EP0620371B1 - Hydraulic system for supply of open or closed hydraulic functions - Google Patents

Hydraulic system for supply of open or closed hydraulic functions Download PDF

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Publication number
EP0620371B1
EP0620371B1 EP94104713A EP94104713A EP0620371B1 EP 0620371 B1 EP0620371 B1 EP 0620371B1 EP 94104713 A EP94104713 A EP 94104713A EP 94104713 A EP94104713 A EP 94104713A EP 0620371 B1 EP0620371 B1 EP 0620371B1
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EP
European Patent Office
Prior art keywords
hydraulic
valve
pressure
feed line
hydraulic system
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP94104713A
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German (de)
French (fr)
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EP0620371A1 (en
Inventor
Manfred Becker
Hilmar Ortlepp
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Deere and Co
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Deere and Co
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B11/00—Servomotor systems without provision for follow-up action; Circuits therefor
    • F15B11/02—Systems essentially incorporating special features for controlling the speed or actuating force of an output member
    • F15B11/04—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed
    • F15B11/05—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed specially adapted to maintain constant speed, e.g. pressure-compensated, load-responsive
    • F15B11/055—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed specially adapted to maintain constant speed, e.g. pressure-compensated, load-responsive by adjusting the pump output or bypass
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/2221—Control of flow rate; Load sensing arrangements
    • E02F9/2225—Control of flow rate; Load sensing arrangements using pressure-compensating valves
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/2221—Control of flow rate; Load sensing arrangements
    • E02F9/2232—Control of flow rate; Load sensing arrangements using one or more variable displacement pumps
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/2278—Hydraulic circuits
    • E02F9/2285—Pilot-operated systems
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/2278—Hydraulic circuits
    • E02F9/2296—Systems with a variable displacement pump
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/20—Fluid pressure source, e.g. accumulator or variable axial piston pump
    • F15B2211/205—Systems with pumps
    • F15B2211/2053—Type of pump
    • F15B2211/20546—Type of pump variable capacity
    • F15B2211/20553—Type of pump variable capacity with pilot circuit, e.g. for controlling a swash plate
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/20—Fluid pressure source, e.g. accumulator or variable axial piston pump
    • F15B2211/25—Pressure control functions
    • F15B2211/253—Pressure margin control, e.g. pump pressure in relation to load pressure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/305—Directional control characterised by the type of valves
    • F15B2211/30505—Non-return valves, i.e. check valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/305—Directional control characterised by the type of valves
    • F15B2211/3056—Assemblies of multiple valves
    • F15B2211/30565—Assemblies of multiple valves having multiple valves for a single output member, e.g. for creating higher valve function by use of multiple valves like two 2/2-valves replacing a 5/3-valve
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/315—Directional control characterised by the connections of the valve or valves in the circuit
    • F15B2211/31523—Directional control characterised by the connections of the valve or valves in the circuit being connected to a pressure source and an output member
    • F15B2211/31529—Directional control characterised by the connections of the valve or valves in the circuit being connected to a pressure source and an output member having a single pressure source and a single output member
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/315—Directional control characterised by the connections of the valve or valves in the circuit
    • F15B2211/31552—Directional control characterised by the connections of the valve or valves in the circuit being connected to an output member and a return line
    • F15B2211/31558—Directional control characterised by the connections of the valve or valves in the circuit being connected to an output member and a return line having a single output member
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/315—Directional control characterised by the connections of the valve or valves in the circuit
    • F15B2211/3157—Directional control characterised by the connections of the valve or valves in the circuit being connected to a pressure source, an output member and a return line
    • F15B2211/31576—Directional control characterised by the connections of the valve or valves in the circuit being connected to a pressure source, an output member and a return line having a single pressure source and a single output member
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/32—Directional control characterised by the type of actuation
    • F15B2211/327—Directional control characterised by the type of actuation electrically or electronically
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/32—Directional control characterised by the type of actuation
    • F15B2211/329—Directional control characterised by the type of actuation actuated by fluid pressure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/40—Flow control
    • F15B2211/405—Flow control characterised by the type of flow control means or valve
    • F15B2211/40515—Flow control characterised by the type of flow control means or valve with variable throttles or orifices
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/40—Flow control
    • F15B2211/405—Flow control characterised by the type of flow control means or valve
    • F15B2211/40576—Assemblies of multiple valves
    • F15B2211/40584—Assemblies of multiple valves the flow control means arranged in parallel with a check valve
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/40—Flow control
    • F15B2211/415—Flow control characterised by the connections of the flow control means in the circuit
    • F15B2211/41509—Flow control characterised by the connections of the flow control means in the circuit being connected to a pressure source and a directional control valve
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/40—Flow control
    • F15B2211/455—Control of flow in the feed line, i.e. meter-in control
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/40—Flow control
    • F15B2211/46—Control of flow in the return line, i.e. meter-out control
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/60—Circuit components or control therefor
    • F15B2211/635—Circuits providing pilot pressure to pilot pressure-controlled fluid circuit elements
    • F15B2211/6355—Circuits providing pilot pressure to pilot pressure-controlled fluid circuit elements having valve means

Definitions

  • the invention relates to a hydraulic system with an adjustable hydraulic pump, the output pressure of which can be controlled as a function of a pressure present at a load signaling connection, a reservoir, at least one hydraulic function with a feed line and a valve arrangement arranged between the hydraulic pump, reservoir and hydraulic function.
  • Modern agricultural tractors today have constant pressure hydraulic systems in which control valves block the flow of liquid from the pump in their neutral position (closed or closed center system). Furthermore, in these systems the hydraulic fluid delivery quantity can be compensated in such a way that only the required fluid quantity is supplied by the pump (power-on-demand).
  • the core of such systems is the so-called load signaling line from the consumer to the load signaling connection of the hydraulic pump, with the aid of which the hydraulic pump adjusts its output pressure at any time as a function of the pressure present at the load signaling connection and thus only provides the necessary requirements. In this way, energy can be saved to a considerable extent.
  • control units are usually designed as constant flow valves that are open in their central position (open center design) or as constant pressure valves that are closed in their central position (closed center design), they do not always have the necessary load signaling connection. If, for example, a control valve of the tractor hydraulic system described above is used to control the fluid flow to the hydraulic functions of an attachment with a constant pressure request, the hydraulic pump of the tractor must be operated continuously at maximum operating pressure. This results in higher power losses than necessary. This also increases fuel consumption and the result is an additional heat load.
  • valve kits which are usually supplied for attachments with constant pressure hydraulic systems, in order to be able to connect them to tractors with constant current hydraulic systems.
  • an electrical control signal from the attachment is used to control a relief valve of the valve kit.
  • the operator In this mode of operation, the operator must carefully adjust the tractor valve that supplies the hydraulic fluid to keep power losses to a minimum. Even with such an attitude, there is still an uninterrupted flow of liquid, when the implement function is not operated, which results in undesirable loss of performance.
  • the object on which the invention is based is seen in providing a solution for a hydraulic system of the type mentioned at the outset by means of which the problems described can be overcome.
  • the hydraulic system should enable a simple and effective interface between different attachment functions and a load-reporting hydraulic system with a compensated amount of liquid, in which the hydraulic pump pressure is limited to the required level.
  • This interface is not intended to require extensive hydraulic installation work or valve modifications in order to obtain a load reporting signal when using different implement functions, by means of which the hydraulic pump can be controlled.
  • a valve arrangement which, in a rest position, closes a passage between the hydraulic function and the load signaling connection and opens in an operating position.
  • a valve of the valve assembly includes a spool which is urged into its rest position by a spring. Furthermore, the slide is exposed to a differential pressure and opens the valve when a differential pressure value corresponding to the spring force is exceeded. Which pressures are used to form the differential pressure depends on the hydraulic function used.
  • a hydraulic system of this type can generate a load signal for any hydraulic functions by means of which the hydraulic pump can be controlled. It provides a simple and effective interface between the hydraulic pump and hydraulic function through which the hydraulic pump outlet pressure can be limited to the required level. No extensive hydraulic installations or valve modifications are required to obtain a usable load signal despite a change between different hydraulic functions.
  • the hydraulic function is designed as an open constant-current hydraulic system, in which the associated control valve drains the hydraulic fluid into the reservoir in its neutral position (open-center design), the spring-loaded side of the control spool with the reservoir and its other side with the hydraulic function leading supply line connected. If the control valve of the hydraulic function is in its neutral position, the hydraulic fluid can flow freely from the supply line into the reservoir. Both sides of the control slide to the reservoir are relieved of pressure so that the control slide blocks the passage of the valve (between the feed line and the load signaling connection) due to the spring force.
  • the load signaling connection is preferably connected to the reservoir via a throttle point, so that the pressure at the load signaling connection can gradually decrease even when the valve is closed.
  • the output pressure of the hydraulic pump is regulated down to the standby pressure.
  • the pump outlet is preferably connected to the feed line by a channel containing an orifice, through which a permanent control current is maintained. As a result of this control current, the pressure in the supply line separated from the storage container rises to the pump outlet pressure.
  • a check valve is preferably provided in the feed line, which only allows liquid flow from the valve to the hydraulic function, but prevents backflow.
  • This check valve is expediently bridged by a throttled channel, in order to allow a gradual pressure reduction in the supply line even when the check valve is closed and to apply the pressure of the hydraulic function to the load signaling connection.
  • the hydraulic function is designed as a constant-pressure hydraulic system that is closed in its central position and in which the associated control valve blocks the supply line in its neutral position (closed-center design), the spring-loaded side of the control spool with the supply line leading to the hydraulic function and the other side of the Control spool connected to the pump outlet.
  • the feed line is preferably connected to the pump outlet via a channel containing an orifice. If the control valve of the hydraulic function is in its neutral position, the supply line is blocked. A gradual pressure equalization takes place via the channel, so that the output pressure of the hydraulic pump is present on both sides of the control slide and the control slide assumes its closed position as a result of the force. This disconnects the load detection connection from the supply line.
  • the load signaling connection is preferably connected to the reservoir via a throttle point, so that the pressure at the load signaling connection can gradually decrease even when the valve is closed.
  • the output pressure of the hydraulic pump is regulated down to the standby pressure.
  • a changeover valve is preferably provided, by means of which either the higher of the two pressures of the pump outlet or the feed line can be applied to the side of the control slide opposite the spring. If the pressure in the supply line is higher than the pump pressure due to a load in the hydraulic function, this is reported via the shuttle valve to the second side of the control spool opposite the spring. The spool moves against the force of the spring and on its first side prevailing lower pressure in the open position of the valve, so that the pump outlet pressure is present at the load signaling connection and the pump regulates. As soon as the pump pressure exceeds the pressure in the supply line, the shuttle valve switches back to the pump outlet pressure.
  • a check valve is preferably provided in the feed line, which prevents liquid backflow from the hydraulic function to the valve.
  • the check valve serves to secure a load on the hydraulic function and avoids an initial pressure drop in the hydraulic function when the control valve is opened against a load pressure.
  • the check valve is expediently bridged by a throttled channel so that, in the event that the control valve is closed against a high load pressure and therefore the check valve is also blocked, a gradual pressure reduction in the supply line is possible and the load signaling connection is pressurized with the pressure of the hydraulic function.
  • the valve preferably controls a second passage through which the pump outlet can be connected to the supply line.
  • This passage which serves to supply the hydraulic function with hydraulic fluid and pressure, is closed or opened at the same time as the connection between the feed line and the load signaling connection.
  • This passage expediently contains an adjustable throttle point, which can be formed by an adjustable rotary slide valve. With the valve open, this enables current control of the hydraulic fluid flowing from the hydraulic pump to the hydraulic function while maintaining the advantages of the load reporting system according to the invention. Furthermore, in particular when using a hydraulic function with the control valve closed in its central position, the pressure drop generated above the throttle point can serve to stabilize the system.
  • FIG. 1 essentially shows a hydraulic pump 10, a control valve 12 with a downstream hydraulic cylinder 14 and a valve arrangement 16 arranged between the hydraulic pump 10 and the control valve 12.
  • the hydraulic pump 10 is a hydraulic pump of a tractor, not shown, which is designed as a variable displacement pump and the output pressure of which is controlled as a function of a pressure present at its load signaling connection 18.
  • the pump outlet pressure is, for example, always 30 bar above the load signaling pressure, provided the system pressure of 200 bar has not yet been reached.
  • the load signaling connection 18 is connected to a storage container 22 via a throttle point 20.
  • the load reporting pressure can slowly decrease via this throttle point 20. If there is no load signal pressure, the hydraulic pump 10 regulates and releases, for example, a standby pressure of 30 bar.
  • the valve arrangement 16 can be designed as a valve block with hydraulic connections that can be fixedly mounted on the tractor.
  • the control valve 12 and the hydraulic cylinder 14, however, can be components of an attachment, not shown, which can be optionally attached to the tractor.
  • the inputs of the control valve 12 are via flexible lines and not shown Quick fasteners connected to corresponding hydraulic connections of the valve block.
  • the control valve 12 of FIG. 1 is a 4/3-way valve, one input of which is connected to the outlet of the valve arrangement 16 and the other input of which is connected to the reservoir 22. In the central neutral position of the control valve 12, its two inputs are connected to one another, so that a constant current hydraulic circuit (closed center circuit) is formed.
  • the two cylinder spaces of the hydraulic cylinder 14 can optionally be connected to the outlet pressure of the valve arrangement 16.
  • valve arrangement 16 The heart of the valve arrangement 16 is a valve 24, through which two passages can be blocked or opened. Although these two valve functions can in principle also be implemented by using two separate valves, the use of only one control slide 26 permits a simple and compact structure.
  • a first input 1 of the valve 24 is connected to the pump outlet via an adjustable throttle point 28 which is designed as a rotary slide valve and which serves for current control, while a second input 2 of the valve 24 is connected to the load-signaling connection 18 of the hydraulic pump 10.
  • the two outputs 3 and 4 of valve 24 corresponding to inputs 1 and 2 are connected to one another. They are connected together via a check valve 30 and a throttle point 32 arranged parallel to this to a feed line 34 which connects the valve arrangement 16 to the control valve 12. Furthermore, the outputs 3 and 4 are connected to the pump output via a channel 36, which contains an orifice 38.
  • the control slide 26 of the valve 24 is loaded on one side by a spring 40 which urges the control slide 26 into its closed position, in which both passages are blocked. Furthermore, each of the two ends of the control slide 26 is exposed to a control pressure which tries to force the control slide 26 into the opposite position.
  • the control connections of the valve 24 are each connected to a changeover valve 42, 44.
  • the two changeover valves 42, 44 are each 3/2-way valves. They are mechanically coupled to one another, which is indicated by the rod 46, and can be switched over together in any manner (for example electrically, hydraulically or mechanically) by an actuating element 48.
  • the two changeover valves 42, 44 are expediently implemented by a common valve slide. They were only shown as two separate parts for the sake of clarity.
  • the position of the changeover valves 42, 44 shown in FIG. 1 corresponds to the open center operation, in which a hydraulic function which is open in the middle position and is designed for constant current operation is connected to the valve arrangement 16.
  • the control connection of the valve 24, which is on the side of the spring 40 is connected to the reservoir 22 and the other control connection is connected to the supply line 34 leading to the control valve 12.
  • the hydraulic system shown in FIG. 1 works as follows:
  • the supply line 34 is connected to the reservoir 22 and is depressurized. So that the two control connections of the valve 24 are connected to the reservoir 22, so that the control slide 26 shifts due to the force of the spring 40 into its position shown in Fig. 1 and both passages locks.
  • the hydraulic pump 10 does not deliver any hydraulic fluid to the hydraulic function 12, 14. If a pressure is still present at the load signaling connection 18, it is reduced via the throttle point 20 to the reservoir 22. The hydraulic pump 10 regulates down to its standby pressure.
  • control valve 12 If the control valve 12 is moved into a working position, the outflow from the feed line 34 to the reservoir 22 is blocked. A permanent control current flows through the orifice 38 and the channel 36, through which a pressure builds up in the feed line 34. This pressure communicates via the changeover valve 44 to the control connection of the valve 24 opposite the spring 40 and moves the control slide 26 into its open position in which the two passages are open.
  • the hydraulic pump 10 now supplies hydraulic fluid to the hydraulic cylinder 14 via the throttle point 28, the valve 24, the check valve 30, the supply line 34 and the control valve 12, so that the hydraulic cylinder 14 performs the desired movement. Furthermore, the load signaling connection 18 of the hydraulic pump 10 is connected to the pressure of the supply line 34, so that the hydraulic pump 10 regulates and provides its maximum system pressure for supplying the hydraulic function.
  • control valve 12 If the control valve 12 is brought back into its central position in order to interrupt the actuation of the hydraulic cylinder, the supply line 34 is depressurized again, the valve 24 closes and the hydraulic pump 10 regulates to its standby pressure.
  • the check valve 30 prevents a load drop.
  • the throttle point 32 lying in parallel with the check valve 30 enables a leakage current against the blocking direction of the check valve 30, so that a gradual pressure equalization can take place.
  • this throttle point 32 is not such.
  • a check valve 50 is arranged between the feed line 34 and the reservoir 22, which allows hydraulic fluid to be sucked in from the reservoir 22 if necessary.
  • FIG. 2 The hydraulic system shown in FIG. 2 is essentially identical to that shown in FIG. 1. The same reference numbers have therefore been used for the same components.
  • the hydraulic system is used to supply a constant-current hydraulic function that contains an open-center control valve 12, in FIG. 2 a constant-pressure hydraulic function with a closed-center control valve 13 is shown as a consumer.
  • the changeover valves 42, 44 shown in FIG. 2 are accordingly in their position for closed-center operation.
  • a shuttle valve 52 is arranged between the pump outlet and the feed line 34, the center connection of which can be connected via the changeover valve 44 to the control connection of the valve 24 opposite the spring 40. Although this shuttle valve 52 is also shown in FIG. 1, it has not yet been described since it has no significance for the open center operation.
  • the hydraulic system shown in FIG. 2 works as follows:
  • control valve 13 If the control valve 13 is in its neutral position, the supply line 34 is blocked.
  • the pump outlet pressure is present in it, which is communicated via the orifice 38, the channel 36 and the orifice 32 or the check valve 30.
  • the pump outlet pressure is also present at the two control connections of the valve 24 via the orifice 38 and the changeover valve 42 or via the changeover valve 52 and the changeover valve 44.
  • the control slide 26 of the valve 24 is therefore held due to the force of the spring 40 in its closed position, in which both passages are closed. If a pressure is still present at the load signaling connection 18, it is reduced via the throttle point 20 to the reservoir 22.
  • the hydraulic pump 10 regulates down to its standby pressure.
  • control valve 13 If the control valve 13 is switched into a working position, the pressure drops in the supply line 34, and the control connection of the valve 24 on the side of the spring 40 is relieved via the channel 36 and the changeover valve 42.
  • the control slide 26 is moved by the pump outlet pressure present at the other control connection into its open position, in which there is a free flow from the hydraulic pump 10 to the control valve 13. Furthermore, the pressure of the supply line 34 is present at the load signaling connection, so that the load signal required for pump control is given and the hydraulic pump 10 is regulated.
  • the pressure drop generated over the adjustable throttle point 28 serves to stabilize the system.
  • the pressure in the feed line 34 switches the shuttle valve 52 from its position shown, so that the feed line 34 via the shuttle valve 52 and the switch valve 44 with the the spring 40 opposite control connection of the valve 24 is connected.
  • the shuttle valve 52 ensures that the higher of the pressures of the pump outlet or the supply line is present at the control connection.
  • the check valve 30 also serves to secure a load on the hydraulic cylinder 14.
  • the throttle point 32 allows a pressure reduction in the supply line 34 if the control valve 13 is closed against a high load pressure.
  • the passage opening of the throttle point 32 is generally dimensioned smaller than that of the orifice 38, so that the pressure at the control connection of the valve 24 located on the spring side is primarily influenced by the pump outlet pressure.
  • valve block 60 which essentially contains the elements of the valve arrangement 16 shown in FIGS. 1 and 2. Elements with the same effect have therefore been given the same reference symbols.
  • the valve block 60 has a pump connection 62 which can be connected to a hydraulic pump 10, a tank connection 64 which can be connected to a reservoir 22, a working connection 66 which can be connected to a hydraulic function via a feed line 34 and one to the load-reporting connection 18 of the hydraulic pump 10 connectable signaling connection 68.
  • a control slide 26 is slidably guided, which contains two control sections 72, 74 and is forced into its left position according to FIG. 3 by the force of a spring 40.
  • the first control section 72 opens or closes a passage 76 between the pump connection 62 and the working connection 66, while the second control section 74 opens or closes a passage 78 between a channel 36 and the signaling connection 68.
  • the control slide 26 is shown in its right position, in which both passages 76, 78 are open.
  • the right end face of the control slide 26 is connected to a changeover valve 42, through which it can be connected either to the tank connection 64 or to the pump connection 62 via a channel 36 containing an orifice 38.
  • the left end face of the control slide 26 can be connected to the working connection 66 by a shuttle valve 52 or to the pump connection 62 via a changeover valve 44.
  • the shuttle valve 52 is designed such that it applies the higher of the two pressures, which act on the working connection 66 or on the pump connection 62, to the left end face of the control slide 26.
  • the two changeover valves 42, 44 are shown in their closed center position. By twisting, they can be brought into their open center position.
  • a valve insert 80 is inserted into the bore of the working connection 66 and counteracts the force of a spring 82 an outlet opening is pressed to close it.
  • This valve insert 80 forms the check valve 30. It has a central bore 84 which serves as a throttle point 32 and allows gradual pressure equalization.
  • a throttle point 28 designed as a rotary slide valve is provided in the area of the pump connection 62.
  • a pressure drop can be set on the one hand, so that the load signal is a certain amount, for example by 30 bar, less than the pump outlet pressure.
  • the throttle point 28 can be used to make a current setting.

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Abstract

A hydraulic system is described which has a variable-displacement hydraulic pump (10), the outlet pressure of which can be controlled as a function of a pressure applied to a load-indicating connection (18), a supply tank (22), a hydraulic function (12, 13, 14) with a feed line (34), and a valve arrangement (16) located between hydraulic pump (10), supply tank (22) and hydraulic function (12, 13, 14). In order to produce a load signal absent at the hydraulic function (12, 13, 14), by means of which load signal the hydraulic pump (10) can be regulated, it is proposed that a valve (24) be arranged between the feed line (34) and the load-indicating connection (18). A control spool (26) of the valve (24) is pushed by a spring (40) and a pressure acting on its first side into a closed position and by a pressure acting on its second side into an open position in which a control connection between the feed line (34) and the load-indicating connection (18) is open. Reversing valve means (42, 44) are provided, by means of which different pressures can alternatively be applied to the first and the second side of the control spool (26). When using a hydraulic function (12, 14) with a constant-flow hydraulic circuit, the first side of the control spool (26) is connected to the supply tank (22) and the second side of the control spool (26) is connected to the feed line (34) by the reversing valve means (42, 44), and, when using a hydraulic function (13, 14) with a constant-pressure hydraulic system, the first side of the control spool (26) is connected to the feed line (34) and the second side of the control spool (26) is connected to the pump outlet by the reversing valve means (42, 44). <IMAGE>

Description

Die Erfindung betrifft ein Hydrauliksystem mit einer verstellbaren Hydraulikpumpe, deren Ausgangsdruck in Abhängigkeit eines an einem Lastmeldeanschluß anstehenden Drucks steuerbar ist, einem Vorratsbehälter, wenigstens einer Hydraulikfunktion mit einer Zuführleitung und einer zwischen Hydraulikpumpe, Vorratsbehälter und Hydraulikfunktion angeordneten Ventilanordnung.The invention relates to a hydraulic system with an adjustable hydraulic pump, the output pressure of which can be controlled as a function of a pressure present at a load signaling connection, a reservoir, at least one hydraulic function with a feed line and a valve arrangement arranged between the hydraulic pump, reservoir and hydraulic function.

Moderne landwirtschaftliche Schlepper verfügen heute über Konstantdruck-Hydrauliksysteme, bei denen Steuerventile in ihrer Neutralstellung den Flüssigkeitsdurchfluß von der Pumpe sperren (geschlossenes oder Closed-Center-System). Ferner kann bei diesen Systemen die Hydraulikflüssigkeitsabgabemenge derart kompensiert werden, daß lediglich die benötigte Flüssigkeitsmenge von der Pumpe geliefert wird (Power-on-Demand). Kernpunkt derartiger Systeme ist die sogenannte Lastmeldeleitung vom Verbraucher an den Lastmeldeanschluß der Hydraulikpumpe, mit deren Hilfe die Hydraulikpumpe jeder Zeit ihren Ausgangsdruck in Abhängigkeit des am Lastmeldeanschluß anstehenden Drucks einstellt und damit nur den notwendigen Bedarf zur Verfügung stellt. Hierdurch läßt sich Energie in erheblichem Maße einsparen.Modern agricultural tractors today have constant pressure hydraulic systems in which control valves block the flow of liquid from the pump in their neutral position (closed or closed center system). Furthermore, in these systems the hydraulic fluid delivery quantity can be compensated in such a way that only the required fluid quantity is supplied by the pump (power-on-demand). The core of such systems is the so-called load signaling line from the consumer to the load signaling connection of the hydraulic pump, with the aid of which the hydraulic pump adjusts its output pressure at any time as a function of the pressure present at the load signaling connection and thus only provides the necessary requirements. In this way, energy can be saved to a considerable extent.

Die in der Landwirtschaft verwendeten Anbaugeräte sind vermehrt mit eigenen Steuergeräten zur Ansteuerung ihrer Hydrauliksysteme ausgestattet. Um eine aufwendige Doppelbedienung von traktoreigenem Steuergerät und anbaugeräteseitigem Steuergerät zu umgehen, wäre es vorteilhaft, wenn sich letztere ohne weitere Zusatzmaßnahmen unmittelbar an das traktoreigene Hydrauliksystem anschließen ließen. Da die anbaugeräteseitigen Steuergeräte jedoch meistens als Konstantstromventile, die in ihrer Mittelstellung offen sind (Open-Center-Bauweise), oder als Konstantdruckventile, die in ihrer Mittelstellung geschlossen sind (Closed-Center-Bauweise), ausgeführt sind, verfügen sie nicht immer über den notwendigen Lastmeldeanschluß. Wird beispielsweise ein Steuerventil des oben schriebenen Schlepperhydrauliksystems verwendet, um den Flüssigkeitsstrom zu den Hydraulikfunktionen eines Anbaugerätes mit Konstantdruckanforderung zu steuern, so muß die Hydraulikpumpe des Schleppers ständig bei maximalem Betriebsdruck betrieben werden. Hierdurch entstehen höhere Leistungsverluste als erforderlich. Damit steigt auch der Treibstoffverbrauch, und eine zusätzliche Wärmebelastung ist die Folge.The attachments used in agriculture are increasingly equipped with their own control devices for controlling their hydraulic systems. In order to avoid complex double operation of the tractor's control unit and the control unit on the implement side, it would be advantageous if the latter could be connected directly to the tractor's hydraulic system without any additional measures. Since the implement side However, control units are usually designed as constant flow valves that are open in their central position (open center design) or as constant pressure valves that are closed in their central position (closed center design), they do not always have the necessary load signaling connection. If, for example, a control valve of the tractor hydraulic system described above is used to control the fluid flow to the hydraulic functions of an attachment with a constant pressure request, the hydraulic pump of the tractor must be operated continuously at maximum operating pressure. This results in higher power losses than necessary. This also increases fuel consumption and the result is an additional heat load.

Eine Lösung dieses Problems könnte darin gesehen werden, auf dem Anbaugerät eine hydraulische Lastmeldeleitung zu installieren, die den Hydraulikdruck der Anbaugerätefunktion erfaßt und an den Lastmeldeanschluß der traktorseitigen Hydraulikpumpe meldet. Dieser Lösungsweg erfordert jedoch Veränderungen an der Anbaugerätehydraulik (Hydraulikkreis und Ventilanordnung), was insbesondere dann sehr kompliziert und teuer werden kann, wenn mehrere Funktionen berücksichtigt werden müssen (siehe auch ÖLHYDRAULIK UND PNEUMATIK, Bd. 36,Nr. 4, April 1992, MAINZ, seiten 234-241, Heinrich lödige "Nutzbare leistung einer LS-Hydraulik", Abb. 4 als nächster Stand der Technik und Grundlage des Oberbegriffes).A solution to this problem could be seen in installing a hydraulic load signaling line on the implement, which detects the hydraulic pressure of the implement function and reports it to the load signaling connection of the tractor-side hydraulic pump. However, this solution requires changes to the implement hydraulics (hydraulic circuit and valve arrangement), which can be very complicated and expensive, in particular, if several functions have to be taken into account (see also OIL HYDRAULICS AND PNEUMATICS, Vol. 36, No. 4, April 1992, MAINZ, pages 234-241, Heinrich lödige "Usable performance of an LS hydraulic system", Fig. 4 as the next state of the art and the basis of the generic term).

Eine andere Lösung erfordert die Verwendung von Ventilbausätzen, die üblicherweise für Anbaugeräte mit Konstantdruck-Hydrauliksystemen geliefert werden, um diese an Schleppern mit Konstantstrom-Hydrauliksystemen anschließen zu können. Bei einem derartigen Ventilbausatz wird ein elektrisches Steuersignal des Anbaugerätes verwendet, um ein Entlastungsventil des Ventilbausatzes anzusteuern. Bei dieser Betriebsweise muß die Bedienungsperson das Schlepperventil, das die Hydraulikflüssigkeit liefert, sorgfältig einstellen, um Leistungsverluste klein zu halten. Selbst mit einer solchen Einstellung herrscht auch dann ein ununterbrochener Flüssigkeitsstrom, wenn die Anbaugerätefunktion nicht betätigt wird, was unerwünschte Leistungsverluste zur Folge hat.Another solution requires the use of valve kits, which are usually supplied for attachments with constant pressure hydraulic systems, in order to be able to connect them to tractors with constant current hydraulic systems. In such a valve kit, an electrical control signal from the attachment is used to control a relief valve of the valve kit. In this mode of operation, the operator must carefully adjust the tractor valve that supplies the hydraulic fluid to keep power losses to a minimum. Even with such an attitude, there is still an uninterrupted flow of liquid, when the implement function is not operated, which results in undesirable loss of performance.

Die der Erfindung zugrunde liegende Aufgabe wird darin gesehen, für ein Hydrauliksystem der eingangs genannten Art eine Lösung anzugeben, durch die sich die geschilderten Probleme überwinden lassen. Insbesondere soll das Hydrauliksystem ein einfaches und effektives Interface zwischen unterschiedlichen Anbaugerätefunktion und einem Lastmelde-Hydrauliksystem mit kompensierter Flüssigkeitsmenge ermöglichen, bei der der Hydraulikpumpendruck auf das erforderliche Maß begrenzt wird. Dieses Interface soll keine extensiven Hydraulikinstallationsarbeiten oder Ventilmodifikationen erfordern, um bei Verwendung unterschiedlicher Anbaugerätefunktionen ein Lastmeldesignal zu gewinnen, durch das die Hydraulikpumpe steuerbar ist.The object on which the invention is based is seen in providing a solution for a hydraulic system of the type mentioned at the outset by means of which the problems described can be overcome. In particular, the hydraulic system should enable a simple and effective interface between different attachment functions and a load-reporting hydraulic system with a compensated amount of liquid, in which the hydraulic pump pressure is limited to the required level. This interface is not intended to require extensive hydraulic installation work or valve modifications in order to obtain a load reporting signal when using different implement functions, by means of which the hydraulic pump can be controlled.

Die Aufgabe wird ausgehend von dem Oberbegriff des Patentanspruchs 1 durch den kennzeichnenden Teil dieses Anspruchs 1 gelöst. Zwischen die Hydraulikfunktion und den Lastmeldeanschluß der Hydraulikpumpe ist eine Ventilanordnung vorgesehen, die in einer Ruhestellung einen Durchgang zwischen der Hydraulikfunktion und dem Lastmeldeanschluß schließt und in einer Betriebsstellung öffnet. Ein Ventil der Ventilanordnung enthält einen Steuerschieber, der durch eine Feder in seine Ruhestellung gedrängt wird. Ferner ist der Schieber einem Differenzdruck ausgesetzt und öffnet das Ventil bei Überschreiten eines der Federkraft entsprechenden Differenzdruckwertes. Welche Drücke zur Bildung des Differenzdrucks herangezogen werden, hängt von der verwendeten Hydraulikfunktion ab.The object is achieved on the basis of the preamble of claim 1 by the characterizing part of this claim 1. Between the hydraulic function and the load signaling connection of the hydraulic pump, a valve arrangement is provided which, in a rest position, closes a passage between the hydraulic function and the load signaling connection and opens in an operating position. A valve of the valve assembly includes a spool which is urged into its rest position by a spring. Furthermore, the slide is exposed to a differential pressure and opens the valve when a differential pressure value corresponding to the spring force is exceeded. Which pressures are used to form the differential pressure depends on the hydraulic function used.

Durch ein derartiges Hydrauliksystem läßt sich für beliebige Hydraulikfunktionen ein Lastsignal erzeugen, durch das die Hydraulikpumpe ansteuerbar ist. Es stellt ein einfaches und effektives Interface zwischen Hydraulikpumpe und Hydraulikfunktion dar, durch das sich der Hydraulikpumpenausgangsdruck auf das erforderliche Maß beschränken läßt. Um trotz eines Wechsels zwischen unterschiedlichen Hydraulikfunktionen ein brauchbares Lastmeldesignal zu gewinnen, sind keine extensiven Hydraulikinstallationen oder Ventilmodifikationen erforderlich.A hydraulic system of this type can generate a load signal for any hydraulic functions by means of which the hydraulic pump can be controlled. It provides a simple and effective interface between the hydraulic pump and hydraulic function through which the hydraulic pump outlet pressure can be limited to the required level. No extensive hydraulic installations or valve modifications are required to obtain a usable load signal despite a change between different hydraulic functions.

Ist die Hydraulikfunktion als offenes Konstantstrom-Hydrauliksystem ausgebildet, bei dem das zugehörige Steuerventil in seiner Neutralstellung die Hydraulikflüssigkeit in den Vorratsbehälter ableitet (Open-Center-Bauweise), so wird die federbelastete Seite des Steuerschiebers mit dem Vorratsbehälter und seine andere Seite mit der zur Hydraulikfunktion führenden Zuführleitung verbunden. Befindet sich hierbei das Steuerventil der Hydraulikfunktion in seiner Neutralstellung, so kann die Hydraulikflüssigkeit aus der Zuführleitung frei in den Vorratsbehälter abfließen. Dabei sind beide Seiten des Steuerschiebers zum Vorratsbehälter druckentlastet, so daß der Steuerschieber infolge der Federkraft den Durchgang des Ventils (zwischen Zuführleitung und Lastmeldeanschluß) sperrt. Vorzugsweise steht der Lastmeldeanschluß über eine Drosselstelle mit dem Vorratsbehälter in Verbindung, so daß sich auch bei geschlossenem Ventil der am Lastmeldeanschluß anstehende Druck allmählich abbauen kann. Hierbei wird der Ausgangsdruck der Hydraulikpumpe auf den Bereitschaftsdruck herunter geregelt.If the hydraulic function is designed as an open constant-current hydraulic system, in which the associated control valve drains the hydraulic fluid into the reservoir in its neutral position (open-center design), the spring-loaded side of the control spool with the reservoir and its other side with the hydraulic function leading supply line connected. If the control valve of the hydraulic function is in its neutral position, the hydraulic fluid can flow freely from the supply line into the reservoir. Both sides of the control slide to the reservoir are relieved of pressure so that the control slide blocks the passage of the valve (between the feed line and the load signaling connection) due to the spring force. The load signaling connection is preferably connected to the reservoir via a throttle point, so that the pressure at the load signaling connection can gradually decrease even when the valve is closed. The output pressure of the hydraulic pump is regulated down to the standby pressure.

Wird das Steuerventil der Hydraulikfunktion in eine Arbeitsposition geschaltet, so ist der freie Abfluß von der Zuführleitung zum Vorratsbehälter unterbrochen. Für diesen Fall ist vorzugsweise der Pumpenausgang mit der Zuführleitung durch einen eine Blende enthaltenden Kanal verbunden, durch den ein permanenter Steuerstrom aufrecht erhalten wird. Durch diesen Steuerstrom steigt in der von dem Vorratsbehälter getrennten Zuführleitung der Druck bis auf den Pumpenausgangsdruck an.If the control valve of the hydraulic function is switched to a working position, the free outflow from the supply line to the reservoir is interrupted. In this case, the pump outlet is preferably connected to the feed line by a channel containing an orifice, through which a permanent control current is maintained. As a result of this control current, the pressure in the supply line separated from the storage container rises to the pump outlet pressure.

Dieser Druckaufbau teilt sich der der Feder gegenüberliegenden Seite des Steuerschiebers mit, wodurch sich der Steuerschieber gegen die Kraft der Feder verschiebt und das Ventil öffnet. Bei geöffnetem Ventil teilt sich der an der Hydraulikfunktion anstehende Druck dem Lastmeldeanschluß der Hydraulikpumpe mit und bildet das gewünschte Lastsignal zur Pumpenregelung.This build-up of pressure communicates with the side of the control spool opposite the spring, as a result of which the control spool moves against the force of the spring and the valve opens. When the valve is open, the pressure at the hydraulic function communicates to the load signaling connection of the hydraulic pump and forms the desired load signal for pump control.

Wird das Steuerventil der Hydraulikfunktion gegen einen Lastdruck geöffnet, so sollte ein Druckabfall vermieden werden. Hierfür ist vorzugsweise in der Zuführleitung ein Rückschlagventil vorgesehen, das lediglich einen Flüssigkeitsfluß von dem Ventil zu der Hydraulikfunktion erlaubt, jedoch einen Rückfluß unterbindet. Dieses Rückschlagventil ist zweckmäßigerweise durch einen gedrosselten Kanal überbrückt, um auch bei geschlossenem Rückschlagventil einen allmählichen Druckabbau in der Zuführleitung zu ermöglichen und den Lastmeldeanschluß mit dem Druck der Hydraulikfunktion zu beaufschlagen.If the control valve of the hydraulic function is opened against a load pressure, a pressure drop should be avoided. For this purpose, a check valve is preferably provided in the feed line, which only allows liquid flow from the valve to the hydraulic function, but prevents backflow. This check valve is expediently bridged by a throttled channel, in order to allow a gradual pressure reduction in the supply line even when the check valve is closed and to apply the pressure of the hydraulic function to the load signaling connection.

Schaltet das Steuerventil zurück in seine Neutralstellung, so wird die Zuführleitung wieder zum Vorratsbehälter entlastet, und der Steuerschieber kehrt durch die Kraft der Feder in die das Ventil schließende Stellung zurück. Der am Lastmeldeanschluß der Hydraulikpumpe anstehende Druck wird über eine Drosselstelle in den Vorratsbehälter abgebaut, und der Ausgangsdruck der Hydraulikpumpe fällt auf den Bereitschaftsdruck ab.If the control valve switches back to its neutral position, the supply line to the reservoir is relieved, and the control slide returns to the valve closing position by the force of the spring. The pressure at the hydraulic pump's load signaling connection is reduced via a throttle in the reservoir, and the output pressure of the hydraulic pump drops to the standby pressure.

Ist die Hydraulikfunktion als in seiner Mittelstellung geschlossenes Konstantdruck-Hydrauliksystem ausgebildet, bei dem das zugehörige Steuerventil in seiner Neutralstellung die Zuführleitung sperrt (Cosed-Center-Bauweise), so wird die federbelastete Seite des Steuerschiebers mit der zur Hydraulikfunktion führenden Zuführleitung und die andere Seite des Steuerschiebers mit dem Pumpenausgang verbunden. Vorzugsweise steht die Zuführleitung über einen eine Blende enthaltenden Kanal mit dem Pumpenausgang in Verbindung. Befindet sich hierbei das Steuerventil der Hydraulikfunktion in seiner Neutralstellung, so ist die Zuführleitung blockiert. Über den Kanal erfolgt ein allmählicher Druckausgleich, so daß auf beiden Seiten des Steuerschiebers der Ausgangsdruck der Hydraulikpumpe ansteht und der Steuerschieber infolge der derkraft seine Schließstellung einnimmt. Damit ist der Lastmeldeanschluß von der Zuführleitung getrennt. Vorzugsweise steht der Lastmeldeanschluß über eine Drosselstelle mit dem Vorratsbehälter in Verbindung, so daß sich auch bei geschlossenem Ventil der am Lastmeldeanschluß anstehende Druck allmählich abbauen kann. Hierbei wird der Ausgangsdruck der Hydraulikpumpe auf den Bereitschaftsdruck herunter geregelt.If the hydraulic function is designed as a constant-pressure hydraulic system that is closed in its central position and in which the associated control valve blocks the supply line in its neutral position (closed-center design), the spring-loaded side of the control spool with the supply line leading to the hydraulic function and the other side of the Control spool connected to the pump outlet. The feed line is preferably connected to the pump outlet via a channel containing an orifice. If the control valve of the hydraulic function is in its neutral position, the supply line is blocked. A gradual pressure equalization takes place via the channel, so that the output pressure of the hydraulic pump is present on both sides of the control slide and the control slide assumes its closed position as a result of the force. This disconnects the load detection connection from the supply line. The load signaling connection is preferably connected to the reservoir via a throttle point, so that the pressure at the load signaling connection can gradually decrease even when the valve is closed. The output pressure of the hydraulic pump is regulated down to the standby pressure.

Wird das Steuerventil der Hydraulikfunktion in eine Arbeitsposition geschaltet, so fällt in der Zuführleitung der Druck ab. Dadurch wird die Federseite des Steuerschiebers druckentlastet, und der Steuerschieber wird durch den auf seiner anderen Seite anstehenden Pumpenausgangsdruck gegen die Federkraft in seine Öffnungsstellung verschoben. Bei geöffnetem Ventil teilt sich der an der Hydraulikfunktion anstehende Druck dem Lastmeldeanschluß der Hydraulikpumpe mit und bildet das gewünschte Lastsignal zur Pumpenregelung.If the control valve of the hydraulic function is switched to a working position, the pressure in the supply line drops. As a result, the spring side of the control slide is relieved of pressure and the control slide is displaced into its open position against the spring force by the pump outlet pressure present on its other side. When the valve is open, the pressure at the hydraulic function communicates to the load signaling connection of the hydraulic pump and forms the desired load signal for pump control.

Vorzugsweise ist ein Wechselventil vorgesehen, durch das wahlweise der höhere der beiden Drücke des Pumpenausgangs oder der Zuführleitung an die der Feder gegenüberliegende Seite des Steuerschiebers anlegbar ist. Ist in der Zuführleitung aufgrund einer Last der Hydraulikfunktion der Druck höher als der Pumpendruck, so wird dieser über das Wechselventil auf die der Feder gegenüberliegende, zweite Seite des Steuerschiebers gemeldet. Der Steuerschieber bewegt sich gegen die Kraft der Feder und den auf seiner ersten Seite herrschenden geringeren Druck in Öffnungsstellung des Ventils, so daß der Pumpenausgangsdruck an dem Lastmeldeanschluß ansteht und die Pumpe aufregelt. Sobald der Pumpendruck den Druck in der Zuführleitung überschreitet, schaltet das Wechselventil wieder auf den Pumpenausgangsdruck um.A changeover valve is preferably provided, by means of which either the higher of the two pressures of the pump outlet or the feed line can be applied to the side of the control slide opposite the spring. If the pressure in the supply line is higher than the pump pressure due to a load in the hydraulic function, this is reported via the shuttle valve to the second side of the control spool opposite the spring. The spool moves against the force of the spring and on its first side prevailing lower pressure in the open position of the valve, so that the pump outlet pressure is present at the load signaling connection and the pump regulates. As soon as the pump pressure exceeds the pressure in the supply line, the shuttle valve switches back to the pump outlet pressure.

Auch bei der Anwendung einer Hydraulikfunktion mit einem in seiner Neutralstellung geschlossenen Steuerventil ist vorzugsweise in der Zuführleitung ein Rückschlagventil vorgesehen, das einen Flüssigkeitsrückfluß von der Hydraulikfunktion zu dem Ventil unterbindet. Auch hier dient das Rückschlagventil der Absicherung einer Last an der Hydraulikfunktion und vermeidet einen anfänglichen Druckabfall in der Hydraulikfunktion, wenn das Steuerventil gegen einen Lastdruck geöffnet wird. Das Rückschlagventil ist zweckmäßigerweise durch einen gedrosselten Kanal überbrückt, um für den Fall, daß das Steuerventil gegen einen hohen Lastdruck geschlossen und daher auch das Rückschlagventil gesperrt wird, einen allmählichen Druckabbau in der Zuführleitung zu ermöglichen und den Lastmeldeanschluß mit dem Druck der Hydraulikfunktion zu beaufschlagen.Even when using a hydraulic function with a control valve closed in its neutral position, a check valve is preferably provided in the feed line, which prevents liquid backflow from the hydraulic function to the valve. Here, too, the check valve serves to secure a load on the hydraulic function and avoids an initial pressure drop in the hydraulic function when the control valve is opened against a load pressure. The check valve is expediently bridged by a throttled channel so that, in the event that the control valve is closed against a high load pressure and therefore the check valve is also blocked, a gradual pressure reduction in the supply line is possible and the load signaling connection is pressurized with the pressure of the hydraulic function.

Schaltet das Steuerventil zurück in seine Neutralstellung, so wird die Zuführleitung wieder gesperrt. Da die Zuführleitung über einen eine Blende enthaltenden Kanal mit dem Pumpenausgang in Verbindung steht, erfolgt ein allmählicher Druckausgleich, so daß auf beiden Seiten des Steuerschiebers der Ausgangsdruck der Hydraulikpumpe ansteht und der Steuerschieber infolge der Federkraft seine Schließstellung einnimmt. Bei geschlossenem Ventil wird der am Lastmeldeanschluß der Hydraulikpumpe anstehende Druck über eine Drosselstelle in den Vorratsbehälter abgebaut, und der Ausgangsdruck der Hydraulikpumpe fällt auf den Bereitschaftsdruck ab.If the control valve switches back to its neutral position, the supply line is blocked again. Since the supply line is connected to the pump outlet via a duct containing an orifice, there is a gradual pressure compensation, so that the outlet pressure of the hydraulic pump is present on both sides of the control slide and the control slide assumes its closed position due to the spring force. When the valve is closed, the pressure at the hydraulic pump's load signaling connection is reduced via a throttle in the reservoir, and the output pressure of the hydraulic pump drops to the standby pressure.

Das Ventil steuert vorzugsweise einen zweiten Durchgang, durch den der Pumpenausgang mit der Zuführleitung verbindbar ist. Dieser Durchgang, der der Druck- und Hydraulikflüssigkeitsversorgung der Hydraulikfunktion dient, wird gleichzeitig mit der Verbindung zwischen der Zuführleitung und dem Lastmeldeanschluß geschlossen bzw. geöffnet. In diesem Durchgang ist zweckmäßigerweise eine verstellbare Drosselstelle enthalten, die durch einen einstellbaren Drehschieber gebildet sein kann. Dieser ermöglicht bei geöffnetem Ventil eine Stromregelung der von der Hydraulikpumpe zu der Hydraulikfunktion fließenden Hydraulikflüssigkeit unter Beibehaltung der Vorteile des erfindungsgemäßen Lastmeldesystems. Ferner kann insbesondere bei Verwendung einer Hydraulikfunktion mit in seiner Mittelstellung geschlossenem Steuerventil der über der Drosselstelle erzeugte Druckabfall zur Stabilisierung des Systems dienen.The valve preferably controls a second passage through which the pump outlet can be connected to the supply line. This passage, which serves to supply the hydraulic function with hydraulic fluid and pressure, is closed or opened at the same time as the connection between the feed line and the load signaling connection. This passage expediently contains an adjustable throttle point, which can be formed by an adjustable rotary slide valve. With the valve open, this enables current control of the hydraulic fluid flowing from the hydraulic pump to the hydraulic function while maintaining the advantages of the load reporting system according to the invention. Furthermore, in particular when using a hydraulic function with the control valve closed in its central position, the pressure drop generated above the throttle point can serve to stabilize the system.

Weitere vorteilhafte Ausgestaltungen und Weiterbildungen der Erfindung gehen aus den Unteransprüchen hervor.Further advantageous refinements and developments of the invention emerge from the subclaims.

Anhand der Zeichnung, die Ausführungsbeispiele der Erfindung zeigt, werden nachfolgend die Erfindung sowie weitere Vorteile und vorteilhafte Weiterbildungen und Ausgestaltungen der Erfindung näher beschrieben und erläutert.With reference to the drawing, which shows exemplary embodiments of the invention, the invention and further advantages and advantageous developments and refinements of the invention are described and explained in more detail below.

Es zeigt:

Fig. 1
die schematische Darstellung eines erfindungsgemäßen Hydrauliksystems, an das eine Open-Center-Hydraulikfunktion angeschlossen ist,
Fig. 2
die schematische Darstellung eines erfindungsgemäßen Hydrauliksystems, an das eine Closed-Center-Hydraulikfunktionangeschlossen ist und
Fig. 3
die Schnittdarstellung einer zwischen einer Hydraulikpumpe und einer Hydraulikfunktion anzuordnenden Ventilanordnung.
It shows:
Fig. 1
the schematic representation of a hydraulic system according to the invention, to which an open center hydraulic function is connected,
Fig. 2
the schematic representation of a hydraulic system according to the invention, to which a closed center hydraulic function is connected and
Fig. 3
the sectional view of a valve assembly to be arranged between a hydraulic pump and a hydraulic function.

Aus Fig. 1 geht im wesentlichen eine Hydraulikpumpe 10, ein Steuerventil 12 mit nachgeordnetem Hydraulikzylinder 14 und eine zwischen der Hydraulikpumpe 10 und dem Steuerventil 12 angeordnete Ventilanordnung 16 hervor.1 essentially shows a hydraulic pump 10, a control valve 12 with a downstream hydraulic cylinder 14 and a valve arrangement 16 arranged between the hydraulic pump 10 and the control valve 12.

Bei der Hydraulikpumpe 10 handelt es sich um eine Hydraulikpumpe eines nicht dargestellten Schleppers, die als Verstellpumpe ausgebildet ist und deren Ausgangsdruck in Abhängigkeit eines an ihrem Lastmeldeanschluß 18 anstehenden Drucks gesteuert wird. Der Pumpenausgangsdruck liegt dabei beispielsweise immer um 30 bar über dem Lastmeldedruck, sofern der Systemdruck von 200 bar noch nicht erreicht ist. Der Lastmeldeanschluß 18 steht über eine Drosselstelle 20 mit einem Vorratsbehälter 22 in Verbindung. Über diese Drosselstelle 20 kann sich der Lastmeldedruck langsam abbauen. Liegt kein Lastmeldedruck vor, so regelt die Hydraulikpumpe 10 ab und gibt beispielsweise einen Bereitschaftsdruck von 30 bar ab.The hydraulic pump 10 is a hydraulic pump of a tractor, not shown, which is designed as a variable displacement pump and the output pressure of which is controlled as a function of a pressure present at its load signaling connection 18. The pump outlet pressure is, for example, always 30 bar above the load signaling pressure, provided the system pressure of 200 bar has not yet been reached. The load signaling connection 18 is connected to a storage container 22 via a throttle point 20. The load reporting pressure can slowly decrease via this throttle point 20. If there is no load signal pressure, the hydraulic pump 10 regulates and releases, for example, a standby pressure of 30 bar.

Die Ventilanordnung 16 kann als ein am Schlepper fest montierbarer Ventilblock mit Hydraulikanschlüssen ausgebildet sein. Das Steuerventil 12 und der Hydraulikzylinder 14 können hingegen Bestandteile eines nicht dargestellten Anbaugerätes sein, das wahlweise an dem Schlepper befestigbar ist. Zur Herstellung der Hydraulikverbindung werden die Eingänge des Steuerventils 12 über flexible Leitungen und nicht dargestellte Schnellverschlüsse mit entsprechenden Hydraulikanschlüssen des Ventilblocks verbunden. Bei dem Steuerventil 12 der Fig. 1 handelt es sich um ein 4/3-Wegeventil, dessen einer Eingang mit dem Ausgang der Ventilanordnung 16 und dessen anderer Eingang mit dem Vorratsbehälter 22 in Verbindung steht. In der mittleren Neutralstellung des Steuerventils 12 sind dessen beide Eingänge miteinander verbunden, so daß sich ein Konstantstrom-Hydraulikkreis (Closed-Center-Kreis) ausbildet. Durch Umschalten des Steuerventils 12 lassen sich wahlweise die beiden Zylinderräume des Hydraulikzylinders 14 an den Ausgangsdruck der Ventilanordnung 16 anschließen.The valve arrangement 16 can be designed as a valve block with hydraulic connections that can be fixedly mounted on the tractor. The control valve 12 and the hydraulic cylinder 14, however, can be components of an attachment, not shown, which can be optionally attached to the tractor. To establish the hydraulic connection, the inputs of the control valve 12 are via flexible lines and not shown Quick fasteners connected to corresponding hydraulic connections of the valve block. The control valve 12 of FIG. 1 is a 4/3-way valve, one input of which is connected to the outlet of the valve arrangement 16 and the other input of which is connected to the reservoir 22. In the central neutral position of the control valve 12, its two inputs are connected to one another, so that a constant current hydraulic circuit (closed center circuit) is formed. By switching the control valve 12, the two cylinder spaces of the hydraulic cylinder 14 can optionally be connected to the outlet pressure of the valve arrangement 16.

Kernstück der Ventilanordnung 16 ist ein Ventil 24, durch das sich zwei Durchgänge jeweils sperren oder öffnen lassen. Diese beiden Ventilfunktionen lassen sich zwar grundsätzlich auch durch Anwendung zweier separater Ventile realisieren, die Verwendung lediglich eines Steuerschiebers 26 läßt jedoch einen einfachen und kompakten Aufbau zu.The heart of the valve arrangement 16 is a valve 24, through which two passages can be blocked or opened. Although these two valve functions can in principle also be implemented by using two separate valves, the use of only one control slide 26 permits a simple and compact structure.

Ein erster Eingang 1 des Ventils 24 steht über eine als Drehschieber ausgebildete verstellbare Drosselstelle 28, die der Stromregelung dient, mit dem Pumpenausgang in Verbindung, während ein zweiter Eingang 2 des Ventils 24 mit dem Lastmeldeanschluß 18 der Hydraulikpumpe 10 verbunden ist. Die beiden zu den Eingängen 1 und 2 korrespondierenden Ausgänge 3 und 4 des Ventils 24 sind miteinander verbunden. Sie stehen gemeinsam über ein Rückschlagventil 30 und eine hierzu parallel angeordnete Drosselstelle 32 mit einer Zuführleitung 34 in Verbindung, die die Ventilanordnung 16 mit dem Steuerventil 12 verbindet. Ferner sind die Ausgänge 3 und 4 über einen Kanal 36, der eine Blende 38 enthält, mit dem Pumpenausgang verbunden.A first input 1 of the valve 24 is connected to the pump outlet via an adjustable throttle point 28 which is designed as a rotary slide valve and which serves for current control, while a second input 2 of the valve 24 is connected to the load-signaling connection 18 of the hydraulic pump 10. The two outputs 3 and 4 of valve 24 corresponding to inputs 1 and 2 are connected to one another. They are connected together via a check valve 30 and a throttle point 32 arranged parallel to this to a feed line 34 which connects the valve arrangement 16 to the control valve 12. Furthermore, the outputs 3 and 4 are connected to the pump output via a channel 36, which contains an orifice 38.

Der Steuerschieber 26 des Ventils 24 ist einseitig durch eine Feder 40 belastet, die den Steuerschieber 26 in seine Schließstellung drängt, in der beide Durchgänge versperrt sind. Ferner ist jedes der beiden Enden des Steuerschiebers 26 einem Steuerdruck ausgesetzt, der den Steuerschieber 26 in die jeweils gegenüberliegende Stellung zu drängen versucht. Die Steueranschlüsse des Ventils 24 stehen je mit einem Umschaltventil 42, 44 in Verbindung. Die beiden Umschaltventile 42, 44 sind jeweils 3/2-Wegeventile. Sie sind miteinander mechanisch gekoppelt, was durch die Stange 46 angedeutet ist, und lassen sich auf beliebige Weise (z. B. elektrisch, hydraulisch oder mechanisch) durch ein Betätigungselement 48 gemeinsam umschalten. Die beiden Umschaltventile 42, 44 werden zweckmäßigerweise durch einen gemeinsamen Ventilschieber realisiert. Sie wurden lediglich wegen der besseren Anschaulichkeit als zwei gesonderte Teile dargestellt.The control slide 26 of the valve 24 is loaded on one side by a spring 40 which urges the control slide 26 into its closed position, in which both passages are blocked. Furthermore, each of the two ends of the control slide 26 is exposed to a control pressure which tries to force the control slide 26 into the opposite position. The control connections of the valve 24 are each connected to a changeover valve 42, 44. The two changeover valves 42, 44 are each 3/2-way valves. They are mechanically coupled to one another, which is indicated by the rod 46, and can be switched over together in any manner (for example electrically, hydraulically or mechanically) by an actuating element 48. The two changeover valves 42, 44 are expediently implemented by a common valve slide. They were only shown as two separate parts for the sake of clarity.

Die in Fig. 1 dargestellte Stellung der Umschaltventile 42, 44 entspricht dem Open-Center-Betrieb, bei der eine in Mittelstellung offene Hydraulikfunktion, die für einen Konstantstrombetrieb ausgelegt ist, an die Ventilanordnung 16 angeschlossen ist. In dieser Stellung ist der Steueranschluß des Ventils 24, der auf der Seite der Feder 40 liegt, mit dem Vorratsbehälter 22 und der andere Steueranschluß mit der zum Steuerventil 12 führenden Zuführleitung 34 verbunden.The position of the changeover valves 42, 44 shown in FIG. 1 corresponds to the open center operation, in which a hydraulic function which is open in the middle position and is designed for constant current operation is connected to the valve arrangement 16. In this position, the control connection of the valve 24, which is on the side of the spring 40, is connected to the reservoir 22 and the other control connection is connected to the supply line 34 leading to the control valve 12.

Die Funktionsweise des in Fig. 1 dargestellten Hydrauliksystems ist folgende:The hydraulic system shown in FIG. 1 works as follows:

Befindet sich das Steuerventil 12 in seiner Neutralstellung, so ist die Zuführleitung 34 mit dem Vorratsbehälter 22 verbunden und drucklos. Damit sind die beiden Steueranschlüsse des Ventils 24 mit dem Vorratsbehälter 22 verbunden, so daß sich der Steuerschieber 26 infolge der Kraft der Feder 40 in seine in Fig. 1 dargestellte Lage schiebt und beide Durchgänge sperrt. Die Hydraulikpumpe 10 liefert keine Hydraulikflüssigkeit an die Hydraulikfunktion 12, 14. Falls am Lastmeldeanschluß 18 noch ein Druck ansteht, baut sich dieser über die Drosselstelle 20 zum Vorratsbehälter 22 ab. Die Hydraulikpumpe 10 regelt auf ihren Bereitschaftsdruck runter.If the control valve 12 is in its neutral position, the supply line 34 is connected to the reservoir 22 and is depressurized. So that the two control connections of the valve 24 are connected to the reservoir 22, so that the control slide 26 shifts due to the force of the spring 40 into its position shown in Fig. 1 and both passages locks. The hydraulic pump 10 does not deliver any hydraulic fluid to the hydraulic function 12, 14. If a pressure is still present at the load signaling connection 18, it is reduced via the throttle point 20 to the reservoir 22. The hydraulic pump 10 regulates down to its standby pressure.

Wird das Steuerventil 12 in eine Arbeitsstellung verschoben, so ist der Abfluß von der Zuführleitung 34 zum Vorratsbehälter 22 gesperrt. Über die Blende 38 und den Kanal 36 fließt ein permanenter Steuerstrom, durch den sich ein Druck in der Zuführleitung 34 aufbaut. Dieser Druck teilt sich über das Umschaltventil 44 dem der Feder 40 gegenüberliegenden Steueranschluß des Ventils 24 mit und verschiebt den Steuerschieber 26 in seine Öffnungsstellung, in der die beiden Durchgänge geöffnet sind. Jetzt liefert die Hydraulikpumpe 10 über die Drosselstelle 28, das Ventil 24, das Rückschlagventil 30, die Zuführleitung 34 und das Steuerventil 12 Hydraulikflüssigkeit an den Hydraulikzylinder 14, so daß dieser die gewünschte Bewegung ausführt. Ferner ist der Lastmeldeanschluß 18 der Hydraulikpumpe 10 mit dem Druck der Zuführleitung 34 verbunden, so daß die Hydraulikpumpe 10 aufregelt und ihren maximalen Systemdruck zur Versorgung der Hydraulikfunktion zur Verfügung stellt.If the control valve 12 is moved into a working position, the outflow from the feed line 34 to the reservoir 22 is blocked. A permanent control current flows through the orifice 38 and the channel 36, through which a pressure builds up in the feed line 34. This pressure communicates via the changeover valve 44 to the control connection of the valve 24 opposite the spring 40 and moves the control slide 26 into its open position in which the two passages are open. The hydraulic pump 10 now supplies hydraulic fluid to the hydraulic cylinder 14 via the throttle point 28, the valve 24, the check valve 30, the supply line 34 and the control valve 12, so that the hydraulic cylinder 14 performs the desired movement. Furthermore, the load signaling connection 18 of the hydraulic pump 10 is connected to the pressure of the supply line 34, so that the hydraulic pump 10 regulates and provides its maximum system pressure for supplying the hydraulic function.

Wird das Steuerventil 12 wieder in seine Mittelstellung gebracht, um die Betätigung des Hydraulikzylinders zu unterbrechen, so wird die Zuführleitung 34 wieder drucklos, das Ventil 24 schließt und die Hydraulikpumpe 10 regelt auf ihren Bereitschaftsdruck runter.If the control valve 12 is brought back into its central position in order to interrupt the actuation of the hydraulic cylinder, the supply line 34 is depressurized again, the valve 24 closes and the hydraulic pump 10 regulates to its standby pressure.

Wird das Steuerventil 12 gegen einen Lastdruck des Hydraulikzylinders 14 geöffnet, so verhindert das Rückschlagventil 30 einen Lastabfall. Die zu dem Rückschlagventil 30 parallelliegende Drosselstelle 32 ermöglicht jedoch einen Leckstrom entgegen der Sperrichtung des Rückschlagventils 30, so daß ein allmählicher Druckausgleich erfolgen kann. Für die Open-Center-Anwendung ist diese Drosselstelle 32 jedoch nicht derlich.If the control valve 12 is opened against a load pressure of the hydraulic cylinder 14, the check valve 30 prevents a load drop. However, the throttle point 32 lying in parallel with the check valve 30 enables a leakage current against the blocking direction of the check valve 30, so that a gradual pressure equalization can take place. For the open center application, however, this throttle point 32 is not such.

Für den Fall, daß das Steuerventil 12 gegen einen Unterdruck im Hydraulikzylinder 14 geöffnet wird, ist zwischen der Zuführleitung 34 und dem Vorratsbehälter 22 ein Rückschlagventil 50 angeordnet, das im Bedarfsfall ein Nachsaugen von Hydraulikflüssigkeit aus dem Vorratsbehälter 22 ermöglicht.In the event that the control valve 12 is opened against a negative pressure in the hydraulic cylinder 14, a check valve 50 is arranged between the feed line 34 and the reservoir 22, which allows hydraulic fluid to be sucked in from the reservoir 22 if necessary.

Das in Fig. 2 dargestellte Hydrauliksystem ist in wesentlichen Einzelheiten identisch mit dem in Fig. 1 dargestellten. Daher wurden für gleiche Bauteile die selben Bezugsziffern verwendet.The hydraulic system shown in FIG. 2 is essentially identical to that shown in FIG. 1. The same reference numbers have therefore been used for the same components.

Ein wesentlicher Unterschied der beiden Hydrauliksysteme ist in ihrer Anwendung zu sehen. Während gemäß Fig. 1 das Hydrauliksystem der Versorgung einer Konstantstrom-Hydraulikfunktion dient, die ein Open-Center-Steuerventil 12 enthält, ist in Fig. 2 als Abnehmer eine Konstantdruck-Hydraulikfunktion mit einem Closed-Center-Steuerventil 13 dargestellt. Entsprechend befinden sich die in Fig. 2 dargestellten Umschaltventile 42, 44 in ihrer Stellung für den Closed-Center-Betrieb. Ferner ist zwischen dem Pumpenausgang und der Zuführleitung 34 ein Wechselventil 52 angeordnet, dessen Mittelanschluß über das Umschaltventil 44 mit dem der Feder 40 gegenüberliegenden Steueranschluß des Ventils 24 verbindbar ist. Dieses Wechselventil 52 ist zwar auch in Fig. 1 dargestellt, wurde jedoch noch nicht beschrieben, da es für den Open-Center-Betrieb keine Bedeutung hat.A significant difference between the two hydraulic systems can be seen in their application. 1, the hydraulic system is used to supply a constant-current hydraulic function that contains an open-center control valve 12, in FIG. 2 a constant-pressure hydraulic function with a closed-center control valve 13 is shown as a consumer. The changeover valves 42, 44 shown in FIG. 2 are accordingly in their position for closed-center operation. Furthermore, a shuttle valve 52 is arranged between the pump outlet and the feed line 34, the center connection of which can be connected via the changeover valve 44 to the control connection of the valve 24 opposite the spring 40. Although this shuttle valve 52 is also shown in FIG. 1, it has not yet been described since it has no significance for the open center operation.

Die Funktionsweise des in Fig. 2 dargestellten Hydrauliksystems ist folgende:The hydraulic system shown in FIG. 2 works as follows:

Befindet sich das Steuerventil 13 in seiner Neutralstellung, so ist die Zuführleitung 34 blockiert. In ihr steht der Pumpenausgangsdruck an, der sich über die Blende 38, den Kanal 36 und die Blende 32 bzw. das Rückschlagventil 30 mitteilt. Der Pumpenausgangsdruck steht über die Blende 38 und das Umschaltventil 42 bzw. über das Wechselventil 52 und das Umschaltventil 44 auch an den beiden Steueranschlüssen des Ventils 24 an. Der Steuerschieber 26 des Ventils 24 wird daher infolge der Kraft der Feder 40 in seiner dargestellten Schließstellung gehalten, in der beide Durchgänge geschlossen sind. Falls am Lastmeldeanschluß 18 noch ein Druck ansteht, baut sich dieser über die Drosselstelle 20 zum Vorratsbehälter 22 ab. Die Hydraulikpumpe 10 regelt auf ihren Bereitschaftsdruck runter.If the control valve 13 is in its neutral position, the supply line 34 is blocked. The pump outlet pressure is present in it, which is communicated via the orifice 38, the channel 36 and the orifice 32 or the check valve 30. The pump outlet pressure is also present at the two control connections of the valve 24 via the orifice 38 and the changeover valve 42 or via the changeover valve 52 and the changeover valve 44. The control slide 26 of the valve 24 is therefore held due to the force of the spring 40 in its closed position, in which both passages are closed. If a pressure is still present at the load signaling connection 18, it is reduced via the throttle point 20 to the reservoir 22. The hydraulic pump 10 regulates down to its standby pressure.

Wird das Steuerventil 13 in eine Arbeitsstellung geschaltet, so fällt in der Zuführleitung 34 der Druck ab, und der auf der Seite der Feder 40 liegende Steueranschluß des Ventils 24 wird über den Kanal 36 und das Umschaltventil 42 entlastet. Der Steuerschieber 26 wird durch den an dem anderen Steueranschluß anstehenden Pumpenausgangsdruck in seine Öffnungsstellung bewegt, in der ein freier Durchfluß von der Hydraulikpumpe 10 zu dem Steuerventil 13 gegeben ist. Ferner steht an dem Lastmeldeanschluß der Druck der Zuführleitung 34 an, so daß das zur Pumpenregelung erforderliche Lastsignal gegeben ist und die Hydraulikpumpe 10 aufregelt. Der über der einstellbaren Drosselstelle 28 erzeugte Druckabfall dient zur Stabilisierung des Systems.If the control valve 13 is switched into a working position, the pressure drops in the supply line 34, and the control connection of the valve 24 on the side of the spring 40 is relieved via the channel 36 and the changeover valve 42. The control slide 26 is moved by the pump outlet pressure present at the other control connection into its open position, in which there is a free flow from the hydraulic pump 10 to the control valve 13. Furthermore, the pressure of the supply line 34 is present at the load signaling connection, so that the load signal required for pump control is given and the hydraulic pump 10 is regulated. The pressure drop generated over the adjustable throttle point 28 serves to stabilize the system.

Mit dem Zurückfahren des Steuerventils 13 in seine mittlere Stellung wird die Zuführleitung 34 wieder gesperrt. Über die Blende 38 erfolgt ein Druckausgleich. Damit stellt sich wieder an beiden Steueranschlüssen des Ventils 24 der gleiche Druck, nämlich der Pumpenausgangsdruck ein, und der Steuerschieber 26 des Ventils 24 bewegt sich infolge der Kraft der Feder 40 in seine Schließstellung.When the control valve 13 moves back into its central position, the feed line 34 is blocked again. Pressure compensation takes place via the orifice 38. This results in the same pressure, namely the pump outlet pressure, and the control slide at both control connections of the valve 24 26 of the valve 24 moves into its closed position due to the force of the spring 40.

Herrscht in der Zuführleitung 34 aufgrund einer Last des Hydraulikzylinders 14 ein höherer Druck als der Pumpenausgangsdruck, so schaltet der Druck in der Zuführleitung 34 das Wechselventil 52 aus seiner dargestellten Stellung um, so daß die Zuführleitung 34 über das Wechselventil 52 und das Umschaltventil 44 mit dem der Feder 40 gegenüberliegenden Steueranschluß des Ventils 24 in Verbindung steht. Das Wechselventil 52 sorgt dafür, daß jeweils der höhere der Drücke des Pumpenausgangs oder der Zuführleitung an dem Steueranschluß ansteht. Somit öffnet das Ventil 24 auch dann, wenn beim Umschalten des Steuerventils 13 in seine Arbeitsstellung der Druck im Hydraulikzylinder 14 höher ist als der Pumpenausgangsdruck. Das Rückschlagventil 30 dient auch hier der Absicherung einer am Hydraulikzylinder 14 anstehenden Last. Die Drosselstelle 32 läßt einen Druckabbau in der Zuführleitung 34 zu, falls das Steuerventil 13 gegen einen hohen Lastdruck geschlossen wird. Die Durchtrittsöffnung der Drosselstelle 32 wird in der Regel kleiner bemessen als die der Blende 38, so daß der Druck an dem auf der Federseite liegenden Steueranschluß des Ventils 24 in erster Linie durch den Pumpenausgangsdruck beeinflußt wird.If a higher pressure than the pump outlet pressure prevails in the feed line 34 due to a load of the hydraulic cylinder 14, the pressure in the feed line 34 switches the shuttle valve 52 from its position shown, so that the feed line 34 via the shuttle valve 52 and the switch valve 44 with the the spring 40 opposite control connection of the valve 24 is connected. The shuttle valve 52 ensures that the higher of the pressures of the pump outlet or the supply line is present at the control connection. Thus, the valve 24 opens even when the pressure in the hydraulic cylinder 14 is higher than the pump outlet pressure when the control valve 13 is switched to its working position. The check valve 30 also serves to secure a load on the hydraulic cylinder 14. The throttle point 32 allows a pressure reduction in the supply line 34 if the control valve 13 is closed against a high load pressure. The passage opening of the throttle point 32 is generally dimensioned smaller than that of the orifice 38, so that the pressure at the control connection of the valve 24 located on the spring side is primarily influenced by the pump outlet pressure.

Aus Fig. 3 geht ein Ventilblock 60 hervor, der im wesentlichen die Elemente der in den Figuren 1 und 2 dargestellten Ventilanordnung 16 enthält. Gleichwirkende Elemente wurden daher mit den selben Bezugszeichen belegt.3 shows a valve block 60 which essentially contains the elements of the valve arrangement 16 shown in FIGS. 1 and 2. Elements with the same effect have therefore been given the same reference symbols.

Der Ventilblock 60 hat einen mit einer Hydraulikpumpe 10 verbindbaren Pumpenanschluß 62, einen mit einem Vorratsbehälter 22 verbindbaren Tankanschluß 64, einen über eine Zuführleitung 34 mit einer Hydraulikfunktion verbindbaren Arbeitsanschluß 66 und einen mit dem Lastmeldeanschluß 18 der Hydraulikpumpe 10 verbindbaren Meldeanschluß 68. In einer Bohrung 70 des Ventilblocks 60 ist ein Steuerschieber 26 verschiebbar geführt, der zwei Steuerabschnitte 72, 74 enthält und durch die Kraft einer Feder 40 in seine gemäß Fig. 3 linke Stellung gedrängt wird. Der erste Steuerabschnitt 72 öffnet oder verschließt eine Passage 76 zwischen dem Pumpenanschluß 62 und dem Arbeitsanschluß 66, während der zweite Steuerabschnitt 74 eine Passage 78 zwischen einem Kanal 36 und dem Meldeanschluß 68 öffnet oder verschließt. Der Steuerschieber 26 ist in seiner rechten Stellung dargestellt, in der beide Passagen 76, 78 geöffnet sind.The valve block 60 has a pump connection 62 which can be connected to a hydraulic pump 10, a tank connection 64 which can be connected to a reservoir 22, a working connection 66 which can be connected to a hydraulic function via a feed line 34 and one to the load-reporting connection 18 of the hydraulic pump 10 connectable signaling connection 68. In a bore 70 of the valve block 60, a control slide 26 is slidably guided, which contains two control sections 72, 74 and is forced into its left position according to FIG. 3 by the force of a spring 40. The first control section 72 opens or closes a passage 76 between the pump connection 62 and the working connection 66, while the second control section 74 opens or closes a passage 78 between a channel 36 and the signaling connection 68. The control slide 26 is shown in its right position, in which both passages 76, 78 are open.

Die rechte Stirnseite des Steuerschiebers 26 ist mit einem Umschaltventil 42 verbunden, durch das sie wahlweise mit dem Tankanschluß 64 oder über einen eine Blende 38 enthaltenden Kanal 36 mit dem Pumpenanschluß 62 verbindbar ist. Die linke Stirnseite des Steuerschiebers 26 ist durch ein Wechselventil 52 wahlweise mit dem Arbeitsanschluß 66 oder über ein Umschaltventil 44 mit dem Pumpenanschluß 62 verbindbar. Das Wechselventil 52 ist derart ausgelegt, daß es jeweils den höheren der beiden Drücke, die am Arbeitsanschluß 66 oder am Pumpenanschluß 62 wirken, an die linke Stirnseite des Steuerschiebers 26 anlegt. Die beiden Umschaltventile 42, 44 sind in ihrer Closed-Center-Stellung dargestellt. Durch Verdrehen lassen sie sich in ihre Open-Center-Stellung bringen.The right end face of the control slide 26 is connected to a changeover valve 42, through which it can be connected either to the tank connection 64 or to the pump connection 62 via a channel 36 containing an orifice 38. The left end face of the control slide 26 can be connected to the working connection 66 by a shuttle valve 52 or to the pump connection 62 via a changeover valve 44. The shuttle valve 52 is designed such that it applies the higher of the two pressures, which act on the working connection 66 or on the pump connection 62, to the left end face of the control slide 26. The two changeover valves 42, 44 are shown in their closed center position. By twisting, they can be brought into their open center position.

Es sei hervorgehehoben, daß an Stelle der Umschaltventile 42, 44 auch andere Mittel zur Umschaltung zwischen Konstantdruck- und Konstantstrom-Betrieb eingesetzt werden können. Beispielsweise können einfache Stopfen verwendet werden, um die für den jeweiligen Betrieb nicht erforderlichen oder störenden Kanäle zu verschließen.It should be emphasized that other means for switching between constant pressure and constant current operation can be used instead of the changeover valves 42, 44. For example, simple plugs can be used in order to close the channels which are not required or are disruptive for the respective operation.

In die Bohrung des Arbeitsanschlusses 66 ist ein Ventileinsatz 80 eingesetzt, der durch die Kraft einer Feder 82 gegen eine Austrittsöffnung gedrückt wird, um diese zu verschließen. Dieser Ventileinsatz 80 bildet das Rückschlagventil 30. Er weist eine zentrale Bohrung 84 auf, die als Drosselstelle 32 dient und einen allmählichen Druckausgleich zuläßt.A valve insert 80 is inserted into the bore of the working connection 66 and counteracts the force of a spring 82 an outlet opening is pressed to close it. This valve insert 80 forms the check valve 30. It has a central bore 84 which serves as a throttle point 32 and allows gradual pressure equalization.

Im Bereich des Pumpenanschlusses 62 ist eine als Drehschieber ausgebildete Drosselstelle 28 vorgesehen. Durch diese Drosselstelle 28 läßt sich zum einen ein Druckabfall einstellen, so daß das Lastmeldesignal um einen bestimmten Betrag, beispielsweise um 30 bar, kleiner ist als der Pumpenausgangsdruck. Zum anderen läßt sich durch die Drosselstelle 28 eine Stromeinstellung vornehmen.In the area of the pump connection 62, a throttle point 28 designed as a rotary slide valve is provided. By means of this throttle point 28, a pressure drop can be set on the one hand, so that the load signal is a certain amount, for example by 30 bar, less than the pump outlet pressure. On the other hand, the throttle point 28 can be used to make a current setting.

Claims (12)

  1. A hydraulic system with an adjustable hydraulic pump (10), whose output pressure can be controlled in dependence on a pressure present on a load signal port (18), a reservoir (22), at least one hydraulic function (12, 14) with a feed line (34) and a valve arrangement (16) arranged between the hydraulic pump (10), the reservoir (22) and the hydraulic function (12, 14), this arrangement comprising a control slider (26) of a valve (24), on which a spring force acts and which is urged into a closed position by a pressure acting on its first end and into an open position by a pressure acting on its second end, characterized in that the valve (24) is arranged in a control connection between the feed line (34) and the load signal port (18) and opens and closes this and in that the valve (24) further opens a passage (76) between the pump outlet and the feed line (34) in its open position and blocks this passage (76) in its closed position.
  2. A hydraulic system according to claim 1, characterized in that the hydraulic function (12, 14) is in the form of an open hydraulic system and in that the control slider (26) of the valve (24) is subjected at one end to the force of a spring (40) and the pressure obtaining in the reservoir (22) and is urged thereby into a closed position and is subjected at the other end to the pressure in the feed line (34) and is urged by this into an open position, in which a control connection is opened between the feed line (34) and the load signal port (18).
  3. A hydraulic system according to claim 1, characterized in that the hydraulic function (13, 14) is in the form of a closed hydraulic system and in that the control slider (26) of the valve (24) is subjected at one end to the force of a spring (40) and the pressure obtaining in the feed line (34) and is urged by this into a closed position, and is subjected at the other end to the pump pressure and is urged by this into an open position, in which a control connection is opened between the feed line (34) and the load signal port (18).
  4. A hydraulic system according to any of claims 1 to 3, characterized in that means (42, 44) are provided through which different pressures can be applied selectively to the first and second ends of the control slider (26).
  5. A hydraulic system according to claim 4, characterized in that, when using a hydraulic function (12, 14) with an open hydraulic circuit the first end of the control slider (26) can be connected by the means (42, 44) to the reservoir (22) and the second end of the control slider (26) to the feed line (34) and in that, when using a hydraulic function (13, 14) with a closed hydraulic system, the first end of the control slider (26) can be connected by the means (42, 44) to the feed line (34) and the second end of the control slider (26) to the pump output.
  6. A hydraulic system according to any of claims 1 to 5, characterized in that the pump output is connected to the feed line (34) through a channel (36) containing an orifice (38).
  7. A hydraulic system according to any of claims 1 to 6, characterized in that a shuttle valve (52) is provided, to which the pump pressure and the pressure in the feed line (34) are applied and which selectively applies the higher of the two pressures to the second end of the control slider (26).
  8. A hydraulic system according to any of claims 1 to 7, characterized in that the load signal port (18) is connected to the reservoir (22) through a restriction (20).
  9. A hydraulic system according to any of claims 1 to 8, characterized in that an adjustable restriction (28) is disposed in the connection between the pump output and the feed line (34).
  10. A hydraulic system according to any of claims 1 to 9, characterized in that a check valve (30) is provided between the output of the valve (24) and the feed line (34) and allows fluid flow only from the valve (24) to the feed line (34).
  11. A hydraulic system according to claim 10, characterized in that the check valve (30) is bypassed by a restriction (32)
  12. A hydraulic system according to any of claims 1 to 11, characterized in that a check valve (50) is provided between the feed line (34) and the reservoir (22) and allows fluid flow only from the reservoir (22) to the feed line (34).
EP94104713A 1993-04-05 1994-03-24 Hydraulic system for supply of open or closed hydraulic functions Expired - Lifetime EP0620371B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE4311191A DE4311191C2 (en) 1993-04-05 1993-04-05 Hydraulic system for supplying open or closed hydraulic functions
DE4311191 1993-04-05

Publications (2)

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EP0620371A1 EP0620371A1 (en) 1994-10-19
EP0620371B1 true EP0620371B1 (en) 1997-09-03

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EP94104713A Expired - Lifetime EP0620371B1 (en) 1993-04-05 1994-03-24 Hydraulic system for supply of open or closed hydraulic functions

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US (1) US5419129A (en)
EP (1) EP0620371B1 (en)
AT (1) ATE157747T1 (en)
CA (1) CA2120052C (en)
DE (2) DE4311191C2 (en)
DK (1) DK0620371T3 (en)

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Also Published As

Publication number Publication date
DK0620371T3 (en) 1998-04-20
DE4311191A1 (en) 1994-10-13
CA2120052A1 (en) 1994-10-06
DE4311191C2 (en) 1995-02-02
US5419129A (en) 1995-05-30
ATE157747T1 (en) 1997-09-15
DE59403919D1 (en) 1997-10-09
EP0620371A1 (en) 1994-10-19
CA2120052C (en) 1999-11-02

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