EP2344700B1 - Device for compensating for hydraulic effective pressures - Google Patents

Description

The invention relates to a device for compensating hydraulic effective pressures in a hydraulic accumulator and in a Hydroaktuator a hydraulic system with a directional control valve for blocking a fluid connection between the Hydroaktuator and the hydraulic accumulator, the directional control valve in its release state establishes a direct fluid connection between the hydraulic actuator and the hydraulic accumulator and this Disconnects fluid communication in its blocking state, and a control valve means having a leading from the directional control valve to the hydraulic accumulator storage line leading from a piston side of the lifting cylinder to the directional valve first line branch and leading from a rod side of the lifting cylinder to the directional control valve second line branch, in response to the transfer of the Directional valve can be activated in the blocking state, which makes a pressure equalization when exceeding a predetermined difference of the effective pressures and which contains a drain valve, the by a e, the predetermined size exceeding difference of the effective pressures can be blocked in its release state in which a pressure difference reducing discharge path to the tank side of the hydraulic system is formed.

In hydraulic systems in which hydroactuators are used, for example for support or lifting systems, it is state of the art, for cushioning or movement damping of moving through the hydraulic actuator components, hydraulic accumulator as hydraulically coupled to the actuator Insert spring or damper element. In some work situations such systems, however, an unsprung, rigid operative connection between the actuator and the device operated by this required, for example, if it is a hydraulically operated boom, which is to form a rigid support element, or uni a working device, the vibration-free controlled in use shall be. In view of these requirements, the connection between the relevant actuator and the hydraulic accumulator must be blocked. When working with locked suspension, the differential pressure in the hydroactuator changes according to the work to be performed by this. Now, if the system is transferred from the state of the locked suspension back into the state with activated hydraulic accumulator, leads a difference in the differential pressure between the hydraulic accumulator and actuator to an uncontrolled movement on the actuator, which is a threat to the system and a security risk for system operators.

A device of the type mentioned is out EP 1 571 267 A2 known. The known suspension device is characterized in that the storage device is brought to approximately the same pressure before activating the suspension, which is present as a support pressure in the drive part, and that for the pertinent adjustment of the accumulator pressure, a differential pressure switch is used. As control pressures are applied to the pressure difference switch on the one hand, the accumulator pressure of the memory device, which is tapped at a corresponding node, and on the other hand, the pressure in the connecting line between the drive part and the directional control valve, more precisely in the first leg. Two further inputs of the differential pressure switch open respectively to the control input side of a charging valve and a discharge valve. Depending on the pressure difference between the storage pressure of the storage device and the piston-side pressure in the first leg of the line, the accumulator pressure is increased via the charging valve or lowered via the drain valve.

In the known device, the hydraulic accumulator is loaded as part of the storage device directly from the hydraulic system of the working machine, here a wheel telehandler. As a result, the risk of uncontrolled movement when transferring the system from the state of the locked suspension is avoided in the state with released suspension because the respective effective pressures of the hydraulic accumulator and the Hydroaktuators are adapted to each other.

The object of the invention is to realize a compensation of hydraulic working pressures with a smaller number and a simpler, less susceptible to malfunctioning design of components.

This object is achieved by a device having the features of claim 1 in its entirety. A device according to the invention for compensating hydraulic effective pressures in a hydraulic accumulator and in a hydraulic actuator having at least one lifting cylinder of a hydraulic system is characterized in that in order to bypass the directional valve in the blocking state from the first and second line branch respectively a fluid path is guided to the storage line, and that in the respective fluid path directed to the piston or rod side check valve arranged such that from the piston or rod side of the lifting cylinder forth each of the higher differential pressure across the respective fluid path by opening the respective check valve at a pressure in the hydraulic accumulator excess pressure differential at the piston or Bar side is releasable, can be guided over the storage line to the hydraulic accumulator.

If in the state of the locked suspension of effective pressure in the hydraulic accumulator is less than the given in the respective working situation differential pressure in Hydroaktuator, a pressure compensation in a conventional manner simply take place in that the hydraulic actuator via a check valve, the hydraulic accumulator to the constant pressure charges the Check valve closes when pressure equality. A particular advantage of the invention, however, is that when prevailing in the hydraulic accumulator higher pressure this is reduced by pressure release to the tank side of the hydraulic system out. By the control valve device ensures that the equalization of the effective pressures not only by charging the hydraulic accumulator, but a charging of the hydraulic accumulator can be done only up to a pressure level at which the prescribed pressure difference is not exceeded, because upon reaching this pressure difference of the pressure compensation over the Discharge valve to the tank side of the system out.

In a preferred application of the invention is provided as Hydroaktuator at least one lifting cylinder of a working machine, the lifting force generating piston side and the rod side are connected to a control block of the machine, the piston side of the lifting cylinder via the directional control valve with the hydraulic accumulator is connected and the control valve means a connection to the hydraulic accumulator and fluid paths to the piston side and the rod side of the lift cylinder, both of which fluid paths contain check valves that release the fluid path only to the higher effective pressure side leading the lift cylinder.

In a particularly advantageous manner, the arrangement can be made such that a discharge valve is provided in the form of a pressure balance, which releases in the release state leading to the tank side discharge path from the connection with the hydraulic accumulator ago and released from the respective, leading to the lifting cylinder fluid path.

To avoid noise or damage to the hydraulic accumulator, the arrangement may be such that the discharge process from the reservoir to the tank side only occurs when the pressure difference is slightly greater than zero. It can be effective on the pressure compensator a the effect of the closing pressure amplifying bias.

In particularly advantageous embodiments, the pressure compensator on a spool, which is loaded for its displacement in the locking position on a piston surface both with the closing pressure from the hydraulic circuit and is loaded with the force of a biasing spring.

• Fig. 1 eine schematisch vereinfacht gezeichnete Seitenansicht einer mobilen Arbeitsmaschine in Form eines Radladers, versehen mit einem Ausführungsbeispiel der erfindungsgemäßen Vorrichtung;
• Fig. 2 eine Symboldarstellung der Schaltung des Hydrauliksystems des Ausführungsbeispieles der erfindungsgemäßen Vorrichtung, dargestellt im Betriebszustand mit freigegebener Federung;
• Fig. 3 eine der Fig. 2 entsprechende Darstellung, wobei der Betriebszustand mit einem Wirkdruck im Hydrospeicher, der kleiner ist als der Wirkdruck auf der Kolbenseite des Hubzylinders, eingezeichnet ist;
• Fig. 4 eine entsprechende Darstellung, wobei der Wirkdruck im Speicher größer als auf der Kolbenseite des Hubzylinders ist;
• Fig. 5 eine entsprechende Darstellung, bei der der Wirkdruck auf der Stangenseite des Hubzylinders größer als auf der Kolbenseite oder im Hydrospeicher ist;
• Fig. 6 eine Funktionsskizze einer als Ablassventil des Ausführungsbeispieles dienenden Druckwaage;
• Fig. 7 eine Symboldarstellung der Druckwaage von Fig. 6 und
• Fig. 8 einen Längsschnitt eines als Druckwaage dienenden Schieberventils, das in einen nicht dargestellten Ventilblock einsetzbar ist.

The invention with reference to an embodiment shown in the drawing will be explained in detail. Show it:

• Fig. 1 a schematically simplified drawn side view of a mobile machine in the form of a wheel loader, provided with an embodiment of the device according to the invention;
• Fig. 2 a symbol representation of the circuit of the hydraulic system of the embodiment of the device according to the invention, shown in the operating state with released suspension;
• Fig. 3 one of the Fig. 2 corresponding representation, the operating state with an effective pressure in the hydraulic accumulator, which is smaller than the differential pressure on the piston side of the lifting cylinder, located;
• Fig. 4 a corresponding representation, wherein the differential pressure in the memory is greater than on the piston side of the lifting cylinder;
• Fig. 5 a corresponding representation in which the differential pressure on the rod side of the lifting cylinder is greater than on the piston side or in the hydraulic accumulator;
• Fig. 6 a functional diagram of serving as a drain valve of the embodiment pressure compensator;
• Fig. 7 a symbolic representation of the pressure balance of Fig. 6 and
• Fig. 8 a longitudinal section of a pressure compensator serving as a slide valve, which is used in a valve block, not shown.

The Fig. 1 shows a mobile machine in the form of a wheel loader 1, with the blade 3, a lifting cylinder 5 is coupled. This forms the Hydroaktuator of the embodiment of the device according to the invention to be described here. Accordingly, in the pressure supply, the lifting force for the blade 3 generating piston side 7 of the lifting cylinder 5 on the in Fig. 1 not shown hydraulic components with a in Fig. 1 only symbolically indicated hydraulic accumulator 9 in conjunction.

The Fig. 2 to 5 show in symbol representation, the circuit of the hydraulic system in each case different operating conditions. Fig. 2 shows the condition with released suspension. A control block 13 of the working machine (wheel loader 1) with a pressure supply device, which is not shown, is connected to the controlled supply of the lifting cylinder 5 with the piston side 7 and the rod side 15. A valve assembly 11 forming the main part of the hydraulic system has inputs 17 and 19 to which the piston side 7 and the rod side 15 of the lifting cylinder 5 are connected. At outputs 21 and 23 of the valve assembly 11 of the hydraulic accumulator 9 and the tank 25 of the hydraulic system are connected.

As mentioned in Fig. 2 the state of the released suspension is shown. In this case, there is a directional control valve 27 due to its mechanical spring bias 29 in its release state, the piston side 7 is connected at the port 17 directly to the hydraulic accumulator 9 at the output 21 and the rod side 15 of the lifting cylinder 5 via the input 19 directly to the tank 25 at the output 23 are connected. In this operating state, the other hydraulic components are not involved in the operation, ie that the system causes a conventional suspension / damping of the activity of the lifting cylinder 5.

As mentioned, suspension is unfavorable or harmful in certain work situations. When a blade 3 of a loader 1 is actuated, for example, a compression or rebounding with regard to the accuracy of the position adjustment of the blade 3 has an unfavorable effect. The transfer of the system in the state of the locked suspension happens in such a way that by supplying a hydraulic control pressure via a control line 50, the directional control valve 27 is brought against the bias voltage 29 in the blocking state, which will be explained in more detail below.

The Fig. 3 to 5 illustrate three different operating modes with each suspension suspension. This refers to the Fig. 3 to the state in which the operating condition on the piston side 7 of the lifting cylinder 5, a higher effective pressure prevails as in the hydraulic accumulator 9. Accordingly, in Fig. 3 shown with thicker line drawn the higher pressure fluid connections, namely from the input 17 of the valve assembly 11 to the locked directional control valve 27 via a first line branch 31 and the first line branch 31 via a dicklinig dashed closing pressure control line 33 to a control port 35 of a drain valve 37th This control connection 35 is referred to here as a second control connection. According to the prevailing in the first leg 31 differential pressure, which is higher than that in the marked with thin line second leg 39 at the entrance 19 and on the rod side 15 of the lifting cylinder 5, connected to the first line branch 31 first check valve 41 is opened so that about a storage line 43 of the memory 9 is charged at the output 21 to the pressure of the piston side 7. In this state, the second check valve 45 is closed in the same direction as the first-mentioned check valve 41 between the storage line 43 and input 19. This arrangement of the check valves 41 and 45 causes from the inputs 17 and 19 forth each of the higher effective pressure via a respective fluid path, which is formed by opening one or the other check valve 41, 45, in the system takes effect. Furthermore, another check valve 46 is connected in the connecting line to the memory 9 between the two connection points of the first and second check valve 41 and 45, which is directed to the memory 9 in its pertinent closed position.

Another control port 47 of the drain valve 37, which is referred to here as the first control port, via a control valve 49, if this in his in Fig. 3 shown opening state is connected to the storage line 43, which in turn, according to one or the other fluid path, that is, depending on which of the check valves 41 or 45 is opened, is connected to the input 17 or the input 19. At the in Fig. 3 the state over the first check valve 41 leading fluid path to the higher differential pressure leading input 17. The prevailing over the open control valve 49 at the first control port 47 pressure also serves as a hydraulic control pressure, the directional control valve 27, by its spring tension 29 in the opening state is biased, hydraulically in the in Fig. 3 shown closed state and thus brings the entire system in the state of the locked suspension.

At the in Fig. 2 the previously-mentioned released suspension state is the control valve 49 in its closed state, which is caused by its actuating magnet 51 is energized, so that the valve 49 is closed against its opening spring 52. As a result, in the state of the released suspension, the first control connection 47 of the discharge valve 37 and the control line 50 of the directional valve 27 are depressurized by connection to the tank side 25. The bias voltage 29 therefore keeps the directional control valve 27 in its open state. If the energization of the actuating magnet 51 is interrupted and the control valve 49 is opened, then via the control line 50, the directional control valve 27 against its bias 29 hydraulically controlled in the locked state and the system goes into the state of the locked suspension, as in Fig. 3 to 5 is shown.

At the in Fig. 3 shown state where the prevailing in the first leg 31 higher effective pressure on the first check valve 41 and the storage line 43, the hydraulic accumulator 9 prevail at the first control port 47 and the second control port 35 of the discharge valve 37 each have the same pressures, namely via the control line 33 from the input 17 ago and via the open first check valve 41 and the open control valve 49 also from the input 17 ago. As a discharge valve 37, a pressure compensator is provided, which is in this steady-state pressure at the control terminals 47 and 35 in the closed state. In this closed state, the discharge valve 47 does not form a discharge path from the inlet connection 53 to an outlet connection 55 which leads via a discharge line 57 via the outlet 23 to the tank 25. From the storage line 43, which is connected via an overpressure protection forming pressure relief valve 59 to the output 23 and the tank 25, therefore, no discharge process takes place. A likewise connected to the storage line 43 drain valve, which is opened manually only for maintenance purposes, is denoted by 61.

The Fig. 4 shows in contrast a state in which, also with locked suspension, the differential pressure in the hydraulic accumulator 9 is higher than the operational condition on the piston side 7 of the lifting cylinder 5 and thus via the input 17 in the valve assembly 11 effective system pressure. To do this in Fig. 4 to illustrate, the storage line 43 is shown in the Fig. Upper part with a thick solid line and in its lower part of the pipe with a thick dashed line. According to the prevailing in the hydraulic accumulator 9 higher effective pressure than in the lifting cylinder 5, the first check valve 41 is closed.

The higher effective pressure of the hydraulic accumulator 9 is thus applied to the first control connection 47 of the discharge valve 37 via the non-energized control valve 49 which is opened by the spring tension 52, while the second control connection 35 leads via the line branch 31 to the lower differential pressure of the input 17.

As already mentioned, the discharge valve 37 has a pressure compensator, which in Fig. 7 in symbol representation and in Fig. 6 is shown in the form of a functional sketch. Fig. 8 shows a longitudinal section of a practical embodiment. As can be seen, it is a slide valve with the valve housing 63 axially movable slide piston 65, shown in the closed position, which is effected by a force acting on the second control port 35 hydraulic closing pressure, reinforced by a mechanical biasing force, the Fig. 6 and 7 designated 67. The discharge valve 37 opens by an opening hydraulic pressure acting on the first control port 47, provided that the opening pressure at the spool 65 causes a higher opening force than the closing pressure prevailing at the control port 35, amplified by the biasing force 67. In other words, condition is that the discharge valve 37 opens to form a discharge path from the inlet port 53 to the outlet port 55 and thus to the tank 25, that applies to the forces acting on the spool 65 forces, the closing force resulting from the pressure at the second control terminal 35, plus the mechanical bias 67th results, is lower than the opening force, generated by the hydraulic pressure at the first control terminal 47th So: $${\mathrm{F}}_{\mathrm{Vorspa}\mathrm{,}}\mathrm{+}{\mathrm{F}}_{\mathrm{print}\mathrm{35}}\mathrm{<}{\mathrm{F}}_{\mathrm{print}\mathrm{47}}$$

In the state of Fig. 4 Accordingly, the pressure from the hydraulic accumulator 9 is discharged so far, according to the interpretation of the discharge valve 37 forming pressure compensator, namely the effective piston surfaces and the effective biasing force 67, only a given, intended, low pressure surplus between memory 9, and thus the input terminal 53, relative to the control terminal 35, ie the lifting cylinder 5, remains. This means that a discharge process can not lead to the reduction of the pressure in the hydraulic accumulator 9 to the value zero.

In an advantageous embodiment, it can be provided here that a pressure level of about 8 bar is present as the opening pressure difference predetermined by the piston geometry and the prestressing force 67. The Fig. 8 shows an embodiment in which engage on a two-part spool 65 for generating the biasing force 67, two coil springs 69 and 71 which bias the piston 65 in the figure to the right in the illustrated closed position, in which the input terminal 53, located in the in Fig. Right side axial end of the valve body 53 is located opposite the output port 55 is locked. In addition to the biasing force 67, the hydraulic pressure of the second control port 35 acts on the left side of the piston 65 in FIG ,

In order to ensure that the pressure at the inlet port 53 does not become effective as an effective control pressure which determines the behavior of the pressure compensator, it is essential that the pressure in Fig. 6 at 73 indicated piston surface, to which the control edges 75 and 77 adjacent to the terminals 53 and 55, is substantially smaller than the effective piston surfaces 79, 79a and 81 at the pressure chambers at the control port 47 and control port 35th

The Fig. 5 refers to a further state in which at the input 19 of the valve assembly 11, the higher effective pressure prevails, compared with the Pressure at the input 17 or the pressure in the hydraulic accumulator 9. Such an operating condition arises when running a device on an obstacle when operating a work machine with locked suspension. This may for example be the case when a mobile device, such as a wheel loader 1, runs with its blade 3 on an elevation forming an obstacle, whereby the standing on the blade 3 weight of the wheel loader 1, the piston of the respective lifting cylinder 5 in the rod side 15th shifts, creating an overpressure on the rod side 15. Via the inlet 19 and the second check valve 45 opening in this state, this overpressure is effective, as well as via the open control valve 49 at the first control port 47 of the drain valve 37, so that in the fulfillment of the opening condition, ie a higher pressure at the port 53 relative to the Control terminal 35 which is connected via the first line branch 31 to the input 17, the discharge valve 37 opens, which in turn the discharge path to the tank 25 is opened, whereby the pressure relief of the storage line 43 is carried out. The higher pressure in the control port 47 ensures that the valve 37 is not in the locked position.

How the particular Fig. 6 and 8th show, the actual pressure compensator is formed by the coil spring 69 and by the effective pressure surfaces of the axially displaceable spool 65. The locking piston is designed as a control slide is in turn formed by the coil spring 71 and the effective piston surface 81 of the said piston piston part. The one with 65 in Fig. 6 designated piston can, as in Fig. 6 imaged to be made in several parts to form such a check valve, that is, the multi-part design prevents when the port 55, a higher pressure than the pressure is formed by the biasing forces of the coil springs 69 and 71 plus the effective pressure force through the Pressure at the second control port 35, it to open the valve seat 55 and so far to an unwanted backflow the fluid enters the system. If you want to dispense with the pertinent check valve function, the indicated spool assembly can also be integrally formed (not shown).

By the invention is thus ensured that is given as a safety function of the pressure equalization in all modes. It is understood that the construction of the drain valve 37, as shown by the Fig. 6 and 8th is not mandatory. Any valve construction whose function corresponds to the above-mentioned opening and closing conditions can be used. Also, the in Fig. 8 shown construction of the two-part slide piston 65 is not mandatory, in which the piston part located on the right in this figure at the input port 53 forms a check valve, which is loaded by the designated spring 69 with low closing force. In this construction, the designated 71 closing spring forms the main part of in Fig. 6 and 7 with 67 designated bias, which increases the closing force of the valve.

Claims (11)

1. A device for compensating for hydraulic effective pressures in a hydraulic accumulator (9) and in a hydraulic actuator of a hydraulic system having at least one lifting cylinder (5), comprising

   - a directional valve (27) for blocking a fluid connection between the hydraulic actuator (5) and the hydraulic accumulator (9), in its release state the directional valve (27) establishing a direct fluid connection between the hydraulic actuator (5) and the hydraulic accumulator (9) and interrupting this fluid connection in its blocked state, and

   - a control valve means (11) which has an accumulator line (34) leading from the directional valve (27) to the hydraulic accumulator (9), a first line branch (31) leading from a piston side (7) of the lifting cylinder (5) to the directional valve (27), and a second line branch (39) leading from a rod side (15) of the lifting cylinder (5) to the directional valve (27), which can be activated depending on the transfer of the directional valve (27) into the blocked state, which carries out pressure compensation when a predetermined difference of effective pressures is exceeded, and which contains a drainage valve (37) which can be blocked by a difference of effective pressures exceeding the predetermined value into its release state in which a drainage path (57) which reduces the pressure difference is formed toward the tank side (25) of the hydraulic system,

   - characterised in that in order to bypass the directional valve (27) in the blocked state of the first (31) and second line branch (39) a respective fluid path to the accumulator line (43) is taken; and

   - that there is arranged in the respective fluid path a non-return valve (41, 45) directed towards the piston or rod side (7, 15) such that from the piston or rod side (7, 15) of the lifting cylinder (5) respectively the higher effective pressure can be carried via the respective fluid path, which can be cleared on the piston or rod side (7, 15) by opening the respective non-return valve (41, 45) with an effective pressure exceeding the pressure in the hydraulic accumulator (9), and via the accumulator line (43) to the hydraulic accumulator (9).
2. The device according to Claim 1, characterised in that the hydraulic actuator is at least one lifting cylinder (5) of a machine (1) the piston side (7) of which producing a lifting force and the rod side (17) of which are connected to a control block (13) of the machine (1).
3. The device according to any of the preceding claims, characterised in that there is a drainage valve in the form of a pressure compensator (37) which in the release state clears the drainage path (57) leading to the tank side (25) from the accumulator line (43) to the hydraulic accumulator (9) and from the respectively cleared fluid path leading to the lifting cylinder (5).
4. The device according to any of the preceding claims, characterised in that the pressure compensator (37) has an input port (53) connected to the hydraulic accumulator (9), an output port (55) connected to the tank (25), a first control port (47) for the supply of an unblocking pressure, and a second control port (35) for the supply of a closing pressure.
5. The device according to any of the preceding claims, characterised in that the second control port (35) is connected to the piston side (7) of the lifting cylinder (5).
6. The device according to any of the preceding claims, characterised in that a preload (67) which amplifies the action of the closing pressure on the second control port (35) takes effect on the pressure compensator (37).
7. The device according to any of the preceding claims, characterised in that the pressure compensator (37) has a slide valve piston (65) which for its displacement into the blocking position on one piston area (81) can be loaded both with the closing pressure prevailing on the second control port (35) and also with the force of a preload spring (69, 71), and that the other piston area (79a) can be loaded with the unblocking pressure which prevails on the first control port (47).
8. The device according to any of the preceding claims, characterised in that the effective piston area (81) of the slide valve piston (65) which borders the second control port (35) is greater than the effective piston area (79) which borders the first control port (47).
9. The device according to any of the preceding claims, characterised in that the input port (53) of the pressure compensator (37) on the end of the slide valve piston (65) opposite the preload spring (69, 71) is formed by the axial end-side opening of the slide housing (63), and that there is one control edge (77, 75) at a time on the assigned end region of the slide valve piston (65) and on the slide housing (63) between its end-side opening and the first control port (47) which is offset axially to the inside in the housing (63).
10. The device according to any of the preceding claims, characterised in that the directional valve (27) is mechanically preloaded into the release state and can be hydraulically directed into the blocking state.
11. The device according to any of the preceding claims, characterised in that in the opening state a control valve (49) connects the fluid path of the control valve means (11) which carries the higher effective pressure to the first control port (47) of the pressure compensator (37) and delivers to the directional valve (27) the hydraulic pressure which blocks it.

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