DE2834421A1 - STEERING VALVE WITH CLOSED CENTER - Google Patents

Description

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Field of application, state of the art

The invention relates to a steering valve with a closed center, in which the inlet of a pressure source is closed in the neutral position. Such a thing In contrast to one with an open center, the steering valve has a constant neutral flow of the fluid requires the advantage that when the steering is not actuated because of the lack of circulation losses, less energy is consumed.

Such steering valves are mainly used in hydraulic steering systems, so those in which one mechanical connection between the actuating device (steering handwheel) and a servomotor for the one to be steered Vehicle parts consists. Here hydraulic support is only available when cornering, but not when driving straight ahead, for example on motorways, so that considerable energy savings can be achieved when driving straight ahead is.

The invention is also applicable to hydrostatic steering, that is, those in which a mechanical connection is not present between the actuating device and the servomotor. Vehicles equipped in this way are for high speeds are not permitted. Here, however, there should be an energy loss due to the circulation of the fluid. should be avoided if a certain steering angle remains unchanged, for example if a work machine carries out work with the steering angle unchanged, at rest or in motion.

Steering valves with a closed center are also used with advantage in steering systems with central hydraulics, so that for other consumers such as brakes or a level

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regulation of full working pressure

Steering valves with a closed center, in which one or two seat valves are provided on the inlet side, are known from DS-OSn 21 Jl 2j6 and 24 46 841 and DE-AS 1 186 747. These seat valves are closed in the neutral position, so that no circulation losses then occur.

When the steering is turned, the or one of the inlet seat valves is mechanically activated after the response play has been used up Stop, i.e. sudden rigidity of a connection from the actuating device to the valve. As a result, pressure fluid suddenly shoots into the respective pressure chamber of a servomotor too much for the jammed vehicle parts. The episode is one Discontinuity in the attachment process that occurs in steering valves of this type could not be eliminated so far.

Task and solution

The present invention seeks to provide a closed center steering valve with poppet valves, which work in such a way that no discontinuity occurs during the articulation process, but with the advantage of a proportional reaction should be retained from the pressure chamber to the actuating device.

This object is achieved by the invention according to claim 1 solved..

Seat valves according to claim 1 can, in addition to the inlet from the pressure source to the servomotor, also in the return from the servomotor be arranged to an equalizing tank. In the case of poppet valves according to the prior art, the Valve body closed by the pressure prevailing in the inlet chamber of the valve against the force of the closing spring held. The combustion chamber is therefore the inlet chamber for the valve. In the invention, the arrangement is just the opposite:

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The spring space is the drain space and the closing spring holds the valve is closed against the pressure drop at the valve, i.e. in the neutral position for the inlet seat valves against the full pressure of the pressure source.

The locking force of the closing spring is reduced by introducing manual force. This reduces the pressure difference between the inlet and outlet areas of the valve. The drain space of the valve is in communication with one of the Working spaces of the servomotor. The reduction in the pressure difference means a controlled build-up of pressure in the Working space depending on the manual force applied.

By applying manual force to the closing spring instead of the valve body, there are discontinuities in the articulation process avoided.

For the principle of the invention, it is irrelevant whether a power transmission to the control spring (s) is tapped directly from a steering spindle, from a part of a steering gear or a part following the steering gear.

Developments of the invention

A further development according to claim 2 enables the seat valves to be installed in a favorable manner in the steering valve. One of the rotating parts can be operated from the steering spindle, while the other has a pinion, which engages in a rack or actuates a hand and posing pump for a hydrostatic steering system.

By a development according to claim 3, the closing spring the seat valve or valves designed so that they can be accommodated well in one of the rotating parts or between the rotating parts and that there is a relatively large amount of space for spring material

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is available.

In steering systems, in particular for passenger cars, a steering behavior is desired in which the relationships between the hydraulic servo pressure and the manual force are different in three areas. In one area on both sides of the neutral position, only manual force should act on the steering. Beyond a certain limit force, the pressure in the working space of the servomotor should increase linearly with manual force, whereby initially relatively large changes in manual force are required for each change in pressure and then beyond the so-called cut-off point, the pressure rises sharply with only minor changes in manual force. These two areas are called "fine tax area ^v" and "cut-off area". The fine control area is essential for normal driving, where only lower steering forces are required, whereas the cut-off area is necessary for parking.

By a development according to claim 5, the steering valve designed so that it has different effects in the fine control area and cutting area. It is In addition, a fine control spring is provided, which is only effective in the fine control range. The clipping point becomes reached when the travel of the fine control spring is used up. In cooperation with the torsion spring, the particular can be designed as a torsion bar, there is a relatively large angle of rotation in the fine control range. At the By twisting the torsion spring, the manual force introduced is split up into a portion that is directly referred to as mechanical Steering portion is passed on from one to the other rotating part, and into another portion that is directed to the The closing spring of the seat valve acts. This results in a flat rise in the characteristic curve in the fine control range of the working pressure over the hand force.

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As soon as the cut-off point is reached, there is an increase hand force fully on the closing spring. Since no significant twisting path is required for this is, the torsion spring is practically no further twisted in the cut-off area. This achieves at only slight further increase in handicraft, large increases in pressure.

By a development of the invention according to claim io v / earth seat valves created that are independent of the pressure in the inlet chamber. Such valves are suitable for non-constant Pressure sources, for example pumps with accumulator charging valves with switching differential.

According to a development according to claim 16, there are two Seat valves are arranged within the rotating parts in such a way that one steering direction is one, and one is the other other opens.

His further development according to claim 17 relates to the case that both seat valves have separate drainage spaces, of which, for example, one with the one Working space and the other are connected to the other working space of the servomotor.

A further development according to claim 18, on the other hand, relates to the case where both seat valves share a common drainage space to have. Such an arrangement is applicable, for example, when a device, the "pressure fluid dem Allocates one or the other working space of the servomotor, basically just a single seat valve connected upstream shall be. Since this seat valve must open in both steering directions, it is here by two seat valves shown, of which only one comes into operation. Spring material is saved here as a result, that both seat valves have a common closing spring.

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Explanation of the invention

Embodiments of the invention are described below with reference to the drawings.

1 and 2 show in cross section and axial section, respectively, a steering valve with a first embodiment of FIG Seat valves.

Fig. 3 shows a desired characteristic of the steering system.

FIG. K shows a second embodiment of a seat valve in cross section corresponding to FIG.

Fig. Ka. Shows a detail of a variant of the second embodiment.

FIG. 5 shows, in a cross section corresponding to FIG. 1, a third embodiment of a seat valve, namely a pressure balanced valve.

6 and 7 are schematic circuit diagrams of hydraulic steering systems in which seat valves according to the invention are usable.

FIG. 8 shows, in a cross section corresponding to FIG. 1, two seat valves which can be actuated in opposite directions and which have a common one Closing spring and

Fig. 9 shows characteristics of a hydraulic steering system accordingly Fig. 7

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First embodiment

The embodiment according to FIGS. 1 and 2 shows a steering valve , in which two parts rotatable one inside the other and in a housing ("rotating parts") for holding and actuating zv / ei inlet seat valves are used. The rotating parts can after Are a rotary valve to form outlet adjustment throttles serve, which is not shown here and is not the subject of the present invention.

An outer rotating part 12 is rotatably mounted in a housing 10 with a seal. Inside the outer rotating part 12, an inner rotating part 14 is rotatably mounted. Both rotating parts are connected to one another by a torsion spring bar Io. The right end of the torsion spring bar is anchored in the inner rotating part 14, the left end in the outer rotating part 12 in a rotationally fixed manner. In the outer rotating part 12 two annular chambers l8a and l8b are provided, each with a working space here are not shown servomotor in connection. The servomotor acts on the steered vehicle parts. One the rotating part, preferably the inner rotating part 14, is non-rotatable with the steering spindle to be actuated by the steering handwheel connected, the other rotating part with the steered vehicle parts, for which purpose it has a rack pinion 20 which engages in a rack 21.

In the outer rotating part 12 and its annular chambers 18a and -b, the two inlet seat valves 22a and -b are housed. The arrangement of the seat valve 22a is described with reference to FIG. 1. Indices "a" are largely omitted here. The seat valve has a valve seat 24 in the outer rotating part 12. The inlet chamber 28 of this seat valve has

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a connection to the pressure source through a longitudinal channel 30 in the outer rotating part 12. The longitudinal channel 30 is standing via an inclined channel 32, a room 33 and a Axial channel 34 in connection with the pressure source. In each of the two annular chambers l8a and -t> is a closing spring provided in the form of an approximately circular arc-shaped spiral spring. In the following it is called "bow spring" called. It is shown in Fig. 1 only with 36, in Fig. denoted by 36a and b, respectively. The top left end (Fig. L) the bow spring 36 presses a valve ball 38 against the Valve seat 24, while its right upper end in a Recess 39 of the outer rotating part 12 is supported. The force with which the bow spring 36 the valve ball 38, corresponds to the generally constant pressure of the pressure source plus a certain overpressure. The bow spring 36th is only at its two upper ones Fixed ends and is otherwise free in the annular chamber l8.

For pressure control in the fine control area is also a fine control spring, here in the form of a helical compression spring 40, is provided. Your left end is supported on the bow spring 36 near the end of the valve body from and surrounds a stop pin 42. The right end of the Helical compression spring 40 is supported on a collar 44 of a pin 46 which is displaceable in the outer rotating part 12 is mounted, in a direction approximately tangential to the circumference of the inner rotating part 14. The right end of the pin 46 can -of a nose 48 of the inner rotary part 14 to be pressed to the left against the compression spring 40, the arc spring on the force exerted on the valve ball is reduced more and more. Eventually touched the left end of the pen 46 the right end of the stop pin 42.

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This is the end of the fine control range. In the subsequent cut-off area, the increases The pressure regulated by the poppet valve in the working space with manual force on the steering wheel increases significantly more than in the fine control area. The torsion bar 16 is practically no longer twisted in this case.

In the annular chamber l8b (Fig. 2), the seat valve 22b is housed opposite to the seat valve 22a, namely a mirror image of the perpendicular 50 in Fig'.l, The annular chambers are sealed from one another and to the outside by seals 51.

Function of the first embodiment

When turning the steering wheel, a torque builds up depending on the resistance of the wheels to be steered inner and outer turned part. A certain part of this torque is absorbed by the torsion spring bar 16, the Rest of the compression springs 40 of the two valves. If the inner rotating part 14 is opposite to the outer rotating part 12 rotated clockwise in Fig. 1, the pin 46 compresses the compression spring 40 and decreases thus the locking force of the arc spring 3c acting on the valve ball 38. To the extent that this locking force is dismantled, builds up in the annular chamber l8 and the associated working space of the servomotor Pressure on.

Fig. 3 shows the relationships between one on the steering wheel manual force F exerted and that effective in the respective pressure chamber of the servomotor. Pressure P. When rising the manual force from the neutral position 0 is initially no

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Pressure built up until the limit force G- is reached. there the fine control range begins along straight line 59. » the one for steering on a straight line with small steering angles but a good feeling of the driver for the road surface is essential. Beyond a certain force, .the dem Corresponds to cut-off point A, the pressure should be significantly steeper with only slightly increasing hand force increase, namely along the characteristic curve 60 of the cut-off area.

As Fig. 1 shows, the cut-off point is reached when the left end of pin 46 contacts stop pin 42. The compression spring 40 and the torsion spring bar 16 are then not or only slightly stretched further. With only a little Further increasing manual force results in strong pressure changes according to the straight line oO. (In the clipping area the torsion bar 16 can practically no longer be tensioned, since the path of the arc spring 36 for actuation of the seat valve 22 is negligibly small).

Second embodiment

In the embodiment according to FIG. 4 were the same or very similar components to the first example provided with the same reference numerals. These parts are no longer described here.

Instead of the helical compression spring * 40 there is a spiral spring 52 is provided, the lower, bent and slightly angled end 54 with the help of a clamp 56 on the Bow spring 36 is attached. The pin 46 is in an eccentric transverse bore 58 of the outer rotating part 12

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mounted tangentially to the circumference of the inner rotating part 14 displaceably. It lies between the nose 48 of the inner Rotary part and the upper, free end of the spiral spring 52.

Pig. 4a shows a variant of the second embodiment. Bow spring J> 6 and spiral spring 52 'are formed in one piece here, so that the clip 56 is omitted.

The function of the second embodiment (Fig. 4 or 4a) is practically the same as that of the first. The spiral spring 52 or 52 'is effective in the fine control range. As soon its upper end is a stop surface 57 of the bow spring 36 touches the clipping area.

Third embodiment

In the third embodiment shown in FIG. 5, a pressure-balanced valve is accommodated within the valve bore 67. It has a one-piece component 65, with a thickened, 6y in the valve bore slidable portion 66 69 with longitudinal channels on the left of this section is the here cone-shaped valve body 68. To the right is a piston 70 slidably sealingly in the valve hole 6j is. The effective cross section of the piston 70 is the same as that of the valve seat 24. To the right of the piston 70, a piston 72 of a smaller pressure gauge is provided, which is guided in a suitable bore 74 with a seal. The pistons 70 and 72 abut one another, but can also be designed in one piece. A pressure-relieved annular space 76 is located at the joint between the two pistons. The arc spring 36 engages with a ball extension 77, 78 in recesses in the piston 72 and in the valve body 68.

For the fine control area, there is again a helical compression spring 40 provided between the inner

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Rotary part 14 and the bow spring 36 is effective.

In addition, an additional spring 80 is provided which surrounds a pin 82 connected to the arc spring 36 and between the bow spring 36 and the outer rotating part 12 is effective. The auxiliary spring 80 holds the inlet poppet valve 22 closed when the steering valve is depressurized.

In the embodiments according to FIGS. 4 and 5 is also a second identical valve arranged reversed in a second ring chamber, just like it has been described with reference to FIGS. 1 and 2. Instead of the helical compression springs 40 and 80, spiral springs can be used can be used in the manner of spiral springs 52 or 52 '.

Function of the third embodiment

When the inner rotating part 14 is rotated with respect to one another the outer rotating part 12 counterclockwise in Fig. 5, the locking force is reduced, so that a pressure can build up in the annular chamber l8 which corresponds to the force exerted on the steering handwheel.

The cut-off point is reached again, - when the mutually facing ends of the pin 46 and the stop pin 42 touch each other.

The pressure building up in the annular space 18 acts on the one hand on the valve body 68 in the closing direction, on the other hand in the opposite direction on the piston 72, the cross section of which is smaller than that of the valve seat 24. The pressure in the annular space 18 can, however do not act on the piston 70, since the upstream annular space 76 against the expansion tank is relieved of pressure. This construction ensures that only a part of the pressure effective in the annular space 18

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acts as a locking force on the valve body 68. This part of the pressure or differential pressure is by design the cross-sections of the valve seat and of the piston 72 can be selected as desired. The differential pressure increases with the pressure building up in the annular space 18.

Associated circuits of steering systems

The above-described steering valves according to FIGS. 1, 2, 4 and 4a set constant or only slightly fluctuating supply pressure in advance. They are advantageously supplied by a high pressure pump 84 (FIGS. 6 and 7), which their delivery flow automatically regulates back when the desired high pressure is reached, so that only hydraulic fluid is conveyed is, insofar as it is processed by the steering, and to »make up for leakage losses. With radial piston pumps with suction control, pressure control can be implemented with a simple valve 86. Will turn into the steering system Hydraulic accumulator 88 (FIG. 6) installed, a relatively small high-pressure pump 84 can be used as the accumulator covers short-term consumption peaks in the steering. aside from that

further consumers can be operated with the memory and safeguards can be implemented in the event of a pump failure.

For the embodiment according to FIG. 5, there is a constant supply pressure not mandatory.

Fig. 6 shows in a basic diagram how the inlet seat valves of the three examples described so far can be arranged. The two are connected to an inlet line 89 supplied by the high pressure pump 84 Inlet seat valves 22a and b connected. Her

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Spring chambers or annular chambers l8a and b are connected to the two working chambers 90a and b of the servomotor. In the two drainage lines 92a and b of the working spaces to an expansion tank 94, path-controlled Adjusting throttles 96a and b are switched on. .

Fig. 7 is a schematic diagram of a steering system of others Type in which one for the allocation of hydraulic fluid to the working spaces 90a and b of the servomotor Rotary valve 97 is used. An inlet seat valve 98 is connected between the pressure source and the rotary slide valve. The rotary valve also controls the return from the working spaces to the expansion tank 94. In the return A seat valve I08 is switched on to the expansion tank. The seat valves 98 and I08 can in the same way be designed and operated by common rotating parts. The fourth, described below Embodiment relates to such seat valves. These must be operable in both steering directions.

Fourth embodiment

As Fig. 8 shows, two seat valves 98a and b are provided, which have a common inlet channel 110, which ends in two oppositely facing valve seats 112a and b. Be attached to these valve seats two valve balls 11 4a and b pressed by a common, arcuate closing spring II6. Both valves open into a common drain space IIS, for actuation of the two valves is a cam 120 on the inner rotating part 14, which on two pins 46a and b in opposite directions Acts directions. Both pins are as in the first embodiment (Fig. 1) with collars 44a and b equipped, on which helical compression springs 40 a and b are supported, which in the manner described on the

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Arc or closing spring Ho act.

The puncture is the same for each direction of rotation as described with reference to the first embodiment.

Such a double seat valve can be used both as an inlet seat valve 93 according to FIG. 7 and as an outlet seat valve 108 use.

By appropriately dimensioning the closing springs 116 .and the compression coil springs 40a and b of the valves 98 and I08 it must be ensured that the valve I08 is always one to a pressure difference Zip higher pressure holds the balance than the valve 98. These relationships are shown in FIG. 9. There the characteristic curve 59-60 corresponds to the inlet valve 98 and a characteristic curve 122-12 ^ the outlet valve IO8.

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Claims (1)

ZAHtIRADPABRIK PRIEDRICRSHAFEN λλλ / / Public Company Ζ83442 | Friedrichshafen STEERING VALVE WITH CLOSED CENTER 1.8, 1978 7I-29 S / P Claims Steering valve with a closed center with at least two seat valves, characterized in that - That the spring chamber (18, II8) of the seat valves (22, 112) is the drainage chamber and the closing spring {J> o, Ho) counteracts the force that is created by the pressure drop occurring at the seat valve and - That parts which are in drive connection with the actuation device of the vehicle (14, 46) attack the closing springs in such a way that when the steering wheel is turned, the force of the Steering direction corresponding closing spring is reduced. 2. Steering valve according to claim 1, characterized in that - that it has two mutually rotatable parts (rotating parts .12, 14), - That the first rotating part (12) has at least two valve seats (24, 112) and at least one inlet space (28, 110) contains, 030007/0396 ORIGINAL INSPECTED - 2 - 71-29 - that the at least one closing spring (j> 6, 116) is supported on the valve body (s) (38, 114) and the first rotating part (12) and - That one from the second rotating part (14) can be actuated Plunger (46) on a closing spring (36, 116) in the sense of a reduction in the associated Valve body (38, 68, 114) exerted closing force acts. 3. Steering valve according to claim 2, characterized geke η η -. draws that the second rotary part ( ^r inner rotary part "14) is rotatably mounted within the first (" outer rotary part "12) and that at least one closing spring (36, II6) is held on the outer rotary part, which is arcuate, on one or two valve bodies (38, 68, 114) acts and surrounds the inner rotating part. 4. Steering valve according to claim 3. » characterized, - That the plunger (46) in the outer rotating part (12) can be displaced approximately tangentially to the inner rotating part (14) are housed, - That their inner ends each with an approximately radial surface (48j to 120) of the inner rotating part (14) cooperate and - That their outer ends on the associated closing spring (36, 116) near the valve seat end attack. 030007 / 039Ö 28 34 W. 5. Steering valve according to one of the preceding claims, characterized in that between the outer and inner rotating part (12 ₃ 14) a torsion spring (16) and between the part (46) in drive connection with the actuating device of the vehicle and the closing spring (^ 6, 116) a further spring (fine control spring 40, 52) are arranged in such a way that the part (46) which is in drive connection with the actuating device acts on the closing spring by a direct stop only after the spring travel of the fine control spring has been exhausted. 6. Steering valve according to claim 5, characterized in that the fine control spring is a spiral spring (52, 52 ') is connected to the closing spring (36) is firmly connected (Fig. 4 and 4a). 7. Steering valve according to claim 6, characterized in that the spiral spring (52) to the
Closing spring (36) is clamped. 8. Steering valve according to claim 6, characterized in that the spiral spring (52 ') with the Closing spring (36) is formed in one piece. 9. Steering valve according to claim 5, characterized in that the fine control spring (4o) a Helical compression spring is. 10. Steering valve according to one of the preceding claims, characterized in that - that the seat valves from the pressure in the inlet chamber (28) are independent in that this pressure is applied to mutually opposing equal cross-sections on both sides a valve tappet (66) acts, 030007/0396 - 4 - 71-29 - That the valve tappet is in drive connection with on its side facing away from the valve body (68) a piston (72) guided under a seal, the cross section of which is smaller than that of the valve seat (24) and its free end face from the pressure in the drain and spring chamber (18) is applied and - That the arcuate closing spring (36) presses the valve body (68) and piston (72) against each other (Fig. 5). 11. Steering valve according to claim 10, characterized in that the end face of the piston (72) facing the valve tappet (66 ) is relieved of pressure (space 76). 12. Steering valve according to claim 10 or 11, characterized in that to hold the pressure zero an additional spring (80) is provided which engages the outer rotating part (12) and the closing spring (36) presses against the valve body (68). 13. Steering valve according to claim 12, characterized in that the additional spring (80) on the the end of the closing spring (36) adjacent to the piston (72) acts. 14. Steering valve according to claim 12 or 13, characterized in that the additional spring is a on the closing spring (36) attached is a spiral spring (not shown). 15 · Steering valve according to claim 12 or I3, characterized in that the additional spring (80) is a helical compression spring. .030007 / 0398 - 5 - 71-29 Ιό. Steering valve according to one of the preceding claims, characterized in that there are two Seat valves (22; 98a, 98b ·), one of which can be actuated in one steering direction and the other in the other. 17. Steering valve according to claim l6, characterized in that the two seat valves each have one have arcuate closing spring (36) and axially against each other offset and housed with opposite opening directions in the rotating parts and have different drainage areas (Pig. 1, 2, 4, 4a, 5). 18. Steering valve according to claim 16, characterized in that both seat valves (98a, b) according to Opposite sides opening valve seats have that a common closing spring (llö) to The purpose of locking both valve bodies is to ensure that both seat valves have a common drainage space (II8) and that two tappets (46a, b) act in opposite directions on the same closing spring (Fig. 8), 030007/0396