GB2063192A - Hydraulic control apparatus, particularly steering apparatus - Google Patents

Abstract

In a hydraulic control apparatus comprising a piston-cylinder assembly (1), a control valve (9) which is connected by two operating connections (14,16) to those two parts (7,8) of the cylinder on opposite sides of the piston (4) and by a tank connection (17) to a tank (18) and which comprises an axially movable, spring-loaded valve spool (12) having ends exposed to the pressure obtaining in a respective one of two control pressure chambers (19, 20) connectible to a respective connection of a power pump (38) by a check valve means (36) and to a respective connection of a manually operable control pump (31), the piston-cylinder assembly comprises a differential piston, the operating connection (4) connected to that part (7) of the cylinder defined, in part, by the face of the piston of smaller area, is permanently connected to one (19) of the control pressure chambers and is isolated from the tank connection, and two valve openings (29,30) are provided the cross-sections of which vary, in opposite senses, in accordance with movement of the spool, the other control pressure chamber (20) being connectible to the other operating connection (16) by one of the openings (29) and that connection being connectible to the tank by the other opening (30). <IMAGE>

Description

SPECIFICATION Hydraulic control apparatus, particularly steering apparatus This invention relates to a hydraulic control apparatus, particularly a steering apparatus, comprising a control valve device which is connected by way of a first and a second operating connection to a respective pressure chamber of a piston-cylinder unit and by way of a tank connection to a tank and which comprises a valve slide loaded by neutral position springs and at the end by the pressure in two control pressure chambers which are connected to a respective connection of a control pump adjustable by a manual actuating element and to a main pump by way of a check valve device.

In a known control apparatus ofthis kind (FR-PS 14 65 422, Figure 4) the valve slide has two collars which close the operating connections in the neutral position and, upon displacement of the valve slide connects one operating connection to one of the control pressure chambers and the other operating connection to the tank connection. The main pump is connected by a respective one of two check valves directly to each control pressure chamber and in the neutral position by way of a short-circuit path to the tank connection. Upon adjustment of the manual actuating element, the pressure in the two control pressure chambers is changed so that the valve slide is displaced out of its neutral position.Pressure medium will then flow from the main pump by way of a check valve, the control pump and the said one control pressure chamber into the said one pressure chamber of the piston-cylinder unit whereas the other pressure chamber is connected to the tank.

Both pressure chambers of the piston-vylinder units have the same effective area. In this case it is a disadvantage that the manual actuating element must first traverse a certain idling distance before the piston-cylinder unit can be moved because the control slide must first be moved by a certain distance before the said one operating connection can be fed with pressure fluid.

The invention is based on the problem of providing a hydraulic control apparatus of the aforementioned kind in which adjustment of the manual actuating element immediately leads to adjustment of the piston-cylinder unit, i.e. without any lost motion zone in the region of the neutral position.

This problem is solved in accordance with the invention in that the piston-cylinder unit comprises a differential piston, that the operating connection leading to the pressure chamber of smaller effective area is permanently connected to the first control pressure chamber and is separated from the tank connection, and that two throttles are provided which are adjustable in opposite senses by the valve slide and of which one throttle connects the second control pressure chamber to the second operating connection and the other throttle connects the second operating connection to the tank connection.

In this construction, the two oppositely adjustable throttles form a pressure divider. The pressure derived between the two throttles produces in the pressure chamber of larger effective area of the piston-cylinder unit a force which is compared with a force produced by the unreduced pressure in the pressure chamber of smaller effective area. With the aid of the control pump adjustable by the manual actuating element, pressure differences result in the two control pressure chambers, by reason of which the valve slide is displaced. This displacement immediately leads to a pressure change between the two throttles and thus to a displacement of the piston in the one or other direction. A further advantage is that external forces acting on the piston lead to displacement of the valve slide such that the external force is compensated by hydraulic forces.In addition, the occurrence of this external force is noticeable at the manual actuating element by way of the control pump so that opposite control can also be exerted by hand.

In a particularly simple embodiment, for the purpose of forming both throttles an annular groove connected to the second operating connection cooperates in the housing of the control valve device with a collar on the valve slide that has a shorter axial length than the annular groove. A very simply constructed valve slide in a very simply constructed housing will therefore be sufficient to achieve the desired result.

It is advisable to use a pressure-controlled main pump. This ensures that one always starts from the same pressure level, which simplifies the design of the two throttles in comparison with the effective areas of the two pressure chambers of the pistoncylinder unit.

In a preferred embodiment, the check valve device comprises a single check valve and the main pump is connected by way of this check valve to the second control pressure chamber and by way of the series circuit of the check valve and control pump to the first control pressure chamber. This results in a simpler construction than if one uses the conventional two check valves but it does not affect the function.

In addition, the check valve may be springinfluenced. This ensures that slight fluctuations in the column of pressure medium or vibrations of the kind occurring during the travel of a vehicle will not lead to malfunctioning.

Preferably, both control pressure chambers are connected to the tank by a respective check valve which opens towards them. This permits emergency operation solely with the aid of the control pump if the main pump fails.

For emergency operation is also favourable if the tank connection of the control valve is connected to the tank by way of a spring influenced check valve opening towards the control valve.

The present invention also provides a hydraulic control apparatus comprising a piston-cylinder assembly, a control valve which is connected by two operating connections to those two parts of the cylinder on opposite sides of the piston and by a tank connection to a tank and which comprises an axially movable, spring-loaded valve spool, each end of the spool being exposed, in use, to the pressure obtaining in a respective one of two control pressure chambers each chamber being connectible to a respective connection of a power pump by a check valve means and to a respective connection of a manually operable control pump, wherein the piston-cylinder assembly comprises a differential piston, the operating connection connected to that part of the cylinder defined, in part, by the face of the piston of smaller area, is permanently connected to one ('the first') of the control pressure chambers and is isolated from the tank connection, and two valve openings are provided the cross-sections of which vary, in opposite senses, in accordance with movement of the spool, the other ('the second') control pressure chamber being connectible to the other operating connection by one of the openings and that connection being connectible to the tank by the other opening.

A hydraulic control apparatus constructed in accordance with the invention will now be described, by way of example, with reference to the accompanying drawing the single figure of which illustrates the apparatus in circuit form.

Referring to the accompanying drawing, a pistoncylinder unit 1 comprises a cylinder 2, a differential piston 4 and a piston rod 3, which, through a linkage 5, turns a wheel 6 to be steered. The cylinder is divided by the piston 4 into two compartments or pressure chambers 7 and 8, the compartment 7 being defined, in part, by the piston face having the smaller area F1 and the compartment 8 being defined, in part, by the piston face having the larger area F2.

A control valve 9 comprises a housing 10 with a bore 11 and an axially movable valve spool 12. In the housing there is an annular groove 13 which com municateswith a first operating connection 14 leading to the pressure chamber 7. A second annular groove 5 communicates with a second operating connection 16 which leads to the pressure chamber 8. Further, there is a tank connection 17 leading to the tank 18. The ends of the spools are exposed to the pressure in two control pressure chambers 19 and 20. In the control pressure chamber 19 there is a neutral position spring 21 which acts on an apertured disc 22. The disc 22 is supported either against a step 23 of the housing or against a respective end of the valve slide 12. A neutral position spring 24 in the control pressure chamber 20 is supported on an apertured disc 25.The drill 3 abuts either a step 26 in the housing or the other end of the valve slide 12. A first collar 27 on the valve slide 12 isolates the control pressure chamber 19 from the central chamber connected to the tank connection 17. Together with the annular groove 16, a second collar 28 of shorter axial width than the annular groove 15 defines two openings or throttles 29 and 30 the cross-sections of which vary in opposite senses in accordance with displacement of the valve slide 20.

A control pump 31 is adjustable by way of a manual actuating element 32 (for example, a steering wheel). The two sides of the control pump 31 are connected to connecting conduits 33 and 34, respectively, which lead to the control pressure chambers 19 and 20, respectively. The connecting conduit 34 is in addition connected by way of a spring-influenced check valve 36 to the pressure side 37 of a main pump 38 which has a pressure compensating device 39 for holding the output pressure constant. Two suction paths 40 40' each having a check valve 41, 41' lead from the connecting conduits 33 and 34 to the tank 18.The tank connection 17 is associated with a check valve 42 which is so strongly loaded by a spring that, during emergency operation, the valve slide 12 can be displaced towards the left (as seen in the drawing) under the pressure produced by the control pump 31 without the check valve 42 opening.

The operation of the control apparatus is as follows.

In the illustrated neutral position, the main pump 38 produces a pressure P0. The pressure P1 in the control pressure chamber 19 and the pressure P2 in the control pressure pressure chamber 20 are substantially equal to P0. The pressure P1 also obtains in the pressure chamber 7. On the other hand, in the pressure chamber 8 there is a pressure P3 because, by way of the check valve 36 and the two throttles 29 and 30, there is a permanent small flow of pressure medium leading to a division of pressure at the operating connection 16. The ratio of the throttle resistances in the neutral position is selected so that in the neutral position P1 x F1 = P3 x F2. By reason of this equilibrium of forces, the piston 4 remains stationary.

Upon anti-clockwise rotation of the actuating element 32 P1 is increased slightly. The valve slide 12 is correspondingly displaced towards the right (as seen in the drawing). The resistance of the throttle 29 increases whilst that of the throttle 30 drops. Consequently the reduced pressure P3 drops. The piston 4 is therefore moved to the right. Pressure fluid is delivered by the main pump 38 by way of the check valve 36, the control pump 31 and the control pressure chamber 19 into the pressure chamber 7 whilst pressure fluid can simultaneously flow out of the pressure chamber 8 by way of the throttle 30 to the tank 18.

If the actuating element is turned clockwise, the valve slide 12 is displaced to the left. The intermediate pressure P3 between the throttles 29 and 30 therefore increases. The piston 4 is pushed to the left. Pressure fluid flows from the main pump 38 by way of the check valve 36 and the control pressure chamber 20 to the pressure chamber 8. The pressure fluid displaced out of the pressure chamber 7 is delivered, by the control pump, into the pressure chamber 8.

If the main pump fails, emergency operation can be maintained using the control pump 31. If the piston 4 is to be displaced to the left, the additionally required pressure fluid can be fed by way of the suction conduit 40', the check valve 41' as well as the control pump 31 to the pressure chamber 8. If displacement of the piston 4 is desired to the right, the required pressure fluid can be fed by way of the suction conduit 40, the check valve 41 as well as the control pump 31 to the pressure chamber 7, it being possible, then for the fluid delivered by the pressure chamber 8 to flow to the tank 18 by way of the check valve 42.

If an external force acts on the piston 4 in the direction of the arrow X while the actuating element 32 is held tight, the piston 4 is displaced slightly to the left, whereby the valve slide 12 is moved to the right as a result of the pressure rise in the control pressure chamber 19. This increases the resistance of the throttle 29 which leads to a reduction in the pressure P3. This corresponds to compensation of the external force. At the same time, the increase in pressure of P1 becomes noticeable at the control pump 31 by way of a corresponding pulse so that the user encounters a slight impact on the actuating element 32 and can exert appropriate control.If the force acts opposite to the direction of the arrow X, the conditions are similar except that the valve slide 12 is displaced to the left, whereby the pressure P3 is increased and the external force is compensated in this manner.

If the actuating element 32 is not being held tight on the occurrence of the external force, it will turn depending on the displacement of the piston 4. On the occurrence of the external force, it is also possible to brake the displacement of the piston by applying a braking torque to the actuating element 32. If the external force is not very large, there are no objections to assist the displacement of the piston that is caused thereby with a like-acting adjustment of the actuating element.

The conduit 37 can also be connected directly to the connecting conduit 33 by way of a further check valve similar to the check valve 36. Further, the check valves 41,41' may be combined as a single check valve bridging only the main pump 38 if, in emergency control operation, the forces that are necessary to open the check valve 36 or the further, similar check valve, can be tolerated.

Claims (9)

1. A hydraulic control apparatus comprising a piston-cylinder assembly, a control valve which is connected by two operating connections to those two parts of the cylinder on opposite sides of the piston and by a tank connection to a tank and which comprises an axially movable, spring-loaded valve spool, each end of the spool being exposed, in use, to the pressure obtaining in a respective one of two control pressure chambers, each chamber being connectible to a respective connection of a power pump by a check valve means and to a respective connection of a manually operable control pump, wherein the piston-cylinder assembly comprises a differential piston, the operating connection connected to that part of the cylinder defined, in part, by the face of the piston of smaller area, is permanently connected to one ('the first') of the control pressure chambers and is isolated from the tank connection, and two valve openings are provided the crosssections of which vary, in opposite senses, in accordance with movement of the spool, the other ('the second') control pressure chamber being connectible to the other operating connection by one of the openings and that connection being connectible to the tank by the other opening.

2. A control apparatus as claimed in claim 1, in which each opening is formed between a collar on the valve spool and a respective edge of an annular groove provided in the wall of a bore in which the spool is movable, the collar having a shorter axial width than that of the annular groove.

3. A control apparatus as claimed in claim 1 or claim 2, in which the power pump is pressure controlled.

4. A control apparatus as claimed in any one of claims 1 to 3, in which the check valve means comprises a single check valve and the power pump is connected by this check valve to the second control pressure chamber and by the series circuit of the check valve and the control pump to the first control pressure chamber.

5. A control apparatus as claimed in any one of claims 1 to 4, in which the check valve means is spring-loaded.

6. A control apparatus as claimed in any one of claims 1 to 5, in which each control pressure chamber is connected to the tank by a respective one of two check valves which is openable towards it.

7. A control apparatus as claimed in any one of claims 1 to 6, in which the tank connection of the control valve is connected to the tank by a spring loaded check valve which is openable towards the control valve.

8. A hydraulic control apparatus, particularly a steering apparatus, comprising a control valve de vice which is connected by way of a first and a second operating connection to a respective press ure chamber of a piston-cylinder unit and by way of a tank connection to a tank and which comprises a valve slide loaded by neutral position springs and at the end by the pressure in two control pressure chambers which are connected to a respective connection of a control pump adjustable by a manual actuating element and to a main pump by way of a check valve device, wherein the piston cylinder unit comprises a differential piston, the operating connection leading to the pressure cham ber of small effective area is permanently connected to the first control pressure chamber and is sepa rated from the tank connection, and two throttles are provided which are adjustable in opposite senses by the valve slide and of which one throttle connects the second control pressure chamber to the second operating connection and the other throttle connects the second operating connection to the tank connec tion.

9. A hydraulic control apparatus substantially as hereinbefore described with reference to, and as shown in the accompanying drawing.