GB1594279A

GB1594279A - Hydraulic steering devices

Info

Publication number: GB1594279A
Application number: GB2611/78A
Authority: GB
Original assignee: Danfoss AS
Current assignee: Danfoss AS
Priority date: 1977-01-24
Filing date: 1978-01-23
Publication date: 1981-07-30
Also published as: IT1107003B; DK143594B; AR215674A1; JPS53116635A; DK552877A; DE2702692A1; FR2377922A1; FR2377922B1; DE2702692C2; AU3260678A; IT7867122A0; BR7800387A; AU511675B2; DK143594C; CA1091131A

Description

(54) IMPROVEMENTS IN AND RELATING TO HYDRAULIC STEERING DEVICES (72) We, DANFOSS A/S, a Danish company, of DK 6430 Nordborg, Denmark, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a controller for use in hydraulic steering systems.

The present invention provides a controller for use in hydraulic steering systems and comprising an inlet for connection to a source of fluid under pressure, an outlet for returning fluid to a tank, a pair of fluid ports for connection to a fluid pressure operated device, a valve including two cooperable tubular valve elements, one of the valve elements being seated in a bore provided in a housing of the controller, and the other valve element being seated within the said one valve element, a control element for effecting relative displacement between the two valve elements in either of two opposite directions, metering means serving, in use, to meter fluid from the inlet to one of the ports in dependence on movement of the control element, the valve acting as a reversing valve for the said fluid ports and as a commutator valve for the metering means and including a number of axially spaced valve openings for fluid flowing between the inlet, the fluid ports and the outlet, the openings being provided between the said one valve element and the wall of the bore and each being in the form of an annular chamber or comprising several orifices arranged in annular formation, adjacent valve openings which are, in use, at relatively high and low pressures respectively being separated by a respective auxiliary annular chamber provided between the said one valve element and the said wall, each auxiliary chamber being connected to receive fluid from the inlet via a check valve.

The provision of the auxiliary chambers serves to prevent leakage, when the controller is passing fluid to the device under control, between adjacent valve openings at different pressures. When the device under control is in the form of a steering cylinder and the inlet pressure is reduced, for example if the inlet is connected to tank (as it usually is in the neutral position of the controller) then each auxiliary chamber will be at that reduced pressure. If the steering cylinder is loaded by an external force it is possible for the pressure fluid to leak from a valve opening connected to the steering cylinder into an adjacent auxiliary chamber resulting in drifting movement of the steering cylinder. That leakage is prevented in the controller of the invention by the provision of the check valve.

If the valve openings comprise four axially spaced annular chambers (hereinafter referred to as main chambers), one of the main chambers being connected to the inlet, the other three main chambers being spaced away, in the same axial sense, from the said one main chamber, the main chamber next to the said one main chamber being connected to one of the fluid ports, its next, in the same axial sense, adjacent main chamber being connected to the other fluid port and the remaining main chamber being connected to the outlet, it is of advantage if two auxiliary chambers are provided, one of the auxiliary chambers being provided between the two main chambers connected to the fluid ports and the other auxiliary chamber being connected between the said remaining main chamber and its adjacent main chamber.

If one of the valve openings comprises a plurality of commutator orifices which are provided in the said one valve element and are angularly equispaced around the axis of that element, the commutator orifices being provided between the said one main chamber and its next adjacent main chamber, it is of advantage if a further auxiliary annular chamber is provided between the said one valve element and the said wall and between the said orifices and the main chamber adjacent to the said one main chamber.

The metering means may include a rotary metering element which is connected to the said one valve element by a drive shaft one end of which is connected to the rotary metering element and the other end of which is provided with a transverse drive pin, opposite ends of the pin being connected to the outer valve element. In that case it is preferred if the transverse pin is disposed between the said other auxiliary chamber and the said remaining main chamber.

From a constructional point of view it is of advantage if a passage is provided in the housing which extends alongside the housing bore and is connected by respective radial bores to the said auxiliary chambers and to a valve opening connected to the inlet.

Each auxiliary chamber may be defined by a groove, preferably formed in the said one valve element.

The check valve can, with advantage, be provided in the said passage and be located between the radial bore connected to the valve opening connected to the inlet and the radial bore connected to the said further auxiliary chamber.

A hydraulic steering controller constructed in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawing, the single figure of which is a diagrammatic longitudinal section of the controller.

Referring to the accompanying drawing, the illustrated control device comprises a housing 1 with a bore 2 in which there is disposed an outer rotary valve sleeve (or commutator) 3; an inner rotary spool 4 being mounted in the sleeve. The spool 4 is provided with a coupling 5 for a steering column shaft not shown, and can be turned- both clockwise and anticlockwise-through a limited angle relative to the sleeve 3 against the force of leaf springs 6. This angle is predetermined by movement of a transverse pin 7-which is firmly connected to the sleeve 3-in a pair of diametrically opposed circumferentially extending slots or apertures 8 in the spool 4, the transvese pin 7 being fixed to one end of a cardan shaft 61.

The other end of the shaft 61 is connected to an externally toothed or lobed gear wheel 9 forming part of a gerotor-type rotary metering device 10, the device also comprising an internally-toothed or lobed gear ring 11. The ring 11 is fixed and the wheel 9 rotates about its own axis; the axis of the wheel orbiting about the axis of the ring. The ring 11 together with an end plate 12 and an intermediate plate 13, are secured to the housing 1 by bolts 14. Working chambers are defined between the plates 12 and 13 and between the teeth of the wheel 9 and ring 11.

The housing 1 comprises an inlet connection 15 which can be connected to a pump 16, as well as an outlet connection 17 which can be connected to a tank 18. In addition, two connections 19 and 20 are indicated diagrammatically-they are disposed in a sectional plane that lies at an angle to the plane of the figure-which can be connected to two operating conduits 21 and 22 leading to a steering cylinder or motor 23 which, in this case, comprises a cylinder 24 and piston 25 and serves to provide steering adjustment for a wheel 26 formed in the wall of the bore 2 and at the sliding face between that wall and the sleeve 3, are four, axially spaced, annular grooves. A first annular groove 27 is connected by a passage 28 to the inlet 15. A second annular groove 29 is connected to the operating conduit connection 19 and a third annular groove 30 to the operating conduit connection 20. The fourth annular groove 31 is connected by a conduit 32 to the outlet 17. Between the two conduits 28 and 32 there is a connecting passage 33 with a check valve 34 which opens if there is a higher pressure at the tank connection 17 than at the pump connection 15.

Leading from the bore 2 there are a plurality of distributing or control orifices 35 each of which has a radial portion extending to the wall of the bore 2 a 1d an axial portion which extends to a respective one of the working chambers formed by the metering device motor 10. Each aperture 35 alternately supplies fluid to or leads fluid from its working chamber.

The sleeve 3 as well as the spool 4 have radially extending neutral position orifices 36 and 37, respectively, which are in registry in the neutral position of the controller and connect the first annular groove 27 to the interior 38 of the spool 4. This interior communicates with the fourth annular groove 31 which is at tank pressure, via the slots 8, longitudinal grooves 39 in the spool 4 and radial holes 40 in the sleeve 3. In the neutral position, therefore, the pump connection 15 is connected to the tank connection 17 and the pressure at the pump connection 15 therefore drops correspondingly.

The relative position of the spool 4 and sleeve 3 shown in the drawing occurs when the piston 25 is moved to the right by rotation of the steering column. In this condition, the neutral position orifices 37 and 38 are displaced with respect to one another and are closed. Pressure fluid then passes from the first annular groove 27 through radial holes 41 formed in the sleeve 3 to an annular groove 42 in the spool 4 and then through axial passages 43 formed in the spool 4 to radially extending circumferentially spaced commutator holes 44 which register with the control orifices 35. Pressure fluid therefore passes through some of the orifices 35 to the metering device 10 and is returned from the latter to other of the control orifices 35, the outflowing pressure fluid reaching axial passages 46 formed in the spool 4 via radially extending circumferentially spaced commutator holes 45 (which alternate circumferentially with the bores 44). From here the fluid passes to the second annular groove 29 via radial holes 47 and then arrives at the cylinder 23 via the connection 19. The return fluid from the cylinder 23 arrives in the third annular groove 30 via the connection 20 and then passes through radial holes 48 (in the sleeve) and 49 (in the spool) to the interior 38 and finally to the fourth annular groove 31 at tank pressure.

On rotation of the steering shaft in the opposite sense, pressure fluid is fed from the metering device 10 into the third annular groove 30 and then back to the tank via the cylinder 23 and the second annular groove 29.

In the illustrated position, therefore, the first annular groove 27 is at fuel pump pressure Pp, the second annular groove 29 is at operating pressure PL which corresponds to the reduced pump pressure after passage of fluid through the measuring motor 10, whilst there is tank pressure PT in the fourth annular groove 31 and a pressure PR equal to the tank pressure PT in the third annular groove 30. As a result of the pressure differences pressure fluid could-in the absence of further grooves described below-leak out of the second annular groove 29 along the sliding face between the sleeve 3 and the wall of the bore 2 to the third annular groove 30. Since this is pressure fluid that has already been metered by the device 10, the rotational movement of the gear wheel 9 will not effect acorresponding movement of the piston 25. Similarly, when the steering column has been rotated in the opposite direction, pressure fluid could leak out of the third annular groove 30 to the second annular groove 29 and to the fourth annular groove 31. The discrepancy in movement of the culinder 23 and device 10 is particularly noticeable when the cylinder 23 has reached an end position because the metering device 10 will continue to operate depending on the extent of the leakage flow. This leads to undesirable slip which is different for both directions of steering.

This disadvantage is avoided in that two auxiliary annular grooves 50 and 51 are provided between the second annular groove 29 and the third annular groove 30 as well as between the third annular groove 30 and the fourth annular groove 31 and/or the transvese pin 7. Both auxiliary grooves are connected by radial holes 52 and 53 to an axial hole 54 which, in turn, communicates with the first annular groove 27 via a radial hole 55. Consequently pump pressure obtains in each of the auxiliary annular grooves 50 and 51. This prevents leakage flow of pressure fluid that has already been metered by the device 10. The fact that pressure fluid can pass from the auxiliary annular grooves into the annular grooves at tank pressure does not materially affect the accuracy of operation.

Further, a third auxiliary annular groove 56 is also provided between the control orfices 35 and the second annular groove 29, this groove 56 being connected by a radial hole 57 to the longitudinal hole 54 and therefore being at pump pressure. The groove 56 prevents the passage of measured pressure fluid from the downstream (and of course also the upstream) control orifices into the second annular groove 29 when this is at tank pressure PT, which improves the steering accuracy and symmetry during steering.

A check valve 58 influenced by a spring 59 is inserted in the longitudinal hole 54. This check valve closes when the pressure in the auxiliary annular grooves 50, 51 or 56 becomes larger than the pressure at the pump connection 15. This can occur in the neutral position, when the pressure at the pump connection 15 is only slightly higher than the pressure at the tank connection 17, if an external force is imposed on the cylinder 23 giving rise to a higher pressure in the annular groove 29 or 30 than the pressure at the pump connection 15. Although this pressure could result in the passage of pressure fluid into the auxiliary annular grooves 50, 51 or 56, no fluid can leak out of these because of the check valve 58 and consequently there is no adjustment of the cylinder.

The drawing shows in broken lines that the pump 16 is provided with a regulator 60, in this case a shunt valve, so that the pump pressure can be varied as required. In this manner of regulation the pressure at the pump inlet 15 can also become smaller than the pressure in the annular grooves 29 or 30 if an external force occurs at the operating motor.

It will be seen from the above description that the sleeve 3 tends to follow-up movement of the spool 4, the controller returning to its neutral condition when the gear wheel 9 has completed the same angular movement as that applied to the spool 4 by means of the steering column.

Further, the direction in which fluid flows to the steering cylinder 23 depends upon the direction in which the spool 4 is rotated.

The spool 4 and sleeve 3 act as a reversing valve for the fluid connections 19 and 20 and the sleeve 3 and the wall of the bore 2 act as a commutator valve for the working chambers of the metering device 10.

The grooves 46 alternate, circumferentially, with another set of similar grooves (not shown) which are axially displaced relative to the grooves 46 and which allow pressure fluid to be fed from the metering device 10 into the groove 30 when the steering shaft is turned in the said opposite sense.

Claims

WHAT WE CLAIM IS:-

1. A controller for use in hydraulic steering systems and comprising an inlet for connection to a source of fluid under pressure, an outlet for returning fluid to a tank, a pair of fluid ports for connection to a fluid pressure operated device, a valve including two cooperable tubular valve elements, one of the valve elements being seated in a bore provided in a housing of the controller, and the other valve element being seated within the said one valve element, a control element for effecting relative displacement between the two valve elements in either of two opposite directions, metering means serving, in use, to meter fluid from the inlet to one of the ports in dependence on movement of the control element, the valve acting as a reversing valve for the said fluid ports and as a commutator valve for the metering means and including a number of axially spaced valve openings for fluid flowing between the inlet, the fluid ports and the outlet, the openings being provided between the said one valve element and the wall of the bore and each being in the form of an annular chamber or comprising several orifices arranged in annular formation, adjacent valve openings which are, in use, at relatively high and low pressures respectively being separated by a respective auxiliary annular chamber provided between the said one valve element and the said wall, each auxiliary chamber being connected to receive fluid from the inlet via a check valve.

2. A controller as claimed in claim 1, in which the valve openings comprise four axially spaced annular chambers (hereinafter referred to as main chambers), one of the main chambers being connected to the inlet, the other three main chambers being spaced away, in the same axial sense, from the said one main chamber, the main chamber next to the said one main chamber being connected to one of the fluid ports, its next, in the same axial sense, adjacent main chamber being connected to the other fluid port and the remaining main chamber being connected to the outlet, two auxiliary annular chambers being provided, one of the auxiliary chambers being provided between the two main chambers connected to the fluid ports and the other auxiliary chamber being connected between the said remaining main chamber and its adjacent main chamber.

3. A controller as claimed in claim 1 or claim 2, in which each of the annular chambers comprising a valve opening is defined by a groove.

4. A controller as claimed in claim 3, in which each groove is formed in the said wall.

5. A controller as claimed in claim 2 or claim 3 or claim 4 when appendant to claim 2, in which one of the valve openings comprises a plurality of commutator orifices which are provided in the said one valve element and are angularly equispaced around the axis of that element, the commutator orifices being provided between the said one main chamber and its next adjacent main chamber, wherein a further auxiliary annular chamber is provided between the said one valve element and the said wall and between the said orifices and the main chamber adjacent to the said one main chamber.

6. A controller as claimed in any one of claims 1 to 5 in which each auxiliary chamber is defined by a groove.

7. A controller as claimed in claim 6, in which each auxiliary chamber is defined by a groove formed in the said one valve element.

8. A controller as claimed in any one of claims 1 to 7, in which the metering means includes a rotary metering element which is connected to the said one valve element by a drive shaft one end of which is connected to the rotary metering element and the other end of which is provided with a transverse drive pin, opposite ends of the pin being connected to the outer valve element.

9. A controller as claimed in claim 8 when appendant to claim 2, in which the transverse pin is disposed between the said other auxiliary chamber and the said remaining main chamber.

10. A controller as claimed in any one of claims 1 to 9, in which a passage is provided in the housing which extends alongside the housing bore and is connected by respective radial bores to the said auxiliary chambers and to a valve opening connected to the inlet.

11. A controller as claimed in claim 10 when appendant to claim 5, in which the check valve is provided in the said passage and is located between the radial bore connected to the valve opening connected to the inlet and the radial bore connected to the said further auxiliary chamber.

12. A controller substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.