WO2008022370A1

WO2008022370A1 - Hydraulic power steering valve

Info

Publication number: WO2008022370A1
Application number: PCT/AU2007/001088
Authority: WO
Inventors: Klaus Juergen Roeske
Original assignee: Bishop Innovation Limited
Priority date: 2006-08-24
Filing date: 2007-08-06
Publication date: 2008-02-28

Abstract

A rotary valve for a hydraulic power steering gear. The valve comprises an input shaft relatively rotatable within a sleeve. The input shaft and sleeve each have an array of longitudinal slots that are arranged together to form a plurality of parallel hydraulic wheatstone bridges. Either the array of slots in the sleeve or the input shaft is evenly spaced around its axis with its slots alternating between a first and second type of slot. The first type of slot communicates with a supply of hydraulic fluid. The second type of slot is extended to provide a return path for hydraulic fluid, and the second type of slot is narrower than the first type of slot.

Description

HYDRAULIC POWER STEERING VALVE

TECHNICAL FIELD

The present invention relates to rotary valves for vehicle hydraulic power steering gears.

BACKGROUND

The general method of operation of rotary hydraulic power steering valves is well known as described in US Patent 3,022,772 (Zeigler et al). Such valves typically comprise an input shaft, connected to the steering wheel of the vehicle, and a sleeve journalled on the input shaft. The sleeve is connected to a driving member, such as a gear pinion, and the input shaft is connected to the driving member by a torsion bar such that torque applied to the input shaft causes relative rotation between the input shaft and the sleeve.

The input shaft typically has an array of longitudinal slots of equal width on its outside diameter, evenly spaced around its axis. The sleeve also has an array of longitudinal slots of equal width in its bore, evenly spaced around its axis. The slots in the input shaft and sleeve are arranged in an underlapping relationship to form a series of longitudinally extending orifices that open and close as the input shaft and sleeve rotate relative to each other. Typically the sleeve and input shaft each have six or eight slots arranged as three or four hydraulic wheatstone bridges respectively to direct hydraulic fluid to either side of a hydraulic assist cylinder in response to relative rotation of the sleeve and input shaft.

Conventionally, the slots in the sleeve and the input shaft are blind ended with drilled holes in the sleeve and input shaft providing communication to the supply of hydraulic fluid, the hydraulic assist cylinder and a return path for the hydraulic fluid. The slots in the input shaft are typically arcuate and are formed by a milling cutter. The slots in a sleeve may also be arcuate and can be machined by a slotting process using a machine such as described in US Patent 4,154,145 (Bishop). US Patent 5,131 ,430 (Roeske et al) describes an alternative valve arrangement in which the slots in the sleeve alternate between supply slots and return slots. The supply slots communicate with a supply of hydraulic fluid through drilled holes in the sleeve. The return slots are extended such that they break out of the end of the sleeve to provide a return path for the hydraulic fluid, instead of having drilled holes. The extended sleeve slots may be machined by slotting using a method described in US Patent 6,082,940 (Roeske).

US Patent 3,393,608 (Saunders) describes another alternative valve arrangement in which the slots in the input shaft alternate between supply slots and return slots. The supply slots communicate with a supply of hydraulic fluid through drilled holes in the sleeve. The return slots are extended along the input shaft to provide a return path for the hydraulic fluid, instead of having drilled holes.

To control the boost characteristic and hydraulic noise of a rotary power steering valve, the edges of the input shaft slots must be accurately contoured. These metering edges form one side of the longitudinally extending orifices described above. Their profile is typically shaped as one or more chamfers. A machine as described in US Patent 5,439,412 (Bishop) may be used to accurately grind the metering edges.

The aspect ratio of the longitudinally extending orifices is defined as their length divided by their depth. To minimise the hydraulic noise of a valve, it is desirable to make the aspect ratio as high as possible. For a given required total orifice area this can be achieved by either maximising the length of the orifices, and hence the length of the slots, or by increasing the total number of slots. Constraints on overall valve length and other factors mean that it may not be practical to lengthen the slots and it is difficult to package more slots in a conventional valve design.

It is an object of the present invention to provide a rotary valve for a hydraulic power steering gear that ameliorates at least one of the problems of the prior art, or at least provides a useful alternative. SUMMARY OF INVENTION

The present invention consists of a rotary valve for a hydraulic power steering gear comprising a first valve member having a first array of longitudinal slots, a second valve member, relatively rotatable to said first valve member, having a second array of longitudinal slots, said first and second arrays of longitudinal slots each having the same even number of slots and co-operating to form a plurality of parallel hydraulic wheatstone bridges responsive to the relative rotation of said first and second valve members, said first array of slots being substantially evenly spaced around the axis of said first member and alternating between a first and a second type of slot, each of said first type of slot being adapted to communicate with a supply of hydraulic fluid and at least one end of each of said second type of slot being extended to provide a return path for hydraulic fluid, characterised in that said second type of slot is narrower than said first type of slot.

In one preferred embodiment, said first valve member comprises a sleeve and said second valve member comprises an input shaft rotatable within said sleeve, said first array of slots being in the bore of said sleeve, and said second array of slots being on the outside diameter of said input shaft.

In another preferred embodiment, said second valve member comprises a sleeve and said first valve member comprises an input shaft rotatable within said sleeve, said second array of slots being in the bore of said sleeve, and said first array of slots being on the outside diameter of said input shaft.

Preferably, said first array of slots comprises ten slots.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a longitudinal sectional view of a first embodiment of a rotary hydraulic power steering valve in accordance with the present invention, shown installed in a steering gear. Fig. 2 is a cross sectional view through H-II of the valve shown in Fig. 1.

Fig. 3 is a longitudinal sectional view of a second embodiment of a rotary hydraulic power steering valve in accordance with the present invention, shown installed in a steering gear.

Fig. 4 is a cross sectional view through IV-IV of the valve shown in Fig. 3.

BEST MODE OF CARRYING OUT THE INVENTION

Figs. 1 and 2 show a first embodiment of a rotary hydraulic power steering valve 1 in accordance with the present invention, comprising an input shaft 2 and a sleeve 3. Sleeve 3 is journalled on input shaft 2 such that they are rotatable relative to each other. Fig. 1 shows valve 1 installed in a housing 4 of a power steering gear, comprising upper housing 5 and lower housing 6. Sleeve 3 is rotatable in the bore 7 of upper housing 5.

Sleeve 3 is rotationally connected to a pinion 9 by a drive pin 10. Pinion 9 is supported by bearing 11. A torsion bar 12 is press fit into pinion 9 at one end and connected at the other end to input shaft 2 by a pin 13. Input shaft 2 is supported by roller bearing 14 and by being journalled on the pinion end of torsion bar 12. The arrangement is such that torque applied to input shaft 2 causes relative rotation between input shaft 2 and sleeve 3.

A supply port 16 in upper housing 5 communicates with a supply of hydraulic fluid, typically comprising a pump and a reservoir (not shown). Ports 18 and 19 communicate with either side of a double acting hydraulic assist cylinder (not shown). Return port 17 returns hydraulic fluid to the reservoir. Seals 20 and 21 prevent hydraulic fluid leaking from upper housing 5. Teflon seals 22 seal between sleeve 3 and bore 7.

Sleeve 3 has an array of ten slots 24, 25 in its bore 30, substantially evenly spaced around its axis 23 such that the angle 26 between the centres of any pair of adjacent slots 24, 25 is approximately 36°. The slots 24, 25 in sleeve 3 alternate between a first type of slot 24 and a second type of slot 25. Slots 24 communicate with a supply of hydraulic fluid through supply port 16 and holes 27 drilled through sleeve 3. Slots

24 are arcuate and blind ended, and may be made by a slotting process using a machine such as described in US Patent 4,154,145 (Bishop). Slots 25 are extended such that they break out one end 28 of sleeve 3 to provide a return path for hydraulic fluid that communicates with return port 17. Slots 25 also break out the other end 29 of sleeve 3 to provide a return path for hydraulic fluid that leaks into cavity 31. The break out at end 28 is deeper than the break out at end 29 because end 28 provides a return path for all hydraulic fluid flowing through valve 1 , whereas only a small amount of leakage hydraulic fluid flows through the break out at end 29. Slots 25 may be machined by slotting using a method described in US Patent 6,082,940 (Roeske).

Slots 24 have a width 33, and slots 25 have a width 34. Slots 25 are narrower than slots 24. As an example, a sleeve 3 having a bore 30 diameter of 22mm may have slots 24 that are 4mm wide and slots 25 that are 2.5mm wide. It is possible for slots

25 to be relatively narrow because there is no necessity to drill return holes through them since hydraulic fluid returns through their ends.

Input shaft 2 also has an array of ten slots 36, arranged in an underlapping relationship with sleeve slots 24, 25 to form twenty longitudinally extending orifices 37. Slots 36 are arcuate and blind ended, and all have the same width 41. Slots 36 can be machined using a circular milling cutter. As a result of the even spacing and alternating width of sleeve slots 24, 25, input shaft slots 36 are not evenly spaced around axis 23 as can clearly be seen in Fig. 2. Holes 39 and 40 communicate with ports 18 and 19 respectively to direct hydraulic fluid from input shaft slots 36 to either side of a hydraulic assist cylinder. Chamfer like metering edges 38 are accurately ground on the edges of slots 36. The arrangement is such that five parallel hydraulic wheatsone bridges are formed that are responsive to the relative rotation of sleeve 3 and input shaft 2 in the manner described in US Patent 3,022,772 (Zeigler et al).

The relatively narrow width of return sleeve slots 25, compared with supply slots 24, allows more slots to be packaged than would be otherwise be practical in a conventional valve of the same size having even slot width in both the sleeve and the input shaft, thereby increasing the aspect ratio of the longitudinally extending orifices and minimising the hydraulic noise generated by the valve. As an example, it is usually only practical to package eight slots in each of the sleeve and input shaft of a conventional valve having a sleeve bore of 22mm with even slot width in the sleeve and input shaft. However, the narrow width return slots of the present invention allow ten slots in each of the sleeve and input shaft to be packaged in the same size valve. Likewise, the present invention allows eight or more slots to be packaged in a valve size that would be usually only be suited to packaging six slots using a conventional design. Furthermore the present invention can be used to package more than ten slots, such as twelve slots in each of the sleeve and input shaft.

Figs. 3 and 4 show a second embodiment of a rotary hydraulic power steering valve 1a in accordance with the present invention, comprising an input shaft 2a and a sleeve 3a. Valve 1a operates in a similar manner to valve 1 shown in Figs. 1 and 2 except that the supply slots 24a and return slots 25a of valve 1 a are on the outside diameter 43 of input shaft 2a, rather than in the sleeve.

Input shaft 2a has an array of ten slots 24a, 25a on its outside diameter 43, substantially evenly spaced around its axis 23 such that the angle 26 between the centres of any pair of adjacent slots 24a, 25a is approximately 36°. The slots 24a, 25a in input shaft 2a alternate between a first type of slot 24a and a second type of slot 25a. Slots 24a communicate with a supply of hydraulic fluid through supply port 16 and holes 27a drilled through sleeve 3a. Slots 24a are arcuate and blind ended. Slots 25a are extended such that they break out one end 28a of the outside diameter 43 of input shaft 2a to provide a return path for hydraulic fluid that communicates with return port 17. Slots 25a are also extended at their other end 44 such that they communicate with cavity 31 to provide a return path for hydraulic fluid that leaks into cavity 31. Slots 24a and 25a may be machined using a circular milling cutter, with the cutter being fed axially to extend slots 25a. Chamfer like metering edges 38 are accurately ground on the edges of slots 24a, 25a. Slots 24a have a width 33a, and slots 25a have a width 34a. Slots 25a are narrower than slots 24a. As an example, an input shaft 2a having an outside diameter 43 of 22mm may have slots 24a that are 4mm wide and slots 25a that are 2.5mm wide. It is possible for slots 25a to be relatively narrow because there is no necessity to drill return holes through them since hydraulic fluid returns through their ends.

Sleeve 3a also has an array of ten slots 36a, arranged in an underlapping relationship with input shaft slots 24a, 25a to form twenty longitudinally extending orifices 37. Slots 36a are arcuate and blind ended, and all have the same width 41a. As a result of the even spacing and alternating width of input shaft slots 24a, 25a, sleeve slots 36a are not evenly spaced around axis 23 as can clearly be seen in Fig. 4. Holes 39a and 40a communicate with ports 18 and 19 respectively to direct hydraulic fluid from sleeve slots 36a to either side of a hydraulic assist cylinder.

Valve 1a has the same advantages as valve 1 shown in Figs. 1 and 2 in that the relatively narrow width of return input shaft slots 25a, compared with supply slots 24a, allows more slots to be packaged than would be otherwise be practical in a conventional valve of the same size having even slot width in both the sleeve and the input shaft.

In other not shown embodiments of the invention, the sleeve and input shaft slots may be made by other methods such that their shape is other than arcuate. For example, the sleeve slots may be broached. Also, the metering edges may be made by methods other than grinding, such as by cold forming. The metering edges may also have a different contour on the upstream and downstream edges.

In other not shown embodiments of the invention, the return slots may only be extended at one end to provide a return path only for the main flow through the valve with some other means, such as a hole in the input shaft, being provided to return leakage fluid from the other end of the valve.

The term "comprising" as used herein is used in the inclusive sense of "including" or "having" and not in the exclusive sense of "consisting only of.

Claims

1. A rotary valve for a hydraulic power steering gear comprising a first valve member having a first array of longitudinal slots, a second valve member, relatively rotatable to said first valve member, having a second array of longitudinal slots, said first and second arrays of longitudinal slots each having the same even number of slots and co-operating to form a plurality of parallel hydraulic wheatstone bridges responsive to the relative rotation of said first and second valve members, said first array of slots being substantially evenly spaced around the axis of said first member and alternating between a first and a second type of slot, each of said first type of slot being adapted to communicate with a supply of hydraulic fluid and at least one end of each of said second type of slot being extended to provide a return path for hydraulic fluid, characterised in that said second type of slot is narrower than said first type of slot.

2. A rotary valve for a hydraulic power steering gear as claimed in claim 1 wherein said first valve member comprises a sleeve and said second valve member comprises an input shaft rotatable within said sleeve, said first array of slots being in the bore of said sleeve, and said second array of slots being on the outside diameter of said input shaft.

3. A rotary valve for a hydraulic power steering gear as claimed in claim 1 wherein said second valve member comprises a sleeve and said first valve member comprises an input shaft rotatable within said sleeve, said second array of slots being in the bore of said sleeve, and said first array of slots being on the outside diameter of said input shaft.

4. A rotary valve for a hydraulic power steering gear as claimed in claim 1 wherein said first array of slots comprises ten slots.