WO1999011503A1

WO1999011503A1 - Power steering valves

Info

Publication number: WO1999011503A1
Application number: PCT/AU1998/000697
Authority: WO
Inventors: Andrew William Hassett; Stephen Spain; Ellis John Taylor
Original assignee: Bishop Steering Pty Ltd
Current assignee: Bishop Steering Pty Ltd
Priority date: 1997-09-03
Filing date: 1998-08-27
Publication date: 1999-03-11
Anticipated expiration: 2000-03-03
Also published as: AUPO894997A0

Abstract

A hydraulic valve for a power steering gear comprising a sleeve journalled on an input-shaft (2). The sleeve having a torsion bar (1) connected thereto via a driven member, the input-shaft having an axially extending bore (6). The torsion bar (1) having an axially extending bore (4) in a fixing end thereof, the fixing end being remote from the driven member and located within the bore (6) of the input-shaft. The surface of the input-shaft bore (6) and the outer surface of the fixing end of the torsion bar (1) forming an interface therebetween. At least one diametral member (5) is press-fitted within the axial bore of the torsion bar and a keying formation (7) is disposed on at least a portion of one or both surfaces forming said interface. In a second embodiment two diametral members (5) are press-fitted within the axial bore (4).

Description

POWER STEERING VALVES

Technical Field

This invention relates to hydraulic power steering gears for motor vehicles and, in particular, to a method of connecting an input-shaft and a torsion bar in the rotary valve of such a power steering gear.

Background

Typically rotary valves for hydraulic power steering include an input-shaft, usually connected to the steering wheel of the vehicle by a flexible joint, and having in its outer periphery a plurality of blind ended, axially extending grooves separated by lands. Journalled on the input-shaft is a sleeve having in its bore an array of axially extending blind ended slots matching the grooves in the input-shaft, but in underlap relationship thereto, the slots of the one being wider than the lands of the other so defining a set of axially extending orifices which open and close when relative rotation occurs between the input-shaft and the sleeve. These orifices are ported as a network such that they form sets of hydraulic Wheatstone bridges which act in parallel.

Drilled passages in the input-shaft and sleeve, together with circumferential grooves in the periphery of the sleeve, serve to communicate oil between the grooves in the input-shaft and the slots in the sleeve, an engine driven oil pump, and right-hand and left-hand hydraulic assist cylinder chambers incorporated in the steering gear.

SUBSΉTUTE SHEET (Rule 26) A torsion bar incorporated in the input-shaft serves to urge the input-shaft and sleeve towards a neutral, centred condition when no power assistance is required. When input torque is applied by the driver to the steering wheel, the torsion bar deflects, causing relative rotation of the sleeve and input-shaft from the neutral condition. This so called "valve operating angle" imbalances the sets of hydraulic Wheatstone bridges and hence causes a differential pressure to be developed between the right-hand and left-hand hydraulic assist cylinder chambers. The "boost characteristic" of the rotary valve, that is the functional relationship between the above mentioned input torque and differential pressure, is determined for a given steering gear application by the geometry of axially extending contours formed on the edges of the grooves of the input-shaft adjacent to its outside diameter.

The general method of operation of such conventional rotary valves is well known in the art of power steering design and so will not be described in any greater details in this specification. An excellent description of this operation is contained in US Pat. No. 3,022,772 (Ziegler), commonly held as being the "original" patent disclosing the rotary valve concept.

It is a requirement of operation of most steering gears that the left and right turn hydraulic assist characteristics be as nearly as possible identical, and this symmetry of operation can only be established at the time of assembly of the valve due to the finite tolerances assigned to the various components involved. Great accuracy is required in determining the neutral position of the valve components to ensure this symmetry. Moreover, once this position is determined, it must be retained for the life of the steering gear.

For most power steering gears the theoretically ideal neutral position of the input-shaft and sleeve components can be defined as the position about which an equal angular

SUBSTrrUTE SHEET (Rule 26) rotation or an equal input torque applied to the input-shaft in either direction, with respect to the sleeve, will result in equal magnitudes of differential pressure of hydraulic fluid being supplied to the left and right assist cylinders during valve operation. The operation of determining and fixing the neutral position is referred to as a "balancing" operation and typically involves adjustment of the angular disposition of the input-shaft with respect to the torsion bar whilst angular rotation of the input-shaft with respect to the sleeve, or alternatively the input torque applied to the input-shaft (which is temporarily locked to the torsion bar), is measured against the valve inlet pressure.

According to the most common present practice, the fixing end of the torsion bar is secured to the input-shaft by a pin pressed through a diametrically disposed hole drilled and reamed through both components during the assembly operation which is performed in a "balancing" machine.

Such balancing machines take many different formats and may be either a conventional hydraulic balancing machine or a pneumatic balancing machine as described in International Patent Application No. PCT/AU95/00774 (Baxter et. al.).

In typical hydraulic balancing machines the driven member (ie. the pinion or worm) and the end of the torsion bar protruding through the upper end of the input-shaft are both rotationally clamped such that the torsion bar is in its undeflected state. The input- shaft is clamped to a vernier drive mechanism capable of imparting very fine angular displacements to the input-shaft relative to the driven member, and hence the sleeve. After establishing oil supply to the valve at required flow rate and temperature, the input-shaft is rotationally displaced in one direction until inlet pressure corresponds to a predetermined check point pressure and the corresponding magnitude of this displacement recorded. The input-shaft is then rotated in the opposite direction until the measured pressure again equals the predetermined check point pressure and a displacement magnitude is similarly recorded. The mean (half way point) of these two angular displacements is then calculated and the input-shaft rotated to this position and clamped. The aforementioned hole is then drilled and reamed and the pin pressed in. The force required to insert the pin is frequently monitored as a measure of the interference fit existing between the reamed hole and pin; also a "push-out" test is often performed to check for pin retention up to a predetermined force on the pin. In other alternative arrangements of hydraulic balancing machines, the input-shaft is rotationally clamped and the driven member (and hence the torsion bar) is rotationally driven during the balancing operation.

In any case, however, there are a number of disadvantages associated with the methodology used by such machines. Firstly, the drilling and reaming operations are time consuming, due to the need to provide a hole of high accuracy and good surface finish for the subsequent interference fitting of the pin. Secondly, the alignment of the pin to the hole is critical for correct fitting. It frequently happens during balancing that, having determined the correct neutral position, the precise angular disposition of the input-shaft and torsion bar is disturbed due to cutting forces applied by the drilling or reaming operation or, indeed, the very large forces necessary for pin insertion. It is therefore found that, on inspection of the completed steering gear or valve, hydraulic operation is no longer symmetrical, requiring the valve assembly be extensively reworked or, alternatively, scrapped. Thirdly there is a significant cost associated with consumables used during such balancing operations such as drills, reamers, cutting fluids, etc., and means must be provided in the machines to remove the swarf generated by the metal cutting operations so that contamination of the valve is avoided. A method for fastening an input-shaft and a torsion bar which overcomes some of the above mentioned problems associated with drilling, reaming and pinning is disclosed in

US Patent No. 5,431 ,379 (Takagi). This method requires a ball-receiving hole to be bored in the end of the torsion bar. The end of the torsion bar is inserted into a bore in the input-shaft and a ball is pressed into the hole to provide an interference fit between the input-shaft and the torsion bar. Subsequently, the peripheral edge of the hole in the torsion bar is elliptically deformed so as to retain the ball in the hole and the torsion bar in the input-shaft. A drawback of this method is that the elliptical deformation is necessary to strengthen the connection between the torsion bar and the input-shaft, as the ball pressed into the bore alone does not provide sufficient connection strength. The elliptical deformation of the torsion bar requires equipment in addition to the equipment of inserting the ball into the bore.

The present invention seeks to improve the connection strength associated with inserting a ball or cylindrical member into an axial bore of the torsion bar without the need of elliptical deformation of the end of the torsion bar, whilst still maintaining a lesser degree of processing precision during balancing as demanded with prior art pinning operations.

Summary of Invention

A first aspect of the present invention consists in a hydraulic valve for a power steering gear, the valve comprising a sleeve journalled on an input-shaft, the sleeve having a torsion bar connected thereto via a driven member, the input-shaft having an axially extending bore, the torsion bar having an axially extending bore in a fixing end thereof, the fixing end being remote from the driven member and located within the bore of the input-shaft, the surface of the input-shaft bore and the outer surface of the fixing end of the torsion bar forming an interface therebetween, characterised in that at least one diametral member is press-fitted within the axial bore of the torsion bar and a keying formation is disposed on at least a portion of one or both surfaces forming said interface.

In a first embodiment the keying formation comprises a knurl, flutes, serration or spline disposed on the outer surface of the fixing end of the torsion bar.

In a second embodiment the keying formation comprises a substantially annular projection disposed on the outer surface of the fixing end of the torsion bar and at least partially fills an annular recess disposed on the surface of the input-shaft bore.

Preferably, for both first and second embodiments, the at least one diametral member comprises two diametral members. Preferably one of these two diametral members is larger in diameter than the other, and is preferably located between the open end of the torsion bar bore and the other diametral member.

Preferably the diametral member is a substantially spherical member (or ball), or alternatively a substantially cylindrical member with its cental axis aligned with the axially extending bore of the torsion bar.

A second aspect of the present invention consists in a hydraulic valve for a power steering gear, the valve comprising a sleeve journalled on an input-shaft, the sleeve having a torsion bar connected thereto via a driven member, the input-shaft having an axially extending bore, the torsion bar having an axially extending bore in a fixing end thereof, the fixing end of the torsion bar being remote from the driven member and located within the bore of the input shaft, the surface of the input-shaft bore and the outer surface of the fixing end of the torsion bar forming an interface therebetween,

SUBSΗTUTE SHEET (Rule 26) characterized in that at least two diametral members are press-fitted within the axial bore of the torsion bar.

Preferably one of these two diametral members is larger in diameter than the other, and is preferably located between the open end of the torsion bar bore and the other diametral member.

Preferably the diametral member is a substantially spherical member (or ball), or alternatively a substantially cylindrical member with its central axis aligned with the axially extending bore of the torsion bar.

Preferably a keying formation is disposed on at least a portion of one or both surfaces forming the interface.

Preferably the keying formation comprises a knurl, flutes, serration or spline disposed on the outer surface of the fixing end of the torsion bar. Alternatively the keying formation comprises a substantially annular projection disposed on the outer surface of the fixing end of the torsion bar and at least partially fills an annular recess disposed on the surface of the input-shaft bore.

For all of the above mentioned aspects of invention a pin may be press-fitted within a hole which is substantially diametrically disposed through the input-shaft and the fixing end of the torsion bar.

Description of the Drawings

The present invention will now be described by way of non-limiting examples with reference to the following drawings. Fig. 1 shows a hydraulic valve assembly according to a first preferred embodiment of the first aspect of the present invention;

Fig. 2 is a partial sectional view of this first preferred embodiment of the input-shaft and torsion bar connection according to the first aspect of the present invention;

Fig. 3 is a partial sectional view of an alternative first preferred embodiment of the input-shaft and torsion bar connection according to the first aspect of the present invention;

Fig. 4 is a partial sectional view of still another alternative first preferred embodiment of the input-shaft and torsion bar connection according to the first aspect of the present invention;

Figs. 5a and 5b are partial sectional views of a second preferred embodiment of the input-shaft and torsion bar connection according to the first aspect of the present invention; and

Fig. 6 is a partial sectional view of a preferred embodiment of the input-shaft and torsion bar connection according to the second aspect of the second invention.

Best Mode for Carrying Out Invention

The hydraulic valve in Fig. 1 is contained within housing 16, and comprises input-shaft 2 having sleeve 17 journalled thereon. The manner in which input-shaft 2 and sleeve 17 operate to direct oil to and from an hydraulic pump and assist cylinders (not shown) is well known in the art and will not further be described here. The lower end of input- shaft 2 is journalled on the lower end of torsion bar 1 via a bush 18, the former axially protruding from a driven member, or pinion 19 in this case. A sleeve drive pin 20 radially protrudes from pinion 19 and engages a hole in the skirt of sleeve 17 to provide a substantially slack-free connection between sleeve 17 and pinion 19. The lower end of torsion bar 1 is firmly connected to pinion 19 by some convenient manner such as swaging. In this manner sleeve 17 is effectively connected to the lower end of torsion bar 1 via the driven member ie. pinion 19.

Embodiments of the two aspects of the present invention are now described with like reference numerals being used for like components of the embodiments.

A first embodiment of the first aspect of present invention is shown in Fig. 2 in which fixing end 3 of torsion bar 1 is provided with an axial bore 4 for receiving a diametral member in the form of a ball (or substantially spherical member) 5. In the present specification a "diametral member" is defined as being a member with a substantially circular cross section. Fixing end 3 of torsion bar 1 is disposed within axial bore 6 that extends the entire length of input-shaft 2, thereby forming an interface between outside surface 7 of fixing end 3 and surface 14 of bore 6. The diameter of ball 5 is slightly larger than the inner-diameter of bore 4, whilst outside cylindrical surface 7 of fixing end 3 is knurled. During assembly, when ball 5 is pressed into bore 4, a portion of fixing end 3 forming the peripheral wall 9 of bore 4 is deformed, expanding the outer diameter of fixing end 3 such that outside surface 7 extends outwardly and its knurling "keys" with surface 14 of bore 6 thereby connecting torsion bar 1 to input-shaft 2 in an interference fit. The keying action is achieved by the knurl crests in outside surface 7 contacting surface 14 of bore 6 with localised regions of high stress occurring at the points of engagement between the knurl crests and surface 14. These localised regions of high stress cause local deformation of surface 14, thereby keying torsion bar 1 to input-shaft 2 and hence preventing relative axial and rotational movements therebetween. An O-ring is fitted in groove 8 of fixing end 3 to seal hydraulic oil within the valve such that it does not leak out between input-shaft 2 and torsion bar 1 at the interface of outside surface 7 and surface 14.

An alternative first embodiment of the first aspect of the present invention is shown in Fig. 3 in which fixing end 3 of torsion bar 1 is provided with axial bore 4 for receiving ball 5, in a similar manner to that of the previous embodiment. However, whilst fixing end 3 of torsion bar 1 is disposed within axial bore 6 thereby forming an interface therebetween, a splined (or fluted) outside surface 7a is used instead of the previous knurled surface 7. During assembly, when ball 5 is pressed into bore 4 in a like manner to the previous embodiment, a keying action occurs between splined (or fluted) outside surface 7a and surface 14 of axial bore 6, thereby connecting torsion bar 1 to input- shaft 2 in an interference fit. It should be understood that in other, not shown, embodiments serrations or other keying formations other than splines, flutes or knurling, as described in the abovementioned embodiments, may be used.

A still another alternative first embodiment of the first aspect of the present invention is shown in Fig. 4. In this case the diametral member is in the form of a substantially cylindrical member 15 with its central axis aligned with the axially extending bore 4 of the fixing end 3 of torsion bar 1. Member 15 is preferably round cornered as shown in Fig. 4 to provide a smooth "lead in" when press-fitting the member into bore 4. Cylindrical member 15 may alternatively be slightly "barrel" shaped (ie. it may have a larger diameter at its middle than at its ends) or may be slightly cylindrically tapered, in both cases the aim again being to provide a smooth "lead in".

A second embodiment of the first aspect of the present invention is shown in Figs. 5a and 5b in which fixing end 3 of torsion bar 1 is provided with axial bore 4 for receiving diametral members in the form of two balls 5 and 5a. Fixing end 3 of torsion bar 1 is disposed within axial bore 6 that extends the entire length of input-shaft 2, thereby forming an interface between surface 7 of fixing end 3 and surface14 of bore 6. Prior to assembly, annular ridge 11 is disposed on inner surface 10 of wall 9 which surrounds bore 4 as shown in Fig. 5a. An annular groove 12 is disposed on surface 14 of bore 6. The diameter of ball 5 is slightly larger than the diameter of bore 4. During assembly, when ball 5 is pressed into bore 4, ridge 11 is forced radially outwardly, displacing material 13 on the outer surface of wall 9 into groove 12 and thereby keying torsion bar

1 to input-shaft 2 as shown in Fig. 5b. As material 13 partially fills groove 12, and the comer edges of groove 12 "bite" into the outer surface of wall 9, this keying action prevents relative axial and rotational movements between torsion bar 1 and input-shaft 2. Second ball 5a, which is preferably slightly larger in diameter than ball 5, is then inserted into bore 4, thereby causing the crests of splined surface 7a to locally deform surface 14 of bore 6 and enhancing the strength of the connection between input-shaft

2 and torsion bar 1 in a similar manner to that described in reference to the first embodiment. It should however be noted that, in other not shown embodiments, the spline on surface 7a may be absent or replaced by some other keying formation such as knurling, flutes, or serrations. Also, whilst this second embodiment is shown as preferably utilising two balls 5 and 5a, it should be understood that in a similar (not shown) embodiment only a single ball 5 may be used. Also, in some applications, one or more cylindrical members could be used in place of one or more balls. Alternatively, a mixture of balls and cylindrical members could be used to achieve the necessary keying action.

It should be understood that in all the above mentioned embodiments for the first aspect of the present invention, keying formations may be provided on surface 14 instead of, or in addition to, the formations on surface 7. An embodiment of the second aspect of invention is shown in Fig. 6 in which fixing end 3 of torsion bar 1 is provided with axial bore 4 for receiving two balls 5 and 5a, in a similar manner to that of the second embodiment of the first aspect of invention. However, whilst fixing end 3 of torsion bar 1 is disposed within axial bore 6, thereby forming an interface therebetween, this embodiment does not utilise keying formations such knurls, flutes, serrations, splines, ridges and grooves of any kind, and relies solely on surface frictional forces at the interface between surface 7 of fixing end 3 and surface 14 of bore 6 imposed by the balls 5 and 5a when they are press-fitted into bore 4. In a similar manner to the second embodiment of the first aspect of invention, the second ball 5a is preferably slightly larger in diameter than ball 5.

In all of the above mentioned embodiments of connecting the input-shaft to the torsion bar, insertion of the ball(s) and/or cylindrical member(s) may take place after the neutral position has been determined when the valve is being balanced in a hydraulic or pneumatic balancing machine. It should be understood that the connection of the input-shaft and torsion bar in accordance with the present invention may in some instances only be for the purpose of maintaining the neutral position of the valve whilst the valve is removed and transported to another station remote from the balancing machine. At this remote station a conventional diametrically disposed hole may be drilled through the input-shaft and torsion bar and a pin may be pressed therein to provide a failsafe function for the connection.

It should be obvious to those skilled in the art that numerous variations and modifications could be made to the hydraulic valve without departing from the spirit and scope of the invention.

Claims

CLAIMS:

1. A hydraulic valve for a power steering gear, the valve comprising a sleeve journalled on an input-shaft, the sleeve having a torsion bar connected thereto via a driven member, the input-shaft having an axially extending bore, the torsion bar having an axially extending bore in a fixing end thereof, the fixing end being remote from the driven member and located within the bore of the input-shaft, the surface of the input-shaft bore and the outer surface of the fixing end of the torsion bar forming an interface therebetween, characterised in that at least one diametral member is press-fitted within the axial bore of the torsion bar and a keying formation is disposed on at least a portion of one or both surfaces forming said interface.

2. A hydraulic valve for a power steering gear as claimed in claim 1 , wherein said keying formation comprises a knurl disposed on the outer surface of the fixing end of the torsion bar.

3. A hydraulic valve for a power steering gear as claimed in claim 1 , wherein said keying formation comprises at least one flute disposed on the outer surface of the fixing end of the torsion bar.

4. A hydraulic valve for a power steering gear as claimed in claim 1 , wherein said keying formation comprises at least one serration disposed on the outer surface of the fixing end of the torsion bar.

A hydraulic valve for a power steering gear as claimed in claim 1 , wherein said keying formation comprises at least one spline disposed on the outer surface of the fixing end of the torsion bar.

6. A hydraulic valve for a power steering gear as claimed in claim 1 , wherein said keying formation comprises a substantially annular projection disposed on the outer surface of the fixing end of the torsion bar and at least partially fills an annular recess disposed on the surface of the input-shaft bore.

7. A hydraulic valve for a power steering gear as claimed in any one of the preceding claims, wherein said at least one diametral member comprises two diametral members.

8. A hydraulic valve for a power steering gear as claimed in claim 7, wherein one of said two diametral members is larger in diameter than the other and is located between the open end of the torsion bar bore and the other diametral member.

9. A hydraulic valve for a power steering gear as claimed in any one of the preceding claims, wherein said at least one diametral member is a substantially spherical member.

10. A hydraulic valve for a power steering gear as claimed in any one of claims 1 to 8, wherein said at least one diametral member is a substantially cylindrical member with its cental axis aligned with the axially extending bore of the torsion bar.

11. A hydraulic valve for a power steering gear as claimed in any one of the preceding claims wherein a pin is press-fitted within a hole which is substantially diametrically disposed through the input-shaft and the fixing end of the torsion bar.

12. A hydraulic valve for a power steering gear, the valve comprising a sleeve journalled on an input-shaft, the sleeve having a torsion bar connected thereto via a driven member, the input-shaft having an axially extending bore, the torsion bar having an axially extending bore in a fixing end thereof, the fixing end of the torsion bar being remote from the driven member and located within the bore of the input shaft, the surface of the input-shaft bore and the outer surface of the fixing end of the torsion bar forming an interface therebetween, characterized in that at least two diametral members are press-fitted within the axial bore of the torsion bar.

13. A hydraulic valve for a power steering gear as claimed in claim 12, wherein one of said two diametral members is larger in diameter than the other and is located between the open end of the torsion bar bore and the other diametral member.

14. A hydraulic valve for a power steering gear as claimed in claims 12 or 13, wherein said at least one diametral member is a substantially spherical member.

15. A hydraulic valve for a power steering gear as claimed in claims 12 or 13, wherein said at least one diametral member is a substantially cylindrical member with its cental axis aligned with the axially extending bore of the torsion bar.

16. A hydraulic valve for a power steering gear as claimed in claims 12 to15, wherein a keying formation is disposed on at least a portion of one or both surfaces forming the interface.

17. A hydraulic valve for a power steering gear as claimed in claim 16, wherein said keying formation comprises a knurl disposed on the outer surface of the fixing end of the torsion bar.

18. A hydraulic valve for a power steering gear as claimed in claim 16, wherein said keying formation comprises at least one flute disposed on the outer surface of the fixing end of the torsion bar.

19. A hydraulic valve for a power steering gear as claimed in claim 16, wherein said keying formation comprises at least one serration disposed on the outer surface of the fixing end of the torsion bar.

20. A hydraulic valve for a power steering gear as claimed in claim 16, wherein said keying formation comprises at least one spline disposed on the outer surface of the fixing end of the torsion bar.

21. A hydraulic valve for a power steering gear as claimed in claim 16, wherein said keying formation comprises a substantially annular projection disposed on the outer surface of the fixing end of the torsion bar and at least partially fills an annular recess disposed on the surface of the input-shaft bore.

22. A hydraulic valve for a power steering gear as claimed in any one of claims 12 to 21 wherein a pin may be press-fitted within a hole which is substantially diametrically disposed through the input-shaft and the fixing end of the torsion bar.