GB2091181A

GB2091181A - Power steering apparatus

Info

Publication number: GB2091181A
Application number: GB8138048A
Authority: GB
Original assignee: Jidosha Kiki Co Ltd
Current assignee: Jidosha Kiki Co Ltd
Priority date: 1980-12-19
Filing date: 1981-12-17
Publication date: 1982-07-28
Also published as: AU7866681A; ES8300603A1; DE3150063C2; FR2496583B1; FR2496583A1; DE3150063A1; AU525585B2; ES508117A0; GB2091181B

Abstract

A control valve of rotary type controls a flow of hydraulic fluid by relative rotational displacement between a pair of elements (13, 14) of the valve. A C-shaped spring (12) preloads the elements to a neutral position and is resiliently deformed upon movement of the elements from that neutral position. The spring is displaced only in a plane perpendicular to the rotary valve axis, and is constrained against movement out of that plane. In one form, this is achieved by transmitting the spring load through projections consisting of a pair of projections (11, 17) rotatable with one of the valve elements and a further projection (10) rotatable with the other of said elements and disposed axially intermediate said pair of projections. By such means the gap opened by the increasing diameter of the spring as it is deformed does not interfere with the accurate and reliable return of the valve to the neutral position. In another form, the spring is constrained between a snap ring and a shoulder on the valve element 14. <IMAGE>

Description

SPECIFICATION Power steering apparatus The invention relates to a power steering apparatus, in particular, to a power steering apparatus including a control valve of rotary type for controlling the supply to or displacement from a power cylinder of hydraulic fluid.

A control valve of rotary type comprises a valve rotor which may be provided in integral manner with an input shaft which is connected to a steering wheel, for example, and a valve sleeve integrally connected to an output shaft, which may be connected to steerable road wheels, and rotatable around the valve rotor. In operation, it controls the supply to or displacement from a power cylinder of hydraulic fluid in response to the direction of relative angular displacement between the input and the output shaft or between the valve rotor and the valve sleeve from a neutral condition. In the conventional arrangement, the input and the output shaft are connected together by a torsion bar, the torsional force of which is effective to maintain the valve rotor and the valve sleeve in their neutral condition whenever the control valve is inoperative.However, it will be appreciated that with a torsion bar, the valve rotor and the valve sleeve must be maintained in their neutral condition when the torsional force of the bar is zero in either direction. As a consequence, it is impossible to apply a preload between the input and the output shaft when the torsion bar arrangement is employed.

To accommodateforthis difficulty, there has been proposed a power steering apparatus in which in addition to or in place of the torsion bar, a substantially C-shaped spring is used which is formed by providing a notch or hiatus partly in a ring-shaped spring member, with projections each integral with the input and the output shaft, respectively, resiliently held between the end faces of the notch formed in the C-shaped spring to permit a preload to be applied while simultaneously maintaining the both shafts in their neutral condition.

However, when a power steering apparatus of the kind described immediately above is employed, if a gap is present between the inner peripheral surface of the C-shaped spring and the outer peripheral surface of a member such as a valve sleeve, for example, which is located inside the spring, a relative rotation between the input and the output shaft to cause a movement of the pair of projections held in the notch of the spring away from each other may cause the spring to tilt out of the original plane, substantially precluding the application of a resilient bias which causes the both projections to be returned to their neutral positions until the spring abuts against the outer peripheral surface of the valve sleeve to prevent any further tilting thereof.If the original gap is removed, as the projections are displaced with widening of the notch or the spacing between the circumferential end faces of the Cshaped spring, an increase in the inner diameter of the spring necessarily produces a gap between the inner peripheral surfaces thereof and the outer peripheral surface of the valve sleeve, again causing the spring to tilt while holding the both projections therein. It then follows that an arrangement which involves the gap mentioned above may not accurately and reliably return the valve rotor and the valve sleeve to their neutral positions. If the original gap is removed, a tilting of the spring as it is operated causes differential resilient biases to be applied to the pair of projections, which may adversely influence the reaction sensed when steering.

According to one aspect of the invention a power steering apparatus in which tilting of a biasing or preloading spring out of a plane perpendicular to the common axis of an input shaft and an output shaft is prevented when a preload is applied across these shafts by the resilience of the spring acting on respective projections rotating one with the input shaft and one with the output shaft, thus enabling a rotary control valve to be reliably maintained in its neutral condition.This may be accomplished by providing a control means on either one of the input and output shafts and/or on a control valve element, and which engages with the circumferential end face of a notch formed in or the axial end face of a C-shaped preloading or biasing spring to prevent a movement of the spring in a direction misaligned from the plane in which the spring is originally disposed or which is perpendicular to the axis of the control valve element, including both a tilting and an axial displacement, while allowing a movement of the spring in such plane.

According to another feature of the invention, the construction of the control means can be simplified by providing a plurality of projections on either the input or the output shaft for causing a flexure of the C-shaped spring while disposing the projection provided on the other shaft between the plurality of projections.

According to a further feature of the invention, the accuracy of operation of the control valve of a power steering apparatus is improved by providing a plurality of projections on the output shaft, coupling a control valve element with the output shaft by means of a pin, and holding a projection on the input shaft and the plurality of projections on the output shaft in a notch formed in a C-shaped spring, thus preventing the resilience of the C-shaped spring from acting upon the valve element.

Other features of the invention will become apparent from the following description with reference to the attached drawings. In the drawings: Figure 1 is a side elevation, partly in longitudinal section, of an embodiment of the invention; Figure 2 is an exploded, perspective view of the main parts shown in Figure 1; Figures 3 and 4 are cross sections taken along the lines Ill-Ill and IV-IV shown in Figure 1; Figure 5 is a schematic illustration of the relationship between the projections and the C-shaped spring in its neutral condition; Figure 6 is a schematic illustration of the relationship between the projections and the C-shaped spring when the input shaft is driven for rotation in one direction; Figure 7 is an enlarged view of the projections and the C-shaped spring according to a modification;; Figure 8 is a side elevation, partly in longitudinal section, of another embodiment of the invention; Figure 9 is a cross section taken along the line IX-IX shown in Figure 8; figure 70 is a schematic illustration of the relationship between the projections and the C-shaped spring as the input shaft is rotated in one direction; Figure 77 is a side elevation, partly in longitudinal section, of a further embodiment of the invention; Figure 12 is an exploded, perspective view the main parts shown in Figure 11; and Figure 13 is a cross section taken along the line XIII-XIII shown in Figure 11.

Referring to the drawings, and particularly to Figure 1, there is shown an input shaft 1 which is disposed on the some axis as an output shaft 2. On its free end, the input shaft 1 is formed with an extension 3 which is aligned with the axis thereof and which is rotatably fitted into a bushing 4 which is in turn fitted into the axial end of the output shaft 2 in alignment with the axis thereof. Under this condition, both the input and the output shaft 1,2 are rotatably journalled in a housing 5 by means of bearings 6. The input shaft 1 is connected to a steering wheel, not shown, while a portion of the output shaft 2 adjacent to the other end thereof is formed with a helical pinion 7, which meshes with a rack connected to steerable road wheels, not shown, generally in the similar manner as a conventional power steering apparatus of rack and pinion type.

Referring to Figures 1 to 3, a substantially polygonal member 8 is formed on the free end of the input shaft 1 substantially at the root of the extension 3, and is received in a groove 9 formed in the adjacent end of the output shaft 2 with a given circumferential clearance therebetween. In this manner, a relative rotation is permitted between the input and the output shaft 1,2 as limited by the magnitude of the clearance. A pair of projections 10, 11 are formed on the input shaft 1 and the output shaft 2, respectively, in the region of the polygonal member 8 and the groove 9, respectively. A valve sleeve 14, to be described later, includes a step 14b on which a projection 17 is integrally formed thereon.These projections 10, 11 and 17 are held sandwiched between the opposite circumferential end faces of a notch 12a formed in a C-shaped spring 12 which is disposed in surrounding relationship with the polygonal member 8 and the groove 9.

When unstressed, the notch 12a of the C-shaped spring 12 has a circumferential length t which is less than a corresponding dimension of the projections 10, 11 and 17, all of which has a common size (see Figure 2). Hence, a desired preload can be applied across the input and the output shaft 1,2 by disposing the projections 10,11 and 17 held sandwiched in the notch of the C-shaped spring 12. It should be apparent that when an external force is not applied to either the input or the output shaft 1, 2, the polygonal member 8 is maintained in its neutral position as viewed in the direction of rotation within the groove 9, by means of the C-shaped spring 12.

A valve rotor 13 is directly formed on the input shaft 1, and the valve sleeve 14 is rotatably fitted over the valve rotor 13, thus forming a control valve of rotary type which is basically known in the art. The end of the valve sleeve 14 located nearer the output shaft 2 is formed as a hollow cylinder 14a which can be fitted over a portion 2a of the output shaft 2 on which the projection 11 is formed. The hollow cylinder 14a is formed with an axial slot 15 of a width which coincides with the circumferential dimension of the projection 11, and is also formed with a through-opening 16 which permits the projection 10 to extend therethrough and which permits a circumferential displacement of the projection 10 therein.

As will be evident by reference to Figures 1 and 3, the hollow cylinder 14a is situated inside the Cshaped spring 12, with the slot 15 being engaged by the projection 11 to provide an integral connection between at least the output shaft 2 and the valve sleeve 14 as far as the rotation is concerned, and the projection 10 loosely extending through the opening 16 with a given spacing on either side, as viewed at least in the direction of rotation. The projection 17 is integrally formed on the step 1 4b which is formed on the end of the hollow cylinder 14a, and is located in alignment with the axial slot 15 as viewed in the circumferential direction and extends toward the projection 11, as indicated in Figure 2.While it may be difficult to provide the projection 17 integrally with the valve sleeve 14 as by machining, it can be easily manufactured by utilizing a sintered material.

Conversely, the projection 17 may be formed as a pin separately from the valve sleeve 14, and the pin may be fixed to the valve sleeve 14 as by a press fit.

As shown in Figure 5, in their neutral condition, the projections 10,11 and 17 are maintained in alignment with each other by the resilience of the C-shaped spring 12, with the projections 11, 17, located on the output shaft side, being located on the opposite axial sides of the projection 10 on the input shaft 1. Consequently, when the input shaft 1 rotates in one direction to produce a relative rotation between the projection 10 on one hand and the projections 11, 17 on the other against the resilience of the C-shaped spring 12, as shown in Figure 6, it will be seen that one of the circumferential end faces of the notch 12a formed in the C-shaped spring 12 is supported at two points defined by the projections 11,17. As a consequence, if there is a gap of an increased magnitude between the inner peripheral surface of the spring 12 when unstressed and the hollow cylinder 1 4a of the valve sleeve 14, the tendency for the spring 12 to tilt relative to the axial direction of the input shafts 1, 2 is avoided. In this manner, the control valve can be maintained in its neutral condition in an accurate and a reliable manner, allowing a sensitive, play-free steering response to be obtained. Any gap between the spring 12 and the valve sleeve 14 is allowed, requiring no particular accuracy in fabricating the spring 12, which therefore can be easily provided.

The control valve comprising the valve rotor 13 and the valve sleeve 14 merely causes a circulation of hydraulic fluid from a pump, not shown, when it assumes the neutral condition shown. Specifically, referring to Figures 1 and 4, the hydraulic fluid from the pump passes through a supply opening 20 formed in the housing 5, and through an annular groove 21 and radial passages 22, both formed in the valve sleeve 14, into axially extending supply grooves 23 which is formed in the valve rotor 13, and thence into a pair of axially extending grooves 24 and 25 formed in the inner surface of the valve sleeve 14 so as to be overlapping with the opposite circumferential ends of the grooves 23, and into axially extending discharge grooves 26 each formed in the valve rotor 13 so as to be overiapping with both of a pair of grooves 24, 25. Upon entering the discharge grooves 26, the hydraulic fluid flows therealong to the region of the abutting ends of the input and the output shaft 1,2 and thence through the opening 16 and the notch 1 2a in the spring 12 to the outside of the valve sleeve 14, where it returns to the suction side of the pump through a discharge port 27 formed in the housing 5. The grooves 24 located on one side of the supply grooves 23 communicate with one of chambers of the power cylinder, not shown, through radial passages 28, an annular groove 29 and a supply/discharge port 30 formed in the housing 5. Similarly, the other grooves 25 communicate with the other chamber of the power cylinder through radial passages 31, an annular groove 32 and a supply/discharge port 33.

However, in the neutral condition, each supply groove 23 exhibits a substantially equal flow area with respect to each of the grooves 24,25, located on the opposite sides thereof, and hence there occurs no pressure differential between the grooves 24, 25, thus maintaining the power cylinder inoperative.

However, when the input shaft 1 rotates in one direction, there occurs a relative rotation between the projection 10 on one hand and the projections 11, 17 on the other, or between the valve rotor 13 and the valve sleeve 14, against the resilience of the C-shaped spring 12, producing a difference in the flow area between each supply groove 23 and the grooves 24, 25 located on the opposite sides thereof depending on the direction of rotation. As a result, a pressure differential is produced between the grooves 24,25 and causes the power cylinder to be operated, thus imparting an auxiliary force in the direction to be steered, as is well known in the art.

In the embodiment described above, the projec- tion 11 is fixedly mounted on the output shaft 2, and is utilized to provide an integral connection between the output shaft 2 and the valve sleeve 14 as far as the rotation is concerned. However, any suitable means may be utilized to provide such an integral connection between the output shaft 2 and the valve sleeve 14, and the projection 11 may be mounted on the valve sleeve 14.

Figure 7 shows a modification. In this instance, the projection 17 is formed by a sintering operation, and the load imposed upon this projection is reduced by providing a spacing L1 between the projections 10, 11 which is less than a spacing L2 between the projections 10, 17 as the input shaft is rotated in one direction to cause a relative rotation between the projection 10 on one hand and the projections 11, 17 on the other against the resilience of the C-shaped spring 12.

More specifically, the load F imposed upon the projection 10 by the resilience of the C-shaped spring 12 is equal to the resultant of loads F1, F2 imposed upon the respective projections 11, 17 and is oppositely directed from the latter. Consequently, the ratio of the loads F1 and F2 is in inverse proportion to the ratio of the spacings L1 and L2 from the projection 10. In other words, the magnitude of the load is reduced as further removed from the projection 10. By disposing the projection 10 close to the projection 11, the load F2 imposed upon the projection 17 can be reduced as compared with the load F1 imposed upon the projection 11, thus effectively preventing any damage which may be caused to the projection 17 which is formed of a relatively brittle material.

When the spring 12 is expanded by moving the projections 11, 17 relative to the other projection 10 as shown in Figure 6, the projection 10 contacts the spring 12 at a single point P. If the point P is largely displaced from the central position where b1 = b2, as viewed in the axial direction, the end face of the notch 1 2a against which the projection 10 abuts will be located askew with respect to the axial direction if the other end face is located in the axial direction, and this may cause a change in the magnitude of the spring constant. To prevent this, it is desirable that the point of contact P be located centrally along the circumferential end face of the spring 12 as viewed in the axial direction.However, if it is necessary to locate the point P offset from the central position for design reason, the spring constant may be chosen in consideration of the angular displacement which would occur about the point P. Alternatively, a plurality of projections 10 may be provided. As a further alternative, the projection 10 may be formed to present a square cross section to increase the area of contact with the spring 12, thus minimizing the angular displacement.

Figures 8 to 10 show another embodiment of the invention in which one end of the output shaft 2 is configured in the form of a sleeve 2b in which the input shaft 1 is received with a bearing 40 interposed therebetween. A pair of axially spaced and radially outwardly extending pins 41,42 are fixedly mounted in the sleeve 2b, between which a through-opening 43 is formed in the sleeve through which a pin 44 mounted on the valve rotor 13 projects. A C-shaped spring 12 which is similar to that illustrated in the previous embodiment is disposed in surrounding relationship with the sleeve 2b. The spring 12 holds the respective pins 41,42 and 44 in its notch, thus applying a given preload across the input and the output shaft 1, 2. It is to be noted that the C-shaped spring 12 is disposed between a step 2formed on the sleeve 2b and a snap ring 46, and thus is constrained from axial movement. The valve sleeve 14 and the sleeve 2b of the output shaft 2 are integrally coupled together by means of a stud 45 which is embedded into the both members. As a relative angular displacement occurs between the input and the output shaft 1, 2, the valve rotor 13 rotates relative to the valve sleeve 14, thus controlling the supply to or displacement from a power cylinder, not shown, of a hydraulic fluid. Figure 10 shows such a relative rotation between the input and the output shaft 1, 2.As shown, the pair of pins 41, 42 abut against dne of the circumferential end faces of the spring 12, thus preventing a tilting movement thereof. In this embodiment, the spring 12 does not interfere or engage with the valve sleeve 14, which is therefore not directly subject to the resilienc of the spring 12.Asa result, the valve sleeve 14is permitted to rotate accurately about the axis, assuring an increased accuracy of controlling the supply or discharge of the hydraulic fluid.

Figure 9 shows that the fitting engagement between the input and the output shaft 1, 2 is provided as a so-called "fail safe" arrangement. Specifically, the periphery of the input shaft 1 is provided with a plurality of axially extending, circumferentially spaced ribs 47 while the inner periphery of the output shaft 2 is formed with a plurality of circumferentially spaced, axially extending flutes which receive the ribs 47 to permit a relative rotation therebetween.

The operation of the embodiment shown in Figures 8 to 10 is basically similar to that of the embodiment initialiy mentioned, and therefore will not be described again.

Figures 11 to 13 show a further embodiment of the invention. In this embodiment, the C-shaped spring 12 is constrained against axial movement by being held between the step 14b on the valve sleeve 14 and a snap ring 50 which is detachably mounted in a circumferential groove 14cformed in the valve sleeve 14. Consequently, the freedom of movement ofthe C-shaped spring 12 in the axial direction is determined by the tolerance between the step 1 4b of the valve sleeve 14 and the spring 12 and the tolerance between the snap ring 50 and the spring 12 alone. As the spring 12 flexes outwardly, it is urged by the projections 10, 11, thus avoiding a tilting thereof. Because the snap ring 50 is detachable, the assembly and the disassembly are facilitated.

In this embodiment, the projection 11 is fixedly mounted on the output shaft 2 and is used to provide an integral connection between the output shaft 2 and the valve sleeve 14 as far as the rotation is concerned. However, suitable means may be utilized to provide such an integral connection between the output shaft and the valve sleeve, and the projection 11 may be formed on the valve sleeve. Alternatively, the valve rotor may be formed on the output shaft while the valve sleeve may be formed on the input shaft in a manner opposite from that illustrated in the embodiments.

It will be seen that each of the embodiments described above relates to a power steering apparatus including a control valve which comprises a valve rotor and a valve sleeve as its control elements. However, it should be understood that the invention is equally applicable to a power steering apparatus including other kinds of control valves of rotary type, for example, a disc-shaped control valve.

While the invention has been specifically shown and described above in connection with several embodiments thereof, it should be understood that a number of changes and modifications therein will readily occurto those skilled in the art.

Claims

1. A power steering apparatus including an input shaft to be connected to a steering wheel, and output shaft disposed on the common axis as the input shaft to be connected to steerable road wheels, control valve elements mounted on the respective shafts, a pair of projections disposed for integral rotation with the respective control valve elements, and a substantially C-shaped spring having a notch therein in which the both projections are held sandwiched to maintain the control valve elements in their neutral condition, the control valve elements being adapted to control the flow of a hydraulic fluid to or from a power cylinder by rotating relative to each other in response to a relative rotational displacement between the input and output shafts while causing a flexure of the spring, control means being provided between the relatively rotatable shafts and/or control valve elements for engaging with a circumferential end face of the notch formed in the C-shaped spring or the axial end face thereof to permit a movement of the spring in a plane which is perpendicular to the shaft axis while constraining the spring from movement in any other direction.

2. A power steering apparatus according to Claim 1, further characterized in that the control means comprises a plurality of projections provided on either the input or the output shaft side, and a single projection provided on the other side and located intermediate the plurality of projections, the C-shaped spring holding these projections sandwiched in the notch formed therein.

3. A power steering apparatus according to Claim 2, further characterized in that the plurality of projections are provided on the output shaft side.

4. A power steering apparatus according to Claim 3, further characterized in that one of the plurality of projections provided on the output shaft side is disposed on the associated control valve element.

5. A power steering apparatus according to Claim 3 in which the plurality of projections are formed on the output shaft.

6. A power steering apparatus according to Claim 5, further characterized in that the output shaft and the control valve element are integrally coupled together by means of a pin.

7. A power steering apparatus according to any one of Claims 4 and 6, further characterized in that the control valve element is formed as a valve sleeve.

8. A power steering apparatus according to Claim 1 in which one of the control valve elements is a valve sleeve while the other control valve element is a valve rotor having one of the pair of projections integral therewith and disposed inside the valve sleeve, the valve sleeve being formed with a through-opening through which the free end of the projection on the valve rotor projects externally, with a given clearance being defined between the projection and the through-opening as viewed in the direction of rotation of the valve sleeve, the valve sleeve being provided with the other projection which is adapted to rotate integrally therewith, the both projections being maintained at given positions by the resilience of the C-shaped spring which is disposed in surrounding relationship with the valve sleeve, the valve sleeve including a step which is located in abutment against one side of the spring, the other side of which bears against a fixing member mounted on the valve sleeve, whereby the C-shaped spring is aliowed to move in a plane perpendicular to the axis while constraining it from movement in any other direction.

9. A power steering apparatus according to Claim 8 in which the fixing member comprises a snap ring fitted over the outer periphery of the valve sleeve.

10. A power steering apparatus comprising coaxial input and output shafts and respective elements of a rotary control valve being mounted on said shafts, for relative rotation therebetween, to control the flow of fluid to a power steering motor, said control valve elements being biased or preloaded to a neutral position of the valve by a substantially C-shaped spring resiliently deformable in a plane perpendicular to the shafts upon relative rotation of the valve elements from said neutral position, said spring being engaged by control means that constrain the spring from movement in directions transverse to said plane.

11. A power steering apparatus constructed and arranged for use and operation substantially as described herein with reference to any of the embodiments iliustrated in the accompanying drawings.