GB1591309A - Steering systems and steering gears therefor - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO STEERING SYSTEMS AND STEERING GEARS THEREFOR (71 We, CAM GEARS LIMITED of 45 Wilbury Way, Hitchin, Hertfordshire, SG4 OTU, a British Company, 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 state ment:- This invention relates to steering systems and steering gears therefore and is particularly concerned with such a system and gear for power assisted vehicle steering which is an improvement in, or modification of, the invention which is the subject of our Complete Specification No. 1,465,901.

According to the present invention there is provided a steering gear assembly for a power assisted vehicle steering system comprising an input component and an output component mounted in a housing for rotation about a common longitudinal axis, the input and output components being interconnected by an elastic torsion bar so that said components can exhibit rotation relative to each other while twisting is effected in the torsion bar; valve means which is intended to regulate the supply of pressure fluid to a steering servo motor and which valve means is controlled by relative rotation between the input and output components; a tubular member which is substantially rigid with one but not the other of said components and within which tubular member the torsion bar extends, and a clutch means comprising a recess in the tubu 'lar member and a detent which is relative to said recess and radially displaceable relative to the longitudinal axis, the detent being capable of co-operating with the recess for clutching the tubular member to the input component or the output component, as the case may be whichever of said components does not have the tubular member as a rigid extension thereof, in response to fluid pressure when such is applied to urge the detent into engagement with the recess, the arrangement of the assembly being such that, when installed in a vehicle steering system', pressure fluid from a vehicle speed responsive source may act upon the detent and cause said en engagement and thereby restrain relative rotation between the input and output components with consequential decrease in vehicle steering power assistance with increase in vehicle speed.

Further according to the present invention there is provided a power assisted vehicle steering system comprising a steering gear assembly as specified in the immediately preceding paragraph in which the valve means regulates the supply of pressure fluid to a steering servo motor in the system; a vehicle speed responsive source of fluid pressure, and means for leading pressure fluid from said source to act upon the detent and cause engagement of the clutch means and thereby restrain relative rotation between the input and output components with consequential decrease in vehicle steering power assistance with increase in vehicle speed.

Still further according to the present invention there is provided a vehicle having a power assisted steering system comprising an input component and an output component mounted in a housing for rotation about a common longitudinal axis, the input and output components beng interconnected by an elastic torsion bar so that said components can exhibit rotation relative to each other while twisting is effected in the torsion bar; valve means which is intended to regulate the supply of pressure fluid to a steering servo motor and which valve means is controlled by relative rotation between the input and output components; a tubular member which is substantially rigid with one but not the other of said components and within which tubular member the torsion bar extends; fluid pressure responsive clutch means for clutching the tubular member to the input component or the output component, as the case may be whichever of said components .does not have the tubular member as a rigid extension thereof, in response to fluid pressure when such is applied to the clutch means, and a source of pressure fluid which is responsive to vehicle speed, said pressure fluid acting upon the clutch means to effect said clutching whereby relative rotation between the input and output components is increasingly restrained with a consequential decrease in vehicle steering power assistance as the vehicle speed increases.

In the present invention the tubular member forms a substantially rigid extension of either the input or output component (for example it may be formed integral with that component) so that any torque responsive characteristics in the tubular member may be considered negligible in comparison with those of the torsion bar. As a consequence, and for so long as the detent is not in driving engagement with the recess of the tubular member, the input and output components can exhibit rotation relative to each other and so develop a twist in, or change the amount of twisting of, the torsion bar; however, when the detent is urged by fluid pressure into firm engagement with the recess to clutch together the tubular member with the input or output component as the case may be, the torsion bar is effectively shunted so that, during normal usage of the steering gear assembly, relative rotation between the input and output components is restrained and thereby power assistance to vehicle steering is removed. It is likely that the extent of driving engagement between the detent and the recess will be progressive as the vehicle speed increases and as such there will be a progressively increasing resistance to restrain relative rotation between the input and output components (with a consequential progressive decrease in power assistance which is provided to the steering) until such time as the detent is in firm engagement with the recess. The recess which cooperates with the detent (and of which there may be more than one set of co-operating recesses and detents as discussed in our aforementioned Specification No. 1,465,901) may be designed to have a progressive camlike effect on the detent which is urged into driving engagement therewith so that such engagement is progressive as aforementioned.

The or each detent is preferably in the form of a ball or plunger with a spherically profiled end for engagement with the recess.

As an alternative to the aforementioned integral structure, the tubular member may be in the form of a tube rigidly connected to the input component or the output component as appropriate. For example, with the output component in the form of a pinion in a rack and pinion steering gear or a worm in a worm and sector steering gear, the tubular member may comprise a tube which is connected as a rigid extension of, and co-axial with, a shaft of such pinion or worm.

Torque responsive steering gears and systems of the general kind to which the present invention relates are well known in the art and as such the particular structures of the valve means which is utilised in the gear assembly and the steering servo motor which is incorporated in the system may each be of a type well known in the art and which need not be discussed in detail herein. For example, the valve means controlled by relativerotation between the input and output components may be of the kind described in our Patent No. 1,223,551 whereby the aforementioned relative rotation imparts axial displacement to a valve element for controlling fluid flow to the servo motor or may be of the kind described in our Specification No.

1,465,901, whereby the input and output components can be regarded as valve elements (or extensions thereof) relative rotation between which causes rotational adjustment between valve ports and lands to control fluid flow to the servo motor. The servo motor may conveniently be a double acting piston and cylinder arrangement incorporated as part of the steering linkage.

One embodiment of a steering gear assembly constructed in accordance with the present invention will now be described by way of example only with reference to the accompanying illustrative drawings in which: Figure 1 is a longitudinal section through the assembly, and Figure 2 is a section of the assembly taken on the line A-A of Figure 1.

Many of the elements in the drawings will be recognisable to those familiar with power assisted vehicle steering systems and a detailed description of such elements is therefore considered unncessary.

The steering gear illustrated is applied to rack and pinion vehicle steering with a rack bar 1 driven by a pinion 2 in a housing or steering box 3, the driver's wheel being connectable by a steering column (not shown) to a tubular input shaft 4. The basic hydraulic system is omitted but may be assumed to include an engine driven pump supplied by a reservoir (5) to which its output flow ultimately returns, such engine driven pump delivering fluid pressure to an input port 6 of the housing from which fluid flow is controlled by a valve mechanism 7 to be directed through outlet ports (not shown) to a servo motor (not shown) for power assistance; fluid displaced from the servo motor can return to the reservoir 5 by way of a port 8 of the housing.

The input shaft 4 is rotatably mounted in the housing 3 co-axially with the axis of the pinion 2 and this shaft 4 receives an elastic torsion bar 9. One end of the bar 9 is rigidly connected by a pin 10 to a shaft 11 of the pinion 2 and the other end of the rod 9 is rigidly connected by a pin 12 to the input shaft 4. The torsion bar 9 acts in a manner which is well known in conventional steering gears for power assisted vehicle steering systems whereby upon rotation of the input shaft 4 such shaft may exhibit rotation relative to the pinion 2 while a twist is progressvely developed in the torsion bar the torque of which resists such relative rotation. Relative rotation between the shaft 4 and pinion 2 causes an adjustment in the valve mechanism 7 so that fluid flow through the valve to the servo motor is appropriately controlled to provide the required power assistance. The structure of the valve mechanism 7 and the manner in which its adjustment is effected as a result of relative rotation between the input shaft 4 and pinion 2 may be well known in the art; in the present example the valve mechanism 7 and the manner of its adjustment are similar to that described in our Patent No.

1,223,551, whereby the shaft 4 carries a sleeve 15 which is capable of axial movement on the shaft but is restrained from circumferential movement relative thereto. The sleeve 15 is provided with track followers in the form of pegs 16 engaging with helical tracks 17 provided on the pinion shaft 11 so that, upon relative rotation between the shaft 4 and the pinion shaft 11, the pegs 16 are displaced along the tracks 17 to cause movement of the sleeve 15 axially within the housing 3. The sleeve 15 is connected to a valve sleeve element 18 which is axially slidable in unison therewith and serves to control fluid flow through the valve mechanism 7.

The torsion bar 9 extends through a cylindrical tube 13 which is received with radial clearance within the end of the tubular input shaft 4. One end of the tube 13 is located within a socket 14 in the pinion shaft 11 to which it is rigidly connected. The tube 13 is substantially co-axial with the axis of rotation for the pinion 2 and effectively forms a rigid extension of the pinion shaft 11 so that there are no, or negligible, torque responsive characteristics exhibited by the tube 13 as compared with those of the torsion bar 9.

Located in the tube 13 adjacent to the free end thereof are a pair of diametrically opposed recesses in the form of holes 19 in the wall of the tube and which are of bevelled or cam profile in the section taken radially of the tube 13 (as shown in Figure 2). Extending radially through the wall of the input shaft 4, substantially in radial alignment with each of the holes 19, are a pair of cylindrical bores 20 each of which serves as a detent housing.

Located as a close sliding fit one within each of the bores 20 are a pair of spherical balls 21. The radially outer faces of the balls 21 are located in an annular chamber 22 of the housing 3 which chamber communicates with a secondary input port 23 to which is connected the output from a transmission driven pump 24 which draws hydraulic fluid from the reservoir 5. The fluid pressure output of pump 24 increases and decreases in accordance with an increase or decrease respectively in vehicle speed and as a result of an increase in such pressure the balls 21 are urged radially inwardy to engage within the holes 19. The outcome of this latter effect is that, in the extreme, the balls 21 may actually lock the input shaft 4 to the rigid tube extension 13 of the pinion shaft 11. A lock when thus formed in effect causes the torsion bar 9 to be shunted so that, during normal usage of the steering gear, relative rotation cannot take place between the input shaft 4 and the pinion shaft 11 and power assistance is not applied. By providing the recesses 19 with a bevelled or cam profile a chosen relationship may be achieved during the engagement of the balls 21 with the recesses 19 and the fluid pressure from the pump 24 until such time as the aforementioned extreme locking condition is effected. As such the decrease in the torsion responsive characteristic exhibited by the torsion bar 9 may be gradual and therefore the decrement of power assistance with increment of speed may be graduated.

Although in the extreme the balls 21 may lock the input shaft 4 to the pinion shaft 11 (through the tube 13) so that the steering is substantially direct between the input and output components of the gear, if, for example in an emergency, an excessive steering force is applied to the input shaft 4 it is envisaged that the exertion of such a high torque on the input shaft may cause the balls 21 to be displaced from the recesses 19 and power assistance would resume.

WHAT WE CLAIM IS: 1. A steering gear assembly for a power assisted vehicle steering system comprising an input component and an output component mounted in a housing for rotation about a common longitudinal axis, the input and output components being interconnected by an elastic torsion bar so that said components can exhibit rotation relative to each other while twisting is effected in the torsion bar; valve means which is intended to regulate the supply of pressure fluid to a steering servo motor and which valve means is controlled by relative rotation between the input and output components; a tubular member which is substantially rigid with one but not the other of said components and within which tubular member the torsion bar extends, and a clutch means comprising a recess in the tubular member and a detent which is displaceable relative to said recess and radially relative to the longitudinal axis, the detent being capable of co-operating with the recess for clutching the tubular member to the input component or the output component, as the case may be whichever of said components does not have the tubular member as a rigid extension thereof, in response to fluid pressure when such is applied to urge the detent

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. gears for power assisted vehicle steering systems whereby upon rotation of the input shaft 4 such shaft may exhibit rotation relative to the pinion 2 while a twist is progressvely developed in the torsion bar the torque of which resists such relative rotation. Relative rotation between the shaft 4 and pinion 2 causes an adjustment in the valve mechanism 7 so that fluid flow through the valve to the servo motor is appropriately controlled to provide the required power assistance. The structure of the valve mechanism 7 and the manner in which its adjustment is effected as a result of relative rotation between the input shaft 4 and pinion 2 may be well known in the art; in the present example the valve mechanism 7 and the manner of its adjustment are similar to that described in our Patent No. 1,223,551, whereby the shaft 4 carries a sleeve 15 which is capable of axial movement on the shaft but is restrained from circumferential movement relative thereto. The sleeve 15 is provided with track followers in the form of pegs 16 engaging with helical tracks 17 provided on the pinion shaft 11 so that, upon relative rotation between the shaft 4 and the pinion shaft 11, the pegs 16 are displaced along the tracks 17 to cause movement of the sleeve 15 axially within the housing 3. The sleeve 15 is connected to a valve sleeve element 18 which is axially slidable in unison therewith and serves to control fluid flow through the valve mechanism 7. The torsion bar 9 extends through a cylindrical tube 13 which is received with radial clearance within the end of the tubular input shaft 4. One end of the tube 13 is located within a socket 14 in the pinion shaft 11 to which it is rigidly connected. The tube 13 is substantially co-axial with the axis of rotation for the pinion 2 and effectively forms a rigid extension of the pinion shaft 11 so that there are no, or negligible, torque responsive characteristics exhibited by the tube 13 as compared with those of the torsion bar 9. Located in the tube 13 adjacent to the free end thereof are a pair of diametrically opposed recesses in the form of holes 19 in the wall of the tube and which are of bevelled or cam profile in the section taken radially of the tube 13 (as shown in Figure 2). Extending radially through the wall of the input shaft 4, substantially in radial alignment with each of the holes 19, are a pair of cylindrical bores 20 each of which serves as a detent housing. Located as a close sliding fit one within each of the bores 20 are a pair of spherical balls 21. The radially outer faces of the balls 21 are located in an annular chamber 22 of the housing 3 which chamber communicates with a secondary input port 23 to which is connected the output from a transmission driven pump 24 which draws hydraulic fluid from the reservoir 5. The fluid pressure output of pump 24 increases and decreases in accordance with an increase or decrease respectively in vehicle speed and as a result of an increase in such pressure the balls 21 are urged radially inwardy to engage within the holes 19. The outcome of this latter effect is that, in the extreme, the balls 21 may actually lock the input shaft 4 to the rigid tube extension 13 of the pinion shaft 11. A lock when thus formed in effect causes the torsion bar 9 to be shunted so that, during normal usage of the steering gear, relative rotation cannot take place between the input shaft 4 and the pinion shaft 11 and power assistance is not applied. By providing the recesses 19 with a bevelled or cam profile a chosen relationship may be achieved during the engagement of the balls 21 with the recesses 19 and the fluid pressure from the pump 24 until such time as the aforementioned extreme locking condition is effected. As such the decrease in the torsion responsive characteristic exhibited by the torsion bar 9 may be gradual and therefore the decrement of power assistance with increment of speed may be graduated. Although in the extreme the balls 21 may lock the input shaft 4 to the pinion shaft 11 (through the tube 13) so that the steering is substantially direct between the input and output components of the gear, if, for example in an emergency, an excessive steering force is applied to the input shaft 4 it is envisaged that the exertion of such a high torque on the input shaft may cause the balls 21 to be displaced from the recesses 19 and power assistance would resume. WHAT WE CLAIM IS:

1. A steering gear assembly for a power assisted vehicle steering system comprising an input component and an output component mounted in a housing for rotation about a common longitudinal axis, the input and output components being interconnected by an elastic torsion bar so that said components can exhibit rotation relative to each other while twisting is effected in the torsion bar; valve means which is intended to regulate the supply of pressure fluid to a steering servo motor and which valve means is controlled by relative rotation between the input and output components; a tubular member which is substantially rigid with one but not the other of said components and within which tubular member the torsion bar extends, and a clutch means comprising a recess in the tubular member and a detent which is displaceable relative to said recess and radially relative to the longitudinal axis, the detent being capable of co-operating with the recess for clutching the tubular member to the input component or the output component, as the case may be whichever of said components does not have the tubular member as a rigid extension thereof, in response to fluid pressure when such is applied to urge the detent

into engagement with the recess, the arrangement of the assembly being such that, when installed in a vehicle steering system, pressure fluid from a vehicle speed responsive source may act upon the detent and cause said engagement and thereby restrain relative rotation between the input and output components with consequential decrease in vehicle steering power assistance with increase in vehicle speed.

2. A steering gear assembly as claimed in claim 1 in which the tubular member is integral with the component from which it extends.

3. A steering gear assembly as claimed in claim 1 in which the tubular member comprises a substantially cylindrical tube which is rigidly connected to the component from which it extends.

4. A steering gear assembly as claimed in any one of the preceding claims wherein the component which does not have the tubular member as a rigid extension thereof has a tubular portion, said tubular portion and tubular member being received one within the other and the clutch means being arranged for clutching the tubular member to the tubular portion in response to fluid pressure when such is applied to the clutch means.

5. A steering gear assembly as claimed in claim 4 wherein the tubular portion is an integral extension of the input component or the output component as the case may be and receives the tubular member.

6. A steering gear assembly as claimed in either claim 4 or claim 5 in which the tubular portion has a radially extending bore in the .wall thereof which bore is substantially in radial alignment with the recess in the tubular member, and in which the detent is housed in the bore to be radially slidable therein in response to fluid pressure when such is applied to the clutch means to effect engagement of the clutch by co-operation of the detent with both the bore and the recess.

7. A steering gear assembly as claimed in any one of the preceding claims wherein the recess of the clutch means comprises a radially extending bore in the wall of the tubular member.

8. A steering gear assembly as claimed in any one of the preceding claims wherein the output component comprises a pinion in a rack and pinion steering gear and the tubular member is a rigid extension of a shaft of such pinion with which it is substantially co-axial.

9. A steering gear assembly as claimed in any one of the preceding claims wherein the recess which co-operates with the detent is shaped to provide a progressive cam-like effect on the detent so that the clutching is progressive as the detent is urged under progressively increasing fluid pressure into cooperation with the recess.

10. A steering gear assembly substantially as herein described with reference to the accompanying illustrative drawings.

11. A power assisted vehicle steering system comprising a steering gear assembly as claimed in any one of the preceding claims in which the valve means regulates the supply of pressure fluid to a steering servo motor in the system; a vehicle speed responsive source of fluid pressure, and means for leading pressure fluid from said source to act upon the detent and cause engagement of the clutch means and thereby restrain relative rotation between the input and output components with consequential decrease in vehicle steering power assistance with increase in vehicle speed.

12. A vehicle having a power assisted steering system comprising an input component and an output component mounted in a housing for rotation about a common longitudinal axis, the input and output components being interconnected by and elastic torsion bar so that said components can exhibit rotation relative to each other while twisting is effected in the torsion bar; valve means which is intended to regulate the supply of pressure fluid to a steering servo motor and which valve means is controlled by relative rotation between the input and output components; a tubular member which is substantially rigid with one but not the other of said components and within which tubular member the torsion bar extends; fluid pressure responsive clutch means for clutching the tubular member to the input component or the output component, as the case may be whichever of said components does not have the tubular member as a rigid extension thereof, in response to fluid pressure when such is applied to the clutch means, and a source of pressure fluid which is responsive to vehicle speed, said pressure fluid acting upon the clutch means to effect said clutching whereby relative rotation between the input and output components is increasingly restrained with a consequential decrease in vehicle steering power assistance as the vehicle speed increases.