GB2114702A

GB2114702A - Vehicle steering gear

Info

Publication number: GB2114702A
Application number: GB08230588A
Authority: GB
Inventors: Frederick John Adams
Original assignee: TRW Steering Systems Ltd
Current assignee: TRW Steering Systems Ltd
Priority date: 1981-10-27
Filing date: 1982-10-26
Publication date: 1983-08-24
Also published as: GB2114702B

Abstract

Vehicle steering gear comprises an input gear 46 meshing with an intermediate gear 48 carrying a pinion gear 50 which drives a rack bar 52 by meshing with a first array of teeth 70 thereon. A further array of teeth 74 on the rack bar 52 meshes with an output gear 54 (e.g. a pinion or sector gear) to which an output shaft 40 is connected. The input gear can be re- positioned around the intermediate gear and the attitude of the output shaft can be adjusted by angular adjustment of the arrays of teeth at opposite ends of rack bar 52 whereby a large range of steering gear geometry requirements can be accommodated. <IMAGE>

Description

SPECIFICATION Vehicle steering gear This invention relates to vehicle steering gear, for example steering gear suitable for use in trucks and other heavy duty road vehicles. The invention makes provision for the inclusion of a servo-mechanism to provide power assistance in operation of the steering gear.

A problem which has arisen in the design of vehicle steering gear in recent years relates to the requirement for improved fuel efficiency in road vehicles, and the consequential need to reduce air resistance, and hence to reduce the height of the driver's cab in road trucks.

Reduction of cab height has the effect that the space available for steering gear is reduced and existing steering gear can no longer be satisfactorily accommodated.

An object of the present invention is to provide vehicle steering gear, and a vehicle incorporating such steering gear, providing improvements in relation to the spacial considerations discussed above, and/or providing improved versatility in its applications.

According to one aspect of the invention there is provided vehicle steering gear comprising: a pinion gear mounted for angular movement in response to a steering input; a rack bar having a longitudinally extending array of teeth in meshing engagement with the pinion gear, the rack bar being longitudinally movable by the pinion gear in response to angular movement of that gear; a further array of teeth on the rack bar; a sector gear mounted for angular movement and in meshing engagement with said further array of teeth on the rack bar so as to be angularly moved in response to longitudinal movement of the rack bar; and an output shaft extending from the sector gear and which is angularly moved in unison with the sector gear to provide a steering output.

According to second aspect of the invention there is provided vehicle steering gear comprising: an input gear mounted for angular movement in response to a steering input; an intermediate gear in meashing engagement with the input gear and angularly movable thereby in response to a steering input; a pinion gear angularly movable in unison with the intermediate gear; a rack bar having a longitudinally extending array of teeth in meshing engagement with the pinion gear, the rack bar being longitudinally movable by the pinion gear in response to angular movement of that gear; a further array of teeth on the rack bar; an angularly movable sector gear in meshing engagement with said further array of teeth on the rack bar so as to be angularly moved in response to longitudinal movement of the rack bar; and an output shaft extending from the sector gear and which is angularly moved in unison with the sector gear to provide a steering output.

Preferably a housing of the vehicle steering gear is adapted to allow adjustment of the position of said input gear around the axis of angular movement of said intermediate gear by angular adjustment of a portion of said housing relative to the remainder of said housing.

The input gear may be provided on an input shaft mounted in an associated housing, the housing being adapted to allow the input gear to be mounted in either of two alternative positions in which the input shaft is on opposite sides of said intermediate gear.

The arrays of teeth on the rack bar may be positioned thereon so as to be radially aligned when viewed in the longitudinal direction of the rack bar, or said arrays of teeth may be displaced from such alignment--according to the geometry requirements of the steering gear and the desired location and attitude of the output shaft.

Alternatively, the two portions of said rack bar which are formed with said arrays of teeth may be arranged to be angularly displaceable relative to each other about the longitudinal axis of the rack bar whereby the attitude of the output shaft can be adjusted about the longitudinal axis of the rack bar.

A servo motor may be provided to act on the rack bar to provide power assistance for the steering gear. The servo motor may comprise a piston provided on the rack bar and sliding in a cylinder formed by a portion of the housing of the steering gear. Said piston may be provided on the rack bar between the arrays of teeth formed thereon.

The mechanical advantage provided by the meshing engagement of the pinion gear with the rack bar may be arranged to vary along the length of the travel of the rack bar.

Where the steering gear for a heavy duty road vehicle such as a truck is provided with a servo motor to act on the rack bar to provide power assistance for the steering gear, the arrangement is preferably such that the mechanical advantage for the transmission of drive from said pinion gear to said rack bar is a minimum in the central region of the travel of the rack bar, and is higher in the end regions thereof.

The array of teeth on the rack bar in meshing engagement with said pinion gear is preferably formed on a concave portion of the edge of the rack bar. The pinion gear may be eccentrically mounted with respect to the axis of the intermediate gear.

In this specification, references to the mechanical advantage of the driving connection between the pinion gear and the rack bar are to be interpreted as follows. The mechanical advantage for the transmission of drive from the pinion gear to the rack bar is to be understood to be greater when a given angular movement of the pinion gear produces a given lengthwise movement of the rack bar (measured along the longitudinal axis of the rack bar) and when the same angular movement of the pinion gear produces a greater lengthwise movement of the rack bar. Thus, a higher mechanical advantage for the transmission of drive from the pinion gear to the rack bar results in less angular movement at the output shaft of the steering gear from a given input angular movement than does a lower mechanical advantage.

In an embodiment of the invention described below, the arrangement is such that the mechanical advantage of the driving connection between the pinion gear and the rack bar is a minimum in the central region of the travel of the rack bar, which is the straight-ahead position for the steering gear when installed on a vehicle, and this provides, in combination with the power assistance also provided in the embodiment, more effective actuation of the power assistance system in the straight-ahead position of the steering gear. Somewhat smaller angular movements of the vehicle's steering wheel are needed at the straight ahead position in order to produce a given angular steering movement of the vehicle's wheels, and as a result the actuation of the power assistance system's control valve is more finely or delicately controlled than would otherwise be the case.

The invention also provides steering gear wherein the arrangement is such that the mechanical advantage for the transmission of drive from the pinion gear to the rack bar is a maximum in the central region of the travel of the rack bar (that is, the straight ahead position of the vehicle), as is appropriate for manual steering systems.

The invention also provides a vehicle incorporating steering gear as defined above. The steering gear may be mounted so that the axis of rotation of the output shaft extends in an upward direction.

The steering gear may be mounted with the rack bar above the intermediate gear and with an input shaft connecting said input gear to a driver's steering wheel of the vehicle, the input shaft also being located above said intermediate gear. Said output shaft may be located on the opposite side of the steering gear from the input shaft, the output shaft being connected to a steering lever and an associated drag link which are located below the level of the steering gear. Alternatively, said output shaft may be provided on the same side of the steering gear as the input shaft, the output shaft being connected to a steering lever and a drag link which are located above the level of the steering gear.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 shows a diagrammatic representation of a vehicle incorporating steering gear in which an output shaft of the steering gear is arcuately movable about an upwardly extending axis; Fig. 2 shows a plan view of steering gear suitable for use in the vehicle of Fig. 1, the output shaft being adjustable in attitude relative to the input shaft and being shown in this Figure in a horizontal attitude; Fig. 3 shows an end view of the steering gear of Fig. 2, the direction of viewing being indicated by arrow Ill in Fig. 2, this view showing the small height or depth requirement of the steering gear and also including, in dotted lines, three optional further positions for the output shaft and an alternative optional position of an input shaft and its associated housing;; Fig. 4 shows a section through the steering gear in the plane indicated by arrows IV--IV in Fig. 2; Fig. 5 shows a further section through the steering gear, illustrating the relationship of a pinion gear, a rack bar and a sector gear, the view being a composite section taken in the plane indicated by arrows VA-VA in the area of the pinion and in the plane VB--VB in the area of the sector gear; Fig. 6 shows a further embodiment of steering gear according to the invention, this embodiment not incorporating a servo motor to provide powerassistance, and this Figure showing a section through the steering gear similar to that of Fig. 4;; Fig. 7 shows a section through the steering gear of Fig. 6, the section being similar to that of Fig. 5 and taken in the planes indicated by arrows VI lA-VI IA and VIIB--VIIB in Fig. 6; Fig. 8 shows a view similar to that of Fig. 1 of a vehicle incorporating the steering gear of Figs. 2 to 5 and with the input gear assembly arranged in the position indicated in dotted lines in Fig. 3 so as to further reduce the height requirements of the steering gear; Fig. 9 shows a view otherwise similar to that of Fig. 8 but in which the output shaft of the steering gear is arranged on the upper side of the steering gear housing so as to even further reduce the height requirements of the total steering mechanism; and Fig. 10 shows, in a view similar to that of a portion of Fig. 7, a section through steering gear incorporating a modified rack bar and pinion assembly.

As shown in Fig. 1, a road vehicle in the form of a truck 10 has steerable road wheels 12 controlled by a driver's steering wheel 14 through steering gear 16, a steering lever 1 8 and a drag link 20.

A driver's cab (not shown) is mounted on the chassis 22 of the vehicle and is pivotable forwards, (with respect to forward direction F of travel of the vehicle) about a horizontal axis 24.

In Fig. 1, dimension H represents the height of axis 24 above the chassis 22, and this dimension is significantly reduced as compared with existing steering gear, particularly such gear requiring the use of a horizontal axis output shaft and a steering lever moving in a vertical plane and corresponding to lever 18.

The construction of steering gear 1 6 will now be described in detail with reference, firstly, to the embodiment shown in Figures 2 to 5.

Vehicle steering gear 26 as shown in Figs. 2 to 5 comprises a gear housing 28 forming a fluidtight casing in which the movable components of the gear are supported and in which lubricant therefore is contained. Housing 28 comprises an input shaft and valve housing 30, an intermediate gear housing 32, a generally horizontally extending rack bar housing 34 and an output shaft housing 36.

An input shaft 38 is journalled for rotation in housing 32 and an output shaft 40 is journalled for rotation in housing 36. The shaft 38 is connected to vehicle steering wheel 14, and output shaft 40 has a tapered splined portion 42 to receive a complementary steering lever (not shown in Figs. 2 to 5) which is retained in position by a nut 44.

As shown in Figs. 4 and 5, steering gear 26 further comprises an input gear 46, an intermediate gear 48 meshing with the input gear and providing a reduction in drive ratio (or an increase in mechanical advantage), a pinion gear 50, a rack bar 52 and a sector output gear 54.

Input shaft 38 is journalled for rotation about an axis 56 and drive is transmitted through a torsion bar 58 to a rotary valve 60 and to input gear 46 which likewise is rotatable about axis 56.

Input gear 46 meshes with intermediate gear 48 which is mounted on bearing 62, 64 for rotation about an axis 66 inclined with respect to input shaft axis 56.

Pinion gear 50 is formed on a shank 68 integral with intermediate gear 48 and meshes with an array of teeth 70 on rack bar 52. Rack bar 52 is mounted for lengthwise sliding movement in housing 34, the mesh between the rack bar and pinion gear 50 being adjustable by means of a yoke 72 which is itself constructed and arranged as in conventional rack and pinion gears. Rack bar 52 is formed with a second or further array of teeth 74 at the other end of the rack bar from teeth 70. Teeth 74 of the rack bar mesh with the teeth 76 of sector gear 54 whereby reciprocating linear movement of the rack bar in the direction indicated by double-headed arrow R effects angular movement of the sector gear about its longitudinal axis 78 which extends at right angles to direction R.

Output shaft 40 is rigidly fixed to sector gear 54 for rotation about axis 78, and it can now be seen that rotation of pinion gear 50 by input shaft 38 causes lengthwise displacement of rack bar 52 and arcuate displacement of sector 54 and hence of output shaft 40.

Located between the two toothed end portions of rack bar 52 is a piston 80 which is slidably located in housing 34 and connected to a supply of hydraulic fluid under pressure and controlled by rotary valve 60 whereby hydraulic pressure is supplied to the appropriate side of piston 80 so as to supplement the torque exerted on output shaft 40.

In use, input shaft 38 is connected to a steering wheel 14 of a vehicle and output shaft 40 is connected to steering lever 1 8 and drag link 20. Turning movement of shaft 38 itself transmits torque to output shaft 40, as already described, and this torque is supplemented by torque generated as a result of the supply of hydraulic fluid under pressure to the appropriate side of piston 80 under the control of rotary valve 60.

Provision is made for adjustment of the mesh of pinion gear 50 with rack bar 52 by means of a mushroom-headed adjustment screw 82 and an associated lock nut 84. A corresponding adjustment screw 86 is provided for sector gear 54.

Among modifications which could be made in the above embodiment are the following: 1. The use of a plain non-bevelled intermediate gear in place of gear 48, with a corresponding adjustment of axis 56.

2. Input gear 46 may be located at any suitable position around the periphery of intermediate gear 48 instead of at the position shown.

3. Input shaft 38 can be provided on the opposite side of housing 28, that is, on the same side of intermediate gear 48 as shank 68.

4. Output shaft 40 can be provided on the opposite side of housing 34 from its position as shown in the drawings i.e. displaced through 1800.

5. Output shaft 40 can be provided at any desired angle between the two positions referred to in 4 above by providing a pivotal connection between the two toothed portions of rack bar'52, the pivot axis being the longitudinal axis of the rack bar. With such provision, the output shaft and its portion of rack bar 52 together with the corresponding end portion of housing 34 can simply be turned through the appropriate angle about the longitudinal axis of the rack bar and then re-secured to the remainder of housing 28.

In this way output shaft 40 can be arranged so as to be vertical.

6. Variation of the ratio of the drive by changing the helix angle of the teeth of input gear 46 and/or of pinion gear 50. The drive ratio can also be changed by changing the pitch circle diameter of sector gear 54. In the above embodiment the drive ratio is 24:1.

In the embodiment of Figs. 6 and 7, the steering gear is simplified by the omission of the servo motor provided by piston 80 in the above embodiment.

The principal components of this embodiment are an input shaft 88 having an input gear 90 driving an intermediate gear 92 having a pinion gear 94 which itself meshes with a first set of teeth 96 on a rack bar 98 while a second set of teeth 100 thereon mesh with a sector gear 102 which is fast with an output shaft 104.

The rack bar is adjustably mounted for sliding movement under the control of yokes 106 and 108.

The steering gear of this embodiment operates substantially as described above save that it is torque derived solely from input shaft 88 which is transmitted to output shaft 104.

In the embodiment of Fig. 8 the parts corresponding to those of Fig. 1 are given the same reference numerals as in Fig. 1.

In this embodiment, advantage has been taken of the versatility of the steering gear assembly 16, in respect of adjustment of the main components of the steering gear to vary the geometry of the assembly and to achieve a more compact layout.

The internal structure of steering gear 16 in Fig. 8 is as described above in relation to Figs. 2 to 5. As already indicated, the housing 30 for the input shaft 38 can be position-adjusted around the axis 110 of intermediate gear 48. Such adjustment is permitted by the intermediate gear housing 32 and its associated mounting bolts 112. In addition to such adjustment, as indicated in Fig. 3, input shaft housing 30 can be mounted in the dotted line position indicated in Fig. 3 by reference numeral 30A, with input shaft 38 correspondingly indicated as 38A. In this latter position of input shaft 38A it is on the same side of intermediate gear 48 as rack bar 52 and as can be seen in Fig. 3 the overall depth of the assembly with the input shaft in this position is significantly reduced as compared with the alternative position of the input shaft shown in full lines.

It will be understood that the input gear 46 of input shaft 38 meshes with intermediate gear 48 in exactly the same way in both positions of the input shaft.

In this embodiment, the arrays of teeth on the rack bar (not shown in Fig. 8) are radially aligned as viewed in the axial direction of the rack bar, so that the axis 114 of angular movement of the output shaft 40 extends parallel to the axis 110 of rotation of the intermediate gear 48. Alternative attitudes of the output shaft axis can be readily achieved by arranging the sets of rack bar teeth so as to be displaced from such alignment-or by providing a pivot between the ends of the rack bar permitting angular adjustment of the arrays of teeth while still transmitting steering forces.

Fig. 3 shows at 42, in full lines, a first position of the output shaft with the arrays of rack bar teeth displaced from radial alignment with each other by 900. At 42A there is shown a first alternative position of the output shaft in which it meshes with teeth on the rack bar which are displaced 1800 from the teeth corresponding to the output shaft position 42.

At 42B there is shown a second alternative output shaft position requiring an array of teeth on the rack bar displaced by a further 900 in the same direction from the teeth required for the output shaft position 42A. And at 42C there is shown the output shaft position corresponding to that of output shaft 42 but with the output shaft on the opposite side of housing 28. A fifth position of the output shaft, displaced a further 900 anti-clockwise (as shown in Fig. 3) from the 42C position is also available. The axes of rotation of the output shaft in these positions are indicated by reference numerals 114, 11 4A, 11 4B, 11 4C and 114D.

In the Fig. 8 embodiment the attitude of the output shaft is that of axis 11 4D, and the whole gear assembly is mounted with the rack bar above the intermediate gear and the input shaft 38A likewise located above the intermediate gear.

With the output shaft of the steering gear on the opposite side of the gear from the output shaft, the steering lever 1 8 and drag link 20 are located below the steering gear housing, as in the Fig. 1 embodiment.

In the embodiment of Fig. 9, the steering drive input arrangements are substantially the same as in Fig. 8, but the attitude of the output shaft is that of axis 114B in the Fig. 3 i.e. parallel to the intermediate gear and on the same side of the gear housing 28 as the input shaft 38A. In this way, the steering gear 16 is positioned below the level of steering lever 18 and drag link 20, thereby further reducing the height requirements of the steering gear assembly.

It will be noted that in the Fig. 8 embodiment the cab pivot axis 24 is located level with the chassis 22 of the vehicle i.e. dimension H of Fig. 1 is reduced to zero by the modified steering gear geometry. However, in the Fig. 9 embodiment, cab pivot axis 24 is positioned well below the level of chassis 22, thereby making a still greater improvement in the cab height requirements of the steering gear.

In the embodiment of Fig. 10, parts corresponding to those of the embodiment of Figs. 6 and 7 are designated by the same reference numerals as in Figs. 6 and 7.

The axis of intermediate gear 92 is identified by reference numeral 1 50 and pinion gear 1 52 is mounted eccentrically with respect thereto, the centre of the pinion gear being identified as 1 54.

Rack bar 1 56 is otherwise constructed as in Figs. 6 and 7, but has a concave edge profile at one end where it is formed with an array of teeth 1 58 for meshing engagement with pinion gear 152.

The profiles of the teeth on rack bar 1 56 and pinion gear 1 52 are as shown. The arrangement is such that the mechanical advantage provided by the driving connection between the pinion gear and the rack bar for the transmission of drive from the pinion gear to the rack bar is less in the central region of the array of teeth 1 58 than at the ends thereof.

In this way, sensitive actuation of the control valve of the power assistance system is achieved.

It will be appreciated from Fig. 10 that the angular movement of pinion gear 1 52 between the ends of the array 1 58 of teeth is approximately one complete turn or 3600 of angular movement.

In operation, this embodiment functions substantially as described in connection with the other embodiments. Slightly smaller angular movement of the steering wheel of the vehicle is needed in the straight ahead position, giving fine control over vehicle steering. The lower mechanical advantage of the steering gear at the ends of its travel is of no significance on account of the power assistance provided.

Among the advantages provided by the embodiments of the invention described above are the compact form of the steering gear and the reduced vehicle cab height permitted thereby, this deriving a part at least from the provision of a horizontally-extending rack bar through which torque-generating thrust is transmitted to the output shaft. Moreover, the provision of such a rack bar enables considerable variation to the attitude of the output shaft to be easily provided for, whereby the steering gear can be readily manufactured for a variety of vehicle steering gear geometry requirements. Also, the input gear and intermediate gear arrangement permits simple adaptation of the steering gear for a variety of drive input shaft positions. The provision of the rack bar likewise greatly simplifies the provision of a servo motor to give power assistance during steering operations.

Claims

1. Vehicle steering gear comprising: a pinion gear mounted for angular movement in response to a steering input; a rack bar having a longitudinally extending array of teeth in meshing engagement with the pinion gear, the rack bar being longitudinally movable by the pinion gear in response to angular movement of that gear; a further array of teeth on the rack bar; an output gear mounted for angular movement and in meshing engagement with said further array of teeth on the rack bar so as to be angularly moved in response to longitudinal movement of the rack bar; and an output shaft extending from the output gear and which is angularly moved in unison with the output gear to provide a steering output.

2. Vehicle steering gear comprising: an input gear mounted for angular movement in response to a steering input; an intermediate gear in meshing engagement with the input gear and angularly movable thereby in response to a steering input; a pinion gear angularly movable in unison with the intermediate gear; a rack bar having a longitudinally extending array of teeth in meshing engagement with the pinion gear, the rack bar being longitudinally movable by the pinion gear in response to angular movement of that gear; a further array of teeth on the rack bar; an angularly movable sector gear in meshing engagement with said further array of teeth on the rack bar so as to be angularly moved in response to longitudinal movement of the rack bar; and an output shaft extending from the sector gear and which is angularly moved in unison with the sector gear to provide a steering output.

3. Vehicle steering gear according to claim 2 wherein a housing of the steering gear is adapted to allow adjustment of the position of said input gear around the axis of angular movement of said intermediate gear by angular adjustment of a portion of said housing relative to the remainder of said housing.

4. Vehicle steering gear according to claim 2 or claim 3 wherein said input gear is provided on an input shaft mounted in an associated housing, the housing being adapted to allow the input gear to be mounted in either of two alternative positions in which the input shaft is on opposite sides of said intermediate gear.

5. Vehicle steering gear according to any one of the preceding claims wherein said arrays of teeth on said rack bar are positioned thereon so as to be radially aligned when viewed in the longitudinal direction of the rack bar.

6. Vehicle steering gear according to any one of claims 1 to 4 wherein said arrays of teeth on said rack bar are positioned thereon so as to be angularly displaced from each other when viewed in the longitudinal direction of the rack bar.

7. Vehicle steering gear according to any one of the preceding claims wherein the two portions of said rack bar which are formed with said arrays of teeth are constructed to be angularly displaceable relative to each other about the longitudinal axis of the rack bar whereby the attitude of said arrays of teeth can be adjusted about the longitudinal axis of the rack bar relative to each other.

8. Vehicle steering gear according to any one of the preceding claims wherein the mechanical advantage provided by the meshing engagement of said pinion gear with said rack bar varies along the length of the travel of the rack bar.

9. Vehicle steering gear according to claim 8 wherein the arrangement is such that the mechanical advantage for the transmission of drive from said pinion gear to said rack bar is a minimum in the central region of the travel of said rack bar and is higher in the end regions thereof.

10. Vehicle steering gear according to clalm 8 or claim 9 wherein the array of teeth on the rack bar in meshing engagement with said pinion gear are formed on a concave portion of the edge of said rack bar.

11. Vehicle steering gear according to claim 10 wherein the pinion gear is eccentrically mounted with respect to the axis of said intermediate gear.

12. Vehicle steering gear according to claim 8 wherein the arrangement is such that the mechanical advantage for the transmission of drive from the pinion gear to the rack bar is a maximum in the central region of the travel of the rack bar.

1 3. Vehicle steering gear according to any one of the preceding claims wherein a servo motor is provided to act on the rack bar to provide power assistance for said steering gear.

14. Vehicle steering gear according to claim 13 wherein said servo motor comprises a piston provided on the rack bar and sliding in a cylinder formed by a portion of a housing of the steering gear.

1 5. Vehicle steering gear according to claim 14 wherein said piston is provided on said rack bar between said arrays of teeth formed thereon.

1 6. Vehicle steering gear constructed and arranged substantially as described herein with reference to the accompanying drawings.

17. A vehicle comprising steering gear as claimed in any one of the preceding claims.

18. A vehicle according to claim 17 wherein the axis of angular movement of said output shaft extends in an upward direction.

1 9. A vehicle according to claim 1 7 or claim 18 wherein the steering gear is mounted with said rack bar located above said intermediate gear and with an input shaft connecting said input gear to a driver's steering wheel of the vehicle, the input shaft also being located above said intermediate gear.

20. A vehicle according to claim 19 wherein said output shaft is located on the opposite side of the steering gear from said input shaft, the output shaft being connected to a steering lever and an associated drag link which are located below the level of the steering gear.

21. A vehicle according to claim 1 9 wherein said output shaft is located on the same side of the steering gear as said input shaft, said output shaft being connected to a steering lever and a drag link which are located above the level of the steering gear.

New claims or amendments to claims filed on 5 May 1983.

Superseded claim 1.

New or amended claims: Claims 2-21 renumbered as 1-20 and appendices corrected.