GB2085380A - Power assisted vehicle steering gear - Google Patents

Abstract

Vehicle steering gear 10 comprises input and output shafts 12 and 14 drivably connected by gearing 16 including a worm-type input gear 46 and a sector output gear 52. A fluid-driven reversible servo-motor is operable to increase the torque applied to the output shaft and comprises a vane 60 mounted on output shaft 14 and axially spaced from and axially aligned with output gear 52, the vane dividing a pressure chamber 58 into two chamber portions 62 and 64 to which hydraulic fluid is supplied by means of a control valve 78 responsive to rotation of input gear 46. Cam means 86 permits adjustment of the mesh of the input and output gears. <IMAGE>

Description

SPECIFICATION Vehicle steering gear This invention relates to vehicle steering gear suitable for use, for example, in lorries and other road vehicles. More particularly, the invention relates to vehicle steering gear of the power-assisted kind incorporating a fluid-driven reversible servomotor operable to increase the torque applied to an output shaft of the steering gear.

In order to improve a currently available steering gear, several factors need to be considered. Firstly, there is the requirement for reduced size or space arising from fuel economy factors which have dictated a reduction in size of vehicle cabs. Then there is a requirement for reduced complexity, especially so far as concerns the sealing of the servomotor and the setting up of the steering gear.

There is also the related requirement for improved reliability. Other factors include the need in certain steering gear layouts for non-parallel input and output shafts and the provision for adjustment during the life of the mechanism of the mesh of gearing connecting input and output shafts of the steering gear.

An object of the present invention is to provide a vehicle steering gear offering improvements in relation to one or more of the factors discussed above and/or a better compromise between manufacturing cost and the above factors.

According to the invention there is provided vehicle steering gear comprising: an input shaft; an output shaft; gearing connecting the input shaft to the output shaft whereby the former can turn the latter; and a fluid-driven reversible servo-motor operable to increase the torque applied to the output shaft; wherein the servo-motor comprises: a chamber; a vane mounted for angular movement in the chamber about an axis, the vane dividing the chamber into two chamber portions; and sealing means on the vane for sliding engagement with the chamber as the vane moves and forming a seal between the chamber portions.

Preferably the vane is mounted on the output shaft for angular movement about the axis of the output shaft. The gearing may comprise an input gear mounted on the input shaft and in meshing engagement with an output gear mounted on the output shaft, the vane being mounted on the output shaft at a position axially spaced from the output gear. The output gear may comprise a toothed sector and the vane is preferably axially aligned with the sector that is to say the vane is in line with the sector as viewed in the axial direction of the output shaft. The input gear may comprise a worm gear and the input shaft may be inclined at up to ninety degrees with respect to the output shaft.The input shaft and the input gear are preferably mounted so as to be angularly adjustable relative to the output gear, whereby the mesh of the input and output gears can be adjusted, cam means being provided to effect such angular adjustment.

The invention also provides vehicle steering comprising : an input shaft carrying an input gear; an output shaft carrying an output gear meshing with the input gear, whereby the input shaft can turn the output shaft; and a fluid-driven reversible servo-motor operable to increase the torque applied to the output shaft and comprising a chamber, and vane means slidable in the chamber under the action of fluid pressure supplied to two portions of the chamber; wherein the output gear comprises a toothed sector mounted on the output shaft and said chamber and vane means are also mounted on the output shaft so as to be axially spaced from and axially aligned with the sector.

According to a further aspect of the invention there is provided vehicle steering gear comprising: an input shaft; an output shaft; gearing connecting the input shaft to the output shaft whereby the former can turn the latter; and a fluid-driven reversible servo-motor operable to increase the torque applied to the output shaft; wherein the input gear comprises a worm gear and the input shaft is inclined with respect to the output shaft.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a section through vehicle steering gear according to the invention, the section being taken in a plane containing the axis of an output shaft of the steering gear; Figure 2 shows a section on the lines ll-ll in Figure 1; Figure 3 shows a section on the line Ill-Ill in Figure 1; and Figure 4 shows, in a view similar to that of Figure 1, the steering gear of Figure 1 incorporating a modified bearing arrangement for the output shaft.

Figures 1,2 and 3 show power-assisted steering gear suitable for use in lorries and other road vehicles.

As shown in Figure 1, the vehicle steering gear 10 comprises an input shaft 12, an output shaft 14 and gearing 16 connecting the input shaft to the output shaft whereby the former can turn the latter. A fluid-driven reversible servo-motor 18 forming part of the steering gear is operable to increase the torque applied to the output shaft 14.

Input shaft 12 is journalled for rotation about an axis 20 in a primary housing 22 which is adjustably mounted on a second housing 24 forming the main body of the steering gear.

Secondary housing 24 is a substantial structure comprising a first end plate 26, a second end plate 28 and an intermediate tubular member 30, the housing being secured together by bolts 32 and rendered fluid-tight by seals/gaskets 34.

Output shaft 14 is formed with splines 36 for driving engaement with an output lever (not shown) to be held in position by a retaining nut 38. Shaft 14 isjournalled in housing 24 for rotation about an axis 40, which is at right angles to input shaft axis 20, on bearings 42 and 44.

Gearing 16 interconnecting input shaft 12 and output shaft 14 comprises an input gear in the form of a worm gear 46 mounted on input shaft 12 which is journalled on bearings 48 and 50, and an output gear 52 mounted on output shaft 14 and in meshing engagement with gear 46. The output gear 52 is in the form of a toothed sector drivably secured by a key 54 and an associated threaded plug 56 to output shaft 14.

Servo-motor 18 comprises a sector-shaped chamber 58 defined by end plates 26,28 and tubular member 30, and a vane 60 mounted for angular movement in chamber 58 about the axis 40 of output shaft 14, the vane dividing chamber 58 into chamber portions 62 and 64.

Sealing means 66 is provided on vane 60 for sliding engagement with chamber 58 and vane 60 moves angularly therein, the sealing means forming a fluid-tight seal between chamber portions 62 and 64 (Figure 3).

Vane 60 comprises a generally finger-shaped vane member 68 projecting radially from an annular hub 70 which is, for example keyed or splined to output shaft 14 so as to be drivably secured thereto. Vane 60 is mounted on the output shaft at a position axially spaced from output gear 52 and axially aligned with the output gear i.e. in line with the output gear as viewed in the axial direction of shaft 14. Vane 60 may be integral with shaft 14 if required.

Sealing means 66 comprises an inner seal 72 and an outer seal 74 located in recesses formed in vane 60 and extending around the periphery of the vane.

Inner seal 72 is of rubber whereas the outer seal 74 is of nylon, the rubber providing the force necesary to push the nylon outwardly into propersealing en gagementwith the walls of the chamber 58. If required the rubber inner seal 72 can be replaced by a corrugated metal strip to bias the outer seal into its sealing engagement.

Inner seal 72 comprises (see Figure 3) two circular shaft seals 76 joined by a longitudinal seal 78 extending along the periphery of the vane for sealing engagement with the chamber.

The nylon parts of sealing means 66 are L-shaped and are cut away at their outer ends (at the small leg of the L) so as to inter-engage with each other to prevent, as far as possible, any passage of fluid between chamber portions 62 and 64. The nylon part of sealing means 66 is in two parts to allowfor machining tolerances of tubular member 30 of secondary housing 24.

Chamber portions 62 and 64 are connected to a hydraulic circuit comprising a pump driven by the enging of the vehicle, a reservoir and a control valve 78 associated with input shaft 12. Valve 78 comprises a rotary valve member 80 which is recessed to provide fluid passageways which co-operate with bores and recesses in a valve housing 82 which is bolted to the main body 24 of the steering gear.

Rotary valve member 80 is pegged to input worm gear 46 which is itself drivably connected to input shaft 12 by a torsion bar 84 which extends into the bored out interior of the worm gear 46. Conventional hydraulic connections are provided between control valve 78 and chamber portions 62, 64 and the hydraulic pump and the reservoir.

Input shaft 12 and its associated worm gear 46 is arranged at a nominal ninety degree inclination with respect to axis 40 of output shaft 14. This inclination can be adjusted so as to adjust the mesh of the input and output gears 46 and 52 by cam means 86.

Primary housing 22 is connected by a pivot pin 88 to secondary housing 24 whereby the primary housing can effectively pivot about a point 90. Such pivotal movement is effected by a rotatable cam member 92 located in a slot 94 provided in housing 22. Adjustment of cam member 92 varies the mesh of the input and output gears 46 and 52 so as to take up any lost motion which have developed during use.

In use, input shaft 12 is connected to the steering wheel of the vehicle and is rotated by the driver. The input torque thus supplied is transmitted to input gear 46 through torsion bar 84. Rotary movement of input gear 46 actuates rotary valve member 80 and also directly transmits torque to output gear 52 and output shaft 14 itself.

Actuation of rotary valve member 80 causes the supply to chamber portion 62 or 64 of servo-motor 18 of hydraulic fluid under pressure whereby the difference in pressure between the opposite sides of vane 60 causes torque to be applied to output shaft 14.

In the embodiment of Figure 4, the steering gear is otherwise constructed and arranged substantailly as described above but it is provided with thrust bearings 96 in place of the simple sleeve-type bearings 42 and 44 of the embodiment described above. Thrust bearings 96 each comprise two ball races 98 and associated tracks 100 so as to accommodate end thrust applied to output shaft 14.

Clearances 104 are provided between the output shaft and its housing 106 to accommodate any end float of the shaft.

Among the advantages of the embodiments described above are the following: 1. Compact size arising from the disposition of vane 60 in relation to sector output gear 52, and other factors.

2. Simplicity of construction and sealing arrangements. The single sealing means 66 serves to divide chamber 58 into the two chamber portions 62 and 64. This feature has benefits in relation to reliability in service.

3. Simplified setting-up procedure arising from the provision of adjustment for the meshing engagement of gears 46 and 52.

4. Simple arrangement for non-parallel input and output shafts with a minimum of meshing gears.

5. Low weight to power output ratio and facility to change the velocity ratio by changing the helix angle of the teeth of the input or output gears.

6. Very robust gearing arrangement which is tolerant of misalignment and lack of squareness.

Among modifications which could be made in the embodiment are the changing of the relative inclination of the input and output shafts.

Claims (12)

1. Vehiclesteering gearcomprising: an input shaft; an output shaft; gearing connecting the input shaft to the output shaft whereby the former can turn the latter; and a fluid-driven reversible servo-motor operable to increase the torque applied to the output shaft; wherein the servo-motor comprises: a chamber; a vane mounted for angular movement in the chamber about an axis, the vane dividing the chamber into two chamber portions; and sealing means on the vane for sliding engagement with the chamber as the vane moves and forming a seal between the chamber portions.

2. Gear according to claim 1 wherein said vane is mounted on the output shaft for angular movement about the axis of the output shaft.

3. Gear according to claim 1 or claim 2 wherein said gearing comprises an input gear mounted on said input shaft and in meshing engagement with an output gear mounted on said output shaft, said vane being mounted on the output shaft at a position axially spaced from said output gear.

4. Gear according to claim 3 wherein said output gear comprises a toothed sector and the vane is axially aligned with the sector.

5. Gear according to claim 3 or claim 4 wherein said input gear comprises a worm gear and said input shaft is inclined with respect to said output shaft.

6. Gear according to any preceding claim wherein said sealing means comprises two circular shaft seals joined by a longitudinal seal to extend along the periphery of the vane for sealing engagement with the chamber.

7. Gear according to claim 5 wherein said input shaft and said input gear are mounted so as to be angularly adjustable relative to said output gear; whereby the mesh of the input and output gears can be adjusted, cam means being provided to effect such angular adjustment.

8. Vehicle steering gear comprising : an input shaft carrying an input gear; an output shaft carrying an output gear meshing with the input gear, whereby the input shaft can turn the output shaft; and a fluid-driven reversible servo-motor operable to increase the torque applied to the output shaft and comprising a chamber, and vane means slidable in the chamber under the action of fluid pressure supplied to two portions of the chamber; wherein the output gear comprises a toothed sector mounted on the output shaft and said chamber and vane means are also mounted dn the output shaft so as to be axially spaced from and axially aligned with the sector.

9. Vehicle steering gear comprising : an input shaft; an output shaft; gearing connecting the input shaft to the output shaft whereby the former can turn the latter; and a fluid-driven reversible servo-motor operable to increase the torque applied to the output shaft; wherein the input gear comprises a worm gear and the input shaft is inclined with respect to the output shaft.

10. Gear according to claim 9 wherein said input shaft and said input gear are mounted so as to be angularly adjustable relative to said output gear; whereby the mesh of the input and output gears can be adjusted, cam means being provided to effect such angular adjustment.

11. Vehicle steering gear substantially as described herein and as illustrated in the accompanying drawings.

12. Avehiclecomprising steering gear as claimed in any preceding claim.