GB2236724A

GB2236724A - Power-assisted steering gear

Info

Publication number: GB2236724A
Application number: GB8922005A
Authority: GB
Inventors: Frederick John Adams
Original assignee: TRW Steering Systems Ltd
Current assignee: TRW Steering Systems Ltd
Priority date: 1989-09-29
Filing date: 1989-09-29
Publication date: 1991-04-17
Also published as: GB8922005D0; DE4030625C2; IT9021572A0; IT9021572A1; IT1243042B; DE4030625A1

Abstract

Steering unit (1) (which may comprise a conventional rack and pinion) has a transmission shaft (5) rotatable relative to a housing (2) about axis (6). An input shaft (20) rotatable in response to a steering input torque has its axis (21) parallel to the axis (6) and eccentric therewith. The transmission shaft (5) has a concentric toothed gear (11) rotatable therewith and engaging with a toothed gear (22) concentric and rotatable with the input shaft (20). The input shaft (20) is rotatable in a carrier (14) pivotally mounted by bolt (15) on the housing (2). In response to rotation of the input shaft (20), a resultant reaction between the engaging gears (11) and (22) pivotally displaces the carrier (14) arcuately about the bolt axis (17). This pivotal displacement serves to actuate, through boss (23) on the carrier and linkage (24), control means (25) for a hydraulic or electric servo motor (9) to assist the intended steering manoeuvre. In a modification the driving engagement between the gears (11) and (22) can be provided by use of an internally toothed gear meshing with an externally toothed gear. <IMAGE>

Description

TITLE "A power assisted steering gear"

TECHNICAL FIELD & BACKGROUND AlT

The present invention relates to a Power assisted steering gear of the kind having a shaft rotatable in response to a steering input torque and in which rotary motion of such shaft is translated by a steering unit to substantially linear motion to provide a steering output. The steering unit mentioned may be in the form of rack and pinion, worm and roller,, cam and lever or re-circulating ball-nut type, all of which are well known in the steering art. In applying these known steering units to a power assisted steering gear it is conventional to provide a servo motor such as an hydraulic ram or electric motor to a steerinq output component of the gear or unit and control means for the servo motor. The control means is adjustable in response to the steering input to control the -actuation of the servo motor, usually hydraulically or electrically as implied abover whereby the servo motor provides power assistance to a steering manoet;vre consistent with an applied steering input. Generally the control means for the servo motor is in the form of an electrical switch device or hydraulic valve associated with the shaft through which the steering input is applied. it is desirable that the adjustment of the control means in response to a steering input is achieved by means of a robust and reliable structure which responds accurately to a steering input torque and can readily and economically be fitted or assembled in the steering gear,, preferably without disrupting the relationship between the components of the steering unit; it is an object of the present invention to Provide a power assisted steering gear which lends itself to satisfy these desirable characteristics.

STATEMENT OF INVENTION & ADVANTAGES

According to,the present invention there is provided a power assisted steering gear comprising a steering unit having a transmission shaft rotatable relative to a housing, said transmission shaft having a first toothed cear rotatable and concentric therewith and said unit translatina rotary motion of the transmission shaft to substantially linear motion to provide a steering output; an input shaft eccentri-c with the transmission shaft and rotatable in response to a steering input torque, said input shaft having a second toothed gear rotatable and concentric therewith and being rotatably mounted by a carrier pivotally mounted relative to said housing; said first and second toothed gears being in driving engagement whereby in response to rotation of the input shaft a resultant reaction between the first and second gears pivotally displaces the carrier arcuately, and wherein said pivotal displacement adjusts means for controlling power assistance to said steering output. Preferably the transmission shaft is rotatable about a first axis, the input shaft is rotatable about a second axis which is substantially parallel with and eccentric to the first axis, and the carrier is mounted for pivotal movement about a third axis which is substantially parallel to said first and second axes.

It is to be realised that by the term "toothed gear" 25 as used throuqhout this Specification we include equivalent components by which rotary torque can be transmitted from the input shaft to the transmission shaft; for example a toothed gear can be in the form of a pin wheel as is well known in the gearing art.

The present invention was primarily developed for steering units of - the rack and pinion kind but may be applied with advantage to other type steerinq units such as worm and roller, cam and lever or recirculating ball-nut, each of which conventionally has a transmission shaft which is rotatable in response to a steering input torque and 3 gear components which translate such rotary motion to substantially linear motion to provide a steerinc output. Usually the components of the steering unit are assembled within the housing which may also carry or incorporate a servo motor such as an hydraulic ram or electric motor, for the steering gear.

The control means for the servo motor, such as an electrical switch device for an electric motor or pump or an hydraulic valve for controlling fluid flow to a ram, is adjusted in response to pivotal displacement of the carrier and preferably the carrier is pivotally mounted by a pin, bolt or similar component on an outer side of the housing for the steering unit with the first and second toothed gears of the transmission and input shafts in driving engagement (such driving engagement may be direct or indirect). With such an arrancement the input shaft and its toothed gear together with the carrier can conveniently be assembled with the steering unit fitted to the exterior of the housing for such unit without disrupting the internal components (which may be conventional) of the steering unit.

The first and second toothed gears may be integrally formed with their respective shafts or secured for rotation therewith. The eccentricity between the axes of the input and transmission shafts will permit the first and second toothed qears, when in direct driving enqaqement, both to have meshing external gear teeth, or one shaft to have external gear teeth which mesh with internal gear teeth of the other shaft. It will be appreciated however that many variations are possible in the tooth form of the first and second toothed gears and also in the arrangement whereby drive is transmitted from the input shaft to the transmission shaft in response to a steering input torque.

Preferably the carrier is adjustable or biased radially with respect to the third axis to adjust or bias 4 the first and second toothed gears into drivinc engagement and alleviate "lost motion" in the transmission through those qears. Preferably the carrier is pivotally mounted to the housing of the steering unit by a pin or similar component as aforementioned which provides the third axis and is spring loaded or otherwise resiliently biased relative to the pin component to urce the carrier radially relative to the third axis in a sense which biases the teeth of the second gear into direct driving engagement with the teeth of the first cear. The carrier can conveniently comprise a subsidiary housing within which are located the first and second toothed gears.

DRAWINGS One embodiment of a power assisted steering gear constructed in accordance with the present invention and incorporatinq a rack and pinion type steering unit will now be described, by way of example only, with reference to the accompanying illustrative drawings in which:- Figure 1 includes a section through the steering ynit parallel with the pinion axis and illustrates direct driving enqagement between externally toothed involute spur gears on input and transmission shafts of the steerinc gear; Figure 2. shows a modification of the qear in Figure 1 in which driving engagement between the input and transmission shafts As effected between an internally toothed gear and an externally toothed gear on those respective shafts; Figure 3 shows a modification of the gear in Figure 2 whereby the internally toothed gear of the input shaft is in the form of a pih wheel gear, and Figure 4 is a part section of the line IV-IV of the qear shown in Figure 3.

DETAILED DESCRIPTION OF DRAWINGS

The power astisted steering gear illustrated includes what may be reqarded as a conventional rack and pinion steering unit 1 having a housina 2 within which is a pinion 4 mounted by bearings 3. The pinion 4 has an integral coaxial (transmission) shaft 5. The pinion and its shaft are rotatable about an axis 6 and the pinion is in drivinq engagement with teeth of a longitudinally extending rack bar 7 which is biased into engagement with the pinion by a spring loaded yoke 8 in the housinc 2. The pinion 4 and its transmission shaft 5 are rotated in response to a steering input torque to drive the rack bar 7 longitudinally relative to the housing 2 and provide a steering output which, when the rack bar is coupled as part of a conventional steerinq linkage in a vehicle, effects in a steering manoeuvre. For providing power assistance the rack bar 7 has associated therewith a servo motor 9 which is actuated in response to the steerinq input to assist in the longitudinal displacement of the rack bar (through a linkaqe generally indicated at 10) consistent with the steering input. 0 The transmission shaft 5 extends from the housinq 1 and, externally of the housing, has an externally toothed involute spur gear wheel 11 which is rotatable and concentric therewith. The gear 11 may be integral with the shaft 5 or secured for rotation therewith for example by a nut 12.

The gear 11 is located within a chamber 13 of a subsidiary housing provided by a carrier 14. The carrier 14 is retained on the housing 2 by a bolt 15 the shank 16 of which extends through a bore 29 in the carrier 14 to screw threadedly engage with the housing 2. The carrier 14 is mounted for pivotal movement on the shank 16 of the bolt and about the axis 17 thereof. Pads of low friction material 18 may be provided between the opposing faces of the carrier 14 and the housing 2 and bolt head respectively to facifitate pivotal movement of the carrier 14 about the 6 axis 17, the latter axis being substantially parallel with the transmission shaft axis 6.

Mounted by bearings 19 in the carrier 14 is an input shaft 20 which is rotatable about its axis 21, the latter being substantially parallel with the axes 6 and 17 and spaced or eccentric to the axis 6. Carried by or inteqral with the input shaft 20 for concentric rotation threwith is an involute externally tdoithed spur gear wheel 22 that is located in the chamber 13 in direct driving engagement with the toothed crear 11.

Projectinq from the exterior of the carrier housing 14 (conveniently integrally formed therewith) and radially of the axis 17 is a boss or similar projection 23 which is intended to adjust, conveniently through a coupling indicated at 24, control means 25 for the servo motor 9.

The input shaft 20 is intended to be rotated in response to a steering input torque which is applied to the steering gearr typically by rotation of a steering wheel column. In response to rotation of the input shaft 20 and its gear 22, drive is imparted through the gear lland transmission shaft 5 to rotate the pinion 4 and effect in longitudinal displacement of the rack bar 7 to provide a steering output. Howeverr as a reaction to the drive which is imparted between the toothed gears 22 and 11 and when there is a resistance to rotation of the gear 11 during a steering manoeuvre, the shaft axis 21 will be urged circumferentially about the shaft axis 6 with a consequence that the carrier housing 14 will be arcuately displaced with the sh.aft 20 about the bolt axis 17 and in a direction compatible with the direction in which the input shaft 20 is rotated. This arcuate displacement of the carrier 14 and its boss 23 serves to adjust the control means 25 to actuate the servo motor 9 and provide power assistance (through the link 10) to the displacement of the rack bar 7 in a, direction and to an extent which is 7 consistent with the applied steerinq input torque.

To provide and maintain efficient meshinq encacement between the toothed cears 11 and 22 and alleviate lost motion between the encaqinq teeth thereof, the -carrier 14 is biased radially relative to the bolt shank 16 and on the side of the bolt shank which is remote from the input shaft 20 to urge the gear 22 into.enaaqement with the gear 11. The biasing is provided by a cup 26 which is in sliding abutment with the bolt shank 16 and is biased relative to the carrier 14 into such abutment by a compression spring 27. The sprinq 27 reacts between the cup 26 and a plug 28 which is screw adjustable on the carrier 14. It will be seen that the biasina force provided by the plug 26 and spring 27 can be varied by adjustment of the plug 28 to increase or decrease the force with which the gears 11 and 22 are urged into driving engagement. To permit such a variation in the drivinq engagement a radial clearance is provided between the bolt shank and bore 29 of the carrier 14. 10 It will be realised from Figure 1 that the radial spacing or eccentricity D provided between the axes of the transmission and input shafts 5 and 20 will permit numerous variations and combinations in the dimensions of the toothed gear wheels 11 and 22 to provide a one-to-oner a step-up or step-down drive ratio and that such eccentricity may be determined as convenient for mountinq the gear unit 1 and carrier 14 within the steering system of a vehicle.

The form of control means 25 and servomotor 9 will be determined as appropriate f o r the particular characteristics of the steering unit or steering gear as will be appreciated by those skilled in the art. For example where the servo motor 9 is hydraulic such as a double acting ram the control means 25 may comprise a spool valve which is M5usted through the linkage 24 to determine 8 the fluid flow to and from the ram as aDProT)riate; where the servo motor 9 is an electric motor the control means 25 may comprise a switch device the adjustment of which determines the direction of running for the electric motor (such electric motor serving for exampl'e either to assist the steering movement directly or to actuate an hypraulic pump which assists the steering movement).

In the modification shoin' in Figure 2 the transmission shaft 5 of the pinion 4 is formed at the end thereof which projects from the housing 1 with an externally toothed involute spur gear 11A, the diameter of which is considerably less than that of the gear wheel 11 in Ficure 1. The gear 11A projects into a carrier in the form of a frame 14A which serves a similar purpose to the housinq carrier 14 in Figure 1, carries the external boss 23 and is pivotally mounted by the bolt 15 on the housing 2 for arcuate displacement about the bolt shank axis 17. Rotatably mounted by bearings 19A within the carrier frame is the input shaft 20 with its axis 21 parallel with the axes 6 and 17 and eccentric with the axis 6. The end.20A of the input shaft 20 adjacent to the housing 2 is bell shaped and provided with an internal involute spur toothed gear wheel 22A that is concentric with the axis 21. Received within the bell end 20A of the shaft 20 and in driving engagement with the internal gear wheel 22A is the external gear wheel 11A. The gears 11A and 22A are biased into engagement, similarly to the Figure 1 arrangement, radially relative to the bolt shank 16 by the spring loaded cup 26 which reacts between the bolt shank and the carrier frame 14A.

The arrangement shown in Figure 2 operates in substantially the same manner as that in Figure 1 whereby in response to a steering input torque being applied to the input shaft 20, the driving engagement between the toothed gears 22A and 11A imparts rotation to the pinion 4 to 9 displace the rack bar 7. The reaction from the transmission of drive between the gear teeth (in response to a resistance to such transmission) causes the carrier frame 14A to be arcuately displaced about the bolt axis 17.

This arcuate displacement of the boss 23 adjusts the control means 25 to actuate the servo motor 9 and impart power assistance to displacement of the rack bar 7. it will be seen from Ficiure 2 that by the use of an internal array of gear teeth 22A engacing with the external array of gear teeth llAy it is possible for the eccentricity D1 between the axes 6 and 21 of the transmission and input shafts to be considerably less than that which is likely to be achieved using the Figure 1 arrangement. The Figure 2 arrangement may therefore be considered more appropriate than the Figure 1 arrangement for use in particular steering gear installations.

In Figure 2 a flexible boot or cover 30 is conveniently provided to extend between the housina 2 and shaft 20 to enclose the carrier frame 14A and components associated therewith (other than for the boss 23 which may extend through the boot).

In a modification of the Figure 2 gear as shown in Figures 3 and 4, the internal spur toothed gear wheel 22A provided in the bell shaped end 20A of the input shaft 20 in Figure 2 is replaced by a pin wheel gear 40. The gear 40 is concentric with the shaft axis 21 and has a circumferentially spaced array of cylindrical pins 41 sec-ured in complementary bores 42 and part cylindrical seatings 43 in the bell shaped end 20A with the axis of each pin parallel to the axis 21. The cylindrical surfaces of the pins 41 stand proud of their seatings 43 to project radially inwardly (relative to the axis 21) of the bell end 20A and provide the equivalent of an internally toothed gear wheel. The transmission shaft 5 carries for concentric rotation therewith an externally toothed gear wheel the teeth 11B of which are suitably profiled, as is well known in the art, for driving engagement with the pins 41 as shown in Figure 4.

In Figure 3 the carrier frame 14A is pivotally mounted 5 by the bolt 15 to a mounting plate 2A welded on the side of the housing 2 (and effectively forminq a part thereof); the transmission shaft 5 is received within a sleeve SA of the externally toothed gear hB to which it is secured for rotation. and the bolt 15 extends through a bush 15A of low 10 friction material in the frame 14A.

a 7 0

Claims

1 A power assisted steering gear comprising a steerinq unit having a transmission shaft rotatable relative to a housing, said transmission shaft having a first toothed gear rotatable and concentric therewith and said unit translating rotary motion of the transmission sbaft to substantially linear motion t.0 provide a steerinq output; an input shaft eccentric with the transmission shaft and rotatable in response to a steering input torque, said input shaft having a second toothed gear rotatable and concentric therewith and being rotatably mounted by a carrier pivotally mounted relative to said housing; said first and second toothed gears being in drivinq enqagement whereby in response to rotation of the input shaft a resultant reaction between the first and second qears pivotally displaces the carrier arcuately, and wherein said pivotal displacement adjusts means for controlling power assistance to said steering output.

2. A gear as claimed in claim 1 in which the transmission 20 shaft is rotatable about a first axis, the input shaf is rotatable about a second axis which is substantially parallel with and eccentric to the first axis, and the carrier is mounted for pivotal movement about a third axis which is substantially parallel to said first and second axes.

3. A gear as claimed in either claim 1 or claim 2 in which the first toothed gear is in direct driving engagement with the second toothed gear.

4. A gear as claimed in claim 3 in which both the first 30 and second toothed gears have external qear teeth.

5. A gear as claimed in claim 3 in which one of said first and second toothed gears has external gear teeth and the other of said toothed qears has internal gear teeth.

6. A qear as claimed in claim 5 in which the second 35 toothed a-ear has'said internal gear teeth located in an 12 open end of the input shaft and said first toothed gear with external gear teeth is located within the open end of the input shaft.

7. A gear as claimed in any one of the preceding claims 5 in which the carrier is pivotally mounted on an outer side of the housing for the steering unit.

8. A gear as claimed in claim 7 in which the carrier comprises a subsidiary housing within which are located the first and second toothed gears.

9. A gear as claimed in any one of the preceding claims in which means is provided for adjusting or biasing the carrier relative to the housing to adjust or bias the first and second toothed gears into driving engagement.

10. A gear as claimed in claim 9 in which the carrier is 15 pivotally mounted by bolt or pin means to be arcuately displaceable about an axis of said bolt or pin means and the carrier is adjustable or biased radially with respect to said axis of the bolt or pin means.

11. A cear as claimed in claim 10 in which radial biasing 20 between the carrier and said bolt or pin means is provided by a spring loaded component which reacts between said carrier and the bolt or pin means and which spring loading is adjustable for adjusting the biasinq with which the f irst and second toothed gears are urged into driving engagement

12. A gear as claimed in any one of the precedinq claims in which said means for controlling power a ssistance and which is adjusted by pivotal displacement of the carrier comprises a valve or switch device.

13. A power assisted steering gear substantially as herein described with reference to Figure 1 of the accompanying illustrative drawings.

14. A steering gear as claimed in claim 13 and modified substantially as herein described with reference to Figure 2 or to Figures 3 and 4 of the accompanying illustrative 9 1 13 1 drawings.

1 0 v Publish d 1991 at The Patent Office, State House. 66171 High Holborn. London WC1 R 47?.Furthe"copies may be obtained from ca C, Sales Branch. Unit 6, Nine Mile Point CWrnfelinfach. Cross Keys. Nert NPI 7HZ. Printed by Multiple. techniques ltd. St Mary Cray. Kent.