GB2212463A

GB2212463A - Power-assisted steering gear

Info

Publication number: GB2212463A
Application number: GB8825986A
Authority: GB
Inventors: Mohammed Ali Hajihosseinloo; Roy Sidney Campbell
Original assignee: Burman and Sons Ltd
Current assignee: Burman and Sons Ltd
Priority date: 1987-11-14
Filing date: 1988-11-07
Publication date: 1989-07-26
Anticipated expiration: 2008-11-07
Also published as: GB8825986D0; GB2212463B; GB8726720D0

Abstract

A power-assisted vehicle steering gear comprises an hydraulically actuated means which is controlled by a main valve having a pair of relatively rotatable parts such as parts 12 and 13, and includes means for resisting such relative rotation between parts 12 and 13. The resisting means comprising a plurality of bails 22 which are each located in one of a series of axially extending circumferentially spaced bores or recesses 21 formed in a ring 19 which is connected to said part 12 so as to be rotatable therewith, each of said balls 22 projecting axially outwardly into an opposed pocket formed in a flange 23 which is connected to said part 13 so as to be rotatable therewith. The strength of said resisting means is variable in strength in dependence upon a chosen parameter or parameters, for example, vehicle speed. In the aforesaid example pressurised oil is applied to said bores or recesses, the pressure of such pressurised oil being variable by means of a pressure control valve in dependence upon the aforesaid chosen parameter or parameters. In an alternative example said ring and said flange are urged towards each other by adjustable resilient means such as a coiled compression spring. <IMAGE>

Description

"POWER-ASSISTED STEERING GEAR" This invention relates to steering gear and specifically to a power-assisted steering gear which is intended for use on a vehicle.

Such power assisted steering gear is provided for the purpose of reducing the manual effort which in use has to be exerted by a vehicle driver when it is desired to turn the driver-actuable steering wheel of the vehicle in which the steering gear is mounted.

It is however important to preserve some "feel" or resistance in the steering mechanism in order that a better control of the vehicle can be achieved.

Nevertheless it is preferable that the degree of such "feel" or resistance should not be constant but should be variable in dependence upon the speed of the vehicle or upon some other chosen parameter or parameters. Thus, in the former case, at relatively low vehicle speeds, such as for example would be employed when parking manoeuvres are being effected, the degree of power assistance required is greater than that needed at relatively high vehicle speeds.

The object of the present invention is to provide a power-assisted steering gear which incorporates an improved form of means for varying the degree of power assistance provided by the gear in dependence upon vehicle speed or some other chosen parameter or parameters.

In accordance with the present invention, there is provided a power-assisted vehicle steering gear comprising an hydraulically-actuated means controlled by a main valve and which is arranged to augment the force applied to the steerable wheels of the vehicle when the associated steering wheel is turned by the vehicle driver, said main valve comprising a pair of relatively rotatable parts of which one in use is connected to said vehicle steering wheel, and means for resisting such relative rotation between said parts, said resisting means being in use variable in strength in dependence upon a chosen parameter or parameters, said resisting means comprising a plurality of balls or rollers which are each located in one of a series of axially extending circumferentially spaced bores or recesses formed in an end face of a ring so as to project axially outwardly from the associated bore or recess into an opposed pocket formed in a flange, said ring and said flange being respectively connected to said relatively rotatable parts of said main valve.

In this arrangement there may be provided a pump and a pressure control valve which is arranged in use to control hydraulic pressure which is applied to second hydraulically actuated means which actuate said resisting means, said pressure control valve being adjustable by means which are responsive to said chosen parameter or parameters.

Conveniently, the aforesaid pressure control valve is electronically operated and is adjustable by means of a microprocessor or other mechanism which is responsive to the chosen parameter or parameters. Thus where a microprocessor is provided it may have an input or inputs relating to vehicle speed and/or another parameter or parameters such as, for example, oil temperature, ambient temperature, road conditions, steering wheel angle, effective radial acceleration, and axial acceleration or deceleration, and an output which is connected to the pressure control valve for the purpose of varying the pressure controlled by the valve until the desired pressure is achieved.

In one particular example the aforesaid ring is formed on or connected to the outer sleeve of said main valve whereas the flange is connected to the inner core of said main valve. The inner end of each of said pockets is preferably profiled (curved) to any desired shape and the arrangement is such that turning of the vehicle steering wheel from a central or neutral position will have the effect of turning said inner core of the main valve relative to the outer sleeve and thus of turning said flange relative to said ring. This will also have the effect of rolling each ball or roller to displace it inwardly into its bore or recess in the ring, the profiled inner end of the associated pocket exerting a kind of cam action on the ball or roller.The bores or recesses themselves may each have a piston which engages at one end with the associated ball or roller and said engaging end may also be of profiled (curved) form.

Hydraulic pressure will in use be applied to said bores or recesses in said ring and the pressure applied (which is variable in dependence upon the chosen parameter or parameters) will provide a resistance to such inward movement of said balls or rollers into their respective bores or recesses. In an alternative arrangement each of said axially extending bores or recesses may be provided with a spring-loaded plunger having a stem which engages the associated ball or roller, a spring acting on said plunger to force the stem into engagement with the associated ball or roller. In this case pressurised-oil controlled by said pressure control valve is in use introduced into each bore or recess to counter-act the pressure exerted by the spring acting on the plunger.

In another example said ring and said flange are urged towards each other by adjustable resilient means in the form of a coiled compression spring and the degree of compression applied to said spring (and thereby the force which urges the ring and the flange towards each other) is adjustable by means of a screw threaded mechanism. Further said screw threaded mechanism can itself be adjusted by means of a stepper motor or other device which can itself be controlled by a microprocessor having an input or inputs receiving signals from a sensor or sensors monitoring the chosen parameter or parameters.

The aforesaid relatively rotatable parts of the main valve will themselves be interconnected by a torsion bar which will provide stiffness in the steering system.

The invention will now be more particularly described with reference to the accompanying drawings wherein Figure 1 is a partly schematic, partly sectional elevation of one example of a steering gear in accordance with the invention, Figure la is a scrap view showing a variation of one of the features seen in Figure 1, and Figure 2 is a sectional view showing part of an alternative construction in accordance with the invention.

Referring firstly to Figure 1 there is shown therein a power-assisted steering gear which is arranged in use to be mounted in a vehicle so as to be operatively connected to the steerable wheels of the vehicle. To this end the steering gear as shown in the drawing is of the rack and pinion variety (but is not restricted to this type of steering mechanism), there being provided a rotatable pinion 10 and a rack 11, the latter being connected to said steerable road wheels and also being connected to an hydraulic ram (not shown) of any known form.The pinion 10 is integrally connected to the outer sleeve 12 of a main valve having an inner core 13, said sleeve 12 and inner core 13 being relatively rotatable and said inner core being extended at that end of the valve remote from said pinion 10 to form a spindle 13a which in use will be connected to the steering column and steering wheel of the vehicle in which the gear is mounted.

Pressurised oil is supplied by means of a main pump (not shown) to said main valve ( return oil being fed to a reservoir 14 which supplies oil to said pump) and the arrangement is such that when the vehicle steering wheel is turned to turn said spindle 13a and inner core 13 of the main valve to either side of a neutral or straight ahead position, then pressurised oil will be directed through slots and passages formed in said main valve to one end or the other of the aforesaid hydraulic ram connected to the rack 11 and thereby effect the desired turning movement of the steerable vehicle wheels. Such an arrangement is known and forms no part of the present invention.

There is however provided a further pump 14a which may be arranged in use to be driven by a small d.c.

motor or by the engine of the vehicle in which the gear is mounted, said pump delivering pressurised oil through a pressure control valve 15. Oil passing through said pressure control valve 15 flows at a pre-determined pressure via a line 16 and suitable drilling 17 into an annul us 18 formed in a ring 19 which is connected by a pair of pins 19a (only one shown) to said sleeve 12, said annul us being connected by radial drillings 20 to a plurality of bores suc- are indicated by reference numeral 21, each of sai bores serving to locate a roller or, as shown, a ba - 22.There is also provided a flange 23 which is connected by a pin 24 to the inner core 13 of said main valve so as to be rotatable therewith, said p-- 24 also serving to connect said inner core 13 to ore end of a torsion bar 25 of which the other end is connected to said sleeve 12 by a pin 26. Said flar is formed with a plurality of pockets 27 and as sh-- in the drawing the balls 22 project from their bor- and into corresponding aligned pockets 27.

The closed end of each pocket 27 is formed to any desired shape or profile. Thus in order that rela . - rotation can occur between the inner core 13 and outer sleeve 12 of the main valve it is necessary said balls 22 should move from neutral positions as seen in Figure 1 (corresponding to a straight aheac steering position) to positions (into which they wt have rolled) further into their associated bores 2'.

return oil flowing back into reservoir 14 via grooves formed in that face of flange 23 which is adjacent ring 19 (one of such grooves being indicated by reference 27a),drilling 28 and line 29. It will of course be understood that the amount or rate of such displacement of said balls 22 into their bores 21 for any given degree of rotation of the inner core 13 wi depend on the profile of the closed ends of said pockets 27. The aforesaid pressure control valve 15 feeds 3i 1 via said line 16 and drilling 17 as above described into the annulus 18 and thence via drillings 20 so as to urge the balls 22 outwardly and into engagement with the pockets 27.This provides a resistance to relative rotation between the aforesaid two relative y rotatable parts (i.e. sleeve 12 and inner core 13) of the main valve through the medium of which oil will be supplied, as previously explained, to the hydraulic ram connected to said rack 11.

The oil pressure which is exerted on said balls 22 to urge them towards and into the pockets 27 is however varied by the aforesaid pressure control valve 15.

To this end there is provided means such as for example a microprocessor 30 which has one or more inputs 31 related to the chosen parameter or parameters. Thus in use where (for example) vehicle speed is being monitored, at relatively high vehicle speed the pump 14a supplies oil to the pressure control valve 15 which at such relatively high vehicle speeds is set by the aforesaid microprocessor 30 to provide the required relatively high pressure which will then press the balls 22 into their pockets 27.

At relatively low vehicle speeds however the microprocessor will act to set the pressure control valve 15 to a state to lower the hydraulic pressure and thus make it easier to turn the spindle 13a (via the vehicle steering wheel) and thus provide a greater power assistance to steering movements of the steerable wheels as may be required for example when parking or manoeuvring at relatively low speeds.

In the event of failure of the main hydraulic pressure used by the aforementioned hydraulic ram, a direct mechanical connection can be established by inter-engageable lugs formed respectively on or connected to the sleeve 12 and inner core 13, one such lug being indicated by reference numeral 32. It is also possible to use a bladder to transmit the desired hydraulic pressure to the balls 21.

Also, as shown in Figure 1, there is provided a booster cylinder 33 which will come into operation in the event of an emergency caused by failure of the pump 14a. Said booster cylinder is provided, intermediate its ends with a diaphragm 34 which separates pressurised gas 35 from hydraulic fluid 36 so that on failure of the pump 1 4a or fluid connections thereto, the gas 35 will expand to cause the diaphragm 34 to express the fluid 36 into the pressure control valve 15 and thence to the annul us 18.

In an alternative arrangement shown in scrap view la, each bore 21 has a plunger 37 loaded by a spring 38 and having a stem 39 which projects through a partition 40 to engage an associated ball 22, the spring 38 thus applying pressure to the ball to force it into its pocket 27. The pressure applied by the spring is reduced by admitting oil from the pressure control valve 15 via a port 41.

Referring now to Figure 2 there is shown therein an alternative construction in accordance with the present invention. In this construction there is provided a main control valve as before, said valve having an outer sleeve 42 which is integrally connected to a pinion forming part of a rack and pinion assembly which is itself connected to the steerable road wheels of the vehicle via the intermediary of an hydraulic ram and said main control valve also includes an inner core 43 which projects at one end 43a from a casing 44, said end 43a being connectible to. the steering column of the vehicle.

Thus in use said inner core or spindle 43 can be turned by angular movement of the vehicle steering wheel.

Said inner core 43 adjacent to its right-hand end as seen in Figure 2 extends through a gear 45 mounted so that it can both rotate and slide axially relative to said inner core 43 and at one axial end of said gear 45 there is provided a flange 46 formed around its periphery with a screw thread 47 which engages with a co-acting screw thread 48 formed within said casing 44.

Said gear 45 engages with a rack 49 connected to a stepper motor 50 which is arranged to be actuated in any convenient manner by means responsive to the vehicle speed or any other chosen parameter or parameters.

The aforesaid flange 46 engages on its outer side bearings 51 located in grooves formed in a pressure plate 52 which is also freely mounted on said inner core 43 and said pressure plate itself engages one end of a coiled compression spring 53. The other end of said spring 53 engages a further plate 54 in which is formed a series of recesses such as grooves or pockets 55 which are opposed by similar grooves or pockets 56.

Said grooves 55 and 56 serve to locate a series of balls 56a formed in a ring 57 which is connected by means of pins 58 to the aforesaid outer sleeve 42 of the main control valve. It will be understood therefore that if it is required to turn the inner core 43 relative to the outer sleeve 42 of the main control valve then the plate 54 has to be displaced to the right as seen in the drawing from the neutral or central position of the steering gear which is illustrated in Figure 2.

Such displacement of plate 54 is resisted by the pressure exerted by the coiled spring 53 and such pressure is varied by relative axial movement of the gear 45 and flange 46 when the stepper motor 50 is actuated. Thus such actuation of the stepper motor will effect a linear movement of the rack 49 which in turn is converted into an angular movement of said gear 45 and by virtue of the interacting screw threads 47 and 48 said gear 45 and flange 46 assembly will be moved axially along the inner core 43 so as either to increase or decrease the pressure exerted by the coiled spring 53 on the plate 54. It is therefore arranged that, for example, at relatively low vehicle speeds the stepper motor 50 will be actuated so as to move the assembly comprising the gear 45 and flange 46 to the right (as seen in Figure 2) along the inner core 43 in order to reduce the compression of the coiled spring 53 and thereby reduce the resistance provided by the balls 56a within the respective sets of grooves or pockets 55 and 56 against relative rotation between said inner core 43 and outer sleeve 42. In a variation of the above-mentioned construction it can be arranged that the stepper motor 50 is connected to a gear (not shown) which can be angularly displaced in a series of steps by the stepper motor, said gear engaging the aforementioned gear 45.

Claims

Claims:

1. A power-assisted vehicle steering gear comprising an hydraulically-actuated means controlled by a main valve and which is arranged to augment the force applied to the steerable wheels of the vehicle when the associated steering wheel is turned by the vehicle driver, said main valve comprising a pair of relatively rotatable parts of which one in use is connected to said vehicle steering wheel, and means for resisting such relative rotation between said parts, said resisting means being in use variable in strength in dependence upon a chosen parameter or parameters, said resisting means comprising a plurality of balls or rollers which are each located in one of a series of axially extending circumferentially spaced bores or recesses formed in an end face of a ring so as to project axially outwardly from the associated bore or recess into an opposed pocket formed in a flange, said ring and said flange being respectively connected to said relatively rotatable parts of said main valve.

2. A steering gear as claimed in Claim 1 wherein there is provided a pump and a pressure control valve which is arranged in use to control hydraulic pressure which is applied to second hydraulically actuated means which actuate said resisting means, said pressure control valve being adjustable by means which are responsive to said chosen parameter or parameters.

3. A steering gear as claimed in Claim 2 wherein said pressure control valve is electronically operated and is adjustable by means of a microprocessor which is responsive to the chosen parameter or parameters.

4. A steering gear as claimed in Claim 3 wherein said ring is formed on or connected to the outer sleeve of said main valve and the flange is connected to the inner core of said main valve.

5. A steering gear as claimed in any one of the preceding claims wherein the inner end of each pocket is formed to a curved configuration.

6. A steering gear as claimed in any one of the preceding claims wherein each of said bores or recesses contains a piston which engages at one end the associated ball or roller.

7. A steering gear as claimed in any one of Claims 2-6 wherein pressurised oil controlled by said pressure control valve is in use introduced into said axially extending bores or recesses.

8. A steering gear as claimed in any one of Claims 1-5 wherein each of said axially extending bores is provided with a spring-loaded plunger having a stem which engages the associated ball or roller, pressurised oil controlled by said pressure control valve being in use introduced into said bore or recess to counter-act the pressure exerted by the spring which acts on said plunger.

9. A steering gear as claimed in Claim 6 wherein each of said pistons is shaped at that end which engages the associated ball or roller to a curved configuration.

10. A steering gear as claimed in Claim 1 wherein said ring and said flange are urged towards each other by adjustable resilient means.

11. A steering gear as claimed in Claim 10 wherein the force exerted by said resilient means is adjustable by screw threaded means.

12. A steering gear as claimed in Claim 11 wherein said screw threaded means is adjusted by a stepper motor which is itself responsive to variations in a chosen parameter or parameters.

13. A steering gear substantially as hereinbefore described with reference to Figure 1, or Figure 2 modified as shown in Figure la, or Figure 2.