GB2046685A

GB2046685A - Power-assisted steering gear

Info

Publication number: GB2046685A
Application number: GB8009685A
Authority: GB
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1979-04-04
Filing date: 1980-03-21
Publication date: 1980-11-19
Also published as: ES8100994A1; GB2046685B; BR8002066A; FR2453067B1; JPS55152671A; JPS6257544B2; DE2913484A1; FR2453067A1; SE8002563L; PL223192A1; DE2913484C2; SE443541B; IT1127422B; IT8048329A0; ES490119A0

Abstract

A power-assisted steering gear has reaction means to provide a "road feel" at the steering wheel. The gear includes a steering spindle comprising a first part 1 and a second part 2. The first part is formed with a rotary valve 3 and the second part 2, which is constructed as a steering worm, is formed with a control bush 5 cooperating with the valve 3 which is connected to the steering worm via a torsion rod 6. The steering worm is operatively connected by way of recirculating balls 14 to a power piston 13 which is axially slidable in a gear casing 12 and meshes with a steering sector 16. The torsion rod 6 is surrounded by a hollow reaction piston 20 which is supported on the two ends 23, 24 of the torsion rod 6. The adjacent ends of the reaction piston 20 and the first steering spindle part 1 are formed with complementary V-shaped recesses 21,22 which upon assembly of the two elements 1 and 20 form, in conjunction with the peripheral surface of the end 23 of rod 6, a peripheral zig-zag channel which serves to guide a row of balls 25. The channel with the balls 25 constitutes centring means for the rotary valve 3, 5. At its end remote from the centring means the reaction piston 20 forms a chamber 30 which accommodates a centring spring 31 and which is connected to a working pressure duct 34, 35. <IMAGE>

Description

SPECIFICATION Power-assisted steering gear, more particularly for motor vehicles This invention relates to a power-assisted steering gear, more particularly for motor vehicles, having a casing, a pressure oil control means, a means for producing a reaction force which can be 'felt at the steering wheel, and a steering spindle comprising a first and a second part, the two steering spindle parts being inter-connected via a torsion rod for the purpose of re-setting the pressure oil control means to the neutral position, the first steering spindle part being connectable to a steering wheel and second steering spindle part being connected via a steering worm and recirculating balls to a power piston which is slidable into the steering gear casing and which meshes with a steering sector carrying a steering arm shaft.

Such a power-assisted steering gear is known, for example, from German Patent Specification 11 33 642, which discloses a first steering spindle part having a forked end by means of which two control pistons are adjusted, which are mounted transversely in relation to the steering spindle axis in a steering worm head formed on the second steering spindle part. The two steering spindle parts can be rotated in relation to one another by the amount of a predetermined control path against the force of a torsion rod. Areas of different sizes are formed on the end faces of the two control pistons, so that during steering a differential piston area acted upon by the working pressure is operative on one control piston, such area producing at the steering spindle a counter force communicating a "road feel".A reaction system of this kind is limited to use with piston valves as a pressure oil control system. Quite apart from this, two piston valves incorporated transversely in relation to the steering spindle axis and at a distance therefrom occupy a relatively large radial space.

The invention aims at providing a relatively simple reaction system, which leaves the outer contours of the steering transmission unchanged, when a rotary valve is used in a power-assisted steering system of the foregoing kind. As a result, the power-assisted steering system can be produced without considerable constructional alterations either with or without a hydraulic reaction, as required by the user.

Accordingly, the present invention consists in a power-assisted steering gear, more particularly for motor vehicles, having a casing, a pressure oil control means, a means for producing a reaction force which can be felt at the steering wheel, and a steering spindle comprising a first and a second part, the two steering spindle parts being inter connected via a torsion rod for the purpose of re setting the pressure oil control means to the neutral position, the first steering spindle part being connectable to a steering wheel and the second steering spindle part being connected via a steering worm and recirculating balls to a power piston which is slidable in the steering gear casing and which meshes with a steering sector carrying a steering arm shaft, characterised by the following features:: a rotary valve formed on the first steering spindle part is connected via the torsion rod to the steering worm, carrying a control bush, of the second steering spindle part; the torsion rod is surrounded by a hollow reaction piston which is supported at the torsion rod ends; arranged between the first steering spindle part and one end of the reaction piston is a centring means formed by parallel inclined surfaces and balls disposed therebetween; disposed in a chamber at the end of the reaction piston remote from the centring means is a centring spring bearing against the reaction piston; the chamber of the reaction piston is connected to a pressure duct.

The hollow reaction piston, which can be acted upon by any required pressure, is accommodated inside the steering worm. The torsion rod, on whose thickened ends the reaction piston is guided, extends through its bore. The reaction piston bears via inclined surfaces, with which one of its end faces is formed, and a row of balls, against complimentary inclined surfaces of the first steering spindle part carrying the rotary valve and the steering wheel. The result is a centring device which is operative in both steering directions and whose return force is boosted by a pressure, for example, the working pressure, operating on the reaction piston. The constructional members required for this purpose are so mounted as to require no additional space.

The power-assisted steering gear can therefore be assembled from prefabricated parts at very low cost, with or without hydraulic reaction, as required.

It is true that French Patent Specification 1 505 333 (e.g., Fig. 7) discloses how in a powerassisted steering gear controlled by a rotary valve, the two facing steering spindle ends of a divided steering spindle can bear against one another with pre-stressing via cutaway portions, having inclined surfaces, and interposed anti-friction members. To produce the pre-stressing, the two steering spindle parts are interconnected via a rod, with the interposition of cup springs. Provision is also made to increase pre-stressing during steering by the working pressure, which is conducted to a reaction piston bearing against the rod. Quite apart from the fact that this known reaction system is used inside a different steering construction, the associated constructional and manufacturing costs are relatively high.Moreover, the constructional members are so nested inside the rotary valve that resilient changes in shape due to pressure may result in jamming.

In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example an embodiment thereof, and in which: Fig. 1 is a longitudinal section through a steering system in accordance with the invention, and Fig. 2 shows an enlarged view of a detail of Fig.

1.

A two-part steering spindle comprises a first steering spindle part 1, carrying a rotary valve 3, and a second steering spindle part 2 which is constructed as a steering worm on which is formed a control bush 5 cooperating with the rotary valve 3. A steering wheel (not shown) is operatively connected to the steering spindle part 1. The two steering spindle parts 1 and 2 are resiliently connected to one another via a torsion rod 6. The steering spindle part 2 is entrained by the steering spindle part 1 after a control path, determined by splines 7, against the force of the torsion rod 6 is overcome. Within the control path the rotary valve 3 effects a rotary movement in relation to the control bush 5, so that pressure oil is supplied to a pressure chamber 10 or 11, in dependence on the direction of rotation.The way in which a rotary valve of this kind operates is widely known and can be gathered, for example, from German Offenlegungsschrift 26 37 458.

The separation of the two pressure chambers 10 and 11 is effected by a power piston 13 sliding in a steering gear casing 12. The power piston 13 engages via recirculating balls 14 the steering worm of the steering spindle part 1. The power piston 13 also engages via teeth 1 5 a steering sector 1 6 connected to a steering arm shaft (not shown). To absorb the axial force, the second steering spindle part 2 connected to the steering worm is supported in a thrust bearing 1 7.

Mounted in a bore 1 8 in the second steering spindle part 2 is a reaction piston 20 which is supported by the thickened ends 23 and 24 of the torsion rod 6. The top end (as viewed in Fig. 1) of the reaction piston 20 is formed with a V-shaped milled recess, while the bottom end of the first steering spindle part 1 is machined complementarily, so that opposite parallel inclined surfaces 21 and 22 are produced after assembly of the two elements. These inclined surfaces cooperate with the surface of the thickened end 23 of the torsion rod 6 to produce a zig-zag groove which extends over the periphery and contains a row of balls 25. The inclined surfaces 21 and 22 and the balls 25 co-operate to provide a centring means for the valve device consisting of the rotary valve 3 and the control bush 5.

The thickened end 23 of the rod 6 is connected via a pin 26 to the first steering spindle part 1. The other thickened end 24 is attached together with a bush 27 by means of a pin 28 to the second steering spindle part 2. As shown in Fig. 2, a chamber 30 is formed by the bush 27 and the thickened end 24 in which chamber is located a pre-stressed compression spring 31, bearing via an annular disc 29 against the reaction piston 20.

By way of the reaction piston 20 and the centring means 21,22 and 25, the spring 31 exerts a predetermined centring force on the rotary valve 3. To facilitate axial slidability, the reaction piston 20 bears against the thickened end 24 via balls 32. The balls 32 have the further advantage that when suitably selected they can make for any existing manufacturing tolerances.

A pressure operative during steering can be introduced into the chamber 30. As shown in Fig.

1, for example, a pump connection 33 extending to the slide valve 3, 5 can be connected via casing bores 34 and 35 to the chamber 30. As a result, the working pressure in the particular pressure chamber 10 or 11 acts on one end face 36 of the reaction piston 20. The force of the working pressure at the end face 36 therefore operates in addition to the force of the spring 31 on the reaction piston 20, which in turn exerts via the centring means 21, 22, 25 a corresponding resetting force on the first steering spindle part 1 and therefore on the steering wheel. In this way a road feel dependent on the steering resistance at the steered wheels is communicated to the driver.

Instead of the working pressure, a driving speed-dependent pressure, which is produced by a pump driven by the gearbox output shaft, can be introduced into the chamber 30. In that case the casing bores 34 and 35 connected to the pump connection 33 are dispensed with and a connection is provided in a cover 1 9 for a line disposed outside the casing 12. In that case the reaction force which can be felt at the steering wheel increases with increasing driving speed and decreasing steering resistance. A further possibility is to use a reaction pressure as disclosed in German Patent Application P 28 51 773.

The pump connection 33 is connected via an annular groove 34' and a number of bores 35' in the control bush 5 to axial grooves 37 in the rotary valve 3. In the neutral position of the rotary valve 3, 5 which is shown in Fig. 1 , the pressure oil passes via further axial grooves 38 and a transverse bore 39 into a central bore 40, from which the pressure oil flows via a transverse bore 41 and the splines 7 constructed with clearance into a bore 1 8 of the second steering spindle part 2, and finally into an annular duct 43 connected to an oil reservoir connection 42. The pressure oil flows through the steering gear unpressurised, that is steering is not effected.

When the steering spindle part 1 is rotated, that pressure oil passes either via axial grooves 44 and radial bores 45 in the control bush 5 into the pressure chamber 11, or via axial grooves 46, radial bores 47, an annular duct 48 and the spindle screwthreading into the pressure chamber 10.

If the power-assisted steering system described above is to be constructed without reaction force, for example, for slowly travelling building site vehicles, the reaction piston 20 is dispensed with and a torsion rod somewhat shortened at the ends is incorporated. The bush 27 with the centring spring 31 and the balls 32 are also dispensed with. In this way the power-assisted steering system can be adapted to its intended use by slight constructional changes.

Claims

1. A power-assisted steering gear, more particularly for motor vehicles, having a casing, a pressure oil control means, a means for producing a reaction force which can be felt at the steering wheel, and a steering spindle comprising a first and a second part, the two steering spindle parts being interconnected via a torsion rod for the purpose of re-setting the pressure oil control means to the neutral position, the first steering spindle part being connectable to a steering wheel and the second steering spindle part being connected via a steering worm and recirculating balls to a power piston which is slidable in the steering gear casing and which meshes with a steering sector carrying a steering arm shaft, characterised by the following features:: a rotary valve formed on the first steering spindle part is connected via the torsion rod to the steering worm, carrying a control bush, of the second steering spindle part; the torsion rod is surrounded by a hollow reaction piston which is supported at the torsion rod ends; arranged between the first steering spindle part and one end of the reaction piston is a centring means formed by parallel inclined surfaces and balls disposed therebetween; disposed in a chamber at the end of the reaction piston remote from the centring means, is a centring spring bearing against the reaction piston; the chamber of the reaction piston is connected to a pressure duct.

2. A power-assisted steering gear according to claim 1, wherein to facilitate axial slidability of the reaction piston, the end of the reaction piston remote from the centring means bears via balls against the adjacent end of the torsion rod.

3. A power-assisted steering gear according to claim 1 or 2, wherein the chamber of the reaction piston can be acted upon by a pressure of predetermined characteristic value (e.g., the working pressure or travel-speed-dependent pressure).

4. A power-assisted steering gear according to any of claims 1 to 3, wherein the reaction piston and the first steering spindle part adjacent the torsion rod are so formed with a V-shaped milled recess that after assembly of the two elements the parallel inclined surfaces are produced which cooperate with the thickened end of the torsion rod to form a zig-zag channel which extends over the periphery arid contains a row of balls.

5. A power-assisted steering gear according to any of claims 1 to 4, wherein the reaction piston and the associated chamber are disposed inside the steering worm.

6. A power-assisted steering gear, substantially as herein described with reference to and as shown in the accompanying drawings.