GB2062560A - Control valve for power- assisted steering gear - Google Patents

Abstract

A control valve for a power- assisted steering gear intended for use in road vehicles comprises a sleeve (12) and an inner core (14) which are co-axial and relatively rotatable, the interior of the sleeve and the exterior of the inner core being each provided with axially extending recesses which have closed ends arranged so that the recesses of the sleeve co-act with the recesses of the inner core to control the flow of pressurised fluid through the control valve. Each of the recesses (28, 29, 30 and 31) in the interior of the sleeve (12) is provided with at least one pair of laterally directed extensions (41 and 42) which extend respectively from the two opposite sides of the associated recess, to provide a more gradual onset of power assistance. The recesses (28, 29, 30, 31) in the sleeve (12) together with the extensions (41, 42) may be formed by electro-chemical or electrical discharge machining. <IMAGE>

Description

SPECIFICATION Manufacture of power-assisted steering gear This invention relates to the manufacture of a power-assisted steering gear which is intended for use in road vehicles and which incorporates a fluid-pressure actuated piston and cylinder unit and a control valve which serves to control the flow of pressurised fluid into and out of said unit and which is itself actuable in use by the driver of a vehicle in which the steering gear is mounted.

The aforesaid control valve conveniently comprises a pair of co-axial, relatively rotatable parts, namely an outer sleeve-like part and an inner part, recesses being provided in the interior surface of the outer part and in the exterior surface of the inner part for use in controlling the flow of pressurised fluid through the steering gear.

The object of the present invention is to provide an improved control valve for use in a powerassisted steering gear as above-described.

In accordance with the invention there is provided, for use in a power-assisted steering gear, a control valve comprising a pair of co-axial, relatively movable parts, namely an outer sleevelike part and an inner part, the interior surface of the outer part and the exterior surface of the inner part being each provided with a plurality of axially extending recesses which each have closed ends, the recesses of the outer part co-acting in use with the recesses of the inner part to control the flow of pressurised fluid through the control valve, wherein each of the recesses provided in the interior surface of the outer part is formed with at least one pair of laterally directed extensions which extend respectively from the two opposite sides of the recess.

Preferably, said recesses in the outer part, together with their laterally directed extensions, are formed by means of electro-chemical machining or by electrical discharge machining, i.e. spark erosion machining.

The co-acting recesses in the exterior surface of the inner part of the control valve are conveniently of straight-sided configuration and may be formed by means of a cutting tool, or by a rolling process or by electro-chemical machining or by electrical discharge machining.

The invention will now be more particularly described with reference to the accompanying drawings wherein Figure 1 is a sectional elevation showing one example of a control valve in accordance with the invention and for use in a power-assisted steering gear, Figure 2 is a sectional view taken on the line 2-2 of Figure 1, Figure 3 is a sectional view taken on the line 3-3 of Figure 1, Figure 4 is a developed view showing the recesses in the outer and inner parts of the control valve seen in Figure 1, Figures 2-4 all being drawn with said parts being in a position which would correspond in use to a "straight ahead" position of the associated steering gear, and Figures 5 and 6 are views similar to Figures 2 and 4 but showing an alternative embodiment of a control valve in accordance with the invention.

Referring firstly to Figure 1 there is shown therein a control valve which forms parts of a power-assisted steering gear, said gear including a rack 10 which meshes with a pinion 11, said rack 10 being connected to or forming part of a fluidpressure actuated piston and cylinder unit (not shown). The pinion 11 has at one end an integral extension 12 which forms the outer or sleeve-like part of the control valve, said part 12 being mounted in a housing 13. The other or inner part of said control valve 14 projects into the interior of the outer part 12 and at its outer end said part 14 is formed with splines 15a whereby it can be connected in use to a shaft (not shown) which is rotatable by the driver of the vehicle in which the steering gear is installed.Furthermore said outer and inner parts 12 and 14 of the control valve are inter-connected by means of a torsion bar 15, one end of said bar being connected by a pin 8 to the part 14 and the other end by a pin 9 to the part 12. The housing 13 is provided with a port 16 which receives pressurised fluid from an engine driven pump, a port 17 which is adapted to return fluid to the pump and two further ports 18 and 19 which serve to direct oil respectively to the opposite ends of the aforementioned piston and cylinder unit when it is desired to effect a turning movement of the vehicle.

The exterior surface of said inner part 14 of the control valve is formed around its periphery with a plurality of axially extending recesses which are indicated in Figure 2 by reference numerals 21, 23, 25 and 27 and which each comprise a straight groove which is of constant width across its length. The developed form of each recess 21, 23, 25 and 27 is thus of rectangular configuration as seen in Figure 4.

The outer part 12 of the control valve is also provided with a plurality of axially extending recesses indicated respectively by reference numerals 28,29,30 and 31 and each of these recesses is relatively shallow but wider than the aforementioned recesses 21, 23, 25 and 27 formed on the exterior surface of the inner part 14.

Referring to Figures 2 and 3 which show the two parts 12 and 14 of the control valve in a position which corresponds to the "straight ahead" position of the steering gear, pressurised fluid will enter the valve through port 1 6 and will then flow round annul us 32 between the outer part 12 and the housing 13.Said fluid will then pass through ports 33 and 34 formed in said outer part 12 and will then be able to flow between the exterior surface of the inner part 14 and the interior surface of the outer part 12 until it reaches further ports 35 and 36 from which it can flow into an annulus 37 formed between the interior of the inner part 14 and the exterior of said torsion bar 1 5. From said annulus 37 (see Figure 3) the fluid can then flow via further ports 38 and 39 into another annulus 40 between the outer part 14 and the housing 13 and from said annulus the fluid can flow out of the housing via the return port 17.In this position therefore fluid will circulate freely through the control valve via the engine driven pump and no fluid will be directed through either of the ports 18 and 19 so that no pressure will be applied to the aforementioned piston and cylinder unit.

The developed view of Figure 4 shows in more detail the shape of the aforementioned recesses 21,23,25 and 27 in the inner part 14 of the control valve and the recesses 28-31 in the outer part 12 of the control valve. The recesses in the inner part 14 are shown in full lines and the recesses in the outer part 12 are shown in broken lines. As will be seen from Figure 4 each of the last-mentioned set of recesses is formed with at least one pair of laterally directed extensions (more than one pair may be provided if desired), indicated by reference numerals 41 and 42 which extend respectively from the two opposite sides of the associated recess.Conveniently each of said recesses 28, 29, 30 and 31 together with each associated pair of extensions 41 and 42 are formed in the interior surface of the outer part 12 by means of electro-chemical machining or by electrical discharge machining, either of such methods enabling the recesses to be formed after said part 12 has been hardened and ground to the required size.In the developed view shown in Figure 4 the recesses in the interior surface of the outer part 12 and the recesses in the exterior surface of the inner part 14 are arranged in a relationship which corresponds to the "straight ahead" position of the associated steering gear and in this position the recesses in the interior surface of the outer part 12 overlap the recesses in the exterior surface of the inner part 14 so that fluid can flow freely between the interior of said outer part 12 and the exterior of said inner part 14 as previously explained.However when a steering movement is effected the recesses in the exterior surface of the inner part 14 will be moved relative to the recesses in the interior surface of the inner part 12 to prevent a flow of fluid around the whole of the exterior of said inner part 14 but the provision of the aforementioned extensions 41 and 42 formed in the recesses of the outer part 12 will provide for a more gradual cut-off from the previous initial position of the recesses in which a recess in the outer part bridges two adjacent recesses of the inner part and this will give a more gradual build up of pressure which will be applied to the aforementioned piston and cylinder unit so that there will not be a sudden change from a situation in which no power assistance is being provided to the steering and the situation in which full power assistance is being rendered.Whilst a steering movement is being effected it is of course to be understood that the flow of pressurised fluid through the valve will be altered so that fluid will flow to the aforesaid piston and cylinder unit through one of said ports 18, 19 and return to the valve through the other port.

Referring now to the alternative construction shown in Figures 5 and 6, the control valve comprises an outer part 12, an inner part 14, a torsion bar 1 5 and a housing 13 as before. Said outer part is also provided with recesses 28, 29, 30 and 31 which each have at least one pair of lateral extensions 41,42 as before. In this case however, the exterior of the inner part 14 is provided with four recesses 43, 44, 45 and 46 which are each in the form of a straight groove of constant width throughout its length, each such recess extending into the exterior surface of the inner part 14.In addition however said inner part is formed with four further straight recesses 47, 48, 49 and 50 which each communicate with shallower, wider recesses indicated respectively by reference numerals 47a, 48a, 49a and 50a.

Each of the recesses in the exterior of the inner part are however (as is the case with the firstdescribed construction) of straight-sided configuration whereas each of the recesses in the interior of the outer part is provided with at least one pair (more than one pair may be provided if desired) of lateral extensions 41 and 42 which will act in use to give a more gradual change from a straight-ahead position when no power assistance is being provided and a steering position in which such power assistance is being given.

The recesses 21, 23,25 and 27 in the first described construction, or the recesses 43-46 and the recesses 47-50 together with recesses 47a, 48a, 49a and 50a in the second described construction can be formed if desired by means of a cutting tool which is brought physically into contact with the inner part 41. Alternatively such recesses may be formed by a rolling operation or, if desired, by means of electro-chemical machining or by electrical discharge machining. In any event however the recesses in the exterior surface of the inner part are straight-sided and are formed in one operation or one set of operations i.e. in one machine. Similarly, the recesses 28-31, together with their lateral extensions 41 and 42, formed in the interior surface of the outer part are formed in one operation in one machine so that all the required recesses in the two parts of the control valve are formed in two operations.

Such an arrangement represents a considerable saving over methods commonly used at present where for example the recesses formed in the interior surface of the outer part are straight-sided and are formed by electro-chemical machining and the recesses in the exterior surface of the inner part are formed by means of a mechanical (e.g. cutting) operation, lateral extensions to the inner part recesses then being formed by electrochemical machining or by mechanical methods, representing three operations in all.

Claims (4)

1. A control valve for use in a power-assisted steering gear comprising a pair of co-axial, relatively movable parts, namely an outer sleevelike part and an inner part, the interior surface of the outer part and the exterior surface of the inner part being each provided with a plurality of axially extending recesses which each have closed ends, the recesses of the outer part co-acting in use with the recesses of the inner part to control the flow of pressurised fluid through the control valve, wherein each of the recesses provided in the interior surface of the outer part is formed with at least one pair of laterally directed extensions which extend respectively from the two opposite sides of the recess.

2. A control valve as claimed in Claim 1 wherein said recesses in the outer part of the control valve, together with their laterally directed extensions, are formed by means of electrochemical machining or by electrical discharge machining.

3. A control valve as claimed in Claim 1 or Claim 2 wherein each of the recesses formed in the exterior surface of the inner part are of straight-sided configuration.

4. A control valve for use in a power-assisted steering gear substantially as hereinbefore described with reference to and as shown in the accompanying drawings.