GB1600822A - Hydraulically-actuated vehicle steering mechanism - Google Patents

Description

(54) HYDRAULICALLY-ACTUATED VEHICLE STEERING MECHANISM (71) We, BURMAN & SONS LIMITED a British Company, of Wychall Lane, Kings Norton, Birmingham B38 8AB, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to hydraulically actuated vehicle steering mechanism that is especially (but not exclusively) intended for use in off-road vehicles such as earthmoving equipment, fork lift trucks and agricultural machines, the mechanism being of the kind which includes piston and cylinder means which are adapted to be connected to the steerable wheels of the vehicle so that fluid pressure applied to said piston and cylinder means will in use effect the desired steering movements of said wheels.

The object of the present invention is to provide an improved hydraulically actuated vehicle steering mechanism of the abovementioned kind.

In accordance with the invention there is provided an hydraulically actuated vehicle steering mechanism of the kind including piston and cylinder means connectible in use to the steerable wheels of a vehicle wherein there is provided a power actuated hydraulic pump, an hydraulic pump-motor unit and a control valve, said control valve comprising a pair of concentric valve members which are interconnected by a torsion bar so as to be angularly movable relative to each other but secured against relative axial movement, one of said members being rotatable by the driver of the vehicle in which in use the mechnism is fitted and the other of said members being rotatable by the rotor of said pumpmotor unit, said valve members being arranged so that when the mechanism is in a neutral or straight ahead condition, the relative angular positions of said members is such as to permit a free flow of fluid through the valve from said pump to a reservoir whereas relative angular movement between the two valve members consequent upon a steering action of the driver in either direction of rotation will initially cut off said free flow of fluid through the valve.

The invention will now be more particularly described with reference to the accompanying drawings wherein.

Figure 1 is an elevation of part of one example of a vehicle steering mechanism constructed in accordance with the invention, Figure 2 is an end view of the unit seen in Figure 1 looking in the direction of arrow 'A', but with a cover plate removed, Figure 3 is a sectional view taken on the line 3-3 of Figure 2, Figure 4 is an elevation of the inner valve member and sleeve assembly forming part of the unit seen in Figure 3, said assembly being shown in a position for, say a righthand turn, Figures 5 and 6 are respectively sections on lines H-H and J-J of Figure 4, but illus- trating fluid flow paths in the neutral or straight ahead condition of the mechanism, and Figures 7-13 are respectively sections on lines D-D, H-H, E-E, C-C, G-G, F-F, and J-J of Figure 4, these figures illustrating fluid flow paths for a right-hand turn.

Referring now to the drawings, Figure 1 shows a combined control valve and hydraulic pump-motor unit but it is to be understood that an hydraulically actuated vehicle steering mechanism in accordance with the invention will also include a power actuated hydraulic pump (not shown) which may be of any suitable form and which in use will be conveniently driven by the engine of the vehicle in which the mechanism is mounted. The mechanism will also include piston and cylinder means (not shown) connectible in use to the steerable wheels of the vehicle.

The unit shown in Figure 1 comprises a combined control valve, generally indicated by reference numeral 10, and an hydraulic pump-motor unit generally indicated by reference numeral 11. Said pumpmotor unit (see Figure 2) includes a stator 12 and a rotor 13, the rotor being mounted eccentrically with regard to the stator and both the stator and the rotor having lobes to form cavities between the stator and the rotor which vary in volume as the rotor rotates within the stator. Thus in the position shown in Figure 2 pressurised fluid admitted for example into cavities 14, 15 and 16 will have the effect of rotating the rotor to express fluid from cavities 17 and I8.

Figure 1 shows external connections 19 and 20, connection 19 being used to lead a supply of pressurised fluid to the control valve from the engine driven pump, whereas connection 20 provides a port through which fluid can flow from the control valve to a reservoir (not shown). The control valve itself comprises a pair of concentric valve members namely an inner valve member 21 and an outer sleeve 22. The inner member 21 projects from the housing 23 of the valve and is formed at its outer end with splines 24 by means of which said inner member 21 can be connected in use to a driver rotatable shaft which in turn would be connected to the steering wheel of the associated vehicle.

Turning now to Figure 3, said inner valve member 21 is hollow and is connected internally at its splined end to one end of a torsion bar 25 by means of a pin 26.

The other end of said torsion bar 25 is connected as by means of a brazing ring 27 to a collar 28 having a forked end which receives the forked end of a wobble shaft 29 shaped at its outer end 30 to engage the interior of said rotor 13. A driving pin 31 extends through the forked ends of said collar 28 and the wobble shaft 29 and said drive pin also extends through a pair of elongated holes formed in opposite sides of the inner valve member 21, the outer ends of said drive pin 31 being located in circular holes formed in opposite sides of the sleeve member 22. The housing 23 also includes a port 32 which is connected to one side (for example the right-hand side) of the aforementioned piston and cylinder means which in use are connected to the steerable wheels of the vehicle. Said housing 23 also has another port (not shown) which would be connected to the left-hand side of said piston and cylinder means.

Reference is now made to Figures 5 and 6 which are respectively sections taken on the lines H-H and J-J of Figure 4, the latter showing the sleeve member 22 from which projects at one end the splined end 24 of the inner valve member 21 and, from the other end, the end 30 of the wobble shaft 29, said Figures 5 and 6 showing fluid flow paths when the control valve is set in a straight ahead or neutral position. Thus pressurised fluid entering the housing 23 through the connection 19 will first flow into a relatively wide annulus 33 formed in the interior of the bcre in the housing 23 which houses said sleeve member 22 and from said annulus 33 the fluid can flow through said sleeve member 22 via two sets of circumferentially spaced drillings indicated in Figure 4 by reference numerals 34 and 35. The drillings 34 and 35 will provide a fluid flow path for initiating a steering movement of the steerable wheels of the vehicle but in the straight ahead or neutral position there will be no tendency for such steering movement to be effected since the drillings 34 and 35 will provide a fluid flow path to the reservoir via the connection 20. Thus said drillings 35 will enable the pressurised fluid to flow into short shallow transfer grooves 36 formed in the interior surface of the sleeve member 22.

In the straight ahead position said transfer grooves 36 communicate with further grooves formed on the exterior of the inner valve member 21 which in turn communicate with further drillings 38- in the sleeve member 22 and said drillings 38 communicate with an annulus 39 which itself communicates with the connection 20. Thus in the straight ahead position fluid can flow freely through the valve between connections 19 and 20 via annulus 33, drillings 35, transfer grooves 36, grooves 37, drillings 38, and annulus 39. Furhter grooves 40 are formed on the exterior of the inner valve member 21 and these grooves in the straight ahead condition contain fluid which both lubricates and balances said valve member 21 relative to the sleeve member 22.

If now a steering movement is initiated for example by turning the inner valve member 21 in a clockwise direction relative to the sleeve member 22 in order to initiate, say, a right-hand turn, the flow paths indicated in Figures 5 and 6 will now be changed to those indicated respectively in Figures 8 and 13. Thus referring to Figure 13 it will be seen that the slots 37 in the inner member 21, whilst still in communication with the transfer slots 36 of the sleeve member 22 will now be out of communication with the drillings 38 so that fluid cannot now pass directly between the connection 19 and connection 20. On the other hand, referring to Figure 8, pressurised fluid flowing through the connection 19 and the relatively wide annulus 33 will now be able to pass through the drillings 34 and thence along slots 41 formed in the exterior of the inner member 21 which will then be in communication with further drillings 42 (see Figures 4 and 9) which supply an annulus 43 formed in the interior of the housing 23. Said annulus 43 in turn feeds further grooves 44 formed in the exterior of said sleeve member 22 and some of said grooves 44 are in communication with drillings 45 formed in the housing 23 (see Figure 10) which will then direct the pressurised fluid into the aforesaid cavities 14, 15 and 16 between the rotor and the stator of the pump-motor unit. This will cause the rotor to turn, thereby expressing fluid from cavities 17 and 18 as previously mentioned, such fluid returning via further drillings 46 (see Figure 10) formed in the housing 23.

From the drillings 46 the returning fluid enters drillings 47 formed in the sleeve member 22 and said drillings 47 feed an annulus 48 which itself feeds further grooves 49 formed on the exterior of the inner member 21. These grooves 49 (see Figure 11) direct fluid through drillings 50 in the sleeve member 22 and thence to an annulus 51 which is connected to the port 32 directing fluid to the right-hand end of the piston and cylinder means connected to the steerable wheels. At the same time, fluid expelled from the left-hand end of said piston and cylinder means will enter the housing 23 by a connection not shown in Figures 1 and 3 but which lies in the plane of section F-F of Figure 4 and which is indicated in Figure 12 by reference numeral 52. Such returned fluid then enters an annulus 53 formed in the bore of the housing from whence it flows through drillings 54 into the grooves 40 formed in the exterior of valve member 21 and thence (see Figure 13) through drillings 38 into annulus 39 and back to the reservoir 20. The steerable wheels will now turn and, since the rotor 13 will also be turning, the wobble shaft 31 connected thereto will also turn, thus taking with it the drive pin 31 which will then turn the sleeve member 22 so as to restore it to its initial angular position relative to the inner member 21. No more fluid will then pass to the pump-motor unit since the grooves 37 will again establish communication between the transfer grooves 36 and drillings 38 to enable fluid to flow freely again through the valve between connections 19 and 20.

It is to be understood that when the inner valve member 21 is turned by the driver to initiate a steering movement the torsion bar 25 will initially be torsionally strained as the inner member 21 turns angularly relative to the sleeve member 22. As fluid is directed into said cavities between the rotor and the stator however the rotor will start to turn and the torsion bar 25 will then be "unwound" as the sleeve member 22 turns in the same direction as the initial turning movement of the valve member 21 until, as previously explained, the two valve members 21 and 22 will be reset in their original relative angular positions. The steerable wheels of the vehicle can of course be turned back into the straight ahead position when the desired turn of the vehicle has been executed by reversing the turning movement of the inner member 21 and a flow in the reverse direction will then take place through the pump-motor unit. The latter will thus act as a metering unit whilst steering is taking place.

With the above described construction it will be appreciated that although the valve members 21 and 22 are relatively angularly movable they will be prevented from relative axial movement, the free flow of fluid through the valve when the mechanism is in a straight ahead or neutral position being cut off by the initial angular movement of one valve member namely the inner valve member relative to the other valve member. This in fact makes for a very compact construction and economy and precision in manufacture can be achieved by forming all the aforesaid grooves in the valve members by means of an electrochemical machining process or by spark erosion machining.

WHAT WE CLAIM IS:- 1. An hydraulically actuated vehicle steering mechanism of the kind including piston and cylinder means connectible in use to the steerable wheels of a vehicle wherein there is provided a power actuated hydraulic pump, an hydraulic pump-motor unit and a control valve, said control valve comprising a pair of concentric valve members which are interconnected by a torsion bar so as to be angularly movable relative to each other but secured against relative axial movement, one of said members being rotatable by the driver of the vehicle in which in use the mechanism is fitted and the other of said members being rotatable by the rotor of said pump-motor unit, said valve members being arranged so that when the mechanism is in a neutral or straight ahead condition, the relative angular positions of said members is such as to permit a free flow of fluid through the valve from said pump to a reservoir whereas relative angular movement between the two valve members consequent upon a steering action of the driver in either direction of rotation will initially cut off said free flow of fluid through the valve.

2. A vehicle steering mechanism as claimed in Claim 1 wherein one end of said torsion bar is connected to one of said valve members so as to be rotatable therewith and the other end of said torsion bar is connected both to the other valve member and to the rotor of said pump-motor unit

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. formed in the housing 23 (see Figure 10) which will then direct the pressurised fluid into the aforesaid cavities 14, 15 and 16 between the rotor and the stator of the pump-motor unit. This will cause the rotor to turn, thereby expressing fluid from cavities 17 and 18 as previously mentioned, such fluid returning via further drillings 46 (see Figure 10) formed in the housing 23. From the drillings 46 the returning fluid enters drillings 47 formed in the sleeve member 22 and said drillings 47 feed an annulus 48 which itself feeds further grooves 49 formed on the exterior of the inner member 21. These grooves 49 (see Figure 11) direct fluid through drillings 50 in the sleeve member 22 and thence to an annulus 51 which is connected to the port 32 directing fluid to the right-hand end of the piston and cylinder means connected to the steerable wheels. At the same time, fluid expelled from the left-hand end of said piston and cylinder means will enter the housing 23 by a connection not shown in Figures 1 and 3 but which lies in the plane of section F-F of Figure 4 and which is indicated in Figure 12 by reference numeral 52. Such returned fluid then enters an annulus 53 formed in the bore of the housing from whence it flows through drillings 54 into the grooves 40 formed in the exterior of valve member 21 and thence (see Figure 13) through drillings 38 into annulus 39 and back to the reservoir 20. The steerable wheels will now turn and, since the rotor 13 will also be turning, the wobble shaft 31 connected thereto will also turn, thus taking with it the drive pin 31 which will then turn the sleeve member 22 so as to restore it to its initial angular position relative to the inner member 21. No more fluid will then pass to the pump-motor unit since the grooves 37 will again establish communication between the transfer grooves 36 and drillings 38 to enable fluid to flow freely again through the valve between connections 19 and 20. It is to be understood that when the inner valve member 21 is turned by the driver to initiate a steering movement the torsion bar 25 will initially be torsionally strained as the inner member 21 turns angularly relative to the sleeve member 22. As fluid is directed into said cavities between the rotor and the stator however the rotor will start to turn and the torsion bar 25 will then be "unwound" as the sleeve member 22 turns in the same direction as the initial turning movement of the valve member 21 until, as previously explained, the two valve members 21 and 22 will be reset in their original relative angular positions. The steerable wheels of the vehicle can of course be turned back into the straight ahead position when the desired turn of the vehicle has been executed by reversing the turning movement of the inner member 21 and a flow in the reverse direction will then take place through the pump-motor unit. The latter will thus act as a metering unit whilst steering is taking place. With the above described construction it will be appreciated that although the valve members 21 and 22 are relatively angularly movable they will be prevented from relative axial movement, the free flow of fluid through the valve when the mechanism is in a straight ahead or neutral position being cut off by the initial angular movement of one valve member namely the inner valve member relative to the other valve member. This in fact makes for a very compact construction and economy and precision in manufacture can be achieved by forming all the aforesaid grooves in the valve members by means of an electrochemical machining process or by spark erosion machining. WHAT WE CLAIM IS:-

1. An hydraulically actuated vehicle steering mechanism of the kind including piston and cylinder means connectible in use to the steerable wheels of a vehicle wherein there is provided a power actuated hydraulic pump, an hydraulic pump-motor unit and a control valve, said control valve comprising a pair of concentric valve members which are interconnected by a torsion bar so as to be angularly movable relative to each other but secured against relative axial movement, one of said members being rotatable by the driver of the vehicle in which in use the mechanism is fitted and the other of said members being rotatable by the rotor of said pump-motor unit, said valve members being arranged so that when the mechanism is in a neutral or straight ahead condition, the relative angular positions of said members is such as to permit a free flow of fluid through the valve from said pump to a reservoir whereas relative angular movement between the two valve members consequent upon a steering action of the driver in either direction of rotation will initially cut off said free flow of fluid through the valve.

2. A vehicle steering mechanism as claimed in Claim 1 wherein one end of said torsion bar is connected to one of said valve members so as to be rotatable therewith and the other end of said torsion bar is connected both to the other valve member and to the rotor of said pump-motor unit

so as to be rotatable both with said other valve member and with said rotor.

3. An hydraulically actuated vehicle steering mechanism substantially as hereinbefore described with reference to and as shown in the accompanying drawings.