THIS INVENTION relates to vehicle steering. In particular, it relates to a road vehicle, to a steering member for a road vehicle, and to a suspension strut for a road vehicle.

The invention provides a road vehicle which includes : a chassis suspended on a set of road wheels, including a pair of steerable front wheels ; a user-operable steering control mounted on the chassis; two elongated steering members, one associated with each front wheel, each steering member being mounted on the chassis for pivotal displacement about an upright pivot axis, and each steering member being connected to the associated wheel for transmitting a steering torque along the length thereof to the associated front wheel ; and a steering linkage connecting the steering members respectively to the steering control for effecting synchronous pivotal displacement of the frontwheels about associated upright steering axes, there being a vertical spacing in the lengthwise direction of each steering member between the connection of that steering member to the associated front wheel and the connection of that steering member to the steering linkage, said spacing being variable in response to operative displacement of the associated front wheel towards and away from the chassis, such that the position of the connection of the steering linkage to each steering member remains fixed relative to the chassis, irrespective of operative displacement of the front wheels towards and away from the chassis.

The mounting of the steering member on the chassis may be spaced above the connection of the steering shaft to the associated wheel, each steering member typically being an upright steering shaft which is mounted at or adjacent an upper end thereof on the chassis and is connected at or adjacent a lower end thereof to the associated front wheel.

Differently defined, the inventor provides in a road vehicle of the type having a chassis suspended on a set of wheels including a pair of front wheels which are interconnected by a user-operable steering mechanism for steering the vehicle by synchronous pivotal displacement of the front wheels respectively about associated upright steering axes, the improvement whereby: the steering mechanism includes a pair of steering shafts, one associated with each front wheel, each steering shaft being capable of transmitting torque and angular displacement along the length thereof about the associated steering axis, each steering shaft being pivotally mounted on the chassis to be pivotable relative to the chassis about the associated steering axis and each front wheel being connected to the associated steering shaft so that said wheel is pivotally displaceable about the associated steering axis in response to pivoting of the steering shaft about said associated steering axis, and each shaft being operatively connected to a user-operable steering control of the vehicle by a steering linkage, such that each steering shaft is pivotally displaceable about its associated steering axis, synchronously with the other shaft, to transmit a steering torque to the associated wheel in response to operation of the steering control by a user, there being a vertical spacing in the axial direction of each steering axis between the connection of each wheel to the associated steering shaft, and the pivotal mounting of that shaft on the chassis, said spacing being variable in response to operative downward displacement of the associated wheel away from the chassis and operative upward displacement of said wheel towards the chassis, the position of the connection of the steering shaft to the steering linkage being fixed relative to the position of the mounting of the steering shaft on the chassis.

Preferably, each steering shaft is variable in length, being connected at a low level to the associated wheel, and being mounted at a high level on the chassis, such that an upper portion of the steering shaft is anchored against longitudinal movement along the length of the shaft relative to the chassis. Each steering shaft will in such case typically be a telescopic shaft, comprising a pair of longitudinally aligned elongated members forming upper and lower portions of the shaft which are telescopically connected such that one of the members is longitudinally slidable relative to the other member, e. g. piston-and-cylinder fashion.

To permit transmission of torque by each steering shaft along its length, the shaft members will be rotationally keyed to each other, e. g. by means of longitudinally extending splines on one of the telescopic members, which splines are slidably received in complementary grooves in the other telescopic member, or vice versa.

Each member of the telescopic steering shaft may have a longitudinally extending oil flow passage therethrough, the passages being connected in-line with each other to form an oil flow path along the length of the interior of the steering shaft.

Advantageously, the steering shaft includes a pumping arrangement for automatically pumping oil from an inlet at a lower end of the steering shaft to an outlet at an upper end of the steering shaft, along the passages, in response to operative reciprocating telescoping of the steering shaft.

In a particular embodiment of the invention, the steering shaft is co-axially located in a hollow interior of an elongated telescopic housing which comprises a pair of longitudinally aligned hollow tubes which are connected together piston-and-cylinder fashion, an upper one of the tubes being anchored against longitudinal displacement relative to the chassis and being anchored against longitudinal displacement relative to the upper shaft member, the other, lower tube of the housing being anchored against longitudinal displacement relative to the lower member of the steering shaft, and the steering shaft being pivotable about its lengthwise direction relative to the housing, to transmit torque and angular displacement to the associated wheel for steering of the vehicle.

The telescopic housing is typically sealed, so that a lower end of an annular space between the exterior of the steering shaft and the interior surface of the housing forms an oil sump, the oil flow path including an oil inlet in the lower shaft member for providing an oil flow connection between the oil sump and the passage in the lower shaft member, a one-way inlet valve being provided in the inlet for permitting oil flow into the oil flow path, the oil flow path further including an outlet at or adjacent an upper end of the passage in the upper shaft member, an intermediate one-way valve being connected in- line in the oil flow path between the inlet and the outlet for permitting oil flow from the inlet to the outlet, the intermediate one-way valve being connected to the upper shaft member

for movement therewith towards and away from the inlet upon reciprocating telescoping of the members between retracted and extended conditions of the shaft.

It will be appreciated that a chamber is thus formed in the steering shaft between the one-way inlet valve and the intermediate valve, such that when the intermediate one-way valve is displaced towards the inlet valve upon retraction or shortening of the steering shaft, oil and/or air in the chamber will be forced through the intermediate valve towards the outlet, while the inlet valve is automatically closed to prevent flow of air and/or oil from the chamber into the sump, and when the intermediate valve is displaced away from the inlet valve in response to extension or lengthening of the steering shaft, the intermediate valve closes to prevent flow of oil or air from the upper shaft member into the chamber, while oil is automatically drawn from the sump through the inlet valve. Oil from the sump is thus displaceable through the chamber along the oil flow passage in response to operative reciprocating lengthening and shortening of the steering shaft, the outlet of the oil flow path being arranged to eject oil on to the walls of the upper housing tube for lubrication of the tubes of the housing where they telescope relative to each other. The arrangement of valves and passages in each steering shaft thus forms an automatic pumping arrangement.

Each steering shaft is c-axially arranged with a coiled suspension spring under compression, the suspension spring acting in the longitudinal direction of the steering shaft to urge the telescopic members of the steering shaft away from each other, towards an extended condition, so that, in use, a portion of the load of the chassis and a body of the vehicle is transferred from the chassis to the wheel by the spring, the unit formed by the steering shaft and the suspension spring thus serving as a suspension strut.

The housing may additionally be provided with a longitudinally arranged damper, often referred to as a shock-absorber, for damping relative movement between the shaft members of the steering shaft, and thus between the telescopic tubes of the housing, away from and towards each other. The damper may be a conventional shock-absorber located longitudinally in the oil flow passage. Instead, the steering shaft may be arranged to act as a damper.

It should be appreciated that the suspension unit formed by the telescopic housing, the steering shaft housed in the housing, the suspension spring, and the damper can form a unitary suspension strut.

Each steering shaft may be connected to the chassis in a manner similar to a conventional MacPherson strut, being flexibly connected to the chassis at its upper end such that the upper end of the steering shaft is anchored against longitudinal displacement along the length of the steering shaft relative to the chassis, and being pivotally connected at its lower end to a link which is, in turn, pivotally connected to the chassis to pivot about a horizontally extending pivot axis, so that, when the associated wheel is displaced towards and away from the chassis, the pivotal connection between the steering shaft and the link causes the wheel to describe an arc about the link pivot axis.

Instead, the steering shaft may be connected at its upper end to the chassis such that the upper shaft member is pivotally displaceable about its longitudinal axis relative to the chassis, said longitudinal axis being fixed relative to the chassis and the upper shaft member being anchored against longitudinal displacement relative to the chassis, the upper shaft member including an articulated universal joint between its connection to the chassis and its telescopic connection to the lower shaft member, the lower shaft member being pivotally connected at or adjacent its lower end to a link which is, in turn, pivotally connected to the chassis to pivot about a horizontal pivot axis, so that operative displacement of the wheel towards or away from the chassis causes the wheel to describe an arc about the link pivot axis. By universal joint is meant a coupling between two intersecting shafts such that the transmission of substantially only torque and axial forces between the shafts are permitted.

The link may be a transverse link, the link pivot axis extending in the fore- and-aft direction of the vehicle at more or less the same low level as the connection of the link to the steering shaft. Instead, the link pivot axis may extend transversely to the fore- and-aft direction, either leading or trailing the wheel.

In a further embodiment of the invention, the upper steering shaft member is rigidly connected to the housing, permitting only pivotal displacement of the upper shaft member relative to its longitudinal axis, the shaft being rigid, such that, upon operative

displacement of the associated wheel towards or away from the chassis, the connection between the wheel and the steering shaft moves along a straight line relative to the chassis, typically parallel to the steering axis of the associated wheel. Typically, the steering shaft is oriented such that the lengthwise direction of the steering shaft is more or less vertical.

The invention extends to a steering member for forming part of a vehicle as defined above.

The invention also extends to a suspension strut for forming part of a vehicle as defined above.

According to another aspect of the invention, there is provided a road vehicle having a chassis suspended on a set of road wheels, the vehicle including, for at least some of the wheels : an elongated suspension strut associated with each of said wheels and comprising an elongated guide member which is variable in length in a longitudinal direction thereof, a suspension spring arranged in parallel with the guide member to resist changes in length of the guide member and to transfer a suspension load from the chassis to the associated wheel, the guide member being connected at or adjacent a lower end thereof to the associated wheel, and the guide member being connected at or adjacent its upper end to the chassis, such that upon operative displacement of the wheel towards and away from the chassis, the locus of the connection between the wheel and the strut is a line having a fixed orientation relative to the chassis.

The invention will now be described by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a schematic three-dimensional view of a vehicle according to the invention, showing, schematically, a steering and independent suspension system for two front wheels of the vehicle ; Figure 2 is a schematic longitudinal sectional view, on an enlarged scale, of a suspension strut forming part of the vehicle of Figure 1;

Figure 3 is a schematic front elevation of a further embodiment of a steering and independent suspension system of a vehicle in accordance with the invention; Figure 4 is a view corresponding to Figure 2 of a lower part of a suspension strut forming part of a further embodiment of a suspension system according to the invention; Figure 5 is a view corresponding to Figure 4 of an upper part of the suspension strut of Figure 4; and Figure 6 is a view corresponding to Figure 3 of yet a further embodiment of a steering and suspension system of a vehicle in accordance with the invention.

In Figure 1 of the drawings, reference numeral 10 generally indicates a vehicle in accordance with the invention. In conventional fashion, the vehicle 10 has a chassis 12 (only part of which is shown in Figure 2) which is suspended on a set of road wheels 14 including a pair of front wheels 16. The vehicle 10 is steerable by synchronous pivotal displacement of the front wheels 16 respectively about associated upright steering axes 18, steering of the front wheels 16 being achieved by a steering mechanism 20 connecting the front wheels 16.

The steering mechanism 20 includes a pair of steering members in the form of steering shafts 22, one associated with each front wheel 16, for transmitting a steering torque along the length of the shaft 22 to the associated front wheel 16, pivotally to displace the front wheel 16 about its steering axis 18. To this end, each front wheel 16 is mounted on a stub axle 24 (Figure 2) which is integral with the associated steering shaft 22, the stub axle 24 projecting transversely from the steering shaft 22 at a low level. Each wheel 16 is rotatably mounted on the associated stub axle 24 to rotate about an axis of rotation 25 which is at an included angle of slightly more than 90° to the steering axis 18.

Each steering shaft 22 is pivotally mounted on the chassis 12 such that it is longitudinally aligned with the associated steering axis 18, being pivotally displaceable relative to the chassis 12 about the associated steering axis 18.

Each steering shaft 22 is located in a hollow interior of an elongated telescopic housing 26, being longitudinally aligned with the housing 26. Each housing 26 comprises a pair of longitudinally aligned hollow tubes 28,30 which are slidably connected together piston-and-cylinder-fashion.

The housing 26 is vertically oriented, the tube 30 being the upper tube and being fixedly mounted on the chassis 12 such that the upper tube 30 is anchored against longitudinal displacement relative to the chassis 12, as well as being anchored against pivotal displacement relative to the chassis 12 about the steering axis 18. The tubes 28, 30 are slidably connected together in longitudinal alignment, an upper end of the lower tube 28 being received in the upper tube 30, the upper and lower tubes 30,28 being rotationally keyed together by means of axially extending radially inwardly projecting ribs 32 on an interior surface of the upper tube 30, which ribs 32 are received in complementary axially extending grooves in the radially outer surface of the lower tube 28.

The housing 26 is thus variable in length by telescoping of the upper and lower tubes 30, 28.

Each steering shaft 22 is a telescopic shaft, comprising a pairof longitudinally aligned elongated shaft members 36,38. The shaft members 36,38 are telescopically slidably connected together and longitudinally aligned, being rotationally keyed to each other by longitudinally extending splines 40 on the shaft member 36, which is the lower shaft member, the splines 40 being slidably received in complementary grooves in the upper shaft member 38, so that each steering shaft 22 is variable in length, and is capable of transmitting torque and angular displacement along its length.

As mentioned above, each steering shaft 22 is located within the associated housing 26, the upper shaft member 38 being anchored against longitudinal displacement relative to the upper tube 30, and the lower shaft member 36 being anchored against longitudinal displacement relative to the lower tube 28 of the housing 26. However, each shaft member 36,38 is journalled in an associated thrust bearing 42, such that the upper shaft member 38 is rotatable relative to the upper tube 30, and the lower shaft member 36 is rotatable relative to the lower tube 28. In this example, each shaft member 36,38 is connected to its associated tube 28,30, on the one hand, by the associated thrust bearing 42 which spaces an associated shoulder 68 on the shaft member 36,38 from an end wall 70 of the associated tube 28,30, to transmit longitudinal forces between the respective shaft members 36,38 and the associated tubes 28,30 in one direction, and, on the other hand, a pairof circlips 72, respectively located in circumferentially extending grooves in the steering shaft 22 immediately outside of the housing 26, to transmit longitudinal forces between the respective shaft members 36,38 and the associated tubes 28,30 in the

opposite direction. The telescopic steering shaft 22 and the telescopic housing 26 are thus connected together for equal and synchronous variations in length, but the steering shaft 22 is rotatable within the housing 26.

The upper shaft member 38 is connected at a high level, above the housing 26, to a steering arm 44 which forms part of a steering linkage 46 of the steering mechanism 20 and connecting the steering shaft 22 to a user-operable steering control in the form of a steering wheel 48. As can best be seen in Figure 1 of the drawings, the steering linkage 46 connects the steering shafts 22 to the steering wheel 48 such that turning of the steering wheel 48 causes synchronous pivotal displacement of the steering shafts 22, and thus of the wheels 16, about the associated steering axes 18. The steering linkage 46 includes a steering bar47 which is shorterthan the transverse spacing between the front wheels 16, the steering bar 47 being pivotally connected at each end thereof to the associated steering arm 44. This steering linkage 46 causes the front wheels 16 in conventional fashion to be synchronously pivotally displaced at different rates, to allow the wheels to follow circles of different radii during cornering.

The housing 26 is sealed to be fluid-tight against fluid flow, inter alia by a sealing ring 50 which extends around the lower tube 28 and is located in a circumferentially extending recess 52 formed by a lower edge of the upper tube 30, while an opening 54 in the end wall 70 of the lower tube 28 through which the steering shaft 22 passes is sealed in conventional fashion. A lower end of an annular space 56 between the exterior of the steering shaft 22 and the interior surface of the housing 26 can thus form a sealed oil sump. The housing 26 is, in use, indeed provided with a charge of oil 76.

The shaft members 36,38 respectively have longitudinally extending passages 58,60 therethrough, the passages 58,60 being connected in-line with each other to form an oil flow path along the length of the interior of the steering shaft 22.

The lower shaft member 36 provides an inlet 74 to the oil flow path, the inlet 74 being located at a low level, to connect the passage 58 to the sump. A one-way or non- return inlet valve 62 is provided adjacent the inlet 74 for permitting oil flow only from the sump into the passage 58. A number of outlets 64 are provided adjacent an upper end of the upper shaft member 38, the outlets 64 being in oil flow communication with the

passage 60 in the upper shaft member 38. In this example there are three outlets 64, which are equally circumferentially spaced, through the shaft 22. An intermediate non- return or one-way valve 66 is connected in-line in the oil flow path between the inlet 74 and the outlets 64, for permitting oil flow, along the flow path only from the inlet 74 to the outlet 64. The intermediate valve 66 is connected to the upper shaft member 38 for movement therewith towards and away from the inlet 74.

The portion of the passage 58 in the lower shaft member 36 between the inlet valve 62 and the intermediate valve 66 forms a chamber which is variable in size in response to displacement of the intermediate valve 66 towards or away from the inlet valve 62.

An annular splash plate 80 is connected to the upper shaft member at a position below and adjacent the outlets 64. The splash plate 80 closes the annular space between the exterior of the shaft 22 and the interior of the housing 26, with a small annular working gap between the periphery of the splash plate 80 and the upper tube 30.

Although not shown in Figures 1 and 2 of the drawings, for ease of illustration, each housing 26 is provided with a coiled suspension spring 78 (see Figure 3) under compression, the spring 78 being longitudinally aligned with the housing 26 and acting to prevent the tubes 28,30 of the housing 26 from telescoping into a retracted condition. In this example, the spring is located around the housing, to act between the tubes 28,30. However, it is envisaged that the spring could be located in the annular space 56 between the shaft 22 and the housing 26. Instead, the tubes 28,30 or the shaft members 36,38 can be prevented from telescopically retracting by an otherwise conventional pneumatic suspension system. In other embodiments of the invention, for force-transmission considerations, it is possible to arrange the spring 78 such that it acts between the upper tube 30 and the stub axle 24, thus avoiding possible failure of the lower circlip 72.

A damper (not shown) in the form of a conventional shock-absorber is also provided in parallel with the spring, to damp oscillation thereof. Although not illustrated, the steering shaft 22 can instead be adapted to serve as the damper. This can be done,

for instance, by providing a narrow orifice in the oil flow passage through which oil 76 is to be forced.

In use, when the vehicle 10 moves over uneven terrain, or during cornering, the wheels 16 are displaced away from and towards the chassis 12 of the vehicle 10.

Since the upper tube 30 is rigidly connected to the chassis 12, the lower tube 28 and the lower shaft member 36, which are both anchored relative to the associated wheel 16, slide telescopically relative to the upper tube 30 and the upper shaft member 38. The wheel 16 is thus guided along a rectilinear path whose locus is parallel to the steering axis 18, provided that there is no rotation of the shaft 22 relative to the housing 26. I n other words, the wheels 16 are displaced linearly, as opposed to conventional arcuate displacement thereof, when there is no turning of the wheels 16. The load of the wheel 16 is transferred through the stub axle 24 to the lower tube 28, and via the compression spring 78 to the upper tube 30.

This relative displacement of the tubes 28,30 causes reciprocating displacement of the intermediate valve 66 towards and away from the inlet valve 62, so that, when the intermediate valve 66 is displaced towards the inlet valve 62 upon shortening of the steering shaft 22, oil 76 and/or air in the chamber defined between the valves 62,66 will be forced through the intermediate valve 66 towards the outlets 64, the inlet valve 62 automatically closing to prevent flow of air and/or oil 76 from said chamber into the sump. Oppositely, when the intermediate valve 66 is displaced away from the inlet valve 62 upon lengthening of the steering shaft 22, the intermediate valve 66 automatically closes to prevent flow of oil 76 or air from the upper shaft member 38 into said chamber, and oil is automatically drawn into the chamber from the sump through the inlet 74 and the inlet valve 62. Oil 76 from the sump is thus displaced through the chamber and along the passages 58,60 in response to reciprocating lengthening and shortening of the steering shaft 22, so that oil is ejected from the outlets 64 on to the splash plate 80. The splash plate 80 guides oil 76 to the interior surface of the upper tube 30, to lubricate the connection between the upper tube 30 and the lower tube 28.

Steering of the vehicle 10 is achieved by turning of the steering wheel 48 by a driver of the vehicle 10, which causes, through the steering linkage 46, each steering arm 44 to exert a steering torque on an upper end of the associated upper shaft member 38.

This steering torque is transmitted along the length of the steering arm 22 to the wheel 16, so that, when the steering torque is sufficiently great, the steering shaft 22 and the wheel 16 pivot about the steering axis 18. Since the steering linkage 46 and the upper tube 30 are fixed in elevation relative to the chassis 12, the vertical spacing of the wheel 16 from the chassis 12 does not affect steering of the wheel 16.

As mentioned above, during movement of the wheel 16 towards and away from the chassis 12, and in the absence of any pivoting of the shaft 22 in the housing 26, the wheel 16 is guided along a path which describes a line parallel to the steering axis 18, due to telescoping of the housing 16 and steering shaft 22.

It will be appreciated that the connection of the lower tube 28 and the upper tube 30 respectively to the steering shaft 22, as described with reference to Figures 1 and 2, may not be sufficiently strong to withstand the stresses caused, in use, by the transfer of load forces between the chassis 12 and the associated road wheel 16. Figures 4 and 5 show a development of the invention which addresses this potential difficulty. In Figures 1-3 and 4-5 of the drawings, like reference numerals indicate like parts, unless otherwise indicated.

With reference to Figure 4, as is the case in the embodiment shown in Figures 1 to 3, the lower thrust bearing 42 engages the shoulder 68 on the lower shaft member 36. However, the lower end wall 70 is omitted, so that the lower tube 28 is open ended. Two lock nuts 82 are screwingly engaged with the lower tube 28, by means of an external screw-thread on each nut 82, which external screw-thread is engaged with an internal screw-thread in the lower tube 28. An annular seal 84 in an upwardly opening cup- shaped metal housing 86 is sandwiched between the upper one of the nuts 82 and the bearing 42, the curved outer periphery of the wall of the cup of the housing 86 being threaded (not shown) and sealingly screwed into the screw-thread of the lower tube 28.

In contrast to the suspension system of Figures 1 to 3, the stub axle 24 is not an integral part of the steering shaft 22, but is fast with a sleeve 88 in which a lower end of the lower member 36 of steering shaft 22 is received. The sleeve 88 has a circular cylindrical passage 100 in which the end of the lower shaft member 36 of shaft 22 is located, the lower extremity of the shaft 22 forming a threaded stud 102 which is screwingly

engaged with the sleeve 88 by means of a complementary internal screw-thread in a lower part of the passage 100. The sleeve 88 is locked in position on the shaft 22 by a lock nut 104 screwed on to part of the stud 102 which protrudes downwardly from the sleeve 88, such that the lock nut 104 abuts upwardly against the sleeve 88.

Furthermore, the sleeve 88 has a pair of diametrically opposed transverse threaded bores 106 which project radially from the steering axis 18, each bore 106 housing an Allen screw 108 which has been screwed radially inwardly into abutment with the steering shaft 22. The radially inner end of each Allen screw 108 is received in a complementary shallow depression 110 in the steering shaft 22, so that the sleeve 88 is rotationally keyed to the shaft 22.

Figure 5 shows the connection between the steering shaft 22 and the upper tube 30. To anchor the shaft 22 against longitudinal movement relative to the upper tube 30, the steering shaft 22 is journalled in an annular collar 112 which is in abutment with the upper end wall 70 of the tube 30. Similarly to the sleeve 88, the collar 112 has a pair of diametrically opposed threaded bores 114 which project radially from a central passage in the collar 112 through which the shaft 22 passes, an Allen screw 116 being received in each bore 114 to key the collar 112 axially to the shaft 22 by engaging an associated outwardly facing circumferential groove or channel in the shaft 22.

It is an advantage of the vehicle described with reference to Figures 1 and 2 of the drawings that the components of the steering linkage 46, such as the steering arms 44 and the steering bar47, are isolated from operative movement of the front wheels 16 towards and away from the chassis 12, the geometry, position and relative orientation of the component parts of the steering linkage 46 being independent of the spacing of the front wheels 16 from the chassis 12. Unlike conventional steering systems, the pivotal position of each front wheel 16 about the steering axis 18 thus remains unaffected by up- and-down movement of the wheels 16. This independent steering system promotes accurate and reliable steering with increased precision of steering, which is particularly advantageous during cornering.

Furthermore, as the locus of the connection between the wheel 16 and the steering shaft 22 is, in the absence of steering, a straight line, as opposed to an arc in conventional suspension systems, the camber of the front wheels 16 remains constant during operation.

If the steering shaft 22, and thus the lengthwise direction of the steering shaft 22 and the housing 26, are vertical, the track of the vehicle 10, i. e. the transverse distance between the front wheels 16, does not change when both wheels 16 are simultaneously displaced towards or away from the chassis 12.

This constant track and camber of the front wheels 16, as well as the independent steering, reduce wear on front tyres of the vehicle 10, during use.

It will be appreciated that the steering system described above facilitates the provision of four-wheel steering in a four-wheel road vehicle. For instance, a suspension strut comprising a housing 26, steering shaft 22, spring 78 and damper, as described with reference to Figures 1 and 2, can additionally be provided for each rear wheel 14. The steering shaft 22 associated with each rear wheel 14 can then be connected to the steering wheel 48 by an extended steering linkage. The geometry of this steering linkage will be independent from the wheels 14, being fixed relative to the chassis 12, obviating many of the difficulties encountered during otherattempts at producing a practically applicable four- wheel steering system.

Figure 3 shows another embodiment of a vehicle suspension and steering system in accordance with the invention, with like reference numerals indicating like parts in Figures 1,2 and 3. Figure 3 shows only the independent steering arrangement for one of the front wheels 16, which includes a suspension strut 90 in an arrangement similar to that of a MacPherson strut. The strut 90 comprises an elongate housing 26 similar to that described in detail with reference to Figures 1 and 2, having a telescopic steering shaft 22 located in a hollow interior thereof. The upper shaft member 38 is flexibly connected to the chassis 12 by a conventional flexible mounting bracket 92, and the upper shaft member 38 is connected to a steering arm 44 for pivoting the steering shaft 22 about the steering axis 18. In this drawing, the spring, indicated by reference numeral 78, is shown.

The lower end of the of the lower steering shaft member 36 is pivotally connected to a transverse link, or wishbone 94, the wishbone 94 in turn being pivotable about a horizontal pivot axis 96 extending in the fore-and-aft direction of the vehicle 10.

In this embodiment, the connection between the strut 90 and the wheel 16 moves in an arc about the wishbone pivot axis 96 in use, as is the case with conventional MacPherson struts. The advantages of constant track and camber are thus not displayed by this embodiment. However, the advantages related to isolation of the steering mechanism 40 from the vertical spacing of the wheels 16 are still present, while retro-fitting of the suspension strut 90 is facilitated by the MacPherson-strut-like construction shown in Figure 3.

In Figure 6 of the drawings, reference numeral 130 generally indicates a further embodiment of a suspension and steering strut in accordance with the invention, like reference numerals indicating like parts in Figures 1 to 5 and in Figure 6. Similar to Figure 3, Figure 6 shows only the independent steering arrangement of one of the front wheels 16, and includes the suspension strut 130 in an arrangement largely similar to that of the strut 90 of Figure 3. The main distinction between the strut 130 of Figure 6 and the strut 90 of Figure 3 is that the upper shaft member 38 has an articulated universal joint 132 at a position along its length. The upper shaft member 38 thus comprises two sub-shafts 134,136 which are connected together by the universal joint 132 in the form of a Hook's coupling which consists of two forks connected to an intermediate cross. The joint 132 thus transmits torque and axial forces from one sub-shaft to the other but permits substantially unrestricted pivoting about either, or both, of a pair of orthogonal pivot axes which are transverse to the shaft member 38, intersecting at the joint 132.

The upper sub-shaft 134 is connected to the chassis 12 such that it is freely pivotable about its longitudinal axis 18 but is longitudinally anchored to the chassis 12. The longitudinal axis of the upper sub-shaft 134 extends vertically, being aligned with the steering axis 18 of the associated front wheel 16.

It is an advantage of the strut 130 of Figure 6 that, unlike the strut 90 of Figure 3, orientation of the steering axis 18 is completely unaffected by operative displacement of the wheel 16 relative to the chassis 12, since although the connection of

the wheel 16 to the stub axle 24 describes an arc about the link pivot axis 96, articulation of the universal joint 132 completely isolates the upper sub-shaft 134 from a lateral component of the wheel's movement, the sub-shafts 134,136 pivoting relative to each other but the upper sub-shaft 134 remaining vertical. Steering torque is, however, still transmissible by means of the steering shaft 22, through the universal joint 132.

It should be appreciated that a similar arrangement can be formed with a leading-or trailing link, in which a link similar to the wishbone-link 94 is arranged to pivot about a pivot axis 96 which extends transversely to the fore-and-aft direction of the vehicle 10, either leading or trailing the wheel 16 in the fore-and-aft direction.

It should further be appreciated that although each example explained above shows a combined steering shaft and suspension strut, a steering shaft can be provided in combination with a conventional suspension system. In such case, the steering shaft will not bear part of the load of the chassis and body of the vehicle and will thus not include a suspension spring and/or damper. The steering shaft will still, however, isolate the steering linkage from operative movement of the front wheels 16 relative to the body.