WO2019180443A1

WO2019180443A1 - Vehicle drive unit and suspension arrangement

Info

Publication number: WO2019180443A1
Application number: PCT/GB2019/050805
Authority: WO
Inventors: Anthony Richard Glover
Original assignee: Mclaren Applied Technologies Limited
Priority date: 2018-03-21
Filing date: 2019-03-21
Publication date: 2019-09-26
Also published as: GB201804533D0; EP3768539A1; GB201903922D0; GB2573869A

Abstract

A vehicle having: a body; a suspension member mounted to the body so as to be movable relative to the body; a drive wheel mounted so as to be capable of rotating relative to the suspension member; and a primary drive unit mounted to the suspension member, the drive unit being configured to apply a drive torque to the rear wheel which is reacted against a reaction force applied to the suspension member, the drive unit being movably mounted to the suspension member in such a way that the reaction force can cause motion of the suspension member relative to the body.

Description

VEHICLE DRIVE UNIT AND SUSPENSION ARRANGEMENT

This invention relates to a vehicle drive arrangement.

The conventional design of motorcycle involves a frame, a rear wheel which is driven and a front wheel. The frame carries a drive source such as an internal combustion (1C) engine. The rear wheel is mounted to the frame on a swing arm. The swing arm extends generally longitudinally (i.e. with an extent in the motorcycle’s X direction) and can pivot relative to the frame about the lateral direction of the vehicle (i.e. parallel to the motorcycle’s Y direction) to provide suspension motion of the rear wheel. The pivot point between the swing arm and the frame is forward of the rear wheel. The drive source is coupled to the rear wheel by a belt, chain or drive shaft.

When such a motorcycle is accelerating, weight is transferred to the rear of the motorcycle. This tends to compress the rear suspension. This tendency is known as squat. Squat affects the geometry of the motorcycle and can alter its handling characteristics. Therefore, it is desirable to limit the extent to which the drive torque alters the motorcycle’s geometry. This is an important aspect of motorcycle design.

One way to resist squat is to stiffen the rear suspension, but this adversely affects handling on rough surfaces. Another approach is to harness other forces on the motorcycle so they counteract squat. First, if the swing arm is positioned so the rear wheel axis is below the pivot point of the swing arm, the force due to the drive torque reacting against the road surface can inherently resist squat. Second, in the case of a chain-driven rear wheel, if the top chain run is above the pivot point of the swing arm then tension in the top chain run as the rear wheel is driven will also provide a pro- squat characteristic. In a basic design of shaft-driven motorcycle, the drive shaft is carried by the swing arm and terminates in a final bevel gear by which it drives the rear wheel. This can cause excessive anti-squat behaviour. One way to counter that is a parallelogram suspension mechanism, which involves the final bevel gear being carried by an additional body mounted to the rear end of the swing arm. (See EP 1 379 428). The additional body can rotate relative to the swing arm and is restrained by a tie rod to the motorcycle’s frame. To accommodate the motion of the additional body, the drive shaft is made flexible, for example by the inclusion of two universal joints.

If the motorcycle’s primary drive source is an electric motor then it can be mounted to the frame and can drive the rear wheel through a chain/belt or a shaft, in an analogous way to an IC engine. Alternatively, an electric motor can be carried by the swing arm and can drive the hub of the rear wheel either directly or through a gear train. The motor torque can be reacted to the swing arm, or the motor can be attached by a tie rod to the motorcycle’s frame in a similar way to the additional body of a shaft drive mechanism. A problem with an electric motor being carried by the swing arm rather than the frame of the motorcycle is generally that if it is carried by the swing arm then it contributes to the unsprung mass of the vehicle.

Hub motors are known in automobiles as a primary source of drive. It is also known for the rear wheels of an automobile to be mounted on trailing arms.

It is known to provide springs and dampers between the body or frame of a vehicle and its suspension parts so as to tune the vehicle’s ride behaviour. It is also known to include an inerter device (see WO 03/005142), which applies a resistive force dependent on the acceleration between its terminals.

There is a need for an improved mechanism for driving a vehicle such as motorcycles.

According to one aspect there is provided a vehicle having: a body; a suspension member mounted to the body so as to be movable relative to the body; a drive wheel mounted so as to be capable of rotating relative to the suspension member; and a primary drive unit mounted to the suspension member, the drive unit being configured to apply a drive torque to the rear wheel which is reacted against a reaction force applied to the suspension member, the drive unit being movably mounted to the suspension member in such a way that the reaction force can cause motion of the suspension member relative to the body.

According to a second aspect there is provided a vehicle having: a body; a suspension member mounted to the body so as to be movable relative to the body; a drive wheel rotatably mounted to the suspension member; and a primary drive unit mounted to the suspension member, the drive unit being configured to apply a drive torque to the rear wheel which is reacted against a reaction force applied to the suspension member, the drive unit being movably mounted to the suspension member in such a way that the position of the drive unit relative to the suspension member varies with the position of the suspension member relative to the body.

According to a third aspect there is provided a vehicle having: a body; a suspension member mounted to the body so as to be movable relative to the body; a spring mechanism whereby the body of the vehicle is sprung for vertical motion relative to the suspension member; a drive wheel rotatably mounted to the suspension member; and a primary drive unit mounted to the suspension member, the drive unit being configured to apply a drive torque to the rear wheel which is reacted against a reaction force applied to the suspension member, the drive unit being movably mounted to the suspension member in such a way that the mass of the drive unit does not fully contribute to unsprung mass of the vehicle.

The drive unit may be movably mounted to the suspension member in such a way that the position of the drive unit relative to the suspension member varies with the position of the suspension member relative to the body. The drive unit may be coupled to the body by a mechanical linkage. The drive unit may be coupled to the suspension member by a mechanical linkage. The or each such mechanical linkage may be configured to cause specified motion of the drive unit.

The drive wheel may be movable relative to the body by virtue of motion of the suspension member relative to the body. The drive unit may be mounted to the suspension member such that, on motion of the suspension member relative to the body, the amplitude of motion of the centre of mass of the drive unit relative to the body over at least part of the range of motion of the drive unit is less than the amplitude of motion of the centre of mass of the drive wheel relative to the body.

The body of the vehicle may be sprung for vertical motion relative to the suspension member. To this end, an elastic element may be configured to act between the body and the suspension member. The suspension member may be movable coupled to the vehicle body, e.g. via a revolute joint. The drive unit may be movably mounted to the suspension member in such a way that over at least part of the range of motion of the drive unit the mass of the drive unit does not fully contribute to unsprung mass of the vehicle. The drive unit may move in the same sense relative to the body as the suspension member and or the wheel.

The drive wheel may be movable relative to the body by virtue of motion of the suspension member relative to the body. The drive unit may be mounted to the suspension member such that, on motion of the suspension member relative to the body, motion of the centre of mass of the drive unit relative to the body is, over at least part of the range of motion of the drive unit, in a direction at least partially opposing (or exactly opposite to) the direction of motion of the centre of mass of the drive wheel relative to the body.

The suspension member may be rotatably mounted to the body.

The suspension member may be translationally mounted to the body.

The suspension member may be a suspension arm. The suspension member may be a wheel carrier.

The drive unit may be rotatably mounted to the suspension member.

The drive unit may be capable of converting energy from a non-mechanical form into motion so as to apply the drive torque to the wheel. The drive unit may be configured so that rotation of a drive shaft of the drive unit may contribute to inertance of the vehicle’s suspension system as provided by the suspension member.

The suspension member may be mounted to the body for rotation about a suspension axis parallel to the rotation axis of the drive wheel.

The suspension axis may be forward of the rotation axis of the drive wheel.

The centre of gravity of the drive unit may be located between a first plane extending in the Y/Z directions of the vehicle through the suspension axis and a second plane extending in the Y/Z directions of the vehicle through the rotation axis of the drive wheel.

The drive wheel may be a rear wheel of the vehicle.

The centre of gravity of the drive unit may be offset from the rotation axis of the drive wheel.

The drive wheel may be movable in the Z direction of the vehicle by virtue of rotation of the suspension member relative to the body of the vehicle. The drive unit may be movably mounted to the suspension member in such a way that as the suspension member moves away from the mid-point of its travel the drive unit moves a smaller distance in the Z direction than the drive wheel.

The drive wheel may be movable in the Z direction of the vehicle by virtue of rotation of the suspension member relative to the body of the vehicle. The drive unit may be movably mounted to the suspension member in such a way that as the suspension member moves away from the mid-point of its travel the drive unit moves a smaller distance in the Z direction than a portion of the suspension member located in the same Y/Z plane of the vehicle as the drive unit. The drive unit may be mounted to the suspension member so as to be rotatable relative to the suspension member about the rotation axis of the drive wheel.

The vehicle may comprise a tie rod coupling the drive unit to the body of the vehicle so as to cause the drive unit to move relative to the suspension member as the suspension member moves relative to the body. The tie rod may be of any suitable shape.

The drive unit may be coupled to the rear wheel by a first flexible coupling to apply the drive torque to the rear wheel. The flexible coupling could be an endless drive loop such as a belt or chain, or a flexible joint such as a universal or constant velocity joint.

The drive unit may be coupled to the suspension member by a flexible coupling to apply the reaction torque to the suspension member.

The drive unit may be coupled to the suspension member so as to apply the reaction torque about the rotation axis of the drive wheel.

The drive unit may be coupled to the suspension member so as to apply the reaction torque in the opposite direction to the drive torque.

The drive unit may be coupled to drive a differential gear arrangement. The differential gear arrangement may form the drive torque and the reaction torque differentially to each other.

The drive unit may have a housing and an output shaft, the drive unit may be configured to drive the output shaft to rotate relative to the housing, the housing may be mounted rotatably with respect to the suspension member, and the output shaft may be coupled to the drive wheel to provide the drive torque and the housing may be coupled to the suspension member to provide the reaction torque. The wheel may be mounted to the suspension member by a revolute joint.

The said suspension member may be mounted to a further suspension member by a first revolute joint and the wheel is mounted to the further suspension member by a second revolute joint, the axes of the first and second revolute joints being parallel and spaced apart.

The drive unit may be an electric motor.

The vehicle may be a motorcycle.

The drive unit is a primary drive unit. The drive unit may convert energy to mechanical energy from at least one other form. For example, the drive unit may be or comprise an internal combustion engine or an electric motor, or a combination of such devices. The drive unit may be or comprise a kinetic energy storage device. Such a device may store energy, e.g. from braking the vehicle, and may then be controllable to release stored energy to drive the vehicle. The drive unit may be arranged so that mechanical energy from the drive unit can drive the drive wheel to rotate relative to the body. The drive unit may be controllable, e.g. by an occupant of the vehicle, to provide energy to the drive wheel. The vehicle may comprise a conduit for providing energy in a non-mechanical form from the body of the vehicle to the primary drive unit. That may, for example, be an electric cable or a fuel hose. The primary drive unit may be configured to convert energy provided via the conduit to drive the drive wheel.

The rotation of which the drive wheel is capable relative to the suspension member may be rotation by which the drive wheel can drive the vehicle to move. The drive wheel may be rotatably mounted to the suspension member by a revolute joint attaching the wheel to the suspension member. The wheel may be capable of revolving about that joint to drive the vehicle.

The suspension member may be attached to the body by a first revolute joint. The drive wheel may be attached to the suspension member by a second revolute joint. The axis of that second revolute joint may be the axis about which the wheel moves to drive the vehicle. The suspension member may be rigid. In that way, the drive wheel may be constrained by the suspension member so that the axis of the second revolute joint can only move relative to the body about the axis of the first revolute joint.

The vehicle may be configured so that the reaction force is reacted through a flexible belt. The flexible belt may be arranged to act about the centre of the drive wheel. The flexible belt may be an endless belt. The flexible belt may be a unitary element or may be made of multiple links, e.g. in the form of a chain.

The drive unit may be configured to drive the drive wheel through a flexible belt. The flexible belt may be an endless belt. The flexible belt may be a unitary element or may be made of multiple links, e.g. in the form of a chain.

The vehicle may be configured so that the drive wheel is capable of (i) suspension motion relative to the body of the vehicle and (ii) drive rotation relative to the body of the vehicle. The suspension motion may be sprung motion. The vehicle may comprise a spring by which the suspension motion is resisted. The spring may be any suitable form of spring, for example a coil spring, a torsion spring, a leaf spring, a gas spring or a combination thereof. The suspension member may carry the drive wheel so as to define the form of the suspension motion. The suspension motion may be, or may substantially be, rotational motion. The wheel may be capable of rotating 360° in drive rotation. The drive unit and the drive wheel may be carried by the suspension member. An axis may be defined extending between (i) the point on the suspension member by which it is most closely attached to the body of the vehicle and (ii) the point on the suspension member by which it is most closely attached to the drive wheel. The projection of the centre of mass of the drive unit on to that axis may be located between those two points. This can help to reduce the contribution of the mass of the drive unit to the unsprung mass of the vehicle. The distance between the first of those points and the projection of the centre of mass of the drive unit on to that axis may be less than 90% or less than 80% of the distance between the two points. The system may be designed so as achieve a desired level of suspension movement of the driven wheel as a function of the torque applied by the drive unit. Thus the reaction force may tune the suspension movement as a function of drive unit torque.

The present invention will now be described by way of example with reference to the accompanying drawings. In the drawings:

Figure 1 is a side view of a motorcycle having an electric drive mechanism.

Figure 2 is an enlarged side view of part of the rear portion of the motorcycle of figure 1 .

Figure 3 is a view of the rear of the motorcycle of figure 1 from below, with the wheel and tyre in cross-section and partially shown.

Figure 4 is a schematic plan view of a first form of differential drive mechanism.

Figure 5 is a schematic plan of a second form of differential drive mechanism.

Figure 6 shows a rear view common to alternative embodiments of suspension systems.

Figures 7 and 8 are a schematic side views of alternative embodiments of a suspension system as shown in figure 6 including wheel driving mechanisms.

In the description below, references to directions such as above, below, in front or behind are with respect to the motorcycle when it is unladen and at rest on a smooth horizontal surface.

Figure 1 shows a motorcycle. The motorcycle has a frame or body 1 . The body is a generally rigid structure. It may be made from a lattice of structural members, moulded as a single rigid body or formed in any other suitable way. A fork 2 is mounted to the front of the body. The fork can be rotated relative to the body about a steer axis 3. Handle bars 4 are mounted to the upper end of the fork. A front ground-engaging or road wheel 5 is mounted to the lower end of the fork. A seat 6 for an occupant is on the upper part of the body. A rigid swing arm 7 is mounted to the body 1 at a revolute joint 8. The rotation axis 9 (see figure 3) of the joint 8 is transverse to the motorcycle, parallel to the Y axis of the motorcycle. The joint 8 constitutes the pivot point of the swing arm. The swing arm 7 is a trailing arm. The swing arm extends generally rearwardly from the pivot point 8. A rear ground-engaging or road wheel 10 is mounted on the swing arm at a rear wheel revolute bearing 1 1 . The rear wheel is free to rotate relative to the swing arm about an axis 12 (see figure 3) transverse to the motorcycle, parallel to the Y axis of the motorcycle. A spring 13 and a damper 14 are connected between the swing arm 7 and the body 1 to resist motion of the swing arm relative to the body. As will be described below, the motorcycle is driven by an electric motor 20. The electric motor acts as a primary drive for the motorcycle. The body carries a charge store 15, such as a battery, from which the motor can be powered.

The frame 1 is suspended by spring 13 and damper 14 at the rear, and by a spring and damper in the forks 2. The frame 1 represents the sprung mass of the motorcycle.

In essence, the motor is mounted to the swing arm in such a way that it can move relative to the swing arm under the action of a coupling strut 21 between the motor and to the body of the motorcycle. The motor applies a torque between the swing arm and the rear wheel in order to drive the rear wheel to rotate and thereby impart motive force to the motorcycle.

As shown in figure 3, the swing arm 7 has a first mounting structure 23 at its forward end. This comprises a fork whose tips sit on either side of the frame. The swing axis 9 of the swing arm passes through the fork tips. The swing arm has a second mounting structure 24 at its rear end. This comprises a shell which carries the rear wheel bearing. The rear wheel is attached to the second mounting structure by a threaded fastener arrangement 25 (e.g. a wheel bolt and wheel nut) which passes through the second mounting structure. The swing arm has a longitudinally extending beam 26 which extends between the first mounting structure 23 and the second mounting structure 24. The beam 26 is narrower in the Y direction than the first and second mounting structures.

The rear wheel 10 comprises a wheel body 70 and a tyre 27 which runs around the rim 28 of the wheel body. The wheel body has a hub 29 and spokes 30. The spokes extend radially and join the hub to the rim. The rear wheel fastener 25 passes through the hub 29. The hub is clamped to the rear mounting structure 24 of the swing arm.

The motor 20 is carried by a bracket 40. The bracket is rigid. The bracket is movably attached to the swing arm at a location offset from the motor. The bracket is attached to the swing arm by a revolute joint. The axis of the revolute joint is coincident with the axis 12 of the rear wheel. Conveniently, the bracket is mounted to the swing arm by a bearing 41 which surrounds the structure 24 of the swing arm to which the wheel is attached. In the motorcycle’s Y direction the bearing 41 may be located between the wheel hub 29 and the longitudinally extending strut 26 of the swing arm. This is a compact way of mounting the bracket. However, the bracket could be mounted in other ways. For example, it could be clamped to the swing arm by the rear wheel fastener 25. In this example, the bracket is a single component, but it could be formed of multiple parts that are articulated with respect to each other. In this example the bracket is attached by a revolute joint to the swing arm, but it could be mounted in other ways, for example on a four-bar linkage.

The bracket 40 is coupled to the frame 1 of the motorcycle by a tie rod 21. The tie rod 21 can pivot with respect to the frame at a joint 71 and with respect to the bracket at a joint 72. The tie rod is rigid. The length of the tie rod may be adjustable, e.g. by a threaded joint, in order to allow the suspension behaviour to be adapted easily. The tie rod 21 causes the bracket 40 to move with respect to the swing arm 7 as the swing arm moves with respect to the frame 1 . The tie rod 21 can be configured in any suitable way to achieve desired motion of the bracket 40. For example, its length and its attachment points to the frame and the bracket can be chosen as needed. It is preferred that the tie rod is configured so that when the swing arm moves, the bracket rotates with respect to the swing arm in the opposite direction to that in which the swing arm rotates with respect to the frame. To achieve this, the tie rod may be attached to the bracket at a point forwards of the rotation axis 12 of the rear wheel and/or of the rotation axis of the bracket 40 with respect to the swing arm. The tie rod can conveniently be attached to the frame at a point above the swing arm 7. The tie rod may be attached directly to the bracket 40 or indirectly: for example by being attached to the housing of the motor 20 which is carried by the bracket.

The motor 20 is attached to the bracket 40. Preferably the motor is attached to the bracket at a location forward of the axis 12 of the rear wheel. The motor is supplied with power from the battery 15 by supply cable 16. The motor 20 is arranged to drive the rear wheel in the manner discussed below. The motor may also act as a generator to brake the rear wheel and thereby charge the battery 15.

The motor drives a rotor to rotate relative to a stator. The rotor rotates relative to the stator about a rotor axis 50. The rotor axis runs transverse to the motorcycle. The rotor axis is parallel to the Y axis of the motorcycle.

The motor is arranged to apply torque differentially between the swing arm 7 and the rear wheel 10 in order to drive the motorcycle. The drive torque is reacted against the swing arm.

Figures 4 shows a first way in which this can be done. The motor 20 has a body 51 which is fast with the stator 52 of the motor. The motor is configured to drive the rotor 53 to rotate relative to the stator about the rotor axis 50. In the example of figures 4 and 5, the body 51 of the motor is attached rigidly to the bracket 40. The rotor drives a differential gear mechanism 54. The differential gear mechanism is an epicyclic mechanism and comprises a sun wheel 55, planet gears 56 which engage with the exterior of the sun wheel and an internally toothed gear 57 which engages the planet gears. This arrangement permits a differential drive to be taken between the planet gears and the internally toothed gear 57. A first drive belt 58 engages a carrier 62 for the planet gears and couples to toothing 59 which is fast with the swing arm 7. The first drive belt enables the motor to apply torque against the swing arm. This will tend to cause the bracket 40 to rotate around its revolute joint to the swing arm, and due to the presence of the tie rod 21 , that will tend to cause the swing arm 7 to move relative to the frame. A second drive belt 60 engages the outer gear 57 and couples to a gear 61 which is fast with the hub of the rear wheel. The second drive belt enables the motor to apply torque to the rear wheel to drive it to rotate. The action of the differential is such that the drive torque to the rear wheel is reacted against the swing arm. The drive torque is reacted against the swing arm about the rotation axis of the rear wheel. The motor is coupled to the swing arm such that when the motor applies a drive torque to the rear wheel in a direction such as to propel the motorcycle forwards, the reaction torque against the swing arm will tend to force the free, rear end of the swing arm 7 downwards relative to the frame 1 .

The first and second belts could be coupled to the differential gear in different ways. For example, the first belt could be coupled to the outer gear 57 and the second belt could be coupled to the planet wheels. Or the rotor could drive the outer gear and one of the belts could be coupled to the sun wheel. Other differential drive gear mechanisms are possible.

Figure 5 shows a second way in which a differential drive can be developed between the swing arm and the rear wheel. The body 51 of the motor 20 is mounted to the bracket 20 by a revolute joint 65 so that it is free to rotate with respect to the bracket about an axis parallel to the rotor axis 50 of the motor. First drive belt 58 engages the body of the motor, which is fast with the motor’s stator, and couples to gear 59 which is fast with the swing arm 7. The first drive belt enables the motor to apply torque against the swing arm. This will tend to cause the bracket 40 to rotate around its revolute joint to the swing arm, and due to the presence of the tie rod 21 , that will tend to cause the swing arm 7 to move relative to the frame. Second drive belt 60 engages the rotor 53 of the motor and couples to a gear 61 which is fast with the hub of the rear wheel. The second drive belt enables the motor to apply torque to the rear wheel to drive it to rotate. Because the body of the motor is free to rotate about the rotor axis, the action of mechanism described above is such that the drive torque to the rear wheel is reacted against the swing arm. The drive torque is reacted against the swing arm about the rotation axis of the rear wheel. The motor is coupled to the swing arm such that when the motor applies a drive torque to the rear wheel in a direction such as to propel the motorcycle forwards, the reaction torque against the swing arm will tend to force the free, rear end of the swing arm 7 downwards relative to the frame 1 . In this embodiment the reaction torque is applied about the rear wheel axis, but it could be applied about another axis. Preferably it is applied about an axis parallel with the wheel axis.

The first and second drive belts may be endless belts. The first and second drive belts may independently be chains, toothed belts, friction belts or any other suitable flexible couplings. Since the motion of the swing arm is limited, the motion of the first belt is limited. The first belt could be replaced by mutually pivotable rigid rods. Instead of belts, torque could be transmitted from the motor to the rear wheel and/or the swing arm by a respective gear train or a drive shaft.

In the examples of both figures 4 and 5, the motor is coupled to the swing arm 7 and the wheel 10 in such a way that the torques applied to the swing arm 7 and the wheel 10 are proportional. The two torques are applied with independent rotational speed.

Preferably the motor is located on the bracket 40 such that its centre of gravity and/or the rotor axis 50 are located forward of the rotation axis 12 of the rear wheel when the swing arm 7 is in the mid-point of its travel and/or for all operational configurations of the swing arm. Preferably the centre of gravity of the motor in combination with the bracket 40 and optionally the belts 58, 60 or the alternative drive means to them is located forward of the rotation axis 12 of the rear wheel when the swing arm 7 is in the mid-point of its travel and/or for all operational configurations of the swing arm. Preferably the centre of gravity of the motor, optionally in combination with the bracket 40, and optionally in combination with the belts 58, 60 or the alternative drive means to them, is offset from the rotational axis 12 in the longitudinal (X) direction of the motorcycle. The tie rod 21 constrains the movement of the centre of gravity of the bracket 40 and motor 20 relative to the sprung mass of the frame 1 as the rear suspension is deflected: i.e. as the swing arm 7 moves about its axis 9.

It is preferred that the tie rod is arranged to extend substantially vertically from the bracket 40 to the frame 1 . It is preferred that flexible joint 71 is located substantially vertically above flexible joint 72. It is preferred that flexible joint 72, by which the tie rod 21 is attached to the bracket 40 is located near and/or substantially vertically in line with the combined centre of gravity of the motor 20 and the bracket 40. These features can result in that combined centre of gravity remaining substantially fixed in position relative to the sprung mass of the motorcycle as the rear suspension deflects. This can result in the mass of the motor 20 and the bracket 40 having substantially no effect on the suspension characteristics of the motorcycle. Mechanisms other than a tie rod may be used to provide motion of the motor relative to the suspension arm. For example, an electronic control unit may be used to modulate the torque applied by the motor 20, or to control another rotational or linear actuator to set the position of the motor 20 relative to the suspension arm in dependence on the configuration of the suspension arm relative to the frame 1 . Alternatively, a hydraulic actuator may be used to move the motor 20 relative to the frame, the hydraulic actuator being driven by a hydraulic feed from a hydraulic sensor coupled between the swing arm and the frame at a location offset from the motor.

The bracket 20 is linked to the frame by tie rod 21 so that for a given amount of suspension motion of the swing arm 7 away from its resting position, the vertical motion of the centre of gravity of the motor 20 and bracket 40 in combination is less than the vertical motion of the rear wheel axis 12. This results in an anti-squat tendency. That anti-squat tendency can be offset by the reaction torque developed by the motor against the swing arm through belt 58. The balance between these behaviours can be tuned by suitable selection of the geometry of tie rod 21 and the effective gear ratio of belt 58. The electric motor 20 is mounted to the suspension arm, rather than being mounted to the body as is the case in many conventional motorcycles. This can reduce total weight due to a reduction in the length of the drive train to the rear wheel. It can also provide packaging advantages, since the motor can be located outside the motorcycle frame, and aerodynamic advantages, since the vehicle will not have a drive chain running from the body to the rear wheel which allows the rider to be packaged in a more aerodynamic position. GB 2 424 631 shows a motorcycle configuration in which the rider can be packaged in a more aerodynamic position than is conventional. The drive arrangement described herein may advantageously be incorporated in a motorcycle of the type described in GB 2 424 631 .

It can be noted that in the embodiment of figure 4 the inertia of the rotor 53 as it rotates can provide suspension inertance. This can be tuned through selection of the mass of the rotor and the operating speed of the motor, which can be separated from the drive speed of the motorcycle through the choice of the effective gear ratio of belt 60. In some situations it may, if desired, be possible to inertia-compensate the rotor, sometimes fully, by modulating the motor torque so as to reduce the impact of suspension movement on torque to the rear wheel. This can reduce the effect of the motor’s inertia on suspension load. In the embodiment of figure 5 the inertia of the rotor 53 as it rotates, and the inertia of the stator 52 as it rotates, can provide suspension inertance. These can be tuned through selection of the masses of the rotor and the stator and the operating speed of the motor, which can be separated from the drive speed of the motorcycle through the choice of the effective gear ratio of belt 60. In some situations it may, if desired, be possible to fully inertia-compensate the rotor by modulating the motor torque so as to reduce the impact of suspension movement on torque to the rear wheel. If the motor is attached so that it moves opposite to the wheel, with respect to the motorcycle body, then its effect on unsprung mass can be reduced. The motor could be mounted so that its motion cancels some or all of the unsprung mass of rear suspension system and/or the wheel. The amount of cancellation will depend on the mass of the motor and the extent to which it moves with suspension motion. The motor could be mounted so that there is in effect substantially zero unsprung mass due to the rear suspension and wheel. The inertance provided by the rotor 53 can also be used to reduce the natural frequency of the suspension motion.

In the examples given above, the suspension arm is attached to the body by a revolute joint, so the suspension arm can move in pure rotation relative to the vehicle body. Alternatively, the suspension arm may be mounted in other ways, for example by a four-bar linkage, in which case the suspension arm may be capable of moving with compound rotation with respect to the frame.

Figures 6, 7 and 8 show alternative arrangements.

Figure 6 is a view of a vehicle’s drive wheel 70 in a Y/Z plane. The drive wheel is mounted to rotate with respect to a wheel carrier 71 . The wheel carrier is mounted to the body 72 of a vehicle by a member 73, which may be in the form of a wishbone. The member 73 can rotate with respect to the body in the vehicle’s X axis on joints 74. The wheel carrier may be mounted so that it can also rotate in the vehicle’s X axis with respect to the member 73, on joints 85. A suspension strut 76 couples the wheel carrier 71 to the vehicle body 72 so as to suspend the body over the wheel carrier. The suspension strut 76 may provide springing and/or damping of suspension motion. For clarity the drive components and their supports as shown in figures 7 and 8 are omitted from figure 6.

Figure 7 is a view of a drive arrangement for the wheel 70. Figure 7 is a view in an X/Z plane. The suspension parts shown in figure 6 are omitted for clarity. A rigid wheel arm 82 is suspended from the body 72 of the vehicle by a link 80. The wheel arm 82 may be considered a suspension member. The link 80 may be provided with revolute joints to one or both of body 72 and wheel arm 82. A motor 91 is mounted on the wheel arm. The stator 87 of the motor is mounted to the wheel arm by a revolute joint. The axis of the revolute joint is parallel to the rotation axis 89 of the wheel 70. It is generally parallel to the vehicle’s Y axis. The motor can drive its rotor 88 to rotate with respect to the stator. A first drive belt 81 couples the rotor to a drive gear 83. The drive gear is rotationally fast with the wheel 70 and hence can rotate with respect to the wheel carrier 71 . A second drive belt 86 connects the stator 87 to the wheel carrier 71 . The second drive belt could be replaced with a rigid link. The wheel arm 82 is coupled by a revolute joint to the wheel carrier so that it can rotate with respect to both the wheel 70 and the wheel carrier 71 . The rotation axis of that revolute joint is preferably parallel to the wheel axis. In this case it is coincident with the wheel axis.

In the arrangement of figure 7, the motor can drive the wheel to rotate using belt 81 driven by rotor 88. The resulting reaction torque at the motor, from stator 87, is reacted to the wheel carrier 71 . This arrangement can provide similar suspension properties to the other arrangements described above.

Figure 8 shows a second alternative arrangement. In the arrangement of figure 8 the wheel arm 82 is suspended from a motor carrier 77 by a revolute joint about axis 90. The wheel arm 82 and the motor carrier 77 may be considered suspension members. Axis 90 is preferably parallel to the axis of wheel 70. Motor carrier 77 is suspended from the body 72 of the vehicle by one or more connectors 79’, 79”. These may each have revolute joints to the vehicle body and/or to the motor carrier. The stator 87 of motor 91 is rigidly attached to the motor carrier 77. The rotor 88 of the motor is coupled by a drive belt to the drive gear 83, and can thereby drive wheel 70 to rotate relative to the wheel carrier 71. In this arrangement, the reaction torque at the motor acts against motor carrier 77. This arrangement has fewer opportunities for tuning the relationship between the drive force on the wheel and its reaction force than other arrangements discussed above, but it can provide benefits of decoupling motor inertia from suspension motion through similar principles to the other arrangements discussed above.

In the arrangements of figures 7 and 8 the wheel arm 82 and the motor carrier 77 could be coupled to the vehicle body in other ways, for example by revolute joints, swinging rods or elastic bushings.

When the suspension system comprising the rear wheel is moving relative to the body of the vehicle the system behaves as if the system has an unsprung mass. The unsprung mass is considered to be the effective mass of the suspension system as it moves relative to the body of the vehicle. The effective mass is a component in the inertia of the suspension system as it moves relative to the body of the vehicle. In embodiments described above, the motor is arranged so that over at least part of the range of motion of the suspension system the motor’s contribution to the unsprung mass of the suspension system comprising the rear wheel is less than the static mass of the motor. Preferably that includes at least a central part of the range of motion, and/or a part of the range of motion corresponding to the neutral position of the suspension system when an 80kg rider load is seated on a seat of the vehicle. The motor may be coupled to the remainder of the suspension system and/or to the body of the vehicle such that when the wheel moves in one direction (e.g. bump or rebound) relative to the body of the vehicle the motor moves in the other direction. This relationship may obtain through the whole or a part of the motion of the suspension system. Preferably that includes at least a central part of the range of motion, and/or a part of the range of motion corresponding to the neutral position of the suspension system when an 80kg rider load is seated on the vehicle. When the system is configured so that the motor moves in the opposite direction to (e.g.) the wheel, movement of the motor can at least partially offset the movement of the mass of the wheel, and optionally the mass of other components of the suspension system in addition to the wheel. Thus, the unsprung mass of the wheel and optionally other components of the suspension system in addition can be partially or fully compensated. When the unsprung mass of the suspension system is fully compensated it may behave as if it has zero unsprung mass. Through suitable choice of the mass of the motor and its movement relative to the remainder of the suspension system the suspension system may be overcompensated such that it behaves as if it has negative unsprung mass. The motor may be configured so that its motion contribute to inertance of the suspension system.

Thus, the motor be arranged to may move in a common sense with the wheel it can drive: i.e. towards the body of the vehicle when the body moves towards the body of vehicle and vice versa; or in an opposite sense to the wheel it can drive: i.e. towards the body of the vehicle when the body moves away from the body of the vehicle and vice versa. In the latter case, the motor may move in a direction that at least partially opposes the direction of motion of the wheel. It may move in a direction that exactly opposes the direction of motion of the wheel.

In the examples given above, the motor is used to drive a motorcycle. The same arrangement may be used to drive other vehicles, for example four-wheeled vehicles such as automobiles. The arrangement is especially suitable for driving road wheels mounted on trailing suspension arms. The arrangement may be applied to front wheels instead of rear wheels. In that case the mechanism may be adapted so that its sense of operation is reversed in order that it provides front anti-jack behaviour.

The electric motor could be substituted by or supplemented with another source of primary motive drive, for example an internal combustion engine or a kinetic energy storage device. That could be carried and could provide drive in the same way as the motor described above.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

1 . A vehicle having:

a body;

a suspension member mounted to the body so as to be movable relative to the body;

a drive wheel mounted so as to be capable of rotating relative to the suspension member; and

a primary drive unit mounted to the suspension member, the drive unit being configured to apply a drive torque to the rear wheel which is reacted against a reaction force applied to the suspension member, the drive unit being movably mounted to the suspension member in such a way that the reaction force can cause motion of the suspension member relative to the body.

2. A vehicle as claimed in claim 1 , wherein the drive unit is movably mounted to the suspension member in such a way that the position of the drive unit relative to the suspension member varies with the position of the suspension member relative to the body.

3. A vehicle as claimed in claim 1 or 2, wherein the drive wheel is movable relative to the body by virtue of motion of the suspension member relative to the body, and the drive unit is mounted to the suspension member such that, on motion of the suspension member relative to the body, the amplitude of motion of the centre of mass of the drive unit relative to the body over at least part of the range of motion of the drive unit is less than the amplitude of motion of the centre of mass of the drive wheel relative to the body.

4. A vehicle as claimed in any preceding claim, wherein the body of the vehicle is sprung for vertical motion relative to the suspension member and the drive unit is movably mounted to the suspension member in such a way that over at least part of the range of motion of the drive unit the mass of the drive unit does not fully contribute to unsprung mass of the vehicle.

5. A vehicle as claimed in any preceding claim, wherein the drive wheel is movable relative to the body by virtue of motion of the suspension member relative to the body, and the drive unit is mounted to the suspension member such that, on motion of the suspension member relative to the body, motion of the centre of mass of the drive unit relative to the body is over at least part of the range of motion of the drive unit in a direction at least partially opposing the direction of motion of the centre of mass of the drive wheel relative to the body.

6. A vehicle having:

a body;

a drive wheel rotatably mounted to the suspension member; and

a primary drive unit mounted to the suspension member, the drive unit being configured to apply a drive torque to the rear wheel which is reacted against a reaction force applied to the suspension member, the drive unit being movably mounted to the suspension member in such a way that the position of the drive unit relative to the suspension member varies with the position of the suspension member relative to the body.

7. A vehicle as claimed in claim 6, wherein the drive wheel is movable relative to the body by virtue of motion of the suspension member relative to the body, and the drive unit is mounted to the suspension member such that, on motion of the suspension member relative to the body, the amplitude of motion of the centre of mass of the drive unit relative to the body is over at least part of the range of motion of the drive unit less than the amplitude of motion of the centre of mass of the drive wheel relative to the body.

8. A vehicle as claimed in claim 6 or 7, wherein the body of the vehicle is sprung for vertical motion relative to the suspension member and the drive unit is movably mounted to the suspension member in such a way that over at least part of the range of motion of the drive unit the mass of the drive unit does not fully contribute to unsprung mass of the vehicle.

9. A vehicle as claimed in any of claims 6 to 8, wherein the drive wheel is movable relative to the body by virtue of motion of the suspension member relative to the body, and the drive unit is mounted to the suspension member such that, on motion of the suspension member relative to the body, motion of the centre of mass of the drive unit relative to the body is over at least part of the range of motion of the drive unit in a direction at least partially opposing the direction of motion of the centre of mass of the drive wheel relative to the body.

10. A vehicle having:

a body;

a spring mechanism whereby the body of the vehicle is sprung for vertical motion relative to the suspension member;

a drive wheel rotatably mounted to the suspension member; and

a primary drive unit mounted to the suspension member, the drive unit being configured to apply a drive torque to the rear wheel which is reacted against a reaction force applied to the suspension member, the drive unit being movably mounted to the suspension member in such a way that the mass of the drive unit does not fully contribute to unsprung mass of the vehicle.

1 1 . A vehicle as claimed in claim 10, wherein the drive wheel is movable relative to the body by virtue of motion of the suspension member relative to the body, and the drive unit is mounted to the suspension member such that, on motion of the suspension member relative to the body, the amplitude of motion of the centre of mass of the drive unit relative to the body is less than the amplitude of motion of the centre of mass of the drive wheel relative to the body.

12. A vehicle as claimed in any preceding claim, wherein the suspension member is rotatably mounted to the body.

13. A vehicle as claimed in any preceding claim, wherein the suspension member is translationally mounted to the body.

14. A vehicle as claimed in any preceding claim, wherein the suspension member is a suspension arm.

15. A vehicle as claimed in any preceding claim, wherein the suspension member is a wheel carrier.

16. A vehicle as claimed in any preceding claim, wherein the drive unit is rotatably mounted to the suspension member.

17. A vehicle as claimed in any preceding claim, wherein the drive unit is capable of converting energy from a non-mechanical form into motion so as to apply the drive torque to the wheel.

18. A vehicle as claimed in any preceding claim, wherein rotation of a drive shaft of the drive unit contributes to inertance of the vehicle’s suspension system as provided by the suspension member.

19. A vehicle as claimed in any preceding claim, wherein the suspension member is mounted to the body for rotation about a suspension axis parallel to the rotation axis of the drive wheel.

20. A vehicle as claimed in claim 19, wherein the suspension axis is forward of the rotation axis of the drive wheel.

21. A vehicle as claimed in claim 19 or 20, wherein the centre of gravity of the drive unit is located between a first plane extending in the Y/Z directions of the vehicle through the suspension axis and a second plane extending in the Y/Z directions of the vehicle through the rotation axis of the drive wheel.

22. A vehicle as claimed in any preceding claim, wherein the drive wheel is a rear wheel of the vehicle.

23. A vehicle as claimed in any preceding claim, wherein the centre of gravity of the drive unit is offset from the rotation axis of the drive wheel.

24. A vehicle as claimed in any preceding claim, wherein the drive wheel is movable in the Z direction of the vehicle by virtue of rotation of the suspension member relative to the body of the vehicle, and the drive unit is movably mounted to the suspension member in such a way that as the suspension member moves away from the mid- point of its travel the drive unit moves a smaller distance in the Z direction than the drive wheel.

25. A vehicle as claimed in any preceding claim, wherein the drive wheel is movable in the Z direction of the vehicle by virtue of rotation of the suspension member relative to the body of the vehicle, and the drive unit is movably mounted to the suspension member in such a way that as the suspension member moves away from the mid- point of its travel the drive unit moves a smaller distance in the Z direction than a portion of the suspension member located in the same Y/Z plane of the vehicle as the drive unit.

26. A vehicle as claimed in any preceding claim, wherein the drive unit is mounted to the suspension member so as to be rotatable relative to the suspension member about the rotation axis of the drive wheel.

27. A vehicle as claimed in any preceding claim, comprising a tie rod coupling the drive unit to the body of the vehicle so as to cause the drive unit to move relative to the suspension member as the suspension member moves relative to the body.

28. A vehicle as claimed in any preceding claim, wherein the drive unit is coupled to the rear wheel by a first flexible coupling to apply the drive torque to the rear wheel.

29. A vehicle as claimed in any preceding claim, wherein the drive unit is coupled to the suspension member by a flexible coupling to apply the reaction torque to the suspension member.

30. A vehicle as claimed in any preceding claim, wherein the drive unit is coupled to the suspension member so as to apply the reaction torque about the rotation axis of the drive wheel.

31. A vehicle as claimed in any preceding claim, wherein the drive unit is coupled to the suspension member so as to apply the reaction torque in the opposite direction to the drive torque.

32. A vehicle as claimed in any preceding claim, wherein the drive unit is coupled to drive a differential gear arrangement, and the differential gear arrangement forms the drive torque and the reaction torque differentially to each other.

33. A vehicle as claimed in any of claims 1 to 31 , wherein the drive unit has a housing and an output shaft, the drive unit is configured to drive the output shaft to rotate relative to the housing, the housing is mounted rotatably with respect to the suspension member, and the output shaft is coupled to the drive wheel to provide the drive torque and the housing is coupled to the suspension member to provide the reaction torque.

34. A vehicle as claimed in any preceding claim, wherein the wheel is mounted to the suspension member by a revolute joint.

35. A vehicle as claimed in any of claims 1 to 33, wherein the suspension member is mounted to a further suspension member by a first revolute joint and the wheel is mounted to the further suspension member by a second revolute joint, the axes of the first and second revolute joints being parallel and spaced apart.

36. A vehicle as claimed in any preceding claim, wherein the drive unit is an electric motor.

37. A vehicle as claimed in any preceding claim, wherein the vehicle is a motorcycle.