Technical Field

The present invention relates to a double wishbone independent suspension system for a motor vehicle.

Background

The majority of motor vehicles are provided with a suspension system capable of absorbing the impact of variations in a road surface. Absorbing this impact helps to provide a smoother ride for both the passengers and other objects carried by the motor vehicle. Whilst there are various different types of suspension systems, a common type of suspension is an independent double wishbone suspension. Independent double wishbone suspension systems typically comprise a double wishbone positioned at each wheel on the vehicle in combination with a spring and a shock absorber.

Double wishbone independent suspension systems typically comprise an upper wishbone and lower wishbone each attached at a bifurcated end to a vehicle chassis and connected at their other end to a wheel. In order for the suspension to absorb the frequent loads which are applied to the wheel, a shock absorber is typically affixed to one of the wishbones and the chassis and a coiled spring is also often attached to one of the wishbones and to the vehicle chassis. The purpose of the shock absorber is to absorb the shocks as the wheel travels over the uneven surface. The coiled spring provides a restoring force which allows the wheel to move relative to the surface and then to return to its stable position as the surface allows.

As the wheel moves relative to the chassis, the angle of the wheel relative to the vehicle and the ground is controlled by the components of the suspension system. Typically, as a wheel passes over an uneven surface the angle of the wheel with respect to the surface changes. This angle is known as the camber angle and is defined as the angle between the wheel's vertical axis and a line perpendicular to the surface the wheel is resting on. The camber angle ultimately defines how much of the wheel is in contact with the surface. For instance, when the camber angle is zero degrees, the wheel is completely flat and thus the entire width of the tyre rests upon the surface. However, when the camber angle is greater than zero the wheel is effectively tilting and thus part of the tyre no longer comes into contact with the surface, or at least with a reduced force. The camber angle is also important for drive characteristics when a vehicle turns. As a vehicle turns, the weight of the vehicle is shifted to different sides of the vehicle causing the suspension in some parts to be placed under an increased load. In order to provide appropriate camber angles, prior art suspension systems typically comprise upper and lower wishbones which have different lengths. By having different length wishbones, the arc that the wheel can travel along can be controlled to provide appropriate camber angles. Therefore, it can be ensured that an appropriate camber angle can be achieved even when the vehicle is turning, so that a sufficient portion of the vehicle's wheels remains in contact with the surface.

The upper wishbone arm is also often designed to accommodate the spring or shock absorber passing through it from the lower wishbone arm and thus is typically larger than the lower one.

Summary

The present invention seeks to provide a different arrangement and when viewed from a first aspect provides a vehicle chassis having upper and lower mounting points thereon and an independent double control arm suspension arrangement mounting a wheel of the vehicle and comprising:

an upper control arm and a lower control arm each having an identical shape and construction, the upper control arm having an upper pivot end and the lower control arm having a lower pivot end, the upper pivot end being attached to the upper mounting point and the lower pivot end being attached to the lower mounting point such that the upper control arm and upper control arm can pivot relative to the chassis and an upper oscillatory end and a lower oscillatory end are capable of oscillating along a fixed arc defined by the upper control arm and lower control arm respectively; and a support for the motor vehicle wheel connected to the upper oscillatory end and the lower oscillatory end.

Thus it will be appreciated by a person skilled in the art that the present invention provides an improved independent double wishbone suspension using an identical upper and lower control arm. This reduces the total number of different components needed to produce the suspension system. The reduction in the number of different components significantly reduces the cost of design, manufacture and distribution of the suspension system as only a single type of control arm needs to be produced, stocked etc.

It will be appreciated that since they are the same length, both the upper and lower control arm will have an arc with an identical radius. In a standard installation this would lead to undesirable camber angles and dynamic performance. However the Applicant has realised that suitable control of the wheel attached to the control arms can be achieved by carefully choosing the positions of the mounting points of the control arms as specified in accordance with the invention such that their arcs are positioned relative to one another so as to provide appropriate wheel kinematics. As a result the Applicant has realised that different length wishbones are not required.

The Applicant has appreciated that the amount of halftrack change experienced by the wheel, and subsequently the tyres, is an important consideration for suspension systems. Halftrack change is the amount of lateral translation of the tyre contact patch during bump and rebound travel. Typically, short wishbones that travel on small arcs produce a large amount of halftrack change. A large amount of halftrack change can cause excessive tyre wear as the tyre is caused to move laterally along a surface which causes wear. Not only does this result in increased running costs, the increased lateral movement can lead to undesirable drive feel, for example the vehicle may feel less refined and it may cause the vehicle to uncontrollably move around on particularly bumpy roads as the tyre experiences larger lateral forces. It has been appreciated by the Applicant that there are various parameters of the suspension system which can be tuned in order to minimise the amount of halftrack change. By increasing the length of the control arms the amount of halftrack change may be reduced. In addition or alternatively, in a set of embodiments the upper mounting point and lower mounting point are chosen such that the amount of halftrack change is minimsed. By way of example, the upper and lower mounting points may be inboard of the typical mounting points on the chassis thus allowing the use of longer control arms. In a preferred set of embodiments the independent double control arm suspension arrangement is arranged such that the halftrack change is no more than ± 0.10 m/m, e.g. no more than ± 0.05 m/m, e.g. no more than ± 0.02 m/m. I.e. if the suspension system travels 100 mm there would be no more than 2 mm of halftrack change. As discussed above, the level of camber gain also impacts the amount of tyre wear. For example, if the camber gain is too high or too low it can lead to increased wear on the inside or outside edges of the tyres. In a set of embodiments the independent double control arm suspension arrangement is arranged so as to provide -20 to -30 degrees/m of camber gain. I.e. if the syspension system travels 100mm there would be between -2 and -3 degrees of camber gain. This may be achieved by, for example, tuning the length of the control arms, tuning the position of the upper and lower mounting points, and tuning the position of the arcs of each control arm.

In a set of embodiments the upper and lower control arms have bifurcated ends. In such a set of embodiments the bifurcated ends preferably form the pivot ends which are mounted to the vehicle chassis. Attaching the control arm to the chassis by its bifurcated ends would normally be done such that it can only move in a single direction e.g. upwards and downwards to ensure stability.

In order for the upper and lower control arms to be sufficiently strong to cope with the loads which they experience as the vehicle goes over uneven ground, the upper and lower control arms may be manufactured out of particularly high strength materials for example steel or carbon fibre, or manufactured in a particularly strong shape or form.

In a set of embodiments both the upper and lower control arm each comprise a respective cross member connecting each side of the bifurcated wishbone. The cross member may help to increase the rigidity of the control arm thus improving its suitability for use in a vehicle suspension system which is likely to be frequently exposed to relatively high loads.

It will be appreciated that there are various measures of the angle of the wheel and the suspension system which define how the wheel responds to an uneven surface. The castor angle is the angle between a line extending along a projection of the wheel support and a line perpendicular to the surface on which the vehicle wheel is resting. In a set of embodiments the upper and lower mounting points on the chassis are offset such that upper and lower control arms are offset longitudinally relative to one another, providing a suspension system that has a positive castor angle. A positive castor angle is when the support is angled away from the direction of travel of the vehicle. This is known to make the vehicle easier to drive and improve its directional stability.

In a set of embodiments the independent double control arm arrangement specified in accordance with the invention is used on wheels at different longitudinal points on the vehicle - e.g. front and back. This further enhances the advantage of requiring fewer different parts in order to produce a vehicle. In a set of such embodiments each of the wheels of the vehicle is mounted as set out in accordance with the invention - i.e. has at least identical upper and lower control arms. The Applicant has recognised that where common suspension components are used throughout a vehicle, their mounting may be different between longitudinally spaced wheels. Thus in a further set of embodiments, the upper mounting point and lower mounting point differ between the longitudinal position of the wheel for which the independent double control arm arrangement is used. It will be appreciated that adjusting the mounting points adjusts the positioning of the upper and lower control arms and can assist in making the suspension more appropriate for the position of the vehicle in which it is being used. For example, if the suspension is mounted on a part of the vehicle which is likely to be heavily laden, such as the rear for a heavy goods vehicle, the suspension can be adjusted accordingly so as to be appropriate to support heavier loads and still be capable of absorbing impacts. In prior art suspension systems a four wheeled vehicle would require four different control arms in order to provide an appropriate suspension performance at the front and rear (with the same components being used on left and right sides). Embodiments of the present invention however require only one type of control arm and thus significantly reduces the cost involved in producing the components for the suspension system of the vehicle.

Additionally, adjusting the positioning of the control arms depending on the position of the independent double control arm arrangement is particularly advantageous in vehicles where there is an uneven torque split between different wheels. In a set of embodiments the upper mounting point and/ or the lower mounting point and/ or the length of the support are chosen to prevent squatting and/or diving of the vehicle when torque and/or braking force is applied to the wheels. Squatting is understood to be when one end of the vehicle dips and/or the other end rises as torque is applied to the wheels.

In a set of embodiments the control arm is shaped so as to accommodate other vehicle components. This is particularly advantageous as the control arm is used universally as both the upper and lower control arms and therefore it may be necessary for either control arm to accommodate other suspension components. This would mean that the control arms could be used with standard suspension components without requiring specific components to be made bespoke for use with the control arms. Shaping the control arm in such a way that it accommodates other suspension components may also be advantageous as it may mean that the other suspension components can be mounted to other parts of the suspension system. For example, the spring and/or damper maybe attached directly to the support. This may mean that the control arm does not need to be made with mounting points for the attachment of other suspension components. This may reduce the complexity of the control arms and thus may reduce the amount of material and/or the material strength required to suitably manufacture the control arms. As the control arms are identical across the vehicle this may significantly reduce the cost of making the suspension systems on the vehicle.

However, it has been appreciated that it may not always be possible to mount the other suspension components to components other than the control arms and thus the control arms may be shaped so as to directly accommodate other suspension components. In a set of embodiments a shock absorber is positioned between one of the control arms and the chassis. In a further set of embodiments the shock absorber is positioned between the lower control arm and the chassis. In such embodiments the control arm maybe shaped such that a suspension spring can be mounted to the lower control arm and pass through the upper control arm without coming into contact with the upper control arm. It will be appreciated that the control arm may take various forms in order for it to appropriate for accommodating other vehicle components. In embodiments where the control arm has a wishbone shape with bifurcated ends and a cross member, the cross member may be positioned closer to the apex of the wishbone than the bifurcated ends such that the freedom for other components to be

incorporated within the control arm is increased. As the cross member improves the rigidity of the control arm, it is recognised that moving it further towards the apex of the control arm may reduce its ability to strengthen the control arm. However the consequent need to strengthen it may be outweighed by the other advantages achievable in accordance with the invention. Alternatively, the cross member may be positioned further from the apex of the control arm than the bifurcated ends so as to increase the central space within the control arm. In either case, designing the control arm such that it can be used with a range of other components increases its applicability to a larger range of vehicles which have different suspension set-ups and use different components. In a set of embodiments a resilient member is positioned between one of the control arms and the chassis. Whilst the resilient member may take various forms, in a set of embodiments the resilient member is a metal coil spring. In a set of embodiments the resilient member is positioned between the upper control arm and the chassis.

Positioning the resilient member between the upper control arm and the chassis is advantageous as the control arm does not have to be designed to allow the resilient member to pass through the control arm, which may be required, as outlined above, if the resilient member was positioned between the lower control arm and the chassis. This is particularly relevant in cases where the suspension system is used on

commercial vehicles where the resilient member may be relatively large in order to be appropriate for the larger weights of commercial vehicles.

Whilst the double wishbone suspension in accordance with the present invention can be used on a range of different vehicles, the Applicant has appreciated that it is particularly useful on commercial vehicles. As commercial vehicles typically have a larger width, their suspension systems are generally larger than typical cars. As a result, the length of the control arms for commercial vehicles are typically larger and as a result it is easier to reduce the halftrack change and obtain the desired camber gain when the system is used on commercial vehicles. The present invention makes it more economically viable to use independent suspension on a commerical vehicle and as a result the camber compensation can be controlled. This can help to reduce tyre wear which is an important consideration for commercial vehicles.

In a set of embodiments the vehicle has a maximum authorised mass of between 2 to 30 tonnes, e.g. 2-26 tonnes. The maximum authorised mass (MAM) is defined to be the maximum weight of a vehicle including the maximum load which it can carry safely on the road.

The Applicant has appreciated that the control arms may be mounted in various different ways to provide the desired wheel kinematics and this may vary depending on the particular type or application of a certain vehicle. However the Applicant has recognised a particularly favourable configuration and when viewed from a second aspect provides a vehicle chassis having upper and lower mounting points thereon and an independent double control arm suspension arrangement mounting a wheel of the vehicle and comprising: an upper control arm and a lower control arm each having an identical shape and construction, the upper control arm having an upper pivot end and the lower control arm having a lower pivot end, the upper pivot end being attached to the upper mounting point and the lower pivot end being attached to the lower mounting point such that the upper control arm and upper control arm can pivot relative to the chassis and an upper oscillatory end and a lower oscillatory end are capable of oscillating along a fixed arc defined by the upper control arm and lower control arm respectively;

a support for the motor vehicle wheel connected to the upper oscillatory end and the lower oscillatory end;

wherein the height of the upper mounting point, the height of the lower mounting point and the length of the support are such that in a rest position the lower oscillatory end is angled towards the ground, the upper oscillatory end is angled upwards, and the support is angled such that its upper part connected to the upper oscillatory end is angled away from vertical and away from the wheel.

It has been appreciated by the Applicant that the specific setup of the mounting points described above, with respect to this second aspect of the invention, provides a suspension system which delivers appropriate wheel kinematics. Brief Description of the Drawings

Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. l shows a schematic front view of a part of a vehicle chassis and suspension system in accordance with the present invention;

Fig. 2 shows a schematic side view of the vehicle chassis of Fig. l;

Fig. 3 shows a perspective view of a vehicle chassis comprising an identical double control arm suspension in accordance with the invention;

Fig. 4 shows a front view of the vehicle chassis of Fig. 3;

Fig. 5 shows a top view of the vehicle chassis of Figs 3 and 4;

Fig. 6 shows an end view of the vehicle chassis of Figs 3 to 5; and

Fig. 7 shows a table containing data of the geometric parameters of different suspension systems. Detailed Description

Figure 1 shows a schematic representation of an identical double wishbone suspension in accordance with the present invention. The suspension arrangement 2 comprises an upper control arm 4 and lower control arm 6 which are identical in shape and construction. The upper control arm 4 has an upper oscillatory end 8 and an upper pivot end 10. The lower control arm 6 has a lower oscillatory end 12 and a lower pivot end 14. The upper pivot end 10 is attached to an upper mounting point on a chassis (not shown) at a first height 16 above the ground. The lower pivot end 14 is attached to a lower mounting point on the chassis at a second height 18 above the ground.

A support member 20 extends between the upper oscillatory end 8 and lower oscillatory end 12. Attached to the support member 20 is a wheel support member 22 to which a wheel 24 is attached so that the wheel 24 rests on the ground 26. A first dashed line 28 represents a line running through the centre of the wheel 24 which is perpendicular to the ground 26. A second dashed line 30 represents an extrapolation of the plane of the support member 20 when the vehicle is at rest on level ground. The wheel-support angle 32 represents the angle between the second dashed line 30 and the first dashed line 28. The ground offset distance 34 is the horizontal distance between the first dashed line 28 and the second dashed line when each line is extrapolated to intersect with the ground 26. The wheel offset 36 is the horizontal distance between the centre of the wheel 26 and the support member 20.

The camber angle of the wheel 24 is defined as the angle between a radial line passing through the edge of the wheel 24 and a vertical line. The depiction in Fig. 1 shows no appreciable camber.

It will be appreciated that the orientation of the wheel 24, along with its camber angle and roll centre will vary as the wheel passes over uneven ground 26. The first height 16, second height 18 and the length of the support 20 are chosen in order to give the desired orientation characteristics of the wheel 24. The first height 16, second height 18 and length of support 20 ensure that at rest the suspension 2 is in the configuration seen in Figure 1, i.e. the support 20 is angled away from the wheel 24, the upper oscillatory end 8 is angled upwards and the lower oscillatory end 12 is angled towards the ground 26. Setting up the suspension 2 in this way helps to achieve the desired wheel 24 characteristics when the wheel 24 passes over uneven surfaces. The wheel-support angle 32 is determined by the angle of the support member 20. The ground offset distance 34 and the wheel offset 36 are determined by the length of the wheel support member 22 and the angle of the support member 20. These parameters are tuned depending on the specific application of the suspension system. However, generally it is desirable that the ground offset distance 34 and wheel offset 36 are minimised as they directly affect steering feel. If the suspension is supporting a wheel which is driven, the ground offset distance 34 is preferably negative. Whilst the wheel- support angle 32 may vary depending on the desired steering feel, the desired amount of camber with steer, the amount of camber with steer, the chassis height with steer and tyre loading with steer, the wheel-support angle 32 maybe around 8 degrees.

Figure 2 shows an end view of the wheel 24 viewed from the inside-out, i.e. from the chassis looking out towards the wheel. A vertical line 38 represents a vertical bisecting plane that runs through the centre 39 of the wheel 24. A third dashed line 40 represents the line of the support member 20 when viewed from the angle shown in this Figure. The castor angle 42 is the angle between the third dashed line 40 and the vertical plane 28. The castor offset 44 is the horizontal distance between the centre of the wheel 24 and the support 20. The mechanical trail 46 is the perpendicular distance from the third dashed line 40 and the point at which the wheel 24 intersects the ground 26. The castor trail 48 is the distance along the ground 26 between the point of intersection of the wheel 24 and the ground and the point of intersection between the third dashed line 40 and the ground 26. It can be seen that by offsetting the upper control arm 4 and lower control arm 6 longitudinally, the castor angle 42 can be determined as required so that the desired wheel centring and steering feel can be achieved and may be set at, for example, approximately 3 degrees. The offset is adjusted so that a lower ball joint 50, which connects the lower control arm 6 and support member 20, is ahead of an upper ball joint 52, which connects the upper control arm 4 and support 20. This is particularly advantageous when used on the front wheels of a vehicle.

Figure 3 shows a perspective view of a vehicle chassis 54 in accordance with the present invention. It can be seen that the upper control arm 4 is attached to upper mounting points 56 on the chassis 54 and the lower control arm 6 is attached to lower mounting points 58. The upper control arm 4 and lower control arm 6 also both comprise a cross member 60. A coiled spring 66 is positioned between the upper control arm 4 and the chassis 54. A shock absorber 68 is connected to the lower control arm 6 and to the chassis 54. Further shown is a steering wheel 70. The steering wheel 70 is operatively connected to the steering arms 72 which are connected to the wheel mount 74. The support 20 connects the upper control arm 4 and lower control arm 6.

When the vehicle passes over uneven ground a wheel may be displaced vertically upwards causing the control arms 4, 6 to pivot about their attachment points 56, 58. As the wheel is displaced vertically upwards the upper control arm 4 pivots upwards such that it causes the spring 66 to compress. As the upper control arm 4 pivots upwards, the lower control arm 6 is brought upwards by the support member 20 which connects the two control arms 4, 6. As the lower control arm 6 is brought upwards its motion is resisted by the spring 66. The shock absorber 68 damps the motion of the lower control arm 6, and thus the upper control arm 4. The spring 66 resists the motion of the control arms 4, 6 and provides a restoring force to move the control arms 4, 6 into their rest position. As the wheel is displaced by the uneven ground the control arms 4, 6 both pivot upwards, and then as the ground evens out the spring 66 forces the control arms 4, 6 back into their rest position.

It will be appreciated that when the wheel passes over a protrusion in the ground it will be forced upwards and thus cause the spring 66 to compress. However, the wheel may pass over cavities in the ground at which point the spring 66 expands further so that the wheel remains in contact with the ground. As the wheel moves downwards the shock absorber 68 still damps the motion of the wheel ensuring that a smooth ride is provided.

Figure 4 shows a front view of the vehicle. Here it can be seen that the upper mounting point 56 and lower mounting point 58 are offset with respect to the vertical line A-A, i.e. they are offset along a lateral/transverse direction of the chassis. By offsetting the mount points 56, 58, the position of the arc that each control arm 4, 6 travels along can be adjusted. By adjusting the position of the arcs the kinematics of the wheel can be controlled. The length of the support member 20 is also apparent in this Figure. It can be seen that the length is chosen such that in the rest position the lower control arm 6 is angled downwards, the upper control arm 4 is angled upwards and the support member 20 is angled towards the vehicle chassis 54. Similarly to choosing suitable positions for the mounting points 56, 58, by choosing the right length of the support 20, the point along the arc at which the upper oscillatory end 8 and lower oscillatory end 12 start in the rest position can be determined. By adjusting the start position of each oscillatory end 8, 12 it is possible to control the wheel kinematics.

Figure 5 shows a top view of the vehicle chassis 54. This Figure also demonstrates how the upper mounting point 56 and lower mounting point 58 are offset with respect to the vertical line A-A, i.e. they are offset along a lateral/transverse direction of the chassis. In addition to this, the mounting points 56, 58 are also offset with respect to the line B- B, i.e. they are offset along a longitudinal direction of the chassis. This longitudinal offset sets the castor angle previously discussed with respect to Figure 2.

Figure 6 shows an end on view of the suspension system viewed from the wheel attachment point 74. It can be seen how the control arms 4, 6 are designed so as to incorporate the other component of the vehicle, for example, the spring 66 and shock absorber 68. It is also seen that the control arms 4, 6 are able to accommodate the steering arm 72. Whilst only the chassis 54 of a single axle has been shown so far it will be appreciated that the arrangement of identical control arms 4, 6 can be used at any point on a vehicle. Typically torque is split unevenly between the front and rear wheels on a vehicle. When a torque is applied to the wheels it can cause the vehicle to 'squat', i.e. the front of the vehicle raises and the rear lowers. By carefully tuning the positioning of the upper control arm 4 and lower control arm 6 on both the front and rear wheels it is possible to minimise the amount to which the vehicle 'squats'. Similarly when a vehicle is braked, the vehicle maybe caused to 'dive', again the positioning of the upper control arm 4 and the lower control arm 6 can be tuned to minimise the negative affects of this characteristic. The 'squat' derivation can be determined using Figure 7. If no anti-squat or anti-dive effects are implemented when a longitudinal force is applied at the wheel contact patch, there will be no vertical movement of the wheel. This would be the case if the control arms 4,6 were parallel. By tuning the position of the mounting points and the control arms 4, 6, the planes projected through the control arms 4, 6 will intersect and this results in anti-squat or anti-dive characteristics. In this instance when a longitudinal force is applied at the wheel contact patch, this will result in a vertical displacement of the wheel. Anti-dive may be used on the front of the vehicle and anti- squat would be used at the rear of the vehicle. On the front suspension setup the lower wishbone rear pickup point is raised, and on the rear suspension, the lower wishbone front pickup point is raised. Figure 7 shows a table detailing various geometric parameters of three different suspension systems. The first column provides a brief description of the types of geometric parameters, the second column provides the units for each parameer, the third column provides data for a suspension system according to the prior art in which the upper and lower wishbones are of a different length, the fourth column provides data for the suspension system of column three which has been modified to fit a particular vehicle, column five shows the data for a suspension system according to the present invention in which the upper and lower wishbones are identical in length and are fitted to the same vehicle as the one used for the data in column four and column six provides the target values for each specific parameter. The table illustrates data relevant to the front suspension of the particular vehicle.

The first set of geometric parameters indicated by 'STATIC GEOMETRY provide information as to the geometric parameters and features of the system when it is static, i.e. not under a load. The second set of parameters indicated by 'KINEMATIC

GEOMETRY provide information relating to the suspension system as it experiences a load.

Referring first to the parameters of the 'STATIC GEOMETRY', it can be seen that many of the parameters of the suspension system according to an embodiment of the present invention are similar to and often improved, when considering the target parameters, over the prior art systems. For example, the caster angle of the suspension system according to the present invention is closer to the target value that the prior art systems. Referring to the 'KINEMATIC GEOMERTY parameters, it can be seen that the parameters of the suspension system according to an embodiment of the present invention are generally similar to the prior art systems. For example, it can be seen that camber gain is within the specified target range. In fact, the camber gain is less than the camber gain of the prior art systems, and thus the tyre wear may be reduced. As explained previously this is particularly advantageous, especially for commercial vehicles. The fact that the suspension system according to the present invention, which utilises an identical upper and lower wishbone, displays similar geometric properties to prior art systems, and in some aspects improves over them, proves the usability of such a system.