Patent Application
20220001712
This invention relates to a suspension and drive mechanism for a steerable wheel of a vehicle. In particular, the invention is described with reference to an electrically powered vehicle.
Implementation of electrically powered vehicles for widespread road transportation presents numerous opportunities and challenges in vehicle design and engineering, even more so when considering fully- or semi-autonomous electric vehicles. One of the overriding opportunities is in exploiting potential efficiencies available to electrically powered vehicles. Some of the ways that electric road vehicles can be made to operate in a more efficient manner includes reducing overall vehicle weight, optimising efficiency of conversion from stored energy to vehicle movement (i.e. drivetrain efficiency), and optimising vehicle body size and interior space available for a given platform.
Electric drive units (drive assemblies) suitable for propelling road vehicles allow for greater flexibility in placement of the motor or motors within the vehicle. Whereas the size and complexity of an internal combustion engine requires the engine to be generally centralised (at least laterally) and drive two or more wheels through a mechanical transmission, more compact electric motors can be distributed in various ways within the vehicle structure. For example, a four wheel electric road vehicle may have an electric drive unit incorporated into each of the front and/or rear wheel assemblies, to drive the front and/or rear wheels directly. This arrangement can lead to enhanced efficiency through reduced mechanical transmission losses, as well as lower vehicle weight through reduced powertrain componentry.
Additionally, the two or four wheels on a vehicle used for steering require a substantial amount of space within the vehicle body envelope due to the arc of travel of the wheels as they travel from lock to lock according to the steering wheel input. This is particularly true with vehicle fitted with direct drive wheel motors fitted within the wheel that can limit the optimal placement of the steering pivot points.
When viewed from above, the envelope a wheel requires to steer is determined by the distance from the outermost point on the wheel to the pivot point, often known as the virtual king pin, about which the wheel assembly rotates during steering input.
If this pivot point ran through the centre of the tyre in a vertical plane then this distance would be minimised as the tyre would spin on its own axis, and the envelope required would also be at a minimum. In practice, it is difficult locate the pivot points in this position and for a conventional vehicle this placement gives rise to a range of poor vehicle handling characteristics, such as no self-centering and limited driver feedback.
Therefore the pivot point usually sits adjacent to the inside edge of the wheel defined by the king pin or steering arm location which means that the envelope required is not minimised due to the need to trade-off this space for vehicle steering and handling dynamics.
Ackermann steering takes this concept further by separating the steering movement into two pivots, one near the hub of each wheel to minimise tyre scrubbing during steering.
Suspension movement then introduces variations in camber and in directional alignment (toe-in or toe-out) to complicate this basic steering geometry, which is further compounded by castor angle, camber angle, king-pin inclination, and offset or scrub radius. Each one of these adjustments is designed to introduce or reduce certain vehicle handling characteristics at all expected vehicle speeds. Often any poor handling characteristics are amplified by the speed the vehicle is travelling at.
The combination of all these factors result in a significant area that needs to be provided for under the vehicle body to ensure the wheels can move freely from lock to lock without any binding against the vehicle chassis or bodywork.
Castor angle is introduced into traditional steering mechanisms to promote a degree of “self-centring” action into the steering. This helps with directional stability of the vehicle and reduces wandering. Improper castor settings will require the driver to move the steering wheel both into and out of each turn, making it difficult to maintain a straight line.
When vehicles are fitted with an electronically actuated steering configuration that is required for full autonomous control, the actuation of the steering input can fight with the natural self-centring behaviour giving rise to a hysteresis effect, especially as the vehicle returns to straight line direction from a turn. There is then a trade-off between how much the steering response is dampened to reduce the overshoot with the dynamic response of the steering to turn the vehicle quickly.
The overall dimensions of the vehicle become important for a range of reasons. With electric vehicles there are thresholds around speed of travel and size of vehicle that then dictate what design and compliance standards apply. It is challenging to maximise interior space while maintaining a compact vehicle size. Therefore, minimising the intrusion of wheel arches and the overall wheel envelope into the passenger area becomes vital to ensure the interior space can be fully utilised.
In consideration of the above, embodiments of the present invention aim to provide an improved suspension and drive mechanism for a steerable wheel of a vehicle, particularly insofar as applied to autonomous electric road vehicles.
In accordance with an aspect of the present invention consists of a suspension and drive mechanism for a steerable wheel of a vehicle, comprising:
Preferably said control arms are arranged to minimise the envelope within which said wheel requires to steer.
Preferably said control arms are arranged such that said virtual steering pivot axis remains substantially vertical above the contact patch of said wheel to minimise envelope within which said wheel requires to steer.
Preferably at the end of the steering rotation of said wheel said virtual pivots are substantially vertically above the centre of the contact patch of said wheel to minimise envelope said wheel requires to steer.
Preferably said virtual steering pivot axis point of contact with the ground translates backwards for the outside wheel of turn and translates forward for the inside wheel of turn relative to said wheel during steering to minimise envelope said wheel requires to steer.
Preferably the castor axis point of contact with the ground for said wheel can remain in substantially the same position when said wheel is straight or turned.
Preferably the virtual steering pivot axis change reduces vehicle drop effect and thereby reduces self-centering effects of the steering to minimised.
Preferably the varying of said virtual steering pivot axis reduces vehicle body roll effects by lifting the outside of said wheel in a turn.
Preferably in another embodiment said front and rear upper control arms are replaced by a wishbone suspension arm.
Preferably in another embodiment said front and rear lower control arms are replaced by a wishbone suspension arm.
Preferably in a further embodiment said front and rear upper control arms are replaced by a suspension strut rigidly attached to said wheel support assembly.
The advanced steering and suspension geometry allows for effective vehicle space utilisation for application in electric vehicles with two or four wheel that pivot for steering.
In embodiments the suspension mechanism is adapted for use with electric vehicles employing an in-wheel electric drive unit wherein space within the vehicle wheel that may ordinarily be utilised for placement of suspension couplings is constrained by placement of the in-wheel electric drive unit. The electric drive unit may include, but is not limited to a brake, gearbox, motor controller, cooling system as part of the assembly.
Embodiments of the invention aim to provide an advanced electric vehicle wheel suspension and steering geometry designed to minimise the space required to accommodate the wheels being steered within the vehicle body envelope. This disclosed system utilises advanced kinematic principles to introduce a variable pivot point which moves to ensure the resultant wheel position is at the most favourable location within the vehicle body envelope as the wheel moves through its arc during full lock to lock travel for a given steering angle.
By utilising a five-link suspension configuration, the length and connection points of each suspension element can be chosen to vary the virtual pivot point depending on how much steering angle has been introduced. A pair of lower suspension control arms and a pair of upper suspension control arms are combined with the steering arm to support and control the wheel position.
When viewed from above the virtual pivot point moves in a non-linear path of varying radius to optimise the wheel location within the vehicle body envelope. At the same time the rate of change of the Ackerman geometry is controlled for a given turn angle whilst maintaining control over castor/bump steer and other suspension dynamics.
The length of each control arm and the offset and location of the pivot point is carefully chosen to avoid any over travel, over centre or binding of the control arms.
Extrapolation of the upper and lower control arms create their own virtual pivot points at the effective intersection thereof, with a line between the virtual pivot points representing a virtual and variable king pin axis.
By adopting its most favourable position relative to the vehicle's body at any point of its travel, the envelope required to accommodate the wheel underneath the vehicle's body is reduced, allowing for highly efficient space utilisation, with resultant reduction in vehicle body size and overall weight.
A further refinement can be implemented for low speed autonomous vehicles wherein the geometry of the five-link suspension may be adjusted to remove any tendency to self-centre, whilst retaining its directional stability regardless of the steering angle. Coupling this suspension with an autonomous control allows for smooth operation of the steering especially back to centre with no noticeable hysteresis or overshot in steering wheel turn angle.
Further disclosure, objects, advantages and aspects of the present invention may be better understood by those skilled in the relevant art by reference to the following description of preferred embodiments taken in conjunction with the accompanying drawings, which are given by way of illustration only and thus not limitative of the present invention, and in which:
An embodiment of an electric vehicle suspension and steering system is described hereinbelow with reference to the accompanying drawings. The suspension system as disclosed herein addresses:
An elevated front perspective view of the suspension system according to an embodiment of the invention is shown in
Suspension assembly 40 shown in
Suspension assembly 40 comprises upper and lower pairs of control arms that couple the chassis 18 to the upright 22. Specifically, front and rear upper control arms 55, 50 couple the chassis to the upright above the rolling axis of the wheel, in use, and front and rear lower control arms 65, 60 couple the chassis to the upright below the wheel rolling axis. Front and rear upper control arms 55,50 have respective chassis mounts 56, 51 which incorporate ball joints to allow articulated movement of the control arms relative to the chassis mounts. The other ends of the front and rear upper control arms are coupled to upright 22 at mounts 57, 52 which also include ball joints. The front and rear lower control arms are similarly arranged below the wheel rolling axis, with respective chassis mounts 66, 61 and upright mounts 67, 62. A suspension strut assembly 80, for example including one or more springs and dampers, has a lower end coupled to the front lower control arm 65 at 84 and an upper end in use coupled to the chassis at 82. A steering arm 70 is also provided, extending between a steering control assembly 72 and a ball joint coupling 71 to the upright 22. The steering arm upright coupling 71 is positioned intermediate the upper and lower control arm mounts and offset from in a forward direction therefrom.
In this exemplary embodiment the upper and lower pairs of control arms are arranged in a substantially similar configuration, respectively above and below the wheel rolling axis. This arrangement is such that the upper and lower pairs of control arms each establish a respective virtual pivot point, wherein a line between these virtual pivot points represents a virtual and variable king-pin axis or steering axis.
The effects of the suspension and steering geometry enabled by the suspension assembly according to embodiments of the invention are illustrated diagrammatically in
In
As well as addressing control and handling characteristics that may be applicable to autonomous vehicles, the suspension system according to embodiments of the invention can be used to optimize vehicle body allowances for steered wheel pivoting. This effect is illustrated in
When viewed from above, the envelope a wheel requires is determined by the distance from the outermost point on the wheel to the pivot point, often known as the virtual king pin, about which the wheel assembly rotates during steering input. If this pivot point ran through the centre of the tyre in a vertical plane then this distance would be minimised as the tyre would spin on its own axis, and the envelope required would also be at a minimum. In practice, having the pivot point fixed in this position would traditionally be seen to provide a range of poor vehicle handling characteristics, but can be well suited to an automated steering vehicle. Therefore, the pivot point usually sits adjacent to the inside edge of the wheel defined by the king pin or steering arm location which means that the envelope required is not minimised due to the need to trade-off this space for vehicle steering and handling dynamics. The suspension and steering system as described herein, however, is able to optimize the vehicle body envelope required to accommodate the steered wheels while maintaining favourable vehicle handling characteristics.
Also of note in the
What should be understood is that a “virtual pivot axis” is created by a line passing through two (upper and lower) virtual pivot points. With reference again to
Another feature is that of self-levelling or jacking achieved through the geometry of the suspension mechanism in combination with the mounting position of suspension strut 80 to lower control arm 65 as shown in
In the abovementioned embodiment, vehicle 10, has four steerable and electrically driven wheels 14,16. However, it should be understood that in a not shown embodiment, the vehicle may only have two of its wheels steerably and electrically driven.
The structure and implementation of embodiments of the invention has been described by way of non-limiting example only, and many additional modifications and variations may be apparent to those skilled in the relevant art without departing from the spirit and scope of the invention described.
Any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material forms part of the prior art base or common general knowledge in the relevant art in Australia or elsewhere on or before the priority date of the disclosure and claims herein.
Throughout this specification and the claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018904353 | Nov 2018 | AU | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/AU2019/000142 | 11/15/2019 | WO | 00 |
