Motor vehicle wheel suspension

Land vehicles – Wheeled – Running gear

Patent

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Details

280675, B60G 702

Patent

active

044589158

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

This invention relates to motor vehicle wheel suspensions, and is of particular utility in independent steerable front wheel suspensions.
A major problem with all front wheel suspensions is known in the industry as "shimmy". This is caused inter alia by the front wheels or a front wheel being out of balance. In the remainder of this specification reference will be made to one wheel, it being understood that similar considerations apply to the corresponding road wheel at the other side of the vehicle. Rotation of an out of balance wheel creates an out of balance force directed radially of the wheel and rotating with the wheel. At certain critical vehicle speeds, hereinafter called "critical wobble speed", typically about 25 m.p.h., about 55 m.p.h., and about 85 m.p.h., a resonant condition occurs and the wheel oscillates in a certain mode characteristic of the suspension. The base frequency of this oscillation is of the order of 10 Hz with harmonics at approximately 5 and 18 Hz. The lower the frequency the greater the amplitude of the oscillation; and the higher the frequency the lower the amplitude. In most known front suspensions, these oscillations are transmitted through a steering linkage and steering mechanism to the steering wheel, and this causes discomfort to the driver. In order to avoid this problem, it is known to carefully balance the wheels but this solution requires additional operation during vehicle manufacture and rebalancing of the wheels in service as the tires wear or are replaced or the balancing weights are lost.
It is therefore an object of the present invention to provide an improved vehicle wheel suspension which will be tolerant of wheel imbalance so that wheel balancing is either avoided completely or is necessary less frequently or is required to less accurate standards.
We have realised and confirmed by experiment and calculation that the wheel oscillations caused by the rotating out of balance forces are of limited amplitude even if the wheel is substantially free to move longitudinally of the vehicle. As the wheel is displaced forwardly by the unbalance force it tends to turn inwardly (toe in) and as the wheel is displaced rearwardly it tends to turn outwardly (toe out), because the unbalance forces when acting forwardly or rearwardly have a turning movement about the king pin axis of the wheel. The magnitude of toe in and toe out movement caused by the out of balance forces is greater in suspensions with a large offset from the king pin axis.
The present invention utilises a novel compliance device in combination with appropriate modification of the geometry of the suspension to reduce, not the oscillations, but the transmission of them to the steering wheel or in the case of a rear suspension, to the body.
It is well known to fit a "compliance device" in the suspension of a motor vehicle. This device provides a resilient connection of the wheel to the vehicle and is intended to reduce noise, vibration and harshness transmitted to the sprung part of the vehicle from the road surface.
The novel compliance device of the invention permits limited forward and rearward displacement of the wheel spindle relative to the vehicle. Its longitudinal resistance for such limited forward and rearward displacement must be proportionately less than that required to overcome the friction in the steering gear linkage.
Hitherto the steering link and suspension arm have in many vehicles approximately constituted a parallelogram (that is the pivot points of the steering link and suspension arm and their respective connections to the wheel are at the four corners of the parallelogram) so that as the wheel is displaced longitudinally as permitted by the compliance device the road wheel is not turned. In some vehicles the steering link and suspension arm have not constituted a parallelogram. This has not been to achieve any special result but has been dictated by package requirements.
In the case of rear wheel suspensions, the oscillations of the rear wheels due to the wheels being out

REFERENCES:
patent: 3178202 (1965-04-01), Kozicki
patent: 3942815 (1976-03-01), Schwenk et al.
patent: 4273356 (1981-06-01), Sakata et al.

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