It is known to provide an electrically actuated steering assembly which employs an electric motor as a source of assistance torque for the driver. This is connected to a steering column via a gearbox. The electric motor, its associated drive and control circuit, and the gearbox, can be mounted upon the steering column shaft so that the shaft supports the weight of the assembly. The steering column and gearbox may form a single steering column assembly.
It is also known that the steering column can be fixed to the vehicle body by means of a substantially horizontal pivot which has its axis of rotation substantially perpendicular to the axis of the steering column shaft. The steering column can thus be tilted about the pivot so as simultaneously to enable height and rake adjustments of the steering wheel to be achieved. The use of such a simple pivoting steering column is well known in the art.
A problem arises when the use of a tiltable steering column is combined with an electrically actuated steering assembly. The motor applies an assistance torque to the steering column via the gearbox as required but, in doing so, generates a reaction torque which must be absorbed through the pivot into the vehicle body. Due to cost restraints during design, there is often a degree of free play in the pivot, and the effect of the reaction torque is to cause the steering column to move slightly about the pivot pin. This movement can produce unwanted noise and vibration in the steering column, for example whenever the torque of the motor varies.
One solution to the problem of reacting the torque generated by the motor would be the use of high precision bushings or by ensuring that there is no clearance at the pivot. However, this use of "over-engineering" to remove the symptoms of vibration does not effectively remove the source of the problem, and the problem would re-appear with wear of the pivot bushes.
USPTO Backgrounds
USPTO Backgrounds