Patent ID: 8695751
Filing Date: 2014-04-15
Classification: B62D,F16H,Y10T

Abstract:
1. A gearbox assembly for an electric power steering apparatus comprising: an electric power assisted steering system comprising a housing, an electric motor fixed relative to the housing having a stator and a rotor, an input shaft operatively connected to the rotor, the input shaft supported at a first end furthest from the motor by a first bearing means and at a second end by a second bearing means, an output shaft operatively connected to a steering column which carries a wheel gear which is fixed relative to the housing and which meshes with a worm gear, and a torque sensor adapted to produce an output signal indicative of the torque in the output shaft, the motor being adapted to apply a torque to the output shaft dependent upon the output signal from the torque sensor, and in which the worm gear provided on the input shaft is adapted to mesh with a wheel gear on the output shaft, further comprising resilient biasing means adapted to act upon the first bearing means to bias the input shaft towards the wheel gear; in which the biasing means comprises a spring assembly which acts between the housing and the first bearing means, in which in a neutral position of the gearbox assembly the worm gear and wheel gear are fully engaged and the spring assembly applies a biasing force onto the first bearing means in a first direction away from the neutral position so as to ensure that the worm gear and wheel gear are fully engaged, the spring assembly also providing a resisting force against movement of the first bearing means in a second direction, opposed to the first direction, in the event that the worm gear and wheel gear try to disengage, wherein the spring assembly has a spring rate which has a step change about the neutral position such that the rate of change in the force exerted by the spring assembly on the first bearing means as the spring assembly moves in the first direction from the neutral position is lower than the rate of change in the force as the spring assembly moves in the second direction away from the neutral position.