Gearbox assembly for an electric power steering assembly

Abstract

A gearbox assembly for an electric power assisted steering apparatus. The assembly comprises a gearbox housing which houses a worm shaft and a gear wheel, the worm shaft being supported relative to the housing by a main bearing assembly at an end closest to the motor and by a tail bearing assembly, at an end furthest from the motor, comprising an inner race and an outer race separated by bearing elements. The gearbox assembly further comprises a first guiding surface upon which the outer race is supported, the outer race being able to move by rolling along the guiding surface when a radial load is applied to the tail bearing assembly by the worm shaft, and a guide device which contacts both the outer bearing and a second guiding surface, the biasing spring acting upon the tail bearing assembly indirectly by acting upon the guide device which in turn acts upon the bearing assembly. The gear wheel i supported by an output shaft having at least one end that provides a take-off from the gearbox assembly. The tail bearing assembly is free to move relative to the housing through a limited range of motion that enables the worm shaft to move radially away from the axis of the wheel gear. The apparatus further includes a biasing spring that applies a biasing force to the tail bearing assembly that biases the worm shaft into engagement with the wheel gear.