Torque sensors

Abstract

A torque sensor for use in an electric power assisted steering system comprises a first shaft, a second shaft, and a torsion bar, a hollow sleeve that is secured to the first shaft and extends along the torsion bar to at least partially axially overlap the second shaft, angular deflection indicating means that produce a signal that is dependent on the angular deflection of the first shaft relative to the second shaft as a torque is applied across the torque sensor that causes the torsion bar to twist, at least one drive dog fixed to the sleeve and at least one corresponding drive dog fixed to the second shaft, in normal operation the two dogs being offset so that they permit a defined range of angular deflection of the torsion bar but will engage each other to provide a path for torque to be transferred from the first shaft to the second shaft in the event of a failure of the torsion bar, and a connecting element which has a first part that is secured within a bore in one of the second shaft and the sleeve, the connecting element having a second part that extends into a feature of the other of the second shaft and the sleeve, at zero torque across the torque sensor the connecting element being spaced circumferentially from the feature by an angular distance greater than the spacing between the drive dogs and spaced from the feature in a direction along the axis of the shafts that is less than the overlap of the drive dogs in that direction to prevent the shafts moving apart in the event of failure of the torsion bar by an amount that would otherwise prevent the drive dogs engaging.