Power assisted steering mechanism

A power assisted steering mechanism for a vehicle, the mechanism including electrically powered drive means for driving the steering mechanism, the drive means including a drive shaft having an input shaft portion drivingly connected to an output shaft portion by resilient means such that rotation of the input shaft portion causes relative rotational displacement between the input shaft portion and the output shaft portion in dependence on the load applied to the output shaft portion, sensor means arranged to produce signals in response to the direction and amount of relative displacement between the input and output shaft portions and an electric motor for driving said output shaft in response to the signals produced by the sensor means, the sensor means comprises a magnetic inductance sensor including an annular core formed of a magnetic material which is arranged to be co-axial with the input and output shaft portions, the core having an annular air gap to define opposed sets of poles on opposite sides of the air gap, a magnetic generating coil operable to generate flow of magnetic flux through the core and between the opposed sets of poles, one of the sets of poles including at least two concentric sensor poles having associated inductance coils for sensing flow of magnetic flux through the associated sensor pole, and a pair of groups of radially extending vanes located within said annular air gap, one group of vanes being mounted on the output shaft portion and the other groups of vanes being mounted on the input shaft portion, the vanes being made of a magnetic material and serving to conduct magnetic flux between the opposed sets of poles, the vanes of one group being axially spaced from the vanes of the other group and being arranged such that on movement of the input shaft portion relative to the output shaft portion consequential relative movement of the groups of vanes causes the impedance across the air gap to alter and cause a greater or lesser amount of the magnetic flux to flow through one or other of the sensor poles.