ELECTRIC POWER STEERING

摘要

An electromagnetic apparatus, such as an electric power assisted steering system (1), comprising: a mechanical component (5) having a limited range of travel having at least one end position and a motor (6) arranged to apply a force to the mechanical component (5) to cause it to move along its range of travel, in which the motor comprises at least three phases each comprising a phase winding, a rotor and drive circuitry to supply drive currents (12, 13, 14) to each of the phases dependent upon the position of the rotor relative to the phase windings, and in which the apparatus is arranged such that when the mechanical component (5) is at an end position in use, the magnitude of the drive current supplied to at least one phase of the motor (6) is substantially at a minimum, and in which the drive circuitry is arranged so as to provide, in use, cyclic drive signals to each phase as the rotor rotates, where the drive signals applied to each phase are out of phase with the drive signals provided to other phases.