US 8,751,111 B2 · Controlling motors in electric power assisted steering systems

Abstract

A method of controlling an electric motor in an electric power assisted steering system, the motor being arranged so as to apply a force to part of a steering mechanism of a vehicle, in which the method comprises calculating a force demand indicative of an assistance force dependent upon the torque applied by a user (TD) to the steering mechanism that it is to be applied to the steering mechanism to reduce the exertion required by the user to steer the vehicle; combining the force demand with an overlay force demand (TER) indicative of a force which it is desired to overlay over the assistance force, to generate a combined assistance force (TA); and controlling the motor according to the combined assistance force, such that together with the force applied by the user, a total force is applied to the steering mechanism, in which, in order to generate the combined assistance force the torque applied by the user is subjected to a non-linear boost function and in which the overlay force demand is combined with the force demand such that, for an arbitrary change in the overlay force demand the change in the total force is independent of the torque applied by the user over a range of torques applied by the user.

Claims29

Dependent claims

calculating a force demand indicative of an assistance force dependent upon a torque applied by a user to the steering mechanism that is to be applied to the steering mechanism to reduce the exertion required by the user to steer the vehicle;
combining the force demand with an overlay force demand, the overlay force demand being indicative of a force which is desired to overlay over the assistance force, to generate a combined assistance force;
and
controlling the electric motor according to the combined assistance force, such that together with a force applied by the user, a total force is applied to the steering mechanism, wherein, in order to generate the combined assistance force,
the torque applied by the user is subjected to a non-linear boost function, and further wherein
the overlay force demand is combined with the force demand such that, for an arbitrary change in the overlay force demand, a change in the total force is independent of the torque applied by the user over a range of torques applied by the user.

3 more elements

An electric power assisted steering system comprising:

a steering wheel;
a steering mechanism which operatively couples the steering wheel to road wheels of a vehicle;
an electric motor that applies a force to part of the steering mechanism;
a torque sensor that provides a torque signal indicative of a torque carried by part of the steering mechanism;
and
a control unit that controls the motor by generating a force demand signal indicative of an assistance force, dependent upon the torque signal, that is to be applied to the steering mechanism to reduce an exertion required by a user to steer the vehicle,
the control unit having an input for the torque signal and an input for an overlay force demand signal being indicative of a force which it is desired to overlay over the assistance force,
the control unit including a boost unit that applies a non-linear boost function to the torque signal, and
the control unit also combining the torque signal and the overlay force demand signal to create a combined assistance force signal so as to control the electric motor such that a total force including the combined assistance force and the force applied by a user is applied to the steering mechanism such that, for an arbitrary change in the overlay force demand signal, the change in the total force is independent of the torque applied by the user over a range of values of the torque applied by the user.

6 more elements

Dependencies are inferred from the claim text.

Controlling motors in electric power assisted steering systems

Life of this patent

Controlling motors in electric power assisted steering systems

Life of this patent

Abstract

Claims29