Electrical power assisted steering system
AssigneeZF Automotive UK Limited
InventorsTim Sworn, George Dibben, Kannan Natesan, Birk Junghanns
Life of this patent
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Abstract
An electric power assisted steering assembly comprises a steering mechanism which operatively connects a steering wheel to the roadwheels of a vehicle, a sensor adapted to produce a first output signal indicative of the torque carried by a portion of the steering mechanism and to produce a second output signal indicative, an electric motor, a signal processing unit having a lead-lag filter to produce an overall torque demand signal, and a motor drive stage adapted to provide a drive current to the motor responsive to the torque demand signal.
Claims7
An electric power assisted steering assembly comprising:
- a steering mechanism which operatively connects a steering wheel to roadwheels of a vehicle;
- a first sensor adapted to produce a first output signal indicative of a torque carried by a portion of the steering mechanism;
- a second sensor adapted to produce a second output signal indicative of an angular velocity of the portion of the steering mechanism, wherein the first and second sensors are one of implemented in a single sensor device or as separate sensor devices;
- a speed sensor adapted to produce a third output signal indicative of a speed of the vehicle;
- an electric motor operatively connected to the steering mechanism;
- a signal processing unit being configured to:
- receive the first, second, and third output signals;
- produce an assistance torque component based on the first output signal;
- apply the second output signal to a filter to produce a damping component equivalent to a filtered first column velocity signal, wherein the filter comprises a gain term constant, a pole and a zero, the gain term constant is set based on the speed of the vehicle, and wherein one of a corner frequency of the pole is set greater than a corner frequency of the zero so that the filter functions as a lag filter or the corner frequency of the zero is set greater than the corner frequency of the pole so that the filter functions as a lead filter;
- determine an overall torque demand representative of a torque to be a applied to the steering mechanism by the motor by subtracting the damping component from the assistance torque component;
- and
- a motor drive stage adapted to provide a drive current to the electric motor based on the determined overall torque demand.
A method of producing a damping component for use in an electric power assisted steering system, the method comprising the steps of:
- receiving an output signal indicative of a torque carried by a portion of a steering mechanism that operatively connects a steering wheel to roadwheels of a vehicle;
- receiving a second output signal indicative of an angular velocity of the portion of the steering mechanism;
- receiving a speed signal generated by a speed sensor indicative of a speed of the vehicle;
- producing an assistance torque component based on the first output signal;
- applying the second output signal to a filter to produce the damping component, wherein the filter comprises a gain term constant, a pole and a zero, the gain term constant is set based on the speed of the vehicle, and wherein one of a corner frequency of the pole is set greater than a corner frequency of the zero so that the filter functions as a lag filter or the corner frequency of the zero is set greater than the corner frequency of the pole so that the filter functions as a lead filter;
- subtracting the damping component from the assistance torque component to produce an overall torque demand;
- and
- applying an overall torque demand signal representative of the overall torque demand to the steering mechanism, wherein the overall torque demand signal is applied by a motor.
Dependencies are inferred from the claim text.