Electric power assisted steering system

A control system for use with an electrical power assisted steering system including a center tapped battery having a first terminal with a voltage above the voltage at the center tap and a second tap having a voltage below the voltage at the center tap, a bi-directional electric motor having two terminals, one terminal being connected to the center tap of the battery, and an operator controlled steering mechanism coupled to the motor so that torque from the motor assists in turning the steering mechanism, the control system comprising:

• sensor means for sensing the displacement and direction of the rotation of the steering mechanism;
• first switching means electrically connected between one terminal of the battery and the first terminal of the motor to permit energization of the motor in a first direction;
• second switching means electrically connected between the other terminal of the battery and the second terminal of the motor to permit energization of the motor in a direction opposite said first direction;
• and
• control means responsive to the sensor means, for selectively energizing either said first switching means or said second switching means to energize the motor to turn in a direction to provide power assist to the operator, and including a means for generating a pulse width modulated signal to the selected switching means, said selected switching means operative to energize the motor to develop torque proportional to the width of the pulse signals.

An electrical power assisted steering system for a wheeled vehicle comprising:

• operator controlled steering mechanism;
• a steering shaft connected between the steering mechanism and at least one steerable wheel of the vehicle;
• a battery having a first terminal at a positive voltage, a second terminal at a ground voltage, and a center tap;
• a permanent magnet electric motor coupled to a steering shaft to apply torque to the steering shaft to turn the steerable wheel, the motor having two terminals, one of said terminals being electrically connected to the center tap of the battery;
• a sensor mounted between the steering mechanism and the steering shaft to sense the displacement and direction of rotation of the steering mechanism and to generate signals proportional thereto;
• means for sensing the speed of the vehicle;
• means for sensing the current flowing through the motor;
• a control circuit for generating a pulse width modulated signal, the pulse width being directly proportional to the displacement of the steering mechanism and the amount of current flowing through the motor and inversely proportional to the speed of the vehicle, said pulse width modulated signal being generated on a first output of the control circuit when the steering mechanism is turned in a first direction and a second output of the control circuit when the steering mechanism is turned in the opposite direction;
• a first transistor, responsive to the first output of the control circuit, electrically connected between the first terminal of the battery and the other of said terminals of the motor for energizing the motor to turn in a first direction in proportion to the width of the pulses;
• and
• a second transistor, responsive to the second output of the control circuit, electrically connected between the other of said terminals of the motor and the second terminal of the battery for energizing the motor to turn in a direction opposite to said first direction in proportion to the width of the pulses.