Electric power assisted steering system

• US 4,624,334 A
• Filed: 08/30/1984
• Issued: 11/25/1986
• Est. Priority Date: 08/30/1984
• Status: Expired due to Fees

• Current Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Original Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Inventors: O'Neil, Walter K., Kelledes, William L.
• Primary Examiner(s): Dolinar, Andrew M.
• Application Number:
  US06/646,371
• Time in Patent Office: 817 Days
• Field of Search: 180/79.1, 180/142, 318/293, 318/300
• US Class Current: 180/446
• CPC Class Codes: B62D 5/046 Controlling the motor
• CPC Class Codes: B62D 5/0463 calculating assisting torque from the motor based on driver input
• CPC Class Codes: B62D 5/0493 detecting processor errors, e.g. plausibility of steering direction

Abstract

An electrical power assisted steering system for a vehicle. The system includes a battery, having two terminals at different voltages and a center tap, and a bidirectional electric power assist motor having two terminals, one terminal being connected to the center tap of the battery. In an electric vehicle, said battery would be the traction battery. A control circuit responds to movement of the vehicle'"'"'s steering wheel to generate a pulse width modulated (PWM) signal to drive the motor to assist in steering. The pulse widths are directly proportional to the driver'"'"'s rotational displacement of the steering wheel and the amount of current flowing through the motor and inversely proportional to the speed of the vehicle. The PWM signal is applied to a selected one of two driving transistors, the first of which is connected between one of the terminals of the battery and the free terminal of the motor, the other of which is connected between the other terminal of the battery and the free terminal of the motor. Upon receipt of the PWM signal, the selected driving transistor connects the motor to its associated terminal of the battery to cause the motor to turn in a desired direction and deliver torque proportional to the width of the pulses. Also disclosed are monitoring circuits which monitor the operation of the control circuit and disconnect the motor from the battery when a malfunction is detected.

Claims

1. An electrical power assisted steering system for a vehicle comprising:

operator controlled means for steering the vehicle;

a steering shaft connected between the operator controlled means and at least one steerable wheel of the vehicle;

a voltage source having a first and second terminal, said first terminal being at a higher voltage than said second terminal, and a center tap;

a bi-directional electrical motor having two terminals, one terminal being connected to the center tap of the voltage source, for providing additional torque to the steering shaft;

means for coupling the motor to the steering shaft;

sensor means for generating a signal indicative of the displacement and rotation of the operator controlled means by an operator; and

control means for controlling the operation of the motor in response to signals from the sensor means, the control means including

a first switching means electrically connected between the first terminal of the voltage source and the other terminal of the motor for selectively energizing the motor to turn in a first direction to thereby provide power assisted steering in said first direction,

a second switching means electrically connected between said other terminal of the motor and the second terminal of the voltage source for selectively energizing the motor to turn in a direction opposite to said first direction to thereby provide power assisted steering in said opposite direction, and

a means for generating pulse width modulated signals selectively to either the first or second switching means, said first and second switching means being responsive to the pulse width modulated signals to energize the motor to turn in proportion to the width of the pulse signals.

2. The electrical power assisted system of claim 1 wherein the widths of the pulses generated by the control means are a function of the displacement of the operator controlled means, the current flow through the motor, and the speed of the vehicle.

3. The electrical power assisted steering system of claim 2 wherein the control means includes monitoring means for detecting improper operation of the control means and, when improper operation is detected, for preventing the motor from providing torque to the steering shaft.

4. The electric power assisted steering system of claim 3 wherein the control means further includes means, responsive to the speed of the vehicle, for reducing the torque generated by the motor inversely in proportion to the speed of the vehicle.

5. The electrical power assisted steering system of claim 2 wherein the motor is a permanent magnet DC electric motor and the voltage source is a traction battery.

6. 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.

7. The control system of claim 6 wherein the width of the pulse signals generated by the control means varies as a function of the displacement of the steering mechanism, the current flow through the motor, and the speed of the vehicle.

8. The control system of claim 7 wherein the control means includes a plurality of circuits and means for monitoring at least one circuit of the control means to detect a malfunction of said at least one circuit and, when a malfunction is detected, for preventing the generation of torque by the motor.

9. The control system of claim 8 wherein the control means includes means for varying the torque generated by the motor inversely in proportion to the speed of the vehicle.

10. 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.

11. The electrical power assisted steering system of claim 10 wherein the control circuit includes a plurality of circuits and a plurality of circuit monitors for detecting improper operation of the circuits and for disconnecting the motor from the battery when improper operation of any circuit is detected.