Electrical power assisted steering system

Claim 2

An electrical power assisted steering system for a vehicle comprising: operator controlled means (12) for steering the vehicle; a steering shaft (18) connected between the operator controlled means (12) and at least one steerable wheel (14) of the vehicle; a voltage source (20) having a first and second terminal, said first terminal being at a higher voltage than said second terminal, and a center tap; a bidirectional electric motor (10) having two terminals, one terminal being connected to the center tap of the voltage source (20) for providing torque to the steering shaft; means (16) for coupling the motor to the steering shaft; sensor means (30) for generating a signal indicative of the displacement and direction of rotation of the operator controlled means (12) by an operator; and control means (28) for controlling the operation of the motor (10) in response to signals from the sensor means (30), the control means, including a firft switching means (24), electrically connected between the first terminal of the voltage source (20) and the other terminal of the motor (10) for selectively energizing the motor to turn in a first direction to thereby provide power assisted steering in said first direction, and including a second switching means (26), electrically connected between said other terminal of the motor (10) and the second terminal of the voltage source (20) for selectively energizing the motor to turn in the directly opposite to said first direction to thereby provide power assisted steering in said opposite direction.

Claim 3

The electric power assisted steering system of Claim 1 wherein the control means (28) further includes means (34,46), responsive to the speed of the vehicle, for reducing the torque generated by the motor inversely in proportion to the speed of the vehicle.

Claim 4

The electricl power assisted steering system of Claim 1 wherein the control means (28) generates pulse width modulated signals selectively to the first or second switching means (24,26), the width of the pulses being a function of the displacement of the operator controlled means, said first and second switching means responsive to the pulse width modulated signals to energize the motor to turn in proportion to the width of the pulses.

Claim 5

The electrical power assisted steering system of Claim 3 wherein the widths of the pulses generated by the control means (28) are a function of the displacement of the operator controlled means (12), the current flow through the motor (10) and the speed of the vehicle.

Claim 6

The electrical power assisted steering system of Claim 1 wherein the control means (28) includes monitoring means (80,82) 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 (18).

Claim 7

The electrical power assisted steering system of Claim 1 wherein the motor (10) is a permanent magnet DC electric motor and the voltage source (20) is a traction battery.

Claim 8

A control system, for use with an electrical power assisted steering system for a vehicle including a center tapped battery (20) having a first terminal with a voltage above the voltage at the center tap and a second terminal having a voltage below the voltage at the center tap, a bidirectional electric motor (10) having two terminals, one terminal being connected to the center tap of the battery, an operator controlled steering mechanism (12) coupled to the motor (10) so that torque from the motor assists in turning the steering mechanism, the control system comprising: sensor means (30) for sensing the displacement and direction of rotation of the steering mechanism; first switching means (24) electrically connected between one terminal of the battery (20) and the other terminal of the motor (10) to permit energization of the motor in a first direction; second switching means (26) electrically connected between the other terminal of the battery (20) and said other terminal of the motor (10) to permit energization of the motor in a direction opposite said first direction; and control means (28), responsive to the sensor means (30), for selectively energizing either said first switching means (24) or said second switching means (26) to energize the motor (10) to turn in a direction to provide power assisted steering to the operator.

Claim 9

A control system, for use with an electrical power assisted steering system for a vehicle including a center tapped battery (20) having a first terminal with a voltage above the voltage at the center tap and a second terminal having a voltage below the voltage at the center tap, a bidirectional electric motor (10) having two terminals, one terminal being connected to the center tap of the battery, an operator controlled steering mechanism (12) coupled to the motor (10) so that torque from the motor assists in turning the steering mechanism, the control system comprising: sensor means (30) for sensing the displacement and direction of rotation of the steering mechanism; first switching means (24) electrically connected between one terminal of the battery (20) and the other terminal of the motor (10) to permit energization of the motor in a first direction; second switching means (26) electrically connected between the other terminal of the battery (20) and said other terminal of the motor (10) to permit energization of the motor in a direction opposite said first direction; and control means (28), responsive to the sensor means (30), for selectively energizing either said first switching means (24) or said second switching means (26) to energize the motor (10) to turn in a direction to provide power assisted steering to the operator.

Claim 10

The control system of Claim 7 wherein the control means (28) includes means (34,36) for varying the torque generated by the motor inversely in proportion to the speed of the vehicle.

Claim 11

The control system of Claim 7 wherein the control means (28) generates a pulse width modulated signal to the selected switching means (24,26), the width of the pulses being proportional to the displacement of the steering mechanism (12); said selected switching means (24,26) operative to energize the motor to develop torque proportional to the width of the pulses.

Claim 12

The control system of Claim 9 wherein the width of the generated pulses varies as a function of the displacement of the steering mechanism (12), the current flow through the motor (10) and the speed of the vehicle.

Claim 13

The control system of Claim 7 wherein the control means (28) includes a plurality of circuits (30,34, 44-72) and means (74-82) 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 (10).

Claim 14

An electrical power assisted steering system for a wheeled vehicle comprising; operator controlled steering mechanism (12); a steering shaft (18) connected between the steering mechanism (12) and at least one steerable wheel (14) of the vehicle; a battery (20) having a first terminal at a positive voltage, a second terminal at a ground voltage, and a center tap; a permanent magnet electric motor (10) coupled to a steering shaft (18) to apply torque to the steering shaft to turn the steerable wheel (14), the motor having two terminals, one of said terminals being electrically connected to the center tap of the battery (20); a sensor (30) mounted between the steering mechanism (12) and the steering shaft (18) to sense the displacement and direction of rotation of the steering mechanism and to generate signals proportional thereto; means (32) for sensing the speed of the vehicle; means (22) for sensing the current flowing through the motor; a control circuit (28) for generating a pulse width modulated signal, the pulse width being directly proportional to the-displacement of the steering mechanism (12) and the amount of current flowing through the motor (10) 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 (24) 1 responsive to the first output of the control circuit, electrically connected between the first terminal of the battery (20) and the other of said terminals of the motor (10) for energizing the motor to turn in a first direction in proportion to the width of the pulses; and a second transistor (26), responsive to the second output of the control circuit, electrically connected between the other of said terminals of the motor (10) and the second terminal of the battery (20) for energizing the motor to turn in a direction opposite to said first direction in proportion to the width of the pulses.

Claim 15

An electrical power assisted steering system for a wheeled vehicle comprising; operator controlled steering mechanism (12); a steering shaft (18) connected between the steering mechanism (12) and at least one steerable wheel (14) of the vehicle; a battery (20) having a first terminal at a positive voltage, a second terminal at a ground voltage, and a center tap; a permanent magnet electric motor (10) coupled to a steering shaft (18) to apply torque to the steering shaft to turn the steerable wheel (14), the motor having two terminals, one of said terminals being electrically connected to the center tap of the battery (20); a sensor (30) mounted between the steering mechanism (12) and the steering shaft (18) to sense the displacement and direction of rotation of the steering mechanism and to generate signals proportional thereto; means (32) for sensing the speed of the vehicle; means (22) for sensing the current flowing through the motor; a control circuit (28) for generating a pulse width modulated signal, the pulse width being directly proportional to the-displacement of the steering mechanism (12) and the amount of current flowing through the motor (10) 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 (24) 1 responsive to the first output of the control circuit, electrically connected between the first terminal of the battery (20) and the other of said terminals of the motor (10) for energizing the motor to turn in a first direction in proportion to the width of the pulses; and a second transistor (26), responsive to the second output of the control circuit, electrically connected between the other of said terminals of the motor (10) and the second terminal of the battery (20) for energizing the motor to turn in a direction opposite to said first direction in proportion to the width of the pulses.

Claim 16

The electrical power assisted steering system of Claim 12 wherein the control circuit (28) includes a plurality of circuits (30,34, 44-72) and a plurality of circuit monitors (74-82) for detecting improper operation of the circuits and for disconnecting the motor (10) from the battery (20) when improper operation of any circuit is detected.