Power steering apparatus

1. An apparatus for use in turning steerable vehicle wheels, said apparatus comprising:

a power steering motor assembly connected with the steerable vehicle wheels, said power steering motor assembly includes first and second power steering motors which are connected with the steerable vehicle wheels;

a first pump which is connected with said power steering motor assembly and is driven by an engine of the vehicle to supply fluid under pressure to said power steering motor assembly;

a second pump which is connected with said power steering motor assembly;

an electric motor which is connected with said second pump and is operable to drive said second pump to supply fluid under pressure to said power steering motor assembly; and

control apparatus connected with said electric motor to effect operation of said electric motor to drive said second pump when said power steering motor assembly requires fluid in addition to fluid supplied by said first pump, said first and second power steering motors being operable to effect turning movement of the steerable vehicle wheels under the influence of fluid supplied by said first pump until said control apparatus effects operation of said electric motor to drive said second pump, said first and second power steering motors being operable to effect turning movement of the steerable vehicle wheels under the influence of fluid supplied by said first and second pumps when said electric motor is operated to drive said second pump.

2. The apparatus as set forth in claim 1 wherein said control apparatus includes a torque sensor which is connected with said power steering motor assembly and is operable to provide an output signal which varies as a function of variations in torque transmitted from a hand wheel to said power steering motor assembly, and a controller which is connected with said torque sensor and said electric motor to vary an operating speed of said electric motor as a function of variations in the output signal from said torque sensor.

3. The apparatus as set forth in claim 1 wherein said control apparatus includes a flow sensor which is connected in fluid communication with at least one of said first and second pumps and is operable to provide an output signal which varies as a function of variations in fluid flow from at least said one of said first and second pumps, and a controller which is connected with said flow sensor and said electric motor to vary an operating speed of said electric motor as a function of variations in the output signal from said flow sensor.

4. The apparatus as set forth in claim 1 wherein said control apparatus includes a flow sensor which is connected in fluid communication with said power steering motor assembly and is operable to provide an output signal which varies as a function of variations in fluid flow from said power steering motor assembly, and a controller which is connected with said flow sensor and said electric motor to vary an operating speed of said electric motor as a function of variations in the output signal from said flow sensor.

5. The apparatus as set forth in claim 1 wherein said control apparatus includes a flow sensor which is connected in fluid communication with said first and second pumps and is operable to provide an output signal which varies as a function of variations in fluid flow from said first and second pumps, and a controller which is connected with said flow sensor and said electric motor to vary an operating speed of said electric motor as a function of the output from said flow sensor.

6. The apparatus as set forth in claim 1 wherein said first and second power steering motors are connected with a single control valve which is operable in response to rotation of a hand wheel to direct fluid flow to said first and second power steering motors to effect turning movement of the steerable vehicle wheels under the influence of force transmitted from said first and second power steering motors.

7. The apparatus as set forth in claim 1 wherein said first power steering motor includes a first piston which is movable under the influence of fluid pressure, first rack teeth being connected with said first piston and being disposed in meshing engagement with first output gear teeth connected with a steering linkage connected with the steerable vehicle wheels, said second power steering motor includes a second piston which is movable under the influence of fluid pressure, second rack teeth being connected with said second piston and being disposed in meshing engagement with second output gear teeth connected with the steering linkage.

8. The apparatus for use in turning steerable vehicle wheels, said apparatus comprising:

first and second power steering motors which are connected with the steerable vehicle wheels;

a first pump which is driven by an engine of the vehicle to provide a first source of fluid under pressure;

a second pump which is connected with an electric motor, said electric motor being operable to drive said second pump to provide a second source of fluid under pressure;

a control valve which is connected in fluid communication with said first and second power steering motors and with said first and second pumps, said control valve being operable to direct fluid pressure from only said first pump to said first and second power steering motors in response to rotation of a hand wheel when said electric motor is in a nonoperating condition in which said electric motor is ineffective to drive said second pump, said control valve being operable to direct fluid pressure from said first and second pumps to said first and second power steering motors in response to rotation of the hand wheel when said electric motor is in an operating condition in which said electric motor is effective to drive said second pump;

a sensor which senses when fluid pressure in addition to fluid pressure supplied by said first pump is required to effect operation of said first and second power steering motors; and

control apparatus connected with said sensor and said electric motor to effect operation of said electric motor to drive said second pump in response to said sensor sensing that fluid pressure in addition to the fluid pressure supplied by said first pump is required to effect operation of said first and second power steering motors.

9. The apparatus as set forth in claim 8 wherein said sensor is operable to provide an output signal which varies as a function of variations in torque transmitted from the hand wheel, and a controller is connected with said torque sensor and said electric motor to vary an operating speed of said electric motor as a function of variations in the output signal from said sensor.

10. The apparatus as set forth in claim 8 wherein a flow sensor is connected in fluid communication with at least one of said first and second pumps and is operable to provide an output signal which varies as a function of variations in fluid flow from at least said one of said first and second pumps, a controller is connected with said flow sensor and said electric motor to vary an operating speed of said electric motor as a function of variations in the output signal from said flow sensor.

11. The apparatus as set forth in claim 8 wherein a flow sensor is connected in fluid communication with said control valve and is operable to provide an output signal which varies as a function of variations in fluid flow from at least one of said first and second pumps, a controller is connected with said flow sensor and said electric motor to vary an operating speed of said electric motor as a function of variations in the output signal from said flow sensor.

12. The apparatus as set forth in claim 8 wherein a flow sensor is connected in fluid communication with said first and second pumps and is operable to provide an output signal which varies as a function of variations in fluid flow from said first and second pumps, a controller is connected with said flow sensor and said electric motor to vary an operating speed of said electric motor as a function of the output from said flow sensor.

13. The apparatus as set forth in claim 8 wherein said first power steering motor includes a first piston which is movable under the influence of fluid pressure, first rack teeth being connected with said first piston and being disposed in meshing engagement with first output gear teeth connected with a steering linkage connected with the steerable vehicle wheels, said second power steering motor includes a second piston which is movable under the influence of fluid pressure, second rack teeth being connected with said second piston and being disposed in meshing engagement with second output gear teeth connected with the steering linkage.