Apparatus for use in turning steerable vehicle wheels

1. An apparatus for use in turning steerable vehicle wheels during operation of an engine of a vehicle, said apparatus comprising:

a hydraulic power steering motor connected with the steerable vehicle wheels and operable to turn the steerable vehicle wheels,

a pump connected in fluid communication with said hydraulic power steering motor and operable to supply hydraulic fluid to said hydraulic power steering motor during turning of the steerable vehicle wheels, and

a gearset connected with the engine of the vehicle and with said pump, said gearset being operable under the influence of force transmitted from the engine of the vehicle to drive said pump at a first speed during turning of the steerable vehicle wheels at relatively low vehicle speeds, said gearset being operable under the influence of force transmitted from the engine to drive said pump at a second speed during turning of the steerable vehicle wheels at relatively high vehicle speeds, said first speed at which said pump is driven by said gearset during a vehicle steering operation at relatively low vehicle speeds is greater than said second speed at which said pump is driven by said gearset during a vehicle steering operation at relatively high vehicle speeds.

2. An apparatus as set forth in claim 1 further including an electric motor connected with said gear set, said electric motor being operable to vary the speed at which said pump is driven by said gearset.

3. An apparatus set forth in claim 1 wherein said gear set is a differential gear mechanism having an output member connected with said pump, a first input member connected with the engine of the vehicle, and a second input member connected with an electric motor.

4. An apparatus set forth in claim 1 further including a reversible electric motor connected with said gearset, and a controller connected with said reversible electric motor, said controller being operable to effect operation of said reversible electric motor in a first direction during turning of the steerable vehicle wheels at relatively low vehicle speeds, said controller being operable to effect operation of said reversible electric motor in a second direction during turning of the steerable vehicle wheels at relatively high vehicle speeds, said second direction of operation of said electric motor being opposite to said first direction of operation of said electric motor.

5. An apparatus as set forth in claim 1 wherein said gearset is a differential gear mechanism having an output member connected with said pump, a first input member connected with the engine of the vehicle, and a second input member connected with a brake.

6. A vehicle steering system comprising:

a hydraulic power steering gear including a hydraulic motor operatively connectable with steerable vehicle wheels for, when connected with the vehicle wheels, steering the vehicle wheels,

a hydraulic fluid reservoir,

a fixed displacement pump having an inlet port for fluid communication with said reservoir and an outlet port for fluid communication with said steering gear,

a gearset for driving said fixed displacement pump, said gear set including a first input driven by the vehicle engine and a second input controlled by a gearset control mechanism, said first and second inputs causing said fixed displacement pump to be driven at a speed to produce the hydraulic fluid flow for steering the vehicle wheels.

7. A system as defined in claim 6 wherein said control mechanism comprises a reversible variable speed electric motor.

8. A system as defined in claim 6 wherein said control mechanism comprises a brake that when actuated reduces the speed of output of said gearset.

9. A system as defined in claim 6 wherein said gearset comprises a planetary gearset for driving the pump.