Engine-Off Power Steering System

Abstract

Motor vehicles are equipped with a center-closed power steering system to provide power steering assistance in engine-off conditions for reduced fuel consumption. The power steering system includes a hydraulic pump mechanically driven by the engine, a high pressure accumulator, a steering gearbox fluidly connected to the accumulator, and a center closed valve mechanically connected to a driver-operated steering wheel. The valve is configured to selectively control flow of pressurized fluid from the accumulator to the steering gearbox to provide power steering assistance.

1 . A non-hybrid motor vehicle with power steering system, comprising:
 a vehicle frame;   one or more drive wheels rotatably mounted on said vehicle frame;   an internal combustion engine mounted on said vehicle frame, providing all propulsive power to said drive wheels for propelling the non-hybrid motor vehicle;   a hydraulic pump, mechanically driven by the internal combustion engine, for pressurizing fluid;   an accumulator storing under pressure fluid pressurized by the hydraulic pump;   a steering gearbox fluidly connected to the accumulator;   a center closed valve mechanically connected to a driver-operated steering wheel mounted in the vehicle, the valve configured to prevent flow of pressurized fluid from the accumulator to the steering gearbox except when said valve is opened by rotation of the steering wheel away from a neutral central position, the valve further configured to allow flow of pressurized fluid from the accumulator to the steering gearbox when the valve is open, to provide supplemental mechanical assistance in steering the motor vehicle upon rotation of the steering wheel away from a neutral central position, even when the internal combustion engine is turned off.   
     
     
         2 . The vehicle of  claim 1 , further comprising a spring return means to assist return of steering to the neutral center position when torque is no longer being applied by the driver to rotate the steering wheel. 
     
     
         3 . The vehicle of  claim 1 , wherein the valve is further configured when open to meter the flow of pressurized fluid from the accumulator to the steering gearbox in relative proportion to the extent of rotational force applied to the steering wheel. 
     
     
         4 . The vehicle of  claim 3 , wherein the valve is a rotary valve comprising:
 a hollow cylindrical sleeve with an input port fluidly connected to the accumulator, and an output port fluidly connected to the steering gearbox; and   a shaft rotatably positioned within the sleeve, wherein a portion of the outer surface of the shaft is configured to sealingly engage an inner surface of the sleeve in a first shaft rotation position to prevent flow of the pressurized fluid between the input port and the output port, and further including a cavity in the outer surface of the shaft configured to allow flow of the pressurized fluid between the input port and the output port in a second shaft rotation position.   
     
     
         5 . The vehicle of  claim 4 , wherein a V-shaped notch is provided on the outer surface of the shaft between the cavity and the portion of the outer surface of the shaft that is configured to sealingly engage the inner surface of the sleeve, in order to provide a smoother transition in driver feel from the first shaft rotation position, in which no mechanical assistance from the power steering system is provided in steering the motor vehicle, to a second shaft rotation position in which full mechanical assistance from the power steering system is provided in steering the motor vehicle. 
     
     
         6 . The vehicle of  claim 4 , wherein a notch is provided on the inner surface of the sleeve on an edge of the output port, in order to provide a smoother transition in driver feel from the first shaft rotation position, in which no mechanical assistance from the power steering system is provided in steering the motor vehicle, to a second shaft rotation position, in which full mechanical assistance from the power steering system is provided in steering the motor vehicle. 
     
     
         7 . A method of reducing fuel consumption in the non-hybrid vehicle of  claim 1 , comprising:
 turning the internal combustion engine off intermittently in driving conditions when there is no driver torque demand;   sending pressurized fluid from the accumulator to the steering gearbox for power steering assistance upon turning of the non-hybrid vehicle;   cutting off flow of the pressurized fluid from the accumulator to the steering gearbox when the non-hybrid vehicle is not being turned or when power steering assistance is not required.   
     
     
         8 . A method of reducing fuel consumption in a hydraulic hybrid motor vehicle with an internal combustion engine, comprising:
 storing pressurized fluid in a high pressure hydraulic accumulator on the hydraulic hybrid motor vehicle;   turning the internal combustion engine off intermittently in driving conditions;   sending the pressurized fluid to a steering actuation system for power steering assistance upon turning of the hydraulic hybrid motor vehicle;   monitoring vehicle speed;   reducing the pressure of the pressurized fluid supplied to the steering actuation system when the monitored vehicle speed is above a first threshold;   cutting off flow of pressurized fluid from the accumulator to the steering actuation system when the hydraulic hybrid motor vehicle is not being turned or when power steering assistance is not required.   
     
     
         9 . The method of  claim 8 , further comprising adjusting the pressure of the pressurized fluid supplied to the steering actuation system as a function of vehicle speed. 
     
     
         10 . The method of  claim 8 , further comprising using a spring return means to assist return of steering to the neutral center position when torque is no longer being applied by the driver to rotate the steering wheel.