Patent ID: 8561752
Filing Date: 2013-10-22
Classification: B62D

Abstract:
1. A vehicle power steering unit comprising: a steering piston in a hydraulic assist unit to control steering of a vehicle; an engine driven positive displacement hydraulic pump having an input and an output; an accumulator; first valving in hydraulic lines between the output of the hydraulic pump, the accumulator and the hydraulic pump input for controllably coupling the output of the hydraulic pump to the accumulator or the input of the hydraulic pump, the first valving being a two-position three-way valve; second valving in hydraulic lines between the accumulator, a first side of the steering piston and the hydraulic pump input for controllably coupling the first side of the steering piston to the accumulator or to the input of the hydraulic pump; third valving in hydraulic lines between the accumulator, a second side of the steering piston and the hydraulic pump input for controllably coupling the second side of the steering piston to the accumulator or to the input of the hydraulic pump; a steering piston position sensor; first and second pressure sensors coupled to the first and second sides of the steering piston, respectively; and a controller coupled to the first and second pressure sensors, the steering piston position sensor, the first, second and third valving, the controller controlling the first valving to maintain a hydraulic pressure in the accumulator and to return additional hydraulic pump capacity to the hydraulic pump input, and to control the second and third valving to provide a differential pressure across the steering piston responsive to a steering input.