Patent ID: 8833506
Filing Date: 2014-09-16
Classification: B62D

Abstract:
1. A power steering apparatus for a vehicle having a steering wheel and a steerable road wheel, the power steering apparatus comprising: a steering mechanism configured to steer the steerable road wheel in accordance with a steering effort inputted to the steering mechanism through the steering wheel; a power cylinder with a pair of pressure chambers which applies a steering force to the steerable road wheel based on a differential pressure between a pressure of a working fluid in a first one of the pair of pressure chambers and a pressure of the working fluid in a second one of the pair of pressure chambers; a first pump that is rotationally driven to supply the working fluid to the power cylinder by a first drive source; a second pump that is rotationally driven to supply the working fluid to the power cylinder by a second drive source provided separately from the first drive source; a control valve disposed in the steering mechanism and configured to selectively supply the working fluid supplied from the first pump or the second pump to one of the pair of pressure chambers of the power cylinder in accordance with a steering operation of the steering wheel; a first reservoir tank in which the working fluid is reserved; a second reservoir tank in which the working fluid is reserved; a return passage changeover valve disposed between the control valve and the first and second pumps, the return passage changeover valve comprising a valve element accommodating bore and a valve element disposed within the valve element accommodating bore so as to be moveable along an axial direction of the valve element accommodating bore, the return passage changeover valve being configured to communicate the first and second pumps with the control valve regardless of an axial position of the valve element and to communicate one of the first and second reservoir tanks with the control valve in accordance with the axial position of the valve element to thereby carry out changeover between a circulating fluid passage through which the working fluid is circulated to the first reservoir tank and a circulating fluid passage through which the working fluid is circulated to the second reservoir tank, a first check valve disposed between the first pump and the return passage changeover valve, the first check valve being operable to allow only a flow of the working fluid flowing from a side of the first pump toward a side of the return passage changeover valve, and a second check valve disposed between the second pump and the return passage changeover valve, the second check valve being operable to allow only a flow of the working fluid flowing from a side of the second pump toward the side of the return passage changeover valve, wherein when the working fluid is supplied from the first pump, the valve element of the return passage changeover valve is moved to a first axial position in which fluid communication between the control valve and the first reservoir tank is established and fluid communication between the control valve and the second reservoir tank is blocked, and wherein when the working fluid is supplied from the second pump only, the valve element of the return passage changeover valve is moved to a second axial position in which the fluid communication between the control valve and the first reservoir tank is blocked and the fluid communication between the control valve and the second reservoir tank is established.