| 摘要 |
PROBLEM TO BE SOLVED: To provide a power steering system that is simple in structure, high in system reliability, and equipped with an inexpensive emergency power steering circuit in combination. SOLUTION: When a first oil pump 31 to be driven by an engine generates an extent of hydraulic pressure of more than the specified one, this hydraulic pressure is fed to a combined type power steering booster 17, while a pilot- operated directional control valve 35 is switched and thereby discharge oil of a second oil pump 40 is discharged to the drain side. This combined type power steering booster 17 assists the steerage of a wheel of a steering wheel shaft. When hydraulic pressure in the pump 31 goes down to less than the specified one while traveling, the pilot-operated directional control valve 35 is switched and thereby the hydraulic pressure in the pump 40 is fed to an integral type power steering booster 13, assisting the control force of a steering wheel 12. With this, a power steering function is maintainable even in the case where the oil pump 31 gets out of order in course of traveling and/or an oil passage is broken down. |
