| 摘要 |
A pump sytem (16) for delivering hydraulic fluid to a load device, such as a hydraulic brake system. The system automatically switches from larger displacement to smaller displacement as pressure at the outlet increases. The pump system comprises one or more lower pressure pumps (72, 76) and a high pressure pump (74, 78) with an actuator (56) driving all pumps simultaneously. An unloading valve (102) is coupled with each lower pressure pump for dumping the output thereof in response to pressure of the fluid delivered to the load device. The actuator comprises an electromagnetic linear motor (122) which imparts an intake stroke to the pumps and stresses a spring (124) which releases stored energy for imparting the pressure stroke to the pumps. |
