Patent ID: 7690899
Filing Date: 2010-04-06
Classification: B60T,F04B

Abstract:
1. A piston pump comprising: a first piston pump including a first piston and a first pump chamber; a drive apparatus for driving the first piston pump; a second piston pump including a second piston and a second pump chamber having an annular shape to surround the first piston, the second piston operating to follow an operation of the first piston; a pressure release passage formed in communication with the second pump chamber; a relief valve provided at the pressure release passage and defining an upper limit discharge pressure of the second piston pump; wherein when a discharge pressure of the second piston pump is equal to or smaller than the upper limit discharge pressure, a discharge fluid of the second piston pump is added to a discharge fluid of the first piston pump so as to flow into an outlet port, and when the discharge pressure of the second piston pump exceeds the upper limit discharge pressure, the discharge fluid of the second piston pump is released to the pressure release passage through the relief valve and the discharge fluid of the first piston pump only flows to the outlet port; and when a volume of the first pump chamber decreases during movement of the first piston, a volume of the second pump chamber decreases in a state where an entrance of the second pump chamber is closed.