Patent ID: 9683588
Date: 2017-06-20
CPC Classifications: E02F,F15B

Claim:
1. A hydraulic closed circuit system, comprising: a prime mover; a hydraulic pump driven by the prime mover and adapted to deliver a hydraulic fluid in two directions; a single rod type hydraulic cylinder connected to the hydraulic pump via a first hydraulic line and a second hydraulic line to form a closed circuit; a tank; a flushing valve connected between the first and second hydraulic lines and the tank; a charge circuit connected to a lower pressure side hydraulic line of the first and second hydraulic lines by switching of the flushing valve, the charge circuit including a charge pump connected to the first and second hydraulic lines and the tank to supply a hydraulic fluid to each of the first and second hydraulic lines from the tank, and a relief valve connected to the charge pump and the tank to maintain the charge pump at a predetermined pressure; and a control unit configured to; determine which of the first and second hydraulic lines is the lower-pressure side hydraulic line, add a predetermined control pressure to a pressure in the lower-pressure side hydraulic line determined by the first determining section to compute a compensation pressure, compare a magnitude of a pressure in a higher-pressure side hydraulic line of the first and second hydraulic lines with a magnitude of the compensation pressure, and compute a command value to control the flushing valve to connect to one of the first and second hydraulic lines determined by the comparison as the lower-pressure side hydraulic line.