| 摘要 |
PROBLEM TO BE SOLVED: To properly reduce warm-up time by causing rapidly increase of a working fluid temperature at the warming up, and to well keep the heat balance of the working fluid by setting distribution ratio properly at load operation. SOLUTION: This hydraulic circuit branches a return channel 8 from a control valve 4 into a cooling channel 8a and a non-cooling channel 8b. The cooling channel 8a, causing reflow to the return channel 8 to a hydraulic fluid tank 2 via an oil cooler 12, connects a pressure gauge 13 positioned in an upstream side of the cooler 12. The non-cooling channel 8b loops the channel 8 to the tank 2 so as not to pass via the cooler 12. A proportional solenoid operated valve is installed to switch the return channel 8 and the non-cooling channel 8b on the way to the non-cooling channel 8b. The detecting signal of the pressure gauge 13 is transmitted to a controller 15. When the pressure in the return channel 8 is higher than a set value, the hydraulic circuit controls so as to increase the flow rate of a return fluid flowing in the non-cooling channel 8b side decided by the solenoid valve 14, and when the pressure in the channel 8 is lower than the set value, the circuit controls so as to reduce the flow rate of the return fluid in the non-cooling channel 8b side.
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