Patent ID: 11866911
Assignee: KUBOTA CORPORATION
Field: Civil engineering (Other fields)
Classification: CPC E  F | IPC E  F

Claim 6:
7. A work vehicle comprising:
an engine;
a hydraulic pump to be driven by the engine to supply hydraulic fluid;
an oil passage connected to the hydraulic pump through which the hydraulic fluid flows;
an additional oil passage connected in parallel with the oil passage;
a hydraulic motor provided in the oil passage to be rotated by the hydraulic fluid; and
a fan connected to the hydraulic motor to rotate together with the hydraulic motor;
a variable relief valve connected to the oil passage and having a solenoid, the variable relief valve being configured to control a flow rate of the hydraulic fluid flowing through the oil passage in accordance with a current flowing through the solenoid;
an unload valve provided in parallel to the variable relief valve and having an additional solenoid, the unload valve being configured to control a flow rate of the hydraulic fluid flowing through the additional oil passage in response to a current flowing through the additional solenoid; and
circuitry configured to control the magnitude of the current flowing through the solenoid to control a rotational speed of the fan,
the circuitry being configured to supply, when the engine is started, a first current that has a first magnitude to the solenoid such that the hydraulic fluid flows through the oil passage by a first flow rate to rotate the fan connected to the oil passage,
the circuitry being configured to supply, when a rotational speed of the engine becomes larger than a first rotational speed threshold value, a second current that has a second magnitude larger than the first magnitude such that the hydraulic fluid flows through the oil passage by a second flow rate smaller than the first flow rate to reduce the rotational speed of the fan, and
the circuitry being configured to supply, when the rotational speed of the engine becomes larger than a second rotational speed threshold value that is larger than the first rotational speed threshold value, a current to the solenoid to change the rotational speed of the fan, the current corresponding to the temperature of the liquid flowing in the work vehicle,
wherein the circuitry is configured to supply, from the start of the engine till when the rotational speed of the engine exceeds a third rotational speed threshold equal to or greater than the first rotational speed threshold value, a third current having a third magnitude to the additional solenoid of the unload valve to shut off the additional oil passage by the unload valve,
wherein the circuitry is configured to supply, when the rotational speed of the engine exceeds the third rotational speed threshold value, a fourth current that has a fourth magnitude larger than the third magnitude to the additional solenoid to open the unload valve such that the hydraulic fluid flows from the hydraulic pump into the additional oil passage, and
wherein the circuitry is configured to supply, when the rotational speed of the engine is equal to or greater than the third rotational speed threshold and exceeds a fourth rotational speed threshold value which is equal to or less than the second rotational speed threshold value, a current corresponding to the temperature of the liquid to the additional solenoid to change the flow rate of the hydraulic fluid flowing through the additional oil passage.