| 摘要 |
PROBLEM TO BE SOLVED: To make driving and braking state of the driving wheels freely switchable by providing a first four wheel drive mode wherein first and second hydraulic motors output substantially a same transmission torque and a second four wheel drive mode wherein the first hydraulic motor outputs smaller transmission torque than the second hydraulic motor freely switchable. SOLUTION: A shuttle valve 48 is connected between oil passages 22, 23, and a high pressure relief valve 46 and a low pressure relief valve 47 are connected in parallel through a relief pressure selector valve 45 made of an electromagnetic valve. Shutoff and communication are made switchable by excitation of a solenoid. A first four wheel drive mode wherein a solenoid of the selector valve 45 is not excited, hydraulic motors 43, 42 output a substantially same transmission torque, whereas in a second four wheel drive mode wherein the solenoid is excited, the transmission torque of the hydraulic motor 43 is smaller than the torque of the hydraulic motor 42. A two wheel drive selector valve 44 is provided between the oil passages 22, 23 so that driving of a front wheel 9 and a non-driving free revolution of the front wheel 9 can be switched therebetween. This realizes four wheel/two wheel drive and braking freely switchable.
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