| 摘要 |
PROBLEM TO BE SOLVED: To perform a smooth steering operation at a muddy field by switching a front wheel gear shifter from a constant speed driving state to a speed increase driving state when engine load is less than a set value and a steering angle of a front wheel exceeds a set angle and maintaining the front wheel gear shifter in the constant speed driving state under a state that engine load is the set value or more. SOLUTION: When a 'double speed' mode is selected by a pushing operation of a selection switch arranged on a panel part in front of a steering wheel 6, a gear shift control valve is controlled and a front wheel gear shift device TF is controlled in a state that power of driving speed to be peripheral speed equal to peripheral speed of a rear wheel 2 is transmitted to a front wheel 1 when a steering angle of a front wheel 1 detected by a steering angle sensor AS is less than a set angleα. But, when the steering angle of the front wheel 1 exceeds the set angleα, the front wheel gear shift device TF is set to a state that power of driving speed to be higher speed than peripheral speed of the rear wheel 2 is transmitted to the front wheel 1 when engine load is less than the set value and a gear shift of the front wheel gear shift device TF is inhibited when engine load is the set value or more.
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