| 摘要 |
PURPOSE:To enable changeover to be carried out rapidly and lighten the burden of an operator by detecting the slippage of a driving wheel from a difference in rotations between a rear wheel and a front wheel, judging to be slippage when the detected ratio is above a certain reference value, and shifting to four-wheel driving. CONSTITUTION:A rotation sensor 15 is provided opposite to a rotary pulser 13 while a rotation sensor 24 is provided opposite to a rotary pulser 23. The number of revolutions Nf and Nr of front and rear wheels are detected by the sensors 14, 24 and compared with a judgeable number of revolution No to calculate the ratio of the number of revolution Prf between front and rear wheels. If the relation between a changeover rotation standard P24 for shifting a gear from two-wheel to four-wheel driving, and the Prf is, Prf>P24, the rear wheel 1 is judged to be slipping and, when a driving method is not in a four- wheel driving condition, the 2-1-4 automatic changeover part 34 of a control part 3 is shifted to a four-wheel side, and a solenoid valve 25 is excited to make a hydraulic transmission 21 an operating condition, resulting in a four- wheel driving condition in which the front wheel 2 is also driven.
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