| 摘要 |
To ensure the benefits of four-wheel drive when the vehicle is accelerating or when the front wheels are slipping, and to eliminate the disadvantage of undesirably transmitting the braking force to the rear wheels when the vehicle is decelerating or when a braking action is applied to the vehicle, the front wheels and the rear wheels are coupled with each other when the rotational speed of the front wheels is higher than that of the rear wheels, but this coupling is disconnected when the rotational speeds of the front and rear wheels are substantially identical or when the rotational speed of the rear wheels is higher than that of the front wheels. To achieve this irrespective of whether the vehicle is moving forward or rearward, the power transmission system comprises a first pump coupled with the front wheels, a second pump coupled with the rear wheels, communication passages connecting these pumps in series with the inlet of one of them being connected to the outlet of the other, a fluid pressure actuated clutch interposed between the front and rear wheels, and a switching valve for appropriately actuating the clutch according to the difference in the outputs and/or inputs of these pumps.
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