| 摘要 |
A system for a four-wheel drive vehicle for automatically changing a power transmission system of an engine of the vehicle from two-wheel driving to four-wheel driving in accordance with driving conditions. The transmission system is provided for transmitting power from the engine to two main driving wheels, and a clutch is provided for transmitting the power of the engine to auxiliary driving wheels. Speed sensors are provided for producing output signals dependent on the speeds of the main and auxiliary wheels, respectively. A load sensor for sensing the load on the engine is provided. A first computing circuit is provided for producing a slip speed signal from output signals of the speed sensors, and a second computing circuit is provided for producing a reference value dependent on the output of the load sensor and a proportional constant which is a value in relationship between the slip speed and the load on the engine. A comparing circuit is provided for comparing the slip speed signal and the reference value with each other and for producing an output signal when the slip speed signal is higher than the reference value. The output signal of the comparing circuit is applied to a switch to engage the clutch, whereby the four-wheel driving power transmission is established.
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