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- g! F8 E2 H2 |! l8 l4 KThis is a "temporary" all wheel drive system. In normal driving conditions, just one axle (the rear axle normally) is driven. In slippery conditions, another axle is engaged by the driver, whether by a lever or a button. This type of all wheel drive does not have a center differential - when all wheel drive is engaged, the front and rear driveshafts are mechanically connected and rotate at the same speed.8 e8 T) ?4 V. p) k) b! ^* v
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When a vehicle is turning, front wheels travel greater distance than rear wheels. # L* z1 N7 J% [
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Figure: Wheels rotate with different speeds and travel different distances when vehicle is turning& e' R% D3 o7 a9 U, q
part-time-all-wheel-drive-windup
+ z& n8 m# e/ T5 u' h) U" p' GBecause part-time all wheel drive system does not have a center differential, front wheels cannot go faster than rear wheels. This type of all wheel drive cannot be used on pavement. Turning on pavement (even on a wet pavement) with all wheel drive engaged causes transmission windup and increases the chances of the transmission breakdown. When all wheel drive is engaged, the vehicle heavily understeers and this can lead to an accident.
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+ _+ Q2 h$ _* H0 h9 L4 bThe all wheel drive mode on a vehicle with part-time all wheel drive should only be used on surfaces with low traction (mud, snow, ice, sand), for short periods, and at low speeds. When driving on such surfaces, the transmission windup is eliminated by slipping of the wheels.5 k6 a5 z7 p% M5 H
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Note: "Part-time 4wd" mode of the Jeep Cherokee's SelecTrac transmission means "locking of center differential". Jeep's SelecTrac is a selectable all wheel drive system. |
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发表于 2015-11-21 21:33
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