The viscous coupling consists of a housing filled with special oil, in which there are discs, between which there is no rigid mechanical connection. The discs are connected through one to the rear axle drive shaft. When discs slip, i.e. when the front and rear wheels rotate at different speeds, the viscosity of the oil in the viscous coupling increases. Thanks to this, the disks begin to rotate as a whole, and the speeds of rotation of the wheels are aligned. A small difference in rotation speeds is compensated, and an increase in their difference leads to an increase in elastic forces in the viscous coupling so that up to 100% of the engine torque can be transmitted to the rear wheels. The inclusion of the rear wheel drive is so soft and smooth that the driver does not even notice it.
On a normal dry road, the wheels rotate at about the same speed. In this case, most of the moment is transferred to the front wheels. However, if the front wheels turn faster than the rear wheels due to high acceleration torque or poor road conditions, the viscous coupling increases the torque to the rear wheels. When the front wheels slip, almost all of the torque is transferred to the rear axle.
When braking, due to the connection between the front and rear axles, the rear wheels would be difficult to brake. Therefore, all-wheel drive vehicles Opel Vectra/Calibra are equipped with a hydraulic disengaging clutch, which automatically disconnects the viscous coupling when braking. The disengaging clutch is electronically controlled and is involved in a common hydraulic circuit.
When engine braking (when the accelerator pedal is not pressed) all-wheel drive is retained. Thus, braking is transferred to all wheels.
When the engine is turned off, the rear wheels are disengaged. Therefore, towing 4WD vehicles with the front end raised is the same as for front-wheel drive vehicles. If for some reason you need to disable rear-wheel drive. fuse F19 must be removed.
1 - engine crankshaft speed sensor
2 - control valve
3 - pressure switch
4 - diagnostic connector (ALDL)
5 - computer
6 - purity sensor
7 - brake light switch
8 - control lamp for turning on all-wheel drive
All-wheel drive is provided by a computer that has its own memory for fault codes. Simultaneously with the recording of the code of the malfunction that has occurred in the memory, the all-wheel drive symbol flashes or lights up on the instrument panel. Repair of the all-wheel drive system should be carried out only in specialized workshops.
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