The ATT (Active Torque Transfer) or TOD (Torque-on-Demand) system is classified as the Full Time 4 WD system. This is an all-wheel drive system with an active distribution of torque between the front and rear axles, which allows to increase the cross-country ability of the car. The distribution of torque depends on:
– vehicle driving conditions (off-road, slippery or normal road);
– vehicle movement mode (acceleration, braking or uniform movement);
– engine load;
– And so on.
The system consists of:
– sensors (front and rear driveshaft rotational speeds) and switches;
– electronic control unit;
– actuators (electromagnetic clutch, electric motor).
Transfer Case Control Scheme.
Note: in the figure, the abbreviations indicate:
TCCM – electronic control unit;
EMC – electromagnetic clutch;
TPS – signal from the throttle position sensor (G 6 CV) or the accelerator pedal position sensor (J 3);
ABS – anti-lock brake system (ABS) signal;
BR – brake light switch signal;
N – signal of the relay of the sensor-switch of neutral transmission of the check point.
Speed sensors detect the speed of the propeller shafts and transmit a signal to the control unit.
The control unit on the basis of signals from sensors and other control units determines the state of the elements of the vehicle control systems and driving conditions. In accordance with the internal algorithm, the unit makes a decision on the ratio of torques on the front and rear wheels and sends control signals to the actuators.
An electromagnetic clutch mounted in a transfer case is responsible for the compression force of the friction discs in a multi-plate clutch. At the signal of the control unit, the clutch either enhances the compression of the discs (thereby increasing the torque supplied to the front wheels) or reduces the compression force of the discs, which leads to a decrease in the moment on the front wheels.
The electric motor is responsible for the inclusion of a downshift. The reduction gear is engaged when the mode switch is in the “LOW” position.
The ratio of torques between the front and rear wheels is not constant, but changing depending on driving conditions. The ratio can vary from 0: 100 (front: back) to 50:50. Thus, the torque on the front wheels cannot exceed the moment supplied to the rear wheels.
The ratio of moments 0: 100, the system sets only when driving at low speed on good roads. In other cases, the system, depending on the conditions, brings a part of the moment to the front wheels and in severe driving conditions, the ratio of moments reaches 50:50 (front: rear).
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