Toyota all-wheel drive. ATC / DTC coupling

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Eugenio,77
mail@toyota-club.net
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Jan 2011 - Oct 2020


First introduced in 1998, to the end of 2000s ATC (Active Torque Control) was the main type of all-wheel drive - without center differential, automatic connection of the rear wheels by electromechanical coupling mounted on the rear differential carrier.


1 - electromechanical coupling, 2 - drive pinion, 3 - differential carrier, 4 - right driveshaft, 5 - side gear, 6 - pinion gear, 7 - ring gear, 8 - left driveshaft, 9 - differential case.

Design

Electromechanical coupling assembly is mounted to the differential carrier. The outer parts of the main clutch and control clutch are coupled to the front housing, the inner part of the main clutch - to the shaft, the inner part of the control clutch - to the cam. The control clutch - multiple metal plate type, the main clutch - multiple wet plate type.

1 - front housing, 2 - main clutch, 3 - control clutch, 4 - solenoid, 5 - cam, 6 - armature, 7 - piston, 8 - shaft.

Operation

If the solenoid is not energized, thecontrol clutch is not engaged - the drive force is transmitted from the propeller shaft to the front housing is not transmitted to the rear wheels.

When the solenoid is energized by control unit, the armature is attracted to the control clutch to engage it. This causes the cam to rotate and rotational movement of the cam causes the piston to push and engage the main clutch. The drive force is transmitted from the front housing to the rear wheels. The amount of transmitted drive force is controlled steplessly by controlling the amperage applied to the solenoid - the higher current amperge means the greater piston stroke.

1 - front housing, 2 - main clutch, 3 - armature, 4 - control clutch, 5 - solenoid, 6 - control unit, 7 - cam, 8 - piston, 9 - shaft.

The control system automatically maintains the target value of torque transmitted to the rear wheels. When the front wheels slip or during sudden takeoff - drive force at rear wheels is increased, during low-speed cornering - decreasing, during engine braking - rear drive off.

ATC is controlled by ABS control unit or for later models, by separate control unit. The system uses wheel speed sensors, steering wheel position sensor, acceleration sensor, signals of throttle position, engine speed, range, brake pedal and parking brake.


The combination meter indicator (torque distribution diagram) indicates the torque value supplied to axles by the number of segments highlighted.

Control modes

Type 1: With "AUTO" button - modes "AUTO 4WD" and "2WD". At OFF state there is only front-wheel- drive, at ON state - control unit automatically manage torque distribution to the rear wheels.

Indicator light is ON, button pressed - "AUTO 4WD" mode.
Indicator light flashes, button pressed - "AUTO 4WD" mode activation.
Indicator is OFF, button released - "2WD" mode.
Indicator light is ON continuously - ATC system failure.
Indicator light flashes during self-diagnosis.

Type 2: With "LOCK" button - modes "AUTO 4WD" and "LOCK". In AUTO mode control unit automatically manage torque distribution to the rear wheels, at LOCK mode - maintains the highest possible rate of electromechanical coupling locking.

Indicator light is OFF - "AUTO 4WD" mode.
Indicator light is ON - "LOCK" mode.
At speed above 40 km/h the system automatically switches from "LOCK" to "AUTO 4WD".
Indicator light flashes slowly - overheating, ATC control ceases.
Indicator light flashes quickly - ATC control ceases.
Indicator light is ON continuously - ATC system failure.

Type 3: No buttons - constant automatic control of torque distribution.

Type 4: With controller or buttons of "Multi-Terrain Select" - the function of an optimal 4WD control for selected road and off-road conditions.



"Mud&Sand" mode - for cases when it is required to rotate all the wheels, regardless of slipping - mud, snow, sand. 4WD coupling is engaged with maximum force (all-wheel drive is "locked") up to 40 km/h. Difflock emulation is minimal and does not prevent slipping.

"Rock&Dirt" mode - for cases when it is required to provide the maximum torque on the wheels having the best grip - diagonal spin, uneven or non-uniform surfaces. 4WD coupling is engaged with maximum force (all-wheel drive is "locked") up to 25 km/h. Difflock emulation is maximal, the slipping wheel is braked faster and stronger.


New manufacturer's trouble codes related to DTC system:

SAE OBD Flash Cause
C120C79Linear solenoid power supply system malfunction
C124194Low power supply voltage
C128082Engine circuit malfunction
C129696ABS malfunction
C129797Steering angle sensor
C129898Linear solenoid circuit
C129999Cancellation of 4WD control
C133791Diameter of the tire is not uniform
U007386Control module communication bus OFF
U010085Lost communication with ECM / PCM A
U012684Lost communication with steering angle sensor module
U012983Lost communication with brake system control module



The main and mass problem of ATC is the noise from the rear differential area due to contamination and wear of the front bearing of the coupling.

Repair of Toyota ATC 4WD coupling


In the civilized markets this defect is covered by an extended guarantee. For example, the Warranty Enhancement Program ZF4 (for RAV4 2006-12, ~650.000 vehicles) provides a free replacement of ATC coupling within 9 years without mileage restriction.



Toyota all-wheel drive. Review
· ATC/DTC · V-Flex · DTV · i-Four · Torsen · E-Four ·
· C.Diff Auto A241H / A540H · C.Diff Lock · C.Diff Visc · FT-Visc ·





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