Transmission Control Systems: Description and Operation

DESCRIPTION
The active torque transfer system (ATTS) detects the engine torque, transmission gear position, acceleration and cornering condition of the vehicle. This is done by means of the engine speed, manifold absolute pressure (MAP) sensor, backup light switch, front and rear wheel sensors, steering angle sensor, lateral G sensor and the yaw rate sensor. As these data are put in the ATTS control unit, it determines the driving force of the right and left wheels. The then system controls the right and left clutch pressure according to the determined driving force by transmitting the signal to the ATTS unit and thereby distributes the driving force to the right and left wheels.

OPERATION
Acceleration Rate And Distribution Ratio
The driving force distribution rate is set as 8:2 between the outer wheels and inner wheels. The vehicle is equipped with an acceleration mechanism to distribute the driving force with wet clutches (torque is transmitted from the high speed side to the low speed side), where the acceleration ratio is set at 15%.

When Driving Straight Forward (ATTS Not Activated):
- Right and left clutches are OFF.
- The planetary pinion gears, center central gear, right central gear, and left central gear engage each other and rotate as an assembly. Therefore, there is no difference in acceleration between the right and left wheels.








When Turning To The Right (ATTS Activated):
- The right clutch is ON.
- Because the center central gear and right central gear are turning, the rotation speed from the right central gear to the planetary pinion gear increases at a ratio of 30/16, while the speed from the planetary pinion gear to the center central gear decrease at a ratio of 16/26. See the following formula that shows the rotation speed of the center central gear increases at a ratio of approximately 1.15.








When Turning To The Left (ATTS Activated):
- The left clutch is ON.
- The left central gear is fixed.
- Because the planetary pinion gear is engaged with the led central gear, it rotates around the central gears while rotating on its axis.
- When the planetary pinion shaft makes one full turn, the planetary pinion gear turns around the led central gear at a ratio of 32/28. It also turns around the center central gear at a ratio of 16/30. Therefore, the following formula shows that the rotation speed of the right central gear increases at a ratio of approximately 1.15.






ATTS UNIT
The moment control unit is the right/left driving force distribution unit. If consists of a 3-series planetary gear, the right and led clutches, the oil pump, the linear solenoid valve, the right and left shim solenoid valves, the right and left oil pressure sensors, and the oil temperature sensor.

3-SERIES PLANETARY GEAR
The 3-series planetary gear is a set of planetary gears and a carrier with gear ratios that set the speed ratio between the right and left wheels at approximately 1.15. It is not equipped with a ring gear but features a 3-phase parallel layout with a sun gear and a planetary gear.

RIGHT/LEFT CLUTCH
The right and led clutches are a plate-fixing wet multi-plate clutch. They are a pair of clutches that fixes the 3-series planetary gear carrier (when turning to right) or the led central gear (when turning to left) to distribute the torque to the right and led wheels.

OIL PUMP
The oil pump is driven by the led driveshaft. It is a trochoid pump located above the oil level to prevent cavitation caused by air trapped by the oil pump drive gear, and it is designed to produce oil pressure to control the right and left wheels and to feed pressurized lubrication oil to each part.

LINEAR SOLENOID VALVE
The linear solenoid valve regulates the primarily controlled oil pressure from the oil pump to the adequate pressure in accordance with the driving torque, that is distributed to the right and led wheels.

RIGHT/LEFT SHIFT SOLENOID VALVE
The right and led shift solenoid valves are provided for the right and left clutches. They are designed to select the 3-series planetary gear fixing shaft for deceleration, and they supply the oil pressure governed by the linear solenoid valve to the clutch by turning ON or OFF.

RIGHT/LEFT OIL PRESSURE SENSOR
The right and left oil pressure sensors are in the right and left clutch oil lines. After detecting the oil pressure, the sensors transmit the signal to the ATTS control unit.

OIL TEMPERATURE SENSOR
After detecting the ATF temperature in the ATTS unit, the oil temperature sensor transmits the signal to the ATTS control unit.