DCCD Subaru STi Explained:
Differential limiting function of torque-sensitive mechanical LSD mechanism
When torque input is to the center differential by acceleration or deceleration, the torque cam transmits the torque from the sun gear to the planetary shaft, generating force that moves the planetary shaft leftward in the figure given below.
This force moves the main clutch hub mounted to the planetary shaft leftward in the figure, causing the main clutch to be engaged.
Because the main clutch outer periphery is connected to rear wheels through the differential case and its inner periphery to front wheels through the main clutch hub and planetary shaft, engagement of the main clutch causes to limit the differential action of the planetary gear unit.
The main clutch engagement force is determined by the leftward force generated by the torque cam; therefore, the differential limiting force generated by the mechanical LSD automatically changes in proportion to the engine driving force (accelerator pedal travel).
DCCD Subaru STi Explained:
Electromagnet Clutch LSD Mechanism
The electromagnetic clutch LSD mechanism consists of a main clutch, an intermediate clutch, a pilot clutch, an armature, a coil, six balls placed between the pilot clutch hub and intermediate pressure plate and other components.
This LSD mechanism carries out differential limiting by converting braking force of the pilot clutch to main clutch engagement force by the balls and intermediate pressure plate.
While the coil is de-energized, the pilot clutch is freed, allowing the pilot clutch hub, balls and intermediate pressure plate (connected to the sun gear through the main clutch hub) to turn idle with approximately the same rotational speed as the sun gear. In this state, the electromagnetic clutch LSD makes no differential limiting.
When the coil is energized, its magnetic force attracts the armature to engage the pilot clutch. As the result, the pilot clutch hub is locked onto the differential case. (The pilot clutch engagement force varies by current flowing through the coil.)
If rotational difference between the sun and internal gears is generated due to a slip in any of tires with the pilot clutch engaged, a phase difference that depends on the pilot clutch engagement force is generated between the intermediate pressure plate connected to the sun gear and the pilot clutch hub (connected to the internal gear through the differential case).
As the result, the balls placed between the intermediate pressure plate and pilot clutch hub are given a force that presses the intermediate pressure plate leftward, causing the intermediate and main clutches to be engaged with each other.
Connection between the intermediate and main clutch limits the differential action between the sun and internal gears.
The force given to the balls that presses the intermediate pressure plate leftward is determined by the pilot clutch engagement force. Therefore, the differential limiting force of the electromagnetic clutch LSD can be controlled by adjusting the pilot clutch engagement force with current applied to the coil.