Driver-Controllable Center Differential System
Driver-controllable Center Differential SystemFEATURES
^ The driver-controllable center differential system consists of a planetary gear set and electromagnetically engaged variably controlled multi plate clutches, distributing the drive torque to the front and rear wheels at a ratio of 35:65. The driver can optionally change the locking rate of the center differential.
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^ The system optimally controls the restricting action of the center differential using a computer and works together with the ABS control.
^ Hand brake control
When the hand brake is operated, the current to the coil is lowered to forcibly free the center differential.
^ Brake control
Controls the center differential restriction torque toward the free state in response to brake switch input.
^ Center differential control
Based on throttle respondent torque control and slip control as basic controls, the differential restriction torque of the center differential is controlled between the free state and locked state through PWM control. Also, information received from other various switches and sensors are used in correcting the instruction torque for center differential control.
^ Fail-safe control
If a failure such as breakage of the coil drive element is detected, the coil driving power is turned off and warning indication is given on the meter cluster at a 1 Hz cycle to call attention of the driver. If a failure occurs in any of the sensors, a fixed value is substituted for the value from the failed sensor to maintain control as usual, while activating a warning indication on the meter at a 1 Hz cycle to call attention of the driver.
^ ABS control
When the ABS operates, the ABSCU & H/U outputs an activating signal to the center differential control unit to decrease the differential restriction torque of the driver-controllable center differential.
^ Throttle respondent torque control Controls the restriction torque of the center differential in response to the throttle opening. The restriction torque of the center differential calculated for each mode is corrected using particular values, however, basically toward the locked state when the throttle is wide open or toward the free state when the throttle is fully closed.
^ Slip control
Controls the restriction torque of the center differential based on the amount of slip derived from the speed of four wheels.
^ Tight cornering control
A correction value is calculated from the left and right wheel speed ratio and applied to the restriction torque of center differential, which is derived from the throttle respondent, slip control, etc.
^ Volume control
By operating the control dial, the driver can optionally control the restriction torque of the center differential.
^ Cornering control
The restriction torque of center differential is controlled based on a value derived from the throttle opening, lateral G sensor, four wheel speeds, etc.
^ Rear differential oil control
When the rear differential oil temperature rises and the oil temperature switch activates, the center differential restriction torque is controlled toward the free state.
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INPUT AND OUTPUT SIGNALS
DRIVER-CONTROLLABLE CENTER DIFFERENTIAL
^ The driver-controllable center differential consists of a differential case, planetary carrier, planetary gears, electro-magnetic coils, armature, main clutch (multi-plate clutch), pilot clutch, and ball bearings.
^ The engine torque enters the differential case from the transmission's driven shaft. The torque from the differential case is divided into front and rear directions at the planetary carrier; the torque to the front is transferred from the planetary carrier through the planetary gears to the sun gear, while the torque to the rear is transferred from the transfer drive gear (integrated with the planetary carrier) through the driven gear to the propeller shaft.
^ If either of the front or rear wheels spins, the driver-controllable center differential controls the differential action between the front and rear wheels.
^ When current flows through the electromagnetic coils, magnetism is generated at components in the following sequence: electromagnet, differential case, armature (A). The armature is moved to the right (B) by this magnetism causing the pilot clutch to engage, and a magnetic field is formed in the area from the electromagnet, differential case, armature, and to the pilot clutch.
The pilot clutch locks the differential case side and cam 1 side together, thus the rotational speed of the cam 1 and differential case are synchronized. The engagement of the pilot clutch is controlled by adjusting the current flowing through the electromagnetic coils.
^ When a speed difference occurs, a force (B) pushing the cam 2 to the left is generated at the steel balls sandwiched between cam 1 and cam 2, pushing the planetary carrier to the left.
^ When the planetary carrier moves to the left (A), the main clutch is engaged. The main gear locks the planetary gears and the sun gear together to generate a differential action restriction torque.
LATERAL G SENSOR
A lateral G sensor is installed to the body at inside the console. The lateral G sensor detects the acceleration of the vehicle in the lateral direction and controls the differential action restriction torque.
MANUAL MODE SWITCH
The manual mode switch enables the driver to select the mode (auto mode or manual mode) by pressing the switch each time.
CONTROL DIAL
A rotary type switch is provided on the center console enabling the driver to optionally set the front-rear differential action restricting torque in the range between locking rate 0% (free) to 100% (locked). Also, detents are provided between free and locked positions.
DRIVER-CONTROLLABLE CENTER DIFFERENTIAL INDICATOR LIGHT
Driver-controllable indicator lights which indicate the locking rate of the center differential are provided in the meter cluster.
When the driver-controllable center differential is in the auto mode the "AUTO" at the upper part of the meter cluster illuminates, and when in manual mode and the differential restriction torque is varied manually the driver-controllable center differential indicator lights illuminate.
If the control unit detects a fault in a component or unit during self diagnosis, the driver-controllable center differential indicator lights flash until the ignition switch is turned OFF.
Faulty components or units can be identified by reading diagnostic trouble codes (DTC), and faults which occurred in the past can be retrieved from the memory.
DRIVER-CONTROLLABLE CENTER DIFFERENTIAL CONTROL UNIT
The control unit is located behind the glove box at the front passenger's side.
If the control unit detects a fault in a component or unit during self diagnosis, the driver-controllable center differential indicator light (FREE light at the bottom) flashes until the ignition switch is turned OFF.
Faulty components or units can be identified by reading diagnostic trouble codes (DTC), and faults which occurred in the past can be retrieved from the memory. The differential restriction torque of the driver-controllable center differential is controlled based on signals from various sensors and switches, ABS monitor signals and ABS wheel speed signals (from four wheels) from the ABSCU & H/U, and by taking into account the conditions of the road surface and the vehicle.
OPERATION
^ When the vehicle is braked (A) while running:
To enhance safety of the vehicle during braking the restriction force of the center differential is controlled toward the free state.
^ When the vehicle is in between the turn-in point (B) and clipping point (C):
When the vehicle is running from the turn-in point toward the clipping point, the throttle opening increases (vehicle accelerates) and a signal from the lateral G sensor is input. Accordingly the center differential restriction torque is gradually increased to improve the cornering ability.
^ When the vehicle is in between the clipping point (C) and exit point (D):
When the vehicle is running past the clipping point toward the exit point, the input from the lateral G sensor decreases. Accordingly the control interprets this as the vehicle is tracking out from the corner and increases the restricting force of the center differential toward the locked state to maintain traction.