System Description
- GENERAL DESCRIPTION
- The Four Wheel Drive Control System (4WD Control System) consists of the hydraulic control mechanism of the transfer unit, steering angle sensor, wheel speed sensor, skid control ECU, and other components for electronic control.
- Drive force appropriate to vehicle speed and condition is distributed to the front and rear wheels of the vehicle by ECU control of the hydraulic pressure of the center differential control limiting clutch to realize stable running.
- Main components and their functions.MAIN COMPONENT FUNCTIONS
Component Function 4WD Indicator Light (Multi-information Display) Displays a warning to the driver when the system malfunctions Slip Indicator Light Notifies driver that the current road surface is slippery Stop Light Switch Detects the brake operation Throttle Position Sensor Detects the opening angle of the throttle Park/Neutral Position Switch Detects the "P" position Steering Angle Sensor Detects turning of the steering wheel Linear Solenoid (Transfer control solenoid) Controls hydraulic pressure of the center differential control limiting clutch using signals from the 4WD control ECU Skid Control ECU with Actuator Detects the signals from each sensor and outputs them to the 4WD control ECU 4WD Control ECU Detects the signals from each sensor via the skid control ECU to operate the linear solenoid and control the system
- FOUR WHEEL DRIVE CONTROL SYSTEM OUTLINE
- Four wheel drive control system is used as the full-time 4WD mechanism for 4WD vehicles.
- Four wheel control system is a full-time 4WD system that is capable of distributing optimum driving force to the front and rear wheels based on running conditions by electronically controlling the transfer center differential control limiting mechanism.
- This system adopts UF1AE that uses a planetary gear type center differential in the transfer section. A wet type multiple disc clutch in the differential control limiting mechanism and a silent chain are used to transfer driving force to the front wheels.
- Four wheel drive control system function.FOUR WHEEL DRIVE CONTROL SYSTEM OPERATION DESCRIPTION
Operation Description Control at vehicle start up This controls the amount of sideway sliding that occurs at the rear of vehicles when accelerating from a stop to improve acceleration and hill climbing capacity Slip control at vehicle start up This helps prevent the vehicle from sliding sideways, to accelerate from a stop with the steering wheel turned and ensures a stable start up and steerability Slip control This ensures high turning performance and stability not affected by road surface conditions during mid and high speed running Control during acceleration This controls straight-line running when accelerating during mid and high speed running to ensure straight-line capacity and stability of the vehicle
- REFERENCE MECHANISM
- Mechanism of the Center Differential.
- The center differential distributes power from the transmission to the front and rear wheels, and absorbs the rotational difference between the front and rear drive shafts generated when they rotate.
- A planetary gear is used for the center differential, which unevenly distributes the driving force to the front and rear wheels.
- Driving force from the transmission is input by the carrier. The carrier and sun gear are directly controlled by the differential control limiting clutch.
- A compact, lightweight and extremely silent chain is used for the front wheel drive transmission, and the driving force is transferred to the front wheel drive shaft by the sun gear of the center differential.
- Mechanism of the Center Differential Control Limiting Clutch.
- The center differential control limiting clutch is located between the planetary gear and the front wheel driving force distribution section, and consists of discs, plates, and pistons of a wet type multiple disc clutch. The basic structure is the same as that of the automatic transmission clutch.
- The rotational difference generated between the plates and discs creates frictional resistance that transfers torque, and then distributes torque of the center differential control limiting mechanism and of the front and rear wheels.
- Adjustment of differential control limiting force is controlled by changing the hydraulic pressure that functions in the piston.
- Mechanism of the Hydraulic Control (ATF Pressure Control).
- Line hydraulic pressure for transmission control is also used by the transfer to simplify the transfer hydraulic system.
- Line hydraulic pressure from the transmission is controlled by a modulator valve so that it does not rise above a specific pressure. This stabilizes hydraulic control of the linear solenoid valve.
- Hydraulic pressure controlled by the linear solenoid valve operates the control valve. It also controls the slip status of the center differential control limiting clutch by modulating the line hydraulic pressure from the transmission in the linear solenoid.
- Mechanism of the Valve body & Linear Solenoid (Transfer Control Solenoid).
- The valve body is positioned in the lower section of the transfer casing, and has a two-level structure consisting of the upper valve body and the valve body cover. A linear solenoid valve is attached to the upper valve body.
- The linear solenoid is integrated with electromagnetic section and the pressure modulating section. The spool pushes the pressure modulator valve according to the electric current value that makes the electromagnetic section function. The pressure modulating valve then generates hydraulic pressure to resist the pushing force of the spool, so it is possible to obtain hydraulic pressure proportional to the electric current value.
- Mechanism of the Center Differential.