GENERAL INFORMATION

Electronically controlled 4WD has been adopted to ensure the on-road performance, achieve lighter and smaller body, and realize better fuel economy.
The electronically controlled 4WD controls the torque of the electronic control coupling located between the propeller shaft and rear differential. This strategy is enabled by varying the torque distribution to the front and rear wheels from the status closer to the front wheel drive to the status closer to the direct coupling 4WD and realizes the optimal drive force according to the various driving conditions.

AIMS OF DEVELOPMENT

Lightweight and simple construction of the electronically controlled 4WD achieves good fuel efficiency and provides enjoyment of selecting the drive mode.

FUNCTION

The adoption of the electronic control coupling prevents the tight corner braking phenomenon^* and satisfies the traction performance.

note

^*Tight corner braking indicates the following condition. When the 4WD vehicle turns sharply on a pavement at low speed (ex. parallel parking), the rotational radius of the front and rear wheels differs, and this difference can no longer be compensated by the tyre slippage. At this time, the driver feels as if the brake was applied.

The electronically controlled 4WD receives the signals of the throttle position and vehicle speed via CAN^* communication protocol, detects the vehicle driving condition and operation of the driver, and distributes the proper torque to the rear wheels.

note ^*: For more information about CAN (Controller Area Network), refer to GROUP 54C .
Under severe driving condition, the system is protected by minimizing the limitation force of the differential.
During high-speed driving, the fuel efficiency is improved by reducing the limitation force of the differential.
The following drive modes are available according to the drivers’ preference to provide the enjoyment of selecting functions.

Drive mode	Control content	Appeal point
4WD ECO	Minimizes the limitation force of the differential.	High fuel efficiency mode. This mode is ordinary driven on efficient 2WD and provides 4WD performance on wheel slipping conditions.
4WD AUTO	Increases the limitation force of the differential according to the different rotation speed of the front and rear wheels and the throttle position.	Normal mode. This mode achieves adequate 4WD performance on various conditions, dried pavement, wet road, snow road, etc.
4WD LOCK	Further increases the limitation force of the differential compared to the 4WD AUTO.	High traction mode. This mode excels at rough road driving and escape from stuck conditions, in addition, realizes strong 4WD driving from low speed to high speed on ordinary road.

CONSTRUCTION DIAGRAM

System component and function

Parts name	Functional description
Engine ECU	Sends the following signals required by 4WD-ECU via CAN communication. Engine torque signal Throttle position signal Engine speed signal
CVT-ECU or A/T-ECU	Sends the following signals required by 4WD-ECU via CAN communication. Gear position signal
ABS/ASC-ECU	Sends the following signals required by 4WD-ECU via CAN communication. ABS sensor signal (4 wheels speed signal) ABS/ASC operation signal 4WD limitation torque signal
Steering wheel sensor	Sends the following signals required by 4WD-ECU via CAN communication. Steering angle signal
4WD switch	Sends the drive mode switch signal (4WD) to 4WD-ECU.
ECO switch	Sends the ECO ON/OFF signal to 4WD-ECU.
ETACS-ECU	Receives drive mode-related information (4WD ECO, 4WD AUTO, 4WD LOCK), failure information and protection information from the 4WD-ECU, and then sends them to the combination meter.
4WD-ECU	Calculates the optimum differential limitation force judging from the vehicle condition and present drive mode based on the signals from each ECU and switch, and controls the current value flown to the electronic control coupling.
	Controls the indicators (4WD ECO, 4WD AUTO, 4WD LOCK) in the combination meter.
	Controls the self-diagnostic function and fail-safe function.
	Controls diagnostic function (Compatible with M.U.T.-III).
Electronic control coupling	Transmits the torque corresponding to the current value controlled by 4WD-ECU to the rear wheels.
Drive mode indicator	Integrated in the combination meter, and indicates the selected drive mode. When the 4WD system fails or is protected, the "4WD-E" or"LOCK" indicator will flash simultaneously or alternately, and the system will enter the mode which protects automatically the drive system components, and the drive mode changeover with the 4WD switch will become unavailable. <Standard meter> When the 4WD system fails or is protected, a message will be displayed, and the system will enter the mode which protects automatically the drive system components, and the drive mode changeover with the 4WD switch will become unavailable. <High contrast meter> The drive mode signal from 4WD-ECU is sent to the combination meter via ETACS-ECU using CAN communication.
Diagnosis connector	Outputs the diagnosis code and establishes the communication with M.U.T.-III.

GENERAL INFORMATION

AIMS OF DEVELOPMENT

FUNCTION

CONSTRUCTION DIAGRAM

System configuration

Control schematic diagram

Electronically controlled 4WD electric circuit diagram