EST (Electronic Shift Transfer)
EST (ELECTRONIC SHIFT TRANSFER)INTRODUCTION
EST system is a kind of part time 4 wheel drive system and its full name is "Electronic shift transfer". Instead of previous free wheel hub, Free Running Differential (FRRD) was adopted and this one is for Shift On The Fly (SOTF) while vehicle driving. When the vehicle runs with 2WD again, the front axle will be rotated idly due to the vehicle speed and this makes the noise and vibration on the propeller shaft and ring gear set. Therefore FRRD will prevent these phenomena to get a driving stability, efficiency and improved NVH.
When 4WD is selected by driver, a FRRD air pump motor operates and a dog clutch in FRRD is engaged to pinion shaft making s front wheels drive. Therefore the front propeller shaft and the front drive shaft are coupled rotating together. Oppositely, if 2WD is selected by a driver, the dog clutch in a FRRD is disengaged resulting in disconnection between the front propeller shaft and the front drive shaft.
TOD (TORQUE ON DEMAND) OR ATT (ACTIVE TORQUE TRANSFER)
INTRODUCTION
TOD system is a kind of full time 4 wheel drive system and its full name is "Torque on demand". The optimum engine torque distribution ration between front and rear is controlled by TOD transfer case. This transfer case is controlled and operated by independent control module, that is Transfer case control module (TCCM) and it is located under the crash pad on passenger side.
The torque transmission ratio to front and rear side is not fixed and it is changed and controlled continuously depends on the road and vehicle driving condition.
Basically the torque split ratio will be 0:100 (that is "FR" situation) on road driving with low and medium vehicle speed. If there is any amount of slip on the rear wheel, the optimum amount of torque will be distributed to front wheel to get a stable driving performance.
The range of torque split ratio is from 0:100 to 50:50. It means the maximum torque amount of front wheel cannot be higher than rear wheel in any kind of road or vehicle condition.
According to the speed signal of front and rear wheel from each sensor, the engine torque information from engine ECM, Electro Magnetic Clutch (EMC) will be activated and it will result the change of depressing force to the multiple disc clutch. If the force is high, more engine torque will be transmitted to front wheel.
Oppositely, if it becomes low, the torque to front side also will be decreased. It means the slip inside of multiple disc clutch will be increased also. Therefore the oil pump for lubrication of clutch is installed and very important for the overall system durability.
SYSTEM DIAGRAM
ACTIVE TORQUE TRANSFER (ATT)