Control Trac
From Wikipedia, the free encyclopedia
Control Trac is the brand name of a four wheel drive system marketed by Ford Motor Company for their sport-utility vehicles. The system was developed by BorgWarner. The Control-Trac system has three driver selectable modes, "Auto", "4H", and "4L". The "Auto" mode was revolutionary at the time, working transparently to provide four wheel drive when needed and if even more traction was required, a twist of a knob or push of a button provides four wheel drive high or low. Control Trac is used on the Ford Explorer and the Ford Expedition.
[edit] The Modes
The "Auto" mode normally routes all engine power to the rear differential until wheel slippage is detected by electronic sensors. When slippage is detected, an electromagnetic clutch activates in the transfer case, progressively transferring power to the front differential. This mode should be used all the time on the road and in nearly all weather conditions. The "4H" mode locks the center clutch, forcing the front and rear drive shafts to turn at the same speed. This mode should only be used in relatively extreme situations such as off-roading or deep snow or sand. Since the center clutch is locked, turning can cause binding in the drivetrain which can cause damage. "4L" is similar to 4H, but additional low gearing is utilized to maximize torque, such as towing a boat out of water. Due to the low gearing, the fastest one can go in 4L is roughly 20 mph (32kph).
Control Trac should not be confused with similar sounding Control Trac II, as the two are not related.
