ControlTrac
ControlTrac four-wheel drive is the
Availability
ControlTrac made its debut on January 12, 1995, for the 1995
Vehicles available with automatic ControlTrac four-wheel drive | ||
---|---|---|
Vehicle | Model Year | Transfer case |
Ford Explorer | MY1995–2010 | two-speed |
Ford Expedition | MY1997–present | two-speed |
Ford Expedition EL/Max | MY2007–present | two-speed |
Lincoln Navigator | MY1998–2006 | two-speed |
Lincoln Navigator | MY2007–present | single-speed* |
Lincoln Navigator L | MY2007–present | single-speed* |
*Does not have Four Low mode with low range off road reduction gearing.
The fifth generation 2011 Ford Explorer (U502) replaced automatic ControlTrac four-wheel drive with automatic Intelligent four-wheel drive and Terrain Management.[5][6]
Design and development
The idea for an electronically controlled four-wheel drive system emerged at BorgWarner in 1985.
The geared center differential would be used to allow the front and rear drive shafts to turn at different rotational speeds so as to eliminate any "drivetrain binding" or "torque windup" while the system was being used on
Within a year, the controller had become larger and more complex. A breadboard electronic version complete with sensor amplifiers and large control modules consumed the entire back end of a station wagon. Input data came from variable reluctance sensors installed at the front drive shaft, rear drive shaft, throttle, brakes, and steering. The goal was to control clutch actuation by controlling current.[1]
However, as the development process continued, engineers at BorgWarner discovered that, with clever
We asked ourselves: Why do we need a differential? There was all of that iron, all that weight, all that cost. And here, we saw that we could control the clutch pack very precisely without it.
— Ronald A. Schoenbach[1]
The design team gained confidence in their concept in 1989, when they made a breakthrough in the multi-disc clutch's control system. Development of closed-loop control smoothed its operation.[1] Using it, the multi-disc clutch made smaller adjustments, but did it more frequently.[1] The microprocessor would review input from sensors every 20 milliseconds and decide if the front axle needed more torque. Using this technique, the unit's computer watched for drive wheel slip. If it sensed as little as half an rpm difference between the front and rear axles, it sent a power signal to the multi-disc clutch. The clutch engaged, diverting torque to the front axle in 10 percent increments, until it alleviated the drive wheel slip. As a result, the system could control runaway drive wheel speed in as little as a third of a wheel revolution.[1]
Off road testing
Early in the development, BorgWarner had employed a sintered bronze clutch material that exhibited an operating condition commonly known as "stick slip." The slippage had inspired engineers to replace it with a paper-based material mounted atop metal. The paper offered a better coefficient of friction and solved the slippage problem. BorgWarner's automatic transmission components division is credited for the solution.[1]
However, heat proved to be a persistent issue. Excessive heat buildup would burn out the new clutch material. To solve the problem, engineers studied the clutch's torque capacity. It was determined that excessive heat buildup was caused by inadequate clutch torque capacity. Engineers increased the system's capacity and equipped a fleet of test vehicles, which they took to the
Modes
ControlTrac has different drive modes as well as different operational behavior for those drive modes depending on which vehicle it is used in. For example, the Ford Expedition used a new auto lock feature in Auto mode. Auto mode with auto lock was not available on the Explorer at that time.[2]
Two High mode
Predominantly, Explorer was not equipped with Two High mode except in the 1995-1996 model years. In model years 1998-up no Two High was available. Only Auto, Four High and Four Low modes were offered. Two High mode was unique to the Expedition, though it was discontinued between the 1999–2002 model years. Two High mode was reintroduced on the redesigned second generation Expedition (U222) for the 2003 model year and featured a new full front axle disconnect system with vacuum operated front locking hubs that would disconnect the front axle, front differential, and front drive shaft when not needed for quieter, more fuel-efficient operation on pavement.[7] Ford claimed that the improved Two High mode could help increase fuel economy up to half-a-mile per gallon of gasoline.[7] In Two High mode, torque is routed to the rear drive wheels only, imitating rear-wheel drive.
Auto mode
Auto mode was featured on both Explorer and Expedition and allows for all-
In the early 2000s, ControlTrac was updated and introduced in 2002 with more advanced software programming, building on the system's
Four High and Four Low modes
Four High and Four Low modes were also featured on both Explorer and Expedition. Four High mode tells the intelligent locking multi-disc differential to lock, providing a permanently locked 50:50 torque distribution.
Both Four High mode and Four Low mode cannot be used on pavement as "driveline binding" and "torque windup" can occur, causing damage to the four-wheel-drive system.
AdvanceTrac
The automatic ControlTrac four-wheel drive system can be coupled with AdvanceTrac
ControlTrac II
ControlTrac II was a Ford four-wheel drive system based on a viscous coupling unit. The viscous coupling replaced the typical center differential used in four-wheel drive applications. The system worked normally in front wheel drive but in addition to the front wheels being driven, a shaft is powered that runs to the viscous coupling in the rear. If the front wheels slip, the viscous coupling progressively releases torque to the rear wheels. Additionally, the ControlTrac II system provided a mechanical lock of four-wheel drive though there was no low range provided by the system.
ControlTrac II has since been replaced by the automatic Intelligent four-wheel drive system, a similar system with the viscous coupling replaced by a computer controlled clutch. The Intelligent 4WD system functionally acts similar to the ControlTrac II system, with the front wheels being driven predominately with torque being sent to the rear wheels only as conditions dictate. The Intelligent 4WD system also lacks the mechanical lock provided by ControlTrac II.
References
- ^ a b c d e f g h i j k l m n "4-wheel drive steps back to the future". www.designnews.com. Retrieved 2012-09-10.
- ^ a b c "New Ford Expedition Features Borg-Warner Transfer Case". www.thefreelibrary.com. Retrieved 2012-09-11.
- ^ "BorgWarner Products". www.borgwarner.com. Retrieved 2012-09-10.
- ^ a b c "Control Trac® delivers automatic torque split, low-range". www.ford-trucks.com. Retrieved 2012-09-10.
- ^ "2011 Ford Explorer Overview". www.ford-trucks.com. Retrieved 2012-09-10.
- ^ "Intelligent 4WD". www.ford.com. Retrieved 2012-09-10.
- ^ a b c d e "2003 Ford Expedition Overview". www.ford-trucks.com. Retrieved 2012-09-10.
- ^ a b c d "2002 Ford Explorer Overview/Powertrain". www.ford-trucks.com. Retrieved 2012-09-10.