One of the drawbacks of light trucks, including pickups and SUVs, is that a higher center of gravity compromises their stability. According to data from the National Highway Traffic Safety Administration (NHTSA), more than half of SUV driver and passenger deaths are related to rollover incidents.
Electronic Stability Control (ESC) systems, which make pickups and SUVs more stable and thus safer to drive, are making headway in alleviating this problem. According to NHTSA, single-SUV crashes decreased by 67% in vehicles equipped with ESC, and fatalities dropped 63%.
A kink in this solution, however, is that ESC can conflict with traditional four-wheel drive (4WD) systems. ESC is designed to use anti-lock brakes and traction control systems on a per-wheel basis to help drivers maintain vehicle control. But in a typical manual 4WD system, the wheels are coupled together, making single-wheel power delivery impossible.
Limiting use of ESC to vehicles without 4WD is not a practical option. “For starters, SUVs and pickups are much more stable in four-wheel drive mode because you have power going to all four wheels,” explains Dave Bruder, chief engineer for BorgWarner's TorqTransfer Systems Div. “On a two-wheel drive system, your only option to improve brake stability control is to take power away from the engine. But you may need that engine power to get out of a panic situation later on in the [accident] event.”
Bruder adds that 4WD improves overall vehicle traction and control under acceleration. So the next logical move is to ensure that ESC can step into the 4WD equation and function smoothly. That's where the concept of “4WD with a brain” comes in, he says.
“Our Torque-On-Demand system goes a step further and uses electronic controls so that 4WD works in tandem with an ESC system,” he explains. “In a sense, it allows 4WD to get out of the way when the ESC technology needs to go to work.”
Torque-on-Demand technology, notes Bruder, provides drivers with full-time, electronically controlled 4WD for all conditions. Its distinguishing feature is the ability to automatically deliver optimal torque using electronic sensors and microcomputer controls.
In addition to better handling and performance, the system provides more refined tuning, less noise, vibration and harshness, less drag, and — most importantly — improved fuel economy. According to Bruder, the system can decide how much power all of the wheels really need based on wheel speed, throttle position and steering wheel angle.
“Then you have what I call the convenience factor for drivers,” he explains. In an electronically controlled 4WD system, shifting between 2WD and 4WD takes place automatically; the driver does not have to make manual shifts and puts the vehicle in the optimal drive configuration for the conditions.”
Having 4WD that adjusts to driving conditions is critical for safety, he adds. “From my own experience, in a pickup in wet conditions you can get the back end coming around before you even have time to decide whether you need to be in 2WD or 4WD,” Bruder says. “Also, with an electronic 4WD, you are getting better handling and control outside of a panic situation, especially when you are making sharp turns in poor conditions.”
In terms of cooperating with ESC, “smart” 4WD systems can literally get out of the way in a tenth of a second since both ESC and 4WD are functioning in the same electronically controlled environment. “It makes 4WD an enabler for ESC and the overall effort to increase light-truck stability,” he says. “It doesn't conflict with ESC and it provides better handling and stability when the ESC isn't operating.”
Bruder notes that this technology is already available on some SUVs and pickup trucks. “It's all about helping light-truck stability and handling systems evolve. It reflects how automakers are trying to leverage 4WD systems to augment vehicle handling and stability programs,” he says. “By modulating the torque to all of the wheels, we're making light trucks more convenient to operate, get better traction and improve handling, while making sure they are safer.”
