By Jim Kerr
Anti-lock braking, traction control and stability control are features built into new vehicles to help drivers with vehicle control while driving on the road. With the power of electronics available for new vehicles, there are many more technologies now available to assist drivers. While many of them will help on the road, there are some specifically designed for drivers who like getting off the pavement too.
Let’s use the off-road technology in the 2011 Toyota 4Runner as one example. Shift the transfer case into 4WD range, and the vehicle computers will modify the Active Traction Control (ATC) system by applying brakes incrementally on a spinning wheel to redirect the power to tires with traction. This is similar to on-road traction control but the system can redirect power to any wheel without reducing power significantly. If there still isn’t enough traction, a pushbutton electrically locks the rear differential so that power is applied to both rear wheels equally. The Mercedes G 550 also includes an electric front differential lock for maximum traction capabilities but when engaged, the vehicle doesn’t want to turn corners easily. This feature is best used for getting through a tough patch – it then must be disengaged for manoeuvring again.
Other traction-enhancing features of the 4Runner include Hill Start Assist, which aids starting traction on loose or slippery surfaces. If the vehicle starts to roll back, the system gently applies brakes enabling a smooth uphill start.
Another system, Toyota’s Kinetic Dynamic Suspension System (KDSS), controls the operation of the front and rear stabilizer bars with a hydraulic linkage and electric solenoids. On road, the solenoids block oil flow to keep the hydraulic rams on each sway bar fixed in place. When driving on rugged surfaces that would normally reduce the load on one wheel allowing it to spin, KDSS operates the solenoids so the hydraulic cylinders move. This permits the sway bars to move, which in turn allows the suspension to move up and down (articulate) without any restriction from the sway bars. Now the tires are in contact with the ground again and have traction.
Traction can also be enhanced going downhill. There are several SUVs, including the Land Rover Range Rover and the new 2011 Ford Explorer, equipped with Downhill Assist Control (DAC). This feature uses throttle and brake control to regulate the vehicle’s downhill speed automatically. Because wheels are braked individually, the vehicle can travel down steep grades covered in loose dirt or rock with stability.
Another system available on the Toyota 4Runner, FJ Cruiser and Lexus LX570 is Crawl Control. This system is like low-speed cruise control and allows the driver to select one of five speeds, from 1.5 to five km/h. Although similar to Downhill Assist, this system works uphill too, and lets the driver concentrate on steering.
Land Rover, Toyota and now Ford’s new Explorer feature controls to tailor the traction to road conditions. In the Explorer, the driver can select Normal, Mud/ruts, Sand, or Snow mode with a knob on the console. Snow mode smoothes throttle inputs and controls power so the tires don’t spin as easily on slippery surfaces, while Sand mode modifies the traction control so the tires can spin more to keep the vehicle moving in loose sand or gravel. The 4Runner “Terrain Select” knob selects between Mud and Sand, Loose Rock, Mogul or Rock. The Rock mode is for serious off-road climbing where you don’t want the tires spinning as you climb over boulders.
Electronic throttle control modification is used by many manufacturers if 4WD low range is selected. By reducing the rate of the throttle opening in relationship to the movement of the accelerator pedal, the driver has better driving control, especially if the vehicle is bouncing over rough surfaces. Transmission shift points are also often changed when in low range so the transmission holds a gear longer, enabling better control.
Traversing rough off-road terrain still takes a combination of driver control and the ability to “read” the terrain, but electronically controlled systems will help even the best drivers. For those of us who only occasionally travel down a cottage trail, perhaps we don’t need all these systems, but they do help to keep vehicles moving safely.