Suspension Control ( Automatic - Electronic ): Description and Operation

DESCRIPTION
WARNING: THE ELECTRICAL POWER TO THE AIR SUSPENSION SYSTEM MUST BE SHUT OFF PRIOR TO HOISTING, JACKING, OR TOWING AN AIR SUSPENSION VEHICLE. THIS CAN BE ACCOMPLISHED BY TURNING OFF THE AIR SUSPENSION SWITCH LOCATED IN THE REAR JACK STORAGE AREA. FAILURE TO DO SO MAY RESULT IN UNEXPECTED INFLATION OR DEFLATION OF THE AIR SPRINGS WHICH MAY RESULT IN SHIFTING OF THE VEHICLE DURING THESE OPERATIONS.

Automatic Ride Control is a computer-controlled suspension system that uses unique suspension components and two stage (firm and soft) shock absorbers to provide a smooth ride for normal driving conditions without sacrificing handling performance. An air spring integral with each shock absorber provides automatic load leveling and allows vehicle height to be adjusted over a span of 50 mm (2 inches).

A smooth ride is achieved through the selection of lower rate front torsion bars and rear leaf springs, Automatic Ride Control (ARC) specific front and rear anti-roll bars, and soft shock damping. Handling performance is maintained by reading driver and road inputs that, under certain conditions, switch the damping rate of the shock absorbers to firm, minimizing body movement. Driver inputs include braking, throttle position, steering rate and position, and ride control switch selection. Road inputs are sensed by two suspension-mounted height sensors and vehicle speed.

The ARC system adjusts vehicle height on the front and rear axles separately through the use of four solenoid valves, an air compressor, and air lines. Vehicle height (trim level) is set based on the status of the door ajar signal and the transfer case mode selected (automatic four-wheel drive, four-wheel drive high, or four-wheel drive low). The trim level is maintained even with the addition and removal of cargo.

In automatic four-wheel drive, an empty vehicle is fully supported by the front torsion bars and rear leaf springs. This height is referred to as the "base" height. Compressed air is applied to the air springs only when a load is added to the vehicle or a transfer case mode of four-wheel drive high or four-wheel drive low is selected.

In four-wheel drive high, the vehicle is raised about 25 mm (1 inch) to increase body clearance and provide a more controlled ride. The vehicle is returned to the base height to achieve a smooth ride at highway speeds.

Off-road capability is increased by stiffening the suspension and raising the vehicle about 50 mm (2 inches) above the base height when in four-wheel drive low, improving clearance between the ground and the body. In four-wheel drive low, compressed air is added to both the front and rear air springs increasing the spring rate of the front and rear by approximately 60% over the spring rate of the suspension when in automatic four-wheel drive. Damping is set to firm in four-wheel drive low to minimize relative movement between the wheel and body.

The system uses two height sensors, a steering sensor, transfer case inputs, and other vehicle sensors to measure driver and road inputs. The system changes shock damping on the front and rear axle separately depending on these inputs through the use of special, dual-rate damping shocks. The system changes vehicle height on the front and rear axle separately through the use of an air compressor, four air solenoids, various air lines, and the use of an air spring integrated inside each shock.

OPERATION
The ARC system lifts the vehicle when the transfer case is shifted into four-wheel drive high (by rotating the transfer case switch) or four-wheel drive low (rotate the selector switch to the 4 low position, place the transmission in neutral, and tap the brake pedal to engage or disengage 4 low).

The ARC system also holds vehicle height when any door or the rear hatch is opened. The system stores front and rear vehicle height the moment an open door is detected. The system then maintains this height regardless of the addition or removal of load. The system will return to its commanded height when all the doors close or if the speed of the vehicle exceeds 16 km (10 mph).