This section examines automatic load-adjustable shock absorbers. They are also called self-leveling.
When vehicles carry heavy loads, their suspension is compressed, causing the rear of the vehicle to be lower than normal.
As a result, steering becomes lighter, the alignment of the headlights becomes too high, and the compression length of travel of the suspension over bumps is reduced, causing discomfort to passengers.
A lower vehicle handles better on smooth roads, but on a rough road, reduced suspension travel can let harsh road shocks be transmitted to the passenger compartment, and cause discomfort.
An automatic load adjustable suspension system controls the vehicle ride height automatically, according to the load placed over the rear axle.
It consists of air-adjustable shock absorbers fitted to the rear suspension, an electrically-driven compressor and air-dryer assembly, and an electronic control unit, and associated wiring and tubing.
The ECU is mounted to the cross-member over the rear axle and a moveable link connects it to a rear suspension member.
As the vehicle is loaded, the normal suspension springs are compressed, which lowers the height of the vehicle.
When the ignition is switched on, the ECU senses the lowered ride height and switches on the air compressor. Air is directed to the shock absorbers, causing the airbag around them to expand and raise the suspension to the normal trim height.
If the load is removed, the suspension springs expand, raising the height of the vehicle.
The ECU senses the raised ride height, and air is exhausted from the shock absorbers, causing the airbag to deflate, and lower the suspension to the normal trim height.
During normal suspension operation, continual adjustment of vehicle ride height is prevented by a time delay, in the ECU.
This allows the trim height to be adjusted only when the ECU reads an out-of-trim signal for 5 to 15 seconds.
The compressor run-time or exhaust-time is limited to 2 minutes.
This prevents it continuing to operate, if the system develops an air leak, or if an exhaust vent remains open.
