System Operation:
Ride LevelingThe ride level sensor maintains a pre-determined rear suspension "trim height" through the action of the rear struts. When weight is added to the vehicle and the rear suspension drops below the controlled trim height, the ride level sensor provides a ground signal for the suspension relay.
FIG. 1 - "UP" LEVELING:
The relay contacts energize the "charge" and "up" solenoid valves in the solenoid valve block simultaneously. Once energized, the charge solenoid valve closes the return orifice from the hydraulic pump to the fluid reservoir, enabling the system to build pressure. At the same time, the "up" solenoid valve is energized and is opened so that hydraulic system mineral oil (HSMO) is routed through the solenoid valve block, from the hydraulic pump to the rear struts. When trim height is reached, the ride level sensor de-energizes the solenoid valves (Fig. 1).
FIG. 2 - ACCUMULATOR CHARGING PRIORITIZED:
"Up" leveling is blocked and brake accumulator charging is prioritized when accumulator pressure is low (1988 and 1989 models only). The low pressure warning switch contacts open and isolate the suspension relay, preventing the up solenoid valve from being energized (Fig. 2).
FIG. 3 - "DOWN" LEVELING:
When weight is removed from the vehicle and the rear suspension rises above trim height, the ride level sensor provides a ground signal to energize the "down" solenoid. Fluid is then exhausted from the rear struts, lowering the rear of the vehicle (Fig. 3).
The ride level sensor will not respond to out of trim inputs until the condition has existed for at least 20 seconds. The delay ensures that the leveling system will not activate due to normal road irregularities. output signals are cancelled if the trim condition is not achieved within five minutes.
Trapped Line Pressure
Rear suspension system bleeding cannot eliminate all traces of air from the system. To prevent air bubbles from forming, (which may cause rear strut knock and loss of damping), a "trapped line pressure" valve (built into the down solenoid valve) maintains a minimum pressure of 27 BAR (390 psi) in the rear suspension. As a result, the rear of an unloaded vehicle stands approximately 1-1/2 inches above trim height. This unloaded height is called "curb height".
FIG. 2 - ACCUMULATOR CHARGING PRIORITIZED:
Accumulator Charging (1988 and 1989 models only)
The "charge switch" at the brake accumulator senses brake boost pressure. When the pressure is low, the charge switch contacts close, the charge valve solenoid is energized and the charge solenoid valve closes the return orifice to the reservoir. The system builds pressure which forces open a non-return valve in the accumulator and the accumulator is charged with fluid (Fig. 2). When the correct pressure is reached, the charge switch contacts open, the charge valve solenoid is de-energized and fluid is diverted back to the reservoir.