Abstract: A level control system for a motor vehicle with an unsprung mass including a wheel, a sprung mass, and a shock absorber connecting the sprung and unsprung masses comprises fluid power apparatus activatable to level the sprung mass with respect to the unsprung mass, a sensor effective to generate a signal indicating the level of the sprung mass relative to the unsprung mass and apparatus responsive to the sensor to compute the difference between the total times, within a predetermined time period, spent by the level above and below a predetermined trim band and apparatus effective to compare the difference of the times with a reference comprising a predetermined percentage of the predetermined time period and activate the fluid power apparatus if the difference exceeds the reference in magnitude, whereby the system can maintain a narrow trim band while the vehicle is not moving while avoiding unnecessary corrections and cycling due to excursions above and below the trim band during vehicle movement over rough

Abstract: A level control system for a wheeled motor vehicle with sprung and unsprung masses, an accessory the activation of which indicates the probability of an associated vehicle load change, fluid power apparatus activatable to level the sprung mass relative to the unsprung mass and sensor apparatus effective to periodically indicate a trim or out-of-trim level condition according to predetermined criteria further comprises apparatus defining a service mode with a time period shorter than a predetermined activation time of the fluid power apparatus which avoids overshoot in level adjustment, a cruise mode with a time period longer than the out-of-trim duration of a predetermined long highway feature and a decision mode with a time period of duration intermediate the service and cruise time period durations and longer than the period of sprung mass oscillation during vehicle movement.