Automatic vehicle level control

A level control system for a wheeled motor vehicle with sprung and unsprung masses and at least one door having alternative open and closed states, the system having fluid power means activatable to level the sprung mass relative to said unsprung mass within a predetermined trim band, said system comprising:

• sampling sensor means effective to indicate the height of said sprung mass relative to said trim band;
• signal generating means responsive to said sensor means for a selected time period to periodically generate a signal indicating whether said sprung mass is above, within or below said trim band for said time period according to predetermined criteria;
• means defining a service time period shorter than a predetermined activation time of said fluid power means which avoids overshoot in level adjustment, a cruise time period longer than the out-of-trim duration of a predetermined long highway feature and a decision time period of duration intermediate the service and cruise time period durations and longer than the period of sprung mass oscillation during vehicle movement;
• means effective to initiate system operation with vehicle operation and select said decision time period;
• means responsive to a predetermined number of consecutive decision time periods with no above-trim or below-trim signals to select said cruise time period;
• means responsive to an above-trim or below-trim signal in a cruise time period to select said decision time period;
• means responsive to an above-trim or below-trim signal in a decision time period to activate said fluid power means and select said service time period;
• means responsive to a within-trim signal in a service time period to deactivate said fluid power means and select said decision time period;
• a door sensor effective to generate a signal whenever said door changes between an open state and a closed state;
• and
• means responsive to a signal from said door sensor during a cruise time period to immediately initiate a decision time period.

A level control system for a wheeled motor vehicle with sprung and unsprung masses and an ignition switch controlling vehicle operation with on and off states, the system having fluid power means activatable to level the sprung mass relative to said unsprung mass within a predetermined trim band, said system comprising:

• sampling sensor means effective to indicate the height of said sprung mass relative to said trim band;
• signal generating means responsive to said sensor means for a selected time period to periodically generate a signal indicating whether said sprung mass is above, within or below said trim band for said time period according to predetermined criteria;
• means defining a service time period shorter than a predetermined activation time of said fluid power means which avoids overshoot in level adjustment, a cruise time period longer than the out-of-trim duration of a predetermined long highway feature and a decision time period of duration intermediate the service and cruise time period durations and longer than the period of sprung mass oscillation during vehicle movement;
• means effective to initiate system operation with vehicle operation and select said decision time period;
• means responsive to a predetermined number of consecutive decision time periods with no above-trim or below-trim signals to select said cruise time period;
• means responsive to an above-trim or below-trim signal in a cruise time period to select said decision time period;
• means responsive to an above-trim or below-trim signal in a decision time period to activate said fluid power means and select said service time period;
• means responsive to a within-trim signal in a service time period to deactivate said fluid power means and select said decision time period;
• an ignition switch sensor effective to generate a signal whenever said ignition switch assumes an off state;
• and
• means responsive to a signal from said ignition switch sensor to immediately initiate a decision time period and prevent further selection of a cruise time period, said means further maintaining level system operation for at least a predetermined finish time after the ignition switch off state is sensed, whereby the level of the vehicle may be adjusted after it is unloaded.