Vehicle suspension control with actuating circuit protection

Claim 1

A suspension control for a motor vehicle including a solenoid actuator, the solenoid including an actuating coil connected in series with a transistor across an electric power source, the suspension control comprising circuit protection apparatus comprising, in combination: means responsive to sensor elements in the suspension control to generate an on signal when a condition is sensed which requires activation of the solenoid after a predetermined time period of the continuous existence of the condition; an inverter effective to invert the ON signl; oscillator means generating pulses at a constant frequency; counter means responsive to the output of the oscillator means to count the pulses therefrom, the counter means including a reset input provided with the inverted ON signal and being effective to generate an output signal after the appearance of the ON signal at a count corresponding substantially to the predetermined time period at the constant frequency of the oscillator means; a first bistable latch having first and second stable states, a set input and a reset input, the set input being connected to receive the output of the oscillator means such that, subject to the reset input, the first bistable latch attempts to enter its first bistable state at the end of each oscillator pulse; a first logical AND circuit responsive to the first stable state of the first bistable latch and a voltage at the junction of the solenoid coil and transistor indicating excessive current to generate a short signal; a second bistable latch having a set input and a reset input, the set input being connected to receive the output of the counter such that, subject to the reset input, the second bistable latch attempts to enter its first stable state with each output signal of the counter means; a first logical OR circuit connecting the reset input of the second bistable circuit to receive the inverted ON signal and the output of the first logical AND circuit such that the second bistable latch is held in its second stable state in the absence of the ON signal or the existence of the short signal; a second logical AND circuit responsive to the first stable state of the second bistable latch and the ON signal to generate a drive signal to the transistor and otherwise to generate an OFF signal to the transistor, the OFF signal of the second logical AND circuit being provided to the reset input of the first bistable latch to hold the same in its second stable state, whereby the transistor is turned on the predetermined time period after the ON signal first appears and, if an excessive current is detected after a time delay corresponding to the first oscillator pulse, the transistor is turned off again for a time equal to the predetermined time period before being turned on again.