Abstract: A vehicle air suspension can be controlled between a Standard setting of ride height and a lower, Kneel, setting. Movement to or from the Kneel setting is frozen if a door is opened or if the footbrake is applied. Alteration to the Kneel setting is prevented except when the vehicle is stationary. The suspension reverts to the Standard ride height if the vehicle is driven off or the handbrake is released. Movement of the suspension to or from a lower or higher setting is carried out sequentially to prevent headlamp dazzle. If the vehicle becomes partly supported by direct contact between the chassis and the ground (belly-out) this is detected by monitoring signals to ride height control valves and by providing a controlled re-inflation and balancing of the air springs.

Abstract: A circuit for controlling a plurality of inductive loads, includes a plurality of low voltage transistors controlled by a flip-flop so that only one of the low voltage transistors is on at any given time. These low voltage transistors connected one end of respective ones of the loads to one rail of a supply. Diodes connect the other ends of the loads to a common point which is connected to the other rail of the supply by a single high-voltage transistor. Further diodes connect said one end of the respective loads to said other rail to protect the low voltage transistors from high voltages caused by the interruption of current in the loads.

Abstract: A device and method for measuring the rate of change of a pulse train from a transducer includes first counter which counts the number of pulses in a first fixed frequency of pulse train during each interval between the signal pulses. A divider receives the count generated in the preceding interval and divides the frequency f.sub.1 of a second fixed frequency pulse train by this count. This divided pulse train is counted by a second counter for the duration of each interval to provide a ratio of the change in duration to the preceding interval's duration.

Abstract: An i.c. engine fuel control system includes a closed loop roughness control, utilizing a roughness sensor circuit, an integrator which integrates the error between the roughness signal and a reference signal and modifies the fuel flow to the engine via a main fuel control with a variable frequency clock. During acceleration and deceleration the closed loop is interrupted by means of a circuit including two differentiators which are sensitive to throttle opening (speed demand) and actual speed respectively, and switches controlled by these differentiators.

Abstract: An i.e. engine fuel control system includes a main fuel control which controls fuel flow to the engine in accordance with one or more engine operating parameters. The operation of the fuel control can be modified by a roughness sensing circuit which produces a roughness signal output dependent on the magnitude of fluctuations of engine speed. This output is applied to an integrator which provides a limited authority trim signal to the fuel control in accordance with the time integral of the error between the roughness signal and a speed-dependent reference signal generated by a speed-shaping circuit.

Abstract: A solenoid drive circuit includes two output transistors in parallel paths of relatively high and low resistance respectively. The low resistance path transistor is controlled by a voltage comparator arranged to compare the voltage across a common current sensing resistor with a reference voltage. When the input to the circuit is low, the high resistance path transistor is biased on, but where the current is below a set level, only the low resistance path transistor conducts. Only when the comparator changes state as the solenoid current exceeds its set level does switching off of the low resistance path transistor permit the other transistor to turn on. A delay circuit is included which operates to prevent the low resistance path transistor turning on if there is a short circuit across the solenoid.

Abstract: A solenoid control circuit includes a first switching element which connects one side of the solenoid load to earth via a current sensing resistor. The other side of the solenoid load is connected by a second switching element to a supply rail. This second switching element is biased to conduct but can be turned off by either of two comparators which are connected to compare the voltage across the current sensing resistor with two different reference voltages. Each comparator has hysteresis and the circuit operates so that one comparator operates to switch off the second switching element when a predetermined current level is reached and the other comparator operates to switch the second switching elements on and off at lower current levels between said predetermined current level and the lower threshold level of the first comparator.