Vehicle suspension control with relative suspension position sensor and differentiator

A suspension for a vehicle having a sprung mass and an unsprung mass and comprising, in combination:

• an actuator connected between the sprung mass and the unsprung mass;
• a relative suspension position sensor connected between the sprung mass and the unsprung mass for generating an analog relative position signal;
• a digital suspension control for receiving and A/D converting an analog relative suspension velocity signal at a predetermined sampling rate and generating a control signal for the actuator to provide a desired suspension behavior;
• and
• an analog circuit apparatus for deriving the analog relative suspension velocity signal from the analog relative position signal, the analog circuit apparatus comprising, in combination:
• an operational amplifier;
• a first resistor connected in negative feedback from an output of the operational amplifier to an inverting input thereof;
• a circuit input connected through a first capacitor to the inverting input of the operational amplifier, the first resistor and first capacitor together providing a linearly increasing gain and a 90 degree phase lead for differentiating action over a low frequency range of vehicle suspension resonances;
• a second resistor connecting the circuit input to the first capacitor;
• a second capacitor connected from the output of the operational amplifier to the junction of the second resistor and first capacitor, the second resistor and second capacitor together with the first resistor and first capacitor defining a bandpass filter having a high Q with a peaking gain in an intermediate frequency range above the low frequency range of vehicle suspension resonances, the second resistor and second capacitor together providing a decreasing gain from the intermediate frequency range to define a predetermined low gain at a higher aliasing frequency related to the sampling frequency of the digital signal processing apparatus;
• and
• a third capacitor connected in parallel with the first resistor to control the Q of the bandpass filter so as to balance the amplitude of the peaking gain in the intermediate frequency range with the group delay in the lower frequency range of vehicle suspension resonances.