Semi-Active Suspension
Semi-active suspension changes its resistance to suspension motion in response to sensors or control commands but does not generate an arbitrary powered force independent of that motion.
How it differs
The most common implementation is an electronically controlled damper. A proportional valve or magnetorheological fluid changes the damper’s force characteristic as the wheel and body move. The controller can select more or less resistance within the device’s achievable envelope, but the motion across the damper is still required to produce force.
This places semi-active suspension between passive and fully active systems. Passive hardware follows a fixed or mechanically self-adjusting characteristic without an electronic command. Fully active suspension uses powered actuators that can add mechanical energy and move the body or wheel suspension in a commanded direction.
“Semi-active,” “adaptive,” and “electronically controlled” are sometimes used loosely in marketing. Adaptive is the broader term: an adaptive suspension may be semi-active, fully active, or a package that also changes ride height. The exact hardware matters more than the label.
For control boundaries and comparisons with powered systems, see Active Suspension.