Semi-Active Suspension Systems: From Advanced Control Algorithms to Emerging Off-Road and Agricultural Applications.

Semi-active suspension systems combine low power consumption, rapid response, and fail-safe operation by reverting to passive mode after control failure, making them important for intelligent chassis and vibration-control systems. With the development of intelligent actuators, nonlinear modeling, and advanced control methods, this technology is expanding from conventional road vehicles to off-road vehicles and agricultural machinery. Compared with passenger cars, agricultural machinery faces stronger random excitation, time-varying loads, muddy environments, resource-constrained controllers, and requirements for operational accuracy. This review focuses on semi-active damping and vibration-isolation systems for off-road and agricultural applications. Mainstream actuators, control-oriented nonlinear damper models, classical, robust, and adaptive control methods, MPC, DRL, and mechanism-data fusion control are compared in terms of hardware constraints, model accuracy, real-time computation, and agricultural adaptability. Applications in seat/cab isolation, tractor and tracked chassis systems, rollover prevention, and precision implements are summarized. The review shows that semi-active suspension in agricultural machinery is evolving beyond the conventional trade-off between ride comfort and handling stability toward multi-objective coordination of safety, ground-contact stability, operational accuracy, operator protection, and energy consumption.