Estimation of Disturbance Inputs to a Tire Coupled Quarter-car Suspension Test Rig
In this study a real-time open loop estimate of the disturbance displacement input to the tire and an external disturbance force, representing handling and aerodynamic forces, acting on the sprung mass of a quarter-car suspension test rig was generated. This information is intended for use in active control methods applied to vehicle suspensions. This estimate is achieved with two acceleration measurements as inputs to the estimator; one each on the sprung and unsprung masses. This method is differentiated from current disturbance accommodating control, bilinear observers, and preview control methods. A description of the quarter-car model and the experimental test rig is given.
The equations of motion for the quarter-car model are derived in state space as well as a transfer function form. Several tests were run in simulation to investigate the performance of three integration techniques used in the estimator. These tests were first completed in continuous time prior to transforming to discrete time. Comparisons are made between the simulated and estimated displacement and velocity of the disturbance input to the tire and disturbance force input to the sprung mass. The simulated and estimated dynamic tire normal forces are also compared. This process was necessary to select preliminary values for the integrator transfer function to be implemented in real-time.
Using the acceleration measurements from the quarter-car test rig, a quarter-car parameter optimization for use in the estimator was performed. The measured and estimated tire disturbance input, disturbance input velocity, and dynamic tire normal force signals are compared during experimental tests. The results show that the open loop observer provides estimates of the tire disturbance velocity and dynamic tire normal force with acceptable error. The results also indicate the quarter-car test rig behaves linearly within the frequency range and amplitude of the disturbance involved in this study. The resultant access to the disturbance estimate and dynamic tire force estimate in real-time enables pursuit of novel control methods applied to active vibration control of vehicle suspensions.