Vehicle Sideslip Estimation Design, implementation, and experimental validation

Control systems that help the driver avoid accidents, or limit the damage in case of an accident, have become ubiquitous in modern passenger cars. For example, new cars typically have an anti-lock braking system (ABS), which prevents the wheels from locking during hard braking, and they often have an electronic stability control system (ESC), which stabilizes the lateral motion of the vehicle to prevent skidding. Collision warning and avoidance, rollover prevention, crosswind stabilization, and preparation for an impending accident by adjusting seat positions and seat belts are additional examples of control systems for automotive safety. These systems rely on information about the state of the vehicle and its surroundings. To obtain this information, modern cars are equipped with various sensors. For a typical car with an ESC system, necessary measurements include the steering wheel angle, wheel angular velocities, lateral acceleration, and the rate of rotation around the vertical body-fixed axis, known as the yaw rate. These measurements alone contain a great deal of information about the state of the vehicle. The speed of the car can be estimated using the wheel angular velocities, and a linear reference model taking the speed, steering wheel angle, and additional measurements as inputs can be used to predict the behavior of the car under normal driving conditions. The predicted behavior can be compared to the actual behavior of the car; ESC systems, for example, use the brakes to correct the deviation from a yaw reference model when the vehicle starts to skid [1]. Although some quantities are easily measured, others are difficult to measure because of high cost or impracticality. When some quantity cannot be measured directly, it is often necessary to estimate it using the measurements that are available. Observers combine the available measurements with dynamic models to estimate unknown dynamic states. Often, dynamic models of sufficient accuracy are not available, and must be carefully constructed as part of the observer design. The observer estimates can be used to implement control algorithms, as Figure 1 illustrates.