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In this work the effects of vehicle vertical vibrations on the tires/road cornering forces, and then consequently on vehicle lateral dynamics are studied. This is achieved through a ride model and a handling model linked together by a non-linear tire model. The ride model is a half vehicle with four degrees of freedom (bounce and pitch motions for vehicle body and two bounce motions for the two axles). The front and rear suspension are a hydro-pneumatic slow-active systems with 6 Hz cut-off frequency designed based on linear optimal control theory. Vehicle lateral dynamics is modeled as two degrees (yaw and lateral motions) incorporating a driver model. An optimal rear wheel steering control in addition to the front steering is considered in the vehicle model to represent a Four Wheel Steering (4WS) system. The tire non-linearity is represented by the Magic Formula tire model.

The dynamics of vehicles became one of the most important aspects for current developments of electronically controlled steering, suspension and traction/braking systems. However, most of the published research on vehicle maneuverability doesn't take into account the effect of the dynamic tire load and its variation on uneven roads. Clearly, it was stated that using a suitable active suspension system could reduce this dynamic tire load. This dynamic tire load is playing a vital role as it is the major link between the vertical and lateral forces exerted on the road, which affects the lateral dynamics of the vehicle. In this paper, a practical hydro-pneumatic limited bandwidth active suspension system with and without wheelbase preview control is used to study its influence on the vehicle stability in lateral direction. The model is a longitudinal half car with four degrees of freedom.

In this work, the active front steering control is studied using linear three degrees of freedom handling model incorporating the driver’s operation model and vehicle suspension derivatives. The active steering control strategy is based on the optimal control theory. In this design, the active front steering angle is determined based on minimizing all model state variables and full state feedback gains. The results are generated when the model is excited by random wind excitation, which was modeled as quasi-static approach with statistical properties taken from previous work, and presented in frequency domain as power spectral density as well as root mean square values in tables. Significant improvements are achieved for the vehicle handling characteristics using active front steering control in comparison with active four wheel steering and conventional two wheel steering.

In this paper, the vehicle body attitude in response to low frequency dynamic loads experienced during braking, accelerating, cornering, aerodynamics or payload variations can be controlled using an electronically controlled active suspension. Using a four degree of freedom half vehicle model, a composite controller which consists of Linear Quadratic Regulator vibration controller (LQR) plus Proportional-Integral-Derivative controller (PID) has been designed to isolate the body vibration from the road surface irregularities and maintain the body static height constant as well as control the body pitch motion. Vertical step inputs and different longitudinal step braking forces were applied to the body C.G. to simulate the payload variations and emergency braking effects.