As already stated, a road vehicle on pneumatic tires cannot maintain a given trajectory under the effect of external perturbations unless managed by some control device, which is usually a human driver. Its stability solely involves such state variables as the sideslip angle β and the yaw velocity r. In the case of two-wheeled vehicles the capsize motion is intrinsically unstable forcing the driver not only to control the trajectory but stabilize the vehicle. A possible scheme of the vehicle-driver system is shown in Fig. . The driver is assumed to be able to detect the yaw angle ψ, the. | 27 CONTROL OF THE CHASSIS AND BY WIRE SYSTEMS MOTOR VEHICLE CONTROL As already stated a road vehicle on pneumatic tires cannot maintain a given trajectory under the effect of external perturbations unless managed by some control device which is usually a human driver. Its stability solely involves such state variables as the sideslip angle 3 and the yaw velocity r. In the case of two-wheeled vehicles the capsize motion is intrinsically unstable forcing the driver not only to control the trajectory but stabilize the vehicle. A possible scheme of the vehicle-driver system is shown in Fig. . The driver is assumed to be able to detect the yaw angle 3 the angular and linear accelerations 3 r dV dt V2 R and to be able to assess his position on the road X and Y . Moreover the driver receives other information from the vehicle such as forces moments noise vibrations etc. that allow him to assess largely unconsciously the conditions of the vehicle and the road-wheel interactions. Conventional vehicles In all classical vehicles of the second half of the twentieth century up to the 1990s the driver had to perform all control and monitoring tasks. The only assistance came from devices like power steering or power brakes that amplified the force the driver exerted on the controls. In this situation the human controller is fully inserted in the control loop or as usually said the systems include a human in the loop. G. Genta L. Morello The Automotive Chassis Volume 2 System Design 429 Mechanical Engineering Series Springer Science Business Media . 2009 430 27. CONTROL OF THE CHASSIS AND BY WIRE SYSTEMS FIGURE . Simplified scheme of the vehicle-driver system. Actually the driver must control high level functions choice of the trajectory decisions about speed and driving style about manoeuvres like overtaking etc. and intermediate level functions reacting to perturbations coming from the air and the road following the chosen trajectory etc. . Only stability
