Design of Sliding Mode Controller Based Antilock Braking System of a Vehicle

Anti-lock braking system (ABS) is the most common safety system in the vehicles, which works to increase the generated braking force between the tire and the road surface for enhancing passenger safety specifically related to accident avoidance. However, designing an ABS is a challenging task considering the fact that it is highly nonlinear and a time varying system. The interaction between the tires and the road surface, the dynamics of the whole vehicle and the characteristics of key components in ABS are all nonlinear and time varying. Due to the nonlinearities of the brake actuation system, robust braking control system with a faster response is required to handle even sudden, extreme variations in driving conditions with little loss of traction and steering ability. In this thesis, out of the robust controlling mechanisms, a sliding mode controller based antilock braking system of a vehicle is introduced. The objective of this SMC based ABS is to keep the wheel slip at an ideal value so that the tire can still generate lateral and steering forces as well as shorter stopping distances in order to prevent the controlled wheel from becoming fully locked. In order to control the system based on wheel slip, a Quarter car in terms of wheel slip is modelled and the model is validated by using open loop response analysis by using MATLAB. Then a controller is designed and implemented using MATLAB. During our controller design, in order to resolve the drawback of SMC i.e. chattering, a nonlinear integral surface is defined. The designed SMC based ABS and the conventional ABS are then evaluated under dry nominal, dry concrete and dry slippery road types. And also the performance of the two systems are evaluated under three different initial vehicle velocities and the system responses are then compared in terms of wheel speed and stopping distance. As the numerical simulation shows, on a dry nominal road, for an initial vehicle speed of 40 km/hr, the stopping distance that is obtained from the SMC based ABS and the conventional ABS are 14.5000m and 15.7080 m respectively. In the same road type, for an initial velocity of 90 km/hr, the stopping distance that is obtained from the SMC based ABS and the conventional ABS are 73.5122m and 79.6029m respectively. And also for an initial vehicle speeds of 40km/hr and 90km/hr, the braking time of the SMC based ABS is 0.11 Second and 0.39 Second faster than the conventional ABS respectively. At last, the proposed SMC based ABS achieves a robust system, minimum braking time and minimum stopping distance than the conventional ABS for all road types.