Research On Pneumatic Anti-lock Braking System And Acceleration Slip Regulation For Three-axle Vehicle

The three-axle structure of chassis has been widely used in different kinds of vehicle, such as heavy trucks, buses and military off-road vehicles. The pneumatic brake system is normally installed in three-axle vehicle. At present, there are many active safety technologies based on pneumatic brake system have been developed. Anti-lock braking system (ABS) and Acceleration Slip Regulation (ASR) are the most widespread applications in these technologies. Through controlling the slip of wheels, ABS can help the vehicle to make fully use of the road adhesion, shorten the brake distance and improve the stability of vehicle. ASR can reduce the skid state of vehicle by controlling the output torque from engine or applying the drive wheel braking force. The acceleration ability and trafficability of vehicle can be improved in some harsh condition by ASR.The ABS/ASR research in China seldom involves three-axle vehicle. A simulation model has been built based on the feature of three-axle vehicle in this paper. And also the algorithm of ABS/ASR has been developed. After this, we complete the off-line simulation platform to test and analysis the effect of ABS/ASR controllers.1. Three-axle Vehicle Dynamics ModelingThe three-axle vehicle dynamic model has several components, such as engine model, pneumatic bake system model, driveline model, tire model, whole vehicle model, wheel load calculation module and the wheel centre velocity calculation module. There are several features in these models: (1) Engine model is built as first order inertial system with lag response. (2) Pneumatic bake system model consists of two parts. The one is the model which can simulate charging and discharging process in air bake chambers; the other is the model of cam-type brakes. (3) Tire model is built based on the theory of GIM tire model. (4) Driveline and whole vehicle model is built according to the different types of driving forms of three-axle vehicle. (5) Wheel load calculation module can simulate the load transfer during the acceleration process, which is built by force and geometric features analysis of vehicle structure.2. The Control Strategy and Algorithms for ABS/ASR ControllersThere are plenty of algorithms for ABS/ASR controllers, but most of them barely put into practice in real products. The methods which choose for the development of controllers are the logic threshold control and PID. The ABS/ASR controllers, which have a good adaptation in different road conditions, can be embedded in the three-axle vehicle dynamic model. The parameters in ABS logic threshold control is wheel acceleration and slip ratio control. There are two parts in ASR controller, one is brake control model, and the other is engine throttle control model. The ASR brake control method is logic threshold control,which chooses wheel acceleration as the control parameter. The ASR engine throttle control method is PID. The ASR controller will choose the active model between the engine throttle control model and brake control model, according to different vehicle velocity.3. The ABS/ASR Off-line Platform for Three-axle VehicleThe three-axle vehicle dynamic model is built with MATLAB/Simulink development tools. According the parameters of three-axle vehicle, this model can simulate different kinds of vehicle motion in two different drive forms (6×6&6×4), such as acceleration, turning and braking. The road conditions for simulating are high adhesion road, low adhesion road, split-μroad and jump-μroad. The simulation model of three-axle vehicle provides a platform for the control strategy and algorithms research of ABS/ASR controllers. The ABS and ASR brake control methods are developed in MATLAB/Stateflow, but ASR engine throttle PID control is developed in MATLAB/Simulink. The ABS /ASR off-line platform for three-axle vehicle is completed after ABS/ASR controllers embedded in three-axle vehicle dynamic simulation model.4. The Off-line Simulation ResearchThe effectiveness of control strategy and algorithms for ABS/ASR controllers need to be tested on the ABS/ASR off-line platform. Before simulating, the road condition and vehicle state have to be selected. For ABS, the state of vehicle is emergency braking in a fixed initial velocity. The road conditions for ABS test are high adhesion road, low adhesion road, split-μroad and jump-μroad. For ASR, the state of vehicle is turning and acceleration. The drive form is 6×6 and 6×4. The vehicle gear is chosen to be the one which can lead to the more obvious skid of wheels. The road conditions for ASR test are low adhesion road, split-μroad and jump-μroad. After the simulation condition is settled, the ABS/ASR off-line simulation research can be carried out. There are several conclusions, after comparing the vehicle state without ABS/ASR and with ABS/ASR, can be made: the off-platform can achieve functions of ABS/ASR controllers test; ABS/ASR controllers can control the slip and skid of wheels in target area, to achieve anti-lock braking and anti-slip effects. When the adhesion of road is changed, ABS/ASR controller can responds very quickly to adapt the road condition.