Research Of ABS Control Algorithm In Cornering Braking And Its Improvement For Vehicle Lateral Stability

Along with the improvement of highroad, the progress of vehicle technology and the increasing of vehicle velocity, it is more and more important to satisfy the vehicle active security performance. It's reported that many traffic accidents are made by vehicle sideslip when braking. For example, 40 percent traffic accidents take place along with vehicle sideslip when vehicle velocity is 80-100km/h. And 100 percent traffic accidents are made by vehicle sideslip when vehicle velocity is more than 160km/h. It is obvious that it is very important for enhancing the vehicle active security performance how to improve the vehicle lateral stability in the limited condition especially in cornering braking.It is a strong nonlinear and complex work condition when braking, and cornering braking is a more dangerous job. There are the longitudinal force and the lateral force between tire and road in cornering braking, when the longitudinal force occupies the most of the friction force, the lateral force is almost equal to zero. During this course, vehicle will lose the lateral ability of resisting interference and this will result in sideslip, crisis turn and track offset. These situations discussed above will result in traffic accidents. So, the lateral stability is an important evaluating target in cornering braking. In order to ensure the lateral stability, some braking efficiencies will be given up. Therefore, the braking efficiency and the lateral stability should be considered together when designing a vehicle braking control system for cornering braking.The traditional ABS controls the wheel slip ratio to be the optimal slip ratio to ensure that the wheel acquires the biggest longitudinal adhesion coefficient to make the biggest braking force, which improves vehicle braking efficiency. But according to the tireμ?λcurve, the wheel lateral adhesion coefficient is not the biggest in the optimal slip ratio. If the lateral force is not enough for cornering braking, the vehicle will not steer by driver's desire and lose the operating stability, which will result in sideslip, crisis turn and track offset. So, the traditional ABS can't improve the vehicle lateral stability performance in cornering braking.In this paper, the ABS Control Algorithm in cornering braking is designed, according to these problems above and combining with the R & D needs of the project (863 Program"Chang'an export cars independent integration and industrialization - integrated chassis control") taken on by our Laboratory. The ABS target slip ratio is found out under considering the braking efficiency and the lateral stability together in cornering braking and the"target slip ratio-steer angle-initial velocity curve"is be designed. And then the improved ABS by using the"target slip ratio-steer angle-initial velocity curve"is designed. The braked turning-vehicle is controlled by the improved ABS and the traditional ABS severally in the high adhesion road and the low attachment road. Simulation results show that the"target slip ratio-steer angle-initial velocity curve"in cornering braking is correct and the improved ABS is more effective than the traditional ABS to keep the stability of the braked turning-vehicle. The mostly jobs are followed:⑴Based on vehicle dynamics, this paper analyzes the relationship between forces of tires and the vehicle yaw movement in cornering braking and finds out the method of improving the vehicle stability, which is to give different target slip ratios to be followed for ABS in different cornering braking. These target slip ratios must provide the desirable vehicle braking efficiency and the desirable vehicle lateral stability.⑵The ABS target slip ratios in cornering braking are designed by using offline simulations and Particle Swarm Optimization (PSO) method. Firstly, these factors which are relative to the vehicle braking efficiency and the vehicle lateral stability are discussed. And then, according to these factors, the flow chart and the PSO method are designed to find out the ABS target slip ratios. Finally the"target slip ratio-steer angle-initial velocity curves"of ABS on different roads are designed.⑶Joint simulation environment for cornering braking is set up by using CarSim, AMESim and Simulink software, which focuses on the ABS hydraulic modulator modeling based on AMESim. These structural parameters which are needed by the ABS hydraulic modulator modeling are obtained through dissecting hydraulic regulator ABS20-Ⅰ. And the relationship between these structural parameters and their affections to the hydraulic regulators performance is analyzed.⑷The improved ABS is designed with the"target slip ratio-steer angle-initial velocity curves"obtained above and the steer angle obtained by the steer angle sensor. The steer angle sensor can be supplied by EPS. The braked turning-vehicle is controlled by the improved ABS and the traditional ABS severally in the high adhesion road and the low adhesion road. Simulation results show that the improved ABS with the"target slip ratio-steer angle-initial velocity curve"is more effective than the traditional ABS to keep the vehicle lateral stability in cornering braking.The innovations of this thesis are obtaining the"target slip ratio-steer angle-initial velocity curves"based on off-line simulation and Particle Swarm Optimization algorithm and designing the improved ABS based on these curves. The improved ABS improves the vehicle lateral stability effectively and its design provides a novel method for the design and development of automotive braking system.