Study On Hydraulic Bootstrapped Limited Slip System Of Vehicle

With the rapid development of the auto industry and the widespread popularity of the family car, vehicle safety has become an important research subject in auto industry field. Anti-slip control of the cars is always the emphasis and difficulty on the vehicle safety control. There is a higher requirement of anti-slip ability due to the faster and faster driving speed and more and more dreadful driving conditions. Current control methods mainly aim at controling vehicle stability and increasing the traction of the vehicle. Although these control methods have a significant effect, there are still some problems that must be solved urgently. The anti-slip control principle, realizing way and limited slip performance of the limited slip system were studied in this paper.According to the problems existed in limited slip differential (LSD) mechanism used widely in wheeled vehicle currently, a novel hydraulic bootstrapped limited slip differential was proposed. Compared with the other initiative anti-slip differential, one of its obvious characteristic is that a complete hydraulic system is integrated within the differential case. It does not need the sensors to measure the variation of the car driving parameters during the working period and has higher reliability for that there is no circuit within it. By the space cam mechanism, this new LSD can adjust the output pressure automatically to regulate the lock degree of the differential according to the speed difference between the two half axles.The cam mechanism, which is composed of half axle gear and the follower located between the differential case and the half axle gear, is the key part of the differential.A new method was introduced because that the traditional reversal method was not suitable to calculate the work profile surface of the space cam mechanism. Based on the conjugated surface meshing theory and the differential geometry theory, the formulas of the induced normal on contact points, the pressure angle and the working profile surface of the new LSD cam mechanism were deduced clearly. The designing example showed that the value of the pressure angle and the induced normal curvature on every contact point could be got directly by the new method although it was not understandable as reversal method. The conclusion that there was cubic relationship between the hydraulic pressure and the size of the clearance was obtained from those functions. The differential anti-slip ability could be adjusted by changing the size of the clearance. The differential simulated software was developed on the basis of the experiment data provided by North Vehicle Research Institute. The software had been used in the friction disk working condition research after it was checked and accepted by North Vehicle Research Institute. Polynomial fitting is the traditional method to describe the mathematic model of the engine, but the low precision is the great problem and even there are fitting errors on the experiment data points. A new method was developed to establish the engine mathematic model because of the flaws of the traditional way by the Polynomial fitting instead of cubic B-spline algorithm. This method has higher precision and no fitting error on the experiment data points. In order to reflect the influence of the differential working condition affected by road exactly, a custom program language was defined to describe the routine and the road surface condition mathematic model. The Road model could be got exactly by adding friction ratio and surface roughness of the road for analyzing the differential working condition.Finally, the experiment of testing the relationship between the pressure of hydraulic system output and the rotational speed difference of the differential was implemented on the experimental platform made by myself. A half axle was motored by an AC asynchronous motor with the belt, and the pressure of the acting room was measured by a hydraulic pressure meter. The results showed that the pressure environment in the acting room could be established if the rotational speed difference between the two axles exceeded some limit. The system output pressure became higher as the speed difference got bigger, but there was a maximum. The experiment results and the conclusions indicated that the novel hydraulic bootstrapped limited slip differential was correct and practicable.