Research On Vacuum Value Detection Test At The End Of Subcompact’s Brake Line

At present, in the automobile charging process, domestic brake fluid filling machine operates detection and judgment process through vacuum value measured by internal vacuum sensor. Vacuum value measured by filling machine just is local vacuum value near pump inlet which can not accurately reflect the vacuum value in the brake line especially at the end, because of the12-14m length from the vacuum pump to brake line’s farthest end. The defect of vacuum value detection of brake fluid filling machine makes the equipment parameters’ accurate setting and analysis of some typical fault mechanism difficult and uncertain. A set of vacuum value detection system at the end of brake line has been developed through a motor company’s three kinds of subcompacts as the chief source, which can detect vacuum value inside of the load sensing proportioning valve and left rear wheel brake at the braking system’s end. Through comparative analysis of vacuum value between the end of brake line and filling machine, the aim was to research evacuation performance among different models, small leakage and brake soft, rational analysis of equipment parameters and leakage position judging method of faulted car with leaking tube joint, put forward corresponding improvement methods, and provide theoretical basis and technical support for research on problems of brake fluid filling in future.The main work and achievements were as follows:1. A set of vacuum value detection system at the end of brake line based on LabVIEW has been designed and a corresponding test method has been put forward. Sealing detection of combination joint, calibration of acquisition card and sensor and real vehicle debugging of the detection system has been done smoothly. It turned out that tightness and precision of the detection system satisfied the test requirement.2. Through the analysis of evacuation test data of three kinds of normal models, it concluded that model1had the best evaluation effect while model3had the worst evaluation effect. Two reasons of the evacuation difference were analyzed, which were coupling mode of the brake master cylinder and structure of brake pipeline. Some corresponding structure improvement methods have been obtained.3. Through the analysis of vacuum value of evacuation test of normal car, faulted car with small leakage and normal car with additional water inside of brake pipeline, it confirmed that the residual moisture in brake pipeline was the main reason of small leakage and brake soft. Related process of brake pipe fittings has been analyzed and corresponding quality control measures have been put forward.4. In view of the company’s irrational parameter setting of brake fluid filling machine, combined with the test data of normal car, setting method of equipment parameter was analyzed. Improvement schemes of equipment parameters of model1and3have been obtained.5.After detailed theoretical analysis of test data of model1with tube joint leakage in different parts (hose and hard tube joint of rear bridge, tube joint of load sensing proportioning valve, tube joint of two way pipe or four way pipe), a general method of judging leakage position of tube joint has been achieved, which improved the efficiency of maintenance.6.Through the three models’ test data analysis in four kinds of situations, five factors determining brake fluid filling machine’s evacuation effect have been obtained, which were model of vacuum pump, equipment parameters, structure of brake pipeline, residual moisture in brake pipe fitting and sealing performance of brake pipeline.