Study Of Vacuum Booster Test-machine Sound Insulation And Drive System

Noise performance of automobile vacuum booster and master cylinder is one of the most concerned indexes to manufacturers as an important factor of automotive brake noise. A uniform industry standard evaluating this performance has not yet built in China where measure and control of it is still underway. Much cost will be paid on purchasing and maintaining test machines if they are imported. Thus we decide to develop a similar machine to test noise performance of vacuum booster on commission of Jilin Auto-Brake Factory.Noise test machine of vacuum booster and master cylinder is applied to provide data for research and quality personnel by measuring the working noise intensity of vacuum booster, drawing noise curve and finally identifying the possible factor through analyzing amplitude and frequency of noise. Structure of loading system of the machine is designed after a careful study of basic working theory and working process of vacuum booster and its component. Meantime, a general depiction of noise amplitude and frequency analyzing method as well as test environment and measuring device are included in this paper. According to requirement measuring environment and the fact that noise intensity of vacuum booster is rather low, we choose noise insulation cabin as the testing space and NL-32 precise noise analyzing instrument as the measuring device.Requirement of measuring environment is so critical that we pay much attention to the structure design of noise insulation cabin. The detailed structure (see chart 1) and size of the cabin are designed according to sound insulation theory of double-deck board and sound absorption theory of porous resonance sound absorbing board within a large amount of materials referred, using a method of analogy and computing. Exterior surface of the cabin is made of stainless steel board. Sound insulation deck is double layer structure, where the outer layer is cabinetwork board clinging to the stainlesssteel board and the inner layer is porous sound absorbing board with the perforation is 28% of the whole board in area. A sound insulation plasterboard is filled between the inner layer and felt, which is placed 60mm away from outer layer. Design of sound insulation door is much similar to that of the cabin, where a vibration insulation slot(10mm in width) is added into the inner surface to keep the measuring environment away from the vibration of the outer stainless steel board. This structure is proved to be reasonable and effective in cutting down noise by the parallel experiments under normal environment and that with external noise in or out of the cabin.As to the design of loading mechanism of the test machine, intensity requirement, transfer of pushing force and diffusion of vibration and noise between joint are the main consideration. For fixed and rotational joints of the cabin, attenuating materials such as nylon or rubber are selected to make covers and rods to minimize the diffusion of vibration and noise,especially on the designing of the connection part in movitation mechanism we put forward a structure as chart 2 which are proved to be effective in preventing the working space from invasion of outside noise through bindiny mechanism and joints. We arrive at a preferable working level as the decrease of sound and vibration. Optimal test result of booster noise can be made through the best simulation of actual working process. To meetthis requirement, a swing organ is designed in the loading mechanism to bring a swing angle (normally no more than 3.5 ) from the axis during the propelling process of booster. This turned out to be successful in simulating the pedal condition in braking process in a mechanical way.Conclusion can be drawn from structure test that application that: insulation cabin design meets technical specification in noise intensity, structure of the test machine is convenient in operation and the data collected are precise. Characteristic of booster noise is summarized through data analysis and a number of possible causes of brake noise are explored in the end.