| Hydraulic system is widely applied to various occasions,from robotics,aerospace and other precision system to the factory machine tools,steel rolling equipment,vehicles,construction machinery and other kinds of industrial and military fields.Various types of automobile are widely equipped with hydraulic brake system.Automobile hydraulic brake system is one of the important structures.It is related to vehicle safety performance and the safe of driver and the related people.For various reasons,the brake fluid of the automobile hydraulic brake system often contains gas.The brake fluid with air containing will form gas-liquid two-phase flow.Automotive hydraulic brake system is through the brake fluid to transfer mechanical energy.The arise of gas-liquid two-phase flow will make the brake fluid's ability seriously reduce of transmission pressure.It is will also seriously influence the brake performance of the automobile hydraulic brake system.The bulk modulus of the brake fluid with air containing will reduce greatly.The bulk modulus of the hydraulic system is one of the important parameters,which is related to the hydraulic oil's ability to transfer work pressure.The reduction of the bulk modulus will make the braking performance of the brake system reduce seriously.In this thesis,the gas-liquid two-phase flow and bulk modulus of the brake fluid in automotive braking system are studied.In this article,the experiment platform which can be used to observe the gas-liquid two-phase flow is designed and built.The flow pattern of the gas-liquid two-phase flow is identified through using the video processing method.Meanwhile,the bulk modulus of the brake fluid with gas containing is theoretically analyzed.The main study and finding is:(1)Firstly,the experiment platform which can be used to study the gas-liquid two-phase flow and detect the bulk modulus of the brake fluid in automotive braking system is designed.The experiment is mainly use the high-speed camera to get a video in a transparent pipe section in horizontal pipes.In this experimental process,we can obtain the brake fluid's video and the pressure data under gas liquid two phase flow condition of different speed.Meanwhile,the bubbles merge,crush,conversion and other flow pattern's evolution is studied.(2)Secondly,a method of gas-liquid two-phase flow pattern recognition based on video processing was proposed.At the first,it needs to use high-speed camera to obtain the brake fluid's gas-liquid two phase flow videos.When brake pedal is pushed,in order to ensure that the flow pattern video under the condition of high speed movement is clear,the high-speed camera's PFS will be chosen as 10000.Then,using OpenCV and C++,the algorithm has three parts: the improved Vibe motion target detection algorithm,the parameter extraction algorithm and the flow identification algorithm.(3)Then,combined with the actual characteristics of hydraulic braking system,the model of effective bulk modulus of brake fluid is deduced.In this part,combined with the actual characteristics of hydraulic braking system,the ideal gas equation of state,Henry's law,the law of conservation of mass and other related hypothesis theory,the volume of a gas,bulk modulus of gas,volume fraction and the effective bulk modulus of the brake fluid are deduced.(4)At last,the relationship between speed,flow pattern,volume fraction and effective bulk modulus is analyzed.In the transparent pipe studied in this thesis,by analyzing the flow pattern of different speeds,the bubble flow is the most.Bubble flow content is higher;the volume fraction is lower.And the lowest point of the volume fraction is among the speed of 30~40 km/h.Whether the speed is too high or too low,the volume fraction always rises.Effective bulk modulus of brake fluid will decrease with the rising of the volume fraction.When the volume fraction is higher than 1% and continue rise,braking pressure that the brake system require will increase rapidly. |
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