Research On The Pressure Control Of The Hydraulic Braking System Of Low Floor Tram

With the continuous development of the urban economy,the number of motor vehicles has increased exponentially.At the same time that cars provide convenience for people,they have caused huge traffic pressure on urban roads,and major pollutants such as carbon monoxide,sulfur dioxide,and other exhaust gases have seriously affected air quality.Low-floor trams,as a medium-capacity,clean and efficient way of travel,will be more suitable for the transportation environment of future population-intensive cities.However,the core technology of the tram braking system was still monopolized by foreign countries.In recent years,domestic companies have begun to design domestic low-floor trams.CRRC Zhuzhou Electric Locomotive Co.,Ltd.has designed a set of hydraulic brake systems for motor vehicles and trailers.However,in actual tests,the hydraulic brake system circuits have problems such as shock and vibration.Problems still need to be identified for improvement.At present,most of the improvement methods of enterprises are trial and error,which is inefficient.This paper establishes a software simulation model for the active hydraulic system of a low-floor tram,and proposes new solutions for precise control of brake pressure and dead-time compensation of pressure control valves.It provides a new solution for the optimization of difficult hydraulic brake systems.Solve ideas and controls.In this paper,the pressure control of the hydraulic braking system of a low-floor tram is studied.It mainly includes the following:(1)This article analyzes the braking system configuration of low-floor trams and trailers,designs braking schemes for different braking mechanisms in different scenarios,and introduces the working principles of hydraulic braking elements and hydraulic circuits.Based on the relevant criteria,the braking levels and braking force requirements for different loads and different braking scenarios were calculated.(2)Based on AMESIM software,the author is based on the low-floor tram structure of CRRC Zhuzhou Electric Locomotive Co.,Ltd.A complete model of the active hydraulic braking unit of a low-floor tramcar trailer was constructed.Conduct modeling and simulation research,including the establishment of pilot-type proportional pressure reducing valve models,simulation of pilot-stage electromagnet response,accumulator charging simulation,step braking simulation,and accumulator charging simulation during intermittent braking.Finally,a simulation model which is more in line with reality is obtained.(3)This paper discusses several braking pressure control strategies,and compares their advantages and disadvantages in actual systems.A feedback linearized sliding mode control strategy for the high-order model of the electro-hydraulic servo system is designed,and a nonlinear model of the valve-controlled asymmetric cylinder is established.The linear controller of the nonlinear model is used to design a sliding film controller.The simulation study in MATLAB/SIMULINK environment shows that the peak value of error force accounts for about 0.15%of the expected force amplitude.(4)This paper studies the deadband compensation of pilot-operated proportional valves,establishes a mathematical model,and designs the spool current step compensation and position control deadband compensation strategies based on the asymmetric deadband of the proportional valve.Under step control,the dead time is reduced by more than 85%.