China. Keywords: Electronically controled Braking System, Proportional Relay Valve, Simulation, HIL Test

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1 Applied Mechanics and Materials Online: ISSN: , Vol. 437, pp doi: / Trans Tech Publications, Switzerland Simulation and HIL Test for Proportional Relay Valve of Commercial Vehicle Pneumatic EBS Jongchol Han 1,a, Weiqiang Zhao 1,b, Changfu Zong 1,c and Hongyu Zheng 1,d 1 State Key Laboratory of Automotive Simulation and Control, Jilin University, Changchun , China a hjc234@163.com, b @qq.com, c cfzong@yahoo.com.cn, d zhenghy@jlu.edu.cn * Corresponding author: Weiqiang Zhao Keywords: Electronically controled Braking System, Proportional Relay Valve, Simulation, HIL Test Abstract. A simulation tool for proportional relay valve of commercial vehicle pneumatic EBS (Electronically controlled Braking System) has been developed using MATLAB/Simulink environment and validated by testing on hardware-in-the-loop test bench focused on its pressure hysteresis characteristic. The simulation and test results show that the simulation model for proportional relay valve characteristics is reasonable and reliable, and it can be used for hardware and control algorithm development of pneumatic EBS for commercial vehicles. Introduction The simulation of electro-pneumatic components used in brake systems of commercial vehicles is of great importance in order to understand their dynamics for developing a control logic and improve the braking performance. Control on braking force for commercial vehicle EBS is mainly performed by closed loop control of pressure in brake chamber and its response characteristic has great effect on realization of EBS function and braking performance. By experimental measurement, there exists pressure hysteresis characteristic in proportional relay valve which is one of the main components of commercial vehicle pneumatic EBS and this becomes the bottleneck to restrict the braking performance of pneumatic EBS and automotive stability. Analyzing the characteristics of EBS components and system precisely is of great significance in improving the performance of EBS and active safety of automobile, and many researchers carried out the studies on analyzing and simulating the components and system of EBS. An electronic braking system case study was presented which comprises an air supply unit, an EBS modulator, piping, a diaphragm brake chamber and the connected brake mechanism in AMESim 3.0 simulation environment [1]. By the method of experimental measuration, the model of the EBS of commercial vehicles was established and the credibility of the model was validated quantitatively according to the similar degree method and analytical hierarchy process method [2]. A control strategy was proposed to minimize the effect of hysteresis in proportional solenoid valve [3] and a model was developed that could represent the dynamics of air flowing through the components of a pneumatic system configuration, that eventually translates into braking force [4]. Meanwhile a sliding mode braking force observer was introduced to support a sliding mode controller for air-braked heavy vehicles [5]. The objective of this paper is to develop the simulation tool for proportional relay valve of commercial vehicle pneumatic EBS in order to improve the performance of EBS and active safety of vehicles. Modeling of Proportional Relay Valve for Pneumatic EBS Structure and Hysteresis Characteristic of Proportional Relay Valve. The proportional relay valve is used in the EBS to modulate the braking pressure on the front axle. It comprises the proportional solenoid valve, relay valve and pressure sensor (see Fig.1). The electrical actuation and monitoring are carried out by the central module. In the proportional relay valve, the electronically received set values are implemented using a proportional magnetic valve in a control pressure for the relay valve. The proportional relay valves output pressure is proportional to this pressure. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-09/05/16,21:05:58)

2 Applied Mechanics and Materials Vol Fig.1 Mode of function of the proportional relay valve Hysteresis characteristic of the proportional relay valve has a great effect on the braking safety of commercial vehicles. There are many factors that cause hysteresis characteristic of proportional relay valve for pneumatic EBS, for example, characteristics of compressed air itself, internal clearance, working gap, friction between moving parts in valve and etc. One of the main reasons of causing hysteresis is various frictions such as Coulomb friction and viscous friction in valve, and the acting direction of friction force is opposite to each other when increasing and decreasing of pressure. Mathematic Model of Proportional Relay Valve. The mathematic model of proportional relay valve consists of several equations such as motion differential equations to represent the moving parts of valve and pressure change equations in air chambers and so on. A group of equations to demonstrate the dynamic characteristic of proportional relay valve for pneumatic EBS of commercial vehicles are as follows: Absorbing force characteristic of solenoid; = = () (1) where, absorbing force of solenoid, air gap flux density, magnetic permeability (generally, = /), length of maximum gap, cross-sectional area of the movable element, N coil turn number, I input current. Motion differential equation of proportional solenoid valve core; "# = $ & "' ( (" +")+ *, 0 " < "! ( + )"# = $ (& +& )"' ( (" +") ( (" +" " )+( + )* 0 1 2, " (2) " " 345 where, 0 1 pressure in air chamber D (chamber D means the pressure controlling chamber between spool valve in proportional solenoid valve and piston in relay valve), " initial gap between cone valve and spool valve in proportional solenoid valve, mass of cone valve and solenoid moving element, mass of spool valve, ( stiffness of cone valve supporting spring, ( stiffness of spool valve supporting spring, " initial compress quantity of cone valve supporting spring, " initial compress quantity of spool valve supporting spring, & equivalent viscous resistance of cone valve, & equivalent viscous resistance of spool valve. Motion differential equation of relay valve core; 7 8# = & 7 8' ( 7 (8 7 +8)+ 7 * :*;(8') <, 0 8 < 8 6 ( 7 + = )8# = (& 7 +& = )8' ( 7 (8 7 +8) (3) ( = (8 = +8 8 )+( 7 + = )* :*;(8') <, where,0 9 pressure in air chamber E (chamber E means the working chamber of relay valve connected to outlet), 8 initial gap between piston and valve seat in relay valve, 7 mass of piston, = mass of valve seat, ( 7 stiffness of piston supporting spring, ( = stiffness of valve seat supporting spring, 8 7 initial compress quantity of piston supporting spring, 8 = initial compress quantity of valve seat supporting spring, & 7 equivalent viscous resistance of piston, & = equivalent viscous resistance of valve seat, < friction between packing and body of relay valve. Pressure change equation in air chambers;

3 420 Industrial Design and Mechanics Power II 1> 1? = C A E D4> E G I JKE L DM N E F DH DH, 0 0 /0 < JVE BD4> E A R D S F T D UG> I J G > I J W, E > /0 1 E where, X adiabatic coefficient(x = 1.4), Y flow area, S gas constant(s = 287.1[/(X* ()), T absolute temperature of gas(generally T = 313(), ^ volume of air chamber. In above equations, the upper among the couples of symbols represents the characteristic of increasing process while the nether represents the one of decreasing process. The effect of fluid mechanical forces such as unsteady momentum forces and jet momentum forces acting on the valve core was neglected in modeling of the valve core motion. Simulation for Characteristics of Proportional Relay Valve Dynamic Characteristic. Based on the above mathematic model, simulation tool was established using MATLAB/Simulink simulation environment. The dynamic characteristics of proportional relay valve were simulated in various conditions of pressure increasing and pressure decreasing using this simulation system. Most parameters of the proportional relay valve were determined by means of basic geometrical, mass, volume and experimental measurements. Some parameters were specified on the basis of technical documentation and the parameters with higher uncertainty such as Coulomb friction forces, or viscous friction have been estimated. The value of pressure source, the atmospheric pressure and the air temperature in air supply unit were used as initial and boundary conditions for simulation. A simulation result is shown in Fig.2 to represent the pressure response characteristic of proportional relay valve according to the change of input current in step. Hysteresis Characteristic. After having enough time to pass by in simulation, the system reaches to the normal state, at this time the characteristic of system reflects the static characteristic of system. Based on this fact, investigated the hysteresis characteristic of the proportional relay valve at the steady-state while increasing or decreasing the input current signal. The simulation result on hysteresis characteristic of the proportional relay valve is shown in Fig.3. From this simulation curve, it is clear that hysteresis of about 0.23A in maximum is occured during pressure increasing and decreasing process. (4) 0.5 Pressure increasing decreasing Time (s) Fig.2 Pressure response characteristic Fig.3 Hysteresis characteristic Experiment of Proportional Relay Valve on Hardware-in-the-Loop Test Bench Using the hardware in the loop simulation technology, a synthesis test bench for electronically controlled braking system of commercial vehicle was built, and the characteristics of proportional relay valve were verified through the hardware-in-the-loop test. The hardware-in-the-loop test bench for experiment of proportional relay valve is shown in Fig.4.

4 Applied Mechanics and Materials Vol Fig.4 Test bench for experiment of proportional relay valve Time (s) Fig.5 Pressure response test It must be emphasized that the pressure response and the hysteresis characteristic are the most important characteristics from the viewpoint of pneumatic EBS operation. Hence, the experimental verifications of simulation results were focused on pressure response and hysteresis characteristics. According to the requirements of the test, the validation for the characteristics of proportional relay valve is performed in the different test conditions of hardware in the loop test and opened loop test. The pressure response test was carried out in the opened loop test condition and the working pressure of air supply unit was set to 0.5Mpa. The result of pressure response test is shown in Fig.5. It can be seen that the time to reach at 75% of maximum pressure is 157ms. The hysteresis characteristic was tested in the HIL test condition, increasing or decreasing the current of the solenoid, and the working pressure of air supply unit was set to 0.7Mpa. The results of hysteresis characteristic tests are shown in Fig.6. Test (1) Test (2) Test (3) Test (4) Fig.6 Hysteresis characteristic test The test results were compared with the corresponding simulation results. The test results showed generally good agreement with simulation results well and this can explain that the model described above is reasonable. A bit of defference between simulation and test is probably due to several assumption and neglect introduced during modelling process. This model can be used in design, research and development of proportional relay valve, and it becomes the base of improving the hysteresis characteristic compensation of EBS for commercial vehicles.

5 422 Industrial Design and Mechanics Power II Conclusions Static and dynamic characteristics of proportional relay valve for commercial vehicle pneumatic EBS have been simulated by MATLAB/Simulink and validated by test on hardware-in-the-loop test bench focused on its pressure hysteresis characteristic. First, a mathematic model of proportional relay valve has been established on the basis of analyzing the cause of its hysteresis characteristic. Next using MATLAB/Simulink, static, dynamic and hysteresis characteristic of proportional relay valve were simulated. Finally the experiments for characteristics of proportional relay valve were carried out on the HIL test bench and through comparing with simulation results, validated the correctness and reliability of the model and theoretical research. The simulation and test results show that this simulation tool for proportional relay valve of pneumatic EBS developed in this paper is reasonable, and it has been concluded that this simulation tool can be used for base of research and development of commercial vehicle pneumatic EBS. Acknowledgements This work was supported by National Natural Science Foundation of China (No ) and China Postdoctoral Science Foundation ( ) and (2012T50291). References [1] Szente, V., Vad, J., Lóránt, G., and Fries, A., Computational and Experimental Investigation on Dynamics of Electric Braking Systems, SAE Technical Paper , 2011, doi: / [2] Liu Zikai, Chen Hui and et al., Modelling and Simulation for Electronic Braking System of Commercial Vehicles, SAE-C2008T529, p [3] Yuan Jianzong, Chen Hui and et al., Study of EBS Pressure Control Stratege, SAE-C2008E437, p [4] T. Acarman, U. Ozguner, C. Hatipoglu and A.M. Igusky, "Pneumatic Brake System Modeling for Systems Analysis," Truck and Bus Meeting and Exposition, Portland, Oregon, Society of Automotive Engineers, December 4-6, [5] Jonathan I. Miller and David Cebon, A high performance pneumatic braking system for heavy vehicles, Vehicle System Dynamics, Vol. 48, Supplement, 2010,

6 Industrial Design and Mechanics Power II / Simulation and HIL Test for Proportional Relay Valve of Commercial Vehicle Pneumatic EBS /