Design and Simulation of the Assistant Characteristic Curve of the Bus's Cycle Ball Type EHPS

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1 Design and Simulation of the Assistant Characteristic Curve of the Bus's Cycle Ball Type EHPS You Zhuan 1,2, He Ren 1,Li Renhe 2, Liu Qiongqiong 2 1 School of Automobile and Traffic Engineering, Jiangsu University, Zhenjiang, Jiangsu , China 2 Department of Automobile Engineering, Huaian College of Information Technology, Huaian, Jiangsu , China Abstract In order to adapt to the Hydraulic power assist characteristic and the change of power consumption of the bus with the change of the front axle load caused by hydraulic power characteristics, the paper describes the EHPS system's development and application. Introduced the mathematical model of EHPS system is established, and the power assist characteristic of EPS system, analyzed the types and characteristics of the power assist characteristic curves, the mathematical model of the electric hydraulic power steering system of the electric bus is established, and constructed the electronic control hydraulic power steering system (EHPS) to improve the steering portability and energy saving. This paper also studied the design of the fuzzy controller for the power assisted target, meeting the requirement of low speed and energy saving of vehicle. Through the simulation results, it shows that the control strategy is reasonable, providing the theoretical basis for the EHPS system which has good performance on the pure electric bus. Keywords - EHPS; fuzzy controller; control strategy; steering portability; hydraulic power characteristics I. INTRODUCTION In recent years, thanks to the development of electronic control and battery technology, as a new energy vehicle, pure electric bus has been widely studied, at the same time, Development of an electric motor-driven pump unit for Electro-hydraulic power steering with 42V powernet proposed that the hydraulic power steering system had been replaced by the electric hydraulic power steering system [1]. The book Numerical simulation of two-phase flow in injection nozzles: Interaction of cavitation and external jet formation proposed that foreign countries adjusted the speed of the steering motor to improve the power characteristics through the installation of EHPS system on commercial vehicles, thus improving the fuel economy and vehicle stability [2]. CFD study of fluid flow and wall heat transfer in a fixed bed of spheres designed the electric hydraulic power steering system was also installed in the domestic part of the pure electric bus, improving the light of the passenger car to a certain extent [3]. Electric Power Steering(EPS) proposed that EPS mainly included mechanical steering gear, torque angle sensor, gear reducer, clutch, motor, electronic control unit (ECU) and so on. Design & Safety Considerations for Electrical Power Steering (EPS) Systems Based on Automotive Safety Integrity Levels proposed that electronic control unit (ECU) was the core part of EPS, its function was to transfer torque angle sensor and the speed sensor signal analysis and processing, the optimization of torque was calculated, the movement control and clutch motor, power steering [4]. But most of the buses are used in the hydraulic power steering system which is fixed by the rotating speed of the motor, this makes the bus steering difficult at low speed, also because that the motor maintains a constant speed and lead to increased energy consumption. Therefore, it is necessary to research and develop the EHPS system which is suitable for the pure electric bus, which has a better energy saving effect. This paper study the change of front axle load effect on steering performance through the establishment of mathematical model of pure electric bus EHPS system and the AMESim simulation model, designing the control strategy, meeting the requirements of the vehicle for low speed and portability and high speed and good sense of road. Figure 1 is a diagram of the recirculating ball type steering gear 1.Steering gear housing 2. Input shaft 3. Steel ball 4. Rocker gear 5. Steering nut 6. Steering screw Figure 1. Diagram of the recirculating ball type steering gear DOI /IJSSST.a.16.4A ISSN: x online, print

2 Development trend of electric power steering system: At present, the development of electric power steering system, its future development trend is mainly in the following aspects: improving the control system performance and reducing the cost of manufacturing control system. The future of the system will further simplify the system, reducing the size of the control unit and drive unit, control production costs, and reduce prices, so that it has more competitive prices. In improving the control system performance, the performance of the motor is the key factor to control the performance of the control system, the performance of the motor and its matching with the electric power steering system will affect the driver's steering control ability and steering road feeling, so the key problem is to further improve the performance of the motor, eliminate the defects such as the lack of the steering sense caused by the inertia of the motor and the friction force, the system can also be applied to trucks in batches, mainly from the improvement of the reliability of the relevant components of the system, such as the use of non contact torque sensor[5]. The control signal of the system will no longer be confined to the speed and torque, but according to a steering angle, steering speed, lateral acceleration, the front axle gravity signals were consistent with the characteristics of the automobile integrated control, in order to obtain better steering feel. To realize the communication between the system control unit and the other control units in the car, in order to realize the integration of the electronic control system of the whole vehicle. After the electric power steering system, the cab will have a larger space for the layout of passive safety devices, reducing the risk of injury to the crew. Looking to the future, the electric power steering system will be towards a more purely electronic and intelligent direction of development. At present, foreign research mainly focuses on the further optimization of the power characteristics and control performance, and the operation simulator is designed to evaluate the control strategy of EPS system. In the research of control strategy, foreign focuses on the choice of compensation and control strategy based on PID, and researched on fuzzy control. Honda automobile company and Nihon University in the automotive electronic steering system has done a lot of theoretical work and simulator test research, they start from the human vehicle closed loop system, the ideal steering system transmission ratio is designed, so that the steady gain of the automobile does not change with the speed of the vehicle[6]. Mitsubishi Co developed an operating simulator that can be used to evaluate the control strategy of the EPS system, the simulator can be easily calculated with 11 degrees of freedom based on the steering wheel angle, the accelerator pedal position and the position of the brake pedal. The United States of America Liao HIDu, ADAMS using YG dynamic analysis software and MATLAB simulation software based on multi-rigid body EPS system dynamics model of the joint simulation research. Delphi company put forward the introduction of yaw rate feedback system controller, in order to improve the handling and stability of vehicle. South Korea's Kim Jae-Bok, Song Ji-Hoon propose direct control of the steering wheel torque control strategy. Because of the limitation of the automobile power supply system, it is difficult to provide a large power, the research and application of the EPS system is mainly used in the car, and it will be applied to the heavy truck, Hydraulic actuator must also be used. However, with the development of battery technology and the application of 42V electronic equipment in the car, the full electronic steering system will be applied to medium and heavy duty vehicles, at present, the 42V power supply has been applied in some concept cars[7]. This paper has researched about a kind of pure electric city bus, Mark card, and its mode is YS6120DG. The car can get rid of air conditioning and the height removing air conditioning is 2880mm, Kerb mass is 12200kg. The monomer battery manufacturers is CITIC Guoan mengguli Amperex Technology Limited with the model of SPIM It's limited sales to Beijing City, Shanghai city and Shandong Province Electric Bus Demonstration Line operation, the vehicle every six months conducts a safety inspection technology. The ownership of vehicles registered shall not be transferred. The specific parameters are shown in Table 1I TABLE I. SPECIFIC PARAMETERS OF PURE ELECTRIC VEHICLES Parameters Detailed Name vehicles The pure electric city bus Types of vehicles City bus Vehicle models YS6120DG Chinese brands Mark card SDRC car instalment Notice G5(165) Exemption No Dimensions (mm) The total mass(kg) Curb weight(kg) 12200~12500 Rated capacity 80/24-44 Approach / departure angle( ) 6.8/6.5 Suspended before / after hanging 2650/3350 Wheelbase 6100 Axle-load 7000 to Shaft number 2 Maximum speed 80 II. KEY TECHNOLOGY OF EHPS SYSTEM A. Mathematical Model Of EHPS System The force of the steering wheel torque caused by the movement of the nut is equivalent to the force of the screw nut, the EHPS system can be divided into 4 parts, the mechanical steering gear, the motor, the steering control valve and the controller. Therefore, in order to facilitate the study, respectively, the establishment of mechanical steering model, motor model, steering control valve model and controller model, and in the AMESIM it will connect each model for simulation analysis. B. The Model Of Mechanical Steering In this paper, it is studied that the clearance and friction of the steering system are neglected. The motion of the screw, the nut and the gear in the model is shown in Figure 2. DOI /IJSSST.a.16.4A ISSN: x online, print

3 Figure 2. Motion among the screw, the nut and the fan According to Newton's second law, the force balance equation of the nut is: M 1x1 F1F2F3 F4 (1) In formula (1): M 1 is the quality of the nut; x 1 is the nut displacement; F 1 is the left cavity pressure; F 2 is the force of the screw nut; F 3 is the right cavity pressure; F 4 is the tooth fan reaction. The transmission relationship between the nut displacement and the steering wheel angle is: S x1 (2) 2 In formula (2): S is in the lead of the screw angle of steering wheel angle. The pressure of the left and right cavities of the booster cylinder is: F1 p5a, F3 p6a (3) In formula (3): p 5 is the left chamber pressure; p 6 is the right pressure; A is the effective working area of the hydraulic oil. C. Controller Model The signal converter in EHPS system receives the front axle load sensor input, determining the maximum rotation speed of the motor, and then determine the speed of the motor when the bus line is running according to the vehicle speed. When the bus steering, the inverter according to the steering wheel angular speed to calculate the motor speed and through the PID control to make the motor accurately and quickly to achieve the target speed, so as to change the size of the power in real time, and improve energy efficiency[8]. According to the different axle load, the relationship between the speed of the motor and the speed of the steering wheel is made by the method of subsection fitting. Pure electric bus with velocity v (15km/h < v 40 km/h) in the city road, the function of motor speed and vehicle speed and steering wheel angular velocity is: 400 ( 15) ( 17.5), ( ) / s 17.5 (4) 130 n 1430 ( 35), 17.5( ) / s 35( ) / s , 35( ) / s 50( ) / s Mathematical model of steering transmission mechanism: The steering mechanism consists of a steering arm, tie rod, steering knuckle arm, steering the main pull rod, the model between the steering arm and the steering wheel is the steering trapezium structure model for Ackerman, it can guarantee the left and right wheels of deflection, the whole space belongs to the four bar mechanism; Effective arm length in the steering process is changing, in order to facilitate the analysis[9], The steering force in place of the steering wheel is equivalent to the main steering rod, then the steering force on the main draw is as follows: M R F jb n cos 0.5 m (5) In the formula, m is the tie rod length with the unit of m; B is the angle of steering through wheels with the unit of rad; n is the arm length of steering knuckle with the unit of m. The main draw on the steering force is equivalent to the steering arm shaft, that is to obtain the force fan rocker type on the gear tooth: Mg Fjb I jb cos (6) In the formula: I jb is the main steering rod length with the unit of m; is the intersection angle between the main pull rod and steering arm with the unit of rad[10]. D. Electrically Controlled Hydraulic Power Steering System (EHPS) With the wide application of electronic technology in the car, the steering system also enter the electronic control era. An electromagnetic valve is added on the basis of hydraulic power steering system, receiving signal using vehicle speed sensor and steering wheel torque sensor, through the electronic control unit (Control Unit Electrical, referred to ECU) to control the size of the solenoid valve, adjust the hydraulic cylinder output hydraulic oil, to control the size of the steering booster, this is a large number of cars and some commercial vehicles on the use of a large number of EHPS system. Electric control hydraulic power steering system of the power from the motor, and the corresponding electronic control system is installed, when the car does not need to turn, motor does not work, reduce energy consumption. When the car is turning in place or moving at a low speed, ECU control solenoid valve open, the maximum amount of oil, EHPS system to provide a greater power steering, steering more portable[11]. When the vehicle is at a high speed, ECU control flow solenoid valve to reduce the current, the electromagnetic valve to reduce the degree of opening, fuel supply decreases, EHPS system to obtain the steering power to reduce, enhance the road sense of high speed traffic, ensure good handling, stability and safety. Compared with the traditional steering system, EHPS the most obvious advantage is that the ECU can be based on the vehicle speed and steering wheel angle signal in different driving conditions to provide the right direction of power, to a certain extent, solve the contradiction between the sensitivity and portability of the different speed. The introduction of electronic control technology is a major change in the development of power steering technology, the steering characteristics can be adjusted and changed with different driving conditions, lay the foundation for the development of DOI /IJSSST.a.16.4A ISSN: x online, print

4 electric power steering system[12]. Compared with the hydraulic power steering system, the electronic control hydraulic power steering system, the performance has been greatly improved, but the hydraulic device still exists, making the EHPS system still has the shortcoming that the HPS system is not easy to overcome, for example, hydraulic devices, such as oil leakage, pipeline is complex, take up space, and parts are not easy to install, detect and repair. In addition, the hydraulic system to increase a set of electronic control system, so that the cost of the system to improve[13]. Electric power steering system (Electric Power Steering System, referred to as EPS) is a new steering technology developed on the traditional mechanical steering system, in the mechanical system to increase the electronic control devices, signal sensors, power devices, etc.. The steering power of EPS system comes from the motor, the motor is regulated by controlling the current input by the electronic control unit (ECU). Under the control of ECU, by controlling and adjusting the change of the current magnitude and direction of the booster motor, achieve different steering power. EPS system can get a good steering assist in all kinds of vehicle speed. When the steering gear ratio is set, the running speed of the vehicle is higher, EPS system to provide less power or help to provide power, enhance the sense of the road, steering wheel more composed, to enhance the vehicle's handling stability and safety; vehicle speed or in situ steering, EPS system to provide greater power, steering operation is more portable, saving the driver physical, reduce the operation intensity, which is relatively large for the commercial vehicle with the steering axle load, especially for trucks and large passenger cars is particularly important. Assist motor to solve the problem of heavy steering, at the same time, it is also free to design a reasonable steering drive ratio to get a good sense of road, so the, EPS system is regarded as a system capable of achieving accurate steering. The steering wheel torque signal measured by the torque sensor and the vehicle speed signal measured by the vehicle speed sensor are transmitted to the system controller, the controller calculates the required target boost value according to the set of power characteristics; And the target power value will correspond to the corresponding size of the motor target current, this can determine the system at this time the desired target current. At this time the system will be based on the size of the target current control signal to the motor, control the operation of the motor to achieve the appropriate power output. The determination of the power assist characteristics should be able to meet the low speed travel light and high speed stability of the vehicle. It can be seen that the value of the booster motor is based on the realtime speed of the vehicle and the size of the driver's steering force. Function of torque and vehicle speed induction coefficient measured by torque sensor[14]. III. EXPERIMENTAL SIMULATION CURVE AND ANALYSIS The steering gear of ZF8098 is analyzed in this paper, the parameters are shown in Table II. TABLE II. THE STEERING GEAR'S PARAMETERS OF THE TYPE OF ZF8098 Steering Gear Model 8098 For front axle load (Kg) 8300 Boosting cylinder diameter (mm)117 Transmi-ssion rate Armaxie swing angie ±47 Whole ring number 6.5 Input torque (N.M) 8-12 Output torque(n.m) 5500 Max.oil pressure (Mpa) 15 Oil pump flow (L/min) Operation oil N32 hydraulic oil Piston travel (mm) x2 Center moment (mm) 90 Steering wheel diameter 0.5m Low speed steering characteristic analysis: Assume that the steering wheel torque changes according to the sinusoidal variation with the frequency of 0.2Hz, the amplitude is 12.5 N.M. Figure 3 is the situation that when the bus speed is v = 10 km/h, steering assist curves corresponding to the different curves of power steering front axle load. We can see that: with the increase of steering wheel torque, the hydraulic power is increasing; The steering wheel torque is fixed when the front axle load is large, the hydraulic power can provide more EHPS system, to improve the steering portability of bus speed[15]. Figure 3. The steering characteristics in different front axle under load Energy saving analysis of steering: Assuming that the steering wheel torque is step-signal input, the step output value is 12.5 N.M. Figure 4 is the situation that when the bus speed is v = 10 km/h, the power consumption corresponding to different motor axle loads. When steering, the bus's EHPS system using the real-time control of the motor output to control the real-time control the motor's output speed. We can see from Figure 4 that: When the steering wheel torque is fixed, the front axle load is small, the smaller the power consumption of the motor, the DOI /IJSSST.a.16.4A ISSN: x online, print

5 EHPS system considering the front axle load's change can improve the steering front axle load's energy saving. At the same time, the motor's response time is within 0.2s, this shows that the EHPS system can meet the power requirements of rapid response. Figure 4. Motor power consumption in different axle loads IV. CONCLUSIONS Along with the progress and development of automobile related technology, automotive power steering system has experienced several development stages, which are hydraulic power steering system, electronically controlled hydraulic power steering system and electric power steering system. The relationship between the power of the EPS system, the vehicle speed and steering wheel torque, is the content of the power characteristics. This paper introduced the YS6120DG type of electric bus and ZF8098 type of steering gear, established the mathematics model of EHPS system, and simulated and analyzedthe fuzzy controller model as in order to eliminate the adverse effects on the work of the steering system. In this paper, a mathematical model of EHPS system is established, the causes of inertia and friction damping in the system and the influence on the work of the steering system are analyzed. At the same time, the model of EHPS vehicle cycle ball type is established, and the establishment of the model and the vehicle model for joint simulation. Through the experimental analysis, the experimental results show that the compensation control strategy can effectively improve the dynamic performance of the vehicle steering system, such as the response speed, steering portability, and the back of the steering system, improving the working performance of the automobile electric power steering system. ACKNOWLEDGEMENTS This work was supported by the Natural Science Fund project in Jiangsu Province(BK ). REFERENCE [1] HUR J. Development of an electric motor-driven pump unit for Electro-hydraulic power steering with 42V powernet. International Journal of Automotive Technology,vol. 11, No. 4, pp , [2] Yuan W, Schnerr G H. Numerical simulation of two-phase flow in injection nozzles: Interaction of cavitation and external jet formation. Journal of Fluids Engineering, vol. 125, No.6, pp , [3] Jemeisland M Ni,Dixon A G. CFD study of fluid flow and wall heat transfer in a fixed bed of spheres. American Institute of Chemical Engineers Journal, vol. 50, No.5, pp , [4] Paravila O. Jacob. Design & Safety Considerations for Electrical Power Steering (EPS) Systems Based on Automotive Safety Integrity Levels.SAE International, vol. 01, pp. 0994, 2010 [5] Qun Z. The Parameters Design and Simulation for the New Assisted Curve of the Electric Power Steering System. International Journal of Advancements in Computing Technology, vol.5, No. 8, pp , [6] Tang B, Jiang H, Xu Z, et al. Dynamics of electromagnetic slip coupling for hydraulic power steering application and its energysaving characteristics. Journal of Central South University, vol. 22, pp , [7] Jang J S R. Self-learning fuzzy controllers based on temporal backpropagation. Neural Networks, IEEE Transactions on,vol. 3, No.5, pp , [8] Battaini M, Casciati F, Faravelli L. Fuzzy control of structural vibration. An active mass system driven by a fuzzy controller. Earthquake Engineering and Structural Dynamics, vol. 27, No. 11, pp , [9] Huang S J, Lin W C. Adaptive fuzzy controller with sliding surface for vehicle suspension control. Fuzzy Systems, IEEE Transactions on, vol. 11,No. 4, pp , [10] Schouten N J, Salman M, Kheir N. Fuzzy logic control for parallel hybrid vehicles. Control Systems Technology, IEEE Transactions on, vol. 10, No. 3, pp , [11] Zuperl U, Cus F, Milfelner M. Fuzzy control strategy for an adaptive force control in end-milling. Journal of Materials Processing Technology, vol. 164, pp , [12] Huang S J, Lee J S. A stable self-organizing fuzzy controller for robotic motion control. Industrial Electronics, IEEE Transactions on, vol. 47, No. 2, pp , [13] Schelzig H, Simon F, Krischer C, et al. Ex-VivoHemoperfusion (ehps) of Pig-Lungs with Whole Human Blood: Effectsof Complement Inhibitionwith a Soluble CI-Esterase-I nhibitor. Annals of Transplantation, vol. 6, No.3, pp.34-39, [14] Beard M C, Midgett A G, Hanna M C, et al. Comparing multiple exciton generation in quantum dots to impact ionization in bulk semiconductors: implications for enhancement of solar energy conversion. Nano letters, vol. 10,No.8, pp , [15] Kim S H, Shin M C, Chu C N. Development of EHPS motor speed map using HILS system. Vehicular Technology, IEEE Transactions on, vol. 62, No.4, pp , DOI /IJSSST.a.16.4A ISSN: x online, print