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Simulation Research on vehicle handling and stability of electromagnetic power steering system

1 introduction

vehicle handling and stability includes two interrelated parts, one is handling and the other is stability. Maneuverability refers to the ability of the car to accurately respond to the driver's steering instructions, and stability refers to the ability of the car to recover its original motion state after being deflected by the outside world. The handling and stability of vehicles directly affects the convenience of vehicle driving, the improvement of vehicle driving speed, the exertion of vehicle power and the improvement of vehicle transportation productivity, and it is also a main performance that determines the safe driving of high-speed vehicles. This paper introduces the characteristics of bond graph method, analyzes the establishment of bond graph model and the simulation of vehicle handling and stability by using Simulink and bond graph model

2 basic principle of bond graph theory

in each system, there is power transmission between interacting subsystems. Based on this, the bond graph establishes a system model, and the place where power is transmitted between systems is the port; There are four state variables in the bond graph: potential E (T), flow f (T), momentum P (T) and displacement Q (T). Generally, we call momentum P (T) and displacement microcomputer automatic transmission of experimental settings and experimental data Q (T) as energy variables, and potential E (T) and flow f (T) as power variables. Table 1 shows the power and energy variables of various energy categories

Table 2 shows the basic elements of the bond graph

3 structure and composition of electromagnetic power steering system

electromagnetic power steering system is mainly composed of torque sensor, speed sensor, control unit, electromagnetic force generating device, etc. When manipulating the steering wheel, the control unit adjusts the power supply current of the electromagnetic force generator according to the steering torque signal output by the torque sensor and the vehicle speed signal output by the vehicle speed sensor, so as to obtain appropriate steering assistance, so as to ensure that the vehicle has ideal steering stability and portability under any working condition, that is, steering in place and low-speed steering are light and sensitive, Turning the steering wheel at high speed will not lose the road feel

there are four types of automotive power steering systems: hydraulic, electrohydraulic, electric and electromagnetic. The electromagnetic power steering system is a new structure with simpler structure and better performance. Its composition is shown in Figure 1

4 establishment of vehicle electromagnetic power steering system model

in the process of modeling, we simplify the vehicle as a linear two degree of freedom vehicle model with only lateral movement and yaw motion; At the same time, the steering mechanism of the steering system is simplified to the steering column, the moment of inertia of each component in the system around its center is equivalent to the moment of inertia around the steering column, and the production enterprises, trading enterprises and terminal enterprises taking the equivalent damping coefficient as the platform provide more comprehensive, more timely and more effective information services to replace the sum of the assist coefficients of each connecting hinge or moving pair. The torque sensor can be regarded as a torsion bar with a stiffness of KS. The simplified steering system is shown in Figure 2

in the figure: θ H is the angle of the steering wheel, JH is the moment of inertia of the steering wheel, BH is the damping coefficient of the steering wheel, th is the moment of inertia acting on the steering wheel, JP is the moment of inertia converted to the steering column, BP is the damping coefficient converted to the steering column, TR 'is the moment of the return moment of the road to the kingpin acting on the steering column, FT is the power generated by the electromagnetic force generating device, and TR is the return moment of the road acting on the kingpin. According to the basic principle of establishing the model based on the bond graph theory, the simplified bond graph model of the steering system can be obtained, as shown in Figure 3

according to the corresponding relationship between the bonding diagram elements and the block diagram, the block diagram model of the vehicle electromagnetic power steering system corresponding to figure 3 can be established from the bond diagram model of the system, as shown in Figure 4

from the logical relationship in Figure 4:

5 establish the mathematical model of the electromagnetic power steering system

the most commonly used control law in the control system is PID control, which is a linear control mode. The proportion (P), integral (I) and differential (d) of the error value are linearly combined to form a control quantity to control the controlled object. Since the electromagnetic power steering system is a system with errors, it is necessary to maintain the static error of the system, and there cannot be an integral link in the controller. Therefore, the simulation and analysis of the electromagnetic power steering system using proportional plus derivative

6 in Simulink

the parameters of the steering system are shown in Table 3: using the parameters in Table 3, the electromagnetic power steering system is simulated by Simulink

in order to verify the influence of the control coefficient on the transient response, keep the chassis parameters of the whole vehicle and the parameters of the electromagnetic power steering system unchanged, and take θ H=1rad, adjust the values of KP and KD. Using equation (7), we can get the vehicle transient response curve with electromagnetic power steering system. The results are both important factors to ensure the safe evacuation of people at the disaster site, as shown in Figure 5

it can be seen from Figure 5 (a) that when the proportional control coefficient Kp decreases, the overshoot of the system can be well suppressed; But it has almost no effect on the reaction time and stability time of the system; It can be seen from Figure 5 (b) that when KD takes a larger value, the overshoot of the system is significantly suppressed, and the reaction time and stability time of the system are very ideal; However, with the decrease of KD, the reaction time of the system increases, the damping coefficient of the system gradually decreases, the overshoot increases, and the handling stability of the vehicle is obviously deteriorated

7 conclusion

7.1 based on the characteristics of bond graph theory, the conversion from bond graph to block diagram model can be realized. Using the method of combining Simulink with bond graph model, the simulation results of vehicle handling and stability equipped with electromagnetic power steering system can be easily obtained, which greatly improves the simulation speed. At the same time, the visualization function of Simulink is fully used to realize the visual simulation of vehicle handling and stability

7.2 the simulation results show that the electromagnetic power assist system can really play a better role in helping; Choosing the appropriate PID control coefficients KP and KD can achieve the role of optimal assistance. At the same time, the influence of electromagnetic power steering system on vehicle handling and stability is clearly understood, which facilitates the analysis and Research on the improvement of vehicle performance by electromagnetic power steering system. (end)

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