Electronically Controlled Air Suspension Bus Control System Design Fan Wang

Transcription

1 Applied Mechanics and Materials Online: ISS: , Vol. 288, pp doi: / Trans Tech Publications, Switzerland Electronically Controlled Air Suspension Bus Control System Design Fan Wang Shandong Transport Vocational College, Weifang, Shandong , China Keywords: bus; air suspension; control system; conditioning circuit; sensor Abstract: The design of coach electronically controlled air suspension control system was made to be optimized and simplified, especially in hardware. The opto-coupler, inset in the input channels and output channels, let the electric be independent each other between computer system and the external environment and had own reference potential. Interfering signals which maybe make the system not to work by any possibility was suppressed. Practice has proved that reliability, safety and practicality of the control system had been greatly improved. An overview of the structure and principle of the control system The typical bus electronically controlled air suspension (ECAS) is mainly composed of two parts, first part is mainly for the structure of the device, the second is the exhaust gas line and control system. When the bus is traveling on the road, each sensor in the ECAS will continue collecting the vehicle speed signal, the acceleration signal of the body perpendicular to the direction, the steering wheel angle signal, the vehicle height signal, brake signal, gate signal for the control system judgment bus conditions and road conditions to provide real-time basis. ECAS can effectively inhibit the turning roll in driving, brake nod straight bumps and other phenomena, to improve the passenger comfort, handling stability, and for the particular intended use of the bus[1] [2]. Control system hardware design Hardware overall scheme outline Figure 1 shows the design of the bus's electronically controlled air suspension control system hardware diagram[3] and micro-controller selects C8051F series 8051-compatible microcontroller. Fig.1Bus electronically controlled air suspension control system hardware structure All rights reserved. o 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, (# , Pennsylvania State University, University Park, USA-13/09/16,09:55:07)

2 138 Advanced Mechanical Engineering III Hardware system design The body acceleration sensor and signal conditioning circuit Body acceleration sensor can be detected by the road excitation caused by the bus body vibration and body vibration into the corresponding waveform signal based on this signal, the ECU to determine the driving conditions of the bus, in order to adjust the stiffness of air spring, changing the body posture, improving the stability and comfort of buses traveling[4][5]. According to the evaluation of the "standard IS " to bear the body's vibration, the total weighted acceleration rms value for evaluating the smoothness index, the choice of the frequency range of 1~80Hz Butterworth (Butterworth) low-pass active filter accelerometer vibration signal filtering. The circuit diagram was shown in Figure 2. The filter frequency response requirements: in the range of less than the cutoff frequency ωc, with most flat amplitude response, and ω> ωc, amplitude-frequency response decline rapidly. +15V Vin 0.4µF C3 0.4µF + Vout 3K - LM747 Fig. 2 Acceleration sensor signal conditioning circuits The ride height sensors and signal conditioning circuits The ride height sensors for the detection of bus body relative to the axle displacement, according to the ride height sensor input signal, the microprocessor calculates the displacement of the bus body and vibration parameters. Between the photoelectric ride height sensor rod and the suspension arm with a rod, bus driving vibration, body height will change the shading plate connected with a high degree of sensor axis will be the lever driven by rotation. Four pairs of opto-couplers within the sensor, the rotation of the sunshield will influence the photo transistor, s conduction in the opto-coupler, the length and position distribution of the pervious to slot make the sunshield turning within the scope of the provisions in the corner, body height in each position corresponds to a 4" O-OFF" photoelectric signal[6] [7]. In Table 1, body height range was divided into 16 height intervals, each height interval has a corresponding optical signal, the microcontroller according to the four level signals of the sensor input can determine the ride height of the real-time changes. MCU will generally be completed within 1ms a sample because of the unpredictable road conditions in the passenger travel process, the vibration amplitude and frequency of the body changes randomly, the single chip microcomputer according to the sampling time body height at a height interval percentage size determination of body height. Figure 3 is a ride height sensor signal conditioning circuits, the SH1, the SH2, SH3, SH4, the output level signal, the signal after signal conditioning circuit direct input microcontroller. Bus electronically controlled air suspension control system has 4 body height sensors. Steering wheel angle sensor and signal conditioning circuit The steering wheel angle sensor is mainly used to monitor the rotation of the steering wheel angle and direction of rotation, at the same time, the microcontroller may occur based on the current speed of calculation of body roll. Optical steering wheel sensor is installed in the steering column, the sensor within the two light-emitting diodes and two matching photoelectric couplers, when the driver turns the steering -15V

3 Applied Mechanics and Materials Vol wheel through the axis of rotation to drive the shading plate rotation, the number of pulse signals of the microcontroller according to the angle sensor output to calculate the steering wheel turning angle [6]. Table 1 Sensor signals the body height interval corresponding Sensor signal SH1 SH2 SH3 SH4 Body height of range High Low OFF OFF O OFF 15 OFF OFF O O 14 O OFF O O 13 O OFF O OFF 12 O OFF OFF OFF 11 O OFF OFF O 10 O O OFF O 9 O O OFF OFF 8 O O O OFF 7 O O O O 6 OFF O O O 5 OFF O O OFF 4 OFF O OFF OFF 3 OFF O OFF O 2 OFF OFF OFF O 1 OFF OFF OFF OFF 0 D1 3 4 Optocoupler 1 SH1 T1 SH2 R2 Optocoupler 2 R9 C1 5 6 R3 Optocoupler 3 0 T2 SH3 T3 optocoupler 4 1 C3 SH4 R8 T4 2 C4 Fig. 3 Height sensor signal conditioning circuit Figure 4 is the direction of rotation to judge the diagram, the sensor output A, B, two signal pulse width is equal, but A, B, signal phase difference of 90 degrees, the microprocessor according to the A signal goes from high to low power In peacetime, the B signal is high or low to determine the steering [6]. A signal at the falling edge signal B is high, compared with the right turn; A signal falling edge of signal B is low compared with the left turn.

4 140 Advanced Mechanical Engineering III After filtering, level shifting, the steering wheel angle sensor to produce the A, B signal, will be directly input to the MCU. Figure 5 is a signal conditioning circuit diagram, 1and 2 photoelectric couplers produce A, B two pulse signal in the phase difference of ninety degrees, The microcontroller according to the input of the pulse number counter that coach the rotation angle, and combining with the vehicle speed signal can be analyzed and obtained the roll of passenger car. Signal A Turn right O O Turn left Connected mrocontroller Signal B O O Fig. 4 The direction of rotation to determine the schematic R8 Optocoupler 1 Connected mrocontroller R3 T1 Connected rocontroller R2 Optocoupler 2 C1 T2 Fig. 5 Steering wheel angle sensor signal conditioning circuits The vehicle speed sensor and signal conditioning circuit The speed sensor by detecting the transmission output shaft speed or wheel speed to the microprocessor bus speed signal, the microprocessor during the speed and the road surface sensor control body posture control, and ride height control signal provided by the vehicle speed sensor. In this paper, the design, acquisition speed sensor signal conditioning circuit by the magnetic speed sensor, the Schmitt trigger 74LS14 and photoelectric coupler structure, shown in Figure 6. The speed sensor output sinusoidal signal through the Schmitt trigger 74LS14 plastic will become the standard rectangular pulse, pulse counter by the photoelectric coupler input microcontroller C8051F022 microcontroller by calculating the number of input pulses within a certain period of time, we can determine the speed of passenger bus. +5V Vin U1A 1 2 U2 Vout D1 74LS14 TPL521 Fig.6 Speed sensor signal conditioning circuits

5 Applied Mechanics and Materials Vol Control system software design This bus electronically controlled air suspension control system software design mainly in the following seven parts: the main program module of the system, straight damping module, steering roll module, brake module, parking chassis control module, control output module and the interrupt service routine module. Figure 7 is the main program flow chart of the bus designed electronically controlled air suspension control system. start System initialization Each sensor signal acquisition k>µg/ω 2 &&θ>φ Steering roll module 6F<a(t)<8F Gate signal? Straight damping module Parking chassis control Brake signal? Brake module Fig. 7 The main program flow chart Summary Bus electronically controlled air suspension control system design plan is determined, according to design requirements, select a suitable microprocessor, the sensor signal conditioning circuits and software system design, innovation and simplification in the design, taken anti-jamming measures to enhance the noise immunity, and improve control system security, reliability and practicality. References [1] Ma ouliang editor. Car circuit analysis and fault detection [M] Beijing: Machinery Industry Press, [2] Zhao Qiyang. Passenger bus air suspension electronic control system [J]. Bus Technology and Research, 2008 (3): 33 ~ 34. [3] Chen Jiarui editor. Automobile structure on the books. 2 Version [M] Beijing: Mechanical Industry Press, [4] Liu Zhengyu. Electronic circuit design and production [M]. Fuzhou: Fujian Science and Technology Press, [5] Qin Zenghuang editor. Electrical engineering. volume two, Electronic version. 6 [M] Beijing: Higher Education Press, [6] Song Fuchang. Identification and testing of automotive sensors diagram [M] Beijing: Electronic Industry Press, [7] Ma ouliang editor. Automotive electrical and electronic control system. 2 [M] Beijing: Machinery Industry Press,