Applied Mechanics and Materials Online: -- ISSN: -78, Vols. 8-87, pp 9-9 doi:.8/www.scientific.net/amm.8-87.9 Trans Tech Publications, Switzerland The Fault Tolerant Output Selector Based on Fault-detection Considering Realistic Fault Modes for Pedal Simulator of Brake-by-Wire System Jianhu Li, a, Manbok Park,b and Hunmo Kim,c Department of Mechanical Engineering, Sungkyunkwan University, Cheoncheon-dong, Jangan-gu, Suwon, Gyeonggi-do -7, Korea MANDO Corporation, Central R&D Center, - Gomae-dong, Giheung-gu, Yongin-Si, Kyonggi-Do -9, Korea Department of Mechanical Engineering, Sungkyunkwan University, Cheoncheon-dong, Jangan-gu, Suwon, Gyeonggi-do -7, Korea a jenhu7@gmail.com, b ohnnuri@mando.com, c kimhm@me.skku.ac.kr Keywords: Fault tolerant, Fault detection, Pedal simulator, BLS(brake light switch), Fuzzy exception handler. Abstract. A brake pedal simulator in a Brake-by-Wire system is studied for fault tolerant control of the brake pedal signals. This study is conducted for the pedal simulator installed with a sensor that generates two analogue signals. Several realistic fault modes recognized by automotive experts have been analyzed. To solve the fault modes, we propose a fault tolerant output selector that can handle transient, intermittent, or permanent faults. The fault tolerant output selector, based on a fault detection algorithm, uses the BLS(brake light switch) signal and the Acc(acceleration pedal) signal to find faults and isolate them. To confirm the system performance, the fault modes were simulated. The result showed the reliability and safety of the pedal simulator for dealing with unexpected faults.. Introduction The fault tolerant control design has been a main subject for the system safety and reliability. Various fault tolerant control methods and fault tolerant systems have been designed and applied[,,,]. In this paper, a brake pedal simulator of Brake-by-Wire is studied to determine if it can solve some expert-recognized faults. We assume that a dual redundant output rotary position sensor is used for the brake pedal simulator, which generates two analogue signals in half value(~vdc and ~.Vdc). This study proposes a fault tolerant output selector which not only can diagnose faults and isolate them but also can select a reasonable signal to output. The fault modes are classified according to fault causes and simulated to confirm the system performance. The section presents the fault modes and effect analysis and the structure of the fault tolerant output selector. Simulations were done for every fault case, and the results are presented in section. Finally, the conclusions of this study and future works are given in Section. 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, www.ttp.net. (ID:...7, Pennsylvania State University, University Park, USA-//,::8)
Applied Mechanics and Materials Vols. 8-87 97. Structure of Fault Tolerant Output Selector The faults are mainly classified as error or failure: an error is defined as a transient and intermittent fault due to a disturbance like noise and a failure is defined as a permanent fault, and in this case, the system can be restored only when related components are repaired or replaced. Failures are subdivided into the non-signal case, caused by a disconnection or a dead short circuit; the signal-fixation case, caused by a fixation of the pedal sensor travel part; and the offset case, caused by a wrong initial value of the sensor output. All of them are potentially dangerous factors of the drive environment. To overcome these faults, a fault tolerant output selector was designed. As Fig. shows, it consists of the threshold predictor[], threshold level calculator[], fault detector, reconfigurator, exception handler[], fuzzy exception handler[] and signal selector. It works with pedal sensor inputs, BLS(brake light switch) signal input, Acc(acceleration pedal) on/off signal, and the drive information of both the vehicle speed and the distance from the front car. Fig. The structure of the fault output selector []. Fault detector This paper defined the two brake signals as main signal a m (k) and sub signal a s (k) on kth cycle. The fault detector has the error detection algorithm and the failure detection algorithm. The fault detector captures two brake signals and examines if an error exists using the error detection algorithm[], in which the signals are checked if the signal values in the normal range, and then sends the results to reconfigurator. (a) (b) Fig. (a) Flowchart of the failure detection algorithm, (b) Detailed algorithm of the brake signal failure: main signal a m (k) failure detection algorithm and sub signal a s (k) failure detection algorithm.
98 Innovation for Applied Science and Technology Fig. (a) shows the failure detection flow chart that captures additional input signals (BLS on/off and Acc on/off) to decide whether a failure has occurred. As Fig. (a) shows, two brake signals are fault detected by the main signal failure check module and then, by the sub signal failure check module, and then the results are sent to the reconfigurator. Fig. (b) shows the main signal and the sub signal failure detection algorithms. Only when the two brake signals are not in the failure mode conditions, are they designated as failure-free. In Fig. (b), first one is the failure detection algorithm for the main signal a m (k) and second one is the failure detection algorithm for the main signal a s (k).. Reconfigurator and Signal selector As Fig. shows, the reconfigurator decides the switch control signal according to the results of fault detection and sends it to the signal selector. The signal selector chooses which signal to output. Fig. Reconfigurator rules and Internal structure of signal selector As a result, the fault tolerant output selector always decides a reliable output signal. If one of two signals has an error or failure, then the selector chooses another fault-free signal. If both signals are fault-free, the selector calculates the average value of the two signals to output. If all of signals have errors, it selects EH(the exception handler). If two signals are designated as failure, it chooses the output value of FEH(the fuzzy exception handler). The decided output signal will be pass through the saturation part to ensure that its value lies in the normal range(v~v) to protect the brake control system.. Simulation Results We set the sampling time to ms, similar to that of an automobile control system. To simulate the error case, we chose two brake signals of sec: one is the smooth section, and the other is rapid section. After that, a random noise was inserted into both signals and the result was evaluated using the IAE[](Integral of the Absolute magnitude of the Error) value. The e(k) value is the difference between the true value A(k) and output value a(k). The random number N(k) is the value obtained by multiplying multiplied % of the true value A(k) by the random number D(k) in the kth cycle. The random number D(k) is in a fixed range( [-,]). As far as IAE value is concerned, the smaller the better. In Fig., (a) is the first error case in which two brake signals were respectively injected with random noise in the smooth section of optional points and the noise injection time is ms each point; (b) shows the result of eliminating the error value, and the IAE value is.7 in this case; (c) shows the second error case simulated the same way in the rapid section; (d) is the result and IAE value is.99 in this case. These results indicate that most of the errors were eliminated but that the error removal efficiency is affected by some factors such as the signal status, amount of error and the area of the injected error.
Applied Mechanics and Materials Vols. 8-87 99............ (a) (b) (c) (d) Fig. (a) Smooth signal with errors and (b) the result of filtering system; (c) rapid signal with errors and (d) the result of filtering system Fig. (a) shows the failure mode in which one of the brake signals is shut off during braking, and (b) is the result; (c) shows that one of brake signals has an offset failure and (d) is the system output. The signal having the offset value will be removed before braking. When Sub signal has shut off or offset failure, the system logic can handle too............... Time (sec)... Time (sec) (a) (b) (c) (d) Fig. (a) The case of main signal failure and (b) system output in this case; (c) main signal has V offset fault and (b) system output in this case Two types of the fixation failure modes are simulated in Fig.. In the first type, the signal is fixed on the braking process, as shown Fig. (a). In this case, the fault detector needs ms to determine which signal went wrong. Two cycle times are required to detect a fixation failure because of a possible error in another signal. So, there is a little error value on the output signal in this moment as shown in Fig. (b). If the fixation failure happened before braking, then the system will remove that module in advance, as shown in Fig. (c) and (d)............. (a) (b) (c) (d) Fig. (a) The case of sub signal fixed while braking and (b) system output in this case; (c) the case of sub signal already fixed before braking and (d) system output in this case. Fig.7 (a) shows the velocity of the vehicle and the distance from the vehicle ahead when all of brake signals have failure while braking; (b) shows the case in which two brake signals are blocked one after another and (c) shows the system output. At this moment, the system recognizes the driver s brake intention through the signal selector algorithm. After that, the Fuzzy Exception Handler calculates the suitable output value using the fuzzy controller, whose inputs are based on the vehicle speed and the vehicle distance from the front car; (d) shows the system output when all of braking signals are blocked before braking. A little delay time exists because of the gap between the pedal s initial position and the BLS on position.
9 Innovation for Applied Science and Technology speed(km/h) distance(m)...... 8..................... (a) (b) (c) (d) Fig.7 (a) Vehicle speed and vehicle distance from front car[]; (b) Brake signal is failed while braking, (c) System output at this case; (d) System output when brake signals are failed before braking.. Conclusions For lowering manufacturing costs and saving space, we chose the redundant output sensor for the pedal simulator. With these simulation results, we can know the fault tolerant output selector can simply solve the faults various fault modes recognized by experts. The fault tolerant output selector handled not only transient faults like noise, which induces error values, but also permanent faults such as disconnections, short circuits, fixations and offsets. Whatever the fault, the system will find it and decide the proper brake signal to output. Therefore, it can protect drivers and the drive environment. In this research, the BLS (brake light switch) is mainly used for detecting failures. We will upgrade the fault tolerant control system with respect to BLS faults in future work. Acknowledgments This study was supported by the technology innovation business which was conducted by the Korean Ministry of Knowledge and Economy (MKE). References [] Man Ho Kim, Suk Lee, Kyung Chang Lee, A fuzzy predictive redundancy system for fault-tolerance of x-by-wire systems, Elsevier, Vol., pp. -, () [] Rolf Isermann, Editor, Fault-Diagnosis Systems An Introduction from Fault Detection to Fault Tolerance, Springer Publisher, Germany () [] R. Isermann, R. Schwarz, S. Stolzl, Fault-tolerant drive-by-wire systems, IEEE Control Systems Magazine, USA (), Vol., Issue, pp. 8. [] Wongoo Lee, Young OK Lee, Minseok Jang, Choong Woo Lee, Chung Choo Chung, Han Byul Chung, Fault Tolerant Control of Sensor Fault of EPB System, Transactions of KSAE, Korea () [] Jianhu Li, Qing Li, Manbok Park, Hunmo Kim, Permanent Sensor Fault-Tolerant Fuzzy Control for EMB Pedal Simulator, KSAE Anuual Conference and Exhibition, () November-; Daejeon, Korea.
Innovation for Applied Science and Technology.8/www.scientific.net/AMM.8-87 The Fault Tolerant Output Selector Based on Fault-Detection Considering Realistic Fault Modes for Pedal Simulator of Brake-by-Wire System.8/www.scientific.net/AMM.8-87.9