Vehicle Engineering (VE), Volume 3, 2015 www.seipub.org/ve doi: 10.14355/ve.2015.03.001
Development of Test Set for Tire Failure Emergency Braking System Qingzhang Chen*1, Jonathan M. Weaver2, Wei Wang1 1 College of Mechanical Engineering, Automotive Engineering, Changshu Institute of Technology, Suzhou, China 2 College of Engineering &Science, Mechanical Engineering, University of Detroit Mercy, Detroit, USA *1
chenqz1973@sina.com; 2jmweaver@udmercy.edu; 3wangwei@cslg.edu.cn
Abstract To develop tire blowout emergency braking system, one of the key problems is the test method for system calibration. By simulating the process of tire blowout, and transmitting the tire failure signal to the system, the test set carries out every performance experiments, so that the control strategy and the control value can be adjusted according to test results. After developing the tire blowout emergency braking system, we designed the tire blowout simulating device, which can release tire pressure with big flow by controlling a small flow, so that the problem of simulating big flow of tire blowout repeatedly was solved. With this device, we also can simulate the different intensity of tire blowout. The whole test system was built, and the road test was carried out. The results show that the test system can be used to develop the relative emergency braking system, and achieve the experiment of system calibration and performance evaluation. Keywords Vehicle; Emergency Braking System; Device for Tire Blowout Simulation; Test Set; Design
Introduction Tire failure is one of the main factors which cause the fatal traffic accidents. Currently, the Tire Pressure Monitoring System (TPMS) is popularly equipped on vehicles to prevent low tire pressure and avoid tire failure accidents. But it can only remind the driver for slowly tire pressure failure(Fu Jianzhong, et al. ,2006; Xu Lina, et al., 2009). For the situation of urgently tire blow‐out, the characteristics of vehicle motion will be changed after tire blow‐out. It’s easy to cause the driver’s rush irritability operation, once the driver operating improperly, the vehicle will be severely side slipped, drifted, and even overturned(Patwardhan S, et al., 1994; Zbigniew Lozia, et al. 2005; Dang Lu, et al. 2010.). So it is useful to develop an emergency braking system to slow down the velocity of vehicle automatically and smoothly(Qingzhang Chen, 2011; Huang Jiang, et al., 2009) A tire blow‐out emergency automatic braking system can slow down the vehicle automatically into a safety speed and stop the vehicle before it going out of the driver’s control. But during the development and the performance evaluation of the system, how to deal with the relative test, and simulate the process of tire blow‐out are the key problems. The thesis is concerning of the design of tire blow‐out test set system. The Scheme of the System System Hardware Principle The emergency braking system (EBS) for tire blow‐out includes the tire blow‐out monitoring module and automotive braking module. The monitoring module is extended on the TPMS, which is used to identify the tire failure. Once the tire blow‐out happening, the tire failure signal is transmitted by the monitoring module to the emergency braking system through radio frequency identification (RFID). When the tire blow‐out signal is received by EBS, it will determine the braking mode according to the situation of tire failure to slow down the vehicle to a safe speed with expected track in shortest time. The braking and vehicle stability control is realized through adjusting the hydraulic braking pressure of each wheel cylinder.
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The EBS for tire blow‐out is shown as fig.1. Based on the Electro‐Hydraulic Braking system (EHB), a yaw rate signal from the yaw rate sensor and the tire blow‐out signal input are added. The automatic braking is realized by the control unit driving the brake motor pump and each related electromagnetic valves to brake after receiving the tire blow‐out signal. According to the yaw rate and the deviation, the braking state of the vehicle is determined, then the pressure of each cylinder is determined, and the related differential braking is carried out to control the vehicle moving stably. With the wheel speed signals, the slip rate of each wheel is calculated, and the related wheel cylinder valves are droved to carry out anti‐lock brake control.
FIG. 1 SYSTEM HARDWARE PRINCIPLE FIG. 2 THE ACTUATORS OF THE SYSTEM
Actuators of the System The actuators of the system are shown as fig.2. It is made up of conventional brake, the hydraulic power supply parts of the automatic braking, inlet and outlet valves of each wheel cylinder, separating valves and balance valves (Ric Robinette, et al., 1997). During the normal moving of the vehicle, the automatic hydraulic braking pipe maintains certain pre‐pressure under the function of the accumulator. When in the conventional braking, brake pedal is working, and the hydraulic pressure is transferred from the separating valve and balance valve to each wheel cylinder to obtain braking force (the pedal feeling simulator and corresponding parts are not shown in the EHB system). Once there is a tire blow‐out, the automatic braking system is activated. With the working of the separating valves, balance valves and the opening of the inlet valves, braking pressure is transferred from the hydraulic power supply to each wheel cylinder. According to the vehicle yaw rate signal, the controller of the emergency automatic braking system judges the operation condition, and then adjusts the amplitude of the pressure in each wheel cylinder to realize the differential braking, and control the moving trajectory of the vehicle. Design of the Test Set Testing Purposes The testing purposes are as following, (1) Simulate the process of tire blow‐out, including identification of tire failure, testing of the responding rapidity
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of monitoring module, and the reliability of RFID transmitting. (2) Testing of the responding time of the EBS, the braking deceleration of vehicle and the braking stability. (3) The testing for adjusting control value in developing system and calibration test. Design of Tire Blow‐out Simulating Device Fig. 3 shows the schematic diagram of the tire blow‐out simulating device. Pressure air in tire can deflated through an air release control valve (ARCV) which is connected with the tire rim by several pipes, and installed on the wheel through the installing base. These pipes are air release connecting except one for control the balance slider of the ARCV, named control pipe. Different number of pipes can make a different flow of the pressure air blow off, that is to say, the more pipes working means the more serious of tire blow‐out. As shown in fig. 4, the ARCV can be wholly opened when the balance slider sliding to the end of right direction, and be closed when the slider is at the end of left. In our test set, there are three pipes for air release. Each of them connects with the tire rim on one end, and another end connects with the inlet port of ARCV. These pipes are added up to realize big flow of blow off so that the rapid process of tire blow‐out is simulated. The structure of the ARCV is shown in figure 4. There are two chambers A and B, and they are divided by the balance slider. Chamber A connects with tire rim through inlet ports and the pipes. Chamber B connects with tire rim through the control pipe with the two‐position three‐way solenoid valve (2P3W‐SV) on it. The solenoid valve is used to switch whether chamber B connects to tire pressure air or to the open air. When to tire pressure air, the air pressure of chamber B is equal to tire pressure as it is in chamber A. Because the area of balance slider on side A is smaller than side B, the force produced by pressure air on side A is smaller than that on side B, and the balance slider stops on the left side. The outlet port of the ARCV is cut off, and the pressure air in tire does not blow off. When chamber B connects to open air, the air pressure on side A is much larger than that on the side B, and there for the force on side A is much larger than side B, so the balance slider stops on the right side. The outlet port is opened to open air, and the pressure air in chamber A blows off rapidly, than the process of tire blow‐out is simulated. Fig. 5 shows the connection of 2P3W‐SV. The 2P3W‐SV is powered by the battery, and switched by a remote control switch. The static state of it is connecting the control pipe to chamber B, and maintaining tire pressure in chamber B. If the remote control switch is on, then the 2P3W‐SV is in the other position connecting chamber B to open air.
FIG.3 THE SCHEMATIC DIAGRAM OF SIMULATING DEVICE FIG. 4 THE PROFILE STRUCTURE OF THE DEVICE
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The picture of tire blow‐out device is shown as fig. 6. It includes the receiver, transmitter, remote controller, 2P3W‐ SV, and ARCV.
FIG. 5 THE CONNECTION OF 2P3W‐SV FIG. 6 THE PICTURE OF TIRE BLOW‐OUT DEVICE
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信号电压(V)
5 4 3 2 1 0 1
1001
2001
3001
4001
5001 6001 t(ms)
7001
8001
9001 10001
FIG. 8 THE RESPONSE OF VEHICLE YAW RATE BETWEEN WITH AND WITHOUT EBS AT 60KM/H
FIG. 7 THE PICTURE OF ROAD TEST SET
Road Test Set The test vehicle is BJ2500. The average air pressure of the tires is charged to normal (250kPa), and the testing ground is a flat cement road (a vehicle brake system testing ground of a company). The tire blow‐out device is controlled by a remote switch. To detect the changes of speed reducing during the braking process of tire blow‐out in the road test system, a accelerate sensor is installed near the center of mass of the vehicle. The picture of road test set is shown in fig.7. The yaw rate signal, longitudinal accelerate signal and wheel velocity signal are collected by DL750 oscilloscope through which the state of longitudinal driving and yaw rate responding of vehicle are recorded. The oscilloscope mainly collects three ways of signal including trigger signal (CH1), yaw rate signal (CH2) and vehicle accelerating signal (CH3). With this test set, we can simulate the processing of vehicle tire blow‐out. By turning on the remote controller, the electromagnetic valve working, air in tire blows out from four pipes simultaneously. At the same time, the signal of tire blow‐out is sent to the emergency braking system. Certainly, there is time delay for identification of tire blow‐out, so we need to give an estimated delay time for the tire blow‐ out signal. Test Results Shown as Fig. 8, when the speed is 60km/h, and curve 1 is blow‐out trigger signal. Curve 2 is yaw rate output curve without additional tire blow‐out control. Curve 3 is the yaw rate output curve after blow‐out with the emergency braking system. According to curve 2 on Fig. 8, without EBS, in about 2 sec after blow‐out, fluctuation range of yaw rate is bigger at the very beginning. As the vehicle slowed down after a blow‐out happened, yaw rate signal is reduced to about
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2.25 (This is the middle value the yaw rate signal, which means the yaw rate to be approximate to zero). Curve 3 is more stable than curve 2, that’s mainly because of the work of EBS, which made the vehicle easier to keep driving in the original track. Conclusions During the development and the performance evaluation of the EBS system, we designed the test system, including the tire blow‐out simulating device, which can release tire pressure with big flow by controlling a small flow and can simulate the different intensity of tire blow‐out. The whole test system was built, and the road tests were carried out. The results show that the test system can be used to develop the relative emergency braking system, and achieve the experiment of system calibration and performance evaluation. ACKNOWLEDGMENT
This work was supported by ‘The Natural Science Foundation’ (BK2011367) and ‘Six Peak Talents Foundation’ (SZ2010002) of Jiangsu Province funded by the Chinese Government. REFERENCES
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