CAR-Virtual tire pressure sensors in vehicles in the Study of Testing

1 Introduction Modern vehicles of the three major electronic information technology basis include: information collection (sensor technology), information transmission (ICT) and information processing (computer technology), the sensor is a modern vehicle electronic products the forefront of information technology. The tire failure and lead to traffic accidents is evoked one of the main reasons for tires, vehicles and the state of the roads accurate and reliable fault tolerance and continuous monitoring, traditional sensor is difficult to accurately completed a complex task, a system based on computer technology and virtual sensors tire of the road friction, road conditions, tire pressure and tire rotation balance, and other parameters. Virtual sensor is based on the sensor hardware and computer platforms, and through software development from, and will use the software to complete the calibration and sensor calibration to achieve the best performance vehicle control. Sensor data acquisition device through access to dollars Reuters machine, the sensor completed by the computer checks the read sensor parameters, sensors installed and recording work. 2 virtual sensor Vehicle Tire virtual sensor hardware, including some of the major computer systems, excellent performance of wheel speed sensor, wheel pressure sensors, as well as connector and instrumentation. Virtual sensors must also include its software package, namely, data processing procedures, compensation procedures and test handling procedures. Virtual Sensor is a signal processing technology, the system can not be used to estimate placed the physical location of the sensor response. Virtual sensors tires on vehicles on the road and can be further friction between the tire, wheel and tire inflation pressure on the balance of factors affecting tire parameters, multi-sensor fusion system will be drawn from the various sensors combined with the information described by observing systems, in order to get more use of a single sensor more accurate, more concrete conclusions. Using computer technology, virtual sensor can be used only ordinary sensors, wheel speed sensor, wheel torque sensor, and motor vehicles CAN bus to transmit information, then under certain computer algorithm, complete vehicle tire friction model calculation to obtain the round of the effective pressure information. The measurement of input and output shown in Figure 1. The start of the study is estimated pavement friction coefficient, and then estimate the wheel pressure. Attachment 3 of the road One vehicle tire model system is based on the ground machinery mechanics theory, the theoretical know: different ground conditions for the attachment coefficient is different. Vehicles driving force attachment coefficient and vehicle tires sliding to the relationship between the rate of Figure 2. As can be seen from Figure: in a certain attachment coefficient, tires slip rate s = 0, and the driving force of the weight of vehicles φ ratio F / G the most, sliding s transfer rate from. Began to increase, φ attachment coefficient increases when vehicle tires slip rate s = 0.10 ~ 0.20, the maximum coefficient of adhesion φ max, if the slip rate continued to increase, attachment coefficient begin to decline. When s tire slip rate reached 100%, occurred entirely tire slip. Slip rate wheels usually defined as the relative speed with the tangential velocity ratio. Their expression for the formula (1). Attachment coefficient φ φ = F / G. The slip rate is very small circumstances, with the rate of car-blading to meet attachment coefficient of linear equations φ = ks, and the characteristics of the tire, and the friction on the road. Based on the above theory, the state vector describing the use of vehicles sliding state, where the vertical stiffness for pre - and post-wheel radius of the poor. The model showed that precise wheel slip ratio is a function of the driving force with a mean μ white noise, the average white noise was mainly due to the different radius around the wheel caused. Speed sensors detect various working on speed ω tires, and from the CAN bus was sent to the engine's torque various tire M, the model solution through computer can access various preliminary tire slip rate and the attachment coefficient. 4 virtual vehicle tire pressure sensor measurement algorithm At present, foreign countries against the virtual tire pressure sensor detection algorithm a lot of research and development projects, for which there are more than 40 patents, most of the standard wheel speed sensor, the main methods are: Vibration analysis algorithm 4.1 Use rubber tires in the road by the impact of the flexibility, speed of the wheels of the spectrum conduct sample analysis, and removal of vehicles from other parts of the vibration caused by the disturbance. Vibration Analysis of the Fast Fourier Transform FFT detection method completed. The basic idea of this method is to tire as a "spring a damper" system. Under the model and inflatable tire pressure, the best general in the vibration frequency between 40-50 Hz, but there are also other higher or lower frequency. Through the different tire vibration research and screening, monitoring its vibration frequency to obtain the values of normal frequency, and detect the non-normal. Whether or FFT model-based methods in the application of vibration analysis, the measurement should be conducted on the speed filtering. Use the least-squares fitting method, reached an. To improve the ratio of the speed of signal interference. Compensation speed signal waveforms clearly show about a 45 Hz vibration mode, as shown in Figure 3. FFT meter and the use of a low rate through the filter can calculate the average cycle diagram, each test can be automatically calculated as shown in Figure 4 peak. Off-line, they can detect 15% of the tire pressure drop, but consider automatically set thresholds and very low error rate warnings, 30% of the tire pressure drop more credible. FFT is a batch of data, a certain time lag. Figure 4 in the use of a lot of 305 test data. The adoption of a second, "a spring damping" model, the calculation of tire pressure with the relevant parameter values Model-based vibration analysis easy introduction fitting method, is given in Figure 5 is the use of least squares fitting that the vibration mode. The use of such filters, we can reliably within 5 s to 30% of the pressure drop. This filter can be at the lowest 1 OOHz frequency data processing, FFT calculation method than decreased significantly. Use one of only 20 Hz operation Kalman filter, the amount of computation in the same circumstances is more than the capacity of RLS. Figure 6 different tire pressure, the Kalman filter estimate the vibration mode, less than 5 times the original amount of computation, this new method detected 15% of the changes in the speed and pressure RLS algorithm for detecting 30% of the same. 4.2 Based on the tire radius of the tire pressure The most common tire pressure calculation is based on the static nonlinear changes in the rate of margin tires, wheels the same size as when the value close to zero. The road surface friction instructions Kalman Filter slip offsets can well reflect the relative radius of the wheel, linear measurement data is the method of noise response insensitive. To offset sliding around the wheel can detect the relative error using Computable yaw-rate filter wheels before and after the relative error, thus calculated wheel radius. Existing methods of pressure on the wheels of most of the wheel speed based on the static tests, based ω1/ω2 = ω3/ω4, feet superscript code for the wheels (left front wheel 1, and the right front 2, 3 left rear, right rear 4). When vehicles uniform linear or circular motion, the vehicle wheel speed equation value is zero. This signals in the form of low-through of not less than 0 with a non-normal deviation, which can use more than the basic point of TPI value. In addition, the nonlinear transform data from the statistical requirements of the sub-state, the lack of flexural strength, different levels of friction, tire wear and so on limiting the reliability of this method. We found that model-based method can well take into account the above, the use of performance significantly. The improved. The basic filter used by the road friction is directed filter (RFI), high-precision yaw rate (HPY), and absolute speed of instructions (AVI) filter, the latter two tire pressure for the determination of relevant information in table 1. When all the gas slowly leaking from the tires, vehicles with the theoretical value of the radius deviation detection equipment can be used diffusion function keys completed. After field testing, for all the methods are compared, come to the conclusion that in a way the final accuracy, rapid response characteristics, strength and computational complexity of the (low-end model and the low sampling frequency), and other aspects of optimal performance. However, under specified circumstances other methods in certain areas can be used as a good supplement, the final algorithm system should be a multi-algorithm combinations. 5 Conclusion Virtual sensor signals through other sensors measured indirectly information, surveying the road and tire adhesion coefficient and tire pressure value, and need special sensor is very expensive. Through accurate measurement of wheel speed signal vehicles, using computer technology can be friction and tire pressure. Attachment coefficient virtual sensor technology is increasingly mature, introduced engineering applications. Virtual tire pressure sensor technologies currently under consideration, based on research methods the virtual vibration sensor technology, and based on the model of the wheel radius virtual sensor technology. But for the complex and volatile external interference factors need to amend CAN Bus information.