Research On Prediction For Parasitic Parameters And Crosstalk In Automotive Wiring Harness

With the pursuit of higher vehicle safety, comfort and easy handling, the number of automotive electronic equipments increased and the complexity of them increased, too. The hybrid vehicles and electric vehicles exacerbated the trend. The automotive electronic equipments were found all over the automobile body, and the different electronic equipments were connected closely through the wiring harness. The power lines and signal lines from the electronic equipments laid down densely along the automobile chassis and body. The numbers of the wiring harnesses in ordinary automobile were over 1000 generally, and total length of them was to 2000 meters. In such tight connection, the electromagnetic interference among the various electronic equipments became increasingly serious. The interference conducted along wiring harnesses to electronic equipments, and affected electronic equipments performance.The crosstalk in the automotive wiring harnesses was the most important conducted interference. It could increase the noise level of wires in vicinity, destroy data, affect the conduction emission and radiated emissions of system, and make the overall electromagnetic compatibility of automobile a strong decline. The crosstalk came from the inductive and capacitive coupling between parasitic parameters of the wires. The parasitic parameters were the root causes of crosstalk.The parasitic parameters and crosstalk of wires related with the harness geometry layout. As the automobile in static, the height of wires to the ground and distance between wires were constant, and it was the deterministic geometry layout.The parasitic parameters and crosstalk of wires were deterministic values in the deterministic geometry layout. As the automobile in dynamic, automobile acceleration, deceleration, vibration and other factors made the height of wires to ground and the distance between wires change, and it was the nondeterministic geometry layout. The heights and the distance were random variables, and the parasitic parameters and crosstalk were statistical quantities in the nondeterministic geometry layout. The geometry layout of wiring harness was the main clue in the dissertation. The deterministic prediction model for the parasitic parameters and crosstalk in the deterministic geometry layout was proposed. The best and worst case prediction model and the statistical prediction model for the parasitic parameters and crosstalk in the nondeterministic geometry layout were proposed at the same time. The main research of dissertation as follows: The deterministic analytical prediction model was established for the parasitic parameters and the crosstalk of wires in inhomogeneous media based on the image method and electromagnetic field theory related and inductive-capacitive coupling approximation method. According to the image method and the electromagnetic field theory related, the dissertation derived the analytical formula of the parasitic parameters of wires in inhomogeneous media. It can predict parasitic parameters simply, conveniently and fast, according to wire coordinates. The inductance-capacitance coupling approximation is simple, practical, and able to get near-end crosstalk and far-end crosstalk of wires fast based on lossless, weak coupling, electrically small wires. According to actual situation, the parasitic parameters and crosstalk of wires in the automotive harness were calculated with the deterministic analytical prediction model. The result was compared with the EMC Studio simulation software; the conformance was good.The dissertation anglicized factors to affect parasitic parameters and crosstalk of wires in order to find the measures to reduce the parasitic parameters and crosstalk. Focus on the changes of parasitic parameters and crosstalk when the height wire-to-ground and the distance between wires change at the same time.When the automobiles moved, the wires in wiring harness moved together, and the geometry layout of wires in the wiring harness changed, so the parasitic parameters and crosstalk changed with it. A statistical prediction model for the parasitic parameters and crosstalk was proposed according to the Monte Carlo method and Taylor series. The Monte Carlo method was used to calculate the mean value and standard deviation of the parasitic parameters and crosstalk, compared with the analytical method based on Taylor series. In order to understand the statistical properties of the parasitic parameters and crosstalk of wires comprehensively, the probability density function and probability ditribution function of those parameters were established through the mean value and standard deviation, under the assumption of normal parasitic. The uncertainty of geometry layout of wires in the automotive wiring harness makes it random essentially for the parasitic parameters and the crosstalk, therefore statistical model is appropriate to predict the dynamic changes of the parasitic parameters and crosstalk in automotive wire harness and it is most rigorous.When the automobiles moved, the range of wires geometry was limited in the wiring harness. The height to the ground and distance of wires changed in a closed interval. The best and worst-case prediction model was established to predict the dynamic changes of parasitic parameter and crosstalk depended on the endpoint values of them. According to the formulas of the parasitic parameter and crosstalk, when the heights of wires to the ground are the maximum and distance between wires is the minimum the parasitic parameter and crosstalk obtain maximum, and it is the worst-case for the parasitic parameter and crosstalk. When the heights of wires to the ground are the minimum and distance between wires is the maximum the parasitic parameter and crosstalk obtain minimum, and it is the best-case for the parasitic parameter and crosstalk. Therefore, it is possible to predict the dynamic changes of the parasitic parameter and crosstalk through the best and worst-case values of them. The 40 positions of wires pairs were selected randomly within wiring harness, and the parasitic parameters and crosstalk in those positions calculated by the EMC Studio were all in the best and the worst-case prediction interval, it turned out that the best and the worst analytical prediction model was effective. The predictive model was simple, convenient and it can provide a rapid prediction about parasitic parameters and crosstalk of wires, ensure the problem will not be missed especially in the early stage of design absence complete information.While the best and worst-case model can predict dynamic changes of parasitic parameters and crosstalk fast, it took the risk of overestimation or underestimation with the extreme value. In order to improve prediction accuracy, under certain of confidence level, the best and worst-case model was amended based on the mean value and standard deviation.Under the circumstance of 80% confidence leves, the interval estimation for the mean values of parasitic parameters and crosstalk were conducted and confidence intervals were obstained. That the best and worst-case intervals were replaced by the confidence intervals can shorted the length of prediction interval and improve prediction accuracy.