| The braking ablity is one of the major performances for vehicle's active safety, and good braking will guarantee safe working for vehicles. Along with the improvements of vehicle dynamical technology and road conditions, which lead to the increase of automotive loading capacity and driving speed, the importance of vehicle's safety performance is getting more and more emphasized. A practical solution to problems resulting from large braking load of vehicles is the auxiliary braking device.Permanent magnet type eddy current retarder is a novel auxiliary braking device apart form the vehicle's own braking and parking brake system, featuring beneficial to energy saving and environment protection. Based on the principle of electromagnetic interaction, the device redistributes the braking load in time by making use of the strong non-contact braking ability generated by the permanent magnetic field. With this kind of the device, not only is the safety performance enhanced, but also the service life of the main braking system is greatly prolonged, indicating a new direction for auxiliary braking device development. At present, the domestic research on permanent magnet type eddy current retarder is just in its initial stage. Domestic auxiliary braking system manufacturing enterprises are short of their own intellectual properties of permanent magnet type eddy current retarder. Under the background mentioned above, research on permanent magnet type eddy current retarder will not only have academic values, but also be important to improve the vehicle's main braking performance, and lead to scientific and technological progress of vehicle's auxiliary braking system industry of China. Based on the present study and technology of permanent magnet type eddy current retarder at home and abroad, the author made systematic study on the electromagnetic field, braking toque and braking performance of the permanent magnet type eddy current retarder with theoretical analysis, finite element analysis and testing approaches. The major research work and results are summarized as followed: 1. The computation of eddy current and braking torque for permanent magnet type eddy current retarder. Based on the reasonable simplification of the physical model and the consideration of penetration depth, the author derived the formulations to calculating eddy current density and effective current. Furthermore, through computing the equivalent magnetic potential, adding the demagnetization effect to the permanent-magnet and applying the air-gas magnetic flux density expression obtained with method of equivalent magnetic circuit, the author derived the braking torque formulation from the eddy current loss principle. To find the braking principle of the retarder, the equivalent magnetic surface current was calculated. Based on the Maxwell equation and the Rogowski method, the distribution pattern of air gas magnetic field and eddy current density were analyzed, and braking torque formulation for calculating permanent magnet type eddy current retarder was derived. To prove the effectiveness of braking torque theory, experiments were carried out on the test-bed. The results showed that the error between theoretical and experimental results was less than 10%, which is acceptable. It is concluded that the equivalent-magnetic-circuit method could be suitable for the engineering design and the Rogowski method effective for the braking principle theoretical research.2. The finite element analysis of magnetic field and magnetic leakage research. Under the condition of ignoring the rotation effect and demagnetization effect, and with the help of finite element analysis software ANSYS, the author completed the following research:building the finite element model for permanent magnet type eddy current retarder, simulating the static magnetic field distribution of the quasi-braking state, analyzing the relationships among the air-gas magnetic density, various magnetic material characteristics, size of rotor and permanent magnet, air-gas width and thickness of the components. The experimental results showed to be consistent to the theoretical results. Based on the finite element method, the influence of air-gas width, permanent magnet size and magnetic polar number on the leakage coefficient was analyzed, and the magnetic leakage for a novel permanent magnet type eddy current retarder was discussed. The finite element analysis results showed to be consistent to the experimental results. It is concluded that it could be feasible to apply finite element analysis to study the magnetic field characteristics. The simulation result may provide the foundation to the further performance analysis and the optimal parameters selection.3. The research of key techniques for permanent magnet type eddy current retarder. The techniques for selection of material, size, magnetization methods and polar number and thickness were analyzed. Since it is difficult to directly measure the induction current of braking states, the author proposed a Soft measurement method. Behavior of induction current with the variation of rotating speed and air-gap width was obtained based on the simulation analysis. The soft-measuring model of eddy current density for braking state then was built. The results show clearly that RBF neural network based soft-sensing model has high measurement precision, and can play efficiency effect in practice engineering calculation and study.4. The sensitivity research of influential factors of braking performance. In order to learn the relationship between the braking performance and structural parameters, the regression equation with braking torque as the function of five structural parameters (inner radius of rotor, circumferential length of permanent magnet, air-gap width, axial width of rotor, height of permanent magnet) was constructed based on the uniform design and regression analysis. The influential sensitivity of the above five structural parameters on the braking performance was analyzed and their relationships were obtained. Based on the results from sensitivity analysis, the structural parameters of retarder were optimized by the full-arrangement method, aimed at increasing the braking torque. The results showed that the height of permanent magnet was the most significant factor to impact the braking performance and the other factors were inner radius of rotor, air-gap width and axial width of rotor in a descending order. The inner radius of rotor had no significant influence on the braking performance. Structural parameters optimization showed remarkable effect. The research results may be helpful to the selection and optimization of the structural parameters.5. The research of the braking performance for vehicles equipped with permanent magnet type eddy current retarder. The researches in this part include:constructing the dynamics equation for vehicles equipped with permanent magnet type eddy current retarder, analyzing the influence of united braking system witch includes the permanent magnet type eddy current retarder and the vehicle's own braking device on the braking stability based on the ECE law simulation, and comparing the braking performance of single retarder to that of the retarder combined with exhaust braking system in terms of the deceleration distance on flat road and the relationship between speed and slope on slope road, the researching approach being field test combined with theoretical analysis. The results showed that united braking had no significant influence on braking stability if the retarder matches well to the whole vehicle. The equipment of the permanent magnet type eddy current retarder could reduce the deceleration distance and meet the continuous braking requirement in the case of slope less than 5%. The united braking system could further improve the braking capability of vehicles.
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