Electromagnetic Field Analysis for Permanent Magnet Retarder by Finite Element Method

Transcription

1 017 Asia-Pacific Engineering and Technology Conference (APETC 017) ISBN: Electromagnetic Field Analysis for Permanent Magnet Retarder by Finite Element Method Chengye Liu, Xinhua Zhang and Xingang Song ABSTRACT Permanent magnet retarder is a kind of excellent performance brake and is used for auxiliary braking device of heavy automobile. Its advantages include lightweight, energy saving, environmental protection and simple maintenance. In addition, permanent magnet retarder can reduce braking load and thermal degradation effectively of its braking performance, and improve safety of the vehicle. Design optimization of magnetic circuit of retarder by using electromagnetic field analysis method can provide a feasible method for the future development of permanent magnet retarder. INTRODUCTION With the rapid economic development in recent years, road transport has been improving rapidly. Highway network extends in all directions, like vehicle speed, and the time of driving in the mountain road. When the car is running in the mountain area, it takes a long time to continuous braking, and when running in the city, it needed to brake frequently, so the vehicle's braking load becomes more and more. If those braking load is borne by the braking system, it will lead to overheating inevitably, and braking performance degradation, even braking failure, which also makes the brake drum and brake lining life greatly shortened, meanwhile the cost of maintenance and time has also been increased. Therefore, the more practical method is to install auxiliary brake device. Auxiliary brake device is used to make the vehicle speed reduced or stable range at a certain speed when in the downhill running. Compared with the main braking system, the power that the auxiliary braking device absorbed is few, and can remain the power unchanged or substantially unchanged for a long time. The working principle of permanent magnet retarder is similar with the eddy current retarder, instead of electric eddy current retarder s electromagnet, it is with permanent magnets to produce magnetic field. According to the structure, the permanent magnet retarder is divided into two types: Drum-type and Disc- Chengye Liu a, Xinhua Zhang b, Xingang Song c School of Automotive and Traffic Engineering, Jiangsu University of Technology, Changzhou, China a lccyyyy@163.com, b @qq.com, c @qq.com 148

2 type. Disc type is easy to obtain a large braking torque, but the structure is large. Drum type has the advantages of compact structure, convenient arrangement and control. Permanent magnet retarder can realize the lightweight and miniaturization, almost no power consumption, only solenoid valve consume power, long time using while not overheating, maintain the braking force stability and durability, even in the high speed range the braking force is not reduced, and the higher the speed of the drive shaft, the greater of braking force, simple maintenance, only need to periodically check the air gap. As the magnetic field generated by the permanent magnetic is limited, the brake torque generated less, and cannot provide a different braking torque. Permanent magnet retarder is the developing mainstream products in foreign markets currently [1-]. THE STRUCTURE OF PERMANENT MAGNET RETARDER The structure of permanent magnet retarder is shown in Fig.1. The magnet pole alternately are spaced and fixed on the magnet holder. Permanent magnet retarder s stator is generally fixed to the rear of the transmission housing. Rotor is connected with drive shaft through flange. Permanent magnets are mounted on the stator. The working principle is that the rotor rotates in the magnetic field of the permanent magnet, and generates the eddy current, then the eddy current and the magnetic field interacted to produce a braking force which is opposite to the rotating direction of the rotor. Considering the energy side, the retarder works based on the principle that the electromagnetic induction makes kinetic energy of motion transfer into electric energy, then electrical energy is eventually converted into thermal energy, which causes automobile to slow down. Figure 1. The structure of permanent magnet retarder. When braking is required, the magnet holder is rotated to the position corresponds to the magnet pole is shown in Fig.. Due to the barrier of nonmagnetic material, the magnetic circuit is formed between adjacent permanent magnets, magnet pole, rotor and magnet holder. Eddy current is within the rotor drum when rotor rotates, which generates the braking torque. When no braking, the magnet holder is driven by actuating device rotates to the position is shown in Fig.3. In this case the magnetic field does not pass through the rotor due to the high magnetic material, so as not to generate a braking torque. 149

3 Figure. Braking state of permanent magnet retarder. Figure 3. Non-braking state of permanent magnet retarder. In order to make the advantages of permanent magnet retarder miniature and lightweight, it is necessary to optimize the structure of the magnetic circuit, which contains the permanent magnets and the magnet pole. Try not to reduce magnetic flux when braking, and make sure it acts on the rotor. Avoid magnetic flux leakage when no braking and all the above requirements should be met during the design, and taking into account the lightweight, and the cost performance in magnetic circuit design. ELECTROMAGNETIC FIELD ANALYSIS TECHNOLOGY According to Maxwell equations, the stable magnetic field without current area of the formula is allowed: H 0 (1) Introduction of scalar magnetic potential to calculate parameters: m m m H m i j k x y z () We can calculate the partial differential equation for scalar magnetic potential on the basis of the above two equations: m m x m y m z 0 (3) 150

4 Equation 3 in combination with the boundary conditions constitute a boundary value problem, namely problem solving of the mathematical model of stable magnetic field. m m m : x y z 1: m m0 m Bn : n 0 (4) Ω is the solved region, 1 and are the boundary conditions, μ is the magnetic permeability, B n is the normal component of the magnetic flux density vector. It can obtain the magnetic field strength of each component, as long as the solution of a scalar, and perform differential, and determine the magnetic induction intensity of each direction. Due to a combination of permanent magnets and magnet pole existence numerous possible, it is difficult to find the optimal value in the experiment. Therefore, using FEM (Finite Element Method) for electromagnetic field can analyse each type of retarder and selected an optimal scheme [3]. Evaluation of the eddy current density of the rotor is shown in Fig.4. The electromagnetic field analysis method is helpful to the analysis of the eddy current density components, which provides direction for optimizing the gap between the magnet and the magnet pole shape, the rotor and the stator. Figure 4. Evaluation of eddy current density distribution. The theory value can be obtained while comparing with the actual value by the electromagnetic field analysis is shown in Fig.5, and the high degree of overlap, so the method can accurately predict the braking force of permanent magnet retarder [4]. Therefore, magnetic field analysis method can be used in a very short time to make magnetic circuit to meet the requirements of users. 151

5 Figure 5. Evaluation of the braking torque by electromagnetic field analysis. CONCLUSIONS The working principle and the development technology of permanent magnet retarder about auxiliary brake device are introduced in this article. In addition, surface treatment technology, control technology also particularly important in retarder developing. Welding technology is also essential in manufacturing of permanent magnet retarder. For example, the stator and holder is welded, this position with rotation and vibration will cause a large load, thus the welding strength also needs to be evaluated. Currently installed on the crane's high braking force permanent magnet retarder has been developed, the usage range of permanent magnet retarder is gradually expanding. It is demanded for lightweight type permanent magnet retarder nowadays, which can improve fuel economy. We hope to introduce this technology for the future development of permanent magnet retarder to improve vehicle safety and reduce environmental pollution. ACKNOWLEDGEMENT This research was financially supported by the Six talent peaks project in Jiangsu Province (015-JXQC-009). REFERENCES [1] Sharif S, Faiz J, Sharif K. Performance analysis of a cylindrical eddy current brake [J]. IET Electric Power Application, 01, 6(9): [] He Ren, Liu Cunxiang. Simulation of integrated system frictional brake and contactless wheel retarder [J]. Journal of Nanjing University of Science and Technology, 011, 35(5): (in Chinese) [3] Yang Liling. Modeling and simulation of the hydraulic disk brake [D]. Wuhan: Wuhan University of Technology, 009. (in Chinese) [4] Zhang Yan, Liu Chengye, He Ren, et al. Influence of eddy current retarder on vehicle braking force utilization [J], Journal of Traffic and Transportation Engineering, 011, 11(6): (in Chinese) 15