Eddy current braking experiment using brake disc from aluminium series of Al6061 and Al7075

Transcription

1 Eddy current braking experiment using brake disc from aluminium series of Al61 and Al75 M Z Baharom 1,2,a, M Z Nuawi 1,b, G Priyandoko 2,c and S M Harris 1,d 1 Department of Mechanic and Material, Universiti Kebangsaan Malaysia, 460 Bangi, Selangor, Malaysia. 2 Faculty of Mechanical Engineering, Universiti Malaysia Pahang, 260 UMP Pekan, Pahang, Malaysia. a mohamadzairi@ump.edu.my, b zaki@eng.ukm.my, c gigih@ump.edu.my, d salleh@eng.ukm.my Abstract. The electromagnetic braking using eddy current was studied, focused on two series of aluminium as the brake disc which are Al61 and Al75. This paper presents the comparison for both series in a few varied parameters related to eddy current braking such as air-gap, number of turns and brake disc thickness. Optical tachometer has been used along with PULSE analyzer to capture the and time (s). The findings shows that the smaller the air-gap, the larger of electromagnet turns and the thicker disc thickness is, will generate higher braking torque to stop the rotational motion of disc brake and give great performance for eddy current braking. Those parameters that been evaluated also addressed a potential on expanding this knowledge to develop an electromagnetic braking system to replace the conventional braking system. 1. Introduction Eddy current braking system has a lot of advantages compared to the conventional braking system. It can reduce the wear of brake pad, vibration and it is environmental friendly. Eddy current braking was said as environmental friendly because it can reduce the pollution of the wear debris from the brake pad itself [1]. In an early research, it was founded that aluminium is the best material to be use as the brake disc compared to copper and zink [2]. The reactions and eddy current effects on aluminium are more effective than copper and zink. As we know, the motion been slow down by a magnetic drag force that has been produced while a conducting material is moving through a stationery magnet or otherwise [3]. The changing magnetic field will induce eddy current in the conductor [3]. These currents will dissipate energy in the conductor and generate drag force [3]. With an experiment setup that has been done by Gonzalez in his laboratory [4], the research regarding eddy current braking behaviour using electromagnet has been expanded by us which focused on two series of aluminium which are Al61 and Al75. Both series are the most common alloys of aluminium for general purpose use. They have been used for aircraft structures, bicycle components, chassis plates and wheel spacers for car. Therefore, these two series of Aluminium have been chosen to be tested in this eddy current braking experiment as the brake disc.

2 2. Experimental Procedure Figure 1. The experimental setup of eddy current braking experiment using electromagnet. Figure 2. 3D view for the experimental setup of eddy current braking. Figure 1 shows the experiment setup for this study while figure 2 shows the 3D view of the experiment setup. Based on the eddy current braking experiment done before [4], both setups are quite similar with a few additional equipments plug-in. The use of digital tachometer been replaced by optical tachometer which connected to the PULSE analyzer to capture the and time (s). Meaning that it also replaces the function of stopwatch in the previous study by Gonzalez. By doing this, the can be recorded directly and precisely. Besides that, power supply that been used is higher power of 10A to induce the current for electromagnet coil. The experiment also been conducted in the semi-anechoic chamber to reduce the environmental error.

3 The power supply for the motor is a 0-V power supply. It will supply voltage about 11V to 15V for this experiment to achieve speed of rpm to 1 rpm when unloaded. Then, the current will be induced to the electromagnet in increment of 0.5A each. The optical tachometer will record the speed (rpm) of the disc rotational motion. The experiment uses two different thicknesses of disc which are 4mm and 5mm. Therefore, this study will looks on the effect of different series of Al61 and Al75, the air-gap, thickness of the disc and the number of electromagnet turns that been used. In this study, a, V, t, d, I, N will represent the air-gap, voltage supplied to the motor, disc thickness, disc diameter, current induced and number of electromagnet turns, respectively. 3. Results and discussions This section will discussed three parts of this study which are the effect of different air-gap, number of electromagnet turns and material comparison of Al61 and Al75. Graph will shows the effect of parameters evaluated while increasing the current induced. It also shows the decelaration occured on the brake disc when current induced into the system Air-gap effect Al61 Al75 Al61 Al75 Figure 3. Speed vs current for Al61 and Al75 a (1mm), N (2), d (4mm) and V (11V). Figure 4. Speed vs current for Al61 andal75 with a (3mm), N (2), d (4mm) and V (11V). 95 Al61 Al Figure 5. Speed vs current for Al61 andal75 with a (5mm), N (2), d (4mm) and V (11V).

4 Figure 3, figure 4 and figure 5 shows the effect regarding air-gap of 1mm, 3mm and 5mm, respectively, for both series of aluminium. Constant voltage of 11V been supplied to the DC motor with the use of electromagnet with 2 turns. As we can see, the smaller the air-gap between the disc and the iron core of the electromagnet was, the better the eddy current braking effect is. Small air-gap will produce a stronger magnetic field, B as been mentioned by Lee and friends in their research [5]. Higher magnetic flux been induced in the small air-gap of 1mm compared to 3mm & 5mm. It means that drag force has been generated in the smaller air-gap for both Al61 & Al75 disc which will contribute to slow the motion faster Number of electromagnet turns N = 2 N = Figure 6. Speed vs current of Al61 for different number of electromagnet turns with a (1mm), d (4mm) and V (11V). Figure 6 shows the graph of vs for electromagnet with and 2 turns with the air-gap of 1mm, 11V voltage supply and disc thickness of 4mm. During the test, due to safety issue, maximum permissible current that been induced for electromagnet with and 2 turns are 8A and 4.5A, respectively. As we can see in figure 6, the larger the number of turns, the better the braking is. It is parallel to the Lee and friends research as been mentioned that when we increase the number of turns, it will stronger the magnetic field [5]. Speed been dropped from about 98rpm to almost 38rpm with the use of electromagnet with 2 turns and maximum of 4.5A current induced. For electromagnet with turns, the speed just drop to about 81rpm with the maximum of 8A current induced. Large number of electromagnet turns will require a small amount of current to produce higher braking torque compared to less number of turns which needed higher amount of current. It is really important to have an optimum number of electromagnet turns for eddy current braking to save amount of current that will be induced into the system Disc thickness In figure 7 and figure 8 below, we can see the effect of using different thickness for the disc brake using disc material of Al61 and Al75, respectively. For this experiment, disc of 4mm & 5mm in thickness has been tested, with the supplied of 11V to DC motor, air-gap of 1mm and 2 turns electromagnet. Result shows that the larger the disc thickness is, the better the braking is. Torque produced on thicker disc is higher which will approach the DC motor torque in order to stop the motion. Disc with thickness of 5mm shows better deceleration for both materials of Al61 and Al75 compared to 4mm disc thickness.

5 d = 4mm d = 5mm d = 4mm d = 5mm Time (s) Time (s) Figure 7. Speed vs time of Al61 for different disc thickness with a (1mm), N (2) and V (11V). Figure 8. Speed vs time of Al75 for different disc thickness with a (1mm), N (2) and V (11V). 3.4 Comparison of Al61 and Al75 Al61 Al75 Figure 9. Speed vs current for Al61 & Al75 with N (2), a (1mm), d (4mm) and V (11V). From figure 9, we can see the comparison between two series of aluminium which are Al61 and Al75. For this test, the number of electromagnet turns fixed at 2, air-gap of 1mm, disc thickness of 4mm and motor voltage supply at 11V. For current induced of 4A, Al61 has dropped its speed to about 38 rpm compared to Al75 which achieved only 42 rpm. It means that Al61 produced higher braking torque compared to Al75. The electrical conductivity of Al61 and Al75 are 2.73 x 10 7 Ωm -1 and 1.92 x 10 7 Ωm -1, respectively. Higher electrical conductivity influenced the generation of greater breaking torque.

6 4. Conclusion From the experiment, we may conclude that Al61 is better than Al75 to be used as the brake disc material for our electromagnetic braking system using eddy current project. Besides that, we may also conclude that the smaller the air-gap, the larger the number of turns is, and the larger the disc thickness is, will generate higher braking torque and performance for electromagnetic braking. Finding mentioned parameters from this experiment are parallel with the theory. Those parameters that have been evaluated show that there is a potential of developing the electromagnetic braking system to replace the conventional braking system. 5. Acknowledgement The authors would like to thank Faculty of Engineering and Build Environment, Universiti Kebangsaan Malaysia for hosting the place and capital to carry out this study. 6. References [1] K. Kukutschovaa, V. Roubiˇceka, K. Malachovab, Z. Pavliˇckovab, R. Holuˇsab, J. Kubaˇckovac, V. Miˇckac, D. MacCrimmond, P. Filip d Wear Mechanism in Automotive Brake Materials, Wear Debris and its Potential Environmental Impact, International Journal of Wear. [2] M.Z. Baharom, M.Z. Nuawi, G. Priyandoko, S.M. Harris, L.M. Siow Eddy current braking study for brake disc of aluminium, copper and zinc, Regional Engineering Postgraduate Conference. [3] M. Jou, J.K. Shiau, C.C. Sun Design of a Magnetic Braking System, Journal of Magnetism and Magnetic Materials, 4(2006) c234-c236. [4] M.I. Gonzalez Experiments With Eddy Currents: The Eddy Current Brake, European Journal of Physics, 25(2004) [5] K.Lee, K.Park Environmental Optimal Robust Control of a Contactless Brake System Using an Eddy Current, Journal of Mechatronics. [6] O. Uexkull, S. Skerfving, R. Doyle, M. Braungart Carbide Antimony in brake pads a carcinogenic component?, J. Cleaner Prod. 13(2005) [7] R.A. Peters Environmental Effects of Copper in Brake Pad Wear Debris, Brake Pad Partnership, Brake Colloquium & Exhibition. [8] M.T. Thomson. Permanent Magnet Electrodynamic Brakes Design Principles and Scaling Laws, Online Symposium for Electronics Engineers. [9] H. Straky, M. Kochem, J. Schmitt, R. Isermann Influences of Braking System Faults On Vehicle Dynamics, Control Engineering Practice. [10] B.Ebrahimia, M.B Khameseea, M.F Golnaraghib Design and Modelling of a Magnetic Shock Absorber on Eddy Current Damping Effect, Journal of Sound and Vibration, 315 (2008) [11] W.H Li, H. Du Design and Experimental Evaluation of a Magnetorheological Brake, Journal of Advanced ManufacturingTechnology, 21:8-515.