Proceedings of the IEEE International Conference on Automation and Logistics Shenyang, China August 2009
Design, Control and Test of a Magnetorheological Fluid Fan Clutch
ongsheng1,2 and Wang Juan1 Cui Liang2, Wang Jiong 2 and Jiang Xuezheng2
2 College of Mechanic Engineering NanjingUniversity of Science and Technology Nanjing, Nostate 210094, China problems produced by the existing fan-driven types, many researchers have paid much attention into developing a new fan-driven system, which should automatically adjust fan’s rotary speed, simultaneously satisfy the energy saving, environmental protection and working conditions requirements. Its appearance of magnetorheological (MR) [1-7] material provides a new way to solve these problems . MR fan clutch with advantages of output speed adjustable, quick response and low power consumption, which using MR fluids as the transmission medium, provides a new way to resolve the problem. Besides, there are many other advantages of MR fan clutch in engineering applications: reasonablely cooling, reducing fuel consumption, reducing noise, etc. At present, many scholars at home and abroad pay much attention into MR fan clutch’s [8-12] design and theoretical analysis . Based on the national natural science foundation support, this research is developed and aims at a new clutch which is using MR fluids as the transmission medium, and its design, control and test of a MR fluid fan clutch are respectively investigated in detail. II. TORQUE TRANSFER MODEL OF MR CLUTCH There are three types of structures for MR clutch, including disc type, cylinder type and cylindrical type. The cylinder type is actually a combination of cylindrical type and disc type. Disc clutch’s working principle is the same as cylindrical clutch, which both rely on MR fluid as a transmission medium to transmit torque. When the rotational speed of input shaft is ω 1 , MR material reflects on a fluid state and its transmission torque is only a very small viscous torque in the absence of magnetic field. At the external magnetic field, magnetic particles in MR fluid have been magnetized into the distribution of chains along the direction of magnetic line, which results in that MR fluid’s shear stress is rapidly increased. And it shows the characteristics of plastomers. As a result, part of torque for MR clutch can be produced by magnetorheological effect and its magnitude can also be controlled by adjusting its strength of the applied magnetic. Compared viscous torque, torque the yield shearing stress produces, named as the yield shearing torque, and is much more than it. Therefore, the yield shearing torque is selected as the main moment and used to transmit torque. When the shear stress is large enough, output shaft and input shaft can finish a synchronous rotation and achieve a  transmission ratio of 1 . Its calculation model of torque and the magnetic circuit model for MR disc type clutch are shown as Fig.1 and Fig.2: 1 Department of Mechanic and Electronic Engineering University of Jiaxing Jiaxing, Nostate 314001, China email@example.com
Abstract - The research is developed and aims at a new clutch using MRF as the transmission medium. Based on the theory of hydrodynamics and the rheology govern equations of magnetorheological fluids, torque transfer model of magnetorheological clutch is derived. The relationships between some designed parameters and outputted torque are analyzed. According to the magnetic circuit design theory, two designed methods of magnetic circuit for magnetorheological clutch are provided. Using Ansys software, its correctness of the theoretical calculation result is verified. Different spec magnetorheological clutches are designed and processed as test specimens. Besides, three control strategies, including double-control, PD control, fuzzy control, are respectively simulated in Matlab environment in order to analyze and evaluate their effect of temperature control. In order to improve the real-time, reliability and stability, an embedded system based on 89S51 microcontroller is designed and developed. A test and performance analysis platform for magnetorheological clutch is developed. And a series of experiments for magnetorheological clutch have been done, including its static characteristics, output characteristics and speed regulation characteristics. The experimental results proved its controllability of output speed for the designed magnetorheological clutch. Index Terms – Fan, Magnetorheological clutch, Torque, Magnetic circuit, Performance test
I. INTRODUCTION When engine is operating, the gas temperature in combustion chamber usually reaches into the range of 1730～ 2400 , which would easily result in some key heated parts temperature rising and mechanical strength reducing. And even parts fracture accidents may be induced by high temperature. Its function of the engine cooling system is to keep its temperature of engine into an appropriate range under all conditions. As a significant part of the engine cooling system, fan plays a very important role to ensure the appropriate cooling and stability temperature of the engine. To armored vehicle, the engine’s thermal condition should be timely change according the working condition and operating environment variation. Therefore, fan should automatically adjust its rotary speed according to different working conditions. At present, there are two shortcomings with existing fan-driven types: on the one hand, the traditional fandriver (shaft-driven) can not export consecutive rotary speed, and will cause unnecessary engine power loss, excessive cooling and other problems; the other, driver which can achieve consecutive rotary speed (hydraulic or motor-driven) will make the system complex. In order to solve these
978-1-4244-4795-4/09/$25.00 ? 2009 IEEE
In equation (7) and (8),
Ttim is produced by the limit
yield stress, Tvis is produced by the speed difference. According to equation (6), their effects of some important parameters in torque transfer model of MR clutch can be analyzed, including internal diameter of disc R1 , external diameter of disc R2 , its limit shear yield stress of MR
Fig. 1 Torque calculation model
fluid τ B , working clearance h and rotate speed Δω . These analyzed results are showed as Fig.3 and Fig.4.
Fig. 3 Relationship between the output torque and yield stress
Fig. 2 Magnetic circuit model
Take a micro-unit at distance R location in a circle:
dS = 2π r ? dr
Its transmission moment of this micro-unit is:
dT = F ? r = (τ ? dS ) ? r = τ ? 2π r 2 ? dr
The total transmission torque is:
T = ∫ dT = ∫ τ ? 2π r 2 ? dR
Fig. 4 Relationship between yield stress and working clearance
According to MR disc clutch, Bingham fluid model is expressed as:
τ y = τ B + γ = τ B +η
In equation (4), η is its viscosity of MR fluid. When its ring of MR disc clutch is expanded into a straight line, it becomes a parallel plate flow patterns. According to its rotate speed of the import plate, its shear rate of MR fluid at any point of disc clutch shows:
?u r ? Δω = ?y h
Substitute equation (4) and (5) into (3), the torque transfer model of MR clutch could be achieved:
πη ? Δω
2 4 3 ( R2 ? R14 ) + π ( R2 ? R13 )τ B 3
In equation (6), its transmission torque of MR disc clutch can be further divided into two parts:
2 3 Ttim = π ( R2 ? R13 )τ B 3 πη ? Δω 4 Tvis = ( R2 ? R14 ) 2h
As shown in Fig.3, when other parameters are unchanged, torque MR clutch can drive is proportional to its limits yield stress of MR fluid. And its limits yield stress of MR fluid is one of the key factors to its magnitude of transmission torque. Therefore, it will be an effective way to select a proper material, whose limit of yield stress is large in order to improve the output torque, From Fig.4, with the increase of working clearance, the output torque will be reduced. But its range of decrease is small. For example, the torque is only decreased 3Nm from 0.5mm to 2.0mm, which accounts for 11% of the largest output. Its variation of working clearance have little affect on the total output. However, its design of magnetic circuit has a great relationship with working clearance’s magnitude, liquid volume and its fluidity. Working clearance should be comprehensively considered. With the improvement of rotate speed difference, there is little increase for output torque. When the angular velocity increases from 0 to 300, the torque increases about 3Nm, but its proportion accounts for only about 7% the maximum torque. Therefore, in actual engineering field, torque slip contributes on is little in total output torque, and even could be negligible. That is to say, MR clutch can show its performance of constant-moment device. Further, its output torque is approximately to its static torque at a low rotary speed.
Based on many numerical simulation results and some parameters of an automobile clutch, some conclusions can be concluded: 1) MR fluid is one of the key factors effecting on the output torque, but its role of working clearance is not obvious. 2) Transmission torque of MR clutch slightly improves with the increase of rotate speed difference, but which accounts for only the maximum 7% of total torque. Therefore, doing transmission torque calculation, its effect can be completely ignored. 3) External diameter has great affect on transmission torque, but its affect of internal diameter is little. So, doing transmission torque calculation, its effect of internal diameter can be completely ignored. 4) In order to ensure the design meeting the engineering application requirements, some correction factors should added when secondary factors are ignored. Considering the main factors and ignoring the secondary factors, a simplified design formula can be expressed as:
T = f (τ B , R1 , R2 ) 2 3 Ttim = π ( R2 ? R13 )τ B ≈ T 3
According to equation (10) and (11), it is provided that
Ttim should meet the design requirements of torque.
If the requirements were not strict, the internal diameter R1 can be even ignored. The reason is that the torque provided by internal diameter only accounts for less than 10% of the overall output torque. Further, a simplify formula is expressed as: 3 (11) Ttim = 90% ? 2 π R2τ B
In this section, based on the Bingham model of MR fluid and N-S equation of incompressible viscous fluid, torque transfer model of MR clutch is established. Combining its actual requirements of a model of armored vehicle, according to the numerical calculation results, and the magnetic circuit design theory, different spec MR fan clutches are designed and developed (Fig.5). Compared to FL10 magnetic particle clutch, its static torque of the developed MR fan clutches reaches 13Nm under 2A input current, its torque improves 3Nm and its outside diameter is decreased 12mm.
The output torque of MR clutch is directly depended on its yield shear stress of MR fluid. Yield shear stress can be controlled by magnetic induction intensity, and control current is provided by the excitation coils. However, in the actual engineering application, there are many factors affecting the magnetic circuit, which can result in it difficult to accurately describe the magnetic field distribution. Therefore, it is necessary to make some reasonable assumptions and simplify work based on the specific requirements. Considering the develop MR clutch as an axis symmetric structure, some assumptions are showed as follows [3, 12] in magnetic circuit optimization design : 1) Its shell of MR clutch has no magnetic leakage; 2) Friction plate, shell materials and the MR fluid are uniform distribution; 3) The combination surface’s magneto resistance can be ignored; 4) Every place has the same magnetic flux. Based on the above assumptions and combined the basic theory of magnetic circuit design, the magnetic circuit problem is calculated from two different viewpoints, including the average magnetic circuit method and the magnetic circuit law Ohm's law. The magnetic circuit model of MR clutch model is shown as Fig.3. From this model, there is only one loop in the circuit. Because the material which constitutes the magnetic circuit is not an only one, the nonuniform, no branch magnetic circuit method can be used to analyze its magnetic field of MR clutch. As the circuit is no branch, it could be concluded that the magnetic flux through the sectional area of Magnetic circuit is the same based on the principle of continuity of magnetic flux. However, the area and materials of magnetic in each segment are varied, and the magnetic field strength at each location is not the same. In accordance with ampere's law and the relationship between each segment’s magnetic flux and magnetic pressure, the circuit equation is showed as follows:
?∑ H ili = Fm = NI ? ? Bi = f ( H i ) ?Φ = B A i i ?
In H3 ~ H5 magnetic circuit, the areas, which magnetic flux passing through along the direction of magnetic lines, is not the same. Its magnetic circuit equations of MR clutch can be concluded:
dl ? ? Rmi = ∫ l μ S i ? ?Φ R = U = Ni ? ∑ mi ∑ mi
Fig. 5 The developed MR clutch
III. MAGNETIC CIRCUIT OPTIMIZATION OF MR CLUTCH
Known from (12) and (13), some parameters of magnetic circuit design and structure are mutual coupling. Therefore, their selection of certain parameters could has a directly relationship with its magnitude of magnetic motive force, and they will it also be closely related to the coil placement space and affect the installation size. Its aim of the magnetic circuit design is to ensure its working strength of the magnetic field in MR clutch. At the same time, coil turn or electric current should be reduced as
much as possible in order to decrease the magnetic motive force. However, by the magnetic circuit model it can be seen that the decrease of magnetic potential energy means that the magnetic induction intensity wound be lowed, which was bound to increase the size of shell and make clutch size larger. In order to achieve the best design, the optimum design method should be used to solve their mutual coupling problem between the structure parameters and magnetic circuit design. The most reasonable results in all possible options should be searched by the optimized algorithm. In optimized model, the design requirements can be identified as the objective function and the mutual coupling relationships as the constraint conditions. The design problems, which meet equation (11) and (13), can be attributed to minimize multivariable nonlinear binding function. Algorithm standard is:
min f ( x )
Fig. 5 Magnetic induction nephogram
? A* x ≤ b ? s.t. ? Aeq * x = beq ?lb ≤ x ≤ ub ?
IV. CONTROL STRATEGY SIMULATION AND CONTROLLER DESIGN Based on MR fluid clutch, a simulation model of water cooling circulatory system for engine is established in Simulink simulation environment. Three control strategies, including double-control, PD control, fuzzy control, are commonly used in temperature control and are simulated. Fig.6 shows an actual engine’s temperature variation. Fig.7 shows its control effect using fuzzy control method. Further, their controlling effects are analyzed and evaluated. According to the simulation results, three control policies all play a positive role to adjust its equilibrium position of system temperature. Its steady state of temperature can be effectively decreased or uplifted adjusting the output gain values. PD control policy and fuzzy control policy can both maintain engine temperature into a set 80℃, but doublecontrol policy cannot achieve a steady value and its controlling effect is poor compared the other policies. In order to satisfy engineering application requirements, a suit of real-time measuring and controlling system including hardware and software for MR fan clutch is developed, which establishes further the basis of integrated design and engineering implementation for engine cooling system in armored vehicle. The developed system’s hardware includes: ATS89S51 microprocessing chip module, temperature measuring and conditioning module, signal outputting interface module, etc. Besides, a good man-machined interface including LCD and keyboard inputting is also designed. The system has four functions, including data acquisition, signal analysis, data storage, data display. Its software includes: system main program, controlling subprogram, interruption subprogram, data collecting and analyzing subprogram, alarm subprogram, LCD subprogram, etc.
In its circuit design of MR clutch, the magnetic potential energy coil drives can be selected as the objective function: (15) L = f min ( R4 , R5 , H , h, L) = ∑ Hl The constraint conditions can be divided into three parts, including magnetic field constraint, structural constraint and installation constraint. Magnetic field constraint refers to the magnetic induction intensity in the vicinity of the work setting. Structural constraint refers to sufficient placement space to coil. Installation constraint refers to its thickness of MR clutch not larger. In the Matlab environment, the objective optimization function is compiled and the optimized results are obtained. According to Ampere's law, the magnetic motive force could be obtained, and according to its design size of clutch, coil turns and the maximum current could be distributed, wire could also be selected. Because the magnetic circuit of MR clutch is belongs to the repeated short-term work type, the current density is selected J = 8 A / mm 2 . Based on the current security indicators, the maximum current which is allowed to pass through the wire is selected as I max = 2.8 A . In order to further prove its correctness of the theoretical calculation and analysis results, according to finite element analysis software Ansys steps, the optimized entities model of MR clutch is established, and then the numerical simulation of electromagnetic is also carried out. When the largest current 2.8A is applied into coil, magnetic induction nephogram is shown as Fig.5. As shown in Fig.5, it is essentially uniformly distributed in the MR fluid work interval.
?C1 (0 ≤ i ≤ 10%imax ) ? ? T (i ) = ?C2i (10%imax ≤ i ≤ 90%imax ) ? ?C3 (90%imax ≤ i ≤ imax ) ?
Fig. 6 Temperature variation curve
B. Slip properties The relationship between rotate speed difference and torque transmission in fixed current is also researched by test. When the fixed current is 0A, 0.5A and 1A, in different rotate speed difference, clutch transmission torque is shown in Fig.9. According to the theoretical analysis results, its increase magnitude of torque is very small when the rotate speed difference increases. Rotate speed difference has little effect on torque, and even could be neglected. In this experiment, test results show its correctness of theoretical analysis, which is torque almost have no change with speed difference significantly increase. C. Regulation properties When input speed is constant, load torque of load port keeps a constant value. The relationship between output rotate speed and input current is shown as Fig.10. When the current is less than a certain value I c , transmission torque of MR clutch is not sufficient to overcome the load, so there is no output speed for MR clutch. When the current is more than I c , the largest dynamic torque MR clutch produces can overcome the load, and make it working in the slip state. When the current is greater than I b , the static torque of clutch can overcome the load, and the driving member has the same speed with the driven member. D. Load properties Load Characteristic refers to its variation of output rotational speed with the increase of load when input speed of MR clutch and electric current remain a certain value. MR clutch load characteristic curve is shown as Fig.11. When the input speed is a fixed value and the input current is a constant value, if load is less than the maximum static torque Tc clutch provided under the input current, the driving member have the same speed with the driven member. When the load is greater than Tc but less than the maximum dynamic torque Tb MR clutch produces under the current, MR clutch works in the slip state. As its rotate speed is gradually declining, when the load is greater than the maximum dynamic torque Tb , load-side of MR clutch stops turning and keeps in a state of brake.
Fig. 7 Temperature control effect using fuzzy control strategy
V. TEST OF MR CLUTCH In order to deeply and systematically investigate its performance of the developed MR fan clutch, based on DSPACE and JN338 sensor, a performance test and analysis platform for MR fan clutch is also developed. Static characteristics, output characteristics, speed regulation characteristics and load characteristicof MR fan clutch are respectively tested and showed (Fig.8, Fig.9, Fig.10, Fig.11). A. Static mechanical properties When the rotate speed difference is small, it can be approximately seen as the static output to MR clutch. When the output terminal is fixed, and 50r/min rotary speed is transmitted to the input shaft, its torque under different input current is showed as Fig.8. By analyzing their mechanical static characteristic of the developed different specifications MR clutch, some conclusions can be achieved as follows: 1) Based on the developed four groups of friction plate MR clutch, it can be obviously indicated from the transmission moment test data that torque has a directly relationship with its outside diameter of MR clutch. It will increase follow to its increase of outside diameter of MR clutch, which is consistent with the theoretical analysis result. 2) By testing the static transmission torque of MR clutch under different current, it is indicated that torque will be improved with the electric current increase However, its increase of torque can be divided into three regions, which are named as non-controlled areas, linear zones, and saturated zone. In non-controlled areas, its increase of input electric current has no effect on the torque increase. The torque has a linear relationship with input current in linear zones. In the saturated zone, torque keeps basically stationary, and it no longer significantly increased with the electric current increase. The above law could express:
evaluated. Using the developed engine cooling testing device, temperature control experiments has also been done and the experimental results proved its feasibility of the MR clutch applied into engine cooling system. With the help of CAE technology, considering engineering application requirement, the next research will concentrate on its miniaturization and intelligentize of MR clutch. At the same time, the optimized temperature control strategy will also be studied. ACKNOWLEDGMENT
Fig. 8 Static characteristic curve
The research work is supported by the national natural science foundation of China (50675106), the Department of Science & Technology of Zhejiang Province Government foundation (2008C21111), the office of Science & Technology of Jiaxing City Government foundation (2007AY1010) and China Postdoctoral Science Foundation (20080431099). The first author wishes to thank Cui.Liang /NUST for a good previously research work basis, especially contribution to theory model derivation and test platform design. REFERENCES
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Fig. 9 Slip test curve
Fig. 10 Regulation characteristics of experimental curve
Fig. 11 Load characteristics of the experimental curve
VI. CONCLUSIONS Combining theoretical analyzing and performance testing, some key problems of MR clutch applied into engine cooling system are discussed in this paper, which provides the technology foundation for a new intelligent fan-driven type. And some qualitative formulates are followed according to the testing results. The theoretical and experimental results proved its controllability of the MR fan clutch output speed, and its mechanical properties of MR fan clutch are also