Coupling Heat Structure Analysis of the Clutch Pressure Plate in Vehicle Overloaded Start Procession

Transcription

1 Sensors & Transducers 2014 by IFSA Publishing, S. L. Coupling Heat Structure Analysis of the Clutch Pressure Plate in Vehicle Overloaded Start Procession Qi-Tang WANG, Mao-Tao ZHU, Xue-Lai LIU School of Automobile and Traffic Engineering Jiangsu University, Zhenjiang Jiangsu, , China Tel.: , , Received: 24 July 2014 /Accepted: 30 October 2014 /Published: 30 November 2014 Abstract: The will be cracking, erasing, and deformation as a result of reduced ability of clutch during the working process. The dynamic model of the vehicle when it started and the CFD model of pressure plate have been established. A new method which can be used to calculate the heat flux and the heat transfer coefficient has been proposed when after anglicizing the model. A simulation analysis of thermal stress coupling of the has been made in order to calculate temperature distribution and the stress level of the. A new improved solution has been proposed. The result shows that although the plate quality is almost same after the improvement, the temperature peak is reducing about 1 C, the maximum stress decreased 38.6 %, and the axial stiffness improved significantly. Copyright 2014 IFSA Publishing, S. L. Keywords: Pressure plate, Sparking power, Stress, Coupling heat structure, Structural improvements. 1. Introduction The entire vehicle driveline clutch is an important part, can play to ensure a smooth start car, and shift smoothly to prevent transmission overload effect [1]. Pressure plate is one of the main parts of the clutch, in the initial process, the due to slippery ground and produce a lot of heat, pressure plate caused a rapid rise in temperature in a short time, due to the relatively closed environment clutch and can not emit heat, in addition to the constraints and can not freely rotate pieces of deformation, it will produce a higher stress, making the appears ablation, cracking and the clutch appears failure problem in advance by the end, thereby affecting the entire transmission system reliability [2-6]. In order to study the danger point in stresses of the temperature by bonding process conditions, through the analysis of the car ramp at full load 15 % of the initial kinetic model in the transmission system conditions, simulation of clutch engagement mill to produce the slip change of power, rotate speed and slide grinding power; create platen CFD model to calculate the flow of the surrounding air by the during the rotation ; platen, and the bonding process in order to determine accurately the boundary conditions, the heat structure coupling analysis to calculate the in the bonding process, the temperature distribution, stress of the danger point. Finally, the results of the is used to the structural improvements, the strengthening of the heat, the purpose of reducing stress levels, provide the basis for the design and development of the. 2. Boundary Conditions of the Platen 2.1. Determination of the Heat Flux When the car starts, the heat generated on the is caused by the friction work 156

2 generated by the sliding friction in the clutch engagement, heat flux of the friction surface [7]: Φ() t qt () =, (1) S where Φ () t is the per unit time by the heat of the heat transfer area; S is the thermal area; qt () is the unit area per unit time heat flow through. By simplifying the calculation, in the process of clutch engagement when the car starts, the relationship between sliding friction power and heat flux density at a point on the friction plate produced as follows: 3r qt () = Nt (), (2) 2π ( r r ) where r, r are the inner and outer diameters of 1 2 platen; r is the radius of the study points; Nt () is the sliding friction power in a function of time. In the previous literature, the heat flux is speculated by theoretical formula and linearization; But from the formula we can see that the heat flux depends on the slippery ground power, but the slippery ground power is constantly changing through the process of clutch engagement, the value is related with the transmission torque of the transmission system and the rotational speed difference [8, 9]: Nt () = T()[ t ω () t ω ()] t, (3) c e c where T() t is the torque by transmission system; c ω () t is the engine speed; ω () t is the rotate speed of e c transmission system. According to the previous analysis, build the engine and transmission system dynamics model when the car loaded with 15 % in condition of ramp start. Simulate the car starting friction power by using MATLAB/Simulink. As shown in Fig. 1. Fig. 1. Sliding friction power. In the process of clutch engagement, assuming that the heat generated by the friction all absorbed by the and friction plate; and both the ratio of the absorption of heat, and heat flow distribution factor associated with the physical properties of materials, and satisfy the following relations [10]: where λ, 1 K 05. λc ρ = λ c ρ 2 2 2, (4) λ are the coefficients of thermal 2 conductivity of friction plate and ; c 1, c are the heat capacity of the friction plate and 2 ; ρ 1, ρ are the density of friction 2 plate and. Joint formula (2), (3), (4) expression of pressure plate surface heat flow density is: Kq() t 3rT ()[ t ω () t ω ()] t q() t = =, (5) ( ) ( ) c e c K + 1 K + 12π r r 2 1 where q () t is the through surface 1 heat flow per unit time The Determination of Convection Heat Transfer Coefficient Pressure plate in the process of joint, the cooling relies mainly on convective heat transfer with the surrounding air. Therefore, the determination of convection heat transfer coefficient is particularly important. And convective heat transfer coefficient is changing by the speed of the and the surrounding temperature, the past is only the outer diameter of the as the feature sizes in the literature, and unifies the convective heat transfer coefficient to load on the all surfaces. Pressure plate CFD model is established in this paper, through the establishment and calculated according to the situation of air flow speed press plate surface convective heat transfer coefficient of different position; so, speed and structure characteristics of the influence of the convective heat transfer coefficient were taken into account. Medium clutch engagement process speed and convection heat transfer coefficient is shown in Fig. 2 and shown in Table 1. Due to space limitations, the article lists the rad/s, 50, 100 rad/s, 150 rad/s, 200 rad/s under the four characteristics of the rotational speed of the convective heat transfer coefficient of various surfaces of the. 157

3 heat flux into the friction surface of through the programming; there is some convection heat transfer between the rest surface of pressure plate and air, applying the function written corresponding to time piecewise linear interpolation the convective heat transfer coefficient at each feature speeds to the platen surface. Fig. 2. Speed of. Table 1. Convective heat transfer coefficient of pressure plate [W/(m 2 ºC)]. Surface Inside diameter side of the Outer diameter side of the The end face of the pressure plate The top surface of the supporting platform Outer diameter side of the support table Inner diameter side support of the support table Desk side support Thermal-structure Coupling Analysis of Pressure Plate 3.1. The Finite Element Model of Pressure Plate Building three-dimensional models of clutch in CATIA, importing the model appropriately simplified into ANSYS, meshing. Selecting hexahedral Solid186 unit, using the sweeping method to divide. Finite element model of the completion of the division includes 212,590 nodes, 46,079 units. Finite element model of the is shown in Fig Boundary Conditions and Loads Assuming temperature is 25 degree centigrade before the clutch is engaged. Importing the calculated Fig. 3. Finite element model of. There are three rivet holes for loading the drive plate at lugs of, because the tangential and radial relative displacement is not so rigid displacement constraints is imposed. The pressure plate with the previous literature bosses at fixed clamping force is applied in different slip surface grinding, because the car started the process of contacting the and friction plate, there is no heat distortion and clamping force in the same direction of the axial. Therefore, the establishment of an adiabatic friction surface of the elastic support plane, the same plane with friction material sheet material. Fixed constraints imposed on the plane, and with the friction between the friction surfaces is constrained. The main surface contacts with the diaphragm spring clamping force. 4. The Results of Simulation Analysis The peak moment cloud of temperature and stress can be seen from Fig. 4 and Fig. 5 respectively. As can be seen in Fig. 4, the, the peak temperature reach 79.6 C in the bonding process and the high-temperature region focused on slippery ground surface. Since the speed of outer edge of the slippery grows faster, therefore the temperature of the region is highest. The highest temperature point at about 1.2 s, and sparking power peaked almost the same moment. Since the time of engaged in the axial direction is shorter, the heat conduction is not sufficient, so the axial temperature gradient is large. 158

4 Fig. 6. The gap between the platen and the support table changes to right-handed, which can accelerate the speed of air in a certain extent from the interior to the outer guide. The number of rivet holes of each support is increased at the two stations to reduce stress concentration. A blast tendon are added in the middle of Rivet holes and the supporting table, which enhances the axial strength and also shared the stress of rivet holes from the diaphragm spring clamping force in some extent. The quality of increased 2.5 %. Fig. 4. Temperature contours of. From Fig. 5, the stress concentration of the is serious. The maximum stress is in the inner edge of the rivet hole and reaches nearly 170 MPa. Meanwhile, the axial deformation is mm. Since the heated transmission is quick, therefore rapid expansion is in the radial and axial directions and the expansion of the is limited by the rivet holes. Warping in the axial direction, the pressing force of the diaphragm spring, the inertia of rotation of the has a greater centrifugal stresses the rivet hole. Through the temperature contours, the rivet hole is where the greatest change in temperature gradient, which is a main cause of the stress concentration. The stress of slippery surface of is under 40 MPa, which is at the lower stress levels and can not have a greater impact on the reliability of the. (a) The structure before improved (b) The structure after improved Fig. 6. Improved model. Fig. 5. Stress contours of. 5. Pressure Plate Structural Improvement The improvements of structure are made since some for temperature rise too quickly and stress concentration severe cases. The improved model is shown in The calculation of CFD analysis of improved about convective heat transfer coefficients at different speeds are shown in Table 2. Comparison of the two tables, the outer surface of the, the upper end and the side of the supporting units have significantly improved heat dissipation after the improvement. The peak moment of cloud of temperature and stress of improved can be seen from Fig. 7 and Fig. 8 respectively. From Fig. 7, as the heat dissipation improved, the peak temperature is about 78.7 C, reduced 1 C compared with previous. As can be seen from Fig. 8, the maximum value of the improved stress is only MPa, which decreased by about 38.6 % compared with the previous one. Stress concentration is also significantly improved and the axial deformation was only mm, which decreased by about 17.4 % compared with the previous. Axial stiffness significantly strengthened. 159

5 Table 2. Convective heat transfer coefficient of improved. Surface Inside diameter side of the Outer diameter side of the The end face of the The top surface of the supporting platform Outer diameter side of the support table Inner diameter side support of the support table Desk side support coefficient is putted up which considering the speed and structural features. The calculation of the thermal boundary conditions of the coupling structure is applied to the by the method of editing functions. 2) The finite element model of the is made for the thermal structure coupled analysis. During the analysis, an elastic plane as axial support platen is established in order to calculate accurate results. The results show that during the process of engaging the clutch, the maximum temperature of reaches 79.6 C and the temperature gradient is more obvious. Maximum stress reaches nearly 170 MPa. The stress concentrated severely and the region stress danger point of are in the rivet hole edge. 3) The structure improvement of is made for poor thermal environment and serious stress concentration situation. An increase of three rivet holes and six blast muscles and the support table side turned to right-handed are made to improve the situation. After the improvements, the thermal environment is improved and temperature peaks the peak nearly reduces 1 C and stress decreases 38.6 %. Axial stiffness has also been significantly improved. The design and development are provided. References Fig. 7. Temperature contours of. Fig. 8. Stress contours of. 6. Conclusions 1) Through the dynamics model establishment and analysis of automotive driveline starting process, a new formula of heat flux is proposed. By the CFD simulation of starting process, the calculation method of the convective heat transfer [1]. Zhang Fan, Bao Jiping, Finite element analysis and improvement on the thermal stress of the truck clutch, Forestry Machinery & Woodworking Equipment, Vol. 39, Issue 4, 2011, pp [2]. Chen Jinguo, Yin Xiaoliang, Gong Youping, et al, Coupling heat stress analysis of the friction disk in clutch, Mechanical & Electrical Engineering Magazine, Vol. 25, Issue 12, 2008, pp [3]. Huang Feng, Mo Yinmin, Lv Juncheng, Study on the wear mechanism of micro-automobile clutch friction materials, Lubrication Engineering, Vol. 35 Issue 3, 2010, pp [4]. Qi Jiande, Zhou Ranjie, Qu Yanyang, et al, Finite element analysis on the temperature field of the friction pair of mini-vehicle clutch, Mechanical Research and Application, Vol. 44, Issue 4, 2013, pp [5]. Chang-Yi, Pan Hong-Xia, Wu Fei-Long et al, Analysis of clutch temperature rise influence factors, Hebei Agricultural Machinery, Vol. 25, Issue 4, 2011, pp [6]. Yan-Yang, Huang Ji-Xiong, Mo Yi-Min, Research of temperature field in minibus clutch based on FEM, Mechanical Research and Application, Vol. 21, Issue 5, 2008, pp [7]. Yang Yongqiang, Zhou Minggui, Zhang Man, et al, Thermal deformation finite of clutch fiction plate, Machinery Design and Manufacture, Vol. 11, Issue 2, 2007, pp [8]. Hu Jianjun, Li Guanghui, Wu Guoqiang, et al, Accurate calculation of clutch torque transmission during vehicle starting, Automotive Engineering, Vol. 30, Issue 12, 2008, pp

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