Heat-fluid Coupling Simulation of Wet Friction Clutch

Transcription

1 3rd International Conerence on Mechatronics, Robotics and Automation (ICMRA 2015) Heat-luid Coupling Simulation o Wet Friction Clutch Tengjiao Lin 1,a *, Qing Wang 1, b, Quancheng Peng 1,c and Yan Xie 1,d 1 State Key Laboratory o Mechanical Transmission, Chongqing University, China a tjlin@cqu.edu.cn, b qwangcqu@163.com, c @qq.com, d @qq.com Keywords: Clutch, Heat-luid coupling, Temperature distribution, Finite element method Abstract. In order to estimate the heating value o wet multi-plate riction clutch at idle state, the heat-luid coupling simulation o oil way luid ield is carried out. Taking oil way o clutch as research object, dynamic mesh technique is adopted to implement the dynamic simulation about luid ield in disc separation process. Based on the actual state o oil way at the end o disc separation process o disengaging clutch, simulation model about heat-luid coupling o oil way is established through combining energy conservation law with shear heating theory o oil ilm. Then the paper simulates the temperature iled o lubricant, and researches the inluence principle o drive shat speed and lubricant low on lubricant temperature. Results shows: the maximum temperature and exit temperature o lubricant increase gradually as idling speed increases; and they will decrease gradually as inlet low increases. Introduction In marine clutch-reversible gearbox, pair-mounted wet multi-plate riction clutches are in engaging and disengaging condition respectively. While clutch is idling in disengaging condition, there is great speed dierence between riction disc and dual plate. Oil ilm among discs will then emerge luid kinetic energy under shear eect o oil ilm, and heat quantity changes with it. Clutch thereore generates heat, which will truly aect wet multi-plate riction clutch. Currently, research about heat generating problem o riction clutch ocuses on temperature iled calculation o riction disc, etc. Through heat conduct model o riction disc, numerical simulation about heat conduct process o riction disc is realized via FEM [1,2,3]. Along with gradual maturation o CFD technology, heat-luid coupling simulation o complicated luid ield is acceptable by combining computer numerical simulation with graphic display, which involves vortex pipe, rerigerator and so on [5]. However, study about heat-luid coupling o oil way luid ield or riction clutch is still rare. This paper sets up simulation model about heat-luid coupling o oil way on the basis o actual oil way situation obtained by dynamic simulation o disc separation process or clutch. Adopting RNG k-ε vortex model, the oil way luid ield and temperature ield are calculated. Inluence principle o drive shat speed and lubricant low on lubricant temperature is also researched, ater which heating value prediction o idling clutch is realized. Governing Equations o Heat-luid Coupling In the analysis o lubricant heat-luid coupling, RNG k-ε vortex model is employed, and governing equations comprised o mass conversation equation, momentum conversation equation and energy conversation equation are also involved. There the mass conversation equation and momentum conversation equation are used or solving the pressure and velocity o lubricant, and the temperature o lubricant can be obtained by combining the energy conversation equation The authors - Published by Atlantis Press 558

2 ρ ( ρu) ( ρv) ( ρw) = 0 t x y z ( ρu) p + div( ρ uu) = div( µ gradu) ρgx t x ( ρv) p + div( ρ vu) = div( µ gradv) ρgy (2) t y ( ρw) p + div( ρ wu) = div( µ gradw) ρgz t z where the Eq. 1 is mass conversation equation, and the Eq. 2 is momentum conversation equation, in which grad()= ()/ x+ ()/ y+ ()/ z; ρ is lubricant density; μ is dynamic viscosity; p is lubricant pressure. In the RNG k-ε turbulence model, the turbulent kinetic energy equation (Eq. 3) and the turbulent dissipation rate equation (Eq. 4) or incompressible luids can be described as: 3 3 k ( uk i ) 1 µ t k 1 + = µ + + Gk ε t i= 1 xi i= 1 ρ xi σk xi ρ (3) 3 3 ε ( uiε ) 1 µ t ε 1 C ε ε + = µ + + G C t i= 1 xi i= 1 ρ xi σε xi ρ k k * 2 1ε k 2ε (4) where k is turbulent kinetic energy; ε is turbulent dissipation rate; μ t is turbulent viscosity; G k is the * item o turbulent kinetic energy caused by gradient o average velocity; C1ε is the correction coeicient o constant C 1ε o RNG k-ε turbulence model. Conversation law o luid energy can be presented as: the energy increasing rate o micro-element in luid channel equals to the sum o net heat lux entering micro-element and work done on micro-element by volume orce and area orce. Thus energy conservation law o micro-element about clutch lubricant is Eq. 5. ( ρct p ) ( ρvct x p ) ( ρvct y p ) ( ρvct z p ) T T T = ( k ) + ( k ) + ( k ) + Qv (5) t x y z x x y y z z where c is speciic heat o lubricant, T is lubricant temperature and Q is viscous dissipation. p Combining Eq. (1), Eq. (2), Eq. (3), Eq. (4) and Eq. (5), heat-luid coupling o clutch lubricant can be analyzed. v (1) Fluid Dynamic Simulation o Clutch The Structure o Clutch. Fig. 1 is the structure o wet multi-disc riction clutch. When the clutch is idling in disengaging operation, the clearances between discs are illed with oil ejected rom our nozzle groups, and riction discs will separate automatically by inluence o lubricant which then lows out through ive oil exit. Initially, we assume that all discs are evenly distributed, and all clearances between discs are the same. Fluid Dynamic Simulation. The lubricant CD40 is used in clutch, and the density and kinematic viscosity are 880kg/m 3 and m 2 /s at 58 C. The solid and inite element models o oil structure are established in ANSYS. Fig. 2 shows the inite element models o oil structure and boundary conditions, the inlet low is 110L/min and the outlet pressure is an atmospheric pressure. The wall o shell is stationary, the luid near wall is processed with wall unction, and steel discs and gears are rotating clockwise by 1213r/min. Stationary solutions o turbulence model o the separation process are obtained by the 559

3 semi-implicit algorithm with coupled equations o pressure and velocity. The dynamic simulation o the separation process is conducted by using dynamic mesh method. Fig.1. The structure o clutch Fig.2. Finite element model o oil structure Heat-luid Coupling Analysis o Clutch Convective Heat Transer Coeicient. Lubricant low can be divided into three categories: laminar low, transitional laminar low and vortex low. In these dierent low categories, convective heat transer coeicient is related to Prandtl number and Reynolds number. Reynolds number and Prandtl number can be solved by Eq. 6: v ρν Re = d, C ν Pr = (6) λ Eq. 7 shows Nusselt number criterion equation(sieder-tate) and convective heat transer coeicient equation /3 µ = µ w Nu Re Pr, h = Nu λ (7) d where µ and µ w are luid dynamic viscosity determined by luid average temperature and wall temperature respectively. Heat-luid Coupling Analysis. Oil way obtained by dynamic simulation o disc separation process is used to build lubricant heat-luid coupling model or idling clutch. In CFX, total thermal model which takes thermal quantity changes caused by luid kinetic energy into consideration is employed. This subsection analyzes the lubricant temperature distribution o oil way while idling speed o drive shat is 1213r/min and housing speed is 0r/min. Boundary conditions o lubricant way include: (1) ixing wall temperature is 50 C, convective heat transer coeicient is W (m 2 K) -1 ; (2) an atmospheric pressure or exit; (3) inlet oil temperature is 58 C, and inlet volumetric low is 110L/min; (4) housing wall is static, and walls at clutch gear and dual plate rotate clockwise at a speed o 1213r/min. Fig. 3 is Lubricant pressure contour. Lubricant pressure loses greatly at the corners o oil way and the nozzles, and maximum oil pressure occurs at inlet hole. Fig. 4 is Lubricant velocity contour. Lubricant velocity changes greatly at shape mutation places such as oil-separating holes and nozzles, and ater lubricant lows into oil-separating holes, low rate increases as channel diameter decreases. Fig. 3. Lubricant pressure contour Fig. 4. Lubricant velocity contour Temperature contour o oil way obtained by heat-luid coupling simulation is shown in Fig

4 while clutch idling speed is 1213r/min. From the igure, linear velocity dierence increases as diameter gets bigger, and then shear heating o oil ilm gets more serious. In a word, oil temperature increases as diameter gets bigger, and it will decrease to some extent as there exists oil outlet and convective heat transer o clutch housing at the outer diameter. Fig. 5. Lubricant temperature contour Inluence o Applying Working Condition on Lubricant Temperature Inluence o Drive Shat Speed on Lubricant Temperature. This subsection mainly analyzes temperature distribution o oil way at dierent rotation rate while clutch inlet low is 110L/min. Table 1 shows convective heat transer coeicient with dierent rotational speed. Table 1. Convective heat transer coeicient with dierent rotational speed Rotational speed n e /r min Convective heat transer coeicient h/w (m 2 K) Temperature contour o clutch lubricant at dierent drive shat speed is given in Fig. 6. From the igure, the maximum clutch oil temperature increases gradually as rotation rate gets bigger. The maximum temperature and the outlet temperature o lubricant between discs are given in Table 2. From the table, as a comprehensive eect o ilm shear heating and heat taken away by lubricant, clutch outlet temperature increases gradually as speed gets bigger. (a) 834r/min (b) 1000r/min (c) 1400r/min (d) 1600r/min Fig.6. Lubricant temperature contour o the clutch with dierent rotational speed Table 2. The temperature with dierent rotational speed Rotational speed n e /r min Maximum temperature T max / C Outlet temperature T out / C Inluence o Inlet Flow on Lubricant Temperature. This section analyzes temperature 561

5 distribution o oil way at dierent inlet low while clutch idling speed is 1213r/min. Fig. 7 shows temperature contour o clutch lubricant at dierent inlet low. From the igure, the maximum clutch oil temperature decreases gradually as inlet low gets bigger. Table 3 shows the maximum temperature and the outlet temperature o lubricant between discs. From the table, clutch outlet oil temperature decreases gradually as inlet low gets bigger as a comprehensive eect o ilm shear heating and heat taken away by lubricant. (a) 70L/min (b) 90L/min (c) 130L/min (d) 150L/min Fig.7. Lubricant temperature contour o the clutch with dierent inlet low Table 3. Lubricant temperature with dierent inlet low Inlet low rate Q/L min Maximum temperature T max / C Outlet temperature T out / C Conclusions 1) Lubricant temperature is basically unchangeable beore lubricant lows between riction disc, and the maximum temperature is C which occurs at oil ilm between discs. Dierent oil ilm has dierent temperature as each oil ilm has dierent thickness, which means clutch idling heating mainly comes rom lubricant shear between riction discs. 2) Through heat-luid coupling analysis o oil way at dierent idling speed and dierent inlet low, results show: the maximum lubricant temperature and the outlet temperature increase gradually as idling speed gets bigger; and they will decrease gradually as inlet low gets bigger. Acknowledgement The authors are grateul or the inancial support provided by the Fundamental Research Funds or the State Key Laboratory o Mechanical Transmission under Contract No. SKLMT-ZZKT-2012 MS 06. Reerences [1] Yue Hong, Jin Liu, Yungeng Wang. Chinese Jouranl o Mechanical Engineering. 17 (2004) (In Chinese) [2] Jen T C, Nemecek D J. International Journal o Heat and Mass Transer. 51 (2008) [3] Shuangmei Zhao, Hilmas G E, Dharani L R. Wear. 264 (2008) [4] Smith E, Pongjet P. International Communications in Heat and Mass Transer. 35(2008) [5] Xiaobin Zhang, Zhihua Gan, Limin Qiu. Journal o Zhejiang University SCIENCE A. 9 (2008) (In Chinese) 562