International Journal of Advance Engineering and Research Development

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Wendy Short
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1 Scientific Journa of Impact Factor (SJIF): 4.4 Internationa Journa of Advance Engineering and Research Deveopment Voume 3, Issue 3, March -206 e-issn (O): p-issn (P): Study and comparison of torque transmitting characteristics of Asbestos disc cutch and 6 pad ceramic cutch in Ashok Leyand 370 engine Sindavaam Sharath, Dr. Manish Kumar 2 The Institution of Engineers (India), Kokata, India 2 Dept. of Production and Industria Engg., MBM Engineering Coege, Jodhpur, India Abstract Study has been carried out on the torque transmitting characteristics of cutch pates, one having Asbestos as friction materia and the other as ceramic pads, when fitted on Ashok Leyand 360 engine.. Resuts thus obtained are compared to ascertain the reiabe one. Index Terms Asbestos disc cutch, ceramic cutch pate, coefficient of friction, torque transmitted. I. INRODUCTION Conventiona cutch pates are made of Asbestos either mouded around brass, copper or zinc wires or woven and impregnated with rubber or asphat. Use of asbestos in cutch inings is being prohibited by many countries as asbestos dust if inhaed may ead to cancer. Thus ceramic and sintered metas (bronze base and iron base) have repaced asbestos inings. These materias possess higher wear resistance, higher coefficient of friction and can be used at higher temperatures []. Numerica anaysis is carried out to determine the torque transmitting abiities of the cutch pates using uniform pressure theory and uniform wear theory. Statement of the case study is- Can we repace asbestos disc cutch with ceramic cutch pate of simiar dimensions for better reiabiity? II. STRUCTURE Study of the case is carried out on the basis of three different cases. They are: Case I: The torque transmitted by conventiona asbestos disc cutch is determined for uniform pressure and uniform wear conditions. Torque transmitted by the cutch for both the conditions if the asbestos ining is repaced with ceramic materia is cacuated. The resuts thus obtained are anayzed to judge which of the two materias is superior to transmit torque Case II: The torque transmitted by 6- pad ceramic cutch pate is cacuated for uniform pressure and uniform wear conditions. Factor of safety is determined and compared with that of conventiona asbestos cutch disc. Case III: As the cutch inings wear out, the axia oad exerted by compressed springs reduces as the initia compression of springs is reieved by the amount of wear out. The torque transmission characteristics of both asbestos cutch disc and 6- pad ceramic cutch pate are cacuated for the condition when inings have worm out to the permissibe imits as stated by OEM. Resuts are compared with the maximum torque deveoped by engine to state whether there does exist any cutch sip. III. INPUT DATA Ashok Leyand 370 Engine: The eading particuars of Ashok Leyand 370 Engine are as foows [2]: Bore mm Stroke mm Number of cyinders 06 Maximum output KW at 2400 RPM Maximum torque N-m at 600 RPM Asbestos Disc Cutch: The specifications of asbestos disc cutch are as foows [2]: Outer diameter 356 mm Frictiona area (Both sides) 238 cm A rights Reserved

2 Thickness of singe ining Permissibe wear out of ining 6.35 mm 3.8 mm 6- Pad Ceramic Cutch Pate: The specifications of 6- pad ceramic cutch pate are as foows [3]: Outer diameter 356 mm Frictiona area of each pad 4.54 cm 2 Number of pads on either side 06 Thickness of friction pad 6.35 mm Pressure Pate: The specifications of pressure pate are as foows [2]: Number of springs Tota spring force Free ength of spring Stiffness of spring 2 (3 groups of 4 springs) N.88 cm N/cm IV. NUMERICAL ANALYSIS The materia used for friction pads in both the cutch pates are known. Thus the range of vaues of coefficient of friction [] of asbestos ining and ceramic pads are as given beow: Type of materia Coefficient of friction, μ Asbestos ining Ceramic composites In the further study, it is presumed that the coefficient of friction of asbestos ining is 0.25 and for ceramic pads is CASE I: TORQUE TRANSMITTED BY ASBESTOS DISC CLUTCH Given, Frictiona area, A = 69 cm 2 (Singe side of cutch) [2] Axia force, W = N [2] Uniform Pressure Theory: Frictiona torque, T = nμwr () Where, n = Number of contact sides = 2 μ = Coefficient of friction (0.25) [] R = Mean radius of friction surface which is given by [4] R = 2 3 [r 3 r 2 3 r 2 r 2 2 ] Where, r and r 2 are externa and interna radii of friction faces. Outer radius, r = 7.8 cm Area of friction surface, A = π(r 2 r 2 2 ) 69 = π (7.8 2 r 2 2 ) r 2 = 0.94 cm Thus, R= 4.64 cm or m Frictiona torque, T = 2 x 0.25 x x = N-m Factor of safety, F s is given by F s = Frictiona torque Maximum torque produced by engine A rights Reserved 396

F s = 606.787 368.86 =.645 Uniform Wear Theory: Frictiona torque, T = nμwr Where, R = Mean radius of friction surface which is given by [4] Thus, R = 4.37 cm or 0.437 m Frictiona torque, T = 2 x 0.

3 F s = =.645 Uniform Wear Theory: Frictiona torque, T = nμwr Where, R = Mean radius of friction surface which is given by [4] Thus, R = 4.37 cm or m Frictiona torque, T = 2 x 0.25 x x = N-m Factor of safety for this case woud be, R = [ r + r 2 2 ] F s = =.65 TORQUE TRANSMITTED BY CLUTCH DISC WHEN ASBESTOS LININGS ARE REPLACED WITH CERAMIC MATERIAL For ceramic materia, it is presumed that the vaue of coefficient of friction μ is Uniform Pressure Theory: Frictiona torque, T = nμwr Factor of safety is, Uniform Wear Theory: Frictiona torque, T = nμwr Factor of safety is, = = N m F s = = = = N m F s = = CASE II: TORQUE TRANSMITTED BY 6- PAD CERAMIC CLUTCH PLATE Dimensions of ceramic friction pad Given [3], Outer radius of cutch = 7.8 cm Width of the pad = 6.7 cm Distance from centre of the cutch to the inner side of friction pad =. cm Frictiona area of each pad, A s (cacuated) = 4.54 cm A rights Reserved 397

4 The pad of given area can be approximated to a shape of trapezium having the dimensions of parae sides as 7.7 cm and 4.7 cm and height of 6.7 cm. Uniform Pressure Theory: Let the ength of arger parae side be a and ength of smaer parae side be b. Let height of the pad be. Length of the parae side at a distance x from the smaer parae side is given by (a b) b + x Area of the eementary section of thickness dx at a distance of x from the smaer parae side is given by [b + (a b) x] dx Norma or axia force on the eementary area of singe pad [4], δw = Pressure x Area = p [b + (a b) x ] dx Let (a b) be k. Frictiona force on the eementary area acting tangentiay at a distance (x + )m, F r = μ Δw (3) Frictiona torque acting on the eementary area, T r = F r (x + ) Tota frictiona torque acting on the friction surface of singe pad, T s = = μp (bx + b + kx 2 + kx)dx = μp[0.0485x x + 0.5x 3 ] μp(b + kx)(x + )dx = μp = μ W A s Axia force, W = N [2] Area of 6 pads, A = 6 x m 2 = m 2 Tota frictiona torque acting on the cutch pate, T = nμ W A rights Reserved 398

5 Where, n = Number of contact sides = 2 For µ = 0.6 [], Tota frictiona torque acting on the cutch, T = N-m Factor of safety woud be, F s = = 2.09 Uniform Wear Theory: Whie designing machine parts which are subjected to wear due to siding friction, it is assumed that the norma wear is proportiona to the work of friction. The work of friction is proportiona to the product of norma pressure (p) and the siding veocity (V = 2πrN) [4]. Therefore, Norma wear Work of friction pv or pv = K(a constant) or p = K V When the friction surface is new, there is a uniform pressure distribution over the entire contact surface. This pressure wi wear most rapidy where the siding veocity is maximum and this wi reduce the pressure between the friction surfaces. This wearing- in process continues unti the product pv is constant over the entire surface. After this, the wear wi be uniform. Let p be the norma intensity of pressure at a distance (x + ) m from the axis of the cutch. Since the intensity of pressure varies inversey with the distance, therefore p(x + ) = C (A constant) or p = C/(x + ) Norma force on the eementary area, (a b) δw = p [b + x ] dx Tota force acting on the friction surface of singe pad, C W s = (b + kx)dx (x + ) = C (b + kx)dx (x + ) Tota force acting on 6 ceramic pads is, W = 6C (b + kx)dx (x + ) We know that tota axia force, W exerted by the springs on the friction surface is N. Thus, = 6C (b + kx)dx (x + ) Let, x + = t dx = dt At x =, t = 0.222, x =, t = = 6C [b + k(t )]dt t Soving the above equation, we get W = C C = N/m Tota frictiona force acting on the cutch pate, T = n μp(b + kx) (x + A rights Reserved 399

6 T = N-m Factor of safety for this case is, T = nμc (b + kx) (x + )dx (x + ) T = C (b + kx) dx T =.2 C [bx + kx2 2 ] T =.2 C [0.047x x 2 ] T = C F s = =.5 CASE III: CONDITIONS OF CLUTCH SLIP The axia or norma pressure exerted by the springs provides a frictiona force in the circumferentia direction when the reative motion between the driving and driven members tends to take pace. The cutch woud sip when []:. The torque due to frictiona force is ess than the torque to be transmitted. 2. The wear of frictiona ining exceeds the imiting vaue. This amount of wear decompresses the springs and thus axia pressure exerted woud reduce causing sip of cutch. 3. The driving shaft and driven shaft rotate at different speeds. Cutch woud sip unti the anguar veocities of the two shafts become equa or the reative veocity becomes zero. Condition I (Torque due to frictiona force): The frictiona force exerted by the cutch discs in a the above cases is more than the maximum torque deveoped by the engine or in other words the factor of safety for a the cases is more than unity. Thus, there exists no cutch sip due to this frictiona force. For the condition of engine when producing maximum output of 0 HP or KW at 2400 rpm, torque deveoped is given by, T = P P 60 = (4) ω 2πN = π 2400 = N m The torque deveoped at maximum output is aso ess than the frictiona torque acting on the cutch pate and thus cutch sip doesn t occur at this condition. Condition II (Wear of frictiona ining): Given [2], Free ength of the spring =.88 cm Stiffness of the spring = N/cm Tota axia oad exerted by the springs, W = N Tota stiffness of 2 springs = = N/cm Axia oad,w Initia compression of springs = (5) Tota stiffness of springs = = 5.72 A rights Reserved 400

7 The permissibe wear imit of singe cutch ining is given as 3.8 mm [2]. When considering both the contact surfaces, the maximum permissibe wear imit woud be 7.62 mm or cm. Thus we need to cacuate the torque transmission capacity of both the cutch pates when the initia compression of spring is reieved by cm or in other words when the springs are compressed by cm. For asbestos disc cutch: We sha consider the uniform wear theory as the cutch pate is worn out. Tota axia force exerted by the springs, = Stiffness of 2 springs Compression of spring = = N Torque transmitted by the cutch (uniform wear) = nμwr [4] = = N-m We know that maximum torque deveoped by the engine is N-m []. The torque transmitted by worn out asbestos cutch disc under uniform wear condition is more than maximum torque deveoped by engine. Thus cutch woudn t sip even when the inings have worn out up to the permissibe imit. OEM might have decided this imit to provide cearance between cutch reease evers and cutch reease bearing. For 6- pad ceramic cutch pate: Tota axia force exerted by the springs (when inings are worn out), W = N Earier we had derived for uniform wear conditions, W = C or C = Torque transmitted by the cutch = C = N-m = In this case the frictiona torque acting on the friction surfaces of cutch pate is ess than the maximum torque deveoped by the engine. Thus at the condition when engine is deveoping maximum torque and the inings have worn out to the permissibe imit, the cutch pate sips. Hence 6-pad ceramic cutch pate must be repaced when the pads get worn more than the said permissibe imit. Condition III (Reative veocity of driving and driven shafts): The difference in veocities of driving and driven shafts is known as reative veocity at time t and is given by [], ω = dθ dt = dθ dt dθ 2 dt (6) or ω = (ω ω 2 ) T ( I + I 2 I I 2 ) t (7) Where, θ and θ 2 are anguar dispacements of driving and driven shafts (rad) ω and ω 2 are anguar veocity of driving and driven shafts (rad/s 2 ) I and I 2 are moments of inertia of driving and driven shaft (Kg-m 2 ) T is cutch torque (N-m) The cutching operation is compete at the instance when the reative veocity becomes zero. Let at this instance time is t. Equating reative veocity to zero and substituting t = t, we get t = (ω ω 2 )I I 2 (I + I 2 )T It is observed that time required for engaging the cutch or duration of cutch sip is directy proportiona to the difference in the anguar veocities of both the shafts and inversey proportiona to the torque. Aso the tota energy dissipated in the form of frictiona heat during cutching operation is given by [], A rights Reserved 40

8 E = 2 (ω ω 2 ) 2 I I 2 (I + I 2 ) (9) Thus the energy dissipated during cutch sip is independent of the torque and directy proportiona to the square of reative veocity of driving and driven shafts. Aso the frequency of cutching operation is aso an important parameter as the temperature of friction pads increases and requires time to dissipate heat. The duration of cutch sip and energy dissipated coud be cacuated if the vaues of other parameters are known. V. FINAL RESULTS The torque transmission characteristics and state of cutch sip for both the cutch pates have been anayzed. The resuts obtained for various cases are tabuated as given beow: CASE I: Type of theory Uniform pressure theory Uniform wear theory Asbestos disc cutch (µ=0.25) Factor of safety Torque transmitted (N-m) When asbestos ining repaced with ceramic materia (µ=0.6) Factor of safety CASE II: Type of theory Uniform pressure theory Uniform wear theory Asbestos disc cutch (µ=0.25) Factor of safety Torque transmitted (N-m) 6- Pad Ceramic cutch pate (µ=0.6) Factor of safety CASE III: Type of cutch pate Torque transmitted (Nm) by cutch when ining has worn out by 7.62mm [2] Maximum torque deveoped by engine (Nm) [2] Cutch sip Asbestos disc cutch Doesn t exist 6- pad ceramic cutch Exists pate VI. CONCLUSION After the anaysis is carried out on asbestos disc cutch and 6- pad ceramic cutch pate, the foowing statements are made after comparing the resuts:. Conventiona asbestos disc cutch is possessing better factor of safety. But if the asbestos inings are repaced with ceramic materia, the torque transmitted and factor of safety achieved is much higher. 2. When coefficient of friction for ceramic pad is presumed to be 0.6, the cutch pate serves the need though the factor of safety is ess when compared with asbestos disc A rights Reserved 402

9 3. When the engine is deveoping maximum torque, cutch sip doesn t occur in asbestos disc cutch even though the inings have worn out to the permissibe imits. 4. The 6- pad ceramic cutch pate sips when the engine is deveoping maximum torque and the inings have worn out to permissibe imits i.e., 7.62 mm. Finay, it is concuded that as ceramic materia has better torque transmission characteristics, if the asbestos inings are repaced with ceramic materia, then the cutch pate woud yied greater factor of safety. But in case of 6- pad ceramic cutch pate, the design criteria of ceramic pads needs to be revisited in order to increase the factor of safety and aso to eiminate cutch sip. As the wear rate or ife of asbestos ining and ceramic pads is not tested, the time scae for the materia to wear up to permissibe imit coudn t be determined. Thus with the above carried study it is not possibe to comment on the reiabiity of these cutch pates. VII. SCOPE OF FUTURE STUDY Though study coud be conducted on the torque transmission characteristics of various friction materias, it is obvious that wear rate needs to be known to precisey define reiabiity. For a fixed amount of braking the amount of wear of asbestos materia tends to remain fairy constant or increase sighty with respect to temperature, but once the temperature reaches >200 C, the wear increases exponentiay with increasing temperature because of therma degradation of bend components and other chemica changes. Whereas the cermet materias are more thermay resistant than asbestos. The cutch discs need to be tested on a fu brake Dynamometer test bed to determine the wear rate for simiar cutching operations which refects the actua performance of the friction materia [5]. Aso in the study, the vaues of coefficient of friction of frictiona materia are presumed, as exact vaues of the asbestos ining and ceramic composite pads are not known. The ceramic composite materia has coefficient of friction vaues more than 0.4 and is insensitive to grabbing [6]. With the aid of computer simuation software and exact vaues of coefficient of friction of friction pads, better anaysis coud be carried out. An optimized soution thus arrived coud repace conventiona components with more efficient and eco-friendy ones. REFERENCES [] VB Bhandari, Design of machine eements 3e, Mc Graw Hi Education Pvt. Ltd., Pubished 200, Friction cutches, page No [2] Ashok Leyand Service Manua, Pubished 2009, Leading particuars of vehice. [3] Cutch Auto India Ltd., Parts Cataogue, Pubished 205. [4] RS Khurmi and JK Gupta, A text book of machine design 3e, S Chand and Company Ltd., Pubished 2002, Cutches, page No [5] [6] Water Krenke, Ceramic Matrix Composites: Fiber Reinforced Ceramics and their Appications, Wiey VCH, 2 May 2008, Ceramic Cutches, page No. A rights Reserved 403

PHYSICS LOCUS / / d dt. ( vi) mass, m moment of inertia, I. ( ix) linear momentum, p Angular momentum, l p mv l I

PHYSICS LOCUS / / d dt. ( vi) mass, m moment of inertia, I. ( ix) linear momentum, p Angular momentum, l p mv l I 6 n terms of moment of inertia, equation (7.8) can be written as The vector form of the above equation is...(7.9 a)...(7.9 b) The anguar acceeration produced is aong the direction of appied externa torque.