Bezzazi_Experimental-characterization-of-frictional-behaviour-of-clutch-facings-using-Pin-on-disk-machine_2007.pdf

Experimental characterization of frictional behaviour of clutch facings using Pin-on-disk machine M. Bezzazi a, A. Khamlichia,*, A. Jabbouria, P. Reisb, J.P. Davimb a LMMS, De partement de Physique, F.S.T.T, B.P. 416, Tangier, Morocco b Departamento de Engenharia Meca nica, Universidade do Aveiro, Portugal Received 24 January 2006 Available online 1 September 2006 Abstract During the clutch engagement manoeuvre, sliding contact occurs between the pair of clutch facings mounted on the friction disk and the counter faces belonging to the fl ywheel and the pressure plate. The transmitted torque is proportional to the overall coeffi cient of friction which depends essentially on temperature, normal pressure load and relative sliding velocity. In this work, performance of the friction coeffi cient is investigated experimentally. Samples of a commercial clutch facings material have been tested using a Pin- on-disk apparatus. When the previous three parameters are preset constant, this machine provides automatic acquisition of friction coef- fi cient and wear measurements. The obtained results are compared with the classical SAE J661a standard test. It is found that the actual clutch facings material has good fading resistance and a rather stable coeffi cient of friction once running in phase is achieved. ? 2006 Elsevier Ltd. All rights reserved. Keywords: Composites; Thermal; Mechanical; Friction behaviour; Clutch facings 1. Introduction In a vehicle rotary motion is to be transmitted from the primary shaft (motor) to the secondary shaft (gear box) for intermittent periods only. To achieve that, a clutch is required between these two components. The function of the clutch is to produce a soft gradual increase in the angu- lar velocity of the driven shaft until full coupling between the motor and the gear box is achieved. Then, the clutch must act as a permanent coupling transmitting, from the driving shaft to the vehicle wheels, the entire mechanical power without subsequent slip 1. During dry clutch engagement manoeuvre, a transient sliding contact situation occurs between the pair of clutch facings mounted on the friction disk and the counter faces belonging to the fl ywheel and the pressure plate. Through- out this engagement process, heat is generated at the con- tact surface yielding temperature to rise 2. Temperature rise may be very important in case of repetitive engage- ments. Good performances of the clutch facings material such as a stable and suffi ciently high coeffi cient of friction are required in order to operate engagements in an effi cient and regular way. Fading phenomenon which is due to a sudden decrease of the friction coeffi cient as function of temperature must be avoided. Variations in time of the fric- tion coeffi cient during the running in phase or due to mate- rial wear must also remain limited. Other factors in addition to temperature might infl uence the coeffi cient of friction level. They are related to hetero- geneities of the contact surfaces, chemical reactions or physical transformations. But, these mechanisms are both complex and non reproducible. Their eff ects could be, in practice, globally taken into account through the coeffi - cient of friction tolerances. To characterize the tribological behaviour of clutch fac- ings, a lot of standard laboratory tests are usually per- formed by the manufacturers: Raybestos tests in case of 0261-3069/$ - see front matter ? 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2006.07.001 * Corresponding author. Address: 33, Re sidence Al Isma lia, Avenue des F.A.R., Appt. 15B, Tetouan, Morocco. Tel.: +212 67 79 50 68; fax: +212 39 35 07 02. E-mail address: khamlichi7 (A. Khamlichi). Materials and Design 28 (2007) 21482153 Materials the friction coeffi cient decreases with increasing temper- ature and with increasing sliding velocity. Comparison of Pin-on-disk results with those obtained through SAE J661a standard test, which was performed on the same clutch facing material, shows that the usual features regarding the coeffi cient of friction behaviour are identical if diff erences of temperature are incorporated. Using the clutch facing material as the disk in the Pin- on-disk machine enables to eliminate glazing eff ect which is frequently observed on other tests where the friction material is reduced to a small sample which is bonded on the pin like for example the FAST test. The tests carried out in the present study have assessed that the most desired performances of clutch facings are confi rmed for the actual material since a stable a suffi - ciently high coeffi cient of friction is obtained. References 1 Williams JA. Engineering tribology. New York: Oxford University Press; 1994. 2 Khamlichi A, Bezzazi M, Parron Vera MA. Optimizing the thermal properties of clutch facings. J Mater Process Technol 2003;634:142. 3 RIP Test programs. R + D Department, Raybestos, Morbach, Ger- many, 1996. 0.0 0.2 0.4 0.6 0.8 1.0 0101201302402503603704804905 Sliding distance (m) 0.0 0.2 0.4 0.6 0.8 1.0 0101201302402503603704804905 Sliding distance (m) 0.0 0.2 0.4 0.6 0.8 1.0 0101201302402503704804905 Sliding distance (m) Sliding distance (m) 0.0 0.2 0.4 0.6 0.8 1.0 0101201302402503603704804905 0.00 0.20 0.40 0.60 0.80 1.00 0101201302402503603704804903 Sliding distance (m) Fig. 4. Friction coeffi cient versus sliding distance (a) T = 100 ?C; v = 1 m/s; P = 51 N. (b) T = 100 ?C; v = 1 m/s; P = 53 N. (c) T = 100 ?C; v = 3 m/s; P = 56 N. (d) T = 200 ?C; v = 1 m/s; P = 58 N. (e) T = 200 ?C; v = 3 m/s; P = 51 N. 50100150200250300350 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 TemperatureC Friction coefficient 1 2 3 5 6 74 Fig. 5. SAE J661a coeffi cient of friction results for clutch facings material. 2152M. Bezzazi et al. / Materials and Design 28 (2007) 21482153 4 JIS D-4311: Clutch facings for automobiles. Tokyo: Japanese Stan- dards Association, 1995. 5 Nicholson G. Facts about friction. Winchester, Virginia: Gedoran America Limited; 2000. 6 Davim JP. An experimental study of tribological behaviour of the brass