12th IFToMM World Congress, Besançon (France), June18-21, 2007 CK-xxx 1 The influence of cam profile deviations on tribologic parameters for the cam- follower coupler with flat disc from thermal engine C. Onescu * J. –C. Grigore + N. –D. Stănescu ++ University of Piteşti University of Piteşti University of Piteşti Piteşti, Romania Piteşti, Romania Piteşti, Romania Abstract—1In this paper the tribologic parameters in the case of small variations of cam profiles, undulations or small wear, have been numerically computed. It considers one non- technological and one wear camshaft, the cam profile deviations being determined by optical measurements. The parameters as friction velocity, hydrodynamic velocity, sliding coefficient for the theoretical cam are compared with the parameters for non- technological and wear camshafts. Keywords: cam, profile deviation, contact, movement laws, sliding coefficient I. Introduction The cam mechanisms accuracy is treated in different papers with accent on cam. The follower displacement is influenced by the following factors: the technological precision of contact elements; dimensional variation due to thermal deformation; elastic deformation for the cam and follower; clearances from the kinematics joints cam- follower-guide follower. The contact movement law [1,4] correlates the angular field and the friction profile with the motion type (sliding + rolling) and reveals the motion type repartition on the cam and follower friction profile. The geometric and kinematics parameters have influence on the tribologic processes (friction, lubrication, wearing) [5,7], with effects on the coupler components durability and reliability. II. The cam-follower coupler kinematics To study the cam-follower coupler from cinematic point of view we have the model from figure 1. Into the tasks specifications of the automotive engine valve train it gives for the podar angle (ϕ i ), the values for the space (s I ) of the flat follower. In this situation is indicated that the follower velocities and acceleration to be evaluated by numerical derivation, using the finite difference method: ϕ ϕ Δ − = = = − + 2 1 1 ' * i i t t s s d ds s v (1) *E-mail: constantin.onescu@upit.ro + E-mail: jan_grigore@yahoo.com ++ E-mail: s_doru@yahoo.com 2 1 1 2 2 ' ' * ) ( 2 ϕ ϕ Δ − + = = = + − i i i t t s s s d s d s a (2) where s i+1 , s i-1 , s i , one takes from the tables. The numerical values of the follower displacement s i = s i (ϕ i ) it loads on the computer using Excel soft. The derivation step is o 2 = Δϕ . By coupling the calculus algorithm to Excel it determines the variation laws ) ( ϕ s s = , ) ( ' ' ϕ s s = , ) ( " " ϕ s s = for a Kurz cam without profile deviations with r 0 =13,5 mm (basis circle radius), s max = 5,1511 mm (follower’s maximum displacement) – the figure 2. Fig.1 Graphical model to study the contact movement. From [1] it results that the movement laws from intake and exhaust cams are almost identical, and the followers velocities and accelerations have the appropriate values. The valve train elasticity have the influence on the follower’s movement laws but this problem will be treated by dynamics. For these causes it recommends that the contact motion laws to be establish beginning with the accelerations. III. Correlation geometry-kinematics-tribology The correlation between geometry, kinematics and tribology is realized for the cam-flat follower coupler by parameters and relations given in the Table I.