Tribological Study for a Low-Friction Cam/Tappet System Including Tappet Spin

Abstract

changes i n the cantltappet interface friction due to changing operating conditions is adopted and integrated into the analysis. Also included in the study is a model of tappet spin allowing for slip at the camltappet interface. Modeling tappet spin makes it possible to see the effects of the tappet crown radius and cam-taper angle on the interface frictional loss.Tappet rotation is found to be affected by design and operctting conditions, and it is dependent primarily on cumhaft speed. It is shown that the tappet crown radius and cam-tiper angle can be optimized to lower the energy loss.Valvetrain enerby-loss predictions, tappet rotational-speed results, and the effect of tappet spin on energy loss agree with the available experimental data. A, = apparent area of contact, m2 a = Hertzian contact half width, m aa = elliptical contact semi-major axis, nl b = temperature coefficient of viscosity, IPC bb = elliptical contact semi-minor axis, rn c~c = tappettlifter guide radial clearance, m d = distance between tappet and contact centers, m E = equivalent modulus of elasticity, Pa e = distance between cam and tappet centerlines, m eT = distance between contact center and tappet centerline, m F = overall friction force, N F,1 = traction force capacity, N Frz = friction force, N FNS = required traction force for no-slip, N Fps = pushrod-tappet seat side force, N f = overall friction coefficient at cam/ta,~~pet interface fLC = coefficient of mixed friction at the lifter guide h, = lubricant film thickness in the Hertzian contact, m h = specific film thickness (=hole) IT = tappet moment of inertia, kg-m2 kL = lubricant thermal conductivity, Wl(m -"C) L = lift, m eLG = effective length of lifter guide, m M = cam torque, N-m m = slope of lubricant-limiting shear stress-pressure relation P = power loss due to sliding, (N-m)/s p = lubricant pressure, Pa PB = asperity load per unit area ( = WBIA,), ~l r n ' p, = elliptical contact Hertzian pressures, ~l m ' pr, = elliptical contact maximum Hertzian pressure, ~l m ' PH = hydrodynamic load per unit area, ~l n i~ Q = energy loss at the camltappet interface, N-m (2Lc = energy loss at the lifter guide, N-m Re = cam-base radius, m Rc = cam instantaneous radius of curvature, m RE = equivalent contact radius, m RF = tappet foot radius, m Rj-= tappet crown radius, m s = cam-taper angle, degree TB = bulk temperature of lubricated components, and supply -temperature of lubricant, O C TT = traction torque at camltappet interface, N-m TF = friction torque at camltappet interface, N-m TR = friction torque from lifter guide, N-m TLC = lubricant temperature in the lifter guide, "C T N S = overall torque for no-slip traction condition, N-n1 t = time, s VT = non-rotating tappet surface speed with respect to contact, mls Vc = cam surface speed with respect to contact, mls VR = entrainment speed, mls 225 Downloaded by [McGill University Library] at 12:27 05 February 2015 Vs = sliclillg S~CCCI, rills W = tot:~l contact loacl, N WII = frac~ion of loacl carriccl by asperities, N lo = LI t i i~ coti...

Analysis of dynamics and friction resistance in the cam-tappet system

“…Mathematical models allowing prediction of lubricant film-thickness and Hertzian pressures at the cam/tappet contact were presented in Gecim (1992). The model can predict the changes in the cam/tappet interface friction due to changing operating conditions.…”

A study of the measurement of surface temperature at a cam/tappet contact

“…By converting the strain gauge output, the friction force can then be measured. Another strain gauge (6) is also used to measure the cam (5) load at the same time. All measurements were carried out under engine motoring conditions on an in-line, OHV type DI diesel engine.…”

“…By converting the strain gauge output, the friction force can then be measured. Another strain gauge (6) is also used to measure the cam (5) load at the same time.…”

Measuring tappet rotation in a valvetrain rig when lubricated in a fully formulated oil containing MoDTC-type friction modifier

“…In the literature [5,7,8], limited models have been developed to investigate the influence of tappet rotation. However, the validation of such models (i.e.…”