Flexible Follower Response of a Translating Cam with Four Different Profiles for Rise-Dwell-Fall-Dwell motion
The flexible follower response of a translating cam with four different profiles for rise-dwell-fall-dwell (RDFD) motion is investigated. The cycloidal displacement motion, the modified sinusoidal acceleration motion, the modified trapezoidal acceleration motion, and the 3-4-5 polynomial motion are employed to describe the rise and the fall motions of the follower and the associated four kinds of cam profiles are studied. Since the follower flexibility is considered, the contact point of the roller and the cam is an unknown. Two geometric constraints formulated to restrain the unknown position are substituted into Hamilton’s principle with Lagrange multipliers. Applying the assumed mode method, one can obtain the governing equations of motion as non-linear differential-algebraic equations. The equations are solved using Runge-Kutta method. Then, the responses of the flexible follower undergoing the four different motions are investigated in time domain and in frequency domain. Keywords—translating cam, flexible follower, rise-dwell-falldwell, response
Stability of motion of the cam–follower system
Abstract In this paper, the dynamics of cam mechanism is analyzed. The mechanism is modeled as a cam–follower-driveshaft system where the flexibility of the camshaft and of the follower are considered. The non-linear and damping properties of the system are also taken into consideration. For constant angular velocity of the cam the mechanism is modeled as a two-degree-of-freedom system. The mathematical model of the system is described with two coupled parametrically excited non-linear second-order differential equations. The stability of motion of the system is investigated. Based on the criterion of stability the method for obtaining cam profile is developed. The conditions for stable and asymptotic stable motion of the follower are analytically determined. The obtained analytical results are compared numerical ones. The solutions are in good agreement.
Effect of DLC coatings on wear in automotive applications
Abstract Diamond like carbon (DLC) coatings have been investigated for application in the automotive valve train and, in particular, the camshaft drive assembly. The drive assembly can have various force transfer devices, such as an overhead bucket tappet assembly or a cam follower assembly. Force transfer devices operate in severe tribological contact situations with maximum Hertzian stresses approaching 1 GN m−2 and temperatures in the range 100–150°C. Lubrication is often partially starved and, therefore, the thermochemical properties and surface finish of the components are critical to their successful operation. For motor sport applications, DLC offers improved wear resistance over steel alone; and for passenger vehicles, the high hardness and commensurately lower friction coefficient that DLC gives against steel counterfaces offers improvements in fuel economy and lower wear. This paper presents the results from an investigation of the wear of DLC coated shims against standard production camshafts. DLC offers benefits in terms of reducing shim wear, but increases the wear of the camshaft. The wear mechanism observed for DLC is dependent on the oil type, but generally it is a pitting type mechanism. The cam wear occurs by plastic ratchetting. The consequences of the results are discussed in terms of the implementation of such coatings in standard valve train applications.