Understanding Friction in Cam–Tappet Contacts—An Application-Oriented Time-Dependent Simulation Approach Considering Surface Asperities and Edge Effects

Abstract

With the increasing challenges of climate change and scarce resources, the development of sustainable and energy-efficient technical systems is becoming increasingly important. In many applications, the friction losses occurring in contacts have a decisive influence on the overall efficiency. At this point, tribological contact optimization can make an important contribution to increasing the efficiency of technical systems. However, improvements are often associated with a considerable experimental effort. To reduce the development time, additional simulation models can be applied to predict the tribological behavior. This requires the closest possible approximation of the real contact within a numerical model. This paper presents a simulation approach for the time-dependent simulation of a cam–tappet contact. The simulation uses realistic operating conditions as they arise in the valve train of internal combustion engines. The influence of edge effects on the friction behavior is considered by a scaled calculation area and the influence of the surface roughness is investigated using stochastic asperity models. It is shown that the tribological behavior within the contact strongly depends on the surface properties and the load spectrum used. In addition, edge effects on the sides of the contact area have a clear influence on the pressure and film thickness distribution.

Numerical optimization of highly loaded microtextured contacts: understanding and mastering complexity

“…The resulting contact conditions were previously determined by Weschta in a multibody simulation. Due to the high dynamics of the contact, a transient EHL simulation over a complete cycle is numerically very complex already in the nontextured case (Orgeldinger and Tremmel, 2021). The contact width changes significantly over the cycle, so an adaptation and remeshing of the computational domain would be necessary at each time step to be able to capture the texture geometry over the whole circle.…”

“…For the correct description of the pressure distribution, the Reynolds equation is extended with flux factors as described by Patir and Cheng (1979, 1978). The implementation is described in more detail in Orgeldinger and Tremmel (2021).…”

“…Here, the computational domain is scaled in the length direction of the line contact, as presented by Winkler et al (2020), to reduce the computational effort. For a detailed description of the nontextured model, we refer to preliminary work (Orgeldinger and Tremmel, 2021). Figure 1(a) shows a simplified view of the computational domain for the 3D as well as the 2D model.…”

A traction coefficient formula for EHL line contacts operating in the linear isothermal region

“…respectively. Since the objective of the present paper is to obtain a prediction formula for the traction coefficient slope, which is related to the SRR, we are only interested in the former of the two terms in (12), i. e., F τ , given by (13a).…”

“…Wei et al [10] and Xiu-jiang et al [11] developed a 3D mixed lubrication model for rolling point and line contacts operating in the piezoviscous elastic region (PE), in order to investigate friction and temperature development in gears. Orgeldinger et al [12], investigated the friction losses for the time-dependent cam-follower in two-dimensional line contact in the isoviscous elastic (IE) region by using a numerical model. These investigations didn't focus on an SRR low region.…”