Burak A. Gecim

Non-Newtonian Effects of Multigrade Oils on Journal Bearing Performance

This study is aimed at predicting the non-Newtonian effects of multigrade oils on journal bearing performance. The governing differential equation, similar to the Reynolds equation, is derived using a general apparent-viscosity function as the constitutive equation in order to be able to accommodate different rheological equations. Treatment of the non-Newtonian effects is confined to nonlinear viscous behavior. Oil elasticity and normal stress effects are not considered. The problem formulation resembles that of the THD problem, and the governing differential equation contains non-Newtonian factors based on the cross-film integrals of viscosity. The problem is solved by the finite difference technique, and the results show reasonable agreement with the experimental data available in the literature. In order to represent the rheology of multigrade engine oils, a new non-linear viscous constitutive equation is proposed. This equation is fitted to experimental data on the rheology of two multigrade engine o...

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

This study explores the design of a low-friction cam/tappet system. An elastohydrodynamic contact analysis is conducted to predict lubricant film-thickness and Hertzian pressures at the cam/tappet contact. In addition, a mixed-friction model that can predict the changes in the cam/tappet 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 cam/tappet interface

Transient hot spot temperatures at a sliding ceramic contact including surface coating effects

Abstract Prediction of hot spot temperatures at a sliding contact is important primarily from a wear viewpoint. The predictions are based on heat conduction models involving moving heat sources. In the present study, two new concepts are analyzed. The first concept is the prediction of transient hot spot temperatures with temperature-dependent properties (material and thermal) and time-dependent sliding speed. The solution of this non-linear problem with the data representing partially stabilized zirconia (PSZ) and Si3N4 indicates that the duration for the contact to reach 1000 °C was between 1 μs and 1 ms depending on the magnitude of the sliding speed. Accounting for thermal softening during the transient contact resulted in a slower temperature rise and lower peak values than those predicted by the constant hardness models. The contact area was shown to grow to twice its initial size due to thermal softening. The second concept analyzed is the effect of a surface layer on the transient hot spot temperatures. In this context, an equivalent resistance model is introduced which reduces the lengthy algebra usually associated with heat transfer modeling of layered solids. This model is used with the data representing a PSZ coating on a cast iron substrate. A PSZ coating on the order of 10 μm raised the steady hot spot temperature by an order of magnitude from what it would have been with a cast iron substrate alone. A thin PSZ film (e.g. 0.05 μm), whose steady state effect was negligible, had a significant effect at the beginning of the transient.

Modeling and Experimental Validation of Optimized Clamp Loading in a Toroidal-CVT

Efficiency of a toroidal traction drive is measured at different torques, speeds, speed ratios, and temperatures, with an emphasis on the effect of the design traction coefficient on variator efficiency. This is accomplished by independently controlling the trunnion and the clamp pressures representing the variator torque and the clamp load, respectively. Also measured is the effect of roller conformity on variator efficiency. Furthermore, a low-speed and high-temperature test is conducted to observe a potential change in the effective coefficient of traction due to a transition in the lubrication mode. It is shown that, by optimum clamping (without gross slip) the variator efficiency can be increased by 1-to 2-percentage point over the efficiencies measured with nominal clamp loads. Also verified is the rapid decrease in variator efficiency with over clamping above the nominal clamp loads. All test results compared well with model predictions.

Analytical and Experimental Assessment of Some Novel Variable-Valve-Actuation Mechanisms

We describe our analytical and experimental works on three novel variable valve actuation systems. These include a mechanical variable-lift and duration concept, a hydraulic-lost-motion variable-lift system, and a valve-deactivation mechanism with unique features. These devices differ in their complexity and versatility but offer a spectrum of design solutions applicable to a range of products. The strengths and weaknesses of these different approaches are discussed and analyzed, and some test results are presented.

Variable Valve Actuation for Advanced Powertrains

We review variable valve actuation (VVA) concepts and also present the results of our work in the creative synthesis of these devices. We begin with a comprehensive survey of existing VVA devices. We then describe our work on four VVA concepts which we have explored in considerable detail. These include hydraulic lost-motion variable-lift systems, in both the direct acting and the roller-finger-follower configurations, several valve deactivation mechanisms with unique features, a variable valve-lift mechanism, and a variable-lift and duration concept. These devices differ in their complexity and versatility but offer a spectrum of design solutions applicable to a range of products. The strengths and weaknesses of these different approaches are discussed and analyzed, and some test results are presented.Copyright

Power-Transfer Capacity of a Geared-Neutral Transmission

Geared-neutral Continuously Variable Transmission (CVT) designs offer various kinematic advantages including a wide ratio range, and elimination of starting devices. However, they suffer from power re-circulation through the Continuously Variable Unit (CVU), which reduces the overall CVT efficiency and increases the CVU contact temperatures. This, in turn, limits the CVT power rating. In this study, the CVU and the CVT design parameters are optimized simultaneously to yield the highest power capacity. The CVU power capacity estimates are based on an instantaneous CVU-contact-temperature of 180°C. It is shown that a CVU design that yields the maximum power capacity is different from a design that yields the highest CVU efficiency.© 2007 ASME

Comparison of Efficiency Measurements and Simulation Results for Automotive Traction Drives

Mechanical Efficiency of toroidal traction drives is the key parameter for transmission engineers worldwide to accept their use in continuously variable transmissions. In this work, the traction drive efficiencies are investigated analytically as well as experimentally as a function of speed, torque, speed ratio and temperature for two different CVUs. In addition, creep at the traction contact is measured and compared with the prediction of the simulation model. In a stand-alone test rig, the drag torque associated with the power-roller thrust bearing is also measured.