Investigation of the friction power losses of different automotive engine concepts

A project is proposed to put to the test the mechanical efficiency and lubrication requirements of different current automotive internal combustion engine (ICE) concepts by using a combined simulation and measurement approach. An extensive set of friction measurements are planned that cover conventional gasoline and Diesel engines, but also engines stemming from new concepts like downsizing and cylinder deactivation that impose new additional demands on the lubrication. With these experimental data the friction power losses of these engine concepts can be assessed in relation to their nominal power output. This will yield an increased understanding of the mechanical efficiency of current state of the art engine concepts (downsized engines and engines with cylinder deactivation) in comparison to more conventional gasoline and Diesel engines. In addition, entirely new ultra-low viscosity polyglycol based lubricants are investigated in terms of friction reduction in comparison to current low-viscosity hydrocarbon based lubricants. Further, with the aid of these experimental data, the capability of current state of the art simulation methodology to predict friction power losses for the individual subsystems piston assembly and journal bearings is tested and the different specific demands of these subsystems on the optimal rheological properties of the lubricant are investigated. As internal combustion engines utilize only a single lubricant for all these subsystems, a better understanding of the requirements of the individual subsystems on the lubricant allows to derive optimum rheological properties (like dynamic viscosity and shear rate dependency of the lubricant, i.e. HTHS-viscosity) that represent an optimum compromise for all these subsystems. An interesting aspect in this regard are the investigated polyglycol based lubricants that show better shear stability (less non-Newtonian behavior) and, thus, are expected to reduce friction by the employing a further reduced viscosity. The range of simulation methods for this task includes extensive elastohydrodynamic and thermo- elastohydrodynamic simulations with a number of contact models of different complexity to describe mixed lubrication. From a methodology point of view, new aspects like e.g. the role of thermoelastic deformations and the consideration of the surface topographies in the simulation are planned to be investigated. While a broad variety of sophisticated methods exist to investigate these tribological issues, it is unclear to which extent they are sufficient to accurately and reliably predict the tribological operating conditions in these subsystems. With the proposed project it is intended to investigate this question in direct comparison to experimental data for four engine concepts that impose very different demands on lubrication.

Investigation of the friction power losses of different automotive engine concepts To reduce fuel consumption the reduction of engine friction has always been in the focus of the car manufacturers. However, the precise measurement and analysis of engine friction is not as easy as it may appear and for a long-time methods with severe limitations have been used within the automotive industry. Within this project a novel approach, the so-called virtual strip-down method, has been introduced and tested for the first time to three very different engines. This virtual strip-down method has many advantages, most notably it allows to virtually look into the engine and see where the friction is generated. This is a valuable advantage as not all friction losses are equal; while the so-called hydrodynamic losses do not harm the engine but increase only the fuel consumption, the so-called mixed lubrication can cause detrimental wear to the engine. Therefore, it is not only important to know how much friction is generated by the different engine subsystems, but also to understand which type of friction occurs. The introduced virtual strip-down method can also help in this respect as could be shown. Besides the introduction of this novel method, it was also the aim of this project to gain a more detailed understanding how engine friction is affected by the actual engine concept. By engine concept it is meant that conventional gasoline (with low power density), downsized gasoline (with high power density, e.g. turbocharged gasoline engines) and modern Diesel engines operate very differently and involve very different mechanical loads on the components of the engine. All of these points influence also engine friction and, consequently, affect the mechanical efficiency of the powertrain. To better understand and quantify these influences, this novel engine friction analysis method has been applied to three engines from these very different three engine concepts (conventional gasoline, downsized gasoline and modern Diesel engine). Many interesting and new results were obtained in this project which lead to the publication of at least 13 papers in international journals. Wherever possible, the papers were published with open access that means the papers can be accessed free of charge for everyone. The importance of these results was also internationally recognized as the project leader was invited as international keynote speaker to deliver the opening lecture for a Japanese automotive tribology symposium.