Abstract
This work presents the application of a combined approach to investigate the friction losses in a modern four-cylinder passenger-car diesel engine. The approach connects the results from engine friction measurements using the indication method and the results from journal-bearing simulations. The utilization of the method enables a subassembly-resolved friction loss analysis that yields the losses of the piston group, crankshaft journal bearings, and valve train (including the timing drive and crankshaft seals). The engine and engine subassembly friction losses are investigated over the full speed and load range, covering more than 120 engine operation points at different engine media supply temperatures ranging from 70 to 110 ∘ C. The subsequently decreasing lubricant viscosity due to higher engine media supply temperatures allow for the identification of friction reduction potentials as well as possible risks due to an onset of mixed lubrication. Furthermore, additional strip-tests have been conducted to determine the friction losses of the crankshaft radial lip seals, the timing drive, and the crankshaft journal bearings, thus enabling a verification of the calculated journal-bearing friction losses with measurement results. For the investigated diesel engine, a friction reduction potential of up to 21% could be determined when increasing the engine media supply temperature from 70 to 110 ∘ C, at engine speeds higher than n = 1500 rpm and part load operating conditions. At low engine speeds and high load operations, the friction loss reduction potential is considerably decreased and below 8%, indicating mixed lubrication regimes at the piston group and valve train.
Highlights
To improve fuel economy and, in particular, the overall mechanical efficiency, the determination of the friction losses of combustion engines is a crucial topic in modern engine development
The results show that bearing temperature measurements at just one main bearing can lead to differences up to 5 ◦ C in bearing temperature which are provided as input data to the journal-bearing, simulation affecting the calculated results of the journal-bearing friction losses
The results presented are the the calculated results of the individual strip-test stages from Equations (6)–(8) for the friction losses of the valve train, crankshaft seals, and lower timing drive respectively
Summary
To improve fuel economy and, in particular, the overall mechanical efficiency, the determination of the friction losses of combustion engines is a crucial topic in modern engine development. Based on current challenges for manufacturers including stricter CO2 emission limits from the legislative side, changing customer preferences (away from product towards function, e.g., car sharing and car rental) and a general focus on the environmental impact, it is nowadays crucial to develop highly efficient vehicles. Measures to reduce the mechanical losses often show advantages in terms of financial investments compared to hybridization and subsequently increases the overall efficiency of hybrid vehicles [2]. The frictional losses of the base engine are generated by the subassemblies’ piston group, crankshaft journal bearings, valve train, timing drive, and shaft seals
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