Innovative Actuation Concepts for Variable-length Connecting Rods
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AUTHORS
Prof. Dr. Eng. Karsten Wittek is Head of the Laboratory for Piston Engines at Heilbronn University of Applied Sciences (Germany).
Frank Geiger, M. Eng. is Research Assistant at Heilbronn University of Applied Sciences (Germany).
© Heilbronn University
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Innovative Actuation Concepts for Variable-length Connecting Rods At Heilbronn University, an easily integrated hydraulic actuation system for variable-length connecting rods was developed and tested in a vehicle as an alternative to mechanical actuation. A second system, based on electromagnetic actuation, allows infinite length variation and was tested on a test bench.
1 INTRODUCTION 2 THE CHALLENGE 3 HYDR AULIC ACTUATION WITH SEPAR ATE C ONTROL OIL PRESSURE LINE 4 TEST VEHICLE 5 TESTING IN THE VEHICLE 6 ELECTROMAGNE TIC ACTUATION 7 SUMMARY AND OUTLO OK
1 INTRODUCTION
MTZworldwide issue 7-8/2020 reported on the operating behavior of variable-length connecting rods with eccentric piston pin bearings. The integration effort is largely determined by the required actuation system. Previous solutions are usually based on a mechanical actuation unit that has to be integrated into the bottomend structure near the crankshaft, which, depending on the engine, requires major design changes. This is why a hydraulic actuation concept has been developed that requires almost no design changes and no adaptation to the lube oil system. A second system that has been developed is based on electromagnetic actuation and allows infinitely variable compression.
piston on which the pressure prevailing in the supply groove in the connecting rod bearing acts. This means that the main switching valve can be actuated by selectively changing the oil pressure in the main oil channel, for example with a variable oil pump. In the test, the function of this “direct” hydraulic actuation with moderate oil pressure changes can only be demonstrated in a limited operating range. Such a “direct” hydraulic actuation is also reported in [2], whereby an electrically driven additional oil pump is used here to supply the connecting rod bearings with a correspondingly high oil pressure independently of the rest of the engine lubrication system. In the concept presented here, a separate control oil pressure line is implemented in the crankshaft, FIGURE 1. The control pressure line (yellow) is connected to a 3-/2-way valve located in the crankshaft (pilot valve) and is either fluidically connected to the crankcase (violet) or to the supply side (green). An additional groove must be provided in the connecting rod bearing shells to create a separate fluid connection between the VCR connecting rod and the crankshaft. The pilot valve is operated by a solenoid actuator. FIGURE 1 shows the non-energized position. The control oil pressure corresponds to the ambient pressure; the main switching valve is not actuated. The switching position high compression ratio (epsilon, EPSHigh) is active. Alternatively, the main switching valve could have been designed so that the switching position low compression
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