Category: New cars

There Is Nothing Permanent

There Is Nothing Permanent
There Is Nothing Permanent





A traditional constant such as compression ratio will soon become a variable. In principle, this is not news: SAAB showed a prototype engine with a deviating cylinder block several years ago. In the engine, proposed and tested by FEV Motorentechnik from Aachen, the crankshaft can not only rotate, but also shift up and down.

Why is this needed? It is known that to achieve maximum efficiency engines operate on the verge of detonation. But this line is highly dependent on the regime. At full load, and even with turbocharging, a compression ratio of 8: 1 can also become critical. But in the partial load mode, a much larger value is up to 15: 1. Usually the detonation boundary is pushed back, shifting the ignition moment - today electronics can do this instantly and over a wide range. But only a decrease in the lead leads to a decrease in efficiency, which completely kills the whole gain from a high degree of compression.

The output is a change in the volume remaining above the piston at top dead center. FEV Motorentekhnik proposed the VCR (Variable Compression Ratio) device, in which the crankshaft main bearings are mounted on special eccentrics. The latter can be rotated back and forth, thereby moving the axis of rotation of the crankshaft up or down. There is, however, one problem: the gearbox is firmly fixed. How to transmit torque from a floating crankshaft to it? For this, mobile “leashes” were created, thanks to which it is possible to transmit rotation, despite the mutual displacement of the axes of the input and output shafts (see. Fig.). The main thing is that all this mechanics is located in the flywheel, and the eccentrics are inside the usual cylinder block and crankcase.

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