Certainly, the latest invention on a particular topic, as in this case of variable compression, always seems to be the most ingenious, but in this case, it may probably be true. The Dutch company Gomecsys from Naarden, south-east of Amsterdam, is taking a rather different route than previously presented others. The PSA Group is said to have presented a test engine during the last symposium in Aachen.

The description starts with the connecting rod bearings of the crankshaft. At their sliding surfaces eccentrics are fitted as intermediate rings, on which then rotate the big connecting rod eyes. Depending on how the eccentrics are turned to the crankshaft, the pistons have a large or a small stroke and thus also different compression ratios, in the present case from 8 to 16: 1.

Important: The eccentrics on the connecting rod bearings are only slightly twisted to change the stroke and the compression. Otherwise, they act as if they were firmly connected to the connecting rod bearings. Of course, the engine does not have to be stopped every time for changing. At the bottom of the video you can see from the measured values how compression is reduced when accelerating and thus higher load demand to prevent knocking.

How are the eccentrics rotated on the connecting rod bearings of the crankshaft? The picture above and the videos below show different versions. We follow the picture above with a shaft through the middle of the first main bearing of the crankshaft. Of course, this can only reach beyond the first crank arm, otherwise it would disturb the first crank drive. The control is passed through the two gears on the eccentric to another short shaft through the next main bearing. Therefore, each eccentric has two gears.

At the very front of the engine is an electric servomotor, which can change the compression or stroke via a worm drive. Would you change the gear drive to the first shaft already during each rotation, a compression without stroke change or even a stroke change between the first and last two strokes would be possible. The original dream of Atkinson would be fulfilled with a much simpler mechanic. Read more about here.

At first glance, the concept seems to be superior to any other Variable Compression Ratios. One of the first in which Saab raised the Cylinder Head in an engine during runtime, had enormous sealing problems. The others are changing either the crankcase and/or the engine block or at least the reciprocating masses. Except for the FEV design, but that alters the position of the crankshaft and therefore is problematic for the further transmission of torque.

In this concept, only the rotating masses compared to a conventional engine are changed, which can be compensated relatively easily. Well the crankcase gets heavier, but maybe you can save one cylinder by downsizing. Another problem could be the lateral forces on the pistons, which only occur at settings between 8 and 16: 1. The only dangerous opponent would be a turbocharger with integrated electric motor, ie without turbo lag, but this should be much more expensive and does not represent all functions of this concept here. 06/18