Engineers at Gomecsys have conducted intensive research to realize a simple, low-cost and durable mechanism that achieves the desired rotation and adjustment of the eccentrics.
The Generation 3 VCR mechanism with reduced engine friction
Looking at a 2 inline engine as the basis for the mechanism the function of the mechanism is to drive the eccentrics at half the crankshaft speed and in the same direction as the crankshaft. In this way the bearing speed of both the conrod bigend and the eccentric will be half the crankshaft speed. Another important function of the mechanism is to adjust the position of the eccentric in relation to the crankshaft position to be able to change the height of the pistons in tdc position.
To realise this the eccentric gears are driven by two intermediate gears which on their turn are driven by a the small sungear that is connected to a gear at the front of the crankshaft (the satelite gear). The satelite gear is driven by the stationairy actuation ringgear.
The VCR mechanism integrated at the front of the engine
The basic position of the eccentrics, and thus the compression ratio, is modified by the rotation of the actuation ring gear. The eccentric timing adjustment is realized by a double adjustment of the actuation ring gear. So to realize an adjustment of 60 degrees of the eccentric basic position the actuation ring gear needs to be adjusted by 120 degrees. Modification of the actuation ring gear can be realized in many ways but a simple and direct solution is to modify the ring gear with a worm drive. The electric motor can drive the worm very fast and doesn’t need a lot of power because the mechanism wants to move in the desired direction by itself.
To realize a mechanism where the actuation ring gear is stationary the gear ratio between the eccentric gear and the sun gear (for example “4”) has to be twice as high as the gear ratio between the actuation ring gear and the satelite gear situated at the front of the engine.