METHOD FOR PROVIDING VARIABLE COMPRESSION RATIO IN A COMBUSTION ENGINE AND DEVICE FOR THE METHOD

The present invention concerns a method for providing a variable compression ratio in a combustion engine, where the combustion chamber () is formed substantially by a piston bowl in the main piston (), comprising a secondary piston () being displaceable against spring action between an upper/outer position which provides minimal volume of the combustion chamber () and lower/inner position which provides maximum volume of the combustion chamber (), or in a position therebetween depending on introduced air mass before the compression stroke. The method is characterized in arranging said secondary piston () resting on a spring () with substantially constant spring force adapted such that introduced air mass is to be compressed to a predetermined pressure at the end of the compression stroke. The invention also concerns a corresponding device and a diesel engine comprising such a device.