Internal combustion engine

The invention increases a thermal efficiency by increasing the degree of constant volume of a fuel-air mixture at the time of combustion in an internal combustion engine. To achieve this, in an internal combustion engine in which a piston 16 slidably fitted in a cylinder 15 is connected to a crankshaft 19 via a connecting rod 21, a cylinder head 12 in which a combustion chamber 22 is defined is disposed between the piston 16 and the crankshaft 19. As compared with a prior art internal combustion engine in which a combustion chamber is disposed opposite to a crankshaft with a piston put therebetween, a ratio of an increased amount of the volume of the combustion chamber 22 to an increased amount of a crank angle of the piston 16 from the top dead center can be suppressed at a small value. As a result, it is possible to increase the degree of constant volume of a fuel-air mixture at the time of combustion and hence to increase a thermal efficiency of the internal combustion engine. Also, since a tensile load is applied to a connecting rod 21 in an expansion stroke, it is possible to lower a strength of the connecting rod 21 and hence to reduce the weight thereof as compared with the prior art internal combustion engine in which a compressive load is applied to a connecting rod.