A former patent provided for the admission into the cylinder of a charge of scavenging air by means of a mechanically operated valve, this charge being subsequent to that let in by the ports in the ordinary manner.
The invention under consideration relates to the placing of this valve in such a position that it is capable of being operated by the same cam-shaft which actuates the fuel and starting valves in the cylinder head.. The rollers operating the fuel and additional air valves respectively are located diametrically opposite to one another with regard to the cam-shaft, and by means of a headpiece acting on the valve spindle which passes through the scavenging pipe provision is made for increasing the movement of the roller operating the additional air-valve.
For this purpose the roller is mounted centrally on a lever, the fulcrum of which is situated at the extremity furthest from the headpiece.