Portable power tool with improved combustion chamber charging means

A portable power tool comprising:

• a body;
• a bore within said body;
• a piston, slidably mounted within said bore for a movement in one direction from a first position through a power stroke into a second position and in an opposite direction through a return stroke;
• a combustion chamber formed in said body and communicating with said bore at an end remote from said second position of said piston and being arranged to receive a gaseous fuel for ignition and combustion;
• inlet means for admitting said fuel to said combustion chamber;
• outlet means for exhausting residual gases from said combustion chamber;
• valve means operable to control said admission and said exhaust through said inlet means and outlet means respectively;
• supply means for supplying said fuel to said inlet means;
• said valve means, said inlet means, said outlet means and said combustion chamber cooperating so that when said valve means allows communication between said combustion chamber and both said inlet means and said outlet means and said piston is at its first position, said fuel is directed into said combustion chamber in a manner scouring the combustion chamber of residual gases from a preceding cycle of operation of the tool and sweeps said residual gases out through said outlet means prior to the valve means adopting a condition in which said outlet means is closed;
• and ignition means for igniting said fuel in said combustion chamber;
• whereby subsequent combustion of said fuel creates an elevated pressure condition within said combustion chamber which acts on said piston to cause rapid movement under power of said piston, through said power stroke towards said second position, said piston being arranged to effect a required power assisted operation.