Fuel injection arrangement

Claim 1

A fuel injection arrangement for a two-stroke engine, especially for handheld portable tools such as motor-driven saws or the like, the engine having a piston and a cylinder conjointly defining a combustion chamber and having a crankshaft connected to the piston and a crankcase wherein pressure is developed in response to the movement of the piston through a piston stroke, the fuel injection arrangement comprising: control opening means communicating with said crankcase; relief opening means communicating with the combustion chamber; control means operatively connected to the crankshaft for clearing and blocking each of said opening means as a predetermined function of the movement of the piston in the cylinder; said relief opening means being positioned with respect to said control opening means so as to be cleared by said control means when said control means blocks said control opening means; an injection nozzle opening into the combustion chamber; a fuel injection pump including: a housing defining an enclosed work space; membrane means partitioning said work space into a pulse chamber and a return chamber; a pump chamber arranged in said housing; a pump cylinder communicating with said pump chamber; a pump piston connected to said membrane means and being slideably mounted in said pump cylinder so as to be reciprocally movable through a piston stroke away from a start position and back to said start position; and, resilient biasing means for resiliently biasing said pump piston into said start position; fuel supply means connected to said pump chamber for supplying fuel to the latter; fuel metering line means for conducting the fuel from said pump chamber to the engine via said injection nozzle opening; a first connecting line connecting said pulse chamber to the crankcase through said control opening means for charging said pulse chamber with the pressure present in the crankcase for actuating said membrane means to develop an actuating force for driving said pump piston out of said start position against the force of said resilient biasing means and into said pump chamber; a second connecting line connecting said pulse chamber to the combustion chamber via said relief opening means when said relief opening means is cleared by said control means; and, check valve means mounted in said second connecting line so as to open in the direction of said combustion chamber to prevent high pressure developed in said combustion chamber because of incomplete or irregular combustion to reach said pulse chamber and to act on said membrane means.