Fuel injection pump for a two-stroke engine

Claim 1

A fuel injection pump 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 crankcase wherein pressure is developed in response to the movement of the piston, the fuel injection pump comprising: a housing defining an enclosed work space; a membrane partitioning said work space into a pulse chamber and a return chamber; a pump chamber arranged in said housing; 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; a pump cylinder communicating with said pump chamber; a pump piston connected to said membrane and being slideably mounted in said cylinder so as to be reciprocally movable through a piston stroke away from a start position and back to said start position; a connecting line connecting said pulse chamber to the crankcase for charging said pulse chamber with the pressure present in the crankcase for actuating said membrane to develop an actuating force for driving said pump piston into said pump chamber to pump the fuel therein through said fuel metering line means and withdrawing said pump piston away from said pump chamber to draw in a fresh quantity of fuel from said fuel supply means; counterpressure means for generating a counterpressure in said return chamber for changing said piston stroke in dependence upon the rotational speed of the engine thereby changing the quantity of fuel pumped from said pump chamber; and, leaf spring means arranged in said return chamber for resiliently biasing said pump piston toward said start position.