Carburetor arrangement for an internal combustion engine

A hand-held, motor-driven chain saw comprising:

• a two-stroke internal combustion engine for generating a suction underpressure during operation;
• a housing for accommodating said engine therein;
• a tank mounted in close proximity to said engine in said housing for holding fuel and wherein overpressure develops in response to a warming of the fuel caused by the heat developed by the engine during said operation thereof and subsequent to said operation until said engine cools down;
• a carburetor connected to said fuel tank;
• inlet valve means mounted in said housing and adapted for communicating with the fuel tank to admit fuel into the carburetor;
• control means responsive to alternating changes in the pressure in the crankcase of the engine for pumping fuel from the fuel tank, said control means being mounted in said housing directly after said inlet valve means;
• venturi means formed in said housing whereat suction underpressure is developed during the operation of the engine;
• nozzle means for metering fuel into said venturi means;
• fuel conduit means formed in said housing for conducting fuel in a flow direction from said control means to said nozzle means;
• and,
• blocking valve means mounted in said housing and arranged in said conduit means between said control means and said nozzle means, said blocking valve means including:
• valve seat means disposed in surrounding relationship to said fuel conduit means;
• a valve body movably mounted in said housing for movement between a first position whereat said valve body is in contact engagement with said valve seat means to block the flow of fuel through said conduit means and a second position whereat said valve body is lifted from said valve seat means to allow passage of fuel through said conduit means to said nozzle means, said valve body being arranged with respect to said conduit means so as to be biased in said flow direction by fuel pressed against said valve body under the force developed by said overpressure in the tank so as to cause said valve body and said valve seat means to conjointly define a seal-tight blockage of said conduit means when said engine is at standstill and said pressure is present in said tank thereby preventing fuel from said tank from flooding the engine in response to said overpressure;
• actuating means mounted in said housing and responsive to said suction underpressure of the engine during the operation thereof for lifting said valve body from said valve seat to said second position in a direction opposite to said flow direction and said overpressure in said tank thereby permitting fuel to flow through said fuel conduit means to said nozzle means;
• and,
• ventilating valve means arranged in a wall of said tank for responding to an underpressure in said tank to open the same to the ambient and for responding to an overpressure in said tank for closing off the same with respect to the ambient;
• said ventilating valve means being configured as a check valve and including:
• a check valve housing mounted in said wall of said tank and defining a check valve seat;
• a valve closure piece movably mounted in said check valve housing for moving from a first position whereat said valve closure piece is pressed tightly against said check valve seat for sealing off said tank from the ambient in the presence of an overpressure condition therein to a second position spaced from said check valve seat for opening said tank to the ambient in the presence of an underpressure condition therein;
• and,
• a spring mounted in said check valve housing for resiliently biasing said valve closure piece against said check valve seat.

A hand-held, motor-driven chain saw comprising:

• a two-stroke internal combustion engine for generating a suction underpressure during operation;
• a housing for accommodating said engine therein;
• a fuel tank mounted, in close proximity to said engine in said housing for holding fuel and wherein overpressure develops in response to a warming of the fuel caused by the heat developed by the engine during said operation thereof and subsequent to said operation until said engine cools down;
• a carburetor connected to said fuel tank;
• inlet valve means mounted in said housing and adapted for communicating with the fuel tank to admit fuel into the carburetor;
• venturi means formed in said housing whereat suction underpressure is developed during the operation of the engine;
• nozzle means for metering fuel into said venturi means;
• said housing having first and second housing portions disposed on opposite sides of said venturi means;
• control means responsive to alternating changes in the pressure in the crankcase of the engine for pumping fuel from the fuel tank, said control means being mounted in said first housing portion of said housing next to said venturi means and directly after said inlet valve means;
• fuel conduit means formed in said housing for conducting fuel in a flow direction from said control means and around said venturi means to said nozzle means;
• and,
• blocking valve means mounted in said second housing portion of said housing next to said venturi means and arranged in said conduit means between said control means and said nozzle means, said blocking valve means including:
• valve seat means disposed in surrounding relationship to said fuel conduit means;
• a valve body movably mounted in said housing for movement between a first position whereat said valve body is in contact engagement with said valve seat means to block the flow of fuel through said conduit means and a second position whereat said valve body is lifted from said valve seat means to allow passage of fuel through said conduit means to said nozzle means, said valve body being arranged with respect to said conduit means so as to be biased in said flow direction by fuel pressed against said valve body under the force developed by said overpressure in the tank so as to cause said valve body and said valve seat means to conjointly define a seal-tight blockage of said conduit means when said engine is at standstill and said pressure is present in said tank thereby preventing fuel from said tank from flooding the engine in response to said overpressure;
• actuating means mounted in said housing and responsive to said suction underpressure of the engine during the operation thereof for lifting said valve body from said valve seat to said second position in a direction opposite to said flow direction and said overpressure in said tank thereby permitting fuel for flow through said fuel conduit means to said nozzle means;
• and,
• ventilating valve means arranged in a wall of said tank for responding to an underpressure in said tank to open the same to the ambient and for responding to an overpressure in said tank for closing off the same with respect to the ambient;
• said ventilating valve means being configured as a check valve and including:
• a check valve housing mounted in said wall of said tank and defining a check valve seat;
• a valve closure piece movably mounted in said check valve housing for moving from a first position whereat said valve closure piece is pressed tightly against said check valve seat for sealing off said tank from the ambient in the presence of an overpressure condition therein to a second position spaced from said check valve seat for opening said tank to the ambient in the presence of an underpressure condition therein;
• and,
• a spring mounted in said check valve housing for resiliently biasing said valve closure piece against said check valve seat.