Gas and liquid contact apparatus – Fluid distribution – Pumping
Reexamination Certificate
1996-02-09
2001-06-19
Chiesa, Richard L. (Department: 1724)
Gas and liquid contact apparatus
Fluid distribution
Pumping
C261S041500, C261SDIG006
Reexamination Certificate
active
06247681
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a carburetor for an internal combustion engine of a hand-held working tool, especially a diaphragm carburetor comprising a housing and having arranged therein a suction channel with a venturi section. Within the suction channel a throttle is pivotably supported. A control chamber connected with a main fuel channel and an idle channel to the suction channel. A bypass is provided via which, for starting the internal combustion engine, an additional amount of fuel/air mixture is introduced into the suction channel downstream of the throttle.
A diaphragm carburetor for an internal combustion engine is known having a carburetor housing comprising a suction channel with a venturi section and a pivotable throttle arranged in the suction channel. A fuel-filled control chamber is connected via a main fuel channel and an idle channel to the suction channel. In a further housing part connected to the carburetor housing an auxiliary channel is arranged through which during starting of the engine an additional amount of fuel/air mixture is introducible into the suction channel downstream of the throttle. In this embodiment the air supply channel and the fuel supply channel are guided within a mixing channel. At the end of the mixing channel a valve is arranged that opens or closes the access to a further channel which extends to the downstream side of the throttle within the suction channel.
The known arrangement is complicated in its construction and requires additional space external to the actual carburetor housing. Furthermore, a secure sealing at the end of the mixing channel is difficult to achieve so that for safety reasons two independently acting shut-off devices are provided which are arranged in series in the flow direction.
It is therefore an object of the present invention to improve a carburetor of the aforementioned kind such that the auxiliary channel is arranged within the carburetor housing and is inexpensive to manufacture and reliable in its function.
SUMMARY OF THE INVENTION
A carburetor for an internal combustion engine of a hand-held working tool according to the present invention is primarily characterized by:
A housing;
A suction channel with a venturi section arranged in the housing, the suction channel having an inlet and an outlet for allowing air flow therethrough;
A throttle connected in the suction channel so as to be pivotable;
A control chamber;
A main fuel channel connecting the suction channel and the control chamber;
An idle fuel channel connecting the suction channel and the control chamber;
A bypass, comprising an air supply line and a fuel supply line, for introducing an auxiliary fuel/air mixture during a starting operation of the internal combustion engine to a location of the suction channel downstream of the throttle in a direction of air flow; and
A closure means for separately closing off in a closed position the air supply line and the fuel supply line of the bypass so that simultaneously the fuel supply and air supply are shut off before formation of the auxiliary fuel/air mixture.
The bypass comprises preferably a parallel bore extending within the housing parallel to the suction channel and a first transverse bore connecting the suction channel and the parallel bore, wherein the first transverse bore opens into the suction channel downstream of the throttle.
Advantageously, the bypass comprises a second transverse bore connecting the suction channel and the parallel bore at a location upstream of the throttle.
Preferably, the carburetor comprises a third transverse bore, wherein the parallel bore extends perpendicularly through the third transverse bore and wherein the third transverse bore has a diameter that is greater than the diameter of the parallel bore.
Advantageously, the diameter of the parallel bore is 3 mm and the diameter of the third transverse bore is 4 mm.
In a preferred embodiment of the present invention the third transverse bore is a blind bore having an inner end wall and the parallel bore intercepts the third transverse bore near the inner end wall.
Preferably, the fuel supply line is connected to the control chamber and opens into the third transverse bore at the inner end wall.
The fuel supply line preferably comprises a throttle opening.
Advantageously, the throttle opening has a diameter of 0.3 mm.
In another embodiment of the present invention, the closure means is a piston positioned in the third transverse bore so as to be axially displaceable.
The piston preferably has a first end face proximal to the inner end wall for closing off the fuel supply line and an outer cylinder mantle surface for closing off the air supply line.
Advantageously, the first end face of the piston comprises a seal for sealingly contacting the inner end wall of the third transverse bore.
Advantageously, the carburetor further comprises an actuating rod, wherein the piston has a second end face distal to the inner end wall and wherein the actuating rod is connected to the second end face.
Expediently, the carburetor further comprises a spring acting on the piston for biasing the piston into the closed position so as to close the fuel supply line and the air supply line.
Advantageously, the carburetor further comprises a cap for closing off the third transverse bore, wherein the spring is a pressure coil spring supported at the cap and the pressure coil spring.
In yet another embodiment of the present invention, the carburetor further comprises a retaining device for retaining the closure means in an open position, in which the fuel supply line and the air supply line are open, until the starting operation is completed.
Preferably, the retaining device comprises a radial collar connected to the actuating rod and a trottle lever having a free end projecting into a travel path of the radial collar and being movable out of the travel path.
Advantageously, the radial collar comprises a frustoconical outer mantle surface facing away from the housing.
Preferably, the piston has a travel path of 3 to 7 mm between the open position and the closed position.
An especially simple and space-saving arrangement of the bypass is provided when the bypass is comprised of a parallel bore extending within the housing parallel to the suction channel and at least one transverse bore for connecting the parallel bore to the suction channel. This transverse bore opens into the suction channel downstream of the throttle. Expediently, the bypass comprises a second transverse bore which extends from the upstream end of the suction channel to the parallel bore. The parallel bore that forms the bypass extends perpendicularly to a third transverse bore having a diameter that is greater than the diameter of the parallel bore. In a preferred embodiment, the diameter of the parallel bore is preferably approximately 3 mm and the diameter of the third transverse bore is approximately 4 mm.
The third transverse bore is a blind bore. The parallel bore of the bypass intercepts the third transverse bore in the vicinity of the inner end wall of the third transverse bore. A fuel supply channel opens into the third transverse bore at the surface of the end wall. The fuel supply channel extends from the control chamber into the third transverse bore. Due to the design of the third transverse bore as a blind bore, its interception by the parallel bore of the bypass in the vicinity of the inner end wall, and the opening of the fuel supply channel in the area of this inner end wall, it is possible to close off with a single element the supply of fuel and air separately, i.e., before their mixing takes place. Preferably, the closure means for closing off the air supply and the fuel supply is a piston that is longitudinally displaceably guided within the third transverse bore. In the simplest manner, the closing of the fuel supply line and the air supply line is achieved by embodying the end face of the piston as a closure member for the fuel supply channel and by employing the mantle surface of the piston to close off the bore
Andreas Stihl AG & Co.
Chiesa Richard L.
Robert W. Becker & Associates
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