Gas and liquid contact apparatus – Fluid distribution – Pumping
Reexamination Certificate
1999-07-23
2001-05-22
Chiesa, Richard L. (Department: 1724)
Gas and liquid contact apparatus
Fluid distribution
Pumping
C261S064100, C261S069200, C261SDIG006
Reexamination Certificate
active
06234456
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a diaphragm carburetor for an internal combustion engine, especially for a two-stroke engine having in a carburetor housing an intake channel for guiding combustion air into the internal combustion engine. The intake channel has a venturi section and upstream of the venturi section a throttle valve. A fuel-filled control chamber is provided which is connectable by an inlet valve operated by a control diaphragm to the fuel supply channel. A first fuel channel extends from the control chamber to a main outlet valve in the venturi section.
In hand-guided working tools such as motor chainsaws, cutters, trimmers etc., it is common to employ two-stroke engines as a drive means. In order to provide the two-stroke engine with the required fuel/air mixture, diaphragm carburetors are known which comprise in a carburetor housing an intake channel which supplies the combustion air into the internal combustion engine. The intake channel has a venturi section. Upstream of the venturi section a throttle valve is arranged with which the flow cross-section for the intake air can be adjusted as a function of the throttle actuation. The throttle valve cooperates with a full load stop which is unchangeable. Because of manufacturing and assembly tolerances, the flow cross-section for the combustion or intake air is not exactly identical; usually, considerable differences are observed, especially because of deviations of the throttle valve angle in the open position in the range of ±3°.
Furthermore, such a diaphragm carburetor has a fuel-filled control chamber which can be connected by a fuel inlet valve controlled by the control diaphragm to the fuel supply channel. A first fuel channel extends from the control chamber to a main outlet valve that is arranged within the venturi section of the intake channel. A second fuel channel extends from the control chamber to an idle valve which is arranged in the area of the throttle valve of the intake channel. Within the passage way to the main outlet valve as well as in the passage way to the idle valve, control valves in the form of adjusting screws having ends in the form of a valve cone are provided so that the fuel ratio for the respective load condition, i.e., idle condition or full load condition, can be adjusted to the desired &lgr; value. However, with this construction even minimal changes or manufacturing tolerances cause considerable fuel/air ratio changes which remain within the limits set by respective regulations, but the corresponding specifications can be reached only with very high manufacturing and adjusting expenditures. Due to the minimal flow cross-section of these screw valves, multiple disturbing influences are present, for example, due to temperature-depending viscosity changes of the fuel and the soiling of the valve so that a substantial change of the fuel/air mixture composition will result which affects the operational behavior of the combustion engine.
It is therefore an object of the present invention to provide a diaphragm carburetor for an internal combustion engine of the aforementioned kind in which in a simple manner with utmost precision the mixture composition of fuel and air can be adjusted so that a reduced band width of the &lgr; range for full load is achieved.
SUMMARY OF THE INVENTION
According to the present invention it is suggested that the cross-section for the fuel flow to the fuel inlet valve is fixed by at least one main throttle and that a plate valve arranged within the intake channel is acted upon by a lever which cooperates with an adjustable stop with which the flow cross-section for the intake air can be adjusted to a desired rich mixture limit and changed within a limited range in the direction of increasing the cross-section.
The essential advantages of the invention are that, by eliminating the control valve at the fuel side within the main passage way, a simple and inexpensive arrangement is provided and that temperature and soiling effects are minimized. In order to determine the constant fuel flow within the first fuel passage way, i.e., the main passage way, as exactly as possible, a main throttle is provided that is unchangeable (fixed). The lever connected to the plate valve in conjunction with the stop determines the rich mixture limit, i.e., the variable stop allows to adjust an increasing flow cross-section for the combustion air from the rich mixture limit in a direction toward a leaner mixture. Because of the fixed main throttle, the fuel-side adjustment remains at 100%.
According to one embodiment, the flow cross-section for the intake air is determined by the position of the throttle valve, i.e., the lever is connected to the shaft of throttle valve. In the alternative, the lever can also be connected to the shaft of a choke valve arranged upstream of the venturi section so that the flow cross-section for the intake air is determined by the position of the choke valve. The adjusting potential for the combustion air can thus be provided either at either one of the plate valves, i.e., the throttle valve or at the choke valve.
In order to provide a simple adjusting device with respect to manufacture and handling, it is expedient to provide the stop in the form of an adjusting screw that is threaded into a threaded bore of the carburetor housing. In known diaphragm carburetors in which the adjustment of the mixture is carried out with respect to the supplied amount of fuel, it is common to rotate the adjusting screw in a clockwise direction for making the mixture more lean. In order to provide the same kind of actuation with the inventive diaphragm carburetor, the direction of rotation of the adjusting screw should thus be set such that a counter clockwise rotation results in a reduction of the cross-section for the intake air. The adjusting range for the plate valve (choke valve or throttle valve) between a first position for a full load condition, i.e., a rich mixture limit, and an upper limit for the full load condition, i.e., a lean mixture limit, should be within a range of 85% for the rich mixture limit and 100% for the lean mixture limit provided for the intake flow cross-section. Between these positions lies the adjusting range for making the mixture more lean for output optimization or altitude adjustment. This corresponds to the rich mixture stop (the H screw), respectively, the lean mixture stop by limiter caps in known diaphragm carburetors. The pitch of the screw thread should be such that the deflection of the lever about the axis of rotation of the plate valve shaft to accomplish the entire adjusting stroke between the rich mixture limit and the lean mixture limit is provided by a rotation of the adjusting screw of approximately 270°.
REFERENCES:
patent: 3045605 (1962-07-01), Nutten et al.
patent: 3072390 (1963-01-01), Phillips
patent: 3231249 (1966-01-01), Kalert, Jr.
patent: 3275305 (1966-09-01), Nutten
patent: 3791632 (1974-02-01), Donovan
patent: 4104994 (1978-08-01), Phillips
patent: 5283013 (1994-02-01), Gerhardy
patent: 5441673 (1995-08-01), Gerhardy
patent: 5542405 (1996-08-01), Gerhardy
patent: 6059271 (2000-05-01), Gerhardy
Andreas Stihl AG & Co.
Chiesa Richard L.
Robert W. Becker & Associates
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