Patent Application
20140261329
The present disclosure relates generally to a carburetor for a stratified scavenged engine.
A carburetor is used to provide a combustible charge or mixture of fuel and air to an internal combustion engine. The carburetor meters liquid fuel for mixing with air to adjust a fuel-to-air ratio, according to varying engine requirements during engine startup, idle, steady-state operation, and changes in load and altitude.
A diaphragm-type carburetor is typically used with small two-stroke internal combustion engines commonly used in hand-held power tools such as chain saws, weed trimmers, leaf blowers, and the like. In the diaphragm carburetor, a body defines a mixing passage with an air inlet and a downstream fuel-and-air mixture outlet. A throttle valve is disposed in the fuel-and-air mixing passage downstream of the air inlet for controlling delivery of a primary fuel-and-air mixture to the engine. A typical diaphragm fuel metering system includes a metering valve, and a flexible diaphragm carried by the body and partially defining and separating a fuel chamber from the atmosphere. The metering valve and diaphragm control fuel flow from the diaphragm fuel pump to the fuel chamber for delivery from the fuel chamber to the fuel-and-air mixing passage.
A scavenging-type of diaphragm carburetor may be used with some engines to reduce scavenging losses or blow-through of some of the fuel-and-air mixture out of engine exhaust ports. A scavenging carburetor is known to have a fuel-and-air mixture passage and a separate scavenging air passage that both communicate at one end of the carburetor with a clean air source at atmospheric pressure, such as an air filter.
In at least some implementations, a fuel and air supply device for an engine includes a carburetor having a fuel metering assembly including a fuel metering diaphragm that defines at least part of a reference chamber, a scavenging air assembly including an air passage and an air valve within the passage and moveable to alter air flow through the air passage, and a reference passage. The reference passage communicates at one end with the air passage at a location upstream of the air valve and at its other end with the reference chamber to provide a reference air signal through the reference passage to the reference chamber. The reference air signal, in at least some implementations, is taken from a location downstream of an air filter and any other components so it is representative of the air flow at the air valve and accounts for restrictions to air flow caused upstream of the air valve.
In at least some implementations, a fuel and air supply device for an engine includes a fuel and air mixing passage from which a fuel and air mixture is delivered to an engine, a fuel metering assembly including a fuel metering diaphragm that defines at least part of a reference chamber, a scavenging air assembly including an air passage through which a supply of air is provided to an engine, a filter through which air flows to the air passage, and a reference passage. The reference passage communicates at one end with a location downstream of the filter at its other end with the reference chamber. This provides a reference air signal to the reference chamber that accounts for restrictions to airflow caused by the filter.
The following detailed description of preferred embodiments and best mode will be set forth with reference to the accompanying drawings, in which:
Referring in more detail to the drawings,
The carburetor 10 may include a fuel-and-air mixing passage 26 defined by the body 24 into which fuel is supplied by one or more fuel circuits and where the fuel is mixed with air flowing from the filter 14 through the passage 26. The fuel and air mixture flows past a butterfly-type throttle valve 32 disposed in or in communication with the fuel and air mixing passage 26 and into the crankcase of the engine. A choke valve 33 may be provided upstream of the throttle valve 32 in another location within or upstream of the fuel and air mixing passage 26.
The carburetor may include a fuel pump assembly 37 that supplies fuel to a fuel metering assembly 28, as is known in the art. Fuel flows from the fuel pump assembly 37 into a fuel metering chamber 38 of the fuel metering system 28 through a valve (not shown) that is opened and closed by flexing or displacement of a fuel metering diaphragm 40. The fuel metering chamber 38 is defined at least in part between a first side of the diaphragm 40 and the carburetor body 24, and a reference chamber 42 is defined between an opposite side of the diaphragm 40 and a cover plate 43 attached to the body. A pressure within the reference chamber 42 acts on the diaphragm and helps to ensure a relatively constant pressure of fuel in the fuel metering chamber. In use, when the operating engine is idling (and the throttle valve 32 is substantially closed), fuel is supplied from the metering chamber 28 to the mixing passage 26 through idle or low speed ports 45, and when the throttle valve 32 is substantially opened (and thus the engine is operating at high speed and/or load conditions), fuel is supplied to the mixing passage 26 primarily through the main or high speed fuel nozzle 46.
To account for restrictions to the air flowing to the carburetor, such as may be caused by the air filter 14, the reference chamber 42 of the fuel metering assembly 28 is communicated with a location downstream of the air filter 14. In at least some implementations, the reference chamber 42 may be communicated with a location downstream of the air filter 14 and upstream of the air valve 16. In this way, a restriction and pressure drop that may be caused by the air filter 14, particularly as the air filter becomes increasingly clogged or dirty in use, can be communicated with the fuel metering assembly 28 to alter the operation of the fuel metering assembly 28 as a function of the air flow through the air filter 14. Therefore, the carburetor 10 can provide a fuel and air mixture to the engine that has a desired air-fuel ratio even as the filter 14 becomes dirtier over time and as the air flow rate through the filter changes.
As shown in
Certain representative examples of reference passages will be described below with regard to other carburetors. The carburetors described below may be of the same general construction as that previously described, and so the description of the carburetors that follows generally will only focus on the differences in the carburetors and will not include a full description of their construction. Further, the same reference numbers may be used among the carburetors where the components are the same or similar, for ease and clarity of description. However, use of a different reference number for similar components among different carburetors does not mean that the exact same component cannot be used in the different carburetors.
Of course, more than one reference passage may be used in a carburetor, if desired, where each passage may be internal, external or a combination of the two. The three passages 88, 94, 96 could be used together, in any combination of two, or only one might be used in a given carburetor. When multiple reference passages are used, they may communicate at one or both ends independently or conjointly with the air passage or reference passage. That is, the reference passages may be independent from each other, or they may be communicated with each other, i.e., joined or merged between the air passage and reference chamber.
The reference passage(s) in any implementation may communicate with the air passage 18 at any desired location, which may open to any axial, circumferential and radial location of the air passage that is desired. For example, the reference passage 88 opens into the air passage 18 at a location that is axially inwardly spaced and circumferentially spaced in the air passage 18 relative to the location at which the reference passage 96 opens into the air passage 18 (where the axis of the air passage 18 is used as the reference for the terms radial, axial and circumferential). And the reference passage 94 includes the inlet tube 92 so its location of communication with the air passage 18 is radially inwardly spaced relative to the other reference passages 88, 94 which open to the air passage 18 via ports in the sidewall of the air passage body 84.
The various reference passage arrangements may facilitate routing the reference passages from the air passage 18 to the reference chamber, and/or could be used to tune or synchronize phasing of the signal provided through the reference passage(s) to the reference chamber. The air flow rate and timing and magnitude of engine pressure pulses can vary at different locations within the air passage so the system can be tuned for a desired performance during at least some of the engine operating conditions. Further, the length of the reference passage(s), number of turns, radius or sharpness of the turns, material of the passage(s), direction that an inlet of the reference passage(s) is facing (e.g. an inlet tube may be oriented and/or bent so that its inlet is facing in any desired direction such as into or away from the air flow, or any angle in between), and still other factors may be calibrated to provide a desired reference signal to the reference chamber. And the reference pressure signal may be timed or synchronized to provide a desired performance during at least some engine operating conditions. To provide further control, a valve may be provided to selectively close off one or more reference passages where more than one reference passage is provided. The valve could be electrically driven and controlled, with one example being a solenoid valve. This may enhance control of the pressure within the reference chamber. If desired, a calibrated vent/bleed opening may be provided through the cover 43 to communicate the reference chamber with the atmosphere and that may provide a controlled attenuation of the reference signal pressure.
Next, referring again to
While the forms of the invention herein disclosed constitute presently preferred embodiments, many others are possible. It is not intended herein to mention all the possible equivalent forms or ramifications of the invention. It is understood that the terms used herein are merely descriptive, rather than limiting, and that various changes may be made without departing from the spirit or scope of the invention.
This application claims the benefit of U.S. Provisional Application No. 61/783,024 filed Mar. 14, 2013, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61783024 | Mar 2013 | US |
