Patent Application
20170107947
The present disclosure relates generally to carburetors for use with internal combustion engines and, more specifically, to a carburetor with a fuel metering diaphragm.
Carburetors are devices that can be used to mix fuel and air to power combustion engines typically including gasoline powered internal combustion spark ignited engines. A carburetor may include a fuel metering system that helps to control the amount of fuel supplied to air flowing through a mixing passage or main bore of the carburetor for mixing the fuel with air and supplying the mixture to the engine. Some metering systems employ a diaphragm that oscillates or reciprocates during operation to open and close a metering valve admitting fuel to a chamber from which it is supplied to the passage for mixing with air. In use, the large number of cycles experienced by such a diaphragm which typically physically interacts with other components of the metering system such as a valve actuating lever, and continuous exposure to solvent containing fuels, can result in a harsh operating environment that causes wear, degradation and ultimately failure of the diaphragm. In a gasoline powered spark ignited internal combustion so-called small engine the diaphragm must fully open the valve when subjected to only a small pressure differential which is typically a maximum negative pressure of −0.9956 kPa or −0.1444 pounds per square inch and usually about −0.50 kPa or −0.0725 pounds per square inch (psi). This very small differential operating pressure also requires that the portion of the diaphragm within a fuel metering chamber be very flexible particularly since such diaphragm may have a surface area within the metering chamber in the range of about 0.5 square inch to 1.0 square inch.
A carburetor with a main bore or fuel and air mixing passage through a body may include a diaphragm defining part of a fuel metering chamber and movable to actuate the valve and with a flexible portion open to the fuel metering chamber and without a perforation through at least the portion of the diaphragm exposed to the fuel metering chamber. A diaphragm may include at least two convolutions providing an increased surface area within the fuel metering chamber compared to the surface area of a plane exposed to and covering the fuel metering chamber. The convolutions may increase the surface area by at least 20% and the diaphragm may be in the form of a bellows with at least two convolutions. The diaphragm may be made of one or more flexible sheets or foils of metal. The diaphragm may also be made in one piece of a flexible elastomer resistant to degradation and swelling when in continuous contact with liquid fuels.
The following detailed description of certain embodiments and best mode will be set forth with reference to the accompanying drawings, in which:
Referring in more detail to the drawings,
In operation, a demand for fuel at the engine increases air flow through the main bore 16, thus reducing fluid pressure in the metering chamber 18 and at the chamber side 28 of the diaphragm 22. A reference pressure in the reference chamber 24, such as atmospheric pressure, acting on the reference side 26 of the diaphragm 22, moves a portion of the diaphragm 22 toward the main body 20 in a direction that reduces the volume of the metering chamber 18 as fuel is delivered to the main bore 16. In at least some implementations, the diaphragm 22 engages a lever 32 that is coupled to the metering valve 30 and opens the metering valve 30 to allow fuel to flow from the fuel source 14 into the metering chamber 18 to replace the fuel delivered from the metering chamber 18 to the main bore 16. This increases the fluid pressure in the metering chamber 18, reversing the direction of movement of the diaphragm away from the carburetor main body 20 in a direction that increases the volume of the metering chamber 18. This diaphragm movement eliminates or reduces the force on the lever 32 so that the metering valve 30 may close against a valve seat 34, such as under the biasing force of a spring 36 acting on the lever 32 to yieldably bias the metering valve to its closed position. The valve closure causes the metering chamber pressure to decrease and begin a new metering cycle as long as there is a demand for fuel at the engine. The carburetor of
Referring to
In this implementation, the diaphragm 22 is formed from metal and includes more than one convolution 46. Inclusion of at least one convolution 46 makes the surface area of the exposed portion 44 of the flexible diaphragm 22 larger than a projected area of the exposed portion (e.g. large than the portion of an imaginary plane 48 extending between the cover 29 and main body 20 and exposed to the chambers 18, 24). The convolutions 46 increase the flexibility of the diaphragm and increase the range of movement of the diaphragm 22. The larger the convolution(s) 46 (i.e., the greater the surface area of the convolutions), the greater the overall allowable diaphragm movement is.
In at least some implementations, each convolution 46 is defined by curved, bent or otherwise nonlinear portions of the diaphragm 22, that define generally concave or convex sections of the diaphragm. Each convolution 46 may include first and second sections 50, 52 of the diaphragm on opposite sides of and leading to a bend or bight 53. The convolutions 46 thus form concave or convex portions of the diaphragm 22, and the convolutions may be circumferentially complete and oriented about an axis 54 of the diaphragm 22 such that the concave or convex portions are annular. In at least some implementations, multiple convolutions 46 may be provided with both concave and convex convolutions oriented or facing generally axially (e.g. the first and second sections 50, 52—or a centerline between them—may be oriented generally parallel to the axis 54 of the diaphragm, plus or minus forty-five degrees).
In the implementation shown in
A contact portion 56 of diaphragm 22 makes physical contact with other metering system components to actuate the metering valve 30. In the illustrated embodiment, contact portion 56 is part of a boss or raised portion 58 of the diaphragm 22 aligned with an end of the lever 32 and arranged to actuate the lever. The contact portion 56 may be formed in the same piece of material as the remainder of the diaphragm 22, providing a diaphragm 22 with convolutions 46 and a contact portion 56 that are all defined in the same continuous piece of material. In the example shown, the convolutions 46 are defined in a radially outermost area of the exposed portion 44 adjacent to the diaphragm periphery 38 trapped between the cover 29 and body 20, and the contact portion 56 is located radially inwardly spaced from the convolutions 46. Hence, the convolutions 46 are provided where the diaphragm 22 is stiffest (adjacent to the point of connection to the carburetor) to increase the responsiveness and range of motion of the diaphragm 22.
An alternate diaphragm 122 is shown in
In this implementation, a first piece 160 of the diaphragm 122 may be trapped about its periphery 138 between the cover 129 and main body 120, as described above with regard to diaphragm 22 and carburetor 10. The first piece 160 may be annular, include the trapped periphery 138 and extend radially inwardly to an inner edge 162. A second piece 164 of the diaphragm 122 may be coupled to the first piece 160 at a location radially inwardly of the periphery 138 of the first piece 160. In this example, the second piece 164 is also annular and includes an inner edge 166, that is joined at or adjacent to the inner edge 162 of the first piece 160, and extends radially outwardly to an outer edge 168. The second piece 164 is smaller (has smaller outer diameter) than the first piece 160 and the outer edge 168 of the second piece 164 is radially spaced from the cover 129 or main body 120 and arranged within the space between them. The second piece 164 may include a bent or inclined portion 170 near the inner edge 166 so that a main portion of the second piece 164 is axially spaced from the first piece 160, at least in an at rest position as shown in
When so arranged, the third piece 172 radially overlies the inner edges 162, 166 of the first and second pieces 160, 164. With the second piece 164 also welded or otherwise sealed to the first piece 160, the diaphragm 122 is without any openings or penetrations that extend through it (e.g. from the reference chamber 124 to the metering chamber 118), at least within the portion of the diaphragm 122 not trapped between the cover 129 and main body 120. Further, the connection between the three diaphragm pieces 160, 166, 172 provides two convolutions 146 which are shown as being oriented radially relative to the axis 154 of the diaphragm 122. A first convolution 146, defined between the first and second pieces 160, 164, faces radially outwardly (is convex relative to the axis 154). A second convolution 146, defined between the second and third pieces 164, 172, faces radially inwardly (is concave relative to the axis 154). Like the first and second sections 50, 52 in diaphragm 22, bends or inclined portions on either side of the points of connection between the pieces 160, 164, 172 of diaphragm 122 define the convolutions. In diaphragm 122, at least a majority of the second piece 164 may extend generally parallel to the first piece 160 plus or minus forty-five degrees, and at least a majority of the third piece 172 may extend generally parallel to a majority of the second piece 164 plus or minus forty-five degrees. This provides an accordion type or pleated construction of the diaphragm 122 that permits axial movement or flexing of the diaphragm in response to a pressure differential across the diaphragm.
The pieces 160, 164, 172 may be formed from the same material, or different materials as desired. In one example, each piece is formed from the same type of metal, such as a stainless steel. Further, the diaphragm pieces 160, 164, 172 may be sealed together in any desired manner, such as by laser welding, an adhesive, solder, or the like. While three diaphragm pieces are shown defining two convolutions 146, the diaphragm 122 may be formed from more than three pieces and more than two convolutions may be provided. Further, the diaphragm material is preferably stiff enough to prevent the pieces 160, 164, 172 from collapsing onto themselves under their own weight, so that they remain separate, such as is shown in
In this example, the radial overlap provided by the interconnected diaphragm pieces significantly increases the surface area of the exposed portion 144 of the diaphragm 122, which is exposed to the pressure within the metering chamber 118 and the reference chamber 124. The first and second pieces 160, 164 define a cavity 176 at their inner edges 162, 166 and the boss defining the contact portion 156 extends away from the cavity 176. The cavity 176 is exposed to the pressure within the reference chamber 124, as is the exposed portion (i.e. the effective area) of the first piece 160, which is the portion of the first piece 160 that is not overlapped by the cover 129 and main body 120 and extending to the inner edge 162. Likewise, the pressure within the metering chamber 118 acts on the combined surface area of the third piece 172 and the portion of the first piece 160 exposed to the metering chamber 118. In at least some implementations, the effective surface area of the exposed portion 144 of the diaphragm 122 may be about 20% or more greater than the surface area of a plane 148 exposed to the chambers 118, 124 and extending between the cover 129 and main body 120. Thus, the forces on the diaphragm 122 may be greater than if the diaphragm 122 were planar or essentially planar, and the diaphragm 122 may be more responsive to pressures acting on it. That is, the diaphragm 122 may be flexed or moved at a lower differential pressure, and it may move or flex more under a pressure differential of a given magnitude. In at least some implementations, the second piece 164 radially overlaps at least 50% of the first piece 160, and has a surface area that is 40% to 90% as large as the exposed area of the plane 148.
Another diaphragm 322 is shown in
The diaphragms 422 and 522 shown in
The diaphragm 522 shown in
In at least some implementations, the diaphragms shown may all be formed of metal. The metal may be inert to the fuel flowing in the carburetor, or otherwise suitable for use in the fuel. One benefit to this is that the metal material will not swell or crack like some polymeric or composite materials used for diaphragms. The metal material may be relatively thin so that it is flexible under the pressures experienced in use of a carburetor, but strong enough to maintain the convolutions and provide relatively controlled diaphragm movement for repeatable and reliable actuation of the metering valve. The diaphragms may be formed from a metal sheet or foil between 0.1000 mm and 0.0127 mm thick. Representative materials include plastic, stainless steel, nickel, copper, aluminum, titanium, cobalt, cobalt-nickel, alloys thereof, and elastomers such as polyacetal, polyester, polyetheretherketone (PEEK), nylon, UHMW polyethylene. Further, the diaphragm may be formed by any suitable process, such as by stamping, electroforming or hydroforming.
In addition to being suitable for use in various fuels, the metal diaphragms are less sensitive to temperature changes in operation (e.g. retain their flexibility over wider range of temperatures) and dissipate heat more quickly compared to diaphragms made from rubber, polymers or composite materials. The heat conduction properties of metal can also be utilized to warm fuel in the metering chamber facilitate cold engine operation, such as by coupling a heating element or heat source with the diaphragm. Further, the metal diaphragms do not need backing plates commonly used with rubber, polymeric or composite diaphragms for rigidity in the area of the metering valve lever, and/or to prevent abrasion of the diaphragm material by the lever. The backing plates are commonly secured with rivets received within a through hole formed in the diaphragm, which provides a potential leak path. Further, the backing plates (usually including washers) and the rivet add complexity and cost associated with multiple parts, including increased difficulty in handling and assembly, and also issues of tolerance control as each component has its own tolerance variations that contribute to a larger overall assembly tolerance (often referred to as tolerance stack-up). Accordingly, the thin, metal diaphragms which need not include backing plates and related components, can be more dimensionally consistent across a production run of diaphragms and a production run of carburetors.
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 Patent Application Ser. No. 62/243,861, filed on Oct. 20, 2015, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62243861 | Oct 2015 | US |
