Patent Application
20060151893
Applicants claim priority of Japanese Application Ser. No. 2005-070771 filed on Mar. 14, 2005 and Japanese Application Ser. No. 2005-003355 filed on Jan. 11, 2005.
The present invention relates generally to a carburetor for a combustion engine and more particularly to a rotary carburetor.
Known rotary type carburetors are commonly used for small, two stroke combustion engines applied to applications such as handheld chainsaws, leaf blowers, hedge trimmers, and the like. A rotary throttle valve of the carburetor has a generally cylindrical throttle received rotatably in a cylindrical cavity of a body that intersects a fuel-and-air mixing passage extending through the body. The rotary throttle valve rotates about an axis and, via a cam interface between the body and the cylindrical throttle, is also operatively moveable axially within the cylindrical cavity. The axial position of the cylindrical throttle is thus dependent upon the rotational angular placement of the throttle valve between a closed or idle position and a wide open throttle, WOT, position. A through-bore extends transversely through the cylindrical throttle of the rotary throttle valve and variably aligns generally longitudinally with the fuel-and-air mixing passage. The through-bore extends substantially perpendicular to the rotary axis and aligns so that when the carburetor is in the WOT position the through-bore is in substantially full communication with the fuel-and-air mixing passage, and when the through-bore is substantially misaligned or communicating minimally with the mixing passage the rotary throttle valve is either closed or in the idle position.
A fuel feed tube disposed concentrically to the rotary axis projects upward from the body and into the through-bore of the cylindrical throttle to an open distal end. An idle adjustment needle is fixedly attached to and projects downward from the cylindrical throttle, into the through-bore, and through the open distal end of the fuel feed tube. An orifice or jet for flowing liquid fuel into the through-bore communicates through a wall of the fuel feed tube and variably aligns axially with the idle fuel adjustment needle in the tube thereby varying the flow cross section of the orifice. Because the rotating cylindrical throttle is cammed, it moves axially during rotation carrying the idle fuel adjustment needle with it as the fuel feed tube and orifice remain stationary. The flow cross section of the orifice generally increases as the throttle valve moves toward the WOT position.
The idle fuel adjustment needle is threaded to the cylindrical throttle enabling adjustment of the quantity of liquid fuel entering the through-bore generally at idle operating conditions of the engine. When the idle fuel adjustment needle is threaded further into the cylindrical throttle more of the orifice is obstructed thus the flow of liquid fuel through the orifice and into the through-bore is reduced. During engine high speed operation or WOT, the idle fuel adjustment needle has little to no effect on fuel flow through the orifice. Instead, a separate high speed fuel adjustment needle is utilized. The high speed fuel adjustment needle threads into the body of the carburetor to adjustably obstruct a primary fuel feed passage in the body that flows liquid fuel to the fuel feed tube. By threading the high speed fuel adjustment needle further into the body, more of the passage is obstructed and less fuel flows through the orifice of the fuel feed tube at high engine speeds.
During manufacturing assembly of the rotary carburetor, and presuming the valve axis is vertical for purposes of explanation, the cylindrical cavity is typically opened upward for receipt of the rotary throttle and is aligned and supported axially between a bottom of the cylindrical cavity carried by the body and a top cover fastened to the body. A hollow shaft of the rotary throttle disposed concentrically to the rotary axis projects rigidly from the throttle and through the cover to engage a throttle lever having a hole for access to the idle fuel adjustment needle located inside the shaft. Unfortunately, access to the high speed adjustment needle must be provided on the side of the carburetor body and not the top like the idle adjustment needle because the top is generally congested with the cover, throttle lever and cam mechanism of the carburetor. Moreover, the fuel passage leading to the fuel nozzle is located centrally in the carburetor main body, and the high speed adjustment needle must extend into the fuel passage in an axially moveable manner with respect to the passage.
Therefore, when conducting the idle and high speed calibration and operation tests of the carburetor in the assembly line or at the time of servicing, the adjustment must be conducted from two different directions, and this inconveniently complicates the adjustment work. Furthermore, when the carburetor is mounted on the engine, it is necessary to provide access for adjustment of the carburetor from two different directions and locations. This restricts the layout of other auxiliary equipment and component parts.
A versatile rotary carburetor has an idle adjustment needle, a high speed adjustment needle, and preferably an air bypass screw mounted for adjustment externally of the carburetor and that are substantially parallel to one-another and accessible for adjustment from a common direction. The idle adjustment needle preferably threads adjustably into a cylindrical throttle projecting outward from the external surface. The cylindrical throttle is rotatable about and movable along an axis in a cylindrical cavity of the body. The cylindrical cavity intersects a fuel-and-air mixing passage in the body that delivers a controlled mixture of fuel and air to the running engine. A primary fuel feed tube disposed concentrically to the rotary axis projects into a through-bore in the cylindrical throttle which is orientated to adjustably align to the mixing passage as the cylindrical throttle rotates. The idle adjustment needle projects axially into the primary fuel feed tube for variably obstructing an orifice in a cylindrical wall of the tube that generally communicates with the through-bore for delivering liquid fuel to the mixing passage. The cylindrical throttle is preferably cammed to move axially as the throttle rotates thereby moving the idle adjustment needle in and out of the fuel feed tube and varying the flow cross section of the orifice.
The high speed adjustment needle is preferably threaded to the body for adjustably intersecting and obstructing a fuel passage in the body that communicates between a fuel source and the fuel feed tube for the flow of liquid fuel into the mixing passage. Preferably, the air bypass screw threads into the body for adjustably intersecting and obstructing an air bypass passage in the body communicating with the mixing passage at both ends and generally bypassing the rotary throttle valve for adjustable air flow into the mixing passage generally downstream of the rotary throttle valve during engine idling.
Preferably, the body has a base portion that carries an external surface and the mixing passage, and has an opposite face that sealably attaches to a fuel metering chamber assembly that supplies liquid fuel at a controlled pressure to the fuel feed tube. The fuel metering chamber assembly is preferably constructed to be removed from the base portion as a single unit, and when removed, exposes the cylindrical cavity that is open through the face of the base portion for receipt of the throttle during assembly. Preferably, the fuel feed tube is attached rigidly to the fuel metering chamber assembly or is otherwise supported by and is removable from the throttle when the fuel metering chamberr assembly is detached from the base portion of the body.
Objects, features and advantages of this invention include a carburetor with multiple adjustments that are all adjustable from a single direction improving packaging versatility for an engine application. Other advantages include simplified manufacturing assembly, improved work efficiency when adjusting fuel and air flow through the carburetor, and easy disassembly for cleaning and maintenance of internal components such as the fuel feed tube while protecting and making other components less susceptible to damage. The carburetor is of relatively simple design, economical manufacture and assembly robust, reliable, durable and in service has a long useful life.
These and other objects, features and advantages of this invention will be apparent from the following detailed description, appended claims, and accompanying drawings in which:
As best illustrated in
The main body 24 also has an external bottom surface 30 receiving a fuel metering chamber assembly 32, a front end 34 with an inlet opening of the mixing passage 22, an opposite rear end 36 with an outlet opening of the mixing passage 22, and a flanking side 38 spanning horizontally between the front and rear ends 34, 36 and vertically between the top and bottom surfaces 26, 30. Preferably, the flanking side 38 is generally carried by a fuel pump assembly 40 for delivering pressurized fuel to the metering chamber assembly 32, and the rear end 36 of the main body 24 mounts to a combustion engine (not shown).
The mixing passage 22 is divided into upstream and downstream regions 42, 44 by the intersection of the throttle valve 28 received in a cylindrical cavity 48 carried by a base portion 58 of the body 24. A cylindrical throttle or barrel 46 of the rotary throttle valve 28 is received in the cylindrical cavity 48 for rotation about, and axial movement along, an axis 50 disposed substantially perpendicular to the mixing passage 22. A through-bore 52 extends laterally through the cylindrical throttle 46 and, dependent upon the rotational angle, adjustably aligns generally longitudinally to the mixing passage 22 between a closed position that substantially isolates the upstream region 42 from the downstream region 44, and a wide open throttle position that provides maximum communication between the regions through the through-bore 52.
The cylindrical throttle 46 preferably has a relatively large diameter cylinder base member 54 carrying the through-bore 52 and a relatively small diameter coaxial and substantially hollow shaft or stem 56 that projects through and outward from the top surface 26. The shaft 56 is preferably unitary to, or formed in one piece with, the base member 54 and attaches to a throttle lever 60 of the rotary throttle valve 28 at a distal end located externally from the body 24. A connecting member 62 is preferably journalled for rotation to a distal end of the lever 60 disposed radially outward from the shaft 56 for engagement to an end of a linkage or wire of a Bowden cable 64 for remote control of the rotary throttle valve 28.
The lever 60 has a hole 63 concentric with the axis 50 providing access to a preferably slotted head of a fuel idle adjustment needle 65 by a tool 67 such as a screwdriver. The idle adjustment needle 65 is preferably threaded to the inside of the hollow shaft 56 and projects downward along the axis 50 and transversely into the through-bore 52 of the throttle 46. An open distal end of a fuel feed tube 69 receives a distal end or tip of the idle adjustment needle 65 and projects upward along the axis and transversely into the through-bore 52. The fuel feed tube 69 receives liquid fuel from the fuel metering chamber assembly 32 and expels the fuel into the through-bore through a fuel jet or orifice 71 located in the cylindrical wall of fuel feed tube 69, and being adjustably and variably obstructed by the internal idle adjustment needle 65.
Preferably, the rotary throttle valve 28 is biased closed by at least a coiled compression spring 66 disposed about the shaft 56 and compressed axially between an upper underside 68 of the machined base portion 58 of the body 24 and the base member 54 of the cylindrical throttle 46. A cam interface 70 located between a distal, contoured or ramped end 61 of the base member 54 of the cylindrical throttle 46 and a ramped bottom face 72 of the cylindrical cavity 48 that is carried by the body 24, and in conjunction with the axial force of the spring 66, urges the rotary throttle valve 28 toward the closed or idle position. The rotary throttle valve 28 rotates preferably toward the open position and moves axially upward against the biasing force of the spring 66 when actuator wire of the Bowden cable 64 is pulled, and the valve automatically rotates and moves axially downward toward the biased closed position when the Bowden cable is released under the return force of the spring 66 and the cam interface 70. Because the cylindrical throttle 46 is preferably cammed to move axially as the throttle rotates, the idle adjustment needle 65 also moves axially in and out of the fuel feed tube 69 as the rotary throttle valve 28 rotates. Hence, the idle adjustment needle 100 variably obstructs an orifice 71 in the cylindrical wall of the tube 69 that generally communicates with the through-bore 52 for delivering liquid fuel to the mixing passage 22.
As best illustrated in
As best illustrated in
The fuel metering chamber assembly 32 and the fuel pump assembly 40 are generally integrated into the main body 24 of the rotary carburetor 20, are of layered construction, and are disposed generally perpendicular to one another. The carburetor 20 receives liquid fuel preferably from a fuel source such as an on-board fuel tank of an engine-driven apparatus (not shown) and through a barbed connector 78 projecting downward from a side plate 80 of the pump assembly 40 that carries the flanking side 38 of the main body 24. An internal face 82 of the side plate 80 generally disposed opposite the flanking side 38 faces a dry side 84 of a resiliently flexible pump diaphragm 86 having a peripheral edge 88 sealed between an outward face 90 of the base portion 58 and the internal face 82 of the side or flanking plate 80 of the body 24. A pulsating pressure chamber 92 is defined between the internal face 82 of the side plate 80 and the dry side 84 of the diaphragm 86 and communicates typically with a crankcase of the combustion engine (not shown). A pump chamber 94 is defined between an opposite wet side 96 of the pump diaphragm 86 and the outward face 90 of the base portion 58 of the main body 24.
From the pump chamber 94, the pump assembly 40 flows pressurized liquid fuel through a fuel channel 98 in the base portion 58 of the main body 24 and to a metering chamber 98 of the fuel metering chamber assembly 32. The fuel metering chamber assembly 32 has a resiliently flexible, and preferably convoluted, metering diaphragm 100 separating a fuel metering chamber 98 from at atmospheric or reference chamber 114 vented preferably to the atmosphere. The metering diaphragm 100 is generally received between and sealed along a peripheral edge 102 to an external bottom plate 104 of the main body 24 that preferably carries the bottom surface 30, and a mid plate 106 of the main body 24 engaged sealably to the base portion 58. Preferably, gaskets or O-rings 108 provide the necessary sealing between a downward face 110 of the base portion 58 and an upward face 112 of the mid plate 84. The reference chamber 114 of the fuel metering chamber assembly 32 is defined between an opposite dry side 116 of the metering diaphragm 100 and an upward face 118 of the bottom plate 104, and the metering chamber 98 is defined between a wet side 120 of the metering diaphragm 100 and an opposite downward face 122 of the mid plate 106.
A manual prime or purge pump with a flexible bulb 124 of the fuel metering chamber assembly 32 operates in a manner commonly known in the art and has a two-way umbrella valve 126. A peripheral edge 128 of the purge bulb 124 engages sealably between the downward bottom surface 30 of the bottom plate 104 of the main body 24 and a bottom bracket 130.
In operation with the engine running, pressure pulses from the crankcase of the engine are received in the pressure chamber 92 of the pump assembly 40 causing the pump diaphragm 86 to flex into and out of the pressure chamber 92. As the diaphragm 86 flexes into the pressure chamber 92 fuel flows from the remote fuel tank or fuel source, through the connector 78 and corresponding passage 126 and into the expanding pump chamber 94. The passage 126 thereby provides fluid communication between the side plate 80 and the base portion 58 of the body 24 and is interposed by an inlet check valve (not shown) that allows fuel flow into the pump chamber 94 and prevents the back-flow of fuel into the fuel tank. Preferably, the check valve is generally located between the side plate 80 and the base portion 58.
As the pump diaphragm 86 flexes back toward the pump chamber 94 with increasing pressure in the crankcase, the volume of the pump chamber 94 decreases causing displaced fuel to flow through an outlet check valve (not shown) that is generally in a fuel channel 132 that intermittently communicates with the metering chamber 98 through a fuel regulating or metering valve 134 that closes when a sufficient fuel pressure or fuel volume is reached in the metering chamber 98.
As best illustrated in
The regulating valve 134 has an elongated arm 140 having a first end being in riding contact with a center projection 141 of the metering diaphragm 100 and a second end that carries a valve head 142 for sealing against an annular valve seat 144 supported by the cylindrical shoulder 138 of the mid plate 106 and generally communicating with the fuel channel 132 when the valve is open. The valve head 142 is normally biased against the valve seat 144 by a compression spring 146 compressed between the downward face 122 of the mid plate 106 and the pivoting arm 140 at a point preferably located between the first end and a pin 148 fixed to the mid plate 106 and about which the arm 140 pivots. When the regulating valve is open and fuel flows through the fuel channel 132 and into the metering chamber 98, the first end of the arm 140 that is urged upon the diaphragm by the spring 146, lowers with the downward flex of the metering diaphragm 100. This causes the opposite second end to move or pivot upward carrying the valve head 142 until it releasably seals against the valve seat 144 thereby placing the regulating valve 134 in a closed position. The regulating valve 134 remains closed and resists the force of the fuel pressure produced by the fuel pump assembly 40 until fuel exiting the metering chamber 98 reduces chamber pressure causing the pressure in the reference chamber 114 to exceed the pressure in the metering chamber 98. Once exceeded, (i.e. a sufficient differential pressure is created across the metering diaphragm) the metering diaphragm 100 flexes into the metering chamber 98 against any residual biasing force of the extended compression spring 146.
As best illustrated in
As best shown in
As shown in
The short fasteners 170 preferably include a head 176 and threaded shank 178 having a length such that upon fastening the mid plate 106 and bottom plate 104 together, the heads 176 engage the bracket 130 and the threaded shanks 178 are threaded within the threaded blind bores 172 of the mid plate 106, and preferably terminate therein. Accordingly, the short fasteners 170 preferably have a length equal to or less than the stacked height of the assembly 32. Thus, the bottom and mid plates 104, 106 can be attached to one another via the fasteners 170 independent from and without interfering with attachment of the fuel metering chamber assembly 32 to the air-fuel mixing or base portion 58 of the main body 24. Upon attaching the bottom and mid plates 104, 106 to one another via the short fasteners 170, the metering chamber 98 and atmospheric chamber 114 are substantially sealed by the force produced by the short fasteners 170 to prevent entry of contamination therein.
As shown in
The long fasteners 180 have a head 186 and threaded shank 188 with a length such that upon locating the shanks 188 through the aligned through-openings 182, 184, the heads 186 engage the bracket 130 and the threaded shanks 188 extend beyond the mid plate 106 for threaded receipt in threaded blind bores 190 in the base portion 58 of the main body 24. Accordingly, the shanks 188 of the long fasteners 180 preferably have a length greater than the stacked height of the metering chamber assembly 32. As such, the fuel metering chamber assembly 32 can be attached to and removed from the base portion 58 without removing the short fasteners 170 attaching the mid and bottom plates 106, 104 to one another. It should be recognized that the long fasteners 180 could have a length equal to or less than the stacked height of the assembly 32 if a counterbore (not shown) were formed in the bottom plate 104 for receipt of the heads 186 of the fasteners 180 therein. In such a case, the bracket 130 could be fastened to the bottom plate 104 via additional fasteners, if desired.
To facilitate removal of the correct fasteners, 170, 180, preferably the fasteners have head configurations distinguishable from one another. For example, the short fasteners 170 are represented here as pan-head screws, while the long fasteners 180 are represented as hexagonal socket head cap screws.
Accordingly and as illustrated in
As best illustrated in
Moreover, during manufacturing assembly, insertion of the idle and high speed adjustment needles 65, 27 and the air bypass screw 160 into the base portion 58 of the main body 24 is preferably also from the same direction or through the top surface 26 thus simplifying manufacturing by eliminating the need to rotate or reposition the carburetor 20 for each needle insertion. Preferably, both needles 65, 27 and the bypass screw 160 have a head 196 carrying a slot 198 exposed through the top surface 26 for receipt of the same tool 67 during end user adjustment. The idle adjustment needle 65 is protected from debris by a plug 200 press fitted into the hole 63 of the throttle shaft 56.
As previously described, the high speed adjustment needle 27 is preferably inserted through the top surface 26 during assembly and the throttle 46 is preferably inserted through the opposite downward face 110 of the base portion 58 of the main body 24. The modified carburetor illustrated in
While the forms of the invention herein disclosed constitute presently preferred embodiments, others will be readily recognized by those skilled in the art. It is not intended herein to mention all the possible equivalent forms or ramifications of the invention. It is understood that 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. The invention is defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-003355 | Jan 2005 | JP | national |
| 2005-070771 | Mar 2005 | JP | national |
