Applicants claim priority of Japanese Application, Ser. No. 2008-010632, filed Jan. 21, 2008, which is incorporated herein by reference in its entirety.
The present disclosure relates generally to carburetors for combustion engines, and more particularly to a variable venturi carburetor.
Conventionally, there has been a demand to improve carburetors for cleaner exhaust gas, and various structures therefor have been proposed. Some carburetors comprise a sliding throttle valve in which a valve member is translatable to increase and decrease an open area of a fuel and air mixing passage. See, for example, Japanese Utility Model Application No. 51-94686 (Utility Model Application Publication No. 53-012924). It is disclosed in the above publication that in a lower-speed or small opening operation mode of a sliding throttle valve carburetor with a variable venturi, a negative intake pressure at the venturi tends to be larger compared with a butterfly valve carburetor. Such large pressure can make an air fuel mixture ratio overly rich and thereby cause unfavorable performance, unless a needle jet is used to restrict supply of fuel to the venturi.
To address this problem, the above publication proposes use of two separate main jets; one dedicated to the lower-speed mode, and another dedicated to a higher-speed or large opening operation mode. However, in the above publication a needle member is repeatedly moved into and out of a fuel nozzle jet, and abrasion may occur between the needle member and the jet after an extended period of use. Such abrasion can deteriorate the performance of the carburetor compared with its initial performance, and deterioration of fuel consumption efficiency and exhaust performances can be particularly significant in the lower-speed mode.
A carburetor according to one implementation includes a main body defining a bore extending through the main body along an axis, a main passage and a venturi defined within the bore, and a fuel nozzle carried by the main body and including a fuel nozzle outlet in fluid communication with the venturi. The carburetor also includes a valve member translatable with respect to the axis of the bore of the main body to control an open area of the bore, such that in a closed state, the valve member closes the main passage but maintains the venturi at least partially open to allow an amount of air for engine idling to flow therethrough.
According to another implementation, a carburetor includes a main body defining a bore extending through the main body along an axis, a main passage and a venturi defined within the bore, and a throttle shaft carried by the main body. The carburetor also includes a fuel bowl carried by the main body and defining a fuel reservoir, a fuel nozzle carried by the main body and including a fuel nozzle inlet in fluid communication with the fuel reservoir and a fuel nozzle outlet in fluid communication with the venturi. The carburetor further includes a needle valve disposed at the fuel nozzle inlet to variably control flow of fuel through the fuel nozzle inlet, and a needle valve transmission coupled between the throttle shaft and the needle valve to convert rotation of the throttle shaft to translation of the needle valve to adjust an amount of fuel supply.
According to an additional implementation, a carburetor includes a main body defining a bore extending along an axis, a throttle shaft carried by the main body, and a fuel nozzle carried by the main body. The carburetor also includes a needle valve operatively coupled to the fuel nozzle to variably control flow of fuel through the fuel nozzle, and a needle valve transmission coupled between the throttle shaft and the needle valve to convert rotation of the throttle shaft to translation of the needle valve. The transmission includes a cam coupled to the throttle shaft and having a cam surface that at least partially defines a variable air-fuel ratio supplied by the carburetor.
According to a further implementation, a sliding throttle valve carburetor includes a carburetor main body defining an intake bore, a valve member moveable in a direction of a diameter of the intake bore to increase and decrease an open area of the intake bore, and a venturi disposed in the intake bore and having a flow passage narrower than the intake bore. The carburetor also includes a fuel discharge port that opens into the flow passage of the venturi, wherein the valve member is integrally provided with a wall portion such that the wall portion moves with the valve member to open and close openings of the venturi, where the wall portion is disposed so as to move in slidable contact with end surfaces of the venturi defining the openings.
At least some of the objects, features and advantages that may be achieved by at least certain embodiments of the invention include providing a variable venturi carburetor that is less susceptible to deterioration of mileage and exhaust performance after an extended period of use, provides highly accurate fuel supply adjustment with a simple structure, improves fuel vaporization, fuel consumption efficiency, and exhaust characteristics, eliminates inadvertent fluctuation in a fuel flow rate through a jet needle structure, improves precision in fuel flow rate adjustment, allows easy adjustment of the fuel flow rate even after assembly of the apparatus, and is of relatively simple design, economical manufacture and assembly, rugged, durable, reliable, and in service has a long useful life.
Of course, other objects, features and advantages will be apparent in view of this disclosure to those skilled in the art. Various other carburetors embodying the invention may achieve more or less than the noted objects, features or advantages.
These and other objects, features and advantages will be apparent from the following detailed description of exemplary embodiments and best mode, appended claims, and accompanying drawings in which:
Referring in more detail to the drawings,
As shown in
The valve member guide block 4 is disposed so as to cross the intake bore 2 in a vertical direction, and is formed with a main intake passage 4a and a venturi 4b, each of which extends through the guide block 4 in an axial direction along the intake bore 2. The main intake passage 4a and the venturi 4b are opened and closed with respect to the intake bore 2 by movement of the valve member 3. In
In the illustrated embodiment, the valve member 3 assumes a generally H-shaped cross-section including the pair of flat plate portions 3a for opening and closing openings at both ends of the venturi 4b, but the shape of the portions of the valve member 3 for opening and closing the openings of the venturi 4b is not limited to the flat plate shape and may assume, for example, a generally circular outer profile in a plan view when viewed in a direction of opening and closing movement of the valve member 3. In the case that the valve member 3 has a circular outer profile, the valve member supporting portion of the valve member guide block 4 can be formed as a circular hole, and this can make the manufacture of the valve member guide block 4 easier.
Referring to
A throttle shaft 6 is provided in the recess 1a so as to extend in a direction perpendicular to the axis of the intake bore 2 and across the space within the recess 1a. Fixed to an end portion of the throttle shaft 6 that protrudes out of the carburetor main body 1 (a right end portion in
Referring to
Although those of ordinary skill in the art will appreciate that there are many ways to adjust a throttle shaft for idle operation,
Referring to
Referring to
A fuel adjustment rod 13 extends between the recess 1a and the fuel reservoir 11a of the fuel supply adjuster 11, and an end of the adjustment screw 12 abuts an end of the fuel adjustment rod 13 in the recess 1a. The fuel adjustment rod 13 extends through a portion of the valve guide block 4 beside the main intake passage 4a, and is supported so as to be moveable in a direction of its extension. An end of the fuel adjustment rod 13 on a side of the fuel reservoir 11a is connected to one end of an extension member 14, the other end of which is formed with a fork-shaped engagement portion 14a to engage an upper surface of an outer flange 15a of a needle support member 15. Thus, the fuel adjustment rod 13 and the extension member 14 constitute an open/close operation amount transmitting mechanism.
The needle support member 15 fixedly holds a base end of a needle valve or member 16. The needle member 16 may have a substantially constant diameter over substantially its entire length. A fuel nozzle outlet or main fuel discharge port 17 of a fuel nozzle or tubular member 18 opens into the venturi 4b. The needle support member 15 and needle member 16 are inserted into the tubular member 18 and are supported in such a manner that the needle support member 15 and needle member 16 can move relative to the tubular member 18. The needle member 16 is disposed at a fuel nozzle inlet, which may be substantially opposite of the fuel discharge port 17, to control flow of fuel through the fuel nozzle inlet. A fuel nozzle post or pillar-like boss portion 1b (
The needle support member 15 is spring-biased, such as by a cone spring 19 interposed between the bottom of the fuel reservoir 11a (
When the throttle is operated toward the fully-open state, the fuel adjustment rod 13 and the extension member 14 move in a direction as indicated by an arrow B in
Referring to
As also shown in
Further, as shown in
Next, exemplary operation of the carburetor is explained. In the idling state of the carburetor, the fuel supply is conducted through the low speed fuel jet 23 as shown in
The positional relationship among the component parts constituting the variable fuel jet in the idling state is shown in
In a low speed or small opening state where the throttle has been operated in the direction indicated by the arrow A in
As mentioned above, in the conventional sliding throttle valve carburetor, a fuel metering needle member, which is called a jet needle, is inserted into the main fuel discharge port that opens into the intake bore, and the needle member is formed with a converging end portion so as to be able to vary an amount of gap between the needle member and the main fuel discharge port to thereby control the amount of fuel discharge. However, in such a structure, the needle member and the main fuel discharge port can contact each other due to engine vibrations or the like, and this can cause abrasion in the needle member and thus result in unfavorable change in the fuel metering characteristics. The change in the amount of fuel discharge can affect the exhaust gas composition and lead to deteriorated exhaust gas characteristics.
With the presently disclosed exemplary embodiments, there may be no jet needle structure (or needle valve) with a needle member having a converging end portion and moved into and out of the main fuel discharge port 17 that opens into the intake bore 2 and, therefore, the above described problem in the conventional carburetor does not arise. Further, in order to cope with problems such as delay in fuel discharge or poor fuel atomization that could be caused due to the absence of the jet needle structure, the carburetor of the exemplary embodiments disclosed herein is equipped with the venturi 4b as described above to create a large negative pressure acting upon the main fuel discharge port 17. Specifically, the valve member 3 is adapted to be able to open and close openings at both ends of the venturi 4b in the direction of air flow by slidingly moving the flat-plate portions 3a along the end surfaces of the venturi 4b defining the openings. Such a structure can eliminate an expansion space that would otherwise reduce the flow rate inside the venturi, and thus contribute to creating larger negative pressure acting upon the main fuel discharge port 17.
Further, as to the fuel metering, which could be performed in the conventional embodiment by the jet needle structure constituted by the main fuel discharge port 17 and the needle member inserted therein, the fuel metering is achieved by the tubular member 18 that is in flow communication with the main fuel discharge port 17 and the needle member 16 is inserted into the tubular member 18 from an end on the side of the fuel supply adjuster 11 (i.e., from an end away from the main fuel discharge port 17). The needle member 16 can be reciprocally moved along the tubular member 18 to control the amount of fuel that is supplied from the fuel reservoir II a to the main fuel discharge port 17 via the tubular member 18 with a comparable precision as that of the conventional jet needle structure.
Further, it is now possible to reduce or eliminate inadvertent fluctuation in the fuel flow rate in the jet needle structure that can be attributed to conducting fuel metering at a portion where the air flows at a high speed. Control of fuel supply to the fuel discharge port 17 is achieved by controlling the position of the needle member 16 inserted into the tubular member 18 to vary fuel flow through the fuel nozzle inlet. Thus, the fuel metering can be achieved by using the needle member 16 having a substantially equal diameter substantially over its length, and there is no need to use the conventional jet needle structure. This can eliminate a jet needle structure that may suffer abrasion due to engine oscillations or the like.
In other words, the needle member 16 does not need to have a converging end portion to be inserted into and moved out of the tubular member 18, and can have a same diameter to its tip end as described above. This can prevent collision between the needle member 16 and the tubular member 18 with a substantial space therebetween when applied with engine oscillations and the like. Thus, the carburetor disclosed herein is less likely to suffer deterioration with time unlike the conventional jet needle structure, and hence it is possible not only to improve the fuel consumption efficiency and the exhaust characteristics but maintain the favorable exhaust characteristics without deterioration with time. Nonetheless, another implementation could include a conventionally tapered needle member 16 if desired.
Further, in the fuel metering structure as presently disclosed, the free end of the extension of the cam lever 9 that is away from the pivoted end is adapted to slidably contact with the cam 8, and an intermediate portion of the cam lever 9 is adapted to act upon the fuel adjustment rod 13 via the adjustment screw 12. Therefore, an amount of movement of the fuel adjustment rod 13 is smaller than an amount of corresponding movement of the free end of the cam lever 9. Therefore, the adjustment mechanism is less affected by manufacturing or assembly errors regarding the component parts constituting the valve operation transmitting mechanism. This can improve the accuracy of fuel adjustment effected by the adjustment mechanism and/or the accuracy of position control of the needle member to which the amount of operation of the operating means is transmitted via the adjustment mechanism, even in the case where an amount of fuel discharge is particularly sensitive to a change in a valve opening area. In the above structure, the fuel increase/decrease characteristics can be freely altered by changing the cam shape, and therefore, the design change in accordance with the engine characteristics can be achieved easily.
The adjustment screw 12 transmitting the movement of the cam lever 9 to the fuel adjustment rod 13 is placed in the recess 1a. Thus, just by detaching the cover 5, one can access the adjustment screw 12 and rotate it to adjust the relative position of the fuel adjustment rod 13 or the needle member 16 with respect to the valve member 3. This allows an easy adjustment of fuel flow rate even after assembly of the apparatus.
It should be also noted that the fuel adjustment rod 13 is disposed inside of the carburetor main body 1. This eliminates a need for an additional protective structure against an abrupt external force as well as an additional dustproof structure, which would be required and complicate the structure if the fuel adjustment rod 13 were provided outside of the carburetor main body 1. Nonetheless, the rod 13 may be disposed partially or completely outside of the main body 1, if desired.
In the illustrated embodiment, the adjustment screws 12 and the fuel adjustment rod 13 abut each other. The spring-biasing force acting upon the needle support member 15 also pushes the fuel adjustment rod 13 and the extension member 14, which engages the needle support member 15, against the adjustment screw 12. Therefore, though the fuel adjustment rod 13 is not fixedly connected to the adjustment screw 12, the fuel adjustment rod 13 can follow the movements of the adjustment screw 12 in the direction of spring-biasing force without rattling. Further, the total length of the fuel adjustment rod 13 and the extension member 14 can be adjusted by using an insertion bush, and it is possible to press-fit an insertion bush to the fuel adjustment rod 13 by using a jig, for example, to thereby improve the assembly accuracy.
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.
Number | Date | Country | Kind |
---|---|---|---|
2008-010632 | Jan 2008 | JP | national |