The present invention relates generally to the field of carburetion, and more particularly to the field of carburetor venturi structures and accessories.
A carburetor is a device for mixing air and fuel in an internal combustion engine in order to provide a combustible fluid for introduction into a cylinder or other combustion chamber. The carburetor typically has a central bore that is obstructed by a throttle plate which, depending upon the position of the throttle plate admits relatively more or less of the fuel/air mixture into the subsequent or downstream venturi portion of the carburetor. For relatively higher powered engines, the carburetor bore is relatively larger in diameter because a relatively greater amount of fuel and air is needed to support the combustion process that generates the higher power. However, at relatively lower throttle settings, a large bore carburetor becomes relatively inefficient because the smaller volume of the fuel/air mixture occupies the entire large bore volume, thereby reducing both turbulence and mixture velocity and promoting poor mixing of the fuel and air.
A typical engine operates over a wide range of power levels, ranging from the low end associated with idling to the midrange and high end associated with rapid acceleration. Since the air/fuel mixture supplied to the engine is typically provided by a single carburetor, selecting a carburetor having the correct bore size is very important in determining overall engine performance. A relatively smaller carburetor delivers quick and stable power at the low end while lacking sufficient fuel/air delivery at the midrange and top end due to the limited flow capability of the smaller bore. A larger carburetor delivers the desired power from the midrange to the top end while lacking stability, responsiveness and fuel efficiency at the low end due to the relatively slower air speeds associated with lower throttle settings.
Since the vast majority of engines operate with a single carburetor having a fixed bore, most engines have to some degree a poor throttle response otherwise known as throttle lag. This is a commonly encountered problem with many types of sporting vehicles such as motorcycles, all terrain vehicles, scooters, go carts and personal watercraft. The very nature of the vehicle design encourages aggressive driving and sometimes racing.
The type of carburetor typically used in a recreational vehicle uses a flat, sliding plate as the throttling mechanism. An example of such a carburetor is disclosed in U.S. Pat. No. 4,814,115, entitled SLIDE AND PIN TYPE CARBURETOR, issued on Mar. 21, 1989 to Hashimoto et al. A problem often associated with flat slide type carburetors is called fuel puddling or streaking which occurs when liquid fuel exits the pilot jet, flows along the carburetor body and into the engine while remaining in a liquid state. This is a result of insufficient air velocity within the carburetor bore that is needed to promote atomization of the fuel into airborne droplets. After a sufficient quantity of fuel has collected, some of it may (or may not) vaporize at random intervals causing an excessive amount of fuel to be instantaneously sent to the combustion chamber.
Another frequently encountered problem is an erratic idle response that causes the engine speed to fluctuate higher and then lower, or to maintain an engine speed that is higher than an acceptable idle speed even though the throttle has been fully returned to its lowest idle position. Large bore single and twin cylinder two cycle engines are often subject to the erratic idle syndrome. Various theories have been proposed to explain the erratic idle phenomenon. One recent article (SnowTech Magazine, October/November 2003, page 8) attributed idling problem to “ . . . air leaking around the flat slides themselves, and this inconsistency is very likely the cause of the occasional high idle speeds . . . We can compensate for it by adding more fuel to offset the extra air leaking around the flat slides”. A subsequent article (SnowTech Magazine, December 2003, page 13) further stated that carburetors are typically calibrated to be “ . . . as lean as possible for improved fuel economy, and the matter of high idle is little more than a lean condition that is easily remedied by adding more fuel to the low speed circuits . . . [Y]ou have to . . . utilize the pilot air jet, pilot fuel jet and fuel screw to get the right calibration balance . . . You need to be willing to sacrifice 2-3 mpg . . . to get rid of the high idle inconsistencies”. Yet another article (SnowTech Magazine, January/February 2004, page 62) states that discontinuities in idling speed are “being caused by a resonance phenomenon”.
The inventor of the present invention has discovered that in fact the inconsistent idling problem is due to large bursts of air being introduced into the engine followed by bursts of heavy wet fuel that is poorly atomized. The lack of atomization is due to the relatively low air speeds at partial throttle. The flow of the air/fuel mixture at low throttle settings can be better understood with reference to
Numerous efforts have been made to maintain downstream air/fuel mixture velocity. One method is to manufacture an asymmetrical carburetor bore, reducing the cross section of the bore near the bottom and enlarging the cross section near the top, creating an oval cross sectional shape. Another type of device is disclosed in U.S. Pat. No. 4,474,145, entitled FUEL SUPPLY SYSTEM FOR INTERNAL COMBUSTION ENGINE, issued on Oct. 2, 1984 to Boyesen. The Boyesen device is a solid, teardrop shaped obstruction with a decreasing cross section in a downstream direction. While the Boyesen device accomplishes the goal of reducing fluctuations in the velocity of the fuel/air mixture, the device occupies a substantial amount of cross sectional area within the air flow passageway, leading inevitably to absolute velocity losses induced by its presence. Neither of the foregoing schemes is amenable to modifying an existing carburetor in the field due to their relative complexity and need for specialized tooling.
The need exists for a carburetor enhancement that maintains higher air flow velocities within the carburetor bore at initial and low speed throttle settings. A higher air speed results in a more thorough atomization of the fuel. The better the fuel is atomized, the more forgiving the carburetor/engine combination will be to variations in either ambient temperature or altitude for a carburetor of a given size.
The ideal carburetor for all throttle settings would be a relatively large bore carburetor that can be made to behave as a smaller bore carburetor at lower throttle settings. The present invention addresses this goal by providing a simple, cost effective device that can be readily installed in the field without any modification to the existing carburetor. The present invention is a carburetor insert located on the downstream (or engine) side of a carburetor. The carburetor insert includes two discrete pieces, the first of which is a wing like airfoil structure that divides the carburetor bore approximately in half along a horizontal plane.
The airfoil extends downstream beginning at a region closely adjacent to the flat slide throttle plate to a region slightly beyond the end of the carburetor bore. The wing or airfoil includes two oppositely oriented tabs that extend beyond the carburetor bore and which terminate adjacent to the outside of the carburetor body casting. The two tabs serve the purpose of securing or locking the airfoil in place within the carburetor bore. The wing can be altered as required to accommodate one or more oil injection nozzles. A second component of the insert is a ramp like structure. The ramp component is located on the downstream engine side of the carburetor, occupying the bottom half of the carburetor bore. The ramp occupies a region that is in close proximity to the carburetor flat slide, forming an inclined plane or ramp that tapers so as to decrease the available cross sectional area of the lower half of the carburetor bore as the bore extends toward the engine. The ramp like structure terminates at the end of the carburetor bore. Various shapes and dimensions of the ramp may be used to achieve desired airflow values for a given throttle setting. The ramp includes at least two carrier grooves adapted to accept and support the wing component. When joined, the wing and the ramp components together form a second venturi within the carburetor bore, the first venturi being the original upstream venturi present in any carburetor The second venturi created by the present invention is located in the lower half of the carburetor bore and is downstream of the existing standard venturi. The presence of the ramp does not inhibit the normal function of the pilot jet circuit and the choke circuit.
The wing component tends to restrict the air flow to the bottom half of the carburetor bore by preventing the air flow from drifting or looping upwardly toward the top of the carburetor bore when the throttle is only partially open. The ramp component acts as a second venturi which further accelerates the air. The higher velocity of the airflow addresses a number of issues. The throttle response is more nearly instantaneous due to the higher air velocity present at partial throttle settings. This characteristic is valuable in a sport vehicle as the rider is able to accelerate more rapidly as a result of a relatively greater rate of engine power increase as the throttle is opened. The absolute value of the peak engine power produced during the first half of the throttle plate travel is also increased.
The vehicle operator is able to momentarily elevate the front of the vehicle solely by manipulation of the throttle, as may be required, for example, in order to negotiate bumps, inclines, gaps or rough areas. The rider is also able to steer in reliance on the improved throttle response. Engine temperature stabilize relatively more quickly due to the improved fuel atomization resulting from the higher airflow velocity. The improved fuel atomization also contributes to more thorough fuel combustion, resulting in a decrease in harmful emissions.
The present invention addresses the erratic idling problem by properly atomizing the relatively dense, moist fuel with a high velocity air column. Fuel is forced along the ramp by the high velocity air column. The fuel is then forced off of the end of the ramp, becoming airborne and quickly atomizing. The effect of the ramp is to substantially reduce the capillary action of flowing, liquid fuel which can produce streaking and puddling. Since the airflow is prevented from flowing upwardly after passing the carburetor slide, the fuel/air mixture tends to flow along a relatively straight path at a relatively higher rate of speed. The second venturi formed by the ramp tends to further increase the air flow velocity.
Referring generally to
The venturi 14 may be composed of any rigid, fuel resistant material such as metal or plastic. Alternatively, the venturi 14 may be formed within the bore 17 at the time of carburetor manufacture and so may be secured by means other than the lip 18, or the venturi 14 may be integrally formed or machined as the inherent shape of the bore 17 and be composed of the same material as the bore 17.
The venturi 14 may also be manufactured and assembled from multiple discrete pieces. Referring also to
Referring also to
As best seen in
The post 37 has a height 36 of approximately 0.080 inch. The wing 15 is inserted into the grooves 30 and 31 by means of a sliding motion in the direction of arrow 39. The tabs 41 and 42 serve as stops which prevent the wing 15 from sliding completely beyond the venturi lip 18. Further, the tabs 41 and 42 tend to impale or otherwise engage any gasket material or rubber manifold linked to the carburetor, further securing the wing 15 so as not to vibrate or shift in position.
Referring also to
Referring also to
Upon insertion of the venturi 14 into the carburetor bore 17, the actual distance 54 between the trailing edge 25 and the leading edge 53 is somewhat critical, and must reside within the range of 0.025 inch and 0.75 inch. In most installations the distance 54 is optimized in the range of approximately 0.100 inch or less. A spacing 54 of greater than 0.5 inch typically results in an excessive amount of the fuel/air mixture 4 failing to enter the venturi 15, while a spacing of closer than 0.025 inch increases the opportunity for debris or vibration to cause venturi 15 to foul or impede the movement of the throttle plate 7. All of the fuel/air mixture 10 is seen to pass through the venturi 14 and along the inclined venturi surface 52. Substantially none of the fuel/air mixture 10 is permitted to flow into the upper bore region 11 due to the presence of the wing 15.
Although the second venturi 14 is shown entirely beneath the upper bore region 11, in practice the second venturi 14 may assume several configurations. In particular, the venturi 14 does not necessarily need to occupy approximately 180 degrees of the circumference of the carburetor bore 17 as illustrated, but rather may extend for less than sixty degrees, resulting in a venturi 14 that occupies only a relatively small amount of the bore cross section. Further, the venturi 14 does not necessarily need to occupy the lowermost portion of the carburetor bore 17, but rather may be positioned along the sides of the bore. Stated differently, the plane defined by the wing 15 may be substantially horizontal as illustrated, but the combination of the wing 15 and venturi 14 may be inserted into the carburetor bore 17 such that the plane of the wing 15 is vertical or any angle between horizontal and vertical. Further, some carburetors may be constructed in such a manner that the carburetor bore 17 ends substantially at the leading edge 53 of the throttle plate 7. In such cases, the combination of the wing 15 and venturi 14 may be affixed so as to be external to, and an extension of, the carburetor bore 17.
The effects of adding the combined wing 15/venturi 14 to a carburetor 1 are illustrated in
The curve 59 represents the airflow produced by the same carburetor 1 with the installation of the combined venturi 14 and wing 15. At the idle setting of approximately 500 revolutions per minute, point 60 indicates that the airflow velocity is approximately thirty eight percent of the maximum available, resulting in excellent fuel atomization and a steady engine idle. Note that the thirty eight percent of maximum airflow figure is not achieved on curve 57 until point 61, which corresponds to a engine speed of approximately 3700 rpm, which is a typical operational speed achieved during normal cruise operation of the vehicle. In this manner the present invention achieves the steady state engine operating conditions normally associated with engine cruise power settings while the engine is operating in the low power and idling regimes.