Carburetor with displaced idle flow

Details Carburetor with displaced idle flow Carburetor with displaced idle flow

2000-02-23

2001-07-31

Yuen, Henry C. (Department: 3747)

Internal-combustion engines

Charge forming device

Auxiliary control of carburetor fuel metering

C123S585000, C123S339230, C261SDIG006

Reexamination Certificate

active

06267102

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to internal combustion engines and more particularly to a carburetor providing a fuel and air mixture for internal combustion engines.
BACKGROUND OF THE INVENTION
Carburetors are currently used to provide the combustion fuel requirements for a wide range of two cycle and four cycle engines including handheld engines, such as engines for chainsaws and weed trimmers, as well as a wide range of marine engine applications. Diaphragm type carburetors are particularly useful for handheld engine applications wherein the engine may be operated in substantially any orientation, including upside down. Typically diaphragm carburetors have been used with two cycle engines and there is a continuing struggle to reduce the exhaust emissions of these engines to prevent escape to the atmosphere of hazardous hydrocarbon vapors and to comply with increasingly strict governmental regulations regarding the same. Still further, engine manufacturers are continually seeking carburetors which are easier to calibrate and of lower cost.
A conventional diaphragm type carburetor has a high speed fuel circuit and an idle or low speed circuit. Typically, the high speed fuel circuit fuel jet or nozzle is disposed upstream of a throttle valve in a venturi of the carburetor body and the idle circuit has a plurality of fuel jets or nozzles some of which are disposed downstream of the throttle valve within the throttle bore. Each fuel circuit has a separate fuel adjustment needle which cooperates with a valve seat to limit the fuel flow available to the nozzles of its corresponding fuel circuit to control the amount of liquid fuel delivered from the carburetor. When the throttle valve is closed, or nearly so, such as at idle or low speed and low load engine operation, substantially no fuel is provided through the high speed fuel circuit and most, if not all of the engine fuel requirements are supplied through the idle or low speed circuit. When the throttle is wide open, fuel is fed to the engine primarily from the high speed fuel circuit of the carburetor, usually with some fuel supplied from the idle fuel circuit, although, in some systems the idle circuit may be shut off by a valve actuated by the throttle shaft.
To provide a lower cost carburetor, one solution has been to provide a single needle diaphragm carburetor which provides fuel entirely through a single fuel circuit of the carburetor. All of the fuel passes through a single needle valve orifice and out of the same series of holes or nozzles at idle or low speed and low load conditions as well as wide open throttle conditions. Holes of the series are provided both downstream and upstream of the throttle valve of the carburetor in a similar location as that of the idle fuel circuits of a carburetor having both idle and high speed fuel circuits each with a separate adjustment needle valve.
While the single needle diaphragm carburetor is of lower cost, it has poor acceleration characteristics, and an extremely rich idle calibration to partially compensate for the poor acceleration characteristics inherent to this type of system. This rich idle calibration condition can cause poor idle stability and contributes to poor stability of the engine as the engine comes down from high load conditions such as wide open throttle to a low load condition such as idle. The poor come down stability is due to the fact that at wide open throttle a greater quantity of fuel is passing through the fuel nozzles and the fuel circuit than is needed for idle engine operation such that when the throttle valve is subsequently moved from wide open throttle to its idle position an excessive amount of fuel is left in the nozzles and the fuel circuit providing a fuel and air mixture to be delivered to the engine which is excessively rich for engine come down and idle operation. This rich fuel and air mixture reduces engine stability and can even cause the engine to cease to operate.
Despite these significant shortcomings, single needle diaphragm carburetors have been successfully employed in use with piston port and relatively large displacement two-stroke engines. However, many small engine applications, such as for chainsaws, weed trimmers and the like, utilize very small displacement two-stroke engines and four-stroke engines due to the benefits in fuel economy and reduced engine emissions. The above noted shortcomings of the single needle diaphragm carburetor are particularly problematic with these mini four-stroke engines and small two-stroke engines.
SUMMARY OF THE INVENTION
A single needle diaphragm type carburetor has a venturi bore therethrough, a throttle valve in the venturi bore, an idle fuel nozzle downstream of the throttle valve when in its idle position, a high speed fuel nozzle preferably disposed within a venturi portion of the bore upstream of the throttle valve and a supplemental air bleed passage which is open upstream of both the idle and high speed fuel nozzles. Both the idle and high speed fuel nozzles communicate with each other and are fed from the same fuel circuit controlled by a single needle valve which limits the fuel flow to them. The supplemental air bleed passage provides air at idle or low speed and low load engine operation which communicates with the fuel which flows through the needle valve to facilitate delivery of a fuel and air mixture (emulsified fuel) to the idle fuel nozzle. At wide open throttle, this supplemental air flow is routed near the idle fuel nozzle and passes through high speed nozzle along with the fuel that flows therethrough without any significant amount of fuel or air flowing out of the idle fuel nozzle. The supplemental air routed adjacent to the idle nozzle dries out, reduces or eliminates the liquid fuel adjacent thereto such that upon come down of the engine from wide open throttle to idle, there is not an excessive amount of fuel supplied to the idle circuit which avoids an overly rich fuel condition during engine come down. Therefore, the stability of the engine throughout its operating range is dramatically improved. Desirably, this single needle diaphragm type carburetor may be used with a wide variety of engine designs including mini four-stroke engines, two-stroke crank case reed valve engines and two-stroke piston port induction engines.
The high speed fuel nozzle is preferably located closely adjacent to the path of fuel flow at idle such that fuel is readily available to the high speed fuel nozzle when the throttle valve is rapidly opened to improve acceleration performance and stability. Also, when the throttle valve is rapidly opened from its idle position, fuel and air is preferably momentarily drawn out of both the idle fuel nozzle and high speed fuel nozzle to provide a temporary rich fuel and air mixture which also improves the acceleration performance and stability of the engine. Also, desirably, the high speed fuel nozzle is disposed within the venturi portion of the fuel and air mixture bore to take advantage of the high pressure drop therein to facilitate drawing fuel into the fuel and air mixture bore at high speed or high load engine conditions to improve acceleration as well as wide open throttle engine stability and performance.
Objects, features and advantages of this invention include providing a single needle diaphragm carburetor which is extremely easy to calibrate, is easy to adjust after initial calibration, provides improved acceleration, provides excellent performance without an over rich idle calibration, improves engine stability throughout the engine operating range, selectively provides fuel from both the idle fuel nozzle and high speed fuel nozzle without mechanical shut off devices or check valves, provides greatly improved come down stability, provides a fuel nozzle in the venturi portion of the carburetor to take advantage of the greater pressure drop therein, permits the engine to be used in substantially any orientation, permits use of a larger venturi, can provide increased engine horsepower, provides a reduced engine exhau

Affiliated with

Also associated with

Rating

Carburetor with displaced idle flow does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Carburetor with displaced idle flow, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Carburetor with displaced idle flow will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2550064