Gas and liquid contact apparatus – Fluid distribution – Valved
Reexamination Certificate
2001-10-11
2003-07-01
Chiesa, Richard L. (Department: 1724)
Gas and liquid contact apparatus
Fluid distribution
Valved
C261S045000, C261S047000
Reexamination Certificate
active
06585235
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a rotary throttle type carburetor suitable for use with a small internal combustion engine, for powering portable implements such as hand held chain saws, weed trimmers, brush cutters and the like, more particularly to a fuel regulating mechanism for such a rotary throttle type carburetor.
BACKGROUND OF THE INVENTION
Rotary throttle type carburetors are currently used to provide the combustion fuel requirements for a wide range of two-stroke-cycle and four-stroke-cycle engines, including hand held engines, such as engines for chain saws and weed trimmers. Typically these carburetors are diaphragm type utilizing a fuel-metering diaphragm operative to control the delivery of fuel from the carburetor regardless of its orientation. There is an increasing trend to provide a so-called “mini-four-stroke” type small engine in order to achieve better fuel economy and reduced exhaust gas air pollutants as compared to a comparable two-stroke cycle engine. However, the very minute quantity of fuel required to power a mini-four-stroke at idle speed in turn requires that the idle mixture needle be set to establish a very tiny overall idle outlet opening in the fuel jet port of the fuel supply pipe. This in turn can lead to problems of sensitivity to needle tip axial movement as well as clogging from debris in the fuel.
As is well understood in the art, a rotary throttle type carburetor typically comprises a cylindrical throttle valve having a throttle hole disposed in the air intake passage of the carburetor body, and the quantity of combustion air intake to the engine is controlled by rotation of the throttle valve. The quantity of fuel delivered to the engine is controlled by the relative position of a needle attached to the throttle valve that is raised and lowered by a cam that rotates with the throttle valve so that the tip of the mixture needle moves along a fuel jet side port of a fuel supply pipe to vary the open area of the fuel jet port.
There are various known methods for regulating the low speed or idle speed fuel delivery of such rotary valve carburetors. One such method and mechanism is disclosed in Japanese Patent Application Publication No. 110847/1983 and in corresponding German Patent DE 3247603 A1 (1983), FIG. 2 of which is also shown as prior art in FIG. 5 of U.S. Pat. No. 5,709,822 and described therein at column 1, lines 47-60, as follows:
A valve type carburetor disclosed in Japanese Patent Laid-Open No. 110847/1983 is known in which, as shown in FIG. 5, in order to change a flow of air with respect to a fuel pipe
16
which projects toward a throttle hole
17
b
of a rotary throttle valve
17
, that is, in order to change a suction negative pressure exerting on a fuel jet port
16
a
at an idle position of the throttle valve
17
, a through-hole
17
c
opening to an inlet of an air intake passage
44
is provided in a wall portion of the throttle
17
b
of the throttle valve
17
. In this proposal, the inside diameter of the through-hole
17
c
is selected according to the specification of the engine. Therefore, the fuel quantity at the idle position is fixed to a predetermined value and cannot be freely adjusted.
In the system and mechanism of the aforementioned U.S. Pat. No. 5,709,822, and as best seen in
FIG. 3
thereof, an air bleed bypass passage
41
is provided for communicating the main throttle hole or throttle bore
17
b
of the throttle valve
17
with the carburetor intake passage
44
of the carburetor body upstream of the throttle valve. An air quantity regulating needle valve
43
is provided in this bleed passage for adjusting the quantity of bypass air admitted to the rotary throttle valve throttle hole
17
b.
In order not to exceed the permitted maximum adverse emissions limit of EPA and/or CARB exhaust regulations, the air/fuel (A/F) mixture is set at the factory by permanently adjusting the conventional fuel regulating needle
15
so that at idle throttle setting the size of the fuel jet orifice
16
a
is made small enough to establish the maximum fuel delivery at engine idle speed that is permitted in terms of the applicable exhaust gas regulations. This is done while the air bleed bypass regulating needle valve
43
is screwed in to completely close bypass or block passage
41
. Then an anti-tamper closing member (i.e., ball
62
) is forced into the mixture needle mounting hole
47
a
and sealed off (as by adhesive
61
) so that the fuel regulating needle cannot again be regulated from outside.
However the operator can still regulate (i.e., lean out), if desired, the fuel quantity in the engine idle operating range. The quantity of idle bypass air flowing through the bypass air bleed passage
41
for bypass communicating the throttle hole
17
b
of the throttle valve
17
with air intake passage
44
upstream of the throttle valve is regulated by adjusting the air quantity regulating needle valve
43
. If the quantity of air flow through the air passage bypass
41
is thus increased, the A/F mixture becomes leaner, and if this bypass air quantity is decreased, the mixture becomes richer. However, since the maximum concentration of the fuel in the A/F mixture at throttle idle setting has been preset, the idle A/F mixture will not exceed the permitted maximum value of the exhaust gas regulations. That is, even if the air quantity regulating needle valve
43
is fully opened, and even if the air quantity regulating needle valve
43
is removed, the bypass air quantity merely becomes maximum, thus the concentration of the mixture does not become rich because the maximum rate of fuel delivery is independently controlled and has already been preset by the aforementioned factory pre-adjustment of the fuel regulating needle.
Although the adjustment feature of '822 patent air quantity regulating needle valve in the idle bypass passage is a desirable feature in many applications, neither it nor the aforementioned Japanese Laid-Open patent cited therein as prior art to '822 solves the problems of regulating needle sensitivity and clogging of the idle output opening as so established by factory adjustment of the conventional fuel regulating needle.
Moreover, other problems associated with adapting a rotary valve type carburetor to the characteristics of a mini-four-stroke engine are neither recognized nor addressed by these aforementioned prior art documents. For example, there is no way the mechanism can be adjusted to provide a simple enrichment starting system to assist cold start of such an engine (that does not require the addition and use of the current standard choke system for this purpose,) and without affecting wide open throttle (W.O.T.) performance. Also, there is no recognition of nor provision for solving the problem of adjusting the fuel quantity versus engine speed curve produced by the regulated A/F mixture in the range of throttle settings between idle and full throttle to better match the performance requirements for acceleration of the engine in the part throttle range. These problems are particularly acute in small mini-four-stroke engines which are highly sensitive to rich and undesired fuel and air mixture provided to the engine.
OBJECTS OF THE INVENTION
Accordingly, among the objects of the present invention are to provide an improved fuel regulating mechanism for a rotary throttle valve type carburetor, and improved method of operating the same, that overcomes the aforementioned problems, particularly those associated with providing such a carburetor for a mini-four-stroke engine, that provides an improved method of controlling the amount of vacuum or negative pressure exerted on the idle fuel outlet orifice at idle speed setting of the carburetor without significantly reducing the throttle valve opening, that provides a low cost and easy to operate improved starting system for such an engine, as well as other types of engines utilizing rotary throttle valve carburetors, and enables the permanent factory adjustment of the fuel regulating needle to be set “higher” to estab
Chiesa Richard L.
Reising Ethington Barnes Kisselle P.C.
Walbro Corporation
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