Gas and liquid contact apparatus – Fluid distribution – Valved
Reexamination Certificate
2000-02-29
2002-12-31
Chiesa, Richard L. (Department: 1724)
Gas and liquid contact apparatus
Fluid distribution
Valved
C261S041100, C261S041500, C123S184230
Reexamination Certificate
active
06499726
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to engines, and in particular to small gasoline engines, such as those used in lawn and garden implements.
2. Background Art
In a prior naturally aspirated four-cycle engine, such as engine
20
shown in
FIGS. 1-3
, carburetor
22
is provided in which air flowing therethrough is charged with fuel. The admixture of fuel and air flows through intake manifold
24
to which the carburetor is attached, and into intake port
26
of cylinder head
28
. The cylinder head or, in the case of an L-head engine (not shown), the cylinder block, is provided with at least two valves (not shown), one of which is an intake valve past which the fuel/air mixture flows as it is drawn from the head into cylinder
30
having reciprocating piston
32
therein. The other valve is an exhaust valve past which exhaust gases exit cylinder
30
after combustion of the fuel/air mixture. As the piston moves away from the head, the intake valve is opened and the admixture is drawn into the cylinder. The intake valve is then closed and piston moves toward the head, the valves of which are now both closed. The admixture is thus compressed and is then spark-ignited in the conventional way, the expanding combustion gases forcing the piston away from the head, powering the engine. As the piston again approaches the head, the exhaust valve is opened and the exhaust gases are forced from the cylinder. The cycle then repeats as the piston again moves away from the head.
The intake strokes of the piston in the cylinder provide a continuous source of vacuum which acts to draw air through carburetor
22
. The amount of vacuum, however, varies with the speed of the engine, which in turn is regulated by the amount and/or quality of the fuel/air mixture delivered to the cylinder. Referring now to
FIG. 4A
, the airflow passage through carburetor
22
has venturi portion
34
, and the amount and/or quality of the fuel/air mixture delivered to cylinder
30
is controlled through pivoting throttle plate or throttle valve
36
located in the airstream, downstream of venturi throat
38
. The angular position of the throttle plate is controlled by rotation of its attached shaft
40
to vary the amount of air allowed through the carburetor, and thus the pressure of the air at or near the venturi throat and the amount of fuel delivered to that air through open end
42
of tubular main jet nozzle
44
, during off-idle running conditions. Opposite end
46
of main jet nozzle
44
extends into main jet well
48
, and fuel is metered into main jet well
48
from the carburetor's fuel storage bowl
50
through metering jet passage
52
extending therebetween. The fuel in main jet well
48
provides a ready supply of fuel for main jet nozzle
44
.
In its idle position, which is shown in
FIG. 4A
, throttle plate
36
is substantially closed, and only a small amount of air is allowed to be drawn through the carburetor; fuel is supplied to the airstream and is allowed to pass through carburetor
22
by means of idle circuit
54
having a fuel supply orifice located downstream of the throttle plate, or an axially arranged plurality of axially spaced fuel supply orifices
56
,
58
,
60
(as shown), at least one of which is located downstream of throttle plate
36
. Fuel supply orifices
56
,
58
,
60
are sequentially exposed to low air pressure as throttle plate
36
opens from its substantially closed, idle position, to a slightly more open, off-idle position during acceleration from idle as shaft
40
is rotated. This “progressive” system of idle fuel orifices is well known in the art, and is disclosed, for example, in U.S. Pat. No. 4,360,481 to Kaufman, the disclosure of which is expressly incorporated herein by reference. Idle fuel orifices
56
,
58
,
60
are provided in the wall surface of the carburetor's air flow passage, and open into idle fuel chamber
62
which is supplied with liquid fuel by idle circuit
54
. Notably, idle fuel outlets
56
,
58
,
60
may be located in a diverging portion of the carburetor's venturi and airflow passage, the diverging portion serving as a diffuser which causes the pressure of the air flowing past the idle fuel supply orifice(s) to be increased. The flow of the liquid fuel through the idle circuit, and thus the idle speed of the engine, is controlled through an idle feed restrictor comprising screw
64
as shown.
It is to be noted that at least one of the idle fuel orifices (i.e, orifice
56
, the “primary” fuel orifice) is at all times downstream of throttle plate
36
. As the throttle plate is opened slightly during acceleration from idle, first progressive orifice
58
and second progressive orifice
60
sequentially become downstream of the opening throttle plate, and additional fuel/air emulsion is provided therethrough to aid in the engine's smooth acceleration to an off-idle speed. Air is received within chamber
62
through idle air bleed orifice
66
located in the wall surface of the carburetor's air flow passage, upstream of the throttle plate, and is mixed with liquid fuel in chamber
62
to produce therein an idle fuel/air emulsion which is delivered to the airstream through at least idle fuel supply orifice
56
, and perhaps through orifices
58
and/or
60
as well. The admixed air and fuel is then delivered to cylinder
30
to support the idle running condition of the engine.
As the throttle is opened from its idle position, the pressure of the air flowing through venturi throat
38
drops with the increasing speed of air moving therethrough. A main fuel/air emulsion is thus drawn to venturi portion
34
at or near its throat
38
through main jet nozzle
44
to support the faster running condition of the engine. Because throttle plate
36
is now no longer substantially closed, a greater amount of air is allowed to pass through the carburetor; the pressure of the air flowing across the idle fuel outlets
56
,
58
,
60
is increased, and a lesser amount of fuel is provided to the airstream by idle circuit
54
. At high engine running speeds, with throttle plate
36
substantially fully opened, the vacuum condition at or near venturi throat
38
is even greater, owing to the higher velocity of the air flowing therethrough; further, the air pressure at the idle fuel outlets
56
,
58
,
60
is even higher, and still less fuel is delivered to the airstream by idle circuit
54
.
The idle circuit is typically one of two types relative to the main fuel circuit, the latter comprising main jet well
48
and main nozzle
44
: (1) the idle circuit may be a separate circuit entirely which parallels the main circuit, with liquid fuel supplied from the carburetor's fuel supply bowl
50
to the idle circuit and main jet well independently; or (2) as shown in
FIG. 4A
, idle circuit
54
may be “married” to the main fuel circuit by having its supply passageway
68
in exclusive fluid communication with main jet well
48
. Separate idle and main fuel circuits may lead to undesirable emissions during the transition from idle to off-idle running conditions, however, for the pressure of the air flowing across the idle fuel orifices
56
,
58
,
60
may still be low enough to draw fuel therefrom during the transition, causing the engine to temporarily run too rich; thus married systems are often preferred for reduced engine emissions.
In addition to its separated or married main and idle fuel circuits, some carburetors may utilize a third fuel circuit which also provides fuel to the airflow passage, at a location upstream of the throttle plate and intermediate the outlets of the main jet and the idle fuel circuit. This third fuel circuit may be referred to as a “secondary fuel circuit”, for it is secondary to the main fuel circuit from which it may be supplied with fuel. Published PCT International Application WO 98/55757, for example, discloses embodiments of carburetors having such secondary fuel circuits. With reference to
FIGS. 1-4
of this PCT application, a first embodim
Baker & Daniels
Chiesa Richard L.
Tecumseh Products Company
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