Carburetor fuel mixture adjustment assembly

Details Carburetor fuel mixture adjustment assembly Carburetor fuel mixture adjustment assembly

2001-03-29

2002-12-10

Chiesa, Richard L. (Department: 1724)

Gas and liquid contact apparatus

Fluid distribution

Valved

C261SDIG003

Reexamination Certificate

active

06491288

ABSTRACT:

REFERENCE TO RELATED APPLICATION
Applicants claim priority of Japanese patent application, Ser. No. 2000-093638, filed Mar. 30, 2000.
FIELD OF THE INVENTION
This invention relates to a carburetor fuel mixture adjustment assembly, and more particularly to a carburetor fuel mixture adjustment needle valve assembly for an internal combustion engine.
BACKGROUND OF THE INVENTION
It is known for a conventional fuel mixture adjustment assembly
70
as shown in
FIG. 6
, to include a cylindrical needle valve body
50
disposed rotateably within an elongated cylindrical needle valve receptacle
46
in a carburetor body
61
to adjust fuel flow. The fuel flows through a fuel passage
42
from a fuel metering chamber, not shown, and into a fuel-and-air mixing passage
41
via a fuel jet. The fuel passage
42
is intersected by the receptacle
46
at an inner distal end or fuel chamber
44
. Rotation of the needle valve body
50
causes a stem portion
50
having a needle tip
51
of the needle valve body
50
to axially advance into, or retract out of, a fuel chamber
44
of the receptacle
46
. Fuel flows traversely into chamber
44
from an inlet orifice, not shown, which communicates through the cylindrical wall of chamber
44
, and flows out of an outlet passage or orifice
43
aligned concentrically to and communicating axially inward of the fuel chamber
44
. The needle tip
51
projects concentrically into the outlet orifice
43
thereby obstructing fuel flow. The stem portion
52
is spaced or separated radially inward from the wall of the fuel chamber
44
thereby permitting fuel flow between the inlet and outlet orifices.
Axial advancement and retraction of the needle tip
51
within the outlet orifice
43
respectively decreases and increases the amount of fuel that can flow through the orifice
43
by decreasing and increasing the cross-sectional area of the valve restriction through at the orifice
43
. An exteriorly threading portion
57
of the needle valve body
50
disposed concentrically to and axially outward from the stem portion
52
is directly threaded to a cylindrical wall
58
of the carburetor body
61
exposed within the receptacle
46
. The needle valve body
50
is rotated by using a tool such as a screwdriver to engage a screw head
58
of the valve body
50
that protrudes from the carburetor body
61
. In some such assemblies
70
, to prevent inadvertent or uncommanded rotation of the needle valve body
50
within the needle valve receptacle
46
, a tamper-resistant adjustment needle limiter cap is placed over the screw head
50
and is secured to or braced against an adjacent structure, not shown.
Fuel mixture adjustment assemblies
70
of this type include enough clearance between the respective threading portions
57
of the needle valve body
50
and the needle valve receptacle
46
to allow for lateral movement of the needle tip
51
within the outlet orifice
43
when force is applied to the head
58
of the needle valve body
50
. This lateral movement can change the size of the orifice
43
enough to result in fuel flow rate changes of up to twenty percent from an optimum fuel flow rate determined by the manufacturer. Fuel flow rate changes caused by needle “slop”
0
result in excessively rich or lean fuel mixtures that undesirably increase exhaust emissions. Therefore, it is desirable to reduce fuel flow fluctuations through the needle valve assembly and the resulting increase in exhaust emissions by limiting needle slop.
Suppressing unintentional rotation of the needle valve body
50
(possibly from engine vibration) which would result in inadvertent alteration of the fuel mixture is a spring
56
disposed concentrically about the needle valve body
50
and compressed axially. A conventional O-ring
54
prevents the leakage of air through the loose fitted threads within the receptacle
46
and into the sub-atmospheric pressure fuel chamber
46
thereby preventing unstable engine operation. The O-ring
54
seals against a conical annular surface
45
of the carburetor body
61
and a shank portion
53
engaged concentrically between the stem portion
52
and the threading portion
57
of the needle valve body
50
. Since the diameter of the shank portion
53
is less than the diameter of the threading portion
57
the shank portion
53
has an axial inward facing annular surface. The spring
56
is compressed axially between the O-ring
54
and the shank portion
53
or annular surface. The axial forces produced by the compressed spring
56
suppress rotation of the needle valve body
50
and assures that the O-ring
54
remains seated sealably between the carburetor body
61
and the shank portion
53
of the needle valve body
50
. Unfortunately, the O-ring and spring are two additional parts which are costly to manufacture and assemble in the carburetor.
SUMMARY OF THE INVENTION
A carburetor fuel mixture adjustment assembly has a threadable holder which suppresses uncommanded rotation of a needle valve body disposed threadably through the threadable holder within an elongated receptacle extending into a carburetor body. A needle portion of the needle valve body advances and retracts into and out of a fuel passage, which feeds fuel to a fuel-and-air mixing passage within the carburetor, via rotation of the needle valve body to respectively decrease and increase fuel flow through the fuel passage. Preferably, a sealing holder disposed within the receptacle has a stem holder portion and a shank holder portion. The stem holder portion holds a stem portion and thereby assures that a needle portion of the needle valve body remains concentrically disposed within an outlet orifice of a fuel chamber of the receptacle which intersects the fuel passage. The shank holder portion disposed within a sealing chamber of the receptacle provides a seal radially between the needle valve body and a sealing chamber wall of the carburetor body preventing air ingress to the sub-atmospheric fuel chamber.
The threadable holder is prevented from rotating within the receptacle via engagement of a clockwise rotational stop surface and a counterclockwise rotational stop surface of the carburetor body with respective clockwise facing surface and counterclockwise facing surface of the threadable holder. The threadable holder prevents rotation of the sealing holder within the receptacle by engagement of a first rotational stop of the shank holder portion with the clockwise facing surface of the threadable holder and engagment of a second rotational stop of the shank holder portion with the counterclockwise facing surface of the threadable holder. The threadable holder is made of a softer material than the needle valve body so that the threading portion of the needle valve body is capable of tapping or forming thread grooves into the rigidly held threadable holder as the needle valve body is screwed into the receptacle.
Preferably, the threadable holder is tightly fitted within a threading chamber of the receptacle. The bottom of the threading chamber is defined by an axial inner shelf and an axial outer shelf which both face outward with respect to the carburetor body. The ends of the inner and outer shelves are interconnected about a centerline of the receptacle by the clockwise and counter clockwise rotational stop surfaces of the carburetor body. Extended axially inward from the inner perimeter of the resultant annular shelf of the threading chamber is a sealing chamber wherein the shank holder portion of the sealing holder is tightly fitted. Inward of the sealing chamber is a fuel chamber. The shank portion of the needle valve body disposed between the needle portion and the threading portion is axially aligned to the sealing chamber and the needle portion is substantially axially aligned to the fuel chamber.
Objects, features and advantages of this invention include the prevention of air ingress into the fuel passage through the receptacle when the fuel chamber is self atmospheric and the prevention of fuel leakage through the receptacle when the fuel chamber is at atmos

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