Note: Descriptions are shown in the official language in which they were submitted.
~ ~6609~
This invention relates to a compound carburetor
for use in an internal combustion engine having a plurali-
ty of cylinders.
In a compound carburetor for use in an engine
having a plurality of cylinders, a primary air-fuel mixture
passes through one throttle valve and is then distributed
to respective cylinders, a secondary air-fuel mixture is fed
to the respective cylinders through secondary throttle valves
arranged for the respective cylinders and a secondary slow-
running fuel system for controlling the air-fuel ratio at the
beginning of opæ~ing of the secondary throttle valves is prov
ided to smooth the tr-ansit from the primary side to the
secondary side. Howeverl in this type of conventional cc~ound
carburetor, generally, there have been the defect that, as
one secondary slow-running fuel system is distributed to the
secondary throttle valves of the respective cylinders, due to
the fluctuation of the opening of the secondary throttle
valve for each cylinder, the fluctuation of the opening area
of the secondary bypass hole, the difference in the length
and bend of the secondary slow-running mixture path and the
air locking phenomenon during the secondary slow-running
mixture path likely to occur at a high temperature which
are all difficult to technically solve, the air-fuel ratio
of the mixture for each cylinder will fluctuate during the
transit from the primary side to the secondary side and the
transit will no longer be smooth.
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Further, generally, the carburetor body is divided into a
carburetor portion, a manifold portion and a throttle body
portion and is formed by a combination thereof. However~ the
secondary slow-running fuel system or particularly the secon-
dary slow-running mixture path is formed within these respec-
tiveportions, is therefore comparatively long in the total
length and can not help having many bends. Not only this will
be likely to cause an air locking phenomenon when the engine
temperature rises as described above but also it will increase
the flow resistance to cause the aelay of the transit from the
primary side to the secondary side and the unstable jet of the
mixture. Therefore, in order to shorten the total length of
the secondary slow-running mixture path and to decrease the
bends, attempts have been made to arrange the carburetor
portion and throttle body portion in the same plane. However,
there have been defects that this arrangement will not only
increase the useless thickness of the component parts but also
require a large space and cause a leakage due to different
strains of the respective portion by heat.
Therefore, the present invention provides a compound
carburetor for internal combustion engines wherein the transit
from the primary side to the secondary side is smoothly made
and the air-fuel. ratio of a mixture fed to each cylinder does
not fluctuate.
According to the present invention, there is provided
an independent secondary slow-running fuel system
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1 16609~
for one cylinder or each of two cylinders.
According to the present invention therefore there
is provided a compound carburetor comprisiny a primary bore
provided therein with a primary throttle valve and branched
in the downstream part of said primary throttle valve to be
respectively connected to a plurality of cylinders of an engine
a secondary bore arranged adjacently to said primary bore and
branched in the downstream part to be respectively connected
to said plurality of cylinders through secondary throttle
valves arranged respectively for said plurality of cylinders,
and a plurality of secondary slow-running fuel systems set
respectively independently for said plurality of cylinders,
opened respectively in the vicinity of said respective
secondary throttle valves, and cooperating respectively with
said respective secondary throttle valves.
According to a preferred embodiment of the present
invention, the mixture path of the secondary slow-running
fuel system includes a pipe airtightly fitted between one
part and the other part of the carburetor body. Thereby,
the length of the mixture path of the secondary slow-running
fuel system can be made as short as possible and the above
described problems can be solved. The pipe is fitted with an
O-ring made of an elastic sealing material or has a rib
formed at each end and is rnade preferably of such adiabatic
material as a phenol resin.
The present invention will be further illustrated
by way of the accompanying drawings in which:
Fig. 1 is a partly sectioned plan view of an em-
bodiment of a compound carburetor according to the present
inYention;
Fig. 2 is a side view of the compound carburetor
shown in Fig. l;
Fig. 3 is a sectional view showing an embodiment
of a pipe ~orming a part of a mixture path of a secondary
slow-running fueI system; and
Fig. 4 is a sectional view showing another embodi-
ment of a pipe forming a part of a mixture path of a second-
ary slow-n1nning fuel system.
With reference to Figs. 1 and 2, the reference
numeral 1 indicates a carburetor body consisting of a car-
buretor portion la, manifold portion lb and throttle body
poxtion lc, 2 indicates a primary bore and 3 indicates a
primary throttle valve provided on the downstream side of
a venturi portion (not illustrated).
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The primary bore 2 is branched on the ~own~
stream side of the primary throttle vaive 3 and is con-
nected to each cylinder. rrhe reference nurneral 4 indicates
a secondary bore whi;ch is branched on the downstream side
of the venturi portion (not illustrated) and is connected
to each cylinder. The reference numeral 5 inaicates a
secondary throttle shaft passing through each branched
path 4a of the secondary bore 4 in the direction inter-
secting at right angles with the center line of the branch-
ed path 4a and 6 indicates a secondary throttle valve
secured to the secondary throttle shaft 5 within each branch-
ed path 4a. The reference numeral 7 indicates a secondary
- bypass hole provided in the inner wall of each branched
path 4a and 8 indicates a secondary slow-running jet connected
to each secondary bypass hole 7 through each secondary slow-
running mixture path 9. A pipe 10 fitted at one end to the
carburetor portion la and at the other end to the manifold
portion lb is set in each secondary slow-running mixture
path 9, that is, between the part positioned in the carbur-
etor portion la of the path 9 and the part positioned in the
manifold portion lb so as to make the length of the mixture
path 9 as short as possible. In connecting so many holes,
the pitch and size of the holes will likely fluctuate and
problems will likely arise in the concentricity and sealab
ility. However, in the case of this embodiment, as shown in
Fig. 3, O-rings 11 made of an elastic sealing material are
fitted on the outer peripheral portions at both ends of the
pipe 10. Also as shown in Fig. 4, the pipe 10 itself may be
o ~ ~
molded of an elastic sealing material to have ribs lOa
integrally Eormed on the outer peripheral pdrtions a~ both
ends. Further, if such adiabatic material, such as a phenol
resin, is used for the material of the pipe 10, the pipe
will be thermally excellent. The reference numeral 12 in-
dicates a secondary slow-running air jet connected to each
secondary slow-running jet 8 and 13 indicates a secondary
slow-running fuel path connecting each secondary slow-runn-
ing air jet 12 with a ~loat chamber 14. The part from the
secondary bypass hole 7 to the secondary slow-running fuel
path 13 forms a secondary slow-running fuel system and each
secondary slow-running jet 8 can have its size freely selected.
The operation of the above described compound car-
buretor is explained as follows.
~ uring the operation of the engine, if a pedal
(not illustrated) is pressed down for the acceleration,
first the primary throttle valve will open and then the
2~ secondary throttle valve will open to gradually feed a large
amount of a thick air-fuel mixture to each cylinder~ In this
case, during the transit from the primary side to the
secondary side, at the initiation of the opening of the
secondary throttle valve ~, each secondary slow-running
fuel system will act independently on each cylinder. There-
fore, even if the opening of the secondary throttle valve 6
for each cylinder and the opening area of the secondary by-
pass hole 7 fluctuate and the length and bend of the seco-
ndary slow-running mixture path are different, by individ-
ually adjusting the size of each secondary slow-running
jet 8, the fluctuation of the air-fuel ratio for each
cylinder during the above mentioned transit will be able
to be reduced. Further, as the secondary slow-running fuel
systems for the respective cylinders are independent so
as not to interfere with each other, the size of the second-
ary slow-running jet 8 for each cylinder can be freely
g ~
selected and, as a xesult, the air fuel ratio for each
cylinder during the above mentioned transit can be made
opti~lum by taking the thermal factors and vibration cond-
itions into consiaera*ion. Fr~m the above, according-to the
compound carburetor of the present invention, the transit
from the primary side to the secondary side can be made very
smooth Furthex, the length of the sPcondary slow-running
mixture path 9 is so short that substantially no air locking
phenomenon will be generated byl:the temperature rise or the
like. Therefore, the total volume of the secondary slow-
running fuel systems can be made so small and the number of
bends of the secondary slow-running mixture path 9 can be
made so few that the passage resistance will reduce, the
transit delay and unstable jetting of the mixture will be
eliminated and, a~ a result, the response characteristic
will improve. Further, as the secondary slow-running mixture
path g is connected through the pipe 10 in the course, the
freedom of the equipment will increase.
In the above mentioned embodiment, the secondary
slow-running fuel systems are provided independently for the
respective cylinders. However, even if one secondary slow-
running fuel system is provided independently for two cylinders
so as to serve the two cylinders, the same effect will be
able to be obtained. This formation is very advantageous
as to the cost.
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