Air valve type carburetor

An air valve type carburetor of the kind in which a throttle valve is disposed in the downstream portion of a barrel interconnected to an engine via an intake manifold; a main nozzle is disposed upstream of the barrel and is connected to a jet of a float chamber; an air horn disposed on the barrel is connected to an air cleaner via an air connector; an air valve is disposed at the upper part of the main nozzle, faces at its tip the nozzle and is connected to the base end of a metering needle which is inserted into a through-hole of the air horn for free vertical movement therein; and a shield plate is fixed to the shank of the metering needle so as to prevent pressure pulsations inside the air connector from entering the through-hole and being applied to the surface of the fuel.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
This invention is broadly concerned with the field of the technique of 
stabilizing an air-fuel ratio in the high load, high speed range of an air 
valve type carburetor of an engine for vehicles such as a car. 
(2) Description of the Prior Art 
As is well known in the art, a variety of carburetors are available for 
engines of cars or the like and they have both merits and demerits. Among 
them, a so-called air valve type carburetor has gained a wide application 
because it provides excellent high load, high speed performance. 
The air valve type carburetor will be now outlined with reference to FIG. 
1. A barrel 1 is interconnected to an engine, not shown, via an intake 
manifold. When a throttle valve 2 of this barrel 1 is fully open in the 
interlocking arrangement with a throttle valve on the primary side, not 
shown, and the engine operation changes to the high speed, high load 
operation, an air valve 4 of an air horn 3 gradually opens to a balanced 
state in accordance with an intake air quantity against the force of a 
return spring 5 so that a metering needle 7, which is pivotally supported 
by a pin at the tip of a link 6 interconnected to the air valve 4, is 
loosely raised inside a through-hole 8 of the air horn 3, expanding 
metering opening with respect to a jet 10 that is disposed in a float 
chamber 9. The fuel 11 thus metered is applied to a well 12 and is mixed 
and emulsified with bleed air by an emulsion pipe 14 connected to an air 
bleed 13. The mixture is discharged as a rich air-fuel mixture from a main 
nozzle 15 that is disposed between the throttle valve 2 and the air valve 
4. 
An air connector 16, which is disposed on the air horn 3 as shown in the 
drawing, is connected, via a duct 17, to an air cleaner 18 disposed at a 
predetermined position inside an engine room. According to this 
arrangement, the air sucked into the air connecter 16 is applied from the 
air valve 4 to the barrel 1 and is also communicated with the float 
chamber 9 via the through-hole 8 of the metering needle 7. 
Accordingly, the intake air pressure changes with the reciprocating 
revolution of the engine. Intake pulsation occurs especially strongly 
inside the carburetor, disposed separately from the air cleaner, during 
the high load, high speed operation of the engine. 
Intake pulsation also affects the float chamber also from the through-hole 
8 as shown in FIG. 1 in such a manner as to push down the surface of the 
fuel oil immediately below the through-hole 8 in the conelike form. If 
this phenomenon proceeds, the jet 10 sucks the air and the air-fuel 
mixture becomes excessively lean, deteriorating engine drivability. In 
such a case, the excellent high load, high speed performance inherent to 
the air valve type carburetor can no longer be obtained. 
SUMMARY OF THE INVENTION 
The present invention has its technical object in solving the problem of 
the drop of the fuel oil surface resulting from intake pulsation of the 
float jet in the high load, high speed operation range of the conventional 
air valve type carburetor described above. In other words, the present 
invention provides an air valve type carburetor in which a shield plate is 
fixed to the metering needle which is in turn inserted loosely into the 
through-hole of the air horn. The air valve type carburetor of the present 
invention prevents the pressure change resulting from intake pulsation 
from affecting the floating chamber and can be satisfactorily applied to a 
variety of carburetors for various vehicles such as cars.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the embodiment shown in FIGS. 2 and 3, the barrel 1 is interconnected to 
the engine via an intake manifold not shown. A throttle valve 2 is 
disposed downstream of the barrel 1 so as to operate in the mechanical 
interlocking arrangement with another throttle valve on the primary side 
which is not shown. An air horn 3 is fitted onto the barrel 1. An air 
valve 4 is pivotally supported by the air horn 3 and is urged in the 
returning direction by a spring 5. The tip of a side link 6, which is 
integral with the air valve 4, is pivotally supported by a pin at the base 
end of a metering needle 7. 
The metering needle 7 is placed inside a float chamber 9 through a 
through-hole 8 of the air horn 3 and faces the tip of a jet 10 of the 
float chamber 9 so as to meter the fuel 11 and to apply the fuel to a well 
12. The fuel inside the well 12 is mixed with bleed air metered by an 
emulsion hole of an emulsion pipe connected to an air bleed 13, and is 
discharged from a main nozzle 15. 
An air connector 16 is mounted onto the air horn 3 and is connected to an 
air cleaner 18 at a predetermined position via a duct 17. The upper 
portion each of the air valve 4, air bleed 13 and through-hole is 
connected to the inside of the air connecter 16. 
The construction described above is substantially the same as the 
construction of the conventional embodiment shown in FIG. 1. 
In accordance with the present invention, a shield plate 19 is fixed to the 
metering needle 7 at right angles by an industrial adhesive or other 
suitable means. The shield plate is made of a lightweight material such as 
foamed styrol and has a disc-like shape whose diameter is considerably 
greater than that of the through-hole 8. The shield plate is fixed at an 
intermediate part of the metering needle 7 to be inserted into the 
though-hole inside the air connecter 16 such as at a set position in the 
proximity of the through-hole 8 from its lower end under the state in 
which the air valve 4 is fully open so as to correspond to the full open 
state of the throttle valve 2. 
The proximate quantity with respect to the through-hole 8 is such that the 
air flow from the through-hole 8 can be deflected sideways by the shield 
plate 19 as shown in the drawing. 
In accordance with the construction described above, when the car changes 
from the normal driving state to the high load or high speed operation and 
the acceleration pedal is pressed, the throttle valve 2 on the secondary 
side is fully opened in the interlocking arrangement with the operation of 
the throttle valve on the primary side and the air valve 4 gradually opens 
in accordance with the intake air quantity against the force of the return 
spring 5 so that the metering needle 7 rises via the link 6, opens the jet 
10, and meters and applies the fuel 11 to the well 12. The fuel is then 
mixed with the bleed air from the emulsion hole and is discharged as a 
rich air-fuel mixture from the main nozzle 15, providing high torque to 
the engine. 
In the interim, the intake air from the air cleaner causes intake pulsation 
inside the air connecter 16, as described already. However, since the 
disc-like shield plate 19 is fixed to the metering needle 7 at right 
angles at its loose elevating portion with respect to the through-hole 8, 
the intake air, which changes due to pulsation, enters the float chamber 9 
from the through-hole 8. Accordingly, even when a changing pressure is 
applied, it is substantially absorbed and does not act upon the float 
chamber 9, so that the oil level of the fuel 11 is kept flat without being 
pressed. Hence, only the fuel 11 is metered and applied from the jet 10 to 
the well 12 without any intake air. Thus, high torque is generated at the 
set rich air-fuel ratio and satisfactory high load high speed drivability 
can be secured. 
Even if oscillation or the like occurs during driving, the shield plate 19 
has less moment of force because it is made of a light-weight material and 
does not cause the metering needle 7 to displace sideways. 
In the embodiment shown in FIG. 3, the shield plate 19' is straight tapered 
with respect to the through-hole 8 so that the incoming pulsating air from 
the through-hole 8 is more likely to displace sideways. 
In the embodiment shown in FIG. 4, the shield plate has a concave shape so 
as to provide more effective effects than the embodiment shown in FIG. 3. 
In still another embodiment of the invention shown in FIG. 5, the diameter 
of the through-hole 8 is reduced so as to facilitate machining. 
Needless to say, the present invention is not particularly limited to the 
embodiments described above but can be worked in various other 
embodiments. For example, the shield plate may be disposed at upper and 
lower two stages or may be equipped at its peripheral portion with steps 
as a rectifying rib. The shield plate may also be made of a light-weight 
material. 
As described in the foregoing, in the air valve type carburetor, although 
the air cone having the through-hole, into which the metering needle 
connected to the air valve is inserted, is open to the air connector to 
which the air cleaner is connected, the present invention disposes the 
shield plate having a diameter greater or smaller than the diameter of the 
through-hole at a predetermining position of the metering needle loosely 
moving up and down inside the through-hole so as to be right angles to the 
shank of the metering needle, so as to interrupt the air flow between the 
air connector and the float chamber. Accordingly, even when intake 
pulsation occurs inside the air connecter during high load high speed 
operation, the pressure change resulting from pulsation does not act upon 
the float chamber so that push force is not applied to the surface of the 
fuel oil inside the float chamber. This arrangement eventually facilitates 
the air intake from the jet and provides high torque at the rich air-fuel 
ratio as was originally designed. Hence, excellent drivability can be 
obtained. 
Since the shield plate is made of a light-weight material, it creates 
little side displacement of the metering needle when the needle moves up 
and down. The shield plate neither results in the increase in the weight 
of the needle nor in the deterioration of the fuel consumption. 
In accordance with the present invention, further, the shield plate may be 
merely fixed to the metering needle so that the conventional embodiment 
can be employed as such. In producing the carburetor, an additional step 
is limited and hence, the increase in the production cost is negligible. 
Since the construction is simple but has high strength, the apparatus of 
the invention has less trouble, does not require maintenance but has high 
durability.