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Патент USA US2412563

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Dec.17,1946.7
R. D. CURK
CARBURETOR
Filed July 20, 1944
J20WaEm
2,412,563
2,412,563
Patented Dec. 17, 1946
I UNITED STATE s
PATENT‘ orrics
2,412,563
.
CARBURETOR
Ralph D. Curk, Dayton, ,Ohio, assignor to
Chandler-Evans Corporation, South Meriden,
Conn., a corporation of Delaware
’ Application July 20, 1944, Serial No. 545,807 _ r
' 1 Claim.
(01. 261-39)
The present invention relates to the measure
ment of ?ow of a ?uid of variable density, and
particularly to apparatus for measuring the flow
of air for use on a carburetor for an aircraft type
internal combustion engine.
A carburetor may be de?ned as a device for
'
?owing ?uid independently of any variations in
its pressure, and means for correcting the Ven
turi meter for pressure variations independently
of any temperature variations.
A'further object of the invention is to provide
improved means of the class described adapted
for use in connection with a, carburetor for an ‘
controlling the fuel-to-air ratio of the charge
aircraft type internal combustion engine.
supplied to the cylinders of an internal combus
Other objects and advantages of the invention
tion engine. In order to control the proportions
will
become apparent from a consideration of the
10
of the charge, certain types of carburetors now
in common use on aircraft utilize means for,‘
measuring the air ?ow, means for measuring the
fuel ?ow, and means for comparing'thev air and
fuel ?ows and for controlling the fuel ?ow so‘as
to correct it if it is not inthe proper proportio
with respect to the air ?ow. '
appended speci?cation, claim and drawing,- in
which the single figure represents; somewhat dia
. grammatically, a carburetor for an internal com
bustion engine employing the principles . of my
invention. -
.
-
'
Referring to the drawing, there is shown a body
Ill of a carburetor .for an internal combustion en
Since aircraft must operate at different altie ‘
tudes and at widely varying temperatures, the, " - gine of an aircraft. Air enters the carburetor
pressure and temperature, and hence the density, - body Id at an inlet l2 and .?ows thru a‘ Venturi
restriction I4 and a ‘passage [5, past a throttle
of the air. entering-the engine varies widely; In
' ii and a fuel discharge nozzle l8 to an outlet 20.
order to maintain a given fuel-to-air ratio,_th'e
A supercharger may be provided’ between the out
mass of fuel must be proportioned to the mass
let_ 20 and the intake manifold of the engine.
of air entering the engine. Therefore, thedevice ‘ ‘" In-certain
casesthe supercharger may be up
which measures the air ?ow must measure the
stream
from
the inlet I2, or two superchargers
25
mass of air ?owing per unit time rather than
may
be
used,
one‘in
each place.
the velocity of the ?owing air. ~
The Venturi restriction ll produces a pressure
The ‘most common device used to measure the
.difierential between the inlet I2 andthe throat
I
In accordance
air ?ow is the Venturi meter.
" , of. the restriction which varies substantially in
with the laws of ?uid ?ow, a Venturi meter pro
accordance with the squareof the velocity of the
' duces a pressure differential which varies as a 30
function of the velocity of the ?uid ?owing thru - air passing thru the restriction. Since the cross
''sectional area, of the Venturi is constant, this > '
it. If the device is to measure the mass of 'the
pressure differential may be taken as» a measure
?owing air, the pressure differential produced by'
of the volume of air ?owing ‘thru the passage per
the Venturi meter must be corrected for varia
tions in air density.
'_ '_
. 35 unit time.
In order to obtain a pressure differential vary- _
" A correction for air density has been obtained
ing as a function of the mass of air per unit time
in the past by utilizing a sealed bellows ?lled
?owing thru the Venturi H, the pressure differ
with a temperature responsive ?uid to operate a
ential between entrance l2 and the throat of‘
valve controlling the ?ow of air thru a passage
I4 is utilized to create an air ?ow thru
wherein the air ?ow .is induced by the pressure 401‘ ,Venturi
a secondary air passage extending from entrance
differential set up by the Venturi meter. Such
12 to the throat of Venturi M. A plurality of
a valve provides only an approximate correction
impact tubes 22 are provided, whose open ends
for air density, since the correction produced for
' project into the entrance l2 to receive the impact
a given change in temperature is different for
of the entering air. The secondary air passage
each value of pressure. Likewise, the correction 45
may be traced from entrance l2, thru tubes 22,
produced for a given change in pressure is di?er- .
a passage 24 interconnecting the impact tubes,
cut for each temperature encountered.
a conduit 26, a chamber 28 in a pressure meter
It is, therefore, an object of the present inven
generally indicated at 30, a restriction 32,~ a
tion to provide improved'means' for measuring
the rate of ?ow of a mass of ?uid of variable 50 chamber 34 in the pressure meter 30, a conduit
36, past a valve 38 into a chamber 40, and thence
thru a conduit 42 to the throat of Venturi H.
Another object of the invention is to provide
The valve 38 is operated by a sealed bellows 44
means, in connection with a Venturi meter used
mounted in the chamber 40. The bellows 44 is
with a ?uid of variable density, to correct the
' meter for variations in the temperature of the 55 fixed at one end,.so that the positibn of the free
density.
'
,
‘
8,412,568
3
end, to which valve 38 is attached, varies in ac~
ccrdance with the air pressure in the chamber
40. The bellows 44 is preferably ?lled with nitro
‘gen or some other suitable temperature respon
tive fluid, so that the position of valve 38 varies
not only with the pressure but with the tempera
ture of the air in the chamber 40, and hence with
the density of that air.
4
' in response to increasing temperatures so as to
increase the pressure drop across restriction 32
as the temperature increases.
'
I The particular contour selected for valve 38
is a compromise design ofa rather complicated
nature, which depends on the characteristics of
the bellows, and on the particular limitations of
pressure and temperature at which the carburet
The cross-sectional area of restriction 32 is
or is designed to operate on a particular type of
controlled by a valve 33 operated by a bellows 35. 10 aircraft.v The contour of valve 33 must also be
The bellows v35 is ?lled with any suitable tempera
a compromise design. It has been found, how
ture responsive ?uid and is connected thru a
ever, that it is possible to approach more closely
tube 31 of suitable dimensions to a bulb 39 inside
the ideal of theoretical perfect density compen
the air passage in the carburetor body [8. The
sation at all values of temperature and pressure
bulb 39 is ?lled with the same ?uid and operates
by the use of the two valves 33 and 38, than is
to cause an expansion of the bellows 35 and a‘
possible by the use of the valve 38 alone.
closing movement of valve 33 upon an increase
Although I have illustrated the bellows 44 as
‘ in temperature adjacent the bulb 38. The tube
' being responsive to both pressure and tempera
31 should be made as short and as small as pos
ture, the temperature responsive feature may be
sible in order that the valve 33 may respond cor~ 20 eliminated from that bellows, if desired, by .using
rectly to the temperature of the combustion air,
an evacuated bellows. The temperature‘ correc
without regard to the ambient temperature,‘
which may be affected by heat from the engine. -
Although the tube 31 is shown as being quite long
and of substantial diameter in the drawing, it
was so drawn merely forv purposes of facilitating
the illustration.
In the secondary air passage, the pressure dif
ferential between the-entrance I 2 and the throat
of venturi I4‘ is divided into two component 30
pressure drops, one across the restriction 32 and
the other across the valve 38. The valve 38 is
positioned in accordance with the pressure of
_ the air ?owing thru the passage l5. ‘Valve 38 is
moved toward open position as the air pressure
increases and toward closed position as the air
~ pressure decreases.
If the volume of air ?owing
per unit time thru passage I5 remains constant
while its pressure decreases, then the mass of air
tion would then be obtained only from bellows
35 and valve 33.v Under such circumstances, the
contours of both valves would have to be differ
ently designed. Furthermore, it would be desir
able to have the valve 33 work in the opposite
direction. That is, the valve 33 should open as
the temperature increases instead of closing with
increasing temperature as now shown.
By proper design of valves 38 and 33, the pres
sure drop across restriction 32 may be made
to vary substantially in accordance with the mass
of air ?owing thru passage i5. This pressure
differential across restriction 32 acts on the dia
phragm 48 which separates the chambers 23 and
34. The force applied to diaphragm 45 is trans
mitted to a valve 48, onwhich it acts in a closing
direction.
‘
The fuel enters the carburetor from a fuel
is decreased, but the pressure differential set up 40 pump or other source of fuel under superatmos
.byv the venturi i4 remains constant. However,
pheric pressure. It ?ows thru a conduit 50, a
the’movement of valve 38 toward closed position
valve 52 in a pressure regulator generally indi
causes the component pressure ~drop across valve
cated at 54, a conduit 56, a mixture control gen
38 to increase, and the component pressure drop
. erally indicated at 58, a jet system 80, an idle
' ‘across restriction 32 to decrease proportionately, 45 valve I25, a conduit 62, a valve 84 in a‘second
reflecting the decrease in the mass of air ?owing
regulator 86, and a conduit 88 to the fuel. dis—
per unit time.
_
The bellows 44 responds to changes in tempera
charge nozzle I 8. I
The pressure regulator 54 includes a diaphragm
10 separating a pair of expansible chambers 12
ner. . An increase in temperature of that air 50 and ‘I4 and connected at its center to the valve
causes an expension of bellows 44 and so re-'
52. A spring 76 biases the valve 52 toward open
duces the pressure drop across restriction 32 to
position. A restriction 18 connects the chambers
compensate for the decrease in density of the
12 and 14.
air accompanying its increase in temperature.
A portion of the fuel entering pressure regu
Since the volume of bellows 44 is different for 55 lator 54 ?ows thru chamber 74, restriction ‘I8,
each value of external pressure, it may be seen
chamber 72, a conduit 80, a. chamber 82 in the
that the bellows produces a different travel of
pressure meter 30, past the valve 48, and thru a
valve 38 per unit change in temperature for each
conduit 84 to the main air passage l5.
different value of pressure. At sea level, the air
The pressure meter 38 includes a diaphragm 8|
pressure is relatively high,‘ the bellows 44 has a‘ 60 separating the chambers 34 and 82 and a dia
small volume and, therefore, produces a rela
phragm 88 separating the chamber 28 from a
tively small travel per degree change of tem
fourth expansible chamber 90. The valve 48 is
perature. At high altitudes, and consequent low
biased toward closed position by a spring 82.
atmospheric pressures, the bellows 44 has a rela
The chamber 90 is connected thru a conduit 34
tively large volume and hence produces a larger 65 to the fuel conduit 82 downstream from the Jet
travel per degree change in temperature. Under
system 68. The pressure in chamber 90 is there
those circumstances, its effect is to overcompen
fore the same as that in the fuel line downstream
sate for changes in temperature. In other words,
from the jet system. The pressure in chamber 82
instead of correcting the inherent tendency ‘of
is the same as that in chamber 12 of pressure
the carburetor to produce too rich a mixture as 70 regulator 54. The position of diaphragm 18 and
the air density increases due to increase in tem
valve 52 is determined by the balance between the
perature, the valve 38 under those circumstances
spring 18 plus the pressure in chamber 72 acting
over-corrects and causes the carburetor to pro
in a valve opening direction and the pressure in
duce too ‘lean a mixture.
chamber 14 acting in a valve closing direction.
The valve 33 opposes this tendency by closing 75 If the balance between these forces is upset, the
ture of the air in chamber 40 in a similar man
. 2,412,503
5
.
diaphragm ‘I0 and valve 52 move until the balance
is restored. 'Therefore the pressure in chamber .
‘I2 is a measure of the pressure in chamber ‘M,
which is substantially the same as the pressure on
the upstream side of the jet system 60. For any
given constant cross-sectional area of the fuel
passages thru the jet system 60, the pressure dif
, tion.
6
When the differential pressure acting on
diaphragm 46 is small, as under low air ?ow con
ditions, the spring 92v becomes the predominating
ferential across it is a measure of the fuel ?ow
1 thru it.
,
a reliable indication of the volume of air entering
the engine. Provision is made to control the fuel
?ow directly in accordance with the throttle po
sition at such times. The spring 82 in the pres
sure meter 30 acts on valve 48 in a closing direc
This pressure diiferential, or rather a -'
, force acting on valve 48. A closing movement of
smaller pressure differential which is a measure
10 valve 48 causes ‘an increase in the fuel ?ow thru
of the pressure differential across the jet system,
is applied thru the diaphragms 86 and 88 of pres
" increases the pressure in chamber .82 of pressure,
@the main‘ fuel line, since the closure of‘valve 48
sure meter 30 to the valve 48, on which it acts in. ~
meter 30 and hence in chamber ‘I2 of pressure
an opening direction.
regulator 54. Furthermore, the'spring ‘I6 of pres
-
From the foregoing, it may be seen that the 15 sure regulator 54 biases valve. 52 in an opening
valve 48 is positioned in accordance with the bal
or fuel ?ow increasing direction.
ance between two forces, one of which varies in
The idle valve I25 is pivotally attached to a
accordance with the mass of air entering the
lever I28, whose opposite end is connectedby a.
carburetor, and the other in accordance with the
link I30 to an arm I32 ?xed on the shaft I“
mass of fuel entering the carburetor. Further 20 of throttle I6. The idle valve is normally wide
more, the valve 48 controls the mass of fuel en
\ tering the carburetor, since it controls the pres
sure in chamber 82. The pressure in the cham
open when the throttle is beyond a range of po—
sitions near its closed position, usually termed the
idling range. As the throttle moves into the idling
ber 82 is transmitted to chamber ‘I2 of pressure
range, thereby decreasing the air flow, the idle
regulator 54 where it controls the position of valve 25 valve I25 moves toward closed position. At the
52 and hence the pressure on the upstream side of
same time, the springs 92 and ‘I6 cause operation
the jet system 60.
of valve 52 in an opening direction. The valve
The pressure regulator 66 operates to maintain
52 is thereby opened sufficiently so that its re
- a substantially constant pressure on the down
strictive effect on the fuel ?ow is less thanthat
stream side of the Jet system 60 and thereby to 30 of the idle valve I25. Therefore, the fuel flow
prevent variations in pressure at the fuel dis
under idling conditions is controlled primarily by
charge nozzle I8, which may be ue to operation
the valve I25 in accordance with the position of
of the throttle or to variations i engine speed.
g
the throttle, and not by the pressure meter 30
from reaching the downstream side of the jet
in accordance with the mass of air entering the
system and affecting the fuel flow.
_
35 engine.
The pressure regulator 66 includes a pair of ex
Although I have illustrated a particular type of
pansible chambers 96 and 98 separated by a ?ex
carburetor, it will be appreciated by those skilled
ible diaphragm I00, which is attached at its cen
in the art that my invention may be applied with
. ter to the valve 64. A spring I02 biases the valve
equal facility to other types of carburetors. The
64 toward closed position. The chamber 86 is 40 carburetor illustrated may, for example, be modi
connected thru a conduit I04 to the conduit 26
?ed by omitting the pressure regulator 54 and '
and thence thru the passage 24 and impact tubes
placing the valve 48 of the pressure meter 80
22 to the air entrance I2. The chamber 88 is
directly in the fuel line between the pump and
connected to the conduit 62. '
'
the mixture control 58.
The mixture control 58 includes a disc valve I08 45
While I have shown and described a preferred
?xed on a shaft I08. The discvalve I08 controls
embodiment of my invention, other modi?cations
the ?ow of fuel thru ports opening into conduits
thereof will readily occur to those skilled in the
H0 and H2 which lead into the Jet system 88.
art, and I therefore intend my invention- to be
When the disc I08 is in the position illustrated in ' limited only by the appended claim.
full lines in‘the drawing, fuel can ?ow to the jet 50
I claim as my invention:
}
system only thru the conduit H0. This full line
A
carburetor
for
an
internal
combustion
en
position of the disc valve I06 is known as the '
gine, comprising a conduit for combustion air
“lean” position of the mixture control 58. When
the disc valve I00 is in the dottedline position . ?owing to said engine, means associated with said
shown in the drawing, the fuel can ?ow thru both 55 air conduit for producing two unequal pressures
whose di?erence varies in accordance with the
the conduits H0 and H2. The dotted line posi
velocity of the air ?owing therethru, a passage
tion of the disc valve I06 is termed the “rich”-po_
connecting spaced points in said air conduit sub
sition of the mixture control. The disc valve I08
can also be moved to a “cut-off” position wherein -
it cuts off the flow thru both conduits I I0 and I I2.
The conduit IIO conducts fuel either thru a 00
?xed restriction or“ jet II 4, or thru a restriction
Il8 controlled by a valve II8 biased to closed po
sition by a spring I 20. The condui
' conducts
fuel to a ?xed restriction I22.
i'lowing'thru' 65
the restrictions H6 and I22 also ?ows thru an
other restriction I24 which limits the total flow
thru restrictions H8 and I22.
,
ject to said two unequal pressures so that a flow ‘
of air is induced thru said passage by said dif
ference of pressures, ?rst and second valves in
series in said passage for controlling the ?ow of
air therethru, a ?rst sealed ?exible bellows ?lled
with a ?uid having an appreciable coefficient of
thermal expansion and exposed to the air ?owing
thru said passage so that it expands upon a de
crease in pressure or an increase in temperature
of said air, a connection between said ?rst bellows
and said ?rst valve so that expansion of said ?rst
The valve H8 is normally closed, but opens at
moves said ?rst valve in a closing direc
high pressure differentials across the jet system 70 bellows
tion, whereby an increase in air temperature
to increase the fuel-to-air ratio under heavy load
conditions.
At low air ?ows, such as are encountered under
causes an increase in the pressure drop across -
said ?rst valve and a corresponding decrease in
the pressure drop across said second valve, said
idling conditions, the pressure differential set up
?rst bellows having an inherent tendency to over
by the venturi I4 tends to be erratic, and is not 75 compensate for temperature changes under low
2,412,663
._ 7
I
pressure conditions, a second sealed ?exible bel
lows, a bulb in said air conduit ?lled with a fluid
having an appreciable coef?cient of thermal ex
8
drop across said second valve to correct for the
overcompensation produced by said ?rst valve,
said ?rst and second valves cooperating with said
pressure producing means to regulate the pres
pansion, a pressure-transmitting connection be
tween said bulb and said second bellows, so that 5 sure drop across said second valve substantially
in accordance with the mass of air ?owing thru
an increase in the air temperature adjacent said
said conduit per unit time, and means responsive
bulb expands said second bellows,- a connection.
to the pressure drop across said second valve for
between said second bellows and said second valve
controlling the ?ow of fuel to the engine.
so that expansion of .said second bellows closes
said second valve, wherebyan increase in air
"RALPH D. CURK.
temperature causes an increase in the pressure
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