Note: Descriptions are shown in the official language in which they were submitted.
~L~S~L'733
The present invention relates to exhaust gas
recirculation for internal combustion engines and, in
particular, to an exhaust gas recirculation valve in
a motor vehicle exhaust emission system to provide
exhaust gas mass flow rate proportional to effective
opening of the valve alone.
One of the methods used to reduce oxides of
nitrogen emissions from the exhaust gases in an internal
combustion engine is tG recirculate a portion of the
exhaust gas- through the engine air intake upstream of
the intake manifold. To achieve a greater reduction
in the oxides of nitrogen with minimal deterioration
of vehicle drivability, the amount of exhaust gas
recirculation should be proportional to engine air
consumption throughout the normal operating range of
the engine.
Conventionally, exhaust gas recirculation is
effected by pres~ure difference between exhaust gas
pressure and induction vacuum downstream of carburetor
throttle valve and the amount o~ exhaust gas recircu~
latlon is controlled by restricting effective cross
- ectional area of exhaust gas recirculation passage
with exhaust gas recirculation valve in response to
venturi vacuum.
This control method involves a problem that the
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flow rate of exhaust gas recirculation increases as the pressure
difference increases even when the opening of the exhaust gas
recirculation valve remains constant. This is particularly a
problem during low load engine opera-tion, in which the engine
induction vacuum is high and format:ion of oxides of nitrogen is
little, because the flow rate of exhaust gas recirculation
increases excessively.
It is a primary object of the present invention to
provide an exhaust gas recirculation which is simple in
construction but precisely meter the flow rate of the recircu-
lated exhaust gas.
It is another object of the present invention to
tailor the design parameters of a valve member and a tube serving
as a valve port for the valve member.
Other objects and advantages of the present invention
will become apparent from the following description in connec-
tion with the accompanying drawings, in which:
Fig. 1 is a schematic view of an exhaust gas
recirculation system;
Fig. 2 is an enlarged sectional view of the valve
member and the venturi tube serving as the valve port for the
valve member; and
Fig. 3 which appears on the same sheet of drawings as
Fig. 1, is a graph showing the experimental results.
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Referring to Fig. 1, there is shown an internal
combustion engine 10 having an intake passage 12 in-
cluding a carburetor 14 and an exhaust passage 16
through which exhaust gases flow. An exhaust gas
recirculation or EGR valve 18 generally comprises a
motor housing 20 having a circular diaphragm 22 dividing
`the housing into a vacuum chamber 6 and an atmospheric
chamber o. A downwardly projecting valve stem 28 is
c~ntrally attached to the dia`phragm 22. A valve member
24 is attached to the valve stem 28 and has a conical
pintle which cooperates with a venturi tube 26 formed
in a valve body 29 to restrict the flow of exhaust
gases from a runner 30 formed in the ~alve body 29 of
an exhaust gas recirculation or EGR passage to a second
15~ runner 32 formed in the val~e body 29 of the EGR passage.
A coilsd spring 34 disposed in the vacuum chamber 6
serves to normally bias the diaphragm 22, the val~e
stem 28, and the valve member 24 to a minimum opening
position with respect to the venturi tube 26. :
~uring engine operation, the flow conditions in ..
a venturi 36 of a thro*tls bore 38 of the carburetor
14, produce a vacuum signal proportional to engine air
consumption. This vacuum signal is amplified by a
suitable apparatus 40 ~nd the amplified signal is used
Z5 t~ control the op ening ~ ~o~ing of the v~lvc ~ember
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24. This amplified vacuum .signal is applied to the
vacuum chamber 24 of the motor housing 20~
Referring to Fig 2, the valve member 24 and the
venturi tube 26 which are designed according to the
pr.esent invention will be described hereinafter.
The venturi tube 26 has a convergent cone 42 and
a divergent cone 44 which are separated at their smallest
diameters by a throat 46. An inlet port 48 of the
venturi tube 26 fluidly connects with the first runner
30 and from the inlet port 48 the convergent cone 42
leads to the throat 46, while an outlet port 50 o~ the
ven~uri tube 26 fluidly connects with the second runner
32 and to the outlet port 50 the divergent cone 44
leads from the throat 46.
t5 The valve member 24 has a conical lower portion
52 having a relatively small cone angle than the
divergent cone 44, an upper flange portion 54 adapted
to close the outlet port 50 of the venturi tube 26,
and a conical intermediate portion 56 between the base
of the conical lower portio~ 52 and the upper ~langa
portion 54. The conical intermediate portion has a
relatively great cone angle than the conical lower
portion 52. The valve member 24 is coaxially movable
in the venturi tube 26 from a closed position in which
the upper flanga portion 54 closes the outlet port 50
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of the venturi tube 26 to a maximum opening position,
the position illustrated in Fig. 2, in which a smaller
diameter portion of the conical lower portion 52
extends into the convergent cone 42 beyond the throat
46 and a larger diameter portion 52 is disposed in the
outlet port 50 of the venturi tube 26.
The design parameters for the valve member 24 and
the venturi tube 26 are as follows.
Let the effective clearance between the valve
member 24 and the throat 46 of the venturi tube 26 when
the valve member 24 is in the maximum opening position,
the position illustrated i~ Fig. 2, be Ao~ let the
effective sectional area at the inlet port 48 of the
venturi tube 30 when the valve member 24 is in the
~aximum opening position be A1, and let the effective
sectional area between the valve member 24 and the
outlet port 50 of the tube 30 when the valve member 24
is in the maximum opening position be A2. Let the
. diameter of the throat 46 be D, let the axial length
Or the convergent cone 42 be L1 and let the axial length
of the divergent cone 44 be L2. Thsn, the valve member
24 and.the tube 30 should satisfy the following
relationships.
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D is from 5mm to 20mm.
L1 is from 0.5xD to 2.0xD.
L2 is from 2.0xD to 5.0xD.
A1/Ao is from 2 to 10.
A2/Ao is from 2 to 8.
If the venturi tube 26 and the valve mernber 24 are
sized to satisfy these relationships the flow ~elocity
of *he exhaust gas at the throat 46 exceeds,t'he s~nic
velocity when a pressure difference between a static
pressure at the inlet port 4B and a static pressure at
the outlet port 50 reaches a value which ranges from '
1/2 to 1f4 of a critical pressure which is a static
pressure at the throat 46 when the flow velocity of the
exhaust gas at the throat 46 reaches the sonic velocity.
E,xperimcnt was conducted by the inventors of
this invention with a valve member and a venturi tube
having'dimensions as follows.
D=10.Omm, LI=8.0mm, L2=30.0mm, AO=25mm2, A1-100mm2
A2=100~m , A1/Ao=5~ A2/Ao=4
As a resul*, the flow velocity,of the exhaust gas at
the throat of the tube reaches the sonic velocity when
the pressure difference between a static pressure at
~n ~inlet port of the tube and a static pressure at an
outlet port of the venturi tube reaches 110mmHg which
,"25 is 30% of the cr1tical pressure of 360mmHg.The flow
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velocity of the exhaust gas at the throat remains the
sonic velocity even if the pressure difference increases
up to 400mmHg.
Fig. 3 shows characteristic curves (shown in
solid lines~ when the valve member is lifted from the
closed position of the valYe member by 6mm and 10mm,
respectively, showing the experimental results obtained
by th~ expe~iment. :
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