U.S. patent number 3,834,366 [Application Number 05/375,362] was granted by the patent office on 1974-09-10 for exhaust gas recirculation control valve.
This patent grant is currently assigned to General Motors Corporation. Invention is credited to William L. Kingsbury.
United States Patent |
3,834,366 |
Kingsbury |
September 10, 1974 |
EXHAUST GAS RECIRCULATION CONTROL VALVE
Abstract
A vacuum operated valve responsive to exhaust back pressure
controls recirculation of exhaust gases from the intake manifold
exhaust crossover passage to the intake manifold induction
passages.
Inventors: |
Kingsbury; William L. (Madison
Heights, MI) |
Assignee: |
General Motors Corporation
(Detroit, MI)
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Family
ID: |
26936493 |
Appl.
No.: |
05/375,362 |
Filed: |
July 2, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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244378 |
Apr 17, 1972 |
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Current U.S.
Class: |
123/568.29 |
Current CPC
Class: |
F02M
26/56 (20160201); F02B 75/22 (20130101); F02M
26/61 (20160201); F02M 26/58 (20160201); F02M
2026/0025 (20160201) |
Current International
Class: |
F02B
75/22 (20060101); F02M 25/07 (20060101); F02B
75/00 (20060101); F02m 025/06 () |
Field of
Search: |
;123/119A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Burns; Wendell E.
Attorney, Agent or Firm: Veenstra; C. K.
Parent Case Text
This is a continuation of application Ser. No. 244,378, filed Apr.
17, 1972 .
Claims
I claim:
1. An exhaust gas recirculation control valve assembly for use on
an internal combustion engine having an induction passage for air
flow to the engine, a throttle disposed in said induction passage
for controlling air flow therethrough, an exhaust passage for
exhaust gas flow from the engine, and an exhaust gas recirculation
passage having a first portion extending from said exhaust passage
and a second portion extending to said induction passage downstream
of said throttle, said control valve assembly comprising a valve
body having an inlet for receiving exhaust gases from said first
portion of said recirculation passage, an outlet for discharging
exhaust gases to said second portion of said recirculation passage,
valve seat means formed between said inlet and said outlet, and an
orifice formed in said inlet, valve means associated with said
valve seat means for controlling flow of exhaust gases
therethrough, and control means for positioning said valve means to
maintain a substantially constant pressure in the zone between said
orifice and said valve seat means, said control means including
spring means biasing said valve means toward engagement with said
valve seat means, a pressure responsive member connected to said
valve means, means defining a vacuum orifice through which said
member is subjected to the pressure in said induction passage
downstream of said throttle, means defining an air bleed orifice
through which said member is subjected to atmospheric air, a bleed
valve associated with one of said orifices for controlling flow
therethrough and thus regulating the control pressure created by
induction passage vacuum received through said vacuum orifice and
atmospheric air received through said air bleed orifice, pressure
responsive means connected to said bleed valve and subjected to the
pressure in said zone whereby upon an increase in pressure in said
zone said pressure responsive means displaces said bleed valve to
decrease said control pressure to thereby cause said pressure
responsive member to overcome the bias of said spring means and
displace said valve means from said valve seat means and increase
recirculation of exhaust gases, and second spring means biasing
said bleed valve to increase said control pressure whereby upon a
decrease in pressure in said zone said second spring means
displaces said bleed valve to increase said control pressure to
thereby permit said first spring means to displace said valve means
toward said valve seat means and decrease recirculation of exhaust
gases.
2. An exhaust gas recirculation control valve assembly for use on
an internal combustion engine having an induction passage for air
flow to the engine, a throttle disposed in said induction passage
for controlling air flow therethrough, an exhaust passage for
exhaust gas flow from the engine, and an exhaust gas recirculation
passage having a first portion extending from said exhaust passage
and a second portion extending to said induction passage downstream
of said throttle, said control valve assembly comprising a valve
body having an inlet for receiving exhaust gases from said first
portion of said recirculation passage, an outlet for discharging
exhaust gases to said second portion of said recirculation passage,
valve seat means formed between said inlet and said outlet, and an
orifice formed in said inlet, valve means associated with said
valve seat means for controlling flow of exhaust gases
therethrough, and control means for positioning said valve means to
maintain a substantially constant pressure in the zone between said
orifice and said valve seat means, said control means including
spring means biasing said valve means toward engagement with said
valve seat means, a pressure responsive member connected to said
valve means, means defining a vacuum orifice through which said
member is subjected to the pressure in said induction passage
downstream of said throttle, means defining an air bleed orifice
through which said member is subjected to atmospheric air, a bleed
valve associated with said bleed orifice for controlling admission
of air therethrough to vary the control pressure created by
induction passage vacuum received through said vacuum orifice and
atmospheric air received through said air bleed orifice, pressure
responsive means connected to said bleed valve and subjected to the
pressure in said zone whereby upon an increase in pressure in said
zone said pressure responsive means displaces said bleed valve to
decrease admission of air through said bleed orifice and thereby
decreases said control pressure to thereby cause said pressure
responsive member to overcome the bias of said spring means and
displace said valve means from said valve seat means and increase
recirculation of exhaust gases, and second spring means biasing
said bleed valve to permit increased admission of air through said
bleed orifice whereby upon a decrease in pressure in said zone said
second spring means displaces said bleed valve to increase
admission of air through said bleed orifice and thereby increases
said control pressure to thereby permit said first spring means to
displace said valve means toward said valve seat means and decrease
recirculation of exhaust gases.
3. An exhaust gas recirculation control valve assembly for use on
an internal combustion engine having an induction passage for air
flow to the engine, a throttle disposed in said induction passage
for controlling air flow therethrough, an exhaust passage for
exhaust gas flow from the engine, and an exhaust gas recirculation
passage having a first portion extending from said exhaust passage
and a second portion extending to said induction passage downstream
of said throttle, said control valve assembly comprising a valve
body having an inlet for receiving exhaust gases from said first
portion of said recirculation passage, an outlet for discharging
exhaust gases to said second portion of said recirculation passage,
valve seat means formed between said inlet and said outlet, and an
orifice formed in said inlet, valve means associated with said
valve seat means for controlling flow of exhaust gases
therethrough, and control means for positioning said valve means to
maintain a substantially constant pressure in the zone between said
orifice and said valve seat means, said control means including
spring means biasing said valve means toward engagement with said
valve seat means, a hollow valve stem connected to said valve means
and extending outwardly of said valve body, a pressure responsive
assembly having a first diaphragm backing member secured to said
valve stem, a diaphragm having a flexible inner portion defining an
exhaust pressure chamber with said backing member and a flexible
annular outer portion extending radially outwardly from said
backing member, and a second diaphragm backing member defining an
atmospheric air chamber with said inner portion of said diaphragm,
a cover member defining a control pressure chamber with said outer
portion of said diaphragm and said second backing member, said
cover member having means for connecting said control pressure
chamber to said induction passage downstream of said throttle, said
diaphragm and said first backing member having openings for
admitting atmospheric air to said atmospheric air chamber, said
second backing member having an air bleed orifice for admitting
atmospheric air from said atmospheric air chamber to said control
pressure chamber, a bleed valve connected to said inner portion of
said diaphragm and associated with said air bleed orifice for
controlling admission of air to said control pressure chamber, said
hollow stem defining a passage connecting said exhaust pressure
chamber to said zone, whereby upon an increase in pressure in said
zone said inner portion of said diaphragm displaces said bleed
valve to decrease admission of air to said control pressure chamber
through said bleed orifice and thereby decreases the pressure in
said control pressure chamber to thereby cause said pressure
responsive member to overcome the bias of said spring means and
displace said valve means from said valve seat means and increase
recirculation of exhaust gases, and second spring means biasing
said bleed valve to permit increased admission of air to said
control pressure chamber through said bleed orifice whereby upon a
decrease in pressure in said zone said second spring means
displaces said bleed valve to increase admission of air to said
control pressure chamber through said bleed orifice and thereby
increases the pressure in said control pressure chamber to thereby
permit said first spring means to displace said valve means toward
said valve seat means and decrease recirculation of exhaust
gases.
4. The method of operating an internal combustion engine having an
induction passage for air flow to the engine, a throttle disposed
in said induction passage for controlling air flow therethrough, an
exhaust passage for exhaust gas flow from the engine, an exhaust
gas recirculation passage extending from said exhaust passage to
said induction passage downstream of said throttle, a valve
controlling exhaust gas flow through said exhaust gas recirculation
passage, and pressure responsive means for positioning said valve,
said method comprising the steps of
sensing the pressure in said induction passage downstream of said
throttle,
opening an air bleed to increase the pressure sensed from said
induction passage and thereby create a control pressure signal,
subjecting said pressure responsive means to said control pressure
signal,
varying the opening of said air bleed in inverse relationship with
the pressure in said exhaust gas recirculation passage upstream of
said valve whereby said pressure responsive means operates said
valve to create a zone of substantially constant pressure in said
exhaust gas recirculation passage,
and flowing exhaust gases through an orifice into said zone,
whereby the rate of exhaust gas flow through said exhaust gas
recirculation passage varies in accordance with the exhaust gas
pressure in said exhaust passage and is thereby proportional to the
rate of air flow through said induction passage.
5. An exhaust gas recirculation control valve assembly for use on
an internal combustion engine having an induction passage for air
flow to the engine, a throttle disposed in said induction passage
for controlling air flow therethrough, an exhaust passage for
exhaust gas flow from the engine, and an exhaust gas recirculation
passage having a first portion extending from said exhaust passage
and a second portion extending to said induction passage downstream
of said throttle, said control valve assembly comprising a valve
body having an inlet for receiving exhaust gases from said first
portion of said recirculation passage, an outlet for discharging
exhaust gases to said second portion of said recirculation passage,
valve seat means formed between said inlet and said outlet, and an
orifice formed in said inlet, valve means associated with said
valve seat means for controlling flow of exhaust gases
therethrough, and control means for positioning said valve means to
maintain a substantially constant pressure in the zone between said
orifice and said valve seat means, said control means including
spring means biasing said valve means toward engagement with said
valve seat means, a pressure responsive member connected to said
valve means, a housing defining a control pressure chamber having a
vacuum orifice through which said control pressure chamber is
subjected to the pressure in said induction passage downstream of
said throttle and an air bleed orifice through which said control
pressure chamber is subjected to atmospheric air, a bleed valve
associated with said bleed orifice for controlling admission of air
therethrough to vary the control pressure created in said control
pressure chamber by induction passage vacuum received through said
vacuum orifice and atmospheric air received through said air bleed
orifice, means for subjecting said pressure responsive member to
the control pressure in said control pressure chamber, a diaphragm
connected to said bleed valve and subjected to the pressure in said
zone whereby upon an increase in pressure in said zone said
diaphragm displaces said bleed valve to decrease admission of air
to said control pressure chamber through said bleed orifice and
thereby decreases said control pressure to thereby cause said
pressure responsive member to overcome the bias of said spring
means and displace said valve means from said valve seat means and
increase recirculation of exhaust gases, and second spring means
biasing said bleed valve to permit increased admission of air to
said control pressure chamber through said bleed orifice whereby
upon a decrease in pressure in said zone said second spring means
displaces said bleed valve to increase admission of air to said
control pressure chamber through said bleed orifice and thereby
increases said control pressure to thereby permit said first spring
means to displace said valve means toward said valve seat means and
decrease recirculation of exhaust gases.
Description
SUMMARY OF THE INVENTION
This invention relates to exhaust gas recirculation in an internal
combustion engine and more particularly to a novel valve assembly
for controlling exhaust gas recirculation.
Recirculation of exhaust gases has been developed as a method for
reducing formation of oxides of nitrogen during the combustion
process in an internal combustion engine. In general, it is desired
to recirculate the exhaust gases at a rate proportional to the rate
at which combustion air flows into the engine, and valves
responsive to induction passage vacuum or throttle position have
been utilized for this purpose.
It also has been recognized that if exhaust gases were recirculated
through an orifice into a region of substantially atmospheric
pressure in the engine air induction system, variations in exhaust
back pressure would cause the exhaust gas recirculation rate to be
proportional to the combustion air flow rate. However, such a
system would require that the exhaust gases pass through at least a
portion of the carburetor.
This invention provides a novel valve assembly utilizing the
exhaust back pressure to recirculate exhaust gases at a rate
proportional to air flow and in a manner which avoids recirculation
of exhaust gases through the carburetor. In employing this
invention, an exhaust gas recirculation passage is provided which
extends from the engine exhaust passage to the engine air induction
passage at a point downstream of the engine throttle. An orifice is
provided in the recirculation passage, and a valve disposed
downstream of the orifice is operated to create a zone of
substantially constant pressure in the passage irrespective of the
wide variations in exhaust back pressure and induction passage
vacuum. The rate of recirculation of exhaust gases through the zone
thus is proportional to the rate of induction air flow.
In other valve assemblies recently proposed for controlling exhaust
gas recirculation in accordance with exhaust back pressure, the
diaphragm or other member responsive to back pressure has directly
operated the valve member which controls the flow of exhaust gases.
In the design of such a valve assembly, certain limitations are
encountered because the back pressure generally is very low. In the
valve assembly of this invention, on the other hand, the exhaust
gas flow controlling valve member is not directly operated by the
member responsive to exhaust back pressure; instead, the valve
member is positioned by a member operated by an induction passage
vacuum signal and the member responsive to exhaust back pressure
controls that signal.
Several embodiments of this valve assembly are depicted herein, the
details of which as well as other objects and advantages of this
invention are set forth in the remainder of the specification and
are shown in the drawings.
SUMMARY OF THE DRAWINGS
FIG. 1 is a top plan view of an internal combustion engine inlet
manifold having induction and exhaust gas crossover passages, an
insert plate having an exhaust gas recirculation passage mounted on
the manifold, and the exhaust gas recirculation control valve
assembly mounted thereon;
FIG. 2 is a sectional view along line 2--2 of FIG. 1 showing the
induction, exhaust gas crossover, and exhaust gas recirculation
passages and also showing the throttle body portion of a carburetor
mounted on the insert plate;
FIG. 3 is an enlarged sectional view, in elevation, of one
embodiment of the control valve assembly, taken generally along
line 3--3 of FIG. 1;
FIG. 4 is a sectional view, in elevation, of another embodiment of
the control valve assembly; and
FIG. 5 is a sectional view, in elevation, of yet another embodiment
of the control valve assembly which also shows, schematically, an
additional control mode which may be utilized with this
embodiment.
This invention is an improvement over the invention of Robert A.
Bolton claimed in commonly assigned application Ser. No. 245,587
filed Apr. 19, 1972. The improved embodiment of this invention
shown in FIG. 3 was invented by Paul B. Kuehl and is specifically
claimed in commonly assigned application Ser. No. 242,420 filed
Apr. 10, 1972. The embodiment of this invention shown in FIG. 5
includes valve surfaces regulating both the air bleed orifice and
the vacuum orifice; the additional control of the vacuum orifice
was invented by Robert A. Bolton and is specifically claimed in the
aforementioned application Ser. No. 245,587. The FIGS. 4 and 5
embodiments make use of the invention of Edward G. Day and Ernst L.
Ranft claimed in commonly assigned application Ser. No. 220,036
filed Jan. 24, 1972. The FIG. 4 embodiment also makes use of an
invention of Ernst L. Ranft and William F. Thornburgh claimed in
commonly assigned application Ser. No. 314,569 filed Dec. 13,
1972.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIGS. 1 and 2, the combustion air induction
passages for the engine are formed in part by an intake manifold 10
which has a pair of vertical primary riser bores 12 and 14 and a
pair of vertical secondary riser bores 16 and 18. Riser bores 12
and 16 open to an upper horizontal plenum 20 connected forwardly
(leftwardly as viewed in FIG. 1) to a pair of transverse runners 22
and 24 and connected rearwardly (rightwardly as viewed in FIG. 1)
to another pair of transverse runners 26 and 28. Similarly, riser
bores 14 and 18 open to a lower horizontal plenum 30 connected
forwardly to a pair of transverse runners 32 and 34 and rearwardly
to another pair of transverse runners 36 and 38.
Intake manifold 10 also has an exhaust crossover passage 40 which
extends transversely from the left-hand side of manifold 10 beneath
plenums 20 and 30 and receives a portion of the exhaust gases
discharged from the engine combustion chambers.
An insert plate 42 is secured on manifold 10 and has primary riser
bores 44 and 46 and secondary riser bores 48 and 50 which meet,
respectively, riser bores 12, 14, 16, 18 of manifold 10.
A carburetor 52 is secured on insert plate 42 and has primary
throttle bores 54 and 56 which meet, respectively, primary riser
bores 44 and 46 of insert plate 42. Carburetor 52 also has
secondary throttle bores (not shown) which meet secondary riser
bores 48 and 50 of insert plate 42. Throttles 57 are disposed in
the carburetor bores to control induction air flow
therethrough.
A bore 58 in manifold 10 leads upwardly from exhaust crossover
passage 40 to the first portion 60 of an exhaust recirculation
passage formed in insert plate 42. The first portion 60 of the
exhaust recirculation passage leads through a control valve
assembly 62 to a second portion 64 of the exhaust recirculation
passage. This second portion 64 divides into a pair of branches 66
and 68 which lead to the primary riser bores 44 and 46 in insert
plate 42.
It should be appreciated that both portions 60 and 64 of the
exhaust recirculation passage may be integrated in manifold 10
rather than in separate insert plate 42.
FIG. 3 shows one embodiment 62a of control valve assembly 62.
Embodiment 62a comprises a valve body 70 having an inlet 72 for
receiving exhaust gases from first portion 60 of the exhaust
recirculation passage and an outlet 74 for discharging exhaust
gases to second portion 64 of the exhaust recirculation passage. An
orifice member 76 is disposed across inlet 72, and a downwardly
facing valve seat 78 is disposed between inlet 72 and outlet 74. A
valve member 80, associated with valve seat 78, is formed on a
hollow stem 82 carried by a pressure responsive diaphragm 84 and
upwardly biased by a spring 86.
A passage 88 senses the pressure in the zone 90 between orifice
member 76 and valve seat 78 and transmits the zone pressure to the
chamber 92 above a diaphragm 94. Diaphragm 94 operates against the
bias of a spring 96 is response to variations in pressure in zone
90 to position a pilot valve 98 disposed in hollow stem 82.
Hollow stem 82 has lateral openings 100 disposed in the chamber 102
between valve seat 78 and outlet 74 and transmits the induction
passage vacuum present therein past valve 98 through upper lateral
openings 104 to the chamber 106 below diaphragm 84. In operation,
as the pressure in zone 90 increases, diaphragm 94 is depressed to
open valve 98 and admit manifold vacuum through openings 104 to
chamber 106, thereby decreasing the pressure signal in chamber 106.
Diaphragm 84 is then pulled downwardly against the bias of spring
86 to displace valve member 80 from valve seat 78. This operation
permits increased recirculation of exhaust gases. Upon a reduction
in pressure in zone 90, spring 96 raises diaphragm 94 thus closing
valve 98 and permitting the pressure signal in chamber 106 to
increase as air is bled through a slot 108 in valve member 98 from
the chamber 110 between diaphragms 94 and 84. Diaphragm 84 is then
pushed upwardly by spring 86 to displace valve member 80 toward
valve seat 78, thereby reducing recirculation of exhaust gases. In
practice, diaphragms 94 and 84 will move in unison and a
substantially constant pressure will be maintained in zone 90.
The back pressure created in the exhaust passages such as 40 of an
internal combustion engine is generally proportional to the square
of the rate of combustion air flow through the engine induction
passages. The rate of flow of exhaust gases from first portion 60
of the exhaust recirculation passage through an orifice such as 76
into a zone such as 90 of substantially constant pressure is
generally proportional to the square root of the exhaust back
pressure. Thus the rate at which exhaust gases are recirculated is
generally proportional to the rate at which combustion air flows to
the engine.
FIG. 4 shows another embodiment 62b of control valve assembly 62.
It comprises a valve body 112 having an inlet 114 receiving exhaust
gases from first portion 60 of the exhaust recirculation passage
and an outlet 116 discharging exhaust gases to second portion 64 of
the exhaust recirculation passage. An orifice member 118 is
disposed across inlet 114, and an upwardly facing valve seat 120 is
formed about outlet 116. A valve member 122, associated with valve
seat 120, is secured on a stem 124 carried by a pressure responsive
diaphragm 126 and downwardly biased by a spring 128.
The pressure in the zone 130, defined between orifice member 118
and valve seat 120, is applied through lateral openings 132 and a
longitudinal passage 134 in stem 124 to a chamber 136 defined
between the central portion 138 of diaphragm 126 and a dished
diaphragm backing member 140. A chamber 142, defined between
central portion 138 of diaphragm 126 and another dished diaphragm
backing member 144, is maintained at atmospheric pressure by
openings 146 extending through diaphragm 126 and backing member
140. The chamber 148 above diaphragm 126 is subjected to the
pressure in the induction passage downstream of throttles 57 by a
vacuum hose 150 which may be connected to carburetor 52, manifold
10, or second portion 64 of the exhaust recirculation passage.
In operation, as the pressure in zone 130 drops, central portion
138 of diaphragm 126 is pushed downwardly by a spring 152. A valve
member 154 secured to diaphragm portion 138 then is displaced from
an air bleed opening 156 to admit air from chamber 142 to chamber
148. This increases the pressure signal in chamber 148, and spring
128 displaces diaphragm 126, stem 124 and valve member 122 toward
valve seat 120 to reduce recirculation of exhaust gases. Upon an
increase in pressure in zone 130, diaphragm portion 138 moves
upwardly against the bias of spring 152 and valve member 154
reduces air flow through opening 156 into chamber 148. The
resulting reduction in the pressure signal in chamber 148 displaces
diaphragm 126, stem 124, and valve member 122 upwardly from valve
seat 120, thereby increasing recirculation of exhaust gases.
Embodiment 62b also maintains a constant pressure zone, 130,
downstream from an orifice, 118, which receives exhaust gases at
exhaust back pressure and thus provides recirculation of exhaust
gases at a rate proportional to induction air flow.
FIG. 5 shows yet another embodiment 62c of control valve assembly
62. It comprises a valve body 158 having an inlet 160 receiving
exhaust gases from first portion 60 of the exhaust recirculation
passage and an outlet 162 discharging exhaust gases to second
portion 64 of the exhaust recirculation passage. An orifice member
164 is disposed across inlet 160 and an upwardly facing valve seat
166 is disposed between inlet 160 and outlet 162. A valve member
168 associated with valve seat 166 is connected by a stem 170 to a
pressure responsive diaphragm 172.
The pressure in the zone 174 between orifice member 164 and valve
seat 166 is applied through a hose 176 to a chamber 178 below a
diaphragm 180. Diaphragm 180 is biased downwardly by a spring 182
and is lifted upon an increase in pressure in zone 174. A pilot
valve 184 is connected by a stem 186 to diaphragm 180 and controls
an air bleed through an orifice 188 into a vacuum chamber 190. A
fitting 192 on chamber 190 is connected through hoses 194 and 196
to a source of vacuum such as that in carburetor 52 below throttles
57 of that in outlet 162. A second fitting 198 on chamber 190 is
connected by a hose 200 to the chamber 202 above diaphragm 172.
In operation, upon an increase in pressure in zone 174 diaphragm
180 is raised against the bias of spring 182 and valve member 184
reduces air flow through orifice 188 into chamber 190. As the
pressure signal in chamber 190 decreases, diaphragm 172 is raised
against the bias of spring 204 and valve member 168 is displaced
from valve seat 166 to permit increased recirculation of exhaust
gases. Upon a decrease in pressure in zone 174, spring 182
depresses diaphragm 180 and valve member 184 permits increased air
flow through orifice 188 into chamber 190. The increased pressure
signal in chamber 190 is transmitted to chamber 202 and spring 204
lowers diaphragm 172 to displace valve member 168 toward valve seat
166, thus reducing recirculation of exhaust gases. Thus embodiment
62c also is effective to maintain a constant pressure zone, 174,
downstream from an orifice, 164, which receives exhaust gases at
exhaust back pressure and thus provides recirculation of exhaust
gases at a rate proportional to induction air flow.
If desired, a valve 206, responsive to temperature or some other
engine or vehicle operating condition, may be disposed between
hoses 194 and 196 to control application of vacuum to chamber 202
and thus to superimpose a supplemental control on recirculation of
exhaust gases.
In some applications, it may be desirable to provide an additional
surface 208 on valve member 184 to control the effective area of
fitting 192 and thus control application of vacuum to chamber 190.
In other applications, it may be desirable to connect hose 200 to
fitting 192 and hose 194 to fitting 198 whereby valve surface 208
may control application of vacuum to chamber 202.
It will be appreciated that each embodiment of valve assembly 62
may be tailored to prevent recirculation of exhaust gases whenever
the induction passage vacuum is very low, thus preventing any
reduction in power due to charge dilution during wide open throttle
operation.
* * * * *