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Claims  |
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What is claimed is:
1. An exhaust gas recirculation (EGR) control system in combination with 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, a venturi formed in said induction passage and an
exhaust passage for exhaust gas flow from the engine, said EGR control
system comprising:
an EGR passageway interconnecting said exhaust passage and said induction
passage downstream of said throttle for recirculation of the exhaust gases
therethrough;
a restriction formed in said EGR passage for restricting said EGR
passageway;
Egr control valve means disposed in said EGR passageway downstream of said
restriction and operative to increase and reduce the pressure (Pe) in a
passage zone of the EGR passageway between said restriction and said EGR
control valve means, said EGR control valve means including first and
second chambers and a flexible diaphragm separating said first and second
chambers, said first chamber communicating with said induction passage to
receive therein a vacuum from a vacuum source and being arranged such that
upon an increase of the vacuum in said first chamber said diaphragm is
moved in the direction to cause a decrease of the pressure (Pe) to
increase the recirculated flow of the exhaust gases, and said second
chamber being fluidly connected to said induction passage to receive
therein a vacuum created in said induction passage downstream of said
throttle and being arranged such that upon an increase of the vacuum in
said second chamber said diaphragm is moved in the direction to cause an
increase of the pressure (Pe) in said passage zone to reduce the
recirculated flow of the exhaust gases; and
pressure regulating valve means operative to increase and reduce the vacuum
in said first chamber by controlling the flow of atmospheric air admitted
into said first chamber in accordance with the pressure (Pe) in said
passage zone and venturi vacuum in said venturi.
2. An EGR control system as claimed in claim 1, in which said EGR control
valve means further comprises:
a third chamber communicating with the atmosphere;
a second diaphragm having a smaller effective working area than said first
diaphragm separating said first and second chambers, said second diaphragm
separating said second and third chambers;
a valve stem integrally connected at its one end to said first and second
diaphragm to integrally move therewith;
a valve head fixedly connected to the other end of said valve stem;
a valve seat disposed in said EGR passageway, said valve head being
arranged to be sealingly seatable in said valve seat; and
biasing means disposed in said first chamber for urging said first and
second diaphragms in the direction of said valve seat.
3. An EGR control system as claimed in claim 1, in which said EGR control
valve means further comprises:
first passage means providing communication between said second chamber and
said EGR passageway downstream of said EGR control valve means.
4. An EGR control system as claimed in claim 1, further comprising:
second passage means providing communication between said venturi and said
pressure regulating valve means for conducting therethrough venturi vacuum
in said venturi;
third passage means communicating with said second passage means and having
an inlet port communicating with the atmosphere for admitting into said
third passage means atmospheric air to dilute the venturi vacuum in said
second passage means; and
relief valve means operatively connected to said third passage means and
movable relative to said inlet port to open and close same in accordance
with operating conditions of the engine, said relief valve means being
constructed and arranged to normally close said inlet port and to open
same in high speed low load operating condition of the engine to cause
decrease of the flow of the recirculated exhaust gases.
5. An EGR control system as claimed in claim 4, in which said relief valve
means comprises:
a fourth chamber communicating with said first chamber;
a fifth chamber communicating with the atmosphere;
a third flexible diaphragm separating said fourth and fifth chambers and
movable relative to said inlet port of said third passage means to open
same in response to the vacuum in said first chamber being above a
predetermined value; and
biasing means disposed in said fourth chamber for urging said third
diaphragm in the direction of said inlet port of said third passage means
to close same in response to the vacuum in said first chamber being below
a predetermined value, whereby in high speed low load operating condition
of the engine said relief valve means is operated to open said inlet port
of said third passage means to cause decrease of the recirculated flow of
the exhaust gases.
6. An exhaust gas recirculation (EGR) control system in combination with 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, a venturi formed in said induction passage and an
exhaust passage for exhaust gas flow from the engine, said EGR control
system comprising:
an EGR passageway interconnecting said exhaust passage and said induction
passage downstream of said throttle for recirculation of the exhaust gases
therethrough;
a restriction formed in said EGR passageway for restricting said EGR
passageway;
Egr control valve means disposed in said EGR passageway downstream of said
restriction and operative to increase and reduce the pressure (Pe) in a
passage zone of the EGR passageway between said restriction and said EGR
control valve means, said EGR control valve means including first and
second chambers, a flexible diaphragm separating said first and second
chambers and first passage means having at least one orifice and providing
communication between said first and second chambers, said second chamber
being fluidly connected to said induction passage to receive therein a
vacuum created in said induction passage downstream of said throttle and
being arranged such that upon an increase of the vacuum in said second
chamber said diaphragm is moved in the direction to cause an increase of
the pressure (Pe) in said passage zone to reduce the recirculated flow of
the exhaust gases, and said first chamber receiving therein the vacuum in
said second chamber through said passage means and being arranged such
that upon an increase of the vacuum in said first chamber said diaphragm
is moved in the direction to cause a decrease of the pressure (Pe) in said
passage zone to thereby increase the recirculated flow of the exhaust
gases; and
pressure regulating valve means operative to increase and reduce the vacuum
in said first chamber by controlling the flow of atmospheric air into said
first chamber in accordance with the pressure (Pe) in said passage zone
and a venturi vacuum in said venturi.
7. An EGR control system as claimed in claim 6, in which said orifice of
said first passage means is formed in said diaphragm.
8. An EGR control system as claimed in claim 6, in which said first passage
means is disposed outside said first and second chambers.
9. An EGR control system as claimed in claim 6, in which said EGR control
valve means further comprises second passage means providing communication
between said second chamber and said EGR passageway downstream of said EGR
control valve means.
10. An EGR control system as claimed in claim 6, in which said EGR control
valve means further comprises:
a third chamber communicating with the atmosphere;
a second diaphragm having a smaller effective working area than said first
diaphragm separating said first and second chambers, said second diaphragm
separating said second and third chambers;
a valve stem integrally connected at its one end to said first and second
diaphragms to integrally move therewith;
a valve head fixedly connected to the other end of said valve stem;
a valve seat disposed in said EGR passage, said valve head being arranged
to be sealingly seatable in said valve seat; and
biasing means disposed in said first chamber for urging said first and
second diaphragms in the direction of said valve seat.
11. An EGR control system as claimed in claim 6, further comprising:
third passage means providing communication between said venturi and said
pressure regulating valve means for conducting therethrough venturi vacuum
in said venturi;
fourth passage means communicating with said third passage means and having
an inlet port communicating with the atmosphere for admitting into said
fourth passage means atmospheric air to dilute the venturi vacuum in said
third passage means; and
relief valve means operatively connected to said fourth passage means and
movable relative to said inlet port to open and close same in accordance
with operating conditions of the engine, said relief valve means being
constructed and arranged to normally close said inlet port and to open
same in high speed low load operating condition of the engine to cause
decrease of the recirculated flow of the exhaust gases.
12. An EGR control system as claimed in claim 6, in which said relief valve
means comprises:
a fourth chamber communicating with said first chamber;
a fifth chamber communicating with the atmosphere;
a third flexible diaphragm separating said fourth and fifth chambers and
movable relative to said inlet port of said fourth passage means to open
same in response to the vacuum in said first chamber being above a
predetermined value; and
biasing means disposed in said fourth chamber for urging said third
diaphragm in the direction of said inlet port of said fourth passage means
to thereby close same in response to the vacuum in said first chamber
being below a predetermined value, whereby in high speed low load
operating condition of the engine said relief valve is operated to open
said inlet port of said fourth passage means to cause decrease of the
recirculated flow of the exhaust gases. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates generally to exhaust gas recirculation in an
internal combustion engine and more particularly to an improvement in an
EGR (Exhaust gas Recirculation) control system for controlling
recirculation of exhaust gases back to the intake.
It is well known in the art that a portion of exhaust gases emitted from an
internal combustion engine is recirculated back to an intake system of the
engine for thereby reducing formation of oxides of nitrogen during the
combustion process in the engine. However, since this exhaust gas
recirculation considerably effects the combustion in the engine and
consequently the operating efficiency of the engine, the exhaust gas
recirculation must be strictly controlled in respect to the operating
conditions of the engine. In general, for the purpose of achieving
efficient reduction in formation of oxides of nitrogen without impairing
the operating efficiency or the power output of the engine, it is desired
to recirculate the exhaust gases at a rate proportional to the rate at
which combustion air flows into the engine, viz., it is desired to
maintain at a predetermined or constant value the EGR ratio, which is the
ratio of the recirculated amount of exhaust gases to the amount of air
inducted to the engine, by weight. On the other hand, for the purpose of
improving the fuel consumption of the engine, it is desired to reduce the
EGR ratio below the above-mentioned predetermined value during particular
operating conditions of the engine, e.g., during high speed low load
operating conditions of the engine. Accordingly, it is necessary to
control exhaust gas recirculation with enough consideration for the
operating efficiency of the power output and the fuel consumption of the
engine.
As an expedient for attaining this purpose, an EGR control system has been
proposed by the same applicant as this application, which system is
disclosed in U.S. Pat. application No. 817,994, filed July 21, 1977. For
explanation of the background of this invention, this EGR control system
is shown in FIG. 1 of the accompanying drawings of this application.
In FIG. 1, designated by the reference numeral 10 is an induction passage
of an internal combustion engine (not shown), by 12 a venturi formed in
the induction passage, and by 14 a throttle in the form of a rotatable
throttle valve disposed in the induction passage 10 for controlling air
flow to the engine. This EGR control system comprises an EGR passage 16
interconnecting an exhaust passage (not shown) and the induction passage
10 downstream of the throttle 14, a restriction or an orifice 18 formed in
the EGR passage 16 for restriction of same and an EGR control valve 20
disposed in the EGR passage 16 downstream of the restriction 18. The EGR
control valve 20 includes a flexible diaphragm 22, and first and second
fluid chambers 23 and 24 separated by the diaphragm 22 from each other.
The fluid chamber 23 communicates with the induction passage 10 downstream
of the throttle 14 through a passage 25 for receiving therein a suction
vacuum, and the fluid chamber 24 communicates with the atmosphere through
a port 24'. A valve stem 26 is fixedly connected at its one end to the
diaphragm 22 so as to be movable therewith as one body. A valve head 27 is
integrally connected to the other end of the valve stem 26 and is
sealingly seatable on a valve seat 28 disposed in the EGR passage 16
downstream of the restriction 18. A spring 29 is disposed in the fluid
chamber 23 for urging the diaphragm 22 in the direction of the valve seat
28. By the EGR control valve 20 thus constructed and arranged as above,
the EGR passage 16 is provided with a chamber or a passage zone 16'
defined between the restriction 18 and the EGR control valve 20. A
pressure regulating valve assembly 30 is provided for controlling the flow
of atmospheric air admitted into the fluid chamber 23 for dilution of the
suction vacuum therein in accordance with a venturi vacuum in the venturi
12 and the pressure (Pe) in the passage zone 16' defined between the
orifice 18 and the EGR control valve 20. For that purpose, the pressure
regulating valve assembly 30 includes four chambers 31, 32, 33 and 34, and
three diaphragms 36, 38 and 40 respectively separating the above four
chambers as shown in the drawing. These three diaphragms 36, 38 and 40 are
fixedly connected to each other so that they are operated as one body. The
chamber 31 communicates with the atmosphere through openings 42 and
further with the passage 25 through a passage 44 which has an inlet port
44' disposed in the chamber 31. The chamber 32 communicates with the
venturi 12 through a passage 46 for receiving therein the venturi vacuum.
The chamber 33 communicates with the atmosphere through an opening 33'.
The chamber 34 communicates with the passage zone 16' of the EGR passage
16 through a passage 47 for receiving therein the pressure (Pe) in the
passage zone 16'. The diaphragm 36 is cooperative with the inlet port 44'
of the passage 44 to create a valve effect, viz., the diaphragm 36 is
movable relative to the inlet port 44' to control the flow of atmospheric
air admitted into the passage 44.
The pressure regulating valve assembly 30 thus described briefly is thus
operative to increase and reduce the vacuum in the chamber 23 of the EGR
control valve 20 in accordance with the venturi vacuum and the pressure
(Pe) as follows.
Upon an increase of the venturi vacuum in response to an increase of the
amount of air to the engine, the diaphragms 36, 38 and 40 are integrally
moved in the direction to close the inlet port 44' to reduce the flow rate
of atmospheric air admitted into the passage 44 thus reducing dilution of
the vacuum in the chamber 23 of the EGR control valve 20. As a result, the
degree of opening of the EGR control valve 20 is increased thus causing
decrease of the pressure (Pe) in the passage zone 16' and therefore the
pressure in the chamber 34 of the pressure regulating valve assembly 30.
When the pressure (Pe) in the passage zone 16' and therefore the pressure
in the chamber 34 of the pressure regulating valve assembly 30 are thus
reduced, the diaphragms 36, 38 and 40 are, on the contrary, actuated to
move in the direction to open the inlet port 44' of the passage 44 to
increase the flow rate of atmospheric air into the passage 44. As a
result, the dilution of the vacuum in the chamber 23 is increased to
reduce the degree of opening of the EGR control valve 20 thus causing an
increase of the pressure (Pe) in the passage zone 16'. By the repetition
of an operation thus described as above, the degree of opening of the EGR
control valve 20 and therefore the pressure (Pe) in the passage zone 16'
are converged to the values in which the pressure (Pe) is proportioned to
the venturi vacuum so that the flow rate of recirculated exhaust gases is
increased and reduced in accordance with increase and decrease of the
venturi varuum.
In this EGR control system, the amount of recirculated exhaust gases
through the EGR passage 16 is a function of the pressure differential
across the restriction 18, viz., upstream and downstream of the
restriction 18, and the size of the restriction 18. In this regard, the
pressure in the EGR passage upstream of the restriction 18 is
approximately equal to the pressure in the exhaust passage (not shown).
The exhaust passage pressure is a positive pressure the absolute value of
which is relatively small, in other words, the exhaust passage pressure
varies within a relatively narrow range through the flow rate of exhaust
gases passing through the exhaust passage varies within a relatively wide
range in response to the variations of the operating conditions of the
engine. Therefore, when the absolute value of the pressure (Pe) in the
passage zone 16' is set at a desirable large value as compared to the
pressure in the EGR passage upstream of the restriction 18 and is
controlled by the EGR control valve 20 in a manner as has been explained
hereinbefore, the pressure differential across the restriction 18 is
proportioned to the flow rate of combustion air to the engine.
Accordingly, the flow rate of recirculated exhaust gases is controlled in
proportion to the flow rate of combustion air flowing into the engine.
This EGR control system further has such a function as follows: When the
pressure (Pe) in the passage zone 16' changes regardless of the venturi
vacuum by the effect of the variations of the suction vacuum in the
induction passage 10, the pressure regulating valve assembly 30 operates
the EGR control valve 20 to move in the direction to cancel the variations
of the pressure (Pe) having been resulted as above. To explain this
function of the EGR control system in more detail, when the pressure (Pe)
is a negative pressure and this is increased regardless of the venturi
vacuum, the diaphragms 36, 38 and 40 are integrally moved in the direction
to open the inlet port 44' by the amount corresponding to the increase of
the pressure (Pe). As a result, the degree of opening of the EGR control
valve 20 is reduced in a manner as has been explained hereinbefore, thus
cancelling the influence of the fluctuations of the suction vacuum on the
pressure (Pe). The pressure (Pe) is thus restored to its initial value.
Accordingly, the flow rate of recirculated exhaust gases is assuredly
prevented from being varied irrespective of the venturi vacuum.
A relief valve 48 is provided in the EGR control system and which includes
a flexible diaphragm 50 and two fluid chambers 52 and 54 separated by the
diaphragm 50 from each other. The fluid chamber 52 communicates with the
passage 25 at a location thereof between orifices 56 and 58 through a
passage 59. The fluid chamber 54 communicates with the atmosphere through
a port 60. A passage 61 is provided which communicates with the passage 46
and has an inlet port 61' located in the chamber 54 for admitting into the
passage 61 atmospheric air. The diaphragm 50 is cooperative with the inlet
port 61' to create a valve effect, viz., the diaphragm 50 is movable
relative to the inlet port 61' between two positions to open and close
same to control admission of atmospheric air into the passage 61. A spring
62 is disposed in the chamber 52 for urging the diaphragm 50 in the
direction of the inlet port 61', viz., in the direction to close the inlet
port 61'. The chamber 52 thus constructed and arranged receives therein
two vacuum signals, one of which is a suction vacuum conducted to the
chamber 52 through the orifice 56 and the other of which is a vacuum
prevailing in the chamber 23 of the EGR control valve and conducted to the
chamber 52 through the orifice 58. Accordingly, the vacuum prevailing in
the chamber 52 is a vacuum composed of the above two vacuum signals, and
the vacuum in the chamber 52 increases and decreases in accordance with a
vacuum prevailing in the chamber 23 of the EGR control valve. Since the
suction vacuum increases as the load on the engine decreases and the
venturi vacuum increases as the RPM of the engine speed increases, the
vacuum in the chamber 52 is maximized upon a high speed low load operating
condition of the engine. When the vacuum in the chamber 52 is above a
predetermined value upon high speed low load operating condition of the
engine, the diaphragm 50 is operated to move against the bias of the
spring 62 into the position where it opens the inlet port 61' of the
passage 61. The vacuum in the chamber 32 of the pressure regulating avle
assembly 30 is therefore reduced by the atmospheric air thus causing a
decrease of the vacuum in the chamber 23 of the EGR control valve 20. As a
result, the degree of opening of the EGR control valve 20 is reduced
whereby the flow rate of recirculated exhaust gases is temporarily
modified to a decreased value in this high speed low load operating
condition of the engine.
Since the formation of oxides of nitrogen during combustion process of the
engine does not take place appreciably when the engine is operated in high
speed low load operating condition, the above reduction of the flow rate
of recirculated exhaust gases in this operating condition of the engine
does not cause any drawback to the emission control effect achieved by the
EGR control system, but the combustion efficiency of the engine is
improved markedly. As a result, the operating efficiency of the engine,
e.g., fuel consumption and operation stability of the engine, is improved.
In this EGR control system as have been thus explained, the spring
constant, viz., the ratio of supplied force to resulting deflection, of
the spring 29 shall be set to a small value so that the vacuum prevailing
in the chamber 23 of the EGR control valve 20 in high load operating
condition of the engine can cause the diaphragm 22 to move against the
bias of the spring 29 to the position where the EGR control valve 20
provides a predetermined opening degree thereof, because in high load
operating condition of the engine the suction vacuum created in the
induction passage 10 downstream of the throttle 14 and therefore the
vacuum in the chamber 23 of the EGR control valve 20 are reduced to
relatively small absolute values.
However, when such a weak spring is employed, the vacuum in the chamber 23
in low speed low load operating condition of the engine shall be set to a
value approximately equal to zero, viz., the pressure in the chamber 23
shall be set to a value approximately equal to the atmospheric pressure,
so that the EGR control valve 20 with such a weak spring 29 can close
sealingly and assuredly in low speed low load operating condition of the
engine. Furthermore, when such a weak spring is employed, the vacuum in
the chamber 23 corresponding to high speed low load operating condition of
the engine cannot be set to a large value because the bias of such a weak
spring can be overcomed by a relatively small counter force.
For this reason, the variable range of the vacuum in the chamber 23 between
maximum and minimum values is compelled to be set narrow.
This narrow variable range of the vacuum in the chamber 23 causes such
drawbacks of the EGR control system that the operation of the EGR control
valve 20 tends to be unstable and the magnitude of the vacuum to open the
relief valve 48 is likely to fluctuate over a wide range relative to the
variable range of the vacuum in the chamber 23. This results in
deterioration of the accuracy of EGR control and therefore lack of the
reliability of the EGR control system.
This EGR control system further encounters a drawback of poor
responsiveness that upon deceleration of a vehicle vehicle with release of
the accelerator pedal it takes a rather long response time until the EGR
control system discontinues the exhaust gas recirculation. This is due to
the fact that the vacuum having prevailed in the chamber 23 of the EGR
control valve 20 remains therein for a relatively long time, viz., it
takes a relatively long time to dilute the vacuum in the chamber 23 below
a predetermined value.
It is accordingly an object of the present invention to improve an EGR
control system of the foregoing type.
It is another object of the present invention to provide an improved EGR
control system in which the variable range of the vacuum effective to
operate an EGR control valve incorporated therein is enlarged to a
desirably wide range whereby the operation of the EGR control system
becomes stable.
It is a further object of the present invention to provide an improved EGR
control system in which a relief valve incorporated therein operates with
an increased accuracy in response to a predetermined high speed low load
operating condition of the engine.
It is a still further object of the present invention to provide an
improved EGR control system which discontinuous the exhaust gas
recirculation with an improved responsiveness in a predetermined high
speed low load operating condition of the engine.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and advantages of the present invention will become
more apparent from the following description taken in conjunction with the
accompanying drawings, in which:
FIG. 1 is a schematic view of a formerly proposed EGR control system as per
the introduction of this specification;
FIG. 2 is a schematic view of a first preferred embodiment of an EGR
control system according to the present invention;
FIG. 3 is an enlarged schematic view showing the arrangement of diaphragms
incorporated in the EGR control system of FIG. 2;
FIG. 4 is a schematic view of a second preferred embodiment of an EGR
control system according to the present invention in which parts thereof
common to FIG. 2 are omitted; and
FIG. 5 is a schematic view of a third preferred embodiment of an EGR
control system according to the present invention in which parts thereof
common to FIG. 2 are omitted.
DETAILED DESCRIPTIONS TO THE PREFERRED EMBODIMENTS
This invention is based on the EGR control system illustrated in FIG. 1 and
contemplates mainly to improve its EGR control valve 20 such that the
movement of the diaphragm 22 is further affected by a vacuum applied
thereto at the opposite side to the chamber 23 to reduce the action of the
vacuum in the chamber 23. Therefore, like elements as those used in the
EGR control system of FIG. 1 are used in FIGS. 2, 4 and 5, and they have
been given the same numerals and will not be described again for brevity.
Referring to FIG. 2, an EGR control system, first embodiment of the present
invention, comprises an EGR control valve 80 which includes two flexible
diaphragms 82 and 84 and three fluid chambers 86, 88 and 90. The fluid
chamber 86 communicates with the induction passage 10 downstream of the
throttle 14 through the passage 25 to receive therein a suction vacuum .
The fluid chamber 88 is fluidly connected to the induction passage 10
downstream of the throttle 14 to receive therein a suction vacuum through
the EGR passage 16 and a passage 92 providing communication between the
chamber 88 and the EGR passage 16 downstream of the EGR control valve 80.
The fluid chamber 90 communicates with the atmosphere. The diaphragm 82
has a larger effective working area than the diaphragm 84 and separates
the chambers 86 and 88, and the diaphragm 84 separates the chambers 88 and
90. The above-mentioned effective working area means the part of the
diaphragm enclosed within or defined by an effective diameter which part
of the diaphragm is flexed or moved upwardly and downwardly as viewed in
the drawing in response to the variations of the vacuum acting thereon. As
shown in FIG. 3, the diaphragm 82 is constructed to have a effective
working area S.sub.1 which is larger than the effective working area
S.sub.2 of the diaphragm 84. The peripheral part of the diaphragm 82 or 84
excluded by the effective diameter is constructed to counteract the
displacement of the inner part of the diaphragm included within the
effective diameter.
In this instance, the passage 92 for conducting suction vacuum to the
chamber 88 is of a considerably short length. Since suction vacuum created
in the induction passage 10 also prevails in the part of EGR passage 16
downstream of the EGR control valve 80, the chamber 88 receives therein a
suction vacuum through such a passage 92 of a short length.
The diaphragms 82 and 84 are integrally interconnected to be movable as one
body and are connected to one end of a valve stem 94. The other end of the
valve stem 94 is fixedly connected with a valve head 96 which is sealingly
seatable in a valve seat 98 disposed in the EGR passage 16 downstream of
the restriction 18. The valve head 96 is cooperative with the valve seat
98 to increase and reduce the opening degree of the EGR control valve 80
in accordance with upward and downward movements of the diaphragms 82 and
84. A spring 100 is disposed in the chamber 86 for urging the diaphragms
82 and 84 in the direction of the valve seat 98, i.e. in the direction to
cause the valve head 96 to seat in the valve seat 98.
The EGR control system of this invention is not provided with the orifice
58 which is arranged in the EGR control system of FIG. 1, viz., the
chamber 52 of the relief valve 48 communicates directly with the chamber
86 of the EGR control valve 80 and the chamber 31 of the pressure
regulating valve assembly 30 without passage through such an orifice 58 as
is provided in the EGR control system of FIG. 1. By this omission of the
orifice 58, the vacuum in the chamber 52 of the relief valve 48 is
substantially equal to the vacuum in the chamber 86 of the the EGR valve
80, on the other hand, in the EGR control system of FIG. 1 the vacuum in
the chamber 52 is a vacuum composed of two vacuum signals as has been
described referring to FIG. 1.
By thus constructing and arranging the EGR control system, the
correspondency between the magnitude of the vacuum in the chamber 86 and
the degree of opening of the EGR control valve 80 is improved optimally by
the effect of the vacuum in the chamber 88, viz., the vacuum in the
chamber 86 is multiplied by the effect of the vacuum in the chamber 88 to
correspond to the same degree of opening of the EGR control valve.
This multiplication of the vacuum in the chamber 86 is obtained as follows:
When assuming S.sub.1 and S.sub.2 as the effective working areas of the
diaphragms 82 and 84 respectively, Pb as the vacuum prevailing in the
chamber 86 and Pa as the vacuum prevailing in the chamber 88, the
diaphragm 82 receives a force expressed by Pb.S.sub.1 in the direction to
open the EGR control valve 80 and further receives a force expressed by
Pa(S.sub.1 -S.sub.2) and a biasing force F by the spring 100 in the
direction to close the EGR control valve 80. The EGR control valve 80
therefore tends to reduce its degree of opening by the amount
corresponding to the effect of the vacuum in the chamber 88. However, when
the degree of opening of the EGR control valve is thus reduced below a
predetermined degree of opening corresponding to the operating condition
of the engine, the pressure (Pe) in the passage zone 16' is increased,
viz., since the pressure (Pe) is normally a negative pressure the vacuum
(Pe) is reduced. Since the pressure (Pe) thus increased is conducted to
the chamber 34 of the pressure regulating valve assembly 30, the diaphragm
40 is caused to move upwardly as viewed in the drawing together with the
diaphragms 36 and 38 thus causing a decrease of the flow rate of
atmospheric air into the passage 44 through the inlet port 44'. The amount
of atmospheric air fed to the chamber 86 for dilution of the vacuum
therein is thus reduced, and consequently the vacuum in the chamber 86 is
increased, viz., the absolute value of the vacuum in the chamber 86 is
increased.
Accordingly, the thus increased amount of the vacuum in the chamber 86
causes the diaphragms 82 and 84 to move upwardly cancelling the influence
of the vacuum in the chamber 88 whereby the EGR control valve 80 retains
the former predetermined degree of opening.
From the above description, it is appreciated that by the action of the
vacuum in the chamber 88 on the diaphragm 82 against the action of the
vacuum in the chamber 86 on same the vacuum in the chamber 86 is
multiplied to correspond to the same degree of opening of the EGR control
valve. In other words, when the EGR control system of FIG. 2 and the EGR
control system of FIG. 1 in a condition in which their EGR control valves
are operated to provide the same degree of opening, the absolute value of
the vacuum in the chamber 86 is larger than same in the chamber 23.
As will be further appreciated, the provision of this chanmber 88 does not
alter the EGR control characteristics of the EGR control system of this
invention as compared to the EGR control system of FIG. 1. Because, when
the venturi vacuum in the venturi 12 is increased in response to the
increase of the flow rate of intake air to the engine, the diaphragm 38 is
moved upwardly together with the diaphragms 36 and 40 to reduce the amount
of atmospheric air admitted to the passage 44 thus causing increase of the
vacuum in the chamber 86. As a result, the degree of opening of the EGR
control valve 80 is increased thus causing decrease of the pressure (Pe)
in the passage zone 16'. Resultantly, the pressure differential across the
restriction 18 is increased to increase the flow rate of recirculated
exhaust gases such that the EGR ratio is maintained at a predetermined
value. When, on the contrary, the venturi vacuum is decreased in response
to the decrease of the flow rate of intake air to the engine, the degree
of opening of the EGR control valve 80 is decreased thus causing the
decrease of the pressure differential across the restriction 18 whereby
the EGR ratio is maintained at a predetermined value by reducing the flow
rate of recirculated exhaust gases by the amount corresponding to the
decrease of the venturi vacuum.
The pressure (Pe) in the passage zone 16' downstream of the restriction 18
fluctuates influenced by the variations of the suction vacuum prevailing
in the part of the EGR passage 16 downstream of the EGR control valve 80,
thus causing the variations of the EGR ratio, e.g., when the suction
vacuum is increases the EGR ratio is increased to a value larger than a
predetermined value. This fluctuation of the pressure (Pe) is compensated
in a similar manner as has been explained with respect to the EGR control
system of FIG. 1, viz., by a feed of the pressure (Pe) to the chamber 34
of the pressure regulating valve assembly 30.
Accordingly, it will be appreciated that the control of the pressure (Pe)
conducted in the EGR control system according to the present invention
contributes to provide two different effects, one of which is a
multiplication effect of multiplying the vacuum in the chamber 86 in
accordance with the suction vacuum fed to the chamber 88, and the other of
which is a compensation effect of compensating the fluctuations of the EGR
ratio resulted from the variations of the suction vacuum.
From the foregoing description, it will be appreciated that the vacuum in
the chamber 86 is multiplied increasingly as the suction vacuum fed to the
chamber 88 increases. Accordingly, the variable range of the vacuum in the
chamber 86 is expanded wider as compared to the variable range of the
vacuum in the chamber 23 in the EGR control system of FIG. 1. Furthermore,
even when the EGR control valve 80 is operated to provide a relatively
small degree of opening as compared to its maximum degree of opening, the
absolute value of the vacuum in the chamber 86 is held at relatively large
value as compared to the vacuum in the chamber 23 of FIG. 1. This means
that a certain amount of variation in the vacuum in the chamber 86 results
in a relatively small amount of variation in the degree of opening of the
EGR control valve 80 as compared to a similarly resulting amount of
variation in the EGR control system of FIG. 1. Therefore, the operation of
the EGR control system of FIG. 2 is stable, viz., the performance
characteristics of the EGR control system of FIG. 2 is stable and
therefore reliable, whereas the operation of the EGR control system of
FIG. 1 is rather unstable because the EGR control system of FIG. 1 varies
the degree of its EGR control valve opening relatively largely in response
to a relatively small amount of variation in the vacuum for actuating the
EGR control valve, viz., the EGR control system of FIG. 1 has ON-OFF type
performance characteristics.
Upon a sudden decelerati | | |
