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BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas recirculation control
system, and, more particularly, relates to an exhaust gas recirculation
control system which is particularly suited for application to a diesel
engine.
The exhaust gas recirculation in diesel engines is to replace a part of the
air inhaled into the cylinders of the engine that is generally in excess
of that which is required for combustion of the fuel injected into the
cylinders of the engine, by recirculated exhaust gas, in order to suppress
emission of harmful NOx pollutants. In this diesel engine exhaust gas
recirculation, it is desirable that the amount of air which is replaced by
exhaust gas should be proportional to the amount of air which is in excess
of the actual air requirement for combustion of the actual amount of fuel
injected, so that maximum possible amount of excess air is reduced from
the air/gas flow supplied to the cylinders of the engine, without causing
unstable combustion of fuel in the cylinders, while accomplishing maximum
effect of suppressing NOx emission, over the entire operational region of
the engine. Since the excess air ratio in the diesel engine decreases as
the load on the engine increases, it is necessary to control the exhaust
gas recirculation quantity so that the exhaust gas recirculation ratio
decreases, as the load on the engine increases. The exhaust gas
recirculation ratio is defined as the ratio of the quantity of exhaust gas
recirculated and introduced into the inlet system of the engine so the
total quantity of inlet gases inhaled by the engine, which is the sum of
the quantity of the recirculated exhaust gases and the amount of fresh air
inhaled by the engine.
The power output of or the load on a diesel engine is controlled by the
amount of fuel injected per unit time, and, therefore, it is not generally
possible, with a diesel engine, to perform control of exhaust gas
recirculation, according to the load on the engine, by using a diaphragm
operated type exhaust gas recirculation control valve which responds to
inlet manifold vacuum, as is done commonly with gasoline engines.
Accordingly, therefore, in the prior art, in a diesel engine the
conventional exhaust gas recirculation control valve has been directly
connected to and operated by either the accelerator pedal linkage of the
vehicle, or the control lever of the fuel injection pump, so that the
exhaust gas recirculation control valve has been operated according to the
operation of the accelerator lever, or the control lever.
This form of control means for exhaust gas recirculation is fairly easy and
simple to manufacture, but there is a problem that it tends to increase
the amount of force required for manipulation of the accelerator pedal,
and thereby may deteriorate the operational feeling of the accelerator
pedal and therefore the drivability of the vehicle.
As an alternative system for controlling diesel exhaust gas recirculation,
there has been proposed a system which comprises a diaphragm type exhaust
gas recirculation control valve, the diaphragm device being actuated by
vacuum provided by a pneumatic governor diaphragm chamber installed in the
fuel injection pump. However, with this system of exhaust gas
recirculation control, the problem arises that it is not really possible
to obtain enough power for operating the exhaust gas recirculation control
valve from the vacuum supplied by the pneumatic governor diaphragm
chamber, because the vacuum present in this pneumatic governor diaphragm
chamber is basically relatively small. Further, because of this, there
arises the problem that the position of the exhaust gas recirculation
control valve may be directly displaced by the dynamic pressure of the
inlet air flow and/or the recirculating exhaust gas flow.
As another possible solution to the problem of diesel exhaust gas
recirculation control, the possibility has been explored of controlling
exhaust gas recirculation quantity continuously to the appropriate and
correct value by measuring the amount of fuel injected to the combustion
chambers of the engine per one cycle, and by opening and closing an
exhaust gas recirculation control valve by a pressure type and/or electric
type actuator, based upon these measurements. However, in this case, the
control system as a whole becomes very complicated, and various problems
occur when it is in practice mounted to an operating automobile.
SUMMARY OF THE INVENTION
The present invention arises from the remarking by the present inventor of
the fact that, although theoretically and desirably the ratio of exhaust
gas recirculation should be varied smoothly and continuously as the load
on the engine varies, in actual practice this smooth variation is not
strictly necessary for effective control, and in practice if the rate of
exhaust gas recirculation were varied in a two step manner, this would
provide a very satisfactory improvement in performance over ON/OFF
control. That is, although the ideal curve of the relationship between
engine load and exhaust gas recirculation ratio should be a smoothly
curved line, nevertheless an approximation to this smoothly curved line by
a two step bar chart, if it provides advantages with regard to simplicity,
cost of manufacture and reliability of operation, may be acceptable.
Therefore, it is the object of the present invention to provide an exhaust
gas recirculation control system, for a diesel engine, which is simple,
and yet provides a performance of control of exhaust gas recirculation
ratio which approximately satisfies the ideally required characteristics
for exhaust gas recirculation.
This, and other, objects, are achieved, according to the present invention,
in a diesel engine, comprising an exhaust system, an inlet system, and an
exhaust gas recirculation system, by an exhaust gas recirculation control
system, comprising: an exhaust gas recirculation control valve, which
controls the amount of exhaust gas recirculated from the exhaust system of
the engine to the inlet system through the exhaust gas recirculation
system; and a means for actuating the exhaust gas recirculation control
valve, which positions the exhaust gas recirculation control valve
selectively and steppedly at one of three states, that are: a first state
in which it provides substantially zero exhaust gas recirculation ratio, a
second state in which it provides a medium exhaust gas recirculation
ratio, and a third state in which it provides a maximum exhaust gas
recirculation ratio, according to the load on the engine.
According to a particular feature of the present invention, the exhaust gas
recirculation control valve actuating means may conveniently comprise a
multi-action diaphragm actuator which includes first and second diaphragms
which define first and second diaphragm chambers and a stem operatively
related with the first and second diaphragms, the stem being located at a
first shift position when either of the first and second diaphragm
chambers is not supplied with operating fluid pressure, at a second shift
position when only the first diaphragm chamber is supplied with operating
fluid pressure, and at a third shift position when both the first and
second diaphragm chambers are supplied with operating fluid pressure, and
a fluid flow control means which controls supply of the operating fluid
pressure to the first and second diaphragm chambers according to the load
on the engine.
According to a further particular feature of the present invention, the
operating fluid pressure supply control means may desirably comprise an
electric switch which detects displacement of a fuel metering element such
as a control lever, a control rack, or a spill ring of a fuel injection
pump in three stages, and first and second electromagnetic valves which
are controlled by the switch and control supply of the operating fluid
pressure to the first and second diaphragm chambers, respectively.
According to another particular feature of the present invention, the
operating fluid pressure which is controlled by the two electromagnetic
valves may be a fluid pressure produced by a pump operated by the diesel
engine.
Further, according to yet another particular feature of the present
invention, the exhaust gas recirculation control valve may desirably be so
adapted that, when exhaust gas recirculation ratio is increased, it
further restricts the passage of intake fresh air. As, in a diesel engine,
the vacuum present in the inlet manifold is relatively low (that is, the
pressure therein is relatively near atmospheric) compared to that present
in the inlet manifold of a gasoline engine, there is a possibility that
the actual amount of exhaust gas recirculated cannot be increased by more
than a certain amount, even when the exhaust gas recirculation control
valve is quite wide open, if it is provided in the exhaust gas
recirculation passage, especially when the engine load is low. On the
other hand, if, as explained above, the intake air passage is more
throttled, by the exhaust gas recirculation control valve, when the
exhaust gas recirculation ratio is to be increased, the absolute amount of
exhaust gas recirculated increases to approximately the same extent as the
amount of inhaled fresh air is decreased. By this arrangement, even at low
engine load, it is possible to obtain the necessary exhaust gas
recirculation ratio, and the necessary amount of recirculation of exhaust
gases.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the following
description of several preferred embodiments thereof, which is to be taken
in conjunction with the accompanying drawings. It should be clearly
understood, however, that the description of the embodiments, and the
drawings, are all of them provided purely for the purposes of illustration
and exemplification only, and are in no way to be taken as limitative of
the scope of the present invention. In the drawings:
FIG. 1 is a somewhat schematic diagram, showing a diesel engine which is
equipped with an embodiment of the exhaust gas recirculation control
system of the present invention;
FIG. 2 is a sectional illustration of part of the embodiment of the exhaust
gas recirculation control system of the present invention, which
incorporates a flapper-type exhaust gas recirculation control valve, and
of part of the intake duct of the diesel engine, showing their
construction in detail;
FIG. 3 is a side view particularly showing an electrical switching system
incorporated in the exhaust gas recirculation system of the present
invention;
FIG. 4 is a graph, in which engine torque is the ordinate and engine rpm is
the abscissa, showing an example of three lines A, B, and C, which divide
from one another the three stages of operation I, II, and III, effected by
the exhaust gas recirculation control system according to the present
invention;
FIG. 5 is a graph, in which exhaust gas recirculation ratio is the ordinate
and engine torque is the abscissa, showing an example of the three-stage
performance of exhaust gas recirculation, effected by the exhaust gas
recirculation control system of the present invention; and
FIG. 6 is a view similar to FIG. 2, partially in cross section, of a second
embodiment of the exhaust gas recirculation control device according to
the present invention, in which a different type exhaust gas recirculation
control valve is used.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, the reference numeral 1 denotes a diesel
engine which inhales air through an air cleaner 2, an inlet duct 3, in
which an exhaust gas recirculation control valve 4 is incorporated, and an
inlet manifold 5, mixes with this air and combusts it in the combustion
chambers, the fuel being injected directly into the combustion chambers by
a fuel injection pump 7, and exhausts exhaust gases through an exhaust
manifold 6.
Fuel injection valves corresponding to the various cylinders of the engine
are incorporated in the engine so as each to be giving, on every
compression stroke of the corresponding piston, a prescribed amount of
liquid fuel, at high pressure, from the fuel injection pump 7, and to
inject this prescribed amount of liquid fuel into the corresponding
cylinder of the engine. The size of this prescribed amount of liquid fuel
is regulated by the position of a control lever 9 of the fuel injection
pump 7. One end of this control lever 9 is connected to one end of a shaft
8, as can be schematically seen in FIG. 1, and the shaft 8 extends into
the fuel injection pump 7 and directly controls its output amount. The
other end of this control lever 9 is pivotally connected by a pin 10 (FIG.
3) to the accelerator pedal (not shown) of the automobile in which this
diesel engine is incorporated, through a linkage system which is not shown
in the figures. When the accelerator pedal of the vehicle is depressed,
the control lever 9 is rotated in the clockwise direction, as seen in FIG.
3, and this direction of rotation of the control lever 9 and the shaft 8
is in the direction of increasing the magnitude of the above mentioned
prescribed amount of charge of liquid fuel supplied to each cylinder of
the engine on its compression stroke.
Thereby, the load on the engine, that is to say, the amount of power
developed by the engine, is increased, according to the clockwise rotation
of the above mentioned control lever 9 or the associated shaft 8 of the
fuel injection pump 7, due to the progressive depression of the
accelerator pedal of the vehicle.
An exhaust gas recirculation passage 11 is provided with its one end
connected to a middle portion of the exhaust manifold 6 and the other end
connected to the exhaust gas recirculation control valve 4. Through this
exhaust gas recirculation passage 11, a part of the exhaust gas produced
by the diesel engine 1 is recirculated and directed to the inlet manifold
5, and the amount of flow of this exhaust gas is controlled in an ongoing
fashion by the exhaust gas recirculation control valve 4.
Referring particularly now to FIG. 2, which shows the exhaust gas
recirculation control valve 4 in more detail, this exhaust gas
recirculation control valve 4, which in this embodiment is a flapper-type
exhaust gas recirculation control valve, comprises a casing 13, which is
generally connected between the inlet manifold 5 and the inlet duct 3, and
which defines within itself an inlet passage 12, which connects the inlet
duct 3 to the inlet manifold 5. On one side of this casing 13 (the upper
side in FIG. 2), is connected an elbow pipe 15, which opens into the inlet
passage 12 via an exhaust gas recirculation valve seat 14. The end of the
elbow pipe 15 remote from the casing 13 is connected, by a nut 16, to an
end of a tubular element which constructs the exhaust gas recirculation
passage 11.
Further, the casing 13 supports rotatably a shaft 17, and on this shaft 17,
inside the inlet passage 12, is fixedly attached one edge of the flapper
valve element 18. Thus, this flapper valve element 18 is so adapted that
it may move between a position, designated in FIG. 2 by I, in which it
rests against the exhaust gas recirculation valve seat 14 and completely
closes off the elbow pipe 15, and therefore the exhaust gas recirculation
passage 11, from communication with the inlet passage 12, through an
intermediate position, designated in FIG. 2 by II, in which it is partly
moved away from this contact with the exhaust gas recirculation valve seat
14 so as to allow partial or restricted communication of the elbow pipe
15, and therefore the exhaust gas recirculation passage 11, with the inlet
passage 12, to a third position, designated in FIG. 2 by III, in which it
is moved so far away from contact with the exhaust gas recirculation valve
seat 14 that the communication of the elbow pipe 15, and therefore the
exhaust gas recirculation passage 11, with the inlet passage 12 is
substantially free, with no substantial restriction being applied thereto
by the flapper valve element 18. Further, according to a particular
feature of this embodiment of the present invention, when the flapper
valve element 18 is in this third position III, which is the full open
position wherein the elbow pipe 15 and the exhaust gas recirculation
passage 11 are substantially connected with the inlet passage 12 with no
substantial restriction being applied therebetween, the flapper valve
element 18 is also at this time providing substantial restriction to the
flow of fresh air from the air cleaner 2, through the inlet duct 3, and
through the inlet passage 12 to the inlet manifold 5.
The shaft 17 is biased in the anticlockwise direction in FIG. 2 by a
twisted coil spring which is not shown in the drawings. Further, one one
end of the shaft 17 (outside the casing 13) there is fixedly connected one
end of a lever 19, and to the other end of this lever 19 there is
pivotally connected one end of a connecting rod 20. The other end of this
connecting rod 20 is connected to the multi-action diaphragm actuated
control device 21, which will be explained hereinafter, and, as will be
seen, by the action of the multi-action diaphragm activated control device
21, via the connecting rod 20, the lever 19, and the shaft 17, the flapper
valve 18 is moved between its various positions I, II, and III. The length
of the connecting rod 20 may be adjusted by an adjusting device 72, which
adjusts its effective length.
The multi-action diaphragm activated control device 21 is fixed to the
casing 13 of the exhaust gas recirculation control valve 4 by a mounting
device 22. This multi-action diaphragm activated control device 21
comprises a first diaphragm 24 and a second diaphragm 25. These diaphragms
24 and 25 are fitted within a casing 23, in a stacked relationship, and,
as seen in FIG. 2, the first diaphragm 24 defines an atomospheric pressure
chamber 26 above itself, between itself and the casing 23. Further,
between the first diaphragm 24 and the second diaphragm 25 and the casing
23, there is defined a first diaphragm chamber 27, and, further, the
second diaphragm 25 defines a second diaphragm chamber 28 below itself,
between itself and the casing 23.
An operating rod 31 is connected, at its one end, to the first diaphragm 24
by discs 29 and 30, and the other end of this operating rod 31 is
connected to the connecting rod 20, via a slot 32, which allows a certain
amount of free play between the connecting rod 20 and the operating rod
31. Further, the second diaphragm 25 supports, above it in FIG. 2, a first
stopper 36, via discs 33 and 34, and a connecting member 35. Further, a
fixed stopper plate 37 is mounted to the casing 23, above the second
diaphragm 25, so that the second diaphragm 25 is prevented from moving
upwards in FIG. 2 further than a certain predetermined position, by the
coming into contact of the fixed stopper plate 37 and the disc 33, which
is attached to the second diaphragm 25 on its upper side. Further, to the
casing 23, below the second diaphragm 25, there is fixed a second stopper
38, which therefore restricts movement downwards in FIG. 2 of the second
diaphragm 25 beyond another certain predetermined position. The position
of this second stopper 38 may be adjusted in height and fixed in the
vertical direction in FIG. 2 by the use of an adjusting screw 39.
Between the first diaphragm 24 and the second diaphragm 25 there is fitted
a first compression coil spring 41, which bears between the disc 30 and
the disc 33, and between the second diaphragm 25 and the lower part in
FIG. 2 of the casing 23 there is fitted a second compression coil spring
42, both these compression coil spring 41 and 42 being fitted at a
predetermined loading. Through the casing 23, there are fitted a first
inlet port 43, which leads a fluid pressure (vacuum in this embodiment)
the production of which will be explained hereinunder into the first
diaphragm chamber 27, and a second inlet port 44, which leads another
fluid pressure (also vacuum in this embodiment) the production of which
will be explained later into the second diaphragm chamber 28.
The operation of this multi-action diaphragm activated control device 21 is
as follows.
When vacuum is not supplied to either of the first inlet port 43 and the
second inlet port 44, then neither the first diaphragm chamber 27 nor the
second diaphragm chamber 28 is supplied with vacuum, but these diaphragm
chambers 27 and 28 are both supplied with atmospheric pressure, and then,
at this time, the multi-action diaphragm activated control device 21 is in
the state shown in FIG. 2, by the biasing actions of the compression coil
springs 41 and 42, and the flapper valve 18 is turned in the anticlockwise
direction by the action of the spring (not shown), as seen in FIG. 2, so
that this flapper valve 18 is kept in the full closed position I, as seen
in FIG. 2, wherein it closes off completely the passage of recirculated
exhaust gases. On the other hand, if vacuum which is greater than a
predetermined value is introduced into the first diaphragm chamber 27 via
the first inlet port 43, the first diaphragm 24 is moved downwards in FIG.
2 to a position where the disc 30 attached to its lower side is in contact
with the first stopper 36, against the opposing spring force of the first
compression coil spring 41, and thereby the lever 19 is rotated, via the
operating rod 31 and the connecting rod 20, in the clockwise direction in
FIG. 2, through a first predetermined angle. By this rotation of the lever
19, via the shaft 17, the flapper valve 18 is moved to the half open
position, which is shown as II in FIG. 2, wherein the passage of
recirculated exhaust gases is allowed at a certain intermediate amount.
Yet further, if vacuum which is greater than certain predetermined values
is introduced into both the first diaphragm chamber 27 and the second
diaphragm chamber 28 at the same time, via the first inlet port 43 and the
second inlet port 44, respectively, then the second diaphragm 25 will move
downwards in FIG. 2 to the position where the disc 34 attached to its
lower side is in contact with the second stopper 38, against the spring
force of the second compression coil spring 42, and also, as described
above, the first diaphragm 24 will move downwards in FIG. 2 to the
position where the disc 30 attached to its lower side is in contact with
the first stopper 36, which is attached to the upper side of the second
diaphragm 25. Thus, in this state, the first diaphragm 24 is moved to a
lower position in the figure than was the case in the above described set
of circumstances in which only the first diaphragm chamber 27, and not the
second diaphragm chamber 28, was supplied with vacuum, and thereby the
lever 19 is rotated, via the operating rod 31 and the connecting rod 20,
in the clockwise direction through a second predetermined angle which is
greater than the first predetermined angle described above. Thereby, via
the shaft 17, the flapper valve 18 is moved in the clockwise direction to
its full open position shown in FIG. 2 by III, wherein it substantially
does not hinder the passage of recirculated exhaust gases.
Thereby, according to selective supply of vacuum to the first inlet port 43
or to both the first and second inlet ports 43 and 44 of the multi-action
diaphragm activated control device 21, this multi-action diaphragm
activated control device 21 provides a two-step performance of moving the
flapper valve 18.
Supply of vacuum to the first inlet port 43 of the multi-action diaphragm
activated control device 21, and therefore to the first diaphragm chamber
27 thereof, is provided, from a vacuum generating pump 49, which in this
embodiment is coupled, as may be schematically seen in FIG. 1, to the
diesel engine 1, via pipes 48 and 47, a first electromagnetic valve 46,
and a pipe 45. Thus, by the opening and closing operation of the first
electromagnetic valve 46, supply of vacuum may be selectively provided to
the first diaphragm chamber 27 of the multi-action diaphragm activated
control device 21. It should be noted that the first electromagnetic valve
46 is so adapted that, when it is not providing supply of vacuum from the
pump 49 to the first inlet port 43 and the first diaphragm chamber 27 of
the multi-action diaphragm activated control device 21, it is providing
atmospheric pressure thereto instead.
Further, supply of vacuum to the second inlet port 44 of the multi-action
diaphragm activated control device 21, and thereby to the second chamber
28 thereof, is provided, from the pump 49, via pipes 48 and 52, a second
electromagnetic valve 5, and a pipe 50. Thereby, the vacuum generated by
the pump 49 is selectively introduced to the second diaphragm chamber 28
of the multi-action diaphragm activated control device 21, under the
control of the second electromagnetic valve 51. It should be noted that
the second electromagnetic valve 51 is so adapted that, when it is not
providing supply of vacuum from the pump 49 to the second inlet port 44
and the second diaphragm chamber 28 of the multi-action diaphragm
activated control device 21, it is providing atmospheric pressure thereto
instead.
The structure of the first and second electromagnetic valves 46 and 51 may
be the same, and, in the shown embodiment, it is. Each of them has a valve
element 55 or 60 which is movable to the right in FIG. 2, so as to block
the atmosphere inlet port 56 or 61, by magnetic force generated by an
electromagnetic coil 53 or 58, and which is also movable to the left in
FIG. 2, so as to block the negative pressure port 54 or 59, by negative
pressure which is present in the negative pressure port 54 or 59. This
negative pressure port 54 or 59 is connected, via a pipe 47 or 52, to the
pipe 48 which leads to the vacuum generating pump 49.
Thus, when the electromagnetic coil 53 or 58 receives supply of electric
current, then it provides magnetic force, and the valve element 55 or 60
is attracted rightwards in FIG. 2, and thereby the negative pressure port
54 or 59 is communicated with the outlet ports 57 or 62, which is
connected via the pipe 45 or 50 with the first inlet port 43 or the second
inlet port 44 of the multi-action diaphragm activated control device 21,
and further, by the rightward motion of the valve element 55 or 60, the
atmospheric inlet port 56 or 61, which leads to the atmosphere, is closed.
On the other hand, when the electric coil 53 or 58 is not supplied with
electric current, then it does not provide magnetic force, and thereby the
valve element 55 or 60 is pulled leftwards in FIG. 2 by the vacuum which
is present in the negative pressure port 54 or 59, and closes this vacuum
negative pressure port 54 or 59. Therefore, the atmospheric inlet port 56
or 61 is communicated with the inlet port 57 or 62, and thereby, via the
pipe 45 or 50, with the first inlet port 43 or the second inlet port 44 of
the multi-action diaphragm activated control device 21.
The electromagnetic coils 53 and 58 of the first and second electromagnetic
valves 46 and 51 are individually supplied selectively with electric
current from a battery electric current source 63, under the control of an
electric switching system 64, which is shown in more detail in FIG. 3. The
electric switching system 64 comprises a first disc member 65 and a second
disc member 66, which are both composed of insulating material, and which
are fixedly attached to the shaft 8 of the diesel fuel injection pump 7.
On the first disc member 65 and the second disc member 66 are mounted
respectively a first contact plate 67 and a second contact plate 68,
around parts of their circumferences, and these first and second contact
plates 67 and 68 are made of electrically conducting material.
To one side of the shaft 8 are provided the first and second contact levers
69 and 70, which are electrically connected respectively to the coil 53 of
the first electromagnetic valve 46, and to the coil 58 of the second
electromagnetic valve 51, and which respectively bear upon the first
contact plate 67 and the second contact plate 68, in a sliding and
electrically conductive fashion. Further, the first contact plate 67 and
the second contact plate 68 are grounded. Thereby, as the shaft 8 rotates
to control the amount of diesel fuel provided to the cylinders of the
engine by the diesel fuel injection pump 7, the first and second disc
members 65 and 66 rotate, and the contact levers 69 and 70 slide along the
contact plates 67 and 68, and establish electrical contact therewith, or
break electrical contact therewith.
Thereby, the one ends of the coils 53 and 58 of the first and second
electromagnetic valves 46 and 51 are selectively connected to ground.
Further, as seen in FIG. 1, the other ends of these electric coils 53 and
58 of the first and second electromagnetic valves 46 and 51 are connected
to the battery electric source 63. Thereby, according to the exact
particular amount of rotation of the shaft 8 of the diesel fuel injection
pump 7, one, both, or neither of the electromagnetic valves 46 and 51 may
be energised.
In more detail, when the shaft 8 of the fuel injection pump 7 is in a
position between the idling position of the pump, denoted by X in FIG. 3,
and the position denoted by A, which is at a predetermined angle Ta away
from the idling position X, the contact plate 67 is in electrical contact
with the first contact lever 69, and thereby electrical power is supplied
to the electromagnetic coil 53 of the first electromagnetic valve 46.
Similarly, when the shaft 8 of the diesel fuel injection pump 7 is between
the idling position of the pump X and the position denoted by B, which is
at a second predetermined angle Tb away from the idling position X, said
second predetermined angle Tb being a little smaller than the
abovementioned first predetermined angle Ta, the second contact plate 68
is in electrical contact with the second contact lever 70, and thereby
electrical power is provided to the electromagnetic coil 58 of the second
electromagnetic valve 51.
Therefore, as the shaft 8 of the fuel injection pump 7 turns progressively
between the idling position X and the engine full load or maximum power
position C, which is at a third predetermined angle Tc away from the fuel
injection pump 7 idling position, the operation of the electric switching
device 64 is as follows.
First, when the shaft 8 of the fuel injection pump 7 is between the idling
position X and the position B, which is at the angle Tb away from the
idling position X, then the first contact plate 67 is in contact with the
second contact lever 70. Therefore, electrical power is provided to both
of the electromagnetic coils 53 and 58 of the first and the second
electromagnetic valves 46 and 51. Thereby, the valve elements 55 and 60 of
the first and second electromagnetic valves 45 and 61 are both attracted
in the rightwards direction in FIG. 2, and thereby the negative pressure
ports 54 and 59 are both communicated with their respective outlet ports
57 and 62, so that vacuum is provided from the pump 49 through the pipe
48, through both the pipes 47 and 52, through both the first and second
electromagnetic valves 46 and 51, and through both the pipes 45 and 50 and
the first inlet port 43 and the second inlet port 44, to both the first
diaphragm chamber 27 and the second diaphragm chamber 28 of the
multi-action diaphragm activated control device 21. Therefore, as
described above, the multi-action diaphragm activated control device 21
opens the flapper valve 18 to its maximum open position, as shown in FIG.
2 by III, so that exhaust gas recirculation is performed to the maximum
amount.
Further, according to the above described particular feature of this
embodiment of the present invention, by the fact that in this condition
the inlet passage 12 is restricted by the fully opened flapper valve 18,
not only is the maximum amount of exhaust gas recirculation provided,
according to the full open position of the flapper valve 18, but also the
flow resistance of the inlet passage 12 to the flow of fresh air from the
air cleaner 2 to the inlet manifold 5 is increased, and thereby the ratio
of exhaust gas recirculation is further increased, which, as explained
above, is very desirable.
Second, when the shaft 8 of the diesel fuel injection pump 7 is rotated
beyond the position B, but not as far as the position A, so that the angle
through which it has moved is greater than Tb but less than Ta, then the
second contact plate 68 comes out of contact with the second contact lever
70, and only the first contact plate 69 remains in contact with the first
contact lever 69. In this case, the electromagnetic coil 53 of the first
electromagnetic valve 46 is provided with electrical power, and thereby
its valve element 55 is moved rightwards in FIG. 2, thus communicating the
negative pressure vacuum port 54 to the outlet port 57, and providing, via
the pipe 45 and the first inlet port 43, the first diaphragm chamber 27 of
the multi-action diaphragm activated control device 21 with vacuum from
the pump 49, while, on the other hand, the electromagnetic coil 58 of the
second electromagnetic valve 51 does not receive electrical power, and
thereby its valve element 60 is moved leftwards in FIG. 2 and blocks the
negative pressure port 59, while opening the atmospheric inlet port 61,
whereby atmospheric pressure is introduced, via the pipe 50, and the
second inlet port 44, to the second diaphragm chamber 28 of the
multi-action diaphragm activated control device 21. Thereby, as explained
above, the multi-action diaphragm activated control device 21 provides a
position for the flapper valve 18, which is the intermediate or half open
position denoted by II in FIG. 2, and thus reduces the amount of fluid
flow of exhaust gas recirculation, as compared with the first situation
described above, to an intermediate flow level.
Further, if the shaft 8 of the diesel fuel injection pump 7 is further
rotated, beyond the angular position denoted by A, to a position between
the angular position A and the angular position C, so that the angle
through which it has moved from the idling position X is greater than Ta,
then in this state the first contact plate 67 is out of contact with the
first contact lever 69, and also the second contact plate 68 is out of
contact with the second contact lever 70. Thereby, no electrical power is
supplied to either the electromagnetic coil 58 of the second
electromagnetic opening and closing valve 51. In this case, the valve
elements 55 and 60 are both of them in their leftwards positions in FIG.
2, and thereby the negative pressure ports 54 and 59 are both closed, and
the atmospheric inlet ports 56 and 61 are both open, whereby atmospheric
pressure is introduced, via the pipes 45 and 50, and the first inlet port
43 and the second inlet port 44, to both the first diaphragm chamber 27
and the second diaphragm chamber 28 of the multi-action diaphragm
activated control device 21. Thereby, as explained above, the multi-action
diaphragm activated control device 21 provides a position for the flapper
valve 18 which is the fully closed position, denoted by I in FIG. 2.
Thereby, exhaust gas recirculation is effectively stopped.
Thus, it is seen that the electrical switching device 64 provides,
selectively, a three-way signal, showing whether the amount of load upon
the diesel engine, that is to say, the amount of fuel provided at each
compression stroke of the piston of a cylinder of the engine to that
cylinder by the diesel fuel injection pump 7, is either in a first region
higher than a first predetermined value, in a second region between the
first predetermined value and a second predetermined value, or in a third
region below the second predetermined value. This three-way signal is
acted on by the means which comprises the two electromagnetic valves 46
and 51, the multi-action diaphragm activated control device 21, and the
exhaust gas recirculation valve 4, to provide a threeway performance of
control of exhaust gas recirculation.
In FIG. 4 is shown a graph, in which engine torque is the ordinate and
engine rpm is the abscissa, showing the characteristics of a diesel
internal combustion engine, as regards the torque and rpm combinations
provided by the above mentioned three positions of the shaft of the diesel
fuel injection pump 7. Thus, the line denoted by A in FIG. 4 shows the
various possible combinations of rpm and torque available when the shaft 8
of the diesel fuel injection pump 7 is at the position A in FIG. 3; the
line denoted by B in FIG. 4 shows the various combinations of engine
torque and engine rpm available when the shaft 8 of the diesel fuel
injection pump 7 is at the position B in FIG. 3; and the line denoted by C
in FIG. 4, similarly, shows the various possible combinations of engine
torque and engine rpm available when the shaft 8 of the diesel fuel
injection pump 7 is at the position C in FIG. 3, which is the full load
position. As shown in FIG. 4, in the high load area I, which is located
between the lines A and C, the flapper valve 18 of the exhaust gas
recirculation valve 4 is in its fully closed position I, and exhaust gas
recirculation is not performed. Further, in the area II of middle load,
which is between the lines A and B, the flapper valve 18 of the exhaust
gas recirculation control valve 4 is in its position II, wherein exhaust
gas recirculation is performed to a moderate degree. Moreover, in the low
load area III, which is the area below the line B in FIG. 4, the flapper
valve 18 of the exhaust gas recirculation valve 4 is in its position III,
and exhaust gas recirculation is performed at the maximum level.
This performance is more clearly shown in FIG. 5, which is a graph, drawn
for a representative fixed value of engine revolution speed, in which
exhaust gas recirculation ratio is the ordinate, and engine torque is the
abscissa, and in which the line designated by D is a line which shows the
limit for effective exhaust gas recirculation. That is, if exhaust gas
recirculation is performed at a higher amount, which is above the line D
in FIG. 5, sufficient oxygen is not available for combustion of the fuel
injected into the cylinders of the engine, and, problems arise with regard
to the emission of HC, CO, and various other unburnt hydrocarbons, such as
soot. Therefore, in order to maintain proper and ideal operation of the
engine, the ideal amount of exhaust gas recirculation to be provided is
shown by the line D in FIG. 5.
Therefore, this line D shows the ideal amount of exhaust gas recirculation
for a particular combination of engine load and engine rpm. However, in
practice, to arrange for an exhaust gas recirculation control means to
provide exactly this amount of exhaust gas recirculation is, as explained
above, excessively costly, and is prone to operational difficulties.
Therefore, according to the present invention, exhaust gas recirculation
is provided according to a characteristic shown by the line denoted by E
in FIG. 5, as an approximation to the ideal performance of exhaust gas
recirculation. The approximation provided by this line E is so arranged
that it definitely never rises above the line D. This is so as definitely
to eliminate the possibility of excessive production of HC, CO, and
unburnt hydrocarbons such as soot in the exhaust gases of the diesel
engine. At the same time, in view of the fact that the amount of exhaust
gas recirculation provided by the exhaust gas recirculation control system
of the present invention, according to the line E in FIG. 5, is
substantially close to the line D, the reduction of emission of NOx by the
device of the present invention is, substantially, acceptable. The three
stages denoted by I, II, and III denote the three positions available for
the flapper valve 18, as explained above with reference to FIG. 4. In the
example shown in FIG. 5, the exhaust gas recirculation ratio in the fully
closed position I is approximately 0%; the exhaust gas recirculation ratio
provided in the part open position II is approximately 25%; and the
exhaust gas recirculation ratio provided in the full open position III is
approximately 50%.
In the shown embodiment, it is possible to adjust together the part open
position II of the flapper valve 18 and the full open position III of the
flapper valve 18, by adjusting the effective length of the connecting rod
20, by the operation of the length adjusting means 72, as explained above.
Further, the full open position III of the flapper valve 18 can be altered
independently of the part open position II of the flapper valve 18, by
adjusting the position of the second stopper 38, by the use of the screw
39, as also explained above.
In FIG. 6, a second embodiment of the exhaust gas recirculation control
device according to the present invention is shown, in partial section. In
this second embodiment, a disc-valve-and-seat-type exhaust gas
recirculation control valve is used, instead of the flapper-type exhaust
gas recirculation valve used in the first embodiment. In more detail, the
exhaust gas recirculation control valve 4 is provided with a disc valve
18', which by its movement upwards and downwards in the figure opens and
closes an exhaust gas recirculation control port 14', which is formed at
the end of the elbow pipe 15'. This disc valve 18' is directly connected,
via the rod 31', to the multi-action diaphragm activated control device
21, with sealing being performed by a seal member 71. Thus, the disc valve
18' is directly moved by the multi-action diaphragm activated control
device 21.
The other illustrated parts in this embodiment correspond, respectively, to
the parts of the first embodiment which are designated by the same
reference numbers. Further, the parts of this second embodiment which are
not shown are similar to those in the first embodiment.
The operation of this second embodiment is similar to the operation of the
first embodiment. That is to say, when both the first inlet port 43 and
the second inlet port 44 of the multi-action diaphragm activated control
device 21 | | |
