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Description  |
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This invention relates to four-cycle internal combustion engines operated
on lean air/fuel mixtures and having an exhaust gas reactor in their
exhaust means to oxidize unburned constituents of the fuel, and to means
for operating the engine, so as to protect the exhaust gas reactor from
thermal damage.
In internal combustion engines having exhaust gas reactors disposed in
their exhaust system, unburned fuel constituents in the exhaust gases are
oxidized to form innocuous substances. One common type of reactor is a
thermal reactor that constitutes a chamber kept at a suitable temperature,
and in which the exhaust gases reside for a sufficient time that the
unburned constituents are oxidized. Still another known reactor is the
catalytic type, wherein a catalyst element is disposed in the stream of
exhaust gases where it promotes and catalyzes the oxidations.
Prior art systems have been devised to oxidize the unburned constituents,
but they have involved considerable economic disadvantages. For example,
for rich-running engines air injection systems are known for injecting air
into the exhaust gases to provide sufficient oxygen for the process. The
additional equipment and controls needed for this system are costly. They
must be of high quality in order to provide a satisfactory life and
reliability. In addition, their reactors are subject to thermal damage
during deceleration, and therefore must be made more rugged and costly so
as to resist this damage. For example, the materials for a thermal reactor
useful in one well-known prior art system cost nearly five times as much
as the simpler thermal reactor which can be used in this invention.
The use of a thermal reactor with an engine which is set to run on a lean
mixture is known. It does have the disadvantage of a theoretical poor
efficiency on cold starts. Also, in prior art systems of this type, the
higher temperatures which were utilized required the more expensive
construction.
It is an object of this invention to provide simple, reliable and
relatively inexpensive means to enable an engine to operate effectively on
a lean air/fuel mixture with a relatively inexpensive exhaust gas reactor
having a long life. The term "exhaust gas reactor" is used herein to mean
a catalytic element, or a thermal reactor which includes a residence
chamber. This invention enables one to enjoy both the advantages of lean
engine operation and the use of a catalytic element, which have heretofore
been incompatible with each other, or of an inexpensive thermal reactor,
which has heretofore not been practical.
There are substantial advantages in operating an internal combustion engine
with mixtures which are not richer than stoichiometric, and especially
with mixtures which are leaner than stoichiometric. A "stoichiometric
mixture" is one in which, when the combustion is completed as far as the
limiting substance (fuel or oxygen) permits, there will be neither excess
oxygen nor excess fuel remaining. The numerical value of the
"stoichiometric ratio" when gasoline is consumed is about 15; that is, the
carburetor passes about 15 formula weights of air for every formula weight
of gasoline introduced into the air stream. The term "fuel" as used herein
means gasoline and similar liquid hydrocarbon fuels. Leaner mixtures have
a relatively larger numerical value of their air/fuel ratio and have
excess oxygen. "Lean mixtures" are here defined as mixtures with an
air/fuel ratio greater than the stoichiometric. The term "ratio" is
sometimes used interchangeably with its numerical value. In contrast,
richer mixtures have a relatively smaller air/fuel ratio. "Rich mixtures"
are here defined as mixtures with an air/fuel ratio lesser than
stoichiometric. There is insufficient oxygen in a rich mixture to consume
all of its fuel.
During normal operation of an engine on a lean mixture, the exhaust gas
contains residual oxygen. Under these conditions, it is unnecessary to
supply additional air to the exhaust system for oxidizing the unburned
constituents in the exhaust gas. Furthermore, the amount of unburned
constituents in the exhaust gas from an internal combustion engine which
is operated with a lean mixture is generally small. Therefore, a
relatively small thermal load is imposed on the reactor, and heat
generation in the reactor can be maintained at a low level. Durability of
the catalyst in a catalytic reactor, or of the shell of a thermal reactor,
is thereby significantly improved as contrasted with rich-mixture
operation where supplementary oxygen is added in the exhaust system and
the oxidation occurs in the reactor, where the generated heat imposes a
very substantial thermal stress on the reactor which increases its cost
and reduces its durability. The foregoing favorable situation pertains in
"normal" conditions, which conditions are defined as those which do not
involve acceleration, deceleration, starting, or operation under heavy
load.
However, when decelerating an engine that is provided with fuel-supplying
means such as a carburetor, or with a fuel injector, set to deliver a lean
mixture under normal conditions, circumstances occur which produce exhaust
gases that can subject the reactor to an unacceptable thermal overload. A
principal cause of such an overload is misfiring, wherein the charge is
not consumed in the combustion chamber, but instead flows unoxidized to
the reactor, where it oxidizes and can create a thermal overload. The term
"deceleration conditions" as used herein is inclusive of typical slowing
down under "engine-brake" conditions, of coasting downhill, and of
down-shifting.
The tendency of an engine to misfire is aggravated by extreme values of the
air/fuel mixture. A mixture which is either too rich or too lean can
misfire. A transient too-rich condition can occur during deceleration
immediately after the engine throttle valve means is rapidly closed. At
that moment, the pressure in the intake passage decreases abruptly. As a
consequence, liquid fuel which was previously deposited on the wall
surfaces of the intake passage is instantaneously vaporized, with the
result that an excessively fuel-rich mixture is momentarily introduced
into the combustion chamber, and can misfire. A transient too-lean
condition can occur immediately after the foregoing too-rich condition
(deceleration continuing), because then the pressure in the induction
means is low (lower than at idle), and a conventional carburetor or fuel
injector will supply a leaner-than-normal mixture because the amount of
fuel supplied to it in response to the induction means pressure is more
nearly related to air flow at idle conditions that it is to the more rapid
air flow which occurs at deceleration conditions. Such a too-lean
condition persists for the duration of the deceleration. In summary, under
the first of these conditions, a too-rich, possibly misfiring, mixture
will initially be supplied, and under the second, a too-lean, possibly
misfiring, mixture will be supplied.
Also, the tendency to misfire is related to the "residual fraction". This
term is defined as follows:
##EQU1##
The term "amount" refers to weight, or to volume measured at like
temperature and pressure. As the numerical value of the residual fraction
decreases, so also does the tendency of the engine to misfire.
The induction means pressure is low under deceleration conditions. It is a
fact that, as the pressure in the induction means decreases, the residual
fraction, and the tendency to misfire, increase. Accordingly, the mixture
under these conditions should be enriched. By enriching it, the
possibility of misfiring because of the tendency of the residual fraction
to increase is opposed.
By preventing misfiring, the oxidation of the fuel to consume the available
oxygen tends primarily to be completed in the combustion chamber, and a
relatively inexpensive, small and simple exhaust gas reactor can be used,
because the thermal load on it is minimal, and it is not subjected to
excessive thermal stress.
In addition, to protect the exhaust gas reactor in case of malfunction of
the mechanism which prevents misfiring, means responsive to an excessive
temperature can be provided for enriching the air/fuel mixture.
The present invention comprises an induction means, a throttle, a
combustion chamber, an exhaust conduit, and an exhaust gas reactor in the
exhaust conduit downstream from the combustion chamber. Means is not
provided to supply air directly to the exhaust conduit. Means is provided
for controlling the air/fuel ratio of a mixture supplied to the combustion
chamber of an engine set to operate normally on a lean air/fuel mixture to
prevent misfiring and consequent excessive thermal load on the exhaust gas
reactor under deceleration conditions. According to the preferred method
of the present invention, under deceleration conditions, mixture supplied
to the combustion chamber is at first leaned for a limited time and, after
a predetermined time, is enriched to produce under both circumstances a
mixture having an air/fuel ratio on which mixture the engine tends not to
misfire under deceleration conditions. As a consequence, the engine
operates smoothly in this transient condition (deceleration), and the
exhaust gas reactor is protected. The exhaust gas reactor requires no
protection under normal load conditions, because the engine operates
smoothly and without misfiring on a lean mixture under these conditions.
According to a preferred but optional feature of the invention, a
supplementary air valve is provided which is responsive to pressure in the
induction means, whereby to supply supplementary air for a limited time to
the mixture in the induction means when the throttle is first closed under
deceleration conditions.
According to another preferred but optional feature of the invention, the
carburetor may be provided with a fuel nozzle controlled by a valve which
is adapted to be opened at an induction means pressure which is respective
to deceleration conditions, and supply additional fuel. Alternatively, the
carburetor may include a low load fuel circuit with air-bleed means
responsive to such conditions, or starter nozzle means may be utilized for
supplying the additional fuel. As a further alternative, a source of air
provided under normal conditions may be terminated during deceleration
conditions.
According to yet another optional feature of the invention, the engine
ignition may be advanced under deceleration conditions, thereby to improve
combustion of the lean mixture and further to suppress any tendency to
misfire.
Despitie the aforementioned features, or perhaps because of their
malfunction, momentary misfiring might still occur in the engine, which
could cause an excessive thermal load to be exerted on the exhaust gas
reactor. Therefore, according to still another optional feature of this
invention, thermosensitive means responsive to the temperature of the
reactor is provided to enrich the mixture in the induction means when the
temperature of the reactor reaches a critical value. This reduces the
tendency of the engine to misfire, because misfiring is less likely to
occur with richer mixtures than with leaner mixtures. Also, residual
oxygen in the exhaust gas will be decreased, because the additional fuel
will have consumed it before it reaches the exhaust gas reactor. Less
oxidation then occurs in the reactor, and it is kept at a safe temperature
.
This invention will be fully understood from the following detailed
description and the accompanying drawings in which:
FIG. 1 is a side elevation, partly in cutaway cross-section and partly in
schematic notation, of an engine incorporating the invention;
FIG. 2 is an axial section of a modified form of carburetor useful with
this invention;
FIG. 3 is an axial section, partly in schematic notation, showing another
embodiment of the invention;
FIG. 4 is a fragmentary view of a portion of FIG. 3;
FIGS. 5a and 5b are fragmentary views of a control in two different
positions taken at lines 5--5 in FIG. 4; and
FIG. 6 is a schematic drawing illustating the theory of this invention.
In FIG. 1 the invention is applied to a four-cycle internal combustion
engine having a V-shaped arrangement of cylinders 1. Each cylinder
includes a combustion chamber 2 which is connected through intake valve
means 3 to an intake passage 4. Each combustion chamber is also connected
through an exhaust valve means 5 to an exhaust pipe or conduit 6. The
intake passage comprises induction means to supply a charge to be ignited
in the combustion chamber. The exhaust condition comprises exhaust means
to carry away the spent charge from the combustion chamber.
In exhaust conduit 6, there is disposed an exhaust gas reactor 7. Exhaust
gases flow through it. The catalytic type may have a conventional
catalytic structure with a skeleton (not shown) of heat-resistant ceramic
material having a catalyst deposited thereon. Its purpose is to accelerate
by catalysis the oxidation of unburned constituents of the fuel by the
oxygen. The thermal reactor is a chamber of suitable size and dimensions,
such that the exhaust gases reside therein for a period of time sufficient
for the oxidation to occur. Either type may be used in this system.
There is no direct supply of air to the exhaust conduit. It communicates
with the atmosphere only downstream from the exhaust gas reactor, where it
discharges the spent gases to atmosphere. The particular type of catalytic
element or even of exhaust gas reactor used is immaterial to this
invention. Any type may be used provided that conditions are provided
which are conducive to the oxidation of the unburned constituents.
The intake passage 4 for each of the combustion chambers is connected to an
intake manifold 8 which in turn is in fluid communication with a
carburetor 9. The carburetor 9 shown in the drawing is a two-barrel type
having a primary and a secondary bore or barrel 10 and 11, respectively.
Bores 10 and 11 are respectively provided with venturi elements 12 and 13.
The venturi elements are respectively provided with main fuel nozzles 18
and 19 connected through air-bleed means 14 and 15 to float chambers 16
and 17, respectively.
Primary bore 10 is provided with a throttle valve 20. It has two slow ports
23 and 24, that are connected through an air-bleed 22 to the float chamber
16. Similarly, the secondary bore 11 is provided with a throttle valve 21
and has a port 26 opening into the passage through the wall thereof. Port
26 is connected through an air-bleed 25 to the float chamber 17.
Throttle valve 21 is normally in the illustrated fully-closed position so
that only the primary side of the carburetor is brought into operation at
relatively low and normal load operation. During high load operations, the
throttle valve 21 is opened after the throttle valve 20 is fully opened so
that both the primary and the secondary side of the carburetor are brought
into operation. A portion of the exhaust pipe is extended as shown by 6a
in the drawing to a position beneath intake manifold 8 so as to direct a
portion of the exhaust gas thereinto to preheat the intake air in manifold
8. This carburetor is set to provide a lean air/fuel mixture at normal
conditions.
In the illustrated embodiment, a supplementary fuel port 27 is formed in
bore 10. Port 27 is also connected through a passage 28 to the slow port
23. For controlling fluid flow through the supplementary fuel port 27, a
needle valve 29 is secured to a diaphragm 30 of diaphragm means 31.
Diaphragm 30 divides the interior of the diaphragm means 31 into an
atmospheric pressure chamber 32 and a suction pressure chamber 33. Chamber
33 is connected through a suction pressure surge tank 34 to intake passage
4.
Needle valve 29 is normally biased toward the right in FIG. 1 under the
influence of a spring 35 so as normally to close port 27. It is displaced
toward the left by diaphragm means 31 so as to open port 27 when the
suction (vacuum) pressure in intake passage 4 is reduced to some
predetermined value.
An armature 36 is formed at one end of needle valve 29. A solenoid coil 37
surrounds the armature to form a solenoid means. The solenoid coil 37
includes wiring which is connected through an ignition switch 38 and a
thermoswitch 39 to an electric power source 40.
Thermoswitch 39 is controlled by a heat-sensitive element 39a disposed in
the exhaust conduit so as to sense the temperature of the exhaust gas
reactor. Thermoswitch 39 is closed when the temperature of the exhaust gas
reactor reaches a predetermined upper value.
The ignition system of the engine includes a distributor 43 for
controllling ignition coil means 42 connected to ignition plugs 41. The
distributor 43 has spark advance means 44 that is connected to diaphragm
means 45. Diaphragm means 45 is adapted to be actuated by suction in the
intake passage. Diaphragm means 45 includes a diaphragm 45b connected
through a connecting rod 45a to the distributor 43. Chambers 45c and 45d
are formed on opposite sides of diaphragm 45b which are selectively
connectible to intake passage 4 through valve 45a. Valve 45e serves
alternately to connect one or the other of chambers 45c and 45d to intake
passage 4, and the remaining one to the atmosphere.
Diaphragm means 90 for controlling valve 45e includes a diaphragm 90a which
is connected to valve 45e. The diaphragm thereby acts as an actuator for
valve 45e. A chamber 90b defined at the right side of the diaphragm 90a is
connected to intake passage 4. A return spring 90c is provided in the
chamber 90b. Diaphragm means 90 is actuated by suction to intake passage
4. During idling operation, the pressure in the intake passage 4, while
subatmospheric, is not at the lowest operating level of the intake
passage. The pressure at deceleration conditions is lower. At idling
pressures diaphragm 90a is urged toward the left in FIG. 1 under the
influence of spring 90c so as to set valve 45e to the setting shown in the
drawing. Suction in the intake passage 4 is then introduced into the
chamber 45d to move the diaphragm 45b upwardly in FIG. 1. The distributor
43 will thereby be rotated counterclockwise to retard the ignition timing.
During deceleration, the suction in the intake passage 4 is increased
(i.e., the pressure is still lower) from the pressure which existed during
the idling operation. The condition of valve 45e is then reversed so as to
communicate the suction from intake passage 4 into chamber 45c instead of
into chamber 45d. This is a substantial suction, and moves diaphragm 45b
and rod 45a downwardly. The distributor is thereby rotated clockwise so
that ignition timing is advanced, perhaps 35.degree. to 45.degree. before
top dead center. This occurs when the intake suction reaches a
predetermined value characteristic of deceleration conditions. Advancement
of the ignition timing tends to repress the tendency to misfire.
In the illustrated engine, the throttle valve 20 is opened to some extent
even during idling operation. It allows a certain amount of mixture to
flow into the combustion chamber. This increases the rate at which
air/fuel mixture ("charge") is supplied to the combustion chambers during
idling operation. In order to prevent the idling engine speed from being
undesirably rapid due to this increased flow of intake mixture, the
ignition timing is retarded. As previously described, when the intake
pressure reaches a predetermined suitably low value ("high suction" or
"high vacuum"), the diaphragm means 45 is operated to move spark advance
means 44 in the ignition-retarding direction. Thereby it is possible to
maintain a relatively low idling speed, even though a relatively large
amount of intake mixture is introduced into the cylinders.
During normal, relatively low load, operation of the engine, only the
throttle valve 20 is opened, and mixture is principally introduced through
the primary bore 10. During high load (also normal) operation, the
throttle valve 20 is fully opened, and the throttle valve 21 is also
opened, so that the mixture is introduced through both of bores 10 and 11.
At this point it will be observed that a carburetor is only one means for
supplying fuel for the air/fuel mixture. A fuel injector is another. Both
will inject fuel into the intake manifold or other induction means
upstream from the combustion chambers and downstream from the throttle in
response to pressure in the induction means. They are fully equivalent.
As previously described, a fuel-lean mixture is introduced into the engine
combustion chambers 2 to fuel the engine at normal conditions, and the
exhaust gas will therefore include a certain amount of residual oxygen.
The exhaust gas, including any unburned constituents, flows through the
exhaust conduit, where it enters the exhaust gas reactor, there to contact
the catalytic element when a catalytic reactor is used, or to reside in
the chamber of thermal reactor long enough for oxidation to occur,
depending on which type is used.
The unburned constituents are oxidized by the residual oxygen. Because it
utilizes oxygen which is present in the spent lean charge from the
combustion chambers when the engine is not decelerating, the process in
the exhaust gas reactor does not require supplementary air from the
atmosphere, and because the mixture is initially lean, there is little to
oxidize. Therefore, no means is needed to inject air directly into the
exhaust conduit, and the exhaust gas reactor can be of minimum size and
complexity.
However, under deceleration conditions, there is a time when additional air
is needed. Means is provided to supply this air to the induction means
upstream from the combustion chambers. An air cleaner 46 is placed
upstream from the inlet portion of the carburetor 9. For the said purpose,
a supplementary air valve 47 forms a bypass for air flow between air
cleaner 46 and intake manifold 8.
During deceleration, an abrupt decrease in pressure occurs immediately
after the closure of the throttle valve. Because of this, fuel which was
deposited on the intake passage wall during normal operation will
spontaneously be vaporized. Therefore, an excessively fuel-rich mixture
momentarily be introduced into the combustion chambers which could
misfire. Valve 47 serves to supply additional air to the intake passage
during this time to dilute the mixture and to maintain the ratio at a
value which will not cause misfire.
Valve 47 includes a valve member 49 secured to the diaphragm 48, and a
valve bore 50. Flow through the bore is controlled by valve member 49.
Diaphragm 48 is subjected to the intake pressure at the downstream side of
the throttle valve 21. During deceleration, diaphragm 48 is actuated by
the intake pressure (which is sub-atmospheric) to move valve member 49 and
open valve bore 50. Thus, supplementary air is supplied from the air
cleaner 46 to the intake manifold. Diaphragm 48 is pierced by an aperture
48a so that the diaphragm tends to return to its original position after
the conclusion of a suitable time delay following closure of the throttle
valve. The size of this orifice or aperture is selected to provide the
desired time delay. The larger it is, the smaller the delay. Valve bore 50
will then be closed by the valve member 49 to terminate the supply of
additional air.
After the above-described initial rich event, the mixture becomes too lean.
This is because a conventional carburetion means (carburetor or fuel
injector) responds to the low induction pressure of deceleration much as
it would to an idling demand, and the amount of fuel supplied by it is
insufficient to create, with the more rapid flow of air, a suitable
non-misfiring mixture. Therefore, the mixture ratio must be changed, and a
convenient means to do so is to supply additional fuel and to maintain the
mixture ratio at a suitable value. For this purpose, suction in intake
passage 4 is transmitted through surge tank 34 into suction chamber 33 of
the diaphragm means 31. Diaphragm 30 moves toward the left, and moves
needle valve 29 to open the supplementary fuel port 27. The construction
is such that this movement involves a time delay, for example about 1 to 2
seconds after the throttle valves are closed. The delay can be selected by
selecting an appropriate size of surge tank, or by placing a restrictor or
orifice in the lines. The system is adjusted so that supplementary
("additional") fuel starts about the time the supplementary ("additive")
air stops.
Additional fuel is supplied from bore 10 through manifold 8 and intake
passage 4 to the combustion chamber 2. The supply of supplementary fuel is
continued for the duration of the deceleration operation. The numerical
value of the air/fuel ratio to be maintained will be discussed below. It
is such that misfiring is averted. The oxygen in the intake mixture will
be substantially consumed in the combustion chamber. A combustible mixture
does not reach the exhaust gas reactor where combustion catalyzed by it
might impose a thermal overload. Oxidation at the exhaust gas reactor is
suppressed due to the lack of oxygen to maintain the oxidation. This
protects the exhaust gas reactor from being subjected to an excessive
thermal load, and enhances its durability, regardless of which type of
reactor is used.
During operation of the engine, despite the usage of the features of this
invention, or perhaps because of a momentary malfunction of them,
misfiring might occur. Then, unless care were taken, unburned mixture
would reach the exhaust gas reactor, and the fuel would be oxidized
therein, perhaps exerting an excessive thermal load on it. This can be
opposed by supplying additional fuel to the induction means so that the
oxygen will somehow be consumed before the mixture reaches the catalytic
element, and perhaps also by preventing misfiring.
To detect excessive temperature and reverse the tendency to overheat,
thermoswitch 39 will be closed when the exhaust gas reactor reaches a
predetermined critical temperature so as to energize the solenoid 37 and
move the needle valve 29 toward the left in FIG. 1. This will open the
supplementary fuel port 28 and provide supplementary fuel to the charge.
The exhaust gas reaching the exhaust gas reactor will then be
substantially free from residual oxygen, and oxidation of fuel in the
exhaust gas reactor will be suppressed. The temperature of the catalyst
will thereby be maintained at a safe level.
An alternate means to provide this thermal overload protection is
illustrated as a circuit 200, also under the control of thermoswitch 39a.
To show that it is an alternative construction, the common terminal of a
selector switch 201 is connected to lead 202. One terminal 203 is
connected to winding 37. Terminal 204 is connected to lead 204a. Lead 204a
connects to a valve actuator 205 which is grounded at 206. This valve
actuator, when actuated, closes normally-open air valve 207. Valve 207
supplies air to the induction system through air conduits 208 and 209 from
the air cleaner, bypassing the carburetor under normal operating
conditions. Air from these conduits forms part of the mixture under normal
conditions. The carburetor is set to provide a lean mixture with air
passed by the throttle and by this valve. When the mixture is to be
enriched in response to overheating in the reactor, switch 39 is closed,
and actuator 205 closes air valve 206. This will enrich the mixture. It is
obvious that any carburetor would be differently set for each of the two
settings of selector switch 201, and that in practice only one of these
systems will be used on any engine. The two are shown on this engine
solely for purposes of illustration of the two embodiments. The solid-line
setting of switch 201 is for the preferred system. The dotted-line setting
is for the alternative system just described.
FIG. 2 shows an example in which the supply of supplementary fuel is made
by utilizing slow speed ports in the carburetor. In all of the Figs.,
corresponding parts are shown by the same reference numbers as in the
other embodiments. As shown by arrow 51, fuel from the primary float
chamber (not shown) is introduced into a passage 52 and passed through an
air-bleed 14 into a main fuel nozzle 18 to be discharged into the venturi
element 12. Passage 52 is provided with a branch passage 53 which is
connected to a passage 54 leading to slow ports 23 and 24. Further, the
passage 54 is connected to a diluting air passage 55. The fuel introduced
from the air-bleed 22 into the passage 54 is diluted by air from passage
55 and is discharged from slow ports 23 and 24 into bore 10.
Air passage 55 is pr | | |
