Engine system

An engine system comprises an internal combustion engine and an exhaust gas treatment system, such as a three-way catalytic converter or an oxidation catalytic converter. The engine has an additional intake means, in addition to a main intake means for admitting by induction an air fuel mixture to a combustion chamber, for admitting under pressure above atmospheric pressure air to the combustion chambers during a period initiating during the exhaust stroke and terminating during the intake stroke for the purpose of expelling residual gas from the combustion chamber to bring about a stable combustion.

BACKGROUND OF THE INVENTION 
The present invention relates to an engine system and more particularly to 
an engine system having an internal combustion engine and an exhaust gas 
treatment system. 
An engine system is known which comprises a three-way catalytic converter 
in which engine exhaust gases flowing therethrough are exposed to a 
catalytic substance which, given the proper air-fuel ratio in the exhaust 
gases, will promote simultaneous oxidation of CO and HC and reduction of 
NOx. In such an engine system, because an air fuel mixture supplier is so 
controlled as to effect combustion at stoichiometry, fuel economy is 
poorer than an engine system in which lean combustion takes place. 
Moreover, the known engine system can not yield power output high enough 
to meet demand when high power output is required. 
Another known engine system comprises an oxidation catalytic converter 
which has a catalytic substance which will promote oxidation of CO and HC. 
In such an engine system, because an air fuel mixture supplier is so 
controlled as to effect lean combustion, fuel consumption increases and 
power output decreases when the engine operates under light load 
conditions. These results are attributable to the fact that the ratio of 
residual gas to fresh air fuel mixture in a charge in a combustion chamber 
increases abruptly under these conditions bringing about rough combustion 
leading to rough engine operation. 
SUMMARY OF THE INVENTION 
It is an object of the invention to improve fuel economy and power output 
of an engine system having an internal combustion engine and an exhaust 
gas treatment system. 
An engine system according to the invention results from the recognition 
that the so called engine stability is affected by G/F, rather than A/F, 
of a charge in a combustion chamber and there is a limit value in G/F 
above which the engine stability is not acceptable to ordinary use as a 
prime mover of an automobile, where, G=(intake air portion of the 
charge)+(residual gas portion of the charge). This means that if the 
residual gas portion of the charge could be replaced with the same amount 
of pure air, the same engine stability could be obtained with less fuel, 
resulting in low fuel consumption. This results from the fact that the 
pure air replacing the residual gas portion will help burning of fuel, 
while the residual gas of the charge, if not replaced, will make the 
burning of fuel difficult. 
The engine system according to the invention results from the further 
recognition that the residual gas portion of the charge will vary greatly 
over various operating conditions of the engine and in particular will 
increase abruptly when the engine operates under partial load conditions, 
which will be frequently used when operating an automobile in which the 
engine system is adapted be installed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1-5 the first embodiment of an engine system of the 
invention will be described hereinafter. 
As shown in FIG. 1, the engine system includes an internal combustion 
engine 1 which has a cylinder block 2 formed with at least one cylinder 
2a, a piston 3 slidable in cylinder 2 for reciprocal movement therein and 
a cylinder head 4 secured to cylinder block 2 to close cylinder 2a. 
Cylinder block 2, piston 3 and cylinder head 4 cooperate to form within 
cylinder 2a a combustion chamber 5. Cylinder head 4 has an intake port 
bore 6 (see FIG. 2), an exhaust port bore 7 and a second or additional 
intake port bore 8, all opening to combustion chamber 5. An intake valve 
6a cooperating with intake port bore 6, an exhaust valve 7a cooperating 
with exhaust port bore 7, and a second intake or air inlet valve 8a 
cooperating with additional intake port bore 8 are supported by cylinder 
head 4 (see FIGS. 1 and 2). Denoted by the reference numeral 5a in FIG. 2 
is an electrode of a spark plug. 
An air fuel mixture supplier which is in the form of a carburetor 9 in this 
embodiment, although other measures may be employed, is connected to 
intake port bore 7 through an induction conduit 10 so that an air fuel 
mixture will be admitted by induction to combustion chamber 5 via intake 
valve 6a during the intake stroke of piston 3. A source of pressurized air 
11 is connected to additional intake port bore 8 through an air admission 
conduit 12 to admit under pressure above atmospheric pressure air to 
combustion chamber 5 via air inlet valve 8a. In practice air shall be 
admitted to combustion chamber 5 under pressure ranging from 1.2 
kg/cm.sup.2 to 2.0 kg/cm.sup.2. The flow of air passing through air 
admission conduit 12 is controllably varied by a flow control device 13 so 
that, at least, substantially the same amount of air as that of the 
residual gas or greater than the latter will be admitted to combustion 
chamber 5 during the exhaust stroke. Source of pressurized air 11 includes 
a surge tank 14 having an outlet connecting with air admission conduit 12, 
an air pump 15 and an air cleaner 16. Air pump 15 is connected to an 
engine crankshaft, not shown in FIG. 1, by a mechanical drive, not shown, 
to transfer, under pressure above atmospheric pressure, air to surge tank 
14. An exhaust conduit 17 connects exhaust port bore 7 to an exhaust gas 
treatment system 18 to direct engine exhaust gases toward exhaust gas 
treatment system 18. 
Exhaust gas treatment system 18 includes a three-way catalytic converter 19 
in this embodiment which is a device of the type in which exhaust gases 
flowing therethrough are exposed to a catalytic substance which, given the 
proper air-fuel ratio in the exhaust gases, will promote simultaneous 
oxidation of CO and HC and reduction of NOx. 
Exhaust conduit 17 is provided with an exhaust sensor in the form of an 
oxygen sensor 20. Oxygen sensor 20 is preferably of the known type which, 
when exposed to engine exhaust gases at high temperatures, generates an 
output voltage signal Z which changes appreciably as the air-fuel ratio 
(A/F) of the exhaust gases passes through the stoichiometric level. Signal 
Z is fed to an electronic controller 21 where the difference between 
signal Z and a reference R is obtained. Reference R is chosen to be a 
constant voltage which is substantially equal to a voltage level of signal 
Z generated by oxygen sensor 20 when A/F of exhaust gases at a measured 
point by oxygen sensor 20 is the stoichiometric level. Controller 21 
generates a command signal to be supplied to an air-fuel ratio controller 
22. Air-fuel ratio controller 22 in this embodiment is of the known type 
which controls, with a solenoid valve 23, air bled to an air fuel metering 
system of carburetor 9 so as to reduce the difference between signal Z and 
reference R. Flow control device 13 will be described in detail referring 
to FIGS. 3 to 5. Flow control device 13 includes a metering valve 30 
fluidly disposed in air admission conduit 12 (see FIG. 3). A vacuum servo 
31 is mounted on air admission conduit 12 and has a diaphragm 31a to which 
the valve stem of metering valve 30 is fixedly connected, an atmospheric 
chamber 31b below (viewing FIG. 3) diaphragm 31a, a vacuum chamber 31c 
above (viewing FIG. 3) diaphragm 31a, and a spring 31d mounted within 
vacuum chamber 31c to act against diaphragm 31a to bias metering valve 30 
to the illustrated closed position in which air admission conduit 12 is 
closed by valve 30. A vacuum conduit 31e connects the outlet of a source 
of constant vacuum, in the form of a vacuum accumulator 32, to vacuum 
chamber 31c. Vacuum accumulator 32 is connected to a source of engine 
induction vacuum, such as induction conduit 10 (see FIG. 1), through a 
check valve 33. A pressure regulator 34 is mounted on vacuum accumulator 
32 to keep the pressure within accumulator 32 constant irrespective of the 
engine operating conditions. Vacuum conduit 31e is provided with an 
orifice 35 therein and an air bleed conduit 36 has one end connected to 
the vacuum conduit 31e at a location intermediate orifice 35 and vacuum 
chamber 31c. An air bleed orifice 37 is provided within air bleed conduit 
36 at an opposite end thereof. A solenoid valve 38 is arranged to control 
flow through air bleed conduit 36. When not energized, solenoid valve 38 
closes air bleed conduit 36, while, when energized, it opens air bleed 
conduit 36. A control circuit 40, only diagrammatically shown in FIG. 3, 
is electrically circuited with solenoid valve 38. 
The control circuit 40 comprises a clock counter 41 which generates a reset 
signal 42 at regular intervals. Reset signal 42 is fed to an integrator 43 
and also to a flip flop 44 to reset them. An electrical signal 45 
representing the engine speed (the engine r.p.m.) is fed to integrator 43. 
An output signal voltage 46 from integrator 43 rises at a faster rate when 
the engine speed is high than when the engine speed is low. Output signal 
voltage 46 is fed to a comparator 47 to which a reference signal voltage 
48 representing the engine induction vacuum is fed. Reference signal 
voltage 48 is higher when the engine induction vacuum is high, i.e., when 
engine load is low, than when the induction vacuum is low, i.e., when 
engine load is high. Comparator 47 feeds a reset signal 49 to the flip 
flop 44 when signal 46 exceeds signal 48. Since the time period after the 
instance of reset signal 42 to the instance of reset signal 49 is variable 
in response to the engine speed and induction vacuum, flip flop 44 will 
generate a pulse signal 50 having a pulse width variable in response to 
the engine speed and induction vacuum. Pulse signal 50 is amplified by 
means of a power amplifier 51 and then fed to solenoid valve 38 to 
energize the solenoid for a time corresponding to the pulse width. 
FIG. 4A shows a timing diagram representing the condition that the engine 
speed is high and induction vacuum is low, while FIG. 4B shows a timing 
diagram representing the condition that the engine speed is low and 
induction vacuum is high. FIG. 5 shows a graph plotting the required 
amount of air for expelling the residual gas from combustion chamber 5 as 
against the engine speed and induction vacuum. It will now be understood 
that with metering valve 30 the amount of air to be admitted into 
combustion chamber 5 through additional intake port bore 8 (see FIG. 1) 
will be varied as shown in FIG. 5. 
Connected to intermediate power amplifier 51 and solenoid valve 38 is a 
normally closed solenoid switch 52 whose solenoid 52a is circuited with a 
throttle sensitive switch 53. Throttle sensitive switch 53 is of the known 
type which is closed when a throttle valve of carburetor 9 is fully 
opened. Therefore, solenoid 52a is energized to open switch 52 to prevent 
energization of solenoid valve 38, keeping air bleed conduit 36 closed, 
applying vacuum in vacuum accumulator 32 to vacuum chamber 31c thereby 
fully opening metering valve 30. 
During the exhaust stroke exhaust valve 7a opens and piston 3 moves 
upwardly from the bottom dead center, and air inlet valve 8a opens to 
admit air to combustion chamber 5 for the purpose of expelling the 
residual gas from combustion chamber 5. Air inlet valve 8a opens fully to 
permit entry of a great amount of air, enough to expel substantially all 
of the residual gas from the combustion chamber before exhaust valve 7a 
closes. 
During the intake stroke intake valve 6a opens, exhaust valve 7a closes and 
piston 4 moves downwardly from the top dead center position. During the 
initial descent of piston 3, air inlet valve 8a closes. Air fuel mixture 
having an air fuel (A/F) ratio continuously adjusted by carburetor 9 is 
admitted by induction to combustion chamber 5. 
It will be noted that the residual gas in the charge in combustion chamber 
5 becomes negligible and the charge is composed of air admitted to 
combustion chamber 5, via air inlet valve 8a, during the exhaust stroke to 
expel the residual gas and of an air fuel mixture admitted to combustion 
chamber 5, via intake valve 6a, during the intake stroke. This means that 
the effective cylinder volume is increased by a volume which is equal to 
the volume of the residual gas expelled from combustion chamber 5 by 
admission of air via air inlet valve 8a. As a result, power output as well 
as fuel consumption can be improved. 
Referring to the operation of flow control device 13 shown in FIG. 3, 
during engine operation under idle and deceleration conditions when 
throttle opening sensitive switch 53 is open, solenoid 52a is not 
energized so that switch 52 is closed to permit solenoid actuated air 
bleed control valve 38 to variably open air bleed conduit 36 in response 
to pulse signal 50 which is a function of engine speed and induction 
vacuum. It will be noted that under these conditions metering valve 30 
controllably varies the amount of air passing through conduit 12 to meet 
varying demands for a variety of operating conditions. During engine 
operation under full load or full throttle conditions throttle sensitive 
switch 53 is closed to energize solenoid 52a thus opening switch 52. 
Opening switch 52 prevents current from flowing through solenoid actuated 
control valve 38, closing air bleed conduit 36 thereby to permit vacuum 
within vacuum accumulator 32 to be transmitted to vacuum chamber 31c 
causing flow metering valve 30 to fully open conduit 12. Therefore, under 
full load conditions, an amount of air greater than the amount of residual 
gas is admitted to combustion chamber 5 during the exhaust stroke before 
exhaust valve 7a closes permitting a considerable amount of air to flow 
out of combustion chamber 5 to exhaust conduit 17. This will cause oxygen 
sensor 20 to generate a level of signal Z which causes air fuel ratio 
controller 22 to adjust A/F of air fuel mixture supplied to combustion 
chamber 5 to the richer side than stoichiometry. Enrichment of air fuel 
mixture supplied to combustion chamber 5 will increase engine power output 
to meet demands for full load conditions. This will be hereinafter 
explained in detail. 
Characterization of a closed loop control system comprising oxygen sensor 
20, electric controller 21 and air fuel ratio controller 22 is such that 
A/F supplied to combustion chamber 5 is varied to obtain a fixed A/F in 
the exhaust gases in exhaust conduit 17 upstream of the point measured by 
oxygen sensor 20. When the amount of air flowing out of combustion chamber 
5 into exhaust conduit 17 through exhaust valve 7a during the exhaust 
stroke is negligible, as is the case when the engine operates under idle, 
deceleration and partial load conditions, A/F in the exhaust gases 
represents A/F in the charge in combustion chamber 5 and therefore A/F in 
the charge is kept around stoichiometry. When a considerably large amount 
of air flows out of combustion chamber 5 into exhaust conduit 17 together 
with the exhaust gases, as is the case when the engine operates under full 
load conditions, there occurs a considerable dilution of engine exhaust 
gases with the air. Therefore, A/F in the exhaust gases no longer 
represents A/F in the charge in combustion chamber 5. Since A/F in the 
charge is adjusted so that exhaust gases resulting from combustion of the 
charge will have A/F which after dilution with the air will approach 
stoichiometry at the point measured by the oxygen sensor upstream of the 
three-way catalytic converter 19, A/F in the charge in combustion chamber 
5 under full load engine operating conditions is rich and combustion of 
such rich charge will result in an increase of engine power output. 
It will be noted that although A/F in the charge in combustion chamber 5 is 
rich under full load engine operating conditions, A/F in exhaust gases 
upstream of catalytic converter 19 can be kept around levels around which 
the simultaneous oxidation of CO and HC and reduction of NOx within 
catalytic converter 19 are maintained. 
When it is desired to reduce the NOx level further, exhaust gas 
recirculation is effected through an exhaust gas recirculation (EGR) 
conduit 24 leading from exhaust conduit 17 at upstream of oxygen sensor 20 
to induction conduit 10 downstream of the carburetor throttle valve. Flow 
of exhaust gases passing through EGR conduit 24 can be controllably varied 
in response to engine operating conditions by means of a conventional EGR 
valve 25. The use of EGR makes possible a substantial cut in the reaction 
capacity for NOx of three-way catalytic converter 19. 
Although in the previously described embodiment a closed loop A/F control 
system which varies A/F supplied to combustion chamber 5 is employed, it 
is possible to employ a closed loop air control system which controls, 
instead of A/F supplied to combustion chamber 5, the amount of air 
admitted to combustion chamber 5 via air inlet valve 8a. When the closed 
loop air control system is employed, carburetor 9 is set rich and A/F in 
the charge is adjusted around stoichiometry after dilution of air admitted 
to combustion chamber 5 via air inlet valve 8a. Closed loop air control 
may be effected with a bypass conduit 26 having one end connected to 
conduit 12 upstream of flow metering valve 30 of flow control device 13 
and the opposite end connected to conduit 12 downstream of flow metering 
valve 30 thereof (see FIGS. 1 and 3). Bypass conduit 26 is provided with a 
solenoid actuated flow control valve 27 circuited to receive a command 
signal from electronic controller 21. Characterization of closed loop air 
control system is such that the amount of additional air supplied through 
bypass conduit 26 is increased by valve 27 when A/F in the exhaust gases 
in exhaust conduit 17 upstream of oxygen sensor 20 is richer than 
stoichiometry, while it is decreased by valve 27 when the A/F is leaner 
than stoichiometry. In order to adjust A/F in the charge to stoichiometry, 
the amount of air admitted to combustion chamber 5 via air inlet valve 8a 
is controlled mainly by means of flow control device 13 to meet demands 
for scavenging combustion chamber 5 and additionally by means of control 
valve 27 for diluting air fuel mixture admitted to combustion chamber 5 
when the engine operates under idle, deceleration and partial load 
conditions. When high engine power output is required, control valve 27 is 
closed to prevent flow of air through bypass conduit 26 such as by 
isolating the valve 27 from the demanded signal from electric controller 
21 to enrich A/F in the charge in combustion chamber 5. 
In the case that the closed loop air control system is employed, switch 52 
(see FIG. 3) is kept closed. 
It will be appreciated from the previous description that in an engine 
system according to the invention the charge in combustion chamber 5 is 
conditioned favorably for satisfactory combustion. 
It will also be appreciated that emission levels from an engine system 
according to the invention are low. 
It will also be appreciated that, when required, an engine system according 
to the invention can yield high power. 
Referring to the second embodiment of an engine system shown in FIG. 6, 
this embodiment differs from the previously described first embodiment in 
that: 
Although the exhaust gas treatment system 18 takes the form of three-way 
catalytic converter 19 and a closed loop control system including oxygen 
sensor 20, control circuit 21 and an air fuel ratio control actuator 22 is 
used in the first embodiment, exhaust gas treatment system 18 takes the 
form of an oxidation catalytic converter 60 in this embodiment so that 
such a closed loop control system as used in the first embodiment is 
unnecessary and is eliminated. Oxidation catalytic converter 60 is a 
device in which exhaust gases flowing therethrough are exposed to a 
catalytic substance which will promote oxidation of CO and HC. 
Explaining the FIG. 6 embodiment in more detail, the air fuel ratio of the 
mixture admitted to combustion chamber 5 is variably adjusted by a 
carburetor, not shown. Setting of the carburetor is made and/or the 
opening timing of air inlet valve 8a is set so that air fuel ratio of the 
charge, which is composed of air fuel mixture admitted to combustion 
chamber 5 via intake valve 6a (see FIG. 2) and air admitted to combustion 
chamber 5 via air inlet valve 8a, becomes lean to bring about a lean 
combustion which results in exhaust gases that are suitable for oxidation 
within oxidation catalytic converter 60. It will be noted that A/F in the 
charge becomes leaner than that in the air fuel mixture admitted to 
combustion chamber 5 via intake valve 6a because the mixture is diluted by 
air admitted to combustion chamber 5 via air inlet valve 8a. 
Delaying the opening timing of air inlet valve 8a by means of a suitable 
variable value timing device will increase the valve opening duration 
after exhaust valve 7a has closed, resulting in an increase in the 
proportion of air from air inlet valve 8a to the charge in combustion 
chamber 5. Thus it will be noted that dilution of fresh mixture from 
intake valve 6a can, if desired, be brought about by increasing the valve 
opening duration. 
A/F in air-fuel mixture admitted to combustion chamber 5 via intake valve 
6a (see FIG. 2) shall be determined taking the following factors into 
account. Stable combustion will be hampered although the oxygen content 
resulting from such combustion increases when the charge in combustion 
chamber 5 becomes excessively lean. Oxygen content in the exhaust gases 
decreases although stable combustion is insured when the charge in 
combustion chamber approaches stoichiometry from the lean side. 
In order to bring about a stable lean combustion, the charge in combustion 
chamber 5 is swirled by a jet of air admitted to combustion chamber via 
air inlet valve 8a to make better mixing of fuel with air. As shown in 
FIG. 2 air inlet valve 8a is formed with a valve shroud 8b to cause air to 
swirl around the cylinder axis although other arrangement or construction 
including complicated port configuration can be employed. 
The engine exhaust gases are directed by exhaust conduit 17 toward 
oxidation catalytic converter 60 where oxidation of HC and CO in the 
exhaust gases takes place and then they are discharged to the ambient 
atmosphere. 
Due to the elimination of the residual gas and stable combustion of lean 
mixture, HC and CO levels in the exhaust gases are low lightening the 
burden on oxidation catalytic converter 60 and the amount of oxygen in the 
exhaust gases is sufficient for oxidation of HC and CO in the converter 
60. Thus a secondary air supply system is simplified or unnecessary. 
When, for yielding high power output, the setting of carburetor is made 
rich so that A/F in the charge for power output is brought about, air to 
be admitted to combustion chamber 5 via air inlet valve 8a may be 
discharged to exhaust conduit 17 via a change-over valve, shown in dashed 
lines which communicates with a nozzle 61 shown in dashed lines in FIG. 6 
or the amount of air admitted after exhaust valve 7a closes may be reduced 
while increasing the amount of air admitted during the exhaust stroke such 
as by advancing the closing timing of air inlet valve 8a under this engine 
operating condition. 
In operation air having been filtered by air cleaner 16 is supplied to 
surge tank 14 and accumulated therein at a certain pressure above 
atmospheric pressure by means of air pump 15 which is driven by the engine 
crankshaft 62 through a pulley 63 and a belt 64. 
The pressure at which air is accumulated in surge tank 14 may be increased 
with the engine revolution speed, if desired. 
Air accumulated at constant pressure in surge tank 14 is admitted to 
combustion chamber 5 via air inlet valve 8a. Flow of air is controlled in 
response to induction vacuum and engine speed by means of a flow control 
device 13' which is substantially similar to that illustrated in FIG. 3 
except that switch 52 is eliminated. 
Air inlet valve 8a is kept open from the final portion of the exhaust 
stroke to the initial portion of the subsequent intake stroke to admit 
under pressure air to combustion chamber 5 to expel the residual gas out 
of combustion chamber 5 before exhaust valve 7a closes. 
As a result, because the amount of residual gas contained in the charge is 
negligible and the charge generally consists of fresh air fuel mixture 
from intake valve 6a and air having replaced the residual gas, stable 
combustion will take place even if A/F in the charge is very lean. It will 
also be noted that effective cylinder volume increases by a volume 
corresponding to the volume of residual gas expelled out of combustion 
chamber 5 causing an increase of engine power output. 
The amount of air admitted to combustion chamber 5 per each opening 
duration of air inlet valve 8a shall be controlled so that A/F in the 
charge in combustion chamber 5 is kept lean. 
It will be noted from the previous description of the embodiment 
illustrated in FIG. 6 that due to such a lean combustion as previously 
described, HC and CO in the exhaust gases will be sufficiently oxidized in 
oxidation catalytic converter 60 without secondary air supply to exhaust 
conduit 17 which, if employed, might lower the exhaust temperature slowing 
the oxidation reaction speed in converter 60. 
It will also be noted that with varying the excess amount of air admitted 
to combustion chamber 5 during the exhaust stroke, it is possible to 
adjust A/F in the exhaust gases to the desired level that is suitable for 
treatment in catalytic converter 60. 
The third embodiment shown in FIG. 7 differs from the second embodiment in 
that exhaust treatment system 18 includes a thermal reactor 70 instead of 
oxidation catalytic converter 60. Denoted by the reference numeral 71 in 
this Figure is a muffler. 
The fourth embodiment shown in FIG. 8 differs from the third embodiment in 
that treatment system 18 includes an oxidation catalytic converter 75 
mounted in the exhaust system downstream of a thermal reactor 76. In this 
case since the remaining HC and CO not oxidized in thermal reactor 76 will 
be oxidized by oxidation converter 75, the oxidation capacities of thermal 
reactor 76 and oxidation converter 75 are small and they can be made of 
compact size. 
Although not shown in FIGS. 6-8, NOx reduction may be effected by arranging 
an EGR conduit and an EGR flow control valve as shown in FIG. 1, if 
desired. 
FIG. 9 shows a preferred cylinder head construction applicable to any one 
of the previously described embodiments. For the purpose of keeping the 
exhaust gases high enough for sufficient treatment in exhaust gas 
treatment system 18, each two adjacent exhaust port bores are joined to 
form a so-called Siamesed exhaust port 80 and a port liner 81 is mounted 
in each Siamesed exhaust port 80. Denoted by the reference numeral 82 is 
an intake manifold.