U.S. patent application number 13/991319 was filed with the patent office on 2013-10-03 for exhaust heating device for internal combustion engine and control method therefor.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The applicant listed for this patent is Naoki Takeuchi. Invention is credited to Naoki Takeuchi.
Application Number | 20130255230 13/991319 |
Document ID | / |
Family ID | 46244197 |
Filed Date | 2013-10-03 |
United States Patent
Application |
20130255230 |
Kind Code |
A1 |
Takeuchi; Naoki |
October 3, 2013 |
EXHAUST HEATING DEVICE FOR INTERNAL COMBUSTION ENGINE AND CONTROL
METHOD THEREFOR
Abstract
An internal combustion engine in which first and second
turbochargers are incorporated in series has first and second
bypass passages bypassing exhaust turbines of the first and second
turbochargers and two opening/closing valves for opening/closing
the first and second bypass passages respectively. An exhaust gas
heating device for heating exhaust gas being led to an exhaust
purifying device from the engine is disposed in an exhaust passage
so as to be located upstream of a confluent portion of the exhaust
passage and the second bypass passage and downstream of the turbine
of the second turbocharger. A valve capable of regulating the flow
rate of exhaust gas flowing in the exhaust passage is disposed in
the exhaust passage so as to be located downstream of a branched
portion of the exhaust passage and the second bypass passage and
upstream of the turbine of the second turbocharger.
Inventors: |
Takeuchi; Naoki;
(Susono-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Takeuchi; Naoki |
Susono-shi |
|
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi, Aichi
JP
|
Family ID: |
46244197 |
Appl. No.: |
13/991319 |
Filed: |
December 17, 2010 |
PCT Filed: |
December 17, 2010 |
PCT NO: |
PCT/JP2010/007332 |
371 Date: |
June 3, 2013 |
Current U.S.
Class: |
60/274 ;
60/320 |
Current CPC
Class: |
Y02T 10/26 20130101;
F02B 37/004 20130101; Y02T 10/144 20130101; F02B 37/013 20130101;
F01N 2610/03 20130101; F01N 2340/06 20130101; Y02T 10/12 20130101;
F01N 3/00 20130101; F02B 37/18 20130101; F01N 3/36 20130101; F01N
3/2033 20130101 |
Class at
Publication: |
60/274 ;
60/320 |
International
Class: |
F01N 3/00 20060101
F01N003/00 |
Claims
1-6. (canceled)
7. An exhaust heating device for heating exhaust gas being led to
an exhaust purifying device from an internal combustion engine
having a first bypass passage bypassing an exhaust turbine of a
first exhaust turbocharger, a second bypass passage bypassing an
exhaust turbine of a second exhaust turbocharger, and two
opening/closing valves for opening or closing the first and second
bypass passages independently of each other, the first exhaust
turbocharger and the second exhaust turbocharger that is disposed
in an exhaust passage so as to be located upstream of the first
turbocharger and is used in mainly a lower speed range of the
internal combustion engine, the first and second turbochargers
being incorporated in series on the exhaust passage, wherein the
exhaust heating device is disposed in the exhaust passage so as to
be located upstream of a confluent portion of the exhaust passage
and the second bypass passage and downstream of an exhaust turbine
of the second turbocharger; and a valve capable of regulating the
flow rate of exhaust gas in the exhaust passage is disposed in the
exhaust passage so as to be located downstream of a branched
portion of the exhaust passage and the second bypass passage and
upstream of the exhaust turbine of the second exhaust
turbocharger.
8. The exhaust heating device for the engine as claimed in claim 7,
wherein the exhaust heating device includes a fuel supply valve for
supplying fuel to the exhaust passage, and ignition means for
igniting and conflagrating the fuel supplied from the fuel supply
valve to the exhaust passage.
9. The exhaust heating device for the engine as claimed in claim 8,
wherein an oxidation catalytic converter is provided in the exhaust
passage between the ignition means and the exhaust purifying
device.
10. The exhaust heating device for the engine as claimed in claim
8, wherein when the fuel is ignited by using the ignition means,
the opening of the valve is regulated in such a manner that the
flow rate of the exhaust gas passing the exhaust turbine of the
second turbocharger becomes smaller than that of the exhaust gas in
the second bypass passage.
11. The exhaust heating device for the engine as claimed in claim
9, wherein when the fuel is ignited by using the ignition means,
the opening of the valve is regulated in such a manner that the
flow rate of the exhaust gas passing the exhaust turbine of the
second turbocharger becomes smaller than that of the exhaust gas in
the second bypass passage.
12. A control method for the exhaust heating device as claimed in
claim 7, comprising the steps of: determining whether or not the
exhaust purifying device is activated; detecting an engine speed of
the engine; setting the opening of the valve based on the detected
engine speed of the engine; and driving the valve in such a manner
as to achieve a set opening when it is determined that the exhaust
purifying device is not activated so as to lead the exhaust gas to
the turbine of the second turbocharger at a predetermined flow rate
and actuate the exhaust heating device.
13. A control method for the exhaust heating device as claimed in
claim 8, comprising the steps of: determining whether or not the
exhaust purifying device is activated; detecting an engine speed of
the engine; setting the opening of the valve based on the detected
engine speed of the engine; and driving the valve in such a manner
as to achieve a set opening when it is determined that the exhaust
purifying device is not activated so as to lead the exhaust gas to
the turbine of the second turbocharger at a predetermined flow rate
and actuate the exhaust heating device.
14. The control method as claimed in claim 12, wherein the step of
driving the valve in such a manner as to achieve the set opening
when it is determined that the exhaust purifying device is not
activated so as to lead the exhaust gas to the turbine of the
second turbocharger at a predetermined flow rate and actuate the
exhaust heating device includes a step of driving the second
opening/closing valve in such a manner as to turn the second bypass
passage into a fully open state.
15. The control method as claimed in claim 13, wherein the step of
driving the valve in such a manner as to achieve the set opening
when it is determined that the exhaust purifying device is not
activated so as to lead the exhaust gas to the turbine of the
second turbocharger at a predetermined flow rate and actuate the
exhaust heating device includes a step of driving the second
opening/closing valve in such a manner as to turn the second bypass
passage into a fully open state.
Description
TECHNICAL FIELD
[0001] The present invention relates to an exhaust heating device
that increases a temperature of exhaust gas in order to activate an
exhaust purifying device and keep the exhaust purifying device in
an activated state in an internal combustion engine that is
provided with the exhaust purifying device.
BACKGROUND ART
[0002] A turbocharger that relatively easily achieves an
improvement in output from an internal combustion engine has a
tendency to bring about a drop in fuel efficiency at the same time.
In recent years, in order to meet the strong demand for an
improvement in fuel efficiency of an internal combustion engine
incorporating such a turbocharger therein, an internal combustion
engine in which two turbochargers having different characteristics
are incorporated is proposed in Patent Literature 1 and Patent
Literature 2. In either case, there are provided a first
turbocharger that mainly functions in a low speed range of the
internal combustion engine and a second turbocharger that mainly
functions in other speed ranges, the turbochargers being arranged
in series or parallel with respect to intake and exhaust
passages.
[0003] Meanwhile, in order to cope with strict emission standards
set for an internal combustion engine, it is necessary to promote
the activation of an exhaust purifying device at the start of the
internal combustion engine, maintain its activated state during the
operation of the engine, and so on. Therefore, Patent Literature 3
and the like have proposed an internal combustion engine in which
an exhaust heating device is incorporated in an exhaust passage
upstream of an exhaust purifying device. This exhaust heating
device generates heated gas in exhaust gas and supplies this
generated heated gas to the exhaust purifying device disposed
downstream, to thus promote the activation of the exhaust purifying
device and maintain its activated state. To do so, the exhaust
heating device generally includes a fuel supply valve which
supplies fuel to the exhaust passage and an igniter such as a glow
plug which heats and ignites the fuel to generate heated gas.
Furthermore, there has been also known an exhaust heating device in
which a compact oxidation catalytic converter is incorporated in
the exhaust passage downstream of the igniter in order to increase
the temperature of the heated gas. Although this oxidation
catalytic converter has its own heat generation function and a
function for reforming fuel to a low-carbon component, it has a
structure different from that of an oxidation catalytic converter
that is used as a part of the exhaust purifying device.
CITATION LIST
Patent Literature
[0004] PTL 1: Japanese Patent Laid-Open No. 2008-255902 [0005] PTL
2: Japanese Patent Laid-Open No. 2009-270470 [0006] PTL 3: Japanese
Patent Laid-Open No. 2006-112401
SUMMARY OF INVENTION
Technical Problem
[0007] It is evident that in the future, an internal combustion
engine that is able to achieve both good output characteristics and
fuel efficiency and clean exhaust gas will be important technology.
From this viewpoint, it has been construed that an exhaust heating
device is further incorporated in an internal combustion engine
incorporating the above-described two-stage exhaust turbocharger
therein.
[0008] In the case of an operating state where an intake flow rate
with respect to the internal combustion engine is large in the
exhaust heating device disclosed in Patent Literature 3, a flow
rate of exhaust gas flowing through an exhaust passage also is
relatively increased. Therefore, the fuel that is supplied to the
exhaust passage from a fuel supply valve in the exhaust heating
device cannot remain around the igniter. Even if the fuel can be
ignited, a flame is blown out by the flow of the exhaust gas, and
therefore, there is a possibility that unburned fuel flows toward
the exhaust purifying device.
[0009] On the other hand, in the internal combustion engine in
which the two-stage exhaust turbocharger is incorporated, an
exhaust flow rate basically tends to become large. Moreover, the
exhaust gas passes through each of exhaust turbines of the two
turbochargers, and therefore, the temperature of the exhaust gas
greatly drops due to the release of the heat to the outside and a
heat capacity of the exhaust turbines per se. As a result, the
above-described inconvenience more prominently occurs, and
therefore, the exhaust heating device can be actuated only at a
small exhaust flow rate, such as deceleration of a vehicle.
[0010] An object of the present invention is to provide an exhaust
heating device capable of stably and continuously igniting fuel in
an internal combustion engine incorporating two-stage exhaust
turbochargers therein.
Solution to Problem
[0011] A first aspect of the present invention is featured by an
exhaust heating device for heating exhaust gas being led to an
exhaust purifying device from an internal combustion engine having
a first bypass passage bypassing an exhaust turbine of a first
exhaust turbocharger, a second bypass passage bypassing an exhaust
turbine of a second exhaust turbocharger, and two opening/closing
valves for opening or closing the first and second bypass passages
independently of each other, the first turbocharger and the second
turbocharger that is disposed in an exhaust passage so as to be
located upstream of the first turbocharger and is used in mainly a
lower speed range of the engine, the first and second turbochargers
being incorporated in series on the exhaust passage, wherein the
exhaust heating device is disposed in the exhaust passage so as to
be located upstream of a confluent portion of the exhaust passage
and the second bypass passage and downstream of an exhaust turbine
of the second turbocharger; and a valve capable of regulating the
flow rate of exhaust gas in the exhaust passage is disposed in the
exhaust passage so as to be located downstream of a branched
portion of the exhaust passage and the second bypass passage and
upstream of the turbine of the second turbocharger.
[0012] According to the present invention, in the case where the
exhaust heating device need be operated, most of the exhaust gas is
introduced to the second bypass passage, and then, the opening of
the valve is regulated, so that a part of the exhaust gas is
introduced to the exhaust heating device through the turbine of the
second turbocharger. Heated gas generated by the operation of the
exhaust heating device is converged with the exhaust gas flowing in
the second bypass passage at the confluent portion of the exhaust
passage and the second bypass passage, and then, flows into the
exhaust purifying device.
[0013] The exhaust heating device for the engine according to the
present invention may include a fuel supply valve for supplying
fuel to the exhaust passage, and ignition means for igniting and
conflagrating the fuel supplied from the fuel supply valve to the
exhaust passage. In this case, an oxidation catalytic converter may
be arranged in the exhaust passage between the ignition means and
the exhaust purifying device. Moreover, when the fuel is ignited by
using the ignition means, it is preferable that the opening of the
valve should be regulated in such a manner that the flow rate of
the exhaust gas passing the turbine of the second turbocharger
becomes smaller than that of the exhaust gas in the second bypass
passage.
[0014] A second aspect of the present invention is featured by a
control method for the exhaust heating device according to the
first aspect of the present invention comprising the steps of:
determining whether or not the exhaust purifying device is
activated; detecting an engine speed of the engine; setting the
opening of the valve based on the detected engine speed of the
engine; and driving the valve in such a manner as to achieve a set
opening when it is determined that the exhaust purifying device is
not activated so as to lead the exhaust gas to the turbine of the
second turbocharger at a predetermined flow rate and actuate the
exhaust heating device.
[0015] According to the present invention, in the case of the
operating state in which no exhaust gas need be introduced to the
second turbocharger, for example, in the case where the engine is
out of a low speed region, the opening of the valve that is closed
is regulated so as to introduce the exhaust gas also to the turbine
of the second turbocharger at a predetermined flow rate while the
exhaust heating device is operated. The resultant heated gas is
converged with the exhaust gas flowing in the second bypass passage
at the confluent portion of the exhaust passage and the second
bypass passage, and then, flows into the exhaust purifying
device.
[0016] In the control method for the exhaust heating device
according to the second aspect of the present invention, the step
of driving the valve in such a manner as to achieve the set opening
when it is determined that the exhaust purifying device is not
activated so as to lead the exhaust gas to the turbine of the
second turbocharger at a predetermined flow rate and actuate the
exhaust heating device may include a step of driving the second
opening/closing valve in such a manner as to turn the second bypass
passage into a fully open state.
Advantageous Effects of Invention
[0017] According to the present invention, even the engine
incorporating the two-stage exhaust turbochargers therein can
stably actuate the exhaust heating device by regulating the opening
of the valve. In addition, the heated gas can be efficiently mixed
with the exhaust gas in the second bypass passage at the confluent
portion with the exhaust passage.
[0018] In the case where the oxidation catalytic converter is
incorporated in the exhaust passage between the ignition means and
the exhaust purifying device, the heated gas can be more
efficiently increased in temperature.
[0019] In the case where the opening of the valve is regulated in
such a manner that the flow rate of the exhaust air in the first
exhaust passage is smaller than that of the exhaust air in the
second exhaust passage, the stable heated gas can be more securely
generated.
[0020] In the case where the opening of the valve is regulated in
such a manner that the flow rate of the exhaust air passing the
turbine of the second turbocharger is smaller than that of the
exhaust air in the second bypass passage and the ignition means
ignites the fuel, the stable heated gas can be more securely
generated.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1 is a conceptual diagram of one embodiment of an
exhaust heating device for an internal combustion engine according
to the present invention;
[0022] FIG. 2 is a control block diagram of main components in the
embodiment illustrated in FIG. 1;
[0023] FIG. 3 is a graph expressing the relationship between an
engine speed and a turbine speed; and
[0024] FIG. 4 is a flowchart illustrating control procedures for
the exhaust heating device in the embodiment illustrated in FIG.
1.
DESCRIPTION OF EMBODIMENTS
[0025] An embodiment in which the present invention is applied to a
compression-ignition type internal combustion engine incorporating
a series-type two-stage exhaust turbocharger will be explained in
detail with reference to FIGS. 1 to 4. The present invention is
not, however, limited to the embodiment, and the construction
thereof may be freely modified according to required
characteristics. The present invention is effectively applied also
to a spark ignition type internal combustion engine in which
gasoline, alcohol, LNG (Liquefied Natural Gas), or the like is used
as fuel to be ignited by a spark plug, for example.
[0026] Main components of an engine system in the present
embodiment are schematically illustrated in FIG. 1, and the control
block thereof is illustrated in FIG. 2, wherein a valve mechanism
for intake and exhaust, an EGR system, and the like are omitted for
the sake of convenience. An engine 10 in the present embodiment is
a compression-ignition multicylinder (four cylinders in the
embodiment shown in FIG. 1) internal combustion engine that
spontaneously ignites light oil as fuel by injecting the fuel
directly into a combustion chamber 12 in a compressed state through
a fuel injection valve 11. However, the engine 10 may be a single
cylinder internal combustion engine from the viewpoint of the
characteristics of the present invention. The amount of fuel
supplied to the combustion chamber 12 through the fuel injection
valve 11 as well as its injection timing is controlled by an ECU
(Electronic Control Unit) 14 based on the position of an
accelerator pedal 13 depressed by a driver and the operating state
of a vehicle. The position of the depressed accelerator pedal 13 is
detected by an accelerator position sensor 15, and the detected
information is input into the ECU 14 and used for setting the
amount of fuel to be injected from the fuel injection value 11.
[0027] An intake pipe 17 that is connected to the engine 10 by way
of an intake manifold 16 defines an intake passage 18 together with
the intake manifold 16. The intake pipe 17 has a branched portion
20d and a confluent portion 20c of an intake bypass pipe 20
defining an intake bypass passage 19 upstream and downstream
thereof. That is to say, both ends of the intake bypass pipe 20 are
connected to the intake pipe 17 via the branched portion 20d
upstream of the intake passage 18 and the confluent portion 20c
downstream of the intake passage 18. In other words, a portion of
the intake pipe 17 that is located between the branched portion 20d
and the confluent portion 20c is arranged in parallel to the intake
bypass passage 20. Hereinafter, the intake passage 18 upstream of
the branched portion 20d is called a first intake passage 18f for
the sake of convenience, and further, a portion defined by the
intake pipe 17 that is located between the branched portion 20d and
the confluent portion 20c is called a second intake passage 18s for
the sake of convenience.
[0028] An airflow meter 20 and an intake temperature sensor 21 are
disposed in the intake pipe 17 further upstream of the branched
portion 20d. Pieces of information related to an intake flow rate
and an intake temperature that are detected by the airflow meter 20
and the intake temperature sensor 21, respectively, are input into
the ECU 14. The ECU 14 corrects the amount of fuel injected from
the fuel injection valve 11 based on the information detected by
the airflow meter 20 and the intake temperature sensor 21.
[0029] An intercooler 23 that cools intake air in order to increase
the filled density of the intake air flowing through the intake
passage 18 and a throttle valve 24 that adjusts the opening of the
intake passage 18 are provided in the intake pipe 17 further
downstream of the confluent portion 20c. The throttle valve 24 in
the present embodiment is electrically connected to the accelerator
pedal 13 such that the opening of the intake passage 18 is
corrected by the ECU 14 according to the operating state of the
vehicle with respect to the position of the accelerator pedal 13
whose position is adjusted by the driver. Here, a throttle valve 24
that is mechanically connected to the accelerator pedal 13 may be
adopted such that the opening of the intake passage 18 accurately
corresponds to the position of the accelerator pedal 13.
[0030] In the intake bypass pipe 20 is disposed an intake bypass
valve 25 for opening or closing the intake bypass passage 19. To
the intake bypass valve 25 is connected a bypass valve driving
motor 26. The ECU 14 controls the operation of the bypass valve
driving motor 26 according to the operating state of the vehicle so
as to switch the opening or closing operation of the intake bypass
valve 25.
[0031] An exhaust pipe 28 that defines an exhaust passage 27 has a
branched portion 30d and a confluent portion 30c of a first exhaust
bypass pipe 30 defining a first exhaust bypass passage 29 upstream
and downstream thereof. That is to say, both ends of the first
exhaust bypass pipe 30 are connected to the exhaust pipe 28 at the
branched portion 30d upstream of the exhaust passage 27 and the
confluent portion 30c downstream of the exhaust passage 27. In
other words, a portion (hereinafter this portion is referred to as
a first exhaust passage 27f for the sake of convenience) of the
exhaust pipe 27 that is located between the branched portion 30d
upstream of the exhaust passage 27 and the confluent portion 30c
downstream of the exhaust passage 27 is arranged in parallel to the
first exhaust bypass passage 29. In the first exhaust bypass pipe
30 is disposed a first exhaust bypass valve 31 for opening or
closing the first exhaust bypass passage 29. The ECU 14 is adapted
to control the opening or closing operation based on the operating
state of the vehicle. To the first exhaust bypass valve 31 in the
present embodiment is connected the bypass valve driving motor 26
together with the intake bypass valve 25. The first exhaust bypass
passage 29 is designed to be opened or closed in substantially
reverse association with the opening or closing operation of the
intake bypass valve 25. Here, an individual actuator may be
connected to the first exhaust bypass valve 31 so as to open or
close the first exhaust bypass passage 29 independently of the
intake bypass valve 25.
[0032] The exhaust pipe 28 that is located further upstream of the
branched portion 30d of the first exhaust bypass pipe 30 further
includes a branched portion 33d and a confluent portion 33c of a
second exhaust bypass pipe 33 defining a second exhaust bypass
passage 32 upstream and downstream thereof, respectively. That is
to say, both ends of the second exhaust bypass pipe 33 are
connected to the exhaust pipe 28 via the branched portion 33d
upstream of the exhaust passage 27 and the confluent portion 33c
downstream thereof. In other words, a portion (hereinafter this
portion is referred to as a second exhaust passage 27s for the sake
of convenience) of the exhaust pipe 27 that is located between the
branched portion 33d upstream of the exhaust passage 27 and the
confluent portion 33c downstream of the exhaust passage 27 is
arranged in parallel to the second exhaust bypass passage 32. In
the second exhaust bypass pipe 33 is disposed a second exhaust
bypass valve 34 for opening or closing the second exhaust bypass
passage 32. The ECU 14 controls the opening or closing operation of
the second exhaust bypass valve 34 based on the operating state of
the vehicle. In the present embodiment, a second bypass valve
driving motor 35 is connected to the second exhaust bypass valve 34
so as to control the opening or closing operation of the second
exhaust bypass valve 34 via the second bypass valve driving motor
35.
[0033] A first turbocharger 36 is arranged so as to span between
the first intake passage 18f and the first exhaust passage 26f,
wherein its compressor 36a is located in the first intake passage
18f whereas its exhaust turbine 36b is located in the first exhaust
passage 27f. Consequently, the first exhaust bypass passage 29
branched from the first exhaust passage 27f at the branched portion
30d merges with the exhaust passage 27 at the downstream confluent
portion 30c together with the first exhaust passage 27f while
bypassing the exhaust turbine 36b of the first turbocharger 36.
Moreover, a second turbocharger 37 that is mainly used in the low
speed range of the engine 10 more than the first turbocharger 36 is
arranged so as to span between the second intake passage 18s and
the second exhaust passage 27s. A compressor 37a of the second
turbocharger 37 is located in the second intake passage 18s. In the
meantime, an exhaust turbine 37b of the second turbocharger 37 is
located in the second exhaust passage 27s defined by the second
exhaust bypass pipe 33. Therefore, the second exhaust bypass
passage 32 branched from the second exhaust passage 27s at the
branched portion 33d merges with the exhaust passage 27 further
upstream of the branched portion 30d together with the second
exhaust passage 27s at the downstream confluent portion 33c while
bypassing the exhaust turbine 37b of the second turbocharger
37.
[0034] To the exhaust pipe 28 that is located downstream of the
confluent portion 30c with the first exhaust bypass pipe 30 is
connected an exhaust purifying device 38 for rendering hazardous
substances produced by combustion of an air-fuel mixture inside of
the combustion chamber 12 harmless. The exhaust purifying device 38
in the present embodiment is provided with an oxidation catalytic
converter 39, a tertiary catalyst, and a NO.sub.x catalyst in order
upstream of the exhaust passage 27. Here, only the oxidation
catalytic converter 39 provided most upstream is illustrated for
the sake of convenience. The oxidation catalytic converter 39
incorporates therein a catalyst temperature sensor 40 for
outputting a detected temperature (hereinafter referred to as a
catalyst temperature) T.sub.n of the oxidation catalytic converter
39 to the ECU 14.
[0035] In the second exhaust passage 27s upstream of the exhaust
turbine 37b of the second turbocharger 37 and downstream of the
branched portion 33d of the second exhaust bypass pipe 33 is
disposed a flow regulating valve 41 capable of regulating the flow
rate of exhaust air in the second exhaust passage 27s. Moreover, to
the flow regulating valve 41 is connected a valve opening sensor 42
for detecting the opening of the flow regulating valve 41.
Information detected by the valve opening sensor 42 is designed to
be input into the ECU 14. To the flow regulating valve 41 is
connected a regulation valve driving motor 43 whose operation is
controlled by the ECU 14. Therefore, the opening of the flow
regulating valve 41 is regulated based on the operating state of
the vehicle and information detected by the valve opening sensor
42.
[0036] Incidentally, the opening or closing operation of the second
exhaust bypass valve 34 by the second bypass valve driving motor 35
is designed to be basically driven inversely to the opening or
closing operation of the flow regulating valve 41. More
specifically, only in the case of the fully opened state of the
flow regulating valve 41, the second exhaust bypass valve 34 is
kept in the fully closed state. To the contrary, in the case where
exhaust air is introduced onto the second exhaust bypass passage
27s, the openings of the second exhaust bypass valve 34 and the
flow regulating valve 41 are controlled so as to achieve a required
turbocharging pressure.
[0037] An exhaust heating device 44 is incorporated in the second
exhaust passage 27s downstream of the exhaust turbine 37b of the
second turbocharger 37 and upstream of the confluent portion 33c of
the second exhaust bypass pipe 33. The exhaust heating device 44 is
adapted to produce heated gas, supply it to the exhaust purifying
device 38 disposed downstream, activates it, and maintains its
activated state. The exhaust heating device 44 in the present
embodiment is provided with a fuel supply valve 45, a glow plug 46
serving as igniting means according to the present invention, and
an auxiliary oxidation catalytic converter 47 in this order from
upstream.
[0038] The fuel supply valve 45 is adapted to supply the fuel into
the second exhaust passage 27s. The ECU 14 controls supply timing
and supply amount based on whether or not the exhaust purifying
device 38 is activated and the vehicle is operated. The operation
of supplying the fuel from the fuel supply valve 45 into the second
exhaust passage 27s is performed when the exhaust purifying device
38 is inactive. Consequently, even when it is unnecessary to
introduce the exhaust gas to the second exhaust passage 27s, that
is, to make the second turbocharger 37 function, the exhaust
heating device 44 is operated, as required. On the other hand, even
when the exhaust gas is introduced to the second exhaust passage
27s so as to make the second turbocharger 37 function, the exhaust
heating device 44 is operated, as required.
[0039] The glow plug 46 is designed to ignite the fuel that is
supplied from the fuel supply valve 45 into the second exhaust
passage 27s and cannot be spontaneously ignited. A direct-current
power supply and a booster circuit, not illustrated, are connected
to the glow plug 46 in order to supply power to the glow plug 46.
The surface temperature of the glow plug 46 is controlled by the
ECU 14. The glow plug 46 may be replaced with a ceramic heater or
the like as the igniting means according to the present
invention.
[0040] The auxiliary oxidation catalytic converter 47 is disposed
in the exhaust passage 27 between the glow plug 46 and the exhaust
purifying device 38. Although the auxiliary oxidation catalytic
converter 47 is disposed on the second exhaust passage 27s upstream
of the confluent portion 33c in the present embodiment, it may be
disposed on the exhaust passage 27 downstream of the confluent
portion 33c. The auxiliary oxidation catalytic converter has a
smaller cross-sectional area than that of the second exhaust
passage 27s, and therefore, enables a part of exhaust gas not to
pass therethrough. That is to say, the flow rate of the exhaust gas
passing the auxiliary oxidation catalytic converter 47 is lower
than that of the exhaust gas that does not pass there, so that the
temperature of the exhaust gas passing the auxiliary oxidation
catalytic converter 47 can be further increased. When the auxiliary
oxidation catalytic converter 47 is satisfactorily increased in
temperature, that is, activated, power to the glow plug 46 can be
cut so as to directly burn the air-fuel mixture inside of the
auxiliary oxidation catalytic converter 47. However, when the
auxiliary oxidation catalytic converter 47 is not activated, such
as at the time of the cold start of the engine 10, it is necessary
to supply power to the glow plug 46. When the temperature of the
auxiliary oxidation catalytic converter 47 becomes high,
hydrocarbons having a large carbon number in an unburned air-fuel
mixture are decomposed so as to be reformed into highly reactive
hydrocarbons having a small carbon number. In other words, on one
hand, the auxiliary oxidation catalytic converter 47 functions as a
rapid heat generating element that generates heat at a high speed
per se, and on the other hand, also functions as a fuel reforming
catalyst that generates reformed fuel. In the present embodiment,
there is provided an auxiliary temperature sensor 48 that detects
the temperature of the auxiliary oxidation catalytic converter 47
(hereinafter referred to as an auxiliary catalyst temperature)
T.sub.Sn and outputs it to the ECU 14. Thereafter, the ECU 14
determines based on the information detected by the auxiliary
temperature sensor 48 whether or not the power is supplied to the
glow plug 46.
[0041] In this manner, heated gas is generated on the second
exhaust passage 27s, and the high-temperature exhaust gas passes
the auxiliary oxidation catalytic converter 47 so that its
temperature is further increased, and the unburned gas is burned by
the auxiliary oxidation catalytic converter 47 or is reformed into
highly active hydrocarbons. And then, these kinds of gas are mixed
with the exhaust gas flowing in the second exhaust bypass passage
32 at the confluent portion 33c, to be thus supplied toward the
exhaust purifying device 38. As a result, it is possible to quickly
activate the exhaust purifying device 38 and maintain its activated
state even while the vehicle travels.
[0042] Incidentally, in order to enhance the ignitability of the
fuel that is injected from the fuel supply valve 45 into the second
exhaust passage 27s, it is effective to provide a plate-shaped
vaporization promoting member in such a manner as to face the fuel
supply valve 45 and the glow plug 46. This vaporization promoting
member has the function of scattering and atomizing fuel, or
promoting vaporization of the fuel when the fuel injected from the
fuel supply valve 45 collides therewith.
[0043] The characteristics of the first and second turbochargers 36
and 37 in the present embodiment are illustrated in FIG. 3. The
first turbocharger 36 that has a relatively large inertia mass
hardly has any supercharging ability in a range in which an engine
speed, that is, an engine speed N.sub.n per unit time is less than
a predetermined speed N.sub.R (hereinafter referred to as a
turbocharged state determining speed). That is to say, the first
turbocharger 36 exhibits the supercharging ability in the range in
which the engine speed N.sub.n is higher than and equal to the
turbocharged state determining speed N.sub.R. In contrast, the
second turbocharger 37 that has a relatively small inertia mass is
designed to exhibit the supercharging ability in the range of the
low engine speed in which the first turbocharger 36 cannot
function. Consequently, the ECU 14 actuates the second turbocharger
37 without actuating the first turbocharger 36 in the case where
the engine speed N.sub.n is lower than the turbocharged state
determining speed N.sub.R. Specifically, the ECU 14 maintains the
first exhaust bypass valve 31 and the flow regulating valve 41 in
basically substantially the fully open state whereas maintains the
intake bypass valve 25 and the second exhaust bypass valve 34 in
the fully closed state. In contrast, the ECU 14 actuates the first
turbocharger 36 without actuating the second turbocharger 37 in the
case where the engine speed N.sub.n is higher than and equal to the
turbocharged state determining speed N.sub.R. Specifically, the ECU
14 maintains the exhaust bypass valve 31 and the flow regulating
valve 41 in the fully closed state whereas maintains the intake
bypass valve 25 and the second exhaust bypass valve 34 in basically
substantially the fully open state. In this manner, the crank angle
sensor 49 detects the crank angle phase of the engine 10, and then,
inputs the detected information into the ECU 14. The ECU 14
calculates the engine speed N.sub.n based on the information output
from the crank angle sensor 49.
[0044] When it is necessary to supply fuel from the fuel supply
valve 45 to the second exhaust passage 27s so as to activate the
exhaust purifying device 38, only a part of the exhaust gas is
allowed to flow in the second exhaust passage 27s. Specifically,
the flow regulating valve 41 is slightly closed in the fully open
state or is slightly opened in the fully closed state, and further,
the opening of the second exhaust bypass valve 34 is controlled in
such a manner that the exhaust gas is introduced in the amount to
be supplied to the second exhaust passage 27s. In this manner, the
fuel to be injected from the fuel supply valve 45 to the second
exhaust passage 27s is ignited by the glow plug 46, and thus, is
turned into heated gas without any extinguishing. The heated gas is
mixed with the exhaust gas flowing from the second exhaust bypass
passage 32 at the confluent portion 33c to the second exhaust
bypass pipe 33. This promotes the activation of the exhaust
purifying device 38.
[0045] The ECU 14 controls the actuation of the intake bypass valve
25, the first and second exhaust bypass valves 31 and 34, the flow
regulating valve 34, and the exhaust heating device 44, that is,
the fuel supply valve 45 and the glow plug 46. The control with
respect to these members is performed in accordance with a preset
program based on the operating state of the vehicle and detection
signals from the auxiliary temperature sensor 48 and the catalyst
temperature sensor 40, as follows. Specifically, when the
temperature T.sub.n of the oxidation catalytic converter 39 is
lower than a temperature (hereinafter referred to as an activation
index temperature) T.sub.R as the index of its activation based on
the detection signal from the catalyst temperature sensor 40, it is
determined that the exhaust purifying device 38 is not activated,
thus actuating the exhaust heating device 44. In contrast, when the
catalyst temperature T.sub.n is higher than and equal to the
activation index temperature T.sub.R, it is determined that the
exhaust purifying device 38 is activated, thus stopping the
actuation of the exhaust heating device 44. Moreover, when the
temperature T.sub.Sn of the auxiliary oxidation catalytic converter
47 is lower than a temperature (hereinafter referred to as an
activation index temperature) T.sub.SR as the index of its
activation, it is determined that the auxiliary oxidation catalytic
converter 47 is not activated, thus supplying the power to the glow
plug 46. In contrast, when the auxiliary catalyst temperature
T.sub.Sn is higher than and equal to the activation index
temperature T.sub.SR, it is determined that the auxiliary oxidation
catalytic converter 47 is activated, thus stopping the power supply
to the glow plug 46. In the meantime, in the case where the exhaust
heating device 44 is actuated in the state in which the engine
speed N.sub.n is higher than and equal to the turbocharged state
determining speed N.sub.R, the flow regulating valve 41 in the
fully closed state is just maintained in a slightly open state.
That is to say, the intake bypass valve 25 and the second exhaust
bypass valve 34 can remain in the fully open state whereas the
first exhaust bypass valve 31 can remain in the fully closed state.
In this manner, a part of the exhaust gas is introduced to the
second exhaust passage 27s, thus igniting the fuel and preventing
any extinguishing (exemplified by characteristics indicated by an
arrow A in FIG. 3). In contrast, it is possible that the fuel
cannot be ignited or is extinguished when the intake bypass valve
25 and the second exhaust bypass valve 34 remain in the fully
closed state whereas the first exhaust bypass valve 31 and the flow
regulating valve 41 remain in the fully open state in the case
where the engine speed N.sub.n is lower than the turbocharged state
determining speed N.sub.R. In this case, the flow regulating valve
41 in the fully open state remains in a slightly open state and the
opening of the second exhaust bypass valve 34 in the fully closed
state is controlled in such a manner that the exhaust gas is
introduced in the amount to be supplied to the second exhaust
passage 27s. As a consequence, most of the exhaust gas is
introduced to the second exhaust bypass passage 32, so that the
fuel to be supplied to the second exhaust passage 27s cannot be
extinguished (exemplified by characteristics indicated by an arrow
B in FIG. 3).
[0046] In this manner, the opening of the flow regulating valve 41
is regulated in such a manner as not to extinguish the fuel to be
supplied to the second exhaust passage 27s from the fuel supply
valve 45 in the above-described exhaust heating device 44. In other
words, the flow rate of the exhaust gas to be introduced into the
second exhaust passage 27s is smaller than that of the exhaust gas
flowing in the second exhaust bypass passage 32. More particularly,
the ECU 14 sets the opening of the flow regulating valve 41 via the
regulation valve driving motor 43 such that the exhaust gas flows
in the second exhaust passage 27s in such a flow rate as not to
extinguish a flame generated by the ignition of the fuel inside of
the second exhaust passage 27s. In this manner, the exhaust gas at
the predetermined flow rate that cannot extinguish a flame can flow
in the second exhaust passage 27s, and therefore, the heated gas
obtained by the exhaust heating device 44 can be introduced to the
exhaust purifying device 38.
[0047] A control procedure of the above-described exhaust heating
device 44 is illustrated in a flowchart in FIG. 4. Specifically, it
is determined in step S11 whether or not the temperature T.sub.n of
the oxidation catalytic converter 39 that is detected by the
catalyst temperature sensor 40 is lower than the activation index
temperature T.sub.R. Here, when it is determined that the exhaust
heating device 44 need not be actuated since the catalyst
temperature T.sub.n is higher than or equal to the activation index
temperature T.sub.R, that is, the oxidation catalytic converter 39
is activated, the determining processing in step S11 is repeated
without performing any processing. In contrast, when it is
determined in step S11 that the catalyst temperature T.sub.n is
lower than the activation index temperature T.sub.R, that is, the
oxidation catalytic converter 39 is not activated so that the
exhaust heating device 44 need be actuated, the control routine
proceeds to step S12. In step S12, it is determined whether or not
the temperature T.sub.Sn of the auxiliary oxidation catalytic
converter 47 to be detected by the auxiliary temperature sensor 48
is lower than the activation index temperature T.sub.SR. Here, the
auxiliary catalyst temperature T.sub.Sn is lower than the
activation index temperature T.sub.SR, that is, the auxiliary
oxidation catalytic converter 47 remains inactivated. Therefore, in
the case where it is determined that the power need be supplied to
the glow plug 46, the control routine proceeds to step S13. In step
S13, it is determined whether or not a flag for supplying the power
to the glow plug 46 is set. Since at first, the flag is not set,
the control routine proceeds to step S14 in which the flag is set,
and further, the power is supplied to the glow plug 46 in step S15.
Furthermore, in step S15, the intake bypass valve 25, the first and
second exhaust bypass valves 31 and 34, and the flow regulating
valve 41 are opened or closed based on the engine speed
N.sub.n.
[0048] For example, in the case where the engine speed N.sub.n is
lower than the turbocharged state determining speed N.sub.R, the
intake bypass valve 25 and the second exhaust bypass valve 34 are
fully closed whereas the first exhaust bypass valve and the flow
regulating valve 41 are fully opened. Consequently, the openings of
the flow regulating valve 41 and the second exhaust bypass valve 34
are controlled such that the fuel supplied to the second exhaust
passage 27s flows at such a flow rate as not to extinguish the
flame when the fuel is ignited by the flow plug 46. More
specifically, the flow regulating valve 41 is closed in the fully
open state, and further, the opening of the second exhaust bypass
valve 34 is controlled, so that the exhaust gas is introduced to
the second exhaust passage 27s in the necessary amount. In this
manner, the amount of the exhaust gas flowing in the second exhaust
passage 27s is reduced whereas the residual exhaust gas is
introduced to the first exhaust bypass passage 32. In contrast, in
the case where the engine speed N.sub.n is higher than and equal to
the turbocharged state determining speed N.sub.R, the intake bypass
valve 25 and the second exhaust bypass valve 34 are fully open
whereas the first exhaust bypass valve 31 and the flow regulating
valve 41 are fully closed. Consequently, the flow regulating valve
41 is slightly opened in the fully closed state in such a manner as
to ignite the fuel supplied to the second exhaust passage 27s, so
that a part of the exhaust gas is introduced also to the second
exhaust passage 27s.
[0049] Next, the fuel is injected from the fuel supply valve 45
toward the second exhaust passage 27s in step S17. In this manner,
the fuel is ignited on the second exhaust passage 27s, on which the
exhaust gas slightly flows, and further, the resultant heated gas
is further increased in temperature by the auxiliary oxidation
catalytic converter 47. The heated gas is mixed with the exhaust
gas flowing at the confluent portion 33c to the first exhaust
bypass passage 32, and then, is introduced to the exhaust purifying
device 38 whose temperature is increased. Subsequently, it is
determined in step 18 whether or not the catalyst temperature
T.sub.n detected by the catalyst temperature sensor 40 is higher
than and equal to the activation index temperature T.sub.R. Here,
the catalyst temperature T.sub.n is lower than the activation index
temperature T.sub.R, that is, the oxidation catalytic converter is
inactive. Therefore, in the case where it is determined that the
operation of the exhaust heating device 44 need be continued, the
control routine returns to step S12, and therefore, the foregoing
processing is repeated. In contrast, in the case where it is
determined that the actuation of the exhaust heating device 44 need
be stopped since the catalyst temperature T.sub.n is higher than
and equal to the activation index temperature T.sub.R, that is, the
oxidation catalytic converter 39 becomes active, the control
routine proceeds to step S19. In step S19, it is determined whether
or not the flag is set. When the flag is determined to be set, the
power supply to the glow plug 46 is stopped in step S20, and then,
the flag is reset in step S21. Thereafter, the fuel supply from the
fuel supply valve 45 is stopped in step S22, and further, the valve
opening control is ended in step S16. Hence, the control routine
returns to the determination in step S11. In this manner, the
intake bypass valve 25, the first and second exhaust bypass valves
31 and 34, and the flow regulating valve 41 can be controlled to be
opened or closed such that the first and second turbochargers 36
and 37 can be most efficiently operated according to the engine
speed N.sub.n.
[0050] On the other hand, in the case where it is determined that
the flag is set in the previous step S13, that is, the power is
supplied to the glow plug 46, the control routine jumps to step
S16, thus continuing the operation of the exhaust heating device
44.
[0051] Moreover, since the auxiliary catalyst temperature T.sub.Sn
is higher than and equal to the activation index temperature
T.sub.SR in the previous step S12, that is, the auxiliary oxidation
catalytic converter 47 is active, the control routine proceeds to
step S23 when it is determined that the power need not be supplied
to the glow plug 46. It is determined in step S23 whether or not
the flag is set. In the case where it is determined that the flag
is set, that is, the power is supplied to the glow plug 46, the
control routine proceeds to step S24 where the power supply to the
glow plug 46 is stopped. Next, the flag is reset in step S21.
Thereafter, the control routine proceeds to the previous step S16,
thus continuing the operation of the exhaust heating device 44. In
contrast, when it is determined that the flag is not set in step
S23, that is, no power is supplied to the glow plug 46, the control
routine jumps to step S16, thus continuing the operation of the
exhaust heating device 44.
[0052] Incidentally, when no problem arises even though the fuel
injected from the fuel supply valve 45 to the second exhaust
passage 27s is extinguished, it should be understood that the
exhaust heating device 44 can be actuated in an arbitrary operating
state.
[0053] It is to be noted that the present invention shall be
construed solely from the matters described in the claims thereof,
and the foregoing embodiment includes not only the matters
described above but any modifications and alterations encompassed
by the concept of the present invention. In other words, all the
matters in the foregoing embodiment are not to limit the present
invention, but include any configurations which may be directly
irrelevant to the present invention and can be optionally changed
according to the usage, purpose, and the like.
REFERENCE SIGNS LIST
[0054] 10 Engine [0055] 11 Fuel injection valve [0056] 12
Combustion chamber [0057] 13 Accelerator pedal [0058] 14 ECU [0059]
15 Accelerator position sensor [0060] 16 Intake manifold [0061] 17
Intake pipe [0062] 18 Intake passage [0063] 18f First intake
passage [0064] 18s Second intake passage [0065] 19 Intake bypass
passage [0066] 20 Intake bypass pipe [0067] 20d Branched portion
[0068] 20c Confluent portion [0069] 21 Airflow meter [0070] 22
Intake temperature sensor [0071] 23 Intercooler [0072] 24 Throttle
valve [0073] 25 Intake bypass valve [0074] 26 Bypass valve driving
motor [0075] 27 Exhaust passage [0076] 27f First exhaust passage
[0077] 27s Second exhaust passage [0078] 28 Exhaust pipe [0079] 29
First exhaust bypass passage [0080] 30 First exhaust bypass pipe
[0081] 30d Branched portion [0082] 30c Confluent portion [0083] 31
First exhaust bypass valve [0084] 32 Second exhaust bypass passage
[0085] 33 Second exhaust bypass pipe [0086] 33d Branched portion
[0087] 33c Confluent portion [0088] 34 Second exhaust bypass valve
[0089] 35 Second bypass valve driving motor [0090] 36 First
turbocharger [0091] 36a Compressor [0092] 36b Exhaust turbine
[0093] 37 Second turbocharger [0094] 37a Compressor [0095] 37b
Exhaust turbine [0096] 38 Exhaust purifying device [0097] 39
Oxidation catalytic converter [0098] 40 Catalyst temperature sensor
[0099] 41 Flow regulating valve [0100] 42 Valve opening sensor
[0101] 43 Regulation valve driving motor [0102] 44 Exhaust heating
device [0103] 45 Fuel supply valve [0104] 46 Glow plug [0105] 47
Auxiliary oxidation catalytic converter [0106] 48 Auxiliary
temperature sensor [0107] 49 Crank angle sensor [0108] N.sub.n
Engine speed [0109] N.sub.R Turbocharged state determining speed
[0110] T.sub.n Catalyst temperature [0111] T.sub.R Activation index
temperature [0112] T.sub.Sn Auxiliary catalyst temperature [0113]
T.sub.SR Activation index temperature
* * * * *