U.S. patent application number 12/069666 was filed with the patent office on 2008-08-21 for homogeneous charge compression ignition engine and air intake and exhaust system thereof.
Invention is credited to Hiroshi Kuzuyama.
Application Number | 20080196406 12/069666 |
Document ID | / |
Family ID | 39678116 |
Filed Date | 2008-08-21 |
United States Patent
Application |
20080196406 |
Kind Code |
A1 |
Kuzuyama; Hiroshi |
August 21, 2008 |
Homogeneous charge compression ignition engine and air intake and
exhaust system thereof
Abstract
An EGR passage partially refluxes exhaust gas to a combustion
chamber as an EGR gas. A heat exchanger cools the EGR gas. A
heating intake passage branches off from a branching portion formed
in a portion of an intake passage on an upstream side of a
downstream end of the EGR passage, and its downstream end
communicates with a portion of the EGR passage on an upstream side
of the heat exchanger. A switch valve adjusts respective amounts of
intake air passing through the intake passage and through the
heating intake passage. When an EGR valve is closed, an ECU
switches the switch valve such that the intake air passes through
one of the intake passage and the heating intake passage; when the
EGR valve is open, the ECU switches the switch valve such that the
intake air passes solely through the intake passage.
Inventors: |
Kuzuyama; Hiroshi;
(Aichi-ken, JP) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
3 WORLD FINANCIAL CENTER
NEW YORK
NY
10281-2101
US
|
Family ID: |
39678116 |
Appl. No.: |
12/069666 |
Filed: |
February 12, 2008 |
Current U.S.
Class: |
60/604 ; 123/295;
60/605.2 |
Current CPC
Class: |
Y02T 10/146 20130101;
F02B 29/0418 20130101; Y02T 10/12 20130101; F02B 1/12 20130101;
F02M 35/10255 20130101; Y02T 10/30 20130101; F02M 21/047 20130101;
F02M 21/0239 20130101; F02M 26/28 20160201; Y02T 10/32
20130101 |
Class at
Publication: |
60/604 ; 123/295;
60/605.2 |
International
Class: |
F01K 23/06 20060101
F01K023/06 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 21, 2007 |
JP |
2007-040404 |
Claims
1. A homogeneous charge compression ignition engine, comprising: a
combustion chamber; an intake passage serving as a passage for
intake air to the combustion chamber; an exhaust passage serving as
a passage for exhaust gas from the combustion chamber; an EGR
passage, communicating with the exhaust passage and the intake
passage, for refluxing a part of the exhaust gas from the
combustion chamber to the combustion chamber as an EGR gas; a heat
exchanger, provided at some midpoint in the EGR passage, for
cooling the EGR gas; an EGR valve, provided at some midpoint in the
EGR passage, for adjusting an opening and closing of the EGR
passage; a heating intake passage which branches off from a
branching portion formed in a portion of the intake passage on an
upstream side of a downstream end of the EGR passage and whose
downstream end communicates with a portion of the EGR passage on an
upstream side of the heat exchanger; a switch valve for adjusting
respective amounts of intake air passing through the portion of the
intake passage on a downstream side of the branching portion and
through the heating intake passage; and a control means which, when
the EGR valve is closed, switches the switch valve such that, on
the downstream side of the branching portion, the intake air
flowing into the combustion chamber passes through at least one of
the intake passage and the heating intake passage, and which, when
the EGR valve is open, switches the switch valve such that, on the
downstream side of the branching portion, the intake air flowing
into the combustion chamber passes solely through the intake
passage.
2. A homogeneous charge compression ignition engine according to
claim 1, wherein, in the EGR passage, the EGR valve is provided on
the upstream side of the downstream end of the heating intake
passage.
3. A homogeneous charge compression ignition engine according to
claim 1, wherein the switch valve is provided at the branching
portion.
4. A homogeneous charge compression ignition engine according to
claim 1, wherein the switch valve and the EGR valve are provided at
a communication portion between the heating intake passage and the
EGR passage.
5. A homogeneous charge compression ignition engine according to
claim 1, wherein the heat exchanger is one through which
circulation coolant of an engine passes.
6. An air intake and exhaust system for use in a homogeneous charge
compression ignition engine having a combustion chamber and an
exhaust passage serving as a passage for exhaust gas from the
combustion chamber, the air intake and exhaust system comprising:
an intake passage leading to the combustion chamber; an EGR
passage, communicating with the exhaust passage and the intake
passage, for refluxing the exhaust gas from the combustion chamber
to the combustion chamber as an EGR gas; a heat exchanger, provided
at some midpoint in the EGR passage, for cooling the EGR gas; an
EGR valve, provided at some midpoint in the EGR passage, for
opening and closing the EGR passage; a heating intake passage which
branches off from a branching portion formed in a portion of the
intake passage on an upstream side of a downstream end of the EGR
passage and whose downstream end communicates with a portion of the
EGR passage on an upstream side of the heat exchanger; a switch
valve for adjusting respective amounts of intake air passing
through the intake passage and through the heating intake passage
on a downstream side of the branching portion; and a control means
which, when the EGR valve is closed, switches the switch valve such
that, on the downstream side of the branching portion, the intake
air flowing into the combustion chamber passes through at least one
of the intake passage and the heating intake passage, and which,
when the EGR valve is open, switches the switch valve such that, on
the downstream side of the branching portion, the intake air
flowing into the combustion chamber passes solely through the
intake passage.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a homogeneous charge
compression ignition engine and an air intake and exhaust system
thereof for refluxing exhaust gas to a combustion chamber as an EGR
gas.
[0003] 2. Description of the Related Art
[0004] In recent years, in the field of internal combustion
engines, attention is being given to a homogeneous charge
compression ignition engine capable of attaining a satisfactory
fuel efficiency and thermal efficiency, and various studies are
being conducted in this regard. In most homogeneous charge
compression ignition engines, fuel and air are mixed with each
other in an intake passage, and the resultant air fuel mixture is
supplied to a combustion chamber. Further, the air fuel mixture
trapped in the combustion chamber undergoes self-ignition during
compression stroke with an increase in temperature and pressure due
to rising of a piston. As is known in the art, in such a
homogeneous charge compression ignition engine, the operation range
allowing stable control of the homogeneous charge compression
ignition (HCCI) is still rather small, which is a problem to be
solved in putting this engine into practical use. In view of this,
with a view toward solving this problem, an attempt is being made
to put into practical use a homogeneous charge compression ignition
engine as applied to a stationary engine whose normal operation
range is relatively small, such as a gas heat pump (GHP) gas
engine. Further, there has also been proposed an engine in which
operational switching is effected as appropriate such that
homogeneous charge compression ignition is effected in a range near
a low/medium rotation and low/medium load range, which is
frequently adopted in actual operation, and that spark ignition
(SI) is effected in a high rotation range and an ultra-low load and
high load range.
[0005] In a homogeneous charge compression ignition engine, the
operation range allowing stable control of the homogeneous charge
compression ignition is small. In the following, this problem will
be discussed in detail. For example, in the low load operation
range, the amount of air fuel mixture supplied to the combustion
chamber is small, and the in-cylinder temperature does not easily
increase, so the ignition property deteriorates, and a misfire is
liable to occur. As is known in the art, in order to suppress
occurrence of a misfire, there is adopted a method using a
so-called internal EGR, according to which a negative overlapping
period is provided in the valve timing of the intake valve and the
exhaust valve so that a part of the gas already burnt may be
allowed to remain in the combustion chamber for the next cycle of
combustion. By thus utilizing the internal EGR, the internal EGR
gas at high temperature and the air fuel mixture newly supplied to
the combustion chamber are mixed with each other to increase the
in-cylinder temperature, so the ignition property at the time of
homogeneous charge compression ignition is improved, thus
suppressing occurrence of a misfire. However, under a still worse
condition as in the case of a low outdoor air temperature, the
temperature in the combustion chamber is low, and a
high-temperature internal EGR is hard to obtain, so even when an
internal EGR is used, homogeneous charge compression ignition is
rather hard to effect, and there is a fear of occurrence of a
misfire.
[0006] Apart from the internal EGR, there is known, as a means for
increasing the in-cylinder temperature of the combustion chamber
of, for example, a diesel engine, a means which prevents occurrence
of a misfire by causing heated intake air (air fuel mixture)
previously heated by a heating mechanism such as a heat exchanger
to flow into the combustion chamber, that is, by performing intake
air heating.
[0007] On the other hand, in a homogeneous charge compression
ignition engine, there occurs in the high load operation range an
abnormal combustion such as knocking or premature ignition. As is
known in the art, in order to suppress occurrence of such an
abnormal combustion, there is utilized an external exhaust gas
recirculation (EGR). Since the external EGR gas immediately after
its extraction from the exhaust passage is at high temperature, it
is cooled by an EGR cooler provided at some midpoint in the EGR
passage so that the volumetric efficiency of the intake air may not
be deteriorated. Further, by refluxing the EGR gas cooled by the
EGR cooler into the combustion chamber, the combustion in the
combustion chamber is slowed down due to an increase in inert
gas.
[0008] As an example of the heat exchanger as the heating device or
the heat exchanger as the EGR cooler, JP 2005-517857 A cited herein
as Patent Document 1 discloses a technique according to which the
heating of the intake air and the cooling of the external EGR gas
are effected by using a heat exchanger 12 (see FIG. 2 of Patent
Document 1 described above). In this technique, the heat exchange
mechanism is made relatively simple by effecting the cooling of the
EGR gas and the intake air heating with the same coolant.
[0009] However, while having a single casing, the heat exchanger of
Patent Document 1 described above contains a first heat exchange
portion and a second heat exchange portion that are separate from
each other, and the cooling of the EGR gas and the intake air
heating are effected in each of those separate systems, i.e.,
within each of the first heat exchange portion and the second heat
exchange portion. Thus, while it can achieve space saving as
compared with the related-art technique using two heat exchangers,
the technique as disclosed in Patent Document 1 described above
involves an increase in size of the heat exchanger as compared with
an ordinary heat exchange system consisting of a single heat
exchanger. Further, in an internal combustion engine using the heat
exchanger of Patent Document 1 described above, it is necessary to
connect to the single heat exchanger a large number of pipes,
including pipes constituting the intake passage and the EGR passage
and a pipe for coolant, resulting in a rather strict limitation in
terms of design in arranging them around the internal combustion
engine.
SUMMARY OF THE INVENTION
[0010] It is accordingly an object of the present invention to
provide a homogeneous charge compression ignition engine and an air
intake and exhaust system thereof which help to achieve further
space saving and which allow EGR gas cooling and intake air
heating.
[0011] In order to achieve the above-mentioned object, a
homogeneous charge compression ignition engine according to the
present invention includes: a combustion chamber; an intake passage
serving as a passage for intake air to the combustion chamber; an
exhaust passage serving as a passage for exhaust gas from the
combustion chamber; an EGR passage, communicating with the exhaust
passage and the intake passage, for refluxing a part of the exhaust
gas from the combustion chamber to the combustion chamber as an EGR
gas; a heat exchanger, provided at some midpoint in the EGR
passage, for cooling the EGR gas; an EGR valve, provided at some
midpoint in the EGR passage, for adjusting an opening and closing
of the EGR passage; a heating intake passage which branches off
from a branching portion formed in a portion of the intake passage
on an upstream side of a downstream end of the EGR passage and
whose downstream end communicates with a portion of the EGR passage
on an upstream side of the heat exchanger; a switch valve for
adjusting respective amounts of intake air passing through the
portion of the intake passage on a downstream side of the branching
portion and through the heating intake passage; and a control means
which, when the EGR valve is closed, switches the switch valve such
that, on the downstream side of the branching portion, the intake
air flowing into the combustion chamber passes through at least one
of the intake passage and the heating intake passage, and which,
when the EGR valve is open, switches the switch valve such that, on
the downstream side of the branching portion, the intake air
flowing into the combustion chamber passes solely through the
intake passage.
[0012] Further, in order to achieve the above-mentioned object, an
air intake and exhaust system for use in a homogeneous charge
compression ignition engine according to the present invention is
used for a homogeneous charge compression ignition engine having a
combustion chamber and an exhaust passage serving as a passage for
exhaust gas from the combustion chamber. The air intake and exhaust
system includes: an intake passage leading to the combustion
chamber; an EGR passage, communicating with the exhaust passage and
the intake passage, for refluxing the exhaust gas from the
combustion chamber to the combustion chamber as an EGR gas; a heat
exchanger, provided at some midpoint in the EGR passage, for
cooling the EGR gas; an EGR valve, provided at some midpoint in the
EGR passage, for opening and closing the EGR passage; a heating
intake passage which branches off from a branching portion formed
in a portion of the intake passage on an upstream side of a
downstream end of the EGR passage and whose downstream end
communicates with a portion of the EGR passage on an upstream side
of the heat exchanger; a switch valve for adjusting respective
amounts of intake air passing through the intake passage and
through the heating intake passage on a downstream side of the
branching portion; and a control means which, when the EGR valve is
closed, switches the switch valve such that, on the downstream side
of the branching portion, the intake air flowing into the
combustion chamber passes through at least one of the intake
passage and the heating intake passage, and which, when the EGR
valve is open, switches the switch valve such that, on the
downstream side of the branching portion, the intake air flowing
into the combustion chamber passes solely through the intake
passage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] In the accompanying drawings;
[0014] FIG. 1 is an overall schematic view of a homogeneous charge
compression ignition engine and an air intake and exhaust system
thereof according to an embodiment of the present invention;
[0015] FIG. 2 is a chart illustrating how an EGR valve and a switch
valve of the homogeneous charge compression ignition engine of FIG.
1 are controlled;
[0016] FIG. 3 is a schematic view of the operation ranges when the
homogeneous charge compression ignition engine of FIG. 1 is
used;
[0017] FIG. 4 is an overall schematic view of a first modification
of the homogeneous charge compression ignition engine of FIG.
1;
[0018] FIG. 5 is an overall schematic view of a second modification
of the homogeneous charge compression ignition engine of FIG. 1;
and
[0019] FIG. 6 is an enlarged schematic view illustrating an
operation range allowing homogeneous charge compression ignition
without using any supercharger in the homogeneous charge
compression ignition engine of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] In the following, a preferred embodiment of the present
invention will be described with reference to the drawings.
(Overall Construction)
[0021] With reference to FIG. 1, the overall construction of a
homogeneous charge compression ignition engine and an air intake
and exhaust system thereof according to an embodiment of the
present invention will be described. In the following description,
the term "intake air" means a gas supplied into a combustion
chamber (e.g., mixture of intake air and gas fuel or mixture of
intake air, gas fuel, and external EGR), and the term "air fuel
mixture" means a mixture of intake air and gas fuel.
[0022] As shown in FIG. 1, a homogeneous charge compression
ignition engine 1 has a combustion chamber 10, an intake passage
11p leading to the combustion chamber 10, and an exhaust passage
12p constituting a passage for the exhaust gas from the combustion
chamber 10, and effects switching as appropriate between spark
ignition and homogeneous charge compression ignition according to
the operating conditions (load and engine RPM). In this way, by
switching between homogeneous charge compression ignition and spark
ignition according to the operating conditions, it is possible to
attain both the high fuel efficiency due to homogeneous charge
compression ignition and the satisfactory starting property and
high output due to spark ignition.
[0023] Further, the homogeneous charge compression ignition engine
1 has a supercharger 11t, a throttle 3, a fuel valve 2v (fuel
supply amount adjusting device), a heating intake passage 20p, a
switch valve 11v, an EGR passage 30p, an EGR valve 30v, a heat
exchanger 40, an intake valve 51v, an exhaust valve 52v, and an
ignition plug 53c. (Those components will be described in detail
below). Further, the homogeneous charge compression ignition engine
1 has an electronic control unit (ECU, which corresponds to a
control device) 5. Electrically connected to the ECU 5 are control
cables 5a through 5i corresponding to the exhaust valve 52v, the
ignition plug 53c, the intake valve 51v, the EGR valve 30v, the
switch valve 11v, the throttle 3, the fuel valve 2v, a bypass
control valve 40v, and the supercharger 11t, respectively. Further,
the ECU 5 controls the operation of the exhaust valve 52v, the
ignition plug 53c, the intake valve 51v, the EGR valve 30v, the
switch valve 11v, the throttle 3, the fuel valve 2v, the bypass
control valve 40v, and the supercharger 11t.
(Regarding the Air Intake and Exhaust System)
[0024] An air intake and exhaust system 60 of the homogeneous
charge compression ignition engine 1 of this embodiment is used to
supply intake air to the combustion chamber 10, to scavenge exhaust
gas from the combustion chamber 10, etc., and includes the intake
passage 11p, the exhaust passage 12p, the heating intake passage
20p, the switch valve 11v, the EGR passage 30p, the EGR valve 30v,
the heat exchanger 40, and the ECU 5. Further, apart from the
above-mentioned intake air supply, etc., the air intake exhaust
system 60 performs mixing of external EGR with air fuel mixture,
intake air heating, etc.
(Mixer)
[0025] The homogeneous charge compression ignition engine 1 has a
mixer 4 at some midpoint in the intake passage 11p; a gas fuel is
supplied to the mixer 4 through a fuel supply path 2p communicating
with the mixer 4. (That is, fuel supply path 2p serves as the
passage for the gas fuel, and communicates with intake passage
11p). Further, air and the fuel are mixed with each other at the
mixer 4.
(Fuel Valve)
[0026] The fuel valve 2v is provided at some midpoint in the fuel
supply path 2p. Further, under control of the fuel valve 2v by the
ECU 5, the degree of opening of the fuel valve 2v is adjusted,
whereby the amount of gas fuel supplied to the intake passage 11b
is adjusted.
(Throttle)
[0027] As shown in FIG. 1, the throttle 3 has a step motor (not
shown) for driving a shaft 3c and a valve portion 3v, and the valve
portion 3c is rotatable around the shaft 3c. Further, the ECU 5
controls the step motor of the throttle 3, whereby the degree of
opening of the passage is adjusted by the valve portion 3v, thereby
adjusting the amount of intake air supplied to the combustion
chamber 10 through the intake passage 11p.
(Supercharger)
[0028] The supercharger 11t is of an electric turbo type whose
supercharging pressure is variable, and is formed as a centrifugal
compressor driven by an electric motor M. The supercharger 11t is
arranged at some midpoint in the intake passage 11p. Further, a
bypass route 40a and a main route 40b are respectively connected to
the upstream side of the supercharger 11t and to the outlet portion
of the supercharger 11t, and communication through those routes is
provided for the intake passage 11p. At some midpoint of the bypass
route 40a, there is provided a bypass control valve 40v for opening
and closing the bypass route 40a.
[0029] When the supercharger 11t is not used, the electric motor M
is controlled to be kept at rest, and the bypass control valve 40v
is controlled to be kept open. As a result, the bypass route 40a
functions as a normal intake passage. On the other hand, when
performing supercharging by using the supercharger 11t, the
electric motor M is controlled to be driven to be rotated, and the
bypass control valve 40v is controlled to be closed. As a result,
the main route 40b functions as a supercharging passage.
(Combustion Chamber)
[0030] The combustion chamber 10 is an internal space defined in
the internal combustion engine by a cylinder and a piston; a piston
50 reciprocates vertically as seen in the drawing. The air fuel
mixture is supplied to the combustion chamber 10 through the intake
passage 11p. After the combustion, the exhaust gas is discharged
through the exhaust passage 12p. The intake valve 51v and the
exhaust valve 52v are arranged at the opening of the intake passage
11p to the combustion chamber 10 and at the opening of the exhaust
passage 12p to the combustion chamber 10, respectively. Those
valves are opened and closed as appropriate upon rising and
lowering of the piston 50 during the strokes of intake,
compression, combustion/expansion, and exhaust, thereby effecting
intake and exhaust. More specifically, the intake valve 51v and the
exhaust valve 52v are respectively driven to be opened and closed
by cams 51c and 52c formed on the outer peripheries of camshafts
(not shown), and their opening/closing timing (phase with respect
to the crank angle) is varied by a well-known variable valve timing
mechanisms provided on the camshafts. The ignition plug 53c is used
for ignition at the time of spark ignition, and its operation is
controlled by the ECU 5.
(EGR Passage)
[0031] The exhaust gas from the combustion chamber 10 passes
through the exhaust passage 12p, and is discharged to the exterior
through an exhaust port (not shown); a part of the exhaust gas
discharged into the discharge passage 12p is supplied to the
combustion chamber 10 again. The EGR passage 30p serves to reflux a
part of the exhaust gas from the combustion chamber 10 to the
combustion chamber 10 as EGR gas; it branches off from the exhaust
passage 12p at a branching position 12b, and a downstream end 30b
thereof communicates with the intake passage 11p. As a result, the
inner space of the exhaust passage 12p and that of the intake
passage 11p communicate with the inner space of the EGR passage 30p
at the upstream end (branching position 12b) and the downstream end
30b of the EGR passage 30p.
[0032] Halfway through the EGR passage 30p, there are provided the
EGR valve 30v for adjusting the opening/closing condition of the
EGR passage 30p and the heat exchanger 40 for cooling the EGR gas
in that order from the upstream side (with respect to the flowing
direction of the EGR gas). Further, as described below, the EGR
passage 30p has a communicating portion 20b between the EGR valve
30v and the heat exchanger 40, establishing communication with the
downstream end of the heating intake passage 20p.
(Heat Exchanger)
[0033] The heat exchanger 40 is provided at some midpoint in the
EGR passage 30p, and functions as a cooling device for the EGR gas.
Further, in the case where the switch valve 11v has been switched
so as to allow passage of intake air (air fuel mixture) through the
heating intake passage 20p, the heating exchanger 40 also functions
as an intake air heating device.
[0034] The heat exchange medium of the heat exchanger 40 is the
circulation coolant of the engine; through passing of this
circulation coolant through its interior, the heat exchanger 40
functions as a heat exchange device (see arrows A and A' in FIG.
1). The circulation coolant that has attained high temperature as
the result of cooling the cylinder block during operation of the
engine is circulated through a radiator outside the engine, and is
cooled at the radiator, whereby the temperature of the coolant is
maintained at approximately 70 to 80 degrees.
(Heating Intake Passage)
[0035] Heating intake passage 20p constitutes a part of the intake
passage when performing intake air heating, and branches off from a
branching portion 11b formed on the upstream side of the downstream
end 30b of the EGR passage 30p (with respect to the flowing
direction of the intake air) in the intake passage 11p. The
downstream end of the heating intake passage 20p is formed so as to
communicate with the upstream side of the heat exchanger 40 in the
EGR passage 30p (upstream side with respect to the flowing
direction of the EGR gas) at the communicating portion 20b.
(Switch Valve)
[0036] The switch valve 11v serves to adjust the amount of intake
air (air fuel mixture) passing through the part of the intake
passage 11p on the downstream side of the branching portion 11b
(with respect to the flowing direction of the intake air) and
through the heating intake passage 20p. The air fuel mixture sent
from the upstream side to the branching portion 11b passes the
branching portion 11b. After that, the proportion in which it
circulates through the two circulation passages of the intake
passage 11p and the heating intake passage 20p, on the downstream
side of the branching portion 11b, is determined by adjustment of
the switch valve 11v. More specifically, switching is effected in
one of the following patterns: (a) a route in which, on the
downstream side of the branching portion 11b, all the air fuel
mixture passes through the intake passage 11p as it is and flows
into the combustion chamber 10 (intake passage: 100%), (b) a route
in which, on the downstream side of the branching portion 11b, all
the air fuel mixture passes through the heating intake passage 20p
to pass through a part of the EGR passage 30p before passing
through the intake passage 11p again to flow into the combustion
chamber 10 (heating intake passage: 100%), and (c) a route which is
somewhere between the above two routes (i.e., route in which, on
the downstream side of branching portion 11b, a part of the air
fuel mixture passes through intake passage 11p, with a part of the
air fuel mixture passing through heating intake passage 20p).
[0037] More specifically, the switch valve 11v contains a valve
(not shown) for the intake passage 11p and a valve (not shown) for
the heating intake passage 20p, each of which is controlled to be
opened or closed, whereby the respective amounts of intake air
passing through the portion of the intake passage 11p on the
downstream side of the branching portion 11b and through the
heating intake passage 20p are adjusted. While in this embodiment
the switch valve is constructed as described above, this should not
be construed restrictively.
(ECU)
[0038] The ECU 5 controls the switch valve 11v as follows: First,
when the EGR valve 30v is closed, the switch valve 11v is switched
such that the air fuel mixture flowing into the combustion chamber
10 passes, on the downstream side of the branching portion 11b
(with respect to the intake air flowing direction), through at
least one of the intake passage 11p and the heating intake passage
20p. On the other hand, when the EGR valve 30v is open, the switch
valve 11v is switched such that the air fuel mixture flowing into
the combustion chamber 10 passes solely through the intake passage
11p on the downstream side of the branching portion 11b (i.e., air
fuel mixture does not pass through heating intake passage 20p, with
all the air fuel mixture passing through intake passage 11p).
(Regarding Exhaust Gas and External EGR)
[0039] Next, the exhaust gas and the external EGR will be
described. During homogeneous charge compression ignition, an
abnormal combustion is liable to occur in the operation range on
the high load side. In view of this, in the homogeneous charge
compression ignition engine 1, by opening the EGR valve 30v in the
operation range on the high load side, the EGR gas is cooled by the
heat exchanger 40 provided at some midpoint in the EGR passage 30p,
and is supplied to the combustion chamber 10 together with the air
fuel mixture, whereby the combustion in the combustion chamber 10
is slowed down.
(Regarding Internal EGR)
[0040] Next, the internal EGR will be described. The homogeneous
charge compression ignition engine 1 has a negative overlapping
period for the valve timing during homogeneous charge compression
ignition operation. Here, the negative overlapping period is a
period in which both the exhaust valve 52v and the intake valve 51v
are closed near the exhaust top dead center, with the exhaust valve
52v being closed before the exhaust top dead center is reached. As
a result, it is possible to allow a part of the already burned gas
(internal EGR gas) to remain in the combustion chamber 10 for the
next cycle of combustion. By providing the negative overlapping
period and by utilizing the internal EGR, the internal EGR gas that
is at high temperature is mixed with the air fuel mixture newly
supplied into the combustion chamber 10 to increase the in-cylinder
temperature, so the ignition property at the time of homogeneous
charge compression ignition is improved. Further, by controlling
the length of the negative overlapping period, it is possible to
control the ignition time to some degree.
(Supercharging and External EGR)
[0041] Next, supercharging and the external EGR will be described.
During high load operation, the supply amount of the air fuel
mixture including gas fuel increases, so the ignition property is
improved to an excessive degree, and knocking attributable to too
intense a combustion is liable to occur. In order to suppress the
occurrence of knocking, it is necessary to reduce the internal EGR
amount in the combustion chamber 10 for the purpose of reducing the
ignition property. Thus, control is effected to reduce the negative
overlapping period. However, a reduction in the internal EGR
simultaneously causes a lag in ignition timing and a reduction in
combustion rate, so it is impossible to control the ignition timing
and the combustion rate as they are in a properly balanced manner.
In view of this, the ignition timing is first controlled by raising
the intake air temperature through supercharging, maintaining a
proper timing. Further, when the engine operation range is on the
high load side, external EGR is performed to suppress abnormal
combustion, slowing down the combustion.
(Operation)
[0042] Next, an operation of the homogeneous charge compression
ignition engine 1, constructed as described above, will be
illustrated. First, in the operation range where spark ignition is
effected, the ECU 5 controls the ignition plug 53c, etc., thereby
effecting spark ignition.
[0043] In the operation range where homogeneous charge compression
ignition is effected, the ECU 5 performs the following control.
First, the air fuel mixture produced at the mixer 4 passes the
intake passage 11p while being adjusted in intake amount by the
throttle 3, and reaches the position of the branching portion 11b
where the switch valve 11v is arranged.
[0044] Further, when the EGR valve 30v is closed, the switch valve
11v is switched such that the air fuel mixture flowing into the
combustion chamber 10 passes at least one of the intake passage 11p
and the heating intake passage 20p on the downstream side of the
branching portion 11b. Here, when the air fuel mixture passes the
heating intake passage 20p, the air fuel mixture passes the heat
exchanger 40, so the heating of the air fuel mixture is effected at
the heat exchanger 40. Thus, the air fuel mixture, which is at
around the outdoor air temperature, passes the heating intake
passage 20p, and is supplied to the combustion chamber 10 in a
state in which its temperature has been previously raised by
several to several tens of degrees. When, for example, the outdoor
air temperature is low, the temperature in the combustion chamber
is low, and it is difficult to obtain a high temperature internal
EGR, so homogeneous charge compression ignition does not easily
occur; thus, when homogeneous charge compression ignition is
effected, there is a fear of occurrence of a misfire. However, by
thus causing a previously heated intake air (air fuel mixture) to
flow into the combustion chamber 10, it is possible to suppress
occurrence of a misfire and to enlarge the operation range where
homogeneous charge compression ignition is possible.
[0045] The case in which the EGR valve 30v is closed corresponds to
the case in which the engine is in the operation range where there
is no need to use external EGR. As shown in FIG. 3, an operation
range is determined by engine load and engine RPM; the homogeneous
charge compression ignition range (operation range suitable for
homogeneous charge compression ignition) corresponds to the central
portion of the drawing. Of this homogeneous charge compression
ignition range (including ranges indicated by symbols a, b, c, and
d), the ranges a, b, and c are operation ranges where no external
EGR is used.
[0046] When the EGR valve 30v is open, the switch valve 11v is
switched such that the air fuel mixture flowing into the combustion
chamber 10 passes solely through the intake passage 11p on the
downstream side of the branching portion 11b. That is, when the EGR
valve 30v is open, the switch valve 11v is controlled such that no
air fuel mixture passes through the heating intake passage 20p.
[0047] Further, since the EGR valve 30v is open, a part of the
exhaust gas from the combustion chamber circulates through the EGR
passage 30p, and is cooled by the heat exchanger 40 before flowing
into the intake passage 11p from the downstream end 30b
communicating with the intake passage 11p and refluxing to the
combustion chamber 10. (That is, both the air fuel mixture and the
external EGR gas are sent to the combustion chamber 10). In this
way, when the EGR valve 30v is in the open state, the heat
exchanger 40 functions as a cooling device for the external
EGR.
[0048] In the high load operation range, abnormal combustion such
as knocking or premature ignition occurs; however, by thus
utilizing the external EGR, it is possible to suppress occurrence
of abnormal combustion. More specifically, the external EGR gas,
which is at high temperature (e.g., approximately 300.degree. C.
before reaching the heat exchanger), is cooled by the heat
exchanger (EGR cooler) 40 provided at some midpoint in the EGR
passage 30p. Further, the cooled EGR gas refluxes into the
combustion chamber 10, whereby the combustion in the combustion
chamber 10 is slowed down due to an increase in inert gas, and
occurrence of abnormal combustion in the combustion chamber 10 is
suppressed.
[0049] The case in which the EGR valve 30 is open corresponds to
the case in which the engine is in the operation range where it is
necessary to use the external EGR. FIG. 3 shows operation ranges
that are determined by engine load and engine RPM; of the
homogeneous charge compression ignition ranges (ranges a through
d), the range d is the operation range where the external EGR is
used. More specifically, in the high load operation range, the
external EGR is utilized as supercharging of the air fuel mixture
is effected. As a result, it is possible to both secure the
requisite ignition property and slow down the combustion due to an
increase in intake air temperature caused by supercharging and due
to a local reduction in temperature attributable to the external
EGR, with the result that it is possible, in the range on the high
load side, to enlarge the range where homogeneous charge
compression ignition is possible.
(Control Example for the Homogeneous Charge Compression Ignition
Engine and the Air Intake and Exhaust System)
[0050] Next, a control example for the homogeneous charge
compression ignition engine 1 and the air intake and exhaust system
60 will be described with reference to FIG. 2. FIG. 2 is a chart
illustrating the opening/closing control and switching control of
the EGR valve 30v and the switch valve 11v of the homogeneous
charge compression ignition engine 1. The horizontal axis of FIG. 2
indicates the magnitude of the engine load. The upper chart in FIG.
2 illustrates the opening degree of the EGR valve. In this chart,
the lowermost portion (see portion (i) of FIG. 2) corresponds to
the state in which the EGR valve 30v is closed, and the opening
degree of the EGR valve 30v increases as the line extends upwards
therefrom (see portion (ii) of FIG. 2). The lower chart in FIG. 2
illustrates how the switch valve 11v is switched. In this chart,
the uppermost position (see portion (1) of FIG. 2) corresponds to
the state in which all the air fuel mixture is passing through the
heating intake passage 20p on the downstream side of the branching
portion 11b, and the lowermost position (see portion (3) of FIG. 2)
corresponds to the state in which all the air fuel mixture is
passing through the intake passage 11p on the downstream side of
the branching portion 11b. The intermediate position (see portion
(2) of FIG. 2) corresponds to the intermediate state, that is, the
state in which, on the downstream side of the branching portion
11b, a part of the air fuel mixture passes through the intake
passage 11p, with a part of the air fuel mixture passing through
the heating intake passage 20p.
[0051] Further, as shown in FIG. 2, in the homogeneous charge
compression ignition engine 1, the operation range is divided
according to the engine load into an NA (natural aspiration) range,
a supercharging range, a supercharging/external-EGR range, etc.,
and operation control is effected according to each load range. The
horizontal axis in FIG. 2 indicates a part of the entire range,
which means there exist a range of lower load and a range of higher
load than the range shown in the drawing.
[0052] As shown in FIG. 2, in the NA range and the supercharging
range, the EGR valve 30v is in the closed state, and the heating
intake passage 20p and the intake passage 11p are used as the
intake path. That is, the external EGR is not used, but the heat
exchanger 40 is used solely for intake air heating.
[0053] In the supercharging/external-EGR range, the EGR valve 30v
is in the open state, and the heating intake passage 20p is not
used at all. That is, solely the external EGR is used, and the heat
exchanger 40 is used solely as the EGR cooler for cooling the
external EGR gas.
[0054] The control illustrated in FIG. 2 is only shown by way of
example; the control of the EGR valve 30v and the switch valve 11b
is not restricted to the one shown in the drawing.
(Effects)
[0055] In the following, effects of the present invention as
compared with those of a diesel engine will be described. In a
diesel engine, intake air heating is effected for the purpose, for
example, of suppressing generation of unburned fuel component and
white smoke during low load operation as in the case of engine
start. Further, by using external EGR, exhaust gas, which is an
inert gas, is supplied to the combustion chamber, and the maximum
combustion temperature is lowered to reduce the amount of nitrogen
oxides generated. To elaborate on this, in the diesel engine, fuel
is directly injected into the combustion chamber, so generation of
differing concentrations of fuel in the combustion chamber is
inevitable, whereby a high temperature portion is locally
generated, resulting in generation of a large amount of nitrogen
oxides. That is, in the diesel engine, external EGR is used for the
purpose of suppressing generation of nitrogen oxides; in
particular, in recent years, when countermeasures against exhaust
gas are being emphasized, the operation range in which it is used
along with intake air heating is being enlarged in the low load
operation range.
[0056] On the other hand, in homogeneous charge compression
ignition, during low load operation as in the case of low outdoor
air temperature and during medium load operation, an improvement in
ignition property is achieved by heating the intake air (air fuel
mixture), and occurrence of a misfire is suppressed. Further, in
homogeneous charge compression ignition, the use of external EGR
during high load operation is effective in view of suppression of
knocking. However, during low load operation as in the case of low
outdoor air temperature and during medium load operation, the use
of external EGR is not desirable in view of deterioration in
ignition property. That is, in homogeneous charge compression
ignition, intake air heating helps to achieve an improvement in
ignition property and external EGR suppresses ignition property, so
they are used in different operation ranges, which means external
EGR and intake air heating are not used simultaneously.
[0057] To elaborate on this, in homogeneous charge compression
ignition, an air fuel mixture obtained by substantially uniformly
mixing fuel and air with each other is caused to undergo self
ignition in the combustion chamber, so, as compared with a diesel
engine in which fuel exists in an uneven fashion, and as compared
with spark ignition (as in the case of a gasoline engine, for
example) in which a local high temperature portion is generated in
the flame, a local high temperature portion is not generated
easily, and the maximum combustion temperature is low. Thus, the
amount of nitrogen oxides generated is small, and there is no need
to use external EGR for the purpose of suppressing generation of
nitrogen oxides.
[0058] As described above, in the homogeneous charge compression
ignition engine 1, the use of external EGR and intake air heating
are not effected simultaneously, so the heat exchanger 40 only
effects one of the cooling of EGR gas and intake air heating
according to the operation range (which is determined according to
the engine load and the engine RPM). Thus, due to the
above-mentioned construction of the homogeneous charge compression
ignition engine 1, the heat exchanger 40, which is used as the EGR
cooler, can also be used for intake air heating without involving a
change in construction, so, even when compared with a generally
adopted construction which uses a single heat exchanger having only
one heat exchange portion, there is involved no increase in the
size of the heat exchanger. Thus, with the simple construction, it
is possible to effect cooling of the EGR gas and intake air
heating. Further, by using an existing EGR passage having an EGR
cooler, it is possible to realize the above-mentioned construction
through a change in and addition of a simple piping structure.
Further, there is no need to connect to a single heat exchanger a
large number of pipes, including the pipes constituting the intake
passage and the EGR passage and the pipe for coolant, and the
restrictions in terms of design in arranging the pipes around the
internal combustion engine are mitigated, so it is possible to
achieve further space saving and conduct cooling of the EGR gas and
intake gas heating.
[0059] Further, in the EGR passage 30p, the EGR valve 30v is
provided on the upstream side of the downstream end of the heating
intake passage 20p (communicating portion 20b), so, in the EGR
passage 30p, the heated intake air (air fuel mixture) is not
allowed to flow into the upstream side of the communicating portion
20b, and it is possible to reflux the heated intake air to the
combustion chamber 10 via the portion of the EGR passage 30p on the
downstream side of the communicating portion 20b and the intake
passage 11p. Further, when the EGR valve is closed, it is possible
to prevent EGR gas from flowing into the heating intake passage
20p.
[0060] Further, the switch valve 11v is provided at the branching
portion 11b, so it is possible to send the intake air (air fuel
mixture) heated by the heat exchanger 40 positively into the
heating intake passage 20p. On the other hand, the intake air (air
fuel mixture) not passing through the heat exchanger 40 does not
enter the heating intake passage 20p, all of it passing through the
intake passage 11p. Thus, the circulation of the intake air is
effected efficiently.
[0061] Further, the heat exchanger 40, through which the
circulation coolant of the engine passes, can utilize the engine
heat, making it possible to effect the cooling of the EGR gas and
the intake air heating with a still simpler construction.
[0062] Further, with its simple construction, the air intake and
exhaust system 60 of the homogeneous charge compression ignition
device of the present invention described above can effect the
cooling of EGR gas and intake gas heating. Further, by utilizing an
existing EGR passage having an EGR cooler, it is possible to
realize the above construction through a change in and addition of
a simple piping structure.
(Regarding Expansion of the Range Allowing Operation)
[0063] Further, it is possible to expand the range allowing
operation toward the low load side by using the homogeneous charge
compression ignition engine 1 and the air intake and exhaust system
60. This will be described with reference to FIG. 3. FIG. 3 is a
schematic view illustrating the operation range in the case in
which the homogeneous charge compression ignition engine 1 is used;
the horizontal axis indicates engine RPM, and the vertical axis
indicates engine load.
[0064] In FIG. 3, the central portion indicated by symbol HCCI
corresponds to the range where homogeneous charge compression
ignition is effected, and the remaining, peripheral range thereof
corresponds to the spark ignition (SI) range. In this way,
operation is conducted while effecting switching as appropriate
between homogeneous charge compression ignition and spark ignition
according to the engine load and the engine RPM.
[0065] Further, in the case of an engine performing no intake air
heating, it is only in the range b in FIG. 3 that operation is
conducted by natural aspiration. That is, when no intake air
heating is conducted, operation is conducted through spark ignition
in the range a of the drawing. However, in the case in which intake
air heating is effected as in the homogeneous charge compression
ignition engine 1, homogeneous charge compression ignition
operation is possible not only in the range b but also in the range
a.
[0066] In the following, this will be described more specifically.
First, in the homogeneous charge compression ignition in the range
a, which is a low load range, a misfire is liable to occur since
the amount of fuel supplied is small. However, by performing intake
air heating in the range a, that is, by closing the EGR valve 30v
and effecting switching at the switch valve 11v such that the
intake air (air fuel mixture) passes through the heating intake
passage 20p, an improvement in ignition property is achieved, and
occurrence of a misfire can be suppressed, so homogeneous charge
compression ignition is possible. As a result, it is possible to
expand the range allowing operation toward the low load side.
[0067] By performing the above-mentioned control in the homogeneous
charge compression ignition engine 1, it is possible to expand the
range allowing operation toward the low load side (range a).
Further, by adjusting the switch valve 11v as appropriate, the
amounts of intake air distributed to the intake passage 11p and the
heating intake passage 20p are controlled according to the outdoor
air temperature, whereby it is possible to adjust the temperature
of the intake air flowing into the combustion chamber 10. Thus,
irrespective of the outdoor air temperature, it is possible to
expand the operation range toward the low load side by adjustment
of intake air distribution. In the range c of the drawing,
operation is effected by supercharging, and, in the range d of the
drawing, operation is possible by supercharging and utilization of
external EGR.
(Modifications)
[0068] Next, modifications of the homogeneous charge compression
ignition engine of the above embodiment will be described with
reference to FIGS. 4 and 5; the description will center on the
differences between the above embodiment and the modifications.
FIG. 4 is an overall schematic view of a homogeneous charge
compression ignition engine according to a first modification, and
FIG. 5 is an overall schematic view of a homogeneous charge
compression ignition engine according to a second modification. The
portions that are the same as those of the above embodiment are
indicated by the same reference numerals, and a description thereof
will be omitted.
(First Modification)
[0069] First, a first modification will be described. As shown in
FIG. 4, in a homogeneous charge compression ignition engine 100 and
an air intake and exhaust system 160 according to this
modification, a switch valve 111v and an EGR valve 130v are
provided at the communicating portion 20b between the heating
intake passage 20p and an EGR passage 130p. More specifically, the
switch valve 111v, which is an opening/closing valve, is provided
at the connecting portion between the heating intake passage 20p
and the EGR passage 130p, and the EGR valve 130v, which is an
opening/closing valve, is provided in the portion of the EGR
passage on the upstream side of the connecting portion 20b. Here, a
control cable 105d (105e) connecting the switch valve 111v and the
EGR valve 130v to an ECU 105 is one obtained by integrating the
control cables 5d and 5e of the above embodiment. In this
modification, the switch valve and the EGR valve are arranged at
one position in the form of a valve 100v, so it is possible to form
the homogeneous charge compression ignition engine and the air
intake and exhaust system in a simple construction.
(Second Modification)
[0070] First, a second modification will be described. As shown in
FIG. 5, in a homogeneous charge compression ignition engine 200 and
an air intake and exhaust system 260 of this modification, an EGR
valve 230v is provided near the communicating portion 20b
(downstream end of the heating intake passage) between the heating
intake passage 20p and an EGR passage 230p, and is provided on the
upstream side with respect to the flowing direction of the EGR gas
in the EGR passage 230p. With this construction also, it is
possible to obtain the same effect as that of the above-mentioned
embodiment.
[0071] The present invention is not restricted to the
above-mentioned embodiment but can be carried out in various
modifications without departing from the scope as defined in the
claims.
[0072] For example, while in the above embodiment the fuel supply
path 2p is arranged so as to communicate with the portion of the
intake passage 11p on the upstream side of the branching portion
11b, this should not be construed restrictively. For example, it
may also communicate with the portion of the intake passage 11p on
the downstream side of the connecting portion (downstream end 30b)
to the EGR passage 30p (see the position indicated by arrow C of
FIG. 1). By arranging the fuel supply path 2p as in the above
embodiment or at the position indicated by the arrow C, it is
possible to supply fuel halfway through the route for intake air no
matter which of the intake passage 11p and the heating intake
passage 20p may be selected by the switch valve 11v. On the other
hand, when the fuel supply path is arranged at a position in the
portion of the intake passage 11p between the branching portion 11b
and the connecting portion (downstream end 30b) (see the position
indicated by arrow B of FIG. 1), the communicating position of the
fuel supply path is not halfway through the route for the intake
air when the heating intake passage 20p is selected, so the fuel
supply becomes rather incomplete, which is not desirable.
[0073] Further, while in the above embodiment the throttle 3 is
arranged in the portion of the intake passage 11p on the upstream
side of the branching portion 11b, this should not be construed
restrictively; it may also be provided on the downstream side of
the connecting portion to the EGR passage 30p (downstream end 30b)
(see the position indicated by arrow C of the drawing). By
arranging the throttle 3 at the position of the above embodiment or
at the position indicated by the arrow C, it is possible to send
intake air forwards or suck intake air in from the rear side no
matter which of the intake passage 11p and the heating intake
passage 20p may be selected by the switch valve 11v. On the other
hand, when the throttle is arranged at a position in the portion of
the intake passage 11p between the branching portion 11b and the
connecting portion (downstream end 30b) (see the position indicated
by arrow B of FIG. 1), the adjustment of the amount of intake air
becomes rather difficult when the heating intake passage 20p is
selected, which means this arrangement is undesirable.
[0074] Further, while in the above embodiment the internal EGR is
utilized so as to expand the operation range allowing homogeneous
charge compression ignition mainly toward the low load side, and
the supercharger 11t is utilized so as to expand the operation
range toward the high load side, this arrangement is not
indispensable. When no internal EGR or supercharger is used, the
operation range allowing homogeneous charge compression ignition is
reduced; it is possible, however, to apply the present invention in
such cases and to utilize intake air heating and external EGR.
Further, as the device for expanding the operation range allowing
homogeneous charge compression ignition, there has been proposed
increasing of the compression ratio in the combustion chamber
instead of using internal EGR; the present invention is also
applicable to such a homogeneous charge compression ignition
engine.
[0075] Further, while the above embodiment has been described on
the assumption that the present invention is to be applied to an
internal combustion engine using gas fuel, there are no particular
limitations in this regard; it is also applicable to other types of
internal combustion engine such as a gasoline engine. For example,
in the case of a gasoline engine, it is possible to use, instead of
the mixer of the above embodiment, some other fuel supply device
such as a carburetor or injector as appropriate as the fuel supply
device.
[0076] Further, while in the above embodiment the circulation
coolant of the engine is used as the heat exchange medium of the
heat exchanger 40, this should not be construed restrictively. For
example, when the gas engine of the above-mentioned embodiment is
applied to the use of gas heat pump, it is also possible to use the
hot water tubing for heating already existing in the apparatus.
There are no particular limitations regarding the heat exchange
medium to be used as long as it is at a temperature higher than the
low outdoor air temperature and lower than the temperature of the
EGR gas (exhaust gas).
[0077] Further, while in the above embodiment the supercharger 11t
is used so as to expand the operation range allowing homogeneous
charge compression ignition, this is not indispensable. When it is
not so necessary to expand the operation range allowing homogeneous
charge compression ignition toward the high load side, it is also
possible to omit the control by the supercharger and the external
EGR. The case in which it is not so necessary to expand the
operation range toward the high load side corresponds, for example,
to a case in which the operation range normally used is restricted
to the low and medium load ranges as in the case of some stationary
engines. Further, while it is not so effective as in the case in
which a supercharger is used, it is also possible to expand the
operation range allowing homogeneous charge compression ignition
without using any supercharger as in the case of the range e of
FIG. 6 if the external EGR is also used on the high load side under
the control by the internal EGR, that is, in a state in which the
internal EGR is reduced, with the amount of air fuel mixture sucked
in increased. In FIG. 6, the ranges a, b, and e are ranges in which
the amount of the internal EGR gas is controlled; the range a is a
range in which intake air heating is effected at the time of low
outdoor air temperature and low load to suppress occurrence of a
misfire, and the range e is a range in which the external EGR is
also used at the time of high load to suppress knocking and expand
the operation range.
* * * * *