U.S. patent application number 12/354903 was filed with the patent office on 2009-07-23 for evaporative fuel treatment apparatus for internal combustion engine.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Masakatsu Nagai, Tomohiro Nakano, Takahiro Uchida, Shuji Yuda.
Application Number | 20090183500 12/354903 |
Document ID | / |
Family ID | 40875351 |
Filed Date | 2009-07-23 |
United States Patent
Application |
20090183500 |
Kind Code |
A1 |
Uchida; Takahiro ; et
al. |
July 23, 2009 |
EVAPORATIVE FUEL TREATMENT APPARATUS FOR INTERNAL COMBUSTION
ENGINE
Abstract
An evaporative fuel treatment apparatus for an internal
combustion engine includes: a communication portion that
communicates a plurality of branch passages with one another at
positions downstream of the plurality of throttle valves; a purge
passage that introduces purge gas, containing evaporative fuel, to
the communication portion; an air supply passage that flows
dilution air, which is used to dilute the evaporative fuel, into
the purge passage; a first flow rate changing portion that is
provided in the air supply passage and that is able to change the
inflow of the dilution air; and a control unit that controls the
first flow rate changing portion.
Inventors: |
Uchida; Takahiro;
(Toyota-shi, JP) ; Yuda; Shuji; (Gotenba-shi,
JP) ; Nagai; Masakatsu; (Hiratsuka-shi, JP) ;
Nakano; Tomohiro; (Nagoya-shi, JP) |
Correspondence
Address: |
GIFFORD, KRASS, SPRINKLE,ANDERSON & CITKOWSKI, P.C
PO BOX 7021
TROY
MI
48007-7021
US
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Aichi-Ken
JP
|
Family ID: |
40875351 |
Appl. No.: |
12/354903 |
Filed: |
January 16, 2009 |
Current U.S.
Class: |
60/295 ;
60/324 |
Current CPC
Class: |
Y02T 10/40 20130101;
F02D 41/0032 20130101; F02M 25/0827 20130101; Y02T 10/42 20130101;
F02D 41/0002 20130101; F02D 41/0085 20130101 |
Class at
Publication: |
60/295 ;
60/324 |
International
Class: |
F01N 3/00 20060101
F01N003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 18, 2008 |
JP |
JP2008-009003 |
Claims
1. An evaporative fuel treatment apparatus for an internal
combustion engine, comprising: a plurality of branch passages that
respectively communicate with a plurality of cylinders; a plurality
of throttle valves that are respectively provided in the plurality
of branch passages, wherein each of the plurality of throttle
valves is able to change the amount of air taken into a
corresponding one of the plurality of cylinders; a balancing
passage that communicates the plurality of branch passages with one
another at positions downstream of the plurality of throttle
valves; a communication portion that communicates the plurality of
branch passages with one another at positions downstream of the
plurality of throttle valves; a purge passage that introduces purge
gas, containing evaporative fuel generated in a fuel tank, to the
communication portion; an air supply passage that flows dilution
air, which is used to dilute the evaporative fuel, into the purge
passage; a first flow rate changing portion that is provided in the
air supply passage and that is able to change the inflow of the
dilution air; and a control unit that controls the first flow rate
changing portion such that the inflow of the dilution air is
changed on the basis of a comparison between the concentration of
the evaporative fuel and a predetermined concentration determined
on the basis of an operating state of the internal combustion
engine.
2. The evaporative fuel treatment apparatus for an internal
combustion engine according to claim 1, wherein the flow passage
area of the communication portion is smaller than the flow passage
area of the balancing passage.
3. The evaporative fuel treatment apparatus for an internal
combustion engine according to claim 1, wherein the dilution air is
air taken from an intake system upstream of the plurality of
throttle valves.
4. The evaporative fuel treatment apparatus for an internal
combustion engine according to claim 1, further comprising a second
flow rate changing portion that changes the flow rate of the purge
gas introduced from the fuel tank to the purge passage, wherein the
control unit controls the second flow rate changing portion such
that the flow rate of the purge gas introduced to the purge passage
reduces, when an actual flow rate of dilution air, which is
changeable by the first flow rate changing portion, is smaller than
a predetermined flow rate of the dilution air by which the
concentration of the evaporative fuel is reduced below the
predetermined concentration.
5. The evaporative fuel treatment apparatus for an internal
combustion engine according to claim 1, further comprising a
concentration determination portion that determines the
concentration of the evaporative fuel, wherein the control unit
controls the first flow rate changing portion such that the inflow
of the dilution air increases, when the determined concentration of
the evaporative fuel is higher than the predetermined
concentration, and controls the first flow rate changing portion
such that the inflow of the dilution air reduces, when the
determined concentration of the evaporative fuel is lower than the
predetermined concentration.
6. The evaporative fuel treatment apparatus for an internal
combustion engine according to claim 1, further comprising an
intake air flow rate detector that is provided in the intake system
upstream of a branch position at which the branch passages branch
off and that detects the flow rate of intake air, wherein the air
supply passage takes air out of the intake system downstream of the
intake air flow rate detector and upstream of the branch position
and flows the taken out air into the purge passage.
7. The evaporative fuel treatment apparatus for an internal
combustion engine according to claim 6, further comprising a surge
tank that is arranged downstream of the intake air flow rate
detector and upstream of the branch position and that forms part of
the intake system, wherein the air supply passage takes air out of
the surge tank and flows the taken out air into the purge
passage.
8. The evaporative fuel treatment apparatus for an internal
combustion engine according to claim 1, further comprising a mixing
promoting portion that is provided between the communication
portion and a connecting position at which the air supply passage
is connected to the purge passage, and that promotes mixing of air
introduced through the air supply passage with purge gas introduced
to the purge passage.
9. The evaporative fuel treatment apparatus for an internal
combustion engine according to claim 8, wherein the purge passage
meanders between the communication portion and the connecting
position to form the mixing promoting portion.
10. An evaporative fuel treatment apparatus for a multi-cylinder
internal combustion engine that includes a pair of first and second
banks respectively having a plurality of cylinders, comprising: a
plurality of branch passages that respectively communicate with the
plurality of cylinders in each bank; a plurality of throttle valves
that are respectively provided in the plurality of branch passages
in each bank, wherein each of the plurality of throttle valves is
able to change the amount of air taken into a corresponding one of
the plurality of cylinders; a balancing passage that communicates
the plurality of branch passages with one another at positions
downstream of the plurality of throttle valves in each bank; a
communication portion that communicates the plurality of branch
passages with one another at positions downstream of the plurality
of throttle valves in the first bank; a purge passage that
introduces purge gas, containing evaporative fuel generated in a
fuel tank, to the communication portion in the first bank; an air
supply passage that flows dilution air, which is used to dilute the
evaporative fuel, into the purge passage in the first bank; a first
flow rate changing portion that is provided in the air supply
passage in the first bank and that is able to change the inflow of
the dilution air; and a control unit that controls the opening
degrees of the plurality of throttle valves in the second bank so
that the amount of air taken into the second bank reduces by a
differential flow rate, when an actual flow rate of dilution air
that is changeable by the first flow rate changing portion is
smaller than a predetermine flow rate of the dilution air used to
reduce the concentration of the evaporative fuel below a
predetermined concentration determined on the basis of an operating
state of the internal combustion engine, wherein the differential
flow rate is a difference between the predetermined flow rate and
the actual flow rate.
11. The evaporative fuel treatment apparatus for an internal
combustion engine according to claim 10, wherein the flow passage
area of the communication portion is smaller than the flow passage
area of the balancing passage.
12. The evaporative fuel treatment apparatus for an internal
combustion engine according to claim 10, wherein the dilution air
is air taken from an intake system upstream of the plurality of
throttle valves.
13. The evaporative fuel treatment apparatus for an internal
combustion engine according to claim 10, wherein the control unit
controls the opening degrees of the plurality of throttle valves in
the second bank so that the amount of air taken into the second
bank is determined so that combustion in the cylinders of the
second bank is occurable and/or is larger than a lower limit intake
air amount determined on the basis of an air-fuel ratio required in
the second bank.
14. An evaporative fuel treatment apparatus for a multi-cylinder
internal combustion engine that includes a pair of first and second
banks respectively having a plurality of cylinders, comprising: a
plurality of branch passages that respectively communicate with the
plurality of cylinders in each bank; a plurality of throttle valves
that are respectively provided in the plurality of branch passages
in each bank, wherein each of the plurality of throttle valves is
able to change the amount of air taken into a corresponding one of
the plurality of cylinders; a balancing passage that communicates
the plurality of branch passages with one another at positions
downstream of the plurality of throttle valves in each bank; a
communication portion that communicates the plurality of branch
passages with one another at positions downstream of the plurality
of throttle valves in each bank; a purge passage that introduces
purge gas, containing evaporative fuel generated in a fuel tank, to
the communication portion in the first bank; a first air supply
passage that flows dilution air, which is used to dilute the
evaporative fuel, from an intake system upstream of the plurality
of throttle valves into the purge passage in the first bank; a
second air supply passage that flows upstream air, in the second
bank, from an intake system upstream of the plurality of throttle
valves into the communication portion of the second bank; a first
flow rate changing portion that is provided in the first air supply
passage in the first bank and that is able to change the inflow of
the dilution air; a second flow rate changing portion that is
provided in the second air supply passage in the second bank and
that is able to change the inflow of the upstream air; and a
control unit that controls the first flow rate changing portion
such that the inflow of the dilution air is changed on the basis of
a comparison between the concentration of the evaporative fuel and
a predetermined concentration determined on the basis of an
operating state of the internal combustion engine, and that
controls the second flow rate changing portion such that the inflow
of the dilution air is equalized to the inflow of the upstream
air.
15. The evaporative fuel treatment apparatus for an internal
combustion engine according to claim 14, wherein the flow passage
area of the communication portion is smaller than the flow passage
area of the balancing passage.
16. The evaporative fuel treatment apparatus for an internal
combustion engine according to claim 1, further comprising: a
second flow rate changing portion that changes the flow rate of the
purge gas introduced from the fuel tank to the purge passage; a
pressure measurement portion that measures a purge pressure at a
position downstream of the second flow rate changing portion; and
an estimation unit that estimates the purge pressure on the basis
of an operating state of the internal combustion engine, wherein
the control unit controls the first flow rate changing portion such
that the inflow of the dilution air is maintained at a constant
value, when the pressure measurement portion fails.
17. The evaporative fuel treatment apparatus for an internal
combustion engine according to claim 10, further comprising: a
second flow rate changing portion that changes the flow rate of the
purge gas introduced from the fuel tank to the purge passage; a
pressure measurement portion that measures a purge pressure at a
position downstream of the second flow rate changing portion; and
an estimation unit that estimates the purge pressure on the basis
of an operating state of the internal combustion engine, wherein
the control unit controls the first flow rate changing portion such
that the inflow of the dilution air is maintained at a constant
value, when the pressure measurement portion fails.
18. The evaporative fuel treatment apparatus for an internal
combustion engine according to claim 14, further comprising: a
second flow rate changing portion that changes the flow rate of the
purge gas introduced from the fuel tank to the purge passage; a
pressure measurement portion that measures a purge pressure at a
position downstream of the second flow rate changing portion; and
an estimation unit that estimates the purge pressure on the basis
of an operating state of the internal combustion engine, wherein
the control unit controls the first flow rate changing portion such
that the inflow of the dilution air is maintained at a constant
value, when the pressure measurement portion fails.
Description
INCORPORATION BY REFERENCE
[0001] The disclosure of Japanese Patent Application No.
2008-009003 filed on Jan. 18, 2008 including the specification,
drawings and abstract is incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a technical field of an evaporative
fuel treatment apparatus for an internal combustion engine, which
treats evaporative fuel generated in a fuel tank.
[0004] 2. Description of the Related Art
[0005] An evaporative fuel treatment apparatus for an internal
combustion engine of this type is, for example, described in
Japanese Utility Model Publication No. 3-53009 (JP-Y-3-53009).
JP-Y-3-53009 describes an evaporative fuel treatment apparatus that
is applied to an internal combustion engine in which a throttle
valve is arranged in each independent intake pipe provided for each
cylinder. In this evaporative fuel treatment apparatus, the
independent intake pipes are in fluid communication with all the
cylinders via a communication pipe, which is common to all the
cylinders, at positions downstream of the throttle valves, and then
the communication pipe is connected to a purge pipe that introduces
purge gas containing evaporative fuel generated in a fuel tank. In
addition, Japanese Patent Application Publication No. 7-189820
(JP-A-7-189820) describes an evaporative fuel treatment apparatus
in which an assist air type fuel injection valve is arranged in
each independent intake passage provided for each cylinder, a purge
passage is connected to an assist air passage that feeds air to the
fuel injection valve, and then purge gas is supplied together with
assist air through the fuel injection valve to each independent
intake passage. Moreover, a technique is suggested, which, in an
internal combustion engine in which a throttle valve is arranged in
each of the above described independent intake pipes, a throttle
portion (opening area is invariable) is provided in an air supply
passage.
[0006] On the other hand, for example, Japanese Patent Application
Publication No. 08-144818 (JP-A-08-144818) describes a technique
that, in a V-engine that has an independent intake system and
exhaust system in each bank, a purge passage is switched to stop
the inflow of purge gas bank by bank. In addition, Japanese Patent
Application Publication No. 5-79359 (JP-A-5-79359) describes a
multi-cylinder internal combustion engine that includes an
independent throttle valve provided in an intake passage of each
cylinder and a second throttle valve provided in a common intake
passage upstream of the independent throttle valves. Moreover, a
technique is suggested, which a pressure in the intake pipe is
calculated to efficiently cause purge gas to flow into the internal
combustion engine.
[0007] These apparatuses introduce purge gas to positions
downstream of the throttle valves through the communication pipe;
however, this may cause an abrupt change in air-fuel ratio because
the directly introduced evaporative fuel has a high concentration.
Specifically, in a single throttle valve type in which a single
throttle valve is provided to control the amount of intake air, a
surge tank is provided downstream of the throttle valve. Thus,
evaporative fuel (so-called, vapor) may be diluted by a large
amount of air that is storable in the surge tank, so the need for
an exclusive dilution device other than the surge tank is low. In
contrast, in an independent throttle valve type in which a
plurality of throttle valves are provided and actuated
independently of one another, it is impossible to provide space for
storing air, like a surge tank, for each cylinder. Thus, it is
generally difficult to dilute evaporative fuel. Furthermore, when
the absolute amount of intake air required by the internal
combustion engine is small as in the case of idling, the amount of
intake air that is usable for diluting evaporative fuel is also
small. In addition, because the rotational speed of the internal
combustion engine is controlled by the throttle valves during
idling, it is necessary to ensure an allowable range within which
the throttle valves are actuated to a closing side; however, in the
independent throttle valve type, the leakage flow rate of the
throttle valve for each cylinder needs to be considered and,
therefore, the margin for closing the throttle valve necessarily
decreases.
SUMMARY OF THE INVENTION
[0008] The invention provides an evaporative fuel treatment
apparatus for an internal combustion engine, which is able to
appropriately treat evaporative fuel while suppressing an abrupt
change in air-fuel ratio.
[0009] A first aspect of the invention provides an evaporative fuel
treatment apparatus for an internal combustion engine. The
evaporative fuel treatment apparatus includes: a plurality of
branch passages that respectively communicate with a plurality of
cylinders; a plurality of throttle valves that are respectively
provided in the plurality of branch passages, wherein each of the
plurality of throttle valves is able to change the amount of air
taken into a corresponding one of the plurality of cylinders; a
balancing passage that communicates the plurality of branch
passages with one another at positions downstream of the plurality
of throttle valves; a communication portion that communicates the
plurality of branch passages with one another at positions
downstream of the plurality of throttle valves; a purge passage
that introduces purge gas, containing evaporative fuel generated in
a fuel tank, to the communication portion; an air supply passage
that flows dilution air, which is used to dilute the evaporative
fuel, into the purge passage; a first flow rate changing portion
that is provided in the air supply passage and that is able to
change the inflow of the dilution air; and a control unit that
controls the first flow rate changing portion such that the inflow
of the dilution air is changed on the basis of a comparison between
the concentration of the evaporative fuel and a predetermined
concentration determined on the basis of an operating state of the
internal combustion engine.
[0010] According to the evaporative fuel treatment apparatus for an
internal combustion engine in the first aspect, the balancing
passage communicates the plurality of branch passages with one
another at positions downstream of the plurality of throttle
valves. The balancing passage implements the function of equalizing
the pressures in the intake pipes corresponding to the respective
cylinders, that is, a so-called balancing function. Specifically,
the balancing passage is able to reduce variations in the amounts
of air that flows through the throttle valves and the amounts of
air taken into the respective cylinders. In other words, the
negative pressures (that is, the amounts of intake air) in the
respective cylinders downstream of the throttle valves are
equalized. Note that the flow passage area according to the aspects
of the invention means the cross-sectional area of a passage
through which fluid flows.
[0011] The flow passage area of the communication portion may be
smaller than the flow passage area of the balancing passage. With
the above configuration, the pressure in the communication portion
is higher than the pressure in each branch passage because of the
flow resistance of the communication portion. Thus, steady flow is
formed. Specifically, the communication portion may be a passage
having a narrow diameter such that pulsation does not occur inside
or considerably small pulsation occurs.
[0012] The purge passage utilizes the steady flow to introduce
purge gas, containing evaporative fuel generated in the fuel tank,
to each branch passage through the communication portion and
finally introduces the purge gas to each cylinder. Thus, because
purge gas is introduced into the branch passages, evaporative fuel
may be treated without releasing the evaporative fuel to the
atmosphere.
[0013] The plurality of throttle valves are respectively provided
in the plurality of branch passages, and each of the plurality of
throttle valves is able to change the amount of air taken into a
corresponding one of the plurality of cylinders.
[0014] The air supply passage may flow dilution air, which is used
to dilute the evaporative fuel, from an intake system upstream of
the plurality of throttle valves into the purge passage. With this
configuration, purge gas introduced into the branch passages is
diluted with dilution air introduced through the air supply
passage.
[0015] Particularly, under the control of the control unit, the
first flow rate changing portion changes the flow rate of the
dilution air on the basis of a comparison between the concentration
of the evaporative fuel and a predetermined concentration
determined on the basis of an operating state of the internal
combustion engine. In other words, the flow rate of the dilution
air is uniquely changed on the basis of a comparison in magnitude
between the concentration of the evaporative fuel and the
predetermined concentration. Here, the "operating state" according
to the aspects of the invention may mean various states that
quantitatively or qualitatively indicates the state of the internal
combustion engine, such as the rotational speed of the internal
combustion engine, the load on the internal combustion engine, such
as the amount of fuel injection or the amount of intake air, the
speed of a vehicle equipped with the internal combustion engine, or
the driver's accelerator operation amount of a vehicle equipped
with the internal combustion engine. In addition, the
"concentration of evaporative fuel" according to the aspects of the
invention may mean the concentration of evaporative fuel contained
in purge gas or may basically mean "percent by weight" throughout.
Alternatively, as long as the same evaporative fuel is referenced,
the "concentration of evaporative fuel" may be percent by volume.
Alternatively, in terms of the meaning that the relative rate of
evaporative fuel in purge gas, the "concentration of evaporative
fuel" may be dimensionless.
[0016] Specifically, when the concentration of evaporative fuel is
higher than the above described predetermined concentration, the
first flow rate changing portion increases the inflow of dilution
air. On the other hand, when the concentration of evaporative fuel
is lower than the above described predetermined concentration, the
first flow rate changing portion reduces the inflow of dilution
air. More specifically, the concentration of evaporative fuel may
be controlled so as to converge on the predetermined concentration
over time. Alternatively, the concentration of evaporative fuel may
be controlled so as to be lower than the predetermined
concentration. Thus, purge gas that contains a remarkably high
concentration of evaporative fuel above the predetermined
concentration is substantially or completely not introduced into
the branch passages. Thus, it is possible to suppress variations in
the air-fuel ratio due to purge gas among the branch passages and
among the cylinders and, therefore, it is possible to appropriately
prevent an abrupt change in the air-fuel ratio. Alternatively,
purge gas that contains a remarkably low concentration of
evaporative fuel below the predetermined concentration is
substantially or completely not introduced into the branch
passages. Thus, it is possible to appropriately prevent an abrupt
change in the air-fuel ratio due to purge gas.
[0017] Particularly, the first flow rate changing portion increases
the inflow of dilution air that flows through the air supply
passage. Thus, it is possible to effectively prevent purge gas that
contains an unnecessarily high concentration of evaporative fuel
from being introduced to the branch passages due to a negative
pressure generated at positions downstream of the throttle valves,
for example, when the opening degrees of the throttle valves are
reduced. Thus, the rotational speed of the internal combustion
engine is easily maintained at a low rotational speed. Typically,
in addition to the control of the opening degree of each throttle
valve, the first flow rate changing portion adjusts the inflow of
dilution air. Thus, it is possible to stabilize the control of the
air-fuel ratio at a low rotational speed, such as during idling,
and, therefore, it is possible to stabilize the operating state at
a low rotational speed.
[0018] As described above, according to the evaporative fuel
treatment apparatus for an internal combustion engine in the first
aspect, because purge gas introduced into the branch passages is
diluted by air introduced through the air supply passage, purge gas
that contains a remarkably high concentration of evaporative fuel
is substantially or completely not introduced into the branch
passages. Thus, it is possible to suppress variations in the
air-fuel ratio due to purge gas among the cylinders and, therefore,
it is possible to appropriately prevent an abrupt change in the
air-fuel ratio.
[0019] If, without changing the inflow of dilution air on the basis
of the vapor concentration by the first flow rate changing portion,
the opening degree of each throttle valve is controlled alone,
high-concentration purge gas is drawn into the cylinders, so the
air-fuel ratio varies among the cylinders due to the purge gas, and
the air-fuel ratio abruptly changes. Alternatively, variations in
the air-fuel ratio among the cylinders increase when the
distribution of purge gas to the cylinders varies due to the
influence of pulsation, or the like. This causes deterioration in
drivability, such as engine vibration, or causes decrease in
stability of the control of the air-fuel ratio. In addition,
exhaust emission deteriorates.
[0020] A second aspect of the invention provides an evaporative
fuel treatment apparatus for a multi-cylinder internal combustion
engine that includes a pair of first and second banks respectively
having a plurality of cylinders. The evaporative fuel treatment
apparatus includes: a plurality of branch passages that
respectively communicate with the plurality of cylinders in each
bank; a plurality of throttle valves that are respectively provided
in the plurality of branch passages in each bank, wherein each of
the plurality of throttle valves is able to change the amount of
air taken into a corresponding one of the plurality of cylinders; a
balancing passage that communicates the plurality of branch
passages with one another at positions downstream of the plurality
of throttle valves in each bank; a communication portion that
communicates the plurality of branch passages with one another at
positions downstream of the plurality of throttle valves in the
first bank; a purge passage that introduces purge gas, containing
evaporative fuel generated in a fuel tank, to the communication
portion in the first bank; an air supply passage that flows
dilution air, which is used to dilute the evaporative fuel, into
the purge passage in the first bank; a first flow rate changing
portion that is provided in the air supply passage in the first
bank and that is able to change the inflow of the dilution air; and
a control unit that controls the opening degrees of the plurality
of throttle valves in the second bank so that the amount of air
taken into the second bank reduces by a differential flow rate,
when an actual flow rate of dilution air that is changeable by the
first flow rate changing portion is smaller than a predetermine
flow rate of the dilution air used to reduce the concentration of
the evaporative fuel below a predetermined concentration determined
on the basis of an operating state of the internal combustion
engine, wherein the differential flow rate is a difference between
the predetermined flow rate and the actual flow rate.
[0021] According to the evaporative fuel treatment apparatus for an
internal combustion engine in the second aspect, in a
multi-cylinder internal combustion engine that includes a pair of
first and second banks respectively having a plurality of
cylinders, such as a V-engine, the plurality of branch passages
respectively communicate with the plurality of cylinders in each
bank. The plurality of throttle valves are respectively provided in
the plurality of branch passages in each bank, and each of the
plurality of throttle valves is able to change the amount of air
taken into a corresponding one of the plurality of cylinders. The
balancing passage communicates the plurality of branch passages
with one another at positions downstream of the plurality of
throttle valves in each bank. The communication portion in the
first bank communicates the plurality of branch passages with one
another at positions downstream of the plurality of throttle
valves. The flow passage area (cross-sectional area) of the
communication portion may be smaller than the flow passage area of
the balancing passage. The purge passage in the first bank
introduces purge gas, containing evaporative fuel generated in a
fuel tank, to the communication portion. The air supply passage in
the first bank flows dilution air, which is used to dilute the
evaporative fuel, into the purge passage. The first flow rate
changing portion in the first bank is provided in the air supply
passage and is able to change the inflow of the dilution air. The
dilution air may be air taken from an intake system upstream of the
plurality of throttle valves.
[0022] Particularly, when an actual flow rate of dilution air that
is changeable by the first flow rate changing portion is smaller
than a predetermine flow rate of the dilution air used to reduce
the concentration of the evaporative fuel below a predetermined
concentration determined on the basis of an operating state of the
internal combustion engine, under the control of the control unit,
the opening degrees of the plurality of throttle valves in the
second bank are controlled so that the amount of air taken into the
second bank reduces by a differential flow rate, which is a
difference between the predetermined flow rate and the actual flow
rate. In addition, not only the differential in flow rate is
controlled, but also a target number of revolutions of the engine
is maintained.
[0023] If the inflow of dilution air used to dilute purge gas that
contains evaporative fuel is insufficient, and when the flow rate
of purge gas, containing evaporative fuel and flowing into the
internal combustion engine, is restricted by the above described
second flow rate changing portion, such as the purge gas variable
throttle valve, in order to prevent engine stop and poor
drivability due to imbalanced distribution of evaporative fuel
among the cylinders, evaporative fuel contained in purge gas also
reduces. As a result, the total amount of evaporative fuel drawn
into the internal combustion engine reduces and, therefore, purge
gas flows out to the atmosphere.
[0024] In contrast, according to the evaporative fuel treatment
apparatus for an internal combustion engine in the second aspect,
when an actual flow rate of dilution air that is changeable by the
first flow rate changing portion is smaller than a predetermine
flow rate of the dilution air used to reduce the concentration of
the evaporative fuel below a predetermined concentration determined
on the basis of an operating state of the internal combustion
engine, under the control of the control unit, the opening degrees
of the plurality of throttle valves in the second bank are
controlled so that the amount of air taken into the second bank
reduces by a differential flow rate, which is a difference between
the predetermined flow rate and the actual flow rate. Thus, it is
possible to additionally assign air, which is originally assigned
to the second bank, to the first bank by the differential flow
rate. Hence, in the first bank, it is possible to ensure dilution
air by the above described predetermined flow rate. Thus, it is not
necessary that the above second flow rate changing portion, such as
a purge gas variable throttle valve, reduces the flow rate of purge
gas introduced to the purge passage, and the total amount of
evaporative fuel drawn into all the cylinders of the pair of banks
is not reduced. Hence, it is possible to prevent purge gas from
being released to the atmosphere.
[0025] Particularly, the necessary inflow of dilution air used to
dilute evaporative fuel in the first bank is ensured while the
total amount of air taken into both the banks is not varied. This
makes it easy to maintain the rotational speed of the internal
combustion engine at a low rotational speed and at a target
rotational speed. This is because a drive shaft is shared between
the first bank and the second bank, the total of the amount of air
taken into the first bank and the amount of air taken into the
second bank ensures the amount of air that achieves a target torque
by which a low rotational speed may be maintained. Typically, in
addition to the control of the opening degree of each throttle
valve of the first bank and the adjustment to increase the inflow
of dilution air by the first flow rate changing portion, by
controlling each throttle valve of the second bank to reduce the
opening degree, it is possible to stabilize the control of the
air-fuel ratio at a low rotational speed, such as during idling,
and, therefore, it is possible to stabilize the operating state at
a low rotational speed.
[0026] A third aspect of the invention provides an evaporative fuel
treatment apparatus for a multi-cylinder internal combustion engine
that includes a pair of first and second banks respectively having
a plurality of cylinders. The evaporative fuel treatment apparatus
includes: a plurality of branch passages that respectively
communicate with the plurality of cylinders in each bank; a
plurality of throttle valves that are respectively provided in the
plurality of branch passages in each bank, wherein each of the
plurality of throttle valves is able to change the amount of air
taken into a corresponding one of the plurality of cylinders; a
balancing passage that communicates the plurality of branch
passages with one another at positions downstream of the plurality
of throttle valves in each bank; a communication portion that
communicates the plurality of branch passages with one another at
positions downstream of the plurality of throttle valves in each
bank; a purge passage that introduces purge gas, containing
evaporative fuel generated in a fuel tank, to the communication
portion in the first bank; a first air supply passage that flows
dilution air, which is used to dilute the evaporative fuel, from an
intake system upstream of the plurality of throttle valves into the
purge passage in the first bank; a second air supply passage that
flows upstream air, in the second bank, from an intake system
upstream of the plurality of throttle valves into the communication
portion of the second bank; a first flow rate changing portion that
is provided in the first air supply passage in the first bank and
that is able to change the inflow of the dilution air; a second
flow rate changing portion that is provided in the second air
supply passage in the second bank and that is able to change the
inflow of the upstream air; and a control unit that controls the
first flow rate changing portion such that the inflow of the
dilution air is changed on the basis of a comparison between the
concentration of the evaporative fuel and a predetermined
concentration determined on the basis of an operating state of the
internal combustion engine, and that controls the second flow rate
changing portion such that the inflow of the dilution air is
equalized to the inflow of the upstream air.
[0027] According to the evaporative fuel treatment apparatus for an
internal combustion engine in the third aspect, in a multi-cylinder
internal combustion engine that includes a pair of first and second
banks respectively having a plurality of cylinders, such as a
V-engine, the plurality of branch passages respectively communicate
with the plurality of cylinders in each bank.
[0028] The plurality of throttle valves are respectively provided
in the plurality of branch passages in each bank, and each of the
plurality of throttle valves is able to change the amount of air
taken into a corresponding one of the plurality of cylinders. The
balancing passage communicates the plurality of branch passages
with one another at positions downstream of the plurality of
throttle valves in each bank.
[0029] The communication portion communicates the plurality of
branch passages with one another at positions downstream of the
plurality of throttle valves in each bank. The flow passage area
(cross-sectional area) of the communication portion may be smaller
than the flow passage area of the balancing passage.
[0030] The purge passage introduces purge gas, containing
evaporative fuel generated in a fuel tank, to the communication
portion in the first bank.
[0031] The first air supply passage flows dilution air, which is
used to dilute the evaporative fuel, from an intake system upstream
of the plurality of throttle valves into the purge passage in the
first bank.
[0032] The second air supply passage flows upstream air, in the
second bank, from an intake system upstream of the plurality of
throttle valves into the communication portion of the second
bank.
[0033] The first flow rate changing portion is provided in the
first air supply passage in the first bank and is able to change
the inflow of the dilution air.
[0034] The second flow rate changing portion is provided in the
second air supply passage in the second bank and is able to change
the inflow of the upstream air.
[0035] Thus, the flow resistance of air that flows through the
communication portion, the purge passage, the first air supply
passage and the first flow rate changing portion in the first bank
may be equalized to the flow resistance of air that flows through
the communication portion, the second air supply passage and the
second flow rate changing portion in the second bank. Thus, it is
possible to coincide the amount of air that flows through the
throttle valves and first air supply passage of the first bank with
the amount of air that flows through the throttle valves and second
air supply passage of the second bank.
[0036] Particularly, under the control of the control unit, the
first flow rate changing portion changes the inflow of dilution air
on the basis of a comparison between the concentration of the
evaporative fuel and a predetermined concentration determined on
the basis of an operating state of the internal combustion engine.
In addition to this, under the control of the control unit, the
second flow rate changing portion changes the inflow of upstream
air so as to be equal to the inflow of dilution air.
[0037] If the flow resistance of air that flows through the
communication portion, the purge passage, the first air supply
passage and the first flow rate changing portion in the first bank
cannot be made substantially equal to the flow resistance of air
that flows through the communication portion, the second air supply
passage and the second flow rate changing portion in the second
bank, that is, if the amount of air that flows through the throttle
valves and first air supply passage of the first bank does not
coincide with the amount of air that flows through the throttle
valves and second air supply passage of the second bank, the range
of characteristics of the opening degree of each throttle valve in
the first bank differs from the range of characteristics of the
opening degree of each throttle valve in the second bank. Thus, for
example, control of the air-fuel ratio at a low rotational speed,
such as during idling, becomes unstable. In other words, if the
first flow rate changing portion is provided for the first bank and
no second flow rate changing portion is provided for the second
bank, the operation of each throttle valve in the first bank, to
which purge gas that contains evaporative fuel flows, causes
relatively small rate of change in the amount of intake air against
the opening degree of each throttle valve, and the amount of intake
air does not change much only by varying the opening degree of each
throttle valve in some degree. In contrast, the operation of each
throttle valve in the second bank, to which no purge gas that
contains evaporative fuel flows, causes relatively large rate of
change in the amount of intake air in association with the opening
degree of each throttle valve, and the amount of intake air
relatively changes by a large amount even when the opening degree
of each throttle valve is varied a little.
[0038] In detail, the resolution of control of the opening degree
of each throttle valve is restricted by hardware. For example, 0.03
degree is the minimum unit of control of the opening degree of each
throttle valve. Thus, when the throttle valves having largely
different opening degree characteristics are used respectively in
both banks, a variation in the amount of intake air per the above
described minimum unit, that is, an increase or a decrease in
actual rotational speed of the internal combustion engine, varies
between both banks. Thus, there is a possibility that variations in
rotational speed during idling may occur in at least one of the
banks.
[0039] In contrast, according to the evaporative fuel treatment
apparatus for an internal combustion engine in the third aspect,
under the control of the control unit, the first flow rate changing
portion changes the inflow of dilution air on the basis of a
comparison between the concentration of the evaporative fuel and a
predetermined concentration determined on the basis of an operating
state of the internal combustion engine. In addition to this, under
the control of the control unit, the second flow rate changing
portion equalizes the inflow of dilution air to the inflow of
upstream air. Thus, because it is possible to control both banks
substantially in the same manner, it is possible to suppress
variations in rotational speed due to a torque difference caused by
a difference in the amount of air between both banks during
idling.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The features, advantages, and technical and industrial
significance of this invention will be described in the following
detailed description of example embodiments of the invention with
reference to the accompanying drawings, in which like numerals
denote like elements, and wherein:
[0041] FIG. 1 is a block diagram that shows a relevant portion of
an internal combustion engine to which an evaporative fuel
treatment apparatus according to a first embodiment of the
invention is applied;
[0042] FIG. 2 is a schematic cross-sectional view that is taken
along the line II-II in FIG. 1;
[0043] FIG. 3 is a flowchart that shows the control process flow of
an ECU that controls the evaporative fuel treatment apparatus for
the internal combustion engine according to the first embodiment of
the invention;
[0044] FIG. 4A is a graph that schematically shows the relationship
between an operating state of the internal combustion engine and a
predetermined concentration according to the first embodiment of
the invention;
[0045] FIG. 4B is a graph that schematically shows the relationship
between the inflow of dilution air, which is determined on the
basis of the predetermined concentration in FIG. 4A, and an
operating state of the internal combustion engine;
[0046] FIG. 5A is a graph that shows changes in the operating state
of the internal combustion engine according to the first embodiment
of the invention;
[0047] FIG. 5B is a graph that shows changes in the inflow of
dilution air according to the first embodiment of the
invention;
[0048] FIG. 5C is a graph that shows changes in the concentration
of evaporative fuel (so-called, vapor) according to the first
embodiment of the invention;
[0049] FIG. 6 is a schematic diagram that shows the basic
configuration of an evaporative fuel treatment apparatus for an
internal combustion engine according to a second embodiment of the
invention;
[0050] FIG. 7A is a bar graph that shows the distribution of the
amount of intake air during normal idling and when dilution air is
increased, in a pair of banks according to the second embodiment of
the invention;
[0051] FIG. 7B is a graph that adds the differential flow rate to
FIG. 7A;
[0052] FIG. 8 is a schematic diagram that shows the basic
configuration of an evaporative fuel treatment apparatus for an
internal combustion engine according to a third embodiment of the
invention;
[0053] FIG. 9A is a bar graph that shows the distribution of the
amount of intake air during idling in a pair of banks according to
a comparative embodiment;
[0054] FIG. 9B is a graph that shows the relationship between the
opening degree of a throttle valve and the amount of intake air
through the throttle valve, in the pair of banks according to the
comparative embodiment;
[0055] FIG. 9C is a bar graph that shows the distribution of the
amount of intake air during idling in a pair of banks according to
the third embodiment of the invention;
[0056] FIG. 10 is a flowchart that shows the operating principle of
an evaporative fuel treatment apparatus for an internal combustion
engine according to a fourth embodiment of the invention;
[0057] FIG. 11 is another flowchart that shows the operating
principle of the evaporative fuel treatment apparatus for an
internal combustion engine according to the fourth embodiment of
the invention;
[0058] FIG. 12A is a graph that shows a common example of the
relationship among a purge pressure, at a position downstream of a
purge gas variable throttle valve and upstream of a purge passage,
an intake pipe pressure, and the opening degree of a variable flow
rate valve; and
[0059] FIG. 12B is a graph that shows a common example of the
relationship between the flow rate of purge gas and a purge
pressure at a position downstream of the purge gas variable
throttle valve and upstream of the purge passage.
DETAILED DESCRIPTION OF EMBODIMENTS
[0060] First, the basic configuration of an evaporative fuel
treatment apparatus for an internal combustion engine according to
a first embodiment of the invention will be described with
reference to FIG. 1 and FIG. 2. FIG. 1 is a block diagram that
shows a relevant portion of the internal combustion engine to which
the evaporative fuel treatment apparatus according to the first
embodiment of the invention is applied. FIG. 2 is a schematic
cross-sectional view that is taken along the line II-II in FIG.
1.
[0061] The internal combustion engine 1 includes cylinders 2, an
intake passage 3, branch passages 3a, a surge tank 3b, throttle
valves 7, a balancing passage 9, a purge passage 10, a
communication portion 10a, a mixing promoting portion 10b, a
canister 11, an air introducing pipe 11a, an air supply passage 12,
a purge gas variable throttle valve 14, a purge pressure sensor 15,
an air-fuel ratio sensor 19, and a fuel tank 20.
[0062] The internal combustion engine 1 is an in-line four-cylinder
spark ignition internal combustion engine (multi-cylinder internal
combustion engine) in which the four cylinders 2 are arranged in
one direction. Each cylinder 2 is connected to the intake passage 3
and an exhaust passage 4. The intake passage 3 includes the branch
passages 3a branched in correspondence with the cylinders 2 and the
surge tank 3b connected to the branch passages 3a. An air cleaner 5
for filtering air is provided upstream of the surge tank 3b. An air
flow meter 6 is provided in the intake passage 3 downstream of the
air cleaner 5 and upstream of a position at which the branch
passages 3a branch off. The air flow meter 6 is able to detect the
flow rate of intake air. The throttle valve 7 is provided one by
one in each branch passage 3a. The opening degree of each throttle
valve 7 may be adjusted so that the flow rate of intake air is
adjustable. An injector 8 that injects fuel is provided downstream
of each throttle valve 7 one by one in each branch passage 3a. Each
throttle valve 7 is attached to a valve shaft 7a that extends
through the branch passages 3a, and the valve shaft 7a is driven by
an actuator 7b for rotation. Thus, each throttle valve 7 serves as
a so-called independent throttle valve. Note that the air flow
meter 6 constitutes a specific example of an intake air flow rate
detector according to the aspects of the invention.
[0063] As shown in FIG. 2, the balancing passage 9 is provided
downstream of the throttle valves 7. The balancing passage 9
communicates the branch passages 3a with one another at positions
downstream of the throttle valves 7 in order to reduce a difference
in pressure among the branch passages 3a. In addition, the purge
passage 10 is connected to the branch passages 3a so as to face the
balancing passage 9. The purge passage 10 introduces purge gas
containing vapor (evaporative fuel) generated in the fuel tank 20.
The purge passage 10 has the communication portion 10a that
communicates the branch passages 3a with one another at positions
downstream of the throttle valves 7. The flow passage area of the
communication portion 10a is smaller than the flow passage area of
the balancing passage 9. The absolute size of the flow passage area
of the communication portion 10a may be set as appropriate. The
flow passage area of the communication portion 10a is desirably set
to a size such that pulsation does not occur in the communication
portion 10a or considerably small pulsation occurs.
[0064] As shown in FIG. 1, the purge passage 10 is connected to the
fuel tank 20 through the canister 11 that adsorbs evaporative fuel.
The canister 11 is a known one that adsorbs evaporative fuel,
introduced from the fuel tank 20, with internal activated carbon
while air is introduced through the air introducing pipe 11a that
opens to the atmosphere.
[0065] The purge gas variable throttle valve 14 is provided
downstream of the canister 11 toward the purge passage 10 as a
purge gas flow rate changing portion that changes the flow rate of
purge gas. The purge gas variable throttle valve 14 is able to
adjust the opening degree so that the flow rate of purge gas
introduced to the purge passage 10 is adjustable. Note that the
purge gas variable throttle valve 14 is a specific example of a
second flow rate changing portion according to the aspects of the
invention.
[0066] The air supply passage 12 is connected between the purge gas
variable throttle valve 14 and the purge passage 10, and introduces
air into the purge passage 10. The other end of the air supply
passage 12 is connected to the surge tank 3b.
[0067] A variable flow rate valve 13 is provided in the air supply
passage 12. The variable flow rate valve 13 serves as a flow rate
changing portion that changes the flow rate of air flowing from the
air supply passage 12 to the purge passage 10. The variable flow
rate valve 13 is able to adjust the opening degree so that the flow
rate of air flowing into the purge passage 10 is adjustable. As air
flows from the air supply passage 12 into the purge passage 10,
purge gas that flows through the purge passage 10 is diluted by the
air. Note that the variable flow rate valve 13 is a specific
example of a first flow rate changing portion according to the
aspects of the invention.
[0068] The mixing promoting portion 10b is provided downstream of a
position at which the air supply passage 12 is connected to the
purge passage 10. The mixing promoting portion 10b promotes mixing
of purge gas with air. The mixing promoting portion 10b is formed
of the meandering purge passage 10, and serves as a specific
example of a mixing promoting portion according to the aspects of
the invention.
[0069] The air-fuel ratio sensor 19 is provided in the exhaust
passage 4. The air-fuel ratio sensor 19 may be configured to be
able to estimate an air-fuel ratio in each cylinder 2.
[0070] The purge pressure sensor 15 measures a pressure at a
position downstream of the purge gas variable throttle valve 14 and
upstream of the purge passage 10. Note that the purge pressure
sensor 15 is a specific example of a pressure measurement portion
according to the aspects of the invention.
[0071] An engine control unit (ECU) 16 controls various components
that constitute the internal combustion engine 1. Note that the ECU
16 is a specific example of a control unit according to the aspects
of the invention.
[0072] According to the above embodiment, because the flow passage
area of the communication portion 10a is smaller than that of the
balancing passage 9, the pressure in the communication portion 10a
is higher than that in each branch passage 3a due to the flow
resistance of the communication portion 10a. Thus, steady flow is
formed as shown by the arrows in FIG. 2. Purge gas is introduced
into the branch passages 3a using that steady flow, so evaporative
fuel may be treated without being released to the atmosphere.
[0073] Particularly, according to the present embodiment, the flow
rate of air used to dilute the purge gas that is introduced into
the branch passages 3a may be changed by the variable flow rate
valve 13 provided in the air supply passage 12. Thus, when purge
gas that contains a high concentration of evaporative fuel is
introduced to the branch passages 3a, the variable flow rate valve
13 increases the flow rate of air to thereby make it possible to
suppress an abrupt change in the air-fuel ratio toward the rich
side. Note that the air-fuel ratio is determined on the basis of
the number of revolutions of the internal combustion engine and the
load on the internal combustion engine.
[0074] On the other hand, when purge gas that contains a low
concentration of evaporative fuel is introduced to the branch
passages 3a, the variable flow rate valve 13 reduces the flow rate
of air to thereby make it possible to suppress an abrupt change in
the air-fuel ratio toward the lean side. Specifically, the variable
flow rate valve 13 provided in the air supply passage 12 is able to
reduce the flow rate of air, flowing from the air supply passage 12
into the purge passage 10. This can prevent unnecessary air from
flowing into the purge passage 10 when the opening degrees of the
throttle valves 7 are reduced. Thus, the internal combustion engine
1 is easily maintained at a low rotational speed and, therefore,
for example, the rotational speed of the internal combustion engine
1 is stable during idling.
[0075] In addition to or in place of this, as described above, the
opening degree of the purge gas variable throttle valve 14 may be
adjusted so that the flow rate of purge gas introduced to the purge
passage 10 is adjustable. Then, when purge gas that contains an
extremely high concentration of evaporative fuel is introduced to
the branch passages 3a, and when it is difficult to suppress an
abrupt change in the air-fuel ratio toward the rich side only by
increasing the flow rate of air using the variable flow rate valve
13, the purge gas variable throttle valve 14 reduces the flow rate
of purge gas introduced to the purge passage 10. Thus, evaporative
fuel introduced to the branch passages 3a may be reduced, so it is
possible to further appropriately and quickly suppress an abrupt
change in the air-fuel ratio toward the rich side.
[0076] In addition, the position, at which air is taken out into
the air supply passage 12, is located downstream of the air flow
meter 6 and, therefore, purge gas is diluted by the air that is
measured by the air flow meter 6. Thus, the amount of fuel
injection may be determined by allowing for the amount of air used
for dilution and, as a result, it is possible to further suppress
variations in the air-fuel ratio. In addition, the air is taken out
from the surge tank 3b, so it is possible to prevent intake
pulsation from influencing supply of air through the air supply
passage 12. Furthermore, the mixing promoting portion 10b is formed
by meandering the purge passage 10. Thus, no additional component
other than the purge passage 10 is required, so the number of
components that implement the mixing promoting portion may be
reduced.
[0077] Next, the operation principle of the evaporative fuel
treatment apparatus for an internal combustion engine according to
the first embodiment of the invention will be described with
reference to FIG. 3 to FIG. 5C. FIG. 3 is a flowchart that shows
the control process flow of the ECU that controls the evaporative
fuel treatment apparatus for an internal combustion engine
according to the first embodiment of the invention. FIG. 4A is a
graph that schematically shows the relationship between an
operating state of the internal combustion engine and a
predetermined concentration according to the first embodiment of
the invention. FIG. 4B is a graph that schematically shows the
relationship between the inflow of dilution air, which is
determined on the basis of the predetermined concentration in FIG.
4A, and an operating state of the internal combustion engine. FIG.
5A is a graph that shows changes in the operating state of the
internal combustion engine according to the first embodiment of the
invention. FIG. 5B is a graph that shows changes in the inflow of
dilution air according to the first embodiment of the invention.
FIG. 5C is a graph that shows changes in the concentration of
evaporative fuel (so-called, vapor) according to the first
embodiment of the invention. Note that the ordinate axis of FIG. 5A
represents a vehicle speed (km/h), and the abscissa axis of FIG. 5A
represents time. The ordinate axis of FIG. 5B represents the inflow
of dilution air, and the abscissa axis of FIG. 5B represents time.
The ordinate axis of FIG. 5C represents a vapor concentration (%),
and the abscissa axis of FIG. 5C represents time.
[0078] As shown in FIG. 3, under the control of the ECU 16, it is
determined whether an execution condition for executing purge
control in which purge gas containing evaporative fuel is
appropriately diluted by dilution air is satisfied (step S101).
When it is determined that the execution condition for executing
the purge control is satisfied (step S101: Yes), under the control
of the ECU 16, the flow rate of purge gas introduced to the purge
passage 10 is determined on the basis of the operating state of the
internal combustion engine, and then the opening degree of the
purge gas variable throttle valve 14 and the duration during which
the opening degree of the purge gas variable throttle valve 14 is
maintained, so-called purge rate pgr, are calculated (step
S102).
[0079] Subsequently, under the control of the ECU 16, the
concentration of vapor (vapor concentration) fgpg per one percent
of the purge rate is calculated (step S103). Note that at this
time, the average fgpgsm of the vapor concentration fgpg (average
vapor concentration fgpgsm) for a predetermined duration may be
calculated. Particularly, the vapor concentration fgpg or the
average vapor concentration fgpgsm is a specific example of a
predetermined concentration determined on the basis of an operation
state of the internal combustion engine according to the aspects of
the invention. Specifically, as shown in FIG. 4A, the predetermined
concentration may be determined on the basis of the number of
revolutions or rotational speed of the internal combustion engine
and the load on the internal combustion engine, such as the amount
of fuel injection or the amount of intake air. FIG. 4A shows the
relationship among the number of revolutions of the internal
combustion engine, the load on the internal combustion engine, and
four predetermined concentrations A, B, C and D.
[0080] Then, under the control of the ECU 16, the amount of
required dilution air qiscvt (required dilution air amount qiscvt)
is calculated on the basis of the average vapor concentration
fgpgsm (step S104). Note that at this time, the average qiscvtsm of
the required dilution air amount qiscvt (average required dilution
air amount qiscvtsm) for a predetermined duration may be
calculated. Specifically, as shown in FIG. 4B, the required
dilution air amount qiscvt or the average required dilution air
amount qiscvtsm may be determined on the basis of the number of
revolutions or rotational speed of the internal combustion engine
and the load on the internal combustion engine, such as the amount
of fuel injection or the amount of intake air, which are variables
used to determine the vapor concentration. FIG. 4B shows the
relationship among the number of revolutions of the internal
combustion engine, the load on the internal combustion engine, and
four required dilution air amounts (dilution air amounts) A', B',
C' and D'.
[0081] Next, under the control of the ECU 16, it is determined
whether an actual vapor concentration is higher than a
predetermined concentration (step S105). When it is determined that
the actual vapor concentration is higher than the predetermined
concentration (step S105: Yes), the required dilution air amount
calculated as described above is multiplied by an increasing
correction coefficient (step S106). Typically, the increasing
correction coefficient may be larger than 1, for example,
"1.5".
[0082] On the other hand, as a result of the determination in step
S105, when it is determined that the actual vapor concentration is
not larger than the predetermined concentration (step S105: No),
the required dilution air amount calculated as described above is
multiplied by a reducing correction coefficient (step S107).
Typically, the reducing correction coefficient may be smaller than
1, for example, "0.8".
[0083] Note that the above described operating principle may be a
feedback control or may be a feedforward control as long as the
inflow of dilution air is changed on the basis of whether the vapor
concentration is high or low.
[0084] As described above, according to the first embodiment,
because purge gas introduced into the branch passages is diluted by
air introduced through the air supply passage, purge gas that
contains a remarkably high concentration of evaporative fuel is
substantially or completely not introduced into the branch
passages. Thus, it is possible to suppress variations in the
air-fuel ratio due to purge gas among the cylinders and, therefore,
it is possible to appropriately prevent an abrupt change in the
air-fuel ratio.
[0085] Specifically, as shown in FIG. 5A, in a state where a
vehicle equipped with the internal combustion engine according to
the first embodiment changes in speed, when the vapor concentration
remarkably increases, as shown in FIG. 5B, the variable flow rate
valve 13 appropriately increases the inflow of dilution air on the
basis of the increased vapor concentration. Thus, as shown in FIG.
5C, it is possible to remarkably suppress variations in the vapor
concentration.
[0086] If, without changing the inflow of dilution air on the basis
of the vapor concentration by the variable flow rate valve 13, the
opening degree of each throttle valve is controlled alone, as shown
by the dotted line corresponding to the comparative embodiment in
FIG. 5C, high-concentration purge gas is drawn into the cylinders,
so the air-fuel ratio varies among the cylinders due to the purge
gas, and the air-fuel ratio abruptly changes. Alternatively, in the
comparative embodiment, variations in the air-fuel ratio among the
cylinders increase when the distribution of purge gas to the
cylinders varies due to the influence of pulsation, or the like.
This causes deterioration in drivability, such as engine vibration,
or causes decrease in stability in the control of the air-fuel
ratio. In addition, exhaust emission deteriorates.
[0087] In contrast, in the first embodiment, in addition to the
control of the opening degree of each throttle valve, the variable
flow rate valve 13 changes the inflow of dilution air on the basis
of the concentration of evaporative fuel (vapor concentration).
Thus, the influence of variations in the concentration of purge gas
is reduced, and control of the air-fuel ratio in an operating state
in which the amount of intake air is small, such as during idling,
is stabilized. Hence, it is possible to stabilize the operating
state at a low rotational speed.
[0088] Next, an evaporative fuel treatment apparatus for an
internal combustion engine according to a second embodiment of the
invention will be described with reference to FIG. 6 to FIG. 7B.
FIG. 6 is a schematic diagram that shows the basic configuration of
the evaporative fuel treatment apparatus for an internal combustion
engine according to the second embodiment of the invention. FIG. 7A
and FIG. 7B are bar graphs that show the distribution of the amount
of intake air during normal idling and when dilution air is
increased, in a pair of banks according to the second embodiment of
the invention. Note that in the second embodiment, like reference
numerals denote like components to those of the above described
first embodiment, and the description thereof will be omitted where
appropriate.
[0089] As shown in FIG. 6, a right bank bk1 that constitutes the
internal combustion engine 1 includes cylinders (not shown), an
intake passage 3, branch passages 3a, a surge tank 3b, throttle
valves (not shown), a balancing passage 9, a purge passage 10, a
communication portion 10a, a mixing promoting portion 10b, a
canister 11, an air introducing pipe 11a, an air supply passage 12,
a variable flow rate valve 13, a purge gas variable throttle valve
14, a purge pressure sensor (not shown), an air-fuel ratio sensor
(not shown), and a fuel tank 20. Note that the right bank bk1 is a
specific example of a "first bank" according to the aspects of the
invention.
[0090] In addition, a left bank bk2 that constitutes the internal
combustion engine 1 includes cylinders (not shown), an intake
passage 3, branch passages 3a, a surge tank 3b, throttle valves
(not shown), a balancing passage 9, an air-fuel ratio sensor (not
shown), and a fuel tank (not shown). Note that the left bank bk2 is
a specific example of a "second bank" according to the aspects of
the invention.
[0091] Particularly, in the second embodiment, when the actual flow
rate of dilution air that is changeable by the variable flow rate
valve 13 is smaller than the above described required dilution air
amount used to decrease the concentration of evaporative fuel
(vapor concentration) below a predetermined concentration that is
determined on the basis of the operating state of the internal
combustion engine, under the control of the ECU 16, the opening
degrees of the plurality of throttle valves in the left bank bk2
are controlled so that the amount of air taken into the left bank
bk2 is reduced by a differential flow rate, which is a difference
between the required amount and the actual flow rate. In addition,
not only the differential in flow rate is controlled, but also a
target number of revolutions of the engine is maintained. Note that
the required dilution air amount is a specific example of a
"predetermined flow rate of dilution air" according to the aspects
of the invention.
[0092] If the inflow of dilution air used to dilute purge gas that
contains evaporative fuel (vapor) is insufficient, and when the
flow rate of purge gas, containing evaporative fuel and flowing
into the internal combustion engine, is restricted by the above
described second flow rate changing portion, such as the purge gas
variable throttle valve, in order to prevent engine stop and poor
drivability due to imbalanced distribution of evaporative fuel
among the cylinders, evaporative fuel contained in purge gas also
reduces. As a result, the total amount of evaporative fuel drawn
into the internal combustion engine reduces and, therefore, purge
gas may flow out to the atmosphere.
[0093] In contrast, according to the second embodiment, when the
actual flow rate of dilution air that is changeable by the variable
flow rate valve 13 is smaller than the above described required
dilution air amount used to decrease the concentration of
evaporative fuel below a predetermined concentration that is
determined on the basis of the operating state of the internal
combustion engine, under the control of the ECU 16, the opening
degrees of the plurality of throttle valves in the left bank bk2
are controlled so that the amount of air taken into the left bank
bk2 is reduced by a differential flow rate, which is a difference
between the required amount and the actual flow rate. Thus, it is
possible to additionally assign air, which is originally assigned
to the left bank bk2, to the right bank bk1 by the differential
flow rate. Hence, in the right bank bk1, it is possible to ensure
the above described required dilution air amount. Thus, the purge
gas variable throttle valve 14 need not to reduce the flow rate of
purge gas introduced to the purge passage, and the total amount of
evaporative fuel drawn into all the cylinders of the pair of banks
is not reduced. Hence, it is possible to reliably prevent purge gas
from being released to the atmosphere.
[0094] Specifically, as shown in FIG. 7A, during normal idling, the
amount of air taken into the right bank is substantially equal to
the amount of air taken into the left bank. At this time, the
amount of air taken into the right bank is the sum of the following
four different intake air amounts. That is, the amount of air taken
into the right bank is the sum of the amount of intake air from the
variable flow rate valve, the amount of intake air from the
throttle valves, the flow rate of air that leaks from the throttle
valves and the flow rate of air that leaks from the variable flow
rate valve. On the other hand, the amount of air taken into the
left bank is the sum of the following two different intake air
amounts. That is, the amount of air taken into the left bank is the
sum of the amount of intake air from the throttle valves and the
flow rate of air that leaks from the throttle valves.
[0095] Particularly, when the inflow of dilution air to the purge
passage is increased in the right bank, the amount of air taken
into the right bank is larger by the differential flow rate
corresponding to the above increase than the amount of air taken
into the left bank. At this time, in the right bank, among the
above described four different intake air amounts, the amount of
intake air from the variable flow rate valve increases by the
differential flow rate. On the other hand, in the left bank,
between the above described two different intake air amounts, the
amount of intake air from the throttle valves reduces by the
differential flow rate.
[0096] Particularly, the necessary inflow of dilution air used to
dilute evaporative fuel in the right bank bk1 is ensured while the
total amount of air taken into both banks is not varied. This makes
it easy to maintain the rotational speed of the internal combustion
engine at a low rotational speed and at a target rotational speed.
This is because a drive shaft is shared between the right bank bk1
and the left bank bk2, the total of the amount of air taken into
the right bank bk1 and the amount of air taken into the left bank
bk2 ensures the amount of air that achieves a target torque by
which a low rotational speed may be maintained. Typically, in
addition to the control of the opening degree of each throttle
valve of the right bank bk1 and the adjustment to increase the
inflow of dilution air by the variable flow rate valve 13, by
controlling each throttle valve of the left bank bk2 to reduce the
opening degree, it is possible to stabilize the control of the
air-fuel ratio at a low rotational speed, such as during idling,
and, therefore, it is possible to stabilize the operating state at
a low rotational speed.
[0097] Note that under the control of the ECU, the opening degrees
of the plurality of throttle valves in the left bank are controlled
on the basis of the following conditions. That is, the amount of
air taken into the left bank is determined so that combustion in
the cylinders of the left bank is occurable and/or the amount of
air taken into the left bank is larger than a lower limit intake
air amount determined on the basis of the air-fuel ratio required
in the left bank. Thus, it is possible to avoid the operating state
in which misfire occurs in the left bank or a torque assigned to
the left bank cannot be generated because of a reduction in the
amount of intake air in the left bank. Thus, it is possible to
generate a target torque by the combination of both banks of the
internal combustion engine.
[0098] Next, an evaporative fuel treatment apparatus for an
internal combustion engine according to a third embodiment of the
invention will be described with reference to FIG. 8 to FIG. 9C.
FIG. 8 is a schematic diagram that shows the basic configuration of
the evaporative fuel treatment apparatus for an internal combustion
engine according to the third embodiment of the invention. FIG. 9A
is a bar graph that shows the distribution of the amount of intake
air during idling in a pair of banks according to a comparative
embodiment. FIG. 9B is a graph that shows the relationship between
the opening degree of a throttle valve and the amount of intake air
through the throttle valve, in the pair of banks according to the
comparative embodiment. FIG. 9C is a bar graph that shows the
distribution of the amount of intake air during idling in a pair of
banks according to the third embodiment of the invention. Note that
in the third embodiment, like reference numerals denote like
components to those of the above described first and second
embodiments, and the description thereof will be omitted where
appropriate.
[0099] As shown in FIG. 8, a right bank bk1 that constitutes the
internal combustion engine 1 includes cylinders (not shown), an
intake passage 3, branch passages 3a, a surge tank 3b, throttle
valves (not shown), a balancing passage 9, a purge passage 10, a
communication portion 10a, a mixing promoting portion 10b, a
canister 11, an air introducing pipe 11a, an air supply passage 12,
a variable flow rate valve 13, a purge gas variable throttle valve
14, a purge pressure sensor (not shown), an air-fuel ratio sensor
(not shown), and a fuel tank 20. Note that the right bank bk1 is
another specific example of a "first bank" according to the aspects
of the invention.
[0100] In addition, a left bank bk2 that constitutes the internal
combustion engine 1 includes cylinders (not shown), an intake
passage 3, branch passages 3a, a surge tank 3b, throttle valves
(not shown), a balancing passage 9, a purge passage 10, a
communication portion 10a, a mixing promoting portion 10b, an air
supply passage 12, a variable flow rate valve 13, an air-fuel ratio
sensor (not shown), and a fuel tank (not shown). Note that the left
bank bk2 is another specific example of a "second bank" according
to the aspects of the invention.
[0101] Thus, the flow resistance of air that flows through the
communication portion 10a, the purge passage 10, the air supply
passage 12 and the variable flow rate valve 13 in the right bank
bk1 may be equalized to the flow resistance of air that flows
through the communication portion 10a, the air supply passage 12
and the variable flow rate valve 13 in the left bank bk2. Thus, it
is possible to coincide the amount of air that flows through the
throttle valves and the air supply passage 12 in the right bank bk1
with the amount of air that flows through the throttle valves and
the air supply passage 12 in the left bank bk2. Particularly, it is
desirable because the flow resistances of air is equalized by
providing the mixing promoting portion for each of the right bank
bk1 and the left bank bk2.
[0102] Particularly, under the control of the ECU 16, the variable
flow rate valve 13 of the right bank bk1 changes the inflow of
dilution air on the basis of a comparison between the concentration
of evaporative fuel and a predetermined concentration determined on
the basis of the operating state of the internal combustion engine.
In addition to this, under the control of the ECU 16, the variable
flow rate valve 13 of the left bank bk2 changes the inflow of
upstream air so as to be equal to the inflow of the dilution
air.
[0103] If the flow resistance of air that flows through the
communication portion 10a, the purge passage 10, the air supply
passage 12 and the variable flow rate valve 13 in the right bank
bk1 cannot be made substantially equal to the flow resistance of
air that flows through the communication portion 10a, the purge
passage 10, the air supply passage 12 and the variable flow rate
valve 13 in the left bank bk2, that is, if the amount of air that
flows through the throttle valves and the air supply passage 12 in
the right bank does not coincide with the amount of air that flows
through the throttle valves and the air supply passage 12 in the
left bank, the range of characteristics of the opening degree of
each throttle valve in the right bank differs from the range of
characteristics of the opening degree of each throttle valve in the
left bank. Thus, for example, control of the air-fuel ratio at a
low rotational speed, such as during idling, becomes unstable. In
other words, if the variable flow rate valve 13 is provided for the
right bank and no variable flow rate valve 13 is provided for the
left bank, as shown by the black solid curve S1 in FIG. 9B, the
operation of each throttle valve in the right bank, to which purge
gas containing evaporative fuel flows, causes relatively small rate
of change in the amount of intake air against the opening degree of
each throttle valve, and the amount of intake air does not change
much only by varying the opening degree of each throttle valve in
some degree. On the other hand, as shown by the black solid curve
S2 in FIG. 9B, the operation of each throttle valve in the left
bank, to which no purge gas containing evaporative fuel flows,
causes relatively large rate of change in the amount of intake air
against the opening degree of each throttle valve, and the amount
of intake air changes by a large amount even when the opening
degree of each throttle valve is varied a little. Specifically, as
shown in FIG. 9A, when the amount of air taken into the right bank
is substantially equalized to the amount of air taken into the left
bank during idling, the amount of air taken into the right bank is
the sum of four different intake air amounts (that is, the amount
of intake air from the variable flow rate valve, the amount of
intake air from the throttle valves, the flow rate of air that
leaks from the throttle valves, and the flow rate of air that leaks
from the variable flow rate valve). On the other hand, the amount
of air taken into the left bank is the sum of two different intake
air amounts (that is, the amount of intake air from the throttle
valves and the flow rate of air that leaks from the throttle
valves). Thus, because in the right bank, the percentage of the
amount of intake air from the throttle valves and the flow rate of
air that leaks from the throttle valves is small, the control of
the opening degree of the throttle valves of the right bank less
influences the amount of intake air of the right bank than that of
the left bank. On the other hand, because in the left bank, the
percentage of the amount of intake air from the throttle valves and
the flow rate of air that leaks from the throttle valves is
substantially 100%, the control of the opening degree of the
throttle valves of the right bank remarkably more influences the
amount of intake air of the right bank than that of the right
bank.
[0104] In detail, the resolution of control of the opening degree
of each throttle valve is restricted by hardware. For example, 0.03
degree is the minimum unit of control of the opening degree of each
throttle valve. Thus, when the throttle valves having largely
different opening degree characteristics are used respectively in
both banks, a variation in the amount of intake air per the above
described minimum unit, that is, an increase or a decrease in
actual rotational speed of the internal combustion engine varies
between both banks. Thus, there is a possibility that variations in
rotational speed during idling may occur in at least one of the
banks.
[0105] In contrast, according to the third embodiment, under the
control of the ECU 16, the variable flow rate valve 13 in the right
bank changes the inflow of dilution air on the basis of a
comparison between the concentration of evaporative fuel and a
predetermined concentration determined on the basis of the
operating state of the internal combustion engine. In addition to
this, under the control of the ECU 16, the variable flow rate valve
13 in the left bank changes the inflow of upstream air so as to be
equalized to the inflow of dilution air. Thus, because both banks
may be controlled substantially in the same manner, it is possible
to suppress variations in rotational speed due to a torque
difference caused by a difference in the amount of intake air
between both banks during idling. Specifically, because the same
range of the opening degree characteristics of each throttle valve
may be used in both banks of the internal combustion engine, it is
possible to stabilize the control of the air-fuel ratio at a low
rotational speed, such as during idling, in both banks.
[0106] Specifically, as shown in FIG. 9C, the amount of air taken
into the right bank is the sum of four different intake air amounts
(that is, the amount of intake air from the variable flow rate
valve, the amount of intake air from the throttle valves, the flow
rate of air that leaks from the throttle valves, and the flow rate
of air that leaks from the variable flow rate valve). Almost
similarly, the amount of air taken into the left bank is the sum of
four different intake air amounts (that is, the amount of intake
air from the variable flow rate valve, the amount of intake air
from the throttle valves, the flow rate of air that leaks from the
throttle valves, and the flow rate of air that leaks from the
variable flow rate valve). In this way, the percentage of the
amount of intake air from the throttle valves and the flow rate of
air that leaks from the throttle valves is substantially equalized
between the right bank and the left bank. Thus, under the simple
control of the ECU 16, the control of the opening degrees of the
throttle valves of the right bank is substantially similar to the
control of the opening degrees of the throttle valves of the left
bank while, for example, during idling, it is possible to
substantially equalize the amount of air taken into the right bank
with the amount of air taken in to the left bank.
[0107] Next, an evaporative fuel treatment apparatus for an
internal combustion engine according to a fourth embodiment of the
invention will be described with reference to FIG. 10 to FIG. 12B.
FIG. 10 is a flowchart that shows the operating principle of the
evaporative fuel treatment apparatus for an internal combustion
engine according to the fourth embodiment of the invention. FIG. 11
is another flowchart that shows the operating principle of the
evaporative fuel treatment apparatus for an internal combustion
engine according to the fourth embodiment of the invention. Note
that in the fourth embodiment, like reference numerals denote like
components to those of the above described first to third
embodiments, and the description thereof will be omitted where
appropriate. FIG. 12A is a graph that shows a common example of the
relationship among a purge pressure, at a position downstream of a
purge gas variable throttle valve 14 and upstream of a purge
passage 10, an intake pipe pressure, and the opening degree of a
variable flow rate valve. FIG. 12B is a graph that shows a common
example of the relationship between the flow rate of purge gas and
a purge pressure at a position downstream of the purge gas variable
throttle valve 14 and upstream of the purge passage 10.
[0108] As shown in FIG. 10, under the control of the ECU 16, it is
determined whether an execution condition for executing purge
control in which purge gas containing evaporative fuel is
appropriately diluted by dilution air is satisfied (step S201).
When it is determined that the execution condition for executing
the purge control is satisfied (step S201: Yes), under the control
of the ECU 16, it is determined whether an abnormality is occurring
in the purge pressure sensor 15 (step S202). When an abnormality is
occurring in the purge pressure sensor 15 (step S202: Yes), under
the control of the ECU 16, a purge pressure t_mv at a position
downstream of the purge gas variable throttle valve 14 and upstream
of the purge passage 10 is estimated on the basis of the operating
state of the internal combustion engine, such as the rotational
speed of the internal combustion engine and the opening degree of
each throttle valve of the internal combustion engine.
Particularly, at the time of the estimation, the opening degree of
the variable flow rate valve 13 is set to a fixed value to thereby
control the inflow of dilution air to a constant value. This can
compensate for general characteristics that the correlation greatly
changes between the purge pressure and the intake pipe pressure at
a position downstream of the purge gas variable throttle valve 14
in accordance with a variation in the opening degree of the
variable flow rate valve 13, as shown by the opening degree a,
opening degree b, opening degree c, opening degree d and opening
degree e in FIG. 12A. Note that the control process of the variable
flow rate valve 13 will be described later. Thus, under the
condition that the inflow of dilution air is a constant value, the
ECU 16 is able to highly accurately estimate a purge pressure t_mv
at a position downstream of the purge gas variable throttle valve
14 and upstream of the purge passage 10. Thus, because the flow
rate of evaporative fuel may be highly accurately determined on the
basis of the estimated purge pressure, by controlling the flow rate
of purge gas on the basis of the inflow of dilution air fixed as
described above (fixed to a constant value), it is possible to
prevent purge gas containing a remarkably high concentration of
evaporative fuel from being introduced into each branch passage.
Hence, it is possible to suppress variations in the air-fuel ratio
due to purge gas among the cylinders and, as a result, it is
possible to appropriately prevent an abrupt change in the air-fuel
ratio. This is because, as shown in FIG. 12B, the flow rate of
purge gas may be highly accurately predicted on the basis of the
highly accurately estimated purge pressure.
[0109] On the other hand, as a result of the determination of the
above described step S202, when no abnormality is occurring in the
purge pressure sensor 15 (step S202: No), because the purge
pressure sensor 15 operates normally, the atmospheric pressure is
added to the measured value of the purge pressure sensor 15, and
the standard atmospheric pressure is subtracted from the resultant
value. Thus, the ECU 16 corrects a purge pressure t_mv at a
position downstream of the purge gas variable throttle valve 14 and
upstream of the purge passage 10 (step S204).
[0110] Specifically, the correction value (ppg) of the purge
pressure t_mv is derived from the following Expression (1).
Correction value of purge pressure t.sub.--mv=klsm/{klmaxb+(1-kpa)}
(1) [0111] where klsm denotes an intake air amount, [0112] klmaxb
denotes the amount of air when the throttle valve is fully opened,
and [0113] kpa denotes an atmospheric pressure correction
coefficient.
[0114] Next, under the control of the ECU 16, the opening degree of
the purge gas variable throttle valve 14 and the purge rate, which
is a duration during which the opening degree is maintained, are
determined on the basis of the estimated or corrected purge
pressure t_mv and the number of revolutions of the internal
combustion engine. At this time, the relationship among the
estimated or corrected purge pressure t_mv, the number of
revolutions of the internal combustion engine, and the purge rate
may be uniquely determined through a map, function, simulation, or
the like. Note that the purge rate may be replaced with a purge
rate that is obtained by dividing the flow rate of purge gas when
the duty ratio of the purge gas variable throttle valve 14 is 100%
by the intake air amount, that is, a so-called full open purge
rate.
[0115] Next, the control process of the variable flow rate valve 13
will be described with reference to FIG. 11.
[0116] As shown in FIG. 11, under the control of the ECU 16, the
controlled variable of the opening degree of the variable flow rate
valve 13 during idling is calculated (step S301).
[0117] Subsequently, under the control of the ECU 16, it is
determined whether an execution condition for executing purge
control in which purge gas containing evaporative fuel is
appropriately diluted by dilution air is satisfied (step S302).
When it is determined that the execution condition for executing
the purge control is satisfied (step S302: Yes), under the control
of the ECU 16, it is determined whether an abnormality is occurring
in the purge pressure sensor 15 (step S303). When an abnormality is
occurring in the purge pressure sensor 15 (step S303: Yes), under
the control of the ECU 16, the opening degree of the variable flow
rate valve 13 is set to a fixed value to thereby control the inflow
of dilution air to a constant value. Alternatively, under the
control of the ECU 16, the opening degree of the variable flow rate
valve 13 is restricted to thereby limit the inflow of dilution air
(step S304).
[0118] Then, under the control of the ECU 16, the controlled
variable of the opening degree of each throttle valve during idling
is calculated and determined (step S305).
[0119] After that, under the control of the ECU 16, the opening
degree of the variable flow rate valve 13 is calculated and
determined on the basis of the above described controlled variable
of the opening degree of each throttle valve (step S306).
[0120] Here, the purge pressure sensor 15 that measures the
pressure at a position downstream of the purge gas variable
throttle valve 14 and upstream of the purge passage 10 will be
described in detail. According to the research by the inventors of
the application, evaporative fuel is drawn into the internal
combustion engine by the negative pressure in the intake pipe, so
the amount of purge gas drawn into the cylinder increases as the
amount of air that flows through the corresponding throttle valve
reduces. In this case, in regard to the air-fuel ratio in each
cylinder, the cylinder draws a larger amount of evaporative fuel
when the amount of air that flows through the corresponding
throttle valve is small despite a rich air-fuel ratio. This
promotes the air-fuel ratio to be further rich. Then, to solve this
problem, the communication portion is provided separately from the
balancing passage, and the diameter of the communication portion
(for example, 4 mm diameter) is reduced. Thus, the balancing
function is suppressed to improve equal distribution. In this case,
the communication portion serves as an orifice (air-flow
resistance), and the pressure in the intake pipe is lower than the
pressure in the purge passage 10 and is lower than the pressure
downstream of the purge gas variable throttle valve 14. In
addition, to further increase the purge rate, or to increase the
pressure in the purge passage, fresh air is drawn into the purge
passage through the variable flow rate valve 13 and mixed with
purge gas. In this case, a variation in the amount of fresh air
introduced through the variable flow rate valve 13 influences the
pressure in the purge passage 10 and the pressure downstream of the
purge gas variable throttle valve 14. In addition, as for the
characteristics of the independent throttle valve, the average of
the pressure in the intake pipe is determined on the basis of a
negative pressure generated at the time when an intake valve is
opened and a pressure difference based on the opening degree of the
throttle valve when the intake valve is closed thereafter.
Generally, there is no linear correlation between the amount of
intake air and the average pressure in the intake pipe. On the
basis of the above principle, there is no correlation between the
pressure downstream of the purge gas variable throttle valve 14,
which is a variable parameter of the flow rate of purge gas, and
the amount of intake air. For this reason, it is technically
difficult to estimate the pressure downstream of the purge gas
variable throttle valve 14 on the basis of the amount of intake air
and the number of revolutions or rotational speed of the internal
combustion engine. In contrast, according to the fourth embodiment,
the purge pressure sensor 15 is provided and directly measures the
pressure at a position downstream of the purge gas variable
throttle valve 14 and upstream of the purge passage 10. Thus, it is
possible to accurately control the variation of the amount of drawn
purge gas.
[0121] The aspects of the invention are not limited to the above
described embodiments but they may be modified into various
alternative embodiments. For example, the aspects of the invention
are not limited to a gasoline engine. The aspects of the invention
may be applied to various internal combustion engines that utilize
diesel or other fuel instead.
[0122] The aspects of the invention are not limited to the
embodiments described above. The aspects of the invention may be
appropriately modified without departing from the scope or spirit
of the invention interpreted from the appended claims and entire
specification. The scope of the invention also encompasses the thus
modified evaporative fuel treatment apparatus for an internal
combustion engine.
[0123] While the invention has been described with reference to
example embodiments thereof, it should be understood that the
invention is not limited to the example embodiments or
constructions. To the contrary, the invention is intended to cover
various modifications and equivalent arrangements. In addition,
while the various elements of the example embodiments are shown in
various combinations and configurations, which are example, other
combinations and configurations, including more, less or only a
single element, are also within the spirit and scope of the
invention.
* * * * *