U.S. patent number 10,385,789 [Application Number 15/607,382] was granted by the patent office on 2019-08-20 for control device for internal combustion engine for selecting operation to calculate target throttle opening degree based on prediction of temporary reduction in charging efficiency of fresh air in acceleration.
This patent grant is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The grantee listed for this patent is TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Yoshiyuki Kageura, Yushi Shibaike, Satoru Tanaka.
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United States Patent |
10,385,789 |
Shibaike , et al. |
August 20, 2019 |
Control device for internal combustion engine for selecting
operation to calculate target throttle opening degree based on
prediction of temporary reduction in charging efficiency of fresh
air in acceleration
Abstract
A control device predicts whether temporary reduction occurs to
a charging efficiency of fresh air in an in-cylinder gas by an
influence of an EGR rate of the in-cylinder gas, which increases
later than increase of a charging efficiency of the in-cylinder
gas, if a first arithmetic operation is applied to calculating a
target throttle opening degree based on a target charging
efficiency which is increasing, in a case of shifting to an
acceleration operation, by using a prediction model expressing
dynamic characteristics of an internal combustion engine. When it
is predicted that temporary reduction occurs to the charging
efficiency of the fresh air, the control device calculates the
target throttle opening degree by a second arithmetic operation by
which an increase speed of a throttle opening degree is restrained
more than by the first arithmetic operation, instead of calculating
the target throttle opening degree by the first arithmetic
operation.
Inventors: |
Shibaike; Yushi (Susono,
JP), Kageura; Yoshiyuki (Shizuoka-ken, JP),
Tanaka; Satoru (Yokohama, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
TOYOTA JIDOSHA KABUSHIKI KAISHA |
Aichi-ken |
N/A |
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI KAISHA
(Aichi-ken, JP)
|
Family
ID: |
60327548 |
Appl.
No.: |
15/607,382 |
Filed: |
May 26, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170350326 A1 |
Dec 7, 2017 |
|
Foreign Application Priority Data
|
|
|
|
|
Jun 6, 2016 [JP] |
|
|
2016-112908 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02D
43/04 (20130101); F02D 41/0007 (20130101); F02D
21/08 (20130101); F02D 41/0047 (20130101); F02P
5/1502 (20130101); F02D 41/10 (20130101); F02D
23/02 (20130101); F02D 2009/022 (20130101); F02B
37/12 (20130101); Y02T 10/144 (20130101); F02D
2041/0017 (20130101); F02D 21/06 (20130101); F02D
41/04 (20130101); F02D 2021/083 (20130101); Y02T
10/12 (20130101); F02P 5/145 (20130101); F02D
41/02 (20130101); F02B 37/18 (20130101); F02D
2009/0235 (20130101); Y02T 10/40 (20130101); F02P
5/04 (20130101); F02M 26/06 (20160201); F02D
2009/0284 (20130101); F02D 2009/0222 (20130101); F02D
2009/0201 (20130101); Y02T 10/47 (20130101); F02D
2200/0402 (20130101) |
Current International
Class: |
F02D
21/08 (20060101); F02D 41/00 (20060101); F02P
5/15 (20060101); F02D 43/04 (20060101); F02D
41/10 (20060101); F02D 23/02 (20060101); F02D
9/02 (20060101); F02D 41/04 (20060101); F02P
5/145 (20060101); F02B 37/12 (20060101); F02B
37/18 (20060101); F02M 26/06 (20160101); F02P
5/04 (20060101); F02D 21/06 (20060101); F02D
41/02 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2000-002143 |
|
Jan 2000 |
|
JP |
|
2010-001796 |
|
Jan 2010 |
|
JP |
|
2012-007547 |
|
Jan 2012 |
|
JP |
|
2012-067607 |
|
Apr 2012 |
|
JP |
|
2014-152716 |
|
Aug 2014 |
|
JP |
|
2014-211090 |
|
Nov 2014 |
|
JP |
|
Primary Examiner: Hamaoui; David
Attorney, Agent or Firm: Hauptman Ham, LLP
Claims
What is claimed is:
1. A control device for an internal combustion engine having a
compressor disposed in an intake passage, a throttle disposed
downstream from the compressor in the intake passage, and an EGR
valve disposed in an EGR passage connecting an exhaust passage and
an upstream side from the compressor in the intake passage, the
control device configured to operate the throttle so as to increase
a charging efficiency of an in-cylinder gas, and operate the EGR
valve to increase an EGR rate of the in-cylinder gas, in an
acceleration operation, the control device comprising: at least one
processor; and at least one memory including at least one computer
program, the at least one memory and the at least one computer
program configured to cause the at least one processor, in the
acceleration operation, to increase a target charging efficiency in
accordance with a magnitude of acceleration requested of the
internal combustion engine, calculate a target throttle opening
degree based on the target charging efficiency, and select to
calculate the target throttle opening degree by one of a first
arithmetic operation, and a second arithmetic operation by which an
increase speed of a throttle opening degree is restrained more than
by the first arithmetic operation, and predict, by using a
prediction model expressing dynamic characteristics of the internal
combustion engine, whether temporary reduction occurs to a charging
efficiency of fresh air in the in-cylinder gas by and during an
increase of the EGR rate of the in-cylinder gas after an increase
of the charging efficiency of the in-cylinder gas when the first
arithmetic operation is applied to calculation of the target
throttle opening degree based on the target charging efficiency
which is increasing, in a case of shifting to the acceleration
operation, wherein the at least one processor is caused to select
to calculate the target throttle opening degree by the first
arithmetic operation in response to a prediction that no temporary
reduction occurs to the charging efficiency of the fresh air in the
in-cylinder gas, and select to calculate the target throttle
opening degree by the second arithmetic operation in response to a
prediction that temporary reduction occurs to the charging
efficiency of the fresh air in the in-cylinder gas, and wherein the
at least one processor is caused to predict, by using the
prediction model, an increase speed of the charging efficiency of
the in-cylinder gas, and an increase speed of a charging efficiency
of an EGR gas in the in-cylinder gas, that are obtained when the
throttle is operated by using the target throttle opening degree
calculated by the first arithmetic operation, and compare the
predicted increase speed of the charging efficiency of the
in-cylinder gas with the predicted increase speed of the charging
efficiency of the EGR gas in the in-cylinder gas, and determine
that temporary reduction occurs to the charging efficiency of the
fresh air in the in-cylinder gas when the predicted increase speed
of the charging efficiency of the EGR gas in the in-cylinder gas is
higher than the predicted increase speed of the charging efficiency
of the in-cylinder gas.
2. The control device according to claim 1, wherein the at least
one processor is caused to in the first arithmetic operation,
calculate a throttle opening degree for achieving the target
charging efficiency as the target throttle opening degree, and in
the second arithmetic operation, acquire a target EGR rate,
calculate an estimated EGR rate of all gases passing through an
intake valve, correct the target charging efficiency by subtracting
a charging efficiency corresponding to a difference between the
target EGR rate and the estimated EGR rate from the target charging
efficiency, and calculate a throttle opening degree for achieving
the corrected target charging efficiency as the target throttle
opening degree.
3. The control device according to claim 1, wherein the at least
one processor is caused, in the acceleration operation, to input
into the prediction model an atmospheric pressure, an opening
degree of the EGR valve, and a throttle opening degree calculated
by using the first arithmetic operation for achieving the target
charging efficiency, and predict, by using (a) the prediction
model, (b) the input atmospheric pressure, (c) the input opening
degree of the EGR valve, and (d) the input throttle opening degree
calculated by using the first arithmetic operation for achieving
the target charging efficiency, a charging efficiency of the
in-cylinder gas, and a charging efficiency of an EGR gas in the
in-cylinder gas, and predict, by using (i) the predicted charging
efficiency of the in-cylinder gas and (ii) the predicted charging
efficiency of the EGR gas in the in-cylinder gas, whether temporary
reduction occurs to the charging efficiency of the fresh air in the
in-cylinder gas by and during the increase of the EGR rate of the
in-cylinder gas after the increase of the charging efficiency of
the in-cylinder gas.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This application is based on and claims the benefit of Japanese
Patent Application No. 2016-112908, filed on Jun. 6, 2016, which is
incorporated by reference herein in its entirety.
BACKGROUND
Field
The present invention relates to a control device for an internal
combustion engine, and particularly relates to a control device for
an internal combustion engine including a supercharger and an EGR
device.
Background Art
As described in JP 2014-152716 A, in an internal combustion engine
where an outlet of an EGR passage is provided upstream of a
compressor in an intake passage, at a time of start of an
acceleration operation, it takes a lot of time for EGR gas that
flows out into the intake passage from the outlet of the EGR
passage to reach a combustion chamber first. Consequently, in a
period until the EGR gas firstly reaches the combustion chamber, an
EGR rate in the combustion chamber becomes excessively low with
respect to a target EGR rate. When the EGR gas reaches the
combustion chamber after a while, a fresh air amount in a cylinder
is abruptly reduced because the EGR rate of the gas entering into
the cylinder suddenly increases, whereby a torque level difference
occurs.
In order to prevent this, the art proposed in JP 2014-152716 A
estimates the EGR rate in the outlet of the EGR passage, and
corrects a target throttle opening degree to a closing side more as
the EGR rate is higher in at least the period until the EGR gas
reaches the combustion chamber when the EGR rate is larger than a
predetermined value.
SUMMARY
In an acceleration operation, correcting the target throttle
opening degree to a closing side leads to reduction in
responsiveness of torque by retarding increase in a charging
efficiency. Therefore, if an influence which an arrival delay of
the EGR gas has on torque is small, the target throttle opening
degree is not desired to be corrected to the closing side. In this
regard, the above described conventional art does not perform
correction of the target throttle opening degree when the EGR rate
in the outlet of the EGR passage is the predetermined value or
less.
To be sure, the EGR rate in the outlet of the EGR passage is one
parameter that indicates the influence which the arrival delay of
the EGR gas has on torque. However, it cannot be determined based
on only the EGR rate in the outlet of the EGR passage whether or
not the fresh air amount in a cylinder is temporarily reduced due
to the arrival delay of the EGR gas and thereby a torque level
difference occurs. Consequently, the above described conventional
art has a possibility of performing correction of the target
throttle opening degree although there is no possibility of
occurrence of a torque level difference, and reducing
responsiveness of torque needlessly.
The present disclosure is made in the light of the aforementioned
problem, and has an object to provide a control device for an
internal combustion engine capable of restraining a torque level
difference due to an arrival delay of EGR gas without reducing
responsiveness of torque more than necessary in an acceleration
operation of the internal combustion engine.
A control device according to the present disclosure is a control
device for controlling an internal combustion engine including a
compressor disposed in an intake passage, a throttle disposed
downstream from the compressor in the intake passage, and an EGR
valve disposed in an EGR passage connecting an exhaust passage and
an upstream side from the compressor in the intake passage.
Further, the control device according to the present disclosure is
a control device configured to operate the throttle so as to
increase a charging efficiency of an in-cylinder gas, and operates
the EGR valve to increase an EGR rate of the in-cylinder gas, in an
acceleration operation. The control device according to the present
disclosure is further configured as follows.
The control device according to the present disclosure comprises
target charging efficiency determination means, target throttle
opening degree arithmetic operation means, and prediction means.
The control device according to the present disclosure may be
configured as a computer including at least one processor and at
least one memory. The computer may be configured to function as the
target charging efficiency determination means, the target throttle
opening degree arithmetic operation means, and the prediction means
by at least one computer program stored in at least the one memory
being executed by at least the one processor.
The target charging efficiency determination means is configured to
determine a target charging efficiency that is a target value of
the charging efficiency of the in-cylinder gas, and is configured
to increase the target charging efficiency in accordance with a
magnitude of acceleration that is requested to the internal
combustion engine. The request for acceleration to the internal
combustion engine may include a request that is inputted by a
driver via an operation of an operation member. Further, a request
for acceleration to the internal combustion engine may be supplied
from a control system of a cruise control device, or a control
system of an autonomous drive device. Note that in the present
specification, a "charging efficiency of the in-cylinder gas" means
a ratio of a mass of all gases in a cylinder, that is, all gases
including fresh air and an EGR gas to a mass of air corresponding
to a stroke volume. When a "charging efficiency" is simply
mentioned, it means the charging efficiency of the in-cylinder gas,
unless described otherwise. Further, when a "charging efficiency of
fresh air" is mentioned, it means a ratio of a mass of fresh air
entering into the cylinder to the mass of air corresponding to the
stroke volume. Further, when a "charging efficiency of the EGR gas"
is mentioned, it means a ratio of a mass of the EGR gas that enters
into the cylinder to the mass of the air corresponding to the
stroke volume.
The target throttle opening degree arithmetic operation means is
configured to calculate a target throttle opening degree that is
the target value of the opening degree of the throttle from the
target charging efficiency. In detail, the target throttle opening
degree arithmetic operation means is configured to be able to
select calculation of the target throttle opening degree by a first
arithmetic operation, and calculation of the target throttle
opening degree by a second arithmetic operation by which an
increase speed of a throttle opening degree is restrained more than
by the first arithmetic operation. In more detail, the target
throttle opening degree arithmetic operation means is configured to
select calculation of the target throttle opening degree by the
first arithmetic operation as standard setting, and select
calculation of the target throttle opening degree by the second
arithmetic operation when a condition for switch of selection that
will be described later is established.
The second arithmetic operation may be to correct the target
throttle opening degree calculated in the first arithmetic
operation to a closing side. For example, if the first arithmetic
operation is to calculate the throttle opening degree for achieving
the target charging efficiency as the target throttle opening
degree, in the second arithmetic operation, the target charging
efficiency may be corrected to a decreasing side, and the throttle
opening degree for achieving the corrected target charging
efficiency may be calculated as the target throttle opening degree.
Acquiring the target EGR rate, calculating the estimated EGR rate
of all the gases passing through the intake valve, and subtracting
the charging efficiency corresponding to the difference between the
target EGR rate and the estimated EGR rate from the target charging
efficiency may be performed as a procedure of correcting the target
charging efficiency to the decreasing side.
The prediction means is configured to predict whether the condition
for switch to calculation of the target throttle opening degree by
the second arithmetic operation from calculation of the target
throttle opening degree by the first arithmetic operation is
established by using the prediction model expressing the dynamic
characteristics of the internal combustion engine. In detail, the
condition for switching selection is that temporary reduction
occurs to the charging efficiency of the fresh air by an influence
of the EGR rate of the in-cylinder gas which increases later than
increase of the charging efficiency of the in-cylinder gas, if the
first arithmetic operation is applied to calculation of the target
throttle opening degree based on the target charging efficiency
which is increasing, in a case of shifting to the acceleration
operation. That is, when temporary reduction of the charging
efficiency of the fresh air that is the cause of a torque level
difference occurs when calculation of the target throttle opening
degree by the first arithmetic operation is also continued in the
acceleration operation, switch to calculation of the target
throttle opening degree by the second arithmetic operation is
performed.
Whether temporary reduction occurs to the charging efficiency of
the fresh air may be predicted by a procedure as follows, for
example. First, an increase speed of the charging efficiency of the
in-cylinder gas, and an increase speed of the charging efficiency
of the EGR gas, which are obtained when the throttle is operated by
using the target throttle opening degree which is calculated by the
first arithmetic operation, are predicted by using a prediction
model. Subsequently, when the increase speed of the charging
efficiency of the EGR gas is higher than the increase speed of the
charging efficiency of the in-cylinder gas, it is determined that
temporary reduction occurs to the charging efficiency of the fresh
air. A difference between the increase speed of the charging
efficiency of the in-cylinder gas and the increase speed of the
charging efficiency of the EGR gas corresponds to an increase speed
of the charging efficiency of the fresh air. Therefore, when the
increase speed of the charging efficiency of the EGR gas is higher
than the increase speed of the charging efficiency of the
in-cylinder gas, the increase speed of the charging efficiency of
the fresh air is negative, and this shows that the charging
efficiency of the fresh air is reduced.
The prediction model for use in prediction may be configured to
include at least the throttle opening degree in an input, and
include at least the charging efficiency of the fresh air or the
increase speed of the charging efficiency of the fresh air in an
output. Further, the prediction model may be configured as a
combination of a plurality of element models. For example, the
prediction model may be configured by combining a supercharging
model in which a relationship between a flow rate of a gas passing
through the intake valve and a compressor flow rate is modeled, an
intake model in which a relationship between the compressor flow
rate, the throttle opening degree and the flow rate of the gas
passing through the intake valve is modeled, and an EGR model in
which a relationship between the compressor flow rate, an EGR valve
opening degree and the EGR rate is modeled.
The supercharging model, the intake model, and the EGR model may be
each configured as a combination of a plurality of element models.
The supercharging model may be configured by combining a turbo
rotational speed model in which a relationship between the flow
rate of the gas passing through the intake valve and a turbo
rotational speed is modeled, and a compressor model in which a
relationship between the turbo rotational speed, a compressor
downstream pressure and the compressor flow rate is modeled, for
example. Further, an air cleaner model in which a relationship
between a flow rate of air which is taken into the intake passage
and a pressure loss in an air cleaner is modeled is included in the
supercharging model, and pressure of air after passing through the
air cleaner may be used as an input to the compressor model.
Further, if the internal combustion engine includes an air bypass
valve, an air bypass valve model in which a relationship between
the operation state of the air bypass valve and the flow rate of a
gas that is returned to upstream of the compressor is modeled may
be included in the supercharging model. If the internal combustion
engine includes an actuator for controlling the turbo rotational
speed like a wastegate valve or a variable nozzle, an operation
state of the actuator may be used as one of inputs to the turbo
rotational speed model, and an actuator response model in which a
response characteristic of the actuator are modeled may be included
in the supercharging model.
The intake model may be configured by combining a throttle model in
which a relationship between an upstream pressure of the throttle,
a downstream pressure of the throttle, the throttle opening degree,
and a flow rate of gas passing through the throttle is modeled, an
intake manifold model in which a relationship between a flow rate
of gas flowing into an intake manifold, a flow rate of gas flowing
out of the intake manifold, and a pressure of the intake manifold
is modeled, and an intake valve model in which a relationship
between the pressure of the intake manifold and the flow rate of
the gas passing through the intake valve is modeled, for example.
Further, an intercooler model in which a relationship between a
flow rate of gas flowing into an intercooler, a flow rate of gas
flowing out of the intercooler, and an outlet pressure of the
intercooler is modeled may be included in the intake model.
The EGR model may be configured by combining an EGR valve model in
which a relationship between the compressor flow rate, the EGR
valve opening degree and the EGR rate is modeled, and an EGR
diffusion model in which a change with respect to time of the EGR
rate by diffusion of the EGR gas in a path from the EGR valve to
the intake valve is modeled, for example.
According to the control device for an internal combustion engine
according to the present disclosure, if it is predicted that
temporary reduction occurs in the charging efficiency of fresh air
by applying the first arithmetic operation to calculation of the
target throttle opening degree in an acceleration operation by the
prediction model expressing the dynamic characteristics of the
internal combustion engine, the target throttle opening degree is
calculated in accordance with the second arithmetic operation by
which the increase speed of the throttle opening degree is
restrained more than by the first arithmetic operation, instead of
the first arithmetic operation. Consequently, the torque level
difference due to a delay in arrival of the EGR gas can be
restrained without reducing responsiveness of torque more than
necessary.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a diagram illustrating a configuration outline of an
internal combustion engine according to the present disclosure;
FIG. 2 is a block diagram illustrating functions included by the
control device according to the present disclosure;
FIG. 3 is a diagram illustrating an example of changes with time of
a charging efficiency of all gases, a charging efficiency of fresh
air and a charging efficiency of an EGR gas at a time of an
acceleration operation;
FIG. 4 is a diagram illustrating an example of a relationship
between a target EGR rate and an estimated EGR rate at the time of
an acceleration operation;
FIG. 5 is a diagram illustrating another example of changes with
time of the charging efficiency of all gases, the charging
efficiency of fresh air and the charging efficiency of the EGR gas
at the time of an acceleration operation;
FIG. 6 is a flowchart illustrating a control flow of throttle
opening degree control according to the present disclosure;
FIG. 7 is a time chart illustrating an example of an operation of
the internal combustion engine in a case where the throttle opening
degree control according to the present disclosure is executed;
FIG. 8 is a time chart illustrating another example of the
operation of the internal combustion engine in the case where the
throttle opening degree control according to the present disclosure
is executed;
FIG. 9 is a block diagram illustrating an example of a
configuration of a prediction model for use in prediction of a
change speed of the charging efficiency of fresh air; and
FIG. 10 is a block diagram illustrating another example of the
configuration of the prediction model for use in prediction of the
change speed of the charging efficiency of fresh air.
DETAILED DESCRIPTION
Hereinafter, an embodiment of the present invention will be
described with reference to the drawings. Note that when the
numerals of the numbers, the quantities, the amounts, the ranges
and the like of the respective elements are mentioned in the
embodiment shown as follows, the present invention is not limited
to the mentioned numerals unless specially explicitly described
otherwise, or unless the invention is explicitly specified by the
numerals theoretically. Further, the structures, steps and the like
that are described in the embodiment shown as follows are not
always indispensable to the invention unless specially explicitly
shown otherwise, or unless the invention is explicitly specified by
the structures, steps and the like theoretically.
1. Configuration of Internal Combustion Engine
FIG. 1 is a diagram illustrating a configuration outline of an
internal combustion engine according to the embodiment. The
internal combustion engine (hereinafter, simply described as an
engine) 1 is a spark ignition type engine, and has an engine block
3, and an engine head 2 that is disposed on the engine block 3. In
the engine block 3, a plurality of cylinders not illustrated are
formed. In the engine head 2, a number of devices and actuators
such as an intake valve and a valve mechanism that drives the
intake valve, an exhaust valve and a valve mechanism that drives
the exhaust valve, an ignition plug and a fuel injection valve that
are not illustrated are mounted.
An intake passage 4 and an exhaust passage 6 are connected to the
engine head 2. In the intake passage 4, an air cleaner 10, an air
flow sensor 12, a compressor 22, an intercooler 14 and an
electronic control type throttle 16 are disposed in this order from
upstream of the intake passage 4 to the engine head 2. In the
exhaust passage 6, a turbine 24 that configures a turbocharger 20
with the compressor 22, and a catalyst device 8 are disposed in
this order from the engine head 2 to downstream. Further, in the
exhaust passage 6, a bypass passage 26 that bypasses the turbine 24
is provided, and a wastegate valve 28 is disposed in the bypass
passage 26.
The engine 1 includes an EGR device 30 that recirculates a part of
exhaust gas to the intake passage 4 from the exhaust passage 6. The
EGR device 30 is configured by an EGR passage 32, an EGR cooler 36
and an EGR valve 34. The EGR passage 32 connects the exhaust
passage 6 downstream of the catalyst device 8 and the intake
passage 4 upstream of the compressor 22. The EGR cooler 36 is
provided in the EGR passage 32, and cools exhaust gas flowing in
the EGR passage 32, that is, EGR gas. The EGR valve 34 is provided
in the EGR passage 32 downstream from the EGR cooler 36 in a
direction of a flow of the EGR gas.
The engine 1 includes a control device 100. To the control device
100, various sensors including an accelerator opening degree sensor
40 are connected in addition to the air flow sensor 12. The control
device 100 controls an operation of the engine 1 by operating
various devices and actuators included by the engine 1, based on
information obtained with these sensors. The control device 100 is
an ECU (Electronic Control Unit) having at least one CPU, at least
one ROM, and at least one RAM. Note that the control device 100 may
be configured by a plurality of ECUs. In the control device 100,
computer programs stored in the ROM are loaded onto the RAM, and
are executed by the CPU, whereby various functions relating to
engine control are realized.
2. Functions Included by Control Device
FIG. 2 is a diagram in which a function relating to control of an
opening degree of the throttle 16, a function relating to control
of an opening degree of the EGR valve 34, and a function relating
to control of an opening degree of the wastegate valve 28 are
especially extracted from the various functions included by the
control device 100 and are expressed in blocks. Although the
control device 100 includes various functions other than these
functions, illustration of the various functions is omitted. In
FIG. 2, arithmetic operation units 101 to 115 are assigned to the
respective functions. Note that the respective arithmetic operation
units 101 to 115 do not exist as hardware, but are virtually
realized when exclusive software stored in the ROM is executed in
the CPU. Hereinafter, the functions relating to throttle opening
degree control, EGR valve opening degree control and wastegate
valve opening degree control that the control device 100 has will
be described with use of FIG. 2.
The arithmetic operation unit 101 calculates a charging efficiency
of fresh air requested of the engine 1 (hereinafter, described as a
request fresh air charging efficiency). In the calculation, a map
in which the request fresh air charging efficiency is related to
the accelerator opening degree is used. By referring to the map,
the request fresh air charging efficiency corresponding to the
accelerator opening degree is obtained. However, when a vehicle
includes a cruise control device, the request fresh air charging
efficiency is determined in accordance with a magnitude of
acceleration required by a control system of the cruise control
device. Further, when the vehicle includes an autonomous drive
device, the request fresh air charging efficiency is determined in
accordance with a magnitude of acceleration requested by a control
system of the autonomous drive device.
An arithmetic operation unit 102 calculates estimated values of
various state quantities of the engine 1. The estimated values that
are calculated include an estimated value of a charging efficiency
of an in-cylinder gas, that is, all gases (hereinafter, described
as an estimated all-gasses charging efficiency), an estimated value
of an EGR rate of a gas passing through the intake valve
(hereinafter, described as an estimated EGR rate), and an estimated
value of a charging efficiency of the EGR gas in the in-cylinder
gas (hereinafter, described as an estimated EGR charging
efficiency). The estimated values of these state quantities are
calculated by using an estimation model in which dynamic
characteristics of the engine 1 are modeled. The estimation model
has a common configuration to a prediction model that will be
described later. In the prediction model that will be described
later, change of the state quantities in a predetermined prediction
period in the future from a present point of time is predicted,
whereas in the calculation by the estimation model, estimated
values of the state quantities at the present point of time are
calculated by using an engine model of substantially the same
configuration as calculation by the prediction model.
An arithmetic operation unit 103 calculates a charging efficiency
that is requested of the engine 1 (hereinafter, described as a
request charging efficiency) by adding up the request fresh air
charging efficiency calculated by the arithmetic operation unit
101, and the estimated EGR charging efficiency calculated by the
arithmetic operation unit 102. Since introduction of fresh air is
inhibited by introduction of the EGR gas, the request charging
efficiency which is a charging efficiency of all of in-cylinder
gases including not only fresh air but also the EGR gas is
calculated in order to ensure a necessary amount of fresh air (an
amount of fresh air that is requested) by additionally opening the
throttle 16.
An arithmetic operation unit 104 calculates an upper limit value of
a charging efficiency with the state of the engine 1 taken into
consideration (hereinafter, described as an upper limit charging
efficiency). In detail, the upper limit charging efficiency is a
maximum charging efficiency that is realizable at a next arithmetic
operation time after one control period. A value that can be
obtained by adding a maximum change amount of the charging
efficiency per one control period to the estimated all-gas charging
efficiency may be set as the upper limit charging efficiency. In
the calculation, a map in which the upper limit charging efficiency
is related to information indicating the state of the engine 1 at
present such as the engine speed and the intake air temperature is
used. Alternatively, the upper limit value of the charging
efficiency may be calculated by using the aforementioned engine
model.
An arithmetic operation unit 105 selects smaller one of the request
charging efficiency calculated by the arithmetic operation unit 103
and the upper limit charging efficiency calculated by the
arithmetic operation unit 104. Subsequently, the arithmetic
operation unit 105 determines the selected charging efficiency as
the target charging efficiency to be given to the engine 1. The
request charging efficiency is only an unilateral request from a
driver or the control system of the autonomous drive device or the
like, and therefore may be an unrealistic value in the state of the
engine 1 at present. In the arithmetic operation unit 105, the
target charging efficiency that is realizable by the engine 1 is
determined by restricting the request charging efficiency to a
realistic value with the state of the engine 1 taken into
consideration. In particular, at the acceleration operation time in
which the request charging efficiency drastically increases, the
request charging efficiency tends to be larger than the upper limit
charging efficiency, and the target charging efficiency is
restricted by the upper limit charging efficiency.
An arithmetic operation unit 107 selects a smaller one of the
target charging efficiency determined by the arithmetic operation
unit 105, and a corrected target charging efficiency that is
calculated by an arithmetic operation unit 106 that will be
described later. Subsequently, the arithmetic operation unit 107
determines the selected charging efficiency as a final target
charging efficiency. Consequently, if the corrected target charging
efficiency calculated by the arithmetic operation unit 106 is
smaller than the original target charging efficiency, the corrected
target charging efficiency is determined as the final target
charging efficiency, but otherwise, the target charging efficiency
is directly determined as the final target charging efficiency.
An arithmetic operation unit 108 calculates a target opening degree
of the throttle 16 (hereinafter, described as a target throttle
opening degree) based on the final target charging efficiency
determined by the arithmetic operation unit 107. In calculation of
the target throttle opening degree, an inverse model of an intake
model in which a response of the charging efficiency to an
operation of the throttle 16 is modeled by a physical expression is
used. The intake model may be configured by combining a throttle
model, an intake manifold model and an intake valve model (each of
the models will be described in detail later). By solving the
inverse model of the intake mode, the target throttle opening
degree for achieving the final target charging efficiency with high
responsiveness is obtained.
The target throttle opening degree which is calculated by the
arithmetic operation unit 108 is outputted to a driver that
operates the throttle 16. The arithmetic operation unit 108
provides a predetermined delay time period (approximately 32 msec
corresponding to several control periods, for example) for throttle
delay control in a period from calculation of the target throttle
opening degree until output. The target throttle opening degree can
be regarded as a throttle opening degree in the future by the delay
time period. If the future throttle opening degree is found, a
charging efficiency at that point of time can be also predicted,
and from the predicted charging efficiency, an amount of fuel which
should be injected by the fuel injection valve can be accurately
calculated. Consequently, the target throttle opening degree
calculated by the arithmetic operation unit 108 is also used in
prediction of the charging efficiency at the point of time in the
future by the delay time period, in the throttle delay control.
An arithmetic operation unit 109 calculates a target intake
manifold pressure based on the final target charging efficiency
determined by the arithmetic operation unit 107. A flow rate of the
gas passing through the intake valve is calculated from the final
target charging efficiency and the engine speed. In calculation of
the target intake manifold pressure, an inverse model of the intake
valve model in which a relationship between the flow rate of the
gas passing through the intake valve and the intake manifold
pressure is modeled is used. By solving the inverse model of the
intake valve model, the target intake manifold pressure for
achieving the final target charging efficiency with high
responsiveness is obtained.
An arithmetic operation unit 110 calculates a target opening degree
of the wastegate valve 28 (hereinafter, described as a target WGV
opening degree) based on the target intake manifold pressure
determined by the arithmetic operation unit 109. A pressure that is
obtained by adding a predetermined pressure loss to an intake
manifold pressure (a pressure at a downstream side of the throttle)
is a supercharging pressure (a pressure at an upstream side of the
throttle), and the supercharging pressure depends on the opening
degree of the wastegate valve 28. Therefore, in determination of
the target WGV opening degree, a map in which the target WGV
opening degree is related to information on the supercharging
pressure and the like is used.
An arithmetic operation unit 111 determines a target EGR rate that
is given to the engine 1. In determination of the target EGR rate,
a map in which the target EGR rate is related to information
indicating an operation state of the engine 1 at present (for
example, the engine speed and the charging efficiency) is used.
An arithmetic operation unit 112 calculates a target opening degree
of the EGR valve 34 (hereinafter, described as a target EGR valve
opening degree) based on the target EGR rate determined by the
arithmetic operation unit 111. In determination of the target EGR
valve opening degree, a map in which the target EGR valve opening
degree is related to the information on the target EGR rate and the
like is used.
The arithmetic operation unit 106 performs correction to the target
charging efficiency calculated by the arithmetic operation unit
105. The correction is performed to restrain a torque level
difference that occurs at the time of acceleration of the engine
1.
The torque level difference will be specifically described. At the
start of an acceleration operation, the throttle 16 is opened
significantly first in accordance with a magnitude of acceleration
that is requested by the driver or the control system of the
autonomous drive device or the like. Furthermore, in a case of
shifting to a high load from a low load with no EGR gas being
introduced, the target EGR rate is set at a value larger than zero
halfway through the shift, in order to enhance fuel consumption
performance and exhaust gas performance, and introduction of the
EGR gas is started.
FIG. 3 is a diagram illustrating an example of changes with time of
the charging efficiency of the in-cylinder gas (hereinafter,
described as the charging efficiency of all the gases) at the time
of an acceleration operation, the charging efficiency of fresh air
in the in-cylinder gas, and the charging efficiency of the EGR gas
in the in-cylinder gas. Since there is some distance from the EGR
valve 34 and the combustion chamber, a state where no EGR gas
reaches the combustion chamber continues for some period from the
start of acceleration, and only the charging efficiency of fresh
air increases. When the EGR gas reaches the combustion chamber
through the intake valve after a while, the charging efficiency of
the EGR gas increases from that point of time, and the charging
efficiency of fresh air is reduced by an increase amount of the
charging efficiency of the EGR gas. The reduction in the charging
efficiency of fresh air is only temporary, and the charging
efficiency of fresh air soon changes to increase from reduction, as
a result that the target charging efficiency further increases and
supercharging by the turbocharger 20 is started. However, as a
result that the charging efficiency of fresh air is reduced even
temporarily, the torque of the engine 1 is temporarily reduced or
is stagnate halfway through the increase of the torque. That is, a
torque level difference occurs.
In order to restrain the torque level difference like this, in the
embodiment, the target charging efficiency is set to be lower than
a value determined from the upper limit charging efficiency to
restrain introduction of fresh air into the combustion chamber,
until the influence of a delay in arrival of the EGR gas is
eliminated.
FIG. 4 is a diagram illustrating an example of a relationship
between the target EGR rate at the time of an acceleration
operation, and the estimated EGR rate of the gas passing through
the intake valve. There is a time delay corresponding to a time
period that is taken until the EGR gas passing through the EGR
valve 34 reaches the combustion chamber, until the estimated EGR
rate changes after the target EGR rate changes. In that period, the
target EGR rate is larger than the estimated EGR rate, and a
difference between both of them becomes larger as the target EGR
rate increases. When the estimated EGR rate starts to increase
shortly, the difference between the target EGR rate and the
estimated EGR rate becomes gradually small, and the difference
between both of them becomes zero when the estimated EGR rate
catches up with the target EGR rate. In this embodiment, the target
charging efficiency is corrected by subtracting the charging
efficiency corresponding to the difference between the target EGR
rate and the estimated EGR rate from the target charging
efficiency, and the target throttle opening degree is calculated
based on the corrected target charging efficiency. In this way, an
increase speed of the charging efficiency of fresh air is
restrained just before the EGR gas reaches the combustion chamber,
and the charging efficiency of fresh air can be prevented from
abruptly reducing when the EGR gas reaches the combustion
chamber.
Returning to FIG. 2 again, explanation of the functions included by
the control device 100 will be continued. An arithmetic operation
unit 113 is provided to calculate a charging efficiency correction
amount that is used in correction of the target charging efficiency
by the arithmetic operation unit 106. The arithmetic operation unit
113 calculates the charging efficiency correction amount for use in
correction of the target charging efficiency based on the target
EGR rate calculated by the arithmetic operation unit 111, the
estimated EGR rate and the estimated all-gas charging efficiency
that are calculated in the arithmetic operation unit 102. The
charging efficiency correction amount is defined as the charging
efficiency corresponding to the difference between the target EGR
rate and the estimated EGR rate. By multiplying the difference
between the target EGR rate and the estimated EGR rate by the
estimated all-gas charging efficiency, the arithmetic operation
unit 113 calculates the charging efficiency correction amount.
The charging efficiency correction amount calculated by the
arithmetic operation unit 113 is inputted to the arithmetic
operation unit 106 via an arithmetic operation unit 114. When the
charging efficiency correction amount calculated by the arithmetic
operation unit 113 is inputted to the arithmetic operation unit 106
by the arithmetic operation unit 114, the arithmetic operation unit
106 corrects the target charging efficiency by subtracting the
charging efficiency correction amount from the target charging
efficiency calculated by the arithmetic operation unit 105, and
outputs the corrected target charging efficiency that is obtained
thereby to the arithmetic operation unit 107.
The arithmetic operation unit 114 can select an output from the
charging efficiency correction amount calculated by the arithmetic
operation unit 113 and a zero value. When the zero value is
selected as the output of the arithmetic operation unit 114,
correction of the target charging efficiency by the charging
efficiency correction amount is not performed. Standard setting of
the output of the arithmetic operation unit 114 is a zero value,
and only in a period in which a switching signal is inputted from
the arithmetic operation unit 115, the output of the arithmetic
operation unit 114 is switched from the zero value to the charging
efficiency correction amount calculated by the arithmetic operation
unit 113.
The arithmetic operation unit 115 inputs the switching signal to
the arithmetic operation unit 114 only when a predetermined
condition for switching selection is established. The condition for
switching selection is that it is predictable that temporary
reduction occurs to the charging efficiency of fresh air by the
influence of the EGR rate of the in-cylinder gas which increases
later than increase in the charging efficiency if the target
throttle opening degree is calculated from the target charging
efficiency which is not corrected in the case of shifting to the
acceleration operation. In other words, the arithmetic operation
unit 115 does not input the switching signal to the arithmetic
operation unit 114 if there is no possibility of the torque level
difference even if the target charging efficiency calculated by the
arithmetic operation unit 105 is directly used in calculation of
the target throttle opening degree. Hereinafter, the case having no
possibility of a torque level difference will be described in
detail by using FIG. 5.
FIG. 5 is a diagram illustrating another example of the changes
with time of the charging efficiency of all the gases, the charging
efficiency of fresh air and the charging efficiency of the EGR gas
at the time of an acceleration operation. In this example, the
state where no EGR gas reaches the combustion chamber also
continues for a while from the start of acceleration, so that after
the charging efficiency of all of the gases starts to increase, the
charging efficiency of the EGR gas starts to increase later than
increase of the charging efficiency of all the gases. Increase of
the charging efficiency of fresh air is restrained by the increase
amount of the charging efficiency of the EGR gas. However, when the
increase speed of the charging efficiency of the EGR gas is
gradual, temporary reduction occurs to the increase speed of the
charging efficiency of the fresh air, but the charging efficiency
itself of the fresh air continues to increase without reducing.
When the charging efficiency of the fresh air continues to
increase, a state where a torque level difference due to reduction
in torque of the engine 1 occurs is not brought about. Therefore,
if the charging efficiency of the fresh air changes as in the
example illustrated in FIG. 5, it is more preferable to control the
opening degree of the throttle 16 in accordance with the target
charging efficiency than correcting the target charging efficiency
based on the charging efficiency corresponding to the difference
between the target EGR rate and the estimated EGR rate, in the
respect that responsiveness of torque to the request of
acceleration can be ensured.
Returning to FIG. 2 again, the arithmetic operation unit 115 will
be described. When the operation is shifted to the acceleration
operation, the arithmetic operation unit 115 predicts whether
temporary reduction occurs to the charging efficiency of the fresh
air when correction of the target charging efficiency is not
performed, by using a prediction model that will be described
later. Whether temporary reduction occurs to the charging
efficiency of the fresh air can be predicted by comparing the
increase speed of the charging efficiency of all the gases, and the
increase speed of the charging efficiency of the EGR gas. When the
increase speed of the charging efficiency of the EGR gas is higher
than the increase speed of the charging efficiency of all the
gases, the increase speed of the charging efficiency of the fresh
air, which is the difference between the increase speed of the
charging efficiency of all the gases and the increase speed of the
charging efficiency of the EGR gas, becomes a negative value. The
increase speed of the charging efficiency of the fresh air being
negative means that the charging efficiency of the fresh air
reduces at each cycle.
In detail, the arithmetic operation unit 115 firstly predicts a
change of the throttle opening degree in the case of not performing
correction of the target charging efficiency. When the change is
within a delay time period of the throttle delay control, the
target throttle opening degree which is calculated from the target
charging efficiency which is not corrected can be regarded as a
future throttle opening degree. As for the throttle opening degree
of the future later than the delay time period of the throttle
delay control, prediction may be performed on the assumption that
the change speed of the throttle opening degree is constant. The
arithmetic operation unit 115 predicts a change of the increase
speed of the charging efficiency of all the gases and a changes of
the increase speed of the charging efficiency of the EGR gas in the
predetermined prediction period of the future later than the
present point of time, based on the predicted throttle opening
degree. When the increase speed of the charging efficiency of the
EGR gas is predicted to be larger than the increase speed of the
charging efficiency of all the gases at least once, within the
prediction period, the arithmetic operation unit 115 inputs a
switching signal to the arithmetic operation unit 114 in a period
until the acceleration operation is ended.
Contents of the arithmetic units 101 to 115 included by the control
device 100 are as described above. In relation with the claims of
the present application, the arithmetic operation units 101, 102,
103, 104 and 105 configure target charging efficiency determination
means. Further, the arithmetic operation units 106, 107, 108, 113
and 114 configure target throttle opening degree arithmetic
operation means. When the output of the arithmetic operation unit
114 is zero, it indicates that a first arithmetic operation is
selected in the target charging efficiency determination means, and
when the output of the arithmetic operation unit 114 is the input
value from the arithmetic operation unit 113, it indicates that a
second arithmetic operation is selected in the target charging
efficiency determination means. The arithmetic operation unit 115
configures prediction means.
3. Control Flow of Throttle Opening Degree Control
Throttle opening degree control to restrain the torque level
difference at the time of an acceleration operation is performed by
the control device 100 which is configured as described above. FIG.
6 is a flowchart illustrating a control flow of the throttle
opening degree control that is executed by the control device
100.
In step S1, the control device 100 takes in the accelerator opening
degree which is measured by the accelerator opening degree sensor
40. Next, in step S2, the control device 100 calculates the request
charging efficiency based on the accelerator opening degree which
is taken in, in step S1. Note that when the vehicle includes a
cruise control device, the request charging efficiency may be
calculated based on the request for acceleration from the control
system thereof. Further, when the vehicle includes an autonomous
drive device, the request charging efficiency may be calculated
based on the request for acceleration from the control system
thereof. Subsequently, in step S3, the control device 100 restricts
the request charging efficiency calculated in step S2 by the upper
limit charging efficiency, and thereby calculates the target
charging efficiency which is realizable by the engine 1.
Next, in step S4, the control device 100 determines whether the
present point of time is the point of time of start of the
acceleration operation. The determination can be performed based on
the accelerator opening degree and the changing speed thereof.
Alternatively, when a deviation of a threshold value or more occurs
between the request charging efficiency and the estimated all-gas
charging efficiency due to increase in the request charging
efficiency, a time point thereof may be regarded as the time point
of start of the acceleration operation. A time point of end of the
acceleration operation can be regarded as a time point at which the
estimated all-gas charging efficiency catches up with the request
charging efficiency and the difference thereof reaches the
threshold value or less, for example.
When the present time point is determined as the time point of
start of the acceleration operation in the determination in step
S4, step S5 is selected. In step S5, the control device 100
predicts whether the increase speed of the charging efficiency of
the EGR gas ever becomes higher than the increase speed of the
charging efficiency of all the gases in the period of the
acceleration operation, by the future prediction using the
prediction model which will be described later. When a result of
the determination in step S4 is negative, step S5 is skipped, and
step S7 is selected as next processing. Therefore, determination in
step S5 is performed only once at the time point of start of the
acceleration operation, and thereafter, the determination in step
S5 is not performed.
When it is predicted that the increase speed of the charging
efficiency of the EGR gas becomes higher than the increase speed of
the charging efficiency of all the gases in the determination in
step S5, step S6 is selected. In step S6, the control device 100
determines to carry out correction of the target charging
efficiency. When the determination is performed, a switching signal
is inputted to the arithmetic operation unit 114 from the
arithmetic operation unit 115 that configures the control device
100. When the result of the determination in step S5 is negative,
step S6 is skipped, and step S7 is selected as next processing.
In step S7, the control device 100 determines presence or absence
of correction of the target charging efficiency. When it is
determined to carry out correction of the target charging
efficiency in step S6, the determination result in step S7 is
affirmative, and step S8 is selected. When the determination result
in step S7 is negative, step S8 is skipped, and step S9 is
selected.
In step S8, the control device 100 calculates the charging
efficiency corresponding to the difference between the target EGR
rate and the estimated EGR rate of the gas passing through the
intake valve, and uses this charging efficiency as the charging
efficiency correction amount to the target charging efficiency.
That is, the control device 100 subtracts the charging efficiency
correction amount from the target charging efficiency, and reduces
the target charging efficiency by the charging efficiency
correction amount. In the relationship with the claims of the
present application, performing the processing in step S8
corresponds to selection of the second arithmetic operation, and
skipping the processing in step S8 corresponds to selection of the
first arithmetic operation.
Next, in step S9, the control device 100 calculates the target
throttle opening degree corresponding to the target charging
efficiency. The target charging efficiency for use in the
calculation is the target charging efficiency corrected in step S8
when the correction processing in step S8 is performed, and is the
target charging efficiency calculated in step S3 when the
correction processing in step S8 is not performed. Subsequently, in
step S10, the control device 100 controls the opening degree of the
throttle 16 based on the target throttle opening degree calculated
in step S9.
4. Operation of Engine in Case of Throttle Opening Degree Control
being Executed
When the above described control flow is executed, at the time of
acceleration from a low load with no EGR gas being introduced, the
engine 1 is operated as illustrated in time charts in FIGS. 7 and
8, for example. The respective time charts illustrate changes with
times of the charging efficiencies of fresh air, the EGR rates and
the throttle opening degrees, in sequence from the top.
FIG. 7 illustrates an operation of the engine 1 as a result of
throttle opening degree control which is adopted when it is
predicted that the increase speed of the charging efficiency of the
EGR gas becomes higher than the increase speed of the charging
efficiency of all the gases.
In a time chart of the charging efficiency of fresh air, a broken
line assigned with a label "request value" shows a change with time
of the request charging efficiency. By restricting the request
charging efficiency to a realistic value with the state of the
engine 1 taken into consideration, the target charging efficiency
(the target charging efficiency before correction) realizable by
the engine 1 is determined. A curved line assigned with a label
"target value (before correction)" shows the change with time of a
proportion of the fresh air in the target charging efficiency
before correction. A curved line assigned with a label "target
value" shows a change with time of a proportion of the fresh air in
the target charging efficiency after correction. A curved line
assigned with a label "actual value" shows a change with time of
the actual charging efficiency of the fresh air.
In a time chart of the EGR rate, a curved line assigned with a
label of "target value" shows a change with time of the target EGR
rate. A curved line assigned with a label of "estimated value"
shows a change with time of the estimated EGR rate of the gas
passing through the intake valve. When the target EGR rate and the
estimated EGR rate change as illustrated in this time chart,
according to the throttle opening degree control of the embodiment,
the charging efficiency corresponding to the difference between the
target EGR rate and the estimated EGR rate is calculated as the
charging efficiency correction amount. The "target value" of the
charging efficiency of the fresh air illustrated in the time chart
in an upper tier is obtained by subtracting the charging efficiency
correction amount from the "target value (before correction)" of
the charging efficiency of the fresh air.
In the time chart of the throttle opening degree, the curved line
assigned with a label of "throttle opening degree (without
restriction)" shows a change with time of the throttle opening
degree in a case of the target throttle opening degree being
calculated based on the target charging efficiency before
correction. The curved line assigned with a label of "throttle
opening degree (with restriction)" shows a change with time of the
throttle opening degree in a case of the target throttle opening
degree being calculated based on the target charging efficiency
after correction. The target charging efficiency corrected by the
charging efficiency correction amount is used in calculation of the
target throttle opening degree, whereby the target throttle opening
degree is corrected to the closing side before and after the EGR
gas reaches the combustion chamber. The throttle 16 is controlled
based on the target throttle opening degree, whereby the increase
speed of the throttle opening degree is restrained as shown by
"throttle opening degree (with restriction)". Thereby, the charging
efficiency of the fresh air smoothly changes even before and after
the EGR gas reaches the combustion chamber, and the torque level
difference due to an arrival delay of the EGR gas is
restrained.
FIG. 8 illustrates an operation of the engine 1 as a result of
throttle opening degree control that is adopted when it is
predicted that the increase speed of the charging efficiency of the
EGR gas does not become higher than the increase speed of the
charging efficiency of all the gases.
In a time chart of the charging efficiency of the fresh air, a
broken line assigned with a label of "request value" shows a change
with time of the request charging efficiency. A curved line
assigned with a label of "target value" shows a change with time of
a proportion of the fresh air in the target charging efficiency
obtained by restricting the request charging efficiency to a
realistic value with the state of the engine 1 taken into
consideration. A curved line assigned with a label of "actual
value" shows a change with time of an actual charging efficiency of
the fresh air.
In a time chart of the EGR rate, a curved line assigned with a
label of "target value" shows a change with time of the target EGR
rate. A curved line assigned with a label of "estimated value"
shows a change with time of the estimated EGR rate of a gas passing
through the intake valve. When the change speed of the estimated
EGR rate is low as illustrated in the time chart, the increase
speed of the charging efficiency of the EGR gas is also low, and
does not become higher than the increase speed of the charging
efficiency of all the gases. In this case, according to the
throttle opening degree control of the embodiment, correction of
the target charging efficiency by the charging efficiency
corresponding to the difference between the target EGR rate and the
estimated EGR rate is not performed.
A curved line illustrated in a time chart of the target throttle
opening degree shows a change with time of the throttle opening
degree in a case of the target throttle opening degree being
calculated based on the target charging efficiency. Correction to
the target charging efficiency is not performed, whereby the
throttle opening degree increases without the increase speed
thereof being restrained. Thereby, the charging efficiency of the
fresh air can be increased at the highest speed, and responsiveness
of torque to the request for acceleration is ensured.
5. Configuration of Prediction Model
Next, a prediction model for use in prediction of the change speed
of the charging efficiency of the fresh air will be described. FIG.
9 is a block diagram illustrating an example of a configuration of
the prediction model. The prediction model is configured by a
plurality of element models, that is, a wastegate valve response
model M1, a turbo rotational speed model M2, a compressor model M3,
an intercooler model M4, a throttle model M5, an intake manifold
model M6, an intake valve model M7, an air cleaner model M8, an air
bypass valve model M9, an EGR valve model M10 and EGR diffusion
models M11, M12 and M13. FIG. 9 illustrates only main flows of
information out of flows of information among the element models.
Therefore, the flows of the information among the element models
are not limited to the example illustrated in FIG. 9. Hereinafter,
contents of the element models included by the prediction model
will be described. However, these element models are all well
known, and therefore, explanation concerning design matters such as
mathematical expressions expressing the respective element models
and maps will be omitted here.
The wastegate valve response model M1 is a model for calculating a
diaphragm differential pressure "dP.sub.wgv" of the wastegate valve
28 from an instruction opening degree "D.sub.wgv" to the wastegate
valve 28. The wastegate valve response model M1 is a model in which
a response characteristic of the diaphragm differential pressure to
the instruction opening degree is modeled, and is specifically
expressed by a dead time element and a first order lag element. In
the future prediction by the arithmetic operation unit 115, the
instruction opening degree which is inputted to the wastegate valve
response model M1 is full opening until the throttle opening degree
is fully opened, and is switched to full closing after the throttle
opening degree is fully opened. Note that if a response delay of
the wastegate valve 28 is such a delay that is ignorable, the
wastegate valve response model M1 may be omitted.
The turbo rotational speed model M2 is a model of a rotation
behavior of the turbine 24. A difference between energy that is
added to the turbine 24 and energy that is consumed by the
compressor 22 is proportional to a change rate of the rotational
speed of the turbine 24. Under the physical relationship, a
relationship that is established between a flow rate of all the
gasses passing through the intake valve (hereinafter, described as
an intake valve flow rate), the diaphragm differential pressure of
the wastegate valve 28 and the turbo rotational speed is modeled as
the turbo rotational speed model M2. In the turbo rotational speed
model M2, the diaphragm differential "dP.sub.wgv" calculated in the
wastegate valve response model M1, and an intake valve flow rate
"m.sub.c" calculated in the intake valve model M7 that will be
described later are inputted, and a turbo rotational speed
"N.sub.tb" is calculated from the input information on them.
The compressor model M3 is a model in which a compression
characteristic of the compressor 22 is modeled. A relationship that
is established between a pressure ratio between the upstream side
and the downstream side of the compressor 22, the turbo rotational
speed, and a flow rate of a gas passing through the compressor 22
(hereinafter, described as a compressor flow rate) is modeled as
the compressor model M3. In the compressor model M3, information on
the turbo rotational speed "N.sub.tb" that is calculated in the
turbo rotational speed model M2, a supercharging pressure
"P.sub.cmp" that is calculated in the intercooler model M4 that
will be described later, an air cleaner downstream pressure
"P.sub.ac" that is calculated in the air cleaner model M8 that will
be described later and the like is inputted. From the input
information on them, a compressor flow rate "m.sub.cmp" is
calculated, and a compressor downstream temperature "T.sub.cmp" is
calculated.
The intercooler model M4 is a physical model that is constructed
based on a conservation law concerning gas in the intercooler 14 in
the intake passage 4. As the intercooler model M4, a formula of an
energy conservation law and a formula of a flow rate conservation
law are specifically used. In the intercooler model M4, information
on a flow rate obtained by subtracting an air bypass valve flow
rate (a flow rate of gas passing through an air bypass valve)
"m.sub.abv" that is calculated in the air bypass valve model M9
that will be described later, from the compressor flow rate
"m.sub.cmp" that is calculated in the compressor model M3, the
compressor downstream temperature "T.sub.cmp" calculated in the
compressor model M3, a throttle flow rate (a flow rate of gas
passing through the throttle 16) "m.sub.t" that is calculated in
the throttle model M5 that will be described later and the like is
inputted. From the input information on them, a supercharging
pressure "p.sub.cmp" is calculated, and an intercooler outlet
temperature "T.sub.ic" is calculated.
The throttle model M5 is a model for calculating a throttle flow
rate from the throttle opening degree. Specifically, a throttle
formula (or also referred to as an orifice flow rate formula) that
has a pressure ratio between the upstream side and the downstream
side of the throttle 16, an upstream temperature of the throttle
16, a passage area determined by the throttle opening degree, and a
flow rate coefficient as parameters is used as the throttle model
M5. In the throttle model M5, information on the supercharging
pressure "P.sub.cmp" and the intercooler outlet temperature
"T.sub.ic" that are calculated in the intercooler model M4, an
intake manifold pressure "P.sub.m" that is calculated in the intake
manifold model M6 that will be described later and the like is
inputted. Further, a throttle opening degree "TA" in a case where
correction of the target charging efficiency is not performed,
which is predicted separately, is inputted to the throttle model
M5. Subsequently, a throttle flow rate "m.sub.t" is calculated from
the input information on them.
The intake manifold model M6 is a physical model that is
constructed based on a conservation rule concerning air in the
intake manifold. As the intake manifold model M6, a formula of an
energy conservation law and a formula of a flow rate conservation
law are specifically used. In the intake manifold model M6,
information on the throttle flow rate "m.sub.t" calculated in the
throttle model M5, an intake valve flow rate "m.sub.c" that is
calculated in the intake valve model M7 that will be described
later and the like is inputted, and the intake manifold pressure
"P.sub.m" is calculated from input information on them.
The intake valve model M7 is a model based on an experimental
result of investigating a relationship between the intake valve
flow rate and the intake manifold pressure. By an empirical rule
obtained by an experiment, the relationship between the intake
valve flow rate and the intake manifold pressure is approximated by
a broken line (or a straight line) that monotonously changes in the
intake valve model M7. A coefficient of an equation of the broken
line (or the straight line) is not a constant, but a variable that
is determined by the engine speed or the like. In the intake valve
model M7, information on the engine speed and the like is inputted,
in addition to the intake manifold pressure "P.sub.m" that is
calculated in the intake manifold model M6, and the intake valve
flow rate "m.sub.c" is calculated from the input information on
them. Subsequently, the intake valve flow rate "m.sub.c" is
converted into a flow rate per one cycle by using the engine speed,
and a ratio to a mass of air corresponding to a stroke volume is
calculated, whereby the charging efficiency of all the gases is
calculated. In the calculation, a present value of the engine speed
may be used.
The air cleaner model M8 is a model for calculating a pressure loss
that occurs in the air cleaner 10. The air cleaner model M8
calculates a value obtained by subtracting a pressure loss from the
atmospheric pressure "P.sub.a" as the air cleaner downstream
pressure "P.sub.ac". For the atmospheric pressure "P.sub.a", a
standard atmospheric pressure stored in the memory of the ECU may
be used as a preset value, or a value of the atmospheric pressure
under each situation measured by the atmospheric pressure sensor
may be used. The pressure loss can be calculated from a flow rate
of fresh air that passes through the air cleaner 10. A flow rate
"m.sub.ga" of the fresh air that passes through the air cleaner 10
can be roughly calculated by correcting a flow rate that is
obtained by subtracting the air bypass valve flow rate "m.sub.abv"
from the compressor flow rate "m.sub.cmp" by an EGR rate
"R.sub.egr1" in the outlet of the compressor 22. If the pressure
loss of the air cleaner 10 is such a degree as to be ignorable, the
air cleaner model M8 may be omitted.
The air bypass valve model M9 is a model for calculating a flow
rate of a gas that is returned to an upstream side from the
downstream side of the compressor 22 by the air bypass valve not
illustrated. As the air bypass valve model M9, a throttle formula
is used as in the throttle model M5. In the air bypass valve model
M9, information on the air cleaner downstream pressure "P.sub.ac"
that is calculated in the air cleaner model M8, the supercharging
pressure "P.sub.cmp" that is calculated in the intercooler model
M4, an opening degree of the air bypass valve and the like is
inputted, and from the input information on them, the air bypass
valve flow rate "m.sub.abv" is calculated. When the engine 1 does
not include an air bypass valve, the air bypass valve model M9 is
omitted.
The EGR valve model M10 is a model for calculating the flow rate
(hereinafter, described as the EGR valve flow rate) of the EGR gas
that passes through the EGR valve 34. As a formula for calculating
the EGR valve flow rate, a throttle formula can be used as in the
throttle model M5 and the air bypass valve model M9. However, the
upstream pressure and the downstream pressure of the EGR valve 34
both depend on the flow rate of fresh air, and therefore, the EGR
valve flow rate can be expressed by a function (a function obtained
by modifying the throttle formula) of the opening degree of the EGR
valve 34 and the flow rate of the fresh air. In the EGR valve model
M10, based on the flow rate "m.sub.egr" of fresh air and an opening
degree "th.sub.egr" of the EGR valve 34, the EGR valve flow rate
"m.sub.egr" is calculated from the aforementioned function. For the
EGR valve opening degree "th.sub.egr", a value determined based on
the charging efficiency calculated from the intake valve flow rate
"m.sub.c" is used. By calculating a ratio of the EGR valve flow
rate "m.sub.egr" calculated in the EGR valve model M10, and a flow
rate obtained by adding the EGR valve flow rate "m.sub.egr" to the
flow rate "m.sub.ga" of fresh air, an EGR rate "R.sub.egr0" in the
outlet of the EGR valve 34 is obtained.
The EGR diffusion model M11 is a model in which a change with time
of the EGR rate by diffusion of EGR gas in the compressor 22 is
modeled, and is specifically expressed by a dead time element and a
first order lag element. The dead time is a time necessary for gas
to pass through the compressor 22, and is related to the upstream
temperature, the upstream pressure and the flow rate of fresh air
of the compressor 22. A time constant of the first order lag
element is a parameter indicating a degree of diffusion of the EGR
gas in the compressor 22, and is related to the flow rate of fresh
air. In the EGR diffusion model M11, the EGR rate "R.sub.egr0" in
the outlet of the EGR valve 34 is processed with the dead time
element and the first order lag element, whereby the EGR rate
"R.sub.egr1" in the outlet of the compressor 22 is calculated.
The EGR diffusion model M12 is a model in which a change with time
of the EGR rate by diffusion of the EGR gas in the throttle 16 is
modeled, and is specifically expressed by a dead time element and a
first order lag element. A dead time is a time that is necessary
for gas to pass through the throttle 16, and is related to the
upstream temperature, the upstream pressure and the flow rate of
fresh air of the throttle 16. A time constant of the first order
lag element is a parameter indicating a degree of diffusion of the
EGR gas in the throttle 16, and is related to the flow rate of
fresh air. In the EGR diffusion model M12, the EGR rate
"R.sub.egr1" in the outlet of the compressor 22 is processed with
the dead time element and the first order lag element, whereby the
EGR rate "R.sub.egr2" in the outlet of the throttle 16 is
calculated.
The EGR diffusion model M13 is a model in which a change with time
of the EGR rate by diffusion of the EGR gas in the intake valve is
modeled, and is specifically expressed by a dead time element and a
first order lag element. A dead time is a time that is necessary
for gas to pass through the intake valve, and is related to an
upstream temperature, an upstream pressure and a flow rate of fresh
air of the intake valve. A time constant of the first order lag
element is a parameter indicating a degree of diffusion of the EGR
gas in the intake valve, and is related to the flow rate of fresh
air. In the EGR diffusion model M13, the EGR rate "R.sub.egr2" in
the outlet of the throttle 16 is processed with the dead time
element and the first order lag element, whereby the EGR rate
"R.sub.egr3" in the outlet of the intake valve is calculated. Note
that the three EGR diffusion models M11, M12 and M13 may be
combined into one, and configured as a single EGR diffusion
model.
By multiplying the intake valve flow rate "m.sub.c" that is
calculated in the intake valve model M7 by the EGR rate
"R.sub.egr3" calculated in the EGR diffusion model M13, a flow rate
"m.sub.egr" of the EGR gas passing through the intake valve is
calculated. Subsequently, the flow rate "m.sub.egr" of the EGR gas
is converted into a flow rate per one cycle by using the engine
speed, and a ratio to a mass of air corresponding to the stroke
volume is calculated, whereby the charging efficiency of the EGR
gas is calculated.
The arithmetic operation unit 115 of the control device 100 repeats
calculation by the prediction model configured as above by a number
of times corresponding to a prediction period. When a divided time
period of prediction is set as .DELTA.t, calculation by the
prediction model is repeated by the number of times obtained by
dividing the prediction period by the time period .DELTA.t.
However, the time period .DELTA.t is only a parameter in
calculation, and is not an actual time period. The control device
100 executes repetitive calculation of the number of times
corresponding to the prediction period, in a single arithmetic
operation period.
In calculation by the prediction model, a series of calculations
shown below is performed at processing of each time. First, an
outline of calculation for predicting the increase speed of the
charging efficiency of all the gases is as follows.
(a1) From the change speed of the throttle opening degree, the
throttle opening degree "TA" of the future by the time period
.DELTA.t is predicted.
(a2) From the throttle opening degree "TA", the intake manifold
pressure "P.sub.m" of the future by the time period .DELTA.t is
predicted by using the throttle model M5 and the intake manifold
model M6.
(a3) From the intake manifold pressure "P.sub.m", the intake valve
flow rate "m.sub.c" of the future by the time period .DELTA.t is
predicted by using the intake valve model M7.
(a4) From the intake valve flow rate "m", the turbo rotational
speed "N.sub.tb" of the future by the time period .DELTA.t is
predicted by using the turbo rotational speed model M2.
(a5) From the turbo rotational speed "N.sub.tb", the compressor
flow rate "m.sub.cmp" and the compressor downstream temperature
"T.sub.cmp" of the future by the time period .DELTA.t are
calculated by using the compressor model M3.
(a6) From the compressor flow rate "m.sub.cmp" and the compressor
downstream temperature "T.sub.cmp", the supercharging pressure
"P.sub.cmp" and the intercooler outlet temperature "T.sub.ic" of
the future by the time period .DELTA.t are calculated by using the
intercooler model M4.
A series of calculations of the above is performed by processing of
one time, and the intake valve flow rate "m.sub.c" of the future by
the time period .DELTA.t is calculated at the processing of each
time. Subsequently, from the intake valve flow rate "m.sub.c", the
charging efficiency of all the gases is calculated, and the
increase speed of the charging efficiency of all the gases is
calculated from a difference between the value of this time and a
value of a previous time of the charging efficiency of all the
gases. The supercharging pressure "P.sub.cmp" and the intercooler
outlet port temperature "T.sub.ic" which are calculated in (a6) in
the end are used as inputs to the throttle model M5 in processing
of a next time.
Next, an outline of calculation for predicting the increase speed
of the charging efficiency of the EGR gas is as follows.
(b1) From the change speed of the throttle opening degree, the
throttle opening degree "TA" of the future by the time period
.DELTA.t is predicted.
(b2) From the throttle opening degree "TA", the intake manifold
pressure "P.sub.m" of the future by the time period .DELTA.t is
predicted by using the throttle model M5 and the intake manifold
model M6.
(b3) From the intake manifold pressure "P.sub.m", the intake valve
flow rate "m.sub.c" of the future by the time period .DELTA.t is
predicted by using the intake valve model M7.
(b4) From the intake valve flow rate "m.sub.c", the turbo
rotational speed "N.sub.tb" of the future by the time period
.DELTA.t is predicted by using the turbo rotational speed model
M2.
(b5) From the turbo rotational speed "N.sub.tb", the compressor
flow rate "m.sub.cmp" and the compressor downstream temperature
"T.sub.cmp" of the future by the time period .DELTA.t are
calculated by using the compressor model M3.
(b6) From the compressor flow rate "m.sub.cmp", the flow rate
"m.sub.ga" of fresh air of the future by the time period .DELTA.t
is calculated.
(b7) From the flow rate "m.sub.ga" of fresh air, the flow rate
"m.sub.egr" of the EGR gas of the future by the time period
.DELTA.t is calculated by using the EGR valve model M10 and the EGR
diffusion models M11, M12 and M13.
A series of calculations in the above is performed by processing of
one time, and the flow rate "m.sub.c," of the EGR gas of the future
by the time period .DELTA.t is calculated at the processing of each
time. Subsequently, from the flow rate "m.sub.egr" of the EGR gas,
the charging efficiency of the EGR gas is calculated, and from a
difference between a value of this time and a value of a previous
time of the charging efficiency of the EGR gas, the increase speed
of the charging efficiency of the EGR gas is calculated.
The arithmetic operation unit 115 of the control device 100
compares the increase speed of the charging efficiency of all the
gases calculated in this way, and the increase speed of the
charging efficiency of the EGR gas at each time. As described
above, when the increase speed of the charging efficiency of the
EGR gas becomes larger than the increase speed of the charging
efficiency of all the gases, the increase speed of the charging
efficiency of fresh air becomes negative, and therefore it can be
predicted that temporary reduction occurs to the charging
efficiency of fresh air.
6. Another Example of Configuration of Prediction Model
FIG. 10 is a block diagram illustrating another example of a
configuration of a prediction model for use in prediction of the
change speed of the charging efficiency of fresh air. The
prediction model is a model that is simplified more than the
prediction model illustrated in FIG. 9, and is configured by three
element models, that is, a supercharging model M21, an intake model
M22 and an EGR model M23. FIG. 10 describes only main flows of
information out of flows of information among the element models.
Therefore, the flows of the information among the element models
are not limited to the example illustrated in FIG. 10. Hereinafter,
contents of the three element models included by the prediction
model will be described.
The supercharging model M21 is a model in which a relationship
between the intake valve flow rate, the atmospheric pressure and
the compressor flow rate is modeled, and corresponds to what is
obtained by integrating the turbo rotational speed model M2 and the
compressor model M3 in the prediction model illustrated in FIG. 9.
The compressor flow rate can be expressed by a function having the
intake valve flow rate and the atmospheric pressure as variables.
In the supercharging model M21, the intake valve flow rate
"m.sub.c" calculated in the intake model M22 that will be described
later and the atmospheric pressure "P.sub.a" are inputted, and the
compressor flow rate "m.sub.cmp" is calculated by using the
aforementioned function. A fixed value may be used as the
atmospheric pressure. In that case, the compressor flow rate can be
expressed by a function having only the intake valve flow rate as a
variable.
The intake model M22 is a model in which a relationship between the
compressor flow rate, the throttle opening degree and the intake
valve flow rate is modeled, and corresponds to what is obtained by
integrating the intercooler model M4, the throttle model M5, the
intake manifold model M6 and the intake valve model M7 in the
prediction model illustrated in FIG. 9. The intake valve flow rate
can be expressed by a function having the compressor flow rate and
the throttle opening degree as variables. In the intake model M22,
the compressor flow rate "m.sub.cmp" that is calculated in the
supercharging model M21, and the throttle opening degree "TA" in
the case of not performing correction of the target charging
efficiency, which is predicted separately, are inputted, and the
intake valve flow rate "m.sub.c" is calculated by using the
aforementioned function. Subsequently, the intake valve flow rate
"m.sub.c" is converted into the flow rate per one cycle by using
the engine speed, and a ratio to a mass of air corresponding to the
stroke volume is calculated, whereby the charging efficiency of all
the gases can be calculated.
The EGR model M23 is a model in which a relationship between the
compressor flow rate, the EGR valve opening degree and the EGR rate
is modeled, and corresponds to what is obtained by integrating the
EGR valve model M10, the EGR diffusion models M11, M12 and M13 in
the prediction model illustrated in FIG. 9. The EGR rate can be
expressed by a function having the compressor flow rate and the EGR
valve opening degree as variables. In the EGR model M23, the
compressor flow rate "m.sub.cmp" calculated in the supercharging
model M21, and the EGR valve opening degree "th.sub.egr" that is
separately predicted are inputted, and the EGR rate "R.sub.egr" is
calculated by using the aforementioned function.
By multiplying the intake valve flow rate "m.sub.c" calculated in
the intake model M22 by the EGR rate "R.sub.egr" calculated in the
EGR model M23, the flow rate "m.sub.egr" of the EGR gas that passes
through the intake valve is calculated. Subsequently, the flow rate
"m.sub.egr" of the EGR gas is converted into the flow rate per one
cycle by using the engine speed, the ratio to a mass of air
corresponding to the stroke volume, whereby the charging efficiency
of the EGR gas is calculated.
If the increase speed of the charging efficiency of all the gases
and the increase speed of the charging efficiency of the EGR gas
can be respectively predicted based on the throttle opening degree
in the case of not performing correction of the target charging
efficiency, the prediction model which is simplified as illustrated
in FIG. 10 may be used.
7. Other Embodiments
As the second arithmetic operation by which the increase speed of
the throttle opening degree is restrained more than by the first
arithmetic operation, restricting the change amount per one control
period of the target throttle opening degree with a guard value may
be adopted. The guard value in that case may be a fixed value, or
may be a function having a difference between the target EGR rate
and the estimated EGR rate as a variable.
* * * * *