U.S. patent application number 13/824483 was filed with the patent office on 2013-07-25 for fuel supply method.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The applicant listed for this patent is Toshihiro Mori. Invention is credited to Toshihiro Mori.
Application Number | 20130186071 13/824483 |
Document ID | / |
Family ID | 47755447 |
Filed Date | 2013-07-25 |
United States Patent
Application |
20130186071 |
Kind Code |
A1 |
Mori; Toshihiro |
July 25, 2013 |
FUEL SUPPLY METHOD
Abstract
The method of the present invention calculates based on the
status of the exhaust emission purifier, a required supply of fuel
to be supplied from the fuel supply valve to the exhaust passage,
reads a unit fuel supply L.sub.U in accordance with a energized
time t.sub.U for the fuel supply valve per one shot, supplies with
a driving cycle depending on the required supply, fuel in the unit
supply to the exhaust passage, when
E.sub.DT-E.sub.DU<E.sub.A-(L.sub.U-g) is established, the
energized time t.sub.UT corresponding to the target fuel supply is
interpolated as a function of (L.sub.U/g) and the target fuel
supply L.sub.U is updated as a new unit supply L.sub.U, and the
function of (L.sub.U/g) is supplied as a new energized time t.sub.U
from the fuel supply valve to the exhaust passage.
Inventors: |
Mori; Toshihiro;
(Suntou-gun, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mori; Toshihiro |
Suntou-gun |
|
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi, Aichi
JP
|
Family ID: |
47755447 |
Appl. No.: |
13/824483 |
Filed: |
August 30, 2011 |
PCT Filed: |
August 30, 2011 |
PCT NO: |
PCT/JP2011/004843 |
371 Date: |
March 18, 2013 |
Current U.S.
Class: |
60/274 |
Current CPC
Class: |
F01N 13/02 20130101;
F01N 2610/03 20130101; F01N 2900/0422 20130101; F01N 2900/1404
20130101; F01N 2560/025 20130101; F01N 2900/1402 20130101; F01N
3/035 20130101; F01N 3/0842 20130101; F01N 3/0871 20130101; F01N
2900/0412 20130101; F01N 3/106 20130101; Y02T 10/47 20130101; F01N
3/025 20130101; F01N 9/002 20130101; F01N 2610/107 20130101; Y02T
10/40 20130101; F01N 9/00 20130101; F01N 2900/0418 20130101; F01N
3/10 20130101 |
Class at
Publication: |
60/274 |
International
Class: |
F01N 3/10 20060101
F01N003/10 |
Claims
1-9. (canceled)
10. A method for supplying fuel from a fuel supply valve to an
exhaust passage at an upstream side of an exhaust emission
purifier, the method comprising the steps of: calculating, based on
the status of the exhaust emission purifier, a required supply of
fuel to be supplied from the fuel supply valve to the exhaust
passage; reading a unit fuel supply L.sub.U to be supplied to the
exhaust passage in accordance with a energized time t.sub.U to the
fuel supply valve per one shot; intermittently supplying, with a
driving cycle depending on the required supply, fuel of the unit
fuel supply L.sub.U from the fuel supply valve to the exhaust
passage; reading the maximum tolerance E.sub.A corresponding to the
unit supply L.sub.U; reading the maximum variation error E.sub.DU
of the fuel supply valve corresponding to the unit supply L.sub.U;
calculating, regard to the fuel the unit supply L.sub.U, an actual
fuel supply g actually supplied to the exhaust passage; setting a
target fuel supply L.sub.UT that is less than the unit supply
L.sub.U by a certain amount; reading the maximum variation error
E.sub.DT of the fuel supply valve corresponding to the target fuel
supply L.sub.UT; judging whether
E.sub.DT-E.sub.DU<E.sub.A-(L.sub.U-g) is established or not;
interpolating, when it is judged that
E.sub.DT-E.sub.DU<E.sub.A-(L.sub.U-g) is established, an
energized time T.sub.UT to the fuel supply valve corresponding to
the target fuel supply L.sub.UT as a function of (L.sub.U/g); and
updating the target fuel supply L.sub.UT as a new unit fuel supply
L.sub.U and using the function of (L.sub.U/g) as a new energized
time t.sub.U to drive the fuel supply valve to supply fuel to the
exhaust passage.
11. The method as claimed in claim 10, wherein: the step of reading
a unit fuel supply L.sub.U to be supplied to the exhaust passage in
accordance with an energized time t.sub.U to the fuel supply valve
per one shot reads the latest updated unit supply L.sub.U.
12. The method as claimed in claim 10, wherein when fuel to be
supplied from the fuel supply valve in accordance with the required
supply at every driving cycle of the fuel supply valve is in an
amount exceeding the double of the unit fuel supply, a half of the
to-be-supplied amount is supplied.
13. The method as claimed in claim 11, wherein when fuel to be
supplied from the fuel supply valve in accordance with the required
supply at every driving cycle of the fuel supply valve is in an
amount exceeding the double of the unit fuel supply, a half of the
to-be-supplied amount is supplied.
14. The method as claimed in claim 10, wherein the state of the
exhaust emission purifier for calculating the required supply is a
temperature of the exhaust emission purifier or an air/fuel ratio
of exhaust flowing therein, and the method further comprises a step
of judging, by carrying-out of the step of intermittently supplying
fuel from the fuel supply valve to the exhaust passage for the
energized time t.sub.U, whether the temperature of the exhaust
emission purifier or the air/fuel ratio of the exhaust flowing
therein is convergent or not and, only when it is judged that the
temperature of the exhaust emission purifier or the air/fuel ratio
of the exhaust flowing therein is convergent, the step of judging
whether E.sub.DT-E.sub.DU<E.sub.A-(L.sub.U-g) is established or
not is carried out.
15. The method as claimed in claim 14, wherein the step of judging
whether the temperature of the exhaust emission purifier or the
air/fuel ratio of the exhaust flowing therein is convergent or not,
includes a step of judging whether at least one of the temperature
of the exhaust emission purifier and the change rate thereof is
within a predetermined range or not, or whether at least one of the
air/fuel ratio of the exhaust flowing in the exhaust emission
purifier and the change rate thereof is within a predetermined
range or not.
16. The method as claimed in claim 10, wherein when the sum of a
detection error of the air/fuel ratio and a detection error of an
air-intake amount is less than the maximum tolerance, the step of
judging whether E.sub.DT-E.sub.DU<E.sub.A-(L.sub.U-g) is
established or not is carried out.
17. The method as claimed in claim 10, further comprising a step of
judging whether an amount of HC passing through the exhaust
emission purifier has a value equal to or less than a predetermined
value, and when it is judged that an amount of HC passing through
the exhaust emission purifier has a value equal to or less than a
predetermined value, the step of judging whether
E.sub.DT-E.sub.DU<E.sub.A-(L.sub.U-g) is established or not is
carried out.
18. The method as claimed in claim 10, further comprising a step of
judging whether a value E.sub.T/.DELTA.T.sub.C obtained by dividing
a detection temperature error E.sub.T of the exhaust emission
purifier by the rate .DELTA.T.sub.C of temperature increase of the
exhaust emission purifier per unit time is smaller than the maximum
tolerance E.sub.A or not, and when it is judged that
E.sub.T/.DELTA.T.sub.C<E.sub.A is established, the step of
judging whether E.sub.DT-E.sub.DU<E.sub.A-(L.sub.U-g) is
established or not is carried out.
19. The method as claimed in claim 18, further comprising a step of
judging whether an amount of HC passing through the exhaust
emission purifier has a value equal to or less than a predetermined
value and, only when it is judged that an amount of HC passing
through the exhaust emission purifier has a value equal to or less
than a predetermined value, the step of judging whether
E.sub.T/.DELTA.T.sub.C<E.sub.A is established or not is carried
out.
Description
TECHNICAL FIELD
[0001] The present invention relates to a fuel supply method for
allowing an internal-combustion engine including an exhaust
emission purifier to efficiently perform the activation processing
and the regenerating processing of the exhaust emission
purifier.
BACKGROUND ART
[0002] In recent years, for complying with strict exhaust gas
regulations applied to an internal combustion engine, it is
necessary to activate an oxidation catalytic converter which
comprises an exhaust emission purifier at the time of starting up
the engine, or to maintain an activated status of the converter in
an actuation of the engine. Therefore, Patent Literature 1 has
proposed an internal combustion engine in which an exhaust gas
heating system is incorporated in an exhaust passage upstream of
the exhaust emission purifier. The exhaust gas heating system
generates a burning gas in an exhaust gas, and supplies the
generated burning gas to the exhaust emission purifier at the
downstream thereof, thereby activating the purifier and maintaining
the activated status thereof. Therefore, the exhaust gas heating
system is generally provided with a fuel supplying valve for
supplying fuel to the exhaust passage and an igniting unit such as
a glow plug for heating the fuel to be ignited, thereby generating
a burning gas.
CITATION LIST
Patent Literature
[0003] PTL: Japanese Patent Laid-open No. 2010-059836
SUMMARY OF INVENTION
Technical Problem
[0004] When controlling the fuel supplied from a fuel supply valve
to an exhaust passage, the hunting of the control is preferably
avoided by minimizing a change in the exhaust temperature or a
change in the air/fuel ratio caused by the fuel supplied from the
fuel supply valve to the exhaust passage.
[0005] On the other hand, the fuel supply valve for supplying fuel
to the exhaust passage in the conventional exhaust heating unit
disclosed in PTL 1 for example basically has the same configuration
as that of a fuel injection valve for injecting fuel pressurized at
a predetermined driving cycle. Thus, the hunting of the control can
be effectively avoided by minimizing the driving cycle to the fuel
supply valve, by minimizing the energized time per one shot, and by
minimizing the amount of fuel supplied to the exhaust passage
during the energized time per one shot.
[0006] However, in the case of the conventional fuel supply valve,
it has been known that the reduction of the energized time per one
shot causes a sudden increase of the variation of the amount of the
fuel supplied to the exhaust passage. This is caused by the
structure of the fuel supply valve itself and an influence by the
viscosity of the fuel itself, meaning that different amounts of
fuel are supplied to the exhaust passage depending on the
manufacturing tolerances of the individual fuel supply valves. Due
to the technical background of the fuel supply valve as described
above, blindedly minimizing the energized time per one shot is
essentially impossible. Thus, the energized time per one shot has
been conventionally determined so that the maximum variation error
of the fuel supply caused by the manufacturing tolerances of the
individual fuel supply valves for example is equal to or lower than
the maximum tolerance of the amount of the fuel supplied to the
exhaust passage during the energized time per one shot to the fuel
supply valve.
[0007] Thus, the conventional exhaust heating unit has a
disadvantage as described below. That is, when the amount of fuel
supplied to the exhaust passage is not so high, the driving cycle
of the fuel supply valve is increased to thereby deteriorate the
fuel ignitability. Furthermore, a change in the exhaust temperature
or the air/fuel ratio is increased depending on when fuel is
supplied and when no fuel is supplied, thus causing the hunting
phenomenon of the control.
[0008] It is an objective of the present invention to provide a
method for supplying fuel that can reduce the energized time per
one shot to the fuel supply valve than in the case of the
conventional structure.
Solution to Problem
[0009] The present invention is in a method for supplying fuel from
a fuel supply valve to an exhaust passage at an upstream side of an
exhaust emission purifier, the method comprises the steps of
calculating, based on the status of the exhaust emission purifier,
a required supply of fuel to be supplied from the fuel supply valve
to the exhaust passage; reading a unit fuel supply L.sub.U to be
supplied to the exhaust passage in accordance with a energized time
t.sub.U to the fuel supply valve per one shot; intermittently
supplying, with a driving cycle depending on the required supply,
fuel of the unit fuel supply L.sub.U from the fuel supply valve to
the exhaust passage; reading the maximum tolerance E.sub.A
corresponding to the unit supply L.sub.U; reading the maximum
variation error E.sub.DU of the fuel supply valve corresponding to
the unit supply L.sub.U; calculating, regard to the fuel the unit
supply L.sub.U, an actual fuel supply g actual supplied to the
exhaust passage; setting a target fuel supply L.sub.UT that is less
than the unit supply L.sub.U by a certain amount; reading the
maximum variation error E.sub.DT of the fuel supply valve
corresponding to the target fuel supply L.sub.UT; judging whether
E.sub.DT-E.sub.DU<E.sub.A-(L.sub.U-g) is established or not;
interpolating, when it is judged that
E.sub.DT-E.sub.DU<E.sub.A-(L.sub.U-g) is established, a
energized time T.sub.UT to the fuel supply valve corresponding to
the target fuel supply L.sub.UT as a function of (L.sub.U/g); and
updating the target fuel supply L.sub.UT as a new unit fuel supply
L.sub.U and using the function of (L.sub.U/g) as a new energized
time t.sub.U to drive the fuel supply valve to supply fuel to the
exhaust passage.
[0010] In the method for supplying fuel according to the present
invention, the step of reading a unit fuel supply L.sub.U to be
supplied to the exhaust passage in accordance with a energized time
t.sub.U to the fuel supply valve per one shot may read the latest
updated unit supply L.sub.U.
[0011] When fuel to be supplied from the fuel supply valve in
accordance with the required supply at every driving cycle of the
fuel supply valve is in an amount exceeding the double of the unit
fuel supply, a half of the to-be-supplied amount may be
supplied.
[0012] The state of the exhaust emission purifier for calculating
the required supply is a temperature of the exhaust emission
purifier or an air/fuel ratio of exhaust flowing therein, and the
method may further comprise a step of judging, by carrying-out of
the step of intermittently supplying fuel from the fuel supply
valve to the exhaust passage for the energized time t.sub.U,
whether the temperature of the exhaust emission purifier or the
air/fuel ratio of the exhaust flowing therein is convergent or not.
In this instance, only when it is judged that the temperature of
the exhaust emission purifier or the air/fuel ratio of the exhaust
flowing therein is convergent, the step of judging whether
E.sub.DT-E.sub.DU<E.sub.A-(L.sub.U-g) is established or not may
be carried out. In this case, the step of judging whether the
temperature of the exhaust emission purifier or the air/fuel ratio
of the exhaust flowing therein is convergent or not may include a
step of judging whether at least one of the temperature of the
exhaust emission purifier and the change rate thereof is within a
predetermined range or not, or whether at least one of the air/fuel
ratio of the exhaust flowing in the exhaust emission purifier and
the change rate thereof is within a predetermined range or not.
[0013] When the sum of a detection error of the air/fuel ratio and
a detection error of an air-intake amount is less than the maximum
tolerance, the step of judging whether
E.sub.DT-E.sub.DU<E.sub.A-(L.sub.U-g) is established or not may
be carried out.
[0014] The method may further comprise a step of judging whether an
amount of EC passing through the exhaust emission purifier has a
value equal to or less than a predetermined value. In this
instance, when it is judged that an amount of HC passing through
the exhaust emission purifier has a value equal to or less than a
predetermined value, the step of judging whether
E.sub.DT-E.sub.DU<E.sub.A-(L.sub.U-g) is established or not may
be carried out.
[0015] The method may further comprise a step of judging whether a
value E.sub.T/.DELTA.T.sub.C obtained by dividing a detection
temperature error E.sub.T of the exhaust emission purifier by the
rate .DELTA.T.sub.C of temperature increase of the exhaust emission
purifier per unit time smaller than the maximum tolerance E.sub.A
or not. In this instance, when it is judged that
E.sub.T/.DELTA.T.sub.C<E.sub.A is established, the step of
judging whether E.sub.DT-E.sub.DU<E.sub.A-(L.sub.U-g) is
established or not may be carried out. In this case, the method may
further comprise a step of judging whether an amount of HC passing
through the exhaust emission purifier has a value equal to or less
than a predetermined value. In this instance, only when it is
judged that an amount of HC passing through the exhaust emission
purifier has a value equal to or less than a predetermined value,
the step of judging whether E.sub.T/.DELTA.T.sub.C<E.sub.A is
established or not may be carried out.
Advantageous Effects of Invention
[0016] According to the method for supplying fuel of the present
invention, a unit supply of fuel can be reduced without exceeding
the maximum tolerance. This can consequently reduce the driving
cycle of the fuel supply valve, thus suppressing the hunting
phenomenon of the control than in the case of the conventional
structure.
[0017] In order to read the unit supply L.sub.U of fuel supplied to
the exhaust passage, the updated latest unit supply L.sub.U can be
read to thereby improve the initial accuracy when the fuel supply
is reduced.
[0018] when the fuel amount to be supplied from the fuel supply
valve at every driving cycle of the fuel supply valve in accordance
with a required supply exceeds the double of the unit fuel supply,
a half of the to-be-supplied amount can be supplied to thereby
suppress a sudden change in the fuel supply per one shot. This can
consequently further suppress the hunting phenomenon of the control
due to a change in the fuel supply. Furthermore, the main effect of
the invention can be continuously obtained by continuously
supplying the unit supply of fuel as long as possible.
[0019] Only when the temperature of the exhaust emission purifier
or the air/fuel ratio of the exhaust flowing therein is convergent,
a step is performed to determine whether
E.sub.DT-E.sub.DU<E.sub.A-(L.sub.U-g) is established or not. By
doing this, a control under a transitional control can be avoided.
This can consequently further suppress the hunting phenomenon of
the control. In particular, a control under a transitional control
can be securely avoided by judging whether at least one of the
temperature of the exhaust emission purifier and the change rate
thereof is within a predetermined range or whether at least one of
the air/fuel ratio of the exhaust flowing in the exhaust emission
purifier and the change rate thereof is within a predetermined
range or not.
[0020] When the sum of the detection error of the air/fuel ratio
and the detection error of the air-intake amount is lower than the
maximum tolerance, whether E.sub.DT-E.sub.DU<E.sub.A-(L.sub.U-g)
is established or not can be judged to thereby securely maintain a
reliable control.
[0021] When the HC amount passing through the exhaust emission
purifier is judged to be equal to or less than a predetermined
value, whether E.sub.DT-E.sub.DU<E.sub.A-(L.sub.U-g) is
established or not can be judged to thereby securely maintain a
reliable control.
[0022] When it is judged that the value E.sub.T/.DELTA.T.sub.C
obtained by dividing the detection temperature error E.sub.T of the
exhaust emission purifier by the rate .DELTA.T.sub.C of temperature
increase of the exhaust emission purifier per unit time is lower
than the maximum tolerance E.sub.A, whether
E.sub.DT-E.sub.DU<E.sub.A-(L.sub.U-g) is established or not can
be judged to thereby obtain a similar effect. In particular, only
when the HC amount passing through the exhaust emission purifier is
judged to be equal to or less than the predetermined value, whether
E.sub.T/.DELTA.T.sub.C<E.sub.A or not can be judged to thereby
further maintain a reliable control.
BRIEF DESCRIPTION OF DRAWINGS
[0023] FIG. 1 is a conceptual diagram schematically illustrating a
vehicle engine system including an exhaust heating unit according
to the present invention;
[0024] FIG. 2 is a control block diagram illustrating the main part
of the embodiment shown in FIG. 1;
[0025] FIG. 3 is a graph schematically illustrating the required
supply corresponding to the driving cycle of the furl supply in the
embodiment shown in FIG. 1;
[0026] FIG. 4 is a graph schematically illustrating the energized
time of the fuel supply valve and the maximum tolerance thereof and
the maximum variation error of the individual fuel supply
valves;
[0027] FIG. 5 is a graph schematically illustrating the
characteristic of an airflow meter;
[0028] FIG. 6 is a graph schematically illustrating the
characteristic of an air/fuel ratio sensor;
[0029] FIG. 7 is a graph schematically illustrating the relation
between the amount of HC in the exhaust and the lean shift amount
of the detection value by the air/fuel ratio sensor;
[0030] FIG. 8 is a map schematically illustrating the relation
between the reaction rate of the catalyst temperature and the
catalyst and the HC amount in the exhaust and the O.sub.2
concentration;
[0031] FIG. 9 is a flowchart showing, together with FIG. 10, the
procedure for setting, in the embodiment shown in FIG. 1, the fuel
supply from the fuel supply valve per one shot in a catalyst
activation mode;
[0032] FIG. 10 is a flowchart showing, together with FIG. 9, the
procedure for setting the fuel supply from the fuel supply valve
per one shot in the catalyst activation mode;
[0033] FIG. 11 is a flowchart showing the details of the subroutine
of the fuel addition in the flowchart shown in FIG. 9;
[0034] FIG. 12 is a flowchart showing, together with FIG. 13, the
procedure for setting the fuel supply from the fuel supply valve
per one shot in a catalyst regenerating mode; and
[0035] FIG. 13 is a flowchart showing, together with FIG. 12, the
procedure for setting the fuel supply from the fuel supply valve
per one shot in the catalyst regenerating mode.
DESCRIPTION OF EMBODIMENTS
[0036] An embodiment in which the present invention is applied to a
compression ignition type internal combustion engine will be in
detail explained with reference to FIG. 1 to FIG. 13. The present
invention is not, however, limited to the embodiment, and the
construction thereof may be freely modified corresponding to
required characteristics. The present invention is effectively
applied to a spark ignition type internal combustion engine in
which gasoline, alcohol, LNG (Liquefied Natural Gas) or the like is
used as fuel to be ignited by a spark plug, for example.
[0037] FIG. 1 schematically illustrates the main part of the engine
system in this embodiment. FIG. 2 illustrates the control blocks of
the main part. FIG. 1 does not illustrate a valve actuating
mechanism for the intake and exhaust of the engine 10 and a
throttle mechanism and a silencer as well as a general EGR
apparatus as an auxiliary machine of the engine 10 for example.
FIG. 1 also does not illustrate a part of various sensors required
for the smooth operation of the engine 10 and the above-described
auxiliary machines.
[0038] The engine 10 in this embodiment is a multicylinder
internal-combustion engine in which fuel of light oil is directly
injected from a fuel injection valve 11 to a combustion chamber 10a
in a compressed state to thereby cause spontaneous ignition.
However, according to the characteristic of the present invention,
the engine 10 also may be a single-cylinder internal-combustion
engine.
[0039] A cylinder head 12 includes an intake port 12a and an
exhaust port 12b opposed to the combustion chamber 10a. The
cylinder head 12 includes a valve actuating mechanism (not shown)
including an intake valve 13a for opening and closing the intake
port 12a and an exhaust valve 13b for opening and closing the
exhaust port 12b. The fuel injection valve 11 opposed to the center
of the upper end of the combustion chamber 10a is also mounted on
the cylinder head 12 so as to be positioned between the intake
valve 13a and the exhaust valve 13b.
[0040] The amount and the injection timing of the fuel injected
from the fuel injection valve 11 into the combustion chamber 10a is
controlled by the Electronic Control Unit (ECU) 15 based on the
vehicle operating condition including the depression amount of the
accelerator pedal 14 by the driver. The depression amount of the
accelerator pedal 14 is detected by an accelerator opening sensor
16. The detection information is outputted to the ECU 15.
[0041] The ECUI 15 includes: an operating status determining
section 15a for determining the vehicle operating condition based
on the information from this accelerator opening sensor 16 and
various sensors for example (which will be described later); a fuel
injection setting unit 15b; and a fuel injection valve driving unit
15c. The fuel injection setting unit 15b sets, based on the
determination result by the operating status determining section
15a, the injection amount and the injection timing of fuel from the
fuel injection valve 11. The fuel injection valve driving unit 15c
controls the operation of fuel injection valve 11 so that the fuel
in an amount set by the fuel injection setting unit 15b is injected
from the fuel injection valve 11 at the set timing.
[0042] The cylinder block in which the piston 17a reciprocates is
mounted on a crank angle sensor 18. The crank angle sensor 18
detects the rotation phase of the crankshaft 17c connected via a
connecting rod 17b to the piston 17a (i.e., a crank angle) to
output this to the ECU 15. The operating status determining section
15a of the ECU 15 determines, based on the information from this
crank angle sensor 18, the rotation phase of the crankshaft 17c and
the engine rotational speed as well as the vehicle speed for
example on a real-time basis.
[0043] An air-intake pipe 19 connected to the cylinder head 12 so
as to communicate with the intake port 12a defines the air-intake
passage 19a together with the intake port 12a. The exhaust pipe 20
connected to the cylinder head 12 so as to communicate with the
exhaust port 12b defines the exhaust passage 20a together with the
exhaust port 12b.
[0044] An exhaust turbo-supercharger (hereinafter simply referred
to as a supercharger) 21 is provided so as to connect the
air-intake pipe 19 and the exhaust pipe 20. This supercharger 21
uses the kinetic energy of the exhaust flowing in the exhaust
passage 20a to supercharge the combustion chamber 11a to increase
the intake filling efficiency. The supercharger 21 in this
embodiment is a turbocharger in which the main part is composed of
a compressor 21a and an exhaust turbine 21b rotating with this
compressor 21a in an integrated manner. The compressor 21a is
provided on the midway of the air-intake pipe 19 positioned at the
upstream of the surge tank 19b provided on the midway of the
air-intake pipe 20. The exhaust turbine 21b is provided on the
midway of the exhaust pipe 20 connected to the cylinder head 12 so
as to communicate with the exhaust port 12b. In order to reduce the
intake temperature heated via the compressor 21a by the heat
transfer from the exhaust turbine 21b subjected to a
high-temperature exhaust, an intercooler 21c is provided. This
intercooler 21c is provided on the midway of the air-intake passage
19a between the compressor 21a and the surge tank 19b provided on
the midway of the air-intake pipe 19.
[0045] The air-intake pipe 19 provided at the upstream of the
compressor 21a of the supercharger 21 includes an airflow meter 22
that detects the flow rate V.sub.A of the intake flowing in the
air-intake passage 19a (which will be hereinafter referred to as an
air-intake amount) to output this to the ECU 15.
[0046] An exhaust emission purifier 23 is provided on the midway of
the exhaust pipe 20 between the exhaust turbine 21b of the
supercharger 21 and a silencer (not shown). The exhaust emission
purifier 23 functions to detoxify the toxic substance generated by
the combustion of mixed air in the combustion chamber 10a. The
exhaust emission purifier 23 in this embodiment includes, in an
order from the upstream side, generally well-known Nitrogen Oxides
(NO.sub.X) storage catalytic converter 23a, Diesel Particulate
Filter (DPF) 23b, and an oxidation catalytic converter 23c.
[0047] An exhaust heating unit 24 is provided on the midway of the
exhaust passage 20a between the exhaust port 12b and the exhaust
turbine 21b of the supercharger 21. This exhaust heating unit 24
functions to heat the exhaust from the engine 10 to the exhaust
emission purifier 23 to activate the oxidation catalytic converter
23c of the exhaust emission purifier 23 and to maintain the active
condition or functions to subject the DPF 23b to a regenerating
processing or the NO.sub.X storage catalytic converter 23a to a
deoxidation processing. The exhaust heating unit 24 in this
embodiment includes a fuel supply valve 24a and a glow plug 24.
[0048] The amount of the fuel supplied from the fuel supply valve
24a mounted on the exhaust pipe 20 to the exhaust passage 20a is
set, based on the determination result by a fuel supply requirement
determining section 15d of the ECU 15 (which will be described
later), by the fuel supply setting section 15e of the ECU 15. The
fuel supply valve driving section 15f of the ECU 15 controls the
operation of the fuel supply valve 24a so that the fuel in an
amount set by fuel supply setting section 15e is supplied from the
fuel supply valve 24a to the exhaust passage 20a.
[0049] The glow plug 24b for igniting the fuel supplied from the
fuel supply valve 24a to the exhaust passage 20a is fixed to the
exhaust pipe 20 so that the heat-generating portion thereof
protrudes to the exhaust passage 20a to be opposed to an injection
region of the fuel injected from the fuel supply valve 24a. This
glow plug 24b is connected to an in-vehicle power source (not
shown) via the glow plug driving section 15g of the ECU 15. The
glow plug driving section 15g switches ON/OFF of the conduction of
the glow plug 24b based on the determination result by the fuel
supply requirement determining section 15d of the ECU 15.
[0050] The exhaust passage 20a at the upstream side of the fuel
supply valve 24a includes a first exhaust temperature sensor 25.
This first exhaust temperature sensor 25 detects the exhaust
temperature T.sub.I flowing in the DPF 23b to output this to the
ECU 15.
[0051] The exhaust passage 20a between the NO.sub.X storage
catalytic converter 23a and the DPF 23b has an air/fuel ratio
sensor 26. This air/fuel ratio sensor 26 detects the air/fuel ratio
R.sub.N of the exhaust flowing therein to output this to the ECU
15. The DPF 23b and the oxidation catalytic converter 23d have
therebetween a catalyst temperature sensor 27 that detects the
temperature T.sub.C of the oxidation catalytic converter 23c to
output this to the ECU 15. The exhaust passage 20a at the
downstream side of the oxidation catalytic converter 23c has the
second exhaust temperature sensor 28 that detects the exhaust
temperature T.sub.O having passed through the oxidation catalytic
converter 23c to output this to the ECU 15.
[0052] The fuel supply requirement determining section 15d of the
ECU 15 determines, based on the determination result of the
operation condition by the operating status determining section
15a, the necessity of the activation of the oxidation catalytic
converter 23c and the necessities of the regenerating processing in
the DPF 23b and the NO.sub.X deoxidation processing in the NO.sub.X
storage catalytic converter 23a. When this fuel supply requirement
determining section 15d determines that the activation of the
oxidation catalytic converter 23c as well as the regenerating
processing in the DPF 23b and the NO.sub.X deoxidation processing
in the NO.sub.X storage catalytic converter 23a are required, then
the addition of fuel through the fuel supply valve 24a will be
performed. The determination result by this fuel supply requirement
determining section 15d is outputted to the glow plug driving
section 15g of the ECU 15, the fuel supply setting section 15e, and
a unit fuel supply updating section 15h (which will be described
later).
[0053] The fuel supply requirement determining section 15d of the
ECU 15 determines that there is a fuel supply requirement (i.e.,
the exhaust heating unit 24 must be operated) when any of the
following cases "a" to "d" occurs.
a: a case where the oxidation catalytic converter 23c is inactive
or is expected to be inactive. b: a case where the DPF 23b is
clogged by the deposition of HC. a case where the storage of
NO.sub.X by the NO.sub.X storage catalytic converter 23a is in a
saturated condition. d. a case where the regenerating processing of
the DPF 23b is required even when the DPF 23b is not clogged. The
case "a" can be judged based on the temperature information
T.sub.I, T.sub.O, and T.sub.C from the first exhaust temperature
sensor 25 and the second exhaust temperature sensor 26 as well as
the catalyst temperature sensor 27. The case "b" can be judged
based on the accumulated operating time of the engine 10 or the
accumulated fuel injection amount from the fuel injection valve 11
for example and also can be judged by an exhaust pressure sensor.
The case "c" can be similarly judged based on the accumulated
operating time of the engine 10 or the accumulated fuel injection
amount from the fuel injection valve 11 for example.
[0054] In order to maintain the correct performance of the exhaust
emission purifier 23, the fuel supply setting section 15e of the
ECU 15 sets the fuel amount to be supplied to the exhaust passage
20a (hereinafter referred to as a required supply) to L.sub.TA and
L.sub.TR.
[0055] More specifically, based on the exhaust temperature T.sub.I
and the air suction amount V.sub.A per a predetermined time (e.g.,
1 second), the activation required fuel supply L.sub.TA to be
supplied to the exhaust passage 20a in order to maintain the active
condition of the oxidation catalytic converter 23c is set based on
the following formula (1). The exhaust temperature T.sub.I is the
exhaust temperature that flows at the upstream side of the
oxidation catalytic converter 23c and that flows in the exhaust
passage 20a proximal to the oxidation catalytic converter 23c. The
exhaust temperature T.sub.I will be hereinafter referred to as a
catalyst upstream exhaust temperature. The air suction amount
V.sub.A per a predetermined time (which will be hereinafter
referred to as an air-intake amount) is acquired from the airflow
meter 22.
L.sub.TA={(T.sub.L-T.sub.I)V.sub.AC}/J (1)
In the formula, T.sub.L means the lowest temperature at which the
oxidation catalytic converter 23c is in an active condition and is
stored in the fuel supply setting section 15e in advance. C shows
the air specific heat. J shows the heat generation amount of the
fuel supplied to the exhaust passage 20a and is also stored in the
fuel supply setting section 15e in advance. The catalyst upstream
exhaust temperature T.sub.I is acquired from the first exhaust
temperature sensor 25.
[0056] When the fuel supply requirement determining section 15d
determines that the regenerating processing by the DPF 23b
constituting the exhaust emission purifier or the NO.sub.X
deoxidation processing by the NO.sub.X storage catalystic converter
is required, then the regenerating required fuel supply L.sub.TR to
be supplied to the exhaust passage 20a is set based on the
following formula (2).
L.sub.TR=V.sub.A/R.sub.T)-q (2)
[0057] In this formula, R.sub.T shows the air/fuel ratio as a
command of the exhaust flowing through the exhaust passage 20a to
the exhaust emission purifier 23 (hereinafter referred to as a
target air/fuel ratio) and is stored in the fuel supply setting
section 15e in advance. In this formula, q shows the injection
amount of the fuel injected from the fuel injection valve 11 to the
combustion chamber 10a of the engine 10 and is acquired from the
fuel injection valve driving unit 15c.
[0058] The information regarding the required fuel supplies
L.sub.TA and L.sub.TR set by the fuel supply setting section 15e
(which will be hereinafter collectively referred to as a required
fuel supply L.sub.T for convenience) is outputted to the fuel
supply valve driving section 15f and the unit fuel supply updating
section 15h of the ECU 15.
[0059] The fuel supply valve driving section 15f performs, at every
calculation cycle t.sub.P, a processing to multiply the required
fuel supply L.sub.T set by the fuel supply setting section 15e with
the calculation cycle t.sub.P (e.g., 20 milliseconds) to totalize
the resultant values. When the fuel totalized value obtained at
every calculation cycle t.sub.P reaches the unit fuel supply
L.sub.U updated by the unit fuel supply updating section 15h, the
energized time t.sub.U corresponding to this unit fuel supply
L.sub.U is given to the fuel supply valve 24a. At the same time,
the fuel totalized value is updated to a value obtained by
(totalized value-unit supply L.sub.U). Then, the fuel totalization
processing is repeated to drive the fuel supply valve 24
intermittently. Therefore, the higher the required fuel supply
L.sub.T per a predetermined time is, the shorter the driving
interval of the fuel supply valve 24a is. The lower the required
supply L.sub.T per a predetermined time is, the longer the driving
interval of the fuel supply valve 24a is. The driving information
from the fuel supply valve driving 15f to the fuel supply valve 24a
is outputted to the surplus tolerance calculating section 15i of
the ECU 15.
[0060] When the engine 10 is in a transitional operating condition
(e.g., in a sudden acceleration requiring the supply of a large
amount of fuel within a short time), the driving cycle t.sub.C of
the fuel supply valve 24a must be synchronized with the fuel burst
interval of the respective cylinders of the engine 10. As a result,
there may be a case where, even when the unit fuel supply L.sub.U
is supplied to the exhaust passage 20a at every driving cycle
t.sub.C matching the fuel burst interval of the respective
cylinders of the engine 10, the fuel supply ratio is insufficient
to thereby fail to provide an appropriate control. In this
embodiment, only when the required supply .DELTA.L.sub.T to be
supplied at every driving cycle t.sub.C of the fuel supply valve
24a (=.DELTA.L.sub.At.sub.C, .DELTA.L.sub.TRt.sub.C) exceeds the
double of the unit fuel supply L.sub.U, a half of the required fuel
supply L.sub.T multiplied with the driving cycle t.sub.C is
supplied from the fuel supply valve 24a to the exhaust passage 20a.
FIG. 3 schematically illustrates the change of the required fuel
supply .DELTA.L.sub.T to be supplied at the respective times
t.sub.1 to t.sub.5 with the shortest driving cycle t.sub.C of the
fuel supply valve 24a. In FIG. 3, the required fuel supply
.DELTA..sub.T accumulates in the period of time t.sub.1 to time
t.sub.3 to exceed the unit fuel supply L.sub.U. At the time t.sub.3
and time t.sub.4 at which the required fuel supply L.sub.T at every
driving cycle t.sub.C exceeds the double of the unit fuel supply
L.sub.U, not the unit fuel supply L.sub.U but fuel in an amount of
.DELTA.L.sub.T/2 is supplied. Thus, after the time t.sub.5, the
required fuel supply .DELTA.L.sub.T at every driving cycle t.sub.C
is convergent to a value smaller than the double of the unit fuel
supply L.sub.U. Thus, the unit fuel supply L.sub.U is supplied as
in the case of the time t.sub.1 and time t.sub.2. This can
consequently suppress a delay of a control and can suppress a
sudden change of the fuel supply supplied from the fuel supply
valve 24a to the exhaust passage 20a.
[0061] The ECU 15 includes a convergence determining section 15j in
addition to the above-described operating status determining
section 15a and fuel supply valve driving section 15f for
example.
[0062] The convergence determining section 15j determines, based on
the determination result of the operating condition from the
operating status determining section 15a, whether the oxidation
catalytic converter 23c reaches, by the supply of fuel from the
fuel supply valve 24a, to the target activation temperature T.sub.T
and is in a stable condition or not. The convergence determining
section 15j also determines whether the air/fuel ratio R.sub.N
reaches, by the supply of fuel from the fuel supply valve 24a, to
the target air/fuel ratio R.sub.T and is in a stable condition or
not.
[0063] The convergence determining section 15j determines that the
temperature of the oxidation catalytic converter 23c is convergent
in the vicinity of the target activation temperature T.sub.T and is
in a stable condition when the following two conditions are
satisfied. The first condition is that that the absolute value of
the value obtained by deducting from the target activation
temperature T.sub.T the temperature of the exhaust flowing in the
exhaust passage 20a proximal to the oxidation catalytic converter
23c at the downstream side of the oxidation catalytic converter 23c
(which will be hereinafter referred to as a catalyst downstream
exhaust temperature) is lower than a positive threshold value
T.sub.R set in advance. The second condition is that the absolute
value of a rate dT.sub.O of change in the exhaust temperature
T.sub.O is smaller than the threshold value dT.sub.R set in advance
(which is generally has a positive value close to 0). As a result,
it can be securely judged that the engine 10 does not have a
transitional operating condition. However, another configuration
also may be used where the oxidation catalytic converter 23c has a
temperature convergent to the neighborhood of the target activation
temperature T.sub.T only when any of the conditions is
satisfied.
[0064] Similarly, the convergence determining section 15j
determines that the exhaust flowing in the exhaust passage 20a has
the air/fuel ratio R.sub.N that is convergent ant stable at the
neighborhood of the target air/fuel ratio R.sub.T when the
following two conditions are satisfied. The first condition is that
the absolute value of the value obtained by deducting, from the
target air/fuel ratio R.sub.T, the air/fuel ratio R.sub.N acquired
by the air/fuel ratio sensor 26 is smaller than the positive
threshold value dR.sub.R set in advance. The second condition is
that the rate dR.sub.N of change of the air/fuel ratio R.sub.N has
an absolute value smaller than the positive threshold value
dR.sub.R set in advance (which is generally has a positive value
close to 0). As a result, it can be securely judged that the engine
10 does not have a transitional operating condition. However,
another configuration also may be used where the exhaust flowing in
the exhaust passage 20a has the air/fuel ratio R.sub.N that is
convergent in the vicinity of the target air/fuel ratio R.sub.T
only when any of the conditions is satisfied.
[0065] By the determination processing by the convergence
determining section 15j as described above, it is possible to
confirm that the engine 10 is not in a transitional operating
condition. Thus, the exhaust heating unit 24 can be subjected to a
smooth control. This determination result is outputted to the
surplus tolerance calculating section 15j.
[0066] FIG. 4 schematically illustrates the relation among the unit
fuel supply L.sub.U and the maximum tolerance E.sub.A as well as
the maximum variation error E.sub.D. It is noted that values are
not positive or negative values around 0 as a center but are
conveniently represented as absolute values on the basis of
percentage. The maximum tolerance E.sub.A shows, with regard to the
unit fuel supply L.sub.U set by the unit fuel supply updating
section 15h, a target control (e.g., a dislocation value for which
a temperature increase control of the oxidation catalytic converter
23c or the air/fuel ratio control of the exhaust can be
convergent). The maximum tolerance E.sub.A can be represented as a
value equal to or less than the unit supply L.sub.U. Thus, the
maximum tolerance E.sub.A represented by percentage can be
basically represented as a fixed value regardless of the magnitude
of the unit supply L.sub.U. On the other hand, the maximum
variation error E.sub.D of the fuel supply, which is caused by the
mechanical characteristic of the fuel supply valve 24a itself or
the viscosity of the fuel itself for example, tends to rapidly
increase as shown by the solid line of FIG. 4 with the decrease of
the unit fuel supply L.sub.U. Thus, when the unit fuel supply
L.sub.U is tried to be less than the unit fuel supply at which the
maximum tolerance E.sub.A is equal to the maximum variation error
E.sub.D (this unit fuel supply will be hereinafter referred to as a
reference unit fuel supply L.sub.UC), the maximum variation error
E.sub.D must be considered. Theerfore, the maximum tolerance
E.sub.A must be further estimated to be smaller in consideration of
the difference between the maximum variation error E.sub.D and the
maximum tolerance E.sub.A so that the unit fuel supply L.sub.U has
an error that is smaller than (E.sub.A-E.sub.D).
[0067] The surplus tolerance calculating section 15i stores therein
the map as show in FIG. 4. The surplus tolerance calculating
section 15i deducts, from the totalized value .SIGMA.L.sub.D of the
unit fuel supply L.sub.U set by the unit fuel supply updating
section 15h, the fuel supply to be actually supplied to correspond
to the totalized value .SIGMA.L.sub.U (hereinafter referred to as
an actual fuel supply) to calculate the supply error E.sub.U. Then,
the surplus tolerance calculating section 15i deducts the
calculated supply error E.sub.U from the maximum tolerance E.sub.A
corresponding to the current unit supply L.sub.U stored in the map
of FIG. 4 to calculate the amount .DELTA.E.sub.A of the surplus
tolerance. The totalized value .SIGMA.L.sub.U is an instruction
value of the amount of the fuel that is driven, during the
detection period of the intake amount V.sub.A, by an instruction
from the fuel supply valve driving section 15f and that is supplied
from the fuel supply valve 24a to the exhaust passage 20a. Thus,
the supply error E.sub.U can be represented by (.SIGMA..sub.U-g).
The actual fuel supply g is calculated based on the following
formula.
g=(.DELTA.T.sub.IV.sub.AC) (3)
In the formula, .DELTA.T.sub.I shows a difference between T.sub.I
detected by the first exhaust temperature sensor 25 and the exhaust
temperature T.sub.O detected by the second exhaust temperature
sensor 28 and is represented by .DELTA.T.sub.I=T.sub.O-T.sub.I.
Thus, the amount .DELTA.E.sub.A of the surplus tolerance is
represented as shown by the following formula (4).
.DELTA.E.sub.A=E.sub.A-.SIGMA.L.sub.U+(.DELTA.T.sub.IV.sub.AC/J)
(4)
The amount .DELTA.E.sub.A of the surplus tolerance calculated by
the surplus tolerance calculating section 15i is outputted to the
unit fuel supply updating section 15h.
[0068] The unit fuel supply updating section 15h in this embodiment
updates the fuel supply per one energized time t.sub.U supplied
from the fuel supply valve 24a to the exhaust passage 20a (i.e.,
the unit fuel supply L.sub.U) and outputs the updated unit fuel
supply L.sub.U to the fuel supply valve driving section 15f. In
this embodiment, the initial value L.sub.US of the unit fuel supply
L.sub.U is stored in advance in the unit fuel supply updating
section 15h. Thus, such a control is carried out that stepwisedly
reduces the unit fuel supply L.sub.U from this initial value
L.sub.US by a certain amount of the target unit fuel supply
L.sub.UT. Basically, the unit fuel supply L.sub.U is updated to
have a smaller value so that, with regard to the required fuel
supply L.sub.T set by the fuel supply setting section 15e, the unit
fuel supply L.sub.U is supplied with the shortest addition interval
(the driving cycle t.sub.C of the fuel supply valve 24a) as
possible. In this case, the initial value L.sub.US of the unit fuel
supply is set to a value sufficiently higher than the reference
unit fuel supply L.sub.UC. The target unit fuel supply L.sub.UT is
set to a value smaller than the current unit fuel supply L.sub.U by
a predetermined amount and is updated to have a smaller value, when
possible, by the update processing.
[0069] More particularly, fuel of the target unit fuel supply
L.sub.UT smaller than the current unit fuel supply L.sub.U by a
certain amount is set. A different processing is performed
depending on the case where the target unit fuel supply L.sub.UT is
higher than the reference unit fuel supply L.sub.UC and the case
where the target unit fuel supply L.sub.UT is lower than the
reference unit fuel supply L.sub.UC. Specifically, when the target
unit fuel supply L.sub.UT is higher than the reference unit fuel
supply L.sub.UC, there is no need to consider the maximum variation
error E.sub.D. Thus, when the supply error E.sub.U calculated by
the surplus tolerance calculating section 15i is lower than the
maximum tolerance E.sub.A, the target unit fuel supply L.sub.UT is
updates as a new unit fuel supply L.sub.U.
[0070] When the target unit fuel supply L.sub.UT is lower than the
reference unit fuel supply L.sub.UC, then the target unit fuel
supply L.sub.UT is set to have a value smaller than the current
unit fuel supply L.sub.U by a certain amount. The maximum variation
error E.sub.DT of the target unit fuel supply L.sub.UT and the
maximum variation error E.sub.DU of the current unit fuel supply
L.sub.U are read out from the map of FIG. 4. Then, the amount
.DELTA.E.sub.D of the surplus variation error obtained by deducting
from the maximum variation error E.sub.DT corresponding to the
target unit fuel supply L.sub.UT the maximum variation error
E.sub.DU corresponding to the current unit fuel supply L.sub.U
(=E.sub.DT-E.sub.DU) is compared with the amount .DELTA.E.sub.A of
the surplus tolerance given from the surplus tolerance calculating
section 15i. Then, when it is judged that the amount .DELTA.E.sub.A
of the surplus tolerance is lower than the amount .DELTA.E.sub.D of
the surplus variation error, the target unit fuel supply L.sub.UT
is updated as a new unit fuel supply L.sub.U.
[0071] In any of the cases, the energized time t.sub.U
corresponding to the updated unit fuel supply L.sub.U is
interpolated as shown in the following formula (5).
t.sub.U=t.sub.UT>k(.SIGMA.L.sub.U/g) (5)
[0072] The energized time t.sub.U corresponding to the updated unit
fuel supply L.sub.U also can be interpolated by any appropriate
function formula other than the formula (5) including
(.SIGMA.L.sub.U/g) as a variable. For example, the following
formula (6) also can be used.
t.sub.U=t.sub.UT+(.SIGMA.L.sub.U/g) (6)
[0073] Furthermore, it is also effective to multiply
(.SIGMA.L.sub.U/a) in order to suppress a sudden change of the
right sides of the formulae (5) and (6), with such an interpolation
coefficient that is higher than 0 and that is equal to 0 and that
is equal to or lower than 1. By including such an interpolation
coefficient in the formulae (5) and (6), it is possible to avoid an
adverse influence by an error of sensors for example used to
calculate the unit fuel supply L.sub.U and the actual fuel supply g
or the calculation of the energized time t.sub.U during a
transitional operating condition of the vehicle. This interpolation
coefficient can be set in advance based on the magnitude of the
error based on the resolution of the sensors for example or the
vehicle transitional operating condition for example.
[0074] As described above, based on the actual fuel supply g
corresponding to the unit fuel supply L.sub.U, the energized time
t.sub.UT corresponding to the target unit fuel supply L.sub.UT is
interpolated. By doing this, even when the current unit fuel supply
L.sub.U is reduced to the target unit fuel supply L.sub.UT, the
resultant error can be equal to or lower than the maximum tolerance
E.sub.A. Thus, when the amount .DELTA.E.sub.A of the surplus
tolerance exceeds the amount .DELTA.E.sub.D of the surplus
variation error and the current unit fuel supply L.sub.U is reduced
to the target unit fuel supply L.sub.UT this exceeds the maximum
tolerance E.sub.A. Thus, no update of the unit fuel supply L.sub.U
is performed.
[0075] As described above, the smaller the unit fuel supply L.sub.U
is when compared with the required fuel supply L.sub.T, fuel is
supplied from the fuel supply valve 24a to the exhaust passage 20a
with a shorter driving cycle t.sub.C. As a result, fuel supplied to
the exhaust passage 20a shows a smaller temporal fluctuation range,
thus providing a smaller fluctuation range of the air/fuel ratio
R.sub.N in the exhaust in particular.
[0076] The unit fuel supply updating section 15h in this embodiment
includes an update availability determining section 151 to
determine the availability of the above-described update processing
of the unit fuel supply L.sub.U and the energized time t.sub.U.
When this update availability determining section 151 determines
that the following conditions (A) (C) (E), and (B) or (D) are
satisfied, this update availability determining section 151 allows
the update of the unit fuel supply L.sub.U and the energized time
t.sub.U by the unit fuel supply updating section 15h. When this
update availability determining section 151 determines that the
following conditions (A), (C), (E), and (B) or (D) are not
satisfied on the other hand, this update availability determining
section 151 does not allow the update of the unit fuel supply
L.sub.U and the energized time t.sub.U by the unit fuel supply
updating section 15h. Then, unit fuel supply updating section 15h
stores the current unit fuel supply L.sub.U and energized time
t.sub.U as the latest unit fuel supply L.sub.U and energized time
t.sub.U.
.DELTA.E.sub.A>.DELTA.E.sub.D (A)
E.sub.A>E.sub.VA+E.sub.RT (B)
E.sub.A>(E.sub.T/E.sub.TC) (C)
E.sub.A>E.sub.U (E)
[0077] With regard to (A), when the amount .DELTA.E.sub.A of the
surplus tolerance exceeds the amount .DELTA.E.sub.D of the surplus
variation error as described above, the unit fuel supply L.sub.U is
not updated because the current unit fuel supply L.sub.U reduced to
the target unit fuel supply L.sub.UT in this case exceeds the
maximum tolerance E.sub.AT.
[0078] With regard to (B), it has been well-known that the airflow
meter 22 and the air/fuel ratio sensor 26 have a unique measurement
error due to the detection system thereof. FIG. 5 shows the
relation between the air-intake amount by the airflow meter 22 and
the measurement error. FIG. 6 shows the relation between the
air/fuel ratio R.sub.N by the air/fuel ratio sensor 26 and the
measurement error. When the regenerating required fuel supply
L.sub.TR is calculated based on the above formula (2), the
air-intake amount V.sub.A detected by the airflow meter 22 and the
air/fuel ratio R.sub.N of the exhaust detected by the air/fuel
ratio sensor 26 include the measurement errors E.sub.VA and
E.sub.RT as shown in FIG. 5 and FIG. 6, respectively. As a result,
some combination of the measurement errors E.sub.VA and E.sub.RT
may exceed the maximum tolerance E.sub.A for the regenerating
required fuel supply L.sub.TR. To solve this, in this embodiment,
the air/fuel ratio R.sub.N of the exhaust is controlled so that,
when the sum (%) of the measurement errors E.sub.VA and E.sub.RT of
by the airflow meter 22 and the air/fuel ratio sensor 26 exceeds
the maximum tolerance E.sub.A, the above target unit fuel supply
L.sub.UT is not updated as a new unit fuel supply L.sub.U. The
above formula (5) is not also calculated.
[0079] With regard to (C), it has been known that the detection
value R.sub.N of the air/fuel ratio sensor 26 is dislocated to the
lean side in proportion to the HC amount included in the exhaust
(so-called lean shift). Thus, the error of the detection value
R.sub.N by the air/fuel ratio sensor due to this lean shift amount
.DELTA.E.sub.S must be lower than the maximum tolerance E.sub.A of
the unit fuel supply L.sub.U. Thus, when the lean shift amount
.DELTA.E.sub.S is too large, the above target unit fuel supply
L.sub.UT is not updated as a new unit fuel supply L.sub.U.
Similarly, the calculation of the above formula (5) also must not
be performed. In this embodiment, when the value .omega.g obtained
by multiplying the HC purification rate .omega. by the exhaust
emission purifier 23 with the actual fuel supply g is lower than
the lean shift amount .DELTA.E.sub.S, then the above target unit
fuel supply L.sub.UT is updated as a new unit fuel supply L.sub.U
and the above formula (5) is calculated. When the value .omega.g
obtained by multiplying the HC purification rate .omega. by the
exhaust emission purifier 23 with the actual fuel supply g is equal
to or larger than the lean shift amount .DELTA.E.sub.S on the other
hand, the above target unit fuel supply L.sub.UT is not updated as
a new unit fuel supply L.sub.U and the above formula (5) is not
performed.
[0080] FIG. 7 schematically illustrates the relation between the HC
amount included in the exhaust passing through the exhaust passage
20a including the air/fuel ratio sensor 26 and the lean shift
amount .DELTA.E.sub.S in the air/fuel ratio sensor 26. The
operating status determining section 15a of the ECU 15 stores
therein the map as shown in FIG. 7 in advance. The HC amount
included in the exhaust is calculated by the fuel supply valve
update availability determining section 151 based on the air-intake
amount V.sub.A and, the fuel injection amount from the fuel
injection valve 11, and the fuel supply from the fuel supply valve
24a. The HC purification rate u by the exhaust emission purifier 23
can be calculated by dividing the HC reaction rate v by the exhaust
emission purifier 23 by the exhaust flow rate (which is the
air-intake amount V.sub.A in this case). The reaction rate v in the
exhaust emission purifier 23 can be calculated based on the
relation among the HC amount and O.sub.2 concentration in the
exhaust and the catalyst temperature. FIG. 8 illustrates the
relation among the HC amount and O.sub.2 concentration in the
exhaust and the catalyst temperature as described above. The fuel
supply valve update availability determining section 151 stores
therein the map as shown in FIG. 8. The fuel supply valve update
availability determining section 151 reads the reaction rate V
based on the catalyst temperature T.sub.C and the HC amount and
O.sub.2 concentration in the exhaust. Next, the air-intake amount
V.sub.A by the airflow meter 22 is divided by information to
calculate the HC purification rate .omega.. Then, the HC
purification rate .omega. is multiplied with the actual fuel supply
g calculated based on the above formula (3) and the result is
compared with the above lean shift amount .DELTA.E.sub.S. Then,
only when .DELTA.E.sub.S>(v/V.sub.A)g is established, the unit
fuel supply updating section 15h updates the unit fuel supply
L.sub.U and the energized time t.sub.U.
[0081] With regard to (D), when a control is carried out based on
the activation required fuel supply L.sub.TA, an influence by the
detection error of the catalyst temperature sensor 27 must be
avoided. Thus, it is judged whether the value
(E.sub.T/.DELTA.T.sub.C) obtained by dividing the detection
temperature error of the exhaust emission purifier 23 (i.e., the
detection error E.sub.T of the catalyst temperature T.sub.C
detected by the catalyst temperature sensor 27) by the rate
.DELTA.T.sub.C of temperature increase of the exhaust emission
purifier 23 per unit time is smaller than the maximum tolerance
E.sub.A or not. When E.sub.A>(E.sub.T/.DELTA.T.sub.C) is
established. Then, the unit supply L.sub.U and the energized time
t.sub.U are updated.
[0082] With regard to (E), when the target unit fuel supply
L.sub.UT is more than the reference unit fuel supply L.sub.UC and
the supply error E.sub.U is larger than the maximum tolerance
E.sub.A, the target unit fuel supply L.sub.UT cannot be updated as
a new unit fuel supply L.sub.U.
[0083] FIG. 9 to FIG. 11 illustrate the flow of the fuel supply
control in this embodiment in the catalyst activation mode to
maintain the oxidation catalytic converter 23c as described above
in an activated state. First, the step S11 determines whether there
is a fuel supply request or not. When it is judged that there is a
fuel supply request (i.e., when it is judged that the activation of
the oxidation catalytic converter 23c in the exhaust emission
purifier 23 is required), the processing proceeds to the step S12
to calculate the activation required fuel supply L.sub.TA. Next,
the step S13 acquires the unit fuel supply L.sub.U from the unit
fuel supply updating section 15h of the ECU 15. Then, the step S14
drives the fuel supply valve 24a to start supplying fuel to the
exhaust passage 20a.
[0084] FIG. 11 illustrates the subroutine of the fuel supply.
Specifically, the step S141 determines whether the required fuel
supply .DELTA.L.sub.TA per unit time is less than double of the
unit fuel supply L.sub.U or not. When the required fuel supply
.DELTA.L.sub.TA per unit time is less than double of the unit fuel
supply L.sub.U (i.e., there is no particular problem when fuel is
continuously supplied in the unit fuel supply L.sub.U), the
processing proceeds to the step S142 to supply fuel with the unit
fuel supply L.sub.U. Next, the step S143 determines whether a fuel
supply flag is set or not. At an initial stage, no fuel supply flag
is set. Thus, the processing proceeds to the step S144 to set a
fuel supply flag. Then, the step S145 determines whether there is a
fuel supply request or not. When it is judged that there is a fuel
supply request (i.e., there is still a need to activate the
oxidation catalytic converter 23.sub.C in the exhaust emission
purifier 23), then the processing returns to the main flow of FIG.
10 to carry out the step S15 (which will be described later). When
the step S145 determines that there is no fuel supply request
(i.e., there is no need to activate the oxidation catalytic
converter 23.sub.C in the exhaust emission purifier 23), the
processing returns to the main flow of FIG. 9 to carry out the step
S30 (which will be described later).
[0085] On the other hand, when the step S141 determines that the
required fuel supply .DELTA.L.sub.TA per unit time exceeds the
double of the unit fuel supply L.sub.U (i.e., when it is judged
that the continued supply of fuel in the unit fuel supply L.sub.U
causes an insufficient fuel supply), the processing proceeds to the
step S146. Then, fuel in the amount of a half of the required fuel
supply .DELTA.L.sub.TA per unit time is supplied through the fuel
supply valve 24a to the exhaust passage 20a. Then, steps after the
above step S143 are carried out.
[0086] The step S15 determines whether the new target unit fuel
supply L.sub.UT set to the current unit fuel supply L.sub.U is less
than the reference unit fuel supply L.sub.UC or not. At an initial
stage, the newly-set target unit fuel supply L.sub.UT is equal to
or more than the reference unit fuel supply L.sub.UC. Thus, the
processing proceeds to the step S16 to allow the surplus tolerance
calculating section 15i to calculate the supply error E.sub.U.
Next, the step S17 determines whether the supply error E.sub.U is
smaller than the maximum tolerance E.sub.A or not. When it is
judged that the supply error E.sub.U is smaller than the maximum
tolerance E.sub.A (i.e., when it is judged that the unit fuel
supply L.sub.U can be updated), the processing proceeds to the step
S18. Then, the set target unit fuel supply L.sub.UT is updated as a
new unit fuel supply L.sub.U and the energized time t.sub.U to the
corresponding fuel supply valve 24a is interpolated as shown in the
formula (5). Then, the processing again returns to the step S11.
When the step S17 determines that the supply error E.sub.U is equal
to or larger than the maximum tolerance E.sub.A (i.e., it is judged
that the unit fuel supply L.sub.U cannot be updated), the current
unit fuel supply L.sub.U and the energized time t.sub.U are
directly maintained. Then, the processing again returns to the step
S11.
[0087] When the above step S15 determines that the target unit fuel
supply L.sub.UT newly set to the current unit fuel supply L.sub.U
is less than the reference unit fuel supply L.sub.UC, (i.e., when
it is judged that the maximum variation error E.sub.D must be
considered), then the processing proceeds to the step S19. Then, it
is judged whether the absolute value of the value obtained by
deducting the current catalyst downstream exhaust temperature
T.sub.O from the target activation temperature T.sub.T of the
oxidation catalytic converter 23c is smaller than the threshold
value T.sub.R or not. When it is judged that the absolute value of
the value obtained by deducting the current catalyst downstream
exhaust temperature T.sub.O from the target activation temperature
T.sub.T of the oxidation catalytic converter 23c is less than the
threshold value T.sub.R (i.e., when it is judged that the oxidation
catalytic converter 23.sub.C reaches the activation temperature),
then the processing proceeds to the step S20. Then, it is judged
whether the rate dT.sub.O of exhaust temperature change in
downstream of the catalyst is less than the threshold value
dT.sub.R or not. When the rate dT.sub.O of exhaust temperature
change in downstream of the catalyst is smaller than the threshold
value dT.sub.R (i.e., when the oxidation catalytic converter
23.sub.C has a temperature that is converged and stable at the
activation temperature), then the processing proceeds to the step
S21. Then, the supply error E.sub.U is calculated. The step S22
calculates the amount .DELTA.E.sub.A of the surplus tolerance. The
step S23 calculates the amount .DELTA.E.sub.D of the surplus
variation error.
[0088] When the above step S19 determines that the absolute value
of the value obtained by deducting the current catalyst downstream
exhaust temperature T.sub.O from the target activation temperature
T.sub.T is equal to or larger than the threshold value T.sub.R
(i.e., when it is judged that the oxidation catalytic converter 23c
is converged at the activation temperature), then the processing
returns to the step S11. in this case, it is noted that the current
unit fuel supply L.sub.U and energized time t.sub.U are maintained
continuously. Similarly, when the step S20 determines that the
exhaust temperature change rate dT.sub.CO is equal to or more than
the threshold value dT.sub.R (i.e., when the oxidation catalytic
converter 23c is not converged at the activation temperature), the
processing returns to the step S11 while maintaining the current
unit fuel supply L.sub.U and energized time t.sub.U.
[0089] After the step S23, the step S24 determines whether the
amount .DELTA.E.sub.A of the surplus tolerance is more than the
amount .DELTA.E.sub.D of the surplus variation error or not. When
it is judged that the amount .DELTA.E.sub.A of the surplus
tolerance is larger than the amount .DELTA.E.sub.D of the surplus
variation error (i.e., it is judged that the unit fuel supply
L.sub.U can be updated to a reduced amount), the processing
proceeds to the step S29. Then, it is judged whether the value
(E.sub.T/.DELTA.T.sub.U) obtained by dividing the detection error
E.sub.T of the catalyst temperature T.sub.C by the rate
.DELTA.T.sub.C of temperature increase of the exhaust emission
purifier 23 per unit time is less than the maximum tolerance
E.sub.A or not. When it is judged that the value of
(E.sub.T/.DELTA.T.sub.C) is smaller than the maximum tolerance
E.sub.A (i.e., when it is judged that the unit fuel supply L.sub.U
can be updated to a reduced amount), the processing proceeds to the
step S18. When it is judged that the value of (E.sub.T/T.sub.C) is
equal to or larger than the maximum tolerance E.sub.A (i.e., when
it is judged that the unit fuel supply L.sub.U cannot be updated to
a reduced amount), the current unit fuel supply L.sub.U and
energized time t.sub.U are directly maintained and the processing
returns to the step S11. Similarly, when the step S24 determines
that amount .DELTA.E.sub.A of the surplus tolerance is equal to or
less than the amount .DELTA.E.sub.D of the surplus variation error
(i.e., when it is judged that an updated unit fuel supply L.sub.U
deviates from the maximum tolerance E.sub.A), then the current unit
fuel supply L.sub.U and energized time t.sub.U are maintained.
Then, the processing returns to the step S11.
[0090] On the other hand, when the above step S11 determines that
there is no fuel supply request (i.e., it is judged that there is
no need to activate the oxidation catalytic converter 23 in the
exhaust emission purifier 23), then the processing proceeds to the
step S30 to determine whether a fuel supply flag is set or not.
When it is judged that the fuel supply flag is set, (i.e., when it
is judged that the fuel supply from the fuel supply valve 24a to
the exhaust passage 20a continued), then the processing proceeds to
the step S31 to stop the fuel supply processing. Then, the step S32
resets the fuel supply flag to thereby complete a series of
controls. When the above step S30 determines that no fuel supply
flag is set (i.e., when it is judged that the processing to supply
fuel from the fuel supply valve 24a to the exhaust passage 20a is
not performed), the processing is completed without doing
anything.
[0091] As described above, when the amount .DELTA.E of the surplus
tolerance is less than the amount .DELTA.E.sub.D of the surplus
variation error, the unit fuel supply L.sub.U is updated to a
smaller target unit fuel supply L.sub.UT. As a result, the
oxidation catalytic converter 23c can have a narrower temperature
amplitude to reduce the wasteful fuel supply, thus improving fuel
consumption. At the same time, even the reduced unit fuel supply
L.sub.U can be always less than the maximum tolerance, thus
securely maintaining a desired control accuracy.
[0092] In the above-described embodiment, the temperature of the
oxidation catalytic converter 23c was controlled. However, a
similar control configuration also can be used when the air/fuel
ratio of the exhaust is controlled.
[0093] FIG. 12 and FIG. 13 show the flow of the fuel supply control
in this embodiment in the catalyst regenerating mode for performing
the regenerating processing by the DPF 23b and the deoxidation
processing by the NO.sub.X storage catalytic converter 23a
constituting the exhaust emission purifier 23 as described above.
The steps S41 to S48, S51 to S54, and S60 to S62 in this embodiment
are basically the same as the steps S11 to S18, S21 to S24, and S30
to S32 in the above flowcharts shown in FIG. 9 and FIG. 10.
However, the regenerating required fuel supply L.sub.TR in the step
S42 is calculated by the formula (2). The fuel supply subroutine of
S44 has the same procedure as that of the above embodiment shown in
FIG. 11.
[0094] When the step S45 determines that the target unit fuel
supply L.sub.UT newly set to the current unit fuel supply L.sub.U
is less than the reference unit supply L.sub.UC (i.e., when it is
judged that the maximum variation error E.sub.D must be
considered), the processing proceeds to the step S49. Then, it is
judged whether the absolute value of the value obtained by
deducting the air/fuel ratio value R.sub.N from the target air/fuel
ratio value R.sub.T is smaller than the positive threshold value
R.sub.R set in advance or not. When it is judged that the absolute
value of the value obtained by deducting the air/fuel ratio value
R.sub.N from the target air/fuel ratio value R.sub.T is less than
the positive threshold value R.sub.R set in advance (i.e., when it
is judged that the current air/fuel ratio R.sub.N substantially
reaches the target air/fuel ratio R.sub.T). Then, the processing
proceeds to the step S50. Then, it is judged whether the rate
dR.sub.N of change of air/fuel ratio detected by the air/fuel ratio
sensor 26 has an absolute value that is less than the threshold
value dR.sub.R or not. When it is judged that the rate dR.sub.N of
change of the air/fuel ratio R.sub.N has an absolute value smaller
than the threshold value dR.sub.R (i.e., when it is judged that the
exhaust flowing in the exhaust passage 20a has the air/fuel ratio
R.sub.N that is converged and stable at the target air/fuel ratio
R.sub.T), the processing proceeds to the step S51 to calculate the
amount .DELTA.E.sub.A of the surplus tolerance.
[0095] When the step S49 determines that the absolute value of the
value obtained by deducting the current air/fuel ratio value
R.sub.N from the target air/fuel ratio value R.sub.T is equal to or
larger than the threshold value R.sub.R(i.e., when it is judged
that the current air/fuel ratio R.sub.N is not converged at the
target air/fuel ratio R.sub.T), then the processing returns to the
step S41. In this case, it is noted that the current unit fuel
supply L.sub.U and the energized time t.sub.U are maintained. When
the step S50 determines that the absolute value of the rate
dR.sub.N of change of the air/fuel ratio is equal to or more than
the threshold value R.sub.R (i.e., when it is judged that the
exhaust flowing in the exhaust passage 20a has the air/fuel ratio
R.sub.N that does not reach the target air/fuel ratio R.sub.T and
is unstable), the processing also returns to the step S41. In this
case, the current unit fuel supply L.sub.U and the energized time
t.sub.U are similarly maintained.
[0096] After the step S53, the step S54 determines whether amount
.DELTA.E.sub.A of the surplus tolerance is more than the amount
.DELTA.E.sub.D of the surplus variation error or not. When the
amount .DELTA.E.sub.A of the surplus tolerance is larger than the
amount .DELTA.E.sub.D of the surplus variation error, (i.e., when
it is judged that the unit fuel supply L.sub.U can be updated and
reduced), then the processing proceeds to the step S55. Then, it is
judged whether the sum of the measurement errors E.sub.VA and
E.sub.RT of the airflow meter 22 and the air/fuel ratio sensor 26
is less than the maximum tolerance E.sub.A or not. When it is
judged that the sum of the measurement errors E.sub.VA and E.sub.RT
of the airflow meter 22 and the air/fuel ratio sensor 26 is smaller
than the maximum tolerance E.sub.A, (i.e., when it is judged that
the unit fuel supply L.sub.U can be updated and reduced), the
processing proceeds to the step S56. Then, the HC amount in the
exhaust is calculated. The step S57 calculates the lean shift
amount .DELTA.E.sub.S in the air/fuel ratio sensor 26. The step S58
calculates the catalyst purification rate .omega.. When the step
S55 determines that the sum of the measurement errors E.sub.VA and
E.sub.RT is less than the maximum tolerance E.sub.A, (i.e., when it
is judged that the unit fuel supply L.sub.U cannot be updated and
reduced), then the processing returns to the step S41 while
maintaining the current unit fuel supply L.sub.U and energized time
t.sub.U.
[0097] After the step S58, the step S59 determines whether the
above lean shift amount .DELTA.E.sub.S is less than a value
obtained by multiplying the HC purification rate .omega. with the
actual fuel supply g or not. When it is judged that the above lean
shift amount .DELTA.E.sub.S is less than a value obtained by
multiplying the HC purification rate .omega. with the actual fuel
supply g, the processing proceeds to the step S48. When it is
judged that the above lean shift amount .DELTA.E.sub.S is equal to
or larger than a value obtained by multiplying the HC purification
rate .omega. with the actual fuel supply g (i.e., when it is judged
that the unit fuel supply L.sub.U cannot be updated and reduced),
then the processing returns to the step S41 while maintaining the
current unit fuel supply L.sub.U and energized time t.sub.U.
[0098] As described above, similarly in this embodiment, when the
amount .DELTA.E of the surplus tolerance is less than the amount
.DELTA.E.sub.D of the surplus variation error, the unit fuel supply
L.sub.U is updated to a smaller target unit fuel supply L.sub.UT.
As a result, the oxidation catalytic converter 23c can have a
narrower temperature amplitude to reduce the wasteful fuel supply,
thus improving fuel consumption. At the same time, even the reduced
unit fuel supply L.sub.U can be always less than the maximum
tolerance, thus securely maintaining a desired control
accuracy.
[0099] It should be noted that, the present invention should be
interpreted based only upon the matters described in claims, and in
the aforementioned embodiments, all changes and modifications
included within the spirit of the present invention can be made
other than the described matters. That is, all the matters in the
described embodiments are made not to limit the present invention,
but can be arbitrarily changed according to the application, the
object and the like, including every construction having no direct
relation to the present invention.
REFERENCE SIGNS LIST
[0100] dT.sub.O Rate of exhaust temperature change [0101] dT.sub.R
Threshold value [0102] dR.sub.N Rate of change of air/fuel ratio
[0103] dR.sub.R Threshold value [0104] .DELTA.E.sub.A Surplus
amount of tolerance [0105] .DELTA.E.sub.D Surplus amount of
variation error [0106] .DELTA.E.sub.S Lean shift amount in air/fuel
ratio sensor [0107] .DELTA.L.sub.T Required supply to be supplied
at every driving cycle of fuel supply valve [0108] .DELTA.T.sub.C
Rate of temperature increase of exhaust emission purifier per unit
time [0109] E.sub.A Maximum tolerance in unit fuel supply [0110]
E.sub.D Maximum variation error in unit fuel supply [0111] E.sub.U
Supply error [0112] E.sub.RT Measurement error by air/fuel ratio
sensor [0113] E.sub.T Measurement error by catalyst temperature
sensor [0114] E.sub.VA Measurement error by airflow meter [0115] g
Actual fuel supply [0116] L.sub.TA Activation required fuel supply
[0117] L.sub.TR Regenerating required fuel supply [0118] L.sub.T
Required fuel supply [0119] L.sub.U Unit fuel supply [0120]
L.sub.UC Reference unit fuel supply [0121] L.sub.US Initial value
of unit fuel supply [0122] L.sub.UT Target unit fuel supply [0123]
R.sub.N Air/Fuel ratio in exhaust [0124] R.sub.T Target air/fuel
ratio [0125] R.sub.R Threshold value [0126] t.sub.C Driving cycle
of fuel supply valve [0127] t.sub.1 to t.sub.5 Time [0128] T.sub.C
Temperature of oxidation catalytic converter [0129] T.sub.O Exhaust
temperature at downstream of catalystff [0130] T.sub.T Target
activation temperature [0131] T.sub.R Threshold value [0132] v HC
Reaction rate in exhaust emission purifier [0133] V.sub.A
Air-intake amount [0134] .omega. HC Purification rate by exhaust
emission purifier [0135] 10 Engine [0136] 10a Combustion chamber
[0137] 11 Fuel injection valve [0138] 12 Cylinder head [0139] 12a
Intake port [0140] 12b Exhaust port [0141] 13a intake valve [0142]
13b Exhaust valve [0143] 14 Accelerator pedal [0144] 15 ECU [0145]
15a Operating status determining section [0146] 15b Fuel injection
setting section [0147] 15c Fuel injection valve driving section
[0148] 15d Fuel supply requirement determining section [0149] 15e
Fuel supply setting section [0150] 15f Fuel supply valve driving
section [0151] 15g Glow plug driving section [0152] 15h Unit fuel
supply updating section [0153] 15i Surplus tolerance calculating
section [0154] 15j Convergence determining section [0155] 15l
Update availability determining section [0156] 16 Accelerator
opening sensor [0157] 17 Cylinder block [0158] 17a Piston [0159]
17b Connecting rod [0160] 17c Crankshaft [0161] 18 Crank angle
sensor [0162] 19 Air-intake pipe [0163] 19a Air-intake passage
[0164] 19b Surge tank [0165] 20 Exhaust pipe [0166] 20a Exhaust
passage [0167] 21 Supercharger (Turbocharger) [0168] 21a Compressor
[0169] 21b Exhaust turbine [0170] 21c intercooler [0171] 22 Airflow
meter [0172] 23 Exhaust emission purifier [0173] 23a NO.sub.X
Storage catalytic converter [0174] 23b DPF [0175] 23c Oxidation
catalytic converter [0176] 24 Exhaust heating unit [0177] 24a Fuel
supply valve [0178] 24b Glow plug [0179] 25 First exhaust
temperature detecting sensor [0180] 26 Air/Fuel ratio detecting
sonsor [0181] 27 Catalytic converter temperature detecting sensor
[0182] 28 Second exhaust temperature detecting sensor
* * * * *