U.S. patent application number 11/515867 was filed with the patent office on 2007-03-15 for fuel injection control device and control method for internal combustion engine and recording medium recorded with program realizing control method.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Hiroaki Tsuji.
Application Number | 20070056557 11/515867 |
Document ID | / |
Family ID | 37833273 |
Filed Date | 2007-03-15 |
United States Patent
Application |
20070056557 |
Kind Code |
A1 |
Tsuji; Hiroaki |
March 15, 2007 |
FUEL INJECTION CONTROL DEVICE AND CONTROL METHOD FOR INTERNAL
COMBUSTION ENGINE AND RECORDING MEDIUM RECORDED WITH PROGRAM
REALIZING CONTROL METHOD
Abstract
From execution of fuel cut until restoration therefrom in
response to a F/C flag being set, an ECU senses an intake air
amount Q and engine speed NE, calculates the charging efficiency
based on Q and NE, and calculates a basic injection amount TAU_B
based on the charging efficiency. When the F/C flag is reset, the
ECU calculates asynchronous injection requested amount TAU_REQ
based on emission request, calculates upper guard injection amount
ASY_MAX based on TAU_B, inserts ASY_MAX into asynchronous injection
amount TAU_ASY when TAU_REQ is larger than ASY_MAX and inserts
TAU_REQ into asynchronous injection amount TAU_ASY when TAU_REQ is
equal to or below ASY_MAX.
Inventors: |
Tsuji; Hiroaki;
(Nishikamo-gun, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
|
Family ID: |
37833273 |
Appl. No.: |
11/515867 |
Filed: |
September 6, 2006 |
Current U.S.
Class: |
123/326 ;
123/492 |
Current CPC
Class: |
F01N 3/101 20130101;
F01N 13/009 20140601; Y02T 10/40 20130101; Y02A 50/2324 20180101;
Y02A 50/20 20180101; F02D 41/126 20130101; Y02T 10/12 20130101;
Y02T 10/47 20130101; F01N 3/10 20130101; F02D 41/1441 20130101;
F01N 2560/14 20130101; F01N 13/0093 20140601; F01N 2560/025
20130101; F01N 11/007 20130101; Y02T 10/22 20130101 |
Class at
Publication: |
123/326 ;
123/492 |
International
Class: |
F02D 41/12 20060101
F02D041/12 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 15, 2005 |
JP |
2005-268459 |
Claims
1. A fuel injection control device for an internal combustion
engine, executing fuel cut that suppresses fuel supply to the
internal combustion engine when a vehicle state satisfies a
predetermined condition, comprising: means for controlling said
internal combustion engine such that asynchronous injection is
executed when execution of said fuel cut is ceased, setting means
for setting an upper limit value of a fuel injection amount in a
mode of said asynchronous injection, means for calculating a
requested amount of injection for asynchronous injection in order
to improve a function of an exhaust purify device provided at said
internal combustion engine, and means for regulating said fuel
injection amount for asynchronous injection to said upper limit
value when said requested amount of injection is larger than said
upper limit value.
2. The fuel injection control device for an internal combustion
engine according to claim 1, wherein said setting means includes
means for setting said upper limit value based on a basic injection
amount by synchronous injection.
3. The fuel injection control device for an internal combustion
engine according to claim 2, wherein said setting means includes
means for setting said upper limit value relatively higher in a
region where said basic injection amount is large as compared to a
region where said basic injection amount is small.
4. The fuel injection control device for an internal combustion
engine according to claim 1, wherein said fuel cut is executed
after racing.
5. A fuel injection control method for an internal combustion
engine, executing fuel cut that suppresses fuel supply to the
internal combustion engine when a vehicle state satisfies a
predetermined condition, comprising the steps of: controlling said
internal combustion engine such that asynchronous injection is
executed when execution of said fuel cut is ceased, setting an
upper limit value of a fuel injection amount in a mode of said
asynchronous injection, calculating a requested amount of injection
for asynchronous injection in order to improve a function of an
exhaust purify device provided at said internal combustion engine,
and regulating said fuel injection amount for asynchronous
injection to said upper limit value when said requested amount of
injection is larger than said upper limit value.
6. The fuel injection control method for an internal combustion
engine according to claim 5, wherein said step of setting an upper
limit value includes the step of setting said upper limit value
based on a basic injection amount by synchronous injection.
7. The fuel injection control method for an internal combustion
engine according to claim 6, wherein said step of setting an upper
limit value includes the step of setting said upper limit value
relatively higher in a region where said basic injection amount is
large as compared to a region where said basic injection amount is
small
8. The fuel injection control method for an internal combustion
engine according to claim 5, wherein said fuel cut is executed
after racing.
9. A recording medium recorded with a program to realize the fuel
injection control method for an internal combustion engine defined
in claim 5 using an operation unit.
10. A fuel injection control device for an internal combustion
engine, executing fuel cut that suppresses fuel supply to the
internal combustion engine when a vehicle state satisfies a
predetermined condition, said fuel injection control device
including an operation unit, said operation unit adapted to control
said internal combustion engine such that asynchronous injection is
executed when execution of said fuel cut is ceased, set an upper
limit value of a fuel injection amount in a mode of said
asynchronous injection, calculate a requested amount of injection
for asynchronous injection in order to improve a function of an
exhaust purify device provided at said internal combustion engine,
and regulate said fuel injection amount for asynchronous injection
to said upper limit value when said requested amount of injection
is larger than said upper limit value.
11. The fuel injection control device for an internal combustion
engine according to claim 10, wherein said operation unit sets said
upper limit value based on a basic injection amount by synchronous
injection.
12. The fuel injection control device for an internal combustion
engine according to claim 11, wherein said operation unit sets said
upper limit value relatively higher in a region where said basic
injection amount is large as compared to a region where said basic
injection amount is small.
13. The fuel injection control device for an internal combustion
engine according to claim 10, wherein said fuel cut is executed
after racing.
14. A recording medium recorded with a program to realize the fuel
injection control method for an internal combustion engine defined
in claim 6 using an operation unit.
15. A recording medium recorded with a program to realize the fuel
injection control method for an internal combustion engine defined
in claim 7 using an operation unit.
16. A recording medium recorded with a program to realize the fuel
injection control method for an internal combustion engine defined
in claim 8 using an operation unit.
Description
[0001] This nonprovisional application is based on Japanese Patent
Application No. 2005-268459 with the Japan Patent Office on Sep.
15, 2005, the entire contents of which are hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to fuel injection control for
an internal combustion engine, particularly asynchronous injection
control at the time of restoration from a fuel cut mode.
[0004] 2. Description of the Background Art
[0005] When a spark ignition type engine is shifted from a steady
operation state to an accelerating operation state, fuel injection
that is not in synchronization with the engine revolution for the
purpose of increasing fuel (hereinafter, referred to as
asynchronous injection) is conducted aside from fuel injection at
every engine revolution (hereinafter, referred to as synchronous
injection). For example, in the case of a multicylinder engine
mounted on a vehicle, fuel is injected in synchronization into the
intake port by an injector from the later stage of the exhaust
stroke to the intake stroke for each cylinder in a steady operation
state. When an action is made by the driver of the vehicle to open
the throttle valve, asynchronous injection is effected immediately
for all the cylinders. Accordingly, the fuel supply to all the
cylinders is increased without delay corresponding to the increase
of the intake air to avoid dilution of the air-fuel mixture and to
avoid degradation in the vehicle acceleration response. Thus, the
drivability can be improved.
[0006] In such asynchronous injection, a constant amount of fuel is
injected by sensing the accelerating operation state, irrespective
of the crank angle, to avoid degradation in the acceleration
response. However, there is the problem that deviation from the
stoichiometric air-fuel ratio may occur as the number of times of
asynchronous injection increases since the stoichiometric air-fuel
ratio is not taken into account as in synchronous injection.
Japanese Patent Laying-Open No. 08-158920 discloses a correcting
control device during the transition period of electronic fuel
injection that can maintain the stoichiometric air-fuel ratio even
in asynchronous injection. This correcting control device for the
transition period of electronic fuel injection estimates the intake
pipe pressure of a preread crank angle from the time of calculation
to the average timing of each cylinder taking in fuel based on
pressure changes in the past in the intake pipe when fuel injection
is to be effected at one time for all the cylinders. The correcting
control device accommodates synchronous injection effecting fuel
injection of one cycle taking into consideration the stoichiometric
air-fuel ratio based on the estimated pressure, and asynchronous
fuel injection effecting injection of fuel that runs short in
synchronous injection at the time of abrupt acceleration. The
amount of fuel injection for the asynchronous fuel injection is
obtained taking into consideration the stoichiometric air-fuel
ratio by estimating the intake pipe pressure, likewise synchronous
injection. The maximum value of the amount of fuel to be injected
in one cycle is limited in synchronous injection and asynchronous
injection.
[0007] In accordance with this correcting control device, the fuel
injection amount in asynchronous fuel injection is obtained taking
into account the stoichiometric air-fuel ratio by estimating the
intake pipe pressure, likewise synchronous injection, so that
deviation from the stoichiometric air-fuel ratio, even when the
asynchronous fuel injection amount increases, can be suppressed.
Further, by limiting the maximum value of the amount of fuel to be
injected in one cycle in synchronous injection and asynchronous
injection, excessive correction can be suppressed.
[0008] The exhaust system of an engine is generally provided with a
catalytic converter to purify specific components in the exhaust
gas. A three-way catalytic converter is used extensively for such a
catalytic converter to oxidize carbon monoxide (CO) and unburned
hydrocarbon (HC) and to reduce nitrogen oxide (NO.sub.X), which are
the specific three components in exhaust gas, for conversion into
carbon dioxide (CO.sub.2), water vapor (H.sub.2O), and nitrogen
(N.sub.2), respectively.
[0009] The purifying property by the three-way catalytic converter
depends upon the air-fuel ratio of the air-fuel mixture formed in
the combustion chamber. The three-way catalytic converter functions
most effectively when the air-fuel ratio is in the vicinity of the
stoichiometric air-fuel ratio. This is due to the fact that, if the
air-fuel ratio is lean and the amount of oxygen in the exhaust gas
is large, oxidation becomes active whereas reduction becomes
inactive, and if the air-fuel ratio is rich and the amount of
oxygen in the exhaust gas is small, reduction becomes active
whereas oxidation becomes inactive, such that all the three
components set forth above cannot be purified favorably. Therefore,
an engine with a three-way catalytic converter has an output linear
type oxygen sensor provided at the exhaust manifold such that the
air-fuel mixture in the combustion chamber is feedback-controlled
to the stoichiometric air-fuel ratio based on the oxygen
concentration measured by the oxygen sensor. In other words, when
the air-fuel ratio is lean and the amount of oxygen in the exhaust
gas is large, the reduction action becomes inactive, which means
that the action of reducing nitrogen oxide (NO.sub.X) is
deteriorated to degrade the NO.sub.X purifying function.
[0010] The vehicle employs the control to suppress fuel supply
during deceleration in order to improve the fuel economy, i.e.
fuel-cut control. This fuel cut control aims to improve the fuel
economy by reducing fuel supply to the engine as much as possible
in a range that does not spoil the running performance and riding
comfort. In general, fuel supply is suppressed when the engine
speed falls within a predetermined range (equal to or higher than
the fuel-cut speed) during deceleration in which the engine takes
an idling state. Specifically, when the throttle valve is closed
during running and the engine speed is equal to or higher than the
fuel cut speed, supply of fuel is ceased. When the engine speed is
reduced to arrive at the restoration speed that defines the lower
limit of the range (fuel cut restoration speed), fuel supply is
resumed.
[0011] Since fuel injection is suppressed during fuel-cut control,
the air-fuel ratio is rendered lean, and the NO.sub.X purifying
function is degraded. If fuel is injected upon restoration from the
fuel-cut state, the NO.sub.X cannot be purified sufficiently since
the NO.sub.X purifying function by the three-way catalytic
converter is degraded. Therefore, the asynchronous injection based
on emission request set forth above is executed.
[0012] If the fuel injection amount in asynchronous injection is
excessive, the air-fuel ratio will become too rich to cause
backfire. If the fuel injection amount is too low, a sufficiently
rich atmosphere cannot be achieved in the three-way catalytic
converter, leading to the problem that the NO.sub.X purifying
function cannot be improved.
[0013] These problems, however, are not recognized in the
aforementioned Japanese Patent Laying-Open No. 08-158920. Although
the control device disclosed in this publication restricts the
amount of fuel injection per cycle in order to suppress excessive
correction, the problems set forth above are not addressed.
SUMMARY OF THE INVENTION
[0014] In view of the foregoing, an object of the present invention
is to provide a fuel injection control device for an internal
combustion engine that can execute asynchronous injection
appropriately at the time of restoration from a fuel-cut mode.
[0015] When the state of the vehicle satisfies a predetermined
condition, the control device of the present invention controls
fuel injection of the internal combustion engine executing fuel cut
that suppresses fuel supply to the internal combustion engine. The
control device is adapted to control the internal combustion engine
such that asynchronous injection is executed when execution of fuel
cut is ceased, set the upper limit value of the fuel injection
amount in a mode of asynchronous injection, calculate the requested
amount of injection for asynchronous injection in order to improve
the function of an exhaust purify device provided at the internal
combustion engine, and regulate the fuel injection amount for
asynchronous injection to the upper limit value when the requested
amount of injection is higher than the upper limit value.
[0016] In accordance with the present invention, asynchronous
injection is effected to inject fuel to all the plurality of
cylinders at one time when the atmosphere in the three-way
catalytic converter was lean during fuel cut and execution of fuel
cut is ceased (restoration from fuel cut). In order to render the
atmosphere in the three-way catalytic converter as rich as possible
to improve the NO.sub.X purifying function, the fuel injection
amount in asynchronous injection is desirably high. If, however,
this fuel injection amount is excessive, backfire may occur to melt
and deteriorate the catalyst. Therefore, when the requested amount
of injection is higher than the upper limit value, the fuel
injection amount in asynchronous injection is regulated to the
upper limit value. Accordingly, asynchronous injection based on
emission request can be conducted while avoiding the problem of
backfire and the like as well as improving the NO.sub.X purifying
function of the three-way catalytic converter at the time of
restoration from fuel cut. As a result, a fuel injection control
device for an internal combustion engine that can execute
asynchronous injection appropriately at the restoration from fuel
cut can be provided.
[0017] Preferably, the fuel injection control device sets the upper
limit value based on the basic injection amount by synchronous
injection.
[0018] In the present invention, the basic injection amount in a
fuel cut mode is calculated and the upper limit value in
asynchronous injection is set corresponding to the basic injection
amount. Therefore, the upper limit value can be set according to
the operation state of the internal combustion engine and the event
of unnecessarily setting the upper limit value can be avoided.
[0019] Further preferably, the fuel injection control device sets
the upper limit value relatively higher in the region where the
basic injection amount is large as compared to the region where the
basic injection amount is small.
[0020] In the present invention, a high basic injection amount
corresponds to a region of high charging efficiency. In such a
region, the NO.sub.X purifying function of the three-way catalytic
converter is to be improved than the problem of backfire.
Therefore, a relatively high upper limit value is set to achieve
sufficient asynchronous injection.
[0021] Further preferably, fuel cut is executed after racing, i.e.
after increasing the engine speed in a non-load state.
[0022] In accordance with the present invention, fuel cut is
executed after racing to avoid the problem of backfire that is
particularly noticeable at the time of restoration from fuel
cut.
[0023] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 represents a configuration of an engine in a vehicle
to which a fuel injection control device according to an embodiment
of the present invention is incorporated.
[0025] FIG. 2 represents the relationship between the basic
injection amount and upper limit guard injection amount stored in
an engine ECU qualified as a fuel injection control device
according to an embodiment of the present invention.
[0026] FIG. 3 is a flow chart of a control program executed by an
engine ECU qualified as a control device according to an embodiment
of the present invention.
[0027] FIG. 4 is a timing chart representing an engine state under
control of an engine ECU qualified as a control device according to
an embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] Embodiments of the present invention will be described
hereinafter with reference to the drawings. The same components
have the same reference characters allotted, and their designation
and function are also identical. Therefore, detailed description
thereof will not be repeated.
[0029] Referring to FIG. 1, a vehicle to which a fuel injection
control device for an internal combustion engine according to the
present embodiment is incorporated includes an engine 150, an
intake system 152, an exhaust system 154, and an ECU (Electronic
Control Unit) 100.
[0030] Intake system 152 includes an intake manifold 110, an air
cleaner 118, an air flow meter 104, a throttle motor 114, a
throttle valve 112, and a throttle position sensor 116.
[0031] The air taken in through air cleaner 118 passes through
intake manifold 110 to flow to engine 150. Throttle valve 112 is
provided in the course of intake manifold 110. Throttle valve 112
opens/closes by an operation of throttle motor 114. The opening of
throttle valve 112 can be sensed by throttle position sensor 116.
At the intake manifold between air cleaner 118 and throttle valve
112, air flow meter 104 is provided to sense the amount of air
taken in. Air flow meter 104 transmits an intake amount signal
representing the amount of intake air Q to ECU 100.
[0032] Engine 150 includes a coolant pipe 122, a cylinder block
124, an injector 126, a piston 128, a crankshaft 130, a coolant
temperature sensor 106, and a crank position sensor 132.
[0033] A specific number of cylinders are provided in a cylinder
block 124, and a piston 128 is provided in each of the plurality of
cylinders. A mixture of the fuel injected from injector 126 and the
intake air is introduced through intake manifold 110 into the
combustion chamber located above piston 128. The air-fuel mixture
is ignited by a spark plug (not shown) to burn. By this burning,
piston 128 is pushed down. At this stage, the up-and-down motion of
piston 128 is converted into a rotation motion of crankshaft 130
via the crank mechanism. The engine speed NE of engine 150 is
detected by ECU 100 based on a signal sensed by crank position
sensor 132.
[0034] Water coolant pipe 122 is provided in cylinder block 124.
Coolant circulates through coolant pipe 122 by the operation of a
water pump (not shown). The coolant in coolant pipe 122 flows to a
radiator (not shown) connected to coolant pipe 122 to be derived of
heat by a cooling fan (not shown). Coolant temperature sensor 106
is provided above the channel of coolant pipe 122 to sense the
temperature of the coolant in coolant pipe 122. Coolant temperature
sensor 106 transmits a coolant temperature signal corresponding to
the sensed coolant temperature to ECU 100.
[0035] Exhaust system 154 includes an exhaust pipe 108, a first
air-fuel ratio sensor 102A, a second air-fuel ratio sensor 102B, a
first three-way catalytic converter 120A, and a second three-way
catalytic converter 120B. First air-fuel ratio sensor 102A is
provided at the upstream side of first three-way catalytic
converter 120A. Second air-fuel ratio sensor 102B is provided at
the downstream side of first three-way catalytic converter 120A
(upstream side of second three-way catalytic converter 120B). It is
to be noted that only one three-way catalytic converter may be
provided instead.
[0036] Exhaust pipe 108 connected to the exhaust side of engine 150
is connected with first and second three-way catalytic converters
120A and 120B. The exhaust gas generated by the burning of air-fuel
mixture in the combustion chamber of engine 150 first flows to
first three-way catalytic converter 120A. The HC and CO included in
the exhaust gas flowing into first three-way catalytic converter
120A are oxidized at first three-way catalytic converter 120A. The
NO.sub.X included in the exhaust gas flowing to first three-way
catalytic converter 120A is reduced at first three-way catalytic
converter 120A. First three-way catalytic converter 120A is located
in the proximity of engine 150 to be rapidly increased in
temperature even in a cold start mode of engine 150 to exhibit the
catalytic function.
[0037] The exhaust gas is then delivered from first three-way
catalytic converter 120A to second three-way catalytic converter
120B for the purpose of purifying NO.sub.X. First and second
three-way catalytic converters 120A and 102B basically have the
same configuration and function.
[0038] A first oxygen sensor 102A provided at the upstream side of
first three-way catalytic converter 120A and a second oxygen sensor
102B provided at the downstream side of first three-way catalytic
converter 120A and the upstream side of second three-way catalytic
converter 120B sense the concentration of oxygen included in the
exhaust gas that passes through three-way catalytic converter 120A
or three-way catalytic converter 120B. By sensing the oxygen
concentration, the ratio of fuel to air included in the exhaust
gas, i.e. air-fuel ratio, can be identified.
[0039] First and second air-fuel ratio sensors 102A and 102B
generate current corresponding to the oxygen concentration in the
exhaust gas. This current is converted into voltage, for example,
to be applied to ECU 100. Thus, the air-fuel ratio of exhaust gas
at the upstream of first three-way catalytic converter 120A can be
identified by the output signal of first air-fuel ratio sensor
102A. The air-fuel ratio of exhaust gas at the upstream of second
three-way catalytic converter 120B can be identified by the output
signal of second air-fuel ratio sensor 102B. First and second
air-fuel sensors 102A and 102B generate, for example, a voltage of
approximately 0.1 V and a voltage of approximately 0.9V when the
air-fuel ratio is lean and rich, respectively. Air-fuel ratio
control is effected by ECU 100 based on the comparison between a
value converted into the air-fuel ratio according to the generated
voltage value and the air-fuel ratio threshold value.
[0040] First and second three-way catalytic converters 120A and
120B function to oxidize HC and CO and reduce NO.sub.X when the
air-fuel ratio is substantially equivalent to the stoichiometric
ratio, i.e. function to purify HC, CO and NO.sub.X at the same
time. First and second three-way catalytic converters 120A and 120B
exhibit active oxidization and inactive reduction when the air-fuel
ratio is lean and the amount of oxygen in the exhaust gas is high,
and exhibit active reduction and inactive oxidation when the
air-fuel ratio is rich and the amount of oxygen in the exhaust gas
is low. All the aforementioned three components cannot be purified
favorably by the three-way catalytic converters. When the air-fuel
ratio is lean and the amount of oxygen in the exhaust gas is high,
reduction becomes inactive, whereby the action of reducing nitrogen
oxide (NO.sub.X) is reduced to degrade the NO.sub.X purifying
function.
[0041] Engine 150 employs the control to suppress fuel supply
during deceleration in order to improve the fuel economy, i.e. the
so-called fuel-cut control. Fuel supply is suppressed when the
engine speed falls within a predetermined range (at least the fuel
cut speed) during deceleration in which engine 150 is idle.
Specifically, when the throttle valve 112 is closed during running
and the engine speed is equal to or above the fuel cut speed, fuel
supply is ceased. When the engine speed is reduced to arrive at the
restoration speed that defines the lower limit of the range (fuel
cut restoration speed), fuel supply is resumed. This restoration
speed is set to a value that does not cause engine stall and that
can maintain steady revolution of engine 150. When the temperature
of the engine coolant sensed by coolant temperature sensor 106 is
low, the fuel cut speed and fuel cut restoration speed are set at
high values.
[0042] ECU 100 qualified as a fuel injection control device for an
internal combustion engine according to the present invention
executes asynchronous injection (outputs an injection instruction
signal to injector 126 of all cylinders) to render the atmosphere
in three-way catalytic converters 120A and 120B rich at the time of
restoration from fuel cut. Accordingly, the atmosphere of first and
second three-way catalytic converters 120A and 120B, lean in a fuel
cut mode, can be rendered rich at the time of restoration to purify
NO.sub.X. If the amount of fuel injection in this asynchronous
injection is excessive, backfire may occur to melt and deteriorate
the catalyst. Therefore, ECU 100 provides an upper limit guard for
the requested amount by emission request with respect to the fuel
injection amount in asynchronous injection to suppress the
occurrence of backfire.
[0043] The upper limit guard injection amount ASY_MAX (.mu.sec) in
asynchronous injection at the time of restoration from fuel cut
will be described with reference to FIG. 2. FIG. 2 represents the
relationship of upper limit guard injection amount ASY_MAX
(.mu.sec) with respect to basic injection amount TAU_B (.mu.sec)
from injector 126. ASY_MAX(.mu.sec)=f(TAU_B) is established with a
function f.
[0044] It is appreciated from FIG. 2 that upper limit guard
injection amount ASY_MAX (.mu.sec) is low when basic injection
amount TAU_B (.mu.sec) is low, and upper limit guard injection
amount ASY_MAX (.mu.sec) takes a constant value when basic
injection amount TAU_B (.mu.sec) exceeds a predetermined value.
[0045] Basic injection amount TAU_B (.mu.sec) that is the fuel
injection amount for synchronous injection is related to the
charging efficiency of engine 150 (the ratio of the amount of air
actually drawn into the cylinder to the amount of air that is to be
drawn in theoretically, and calculated based on engine speed NE and
intake air amount Q). When the charging efficiency is low, basic
injection amount TAU_B (.mu.sec) is small; when the charging
efficiency is high, basic injection amount TAU_B (.mu.sec) is
large. In the case where engine 150 is in a normal operation state,
the charging efficiency is high and low when the opening of
throttle valve 112 is large and small, respectively.
[0046] Thus, the region of low basic injection amount TAU_B
(.mu.sec) shown in FIG. 2 corresponds to a region of low charging
efficiency. In this region, the melting and deterioration of the
catalyst caused by backfire can be prevented, so that a certain
level of the NO.sub.X purifying function can be exhibited. In
contrast, the region shown in FIG. 2 where basic injection amount
TAU_B (.mu.sec) is high corresponds to a region where the charging
efficiency is high. In such a region, the NO.sub.X purifying
function by first and second three-way catalytic converters 120A
and 120B can be exhibited sufficiently. In view of the foregoing,
the upper limit guard injection amount ASY_MAX (.mu.sec) at the
region where basic injection amount TAU_B (.mu.sec) is low is small
(guarded extensively), whereas the upper limit guard injection
amount ASY_MAX (.mu.sec) at the region where basic injection amount
TAU_B (.mu.sec) is high is large (not guarded extensively).
[0047] The relationship between basic injection amount TAU_B
(.mu.sec) and upper guard injection amount ASY_MAX (.mu.sec) shown
in FIG. 2 is only a way of example, and the present invention is
not limited to the relationship shown in FIG. 2.
[0048] The configuration of the control program executed at ECU 100
qualified as a fuel injection control device according to the
present embodiment will be described hereinafter with reference to
FIG. 3. This program is executed repeatedly at a predetermined
cycle time (for example, 8 msec).
[0049] At step (hereinafter, step abbreviated at S) 100, ECU 100
determines whether a F/C (fuel cut) flag is set or not. This F/C
flag is set and reset when the fuel cut start condition by another
program executed at ECU 100 is satisfied and not satisfied,
respectively. When the F/C flag is set (YES at S100), control
proceeds to S110, otherwise (NO at S100), the process ends.
[0050] At S110, ECU 100 senses the intake air amount Q based on a
signal from air flow meter 104. At S120, ECU 100 senses engine
speed NE based on a signal from crank position sensor 132.
[0051] At S130, ECU 100 calculates the charging efficiency based on
intake air amount Q and engine speed NE. At S140, ECU 100
calculates basic injection amount TAU_B (.mu.sec) based on the
charging efficiency.
[0052] At S150, ECU 100 determines whether the F/C flag is reset or
not. When the F/C flag is reset (YES at S150), control proceeds to
160, otherwise (NO at S150), control returns to S110.
[0053] At S160, ECU 100 calculates asynchronous injection requested
amount TAU_REQ (.mu.sec) based on the emission request. This is the
amount of fuel required to achieve a rich atmosphere for first and
second three-way catalytic converters 120A and 120B to sufficiently
exhibit the NO.sub.X purifying function.
[0054] At S170, ECU 100 calculates upper limit guard injection
amount ASY_MAX (.mu.sec) based on basic injection amount TAU_B
(.mu.sec). Upper limit guard injection amount ASY_MAX (.mu.sec) is
calculated using a function f representing the relationship as
shown in FIG. 2, for example.
[0055] At S180, ECU 100 determines whether asynchronous injection
requested amount TAU_REQ (.mu.sec) is higher than upper limit guard
injection amount ASY_MAX (.mu.sec). When asynchronous injection
requested amount TAU_REQ (.mu.sec) is higher than upper limit guard
injection amount ASY_MAX (.mu.sec) (YES at S180), control proceeds
to S190, otherwise (NO at S180), control proceeds to S200.
[0056] At S190, ECU 100 inserts upper limit guard injection amount
ASY_MAX (.mu.sec) into asynchronous injection amount TAU_ASY
(.mu.sec). At S200, ECU 100 inserts asynchronous injection
requested amount TAU_REQ (.mu.sec) into asynchronous injection
amount TAU_ASY (.mu.sec).
[0057] At S210, ECU 100 outputs an asynchronous injection
instruction signal (injection amount TAU_ASY) to injector 126.
[0058] An operation of ECU 100 realizing the fuel injection control
device of the present embodiment based on the configuration and
flow chart set forth above will be described hereinafter with
reference to FIG. 4.
[0059] <During Fuel Cut>
[0060] When the operation of engine 150 is initiated and the fuel
cut condition is satisfied, the F/C flag is set and fuel cut is
initiated (YES at S100). This corresponds to time t (1) in FIG.
4.
[0061] Although fuel injection will not be actually executed during
fuel cut, basic injection amount TAU_B (.mu.sec) from injector 126
is calculated. Specifically, intake air amount Q to engine 150 is
sensed (S110); engine speed NE is sensed (S120); the charging
efficiency is calculated based on intake air amount Q and engine
speed NE (S130); and basic injection amount TAU_B (.mu.sec) is
calculated based on the charging efficiency (S140).
[0062] Such an operation is repeated during fuel cut. This
corresponds to the state from time t (1) onward, in FIG. 4, and
basic injection amount TAU_B (.mu.sec) is indicated by the dotted
line.
[0063] When the fuel cut condition is no longer satisfied (or when
the fuel cut restore condition is satisfied), the F/C flag is reset
for restoration from a fuel cut mode (YES at S150). This
corresponds to time t (2) of FIG. 4.
[0064] At time t (2), asynchronous injection requested amount
TAU_REQ (.mu.sec) is calculated based on emission request (S160).
Then, upper limit guard injection amount ASY_MAX (.mu.sec) is
calculated based on basic injection amount TAU_B (.mu.sec) and the
relation shown in FIG. 2 (S170).
[0065] <When Regulated by Upper Limit Guard Injection Amount
ASY_MAX>
[0066] When asynchronous injection requested amount TAU_REQ
(.mu.sec) at the time of restoration from fuel cut is high and
larger than upper limit guard injection amount ASY_MAX (.mu.sec)
(YES at S180), upper limit guard injection amount ASY_MAX (.mu.sec)
is inserted into asynchronous injection amount TAU_ASY (.mu.sec)
(S190).
[0067] This is the state indicated by (A) in FIG. 4, and
corresponds to the case where asynchronous injection requested
amount TAU_REQ (.mu.sec) is regulated by upper limit guard
injection amount ASY_MAX (.mu.sec) to be reduced to the level of
upper limit guard injection amount ASY_MAX (.mu.sec).
[0068] By the reduction down to upper limit guard injection amount
ASY_MAX (.mu.sec), the possibility of the catalyst being melted and
deteriorated by backfire in the case where the fuel of asynchronous
injection requested amount TAU_REQ (.mu.sec) is provided by
asynchronous injection can be avoided. Since at least upper limit
guard injection amount ASY_MAX (.mu.sec) is provided in
asynchronous injection at the time of restoration from fuel cut,
the atmosphere of first and second three-way catalytic converters
120A and 120B can be rendered rich, allowing improvement of the
NO.sub.X purifying function.
[0069] <When not Regulated by Upper Limit Guard Injection Amount
ASY_MAX>
[0070] When asynchronous injection requested amount TAU_REQ
(.mu.sec) at the time of restoration from fuel cut is not large and
is equal to or below upper limit guard injection amount ASY_MAX
(.mu.sec) (NO at S180), asynchronous injection requested amount
TAU_REQ (.mu.sec) is inserted into asynchronous injection amount
TAU_ASY (.mu.sec) (S200).
[0071] This state corresponds to (B) in FIG. 4. Asynchronous
injection requested amount TAU_REQ (.mu.sec) is not regulated by
upper limit guard injection amount ASY_MAX (.mu.sec), and only
asynchronous injection requested amount TAU_REQ (.mu.sec) is
injected in an asynchronous manner at the time of restoration from
fuel cut.
[0072] Even in such a case where only the fuel of asynchronous
injection requested amount TAU_REQ (.mu.sec) is injected
asynchronously, the region where the charging efficiency is high
and the emission request is satisfied can be achieved, so that the
atmosphere of first and second three-way catalytic converters 120A
and 120B can be rendered rich sufficiently. Therefore, the NO.sub.X
purifying function can be improved.
[0073] By virtue of the fuel injection control device for an
internal combustion engine according to the present embodiment set
forth above, asynchronous injection based on emission request can
be conducted while avoiding the problem of backfire and the like
and also improving the NO.sub.X purifying function of the three-way
catalytic converter at the time of restoration from fuel cut.
[0074] The problem such as backfire is particularly significant by
asynchronous injection based on emission request at the time of
restoration from fuel cut, subsequent to racing in an idling state
of the engine prior to fuel cut. Therefore, the present invention
is particularly advantageous when the asynchronous injection
control of the present embodiment is effected after idle
racing.
[0075] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *