JP2003065111A - Fuel injection controller for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To securely prevent overheating of an exhaust system without causing unnecessary increase of fuel amount. SOLUTION: When exhaust air temperature TEXT is below a first threshold value T1 which makes it possible to regard that there is no influence for exerting thermal harm to exhaust system constituent parts, increase in fuel amount related to the reduction of exhaust air temperature is not performed to improve fuel consumption. While the exhaust air temperature TEXT reaches a second threshold value T2 which may cause thermal harm to the exhaust system constituent parts from the first threshold value T1, increase of fuel amount related to the reduction of exhaust air temperature is gradually performed to improve fuel consumption and make a linkage up to fuel amount increase compensation performed when the exhaust air temperature TEXT exceeds the second threshold value T2 smooth. When the exhaust air temperature TEXT exceeds the second threshold value T2, increase of fuel amount related to the reduction of exhaust air temperature is performed based on an engine operation condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine fuel for increasing the amount of fuel injection and reducing the exhaust temperature when the exhaust temperature is high, such as during high-load operation of the engine, to prevent damage due to overheating of exhaust system parts such as catalysts. The present invention relates to an injection control device.

[0002]

2. Description of the Related Art Generally, in engine fuel injection control, in a high load operation region where exhaust gas temperature rises, fuel injection is performed in order to prevent exhaust system components such as a catalyst for purifying exhaust gas from overheating and deteriorating. Although the amount is increased to lower the exhaust temperature, the temperature rise of the exhaust system parts is delayed with respect to the rise of the exhaust temperature because the heat capacity of the exhaust system is large, during which unnecessary fuel is increased, There is a problem that it is disadvantageous in terms of fuel efficiency.

Therefore, for example, Japanese Patent Laid-Open No. 8-200120
In the publication, when the power increase set at least based on the engine speed increases with time, the basic fuel injection amount is corrected based on the gradually increased power increase to improve the engine speed. A technique is disclosed in which the fuel injection amount is prevented from being rapidly increased corresponding to the number, and the catalyst is cooled without deteriorating fuel consumption and exhaust emission.

[0004]

However, when the basic fuel injection amount is corrected on the basis of the gradually increased power increase as in the above-mentioned prior art, the fuel injection amount corrected for increase is not necessarily the temperature rise of the exhaust system. Does not necessarily correspond to
There is a possibility that the exhaust system may not be sufficiently overheated, or that the fuel economy may not be sufficiently taken.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fuel injection control device for an engine capable of reliably preventing overheating of the exhaust system without incurring unnecessary fuel increase. .

[0006]

In order to solve the above-mentioned problems, the invention according to claim 1 is a fuel injection control device for an engine for correcting the exhaust temperature reduction by increasing the fuel amount when the exhaust gas temperature is high. First determining means for determining whether or not the exhaust temperature has reached a first threshold which is a temperature threshold that can be regarded as having no harmful effect, and an exhaust system having a temperature higher than the first threshold Second determining means for determining whether or not the exhaust temperature has reached a second threshold, which is a temperature threshold in which heat damage to the components is concerned, and when the exhaust temperature is less than or equal to the first threshold, When the fuel amount increase related to the exhaust gas temperature reduction correction is prohibited and the exhaust gas temperature is between the first threshold value and the second threshold value, the fuel amount increase related to the exhaust gas temperature reduction correction is gradually increased, When the exhaust temperature shifts to a temperature range higher than the second threshold value , Characterized in that an exhaust air temperature reducing correction means for setting a fuel increase according to the exhaust air temperature reducing correction based on the engine operating conditions.

According to a second aspect of the present invention, in the first aspect of the present invention, the exhaust gas temperature reduction correction means is configured to discharge the exhaust gas when the exhaust gas temperature is between the first threshold value and the second threshold value. It is characterized in that the above-mentioned fuel increase amount is gradually increased by adding a gradually increasing correction amount to the correction coefficient of the fuel injection amount related to the temperature reduction correction.

According to a third aspect of the present invention, in the first aspect of the invention, the exhaust gas temperature reduction correction means is configured to discharge the exhaust gas when the exhaust gas temperature is between the first threshold value and the second threshold value. It is characterized in that the correction coefficient of the fuel injection amount relating to the temperature reduction correction is multiplied by a correction rate that gradually increases to gradually increase the fuel increase amount.

That is, according to the first aspect of the present invention, when the exhaust gas temperature is equal to or lower than the first threshold value at which it can be considered that there is no heat damage to the exhaust components, the fuel amount increase related to the exhaust gas temperature reduction correction is prohibited. Then, when the exhaust gas temperature is between the first threshold value and the second threshold value in which heat damage to the exhaust component is concerned, the fuel increase amount related to the exhaust gas temperature reduction correction is gradually increased,
When the exhaust temperature shifts to a temperature range higher than the second threshold value, both the suppression of fuel consumption and the suppression of exhaust temperature overheating can be achieved by setting the fuel increase amount related to the exhaust temperature reduction correction based on the engine operating state. Plan.

In this case, when the exhaust gas temperature is between the first threshold value and the second threshold value, the correction coefficient of the fuel injection amount relating to the exhaust gas temperature reduction correction is set for each control cycle. Is added to the correction amount to be gradually increased, and the fuel increase amount related to the exhaust temperature reduction correction is gradually increased.

Further, according to a third aspect of the invention, when the exhaust gas temperature is between the first threshold value and the second threshold value, the correction coefficient of the fuel injection amount relating to the exhaust gas temperature reduction correction is set for each control cycle. By multiplying the correction rate that gradually increases, the fuel increase amount related to the exhaust temperature reduction correction is gradually increased.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. 1 to 7 relate to the first embodiment of the present invention, FIG. 1 is a flowchart of a fuel injection control routine, FIG. 2 is a flowchart of a power increase correction coefficient setting routine, and FIG. 3 is an output air-fuel ratio increase correction coefficient table. 4 is an explanatory view of a power increase correction coefficient table, FIG. 5 is a time chart showing the relationship between engine load, power increase correction coefficient, and exhaust temperature, FIG. 6 is an overall schematic view of the engine, and FIG. It is a circuit block diagram of a control system.

First, the overall construction of the engine will be described with reference to FIG. In the figure, reference numeral 1 is an engine, and in the present embodiment, a horizontally opposed four-cylinder gasoline engine is shown. Cylinder heads 2 are provided on both left and right banks of a cylinder block 1a of the engine 1, and an intake port 2a and an exhaust port 2b are formed on each cylinder head 2.

An intake manifold 3 is communicated with each intake port 2a of the cylinder head 2, and a throttle valve passage 5 is communicated with the intake manifold 3 via an air chamber 4 in which the intake passages of each cylinder are gathered. An air cleaner 7 is attached to the upstream side of the throttle valve passage 5 via an intake pipe 6, and the air cleaner 7 is in communication with an air intake chamber 8. An exhaust pipe 10 is connected to the exhaust port 2b via an exhaust manifold 9.
A muffler 12 is connected to the exhaust pipe 10 via a catalytic converter 11.

A throttle valve 5a interlocking with an accelerator pedal is provided in the throttle valve passage 5, an intercooler 13 is provided in an intake pipe 6 immediately upstream of the throttle valve passage 5, and an air cleaner for the intake pipe 6 is provided. A resonator chamber 14 is provided on the downstream side of 7.

In the bypass passage 15 which connects the resonator chamber 14 and the intake manifold 3 and bypasses the upstream side and the downstream side of the throttle valve 5a, an ISC (idle speed control) valve for adjusting the idle air amount is provided. 16
Is installed. Further, immediately downstream of the ISC valve 16 is opened when the intake pressure is a negative pressure, and the turbocharger 18
A check valve 17 that closes in the supercharged positive pressure state is installed.

The turbocharger 18 compressor is
The intake pipe 6 is installed downstream of the resonator chamber 14, and the turbine is installed in the exhaust pipe 10. further,
A wastegate valve 19 is provided at the turbine housing inlet of the turbocharger 18, and the wastegate valve 19 is connected to a wastegate valve actuating actuator 20.

Actuator 20 for operating the wastegate
Are partitioned by a diaphragm into two chambers, one forming a pressure chamber communicating with the wastegate control duty solenoid valve 21, and the other forming a spring chamber accommodating a spring for urging the wastegate valve 19 in the closing direction. is doing.

The wastegate controlling duty solenoid valve 21 is provided in a passage that connects the resonator chamber 14 and the compressor downstream of the turbocharger 18 of the intake pipe 6, and an electronic control unit 50 (see FIG. 7) described later. Depending on the duty ratio of the control signal output from
The pressure on the resonator chamber 14 side and the pressure on the compressor downstream side are adjusted to supply the control pressure to the pressure chamber of the wastegate valve operating actuator 20.

That is, the electronic control unit 50 controls the wastegate control duty solenoid valve 21 and operates the wastegate valve actuating actuator 20 to adjust the exhaust gas relief by the wastegate valve 19, thereby making the turbocharger 18 operate. Control the boost pressure.

An injector 22 is exposed immediately upstream of each intake port 2a of each cylinder of the intake manifold 3. Further, the cylinder head 2 is provided with an ignition plug 23 whose tip is exposed to the combustion chamber for each cylinder, and an igniter 25 is connected via an ignition coil 24 connected to the ignition plug 23.

Fuel is pressure-fed to the injector 22 from an in-tank type fuel pump 27 provided in a fuel tank 26 through a fuel filter 28, and a pressure regulator 29 regulates the fuel pressure to the injector 22.

Next, the arrangement of the sensors will be described.
Reference numeral 29 is an absolute pressure sensor, and the intake pipe pressure / atmospheric pressure switching solenoid valve 30 selectively detects the intake pipe pressure (intake pressure in the intake manifold 3) and the atmospheric pressure. Further, in the intake pipe 6, a thermal intake air amount sensor 31 using a hot wire, a hot film or the like is provided immediately downstream of the air cleaner 7. Also, the throttle valve 5a has
A throttle opening sensor 32 for detecting the opening of the throttle valve 5a is connected in series.

The cylinder block 1a of the engine 1
Is equipped with a knock sensor 33,
A cooling water temperature sensor 35 is exposed to a cooling water passage 34 that connects the left and right banks of the cylinder block 1a.
Further, in the exhaust pipe 10, an O2 sensor 36 is exposed at the collecting portion of the exhaust manifold 9, and an exhaust temperature sensor 37 is exposed immediately upstream of the catalytic converter 11.

A crank angle sensor 40 is provided opposite to the outer periphery of the crank rotor 39 pivotally mounted on the crankshaft 1b, and further, a crank angle sensor 40 is provided at a ratio of 1 / l to the crankshaft 1b.
A cam rotor 41 connected to a camshaft 1c that rotates twice
A cylinder discriminating sensor 42 for discriminating the present combustion stroke cylinder, fuel injection target cylinder, or ignition target cylinder is provided in the counter.

Next, the structure of the electronic control system for controlling the engine 1 will be described. Fuel injection control, ignition timing control,
Engine control such as boost pressure control and idle speed control
It is performed by an electronic control unit (ECU) 50 shown in FIG. 7.

The ECU 50 includes a CPU 51, a ROM 52,
A RAM 53, a backup RAM 54, a counter / timer group 55, and an I / O interface 56 are mainly configured by a microcomputer connected to each other via a bus line, and a constant voltage circuit 57, I / O that supplies a stabilized power supply to each unit. Peripheral devices such as a drive circuit 58 and an A / D converter 59 connected to the O interface 56 are built in.

The counter / timer group 55 is for generating various counters such as a free-run counter, a counter for counting the cylinder discrimination sensor signal (cylinder discrimination pulse), a fuel injection timer, an ignition timer, and a periodic interrupt. Various timers such as the regular interrupt timer and the watchdog timer for system abnormality monitoring are collectively referred to for convenience, and various software counter timers are used.

The constant voltage circuit 57 is connected to the battery 61 via the first relay contact of the power supply relay 60 having the two relay contacts, and is also directly connected to the battery 61, and the ignition switch 62 is connected to the constant voltage circuit 57. When the contact of the power relay 60 is closed by being turned on, power is supplied to each part in the ECU 50, while the ignition switch 6
Regardless of whether 2 is ON or OFF, backup RAM is always available
A power supply for backup is supplied to 54. A power supply line for supplying power from the battery 61 to each actuator is connected to the second relay contact of the power supply relay 60.

The input port of the I / O interface 56 is connected to the ignition switch 62 and the knock sensor 3
3, a crank angle sensor 40, a cylinder discrimination sensor 42, a vehicle speed sensor 43 for detecting a vehicle speed, and the like are connected, and further, an absolute pressure sensor 29, an intake air amount via an A / D converter 59. The sensor 31, the throttle opening sensor 32, the cooling water temperature sensor 34, the O2 sensor 36, the exhaust gas temperature sensor 37, etc. are connected, and the battery voltage V
B is input and monitored.

On the other hand, at the output port of the I / O interface 56, the relay coil (not shown) of the fuel pump 27, the ISC valve 16, the wastegate control duty solenoid valve 21, the injector 22, and the intake pressure /
The atmospheric pressure switching solenoid valve 30 and the like are connected via the drive circuit 58, and the igniter 25 is connected.

The CPU 51 processes the detection signals from the sensors and switches input via the I / O interface 56, the battery voltage, etc. in accordance with the control program stored in the ROM 52, and stores various data in the RAM 53. Based on the data, various learning value data stored in the backup RAM 54, fixed data stored in the ROM 52, and the like, the fuel injection amount, the ignition timing, I
The duty ratio of the drive signal for the SC valve 16 and the wastegate control duty solenoid valve 21 is calculated, and engine control such as fuel injection control, ignition timing control, idle speed control, boost pressure control, etc. is performed.

In such engine control, the ECU
When the engine operating condition is in a predetermined high load operating region, 50 executes an exhaust temperature reduction correction for increasing the fuel injection amount and lowering the exhaust gas temperature to prevent overheating of the exhaust temperature TEXT to prevent a catalyst etc. Protect the exhaust system components of. that time,
A first threshold value T1 which is a temperature threshold value with respect to the exhaust gas temperature TEXT that can be regarded as having no heat damage to the exhaust system components;
Second, which is a temperature threshold that may cause heat damage to exhaust system components
Threshold value T2 (> T1) of
Even if the engine operating state is in the high load operating region, the fuel amount increase correction related to the exhaust temperature reduction correction is not performed until the exhaust temperature TEXT reaches the first threshold value T1, and the exhaust temperature TEXT
Is within the range between the first threshold value T1 and the second threshold value T2, the fuel consumption amount is reduced by gradually increasing the fuel increase amount related to the exhaust temperature reduction correction. And the exhaust temperature TEX
When T exceeds the second threshold value T2, the fuel amount increase related to the exhaust temperature reduction correction is set based on the engine operating state.

That is, the ECU 50 has the functions of the first and second determination means and the exhaust temperature reduction correction means according to the present invention. Specifically, the functions of each means are determined by the routines shown in FIGS. To be realized.

The processing relating to the fuel injection control of the present invention executed by the ECU 50 will be described below with reference to the flowcharts of FIGS.

FIG. 1 is a fuel injection control routine executed every predetermined period after the system is initialized. First, in step S101, the intake air amount Q based on the signal from the intake air amount sensor 31 and the engine. A basic fuel injection pulse width Tp (= K × Q / NE; K is an injector characteristic correction constant) that determines the basic fuel injection amount is calculated from the rotational speed NE.

Next, at step S102, a startup amount increasing coefficient K for increasing the amount of fuel at the time of starting to improve the starting performance.
ST is a power increase correction coefficient KPOWER (which will be described later) that is a correction coefficient for the fuel injection amount related to the output air-fuel ratio and the exhaust temperature reduction.
And other correction factors are added to multiply the values, and various correction factors KHOS are set (KHOS ← KST × (KPOWER +
…)).

In a succeeding step S103, a well-known air-fuel ratio allocation coefficient KMR, O2 sensor 36 for compensating the basic fuel injection pulse width Tp for each operation region due to the characteristic peculiarities of the injector 22 and the intake air amount sensor 31. The air-fuel ratio feedback correction coefficient LAMBDA for converging the air-fuel ratio to the target air-fuel ratio based on the output value of the Air-fuel ratio learning correction coefficient KBLRC and the air-fuel ratio correction term (LAMBDA + KBLRC-
1) Multiply the correction term (KHOS + KACC-KDC) by the various correction coefficients KHOS, acceleration increase coefficient KACC, and deceleration decrease coefficient KDC, and the adhesion correction coefficient KX for correcting the effect of fuel adhering to the port wall surface, etc. Set the injection pulse width Te (Te ← Tp × KMR × (LAMBDA + KBLRC-1) × (KHOS
+ KACC-KDC) x KX).

Then, in step S104, the effective fuel injection pulse width Te is added with the ineffective pulse width Ts for compensating the ineffective injection time of the injector 22 which changes according to the battery voltage VB, and the final fuel injection amount is obtained. Is set (Ti ← Te + Ts), the fuel injection pulse width Ti is set in the injection timer of the cylinder #i in step S105, and the routine exits.

Here, the power increase correction coefficient KPOWER used when setting the various correction coefficients KHOS is set by the power increase correction coefficient setting routine shown in FIG. This routine is executed every predetermined period, and first, in step S
In 201, based on the basic injection pulse width Tp representing the engine load and the engine speed NE, the power increase correction coefficient table TBL2 shown in FIG. 4 is referenced with interpolation calculation, and the second power increase correction coefficient KPOWER2 is set. . The second power increase correction coefficient KPOWER2 protects the exhaust system from heat damage of the exhaust temperature TEXT that can be increased when the fuel increase correction related to the output air-fuel ratio and the fuel increase correction related to the output air-fuel ratio are performed. This is for simultaneously performing the fuel amount increase correction for reducing the exhaust gas temperature by cooling the fuel. Here, the power increase correction coefficient table TBL2 uses the basic fuel injection pulse width Tp as an example of the engine load and the engine speed NE as parameters, and outputs air-fuel ratio and exhaust temperature by fuel cooling for protection of exhaust system components. The fuel increase rate that is appropriate for the reduction can be obtained in advance by simulation or experiment, and this is stored in a series of addresses in the ROM 52 as a table of the second power increase correction coefficient KPOWER2. As shown in, the high load operation range (power increase range) in which the correction relating to the output air-fuel ratio and the exhaust gas temperature reduction is performed according to the engine operating state.
And the low load operation range (KPO
WER2 = 0) is set.

In the following step S202, it is determined whether or not the second power increase correction coefficient KPOWER2 is a region where the correction by 0 is not performed. If KPOWER2 = 0, step S203
After setting the second power increase correction coefficient KPOWER2 as the final power increase correction coefficient KPOWER (= 0), the routine exits. That is, during engine low load operation in which the second power increase correction coefficient KPOWER2 is 0, unnecessary fuel increase correction related to output air-fuel ratio and exhaust temperature reduction is not performed.

On the other hand, in step S202, KPOWER2
During the engine high load operation of ≠ 0, the exhaust temperature TEXT and the first and second threshold values T1,
The power increase correction coefficient KPOWER is set according to the comparison result with T2.

That is, first, in step S204, the exhaust gas temperature TEX detected by the exhaust gas temperature sensor 37 is detected.
Compare T with a second threshold T2. Here, the second threshold T
2 is the temperature of exhaust gas, which may cause heat damage to exhaust system components such as catalysts, obtained in advance by simulation or experiment,
It is stored in the ROM 52 as fixed data, and is set to 800 ° C., for example.

Then, in step S204, the exhaust temperature T
When EXT is less than or equal to the second threshold value T2, the routine proceeds to step S205, where the first power increase correction coefficient KPO which is an accurate fuel increase rate for performing the fuel increase correction only for the output air-fuel ratio.
WER1 is the basic fuel injection pulse width Tp representing the engine load
Output air-fuel ratio increase correction coefficient table TBL shown in FIG.
1 is set with reference to interpolation calculation. The output air-fuel ratio increase correction coefficient table TBL1 is accurate to obtain only the output air-fuel ratio without adding the exhaust temperature reduction correction using the basic fuel injection pulse width Tp and the engine speed NE as an example of the engine load as parameters. The fuel increase rate is obtained in advance by simulation or experiment, and is stored in the ROM 5 as a table of the first power increase correction coefficient KPOWER1.
2 is stored in a series of addresses, and as shown in FIG. 3, a high load operation region (output air-fuel ratio increasing region) in which correction related to the output air-fuel ratio is performed according to the engine operating state
And output air-fuel ratio correction is not performed (KPOWER1 = 0)
The low load operation area is set.

In the following step S206, the exhaust temperature TEX
Compare T with the first threshold T1. Here, the first threshold T
1 is a value lower than the second threshold value T2, and the upper limit value of the exhaust temperature that can be regarded as having no influence of the heat damage on the exhaust system components is previously obtained by simulation or experiment, and is set as fixed data in the ROM 52. Is stored in memory, and is set to 780 ° C., for example.

Then, in step S206, the exhaust temperature T
When EXT is less than or equal to the first threshold value T1, it is determined that the exhaust system components are not affected by heat damage, the process proceeds to step S207, and the correction amount COR for gradually increasing the power increase correction coefficient KPOWER is set. The initial value is set to 0, and step S20
After setting the final power increase correction coefficient KPOWER with the first power increase correction coefficient KPOWER1 in (8)
← KPOWER 1) Exit the routine. That is, even if the engine operating state shifts to the high load operating region, the exhaust temperature TEXT
There is a predetermined delay before the rise. Therefore, when the exhaust temperature TEXT is less than or equal to the first threshold value at which it can be considered that the exhaust system components are not affected by heat damage, t1 to t2 in FIG.
As shown in, the output air-fuel ratio increase correction coefficient table TBL
The power increase correction coefficient KPOWER is set by the first power increase correction coefficient KPOWER1 according to 1, and an appropriate fuel increase rate is determined to obtain the output air-fuel ratio. Since this fuel increase rate does not include the fuel increase rate for exhaust temperature reduction correction, the exhaust temperature reduction correction is substantially prohibited, and fuel consumption can be suppressed and fuel consumption can be improved accordingly.

On the other hand, when the exhaust temperature TEXT is higher than the first threshold value T1 in step S206 (that is,
(T1 <TEXT≤T2), as indicated by t2 to t3 in FIG. 5, the power increase correction coefficient KPOWER is gradually increased by the set value SET by the correction amount COR for each set cycle of the routine execution cycle.

That is, when the process proceeds from step S206 to step S209, the previous correction amount COR is set to the set value SET.
Is added to set a new correction amount COR (COR ← CO
R + SET), and then in step S210, in step S2
The final power increase correction coefficient KPOWER is calculated by adding the correction amount COR set in step S209 to the first power increase correction coefficient KPOWER1 obtained in 05 (KPOWER ← K
POWER1 + COR).

Then, in step S211, the upper limit value of the power increase correction coefficient KPOWER is regulated. That is,
Power increase correction coefficient KPOWE calculated in step S210
R is compared with the second power increase correction coefficient KPOWER2. If the power increase correction coefficient KPOWER is less than or equal to the second power increase correction coefficient KPOWER2, the routine is exited. On the other hand, in step S211, the power increase correction coefficient KPO
When WER is higher than the second power increase correction coefficient KPOWER2, the process proceeds to step S203, the upper limit of the value of the power increase correction coefficient KPOWER is restricted by the second power increase correction coefficient KPOWER2, and then the routine exits.

Further, in step S204, when the exhaust temperature TEXT is higher than the second threshold value T2 (t3 in FIG. 5).
After that, it is determined that the exhaust temperature TEXT has reached a temperature at which heat damage to the exhaust system components is suspected, the process proceeds to step S203, and the output air-fuel ratio and exhaust temperature reduction set based on the engine operating state in step S201. After the final power increase correction coefficient KPOWER is set by the second power increase correction coefficient KPOWER2 that is appropriate for performing the fuel increase correction according to (1), the routine is exited.

According to the present embodiment, the fuel amount increase correction relating to the exhaust gas temperature reduction is performed based on the exhaust gas temperature TEXT.
It is possible to accurately perform fuel injection control that achieves both reduction of fuel consumption and reduction of exhaust temperature.

That is, the first threshold value T which can be considered that the exhaust gas temperature TEXT has no influence on the exhaust system components to cause heat damage.
When it is 1 or less, the output air-fuel ratio increase correction coefficient table T
Since the power increase correction coefficient KPOWER1 is set by the first power increase correction coefficient KPOWER1 based on BL1 and the fuel increase related to the exhaust gas temperature reduction is not performed, the fuel consumption can be suppressed correspondingly and the fuel consumption can be improved.

Further, the exhaust temperature TEXT is changed from the first threshold value T1 to the second threshold value T2 which may cause heat damage to the exhaust system components.
Up to, the power increase correction coefficient KPOWER is gradually increased at each set cycle of the calculation cycle, and the fuel temperature is gradually cooled to a value at which exhaust temperature reduction correction can be performed by gradually increasing the fuel consumption. In addition, it is possible to improve the controllability by smoothing the connection to the fuel increase correction by the second power increase correction coefficient KPOWER2 performed when the exhaust temperature TEXT exceeds the second threshold value T2. You can

After the exhaust temperature TEXT reaches the second threshold value T2, the output air-fuel ratio and the fuel cooling for protecting the exhaust system are controlled by using the second power increase correction coefficient KPOWER2 based on the power increase correction coefficient table TBL2. Power increase correction coefficient KPOWE based on the correct fuel increase rate to obtain the exhaust temperature reduction by
By setting R, it is possible to reliably prevent heat damage to exhaust system components due to a rise in exhaust temperature.

In this embodiment, when the exhaust gas temperature TEXT is between the first threshold value T1 and the second threshold value T2, the power increase correction coefficient KPOWER is set to the correction amount COR by the addition term.
However, the power increase correction coefficient KPOWER may be corrected by a correction factor based on the multiplication term, and the power increase correction coefficient KPOWER may be gradually increased.

Next, a second embodiment of the present invention will be described with reference to FIGS. 8 is a flowchart of a fuel injection control routine, FIG. 9 is a flowchart of an exhaust temperature reduction correction coefficient setting routine, FIG. 10 is an explanatory diagram of a full increase coefficient table, FIG. 11 is an explanatory diagram of an exhaust temperature reduction correction coefficient table, and FIG. It is a time chart which shows the relationship between engine load, fuel increase, and exhaust temperature.

The present embodiment is different from the first embodiment in that the output air-fuel ratio is obtained in place of the power increase correction coefficient KPOWER which is the correction coefficient of the fuel injection amount for reducing the output air-fuel ratio and the exhaust temperature. The full increase coefficient KFULL (= first power increase correction coefficient KPOWER1) and the exhaust temperature reduction correction coefficient KRICH related to exhaust temperature reduction are individually set. The same components as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the fuel injection control routine shown in FIG. 8, the process of step S301 is performed instead of step S102 of the above-described first embodiment, and the starting boosting coefficient KST is increased.
, Full increase coefficient KFULL, exhaust temperature reduction correction coefficient KRICH,
And the value obtained by adding the other correction coefficients are multiplied to set various correction coefficients KHOS (KHOS ← KST × (KFULL + KRI
CH + ...)). Here, the full increase coefficient KFULL is set by referring to the full increase coefficient table TBLF shown in FIG. 10 with interpolation calculation based on the engine operating state based on the basic fuel injection pulse width Tp representing the engine load and the engine speed NE. To do. The full fuel increase coefficient table TBLF uses the basic fuel injection pulse width Tp, which is an example of the engine load, and the engine speed NE as parameters, and does not take the exhaust temperature reduction correction into consideration. Is obtained in advance by simulation or experiment,
ROM as a table based on the full increase coefficient KFULL
It is stored in a series of 52 addresses,
As shown in FIG. 10, a high-load operating region (full increase region) in which the output air-fuel ratio is corrected according to the engine load and a low-load operating region in which the output air-fuel ratio is not corrected (KFULL = 0). Is set.

Further, in this embodiment, instead of the power increase correction coefficient setting routine, the exhaust temperature reduction correction coefficient setting routine shown in FIG. 9 is executed every predetermined period. Hereinafter, the ECU 50
The processing relating to the exhaust temperature reduction correction coefficient setting executed by will be described with reference to the flowchart of FIG.

First, in step S401, an exhaust temperature reduction correction coefficient KRICH that determines an appropriate fuel increase rate for reducing the exhaust temperature TEXT by cooling with injected fuel is set to the basic fuel injection pulse width Tp and the engine speed that represent the engine load. Based on the engine operating state according to NE, the exhaust temperature reduction correction coefficient table TBLR shown in FIG. 11 is referred to and set with interpolation calculation. Exhaust temperature reduction correction coefficient table T
The BLR uses a basic fuel injection pulse width Tp, which is an example of an engine load, and an engine speed NE as parameters to obtain an accurate fuel increase rate for performing exhaust temperature reduction correction by a simulation or an experiment, and then removes this. ROM5 as a table based on the temperature reduction correction coefficient KRICH
2 is stored in a series of addresses, and as shown in FIG. 11, an area (exhaust temperature reduction correction area) in which correction related to exhaust temperature reduction is performed and an exhaust temperature reduction related to the engine operating state. Low load operation area without correction (KRICH =
0) and are set.

In the following step S402, it is determined whether the exhaust temperature reduction correction coefficient KRICH is a region where the exhaust temperature reduction correction by 0 is not performed. When KRICH = 0, the exhaust temperature reduction correction coefficient KRICH obtained in step S401 is set. The final exhaust temperature reduction correction coefficient KRICH is set as it is, and the routine is exited.

On the other hand, in step S402, KRICH ≠
When it is 0, the exhaust temperature reduction correction coefficient KRI obtained in step S401 is determined according to the result of comparison between the exhaust temperature TEXT and the first and second threshold values T1 and T2 by the processing from step S403.
CH is corrected using the correction rate RT, and the final exhaust gas temperature reduction correction coefficient KRICH is set.

That is, first, in step S403, the exhaust gas temperature TEXT detected by the exhaust gas temperature sensor 37 is compared with the first threshold value T1 as in the first embodiment.

When the exhaust temperature TEXT is less than or equal to the first threshold value T1, it is determined that the exhaust system components are not affected by heat damage, and the process proceeds to step S404 to set the correction factor RT to 0 (RT ← 0) Then, in the subsequent step S405, the exhaust temperature reduction correction coefficient KRICH obtained in step S401 is multiplied by the correction rate RT (= 0) to set the final exhaust temperature reduction correction coefficient KRICH (KRICH ← KRICH × RT) Exit the routine.

That is, even if the engine operating state shifts to the high load operating region, there is a predetermined delay before the exhaust temperature TEXT rises. Therefore, when the exhaust temperature TEXT is equal to or lower than the first threshold value at which it can be considered that the exhaust system components are not affected by the heat damage, the exhaust temperature reduction correction coefficient KRICH becomes zero as shown by t1 to t2 in FIG. This is set, whereby the exhaust temperature reduction correction is substantially prohibited, and fuel consumption can be suppressed and fuel consumption can be improved accordingly.

On the other hand, when the exhaust gas temperature TEXT is higher than the first threshold value T1 in step S403, step S403
In step 406, the exhaust temperature TEXT is compared with the second threshold value T2.

When the exhaust gas temperature TEXT is equal to or lower than the second threshold value T2 (that is, T1 <TEXT ≦ T2), as shown by t2 to t3 in FIG. Is a set value R1 (for example, R1 = 0.0
02) Gradually increase the exhaust temperature reduction correction coefficient KRI
CH is gradually shifted to a value at which exhaust temperature reduction correction can be performed by fuel cooling by increasing the amount of fuel.

That is, the process proceeds from step S406 to step S407, and the set value R1 is added to the previous correction rate RT to update the correction rate RT (RT ← RT + R1). Then, in a succeeding step S408, the correction rate RT is compared with the upper limit value LIM (= 1) of the correction rate RT to obtain the correction rate RT.
If is less than or equal to the upper limit value LIM, the process proceeds to step S405, and the exhaust temperature reduction correction coefficient KRI obtained in step S401.
After CH is multiplied by the correction factor RT to set the final exhaust gas temperature reduction correction coefficient KRICH (KRICH ← KRICH × RT), the routine exits. On the other hand, in step S408, the correction factor RT
Is larger than the upper limit value LIM, step S409.
Then, the correction rate RT is limited by the upper limit value LIM (= 1) to the upper limit, and the routine exits through step S405.

Further, in step S406, when the exhaust temperature TEXT is higher than the second threshold value T2 (t in FIG. 12).
3 or later), it is determined that the exhaust temperature TEXT has reached a temperature where heat damage to the exhaust system components is concerned, and the exhaust temperature reduction correction coefficient KRICH obtained in step S401 is used as it is as the final exhaust temperature reduction correction coefficient KRICH. Exit the routine as.

According to this embodiment, it is possible to obtain the same effect as that of the first embodiment described above.

That is, when the exhaust gas temperature TEXT is equal to or lower than the first threshold value T1 which can be regarded as having no influence on the exhaust system components for heat damage, the exhaust gas temperature reduction correction coefficient KRICH is set to zero (KRICH = 0) and the fuel is reduced. It is possible to suppress consumption and improve fuel efficiency.

When the exhaust temperature TEXT is between the first threshold value T1 and the second threshold value T2 (T1 <TEXT≤T
2) Adopt a correction rate for the exhaust temperature reduction correction coefficient KRICH, increase the correction rate RT by R1 for each set cycle of the calculation cycle, and correct the exhaust temperature reduction correction coefficient KRICH by cooling the fuel by increasing the fuel quantity. It is possible to improve fuel efficiency by gradually shifting to a value that can perform, and it is possible to improve the controllability by smoothly connecting the exhaust temperature reduction correction coefficient KRICH.

When the exhaust temperature TEXT exceeds the second threshold value T2, which may cause heat damage to the exhaust system components, the value based on the exhaust temperature reduction correction coefficient table TBLR is used as it is to protect the exhaust system. The exhaust temperature reduction correction coefficient KRICH is set according to the appropriate fuel increase rate to obtain the exhaust temperature reduction by the fuel cooling, and the exhaust temperature is reduced by the fuel cooling, so that the heat damage to the exhaust system components due to the exhaust temperature rise is prevented. It can be surely prevented.

In the present embodiment, the correction rate RT is set to 0 when the exhaust temperature TEXT is the first threshold value T1, but the present invention is not limited to this, and the correction rate RT may be set to 0 to 0, for example.
The value may be set to about 0.4.

Further, in the present embodiment, the correction rate RT for the exhaust temperature reduction correction coefficient KRICH is adopted, and the exhaust temperature TEXT
Is between the first threshold value T1 and the second threshold value T2, the correction factor RT is increased by the set value R1 and the correction factor RT is given to the exhaust gas temperature reduction correction coefficient KRICH by the multiplication term.
Although the exhaust temperature reduction correction coefficient KRICH is gradually increased, the exhaust temperature reduction correction coefficient KRICH may be increased by set values depending on the correction amount by the addition term.

[0076]

As described above, according to the present invention, unnecessary fuel increase can be suppressed and fuel consumption can be improved by performing the fuel increase correction for exhaust temperature reduction based on the exhaust temperature. In addition, overheating of the exhaust system can be reliably prevented, and heat damage to the exhaust components can be accurately prevented.

[Brief description of drawings]

FIG. 1 is a flowchart of a fuel injection control routine according to a first embodiment of the present invention.

FIG. 2 is a flow chart of a power increase correction coefficient setting routine.

FIG. 3 is an explanatory diagram of an output air-fuel ratio increase correction coefficient table of the same as above.

FIG. 4 is an explanatory diagram of a power increase correction coefficient table of the same as above.

FIG. 5 is a time chart showing the relationship between the engine load, the power increase correction coefficient, and the exhaust temperature.

FIG. 6 is the same as above, and is an overall schematic view of the engine.

FIG. 7 is a circuit diagram of the electronic control system of the above.

FIG. 8 is a flowchart of a fuel injection control routine according to the second embodiment of the present invention.

FIG. 9 is a flowchart of an exhaust temperature reduction correction coefficient setting routine.

FIG. 10 is an explanatory diagram of a full weight increase coefficient table.

FIG. 11 is an explanatory diagram of an exhaust temperature reduction correction coefficient table of the same.

FIG. 12 is a time chart showing the relationship between engine load, fuel increase, and exhaust temperature as above.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine 37 ... Exhaust temperature sensor 50 ... Electronic control device (1st determination means, 2nd determination means, exhaust temperature reduction correction means) T1 ... 1st threshold value T2 ... 2nd threshold value TEXT ... Exhaust temperature KPOWER ... Power increase correction coefficient (fuel injection amount correction coefficient for exhaust temperature reduction correction) KRICH ... Exhaust temperature reduction correction coefficient (fuel injection amount correction coefficient for exhaust temperature reduction correction) COR ... Correction amount RT ... Correction rate

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 3G084 BA08 BA09 BA13 DA10 DA19                       DA28 DA37 EB12 FA01 FA08                       FA10 FA11 FA20 FA25 FA26                       FA27 FA29 FA38 FA39                 3G091 AA02 AA10 AB01 BA04 BA07                       BA36 CB02 DA02 DC01 EA01                       EA05 EA06 EA07 EA14 FB02                       FB12 FC05 GA06 HB06                 3G301 HA01 HA11 JA02 JA21 JA33                       KA09 LB02 LC01 MA01 MA11                       NA08 NC02 ND04 NE01 PA04Z                       PA07Z PA09Z PA11Z PD02Z                       PD11Z PE03Z PE04Z PE08Z

Claims (3)

[Claims] 1. In a fuel injection control device for an engine, which corrects an exhaust temperature by reducing the amount of fuel when the exhaust gas temperature is high, the exhaust gas is exhausted to a first threshold value which is a temperature threshold value that can be regarded as having no effect on heat damage to exhaust system components. A first determination unit that determines whether or not the temperature has reached, and a second threshold value that is a temperature threshold value that is higher than the first threshold value and that is likely to cause heat damage to exhaust system components. Second determining means for determining whether or not the exhaust temperature has reached; and, when the exhaust temperature is equal to or lower than the first threshold value, the fuel amount increase related to the exhaust temperature reduction correction is prohibited, and the exhaust temperature is equal to the first threshold value. And the second threshold value, the fuel increase amount relating to the exhaust temperature reduction correction is gradually increased, and when the exhaust temperature shifts to a temperature range higher than the second threshold value, Based on the engine operating condition, increase the fuel amount related to exhaust temperature reduction correction. A fuel injection control device for an engine, comprising: 2. The exhaust gas temperature reduction correction means, when the exhaust gas temperature is between the first threshold value and the second threshold value, the correction coefficient of the fuel injection amount relating to the exhaust gas temperature reduction correction is gradually increased. 2. The fuel injection control device for an engine according to claim 1, wherein the fuel increase amount is gradually increased by adding a correction amount that is increased. 3. The exhaust gas temperature reduction correction means, when the exhaust gas temperature is between the first threshold value and the second threshold value, the correction coefficient of the fuel injection amount related to the exhaust gas temperature reduction correction is gradually increased. 2. The fuel injection control device for an engine according to claim 1, wherein the fuel increase amount is gradually increased by multiplying by a correction factor that increases with time.