JPH1054287A - Fuel injection controller for in-cylinder direct injection type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve NOX purification rate by providing a fuel injection controller which can maintain the temperature of a lean NOX catalyst fitted in an exhaust system at an optimum temperature without degrading drivablility. SOLUTION: When catalyst temperature is higher than a targeted value, the degree of sub injection fuel contribution to the combustion is decreased by delay-correcting sub injection timing. As a result, exhaust temperature is lowered, so that the catalyst temperature is lowered. At that time, torque decrease amount due to degraded combustibility is compensated by increasing main injection amount to keep torque constant. When the catalyst temperature is lower than the targeted value, the degree of sub injection fuel contribution to combustion is increased by advance-correcting the sub injection timing. As a result, exhaust temperature is raised, so that the catalyst temperature is raised. At that time, a torque increase amount due to improved combustibility is compensated by decreasing main injection amount to keep torque constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a lean N
The present invention relates to a fuel injection control device for a lean-burn, direct-injection type internal combustion engine having an O _x catalyst and a fuel injection valve in each cylinder.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of fuel economy, a lean burn (lean burn) engine has been developed as a gasoline engine, and the application range of a diesel engine has been expanding. In diesel engines and lean burn engines, fuel is burned under a large excess air ratio, and while HC (hydrocarbon) and CO (carbon monoxide), which are incomplete combustion components, are emitted less,
The amount of emission of NO _x (nitrogen oxide) generated by the reaction between the nitrogen in the air and the unburned oxygen increases, and the amount of unreacted O ₂ in the exhaust gas also increases.

[0003] Therefore, the lean NO _x catalyst which can lean state, that O ₂ is reduced and purify NO _x in the exhaust gas in the state present in excess is used. As the lean NO _x catalyst, a zeolite-based catalyst supporting a transition metal or a noble metal is often used. Although in _the NO _x purification by lean NO _x catalyst requires the presence of a reducing agent such as HC, since it is insufficient in the amount of reducing agent present in the exhaust gas, the reducing agent upstream of the lean NO _x catalyst A sub-injection is performed in which a fuel as a reducing agent is injected into a cylinder under a condition in which a device for adding a fuel is provided, or fuel flows out to a catalyst without burning.

On the other hand, in a direct injection type engine such as a diesel engine, since it is necessary to achieve precise control of high-pressure fuel, a common rail type fuel injection system has recently been developed. This common-rail fuel injection system stores high-pressure fuel generated by a high-pressure pump in a common rail, and injects high-pressure fuel from the common rail to each cylinder of the engine by opening and closing a solenoid valve. The pressure is always controlled to an optimum value by the pressure sensor and the discharge amount control mechanism of the pump.

[0005]

However, lean NO
_The temperature range in which the _x catalyst can reduce and purify NO _x, that is, the temperature window of the lean NO _x catalyst is a very narrow range. Various proposals have been made as countermeasures. For example, JP-A-4-231645, in-cylinder direct injection engine employing a lean NO _x catalyst system and the common rail fuel injection system, for supplying HC as a reducing agent to the lean NO _x catalyst sub By changing the injection timing according to the catalyst temperature, N
A technique for improving the O _x purification rate is disclosed.

According to the above prior art, the early stage of the combustion stroke (expansion stroke) (for example, 60 crank angles after top dead center).
When the sub-injection timing is set to the above, the injected fuel almost burns and contributes to an increase in the exhaust gas temperature, that is, the catalyst temperature. However, since a part of the combustion energy becomes the engine output, the torque increases against the driver's will, which may cause deterioration of the drivability.

[0007] In view of the above situation, an object of the present invention is that the lean-burn internal combustion engine capable of having a lean NO _x catalyst, maintaining the catalyst temperature to optimum temperatures without causing the degradation of vehicle drivability in the exhaust system An object of the present invention is to improve the NO _x purification rate by providing a fuel injection control device capable of performing the above. In addition, an object of the present invention is to contribute to prevention of air pollution.

[0008]

Means for Solving the Problems] was devised in order to achieve the above object, according to the present invention, a fuel injection control apparatus for a cylinder direct injection type internal combustion engine, each provided with a lean NO _x catalyst in an exhaust system a fuel injection control apparatus in the lean combustible and-cylinder direct injection type internal combustion engine with each fuel injection valve into the cylinder, the operating condition detecting means for detecting an engine operating condition of the internal combustion engine, said lean NO _x And a main injection during an intake stroke or a compression stroke and a sub-injection during an expansion stroke or an exhaust stroke according to the engine operating state detected by the operating state detecting means. Injection control amount setting means for setting the injection timing and injection amount of the injection, and setting by the injection control amount setting means according to the catalyst temperature detected by the catalyst temperature detection means. A sub-injection timing correcting means for correcting the set sub-injection timing, and increasing the main injection amount set by the injection control amount setting means when the sub-injection timing is corrected to the retard side by the sub-injection timing correcting means. And a main injection amount correction means for reducing the main injection amount set by the injection control amount setting means when the sub injection timing is corrected to the advance side by the sub injection timing correction means. It is characterized by doing.

[0009] In the fuel injection control device according to the present invention configured as described above, the sub-injection timing during the expansion stroke or the exhaust stroke is corrected according to the catalyst temperature.
That is, when the catalyst temperature is high, the degree to which the fuel of the sub-injection contributes to combustion is reduced by retarding the sub-injection timing, and as a result, the exhaust gas temperature is reduced, and the catalyst temperature is reduced accordingly. Becomes possible. In addition, the decrease in torque due to the deterioration of the flammability is compensated for by increasing the main injection amount, so that the torque is kept constant and the operability does not deteriorate. On the other hand, when the catalyst temperature is low, the degree to which the fuel of the sub-injection contributes to combustion is increased by advancing the sub-injection timing,
As a result, it becomes possible to raise the exhaust gas temperature and accordingly the catalyst temperature. In addition, the increase in torque due to the improvement in the flammability is compensated by the decrease in the main injection amount, so that the torque is kept constant and the operability does not deteriorate.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is an overall configuration diagram of a four-cylinder diesel engine employing a fuel injection control device according to one embodiment of the present invention. Air required for combustion in the engine body 1 is supplied to the engine body 1 via the intake system 2.
At this time, the air is supplied to the air cleaner 3 provided in the intake system 2.
Is filtered. On the other hand, the fuel stored in the fuel tank 10 is pumped by a low-pressure pump 11 and supplied to a high-pressure pump 13 via a low-pressure conduit 12. The high pressure pump 13 pumps fuel to the common rail 15 via the high pressure conduit 14.

The fuel stored in the common rail 15 in a high pressure state is supplied to each fuel injection valve 18 having a three-way solenoid valve 17 through each branch pipe 16, and is injected into each cylinder by each fuel injection valve 18. . A part of the fuel can be returned from the three-way solenoid valve 17 to the fuel tank 10 via the return pipe 19 without being injected from the fuel injection valve 18. Then, the exhaust gas generated in the engine body 1 is discharged from the exhaust system 4. At that time, the exhaust gas is purified by a lean NO _x catalytic converter 5 provided in the exhaust system 4.

An electronic control unit (ECU) 30 is a microcomputer system for executing fuel injection control. According to the programs and various maps stored in the read only memory (ROM) 33, the central processing unit (C)
PU) 31 inputs signals from various sensors into an input port 35.
, An arithmetic process is executed based on the input signal, and various actuator control signals are output via the output port 36 based on the arithmetic result. The random access memory (RAM) 34 is used as a temporary data storage place in the operation / control processing. These components in the ECU are connected by a system bus 32 including an address bus, a data bus, and a control bus.

An accelerator opening sensor 21 for generating an output voltage corresponding to the opening θA of an accelerator pedal (not shown) is connected to an input port 35 of the ECU 30 via an A / D converter 37. . The input port 35 is connected to the crank angle sensor 22 that generates a number of output pulses per unit time in proportion to the engine speed NE. Further, the input port 35 is connected to the cylinder discrimination sensor 23 that generates an output pulse at the compression top dead center of the first cylinder and the fourth cylinder. A pressure sensor 24 for generating an output voltage corresponding to the pressure in the common rail 15 is provided at the input port 35 with an A / D converter 37.
Connected through. In addition, the input port 35
A catalyst inflow exhaust temperature sensor 25 that generates an output voltage according to the temperature of the exhaust gas flowing into the catalytic converter 5 and a catalyst outflow exhaust temperature sensor 26 that generates an output voltage according to the temperature of the exhaust gas flowing out of the catalytic converter 5 are respectively A It is connected via a / D converter 37.

On the other hand, the output port 36 of the ECU 30
A pressure control solenoid valve in the high pressure pump 13 is connected via a drive circuit 38. Then, the ECU 30 determines the amount of fuel pressure to be sent from the high-pressure pump 13 to the common rail 15 based on the output signal of the pressure sensor 24 so that the pressure in the common rail 15 becomes a desired value. Control the solenoid valve. The pressure in the common rail 15 determines the injection rate (fuel injection amount per unit crank angle or unit time) of the fuel injected from the fuel injection valve 18 into each cylinder. The output port 36 is connected to a three-way solenoid valve 17 in the fuel injection valve 18 via a drive circuit 39 and a counter circuit 40. The ECU 30 controls the fuel injection timing and the fuel injection period by controlling the opening and closing of the three-way solenoid valve 17.
Note that the product of the fuel injection rate and the fuel injection period is the fuel injection amount.

FIG. 2 is a flowchart showing a processing procedure of a fuel injection execution routine by the ECU 30. This routine is executed at every fixed crank angle, for example, at a crank angle of 30.
It is executed as an interrupt process every time. First, in step 102, the angle determination counter CNE counts. CNE is incremented by one from 0 to 5 every 30 degrees of crank angle, and after CNE becomes 5, CNE is increased.
NE is set to 0, and is again increased by 1 every 30 degrees of the crank angle.

Next, at step 104, a cylinder discrimination counter CCYL is counted. CCYL is
From 0 to 3, it is incremented by 1 every 180 degrees of the crank angle. After CCYL becomes 3, CCYL is set to 0, and is incremented again by 1 every 180 degrees of the crank angle. The time when CCYL changes indicates the compression top dead center of each cylinder. For example, the time when CCYL is increased to 3 indicates the compression top dead center of the fourth cylinder, and CCYL is 3
The point at which the value is cleared from 0 to 0 indicates the compression top dead center of the second cylinder, and the point at which CCYL is increased to 1 indicates the compression top dead center of the first cylinder. The time when CNE is cleared from 5 to 0 coincides with the time when CCYL changes, and indicates the compression top dead center of each cylinder.

In step 106, CNE and CCYL
Is calculated based on the following formula.
The cylinder nm is a cylinder that is in the compression stroke from the intake stroke. Next, at step 108, it is determined whether or not the CNE has reached a value CNEm to be set in the counter 40 for a main injection start time tm and a main injection period τm to be described later. CN
When E = CNEm, the routine proceeds to step 110, where the main injection start time tm and the main injection period τm from the current time to the main injection start time are set in the counter 40. When the main injection start time tm is set in the counter 40, the counter 40 starts counting, and when the main injection start time tm has elapsed, the main injection is performed. At this time, counting of the main injection period τm is started, and when the main injection period τm has elapsed, the main injection is stopped. If a negative determination is made in step 108, step 110 is skipped and the main injection is not performed.

Next, at step 112, the cylinder ns for which sub-injection is to be executed is calculated based on CNE and CCYL. The cylinder ns is a cylinder in an expansion stroke or an exhaust stroke. Next, at step 114, the CNE counts a sub-injection start time ts and a sub-injection period t
It is determined whether the value CNEs to be set to 0 has been reached. When CNE = CNEs, the routine proceeds to step 116, where the sub injection start time t from the current time to the sub injection start time
s and the sub injection period τs are set in the counter 40.
When the sub-injection start time ts is set in the counter 40,
The counter 40 starts counting, and the sub-injection start time ts
Is elapsed, the sub-injection is executed. At this time, counting of the sub-injection period τs is started, and when the sub-injection period τs elapses, the sub-injection is stopped. If a negative determination is made in step 114, step 116 is skipped and the sub-injection is not performed.

FIG. 3 is a flowchart showing a processing procedure of a fuel injection control amount calculation routine by the ECU 30.
This routine is executed as interrupt processing that occurs in a predetermined time period. First, in step 202, based on the outputs of the accelerator opening sensor 21 and the crank angle sensor 22, the current accelerator opening θA and engine speed N
E is detected. Next, at step 204, the target common rail pressure PCt is calculated according to the detected accelerator opening θA and the engine speed NE. Note that, for this calculation, a predetermined map is stored in the ROM 33 in advance, and interpolation calculation based on this map is executed.
The ECU 30 determines the amount of fuel pressure to be sent from the high-pressure pump 13 to the common rail 15 so that the common-rail pressure PC detected by the pressure sensor 24 becomes the target common-rail pressure PCt. Execute the control for. That is, the feedback control regarding the common rail pressure PC is separately executed.

Next, at step 206, the main injection start time tm, the main injection period τm, and the count values of the angle discrimination counter for setting tm and τm in the counter 40 in accordance with the accelerator opening θA and the engine speed NE. C
NEm is calculated. Note that, for this calculation, a predetermined map is stored in the ROM 33 in advance, and interpolation calculation based on this map is executed. Similarly, step 20
8, the sub-injection start time ts, sub-injection period τs, and t
The count value CNEs of the angle determination counter for which s and τs are to be set in the counter 40 is calculated. Note that, for this calculation, a predetermined map is stored in the ROM 33 in advance, and interpolation calculation based on this map is executed.

Next, at step 210, the current catalyst inflow exhaust gas temperature THEI and catalyst outflow exhaust gas temperature THEO are detected based on the outputs of the catalyst inflow exhaust temperature sensor 25 and the catalyst outflow exhaust temperature sensor 26. Next, at step 212, the actual catalyst temperature THC is estimated based on the detected THEI and THEO. Then, in step 214, the lean NO _x catalyst 5 catalyst temperature deviation ΔT that indicates the actual catalyst temperature THC is how much higher than the target catalyst temperature THCt for achieving high removal rate
HC is calculated. When ΔTHC <0, it indicates that the catalyst temperature THC is lower than the target catalyst temperature THCt.

Next, at step 216, it is determined whether the absolute value of ΔTHC is less than a predetermined value. When the determination result of step 216 is YES, it is considered that correction of the fuel injection control amount for adjusting the catalyst temperature is particularly unnecessary, and this routine is ended. On the other hand, if the decision result in the step 216 is NO, the following fuel injection control amount correction is executed. First, step 2
At 18, the sub-injection timing retard correction amount Δts is calculated according to the catalyst temperature deviation ΔTHC. For this calculation, a predetermined map is stored in the ROM 33 in advance, and an interpolation calculation based on this map is executed. Note that ΔTHC> 0
, That is, the catalyst temperature THC is equal to the target catalyst temperature THC.
When it is higher than t, the sub-injection timing retard correction amount Δts>
0, that is, the delay correction of the sub-injection timing is performed. On the other hand, when ΔTHC <0, that is, when the catalyst temperature THC is lower than the target catalyst temperature THCt, the sub-injection timing retardation correction amount Δts <0, That is, advance correction of the sub-injection timing is performed.

Next, at step 220, an increase correction amount Δτm for the main injection period τm is calculated according to the sub-injection timing retard correction amount Δts. For this calculation, a predetermined map is stored in the ROM 33 in advance, and an interpolation calculation based on this map is executed. Note that when Δts> 0, that is, when the retard correction of the sub-injection timing is performed, the main injection period increase correction amount Δτm> 0, that is, when the main injection period increase correction is performed, while when Δts <0, That is, when the advance angle correction of the sub-injection timing is performed, the main injection period increase correction amount Δτm <0, that is, the decrease correction of the main injection period is performed. In steps 222 and 224, the sub-injection timing ts after correction by the sub-injection timing retardation correction amount Δts and the main injection period τm after correction by the main injection period increase correction amount Δτm are calculated, and this routine ends.

Thus, as shown in FIG.
When the catalyst temperature is higher than the target temperature, the sub-injection timing is retarded and the degree to which the fuel of the sub-injection contributes to combustion decreases, and as a result, the exhaust gas temperature decreases, and accordingly the catalyst temperature decreases. In addition, the purification rate of the catalyst is improved. In addition, the decrease in torque due to the deterioration of the flammability is compensated by the main injection period, that is, the increase of the main injection amount, so that the torque is kept constant and the operability does not deteriorate. Similarly, as shown in FIG. 4B, when the catalyst temperature is lower than the target temperature, the sub-injection timing is advanced and the degree of contribution of the sub-injection fuel to combustion increases, and as a result, The exhaust gas temperature rises, and the catalyst temperature rises accordingly, so that the purification rate of the catalyst improves. Moreover, the increase in torque due to the improvement in the flammability is compensated by the main injection period, that is, the decrease in the main injection amount, so that the torque is kept constant and the operability does not deteriorate.

Although the embodiments of the present invention have been described above, the present invention is of course not limited to these embodiments.

[0027]

As described above, according to the present invention,
Exhaust system lean NO _x catalyst lean combustible fuel injection control device capable of maintaining the catalyst temperature to optimum temperatures without causing the degradation of vehicle drivability in an internal combustion engine having a are provided, NO _x purification rate Is improved. That is, the present invention contributes to prevention of air pollution.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a four-cylinder diesel engine employing a fuel injection control device according to one embodiment of the present invention.

FIG. 2 is a flowchart showing a processing procedure of a fuel injection execution routine by an electronic control unit.

FIG. 3 is a flowchart showing a processing procedure of a fuel injection control amount calculation routine by an electronic control unit.

FIG. 4 is a diagram for explaining correction of a fuel injection control amount according to the present invention.

[Explanation of symbols]

1 ... diesel engine body 2 ... intake system 3 ... air cleaner 4 ... exhaust system 5 ... lean NO _x catalytic converter 10 ... Fuel tank 11 ... low-pressure pump 12 ... a low-pressure conduit 13 ... a high-pressure pump 14 ... high-pressure line 15 ... common rail 16 ... branch pipe DESCRIPTION OF SYMBOLS 17 ... Three-way solenoid valve 18 ... Fuel injection valve 19 ... Return pipe 21 ... Accelerator opening sensor 22 ... Crank angle sensor 23 ... Cylinder discrimination sensor 24 ... Pressure sensor 25 ... Catalyst inflow exhaust temperature sensor 26 ... Catalyst outflow exhaust temperature sensor 30 ... Electronic control unit (ECU) 31 Central processing unit (CPU) 32 System bus 33 Read only memory (ROM) 34 Random access memory (RAM) 35 Input port 36 Output port 37 A / D converter 38 Drive circuit 39 ... Drive circuit 40 ... Counter circuit

Continued on the front page (72) Inventor Toshiaki Tanaka 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation

Claims (1)

[Claims] 1. A fuel injection control device for a lean-burn, direct-injection-type internal combustion engine having a lean NO _x catalyst in an exhaust system and a fuel injection valve in each cylinder. operating condition detecting means for detecting an engine operating condition, the catalyst temperature detecting means for detecting a catalyst temperature of the lean NO _x, in accordance with the engine operating conditions detected by said operating condition detecting means, the intake stroke or compression stroke An injection control amount setting unit for setting an injection timing and an injection amount of a main injection and a sub-injection during a period of an expansion stroke or an exhaust stroke within a period, and the injection is performed according to a catalyst temperature detected by the catalyst temperature detection unit. Sub-injection timing correction means for correcting the sub-injection timing set by the control amount setting means, and the sub-injection timing is corrected to the retard side by the sub-injection timing correction means. When the main injection amount set by the injection control amount setting unit is increased, the sub injection timing is corrected to the advance side by the sub injection timing correction unit. A fuel injection control device for a direct injection type internal combustion engine, comprising: a main injection amount correction means for reducing a set main injection amount.