JP2003120372A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress degradation in exhaust emissions by providing a technique for compensating a shortage or overage of fuel injection quantity irrespective of an operating range in an exhaust emission control device for an internal combustion engine. SOLUTION: The exhaust emission control device for an internal combustion engine comprises an exhaust pressure measuring means 37 for measuring the pressure of exhaust gas, a discharge timing determining means 35 for determining the timing of a discharge of exhaust gas from an internal combustion engine 1, a pressure wave arrival time estimating means 35 for estimating a time from the discharge timing of exhaust gas to the arrival of a pressure wave of the exhaust gas at the exhaust pressure measuring means 37, a fuel quantity estimating means 35 for estimating a shortage or overage of fuel supply quantity according to the pressure of exhaust gas at the time of pressure wave arrival, and a correcting means 35 for correcting the fuel supply quantity according to the estimation result of the fuel quantity estimating means 35.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an exhaust emission control device for an internal combustion engine.

[0002]

2. Description of the Related Art As a technique for purifying nitrogen oxides (NOx) contained in the exhaust gas of an internal combustion engine, a technique for arranging a lean NOx catalyst in the exhaust system of the internal combustion engine has been proposed. As one of the lean NOx catalysts, for example, when the oxygen concentration of the inflowing exhaust gas is high, nitrogen oxides (NOx) in the exhaust gas are absorbed, and when the oxygen concentration of the inflowing exhaust gas is low and a reducing agent is present, An occlusion-reduction type NOx catalyst is known which reduces nitrogen oxide (NOx) that has been absorbed while reducing it to nitrogen (N ₂ ).

When this storage reduction type NOx catalyst is arranged in the exhaust system of an internal combustion engine, when the internal combustion engine is operated in lean combustion and the air-fuel ratio of the exhaust gas becomes high, the nitrogen oxides (NO
x) is absorbed by the NOx storage reduction catalyst and NO
x Nitrogen oxides (NOx) absorbed by the NOx storage reduction catalyst when the air-fuel ratio of the exhaust flowing into the catalyst becomes low
Is released and reduced to nitrogen (N ₂ ).

By the way, since the NOx absorption capacity of the NOx storage reduction catalyst is limited, when the internal combustion engine is operated in lean burn for a long period of time, the NOx absorption capacity of the NOx storage reduction catalyst becomes saturated, and the nitrogen in the exhaust gas is exhausted. Oxides (NOx) are released into the atmosphere without being removed by the NOx storage reduction catalyst.

Therefore, when the NOx storage reduction catalyst is applied to a lean-burn internal combustion engine, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is set before the NOx absorption capacity of the NOx storage reduction catalyst is saturated. Decrease for a short period of time, and storage reduction type N
It is necessary to release and reduce nitrogen oxides (NOx) absorbed by the Ox catalyst.

As a method of lowering the air-fuel ratio of the exhaust gas in this way, a method of adding fuel as a reducing agent to the exhaust gas flowing upstream from the NOx storage reduction catalyst can be exemplified.

When adding such a reducing agent, it is important to accurately control the amount of the reducing agent added according to the nitrogen oxides (NOx) absorbed in the NOx storage reduction catalyst.

This is because if the amount of reducing agent added is excessively large with respect to the nitrogen oxides (NOx) absorbed in the NOx storage reduction catalyst, excess reducing agent will be released into the atmosphere. On the other hand, when the addition amount of the reducing agent is insufficient with respect to the nitrogen oxides (NOx) absorbed in the NOx storage reduction catalyst, the NOx absorption capacity of the NOx storage reduction catalyst becomes saturated, and the nitrogen oxidation in the exhaust gas occurs. This is because the substances (NOx) will be released into the atmosphere without being purified.

[0009] With respect to such a problem, Japanese Patent No. 28450
In the exhaust gas purification device for an internal combustion engine described in Japanese Patent No. 56,
By determining the addition amount of the reducing agent in consideration of the amount of air taken into the internal combustion engine and the oxygen concentration detected by the air-fuel ratio sensor, it is possible to prevent an excessive supply or an insufficient supply of the reducing agent, thereby reducing the amount of the reducing agent. It aims to suppress the deterioration of exhaust emission due to the release of nitrogen oxides (NOx) into the atmosphere.

[0010]

However, in the invention described in the above publication, for example, in an internal combustion engine having a plurality of cylinders, the amount of fuel injection caused by deterioration or individual difference of the fuel injection valve for supplying fuel into the cylinder is generated. Variation was not taken into account. If there is such a variation in the fuel injection amount, the air-fuel ratio of the exhaust gas fluctuates, and therefore the amount of reducing agent required for NOx release and reduction fluctuates, so that the required air-fuel ratio may not be obtained.

On the other hand, in an internal combustion engine having a plurality of cylinders,
Exhaust pipes extending from each cylinder may be combined into one and then connected to the catalyst. In the internal combustion engine configured in this way, even if an air-fuel ratio sensor is installed upstream or downstream of the catalyst to measure the air-fuel ratio, the exhaust gas from each cylinder mixes and reaches the air-fuel ratio sensor. It is difficult to identify from which cylinder the generated exhaust was discharged. Therefore, it is difficult to correct the fuel injection amount for each cylinder with the output signal of the air-fuel ratio sensor.

Further, for example, when the fuel supply amount is small with the intake air amount reduced by the intake throttle valve, the above method can be applied, but it is necessary to supply a large amount of fuel. In this case, it is difficult to apply the correction made at the time of supplying a small amount of fuel as it is. Therefore, when the predetermined condition is not satisfied, the air-fuel ratio cannot be optimized due to the excess or deficiency of the fuel, and there is a possibility that the exhaust emission deteriorates.

Therefore, if the fuel can be accurately supplied even in an operating region where a large amount of reducing agent is required, it is possible to suppress deterioration of exhaust emission.

The present invention has been made in view of the above problems, and in an exhaust gas purification apparatus for an internal combustion engine,
It is an object of the present invention to provide a technique for correcting the excess or deficiency of the fuel injection amount regardless of the operating region, and thereby suppressing the deterioration of exhaust emission.

[0015]

In order to achieve the above object, the exhaust gas purifying apparatus for an internal combustion engine of the present invention employs the following means. That is, fuel supply means for supplying fuel to the internal combustion engine, exhaust pressure measurement means for measuring the pressure of exhaust gas, discharge timing determination means for determining the timing at which exhaust gas is discharged from the cylinder of the internal combustion engine, and discharge timing determination Pressure wave arrival time estimating means for estimating the time from the exhaust discharge timing determined by the means until the exhaust pressure wave reaches the exhaust pressure measuring means, and the pressure wave arrival time from the time estimated by the discharge timing estimating means Fuel amount estimating means for estimating excess or deficiency of the fuel supply amount based on the pressure measured by the exhaust pressure measuring means when the time estimated by the time estimating means has passed, and based on the estimation result of the fuel amount estimating means And a correction unit that corrects the fuel supply amount.

The greatest feature of the present invention is that in an exhaust gas purification apparatus for an internal combustion engine, a pressure wave when exhaust gas is discharged from a cylinder is measured, and an excess or deficiency of fuel supplied to the cylinder is estimated from the measured pressure wave. However, the amount of fuel supplied into the cylinder is corrected based on this result.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, after the fuel is burned in the cylinder, burned gas is discharged from the cylinder and a pressure wave is generated. The pressure wave generated at this time is transmitted through the exhaust gas. The magnitude of this pressure wave has a correlation with the pressure in the cylinder, and the pressure in the cylinder depends on the fuel injection amount supplied to the cylinder. Therefore, the fuel injection amount can be estimated by measuring the magnitude of the pressure wave in the exhaust gas.

In the present invention, the exhaust gas purification apparatus for an internal combustion engine comprises a filter capable of collecting particulate matter in the exhaust gas, and the exhaust gas pressure measuring means measures the pressure difference between the exhaust gas upstream and downstream of the filter. Measuring, the pressure wave arrival time estimating means estimates the time to reach the exhaust pressure measuring means on the upstream side of the filter, the fuel amount estimating means based on the pressure difference between the exhaust gas upstream and downstream of the filter. It is possible to estimate the excess or deficiency of the fuel supply amount.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, the particulate matter contained in the exhaust gas is captured by the filter. The particulate matter captured in this way is burned and removed by the high-temperature exhaust gas discharged from the internal combustion engine during high-load operation, but when the light-load operation continues, it accumulates on the filter and causes clogging. At this time, since the pressure difference before and after the filter becomes large, the clogging of the filter can be detected by measuring the pressure of the exhaust gas upstream and downstream of the filter, and the particulate matter is removed by raising the temperature of the exhaust gas. You can know when to do it.

On the other hand, when the pressure wave generated from the internal combustion engine reaches the filter upstream side of the exhaust pressure measuring means, the pressure on the upstream side increases, and therefore the differential pressure across the filter increases. Since the magnitude of this pressure difference correlates with the amount of fuel supplied to the cylinder of the internal combustion engine, the amount of fuel supplied to the cylinder can be estimated by measuring the magnitude of the pressure difference.

Further, since it takes time for the pressure wave generated in the cylinders to reach the exhaust pressure measuring means, in an internal combustion engine having a plurality of cylinders, the differential pressure measured by the exhaust pressure measuring means is determined by which cylinder. It is necessary to judge whether it is due to the pressure wave generated from. Therefore, the pressure wave arrival time estimating means estimates the time taken for the pressure wave to reach the exhaust pressure measuring means from the cylinder, and can identify from which cylinder the pressure wave is generated.

The filter may carry a NOx absorbent or a catalyst.

In the present invention, the internal combustion engine has a plurality of cylinders, the fuel supply means supplies fuel to each cylinder, and the pressure wave arrival time estimation means determines the pressure wave discharged from each cylinder. Estimating the time to reach the exhaust pressure measuring means, the correcting means determines the cylinder based on the deviation between the exhaust pressure corresponding to a preset fuel supply amount and the exhaust pressure measured by the exhaust pressure measuring means. The fuel supply amount can be corrected every time.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, the fuel injection amount can be corrected for each cylinder based on the magnitude of the pressure wave of the exhaust gas for each cylinder, and the fuel injection amount between the cylinders can be calculated. It can be made uniform.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Specific embodiments of an exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described below with reference to the drawings. Here, the case where the exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied to a diesel engine for driving a vehicle will be described as an example.

FIG. 1 is a diagram showing a schematic configuration of an engine 1 and an intake / exhaust system for the engine 1 to which an exhaust purification system according to this embodiment is applied.

The engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.

The engine 1 is equipped with a fuel injection valve 3 for directly injecting fuel into the combustion chamber of each cylinder 2. Each fuel injection valve 3 is connected to a pressure accumulator (common rail) 4 that accumulates fuel to a predetermined pressure. A common rail pressure sensor 4a that outputs an electric signal corresponding to the pressure of the fuel in the common rail 4 is attached to the common rail 4.

The common rail 4 communicates with a fuel pump 6 via a fuel supply pipe 5. This fuel pump 6
Is a pump that operates using the rotational torque of the output shaft (crankshaft) of the engine 1 as a drive source. A pump pulley 6a attached to the input shaft of the fuel pump 6 is attached to the output shaft (crankshaft) of the engine 1. The crank pulley 1a is connected to the crank pulley 1a via a belt 7.

In the fuel injection system thus constructed, when the rotational torque of the crankshaft is transmitted to the input shaft of the fuel pump 6, the fuel pump 6 is transmitted from the crankshaft to the input shaft of the fuel pump 6. The fuel is discharged at a pressure according to the rotating torque.

The fuel discharged from the fuel pump 6 is
It is supplied to the common rail 4 via the fuel supply pipe 5, accumulated in the common rail 4 to a predetermined pressure, and distributed to the fuel injection valve 3 of each cylinder 2. When a drive current is applied to the fuel injection valve 3, the fuel injection valve 3 opens, and as a result, fuel is injected from the fuel injection valve 3 into the cylinder 2.

Next, an intake branch pipe 8 is connected to the engine 1, and each branch pipe of the intake branch pipe 8 communicates with a combustion chamber of each cylinder 2 through an intake port (not shown). There is.

The intake branch pipe 8 is connected to the intake pipe 9,
The intake pipe 9 is connected to the air cleaner box 10. An air flow meter 11 that outputs an electric signal corresponding to the mass of intake air flowing through the intake pipe 9 is attached to the intake pipe 9 downstream of the air cleaner box 10.

An intake throttle valve 13 for adjusting the flow rate of the intake air flowing through the intake pipe 9 is provided at a portion of the intake pipe 9 located immediately upstream of the intake branch pipe 8. The intake throttle valve 13 is provided with an intake throttle actuator 14 configured by a step motor or the like for driving the intake throttle valve 13 to open and close.

In the intake pipe 9 located between the air flow meter 11 and the intake throttle valve 13, a compressor housing 15a of a centrifugal supercharger (turbocharger) 15 which operates by using heat energy of exhaust gas as a drive source is provided. The
An intercooler 16 for cooling the intake air that has become hot due to being compressed in the compressor housing 15a is provided in the intake pipe 9 downstream of the compressor housing 15a.
Is provided.

In the intake system configured as described above, the intake air flowing into the air cleaner box 10 is cleaned by the air cleaner (not shown) in the air cleaner box 10 to remove dust and dirt from the intake air, and then the intake pipe 9 Through the compressor housing 15a.

The intake air flowing into the compressor housing 15a is compressed by the rotation of the compressor wheel installed in the compressor housing 15a. The intake air that has been compressed in the compressor housing 15a and has a high temperature is cooled in the intercooler 16 and then flows into the intake branch pipe 8 with its flow rate adjusted by the intake throttle valve 13 as necessary. The intake air that has flowed into the intake branch pipe 8 is distributed to the combustion chamber of each cylinder 2 through each branch pipe, and is burned using the fuel injected from the fuel injection valve 3 of each cylinder 2 as an ignition source.

On the other hand, an exhaust branch pipe 18 is connected to the engine 1, and each branch pipe of the exhaust branch pipe 18 communicates with a combustion chamber of each cylinder 2 through an exhaust port (not shown).

The exhaust branch pipe 18 serves as the centrifugal supercharger 15.
Is connected to the turbine housing 15b. The turbine housing 15b is connected to an exhaust pipe 19, and the exhaust pipe 19 is connected downstream to a muffler (not shown).

An occlusion reduction type N is provided in the middle of the exhaust pipe 19.
A particulate filter carrying an Ox catalyst (hereinafter,
Simply called a filter. ) 20 are provided. An exhaust gas temperature sensor 24 that outputs an electric signal corresponding to the temperature of the exhaust gas flowing through the exhaust pipe 19 is attached to the exhaust pipe 19 upstream of the filter 20. Also, filter 2
One end of an upstream introduction pipe 37a for introducing exhaust gas is connected to the upstream side of 0, and one end of a downstream introduction pipe 37b is connected to the downstream side of the filter 20. The other end of the upstream introduction pipe 37a and the other end of the downstream introduction pipe 37b are connected to the differential pressure sensor 37. The differential pressure sensor 37 outputs an electric signal corresponding to the differential pressure of the exhaust gas introduced from the upstream introduction pipe 37a and the downstream introduction pipe 37b.

Exhaust pipe 1 downstream of the above-mentioned filter 20
An exhaust throttle valve 21 for adjusting the flow rate of the exhaust gas flowing through the exhaust pipe 19 is provided in the valve 9. This exhaust throttle valve 2
1, an exhaust throttle valve 2 which is composed of a step motor or the like
An exhaust throttle actuator 22 for driving to open and close 1 is attached.

In the thus constructed exhaust system, the air-fuel mixture (burnt gas) burned in each cylinder 2 of the engine 1 is discharged to the exhaust branch pipe 18 through the exhaust port, and then the exhaust branch pipe 18 is exhausted. Turbine housing 15b of centrifugal supercharger 15
Flow into. The exhaust gas that has flowed into the turbine housing 15b uses the thermal energy of the exhaust gas to rotate the turbine wheel that is rotatably supported in the turbine housing 15b. At that time, the rotational torque of the turbine wheel is transmitted to the compressor wheel of the compressor housing 15a described above.

The exhaust gas discharged from the turbine housing 15b flows into the filter 20 through the exhaust pipe 19, PM in the exhaust gas is collected, and harmful gas components are removed or purified. The exhaust gas from which the PM has been captured by the filter 20 and the harmful gas components have been removed or purified is discharged to the atmosphere via the muffler after the flow rate is adjusted by the exhaust throttle valve 21 as necessary.

Further, the exhaust branch pipe 18 and the intake branch pipe 8 are exhaust gas recirculation passages (hereinafter referred to as EGR passages) for recirculating a part of the exhaust gas flowing in the exhaust branch pipe 18 to the intake branch pipe 8. )
25 are communicated with each other. In the middle of the EGR passage 25, an exhaust valve (hereinafter, referred to as EG, which is composed of a solenoid valve or the like, flows through the EGR passage 25 according to the magnitude of the applied power.
R gas. ) Flow rate adjustment valve (hereinafter,
Use EGR valve. ) 26 are provided.

An EGR valve 26 is provided in the middle of the EGR passage 25.
An EGR cooler 27 that cools the EGR gas flowing through the EGR passage 25 is provided further upstream. A cooling water passage (not shown) is provided in the EGR cooler 27, and a part of the cooling water for cooling the engine 1 circulates.

In the exhaust gas recirculation mechanism constructed as described above, when the EGR valve 26 is opened, the EGR passage 25 is brought into conduction, and a part of the exhaust gas flowing through the exhaust branch pipe 18 is part of the EGR passage 25. To the intake branch pipe 8 via the EGR cooler 27.

At this time, in the EGR cooler 27, heat exchange is performed between the EGR gas flowing in the EGR passage 25 and the cooling water of the engine 1 to cool the EGR gas.

The EGR gas recirculated from the exhaust branch pipe 18 to the intake branch pipe 8 via the EGR passage 25 is introduced into the combustion chamber of each cylinder 2 while being mixed with the fresh air flowing from the upstream side of the intake branch pipe 8. Get burned.

Here, the EGR gas contains an inert gas component such as water (H ₂ O) and carbon dioxide (CO ₂ ) which does not burn by itself and has a high heat capacity. Therefore, when EGR gas is contained in the air-fuel mixture, the combustion temperature of the air-fuel mixture is lowered, and thus nitrogen oxide (NOx)
Is suppressed.

Further, when the EGR gas is cooled in the EGR cooler 27, the temperature of the EGR gas itself is lowered and the volume of the EGR gas is reduced, so that when the EGR gas is supplied into the combustion chamber, the EGR gas is reduced. The ambient temperature of 1 is not unnecessarily increased, and the amount of fresh air (volume of fresh air) supplied into the combustion chamber is not unnecessarily reduced.

Next, the filter 20 according to this embodiment will be described.

FIG. 2 is a sectional view of the filter 20. FIG. 2A is a view showing a cross section in the lateral direction of the filter 20. FIG. 2B is a diagram showing a vertical cross section of the filter 20.

As shown in FIGS. 2A and 2B, the filter 20 is of a so-called wall flow type having a plurality of exhaust flow passages 50 and 51 extending in parallel with each other. These exhaust flow passages are composed of an exhaust inflow passage 50 whose downstream end is closed by a plug 52 and an exhaust outflow passage 51 whose upstream end is closed by a plug 53. The hatched portion in FIG. 2A indicates the plug 53. Therefore, the exhaust inflow passages 50 and the exhaust outflow passages 51 are alternately arranged via the thin partition walls 54. In other words, in the exhaust inflow passage 50 and the exhaust outflow passage 51, each exhaust inflow passage 50 is surrounded by four exhaust outflow passages 51, and each exhaust outflow passage 51 includes four exhaust inflow passages 50.
It is arranged to be surrounded by.

The filter 20 is made of a porous material such as cordierite, so that the exhaust gas flowing into the exhaust gas inflow passage 50 flows in the surrounding partition wall 54 as shown by the arrow in FIG. 2B. It flows out into the adjacent exhaust outflow passage 51.

In the embodiment according to the present invention, each exhaust inflow passage 5
0 and the peripheral wall surface of each exhaust outflow passage 51, that is, each partition wall 54
A carrier layer made of, for example, alumina is formed on both side surfaces of the above and on the inner wall surface of the pores in the partition wall 54, and the occlusion reduction type NOx catalyst is carried on this carrier.

Next, the function of the NOx storage reduction catalyst carried by the filter 20 according to this embodiment will be described.

The filter 20 uses, for example, alumina as a carrier, and potassium (K) and sodium (N) are deposited on the carrier.
a), an alkali metal such as lithium (Li) or cesium (Cs), an alkaline earth such as barium (Ba) or calcium (Ca), and a rare earth such as lanthanum (La) or yttrium (Y). And at least one of them is carried and a noble metal such as platinum (Pt). In the present embodiment, barium (Ba) and platinum (Pt) are supported on a carrier made of alumina, and ceria (Ce ₂ O ₃ ) having an O ₂ storage capacity is further supported.
A storage reduction type NOx catalyst (hereinafter simply referred to as "NOx catalyst") configured by adding is adopted.

The NOx catalyst thus constructed is
When the exhaust gas flowing into the Ox catalyst has a high oxygen concentration, it absorbs nitrogen oxides (NOx) in the exhaust gas.

On the other hand, the NOx catalyst releases the nitrogen oxide (NOx) absorbed when the oxygen concentration of the exhaust gas flowing into the NOx catalyst decreases. At that time, if a reducing component such as hydrocarbon (HC) or carbon monoxide (CO) is present in the exhaust gas, the NOx catalyst converts the nitrogen oxide (NOx) released from the NOx catalyst into nitrogen (N). It can be reduced to ₂ ).

By the way, when the engine 1 is in the lean burn operation, the air-fuel ratio of the exhaust gas discharged from the engine 1 becomes a lean atmosphere and the oxygen concentration of the exhaust gas becomes high.
Nitrogen oxides (NOx) contained in the exhaust gas will be absorbed by the NOx catalyst, but if the lean burn operation of the engine 1 is continued for a long period of time, the NOx absorption capacity of the NOx catalyst will be saturated, and Nitrogen oxides (NOx) are released into the atmosphere without being removed by the NOx catalyst.

Particularly, in a diesel engine such as the engine 1, a lean air-fuel ratio mixture is burned in most operating regions, and accordingly, the exhaust air-fuel ratio becomes lean air-fuel ratio in most operating regions. , N of NOx catalyst
Ox absorption capacity is easily saturated.

Therefore, when the engine 1 is in the lean burn operation, the concentration of oxygen in the exhaust flowing into the NOx catalyst is reduced and the concentration of the reducing agent is increased before the NOx absorption capacity of the NOx catalyst is saturated, and the NOx concentration is increased. It is necessary to release and reduce nitrogen oxides (NOx) absorbed by the catalyst.

As a method of lowering the oxygen concentration in this way, the fuel amount in the exhaust gas is increased, or the amount of EGR gas to be recirculated is increased to increase the soot generation amount to the maximum so that the EGR gas amount is further increased. Although a method of increasing low temperature combustion, exhaust stroke injection, or the like can be considered, in the present embodiment, the filter 2 is used.
A reducing agent supply mechanism for adding fuel (light oil) as a reducing agent to the exhaust gas flowing through the exhaust pipe 19 upstream of 0 is provided, and by adding the fuel from the reducing agent supply mechanism to the exhaust gas,
The oxygen concentration of the exhaust gas flowing into the filter 20 is reduced and the concentration of the reducing agent is increased.

As shown in FIG. 1, the reducing agent supply mechanism is mounted so that its injection hole faces the inside of the exhaust branch pipe 18, and is opened by a signal from the ECU 35 to inject fuel. 28, a reducing agent supply path 29 that guides the fuel discharged from the fuel pump 6 to the reducing agent injection valve 28, and a distribution of the fuel in the reducing agent supply path 29 that is provided in the reducing agent supply path 29. And a shutoff valve 31 for shutting off.

In such a reducing agent supply mechanism, the high-pressure fuel discharged from the fuel pump 6 is applied to the reducing agent injection valve 28 via the reducing agent supply passage 29. And ECU3
The reducing agent injection valve 28 is opened by a signal from 5 and fuel as a reducing agent is injected into the exhaust branch pipe 18.

The reducing agent injected from the reducing agent injection valve 28 into the exhaust branch pipe 18 reduces the oxygen concentration of the exhaust gas flowing from the upstream side of the exhaust branch pipe 18.

The thus formed exhaust gas having a low oxygen concentration flows into the filter 20 and releases nitrogen oxides (NOx) absorbed in the filter 20 while releasing nitrogen (N ₂ ).
Will be reduced to.

After that, the reducing agent injection valve 28 is closed by a signal from the ECU 35, and the addition of the reducing agent into the exhaust branch pipe 18 is stopped.

In this embodiment, fuel is injected into the exhaust gas to add fuel, but instead of this, the amount of recirculated EGR gas is increased to increase the amount of soot generated. After reaching the maximum, low temperature combustion may be performed to further increase the EGR gas amount, and fuel may be injected from the fuel injection valve 3 in the expansion stroke, exhaust stroke, etc. of the engine 1.

The engine 1 configured as described above is provided with an electronic control unit (ECU) 35 for controlling the engine 1. The ECU 35 is a unit that controls the operating state of the engine 1 in accordance with the operating conditions of the engine 1 and the driver's request.

The ECU 35 includes the common rail pressure sensor 4
Various sensors such as a, the air flow meter 11, the exhaust temperature sensor 24, the crank position sensor 33, the water temperature sensor 34, the accelerator opening sensor 36, and the differential pressure sensor 37 are connected via electrical wiring, and the output signals of the various sensors described above. Is input to the ECU 35.

On the other hand, the ECU 35 has a fuel injection valve 3, an intake throttle actuator 14, an exhaust throttle actuator 22, a reducing agent injection valve 28, an EGR valve 26, and a shutoff valve 31.
Etc. are connected via electrical wiring, and the above-mentioned parts are connected to the ECU.
35 can be controlled.

Here, the ECU 35, as shown in FIG. 3, is connected to each other by a bidirectional bus 350, C
The input port 356 includes a PU 351, a ROM 352, a RAM 353, a backup RAM 354, an input port 356, and an output port 357.
And an A / D converter (A / D) 355 connected to.

The input port 356 inputs the output signals of a sensor that outputs a digital signal format signal such as the crank position sensor 33, and outputs those output signals to C.
It is transmitted to the PU 351 and the RAM 353.

The input port 356 includes a common rail pressure sensor 4a, an air flow meter 11, and an exhaust temperature sensor 2.
4, the water temperature sensor 34, the accelerator opening sensor 36, the differential pressure sensor 37, and the like, output signals of sensors that output signals in an analog signal format are input through the A / D 355, and those output signals are input to the CPU 351 or It is transmitted to the RAM 353.

The output port 357 is connected to the fuel injection valve 3,
Intake throttle actuator 14, exhaust throttle actuator 22, EGR valve 26, reducing agent injection valve 28, shutoff valve 3
1 and the like via electric wiring, and outputs control signals output from the CPU 351 to the fuel injection valve 3, the intake throttle actuator 14, the exhaust throttle actuator 2 described above.
2, to the EGR valve 26, the reducing agent injection valve 28, or the shutoff valve 31.

The ROM 352 includes a fuel injection control routine for controlling the fuel injection valve 3, an intake throttle control routine for controlling the intake throttle valve 13, an exhaust throttle control routine for controlling the exhaust throttle valve 21, an EGR valve. EGR control routine for controlling 26, NOx for adding / reducing reducing agent to filter 20 to release / reduce absorbed NOx
Purification control routine, poisoning elimination control routine for eliminating SOx poisoning of the filter 20, P collected in the filter 20
Application programs such as a PM combustion control routine for burning and removing M and a fuel injection amount correction routine for correcting the fuel injection amount from the output signal of the differential pressure sensor 37 are stored.

The ROM 352 stores various control maps in addition to the above application programs. The control map is, for example, a fuel injection amount control map showing the relationship between the operating state of the engine 1 and the basic fuel injection amount (basic fuel injection time), and the fuel showing the relationship between the operating state of the engine 1 and the basic fuel injection timing. Injection timing control map,
An intake throttle valve opening control map showing the relationship between the operating state of the engine 1 and the target opening degree of the intake throttle valve 13, and an exhaust throttle valve opening map showing the relationship between the operating state of the engine 1 and the target opening degree of the exhaust throttle valve 21. Control map, engine 1 operating status and EGR
An EGR valve opening control map showing the relationship with the target opening of the valve 26, a reducing agent addition control map showing the relationship between the operating state of the engine 1 and the target addition of the reducing agent (or the target air-fuel ratio of the exhaust gas), A reducing agent injection valve control map showing the relationship between the target addition amount of the reducing agent and the valve opening time of the reducing agent injection valve 28, and a fuel injection amount correction control map showing the relationship between the output signal of the differential pressure sensor 37 and the fuel correction amount. Etc.

The RAM 353 stores the output signal from each sensor, the calculation result of the CPU 351 and the like. The calculation result is, for example, the engine speed calculated based on the time interval at which the crank position sensor 33 outputs a pulse signal. These data are rewritten to the latest data each time the crank position sensor 33 outputs a pulse signal.

The backup RAM 354 is a non-volatile memory capable of storing data even after the operation of the engine 1 is stopped.

The CPU 351 operates according to the application program stored in the ROM 352 to control the fuel injection valve, intake throttle control, exhaust throttle control, E
GR control, NOx purification control, poisoning elimination control, PM combustion control, fuel injection amount correction control, etc. are executed.

For example, in the NOx purification control, the CPU 35
1 executes a so-called rich spike control in which the oxygen concentration in the exhaust gas flowing into the filter 20 is reduced in a spike-like (short time) manner in a relatively short cycle.

In the rich spike control, the CPU 351
Determines whether the rich spike control execution condition is satisfied every predetermined period. Examples of the rich spike control execution condition include conditions in which the filter 20 is in the active state, the output signal value of the exhaust temperature sensor 24 (exhaust temperature) is equal to or less than a predetermined upper limit value, and the like.

When it is determined that the rich spike control execution condition as described above is satisfied, the CPU 351
Controls the reducing agent injection valve 28 so that the reducing agent injection valve 28 injects fuel as the reducing agent in a spike manner to temporarily change the air-fuel ratio of the exhaust gas flowing into the filter 20 to a predetermined target rich air-fuel ratio. And

Specifically, the CPU 351 has the RAM 35.
Engine speed, accelerator opening sensor 3 stored in 3
6 output signal (accelerator opening), air flow meter 11
Output signal value (intake air amount), output signal of the air-fuel ratio sensor, fuel injection amount, and the like.

The CPU 351 accesses the reducing agent addition amount control map of the ROM 352 with the engine speed, the accelerator opening degree, the intake air amount and the fuel injection amount as parameters, and sets the air-fuel ratio of the exhaust gas to a preset target air-fuel ratio. The amount of addition of the reducing agent (target amount of addition) required to obtain the fuel ratio is calculated.

Subsequently, the CPU 351 accesses the reducing agent injection valve control map of the ROM 352 using the target addition amount as a parameter, and the reducing agent necessary for injecting the target addition amount of the reducing agent from the reducing agent injection valve 28. The valve opening time (target valve opening time) of the injection valve 28 is calculated.

When the target opening time of the reducing agent injection valve 28 is calculated, the CPU 351 opens the reducing agent injection valve 28.

The CPU 351 closes the reducing agent injection valve 28 when the target opening time elapses from the time when the reducing agent injection valve 28 is opened.

As described above, when the reducing agent injection valve 28 is opened for the target opening time, the target addition amount of fuel is injected from the reducing agent injection valve 28 into the exhaust branch pipe 18. Then, the reducing agent injected from the reducing agent injection valve 28 mixes with the exhaust gas that has flowed from the upstream side of the exhaust branch pipe 18 to form an air-fuel mixture having a target air-fuel ratio, and then flows into the filter 20.

As a result, the air-fuel ratio of the exhaust gas flowing into the filter 20 is such that the oxygen concentration changes in a relatively short cycle, so that the filter 20 absorbs and releases / reduces nitrogen oxides (NOx). And will be repeated alternately in a short cycle.

Next, in the poisoning elimination control, the CPU 351
Will perform a poisoning elimination process in order to eliminate the poisoning due to the oxide of the filter 20.

Here, sulfur (S) is used as the fuel for the engine 1.
When such a fuel is burned in the engine 1, sulfur oxides (SOx) such as sulfur dioxide (SO ₂ ) and sulfur trioxide (SO ₃ ) are generated.

Sulfur oxide (SOx) flows into the filter 20 together with exhaust gas and is absorbed by the filter 20 by the same mechanism as nitrogen oxide (NOx).

Specifically, when the oxygen concentration of the exhaust gas flowing into the filter 20 is high, sulfur oxides (S) such as sulfur dioxide (SO ₂ ) and sulfur trioxide (SO ₃ ) in the inflowing exhaust gas are included.
Ox) is oxidized on the surface of platinum (Pt) and absorbed by the filter 20 in the form of sulfate ions (SO ₄ ²⁻ ). Furthermore,
The sulfate ions (SO ₄ ^2- ) absorbed by the filter 20 are
Sulfate (BaS) combined with barium oxide (BaO)
O ₄ ) is formed.

By the way, the sulfate (BaSO ₄ ) is more stable than barium nitrate (Ba (NO ₃ ) ₂ ) and less likely to be decomposed, and is decomposed even when the oxygen concentration of the exhaust gas flowing into the filter 20 becomes low. Instead, they remain in the filter 20.

Sulfate (BaS) in the filter 20
As the amount of O ₄ ) increases, the nitrogen oxides (N
Barium oxide (B) which can participate in the absorption of Ox)
Since the amount of aO) decreases, so-called SOx poisoning occurs in which the NOx absorption capacity of the filter 20 decreases.

As a method of eliminating the SOx poisoning of the filter 20, the ambient temperature of the filter 20 is raised to a high temperature range of about 600 to 650 ° C. and the oxygen concentration of the exhaust gas flowing into the filter 20 is lowered. ,
Barium sulfate (BaSO) absorbed by the filter 20
₄₎ the SO ₃ ^- and SO ₄ ^- and pyrolyzed, followed by SO ₃ ^- and SO ₄
^- it can be exemplified a method of reducing the ^- is reacted with a hydrocarbon in the exhaust gas (HC) and carbon monoxide (CO) gaseous SO ₂ and.

Therefore, in the poisoning elimination processing according to the present embodiment, the CPU 351 first executes the catalyst temperature raising control for raising the bed temperature of the filter 20, and then lowers the oxygen concentration of the exhaust gas flowing into the filter 20. I did it.

In the catalyst temperature raising control, the CPU 351 may, for example, inject fuel secondarily from the fuel injection valve 3 and add fuel to the exhaust gas from the reducing agent injection valve 28 during the expansion stroke of each cylinder 2. Alternatively, those unburned fuel components may be oxidized in the filter 20, and the heat generated during the oxidation may raise the bed temperature of the filter 20.

However, if the temperature of the filter 20 rises excessively,
Since the heat deterioration of the filter 20 may be induced, it is preferable that the secondary injection fuel amount and the additional fuel amount be feedback-controlled based on the output signal value of the exhaust temperature sensor 24.

When the bed temperature of the filter 20 rises to a high temperature range of about 600 ° C. to 650 ° C. due to the catalyst temperature raising process as described above, the CPU 351 causes the reducing agent injection to reduce the oxygen concentration of the exhaust gas flowing into the filter 20. Fuel is injected from the valve 28.

When excessive fuel is injected from the reducing agent injection valve 28, those fuels burn rapidly in the filter 20 and the filter 20 overheats, or excessive fuel injected from the reducing agent injection valve 28 is injected. Since the filter 20 may be unnecessarily cooled by the fuel, the CPU 351 controls the reducing agent injection valve 28 based on the output signal of the air-fuel ratio sensor (not shown).
It is preferable to feedback control the fuel injection amount from.

When the poisoning elimination processing is executed in this way,
When the bed temperature of the filter 20 is high, the oxygen concentration of the exhaust gas flowing into the filter 20 is low, so that barium sulfate (BaSO ₄ ) absorbed by the filter 20 is thermally decomposed into SO ₃ ⁻ and SO ₄ ^−. The SO ₃ ⁻ and SO ₄ ⁻ react with hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas and are reduced, whereby SOx poisoning of the filter 20 is eliminated.

On the other hand, depending on the operating condition of the engine, the PM captured by the filter 20 remains unburned and accumulated, which causes the filter 20 to be clogged. As one of the methods for effectively removing the unburned PM, the temperature increase control by the fuel addition is effective.

By the way, NOx of the NOx storage reduction catalyst or the like
Catalysts and other catalysts have an air-fuel ratio range in which exhaust gas can be purified, and an air-fuel ratio outside this range reduces the exhaust gas purification capability. Further, as described above, the storage reduction type NOx
There is a required air-fuel ratio of exhaust gas in the release / reduction of NOx stored in the catalyst, elimination of SOx poisoning, or temperature increase control of the catalyst or the like. Therefore, it is important to accurately control the air-fuel ratio of exhaust gas. However, since the fuel injection valves 3 may have different fuel injection amounts per unit time due to individual differences and changes over time, air-fuel ratio control is performed on the assumption that all fuel injection valves inject the same amount of fuel. Then, there is a possibility that the required air-fuel ratio cannot be obtained. In particular, in a multi-cylinder engine, the fuel injection amount may differ from cylinder to cylinder even in a steady state, and the air-fuel ratio of the exhaust gas flowing into the catalyst or the like may fluctuate. In such a case, the required air-fuel ratio cannot be obtained even if the fuel injection amounts of all the fuel injection valves are uniformly corrected. Therefore, it is necessary to correct the fuel injection amount for each cylinder, but in the conventional internal combustion engine, since the mounting position of the air-fuel ratio sensor is located downstream of the collecting portion of the exhaust gas discharged from each cylinder, the It was difficult to measure the air-fuel ratio while specifying whether or not it was a thing.

Therefore, in the present embodiment, when the burned gas is discharged from the inside of the cylinder, the inside of the exhaust branch pipe 18 and the exhaust pipe 1
By measuring the magnitude of the pressure wave propagating in the cylinder 9, the fuel injection amount is corrected for each cylinder while obtaining the excess or deficiency of the fuel injection amount for each cylinder. Here, in the present embodiment, focusing on the fact that the magnitude of the pressure wave has a correlation with the amount of fuel injected into the cylinder, the output signal of the differential pressure sensor 37 that measures the differential pressure before and after the filter 20 is output. The fuel injection amount can be corrected based on the size.

Next, a method of correcting the fuel injection amount according to this embodiment will be described.

FIG. 4 is a flow chart showing the flow of fuel injection amount correction according to this embodiment.

This routine is to change the fuel injection valve 3 over time.
It is performed every 10,000 kilometers, for example, in consideration of differences between individuals.

In step S101, it is determined whether the engine 1 is in a steady state. Here, the steady state is
The state in which the engine 1 maintains a constant rotation speed under a constant load, and the valve opening time (load) of the fuel injection valve 3 and the output signal (rotation speed) of the crank position sensor 33 are within a constant range. Sometimes it is determined to be a steady state. here,
The steady state is set because, in a transient state in which the rotation speed or the load changes with time, the fuel injection amount also changes and it becomes impossible to determine the variation between the cylinders.

If the affirmative judgment is made in step S101, the routine proceeds to step S102, while if the negative judgment is made, this routine is once ended.

In step S102, based on the number of revolutions of the engine 1 and the fuel injection amount, the cylinder 2 is connected to the upstream side introduction pipe 3
The time to reach 7a is calculated. The pressure wave generated from the inside of the cylinder 2 propagates in the exhaust branch pipe 18 and the exhaust pipe 19 at the speed of sound, but the speed at this time varies depending on the exhaust state. Therefore, the temperature of exhaust gas and the like are calculated from the engine speed obtained from the output signal of the crank position sensor 33 at this time and the valve opening time of the fuel injection valve 3 calculated by the ECU 35 to obtain the speed at which the pressure wave is transmitted. At this time, the engine speed, the fuel injection amount, and the time during which the pressure wave is transmitted are mapped in advance, and the output signal of the crank position sensor and the ECU
The transmission time (hereinafter referred to as a delay time) of the pressure wave may be calculated by substituting the calculated valve opening time of the fuel injection valve 3 of 35.

The delay time thus obtained is R
It is stored in AM353.

In step S103, the reading timing of the differential pressure sensor is calculated from the valve opening timing of the exhaust valve (not shown) and the delay time calculated in step S102. Since the exhaust valve opens and closes in conjunction with the rotation of the crankshaft (not shown), it is possible to know the opening timing of the exhaust valve from the output signal of the crank position sensor 33. The pressure wave is transmitted to the inside of the exhaust branch pipe 18 at the same time when the exhaust valve is opened, and then passes through the inside of the exhaust pipe 19 to reach the upstream side inlet 37.
reach a. Further, the pressure wave reaches the differential pressure sensor 37 from the upstream introduction port 37a. At this time, since the pressure wave has not reached the downstream introduction port 37b, the pressure on the upstream side of the differential pressure sensor 37 becomes high, and the differential pressure sensor 37 outputs a signal indicating a large differential pressure.

In step S104, the output signal of the differential pressure sensor 37 is read. The CPU 351 executes the step S10.
The output signal of the differential pressure sensor 37 is read at the read timing calculated in 3.

In step S105, a correction value for the amount of fuel injected from the fuel injection valve 3 is calculated. The rotational speed, the load, and the average value of the output signal of the differential pressure sensor 37 when the pressure wave after opening the exhaust valve reaches the differential pressure sensor 37 are mapped to R
It is stored in the OM 352 in advance. The CPU 351 substitutes the rotation speed and the load into this map to calculate the average value of the output signals of the differential pressure sensor 37. Next, the CPU 351
The deviation between this average value and the actual measurement value of the differential pressure sensor 37 read in step S104 is calculated. Here, since the magnitude of the pressure wave is correlated with the amount of fuel injected into the cylinder,
The deviation correlates with the amount of fuel injected into the cylinder. Therefore, if the relationship between the deviation and the excess / deficiency of fuel is mapped in advance, the deviation can be substituted into the map to calculate the excess / deficiency of fuel. The excess / deficiency amount of fuel calculated at this time is a fuel amount that needs to be corrected, and the RAM 35 is used as a correction value for the fuel amount for eliminating this excess / deficiency amount.
Store in 3.

In step S106, the corrected output signal of the differential pressure sensor 37 is used as an average value and a new backup R is performed.
It is stored in the AM 354. In step S105 of the routine from the next time, the fuel injection amount is corrected using the average value of the differential pressure sensor 37 stored in the backup RAM 354.

The average value of the corrected differential pressure sensor 37 is not used in the next routine, and the ROM 3
It is also possible to calculate the fuel injection amount by using the average value of the output signals of the differential pressure sensor in the initial state read from 52. In this case, the process of step S106 is unnecessary.

In this way, the correction value of the fuel injection amount of each cylinder can be obtained.

After that, the ECU 35 performs fuel injection by adding the correction value calculated in this routine at the time of fuel injection of each cylinder.

As described above, according to this embodiment, the fuel injection amount can be corrected.

Here, conventionally, the fuel injection amount is corrected based on the fluctuation of the engine speed in the idle state.
When the fuel injection amount is small, the fuel injection amount can be corrected by such a method, but when the fuel injection amount increases, the injection amount that must be corrected fluctuates and it is difficult to perform the correction. there were.

On the other hand, in the present embodiment, the fuel injection amount can be corrected from the magnitude of the pressure wave propagating in the exhaust gas, so that the fuel injection amount can be corrected even in the medium-high speed region where the fuel injection amount is large. It will be possible.

[0125]

In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the fuel injection amount can be obtained based on the magnitude of the pressure wave propagating in the exhaust gas, and the fuel injection amount for each cylinder can be obtained even in a state other than the light load state. The injection amount can be corrected.

Therefore, the air-fuel ratio of the exhaust gas can be accurately controlled for each cylinder, so that the variation of the air-fuel ratio can be suppressed and the deterioration of the exhaust emission can be suppressed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an engine to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention is applied and an intake / exhaust system thereof.

FIG. 2A is a diagram showing a lateral cross section of a particulate filter. (B) is a figure which shows the longitudinal cross section of a particulate filter.

FIG. 3 is a block diagram showing an internal configuration of an ECU.

FIG. 4 is a flowchart showing a flow of fuel injection amount correction according to the embodiment of the present invention.

[Explanation of symbols]

1 ... Engine 1a: Crank pulley 2 ... Cylinder 3 ... Fuel injection valve 4 ... Common rail 4a ... Common rail pressure sensor 5 ... Fuel supply pipe 6 ... Fuel pump 6a ... Pump pulley 8 ... Intake branch pipe 9 ... Intake pipe 18 ... Exhaust branch pipe 19 ... Exhaust pipe 20 ... Particulate filter 21 ... Exhaust throttle valve 24 ... Exhaust gas temperature sensor 25 ... EGR passage 26 ... EGR valve 27 ... EGR cooler 28 ... Reducing agent injection valve 29 ... Reductant supply path 31 ... Shut-off valve 33 ... Crank position sensor 34 ... Water temperature sensor 35 ... ECU 36 ... Accelerator opening sensor 37 ... Differential pressure sensor

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masaaki Kobayashi             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. (72) Inventor Daisuke Shibata             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. (72) Inventor Shinobu Ishiyama             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. (72) Inventor Tomoyuki Ono             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. (72) Inventor Akihiko Negami             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. F-term (reference) 3G090 AA02 BA01 CB04 CB25 DA12                       DA13 EA06 EA07                 3G091 AA02 AA10 AA11 AA18 AB06                       AB13 BA01 BA08 BA11 BA14                       CA18 CB01 CB07 DA02 DC03                       EA01 EA05 EA07 EA16 EA17                       EA32 FC04 GA06 HA14 HB05                       HB06                 3G301 HA02 HA06 HA11 HA13 JA05                       JA21 JA24 JA25 KA21 LB11                       LC01 MA11 NA08 NB03 NC07                       ND03 PA01Z PB08Z PD14Z                       PE03Z PE08Z PF03Z

Claims (3)

[Claims] 1. A fuel supply means for supplying fuel to an internal combustion engine, an exhaust pressure measuring means for measuring a pressure of exhaust gas, and an exhaust timing determining means for determining a timing at which exhaust gas is discharged from a cylinder of the internal combustion engine. The pressure wave arrival time estimating means for estimating the time from the discharge timing of the exhaust gas determined by the discharge timing determining means to the arrival of the pressure wave of the exhaust gas in the exhaust pressure measuring means, and the time estimated by the discharge timing estimating means Fuel amount estimating means for estimating excess or deficiency of the fuel supply amount based on the pressure measured by the exhaust pressure measuring means when the time estimated by the pressure wave arrival time estimating means has elapsed, and estimation of the fuel amount estimating means An exhaust emission control device for an internal combustion engine, comprising: a correction unit that corrects the fuel supply amount based on a result. 2. The exhaust gas purification apparatus for an internal combustion engine comprises a filter capable of collecting particulate matter in exhaust gas, and the exhaust gas pressure measuring means measures a pressure difference between exhaust gas upstream and downstream of the filter, The pressure wave arrival time estimation means estimates the time to reach the exhaust pressure measurement means on the upstream side of the filter, and the fuel amount estimation means determines the fuel supply amount based on the pressure difference between the exhaust gas upstream and downstream of the filter. The exhaust gas purification device for an internal combustion engine according to claim 1, wherein excess or deficiency is estimated. 3. The internal combustion engine has a plurality of cylinders, the fuel supply means supplies fuel to each cylinder, and the pressure wave arrival time estimation means determines that the pressure wave discharged from each cylinder is the exhaust pressure. Estimating the time to reach the measurement means, the correction means is a fuel for each cylinder based on the deviation between the exhaust pressure corresponding to a preset fuel supply amount and the exhaust pressure measured by the exhaust pressure measurement means. The exhaust emission control device for an internal combustion engine according to claim 1 or 2, wherein the supply amount is corrected.