JP2002364439A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of accurately finding a back-and-forth differential pressure of a filter in an exhaust emission control device for an internal combustion engine. SOLUTION: This exhaust emission control device has the filter 20 capable of capturing fine particles in exhaust emission of the internal combustion engine 1 for a certain period; a differential pressure detection means 37 detecting the differential pressure between the rear and the front of the filter 20 from pressure of the exhaust emission before and after the filter 20; and a correction means 35 correcting a detection value of the differential pressure detection means 37 when the internal combustion engine 1 is stopped after a perfect warming-up state of the internal combustion engine 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purification device for an internal combustion engine.

[0002]

2. Description of the Related Art Diesel engines are economical, but have a particulate matter typified by soot, which is a suspended particulate matter contained in exhaust gas.
Hereinafter, it is referred to as “PM” unless otherwise specified. ) Removal is an important issue. For this reason, a technique of providing a particulate filter (hereinafter, simply referred to as “filter”) for trapping PM in an exhaust system of a diesel engine so that PM is not released into the atmosphere is well known.

[0003] This filter can prevent PM in exhaust gas from being once collected and released into the atmosphere. However, PM trapped in the filter may accumulate on the filter and cause clogging of the filter. When this clogging occurs, the pressure of the exhaust gas upstream of the filter increases, which may cause a decrease in the output of the internal combustion engine or damage to the filter. In such a case, the PM deposited on the filter can be removed by igniting and burning. Removing PM accumulated on the filter in this way is called filter regeneration.

[0004] Regeneration of a filter is sometimes performed based on the amount of PM collected by the filter. For example, the amount of trapped PM can be estimated from the differential pressure of the exhaust gas before and after the filter. One of the methods for detecting the differential pressure is a method using a differential pressure sensor provided before and after the filter. However, some differential pressure sensors have an output error from the time of manufacture, and others have an output error due to aging during use, PM adhesion, and the like. Further, the output value of the differential pressure sensor fluctuates with a change in temperature, and this output characteristic differs for each differential pressure sensor.

A method of correcting these errors and the like is, for example,
It is described in U.S. Pat. No. 4,574,589. According to this, when the engine is stopped, the actual differential pressure before and after the filter becomes 0, so the output signal of the differential pressure sensor as a reference at this time is obtained in advance, and the output signal value from the differential pressure sensor and this reference Can be obtained as a correction value. Then, the difference between the output signal value from the differential pressure sensor obtained during the operation of the internal combustion engine and the obtained correction value is the corrected differential pressure.

[0006]

However, since the output signal from the differential pressure sensor fluctuates depending on the ambient temperature around the differential pressure sensor, the temperature of the sensor itself, and the like, the timing for obtaining the correction value is important. That is, even if the differential pressure is 0, if the ambient temperature around the differential pressure sensor, the temperature of the sensor itself, or the like is different, the differential pressure sensor transmits a different output signal, so that the correction value varies. In particular, when the engine is stopped before the warm-up of the internal combustion engine is completed, or when a long time has elapsed since the engine was stopped, the ambient temperature around the differential pressure sensor and the temperature of the sensor itself are completely warmed up. Therefore, accurate correction becomes difficult.

If a certain amount of error always occurs in the differential pressure sensor irrespective of the magnitude of the differential pressure, the correction can be made by the above method. Cannot be corrected by the above method.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an exhaust purification device for an internal combustion engine is provided.
It is an object of the present invention to provide a technique capable of accurately obtaining a differential pressure across a filter.

[0009]

Means for Solving the Problems To achieve the above object, an exhaust gas purifying apparatus for an internal combustion engine according to the present invention employs the following means. That is, a filter capable of capturing particulates in the exhaust gas of the internal combustion engine for a period of time, a differential pressure detecting means for detecting a differential pressure across the filter from the pressure of the exhaust gas before and after the filter, and after the internal combustion engine is completely warmed up. And a correcting means for correcting the value detected by the differential pressure detecting means while the engine is stopped.

The most significant feature of the present invention is that the exhaust gas purifying apparatus for an internal combustion engine includes a differential pressure detecting means for detecting a differential pressure across the filter and a correcting means for correcting the differential pressure detecting means,
If the correction is performed only when the engine is stopped after the internal combustion engine is completely warmed up, the atmosphere of the differential pressure detecting means becomes a constant temperature and the differential pressure becomes zero.
Therefore, an effect of enabling accurate correction can be achieved.

In the exhaust gas purifying apparatus for an internal combustion engine thus configured, PM contained in the exhaust gas is collected by the filter.

The PM trapped by the filter burns when the temperature of the exhaust gas is high, for example, when the internal combustion engine is operated in a high-speed high-load region. However, if the operation in the light load region continues for a long time, the PM trapped in the filter accumulates without burning. PM deposited in this way is
This may cause filter clogging.

Therefore, the differential pressure detecting means detects the pressure before and after the filter, estimates the amount of deposited PM, and when the amount of deposited PM is large, adjusts the amount of fuel supplied to the internal combustion engine and adds a reducing agent in the exhaust gas. Then, the PM is burned and removed.

The output characteristic of the differential pressure detecting means has an output characteristic peculiar to each differential pressure detecting means, and the output signal fluctuates due to deterioration with time or the like. Will be Since the output signal from the differential pressure detecting means fluctuates depending on the temperature of the differential pressure detecting means and the ambient temperature, the output signal is corrected after the internal combustion engine is completely warmed up and after the internal combustion engine is stopped. A correction value for the signal is determined. At this time, since the internal combustion engine is stopped, the ambient temperature around the differential pressure detecting means becomes substantially constant,
In addition, since the peripheral members have been heated up to a predetermined temperature since they have been completely warmed up, heat is not taken away. Since there is no flow of exhaust gas, the actual differential pressure before and after the filter becomes zero. In this manner, the correction value of the differential pressure detecting means can be obtained at a substantially constant predetermined temperature, so that accurate correction can be performed.

In the present invention, the correction means obtains a difference between a value obtained in advance and a detection value of the differential pressure detecting means, and adds the difference to a detection value of the differential pressure detecting means to thereby obtain a differential pressure. The detection means can be corrected.

When the output signal of the differential pressure detecting means has an error of a certain value, the error can be corrected by adding or subtracting the error to the output signal from the differential pressure detecting means. Become.

According to the present invention, there is provided an EGR device for recirculating a part of the exhaust gas to the intake system of the internal combustion engine, and when the EGR gas amount is increased more than usual, the correcting means corrects the differential pressure detecting means. It can be carried out.

If the amount of EGR gas is increased more than usual during operation of the internal combustion engine, most of the exhaust gas is recirculated, so that the amount of exhaust gas flowing through the filter decreases. For this reason, regardless of the amount of PM deposited on the filter, the pressure difference before and after the filter hardly changes.

If the output signal value serving as a reference for the differential pressure detecting means in such a state is obtained in advance, the deviation of the output signal at this time can be obtained, and the output signal can be corrected.

In the present invention, the correcting means corrects the differential pressure detecting means based on a detected value of the differential pressure detecting means when the EGR gas amount is increased more than usual and a normal value obtained in advance. Can be performed.

This makes it possible to correct the output signal from the differential pressure detecting means having the characteristic that the output signal fluctuates at a certain ratio with respect to the differential pressure before and after the filter.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific embodiment of a heat storage device for an internal combustion engine according to the present invention will be described below with reference to the drawings. Here, the case where the heat storage device 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. <First Embodiment> FIG. 1 is a diagram showing a schematic configuration of an engine 1 to which an exhaust gas purification apparatus according to the present invention is applied and an intake / exhaust system thereof.

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

The engine 1 has 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 accumulation chamber (common rail) 4 for accumulating fuel up to a predetermined pressure. The common rail 4 is provided with a common rail pressure sensor 4a that outputs an electric signal corresponding to the pressure of the fuel in the common rail 4.

The common rail 4 communicates with a fuel pump 6 through 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 driving 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. And is connected via a belt 7 to the crank pulley 1a.

In the fuel injection system thus configured, 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 corresponding to the rotating torque.

The fuel discharged from the fuel pump 6 is
The fuel 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 valves 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 via an intake port (not shown). I have.

The intake branch pipe 8 is connected to an intake pipe 9.
This intake pipe 9 is connected to an air cleaner box 10. An air flow meter 11 that outputs an electric signal corresponding to a mass of the intake air flowing through the intake pipe 9 is provided in an intake pipe 9 downstream of the air cleaner box 10 and a temperature corresponding to the temperature of the intake air flowing through the intake pipe 9. And an intake air temperature sensor 12 that outputs a detected electric signal.

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

A compressor housing 15a of a centrifugal supercharger (turbocharger) 15 which operates using heat energy of exhaust gas as a driving source is provided in an intake pipe 9 located between the air flow meter 11 and the intake throttle valve 13. And
An intercooler 16 for cooling intake air, which has been compressed in the compressor housing 15a and has become high temperature, 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 passes through the intake pipe 9 after dust or the like in the intake is removed by an air cleaner (not shown) in the air cleaner box 10. And flows into the compressor housing 15a.

The intake air flowing into the compressor housing 15a is compressed by rotation of a compressor wheel provided in the compressor housing 15a. The intake air that has been compressed in the compressor housing 15a and has become high temperature is cooled by the intercooler 16, and then flows into the intake branch pipe 8 with the flow rate adjusted by the intake throttle valve 13 as necessary. The intake air flowing into the intake branch pipe 8 is distributed to the combustion chamber of each cylinder 2 via 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 the combustion chamber of each cylinder 2 via an exhaust port (not shown).

The exhaust branch pipe 18 is connected to the centrifugal turbocharger 15.
Of 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).

In the middle of the exhaust pipe 19, a storage reduction type N
A particulate filter supporting an Ox catalyst (hereinafter, referred to as a particulate filter)
Simply called a filter. ) 20 are provided. An exhaust temperature sensor 24 that outputs an electric signal corresponding to the temperature of exhaust flowing through the exhaust pipe 19 is attached to the exhaust pipe 19 upstream of the filter 20. Filter 2
One end of an upstream introduction pipe 37a for introducing exhaust gas is connected to the upstream, and one end of a downstream introduction pipe 37b is connected to the downstream of the filter 20. The other ends of the upstream introduction pipe 37a and the downstream introduction pipe 37b are connected to a 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.

The exhaust pipe 1 downstream of the filter 20
An exhaust throttle valve 21 for adjusting the flow rate of exhaust flowing through the exhaust pipe 19 is provided at 9. This exhaust throttle valve 2
The exhaust throttle valve 2 includes a step motor and the like.
An exhaust throttle actuator 22 that drives the opening and closing of the exhaust throttle 1 is mounted.

In the exhaust system configured as described above, the air-fuel mixture (burned gas) burned in each cylinder 2 of the engine 1 is discharged to the exhaust branch 18 via the exhaust port, and then from the exhaust branch 18. Turbine housing 15b of centrifugal turbocharger 15
Flows into The exhaust gas flowing into the turbine housing 15b rotates a turbine wheel rotatably supported in the turbine housing 15b by using thermal energy of the exhaust gas. At this 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 a filter 20 via an exhaust pipe 19, where PM in the exhaust gas is collected and harmful gas components are removed or purified. The exhaust gas from which PM has been collected by the filter 20 and harmful gas components have been removed or purified is discharged to the atmosphere via a muffler after the flow rate is adjusted by an exhaust throttle valve 21 as necessary.

The exhaust branch pipe 18 and the intake branch pipe 8 are connected via an exhaust gas recirculation passage (EGR passage) 25 for recirculating a part of exhaust flowing through the exhaust branch pipe 18 to the intake branch pipe 8. Are in communication. In the middle of the EGR passage 25, a solenoid valve or the like is provided.
A flow control valve (EGR valve) 26 for changing the flow rate of exhaust gas (hereinafter, referred to as EGR gas) flowing through the passage 25 is provided.

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

In the exhaust gas recirculation mechanism configured as described above, when the EGR valve 26 is opened, the EGR passage 25 becomes conductive, and a part of the exhaust gas flowing through the exhaust branch pipe 18 is partially discharged. And is guided to the intake branch pipe 8 through the EGR cooler 27.

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

The EGR gas recirculated from the exhaust branch pipe 18 to the intake branch pipe 8 via the EGR passage 25 is guided to the combustion chamber of each cylinder 2 while mixing with fresh air flowing from the upstream of the intake branch pipe 8. I will

Here, the EGR gas contains an inert gas component such as water (H ₂ O) or carbon dioxide (CO ₂ ) which does not burn itself and has endothermic properties. Therefore, if EGR gas is contained in the air-fuel mixture,
The combustion temperature of the air-fuel mixture is lowered, so that nitrogen oxides (NO
x) is suppressed.

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

Next, the filter 20 will be described.

FIG. 2 shows the structure of the filter 20. In addition,
2A shows a cross section of the filter 20 in the horizontal direction, and FIG. 2B shows a cross section of the filter 20 in the vertical direction. As shown in FIGS. 2A and 2B, the filter 20 is a so-called wall flow type having a plurality of exhaust passages 50 and 51 extending in parallel with each other. These exhaust passages are constituted by 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. Note that FIG.
In FIG. 5A, the hatched portion indicates the plug 53. Accordingly, the exhaust inflow passages 50 and the exhaust outflow passages 51 are alternately arranged with the thin partition walls 54 interposed therebetween. In other words, the exhaust inflow passage 50 and the exhaust outflow passage 51 are arranged such that each exhaust inflow passage 50 is surrounded by the four exhaust outflow passages 51 and each exhaust outflow passage 51 is surrounded by the four exhaust inflow passages 50.

The filter 20 is formed of a porous material such as cordierite, so that the exhaust gas flowing into the exhaust inflow passage 50 flows through the surrounding partition wall 54 as shown by an arrow in FIG. Then, 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 layer of a carrier made of, for example, alumina is formed on both side surfaces and on the inner wall surface of the pores in the partition wall 54, and the storage reduction type NOx catalyst is carried on this carrier.

Next, the operation of the storage reduction type NOx catalyst carried on the filter 20 according to the present embodiment will be described.

The filter 20 uses, for example, alumina as a carrier, and places potassium (K), sodium (N) on the carrier.
a) Alkali metals such as lithium (Li) or cesium (Cs), alkaline earths such as barium (Ba) or calcium (Ca), and rare earths such as lanthanum (La) or yttrium (Y). And a noble metal such as platinum (Pt). In the present embodiment, a description will be given of an example of an occlusion reduction type NOx catalyst constituted by supporting barium (Ba) and platinum (Pt) on a carrier made of alumina.

The NOx catalyst having the above-described structure is used for the Nx catalyst.
When the oxygen concentration of the exhaust gas flowing into the Ox catalyst is high, nitrogen oxides (NOx) in the exhaust gas are absorbed.

On the other hand, when the oxygen concentration of the exhaust gas flowing into the NOx catalyst decreases, the NOx catalyst releases the absorbed nitrogen oxides (NOx). At this time, if reducing components such as hydrocarbons (HC) and carbon monoxide (CO) are present in the exhaust gas, the NOx catalyst converts the nitrogen oxides (NOx) released from the NOx catalyst into nitrogen (N ₂ ) can be reduced.

When the engine 1 is operating 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.
The nitrogen oxides (NOx) contained in the exhaust gas are absorbed by the NOx catalyst. However, if the lean burn operation of the engine 1 is continued for a long time, the NOx absorption capacity of the NOx catalyst is saturated, and Nitrogen oxides (NOx) are released to the atmosphere without being removed by the NOx catalyst.

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

Accordingly, when the engine 1 is operating in the lean burn mode, the oxygen concentration in the exhaust gas 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, thereby increasing the NOx concentration. It is necessary to release and reduce nitrogen oxides (NOx) absorbed by the catalyst.

The exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment includes a reducing agent supply mechanism for adding fuel (light oil) as a reducing agent to exhaust gas flowing through an exhaust pipe 19 upstream of a filter 20. By adding fuel from the 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 on the cylinder head of the engine 1 so that its injection hole faces the inside of the exhaust branch pipe 18, and the valve is opened by a signal from the ECU 35 to inject fuel. A reducing agent injection valve 28, a reducing agent supply passage 29 for guiding the fuel discharged from the fuel pump 6 to the reducing agent injection valve 28, and a reducing agent supply passage 29.
And a shutoff valve 31 for shutting off the flow of the fuel in the reducing agent supply passage 29.

The reducing agent injection valve 28 has an injection hole of the reducing agent injection valve 28 located downstream of a connection portion of the exhaust branch pipe 18 with the EGR passage 25, and has four branch pipes of the exhaust branch pipe 18. It is preferable that the projection is protruded to the exhaust port of the cylinder 2 closest to the collecting portion and is attached to the cylinder head so as to face the collecting portion of the exhaust branch pipe 18.

This prevents the reducing agent (unburned fuel component) injected from the reducing agent injection valve 28 from flowing into the EGR passage 25, and prevents the reducing agent from being centrifuged in the exhaust branch pipe 18 without stagnation. This is to reach the turbine housing 15b of the supercharger.

In the example shown in FIG. 1, the fourth (# 4) cylinder 2 of the four cylinders 2 of the engine 1 is located closest to the collecting portion of the exhaust branch pipe 18, so that the fourth (# 4) cylinder 2 Although the reducing agent injection valve 28 is attached to the exhaust port of the cylinder 2, when the cylinder 2 other than the # 4 (# 4) cylinder 2 is located closest to the collecting portion of the exhaust branch pipe 18, that cylinder is The reducing agent injection valve 28 is attached to the second exhaust port.

Further, the reducing agent injection valve 28 is designed to penetrate a water jacket (not shown) formed in the cylinder head or to be mounted close to the water jacket, and use cooling water flowing through the water jacket. The reducing agent injection valve 28 may be cooled.

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 path 29. And ECU3
In response to the signal from 5, the reducing agent injection valve 28 is opened, 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 flows into the turbine housing 15b together with the exhaust gas flowing from the upstream of the exhaust branch pipe 18.
The exhaust gas and the reducing agent that have flowed into the turbine housing 15b are stirred and uniformly mixed by the rotation of the turbine wheel to form exhaust gas having a low oxygen concentration.

The exhaust gas having a low oxygen concentration formed as described above flows into the filter 20 from the turbine housing 15b via the exhaust pipe 19, and emits nitrogen oxides (NOx) absorbed by the filter 20. It will be reduced to nitrogen (N ₂ ).

Thereafter, 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.

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 a driver's request.

The ECU 35 includes a common rail pressure sensor 4
a, various sensors such as an air flow meter 11, an intake temperature sensor 12, an intake pipe pressure sensor 17, an exhaust temperature sensor 24, a crank position sensor 33, a water temperature sensor 34, an accelerator opening sensor 36, and a differential pressure sensor 37 are connected via electric wiring. Output signals of the various sensors described above are connected to the ECU.
35.

On the other hand, the fuel injection valve 3, the intake throttle actuator 14, the exhaust throttle actuator 22, the EGR valve 26, the shut-off valve 31, the differential pressure sensor 37 and the like are connected to the ECU 35 via electric wiring. Each part is ECU3
5 can be controlled.

Here, as shown in FIG. 3, the ECU 35 is connected to a C
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, such as the crank position sensor 33, and converts those output signals to C.
The data is transmitted to the PU 351 and the RAM 353.

The input port 356 is connected to the common rail pressure sensor 4a, the air flow meter 11,
2. Intake pipe pressure sensor 17, exhaust temperature sensor 24, water temperature sensor 34, accelerator opening sensor 36, differential pressure sensor 3.
7, and the like, input through an A / D 355 of a sensor that outputs a signal in an analog signal format, and transmit those output signals to the CPU 351 and the RAM 353.

The output port 357 is connected to the fuel injection valve 3,
The control signal outputted from the CPU 351 is connected to the intake throttle actuator 14, the exhaust throttle actuator 22, the EGR valve 26, the shut-off valve 31 and the like via electric wiring, and transmits the control signal outputted from the CPU 351 to the fuel injection valve 3, the intake throttle actuator 14 and the like. , Exhaust throttle actuator 22, EGR valve 26,
Alternatively, it transmits to 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, and EGR. Application programs such as an EGR control routine for controlling the valve 26, a PM combustion control routine for burning and removing PM trapped in the filter 20, and a correction value calculation routine for correcting an output signal of the differential pressure sensor 37. I remember.

The ROM 352 stores various control maps in addition to the application programs described above. The control map includes, for example, a fuel injection amount control map indicating a relationship between an operating state of the engine 1 and a basic fuel injection amount (basic fuel injection time), and a fuel indicating a relationship between an operating state of the engine 1 and a 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 of the intake throttle valve 13, and the exhaust throttle valve opening showing the relationship between the operating state of the engine 1 and the target opening of the exhaust throttle valve 21. Degree control map, operating state of engine 1 and EGR
An EGR valve opening control map showing a relationship with a target opening of the valve 26, a reducing agent addition amount control map showing a relationship between an operating state of the engine 1 and a target adding amount of a reducing agent (or a target air-fuel ratio of exhaust), It is a reducing agent injection valve control map or the like showing the relationship between the target addition amount of the reducing agent and the opening time of the reducing agent injection valve 28.

The RAM 353 stores an output signal from each sensor, a calculation result of the CPU 351 and the like. The calculation result is, for example, an engine speed calculated based on a 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 nonvolatile memory capable of storing data even after the operation of the engine 1 is stopped.

The CPU 351 operates in accordance with an application program stored in the ROM 352 to control fuel injection valves, intake throttle control, exhaust throttle control,
Execute GR control, PM combustion control, and the like.

By the way, in the conventional exhaust gas purifying device, the PM accumulated on the filter is burned and removed by the high-temperature exhaust gas discharged when the engine is operated in the region of high rotation and high load. However, since it takes time to burn PM, if the operating region of the engine deviates from the high-speed high-load region before the PM is completely burned and removed, the PM remains unburned. It is difficult to maintain the operating state of the engine suitable for such PM combustion for a long period of time. Therefore, the unburned PM gradually accumulates on the filter, which causes the filter to be clogged.

One method of effectively removing PM remaining after burning is to add fuel to exhaust gas.

Next, PM combustion control by adding fuel to exhaust gas will be described.

In the PM combustion control, the CPU 351 executes a fuel addition control for adding fuel to the exhaust gas flowing into the filter 20.

First, the CPU 351 reads the output signal of the differential pressure sensor 37, and uses the filter 20 stored in the ROM 352 to show the relationship between the differential pressure and the PM accumulation amount.
The amount of PM deposited on the surface is determined.

The CPU 351 determines whether or not the fuel addition control execution condition is satisfied at predetermined intervals.
Examples of the fuel addition control execution conditions include, for example, whether the filter 20 is in an active state, and whether the output signal value (exhaust temperature) of the exhaust temperature sensor 24 is equal to or lower than a predetermined upper limit. can do.

When it is determined that the above-described fuel addition control execution condition is satisfied, the CPU 351 controls the reducing agent injection valve 28 to inject fuel as a reducing agent from the reducing agent injection valve 28. Thereby, the air-fuel ratio of the exhaust gas flowing into the filter 20 is temporarily set to a predetermined target air-fuel ratio.

More specifically, the CPU 351
Engine speed, accelerator opening sensor 3 stored in
6 output signal (accelerator opening), air flow meter 11
The output signal value (intake air amount), fuel injection amount, and the like are read out. Further, the CPU 351 accesses the reducing agent addition amount control map of the ROM 352 using the engine speed, the accelerator opening, the intake air amount, and the fuel injection amount as parameters, and sets the exhaust air-fuel ratio to a preset target air-fuel ratio. Then, the addition amount (target addition amount) of the reducing agent necessary for the calculation is calculated.

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

When the target valve 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 valve opening time has elapsed since the opening of the reducing agent injection valve 28.

When the reducing agent injection valve 28 is opened for the normal target valve opening time, the fuel of the normal target addition amount 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 flowing from the upstream of the exhaust branch pipe 18 to form an air-fuel mixture having a target air-fuel ratio and flows into the filter 20.

As a result, the oxygen concentration of the exhaust gas flowing into the filter 20 changes in a relatively short cycle. Then, the active oxygen is released by the fuel flowing into the filter 20, whereby the PM is transformed into a substance easily oxidized, and the oxidizable amount per unit time is improved. In addition, the addition of fuel removes oxygen poisoning of the catalyst and increases the activity of the catalyst, so that active oxygen is easily released. Then, the PM is oxidized and combusted and removed by the active oxygen.

In the engine 1 having the conventional filter,
In this way, it was possible to remove PM by oxidizing and burning it. However, there is an individual difference in the output signal of the differential pressure sensor 37, and an error may occur in the output signal due to deterioration over time or the like. Therefore, there is a possibility that the timing of performing the PM combustion control is shifted. If the PM removal is delayed, filter 2
0 The pressure of the exhaust gas upstream increases, the output decreases and the filter 2
0 may be damaged. On the other hand, if fuel is added while the amount of PM deposited is small, the number of times of addition increases, leading to deterioration of fuel efficiency.

FIG. 5 is a diagram showing one form of the output signal value when the differential pressure sensor 37 has an error.
In this case, the output value is V0 if no error occurs in the differential pressure sensor 37 when the actual differential pressure is 0, but becomes V1 if an error occurs. Then, even when the actual differential pressure is other than 0, the differential pressure sensor 37 having an error always shows a value higher by (V1-V0).

Therefore, in the present embodiment, a correction value for correcting the output signal of the differential pressure sensor 37 is obtained when the engine is stopped after the complete warm-up, and thereafter, based on the corrected value of the output signal of the differential pressure sensor 37, The amount of PM deposited on the filter 20 is estimated. Here, the complete warm-up means when the temperature of the cooling water circulating in the engine 1 reaches a predetermined temperature or when the differential pressure sensor 3
It may be the time when the temperature of 7 reaches a predetermined temperature. Furthermore,
The reason why the engine is stopped is that the differential pressure across the filter 20 becomes 0 while the engine is stopped, so that the reference becomes clear and the correction value can be easily obtained. On the other hand, even when the engine is operating in a steady state, it is difficult to correct the temperature and pressure of the exhaust gas due to fluctuations.

Next, the differential pressure sensor 37 according to the present embodiment
The method of correcting the output signal of the above will be described.

FIG. 4 is a flowchart showing a flow for obtaining a correction value for correcting the output signal of the differential pressure sensor 37.

The flow for obtaining the correction value shown in FIG. 4 is performed at predetermined time intervals.

In step S101, it is determined whether or not the engine 1 is completely warmed up. The CPU 351 sets R
Access the AM 353 and read the output signal of the water temperature sensor 34. If this value is equal to or higher than the previously determined cooling water temperature in the fully warmed-up state, the CPU 351 determines that it is in the completely warmed-up state and proceeds to step S102. On the other hand, if a negative determination is made, this routine is temporarily terminated without performing the subsequent processing.

In step S102, it is determined whether or not the engine 1 is stopped. The CPU 351 is a RAM
353 is accessed, and the output signal of the crank position sensor 33 is read. If the engine speed Ne obtained from the output signal of the crank position sensor 33 is 0, it is determined that the engine 1 is in the stopped state, and step S103 is performed.
Proceed to. On the other hand, if a negative determination is made, this routine is temporarily terminated without performing the subsequent processing.

In step S103, a timer for detecting the stop time of the engine 1 is started.

In step S104, it is determined whether or not the count time C1 of the timer is longer than a predetermined time Cth.

FIG. 6 is a time chart showing the differential pressure sensor and the engine speed immediately after the engine 1 is stopped. Key switch during engine 1 operation (not shown)
Is rotated to the OFF side, the number of revolutions of the engine 1 becomes 0, but the output signal of the differential pressure sensor 37 fluctuates greatly in this process. This is because the exhaust pipe 1
This is because the pulsation of the exhaust gas during operation of the engine 1 remains in the nozzle 9. Therefore, a correction value of the output signal of the differential pressure sensor 37 is obtained after a lapse of a predetermined time Cth (for example, one second). If a positive determination is made in step S104,
Proceeding to step S105, if a negative determination is made, this routine is terminated once without performing subsequent processing.

In step S105, the output signal V1 of the differential pressure sensor 37 is read.

In step S106, a correction value of the output signal of the differential pressure sensor 37 is obtained. When the engine 1 is stopped, the differential pressure across the filter 20 obtained from the output signal of the differential pressure sensor 37 should be zero. CPU 351
Reads from the ROM 352 the reference output signal value V0 of the differential pressure sensor 37 when the actual differential pressure obtained in advance is 0. The CPU 351 calculates a deviation between the reference output signal value V0 and the output signal V1 of the differential pressure sensor 37, and stores this value as a correction value in the backup RAM 354.

The correction value V obtained in this way is added to the output signal of the differential pressure sensor 37 thereafter, so that the differential pressure sensor 37 can be corrected. That is, the differential pressure Vr after the correction with respect to the output signal V of the differential pressure sensor 37 can be obtained by the following equation.

Vr = V− (V0−V1) Here, in the conventional correction method, the state of the engine at the time of obtaining the correction value has not been considered. Since the output signal of the differential pressure sensor fluctuates depending on the ambient temperature around the differential pressure sensor, the correction value may be erroneously learned when the ambient temperature around the differential pressure sensor when the correction value is obtained is low.

In this respect, in this embodiment, since the correction value is obtained based on the output signal of the differential pressure sensor immediately after the engine is completely warmed up and immediately after the engine is stopped, the ambient temperature around the differential pressure sensor is substantially constant at a predetermined temperature. In this case, a correction value can be obtained, so that accurate correction can be performed.

The correction of the present embodiment is effective when a certain amount of error occurs in the output signal of the differential pressure sensor regardless of the magnitude of the differential pressure. <Second Embodiment> In the present embodiment, the correction performed when a certain amount of error occurs in the output signal of the differential pressure sensor 37 regardless of the magnitude of the differential pressure performed in the first embodiment. in addition,
Correction is also performed when an error of a fixed ratio occurs in the output signal due to the magnitude of the differential pressure.

The correction of the differential pressure sensor 37 in the present embodiment is performed at the time of low-temperature combustion in which the EGR gas is recirculated in a larger amount than usual.

Here, low-temperature combustion will be described.

Conventionally, EG has been used to suppress the generation of NOx.
R has been used. Since the EGR gas has a relatively high specific heat ratio and can absorb a large amount of heat, the combustion temperature in the cylinder 2 decreases as the proportion of the EGR gas in the intake air increases. NOx when combustion temperature drops
The emission amount of NOx also decreases, so that the higher the EGR gas ratio, the lower the amount of NOx emission.

However, when the EGR gas ratio is increased, the amount of soot generation starts to increase rapidly at a certain ratio or more. Normal EGR control has a lower EG than soot starts to increase sharply.
It is performed at the R gas ratio.

However, when the EGR gas ratio is further increased, the soot increases rapidly as described above. However, a peak exists in the amount of generated soot, and the EGR gas ratio further exceeds this peak. With a higher level, the soot will then start to drop sharply and eventually hardly occur.

This is because when the temperature of the fuel and its surrounding gas during combustion in the combustion chamber is lower than a certain temperature, the growth of hydrocarbons (HC) stops at a stage before reaching soot,
This is because when the temperature of the fuel and its surrounding gas becomes higher than a certain temperature, hydrocarbons (HC) grow into soot at a stretch.

Therefore, if the combustion during combustion in the combustion chamber and the temperature of the surrounding gas are suppressed below the temperature at which the growth of hydrocarbons (HC) stops halfway, no soot is generated.
In this case, the endothermic effect of the gas around the fuel when the fuel burns greatly affects the temperature of the fuel and the gas around the fuel, and the amount of heat absorbed by the gas around the fuel, that is, EGR, depends on the amount of heat generated during the combustion of the fuel. By adjusting the gas ratio, it is possible to suppress the generation of soot.

When performing low-temperature combustion, the EGR gas ratio is as follows:
ROM that is obtained in advance by experiments etc. and mapped
352. EGR based on this map
Perform feedback control.

On the other hand, the hydrocarbons (HC) whose growth has stopped halfway before reaching soot are converted to NOx carried on the filter 20.
Combustion purification can be performed using an absorbent or the like.

As described above, in low-temperature combustion, hydrocarbons (HC) whose growth has stopped halfway before reaching soot are basically purified by a NOx absorbent or the like. Therefore NOx
When the absorbent is not activated, the hydrocarbon (H
Since C) is released into the atmosphere without being purified, it is difficult to use low-temperature combustion.

Further, the fuel and the surrounding gas temperature during combustion in the cylinder 2 can be controlled to be lower than the temperature at which the growth of hydrocarbons (HC) stops halfway, because the engine load with a small calorific value due to combustion is relatively small. Is low.

Therefore, in this embodiment, the low-temperature combustion control is performed when the engine 1 is operated at a low rotation speed and a low load and the temperature is within the temperature window of the NOx storage reduction catalyst supported on the filter 20. Is performed.

Whether the temperature is within the temperature window region can be determined based on the output signal of the exhaust gas temperature sensor 24.

As described above, in low-temperature combustion, hydrocarbon (HC) as a reducing agent can be supplied to the NOx storage reduction catalyst while suppressing emission of PM represented by soot, and NOx can be reduced and purified. .

When such low-temperature combustion control is being performed, most of the exhaust gas is recirculated to the intake branch pipe 8, so that
The amount of exhaust passing through the filter 20 is reduced. Therefore, even if PM accumulates on the filter 20, the actual differential pressure has a predetermined value. This value may be obtained in advance by an experiment. As described above, in the present embodiment, the engine 1
Pressure sensor 3 during idle and low-temperature combustion control
7 is corrected.

Here, FIG. 7 is a diagram showing one form of the output signal value when the differential pressure sensor 37 has an error.
Assuming that the reference differential pressure during low-temperature combustion is dpi, the differential pressure sensor 3
7 has no error, the output signal value is V2. On the other hand, the output signal when the differential pressure sensor 37 has an error is, for example, V3. The output signal Va of the differential pressure sensor 37 includes the above-described error of a constant amount that does not depend on the magnitude of the differential pressure and an error that occurs at a constant ratio depending on the magnitude of the differential pressure. Also, when the pressure difference across the filter 20 actually becomes zero,
That is, the output signal of the differential pressure sensor 37 when the engine 1 is stopped is V0 and V1 when there is no error and when there is an error.

From this figure, it can be seen that the corrected output value Vr of the differential pressure sensor 37 can be obtained by the following equation.

Vr = Va− (V1−V0) − ｛V3−V
1− (V2−V0)｝ · (Va−V1) / (V3−V
1) Next, a method for correcting the output signal of the differential pressure sensor 37 according to the present embodiment will be described.

FIG. 8 is a flowchart showing a flow for obtaining a correction value for correcting the output signal of the differential pressure sensor 37.

The flow for obtaining the correction values shown in FIG. 8 is performed at predetermined time intervals.

In step S201, it is determined whether or not the engine 1 is completely warmed up. The CPU 351 sets R
Access the AM 353 and read the output signal of the water temperature sensor 34. If this value is equal to or higher than the cooling water temperature at the time of the fully warmed-up state obtained in advance, the CPU 351 determines that it is in the completely warmed up state and proceeds to step S202. On the other hand, if a negative determination is made, this routine is temporarily terminated without performing the subsequent processing.

In step S202, it is determined whether or not the engine 1 is in an idle state. The CPU 351 sets R
Access AM353 and crank position sensor 33
Is read out. Crank position sensor 33
If the engine speed Ne obtained from the output signal is the idling speed previously obtained, it is determined that the engine 1 is in the idle state, and the process proceeds to step S203. On the other hand, if a negative determination is made, this routine is temporarily terminated without performing the subsequent processing. In the present embodiment, low-temperature combustion control is performed at the time of idling.

In step S203, a timer for detecting the idle time of the engine 1 is started.

In the step S204, it is determined whether or not the count time C1 of the timer is longer than a predetermined time Cth. Here, immediately after the engine 1 enters the idle state, the output signal of the differential pressure sensor 37 is not stable because the exhaust gas pulsation during the operation of the engine 1 remains in the exhaust pipe 19. Therefore, after a lapse of a predetermined time Cth, the differential pressure sensor 3
7 so as to obtain the correction value of the output signal of step S7.
A determination is made in step 4. When an affirmative determination is made, the process proceeds to step S205, and when a negative determination is made, this routine is temporarily terminated without performing the subsequent processing.

In the step S205, the output signal V3 of the differential pressure sensor 37 is read.

In step S206, a corrected value Vr of the output signal of the differential pressure sensor 37 is determined.

Here, in the conventional correction method, the state of the engine when obtaining the correction value is not taken into consideration. Since the output signal of the differential pressure sensor fluctuates depending on the ambient temperature around the differential pressure sensor, the correction value may be erroneously learned when the ambient temperature around the differential pressure sensor when the correction value is obtained is low.

In this regard, in the present embodiment, since the correction value is obtained based on the output signal of the differential pressure sensor during the execution of the low-temperature combustion control after the complete warm-up and at the time of idling, the ambient temperature around the differential pressure sensor is reduced. Since the correction value can be obtained when the differential pressure across the filter 20 is a predetermined value at a substantially constant predetermined temperature, accurate correction can be performed.

In this way, in addition to the correction when a certain amount of error occurs in the output signal of the differential pressure sensor 37 irrespective of the magnitude of the differential pressure, a fixed ratio of the output signal depends on the magnitude of the differential pressure. Correction when an error occurs can also be performed.

[0139]

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the correction value of the output signal can be obtained when the output fluctuation of the differential pressure means is small. It is possible to accurately detect the amount of PM that has occurred.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing both an engine to which an exhaust gas purification device 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 horizontal cross section of a particulate filter. (B) is a figure which shows the longitudinal direction cross section of a particulate filter.

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

FIG. 4 is a flowchart illustrating a flow when obtaining a correction value for correcting an output signal of the differential pressure sensor according to the first embodiment of the present invention.

FIG. 5 is a diagram showing one mode of an output signal value when an error occurs in a differential pressure sensor.

FIG. 6 is a time chart showing the differential pressure sensor and the engine speed immediately after the engine is stopped.

FIG. 7 is a diagram illustrating an example of an output signal value when an error occurs in the differential pressure sensor.

FIG. 8 is a flowchart illustrating a flow when obtaining a correction value for correcting an output signal of a differential pressure sensor according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION 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: Reducing agent supply path 31: Shutoff valve 33 · · · Crank position sensor 34 · · · water temperature sensor 35 · · · ECU 351 · · · CPU 352 · · · ROM 353 · · · RAM 354 · · · backup RAM 36 · · · accelerator opening sensor 37 · · · differential pressure sensor Sa 37a ·· upstream inlet tube 37b ·· downstream side inlet tube

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) F01N 3/02 F01N 3/02 321D 3/28 301 3/28 301C F02D 21/08 301 F02D 21/08 301B 301D 301H 43/00 301 43/00 301T 301W F02M 25/07 570 F02M 25/07 570D 570J F term (reference) 3G062 AA01 ED08 GA01 GA02 GA04 GA06 GA08 GA09 GA21 3G084 AA01 BA00 BA05 BA13 BA19 BA20 BA24 CA07 DA00 FA02 FA07 FA10 FA11 FA20 FA27 FA37 FA38 3G090 AA03 BA01 CA01 CB21 DA03 DA04 DA12 DA18 DB04 EA05 EA06 EA07 EA08 3G091 AA10 AA11 AA18 AB05 AB06 AB13 BA01 CA18 CA26 CB07 DB06 EA01 EA05 EA07 GB02 EB08 GBW 3G092 AA02 AA17 AA18 AB03 BB01 DB03 DC03 DC09 DC10 DC12 D C15 DF08 DG08 EA08 EA17 EA28 EB03 EB06 FA17 FA18 FA37 GA10 HA01Z HA04Z HA05Z HA06X HB03Z HD01Z HD07X HD08Z HD09Z HE03Z HE08Z

Claims (4)

[Claims] 1. A filter capable of capturing particulates in exhaust gas of an internal combustion engine for a period of time, differential pressure detecting means for detecting a differential pressure across the filter from the pressure of exhaust gas before and after the filter, And a correcting means for correcting the detection value of the differential pressure detecting means while the engine is stopped after the engine has stopped. 2. The differential pressure detecting means according to claim 1, wherein said correcting means obtains a deviation between a predetermined value and a detected value of said differential pressure detecting means, and adds the deviation to a detected value of said differential pressure detecting means. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the correction is performed. 3. An EGR device for recirculating a part of exhaust gas into an intake system of an internal combustion engine, wherein the correcting means corrects the differential pressure detecting means when the EGR gas amount is increased more than usual. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1 or 2, wherein: 4. The correction means corrects the differential pressure detection means based on a detected value of the differential pressure detection means when the EGR gas amount is increased more than usual and a normal value obtained in advance. The exhaust gas purifying apparatus for an internal combustion engine according to claim 3, wherein: