JP2003214146A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect an absolute pressure of exhaust gas, in an exhaust emission control device for internal combustion engine provided with a means for detecting a differential pressure between upstream and downstream sides of the collecting mechanism arranged to an exhaust system of the internal combustion engine. <P>SOLUTION: This exhaust emission control device comprises: the collecting mechanism 29 arranged to an exhaust passage of the internal combustion engine; and a differential pressure detecting mechanism 39 introducing upstream and downstream exhaust gas from the collecting mechanism 29 to detect the differential pressure of them. This device is constituted such that any one of the exhaust gas and atmospheric air present more downstream than the collecting mechanism 29 is selectively introduced to the differential pressure detecting mechanism 39, and when there is no need for detecting the differential pressure between upstream and downstream sides of the collecting mechanism 29, the atmospheric air is introduced into the differential pressure detecting mechanism 39. Accordingly, a pressure difference between the exhaust gas and atmospheric air present more upstream than the collecting mechanism 29, that is, the absolute pressure of the exhaust gas, is detected. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a technique for purifying exhaust gas from an internal combustion engine.

[0002]

2. Description of the Related Art In recent years, internal combustion engines mounted in automobiles and the like have been required to have improved exhaust emissions. Particularly, in compression ignition type internal combustion engines (diesel engines) using light oil as fuel, carbon monoxide (CO ), Hydrocarbons (HC), nitrogen oxides (NOx), etc., as well as soot and S contained in exhaust gas.
Fine particles such as OF (Soluble Organic Fraction) (PM:
Particulate Matter) is required to be purified or removed.

Therefore, a particulate filter made of a porous base material having a large number of pores having a very small cross-sectional area is arranged in the exhaust passage of the diesel engine, and the exhaust gas of the diesel engine is placed in the pores of the particulate filter. A method of collecting PM in exhaust gas by flowing it is known.

However, if the PM trapping amount of the particulate filter is excessively increased, the exhaust resistance of the particulate may be increased, and the back pressure acting on the internal combustion engine may be excessively increased accordingly. It is necessary to purify the PM trapped in the fill at an appropriate time to regenerate the PM trapping ability of the particulate filter.

In response to such a demand, in the past, Japanese Patent Laid-Open No.
As described in Japanese Patent Application Publication No. 001-173498,
A differential pressure sensor that detects the differential pressure across the particulate filter is provided, and when the output signal value of the differential pressure sensor exceeds a predetermined value, if the amount of fine particles deposited on the particulate filter exceeds the maximum allowable value. Techniques for determining have been proposed.

[0006]

On the other hand, in recent diesel engines, an oxygen concentration sensor (air-fuel ratio sensor) is provided in the exhaust passage of the diesel engine so that the oxygen concentration in the exhaust gas becomes a desired concentration. A technique for controlling the operating state of the vehicle is known.

By the way, since the oxygen concentration sensor has an output characteristic depending on the pressure, it is necessary to correct the output signal value of the oxygen concentration sensor according to the absolute pressure of the exhaust gas in order to accurately detect the oxygen concentration of the exhaust gas. is there.

However, in the above-mentioned conventional technique,
Since only the differential pressure sensor for detecting the differential pressure across the particulate filter is provided and the absolute pressure of the exhaust cannot be detected, the oxygen concentration of the exhaust cannot be accurately detected.

The present invention has been made in view of the above problems, and exhaust gas purification of an internal combustion engine provided with means for detecting the differential pressure across the trapping mechanism provided in the exhaust system of the internal combustion engine. An object of the present invention is to provide a technique capable of detecting an absolute pressure of exhaust gas in an apparatus.

[0010]

The present invention adopts the following means in order to solve the above problems.

That is, the exhaust gas purifying apparatus for an internal combustion engine according to the present invention is provided in the exhaust passage of the internal combustion engine, and has a trapping mechanism for trapping particulates in the exhaust gas and an exhaust passage upstream of the trapping mechanism. Introducing exhaust gas and exhaust gas in the exhaust passage downstream of the collection mechanism, a differential pressure detection mechanism for detecting a difference in exhaust pressure between the upstream and downstream of the collection mechanism, and upstream or downstream of the collection mechanism. Atmosphere introduction switching means for selectively introducing either one of the exhaust gas in the exhaust passage and the atmosphere to the differential pressure detection mechanism, and the atmosphere instead of the exhaust gas in the exhaust passage upstream or downstream of the collection mechanism. Absolute pressure detection control means for controlling the atmosphere introduction switching means so as to introduce into the differential pressure detection mechanism and detecting the absolute pressure of the exhaust gas downstream and / or upstream of the collection mechanism.

According to the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine, comprising: a trapping mechanism provided in an exhaust passage of an internal combustion engine; and a differential pressure detecting mechanism for detecting a differential pressure across the trapping mechanism. It is necessary to detect the differential pressure across the trapping mechanism by adopting a configuration in which either the exhaust gas in the exhaust passage upstream or downstream of the trapping mechanism or the atmosphere can be selectively introduced to the detection mechanism. When there is not, by introducing the atmosphere to the differential pressure detection mechanism instead of the exhaust gas upstream or downstream of the collection mechanism, the pressure difference between the atmosphere and the exhaust gas downstream or upstream of the collection mechanism, that is, the absolute pressure of the exhaust gas The greatest feature is to detect.

In such an exhaust gas purification apparatus for an internal combustion engine, the absolute pressure detection control means switches the atmosphere introduction switch so as to introduce the atmosphere into the differential pressure detection mechanism instead of the exhaust gas in the exhaust passage upstream (or downstream) from the collection mechanism. Control means.

In this case, the exhaust gas and the atmosphere in the exhaust passage downstream (or upstream) of the collecting mechanism are introduced into the differential pressure detecting mechanism. As a result, the differential pressure detection mechanism detects the differential pressure between the exhaust pressure and the atmospheric pressure downstream (or upstream) of the collection mechanism, and the differential pressure is downstream (or upstream) of the collection mechanism. It corresponds to the absolute pressure of exhaust gas.

At that time, the atmospheric pressure and the exhaust gas in the exhaust passage downstream (or upstream) of the trapping mechanism are introduced into the differential pressure detecting mechanism, and the pressure difference between the exhaust gas and the atmospheric air in the downstream (or upstream) of the trapping mechanism. And the exhaust pressure in the exhaust passage upstream of the trapping mechanism and the exhaust gas in the exhaust passage downstream of the trapping mechanism are introduced into the differential pressure detection mechanism to detect the exhaust pressure upstream and downstream of the trapping mechanism. If the difference between the two is detected, it is also possible to calculate the absolute pressure of the exhaust gas upstream (or downstream) of the collection mechanism using these two differential pressures.

Therefore, the exhaust gas purification apparatus for an internal combustion engine according to the present invention can selectively introduce either the exhaust gas or the atmosphere in the exhaust passage upstream or downstream of the trapping mechanism with respect to the differential pressure detecting mechanism. With this configuration, it is possible to detect both the absolute pressure of exhaust gas upstream of the collection mechanism and the absolute pressure of exhaust gas downstream of the collection mechanism.

Further, the exhaust gas purifying apparatus for an internal combustion engine according to the present invention has an oxygen concentration sensor provided in the exhaust passage upstream and / or downstream of the trapping mechanism and the absolute pressure of the exhaust gas detected by the absolute pressure detection control means. A correction means for correcting the output signal value of the oxygen concentration sensor based on the above may be further provided.

In this case, since the output signal value of the oxygen concentration sensor is corrected based on the absolute pressure of the exhaust gas, the accurate oxygen concentration can be detected regardless of the exhaust gas pressure. .

On the other hand, in the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, when the oxygen concentration sensors are provided upstream and downstream of the trapping mechanism, the output characteristic of the oxygen concentration sensor is the exhaust pressure. The output difference between the upstream side oxygen concentration sensor and the downstream side oxygen concentration sensor when the internal combustion engine is operating at a lean air-fuel ratio and the oxygen storage capacity of the trapping mechanism is saturated, The clogging of the collection mechanism may be determined based on this.

This is because when the internal combustion engine is operating at a lean air-fuel ratio and the oxygen storage capacity of the trapping mechanism is saturated, the oxygen concentration in the exhaust gas upstream of the trapping mechanism and the oxygen concentration of the exhaust gas downstream of the trapping mechanism. Since the oxygen concentration of the exhaust gas is the same, the difference between the output signal value of the upstream side oxygen concentration sensor and the output signal value of the downstream side oxygen concentration sensor at that time is due to the differential pressure across the trapping mechanism. It is based on the knowledge.

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the collecting mechanism may be a particulate filter carrying an oxidation catalyst and a NOx storage agent.

[0022]

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.

<First Embodiment> First, a first embodiment of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described with reference to FIGS.
It will be described with reference to FIG.

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

The internal combustion engine 1 shown in FIG. 1 is a compression ignition type diesel engine having four cylinders 2. In this internal combustion engine 1, a fuel injection valve 3 for injecting fuel directly into the combustion chamber of each cylinder 2 and a crankshaft that is an engine output shaft of the internal combustion engine 1 are rotated every predetermined angle (for example, 15 °). A crank position sensor 4 that outputs a pulse signal,
A water temperature sensor 5 that outputs an electric signal corresponding to the temperature of cooling water flowing through a water jacket (not shown) of the internal combustion engine 1 is attached.

The above-mentioned fuel injection valve 3 is connected to a pressure accumulating chamber (common rail) 7 via a fuel pipe 6. The common rail 7 is connected to a fuel pump 9 attached to a fuel tank 8 via a fuel pipe 10, and is also connected to a fuel tank 8 via a return pipe 11.

When the fuel pressure in the common rail 7 is lower than a preset maximum pressure, the connection portion of the common rail 7 to which the return pipe 11 is connected is closed to disconnect the conduction between the common rail 7 and the return pipe 11. A pressure adjusting valve 12 is provided which opens when the fuel pressure in the common rail 7 becomes equal to or higher than the maximum pressure and allows the common rail 7 and the return pipe 11 to conduct.

A fuel pressure sensor 13 that outputs an electric signal according to the fuel pressure in the common rail 7 is attached to the common rail 7.

In the fuel system thus constructed, the fuel pump 9 pumps up the fuel stored in the fuel tank 8,
The pumped fuel is pressure-fed to the common rail 7 through the fuel pipe 10. At that time, the fuel discharge amount of the fuel pump 9 is feedback-controlled based on the output signal value of the fuel pressure sensor 13 described above.

The fuel supplied from the fuel pump 9 to the common rail 7 is accumulated until the pressure of the fuel reaches a desired target pressure. The fuel accumulated in the common rail 7 up to the target pressure is distributed to the fuel injection valve 3 of each cylinder 2 via the fuel pipe 6. Each fuel injection valve 3 opens when a drive current is applied, and injects the fuel of the target pressure supplied from the common rail 7 into the combustion chamber of each cylinder 2.

In the above fuel system, the common rail 7
When the fuel pressure inside becomes higher than the maximum pressure, the pressure regulating valve 1
2 opens. In this case, a part of the fuel stored in the common rail 7 is returned to the fuel tank 8 via the return pipe 11, and the fuel pressure in the common rail 7 is reduced.

Next, the internal combustion engine 1 is connected to an intake branch pipe 14 formed so that a plurality of branch pipes merge into one collecting pipe. Each branch pipe of the intake branch pipe 14 communicates with the combustion chamber of each cylinder 2 via an intake port (not shown).
The collecting pipe of the intake branch pipe 14 is connected to the intake pipe 15,
The intake pipe 15 is connected to the air cleaner box 16.

At a portion of the intake pipe 15 immediately downstream of the air cleaner box 16, an air flow meter 17 for outputting an electric signal corresponding to the mass of intake air flowing in the intake pipe 15 and a flow in the intake pipe 15 are provided. An intake air temperature sensor 18 that outputs an electric signal corresponding to the intake air temperature is attached.

A compressor housing 1 of a centrifugal supercharger (turbocharger) 19 which operates by using heat energy of exhaust gas discharged from the internal combustion engine 1 as a drive source is provided at a portion of the intake pipe 15 downstream of the air flow meter 17.
9a is provided.

An intercooler 20 for cooling the fresh air that has been compressed in the compressor housing 19a and has a high temperature is provided at a portion of the intake pipe 15 downstream of the compressor housing 19a.

An intake throttle valve 21 for adjusting the flow rate of intake air flowing through the intake pipe 15 is provided at a portion of the intake pipe 15 downstream of the intercooler 20.
The intake throttle valve 21 is provided with an intake throttle actuator 21a for opening and closing the intake throttle valve 21 and an intake throttle valve opening sensor 21b for outputting an electric signal according to the opening degree of the intake throttle valve 21. Has been.

In the intake system configured as described above, the fresh air flowing into the air cleaner box 16 is cleaned by the air cleaner (not shown) in the air cleaner box 16 to remove dust and dirt from the fresh air, and then the intake pipe 15 Through a compressor housing 19a of the centrifugal supercharger 19.

The fresh air flowing into the compressor housing 19a is compressed by the rotation of the compressor wheel installed in the compressor housing 19a. The fresh air that has been compressed in the compressor housing 19 a and has a high temperature is cooled by the intercooler 20.

The fresh air cooled by the intercooler 20 is guided to the intake branch pipe 14 with the flow rate thereof adjusted by the intake throttle valve 21 if necessary. The fresh air introduced into the intake branch pipe 14 is distributed from the collecting pipe of the intake branch pipe 14 to each branch pipe and is introduced into the combustion chamber of each cylinder 2.

The fresh air distributed to the combustion chamber of each cylinder 2 is compressed by a piston (not shown) and burned using the fuel injected from the fuel injection valve 3 as an ignition source.

Next, the internal combustion engine 1 is connected to an exhaust branch pipe 24 formed so that a plurality of branch pipes merge into one collecting pipe. Each branch pipe of the exhaust branch pipe 24 communicates with the combustion chamber of each cylinder 2 through an exhaust port (not shown).
The collecting pipe of the exhaust branch pipe 24 is connected to the exhaust pipe 25a via the turbine housing 19b of the centrifugal supercharger 19.

The portion of the exhaust branch pipe 24 located immediately upstream of the turbine housing 19b and the exhaust pipe 2
5a is connected to a portion located immediately downstream of the turbine housing 19b by a turbine bypass passage 26 that bypasses the turbine housing 19b.

The turbine bypass passage 26 is provided with a wastegate valve 27 having a valve body 27a for opening and closing the turbine bypass passage 26 and an actuator 27b for driving the valve body 27a to open and close.

The actuator 27b is connected to the intake pipe 15 located immediately downstream of the compressor housing 19a via an operating pressure passage 28, and the pressure of fresh air flowing in the intake pipe 15 immediately downstream of the compressor housing 19a, In other words, the valve body 27a is opened and closed by utilizing the pressure (supercharging pressure) of the fresh air compressed in the compressor housing 19a.

Specifically, the actuator 27b holds the valve body 27a in the valve closed position when a pressure lower than a predetermined pressure is applied from the intake pipe 15 through the operating pressure passage 28, and the actuator 27b receives the intake pipe 15 from the intake pipe 15. When a pressure higher than a predetermined pressure is applied through the operating pressure passage 28, the valve body 27a is driven to open.

That is, when the supercharging pressure of the intake air by the centrifugal supercharger 19 reaches or exceeds a predetermined pressure, the actuator 27b
The valve body 27a is opened to bring the turbine bypass passage 26 into conduction, and the flow rate of the exhaust gas flowing into the turbine housing 19b is reduced so that the supercharging pressure does not exceed the predetermined pressure.

The exhaust pipe 25a is connected to an exhaust gas purification mechanism 29 for purifying harmful gas components in exhaust gas, particularly particulates (PM: Particulate Matter). The exhaust purification mechanism 29 is connected to the exhaust pipe 25b, and the exhaust pipe 25b
Is connected downstream to a muffler (not shown). Hereinafter, the exhaust pipe 25a upstream of the exhaust purification mechanism 29 will be referred to as an upstream exhaust pipe 25a, and the exhaust pipe 25b downstream of the exhaust purification mechanism 29 will be referred to as a downstream exhaust pipe 25b.

The exhaust gas purification mechanism 29 is an embodiment of the trapping mechanism according to the present invention, and includes a DPF (Diesel Particulate Filter) for trapping PM contained in the exhaust gas and a wall made of a porous base material. DPNR (Diesel Particulate NOx) in which an oxidation catalyst typified by platinum (Pt) and a NOx storage agent typified by potassium (K) or cesium (Cs) are carried on a flow type particulate filter.
Reduction) catalyst. In the following, the exhaust gas purification mechanism 29 will be referred to as the particulate filter 29.
Shall be called.

An oxygen concentration sensor 38 that outputs an electric signal corresponding to the oxygen concentration of the exhaust gas flowing through the upstream exhaust pipe 25a is attached to the upstream exhaust pipe 25a. The upstream side exhaust pipe 25a and the downstream side exhaust pipe 25b
A differential pressure sensor 39 that outputs an electric signal corresponding to the differential pressure between the exhaust pressure in the upstream exhaust pipe 25a and the exhaust pressure in the downstream exhaust pipe 25b is attached to the.

As shown in FIG. 2, the differential pressure sensor 39 has two gas introducing portions 391 and 392, and corresponds to the pressure difference between the two gases introduced into the two gas introducing portions 391 and 392. The sensor main body 390 which outputs an electric signal is provided. Hereinafter, the gas introducing unit 391 is referred to as a first gas introducing unit 391, and the gas introducing unit 392 is referred to as a second gas introducing unit 392.

The first gas introducing section 391 communicates with the upstream exhaust pipe 25a through the first gas introducing tube 393, and the second gas introducing section 392 connects the second gas introducing section 392 with the second gas introducing section 392. It is connected to the three-way switching valve 395 via the introduction pipe 394.

The three-way switching valve 395 has the above-mentioned second
In addition to the gas introduction pipe 394, the exhaust introduction pipe 396 and the atmosphere introduction pipe 397 are connected, and the three-way switching valve 395 selectively selects one of the exhaust introduction pipe 396 and the atmosphere introduction pipe 397 for the second It is electrically connected to the gas introduction pipe 394. The three-way switching valve 395 is composed of, for example, a vacuum switching valve (VSV).

The above-mentioned exhaust introduction pipe 396 is connected to the above-mentioned downstream side exhaust pipe 25b, and is connected to the above-mentioned atmosphere introduction pipe 39.
7 is open to the atmosphere.

In the differential pressure sensor 39 constructed as described above, when the three-way switching valve 395 connects the second gas introduction pipe 394 and the exhaust introduction pipe 396, as shown in FIG. Exhaust gas pressure Pup upstream of the particulate filter 29 is applied to the first gas inlet 391 of the sensor body 390, and exhaust gas pressure Pdown downstream of the particulate filter 29 is the second gas of the sensor body 390. It will be applied to the introduction part 392.

In this case, the sensor main body 390 is arranged so that the pressure of the exhaust gas upstream of the particulate filter 29: P
An electric signal corresponding to the differential pressure between up and the exhaust pressure downstream of the particulate filter 29: Pdown (hereinafter referred to as the differential pressure across the filter): ΔP (= Pup-Pdown) is output.

When the three-way switching valve 395 connects the second gas introduction pipe 394 and the atmosphere introduction pipe 397,
As shown in FIG. 4, the particulate filter 29
Exhaust pressure upstream: Pup is the sensor body 390
Is applied to the first gas introduction part 391 of the sensor main body 390 and the atmospheric pressure Pa is applied to the second gas introduction part 392 of the sensor main body 390.
Will be applied to.

In this case, the sensor main body 390 is arranged so that the pressure of the exhaust gas upstream of the particulate filter 29: P
An electric signal corresponding to a pressure difference (= Pup-Pa) between up and atmospheric pressure: Pa, in other words, a particulate filter 29.
An electric signal corresponding to the absolute pressure of exhaust gas on the upstream side is output.

As described above, according to the differential pressure sensor 39 of the present embodiment, it is possible to detect the absolute pressure of the exhaust gas in the upstream exhaust pipe 25a only by mounting the three-way switching valve on the existing differential pressure sensor. Becomes

Returning now to FIG. 1, the downstream side exhaust pipe 25
An exhaust throttle valve 33 for adjusting the flow rate of the exhaust gas flowing in the downstream exhaust pipe 25b is attached to b. An exhaust throttle actuator 34 that opens and closes the exhaust throttle valve 33 is attached to the exhaust throttle valve 33.

In the exhaust system configured as described above, the burnt gas burned in the combustion chamber of each cylinder 2 of the internal combustion engine 1 is discharged to the exhaust branch pipe 24 through the exhaust port of each cylinder 2, and then Each branch pipe of the exhaust branch pipe 24 flows into the turbine housing 19b of the centrifugal supercharger 19 through the collecting pipe.

Turbine housing 19 of centrifugal supercharger 19
When the exhaust gas flows into b, the thermal energy of the exhaust gas is converted into the rotational energy of the turbine wheel rotatably supported in the turbine housing 19b. The rotational energy of the turbine wheel is transmitted to the compressor wheel of the compressor housing 19a described above, and the compressor wheel compresses fresh air by the rotational energy transmitted from the turbine wheel.

At this time, when the pressure (supercharging pressure) of the fresh air compressed in the compressor housing 19a rises to a predetermined pressure or higher, the supercharging pressure passes through the working pressure passage 28 and the actuator 27b of the wastegate valve 27. The actuator 27b drives the valve body 27a to open.

When the valve body 27a of the wastegate valve 27 is opened, a part of the exhaust gas flowing through the exhaust branch pipe 24 flows into the upstream side exhaust pipe 25a through the turbine bypass passage 26, so that it flows into the turbine housing 19b. The flow rate of the generated exhaust gas is reduced, and the thermal energy of the exhaust gas flowing into the turbine housing 19b, in other words, the thermal energy converted into the rotational energy of the turbine wheel in the turbine housing 19b is reduced. As a result, the rotational energy transmitted from the turbine wheel to the compressor wheel is reduced, and an excessive increase in boost pressure is suppressed.

The exhaust gas discharged from the turbine housing 19b to the upstream exhaust pipe 25a and the exhaust gas guided from the turbine bypass passage 26 to the upstream exhaust pipe 25a are
From the upstream side exhaust pipe 25a to the particulate filter 29
Flow into. The exhaust gas that has flowed into the particulate filter 29 is discharged to the downstream exhaust pipe 25b after the particulates such as soot contained in the exhaust gas have been purified or removed, and is discharged into the atmosphere through the downstream exhaust pipe 25b.

An exhaust gas recirculation passage (EGR passage) 100 is connected to the exhaust branch pipe 24, and the EGR passage 10
0 is connected to the intake branch pipe 14. The EGR
An EGR valve 101 that opens and closes an opening end of the EGR passage 100 in the intake branch pipe 14 is provided at a connection portion between the passage 100 and the intake branch pipe 14. The EGR
The valve 101 is composed of a solenoid valve or the like, and the opening degree can be changed according to the magnitude of applied power.

In the middle of the EGR passage 100, the EG
An EGR cooler 103 for cooling exhaust gas (hereinafter, referred to as EGR gas) flowing in the R passage 100 is provided.

Two pipes 104 and 105 are connected to the EGR cooler 103, and these two pipes 104 and 105 are connected to each other.
Reference numeral 105 is connected to a radiator 106 for radiating the heat of the cooling water of the internal combustion engine 1 to the atmosphere.

One of the two pipes 104 and 105 is a pipe for guiding a part of the cooling water cooled in the radiator 106 to the EGR cooler 103, and the other pipe 104. 105 is the E
It is a pipe for guiding the cooling water after circulating in the GR cooler 103 to the radiator 106. In the following, the pipe 104 will be referred to as a cooling water introduction pipe 104, and the pipe 1
05 is referred to as a cooling water outlet pipe 105.

An on-off valve 107 for opening and closing the flow path in the cooling water outlet pipe 105 is provided in the middle of the cooling water outlet pipe 105. The on-off valve 107 is composed of an electromagnetic drive valve that opens when drive power is applied.

The exhaust gas recirculation mechanism (E
(GR mechanism), when the EGR valve 101 is opened, EGR
The passage 100 becomes conductive, and a part of the exhaust gas flowing in the exhaust branch pipe 24 passes through the EGR passage 100 and the intake branch pipe 1
Guided to 4.

At this time, if the on-off valve 107 is in the open state, the circulation path connecting the radiator 106, the cooling water introducing pipe 104, the EGR cooler 103 and the cooling water outlet pipe 105 becomes conductive, and the radiator 106 cools. The cooling water circulates in the EGR cooler 103. as a result,
In the EGR cooler 103, heat exchange is performed between the EGR gas flowing in the EGR passage 100 and the cooling water circulating in the EGR cooler 103, and the EGR gas is cooled.

The EGR gas recirculated from the exhaust branch pipe 24 to the intake branch pipe 14 via the EGR passage 100 is supplied to the intake branch pipe 1
Each cylinder 2 while mixing with fresh air flowing from upstream of 4
Of the fuel injection valve 3 and is burned with the fuel injected from the fuel injection valve 3 as an ignition source.

Since the EGR gas contains an inert gas component such as water (H ₂ O) and carbon dioxide (CO ₂ ), if the EGR gas is contained in the mixture, The combustion temperature of air is lowered, and thus the amount of nitrogen oxides (NO _x ) generated can be suppressed.

Further, in the EGR cooler 103, the EGR
When the gas is cooled, the temperature of the EGR gas itself is lowered and the volume of the EGR gas is reduced.
When the R gas is supplied into the combustion chamber, the ambient temperature in the combustion chamber does not unnecessarily rise, and the amount of fresh air (volume of fresh air) supplied into the combustion chamber is unnecessarily reduced. Absent.

The internal combustion engine 1 having the above-described structure is equipped with an electronic control unit (EC) for controlling the internal combustion engine 1.
U: Electronic Control Unit) 35 is installed side by side. The ECU 35 is a unit that controls the operating state of the internal combustion engine 1 in accordance with the operating conditions of the internal combustion engine 1 and the driver's request.

In addition to the crank position sensor 4, the water temperature sensor 5, the fuel pressure sensor 13, the air flow meter 17, the intake air temperature sensor 18, the intake throttle valve opening sensor 21b, the oxygen concentration sensor 38, and the differential pressure sensor 39, the ECU 35 is provided. An accelerator position sensor 37 that outputs an electric signal corresponding to an operation amount (accelerator opening) of an accelerator pedal 36 provided in a vehicle compartment is electrically connected, and output signals of the above-described sensors are input to the ECU 35. It has become so.

On the other hand, the ECU 35 includes a fuel injection valve 3, a fuel pump 9, an intake throttle actuator 21a, an exhaust throttle actuator 34, an EGR valve 101, and an opening / closing valve 10.
7, the three-way switching valve 395, etc. are electrically connected, and the ECU 3
It is possible for 5 to control the above-mentioned respective parts.

Here, the ECU 35, as shown in FIG. 5, is connected to each other by a bidirectional bus 40, CP
U / 41 connected to the input port 45 while having a U41, a ROM 42, a RAM 43, a backup RAM 44, an input port 45, and an output port 46.
A D converter (A / D) 47 is provided.

The input port 45 inputs the output signals of a sensor that outputs a digital signal format signal such as the crank position sensor 4, and sends these output signals to the CPU 41 and the RAM 43 via the bidirectional bus 40. To do.

The input port 45 includes a water temperature sensor 5, a fuel pressure sensor 13, an air flow meter 17, an intake air temperature sensor 18, an intake throttle valve opening sensor 21b, an accelerator position sensor 37, an oxygen concentration sensor 38, and a differential pressure sensor 39.
As described above, the output signals of a sensor that outputs an analog signal format are input via the A / D 47, and those output signals are input via the bidirectional bus 40 to the CPU 41 or the RAM 4
Send to 3.

The output port 46 includes the fuel injection valve 3, the fuel pump 9, the intake throttle actuator 21a, the exhaust throttle actuator 34, the EGR valve 101, and the on-off valve 10.
7, electrically connected to the three-way switching valve 395 and the like via a drive circuit (not shown), and transmits a control signal output from the CPU 41 to each of the above-mentioned units.

The ROM 42 stores a fuel injection control routine, an intake throttle control routine, an exhaust throttle control routine, and E
It stores various application programs such as a GR control routine and a PM regeneration control routine, and also stores various control maps.

The RAM 43 stores the output signal from each sensor, the calculation result of the CPU 41, and the like. The calculation result is, for example, the engine speed calculated based on the time interval at which the crank position sensor 4 outputs a pulse signal. These data are rewritten to the latest data each time the crank position sensor 4 outputs a pulse signal.

The backup RAM 44 is a non-volatile memory capable of storing data even after the operation of the internal combustion engine 1 is stopped.

The CPU 41 operates according to the application program stored in the ROM 42,
In addition to known control such as fuel injection control, fuel pump control, intake throttle control, exhaust throttle control, EGR control, PM regeneration control, oxygen concentration sensor output correction control, which is the gist of the present embodiment, is executed.

The oxygen concentration sensor output correction control in this embodiment will be described below.

Generally, the oxygen concentration sensor has a characteristic that the output signal value changes according to the exhaust pressure.
For example, the output signal value (sensor output ratio) of the oxygen concentration sensor with respect to the actual oxygen concentration becomes "1" when the oxygen concentration sensor is used under the same pressure as the atmospheric pressure, as shown in FIG. . However, when the oxygen concentration sensor is used under a pressure lower than the atmospheric pressure, the sensor output ratio becomes a value less than “1” and at the same time, becomes smaller as the pressure becomes lower. On the other hand, when the oxygen concentration sensor is used under a pressure higher than atmospheric pressure,
The sensor output ratio becomes a value larger than “1” and at the same time, becomes larger as the pressure becomes higher.

In consideration of such circumstances, when the oxygen concentration sensor is arranged upstream of a member such as a particulate filter which has a relatively large pressure loss and the degree of the pressure loss is likely to change, the exhaust gas There is a possibility that the error between the output signal value of the oxygen concentration sensor and the actual oxygen concentration becomes large due to pressure rise or pressure fluctuation.

On the other hand, in the oxygen concentration sensor output correction control according to the present embodiment, control using the output signal value of the oxygen concentration sensor 38, for example, the oxygen concentration of the exhaust gas flowing into the particulate filter 29 is set to the desired oxygen. When performing feedback control of the air-fuel ratio of the air-fuel mixture used for combustion in the internal combustion engine 1 to obtain the concentration, the differential pressure sensor 39 is used as described in the description of FIG.
The absolute pressure of the exhaust gas in 5a is detected, and the output signal value of the oxygen concentration sensor 38 is corrected based on the detected absolute pressure of the exhaust gas.

Specifically, the CPU 41 controls the differential pressure sensor 39 to detect the absolute pressure of the exhaust gas in the upstream exhaust pipe 25a on condition that it is not necessary to detect the differential pressure before and after the filter: ΔP. To do. That is, the CPU 41, as described in the description of FIG.
And the atmosphere introduction pipe 397 are electrically connected to each other.
5 is controlled, and the output signal value (= Pup-Pa) of the sensor main body 390 and the output signal value of the oxygen concentration sensor 38 at that time are read.

Subsequently, the CPU 41 causes the sensor body 390 to
The correction coefficient: A _(Pup-Pa) is calculated using the output signal value (= Pup-Pa) of the parameter as a parameter, and the correction coefficient: A _(Pup-Pa)
Is integrated with the output signal value of the oxygen concentration sensor 38 to calculate the actual oxygen concentration. The correction coefficient mentioned above: A _(Pup-Pa)
Is a coefficient unique to the oxygen concentration sensor 38 and is assumed to be experimentally obtained in advance.

As described above, in the oxygen concentration sensor output correction control according to the present embodiment, the differential pressure sensor 39 is used to detect the absolute pressure of the exhaust gas in the upstream exhaust pipe 25a, and based on the absolute pressure of the exhaust gas, Since the output signal value of the oxygen concentration sensor 38 is corrected by this, it becomes possible to detect the accurate oxygen concentration of the exhaust gas in the upstream exhaust pipe 25a.

Therefore, according to the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment, it becomes possible to detect the absolute pressure of exhaust gas by attaching the three-way switching valve to the existing differential pressure sensor, and thus the particulates. It is possible to accurately determine the oxygen concentration of exhaust gas upstream of the filter.

<Second Embodiment> Next, a second embodiment of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described with reference to FIGS.
A description will be given based on FIG. Here, a configuration different from that of the first embodiment described above will be described, and description of the same configuration will be omitted.

In this embodiment, as shown in FIG. 7, the upstream exhaust pipe 25a and the downstream exhaust pipe 25b have an exhaust pressure in the upstream exhaust pipe 25a and an exhaust pressure in the downstream exhaust pipe 25b. A differential pressure sensor 50 that outputs an electric signal corresponding to the differential pressure between the

As shown in FIG. 8, the differential pressure sensor 50 has two gas introducing portions 501 and 502, and detects the pressure difference between the two gases introduced into the two gas introducing portions 501 and 502. Sensor body 5 that outputs a corresponding electrical signal
It is equipped with 00. In the following, the gas introduction part 501
The gas introduction part 501 is referred to as the gas introduction part 501 and the gas introduction part 502 is referred to as the second gas introduction part 502.

The first gas introducing section 501 is in communication with the three-way switching valve 504 via the first gas introducing tube 503, and the second gas introducing section 502 is the second gas introducing tube 507. Is connected to the downstream side exhaust pipe 25b via.

The three-way switching valve 504 has the above-mentioned first
In addition to the gas introduction pipe 503, the exhaust introduction pipe 505 and the atmosphere introduction pipe 506 are connected, and the three-way switching valve 504 selectively selects either one of the exhaust introduction pipe 505 and the atmosphere introduction pipe 506. The gas introduction pipe 503 is electrically connected.

The above-mentioned exhaust introduction pipe 505 is connected to the upstream side exhaust pipe 25a, and the above-mentioned atmosphere introduction pipe 506 is open to the atmosphere.

In the differential pressure sensor 50 constructed as described above, when the three-way switching valve 504 connects the first gas introduction pipe 503 and the exhaust introduction pipe 505 to each other, as shown in FIG. Exhaust pressure Pup upstream of the particulate filter 29 is applied to the first gas introduction part 501 of the sensor body 500, and exhaust pressure Pdown downstream of the particulate filter 29 is the second gas of the sensor body 500. It will be applied to the introduction part 502.

In this case, the sensor main body 500 is arranged such that the pressure of the exhaust gas upstream of the particulate filter 29: P
Pressure difference between up and the exhaust gas downstream of the particulate filter 29: Pdown (differential pressure before and after the filter): ΔP
An electric signal corresponding to (= Pup-Pdown) will be output.

When the three-way switching valve 504 connects the first gas introducing pipe 503 and the atmosphere introducing pipe 506,
As shown in FIG. 10, the atmospheric pressure: Pa is the sensor body 5
00 is applied to the first gas introduction part 501,
Exhaust pressure downstream of the particulate filter 29: Pdown is the second gas introduction part 5 of the sensor body 500.
02 will be applied.

In this case, the sensor body 500 has an atmospheric pressure:
Pressure difference between Pa and the exhaust gas downstream of the particulate filter 29: Pdown (= Pa-Pdown, hereinafter,
An electric signal corresponding to the atmospheric pressure / exhaust pressure difference) will be output. The absolute value of this output signal value is a value corresponding to the absolute pressure of exhaust gas downstream of the particulate filter 29.

When the absolute pressure of the exhaust gas upstream of the particulate filter 29 is detected by using the differential pressure sensor 50 having the above-mentioned structure, the above-mentioned FIG.
As described above, the three-way switching valve 504 is operated to connect the first gas introduction pipe 503 and the exhaust introduction pipe 505 to detect the differential pressure before and after the filter: ΔP (= Pup-Pdown), and As described in the explanation of FIG. 10 described above, the three-way switching valve 504 is operated to connect the first gas introduction pipe 503 and the atmosphere introduction pipe 506 to detect the atmosphere / exhaust pressure difference (= Pa-Pdown). . Then, by subtracting the atmospheric / exhaust pressure difference (= Pa-Pdown) from the differential pressure across the filter: ΔP (= Pup-Pdown) ((Pup-Pd
own) − (Pa−Pdown) = Pup−Pa), absolute pressure of exhaust gas upstream of the particulate filter 29 (= P)
up-Pa) can be obtained.

Therefore, the differential pressure sensor 5 according to the present embodiment.
According to 0, it becomes possible to detect the absolute pressure of the exhaust gas upstream of the particulate filter 29, as in the first embodiment described above, and the absolute pressure of the exhaust gas is utilized to detect the oxygen concentration sensor 38. It is also possible to correct the output signal value. As a result, the particulate filter 2
It is possible to accurately obtain the oxygen concentration of the exhaust gas upstream of 9.

<Third Embodiment> Next, a third embodiment of the present invention will be described.
The embodiment will be described with reference to FIGS. 11 to 13. Here, a configuration different from that of the first embodiment described above will be described, and description of similar configurations will be omitted.

In this embodiment, as shown in FIG.
Instead of the differential pressure sensor, an upstream oxygen concentration sensor 38a and a downstream oxygen concentration sensor 38b are arranged in the upstream exhaust pipe 25a and the downstream exhaust pipe 25b, respectively.

In response to this, the A / D 47 of the ECU 35 is
12, the water temperature sensor 5, the fuel pressure sensor 13, the air flow meter 17, the intake air temperature sensor 18,
The intake throttle valve opening sensor 21b, the accelerator position sensor 37, the upstream oxygen concentration sensor 38a, and the downstream oxygen concentration sensor 38b are connected.

In this case, the CPU 41 operates in accordance with the application program stored in the ROM 42 and performs well-known control such as fuel injection control, fuel pump control, intake throttle control, exhaust throttle control, EGR control, PM regeneration control and the like. The filter front-back differential pressure detection control, which is the gist of the present embodiment, is executed.

In the filter front-back differential pressure detection control, the CPU 4
1 executes a filter front-back differential pressure detection control routine as shown in FIG. This filter front-back differential pressure detection control routine is a routine stored in advance in the ROM 42, and is a routine that is repeatedly executed by the CPU 41 at every predetermined time (for example, every time the crank position sensor 4 outputs a pulse signal).

In the filter front-back differential pressure detection control routine,
First, in S1301, the CPU 41 first determines the internal combustion engine 1
Determines whether the engine is operating at a lean air-fuel ratio.

If it is determined in S1301 that the internal combustion engine 1 is not operating at the lean air-fuel ratio, the CP
The U41 resets the value of the lean operation counter C to "0" and once ends the execution of this routine. The lean operation counter C described above is a counter that measures the time during which the internal combustion engine 1 is continuously operated at the lean air-fuel ratio.

On the other hand, in S1301, the internal combustion engine 1
Is determined to be operating with a lean air-fuel ratio,
The CPU 41 proceeds to S1302 and activates the lean operation counter: C.

In S1303, the CPU 41 determines whether or not the time measured by the lean operation counter C: C is equal to or longer than a predetermined OSC saturation time. The OSC saturation time described above is from the time when the lean air-fuel ratio operation of the internal combustion engine 1 is started until the oxygen storage capacity of the particulate filter 29 is saturated (the particulate filter 29 cannot store oxygen in exhaust gas). This is the time required and is a value that has been experimentally obtained in advance.

When it is determined in S1303 that the time count of the lean operation counter: C: C is less than the OSC saturation time, the CPU 41 re-executes the processing of S1301 and thereafter.

When it is determined in S1303 that the time count of the lean operation counter C: C is equal to or longer than the OSC saturation time, the CPU 41 proceeds to S1304 and outputs the output signal value of the upstream oxygen concentration sensor 38a: Dup. The output signal value: Ddown of the downstream oxygen concentration sensor 38b is read.

In S1305, the CPU 41 causes the difference between the output signal value Dup of the upstream oxygen concentration sensor 38a and the output signal value Ddown of the downstream oxygen concentration sensor 38b: Ddown: ΔD.
(= Dup-Ddown) is calculated.

In S1306, the CPU 41 causes the CPU 41 to execute the above S1.
The difference calculated in 305: ΔD is the differential pressure across the filter: Δ
Convert to P. Here, when the internal combustion engine 1 is operated at the link air-fuel ratio and the oxygen storage capacity of the particulate filter 29 is saturated, the actual oxygen concentration of the exhaust gas upstream of the particulate filter 29 and the particulate filter 29 Since it matches the actual oxygen concentration of the exhaust gas at the downstream side, the upstream side oxygen concentration sensor 38a and the downstream side oxygen concentration sensor 3 under such a situation.
The difference between the values detected by 8b: ΔD is the differential pressure across the filter:
It can be said that this is due to ΔP.

Therefore, the differential pressure before and after the filter: ΔP and the difference:
It is possible to obtain the differential pressure across the filter: ΔP using the difference: ΔD as a parameter by experimentally obtaining the relation with ΔD in advance and mapping the relationship.

Therefore, in the internal combustion engine 1 having the oxygen concentration sensors 38a and 38b before and after the particulate filter 29, the differential pressure sensor is provided by utilizing the output characteristic of the oxygen concentration sensor according to the change of the exhaust pressure. It is possible to obtain the differential pressure across the filter without the need. As a result, it is possible to determine the amount of trapped PM in the particulate filter 29 using the differential pressure across the filter as a parameter.

[0121]

According to the present invention, the exhaust gas purifying apparatus for an internal combustion engine is provided with a collection mechanism provided in the exhaust passage of the internal combustion engine and a differential pressure detection mechanism for detecting the differential pressure across the collection mechanism. In, when it is not necessary to detect the differential pressure across the collection mechanism, by introducing the exhaust gas upstream or downstream of the collection mechanism and the atmosphere into the differential pressure detection mechanism, in the upstream or downstream of the collection mechanism. It is possible to detect the absolute pressure of exhaust gas.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine according to a first embodiment.

FIG. 2 is a diagram showing a configuration of a differential pressure sensor according to the first embodiment.

FIG. 3 is a diagram (1) for explaining the operation of the differential pressure sensor.

FIG. 4 is a diagram (2) for explaining the operation of the differential pressure sensor.

FIG. 5 is a block diagram showing the internal configuration of the ECU.

FIG. 6 is a diagram showing output characteristics of an oxygen concentration sensor due to pressure change.

FIG. 7 is a diagram showing a schematic configuration of an internal combustion engine according to a second embodiment.

FIG. 8 is a diagram showing a configuration of a differential pressure sensor according to a second embodiment.

FIG. 9 is a diagram (1) for explaining the operation of the differential pressure sensor.

FIG. 10 is a diagram (2) for explaining the operation of the differential pressure sensor.

FIG. 11 is a diagram showing a schematic configuration of an internal combustion engine according to a third embodiment.

FIG. 12 is a block diagram showing an internal configuration of an ECU according to a third embodiment.

FIG. 13 is a flowchart showing a control routine for detecting a differential pressure across the filter.

[Explanation of symbols]

1 ... Internal combustion engine 17 ... Air flow meter 25a ... upstream exhaust pipe 25b ... downstream exhaust pipe 29 ... Particulate filter (collection mechanism) 35 ... ECU 38 ... Oxygen concentration sensor 38a ... upstream oxygen concentration sensor 38b ... downstream oxygen concentration sensor 41 ... CPU 50 ... Differential pressure sensor 500 ... Sensor body 501..First gas introduction section 502 ... Second gas introduction section 503 ... First gas introduction pipe 504 ... Second gas introduction pipe 505 ... 3-way switching valve 506 ... Exhaust gas introduction pipe 507 ... Atmosphere introduction pipe

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 3G084 AA01 BA09 DA04 FA29                 3G090 AA03 BA01 DA03 DA04 DA05                       DA06

Claims (4)

[Claims] 1. A collection mechanism provided in an exhaust passage of an internal combustion engine for collecting fine particles in exhaust gas; exhaust gas in an exhaust passage upstream of the collection mechanism; and exhaust passage downstream of the collection mechanism. Of the exhaust gas, the differential pressure detection mechanism for detecting the difference in the exhaust pressure between the upstream and downstream of the collection mechanism, and either the exhaust gas in the exhaust passage upstream or downstream of the collection mechanism and the atmosphere To selectively introduce the air into the differential pressure detecting mechanism, and the atmosphere introducing switch to introduce the atmosphere into the differential pressure detecting mechanism instead of the exhaust gas in the exhaust passage upstream or downstream of the collecting mechanism. An exhaust gas purifying apparatus for an internal combustion engine, comprising: an absolute pressure detection control means for controlling the means and detecting the absolute pressure of the exhaust gas downstream and / or upstream of the trapping mechanism. 2. An oxygen concentration sensor provided in an exhaust passage upstream and / or downstream of the trapping mechanism, and an output signal of the oxygen concentration sensor based on the absolute pressure of the exhaust gas detected by the absolute pressure detection control means. The exhaust emission control device for an internal combustion engine according to claim 1, further comprising a correction unit that corrects the value. 3. A trapping mechanism provided in an exhaust passage of an internal combustion engine for trapping particulates in exhaust gas; an upstream oxygen concentration sensor provided in an exhaust passage upstream of the trapping mechanism; A downstream oxygen concentration sensor provided in the exhaust passage downstream of the mechanism, and the upstream oxygen concentration when the internal combustion engine is operating at a lean air-fuel ratio and the oxygen storage capacity of the trapping mechanism is saturated. An exhaust gas purification device for an internal combustion engine, comprising: a clogging determination unit that determines clogging of the collection mechanism based on an output difference between a sensor and the downstream oxygen concentration sensor. 4. The exhaust gas purification device for an internal combustion engine according to claim 1, wherein the collection mechanism is a particulate filter carrying an oxidation catalyst and a NOx storage agent.