JP2003138930A - Exhaust emission control device of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize an amount of oxygen released from an oxygen occluding substance in a desorption operation state. SOLUTION: An HC adsorbed catalyst 27 includes: an HC adsorbent 27b which desorbs hydrocarbon adsorbed accompanied with temperature rising while adsorbing hydrocarbon; the oxygen occluding substance; and a catalyst metal. This device comprises: a reduction degree control means 43 which controls an exhaust gas in an upstream side of the HC adsorbed catalyst 27 or in the HC adsorbed catalyst 27 so as to be in a reduction side (rich side) in the desorption operation state in which an HC desorption amount from the HC adsorbent 27b is greater than an HC adsorption amount to the HC adsorbent 27b; a third oxygen concentration sensor 28 which detects as an exhaust air-fuel ratio a reduction degree of the exhaust gas at a downstream side of the HC adsorbed catalyst 27 in an exhaust passage 22; and a correction means 44 which corrects a fuel injection control by the reduction degree control means 43 based on the reduction degree detected by the third oxygen concentration sensor 28.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification apparatus for an engine equipped with an HC adsorption catalyst, and more particularly to a measure for optimizing the degree of reduction of exhaust gas flowing into the HC adsorption catalyst.

[0002]

2. Description of the Related Art Conventionally, there has been known an engine exhaust purification system in which an HC adsorption catalyst is arranged in an exhaust passage and the amount of oxygen flowing into the HC adsorption catalyst is adjusted. The HC adsorption catalyst used in this exhaust purification device generally contains an HC adsorbent, an oxygen storage substance, and a catalytic metal. The HC adsorbent has a property of adsorbing HC (hydrocarbon) in exhaust gas at a low temperature such as cold start of an engine, and desorbing the adsorbed HC along with a temperature rise of the HC adsorbent. ing. The oxygen storage substance has a property of storing oxygen on the oxidation side (lean side) and releasing oxygen on the reduction side (rich side), such as cerium oxide. The catalytic metal has a property of being activated at a temperature equal to or higher than a predetermined temperature to decompose HC, CO and NOx in the exhaust gas to purify the exhaust gas.

When the engine is started, the HC adsorbent adsorbs HC in the exhaust gas purifying apparatus, but when the temperature of the HC adsorbent rises and reaches a predetermined temperature, the adsorbed HC is desorbed. Start. Since the catalytic metal is not yet activated during the elimination of HC, for example, JP-A-10-61426 and JP-A-11-8 are used.
As disclosed in Japanese Patent No. 2111, there is known a technique in which the exhaust gas in the HC adsorption catalyst is made into an oxygen rich state by controlling the air-fuel ratio to the lean side, and HC is decomposed by using oxygen in the exhaust gas. Has been. On the other hand, HC
By controlling the air-fuel ratio to the rich side during desorption of H
It has been proposed that the oxygen concentration in the C adsorption catalyst is controlled to be reduced to approximately 0.5% or less, oxygen is released from the oxygen storage material, and the HC desorbed from the HC adsorbent is decomposed by the released oxygen. .

[0004]

However, in the case where the exhaust gas in the HC adsorption catalyst is controlled to be reduced to approximately 0.5% or less as described above, the HC concentration in the HC adsorption catalyst rises and the HC is completely removed. The problem arises that it can happen that it cannot be decomposed into. Alternatively, even when the amount of HC adsorbed on the HC adsorbing catalyst is reduced, a large amount of oxygen is released from the oxygen storage substance, so that it is necessary to supply oxygen in vain.

The present invention has been made in view of the above point, and an object thereof is to optimize the amount of oxygen released from the oxygen storage substance in the desorption operation state.

[0006]

In order to achieve the above object, the present invention is based on the degree of reduction on the downstream side of the HC adsorbing catalyst in the desorption operation state, and exhaust on the upstream side of the HC adsorbing catalyst. This is to correct the reduction degree control of the gas.

Specifically, the first solution means is an HC adsorbent which is disposed in the exhaust passage of the engine and adsorbs HC while desorbing the adsorbed HC as the temperature rises, and oxygen on the oxidizing side. An oxygen storage material that stores oxygen and releases oxygen on the reduction side, an HC adsorption catalyst containing a catalyst metal that oxidizes HC desorbed from the HC adsorption material, and at least an adsorption amount of hydrocarbons on the HC adsorption material When in a desorption operation state in which the amount of hydrocarbons desorbed from the HC adsorbent exceeds the desorption operation state, exhaust gas in the upstream side of the HC adsorption catalyst or in the HC adsorption catalyst is reduced so that oxygen is released from the oxygen storage material. Based on the degree of reduction detected by the degree-of-reduction detection means, the degree-of-reduction control means for controlling the degree of reduction, the degree-of-reduction detection means for detecting the degree of reduction of the exhaust gas on the downstream side of the HC adsorption catalyst in the exhaust passage, and the degree-of-reduction control Control by means And a correcting means for correcting the.

The second solving means is the same as the first solving means, wherein the correcting means corrects the reduction degree detected by the reduction degree detecting means to be a predetermined value or less.

A third solving means is the above-mentioned first solving means, wherein the reduction degree control means controls the reduction degree of the exhaust gas upstream of the HC adsorption catalyst or in the HC adsorption catalyst to an upstream reference value. At the same time, the correction means corrects the degree of reduction of the exhaust gas detected by the degree-of-reduction detection means to be equal to or less than the upstream reference value and equal to or more than the downstream reference value smaller than the upstream reference value.

A fourth solving means is the above-mentioned first solving means, wherein the reduction degree control means is such that the reduction degree on the downstream side of the HC adsorption catalyst is smaller than the reduction degree reference value on the upstream side. Feedback control of the fuel injection amount is performed so that the value becomes a value.

Further, a fifth solving means is the above-mentioned first solving means, wherein the reduction degree detecting means detects the reduction degree of the exhaust gas as an exhaust air-fuel ratio. The exhaust air-fuel ratio is an expression method that represents the air-fuel ratio of the mixture of fuel and air that directly corresponds to the exhaust gas state from the existing state of the oxygen concentration and the reducing agent concentration of the exhaust gas. 0.7 corresponds to the theoretical air-fuel ratio, and the oxygen concentration at this time is substantially 0 to
It becomes 0.5%. With this as a boundary, the exhaust air-fuel ratio is 14.
When it is 7 or less, the oxygen concentration decreases or is fixed to zero, and the reducing agent concentration increases. On the other hand, the exhaust air-fuel ratio is 1
At 4.7 or higher, the oxygen concentration increases and the reducing agent concentration decreases.

That is, in the above first solving means, the reduction degree control means causes the reduction degree control means to operate at least during the desorption operation state in which the desorption amount of HC from the HC adsorbent exceeds the adsorption amount of HC to the HC adsorbent. The exhaust gas upstream of the adsorption catalyst or in the HC adsorption catalyst is controlled to the reducing side (rich side), that is, to the reducing side so that the oxygen concentration of the exhaust gas is reduced or the reducing agent is increased. That is, by controlling the exhaust gas on the upstream side of the HC adsorption catalyst or in the HC adsorption catalyst to the reduction side, the oxygen concentration is lowered, and oxygen is released from the oxygen storage substance. The released oxygen has high reactivity because it is in an activated state, and purifies HC (hydrocarbon) desorbed from the HC adsorbent.

On the other hand, the reduction degree detection means detects the reduction degree of the exhaust gas on the downstream side of the HC adsorption catalyst, and the correction means corrects the control by the reduction degree control means based on this reduction degree. That is, in the desorption operation state, the exhaust gas in the upstream side of the HC adsorbing catalyst or in the HC adsorbing catalyst is controlled to the reducing side, so that the HC concentration in the HC adsorbing catalyst tends to rise. Since the control by the reduction degree control means is corrected based on the degree of reduction of the exhaust gas on the downstream side of the exhaust gas, it is possible to prevent the exhaust gas from being controlled to the reduction side to such an extent that HC cannot be completely decomposed. That is, it is possible to prevent the exhaust gas from being unnecessarily controlled to the reducing side. Alternatively, when the amount of HC desorbed from the HC adsorption catalyst decreases, it is necessary to cause the oxygen storage substance to store oxygen more than necessary in order to prevent excessive release of oxygen from the oxygen storage substance. Disappear. The above-mentioned degree of reduction corresponds to the concentration of reducing agents such as HC and CO that affect the release of oxygen from the oxygen storage substance.

In the second solving means, the first
In order to correct the control by the reduction degree control means so that the reduction degree detected by the reduction degree detection means becomes equal to or less than a predetermined value, the amount of HC that cannot be decomposed is HC.
It can be prevented from flowing into the adsorption catalyst. That is, since the exhaust gas is prevented from being unnecessarily controlled to the reducing side, it is possible to prevent the fuel consumption from deteriorating.
The predetermined value is equal to or smaller than the reduction degree of the exhaust gas upstream of the HC adsorption catalyst or in the HC adsorption catalyst set by the reduction control means. is there.

In the third solving means, the first
In the solving means, the downstream side reference value is set to a value at which the degree of reduction is smaller than the upstream side reference value, and the degree of reduction control is performed so that the degree of reduction of exhaust gas on the downstream side of the HC adsorption catalyst falls between both reference values. Since the control by the means is corrected, the exhaust gas is prevented from being unnecessarily controlled to the reducing side (rich side), and unnecessary release of oxygen from the oxygen storage substance is prevented. There is no need to store oxygen in the substance more than necessary.

Further, in the fourth solving means, the first
In the solution means, the reduction degree control means performs the control by the feedback control of the fuel injection amount, so that the reduction degree of the exhaust gas can be accurately controlled. Also, H
Since the feedback control is performed so that the degree of reduction of the exhaust gas on the downstream side of the C adsorption catalyst becomes a target value of the degree of reduction smaller than the reduction degree reference value on the upstream side, the exhaust gas is unnecessarily reduced (rich side). Side) can be prevented. On the other hand, when the amount of HC desorbed from the HC adsorption catalyst decreases, it is possible to prevent excessive release of oxygen from the oxygen storage substance.
It becomes unnecessary to store oxygen more than necessary in the oxygen storage material.

[0017]

Embodiment 1 of the present invention will be described in detail below with reference to the drawings.

An engine exhaust gas purification apparatus according to an embodiment of the present invention purifies exhaust gas from a gasoline engine of a cylinder injection type engine. In the above gasoline engine, a plurality of cylinders 2 and a piston 3 reciprocatingly fitted in each cylinder 2 are provided in an engine body 1, and a combustion chamber 4 is provided above the cylinder 2 by the piston 3. It is compartmentalized. A spark plug 6 connected to an ignition circuit 5 is mounted in the combustion chamber 4 at a predetermined position above the combustion chamber 4 as desired.

In the periphery of the combustion chamber 4, the combustion chamber 4
An injector 7 as a fuel supply means for directly injecting fuel is installed therein. A fuel supply circuit having a high-pressure fuel pump, a pressure regulator and the like (not shown) is connected to the injector 7, and the fuel from the fuel tank is adjusted to an appropriate pressure by the fuel supply circuit and supplied to the injector 7. It has become.
Further, the fuel supply circuit is provided with a fuel pressure sensor 8 for detecting the fuel pressure.

The combustion chamber 4 communicates with an intake passage 10 via an intake port provided with an intake valve 9. An air cleaner 11 for filtering intake air, an air flow sensor 12 for detecting an intake air amount, an electric throttle valve 13 for narrowing the intake passage 10, and a surge tank 14 are arranged in this intake passage 10 in this order from the upstream side. It is set up. The electric throttle valve 13 is opened and closed by being driven by a motor 15 without interlocking with an accelerator pedal (not shown). Further, the electric throttle valve 13
A throttle opening sensor 16 for detecting the valve opening of the surge tank 14 is provided at the installation portion of the above, and an intake pressure sensor 17 for detecting the intake pressure is provided at the installation portion of the surge tank 14.

The intake passage 10 on the downstream side of the surge tank 14 is an independent passage branched for each cylinder 2. The downstream end of each independent passage is branched into two and communicates with the intake port. A swirl valve 18 is provided on one side thereof. When the swirl valve 18 is driven by the actuator 19 to be in the closed state, intake air is supplied into the combustion chamber 4 only from the other branch passage, so that a strong intake swirl is generated in the combustion chamber 4. ing.
This intake swirl will be weakened as the swirl valve 18 opens. A swirl valve opening sensor 20 that detects the opening of the swirl valve 18 is provided at the installation portion of the swirl valve 18. Instead of the swirl valve 18, a tumble valve for generating a tumble flow may be installed.

The combustion chamber 4 communicates with an exhaust passage 22 through an exhaust port provided with an exhaust valve 21, and the upstream end of the exhaust passage 22 is branched for each cylinder 2. In the exhaust passage 22, a first oxygen concentration sensor 24 for detecting the oxygen concentration in the exhaust gas, HC (hydrocarbon), CO (carbon monoxide), and NOx in the exhaust gas are arranged in this order from the upstream side.
A conventionally known three-way catalyst 25 having a function of purifying all (nitrogen oxides), and a second oxygen concentration sensor 2 for detecting the oxygen concentration in exhaust gas on the downstream side of the three-way catalyst 25.
6, an HC adsorption catalyst 27 that adsorbs and purifies HC in the exhaust gas, and a third oxygen concentration sensor 28 that detects the oxygen concentration in the exhaust gas on the downstream side thereof.

The first to third oxygen concentration sensors 24 and 2
Reference numerals 6 and 28 detect the degree of reduction of the exhaust gas as an exhaust air-fuel ratio obtained based on the oxygen concentration, and its output is largely inverted (changed) between the lean side and the rich side with the stoichiometric air-fuel ratio as the boundary. Λ sensor, which provides excellent detection accuracy in the vicinity of the stoichiometric air-fuel ratio. The third oxygen concentration sensor 28 constitutes reduction degree detection means for detecting the degree of reduction of exhaust gas on the downstream side of the HC adsorption catalyst 27 as an exhaust air-fuel ratio. In other words, the detection value of the third oxygen concentration sensor 28 influences the release of oxygen from the oxygen storage substance described later,
The degree of reduction of exhaust gas on the downstream side of the HC adsorption catalyst 27 corresponding to the concentration of the reducing agent component such as CO is estimated. The first to third oxygen concentration sensors 2
Instead of the λ sensor, 4, 26, 28 may be constituted by linear oxygen sensors whose output changes linearly according to the air-fuel ratio.

The HC adsorbing catalyst 27 has a function of adsorbing HC discharged particularly during cold start and purifying exhaust gas, and as shown in FIG. 2, a honeycomb structure made of cordierite is used. And a HC adsorbent 27b carried on the wall surface of the through hole formed in the carrier 27a,
It is constituted by a three-way catalyst layer 27c supported by being coated on the surface thereof.

The above-mentioned HC adsorbent 27b is the H gas in the exhaust gas.
A so-called β-type zeolite in which a large number of pores having a pore size suitable for adsorbing and holding C, that is, a pore size of about 7.2 angstrom is formed, is made to impregnate and carry silver (Ag), The HC in the exhaust gas is adsorbed at a low temperature such as during cold start of the
C is eliminated. The silver is supported in order to enhance the HC adsorbing action of β-type zeolite so that the HC can be retained at a higher temperature.

The three-way catalyst layer 27c has a catalyst metal such as palladium (Pd) or platinum (Pt) supported on alumina or the like and a binder made of zirconium (Zr) or the like, and is heated to a predetermined temperature. By activating by
It has a function of oxidizing HC and CO in the exhaust gas and reducing NOx in the exhaust gas to purify it. This purifying function is remarkably exhibited near the stoichiometric air-fuel ratio.

The three-way catalyst layer 27c is heated to a predetermined temperature and activated to generate oxygen in a high oxygen atmosphere having a high oxygen concentration in the exhaust gas (for example, an atmosphere having an oxygen concentration of 0.5% or more). An oxygen storage material that has the function of releasing the stored oxygen as the oxygen concentration in the exhaust gas decreases and becomes a low oxygen atmosphere, such as cerium oxide (CeO2) or cerium Ce and praseodymium Pr. It contains an oxygen storage material such as a complex oxide with a rare earth element. In other words, the oxygen storage material has a property of storing oxygen when the surrounding exhaust gas is on the oxidizing side (lean side) and releasing the stored oxygen when the surrounding exhaust gas is on the reducing side (rich side). is doing.

In the three-way catalyst layer 27c, the HC desorbed from the HC adsorbent 27b is oxidized and purified at a relatively low temperature by the oxidizing action utilizing the oxygen released from the oxygen storage material. It has become. The above HC
The adsorption catalyst 27 is composed of the material forming the three-way catalyst layer 27c and H
It may be configured such that the C adsorbent 27b is integrally mixed.

An EGR passage 29 for returning a part of the exhaust gas to the intake system is connected to the exhaust passage 22.
The EGR passage 29 has an upstream end connected to the upstream side of the first oxygen concentration sensor 24 in the exhaust passage 22, and a downstream end connected between the throttle valve 13 and the surge tank 14 in the intake passage 10. . EGR passage 29
Includes an EGR valve 3 whose opening degree is electrically adjustable.
0 and a lift sensor 31 that detects the lift amount of the EGR valve 30 are provided. The EGR passage 29, the EGR valve 30, and the lift sensor 31 constitute exhaust gas recirculation means.

In the exhaust passage 22, a part of the intake air is introduced from the intake passage 10 to the HC adsorbing catalyst 2 in the exhaust passage 22.
7 is connected to a secondary air supply passage 32 that is sent to the upstream side. The opening and closing of the secondary air supply passage 32 is controlled according to a control signal output from a control unit (ECU) 34 that controls the engine. A flow control valve 33 is provided.

The control unit 34 includes the air flow sensor 12, the throttle opening sensor 16, the intake pressure sensor 17, the swirl valve opening sensor 20, the oxygen concentration sensors 24, 26 and 28, and the lift sensor for the EGR passage 29. The output signal from 31 is input. Also,
The control unit 34 includes a water temperature sensor 35 that detects an engine cooling water temperature, an intake air temperature sensor 36 that detects an intake air temperature, and an atmospheric pressure sensor 3 that detects an atmospheric pressure.
7, the detection signals output from the rotation speed sensor 38 that detects the rotation speed of the engine and the accelerator opening sensor 39 that detects the opening (accelerator operation amount) of the accelerator pedal are input.

The control unit 34 includes an HC determination control means 42, a fuel injection control means 40, an ignition timing control means 41, and a correction means 44.

The HC determination control means 42 compares the temperature _THCE of the HC adsorption catalyst 27, which is derived based on the elapsed time and the operation history measured after the engine is started, with the preset reference temperature. As a result, the HC adsorption / desorption state of the HC adsorption catalyst 27 is determined.

That is, as shown in FIGS. 3 (a) and 3 (b), after the cold start of the engine, only the HC is adsorbed by the HC adsorbent 27b, and the HC is not desorbed from the HC adsorbent 27b. The state continues, and the temperature _THCE of the HC adsorption catalyst 27 gradually rises with the passage of time. Then, as the amount of HC adsorbed gradually increases, the temperature T _{H CE} of the HC adsorption catalyst 27 increases _{.
Reaches the} desorption start temperature _THC1 , the desorption of HC from the HC adsorbent 27b starts. At this time, the HC adsorbent 27b
Adsorption to and desorption from the HC adsorbent 27b are performed in parallel. Then, when the temperature _THCE of the HC adsorbing catalyst 27 further rises, the desorption operation state in which the desorption amount of HC desorbed from the HC adsorbent 27b exceeds the HC adsorption amount adsorbed by the HC adsorbent 27 is reached. The temperature at this time is the desorption operation start temperature T
_HC2 . Then, when the temperature of the HC adsorption catalyst 27 further rises, desorption of HC from the HC adsorbent 27b is completed. The temperature _THCE at this time is _defined as the desorption operation completion temperature _THC3 .

That is, the temperature T _HCE of the HC adsorption catalyst 27 gradually rises with the passage of time, but since the rising speed varies depending on the history after the engine is started, the HC judgment control means 42 is The temperature T _HCE of the HC adsorption catalyst 27 _{depends on} the history of the
Whether the temperature is before reaching _HC2 or the desorption operation completion temperature T
Determine if it has reached _HC3 .

The desorbed amount of HC from the HC adsorbent 27b is based on the oxygen concentration detected by the third oxygen concentration sensor 28 arranged on the downstream side of the HC adsorption catalyst 27. You may make it detect whether it is in the desorption operation state exceeding.

The fuel injection control means 40 is constructed so as to control the fuel injection state injected from the injector 7 according to the operating state of the engine.

The fuel injection control means 40 is judged by the HC judgment control means 42 to be in the initial operation state in which the temperature T _HCE of the HC adsorption catalyst 27 is lower than the desorption operation start temperature _THC2. In this case, the initial injection control for controlling the fuel injection amount is executed so that the average air-fuel ratio in the combustion chamber 4 becomes 14.0.

When the HC adsorbing catalyst 27 is in an operating state in which the HC adsorbing catalyst 27 adsorbs and desorbs HC, the fuel injection control means 40 is in the period from the intake stroke to the ignition timing, and in the latter half of the compression stroke or later. The fuel injection is performed in each of the injection and the early injection before this, and the injector 7 is controlled so as to perform the divided injection at least twice. The fuel injection control means 40 may be configured to perform the split injection in the entire operating region during cold operation, and in the high load region, the fuel is injected only in the intake stroke in order to satisfy the engine output requirement. It may be configured to perform injection. Further, it is not always necessary to directly inject the fuel, and the injector 7 may be arranged in the intake port to supply the mixture of intake air and fuel into the combustion chamber 4. Good.

Further, the fuel injection control means 40 comprises a reduction degree control means 43. The reduction degree control means 43
Indicates that the HC determination control means 42 is the H of the HC adsorption catalyst 27.
The desorption amount of HC from the C adsorbent 27b is determined by the HC adsorbent 27b.
When it is determined that the desorption operation state exceeds the amount adsorbed on the exhaust gas, the initial injection control is stopped, and the exhaust gas contacting the HC adsorption catalyst 27 moves to the reducing side (rich side) where the oxygen concentration is 0.5% or less. Therefore, the oxygen release control for feedback controlling the fuel injection amount is executed. In the oxygen release control, the degree of reduction _OX2 of the exhaust gas on the upstream side of the HC adsorption catalyst 27 is lower than the theoretical air-fuel ratio in the exhaust air-fuel ratio (higher than the degree of reduction equivalent to the theoretical air-fuel ratio).
By controlling the degree of reduction to about 5 and controlling to the rich side, the oxygen concentration of the exhaust gas contacting the HC adsorption catalyst 27 is controlled to 0.5% or less. That is, in the oxygen release control, the degree of reduction of exhaust gas having an exhaust air-fuel ratio of 14.5 is set as the degree of reduction target value on the upstream side of the HC adsorption catalyst 27.

The exhaust air-fuel ratio is an expression method that represents the air-fuel ratio of the mixture of fuel and air that corresponds directly to the exhaust gas state from the existing state of the oxygen concentration and reducing agent concentration of the exhaust gas. When the fuel ratio is 14.7, it corresponds to the theoretical air-fuel ratio, and the oxygen concentration at this time is substantially 0 to 0.5%. When the exhaust air-fuel ratio is 14.7 or less with this as a boundary, the oxygen concentration decreases or is fixed to zero, and the reducing agent concentration increases. At this time, the exhaust gas becomes the reducing side (rich side), and the degree of reduction of the exhaust gas becomes large. On the other hand, when the exhaust air-fuel ratio is 14.7 or more, the oxygen concentration increases and the reducing agent concentration decreases. At this time, the exhaust gas becomes the oxidation side (lean side), and the reduction degree of the exhaust gas becomes small.

In the above oxygen release control, the oxygen concentration contained in the exhaust gas is controlled to be 0.5% or less because the oxygen contained in the exhaust gas contacting the HC adsorption catalyst 27 is controlled. This is because if the concentration is controlled to the oxidation side (lean side) exceeding 0.5%, it becomes difficult for oxygen to be released from the oxygen storage substance contained in the HC adsorption catalyst 27. That is, the reduction degree control means 43 controls the degree of reduction of the exhaust gas with respect to the oxygen storage substance.

In the above oxygen release control, the degree of reduction O _X2 of the exhaust gas on the upstream side of the HC adsorption catalyst 27 detected by the second oxygen concentration sensor 26 is lower than the reduction degree reference value O _X20 corresponding to the exhaust air-fuel ratio of 14.5. Is also higher, the feedback value Qfb2 of the fuel injection amount is reduced by the correction value β1, and conversely, when it is lower than the reduction degree reference value O _X20 corresponding to the exhaust air-fuel ratio of 14.5, the feedback value Qfb2 of the fuel injection amount is corrected. By increasing the value β2, control is performed so that the reduction degree reference value O _X20 on the upstream side of the HC adsorption catalyst 27 becomes the reference value. At this time, by setting the correction value β1 to a value smaller than the correction value β2, it becomes easier to control the exhaust gas on the upstream side of the HC adsorption catalyst 27 to the rich side.

The degree of reduction O _X2 of the exhaust gas on the upstream side of the HC adsorption catalyst 27 is weaker than the degree of reduction corresponding to the exhaust air-fuel ratio of 13.5 (a state where the exhaust air-fuel ratio is large, a state where the reduction degree is small). ) Is preferable. The exhaust gas reduction degree O _X2 on the upstream side of the HC adsorption catalyst 27 is burned in a state in which the reduction strength is stronger than the reduction degree equivalent to the exhaust air-fuel ratio of 13.5 (a state where the exhaust air-fuel ratio is small, a state where the reduction degree is large). In this case, although the release of oxygen from the oxygen storage substance is promoted, since the amount of HC discharged from the engine increases rapidly, some HC is also released from the HC adsorbent 27a, so that H
This is because C cannot be completely purified. And
Reduction degree O of exhaust gas on the upstream side of the HC adsorption catalyst 27
_It is more preferable to control _X2 to a degree of reduction corresponding to an exhaust air-fuel ratio of 14.0 or more and less than 14.7.

The ignition timing control means 41 comprises the ignition circuit 5
A control signal is output to control the ignition timing of the air-fuel mixture according to the operating state of the engine. That is, the ignition timing control means 41 basically sets the ignition timing to M
Although controlled to BT, in the cold operation state of the engine,
When it is confirmed by the HC determination control means 42 that the degree of desorption of HC is large during the split injection, the ignition timing is retarded by a predetermined amount from the MBT, if necessary. Is configured.

The correction means 44 uses the degree of reduction O _X3 detected by the third oxygen concentration sensor 28 in the oxygen release control.
Based on the above, the control by the reduction degree control means 43 of the fuel injection control means 40 is corrected. That is, the degree of reduction corresponding to the exhaust air-fuel ratio of 14.7 (corresponding to the theoretical air-fuel ratio) is set as the target value _OX30 on the downstream side of the HC adsorption catalyst 27, and the correction means 44 is on the downstream side of the HC adsorption catalyst 27. The degree of reduction in the exhaust air-fuel ratio is 14.7
It is configured to correct the feedback control of the fuel injection amount by the reduction degree control means 43 so that the target value O _X30 becomes a considerable amount. In other words, the fuel injection control means 40
Is a target value O at which the reduction degree O _X3 of the exhaust gas on the downstream side of the HC adsorption catalyst 27 is smaller than the reduction degree reference value O _X20 on the upstream side (equivalent to an average air-fuel ratio of 14.5).
_X30 (Average air-fuel ratio of 14.6 to 14.7 equivalent, claim 4
(Corresponding to the target value in 1), feedback control of the fuel injection amount is executed.

In the above oxygen release control, it is judged whether or not the reduction degree O _X3 detected by the third oxygen concentration sensor 28 is higher than the target value O _X30 corresponding to the exhaust air-fuel ratio of 14.6 to 14.7. Target value O equivalent to 14.6 to 14.7 in exhaust air-fuel ratio
When it is higher than _X30 , only when the previously detected reduction degree O _X3 is higher than the target value O _X30 corresponding to the exhaust air-fuel ratio of 14.6 to 14.7, the fuel injection amount feedback value Qfb3
Is reduced by the correction value γ1. Conversely, the third
When the reduction degree O _X3 detected by the oxygen concentration sensor 28 is less than or equal to the target value O _X30 corresponding to the exhaust air-fuel ratio of 14.6 to 14.7, the feedback value Qfb3 of the fuel injection amount is increased by the correction value γ2. ing. Further, the reduction degree O _X3 detected by the third oxygen concentration sensor 28 is 14.6 in terms of exhaust air-fuel ratio.
Is higher than the target value O _X30 equivalent to 14.7, the reduction degree O _X3 detected last time is 14.6 in terms of exhaust air-fuel ratio.
From the target value O _X30 equivalent to 14.7,
The feedback value Qfb3 is not corrected.

The correction value γ1 for reducing the feedback value Qfb3 is set to a value smaller than the correction value γ2 for increasing the feedback value Qfb3. That is, H
Exhaust gas reduction degree O _X3 on the downstream side of the C adsorption catalyst 27
Is continuously higher than the target value _OX30 corresponding to the exhaust air-fuel ratio of 14.6 to 14.7, that is, the feedback value Qfb3 is reduced and corrected only when continuously controlled to the rich side. In addition, by setting the correction value γ1 to be reduced to a value smaller than the correction value γ2 to be increased, the exhaust gas on the upstream side of the HC adsorption catalyst 27 can be easily controlled to the rich side. It should be noted that, when the rich side is continuously controlled, the correction for reducing the feedback value Qfb3 may be prohibited.

Target value on the downstream side of the HC adsorption catalyst 27
By setting O _X30 to the degree of reduction equivalent to the theoretical air-fuel ratio,
It is possible to suppress excessive inflow of HC into the HC adsorption catalyst 27 and prevent excessive control on the reducing side, and also to prevent excessive release of oxygen from the oxygen storage substance to achieve optimum oxygen. The release amount can be obtained, and it becomes unnecessary to store oxygen in the oxygen storage material more than necessary.

The fuel injection control means 40 confirms that the temperature _THCE of the HC adsorption catalyst 27 becomes _{equal to} or higher than the desorption completion temperature _THC3 at which desorption of HC from the HC adsorbent 27b is completed. It is configured to shift from the oxygen release control to the warm operation control in which the fuel injection amount corresponding to the operation state is feedback-controlled. In the warm operation control, the feedback values Qfb2, Qfb3 are reset to zero, and the fuel injection amount is based on the exhaust gas reduction degree O _X1 on the upstream side of the three-way catalyst 25 detected by the first oxygen concentration sensor 24. Controlled.

Further, the fuel injection control means 40, for example, in the stratified charge combustion region during the warm operation, causes the injector 7 to collectively inject the fuel at a predetermined timing of the compression stroke, so that the vicinity of the spark plug 6 is reached. In addition to burning the fuel of the air-fuel mixture in a distributed state, the combustion control is performed in a stratified combustion mode in which the air-fuel ratio of the air-fuel mixture in the combustion chamber 4 is in a lean state of about 30. Further, in the uniform fuel combustion region during the warm operation, the fuel injection control means 40 collectively injects combustion from the injector 7 in the intake stroke, and makes the average air-fuel ratio of the entire combustion chamber 4 approximately the theoretical air-fuel ratio (A /F=14.7), the combustion control in the uniform combustion mode is executed. In the medium-load medium-speed rotation region of the engine, the fuel may be injected by being divided into an intake stroke and a compression stroke.

-Control Operation- The control operation of the engine exhaust gas purification apparatus configured as described above will be described with reference to the flow charts shown in FIGS.

First, when the control operation is started, in step ST11, the air flow sensor 12, the first to third oxygen concentration sensors 24, 26, 28, the water temperature sensor 35,
Intake air temperature sensor 36, atmospheric pressure sensor 37, rotation speed sensor 3
8 and each data corresponding to the detection value of the accelerator opening sensor 39 is input, and the process proceeds to step ST12. In step ST12, the target torque Tr of the engine is set from a preset map based on the accelerator opening and the engine speed, and the process proceeds to step ST13. In step ST13, the basic injection amount Qb of fuel and the basic opening Th ₀ of the electric throttle valve 13 are set from a preset map using the target torque Tr and the engine speed as parameters, and step ST1
Move to 4 and drive the electric throttle valve 13 to step S
Move to T15. The basic injection amount Qb and the basic opening Th ₀ of the electric throttle valve 13 are set so that the air-fuel ratio in the combustion chamber 4 of the engine becomes the stoichiometric air-fuel ratio.

In step ST15, the HC adsorption catalyst 27
The temperature _{THCE of} is derived, and in step ST16, this HC
Based on the temperature T _HCE of the adsorption catalyst 27, it is determined whether or not the operation state is such that HC is desorbed from the HC adsorbent 27b. That is, the temperature T _HCE of the HC adsorption catalyst 27 is derived from the operation history and the like, and this temperature T _HCE is the desorption operation start temperature T _{H C2}
It is determined whether or not it is less than, and it is determined whether or not the state has transitioned to the desorption operation state. The desorption operation start temperature _THC2 is set to, for example, 150 ° C.

When the temperature T _HCE of the HC adsorbing catalyst 27 is _{equal to} or higher than the desorption operation start temperature T _HC2 , the determination in step ST16 becomes NO and the process proceeds to step ST17, where the temperature T _HCE of the HC adsorbing catalyst 27 is desorbing as described above. It is determined whether the temperature is _{equal to} or higher than the operation start temperature T _HC2 and _lower than the desorption operation completion temperature T _HC3 . The desorption operation completion temperature _THC3 is set to 250 ° C., for example. That is, it is determined whether or not the desorption operation state in which the desorption amount of HC desorbed from the HC adsorbent 27b exceeds the adsorption amount of HC adsorbed to the HC adsorbent 27b. When the temperature _THCE of the HC adsorption catalyst 27 is within the above range and the desorption operation state is set, the determination in step ST17 becomes YES and the process proceeds to step ST18.

In step ST18, the second oxygen concentration sensor
Exhaust on the upstream side of the HC adsorption catalyst 27 detected by the server 26
Gas gas reduction degree O_X2Is the preset reducing degree group on the upstream side
Quasi-value O _X20(Exhaust air-fuel ratio is equivalent to 14.5)
The original strength is strong). And HC adsorption touch
Reduction degree O of exhaust gas on the upstream side of the medium 27_X2Is above
Flow-side reduction degree reference value O_X20Step ST when higher than
Proceed to 19 and correct the fuel injection amount feedback value Qfb2
Decrease by β1 and proceed to step ST20. On the other hand, the above
Gas gas reduction degree O_X2Is the above-mentioned upstream reduction degree reference value O_X20Since
If it is lower, proceed to step ST21 and set the fuel injection amount
The feedback value Qfb2 is increased by the correction value β2 and the step S
Proceed to T20. That is, when in the desorption operation state
Are burned so that the degree of reduction is equivalent to 14.5 in the exhaust air-fuel ratio.
In the upstream side of the HC adsorption catalyst 27 by increasing or decreasing the material injection amount
Exhaust gas is controlled to the rich side.

In step ST20, the reduction degree O _X3 of the exhaust gas on the downstream side of the HC adsorption catalyst 27 is _calculated from the preset target value O _X30 on the downstream side (corresponding to the exhaust air-fuel ratio of 14.6 to 14.7). Is also high (the degree of return is strong). When the reduction degree O _X3 of the exhaust gas on the downstream side of the HC adsorption catalyst 27 is higher than the target value O _X30 on the downstream side, the process proceeds to step ST22, and the reduction degree O _X3 previously detected by the third oxygen concentration sensor 28. Is higher than the target value O _X30 on the downstream side, and proceeds to step ST23 only when the reduction degree O _X3 is higher than the target value O _X30 on the downstream side, the feedback value of the fuel injection amount. Qfb3 is the correction value γ
Decrease by 1. In addition, last time the third oxygen concentration sensor 2
When the reduction degree O _X3 detected by 8 is less than or equal to the target value O _X30 on the downstream side, the process proceeds to step ST24, and the process proceeds to step ST26 without correcting the feedback value Qfb3.

On the other hand, in step ST20, when the reduction degree O _X3 of the exhaust gas on the downstream side of the HC adsorbing catalyst 27 is less than or equal to the target value O _X30 on the downstream side, step ST
In step 25, the feedback value Qfb3 of the fuel injection amount is increased by the correction value γ2, and the process proceeds to step ST26. In other words, feedback is performed only when the reduction degree O _X3 is continuously higher than the downstream side target value O _X30 corresponding to the exhaust air-fuel ratio of 14.6 to 14.7, that is, when the rich side is continuously controlled. value
By performing the reduction correction of Qfb3 and setting the correction value γ1 for reduction correction to a value smaller than the correction value γ2 for increase correction, the exhaust gas on the upstream side of the HC adsorption catalyst 27 has an oxygen concentration of 0.5. % Reduction side (rich side)
It is easy to control. Further, the target value O _{X30 of the} degree of reduction of the exhaust gas on the downstream side of the HC adsorption catalyst 27 is set to a value equivalent to the stoichiometric air-fuel ratio, and fuel injection is performed based on the degree of reduction O _X3 of the exhaust gas on the downstream side of the HC adsorption catalyst 27. Since the amount is adjusted to be increased or decreased,
It is possible to suppress excessive inflow of C, and
The excessive release of oxygen from the oxygen storage substance of the HC adsorption catalyst 27 is prevented.

That is, as shown in FIG. 3 (c), the amount of HC desorbed from the HC adsorbent 27b of the HC adsorption catalyst 27 is equal to the amount of HC depleted.
The desorption operation state (time T1
From the time T2 to the time T2), the exhaust gas on the upstream side of the HC adsorption catalyst 27 is controlled to have a reduction degree O _X2 on the rich side corresponding to an exhaust air-fuel ratio of 14.5. Also, HC
The exhaust gas on the downstream side of the adsorption catalyst 27 has a reduction degree O _X3.
Is controlled to a degree of reduction corresponding to an exhaust air-fuel ratio of 14.6 to 14.7.

At step ST26, is the degree of reduction O _X1 of the exhaust gas detected by the first oxygen concentration sensor 24 higher than the degree of reduction reference value O _X10 on the upstream side of the three-way catalyst 25 (the degree of reduction is strong)? Determine whether or not. The degree of reduction O _X1 of the exhaust gas is the reduction degree reference value O on the upstream side of the three-way catalyst 25.
When it is lower than _{X10, the} determination in step ST26 is YES, the process proceeds to step ST27, the feedback value Qfb1 of the fuel injection amount is reduced by the correction value α, and the process proceeds to step ST28. On the other hand, when the reduction degree reference value O _X10 or less, the process proceeds from step ST26 to step ST29, the feedback value Qfb1 is increased by the correction value α, and step ST28
Move on to.

In step ST28, the basic injection amount Qb
The final injection amount Qp is derived by adding the above-mentioned respective feedback values Qfb1, Qfb2, Qfb3 to step ST30, and the fuel is injected at step ST31 at the injection timing.

On the other hand, in step ST16, when the temperature of the HC adsorption catalyst 27 is in the initial operating state below the desorption operation start temperature _THC2 , the determination in step ST16 is YES, and the routine proceeds to step ST32. In step ST32, the initial injection amount Qpre is added to the basic injection amount Qb to set the final injection amount Qp so that the average air-fuel ratio in the combustion chamber 4 becomes 14.0. Then, the process proceeds to step ST30. Fuel is injected in step ST31 at the injection timing.

When the temperature T _HCE of the HC adsorption catalyst 27 becomes _{equal to} or higher than the desorption operation completion temperature T _{HC3 in} step ST17, that is, when it is determined that the desorption operation state has ended, step ST33 Go to the feedback value
Qfb2 and feedback value Qfb3 are set to zero, and the process proceeds to step ST26. Then, similarly to the above, steps ST27 and ST29
In step ST28, the feedback value Qfb1 is increased or decreased by the correction value α, and in step ST28, the final injection amount Qp is derived. In other words, the final injection amount Qp is derived by only feedback value Qfb1 which is determined based on the degree of reduction O _X1 of the exhaust gas at the upstream side of the three-way catalyst 25, migrated it from oxygen controlled release in warm operation control Becomes And step
In ST30, step ST31 according to the injection timing
In, fuel injection control is executed. In the warm operation control, feedback control of the fuel injection amount corresponding to the operation state is executed.

[0064]

Other Embodiments of the Invention
The exhaust passage 22 includes a three-way catalyst 25 and a first oxygen concentration sensor 2
4 may be omitted. In this case, in the oxygen release control, the fuel injection control based on the degree of reduction of exhaust gas on the upstream side of the three-way catalyst 25 is omitted.

In the above embodiment, the degree of reduction of the exhaust gas on the upstream side of the HC adsorption catalyst 27 is controlled by the feedback control of the fuel injection amount. However, the control of the degree of reduction of the exhaust gas is performed by the fuel injection amount. The feedback control is not limited to the above, but control by secondary air or the like can be applied.

In the above embodiment, the upstream side reference value O _X20 and the downstream side target value O _X30 of the HC adsorption catalyst 27 are set, and the feedback value is set so that the degree of reduction of the exhaust gas becomes the reference value or the target value, respectively. Although Qfb2 and Qfb3 are corrected, the downstream reference value (corresponding to the downstream reference value in claim 3) is used instead of the feedback control based on the feedback value Qfb2. (Corresponding to the upstream reference value in claim 3), and the correction means 44 sets
The control by the fuel injection control means 40 may be corrected so that the degree of reduction on the downstream side of the HC adsorption catalyst 27 becomes a degree of reduction between the upstream side reference value and the downstream side reference value. That is, if the degree of reduction on the downstream side of the HC adsorption catalyst 27 is not within this interval and is larger than the upstream reference value, then Qb + Qf
While reducing the fuel injection amount by b1 + Qfb2 by a predetermined amount, if it is in the meantime, Qb + Qfb1 + Qf without such correction
The fuel injection amount according to b2 may be directly injected. Even with such a configuration, the HC adsorption catalyst 27 is
Can be prevented from flowing in excessively, and H
It is possible to prevent excessive release of oxygen from the oxygen storage substance of the C adsorption catalyst 27.

[0067]

As described above, according to the inventions of claims 1 and 5, the control by the reduction degree control means is corrected based on the degree of reduction of the exhaust gas on the downstream side of the HC adsorption catalyst. Therefore, in the desorption operation state, it is possible to effectively use the oxygen released from the oxygen storage substance in the HC adsorption catalyst to process the HC and the like in the exhaust gas, and to optimize the release of oxygen. The amount can be controlled. That is, it is possible to prevent the exhaust gas from being unnecessarily controlled to the reducing side, improve fuel efficiency, and suppress excessive supply of oxygen to the HC adsorption catalyst. It becomes unnecessary to store oxygen more than necessary in the oxygen storage material.

Further, according to the second aspect of the present invention, it is possible to reliably prevent the exhaust gas from being unnecessarily controlled to the reducing side to improve the fuel consumption, and at the same time, the HC adsorption catalyst is excessively oxygenated. It is possible to prevent the oxygen storage substance from being supplied to the oxygen storage material, and it becomes unnecessary to store oxygen more than necessary in the oxygen storage material, so that the action and effect of the invention according to claim 1 can be effectively exhibited.

According to the third aspect of the present invention, it is possible to reliably prevent the exhaust gas from being unnecessarily controlled to the reducing side to improve the fuel consumption, and at the same time, to improve the fuel consumption of oxygen to the HC adsorption catalyst. The excessive supply can be reliably prevented, and it becomes unnecessary for the oxygen storage substance to store oxygen more than necessary, so that the action and effect of the invention according to claim 1 can be effectively exhibited.

Further, according to the invention of claim 4, since the degree of reduction of the exhaust gas is controlled by the feedback control of the fuel injection amount, the degree of reduction is accurately controlled by effectively utilizing the fuel injection control. can do.

[Brief description of drawings]

FIG. 1 is an overall view showing an overall configuration of an engine exhaust gas purification apparatus according to an embodiment.

FIG. 2 is a sectional view partially showing the structure of an HC adsorption catalyst.

FIG. 3 (a) is a characteristic diagram showing a driving operation of the HC adsorption catalyst, FIG. 3 (b) is a characteristic diagram showing a temperature change of the HC adsorption catalyst, and FIG. 3 (c) is an upstream side of the HC adsorption catalyst. FIG. 6 is a characteristic diagram showing changes in the degree of reduction of exhaust gas on the side.

FIG. 4 is a flowchart showing the first half of the control operation of the exhaust emission control system for the engine according to the embodiment.

FIG. 5 is a flowchart showing the latter half of the control operation of the engine exhaust gas purification apparatus according to the embodiment.

[Explanation of symbols]

22 Exhaust passage 27 HC adsorption catalyst 27b HC adsorbent 28 Third oxygen concentration sensor (reduction degree detecting means) 43 Reduction degree control means 44 Correction means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02D 41/04 305 F02D 41/04 330M 330 B01D 53/36 103Z (72) Inventor Yashiko Kato Hiroshima Prefecture 3-1, Shinchi Fuchu-cho, Aki-gun F-term in Mazda Co., Ltd. (reference) 3G091 AA11 AA17 AA24 AA28 AB03 AB10 BA01 BA15 CA22 CB02 CB03 DC01 EA01 EA05 EA06 EA07 EA19 EA30 EA34 FA04 GA06 GB06W GB07W GB09Y HA37G HA36G HA36G HA36G HAHA HAX HAHAG HA04 HA13 JA26 KA05 LA01 LA05 LB04 MA01 MA12 MA19 MA23 NC02 ND02 NE14 PA01Z PA09Z PA11Z PB03A PB05A PD03A PD04A PD09A PD12Z PD15Z PE01Z PE03Z 4D048 AA18 AB07 CC32 CC46 DA01 DA02 DA20 EA04

Claims (5)

[Claims] 1. An H which is arranged in an exhaust passage of an engine and which adsorbs HC while desorbing adsorbed HC as the temperature rises.
C adsorbent, an oxygen storage material that stores oxygen on the oxidation side and releases oxygen on the reduction side, and H desorbed from the HC adsorption material.
An HC adsorption catalyst containing a catalytic metal that oxidizes C, and a desorption operation state in which the desorption amount of HC from the HC adsorbent exceeds the adsorption amount of HC to the HC adsorbent at least,
Reduction degree control means for controlling the exhaust gas upstream of the HC adsorption catalyst or the exhaust gas in the HC adsorption catalyst to the reduction side so that oxygen is released from the oxygen storage substance, and the exhaust gas downstream of the HC adsorption catalyst in the exhaust passage. Exhaust gas purification of an engine, comprising: a reduction degree detection means for detecting a reduction degree; and a correction means for correcting the control by the reduction degree control means on the basis of the reduction degree detected by the reduction degree detection means. apparatus. 2. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the correcting unit corrects the degree of reduction detected by the degree-of-reduction detecting unit to be a predetermined value or less. 3. The reduction degree control means according to claim 1, wherein the reduction degree of exhaust gas in the upstream side of the HC adsorption catalyst or in the HC adsorption catalyst is controlled to an upstream side reference value, and the correction means detects the reduction degree. An exhaust gas purifying apparatus for an engine, wherein the degree of reduction of exhaust gas detected by the means is corrected so as to be equal to or lower than the upstream reference value and equal to or higher than a downstream reference value that is smaller than the upstream reference value. 4. The fuel injection amount feedback control according to claim 1, wherein the reduction degree control means sets the reduction degree on the downstream side of the HC adsorption catalyst to a target value having a reduction degree smaller than the reduction degree reference value on the upstream side. An engine exhaust purification device characterized by performing control. 5. The engine exhaust gas purification apparatus according to claim 1, wherein the reduction degree detection means detects the degree of reduction of the exhaust gas as an exhaust air-fuel ratio.