JP2007154692A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To excellently retain exhaust emission control performance when an exhaust gas purifying catalyst is deteriorated. <P>SOLUTION: When it is diagnosed that the exhaust gas purifying catalyst is deteriorated, the valve overlap amount of an intake/exhaust valve is corrected to be increased, ignition timing is corrected to lag its phase, an EGR amount is corrected to be increased, and these correction amounts are set to be increased according to an increase in engine load, so that emissions of NOx and HC (unburnt fuel) from an engine (combustion chamber) are reduced, and also exhaust is circulated to a bypass catalyst arranged by bypassing the exhaust gas purifying catalyst diagnosed as deteriorated. Thereby, emissions discharged from the engine are purified. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine provided with an exhaust gas purification catalyst in an exhaust passage.

In Patent Document 1, a low-temperature catalyst is provided separately from a normal exhaust purification catalyst, and the flow is switched to a low-temperature catalyst with little deterioration by a switching valve, thereby reducing exhaust emission during cold operation. Is disclosed.
Utility Model 1-66420

As is well known, since exhaust purification performance of exhaust purification catalysts deteriorates due to deterioration, the deterioration state of the catalyst is diagnosed, and when it is diagnosed that the catalyst is deteriorated, the catalyst is replaced based on the diagnosis result. I try to let them.
However, until the catalyst is replaced, the exhaust emission deteriorates. Even in the above-mentioned Patent Document 1, the low temperature catalyst is used only when the engine is cold. The deterioration of exhaust emissions could not be avoided.

  The present invention has been made paying attention to such a conventional problem, and it is possible to prevent deterioration of exhaust emission until the catalyst is replaced when the exhaust purification catalyst is diagnosed as being deteriorated. With the goal.

Therefore, the present invention provides an exhaust gas purification apparatus for an internal combustion engine having an exhaust gas purification catalyst in an exhaust passage.
Diagnosing the deterioration state of the exhaust purification catalyst, and when it is diagnosed that the exhaust purification catalyst is deteriorated, increase correction of the valve overlap amount of the intake and exhaust valves, correction of the retard of the ignition timing, increase of the EGR amount Correction is performed, and the flow path is switched to the second exhaust purification catalyst provided by bypassing the exhaust purification catalyst.

In this way, by increasing the valve overlap amount when the exhaust purification catalyst is deteriorated, HC (unburned fuel) discharged from the engine (combustion chamber) due to exhaust blow-back can be reduced and the internal EGR amount can be reduced. The combustion temperature decreases due to the increase in NOx, and NOx can be reduced.
Further, when the exhaust purification catalyst is deteriorated, the ignition timing is retarded to reduce NOx discharged from the engine (combustion chamber) due to a decrease in the combustion temperature, and HC can be reduced due to the afterburning promoting effect.

Further, when the exhaust purification catalyst is deteriorated, the NOx discharged from the engine (combustion chamber) due to the decrease in the combustion temperature can be reduced by increasing the EGR amount.
Further, by switching the flow path to the second exhaust purification catalyst when the exhaust purification catalyst is deteriorated, exhaust emissions such as HC and NOx can be reduced by using the second exhaust purification catalyst that has not deteriorated.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system configuration diagram of a vehicle engine in the embodiment.
Air is sucked into the engine 1 shown in FIG. 1 through an air cleaner 2, an intake duct 3, an electrically controlled throttle chamber 4, an intake collector 5, an intake manifold 6, and an intake valve 7.
Further, a fuel injection valve 9 for directly injecting fuel into the combustion chamber 8 is provided for each cylinder, and the air sucked into the cylinder and the fuel injected from the fuel injection valve 9 are mixed for combustion mixing. Qi is formed.

The air-fuel mixture formed in the combustion chamber 8 is ignited and burned by spark ignition by the spark plug 10.
Combustion exhaust from the engine 1 is discharged via an exhaust valve 11, an exhaust manifold 12, an exhaust duct 13, and a pair of exhaust purification catalysts 14A, B on the upstream side and the downstream side.
Here, the exhaust purification catalysts 14A and 14B have not only a three-way catalyst that purifies HC, CO, and NOx by oxidation / reduction reactions, but also the function of the three-way catalyst, and the exhaust air-fuel ratio is lean. A NOx trap catalyst or the like having a function of trapping NOx in exhaust gas and desorbing and purifying NOx trapped when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio or rich may be used. Of course, the catalyst may be one catalyst without being divided into upstream and downstream.

A part of the exhaust duct 11 on the downstream side of the exhaust purification catalysts 14A, B is bypassed in parallel, and a bypass catalyst 16 having an exhaust purification function similar to that of the exhaust purification catalysts 14A, B is interposed in the bypass passage 15.
In addition, a flow path switching valve 17 that selectively opens the bypass passage 15 and the main passage parallel to the bypass passage 15 is provided at the upstream branch point of the bypass passage 15 in the exhaust duct 11.

Further, an EGR passage (exhaust gas recirculation passage) 18 is provided for communicating the exhaust manifold 12 and the intake collector 5, and when the EGR control valve 19 interposed in the EGR passage 18 is opened, a part of the exhaust is caused by the pressure difference. The air is returned to the intake collector 5.
The electrically controlled throttle chamber 4, the fuel injection valve 8, the spark plug 9, the flow path switching valve 17, and the EGR control valve 19 are controlled by an engine control unit (hereinafter referred to as ECU) 20.

The ECU 20 is configured to include a microcomputer, and performs arithmetic processing on detection signals from various sensors in accordance with a program stored in advance, so that the electric control type throttle chamber 4, the fuel injection valve 8, the spark plug 9, and the EGR control valve 19 are processed. A control signal is output.
The various sensors include an air flow meter 21 that is interposed in the intake duct 3 and detects the intake air amount of the engine 1, a crank angle sensor 22 that outputs a detection signal synchronized with the rotation of the crankshaft, and the pair of exhaust purification catalysts. Air-fuel ratio sensors 23a and 23b are provided on the upstream side and downstream side of 14A and 14B and output air-fuel ratio signals corresponding to the oxygen concentration in the exhaust gas, respectively.

Then, the deterioration diagnosis of the exhaust purification catalysts 14A and 14B is performed based on a known deterioration diagnosis method such as the ratio of the rich / lean reversal cycle of the air / fuel ratio upstream and downstream of the catalyst detected by the two air / fuel ratio sensors 23a and 23b. When the deterioration is diagnosed, various processes for preventing the exhaust emission from deteriorating are executed.
Next, details of the process at the time of catalyst deterioration diagnosis by the ECU 20 will be described with reference to the flowchart of FIG.

In the flowchart of FIG. 2, first, in step S1, it is determined whether or not the catalyst has deteriorated by the deterioration diagnosis of the exhaust purification catalysts 14A and 14B.
Specifically, the ratio of the air-fuel ratio rich / lean inversion period ta detected by the upstream air-fuel ratio sensor 23a to the air-fuel ratio rich / lean inversion period tb detected by the downstream air-fuel ratio sensor 23b (ta When / tb) becomes equal to or greater than a predetermined threshold value, it is diagnosed that the amount of oxygen storage in the catalyst has decreased and deteriorated, and the catalyst diagnosis NG flag is turned ON. It is determined whether or not the catalyst has deteriorated based on the value of the catalyst diagnosis NG flag. When the catalyst diagnosis NG flag is turned ON, a warning lamp is turned on at the same time, whereby the catalyst is replaced at a service factory or the like. The present invention intends to reduce exhaust emission until the catalyst replacement.

When it is diagnosed that the catalyst is not deteriorated, this flow is terminated. When it is diagnosed that the catalyst is deteriorated, the process proceeds to step S2.
In step S2, whether the engine load T (detected by values representative of loads such as fuel injection amount, intake air amount, throttle opening, etc.) T is in a low load region below a threshold a for determining low load. Determine.

When it is determined in step S2 that the load is in the low load range, the process proceeds to step S3, and the valve overlap amount O / L of the intake / exhaust valve is set in a state where the catalyst is not deteriorated as in the following equation. The set amount O / Lnormal is corrected to be increased by a predetermined amount O / Lα set corresponding to the low load.
O / L = O / Lnormal + O / Lα
Next, in step S4, the ignition timing ADV (set as the advance amount from the reference crank angle position) is set at a low load with respect to the set amount ADVnormal that is also set in a state where the catalyst is not deteriorated, as in the following equation. Is retarded by a predetermined amount RETα set corresponding to

ADV = ADVnormal-RETα
Next, in step S5, the exhaust gas recirculation amount EGR to the intake system is set corresponding to the low load with respect to the set amount EGRnormal that is also set in a state where the catalyst is not deteriorated, as in the following equation. Increase correction is performed by a predetermined amount EGRα.
EGR = EGRnormal + EGRα
Next, in step S <b> 13, the flow path switching valve 17 opens the bypass passage 15 and causes the exhaust to flow through the bypass catalyst 16.

On the other hand, if it is determined in step S2 that the load T is not less than a, the process proceeds to step S6, and whether the load T is equal to or less than the threshold b (> a) for determining the medium load, that is, a ≦ T ≦ It is determined whether it is in the middle load range of b.
When it is determined in step S6 that the vehicle is in the medium load region, the process proceeds to step S7, and the predetermined amount O / Lnormally set corresponding to the medium load with respect to the set amount O / Lnormal as shown in the following equation. Increase correction by Lβ (> O / Lα).

O / L = O / Lnormal + O / Lβ
Next, in step S8, the ignition timing ADV is retarded by a predetermined amount RETβ (> RETα) set corresponding to the medium load with respect to the set amount ADVnormal as shown in the following equation.
ADV = ADVnormal-RETβ
Next, in step S9, the exhaust gas recirculation amount EGR is corrected to increase by a predetermined amount EGRβ set corresponding to the medium load with respect to the set amount EGRnormal, as in the following equation.

EGR = EGRnormal + EGRβ
Next, the process proceeds to step S <b> 13, and the exhaust gas is circulated through the bypass catalyst 16.
If it is determined in step S6 that the load T is in a high load range exceeding the threshold value b, the process proceeds to steps S10, 11, and 12, and the valve overlap amount O / L is sequentially calculated as in the following equation. After correcting the ignition timing ADV and the exhaust gas recirculation amount EGR, the routine proceeds to step S13, where the exhaust gas is circulated to the bypass catalyst 16.

O / L = O / Lnormal + O / Lγ where O / Lγ> O / Lβ
ADV = ADVnormal−RETγ where RETγ> RETβ
EGR = EGRnormal + EGRγ where EGRγ> EGRβ
In this way, when it is diagnosed that the exhaust purification catalysts 14A and 14B are deteriorated, the exhaust from the engine 1 is corrected by correcting the valve overlap amount O / L, the ignition timing ADV, and the EGR amount. Emissions can be maintained well.

Specifically, by increasing the valve overlap amount O / L, it is possible to enhance the exhaust blow-back effect, thereby suppressing HC emission from the engine (combustion chamber) and reducing the HC emission amount. Similarly, the ratio of the internal EGR amount in the intake air increases due to the increase in the exhaust blow-back amount, so that the combustion temperature decreases and NOx can also be reduced.
In addition, by correcting the ignition timing to retard, ignition combustion is performed at a timing away from the maximum pressure at the compression top dead center, so that the combustion temperature is lowered and discharged from the engine (combustion chamber). NOx can be reduced, and HC can be reduced by the afterburning promoting effect.

Further, by increasing and correcting the amount of inert EGR gas, it is possible to reduce NOx discharged from the engine (combustion chamber) when the combustion temperature decreases.
By these three corrections, the exhaust emission from the engine is improved as much as possible, and the new or substantially unused new state of the bypass catalyst 16 (first) is used only when the exhaust purification catalysts 14A and 14B are always used. 2), the exhaust emission finally discharged from the bypass catalyst 16 can be maintained sufficiently satisfactorily.

Here, the bypass catalyst 16 is used with a very low use frequency, and is used after reducing the exhaust emission from the engine by performing the above-mentioned various corrections. That's fine.
In addition, since the exhaust emission from the engine gets worse as the load increases, increasing each correction amount according to the increase in load as in this embodiment sets the correction amount necessary and sufficient for exhaust purification. can do.

However, since the driver is notified of catalyst deterioration and the catalyst is replaced, a large correction amount is set within this range so as not to adversely affect the engine, and even if there is a slight decrease in operability, exhaust purification is possible. You may make it give priority to performance.
FIG. 3 shows how various state quantities change in the above embodiment, together with a comparative example in which correction according to the present invention is not performed.

FIG. 4 is a system configuration diagram of a vehicle engine according to an embodiment in which a low-temperature catalyst used when cold is used as the second exhaust purification catalyst.
In the present embodiment, a low-temperature catalyst 32 is interposed in a bypass passage 31 connected in parallel with the upstream side exhaust purification catalyst 14 </ b> A, and the bypass passage 31 and the bypass passage 31 at the upstream branch point of the bypass passage 31 in the exhaust duct 11. A flow path switching valve 33 for selectively opening a main passage in parallel with the main passage is provided.

  The low-temperature catalyst 32 is made of a catalyst material that can be activated even at low temperatures to obtain a good exhaust purification function, or is used in a state in which the catalyst is activated by increasing the temperature by incorporating an electric heater or the like. The flow path switching valve 33 is controlled to open the bypass passage 31 when the water temperature detected by a water temperature sensor (not shown) is below a predetermined value, and the exhaust gas is led to the low temperature catalyst 32. As a result, exhaust emissions during cold operation are well maintained.

  Then, a deterioration diagnosis of the exhaust purification catalysts 14A and 14B is performed in the same manner as in the first embodiment, and when it is determined that the catalyst is deteriorated, an increase correction of the valve overlap amount O / L, an ignition timing ADV And the EGR amount increase correction, and the flow path switching valve 33 is controlled to open the bypass passage 31 so that the exhaust gas is passed through the low temperature catalyst 32 and purified by the low temperature catalyst 32. To.

Since the low temperature catalyst 32 is used only when it is cold, the degree of deterioration is lower than that of the exhaust purification catalysts 14A and 14B. Therefore, good exhaust purification performance is obtained until the deteriorated exhaust purification catalysts 14A and 14B are replaced. Since a catalyst previously provided for low temperatures can be used, the cost can be reduced.
In the embodiment described above, the valve overlap amount O / L increase correction, the ignition timing ADV retardation correction, the EGR amount increase correction, and the switching of the flow path to the second exhaust purification catalyst are all performed. However, even if one of these is omitted and only one is performed, the exhaust purification performance can be improved when the normal exhaust purification catalyst is deteriorated.

The system block diagram of the vehicle engine in 1st Embodiment. The flowchart which shows the detail of the process at the time of the catalyst deterioration diagnosis in embodiment same as the above. The time chart which shows the mode of the change of the various state quantities when the catalyst in embodiment same as the above is diagnosed with the comparative example which does not perform correction | amendment which concerns on this invention. The system block diagram of the vehicle engine in 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Engine 7 ... Intake valve 10 ... Spark plug 11 ... Exhaust valve 13 ... Exhaust duct 14A, B ... Exhaust purification catalyst 15 ... Bypass passage 16 ... Bypass catalyst 17 ... Flow path switching valve 18 ... EGR passage 19 ... EGR control valve 20 ... Engine control unit (ECU)
21 ... Air flow meter 22 ... Crank angle sensor 23a ... Air-fuel ratio sensor (upstream side of catalyst)
23b ... Air-fuel ratio sensor (catalyst downstream side)
31 ... Bypass passage 32 ... Low temperature catalyst 33 ... Flow path switching valve

Claims (8)

In an exhaust gas purification apparatus for an internal combustion engine provided with an exhaust gas purification catalyst in an exhaust passage,
Catalyst deterioration diagnosis means for diagnosing the deterioration state of the exhaust purification catalyst;
A valve overlap amount correcting means for correcting an increase in the valve overlap amount of the intake / exhaust valve when the catalyst deterioration diagnosis means diagnoses that the exhaust purification catalyst is deteriorated;
An exhaust emission control device for an internal combustion engine, comprising:   The load detecting means for detecting the load of the engine is provided, and when the engine load is large, the increase correction amount of the valve overlap amount by the valve overlap amount correcting means is made larger than when the load is small. An exhaust gas purification apparatus for an internal combustion engine as described. In an exhaust gas purification apparatus for an internal combustion engine provided with an exhaust gas purification catalyst in an exhaust passage,
Catalyst deterioration diagnosis means for diagnosing the deterioration state of the exhaust purification catalyst;
An internal combustion engine comprising: an ignition timing retarding correction unit that retards an ignition timing when the catalyst degradation diagnosis unit diagnoses that the exhaust purification catalyst is degraded. Exhaust purification device.   The load detection means for detecting the engine load is provided, and when the engine load is large, the ignition timing retardation correction amount by the ignition timing retardation correction means is made larger than when the engine load is small. Exhaust gas purification device for internal combustion engine. In an exhaust gas purification apparatus for an internal combustion engine provided with an exhaust gas purification catalyst in an exhaust passage,
Catalyst deterioration diagnosis means for diagnosing the deterioration state of the exhaust purification catalyst;
And an EGR amount correcting unit that increases and corrects the recirculation amount (EGR amount) of the exhaust gas to the intake system when the catalyst deterioration diagnosis unit diagnoses that the exhaust purification catalyst has deteriorated. An exhaust gas purification apparatus for an internal combustion engine characterized by the above.   6. The exhaust of the internal combustion engine according to claim 5, further comprising load detection means for detecting engine load, wherein the EGR increase correction amount by the EGR amount correction means is larger when the engine load is large than when the engine load is small. Purification equipment. In an exhaust gas purification apparatus for an internal combustion engine, comprising: a first exhaust gas purification catalyst in an exhaust passage; and a second exhaust gas purification catalyst that bypasses the first exhaust gas purification catalyst;
Catalyst deterioration diagnosis means for diagnosing the deterioration state of the first exhaust purification catalyst;
Flow path switching means for switching the flow path so as to guide the exhaust to the second exhaust purification catalyst when the catalyst deterioration diagnosis means diagnoses that the first exhaust purification catalyst is deteriorated;
An exhaust emission control device for an internal combustion engine, comprising:   8. The exhaust gas purification apparatus for an internal combustion engine according to claim 7, wherein the second exhaust gas purification catalyst is a low temperature catalyst used when the engine is cold.

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