JP3644237B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly to an exhaust gas purification device that purifies exhaust gas immediately after startup.
[0002]
[Prior art]
For purifying exhaust gas discharged from an internal combustion engine of an automobile, a catalyst device carrying a catalyst made of a noble metal (platinum, rhodium, etc.) or other metal has been widely used. Such a catalyst purifies by oxidizing and reducing HC, CO, NOx, etc., which are harmful components in the exhaust gas. By the way, in order to obtain this catalytic action, the exhaust temperature must be high, for example, a temperature around 300 ° C. is required. However, immediately after the start of the internal combustion engine, the exhaust gas temperature is low and does not reach the temperature at which the catalyst is activated (around 300 ° C.), so exhaust harmful components are hardly purified, and a relatively large amount of exhaust harmful substances are released into the atmosphere. There is a problem of being released inside.
[0003]
Therefore, in order to solve the above problem, an exhaust recombustor is further provided on the upstream side of the catalyst device disposed in the exhaust system of the internal combustion engine. Immediately after startup, combustible exhaust gas is supplied to the recombustor. Those which are burned and the catalyst is activated early with the heat of combustion are known (Japanese Laid-open Patent Publication No. 6-508409, etc.). This exhaust purification device does not inject fuel into the exhaust recombustor, but enriches the air-fuel ratio of the internal combustion engine and supplies secondary air to generate combustible exhaust gas containing combustible components and air. The combustible gas is burned by the ignition device, and the catalyst can be activated quickly with a very simple configuration. Moreover, since HC and CO can be purified by combustion even before the catalyst activity, it can be said that this is a very effective means for purifying exhaust gas as a whole.
[0004]
[Problems to be solved by the invention]
However, in the above-described conventional exhaust purification device, there is no problem if the exhaust gas re-combustion is performed immediately from the start, but in practice, the gas in the exhaust gas re-combustor is controlled in the combustible region and ignited. However, since there is a delay of about several seconds, there is a drawback that a relatively large amount of unburned components are released during that period.
[0005]
In particular, as a premise for operating the exhaust recombustor, for example, if the air-fuel ratio of the air-fuel mixture combusted in the internal combustion engine is set to a rich state, the unburned components also increase accordingly. The emission of fuel components is a major problem.
[0006]
One cause of the ignition delay of such an exhaust recombustor is that the exhaust gas that is an inert gas stays in the exhaust passage when the engine is started, so even if combustible gas is generated upstream, By reaching the exhaust gas recombustor, it is diluted by the exhaust gas that has accumulated, and the ignitability is deteriorated. In other words, the mixed gas of the generated combustible gas and the accumulated exhaust gas will not ignite until it reaches an ignitable concentration, and during that time, some of the unburned components will be released to the atmosphere. is there.
[0007]
[Means for Solving the Problems]
Therefore, in order to solve the above-described problem, the present invention replaces the accumulated exhaust gas in the exhaust passage with air before operating the exhaust recombustor, that is, before starting the supply of the combustible gas. Ignition combustion was performed promptly at the start of supply of sex gases. Furthermore, in consideration of the dilution by the replaced air, the amount of secondary air supplied in the initial stage of the exhaust recombustor operation is reduced to achieve more reliable ignition combustion.
[0008]
That is, an exhaust gas purification apparatus for an internal combustion engine according to claim 1 is provided with a catalyst device provided in an exhaust passage of the internal combustion engine, an exhaust gas recombustor provided upstream of the catalyst device and provided with ignition means, In an exhaust gas purification device for an internal combustion engine, comprising: a combustible gas generating means for making exhaust gas supplied to an exhaust recombustor in a combustible state;
Prior to the supply of the combustible exhaust gas by the combustible gas generating means, the replacement means for replacing the exhaust gas staying in the exhaust passage with air before the engine is started or when the engine is not operating after the engine is stopped. It has.
[0009]
The combustible gas generation means includes, for example, a non-burning component supply means for temporarily increasing unburned components in the exhaust gas, and 2 in the exhaust gas upstream of the exhaust recombustor. A secondary air supply device for supplying secondary air. Further, the unburned component supply means comprises air-fuel ratio control means for temporarily setting the air-fuel ratio of the internal combustion engine to a rich state, for example. Alternatively, an individual fuel injection device or the like can be provided.
[0010]
As the replacement means, an appropriate scavenging pump or the like can be used. When the secondary air supply device is provided as described above, the replacement is performed by the secondary air supply device as in claim 4. Means can be configured.
[0011]
The replacement of the exhaust gas and the air in the exhaust passage only needs to be completed when the exhaust recombustor is operated. According to the fifth aspect of the present invention, the secondary air supply device is operated immediately before starting the internal combustion engine to replace the exhaust gas in the exhaust passage with air. According to a sixth aspect of the invention, when the operation of the internal combustion engine is finished, the secondary air supply device is operated to replace the exhaust gas in the exhaust passage with air.
[0012]
In this way, by replacing the exhaust gas in the exhaust passage with air in advance, there is no dilution by the exhaust gas that is an inert gas, and the ignitability is improved, so that ignition combustion can be performed quickly with the supply of combustible gas It becomes.
[0013]
The invention according to claim 7 is characterized in that the secondary air supply amount at the start of exhaust recombustion by the secondary air supply device is corrected to be reduced in consideration of the replaced air amount in the exhaust passage.
[0014]
FIG. 10 is an explanatory diagram showing the amount of gas flowing into the exhaust recombustor at the start of combustion in the exhaust recombustor. In the conventional apparatus, as shown in FIG. Three of the gas, the secondary air, and the residual exhaust gas in the exhaust passage are mixed and flow in. In this case, since the residual exhaust gas is an inert gas, the ignitability is greatly deteriorated. On the other hand, if the residual exhaust gas in the exhaust passage is replaced with air, as shown in (b), since inert gas does not exist, the ignitability is improved. However, as shown in the figure, since the air in the exhaust passage is added to the secondary air, the air-fuel mixture of the rich exhaust gas and the secondary air is further diluted by the air in the exhaust passage, and is slightly diluted. It becomes an air-fuel mixture and a certain ignition delay occurs. On the other hand, as shown in (c), if the secondary air supply amount is corrected to be reduced in consideration of the substituted air amount in the exhaust passage, the mixed gas as a whole becomes an appropriate air-fuel mixture, and ignition combustion is performed more quickly. To.
[0015]
This reduction correction may be continued until all the gas initially present in the exhaust passage passes through the exhaust recombustor. The larger the intake air amount of the internal combustion engine, the greater the amount of exhaust gas, and the shorter the time it takes for the originally existing gas to pass through the exhaust recombustor. Therefore, in the invention of claim 8, the time for correcting the amount of reduction is set based on the intake air amount of the internal combustion engine.
[0016]
【The invention's effect】
According to the present invention, the ignition delay period until the actual recombustion occurs in the exhaust recombustor due to the exhaust gas remaining in the exhaust passage can be shortened. Fuel components are greatly reduced. Therefore, in combination with the early activation of the catalyst by exhaust recombustion, it becomes possible to significantly reduce harmful components discharged at the time of cold start as a whole internal combustion engine.
[0017]
In particular, if the secondary air supply amount is corrected to decrease in consideration of the air amount in the replaced exhaust passage as in claims 7 and 8, the combustible gas having an appropriate concentration from the beginning is discharged to the exhaust recombustor. The ignition combustion can be started more quickly.
[0018]
Further, by replacing the exhaust gas and the air by using the secondary air supply device necessary for exhaust recombustion as in claim 4, it is not necessary to add a new pump or the like. Can be easily realized.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
[0020]
FIG. 1 shows the configuration of an embodiment of the present invention. The exhaust passage 2 of the internal combustion engine 1 is provided with a three-way catalyst device 6 in which a catalyst such as platinum is supported on a carrier made of ceramics or the like, and an exhaust recombustor 5 is disposed upstream of the catalyst device 6. Is provided. This exhaust recombustor 5 includes a spark plug 4 as an ignition means. The ignition plug 4 is connected to an ignition device (not shown) composed of an ignition coil and the like, and spark discharge is performed by the ignition device. In this embodiment, the catalyst device 6 and the exhaust reburner 5 are accommodated in the same casing.
[0021]
A secondary air pump 3 is connected to the upstream side of the exhaust recombustor 5 as a secondary air supply device. Further, the catalyst device 6 is provided with a catalyst temperature sensor 7 for detecting the internal temperature of the catalyst device 6, that is, the catalyst temperature, and the internal combustion engine 1 is provided with a water temperature sensor 9 for detecting the cooling water temperature. Yes. Detection signals from the catalyst temperature sensor 7 and the water temperature sensor 9 are input to the engine control unit 8.
[0022]
The secondary air pump 3 and the ignition device described above are controlled by control signals from the engine control unit 8, respectively, and supply and ignite secondary air during exhaust recombustion, as will be described later. Yes.
[0023]
A fuel injection device 11 is attached to the intake passage 10 of the internal combustion engine 1 so that fuel is injected by an injection signal from the engine control unit 8. This fuel injection amount is basically controlled according to the operating conditions of the internal combustion engine 1, but at the time of exhaust recombustion, the air-fuel ratio is kept rich by increasing the fuel injection amount.
[0024]
The basic operation of the exhaust emission control device will be described. When the internal combustion engine 1 is started (when the ignition switch is turned on), if the internal temperature of the catalyst device 6 is equal to or lower than a predetermined temperature (for example, 300 ° C.), the three-way catalyst Is determined to be inactive. If it is determined as inactive, the secondary air pump 3 is immediately started before cranking, and the exhaust gas remaining in the exhaust passage 2 is pushed out with the secondary air. That is, replacement of residual exhaust gas and air is performed. When the starter switch is turned on and cranking is started, the operation of the exhaust gas recombustor 5 is started at the same time. Specifically, the fuel is injected by the fuel injection device 11 so that the air-fuel ratio becomes very rich (the air-fuel ratio is 10 or less) by a signal from the engine control unit 8. At the same time, the secondary air pump 3 and the spark plug 4 are actuated by the control signal of the engine control unit 8, and supply of secondary air and spark discharge are started.
[0025]
As a result, combustible components (HC, CO, H ₂ ) from the exhaust gas and O ₂ by the secondary air are mixed and supplied to the downstream side, and this is ignited by the spark of the spark plug 4 and exhaust recombustor 5. Burn with. Activation of the catalyst device 6 is promoted by heat generated by the exhaust recombustion. Here, the initial secondary air supply amount is corrected to decrease so that the combustible air-fuel mixture does not become lean in consideration of the air amount existing in the exhaust passage 2, and when a predetermined period has passed, Is returned to the secondary air supply amount.
[0026]
When the internal temperature of the catalyst device 6 becomes higher than a predetermined temperature (for example, 350 ° C.) as a result of this exhaust reburning, it is determined that the three-way catalyst is completely activated, and the discharge of the spark plug 4 is stopped and the secondary air The operation of the pump 3 is stopped, and the exhaust gas reburning in the exhaust gas reburner 5 is terminated. At the same time, the fuel injection amount is controlled so that the air-fuel ratio becomes the stoichiometric air-fuel ratio in order for the three-way catalyst in the catalyst device 6 to work efficiently.
[0027]
As described above, in this exhaust purification device, the ignition delay period until actual recombustion is shortened by replacing the exhaust gas in the exhaust passage 2 with air when the internal combustion engine is started. FIG. 2 is a characteristic diagram for explaining the operation of the present invention. The vertical axis indicates the combustible mixture concentration at the inlet of the exhaust recombustor 5 (the concentration generated on the upstream side is assumed to be 100%). The horizontal axis shows the elapsed time from the start of the operation of the exhaust recombustor 5. In the conventional system in which exhaust gas remains in the exhaust passage 2, there is an ignition delay period due to a slow rise of the combustible mixture concentration in addition to a gas transport delay period from the internal combustion engine 1 to the exhaust recombustor 5. . On the other hand, in the present invention, a sufficient concentration is ensured from the first stage when the gas reaches the exhaust recombustor 5, and the ignition delay period is shortened. Thereby, combined with the early activation of the catalyst, the harmful components discharged during the cold start are significantly reduced as a whole.
[0028]
The above operation will be described more specifically based on the flowchart of FIG. This routine is started at the same time as the ignition switch of the internal combustion engine 1 is turned ON, and is repeatedly executed. A flag FENDEGC and a flag FEGC, which will be described later, are initialized to 0 at the start of control. First, in step 1 (abbreviated as S1 in the figure), it is determined based on the catalyst temperature at the time of starting or the cooling water temperature at the time of starting whether or not it is a condition for operating the exhaust recombustor 5. For example, if the catalyst temperature is 300 ° C. or lower, exhaust recombustion is performed. If it is a condition to be operated, the process proceeds to step 2 to refer to a flag FENDEGC indicating that exhaust reburning has ended. Since it is 0 in the initial state, the process proceeds from step 2 to step 3, and a flag FEGC indicating that the exhaust recombustor 5 is operating is referred to. Since it is also 0 in the initial state, the process proceeds from step 3 to step 4. In step 4, it is determined whether or not the predetermined time T1 has elapsed since the start of the operation of the secondary air pump 3, and the process proceeds to step 5 until the predetermined time T1 elapses to operate the secondary air pump 3. In particular, at this time, the pump drive signal KAP is set to MAXAP corresponding to the maximum flow rate, and exhaust scavenging air is supplied from the secondary air pump 3 into the exhaust passage 2.
[0029]
In the next step 7, it is determined whether the starter switch has been turned ON. If NO, the above processing is continued. Accordingly, the supply of air by the secondary air pump 3 is maximized until the starter switch is turned on or until a predetermined time T1 has elapsed, and the exhaust gas in the exhaust passage 2 is replaced with air. The reason why the air supply by the secondary air pump 3 is maximized is that when the driver turns on the starter switch immediately after turning on the ignition switch, the exhaust gas in the exhaust passage 2 is replaced with air. This is to deal with the fact that sufficient time cannot be secured.
[0030]
If the predetermined time T1 elapses before the starter switch is turned on, the process proceeds from step 4 to step 6 and the secondary air pump 3 is temporarily stopped.
[0031]
When the starter switch is turned on, cranking is started by a starter motor (not shown). That is, in step 8, the air-fuel ratio is set to a rich value, the discharge of the spark plug 4 is started, and the secondary air pump 3 is operated. In particular, at this time, a value obtained by subtracting the correction amount DAP from the basic supply amount TBLKAP is given as the pump drive signal KAP in order to reduce the secondary air supply amount. Here, as shown in FIG. 4, the basic supply amount TBLKAP is set according to the cooling water temperature, and the flow rate increases as the temperature decreases. The air-fuel ratio is also set richer as the temperature is lower. Further, the correction amount DAP takes into account the air present in the exhaust passage 2.
[0032]
In this way, since the combustible exhaust gas is supplied to the exhaust gas recombustor 5 at an appropriate concentration from the beginning, ignition combustion is immediately performed.
[0033]
In step 9, the flag FEGC indicating that the exhaust recombustor 5 is operating is set to 1. Thereby, the process proceeds from step 3 to step 10 thereafter. In step 10, it is determined whether or not a predetermined time T2 has elapsed since the start of the operation of the exhaust recombustor 5, and the secondary air supply amount is reduced as described above until the predetermined time T2 has elapsed. The operation of the exhaust reburner 5 is continued in the corrected state. The predetermined time T2 corresponds to a period until the influence of the air previously introduced into the exhaust passage 2 is eliminated. When the predetermined time T2 has elapsed, the routine proceeds to step 11 where the drive signal KAP for the secondary air pump 3 is set to the basic supply amount TBLKAP.
[0034]
In the flowchart of FIG. 3, only the process at the start of exhaust recombustion is shown. As described above, for example, when the temperature of the catalyst device 6 reaches a predetermined temperature, the operation of the exhaust recombustor 5 is performed. Stops. At this time, the flag FENDEGC is set to 1.
[0035]
In the above embodiment, the starter switch is turned on and cranking is started, and the exhaust gas recombustor 5 is started at the same time. However, when the start of fuel injection is slightly delayed at the start of cranking, Scavenging in the exhaust passage 2 is further ensured. That is, if the intake air is sent to the exhaust passage 2 as it is without injecting fuel for a predetermined period after the cranking is started, the time from the ignition switch ON to the starter switch ON, that is, the secondary air pump Even if the period of replacement by 3 is short, it can be compensated.
[0036]
Next, a second embodiment will be described based on the flowchart of FIG. This is a partial modification of the processing in step 10 described above. FIG. 5 shows only the main part, and the same part as in FIG. 3 is omitted.
[0037]
If the flag FEGC is set to 1 in step 9 described above, the process proceeds to step 31 where the coolant temperature TW is read. In step 32, the intake air amount QA of the internal combustion engine 1 is estimated from the cooling water temperature TW based on the characteristics shown in FIG. Note that the intake air amount QA may be directly detected by an air flow meter (not shown). In the next step 33, the secondary air supply amount correction time TAP is determined from the intake air amount QA based on the characteristics shown in FIG. Then, in step 34, it is determined whether or not the correction time TAP has elapsed since the operation of the exhaust recombustor 5 has started. When the correction time TAP has elapsed, the process proceeds to step 11 described above. The drive signal KAP of the secondary air pump 3 is set to the basic supply amount TBLKAP.
[0038]
That is, in the embodiment of FIG. 3, the correction time for reducing the secondary air is fixedly given, whereas in this embodiment, the correction time TAP is given corresponding to the intake air amount QA. This is because the larger the intake air amount QA, the larger the exhaust gas amount, and the shorter the time until the initial combustible exhaust gas mixed with the remaining air in the exhaust passage 2 passes through the exhaust recombustor 5. In this way, fluctuations in the concentration of the combustible gas in the exhaust recombustor 5 are further reduced.
[0039]
Next, FIGS. 8 and 9 are flow charts showing a third embodiment of the present invention. This embodiment is characterized in that the exhaust gas in the exhaust passage 2 is replaced with air at the end of engine operation.
[0040]
FIG. 8 shows the flow of processing executed when the internal combustion engine 1 is stopped. If it is determined in step 101 that the ignition switch has been turned OFF, the routine proceeds to step 102 where the secondary air pump 3 is operated. The operation of the secondary air pump 3 is continued for a predetermined time TEAP set in advance so as to be sufficient for scavenging (step 103), and when the time TEAP has elapsed, the secondary air pump 3 stops (step 104). A series of control ends.
[0041]
Thus, by scavenging by the secondary air pump 3 at the end of the operation, the exhaust gas in the exhaust passage 2 is surely replaced with air. In particular, since the scavenging time can be set sufficiently long, even when the volume of the exhaust passage 2 is large or the secondary air pump 3 is relatively small, exhaust gas does not remain in the exhaust passage 2 and is completely Can be substituted.
[0042]
By substituting with air in advance in this way, a special replacement process becomes unnecessary at the next start-up. The flowchart in FIG. 9 shows the flow of the process at the time of starting, but this is only the process in which steps 4 to 6 corresponding to the replacement process are omitted from the flowchart in FIG. The detailed explanation is omitted. As shown in FIG. 5, the correction time can be set to correspond to the intake air amount QA.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a mechanical configuration of an exhaust emission control device according to the present invention.
FIG. 2 is a characteristic diagram showing the change over time in the concentration of a combustible mixture at the exhaust recombustor inlet in comparison with the present invention and the prior art.
FIG. 3 is a flowchart showing an embodiment of control of the exhaust gas purification apparatus.
FIG. 4 is an explanatory diagram showing a relationship between a water temperature TW and a basic drive signal TBLKAP for a secondary air pump.
FIG. 5 is a flowchart showing only a main part of the second embodiment.
FIG. 6 is an explanatory diagram showing a relationship between a water temperature TW and an intake air amount QA.
FIG. 7 is a characteristic diagram showing a relationship between an intake air amount QA and a secondary air supply amount correction time TAP.
FIG. 8 is a flowchart of processing at the end of operation according to a third embodiment.
FIG. 9 is a flowchart at the start of operation, similarly showing a third embodiment.
FIG. 10 is an explanatory view showing the amount of gas flowing into the exhaust recombustor in comparison with the conventional one.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Exhaust passage 3 ... Secondary air pump 4 ... Spark plug 5 ... Exhaust recombustor 6 ... Catalyst device 7 ... Catalyst temperature sensor 8 ... Engine control unit 11 ... Fuel injection device

Claims (8)

A catalyst device provided in an exhaust passage of an internal combustion engine, an exhaust recombustor located upstream of the catalyst device and provided with ignition means, and an exhaust gas supplied to the exhaust recombustor in a combustible state In an exhaust gas purification device for an internal combustion engine, comprising:
Prior to the supply of the combustible exhaust gas by the combustible gas generating means, the replacement means for replacing the exhaust gas staying in the exhaust passage with air before the engine is started or when the engine is not operating after the engine is stopped. An exhaust emission control device for an internal combustion engine, comprising: The combustible gas generation means includes unburned component supply means for temporarily increasing unburned components in the exhaust gas, and secondary air for supplying secondary air into the exhaust gas upstream of the exhaust recombustor. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, comprising a supply device. 3. An exhaust purification system for an internal combustion engine according to claim 2, wherein said unburned component supply means comprises air-fuel ratio control means for temporarily setting the air-fuel ratio of the internal combustion engine to a rich state. 4. The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the replacement means is constituted by the secondary air supply device. 5. The exhaust emission control device for an internal combustion engine according to claim 4, wherein the secondary air supply device is operated immediately before starting the internal combustion engine to replace the exhaust gas in the exhaust passage with air. 5. The exhaust gas purification apparatus for an internal combustion engine according to claim 4, wherein the secondary air supply device is operated at the end of the operation of the internal combustion engine to replace the exhaust gas in the exhaust passage with air. The secondary air supply amount at the beginning of exhaust recombustion by the secondary air supply device is corrected to decrease in consideration of the amount of air replaced in the exhaust passage. Exhaust gas purification device for internal combustion engine. 8. The exhaust gas purification apparatus for an internal combustion engine according to claim 7, wherein a time for correcting the reduction is set based on an intake air amount of the internal combustion engine.

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