JP3629953B2 - 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 prevents the discharge of HC immediately after startup by an HC adsorbent interposed in an exhaust passage.
[0002]
[Prior art]
Conventionally, a three-way catalyst supporting a noble metal (platinum, palladium, rhodium, etc.) or other metals has been used for purifying exhaust gas emitted from an internal combustion engine of an automobile. Such a catalyst purifies by oxidizing or reducing HC, CO, NOx, etc., which are harmful components in the exhaust gas, but in order to obtain this catalytic action, the exhaust temperature must be high, For example, a temperature of about 200 to 300 ° C. is generally required for purification using an HC catalyst. 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 above catalyst is activated (for example, 200 ° C. or higher). Therefore, HC is hardly purified, and most of the HC generated in the internal combustion engine is atmospheric. Will be released.
[0003]
Therefore, in addition to a general three-way catalyst device, an HC adsorbent that adsorbs HC under low temperature conditions is arranged in the exhaust system of the internal combustion engine so as to adsorb HC discharged before catalyst activation. Known (Japanese Patent Laid-Open Nos. 6-241028, 7-144119, etc.). This HC adsorbent, for example, uses zeolite or the like, and has a characteristic of adsorbing HC at a low temperature and then desorbing the adsorbed HC when a predetermined desorption temperature is reached. . The desorbed HC is purified by the activated catalyst.
[0004]
JP-A-7-109934 discloses a technique for reducing the amount of HC itself generated from an internal combustion engine by changing the opening and closing timing of the intake and exhaust valves at the time of cold start. Japanese Patent Laid-Open No. 8-158897 discloses that the exhaust pressure is increased by closing the exhaust shutter valve during cold start to suppress the discharge of unburned components, and an HC adsorbent is disposed upstream of the exhaust shutter valve. The configuration is disclosed.
[0005]
[Problems to be solved by the invention]
However, the above-mentioned HC adsorbents, especially zeolite-based adsorbents, have high adsorption efficiency for HC having a large molecular weight, but low adsorption efficiency for HC having a small molecular weight, and thus catalytic activity. In the previous stage, there is a problem that HC having a small molecular weight is easily released to the atmosphere.
[0006]
[Means for Solving the Problems]
FIG. 1 is a characteristic diagram showing the relationship between the opening / closing timing of a general intake / exhaust valve and the amount of HC discharged at the downstream position of the exhaust valve. As shown in this figure, HC is discharged when the exhaust valve starts to open. And two peaks, the vicinity of the piston reaching top dead center. Here, focusing on the molecular weight of each HC, the molecular weight of the first peak is large and the molecular weight of the second peak is small. This latter HC is considered that the liquid fuel remaining in the clevis volume has just been vaporized. Therefore, the molecular weight is smaller than that of the former, and the adsorption efficiency with the HC adsorbent is low.
[0007]
Therefore, in the first invention according to claim 1, the generation of HC having a small molecular weight is suppressed by advancing the opening timing of the intake valve, and the former HC having a large molecular weight is more reliably prevented by the HC adsorbent. Adsorption was performed to greatly reduce the release of HC into the atmosphere.
[0008]
That is, the exhaust gas purification apparatus for an internal combustion engine according to claim 1 is interposed in an exhaust passage of the internal combustion engine and adsorbs HC (hydrocarbon component) in the exhaust,
A variable valve mechanism that is provided at least on the intake valve side of the internal combustion engine and is capable of variably controlling at least the opening timing of the intake valve;
Means for detecting a cold state of the internal combustion engine;
An open / close timing control means for advancing the opening timing of the intake valve when the internal combustion engine is cold;
The that features.
[0009]
If the opening timing of the intake valve is advanced as described above, the exhaust blowback to the intake system increases, and the discharge of HC having a low molecular weight generated near the top dead center of the piston to the exhaust system decreases. Further, if the opening / closing timing on the exhaust valve side is fixed, the valve overlap expands due to the advance of the opening timing of the intake valve in this way, and in an extreme case, instability of combustion occurs and HC Although the production amount itself may increase on the contrary, the molecular weight of HC that increases with the instability of the combustion is relatively large, so that it can be reliably adsorbed by the HC adsorbent. .
[0010]
In the second invention according to claims 3 and 4 , the generation of HC having a small molecular weight in the vicinity of the top dead center is suppressed by advancing the closing timing of the exhaust valve.
[0011]
That is, the exhaust gas purification apparatus for an internal combustion engine according to claims 3 and 4 is provided in an exhaust passage of the internal combustion engine, adsorbs HC (hydrocarbon component) in the exhaust, and
A variable valve mechanism that is provided at least on the exhaust valve side of the internal combustion engine and can variably control at least the closing timing of the exhaust valve;
Means for detecting a cold state of the internal combustion engine;
An opening / closing timing control means for advancing the closing timing of the exhaust valve to before the top dead center when the internal combustion engine is cold;
It has.
[0012]
If the exhaust valve is closed before top dead center in this way, discharge of HC having a small molecular weight in the vicinity of top dead center is suppressed. Accordingly, it is possible to reliably prevent the discharge of HC in combination with the action of adsorbing HC having a relatively large molecular weight by the HC adsorbent.
[0013]
The devices disclosed in Japanese Patent Application Laid-Open No. 7-109934 and Japanese Patent Application Laid-Open No. 8-158897 are designed to reduce the total amount of HC generated from the internal combustion engine regardless of the molecular weight of HC. The characteristics of the HC adsorbent having an excellent adsorption action for HC having a relatively large molecular weight cannot be fully utilized.
[0014]
The HC adsorbent is made of a zeolitic adsorbent as described in claim 5 , for example. As described above, this zeolite adsorbent has high adsorption efficiency for HC having a large molecular weight and low adsorption efficiency for HC having a small molecular weight.
[0015]
Also, the cold state detecting means, as in claims 1 and 3, and detects that said HC absorbent is less than the desorption start temperature. That is, by changing the opening / closing timing only when the adsorption action by the HC adsorbent is obtained, unnecessary deterioration of combustion and the like can be minimized.
[0016]
In the inventions of claims 2 and 4 , the advance amount of the intake valve opening timing or the exhaust valve closing timing is made smaller as the load of the internal combustion engine is lower. Thereby, instability of combustion in a low load region such as idle is suppressed.
[0017]
【The invention's effect】
According to the exhaust gas purification apparatus for an internal combustion engine according to the present invention, when the engine is cold, the HC having a high molecular weight is adsorbed by the HC adsorbent and the HC having a low molecular weight that is difficult to be adsorbed is closed at the intake valve opening timing or the exhaust valve closing time. Since the emission is suppressed by the advance of the timing, as a whole, the amount of HC emission can be reduced to a very low level.
[0018]
In particular, by combining HC adsorbent and variable control of intake / exhaust valve opening / closing timing, the adsorption efficiency of HC adsorbent can be utilized to the maximum, and HC can be significantly reduced with a relatively small capacity of HC adsorbent. This can be realized, and there is no adverse effect of an increase in HC due to deterioration of combustion due to advancement of the opening / closing timing, and HC actually discharged can be greatly reduced.
[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. 2 is a structural explanatory view showing a first embodiment of the present invention, and a piston 3 defining a combustion chamber 4 is slidably fitted to each cylinder 2 of the internal combustion engine 1. A spark plug 5 is disposed at the center. The exhaust passage 7 connected to the combustion chamber 4 via the exhaust valve 6 is provided with a three-way catalyst device 8 serving as a pre-catalytic converter, and HC in the exhaust at the low temperature is disposed downstream thereof. An adsorption catalyst device 9 is interposed as an adsorbent to be adsorbed. In this embodiment, the three-way catalyst device 8 and the adsorption catalyst device 9 are accommodated in the same casing. The adsorption catalyst device 9 is a device in which an adsorption catalyst obtained by mixing a zeolite-based HC adsorption component and a three-way catalyst component such as a noble metal is supported on a carrier made of ceramics, etc., and a part of the adsorbed HC is catalyzed. It has a self-purifying function of oxidizing with. Or it can also be set as the structure which laminated | stacked the adsorption component and the catalyst component. Although not shown, a three-way catalyst device serving as a main catalytic converter is provided further downstream of the adsorption catalyst device 9.
[0021]
In an intake passage 11 connected to the combustion chamber 4 via an intake valve 10, a fuel injection valve 12 is disposed toward the intake valve 10, and a throttle valve 14 and an air flow meter are disposed upstream of the collector 13. 15 are sequentially inserted.
[0022]
Further, a water temperature sensor 16 for detecting the cooling water temperature of the internal combustion engine 1 and a crank angle sensor 17 for detecting the rotation angle of the crankshaft are provided, and detection signals of these sensors are respectively input to the engine control unit 18. Yes. The engine control unit 18 comprehensively controls the fuel injection amount and injection timing by the fuel injection valve 12 and the ignition timing of the spark plug 5 based on these detection signals.
[0023]
The exhaust valve 6 and the intake valve 10 are each driven to open and close by a valve operating mechanism mainly composed of a camshaft. In particular, a control signal from the engine control unit 18 is provided on the intake valve 10 side. Is provided with a variable valve mechanism 19 that can variably control the valve lift characteristics. In this embodiment, as the variable valve mechanism 19, for example, by shifting the phases of the crankshaft and the camshaft, the valve opening timing and the closing timing can be advanced simultaneously by a certain amount without changing the valve operating angle. The thing of a well-known structure is used. It is also possible to use a type that can variably control the valve operating angle as disclosed in JP-A-6-185321.
[0024]
FIG. 3 is a characteristic diagram showing the valve opening / closing timing and the HC emission amount downstream of the exhaust valve 6 in the above embodiment. In the above embodiment, when the internal combustion engine 1 is completely warmed up, the valve lift characteristic of the intake valve 10 is such that an appropriate amount of valve overlap occurs across the piston top dead center position (TDC). Is as indicated by the broken line in FIG. In contrast, when the internal combustion engine 1 is cold after the cold start, the variable valve mechanism 19 is actuated to the advance side by the control signal from the engine control unit 18, and the valve lift characteristic of the intake valve 10 is (A). It becomes like the solid line. Thus, when the intake valve 10 opens relatively early, the negative pressure on the intake passage 11 side acts on the combustion chamber 4 and exhaust blowback occurs. That is, HC having a relatively small molecular weight generated in the vicinity of the piston top dead center position is sucked back into the intake system, and the amount of HC flowing out to the exhaust system decreases as shown by the solid line in FIG. Note that the broken line in (B) indicates the HC emission amount during cold when the valve lift characteristic of the intake valve 10 is maintained at a normal characteristic.
[0025]
On the other hand, HC at the stage where the exhaust valve 6 starts to open has a relatively large molecular weight as described above, and is reliably adsorbed by the adsorption catalyst device 9. Further, when the intake valve 10 is advanced as described above and the valve overlap is enlarged, combustion becomes unstable and HC increases, but the HC accompanying the unstable combustion has a relatively high molecular weight. Can be processed by the adsorption catalyst device 9 in the same manner, and there is no problem.
[0026]
As described above, in this embodiment, by combining the adsorption catalyst device 9 and the advance control of the intake valve 10, the overall HC emission amount when the three-way catalyst device 8 is not activated can be greatly reduced. Can do. Since the adsorption catalyst device 9 has to adsorb only HC having a high molecular weight and a large molecular weight, the adsorption catalyst device 9 is relatively small in size and can sufficiently adsorb, and adsorbs HC having a small molecular weight. A special configuration or the like is not necessary. In addition, since the variable valve mechanism 19 need only be provided on the intake valve 10 side, complication of the configuration of the internal combustion engine 1 can be minimized.
[0027]
The advance control of the intake valve 10 is continued while the adsorption catalyst device 9 is in a low-temperature state that can be adsorbed, and when the desorption temperature (for example, about 200 ° C.) is reached, the normal opening / closing timing is restored. Of course, the temperature of the adsorption catalyst device 9 can be directly detected by using a temperature sensor, but can be estimated, for example, from the cooling water temperature at the start and the operation history after the start.
[0028]
Further, as the advance amount in the advance angle control, a fixed value may be given as ON or OFF, but as shown in FIGS. 4 and 5, the advance angle is increased at a low load according to the load. You may carry out variable control so that quantity may become small. In this way, instability of combustion in a low load region such as idle can be avoided.
[0029]
Next, FIG. 6 shows a second embodiment of the present invention. In this embodiment, the valve operating mechanism on the intake valve 10 side has a fixed valve lift characteristic. Instead, the valve lift mechanism on the exhaust valve 6 side is controlled by a control signal from the engine control unit 18. A variable valve mechanism 20 capable of variably controlling the characteristics is provided. In this embodiment, as the variable valve mechanism 20, the valve opening timing and the closing timing are simultaneously changed without changing the valve operating angle by shifting the phases of the crankshaft and the camshaft as in the first embodiment. Although a configuration capable of a certain amount of advance is used, a configuration capable of variably controlling the valve operating angle can also be used.
[0030]
FIG. 7 is a characteristic diagram showing the valve opening / closing timing and the HC discharge amount downstream of the exhaust valve 6 in the second embodiment. In the second embodiment, when the internal combustion engine 1 has been warmed up, the valve lift characteristic of the exhaust valve 6 is such that an appropriate amount of valve overlap occurs across the piston top dead center position. (A) It is like the broken line, and the closing time is in the position after the top dead center.
[0031]
On the other hand, when the internal combustion engine 1 is cold after the cold start, the variable valve mechanism 20 is actuated to the advance side by the control signal from the engine control unit 18, and the valve lift characteristic of the exhaust valve 6 is (A). It becomes like the solid line. In particular, the advance angle control is performed up to a position where the closing time is before the top dead center. By closing the exhaust valve 6 before top dead center in this way, discharge of HC having a relatively small molecular weight in the vicinity of the piston top dead center position is suppressed, and is discharged to the exhaust system as indicated by the solid line in FIG. The amount of HC, especially the amount of HC with a small molecular weight, is greatly reduced. In addition, the broken line of (B) has shown the HC discharge | emission amount at the time of cold at the time of maintaining the valve lift characteristic of the exhaust valve 6 at a normal characteristic.
[0032]
On the other hand, since the HC at the stage where the exhaust valve 6 starts to open has a relatively large molecular weight as described above, it is reliably adsorbed by the adsorption catalyst device 9 as in the case of the first embodiment. Further, if the closing timing of the exhaust valve 6 is advanced while the operating angle is constant as described above, it is natural that the opening timing is also advanced and the unburned mixture easily flows out to the exhaust system. However, since the HC generated at this stage has a relatively large molecular weight, it can be treated by the adsorption catalyst device 9 without any problem. Not.
[0033]
In each of the above embodiments, the variable valve mechanism is used for only one of the exhaust valve 6 and the intake valve 10. However, in order to realize valve overlap and the like according to operating conditions, the exhaust valve 6 and the intake valve A variable valve mechanism can be used for both of the valves 10.
[0034]
In particular, in the example of FIG. 7, since the valve lift characteristic on the intake valve 10 side is fixed, the valve overlap is 0 during advance control, and the intake valve 10 open timing from the exhaust valve 6 close timing. There is a certain period until the intake valve 10 side is advanced at the same time to ensure an appropriate valve overlap. It is possible to avoid the deterioration.
[Brief description of the drawings]
FIG. 1 is a characteristic diagram showing a relationship between valve opening / closing timing of an intake / exhaust valve and HC emission amount in the related art.
FIG. 2 is a structural explanatory view showing a first embodiment of the present invention.
FIG. 3 is a characteristic diagram showing the relationship between the valve opening / closing timing of the intake / exhaust valve and the HC emission amount in the first embodiment.
FIG. 4 is a characteristic diagram showing a relationship between a load of an internal combustion engine and an advance amount.
FIG. 5 is a characteristic diagram showing valve opening / closing timing when loads are different.
FIG. 6 is a structural explanatory view showing a second embodiment of the present invention.
FIG. 7 is a characteristic diagram showing the relationship between the valve opening / closing timing of the intake / exhaust valve and the HC emission amount in the second embodiment.
[Explanation of symbols]
6 ... Exhaust valve 7 ... Exhaust passage 9 ... Adsorption catalyst device 10 ... Intake valve 19 ... Variable valve mechanism 20 ... Variable valve mechanism

Claims (5)

An HC adsorbent interposed in the exhaust passage of the internal combustion engine and adsorbing HC (hydrocarbon component) in the exhaust;
A variable valve mechanism that is provided at least on the intake valve side of the internal combustion engine and is capable of variably controlling at least the opening timing of the intake valve;
Means for detecting a cold state of the internal combustion engine;
An open / close timing control means for advancing the opening timing of the intake valve when the internal combustion engine is cold;
A exhaust gas purifying apparatus for an internal combustion engine that features,
The exhaust gas purifying apparatus for an internal combustion engine, wherein the cold state detecting means detects that the HC adsorbent is at or below a desorption start temperature . 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the advance amount of the intake valve opening timing is made smaller as the load of the internal combustion engine is lower. An HC adsorbent interposed in the exhaust passage of the internal combustion engine and adsorbing HC (hydrocarbon component) in the exhaust;
A variable valve mechanism that is provided at least on the exhaust valve side of the internal combustion engine and can variably control at least the closing timing of the exhaust valve;
Means for detecting a cold state of the internal combustion engine;
An opening / closing timing control means for advancing the closing timing of the exhaust valve to before the top dead center when the internal combustion engine is cold;
An exhaust purification device for an internal combustion engine comprising:
The exhaust gas purifying apparatus for an internal combustion engine, wherein the cold state detecting means detects that the HC adsorbent is at or below a desorption start temperature. An exhaust purification system of an internal combustion engine according to claim 3 in which the load of the internal combustion engine, characterized in that the lower the smaller the amount of advance of the exhaust valve closing timing. The exhaust purification device for an internal combustion engine according to any one of claims 1 to 4 , wherein the HC adsorbent comprises a zeolite adsorbent.

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