JP4206593B2 - In-cylinder injection internal combustion engine control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for a direct injection internal combustion engine having an HC adsorption catalyst and a three-way catalyst or an oxidation catalyst in an exhaust passage.
[0002]
[Prior art]
Generally, the exhaust passage of an internal combustion engine has a three-way catalyst that simultaneously purifies hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO ₃ ), which are harmful substances in the exhaust gas, and carbonization. An oxidation catalyst is provided for oxidizing and treating unburned components such as hydrogen (HC) and carbon monoxide (CO). However, at the time of cold start of the internal combustion engine, the three-way catalyst and the oxidation catalyst are in a low temperature state, and activation is delayed, so that harmful substances such as HC cannot be efficiently purified. Therefore, an HC adsorption catalyst is also provided, and at the time of cold start, HC contained in the exhaust gas is efficiently adsorbed by this HC adsorption catalyst, and at the same time, the temperature of the exhaust gas heats up with a three-way catalyst or an oxidation catalyst, Various techniques have been proposed in which, when HC is desorbed at a predetermined temperature or more, an activated three-way catalyst or oxidation catalyst purifies the desorbed HC.
[0003]
However, the temperature at which the three-way catalyst is activated to purify HC is higher than the temperature at which the HC adsorption catalyst desorbs HC, and HC cannot be reliably purified during this period. FIG. 5 is a time chart showing the HC generation processing status and temperature change at the time of cold start of the internal combustion engine. The solid line indicates the HC concentration and the exhaust system temperature on the catalyst inlet side, and the dotted line indicates the HC concentration on the catalyst outlet side. The two-dot chain line is the exhaust system temperature at the center of the catalyst. As can be seen from the time chart of FIG. 5, the exhaust gas from the internal combustion engine at the cold start, that is, the temperature on the catalyst inlet side is low and the HC concentration is high, but the HC concentration on the catalyst outlet side is low. It can be seen that the HC adsorption catalyst adsorbs HC in the gas (adsorption period). However, although the HC concentration on the catalyst inlet side decreases with the passage of time, the HC concentration on the catalyst outlet side slightly increases. It can be seen that the temperature on the catalyst inlet side rises and the HC adsorption catalyst reaches the HC desorption temperature and desorbs HC, but the three-way catalyst has not yet reached the activation temperature (desorption period). After that, when a predetermined time elapses and the temperature on the catalyst inlet side rises and the three-way catalyst is activated, HC in the exhaust gas and HC desorbed from the HC adsorption catalyst are purified, and HC on the catalyst outlet side is purified. The concentration will decrease (purification period).
[0004]
Thus, at the time of cold start of the internal combustion engine, the HC adsorption catalyst adsorbs HC in the exhaust gas, but the period from when the HC adsorption catalyst reaches the HC desorption temperature until the three-way catalyst is activated is HC. Can not be purified reliably. Therefore, by providing a heating means for heating the three-way catalyst in the exhaust passage and activating early, HC released from the HC adsorption catalyst can be immediately purified with the three-way catalyst, for example, It is disclosed in JP-A-9-256840 and JP-A-11-82003. This "engine exhaust purification device" disclosed in Japanese Patent Laid-Open No. 9-256840 is provided with an electrocatalyst as a heating means upstream of the HC adsorption catalyst, and is disclosed in Japanese Patent Laid-Open No. 11-82003. The "control device for an internal combustion engine" thus retarded the ignition timing by a predetermined amount in the idle operation region.
[0005]
[Problems to be solved by the invention]
However, as in the “exhaust gas purification device” of Japanese Patent Application Laid-Open No. 9-256840, if an electrocatalyst is separately provided in the exhaust passage and the temperature rises, the number of parts of the exhaust system increases and the electrocatalyst is controlled. The control system must be changed, and the apparatus becomes complicated and expensive. Further, as in the “Control Device for Internal Combustion Engine” of Japanese Patent Application Laid-Open No. 11-82003, when the ignition timing is retarded by a predetermined amount in the idle operation region and the temperature rises, the combustion becomes unstable and not only the engine but also the ignition timing Since the temperature rise effect due to the retard is slow, HC cannot be sufficiently purified with a three-way catalyst.
[0006]
The present invention solves such a problem, and it is possible to improve the purification processing efficiency by reliably suppressing the discharge of hydrocarbons without separately providing a catalyst temperature raising device or making a major change to the engine control system. It is an object of the present invention to provide a control device for an in-cylinder injection internal combustion engine.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a control apparatus for a cylinder injection internal combustion engine according to claim 1 of the present invention is provided with an HC adsorption catalyst for adsorbing hydrocarbons in exhaust gas in an exhaust passage of the internal combustion engine, and the internal combustion engine. A three-way or oxidation catalyst for purifying harmful substances in the exhaust gas is provided downstream of the HC adsorption catalyst in the exhaust passage of the engine. When the means selects the two-stage combustion mode in which the fuel is injected in the expansion stroke or the exhaust stroke after the fuel injection for the main combustion , and then shifts from the idling operation state to the running state, the two-stage combustion mode is switched to the compression slight lean control. I am doing so.
[0008]
Therefore, at the time of cold start of the internal combustion engine, HC in the exhaust gas is adsorbed efficiently by the HC adsorption catalyst, and at the same time, fuel injection is performed even in the expansion stroke, so that the exhaust gas becomes hot and the three-way catalyst immediately rises in temperature. In addition, by injecting fuel even in the exhaust stroke, CO and HC are supplied to the three-way catalyst and immediately heated to be activated and desorbed from the HC adsorption catalyst. The HC that has been removed is purified by the ternary or oxidation catalyst that has already been activated from the beginning of desorption, and the emission of HC can be reliably suppressed to improve the purification efficiency.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0012]
FIG. 1 shows a schematic configuration of a control apparatus for a direct injection internal combustion engine according to an embodiment of the present invention, and FIG. 2 shows a control apparatus for a direct injection internal combustion engine according to the present embodiment applied during cold start of the internal combustion engine. FIG. 3 is a graph showing the amount of HC desorbed with respect to the catalyst temperature, and FIG. 4 is an enlarged cross-sectional view of the HC adsorption catalyst.
[0013]
In the control apparatus for a direct injection internal combustion engine of the present embodiment, as shown in FIG. 1, an internal combustion engine (hereinafter referred to as an engine) 10 is an in-cylinder injection type in-line four cylinder that directly injects fuel into a combustion chamber. In-cylinder injection that is a gasoline engine and can perform fuel injection in the intake stroke (intake stroke injection mode) or fuel injection in the compression stroke (compression stroke injection mode) by switching the fuel injection mode (operation mode) This is a spark-ignition type in-line 4-cylinder gasoline engine. This in-cylinder injection type engine 10 can be easily operated at a stoichiometric air-fuel ratio (stoichiometric), an operation at a rich air-fuel ratio (rich air-fuel ratio operation), or an operation at a lean air-fuel ratio (lean air-fuel ratio). In particular, in the compression stroke injection mode, it is possible to operate at a super lean air / fuel ratio that is larger than the lean air / fuel ratio operation in the intake stroke.
[0014]
A spark plug 12 is attached to the cylinder head 11 of the engine 10 for each cylinder, and an injector 13 having an injection port opened in the combustion chamber 14. A fuel supply device (fuel pump) having a fuel tank is connected to the injector 13 via a fuel pipe (not shown). The fuel in the fuel tank is supplied at a high fuel pressure, and this fuel is supplied from the injector 13 to the combustion chamber 14. Inject at the desired fuel pressure. At this time, the fuel injection amount is determined from the fuel discharge pressure of the fuel pump and the valve opening time (fuel injection time) of the injector 13, and is controlled by the driver 15. Further, a piston 17 is supported on the cylinder 16 of the engine 10 so as to be slidable up and down, and a cavity 18 that is hemispherically recessed is formed on the top surface of the piston 17. Can generate a reverse tumble flow.
[0015]
An intake port 19 and an exhaust port 20 are formed in the cylinder head 11 in a substantially upright direction facing the combustion chamber 14. The intake port 19 is opened and closed by driving an intake valve 21, and the exhaust port 20 is opened and closed by driving an exhaust valve 22. The An intake side camshaft 23 and an exhaust side camshaft 24 are rotatably supported on an upper portion of the cylinder head 11. The intake valve 21 is driven by the rotation of the intake side camshaft 23. The exhaust valve 22 is driven by the rotation.
[0016]
A vane-type crank angle sensor 25 that outputs a crank angle signal SGT at a predetermined crank position of each cylinder is provided, and the crank angle sensor 25 can detect the engine speed. The camshafts 23 and 24 that rotate at half the number of revolutions of the crankshaft are provided with an identification sensor 26 that outputs a cylinder identification signal SGC, and the cylinder identification signal SGC can identify which cylinder the crank angle signal SGT belongs to. It is said that.
[0017]
An intake pipe 28 is connected to the intake port 19 via an intake manifold 27, and an air cleaner 29 is attached to an air intake port of the intake pipe 28. The intake pipe 28 is provided with a throttle body 30. The throttle body 30 is provided with a butterfly throttle valve 31 for opening and closing the flow path, and a throttle position sensor 32 for detecting the opening degree of the throttle valve 31 is attached. It has been. The throttle position sensor 32 outputs a throttle voltage corresponding to the opening degree of the throttle valve 31, and the opening degree of the throttle valve 31 is recognized based on the throttle voltage. Further, a bypass passage 33 is formed in the throttle body 30 for bypassing the intake passage during idling, and an idle speed control valve 34 for opening and closing the bypass passage 33 is provided.
[0018]
On the other hand, an exhaust pipe 36 is connected to the exhaust port 20 via an exhaust manifold 35, and an O ₂ sensor 37 is attached to the exhaust pipe 36. An exhaust purification catalyst device 38 is provided on the downstream side of the exhaust pipe 36, and the exhaust purification catalyst device 38 includes an HC adsorption catalyst 39 and a three-way catalyst (or an oxidation catalyst) 40. Further, a high temperature sensor 41 is attached to the exhaust pipe 36 on the upstream side of the exhaust purification catalyst device 38, and a muffler (not shown) is attached on the downstream side.
[0019]
As shown in FIG. 4, the HC adsorption catalyst 39 constituting the exhaust purification catalyst device 38 is composed of a porous carrier 431, HC as zeolite adsorbing HC, etc., with an adsorption layer 391 as a lower layer and an upper layer thereof. It is configured to carry platinum (Pt), palladium (Pd), rhodium (Rh), etc. as a three-way catalyst layer 401 for purifying HC, and can adsorb and purify HC in the exhaust gas. Yes. Note that platinum or the like may be supported on the lower layer as a three-way catalyst layer, and zeolite or the like may be supported on the upper layer as an HC adsorption layer. The three-way catalyst 40 has a reduction function for purifying harmful substances (HC, CO, NOx) in the exhaust gas. The three-way catalyst 40 is located downstream of the HC adsorption catalyst 39. By being disposed, the HC adsorption catalyst 39 also serves to purify HC that has been desorbed without being purified. However, the three-way catalyst 40 may be omitted when the HC desorbed by only the three-way catalyst layer 401 can be sufficiently purified.
[0020]
The vehicle is provided with an ECU (electronic control unit) 42 having an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), a central processing unit (CPU), a timer counter, and the like. Comprehensive control including the engine 10 is performed. That is, the various sensors 25, 26, 32, 37, and 41 described above are connected to the input side of the ECU 42, and detection information from these sensors is input. On the other hand, the ignition plug 12 and the driver 15 of the injector 13 described above are connected to the output side of the ECU 42 via an ignition coil. The ignition plug 12 and the driver 15 of the injector 13 are connected to various sensors. Optimal values such as the fuel injection amount and ignition timing calculated based on the detected information are respectively output. Thus, an appropriate amount of fuel is injected from the injector 13 at an appropriate timing, and ignition is performed at an appropriate timing by the spark plug 12.
[0021]
Actually, the ECU 42 determines the target in-cylinder pressure corresponding to the engine load, that is, the target average effective pressure Pe, based on the throttle opening information θth from the throttle position sensor 32 and the engine rotational speed information Ne from the crank angle sensor 25. Further, the fuel injection mode is set from a map (not shown) according to the target average effective pressure Pe and the engine rotational speed information Ne. For example, when the target average effective pressure Pe and the engine rotational speed Ne are both small, the fuel injection mode is set to the compression stroke injection mode, and fuel is injected in the compression stroke, while the target average effective pressure Pe increases, or the engine When the rotational speed Ne increases, the fuel injection mode is changed to the intake stroke injection mode, and fuel is injected in the intake stroke. Then, a target air-fuel ratio (target A / F) as a control target is set from the target average effective pressure Pe and the engine speed Ne, and an appropriate amount of fuel injection is determined based on the target A / F.
[0022]
By the way, in this embodiment, when the cold start of the engine 10 is determined (cold start detection means), the fuel injection is performed in the expansion stroke or the exhaust stroke after the fuel injection in the compression stroke for main combustion. By selecting the combustion mode (fuel injection control means), the three-way catalyst 40 is activated so that the HC adsorbed on the HC adsorption catalyst 39 is purified, that is, the target air-fuel ratio in the compression stroke. Is changed to a richer side than the target air-fuel ratio selected at a time other than during cold start (fuel injection control means).
[0023]
That is, when the cold start of the engine 10 is determined from the ON signal of the ignition key switch and the engine water temperature, the ECU 42 selects the two-stage combustion mode in which fuel injection is performed in the compression stroke and the expansion stroke, and the target air-fuel ratio (target A / F) is set, and as described above, an appropriate amount of fuel injection set based on the target A / F is injected in the compression stroke and the expansion stroke. Then, after the fuel for main combustion injected in the compression stroke is ignited and burned, the fuel injected in the expansion stroke further burns, and the exhaust gas becomes high temperature. The original catalyst 40 is heated and activated immediately. On the other hand, the HC adsorption catalyst 39 adsorbs HC in the exhaust gas.
[0024]
The HC desorption temperature from the HC adsorption catalyst 39 is about 150 ° C., and the activation temperature at which the HC can be treated in the three-way catalyst 40 is 250 ° C., but the HC is exhausted by high-temperature exhaust gas over a predetermined time. Since the temperature of the adsorption catalyst 39 and the three-way catalyst 40 is raised quickly, the HC desorbed from the HC adsorption catalyst 39 has a three-way function that the HC adsorption catalyst 39 has from the beginning of the desorption, and the downstream three-way catalyst. Purification is performed by the original catalyst 40.
[0025]
When this cold start is determined, fuel is injected in the exhaust stroke after the expansion stroke injection, or fuel is injected in the exhaust stroke instead of the expansion stroke injection, and CO or HC is converted into a three-way catalyst. The three-way catalyst 40 may be activated at an early stage by supplying it to 40 and raising the temperature. Even in this case, the HC desorbed when the HC adsorption catalyst 39 reaches a predetermined temperature is purified by the three-way catalyst 40.
[0026]
Further, after the cold start is determined and the compression stroke injection and the expansion stroke injection are executed, when the transition from the idling operation state to the running state is performed, the compression light lean control from the two-stage combustion mode, that is, the target air-fuel ratio is set to the theoretical air-fuel ratio. By changing the lean air-fuel ratio from the normal lean air-fuel ratio at which the compression stroke injection is performed to a richer side, the CO and HC are supplied to the three-way catalyst 40 and the temperature is raised. Early activation of the catalyst 40 is continued. This is because the temperature of the three-way catalyst 40 is excessively increased in the two-stage combustion mode when the idling operation state is shifted to the running state, and there is a risk of thermal deterioration, and the durability of the three-way catalyst 40 is taken into consideration.
[0027]
As described above, in the control device for a cylinder injection internal combustion engine of the present embodiment, the compression stroke injection and the expansion stroke are executed at the time of cold start of the engine 10 to increase the temperature of the exhaust gas, and the high temperature exhaust gas causes the three-way catalyst. By activating 40 by raising the temperature, the timing of desorption of HC adsorbed by the HC adsorption catalyst 39 and the activation timing at which the three-way catalyst 40 can treat HC are almost simultaneous, and the HC adsorption catalyst The purification efficiency can be improved by reliably purifying HC by the three-way function or the three-way catalyst 40 of the HC adsorption catalyst 39 before and after HC desorption from 39. Further, in the present embodiment, fuel is injected in the exhaust stroke after the expansion stroke injection, or fuel injection is performed in the exhaust stroke instead of the expansion stroke injection, or the two-stage combustion mode is switched to the compression sludge lean control. Thus, by supplying CO or HC to the three-way catalyst 40 and raising the temperature, the three-way catalyst 40 can be activated early.
[0028]
Here, the HC suppression effect by early activation of the three-way catalyst 40 by the control device for the direct injection internal combustion engine of the present embodiment will be described. The time chart shown in FIG. 2 represents the HC generation processing status and temperature change at the time of cold start, the solid line is the HC concentration and exhaust system temperature on the inlet side of the exhaust purification catalyst device 38, and the dotted line is the outlet side. The HC concentration at 2 and the two-dot chain line are the exhaust system temperature at the center.
[0029]
As can be seen from the time chart of FIG. 2, the exhaust gas discharged from the engine 10 at the time of cold start, that is, the HC concentration on the catalyst inlet side is high, but the HC concentration on the catalyst outlet side is low. It can be seen that the catalyst 39 adsorbs HC in the exhaust gas (adsorption period). Since the period of the two-stage combustion mode immediately after the cold start, the exhaust gas on the catalyst inlet side rises and the HC concentration on the catalyst outlet side decreases, so that the three-way catalyst 40 is activated and is in the exhaust gas It can be seen that the HC is being purified (purification period). Thus, the HC adsorption period by the HC adsorption catalyst 39 immediately shifts to the HC purification period by the activation of the three-way catalyst 40, and the HC desorbed from the HC adsorption catalyst 39 is released to the atmosphere as it is. There is almost no period during which HC can be released during this period.
[0030]
By the way, in the above-described embodiment, the HC adsorption catalyst 39 is configured by supporting zeolite that physically adsorbs HC on a support made of a porous material. However, a transition metal is added to chemically adsorb HC. Also good. In this case, as shown in FIG. 3, by adding a transition metal, the desorption temperature of HC adsorbed on the HC adsorption catalyst can be increased to approach the activation temperature of the three-way catalyst, thereby desorbing HC. The separation timing can be delayed to improve the HC purification efficiency by the three-way catalyst.
[0031]
In the above-described embodiment, the HC adsorption catalyst 39 is provided with a zeolite layer having an HC adsorption function and a platinum layer for purifying HC. However, by providing a three-way catalyst 40 on the downstream side of the HC adsorption catalyst 39, the zeolite As shown in FIG. 4, when the HC adsorption layer 391 and the three-way catalyst layer 401 are provided on the carrier 31 of the HC adsorption catalyst 39, the three-way catalyst 40 on the downstream side may be omitted. . Further, the HC adsorption catalyst 39 may be provided with an HC adsorption function, and an NOx occlusion function that occludes NOx in the exhaust gas when the air-fuel ratio is a lean air-fuel ratio may be integrally provided. In addition, the NOx occlusion function may be provided separately. In this case, it is desirable to provide a three-way catalyst upstream or downstream of the HC adsorption + NOx storage catalyst or the HC adsorption catalyst + NOx storage catalyst. That is, as long as HC is adsorbed first and then desorbed HC is purified, an oxidation catalyst may be used instead of a three-way catalyst, and any form is used in consideration of vehicle mounting characteristics and the like. May be.
[0032]
【The invention's effect】
As described above in detail in the embodiment, according to the control apparatus for a cylinder injection internal combustion engine of the invention of claim 1, the HC adsorption catalyst and the three-way or oxidation catalyst are provided in the exhaust passage of the internal combustion engine, and the internal combustion engine Since the two-stage combustion mode in which the fuel is injected in the expansion stroke or the exhaust stroke after the fuel injection for the main combustion at the cold start of the internal combustion engine is selected, the HC in the exhaust gas is adsorbed by the HC at the cold start of the internal combustion engine. At the same time as the catalyst is adsorbed efficiently, the exhaust gas becomes hot due to the expansion stroke injection, and the three-way catalyst rises in temperature and is activated early, and the exhaust stroke injection supplies CO and HC to the three-way catalyst. As a result, the temperature is raised and activated early, and the HC adsorbed by the HC adsorption catalyst is surely purified by the three-way or oxidation catalyst, and the emission efficiency is improved by reliably suppressing the discharge of HC. improves Door can be.
[0033]
According to the control device for a cylinder injection internal combustion engine of the second aspect of the present invention, the HC adsorption catalyst and the three-way or oxidation catalyst are provided in the exhaust passage of the internal combustion engine, and the compression stroke and expansion are performed when the internal combustion engine is cold-started. Since the two-stage combustion mode in which fuel injection is performed in the stroke or the exhaust stroke is selected and the target air-fuel ratio in the compression stroke is changed to the richer side than the target air-fuel ratio selected outside the cold start, At the time of cold start of the internal combustion engine, the HC in the exhaust gas is efficiently purified by the HC adsorption catalyst, and at the same time, the target air-fuel ratio is changed to the concentrating side, and CO and HC are supplied to the three-way catalyst to raise the temperature early. Thus, the HC adsorbed on the HC adsorption catalyst is surely purified by the three-way or oxidation catalyst, and the purification efficiency can be improved by reliably suppressing the discharge of HC.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a control device for a direct injection internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a time chart showing HC generation processing status and temperature change at the time of cold start of the internal combustion engine to which the control device for a direct injection internal combustion engine of the present embodiment is applied.
FIG. 3 is a graph showing the amount of HC desorption with respect to the catalyst temperature.
FIG. 4 is an enlarged cross-sectional view of an HC adsorption catalyst.
FIG. 5 is a time chart showing the HC generation processing status and temperature change at the time of cold start of the internal combustion engine.
[Explanation of symbols]
10 Engine (Internal combustion engine)
12 Spark plug 13 Injector 14 Combustion chamber 36 Exhaust pipe (exhaust passage)
23 Exhaust purification catalyst device 38 Exhaust purification catalyst device 39 HC adsorption catalyst 40 Three-way catalyst 41 High temperature sensor 42 Electronic control unit, ECU (cold start detection means, fuel injection control means, fuel injection control means)

Claims (1)

In a cylinder injection internal combustion engine that directly injects fuel into a combustion chamber,
An HC adsorption catalyst provided in the exhaust passage of the internal combustion engine and adsorbing hydrocarbons in the exhaust gas;
A three-way or oxidation catalyst that is provided downstream of the HC adsorption catalyst in the exhaust passage of the internal combustion engine and purifies harmful substances in the exhaust gas;
Cold start detection means for determining the cold start of the internal combustion engine;
When the cold start detection means determines that the internal combustion engine is cold started, the two-stage combustion mode in which fuel injection is performed in the expansion stroke or the exhaust stroke is selected , and then when the transition from the idle operation state to the traveling state is made, the two-stage combustion mode is selected. A control device for a direct injection internal combustion engine, comprising: fuel injection control means for switching from a combustion mode to a compression-slight lean control.

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