JP2000145511A - Exhaust gas temperature raising device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily raise exhaust gas temperature by controlling an engine control parameter for stratified combustion at the time of an engine operation which requires the raising of exhaust gas temperature, and injecting adding fuel by a fuel injection valve during an intermediate time of an expansion stroke after main combustion or an expansion stroke after that. SOLUTION: In an ECU 23, various kinds of the quantity of engine operating state of a catalyst temperature Tcc, a cooling water temperature Tw, engine rotating speed Ne, an intake temperature Ta, and the like is read at the time of an operation of an engine 1, the catalyst temperature Tcc and a catalyst judging temperature Tcw are compared with each other, and it is judged that a catalyst 9 is in an active condition or not. In this case where this judgment is Tcc < Tcw and the catalyst 9 is in an inactive condition, the raising of exhaust gas temperature is controlled. Namely, main fuel injection is performed in a compression lean mode, and its ignition timing is also phase lag-controlled. A target air-fuel ratio is decided using leaning maps which are different according to judgment result at the time of engine cooling or after warming, a main fuel injection time is calculated, and an adding fuel injection time is found out so as to control a fuel injection valve 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus which raises the temperature of exhaust gas during a cold operation of an in-cylinder injection type internal combustion engine in which fuel is directly injected into a combustion chamber, spark ignited and stratified combustion is performed. The present invention relates to an exhaust gas heating device suitable for early activation or the like.

[0002]

2. Related Background Art In recent years, in a spark ignition type internal combustion engine mounted on a vehicle, fuel is directly supplied to a combustion chamber in place of a conventional intake pipe injection type in order to reduce harmful exhaust gas components and improve fuel efficiency. Various direct injection gasoline engines have been proposed. In a cylinder injection type gasoline engine, for example, by injecting fuel from a fuel injection valve into a cavity provided at the top of the piston, an air-fuel mixture having an air-fuel ratio close to the stoichiometric air-fuel ratio is generated around the ignition plug at the time of ignition. Let me. This makes it possible to ignite even with a lean air-fuel ratio as a whole, thereby reducing CO and HC emissions and greatly improving fuel efficiency during idling and low-load driving.

In such a gasoline engine,
The compression stroke injection mode and the intake stroke injection mode are switched according to the operating state of the engine, that is, the engine load. By switching the control mode in this way, during low-load operation, fuel is injected mainly during the compression stroke, and a mixture near the stoichiometric air-fuel ratio is locally formed around the ignition plug or in the cavity, and as a whole, Good stratified combustion can be performed even at a low air-fuel ratio (this control mode is also called a compression lean mode). In the compression stroke injection mode, operation is possible even when the overall air-fuel ratio is set to a large value (for example, an air-fuel ratio of 40), so that a large amount of fresh air intake air and an exhaust gas recirculation amount (EGR amount) are supplied into the cylinder. As a result, the pumping loss can be reduced and the fuel efficiency can be significantly improved. For this reason, it is desirable to improve the fuel economy by expanding the range of operation in the compression stroke injection mode as much as possible.

[0004] On the other hand, during medium to high load operation, fuel is injected mainly during the intake stroke to form a mixture having a uniform air-fuel ratio in the combustion chamber, and a large amount of fuel is burned in the same manner as in an intake pipe injection type gasoline engine. This ensures the required output during acceleration and high-speed running. When such an in-cylinder injection type internal combustion engine is started at a cold start or at a low load operation in an environment where the outside air temperature is low, an exhaust gas purifying device (also referred to simply as a catalyst) disposed in an exhaust passage is activated very quickly after the start. There is a problem that the catalyst that has not been activated or that has been activated is likely to be inactivated by being cooled by the compression lean mode operation (exhaust gas flow rate is high and the exhaust gas temperature may decrease due to lean combustion). In order to cope with such a problem, various methods for raising the temperature of the exhaust gas to activate the catalyst at an early stage have been proposed.

For example, Japanese Patent Application Laid-Open No. 4-183922 discloses a fuel injection valve which is operated again during an expansion stroke or an exhaust stroke of an engine when the intake valve is closed in order to activate the catalyst at an early stage. Inject fuel and reactivate the additional fuel by reactivating the ignition plug in the combustion chamber, or remix the additional fuel into the exhaust gas and reignite by the ignition plug provided in the exhaust passage. A technique has been proposed in which a catalyst is heated to quickly raise the temperature to an activation temperature.

In this prior art, a spark plug in a combustion chamber is restarted in order to reburn and raise the temperature of exhaust gas,
Although an ignition plug is provided separately in the exhaust passage, in the former case, the ignition control logic becomes complicated, and there is a problem that the second ignition energy cannot be sufficiently secured.
Further, there is a problem that the igniter becomes large and the cost increases when trying to sufficiently secure the ignition energy. In the latter case, there is a problem that the number of parts increases and the cost increases.

In this prior art, re-combustion is attempted using an ignition plug provided in an exhaust passage.
Normally, in an in-cylinder injection type internal combustion engine, during the expansion stroke and the exhaust stroke, the fuel from the main fuel injection is almost completely burned, and the number of activated chemical reaction species that become the ignition in the cylinder is reduced. (Eg, gasoline), large amounts of energy (eg, heat, pressure,
Temperature, etc.), as in the prior art, it is sufficient to simply re-activate the fuel injection valve during the expansion stroke or the exhaust stroke to inject additional fuel and reignite using the spark plug. There is a possibility that no energy is given and no reburning takes place. For this reason, there is a problem that the temperature of the exhaust gas cannot be reliably raised and the catalyst cannot be activated early.

Japanese Patent Laid-Open No. 8-1 discloses a method of burning fuel additionally injected during the expansion stroke without using a spark plug.
00638. This proposal, in addition to the normal fuel injection (combustion injection for the main combustion), injects additional fuel during the expansion stroke, ignites this additional fuel by the flame propagation of the main combustion, and reduces the exhaust gas temperature. It is intended to raise the temperature. According to this method, there is an advantage that it is not necessary to re-activate the ignition plug when re-burning,
Further, since the exhaust gas temperature becomes higher than usual, the time until the catalyst is activated can be shortened.

[0009]

However, according to the above-mentioned proposed method, the injection timing of the additional fuel during the expansion stroke is determined by the timing at which the ignition of the main combustion flame (propagation of the hot flame) can be reliably ignited (see Japanese Patent Laid-Open Publication No. No. 8-100638 describes a crank angle of 10 ° to 80 ° ATDC). If the additional fuel is burned at an early stage of such an expansion stroke, a part of the generated thermal energy is taken away by the expansion work, and the exhaust gas temperature, which is the original purpose, cannot be sufficiently increased. In order to obtain a sufficient exhaust gas temperature increase rate, it is necessary to increase additional fuel, and extra fuel is required.

The present invention has been made to solve such a problem. In order to effectively use the combustion energy of the additional fuel for raising the temperature of the exhaust gas, the injection is performed in the middle stage of the expansion stroke or later. It is desirable to provide an exhaust gas heating device capable of reliably burning an additional fuel without providing an additional device to raise the temperature of exhaust gas (exhaust gas). With the goal.

[0011]

According to a first aspect of the present invention, there is provided an exhaust gas heating apparatus having a fuel injection valve for directly injecting fuel into a combustion chamber, at least during a compression stroke. In an exhaust gas heating apparatus for an in-cylinder injection type internal combustion engine that injects fuel from a combustion injection valve and ignites sparks to perform stratified combustion, it operates during engine operation in which exhaust gas heating is required to perform stratified combustion. Engine control means for controlling engine control parameters, and additional fuel control means for injecting additional fuel from the fuel injection valve during the expansion stroke in the middle stage of the expansion stroke after the main combustion during the operation of the engine control means or thereafter. It is characterized by comprising.

The present invention is based on the technical idea that the flame of the main combustion reaches and burns the additional fuel as in the prior art, or the additional fuel is injected into the flame of the main combustion and burned. This is not based on the following findings. FIG. 1 shows a process of combustion of main fuel injected during a compression stroke and combustion of additional fuel injected during an expansion stroke in the middle stage or later of the expansion stroke (hereinafter, these combustions are referred to as “two-stage combustion”). FIG. 2 conceptually illustrates the relationship between the in-cylinder pressure and the change in the crank angle. When the main fuel injection is performed during the compression stroke (crank angle position CA1 in FIG. 2), as shown in FIG. 1A, an air-fuel mixture having a rich portion of fuel and a thin portion around it is formed in the combustion chamber. Is done. In this type of in-cylinder injection type internal combustion engine, the above-described portion having a high fuel concentration (near the stoichiometric air-fuel ratio) is used to stably burn even a lean mixture whose overall air-fuel ratio is leaner than the stoichiometric air-fuel ratio. Is formed around the spark plug, and a substantially central portion of the mixture is ignited by the spark plug (FIG. 1).
(B), crank angle position CA2 in FIG. 2).

If the air-fuel mixture does not ignite, the in-cylinder pressure Pe changes only as the pressure rises due to the reciprocation of the piston and changes as shown by the thin line in FIG. 2 with the change in the crank angle. When the air-fuel mixture ignites, the air-fuel mixture changes as shown by the thick line in FIG. The phenomenon from the ignition to the ignition will be described in more detail with reference to FIG. 3 as well. When gasoline is mixed with air and spark ignited, heat is generated in a normal combustion with heat generation, that is, before the flame reaction. An unprecedented pre-flame reaction (sometimes referred to as a cold flame, but no flame may be observed, so precedes). Preflame reactions are active chemical species (such as C and C) that are effective in driving the chain branching reaction, such as peroxides and formaldehyde.
HO, H ₂ O _2, OH and the like. These are called "pre-flame reaction products"), which proceed by compressing the air-fuel mixture or exposing it to high temperatures. Usually, when a flame nucleus is formed around the discharge by spark ignition, this flame The proinflammatory reaction rapidly proceeds around the nucleus due to the formation of the nucleus (FIG. 1 (d)).

The rapid progress of the preflame reaction can be explained with reference to FIG. FIG. 3 shows the change in the pre-flame reaction product concentration observed at a specific location in the rich fuel mixture, which can lead from ignition to ignition (FIG. 3).
The crank angle position at which ignition occurs from the ignition of (i) corresponds to the “DZ region” shown in FIG. 2). The mixture formed by fuel injection at the crank angle position CA1 is heated by adiabatic compression, during which the preflame reaction product concentration slightly increases (from CA1 to CA2 in FIG. 3). Then, the preflame reaction product concentration rapidly proliferates upon ignition, and when the concentration exceeds a certain equilibrium concentration INTD (CA in FIG. 3).
3) The preflame reaction rate explodes exponentially,
At this time, it is defined as "ignition". At this time, a flame (hot flame) is generated ((d) in FIG. 1), and the process shifts from the "pre-flame reaction" process to the "hot flame reaction" process. As the thermo-flame reaction progresses, the concentration of the pre-flame reaction product at that position sharply decreases,
Instead, CO ₂ and H ₂ O, unburned hydrocarbon THC (Total Hy
The final product concentration (indicated by the dashed line in FIG. 3), called drocarbons, will increase sharply.

At a position adjacent to the position where the hot flame reaction has occurred, the heat of reaction is supplied from the hot flame to start the pre-flame reaction. Here again, the concentration of the pre-flame reaction product rapidly increases, and then the hot-flame reaction starts. Is done. The region (heat flame) in which the thermal flame reaction has been started in this way sequentially propagates outward (FIG. 1 (e), and the phenomenon in which the flame surface propagates in this manner is called "flame propagation". ), The flame reaches the boundary between the low fuel concentration region and the high fuel concentration region. When the boundary is reached, the flame cannot propagate to the region with low fuel concentration, and the flame propagation stops, but the fuel present in the thin mixture portion receives the supply of reaction heat from the rich mixture portion, The pro-inflammatory reaction is sustained, albeit moderately (FIG. 1 (f)).

FIG. 4 shows a change in the concentration of the pre-flame reaction product observed at a specific position in the fuel-air mixture portion where the fuel concentration is low. The crank angle in the middle to late stages of the expansion stroke in which the combustion of the fuel-rich mixture portion ends. It shows that the preflame reaction product is maintained at a high concentration near the position (“WZ region” in FIG. 2). When the additional fuel is injected in this state, the additional fuel is exposed to the high-temperature atmosphere in the cylinder, so that the preflame reaction of the additional fuel proceeds faster than usual (normal temperature). For this reason, if the total amount of the pre-flame product newly generated by this reaction and the pre-flame product remaining in the cylinder after the main combustion exceeds the ignition limit concentration, self-ignition starts, and there is no spark ignition in particular. The additional fuel can be burned.

The present invention according to claim 1 has been made in view of such knowledge, and is added during the middle stage of the expansion stroke after the main combustion, in which the combustion of the rich mixture ends, or during the expansion stroke thereafter. If fuel is injected and the concentration of the preflame reaction product is controlled to a value exceeding the ignition limit concentration in the entire cylinder (at the point of (g) in FIG. 1, CA4 in FIGS. 2 and 4), the spark plug is re-ignited. The fuel can be self-ignited and burned without relying on the propagation of a hot flame (flame propagation) from a rich mixture during the first half of the expansion stroke. Compared to when fuel is injected,
The temperature of the exhaust gas can be reliably increased without a part of the heat energy generated by the additional fuel being taken away by the expansion work. Further, it is preferable to inject the additional fuel into the high-temperature atmosphere after the main combustion (claim 2).

Therefore, the engine control parameters such as the ignition timing and the air-fuel ratio are variously changed so that the concentration of the pre-flame reaction product in the combustion chamber is increased during the middle stage of the expansion stroke in which the combustion of the rich mixture ends and in the expansion stroke thereafter. Experimental data was obtained to allow the residual concentration to exceed the ignition limit concentration. FIG.
Shows the relationship between the exhaust gas temperature and the additional fuel injection timing when the ignition timing TRD and the additional fuel injection timing are variously changed. The experimental conditions were as follows: the intake air amount was kept constant, the main fuel injection amount was set so that the total air-fuel ratio was 30, and the additional fuel amount was added to the main fuel injection amount to make the total air-fuel ratio stoichiometric. The fuel ratio was set so as to be (14.7).

FIG. 6 shows the ignition timing TRD similarly to FIG.
And when the injection timing of the additional fuel is variously changed,
The relationship between the exhaust temperature and the injection timing of the additional fuel is shown. In this case, the main fuel injection amount is set so that the total air-fuel ratio becomes 40, and the additional fuel amount is added to the main fuel injection amount to obtain the total amount of the total fuel. The fuel ratio was set to be the stoichiometric air-fuel ratio (14.7), and the other experimental conditions were set the same as in FIG. That is, in the experiment shown in FIG. 6, the main fuel injection amount is smaller than that in FIG. 5, and the rich mixture portion shown in FIG. 1A is smaller.

FIG. 7 shows a map of the exhaust gas temperature and the amount of unburned hydrocarbons in the exhaust gas using the ignition timing TRD and the injection timing of the additional fuel as parameters from the same experimental results as in FIG. Based on these experimental results, the injection timing of the additional fuel was set at the beginning of the expansion stroke (45 ° AT
When changing from the DC position to the middle stage (65 ° ATDC crank angle), THC (Total Hydraulic
The amount emitted as drocarbons) increases, and the rise in exhaust gas temperature also worsens. On the other hand, when additional fuel is injected after the middle stage of the expansion stroke, a peak of the exhaust gas temperature is obtained at around 90 ° to 100 ° in crank angle. That is, in the initial stage of the expansion stroke and after the middle stage of the expansion stroke, the rise in the exhaust gas temperature itself is almost the same, but when the additional fuel is injected after the middle stage of the expansion stroke, less energy is lost to the expansion work, and the efficiency is increased. This is desirable because it can be well converted to heat energy and the deterioration of fuel efficiency is small.

From the results of these experiments, it has become clear that the more the ignition timing of the main fuel is retarded, the higher the exhaust gas temperature. If the ignition timing is retarded, combustion slows down, delays flame propagation, and extinguishes because the in-cylinder pressure decreases before the flame propagates sufficiently, resulting in an increase in the concentration of the preflame reaction product. Will do. For this reason, it is considered that the combustion speed of the additional fuel was increased and a large temperature raising effect was obtained.

As is clear from the comparison between the experimental results shown in FIGS. 5 and 6, when the main fuel injection amount is set so that the overall air-fuel ratio becomes 40, a large increase in the ignition timing is obtained regardless of the retard amount of the ignition timing. A warm effect can be obtained. It is considered that when the air-fuel ratio is made lean, slow combustion occurs, and the same result as when the ignition timing is retarded is obtained. These experimental results show that the pre-flame reaction product concentration in the combustion chamber remains in the middle stage or later of the expansion stroke after the main combustion, and the pre-flame reaction product concentration becomes the ignition limit concentration after additional fuel is injected. It is suggested that in order to control the value to exceed the value, the combustion of the main fuel should be slowed down by retarding the ignition timing, making the air-fuel ratio lean, or other methods.

Also, as can be seen from the above experimental results, the injection timing of the additional fuel is preferably set at 70 to 110 ° ATDC at a crank angle at which the preflame reaction products increase.
The crank angle set in this way can be defined as an expansion stroke in the middle stage of the expansion stroke or later. The present invention according to claim 3 has been made in view of such knowledge, and the crank angle in the expansion stroke after the main combustion where the combustion of the rich mixture ends is 70 to 110 ° after the top dead center. In addition, by injecting additional fuel and controlling the concentration of the preflame reaction product in the entire cylinder to a value exceeding the ignition limit concentration (FIG. 1 (g), FIG.
And at the time of CA4 in FIG. 4), the additional fuel is self-ignited and burned without reignition of the spark plug and without depending on propagation of the hot flame from the rich mixture (flame propagation) in the first half of the expansion stroke. It is possible to surely raise the temperature of the exhaust gas without a part of the heat energy generated by the additional fuel being taken away by the expansion work, as compared with the case where the additional fuel is injected at the time of the flame propagation as in the prior art. it can. And
In particular, in order to obtain the effect of raising the temperature of the exhaust, the crank angle is 80 to 1
Preferably, it is set to 00 ° ATDC (the invention of claim 4).

Further, when the crank angle is in the range of 70 to 110
In order to make the concentration of the preflame reaction product exceed the ignition limit concentration during the middle or later expansion stroke of ATDC, an ignition timing setting means is provided as an engine control means, and the ignition timing is set to the crank timing. 10 ° BTDC to 5 ° AT at an angle
DC is preferably set (the invention of claim 5), and in consideration of the stability of stratified combustion (main combustion), it is preferable to set 5 ° BTDC to TDC. In this case, an air-fuel ratio setting unit may be provided as the engine control unit, and the air-fuel ratio during stratified combustion may be set to 25 or more (the invention of claim 6).
In consideration of the stability of stratified combustion (main combustion), it is more preferable to set the air-fuel ratio during stratified combustion to about 30 to 40.

However, the air-fuel ratio at the time of stratified combustion is 35
With the above setting (the invention of claim 7), it is not necessary to retard the ignition timing at the time of stratified combustion, and only by adjusting the air-fuel ratio, the pre-flame occurs after the additional fuel injection during the middle stage of the expansion stroke or the subsequent expansion stroke. The reaction product concentration can be controlled to a value exceeding the ignition limit concentration. In any case, the engine control means has at least one of an ignition timing setting means for setting an ignition timing for stratified combustion and an air-fuel ratio setting means for setting an air-fuel ratio for stratified combustion, and the When the engine operation is required, the ignition timing of the stratified combustion is retarded,
Or by controlling the air-fuel ratio of stratified combustion to the lean side,
It is possible to control the preflame reaction product concentration to be close to the ignition limit concentration during the expansion stroke in the middle stage of the expansion stroke or thereafter (before additional fuel injection) (the invention of claim 8).

According to a ninth aspect of the present invention, there is provided an ignition timing setting means for setting an ignition timing for stratified combustion, as an engine control means.
Or, by having one of the air-fuel ratio setting means for setting the air-fuel ratio for stratified combustion, during the operation of the engine in which the exhaust gas temperature is required to rise, the ignition timing or the air-fuel ratio as an engine control parameter for stratified combustion By controlling one of them, the pre-flame reaction product concentration can be controlled to be close to the ignition limit concentration in the middle stage of the expansion stroke or during the expansion stroke thereafter (before additional fuel injection). Then, during the middle stage of the expansion stroke after the main combustion, in which the combustion of the rich mixture ends, or during the expansion stroke thereafter, additional fuel is injected, and the preflame reaction product concentration exceeds the ignition limit concentration in the entire cylinder. (G) in FIG. 1 (at time CA4 in FIGS. 2 and 4), the ignition plug is not reignited, and the propagation of the hot flame (flame propagation) from the rich mixture in the first half of the expansion stroke. It is possible to self-ignite and burn the additional fuel without depending on it, and compared to the case where the additional fuel is injected at the time of flame propagation as in the prior art, a part of the heat energy generated by the additional fuel is used for expansion work. The exhaust gas can be reliably heated without being deprived.

Further, during the operation of the engine in which the temperature of the exhaust gas is required to be raised, the ignition timing of the stratified combustion is controlled to the retard side, or the air-fuel ratio of the stratified combustion is controlled to the lean side, so that the middle stage of the expansion stroke after the main combustion or During the subsequent expansion stroke (before additional fuel injection)
Further, the concentration of the preflame reaction product can be controlled so as to be near the ignition limit concentration (the invention of claim 10). Note that the exhaust gas heating device of the present invention may be any engine that is controlled in a compression stroke injection mode, in which fuel is injected from the combustion injection valve at least during a compression stroke and spark ignition is performed to perform stratified combustion. In addition, the control can be performed in the intake stroke injection mode, and the engine may be controlled by switching between these modes.

The exhaust gas temperature raising device of the present invention is applied to an internal combustion engine provided with an exhaust gas purifying device, and is provided with C in the exhaust gas.
A three-way catalyst having a three-way function for purifying O, HC and NOx, and a lean NOx for mainly purifying NOx during lean combustion
It is suitably applied to an internal combustion engine having a catalyst. An engine having a three-way catalyst downstream of the lean NOx catalyst may be used. In this case, CO and HC that could not be sufficiently purified by the lean NOx catalyst can be reliably purified without hindering NOx purification by the lean NOx catalyst. However, when the lean NOx catalyst has a three-way function, only the lean NOx catalyst may be provided.

[0029]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 8 is a schematic configuration diagram showing one embodiment of a control device for a direct injection gasoline engine according to the present invention mounted on a vehicle. In FIG. 8, reference numeral 1 denotes an in-cylinder in-cylinder in-line four-cylinder gasoline engine (hereinafter simply referred to as an engine) of a spark ignition type, which injects fuel directly into a combustion chamber.
This is an internal combustion engine that performs each expansion and exhaust stroke in one operation cycle, that is, a four-cycle engine. In the engine 1, an intake device, an EGR device 10, etc., including the combustion chamber 1a, are designed exclusively for in-cylinder injection.

The cylinder head of the engine 1 is also provided with an electromagnetic fuel injection valve 8 together with an ignition plug 35 for each cylinder so that fuel is directly injected into the combustion chamber 1a. A hemispherical cavity is formed on the top surface of the piston that reciprocates by sliding in the cylinder at a position near the top dead center where the fuel spray from the fuel injection valve 8 reaches (see the figure). Zu). The theoretical compression ratio of the engine 1 is set higher (about 12 in this embodiment) than that of the intake pipe injection type. A DOHC 4-valve valve mechanism is employed as a valve operating mechanism. An intake-side camshaft and an exhaust-side camshaft are rotatably held above the cylinder head to drive the intake and exhaust valves 4 and 5, respectively. I have.

An intake port 2a is formed in the cylinder head in a substantially upright direction so as to pass through between the two camshafts, and an intake flow passing through the intake port 2a causes a reverse flow to be described later in the combustion chamber 1a. A tumble flow is generated. On the other hand, the exhaust port 3a is formed in a substantially horizontal direction similarly to a normal engine, but has a large-diameter EGR port (not shown) branched diagonally.
In the figure, reference numeral 19 denotes a water temperature sensor for detecting a cooling water temperature Tw. Reference numeral 21 denotes a crank angle signal SG at a predetermined crank position (5 ° BTDC and 75 ° BTDC in this embodiment) of each cylinder.
Reference numeral 34 denotes a crank angle sensor that outputs T, and reference numeral 34 denotes an ignition coil that outputs a high voltage to the ignition plug 35. A camshaft that rotates at half the number of revolutions of the crankshaft is provided with a cylinder discrimination sensor (not shown) that outputs a cylinder discrimination signal SGC, and the signal from this sensor generates a crank angle signal SGT. Determine which cylinder it is.

As shown in FIG. 8, an air cleaner 6a, a throttle body 6b, a stepper motor type idle speed control valve (hereinafter referred to as an idle adjustment valve) is connected to an intake port 2a via an intake manifold 2 having a surge tank 2b. Intake pipe 6 with 16)
Is connected. Further, the intake pipe 6 is provided with a large-diameter air bypass pipe 50a that bypasses the throttle body 6b and introduces intake air into the intake manifold 2. A large-diameter linear solenoid type air pipe is provided in the pipeline. A bypass valve (referred to as an ABV valve) 50 is provided.
The air bypass pipe 50a has a flow passage area similar to that of the intake pipe 6, and when the ABV valve 50 is fully opened, the required amount of intake air in the low to medium speed range of the engine 1 can flow. . On the other hand, the idle adjustment valve 16 is provided with an ABV valve 50.
It has a smaller flow passage area and uses the idle adjustment valve 16 when adjusting the intake air amount with high accuracy.

The throttle body 6b includes a butterfly type throttle valve 7 for opening and closing a flow path, a throttle sensor 14 for detecting accelerator opening information by detecting a throttle opening θth, and an idle sensor for detecting a fully closed state. A switch 15 is provided. Air cleaner 6
a, an intake air temperature sensor 1 for obtaining an intake air density.
2. An atmospheric pressure sensor 13 is provided, and the atmospheric pressure Pa,
A signal corresponding to the intake air temperature Ta is output. Further, near the inlet of the intake pipe 6, a Karman vortex type air flow sensor 1 is provided.
1, which outputs a vortex generation signal proportional to the volume air flow rate Qa per intake stroke.

The above-mentioned EGR port has a large-diameter EGR port.
It is connected downstream of the throttle valve 7 and upstream of the intake manifold 2 via a GR pipe 10b, and a stepper motor type EGR valve 10a is disposed in the pipeline. On the other hand, the exhaust port 3a is connected to an exhaust manifold 3 to which an O ₂ sensor 17 is attached, and further includes an exhaust gas purifying catalytic converter (catalyst) 9 as an exhaust gas purifying catalyst, a muffler (not shown), and the like. The exhaust pipe (exhaust passage) 3b provided is connected. The O ₂ sensor 17 detects the oxygen concentration in the exhaust gas and outputs a detection signal. A catalyst temperature sensor (high temperature sensor) 26 for detecting the temperature of the catalyst or its vicinity (hereinafter referred to as the catalyst temperature) Tcc is attached to the downstream side of the catalyst 9. And, from the combustion chamber 1a, the exhaust manifold 3
After the three harmful components of CO, HC and NOx in the exhaust gas are purified by the catalytic converter 9, the exhaust gas discharged to the muffler is silenced by a muffler and discharged to the atmosphere side. In particular, this engine is an engine that can perform economizing operation while keeping the air-fuel ratio on the lean side (lean side). During lean operation, the normal three-way catalyst alone cannot sufficiently purify NOx in exhaust gas. The catalyst 9 is a combination of a lean NOx catalyst 9a and a three-way catalyst 9b. That is, downstream of the lean NOx catalyst 9a, CO, HC and NOx
Is provided with a three-way catalyst 9b having a three-way function capable of purifying the catalyst. This is because the three-way catalyst 9b is arranged upstream of the lean NOx catalyst 9a, and the NOx in the lean NOx catalyst 9a is reduced.
x Lean NO while not hindering purification
x This is to ensure that CO and HC that could not be sufficiently purified by the catalyst can be purified. When the lean NOx catalyst has a three-way function, the lean NOx
Only one catalyst may be provided.

A fuel tank (not shown) is provided at the rear of the vehicle body. Then, the fuel stored in the fuel tank is sucked up by an electric low-pressure fuel pump and sent to the engine 1 side through a low-pressure feed pipe. The fuel supplied to the engine 1 is supplied to a high-pressure fuel pump (not shown) attached to a cylinder head via a high-pressure feed pipe and a delivery pipe.
The fuel is supplied to each fuel injection valve 8.

An ECU (electronic control unit) is provided in the vehicle interior.
The ECU 23 has an input / output device (not shown) and a storage device (ROM, RAM, non-volatile RAM) for storing control programs, control maps, and the like.
Etc.), a central processing unit (CPU), a timer counter, and the like, and perform overall control of the engine 1. EC
On the input side of U23, switches for detecting the operating status of an air conditioner, a power steering device, an automatic transmission, and the like, which are loads on the engine 1 at the time of operation, are respectively connected, and each detection signal is supplied to the ECU 23. I have. In addition, EC
In U23, in addition to the various sensors and switches described above, a number of switches and sensors (not shown) are connected to the input side, and various warning lights and devices are also connected to the output side. .

The ECU 23 determines the fuel injection mode, the fuel injection amount, the fuel injection end timing, the ignition timing, the amount of EGR gas introduced, etc., based on the input signals from the various sensors and switches described above. The drive control of the fuel injection valve 8, the ignition coil 34, the EGR valve 10a and the like is performed. next,
The normal control of the engine 1, that is, the control when the exhaust gas temperature raising control described later is not performed will be briefly described.

When the engine is started when the engine is cold, the ECU 2
3 selects an intake stroke injection mode and injects fuel so as to have a relatively rich air-fuel ratio. This is because the fuel has a low vaporization rate during a cold period, and therefore, when injection is performed in the compression stroke injection mode, misfires and discharge of unburned fuel are inevitable. The ECU 23 also sets the ABV valve 50 at the time of starting.
Is closed, the intake air to the combustion chamber 1a is supplied from the gap of the throttle valve 7 and the idle adjustment valve 16. still,
The idle adjustment valve 16 and the ABV valve 50 are centrally managed by the ECU 23, and the respective valve opening amounts are determined according to the required introduction amount of intake air (bypass air) bypassing the throttle valve 7.

Until the cooling water temperature TW rises to a predetermined value after the start, the ECU 23 selects the intake stroke injection mode and injects the fuel in the same manner as at the time of the start, and also continuously closes the ABV valve 50. In addition, the control of the idle speed according to the increase or decrease of the load of the auxiliary equipment such as the air conditioner is performed by the idle adjustment valve 16 (the ABV valve 50 is also opened as necessary) as in the intake pipe injection type. . Further, when a predetermined cycle elapses and the O ₂ sensor 17 reaches the activation temperature,
23 starts the air-fuel ratio feedback control according to the output voltage of the O ₂ sensor 17 and purifies the harmful exhaust gas component by the catalyst 9. As described above, when the engine is cold, substantially the same fuel injection control as that of the intake pipe injection type is performed, but since there is no attachment of fuel droplets to the intake port wall surface, control responsiveness and accuracy are improved.

When the warm-up of the engine 1 is completed, the ECU 2
3 retrieves the current fuel injection control area from the fuel injection control map of FIG. 9 based on the target in-cylinder effective pressure (target load) Pe obtained from the throttle opening θth and the like and the engine speed (rotation speed) Ne. In addition to determining the fuel injection mode and the fuel injection amount to drive the fuel injection valve 8, the ABV valve 50 and the E
Valve opening control of the GR valve 45 is also performed.

For example, during low-load / low-speed operation such as idling operation, the compression stroke injection lean region shown by hatching in FIG. 9 is selected, so that the ECU 23 selects the compression stroke injection mode and sets the ABV valve 50 and the EGR valve 10a. The valve is opened according to the operating state to obtain a lean air-fuel ratio (20 to 40 in this embodiment).
Inject fuel so that At this time, the fuel vaporization rate increases, and the intake air flowing from the intake port 2a forms a reverse tumble flow 80 indicated by an arrow as shown in FIG. 10, so that the fuel spray 81 is stored in the piston cavity. Is done. As a result, an air-fuel mixture in the vicinity of the stoichiometric air-fuel ratio is formed around the ignition plug 35 at the time of ignition, and it is possible to ignite even with an extremely lean air-fuel ratio as a whole (for example, about 50 in overall air-fuel ratio). Become. As a result, the emission of CO and HC becomes extremely small, and the emission of NOx is also reduced by the recirculation of exhaust gas. In addition, the pumping loss is reduced by opening the ABV valve 50 and the EGR valve 10a, and the fuel efficiency is greatly improved. And, since the control of the idle speed according to the increase or decrease of the load is performed by increasing or decreasing the fuel injection amount, the control response becomes very high.

In the compression stroke injection mode, the fuel spray injected from the injection valve 8 must ride on the reverse tumble flow and reach the spark plug 35,
The fuel must evaporate by the time it reaches and ignites to form a mixture that is easy to ignite. Average air-fuel ratio is 20
If it is less than the above, an over-rich mixture is locally generated near the spark plug 35 to cause a so-called rich misfire. On the other hand, if it is 40 or more, the mixture exceeds the lean limit and misfire (so-called lean misfire) tends to occur. Therefore, as described later, the timing of starting and ending the fuel injection and the timing of the ignition are accurately controlled, and the average air-fuel ratio is set to 20%.
The range is set to be within a range from 40 to 40. If the range is exceeded, the mode is switched to the intake stroke injection mode described later.

When the vehicle is running at low to medium speeds, a lean region or a stoichiometric feedback region (a stoichiometric air-fuel ratio feedback control region) based on the intake stroke injection mode in FIG. 9 is used depending on the load state and the engine speed Ne. Therefore, E
The CU 23 selects the intake stroke injection mode and injects fuel so as to have a predetermined air-fuel ratio. That is, in the lean region of the intake stroke injection mode, the ABV valve 5 is controlled so as to have a relatively lean air-fuel ratio (for example, about 20 to 23).
In the stoichiometric feedback range (S-FB range), the ABV valve 50 and the EGR are controlled.
Control the opening and closing of the EGR valve 10a.
a is controlled only in a specific region of the stoichiometric feedback range), and the air-fuel ratio feedback control is performed according to the output voltage of the O ₂ sensor 17. As shown in FIG. 11, since the intake air flowing from the intake port 2a forms the reverse tumble flow 80, the fuel injection start timing or the end timing is adjusted to adjust the fuel injection in the lean region (intake lean region) of the intake stroke injection mode. In addition, it is possible to ignite even at a lean air-fuel ratio due to the effect of turbulence due to reverse tumble. still,
In the stoichiometric feedback range, a large output is obtained with a relatively high compression ratio, and harmful exhaust gas components are purified by the catalyst 9.

The ECU 23 selects the intake stroke injection mode and closes the ABV valve 50 at the time of rapid acceleration or high-speed running, so that the ECU 23 selects the intake stroke injection mode, and sets the throttle opening θth and engine speed. Fuel is injected so as to have a relatively rich air-fuel ratio according to the speed Ne and the like. At this time, in addition to the high compression ratio and the fact that the intake flow forms the reverse tumble flow 80, a high output can be obtained by the inertia effect because the intake port 2a is substantially upright with respect to the combustion chamber 1a. Can be

Further, during coasting operation during mid-high speed running, the fuel cut-off region shown in FIG. 9 is set, so that the ECU 23 completely stops fuel injection. As a result, the fuel efficiency is improved, and the emission amount of the harmful exhaust gas component is reduced. The fuel cut is immediately stopped when the engine rotation speed Ne falls below the return rotation speed or when the driver steps on the accelerator pedal.

Next, the exhaust gas temperature raising control procedure according to the present invention will be described with reference to the flowchart shown in FIG. The exhaust gas temperature raising control routine shown in FIG. 12 is repeatedly executed every time the crank angle signal SGT is output from the crank angle sensor 21 while the above-described normal control is being executed.

First, in step S10, the ECU 23 determines the catalyst temperature Tcc, the cooling water temperature Tw, the intake air flow rate Qa,
Throttle opening θth, engine speed Ne, atmospheric pressure Pa
And various engine operating state quantities such as the intake air temperature Ta. Then, the process proceeds to step S12 to determine whether the catalyst 9 is in the active state by comparing the catalyst temperature Tcc with the catalyst determination temperature Tcw. This catalyst determination temperature Tcw is
The catalyst activity target temperature is determined according to the catalyst activity lower limit temperature, and can be set as, for example, a value obtained by adding a predetermined temperature to the catalyst activity lower limit temperature. This catalyst activity lower limit temperature is 4 in the lean NOx catalyst according to the present embodiment.
It is about 00 degrees. It is needless to say that the determination may include not only the catalyst temperature but also a determination as to whether or not a condition for inhibiting the exhaust gas temperature increase control described later is satisfied. For example, immediately after starting, the engine speed Ne
During a period until the engine speed exceeds a predetermined rotational speed or during a certain period of time (for example, about 4 seconds) during which the engine rotational speed stabilizes, or the air amount adjusting means (for example, throttle If there is a change in the opening of the valve, the control may be prohibited. In particular, in the latter case, when the air amount adjusting means changes in the opening direction, the fuel injection amount is increased in accordance with the request for acceleration, and the exhaust gas temperature can increase without the control of the present invention. When the direction changes to the closing direction, the fuel cut control is performed, so that the exhaust gas temperature rise control cannot be performed basically.

If the catalyst temperature Tcc is higher than the catalyst determination temperature Tcw, or if the exhaust gas temperature rise control prohibition condition is satisfied, it is determined that the catalyst 9 is in the active state (step S).
If the result of the determination in step 12 is “Y”, the flow proceeds to step S14. In this step, the normal control described above is executed,
Only the main fuel injection is performed and no additional injection is performed. Therefore, the above-described compression stroke injection mode control or intake stroke injection mode control is executed according to the engine operating state.

If the catalyst temperature Tcc is lower than the catalyst determination temperature Tcw, or if the exhaust gas temperature rise control prohibition condition is not satisfied, it is determined that the catalyst 9 is in an inactive state (step S).
When the result of the determination in step 12 is "N"), the following exhaust gas temperature raising control is executed. In the exhaust gas temperature raising control, the main fuel injection is performed in the compression lean mode, and the ignition timing is also retarded.
More specifically, first, in step S16, the ignition timing TRD is read from the retard map. The ignition timing of the main fuel injection of the exhaust gas temperature raising control is read from the experimental data similar to the experimental results of FIGS. 5 to 7 according to the catalyst temperature Tcc, the target exhaust temperature, the cooling water temperature Tw, and the like. Further, the intake air density is corrected according to the atmospheric pressure Pa and the intake air temperature Ta.
In any case, the ignition timing TRD is 10 ° in crank angle.
It is set to an appropriate value within the range of BTDC to 5 ° ATDC.

Next, at step S18, it is determined whether or not the cooling water temperature Tw is lower than a predetermined determination temperature Two. From the comparison between FIG. 5 and FIG. 6, when performing two-stage combustion,
It is advantageous in terms of the temperature increase effect that the air-fuel ratio at the time of the main fuel injection is set to a value as large as about 40, but when the cooling water temperature Tw is lower than the determination temperature Two (for example, 50 ° C.) when the engine is cold (step S18). If the determination result is affirmative "Y"), the stable combustion at the time of the main fuel injection is prioritized, and in step S20, the target air-fuel ratio AF is read from the lean first map. On the other hand, when the cooling water temperature Tw is equal to or higher than the determination temperature Two (when the determination result in step S18 is negative “N”),
There is no fear of unstable combustion, and in step S22, the target air-fuel ratio AF is read from the lean second map.

Therefore, the target air-fuel ratio read from the lean first map is set to a smaller value than the one read from the lean second map at the same engine operating state quantity. The local air-fuel ratio of the air-fuel mixture formed near 35 is set so as to be an optimum value (theoretical air-fuel ratio) for stable combustion. Therefore, according to the water temperature (according to the combustion state at the time of main fuel injection)
There is an advantage that the target air-fuel ratio can be easily set.

As the engine operation state quantity for reading the target air-fuel ratio from the first and second maps, for example, the engine speed Ne and the target average effective pressure Pe are used. Required to
A map value (AF = f (P
e, Ne)) are set and stored in the storage device of the ECU 23 described above. The target average effective pressure Pe is correlated with the engine output desired by the driver, and the throttle opening θth
And the target average effective pressure map in accordance with the engine speed Ne.

Next, in step S24, the main fuel injection time (opening time of the fuel injection valve 8) Tinjm is calculated by the following equation (M1) using the read target air-fuel ratio AF. Tinjm = K × (Qa × γ / AF) × (Kwt × ...) × Kg + TDEC ... (M1) Here, Kwt, Kaf ..., etc. are various values set according to the engine coolant temperature Tw, etc. This is a correction coefficient and is set according to the engine operating state. Kg is a gain correction coefficient of the injection valve 8, and TDEC is an invalid time correction value, which is set according to the target average effective pressure Pe and the engine speed Ne. K
Is a conversion coefficient for converting the fuel amount into the valve opening time, and is a constant.

When the calculation of the main fuel injection time Tinjm is completed, in the next step S26, the injection time Tinja of the additional fuel is calculated by the following equation (M2). The additional fuel injection amount is set according to the amount of oxygen remaining in the cylinder after the main combustion. That is, the air-fuel ratio obtained from the total fuel injection amount per cycle, which is the sum of the main combustion injection amount and the additional fuel injection amount, and the intake air amount Qa per cylinder, is equal to the target air-fuel ratio (for example, When the main combustion is stabilized at an engine speed of 1500 rpm, the temperature is set to be slightly leaner than the stoichiometric air-fuel ratio (for example, about 15) so as to maximize the exhaust gas temperature rise. Is set.

Tinja = K × Qa × γ ((1 / theoretical AF) − (1 / AF)) × (Kwt × ...) × Kg + TDEC (M2) Thus, the main combustion injection amount and When the calculation of the additional fuel injection amount is completed, main fuel injection and ignition are performed in step S28. The main fuel injection is performed during the compression stroke.
According to the ignition timing TRD set in 6, it is preferable to determine the start timing of the main fuel injection so that the air-fuel mixture can reach a suitable position near the ignition plug 35 at the timing when ignition can be performed most stably. Therefore, in the present embodiment, the main fuel injection start timing is set as a function of the ignition timing TRD, and the fuel injection valve 8 is driven to open at the main fuel injection start timing set in the compression stroke to inject the main fuel. Has started.

Next, the routine proceeds to step S30, where additional fuel is injected at a predetermined time in the middle stage of the expansion stroke. From the experimental results shown in FIGS. 5 to 7, the injection start timing of the additional fuel may be fixed at the middle stage of the expansion stroke, for example, at a crank angle of 90 ° ATDC, but the atmospheric pressure Pa, the intake air temperature Ta, etc. Are set in consideration of the environmental conditions described in (1) and (2) above, taking into account the time when the temperature raising efficiency becomes maximum. Such additional fuel injection start timing may be set experimentally in advance and stored in the above-described storage device of the CPU 23.

When the ECU 23 waits for the arrival of the additional fuel injection start timing set as described above, drives the fuel injection valve 8 to open the valve, and performs the injection of the additional fuel. A pre-flame reaction product is present in a lean mixture portion formed in the chamber 1a at a concentration near the ignition limit, and the pre-flame reaction product generated from the additional fuel injected into the high-temperature atmosphere in the cylinder. Self-ignition exceeds the ignition limit, and combustion of additional fuel is started. The heat energy generated by the additional fuel surely raises the temperature of the exhaust gas without a part of the heat energy being taken away by the expansion work.

In the exhaust gas temperature raising control of the above embodiment,
The injection amount of the additional fuel is set such that the total injection amount including the main fuel injection amount is equal to the target air-fuel ratio in accordance with the operating state, while the total air-fuel ratio per one cylinder is equal to the operating state. However, the present invention is not limited to such a setting method. In some cases, the total air-fuel ratio per one cylinder cycle may be smaller or larger than the stoichiometric air-fuel ratio.
You may make it set as a fixed injection amount which can be reburned.

In the exhaust gas temperature raising control of the above-described embodiment, the ignition timing of the main fuel is retarded to cause slow combustion, and in the middle of the expansion stroke or later, the concentration of the preflame reaction product becomes close to the ignition limit concentration. , But in another embodiment,
The ignition timing of the main fuel is not retarded as compared with the normal operation, and the air-fuel ratio of the main combustion is leaned (lean) to 35 or more to cause slow combustion, and in the middle or later stage of the expansion stroke Alternatively, the pre-flame reaction product concentration can be controlled to a concentration near the ignition limit concentration.

Further, when performing additional fuel injection, injection need not always be performed once, but may be performed a plurality of times. Furthermore, the additional fuel injection may be performed for all cylinders, or may be performed only for a specific cylinder. In the above-described embodiment, the catalyst temperature sensor 26 is provided, and the catalyst temperature Tcc
It is determined whether or not the temperature of the catalyst 9 needs to be raised based on the detection result to determine whether or not to perform the exhaust gas temperature raising control. The catalyst temperature may be estimated based on the above signal, and it may be determined whether or not to perform the exhaust gas temperature increase control based on the estimation result. Further, in order to simplify the control, an engine temperature detecting means at the start which detects whether the engine temperature (cooling water temperature) at the start is equal to or lower than a set temperature, or an elapsed time from the start (the water temperature at the start) (Variable or fixed predetermined time set in accordance with the above), the exhaust gas temperature raising control may be performed based on the output from the elapsed time detecting means for detecting the time until the time reaches the predetermined time.

Further, an operation state in which the exhaust gas temperature raising control is performed is specified, for example, immediately after the engine is started (when the engine speed after the start exceeds a predetermined engine speed, or when the engine speed after the start is stable, the engine speed is kept constant). When the time has passed), during steady running (when the change in throttle opening is small during stratified combustion),
Alternatively, the exhaust gas temperature raising control may be set to be performed for a predetermined time in a specific operation state in which the catalyst may be in an inactive state, for example, at the time of a return idle after the fuel cut.

In this embodiment, when the catalyst is in an inactive state, the target air-fuel ratio is read from the first map or the second map according to the water temperature, and the fuel injection amount and the like are set. In particular, the injection amount ratio between the main injection and the sub injection may be variably set based on the water temperature information without using a map. That is, if the water temperature is low, the injection amount of the main injection is increased to stabilize combustion, and if the water temperature is high, the injection amount of the sub-injection is increased to shorten the total time until the catalyst is activated. May be.

[0063]

As described above in detail, according to the exhaust gas temperature raising apparatus of the present invention, the engine control parameters for stratified combustion are controlled during the operation of the engine requiring the exhaust gas temperature raising. By injecting additional fuel from the fuel injection valve during the middle stage of the expansion stroke after the main combustion or during the expansion stroke thereafter, it is possible to perform the main combustion as in the case where the additional fuel is injected at the time of flame propagation at the beginning of the expansion stroke of the prior art. Since the flame reaches and burns the additional fuel, or the fuel of the main combustion is not self-ignited in the cylinder without injecting and burning the additional fuel, the fuel is generated by the additional fuel compared to the conventional technology. Exhaust gas can be reliably heated without a part of thermal energy being taken away by expansion work.

Further, by injecting the additional fuel into the high-temperature atmosphere after the main combustion as in the additional fuel control means of the exhaust gas heating apparatus of the present invention, the pre-flame reaction of the additional fuel proceeds. Additional fuel can be burned, especially without spark ignition. According to the third aspect of the present invention, the engine control parameters for the stratified combustion are controlled during the operation of the engine in which the exhaust temperature is required to be raised, and after the top dead center at the crank angle during the expansion stroke. By injecting the additional fuel from the fuel injection valve at 70 ° to 110 °, the main combustion flame reaches and burns the additional fuel as in the case of the prior art in which the additional fuel is injected at the beginning of the expansion stroke flame propagation. Or the self-ignition in the cylinder without injecting additional fuel into the flame of the main combustion and burning it, compared to the prior art, a part of the heat energy generated by the additional fuel is taken for expansion work. The temperature of the exhaust gas can be surely raised without being affected.

As in the additional fuel control means of the exhaust gas heating apparatus of the present invention, the injection start timing of the additional fuel is set at 80 ° to 100 ° after the top dead center at the crank angle during the expansion stroke. Thereby, a higher exhaust gas temperature increasing effect can be obtained. According to a fifth aspect of the present invention, the engine control means of the exhaust gas temperature raising apparatus according to the fifth aspect of the present invention comprises:
The ignition timing of the main fuel can be retarded and the combustion can be slowed down because the ignition timing is set to about 5 ° ATDC. The concentration of the pre-flame reaction product remaining in the room can be controlled near the fire concentration limit value. Therefore, self-ignition becomes possible in the cylinder by the injection of the additional fuel, and the temperature of the exhaust gas can be increased.

At this time, like the engine control means of the exhaust gas heating apparatus according to the present invention, an air-fuel ratio setting means for setting the air-fuel ratio during stratified combustion to 25 or more is provided. The fuel can be burned slowly. The engine control means of the exhaust gas temperature raising apparatus according to the present invention is provided with air-fuel ratio setting means for setting the air-fuel ratio during stratified combustion to 35 or more, so that the ignition timing of the main fuel is retarded. Even without this, the main fuel can be slowly burned only by controlling the air-fuel ratio, and the pre-flame reaction product concentration remaining in the combustion chamber during the middle stage of the expansion stroke or the subsequent expansion stroke is brought close to the fire concentration limit value. Can be controlled.

According to another aspect of the present invention, the engine control means of the exhaust gas heating apparatus of the present invention includes an ignition timing setting means for setting an ignition timing for stratified combustion or an air-fuel ratio setting for setting an air-fuel ratio for stratified combustion. Since the ignition timing setting means sets the ignition timing for stratified combustion on the retard side while the air-fuel ratio setting means sets the air-fuel ratio for stratified combustion on the lean side, At the time of engine operation in which exhaust temperature rise is required, the ignition timing of stratified combustion can be retarded, or the air-fuel ratio of stratified combustion can be controlled to be lean, so that the main fuel can be burned slowly. The concentration of the preflame reaction product remaining in the combustion chamber during the middle stage of the expansion stroke or thereafter can be controlled near the fire concentration limit value. Thereby, self-ignition becomes possible after the additional fuel injection, and the temperature of the exhaust gas can be increased.

According to the exhaust gas temperature raising apparatus of the present invention, the ignition timing setting means for setting the ignition timing for stratified combustion or the air-fuel ratio setting means for setting the air-fuel ratio for stratified combustion is provided. When the engine is operated, which requires an exhaust temperature rise, the main fuel can be slowly burned by controlling one of the ignition timing or the air-fuel ratio as an engine control parameter for the stratified combustion, It is possible to control the concentration of the preflame reaction product remaining in the combustion chamber during the middle stage of the later expansion stroke or the subsequent expansion stroke to a value close to the fire concentration limit value. Then, during the control of the engine control parameters for stratified combustion, additional fuel is injected from the fuel injection valve during the middle stage of the expansion stroke after the main combustion or during the subsequent expansion stroke, whereby the flame propagation in the early stage of the expansion stroke of the prior art is performed. Sometimes, as in the case of injecting additional fuel, the flame of the main combustion reaches and burns the additional fuel, or the self-ignition in the cylinder without injecting and burning the additional fuel to the flame of the main combustion. Therefore, compared with the related art, it is possible to surely raise the temperature of the exhaust gas without a part of the heat energy generated by the additional fuel being taken away by the expansion work.

According to a tenth aspect of the present invention, the engine control means of the exhaust gas temperature raising device sets the ignition timing of the stratified combustion to the retard side while the air-fuel ratio setting means sets the ignition timing of the stratified combustion to the retard side.
By setting the air-fuel ratio of the stratified combustion to the lean side, the ignition timing for the stratified combustion is retarded or the air-fuel ratio for the stratified combustion is set to the lean side during an engine operation in which the exhaust gas temperature is required to rise. Control to make the main fuel burn slowly,
The concentration of the pre-flame reaction product remaining in the combustion chamber during the middle stage of the expansion stroke after the main combustion or during the expansion stroke thereafter can be controlled near the fire concentration limit value. Thereby, self-ignition becomes possible after the additional fuel injection, and the temperature of the exhaust gas can be increased.

[Brief description of the drawings]

FIG. 1 is a stroke diagram conceptually illustrating a process of combustion of main fuel injected in a compression stroke and combustion of additional fuel injected in an expansion stroke in a middle stage or later of an expansion stroke.

FIG. 2 is a graph showing a relationship between a change in a crank angle and an in-cylinder pressure during an exhaust gas temperature increase control according to the present invention.

FIG. 3 is a graph showing a change in a concentration of a preflame reaction product generated in a main fuel combustion region in a combustion chamber, which is indicated by a broken circle DZ in FIG. 2;

FIG. 4 is a graph showing a change in concentration of a preflame reaction product occurring in an additional fuel combustion region in a combustion chamber, which is indicated by a broken circle WZ in FIG.

FIG. 5 is a graph showing the relationship between the exhaust gas temperature and the injection timing of the additional fuel when the ignition timing TRD is variously changed, and shows the experimental result data when the main fuel injection amount is set to 30 in the air-fuel ratio. Show.

FIG. 6 is a graph similar to FIG. 5 showing the relationship between the exhaust gas temperature and the injection timing of the additional fuel when the ignition timing TRD is variously changed, and the main fuel injection amount is set to 40 in the air-fuel ratio. The experimental result data in the case is shown.

FIG. 7 is a map diagram showing the exhaust temperature and the amount of unburned hydrocarbons in the exhaust gas, using the ignition timing TRD and the additional fuel injection timing as parameters, from the same experimental results as in FIG.

FIG. 8 is a schematic configuration diagram of an engine control device according to the exhaust gas heating device of the present invention.

FIG. 9 is defined in accordance with the average effective pressure Pe in the cylinder of the engine and the engine speed Ne, and shows a compression stroke injection lean operating range;
4 is an engine control mode map showing an intake stroke injection lean operation region, a stoichiometric feedback operation region, and the like.

FIG. 10 is an explanatory diagram showing a fuel injection mode in a compression stroke injection mode of the direct injection spark ignition type internal combustion engine according to the present invention.

FIG. 11 is an explanatory diagram showing a fuel injection mode in an intake stroke injection mode of the direct injection spark ignition type internal combustion engine according to the present invention.

FIG. 12 is a flowchart for explaining an exhaust gas temperature rise control procedure according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 In-cylinder injection spark ignition type internal combustion engine 1a Combustion chamber 7 Throttle valve 8 Fuel injection valve 9 Exhaust gas purification device (catalyst) 11 Air flow sensor 12 Intake temperature sensor 13 Atmospheric pressure sensor 14 Throttle sensor 19 Cooling water temperature sensor 21 Crank angle Sensor (engine speed sensor) 23 Electronic control unit (ECU) (engine control means, additional fuel control means) 35 Spark plug

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/36 ZAB F01N 3/36 ZABR F02B 17/00 ZAB F02B 17/00 ZABF F02D 41/02 ZAB F02D 41 / 02 ZAB 301 301A 41/34 ZAB 41/34 ZABH 43/00 301 43/00 301J 301B 301E 45/00 301 45/00 301G F02P 5/15 F02P 5/15 B (72) Inventor Hiromitsu Ando Tokyo Metropolitan Port 5-33-8 Shiba-ku, Mitsubishi Motors Industry Co., Ltd. (72) Inventor Toshio Shuto 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation

Claims (10)

[Claims] A fuel injection valve for injecting fuel directly into a combustion chamber, wherein at least at the time of a compression stroke, fuel is injected from the combustion injection valve and spark ignition is performed to perform stratified combustion. A temperature control device that operates during an engine operation that requires an exhaust gas temperature rise to control an engine control parameter for the stratified combustion; and a middle stage of the expansion stroke after the main combustion during the operation of the engine control device. Or an additional fuel control device for injecting additional fuel from the fuel injection valve during an expansion stroke thereafter. 2. The exhaust gas heating apparatus according to claim 1, wherein said additional fuel control means injects said additional fuel into a high-temperature atmosphere after main combustion. 3. An in-cylinder injection type internal combustion engine having a fuel injection valve for directly injecting fuel into a combustion chamber and injecting fuel from the combustion injection valve at least during a compression stroke to perform stratified combustion by spark ignition. In the warming device, an engine control means that operates during operation of an engine that requires an exhaust gas temperature increase to control engine control parameters for the stratified combustion; and a crank angle during the expansion stroke during operation of the engine control means. An exhaust gas heating device comprising: additional fuel control means for starting injection of additional fuel from the fuel injection valve at 70 ° to 110 ° after the top dead center. 4. The exhaust gas according to claim 3, wherein the additional fuel control means sets the injection start timing of the additional fuel to 80 ° to 100 ° after the top dead center at the crank angle during the expansion stroke. Heating device. 5. An exhaust gas heating device according to claim 3, wherein said engine control means includes an ignition timing setting means for setting an ignition timing in a crank angle of 10 ° BTDC to 5 ° ATDC. . 6. The exhaust gas heating apparatus according to claim 5, wherein said engine control means includes air-fuel ratio setting means for setting an air-fuel ratio during stratified combustion to 25 or more. 7. The exhaust gas heating apparatus according to claim 1, wherein said engine control means includes air-fuel ratio setting means for setting an air-fuel ratio during stratified combustion to 35 or more. 8. The engine control means has at least one of an ignition timing setting means for setting an ignition timing for the stratified combustion, and an air-fuel ratio setting means for setting an air-fuel ratio for the stratified combustion, The ignition timing setting means sets the ignition timing for stratified combustion to a retard side, while the air-fuel ratio setting means sets the air-fuel ratio for stratified combustion to a lean side. Item 4. The exhaust gas heating apparatus according to Item 1 or 3. 9. An in-cylinder injection type internal combustion engine having a fuel injection valve for directly injecting fuel into a combustion chamber, wherein fuel is injected from the combustion injection valve at least during a compression stroke and spark ignition is performed to perform stratified combustion. An engine requiring one of an ignition timing setting means for setting an ignition timing for the stratified combustion and an air-fuel ratio setting means for setting an air-fuel ratio for the stratified combustion, An engine control unit that operates during operation to control one of an ignition timing and an air-fuel ratio as an engine control parameter for the stratified combustion; and, during or after the expansion stroke after main combustion during operation of the engine control unit. An additional fuel control means for injecting additional fuel from the fuel injection valve during the expansion stroke of the exhaust gas. 10. The ignition timing setting means sets the ignition timing for stratified combustion to a retard side, while the air-fuel ratio setting means sets the air-fuel ratio for stratified combustion to a lean side. The exhaust gas heating device according to claim 9, wherein: