JP2007002772A - Exhaust temperature control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sufficiently raise exhaust temperature while preventing rich misfire and so on in a combustion chamber, when after burning is promoted by supplying secondary air to an exhaust passage, for the early activation of a catalyst immediately after starting, in an engine for injecting fuel from a fuel injection valve to an intake port. <P>SOLUTION: The minimum required fuel injection quantity Tie for stable combustion in the combustion chamber and a fuel injection quantity Tii for burning by secondary air in an exhaust passage are respectively calculated. Then, the fuel injection quantity Tie is injected in an exhaust stroke, and the fuel injection quantity Tii is injected in an intake stroke. In this case, injection is performed one time over an intake valve opening timing IVO, or divided injection is performed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas temperature control device for an internal combustion engine used for early activation of an exhaust purification catalyst immediately after starting.

Patent Document 1 includes a fuel injection valve that directly injects fuel into a combustion chamber, and a secondary air supply device (air pump) that supplies secondary air to an exhaust passage. In addition to the injection, the fuel is additionally injected between the expansion stroke and the exhaust stroke, and the additionally injected fuel is combusted by the secondary air from the secondary air supply means in the exhaust passage to thereby reduce the exhaust temperature. A device is disclosed which is activated to activate the exhaust purification catalyst immediately after starting.
JP 2002-327619 A

However, the technique described in Patent Document 1 is a technique specific to a direct injection engine in which additional injection is performed in the combustion chamber between the expansion stroke and the exhaust stroke, and cannot be applied to an engine that supplies fuel to the intake passage.
In the case of an engine that supplies fuel to the intake passage, by increasing the fuel supply amount, the in-cylinder A / F is operated to make a large amount of unburned fuel discharged into the exhaust passage, which is supplied as secondary air. It is known that the exhaust temperature can be raised by burning with the secondary air from the device, and the richer the A / F, the higher the exhaust temperature rise effect.

However, rich misfire and deterioration of combustion stability due to over-rich are the bottleneck, and since there is a rich limit, it is the actual situation that the optimum A / F from emission cannot be used.
In view of such a situation, the present invention makes it possible to sufficiently raise the exhaust temperature by making maximum use of secondary air in the exhaust passage while preventing rich misfire in an engine that supplies fuel to the intake passage. An object of the present invention is to provide an exhaust gas temperature control device for an internal combustion engine capable of

  For this reason, in the present invention, when raising the exhaust gas temperature, the fuel injection amount necessary for stable combustion in the combustion chamber, and the fuel injection amount burned by the secondary air from the secondary air supply device in the exhaust passage, Are calculated, the fuel injection amount necessary for the stable combustion is injected in the exhaust stroke, and the fuel injection amount burned by the secondary air is injected in the intake stroke.

  According to the present invention, the fuel injected in the exhaust stroke (before intake valve opening) is vaporized by the intake valve surface temperature and then sucked into the combustion chamber and contributes to combustion, whereas the intake stroke (intake valve) The fuel injected after the opening of the valve is sucked into the combustion chamber in the form of droplets without being vaporized, and is discharged almost without being combusted. Therefore, by setting the fuel amount that is promoted to vaporize even if the fuel injection amount is increased, the combustion A / F in the cylinder does not become excessively rich and deterioration of combustion stability can be prevented, while the exhaust passage As a result, the afterburning amount of the catalyst increases and the exhaust temperature can be significantly increased, so that the catalyst can be activated early and emissions can be reduced.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system diagram of an engine (internal combustion engine) showing an embodiment of the present invention.
An air cleaner 3, an electric throttle valve 4, and an intake manifold (collector) 5 are provided in the intake passage 2 of the engine 1 from the upstream side. The electric throttle valve 4 controls the amount of intake air, and the opening degree is controlled by a step motor or the like that is operated by a signal from an engine control unit (hereinafter referred to as ECU) 30. However, a mechanical throttle valve connected to the accelerator pedal by a wire or the like may be used.

  A fuel injection valve 7 for injecting fuel to the intake port 6 of each cylinder (directed toward the umbrella portion of the intake valve 8) is attached to the branch portion on the outlet side of the intake manifold 5. The fuel injection valve 7 is opened by energizing the solenoid for a time determined by the pulse width based on the injection pulse signal output in synchronization with the engine rotation from the ECU 30, and injects the fuel adjusted to a predetermined pressure. .

The air controlled by the electric throttle valve 4 and the fuel injected from the fuel injection valve 7 are sucked into the combustion chamber 9 of the engine 1 when the intake valve 8 is opened.
The air and fuel sucked into the combustion chamber 9 form an air-fuel mixture, which is ignited and burned by the spark plug 10 at the ignition timing controlled by the ECU 30. The exhaust gas after combustion is discharged to the exhaust passage 12 (exhaust port 13) through the exhaust valve 11. The exhaust passage 12 includes an exhaust port 13 formed for each cylinder in the cylinder head, an exhaust manifold 14 connected to the outlet side thereof, and the like. An exhaust purification catalyst 15 is provided.

  Here, in order to supply the secondary air upstream of the exhaust purification catalyst 15 in the exhaust passage 12, particularly to the exhaust port 13 of each cylinder in the cylinder head, which is a high temperature portion of the exhaust (toward the exhaust valve 11 umbrella), An electric air pump 16 is provided as a secondary air supply device, and its discharge side opens to an exhaust port 13 for each cylinder via an on-off valve (shutoff valve) 17 and further via a distribution gallery 18. The secondary air supply passage 19 is connected. Here, the secondary air is supplied to the exhaust port 13 as long as it is upstream of the catalyst 15 in the exhaust passage 12, and may be any cylinder, cylinder group, or common to all cylinders.

The suction side of the air pump 16 is connected by a pipe 20 to a secondary air outlet 21 provided downstream of the air cleaner 3 of the intake passage 2 (upstream of the air flow meter 33 arranged upstream of the electric throttle valve 4).
The ECU 30 detects an accelerator opening APO detected by an accelerator opening sensor 31, an engine speed N detected by a crank angle sensor 32, an intake air amount Q detected by an air flow meter 33, and an intake temperature sensor 34. The intake air temperature Ta, the engine coolant temperature Tw detected by the water temperature sensor 35, the exhaust air-fuel ratio detected by the air-fuel ratio sensor 36, and the like are input. In addition, although not shown, a signal is also input from an engine key switch having an ignition switch and a start switch.

  The ECU 30 controls the opening degree of the electric throttle valve 4, the fuel injection timing and fuel injection amount of the fuel injection valve 7, the ignition timing of the spark plug 10, and the like based on the engine operating conditions detected from these input signals. . Further, the operation of the air pump 16 and the on-off valve 17 is controlled. The on-off valve 17 is opened when the air pump 16 is turned on and closed when the air pump 16 is turned off, and can be omitted when the air pump 16 itself has a shut-off function when turned off.

Next, the fuel / secondary air control routine executed by the ECU 30 will be described with reference to the flowchart of FIG. This routine is executed every predetermined time during engine rotation.
In S11, the intake air amount Q, the engine speed N, the accelerator opening APO, and the water temperature Tw are read.
In S12, it is determined whether or not cranking is currently being performed (start switch ON).

If it is determined in S12 that cranking is currently in progress, the process proceeds to S13, and the secondary air supply device is stopped. Specifically, power supply to the motor that drives the air pump is cut off, and the on-off valve disposed in the secondary air supply passage is controlled to be closed.
In the next S14, the fuel injection amount Ti for starting and the fuel injection timing IT are calculated. Specifically, the fuel injection amount Ti is calculated by multiplying the basic fuel injection amount Tp by an increase correction coefficient for starting, and the fuel injection timing IT is set to a predetermined timing during the exhaust stroke (before the intake valve is opened). To do.

The basic fuel injection amount Tp is a fuel injection amount corresponding to the theoretical air-fuel ratio with respect to the intake air amount Q, and is calculated every predetermined time by the following equation.
Tp = K × Q / N (where K is a coefficient)
Further, the fuel injection amount in this embodiment is all calculated as the valve opening time of the fuel injection valve.
If it is determined in S12 that the cranking is not currently performed, the process proceeds to S15, and it is determined whether or not the accelerator opening APO is substantially 0 (idle state). If an idle switch is provided in addition to the accelerator opening sensor, it may be determined whether or not the idle switch is ON.

If it is determined in S15 that the accelerator opening APO is substantially 0, the process proceeds to S16, and it is determined whether or not the water temperature Tw is lower than the catalyst warm-up determination water temperature Twth. Here, the catalyst warm-up is determined using the water temperature Tw. However, when a catalyst temperature sensor is provided, the catalyst temperature is used.
If it is determined in S16 that the water temperature Tw is lower than the catalyst warm-up determination water temperature Twth, the process proceeds to S17, and the secondary air supply device is activated. Specifically, predetermined electric power is supplied to the motor that drives the air pump, and the on-off valve disposed in the secondary air supply passage is controlled to be in an open state.

In next S18, it is determined whether or not the value of the timer T is smaller than the secondary air stabilization time Tth. The timer T is a timer that measures an elapsed time since the secondary air supply device is in an operating state, and a desired secondary air flow rate cannot be obtained until the elapsed time becomes equal to or longer than the secondary air stabilization time Tth.
When it is determined in S18 that the value of the timer T is smaller than the secondary air stabilization time Tth, the process proceeds to S19, and the normal fuel injection amount Ti and the fuel injection timing IT are calculated. Specifically, the fuel injection amount Ti (= Tp × COEF × α) is calculated by multiplying the basic fuel injection amount Tp by various correction coefficients COEF and an air-fuel ratio feedback correction coefficient α, and the fuel injection timing IT is in the exhaust stroke. Is set at a predetermined time. The various correction coefficients COEF are a summary of the post-startup increase correction coefficient, the water temperature increase correction coefficient, etc., and the minimum fuel injection amount required for stable combustion is calculated by multiplying the basic fuel injection amount Tp by the various correction factors COEF. The Since the air-fuel ratio feedback correction coefficient α is clamped to 1 before the air-fuel ratio sensor is activated and the secondary air supply device is operating, α is always 1 when this step is executed. The fuel injection timing IT is determined so that the time from the end of fuel injection (Ti) to the intake valve opening timing IVO is a sufficient time (the time during which the injected fuel is sufficiently vaporized by the heat of the intake valve) (FIG. 4 (A)).

  If it is determined in S18 that the value of the timer T is equal to or greater than the secondary air stabilization time Tth, the process proceeds to S20 to calculate the fuel injection amount Ti and the fuel injection timing IT for introducing secondary air. The processing of this step will be described later in detail with reference to FIG. In addition, in the state where the secondary air is stably supplied, the control (riching) for introducing the secondary air is performed in order to prevent deterioration of HC emission.

If it is determined in S15 that the accelerator opening APO is greater than 0, or if it is determined in S16 that the water temperature Tw is equal to or higher than the catalyst warm-up determination water temperature Twth, the process proceeds to S21, and the normal fuel injection amount Ti And the fuel injection timing IT is calculated (similar to S19).
In the next S22, it is determined whether or not the value of the counter C is smaller than a predetermined value Cth. The counter C is a counter that is reset when the fuel control is switched from when the secondary air is introduced to when it is normal, and is counted up every time the engine rotates once.

  When it is determined in S22 that the value of the counter C is smaller than the predetermined value Cth, the process proceeds to S23 and the secondary air supply device is activated. Immediately after switching the fuel control, there is a possibility that the effect of the previous control remains (such as the exhaust stroke of the cylinder in which the fuel injection for introducing the secondary air has already been performed has not ended). This is because the supply of secondary air is cascaded for a while after switching.

When it is determined in S22 that the value of the counter C is equal to or greater than the predetermined value Cth, the process proceeds to S24 and the secondary air supply device is stopped.
Next, the details of the processing of S20 in the routine of FIG. 2 (calculation of the fuel injection amount Ti and the fuel injection timing IT for introducing secondary air) will be described with reference to the flowchart of FIG. 3 (first embodiment). .

  In S31, the fuel injection amount Tie (= Tp × COEF2) during the exhaust stroke (before intake valve opening) is calculated by multiplying the basic fuel injection amount Tp by various correction coefficients COEF2 for introducing secondary air. The exhaust stroke fuel injection amount Tie is the fuel injection amount in the first half of fuel injection executed before the intake valve opening timing IVO (before the intake valve opening timing IVO), and is calculated as the minimum fuel injection amount required for stable combustion. Is done. In addition, since the vaporization time of the injected fuel is shorter than that in the normal exhaust stroke injection, the injection amount considering this is calculated. Specifically, when the conditions such as the water temperature are the same, the various correction coefficients COEF2 for introducing the secondary air are set to values slightly increased from the various correction coefficients COEF for the normal time.

In S32, a rich misfire limit fuel injection amount Tp2 and a maximum fuel injection amount Tim are calculated.
The rich misfire limit fuel injection amount Tp2 is a fuel injection amount at which the air-fuel ratio of the air-fuel mixture in the combustion chamber becomes the rich misfire limit air-fuel ratio, and is calculated by the following equation.
Tp2 = K2 × Q / N (where K2 is a coefficient greater than K)
The maximum fuel injection amount Tim is a fuel injection amount at which the air-fuel ratio of the exhaust gas flowing into the exhaust gas purification catalyst becomes the stoichiometric air-fuel ratio, and is calculated by the following equation using the secondary air flow rate Q2.

Tim = K × (Q + Q2) / N
The secondary air flow rate Q2 is a design flow rate of an air pump for supplying secondary air, and is determined in advance. In the present embodiment, since the fuel control for introducing the secondary air is started after the supply of the secondary air is stabilized, the design flow rate can be used as the secondary air flow rate Q2 in the above equation. In consideration of the effect of exhaust pressure, the value of the secondary air flow rate Q2 may be corrected according to the engine speed N and the intake air amount Q.

  In S33, the intake stroke injection fuel vaporization rate V is calculated based on the water temperature Tw. The intake stroke injection fuel vaporization rate V is a value indicating the proportion of fuel that is vaporized by the ignition timing in the fuel injected during the intake stroke (after the intake valve is opened), and the higher the water temperature Tw, that is, the intake stroke injection. The higher the bore wall temperature to which fuel adheres, the greater the value. In addition to the water temperature Tw, the intake air temperature Ta may be considered. The fuel that has not been vaporized by the ignition timing is vaporized by receiving combustion heat during the expansion stroke, and is discharged together with the already burned gas during the exhaust stroke. This unburned fuel is combusted by the secondary air in the exhaust port and in the exhaust manifold.

In S34, two types of intake stroke fuel injection amounts Tii1, Tii2 are calculated.
One intake stroke fuel injection amount Tii1 is an intake stroke fuel injection amount that makes the air-fuel ratio of the air-fuel mixture in the combustion chamber (the air-fuel mixture formed at the ignition timing) a rich misfire limit air-fuel ratio, and is calculated by the following equation. The
Tii1 = (Tp2-Tie) / V
Here, it is assumed that all of the injected fuel in the exhaust stroke is vaporized by the ignition timing to form an air-fuel mixture, which is subtracted from the rich misfire limit fuel injection amount Tp2 to calculate the margin, and this margin is taken into the intake The intake stroke fuel injection amount Tii1 is calculated by dividing by the stroke injection fuel vaporization rate V. Actually, not all of the injected fuel in the exhaust stroke is vaporized by the ignition timing, but in order to reliably prevent rich misfire, the intake stroke fuel injection amount Tii1 is calculated based on the above assumption.

The other intake stroke fuel injection amount Tii2 is an intake stroke fuel injection amount in which the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is the stoichiometric air-fuel ratio, and is calculated by the following equation.
Tii2 = Tim-Tie
That is, the remainder obtained by subtracting the exhaust stroke fuel injection amount Tie from the maximum fuel injection amount Tim is the intake stroke fuel injection amount Tii2.

  In S35, the smaller one of the two types of intake stroke fuel injection amounts Tii1, Tii2 is set as the final intake stroke fuel injection amount Tii. When Tii1 is selected, the air-fuel ratio of the air-fuel mixture in the combustion chamber at the ignition timing becomes the rich misfire limit air-fuel ratio, and the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is leaner than the stoichiometric air-fuel ratio. When Tii2 is selected, the air-fuel ratio of the air-fuel mixture in the combustion chamber at the ignition timing becomes leaner than the rich misfire limit air-fuel ratio, and the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst becomes the stoichiometric air-fuel ratio.

In S 36, the fuel injection amount Ti (= Tie + Tii) is calculated by adding the exhaust stroke fuel injection amount Tie and the intake stroke fuel injection amount Tii. The fuel injection amount Ti when Tii2 is selected is the maximum fuel injection amount Tim.
In S37, the fuel injection timing IT is calculated based on the exhaust stroke fuel injection amount Tie and the engine speed N. Specifically, the fuel injection timing IT (injection start crank angle) is calculated by subtracting the value obtained by converting the exhaust stroke fuel injection amount Tie into the crank angle at the engine speed N from the intake valve opening timing. In a fuel injection execution routine (not shown) (executed in synchronism with engine rotation), an injection pulse signal having a length corresponding to the fuel injection amount Ti is generated when the crank angle reaches the fuel injection timing IT. Output to. Thereby, the fuel injection for the time of secondary air introduction shown in Drawing 4 (C) can be performed.

Next, the effect of this embodiment will be described.
In the system for supplying secondary air to the exhaust passage for the purpose of early activation of the catalyst at start-up, it is desirable that the in-cylinder combustion A / F be as rich as possible when maximizing the exhaust temperature rise effect. .
However, if the fuel injection amount is increased for the purpose of increasing the unburned HC used for afterburning, all the fuel is promoted to be vaporized by the intake valve, and the inside of the cylinder becomes excessively rich. That is, as shown in FIG. 4 (A), in the fuel control for normal time, the fuel injection timing is set in the middle of the exhaust stroke so that a sufficient vaporization time is taken from the end of fuel injection to the intake valve opening (IVO). As shown in FIG. 4B, when the fuel is enriched with the normal fuel control, vaporization is promoted at the intake valve surface temperature, so that the inside of the cylinder becomes excessively rich. .

As a result, combustion becomes unstable, and engine vibration deteriorates vehicle drivability. In addition, there is a possibility that rich misfire may occur during transient A / F fluctuations. Moreover, if the vaporization of all the supplied fuel is promoted, even the fuel that is to be discharged without combustion is involved in the combustion, so the unburned HC discharged from the combustion chamber is reduced, and the exhaust temperature rise effect can be obtained efficiently. Absent.
Therefore, in the present invention, the fuel injection amount (Tie) necessary for stable combustion in the combustion chamber and the fuel injection amount (Tii) to be burned by the secondary air in the exhaust passage are respectively calculated and required for the stable combustion. The fuel injection amount (Tie) is injected in the exhaust stroke, and the fuel injection amount (Tii) burned by the secondary air is injected in the intake stroke.

In particular, in the present embodiment, as shown in FIG. 4C, the total fuel injection amount of the exhaust stroke fuel injection amount Tie and the intake stroke fuel injection amount Tii in one fuel injection is set as the intake valve opening timing IVO. Inject again.
According to this, the fuel injected in the exhaust stroke (before the intake valve is opened) is sucked into the combustion chamber after being vaporized by the intake valve surface temperature, and injected in the intake stroke (after the intake valve is opened). The fuel is sucked into the combustion chamber as droplets without being vaporized.

Therefore, the fuel injected in the exhaust stroke contributes to combustion in the combustion chamber, whereas most of the fuel injected in the intake stroke is discharged without being burned.
Therefore, by setting the fuel amount that is promoted to be vaporized even if the fuel injection amount is increased, the combustion A / F in the cylinder does not become excessively rich (the combustion A / F is not increased even if the supply A / F is rich). It becomes leaner than that), and deterioration of combustion stability and rich misfire can be prevented. On the other hand, the amount of afterburning in the exhaust passage is increased, and the exhaust temperature can be significantly increased, so that the catalyst can be activated early and emissions can be reduced.

Further, according to the present embodiment, the intake stroke fuel injection amount Tii is the amount obtained by subtracting the exhaust stroke fuel injection amount Tie from the fuel injection amount Tp2 at which the air-fuel ratio of the air-fuel mixture in the combustion chamber becomes the rich misfire limit, and the intake air By calculating based on the vaporization rate V of the stroke injection fuel (when Tii = Tii1), the fuel injection amount can be optimized in consideration of the rich misfire limit.
Further, according to the present embodiment, the intake stroke fuel injection amount Tii is determined from the fuel injection amount Tim at which the air-fuel ratio of the exhaust downstream of the secondary air supply position (catalyst inlet) becomes the stoichiometric air-fuel ratio. By calculating by subtracting Tie (when Tii = Tii2), it is possible to optimize the fuel injection amount in consideration of the purification efficiency of the catalyst. That is, unburned HC is not discharged more than necessary with respect to the supplied secondary air amount, and deterioration of the tail pipe HC can be prevented.

  Further, according to the present embodiment, the intake stroke fuel injection amount includes the margin obtained by subtracting the exhaust stroke fuel injection amount Tie from the fuel injection amount Tp2 at which the air-fuel ratio of the air-fuel mixture in the combustion chamber becomes the rich misfire limit, and the intake stroke From the first intake stroke fuel injection amount Tii1 calculated based on the vaporization rate V of the injected fuel and the fuel injection amount Tim at which the air-fuel ratio of the exhaust downstream from the secondary air supply position (catalyst inlet) becomes the stoichiometric air-fuel ratio. Optimizing the fuel injection amount in consideration of the rich misfire limit and the purification efficiency of the catalyst by setting the smaller one of the second intake stroke fuel injection amount Tii2 calculated by subtracting the exhaust stroke fuel injection amount Tie Can be achieved.

Next, a second embodiment of the present invention will be described with reference to FIGS.
FIG. 5 is a flowchart showing the second embodiment of the process of S20 of the routine of FIG. 2 (calculation of fuel injection amount Ti and fuel injection timing IT for introducing secondary air), which is executed instead of FIG. Is done.
In S41, the exhaust stroke fuel injection amount Tie (= Tp × COEF) is calculated by multiplying the basic fuel injection amount Tp by various correction coefficients COEF. In the present embodiment, since the exhaust stroke injection timing ITe is set in the same manner as the normal injection timing (S46), the exhaust stroke fuel injection amount Tie is calculated using the same various correction coefficients COEF as in the normal time.

In S42, the rich misfire limit fuel amount Tp2 and the maximum fuel injection amount Tim are calculated (similar to S32 in FIG. 3).
In S43, the intake stroke injection fuel vaporization rate V is calculated based on the water temperature Tw (similar to S33 in FIG. 3). Since the intake stroke injection timing of the present embodiment is set in the middle of the intake stroke, when compared at the same water temperature, the intake stroke injection fuel vaporization rate V of the present embodiment is higher than the intake stroke injection fuel vaporization rate V of the first embodiment. Is smaller.

In S44, two types of intake stroke fuel injection amounts Tii1, Tii2 are calculated (similar to S34 in FIG. 3).
In S45, the smaller one of the two types of intake stroke fuel injection amounts Tii1, Tii2 is set as the final intake stroke fuel injection amount Tii (similar to S35 in FIG. 3).
In S46, the exhaust stroke fuel injection timing ITe is calculated based on the exhaust stroke fuel injection amount Tie and the engine speed N. As described above, the exhaust stroke fuel injection timing ITe is set to be the same as the normal injection timing (see FIG. 6).

  In S47, the intake stroke fuel injection timing ITi is calculated based on the intake stroke fuel injection amount Tii and the engine speed N. The intake stroke fuel injection timing ITi is set to a time when the vaporization amount of the injected fuel is minimized (see FIG. 6). If the injection timing is set so that the intake valve reaches the maximum lift when the injected fuel reaches the position of the intake valve, the fuel can easily reach the bore wall as droplets, and the amount of vaporization of the injected fuel is reduced. In addition, the intake air flow velocity when passing through the intake valve (the smaller the vaporization amount, the smaller the vaporization amount) and the time from the flow into the combustion chamber until the ignition timing (the shorter the vaporization amount, the smaller the vaporization amount) are also taken into consideration.

In a fuel injection execution routine (not shown), two injections are performed when effective values are set for the exhaust stroke fuel injection timing ITe and the intake stroke fuel injection timing ITi.
In the present embodiment, a fuel injection amount required for stable combustion in the combustion chamber and a fuel injection amount burned with secondary air in the exhaust passage are respectively calculated, and the fuel injection amount required for the stable combustion is calculated as an exhaust stroke. As shown in FIG. 6, the fuel injection is divided into the exhaust stroke fuel injection amount Tie and the intake stroke fuel injection amount. Tii is injected at different times.

Specifically, the exhaust stroke fuel injection amount Tie is injected in the middle of the exhaust stroke, and the intake stroke fuel injection amount Tii is injected in the middle of the intake stroke.
According to this, the fuel necessary for stable combustion in the combustion chamber is injected at an early stage of the exhaust stroke, and the vaporization time until the intake valve is opened can be taken more sufficiently, and the combustion stability is further improved. Can be made.

On the other hand, the fuel combusted by the secondary air is injected at a time when the intake stroke is late, so that the vaporization time until ignition can be shortened, and the injection timing increases the opening area of the intake valve portion and the intake flow velocity becomes slow. Therefore, it becomes more difficult to vaporize, the afterburning amount is increased, and the exhaust temperature increasing effect can be further enhanced.
It should be noted that if the intake stroke fuel injection is made as late as possible and the injection is terminated near the intake valve closing timing IVC, the vaporization time is shortened and it is difficult to contribute to combustion. However, the injection fuel is set so as not to adhere to the intake valve.

Further, in the case of split injection, the normal combustion portion and the enriched portion can be clearly divided, so that there is an advantage that there is no influence on a slight variation in injection timing.
Next, a third embodiment of the present invention will be described with reference to FIG.
FIG. 7 is a flowchart showing the third embodiment regarding the processing of S20 of the routine of FIG. 2 (calculation of fuel injection amount Ti and fuel injection timing IT for introducing secondary air).

In S51, the same processing as S41 to S45 of the second embodiment (FIG. 5) is performed to calculate the exhaust stroke fuel injection amount Tie and the intake stroke fuel injection amount Tii for the second injection.
In S52, it is determined whether or not the intake stroke fuel injection amount Tii is larger than the minimum fuel injection amount Timin of the fuel injection valve. The minimum fuel injection amount Timin is a value determined in advance by the specifications of the fuel injection valve, and the fuel injection valve cannot inject fuel of an amount smaller than this with high accuracy.

When it is determined in S52 that the intake stroke fuel injection amount Tii is larger than the minimum fuel injection amount Timin of the fuel injection valve, the process proceeds to S53, and the same processing as S46 and S47 in the second embodiment (FIG. 5) is performed. Then, the exhaust stroke fuel injection timing ITe and the intake stroke fuel injection timing ITi are calculated.
If it is determined in S52 that the intake stroke fuel injection amount Tii is less than or equal to the minimum fuel injection amount Timin of the fuel injection valve, the process proceeds to S54, and the same processing as S31 to S37 in the first embodiment (FIG. 3) is performed. Thus, the fuel injection amount Ti and the fuel injection timing IT in one injection are calculated.

  In the present embodiment, a fuel injection amount required for stable combustion in the combustion chamber and a fuel injection amount burned with secondary air in the exhaust passage are respectively calculated, and the fuel injection amount required for the stable combustion is calculated as an exhaust stroke. When the fuel injection amount that is injected by the secondary air and burned by the secondary air is injected in the intake stroke, the intake stroke fuel injection amount is compared with the minimum fuel injection amount of the fuel injection device (fuel injection valve). In response, the single injection in which the total fuel injection amount of the exhaust stroke fuel injection amount and the intake stroke fuel injection amount is injected across the intake valve opening timing, and the exhaust stroke fuel injection amount and the intake stroke fuel injection amount are separated. The divided injection that is injected at this time is switched.

According to the present embodiment, the effect similar to that of the second embodiment can be obtained by the divided injection, and when the amount of the enriched fuel is reduced, switching to the single injection is avoided to avoid the situation where the fuel injection control becomes impossible. it can.
FIG. 8 shows the relationship between the exhaust manifold inlet temperature (° C.) and the HC discharge amount (g / km) 20 seconds after the start (first idle). As can be seen, the emission can be improved by raising the exhaust temperature immediately after starting.

  Fig. 9 shows the transition of the catalyst outlet HC concentration (ppm) over time after start-up according to the exhaust temperature (high, medium, low). This also improves the emission by increasing the exhaust temperature rise. Is shown.

Engine system diagram showing an embodiment of the present invention Flow chart of fuel / secondary air control routine Flowchart of the first embodiment of a subroutine for introducing secondary air Explanatory drawing of fuel control for introducing secondary air according to the first embodiment Flowchart of the second embodiment of the subroutine for introducing secondary air Explanatory drawing of the fuel control for the secondary air introduction of 2nd Embodiment Flowchart of the third embodiment of the subroutine for introducing secondary air Diagram showing the effect of increased exhaust temperature Diagram showing the effect of increased exhaust temperature

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Intake passage 3 Air cleaner 4 Electric throttle valve 5 Intake manifold 6 Intake port 7 Fuel injection valve 8 Intake valve 9 Combustion chamber 10 Spark plug 11 Exhaust valve 12 Exhaust passage 13 Exhaust port 14 Exhaust manifold 15 Exhaust purification catalyst 16 Air pump 17 On-off valve 18 Gallery 19 Secondary air supply passage 20 Piping 21 Secondary air outlet 30 Engine control unit (ECU)
31 Accelerator opening sensor 32 Crank angle sensor 33 Air flow meter 34 Intake air temperature sensor 35 Water temperature sensor 36 Air-fuel ratio sensor

Claims (8)

An internal combustion engine comprising: a fuel injection device that injects fuel into an intake passage; and a secondary air supply device that supplies secondary air to an exhaust passage.
Calculating the fuel injection amount required for stable combustion in the combustion chamber when raising the exhaust temperature and the fuel injection amount combusted by the secondary air from the secondary air supply device in the exhaust passage, An exhaust temperature control device for an internal combustion engine, wherein a fuel injection amount required for stable combustion is injected in an exhaust stroke, and a fuel injection amount burned by the secondary air is injected in an intake stroke.   2. The exhaust temperature of an internal combustion engine according to claim 1, wherein the total fuel injection amount of the exhaust stroke fuel injection amount and the intake stroke fuel injection amount is injected across the intake valve opening timing in one fuel injection. Control device.   2. An exhaust temperature control apparatus for an internal combustion engine according to claim 1, wherein the fuel injection is divided and the exhaust stroke fuel injection amount and the intake stroke fuel injection amount are injected at different timings.   The intake stroke fuel injection amount is compared with the minimum fuel injection amount of the fuel injection device, and the total fuel injection amount of the exhaust stroke fuel injection amount and the intake stroke fuel injection amount is injected across the intake valve opening timing according to the comparison result. 2. The exhaust temperature control device for an internal combustion engine according to claim 1, wherein the one-time injection and the split injection in which the exhaust stroke fuel injection amount and the intake stroke fuel injection amount are injected at different timings are switched.   The intake stroke fuel injection amount is calculated on the basis of the margin obtained by subtracting the exhaust stroke fuel injection amount from the fuel injection amount at which the air-fuel ratio of the air-fuel ratio in the combustion chamber becomes the rich misfire limit, and the evaporation rate of the intake stroke injected fuel The exhaust gas temperature control device for an internal combustion engine according to any one of claims 1 to 4, wherein the exhaust gas temperature control device is an internal combustion engine.   The intake stroke fuel injection amount is calculated by subtracting the exhaust stroke fuel injection amount from the fuel injection amount at which the air-fuel ratio of the exhaust downstream of the secondary air supply position becomes the stoichiometric air-fuel ratio. Item 5. The exhaust gas temperature control device for an internal combustion engine according to any one of Items 4 to 6. The intake stroke fuel injection amount is
The first intake stroke fuel injection amount calculated based on a margin obtained by subtracting the exhaust stroke fuel injection amount from the fuel injection amount at which the air-fuel ratio of the air-fuel ratio in the combustion chamber becomes the rich misfire limit, and the evaporation rate of the intake stroke injected fuel When,
Of the second intake stroke fuel injection amount calculated by subtracting the exhaust stroke fuel injection amount from the fuel injection amount at which the air fuel ratio of the exhaust downstream from the secondary air supply position becomes the stoichiometric air fuel ratio,
The exhaust temperature control device for an internal combustion engine according to any one of claims 1 to 4, wherein the exhaust temperature control device is smaller.   The exhaust gas of the internal combustion engine according to any one of claims 1 to 7, wherein an exhaust gas purification catalyst is provided in the exhaust passage, and the exhaust gas temperature is raised when a temperature increase request for the catalyst is made. Temperature control device.

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