JP2002089320A - Control device of lean-burn engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent sudden change of an engine output torque, by preventing irregularity of fuel control during gradual changeover of an air fuel ratio, when a combustion mode where the air fuel ratio is a rich side air fuel ratio, is changed over to that where the air fuel ratio is a lean side air fuel ratio, in a control device of a lean-burn engine. SOLUTION: When the air fuel ratio is changed over from a second combustion mode where the air fuel ratio is a theoretical air fuel ratio or a ratio of a richer side, to a first combustion mode where the air fuel ratio is that of a leaner side than the theoretical air fuel ratio, the air fuel ratio changeover means 62A carry out tailing processing to gradually changeover the air fuel ratio. The tailing processing starts after a throttle valve driving means 30a drive a throttle valve, depending on the changeover of the combustion mode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lean-burn engine having a combustion mode in which fuel is injected at an air-fuel ratio leaner than the stoichiometric air-fuel ratio and a combustion mode in which fuel is injected near the stoichiometric air-fuel ratio. The present invention relates to a lean-burn engine control device suitable for use.

[0002]

2. Description of the Related Art In recent years, starting with automobile engines,
Lean-burn engines have been developed in which, when the required load on the engine is small, the air-fuel ratio is made leaner than the stoichiometric ratio so that the engine is operated lean to improve fuel efficiency. In particular, in the case of an in-cylinder injection engine that directly injects fuel into a cylinder, stratified combustion in which fuel is injected in the compression stroke and an air-fuel mixture of an appropriate concentration is partially collected only near the spark plug is possible. According to the stratified combustion, an operation with an extremely lean air-fuel ratio (super lean operation) can be performed in the entire cylinder while securing the ignitability of the fuel, and the fuel efficiency can be further improved.

In lean operation (particularly, super-lean operation by stratified combustion), a larger amount of intake air is required to produce the same engine output than in stoichiometric operation. It is necessary to provide a detour air bypass valve to perform intake increase control through this air bypass valve during lean operation, or to perform intake increase control through this ETV during lean operation by making the throttle valve electronically controlled (ETV). is there.

[0004] In such a lean burn engine, the combustion mode of the engine is controlled according to the operating state of the engine.
For example, when the engine output request is small (the engine load is small) or when the engine speed is low, the super lean mode for performing the super lean operation or the lean mode for performing the lean operation is selected, and the engine output request (engine load) is selected.
The combustion mode (for example, stoichiometric mode) that makes the air-fuel ratio richer (for example, stoichiometric) is selected as the engine speed becomes higher as the engine speed increases.

[0005]

The air-fuel ratio (A / F) of the conventional lean-burn engine as described above is greatly different between the lean mode and a combustion mode richer than the lean mode (for example, a stoichiometric mode). Therefore, when a mode is switched between these modes, a switching shock is likely to occur. Therefore, at the time of such mode switching, the air-fuel ratio (A / F) is tailed by tailing the target air-fuel ratio (target A / F).
F) is changed gradually so as to prevent the switching shock.

For example, FIG. 7 is a time chart showing changes in the engine control parameters and the engine operating state when the mode is switched from the stoichiometric mode to the lean mode (here, the super lean mode). (Case 1), and (b) shows a second example (case 2). As shown in FIGS. 7A and 7B, an A / F coefficient [A / F correction coefficient (A / F) for setting the fuel injection amount (fuel injection valve drive time, injector pulse width with respect to the intake air amount). F correction coefficient)] is approximately 1. in the stoichiometric mode.
0, in lean mode it is much smaller than 1.0,
When the mode is switched from the stoichiometric mode to the lean mode, a tailing process is performed to gradually decrease the value from approximately 1.0. This tailing process is performed such that the A / F coefficient is reduced stepwise in synchronization with the crank angle sensor signal (SGT).

[0007] A target opening of the electronically controlled throttle valve (ETV) (a target ETV opening, abbreviated as a target ETV) is calculated in a predetermined time cycle, and is sent to the ETV controller in a communication cycle different from the calculation cycle. Thus, the opening of the ETV is adjusted at a predetermined time period through the ETV controller. When the mode is switched from the stoichiometric mode to the lean mode, the target ETV is increased stepwise in the calculation cycle immediately after the mode switching. On the other hand, the actual ETV opening (actual ETV opening, abbreviated actual ETV) is the target ETV.
The opening degree does not immediately change in response to the switching, but increases with time with a response delay and a very short time. As the actual ETV increases, the volume efficiency Ev also increases. However, the volume efficiency Ev also increases more slowly than the actual ETV with a response delay with respect to the increase in the actual ETV.

[0008] The injector pulse width (INJ pulse width) corresponding to the fuel injection amount is calculated at the SGT falling timing. The INJ pulse width is calculated by multiplying a parameter (volume efficiency Ev) according to the intake air amount by the A / F coefficient. Therefore, if the A / F coefficient decreases, the INJ pulse width decreases and the volume efficiency Ev increases. Then, the INJ pulse width also increases. When switching from the stoichiometric mode to the lean mode, if the reduction of the A / F coefficient and the increase of the volumetric efficiency Ev are performed at appropriate timing, the INJ pulse width changes gradually.

However, the mode switching determination is normally performed by a timer interrupt of a predetermined cycle, whereas the tailing start of the A / F coefficient is performed in synchronization with the SGT (for example, at the timing of the rise of the timing SGT), and E
The change of the TV is performed at a timing based on a timer interrupt command of a predetermined cycle. Therefore, FIG.
When the time point t1 of the mode switching determination and the SGT rising timing t2 immediately after the time point t1 approach each other as in the case 1 shown in FIG. 7, the SGT rising timing (time point t2) immediately follows the timing of the mode switching determination (time point t1). The tailing of the A / F coefficient is started, and the change of the target ETV is performed at the subsequent timer interrupt timing (time t3).
In some cases. In such a case, the situation where the change of the target ETV is too late with respect to the start of the tailing of the A / F coefficient and the volume efficiency Ev does not increase despite the decrease of the A / F coefficient temporarily occurs. At time points t4 to t5, the INJ pulse width temporarily decreases stepwise, causing a temporary decrease in the engine output torque [see the in-cylinder pressure Pi shown in FIG. 7A].

Further, as in Case 2 shown in FIG. 7 (b), if the time point t1 of the mode switching judgment is separated from the SGT rising timing t2 immediately after the time point t1, the timing (time point t1) of the mode switching judgment After some time, SG
The T rise timing (time t2) comes, and at this time t2, tailing of the A / F coefficient starts,
In the vicinity of this time point t2, a timer interrupt is executed and the target E
There may be a case where the TV is changed. In such a case, the target ETV is changed too early with respect to the start of the tailing of the A / F coefficient, and the volume efficiency Ev temporarily increases so as to exceed the decrease in the A / F coefficient. During this period (time t6 to t7), the INJ pulse width increases stepwise for a period of time, causing a period of increase in the engine output torque [see the cylinder pressure Pi shown in FIG. 7B].

As described above, the tailing control of the A / F coefficient is performed in synchronization with the SGT (for example, by the SGT rising interrupt), while the mode switching determination is performed by the timer interrupt of a predetermined cycle. The timing of the mode switching determination within the variance is varied, and the setting of the target ETV is performed by a timer of a predetermined period after receiving the mode switching determination, and the ETV control is performed after transmission and reception of a signal by communication of a predetermined period. As a result, the timing of opening the ETV varies, which causes a large variation in fuel control. As a result, a problem arises in that the engine output torque fluctuates abruptly and the driving feeling of the engine is impaired, and in the case of an automobile engine, the traveling feeling is impaired.

The present invention has been made in view of the above-described problems, and gradually switches the air-fuel ratio when switching from the combustion mode in which the air-fuel ratio is the rich air-fuel ratio to the lean-side air-fuel ratio. It is an object of the present invention to provide a lean-burn engine control device capable of suppressing a variation in fuel control and preventing a sudden change in engine output torque when performing such control.

[0013]

Therefore, in the control apparatus for the lean burn engine according to the present invention, the first combustion mode and the second combustion mode can be switched according to the operation state.
In the first combustion mode, fuel injection is performed so that the air-fuel ratio becomes leaner than the stoichiometric air-fuel ratio. In the second combustion mode, the air-fuel ratio is more concentrated than the lean-side air-fuel ratio. Fuel injection is performed so that the air-fuel ratio becomes richer. At this time, the throttle valve driving means drives the throttle valve so that the air-fuel ratio becomes a target air-fuel ratio set according to the operating state. When switching from the second combustion mode to the first combustion mode, the air-fuel ratio switching means gradually switches the air-fuel ratio. The operation of the air-fuel ratio switching means is started by the operation of the throttle valve driving means. After the start.
Therefore, the air-fuel ratio can be switched in accordance with the control of the throttle valve, and the variation in the fuel control can be suppressed, thereby preventing a sudden change in the engine output torque.

At the time of switching from the second combustion mode to the first combustion mode, the start of the operation of the air-fuel ratio switching means (the start of control for gradually switching the air-fuel ratio) is determined at the time of the start of the operation of the throttle valve driving means. It is preferable that the delay is performed by a predetermined delay time. As a result, the air-fuel ratio can be switched appropriately in accordance with the control of the throttle valve, and the variation in the fuel control can be further suppressed, and the sudden fluctuation of the engine output torque can be reliably prevented ( Claim 2).

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIGS. 1 to 6 show a control device for a lean-burn engine as an embodiment of the present invention. First, the lean-burn engine according to the present embodiment will be described. The lean-burn engine is, for example, a direct injection engine (hereinafter, also referred to as a direct injection gasoline engine or simply an engine) mounted on an automobile, and mounted on the automobile. The configuration is as shown in FIG.

That is, as shown in FIG. 2, the cylinder head 2 of the engine 1
And a fuel injection valve 6 that opens directly into the combustion chamber 5. A piston 8 connected to a crankshaft 7 is provided in the cylinder 3, and a hemispherically concave cavity 9 is formed on a top surface of the piston 8. An intake passage 11 that can communicate with the combustion chamber 5 via an intake valve 10 and an exhaust passage 13 that can communicate with the combustion chamber 5 via an exhaust valve 12 are connected to the cylinder head 2. Although not shown, the intake port is disposed substantially vertically above the combustion chamber 5 and cooperates with the cavity 9 on the top surface of the piston 8 to form a reverse tumble flow due to intake air in the combustion chamber 5. .

A water temperature sensor 16 for detecting a cooling water temperature is provided on a water jacket 15 on the outer periphery of the cylinder 3. A camshaft (not shown) for driving the exhaust valve 12 is provided with a cylinder identification sensor (not shown) for outputting a cylinder identification signal corresponding to the position of the camshaft. Since the engine speed can be calculated based on the crank angle signal,
The crank angle sensor 17 also functions as an engine speed detection unit.

In the intake passage 11, an air cleaner 21, an intake pipe 22, a throttle body 23, a surge tank 24, and an intake manifold 25 are arranged in this order from the upstream side, and an intake port (not shown) is provided at a downstream end of the intake manifold 25. Is provided. The combustion chamber 5 is provided in the throttle body 23.
An electronically controlled throttle valve (ETV) 30 for adjusting the amount of air flowing into the inside is provided. This ETV30
The electronically controlled throttle valve 30b is controlled by a throttle valve actuator (throttle valve driving means) 30a. The opening of the ETV 30 is controlled through an ETV controller 30c. Speed control and control of introduction of a large amount of intake air during lean operation, which will be described later, can also be performed.

Further, an air flow sensor 37 for detecting an intake air flow rate is provided immediately downstream of the air cleaner 21.
The throttle body 23 has a throttle position sensor 38 for detecting the throttle opening of the ETV 30 and an ETV 3
And an idle switch 39 for detecting the fully closed state of 0 and outputting an idle signal. The exhaust system includes an exhaust manifold 2 having an exhaust port 13 from the upstream side.
6, an exhaust pipe 27, and a three-way catalyst 29 for purifying exhaust gas is interposed in the exhaust pipe 27.
6 is provided with an O ₂ sensor 40.

Further, an accelerator position sensor (hereinafter, referred to as APS) 42 for detecting an accelerator pedal depression amount (accelerator position) θap is provided. Although the fuel supply system is not shown, fuel whose pressure has been adjusted to a predetermined high pressure (about several tens of atmospheres (for example, about 2 to 7 MPa)) is guided to the fuel injection valve 6, and the high-pressure fuel is supplied from the fuel injection valve 6. Is to be injected.

Then, the spark plug 4, the fuel injection valve 6, E
In order to control the operation of each engine control element such as the TV 30, an electronic control unit (ECU) 60 having a function as control means of the internal combustion engine is provided. The ECU 60 includes an input / output device, a storage device for storing a control program, a control map, and the like, a central processing unit, a timer and a counter, and the like. The ECU 60 controls each of the above-described engine control elements based on position information and the like.

In particular, the present engine is a direct injection engine, which can perform fuel injection at an arbitrary timing, uniformly mixes and uniformly burns by fuel injection mainly in the intake stroke, and also mainly performs compression stroke in the compression stroke. By the fuel injection, stratified combustion can be performed using the above-mentioned reverse tumble flow. The operation mode of the present engine includes a stoichiometric mode (second stoichiometric mode) in which the air-fuel ratio is maintained near the stoichiometric air-fuel ratio by feedback control based on the detection information of the O ₂ sensor 40.
Combustion mode), an enrichment mode in which the air-fuel ratio is made richer than the stoichiometric air-fuel ratio (second combustion mode), and an ultra-lean combustion using the above-described stratified combustion in which the air-fuel ratio is made leaner than the stoichiometric air-fuel ratio. A super-lean mode (first combustion mode) for super-lean operation is provided.

In the super lean mode (first combustion mode),
The fuel is injected in the compression stroke, and the reverse tumble flow,
Utilizing the cavity 9 on the top surface of the piston 8, the injected fuel is partially collected only in the vicinity of the ignition plug 4, and the other portion performs stratified combustion in which only the air is in a state of only air, thereby improving the ignitability of the fuel. While maintaining the same, an extremely lean air-fuel ratio is used throughout the cylinder to improve fuel efficiency.

In the ECU 60, an engine rotational speed (hereinafter referred to as an engine rotational speed) Ne and an average effective pressure Pe indicating an engine load state are based on a preset map.
Any one of the operation modes is selected according to the target value (target Pe). In the state where the engine speed Ne is small and the target Pe is also small, the super lean operation mode (compression lean operation mode) by the stratified combustion is set. When the selection is made and the engine speed Ne and the target Pe increase, the operation mode is selected in the order of stoichiometry and enrichment.

The engine speed Ne is calculated from the output signal of the crank angle sensor 17, and the target Pe is the engine speed Ne and the accelerator position detected by the APS 42 (or detected by the throttle position sensor 38). Throttle opening degree θth). Here, a control device of the lean burn engine of the present embodiment for performing such engine control will be described with reference to FIG.

As shown in FIG. 1, the ECU 60 includes, as described above, a combustion mode setting means 61 for setting a combustion mode (operation mode) from an engine operation state, a setting of the combustion mode setting means 61 and an engine operation state. (Ne, Pe
Air-fuel ratio setting means 6 for setting a target air-fuel ratio based on
2, the combustion mode setting means 61 and the air-fuel ratio setting means 62
Each functional element is provided such as a fuel injection valve control means 63 and an ETV control means 64 for controlling the operation of the fuel injection valve 6 and the ETV 30 based on each setting and the engine operation state (Ne, Pe, etc.). Of course, in addition to this, it also has a function of controlling various other engine control elements such as a spark plug control means for controlling the spark plug 4.

As described above, the combustion mode setting means 61 selects any one of the combustion modes (operation modes) according to the engine operating state, that is, the engine speed Ne and the target Pe. (Mode switching determination) is performed by a timer interrupt of a predetermined cycle. The engine speed Ne is calculated from the output signal of the crank angle sensor 17 by the engine speed calculation unit 64, and the target Pe is detected by the engine speed Ne and the accelerator position detected by the APS 42 (or detected by the throttle position sensor 38). Is calculated by the target Pe calculating unit 65 from the calculated throttle opening θth).

The air-fuel ratio setting means 62 sets a target air-fuel ratio in accordance with the combustion mode set by the combustion mode setting means 61 and the engine operating state (engine speed Ne and target Pe). In particular, when the combustion mode is switched, the target air-fuel ratio is largely switched, so that the air-fuel ratio setting means 62 has a function as the air-fuel ratio switching means 62A. In the air-fuel ratio switching means 62A, the second combustion mode (for example, the stoichiometric mode)
A so-called tailing process for gradually switching the air-fuel ratio when switching to the combustion mode (super lean mode) is performed. Details of this will be described later. Note that the setting of the target air-fuel ratio and the tailing processing of the target air-fuel ratio are performed in accordance with the crankshaft angle, specifically, in synchronization with the signal (SGT) detected by the crank angle sensor 17 (for example, at every rising timing of the SGT). To).

The fuel injection valve control means 63 calculates an A / F coefficient [with respect to the intake air amount] from the target air-fuel ratio set by the air-fuel ratio setting means 62 (however, during tailing processing, the target air-fuel ratio for tailing processing). Air-fuel ratio coefficient for setting the fuel injection amount (fuel injection valve driving time, injector pulse width)], and set the target fuel injection amount (injector pulse width) from the A / F coefficient and the actual intake air amount Q. Then, the fuel injection timing is set according to the combustion mode set by the combustion mode setting means 61 and the engine operating state (engine speed Ne, target Pe, intake air amount Q, etc.). In this setting, the valve opening timing and the valve closing timing of the fuel injection valve are set corresponding to the crank angle, and the fuel injection valve 6 is controlled based on this. The injector pulse width and the fuel injection timing are set according to the crankshaft angle, specifically, in synchronization with the signal (SGT) detected by the crank angle sensor 17 (for example, at every rising timing of the SGT). Done. The intake air amount Q is calculated by the intake air amount calculation unit 66 based on the detection information of the air flow sensor 37.

In the ETV control means 64, the combustion mode set by the combustion mode setting means 61, the target air-fuel ratio set by the air-fuel ratio setting means 62 (here, the tailing process is ignored), the detected actual intake air amount Q, and the engine operation state (engine speed Ne, target Pe, intake air amount Q, etc.), and the electronically controlled throttle valve (ET
V) 30 target opening (target ETV opening, target ET for short)
V) is set, and based on this, the throttle valve actuator (throttle valve driving means) 30a of the ETV 30 is controlled through the ETV controller 30c. In addition,
The setting of the target ETV, the communication of the set target ETV information, and the control of the throttle valve actuator 30a by the ETV controller 30c are performed at a predetermined cycle (time cycle) individually set.

Here, the tailing process will be described. In the air-fuel ratio switching means 62A, the target air-fuel ratio is largely switched from AF1 to AF2 by the air-fuel ratio setting means 62 in accordance with the switching of the combustion mode (in this case, When the target air-fuel ratio AF1 is immediately reduced, the target air-fuel ratio AF1 immediately before the switching is reduced by a small amount (A / F tailing gain) δ _AF per control cycle to reach the target air-fuel ratio AF2 at the switching destination. The control cycle in this case is in accordance with the crankshaft angle. For example, at every rising timing of the signal (SGT) detected by the crank angle sensor 17, the control cycle is minute from the target air-fuel ratio AF (n-1) of the previous cycle. the amount δ target air-fuel ratio AF for tailing by subtracting _{AF (n) [= AF (} n-
1) −δ _AF ] is set to gradually decrease the air-fuel ratio.

A / F correction coefficient C corresponding to target air-fuel ratio AF
Paying attention to the _AF, the target air-fuel ratio A / F correction coefficient C _AF in accordance with the AF is switched largely to C _AF [L] from the C _AF [S], the previous cycle of the A / F correction coefficient C _AF (N-1)
Target air-fuel ratio C for tailing by subtracting a small amount δ _CAF from
_AF (n) [= C _AF (n-1) -δ _CAF ] is set. However, the tailing is not restricted by the SGT rising timing, and the tailing is started when a preset delay time has elapsed from the time when the ETV 30 started operating in accordance with the switching of the combustion mode. It is supposed to.

That is, as shown in FIG. 5, at time _t01 , the combustion mode changes from the second combustion mode (stoichiometric mode) to the first combustion mode.
When switching to the combustion mode (super lean mode), conventionally, as shown by the thin line in FIG. 5, the target air-fuel ratio AF (n) considering the tailing process at the rising timing of the SGT immediately after this (time t ₀₂ ). ) Is set, and the A / F coefficient is set from the target air-fuel ratio AF (n).
The target ETV is set by a timer interrupt at a time period independent of the rise timing of the ETV, and the opening of the ETV is adjusted (control of the throttle valve actuator 30a).

On the other hand, when the combustion mode is switched from the second combustion mode (stoichiometric mode) to the first combustion mode (super lean mode) at time t ₀₁ ,
As shown by the bold line in FIG. 5, until the actual ETV (actual ETV opening, that is, the actual ETV opening) changes according to the switching of the combustion mode, the target air-fuel ratio A corresponding to the switching of the combustion mode is changed.
Configuring and A / F coefficient F (n) without the time the actual ETV is starts to change (ETV30 starts the operation) has passed a predetermined delay time td from the time t ₀₃ to the t
_{At 04} , tailing starts.

The reason why the tailing of the target air-fuel ratio is started after a predetermined delay time has elapsed since the start of the change of the actual ETV is that the tailing start of the target air-fuel ratio is actually started when the combustion mode is switched to the combustion chamber. This is in order to avoid variations in fuel control in synchronization with a change (increase) in the supplied intake air amount. That is, the target fuel injection amount [injector pulse width (INJ pulse width)] is set from the A / F coefficient (A / F correction coefficient) and the actual intake air amount Q.
Since the / F coefficient changes (decreases here) in accordance with the tailing of the target air-fuel ratio, if the start timing of the tailing of the target air-fuel ratio is earlier than the change (increase) of the actual intake air amount Q, the target fuel injection amount is reduced. If the timing for starting the tailing of the target air-fuel ratio is too late than the change (increase) of the actual intake air amount Q, a temporary increase in the target fuel injection amount is caused.

Such a temporary decrease or increase in the target fuel injection amount causes a sudden change in the engine output torque and impairs the driving feeling of the engine, particularly the driving feeling in the case of an automobile engine. In order to avoid this, the tailing start of the target air-fuel ratio is synchronized with a change (increase) in the intake air amount. The reason why the tailing of the target air-fuel ratio starts after a lapse of a predetermined delay time from the start of the change of the actual ETV is that the start of the change (increase) of the actual intake air amount (see the volumetric efficiency Ev) is E
This takes into account the point that it is delayed from the start (change) of the TV opening. Also, the change (increase) in the actual intake air volume
Is performed gently even after the start, so that tailing processing of the target air-fuel ratio is performed so as to correspond to such a characteristic of the change (increase).

Whether or not the actual ETV has started to change (here, increase) is determined by the actual ETV after the combustion mode switching.
It is determined whether or not the difference between the actual ETV immediately before and the combustion mode switching is equal to or more than a predetermined amount. Therefore, the actual ETV is detected constantly or at a very short cycle. Of course, real ETV
, That is, whether the detected value of the actual ETV has changed (increased) by a predetermined amount or more during a predetermined period (for example, a detection cycle), it can be determined whether the actual ETV has started to change (increase). .

Further, tailing processing of the target air-fuel ratio (A /
(Including tailing of the F coefficient), the target air-fuel ratio and the A / F coefficient are gradually reduced in synchronization with the SGT, such as in the unit of the rising timing of the SGT. At a time different from the timing, the target air-fuel ratio and the A / F coefficient are gradually reduced. Therefore, the time from the start of the tailing process to the rising timing of the next _SGT is shorter than one cycle T _{SGT of the SGT} .

Therefore, the tailing process is performed smoothly.
(Tailing at a uniform rate of change
Prior to the rise timing of this SGT,
A for tailing performed in response to changes in actual ETV
/ F correction coefficient C_AF(0.5) is calculated using FIG.
As shown, the normal gradual decrease (A / F tailing gain) δ
_CAFIn addition, one cycle T of SGT_SGTFirst tailing for
A / F correction coefficient C_AF(0.5) usage period (that is,
One cycle T of SGT_SGT-The tie of the last SGT rise
Time T from the beginning to the start of the tailing process₁₁To
Reduced time) T ₁₂To multiply the ratio of
are doing.

C _AF (0.5) = C _AF (0) −δ _CAF * (T ₁₂ / T _SGT ) where C _AF (0) is the A / F immediately before the start of the tailing process.
The correction coefficient, here, C _AF (0) = C _AF [S]
≒ 1, T ₁₂ = T _SGT −T ₁₁ The tailing A / F correction coefficient C _AF (0.5) for the tailing process after detecting that the actual ETV has started to change. Can be sufficiently calculated during the delay time until the start of.

The tailing A / F correction coefficient C _AF (1), C, which is set at the subsequent SGT rising timing.
_AF (2), C _AF (3),..., C _AF (n) _,. C _AF (n) = C _AF (n−1) −δ _CAF where n is a natural number of 1 or more. The target air-fuel ratio AF for tailing is the original target air-fuel ratio (the target air-fuel ratio set at the time of switching the combustion mode). When AF2 is reached, in other words, when the A / F correction coefficient C _AF (n) for tailing reaches the original A / F correction coefficient (A / F correction coefficient set at the time of switching the combustion mode) C _AF [S] The tailing process of the target air-fuel ratio and the A / F coefficient is terminated.

The control device for a lean burn engine as one embodiment of the present invention is configured as described above.
During the engine operation, for example, as shown in FIG. 3, tailing start processing of the target air-fuel ratio and the A / F coefficient is performed in a main routine that is processed at a predetermined time period, and thereafter, as shown in FIG. , A tailing process of the target air-fuel ratio and the A / F coefficient is performed.

That is, as shown in FIG. 3, first, a target ETV opening (target ETV) is obtained according to each combustion mode (step A10), and the actual ETV opening (actual ETV) is taken in (step A10). A20), it is determined whether or not the combustion mode (A / F mode) is being switched (step A3).
0). If the combustion mode (A / F mode) is not being switched, the delay timer is set to a predetermined delay time (step A40), the A / F tailing flag is cleared (step A50), and the A / F tailing is performed. Do not implement.

On the other hand, if the combustion mode (A / F mode) is being switched, the process proceeds to step A60, where the combustion mode is switched from the stoichiometric or enriched mode to the lean mode (particularly, the super lean mode). If it is determined whether or not there is a switch from the stoichiometric or enriched mode to the lean mode (particularly, the super lean mode), A
No processing relating to / F tailing is performed (the delay timer is set, and the A / F tailing flag is cleared).

The combustion mode is switched from a stoichiometric or enriched mode to a lean mode (particularly, a super lean mode).
If so, the process proceeds to step A70, in which the target ETV opening in the previous mode (see step A10) and the current actual ET
It is determined whether the difference from V (see step A20) is greater than a predetermined value. If the difference between the target ETV opening in the previous mode and the current actual ETV is equal to or smaller than a predetermined value, the processing relating to A / F tailing is not performed (the delay timer is set, and the A / F tailing flag is cleared).

The target ETV opening in the previous mode and the current actual ET
If the difference from V is larger than the predetermined value, the process proceeds to step A80, and it is determined whether the A / F tailing flag is set (A / F tailing is being performed). If the A / F tailing flag has not been set, the countdown of the delay timer is started (step A90). In the next step A100, it is determined whether or not the value of the delay timer has reached 0, and the countdown of the delay timer proceeds. When the value of the delay timer has reached 0, the process proceeds to step A110, where the A / F tailing flag is set. Is set. Then, the process proceeds to step A120 to control the fuel injection by correcting the target fuel injection amount (injector pulse width) by the tailing A / F correction coefficient C _AF (0.5) prior to the rise timing of the SGT.

That is, the A / F immediately before the start of the tailing process
Correction coefficient is C_AF(0), tapered amount (A / F tailing gay
N) to δ_CAFFrom the previous SGT cycle to the previous SGT
From the rising timing to the start of the tailing process
Time T₁₁Time T ₁₂The previous SGT cycle and
The current SGT cycle is T_SGTAnd A is given by
/ F correction coefficient C_AF(0.5) to calculate the target fuel injection
Correct the volume (injector pulse width).

C _AF (0.5) = C _AF (0) −δ _CAF * (T ₁₂ / T _SGT ) where C _AF (0) = 1, T ₁₂ = T _SGT −T ₁₁ Such a predetermined period The SGT rising interrupt routine for A / F tailing is executed independently of the main routine executed in FIG. That is, FIG.
As shown in FIG. 2, the combustion mode (A) from the stoichiometric or enriched mode to the lean mode (particularly, the super lean mode)
/ F mode) (step B10). If there is such a combustion mode switch, the process proceeds to step B30 to determine whether the A / F tailing flag is set. You. If the A / F tailing flag is set in the main routine (step A110), the process proceeds from step B20 to step B30, where the target fuel injection is performed by the tailing A / F correction coefficient C _AF (n) based on the SGT rising timing. The fuel injection is controlled by correcting the amount (injector pulse width).

That is, A /
The F correction coefficient C _AF (0), decreasing amounts of (A / F tailing gain) as [delta] _CAF, A / F correction coefficient C _AF by the following formula
By calculating (n), the target fuel injection amount (injector pulse width) is corrected. C _AF (n) = C _AF (n−1) −δ
_CAF , where n is a natural number of 1 or more, and the A / F correction coefficient C _AF (n) for tailing is
It is determined whether the original A / F correction coefficient (final A / F correction coefficient set at the time of switching the combustion mode) C _AF [S] (step B40), and the A / F correction coefficient for tailing is determined. C _AF (n) is the final A / F correction coefficient C _AF [S]
When the A / F tailing flag is lowered, the A / F tailing flag is cleared, and the A / F tailing process ends (step B5).
0).

As described above, according to the control apparatus for the lean-burn engine of this embodiment, when the mode is switched from the stoichiometric mode or the enriched mode (the second combustion mode) to the lean mode (the first combustion mode), as shown in FIG. As shown in the figure, after waiting for the opening operation of the ETV 40 corresponding to the combustion mode,
Since the / F tailing process is started, the start of the A / F tailing process is not too early than the start of the increase in the intake air amount, and therefore, the A / F tailing process is started even though the intake air amount has not increased. The fuel injection amount (injector pulse width) decrease correction is started, and the fuel injection amount (injector pulse width) is changed as shown in FIG.
Temporary excessive decrease is prevented.

Also, as shown in FIG.
Of the ETV 40 according to the combustion mode
Operation start time t₀₃When the specified delay time has elapsed since
Point t ₀₄The change (increase) in the ETV opening
Actual intake volume delayed from start (see volumetric efficiency Ev)
A / F tailing processing at the start of change (increase)
Is started, and the A / F tailing process is started.
The timing is appropriate. Of course, A / F
The start of the ring process is later than the start of the increase in the intake air volume.
Fuel injection amount (injector pulse
Width) temporarily increases excessively as shown in FIG.
Not even.

As a result, a sudden change in the engine output torque due to the variation in fuel control is prevented, the driving feeling of the engine is improved, and the driving feeling of the automobile engine can be improved. In addition,
The control related to the A / F tailing process as described above is a mode switching from stoichiometric or enriched to lean. Since such mode switching is performed when the engine is in a steady operation, the mode is changed during acceleration (from lean to rich). As compared with the mode switching in which the engine state greatly fluctuates as described above, it is easier to stably perform the control, and highly reliable control can be realized.

The above-described embodiment is merely an example, and the present invention is not limited to this embodiment. Various modifications of the above-described embodiment may be made without departing from the spirit of the present invention. be able to. For example, the first combustion mode is not limited to the super-lean mode by the compression stroke injection, but may be the lean mode by the intake stroke injection. Therefore, the present control device is suitable for the direct injection engine,
Application to other lean-burn engines is also conceivable.

[0054]

As described in detail above, according to the control apparatus for a lean burn engine of the present invention, the air-fuel ratio switching means gradually changes the air-fuel ratio when switching from the second combustion mode to the first combustion mode. The operation of the air-fuel ratio switching means is started after the operation of the throttle valve driving means is started. Therefore, the air-fuel ratio can be switched in accordance with the control of the throttle valve, and the variation in the fuel control can be suppressed, and a sudden change in the engine output torque can be prevented. And, in the case of an automobile engine, an advantage that the running feeling can be improved (claim 1).

Further, at the time of switching from the second combustion mode to the first combustion mode, the start of the operation of the air-fuel ratio switching means is delayed by a predetermined delay time from the start of the operation of the throttle valve driving means, so that the fuel is increased. Variations in control are further suppressed, so that sudden fluctuations in engine output torque can be reliably prevented, and the above-mentioned driving feeling and traveling feeling can be more reliably improved. ).

[Brief description of the drawings]

FIG. 1 is a control block diagram illustrating a control device for a lean burn engine as one embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing a lean burn engine according to one embodiment of the present invention.

FIG. 3 is a flowchart showing control contents according to a control device for a lean burn engine as one embodiment of the present invention.

FIG. 4 is a flowchart showing control contents according to a control device for a lean burn engine as one embodiment of the present invention.

FIG. 5 is a time chart showing a specific example of engine control according to the control apparatus for a lean burn engine as one embodiment of the present invention, wherein (a) shows an injector pulse width;
(B) is the air-fuel ratio coefficient, (c) is the volumetric efficiency, (d) is the actual opening of the ETV, (e) is the target opening of the ETV,
(F) shows the combustion mode, and (g) shows the crank angle sensor signal.

6 is a diagram showing a specific example of engine control according to the control device for a lean burn engine as one embodiment of the present invention, and is a diagram showing an enlarged part A of FIG. 5;

FIG. 7 is a time chart for explaining a problem in control of a conventional lean burn engine.
(B) shows Case 2 respectively.

[Explanation of symbols]

Reference Signs List 1 engine 17 crank angle sensor (engine rotational speed detecting means) as engine operating state detecting means 30 electronically controlled throttle valve (ETV) 30a throttle valve actuator (throttle valve driving means) 37 air flow sensor as engine operating state detecting means 38 engine Throttle position sensor as operating state detecting means 60 ECU 61 Combustion mode setting means 62 Air-fuel ratio setting means 62A Air-fuel ratio switching means 63 Fuel injection valve control means 64 ETV control means

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Satoshi Yoshikawa 5-33-8 Shiba, Minato-ku, Tokyo Inside Mitsubishi Motors Corporation (72) Inventor Nobuaki Murakami 3-33-8 Shiba, Minato-ku, Tokyo Mitsubishi F-term (reference) in the Automotive Industry Co., Ltd. (reference)

Claims (2)

[Claims] 1. A first combustion mode in which fuel injection is performed so that an air-fuel ratio becomes leaner on the lean side than a stoichiometric air-fuel ratio, and enrichment is performed on an air-fuel ratio richer than the lean-side air-fuel ratio. A second combustion mode in which fuel injection is performed to achieve a side air-fuel ratio;
A control device for a lean-burn engine switchable according to an operating state, wherein the throttle valve driving means drives a throttle valve to attain a target air-fuel ratio set according to an operating state; Air-fuel ratio switching means for gradually switching the air-fuel ratio when switching to the first combustion mode, and switching the air-fuel ratio after starting operation of the throttle valve driving means when switching from the second combustion mode to the first combustion mode. A control device for a lean-burn engine, characterized by starting operation of the means. 2. The method according to claim 1, wherein the operation of the air-fuel ratio switching means is started with a delay of a predetermined delay time from the start of operation of the throttle valve driving means when switching from the second combustion mode to the first combustion mode. The control device for a lean-burn engine according to claim 1.