JP3424518B2 - Control device for internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention switches between stratified lean combustion, homogeneous lean combustion, and homogeneous stoichiometric combustion in which the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio, according to operating conditions, and at a predetermined operating condition. The present invention relates to a control device for an internal combustion engine that purges evaporated fuel, and more particularly to a technique for improving air-fuel ratio control accuracy during stratified lean combustion.

[0002]

2. Description of the Related Art Conventionally, in an internal combustion engine equipped with a device for purging evaporated fuel in a fuel tank into an intake system under a predetermined operating condition and treating the same, a homogeneous stoichiometric combustion is considered in consideration of the influence of the purge on the air-fuel ratio control. There is one in which learning of the air-fuel ratio is independently performed according to the presence or absence of purge (Japanese Patent Application Laid-Open No. Hei 5 (1999))
-202816).

Further, in recent years, in order to improve exhaust emission and fuel consumption, there is a homogenous mixture which is made leaner than the stoichiometric air-fuel ratio and is burned (homogeneous lean combustion). The learned value of the air-fuel ratio obtained during combustion is used during homogeneous lean combustion to improve the air-fuel ratio accuracy. In this case, when the learning value during purging is used, the learning value is updated in the direction of decreasing the air-fuel ratio when the evaporative combustion concentration is high, so in the homogeneous lean combustion in which leaning is advanced to the combustion stable limit, If the air-fuel ratio becomes leaner due to the air-fuel ratio learning value, misfire may occur. Therefore, there is a method in which a learning value having a larger value and a higher air-fuel ratio is selected and used from the two kinds of learning values depending on the presence or absence of purging.

On the other hand, most recently, in a gasoline engine, fuel is directly injected into a combustion chamber, and fuel is injected in a compression stroke to form a stratified mixture around the ignition plug to perform stratified combustion, thereby reducing exhaust emissions and fuel consumption. There are some improvements. However, even in the engine that performs the stratified charge combustion, in order to secure the required torque with a limited cylinder volume, it is necessary to inject fuel in the intake stroke to perform homogeneous combustion (homogeneous lean combustion, homogeneous stoichiometric combustion). These combustions are switched according to the operating state.

[0005]

When the air-fuel ratio control is performed by using the learned value in the direction of uniformly increasing the air-fuel ratio in the lean combustion without distinction from the homogeneous lean combustion in the engine which performs the stratified lean combustion, the stratified combustion is performed. In lean combustion, since the air-fuel ratio around the spark plug is made dense, further increasing the air-fuel ratio causes a problem that rich misfire tends to occur.

The present invention has been made in view of the above conventional problems, and provides a control device for an internal combustion engine capable of performing a purge process of evaporated fuel while ensuring stable combustion even in stratified lean combustion. The purpose is to provide.

[0007]

For this reason, the invention according to claim 1 is directed to stratified lean combustion depending on engine operating conditions.
While switching between homogeneous lean combustion and homogeneous stoichiometric combustion in which the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio,
In an internal combustion engine that purges evaporative fuel into an intake system under predetermined operating conditions, an air-fuel ratio feedback correction value is independently learned by the presence or absence of the evaporative fuel purge during the homogeneous stoichiometric combustion, and the feedback correction value is near a reference value. In addition to obtaining the learning value maintained at, the air-fuel ratio control is performed by individually referring to the two kinds of learning values during the stratified lean combustion and the homogeneous lean combustion.

Further, according to a second aspect of the present invention, as shown in FIG. 1, stratified lean combustion, homogeneous lean combustion, and homogeneous stoichiometric combustion in which the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio according to engine operating conditions. In the internal combustion engine, which is equipped with a combustion switching means for switching between and, and an evaporative fuel purging means for purging the evaporative fuel into the intake system under a predetermined operating condition, independently of the presence or absence of the evaporative fuel purge during the homogeneous stoichiometric combustion. The learning means for each purge presence / absence for learning the feedback correction value of the air-fuel ratio to obtain the learning value for maintaining the feedback correction value in the vicinity of the reference value, and the two types of learning respectively in the stratified lean combustion and the homogeneous lean combustion. Constituting stratified lean combustion air-fuel ratio control means for performing air-fuel ratio control by individually referring to values, and homogeneous lean combustion air-fuel ratio control means Characterized in that was.

According to these aspects of the invention, the two types of learning values of the air-fuel ratio learning independently performed according to the presence / absence of the purge during the homogeneous stoichiometric combustion are separately performed for the stratified lean combustion and the homogeneous lean combustion. Air-fuel ratio control is performed by referring to the learned value.
As a result, for each combustion that has the opposite tendency of the air-fuel ratio that facilitates misfire, such as stratified lean combustion and homogeneous lean combustion,
The optimum air-fuel ratio control can be performed with reference to each suitable learning value.

The invention according to claim 3 limits the purge flow rate of evaporated fuel during stratified lean combustion, and
Of the two types of learning values, the air-fuel ratio control is performed with reference to the learning value on the side where the air-fuel ratio becomes thin, and during homogeneous combustion, the learning value on the side where the air-fuel ratio becomes darker among the two types of learning values. Is performed to control the air-fuel ratio.

In this way, during stratified lean combustion,
By limiting the purge flow rate of the evaporated fuel and referring to the learning value on the side where the air-fuel ratio becomes thinner, of the learning value of the air-fuel ratio during non-purging and the learning value of the air-fuel ratio during purging, the air-fuel ratio becomes rich. It is possible to prevent misfire, and at the time of homogeneous lean combustion, refer to the learning value on the side where the air-fuel ratio becomes richer among the learning value of the air-fuel ratio during non-purging and the learning value of the air-fuel ratio during purging. Can prevent misfire due to leaning.

The invention according to claim 4 is characterized in that the fuel is directly injected into the combustion chamber. With the direct injection type, it is possible to easily switch between stratified combustion and homogeneous combustion by setting the injection timing.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a system diagram of an internal combustion engine showing an embodiment. First, this will be described. Air is sucked into a combustion chamber of each cylinder of an internal combustion engine 1 mounted on a vehicle from an air cleaner 2 through an intake passage 3 under the control of an electronically controlled throttle valve 4.

An electromagnetic fuel injection valve 5 is provided so as to directly inject the fuel into the combustion chamber. The fuel injection valve 5 is opened by energizing a solenoid by an injection pulse signal output from a control unit 20 described later in synchronization with the engine rotation in an intake stroke or a compression stroke to open the fuel and regulate the fuel to a predetermined pressure. It is designed to jet.
Then, the injected fuel diffuses into the combustion chamber in the case of the intake stroke injection to form a homogeneous air-fuel mixture, and in the case of the compression stroke injection, forms a concentrated layered air-fuel mixture around the spark plug 6. Based on an ignition signal from a control unit 20 which will be described later, the ignition plug 6 ignites and combusts (homogeneous combustion or stratified combustion). Combustion methods can be divided into homogeneous stoichiometric combustion at the theoretical air-fuel ratio, homogeneous lean combustion (air-fuel ratio 20 to 30), and stratified lean combustion (air-fuel ratio of about 40) in combination with air-fuel ratio control (Fig. 4). See).

Exhaust gas from the engine 1 is discharged from an exhaust passage 7, and an exhaust purification catalyst 8 is interposed in the exhaust passage 7. Further, a canister 10 as an evaporated fuel processing device is provided in order to process the evaporated fuel generated from the fuel tank 9. The canister 10 is an airtight container filled with an adsorbent 11 such as activated carbon, and an evaporated fuel introduction pipe 12 from a fuel tank 9 is connected to the canister 10. Therefore, institution 1
The evaporated fuel generated in the fuel tank 9 while the fuel cell is stopped is guided to the canister 10 through the evaporated fuel introducing pipe 12 and adsorbed there.

The canister 10 also has a fresh air introduction port 13
Is formed and the purge passage 14 is led out. The purge passage 14 is connected to a downstream side of the throttle valve 4 (intake manifold) in the intake passage 3 via a purge control valve 15. The purge control valve 15 is opened by a signal output from a control unit 20 described later under a predetermined condition while the engine 1 is operating. Therefore,
If the purge permission condition is satisfied during the subsequent operation of the engine 1 and the subsequent operation, the purge control valve 15 is opened and the suction negative pressure of the engine 1 acts on the canister 10, resulting in the fresh air introduction port 13
The adsorbent 1 of the canister 10 by the air introduced from the
The evaporated fuel adsorbed on the fuel cell 1 is desorbed, and the purge gas containing the desorbed fuel is sucked through the purge passage 14 to the downstream side of the throttle valve 4 of the intake passage 3, and thereafter, in the combustion chamber of the engine 1. Burned.

The control unit 20 includes a CPU and R
The microcomputer is provided with an OM, a RAM, an A / D converter, an input / output interface, and the like, receives input signals from various sensors, performs arithmetic processing based on the signals, and injects the fuel injection valve 5 and the spark plug 6. And controlling the operation of the purge control valve 15 and the like. As the various sensors, a crank angle sensor 21, which detects the rotation of the crankshaft or the camshaft of the engine 1,
22 is provided. These crank angle sensors 2
1 and 22 have a crank angle of 720 °, where n is the number of cylinders.
For each / n, the reference pulse signal REF is output at a predetermined crank angle position (for example, 110 ° before compression top dead center), and the unit pulse signal POS is output every 1 to 2 °. The engine rotation speed Ne can be calculated from the REF cycle or the like.

In addition to this, an air flow meter 23 for detecting the intake air flow rate Qa upstream of the throttle valve 4 in the intake passage 3,
Accelerator sensor 24 for detecting the accelerator pedal depression amount (accelerator opening) ACC, throttle valve 4 opening TV
A throttle sensor 25 that detects O (including an idle switch that is turned on when the throttle valve 4 is fully closed), a water temperature sensor 26 that detects the cooling water temperature Tw of the engine 1, and a rich / lean exhaust air-fuel ratio in the exhaust passage 7. An O ₂ sensor 27 that outputs a signal corresponding to the vehicle speed, a vehicle speed sensor 28 that detects the vehicle speed VSP, and the like are provided.

Next, the air-fuel ratio control and purge control according to the first embodiment will be described with reference to the flow chart shown in FIG. In step 1, the target equivalence ratio TFBYA, the basic fuel injection amount Tp, and the target purge control valve opening TEVP are read. Here, the target equivalent ratio TFBYA is calculated by a direct search or the like based on the accelerator opening ACC and the engine speed Ne, or the target torque tTe and the engine obtained from the accelerator opening ACC and the engine speed Ne. It is calculated by a search from a map or the like with the rotation speed Ne.
The basic fuel injection amount Tp is calculated as a fuel injection amount at a reference equivalent ratio (= 1) corresponding to the theoretical air-fuel ratio with respect to the cylinder intake air amount Q obtained from the intake air amount Qa detected from the air flow meter and the engine rotation speed Ne. To do. The target purge control valve opening degree TEVP is calculated by searching a map or the like based on the engine speed Ne and the engine load such as the basic fuel injection amount Tp (see FIG. 5).

In step 2, the target equivalent ratio TFBY is
A fuel injection amount Tib, which is a fuel injection amount corresponding to A and is used for a map search of an air-fuel ratio learning value described later, is calculated by the following equation. Tib = TFBYA × Tp In step 3, the engine speed Ne and the lean flag F
Read LEAN.

In step 4, the lean flag FLE is set.
Determine the value of AN. In step 5, a constant LRNALP is set in the map header MAPHD so that the learned value is retrieved from the map that stores the learned value of the air-fuel ratio during the evaporative fuel purge, and in step 6, the engine speed Ne and the fuel injection amount T
Based on ib, the learning value KLBLRC is searched from the map storing the air-fuel ratio learning value during the purge, and the learning value KLBLRC is set as KLBLRC0.

Next, in step 7, a constant BSALP is set in the map header MAPHD so that the learned value is retrieved from the map storing the learned value of the air-fuel ratio during non-purging of the evaporated fuel, and in step 8, the engine rotation speed Ne and the fuel injection are set. Amount Ti
Based on b and b, the learning value KLBLRC is searched from the map storing the air-fuel ratio learning value during non-purging, and the learning value KLBLRC is set as KLBLRC1.

In step 9, stratified lean combustion or homogeneous lean combustion is discriminated by the value of the stratified combustion switching flag FSTR. When it is determined that stratified lean combustion is in progress, in step 10, the output correction coefficient KHEVP is set to a predetermined value less than 1. CST
After making a correction to limit the purge flow rate by setting it to REV, the process proceeds to step 12, and when it is determined that the homogeneous lean combustion is being performed, the output correction coefficient KHEVP is set to 1.0 in step 11 to make a correction to limit the purge flow rate. No, go to step 13.

In step 12, the learned value K during the purge is set.
LBLRC0 is compared with the learning value KLBLRC1 during non-purging, and when it is determined that KLBLRC1 <KLBLRC0, the routine proceeds to step 14 and the learning value KLB during non-purging.
LRC1 is set as the learning value KLBLRC, and if not (KLBLRC1 ≧ KLBLRC0), the process proceeds to step 15 and the learning value KLBLRC0 during purging is set as the learning value KLBLRC.

That is, during the stratified lean combustion, the smaller learning value among the learning values during purging and non-purging, that is, the learning value in the direction of decreasing the air-fuel ratio is selected. On the other hand, similarly in step 13, the learning value KLBLRC during the purge is similarly set.
0 is compared with the learning value KLBLRC1 during non-purging, but when it is determined that KLBLRC1 <KLBLRC0, the routine proceeds to step 15 and the learning value KLBLRC during purging.
0 is set as the learning value KLBLRC, and if not (KLBLRC1 ≧ KLBLRC0), the process proceeds to step 14 and the learning value KLBLRC1 during non-purging is set to the learning value KL.
Set as BLRC.

That is, at the time of homogeneous lean combustion, the larger learning value among the learning values during purging and non-purging, that is, the learning value in the direction of increasing the air-fuel ratio is selected. Next, at step 16, the fuel injection amount Ti is calculated by the following equation using the learned value KLBLRC selected and searched as described above. Ti = Tib × KLBLRC × COEF + Ts COEF is various correction coefficients determined based on the cooling water temperature,
Ts is an invalid injection amount determined by the battery voltage.

In step 17, the opening control value EVP of the purge control valve 15 is calculated by the following equation. Here, as described above, during the stratified lean combustion, the output correction coefficient KHEV
Since P is set to a value less than 1.0, the purge flow rate is limited, and during homogeneous lean combustion, the output correction coefficient K
Since HEVP is set to 1.0, the opening degree of the purge control valve 15 is not specially corrected and the target control value TEV
Controlled by P.

EVP = TEVP × KHEVP In this way, at the time of stratified lean combustion, by limiting the purge flow rate, the smaller learning value of the two kinds of learning values that thins the air-fuel ratio is selected. It is possible to reliably prevent misfire due to enrichment of the air-fuel ratio. On the contrary, during homogeneous lean combustion, conversely, by selecting the larger learning value that makes the air-fuel ratio richer, it is possible to reliably prevent misfire due to lean air-fuel ratio as in the conventional case. In particular, in this embodiment, even if an abnormality occurs in the purge control system such as the purge control valve and erroneous learning is performed, a learning value that is suitable for each combustion is selected to perform good air-fuel ratio control. You can

Also, in step 14, the lean flag FLEA is set.
If it is determined by N that the combustion is not in the lean combustion but in the homogeneous stoichiometric combustion, the process proceeds to step 18 and subsequent steps, and the independent learning of the air-fuel ratio is performed according to the presence or absence of the purge as follows. In step 18, the value of the learning convergence flag FBSLTD is determined to determine whether the learning has converged.

If the value of the convergence determination flag FBSLTD is 0, that is, the air-fuel ratio feedback correction coefficient has not converged, and it is determined that the condition for stopping the purge of the evaporated fuel is the condition, the target of the purge control valve 15 is determined in step 19. Opening control value T
Set EVP to 0 to stop purging. Step 20
Then, the map header MAP is searched so that the learned value is searched from the map that stores the air-fuel ratio learned value during the non-purging of the evaporated fuel.
Set the constant BSALP to HD.

In step 21, the learned value KLBLRC is retrieved from the map storing the learned value of the air-fuel ratio during non-purging based on the engine speed Ne and the fuel injection amount Tib. In step 22, the air-fuel ratio feedback correction coefficient A
Learning is performed so that LPHA approaches a reference value (for example, 1), and the learning value KLBLRC is updated. Here, during the learning, the non-purging is being performed, and the learning value KLBLRC is stored and updated in the storage area dedicated to the non-purging. If the learning convergence is determined and it is determined that the learning has converged, the learning convergence flag F
Set BSLTD to 1.

Next, the routine proceeds to step 16, where the fuel injection amount Ti is calculated using the learning value at the time of non-purging, and step
The opening control value EVP of the purge control valve is calculated at 17, but since the target opening control value TEVP is set to 0 as described above, the opening control value also becomes 0 and the purge is maintained in the stopped state. It On the other hand, when it is determined in step 18 that the learning has converged, the routine proceeds to step 23, where a constant LRNALP is set in the map header MAPHD so that the learned value is searched from the map storing the air-fuel ratio learned value during evaporative fuel purge.
Set.

In step 24, the learned value KLBLRC is retrieved from the map storing the learned value of the air-fuel ratio during the purge, based on the engine speed Ne and the fuel injection amount Tib. In step 25, the air-fuel ratio learning similar to the above is performed and the learning value KLBLRC is updated. Here, at the time of learning, purging is in progress, and the learning value KLBL is stored in a dedicated storage area during purging.
Store and update RC.

Next, the routine proceeds to step 16, where the fuel injection amount Ti is calculated using the learning value at the time of non-purging,
At 17, the opening control value EVP of the purge control valve is calculated.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration and functions of the present invention.

FIG. 2 is a diagram showing a system configuration of an embodiment of the present invention.

FIG. 3 is a flowchart showing a fuel injection amount control and purge control routine in the first embodiment.

FIG. 4 is a combustion switching map according to operating conditions in the above embodiment.

FIG. 5 is a map of the target opening control value of the purge control valve according to the operating conditions.

[Explanation of symbols]

1 Internal combustion engine 5 Fuel injection valve 6 spark plug 9 Fuel tank 10 canisters 11 Adsorbent 12 Evaporative fuel introduction pipe 13 Fresh air inlet 14 Purge passage 15 Purge control valve 20 control unit

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 10-231758 (JP, A) JP 5-202816 (JP, A) JP 9-151771 (JP, A) JP 4- 362221 (JP, A) JP-A-3-281965 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F02D 41/14 F02D 41/02 F02M 25/08

Claims (4)

(57) [Claims] 1. A stratified lean combustion, a homogeneous lean combustion, and a homogeneous stoichiometric combustion in which the air-fuel ratio is feedback-controlled to a stoichiometric air-fuel ratio are switched according to the engine operating conditions, and the evaporated fuel is taken in under a predetermined operating condition. In an internal combustion engine for purging the system, while independently learning the feedback correction value of the air-fuel ratio by the presence or absence of the evaporated fuel purge during the homogeneous stoichiometric combustion to obtain a learning value for maintaining the feedback correction value near the reference value, A control device for an internal combustion engine, wherein air-fuel ratio control is performed by individually referring to the two types of learned values during stratified lean combustion and homogeneous lean combustion. 2. Combustion switching means for switching between stratified lean combustion, homogeneous lean combustion, and homogeneous stoichiometric combustion in which the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio is provided in accordance with engine operating conditions, and predetermined operating conditions are provided. In an internal combustion engine equipped with an evaporated fuel purging means for purging the evaporated fuel into the intake system, the feedback correction value of the air-fuel ratio is independently learned by the presence or absence of the evaporated fuel purge during the homogeneous stoichiometric combustion, and the feedback correction value is calculated. Purge presence / non-learning means for obtaining a learning value maintained near the reference value, and stratified lean combustion for performing air-fuel ratio control by individually referring to the two types of learned values during stratified lean combustion and homogeneous lean combustion, respectively. An internal-combustion-engine control device comprising: a space-time air-fuel ratio control unit and a homogeneous lean-burn time air-fuel ratio control unit. 3. At the time of stratified lean combustion, the purge flow rate of the evaporated fuel is restricted, and the air-fuel ratio control is performed by referring to the learned value of the two types of learned values on the side where the air-fuel ratio becomes thin, to achieve homogeneous combustion. The control device for the internal combustion engine according to claim 1 or 2, wherein the air-fuel ratio control is performed with reference to a learned value on the side where the air-fuel ratio becomes richer, out of the two types of learned values. 4. The control device for an internal combustion engine according to claim 1, wherein the fuel is directly injected into the combustion chamber.