JPH07133735A - Control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent knocking while avoiding deterioration of combustion by suppressing transient leaning only when a target air-fuel ratio exceeds a limit air-fuel ratio under the low atmospheric pressure, and maintaining operating condition to the most leaning air-fuel ratio within a stable combustion range without carrying out any correction by the atmospheric pressure when the target air-fuel ratio is less than the limit air-fuel ratio on the basis of operating condition. CONSTITUTION:A target air-fuel ratio is set to be in lean condition by a setting means 2 in a normal running range detected by an operating condition detecting means 1 so as to carry out lean combustion. A lean side limit air-fuel ratio is set by a limit air-fuel ratio setting means 4 according to the atmospheric pressure detected by an atmospheric pressure detecting means 3 so as to make it nearly a theoretical air-fuel ratio. When an air-fuel ratio in relation to operating condition is in lean condition more than the limit air-fuel ratio, the air-fuel ratio is corrected following the limit air-fuel ratio by an air fuel ratio correcting means 5. Simultaneously, leaning of the air-fuel ratio is suppressed according to reduction of the atmospheric pressure, and the air-fuel ratio is corrected to a delay side by an ignition timing correcting means 6 according to a correction amount corresponding to the atmospheric pressure. Therefore a swiral ratio, ignition timing, and the like are controlled correctly, and lean combustion is stabilized so as to prevent generation of knocking under the low atmospheric pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine adapted to perform lean combustion under a predetermined operating condition, and more particularly to a control device adapted to provide correction at high altitude.

[0002]

2. Description of the Related Art Conventionally, mainly in order to improve the fuel consumption rate, an internal combustion engine is designed to perform lean combustion with an air-fuel ratio (A / F) of about 20 to 22 under predetermined operating conditions. Engine control devices are known. For example, Japanese Patent Laid-Open No. 2-7
No. 0959 discloses that lean combustion is stabilized by giving a strong swirl in a cylinder by a swirl control valve, and an air-fuel ratio sensor provided in an exhaust system causes an actual air-fuel ratio along a target lean air-fuel ratio. There is shown an internal combustion engine with closed loop control.

[0003]

Various elements such as swirl ratio and ignition timing must be properly controlled in order to stably perform the lean combustion as described above.
In high altitudes where the atmospheric pressure is low, there is a problem that the atomization of the fuel supplied from the injection valve deteriorates due to the decrease in the cylinder pressure due to the decrease in atmospheric pressure, and as a result, the lean combustion becomes unstable.

If the air-fuel ratio is simply corrected so as to approach the stoichiometric air-fuel ratio at high altitudes, knocking tends to occur.

[0005]

As shown in FIG. 1, an internal combustion engine control apparatus according to the present invention comprises an operating condition detecting means 1 for detecting an operating condition of an internal combustion engine, and a lean air condition under a predetermined operating condition. A target air-fuel ratio setting means 2 for setting a target air-fuel ratio according to the detected operating conditions so as to obtain a fuel ratio, an atmospheric pressure detection means 3 for detecting atmospheric pressure, and a lean side limit according to the detected atmospheric pressure. A limit air-fuel ratio setting means 4 for setting an air-fuel ratio, an air-fuel ratio correction means 5 for giving the limit air-fuel ratio as a target air-fuel ratio when the target air-fuel ratio corresponding to the operating condition is leaner than the limit air-fuel ratio, And an ignition timing correction means 6 for correcting the ignition timing to the retard side in accordance with the correction amount of the target air-fuel ratio.

[0006]

Under the operating conditions such as the steady running range, the target air-fuel ratio is set to the lean side and lean combustion is performed, but the limit air-fuel ratio setting means 4 detects the atmospheric pressure detected by the atmospheric pressure detecting means 3. Accordingly, the lean side limit air-fuel ratio is set such that the lower the atmospheric pressure, the closer to the stoichiometric air-fuel ratio. And
When the target air-fuel ratio corresponding to the operating condition is leaner than the limit air-fuel ratio, the air-fuel ratio correction means 5 corrects the target air-fuel ratio along this limit air-fuel ratio. That is, the target air-fuel ratio is limited so as not to become leaner than the limit air-fuel ratio. Therefore, in the highlands, leaning of the air-fuel ratio is suppressed in a form corresponding to the decrease in atmospheric pressure so that the stable combustion is maintained. Further, when the air-fuel ratio is corrected corresponding to the atmospheric pressure in this way, at the same time,
The ignition timing correction means 6 corrects the ignition timing to the retard side according to the correction amount. This suppresses the occurrence of knocking.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 2 is a structural explanatory view showing a mechanical structure of a control device according to the present invention, in which 11 is an internal combustion engine and 12
Indicates the intake passage, and 13 indicates the exhaust passage. In the intake passage 12, an electromagnetic fuel injection valve 14 for supplying fuel to each intake port is arranged, and a throttle valve 15 is interposed. This throttle valve 15
The opening degree of is detected by a throttle opening sensor 16 including a potentiometer. On the upstream side of the throttle valve 15, for example, a hot wire type air flow meter 17 for detecting the intake air amount is arranged. Further, a swirl control valve 18, which is a butterfly valve having a notch formed in a part of the valve body, is disposed near the intake port of the intake passage 12. This swirl control valve 18
By closing the inflow direction of intake air at the time of closing,
A strong swirl is generated in the cylinder, and the diaphragm type negative pressure actuator 19 opens and closes the swirl. The negative pressure actuator 19 uses a negative pressure on the downstream side of the throttle valve 15 in the intake passage 12 as an operation source,
Moreover, it is controlled to be ON and OFF via the three-way electromagnetic system 20.

In the exhaust passage 13, a catalytic converter 21 using, for example, a three-way catalyst is interposed, and an air-fuel ratio sensor 22 is arranged upstream of the catalytic converter 21. The air-fuel ratio sensor 22 is composed of a wide area type air-fuel ratio sensor such as an oxygen pump type sensor, and is adapted to obtain an output corresponding to the value of the air-fuel ratio including the lean region.

Reference numeral 23 is a water temperature sensor for detecting the cooling water temperature of the internal combustion engine 11, and 24 is a crank angle sensor for issuing a pulse signal at every predetermined crank angle so as to detect the engine speed.

The control unit 25 to which the detection signals of the various sensors described above are input uses a so-called microcomputer system, and includes a CPU 26 and a ROM.
27, RAM 28, I / O port 29, and the like. The control unit 25 includes an intake air amount detected by the air flow meter 17 and the air-fuel ratio sensor 2
The injection amount and the injection timing of the fuel injection valve 14 are controlled based on the detection signal of No. 2 and the ignition timing of the spark plug 30 is comprehensively controlled. Further, in this embodiment, the atmospheric pressure sensor 31 is built in the control unit 25 to detect the actual atmospheric pressure at the place where the internal combustion engine 11 is operating.

The basic operation of the control device having the above construction will be described. First, as the air-fuel ratio control, the target air-fuel ratio AFT is calculated based on a predetermined map from the intake air amount and the engine speed.
Are sequentially set, and the fuel injection amount is controlled so as to be set accordingly. FIG. 4 is a characteristic diagram showing the characteristic of the target air-fuel ratio AFT. As shown in FIG. 4, the characteristic of the target air-fuel ratio AFT is such that the air-fuel ratio becomes the largest in a predetermined medium speed medium load region. It is set. Then, the injection pulse width applied to the fuel injection valve 14 is controlled according to the target air-fuel ratio AFT. Further, the air-fuel ratio sensor 22 detects the actual air-fuel ratio from the exhaust gas composition, and by multiplying the basic injection pulse width by the feedback correction coefficient calculated based on this detection signal, the actual air-fuel ratio can be accurately calculated. Target air-fuel ratio AF
It is designed to be kept at T. Although the swirl control valve 18 is open at the stoichiometric air-fuel ratio, the three-way solenoid valve 2 is used in the operating region where lean combustion is executed.
The swirl control valve 18 is closed via 0, and a strong swirl is generated in the cylinder.

On the other hand, in a place where the atmospheric pressure is low, such as in a highland, the atomization of the fuel is deteriorated as described above, so that the target air-fuel ratio AFT is set by the lean side limit air-fuel ratio AFL corresponding to the atmospheric pressure value. It is restricted and further leaning is prevented.

As for the ignition timing, the advance value ADV is sequentially set based on the intake air amount and the engine speed based on a predetermined map, but when the swirl control valve 18 is closed. Since the required ignition timing is different in combination with the difference between the air-fuel ratio and the open state, two types of maps are given in advance, and the swirl control valve 18 is opened in the non-lean region. , And the lean region where the swirl control valve 18 is closed, the maps are switched. When the lean air-fuel ratio is limited to the limit air-fuel ratio AFL in high altitudes as described above, the actual required ignition timing deviates from the ignition timing set in this map. Therefore, depending on the correction amount of the air-fuel ratio. Thus, the ignition timing is corrected to the retard side. FIG. 7 shows the relationship between the air-fuel ratio and the required ignition timing under certain operating conditions. As shown in the figure, the leaner the ignition timing, the more the required ignition timing is on the advancing side, and conversely, when it approaches the theoretical air-fuel ratio. , Relatively late. Therefore, if the air-fuel ratio is corrected to be small at high altitudes, knocking is likely to occur at normal ignition timing during lean combustion.

The flow chart of FIG. 3 shows a specific processing flow of the above-described correction control for atmospheric pressure.
This will be described below. The process of FIG. 3 is repeatedly executed, for example, at regular intervals.

First, in step 1, the target air-fuel ratio AFT is set based on the engine operating conditions, specifically, the engine speed and the intake air amount. This is as shown in FIG.
It is searched from the map of characteristics as shown in. Then, in step 2, it is judged from the value of the target air-fuel ratio AFT whether or not it is in the lean region. In the non-lean region, that is, in the case of the stoichiometric air-fuel ratio or the rich air-fuel ratio, the atmospheric pressure does not adversely affect, and therefore the atmospheric pressure correction is not performed.

If it is determined in step 2 that the region is lean, the process proceeds to step 3 and the atmospheric pressure value detected by the atmospheric pressure sensor 31 is read. Then, in step 4, the lean side limit air-fuel ratio AFL is set based on the value of the atmospheric pressure. The limit air-fuel ratio AFL is given in advance in the form of a table having characteristics as shown in FIG. 6 as a limit air-fuel ratio at which stable combustion can be maintained, and a value corresponding to the atmospheric pressure at that time should be searched. Is set by.

Next, at step 5, the target air-fuel ratio AFT obtained from the operating conditions is compared with the limit air-fuel ratio AFL. If the target air-fuel ratio AFT is equal to or less than the limit air-fuel ratio AFL in step 5, stable lean combustion can be performed as it is, and therefore the corrections in step 6 and thereafter are not performed. In this case, the air-fuel ratio is controlled along the target air-fuel ratio AFT, and the ignition timing is controlled by the advance value obtained from the lean ignition timing map. In step 5, when the target air-fuel ratio AFT is larger than the limit air-fuel ratio AFL,
Since the deterioration of combustion due to the decrease in atmospheric pressure occurs, step 6
Then proceed to the correction. In step 6, the target air-fuel ratio AFT and the limit air-fuel ratio AFL are set as the air-fuel ratio correction amount ΔAF.
And the difference (AFT-AFL). Then, in step 7, the ignition timing correction amount ΔADV corresponding to the air-fuel ratio correction amount ΔAF is obtained. Specifically, the air-fuel ratio correction amount Δ
AF and target air-fuel ratio AF at that time obtained from operating conditions
Based on T and T, it is determined from a map of characteristics as shown in FIG. The ignition timing correction amount ΔADV is given as a correction amount to the retard side, and the larger the value, the later the ignition timing. That is, as shown in FIG. 7, even if the air-fuel ratio correction amount ΔAF is the same, if the base air-fuel ratio is different, the required ignition timing changes differently. Map characteristics are set.

After determining the ignition timing correction amount ΔADV in this way, the target air-fuel ratio AFT is corrected in step 8 and the ignition timing is corrected in step 9. That is, in step 8, the target air-fuel ratio ΔAFT
As a substitute for the value obtained from the operating conditions, the limit air-fuel ratio A
The value of FL is given. As a result, as illustrated in FIG. 5, the target air-fuel ratio AFT is limited to the limit air-fuel ratio AFL, and the leanest limit air-fuel ratio is maintained within a range where combustion deterioration does not occur. Further, in step 9, the ignition timing is corrected to the retard side by subtracting the ignition timing correction amount ΔADV from the advance value retrieved based on the predetermined map. In FIG. 5, the engine speed is set to a constant value N1.
The relationship between the load and the air-fuel ratio in the case of (see FIG. 4) is shown.

Therefore, according to the above-described embodiment, in a place where the atmospheric pressure decreases, such as in a highland, the air-fuel ratio becomes excessively lean by suppressing the air-fuel ratio to be equal to or less than the limit air-fuel ratio AFL, and the deterioration of combustion is surely performed. Avoided. Then, as is apparent from FIG. 5, in a region where the target air-fuel ratio AFT obtained from the operating conditions is equal to or lower than the limit air-fuel ratio AFL, correction by atmospheric pressure is not performed, so that a sufficiently lean air-fuel ratio can be maintained, and combustion It is possible to maximize the fuel consumption rate while avoiding the deterioration of fuel consumption. Further, since the ignition timing is corrected to the retard side at the same time when the air-fuel ratio is corrected, knocking can be reliably prevented.

[0021]

As is apparent from the above description, the control device for an internal combustion engine according to the present invention suppresses excessive leaning of the air-fuel ratio when the atmospheric pressure decreases in high altitudes,
Deterioration of combustion is reliably avoided. In particular, the correction is made only when the target air-fuel ratio exceeds the limit air-fuel ratio, and in the region where the target air-fuel ratio obtained from the operating conditions is the limit air-fuel ratio or less,
Since the correction is not performed by the atmospheric pressure, the leanest air-fuel ratio can be maintained within the range where stable combustion can be performed, and the deterioration of combustion can be avoided and the fuel consumption rate can be maximized. Further, since the ignition timing is corrected to the retard side at the same time when the air-fuel ratio is corrected, knocking can be reliably prevented.

[Brief description of drawings]

FIG. 1 is a claim correspondence diagram showing a configuration of the present invention.

FIG. 2 is a structural explanatory view showing an embodiment of a control device according to the present invention.

FIG. 3 is a flowchart showing a flow of atmospheric pressure correction of this embodiment.

FIG. 4 is a characteristic diagram showing characteristics of a target air-fuel ratio with respect to operating conditions.

FIG. 5 is a characteristic diagram showing characteristics of an air-fuel ratio at a constant rotation speed.

FIG. 6 is a characteristic diagram showing characteristics of a limit air-fuel ratio with respect to atmospheric pressure.

FIG. 7 is a characteristic diagram showing a relationship between an air-fuel ratio and a required ignition timing.

FIG. 8 is a characteristic diagram showing a characteristic of an ignition timing correction amount.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Operating condition detection means 2 ... Target air-fuel ratio setting means 2 3 ... Atmospheric pressure detection means 3 4 ... Limit air-fuel ratio setting means 5 ... Air-fuel ratio correction means 6 ... Ignition timing correction means

Claims (1)

[Claims] 1. An operating condition detecting means for detecting an operating condition of an internal combustion engine, and a target air-fuel ratio setting for setting a target air-fuel ratio according to the detected operating condition so that a lean air-fuel ratio is obtained under a predetermined operating condition. Means, an atmospheric pressure detection means for detecting the atmospheric pressure, a limit air-fuel ratio setting means for setting a lean side limit air-fuel ratio according to the detected atmospheric pressure, and a target air-fuel ratio corresponding to the operating condition is the limit air-fuel ratio. When leaner, the air-fuel ratio correction means for giving the limit air-fuel ratio as the target air-fuel ratio, and the ignition timing correction means for correcting the ignition timing to the retard side in accordance with the correction amount of the target air-fuel ratio are provided. A control device for an internal combustion engine, characterized in that: