JPH0357859A - Air-fuel ratio controller of internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent thermal deformation of an internal combustion engine or abnormal increase of the highest wall temperature by compensating the air-fuel ratio of cylinders of the engine, respectively based on the wall temperature in the cylinders, and thereby equalizing a real air-fuel ratio or wall temperature distribution. CONSTITUTION:In an internal combustion engine, respective fuel injection valves 1 are arranged at every cylinder. In this case, wall temperature in the vicinity of a combustion chamber at every cylinder is detected by a means 2. Based fuel injection is set by a means 3 on an operation condition of the engine. Compensation coefficient of the respective cylinders is set by a means 4 based on detected wall temperature by the means 2 under specified operation conditions in the engine. The basic fuel injection set by the means 3 is compensated by a means 5 at every cylinder in response to the compensation coefficient set by a means 4. Consequently, a real air-fuel ratio or wall temperature distribution are respectively equalized at every cylinder, and thermal deformation of the engine or abnormal increase of the highest wall temperature are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to an air-fuel ratio control device for an internal combustion engine, and more particularly to an air-fuel ratio control device that controls the air-fuel ratio for each cylinder.

2. Description of the Related Art Some fuel supply systems for internal combustion engines include fuel injection valves for each cylinder. In addition, conventional air-fuel ratio control devices include those that calculate the required fuel injection amount from engine speed and intake air amount, etc., or perform feedback control based on detection of residual oxygen concentration using O, Senna, etc. is known, but in either case, the fuel injection amount in each cylinder is controlled to be the same, and basically the same air-fuel ratio is maintained in each cylinder (for example, in Japanese Patent Laid-Open No. 1983-1989). 51242
Publications, etc.).

Problems to be Solved by the Invention However, even if control is performed with the aim of achieving the same air-fuel ratio in each cylinder, the layout of the intake and exhaust system is different for each cylinder, and there are also individual differences in the fuel injection valves, so in practice In this case, the air-fuel ratio in each cylinder differs considerably. Therefore, when an attempt is made to make the air-fuel ratio lean in order to reduce fuel consumption, the lean limit is limited at the leanest cylinder due to variations between cylinders, making it impossible to make the engine as a whole lean enough. In other words, as the engine as a whole becomes leaner, there will be extremely lean cylinders, making combustion more likely to become unstable.

In addition, the wall temperature of the combustion chamber is greatly affected by the air-fuel ratio, so
At high loads, etc., the wall temperature distribution becomes uneven due to variations in the air-fuel ratio, causing problems such as thermal deformation of the engine and local increases in maximum wall temperature.

Means for Solving the Problems Therefore, the present invention focuses on the correlation between the wall temperature of the combustion chamber and the air-fuel ratio, and controls the air-fuel ratio for each cylinder based on the wall temperature. . In other words, this issue. The air-fuel ratio control device for an internal combustion engine according to the present invention detects the wall temperature near the combustion chamber of each cylinder in an internal combustion engine in which a fuel injection valve l is arranged for each cylinder as shown in FIG. A detection means 2, a basic fuel injection amount setting means 3 for setting a basic fuel injection amount based on engine operating conditions, and a temperature detection means 2 that detects a correction coefficient for each cylinder under predetermined operating conditions. It is comprised of a correction coefficient setting means 4 that sets based on the wall temperature, and a correction means 5 that corrects the basic fuel injection amount for each cylinder using this correction coefficient.

2. Basic fuel injection amount setting At stage 3, the basic fuel injection amount is set based on the intake air range of the engine, the detection signal of the Ot sensor, etc. Furthermore, the wall temperature detected in each cylinder varies greatly depending on the actual air-fuel ratio of each cylinder, as shown in FIG. 2, and reaches its maximum near the air-fuel ratio 13. A necessary correction coefficient for each cylinder is determined from the variation in the detected wall temperature, and the fuel injection amount for each cylinder is corrected and controlled based on this coefficient. In addition, in the low and medium load range where the lean limit is an issue, the air-fuel ratio of each cylinder is corrected to be uniform, and in the high load range where thermal distortion and maximum wall temperature are issues, the wall temperature itself is made to be uniform. It is good to correct it.

EXAMPLE Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 3 shows an embodiment in which the present invention is applied to an in-line six-cylinder internal combustion engine.

An internal combustion engine main body l2 having six combustion chambers 11 is provided with an intake boat I3 and an exhaust boat 14 in a cross-flow manner, and an intake manifold l5 and an exhaust manifold l6 are connected to each of them. And an electromagnetic fuel injection valve in each intake boat l3! 7 is installed, and supplies fuel to each cylinder individually. This fuel injection valve l7
As is well known, fuel regulated to a predetermined pressure difference is introduced into the intake boat 13, during which time the fuel injection amount is obtained in a form approximately proportional to the valve time, that is, the ON time of the drive pulse signal. It looks like this.

Further, an intake pressure sensor 19 for detecting the intake pressure (Pb) on the downstream side of the throttle valve 18 is attached to the collector portion of the intake manifold 15.
For example, a hot wire type air flow meter 20 for detecting the intake air flow fiGa is installed on the upstream side. Further, an O sensor 2l is installed at the gathering part of the exhaust manifold l6 to output a detection signal related to the residual oxygen concentration.

Further, a rotational speed sensor 22 detects the rotational speed Ne of the internal combustion engine, and a water temperature sensor 23 detects the cooling water temperature TW.
is provided.

Further, a wall temperature sensor 24 consisting of a thermocouple, a thermistor, or the like that detects the wall temperature T in the vicinity of the combustion chamber 11 is individually provided for each cylinder. In detail, as shown in Fig. 4, it is inserted into the wall of the cylinder head 25, and the temperature measurement point at the tip is the combustion chamber! It is located very close to l. In FIG. 4, 26 is a spark plug, 27 is an exhaust valve, 28 is a cylinder block, 29 is a piston, and 30 is a water jacket.

The fuel injection weight of each fuel injection valve 17 described above is individually controlled by a control unit 3l using a microcomputer system. The control unit 31 receives detection signals from the sensors mentioned above, and as described later,
In addition to setting the basic fuel injection amount according to driving conditions,
The system detects variations in the wall temperature of each cylinder and corrects the actual injection amount for each cylinder.

Next, details of this air-fuel ratio control will be explained according to the flowcharts shown in FIGS. 5 to 7.

FIG. 5 is a flowchart showing the main routine of air-fuel ratio control, which is executed every time there is an injection in each cylinder. FIG. 6 shows the correction coefficient determination routine for medium and low loads (step 4), which determines the correction coefficients for each cylinder required during medium and low loads.
FIG. 7 is a flowchart showing details of the high-load correction coefficient determination routine (step 6) that determines the correction coefficient for each cylinder required at high load. In these flowcharts, i such as Ti indicates the cylinder number (i=1.2...6).

First, to explain the flow of the main routine, step l
Various detection signals indicating the engine operating conditions at that time, specifically, intake air flow rate Gax cooling water temperature TW, rotation speed N
Read each signal: e, intake pressure Pb and O, and sensor signal. Next, in step 2, the cooling water temperature TW is compared with a predetermined warm-up completion water temperature, for example, 80°C. Here, if the temperature is 80° C. or lower, air-fuel ratio correction for each cylinder is not performed. That is, intake air flow rate Ga, cooling water temperature TW, intake pressure Pb. The basic fuel injection amount Gro (step! 4) calculated based on the Ot sensor signal is used as is for the final fuel injection amount. li fuel injection QGf(i) (step 15), and fuel injection is performed in accordance with this (step +6).

On the other hand, if the temperature is 80°C or higher, further
svHg region) and a predetermined high load region (Ne≧300O
rpm and Pb≧-100in+Hg) and other regions (Step 7, perform air-fuel ratio control according to each IOL).

In a predetermined medium-low load region, the correction coefficient K(i
) (step 8) and use this to set the basic fuel injection fl
Perform IGfo correction. That is, G f (+) = G f o X (1 +
K(t)) is the injection amount G of the corresponding cylinder i.
f(+) is calculated (step 15). Note that the basic fuel injection amount Gf. is determined based on the intake air flow rate Ga, the cooling water temperature TW, and the intake pressure pb (step 9). In other words, in this region, it is a simple loop control that does not depend on the 0, senna signal.

In a predetermined high load region, the high load correction coefficient Kh(i) for each cylinder i obtained in the high load correction coefficient determination routine (step 6) described later is set as the correction coefficient K(i).
Step ll), using this, the basic fuel injection ffiGf
．． is corrected, and the injection ffiGf(i
) is determined (step 15). Note that the basic fuel injection ffiGf. Settings (Step! 2)
In this case, O and sensor signals are taken into consideration, resulting in closed loop control. In other words, closed loop control is performed so that the amount of fuel supplied to the entire engine has good exhaust purification performance, and within this, the fuel distribution to each cylinder is corrected according to the above correction coefficient K(i). .

In addition, the correction coefficient K(i) is kept at O in areas other than the above-mentioned medium-low load area and high load area (step l3).
, as in the case of cold conditions, no correction is made for each cylinder.

On the other hand, when the operation is in a specific operating range within the above-mentioned medium and low load range, specifically when Ne=1500±100 rpm and Pb=-300±]OxxHg (Step 3), Step 3 The process then proceeds to step 4, in which the medium/low load correction coefficient Kl2(+) for each cylinder i is determined in sequence. The correction coefficient Kff(i) determined here is stored in the memory and updated sequentially. The above-mentioned region is selected as a region that occurs relatively frequently in normal driving conditions and in which the air-fuel ratio is around 13.

In addition, when the operating range is in a specific range among the high load ranges mentioned above, specifically, when Ne=3600±100 rpm and Pb=−60±10xmlg (step 5), the steps from step 5 to 6, the high load correction coefficient Kh(+) for each cylinder i is determined in sequence. The correction coefficient Kh(i) determined here is also stored in the memory and updated sequentially.

Next, the flow of the medium/low load correction coefficient determination routine shown in FIG. 6 will be explained. Note that, as described above, this is executed only after warm-up and under specific operating conditions. First, in step 2l, each temperature f2 detected by each wall temperature sensor 24 is
The wall temperature Ti of i is read. Since this wall temperature Ti is influenced by the height of the cooling water temperature TW at that time, in step 22, the difference (TW
-80) is added and corrected. And step 23
From the wall temperature T of cylinders #l to #6, the average wall temperature Tav, the minimum wall temperature Tmin, and the temperature range ΔT (ΔT=Tav−Tm
in), and the cylinder number with the lowest wall temperature is set as NC.

If the above temperature range ΔT is below a predetermined amount, for example 10°C, the correction coefficient K(2(i) is not updated (step 24), but if it is above 10°C, Medium and low load correction coefficient KI2 for cylinder NQ with minimum wall temperature TmLn
(Try increasing Nu by 0.1 (step 26).

Note that rsignJ in step 26 is simply a coefficient indicating the positive and negative directions, that is, the direction of increase or decrease by 0.1.

In addition, the current temperature range ΔT and the lowest wall temperature cylinder Ne are stored as ΔT o and NQ o, respectively (step 27).
, the current medium-low load correction coefficient determination routine ends.

Then, the next time this routine is executed, it is determined whether the current lowest wall temperature cylinder NC is the same as the previous cylinder NQo (step 25), and if they are the same, the current temperature range is further increased. Determine whether ΔT is smaller or larger than the previous temperature width ΔT0 (step 28
). Here, if it is the same cylinder as the previous time and the temperature width ΔT has decreased, proceed to step 26 and further increase the mid-low load correction coefficient KI2 (NI2') of the corresponding cylinder NQ by 0.1. . Furthermore, if the temperature range ΔT has expanded, the positive/negative direction of the coefficient "sign" is reversed (step 29), and the mid-low load correction coefficient KI2 (N( ) of the corresponding cylinder Nf2 is reversed to 0.1 Incidentally, if the lowest wall temperature cylinder NQ has changed from the previous time, an attempt is made to similarly increase or decrease the mid-low load correction coefficient of that cylinder NI2 by 0.1.

That is, under the operating conditions when this routine is executed, the average air-fuel ratio is approximately around I3. Therefore, as is clear from Figure 2, the wall temperature decreases when the air-fuel ratio is richer or leaner than the average air-fuel ratio, but the air-fuel ratio of the cylinder Ne with the lowest wall temperature is lean. If so, the correction coefficient KQ is
By increasing (N+!), the wall temperature tends to rise.

Therefore, when the correction coefficient determination routine for medium and low loads is repeated and the correction coefficient In(Nl2) gradually increases, the lowest wall temperature Tmtn approaches the average wall iuTaV,
Eventually, the temperature becomes within the range of ΔT<10°C. As a result, the correction coefficient 1n(+) required for the Nl2 cylinder at that time is determined.

Furthermore, if the air-fuel ratio of the cylinder NC with the lowest wall temperature is rich, the wall temperature will further decrease due to an increase in the correction coefficient Ki2 CNQ ). Therefore, the previous temperature range ΔT
By comparison with o (step 28), it is immediately determined that the air-fuel ratio should be leaner, and from then on, Δ'r<1
The correction coefficient In (In 2 ) gradually decreases until it reaches 0°C.

Then, as a result of the correction, if the lowest wall temperature cylinder NQ is different from the previous one, the correction coefficient K+2(i) now necessary for the same cylinder Ne is determined in the same procedure.

Therefore, this correction loss Kff(1) at medium and low load is used (N)
In the medium and low load range, correction control is performed so that the wall temperature of each cylinder and the relatively high temperature side are substantially uniform, and at the same time, the actual air-fuel ratio is maintained substantially uniform around l3. Therefore, combustion instability in some lean cylinders can be prevented, and by keeping the wall temperature as high as possible, combustion and fuel efficiency can be improved.

Next, the flow of the high load correction coefficient determination routine shown in FIG. 7 will be explained. First, in step 31, the wall temperature T of each cylinder i
i is read, and in step 32, the water temperature is corrected using 90°C as the reference temperature. In step 33, the average wall temperature Tav, the minimum wall temperature Tmin, the maximum wall temperature Tmax, and the temperature range ΔTh (ΔTh=Tav−Tmin ), and the temperature range ΔTQ (ΔTQ = Tmax-T av ), and the cylinder number with the lowest wall temperature is Mh, and the cylinder number with the lowest wall temperature is MQ.

For the above minimum wall temperature cylinder MQ, steps 34 to 3
6 and steps 40, 41, and 42, the same processing as the above-mentioned medium/low load correction coefficient determination routine is performed. As a result, the minimum wall temperature Tmin and the average wall temperature Tav
The high load correction coefficient Kh (Ml2) of the cylinder MI2 with the lowest wall temperature is determined so that the temperature difference ΔTQ between the cylinder MI2 and the cylinder MI2 is 10° C. or less.

For the highest wall temperature cylinder Mh, steps 37 to 40
Similar processing is performed by steps 43 and 44. As a result, the maximum wall temperature T m aX and the average wall temperature T
The high load correction determination Kh (Mh) for the maximum wall temperature cylinder Mh is determined so that the temperature difference ΔTh with respect to av is 10° C. or less.

Therefore, in a high load range where this high load correction coefficient Kh (D) is used, correction control is performed so that the wall temperature of each cylinder is equalized to an intermediate wall temperature.As a result, the temperature distribution of the entire engine is made uniform. At the same time, the maximum sacred temperature, which is a problem in high load areas, can be suppressed to a low level, and durability can be improved.

Effects of the Invention As is clear from the above explanation, in the air-fuel ratio control device for an internal combustion engine according to the present invention, the air-fuel ratio of each cylinder is individually corrected based on the wall temperature of the combustion chamber of each cylinder. Therefore, it is possible to equalize the actual air-fuel ratio and temperature distribution of each cylinder.

[Brief explanation of drawings]

Fig. I is a claim correspondence diagram showing the configuration of this invention, Fig. 2 is a characteristic diagram showing the relationship between air-fuel ratio and wall temperature, Fig. 3 is a configuration explanatory diagram showing one embodiment of this invention, and Fig. 4 Figure 5 is a sectional view of the main parts of the engine. FIGS. 6 and 7 are flowcharts showing the flow of air-fuel ratio control processing in this embodiment. l...Fuel injection valve, 2...Temperature detection means, 3...
Basic fuel injection amount setting means, 4...correction coefficient setting means, 5...correction means. Figure 1 Figure 2 Figure 4

Claims (1)

[Claims] (1) In an internal combustion engine in which a fuel injection valve is arranged for each cylinder, there is a temperature detection means for detecting the wall temperature near the combustion chamber of each cylinder, and a basic fuel injection amount based on the engine operating conditions. a basic fuel injection amount setting means for setting a correction coefficient for each cylinder under predetermined operating conditions, a correction coefficient setting means for setting a correction coefficient for each cylinder based on each wall temperature detected by the temperature detection means; An air-fuel ratio control device for an internal combustion engine, comprising a correction means for correcting a basic fuel injection amount for each cylinder.