JPS62261632A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To enable a highly accurate air-fuel ratio control without a response delay by comparing the crank angle, in which the actual value of the cylinder internal pressure of an engine at the time of transient operation attains a maximum, with a target value, and learning the correction quantity of air-fuel ratio at the time of transient in accordance with the deviation. CONSTITUTION:When the operation is discriminated to the in a transient operating condition by a transient condition discriminating means 3 on the basis of the number of revolutions N and intake air quantity Qa from an operating condition detecting means 1, a target value setting means 6 sets the target value theta pmo of the crank angle at which the cylinder internal pressure attains a maximum in accordance with the transient condition. The detected signal P from a cylinder internal pressure detecting means 2 caused by a piezoelectric sensor formed in the washer shape of an ignition plug is input into a means 5, from which the actual value theta pmax of the crank angle at which the cylinder internal pressure attains a maximum is input into a learning means 7. The learning means 7 learns the correction quantity of air-fuel ratio at the time of transient in accordance with the deviation between the target value theta pmp and the actual value theta pmax, and in response to this learning value the fuel injection quantity is corrected by a means 8.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an air-fuel ratio control device for an internal combustion engine.

(Prior art) An electronically controlled air-fuel ratio control device calculates the amount of fuel injection required for one combustion cycle according to the operating state, and sends a drive pulse corresponding to this injection amount to the fuel injection valve in synchronization with engine rotation. However, in order to improve control accuracy, during steady operation, etc., the signal from the air-fuel ratio sensor installed in the exhaust system is feed-punked to obtain a predetermined air-fuel ratio (base air ratio). ing. Also, in order to improve drivability during acceleration, a transient air-fuel ratio is added to the base'g! Rather than the fuel ratio, the air-fuel ratio (transient air-fuel ratio) is used (Japanese Patent Application Laid-open Nos. 54-106736 and 54-1307).
See Publication No. 34. ).

(Problem to be Solved by the Invention) By the way, air-fuel ratio feedback control is performed so that there is no deviation from a target value (often a tolerance range is set around the target value). , when a deviation occurs due to a change in the target value itself due to the transition from a steady state to a transient state, or when a new deviation occurs at the same target value due to changes over time or fuel properties, etc. Although there are long and short periods of time on soil where the amount is within the allowable range, in the end it can be brought within the permissible range.

However, with feedback control based on an air-fuel ratio sensor, there is a response delay before a change in the injection amount (air-fuel ratio) in the intake system appears in the exhaust system, so the air-fuel ratio control accuracy during transient periods cannot be maintained at the same level as during steady-state conditions. It is quite difficult to raise this level. For this reason, if the air-fuel mixture is thinner than the transient air-fuel ratio, the acceleration desired by the driver cannot be obtained, and on the other hand, if the air-fuel mixture is richer, fuel efficiency will deteriorate. This is because transient times are a bottleneck for feedback control, and drivability and fuel efficiency during transient times are influenced by how much the accuracy of air-fuel ratio control during transient times can be improved.

This invention was made to improve the problems of the conventional example, and the crank angle (target value) that provides the maximum value of the cylinder pressure has a correlation with the air-fuel ratio and is almost constant regardless of changes in operating conditions. By focusing on taking the value and using this actual crank angle value 9 pemax as a feedback control signal, it becomes possible to control the air-fuel ratio with high precision without causing a response delay even during transient times. In other words, the air-fuel ratio control device detects the actual value 9pmax of the Kuralev angle at which the cylinder pressure is at its maximum, and performs learning correction so as to eliminate the deviation from the target value θpmo of the crank angle at which the cylinder internal pressure at the time of transition is at its maximum. The purpose is to provide

(Means for Solving the Problems) In the present invention, as shown in FIG. 1, means 1 for detecting the operating state of the engine, means 3 for determining the transient state of the engine, means 4 for calculating the basic fuel injection ii T p so as to achieve the air-fuel ratio; means 2 for detecting the cylinder pressure of the engine; means 5 for detecting the actual value θpmax of the crank angle at which the cylinder pressure becomes maximum; The means 6 for setting the target value 9 p+*o of the crank angle at which the cylinder pressure is maximum at the time, and the correction amount of the air-fuel ratio during the transient period determined according to the deviation between these actual values and the target value are learned. A means 7 and a means 8 for correcting the fuel injection amount during a transient period according to the learned value are provided.

Here, the term "calculation" is used as a concept that includes not only numerical calculations but also operations such as table searches.In addition, the intake air RQa as the engine load and the engine speed N are shown as representative values of the operating state.

(Operation) With this configuration, the value θpmax correlated to the air-fuel ratio
The deviation from the target value 9pmo is determined using the feedback signal, and the correction amount of the air-fuel ratio during the transient period is learned so that this deviation will not occur during the next transient control.

For example, if the current air-fuel mixture becomes leaner than the air-fuel mixture that provides the transient air-fuel ratio due to changes in fuel properties or changes over time in the 8!1 ratio, combustion will be delayed.
The value of taax shifts to the retarded side than 19 pmo,
In this case, the transient air-fuel ratio correction amount is learned so that the air-fuel mixture becomes richer, and is maintained so that no deviation occurs during the 'th transition. Conversely, if the air-fuel mixture at that time is richer than the air-fuel mixture at the transient air-fuel ratio, e pa+ax becomes θ
Since the angle deviates to the advance side compared to pmo, the supplementary No. 7F of the transient air-fuel ratio is learned so that there is no deviation in this case as well.In other words, the deviation from the target value is canceled each time by learning correction using 9911JLX as a feedback signal. Therefore, at the start of transient control, the fuel properties and
The same state that is initially set so that the transient air-fuel ratio is obtained according to state a is always obtained. As a result, it is possible to control the transient air-fuel ratio with high precision even during transient periods, ensuring good operation without being affected by subsequent changes in the air-fuel ratio, such as fuel properties or changes over time. can acquire sexuality.

This will be further explained in Examples below.

(Embodiment) FIG. 2 shows the mechanical configuration of a first embodiment of the present invention applied to an electronically controlled fuel injection engine.

In such an engine, signals from sensors that detect various operating variables are input to the control unit 30, and the control unit 30 calculates the fuel injection !ITi to be supplied to the engine based on these signals. , the electromagnetic fuel injection valve 18 is driven and controlled by a drive pulse based on the calculated injection amount Ti. Such a configuration is publicly known, and the air flow detecting the intake air amount Qa as the engine load is used as a driving state detection means. quantity sensor 20, a crank angle sensor 21 that generates a 1 degree crank angle signal and a reference position signal;
Water temperature sensor 22 that detects cooling water temperature Tw, air-fuel ratio sensor (for example, mi concentration sensor) 24hJ that detects air-fuel ratio
Sensors 15 are MAA pipes, 16 are intake ff' valves, 17 are exhaust pipes, and 19 are spark plugs.

Next, the characteristic part of this invention is that θp has a correlation with the air-fuel ratio.
IIlax (actual value of crank angle at which cylinder pressure is maximum)
is used as a feedback signal to calculate the deviation of the crank angle from the target value θpmo at which the in-cylinder pressure during the transient period is at its maximum.

The calculations and the learning correction based on these deviations are executed by the control unit 30.

First, a known means for detecting the cylinder pressure is used. For example, as shown in Figure @3, the cylinder pressure sensor 25
A to 25D and charge amplifiers 268 to 26D constitute an in-cylinder pressure detection means, and the voltage signal 31 is obtained by converting the charge signal output from each in-cylinder pressure sensor from charge to voltage.
1 to Su4. Here, as the cylinder pressure sensor, a piezoelectric sensor formed in the shape of a washer of one spark plug or a piezoelectric sensor that directly detects the cylinder pressure is well known.

The configuration shown in Figure 13 is an example of a four-cylinder engine, and in order to detect the f9 pmax of the gold cylinder, only the in-cylinder pressure signal in the vicinity of combustion (in a predetermined crank angle range) per cylinder is sufficient. , a multiplexer 27 sequentially selects and outputs the signals of the cylinders that match the ignition order. Furthermore, the signal S2n from the multiplexer 27 is input to the main control circuit 31 via the low frequency vibration detection circuit 28.

This is to remove unnecessary frequency components and effectively extract only the cylinder pressure signal, which is a low frequency component.

Next, the internal operation executed in the main control circuit using the cylinder pressure signal S9 obtained in this way will be explained with reference to the flowchart of FIG. The operation shown in the figure is executed by interrupt processing at a predetermined crank angle (near 50° ATDC) in the expansion stroke for each cylinder. This is because the value of epmax is required as a prerequisite for calculating the injection amount, so this 811
111 (This is because it was decided to perform the calculation of the injection amount after the calculation of LX.

The main control circuit 31 has the functions of means 3 to 8 shown in FIG. 1, and as shown in FIG.
RAM34. Nonvolatile/Mo17 (NVM)35 and I1
It is composed of a microcomputer 31 consisting of 0 ports 36. The numbers in the figure are processing numbers.

First, basic control of the fuel injection amount is the same as before, and the injection ffl T is expressed by the following equation (1).
An injection pulse signal Si corresponding to i is output to the injection valve 18 (step 56).

T i = T pX CoXa + Ts −
(1) Here, 'l'' p(= K-Q a/N,
K is a constant.

) is the basic injection amount determined by the intake air amount Qa and the engine rotation WLN, and is the basic injection amount for obtaining the base air-fuel ratio (steps 41 to 43). In addition, this T-IJ, 1
hTom411MlgeIIsuichi++Mli(s1tM*
Ill;! +l++, 1'7.7 Tan [Renado] -/I"
1, it is temporarily stored as Tpo (step 57).

Further, Co is the sum of various correction coefficients, and in a steady state is given by the following equation (2) (step 65).

Co”KMR+K TW...(2)
However, KMR (=f(Tp-N)) is a mixture ratio correction coefficient, and KTW (=f(Tw, N)) is a water temperature increase correction coefficient. Note that these coefficients are T
It is obtained by table search using p, N or Tw, N as parameters (steps 44 and 45). Also, α
is an air-fuel ratio feed bank correction coefficient determined based on the output value of the air-fuel ratio sensor 24, and Ts is a correction amount based on the battery voltage value.

On the other hand, in order to improve drivability during acceleration (transient time), the acceleration correction coefficient KACC (=f(Tp, N)) is used to obtain a mixture with a lower air-fuel ratio than the base air-fuel ratio.
is added to the correction coefficient of the weight loss (2) (step 47,
52.55).

Note that the amount of change in the basic injection amount ΔTp (=(Tp−Tpo)
XN, where -1110 is Tp for one control period. ) by comparing it with the acceleration judgment reference value ao.
If p≧aQ, it is determined that the vehicle is accelerating (steps 46 and 47). This corresponds to the function of means 3 in FIG.

Next, the characteristic part of this invention will be described. It is that the acceleration correction coefficient KACC learns and corrects the amount that does not match the actual situation due to the fuel properties that occur later or changes over time. Here, KACC is a basic value that provides a correction coefficient during acceleration, and if there are no changes in fuel properties or over time,
The target transient air-fuel ratio should be obtained only with this KACC. However, in reality, these changes cause a deviation from the air-fuel ratio during the transient period, and in this case, since the air-fuel ratio is during a transient period, using the signal from the air-fuel ratio sensor, which is affected by changes in operating conditions, will not respond well. This results in delays and ultimately insufficient accuracy.

Therefore, the correction coefficient DKAC is used as a value to correct KACC.
DKACC is learned so that there is no deviation from the target value θpmo by using the air-fuel ratio correlation value (epmax), which is not affected by changes in operating conditions, as a feedback signal. That is, DKAC
C is increased or decreased to obtain a transient air-fuel ratio, thereby absorbing changes in fuel properties and over time.

Therefore, this DKACC is used as the learning table (DKACC
table) and added to KACC (steps 53, 55).

Next, based on e pmax (learning control is performed in step 40
．． 49-51. Runs at 58-63. That is,
Step 40 corresponds to the function of means 5 in FIG.
is the function of means 6 in the same figure, steps 50.51.58~
63 corresponds to the function of means 7 in the figure, and the control deviation Δep-(=θpIIio-θpmax) is accumulated during acceleration, and the learning value DKACC is rewritten based on this accumulated value ΣΔepm immediately after acceleration. I will pay.

Here, if the air-fuel ratio is a constant value, 9pmo is 15 to 20 in most of the operating Wi range regardless of changes in operating conditions.
"ATDC (constant value). Therefore, 9 pmax
Unlike the air-fuel ratio sensor signal, which has a response delay due to changes in driving conditions, it is not affected by changes in driving conditions, and therefore can be a highly reliable signal equivalent to the air-fuel ratio during acceleration. It is. Note that θ13110 (=
f(T ptN )), for example, it may be obtained by table search using Tp and N as parameters (step 49). However, in the low load range and high load range, a retarded side, that is, a large value, is adopted in both cases due to the relationship with engine stability and knocking level, respectively.

Regarding s epmax, a predetermined crank angle is set around the crank angle at which combustion occurs, and the in-cylinder pressure P obtained over this range and the crank angle at that time are stored in association with each other, and a group of these data is stored. It is sufficient to adopt the crank angle at which P becomes the maximum from among the above (step 40), and the specific method thereof is known to the public.

The deviation Δepm is then integrated over the acceleration period (step 51). Next, the learning correction based on the integrated value B (=ΣΔθpm> is performed immediately after acceleration (steps 58 to 63).

Note that f(DDKACC can also be calculated) that corrects the learning value DKACC based on the integrated value B.
In this case, data processing becomes difficult because the values differ depending on the degree of acceleration. Therefore, standardization is performed by adopting the ratio β (=B/A) obtained by dividing B by the integrated value A (=ΣΔTp) of ΔT and p, and data processing is simplified as a value that does not depend on the degree of acceleration.

In order to speed up the process (steps 48v59), the integrated values A and B are rewritten each time they are integrated (step 54).
).

β thus obtained becomes a parameter representing the deviation from θpmo. For example, if β is larger than the predetermined value β0, it means that e pmax has shifted to the retard side from 9 p+ao during acceleration. From this, at that time D
It is interpreted that this is because the KACC value does not provide a mixture leaner than the target air-fuel ratio during acceleration, and the rise in cylinder pressure is delayed, resulting in a shift to the retarded side. Therefore, in order to achieve the air-fuel ratio during acceleration in this case, it is necessary to increase the amount of fuel by correcting DKACC.

Therefore, if β≧β0, the correction amount D proportional to this β
DKACC (=kl·β, where 1 is a constant 6) is calculated (step 60.61).

Then, based on this DDKACC, the nonvolatile memory 35
The DKACe stored in the DKACC table of is rewritten (step 63). The rewriting method is based on interpolation calculation between grid points of the learning table. In this case, DKAC
A limiter is provided to prevent the value of C from becoming too large.

Note that when β is β0, it almost matches the target value θpmo, so there is no need to replace the old one.
To prevent the air-fuel ratio from becoming too rich, subtract a small value (constant value) k2 from the learning table (step 60,
62.63).

Finally, the values A, B, and β used this time are set to zero in preparation for learning correction during the next acceleration (step 64).

As mentioned above, v! To explain the effect when this is done, the control deviation from the target value θ13 IfO is determined using the value epmax correlated to the air-fuel ratio as a feedback signal, and in order to prevent this deviation from occurring during the next acceleration, the control deviation is determined immediately after acceleration. The DKACC table is rewritten.

For example, if the air-fuel mixture at that time is leaner than the air-fuel mixture at the time of acceleration due to changes in fuel properties or over time, combustion will be delayed, so the value of θpmax is θpm.

Shifts to the retarded side. On the other hand, the learned value DKACC is changed so that the air-fuel mixture becomes richer, and is maintained so that no deviation occurs during the next acceleration.

Conversely, if the air-fuel mixture at that time is richer than the air-fuel ratio air-fuel mixture at the time of acceleration, θpmax will shift to the advanced side than θp If O, so there is no deviation in this case as well. will be rewritten.

In other words, θpIIax is affected by changes in driving conditions! As a value that is not detected, it is optimal as an air-fuel ratio detection signal that can be obtained during a transient period.If this signal is used as a feedback control signal, it is possible to reliably control the acceleration lO air-fuel ratio, and the control deviation can be reduced by learning correction. Solved each time? 1 yen, so at the start of acceleration, the same state as initially set according to the fuel properties and engine state at that time is always obtained. As a result, it becomes possible to control the air-fuel ratio with high precision during transient times, and it is possible to obtain good drivability even during transient times without being affected by later-occurring fuel properties or changes over time.

However, in the conventional example, as long as feedback control is based on an air-fuel ratio sensor, there is a limit to air-fuel ratio control during transient periods, and if there is a change in fuel properties, etc. This can lead to deviations in the air-fuel ratio during transients.

Next, FIGS. 5 to 8 show a flowchart of a second embodiment of the present invention, which is used for interrupt injection amount correction during acceleration (usually when there is an urgent change in the intake throttle valve in the closing direction). In addition to the injection amount (in addition to the injection amount in which an interrupt injection is performed only once), we decided to perform learning correction in the same way.

However, in interrupt injection control, when ΔTp≧a1 (however, al > 110), the learning table (KADD table) is Search, seek, and seek KAD
At step D, the basic interrupt injection fl, the corrected value of T add (K A D D (Steps 80-83). However, the level βI that determines whether or not learning of interrupt injection is necessary satisfies β1≧β0.

Note that one interrupt injection is sufficient, so in order to prevent another interrupt injection, the 7-lag FADD is
= 1 (indicates that interrupt injection has already been performed)
If so, it is not executed (step 71).

Further, assuming sequential injection, one interrupt injection is sufficient, but in the case of group injection, several times may be required. It goes without saying that the present invention can be applied to this case as well.

This example also provides the same effects as the first example.

(Effects of the Invention) As explained above, in this invention, the crank angle at which the in-cylinder pressure is maximum is adopted as the air-fuel ratio equivalent amount that is not affected by changes in operating conditions, and the actual value epmax is used as a feedback control signal to set the target value. Since the learning correction is made to eliminate deviation from epmo, it is possible to reliably control the air-fuel ratio during acceleration, and at the beginning of the transient 1M, it is the same as the initial setting according to the fuel properties and engine status at that time. State is always available. As a result, it becomes possible to control the air-fuel ratio with high precision to the transient air-fuel ratio, and it is possible to obtain good drivability during the transient period by eliminating the effects of later-occurring fuel properties and changes over time.

[Brief explanation of drawings]

Figure tItI1 is a conceptual configuration diagram of this invention. FIG. 2 is a mechanical configuration diagram of the first embodiment of this invention, and FIG. 3 is a mechanical configuration diagram of the first embodiment of the invention.
Block configuration diagram of the Huntroll unit shown in the figure, fJIJ
FIG. 4 is a flowchart illustrating the contents of the operations executed within the main control circuit of this embodiment. FIGS. 5 to 8 are flowcharts illustrating the operations executed in the main control circuit of the second embodiment of the present invention. 1... Operating state detection means, 2... Cylinder pressure detection means,
3... Means for determining the transitional time, 4... Means for calculating the basic fuel injection amount, 5... Means for detecting the actual value of the crank angle at which the in-cylinder pressure becomes maximum, 6... Means for determining the in-cylinder pressure during the transient time. Means for setting a target value of the maximum crank angle, 7... Learning means, 8... Injection amount correction means, 18... Fuel injection valve, 1
9... Spark plug, 20... Air amount sensor, 21.
・・Crank angle sensor, 22・・Water temperature sensor, 24・
...Air-fuel ratio sensor, 25.25A-25D...Cylinder pressure sensor, 26A-26D...Charge amplifier, 27.
...Multiplexer, 28...Low frequency vibration detection circuit,
30...Control unit, 31...Main FLR
lJ 14 circuit. Patent applicant: Hitachi, Ltd. (1 other person)

Claims (1)

[Claims] Means for detecting the operating state of the engine, means for determining the transient state of the engine, means for calculating the basic fuel injection amount so as to achieve a target air-fuel ratio according to the operating state, and means for detecting the cylinder pressure of the engine. a means for detecting the actual value of the crank angle at which the cylinder pressure is maximum; a means for setting a target value for the crank angle at which the cylinder pressure is at its maximum during a transient period; 1. An air-fuel ratio control device for an internal combustion engine, comprising: means for learning the amount of correction of the air-fuel ratio during a transient period determined by the method; and means for correcting the amount of fuel injection during a transient period in accordance with the learned value.