JPS6090940A - Air-fuel ratio controlling apparatus - Google Patents

Abstract

PURPOSE:To raise the accuracy of air-fuel ratio control, by determining a target exhaust temperature on the basis of the intake temperature and the conditions of engine operation, and feed-back controlling the air-fuel ratio to keep the exhaust temperature of an engine at said target exhaust temperature. CONSTITUTION:In operation of an engine, a target base exhaust temperature TEMH is determined from the air-flow rate QA and the engine speed N in a taget-value determining means 21, and then a target exhaust temperature TEM is obtained by correcting the target base exhaust temperature TEMH on the basis of the cooling-water temperature TW and the intake temperature TA representing the conditions of engine operation. Thereafter, comparison is made between the target exhaust temperature TEM and the actual exhaust temperature TE in a comparing means 22, and a base pulse width TPO is calculated in a base pulse width calculating means 23 on the basis of the air-flow rate QA and the engine speed N. Further, a required pulse width TI is obtained by correcting the base pulse width TPO by use of a correction factor or the like that is determined by a correction factor determining means 25 according to the result of the above comparing means 22 and a control zone judging means 24 which judges whether fuel supply is interrupted.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an air-fuel ratio control device for an engine, and particularly to an air-fuel ratio control device that utilizes the correlation between the air-fuel ratio and the exhaust gas temperature.

(Prior art) An example of a device that accurately controls the air-fuel ratio of the intake air-fuel mixture of an engine is the one described in "R E CCS Technical Manual - L Series Engine" (published by Nissan Motor Co., Ltd., June 1970). It has been known. This air-fuel ratio control device corrects the fuel supply amount calculated based on the operating state of the engine based on the output of an oxygen sensor that detects the oxygen concentration in the exhaust gas at the stoichiometric air-fuel ratio to adjust the air-fuel ratio of the engine intake mixture. is controlled to the stoichiometric air-fuel ratio.

However, in such an air-fuel ratio control device,
The air-fuel ratio can only be controlled to the stoichiometric air-fuel ratio, and the lean air-fuel ratio control that has been desired in recent years cannot be performed.

Therefore, the present applicant has previously developed an air-fuel ratio control device (Japanese Patent Laid-Open No. 58-9863) that uses the correlation between the air-fuel ratio and the exhaust temperature.
We proposed Publication No. 7 (see 4). This air-fuel ratio control device stores the correlation between exhaust temperature and air-fuel ratio in advance and stores the control target exhaust temperature in each operating state (indicated by the engine speed and negative 4!J), and stores the correlation between the engine speed and the load. This goal υ1 based on
The air temperature is read out and compared with the actually detected exhaust gas temperature, and the air-fuel ratio is feedback-controlled so that the detected exhaust gas temperature becomes the target exhaust temperature.

However, since this air-fuel ratio control device sets the target exhaust temperature based on engine speed and load, the exhaust temperature fluctuates due to the influence of changes in intake air temperature, and the air-fuel ratio cannot be controlled accurately. There was a risk that they would not be able to do so.

(Purpose of the Invention) Therefore, the present invention sets a target exhaust temperature based on the operating state of the engine and the intake air temperature, and performs feedback control of the air-fuel ratio so that the engine exhaust temperature becomes the target exhaust temperature. The purpose is to improve the accuracy of fuel ratio control.

(Configuration of the Invention) The configuration of the present invention will be explained based on the overall configuration diagram shown in FIG.

The operating state of the engine is detected by the operating state detection means, and the temperature of the intake air of the engine (including both intake air and a mixture of intake air and fuel) is detected by the intake air temperature detection means 7.

Then, the target value setting means 21 sets a target exhaust temperature that has a correlation with the air-fuel ratio based on the operating state of the engine and the intake air temperature G. The exhaust temperature of the engine is detected by the exhaust temperature detection means 9, and the air-fuel ratio is controlled by the air-fuel ratio control means 27 so that the engine exhaust temperature becomes the target exhaust temperature.

(Example) Embodiments of the present invention will be described below based on the drawings.

2 to 10 are diagrams showing one embodiment of the present invention, and this embodiment is applied to a vehicle that performs a swerving motion when no special engine driving force is required for deceleration or stopping.

First, to explain the configuration, in FIG. 2, I is an engine body, and an intake pipe 2 and an exhaust pipe 3 are attached to the engine body 1. The intake pipe 2 includes an air cleaner 4, an air flow meter 5, a throttle valve 6, and an intake air temperature sensor 7.
A fuel injection valve 8 is also removed, and air purified by an air cleaner 4 is introduced into the engine body 1 through the intake pipe 2. The air flow meter 5 detects the air flow IQA regulated by the throttle valve 6, and the intake air temperature sensor (intake air temperature detection means) 7 detects the temperature 'I'' of the air (intake air) introduced into the engine. Fuel is injected into this intake air from the fuel injection valve 3, and the engine body 1
is introduced as a mixture. Note that the intake air temperature sensor 7 may be provided downstream of the fuel injection valve 8 to detect the temperature of the air-fuel mixture, and in this case, the intake air indicates the air-fuel mixture. On the other hand, an exhaust temperature sensor (exhaust temperature detection means) 9 is attached to the exhaust pipe 3 to detect the exhaust temperature 'I''I3. The output signal, the output signal of the intake air temperature sensor 7 that displays the intake air temperature TA, and the output signal of the exhaust temperature sensor 9 that displays the exhaust air temperature TE are input to the control unit IO,
0 further includes a signal from a rotation speed detection means (not shown) for detecting the engine rotation speed N, a signal from a water temperature detection means for detecting the temperature TW of the cooling water of the engine 1, and a signal indicating the terminal voltage VB of the battery. etc. are entered.

Control unit] 0 is an A/D converter [11, I
10 ports 12, MPU 13, ROM 14, RA
Consists of M15 and injection valve drive circuit 16,
Of the signals input to the control unit 10, signals input as analog values are converted to digital values by the A/D converter 11 and input to the I10 port 12, and signals input as digital values are directly input to the I10 port 12. is input. MPU] 3 reads necessary external data from the I10 board 12 according to the program written in the ROMI 4, performs arithmetic processing while exchanging data with the RAM 15, and executes calculations as necessary. The correspondingly processed data is output to the I10 boat 12. The injection valve drive circuit 16 outputs a drive pulse for driving the fuel injection valve 8 based on the signal from the 110 boat 12.

Next, the effect will be explained.

The air-fuel ratio A/F has a close correlation with the engine operating stability S, fuel consumption rate F, and exhaust temperature TE in a certain operating state. FIG. 3 shows these relationships when both the intake air amount and engine speed are constant. Therefore, exhaust temperature '1゛E and air-fuel ratio A/ ]
By clarifying the correlation in all operating conditions, the air-fuel ratio A can be determined based on the exhaust temperature ゛1゛E.
/F can be controlled.

Therefore, in this embodiment, the intake air flow rate QA and the engine speed N are mainly used as factors for displaying the operating state. I''IEM is set, and the air-fuel ratio A/F is controlled by controlling the fuel injection amount so that the actual exhaust gas temperature TE becomes the target exhaust gas temperature TEM.

A block diagram of signal processing in this control unit node IO is shown in FIG. 4. That is, first, the target value setting means 2I determines the basic target exhaust temperature TEMH based on the air flow rate QA and the engine speed N, and then sets the basic target exhaust temperature TEMH to the cooling water temperature TW and the intake air temperature TA, which indicate the operating state of the engine. The target exhaust gas temperature TEM is set by performing correction based on the above. Next, this target exhaust temperature TEM is compared with the actual engine exhaust temperature TE by the comparing means 22.
Compare with. On the other hand, in the basic pulse width calculation means 23, the fuel injection valve 8 is
The basic pulse width "I'PO" of the drive pulse outputted to the control zone is set, and the control zone determining means 24 determines whether the fuel is being adjusted or the accelerator is being fully opened.Then, the correction coefficient is set. Means 5 is the comparison means 2
2 and the results of the control zone discriminating means U, it is determined whether or not to perform feed hack control based on the exhaust gas temperature TE, and a correction coefficient is calculated. is multiplied by the correction coefficient set by the correction coefficient setting means 25 and also by a correction coefficient based on the cooling water temperature, etc., and further corrects the operation delay of the fuel injection valve 8 to calculate the pulse width TI of the drive pulse. ing.

The comparison means 22, the basic pulse calculation means, the control zone discrimination means 24, the correction coefficient setting means and the pulse width calculation means 26 are used to determine whether the engine exhaust temperature TE is the target exhaust temperature T.
Air-3B ratio control means 2 that controls the air-fuel ratio to achieve EM
7.

Next, the signal processing within the control unit 10 will be explained in more detail based on the flowcharts shown in FIGS. 5-7.

First, the setting of the target exhaust temperature TEM and the target exhaust temperature T
A comparison between EM and the detected engine exhaust temperature TE will be explained based on the flowchart of FIG. In addition,
In FIG. 5, S and ~Sob indicate each step of the flow, and this flow runs, for example, every 10 (ms). In step S1, the air flow rate QA input to the I10 port 12, [1 rotation speed N, intake air temperature TA, cooling water temperature TW]
and exhaust temperature TE, and in step S2, RO is adjusted in advance based on the air flow rate QA and engine speed N.
Look up the basic target exhaust temperature TEMH from the data table stored in M14. For example, in the case of A/F = 22 listed as the control target air-fuel ratio in Fig. 3, this data table is given as shown in Fig. 8, and the air flow MQA and engine speed N are given as the operating state. Then, the basic target exhaust gas temperature TEMH is determined. This basic target exhaust gas temperature TEMH corresponds to the control target air-fuel ratio (A/F=22 in the case of FIGS. 3 and 8) in the operating state. Next, in step S3, an intake air temperature correction coefficient KTA is looked up from a data table stored in advance in the ROM 14 based on the intake air temperature TA, and in step S'4, the second basic target exhaust temperature TEMH2 is determined by the following equation. Calculate.

TEMH2=-1"EMHxKTA----(11) The data table that gives this intake air temperature correction coefficient KTA is
For example, given as shown in Fig. 9, ρ temperature correction coefficient K
i' A becomes smaller as the intake air temperature TA becomes lower, and becomes larger as the intake air temperature TA becomes higher, starting from about 40°C. Therefore, the second basic target exhaust temperature TEMH2 is:
The lower the intake air temperature TA is than about 40°C, the basic target exhaust temperature i" E M H is set lower, and the higher the intake air temperature TA is above about 40°C, the basic target exhaust temperature is set.
The temperature is set higher than FE M II. The fact that the second basic target exhaust temperature T E M H2 is set lower than the basic target exhaust temperature i' E M II is based on the relationship between the air-fuel ratio A/F and the exhaust temperature TE in Fig. 3. As is clear, this means that the exhaust temperature TE is set at an air-fuel ratio on the leaner side than the control target air-fuel ratio, and the second basic target exhaust temperature T IJ M H2 is set to a temperature higher than the basic target exhaust temperature TEMH. This means that the exhaust temperature TE is set at an air-fuel ratio that is closer to the control target air-fuel ratio. As a result, the intake air density changes due to the direct change in the exhaust temperature due to the change in the intake air temperature TA, and the air-fuel ratio A
It is possible to correct the change in exhaust gas temperature TE caused by the change in /F. Next, in step s5, a water temperature correction coefficient KTW is looked up from a data table stored in advance in the ROM 14 based on the cooling water temperature TW, and in step s9, a target exhaust gas temperature TEM is calculated using the following equation.

TEM = TEMH2 Fuel ratio A/F
When the cooling water temperature TW is lower than approximately 80"C, it becomes smaller, and as it becomes higher, it becomes larger. However, the water temperature correction coefficient KTW The temperature will rise to 40℃ again.
When the value becomes lower than , the value for correcting the air-fuel ratio A/F to a constant value (
(indicated by a broken line in FIG. 1O) is set to 116, which is larger than Therefore, cooling water/1! ! ] ゛When W is low,
When it is high, the air-fuel ratio A/F is controlled to the Lynch side compared to the target air-fuel ratio LL, and the stability of the engine is improved. And step S? , the target exhaust temperature TEM and the engine exhaust temperature TE detected by the exhaust temperature sensor 9 are set to 1.
By comparison, when 'T' E M <i" E, the flag i" F L G is set at stay 7" S8 (
TFLG=1), 1' E M≧i' When E,
In step s9, lower the flag T I='L G (
TFLG=0), 7 rasog 'f' F L G is 7J1
4 Air temperature TE is higher than the target exhaust temperature TEM, but it is lower than the target exhaust temperature TEM.
= 1 indicates that the air-fuel ratio A/F is leaner than the target air-fuel ratio Ll, and "F L G = 0 indicates that it is leaner."

As described above, the setting of the target exhaust gas temperature TBM and the comparison of the target exhaust gas temperature TEM and the actual exhaust gas temperature TE are completed. A value is set, and it is determined whether or not the sudden drop in exhaust gas temperature TE is within this allowable value range, and the subsequent air-fuel ratio control method is changed. That is, in step sxl of the flowchart in FIG. 5, the allowable fluctuation value MDTB of the actual exhaust gas temperature TE is looked up from the data table previously stored in the ROM 14 based on the engine speed N and the intake air flow rate QA. up, step S
In it, the value obtained by smoothing the old data of exhaust gas temperature TE (old exhaust temperature) TEO and the exhaust temperature T in this process
From E, the change 1DTE of the sudden drop in exhaust gas temperature is calculated using the following equation.

DTE=TEO-TE~------(31) The permissible fluctuation value MDTE for the sudden drop in exhaust gas temperature TE is given, for example, as a value indicated by diagonal lines in FIG. 3.And,
In step 312, the amount of change DTE is set to the allowable variation value M
Compared with DTE, when DTE>MDTE, temp S
Set the exhaust temperature sudden change flag DTFLG at +3 (1
) TFI-G=1), l)'rEs; Ml) TE, step S14. Sudden exhaust temperature change flag D1”
Increase FL G by 1 (DTFLG=0) Step S,
! Proceed to −. The exhaust temperature sudden change flag DTFLG is a flag that indicates whether or not the exhaust temperature 1゛E has suddenly decreased. DTFLG=1 indicates that the exhaust temperature 1゛E has suddenly decreased, and DTFLC ;-〇 indicates that the exhaust temperature decrease of 1゛E is not rapid. Step S
tq, change 1 in step S11] D T
The exhaust gas temperature TE used to calculate E is calculated according to the following formula based on the old exhaust temperature TEOB from the previous process and the current exhaust temperature TF. Store T fE O in the RAM 15.

T I E O = “f’ IE O B x 7 / 8
+ T Ex l / 8 ------- (41 Zunawara, this 11'' exhaust temperature TEO is a weighted calculation from the old exhaust temperature 1' IE 0 +3 from the previous processing and the current exhaust temperature TE) It is.

Next, we will discuss the calculation process of the correction coefficient for feed-hack control of the air-fuel ratio based on the comparison results between the target exhaust temperature TEM and the actual exhaust temperature TE and the comparison results between the permissible fluctuation value MDTE and the amount of change DTE. , will be explained based on the flowchart of FIG. This flow is performed once per crankshaft rotation of the engine l, and is performed from 2S□ to 2S in Fig. 6.
7 shows each step of the flow. First, in step 2S, it is determined whether or not to perform feed hack control.
This is determined by whether or not the fuel is in a full-open position, or whether the accelerator is fully opened. Since this is the time when fuel increase correction is being performed, feed puncture control is not performed. Fuercasoto has not been performed and K
When MR=0, the process advances to the next step 2S2 to perform feedhack control. In step 2S2, the exhaust temperature sudden change flag DTFLG is set (DTFLG-
1) or not (DTFLG=0), and 1) T F
When L G = 1, in step 233, 1
) to the feedbank correction coefficient for 11th processing!・"B
Feed hack by the following formula based on 13? Calculate the di stop coefficient KF13 and proceed to step 2S3, D T
When F L G = O, proceed directly to step 2S4.
Proceed to.

KFB=KFBB+KFBBxO, 03・---(5)
Of course, the exhaust gas temperature TE of engine 1 is within the permissible fluctuation value M I)
“r E” When the fee decreases rapidly to 2, the fee 1
- The hack feed correction coefficient KFB is set to a value 3% larger than the feed hack correction coefficient KFBB used in the previous processing to lynch the air-fuel ratio and improve the stability of the engine. That is, in 2S-4, it is determined whether the flag i"FLG is set or not by 1', and TFLG=1 is determined by 1'.
When = 1, in step 2S, the feed bank correction coefficient K F B is calculated according to 2〇, and 1''
When F L G = O, in step 23G, the feedback correction coefficient KFB is calculated according to equation (7).
Calculate Step 2S・? Proceed to.

KFB=KFBB-KFBBXO,0L----(6
1KFB=KFBB+KFBBxO, 01---17
1, that is, when TFLG=1, the actual exhaust gas temperature TE
is higher than the target exhaust temperature TEM (when the air-fuel ratio A/F is closer to the target air-fuel ratio), so the feed bank correction coefficient KFB is set to a value 1% smaller than the feed bank correction coefficient KFEB used in the previous process. and air fuel ratio A/
F is corrected to the lean side, and when TFLG=0, conversely, it means that the air-fuel ratio A/F is leaner than the target air-fuel ratio, so the feedback correction coefficient KFB is set to 1 from the feed bank correction coefficient KFEB used in the previous process. % to a larger value to correct the air-fuel ratio A/F to the Lynch side. And step 2S.

In this step, the feedback correction coefficient KFB calculated in the above process is stored in RAM15, and the calculation process of the feedbank correction coefficient KFB is completed.

Next, the calculation process of the pulse width of the drive pulse output to the fuel injection valve 8 based on the feed hack correction coefficient KFB calculated by the above-described process will be explained based on the flowchart of FIG. 7. This flow is, for example, 10
It is performed every m5, and 33. in Figure 7. ~3SG indicates each step of the flow. First, step 33. , the basic pulse width TPO is the air flow rate QA and the engine speed N
From this, calculation is performed using the following equation, and the process proceeds to step 3S2.

T P O= K (QA/N) - [81 However, I(
: In constant step 3S2, it is determined whether the accelerator full-open correction coefficient KMR is positive or not. When KMR=0, in step 3S3, the second basic pulse width TPO2 is calculated using the formula (2), and then in step 3S-4 The injection pulse width TP is expressed by the formula α
O), and when KMR=1, step 3S
In step s, the injection pulse width TP is calculated using equation (11), and the process proceeds to step 33Q.

T P O2= T P Ox K F B -----
-(9)TP=TPO2XCOEF---QlTP
=TPOXCOEFX (KMR+1.0)−・−(1
1) However, C0EF is a correction coefficient that performs various corrections such as correction and starting correction based on the cooling water temperature.

That is, when KMR=0, the full throttle correction is not performed, and the above-mentioned feed bank correction coefficient KF
The injection pulse width TP is calculated based on B so that the air-fuel ratio A/F becomes the target air-fuel ratio. When KMR=1,
This is when the fuel injection amount is increased by full throttle correction, and the air-fuel ratio A/F is adjusted based on the full throttle correction coefficient KMH.
The injection pulse width T is set so that F is richer than the target air-fuel ratio.
Calculating P. Then, in step 38G,
As shown in the following equation, the voltage correction pulse width TS is added to the injection pulse width TP to obtain the pulse width TI.

T I = T'P + TS ------- (12) This voltage correction pulse width TS is a pulse width for correcting the operation delay with respect to the drive pulse of the fuel injection valve 8, and the voltage applied to the fuel injection valve 8 is・Set based on note voltage.

That is, the voltage correction pulse width T''S is used to correct changes in the effective valve opening time of the fuel injection valve 8 with respect to the drive pulse, and the fuel injection valve 8 injects fuel into the intake pipe 2 for a period of the injection pulse width TP. Inject inside.

In this way, the target exhaust temperature TEM is set based on the operating state of the engine 1 and the intake air temperature TA, and the air-fuel ratio is determined to be rich or lean depending on whether the actual exhaust gas temperature TE is higher or lower than the target exhaust temperature TEM. Since the air-fuel ratio of the air-fuel mixture introduced into the engine 1 can be controlled by feedbank by determining the air-fuel ratio, the air-fuel ratio A/F can be precisely controlled to the target air-fuel ratio without being affected by fluctuations in the intake air temperature TA. be able to. When the exhaust gas temperature TE suddenly drops to a predetermined value M D TE or more, the air-fuel ratio A/F can be corrected to the rich side, so the stability of the engine 1 can be improved.

(Effects of the Invention) According to the present invention, the target exhaust temperature can be set based on the operating state of the engine and the intake air temperature, and the influence of the intake air temperature on the exhaust temperature can be corrected, so the air-fuel ratio can be adjusted over a wide range. The air-fuel ratio can be precisely controlled to the target air-fuel ratio.

Further, in the above embodiment, when the exhaust gas temperature suddenly decreases, the air-fuel ratio can be controlled to a rich air-fuel ratio, so the stability of the engine can be improved.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of the present invention, and FIGS. 2 to 10 are diagrams showing one embodiment of the air-fuel ratio control device of the present invention.
The figure is an overall schematic diagram, Figure 3 is a diagram showing the relationship between air-fuel ratio, engine operation stability, exhaust temperature, and fuel consumption rate, Figure 4 is a block diagram showing its effect, and Figure 5.6.7 Figure 8 is a flowchart showing the effect, Figure 8 is a diagram showing an example of the target exhaust temperature given by the engine speed and air flow rate, Figure 9 is a diagram showing the relationship between intake air temperature and intake air temperature correction coefficient,
FIG. 10 is a diagram showing the relationship between cooling water temperature and cooling water temperature correction coefficient. 7---Intake air temperature detection means, 9---Exhaust temperature detection means, 211'' target value setting means, 27---Air-fuel ratio control means. Patent Applicant Nissan Motor Co., Ltd. Representative Patent Attorney Arigagun Part 5 Figure 5 S12 Hitya DTFE) t'1DTE D-choji≦, MD-choe S14 ClTl:1Le-=(7C+rFL%=I
5135 7 eof3 ND

Claims (2)

[Claims] (1) Operating state detection means for detecting the operating state of the engine;
an intake air temperature detection means for detecting the intake air temperature of the engine; an exhaust temperature detection means for detecting the exhaust gas temperature of the engine; a target value setting means for setting a target exhaust temperature based on the operating state of the engine and the intake air temperature; JJ[An air-fuel ratio control device characterized by comprising: an air-fuel ratio control means for controlling an air-fuel ratio so that the air temperature becomes a target exhaust gas temperature. (2) In the air-fuel ratio control device according to claim 1, the air-fuel ratio control means sets an allowable variation value that allows a sudden drop in exhaust gas temperature of the engine, and the exhaust temperature exceeds the allowable variation value. An air-fuel ratio control device that controls the air-fuel ratio to the Lynch side when the air-fuel ratio suddenly decreases.