JPH01271627A - Device for controlling air-fuel ratio of internal combustion engine - Google Patents

Abstract

PURPOSE:To get rid of the smoldering of a plug, etc. by gradually reducing air-fuel ratio to measure the lower limit air-fuel ratio selative value for obtaining the required air-fuel ratio lean limit and, together with a reference relative value, obtaining the correcting factor for a quantity increasing characteristic value, at the time of the calibration of a warming-up period. CONSTITUTION:At the time of the calibration of the warming-up period which is detected by a water temperature sensor 46, a control circuit 30 gradually reduces air-fuel ratio by means of a fuel injection valve 26 to detect the change in engine speed in a defined time, thereby measuring a lower limit air-fuel ratio relative value for obtaining the required air-fuel ratio lean limit of an internal combustion engine. A correction factor for a quantity increasing characteristic is obtained from this value and a corresponding reference air-fuel ratio relative value obtained from a quantity increasing characteristic which is previously set by a ROM 70. An internal combustion engine is controlled by an air-fuel ratio determined by a cooling water temperature by the sensor 46, the quantity increasing characteristic, and the correction factor. Thereby, a warming-up quantity increasing correction as the lower limit air-fuel ratio for each internal combustion engine can be performed, while making it possible to cope with secular change by carrying out the calibration from time to time.

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD 1 The present invention relates to an air-fuel ratio control device that controls the actual air-fuel ratio during warm-up operation of an internal combustion engine to be the optimum lower limit air-fuel ratio for each engine and the state of the engine. BACKGROUND OF THE INVENTION Conventionally, electronically controlled fuel injection devices have been known for controlling fuel injection time so that the air-fuel ratio takes an optimum value for internal combustion engines installed in automobiles and the like. The electronically controlled fuel injection system requires a richer air-fuel mixture during warm-up of the internal combustion engine than after warm-up.
During the warm-up period, warm-up increase correction is performed on the basic injection time. The warm-up increase correction is performed with a characteristic such that the lower the cooling water temperature, the larger the air-fuel ratio, and the characteristics of the air-fuel ratio with respect to the cooling water temperature are usually stored in a ROM or the like in a map format.

[Problems to be solved by the invention]

By the way, the above-mentioned characteristics are determined on the average based on experimental data, and are set in a ROM or the like as regular characteristics when manufacturing a vehicle or the like in which an internal combustion engine is mounted. However, the above characteristics are determined to take the air-fuel ratio that will yield the maximum output at each cooling water temperature during warm-up, but the optimal air-fuel ratio during warm-up depends on the individual It changes depending on the internal combustion engine and its operating conditions. In other words, the optimal air-fuel ratio is determined by variations in internal combustion engine manufacturing.
It varies depending on the quality of the engine oil used, the degree of carbon adhesion, etc., and changes over time. Therefore, if the above-mentioned characteristics are made constant regardless of the internal combustion engine or the operating state of the internal combustion engine, the optimum warm-up increase correction will not necessarily be performed. As a result, the air-fuel mixture becomes richer than necessary, causing plug smoldering and deterioration of emissions and fuel efficiency. The present invention has been made to solve the above problems, and its purpose is to enable optimal warm-up increase correction that improves fuel efficiency depending on each internal combustion engine. .

[Means to solve the problem]

The configuration of the invention for solving the above problem is that, when warming up the internal combustion engine, the air-fuel ratio control is performed to control the air-fuel ratio of the fuel supplied to the internal combustion engine based on a preset increase characteristic with respect to the cooling water temperature. In the apparatus, during a warm-up period of the internal combustion engine and when calibrating the increase characteristic, the rotational speed is set to a predetermined value by gradually decreasing the air-fuel ratio and measuring a change in the rotational speed of the internal combustion engine within a predetermined time. Measuring means for measuring a lower limit air-fuel ratio related value related to a lower limit air-fuel ratio in an air-fuel ratio range that maintains the following: the lower limit air-fuel ratio related value; a correction coefficient calculation means for calculating a correction coefficient for the increase characteristic from a reference air-fuel ratio related value determined from the increase characteristic; a correction coefficient storage means for storing the correction coefficient determined by the correction coefficient calculation means; The engine is characterized by comprising an air-fuel ratio correction means for controlling the internal combustion engine at an air-fuel ratio determined from the measured cooling water temperature, the increase characteristic, and the correction coefficient during warm-up operation of the engine. .

[Effect]

In the warm-up operation, for example, when a predetermined calibration start condition is satisfied or a calibration start command is given, the measuring means is activated. The measuring means measures the change in rotational speed of the internal combustion engine over a predetermined period of time when the air-fuel ratio is gradually reduced, and detects the lower limit of the air-fuel ratio, which is the lean limit value, at a stage just before the engine starts hunting. Measure a lower limit air-fuel ratio related value related to the air-fuel ratio. The difference between the lower limit air-fuel ratio-related value and the reference air-fuel ratio-related value determined from the increase characteristics at the cooling water temperature when the value is measured differs depending on the conditions of each internal combustion engine. Therefore, the correction coefficient calculation means is
A correction coefficient for correcting the increase characteristic is calculated from the measured lower limit air-fuel ratio related value and the corresponding reference air-fuel ratio related value, and the correction coefficient storage means stores this value. in this way,
In any warm-up operation after the correction coefficient has been calculated,
The air-fuel ratio is controlled by the air-fuel ratio correction means based on the air-fuel ratio determined from the measured cooling water temperature, the increase characteristic, and the lower limit air-fuel ratio related value. In this way, once the − degree calibration process is executed and the correction coefficient is calculated, the subsequent warm-up operation will be controlled at the optimal lower limit air-fuel ratio according to each engine, and the The adverse effects caused by the warm-up increase correction using the increase characteristic are improved. In particular, since warm-up operation can be controlled at the lower limit air-fuel ratio that is optimal for the internal combustion engine, fuel efficiency during warm-up operation is improved, and plug smoldering and deterioration of driving performance are prevented. Furthermore, by occasionally executing the calibration process for calculating the correction coefficients described above, it is possible to cope with changes over time in the internal combustion engine.

【Example】

The present invention will be described below based on specific examples. FIG. 1 schematically shows an example of an electronically controlled fuel injection type internal combustion engine as an embodiment of the present invention. In the figure, 10 represents the engine body, 12 represents the intake passage, 1
4 represents a combustion chamber, and 16 represents an exhaust passage. The intake air taken in through an air cleaner (not shown) is
The air flow sensor 18 detects the flow rate. The intake air flow rate is controlled by a throttle valve 20 that is linked to an accelerator pedal (not shown). Throttle valve 2
The intake air that has passed through the air is guided into the combustion chamber 14 via the surge tank 22 and the intake valve 24. The fuel injection valve 26 is actually provided for each cylinder, and is controlled to open and close in response to electrical drive pulses sent from the control circuit 3o via the line 28, and is controlled to open and close in response to electrical drive pulses sent from the fuel supply system (not shown). Pressurized fuel is intermittently injected into the intake passage opening near the intake valve 24. The exhaust gas after being burned in the combustion chamber 14 is passed through the exhaust valve 32.
The gas is discharged into the atmosphere through the exhaust passage 16 and a catalytic converter (not shown). The air flow sensor 18 is provided at the intake passageway upstream of the throttle valve 20 and detects the intake air flow rate. air 7
0 - The detection signal of the sensor 18 is sent to the control circuit 3 via the line 34.
sent to 0. The crank angle sensors 38 and 40 provided in the distributor 36 output pulse signals each time the crankshaft rotates 30° and 720°, and when the crank angle 30.
A pulse signal for each crank angle of 720 degrees is sent to the control circuit 30 via a line 42 and a pulse signal for every 720 degrees of crank angle is sent to the control circuit 30 via a line 44, respectively. An output signal from a water temperature sensor 46 that detects the engine cooling water temperature is sent to the control circuit 30 via a line 48. FIG. 2 is a block diagram showing a configuration example of the control circuit 30 shown in FIG. 1. In the figure, the air flow sensor 18, water temperature sensor 46, crank angle sensors 38 and 40, and fuel injection valve 26 are each represented by blocks. The output signals from the air flow sensor 18 and the water temperature sensor 46 are sent to an A/D converter 60 having an analog multiplexer function, and are processed by a microprocessor (MPII).
The signals are sequentially selected and A/D converted in accordance with the instruction signal from 62, resulting in two communication signals. Pulse signals every 30 degrees of crank angle from the crank angle sensor 38 are sent to the MPU via an input/output circuit (110 circuit) 64.
62 and becomes an interrupt request signal for the 30° crank angle interrupt processing routine, and also serves as a clock for incrementing a timing counter provided in the I10 circuit 64. A pulse signal from the crank angle sensor 40 at every crank angle of 72° serves as a reset signal for the timing counter. The register in the input/output circuit (110 circuit) 66 receives and receives the calculated value regarding the injection time T sent from the MP[I62, and starts counting clock pulses when the injection start timing signal is applied from the I10 circuit 64. A binary comparator and drive circuit are provided to compare the binary counter with the contents of these registers and the binary counter. The binary comparator outputs an 11" level injection pulse signal after the injection start timing signal is applied until the contents of the counter become equal to the contents of the register. Therefore, this injection pulse signal has the calculated pulse width T. This injection pulse signal is sent to the fuel injection valve 26 via the drive circuit and energizes it.As a result, an amount of fuel corresponding to the calculated pulse width T is injected.Control circuit 30 An A/D converter 60 and an I10 circuit 64 are connected to the MPU 62, which is the main component of the
and 66, random access memory (RAM) 68,
and a read-only memory (ROM) 70 are connected, and data is transferred via this bus 72. The RAM 68 is backed up by a battery, and includes a maximum speed register 680 and a minimum speed register 681 that store the maximum value Nmax and minimum value Nm1n of the rotational speed H of the internal combustion engine in the period of the pulse signal every 720 degrees of crank angle. , correction coefficient KIIL for each cooling water temperature range,
A correction coefficient memory 682 for storing the calculated injection time T, and an injection time memory 683 for storing the calculated injection time T are formed. In addition, the ROM 70 stores various data necessary for programs and arithmetic processing to be described later, and also stores the increase characteristic showing the relationship between the cooling water temperature THW and the reference increase coefficient during warm-up operation as shown in FIG. Standard increase coefficient table 70
1 is formed. Next, according to FIGS. 3, 4, and 5, MPII 62
Explain how it works. Every time a pulse signal of every 30 degrees of crank angle is input, the fifth
The program shown in the figure is started. In step 300, by reading the timer value, the crank angle is set to 30°.
You can know the time required for rotation. next step 30
2, the timer is cleared to measure the rotation time of the next 30° crank angle. Note that this timer is initially set to 0 when the engine is started. Next, step 30
4, the engine rotation speed N is calculated from the rotation time. This rotational speed N is the minimum rotational speed Nm stored in the minimum speed register 681 in step 306.
1n, and if the measured rotational speed N is smaller than the minimum rotational speed Nm1n, the rotational speed N measured in step 308 is stored in the minimum speed register 681 as the new minimum rotational speed Nm1n. Further, in step 310, the rotation speed Nll1ax stored in the maximum speed register 680 is compared in size, and if the measured rotation speed N is larger than the maximum rotation speed Nmax, the rotation speed N measured in step 312 is is stored in the maximum speed register 680 as the new maximum rotational speed Nmax. Note that the values stored in the maximum speed register 680 and the minimum speed register 681 are cleared to 0 at the beginning of engine startup, and are also cleared to 0 in synchronization with a pulse signal every 720° crank angle. Therefore, the above process is 720°
During one cycle of the crank angle, the maximum speed register 680 and the minimum speed register 681 contain 72
The maximum rotational speed Nmax and minimum rotational speed Nm1n in the 0° crank angle period are obtained. Note that in step 314, other processing that should be executed every 30 degrees of crank angle is executed. The program shown in Figure 3 is a bus signal output from the crank angle sensor 40 at every 720° crank angle.
This is a calibration processing program activated by the A signal. In step 100, it is determined whether the vehicle is in a warm-up state and stopped, and if the conditions are met, steps from step 102 onwards are executed. In step 102, the current cooling water temperature THW is read from the water temperature sensor 46. Since the correction coefficient for correcting the increase characteristic for each individual internal combustion engine depends on the cooling water temperature, the correction coefficient is determined for each temperature range of the cooling water temperature THII, and the correction is carried out for each temperature range k. The coefficient is K
Let it be WLk. Therefore, in the next step 104, the learning area of the correction coefficient KWLb is determined based on the cooling water temperature Tl1ll. When the correction coefficient K11Lk is determined by the - degree calibration process, in order to prevent the subsequent calibration process from being repeatedly executed in short cycles every time the 720 degree CA signal is input, in step 122, the 7-lag PI! NDk is set to "1". Therefore, in step 106, this flag FBNDk becomes "0".
'', it is determined whether or not to perform the calculation of lI4- on the correction coefficient. Note that all flags FEND are initialized to "O" at the engine start timing, so in the first execution cycle, step 10 is
6 is determined as YBS, and the calculation process of the correction coefficient KWL in step 108 and subsequent steps is executed. As a result, after starting the internal combustion engine, the cooling water temperature T 1111. The calculation process of the learning area correction coefficient KWLk determined by is executed only once. In the next step 108, the maximum rotational speed Nmax in the previous 72° crank angle cycle stored in the maximum speed register 680 and the minimum rotational speed Nm1n in the previous 72° crank angle cycle stored in the minimum speed register 681 are read. The difference is calculated to obtain the amount of rotational speed change ΔNE in the previous 720° crank angle cycle. Then, in the next step 110, the maximum speed register 680 is used to obtain the maximum rotation speed Nmax and minimum rotation speed Nm1n in the next 72° crank angle cycle.
and the minimum speed register 681 is cleared. Note that the maximum speed register 680 and the minimum speed register 681 are cleared as initial settings at the starting timing of the internal combustion engine. The above rotational speed change amount ΔNl! represents the short-period fluctuation amount of the rotation speed, and a large rotation speed change amount ΔNE indicates that hunting has occurred in the rotation of the internal combustion engine. Therefore, in the next step 112, it is determined whether or not the rotational speed change amount ΔNB is equal to or less than the set value 3Qrpm. However, in the first execution cycle, the rotational speed change amount ΔH is 0, so the determination in step 112 is made. is Y
ES, and in step 114, a predetermined value ΔpHL1 is subtracted from the current increase coefficient PWL, and the subtracted value is stored as the current increase coefficient FIL. Incidentally, the increase coefficient FIL is initially set to the reference increase coefficient FWLt-t corresponding to the cooling water temperature TIIH when the engine is started. Then, in the next step 116, the reference increase coefficient FWLt,t corresponding to the current cooling water temperature THII is read from the reference increase coefficient table 701, and the current increase coefficient FWL
The correction coefficient K is determined by the ratio to the standard increase coefficient FWL.
WLk is calculated. Then, in the next step 118,
The correction coefficient KWLk is stored in the correction coefficient memory 682 of the RAM 68, and this program ends. and,
After the correction coefficient KIIL is determined, the air-fuel ratio is determined by the reference increase coefficient PlILt-t determined by the cooling water temperature THII at that time according to the program shown in FIG.
and the corresponding correction coefficient K11Lh. Note that the correction coefficient KWL is initially set to "1" in a state where the calibration process has not been executed for -degrees, so the initial air-fuel ratio when the calibration process is executed for the first time is equal to the cooling water temperature T.
It is determined by the reference increase coefficient FlIL+-t corresponding to l1ll. The program shown in FIG. 3 is executed every time an interrupt by the 720° CA signal occurs, and the determination in step 106 is YES, and the determination in step 112 is YES while the short-period rotational speed change amount ΔNil is small. Then, in step 114, the current increase coefficient PwL is decreased, and step 1
16 is a correction factor! ILk is updated, step 118
The value is stored in the correction coefficient memory 682. In this way, while the short-period rotational speed change amount ΔNB is small,
As a result of *Lh being gradually decreased in the increase coefficient FIIL and the correction coefficient, the air-fuel ratio gradually decreases. As a result of the air-fuel ratio gradually decreasing, the rotational speed N of the internal combustion engine
However, if the air-fuel ratio becomes too lean, the rotational speed of the internal combustion engine will hunt, leading to engine stall. Therefore, it is necessary to detect this hunting precursor phenomenon, and this detection is performed by determining the magnitude of the short-period rotational speed change amount ΔNB. In other words, when the air-fuel ratio is gradually decreased, the amount of rotational speed change ΔN (! is 3Qr
It becomes larger than pm. Rotation speed change amount ΔNI! is 3O
rpm, the determination in step 112 becomes No, and the process moves to step 120, where the predetermined value Δ1lIIL2 is calculated from the increase coefficient FIIL in the previous execution cycle.
By setting the added value as the increase coefficient FWL in the actual running cycle, a value related to the lean limit of the air-fuel ratio, that is, the lower limit air-fuel ratio is determined. Then, the process moves to step 122 to indicate that the increase factor has been determined for calibration by 7 lags Fl! NO, is set to "1". Then, in the next step 116, the reference increase coefficient FII
A correction coefficient KIILk for calibrating the increase characteristic is calculated using the increase coefficient FIILO ratio related to the lower limit air-fuel ratio obtained in the actual running cycle for Lt, and the value is stored in the correction coefficient memory 682 in step 118. Ru. As mentioned above, each time the program shown in FIG. 3 is executed during the calibration processing period of machine operation, the correction coefficient KIIL
k changes in a decreasing manner and takes a constant value with a correction coefficient corresponding to the lower limit air-fuel ratio. In this way, while the correction coefficient KWLk is determined, a program for determining the injection time shown in FIG. 4 is activated every 360° or 720° crank angle. In step 200, the intake air amount Q/N per revolution is calculated from the current intake air amount Q input from the air flow sensor 18 and the rotational speed N, and a proportionality constant proportional to the stoichiometric air-fuel ratio is multiplied by 1. Then, the reference injection time TP necessary to obtain the stoichiometric air-fuel ratio is calculated. And step 2
01, the reference increase coefficient FilLt- is read from the correction coefficient memory in accordance with the current cooling water temperature THW. Next, the process moves to step 202, and the reference increase coefficient F
By multiplying IILs-t by the correction coefficient KWLm stored in the correction coefficient memory 682 at that time, an increase coefficient AWL for determining the injection time is calculated. Then, in step 203, the increase coefficient AIIIL is added to the reference injection time TP.
The injection time T is determined by multiplying by a correction coefficient h%F, which is determined based on other factors, and the value is stored in the injection time memory 683 in step 204. Then, based on the value, fuel is injected for the determined injection time T at the optimum injection timing by another program. In this way, the actual air-fuel ratio is changed by determining the injection time T. During the calibration processing period of the warm-up period, the air-fuel ratio gradually decreases, but in the actual warm-up period after the calibration processing is completed, it is controlled at the final value, that is, the lower limit air-fuel ratio. . In the above embodiment, the lower limit air-fuel ratio-related value and the reference air-fuel ratio-related value are embodied as an increase coefficient proportional to the air-fuel ratio, and among them, the reference air-fuel ratio-related value in particular is a standard determined from a preset increase characteristic. It is specified as an increase coefficient. Further, the increase characteristic is a characteristic related to the increase coefficient, and a set value common to internal combustion engines obtained from the increase characteristic is the reference increase coefficient. Therefore, the increase coefficient shown in the above embodiment is just an example, and various values that change in relation to the air-fuel ratio and the pond fuel ratio are adopted as the lower limit air-fuel ratio-related value and the reference air-fuel ratio-related value. Is possible. Furthermore, in the above embodiment, the air-fuel ratio is determined by correcting the increase characteristic with the correction coefficient during actual warm-up operation, but the increase characteristic is corrected with the correction coefficient during calibration and then the corrected increase characteristic is stored. Alternatively, during actual warm-up operation, the air-fuel ratio may be determined according to the corrected increase characteristics. Further, in the above embodiment, the function of the measuring means is mainly realized by the programs shown in FIGS. 3, 4, and 5, which are executed during the calibration processing period until a certain correction coefficient is determined.
The correction coefficient calculation means 9 function calculates the amount of change in rotational speed in a short period Δ
The function of the correction coefficient storage means is realized in step 116 of the execution cycle when N11l is detected to be 3 Orpm or more, and the function of the correction coefficient storage means is realized in step 118 of the same execution cycle and the correction coefficient memory 682. This is realized by the program shown in FIG. 4 that is executed.

【Effect of the invention】

The present invention measures a lower limit air-fuel ratio-related value at which the required air-fuel ratio lean limit of an internal combustion engine can be obtained by gradually decreasing the air-fuel ratio and detecting changes in rotation speed within a predetermined time during calibration processing during a warm-up period. Then, a correction coefficient for the increase characteristic is determined from the measured lower limit air-fuel ratio related value and a corresponding reference air-fuel ratio related value obtained from the preset increase characteristic,
During warm-up operation, the internal combustion engine is controlled using the air-fuel ratio determined from the measured cooling water temperature, increase characteristics, and correction coefficient, so the lower limit air-fuel ratio and It becomes possible to perform a warm-up increase correction, and by occasionally executing a calibration process, it is possible to cope with changes over time. Therefore, it is possible to improve drivability during warm-up operation, eliminate defects such as plug smoldering, and improve emissions and fuel efficiency.

[Brief explanation of the drawing]

FIG. 1 is a mechanical diagram showing the mechanical configuration of an air-fuel ratio control device according to a specific embodiment of the present invention. FIG. 2 is a block diagram showing the electrical configuration of the air-fuel ratio control device. FIG. 3, FIG. 4, and FIG. 5 are flowcharts showing the processing procedure of the CPU used in the air-fuel ratio control device. 6th
The figure is a characteristic diagram showing preset increase characteristics. 10...Engine body 12--Intake passage 14゛°-
Combustion chamber 16" - Exhaust passage 18 ° Air flow sensor 20 Throttle valve 22 Pa Surge tank 24 Intake valve 26 Fuel injection valve 30...
°Control circuit 36...distributor 38.40
... Clann angle sensor patent applicant Nippondenso Co., Ltd. Representative Patent attorney Osamu Fujitani Figure 4 Figure 6

Claims (2)

[Claims] (1) In an air-fuel ratio control device that controls the air-fuel ratio of fuel supplied to the internal combustion engine based on a preset increase characteristic regarding cooling water temperature during warm-up of the internal combustion engine, By gradually decreasing the air-fuel ratio and measuring the change in rotational speed of the internal combustion engine over a predetermined time period, when calibrating the increase characteristic, the lower limit air in the air-fuel ratio range in which the change in rotational speed is maintained at a predetermined value or less is determined. a measuring means for measuring a lower limit air-fuel ratio related value related to a fuel ratio; a reference air-fuel ratio related value determined from the lower limit air-fuel ratio related value and the increase characteristic at the cooling water temperature at the time of measuring the lower limit air-fuel ratio related value correction coefficient calculation means for calculating a correction coefficient for the increase characteristic from the value; correction coefficient storage means for storing the correction coefficient calculated by the correction coefficient calculation means; An air-fuel ratio control device for an internal combustion engine, comprising an air-fuel ratio correction means for controlling the internal combustion engine with an air-fuel ratio determined from the cooling water temperature, the increase characteristic, and the correction coefficient. (2) The lower limit air-fuel ratio related value and the correction coefficient are determined according to a plurality of the cooling water temperatures, and the air-fuel ratio correction means relates the reference air-fuel ratio using the correction coefficient corresponding to the measured cooling water temperature. An air-fuel ratio control device for an internal combustion engine according to claim 1, characterized in that the air-fuel ratio control device for an internal combustion engine corrects the value.