JP3789336B2 - Air-fuel ratio feedback control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air-fuel ratio feedback control apparatus for an internal combustion engine, and more particularly to an apparatus that performs air-fuel ratio feedback control so that combustion does not become unstable when the internal combustion engine is cold.
[0002]
[Prior art]
In general, in an air-fuel ratio feedback control device for an internal combustion engine, an air-fuel ratio sensor is used to detect the air-fuel ratio of the internal combustion engine based on the oxygen concentration in the exhaust gas, and the air-fuel ratio acting in a direction to bring the detected air-fuel ratio closer to the target air-fuel ratio. Air-fuel ratio feedback control is performed in which an air-fuel ratio correction coefficient is obtained and the fuel injection time of the fuel injection valve is corrected using the air-fuel ratio correction coefficient.
[0003]
In such an air-fuel ratio feedback control apparatus, air-fuel ratio control appropriately corresponding to various operating states of the engine is performed, and learning control for improving the accuracy of the air-fuel ratio is also performed at the same time.
[0004]
For example, Japanese Patent No. 3065176 discloses an air-fuel ratio control device for an engine that can sufficiently improve the accuracy of air-fuel ratio learning control even when the cold purge operation temperature is set low.
[0005]
[Problems to be solved by the invention]
In the air-fuel ratio feedback control apparatus as described above, when the internal combustion engine is started, feedback control is started immediately after the air-fuel ratio sensor is activated, and it is considered whether combustion in the internal combustion engine is normally performed. May not have.
[0006]
However, especially when the combustion chamber of the internal combustion engine is at a relatively low temperature, such as when starting from a cold state, the oil drops due to the clearance, and the oil component or fuel entering the combustion chamber of the engine burns. Otherwise, it is exhausted as it is and may adhere to the detection part of the air-fuel ratio sensor. In such a case, the air-fuel ratio sensor recognizes the rich state regardless of the actual air-fuel ratio, and feedback control is performed based on this detected air-fuel ratio, so the fuel injection amount is reduced and the air-fuel ratio becomes lean. It may become too much. Further, if the air-fuel ratio is learned in such a state, a value based on erroneous detection is learned, which is not preferable.
[0007]
In view of the above problems, an object of the present invention is to provide an air-fuel ratio control apparatus that can avoid a state in which the feedback air-fuel ratio becomes lean when the internal combustion engine is started.
[0008]
[Means for Solving the Problems]
An air-fuel ratio feedback control apparatus according to the present invention includes an air-fuel ratio detection unit that detects an air-fuel ratio of an internal combustion engine, an air-fuel ratio setting unit that sets a target air-fuel ratio according to an operating state of the internal combustion engine, and the target air-fuel ratio. Air-fuel ratio correction coefficient calculating means for calculating an air-fuel ratio correction coefficient for feedback control of the air-fuel ratio based on the detected air-fuel ratio, and a lower limit value of the air-fuel ratio correction coefficient according to the temperature at the start of the internal combustion engine And a lower limit limiting means for limiting.
[0009]
According to the present invention, the lower limit value of the air-fuel ratio correction coefficient is limited according to the temperature at the start of the internal combustion engine, so that combustion is not normally performed and the air-fuel ratio detection means erroneously detects the air-fuel ratio. However, combustion does not become unstable because the air-fuel ratio becomes too lean. The air-fuel ratio detecting means is an oxygen sensor such as a proportional oxygen concentration sensor.
[0010]
In another embodiment of the present invention, the lower limit value is limited so as to continue for a period set in accordance with the temperature at the start of the internal combustion engine.
[0011]
According to this aspect, the lower limit value of the air-fuel ratio correction coefficient is limited only for a period set according to the temperature at the start of the internal combustion engine, so that the temperature of the internal combustion engine rises and combustion is performed normally. Then, the calculation of the air-fuel ratio correction coefficient is performed as usual without any restriction.
[0012]
In still another embodiment of the present invention, the air-fuel ratio feedback control device learns the air-fuel ratio correction coefficient to calculate a learning correction term, and calculates the learning correction term during the period. A prohibition means for prohibiting is further provided.
[0013]
According to this aspect, since the calculation of the learning correction term is prohibited during the period set in accordance with the temperature at the start of the internal combustion engine, the air-fuel ratio based on the erroneously detected air-fuel ratio when combustion is not normally performed. Learning the fuel ratio correction coefficient can be avoided.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0015]
FIG. 1 is a diagram showing an overall configuration of an internal combustion engine (hereinafter referred to as “engine”) and its control device including an air-fuel ratio feedback control device according to an embodiment of the present invention. A throttle valve 3 is arranged in the middle of the intake pipe 2 leading to the engine 1. A throttle valve opening (THA) sensor 4 is connected to the throttle valve 3, and an electric signal corresponding to the opening of the throttle valve 3 is output and supplied to an electronic control unit (hereinafter referred to as "ECU") 5. The configuration of the ECU 5 will be described later.
[0016]
The fuel injection valve 6 is provided in each cylinder between the engine 1 and the throttle valve 3 and slightly upstream of an intake valve (not shown) of the intake pipe 2. The fuel in the fuel tank 20 is discharged from a fuel pump (not shown) and supplied to the fuel injection valve 6. The fuel injection valve 6 is electrically connected to the ECU 5, and the valve opening time of the fuel injection is controlled by a signal from the ECU 5. The injected fuel is mixed with the air from the intake pipe 2 to become an air-fuel mixture and supplied to the engine 1.
[0017]
An intake pipe pressure (PB) sensor 8 and an intake air temperature (TA) sensor 9 are attached to the intake pipe 2, and the pressure and intake temperature in the intake pipe are detected and supplied to the ECU 5 as electrical signals.
[0018]
An engine coolant temperature (TW) sensor 10 mounted on the main body of the engine 1 includes a thermistor and the like, detects the engine coolant temperature, outputs a corresponding temperature signal, and supplies the temperature signal to the ECU 5.
[0019]
An engine speed (NE) sensor 11 and a cylinder discrimination (CYL) sensor 12 are attached around the camshaft or crankshaft (not shown) of the engine 1. The engine speed sensor 11 outputs a pulse (hereinafter referred to as “TDC signal pulse”) at each top dead center (TDC) at the start of the intake stroke of each cylinder of the engine 1, and the cylinder discrimination sensor 12 is a predetermined cylinder. A signal pulse is output at the crank angle position. Both pulses are supplied to the ECU 5.
[0020]
A three-way catalyst 14 is provided in the exhaust pipe 13. The three-way catalyst 14 accumulates O ₂ in the exhaust gas when the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is set to a leaner side than the stoichiometric air-fuel ratio and the exhaust gas lean state has a relatively high O ₂ concentration in the exhaust gas. On the contrary, in the exhaust rich state where the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is set to a richer side than the stoichiometric air-fuel ratio and the O ₂ concentration in the exhaust gas is low and the HC and CO components are large, the accumulated O ₂ Has a function of oxidizing HC and CO in the exhaust gas.
[0021]
A proportional oxygen concentration sensor 17 (hereinafter referred to as “LAF sensor”) is attached upstream of the three-way catalyst 14. The LAF sensor 17 outputs an electrical signal substantially proportional to the oxygen concentration (air-fuel ratio) in the exhaust gas and supplies it to the ECU 5.
[0022]
The ECU 5 is composed of a computer, a ROM for storing programs and data, a RAM for storing programs and data necessary for execution and providing a calculation work area, a CPU for executing programs, and input signals from various sensors. An input interface for processing and a drive circuit for sending a control signal to the fuel injection valve 6 and the like are provided. Signals from the aforementioned sensors are received by the input interface and processed according to a program stored in the ROM. In FIG. 1, the ECU 5 is shown as a functional block based on such a hardware configuration.
[0023]
The ECU 5 includes functional blocks of an air-fuel ratio setting unit 31, a fuel injection amount calculation unit 33, an air-fuel ratio correction coefficient calculation unit 35, a lower limit limiting unit 37, a learning correction term calculation unit 39, and a prohibition unit 41.
[0024]
The air-fuel ratio setting means 31 sets a target air-fuel ratio KCMD corresponding to various engine conditions based on the engine parameters such as the engine speed NE, the throttle valve opening THA, and the engine coolant temperature TW.
[0025]
The air-fuel ratio correction coefficient calculating means 35 feedback-controls the air-fuel ratio so that the detected air-fuel ratio KACT calculated from the output of the LAF sensor 17 matches the target air-fuel ratio KCMD when the execution condition of the air-fuel ratio feedback control is satisfied. An air-fuel ratio correction coefficient KAF is calculated.
[0026]
The lower limit value limiting means 37 limits the air-fuel ratio correction coefficient KAF so that it does not fall below a predetermined or lower limit value corresponding to the engine coolant temperature TW for a period set according to the engine coolant temperature TW.
[0027]
The learning correction term calculation means 39 learns the air-fuel ratio correction coefficient KAF and calculates the learning correction term KREF. The learning correction term KREF calculates the learning value of the air-fuel ratio correction coefficient under various engine conditions and uses it as an alternative value or initial value of the air-fuel ratio correction coefficient in order to correct variations in the air-fuel ratio caused by individual engine differences. This is to improve the air-fuel ratio control.
[0028]
The prohibiting means 41 prohibits calculation of the learning correction term KREF while the lower limit value limiting means 37 limits the lower limit value of the air-fuel ratio correction coefficient. This is to prevent learning an air-fuel ratio correction coefficient based on an erroneously detected air-fuel ratio when combustion is not normally performed.
[0029]
The fuel injection amount calculating means 33 calculates the fuel injection time TOUT of the fuel injection valve 6 according to the flowchart shown in FIG.
[0030]
First, in step S201, a basic fuel amount TIM is calculated. The basic fuel amount TIM is specifically the basic fuel injection time of the fuel injection valve 6, and is determined by searching a TI map (not shown) set according to the engine speed NE and the intake pipe pressure PB. The TI map is set so that the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is substantially the stoichiometric air-fuel ratio in the operating state corresponding to the engine speed NE and the intake pipe pressure PB. That is, the basic fuel amount TIM is substantially proportional to the intake air amount per unit time of the engine.
[0031]
Subsequently, based on the target air-fuel ratio KCMD, the air-fuel ratio correction coefficient KAF, the basic fuel amount TIM, and various detected engine parameters, the fuel injection time TOUT is calculated by the following equation (1) (S203).
[0032]
[Expression 1]
TOUT = KTOTAL × KAF × KCMD × TIM (1)
Here, KTOTAL is a coefficient that collectively indicates correction coefficients calculated from the engine coolant temperature TW, the intake air temperature TA, the atmospheric pressure, and the like.
[0033]
The ECU 5 controls to open the fuel injection valve 6 by TOUT determined as described above in synchronization with the TDC signal pulse.
[0034]
FIG. 3 is a flowchart of a process for calculating each air-fuel ratio feedback correction term shown in Expression (1). First, the detected air-fuel ratio KACT of the exhaust is calculated by considering each engine parameter in the output of the LAF sensor 17 installed upstream of the three-way catalyst 14 (S301). Next, a target air-fuel ratio KCMD for optimizing drivability is calculated in consideration of various engine conditions (S303). Then, a main routine of air-fuel ratio (hereinafter referred to as LAF) feedback control, which will be described with reference to FIG. 4, is executed (S305).
[0035]
FIG. 4 is a flowchart of the main routine of LAF feedback control. In this process, after determining the conditions for performing the feedback control, the air-fuel ratio correction coefficient KAF is calculated based on the output of the LAF sensor 17 and the like, and STR (Self Tuning Regulator) feedback control is executed.
[0036]
First, it is determined whether or not the flag F-FC indicating “1” that the fuel is being cut is 1 (S401). If F-FC = 0 and the fuel is not cut, it is determined whether the target air-fuel ratio KCMD is equal to or lower than the air-fuel ratio KCMDWOT when the throttle is fully opened (S403). This KCMDWOT is set to be leaner than the air-fuel ratio at which the LAF sensor 17 compensates for detection accuracy. When KCMD ≦ KCMDWOT, an air-fuel ratio correction coefficient KAF calculation process described later with reference to FIG. 5 is executed (S405). Subsequently, 1 is set to a flag F-LAFFB indicated by “1” that the condition for executing the LAF feedback is satisfied (S407). Thereby, LAF feedback control is executed.
[0037]
If F-FC = 1 in step S401, or if KCMD> KCMDWOT in step S403 and the air-fuel ratio is large and rich, 1.0 is set to the air-fuel ratio correction coefficient KAF (S411), and the flag F- LAFFB is set to 0 (S413), and this routine is terminated. Thus, the LAF feedback control is not executed during fuel cut or when the accelerator is fully open and output is required.
[0038]
FIG. 5 is a flowchart showing the calculation processing of the air-fuel ratio correction coefficient KAF shown in step S405 of FIG. In this process, the air-fuel ratio correction coefficient KAF is calculated so that the detected air-fuel ratio KACT becomes an optimum air-fuel ratio corresponding to various engine states determined from various parameters.
[0039]
An adaptive parameter of the adaptive controller STR is calculated by processing not shown (S501). The parameters calculated here are used in KSTR calculation in step S601 in FIG. Next, a calculation process of a correction term KSTR for adaptive control, which will be described later with reference to FIG. 6, is executed (S503). A value obtained by dividing the calculated adaptive control correction term KSTR by the target air-fuel ratio KCMD is set as the air-fuel ratio correction coefficient KAF (S505), and the calculation process of the KAF learning value KREF described later with reference to FIG. 8 is executed. (S507), and this process ends.
[0040]
FIG. 6 is a flowchart of the calculation process of the adaptive control correction term KSTR.
[0041]
The adaptive control correction term KSTR is calculated according to a predetermined equation using the parameter calculated using STR in step S501 of FIG. 5 (S601). Next, a calculation process of a lower limit value LAFLMTL of an air-fuel ratio correction coefficient (KAF) described later with reference to FIG. 7 is performed (S603). Then, it is determined whether the adaptive control correction term KSTR calculated in step S601 is equal to or greater than the product of the KAF upper limit value LAFLMTH and the target air-fuel ratio KCMD (S605). If KSTR <LAFLMTH · KCMD and the upper limit value is not reached, it is determined whether or not KSTR is equal to or less than the product of the KAF lower limit value LAFLMTL calculated in step S603 and the target air-fuel ratio KCMD (S607).
[0042]
If KSTR ≧ LAFLMTH · KCMD in step S605, the value of LAFLMTH · KCMD is set in KSTR, and 1 is set in flag F-LAFLMT indicating that the normal lower limit value is used in “1” (S613). ). If KSTR ≦ LAFLMTL · KCMD in step S607, the value of LAFLMTL · KCMD is set in KSTR, and 1 is set in flag F-LAFLMT (S613). As described above, when the adaptive control correction term KSTR is equal to or higher than the upper limit value or equal to or lower than the lower limit value, the upper limit value or the lower limit value is set in KSTR.
[0043]
In step S607, if KSTR> LAFLMTL · KCMD and KSTR is between the upper and lower limit values, the flag F-LAFLMT is set to 0 (S609), and this process ends. As described above, the processing shown in FIG. 6 operates so as to change the limit value according to the value of the adaptive control correction term KSTR.
[0044]
FIG. 7 is a flowchart of the air-fuel ratio correction coefficient lower limit value LAFLMTL calculation process. In this process, the lower limit value LAFLMTL of KAF corresponding to the operating state of the engine is calculated.
[0045]
It is determined whether or not a flag F-STMOD indicating 1 in the start mode is 1 (S701). If F-STMOD = 0 and the engine is not in the start mode, the process directly proceeds to step S707. If F-STMOD = 1 and the engine is in the start mode, a value obtained by searching a lower limit table (see FIG. 8) determined according to the engine coolant temperature TW is set to the counter determination value TLAFLMTL (S703). This lower limit table is determined in advance so as to decrease as the engine coolant temperature TW increases. The counter determination value TLAFLMTL corresponds to a period during which the lower limit value is limited according to the engine coolant temperature TW. Subsequently, 0 is set to the flag F-LAFLMTL (S705).
[0046]
It is determined whether or not the timer T20ACR that counts the time from engine start has exceeded the counter determination value TLAFLMTL obtained in step S703 (S707). Since initially T20ACR ≦ TLAFLMTL, the lower limit LAFLMTL, which is a fixed value or a value corresponding to the engine coolant temperature TW, is smaller than the product of the learning value KREFX without purge and the final lower limit LAFLMTLF described in FIG. It is determined whether or not (S709). If LAFLMTL <KREFX · LAFLMTLF, this value is set to the lower limit value LAFLMTL (S711), and this process is terminated. By limiting the lower limit value in this way, it is possible to avoid a situation in which the air-fuel ratio becomes too lean due to erroneous detection of the LAF sensor 17 immediately after engine startup and combustion becomes unstable.
[0047]
If the timer T20ACR exceeds the counter determination value TLAFLMTL in step S707, 1 is set in the flag F-LAFLMTL (S713), and the final value LAFLMTLF is set in LAFLMT (S715).
[0048]
If LAFLMTL ≧ KREFX · LAFLMTLF in step S709, the final value LAFLMTLF is set to LAFLMT without limiting the lower limit value (S715).
[0049]
FIG. 9 is a flowchart of a process for calculating the KAF learning value KREF. The learning value KREF is used to learn KAF under various conditions in order to absorb variations in the air-fuel ratio caused by individual differences between engines, and to use it as a substitute value or initial value for KAF to improve air-fuel ratio detection accuracy. Is.
[0050]
It is determined whether or not the engine cooling water temperature TW is higher than a predetermined water temperature TWREF (S801). If TW ≦ TWREF, the engine coolant temperature is low and the learning value KREF should not be calculated. If TW> TWREF in step S801, it is determined whether or not the flag F-LAFLMTL is 1 (S803). When F-LAFLMTL = 0, since the predetermined period has not elapsed since the engine start, the process proceeds to step S813 without calculating the learning value KREF.
[0051]
If F-LAFLMTL = 1 in step S803, it is determined whether or not the purge delay flag F-PGDLY is 1 (S805). If F-PGDLY = 0 and purge purge is not in progress, the KAF learning value KREF when purge is performed is calculated by processing not shown (S807). Next, it is determined whether or not the purge-off timer TPGOFF is 0 (S809). If TPGOFF = 1, it indicates that the purge is being performed, and the process proceeds to step S813 to determine again whether or not the flag F-PGDLY is 1. Since this time is NO, this processing ends.
[0052]
When F-PGDLY = 1 in step S805 or when TPGOFF = 0 in step S809, purge is not performed, so the KAF learning value KREFX without purge is calculated by processing not shown (S811). . Subsequently, in step S813, it is determined whether or not the flag F-PGDLY is 1. If F-PGDLY = 1 at step S805, the KREFX calculated at step S811 is set to KREF (S815). If TPGOFF = 0 in step S809, F-PGDLY = 0, so step S815 is skipped and the process is terminated.
[0053]
By the processing described above, the operation of the engine and the air-fuel ratio feedback control device at the time of starting is as follows.
[0054]
When the engine is determined to be in the start mode (S701), a period for limiting the lower limit value is determined according to the engine coolant temperature TW (S703), and 0 is set to the flag F-LFLMTL to limit the lower limit value ( S705). The period is a period until the temperature of the combustion chamber of the engine rises sufficiently. During this period, the lower limit value LAFLMTL is compared with the product of the learning value KREFX without purge and the final value of LAFLMTL (S707, S709). If it is determined that the lower limit value LAFLMTL is lower, the lower limit value LAFLMTL is limited ( S711).
[0055]
Since LAFLMTL is used to calculate the lower limit value of the adaptive control correction term KSTR (S607) and KSTR is used to calculate KAF (S505), limiting LAFLMTL is the lower limit value of the air-fuel ratio correction coefficient KAF. Will be limited. Therefore, the lower limit value of the air-fuel ratio correction coefficient KAF is limited during the period.
[0056]
In the prior art, when the LAF sensor 17 is activated, feedback control is started immediately, and the combustion state in the engine is not taken into consideration. For this reason, when the combustion chamber of the engine is at a low temperature, the oil component is exhausted without being burned, and is attached to the detection part of the LAF sensor 17 and may be recognized as an exhaust rich state. In this case, feedback control that makes the air-fuel ratio lean is performed. Therefore, in the present embodiment, in order to prevent such a situation, as described above, the air-fuel ratio correction coefficient KAF is determined during the period determined by the engine coolant temperature TW even when the LAF sensor 17 has erroneously detected the air-fuel ratio. Do not set it below the lower limit. Therefore, it is possible to prevent deterioration of emission and drivability due to the air-fuel ratio becoming too lean and unstable combustion.
[0057]
Further, since F-LAFLMTL = 0 during the above period (S705), the KAF learning term KREF is not calculated (S803).
[0058]
When the above period elapses, 1 is set to the flag F-LAFLMTL (S713), and the mode for using the normal (unrestricted) lower limit value is entered (S715). This is because it is determined that the temperature of the combustion chamber has increased to such an extent that oil burns after a sufficient time has passed, and thus it is not necessary to limit the lower limit value. At this time, calculation of the learning value KREF (or KREFX) is started (S807) because the erroneous detection of the air-fuel ratio feedback coefficient by the LAF sensor is eliminated.
[0059]
Although the present invention has been described above with reference to specific embodiments, the present invention is not limited thereto, and various modifications and alternatives are also included in the scope of the present invention. For example, the limitation of the lower limit value of the air-fuel ratio correction coefficient is performed for a period determined according to the engine coolant temperature. However, when the engine coolant temperature reaches a predetermined temperature, the limitation of the lower limit value ends. May be.
[0060]
【The invention's effect】
According to the present invention, since the means for limiting the lower limit value of the air-fuel ratio correction coefficient according to the temperature of the internal combustion engine is provided, even when the air-fuel ratio sensor shows a richer state than the original air-fuel ratio when starting the internal combustion engine, It is possible to prevent deterioration in emissions and drivability due to the air-fuel ratio becoming too lean and unstable combustion.
[0061]
Further, since the means for prohibiting calculation of the air-fuel ratio learning correction term is provided while the feedback correction coefficient lower limit value is being limited, erroneous learning of the air-fuel ratio can be avoided.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an overall configuration of an engine equipped with an air-fuel ratio feedback control device of the present invention.
FIG. 2 is a flowchart of a process for calculating a fuel injection time TOUT.
FIG. 3 is a flowchart of a process for calculating an air-fuel ratio feedback correction term.
FIG. 4 is a flowchart of a main routine of LAF feedback.
FIG. 5 is a flowchart of a process for calculating an air-fuel ratio correction coefficient KAF.
FIG. 6 is a flowchart of processing for calculating an adaptive control correction term KSTR.
FIG. 7 is a flowchart of a process for calculating an air-fuel ratio correction coefficient lower limit value LAFLMTL.
FIG. 8 is a table for searching for a counter determination value TLAFLMTL corresponding to the engine coolant temperature TW.
FIG. 9 is a flowchart of processing for calculating a KAF learning value KREF.
[Explanation of symbols]
1 Internal combustion engine
5 Electronic control unit
6 Fuel injection valve
8 Intake pipe pressure sensor
10 Engine coolant temperature sensor
11 Engine speed sensor
13 Exhaust pipe
14 Three-way catalyst
17 Proportional oxygen concentration sensor
20 Fuel tank
31 Air-fuel ratio setting means
33 Fuel injection amount calculation means
35 Air-fuel ratio correction coefficient calculation means
37 Lower limit limiting means
39 Learning correction term calculation means
41 Prohibited measures

Claims (2)

Means for detecting the air-fuel ratio of the internal combustion engine;
Air-fuel ratio setting means for setting a target air-fuel ratio according to the operating state of the internal combustion engine;
Air-fuel ratio correction coefficient calculating means for calculating an air-fuel ratio correction coefficient for feedback control of the air-fuel ratio based on the target air-fuel ratio and the detected air-fuel ratio;
Lower limit value limiting means for limiting the lower limit value of the air-fuel ratio correction coefficient over a period set according to the temperature of the internal combustion engine at the time of starting the internal combustion engine;
An air-fuel ratio feedback control device for an internal combustion engine comprising: Learning correction term calculation means for learning the air-fuel ratio correction coefficient and calculating a learning correction term;
Prohibiting means for prohibiting the calculation of the learning correction term during the period;
Further comprising an air-fuel ratio feedback control apparatus for an internal combustion engine according to claim 1.

Images