JP3223472B2 - Control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control system for an internal combustion engine that controls the operation of the internal combustion engine at an air-fuel ratio leaner than a stoichiometric air-fuel ratio immediately after the internal combustion engine is started.

[0002]

2. Description of the Related Art Conventionally, immediately after the start of an internal combustion engine, the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine has been controlled to be richer than the stoichiometric air-fuel ratio to ensure the stability of engine rotation. Since it has become possible to secure the stability of the engine rotation even when the engine is controlled to the lean side, the internal combustion engine that operates the engine by controlling the air-fuel ratio to the lean side until the feedback control of the air-fuel ratio is started is started. A control device has been proposed (for example, Japanese Patent Publication No. 5-31646).

[0003]

However, in the above-described conventional control apparatus for an internal combustion engine, the engine is operated at an air-fuel ratio leaner than the stoichiometric air-fuel ratio immediately after the internal combustion engine is started (hereinafter, referred to as "immediately after the start of the engine"). Lean burn control ”)
Can not be performed in any driving area,
When the engine temperature is lower than or equal to a predetermined temperature (for example, when the atomization of the fuel is deteriorated, or when the engine friction is large, and the combustion state of the fuel is deteriorated), or when the engine temperature is higher than the predetermined temperature (for example, the fuel supply). If the engine is operated with an air-fuel ratio leaner than the stoichiometric air-fuel ratio at a high temperature at which vapor is expected to be generated in the line, problems such as a decrease in stability of engine rotation and a stall of the engine may occur.

Further, when a sudden change in the air-fuel ratio occurs, for example, immediately switching from a state in which the air-fuel ratio is operated on the lean side to an operation based on the stoichiometric air-fuel ratio, there is a problem that engine rotation fluctuation and hunting occur. There was also.

Further, when the vehicle is driven during the lean burn control immediately after the start of the engine, the output torque of the engine is reduced, which causes problems such as stall of the engine and deterioration of the feeling of acceleration.

[0006] Immediately after the internal combustion engine is started, the air-fuel ratio is usually controlled by feedforward control. If the fuel supply state changes due to aging or the like, the fuel cannot be supplied accurately, causing misfire or engine rotation. There was also a problem of causing fluctuations.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it has been found that the engine speed decreases due to lean burn control immediately after engine start, engine stall, and the like at a low temperature below a predetermined temperature or at a high temperature above a predetermined temperature. It is a first object of the present invention to provide a control device for an internal combustion engine capable of preventing a stall of the engine, a deterioration in a feeling of acceleration, and the like caused by running the vehicle during the lean burn control immediately after the start of the engine.

It is a second object of the present invention to provide a control device for an internal combustion engine capable of preventing engine speed fluctuations and hunting due to a rapid air-fuel ratio fluctuation.

Further, there is provided an internal combustion engine control device capable of preventing a misfire or a change in engine speed due to aging or the like when the air-fuel ratio immediately after the start of the internal combustion engine is controlled by feedforward control. As a third object.

A fourth object of the present invention is to provide a control device for an internal combustion engine which can prevent the stability of the engine rotation from being reduced due to misfire of the internal combustion engine and fluctuations in the engine speed.

[0011]

SUMMARY OF THE INVENTION In order to achieve the first object, the present invention provides a control method for an internal combustion engine that controls the operation of the internal combustion engine at an air-fuel ratio leaner than a stoichiometric air-fuel ratio immediately after the start of the engine. in the apparatus, the vehicle equipped with the internal combustion organizations
Operating state detecting means for detecting an in- gear state of the transmission ;
Air-fuel ratio changing means for changing the air-fuel ratio at which the internal combustion engine is operated to an air-fuel ratio richer than the lean air-fuel ratio when the in- gear state is detected by the operating state detecting means And characterized in that:

[0012]

[0013]

[0014]

[0015]

[0016]

[0017]

[0018]

According to the structure of the present invention, when <br/> the gear condition of the vehicle equipped with the internal combustion engine detected by the operating condition detecting means, the air-fuel ratio changing means, leaner than the stoichiometric air-fuel ratio The air-fuel ratio set on the side is changed to the air-fuel ratio on the rich side.

[0019]

[0020]

[0021]

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an internal combustion engine (hereinafter referred to as "engine") and a control device thereof according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an engine.

The intake pipe 2 of the engine 1 communicates with the combustion chamber of each cylinder of the engine 1 via a branch (intake manifold) 11. A throttle valve 3 is provided in the intake pipe 2. Throttle valve opening (θTH) for throttle valve 3
The sensor 4 is connected, outputs an electric signal corresponding to the throttle valve opening θTH, and supplies it to an electronic control unit (hereinafter referred to as “ECU”) 5. An auxiliary air passage 6 that bypasses the throttle valve 3 is provided in the intake pipe 2, and an auxiliary air amount control valve 7
Is arranged. The auxiliary air amount control valve 7 is connected to the ECU 5, and the ECU 5 controls the valve opening amount.

An intake air temperature (TA) sensor 8 is mounted on the intake pipe 2 upstream of the throttle valve 3, and a detection signal is supplied to the ECU 5. An expanded chamber 9 is provided between the throttle valve 3 of the intake pipe 2 and the intake manifold 11, and the chamber 9 has an intake pipe absolute pressure (PB
A) The sensor 10 is attached. PBA sensor 1
The detection signal of 0 is supplied to the ECU 5.

The main body of the engine 1 has an engine water temperature (T
W) The sensor 13 is mounted, and the detection signal is EC
It is supplied to U5. The ECU 5 is connected to a crank angle position sensor 14 that detects a rotation angle of a crankshaft (not shown) of the engine 1, and supplies a signal corresponding to the rotation angle of the crankshaft to the ECU 5. The crank angle position sensor 14 outputs a signal pulse (hereinafter referred to as a “CYL signal pulse”) at a predetermined crank angle position of a specific cylinder of the engine 1, and a top dead center (TDC) at the start of an intake stroke of each cylinder. ) At a crank angle position before a predetermined crank angle (in the case of a four-cylinder engine, the crank angle is 18).
A TDC sensor that outputs a TDC signal pulse and a pulse (hereinafter referred to as a “CRK signal pulse”) at a constant crank angle cycle (for example, a 30-degree cycle) shorter than the TDC signal pulse
), And a CYL signal pulse, a TDC signal pulse, and a CRK signal pulse
It is supplied to U5. These signal pulses are used for various timing controls such as a fuel injection amount (fuel injection time), a fuel injection timing, an ignition timing, and the like, and detection of the engine speed NE.

A fuel injection valve 12 is provided for each cylinder slightly upstream of the intake valve of the intake manifold 11, and each injection valve is connected to a fuel pump (not shown) and electrically connected to the ECU 5. The fuel injection timing and the fuel injection time (valve opening time) are controlled by a signal from the ECU 5. Engine 1 spark plug (not shown) is also EC
It is electrically connected to U5, and the ignition timing θIG is controlled by the ECU5.

The exhaust pipe 16 is connected to a branch portion (exhaust manifold) 1
5 is connected to the combustion chamber of the engine 1. In the exhaust pipe 16, immediately downstream of the portion where the branch portions 15 gather,
Wide area air-fuel ratio sensor (hereinafter referred to as "LAF sensor") 17
Is provided. Further, a three-way catalyst 19 directly below and a three-way catalyst 20 below the floor are arranged downstream of the LAF sensor 17, and an oxygen concentration sensor (hereinafter referred to as an "O2 sensor") is provided between these three-way catalysts 19 and 20. 18 is mounted. The three-way catalysts 19 and 20 are used to remove HC, C in exhaust gas.
Purifies O, NOx, etc.

The LAF sensor 17 includes a low-pass filter 2
The ECU 2 is connected to the ECU 5 via the ECU 2 and outputs an electric signal substantially proportional to the oxygen concentration (air-fuel ratio) in the exhaust gas, and supplies the electric signal to the ECU 5. The output of the O2 sensor 18 has a characteristic that the output sharply changes before and after the stoichiometric air-fuel ratio, and the output becomes high level on the rich side and low level on the lean side from the stoichiometric air-fuel ratio. O2 sensor 18
Is connected to the ECU 5 via a low-pass filter 23, and the detection signal is supplied to the ECU 5.

In the engine 1, the valve timing of the intake valve and the exhaust valve can be switched between two stages: a high-speed valve timing suitable for a high-speed rotation region of the engine and a low-speed valve timing suitable for a low-speed rotation region. It has a mechanism 60. The switching of the valve timing includes the switching of the valve lift amount. Further, when the low-speed valve timing is selected, one of the two intake valves is stopped to stabilize the air-fuel ratio even when the air-fuel ratio becomes leaner than the stoichiometric air-fuel ratio. We have tried to ensure the combustion that we did.

The valve timing switching mechanism 60 switches the valve timing via a hydraulic pressure. An electromagnetic valve and a hydraulic pressure sensor for switching the hydraulic pressure are connected to the ECU 5. The detection signal of the oil pressure sensor is supplied to the ECU 5, and the ECU 5 controls the solenoid valve to perform switching control of the valve timing.

An atmospheric pressure (PA) sensor 21 for detecting an atmospheric pressure is connected to the ECU 5, and a detection signal is supplied to the ECU 5.

The ECU 5 has an input circuit having the functions of shaping the input signal waveforms from the various sensors described above, correcting the voltage level to a predetermined level, converting an analog signal value to a digital signal value, and the like, and a central processing circuit. (CPU), a storage device including a ROM and a RAM for storing various arithmetic programs executed by the CPU, various maps and arithmetic results described below, and drive signals to various solenoid valves such as the fuel injection valve 12 and the ignition plug. And an output circuit for outputting the same.

Based on the various engine operation parameter signals described above, the ECU 5 performs various operations such as lean burn control immediately after engine start, a feedback control operation region corresponding to the outputs of the LAF sensor 17 and the O2 sensor 18 and an open control operation region. The engine operating state is determined, and the fuel injection valve 12 is calculated according to the following equation 1 according to the engine operating state.
Is calculated, and a signal for driving the fuel injection valve 12 is output based on the calculation result.

[0035]

TOUT (N) = TIMF × KTOTAL × K
CMDM × KLAF × KOBSV # N FIG. 2 is a functional block diagram for explaining a method of calculating the fuel injection time TOUT (N) according to the above equation 1, and with reference to this, the fuel injection time TOUT in the present embodiment will be described.
An outline of the calculation method of (N) will be described. Here, N represents a cylinder number, and a parameter with this is calculated for each cylinder. In the present embodiment, the amount of fuel supplied to the engine is calculated as the fuel injection time. Since this corresponds to the amount of fuel injected, TOUT is also called the fuel injection amount or the fuel amount.

In FIG. 2, a block B1 calculates a basic fuel amount TIMF corresponding to the intake air amount. This basic fuel amount TIMF is basically set according to the engine speed NE and the intake pipe absolute pressure PBA. The intake system from the throttle valve 3 to the combustion chamber of the engine 1 is modeled, and its intake system model is modeled. It is desirable to perform the correction in consideration of the delay of the intake air based on the above. In this case, the throttle valve opening θTH and the atmospheric pressure PA are used as detection parameters.
Is further used.

Blocks B2 to B8 are multiplication blocks which multiply and output the input parameters of the blocks. By these blocks, the calculation of the above equation 1 is performed, and the output of the blocks B5 to B8 is used as the fuel injection amount T for each cylinder.
OUT (N) is obtained.

A block B9 includes an engine water temperature correction coefficient KTW set according to the engine water temperature TW, and an EGR correction coefficient K set according to the exhaust gas recirculation amount during execution of the exhaust gas recirculation.
A correction coefficient KTOTAL is calculated by multiplying all the feedforward correction coefficients such as EGR, and is input to the block B2.

The block B21 comprises an engine speed NE,
Target air-fuel ratio coefficient KCM according to intake pipe absolute pressure PBA etc.
D is determined and input to block B22. The target air-fuel ratio coefficient KCMD is the reciprocal of the air-fuel ratio A / F, that is, the fuel-air ratio F
/ A, and takes a value of 1.0 at the stoichiometric air-fuel ratio.
Also called target equivalent ratio. Block B22 corrects the target air-fuel ratio coefficient KCMD based on the O2 sensor output VMO2 input through the low-pass filter 23, and
18 and B23. Block B23 is the KCM
A fuel cooling correction is performed according to the D value, and the final target air-fuel ratio coefficient K
The CMDM is calculated and input to the block B3.

The block B10 includes a low-pass filter 22
The output value of the LAF sensor input through is sampled every time a CRK signal pulse is generated, the sample values are sequentially stored in a ring buffer memory, and a sample value sampled at an optimal timing according to the engine operating state is selected. (LAF sensor output selection processing), block B1
1 and input to the block B18 via the low-pass filter block B16. This LAF sensor output selection processing is based on the fact that the air-fuel ratio that changes depending on the sampling timing cannot be detected accurately, and the time required for the exhaust gas discharged from the combustion chamber to reach the LAF sensor 17 and the LAF.
This takes into account that the reaction time of the F sensor itself changes depending on the engine operating state.

The block B18 includes a PID correction coefficient K by PID control according to the deviation between the detected air-fuel ratio and the target air-fuel ratio.
LAF is calculated and input to block B4.

The block B11 has a function as a so-called observer, and is a collecting portion (mixed gas of exhaust gas discharged from each cylinder) detected by the LAF sensor 17.
The air-fuel ratio of each cylinder is estimated based on the air-fuel ratio of the respective cylinders, and is input to blocks B12 to B15 corresponding to the four cylinders. In FIG. 2, block B12 corresponds to cylinder # 1, block B15 corresponds to cylinder # 2, and block B1.
3 corresponds to cylinder # 3, and block 14 corresponds to cylinder # 4. In blocks B12 to B15, cylinder-by-cylinder correction coefficients KOBSV # N (N = 1 to 4) are controlled by PID control so that the air-fuel ratio of each cylinder (the air-fuel ratio estimated by observer block B11) matches the air-fuel ratio of the collecting section. It is calculated and input to blocks B5 to B8, respectively.

As described above, in the present embodiment, the cylinder-by-cylinder correction coefficient KOBSV # N set according to the air-fuel ratio of each cylinder estimated based on the LAF sensor output is applied to the above equation (1), and The fuel injection amount TOUT (N) is calculated. That is, the variation of the air-fuel ratio for each cylinder is eliminated by the cylinder-specific correction coefficient KOBSV # N, the purification rate of the catalyst is improved, and good exhaust gas characteristics can be obtained in various engine operating states.

In the present embodiment, the functions of the respective blocks shown in FIG. 2 are realized by arithmetic processing by the CPU of the ECU 5. Therefore, the contents of the processing will be specifically described with reference to the flowchart of this processing.

FIG. 3 shows the PID correction coefficient KLAF and the cylinder-specific correction coefficient KOBSV according to the output of the LAF sensor 17.
It is a flowchart of a process of calculating #N. This process is executed every time a TDC signal pulse is generated.

In step S1, it is determined whether or not the engine is in the start mode, that is, whether or not cranking is being performed. If the engine is in the start mode, the process proceeds to the start mode. If it is not the start mode, calculation of the target air-fuel ratio coefficient (target equivalent ratio) KCMD and the final target air-fuel ratio coefficient KCMDM (step S2) and L
An AF sensor output selection process is performed (step S3), and a calculation of the detected equivalent ratio KACT is performed (step S4).
The detected equivalent ratio KACT is obtained by converting the output of the LAF sensor 17 into an equivalent ratio.

Next, it is determined whether or not the activation of the LAF sensor 17 has been completed (step S5). this is,
For example, the difference between the output voltage of the LAF sensor 17 and its center voltage is compared with a predetermined value (for example, 0.4 V), and when the difference is smaller than the predetermined value, it is determined that the activation is completed.

Next, the engine operating state is determined by the LAF sensor 17.
It is determined whether or not the vehicle is in an operation region (hereinafter, referred to as a “LAF feedback region”) in which feedback control is performed based on the output (step S6). This is, for example, L
When the activation of the AF sensor 17 is completed and the fuel cut or the throttle is not fully opened, the LAF feedback region is determined. As a result of this determination, L
Reset flag F when not in AF feedback area
KLAFRESET is set to “1”, and is set to “0” when in the LAF feedback area.

In the following step S7, a reset flag F
It is determined whether or not KLAFRESET is “1”, and
If FRESET = 1, the flow advances to step S8 to set PI
D correction coefficient KLAF is set to “1.0”, cylinder-specific correction coefficient KO
The cylinder-dependent correction coefficient learning value KOBSV described below is set to BSV # N.
#Nsty and the integral term K of PID control
LAFI is set to “0”, and this processing ends. Here, by setting the cylinder-by-cylinder correction coefficient KOBSV # N to the cylinder-by-cylinder correction coefficient learning value KOBSV # Nsty, misfire of the internal combustion engine due to a change in the fuel supply state due to aging or the like during feedforward control, or engine rotation The stability of the engine against fluctuations can be ensured.

On the other hand, in the discrimination of step S7, FKLAF
If RESET = 0, observer stop determination is performed (step S9). This observer stop determination means that, for example, when the engine speed is high, it is difficult to secure the calculation time or the engine speed with insufficient sensor responsiveness is determined in advance as the observer limit speed, and the observer limit speed is detected. When the detected engine speed NE is equal to or higher than the observer limit speed, the engine speed NE is compared with the engine speed NE.
The flag FOBSVST for stopping the process of the observer (block B11) is set to "1", while when the detected engine speed NE is smaller than the observer limit speed, the flag FOBSVST is set to "0".

In the following step S10, flag FOBS
It is determined whether or not VST is "1". If it is "0", a KOBSV # N calculation process, which is an operation performed by the observer, is performed (step S11), while a flag FOBSVS is set.
When T is "1", the value KOBSV # N is replaced with the result of the previous KOBSV # N calculation process instead of performing the KOBSV # N calculation process (step S12). Thus, when the observer is stopped, the previous value KOB
Since SV # N is used, the observer operates and the value KO
When BSV # N is calculated, the calculated value KOBS
V # N needs to be stored. That is, the calculated value KOBSV # N is stored in an area secured at a predetermined position in the RAM, and when the observer stops, the previous value KOBSV # N is read and the value KOBSV # N is updated. As a result, it is possible to prevent misfire and fluctuations in engine rotation due to aging and the like.

Subsequently, using the value KOBSV # N obtained in step S11 or S12, the feedback correction coefficient KLAF is calculated (step S13), and then the present processing is terminated.

FIG. 4 is a flowchart of the process for calculating the final target air-fuel ratio coefficient KCMDM in step S2 of FIG.

In step S21, the engine speed NE
Then, a map is searched according to the intake pipe absolute pressure PBA and a basic value KBS is calculated. It should be noted that a value for idle time is also set in the map.

In the following step S22, it is determined whether or not a condition for executing the lean burn control immediately after the start of the engine is satisfied (lean determination after start). If the condition is satisfied, the after-start lean flag FASTLEAN is set to "1". While “0” is set when the condition is not satisfied. Details of the lean burn control execution conditions will be described later with reference to FIG. Note that the lean burn control immediately after the start is performed for the purpose of preventing an increase in the amount of HC emission and a decrease in the fuel consumption rate in a state where the catalyst is inactive immediately after the start of the engine as before.

Next, in step S23, it is determined whether or not the throttle valve is fully open (WOT). If the throttle valve is fully open, the WOT flag FWOT is set to "1", and if not, it is set to "0". Next, an increase correction coefficient KWOT is calculated according to the engine coolant temperature TW (step S24). At this time, a correction coefficient KXWOT at the time of high water temperature is also calculated.

In the following step S25, the target air-fuel ratio coefficient KCMD is calculated, and then the calculated KCMD value is limited (processing to fall within the range of predetermined upper and lower limits).
Is performed (step S26). The processing in step S25 will be described later with reference to FIG.

In the following step S27, the O2 sensor 18
The activation flag FMO2 is set to "1" when activation is completed, and is set to "0" when activation is not completed. For example, when a predetermined period has elapsed after the start of the engine, it is determined that the activation has been completed.

In step S28, the correction term D of the target air-fuel ratio coefficient KCMD according to the output VMO2 of the O2 sensor 18
Calculate KCMDO2. In this process, the correction term DKCMDO2 is calculated by PID control in accordance with the difference between the O2 sensor output VMO2 and the reference value VREFM.

In step S29, the target air-fuel ratio coefficient KCMD is corrected by the following equation.

KCMD = KCMD + DKCMDO2 Thus, the target air-fuel ratio coefficient KCMD can be set so as to compensate for the deviation of the output of the LAF sensor 17.

In the following step S30, the calculated KCM
A KCMD-KETC table is searched according to the D value to calculate a correction coefficient KETC, and a final target air-fuel ratio coefficient KCMDM is calculated by the following equation.

KCMDM = KCMD × KETC The correction coefficient KETC is to correct the effect in consideration of the fact that the fuel cooling effect by the injection increases as the KCMD value increases and the fuel injection amount increases, KC
The value is set to a larger value as the MD value increases. .

Next, KCMDM value limit processing is performed (step S31), and the KCMD value obtained in step S29 is stored in the ring buffer (step S32), and this processing ends.

FIG. 5 is a flowchart of the after-start lean determination process in step S22 of FIG.

First, it is determined whether or not a transmission (not shown) is in an in-gear state (step S41). If the transmission is not in an in-gear state, it is determined whether or not a predetermined period of time for performing lean burn control immediately after starting the engine has elapsed. (Step S
42).

If it is determined in step S42 that the predetermined time has not elapsed, it is determined whether or not the engine water temperature TW is higher than an upper limit value TWASTLEANH of the engine water temperature at which the lean burn control may be performed immediately after the engine is started. (Step S43), the engine coolant temperature TW is set to the upper limit value TWA
When the engine water temperature is equal to or lower than STLEAN, it is determined whether or not the engine water temperature TW is equal to or lower than a lower limit value TWASTLEANL of the engine water temperature at which the lean burn control may be performed immediately after the engine is started (step S44).

The engine water temperature T is determined in step S44.
When W is higher than the lower limit value TWASTLEANL, it is determined whether or not the fluctuation amount TH of the throttle valve opening exceeds the upper limit THLEAN of the fluctuation amount of the throttle valve opening at which the lean burn control may be performed immediately after the engine is started. (Step S45). Here, the throttle valve opening variation amount TH is determined by the valve opening θ from the throttle valve opening sensor 4.
It is determined by constantly monitoring the TH signal and taking the difference between the currently detected value and the previously detected value.

If it is determined in step S45 that the throttle valve opening variation TH is equal to or less than the upper limit value THLEAN, the absolute value | DME | of the rotation variation of the engine speed may be subjected to lean burn control immediately after the engine is started. It is determined whether or not the rotation fluctuation amount exceeds the upper limit value DMELEAN (step S46). Here, the rotation fluctuation amount | DME |
Is calculated based on the detected engine speed NE, similarly to the throttle valve opening variation TH.

In the determination in step S46, the rotation fluctuation amount | D
When ME | is equal to or less than the upper limit value DMELEAN, it is determined whether or not misfire has been detected (step S47). A specific method for detecting misfire will be described later with reference to FIGS.

If no misfire is detected in the step S47, it is determined whether or not the engine speed NE exceeds an upper limit value NASTLEAN (H, L) having hysteresis, which may perform lean burn control immediately after starting the engine. Is determined (step S48), and the upper limit value NEA is determined.
If it is not more than STREAN (H, L), the magnitude of the load on the engine 1 is determined (step S4).
9). Here, the magnitude of the load applied to the engine 1 is
The determination is made based on the absolute pressure PBA in the intake pipe.

In the determination in step S49, the intake pipe absolute pressure PBA indicates the upper limit value PBASTLE having hysteresis, in which lean burn control may be performed immediately after the engine is started.
If it is less than AN (H, L), the post-start lean flag FASTLEAN is set to "1" (step S5).
0), the lean burn control immediately after the start of the engine is started.

On the other hand, in the discrimination of steps S41 to S49,
If the answer is "yes" (YES), the post-start lean flag FASTLEAN is set to "0".
(Step S51), the lean burn control immediately after the start of the engine is prohibited or stopped.

That is, in this embodiment, when the transmission is in the in-gear state, when the throttle valve opening fluctuation amount TH is large, when the engine speed NE is large, and when the load applied to the engine 1 is large, the driver Predicts that the vehicle is about to run the vehicle, and if the lean burn control is being performed immediately after the engine is started at this time, the lean burn control is stopped. Can be prevented from deteriorating.

The engine water temperature TW is equal to the upper limit value TWA.
When the temperature is higher than STREANH or the lower limit TWA
Since the lean burn control is stopped immediately after the engine is started even when the engine speed is equal to or less than STLEANL, it is possible to prevent a decrease in stability of the engine rotation and a stall of the engine.

Further, when the misfire is detected or when the rotation fluctuation amount | DME | exceeds the upper limit value DMELEAN, the lean burn control immediately after the engine is started is stopped. Can be prevented from decreasing.

FIGS. 6 and 7 are flowcharts of the KCMD calculation process in step S25 of FIG.

First, in step S61 of FIG. 6, the after-start lean flag FASTL set in step S22 of FIG.
It is determined whether or not EAN is “1”, and FASTLEAN = 1
If, the LEAN table is searched to read out each component of the leaning coefficient KLEAN necessary for performing the lean burn control immediately after the engine is started (step S62 in FIG. 7). Here, each component of the leaning coefficient KLEAN is, specifically, a coefficient KLEANTW set in accordance with the engine coolant temperature TW, a coefficient KLEANPA set in accordance with the intake air temperature PA, and an engine speed NE. Determined coefficient KLEANNE, intake pipe absolute pressure P
Coefficient KLEANPBA determined according to BA, Coefficient KLEAN determined according to elapse of time after engine start
AST. Then, the leaning coefficients KLEAN are calculated as the respective coefficients KLEANW, KLEANPA, KLEANN.
It is defined as the result of multiplying E, KLEANPBA and KLEANAST.

FIG. 8 is a diagram showing an example of a lean (LEAN) table storing the values of the respective components (coefficients) of the leaning coefficient KLEAN.

In the figure, (a) shows a coefficient KLEAN.
This is a graph of table data for determining TW, in which the vertical axis indicates coefficient values, and the horizontal axis indicates engine water temperature T.
W is shown. In the figure, the range where the engine water temperature TW is 0 ° C. or lower or 40 ° C. or higher is a region where leaning is prohibited. Therefore, the coefficient KLEANTW is set to “1.0” and the engine water temperature TW is 10 ° C. to 30 ° C. Is a region where leaning can be freely performed, the coefficient KLEANTW is set to “0.9”, and the engine coolant temperature TW is 0 ° C. to 10 ° C.
Alternatively, the range of 30 ° C. to 40 ° C. is a region in which a change in the engine speed is likely to occur due to a sudden change in the air-fuel ratio.
LEANTW is changed linearly.

(B) is a graph of table data for setting the coefficient KLEANPA. The vertical axis indicates the coefficient value, and the horizontal axis indicates the intake air temperature PA.

(C) is a graph of table data for setting the coefficient KLEANNE. The vertical axis indicates the coefficient value, and the horizontal axis indicates the engine speed NE.

(D) is a graph of table data for setting the coefficient KLEANPBA. The vertical axis indicates the coefficient value, and the horizontal axis indicates the intake pipe absolute pressure PBA.

(E) is a graph of table data for setting the coefficient KLEANAST. The vertical axis indicates the coefficient value, and the horizontal axis indicates the elapsed time after the start of the engine.

As can be seen from (b) to (e), the coefficient values of each graph are set similarly to the graph of (a).

Returning to the flowchart of FIG. 7, in the subsequent step S63, the coefficients KLEANTW, KLEANPA, KLE read from the leaning table as described above.
All the signals ANNE, KLEANPB, and KLEANAST are multiplied, and the multiplication result is stored in a temporary area KLEANTMP secured at a predetermined position in the RAM.

Next, the value of a flag FΔLEAN for performing a process of changing the value of the temporary area KLEANMP while gradually changing the leaning coefficient KLEAN (with the width of ΔKLEAN) is determined (step S64), and the value of the flag FΔLEAN is determined. If the value is "0", the value of the post-start lean flag FASTLEAN is determined (step S65). Here, the post-start lean flag FASTLE
In order to use the previous value of AN, an area for storing the previous value is provided, for example, at a predetermined position in the RAM.

If it is determined in step S65 that the lean flag FASTLEAN after the previous start is "0", that is, if the condition for performing the lean burn control is satisfied for the first time this time, the flag FΔLEAN is set to "1" (step S65).
66), the leaning coefficient KLEAN is set to an initial value of 1.
0 (step S67), and the leaning coefficient KLEA is set.
A predetermined value ΔKLEAN is subtracted from N, and the leaning coefficient KLEAN is updated to the subtracted value (step S6).
8).

On the other hand, the flag F
When ΔLEAN is “1”, steps S65 to S67
Skip to step S68.

Next, it is determined whether or not the value of the leaning coefficient KLEAN updated in step S68 is larger than the value of the temporary area KLEANTMP calculated in step S63 (step S69). If larger, the current target air-fuel ratio is determined. The coefficient KCMD is multiplied by the leaning coefficient KLEAN, and the multiplied value is updated with the target air-fuel ratio coefficient KCMD (step S70).

That is, the processing of steps S64 to S69 is performed by changing (decreasing) the leaning coefficient KLEAN by the width of ΔKLEAN while obtaining the value KL calculated in step S63.
This is a process for approaching EANTMP. This allows
It is possible to prevent engine speed fluctuations, hunting, and the like due to rapid changes in the air-fuel ratio.

On the other hand, if it is determined in step S65 that the value of the post-start lean flag FASTLEAN is "1", that is, if the flag FΔLEAN is "0" and this time is the second or subsequent lean burn control, Or, in the determination of step S69, the leaning coefficient KLEAN
Is less than or equal to the value of the temporary area KLEANTMP, the flag FΔLEAN is set to “0” (step S7).
1) The leaning coefficient KLEAN is assigned to the temporary area KLE.
After updating to the value of ANTMP (step S72), the process proceeds to step S70.

On the other hand, in step S61, FASTLE
If AN = 0 and the condition for executing the lean burn control after the start is not satisfied, the engine coolant temperature TW becomes equal to the predetermined coolant temperature TWC.
It is determined whether the temperature is higher than the MD (for example, 80 ° C.) (FIG. 6)
Step S73). When TW> TWCMD holds, the KCMD value is set to the basic value KBS calculated in step S21 in FIG. 4 (step S74), and the process proceeds to step S78. When TW ≦ TWCMD is satisfied, a map set in accordance with the engine coolant temperature TW and the intake pipe absolute pressure PBA is searched, and the low coolant temperature target value KT is determined.
WCMD is calculated (step S75), and it is determined whether or not the basic value KBS is larger than the KTWCMD value (step S76). If KBS> KTWCMD, the process proceeds to step S74, where KBS ≦ KTWCM.
D, the basic value KBS is changed to the low water temperature target value KTW.
CMD (step S77), and step S7
Proceed to 8.

In step S78, step S2 in FIG.
It is determined whether or not the WOT flag FWOT set in step 3 is "1". If FWOT = 0, the process is immediately terminated, and
If WOT = 1, a KCMD value setting process for a high load is performed (step S79), and this process ends. In this process, the KCMD value is compared with the high load increase correction coefficients KWOT and KXWOT calculated in step S24 of FIG.
When the CMD value is smaller than these coefficient values, KCMD
The correction is performed by multiplying the value by a correction coefficient KWOT or KXWOT.

Next, the LAF sensor output selection processing in step S3 in FIG. 3 will be described.

Since the exhaust gas of the engine is exhausted in the exhaust stroke, the behavior of the air-fuel ratio in the exhaust system assembly of the multi-cylinder engine is clearly synchronized with the TDC signal pulse. Therefore, it is necessary to detect the air-fuel ratio by the LAF sensor 17 in synchronization with the TDC signal pulse. However, depending on the sample timing of the sensor output, the behavior of the air-fuel ratio may not be accurately grasped. For example, when the air-fuel ratio of the exhaust system collecting part with respect to the TDC signal pulse is as shown in FIG. 9, the air-fuel ratio recognized by the ECU 5 has a completely different value depending on the sample timing as shown in FIG. In this case, it is desirable to perform sampling at a timing at which the actual output change of the LAF sensor can be grasped as accurately as possible.

Further, the change in the air-fuel ratio also differs depending on the arrival time of the exhaust gas to the sensor and the reaction time of the sensor. The time to reach the sensor is the exhaust gas pressure,
It changes depending on the exhaust gas volume and the like. Furthermore, T
Since sampling in synchronization with the DC signal pulse means sampling based on the crank angle,
Inevitably affected by the engine speed NE. As described above, the optimal timing for detecting the air-fuel ratio largely depends on the engine operating state.

Therefore, in this embodiment, as shown in FIG. 11, the output of the LAF sensor sampled every time a CRK signal pulse (generated at every crank angle of 30 degrees) is stored in a ring buffer (18 storages in this embodiment). And the output value at the optimal timing (the optimal value from the value 17 times ago to the current value) is detected equivalent ratio KA
It is converted to CT and used for feedback control.

FIG. 12 is a diagram showing L in step S3 in FIG.
9 is a flowchart of an AF sensor output selection process.

First, in step S81, the engine speed NE and the intake pipe absolute pressure PBA are read, and then it is determined whether or not the current valve timing is the high-speed valve timing (step S82). As a result, in the case of the high-speed valve timing, a timing map for the high-speed valve timing is searched (step S83), and in the case of the low-speed valve timing, a timing map for the low-speed valve timing is searched (step S84). The LAF sensor output VLAF stored in the ring buffer is selected (step S85), and the process ends.

As shown in FIG. 13, according to the engine speed NE and the intake pipe absolute pressure PBA, the timing map shows that the lower the engine speed NE or the higher the intake pipe absolute pressure PBA, the faster the crank angle position. Is set to select the value sampled in. Here, “early” means a value sampled at a position closer to the previous TDC position (in other words, an old value).
The reason for this setting is that the LAF sensor output is as shown in FIG.
As shown in the above, it is best to sample at a position as close as possible to the actual maximum or minimum value of the air-fuel ratio (hereinafter referred to as "extreme value"), but the extreme value, for example, the first peak value is Assuming that the reaction time of the sensor is constant, FIG.
As shown in the figure, the lower the engine speed NE, the faster the crank angle position. The higher the load, the higher the exhaust gas pressure and exhaust gas volume, the higher the exhaust gas flow rate, and the longer the arrival time at the sensor. Because it hastens.

The high-speed valve timing map is as follows.
For the same engine speed NE or intake pipe absolute pressure PBA, the timing is set to be earlier than the low speed valve timing map. This is because the opening timing of the exhaust valve is earlier at the high-speed valve timing than at the low-speed valve timing.

As described above, according to the processing of FIG. 12, the sensor output VLAF sampled at the optimal timing according to the engine operating state is selected, so that the detection accuracy of the air-fuel ratio can be improved. As a result, the estimation accuracy of the air-fuel ratio for each cylinder by the observer is improved, and the accuracy of the air-fuel ratio feedback control for each cylinder can be improved.

When an abnormality of the CRK sensor is detected, the output of the LAF sensor when the TDC signal pulse is generated is adopted.

Next, the calculation processing of the detected equivalent ratio KACT in step S4 of FIG. 3 will be described. FIG. 15 is a flowchart of the KACT calculation process.

First, in step S101, the above-described FIG.
Sensor output selection value VLAFS selected by the process of step 2
By subtracting the sensor output center value VCENT from EL, a temporary value VLAFTEMP is calculated. Here, the center value VCENT is L when the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio.
This is the AF sensor output value.

Next, it is determined whether or not the VLAFTEMP value is a negative value (step S102).
0 and the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the air-fuel ratio is multiplied by a lean correction coefficient KLBLL to obtain VLAFT.
The EMP value is corrected (step S103), while the VLA is corrected.
When FTEMP ≧ 0 and the air-fuel ratio is richer than the stoichiometric air-fuel ratio, multiply by the rich correction coefficient KLBLR,
The VLAFTEMP value is corrected (step S104).
Here, the lean correction coefficient KLBLL and the rich correction coefficient KLBLR are correction coefficients for variation correction calculated according to the value of the label resistance attached to the LAF sensor. The label resistance value is set in advance according to the result of measuring the characteristics of the LAF sensor, and the ECU 5 reads the value to determine the correction coefficients KLBLL and KLBLR.

In a succeeding step S105, a corrected center value VOUTCNT is added to the temporary value VLAFTTEMP to calculate a corrected output value VLAFE.
The KACT table is searched according to the FE value to calculate the detected equivalent ratio KACT (step S106). here,
The KACT table is a table for calculating the detected equivalent ratio KACT according to the corrected output value VLAFE, and the table center value VOUTCNT is the stoichiometric air-fuel ratio (KACT =
1.0) (grid point data (corrected output value)).

By the above processing, it is possible to obtain the detection equivalent ratio KACT excluding the influence of the characteristic variation of the LAF sensor.

FIG. 16 is a flowchart showing the operation of L in step S6 of FIG.
It is a flowchart of AF feedback area determination processing.

First, in step S121, it is determined whether or not the LAF sensor 17 is in an inactive state. When the LAF sensor 17 is in an active state, it is determined whether or not a flag FFC indicating that fuel cut is being performed is "1". (Step S12)
2) When FFC = 0, it is determined whether or not a flag FWOT indicating “1” indicating that the throttle valve is fully opened is “1” (step S123). It is determined whether or not the battery voltage VBAT detected by the sensor that does not operate is lower than a predetermined lower limit value VBLOW (step S124). ) Is determined (step S125). Then, steps S121 to S
If any of the answers 125 is affirmative (YES), PI
A KLAF reset flag FKLA indicating "1" indicating that the D correction coefficient KLAF should be reset to 1.0 (no correction value).
FRESET is set to "1" (step S12)
7).

On the other hand, if all of the answers in steps S121 to S125 are negative (NO), the KLAF reset flag FKLAFRESET is set to "0" (step S125).
126).

In the following step S128, the O2 sensor 1
8 is in an inactive state, and when it is in an active state, the engine coolant temperature TW is reduced to a predetermined lower limit coolant temperature TWLOW.
(For example, 0 ° C.) (step S)
129). Then, when the O2 sensor 18 is in the inactive state or when TW <TWLOW, the hold flag FKLAFHOLD indicating “1” that the PID correction coefficient KLAF should be maintained at the current value is set to “1” ( Step S131), this process ends. On the other hand, when the O2 sensor 18 is in the active state and TW ≧ TWLOW, it is determined that FKLAFHOLD = 0 (step S13).
0), this process ends.

Next, the PID in step S13 in FIG.
The correction coefficient KLAF calculation processing will be described with reference to FIG.

First, in step S141, it is determined whether or not the hold flag FKLAFHOLD is "1".
When AFHOLD = 1, this processing is immediately terminated, and
If KLAFHOLD = 0, it is determined whether the KLAF reset flag FKLAFRESET is "1" (step S142). As a result, FKLAFRESET =
If it is 1, the process proceeds to step S143, where the PID correction coefficient KLAF is set to "1.0", and the integral control gain KI, the target equivalent ratio KCMD, and the detected equivalent ratio KACT are set.
Is set to "0", and the process ends.

In step S142, FKLAFRESET is set.
If = 0, the process proceeds to step S144, in which a proportional control gain KP, an integral control gain KI, and a differential control gain KD are searched from a map set in accordance with the engine speed NE and the intake pipe absolute pressure PBA. However, in the idle state, an idle gain is adopted. Next, the deviation DKAF between the target equivalent ratio KCMD and the detected equivalent ratio KACT
(K) (= KCMD (k) -KACT (k)) is calculated (step S145), and the deviation DKAF (k) and each of the control gains KP, KI, and KD are applied to the following equation to obtain the proportional term K
LAFP (k), integral term KLAFI (k) and derivative term K
LAFD (k) is calculated (step S146).

KLAFP (k) = DKAF (k) × KP KLAFI (k) = DKAF (k) × KI + KLAFI
(K-1) KLAFD (k) = (DKAF (k) -DKAF (k-
1)) × KD In the following steps S147 to S150, the integral term KLAF
The limit processing of I (k) is performed. That is, KLAFI
(K) Values are predetermined upper and lower limit values KLAFILMTH, KLAF
It is determined whether or not it is within the range of ILMTL (step S
147, S148), KLAFI (k)> KLAFIL
If MTH, KLAFI (k) = KLAFLM
TH (step S150), and KLAFI (k) <K
If LAFILMTL, KLAFI (k) = K
LAFILMTL is set (step S149).

In the following step S151, a PID correction coefficient KLAF (k) is calculated by the following equation.

KLAF (k) = KLAFP (k) + KL
AFI (k) + KLAFD (k) +1.0 Next, the KLAF (k) value is increased to a predetermined upper limit value KLAFLMT.
It is determined whether or not it is greater than H (step S152).
When LAF (k)> KLAFLMTH, KLA
F (k) = KLAFLMTH (step S15
5), end this processing.

In step S152, KLAF (k) ≦ K
If LAFLMTH is satisfied, it is determined whether or not the KLAF (k) value is smaller than a predetermined lower limit value KLAFLMTL (step S153), and KLAF (k) ≧ KLAFLMTL.
If this is the case, the process immediately ends, while KLAF (k)
<KLAFLMTL, KLAF (k) = K
The process ends as LAFMTL (step S154).

According to this process, PID control is performed so that the detected equivalent ratio KACT matches the target equivalent ratio KCMD.
An ID correction coefficient KLAF is calculated.

Next, the process of calculating the cylinder-specific correction coefficient KOBSV # N in step S11 of FIG. 3 will be described.

First, the method of estimating the cylinder-by-cylinder air-fuel ratio by the observer will be described, and then the method of calculating the cylinder-by-cylinder correction coefficient KOBSV # N according to the estimated cylinder-by-cylinder air-fuel ratio will be described.

First, in order to accurately separate and extract the air-fuel ratio of each cylinder from the output of one LAF sensor, it is necessary to consider the detection response delay of the LAF sensor. So LA
When the F sensor was modeled as a first-order lag system and a model shown in FIG. 18 was created, it was confirmed by an experiment that the air-fuel ratio obtained based on this model matched well with the true air-fuel ratio. Here, LAF (t) is the output of the LAF sensor, A / F (t) is the input A / F, and α is the gain. The state equation of this model can be expressed by Equation 2.

[0125]

(Equation 2) When this is discretized by the period ΔT, it becomes as shown in Expression 3, and when this is represented by a block diagram, it becomes as shown in FIG.

[0126]

(Equation 3) When this equation 3 is transformed, it becomes as shown in equation 4.
The value at time (k-1) can be inversely calculated from the value at time k as in Expression 5.

[0127]

(Equation 4)

[0128]

(Equation 5) Specifically, when the Z-conversion of Equation 3 is represented by a transfer function, Equation 6 is obtained. Therefore, the inverse transfer function is multiplied by the current LAF sensor output LAF (k) to obtain the previous input air-fuel ratio. A / F (k-1) can be estimated in real time. FIG. 20 shows a block diagram of the real-time A / F estimator.

[0129]

(Equation 6) Next, a method of separating and extracting the air-fuel ratio of each cylinder based on the true air-fuel ratio obtained as described above will be described.

The air-fuel ratio of the exhaust system assembly is considered to be a weighted average in consideration of the temporal contribution of the air-fuel ratio of each cylinder, and the value at time k is represented by Expression 7. Since the fuel amount (F) is used as the operation amount, the fuel-air ratio F / A is used in Expression 7. The fuel-air ratio F / A in Expression 7 means a true value obtained by correcting the response delay of the sensor obtained by Expression 5.

[0131]

(Equation 7) That is, the air-fuel ratio of the collecting portion is represented by the sum of the past combustion history of each cylinder multiplied by the weight C (for example, 40% for the immediately preceding cylinder, 30% before that, etc.). This model is represented by a block diagram as shown in FIG. 21, and its state equation is as shown in Expression 8.

[0132]

(Equation 8) When the fuel-air ratio of the collecting portion is set to y (k), the output equation can be expressed as Expression 9.

[0133]

(Equation 9) In Equation 9, since u (k) cannot be observed, x (k) cannot be observed even if an observer is designed from this state equation. Therefore, if it is assumed that x (k + 1) = x (k−3) assuming that the air-fuel ratio before 4TDC (that is, the same cylinder) is in a steady operation state in which the air-fuel ratio does not rapidly change, Expression 9 becomes Expression 10. .

[0134]

(Equation 10) FIG. 22 shows that the air-fuel ratio of three cylinders of a four-cylinder engine is 14.7.
When the air-fuel ratio of one cylinder is 12.0,
It is a diagram showing the transition of the output value and the measured value of the model,
It was confirmed that the above model well modeled the exhaust system of a four-cylinder engine. Therefore, the problem of estimating the cylinder-by-cylinder air-fuel ratio from the gathering portion A / F is reduced to the problem of a normal Kalman filter that observes x (k) using the state equation and the output equation shown in Expression 11. When the Riccati equation is solved using the weight matrices Q and R as in Equation 12, the gain matrix K is as shown in Equation 13.

[0135]

[Equation 11]

[0136]

(Equation 12)

[0137]

(Equation 13) From this, when (A-KC) is obtained, it becomes as shown in Expression 14.

[0138]

[Equation 14] Here, the configuration of a general observer is as shown in FIG. 23, but since there is no input u (k) in the model of the present embodiment, a configuration in which only y (k) is input as shown in FIG. This can be expressed by the following equation.

[0139]

(Equation 15) Therefore, the estimated value x hat (k) of the current fuel-air ratio for each cylinder can be calculated from the collective fuel-air ratio y (k) and the estimated value X hat (k) of the past fuel-air ratio for each cylinder. .

Here, the observer that receives y (k) as an input, that is, the system matrix S of the Kalman filter is represented by Expression 16.

[0141]

(Equation 16) In the model of the present embodiment, the load distribution R of the Riccati equation
When the element of Q: the element of Q = 1: 1, the system matrix S becomes
It is given by Expression 17.

[0142]

[Equation 17] FIG. 25 is a block diagram in which the above-described model and an observer are combined, and a simulation result has been obtained in which the cylinder-by-cylinder air-fuel ratio obtained therefrom matches well with the actually measured value. As described above, in this embodiment, since the response delay of the LAF sensor is taken into consideration and an observer is introduced, the air-fuel ratio of each cylinder can be accurately extracted from the air-fuel ratio of the collecting section.

FIG. 26 is a flowchart of the above-described cylinder-by-cylinder air-fuel ratio estimation processing.

In the same figure, in step S161, an observer calculation for high-speed valve timing (ie, a calculation for estimating the air-fuel ratio for each cylinder) is performed, and in the following step S162,
Observer calculation for low-speed valve timing is performed. Then, it is determined whether or not the current valve timing is high-speed valve timing (step S163). If the current valve timing is high-speed valve timing, an observer calculation result for high-speed valve timing is selected (step S164). Then, an observer calculation result for low-speed valve timing is selected (step S165).

As described above, regardless of the current valve timing, the observer calculation for the high-speed and low-speed valve timings is performed together, and according to the current valve timing,
The calculation result is selected because the cylinder-by-cylinder air-fuel ratio estimation calculation requires several calculations to converge. As a result, the accuracy of estimating the cylinder-by-cylinder air-fuel ratio immediately after the switching of the valve timing can be improved.

Next, a method of calculating the cylinder-specific correction coefficient KOBSV # N based on the estimated cylinder-specific air-fuel ratio will be described with reference to FIG.

That is, the target A / F is calculated by dividing the collecting portion A / F by the last calculated value of the average value of the cylinder-specific correction coefficients KOBSV # N of all cylinders, and the cylinder-by-cylinder correction coefficient KO of the # 1 cylinder is calculated.
BSV # 1 is obtained by PID control so that the deviation between the target A / F and the estimated air-fuel ratio A / F # 1 of cylinder # 1 becomes zero. Similar calculations are performed for the # 2 to # 4 cylinders to calculate KOBSV # 2 to # 4.

As a result, the air-fuel ratio of each cylinder converges to the collective air-fuel ratio, and the collective air-fuel ratio converges to the target air-fuel ratio by the PID correction coefficient KLAF. The air-fuel ratio can be converged. Further, a cylinder-by-cylinder correction coefficient learning value KOBSV # Nsty, which is a learning value of the cylinder-by-cylinder correction coefficient KOBSV # N, is calculated and stored by the following equation.

KOBSV # Nsty = C × KOBSV #
N + (1−C) × KOBSV # Nsty (n−1) Here, C is a weight coefficient, and KOBSV # Nsty
(N-1) is the previous learning value.

In the actual operation, the set A /
F is the detected equivalent ratio KACT, and the estimated air-fuel ratio A
/ F # N and target A / F are also calculated as equivalent ratios.

FIG. 28 is a flowchart showing the procedure of misfire determination used in step S47 of FIG.

FIG. 17A shows a CRK process which is executed in synchronism with each generation of the CRK signal pulse. In this process, the generation time interval of the CRK signal pulse (in proportion to the reciprocal of the engine speed). An average value of the parameters (hereinafter, referred to as a "first average value") TAVE is calculated (step S171).

FIG. 13B shows a TDC process executed in synchronism with the generation of each TDC signal pulse. In this process, the first average value TAVE calculated by the CRK process is shown.
(Hereinafter referred to as “second average”) M change amount Δ
Based on M (step S172), it is determined whether or not a misfire has occurred in engine 1 (step S173).

FIG. 29 is a flowchart of a program for calculating the first average value TAVE.

In the step S181, the generation time interval CRMe (n) of the CRK signal pulse is measured. Specifically, every time the crankshaft rotates 30 degrees, the CRMe
(N), CRMe (n + 1), CRMe (n + 2)...

In step S182, 1
The first average value TAVE (n) is calculated as the average value of 12 CRMe values from the previous measurement value CRMe (n-11) to the latest measurement value CRMe (n).

[0157]

(Equation 18) In this embodiment, since the CRK signal pulse is generated every time the crankshaft rotates 30 degrees, the first average value TAVE (n)
Is an average value corresponding to one rotation of the crankshaft. By performing such an averaging process, one revolution of the crankshaft becomes one.
It is possible to remove a primary vibration component of the periodic engine rotation, that is, a noise component due to a mechanical error (manufacturing error, mounting error, etc.) of the pulsar or pickup constituting the crank angle sensor 11.

The engine speed NE is calculated based on the TAVE (n) value.

FIG. 30 is a flowchart showing step S17 in FIG.
2 is a flowchart specifically showing the processing in FIG.

In step S191, the following equation (19) is used.
The calculated value TAVE (n−5) five times before the first average value TAVE
6 TAs from 5) to the latest calculated value TAVE (n)
A second average value M (n) is calculated as the average value of the VE values.

[0161]

[Equation 19] In this embodiment, the engine 1 is a four-cylinder four-cycle engine, and ignition is performed in one of the cylinders every time the crankshaft rotates 180 degrees. Therefore, the second average value (n)
Is the average value of the first average value TAVE (n) for each ignition cycle. By performing such an averaging process, the torque variation of the engine rotation due to combustion is represented by 2
The next vibration component, that is, the vibration component of the crankshaft half rotation cycle can be removed.

In the following step S192, the following equation is used.
High-pass filter processing of the second average value M (n) is performed.
The second average value after the high-pass filter processing is FM (n).

FM (n) = b (1) × M (n) + b (2) × M
(N−1) + b (3) × M (n−2) −a (2) × FM (n−
1) −a (3) × FM (n−2) where b (1) to b (3), a (2) and a (3) are filter transfer coefficients, for example, 0.2096, − 0.4192,
The values are set to 0.2096, 0.3557, and 0.1940. Further, FM (0) and FM (1) each have a value of 0, and the above expression is applied to n having a value of 2 or more.

By this high-pass filter processing, M
(N) The low-frequency component of about 10 Hz or less included in the value is removed, and the influence of vibration transmitted from the driving system to the engine (for example, vibration due to torsion of the crankshaft, road surface vibration transmitted from the tire, etc.) can be removed. it can.

In the following step S193, the variation ΔM of the second average value FM (n) subjected to the high-pass filter processing is set to ΔM.
(N) is calculated by the following equation.

ΔM (n) = FM (n) −FM (n−1) The second average value FM after high-pass filter processing
In (n), since the polarity is inverted with respect to the M (n) value, when a misfire occurs in the engine 1, the M (n) value increases, so the FM (n) value increases in the negative direction, and ΔM (N) The value also tends to increase in the negative direction.

FIG. 31 is a flowchart of a program for performing misfire determination and misfire cylinder determination based on the change amount ΔM calculated as described above.

In step S201, monitor execution conditions,
That is, it is determined whether or not the misfire determination can be performed. The monitoring execution condition is satisfied, for example, when the engine operation state is in a steady state and the engine water temperature TW, the intake air temperature TA, the engine rotation speed NE, and the like are within a predetermined range.

When the monitor execution condition is not satisfied, this program is immediately terminated. When the monitor execution condition is satisfied, whether the change amount ΔM is smaller than a predetermined negative value MSLMT (| ΔM | is | MSLMT | Good or not). Here, the negative predetermined value MSLMT
Is read from a map set in accordance with the engine speed NE and the engine load (intake pipe absolute pressure PBA). The absolute value of the MSLMT value is set to decrease as the engine speed NE increases, and set to increase as the engine load increases.

When the answer to step S202 is negative (NO), that is, when ΔM ≧ MSLMT holds, the program is immediately terminated, and the answer to step S202 is affirmative (YE
S), that is, when ΔM <MSLMT is satisfied, it is determined that a misfire has occurred in the previously ignited cylinder. As described above, when a misfire occurs, the ΔM (n) value increases in the negative direction.

The reason why the misfire is determined to have occurred in the previous ignition cylinder is that a delay occurs due to the high-pass filter processing.

In this embodiment, the misfire determination is made by the above method. However, the present invention is not limited to this, and any method may be used as long as the misfire can be determined.

As described above, according to the present embodiment,
Observe the variation in air-fuel ratio for each cylinder with the observer,
Since the air-fuel ratio is controlled in accordance with the observation result, the lean burn control immediately after the start of the engine can be performed in a wider range, and when the engine state is out of the range, the lean burn control can be performed immediately after the start of the engine. Since the configuration is such that the lean burn control is stopped, it is possible to prevent a decrease in engine speed, a stall, a deterioration in a feeling of acceleration, and the like.

[0174]

As described above, according to the present invention,
In the operating condition detecting means of the vehicle equipped with an internal combustion engine
When the gear state is detected by the air-fuel ratio changing means,
Since the air-fuel ratio than the stoichiometric air-fuel ratio has been set to the lean side is changed richer, deterioration of the stall and acceleration feeling of the engine due to driving the vehicle during the lean-burn control immediately after institutional starting And the like can be prevented.

[0175]

[0176]

[0177]

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an internal combustion engine and a control device thereof according to an embodiment of the present invention.

FIG. 2 is a functional block diagram for explaining a method of calculating a fuel injection time TOUT (N).

FIG. 3 is a flowchart of a process for calculating a PID correction coefficient KLAF and a cylinder-specific correction coefficient KOBSV # N according to the output of the LAF sensor of FIG. 1;

FIG. 4 is a flowchart of a process for calculating a final target air-fuel ratio coefficient KCMDM in step S2 of FIG. 3;

FIG. 5 is a flowchart of a post-start lean determination process in step S23 of FIG. 4;

FIG. 6 is a flowchart of a KCMD calculation process in step S25 of FIG. 4;

FIG. 7 is a flowchart of a KCMD calculation process in step S25 of FIG.

FIG. 8 is a diagram showing a lean table for reading out each coefficient for determining a leaning coefficient KLEAN.

FIG. 9 is a diagram for explaining a relationship between TDC of a multi-cylinder internal combustion engine and an air-fuel ratio of an exhaust system collecting part.

FIG. 10 is a diagram for explaining the quality of a sample timing with respect to an actual air-fuel ratio.

FIG. 11 is a diagram for explaining a method of obtaining an output value at an optimal timing from an LAF sensor output sampled every time a CRK signal pulse is generated.

FIG. 12 is a flowchart of an LAF sensor output selection process in step S3 of FIG. 3;

FIG. 13 is a diagram showing characteristics of a timing map used in the flowchart of FIG.

FIG. 14 is a graph showing sensor output characteristics with respect to the engine speed and the engine load for explaining the characteristics of FIG. 13;

FIG. 15 is a detection equivalent ratio KA in step S4 of FIG. 3;
It is a flowchart of a calculation process of CT.

FIG. 16 is a flowchart of a LAF feedback area determination process in step S6 of FIG. 3;

FIG. 17 is a flowchart of a PID correction coefficient KLAF calculation process in step S13 of FIG. 3;

FIG. 18 is a block diagram showing a model obtained by assuming that the LAF sensor is a first-order delay system.

19 is a block diagram showing a model obtained by discretizing the model of FIG. 18 with a period ΔT.

FIG. 20 is a block diagram illustrating a true air-fuel ratio estimator that models the detection behavior of the LAF sensor.

FIG. 21 is a block diagram illustrating a model showing a behavior of an exhaust system of the internal combustion engine.

FIG. 22 shows that the air-fuel ratio of three cylinders of a four-cylinder engine is 14.7.
When the air-fuel ratio of one cylinder is 12.0,
FIG. 22 is a diagram showing transitions of output values and measured values of the model of FIG. 21.

FIG. 23 is a block diagram showing a configuration of a general observer.

FIG. 24 is a block diagram showing a configuration in a case where the general observer of FIG. 23 is rewritten for the model used in the present embodiment.

25 is a block diagram in which the model in FIG. 21 and the observer in FIG. 23 are combined.

FIG. 26 is a flowchart of a cylinder-by-cylinder air-fuel ratio estimation process.

FIG. 27 is a diagram for explaining a method of calculating a cylinder-specific correction coefficient KOBSV # N based on the cylinder-specific air-fuel ratio estimated by the processing of FIG. 26;

FIG. 28 is a flowchart showing a misfire determination procedure used in step S47 of FIG. 5;

FIG. 29 is a flowchart of a program for calculating a first average value TAVE.

FIG. 30 is a flowchart specifically showing the processing in step S172 of FIG. 28;

FIG. 31 is a flowchart of a program for performing misfire determination and misfire cylinder discrimination based on the change amount ΔM calculated in FIG. 30;
It is.

[Explanation of symbols]

4 throttle valve opening sensor 5 EC U 10 PBA sensor 13 Engine coolant temperature sensor 14 crank angle sensor B11 observers server

──────────────────────────────────────────────────続 き Continuation of the front page (72) Norio Suzuki, Inventor 1-4-1 Chuo, Wako-shi, Saitama Prefecture Honda R & D Co., Ltd. (56) References JP-A-6-288276 (JP, A) JP-A Sho 62-165543 (JP, A) JP-A-60-233331 (JP, A) JP-A-3-225050 (JP, A) JP-A-2-153243 (JP, A) (58) Fields investigated (Int. Cl ^7, DB name) F02D 41/00 -. 41/40 F02D 43/00 - 43/04 F02D 45/00

Claims (1)

(57) [Claims] The control apparatus according to claim 1 an internal combustion engine for operation control in the air-fuel ratio leaner than the stoichiometric air-fuel ratio of the internal combustion engine immediately after the start of the internal combustion engine, the in-gear state of the transmission of a vehicle equipped with the internal combustion organizations Operating state detecting means for detecting, and when the in- gear state is detected by the operating state detecting means, the air-fuel ratio at which the internal combustion engine is operated is set to an air-fuel ratio richer than the lean-side air-fuel ratio. A control device for an internal combustion engine, comprising: air-fuel ratio changing means for changing to a fuel ratio.