JPH11351020A - Lean burn engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress torque shocks during a changeover to a lean air-fuel ratio by optimizing the adaptation of the air-fuel ratio to engine output torque. SOLUTION: A throttle opening criterion TVOLE is selected by interpolation from a throttle-opening criterion table employing engine speed NE as parameter (S50). A determination is then made whether a throttle opening angle TVO, even with a hysteresis as the case may be, is less than the throttle opening criterion TVOLE (S52, S54). If this proposition is acceptable, a throttle opening determination flag FTVO is set to '1' (S53) to change the air-fuel ratio on a stoichiometric or rich level to a lean air-fuel ratio in the range wherein the generated engine torque is held substantially constant, with the result that no torque shocks are produced.

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 a lean burn engine which switches between a stoichiometric air-fuel ratio or a rich air-fuel ratio and a lean air-fuel ratio in accordance with a result of a determination of permission / prohibition of lean burn.

[0002]

2. Description of the Related Art Conventionally, there has been known a lean burn engine which operates at a lean air-fuel ratio in a low and medium load range, thereby improving fuel efficiency by reducing pumping loss and improving theoretical thermal efficiency.

For example, Japanese Patent Application Laid-Open No. 9-287497 discloses that the air-fuel ratio (oxygen) sensor is activated, the engine has been warmed up, the load is in a predetermined lean region, and the rotation speed is predetermined. A technology is disclosed in which lean operation is permitted and the air-fuel ratio is switched to lean when conditions such as a lean region, a second gear position or higher, and a vehicle speed within a predetermined range are satisfied.

[0004]

However, when switching from a stoichiometric air-fuel ratio or a rich air-fuel ratio to a lean air-fuel ratio, if the engine speed is simply switched to a lean air-fuel ratio only in a predetermined lean region, the engine is switched depending on the operating region. Output torques of the motors cause a torque shock.

The present invention has been made in view of the above circumstances, and provides a control device for a lean burn engine that realizes an optimum match with an engine output torque when switching to a lean air-fuel ratio and can reduce a torque shock. With the goal.

[0006]

According to a first aspect of the present invention, a stoichiometric air-fuel ratio or a rich air-fuel ratio is switched between a rich air-fuel ratio and a lean air-fuel ratio in accordance with a result of a determination of permission / prohibition of lean burn. In the control device for a lean-burn engine provided with an air-fuel ratio switching means, as shown in the basic configuration diagram of FIG. 1, determination of a throttle opening indicating a boundary of a region where intake air amounts are substantially equal for each set range of engine speed. A throttle opening determining means for permitting lean burn when a current throttle opening is set to a value equal to or less than the determination value.

That is, according to the first aspect of the present invention, when the current throttle opening is equal to or smaller than the determination value indicating the boundary of the region where the intake air amount set for each set range of the engine speed is substantially equal, the lean state is determined. By permitting the burn and switching to the lean air-fuel ratio, the air-fuel ratio can be switched on the equal torque line of the engine to avoid torque shock.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. 2 to 32 relate to an embodiment of the present invention, FIG. 2 is a flowchart of a cylinder discrimination / engine speed calculation routine, FIG. 3 is a flowchart of a fuel injection amount setting routine, and FIG. 4 is an air-fuel ratio feedback correction coefficient setting. 5 is a flowchart of various correction coefficient setting routines, FIG. 6 is a flowchart of a leaning correction coefficient setting routine, FIGS. 7 and 8 are flowcharts of a leaning permission coefficient setting routine, and FIGS.
FIG. 15 is a flowchart of a lean burn execution possible determination routine, FIG. 16 is a flowchart of a lean burn possible deceleration determination routine, FIG. 17 is a flowchart of a vehicle speed change calculation routine, FIG. 18 is a flowchart of a high catalyst temperature lean burn permission condition determination routine, 19 is a flowchart of a catalyst temperature integration routine, FIG. 20 is a time chart showing a setting state of an air-fuel ratio feedback correction coefficient based on an O2 sensor output, FIG. 21 is an explanatory diagram of a lean upper limit map, and FIG. 22 is a lean target value. FIG. 23 is an explanatory view of a map, FIG. 23 is an explanatory view showing a change in a leaning permission coefficient due to lean burn inhibition / permission, FIG. 24 is an explanatory view of lean burn execution determination conditions, and FIG. 25 is an explanatory view of a throttle opening degree determination value table. FIG. 26 is an explanatory diagram of the deceleration condition in which lean burn is possible, and FIG. FIG. 28 is a time chart showing the relationship among the engine, the cylinder discrimination pulse, the combustion stroke cylinder, the ignition signal, and the injector drive signal.
9 is an explanatory view showing details of a main part of an intake system, FIG. 30 is a front view of a crank rotor and a crank angle sensor, FIG. 31 is a front view of a cam rotor and a cylinder discrimination sensor, and FIG. 32 is a circuit configuration diagram of an electronic control system. .

In FIG. 28, reference numeral 1 denotes a lean burn engine (hereinafter simply abbreviated as "engine") that performs lean burn (lean burn) operation by stratified combustion in substantially the entire region except for a part of the operation region. In the drawings, a horizontally opposed four-cylinder gasoline engine is shown. Cylinder heads 2 are provided in both left and right banks of a cylinder block 1a of the engine 1, respectively, and each cylinder head 2 is formed with an intake port 2a and an exhaust port 2b.

As an intake system of the engine 1, an intake manifold 3 communicates with each intake port 2a, and a throttle valve interlocked with an accelerator pedal through an air chamber 4 in which intake passages of respective cylinders are connected to the intake manifold 3. The throttle chamber 5 in which 5a is interposed communicates. An air cleaner 7 is mounted on the upstream side of the throttle chamber 5 via an intake pipe 6, and a chamber 8 communicates with a middle of an air intake passage connected to the air cleaner 7.

The intake pipe 6 has a throttle valve 5
a bypass passage 9 is connected to the bypass passage 9 to control the idle rotation speed by adjusting the amount of bypass air flowing through the bypass passage 9 according to the valve opening during idling. A valve (ISC valve) 10 is interposed.

Further, an injector 11 is disposed immediately upstream of the intake port 2a of each cylinder of the intake manifold 3. The engine 1 of this embodiment is an SOHC four-valve engine having two intake valves 12 and two exhaust valves 13 for each cylinder. The injector 11 employs, for example, a two-way injection type injector. The two injection valves 1 for each cylinder are arranged such that each injection direction of the injector 11 is directed toward the valve head of each intake valve 12.
Between them, an ignition plug 15 for exposing the discharge electrode portion to the combustion chamber 14 is provided. An igniter 17 is connected to the ignition plug 15 via an ignition coil 16 provided for each cylinder.

As shown in FIG. 29, the intake port 2a
Is formed in the shape of a straight port. At low and medium loads where the amount of intake air is small, the air-fuel mixture flowing from the intake port 2a into the combustion chamber 14 through each intake valve 12 is applied to the combustion chamber 14 as shown in FIG. A so-called tumble flow in the vertical direction is generated as shown by an arrow in FIG. 3, and during the lean air-fuel ratio control, the tumble flow enables stratified combustion, and lean burn is performed. Further, at the time of a high load with a large intake air amount, the air-fuel mixture flowing into the combustion chamber 14 is flow-enhanced by the tumble flow, so that the combustibility is improved. ) Ensures the engine output.

The injector 11 is connected to a fuel tank 19 via a fuel supply passage 18. The fuel tank 19 is provided with an in-tank type fuel pump 20. The fuel from the fuel pump 20 is pumped to the injector 11 and the pressure regulator 22 through a fuel filter 21 interposed in the fuel supply passage 18, and is returned from the pressure regulator 22 to the fuel tank 19 to be supplied to the injector 19. The fuel pressure to 11 is regulated to a predetermined pressure.

A discharge passage 23 for discharging the fuel vapor generated in the fuel tank 19 extends from an upper portion of the fuel tank 19, and communicates with an upper portion of a canister 25 via a two-way valve 24. I have. Inside the canister 25, an adsorbing portion made of activated carbon or the like is provided.
Further, a fresh air introduction port communicating with the atmosphere is opened at a lower portion, and the fresh air from the fresh air introduction port and the evaporated fuel stored in the adsorbing section are mixed as a mixture from the purge passage 26 to the air chamber 4. The air is guided by the negative pressure in the air chamber 4.

Downstream of the canister 25 in the purge passage 26, there is provided a proportional control valve such as a duty solenoid valve or a linear solenoid valve for controlling the amount of fuel vapor purged from the canister 25 into the air chamber 4. A canister purge control (CPC) solenoid valve 27 is interposed.

On the other hand, as an exhaust system of the engine 1, an exhaust pipe 29 is communicated with a collection portion of an exhaust manifold 28 which communicates with each exhaust port 2 b of the cylinder head 2, and a catalytic converter 30 is interposed in the exhaust pipe 29. To the muffler 31. This catalytic converter 30 includes:
For example, NO such as alkali metal, alkaline earth, rare earth, etc.
a NOx storage type catalyst in which an x storage material and a noble metal such as platinum are supported on a carrier such as alumina,
Due to the storage function of Ox and O2, when the oxygen concentration of the exhaust gas is high, HC and CO are oxidized and reduced and NO
Absorb x. Then, when the oxygen concentration in the exhaust gas decreases, the stored NOx is released, and the NOx is reduced and purified by the excess HC and CO that are not oxidized and reduced.

Next, sensors for detecting the operating state of the engine will be described. Air cleaner 7 for intake pipe 6
A thermal intake air amount sensor 32 using a hot wire or a hot film is interposed immediately downstream of the throttle valve 5a provided in the throttle chamber 5 and a throttle opening sensor 33a and a throttle valve 5a. O with fully closed
A throttle sensor 33 having a built-in idle switch 33b for N is connected in series. Further, an intake pipe pressure sensor 34 for detecting the pressure (intake pipe pressure) downstream of the throttle valve 5a as an absolute pressure is connected to the air chamber 4.

The cylinder block 1a of the engine 1
A knock sensor 35 is attached to the cooling water passage 3 communicating the left and right banks of the cylinder block 1a.
6, a cooling water temperature sensor 37 is provided. An exhaust temperature sensor 38 for detecting an exhaust gas temperature immediately upstream of the catalyst and an exhaust temperature sensor 38 for detecting whether the stoichiometric fuel is rich or lean are provided upstream of the catalytic converter 30. An O2 sensor 39 is provided.

The crankshaft 40 of the engine 1
A crank angle sensor 42 is provided on the outer periphery of a crank rotor 41 which is axially mounted on the cam shaft 43. A cylinder discriminating sensor 45 is provided on a cam rotor 44 connected to a cam shaft 43 which makes a half turn with respect to the crank shaft 40. Has been established.

As shown in FIG. 30, the crank rotor 41 has projections 41a, 41b, and 41c formed on the outer periphery thereof, and these projections 41a, 41b, and 41c are connected to the cylinders (# 1 and # 2 cylinders). (# 3, # 4 cylinders) before compression top dead center (BTDC) θ1, θ2, θ3.
In this embodiment, θ1 = 97 ° CA, θ2 = 65 ° C
A, θ3 = 10 ° CA.

As shown in FIG. 31, on the outer periphery of the cam rotor 44, projections 44a, 44b,
A projection 44a is formed at a position θ4 after the compression top dead center (ATDC) of the # 3 and # 4 cylinders.
b is composed of three protrusions, and the first protrusion is A of the # 1 cylinder.
It is formed at the position of TDCθ5. Further, the protrusion 44c
Is formed by two projections, and the first projection is the AT of the # 2 cylinder.
It is formed at the position of DCθ6. In this embodiment,
θ4 = 20 ° CA, θ5 = 5 ° CA, θ6 = 20 ° CA.

As shown in the time chart of FIG. 27, the crank rotor 41 and the cam rotor 44 are rotated by the rotation of the crankshaft 40 and the camshaft 43 in association with the operation of the engine, and each projection of the crank rotor 41 is connected to the crank angle sensor. 42, and θ1, θ2, θ3 (BTDC 97 °, 65
°, 10 ° CA) each crank pulse of engine 1/2
Output every rotation (180 ° CA). On the other hand, between the θ3 crank pulse and the θ1 crank pulse, the cam rotor 4
4 are detected by the cylinder discrimination sensor 45, and a predetermined number of cylinder discrimination pulses are output from the cylinder discrimination sensor 45.

The following electronic control unit (ECU) 5
0, the engine speed NE is calculated based on the input interval time Tθ of the crank pulse output from the crank angle sensor 42, and the order of combustion strokes of each cylinder (for example,
# 1 cylinder → # 3 cylinder → # 2 cylinder → # 4 cylinder) and a value obtained by counting the cylinder discrimination pulse from the cylinder discrimination sensor 45 by the counter, based on the pattern of the combustion stroke cylinder, fuel injection target cylinder and ignition. The cylinder of the target cylinder is determined.

The ECU 50 is provided with the above-described injector 11,
Spark plug 15, ISC valve 10, CPC solenoid valve 2
7 for calculating the control amounts for actuators such as 7 and outputting control signals, that is, engine control such as fuel injection control including air-fuel ratio control, ignition timing control, idle speed control, and evaporative fuel purge control. As shown in FIG. 32, a CPU 51, a ROM 52, a RAM 53, a backup RAM 54, a counter / timer group 55, and an I / O interface 56 are mainly configured by a microcomputer connected to each other via a bus line. , A drive circuit 58 connected to the I / O interface 56, and A /
A peripheral circuit such as a D converter 59 is built in.

The counter / timer group 55 generates various counters such as a free-run counter, a counter for counting the input of a cylinder discrimination sensor signal (cylinder discrimination pulse), a fuel injection timer, an ignition timer, and a periodic interrupt. Timer for inputting a crank angle sensor signal (crank pulse), a timer for measuring the elapsed time after starting the engine, and a watchdog timer for monitoring system abnormalities. The timer is a generic term for convenience, and various other software counters and timers are used.

The constant voltage circuit 57 is connected to a battery 61 via a first relay contact of a power supply relay 60 having two circuit relay contacts.
0 relay coil is connected via an ignition switch 62. The constant voltage circuit 57 is directly connected to the battery 61. When the ignition switch 62 is turned on and the contact of the power supply relay 60 is closed, the constant voltage circuit 57 supplies power to each unit in the ECU 50. Regardless of ON or OFF,
A backup power supply is supplied to the backup RAM 54.

Further, the fuel pump 20 is connected to the battery 61 via a relay contact of a fuel pump relay 63. A power supply line for supplying power from the battery 61 to each actuator is connected to the second relay contact of the power supply relay 60.

The input port of the I / O interface 56 includes an idle switch 33b and a knock sensor 3
5, a crank angle sensor 42, a cylinder discrimination sensor 45, a vehicle speed sensor 46 for detecting a vehicle speed, and a starter switch 47 for detecting an engine start state are connected.
Further, via the A / D converter 59, the intake air amount sensor 3
2, throttle opening sensor 33a, cooling water temperature sensor 3
7, the O2 sensor 39, the exhaust gas temperature sensor 38, and the intake pipe pressure sensor 34 are connected, and the battery voltage VB is input and monitored.

On the other hand, the ISC valve 10, the injector 11, the C
The PC solenoid valve 27 and the relay coil of the fuel pump relay 63 are connected via the drive circuit 58, and the igniter 17 is connected.

In accordance with the control program stored in the ROM 52, the CPU 51 processes the detection signals from the sensors and switches, which are input via the I / O interface 56, the battery voltage, and the like, and stores them in the RAM 53. Based on various data, various learning value data stored in the backup RAM 54, fixed data stored in the ROM 52, etc., the fuel injection amount, the ignition timing, the duty ratio of the control signal for the ISC valve 10, the intake air of the evaporated fuel , And performs engine control such as fuel injection control including air-fuel ratio control, ignition timing control, idle speed control, and evaporative fuel purge control.

In such an engine control system, EC
In U50, it is determined from various conditions whether or not the current operating state is a state in which lean burn can be performed. Based on the determination result, execution / stop of air-fuel ratio feedback correction based on the output of the O2 sensor 39 is determined. , The fuel injection pulse width Ti that determines the final fuel injection amount to be supplied to the engine
Is set as a leaning correction coefficient FLEAN for correcting the amount of reduction.

As is well known, the fuel injection pulse width Ti which determines the final fuel injection amount to be supplied to the engine determines the basic stoichiometric fuel injection amount calculated from the engine speed NE and the intake air amount Q. Various correction coefficients C based on the engine operating state with respect to the basic fuel injection pulse width Tp
It is set by adding a correction mainly including an air-fuel ratio feedback correction coefficient LAMBDA based on the output of the OEF and O2 sensor 39.

The leaning correction coefficient FLEAN is given as one of the correction terms in the various correction coefficients COEF as a subtraction term with respect to other correction terms set in accordance with the engine operating state. (Air-fuel ratio feedback stop; LAMBDA = 1.0), the stoichiometric basic fuel injection pulse width Tp is reduced and corrected to obtain a lean air-fuel ratio.

In this case, when switching from the stoichiometric state (including the rich air-fuel ratio) to the lean air-fuel ratio, a torque shock may occur due to a change in the output torque of the engine. As one of the conditions, the condition that the throttle opening TVO is equal to or less than a set judgment value (throttle opening judgment value TVOLE described later) corresponding to the engine speed NE is provided, and the air-fuel ratio is switched in a region where the output torques are substantially equal. This reduces the torque shock.

That is, the ECU 50 realizes a function as air-fuel ratio switching means for switching between a stoichiometric air-fuel ratio or a rich air-fuel ratio and a lean air-fuel ratio in accordance with the result of the determination of permission / prohibition of lean burn. The function as the throttle opening determination means is also realized.

Hereinafter, the processing related to the lean burn control executed by the ECU 50 will be described with reference to the flowcharts of FIGS.

First, the ignition switch 62 is turned on.
Then, when the power is supplied to the ECU 50, the system is initialized, and each flag and each counter are initialized except for data such as various learning values stored in the backup RAM 54. And the starter switch 47
Is turned on and the engine 1 is started, the cylinder discriminating / engine speed calculating routine of FIG. 2 is executed every time a crank pulse is input from the crank angle sensor 42, discriminating the fuel injection target cylinder and the ignition target cylinder, and The calculation of the number NE is performed.

In this cylinder discriminating / engine speed calculating routine, when the crank rotor 41 rotates in response to engine operation and a crank pulse is input from the crank angle sensor 42, first, in step S1, the current input crank angle is set. Whether the pulse corresponds to the crank angle of θ1, θ2, or θ3 is identified based on the input pattern of the cylinder determination pulse from the cylinder determination sensor 45. In step S2, the input pattern of the crank pulse and the cylinder determination pulse is determined. , The cylinders such as the combustion stroke cylinder, the ignition target cylinder, and the fuel injection target cylinder are determined.

That is, as shown in the time chart of FIG. 27, for example, if there is a cylinder discrimination pulse input between the previous crank pulse input and the present crank pulse input, the current crank pulse becomes θ1 The crank pulse can be identified as a crank pulse, and the crank pulse input next time can be identified as a θ2 crank pulse.

If there is no cylinder discrimination pulse input between the previous and current crank pulse inputs and there is a cylinder discrimination pulse input between the last two previous and previous crank pulse inputs, the current crank pulse will be the θ2 crank pulse. The crank pulse input next time can be identified as the θ3 crank pulse. Further, if there is no cylinder discrimination pulse input between the previous and current times and between the last and last crank pulse inputs, the currently input crank pulse can be identified as the θ3 crank pulse, and the next input crank pulse can be identified. The pulse can be determined as a θ1 crank pulse.

Further, when three cylinder discriminating pulses are inputted (the .theta.5 cylinder discriminating pulse corresponding to the projection 44b) between the previous and current crank pulse inputs, the next top dead center of the compression is # 3 cylinder, and The combustion stroke cylinder is # 1 cylinder, the ignition target cylinder is # 3 cylinder, and the fuel injection cylinder is
It can be determined that the cylinder # 2 is two cylinders behind it.

Two cylinder discrimination pulses are input between the previous and current crank pulse inputs (θ corresponding to the projection 44c).
The next compression top dead center is #
There are four cylinders, the current combustion stroke cylinder is # 2 cylinder, the ignition target cylinder is # 4 cylinder, and the fuel injection target cylinder is # 3
It can be determined as a cylinder.

One cylinder discrimination pulse is input between the previous and current crank pulse inputs (θ corresponding to the protrusion 44a).
When the previous compression top dead center determination is # 4 cylinder, the next compression top dead center is # 1 cylinder,
The current combustion stroke cylinder is # 4 cylinder, the ignition target cylinder is # 1 cylinder, and the fuel injection target cylinder is # 2 cylinder. Similarly, when one cylinder discrimination pulse is input between the previous and current crank pulse inputs and the previous compression top dead center determination was # 3 cylinder, the next compression top dead center is # 2 cylinder, The current combustion stroke cylinder is # 3 cylinder, the ignition target cylinder is # 2 cylinder, and the fuel injection target cylinder is # 1 cylinder.

Thereafter, the process proceeds from step S2 to step S3, in which the time from the previous crank pulse input to the present crank pulse input measured by the crank pulse input interval timer, that is, the crank corresponding to the presently identified crank pulse. The crank pulse input interval time Tθ corresponding to the inter-pulse angle is detected.

This crank pulse input interval time Tθ is
This is the time required for the crank rotor 41 to rotate by a known crank pulse angle previously stored as fixed data in the ROM 52. In the present embodiment, this corresponds to an angle 93 ° CA between the θ3 crank pulse and the θ1 crank pulse. Crank pulse input interval time TO93, crank pulse input interval time corresponding to angle 32 ° CA between θ1 crank pulse and θ2 crank pulse TO32, crank pulse input interval corresponding to angle 55 ° CA between θ2 crank pulse and θ3 crank pulse The time TO55 is detected and stored at a predetermined address in the RAM 53.

Next, the routine proceeds to step S4, where the crank pulse input interval times TO93, TO55, TO32 are read from the RAM 53, and the respective crank pulse input interval times TO93, TO55, TO93 are read.
TO32 is summed to obtain an elapsed time of a crank angle of 180 ° CA (engine half rotation), and a current engine speed NE is calculated based on the elapsed time of the engine half rotation.
Store at the predetermined address of M53 and exit the routine.

After the system initialization, the fuel injection amount setting routine shown in FIG.
The fuel injection pulse width Ti is determined for each fuel injection target cylinder determined by the above-described cylinder determination / engine speed calculation routine. The fuel injection pulse width Ti determines the final fuel injection amount supplied to the engine. You.

In this fuel injection amount setting routine, first,
In step S501, a basic fuel injection pulse width Tp that determines a basic fuel injection amount corresponding to stoichiometry is calculated from the engine speed NE and the intake air amount Q based on an output signal from the intake air amount sensor 32 (Tp ← K). × Q / NE; K is an injector characteristic correction constant). The basic fuel injection pulse width Tp is used when setting various coefficients as a parameter representing the engine load.

Next, in steps S502 and S503,
Various correction coefficients COEF and air-fuel ratio feedback correction coefficient LAMB stored at predetermined addresses in RAM 53
When DA is read, the engine speed N is determined in step S504.
The air-fuel ratio learning value KLR is searched by referring to the air-fuel ratio learning value table of the backup RAM 54 based on E and the basic fuel injection pulse width Tp representing the engine load, and the air-fuel ratio learning correction coefficient KBLRC is set by interpolation calculation.

As is well known, the air-fuel ratio learning value KLR, which is the basis of the air-fuel ratio learning correction coefficient KBLRC,
For each engine operation region based on E and the basic fuel injection pulse width Tp representing the engine load, the air-fuel ratio feedback correction coefficient LAMBDA is learned according to the deviation of the average value from the reference value in a predetermined cycle with respect to the reference value, and the intake air amount sensor 3
This is for correcting variations during production of the intake air amount measuring system such as 2 and the fuel supply system such as the injector 11 and deterioration over time.

Next, proceeding to step S505, the voltage correction pulse width TS for compensating the invalid injection time of the injector 11 is set by referring to the table based on the battery voltage VB. In step S506, the basic fuel injection pulse width Tp is set to various values. The air-fuel ratio is corrected by multiplying the correction coefficient COEF and the air-fuel ratio feedback correction coefficient LAMBDA, the learning correction is performed by multiplying the air-fuel ratio learning correction coefficient KBLRC, and the voltage is corrected by adding the voltage correction pulse width TS to the engine. Fuel injection pulse width Ti that determines the final fuel injection amount to be supplied
(Ti ← Tp × COEF × LAMBDA × K
BLRC + TS). Then, in step S507, the fuel injection pulse width Ti is set in the injection timer of the fuel injection target cylinder, and the routine exits.

As a result, the injection timer for the fuel injection target cylinder is started at a predetermined timing, and the fuel injection pulse width T
The drive pulse signal of i is output to the injector 11 of the fuel injection target cylinder, and a predetermined amount of fuel is injected from the injector 11.

The fuel injection pulse width Ti set in the above-described fuel injection amount setting routine indicates that the lean burn can be executed by the lean burn execution determination routine shown in FIGS. 9 to 15 which is executed at predetermined intervals after the system initialization. When it is determined that the lean burn is permitted, the correction by the air-fuel ratio feedback correction coefficient LAMBDA to the basic fuel injection pulse width Tp corresponding to stoichiometry is stopped (L
AMBDA = 1.0), while various correction coefficients COE
The lean correction coefficient FLEAN, which is one of the correction terms for F, is used to reduce the amount of fuel, and the lean air-fuel ratio (usually A / F
= 22).

Each correction coefficient relating to the setting of the fuel injection pulse width Ti, that is, the air-fuel ratio feedback correction coefficient LAMBDA, various correction coefficients COEF, and the leaning correction coefficient FLEAN which is one of the correction terms in the various correction coefficients COEF. Are respectively set by an air-fuel ratio feedback correction coefficient setting routine shown in FIG. 4, a various correction coefficient setting routine shown in FIG. 5, and a leaning correction coefficient setting routine shown in FIG.

Prior to the description of the lean burn execution feasibility determination routine of FIGS. 9 to 15, the air-fuel ratio feedback correction coefficient setting routine of FIG. 4, the various correction coefficient setting routines of FIG. 5, and the leaning correction coefficient setting of FIG. Routines and routines related to setting parameters used in each routine will be described.

As will be described later, the result of the lean burn execution determination routine shown in FIGS. 9 to 15 is represented by using a lean burn flag FLB. Flag FLB is 1
Is set to indicate lean burn permission, and if it is determined that lean burn cannot be performed, the lean burn flag F
LB is cleared to 0, indicating that lean burn is prohibited.

The air-fuel ratio feedback correction coefficient setting routine of FIG. 4 is executed at predetermined intervals.
In steps 41 to S143, it is determined whether or not the initial conditions based on the engine speed NE and the operation state of the starter switch 47 are satisfied.
It is determined whether the air-fuel ratio feedback condition is satisfied by determining whether the sensor 39 is activated and whether lean burn is prohibited based on the reference result of the lean burn flag FLB.

That is, in step S141, when the engine is not rotating at NE = 0, when the starter switch 47 is turned on, the engine is cranked, and the time after the engine is started is counted by the post-start time counting timer. 4
sec) when any of the conditions in the initial condition is satisfied,
Alternatively, in step S142, the output voltage VO2 of the O2 sensor 39
Does not reach the set value and the state in the predetermined range does not continue for the set time or longer, or when F is set in step S143.
When the lean burn is permitted with LB = 1, it is determined that the feedback condition is not satisfied, and the process proceeds to step S145, where the air-fuel ratio feedback correction coefficient LAMBDA is set to LAMBDA.
= 1.0 and exit from the routine.

In step S141, when the time after the starter switch 47 is turned on from OFF in the engine rotation state of NE ≠ 0 elapses a set time or more and the initial condition is not satisfied, and in step S142, the O2 sensor When it is determined that the output voltage VO2 of 39 is equal to or higher than the set value or within a predetermined range for the set time or longer and the O2 sensor 39 is in the active state and the lean burn of FLB = 0 is prohibited in step S143, the process proceeds to step S144. It is determined whether or not the clamp condition is satisfied.

When the clamp condition in the transient engine operation state is satisfied, such as during acceleration / deceleration or fuel cut, the feedback condition is similarly determined not to be satisfied, and the flow advances to step S146 to set the air-fuel ratio feedback correction coefficient LAMBDA to a predetermined value (normally). , 1.0) and exit the routine.

That is, when the air-fuel ratio feedback condition is not satisfied, the air-fuel ratio feedback correction coefficient LAMBDA
Is 1. The air-fuel ratio feedback correction based on the output from the O2 sensor 39 is stopped by being fixed to O or clamped to a predetermined value. In this case, the lean burn flag FLB becomes FLB =
When 1 (lean burn permitted), the leaning correction coefficient FLEA is added to the various correction coefficients COEF (step S506 in FIG. 3) incorporated in the equation for calculating the fuel injection pulse width Ti.
N is given as a subtraction term, the fuel injection amount is reduced and corrected, and the air-fuel ratio is controlled lean.

On the other hand, when the engine is in a steady operation state in which the clamp condition is not satisfied in step S144, it is determined that the air-fuel ratio feedback condition is satisfied, and the process proceeds to step S147 and subsequent steps.
An air-fuel ratio feedback correction coefficient LAMBDA is set by proportional integral control (PI control) according to the result of comparison between the output voltage VO2 of the O2 sensor 39 and a slice level SLICE, which is a determination value for determining the air-fuel ratio state.

In this embodiment, the slice level SLIC is used.
E is a determination threshold corresponding to the stoichiometric air-fuel ratio, and is determined in step S1.
At 47, the output voltage VO2 of the O2 sensor 39 is read, and the O2 sensor output voltage VO2 is compared with the slice level SLICE to determine whether the current air-fuel ratio is shifted to the rich side or to the lean side with respect to stoichiometry. to decide. Then, when VO2 ≧ SLICE and the air-fuel ratio is shifted to the rich side, the process proceeds to step S148, and the first reversal determination flag FR is referred to.

The first reversal discrimination flag FR is a flag for judging the first time when the air-fuel ratio is reversed from lean to rich or the first time when the air-fuel ratio is reversed from rich to lean. 0 → 1 after inversion from the side to the rich side, and 1 → 0 after inversion from the rich side to the lean side.

Therefore, when the air-fuel ratio is rich and FR = 0
Is the first time when the air-fuel ratio is inverted from the lean side to the rich side, the process proceeds from step S148 to step S149, where the air-fuel ratio feedback correction coefficient LAMBDA is set to P
Skip in the minus direction by the proportional constant PD of the I control (LAMBDA ← LAMBDA-PD), and step S15
The inversion first discrimination flag FR is set at 1 (FR ← 1),
Exit the routine.

When the air-fuel ratio is rich and FR = 1, the air-fuel ratio feedback correction coefficient LAMB has already been obtained.
Since the skip in the negative direction is performed on DA by the proportionality constant PD, the process proceeds from step S148 to step S150, and the air-fuel ratio feedback correction coefficient LAMB
DA is gradually decreased by the integral constant ID of the PI control every time the routine is executed (LAMBDA ← LAMBDA-ID),
The process exits the routine via the above-described step S151.

On the other hand, in step S147, VO2
<If the air-fuel ratio is lean on SLICE, step S1
The process branches to 52, and similarly, the inversion initial discrimination flag FR is referred to. When the air-fuel ratio is lean and FR = 1, it is the first time that the air-fuel ratio has been inverted from the rich side to the lean side, so the process proceeds to step S153, and the air-fuel ratio feedback correction coefficient LAMBDA is increased in the positive direction by the proportionality constant PU. Skip (LAMBDA ← LAMBDA + P
U) In step S155, the first reversal determination flag FR is cleared (FR ← 0), and the routine exits.

When the air-fuel ratio is on the lean side and FR = 0, the air-fuel ratio feedback correction coefficient LAMB has already been obtained.
Since the DA is skipped in the plus direction by the proportionality constant PU, the process proceeds from step S152 to step S152.
Proceeding to S154, the air-fuel ratio feedback correction coefficient LAMBD
A is gradually increased by the integral constant IU of PI control every time the routine is executed (LAMBDA ← LAMBDA + IU), and the process exits the routine via the above-described step S155.

That is, when the air-fuel ratio feedback condition is satisfied, as shown in FIG. 20, when the air-fuel ratio deviates from stoichiometric to the rich side, the air-fuel ratio feedback correction coefficient LAMBDA is reduced by proportional integral control, as shown in FIG.
When the air-fuel ratio deviates from stoichiometric to the lean side, the air-fuel ratio feedback correction coefficient LAMBDA is increased.
Then, the air-fuel ratio feedback correction coefficient LAMBD
By incorporating A into the equation for calculating the fuel injection pulse width Ti (step S506 in FIG. 3), when the air-fuel ratio deviates from stoichiometric to the rich side, the fuel injection amount is reduced and corrected by the air-fuel ratio feedback correction coefficient LAMBDA. When the air-fuel ratio deviates from the stoichiometric direction to the lean side, the fuel injection amount is corrected to increase, thereby controlling the air-fuel ratio to converge to the stoichiometric ratio.

Next, various correction coefficient setting routines shown in FIG. 5 will be described. This routine is executed for a predetermined period (for example,
10 msec). First, in step S161,
The full increase coefficient KFULL is set by referring to the full increase coefficient table stored in the ROM 52 based on the engine speed NE and the basic fuel injection pulse width Tp representing the engine load. This full increase coefficient KFULL is used to protect the catalyst by preventing an abnormal increase in the catalyst temperature by fuel increase correction when the engine operation state is at least one of high speed and high load, and to secure engine output. This is set in the full increase coefficient table shown in FIG.

In the full increase coefficient table of the illustrated example, when the basic fuel injection pulse width Tp is in at least one of the high engine load area and the high engine rotation area, the full increase coefficient KFULL is set to KFULL> 0. Is done. This area is a so-called full increase area in which fuel increase correction is performed by the full increase coefficient KFULL.
Outside this full increase range, the full increase coefficient KFULL
However, KFULL = 0 is set, and the fuel increase correction by the full increase coefficient KFULL is not performed. Further, in the full increase coefficient table, a larger value of the full increase coefficient KFULL is stored as the basic fuel injection pulse width Tp is larger and the engine speed NE is higher, that is, as the load is higher and the engine speed is higher.

In the following step S162, the post-start increase coefficient K
Set the AS. The post-start increase coefficient KAS is for performing a fuel increase correction for a predetermined period immediately after the engine start in order to secure the stability of the engine speed immediately after the engine start, and is based on the cooling water temperature TW by the cooling water temperature sensor 37. After the initial value is set and the engine is started by turning off the starter switch 47 as shown in step S162, KAS
It is gradually reduced until = 0.

Next, at step S163, the water temperature increase coefficient KTW is set by referring to the table based on the cooling water temperature TW. The water temperature increase coefficient KTW determines the fuel increase rate for ensuring the drivability when the engine is cold. As shown in step S163, the lower the cooling water temperature TW,
The water temperature increase coefficient KTW of a large value is stored in the table.

Then, in step S164, the leaning correction coefficient setting routine shown in FIG. 6 is executed to set the leaning correction coefficient FLEAN, and in step S165, various correction items set according to the engine operating state, that is, , The full increase coefficient KFULL, the after-start increase coefficient KAS, the water temperature increase coefficient K
The lean correction coefficient FLEAN is given to TW as a subtraction term, and various correction coefficients COEF are set by the following equations, and the routine exits. COEF ← 1 + KFULL + KAS + KTW-FLEAN

The lean correction coefficient FLEAN is FLB
= 0 (lean burn prohibited), FLEAN = 0, and FLB = 1 (lean burn permitted), FLEAN
When EAN ≠ 0, it is given as a subtraction term in various correction coefficients COEF. As a result, when lean burn is permitted, as described above, the air-fuel ratio feedback correction is stopped, the fuel injection pulse width Ti is reduced by various correction coefficients COEF, and the air-fuel ratio is controlled to lean. .

Next, the leaning correction coefficient setting routine of FIG. 6 for setting the leaning correction coefficient FLEAN will be described. In this routine, first, in step S211
Lean upper limit value FL by interpolation calculation from a two-dimensional map of intake pipe pressure PM (absolute pressure) and engine speed NE
Find EMAX.

The lean upper limit FLEMAX gives the upper limit of the lean air-fuel ratio for each operation region, that is, the misfire limit due to the air-fuel ratio lean, and is based on the intake pipe pressure PM and the engine speed NE as shown in FIG. Set by a two-dimensional map. In this map, as the intake pipe pressure PM (absolute pressure) shifts to a high load area,
A lean upper limit value FLEMAX (for example, FLEMAX = 0.37; a large value for an air-fuel ratio with a large lean ratio);
A / F = 26.5) is stored and the intake pipe pressure PM
In a low-load low-rotation region where the engine speed NE is low and the engine speed NE is low, a lean upper limit FLEMAX (for example, FLEMAX = 0.
29; A / F = 20.7).

Next, the routine proceeds to step S212, where a leaning target value FLENTGT which gives a target value of the lean air-fuel ratio for each operating region is obtained by interpolation from a two-dimensional map of the intake pipe pressure PM and the engine speed NE. The lean target value FLENTGT is set by a two-dimensional map based on the intake pipe pressure PM and the engine speed NE, as in the above-described lean upper limit, and the two-dimensional map includes the intake air pressure as shown in FIG. The higher the pipe pressure PM shifts to the high load region, the larger the leaning target value FLENTGT
Is stored, and in the low-load low-rotation region where the intake pipe pressure PM is low and the engine speed NE is low, a small leaning target value FLENTGT is stored.

In the following step S213, a lean limit target value FLEGDH, which is a target value for changing the air-fuel ratio in accordance with the torque fluctuation due to misfiring in lean burn, ie, the degree of surge, is set. The lean limit target value FLEGDH is updated at predetermined intervals in accordance with the surge level, and is gradually increased in a stable state with no surge to increase the fuel reduction correction amount by the leaning correction coefficient FLEAN to increase the air-fuel ratio. Direction, and when the surge occurs, it is rapidly reduced to make the lean correction coefficient FLEAN.
Thus, the air-fuel ratio is corrected in the rich direction by reducing the fuel loss correction amount due to the above-described operation, and the surge is quickly eliminated.

Then, the lean limit target value FLEGD
After setting H, the process proceeds to step S214, in which the lean limit permission value PFLEGD is set to the lean limit target value FLEGDH.
To obtain the lean limit value FLEGDB, and in step S215, the lean limit value FLEGD
B is multiplied by a lean target value FLENTGT to calculate a final lean limit value FLEANLMT (FL
EANLMT ← FLENTGT × FLEGDB).

The leaning permission coefficient PFLEGD is for gradually changing the air-fuel ratio when switching from stoichiometric (including rich air-fuel ratio) to lean air-fuel ratio to prevent torque shock due to sudden change in air-fuel ratio. The leaning permission coefficient setting routine of FIG. 7 and FIG.
In a steady state in which lean burn is prohibited, PFLEGD is fixed to 0, and in a steady state in which lean burn is permitted, PFLEGD is fixed to 1.0. The value is increased or decreased.

Next, the routine proceeds to step S216, where the lean limit value FLEANLMT is compared with the lean upper limit value FLEMAX previously set in step S211.
If LEMAX> FLEANLMT, the lean limit value FLEANLMT is set as the leaning correction coefficient FLEAN in step S217 (FLEAN ← FLEANLM).
T) Then exit the routine and FLEMAX ≦ FLEANL
In the case of MT, the lean upper limit value FLE is determined in step S218.
MAX is set as the leaning correction coefficient FLEAN (FL
EAN ← FLEMAX) and exit the routine.

That is, the leaning correction coefficient FLEAN
Are the lean upper limit FLEMAX and the lean limit F
LEANLMT, which is set to the smaller value, but in the state of FLEANLMT <FLEMAX, the leaning correction coefficient FLEAN contains the lean limit target value FL.
The lean limit value FLEANLMT that changes according to the EGDH and the lean permission coefficient PFLEGD is reflected. Then, when the correction in the lean direction by the lean limit value FLEANLMT is equal to or greater than the lean upper limit value FLEMAX, the correction in the lean direction is set not to be larger than the correction by the lean upper limit value FLEMAX determined from the map.

Next, the leaning permission coefficient setting routine shown in FIGS. 7 and 8 will be described. This leaning permission coefficient setting routine is executed at predetermined intervals (for example, 40 msec).
First, the lean burn flag FLB is referred to in step S441. If FLB = 1 and the lean burn is permitted, the process proceeds to step S442, where the current lean permitting coefficient PFLEGD is incremented by the increment value KDLEAN.
P (for example, KDLEAMP = 0.00781) is added, and the leaning permission coefficient PFLEGD is increased and updated to a new value (PFLEGD ← PFLEGD + KDLE).
ANP).

Next, the routine proceeds to step S443, where it is determined whether or not the lean permission coefficient PFLEGD has reached the upper limit (1.0). Leaning permission coefficient PFLEGD is fixed at 1.0 (PFLEGD ← 1.0), and the routine exits. When PLEEGD ≦ 1.0, that is, when lean burn is prohibited (FLB = 0), lean burn is permitted (FLB =
When the air-fuel ratio is changed to the transient state in 1), the lean permission coefficient PFLEGD and the set value KPFLEGDL (for example, KPFLEGDL =
0.796).

The above set value KPFLEGDL is an intermediate air-fuel ratio (about A / F = 16 to 18) at which knocking and NOx emission increase when the air-fuel ratio changes in the lean direction from lean burn inhibition to lean burn permission. This is a so-called initial value when the lean permission coefficient PFLEGD is gradually increased.
45, when PFLEGD ≦ KPFLEGDL,
Proceeding to step S446, the set value KPFLEGDL is set in the lean permission coefficient PFLEGD (PFLEGD ←
KPFLEGDL) and exit the routine.

Then, the set value KPFLEGDL is set in the lean permission coefficient PFLEGD, and P is set in step S445.
FLEGD> KPFLEGDL, and after exiting the routine, every time the routine is executed, the leaning permission coefficient PFLEGD is set.
Is gradually increased by an increment value KDLEANP, and step S4
If PFLEGD> 1.0 in 43, step S4
At 44, the lean permission coefficient PFLEGD is fixed at 1.0.

That is, as shown in FIG. 23 (a), when lean burn is prohibited from the state in which lean burn is prohibited and the stoichiometric or rich air-fuel ratio is controlled (PFLEGD = 0), first, the lean burn is started. The permission coefficient PFLEGD is immediately changed from 0 to a set value KPFLEGDL (for example, KPFLEGDL = 0.796) to avoid the intermediate air-fuel ratio, and thereafter, the lean permission coefficient PFLE is set.
GD is incremented by KDLEANP (eg, KDLEANP).
= 0.00781), thereby gradually changing the air-fuel ratio in the lean direction via the leaning correction coefficient FLEAN, thereby preventing a torque shock due to a sudden change in the air-fuel ratio.

On the other hand, in step S441, FLB = 0
When lean burn is prohibited, the process proceeds from step S441 to step S447 to check whether the idle switch 33b is ON. When the idling switch 33b is ON and the idling operation is being performed, at step S448, the set value KDL is set to the decrease DLEANM for gradually decreasing the lean permission coefficient PFLEGD.
Set EANM (for example, KDLEANM = 0.016) (DLEANM ← KDLEANM) and step
Proceeding to S454, if the idle switch 33b is OFF, the value of the decrease DLEANM is set in accordance with the change in the throttle opening TVO in step S449 and thereafter, and in step S4
Proceed to 54.

That is, in step S449, the absolute value of the difference between the current throttle opening TVO and the throttle opening TVOn-3 at the calculation timing at the time of execution of the routine three times before (in this embodiment, the calculation timing 120 msec before) is calculated. The amount of change in throttle opening | TVO-TVOn-3 | is obtained from the value, and this amount of change in throttle opening | TVO-TVOn-3 | is compared with a determination value KDTVOLE1 (for example, equivalent to 60 mV). Then, | TVO-TVOn-3 | <KDTVOLE
If the throttle opening change is relatively small at 1 in step S450, the reduced amount DLEANM is set to the set value KDLEANM1 (for example, KDLEANM1 = 0.0) at step S450.
313) is set (DLEANM ← KDLEANM1)
And proceed to step S454.

In the above step S449, | TVO-T
If VOn-3│≥KDTVOLE1, step S45
In step 1, the throttle opening change amount | TVO-TVOn-3 | is compared with a determination value KDTVOL2 (equivalent to, for example, 240 mV). Then, | TVO-TVOn-3 | <KDTVOL
At E2, when the throttle opening change is in the middle operation state, the set value K is set to the decrease DLEANM at step S452.
DLEANM2 (eg, KDLEANM2 = 0.06
6) is set (DLEANM ← KDLEANM2), and the flow advances to step S454 to | │TVO-TVOn-3│ ≧ KDT
When the throttle valve is in an operating state where the change in the throttle opening is large in VOL2, the set value KDLEANM3 (for example, KDLEANM3 = 0.
1016) is set (DLEANM ← KDLEANM
3) Then proceed to step S454.

In step S454, a leaning permission coefficient PF
LEGD is decreased by the decrease DLEANM and updated to a new value (PFLEGD ← PFLEGD−DLEAN
M), at step S455, the lean permission coefficient PFLEGD
And a set value KPFLEGDR (KPFLEGDR = 0 in the present embodiment) which is the end value of the gradual decrease when the lean permission coefficient PFLEGD is gradually decreased. When PFLEGD> KPFLEGDR, the routine exits. When PFLEGD ≦ KPFLEGDR, the leaning permission coefficient PFLEGD is set to 0 in step S456, and the routine exits (PFLEGD ← 0).

That is, as shown in FIG. 23 (b), when the lean burn is prohibited from the state in which the lean burn is permitted and the lean air-fuel ratio is controlled (PFLEGD = 1), the lean permission coefficient PFLEGD is set. Decrease DLE according to idle operation or change in throttle opening
ANM is used to gradually reduce the value of the lean correction coefficient F
The air-fuel ratio is changed in the stoichiometric direction via LEAN to prevent a torque shock due to a sudden change in the air-fuel ratio. In this case, the steeper the air-fuel ratio is set earlier as the throttle opening change is steeper and the acceleration is greater, the steeper the leaning of the lean permission coefficient PFLEGD.

A lean burn flag FLB indicating lean burn inhibition / permission referred to in each of the above routines
Are set / set in accordance with the result of the lean burn feasibility determination by the lean burn feasibility determination routine of FIGS. 9 to 15 executed at predetermined intervals (for example, every 10 msec).
Cleared.

In this embodiment, the lean burn execution determination is made when the condition (a) to (g) described below is satisfied and the condition satisfying all of these conditions continues for a set time or more. It is determined that burn can be performed. (A) The condition in which the engine warm-up is in the normal state. (B) The condition in which the engine speed is in the low-medium speed range. (C) The condition in which the engine is running normally. After detecting the condition and prohibiting lean burn,
Conditions that enable return to lean burn (f) Conditions in which the catalyst temperature is equal to or lower than the set temperature (g) Conditions in which lean burn can be restarted after the catalyst temperature exceeds the set temperature and lean burn is prohibited

Hereinafter, the lean burn execution feasibility determination routine will be described. In this routine, first, step
In step S11 to step S22, it is determined whether or not the condition (a), that is, the cooling water temperature is within the set range in which the hysteresis for preventing control hunting is provided on the low temperature side and the high temperature side, and the engine warm-up is in a normal state. Is determined. In the determination of the water temperature condition, a first water temperature determination flag FTWL for determining whether the low temperature condition is satisfied and a second water temperature determination flag FTWH for determining whether the high temperature condition is satisfied (both are initialized to 0 at the time of system initialization). When the cooling water temperature satisfies the condition within the set range, FTWL = 1 and FTWH =
Let it be 1.

For this reason, in step S11, the first water temperature determination flag FTWL is referred to, and when FTWL = 0, step S12 is executed.
The upper limit value of the hysteresis width KTWLEL provided on the low temperature side
H (e.g., 80 ° C.) is set to the low-temperature side determination value KTWL.
Set as EL (KTWLEL ← KTWLELH)
Then, the process proceeds to step S14 after setting the determination threshold value when the cooling water temperature rises.

When FTWL = 1 in step S11, the lower limit value KTWLELL (corresponding to, for example, 75 ° C.) of the hysteresis width provided on the low temperature side in step S13 is set as the determination value KTWLEL on the low temperature side (KTWLEL ←).
KTWLELL), and sets the determination threshold value when the cooling water temperature falls, and then proceeds to step S14.

In step S14, the current coolant temperature TW detected by the coolant temperature sensor 37 and the low-temperature side determination value KTWL
EL, and if TW ≧ KTWLEL, it is determined that the low temperature condition is satisfied, and the first water temperature determination flag FTWL is set to 1 in step S15 (FTWL ← 1), and step S17 is performed.
When TW <KTWLEL, the condition on the low temperature side is not satisfied, so the first water temperature determination flag FTWL is determined in step S16.
Is cleared to 0 (FTWL ← 0), and the process proceeds to step S17.

In step S17, the second water temperature determination flag FTWH
When FTWH = 0, the lower limit value KTWLEHL of the hysteresis width provided on the high temperature side in step S18 (for example,
(Equivalent to 100 ° C.) is set as the determination value KTWLEH on the high-temperature side (KTWLEH ← KTWLEHL), and is set as the determination threshold value for the first time of the routine or when the cooling water temperature decreases, and then the process proceeds to step S20.

In step S17, FTWH = 1
, The upper limit value KTWLEHH (e.g., equivalent to 105 ° C.) of the hysteresis width provided on the high temperature side in step S19 is set as the high temperature side determination value KTWLEH (KTW).
(WLEH ← KTWLEHH), and the threshold value is set as a determination threshold when the cooling water temperature rises.

In step S20, the current cooling water temperature TW is compared with the high-temperature side determination value KTWLEH, and TW <KTWL.
In the case of EH, it is determined that the condition on the high temperature side is satisfied, and
In S21, the second water temperature determination flag FTWH is set to 1 (FTWH ←
1) Then, the process proceeds to step S23 and thereafter. If TW ≧ KTWLEH, the condition on the high temperature side is not satisfied, so the second water temperature determination flag FTWH is cleared to 0 in step S22 (FTWH ← 0), and the process proceeds to step S23 and thereafter.

That is, as shown in FIG. 24 (a), when the water temperature rises, the cooling water temperature TW is higher than the upper limit value KTWLELH of the hysteresis width provided on the lower temperature side and lower than the upper limit value KTWLEHH of the hysteresis width provided on the higher temperature side. Also,
When the cooling water temperature TW is lower than the lower limit value KTWLEHL of the hysteresis width provided on the high temperature side and equal to or higher than the lower limit value KTWLELL of the hysteresis width provided on the low temperature side when the water temperature falls, the water temperature condition is satisfied (FTWL = 1 and FTWH). =
1).

In the following steps S23 to S32, the condition (b), that is, the engine speed is within a set range in which hysteresis for preventing control hunting is provided on the low speed side and the high speed side, This is a process for determining whether or not the vehicle is within the range, using two flags similar to the determination of the water temperature condition, a first rotation determination flag FNEL and a second rotation determination flag FNEH. The flags FNEL and FNEH are both initialized to 0 at the time of system initialization. When the engine speed satisfies a condition within a set range, FNEL = 1 and FNEH
= 1.

First, in step S23, the first rotation determination flag FNEL is referred to, and when FNEL = 0, the lower limit value NELEEAN of the hysteresis width provided on the low rotation side in step S24.
(E.g., equivalent to 900 rpm) the hysteresis width KNE
A determination value (NLEEAN + KNLEHS) obtained by adding LEHS (e.g., equivalent to 100 rpm) is compared with the current engine speed NE to determine whether or not the engine speed is equal to or larger than the upper limit of the hysteresis width provided on the low speed side. judge.

Then, NE ≧ NELEA + KNELE
In the case of HS, it is determined that the condition on the low rotation side is satisfied, and step S2 is performed.
5 sets the first rotation determination flag FNEL to 1 (FNEL ←
1) Then, the process proceeds to a step S28, where NE <NELEAN + KN
In the case of ELEHS, the first rotation determination flag FNEL is cleared to 0 in step S27 because the low rotation side condition is not satisfied (F
NEL ← 0), and the process proceeds to step S28.

In step S23, FNEL = 1
In step S26, the above-described lower limit value NELEAN is set in step S26.
Is compared with the current engine speed NE to determine whether the engine speed is lower than the lower limit of the hysteresis width provided on the low speed side. When NE ≧ NELEAN, the process proceeds to step S28 via the above-described step S25 of setting the first rotation determination flag FNEL. When NE <NELEAN, the process proceeds to the above-described step S27 for clearing the first rotation determination flag FNEL. Proceed to S28.

In step S28, the second rotation determination flag FNEH
When FNEH = 0, the process proceeds to step S29 to set the lower limit value NELEEAN of the hysteresis width provided on the low rotation side to the set width KNELEWID (for example, equivalent to 2500 rpm).
Judgment value (NELEAN + KNELEWID)
Is compared with the current engine speed NE to determine whether the engine speed is lower than the lower limit value of the hysteresis width on the high speed side at the first time of the routine or when the speed is decreased.

Then, NE <NELEA + KNELE
In the case of WID, it is determined that the condition on the high rotation side is satisfied and the step is performed.
In S30, the second rotation determination flag FNEH is set to 1 (FNEH ←
1) Then, the process proceeds to step S33 and thereafter, where NE ≧ NELEAN +
In the case of KNELEWID, since the condition on the high rotation side is not satisfied, the second rotation determination flag FNEH is cleared to 0 (FNEH ← 0) in step S32, and the process proceeds to step S33 and subsequent steps.

Also, in step S28, FNEH = 1
In step S31, the current engine speed NE
With the lower limit value NELEAN and the set width KNELWI
Determination value obtained by adding D and the hysteresis width KNELEHS (NLEEAN + KNELEID + KNELEHS)
Then, it is determined whether or not the engine speed has risen to or above the upper limit of the hysteresis width on the high speed side.

Then, NE <NELEAN + KNELE
When WID + KNELEHS, the second rotation determination flag F
Set NEH to 1 Step through the above step S30
Proceed to S33 or later, and NE ≥ NELEN + KNELEWID
+ KNLEHS, the second rotation determination flag FNE
Clear H to 0 After step S32 described above, step S3
Proceed to 3 and later.

That is, as shown in FIG. 24 (b), when the engine speed increases, the engine speed NE becomes equal to the determination value (NELEEAN +) which is the upper limit of the hysteresis width provided on the low engine speed side.
KNELEHS) or more and a determination value (NLEEAN + KNEL) which is an upper limit of the hysteresis width provided on the high rotation side.
When the engine speed NE does not exceed EWID + KNELEHS, or when the engine speed drops, the determination value (NELEA) at which the engine speed NE is the lower limit of the hysteresis width provided on the high engine speed side.
(N + KNELEWID), and is equal to or greater than the determination value NELEAN which is the lower limit of the hysteresis width provided on the low rotation side, the rotation speed condition is satisfied (FNEL = 1 and FNEH).
= 1).

Steps S33 to S44 are processing for judging whether the condition (c), that is, the vehicle speed is normal traveling, is within a set range in which hysteresis for preventing control hunting is set at upper and lower limits. The determination is performed using the vehicle speed determination flag FVSPL and the second vehicle speed determination flag FVSPH. Each flag FVS
PL and FVSPH are both initialized to 0 at the time of system initialization, and when the vehicle speed satisfies a condition within a set range, FVSPL = 1 and FVSPH = 1.

At step S33, the first vehicle speed determination flag FVSP
Referring to L, when FVSPL = 0, the upper limit value KVSLELH (e.g., 18 Km / h) of the hysteresis width provided on the low-speed side in step S34 is set as the low-speed side determination value KVSLEL for the vehicle speed increase (KVSLEL ←). K
VSLELH), and proceeds to step S36.

When FVSPL = 1 in step S33, the lower limit value KVSLELL of the hysteresis width provided on the low speed side in step S35 (for example, equivalent to 16 km / h).
Is set as the determination value KVSLEL on the low speed side when the vehicle speed decreases (KVSLEL ← KVSLELL), and the process proceeds to step S36.

In step S36, the current vehicle speed VSP detected by the vehicle speed sensor 46 is compared with a low-speed determination value KVSLEL. If VSP ≧ KVSLEL, it is determined that the low-speed condition is satisfied, and in step S37 the first vehicle speed is determined. The determination flag FVSPL is set to 1 (FVSPL ← 1), and the process proceeds to step S39. When VSP <KVSLEL, the condition for the low speed side is not satisfied, so the first vehicle speed determination flag FVSP is determined in step S38.
L is cleared to 0 (FVSPL ← 0), and the process proceeds to step S39.

At step S39, the second vehicle speed determination flag FV
Referring to SPH, when FVSPH = 0, the lower limit value KVSLEHL (for example, equivalent to 105 km / h) of the hysteresis width provided on the high speed side in step S40 is set as a determination value KVSLEH for when the vehicle speed increases (KVSLEH ← KVSL).
EHL), and then proceeds to step S42.

When FVSPH = 1 in step S39, the upper limit value KVSLEHH (for example, equivalent to 110 km / h) of the hysteresis width provided on the high speed side in step S41 is set as the determination value KVSLEH when the vehicle speed decreases (KVSLEH). ← KVSLEHH), and then proceeds to step S42.

In step S42, the current vehicle speed VSP is compared with the high speed determination value KVSLEH, and VSP <KVS.
In the case of LEH, it is determined that the condition on the high speed side is satisfied, and the second vehicle speed determination flag FVSPH is set to 1 in step S43 (FVSP
H ← 1) Then, the process proceeds to step S45 and thereafter, and VSP ≧ KVSL
In the case of EH, the condition on the high-speed side is not satisfied, so step S44
To clear the second vehicle speed determination flag FVSPH to 0 (FVSPH ←
0) and then proceed to step S45.

That is, as shown in FIG. 24 (c), the current vehicle speed VSP is equal to or higher than the upper limit value KVSLELH of the hysteresis width provided on the low speed side when the vehicle speed increases, and the upper limit value KVSLEHH of the hysteresis width provided on the high speed side. When the vehicle speed decreases, the vehicle speed condition is satisfied when the lower limit value of the hysteresis width KVSLEHL provided on the high speed side is lower than the lower limit value KVSLELL of the hysteresis width provided on the lower speed side and the vehicle speed condition is higher (FVSPLELL). = 1 and FVSPH
= 1).

Steps S45 to S55 are processing for judging the condition (d), that is, the steady operation state including slow acceleration, in which the condition that the intake pipe pressure PM (absolute pressure) is lower than the judgment value with hysteresis, the throttle opening It is determined whether or not a condition that TVO is smaller than the throttle opening determination value TVOLE described below with hysteresis is satisfied.

The determination with respect to the intake pipe pressure is shown in FIG.
When the intake pipe pressure PM becomes lower than the lower limit value of the hysteresis width (LDLEAN + LDLEID), it is set to 1 to indicate that the condition is satisfied, and the upper limit value of the hysteresis width (LDLEAN + LDLEID + LDLEH).
YS) is performed using an intake pipe pressure determination flag FPM (initial value is 0) which is cleared to 0 when the condition is not satisfied.

For this reason, in step S45, the intake pipe pressure determination flag FPM is referred to, FPM = 0, and the high load operation state (acceleration operation state) in which the accelerator pedal depression amount is large at the first time of the routine or at the time of execution of the previous routine. )
In step S46, the reference pressure value LDLEAN
(E.g., equivalent to 224 mmHg) set value LDLEWI
D (e.g., 175 mmHg) is determined as the lower limit of the hysteresis width (LDLEAN + LDLEID), and this determination value (LDLEAN + LDLEW).
ID) and the current intake pipe pressure PM detected by the intake pipe pressure sensor 34 are compared.

Then, PM <LDLEAN + LDLEW
ID, the intake pipe pressure determination flag FPM is determined in step S47.
Is set to 1 (FPM ← 1), and the process proceeds to step S50, where P
If M ≧ LDLEAN + LDLEID, step S4
9 clears the intake pipe pressure judgment flag FPM to 0 (FPM ←
0) and then proceed to step S50.

In step S45, FPM = 1
When the accelerator is released or the accelerator depression amount is small and the intake pipe pressure is lower than the lower limit value of the hysteresis width, the steps S45 to S48 are performed.
Proceed to the above judgment value (LDLEAN + LDLEWID)
The determination value obtained by adding the hysteresis width LDLEHYS to the upper limit of the hysteresis width is used as the determination value (LDLEA).
(N + LDLEID + LDLEHYS) and the current intake pipe pressure PM.

Then, PM <LDLEAN + LDLEW
ID + LDLEHYS, intake pipe pressure determination flag F
The process proceeds to step S50 via the above-described step S47 for setting PM, and PM ≧ LDLEAN + LDLEID + LDLE
In the case of HYS, the process proceeds to step S50 via the above-described step S49 for clearing the intake pipe pressure determination flag FPM.

In step S50, a throttle opening determination value TVOLE is obtained by interpolation from a throttle opening determination value table using the engine speed NE as a parameter. The throttle opening determination value TVOLE is used to prevent torque shock by switching from stoichiometric (including a rich air-fuel ratio) to a lean air-fuel ratio in a region where the generated torque of the engine is substantially equal. As shown in step S50, the throttle opening determination value TVOLE changes stepwise with respect to the engine speed NE and increases as the engine speed NE increases.

That is, focusing on the intake air amount determined by a predetermined functional relationship between the throttle opening and the engine speed, in a region where the throttle opening is smaller than the predetermined opening, the change in the engine speed is not affected. The intake air amount hardly changes, and the generated torque hardly changes. Therefore,
By switching from stoichiometric (including rich air-fuel ratio) to lean air-fuel ratio in such a region, torque shock can be reduced and the air-fuel ratio can be switched smoothly.

FIG. 25 shows an example of data in the throttle opening degree determination value table. In the idle range of 0 to 800 rpm, a slight change in the throttle opening degree causes a large change in the intake air amount Q and a change in torque. The value of the throttle opening determination value TVOLE is also small, and is 2000 rpm.
In the above description, since the change in the intake air amount Q and the change in torque are small with respect to the change in the throttle opening, the value of the throttle opening determination value TVOLE is constant.

The throttle opening determination value TV
After the OLE is set, the process proceeds to step S51 and thereafter, and it is determined whether or not a condition that the throttle opening TVO is smaller than the throttle opening determination value TVOLE described below with hysteresis is satisfied. This determination is cleared to 0 when the throttle opening TVO becomes larger than the throttle opening determination value TVOLE as the upper limit of the hysteresis width as shown in FIG.
The lower limit value of the hysteresis width (TVOLE-KTVOLEH
S) This is performed by using a throttle opening degree determination flag FTVO (initial value: 0) which is set to 1 when the value becomes equal to or less and indicates that the condition is satisfied.

That is, in step S51, the throttle opening determination flag FTVO is referred to, and when FTVO = 0, a determination value (TVOLE) corresponding to the hysteresis width KTVOLEHS (for example, equivalent to 6 deg) is subtracted from the throttle opening determination value TVOLE in step S52. -KTVOLEHS),
The current throttle opening TVO detected by the throttle opening sensor 33a is compared.

Then, TVO≤TVOLE-KTVOL
At the time of EHS, it is determined that the condition is satisfied, and the throttle opening determination flag FTVO is set to 1 in step S53 (FTVO ← 1).
To step S56 and thereafter, TVO> TVOLE-K
In the case of TVLEHS, it is determined that the condition is not satisfied, and the throttle opening degree determination flag FTVO is cleared to 0 (FTVO ← 0) in step S55, and the process proceeds to step S56.

If FTVO = 1 in step S51, the process proceeds from step S51 to step S54, where the current throttle opening TVO and the throttle opening determination value TVOL are determined.
E, and when TVO ≦ TVOLE, the throttle opening determination flag FTVO is set. After the above-described step S53, the process proceeds to step S56, and when TVO> TVOLE, the throttle opening determination flag FTVO is cleared. After step S55, the process proceeds to step S56 and subsequent steps.

Next, in steps S56 to S61, after the condition (e), that is, the transient state is detected and lean burn is prohibited, it is first determined whether or not the condition for returning to lean burn is satisfied. In step S56, the lean burn possible deceleration determination flag FLBDE is referred to. The lean burn possible deceleration determination flag FLBDE is a flag for detecting a transient state at the time of sudden acceleration or starting and prohibiting the lean burn and then permitting the lean burn again. The initial value is 0 indicating that the lean burn is permitted. It is. Here, the deceleration in the lean burn possible deceleration means a decrease in the speed change.

As a result of referring to the lean burn possible deceleration determination flag FLBDE in step S56, the routine is in the first or current lean burn permission state, and FLBDE = 0.
In step S57, the process proceeds to step S57, where the throttle opening TVO at the calculation timing at the time of execution of the current routine and the calculation timing at the time of execution of the routine four times before (40 m in the present embodiment).
Throttle opening TVO at calculation timing before sec)
n-4 is set to a set value KDLTTH (for example, 1.76 d
eg equivalent).

As a result of the comparison in step S57, the TVO-
When TVOn-4 ≧ KDLTTH, it is determined that rapid acceleration has occurred.
In step S59, the lean burn possible deceleration determination flag FLBDE is set to 1 to inhibit lean burn (FLBDE ← 1).
Then, the process proceeds to step S61, where TVO-TVOn-4 <KDLT
At the time of TH, it is determined that the vehicle is accelerating slowly, and the vehicle speed VSP is further set at step S58 to a set value KVSLEST (eg,
/ H), and whether or not the vehicle is in the starting state.

As a result, when VSP <KVSLEST, it is determined that the vehicle is in the start state. Similarly, in order to inhibit lean burn, the lean burn possible deceleration determination flag FLBDE is set to 1 in step S59, and the routine proceeds to step S61.
If ≧ KVSLEST, the process proceeds directly to step S61. Then, in step S61, the throttle opening degree T for each calculation timing stored in a register or the like in time series is calculated.
VOn-4, TVOn-3, TVOn-2, TVOn-1, TVO are sequentially shifted (TVOn-4 ← TVOn-3, TVOn-3 ← TV
On-2, TVOn-2 ← TVOn-1, TVOn-1 ← TVO),
Proceed to step S62 and subsequent steps.

On the other hand, when FLBDE = 1 in step S56, that is, when the transient state at the time of rapid acceleration or starting is detected and lean burn is prohibited, the process proceeds from step S56 to step S60, and FIG. After the lean burn possible deceleration determination routine is executed to determine whether the return to the lean burn is possible, the process proceeds to the step S62 and subsequent steps via the above-described step S61.

Here, the lean burn possible deceleration determination routine of FIG. 16 will be described. In this lean burn possible deceleration determination routine, it is determined whether or not the vehicle speed has converged to a constant speed as a condition under which the vehicle can return to lean burn.
When the rate of change of the vehicle speed falls from a state greater than the set value to a set value or less, and if any of the conditions for turning on the idle switch 33b is satisfied, the vehicle speed converges to a constant speed and a return to lean burn is possible. Is determined.

Therefore, in the lean burn possible deceleration determination routine, first, in step S91, the throttle opening TVO at the calculation timing at the time of executing the current routine is subtracted from the throttle opening TVOn-4 at the calculation timing four times before. The throttle opening change amount in the closing direction is obtained, and the throttle opening change amount (TVOn−4−TVO) is obtained.
Is compared with a set value KTVLEST (for example, equivalent to 1.32 deg).

Then, TVOn-4-TVO ≧ KTVLE
In the case of ST, it is determined that the throttle is closed by the set opening or more within the time determined from the calculation cycle and the vehicle speed has converged to the constant speed, and step S97 is performed to permit lean burn again.
Clears the lean burn possible deceleration determination flag FLBDE to 0 (FLBDE ← 0), and then sets a vehicle speed change determination flag FDVSP (initial value is 0) which is set to 1 when an acceleration state is determined from a change in vehicle speed in step S98. ) Is cleared to 0 (FDVSP ←
0) and exit the routine.

In step S91, TVOn-4-TV
If O <KTVLAST, the acceleration determination flag FDVSP is referred to in step S92, and if FDVSP = 0, the process proceeds to step S9.
3, the vehicle speed change DVSP calculated at predetermined intervals (for example, every 1 second) by the vehicle speed change calculation routine of FIG. 17 is changed to a set value KDVSLEST (for example, 14K).
m / h).

In the vehicle speed change calculation routine of FIG. 17, in step S101, the vehicle speed VSPOLD3 at the time of execution of the routine three times earlier (the vehicle speed three seconds before in this embodiment) VSPOLD3 is subtracted from the vehicle speed VSP at the time of execution of the current routine to obtain a vehicle speed change DVSP. (DVSP ← VSP-VSPOLD3), and step S10
2, S103 and S104, respectively, the vehicle speed VSPOLD3 at each calculation timing stored in a register or the like in chronological order.
VSPOLD2, VSPOLD1, and VSP are sequentially shifted (VSPOLD3 ← VSPOLD2, VSPOLD2).
2 ← VSPOLD1, VSPOLD1 ← VSP), and exit the routine. Here, the vehicle speed change DVSP is a vehicle speed change amount per unit time (3 seconds in the present embodiment), and represents a change rate of the vehicle speed VSP.

Then, the vehicle speed change DVSP (vehicle speed change rate) calculated by the above-described vehicle speed change calculation routine and the set value KD
As a result of comparison with VSLEST, DVSP ≦ KDVSLES
If it is T and the change in vehicle speed during acceleration is small or during deceleration, the process jumps to step S96, where DV
If SP> KDVSLEST and the vehicle speed change is accelerating greater than the set value, the process proceeds to step S94, and the vehicle speed change determination flag FDVSP is set to 1 (FDVSP ← 1).
Then, the process proceeds to step S96.

In the step S96, the idle switch 33b
Check if is turned ON, and check the idle switch 3
When 3b is OFF, the routine exits as it is, and when the idle switch 33b is ON, the lean burn possible deceleration determination flag FLBDE is cleared to 0 (FLBDE ← 0) in step S97 to permit lean burn again, and step S9
8 clears the vehicle speed change judgment flag FDVSP to 0 (FDVSP ←
0) and exit the routine.

On the other hand, when FDVSP = 1 in step S92, that is, when the vehicle speed change is accelerating larger than the set value, the process proceeds from step S92 to step S95, and the vehicle speed change DVSP is compared with the set value KDVSLEST. And, when DVSP> KDVSLEST,
The routine exits through the above-described step S96 for checking ON / OFF of the idle switch 33b, and the DVSP ≦ KDV
In the case of SLEST, it is determined that the vehicle speed change becomes less than the set value and becomes gradual, and it is determined that the vehicle speed has converged to the constant speed.

That is, for example, when the acceleration due to the accelerator operation by the driver is detected and the lean burn is prohibited, as shown in FIG. 26, the increase in the vehicle speed VSP slows down and the vehicle speed change DVSP (vehicle speed change rate) is set. When the value becomes lower than the set value KDVSLEST from a state larger than the value KDVSLEST, that is, immediately before the transition from the transient state to the steady state, the vehicle is returned to the lean burn. By entering the burn burn, the sensitive shock level can be reduced.

Then, the above-described lean burn possible deceleration determination routine is executed, the process returns to the lean burn possible execution determination routine, and the process proceeds to step S62 through step S61 described above. A catalyst temperature lean burn permission condition determination routine is executed.

As described later, in step S72,
For protecting the catalyst, the temperature of the catalyst is monitored based on the output value of the exhaust gas temperature sensor 38 disposed immediately upstream of the catalytic converter 30, and it is determined whether or not the catalyst temperature has exceeded the upper limit temperature KTCAT which can be used continuously. When the catalyst temperature exceeds the upper limit temperature (at a high catalyst temperature), the lean burn permission period and the lean burn inhibition are set by the high catalyst temperature lean burn permission flag FCAT set by the high catalyst lean burn permission condition determination routine. The period is set alternately.

That is, generally, in the NOx storage type catalyst, the catalyst temperature is higher than a certain level (for example, 510
(° C. or more), the NOx occlusion effect becomes small, and if used continuously, the coating layer on the catalyst surface deteriorates and cannot be recovered. At this high temperature, the stoichiometric operation is prohibited and lean burn operation is performed to recover the coating layer on the catalyst surface, and stoichiometric operation and lean burn operation are alternately performed without progressing deterioration. It is possible.

For this reason, in the high catalyst temperature lean burn permission condition determination routine described below, the amount of heat received by the catalyst is calculated, and the lean burn inhibition / permission at high catalyst temperature is determined based on the amount of heat received by the catalyst. I do. In the present embodiment, the amount of heat received by the catalyst is substituted by the following catalyst temperature integrated value TCATSUM obtained by integrating the instantaneous value TCAT of the catalyst temperature at regular intervals, thereby simplifying the control while avoiding complicated calculations, and I try to improve the nature. That is, first, step
In S121, a high catalyst temperature lean burn permission flag FCAT (initial value is 0 indicating lean burn inhibition) indicating lean burn permission at high catalyst temperature is referred to.

In step S121, FCAT
When = 0, in step S122 the catalyst temperature integrated value TCA
Set TSUM to the set value KTCATSOK (for example, 6553).
5 ° C). The above-mentioned catalyst temperature integrated value TCATTUM
Represents the amount of heat received by the catalyst after the lean burn has been inhibited or restarted at a high catalyst temperature, and is calculated, for example, every 1 second by the catalyst temperature integration routine of FIG. The value is 0 when lean burn is prohibited or when lean burn is restarted.
Is initialized to

That is, in the catalyst temperature integration routine, in step S131, the catalyst temperature instantaneous value TCAT detected by the exhaust gas temperature sensor 38 is added to the previous integrated value TCATTUM.
To update the catalyst temperature integrated value TCATSUM to the latest value.
T).

The set value KTCATSOK represents the amount of heat received by the catalyst at which the lean burn can be restarted after the lean burn is prohibited (shift to the stoichiometric operation) at a high catalyst temperature. Lean burn is prohibited, the air-fuel ratio is set to stoichiometric, and the amount of heat received until the catalyst recovers its function with respect to the lean burn.

Then, at the above step S122, TCATSU
If M <KTCATSOK, the routine exits and TC
When ATSUM ≧ KTCATSOK, the high catalyst temperature lean burn permission flag FCAT is set to 1 (FCAT ← 1) in step S123 to permit the return to lean burn, and in step S126, the catalyst temperature integrated value TCATSUM is cleared (TCATTSUM). ← 0) and exit the routine.

On the other hand, in step S121, FCAT =
When the lean burn is permitted at a high catalyst temperature, the process proceeds from step S121 to step S124, where the catalyst temperature integrated value TCATTUM is set to the set value KTCA.
Compare with TSNG (for example, 65535 ° C). The set value KTCATSNG is a catalyst heat receiving amount at which the lean burn can be continued without advancing the deterioration of the coating layer on the catalyst surface at a high catalyst temperature, or the lean burn is continued at a high catalyst temperature, and the catalyst surface coating is performed. This indicates the amount of heat received by the catalyst that can recover the function of the catalyst by shifting to the above-described stoichiometric operation even if the layer is deteriorated to some extent. When TCATTUM <KTCATSNG, even when the catalyst temperature is high, the catalyst is lean. Judge that it is OK to continue the burn, exit the routine, and
If ≧ KTCATSNG, the high catalyst temperature lean burn permission flag FCAT is cleared to 0 (FCAT ← 0) in step S125 to prohibit lean burn to protect the catalyst,
The routine exits through step S126 in which the catalyst temperature integrated value TCATTUM is cleared to 0.

That is, even when the catalyst temperature exceeds the upper limit temperature at which continuous use can be performed during the execution of the lean burn, the lean burn is prohibited and the lean burn permission is received instead of uniformly inhibiting the lean burn. It is performed alternately for the time specified by the calorific value,
The execution frequency of the lean burn can be maximized while preventing the catalyst from deteriorating, and the fuel efficiency can be improved.

When the lean burn frequency at the time of high catalyst temperature is set according to the above-described lean burn permission condition at high catalyst temperature, in the lean burn feasibility determination routine, steps S63 and S6 are executed.
4, at S65, S66, S67, S68, S69, S70, S71, a first coolant temperature determination flag FTWL, a second coolant temperature determination flag FTWH, a first rotation determination flag FNEL, a second rotation determination flag FNEH, and a first vehicle speed, respectively. Determination flag FVSPL, second vehicle speed determination flag FVSPH, intake pipe pressure determination flag FPM, throttle opening degree determination flag FTV
O, refer to lean burn possible deceleration determination flag FLBDE.

Then, the first water temperature determination flag FTWL and the second
Water temperature determination flag FTWH, first rotation determination flag FNEL, second
A rotation determination flag FNEH, a first vehicle speed determination flag FVSPL, a second vehicle speed determination flag FVSPH, an intake pipe pressure determination flag FPM,
When at least one of the throttle opening degree determination flags FTVO has a value of 0, or when the lean burn possible deceleration determination flag FLBDE is 1, it is determined that the condition for enabling lean burn is not satisfied, and the process proceeds from step S7 to step S7.
Proceeding to 8, the timer TM for measuring the duration for which the condition for enabling the lean burn is satisfied is cleared (TM ← 0), and then the lean burn flag FLB is cleared to 0 in step S79 to inhibit the lean burn (FLB). ← 0) and exit the routine.

A first water temperature judgment flag FTWL, a second water temperature judgment flag FTWH, a first rotation judgment flag FNEL, a second rotation judgment flag FNEH, a first vehicle speed judgment flag FVSPL, a second
When the vehicle speed determination flag FVSPH, the intake pipe pressure determination flag FPM, and the throttle opening degree determination flag FTVO are all 1 and the lean burn possible deceleration determination flag FLBDE is 0, that is, the water temperature condition, rotation speed condition, and vehicle speed condition described above. When all of the intake pipe pressure condition, the throttle opening condition, and the lean burnable deceleration condition are satisfied, steps S63 to S63 are executed.
The process proceeds to step S72 via step 71, and in order to determine the condition (f), the catalyst temperature instantaneous value TCAT is set to the upper limit temperature KTCAT (for example, 5
10 ° C).

Then, when TCAT ≦ KTCAT, the flow directly proceeds to step S74. When the catalyst temperature is higher than TCAT> KTCAT in step S72, the high catalyst temperature lean burn permission flag FCAT set in the above-described high catalyst temperature lean burn permission condition determination routine is referred to in step S73. Then, when FCAT = 0 and the lean burn is prohibited, the lean burn is prohibited by clearing the lean burn flag FLB through the above-described steps S78 and S79, and the routine exits. When FCAT = 1 and the lean burn is permitted, the step is executed. Proceed to S74.

In step S74, the lean burn flag FL
Referring to B, if FLB = 1 and lean burn is currently permitted, the routine exits as it is. Also, FLB
= 0 and the lean burn is currently prohibited, in step S75, the timer TM for measuring the continuation time during which the condition for enabling the lean burn is satisfied is set to the set value TMLE.
(E.g., 520 msec) is checked.

If TM <TMLE, the timer TM is counted up in step S76 (TM ← TM +
1) Then, the process exits the routine. If TM ≧ TMLE, the lean burn flag FLB is set to 1 (FLB ← 1) in step S77 to permit lean burn, and the process exits.

As described above, the lean burn flag FLB set by the above-described lean burn feasibility determination routine is determined by the air-fuel ratio feedback correction coefficient setting routine (step S143 in FIG. 4) and the lean correction coefficient FLEAN.
Is referred to in the leaning permission coefficient setting routine (step S441 in FIG. 7) when setting is performed, and is reflected in the fuel injection control.

When FLB = 1, lean burn is performed with a lean air-fuel ratio, and when FLB = 0, lean burn is prohibited, and operation is performed with stoichiometry (including a rich air-fuel ratio).

[0167]

As described above, according to the present invention, when switching to the lean air-fuel ratio for performing the lean burn,
When the current throttle opening is equal to or smaller than a determination value indicating a boundary of a region where the intake air amount set for each set range of the engine speed is substantially equal, it is determined that lean burn can be performed, and the air-fuel ratio is switched to a lean air-fuel ratio. Therefore, the air-fuel ratio can be switched to the lean air-fuel ratio along the equal torque line of the engine, and excellent effects such as reduction of torque shock by realizing optimum matching with the output torque of the engine can be obtained.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of the present invention.

FIG. 2 is a flowchart of a cylinder discrimination / engine speed calculation routine.

FIG. 3 is a flowchart of a fuel injection amount setting routine;

FIG. 4 is a flowchart of an air-fuel ratio feedback correction coefficient setting routine.

FIG. 5 is a flowchart of a routine for setting various correction coefficients.

FIG. 6 is a flowchart of a leaning correction coefficient setting routine.

FIG. 7 is a flowchart of a leaning permission coefficient setting routine (part 1);

FIG. 8 is a flowchart of a leaning permission coefficient setting routine (part 2);

FIG. 9 is a flowchart of a lean burn execution possibility determination routine (part 1).

FIG. 10 is a flowchart of a lean burn execution possibility determination routine (part 2);

FIG. 11 is a flowchart of a lean burn execution possibility determination routine (part 3).

FIG. 12 is a flowchart of a lean burn execution possibility determination routine (part 4).

FIG. 13 is a flowchart of a lean burn execution possibility determination routine (part 5).

FIG. 14 is a flowchart of a lean burn execution possibility determination routine (part 6).

FIG. 15 is a flowchart of a lean burn execution possibility determination routine (part 7).

FIG. 16 is a flowchart of a lean burn possible deceleration determination routine.

FIG. 17 is a flowchart of a vehicle speed change calculation routine.

FIG. 18 is a flowchart of a high catalyst temperature lean burn permission condition determination routine.

FIG. 19 is a flowchart of a catalyst temperature integration routine.

FIG. 20 is a time chart showing a setting state of an air-fuel ratio feedback correction coefficient based on an O2 sensor output;

FIG. 21 is an explanatory diagram of a lean upper limit value map.

FIG. 22 is an explanatory diagram of a leaning target value map.

FIG. 23 is an explanatory diagram showing a change in a leaning permission coefficient due to lean burn inhibition / permission.

FIG. 24 is an explanatory diagram of lean burn feasibility determination conditions.

FIG. 25 is an explanatory diagram showing an example of data of a throttle opening determination value table.

FIG. 26 is an explanatory diagram of a lean burn possible deceleration condition.

FIG. 27 is a time chart showing a relationship among a crank pulse, a cylinder discrimination pulse, a combustion stroke cylinder, an ignition signal, and an injector drive signal.

FIG. 28 is an overall schematic diagram of an engine.

FIG. 29 is an explanatory diagram showing details of a main part of an intake system.

FIG. 30 is a front view of a crank rotor and a crank angle sensor.

FIG. 31 is a front view of a cam rotor and a cylinder discrimination sensor.

FIG. 32 is a circuit configuration diagram of an electronic control system.

[Explanation of symbols]

1 ... lean burn engine 50 ... ECU (air-fuel ratio switching means, throttle opening determination means) NE ... engine speed TVO ... throttle opening TVOLE ... throttle opening determination value

Claims (1)

[Claims] 1. A lean-burn engine control device comprising air-fuel ratio switching means for switching between a stoichiometric air-fuel ratio or a rich air-fuel ratio and a lean air-fuel ratio in accordance with a result of determination of permission / prohibition of lean burn. A throttle opening determination value indicating a boundary of a region where the intake air amount is substantially equal is set for each set range, and when the current throttle opening is equal to or less than the determination value, a throttle opening determination unit for permitting lean burn is provided. A control device for a lean burn engine, comprising: