JPH08144801A - Air-fuel ratio control for engine - Google Patents

Abstract

PURPOSE: To attain more convenience as a base control software by making clear a criterion concerning which correction items should be changed without having any effect upon the other correction items if no good condition occurs on air-fuel ratio controllability in a certain operating range. CONSTITUTION: According to an engine operating conditions, a combustible limit equivalent ratio ϕtw which shows a combustible limit on the lean side by a relation to cooling water temperature, a maximum output equivalent ratio ϕful which is set under a condition where an engine performs maximum output, an exhaust gas temperature limit equivalent ratio ϕtex for fuel cooling which restrains exhaust gas temperature rising below a designed limit, a catalyst purifying factor best equivalent ratio ϕgas which is set under a condition where exhaust gas is purified, and a fuel consumption best equivalent ratio ϕeco which sets the equivalent ratio at which the best fuel consumption is obtained are set, and the maximum value of them is set as a target equivalent ratio COEF. An in-cylinder suction fuel mass Gfuel per one inspiration stroke corresponding to a target air-fuel ratio where preset theoretical air-fuel ratio F/A is corrected at the target equivalent ratio is computed based on an in-cylinder intake air mass Gair for respective cylinders.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine air-fuel ratio control method for variably setting a target air-fuel ratio based on a theoretical fuel-air ratio according to operating conditions.

[0002]

2. Description of the Related Art Generally, in this type of fuel injection control, L
There are a JETRONIC method and a D-JETRONIC method. Both of them simply calculate the intake air amount based on the measured value of the intake air amount sensor, or based on the intake pipe pressure downstream of the throttle valve. The only difference is whether to calculate the intake air amount. Whether the engine uses the L-Jetronic system or the D-Jetronic system, after the intake air amount is calculated, the target air-fuel ratio is handled in a common calculation process. It is possible to determine the fuel injection amount to be used.

As an engine adopting the L-Jetronic system, there is, for example, one disclosed in Japanese Patent Application Laid-Open No. 2-5745. In this engine, it is assumed that the intake air mass flow rate [mg / sec ² ] detected by the intake air amount sensor was measured at the same time as when it passed through the throttle valve, and the intake air flow into the chamber downstream of this throttle valve was considered. The amount of intake air taken into each cylinder is calculated from the output relationship.

On the other hand, as an engine adopting the D-Jetronic system, there is one disclosed in JP-A-6-185391. In this engine, the amount of intake air into the cylinder is estimated using an equation of state of air. That is, the throttle valve passes through the throttle valve per unit time (Δt) based on the pressure difference between the upstream and downstream sides of the throttle valve, that is, the deviation between the atmospheric pressure and the intake pipe pressure, the throttle effective opening area, and the air density on the upstream side of the throttle valve. The amount of intake air (the amount of air passing through the throttle) is approximately calculated, and then the amount of change in the amount of air filled in the chamber this time is set based on the amount of change in the pressure of the amount of air in the chamber Gb downstream of the throttle valve. Then, the amount of air filled in the chamber this time is regarded as not being sucked into the cylinder, and the cylinder intake air amount per unit time is calculated.

Then, the basic injection amount determined by the in-cylinder intake air amount and the engine speed is multiplied by a correction coefficient for obtaining an appropriate air-fuel ratio according to the engine state at that time, and each injector is injected. Set the fuel injection amount.

[0006]

As described above, conventionally,
When the in-cylinder intake air amount is obtained, the fuel injection amount is calculated based on this in-cylinder intake air amount, and the air-fuel ratio is eventually controlled as the total value of the basic injection amount corrected by various correction factors. It's just that.

Therefore, when a problem occurs in the air-fuel ratio controllability under a certain operating condition, a criterion of which correction term should be changed without affecting other parts to obtain good air-fuel ratio controllability. Is unclear. In other words, even if the intake air amount to each cylinder is accurately estimated, the air-fuel ratio control system based on this intake air amount in the cylinder follows the conventional control system. It is not convenient as a base control software that can be changed to, and a total change is forced.

The present invention has been made in view of the above-mentioned circumstances, and even when a problem occurs in the air-fuel ratio controllability in a certain operating region, a criterion for determining which correction term should be changed becomes clear,
Further, it is an object of the present invention to provide an engine air-fuel ratio control method in which the change is unlikely to affect other parts and which is sufficiently convenient as base control software.

[0009]

In order to achieve the above object, an engine air-fuel ratio control method according to the present invention is an engine air-fuel ratio which corrects a stoichiometric fuel-air ratio by a target equivalence ratio to set a target air-fuel ratio in a steady state. In the fuel ratio control method, the target equivalence ratio is set to a maximum value among a plurality of different required equivalence ratios set based on an engine operating state.
Further, preferably, the required equivalence ratio is a fuel cooling based on at least the engine speed and the engine load, and a flammability limit equivalence ratio that sets a flammability limit increase coefficient on the lean side of the air-fuel ratio. It is characterized in that the exhaust gas temperature limit equivalence ratio sets the usage increase coefficient.

[0010]

[Operation] In the present invention, a plurality of different required equivalence ratios are set according to the engine operating state, and then the maximum value of the respective required equivalence ratios is set as the target equivalence ratio. And
With this target equivalence ratio, the theoretical fuel-air ratio preset or set corresponding to various types of fuel is corrected to set the target air-fuel ratio in the steady state. Therefore, if this theoretical fuel-air ratio is 1,
The target air-fuel ratio is determined by the target equivalence ratio.

Further, as the required equivalence ratio, at least the flammability limit equivalence ratio for setting the flammability limit increase coefficient on the lean side of the air-fuel ratio based on the engine speed and the engine temperature, and the fuel cooling based on the engine speed and the engine load. By adopting the exhaust gas temperature limit equivalence ratio that sets the usage increase coefficient, the flammability limit equivalence ratio is set to a rich equivalence ratio during cold start, etc., and the lean equivalence ratio gradually increases as the temperature shifts to high temperature and high rotation. On the other hand, in the exhaust gas temperature limit equivalence ratio, set the lean equivalence ratio or 0 at low rotation and low load operation, and gradually set to the rich equivalence ratio as shifting to high rotation and high load operation. In the low speed region, the flammable limit equivalence ratio is determined as the target equivalence ratio, while in the high revolution speed and high load region, the exhaust gas temperature limit equivalence ratio is determined as the target equivalence ratio. Etc., the optimum air-fuel ratio is set according to the engine operating condition.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 25 shows an overall schematic view of the engine,
Reference numeral 1 in the figure denotes an engine (in the figure, a horizontally opposed four-cylinder engine is shown), an intake manifold 3 is connected to an intake port 2a of a cylinder head 2, and an air chamber 4 is provided upstream of the intake manifold 3. And the throttle passage 5 is in communication. An air cleaner 7 is provided on the upstream side of the throttle passage 5 via an intake pipe 6.
Is attached, and the air cleaner 7 is communicated with an air intake chamber 8 which is an intake port for intake air. Further, an exhaust pipe 10 is connected to the exhaust port 2b via an exhaust manifold 9, and a catalytic converter 11 is inserted in the exhaust pipe 10 to be connected to a muffler 12.

On the other hand, a throttle valve 5a is provided in the throttle passage 5, an intercooler 13 is provided in the intake pipe 6 immediately upstream of the throttle passage 5, and further,
A resonator chamber 14 is provided downstream of the air cleaner 7 in the intake pipe 6.

Further, a bypass passage 1 for connecting the resonator chamber 14 and the intake manifold 3 to bypass the upstream side and the downstream side of the throttle valve 5a.
5, idle control (IS
C) The valve 16 is interposed. Further, the above ISC valve 1
A check valve 17 which is opened immediately downstream of 6 when the intake pressure is a negative pressure and which is closed when the intake pressure becomes a positive pressure by being supercharged by a turbocharger 18 is interposed.

In the turbocharger 18, a compressor is installed downstream of the resonator chamber 14 of the intake pipe 6, and a turbine is installed in the exhaust pipe 10. Further, a wastegate valve 19 is provided at the turbine housing inlet of the turbocharger 18, and a wastegate valve actuating actuator 20 is connected to the wastegate valve 19.

The waste gate valve actuating actuator 20 is partitioned into two chambers by a diaphragm, one of which forms a pressure chamber communicating with the waste gate valve controlling duty solenoid valve 21, and the other of which forms the waste gate valve 19. A spring chamber is formed that houses a spring that urges in the closing direction.

The wastegate valve controlling duty solenoid valve 21 is interposed in a passage that connects the resonator chamber 14 and the compressor downstream of the turbocharger 18 of the intake pipe 6, and an electronic control unit 50 described later. (ECU; see FIG. 28) according to the duty ratio of the control signal outputted from the control chamber, the pressure on the resonator chamber 14 side and the pressure on the compressor downstream side are adjusted, and the pressure chamber of the waste gate valve operating actuator 20 is adjusted. Supply to.

That is, the wastegate valve controlling duty solenoid valve 21 is controlled by the ECU 50, and the wastegate valve operating actuator 20 is controlled.
Is operated to adjust the exhaust gas relief by the waste gate valve 19, so that the supercharging pressure by the turbocharger 18 is controlled.

An intake pipe pressure sensor 22 for detecting the intake pipe pressure P as an absolute pressure is communicated with the intake manifold 3 through a passage 23, and further, each intake port 2a of each cylinder of the intake manifold 3 is connected. The injector 25 is exposed immediately upstream. Further, an ignition plug 26a whose tip is exposed to the combustion chamber is attached to each cylinder of the cylinder head 2, and an igniter 27 is connected to the ignition plug 26a via an ignition coil 26b provided for each cylinder. Has been done.

The injector 25 includes a fuel tank 2
Fuel is pressure-fed from an in-tank type fuel pump 29 provided inside 8 through a fuel filter 30, and a pressure regulator 31 regulates the fuel pressure to the injector 25.

Also, the air cleaner 7 of the intake pipe 6
A thermal intake air amount sensor 32 using a hot wire or a hot film or the like is provided immediately downstream of the throttle valve 5a, and a throttle opening sensor 33a and an idle switch 33b are built in the throttle valve 5a. Are lined up. Further, an intake air temperature sensor 46 is exposed to the air chamber 4.

Further, a knock sensor 34 is attached to the cylinder block 1a of the engine 1, and a water temperature sensor 36 is exposed to a cooling water passage 35 which connects the left and right banks of the cylinder block 1a.
The O 2 sensor 37 is exposed to the collecting portion of the exhaust manifold 9.

A crank rotor 38 is rotatably mounted on a crank shaft 1b supported by the cylinder block 1a, and a crank angle sensor 39 including an electromagnetic pickup is provided on the outer periphery of the crank rotor 38. Further, a cam angle sensor 41 for discriminating a cylinder, which is composed of an electromagnetic pickup or the like, is provided opposite to a cam rotor 40 connected to the cam shaft 1c of the engine 1. still,
The crank angle sensor 39 and the cam angle sensor 41
Is not limited to a magnetic sensor such as an electromagnetic pickup, but may be an optical sensor.

As shown in FIG. 26, the crank rotor 38 has projections 38a, 38b and 38c formed on the outer periphery thereof, and these projections 38a, 38b and 38c are associated with the cylinders (# 1, # 2 and #). Before # 3, # 4 compression top dead center (BTD
C) It is formed at the positions of θ1, θ2 and θ3, and in the present embodiment, θ1 = 97 ° CA and θ2 = 65 ° C.
A, θ3 = 10 ° CA.

Each protrusion of the crank rotor 38 is detected by the crank angle sensor 39, and the BTDC 97
Crank pulses of °, 65 °, and 10 ° are output every 1/2 engine revolution (every 180 ° CA). Then, the input interval time of each signal is counted by the timer, and the engine speed Ne is calculated.

Further, as shown in FIG. 27, on the outer periphery of the cam rotor 40, there are projections 40a, 40b for cylinder discrimination,
40c is formed, and the projection 40a is formed at the position after compression top dead center (ATDC) θ4 of the # 3 and # 4 cylinders.
0b is composed of three protrusions, and the first protrusion is formed at the ATDCθ5 position of the # 1 cylinder. Further, the protrusion 40c is formed by two protrusions, and the first protrusion is formed at the position of ATDC θ6 of the # 2 cylinder. In this embodiment, θ4 = 20 ° CA, θ5 = 5 ° CA, θ6
= 20 ° CA.

When each protrusion of the cam rotor 40 is detected by the cam angle sensor 41 and the combustion stroke sequence of each cylinder is # 1 → # 3 → # 2 → # 4, the combustion stroke sequence and Cylinder discrimination is made based on the pattern of the cam pulse from the cam angle sensor 41 and the value counted by the counter.

On the other hand, in FIG. 28, reference numeral 50 is an electronic control unit (ECU) 50 for controlling the engine system,
The ECU 50 is mainly composed of two computers, a main computer 51 for performing fuel injection control, ignition timing control and the like, and a dedicated sub computer 52 for performing knock detection processing, and supplies a predetermined stabilizing power to each part. The constant voltage circuit 53 and various peripheral circuits are incorporated.

The constant voltage circuit 53 includes an ECU relay 54.
Is connected to the battery 55 via the relay contact of
A relay coil of the ECU relay 54 is connected to the battery 55 via an ignition switch 56,
When the ignition switch 56 is turned on, the EC
When the relay contact of the U relay 54 is closed, control power is supplied to each of the computers 51 and 52, the constant voltage circuit 53 is directly connected to the battery 55, and the ignition switch 56 is turned on and off.
Regardless of F, the backup power is supplied to the backup RAM 61.

A fuel pump 29 is connected to the battery 55 via a relay contact of a fuel pump relay 57.

The main computer 51 has a CPU 5
8, ROM59, RAM60, backup RAM6
1, a counter / timer group 62, a serial communication interface SCI 63, and an I / O interface 64 are microcomputers connected via a bus line 65, and the backup RAM 61 includes:
Regardless of whether the ignition switch 56 is ON or OFF, backup power is constantly supplied from the constant voltage circuit 53 directly connected to the battery 55 to retain data.

The counter / timer group 62 includes various counters such as a free-run counter, a counter for counting input of cam angle sensor signals, a fuel injection timer, an ignition timer,
For convenience, various timers such as a periodic interrupt timer for generating a periodic interrupt, a timer for measuring an input interval of a crank angle sensor signal, and a watchdog timer for monitoring a system abnormality are collectively referred to for convenience. In addition, various software counters and timers are used.

The sub-computer 52, like the main computer 51, has a CPU 71 and a ROM 7.
2, RAM 73, counter / timer group 74, SCI7
5 and the I / O interface 76 is the bus line 7
7, the main computer 51 and the sub computer 52 are connected to each other by a serial communication line via the SCIs 63 and 75.

The I / O interface 64 of the main computer 51 has an intake port, an intake air amount sensor 32, a throttle opening sensor 33a, and a water temperature sensor 3 at its input ports.
6, O2 sensor 37, intake pipe pressure sensor 22, atmospheric pressure sensor 44, vehicle speed sensor 42, intake air temperature sensor 46, and
The battery 55 is connected via the A / D converter 66, the idle switch 33b, the starter switch 43, the crank angle sensor 39, the cam angle sensor 41, etc. are connected, and further, various sensors and switches not shown. Are connected.

The igniter 27 is connected to the output port of the I / O interface 64, and the ISC valve 16, the injector 25, the relay coil of the fuel pump relay 57, and the waste solenoid valve controlling duty solenoid valve 21 are connected. It is connected via a drive circuit 67, and further various actuators (not shown) are connected.

On the other hand, the I / O of the sub computer 52
The interface 76 has an input port to which the crank angle sensor 39 and the cam angle sensor 41 are connected, and
The knock sensor 34 is connected via the D / D converter 78, the frequency filter 79, and the amplifier 80. The knock detection signal from the knock sensor 34 is amplified to a predetermined level by the amplifier 80, and then the frequency filter 79. The necessary frequency components are extracted by the A / D converter 78.
At, it is converted into a digital signal and input.

The main computer 51 processes the detection signals from the sensors and performs fuel injection amount control, ignition timing control, idle control, etc., while the sub-computer 52 controls the engine speed and engine load. The sample section of the signal from the knock sensor 34 is set on the basis of, and the signal from the knock sensor 34 is A / D converted at high speed in this sample section to faithfully convert the vibration waveform into digital data, and based on this data Determine whether knock has occurred.

The output port of the I / O interface 76 of the sub computer 52 is connected to the input port of the I / O interface 64 of the main computer 51, and the knock determination result of the sub computer 52 is I / O. It is output to the interface 76. Then, in the main computer 51, when the knocking occurrence determination result is output from the sub computer 52, knock data is read from the sub computer 52 from the serial communication line via the SCI 63, and immediately based on this knock data The ignition timing of the cylinder is delayed to avoid knock.

In such engine control, various jobs related to signal input processing from sensors and switches, fuel injection control, ignition timing control, and idle control are handled by one operating system (OS) in the main computer 51. Performed efficiently under control. This O
S is various management functions for vehicle control, and
It has an internal strategy closely related to this management function, systematically combines various jobs, and executes various jobs efficiently by processing at equal time intervals.

The fuel injection control by the main computer 51 will be described below with reference to the routines shown in FIGS. Since the sub computer 52 is a computer dedicated to knock detection processing, its operation description is omitted.

In this embodiment, based on the A / D conversion result processed on the OS side, crank position information, engine speed, etc., the user side job sets the fuel injection amount, ignition timing, etc., and gives these instructions. The values are set in the injection timer and the ignition timer by the OS. Then, a periodic interrupt request for every 10 ms job, every 50 ms job, etc. is output,
In addition, each signal input from the crank angle sensor 39 (BTDC
6 times per engine revolution every 97 °, 65 °, 10 ° CA)
Permits interruption of each crank pulse input job started at.

In each 10 ms job, the fuel injection effective pulse width and fuel injection waste pulse width setting routines shown in FIGS. 1 to 3 and the intake air amount setting routine shown in FIG. 5 are executed. Further, in each 50 ms job, the coefficient setting routine shown in FIG. 6 and the required equivalent ratio setting routine shown in FIGS. 7 to 9 are executed.

In the following description, as shown in FIG. 24, the portion from the downstream side of the throttle valve 5a of the intake system to the upstream side of the intake valve is generically called the intake chamber 6A. Therefore, the intake chamber 6A is a general term for the throttle passage 5, the air chamber 4, the intake manifold 3, and the intake port 2a.

Here, terms used in the following description will be briefly described. Q means mass flow rate [mg / sec], and G means mass per cycle [mg / cycle]. However, in-cylinder intake air mass Gair and in-cylinder intake fuel mass Gfu described later
Since el and the like are inhaled only during the intake stroke, they have substantially the same meaning as the mass per intake stroke. Further, from the left of FIG. 24, Qa is the mass flow rate of air passing through the intake air amount sensor 32 (sensor passing air mass flow rate), M is the air mass of the intake chamber 6A, P is the intake pipe internal pressure of the intake chamber 6A, and Ginj. Is the fuel injection mass, Qc is the cylinder intake air mass flow rate, Gair is the cylinder intake air mass, Gfuel
Indicates the mass of in-cylinder intake fuel.

First, before explaining the routine for setting the effective fuel injection pulse width and the unnecessary fuel injection pulse width shown in FIGS. 1 to 3, the routine for setting the parameters to be taken in this routine will be explained.

In the routine executed every 10 ms job in FIG. 5, the cylinder intake air mass Gair per intake stroke is calculated by the D-Jetronic system. First, in step S41, the intake pipe pressure P on the downstream side of the throttle valve 5a calculated based on the detection value of the intake pipe pressure sensor 22,
The intake air temperature T calculated based on the detection value of the intake air temperature sensor 46 is read, and it is determined in step S42 whether the current intake air temperature T is 50 ° C. or lower, that is, in the normal intake air temperature region, and if T <50 ° C. Sometimes, the process proceeds to step S43, the intake air temperature set value T'is set at the current intake air temperature T, and the process proceeds to step S45. When T ≧ 50 ° C., the intake air temperature setting value T ′ is set to a fixed value of 50 ° C. in step S44, and then the process proceeds to step S45.

By the way, the cylinder intake air mass Gair is
Even if the intake pipe pressure P is constant, it varies depending on the intake air temperature T. Therefore, from the air density σ to the cylinder intake air mass G
It is necessary to calculate air. Assuming that the air density σ in the cylinder is the same as the air density in the intake chamber 6A during the intake stroke, the air density α in the cylinder can be obtained from the following equation by the equation of state of air.

Σ = P × (1−Regr) / (R × T) (1) Regr; EGR rate R; Gas constant FIG. 11 shows the relationship between the cylinder intake air mass Gair and the intake air temperature T. The solid line is the characteristic of the intake air mass (measured intake air amount) obtained by actual measurement, the two-dot chain line is the intake air mass (density proportional intake air amount) obtained according to the air density σ calculated by the above formula (1), and the one-dot chain line is the intake air temperature. The intake air mass (pressure proportional intake air amount) obtained according to the air density σ calculated by fixing T to a certain temperature is shown. As shown in the figure, in the normal intake air temperature region in which the intake air temperature T is 50 ° C. or less, the density-proportional intake air amount exhibits a characteristic substantially in line with the actually measured intake air amount. However, according to the measurement result of the engine with the turbocharger, the intake air temperature T is 50 ° C.
In the region exceeding, the cylinder intake air mass Gair is not sucked in proportion to the air density σ, and the density-proportional intake air amount becomes smaller than the measured intake air amount, and as a result, the air-fuel ratio becomes lean. Will turn into. By the way, originally, in the region where the intake air temperature T is 50 ° C. or higher, correction should be performed using the correction coefficient for each temperature, but the control becomes complicated and the pressure proportional intake air amount substantially matches the measured intake air amount. Since it shows the characteristics,
In this routine, the intake air temperature set value T ′ is fixed at 50 ° C. and the cylinder intake air mass Gair is obtained.
Note that the above-mentioned 50 ° C. is the critical temperature obtained by the experiment, and it differs depending on the engine type to be adopted, so it must be set individually. Further, in the engine in which the EGR device is not mounted as in this embodiment, the EGR rate is zero.

Then, in step S45, the air density σ is calculated by substituting the intake air temperature T in the equation (1) with the intake air temperature set value T ', and in step S46, the air density σ and the stroke volume D are calculated. Based on and, the theoretical intake mass Gth per intake stroke is calculated from the following equation.

Gth ← D × σ (2) Therefore, the theoretical intake air mass Gth is proportional to the intake pipe pressure P unless the intake air temperature set value T ′ is taken into consideration.

Then, in step S47, the cylinder intake air mass Gair is calculated from the following equation based on the theoretical intake mass Gth, and the routine is exited.

Gair ← (Gth−ηb) × ηv × Ktrm (3) ηb: Intake loss mass ηv: Volume efficiency Ktrm: Intake air amount error correction coefficient Relationship between the theoretical intake mass Gth and the cylinder intake air mass Gair Is as shown in FIG. 12, and the theoretical intake mass Gt
It is represented by a linear expression of the horizontal axis contact ηb and the inclination ηv such that the cylinder intake air mass Gair becomes zero before h becomes zero, that is, the intake pipe pressure P becomes a complete vacuum. However, in reality, there is no operating condition such that the cylinder intake air mass Gair becomes zero. Further, the intake loss mass ηb and the volume efficiency ηv per intake stroke are set by referring to a one-dimensional map with interpolation calculation based on the engine speed Ne, as will be described later. Furthermore, since the relationship between the theoretical intake air mass Gth and the in-cylinder intake air mass Gair may not be completely expressed by the linear expression in the intake air amount error correction coefficient Ktrm, the steady-state air amount measurement depending on operating conditions may be performed. This is for correcting such an error amount, and is set by referring to a two-dimensional map with interpolation calculation based on the throttle opening α and the engine speed Ne, for example. FIG. 13 illustrates the characteristics of the two-dimensional map that sets the intake air amount error correction coefficient Ktrm. As shown in this figure, the value of the intake air amount error correction coefficient Ktrm is basically 1.0.

Next, the coefficient setting routine executed in each 50 ms job shown in FIG. 6 will be described. In this routine, the intake air loss mass ηb and the volumetric efficiency ηv
Set.

First, at step S51, the engine speed N
Then, in step S52 and S53, the volumetric efficiency ηv and the intake air loss mass ηb are set by referring to the one-dimensional map with interpolation calculation based on the engine speed Ne, and the routine is exited.

Volumetric efficiency ηv, intake air loss mass ηb
The value of is theoretically 1.0, but it is a value that changes depending on the effect of cam synchronization, etc. for each engine speed,
Further, factors such as high altitude correction and exhaust pressure correction can be added to the volume efficiency ηv.

As described above, in this routine, the cylinder intake air mass Gair is calculated based on the intake pipe pressure P based on a simple calculation formula, and the volume efficiency ηv and the intake loss mass ηb are the primary Since it can be set from the original map, the load on the computer is lightened, and moreover,
As long as the intake pipe pressure P is accurately measured, it can be applied in all regions including the starting time.

By the way, the cylinder intake air mass Gair
Can also be calculated by the L-Jetronic method. A procedure for calculating the cylinder intake air mass Gair using the L-Jetronic method will be described according to the routine executed in each 4 ms job of FIG. The detection time of the intake air amount sensor 32 may be considered to be substantially the same as the detection time of the throttle valve 5a, although it varies depending on the length of the intake conduit up to the throttle valve 5a and the flow velocity.

First, in step S101, the output voltage VAFM from the intake air amount sensor 32 is read, and in the next steps S102 and S103, the output voltage VAFM is transiently corrected. That is, as shown in FIG. 14, according to the experiment,
The change of the output voltage VAFM of the intake air amount sensor 32 with respect to the sudden change of the intake air amount during the transient is 2 of the ideal change.
It shows a sufficiently fast response up to a voltage of / 3, but the remaining 1 /
3 has been shown to respond with a delay having a time constant of about 200 ms. If the relationship between the mass air flow rate Qa passing through the sensor and the output voltage VAFM at this time is expressed by the transfer function of the time constant τ (s), VAFM = (2/3) × Qa + {1 / (3τ (s) +3) } × Qa (4), and the response delay may be corrected by the inverse function of the equation (4). This correction equation is Qa = (1/2) × [3-1 / {(2/3 ) Τ (s) +1}] × VAFM (5)

Since the above time constant τ (s) is 200 ms, if (2/3) τ (s) + 1≈130, then the above equation (5) becomes Qa = (1/2) × (3- (130) VAFM ≈ (1/2) × (3 VAFM-VAFM / 130) (6) That is, from the output voltage VAFM of the intake air amount sensor 32 three times, this output voltage VAFM is 130 m
Subtract the output voltage VAFM delayed by the time constant of s,
If the value is halved, the response delay of the intake air amount sensor 32 during the transition can be easily corrected.

Based on such an idea, the above step S
At 102, a predetermined time constant shown in the following equation is calculated from the first-order lag output voltage VAFMav obtained this time and the present output voltage VAFM (in this routine, an approximate value of 130 ms is 32 × 4 m).
s) based on the weighted average of the first-order lag output voltage V
Calculate AFMav.

VAFMav ← (31 · VAFMav + VAFM) / 32 (7) Next, in step S 103, the output voltage after the transient correction (transient corrected output voltage) V′AFM is calculated from the current output voltage VAFM and the first-order lag output voltage VAFMav. Is calculated from the following formula.

V′AFM ← (3 · VAFM−VAFMav) / 2 (8) As described above, since the transient response delay of the intake air amount sensor 32 can be derived by a simple linear equation, the load on the computer is reduced. Can be reduced.

Then, in step S104, the transient corrected output voltage V'AFM, which has been transiently corrected, is passed through the sensor-passing air mass flow rate Q using a word interpolation table of 32 grids at equal intervals.
In step S105, this sensor passing air mass flow rate Qa is multiplied by the intake air amount error correction coefficient Ktrm to calculate the current sensor passing air mass flow rate Q'a.

The intake air amount error correction coefficient Ktrm is
A coefficient for correcting a steady error in air amount measurement due to operating conditions, and similar to the above-mentioned D-Jetronic system, for example, a two-dimensional map with interpolation calculation based on the throttle opening α and the engine speed Ne. To set (see FIG. 13).

Next, in step S106, it is determined whether the engine has started or not based on the engine speed Ne, and Ne
When <300 rpm, it is determined that the engine is starting, and the step S
The process proceeds to step 107, and when Ne ≧ 300 rpm, it is determined that the engine has been started, and the process proceeds to step S108.

When the routine proceeds to step S107, the in-cylinder intake air mass Gair at the time of starting is set to an initial value and the routine exits.

The reason why the in-cylinder intake air mass Gair is set to an initial value at the time of starting is as follows.

1) The in-cylinder intake air mass Gair is normally calculated by the air flow rate / engine speed, but the calculation result becomes uncertain when both the engine speed and the air flow rate are small. easy.

2) As will be described in step S108 described later, the in-cylinder intake air mass Gair is successively calculated after starting, depending on the history, so an initial value is set when the first routine is executed after starting. Need to be

3) At the time of starting, not by setting a certain injection width at the time of starting, but by setting the in-cylinder intake air mass Gair to an initial value, the in-cylinder intake air can be obtained in all operating regions at the time of starting and after starting. Calculation using the mass Gair becomes possible.

Therefore, at the time of starting, the cylinder intake air mass G
The initial value is set by the estimated value of air. This initial value is calculated from the following equation, for example, by regarding the intake pipe pressure P in the intake chamber 6A as atmospheric pressure, and substituting the intake water temperature with the cooling water temperature.

Initial value = fixed value × atmospheric pressure / cooling water temperature (° K) (9) On the other hand, when it is determined that the engine has been started, the process proceeds to step S108.
The in-cylinder intake air mass Gair is calculated from the intake chamber model shown in the following equation based on the sensor passing air mass flow rate Q′a calculated in step S105, and the routine exits. Gair ← Q′a × Mtch + (MTCS−Mtch) × Gair / MTCS (10) MTCS: Half rotation time The formula (10) is based on the following idea. That is, the intake chamber model can be calculated from the following two equations.

1) Gair = σ × D = M × D / V σ: Air density in intake chamber 6A D: Stroke volume V: Volume in intake chamber 6A (chamber volume) 2) M (new) = Gair ( old) + Qa × Δt−Qc × Δt (new): Current value (old): Value before Δt Δt: Calculation cycle When M and Qc are deleted from the above two equations, the above sensor passage is performed as shown in the following equation. The cylinder intake air mass Gair can be calculated from the air mass flow rate Qa. Gair (new) = Gair (old) + Qa × Δt × D / V −Qc × Δt × D / V (10-1) The cylinder intake air mass flow rate Qc is such that the number of intake strokes per unit time is 4 cycles. In the case of an engine, the number of cylinders x Ne / 2
Therefore, Qc = (number of cylinders / 2) × Ne × Gair, and the above equation (10-1) is: Gair (new) = Gair (old) + Qa × Δt × D / V− (number of cylinders / 2) × Ne × Gair (old) × Δt × D / V = Qa × Δt × D / V + (1- (number of cylinders / 2) × Ne × Δt × D / V) × Gair (old) (10-2) Becomes Here, Δt × D / V = fixed value = Mtch is set, and if the engine to be adopted is four cylinders, the above equation (10-2) is expressed as Gair (new) = Qa × Mtch + (1-2Ne × Mtch) × Gair (old) (10-3). In this routine, for the convenience of calculation, not the engine speed Ne [rps] but the half-revolution time (Ne / 2) is used. If this half-revolution time is referred to as MTCS, the above (10-3) is used. The expression is Gair (new) = Qa * Mtch + Gair (old) * (MTCS-Mtch) / MTCS (10 '), and the expression (10) shown in step S108 is derived.

Then, if this equation (10) is performed for each calculation cycle Δt, the cylinder intake air mass Gair can be sequentially calculated depending on the history.

As described above, in the present embodiment, the difference between the D-Jetronic system and the L-Jetronic system is that the cylinder intake air mass Gair is simply calculated based on the detection value of the intake pipe pressure sensor 22, or the intake air mass Gair is calculated. Whether the in-cylinder intake air mass Gair is calculated based on the detected value of the air amount sensor 32, that is, only the calculation method of the in-cylinder intake air mass Gair is different. In the following routine, the in-cylinder intake air mass Gir
If the air is calculated, the D-Jetronic method and L
The same applies to engines that use either the JETRONIC method.

Next, the required equivalence ratio setting routine for the in-cylinder air-fuel mixture according to the operating conditions will be described with reference to the routines shown in FIGS. This routine is executed by a job every 50 ms, and is a combustible limit equivalent ratio φtw that is a steady required increase.
The maximum output equivalent ratio φful, the exhaust gas temperature limit equivalent ratio φtex, the catalyst purification rate best equivalent ratio φgas, and the fuel efficiency best equivalent ratio φeco are set. Since each of the required equivalent ratios φtw, φful, φtex, φgas, φeco is a steady required increase, a coefficient (air conditioner increase correction coefficient, D) for correcting the air-fuel ratio fluctuation caused by a transient fuel delay or the like in a feedforward manner. The range increase correction coefficient, etc.) or the coefficient for correcting the error of the sensor or the injector (mixing ratio correction coefficient, etc.) is not included. Further, the required equivalent ratios set in this routine are compared at the time of executing the routine of FIG. 1 which will be described later, and the maximum value thereof is adopted as the target equivalent ratio (increase coefficient to the theoretical fuel air ratio F / A) COEF.
The equivalence ratio φ has a relationship of φ = 1 / λ with respect to the excess air ratio ((A / F) actual / (A / F) theory) λ.

First, in step S61, the cooling water temperature Tw and the engine speed Ne are read. Then, step S62
At S65 or S66, the flammability limit equivalent ratio φtw for setting the lean flammability limit increase coefficient on the lean side is set. In step S62, the cooling water temperature Tw and the engine speed Ne.
Based on the above, the two-dimensional map is referred to with interpolation calculation, and the reference combustible limit equivalent ratio Mtw that serves as a reference when setting the combustible limit equivalent ratio φtw is set. This reference flammability limit equivalent ratio M
tw represents the flammability limit on the lean side depending on the relationship with the cooling water temperature Tw. In FIG. 15, this reference flammability limit equivalent ratio M
The characteristic of the two-dimensional map which sets tw is illustrated. As shown in FIG. 15, the axis on the cooling water temperature Tw side is set to be close to the conventional water temperature increase, and at a certain high water temperature, the reference combustible limit equivalent ratio Mtw is set to the lean equivalent ratio. It The axis on the engine speed Ne side is set so as to be able to search all the rotation speed regions including the cranking rotation speed. Cylinder intake air mass Gai
Since r is also set at the time of starting (see the flowchart of FIG. 5 or FIG. 10), the flammability limit equivalent ratio φtw at this time becomes a factor that determines the injection pulse width at the time of starting. In addition, at the time of starting, the standard flammability limit equivalent ratio M
tw is set to a large value, but when it changes to a small value as the engine speed increases after starting, as will be described later, a change in the flammability limit equivalent ratio φtw is performed with a certain first-order lag time constant. By delaying the amount, it is possible to secure an increase in the amount after starting.

Next, at step S63, it is judged from the engine speed or the like whether the engine is in the stalled state. If it is judged that the engine is in the stalled state, the process branches to step S66, and the reference combustible limit equivalent ratio Mtw is used. The flammability limit equivalent ratio φtw is set this time, and the process jumps to step S67. On the other hand, if it is determined that the engine is not in the stalled state, the routine proceeds to step S64, where the reference combustible limit equivalent ratio Mtw and the previous combustible limit equivalent ratio φtw are compared, and Mtw ≧ φt
When w, the required equivalence ratio has been increased, so the process branches to step S66, and the reference combustibility limit equivalence ratio Mtw is used to set the present flammability limit equivalence ratio φtw to respond to the increase request, and then step Jump to S67. On the other hand, Mt
When w <φtw, the required equivalent ratio has been reduced, so the routine proceeds to step S65, where the first-order lag processing is performed by the weighted average of the predetermined time constant (16 × 50 ms in this routine) shown in the following equation. The flammability limit equivalent ratio φtw is set. As a result, the increase in the amount after starting is substantially ensured.

Φtw ← (15φtw + Mtw) / 16 (11) Next, the maximum output equivalent ratio φful is set in step S67 to S70 or S71. First, step S6
In step 7, the throttle opening α is read and step S68
Then, the full increase reference value αth is set based on the engine speed Ne by referring to the one-dimensional map with interpolation calculation. This full increase reference value αth is a reference value for determining whether the engine requires the maximum output, and as shown in FIG.
The characteristics are obtained from the relationship between the engine speed Ne and the throttle opening α and are mapped.

Then, in step S69, the throttle opening α and the full increase reference value αth are compared, and α ≦ α
If th, it is determined that the full amount increase condition is not satisfied, the process proceeds to step S70, the maximum output equivalent ratio φful is set to 0, and the process proceeds to step S72. On the other hand, when α> αth, it is determined that the full increase condition is satisfied, and the process branches to step S71 to set the maximum output equivalent ratio φful to 1.2, that is, the equivalent ratio (full increase) that gives the maximum output of the engine. Set.

The target equivalent ratio COEF is the required equivalent ratios φtw, φful, φtex, which are set by this routine.
Since the maximum value is selectively set from φgas and φeco, when the maximum output equivalent ratio φful is set to 0 in step S70, the maximum output equivalent ratio φf is set.
ul will not be selected for the target equivalence ratio COEF. Also, the amount of increase for suppressing the rise in exhaust gas temperature is
Since the exhaust gas temperature limit equivalence ratio φtex is separately set, the maximum output equivalence ratio φful is approximately 15 to 20 with respect to the theoretical air-fuel ratio A / F (= 14.6) regardless of the engine speed Ne. It should be a% increase.

Then, steps S72 to S79 or S8.
An exhaust gas temperature limit equivalence ratio φtex that sets the fuel cooling increase coefficient to 0 is set. First, in step S72, the basic exhaust gas temperature limit equivalent ratio Mtex is set by referring to the two-dimensional map with interpolation calculation based on the cylinder intake air mass Gair and the engine speed Ne which are examples of the load. The basic exhaust gas temperature limit equivalence ratio Mtex is an increase amount for cooling the fuel in order to suppress the rise of the exhaust gas temperature below the design limit and protect the engine and the exhaust system. FIG. 17 exemplifies the characteristics of the two-dimensional map for setting the basic exhaust gas temperature limit equivalent ratio Mtex. As shown in the figure, it is set to perform a large increase at high load (high Gair) and high rotation. The intake pipe pressure P is adopted instead of the cylinder intake air mass Gair as a parameter for detecting the engine load, and the two-dimensional map is set based on the characteristic based on the relationship between the intake pipe pressure P and the engine speed Ne. You may do it.

Then, in step S73, the basic exhaust gas temperature limit equivalence ratio Mtex is compared with 1.2, which is the full increase value of the maximum output equivalence ratio φful, and M
When tex ≧ 1.2, the process proceeds to step S74, and M
When tex <1.2, the process proceeds to step S76.

Then, when the routine proceeds to step S76, a predetermined time constant (in this routine, 16) is calculated by the weighted average of the present average exhaust gas temperature limit equivalence ratio φtexAV expressed by the following equation.
(× 50 ms) primary delay processing is performed, and the flow proceeds to step S78.

ΦtexAV ← (15 · φtexAV + Mtex) / 16 (12) Further, in step S74, the basic exhaust gas temperature limit equivalent ratio Mtex is compared with the average exhaust gas temperature limit equivalent ratio φtexAV up to the previous time. If Mtex <φtexAV, that is, 1.2 ≦ Mtex <φtexAV, the process proceeds to step S75, and Mtex ≧ φtexAV.
If so, the process proceeds to step S77.

In step S75, the first-order lag processing (32 × 50 ms in this routine) of the predetermined average time is carried out by the weighted average of the current average exhaust gas temperature limit equivalence ratio φtexAV shown in the following equation, and the routine proceeds to step S78.

ΦtexAV ← (31 · φtexAV + Mtex) / 32 (13) On the other hand, when the process proceeds to step S77, the average exhaust gas temperature limit equivalent ratio φtexAV of this time is calculated as a predetermined time constant (in this routine, 128 by the weighted average). (× 50 ms) first-order delay processing is performed, and the flow proceeds to step S78.

ΦtexAV ← (127 · φtexAV + Mtex) / 128 (14) Therefore, when the so-called required equivalence ratio of Mtex <1.2 is thin, the average exhaust gas temperature limit equivalence ratio φtexAV is set with a relatively fast time constant. And Mtex ≧ 1.2,
When the required equivalence ratio of Mtex ≧ φtexAV is high, the average exhaust gas temperature limit equivalence ratio φtexAV is set with a slow time constant.

Then, in step S78, the average exhaust gas temperature limit equivalent ratio φtexAV calculated in step S75, S76 or S77 is compared with the basic exhaust gas temperature limit equivalent ratio Mtex, and when Mtex <φtexAV. In step S79, the basic exhaust gas temperature limit equivalence ratio Mtex is set to the exhaust gas temperature limit equivalence ratio φte this time.
If Mtex ≧ φtexAV, the current exhaust gas temperature limit equivalent ratio φtex is set as the average exhaust gas temperature limit equivalent ratio φtexAV in step S80.

Therefore, the exhaust gas temperature limit equivalence ratio φtex
Is limited to the upper limit by the average exhaust gas temperature limit equivalent ratio φtexAV, and is also limited to the lower limit at the basic exhaust gas temperature limit equivalent ratio Mtex. As a result, the upper limit value of the exhaust gas temperature limit equivalence ratio φtex is the engine speed N
e and the cylinder intake air mass Gair, that is,
According to the average exhaust gas temperature limit equivalence ratio φtexAV set in step S75, S76 or S77, the change is made slowly or relatively quickly. As a result, φtex <φf until the exhaust gas temperature actually approaches the design limit value in a long full-open operation.
Thus, the output can be expected to increase as compared with the case where the fuel cooling component is included in the maximum output equivalent ratio φful as in the conventional case. This exhaust gas temperature limit equivalence ratio φ
tex may be set based on a value obtained by measuring or estimating the exhaust gas temperature.

Then, the process proceeds from step S79 or S80 to step S81, and steps S81 to S85 are performed.
Alternatively, in S86, the catalyst purification rate best equivalent ratio φgas is set. This catalyst purification rate best equivalent ratio φgas is applicable when a three-way catalyst is used as the catalytic converter 11, and when the condition for purifying exhaust gas is satisfied, φgas ← 1.0 is set. Other than, φg
Let as ← 0.

In steps S81 to S84, it is determined whether the operating conditions are such that the exhaust gas must be purified.
This judgment condition is the throttle opening α and the engine speed N.
e, the throttle opening α is 10 ° ≦ α <70 ° (steps S81 and S82), and the engine speed N is N.
When e is 800 rpm ≦ Ne <3000 rpm (steps S83, S84), the catalyst purification rate best equivalent ratio φga
s is set to 1.0 (step S85), and φgas is set to 0 otherwise (step S86).
Note that the above determination conditions are examples, and the exhaust gas purification region can be set arbitrarily according to the characteristics of the engine. Further, for example, instead of the throttle opening α, the intake pipe pressure P and the cylinder intake air mass Gair are adopted. You may. When a lean Nox catalyst is used as the catalytic converter 11, the catalyst purification rate best equivalent ratio φgas is φ in the entire operating range.
Set gas ← 0.

Thereafter, in step S87, the two-dimensional map is referenced with interpolation calculation based on the intake pipe pressure P and the engine speed Ne as an example of the load, and the fuel efficiency best equivalent ratio φeco is set. Exit the routine.

FIG. 18 shows this fuel efficiency best equivalent ratio φeco.
The characteristic of the two-dimensional map for setting is illustrated. As shown in the figure, in each region of this two-dimensional map, the equivalence ratio that can obtain the best fuel consumption rate under the engine operating conditions is preliminarily obtained by experiments and stored.

Here, the relationship between the fuel efficiency best equivalent ratio φeco and the flammability limit equivalent ratio φtw will be briefly described.

If the air-fuel ratio is made lean to the flammability limit equivalent ratio φtw, it is generally impossible to obtain the best fuel economy. However, when the water temperature is low during warming up, it is possible to obtain better combustion by suppressing leaning by the above flammability limit equivalent ratio φtw, rather than making the air-fuel ratio lean to the fuel efficiency best equivalent ratio φeco. In some cases, the fuel efficiency best equivalent ratio φeco is set separately from the flammability limit equivalent ratio φtw. It should be noted that the above catalyst purification rate best equivalent ratio φga
When s is φgas ← 1.0 in the entire operating range, the above fuel efficiency best equivalent ratio φeco is hidden, so that meaning is lost. For example, an exhaust purification system is a lean Nox.
When a catalyst is used, as described above, the catalyst purification rate best equivalent ratio φgas is set to φgas ← 0 in the entire operating range. Therefore, this fuel consumption rate best equivalent ratio φeco is the catalyst purification rate best equivalent ratio. Will also have the element as.
Further, when the fuel efficiency is improved by the stoichiometric air-fuel ratio control using EGR, in the D-Jetronic system, the above (1),
As is clear from the equation (2), the theoretical intake air mass Gth is only the fresh air amount excluding the EGR amount, and in the L-Jetronic system, it is calculated based on the output voltage VAFM of the intake air amount sensor 32. In-cylinder intake air mass Gair
As a result, since the EGR amount is removed and only the fresh air amount is obtained, the air-fuel ratio controllability becomes better when φeco ← 1.0 in the entire operation region. Also, this fuel efficiency best equivalence ratio φ
instead of the intake pipe pressure P, the intake air mass Ga in the cylinder
You may make it set with reference to the two-dimensional map created from the relationship between ir and the engine speed Ne.

Then, using the set values obtained in each of the above routines, 1 is set in steps S1 to S10 of the fuel injection effective pulse width and fuel injection waste pulse width setting routine executed in each 10 ms job of FIGS. The fuel injection mass per cycle is calculated, and the fuel injection effective pulse width Te and the fuel injection waste pulse width Ts are calculated in steps S11 to S24.

First, in step S1, each required equivalence ratio φt set in the required equivalence ratio setting routine for the in-cylinder air-fuel mixture is set.
w, φful, φtex, φgas, φeco are compared, and the maximum value of these required values is determined as the target equivalence ratio COEF.

Next, in step S2, the cylinder intake fuel mass Gfuel per intake stroke into the cylinder is calculated from the following equation.

Gfuel ← Gair × F / A × COEF × Kfb (15) F / A: theoretical fuel-air ratio Kfb: air-fuel ratio feedback correction coefficient where theoretical fuel-air ratio F / A is theoretical air-fuel ratio A / F If the theoretical air-fuel ratio is 14.6, the theoretical fuel-air ratio is 1 /
It becomes 14.6. The stoichiometric air-fuel ratio A / F is the ratio of the minimum air amount required for complete combustion of fuel to the fuel amount, and is a variable in an engine or the like compatible with various types of fuel.

On the other hand, the initial value of the air-fuel ratio feedback correction coefficient Kfb is 1.0, which can be rewritten by an external strategy for performing air-fuel ratio feedback control and air-fuel ratio learning control. Further, by multiplying the theoretical fuel air ratio F / A by the target equivalent ratio COEF, the target air fuel ratio of the in-cylinder mixture according to the operating condition is set. Therefore, the target value of the air-fuel ratio feedback correction coefficient Kfb set when feedback control is performed by the linear A / F sensor is the target equivalent ratio COEF when the theoretical fuel-air ratio F / A is 1.

By the way, the in-cylinder intake fuel mass Gfue
l is the amount of fuel that is desired to be sucked into the cylinder in one stroke, which normally matches the injection amount from the injector 25,
There is a delay in response at the time of transition, so they do not match. That is,
Even if the fuel injection amount from the injector 25 suddenly increases transiently, a part of the fuel is sucked into the cylinder after adhering to the inner wall of the intake port, so that a delay is caused and the fuel is sucked into the cylinder. Fuel quantity increases slowly. Therefore, when the in-cylinder intake fuel mass Gfuel rapidly increases, the fuel amount from the injector 25 is changed to the in-cylinder intake fuel mass Gfuel.
It is necessary to make the feed-forward injection larger than that to make the intake fuel amount into the cylinder equal to the cylinder intake fuel mass Gfuel. The additional fuel mass Gacc per intake stroke at the time of the transition corresponding to this additional increase amount is calculated in the next step S3.
~ S9 is calculated.

First, in step S3, a two-dimensional map (see FIG. 1) is obtained based on the throttle opening α and the engine speed Ne.
9) with interpolation calculation, the index value (static index value) Macc corresponding to the static cylinder intake air mass Gair
Set. This static index Macc indicates the throttle opening α and the engine speed Ne during steady running with little load fluctuation.
If C is held constant, finally, the cylinder intake air mass Ga
It is premised that ir becomes constant. Therefore, if the load fluctuation during traveling can be ignored, the static index Macc can be set from the one-dimensional map with interpolation calculation based on the throttle opening α, as shown in step S31 of FIG. is there.

Also, transiently, there is a delay in the cylinder intake air mass Gair, and it is necessary to obtain the additional fuel mass Gacc corresponding to this delay.

Therefore, in step S4, first, a predetermined time constant assuming an intake delay in the intake chamber 6A (see FIG. 24) (4 × in this routine although it varies depending on operating conditions)
(Fixed to 10 ms) primary delay processing is performed based on the weighted average shown in the following equation, and dynamic cylinder intake air mass G
An index value (dynamic index value) Sacc corresponding to air is calculated.

Sacc ← (3 · Sacc + Macc) / 4 (16) Next, in step S5, the dynamic index value Sacc and
The delay index value Tacc due to fuel adhesion calculated at the time of the previous routine execution is compared. The delay index value Tac
c corresponds to the in-cylinder intake fuel mass Gfuel.

Then, Sacc <Tacc, that is,
A value corresponding to the previous cylinder intake fuel mass Gfuel (Ta
When the value (Sacc) corresponding to the cylinder intake air mass Gair this time is smaller than cc), the routine proceeds to step S6, where the delay index value Tacc is set to the dynamic index value Sac.
As c, the process proceeds to step S8. As a result, Sacc =
It becomes Tacc, and in step S9 described later, the additional fuel mass Gacc becomes 0, and the additional fuel amount is not increased.

On the other hand, Sacc ≧ Tacc, that is, a value (Tac corresponding to the previous cylinder intake fuel mass Gfuel).
When the value (Sacc) corresponding to the in-cylinder intake air mass Gair at this time is increasing or has not changed with respect to c), the process branches to step S7, and this dynamic index S
acc is subjected to the first-order lag processing (8 × 10 ms in this routine) due to fuel adhesion by the weighted average shown in the following equation to obtain the delay index value Tacc due to fuel adhesion this time.
Is calculated and the process proceeds to step S8.

Tacc ← (7 · Tacc + Sacc) / 8 (17) Then, when the process proceeds to step S8, the coefficient Rac is obtained by referring to the one-dimensional map with interpolation calculation based on the engine speed Ne.
Set c.

After that, the process proceeds to step S9, in which 1
The additional fuel mass Gacc per intake stroke is calculated from the following equation.

Gacc ← Racc × (Sacc−Tacc) (18) As shown in the equation (18), a value (Sacc) corresponding to the current cylinder intake air mass Gair and the current cylinder intake fuel mass Gfuel. The difference from the value (Tacc) corresponding to is the increasing pattern that compensates for the shortage due to fuel adhesion.

Thus, this additional fuel mass Gacc
Is based on only the throttle opening α and the engine speed Ne,
Only the amount of change in the cylinder intake air mass Gair is simply detected without delay, and this value is used for calculation.

FIG. 20 shows the above-mentioned index values Macc, Sacc, when the throttle valve 5a is slightly opened during traveling.
The characteristic of Tacc is shown. The static index value Macc increases following the throttle opening α, while the dynamic index value Sacc
Increases with a first-order lag of 4 × 10 ms with respect to the static index value Macc. Further, the delay index value Tacc is
The dynamic index value Sacc increases with a time constant of 8 × 10 ms. Considering that the delay index value Tacc corresponds to the cylinder intake fuel mass Gfuel, the delay of the adhered amount is determined by the dynamic index value Sacc and the delay index value Tacc.
And the difference index value (Sa) in step S9.
cc-Tacc) is multiplied by the coefficient Racc to obtain the additional fuel mass Gacc. By the way, as shown in FIG. 21, it has been clarified from an experiment that the difference index value (Sacc-Tacc) matches the lean spike pattern generated immediately after the opening of the conventional throttle valve 5a. Therefore, if the amount corresponding to this difference index value (Sacc-Tacc) is increased by acceleration, the exhaust air-fuel ratio becomes constant without leaning even during a transition.

The additional fuel mass Gacc is similar to the acceleration increase / acceleration additional pulse.
c is a feedforward amount for making the amount of intake fuel into the cylinder equal to the intake fuel mass in the cylinder Gfuel,
It is not for temporarily making the air-fuel ratio A / F rich during acceleration. Therefore, if it is necessary to make the air-fuel ratio A / F rich at the time of acceleration, the acceleration equivalence ratio φacc during the required equivalence ratio setting routine shown in FIGS. 7 to 9 is selected as a selection branch of the target equivalence ratio COEF. It is naturally conceivable to add as a sixth increase factor.

Further, conventionally, there is a triangle increasing method as a method for calculating the additional fuel mass Gacc. In this triangular amount increasing method, the amount of increase is set on the basis of the movement of the throttle valve, so that the responsiveness is good, but since the primary delay of the amount of fuel sucked into the cylinder is increased while approximating with a triangle, It does not exactly match the lean spike shown, and the air-fuel ratio during transition may become partially rich or lean. Further, in the theoretical fuel adhesion model, there is a response delay and noise of the sensor itself for measuring the intake air amount, so that the performance tends to vary, and sufficient reliability cannot be obtained.

Then, in step S10, the fuel addition mass Gacc is added to the cylinder intake fuel mass Gfuel.
Is added to calculate the fuel injection mass Ginj per cycle. By the way, when the injection timing is set to an early stage and the fuel injection mass Ginj sharply increases at a timing after the injection is completed and before the intake stroke is started,
It is also possible to automatically inject additional fuel, and this fuel injection mass Ginj is the amount of fuel injected from the injector 25 from one intake stroke to one and a half revolutions before, that is, from the time immediately after the end of the intake stroke to the start of the next intake stroke. The total amount is calculated.

Next, in steps S11 to S24, the cylinder-specific fuel injection effective pulse widths Te1 to Te4 and the cylinder-specific fuel injection waste pulse widths Ts1 to Ts4 are calculated (where 1, 2, 3, 4 are Indicates the cylinder number).

First, in step S11, the value of the maximum output equivalent ratio φful is referenced, and in step S12, the value of the exhaust gas temperature limit equivalent ratio φtex is referenced. And φful
= 0 engine does not demand maximum output, and
If the increase due to the exhaust gas temperature limit of φtex = 0 is not requested, the process proceeds to step S13, and the cylinder-by-cylinder injection amount correction coefficient Ktn1 for correcting the cylinder-by-cylinder variation of the air-fuel ratio.
~ Ktn4 is set to 1.0, and the process proceeds to step S18. On the other hand, in the above step S11, φful = 1.2
(Full increase), or in step S12, φtex
When it is determined that ≠ 0, the process branches to step S14, and the one-dimensional map for each cylinder is referenced with interpolation calculation based on the engine speed Ne in steps S14 to S17.
The cylinder-by-cylinder injection amount correction coefficients Ktn1 to Ktn4 are set, and the process proceeds to step S18. Injection amount correction coefficient Ktn
Is for increasing or decreasing the fuel injection amount for each cylinder to uniformly set the air-fuel ratio, and each of the one-dimensional maps stores a value corresponding to the intake characteristic of each cylinder.

By the way, the reason why the fuel injection amount must be changed for each cylinder depending on the operating condition is that the cylinder intake air mass Gair is originally different for each cylinder. Gair should be calculated for each cylinder in consideration of the intake characteristic, and the in-cylinder intake fuel mass Gfuel and the fuel injection mass Ginj should be calculated for each cylinder, but since the calculation load of the CPU becomes heavy,
Using the cylinder-by-cylinder injection amount correction coefficients Ktn1 to Ktn4, the apparent fuel injection effective pulse widths Te1 to T for each cylinder are apparently used.
Corrected e4 [ms].

Further, a particular problem of the variation in the air-fuel ratio among the cylinders is knocking during high load operation. Fluctuations in the air-fuel ratio during medium-low load operation have little effect on exhaust gas, and from the viewpoint of engine vibration, it is desirable that the fuel amounts of all cylinders are the same, because the outputs of the cylinders will be more uniform. Therefore, if a full increase is required,
When it is necessary to obtain the maximum output for all cylinders, and if it is required to increase the amount due to the exhaust gas temperature limit, the temperature rise of the exhaust system etc. of all cylinders should be suppressed within the design limit. Therefore, only in such a case, that is, when the required increase is set on the assumption that the air-fuel ratio between the cylinders is uniform, the fuel injection amount of each cylinder A correction coefficient (cylinder injection amount correction coefficient) for appropriately increasing / decreasing is adjusted and individually controlled so that the air-fuel ratio of the in-cylinder mixture of each cylinder becomes the target air-fuel ratio.

Then, when proceeding to step S18, the overall fuel injection effective pulse width Te_all is calculated from the following equation.

Te_all ← Kmr × Ginj × Kcon (19) Kmr: Pulse width error correction coefficient Kcon: Injector capacity coefficient [sec / g] Here, the pulse width error correction coefficient Kmr is a dynamic flow rate characteristic of the injector 25. Is a non-linearity correction of the engine speed Ne and the fuel injection mass Ginj in this routine.
Based on the above, the two-dimensional map shown in FIG. 22 is set with reference to the interpolation calculation. Also, the injector capacity coefficient K
con is the reciprocal of the static mass flow rate characteristic of the injector 25, and Kcon = 0.1 [sec / g] for an injector that injects 1 gram of fuel for 0.1 second. In addition,
Although this injector capacity coefficient Kcon is a fixed value in this routine, it is used as a variable when the specific gravity or viscosity of the fuel changes in an FFV engine or the like that can handle various types of fuel.

Then, in steps S19 to S22, the fuel injection effective pulse width Te_all is corrected by the cylinder-by-cylinder injection amount correction coefficients Ktn1 to Ktn4 to set the cylinder-by-cylinder fuel injection effective pulse widths Te1 to Te4, respectively.

Thereafter, the process proceeds to step S23, the fuel injection waste pulse width Ts_all [ms] is set based on the battery voltage VB by referring to the one-dimensional map with interpolation calculation, and at step S24, the cylinder-specific fuel injection waste pulse width is set. Ts1 to T
s4 is set by the fuel injection waste pulse width Ts_all, and the routine is exited.

On the OS side, the individual cylinder fuel injection effective pulse widths Te1 to Te4 and the individual cylinder fuel injection waste pulse widths Ts1 to Ts4 are added to calculate the fuel injection pulse width for each cylinder.

The relationship between the width of the voltage pulse applied to the injector 25 (fuel injection pulse width) and the fuel injection mass Ginj is as shown in FIG. 23, and the fuel injection mass Ginj is shown.
Basically, this fuel injection mass Ginj is determined.
Is multiplied by the injector capacity coefficient Kcon to obtain the effective fuel injection pulse width Te, and the effective fuel injection pulse width Te is added to the invalid fuel injection pulse width Ts, which is the ineffective fuel injection pulse width, to determine the fuel injection pulse width. It is calculated.

In the present embodiment, it is determined in the OS whether to inject the fuel of the fuel injection mass Ginj at one time or in two injections. Therefore, the cylinder-by-cylinder fuel injection effective pulse width Te1 is determined. ~ Te4 and the above-mentioned cylinder-by-cylinder fuel injection waste pulse widths Ts1 to Ts4 are passed separately to the OS without being added in advance, and added immediately before the injection setting inside this OS to give the fuel injection pulse width given to each injector. It is calculated. By doing so, even if it is decided to inject the fuel of the fuel injection mass Ginj in two times within the OS,
By adding the fuel injection dead pulse width Ts to the fuel injection effective pulse width Te of / 2, the fuel injection pulse width per time can be easily given.

As described above, according to the present embodiment, for example, when a new fuel adhesion model is developed, the formula (3) or the formula (10) for calculating the cylinder intake air mass Gair is used in the calculation formula. If the flow rate of the injector is non-linear, it is sufficient to correct the effective fuel injection pulse width Te and the unnecessary fuel injection pulse width Ts. As a result, when a problem occurs in the air-fuel ratio controllability in a certain operating range, not only is it clear which part should be changed, but that change is unlikely to affect other parts. Can be expected to be utilized.

[0129]

As described above, according to the present invention,
Since the target equivalence ratio is set to the maximum value among a plurality of different required equivalence ratios set based on the engine operating state, for example, when a problem occurs in the air-fuel ratio controllability in a certain operating region, Not only is the standard for determining which correction term should be changed according to the driving characteristic becomes clear, but the change is unlikely to affect other correction terms, providing convenience as base control software.

Further, by providing at least a flammability limit equivalence ratio and an exhaust gas temperature limit equivalence ratio as the required equivalence ratio, the flammability limit equivalence ratio is set to a rich equivalence ratio at a low temperature start, etc. The lean equivalence ratio is gradually set as the engine speed shifts to high rotation. On the other hand, at the exhaust gas temperature limit equivalence ratio, the lean equivalence ratio or 0 is used during low rotation and low load operation.
In the low rotation speed region, the flammable limit equivalence ratio is set as the target equivalence ratio by gradually setting the rich equivalence ratio as the engine speed shifts to high rotation and high load operation.
The optimum air-fuel ratio can be set according to the engine operating state, such as the exhaust gas temperature limit equivalence ratio being set as the target equivalence ratio in the high rotation and high load range.

[Brief description of drawings]

FIG. 1 is a flowchart showing a routine for setting a fuel injection effective pulse width and a fuel injection waste pulse width, which is executed in each 10 ms job.

FIG. 2 is a flowchart (continuation) showing a routine for setting a fuel injection effective pulse width and a fuel injection dead pulse width, which is executed in every 10 ms job.

FIG. 3 is a flow chart (continuation) showing a routine for setting a fuel injection effective pulse width and a fuel injection dead pulse width, which is executed in each 10 ms job.

FIG. 4 is a flowchart showing a main part of a routine for setting a fuel injection effective pulse width and a fuel injection waste pulse width according to another mode.

FIG. 5 is a flowchart showing a cylinder intake air mass setting routine that is executed in each 10 ms job.

FIG. 6 is a flowchart showing a coefficient setting routine executed in every 50 ms job.

FIG. 7 is a flowchart showing a required equivalent ratio setting routine executed for each 50 ms job.

FIG. 8 is a flowchart showing a required equivalent ratio setting routine executed for each 50 ms job (continued).

FIG. 9 is a flowchart showing a required equivalent ratio setting routine executed for each 50 ms job (continued).

FIG. 10 is a flowchart showing a cylinder intake air mass setting routine executed every 4 ms according to another mode.

FIG. 11 is a characteristic diagram showing a relationship between a cylinder intake air mass and an intake air temperature.

FIG. 12 is a characteristic diagram showing a relationship between a theoretical intake air mass and a cylinder intake air mass.

FIG. 13 is a conceptual diagram of a two-dimensional map for setting an intake air amount error correction coefficient.

FIG. 14 is a characteristic diagram showing the output voltage of the intake air amount sensor during a transition.

FIG. 15 is a conceptual diagram of a two-dimensional map for setting the basic flammability limit equivalence ratio.

FIG. 16 is a characteristic diagram showing a region where the maximum output equivalent ratio is increased.

FIG. 17 is a characteristic diagram of a two-dimensional map for setting the basic exhaust gas temperature limit equivalence ratio.

FIG. 18 is a characteristic diagram of a two-dimensional map that sets the fuel efficiency best equivalent ratio.

FIG. 19 is a conceptual diagram of a two-dimensional map that sets an index value corresponding to a static cylinder intake air mass.

FIG. 20 is a characteristic diagram showing a relationship between a static index value, a dynamic index value, and a delay index value for this dynamic index value.

FIG. 21 is a characteristic diagram showing the relationship between the lean spike and the increase pattern during transient operation.

FIG. 22 is a characteristic diagram of a two-dimensional map for setting a pulse width error correction coefficient.

FIG. 23 is a characteristic diagram showing a relationship between a fuel injection pulse width and a fuel injection mass.

FIG. 24 is an explanatory diagram showing an intake system model of the engine.

FIG. 25 is an overall configuration diagram of an engine

FIG. 26 is a front view of a crank rotor and a crank angle sensor.

FIG. 27 is a front view of a cam rotor and a cam angle sensor.

FIG. 28 is a circuit configuration diagram of the electronic control device.

[Explanation of symbols]

 F / A ... Theoretical fuel-air ratio COEF ... Target equivalence ratio Gair ... Cylinder intake air mass (engine load) Ne ... Engine speed P ... Intake pipe pressure (engine load) Tw ... Cooling water temperature (engine temperature) φeco ... Fuel consumption rate Best equivalent ratio (required equivalent ratio) φful ... Maximum output equivalent ratio (required equivalent ratio) φgas ... Catalyst purification rate Best equivalent ratio (required equivalent ratio) φex… Exhaust gas temperature limit equivalent ratio (required equivalent ratio) φtw… Combustible limit equivalent Ratio (required equivalent ratio)

Claims (2)

[Claims] 1. An air-fuel ratio control method for an engine, wherein a stoichiometric fuel-air ratio is corrected with a target equivalence ratio to set a target air-fuel ratio in a steady state, wherein a plurality of target equivalence ratios are set based on engine operating conditions. An air-fuel ratio control method for an engine, wherein the maximum value is set among different required equivalent ratios. 2. The required equivalence ratio is based on at least the engine speed and the engine temperature, and sets the flammability limit increase coefficient on the lean side of the air-fuel ratio lean, and the fuel cooling based on the engine speed and the engine load. 2. An air-fuel ratio control method for an engine according to claim 1, wherein an exhaust gas temperature limit equivalence ratio is used to set a usage increase coefficient.