JP2002047980A - Engine air-fuel ratio control device - Google Patents

Abstract

(57) [Problem] To improve the function of following a target air-fuel ratio while ensuring stable air-fuel ratio behavior against air-fuel ratio disturbance. SOLUTION: A model value Um obtained by substituting a sensor measurement equivalent ratio φ by a linear air-fuel ratio sensor 35 into an air-fuel ratio response inverse model M2 is processed by a filter F1 to calculate an engine inlet equivalent ratio estimated value Ue. Then, the difference between the value Uf obtained by filtering the feedback correction amount Ui through the filter F2 and the estimated engine inlet equivalent ratio Ue is determined as a disturbance equivalent ratio correction value φd, and the disturbance equivalent ratio correction value φd and the target equivalent ratio φr are obtained. Are calculated as a new feedback correction amount Ui. In the fuel injection amount setting unit M1, the basic fuel injection pulse width is feedback-corrected by the feedback correction amount Ui, and further the correction according to the operating state or the correction by learning is applied to determine the final fuel injection amount. Set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for an engine that achieves both improvement of a target value tracking function and suppression of vibration of the air-fuel ratio behavior.

[0002]

2. Description of the Related Art In recent years, in air-fuel ratio control of an engine, a technology using a wide-range air-fuel ratio sensor whose output value continuously changes according to an air-fuel ratio from rich to lean including a stoichiometric air-fuel ratio has been developed. I have. In the air-fuel ratio feedback control using the wide-range air-fuel ratio sensor, a technique of modeling an air-fuel ratio response and performing control based on the model has been proposed to improve control accuracy.

The control based on the air-fuel ratio response model uses a controller based on proportional-integral-derivative control (PID control) and attempts to optimize its parameters (gain) using a model. JP-A-6-2490
No. 24 discloses a controller to which modern control theory is applied, and Japanese Patent Application Laid-Open No. H8-232718 adopts an adaptive control theory to cope with a change in air-fuel ratio response. A technique for performing control is disclosed. Furthermore, Japanese Patent Application Laid-Open No. H11-210527 discloses a technique of estimating an air-fuel ratio using an observer and performing feedback control of the air-fuel ratio according to PID control.

[0004]

However, the PID
In conventional air-fuel ratio control based on control, the function of following the target value is performed by I control of the deviation between the target air-fuel ratio and the measured air-fuel ratio. Therefore, the phase is always delayed by 90 °. For this reason, if air-fuel ratio disturbances occur due to execution of canister purge or aging of the injector, etc., if the control parameters are increased to enhance the target value tracking function, the air-fuel ratio behavior becomes oscillatory, and conversely, the air-fuel ratio behavior There is a contradiction that when the control parameter is reduced to avoid vibration, the target value tracking function is reduced. This inconsistency is difficult to resolve even by optimizing the control parameters.

The present invention has been made in view of the above circumstances, and provides an air-fuel ratio control device for an engine capable of improving a function of following a target air-fuel ratio while ensuring stable air-fuel ratio behavior against air-fuel ratio disturbances. It is intended to provide.

[0006]

In order to achieve the above-mentioned object, the invention according to claim 1 is an invention in which an equivalence ratio at an engine outlet is modeled from an equivalence ratio at an engine inlet by a first-order or second-order linear differential system. Filter the model value obtained by applying the measured equivalence ratio of the engine outlet measured by the wide area air-fuel ratio sensor to the inverse model of the fuel ratio response model, and calculate the estimated value of the engine inlet equivalent ratio that estimates the equivalent ratio of the engine inlet An engine inlet equivalent ratio estimating means for calculating a disturbance equivalent ratio correction value for estimating an air-fuel ratio disturbance based on a filtered value of an instruction value for an equivalent ratio of an engine inlet and the engine inlet equivalent ratio estimated value. A fuel ratio disturbance estimating means, and a feedback correction for a fuel injection amount corresponding to an equivalent ratio at an engine inlet based on the disturbance equivalent ratio correction value and a target equivalent ratio. Feedback correction amount calculating means for calculating the back correction amount as a new instruction value with respect to the equivalence ratio at the engine inlet; and correcting the fuel injection amount with the feedback correction amount and setting the final fuel injection amount to be supplied to the engine. And a fuel injection amount setting means.

According to a second aspect of the present invention, in the first aspect of the invention, the air-fuel ratio disturbance estimating means filters the instruction value for the equivalence ratio at the engine inlet by adding a correction for eliminating a dead time component. It is characterized by doing.

According to a third aspect of the present invention, in the first aspect of the present invention, a parameter of the filter processing is varied depending on an operation range.

According to a fourth aspect of the present invention, in the first aspect of the invention, the feedback correction amount calculating means calculates a control value by a proportional control or a proportional differential control of a deviation between the target equivalent ratio and the measured equivalent ratio. In addition, the present invention is characterized in that the feedback correction amount is calculated.

According to a fifth aspect of the present invention, in the first aspect of the present invention, a learning means for learning and controlling the feedback correction amount based on the disturbance equivalent ratio correction value is provided.

According to a sixth aspect of the present invention, in the first aspect, the air-fuel ratio disturbance estimating means regulates the disturbance equivalent ratio correction value with a minimum value and a maximum value.

According to a seventh aspect of the present invention, in the first aspect of the invention, the air-fuel ratio disturbance estimating means sets the disturbance equivalent ratio correction value to the air-fuel ratio feedback inhibition when the air-fuel ratio feedback inhibition condition is satisfied. It is characterized in that it is maintained at the value when the condition is satisfied or reset to the set value.

According to an eighth aspect of the present invention, in the first aspect of the invention, the air-fuel ratio disturbance estimating means stores a value of the disturbance equivalent ratio correction value when a condition for executing the canister purge is satisfied, and When the purge condition is canceled, the disturbance equivalent ratio correction value is set to a value stored when the canister purge execution condition is satisfied until a set time elapses.

That is, according to the first aspect of the present invention, the equivalence ratio at the engine outlet is changed from the equivalence ratio at the engine inlet to the primary or secondary.
By applying the measured equivalence ratio at the engine outlet measured by the wide area air-fuel ratio sensor to the inverse model of the air-fuel ratio response model modeled by the following linear differentiation method, the equivalence ratio at the engine inlet and the phase of the measured equivalence ratio are aligned, By filtering the model value obtained from the model, the equivalence ratio at the engine inlet can be stably estimated. Then, the air-fuel ratio disturbance is estimated without a phase delay based on the filtered value of the instruction value for the equivalent ratio at the engine inlet and the estimated value of the engine inlet equivalent ratio, and based on the disturbance equivalent ratio correction value and the target equivalent ratio. The feedback correction amount for feedback-correcting the fuel injection amount corresponding to the equivalent ratio of the engine inlet is calculated as a new instruction value for the equivalent ratio of the engine inlet, and the fuel injection amount is corrected by the feedback correction amount to the engine. Set the final fuel injection amount to be supplied.

In this case, according to the present invention, the instruction value for the equivalence ratio at the engine inlet is filtered by adding a correction for eliminating a dead time component to calculate a disturbance equivalence ratio correction value. Even in a response where the time component cannot be ignored, the followability to the target equivalent ratio is stably improved.

According to the third aspect of the present invention, the influence of high-frequency components such as noise can be eliminated even in an operation region where the air-fuel ratio response is slow, by varying the parameters of the filter processing depending on the operation region.

According to a fourth aspect of the present invention, the response is further improved by calculating a feedback correction amount by adding a control value by a proportional control or a proportional differential control of a deviation between a target equivalent ratio and a measured equivalent ratio. The target value tracking performance is further improved.

According to a fifth aspect of the present invention, the feedback correction amount is learned and controlled based on the disturbance equivalent ratio correction value, so that the air-fuel ratio disturbance can be estimated in a feed-forward manner. And the target value followability during transient operation is improved.

According to a sixth aspect of the present invention, the disturbance equivalent ratio correction value is regulated by a minimum value and a maximum value, thereby avoiding feedback due to an excessive disturbance estimated value, and preventing failure of a wide-range air-fuel ratio sensor and excessive noise. Even if it occurs, erroneous estimation of disturbance is prevented.

According to a seventh aspect of the present invention, when the air-fuel ratio feedback inhibition condition is satisfied, the disturbance equivalent ratio correction value is set to
By maintaining the value at the time when the air-fuel ratio feedback prohibition condition is satisfied or resetting it to a set value, the disturbance equivalent ratio correction value before and after the feedback prohibition condition is satisfied is made a continuous value, thereby preventing erroneous estimation of disturbance.

According to an eighth aspect of the present invention, when the condition for performing the canister purge is satisfied, the value of the disturbance equivalent ratio correction value is stored, and when the canister purge condition is released, the disturbance equivalent ratio is maintained until the set time elapses. By setting the correction value to a value stored when the canister purge execution condition is satisfied, a disturbance equivalent ratio correction value is calculated in a feed-forward manner when the canister purge condition is released, thereby enabling accurate correction.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 7 show a first embodiment of the present invention.
1 is an overall configuration diagram of an engine system, FIG. 2 is a circuit configuration diagram of an electronic control system, FIG. 3 is a functional block diagram of air-fuel ratio control, FIG. 4 is a flowchart of a feedback correction amount calculation routine, and FIG. FIG. 6 is a flow chart of a fuel injection control routine, FIG. 6 is a time chart showing a change in the disturbance equivalent ratio correction value before and after the feedback is prohibited, and FIG. 7 is a time chart showing a change in the disturbance equivalent ratio correction value before and after the canister purge.

First, the overall structure of the engine will be described with reference to FIG. In the figure, reference numeral 1 denotes an engine, and in this embodiment, a horizontally opposed type in which a cylinder block 1a is divided into two banks (a left bank on the right side and a right bank on the left side in the figure) around the crankshaft 1b. 4 shows a four-cylinder engine. 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.

An intake manifold 3 communicates with the intake port 2a. A throttle chamber 5 communicates with the intake manifold 3 through an air chamber 4 in which intake passages of the respective cylinders are gathered. An air cleaner 7 is attached via a pipe 6,
It is communicated with the air intake chamber 8. An exhaust pipe 10 communicates with the exhaust port 2b via an exhaust manifold 9, and a catalytic converter 11 is interposed in the exhaust pipe 10 and communicates with a muffler 12.

The throttle chamber 5 is provided with a throttle valve 5a linked to an accelerator pedal, and a bypass passage 13 for bypassing the throttle valve 5a is branched from the suction pipe 6. The bypass passage 13 is provided with an idle speed control valve (ISC valve) 14 for controlling the idle speed by adjusting the amount of bypass air flowing through the bypass passage 13 at the time of idling. The ISC valve 14
In the present embodiment, the valve opening is adjusted according to the duty ratio of a control signal output from an electronic control device 50 (see FIG. 2) described later.

An injector 15 is disposed immediately upstream of the intake port 2a of each cylinder of the intake manifold 3, and is connected to a fuel tank 17 via a fuel supply path 16. An in-tank type fuel pump 18 is provided in the fuel tank 17, and fuel from the fuel pump 18
The fuel is fed to the injector 15 and the pressure regulator 20 through the fuel filter 19 interposed in the fuel supply passage 16 and returned to the fuel tank 17 from the pressure regulator 20 to regulate the fuel pressure to the injector 15 to a predetermined pressure. Is done.

Further, from the upper part of the fuel tank 17, a discharge passage 21 for discharging the fuel vapor generated in the fuel tank 17 extends, and an adsorbing portion made of activated carbon or the like is provided via a two-way valve 22. The canister 23 communicates with an upper portion of the canister 23. The canister 23 is provided with a fresh air introduction port communicating with the atmosphere at a lower portion, and a purge passage 24 for introducing a mixture (evaporation gas) of fresh air from the fresh air introduction port and the evaporated fuel gas stored in the adsorption section. It extends from the top.

The purge passage 24 is provided with a canister purge control (CPC) duty solenoid valve 25 as an actuator for adjusting a purge amount of the evaporative gas in the middle of the purge passage 24. The purge solenoid 24 is located on the right side of the air chamber 4 downstream of the throttle valve 5a. It is connected to the bank side and opened. The CPC duty solenoid valve 25 is
As with the ISC valve 14, the valve opening is adjusted according to the duty ratio of a control signal output from an electronic control unit 50 (see FIG. 2) described later. On the other hand, an ignition plug 26 that exposes a discharge electrode at the tip to the combustion chamber 1c is attached to each cylinder of the cylinder head 2, and an ignition coil 27 containing an igniter 28 is connected to the ignition plug 26.

Next, sensors for detecting the operating state of the engine will be described. Air cleaner 7 for suction pipe 6
A thermal intake air amount sensor 29 using a hot wire or a hot film or the like is interposed immediately downstream of the throttle valve 5.
A throttle sensor 30 having a built-in throttle opening sensor 30a and an idle switch 30b that is turned on when the throttle is fully closed is provided in series. The air chamber 4 has
A suction pipe pressure sensor 31 for detecting the suction pipe pressure downstream of the throttle valve 5a as an absolute pressure is provided.

The cylinder block 1a of the engine 1
A knock sensor 32 is attached to the cylinder block 1a, and a coolant temperature sensor 34 faces a coolant passage 33 communicating the left and right banks of the cylinder block 1a. Further, a linear air-fuel ratio sensor 35 serving as a wide-range air-fuel ratio sensor is provided upstream of the catalytic converter 11. Are arranged. Further, a crank angle sensor 37 is provided on the outer periphery of a crank rotor 36 axially mounted on the crankshaft 1b of the engine 1, and further, a camshaft 1d which makes a half turn with respect to the crankshaft 1b.
A cylinder discriminating sensor 39 for discriminating the current combustion stroke cylinder, the fuel injection target cylinder, and the ignition target cylinder is provided opposite to the cam rotor 38 connected to the cylinder.

Next, an electronic control unit (ECU) 50 for controlling the engine 1 will be described with reference to FIG. E
The CU 50 mainly includes a microcomputer in which 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 connected to each other via a bus line, and supplies a stabilized power to each unit. Constant voltage circuit 57, I /
A peripheral circuit such as a drive circuit 58 and an A / D converter 59 connected to the O interface 56 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. Timers such as a timer for periodic interruption, a timer for measuring an input interval of a crank angle sensor signal (crank pulse), and a watchdog timer for monitoring a system abnormality are collectively referred to for convenience. A timer is used.

The constant voltage circuit 57 is connected to the battery 61 via the first relay contact of the power supply relay 60 having two relay contacts, and is also directly connected to the battery 61. When the switch is turned on and the contact of the power supply relay 60 is closed, power is supplied to each unit in the ECU 50, while the ignition switch 62 is turned on.
Irrespective of ON / OFF of the backup RAM5
4 is supplied with power for backup. Further, the fuel pump 18 is connected to the battery 61 via a relay contact of the fuel pump relay 63. The power supply relay 60
A power supply line for supplying power from the battery 61 to each actuator is connected to the second relay contact.

The input ports of the I / O interface 56 are connected to an ignition switch 62, an idle switch 30b, a knock sensor 32, a crank angle sensor 37, a cylinder discriminating sensor 39, a vehicle speed sensor 40, and the like. The intake air amount sensor 29, the throttle opening sensor 30a, the suction pipe pressure sensor 31, the cooling water temperature sensor 34, the linear air-fuel ratio sensor 35, and the like are connected via the A / D converter 59, and the battery voltage VB is reduced. Input and monitored. On the other hand, the output ports of the I / O interface 56 are connected to the relay coils of the power supply relay 60 and the fuel pump relay 63, the ISC valve 14, the injector 15, the CPC duty solenoid valve 25, and the like via the drive circuit 58. And an igniter 28 is connected.

In accordance with the control program stored in the ROM 52, the CPU 51
The detection signal from the sensors and switches, the battery voltage, etc., which are input via the CPU 6, are processed, and various data stored in the RAM 53 and various learning value data stored in the backup RAM 54 are stored in the ROM 52. Fuel injection amount, ignition timing, IS
The control duty for the C valve 14, the control duty for the CPC duty solenoid valve 25, and the like are calculated, and engine controls such as air-fuel ratio control (fuel injection control), ignition timing control, idle speed control, and canister purge control are performed.

Here, the air-fuel ratio control by the ECU 50 is as follows.
In feedback control using an air-fuel ratio response model, a control method in which integral control (I control) for a deviation between a target air-fuel ratio and a measured air-fuel ratio is changed to a compensator having a small phase delay is adopted. That is, in the conventional I control that performs the target value tracking function, the phase is always delayed by 90 ° with respect to the deviation between the target air-fuel ratio and the output air-fuel ratio, so that the air-fuel ratio disturbance due to the canister purge execution, the aging of the injector 15, etc. When this occurs, the air-fuel ratio behavior becomes oscillatory if the control parameter is increased in order to enhance the target value tracking function, and conversely, if the control parameter is reduced in order to avoid the vibration of the air-fuel ratio behavior, the target value tracking function decreases. It is difficult to eliminate this contradiction even by optimizing the control parameters. Therefore, in the air-fuel ratio control in the ECU 50, the above-mentioned contradiction is resolved by changing the I control to a compensator having a small phase delay, and both the improvement of the target value tracking function and the suppression of the vibration of the air-fuel ratio behavior are achieved.

FIG. 3 shows the function of the air-fuel ratio feedback control by the ECU 50 using the linear air-fuel ratio sensor 35. The fuel injection amount setting unit M1, the air-fuel ratio response inverse model M2,
The filter F1, F2, the inverse model coefficient calculation unit M3 is a basic configuration, the engine inlet equivalent ratio estimation means according to the present invention,
Air-fuel ratio disturbance estimating means, feedback correction amount calculating means,
The function of the fuel injection amount setting means is realized. The air-fuel ratio response inverse model M2 expresses an air-fuel ratio response model for estimating the exhaust equivalent ratio at the engine outlet from the engine inlet equivalent ratio corresponding to the fuel injection amount to be controlled by a first-order or second-order linear differential equation, This air-fuel ratio response model is solved by an engine inlet equivalent ratio. The air-fuel ratio response inverse model M2 and the filters F1 and F2 realize a compensator with a small phase lag, and achieve a target equivalent while securing a stable air-fuel ratio behavior. The ability to follow the ratio φr is improved.

The coefficient (parameter of the differential equation: inverse model coefficient) in the air-fuel ratio response inverse model M2 is determined by the inverse model coefficient calculator M3 based on the engine speed Ne and the engine load (for example, the suction pipe pressure Pm). It is calculated for each area. Then, a model value Um obtained by substituting the sensor measurement equivalent ratio φ obtained from the measurement value of the linear air-fuel ratio sensor 35 into the air-fuel ratio response inverse model M2 using the inverse model coefficient for each operation region is processed by the filter F1. Then, the engine inlet equivalent ratio is calculated as the estimated engine inlet equivalent ratio Ue. Next, the difference between the value Uf obtained by filtering the feedback correction amount Ui corresponding to the instruction value of the engine inlet equivalent ratio through the filter F2 and the estimated engine inlet equivalent ratio Ue is obtained as a disturbance equivalent ratio correction value φd. The disturbance equivalent ratio correction value φd and the target equivalent ratio φr are added to calculate a new feedback correction amount Ui. The fuel injection amount setting unit M1 performs feedback correction of the basic fuel injection pulse width that determines the basic fuel injection amount corresponding to the intake air amount per stroke with the feedback correction amount Ui, and further performs correction according to the operating state or learning. The fuel injection pulse width which determines the final fuel injection amount is set by adding the above.

In this embodiment, as shown in the following equation (1), an air-fuel ratio response model using a first-order linear differential equation is calculated using a constant a (0 <a <1) for each operating region. Discretize every operation cycle. An equation of an inverse model obtained by solving the discretized model with an engine inlet equivalent ratio u (k) is expressed by the current sensor equivalent ratio φ by the linear air-fuel ratio sensor 35.
(K), a model value Um (K) is obtained by substituting the previous sensor measurement equivalent ratio φ (K-1). This model value Um (K) is an estimated value of the engine inlet equivalent ratio, and the exhaust-side equivalent ratio obtained from the measurement value of the linear air-fuel ratio sensor 35 by the air-fuel ratio response inverse model M2 is used as the fuel to be controlled. The phase can be the same as the engine inlet equivalent ratio corresponding to the injection amount.
The constant b (> 0) in the equation (2) is a constant for each operation region, and is an inverse model coefficient given to the air-fuel ratio response inverse model M2. φ (K) = a × φ (K-1) + (1−a) × u (K) (1) Um (K) = (1 + b) × φ (K) −b × φ (K-1) … (2)

Then, the model value Um (K) from the air-fuel ratio response inverse model M2 is passed through a filter F1 and obtained as an estimated engine inlet equivalent ratio Ue (K) as shown in equation (3). That is, the engine inlet equivalent ratio estimated by the air-fuel ratio response inverse model M2 can be obtained as an engine inlet estimated value stabilized by passing through the filter F1. Ue (K) = (1−q) × Um (K) + q × Ue (K−1) (3) where q: filter coefficient (0 <q <1)

At the same time, as shown in the following equation (4), the current feedback correction amount Ui (K) is passed through the filter F2 to obtain a filter output value Uf (K). Here, the filters F1 and F2 are the same filter. And
As shown in the equation (5), a disturbance equivalent ratio correction value φd (K) is calculated by subtracting the engine inlet equivalent ratio estimated value Ue (K) from the filter output value Uf (K). As shown,
The disturbance equivalent ratio correction value φd (K) is added to the target equivalent ratio φr (K) to calculate a new feedback correction amount Ui (K). Uf (K) = (1−q) × Ui (K) + q × Uf (K−1) (4) φd (K) = Uf (K) −Ue (K) (5) Ui (K) = φd (K) + φr (K)… (6)

In this case, the phase delay of the disturbance equivalent ratio correction value φd (K) with respect to the engine inlet equivalent ratio is determined by the filter F1,
Although depending on F2, by setting the filter coefficient q small, the response can be made sufficiently faster than the air-fuel ratio response model of the equation (1). That is, the phase delay of the disturbance equivalent ratio correction value φd (K) with respect to the engine inlet equivalent ratio can be made so as not to have much influence in the feedback control, and the gain can be made to correspond one-to-one. In the present embodiment, the filters F1,
F2 employs the same filter, but filters F1,
F2 can be set freely.

The above processing is executed by a feedback correction amount calculation routine shown in FIG. 4 and a fuel injection control routine shown in FIG. These routines are executed at predetermined intervals, and the feedback correction amount Ui (K) calculated in the feedback correction amount calculation routine is used in the fuel injection control routine to determine the final fuel injection amount for the injector 15. The width Ti is set.

First, the feedback correction amount calculation routine shown in FIG. 4 will be described. In this routine, the engine speed Ne based on the signal from the crank angle sensor 37 is read in the first step S101, and the suction pipe pressure P based on the signal from the suction pipe pressure sensor 31 is read in step S102.
Read m. Next, the routine proceeds to step S103, where an inverse model coefficient b for each operating region is calculated based on the engine speed Ne and the suction pipe pressure Pm. The inverse model coefficient b is obtained by referring to a table created in advance by simulation or using the experiment together with the simulation with interpolation calculation, and is given to the air-fuel ratio response inverse model as a coefficient for each operation region.

In the following step S104, the output from the linear air-fuel ratio sensor 35 is read, and in step S105,
The equivalent ratio of the exhaust gas is calculated from the output of the linear air-fuel ratio sensor 35, and is set as the sensor measured equivalent ratio φ (K). Then, in step S106, the sensor measurement equivalence ratio φ (K) is given to the air-fuel ratio response inverse model, and the model value Um is calculated in accordance with the above equation (2).
Calculate (K).

Next, the process proceeds to step S107, where the model value Um (K) is filtered by the filter F1 according to the above-described equation (3) to obtain an estimated engine inlet equivalent ratio Ue (K). The current feedback correction amount Ui (K) is filtered by the filter F2 according to the above equation (4) to obtain a filter output value Uf (K).

After that, in step S109, the disturbance equivalent ratio correction value φd (K) is calculated by subtracting the engine inlet equivalent ratio estimated value Ue (K) from the filter output value Uf (K) according to the above equation (5). In step S110, the disturbance equivalent ratio correction value φd (K) is added to the target equivalent ratio φr (K) according to the above equation (6), and a new feedback correction amount Ui (K) is obtained.
Is calculated, and the process exits the routine.

Next, the fuel injection control routine will be described. In this routine, in the first step S201,
A basic fuel injection pulse width Tp that determines a basic fuel injection amount corresponding to an intake air amount per stroke is set. Since the engine 1 of the present embodiment is a mass flow type engine that sets the fuel injection amount based on the intake air amount directly measured by the intake air amount sensor 29, a value obtained by dividing the measured air amount Q by the engine speed Ne. Is multiplied by an injector characteristic constant K to set the basic fuel injection pulse width Tp (Tp ←
K × Q / Ne). In the case of a speed-density type engine in which the intake air amount is estimated from the intake pipe pressure Pm and the engine speed Ne without using the intake air amount sensor, a table using the intake pipe pressure Pm and the engine speed Ne as parameters is provided. The basic fuel injection pulse width Tp is set with reference to the interpolation calculation.

Next, the process proceeds to step S202, in which the learning value LF (K) is added to the feedback correction amount Ui (K) obtained by the above-described air-fuel ratio response inverse model M2 and the filters F1 and F2 to obtain the final correction amount. Uc (K) (Uc (K) ← Ui (K)
+ LF (K)), in step S203, various correction coefficients C based on the engine operating state are added to the basic fuel injection pulse width Tp.
The effective injection pulse width Te is set by multiplying the OEF and the correction amount Uc (K) (Te ← Tp × COEF × Uc
(K)).

Thereafter, in step S204, the injector 1 which depends on the battery voltage is set to the effective injection pulse width Te.
5 is added to the invalid pulse width Ts for compensating for the invalid injection time, and the fuel injection pulse width Ti that determines the final fuel injection amount to be supplied to the engine is set (Ti ← Te + T
s). Then, in step S205, the injection timer of the corresponding cylinder #i is set, and the routine exits.

As a result, it is possible to obtain good followability to a target air-fuel ratio (a target equivalent ratio) while maintaining a stable air-fuel ratio behavior with respect to an air-fuel ratio disturbance due to aging of the canister purge, the injector 15, and the like. This can contribute to a reduction in exhaust emissions.

In this case, during the air-fuel ratio feedback control, when the feedback inhibition condition is satisfied due to fuel cut or the like, the disturbance equivalent ratio correction value φd (K) obtained by the above equation (5) is used when the feedback inhibition condition is satisfied. Or reset to the set value. Then, when the feedback prohibition condition is cancelled, it is desirable to start the calculation of the disturbance equivalent ratio correction value φd (K) after the delay time DTFBN elapses from the time when the condition changes. As a result, as shown in FIG. 6, the disturbance equivalent ratio correction value φd (K) before and after the feedback prohibition condition is satisfied can be made a continuous value, thereby preventing erroneous estimation of disturbance and improving controllability. can do.

As shown in FIG. 7, when the canister purging execution condition is satisfied, the disturbance equivalent ratio correction value φd (K) obtained by the above equation (5) is replaced by the value before the canister purging execution condition is satisfied. When the canister purge condition is released, the disturbance equivalent ratio correction value φd (K) is changed to the value φd (Kd) when the canister purge execution condition is satisfied until the delay time DTFBC elapses from when the condition is changed.
It is desirable to be c. Thus, when the canister purge condition is released, the disturbance equivalent ratio correction value φd (K) can be calculated in a feedforward manner to perform an accurate correction, and controllability can be further improved.

FIG. 8 relates to a second embodiment of the present invention.
It is a functional block diagram of air-fuel ratio control. The second form is the first
A correction for eliminating a dead time component in the air-fuel ratio response is added to the air-fuel ratio control of the embodiment.

That is, the air-fuel ratio response model expressed by the above equation (1) takes the following equation (7) into consideration when considering the dead time.
Indicated by the equation. Therefore, in order to eliminate this dead time component, in the second embodiment, as shown in FIG. 8, compared to the first embodiment, the dead time calculation unit M4 and the dead time delay unit M5
Add. Then, in the dead time calculation unit M4, the engine speed Ne and the engine load (for example, the suction pipe pressure Pm)
The dead time L is calculated on the basis of the feedback correction amount U via the dead time delay unit M5.
Applies to i (K). The dead time L can be obtained by referring to a dead time table created in advance by simulation or experiment or by calculation. φ (K) = a × φ (K−1) + (1−a) × u (K−L) (7) where L: step of dead time

In the dead time delay section M5, the feedback correction amount Ui (K) is delayed by the dead time L and applied to the filter F2.
The feedback correction amount Ui (K) is processed by the following equation (8) with the equation changed to obtain a filter value Uf (K). Uf (K) = q × Ui (KL) + (1−q) × Uf (K−1) (8)

The other processes are the same as those in the first embodiment described above. In the second embodiment, by performing a correction for eliminating the dead time component, an excellent target value tracking can be performed even in a response in which the dead time component cannot be ignored. Nature can be secured.

FIG. 9 relates to a third embodiment of the present invention.
It is a functional block diagram of air-fuel ratio control. The third form is the first
For the embodiment, the filter coefficients q of the filters F1 and F2 are varied according to the operation range.

That is, as shown in FIG. 9, a filter coefficient calculator for calculating a filter coefficient q for each operation region determined by the engine speed Ne and the engine load (for example, the suction pipe pressure Pm) in the first embodiment. By adding M6 and applying the calculated filter coefficient q to the filters F1 and F2, the engine inlet equivalent ratio estimated value Ue is more stabilized.
(K). The filter coefficient q is associated with a constant a for each operating region of the air-fuel ratio response model shown in the equation (1), and the engine speed Ne and the engine load (for example, the suction pipe pressure P
m), an optimal value is obtained in advance by simulation or experiment and stored in a table for each operation region determined by the above. Then, by referring to this table with interpolation calculation, a filter coefficient q for each operation region can be obtained.

The other processing is the same as in the first embodiment.
In the third embodiment, even in a region where the air-fuel ratio response is slow (a region where the constant a is large), the influence of high frequency components such as noise can be eliminated, and controllability can be further improved.

FIGS. 10 and 11 relate to the fourth embodiment of the present invention. FIG. 10 is a functional block diagram of the air-fuel ratio control, and FIG. 11 is a time chart showing a response to an air-fuel ratio disturbance. The fourth embodiment is different from the first embodiment in that when calculating the feedback correction amount Ui (K), proportional differential control (PD control) of the deviation between the target equivalent ratio φr (K) and the sensor measurement equivalent ratio φ (K) is performed. ).

That is, as shown in FIG. 10, the engine speed Ne and the engine load (for example,
A PD control coefficient calculation unit M7 and a PD control unit M8 for calculating a PD control coefficient (P control coefficient Kp and D control coefficient Kd) for each operation region determined by the suction pipe pressure Pm) and a target equivalent ratio φr (K ) And the sensor measurement equivalent ratio φ (K)
(K) is processed by the PD control unit M8. e (K) = φr (K) −φ (K) (9)

The optimum values of the P control coefficient Kp and the D control coefficient Kd are obtained in advance by simulation or experiment for each operation region determined by the engine speed Ne and the engine load (for example, the suction pipe pressure Pm). Store in a table. Then, by referring to this table with interpolation calculation, the P control coefficient Kp and the D control coefficient Kd for each operation region can be obtained.

In the PD control unit M8, the P control coefficients Kp and D for each operating region given from the PD control coefficient calculation unit M7
Using the control coefficient Kd, a deviation e (K) between the target equivalent ratio φr and the sensor measured equivalent ratio φ (K) is processed to obtain a proportional differential value PD (K) shown in Expression (10). Then, as shown in the following equation (11), the feedback correction amount Ui (K) is obtained by correcting the target equivalent ratio φr (K), the disturbance equivalent ratio correction value φd (K), and the proportional differential value PD.
(K). PD (K) = Kp × e (K) + Kd × (e (K) −e (K−1)) / dt (10) Ui (K) = φd (K) + φr (K) + PD (K) (11) where dt: calculation cycle

In the fourth embodiment, the control response is further increased by adding PD control to the first embodiment, and the target value followability can be further improved. That is, FIG.
As shown in (b) and FIG. 11 (c), in the conventional PID control, when an air-fuel ratio disturbance occurs, an oscillating air-fuel ratio behavior accompanied by excessive overshoot is exhibited, and it takes time to converge to the target value. However, the I control that performs the target value tracking function in the PID control is performed by the inverse air-fuel ratio response model M2 and the filter F.
In the air-fuel ratio control of the fourth embodiment in which the compensator is changed to 1, F2, as shown in FIG.
Overshoot can be suppressed to an extremely small value, and the target value can be quickly and stably converged.

In the present embodiment, an example in which PD control is added has been described. However, for simplicity, only P control may be used.

FIGS. 12 and 13 relate to the fifth embodiment of the present invention. FIG. 12 is a functional block diagram of the air-fuel ratio control, and FIG. 13 is a flowchart of a learning value updating routine. The fifth embodiment is different from the first embodiment in that a learning value LF (K) for correcting the basic fuel injection pulse width Tp in the fuel injection amount setting unit M1 is used.
Is updated by learning control based on the disturbance equivalent ratio correction value φd (K).

That is, as shown in FIG. 12, the engine speed Ne and the engine load (for example,
A learning mechanism that sets a learning value LF (K) based on the disturbance equivalent ratio correction value φd (K) and updates the learning value LF (K) when the learning condition is satisfied for each operation region determined by the suction pipe pressure Pm). Add M9. The learning value updating process in the learning mechanism M9 is performed by a learning value updating routine of FIG. 13 executed at predetermined intervals.

In the learning value update routine, first, in step S301, when the learning condition is not satisfied or when the learning value is updated, 0 is set.
Is referred to the value of the learning counter LCNT (K), which is cleared to the above. If LCNT (K) ≠ 0, step S
Proceeding to 303, the learning counter LCNT (K) is counted up (LCNT (K) ← LCNT (K-1) +1), and the LCN
When T (K) = 0, in step S302, the current engine speed Ne and the suction pipe pressure Pm are respectively set to the engine speed initial value Nei and the suction pipe pressure initial value Pmi (Nei ← Ne, Pmi ← Pm). In step S303, the learning counter LCNT (K) is counted up.

Next, in steps S304 to S308, it is checked whether or not the following conditions (a) to (e) are satisfied. (A) │Ne-Nei│> set value DNe (b) │Pm-Pmi│> set value DPm (c) │φd│> set value DFd (d) Feedback prohibition condition (e) Canister purge condition

As a result, if any one of the conditions (a) to (e) is satisfied, the process branches to step S317 from the corresponding step as the learning condition is not satisfied, and the learning counter LCNT (K) is cleared. Do (LCNT (K) ← 0)
Exit the routine. When all of the conditions (a) to (e) are not satisfied, that is, at the time of steady engine operation, it is checked in step S309 whether the learning counter LCNT (K) has reached the set value TC. And LCNT (K)
In the case of を TC, the routine exits and LCNT (K) = T
In the case of C, the learning value is updated in accordance with the sign of the disturbance equivalent ratio correction value φd (K) after step S310 in order to update the learning value.

That is, in step S310, the learning value LF (K) of the current operating region determined by the engine speed Ne and the suction pipe pressure Pm is read from the learning table stored in the backup RAM 54, and the process proceeds to step S310.
In 311, it is checked whether or not the disturbance equivalent ratio correction value φd (K) exceeds 0. If φd (K)> 0, the set value DLF is added to the learning value LF (K) in step S312 to update the value of the corresponding area of the learning table (LF (K) ← LF
(K−1) + DLF), and in step S312, the disturbance equivalent ratio correction value φd (K) is reduced by the learning amount (φd (K) ← φ (K) −D
LF), the learning counter LCNT in step S316
Clear (K) (LCNT (K) ← 0) and exit the routine.

If φd (K) ≦ 0 in step S311, the set value DLF is subtracted from the learning value LF (K) in step S314 to update the value of the corresponding area of the learning table (LF (K ) ← LF (K−1) −DLF), step S315
Increases the disturbance equivalent ratio correction value φd (K) by the learning amount (φ
d (K) ← φ (K) + DLF), the learning counter LCNT (K) is cleared in step S316 (LCNT (K) ← 0), and the routine exits.

As described in the first embodiment, the learning value LF (K) is added to the feedback correction amount Ui (K) to form a final correction amount Uc (K), which is based on the engine operating state. The effective injection pulse width Te is set by multiplying the basic fuel injection pulse width Tp together with the various correction coefficients COEF. The effective pulse width Te reflecting the learning result based on the disturbance equivalent ratio correction value φd (K) is added to the invalid pulse width Ts.
Are added to set the final fuel injection pulse width Ti.

In the fifth embodiment, the learning control based on the disturbance equivalent ratio correction value φd (K) is performed on the first embodiment, so that the air-fuel ratio disturbance can be corrected in a feed-forward manner. As a result, the burden of feedback can be reduced, and the target value followability in a state where the amount of disturbance changes or during transient operation can be improved.

FIG. 14 is a flowchart of a feedback correction amount calculation routine according to the sixth embodiment of the present invention. The sixth embodiment is different from the first embodiment in that the disturbance equivalent ratio correction value φd (K) is set to a minimum value φdmin (<0) and a maximum value φd (K).
A process for saturating with dmax (> 0) is added.

That is, in the feedback correction amount calculation routine shown in FIG. 14, similarly to the first embodiment, if the disturbance equivalent ratio correction value φd (K) is calculated in steps S109 through S108 and step S109, then steps S109 to S109 −1, the disturbance equivalent ratio correction value φd
It is checked whether (K) is smaller than the minimum value φdmin.

If φd (K) <φdmin, the flow advances from step S109-1 to step S109-2 to limit the disturbance equivalent ratio correction value φd (K) to the minimum value φdmin and restrict the lower limit (φd (K) ← φdmin), step S
The disturbance equivalent ratio correction value φd (K) whose lower limit is regulated at 110 is added to the target equivalent ratio φr (K), and a new feedback correction amount U is added.
Calculate i (K) and exit the routine.

In step S109-1, φd (K) ≧
In the case of φdmin, the process proceeds from step S109-1 to step S109-3 to check whether or not the disturbance equivalent ratio correction value φd (K) is larger than the maximum value φdmax. As a result, when φd (K) ≦ φdmax, that is, when the disturbance equivalent ratio correction value φd (K) calculated in step S109 is within the range between the minimum value φdmin and the maximum value φdmax, the process directly proceeds to step S110. Then, a new feedback correction amount Ui (K) is calculated by adding the disturbance equivalent ratio correction value φd (K) to the target equivalent ratio φr (K), and the routine exits.

On the other hand, when φd (K)> φdmax,
The process proceeds from step S109-3 to step S109-4, where the disturbance equivalent ratio correction value φd (K) is restricted to the maximum value φdmax and the upper limit is restricted (φd (K) ← φdmax), and step S1 is performed.
The disturbance equivalent ratio correction value φd (K) whose upper limit has been regulated at 10 is added to the target equivalent ratio φr (K) to add a new feedback correction amount Ui.
Calculate (K) and exit the routine.

In the sixth embodiment, as compared with the first embodiment, feedback due to an excessive disturbance equivalent ratio correction value φd (K) can be avoided, and when the linear air-fuel ratio sensor 35 breaks down or excessive noise occurs. Even in this case, it is possible to prevent erroneous estimation of disturbance and to avoid adverse effects such as engine stall.

[0082]

As described above, according to the present invention, it is possible to improve the function of following a target air-fuel ratio while maintaining a stable air-fuel ratio behavior against an air-fuel ratio disturbance, and to reduce exhaust emissions. Can contribute.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an engine system according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of an electronic control system according to the first embodiment;

FIG. 3 is a functional block diagram of air-fuel ratio control according to the first embodiment;

FIG. 4 is a flowchart of a feedback correction amount calculation routine;

FIG. 5 is a flowchart of a fuel injection control routine according to the first embodiment;

FIG. 6 is a time chart showing a change in a disturbance equivalent ratio correction value before and after the feedback is prohibited.

FIG. 7 is a time chart showing a change in a disturbance equivalent ratio correction value before and after the canister purge is performed.

FIG. 8 is a functional block diagram of air-fuel ratio control according to a second embodiment of the present invention.

FIG. 9 is a functional block diagram of air-fuel ratio control according to a third embodiment of the present invention.

FIG. 10 is a functional block diagram of air-fuel ratio control according to a fourth embodiment of the present invention.

FIG. 11 is a time chart showing a response to an air-fuel ratio disturbance;

FIG. 12 is a functional block diagram of air-fuel ratio control according to a fifth embodiment of the present invention.

FIG. 13 is a flowchart of a learning value updating routine.

FIG. 14 is a flowchart of a feedback correction amount calculation routine according to the sixth embodiment of the present invention;

[Explanation of symbols]

Reference Signs List 1 engine 35 linear air-fuel ratio sensor (wide-range air-fuel ratio sensor) 50 electronic control unit (engine inlet equivalent ratio estimating means, air-fuel ratio disturbance estimating means, feedback correction amount calculating means, fuel injection amount setting means) M2 air-fuel ratio response inverse model F1 , F2 filter φ sensor measured equivalent ratio (measured equivalent ratio) φr target equivalent ratio Um model value Ue engine inlet equivalent ratio estimated value φd disturbance equivalent ratio correction value Ui feedback correction amount Ti fuel injection pulse width (final fuel injection amount)

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F02D 45/00 340 F02D 45/00 340D 368 368G 370 370B F term (reference) 3G084 BA06 BA09 BA13 DA12 EA01 EB15 EB16 EB20 EB24 EC04 FA05 FA07 FA10 FA11 FA20 FA25 FA29 FA38 FA39 3G301 HA01 HA14 JA03 LA04 MA01 MA11 ND05 ND12 ND15 ND25 PA01Z PA07Z PA11Z PC08Z PD04Z PE03Z PE05Z PE08Z PF01Z

Claims (8)

[Claims] 1. A measurement of an engine outlet measured by a wide-range air-fuel ratio sensor to an inverse model of an air-fuel ratio response model in which an equivalent ratio of an engine outlet is modeled by a first-order or second-order linear differential method from an equivalent ratio of an engine inlet. An engine inlet equivalence ratio estimating means for filtering a model value obtained by applying the equivalence ratio to calculate an engine inlet equivalence ratio estimated value that estimates an engine inlet equivalence ratio; and Air-fuel ratio disturbance estimating means for calculating a disturbance equivalent ratio correction value that estimates an air-fuel ratio disturbance based on the processed value and the engine inlet equivalent ratio estimated value, based on the disturbance equivalent ratio correction value and the target equivalent ratio Therefore, the feedback correction amount for performing the feedback correction of the fuel injection amount corresponding to the equivalence ratio at the engine inlet is changed to a new instruction value for the equivalence ratio at the engine inlet. A feedback correction quantity calculating means for calculating Te, corrects the fuel injection amount by the feedback correction amount,
An air-fuel ratio control device for an engine, comprising: fuel injection amount setting means for setting a final fuel injection amount to be supplied to the engine. 2. The engine according to claim 1, wherein the air-fuel ratio disturbance estimating means filters an instruction value for the equivalence ratio at the engine inlet by adding a correction for eliminating a dead time component. Fuel ratio control device. 3. The air-fuel ratio control device for an engine according to claim 1, wherein parameters of the filter processing are varied according to an operation range. 4. The feedback correction amount calculating means calculates the feedback correction amount by adding a control value by proportional control or proportional differential control of a deviation between the target equivalent ratio and the measured equivalent ratio. The engine air-fuel ratio control device according to claim 1. 5. The air-fuel ratio control device for an engine according to claim 1, further comprising learning means for learning and controlling the feedback correction amount based on the disturbance equivalent ratio correction value. 6. An air-fuel ratio control device for an engine according to claim 1, wherein said air-fuel ratio disturbance estimating means regulates said disturbance equivalent ratio correction value with a minimum value and a maximum value. 7. The air-fuel ratio disturbance estimating means, when the air-fuel ratio feedback prohibition condition is satisfied, maintains the disturbance equivalent ratio correction value at the value when the air-fuel ratio feedback prohibition condition is satisfied or resets the correction value to a set value. The engine air-fuel ratio control device according to claim 1, wherein: 8. The air-fuel ratio disturbance estimating means stores the value of the disturbance equivalent ratio correction value when the canister purge execution condition is satisfied, and until the set time elapses when the canister purge condition is released. 2. The air-fuel ratio control device for an engine according to claim 1, wherein the disturbance equivalent ratio correction value is a value stored when a canister purge execution condition is satisfied.