JP2510866B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio control device for an internal combustion engine having an electronically controlled fuel injection device.

<Prior Art> An electronically controlled fuel injection device for an internal combustion engine includes an electromagnetic fuel injection valve in an engine intake system and has parameters of an engine operating state related to an amount of air taken into the engine (for example, engine intake air flow rate and engine intake air flow rate). Set the basic fuel injection amount based on
The final fuel injection amount is obtained by multiplying this by a feedback correction coefficient for air-fuel ratio feedback control, and a drive pulse signal with a pulse width corresponding to this fuel injection amount is obtained at a predetermined timing synchronized with the engine rotation. By outputting the fuel to the fuel injection valve, the fuel injection amount is controlled, and an optimum amount of fuel is injected and supplied to the engine.

Regarding the air-fuel ratio feedback control, an oxygen sensor is provided in the engine exhaust system to detect the air-fuel ratio of the engine intake air-fuel mixture, which is closely related to the oxygen concentration in the engine exhaust,
The detected air-fuel ratio is compared with the stoichiometric air-fuel ratio which is the target air-fuel ratio to determine rich lean, and the feedback correction coefficient is changed based on this to control the air-fuel ratio to the stoichiometric air-fuel ratio.

Specifically, as shown in FIG. 13, the output voltage of the oxygen sensor is compared with the slice level voltage, and when the output voltage is high, it is determined to be rich, and when the output voltage is low, it is determined to be lean. Based on this, proportional feedback and integral (PI) control is used to set and control the feedback correction coefficient. That is, for example, in the case of rich (lean), the feedback correction coefficient is first decreased (increased) by the proportional constant P, and then decreased (increased) by the integration constant I by time synchronization or rotation synchronization to increase the theoretical air-fuel ratio. Control is performed so as to approach the air-fuel ratio (see Japanese Patent Laid-Open No. 60-240840).

<Problems to be solved by the invention> However, in such a conventional air-fuel ratio feedback control, the air-fuel ratio is controlled only by the magnitude relationship with the target air-fuel ratio, and the response of the oxygen sensor to the actual change in the air-fuel ratio. However, when the output voltage of the oxygen sensor crosses the slice level voltage, the actual air-fuel ratio has changed greatly from the target air-fuel ratio to the rich side or lean side, resulting in poor control (Fig. 13). (Hatched portion) also occurs. Therefore, overshoot,
The amount of undershoot increases, and as a result, the fluctuation range of the air-fuel ratio is large and the convergence to the target air-fuel ratio deteriorates, which deteriorates drivability due to surge torque and increases the emissions of CO, HC, NO _x, etc. Is invited.

In view of such conventional problems, the present invention provides a deviation of the air-fuel ratio from the target air-fuel ratio and a differential value (change speed) of the air-fuel ratio.
By setting the feedback correction coefficient based on the above, the fluctuation of the air-fuel ratio can be more effectively suppressed and the convergence to the target air-fuel ratio can be improved, so that hunting due to poor control can be prevented and surge torque (vehicle (Longitudinal vibration) to reduce drivability and improve exhaust purification performance.

<Means for Solving the Problems> For this reason, the present invention, as shown in FIG.
To K means the air-fuel ratio control device for the internal combustion engine.

(A) Engine operating state detecting means for detecting engine operating state (B) Basic fuel injection amount setting means for setting basic fuel injection amount based on the detected engine operating state (C) Detecting engine exhaust gas component Air-fuel ratio detecting means for detecting the air-fuel ratio of the air-fuel mixture sucked into the engine (D) Deviation calculating means for calculating the deviation of the detected air-fuel ratio from the target air-fuel ratio (E) The differential value of the detected air-fuel ratio Differential value calculating means for calculating (F, G) Step value converting means for converting the deviation and the differential value into step values according to their magnitudes (H) The step value of the deviation and the step value of the differential value Feedback correction coefficient step value setting means for setting the feedback correction coefficient step value by referring to a map in which the feedback correction coefficient step value is determined in correspondence with (1) Feedback correction coefficient setting means for setting a feedback correction coefficient for feedback correcting the basic fuel injection quantity (J) The basic fuel injection quantity set by the basic fuel injection quantity setting means and the feedback correction coefficient setting means Fuel injection amount calculation means for calculating the fuel injection amount based on the feedback correction coefficient (K) Fuel injection means for supplying fuel to the engine on / off by a drive pulse signal corresponding to the calculated fuel injection amount <Operation> Based on the engine operating state detected by the engine operating state detecting unit A, the basic fuel injection amount setting unit B sets the basic fuel injection amount substantially corresponding to the target air-fuel ratio.

On the other hand, the air-fuel ratio is detected by the air-fuel ratio detecting means C,
The deviation calculation means D calculates the deviation of the air-fuel ratio from the target air-fuel ratio, and the differential value calculation means E calculates the differential value (change speed) of the air-fuel ratio.

Since the trend of the air-fuel ratio can be predicted by these deviations and differential values, the feedback correction coefficient is set based on these. At this time, first by the step value conversion means F, G,
The deviation and the differential value are converted into step values (fuzzy numbers) according to their magnitudes. Next, the feedback correction coefficient step value setting means H refers to a map in which the feedback correction coefficient step value (fuzzy amount) is determined in correspondence with the deviation step value and the differential value step value, and the feedback correction coefficient step is referred to. Set the value. And
The feedback correction coefficient setting means I sets the feedback correction coefficient in correspondence with the feedback correction coefficient step value.

The fuel injection amount calculation means J calculates the fuel injection amount based on the basic fuel injection amount and the feedback correction coefficient set by the setting means B and I. Then, the fuel injection means K is generated by the drive pulse signal corresponding to the fuel injection amount.
Works.

<Example> An example of the present invention will be described below.

In FIG. 2, air is sucked into an engine 1 from an air cleaner 2 via an intake duct 3, a throttle valve 4, and an intake manifold 5. A fuel injection valve 6 as a fuel injection means is provided for each cylinder in a branch portion of the intake manifold 5. The fuel injection valve 6 is an electromagnetic fuel injection valve that is energized by a solenoid to open, is de-energized, and closes. The fuel injection valve 6 is energized by a drive pulse signal from a control unit 12 described later, and is opened. The fuel which is pressure-fed from the pump and adjusted to a predetermined pressure by the pressure regulator is injected and supplied. Although this example is a multi-point injection system, it may be a single-point injection system in which a single fuel injection valve is provided in common to all cylinders upstream of the throttle valve.

An ignition plug 7 is provided in a combustion chamber of the engine 1 to ignite and burn an air-fuel mixture by spark ignition.

Then, exhaust gas is discharged from the engine 1 through the exhaust manifold 8, the exhaust duct 9, the three-way catalyst 10, and the muffler 11. The three-way catalyst 10 oxidizes CO and HC in exhaust components,
By reducing O _x, is an exhaust purification device that converts to other harmless substances, the conversion efficiency is closely related to the air-fuel ratio of the intake mixture.

The control unit 12 includes a microcomputer including a CPU, a ROM, a RAM, an A / D converter, and an input / output interface, receives input signals from various sensors, performs arithmetic processing as described below, The operation of the fuel injection valve 6 is controlled.

As the various sensors, a hot-wire air flow meter 13 is provided in the intake duct 3 and outputs a voltage signal corresponding to the intake air flow rate Q.

In addition, the crank angle sensor 14 is provided, and in the case of four cylinders, the reference signal and the crank angle 1 for each crank angle of 180 ° are set.
Outputs a unit signal for each ° or 2 °. Here, the engine speed N can be calculated by measuring the period of the reference signal or the number of unit signals generated within a predetermined time.

The water jacket of the engine 1 is provided with a water temperature sensor 15 for detecting the cooling water temperature Tw.

The air flow meter 13, the crank angle sensor 14, and the like are engine operating state detecting means.

Further, an oxygen sensor 16 as an air-fuel ratio detecting means is provided at a collecting portion of the exhaust manifold 8, and detects an air-fuel ratio of the intake air-fuel mixture through an oxygen concentration in the exhaust gas.

The oxygen sensor 16 is, for example, a cylinder having a bottom and a closed end facing the exhaust gas and used as a solid electrolyte for a concentration battery. The oxygen ion conductor is zirconia (ZrO ₂ ). The electromotive force is generated according to the ratio of the oxygen concentration. Then, a platinum catalyst layer formed by vapor-depositing platinum that functions as an oxidation catalyst is provided on the outer surface of the zirconia tube, and in general, a small amount of unburned O ₂ and CO that are present when burned with a rich air-fuel mixture It is well known that the components are combined with each other to make the outside oxygen concentration substantially zero, thereby increasing the inside / outside oxygen concentration ratio to generate a large electromotive force (the characteristic of the broken line in FIG. 3).

However, in this example, a so-called semi-catalyst is formed by forming a platinum catalyst layer or enlarging platinum particles as known from JP-A-59-109853.

As a result, the low-concentration oxygen outside the zirconia tube could not be made to react well with the unburned components and the oxygen concentration could not be quickly reduced to zero, and the electromotive force changed at the theoretical air-fuel ratio where the oxygen concentration suddenly changed. However, it will change gradually as a whole (characteristics of the solid line in FIG. 3).

That is, without the catalytic action of platinum, the ratio of the oxygen concentration inside and outside the zirconia tube becomes small due to the oxygen remaining when the mixture is burned in a rich air-fuel mixture, and sufficient electromotive force cannot be obtained. It consumes a low concentration of oxygen in order to obtain a large electromotive force, but weakening the catalytic action slows down the rise of electromotive force, resulting in an inclined output characteristic as shown by the solid line in FIG. The oxygen sensor 16 is provided.

As a result, not only the on / off detection of whether the air-fuel ratio is rich or lean with respect to the stoichiometric air-fuel ratio but also the air-fuel ratio can be specified and detected.

Here, the CPU of the microcomputer incorporated in the control unit 12 performs a calculation process according to a program (fuel injection amount calculation routine) on the ROM shown as a flowchart in FIG. 4 to control the fuel injection.

The functions as the basic fuel injection amount setting means, the deviation calculating means, the differential value calculating means, the step value converting means, the feedback correction coefficient step value setting means, the feedback correction coefficient setting means, and the fuel injection amount calculating means are achieved by the program. To be done.

Next, with reference to the flowchart of FIG. 4, the state of the arithmetic processing of the microcomputer in the control unit 12 will be described.

This fuel injection amount calculation routine is executed in synchronization with the engine rotation or every predetermined time.

In step 1 (denoted as S1 in the figure; the same applies hereinafter), the intake air flow rate Q detected based on the signal from the air flow meter 13 and the engine speed N detected based on the signal from the crank angle sensor 14 Then, the water temperature Tw detected based on the signal from the water temperature sensor 15 is input. Also, the oxygen sensor 16
Input the output voltage V ₀₂ of.

In step 2, the basic fuel injection amount Tp corresponding to the intake air amount per unit rotation is obtained from the intake air flow rate Q and the engine speed N.
= K · Q / N (K is a constant). Step 2 corresponds to basic fuel injection amount setting means.

In step 3, various correction coefficients COEF = 1 + K _TW + ... Including a water temperature correction coefficient K _TW corresponding to the water temperature Tw are set.

In step 4, it is determined whether or not a predetermined air-fuel ratio feedback control condition is satisfied. Here, the predetermined air-fuel ratio feedback control conditions, the water temperature Tw is a predetermined value or more, also, the oxygen sensor 16 is active and normal, the upper and lower peak value of the output voltage V ₀₂ is, for example, 720 mV or more, 230 mV or less. The condition is that If this condition is not satisfied, proceed to step 5 to stop the air-fuel ratio feedback control and proceed to step S5 where the feedback correction coefficient LAMBDA
Is clamped to the reference value of 1.0.

If the air-fuel ratio feedback control condition is satisfied, proceed to step 6 and refer to the map to output voltage V _{02 of the} oxygen sensor 16.
To the air-fuel ratio λ.

In this embodiment, the output voltage V ₀₂ of the oxygen sensor 16 is converted into the air-fuel ratio λ for processing, but the output voltage V ₀₂ itself can be regarded as the air-fuel ratio for processing.

Next, the routine proceeds to step 7, where the actual N value is referred to by referring to the map in which the target air-fuel ratio λ _tg is determined for each area of the engine operating state according to the engine speed N and the basic fuel injection amount Tp which are the parameters of the engine operating state. The target air-fuel ratio λ _tg corresponding to Tp and is searched. The target air-fuel ratio λ _tg is set to the theoretical air-fuel ratio in the low / medium rotation / low / medium load region, and is set to the rich side in the high rotation / high load region.

Then the deviation (error amount) from the target air-fuel ratio lambda _tg of the air-fuel ratio lambda proceeds to step 8 to calculate the E = λ-λ _tg. The step 8 corresponds to deviation calculating means.

Next, the _routine proceeds to step 9, where the previous air-fuel ratio λ _oLd is subtracted from the current air-fuel ratio λ and the change amount of the air-fuel ratio per unit rotation or unit time, that is, the differential value (change speed) Δ of the air-fuel ratio.
_Calculate E = λ−λ _oLd . The step 9 corresponds to the differential value calculating means.

Next, in step 10, the deviation E and the differential value ΔE are converted into step values (fuzzy numbers) with reference to the maps of FIGS. 5 and 6, respectively. The step 10 corresponds to the step value conversion means.

That is, as for the deviation E, as shown in FIG. 5, the maximum positive value PB, positive intermediate value PM, positive minimum value PS, zero 0, negative minimum value NS, negative intermediate value NM, negative maximum value The value NB is converted into a value in seven steps, and the differential value ΔE is also converted into a value in the same seven steps as shown in FIG.

Next, in step 11, the feedback correction coefficient LAMBDA of the feedback correction coefficient LAMBDA is determined with reference to the map of FIG. 7 in which the step value (fuzzy amount U) of the feedback correction coefficient LAMBDA is determined for each step value of the deviation E and the differential value ΔE. Set a step value (fuzzy amount U). The step 11 corresponds to the air-fuel ratio feedback correction coefficient step value setting means.

When setting the feedback correction coefficient LAMBDA here, so-called fuzzy inference is applied and the fuzzy amount U in that case is calculated.

Fuzzy reasoning (control) is simply described, for example, considering the certainty (fuzzy amount) of a proposition such as making the manipulated variable (control amount) positive or negative with respect to the input amount (detected value),
The operation amount is set by weighting the fuzzy amount.

As a method of setting the fuzzy amount, there is a complicated one in which the fuzzy amount is set for each one step or two steps of the control deviation, and the fuzzy amount is obtained collectively from each fuzzy amount. As a simple method, the differential value ΔE is weighted with the deviation E taken into account
A fuzzy amount U is set as shown in the figure.

That is, when the differential value ΔE corresponding to the change speed of the air-fuel ratio is a large positive value, that is, when the change in the air-fuel ratio in the rich direction is large, it is possible to prevent the air-fuel ratio from becoming excessively rich due to overshoot. Therefore, the feedback correction coefficient LAMBDA should be made small in order to control the air-fuel ratio in the lean direction. However, even if the differential value ΔE is a large positive value, the feedback correction coefficient LAMBDA should be small when the deviation E of the air-fuel ratio from the target air-fuel ratio is a large positive value, that is, when the air-fuel ratio is rich. However, when the deviation E is a large negative value, that is, when the air-fuel ratio is lean, the feedback correction coefficient LAMBDA should not be made too small.

Therefore, the positive value of the fuzzy amount U is made to correspond to the increase setting of the feedback correction coefficient LAMBDA in the rich direction, and the negative value is made to correspond to the decrease setting of the feedback correction coefficient LAMBDA in the lean direction, and the magnitudes of the absolute values are changed. Corresponding to the certainty of the increase / decrease setting, the larger the positive value of ΔE and the larger the positive value of E, the larger the fuzzy amount U becomes with a negative value, and the larger ΔE becomes with a negative value. The larger the value of E and the more negative the value of E, the larger the value of fuzzy U becomes.

In the case of the fuzzy amount U, the maximum positive value is the same as E and ΔE.
Set in 7 steps from PB to maximum negative value NB.

Next, in step 12, the value of the feedback correction coefficient LAMBDA is set corresponding to the step value of the fuzzy amount U
Set the feedback correction coefficient LAMBDA by referring to the map in the figure. The part of step 12 corresponds to the air-fuel ratio feedback correction coefficient setting means.

That is, as shown in FIG. 8, the larger the fuzzy amount U is, the larger the feedback correction coefficient LAMBDA is (for example, PB → 1.10, PM → 1.05). When the fuzzy amount U = 0, LAMBDA = The feedback correction coefficient LAMBDA is set to be smaller as the fuzzy amount U becomes a negative value and becomes larger (for example, NB → 0.09, NM → 0.95).

Note that FIG. 9 shows how the feedback correction coefficient LAMBDA is set.

After setting the feedback correction coefficient LAMBDA in this way, in step 13, the voltage correction amount Ts is set based on the battery voltage. This is for correcting a change in the injection flow rate of the fuel injection valve 6 due to a change in the battery voltage.

Then, in step 14, the fuel injection amount Ti is calculated according to the following equation. The part of step 14 corresponds to the fuel injection amount calculation means.

Ti = Tp / COEF / LAMBDA + Ts When the fuel injection amount Ti is calculated in this way, this is set in the output register, and when the fuel injection timing in synchronization with the predetermined engine speed is reached, the Ti A drive pulse signal having a pulse width is output to the fuel injection valve 6 to inject fuel.

In such fuel injection control, in the air-fuel ratio feedback control, the feedback correction coefficient LAMBDA is based on the deviation E of the air-fuel ratio from the target air-fuel ratio and the differential value (change speed) ΔE of the air-fuel ratio, that is, the change state of the air-fuel ratio. Since it can be predicted and set, the convergence of the air-fuel ratio to the target air-fuel ratio is improved, hunting due to poor control is prevented, surge torque is reduced, operability is improved, and exhaust purification performance is improved. it can.

Next, an example in which the oxygen sensor 16 is changed will be described.

As proposed in Japanese Patent Application No. 62-65844, titanium oxide (TiO ₂ ) or lanthanum oxide (La
₂ O ₃ ) as a carrier to form a NO _x reduction catalyst layer on which a NO _x reduction catalyst such as rhodium (Rh) or ruthenium (Ru) is supported.

Then, when the NO _x concentration in the exhaust gas is high, this high concentration of NO _x is reduced and O ₂ is generated, so that the oxygen concentration including O ₂ obtained by the reduction of this NO _x is detected. As a result, as shown in FIG. 10 (a), the output characteristic of the oxygen sensor shifts to the rich side as compared with the oxygen sensor having no NO _x reduction function.

However, the output characteristic shown in FIG. 10 (a) is an apparent characteristic when the output of the oxygen sensor having no NO _x reduction function is used as a reference.

Considering from the viewpoint of the true oxygen concentration of the exhaust gas, since this is what should be detected including the oxygen content contained in the NO _x, the oxygen sensor having no _the NO _x reduction function, NO _x in the exhaust When the concentration is high, the oxygen content in this NO _x is not detected as the oxygen concentration, and the oxygen concentration is detected as low even when the lean air-fuel mixture that originally has high oxygen concentration is burned, and the output characteristics of the oxygen sensor are As shown by the broken line in FIG. 10 (b), the true stoichiometric air-fuel ratio deviates to the lean side depending on the NO _x concentration. Therefore, when the NO _x concentration is high, the air-fuel ratio is controlled to be leaner than the true stoichiometric air-fuel ratio, further increasing the NO _x concentration.

On the other hand, if the oxygen sensor has a NO _x reducing function, it is possible to detect the true oxygen concentration including the oxygen content in NO _x . Therefore, as shown by the solid line in FIG. ,
The true theoretical air-fuel ratio can be detected regardless of the NO _x concentration, and by performing air-fuel ratio feedback control according to the output voltage of the oxygen sensor, the theoretical air-fuel ratio can be calculated without being affected by the NO _x concentration in the exhaust gas. The air-fuel ratio can be controlled, and the NO _x emission amount can be greatly reduced. Further, since the EGR can be abolished due to the NO _x reduction effect, CO and HC emissions can also be reduced.

In addition, if the NO _x reduction catalyst layer is provided in the tilted oxygen sensor and this control is performed, the convergence to the stoichiometric air-fuel ratio is improved, so that the NO _x reduction effect can be more exerted.

However, not only the tilt-type oxygen sensor but also a normal on-off type oxygen sensor having an output characteristic as shown in FIG. 11 or NO _{x in} this normal on-off type oxygen sensor.
This control can be performed by using a catalyst provided with a reduction catalyst layer and having an output characteristic in which the output voltage is inverted with the true stoichiometric air-fuel ratio as a boundary even when the NO _x concentration increases.

Figure 12 shows an on-off type oxygen sensor or NO
₇ shows a fuel injection amount calculation routine when an oxygen sensor provided with an _x reduction catalyst layer is used.

The difference is that the deviation E is the output voltage V _{02 of the} oxygen sensor.
_Is obtained by subtracting the slice level voltage SL (for example, 500 mV), and the differential value ΔE is obtained by subtracting the previous output voltage V _02oLd from the present output voltage V ₀₂ .

<Effects of the Invention> As described above, according to the present invention, feedback control is performed while predicting the air-fuel ratio change based on the deviation of the detected air-fuel ratio from the target air-fuel ratio and the differential value of the detected air-fuel ratio. By doing so, it is possible to obtain an effect that the convergence to the target air-fuel ratio can be enhanced, the driveability can be improved by reducing the surge torque, and the exhaust gas purification performance can be improved. Further, when setting the air-fuel ratio feedback correction coefficient based on the deviation and the differential value, each step value of the deviation and the differential value is obtained, and the step of the feedback correction coefficient is obtained by referring to the map from these step values. Since the value is obtained and the feedback correction coefficient is set corresponding to this step value, there is an advantage that integration control and the like are not necessary and the control can be simplified.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing the configuration of the present invention, FIG. 2 is a system diagram showing an embodiment of the present invention, FIG. 3 is an output voltage characteristic diagram of an oxygen sensor, and FIG. 4 is a fuel injection amount calculation routine. 5 to 8 are diagrams showing maps used in the same routine, FIG. 9 is a diagram showing how a feedback correction coefficient is set, and FIGS. 10 (a), (b) and 11 are shown. FIG. 12 is an output voltage characteristic diagram of an oxygen sensor shown as another embodiment, FIG. 12 is a flowchart of a fuel injection amount calculation routine shown as another embodiment, and FIG. 13 is a diagram showing how a feedback correction coefficient is conventionally set. Is. 1 ... Engine, 6 ... Fuel injection valve, 12 ... Control unit, 13 ... Air flow meter, 14 ... Crank angle sensor, 16 ... Oxygen sensor

Claims (1)

(57) [Claims] 1. An engine operating state detecting means for detecting an engine operating state, a basic fuel injection amount setting means for setting a basic fuel injection amount based on the detected engine operating state, and an engine exhaust gas component for detecting the engine exhaust component. Air-fuel ratio detecting means for detecting the air-fuel ratio of the air-fuel mixture sucked into the engine, deviation calculating means for calculating the deviation of the detected air-fuel ratio from the target air-fuel ratio, and calculating the differential value of the detected air-fuel ratio Differential value calculation means, step value conversion means for converting the deviation and the differential value into step values according to their magnitudes, and feedback corresponding to the step value of the deviation and the step value of the differential value Feedback correction coefficient step value setting means for setting a feedback correction coefficient step value with reference to a map that defines correction coefficient step values, and the base corresponding to the feedback correction coefficient step value. Feedback correction coefficient setting means for setting a feedback correction coefficient for feedback-correcting the main fuel injection amount; basic fuel injection amount set by the basic fuel injection amount setting means; and feedback correction coefficient set by the feedback correction coefficient setting means And a fuel injection amount calculation means for calculating a fuel injection amount based on the above, and a fuel injection means for injecting and supplying fuel to the engine on and off by a drive pulse signal corresponding to the calculated fuel injection amount. An air-fuel ratio control device for an internal combustion engine, comprising: