JPH11343903A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately control an air-fuel ratio, regardless of environmental changes, by detecting an injection coefficient when an ion current value becomes maximum by increasing or decreasing the injection coefficient, learning this injection coefficient as a reference injection coefficient corresponding to a specified air-fuel ratio and controlling fuel injection amount based on the learned injection coefficient. SOLUTION: At the time of a stationary traveling state, an average value I1 of an ion output detected in an ion current detection circuit 110 for every combustion of a prescribed number of times is calculated and an average value I2 of the ion output is calculated by increasing the present injection coefficient KIN1 by a prescribed value. When increased amount 'I2 -I1 ' of an ion output average value is larger than a decision reference value ΔIREF, an ion output I2 is newly stored as I1 . When 'I2 -I1 ' is smaller than the decision reference value ΔIREF, whether decreased amount 'I2 -I1 ' of the ion output average value is larger than the decision reference value ΔIREF or not is decided. When decreased amount 'I2 -I1 ' is larger, the ion output I2 is newly stored as I1 , next, the injection coefficient KINI is reduced by the prescribed value, an average value of the ion output is calculated and the value is determined for I2 . When the decreased amount 'I2 -I1 ' is smaller, the present injection coefficient KIK1 is stored as a reference injection coefficient KIN1 REF.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for controlling an air-fuel ratio based on an ionic current flowing according to an amount of ions generated by combustion in a cylinder of an internal combustion engine.

[0002]

2. Description of the Related Art As one of methods for detecting the air-fuel ratio of an internal combustion engine, a method has been proposed in which an ion current corresponding to the amount of ions generated in a cylinder is measured, and the air-fuel ratio is detected based on the ion current. I have. That is, when a discharge is caused by the ignition plug and the air-fuel mixture in the cylinder burns, the air-fuel mixture is ionized. When a voltage is applied to the ignition plug while the mixture is in an ionized state, an ionic current flows. This ion current can be detected, and the air-fuel ratio can be detected based on the current value.

For example, Japanese Patent Application Laid-Open No. Hei 7-19151 stores a characteristic diagram showing a relationship between an ion current value and an air-fuel ratio as a map, and refers to the map based on the detected ion current value to obtain an air-fuel ratio. An apparatus for calculating a fuel ratio is disclosed. The air-fuel ratio can be controlled by detecting the air-fuel ratio using such a device and adjusting the amount of fuel supplied to the engine based on the detected air-fuel ratio.

[0004]

Considering the relationship between the ion current value and the air-fuel ratio, the environmental conditions such as humidity change and the ignition plug change even when the air-fuel ratio of the air-fuel mixture to be burned is the same. Or the ion current value changes. Therefore, when trying to accurately control the air-fuel ratio based on the ionic current, it is necessary to consider the degree of influence of all other factors that change the ionic current. However, it is practically difficult to perform the air-fuel ratio control based on the ion current while taking such consideration into account.

In view of the above problems, an object of the present invention is to provide an air-fuel ratio control device based on ion current, which can accurately control the air-fuel ratio regardless of changes in environmental conditions, deterioration of a spark plug, and the like. Is to provide.

[0006]

According to the present invention, there is provided an ion current detecting apparatus for detecting an ion current corresponding to an amount of ions generated by burning an air-fuel mixture in a cylinder of an internal combustion engine. Detecting means, by increasing or decreasing the injection coefficient, which is a coefficient when calculating the injection amount from the air amount, to detect the injection coefficient when the ion current value detected by the ion current detection means is maximum, Reference injection coefficient learning means for learning the detected injection coefficient as a reference injection coefficient corresponding to a specific air-fuel ratio, and injection control means for controlling the fuel injection amount based on the reference injection coefficient learned by the reference injection coefficient learning means And comprising:
An air-fuel ratio control device for an internal combustion engine is provided.

According to the present invention, preferably, the injection control means achieves the target air-fuel ratio based on a target air-fuel ratio according to an engine operating state, the specific air-fuel ratio, and the reference injection coefficient. The fuel injection amount is calculated by multiplying the calculated injection coefficient and the air amount.

[0008]

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

FIG. 1 is an overall schematic diagram of an electronically controlled internal combustion engine provided with an air-fuel ratio control device according to the present invention. The internal combustion engine 1 is an in-line multi-cylinder four-stroke cycle reciprocating gasoline engine mounted on a vehicle. The engine 1 includes a cylinder block 2 and a cylinder head 3. In the cylinder block 2, a plurality of cylinders 4 extending in the up-down direction are arranged side by side in the thickness direction of the paper surface, and a piston 5 is accommodated in each cylinder 4 so as to be reciprocable. Each piston 5
It is connected to a common crankshaft 7 via a connecting rod 6. The reciprocating motion of each piston 5 is converted into a rotational motion of a crankshaft 7 via a connecting rod 6.

[0010] Between the cylinder block 2 and the cylinder head 3, a combustion chamber 8 is provided above each piston 5. The cylinder head 3 is provided with an intake port 9 and an exhaust port 10 for communicating both outer surfaces thereof with the respective combustion chambers 8. In order to open and close these ports 9 and 10, an intake valve 11 and an exhaust valve 12 are supported on the cylinder head 3 so as to be able to reciprocate substantially vertically. In the cylinder head 3,
Above each valve 11, 12, an intake side camshaft 1 is provided.
3 and the exhaust-side camshaft 14 are provided rotatably. Cams 15 and 16 for driving the valves 11 and 12 are attached to the camshafts 13 and 14, respectively. Timing pulleys 17 and 18 provided at ends of the camshafts 13 and 14 are connected to a timing pulley 19 provided at an end of the crankshaft 7 by a timing belt 20.

The intake port 9 is connected to an intake passage 30 having an air cleaner 31, a throttle valve 32, a surge tank 33, an intake manifold 34 and the like. Air (outside air) outside the engine 1 is supplied to the intake passage 3 toward the combustion chamber 8.
0 sequentially passes through the respective parts 31, 32, 33 and 34. An idle adjustment passage 35 that bypasses the throttle valve 32 is provided with an idle rotation speed control valve (ISCV) 36 for adjusting the air flow during idling. Each intake port 9 is provided in the intake manifold 34.
An injector 40 for injecting fuel toward is mounted. The fuel is stored in a fuel tank 41, from which the fuel is pumped by a fuel pump 42, and a fuel pipe 4
3 and is supplied to the injector 40. Then, a mixture of fuel injected from the injector 40 and air flowing in the intake passage 30 is introduced into the combustion chamber 8 via the intake valve 11.

In order to ignite this mixture, an ignition plug 50 is attached to the cylinder head 3. At the time of ignition, the igniter 51 that has received the ignition signal controls the supply and cutoff of the primary current of the ignition coil 52, and the secondary current is supplied to the ignition plug 5 via the ignition distributor 53.
0 is supplied.

The burned air-fuel mixture is guided to the exhaust port 10 via the exhaust valve 12 as exhaust gas. The exhaust port 10 has an exhaust manifold 61 and a catalytic converter 62.
The exhaust passage 60 provided with the above is connected. HC (hydrocarbon), which is an incomplete combustion component, is supplied to the catalytic converter 62.
And a three-way catalyst that simultaneously promotes the oxidation of CO (carbon monoxide) and the reduction of NO _x (nitrogen oxide) generated by the reaction of nitrogen in the air with unburned oxygen. . The exhaust gas thus purified in the catalytic converter 62 is discharged into the atmosphere.

Various sensors are attached to the engine 1. A water temperature sensor 74 for detecting the temperature of the cooling water of the engine 1 is attached to the cylinder block 2. An air flow meter 70 for detecting an intake air flow rate is attached to the intake passage 30. An intake air temperature sensor 73 for detecting the temperature of the intake air is attached near the air cleaner 31 in the intake passage 30.
In the intake passage 30, near the throttle valve 32, a throttle opening sensor 72 for detecting the rotation angle of the shaft is provided. When the throttle valve 32 is in the fully closed state, the idle switch 82 is turned on, and the throttle fully closed signal output from the idle switch 82 becomes active. The surge tank 33 is provided with a vacuum sensor 71 for detecting an internal pressure (intake pressure). An O ₂ sensor 75 for detecting whether the air-fuel ratio of the exhaust gas is rich or lean with respect to the stoichiometric air-fuel ratio is attached to a portion of the exhaust passage 60 upstream of the catalytic converter 62.

The distributor 53 incorporates two rotors that rotate in synchronization with the rotation of the crankshaft 7, and detects the crank angle based on the rotation of one of the rotors to detect the reference position of the crankshaft 7. (C
A) is provided with a crank reference position sensor 80 that generates a reference position detection pulse every 720 ° CA in terms of A), and detects a rotation speed of the crankshaft 7 based on the rotation of the other rotor. Crank angle sensor 81 that generates a rotation speed detection pulse for each CA
Is provided. The vehicle is provided with a vehicle speed sensor 83 that generates a number of output pulses per unit time in proportion to the rotation speed of the transmission output shaft, that is, the vehicle speed.

Engine electronic control unit (engine ECU) 90
Is a microcomputer system that executes fuel injection control, ignition timing control, idle speed control, and the like.
The ignition timing control is based on the engine speed obtained from the crank angle sensor 81 and signals from other sensors, comprehensively determines the state of the engine, determines the optimal ignition timing, and sends an ignition signal to the igniter 51. It is. The idle rotation speed control detects an idle state based on a throttle fully-closed signal from an idle switch 82 and a vehicle speed signal from a vehicle speed sensor 83, and detects a target rotation speed determined by a coolant temperature from a water temperature sensor 74 and an actual rotation speed. The engine speed is compared with the engine speed, the control amount is determined so as to be the target speed in accordance with the difference, and the ISCV 36 is controlled to adjust the air amount, thereby maintaining the optimum idle speed. .

In the fuel injection control, basically, based on the intake air amount of the engine, a fuel injection amount for achieving a predetermined target air-fuel ratio, that is, an injection time by the injector 40 is calculated, and a predetermined crank angle is calculated. At this time, the injector 40 is controlled to inject the fuel. In addition,
The intake air amount of the engine is calculated from the intake air flow rate measured by the air flow meter 70 and the engine rotation speed obtained from the crank angle sensor 81, or the intake pipe pressure and the engine rotation speed obtained from the vacuum sensor 71. Is estimated by Then, air applied when the fuel injection amount calculation is based on the signal from the basic correction, O ₂ sensor 75 based on signals from various sensors such as the throttle opening sensor 72, intake air temperature sensor 73, coolant temperature sensor 74 Fuel ratio feedback correction, etc. are added.

The engine 1 also includes an ion current detection circuit 110 for performing rough air-fuel ratio control based on ions generated in the cylinder after combustion.
Is provided. FIG. 2 is a diagram showing a circuit configuration of the ignition device and the ion current detection circuit 110. Ignition coil 5
One end of the second primary winding 52a is connected to the positive electrode of the battery 100, and the other end is connected to the collector of the switching transistor 51a in the igniter 51. The emitter of the transistor 51a is grounded, and an ignition signal is applied to its base. One end of the secondary winding 52b of the ignition coil 52 is connected to the cathode of the diode 112. Diode 1
The anode 12 is connected to the center electrode 50a of the ignition plug 50 via the distributor 53. The outer electrode 50b of the spark plug 50 is grounded.

The diode 112 and the distributor 5
3 is connected to a diode 114 and a constant voltage power supply 116.
And an ion current detection resistor 118. Therefore, a constant voltage is always applied to the ignition plug 50 by the constant voltage power supply 116. A connection point between the constant voltage power supply 116 and the ion current detection resistor 118 gives an output (voltage signal) of the ion current detection circuit 110. Then, the output of the ion current detection circuit is guided to the engine ECU 90.

Next, an ignition device and an ion current detection circuit 1
The operation of No. 10 will be described. First, when the ignition signal becomes high and the transistor 51a is turned on, a current flows through the primary winding 52a of the ignition coil. Next, when the ignition signal is turned low and the transistor 51a is turned off to cut off the primary current, the secondary winding 5 of the ignition coil 52 is turned off.
A high voltage is induced in 2b, and as a result, a spark discharge occurs in the spark plug 50. That is, when a negative high voltage is applied to the center electrode 50a of the ignition plug 50, spark discharge occurs between the center electrode 50a and the outer electrode (ground electrode) 50b, and the ignition coil secondary winding 52b A current circulates through the ignition plug 50 and the diode 112 to the secondary winding 52b.

The spark discharge at the spark plug 50 causes
When the mixture in the combustion chamber ignites and burns, the mixture is ionized. When the air-fuel mixture is in an ionized state, there is conductivity between both electrodes of the ignition plug 50. In addition, since a voltage is always applied between both electrodes of the ignition plug 50 by the constant voltage power supply 116, an ionic current flows. That is, the ion current is supplied to the constant voltage power supply 116.
From the positive terminal through the ion current detection resistor 118, the ignition plug 50 and the diode 114,
To the negative terminal of Then, the ion current detection resistor 11
8 and the constant voltage power supply 116 have a connection point of “ion current value ×
A voltage of "detection resistance value" appears, and the voltage is supplied to the ECU 90 as an output of the ion current detection circuit.

Note that, even in the same combustion state, the peak value of the output voltage of the ion current detection circuit (hereinafter, simply referred to as ion output) varies for each combustion. However, when the ion output is measured for a certain number of times of combustion in the same combustion state and the average value is obtained, the average value has a certain correlation with the air-fuel ratio.

FIG. 3 is a characteristic diagram showing the relationship between the air-fuel ratio and the average value of ion output over a predetermined number of times. As shown in this figure, the ion output average value becomes maximum near the output air-fuel ratio (the weight ratio of air and fuel (about 12.5) at which the output becomes maximum), and the air-fuel ratio leaner than that also occurs. There is also a tendency for the air-fuel ratio on the rich side to decrease.

By the way, as described above, when environmental conditions such as humidity change or the spark plug deteriorates, the ion output average value changes as shown in FIG. Therefore, when the air-fuel ratio is determined from the ion output average value with reference to the map shown in FIG. 3 when the environment changes or the plug is deteriorated, the detected air-fuel ratio is deviated from the true air-fuel ratio. Becomes

However, even if the characteristic of the ion output average value with respect to the air-fuel ratio changes, the ion output average value has the maximum value near the output air-fuel ratio. That is, the change in the ion output characteristic that occurs when the environment changes or when the plug is deteriorated is a quantitative change, not a qualitative change. From such knowledge, the present invention realizes the air-fuel ratio control based on the ion current as follows.

Generally, the fuel injection amount (mass) is determined according to the amount of air (mass) sucked into the cylinder, and its coefficient is called an injection coefficient. That is, the fuel injection amount G _{FI NJ,} cylinder air amount G _ACYL, the injection coefficient K _INJ
Then, it is represented as G _FINJ ← K _INJ * G _ACYL . Then, the air-fuel ratio of the engine is changed by changing the injection coefficient K _INJ to achieve the target air-fuel ratio.

[0027] Here, the injection coefficient K _INJ when ion output is maximized by allowed to increase or decrease the injection coefficient K _INJ
Is detected, the injection coefficient K _INJ is an injection coefficient that achieves a specific air-fuel ratio, that is, an output air-fuel ratio of 12.5, irrespective of environmental changes and plug deterioration, as shown in FIG. Therefore, in the present invention, first, an injection coefficient that achieves an output air-fuel ratio of 12.5 is obtained from a change in the ion output, and is set as a reference injection coefficient K _INJREF . Next, the target air-fuel ratio R
_{Based on the AFTGT} , the output air-fuel ratio 12.5, and the reference injection coefficient K _{IN JREF} , an injection coefficient K _INJ that achieves the target air-fuel ratio R _AFTGT is calculated. For example, according to the definition of the injection coefficient, the air-fuel ratio and the injection coefficient are regarded as having an inversely proportional relationship, and the target air-fuel ratio R _{AFTGT is} calculated by the following calculation: K _INJ ← K _INJREF * (12.5 / _RAFTGT ) it can be obtained an injection coefficient K _INJ to achieve.

FIG. 5 is a flowchart of a process for learning the reference injection coefficient K _INJREF and _embodies the above description. This learning process is preferably executed once when the vehicle is in a steady running state. First, in step 202, it calculates the average value of the ion output detected for each combustion over the combustion of a predetermined number of times (e.g. 64 times) to it as I _1. Next, at step 204, the current injection coefficient K _{IN J} is increased by a predetermined value ΔK. Then, in step 206, as in step 202, calculates the average value of the detected ion output for each combustion over the combustion of a predetermined number of times, that it with I _2.

[0029] In step 208, increase the amount of ion output average value due to the increased injection coefficient K _INJ "I ₂ -
It is determined whether or not “I ₁ ” is greater than a predetermined determination reference value ΔI _REF . When “I ₂ −I ₁ > ΔI _REF ”, that is, it is determined that the air-fuel ratio is leaner than the vicinity of the output air-fuel ratio 12.5. If so, step 210 replaces I ₂ with a new I ₂
After storing as ₁ , the process loops back to step 204.

On the other hand, in step 208, "I ₂ -I
When it is determined that ₁ ≦ ΔI _REF ”, step 212
Then, it is determined whether or not the decrease amount “I ₁ −I ₂ ” of the ion output average value is larger than a predetermined determination reference value ΔI _REF .
When “I ₁ −I ₂ > ΔI _REF ”, that is, when it is determined that the air-fuel ratio is on the rich side from the vicinity of the output air-fuel ratio of 12.5, the process proceeds to step 214, and I ₂ is newly stored as I ₁ . Next, at step 216, the current injection coefficient K _INJ is reduced by a predetermined value ΔK. Then, in step 218, calculates the average value of the ion output detected for each combustion over the combustion of a predetermined number of times, it was the I _2, it loops back to step 212.

In step 212, "I ₁ -I ₂ ≤Δ
When it is determined to be I _REF ”, the current injection coefficient K _INJ
It is determined that the air-fuel ratio of about 12.5 has been achieved. Therefore, the _routine proceeds to step 220, where the current injection coefficient K _INJ is stored as the reference injection coefficient K _INJREF . With the above processing, the learning processing of the reference injection coefficient K _INJREF is completed.

FIG. 6 is a flowchart of a fuel injection amount calculation process in the case where the air-fuel ratio control based on the ion current is performed. First, in step 302, a current engine operating state is detected from outputs from various sensors. Next, at step 304, based on the detected operation state, the amount of air G _ACYL drawn into the cylinder during the intake stroke is calculated. In step 306, the target air-fuel ratio R _{AFTG T} is determined based on the detected operating state. Next, at step 308, as described above, the injection coefficient K _INJ that achieves the target air-fuel ratio R _AFTGT is obtained by the calculation of, for example, K _INJ ← K _INJREF * (12.5 / _RAFTGT ). Finally, at step 310, the fuel injection amount G _FINJ is determined by the calculation G _FINJ ← K _INJ * G _ACYL .

Although the embodiment of the present invention has been described above, the present invention is not limited to this, and various embodiments can be adopted. For example, various circuit configurations can be considered as the ion current detection circuit. Further, the method of calculating the injection coefficient that achieves the target air-fuel ratio using the output air-fuel ratio and the reference injection coefficient that achieves the output air-fuel ratio is not limited to the above-described arithmetic expression.

[0034]

As described above, according to the present invention,
In the air-fuel ratio control device based on the ionic current, the air-fuel ratio can be accurately controlled regardless of changes in environmental conditions, deterioration of the spark plug, and the like.

[Brief description of the drawings]

FIG. 1 is an overall schematic diagram of an electronically controlled internal combustion engine including an air-fuel ratio control device according to one embodiment of the present invention.

FIG. 2 is a diagram showing a circuit configuration of an ignition device and an ion current detection circuit.

FIG. 3 is a characteristic diagram illustrating a relationship between an air-fuel ratio and an average value of a peak value (ion output) of an output voltage of an ion current detection circuit.

FIG. 4 is a diagram for explaining how the characteristics of the average ion output value with respect to the air-fuel ratio change due to environmental changes, plug deterioration, and the like.

FIG. 5 is a flowchart of a process for learning a reference injection coefficient K _INJREF .

FIG. 6 is a flowchart of a fuel injection amount calculation process when performing air-fuel ratio control based on ion current.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... In-line multi-cylinder 4-stroke cycle reciprocating gasoline engine 2 ... Cylinder block 3 ... Cylinder head 4 ... Cylinder 5 ... Piston 6 ... Connecting rod 7 ... Crankshaft 8 ... Combustion chamber 9 ... Intake port 10 ... Exhaust port 11 ... Intake valve 12 ... Exhaust valve 13 ... Intake side camshaft 14 ... Exhaust side camshaft 15 ... Intake side cam 16 ... Exhaust side cam 17,18,19 ... Timing pulley 20 ... Timing belt 30 ... Intake passage 31 ... Air cleaner 32 ... Throttle valve 33 ... Surge tank 34 Intake manifold 35 Idle adjust passage 36 Idle speed control valve (ISCV) 40 Injector 41 Fuel tank 42 Fuel pump 43 Fuel pipe 50 Spark plug 51 Igniter 52 Ignition coil 53 Ignition distributor 60 ... exhaust passage 61 ... exhaust manifold 62 ... catalytic converter 70 ... air flow meter 71 ... vacuum sensor 72 ... Throttle opening sensor 73 ... intake air temperature sensor 74 ... water temperature sensor 75 ... O ₂ sensor 80 ... crank reference position sensor 81 ... Crank angle sensor 82 Idle switch 83 Vehicle speed sensor 90 Engine ECU 100 Battery 110 Ion current detection circuit

Claims (2)

[Claims] An ion current detecting means for detecting an ion current according to an amount of ions generated by combustion of an air-fuel mixture in a cylinder of an internal combustion engine, and an injection which is a coefficient for calculating an injection amount from an air amount. By increasing or decreasing the coefficient, the injection coefficient at which the ion current value detected by the ion current detection means becomes maximum is detected, and the detected injection coefficient is learned as a reference injection coefficient corresponding to a specific air-fuel ratio. An air-fuel ratio control device for an internal combustion engine, comprising: a reference injection coefficient learning unit; and an injection control unit that controls a fuel injection amount based on a reference injection coefficient learned by the reference injection coefficient learning unit. 2. The injection control means calculates an injection coefficient for achieving the target air-fuel ratio based on a target air-fuel ratio according to an engine operating state, the specific air-fuel ratio, and the reference injection coefficient. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the fuel is injected at an injection amount obtained by multiplying the obtained injection coefficient by the air amount.