JPH11336650A - Combustion state detecting device for internal combustion engine, and control device for the engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the combustion state of an internal combustion engine with simple circuit constitution by providing a current discriminating means for discriminating whether or not an ion current detected by an ion current detecting means is the reference value or less. SOLUTION: A mixture comprising fuel injected from an injector 40, and air flowing in an intake passage 30, is led into a combustion chamber 8 through an intake valve 11. When igniting, an igniter 51 controls the application and cut-off of a primary current of an ignition coil 52, and a secondary current is supplied to a spark plug 50 through an ignition distributor 53. An engine electronic control unit 90 executes fuel injection control, ignition timing control, idling speed control and the like. An engine 1 is provided with an ion current detecting circuit 130 for detecting a combustion state on the basis of ion generated in a cylinder after combustion. The combustion state of the internal combustion engine can thus be detected with simple circuit constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting a combustion state of an internal combustion engine based on ions generated in a cylinder, and a control device for the internal combustion engine using the same.

[0002]

2. Description of the Related Art As one method of detecting the combustion state 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 combustion state is detected based on the ion current. I have. That is, when discharge occurs by the spark plug and the air-fuel mixture in the cylinder burns,
The mixture is ionized. When a voltage is applied to the ignition plug while the mixture is in an ionized state, an ionic current flows. The combustion state can be detected by detecting the ion current and performing an analysis process.

For example, Japanese Patent Application Laid-Open No. 4-308360 discloses that an output voltage of an ion current detection circuit is led to an integration circuit or a peak hold circuit to obtain an integrated value or a peak value, and a combustion state is determined based on the integrated value or the peak value. An apparatus for detecting is disclosed.

[0004]

However, when trying to find the integrated value or peak value of the output voltage of the ion current detection circuit as described above, it is necessary to widen the dynamic range of the processing circuit, and the circuit configuration is complicated. Problem arises.

In view of the above problems, an object of the present invention is to provide a combustion state detecting device for an internal combustion engine which realizes a combustion state detection based on an ion current with a simple circuit configuration. A further object of the present invention is to provide a control device for an internal combustion engine using the combustion state detecting device.

[0006]

In order to achieve the above object, according to a first aspect of the present invention, an ionic current corresponding to an amount of ions generated by combustion of an air-fuel mixture in a cylinder of an internal combustion engine is provided. Current detection means for detecting the ion current, current value determination means for determining whether or not the value of the ion current detected by the ion current detection means is equal to or less than a reference value, and ion current determination means for a predetermined number of combustions Combustion of an internal combustion engine, comprising: counting means for counting the number of times of combustion in which the current value is determined to be equal to or less than the reference value; and combustion determination means for determining a combustion state based on the number of times counted by the counting means. A state detection device is provided.

[0007] According to a second aspect of the present invention, in the combustion state detecting device according to the first aspect, the combustion judging means determines that the number of times counted by the counting means is larger than a predetermined value. It is determined that the combustion is poor.

Further, according to a third aspect of the present invention, in the combustion state detecting device according to the first aspect, the reference value used in the current value determining means is changed according to the engine speed. .

According to a fourth aspect of the present invention, in the combustion state detecting device according to the third aspect, the reference value used in the current value discriminating means is set to a larger value as the engine speed increases. Is changed to

[0010] According to a fifth aspect of the present invention, in the combustion state detecting device according to the first aspect, the determination process by the combustion determination means is executed during a cold first idling, and the property of the fuel is detected. Is done.

According to a sixth aspect of the present invention, there is provided the combustion state detecting device according to any one of the first to fifth aspects, and the combustion state detecting device detects the combustion state. A control device for an internal combustion engine, comprising: a fuel injection control unit that corrects a fuel injection amount according to a combustion state.

[0012]

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 a combustion state detecting 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
Are connected to a common crankshaft 7 via a connecting rod 6. The reciprocating motion of each piston 5 is
The rotational motion of the crankshaft 7 is converted through the connecting rod 6.

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.

To ignite this mixture, an ignition plug 50 is mounted on 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 an exhaust port 10 via an 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.

The engine 1 is provided with various sensors. 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. An intake pressure sensor 71 for detecting the internal pressure (intake pressure) is attached to the surge tank 33. 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 which 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), a crank reference position sensor 80 for generating a reference position detection pulse every 720 ° CA is provided, and the other rotor is used to detect the rotation speed of the crankshaft 7 (engine rotation speed NE). A crank angle sensor 81 that generates a rotation speed detection pulse every 30 ° CA based on the rotation of the crankshaft 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,
Signals from various sensors and switches are input, arithmetic processing is performed based on the input signals, and control signals for various actuators are output based on the arithmetic results. 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 a cold state, the viscosity of the engine oil increases and the friction torque increases. Therefore, the intake air amount is set to be larger than that after warm-up, and the first idle rotation speed is set.

The fuel injection control basically calculates a fuel injection amount for achieving a predetermined target air-fuel ratio, that is, an injection time by the injector 40, based on an intake air amount per one revolution of the engine, and calculates a predetermined time. The injector 40 is controlled to inject fuel when the crank angle is reached. The amount of intake air per one revolution of the engine is calculated from the intake air flow rate measured by the air flow meter 70 and the engine speed obtained from the crank angle sensor 81, or the intake pipe obtained from the intake pressure sensor 71. Estimated by pressure and engine speed. When the fuel injection amount is calculated, the throttle opening sensor 72,
Basic correction based on signals from the respective sensors such as the intake air temperature sensor 73 and the water temperature sensor 74, air-fuel ratio feedback correction based on a signal from the O ₂ sensor 75, and the like are added.

Further, the engine 1 is provided with an ion current detection circuit 130 for detecting a combustion state based on ions generated in the cylinder after combustion. FIG.
FIG. 2 is a diagram showing a circuit configuration of an ignition device and an ion current detection circuit 130. One end of a primary winding 52a of the ignition coil 52 is connected to a positive electrode of the battery 101, and the other end is
Switching transistor 51a in igniter 51
Connected to the collector. The transistor 51a
Are grounded, and an ignition signal is applied to their bases. One end of a secondary winding 52b of the ignition coil 52 is connected to a center electrode 50a of the ignition plug 50 via an ignition distributor 53.
The outer electrode 50b of the spark plug 50 is grounded.

At the other end of the secondary winding 52b of the ignition coil 52, an ion current detection circuit 130 is provided. First, a capacitor 131 serving as an ion current generation power supply is connected to the secondary winding 52b. This capacitor 131
Is connected in parallel with a constant voltage diode (Zener diode) 132 for limiting the voltage charged in the capacitor 131 by the ignition coil secondary current to a constant value. The other end of the capacitor 131 is grounded through a diode 133 that allows current to flow only in the ground direction, and is grounded through an ion current detection resistor 134.

The connection point between the capacitor 131 and the ion current detection resistor 134 is connected to the inverting amplifier circuit 136. The inverting amplifier circuit 136 includes an operational amplifier (op-amp) 1 having a non-inverting input terminal (+ terminal) grounded.
37, an input resistor 138 connected to the inverting input terminal (-terminal) of the operational amplifier 137, and a feedback resistor 139 from the output terminal of the operational amplifier 137 to the inverting input terminal (-terminal). Assuming that the resistance of the input resistor 138 is R _a and the resistance of the feedback resistor 19 is R _f , the voltage amplification is “−R _f / R _a ” as is well known. Then, the output of the inverting amplifier circuit 136 is supplied to the engine ECU 90 as an ion current detection circuit output (voltage signal). Note that R
_a and R _f are larger values than the resistance value R ₁ of the ion current detection resistor 14.

FIG. 3 is a time chart for explaining the operation of the ion current detection circuit 130. First,
When the ignition signal becomes high and the transistor 51a in the igniter 51 is turned on, a current flows through the ignition coil primary winding 52a. Next, when the primary current is cut off by turning off the ignition signal and turning off the transistor 51a, a high voltage is induced in the secondary winding 52b of the ignition coil 52, and as a result, the ignition plug 50 Spark discharge occurs. That is, when a high voltage of negative polarity is applied to the center electrode 50a of the ignition plug 50,
0a and the outer electrode (ground electrode) 50b, a spark discharge occurs, and the capacitor 1
31, constant voltage diode 132, diode 133,
In addition, a discharge current circulating through the ignition plug 50 to the secondary winding 52b flows. In this process, the capacitor 131 is charged to a voltage that matches the zener voltage (about 100 V) of the constant voltage diode 132.

After the end of the discharge, the ignition coil tries to release the residual magnetic energy, and the ignition coil secondary winding 52
b inductance L ₂ and LC resonance between the stray capacitance C ₂ which is formed in the high voltage line 102 occurs, the LC resonance current flows. Therefore LC resonance current detected by the ion current detecting resistor, the ion current waveform after the end of discharge, as shown in I ₁ of FIG. 3, but appears sharp change, which is the residual magnetic noise (LC Resonance noise) and not due to ion current.

[0027] Then, after the LC resonance current I ₁ due to the residual magnetic energy flows, the ion current I ₂ flows. That is, when the air-fuel mixture in the combustion chamber is ignited and burned by the spark discharge in the ignition plug 50, the air-fuel 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 applied between both electrodes of the ignition plug 50 by the charging voltage of the capacitor 131, an ionic current flows. This ionic current flows from one end of the capacitor 131 to the ignition coil secondary winding 52b, the ignition plug 50,
And the capacitor 1 via the ion current detection resistor 134.
31 to the other end. Then, the ion current detection resistor 1
A potential of “−ion current value × detection resistance value” appears at a connection point between the capacitor 34 and the capacitor 131, and the potential is inverted and amplified by the inverting amplifier circuit 136. Finally, the output of the inverting amplifier circuit 136 is used as the output of the ion current detection circuit by the ECU.
90.

By the way, 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) fluctuates for each combustion. But,
When the ion output is measured over a certain number of combustions while in the same combustion state, they show a constant distribution. FIG. 4 is a characteristic diagram showing the distribution of ion output in one good combustion state and one deteriorated combustion state, and the horizontal axis represents ion output.
The vertical axis represents frequency. As shown in this figure, when the combustion state is deteriorated (curve C ₂ ) as compared with the case where the combustion state is good (curve C ₁ ), the ion output becomes
As a whole, it is distributed on the left side, that is, on the side where the value decreases.

[0029] Therefore, as shown in FIG. 4, by detecting the frequency of ion output falls below a predetermined reference value V _R,
Better when the combustion state better than the frequency (corresponding to the area A ₁₎ (curve C _1), (corresponding to the area A ₂₎ The frequency of cases (curve C ₂₎ that the combustion state is worse growing. Therefore, in the present invention, the combustion state is detected by detecting the frequency at which the ion output becomes equal to or less than a certain reference value. In such a combustion state detection process, it is sufficient to provide only means for determining whether or not the ion output is equal to or less than the reference value. There is no need to provide a circuit for detection, and there is an effect that the circuit configuration is simplified.

In other words, when the ion output is a constant reference value V
_When the engine speed NE is constant, the frequency FRQ [%] that becomes equal to or less than _R and the air-fuel ratio A / F representing the combustion state are as follows:
There is a relationship as shown in FIG.
The air-fuel ratio A / F is determined by detecting Q. As shown in FIG. 5, as the air-fuel ratio A / F increases, the frequency FRQ also increases.
When the RQ is determined, the air-fuel ratio A / F is also uniquely determined.

By the way, even in the case of combustion at the same air-fuel ratio, when the engine rotation speed increases, the combustion speed increases, and the amount of ions instantaneously present around the spark plug also increases. growing. As a result, FIG.
The ion output distribution shown in FIG. 6 moves to the right side, that is, the side where the value increases, due to the increase in the engine rotation speed, and becomes the ion output distribution shown in FIG. That is, due to the increase in the engine speed, the curves C ₁ and C shown in FIG.
₂ correspond to the curves C ₁₁ and C ₂₂ shown in FIG. 6, respectively.
Move to.

Therefore, a map of the frequency FRQ and the air-fuel ratio A / F shown in FIG. 5 is provided for each of the plurality of engine speeds NE, that is, the air-fuel ratio A / F is obtained from the frequency FRQ and the engine speed NE. By providing a two-dimensional map, the combustion state may be detected. However, providing such a two-dimensional map increases the number of matching elements in map creation, increases the time spent for matching, and increases the processing load when the ECU performs interpolation calculation based on the map. Is not preferred. Therefore, in the present invention, as shown in FIG. 6, by increasing the determination reference value V _R in accordance with the increase in the engine speed, suffice one-dimensional map for determining the air-fuel ratio A / F from the frequency FRQ Like that. That is, in accordance with increase in engine speed, the reference value V _R shown in Figure 4 is changed to a reference value V _RR shown in FIG.

The upper graph in FIG. 7 shows the engine speed NE.
And reference value V for ion output _RAlso shows the relationship with
It is. Thus, as the engine speed NE increases,
Criterion value V_RIs increased, the lower part of FIG.
As shown in the graph, the ion output is below the judgment reference value
Frequency FRQ becomes independent of the engine speed NE.
Therefore, the amount is equivalent to the air-fuel ratio A / F.

FIG. 8 is a flowchart showing a processing procedure of a combustion state detection routine executed in the ECU 90. This routine is executed to detect the combustion state when the air-fuel ratio feedback control based on the signal from the O ₂ sensor 75 is not executed, and is started after ignition. In particular, a great effect is obtained when the process is executed to detect the fuel property during the cold first idling. That is, when heavy fuel is used, the air-fuel ratio becomes lean during cold first idling, the rotation speed decreases, and the ion output decreases. This can be used to detect the fuel properties. is there.

First, at step 202, the ignition number counter CI is incremented. Then, step 2
In 04, based on the upper graph of Figure 7, ion output determination reference value V _R corresponding to the current engine speed NE is calculated. Next, at step 206, whether the current ion output V is smaller than the reference value V _R by the combustion is determined, at the time of V <V _R proceeds to step 208, whereas,
Proceeds to step 210 when the V ≧ V _R. This determination is easily realized by a comparator provided in the ECU. In step 208, the counter CL for counting the number of combustion ions output V is smaller than the reference value V _R is incremented, the flow proceeds to step 210.

In step 210, the ignition number counter C
I is predetermined ignition count C _R (e.g., 32) whether or not reached is determined, CI <C while the routine is caused to completion when the _R, CI ≧ C step when _R 21
Proceed to 2. In step 212, during combustion over number of times of ignition CI, the frequency of combustion ion output V is less than the reference value V _R FRQ [%] is the FRQ ← 100 * CL / CI becomes operational, is calculated. In step 214, a combustion state (air-fuel ratio) is detected based on the frequency FRQ, and a correction coefficient in fuel injection control is determined based on the detected combustion state. Finally, in step 216, the counters CI and CL are initialized, and this routine ends.

[0037]

As described above, according to the present invention,
It is sufficient to provide only means for determining whether or not the output of the ion current detection circuit is equal to or less than the reference value, so that the combustion state of the internal combustion engine can be detected with a simple circuit configuration.

[Brief description of the drawings]

FIG. 1 is an overall schematic diagram of an electronically controlled internal combustion engine including a combustion state detection device according to 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 time chart for explaining an operation of the ion current detection circuit.

FIG. 4 is a diagram illustrating a distribution of a peak value (ion output) of an output voltage of the ion current detection circuit.

FIG. 5 is a characteristic diagram showing the relationship between the air-fuel ratio and the frequency at which the ion output becomes equal to or lower than a certain reference value when the engine rotation speed is constant.

FIG. 6 is a diagram showing a distribution of ion output when the engine rotation speed is increased.

Shown [7] the relationship between the determination reference value V _R for the engine rotational speed NE and the ion output, and the relationship, between the engine rotational speed and the ion output falls below a predetermined reference value frequency in some air FIG.

FIG. 8 is a flowchart showing a processing procedure of a combustion state detection routine executed by the ECU.

[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 ... intake pressure 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 101 ... battery 102 ... high voltage line 130 ... ion current detection circuit

Claims (6)

[Claims] 1. An ion current detecting means for detecting an ion current corresponding to an amount of ions generated by combustion of an air-fuel mixture in a cylinder of an internal combustion engine, wherein the value of the ion current detected by the ion current detecting means is Current value discriminating means for discriminating whether or not the current value is equal to or less than a reference value; counting means for counting the number of times of combustion in which the ion current value is judged to be equal to or less than the reference value in the predetermined number of combustions; A combustion state detection device for an internal combustion engine, comprising: combustion determination means for determining a combustion state based on the number of times counted by the counting means. 2. The combustion state detection of an internal combustion engine according to claim 1, wherein said combustion judging means judges that the combustion is defective when the number counted by said counting means is larger than a predetermined value. apparatus. 3. The combustion state detecting device for an internal combustion engine according to claim 1, wherein a reference value used in said current value determining means is changed according to an engine speed. 4. The combustion state detecting device for an internal combustion engine according to claim 3, wherein the reference value used in the current value discriminating means is changed to a larger value as the engine speed increases. 5. The combustion state detection device for an internal combustion engine according to claim 1, wherein the determination processing by the combustion determination means is executed during a cold first idling, and a property of the fuel is detected. 6. Any one of claims 1 to 5
A control device for an internal combustion engine, comprising: the combustion state detection device according to any one of the preceding items, and a fuel injection control unit that corrects a fuel injection amount according to a combustion state detected by the combustion state detection device.