JP5904768B2 - Combustion state determination device for internal combustion engine - Google Patents

Description

  The present invention relates to a determination device that determines a combustion state in a cylinder of an internal combustion engine.

  As a method for estimating the combustion state of the fuel in the cylinder, one that detects an ionic current flowing through the electrode of a spark plug during combustion is known (see, for example, Patent Document 1 below). At the time of poor combustion such as over leaning, the combustion becomes excessively slow compared with the normal combustion, the peak of the ionic current is lowered, and the time during which the ionic current is flowing becomes longer. The transition of the ionic current is measured, and it is determined whether the maximum value exceeds the determination threshold or whether the time during which the ionic current exceeds the determination threshold (this threshold is different from the threshold) is short or long. Thus, it is possible to determine whether or not the combustion is normal. Needless to say, if the ion current cannot be detected, a misfire has occurred in the cylinder.

  In detecting the ionic current, it is usual to apply a high bias voltage due to the charge stored in the capacitor to the center electrode of the spark plug (see, for example, Patent Document 2 below).

  However, since the charge stored in the capacitor is released when the ionic current flows, the bias voltage applied to the electrode of the spark plug gradually decreases during the expansion stroke. Therefore, the level of the ion current detected after the middle of the combustion process inevitably decreases, but the conventional method makes a judgment based solely on the measured value of the ion current without considering the decrease of the bias voltage. It was. For this reason, the misjudgment about the combustion state was sometimes caused.

Japanese Patent Application Laid-Open No. 06-034490 JP 2006-200432 A

  The present invention, which has been made by paying attention to the above-mentioned problem for the first time, aims to further improve the accuracy of determination of the combustion state with reference to the ion current.

In the present invention, a circuit for detecting a ionic current flowing through an electrode of a spark plug by applying a bias voltage based on an electric charge stored in a capacitor to detect an ionic current flowing through the electrode is used to determine a combustion state in a cylinder of an internal combustion engine, The ion current detected during the expansion stroke is repeatedly measured, and the amount of charge or capacitor voltage flowing out of the capacitor is calculated from the time series of the measured values. Based on the amount of charge or capacitor voltage, the current during the expansion stroke is calculated . A combustion state determination device for an internal combustion engine is characterized in that a resistance value between the electrodes of the spark plug is obtained and the resistance value during the expansion stroke is compared with a determination threshold value . In addition, in the present invention, a circuit for detecting a ionic current flowing through an electrode of a spark plug by applying a bias voltage based on the charge stored in the capacitor to the electrode of the spark plug is used to determine the combustion state in the cylinder of the internal combustion engine. Then, the ion current is repeatedly measured, the amount of charge flowing out from the capacitor or the capacitor voltage is calculated from the time series of the measured value, and the resistance value between the electrodes of the spark plug is calculated based on the amount of charge or the capacitor voltage. If the amount of charge released from the capacitor, which is repeatedly calculated, is approximately equal to the amount of charge originally stored in the capacitor, the ignition plug is calculated. An internal combustion engine characterized in that information indicating that a failure has occurred is written in a memory, and is notified in a manner appealing to the driver's vision or hearing. To constitute a combustion state determining apparatus.

  ADVANTAGE OF THE INVENTION According to this invention, the precision of the determination of the combustion state which referred the ion current can be improved further.

The figure which shows schematic structure of the internal combustion engine in one Embodiment of this invention. The circuit diagram of the spark ignition device in the embodiment. The figure which shows each transition of the combustion pressure and ion current in each cylinder of an internal combustion engine. The figure which shows transition after the compression stroke of the ionic current in each cylinder of an internal combustion engine.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of a spark ignition type internal combustion engine in the present embodiment. This internal combustion engine is of a direct injection type, and includes a plurality of cylinders 1 (one of which is shown in FIG. 1), an injector 10 that injects fuel into each cylinder 1, An intake passage 3 for supplying intake air to the cylinder 1, an exhaust passage 4 for discharging exhaust from each cylinder 1, an exhaust turbocharger 5 for supercharging intake air flowing through the intake passage 3, and an exhaust passage And an external EGR device 2 that recirculates EGR gas from 4 toward the intake passage 3.

  A spark plug 13 is attached to the ceiling of the combustion chamber of the cylinder 1. FIG. 2 shows an electric circuit for spark ignition. The spark plug 13 receives spark voltage generated by the ignition coil 12 and causes spark discharge between the center electrode and the ground electrode. The ignition coil 12 is integrally incorporated in a coil case together with an igniter 11 that is a semiconductor switching element.

  When the igniter 11 receives an ignition signal o from an ECU (Electronic Control Unit) 0, which is a combustion state determination device for an internal combustion engine, the igniter 11 is first ignited and a current flows to the primary side of the ignition coil 12, and the ignition immediately thereafter. The igniter 11 is extinguished at the timing, and this current is cut off. Then, a self-induction action occurs, and a high voltage is generated on the primary side. Since the primary side and the secondary side share the magnetic circuit and the magnetic flux, a higher induced voltage is generated on the secondary side. This high induction voltage is applied to the center electrode of the spark plug 13, and spark discharge occurs between the center electrode and the ground electrode.

  The ECU 0 detects an ionic current generated in the combustion chamber of the cylinder 1 during the explosion combustion of the fuel, and refers to the ionic current to determine the combustion state.

  As shown in FIG. 2, the electrical circuit for spark ignition has a bias power supply unit 14 for effectively detecting the ionic current, and an amplification that amplifies and outputs a detection voltage corresponding to the amount of the ionic current. The part 15 is attached. The bias power supply unit 14 includes a capacitor 141 that stores a bias voltage, a Zener diode 142 for increasing the voltage of the capacitor 141 to a predetermined voltage, current blocking diodes 143 and 144, and a load that outputs a voltage corresponding to the ion current. A resistor 145. The amplifying unit 15 includes a voltage amplifier 151 typified by an operational amplifier.

  During arc discharge between the center electrode and the ground electrode of the spark plug 13, the capacitor 141 is charged, and then an ion current flows through the load resistor 145 by the bias voltage charged in the capacitor 141. The voltage between both ends of the resistor 145 generated due to the flow of the ionic current is amplified by the amplifying unit 15 and received by the ECU 0 as the ionic current signal h.

  FIG. 3 illustrates respective transitions of the combustion pressure (indicated by a broken line in the figure) and the ionic current (indicated by a solid line in the figure). In the case of normal combustion, the ionic current suddenly flows like a surge at the moment of ignition (inductive discharge), decreases before compression top dead center, and then increases again (capacitive discharge). And, at the same time as the combustion pressure reaches its peak, the ionic current also becomes maximum.

  The intake passage 3 takes in air from the outside and guides it to the intake port of the cylinder 1. On the intake passage 3, an air cleaner 31, a compressor 51 of the supercharger 5, an intercooler 32, an electronic throttle valve 33, a surge tank 34, and an intake manifold 35 are arranged in this order from the upstream side.

  The exhaust passage 4 guides exhaust generated as a result of burning fuel in the cylinder 1 from the exhaust port of the cylinder 1 to the outside. An exhaust manifold 42, a drive turbine 52 for the supercharger 5, and a three-way catalyst 41 are disposed on the exhaust passage 4. In addition, an exhaust bypass passage 43 that bypasses the turbine 52 and a waste gate valve 44 that is a bypass valve that opens and closes the inlet of the bypass passage 43 are provided. The waste gate valve 44 is an electric waste gate valve that can be opened and closed by inputting a control signal l to the actuator, and a DC servo motor is used as the actuator.

  The exhaust turbocharger 5 is configured such that the drive turbine 52 and the compressor 51 are connected and linked in a coaxial manner. Then, the driving turbine 52 is rotationally driven by using the energy of the exhaust gas, and the compressor 51 is pumped by using the rotational force, whereby the intake air is pressurized and compressed (supercharged) and sent to the cylinder 1.

  The external EGR device 2 realizes a so-called high-pressure loop EGR. The inlet of the external EGR passage is connected to a predetermined location upstream of the turbine 52 in the exhaust passage 4. The outlet of the external EGR passage is connected to a predetermined location downstream of the throttle valve 33 in the intake passage 3, specifically to a surge tank 34. An EGR cooler 21 and an EGR valve 22 are also provided on the external EGR passage.

  The ECU 0 is a microcomputer system having a processor, a memory, an input interface, an output interface, and the like.

  The input interface includes a vehicle speed signal a output from a vehicle speed sensor for detecting the vehicle speed, an engine rotation signal b output from an engine rotation sensor for detecting the rotation angle and engine speed of the crankshaft, an accelerator pedal depression amount or a throttle. An accelerator opening signal c output from an accelerator opening sensor that detects the opening of the valve 33 as an accelerator opening, intake air temperature and intake pressure (or supercharging pressure) in the intake passage 3 (especially the surge tank 34). The intake air temperature / intake pressure signal d output from the temperature / pressure sensor for detecting engine, the shift position signal e output from the shift position (gear position) switch, and the cooling output from the water temperature sensor for detecting the cooling water temperature of the internal combustion engine. Cam signal output from cam angle sensor at multiple cam angles of water temperature signal f and intake camshaft , An ion current signal h output from a circuit for detecting an ion current generated by the generation of plasma in the combustion chamber and the combustion of the air-fuel mixture, an operation signal i regarding whether or not the air conditioner is operating, The battery state signal j etc. output from the sensor which detects the parameter | index which suggests a charge state are input. The engine rotation sensor generates a pulse signal b every 10 ° CA (crank angle). The cam angle sensor generates a pulse signal g at an angle obtained by dividing 720 ° CA by the number of cylinders, or every 240 ° CA for a three-cylinder engine. The operation signal i of the air conditioner may be a signal issued from a switch manually operated by the driver to turn on the air conditioner or a signal issued from an auto air conditioner ECU that controls the auto air conditioner system. . The battery status signal j displays, for example, battery current, battery voltage, and battery temperature.

  From the output interface, the opening operation signal k for the throttle valve 33, the opening operation signal l for the waste gate valve 44, the opening operation signal m for the EGR valve 22, and the fuel injection signal for the injector 10. n, an ignition signal o is output to the igniter 11, and a voltage instruction signal p is output to a voltage regulator that controls the output voltage of the alternator that generates power upon receiving the driving force transmitted from the crankshaft.

  The processor of the ECU 0 interprets and executes a program stored in the memory in advance, calculates operation parameters, and controls the operation of the internal combustion engine. The ECU 0 obtains various information a, b, c, d, e, f, g, h, i, j necessary for operation control of the internal combustion engine via the input interface, knows the engine speed, and uses the cylinder 1 Estimate the amount of intake air to be filled. Based on the engine speed and intake air amount, the required fuel injection amount, fuel injection timing (including the number of times of fuel injection for one combustion), fuel injection pressure, ignition timing, EGR amount (or EGR rate) And various operating parameters such as the opening degree of the EGR valve 22 and the electric power generated by the alternator. As the operation parameter determination method itself, a known method can be adopted, and the description thereof will be omitted. The ECU 0 applies various control signals k, l, m, n, o, and p corresponding to the operation parameters via the output interface.

  The ECU 0 of this embodiment repeatedly measures the ionic current, and calculates the amount of charge flowing out from the capacitor 141 and / or the voltage of the capacitor 141 from the time series of the measured values. Then, a resistance value between the center electrode of the spark plug 13 and the ground electrode is obtained based on the charge amount or the capacitor voltage.

If the charge stored in the capacitor 141 is Q, the voltage of the capacitor 141 is V, and the capacitance of the capacitor 141 is C,
Q = CV
This relationship is established. On the other hand, if the resistance value between the center electrode of the spark plug 13 and the ground electrode is R, and the current flowing through the electrode of the spark plug 13 by capacitive discharge after ignition is I,
V = (R + r) I
This relationship is established. r is the resistance value of the load resistor 145. However, this r may be ignored.

Let t be the time that has elapsed since the start of capacitive discharge. At time t = T, the amount of charge Q ′ flowing out of the capacitor 141 is
Q ′ (T) = ∫ ₀ ^T I (t) dt
It is. Actually, the ECU 0 repeatedly samples the ion current signal h at a predetermined cycle, and the ECU 0 integrates the sampling value I (t) multiplied by the sampling cycle to thereby accumulate the charge amount Q ′ (T ) Is calculated.

The amount of charge Q and the capacitor voltage V remaining in the capacitor 141 at the time of t = T are:
Q (T) = Q (0) −Q ′ (T)
V (T) = Q (T) / C
It becomes. Q (0) is the charge amount when the capacitor 141 having the capacitance C is charged to a predetermined voltage.

The resistance value R (T) between the electrodes of the spark plug 13 can be obtained from the sampling value I (T) of the ionic current at the time t = T and the capacitor voltage V (T). That is,
R (T) = {V (T) / I (T)} − r = {Q (0) −∫ ₀ ^T I (t) dt} / {CI (T)} − r
It becomes.

  Basically, the resistance value R indicates a combustion resistance that depends on the amount of ions generated in the combustion chamber by the combustion of fuel. When sufficient combustion is performed, this R decreases, but when combustion is insufficient, R remains large. In particular, when the flame does not ignite or is misfired in which the flame disappears in the middle, R becomes the insulation resistance itself between the center electrode of the spark plug 13 and the ground electrode. In short, it is possible to estimate and determine the combustion state in the cylinder 1 by repeatedly calculating R (t) and referring to the transition or the minimum value.

  For example, if the minimum value of the combustion resistance R (t) is below the determination threshold in the expansion stroke, it is determined that the combustion is normal, and if R (t) does not fall below the determination threshold, it is determined that the combustion is defective or misfiring. Alternatively, if the combustion resistance R (t) in the expansion stroke is less than a certain length during which the combustion resistance R (t) is lower than a determination threshold value (which is different from the threshold value and higher than the threshold value), the normal combustion is determined. If it is longer than the length, it is judged as defective combustion. According to the latter, it is possible to sense an excessive slowing of combustion due to overlean or the like.

  However, carbon or the like gradually adheres and accumulates on the spark plug 13 as aging. This carbon or the like reduces the insulation resistance between the electrodes of the spark plug 13 and increases the leakage current. If the secular change is significant, the ratio of the resistance value R to the decrease in insulation resistance increases, and it becomes difficult to distinguish whether R is due to the generation of ions accompanying combustion or due to adhesion of carbon or the like. In an extreme case, there is a possibility that R takes a value close to the resistance value during normal combustion in spite of poor combustion.

Therefore, it is preferable to know the insulation resistance of the spark plug 13 and use it for diagnosis of the spark plug 13. The charge amount Q stored in the capacitor 141 gradually decreases as the cylinder 1 shifts to the expansion stroke, the exhaust stroke, and the intake stroke of the next cycle in the cylinder 1, but the charge discharge amount Q ′ from the capacitor 141 decreases. When (t) becomes equal to the amount of charge Q (0) originally stored, the insulation resistance between the electrodes of the spark plug 13 is lowered, and the capacitor 141 discharges all charges due to the leakage current between the electrodes. Can be regarded as having done. Therefore, ECU0
Q ′ (t) ≈Q (0)
If the condition is satisfied, it is determined that a failure has occurred in the spark plug 13, information indicating that is written in the memory, and an aspect that appeals to the driver's vision or hearing (for example, a lamp in the cockpit) Are turned on, information is displayed on the display, an alarm is sounded, etc.).

When the condition of the above equation is not satisfied, it is possible to estimate the insulation resistance between the electrodes of the spark plug 13. That is, as shown in FIG. 4, the current I (T _d ) flowing through the electrode of the plug 13 at the time when fuel combustion has already ended, particularly at the time t = T _d after the intake stroke, is a leakage current, The resistance value R (T _d ) calculated for the time point t = T _d is the insulation resistance.

Then, when determining the combustion state, a value obtained by subtracting the insulation resistance R (T _d ) from the calculated resistance value R (t) is defined as a true combustion resistance, and this true combustion resistance {R (t) −R ( T _d )} may be compared with a determination threshold.

  According to the present embodiment, the combustion in the cylinder 1 of the internal combustion engine is performed using the circuit that detects the ion current I flowing through the electrode by applying the bias voltage V due to the charge Q stored in the capacitor 141 to the electrode of the spark plug 13. The state is determined, the ion current I is repeatedly measured, the charge amount Q ′ or the capacitor voltage V flowing out from the capacitor 141 is calculated from the time series of the measured values, and the charge amount Q ′ or the capacitor is calculated. Since the combustion state determination device 0 of the internal combustion engine is characterized in that the resistance value R between the electrodes of the spark plug 13 is obtained based on the voltage V, the bias voltage V is reduced due to the discharge of the charge of the capacitor 141. Considering this, it becomes possible to estimate the combustion state more accurately.

  The present invention is not limited to the embodiment described in detail above. In the above-described embodiment, the combustion resistance R is obtained, and the combustion state determination in which the combustion resistance R is compared with the determination threshold value is considered. However, the combustion resistance R is a huge value, and it is not always easy to handle the ECU 0 as a combustion state determination device. That is, it may be necessary to take measures to avoid the occurrence of rounding errors in the processor.

  In view of the above circumstances, it is conceivable to compare the determination threshold value of the ionic current I itself with the conventional determination method. In this case, based on the charge amount Q ′ flowing out from the capacitor 141 or the capacitor voltage V, correction is performed to raise the value of the ion current I to be compared with the determination threshold value.

For example, assume that the bias voltage applied to the center electrode of the spark plug 13 is constant and does not decay, and the amount of ion current flowing under this assumption is calculated. Under a constant bias voltage V (0),
V (0) = {R (t) + r} {I (t) + I ′ (t)}
This relationship is established. V (0) is a predetermined voltage. I (t) is an actually measured value of the ionic current. I ′ (t) is a correction amount added to the measured value of the ionic current.

Thus, regarding the combustion resistance R (t),
R (t) + r = V (t) / I (t)
From the fact that
I (t) + I ′ (t) = V (0) I (t) / V (t) = CV (0) I (t) / Q (t)
As a result, the ion current amount {I (t) + I ′ (t)} to be compared with the determination threshold value with the correction amount taken into account can be obtained.

  The ECU 0 as the combustion state determination device determines normal combustion if the maximum value of the ion current amount {I (t) + I ′ (t)} exceeds the determination threshold in the expansion stroke, and determines the ion current amount {I (t) + I. If '(t)} does not exceed the determination threshold, it is determined that the combustion is defective or misfiring. Alternatively, if the ion current amount {I (t) + I ′ (t)} exceeds the determination threshold value (this threshold value is lower than the threshold value, which is different from the threshold value) during the expansion stroke, the length is less than a certain length. If it is longer than a certain length, it is determined as defective combustion.

  Other specific configurations of each part can be variously modified without departing from the spirit of the present invention.

  The present invention can be applied to control of an internal combustion engine mounted on a vehicle or the like.

0 ... Combustion state determination device (ECU)
DESCRIPTION OF SYMBOLS 1 ... Cylinder 13 ... Spark plug 14 ... Bias power supply part 141 ... Capacitor 15 ... Amplification part

Claims (2)

A circuit for detecting a ionic current flowing through an electrode of a spark plug by applying a bias voltage based on an electric charge stored in a capacitor and detecting an ionic current flowing through the electrode to determine a combustion state in a cylinder of an internal combustion engine,
The ion current detected during the expansion stroke is repeatedly measured, and the amount of charge or capacitor voltage flowing out of the capacitor is calculated from the time series of the measured values. Based on the amount of charge or capacitor voltage, the current during the expansion stroke is calculated . A combustion state determination device for an internal combustion engine, wherein a resistance value between electrodes of a spark plug is obtained and the resistance value during the expansion stroke is compared with a determination threshold value . A circuit for detecting a ionic current flowing through an electrode of a spark plug by applying a bias voltage based on an electric charge stored in a capacitor and detecting an ionic current flowing through the electrode to determine a combustion state in a cylinder of an internal combustion engine,
Whether ion current is measured repeatedly, the amount of charge or capacitor voltage flowing out of the capacitor is calculated from the measured time series, and the resistance value between the electrodes of the spark plug is calculated based on the amount of charge or capacitor voltage. Or it adds correction to the measured value of ion current,
When the amount of charge released from the capacitor, which is repeatedly calculated, is approximately equal to the amount of charge originally stored in the capacitor, information indicating that a failure has occurred in the spark plug is written in the memory and the operation is performed. A combustion state determination device for an internal combustion engine, which is notified in a manner appealing to a person's vision or hearing.

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