JP5907715B2 - 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 and refers to the ionic current flowing through the electrode of the spark plug during combustion is known (see, for example, Patent Document 1 below). During poor combustion such as over lean, the peak of the ionic current is lower than during normal combustion. It is possible to determine whether or not the combustion in the cylinder is normal by measuring the transition of the ion current and comparing the measured value with a threshold value for determination.

  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).

  By the way, as the use period of the spark plug becomes longer, deposits such as fuel components, lubricating oil, and additives gradually adhere to and accumulate on the electrodes. This deposit works like an electrical resistance that reduces the amount of ionic current flowing through the electrode of the spark plug, so even if the fuel burns properly and ions are generated in the combustion chamber, the measured value of the ionic current is There is a possibility that the determination threshold value is not exceeded and it is erroneously determined that it is a combustion failure or misfire.

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

  An object of the present invention is to further improve the accuracy of determination of a combustion state with reference to an ionic current.

In the present invention, a circuit that detects the ionic current flowing through the electrode of the spark plug during combustion is used to determine the combustion state in the cylinder of the internal combustion engine, and flows through the electrode of the spark plug through the circuit. The current is measured repeatedly, and it is determined that the combustion state in the cylinder is normal on the condition that the current value based on the time series exceeds the threshold value, and the current value based on the measured time series does not exceed the threshold value. when the the length of the generation period of the current value based on the time series, the integral amount of the current value, with reference to the transition of the change of generation time and current value of the current value, or the combustion state in the cylinders is normal poor The combustion state determination device for an internal combustion engine is characterized by determining whether or not.

  In addition, if the current value is generated even at the time when it is thought that combustion in the cylinder has ended, the current is measured by further increasing the gain of the circuit at the time of subsequent current measurement, Then, it may be determined whether the combustion state in the cylinder is normal or defective. Then, it is possible to avoid the problem that the measured value of the current is unduly raised due to “ground floating” in which the ground level of the circuit is separated from the ground.

  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 the ionic current in the cylinder of an internal combustion engine. The figure which shows the relationship between the combustion state in the cylinder of an internal combustion engine, and transition of the detected electric current. The flowchart which shows the example of a procedure of the process which the combustion state determination apparatus of the embodiment performs.

  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 and an exhaust passage 4 for discharging exhaust from each cylinder 1 are provided.

  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, in this embodiment, a circuit for detecting an ionic current is added to the electric circuit for spark ignition. This detection circuit includes a bias power supply unit 14 for effectively detecting an ionic current, and an amplification unit 15 that amplifies and outputs a detection voltage corresponding to the magnitude of the ionic current. 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 by 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 exemplifies transitions of the ion current (shown by a solid line in the figure) and the combustion pressure in the cylinder 1 (in-cylinder pressure; shown by a broken line in the figure). In the case of normal combustion, the ionic current cannot be detected during the discharge for ignition. In the case of normal combustion, the ionic current decreases by a chemical reaction before the compression top dead center after the end of spark ignition, and then increases again by thermal dissociation. In addition, the ionic current reaches a maximum almost simultaneously with the peak of the combustion pressure.

  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, an electronic throttle valve 33, a surge tank 34, and an intake manifold 35 are arranged in this order from the upstream.

  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 and a three-way catalyst 41 are disposed on the exhaust passage 4.

  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, a temperature / pressure sensor that detects intake air temperature and intake air pressure in the intake passage 3 (particularly, the surge tank 34). The intake air temperature / intake pressure signal d output from the engine, the shift position signal e output from the shift position (gear position) switch, the coolant temperature signal f output from the water temperature sensor for detecting the coolant temperature of the internal combustion engine, the intake camshaft Cam signal g output from the cam angle sensor at a plurality of cam angles, Indicates an ion current signal h output from a circuit for detecting ion current generated as a result of zuma generation and air-fuel mixture combustion, an operation signal i regarding whether or not the air conditioner is operating, and a state of charge of the in-vehicle battery. A battery state signal j output from a sensor that detects the index is 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, an opening operation signal k for the throttle valve 33, a fuel injection signal n for the injector 10, an ignition signal o for the igniter 11, and an alternator that generates electric power by receiving driving force from the crankshaft. A voltage instruction signal p or the like is output to a voltage regulator that controls the output voltage.

  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. Various operating parameters such as required fuel injection amount, fuel injection timing (including the number of fuel injections per combustion), fuel injection pressure, ignition timing, and power generated by the alternator based on the engine speed and intake air amount. To decide. 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, n, o, and p corresponding to the operation parameters via the output interface.

  The ECU 0 of this embodiment refers to the ion current signal h flowing through the spark plug 13 of each cylinder 1 and determines whether the fuel combustion in the cylinder 1 is normal or defective.

  At the time of poor combustion such as over leaning, the combustion is excessively slow compared with that at the time of normal combustion, and the peak of the ion current peak due to thermal dissociation shown in FIG. 3 is lowered. Needless to say, when a misfire occurs in the cylinder 1, no ion current flows in the first place. Therefore, the ECU 0 repeatedly samples the current signal h at a predetermined cycle, and obtains a time series of measured values of the current flowing through the electrode of the spark plug 13 of the cylinder 1. And the time series of the measured value acquired through the period during which the combustion is expected to continue during the expansion stroke of the target cylinder 1 is compared with a predetermined determination threshold value. As shown in FIG. 4A, if at least a part of the time series of measured values exceeds the determination threshold value, it can be determined that the current combustion in the cylinder 1 has been performed normally.

  However, even if the time series of measured values does not exceed the determination threshold, it cannot be immediately determined that the combustion in the cylinder 1 is defective or misfiring. Deposits adhere to the electrodes of the spark plug 13 as aging. This deposit reduces the level of the ionic current signal h detected through the resistor 145 of the detection circuit. If the deposit is significantly accumulated, as shown in FIG. 4B, the measured value of the ionic current due to thermal dissociation does not exceed the determination threshold value even though the target cylinder 1 is burning normally. obtain.

  On the other hand, even if no ion or plasma is generated in the combustion chamber due to misfire, as shown in FIG. 4C, a noise current h flows through the load resistor 145 of the detection circuit, and this is caused by the combustion of the fuel. There is also a risk of erroneous detection of current. Furthermore, when a “ground floating” occurs in which the ground level of the detection circuit is separated from the ground (0 V), the measured value of the current h flowing through the load resistor 145 is unduly raised as shown in FIG. Will be. Incidentally, the ground floating is often caused by wiring resistance when a large current flows through an on-vehicle electric load such as an illumination lamp, a fan motor, or an audio device.

  Therefore, when the measured value of the current flowing through the electrode of the spark plug 13 does not exceed the determination threshold, it is determined and specified whether the level of the ionic current signal h during normal combustion is reduced, noise, or ground floating. There is a need.

  As shown in FIG. 4B, the waveform of the ion current signal h during normal combustion continuously takes a positive value for a certain length during the expansion stroke. Then, it becomes 0 or almost 0 at the time when the combustion ends, particularly after the exhaust stroke.

  On the other hand, as shown in FIG. 4C, the waveform of the current signal h due to noise frequently fluctuates in comparison with the ion current caused by combustion. Moreover, even when the combustion during the expansion stroke should continue, the frequency of becoming 0 or a small value close to 0 is high. That is, the waveform of the current signal h is not continuous and is interrupted.

  In addition, as shown in FIG. 4D, the current signal h due to ground floating continues to take a positive value even after the intake stroke.

  FIG. 5 shows a procedure example of processing executed by the ECU 0 when determining the combustion state in each cylinder 1. First, the ECU 0 obtains a time series of measured values of the current h at a time when the ion current may be detected, which is obtained by sampling during a period in which the combustion during the expansion stroke of the target cylinder 1 is expected to continue. Compared with the determination threshold (step S1). When at least a part of the time series of measured values exceeds the determination threshold, it is determined that the current combustion in the cylinder 1 has been performed normally (step S2).

  If the time series of the measured values does not exceed the determination threshold, the measured values of the current h sampled during the above period are integrated over time, and the integrated amount is compared with a required determination reference value (step S3). . The integration amount can be approximately calculated by integrating the time series of measurement values. If the integration amount of the measured value of the current h is below the determination reference value, it is determined that the current combustion in the cylinder 1 is defective or misfired without burning (step S7). The current signal h in this case is considered to be noise.

  Further, the time series of measured values sampled during the above period is not 0 or a small value close to 0, but the continuous time length (or the current signal h remains positive for the above sampling period). The ratio of consecutive periods) is compared with a required determination reference value (step S4). If the continuous time of the waveform of the current h is less than the determination reference value, it is determined that the current combustion in the cylinder 1 is defective or misfired without burning (step S7). The current signal h in this case is also considered to be noise.

  In addition, the measured value of the current h sampled during the above period is time-differentiated for each fixed period (which may coincide with the sampling period), and the differential amount for each fixed period (or the change per unit time) The average of the absolute values of) is compared with a required determination reference value (step S5). The differential amount at a certain time can be approximately calculated by subtracting the measured value sampled at the most recent time from the measured value sampled at that time. If the average of the absolute value of the differential value of the measured value of the current h exceeds the criterion, it is determined that the current combustion in the cylinder 1 is defective or misfired without burning (step S7). The current signal h in this case is also considered to be noise.

  Even if the tests in steps S3 to S5 are passed, normal combustion is not necessarily performed in the target cylinder 1. This is because the current signal h may be biased due to floating ground. If the test in steps S3 to S5 is passed, sampling is performed at the time when combustion in the target cylinder 1 should end, for example, during the exhaust stroke after the expansion bottom dead center or during the next intake stroke. It is determined whether the measured value of the current h is 0 or larger than a predetermined value close to 0 (step S6). If the measured value of the current h at the time when combustion is considered to have ended is greater than 0 or a predetermined value close to 0, it is considered that a ground float has occurred, and the current combustion in the cylinder 1 is normal. It is determined that it is at least unclear whether there is a possibility of combustion failure or misfire (step S7). On the contrary, if the measured value of the current h at the time when it is considered that the combustion has ended is 0 or less than a predetermined value close to 0, it is determined that the current combustion in the cylinder 1 is normally performed ( Step S2).

  In this embodiment, a circuit for detecting a ionic current flowing through an electrode of a spark plug 13 by applying a bias voltage based on the electric charge stored in the capacitor 141 and detecting the ionic current flowing through the electrode is used to determine the combustion state in the cylinder 1 of the internal combustion engine. The current flowing through the electrode of the spark plug 13 is repeatedly measured via the circuit, and the combustion state in the cylinder 1 is normal on the condition that the current value based on the time series exceeds the threshold value. On the other hand, if the current value based on the time series of measured values does not exceed the threshold value, the length of the current value generation period based on the time series, the integration amount of the current value, the generation time of the current value, or the change in the current value The combustion state determination device 0 that determines whether the combustion state in the cylinder 1 is normal or defective is configured with reference to at least one of the transitions.

  According to the present embodiment, even if the level of the ionic current signal h is decreased due to the secular change of the spark plug 13, it is possible to accurately determine whether or not the fuel is normally burned in the cylinder 1. . In addition, since the probability of misjudging normal combustion as defective combustion or misfire is reduced, it is not necessary to perform maintenance that is originally unnecessary on the internal combustion engine itself, which contributes to a reduction in operating costs.

  The present invention is not limited to the embodiment described in detail above. In step S6, when the current value is generated even when it is considered that the combustion in the cylinder 1 has ended (the measured value of the current h at that time is a positive value), that is, the detection of the ionic current. When it is assumed that a ground float has occurred in the circuit, the gain of the detection circuit, specifically the gain of the voltage amplifier 151, is measured when the current h is measured in the expansion stroke of the cylinder 1 from the next time. It is preferable that the current h be sampled and measured to determine the combustion state in the cylinder 1 after further increase.

  Since the bias added to the waveform of the current h due to the ground floating does not increase even if the gain of the amplifier 151 is increased, steps S1 to S7 are performed with a relatively small influence of the ground floating on the waveform of the current h. This makes it possible to further improve the determination accuracy of the combustion state.

  In addition, the specific configuration of each part, the specific processing procedure, and the like 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)

Using a circuit that detects an ionic current flowing through the electrode of the spark plug during combustion, the combustion state in the cylinder of the internal combustion engine is determined,
The current flowing through the electrode of the spark plug is repeatedly measured through the circuit, and it is determined that the combustion state in the cylinder is normal on the condition that the current value based on the time series exceeds a threshold value,
When the current value based on time series of measurements did not exceed the threshold, the reference length of the generation period of the current value based on the time series, the integral amount of the current value, the transition of change in generation timing and the current value of the current And determining whether the combustion state in the cylinder is normal or defective. If the current value is generated even at the time when the combustion in the cylinder is considered to have ended, the current is measured by further increasing the gain of the circuit at the time of the subsequent current measurement, and then The combustion state determination device for an internal combustion engine according to claim 1, wherein it is determined whether the combustion state in the cylinder is normal or defective.

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