JP2020037884A - Abnormal determination device of ignition plug - Google Patents

Abstract

To replace an ignition plug at suitable timing.SOLUTION: This is an abnormality determination device 100 for an ignition plug. An ignition plug 25 includes a pair of electrodes 250. The abnormality determination device 100 includes an ignition section 251 which is ignited by applying ignition energy to the pair of the electrodes 250. A control section 10 includes an abnormality determination section 101 for determining abnormality of the ignition plug 25 which is caused by abrasion of the pair of the electrodes 250. The abnormality determination section 101 operates the ignition plug 25 by applying determination ignition energy smaller than the ignition energy to the pair of the electrodes 250 when an abrasion amount of the pair of the electrodes 250 is equal to or more than a prescribed value, and ignitability of an air-fuel mixture is determined. It is determined that the ignition plug 25 is in an abnormal state when the ignitability of the air-fuel mixture is deteriorated.SELECTED DRAWING: Figure 12

Description

  The disclosed technology relates to a spark plug abnormality determination device.

  Usually, an ignition plug is installed in an engine that ignites (or ignites) an air-fuel mixture to perform combustion. The spark plug has a pair of electrodes (a center electrode and a ground electrode) facing the inside of the combustion chamber. The center electrode and the ground electrode face each other with a slight gap. By applying a predetermined voltage between these electrodes, a discharge occurs between these electrodes. Thereby, a flame nucleus is formed in the air-fuel mixture, and the air-fuel mixture is ignited by the growth of the flame nucleus.

  The center electrode and the ground electrode are worn by the discharge. As the wear progresses, the gap increases and the discharge voltage required for ignition increases accordingly. If the discharge voltage is excessively high, there is a possibility that the applied voltage applied between the electrodes becomes insufficient and a misfire occurs, or the applied voltage exceeds the durability of the spark plug and the spark plug is damaged.

  Therefore, the spark plug is a consumable that needs to be replaced periodically. The replacement timing is generally set uniformly for each predetermined traveling distance.

  However, the amount of electrode wear depends on the operating state of the engine. Therefore, the timing of actually replacing the spark plug depends on the driving technique and preferences of the user, and varies among individual engines.

  Thereby, the replacement timing of the spark plug is usually set to the safe side in consideration of the variation of each engine. As a result, a user who has not yet reached the timing to replace the spark plug may replace the spark plug.

  Therefore, it is preferable to measure the wear amount of the electrodes according to the operating state of each engine and to determine the timing of replacing the spark plug individually, since it is possible to replace the spark plug at an appropriate timing even if there is variation.

  On the other hand, Patent Literature 1 discloses a method for estimating a gap length (gap size) of a worn electrode in a general spark ignition engine based on an operation state of the engine.

  That is, Patent Document 1 shows that the gap length can be estimated from three parameters at the time of ignition, which are composed of discharge time, in-cylinder gas density, and in-cylinder gas flow rate. Is shown.

  In Patent Literature 1, the gap length is estimated during the operation of the engine using the relational expression, and when the gap length becomes equal to or larger than a preset value, the abnormality of the spark plug is notified by lighting a warning lamp or the like.

JP-A-2006-53314

  According to the technique disclosed in Patent Literature 1, the gap length can be individually estimated, so that it is possible to expect replacement of the spark plug at an appropriate timing.

  However, according to the technique disclosed in Patent Document 1, it is necessary to accurately measure the in-cylinder gas flow velocity near the electrode, and it is difficult to estimate the gap length with high accuracy.

  In contrast, by estimating the amount of wear that increases over time by accumulating the amount of wear caused by each ignition, the worn electrode is added by adding the estimated amount of wear to the gap of an unused spark plug. To estimate the gap length.

  However, even in the gap of an unused spark plug, there is a variation (initial variation) based on the tolerance. This initial variation also affects the timing of replacing the spark plug, as well as the amount of wear.

  In particular, in an engine having a high compression ratio in which the in-cylinder pressure increases during combustion as compared with a conventional spark ignition engine, such as an engine that performs SPCCI combustion described later, the tendency becomes more remarkable. Therefore, in an engine with a high compression ratio, not only the effects due to wear but also the effects due to initial variations are important issues that cannot be ignored.

  That is, as the in-cylinder pressure during combustion increases, the discharge voltage also increases accordingly. Therefore, the applied voltage must be increased accordingly. However, when the applied voltage is increased, the wear is apt to proceed.

  Therefore, it is conceivable to reduce the discharge voltage by decreasing the gap length as compared with the conventional case, as the in-cylinder pressure increases. However, when the gap length is reduced, the influence of the discharge increases and the electrodes are easily worn. Further, even with the same amount of wear, if the gap length is small, the influence on the change in the amount of wear increases.

  As a result, the replacement timing of the spark plug is shortened, and the replacement of the spark plug is required more frequently than before. Further, the variation in the timing of replacing the spark plug is also increased, and inappropriate replacement is increased. Therefore, even if the wear amount can be estimated with high accuracy, the replacement of the spark plug cannot be performed at an appropriate timing unless the initial variation is taken into account.

  On the other hand, the present inventors have examined the relationship between the gap length and the ignitability (the sensitivity of the air-fuel mixture to ignition), and the details will be described later. They found that it was possible to determine the spark plug abnormality due to electrode wear, and completed a new technology.

  In other words, the purpose of the disclosed technology is to determine whether or not the spark plug can be replaced at an appropriate timing even with an engine having a high compression ratio, not to mention an engine having a conventional compression ratio. It is to provide a device.

  The disclosed technology relates to an abnormality determination device for a spark plug mounted on an engine.

  The engine has a combustion chamber partitioned in a cylinder such that the volume is changed by a reciprocating piston. The spark plug has an electrode pair consisting of a ground electrode and a center electrode facing the combustion chamber with a predetermined gap therebetween.

  The abnormality determination device includes: a measurement unit that measures a parameter related to the operation of the engine; and an ignition that ignites an air-fuel mixture formed inside the combustion chamber by applying a predetermined ignition energy to the electrode pair. A control unit that is electrically connected to each of the measurement unit and the ignition unit, and that outputs a signal to the ignition unit based on a signal input from the measurement unit. The control unit has an abnormality determination unit that determines abnormality of the ignition plug caused by wear of the electrode pair.

  A first determination process in which the abnormality determination unit determines whether an amount of wear of the electrode pair, which increases according to an operation state of the engine, is equal to or more than a predetermined value; A second determination process for activating the spark plug by applying a determination ignition energy smaller than the ignition energy to the electrode pair when the value becomes equal to or more than the ignition energy; and applying the determination ignition energy to the electrode pair. Then, a third determination process of determining the ignitability of the air-fuel mixture is performed. Then, when it is determined in the third determination process that the ignitability of the air-fuel mixture is reduced, it is determined that the ignition plug is abnormal.

  That is, the ignition plug abnormality determination device includes a control unit having an abnormality determination unit, and the abnormality determination unit is configured to determine an abnormality of the ignition plug caused by wear of the electrode pair. Have been.

  The abnormality determination unit determines by a first determination process that the wear amount of the electrode pair has increased to a certain degree or more. By doing so, the frequency of subsequent processing is reduced, and efficient determination control can be realized.

  Then, the abnormality determination unit activates the ignition plug by applying a determination ignition energy smaller than the ignition energy to the electrode pair, that is, by lowering the applied voltage to make the ignition more difficult than the current state (second determination process). . Then, the ignitability of the air-fuel mixture is determined (third determination process).

  Although the details will be described later, the present inventors have examined the relationship between the gap length (including the wear amount and the initial variation) and the ignitability. As the gap length increases, the ignitability initially improves, but to some extent It has been found that the ignitability sharply decreases when the size becomes large, and an inflection point where the ignitability changes greatly is recognized. Therefore, the ignitability of the air-fuel mixture is determined in a state in which ignition is more difficult than in the current situation, and when it is determined that the ignitability of the air-fuel mixture has decreased, the ignition plug is determined to be abnormal.

  By doing so, it is possible to judge that the ignitability sharply decreases soon under the present conditions, and that the gap length is at a level that requires replacement of the spark plug. Therefore, according to the ignition plug abnormality determination device, it is possible to appropriately determine the abnormality of the ignition plug due to the increase in the gap length.

  The abnormality determining unit may output a signal requesting replacement of the spark plug when the spark plug is determined to be abnormal in the third determination process.

  Then, the user can replace the spark plug at an appropriate timing.

  In the first determination process, a signal input from the measurement unit every time combustion is performed in the combustion chamber and the number of times the spark plug is ignited in accordance with the combustion are integrated over time. By performing the process, a wear amount estimation process of estimating the wear amount of the electrode pair is performed, and using the estimated wear amount of the electrode pair, it is determined whether or not the predetermined value or more, It may be.

  That is, the abnormality determination unit estimates the amount of wear generated at the electrode pair for each ignition according to the operating state of the engine, and estimates the total amount of wear by integrating the amounts. Therefore, it is possible to reduce the influence of variations among the engines, and to accurately estimate the amount of wear of the electrode pair. Such a highly accurate estimation of the wear amount of the electrode pair makes it possible to not execute the second determination processing or the like until the wear amount is near the limit. Therefore, more efficient determination control can be realized.

  The ignition unit has an ignition coil that applies a voltage corresponding to an energization time to the electrode pair, and the ignition coil is energized according to a required voltage set according to a state inside the combustion chamber. In the second determination process, the energization time may be shortened so that a predetermined determination voltage lower than the required voltage is applied to the electrode pair.

  Then, it is possible to adjust the determination voltage applied to the electrode pair only by changing the time for energizing the ignition coil. Therefore, control efficiency can be improved.

  In the first determination process, the first electrode comprises a wear amount per unit time of the center electrode, a first wear amount estimation value in which the wear amount increases as the engine speed and load increase, and a first wear amount per unit time of the ground electrode. And the second pair of estimated wear amounts having a size different from the first estimated wear amount and having a larger wear amount as the engine speed and the load are higher. May be performed.

  The wear of the electrode pair differs between the center electrode and the ground electrode. The center electrode is mainly dominated by wear due to induction discharge, whereas the ground electrode is mainly dominated by wear due to capacitive discharge. Therefore, taking into account these differences in characteristics, the electrode pair wear is determined for each electrode based on the amount of wear (the first estimated value of wear and the second estimated value of wear) corresponding to the operating state of the engine. Estimate the amount. By doing so, highly accurate estimation of the wear amount of the electrode pair can be performed.

  In this case, when the engine speed and the load are compared under the same condition, the second estimated wear amount may be set to a value larger than the first estimated wear amount. .

  Due to the difference in characteristics, the amount of wear tends to be larger in the ground electrode than in the center electrode. Therefore, by setting the second estimated value of the wear amount to a relatively larger value than the first estimated value of the wear amount, the difference in the amount of wear based on the characteristics of each electrode becomes clear, and more accurate estimation can be performed. I can do it.

  The engine may have a geometric compression ratio of 16 or more.

  As described above, the disclosed ignition plug abnormality determination device is particularly effective for an engine having a high compression ratio. Therefore, if the geometric compression ratio of the engine to which the disclosed abnormality determination device for a spark plug is applied is 16 or more, the effect can be effectively exhibited.

  In particular, in this case, the control unit outputs a signal to the ignition unit so that the air-fuel mixture formed inside the combustion chamber is ignited at a predetermined timing. After starting the accompanying combustion, a predetermined compression ignition combustion in which the remaining unburned air-fuel mixture burns by self-ignition may be performed in the engine.

  That is, the present invention is applied to an engine that performs SPCCI combustion. Then, since the spark plug can be replaced without excess and deficiency, and the spark plug can be used in an appropriate state, stable combustion control can be performed even in advanced combustion control. Therefore, SPCCI combustion can be appropriately performed.

  According to the disclosed technology, it is possible to replace the spark plug at an appropriate timing, not to mention an engine having a high compression ratio, as well as an engine having a conventional compression ratio.

FIG. 2 is a diagram illustrating a configuration of an engine. It is a figure which illustrates the structure of a combustion chamber. The upper figure is a plan view equivalent view of a combustion chamber, and the lower figure is II-II sectional drawing. FIG. 2 is a plan view illustrating a configuration of a combustion chamber and an intake system. It is a figure which illustrates a spark plug and an ignition device. FIG. 2 is a block diagram illustrating a configuration of an engine control device. It is a figure which illustrates the waveform of SPCCI combustion. It is an example of an engine map. FIG. 4 is a diagram for explaining a relationship between the number of combustion cycles and a gap length. 4 is a graph showing a relationship between a discharge voltage and an integrated value of an in-cylinder pressure and a gap length. FIG. 3 is a block diagram illustrating a main configuration related to the abnormality determination device. It is a figure showing a wear amount distribution map. The upper diagram (a) shows a distribution map of the estimated wear amount of the center electrode. The lower diagram (b) shows a wear amount distribution map of the ground electrode. It is a graph showing the relationship between gap length and ignitability. It is a figure which shows an example of the flow of abnormality determination control of a spark plug.

  Hereinafter, embodiments of the disclosed technology will be described in detail with reference to the drawings. However, the following description is merely an example in nature, and does not limit the present invention, its application, or its use. The following description is an example of an abnormality determination device for an engine and a spark plug.

<Engine>
1 to 3 illustrate an engine 1 to which a disclosed abnormality determination device for a spark plug is applied. The engine 1 is a four-stroke engine in which the combustion chamber 17 operates by repeating an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. The engine 1 is mounted on a four-wheeled vehicle. When the engine 1 operates, the automobile runs. The fuel of the engine 1 is gasoline in this configuration example. The fuel may be a liquid fuel containing at least gasoline. The fuel may be gasoline containing, for example, bioethanol.

  The engine 1 includes a cylinder block 12 and a cylinder head 13 mounted thereon. A plurality of cylinders 11 (cylinders) are formed inside the cylinder block 12. 1 and 2, only one cylinder 11 is shown. The engine 1 is a multi-cylinder engine.

  The piston 3 is slidably inserted in each cylinder 11. The piston 3 is connected to a crankshaft 15 via a connecting rod 14. The piston 3 defines a combustion chamber 17 together with the cylinder 11 and the cylinder head 13. That is, the combustion chamber 17 is partitioned in a cylinder such that the volume changes with the reciprocating piston. The “combustion chamber” may be used in a broad sense. That is, the “combustion chamber” may mean a space formed by the piston 3, the cylinder 11, and the cylinder head 13 regardless of the position of the piston 3.

  The lower surface of the cylinder head 13, that is, the ceiling surface of the combustion chamber 17 is constituted by an inclined surface 1311 and an inclined surface 1312 as shown in the lower diagram of FIG. The inclined surface 1311 is inclined upward from the intake side toward the injection axis X2 of the injector 6 described later. The slope 1312 has an upward slope from the exhaust side toward the injection axis X2. The ceiling surface of the combustion chamber 17 has a so-called pent roof shape.

  The upper surface of the piston 3 protrudes toward the ceiling surface of the combustion chamber 17. A cavity 31 is formed on the upper surface of the piston 3. The cavity 31 is recessed from the upper surface of the piston 3. In this configuration example, the cavity 31 has a shallow dish shape. The center of the cavity 31 is shifted to the exhaust side from the center axis X1 of the cylinder 11.

  The geometric compression ratio of the engine 1 is set to 10 or more and 30 or less. For example, the geometric compression ratio of the engine 1 may be 16 or more, which is higher than that of a general spark ignition engine. As described later, the engine 1 performs SPCCI combustion that combines SI combustion and CI combustion in a part of the operating range. The SPCCI combustion controls the CI combustion by utilizing the heat generated by the SI combustion and the pressure increase. The engine 1 is a compression ignition type engine.

  However, in the engine 1, it is not necessary to increase the temperature of the combustion chamber 17 when the piston 3 reaches the compression top dead center (that is, the compression end temperature). The engine 1 can set the geometric compression ratio relatively low. Reducing the geometric compression ratio is advantageous for reducing cooling loss and mechanical loss.

  The geometric compression ratio of the engine 1 is 14 to 17 in a regular specification (a low octane fuel having an octane number of about 91), and 15 in a high octane specification (a high octane fuel having an octane number of about 96). To 18 may be used.

  An intake port 18 is formed in the cylinder head 13 for each cylinder 11. The intake port 18 has a first intake port 181 and a second intake port 182, as shown in FIG. The intake port 18 communicates with the combustion chamber 17. Although not shown in detail, the intake port 18 is a so-called tumble port. That is, the intake port 18 has a shape such that a tumble flow is formed in the combustion chamber 17.

  The intake port 18 is provided with an intake valve 21. The intake valve 21 opens and closes between the combustion chamber 17 and the intake port 18. The intake valve 21 opens and closes at a predetermined timing by a valve operating mechanism. The valve operating mechanism may be a variable valve operating mechanism that changes valve timing and / or valve lift. In this configuration example, as shown in FIG. 4, the variable valve mechanism has an intake electric S-VT (Sequential-Valve Timing) 23. The intake electric S-VT 23 continuously changes the rotation phase of the intake camshaft within a predetermined angle range. The valve opening timing and the valve closing timing of the intake valve 21 change continuously. Note that the intake valve operating mechanism may have a hydraulic S-VT instead of the electric S-VT.

  An exhaust port 19 is formed in the cylinder head 13 for each cylinder 11. The exhaust port 19 also has a first exhaust port 191 and a second exhaust port 192, as shown in FIG. The exhaust port 19 communicates with the combustion chamber 17.

  The exhaust port 19 is provided with an exhaust valve 22. The exhaust valve 22 opens and closes between the combustion chamber 17 and the exhaust port 19. The exhaust valve 22 opens and closes at a predetermined timing by a valve operating mechanism. This valve operating mechanism may be a variable valve operating mechanism that changes valve timing and / or valve lift. In this configuration example, as shown in FIG. 4, the variable valve mechanism has an exhaust electric S-VT24. The exhaust electric S-VT 24 continuously changes the rotation phase of the exhaust camshaft within a predetermined angle range. The valve opening timing and the valve closing timing of the exhaust valve 22 change continuously. The exhaust valve mechanism may have a hydraulic S-VT instead of the electric S-VT.

  The intake electric S-VT 23 and the exhaust electric S-VT 24 adjust the length of the overlap period during which both the intake valve 21 and the exhaust valve 22 are opened. When the length of the overlap period is increased, the residual gas in the combustion chamber 17 can be scavenged. Further, by adjusting the length of the overlap period, internal EGR (Exhaust Gas Recirculation) gas can be introduced into the combustion chamber 17. The internal EGR system includes an intake electric S-VT23 and an exhaust electric S-VT24. Note that the internal EGR system is not always configured by the S-VT.

  The injector 6 is attached to the cylinder head 13 for each cylinder 11. The injector 6 injects fuel directly into the combustion chamber 17. The injector 6 is an example of a fuel injection unit. The injector 6 is provided at a valley of the pent roof where the inclined surfaces 1311 and 1312 intersect. As shown in FIG. 2, the injection axis X2 of the injector 6 is located on the exhaust side of the center axis X1 of the cylinder 11. The injection axis X2 of the injector 6 is parallel to the central axis X1. The injection axis X2 of the injector 6 coincides with the center of the cavity 31. The injector 6 faces the cavity 31. Note that the injection axis X2 of the injector 6 may coincide with the center axis X1 of the cylinder 11. In the case of this configuration, the injection axis X2 of the injector 6 may coincide with the center of the cavity 31.

  Although not shown in detail, the injector 6 is configured by a multi-injection type fuel injection valve having a plurality of injection ports. The injector 6 injects the fuel such that the fuel spray spreads radially from the center of the combustion chamber 17 as shown by a two-dot chain line in FIG. In the present configuration example, the injector 6 has ten injection holes, and the injection holes are arranged at equal angles in the circumferential direction.

  A fuel supply system 61 is connected to the injector 6. The fuel supply system 61 includes a fuel tank 63 configured to store fuel, and a fuel supply path 62 that connects the fuel tank 63 and the injector 6 to each other. A fuel pump 65 and a common rail 64 are provided in the fuel supply path 62. The fuel pump 65 pumps fuel to the common rail 64. The fuel pump 65 is a plunger pump driven by the crankshaft 15 in this configuration example. The common rail 64 stores the fuel pumped from the fuel pump 65 at a high fuel pressure. When the injector 6 opens, the fuel stored in the common rail 64 is injected into the combustion chamber 17 from the injection port of the injector 6. The fuel supply system 61 can supply the fuel at a high pressure of 30 MPa or more to the injector 6. The pressure of the fuel supplied to the injector 6 may be changed according to the operating state of the engine 1. Note that the configuration of the fuel supply system 61 is not limited to the above configuration.

(Spark plug)
An ignition plug 25 is attached to the cylinder head 13 for each cylinder 11. The spark plug 25 forcibly ignites the mixture in the combustion chamber 17. In this configuration example, the spark plug 25 is disposed closer to the intake side than the center axis X1 of the cylinder 11. The spark plug 25 is located between the two intake ports 18. The ignition plug 25 is attached to the cylinder head 13 so as to be inclined downward from the upper side toward the center of the combustion chamber 17. As shown in FIG. 2, the electrode of the ignition plug 25 faces the inside of the combustion chamber 17 and is located near the ceiling surface of the combustion chamber 17. Note that the ignition plug 25 may be arranged on the exhaust side of the center axis X1 of the cylinder 11. Further, the spark plug 25 may be arranged on the central axis X1 of the cylinder 11.

  An ignition device 251 is electrically connected to the ignition plug 25 (also simply referred to as connection). The ignition device 251 (an example of an ignition unit) is connected to the battery 252 and supplies electric power to the ignition plug 25 (the details of the ignition plug and the ignition device 251 will be described later).

  An intake passage 40 is connected to one side of the engine 1. The intake passage 40 communicates with the intake port 18 of each cylinder 11. The gas introduced into the combustion chamber 17 flows through the intake passage 40. An air cleaner 41 is provided at an upstream end of the intake passage 40. The air cleaner 41 filters fresh air. A surge tank 42 is provided near the downstream end of the intake passage 40. The intake passage 40 downstream of the surge tank 42 forms an independent passage that branches off for each cylinder 11. The downstream end of the independent passage is connected to the intake port 18 of each cylinder 11.

  A throttle valve 43 is provided between the air cleaner 41 and the surge tank 42 in the intake passage 40. The throttle valve 43 adjusts the amount of fresh air introduced into the combustion chamber 17 by adjusting the opening degree of the valve. That is, the throttle valve 43 constitutes an “air adjustment unit” that adjusts the amount of air supplied to each combustion chamber 17 by increasing or decreasing it.

  In the intake passage 40, a supercharger 44 is disposed downstream of the throttle valve 43. The supercharger 44 supercharges the gas introduced into the combustion chamber 17. In this configuration example, the supercharger 44 is a mechanical supercharger driven by the engine 1. The mechanical supercharger 44 may be of a Roots type, a Richolm type, a vane type, or a centrifugal type.

  An electromagnetic clutch 45 is interposed between the supercharger 44 and the engine 1. The electromagnetic clutch 45 transmits a driving force from the engine 1 to the supercharger 44 between the supercharger 44 and the engine 1 or interrupts the transmission of the driving force. As will be described later, the supercharger 44 is switched on and off when the ECU 10 switches between disconnection and connection of the electromagnetic clutch 45.

  An intercooler 46 is provided downstream of the supercharger 44 in the intake passage 40. The intercooler 46 cools the gas compressed in the supercharger 44. The intercooler 46 may be configured, for example, as a water-cooled type or an oil-cooled type.

  A bypass passage 47 is connected to the intake passage 40. The bypass passage 47 connects the upstream portion of the supercharger 44 and the downstream portion of the intercooler 46 in the intake passage 40 with each other so as to bypass the supercharger 44 and the intercooler 46. An air bypass valve 48 is provided in the bypass passage 47. The air bypass valve 48 adjusts the flow rate of gas flowing through the bypass passage 47.

  The ECU 10 fully opens the air bypass valve 48 when the supercharger 44 is turned off (that is, when the electromagnetic clutch 45 is disconnected). Gas flowing through the intake passage 40 bypasses the supercharger 44 and is introduced into the combustion chamber 17 of the engine 1. The engine 1 operates in a non-supercharged state, that is, in a state of natural intake.

  When the turbocharger 44 is turned on, the engine 1 operates in a supercharged state. The ECU 10 adjusts the opening of the air bypass valve 48 when the turbocharger 44 is turned on (that is, when the electromagnetic clutch 45 is engaged). Part of the gas that has passed through the supercharger 44 flows back to the upstream of the supercharger 44 through the bypass passage 47. When the ECU 10 adjusts the opening of the air bypass valve 48, the supercharging pressure of the gas introduced into the combustion chamber 17 changes. It should be noted that the supercharging time is defined as a time when the pressure in the surge tank 42 exceeds the atmospheric pressure, and the non-supercharging time is defined as a time when the pressure in the surge tank 42 becomes equal to or less than the atmospheric pressure. Is also good.

  In this configuration example, a supercharging system 49 is configured by the supercharger 44, the bypass passage 47, and the air bypass valve 48.

  The engine 1 has a swirl generator that generates a swirl flow in the combustion chamber 17. The swirl generator has a swirl control valve 56 attached to the intake passage 40, as shown in FIG. The swirl control valve 56 is disposed in the secondary passage 402 of the primary passage 401 connected to the first intake port 181 and the secondary passage 402 connected to the second intake port 182. The swirl control valve 56 is an opening control valve that can narrow the cross section of the secondary passage 402. When the degree of opening of the swirl control valve 56 is small, the flow rate of intake air flowing from the first intake port 181 into the combustion chamber 17 is relatively large, and the flow rate of intake air flowing from the second intake port 182 into the combustion chamber 17 is relatively high. Since it is small, the swirl flow in the combustion chamber 17 becomes strong. If the degree of opening of the swirl control valve 56 is large, the flow rate of intake air flowing into the combustion chamber 17 from each of the first intake port 181 and the second intake port 182 becomes substantially equal, so that the swirl flow in the combustion chamber 17 is weak. Become. When the swirl control valve 56 is fully opened, no swirl flow occurs. Note that the swirl flow circulates counterclockwise in FIG. 3 as indicated by the white arrow (see also the white arrow in FIG. 2).

  An exhaust passage 50 is connected to the other side of the engine 1. The exhaust passage 50 communicates with the exhaust port 19 of each cylinder 11. The exhaust passage 50 is a passage through which the exhaust gas discharged from the combustion chamber 17 flows. Although not shown in detail, an upstream portion of the exhaust passage 50 constitutes an independent passage branched for each cylinder 11. The upstream end of the independent passage is connected to the exhaust port 19 of each cylinder 11.

  An exhaust gas purification system having a plurality of catalytic converters is provided in the exhaust passage 50. Although not shown, the upstream catalytic converter is disposed in the engine room. The upstream catalytic converter has a three-way catalyst 511 and a GPF (Gasoline Particulate Filter) 512. The downstream catalytic converter is located outside the engine room. The downstream catalytic converter has a three-way catalyst 513. Note that the exhaust gas purification system is not limited to the configuration shown in the figure. For example, the GPF may be omitted. Further, the catalytic converter is not limited to one having a three-way catalyst. Furthermore, the arrangement order of the three-way catalyst and the GPF may be appropriately changed.

  An EGR passage 52 constituting an external EGR system is connected between the intake passage 40 and the exhaust passage 50. The EGR passage 52 is a passage for returning a part of the exhaust gas to the intake passage 40. The upstream end of the EGR passage 52 is connected between the upstream catalytic converter and the downstream catalytic converter in the exhaust passage 50. The downstream end of the EGR passage 52 is connected to an upstream portion of the supercharger 44 in the intake passage 40. The EGR gas flowing through the EGR passage 52 enters the intake passage 40 upstream of the supercharger 44 without passing through the air bypass valve 48 of the bypass passage 47.

  The EGR passage 52 is provided with a water-cooled EGR cooler 53. The EGR cooler 53 cools the exhaust gas. An EGR valve 54 is also provided in the EGR passage 52. The EGR valve 54 adjusts the flow rate of the exhaust gas flowing through the EGR passage 52. By adjusting the opening of the EGR valve 54, it is possible to adjust the amount of recirculated exhaust gas, that is, the amount of external EGR gas.

  In this configuration example, the EGR system 55 includes an external EGR system and an internal EGR system. The external EGR system can supply exhaust gas having a lower temperature than the internal EGR system to the combustion chamber 17.

(Spark plug and ignition device)
As shown in FIG. 4, the spark plug 25 has a pair of electrodes (electrode pair 250) facing the inside of the combustion chamber 17. Each of the electrode pairs 250 includes a ground electrode 250a and a center electrode 250b formed using a material such as a nickel alloy, platinum, and an iridium alloy. The ground electrode 250a and the center electrode 250b face each other with a gap having a predetermined size (gap length G) therebetween.

  When ignition energy is applied to these electrode pairs 250 (specifically, a high voltage is applied instantaneously), discharge occurs between the electrode pairs 250. Thereby, a flame kernel is formed. As the flame kernel grows, the air-fuel mixture formed inside the combustion chamber 17 is ignited.

  When the gap length G is small, the heat of the fuel is absorbed by the ground electrode 250a and the center electrode 250b, and the formation and growth of the flame nucleus is hindered (so-called cooling loss). Therefore, in the engine 1, the gap length G is set to at least 0.5 mm or more (the initial value of the gap length G ≧ 0.5 mm).

  An ignition device 251 is connected to the ignition plug 25 to supply power to the electrode pair 250. The ignition device 251 includes an ignition coil 251a, an igniter 251b, a discharge ammeter 251c, and the like. The ignition coil 251a includes a primary coil 251a1, a secondary coil 251a2, a core 251a3, and the like.

  One end of the primary coil 251a1 is connected to the battery 252. The other end of the primary coil 251a1 is connected (grounded) to a reference potential via an igniter 251b connected to the ECU 10. One end of the secondary coil 251a2 is connected to each ignition plug 25 (specifically, the center electrode 250b) via a distributor (device for distributing electric power to the ignition plug 25 of each cylinder 11) not shown.

  The other end of the secondary coil 251a2 is connected (grounded) to a reference potential via a discharge ammeter 251c connected to the ECU 10. The discharge ammeter 251c measures the current value of the current flowing through the secondary coil 251a2, and outputs a signal to the ECU 10. The secondary coil 251a2 has a larger number of turns than the primary coil 251a1. The igniter 251b switches between an ON state in which the power of the battery 252 is supplied to the primary coil 251a1 and an OFF state in which the power of the battery 252 is not supplied to the primary coil 251a1, according to a signal input from the ECU 10.

  When the igniter 251b is turned on, the primary coil 251a1 is energized, and a magnetic field is generated in the ignition coil 251a. Thereafter, when the igniter 251b is turned off at a predetermined timing, a current flows through the secondary coil 251a2 by electromagnetic induction to generate a voltage. Since the number of turns of the secondary coil 251a2 is larger than the number of turns of the primary coil 251a1, a high voltage is generated in the secondary coil 251a2. When the high voltage is applied to the electrode pair 250, the air-fuel mixture formed inside the combustion chamber 17 is ignited.

  The ignition timing is determined by the timing at which the primary coil 251a1 is energized. Further, the magnitude of the voltage (applied voltage) applied to the electrode pair 250 is determined by the energization time (dwell time) to the primary coil 251a1. That is, the applied voltage is correlated with the dwell time. Usually, in order to perform stable ignition, the applied voltage is set to be higher than the voltage required for discharging (discharge voltage).

  The discharge voltage is proportional to the gap length G and the internal pressure of the combustion chamber 17 at the time of ignition. In normal control, the gap length G is regarded as a constant value, so that the ignition device 251 applies a predetermined voltage (required voltage) corresponding to the internal pressure of the combustion chamber 17 at the time of ignition to the electrode pair 250 in response to a request from the ECU 10. Is applied.

  Specifically, the ECU 10 determines a voltage to be applied to the electrode pair 250 based on an internal pressure of the combustion chamber 17 obtained from an input signal of the in-cylinder pressure sensor SW6, an applied voltage obtained from an input signal of the discharge ammeter 251c, and the like. Required voltage). In this engine 1, the required voltage is set to be at least 10 kV or more.

  On the other hand, the ignition device 251 adjusts the dwell time based on the set required voltage so that a dischargeable voltage is applied to the electrode pair 250. If the required voltage is high, the dwell time is increased, and if the required voltage is low, the dwell time is reduced. When the engine 1 is operating, the ignition coil 251a is energized according to a state inside the combustion chamber 17, that is, a required voltage set according to the internal pressure of the combustion chamber 17.

(ECU)
The engine 1 is provided with an ECU (Engine Control Unit) 10 for controlling its operation. The ECU 10 is a controller based on a known microcomputer, and as shown in FIG. 5, a central processing unit (CPU) 10a that executes a program, and a RAM (Random Access Memory) or a ROM, for example. (Read Only Memory) and a memory 10b for storing programs and data, and an input / output bus 10c for inputting and outputting electric signals. The ECU 10 is an example of a “control unit”.

  Various sensors SW1 to SW17 are connected to the ECU 10, as shown in FIGS. The sensors SW1 to SW17 output signals to the ECU 10. These sensors SW1 to SW17 are examples of a “measurement unit” that measures various parameters related to the operation of the engine 1. The contents of these sensors SW1 to SW17 are shown below.

Airflow sensor SW1: disposed downstream of air cleaner 41 in intake passage 40 and measures the flow rate of fresh air flowing through intake passage 40 First intake air temperature sensor SW2: disposed downstream of air cleaner 41 in intake passage 40; , Which measures the temperature of fresh air flowing through the intake passage 40. The first pressure sensor SW3 is disposed downstream of the connection position of the EGR passage 52 in the intake passage 40 and upstream of the supercharger 44, and The second intake air temperature sensor SW4 is disposed downstream of the supercharger 44 in the intake passage 40 and upstream of the connection position of the bypass passage 47, and flows out of the supercharger 44. A second pressure sensor SW5 for measuring the temperature of the gas, which is attached to the surge tank 42 and measures the pressure of the gas downstream of the supercharger 44. In-cylinder pressure sensor SW6: attached to cylinder head 13 corresponding to each cylinder 11 and measures pressure in each combustion chamber 17 Exhaust temperature sensor SW7: disposed in exhaust passage 50 and discharged from combustion chamber 17 measuring the temperature of the exhaust gas linear O ₂ sensor SW8: disposed upstream of the catalytic converter upstream of the exhaust passage 50 and measures the oxygen concentration in the exhaust gas lambda O ₂ sensor SW9: three upstream of the catalytic converter Water temperature sensor SW10, which is arranged downstream of the main catalyst 511 and measures the oxygen concentration in the exhaust gas, is attached to the engine 1 and measures the temperature of cooling water. Crank angle sensor SW11: is attached to the engine 1 and cranks. Accelerator opening sensor SW12 for measuring rotation angle of shaft 15: accelerator pedal The intake cam angle sensor SW13: attached to the engine 1 and measures the rotation angle of the intake camshaft. The exhaust cam angle sensor SW14: engine 1 attached to the structure and measures the accelerator opening corresponding to the operation amount of the accelerator pedal. EGR differential pressure sensor SW15: disposed in the EGR passage 52 and measuring the upstream and downstream differential pressures of the EGR valve 54. Fuel pressure sensor SW16: of the fuel supply system 61 A third intake air temperature sensor SW17 attached to the common rail 64 and measuring the pressure of the fuel supplied to the injector 6 is attached to the surge tank 42 and is introduced into the combustion chamber 17 in other words, the temperature of the gas in the surge tank 42. Measure the temperature of the intake air.

  The discharge ammeter 251c of the ignition device 251 also outputs a signal to the ECU 10. Therefore, the measurement unit also includes the discharge ammeter 251c.

  The ECU 10 determines the operating state of the engine 1 based on the signals of the sensors SW1 to SW17 and the discharge ammeter 251c, and calculates the control amount of each device according to a predetermined control logic. The control logic is stored in the memory 10b. The control logic includes calculating a target amount and / or a control amount using the map stored in the memory 10b.

  The ECU 10 sends an electric signal related to the calculated control amount to the injector 6, the intake electric S-VT 23, the exhaust electric S-VT 24, the fuel supply system 61, the throttle valve 43, the EGR valve 54, and the electromagnetic clutch 45 of the supercharger 44. , The air bypass valve 48, the swirl control valve 56, the alarm 57, and the ignition device 251. The annunciator 57 is a device that notifies an occupant of an alarm or the like, and includes, for example, a lamp or the like displayed on an instrument panel.

(SPCCI combustion concept)
The engine 1 performs combustion by compression self-ignition in a predetermined operating state with a primary purpose of improving fuel efficiency and exhaust gas performance. In the combustion by self-ignition, when the temperature in the combustion chamber 17 before the start of compression varies, the timing of self-ignition greatly changes. Therefore, the engine 1 performs SPCCI combustion that combines SI combustion and CI combustion.

  In the SPCCI combustion, the ignition plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17 so that the air-fuel mixture performs SI combustion by flame propagation and generates heat in the combustion chamber 17 by the heat generated by the SI combustion. This is a mode in which the unburned air-fuel mixture performs CI combustion by self-ignition due to an increase in temperature and an increase in pressure in the combustion chamber 17 due to flame propagation (partial compression ignition combustion).

  By adjusting the calorific value of the SI combustion, it is possible to absorb the temperature variation in the combustion chamber 17 before the start of compression. By adjusting the ignition timing by the ECU 10, the air-fuel mixture can self-ignite at the target timing.

  In SPCCI combustion, heat generation during SI combustion is more moderate than heat generation during CI combustion. As illustrated in FIG. 6, the waveform of the heat release rate in the SPCCI combustion has a rising slope smaller than the rising slope in the CI combustion waveform. Also, the pressure fluctuation (dp / dθ) in the combustion chamber 17 becomes gentler during SI combustion than during CI combustion.

  When the unburned air-fuel mixture self-ignites after the start of SI combustion, the slope of the heat release rate waveform may change from small to large at the timing of self-ignition. The waveform of the heat release rate may have an inflection point X at the timing θci at which the CI combustion starts.

  After the start of CI combustion, SI combustion and CI combustion are performed in parallel. Since the CI combustion generates more heat than the SI combustion, the heat generation rate is relatively large. However, since the CI combustion is performed after the compression top dead center, the slope of the waveform of the heat release rate is prevented from becoming too large. The pressure fluctuation (dp / dθ) during CI combustion also becomes relatively moderate.

  The pressure fluctuation (dp / dθ) can be used as an index representing combustion noise. As described above, in the SPCCI combustion, since the pressure fluctuation (dp / dθ) can be reduced, it is possible to prevent the combustion noise from becoming too large. The combustion noise of the engine 1 is kept below an allowable level.

  When the CI combustion ends, the SPCCI combustion ends. CI combustion has a shorter combustion period than SI combustion. SPCCI combustion has an earlier combustion end timing than SI combustion.

The heat-release-rate waveform of SPCCI combustion, a first heat generation rate portion Q _SI formed by SI combustion, and the second heat generating section Q _CI formed by CI combustion, but formed continuous in this order Have been.

Here, the SI ratio is defined as a parameter indicating the characteristics of SPCCI combustion. The SI rate is defined as an index related to the ratio of the amount of heat generated by SI combustion to the total amount of heat generated by SPCCI combustion. The SI ratio is a ratio of the amount of heat generated by two combustions having different combustion modes. When the SI ratio is high, the ratio of SI combustion is high, and when the SI ratio is low, the ratio of CI combustion is high. The SI rate may be defined as the ratio of the amount of heat generated by SI combustion to the amount of heat generated by CI combustion. That is, in SPCCI combustion, the crank angle at which the CI combustion starts as CI combustion start time Shitaci, in the waveform 801 shown in FIG. 6, the area _{Q SI} the SI combustion also advance side than Shitaci, slow including Shitaci angle from the area _{Q CI} of CI combustion is a side, it may be SI index ₌ Q SI _{/ Q CI.}

  The engine 1 may generate a strong swirl flow in the combustion chamber 17 when performing SPCCI combustion. More specifically, the engine 1 generates a strong swirl flow in the combustion chamber 17 when performing the SPCCI combustion of the air-fuel mixture leaner than the stoichiometric air-fuel ratio. A strong swirl flow may be defined as a flow having a swirl ratio of, for example, 4 or more. The swirl ratio can be defined as a value obtained by dividing the value obtained by measuring and integrating the intake flow lateral angular velocity for each valve lift by the engine angular velocity. Although not illustrated, the intake flow lateral angular velocity can be obtained based on measurement using a known rig tester.

  When a strong swirl flow is generated in the combustion chamber 17, the outer peripheral portion of the combustion chamber 17 becomes a strong swirl flow, while the swirl flow in the central portion becomes relatively weak. When the injector 6 injects fuel into the combustion chamber 17 where a strong swirl flow is formed, the fuel mixture in the center of the combustion chamber 17 is relatively rich and the fuel mixture in the outer periphery is relatively rich in fuel. It becomes thin, and the mixture can be stratified.

(Basic engine control)
The ECU 10 operates the engine 1 according to the control logic stored in the memory 10b.

  That is, the ECU 10 determines the operating state of the engine 1 based on the signals from the sensors SW1 to SW17, sets the target torque, and sets the state in the combustion chamber 17 so that the engine 1 outputs the target torque. Calculation for adjusting the amount, the injection amount, the injection timing, and the ignition timing is performed.

  When performing the SPCCI combustion, the ECU 10 controls the SPCCI combustion using two parameters, the SI ratio and θci. Specifically, the ECU 10 determines the target SI ratio and the target θci corresponding to the operating state of the engine 1 and sets the combustion chamber 17 so that the actual SI ratio matches the target SI ratio and the actual θci becomes the target θci. And the ignition timing.

  The ECU 10 sets a low target SI ratio when the load on the engine 1 is low, and sets a high target SI ratio when the load on the engine 1 is high. When the load of the engine 1 is low, the suppression of the combustion noise and the improvement of the fuel economy are compatible with each other by increasing the ratio of the CI combustion in the SPCCI combustion. When the load of the engine 1 is high, increasing the ratio of SI combustion in SPCCI combustion is advantageous for suppressing combustion noise.

(Engine operating area)
FIG. 7 illustrates a map (at a warm state) related to the control of the engine 1. The map is stored in the memory 10b of the ECU 10. The map is roughly divided into three areas according to the level of the load and the level of the rotation speed. Specifically, the three regions include the low load region A1 including the idling operation and extending to the low rotation speed and the middle rotation region, the middle and high load regions A2, A3, A4, and the low load region higher in load than the low load region A1. This is a high rotation region A5 having a higher rotation speed than the load region A1, the medium and high load regions A2, A3, and A4. The medium and high load regions A2, A3, and A4 also include a medium load region A2, a high load medium rotation region A3 having a higher load than the middle load region A2, and a high load low rotation having a lower rotation speed than the high load medium rotation region A3. It is divided into an area A4.

  Here, the low rotation region, the middle rotation region, and the high rotation region are respectively obtained by dividing the entire operation region of the engine 1 into approximately three equal parts of the low rotation region, the middle rotation region, and the high rotation region in the rotation speed direction. The low rotation region, the middle rotation region, and the high rotation region may be used. In the example of FIG. 7, the rotation speed is low when the rotation speed is less than N1, high when the rotation speed is N2 or more, and is medium when the rotation speed is N1 or more and less than N2. The rotation speed N1 may be, for example, about 1200 rpm, and the rotation speed N2 may be, for example, about 4000 rpm.

  The low load region may be a region including a light load operation state, the high load region may be a region including a fully open load operation state, and the medium load region may be a region between a low load region and a high load region. Further, the low load region, the medium load region, and the high load region are respectively obtained by dividing the entire operation region of the engine 1 in the load direction into approximately three equal parts of the low load region, the medium load region, and the high load region. It may be a low load area, a medium load area, and a high load area.

  The engine 1 performs SPCCI combustion in the low load region A1, the medium load region A2, the high load medium rotation region A3, and the high load low rotation region A4. The engine 1 also performs SI combustion in the high rotation region A5.

  For example, in the low load region A1, the air-fuel ratio of the air-fuel mixture (the value of the air-fuel ratio at the time of ignition, A / F) is leaner than the stoichiometric air-fuel ratio in the entire combustion chamber 17 (that is, the excess air ratio λ>). 1). More specifically, the A / F of the air-fuel mixture in the entire combustion chamber 17 is 25 or more and 31 or less. Therefore, when the engine 1 is operating in the low load region A1, the engine 1 performs SPCCI combustion under a condition where the air-fuel ratio is lean (lean SPCCI combustion).

  That is, when the engine 1 is operating in the low load region A1, after the fuel injection ends, the ECU 10 determines that the actual SI ratio matches the target SI ratio and the actual θci becomes the target θci, A signal is output to the ignition device 251 so that the ignition plug 25 ignites the air-fuel mixture at a predetermined timing immediately before the ignition.

<Ignition device for spark plug>
The spark plug abnormality determination device (also simply referred to as abnormality determination device 100) is a device that determines whether the ignition plug 25 has an abnormality. In the engine 1, the abnormality determination device 100 includes the ECU 10, the sensors SW1 to SW17, the ignition device 251 and the like (see FIG. 10). The configuration of the abnormality determination device 100 can be appropriately changed according to specifications.

  The spark plug 25 is a consumable that needs to be replaced periodically. In the case of this engine 1, SPCCI combustion is performed, so that the geometric compression ratio is higher than that of a general spark ignition type engine. That is, the internal pressure (in-cylinder pressure) of the combustion chamber 17 during combustion is relatively high. Therefore, the electrode pair 250 is easily worn, and the spark plug 25 needs to be replaced frequently. Abnormality judging device 100 is used particularly for judging such a replacement timing of spark plug 25.

(Relationship between electrode pair wear and spark plug replacement timing)
The electrode pair 250 wears out each time ignition occurs. That is, each of the center electrode 250b and the ground electrode 250a is consumed by the discharge. Wear of the center electrode 250b mainly due to the induced discharge is dominant. On the other hand, the ground electrode 250a is mainly dominated by wear due to capacitive discharge. Each time the ignition is performed, the center electrode 250b and the ground electrode 250a are gradually consumed according to the intensity of the discharge, and the gap length G increases. Since the mechanism of consumption of these electrodes is known, detailed description thereof is omitted.

  The amount of wear of the electrode pair 250 varies depending on the operating state of the engine 1. Therefore, the timing of replacing the spark plug 25 depends on the driving technique and preferences of the user, and varies among the engines 1. On the other hand, the replacement timing of the spark plug 25 is generally set uniformly for each predetermined traveling distance based on an empirical rule. The replacement timing of the spark plug 25 is set on the safe side in consideration of the variation.

  Therefore, if the replacement timing of the spark plug 25 is uniformly set to the safe side as in the past, a user who has not actually reached the timing to replace the spark plug 25 can replace the spark plug 25 which can still be used sufficiently. It may also happen.

  This point will be specifically described with reference to FIG. FIG. 8 schematically shows the relationship between the number of combustion cycles (corresponding to the traveling distance) and the gap length G. A graph L1 shows a change in the gap length G with time of a general spark ignition type engine. A graph L2 represents a change in the gap length G of the engine 1 over time. GL1 and GL2 represent the upper limit values of the gap length G of the general spark ignition engine and the engine 1, respectively.

  The discharge voltage can be linearly approximated to the converted electrode distance (integrated value of the in-cylinder pressure and the gap length G) according to Paschen's law. That is, as shown in FIG. 9, the discharge voltage is proportional to the in-cylinder pressure (for example, charging efficiency / volume of the combustion chamber 17 at the time of ignition) and the integrated value of the gap length G. Therefore, when the in-cylinder pressure during combustion increases, if the gap length G is the same, the discharge voltage increases accordingly.

  This correlation is the same for the applied voltage or the required voltage. Therefore, in FIG. 9, the discharge voltage can be replaced with the applied voltage or the required voltage.

  Therefore, when the gap length is increased and the discharge voltage is increased, the applied voltage or the required voltage must be increased in accordance with the increase in the discharge voltage, but the voltage of the battery 252 may be insufficient. For this reason, in the engine 1, the initial gap length G is made smaller than that of the conventional spark ignition type engine in order to lower the discharge voltage as the in-cylinder pressure increases (in FIG. 8, from GS1 to GS2 in FIG. 8). To).

  However, when the gap length G is reduced, the influence of the discharge is increased and the electrodes are easily worn (the inclination of the graph L1 <the inclination of the graph L2). As a result, the replacement timing of the spark plug 25 is shortened, and replacement at a higher frequency than in the related art is required. In addition, if the electrode is easily worn, the variation increases accordingly (variation width D1 in graph L1 <variation width D2 in graph L2).

  As a result, when the replacement timing of the spark plug 25 is set on the safe side in consideration of the variation width D2, as shown by the arrow lines R1 and R2 in FIG. The period during which the user replaces the spark plug 25 at an inappropriate timing is longer than that of the expression engine.

  Further, even with the same variation, if the gap length G is small, the influence on the replacement timing is increased accordingly. For example, when the gap length G of 1 mm is set to 0.5 mm, the wear of 0.1 mm is increased by 10% in the former case and increased by 20% in the latter case. Therefore, as the gap length G decreases, the influence on the replacement timing of the spark plug 25 increases.

  In addition, the gap length G has a variation (initial variation) based on the tolerance even when the spark plug 25 is not used (GS1, GS2). This initial variation also affects the replacement timing of the spark plug 25 together with the amount of wear. Although it depends on the specifications of the spark plug 25, there is a possibility that the traveling distance may have an effect of several hundred to several thousand km only by the initial variation.

  On the other hand, in the abnormality determination device 100, the abnormality of the ignition plug 25 caused by the wear of the electrode pair 250 can be effectively determined so that the replacement of the ignition plug 25 can be performed at appropriate timing with no excess or shortage. It is devised.

(Abnormality judgment unit)
FIG. 10 shows a main configuration related to the abnormality determination device 100. The ECU 10 includes an abnormality determination unit 101. The abnormality determination unit 101 determines whether or not there is an abnormality in the spark plug 25 caused by wear of the electrode pair 250. Signals from the sensors SW1 to SW17, such as a signal from the in-cylinder pressure sensor SW6, and a signal from the discharge ammeter 251c of the ignition device 251 are input to the abnormality determination unit 101. Then, based on these signals, abnormality determination unit 101 outputs a signal to ignition device 251 in order to execute a predetermined process of determining abnormality of spark plug 25 due to wear of electrode pair 250.

  Specifically, the abnormality determination unit 101 performs a first determination process, a second determination process, a third determination process, and the like. Then, when the abnormality determination unit 101 determines in the third determination process that the ignitability of the air-fuel mixture has decreased, the abnormality caused by the wear of the electrode pair 250 is detected in the ignition plug 25. It is determined that there is.

(First determination process)
In the first determination process, a process is performed to determine whether the amount of wear of the electrode pair 250 that increases according to the operating state of the engine 1 is equal to or greater than a predetermined value (wear reference value).

  More specifically, each time combustion is performed in the combustion chamber 17, a time-based integration is performed using a signal input from each of the sensors SW1 to SW17 and the number of times the ignition plug 25 is ignited with the combustion. Perform processing. By doing so, a wear amount estimation process for estimating the wear amount of the electrode pair 250 is performed. Using the estimated wear amount of the electrode pair 250, it is determined whether or not the wear amount is equal to or more than the wear reference value.

  The abnormality determination unit 101 is provided with two maps (estimated wear amount distribution maps) corresponding to the operating state of the engine 1 in order to execute the first determination process. These estimated wear amount distribution maps correspond to the center electrode 250b and the ground electrode 250a, respectively, and are set based on a wear estimation formula corresponding to the wear characteristics of the center electrode 250b and the ground electrode 250a, respectively. .

  Each wear estimation formula is configured based on the results of various tests such as a durability test and a rig test. A specific example will be described.

(Estimation formula for wear of ground electrode 250a)
Estimated wear amount of ground electrode 250a = constant × plug capacity × (total gas filling amount / in-cylinder volume at ignition−constant) square × times of ignition

(Estimation formula for wear of center electrode 250b)
Estimated wear amount of the center electrode 250b = constant × (in-cylinder pressure at ignition / in-cylinder temperature at ignition) square × ignition frequency × time integral of discharge current

  Here, the terms “total gas charge / in-cylinder volume at ignition” and “cylinder pressure at ignition / in-cylinder temperature at ignition” respectively correspond to the in-cylinder density. The term “time integration value of discharge current” is a value related to the discharge characteristics of the ignition coil 251a.

  FIG. 11 shows an example of each estimated wear amount distribution map. FIG. 11 (a) in the upper part of FIG. 11 shows the estimated wear amount distribution map (first estimated wear amount distribution map) of the center electrode 250b. FIG. 11B at the bottom of FIG. 11 illustrates a wear amount distribution map (second wear estimated amount distribution map) of the ground electrode 250a. In each of the estimated wear amount distribution maps, the amount of wear estimated to occur per unit time is set according to each rotational speed and each load of the engine 1.

  That is, the first estimated wear amount distribution map includes the amount of wear of the center electrode 250b per unit time, and the estimated value of the wear amount (first amount) corresponding to each rotation speed of the engine 1 and each load (intake charge amount). Wear amount). The second estimated wear amount distribution map includes the amount of wear of the ground electrode 250a per unit time, and an estimated value of the wear amount (second estimated wear amount) corresponding to each rotation speed and each load of the engine 1 is set. Have been.

  Both the first estimated wear amount and the second estimated wear amount tend to increase as the load on the engine 1 increases. Both the first estimated wear amount and the second estimated wear amount tend to increase as the rotation speed of the engine 1 increases. Both the first estimated wear amount and the second estimated wear amount tend to change more greatly with a change in load than the rotation speed of the engine 1.

  Further, when the rotation speed and the load of the engine 1 are compared under the same conditions, the second estimated wear amount is set to a value larger than the first estimated wear amount. That is, in the engine 1 in which the SPCCI combustion is performed, the ground electrode 250a tends to be worn more easily than the center electrode 250b.

  When the engine 1 is operating, the abnormality determination unit 101 inputs a signal from each of the sensors SW1 to SW17. For example, the in-cylinder pressure at the time of ignition is obtained based on a signal input from the in-cylinder pressure sensor SW6, and the in-cylinder volume at the time of ignition is obtained based on a signal input from the crank angle sensor SW11.

  Then, the abnormality determination unit 101 obtains the rotation speed and load of the engine 1 and the state quantity in the cylinder at the time of operation, and uses the first estimated wear amount distribution map and the second estimated wear amount distribution map, An estimated wear amount per ignition of the center electrode 250b and the ground electrode 250a according to the rotation speed and the load of the engine 1 is calculated. Then, the abnormality determination unit 101 acquires the estimated wear per ignition of the electrode pair 250 by adding the estimated wear per ignition of the center electrode 250b and the ground electrode 250a.

  Each time the engine 1 ignites, the abnormality determination unit 101 acquires the estimated wear amount per ignition of the electrode pair 250 and accumulates the acquired estimated wear amount per ignition. By doing so, the abnormality determining unit 101 estimates the amount of wear of the electrode pair 250 that increases according to the operating state of the engine 1.

  As described above, the abnormality determination unit 101 estimates the amount of wear generated in the electrode pair 250 for each ignition while considering the wear characteristics of each electrode according to the operating state of the engine 1, and integrates the amount of wear. Thus, the total amount of wear is estimated. Therefore, the influence of the variation due to the difference in the operation history of the engine 1 can be reduced, and the wear amount can be estimated with high accuracy.

  However, even if the wear amount can be estimated with high accuracy only by the first determination processing, the initial variation is not taken into account. Therefore, if the spark plug 25 is replaced based on the wear amount estimated in the wear amount estimation process, the spark plug 25 may still need to be replaced at inappropriate timing.

  Therefore, in the abnormality determination device 100, the wear amount estimation processing is used as a pre-processing in determining abnormality of the spark plug 25. That is, the first determination process is performed before the second determination process and the third determination process for actually determining the replacement timing of the spark plug 25, and the frequency of performing the second determination process and the third determination process is reduced. Therefore, a wear amount estimation process is performed.

  Specifically, a wear reference value having a predetermined wear amount, which is larger than the initial value of the gap length G and smaller than the upper limit value of the gap length G (the limit value at which ignition can be appropriately performed), is sent to the abnormality determination unit 101. Is set. Although the wear reference value can be adjusted as appropriate, it is preferable for the purpose to be closer to the upper limit value of the gap length G.

  Then, the abnormality determination unit 101 performs a process of determining whether or not the wear amount of the electrode pair 250 estimated in the wear amount estimation process is equal to or greater than the wear reference value, and the wear amount is equal to or greater than the wear reference value. If it does, the following second determination process is executed.

(Second determination process)
In the second determination process, utilizing the relationship between the gap length G and the ignitability, it is determined whether or not the gap length G taking into account not only the wear amount but also the initial variation has reached the timing at which the spark plug 25 should be replaced. Is determined. Specifically, a process of operating the ignition plug 25 is performed by applying the determination ignition energy smaller than the original ignition energy to the electrode pair 250.

(Relationship between gap length G and ignitability)
The present inventors have examined the relationship between the gap length G and the ignitability (the sensitivity of the air-fuel mixture to ignition). As a result, it was found that an inflection point at which the ignitability greatly changes with a change in the gap length G is recognized. discovered.

  FIG. 12 illustrates a graph showing the relationship between the gap length G and the ignitability. Since the initial gap length G is relatively small, the ground electrode 250a and the center electrode 250b are close to each other. Therefore, heat generated between the ground electrode 250a and the center electrode 250b by the discharge is easily absorbed by these electrodes. That is, the cooling loss is large. The ignitability is relatively low because heat is taken by the cooling loss.

  As the electrode wear progresses and the gap length G increases, the ground electrode 250a and the center electrode 250b move away from each other. As a result, the cooling loss is reduced, and the ignitability gradually increases.

  On the other hand, when the gap length G increases, the discharge voltage increases accordingly, making ignition difficult. These contradictory properties interact with the increase in the gap length G. Therefore, the present inventors have found that when the gap length G is increased to some extent, a phenomenon in which the ignitability sharply decreases is recognized. The present inventors have conceived of using the inflection point of ignitability observed in this phenomenon in determining abnormality of the ignition plug 25 due to wear of the electrode.

  That is, at the stage where the spark plug 25 is normal, that is, at the stage where the gap length G (actual gap length G ′) including the wear amount and the initial variation has not reached the timing to replace the spark plug 25, the actual gap length G As' increases, the ignitability also increases.

  Therefore, at this stage, if the required voltage is applied to the electrode pair 250 under normal control, only stable ignition of the air-fuel mixture can be performed.

  Therefore, the applied voltage is reduced, and ignition energy (ignition energy for determination) smaller than the ignition energy to be originally applied is applied to the electrode pair 250, and the ignition plug 25 is operated, that is, discharged. Specifically, the energization time (dwell time) is adjusted to be shorter so that a predetermined determination voltage lower than the required voltage is applied to electrode pair 250. By doing so, it is possible to forcibly reproduce a state in which ignition is more difficult than the current state.

(Third determination process)
In the third determination process, when the determination ignition energy is applied to the electrode pair 250, a process of determining the ignitability of the air-fuel mixture is performed. That is, the ignitability of the air-fuel mixture is determined in a state where ignition is more difficult than in the current situation.

  As a result, if no decrease in the ignitability is observed, the ignitability does not decrease even at the determination voltage lower than the required voltage. It can be determined that it is not.

  On the other hand, when a decrease in ignitability is recognized, the actual gap length G ′ is close to the inflection point, and even when the required voltage is applied as usual, the ignitability rapidly decreases shortly, It can be determined that the spark plug 25 is abnormal, that is, at a level that requires replacement of the spark plug 25.

  The determination ignition energy, specifically, the determination voltage or dwell time can be appropriately set according to the specifications. For example, if the determination is made based on the presence or absence of a misfire, the determination can be made relatively easily. However, in that case, there is a possibility that torque fluctuation or the like may be caused.

  In the case of the engine 1, since the in-cylinder pressure sensor SW6 is provided, the ignitability is determined using this. If the in-cylinder pressure sensor SW6 is used, it is possible to accurately determine a decrease in ignitability without causing a misfire. Specifically, a predetermined value (ignitability reference value) corresponding to the detection value of in-cylinder pressure sensor SW6, which is a criterion for ignitability, is set in advance in abnormality determination section 101.

  The ignitability reference value may be the detection value of the in-cylinder pressure sensor SW6 itself, or may be a specific value related to ignitability obtained by calculating from the detection value of the in-cylinder pressure sensor SW6. The abnormality determination unit 101 determines the ignitability of the air-fuel mixture by comparing the detection value of the in-cylinder pressure sensor SW6 with the ignitability reference value.

(Abnormality determination control of spark plug 25)
FIG. 13 illustrates a flow of abnormality determination control of the ignition plug 25 by the abnormality determination device 100.

  The ECU 10 (the abnormality determination unit 101) determines the operating state of the engine 1 based on signals input from the sensors SW1 to SW17 and the like (step S1). For example, the in-cylinder pressure is obtained using a signal input from the in-cylinder pressure sensor SW6, the load (torque) of the engine 1 is obtained using a signal input from the accelerator opening sensor SW12, the crank angle sensor SW11 Or the number of revolutions of the engine 1 is obtained using a signal input from

  Next, the ECU 10 executes the above-described first determination processing based on these input signals (step S2). That is, it is determined whether or not the estimated value of the wear amount of the electrode pair 250 that increases according to the operating state of the engine 1 is equal to or greater than a predetermined value (wear reference value).

  As a result, when the estimated value of the wear amount of the electrode pair 250 is less than the wear reference value (No in step S2), the ECU 10 determines that the spark plug 25 is normal, that is, the actual gap length G 'needs to be replaced. It is determined that it is not so large (step S20). Such control is performed, for example, in a case where the wear of the electrode pair 250 has not progressed and there is a sufficient margin until the timing of replacing the spark plug 25.

  Then, in this case, until the predetermined number of ignitions, for example, 100,000 times, has elapsed, the result of the determination as normal is held, and the process returns (step S21). Since the abrasion of the electrode does not progress rapidly, it is not preferable to perform the determination process frequently. Therefore, it is preferable to determine the abnormality of the spark plug 25 at an appropriate frequency according to the operating state of the engine 1.

  The number of ignitions (the number of retained ignitions) at which the determination result of normal is held is set according to the specification. For example, the number of times of holding ignition may be set so as to decrease gradually each time step S20 is repeated.

  On the other hand, when the estimated value of the wear amount of the electrode pair 250 is equal to or larger than the wear reference value (Yes in step S2), the ECU 10 needs to change the actual gap length G ′ due to the progress of the electrode wear. It is determined that the level has been reached, and the above-described second determination process is started. Such control is performed, for example, in a case where the wear of the electrode pair 250 progresses to such an extent that the influence of the initial variation is exerted, and the timing to replace the spark plug 25 comes soon.

  As described above, by performing the first determination processing in advance, the frequency of executing the second determination processing and the third determination processing can be significantly reduced. In the first determination process, the amount of wear according to the operating state of the engine 1 can be estimated with high accuracy. Therefore, the execution of the second determination process and the third determination process is suppressed to near the limit value of the actual gap length G ′. Can be. Thereby, the efficiency of the abnormality determination control of the ignition plug 25 can be improved. Even if a torque fluctuation occurs with the second determination processing, the torque fluctuation can be suppressed.

  When the second determination process is started, the ECU 10 first detects an in-cylinder pressure based on a signal input from the in-cylinder pressure sensor SW6, and calculates a determination voltage value from the detected in-cylinder pressure value (step S3). That is, the ECU 10 obtains the applied voltage necessary for stably igniting the air-fuel mixture from the detected in-cylinder pressure according to the normal control, and obtains the required voltage corresponding thereto. In the case of normal control, the ECU 10 adjusts the dwell time so that a voltage corresponding to the required voltage is applied to the electrode pair 250, and energizes the primary coil 251a1 at an appropriate timing.

  On the other hand, in this abnormality determination control, the ECU 10 calculates a predetermined determination voltage smaller than the required voltage based on the acquired required voltage in order to forcibly reproduce a state in which ignition is more difficult than the current state. . The value of the determination voltage may be a constant value, or may be changed according to the required voltage or the like.

  The ECU 10 calculates a dwell time for determination based on the calculated voltage for determination (step S4). The dwell time for determination is shorter than the dwell time corresponding to the required voltage. Therefore, the energization time to the primary coil 251a1 becomes relatively short, and accordingly, the applied voltage also decreases, and the determination voltage can be applied to the electrode pair 250.

  Then, the ECU 10 outputs a signal to the ignition device 251 to operate the ignition plug 25 so as to ignite at a predetermined timing (step S5). Thereby, the determination voltage is applied to the electrode pair 250, and the air-fuel mixture formed inside the combustion chamber 17 is ignited.

  The ECU 10 determines the ignitability of the air-fuel mixture by the ignition at that time based on the signal input from the in-cylinder pressure sensor SW6 (step S6). Specifically, the ECU 10 compares the detection value of the in-cylinder pressure sensor SW6 with a predetermined value (ignition reference value).

  As a result, if the detected value of the in-cylinder pressure sensor SW6 is equal to or greater than the ignitability reference value (No in step S6), the ECU 10 determines that the spark plug 25 is normal, that is, the actual gap length G 'is large enough to require replacement. It is determined that it is not (step S20).

  Then, in this case, until the predetermined number of ignitions, for example, 1000 times, which is smaller than the case of the first determination process, e.g., 1000 times, the determination result of normality is held and the process returns (step S21). Further, similarly to the case of the first determination process, the number of ignitions (the number of retained ignitions) for holding the determination result of normal may be set to be gradually reduced each time step S20 is repeated.

  On the other hand, when the detection value of the in-cylinder pressure sensor SW6 is less than the ignitability reference value (Yes in step S6), the ECU 10 determines that the actual gap length G ′ is close to the upper limit value, and the ignitability will soon be abrupt. , That is, it is determined that the spark plug 25 is abnormal (step S7).

  Then, in this case, the ECU 10 outputs a signal requesting replacement of the spark plug 25 to the alarm 57, and notifies the user that the spark plug 25 needs to be replaced (step S8).

  Thus, according to the spark plug abnormality determination device 100 disclosed herein, the spark plug 25 can be replaced at an appropriate timing.

  In particular, in the engine 1, when operating in the low load region A1, lean SPCCI combustion with a lean air-fuel ratio is performed. Lean SPCCI combustion is less likely to propagate a flame than SPCCI combustion at or near the stoichiometric air-fuel ratio. Therefore, in lean SPCCI combustion, SI combustion tends to be unstable. That is, it is difficult to ignite the mixture. Also, it is difficult to control the start timing of CI combustion, that is, to control θci. Therefore, the abnormality determination device 100 is effective for the engine 1 in which lean SPCCI combustion is performed.

  The ignition plug abnormality determination device according to the disclosed technology is not limited to the above-described embodiment, but also includes various other configurations.

  For example, the engine to be applied is not limited to an engine that performs SPCCI combustion. It can also be applied to ordinary spark ignition engines. Particularly, it is suitable for an engine having a high compression ratio.

  The in-cylinder pressure sensor is not essential. It is possible to determine a decrease in ignitability even with a crank angle sensor. However, if the in-cylinder pressure sensor is used, it is possible to determine a decrease in ignitability with high accuracy. As a result, torque fluctuations due to misfire can be suppressed, so that it is preferable to use an in-cylinder pressure sensor.

1 engine 10 ECU (control unit)
25 spark plug 100 abnormality determination device 101 abnormality determination unit 250 electrode pair 250a ground electrode 250b center electrode 251 ignition device (ignition unit)
SW1 to SW17 Sensor (measurement unit)
G gap length

Claims (8)

An abnormality determination device for a spark plug mounted on an engine,
The engine has a combustion chamber partitioned in a cylinder such that the volume is changed by a reciprocating piston,
The ignition plug has an electrode pair consisting of a ground electrode and a center electrode facing each other with a predetermined gap facing the combustion chamber,
The abnormality determination device,
A measuring unit that measures parameters related to the operation of the engine,
By applying a predetermined ignition energy to the electrode pair, an ignition unit that ignites a mixture formed inside the combustion chamber,
A control unit that is electrically connected to each of the measurement unit and the ignition unit, and outputs a signal to the ignition unit based on a signal input from the measurement unit.
With
The control unit has an abnormality determination unit that determines abnormality of the spark plug caused by wear of the electrode pair,
The abnormality determination unit,
A first determination process of determining whether the amount of wear of the electrode pair that increases according to the operating state of the engine is equal to or greater than a predetermined value;
A second determination process for operating the ignition plug by applying a determination ignition energy smaller than the ignition energy to the electrode pair when the wear amount of the electrode pair is equal to or greater than the predetermined value;
A third determination process of determining the ignitability of the air-fuel mixture when the determination ignition energy is applied to the electrode pair;
Run
An abnormality determination device for an ignition plug, which determines that the ignition plug is abnormal when it is determined in the third determination process that the ignitability of the air-fuel mixture is reduced. The spark plug abnormality determination device according to claim 1,
The abnormality determination device for an ignition plug, wherein the abnormality determination unit outputs a signal requesting replacement of the ignition plug when it is determined in the third determination process that the ignition plug is abnormal. The abnormality determination device for a spark plug according to claim 1 or 2,
In the first determination process,
By performing a chronological integration process using a signal input from the measuring unit and the number of times the ignition plug is ignited in accordance with the combustion, each time the combustion is performed in the combustion chamber, A wear amount estimation process for estimating the wear amount of the electrode pair is performed,
An abnormality determination device for a spark plug, wherein it is determined whether or not the estimated wear amount of the electrode pair has exceeded the predetermined value. The spark plug abnormality determination device according to claim 1,
The ignition unit has an ignition coil that applies a voltage corresponding to an energization time to the electrode pair,
The ignition coil is configured to be energized according to a required voltage set according to a state inside the combustion chamber,
In the second determination process,
An abnormality determination device for an ignition plug, wherein the energization time is shortened so that a predetermined determination voltage lower than the required voltage is applied to the electrode pair. The spark plug abnormality determination device according to claim 1,
In the first determination process,
A first wear amount estimated value comprising a wear amount per unit time of the center electrode, wherein the wear amount increases as the rotation speed and the load of the engine increase.
A second wear amount estimated value, which is made up of the amount of wear per unit time of the ground electrode and has a size different from the first wear amount estimated value, and the amount of wear increases as the engine speed and load increase, On the basis of the,
A spark plug abnormality determination device, wherein a wear amount estimation process for estimating the wear amount of the electrode pair is performed. The abnormality determination device for a spark plug according to claim 5,
An abnormality determination device for a spark plug, wherein when the engine speed and the load are compared under the same conditions, the second estimated wear amount is set to a value larger than the first estimated wear amount. . The spark plug abnormality determination device according to any one of claims 1 to 6,
The spark plug abnormality determination device, wherein the engine has a geometric compression ratio of 16 or more. The abnormality determination device for a spark plug according to claim 7,
The control unit outputs a signal to the ignition unit so that the air-fuel mixture formed inside the combustion chamber is ignited at a predetermined timing, so that a part of the air-fuel mixture starts combustion accompanied by flame propagation. An ignition plug abnormality determination device, wherein predetermined compression ignition combustion is performed in the engine after the remaining unburned air-fuel mixture burns by self-ignition.

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