JP7382019B2 - Spark plug wear estimation device and abnormality determination device - Google Patents

Description

The present invention relates to a spark plug wear amount estimating device and an abnormality determining device.

A spark plug is installed in an engine that ignites a mixture to cause combustion. A spark plug has a pair of electrodes (a center electrode and a ground electrode) that face the inside of a 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 is generated between these electrodes. As a result, a flame kernel is formed in the air-fuel mixture, and as the flame kernel grows, the air-fuel mixture is ignited.

The center electrode and ground electrode are worn out by discharge. As wear progresses, the gap becomes larger and the discharge voltage required for ignition increases accordingly. If the discharge voltage becomes too high, there is a risk that the applied voltage applied between the electrodes will be insufficient and a misfire will occur, or that the applied voltage will exceed the durability of the spark plug and damage the spark plug.

Therefore, spark plugs are consumable items that need to be replaced regularly. Generally, the replacement timing is uniformly set for each predetermined mileage.

However, the amount of electrode wear varies depending on the operating conditions of the engine. Therefore, the timing at which spark plugs should actually be replaced depends on the user's driving skills and preferences, and varies from engine to engine.

As a result, the spark plug replacement timing is usually set on the safe side, taking into account variations in individual engines. As a result, there may be cases where a user replaces the spark plug before it is actually time to replace the spark plug.

Therefore, it would be preferable to measure the wear amount of the electrodes according to the operating conditions of each engine and to determine the timing for replacing the spark plugs individually, since the spark plugs can be replaced at the appropriate timing even if there are variations.

Patent Document 1 discloses a method for estimating the gap length (gap size) of a worn electrode in a general spark ignition engine based on the operating state of the engine. Patent Document 1 shows that it is possible to estimate the gap length from three parameters at the time of ignition, including discharge time, in-cylinder gas density, and in-cylinder gas flow rate, and also calculates the gap length from these parameters. This shows the relational expression that can be used.

In Patent Document 1, the gap length is estimated during engine operation using the relational expression, and when the gap length exceeds a preset value, an abnormality of the spark plug is notified by lighting a warning light or the like.

Unexamined Japanese Patent Publication No. 2016-53314

By the way, some engines perform early ignition (also called advance ignition) to pre-activate the air-fuel mixture on the advance side (for example, in the intake stroke) of the main ignition that ignites the air-fuel mixture. be. That is, although early ignition does not substantially cause flame propagation of the mixture due to insufficient temperature, it does cleave the fuel components to form hydrogen peroxide and formaldehyde, and from these components e.g. OH radicals are generated. The air-fuel mixture will be activated. By activating this air-fuel mixture in advance, ignition by the subsequent main ignition can be reliably performed and the combustion speed can be increased.

When estimating the amount of wear on a spark plug (electrode pair), conventionally, the amount of wear per early ignition is the same as the amount of wear per one main ignition, or the amount of wear due to early ignition is more advanced than the main ignition. However, the actual situation was that the ignition was performed at a timing when the cylinder pressure was lower than the main ignition, so the amount of wear would be smaller than the amount of wear per main ignition.

However, a detailed examination of the amount of wear when performing early ignition revealed that the amount of wear per early ignition is greater than the amount of wear per one main ignition. When we investigated the cause of this, we found that during early ignition, a large flow velocity flows toward the exhaust side (exhaust port side) within the combustion chamber, but a stagnation of this large flow velocity occurs on the side of the center electrode. As a result, the side surface of the center electrode wears out in a moth-eaten pattern. They also learned that wear progresses quickly from the moth-eaten worn part to the entire center electrode.

The present invention was made based on the knowledge as described above, and its first object is to provide a spark plug that enables accurate estimation of the wear amount of the spark plug when performing early ignition and main ignition. An object of the present invention is to provide a wear amount estimating device.

A second object of the present invention is to provide a spark plug abnormality determination device that can accurately determine the abnormality of a spark plug based on the results of estimating the wear amount of the spark plug.

In order to achieve the first objective, the present invention adopts the following solution method. That is,
It is arranged on the ceiling wall of the combustion chamber in a reciprocating engine, and is used to perform early ignition to activate the air-fuel mixture on the advance side of the main ignition that ignites the air-fuel mixture in the combustion chamber, relative to the engine operating range. A spark plug wear amount estimating device comprising a center electrode and a ground electrode, which is configured to operate in a low speed and low load range,
Wear amount estimating means for estimating the wear amount per early ignition and the wear amount per main ignition of the center electrode of the spark plug in the low speed/low load range, respectively;
Wear amount integration that obtains a wear amount integrated value by integrating the amount of wear of the center electrode per one early ignition of the spark plug estimated by the wear amount estimating means and the amount of wear of the center electrode per one main ignition. means and
Equipped with
The wear amount estimating means calculates the wear amount of the center electrode of the spark plug per main ignition in the low speed/low load range based on a predetermined calculation formula using a constant discharge current value as a parameter. Estimated by
The wear amount estimating means calculates the wear amount per early ignition of the center electrode of the spark plug in the low speed/low load range based on the predetermined calculation formula using the constant discharge current value as a parameter. By adding a predetermined amount to the calculated value, the wear amount of the center electrode is estimated to be larger than the amount of wear of the center electrode during main ignition.
(corresponding to claim 1).

According to the above-mentioned solution method, the amount of wear of the spark plug can be estimated with high accuracy based on the knowledge that the amount of wear per ignition is greater in early ignition than in main ignition.

A preferred embodiment based on the above solution method is as follows.

The wear amount estimating means includes a first wear amount estimating means based on capacitive discharge of the spark plug, and a second wear amount estimating means based on the induced discharge of the spark plug,
The wear amount estimating means calculates the amount of wear per early ignition by adding up the amount of wear estimated by the first wear amount estimating means and the amount of wear estimated by the second wear amount estimating means. In contrast, it is estimated as a value obtained by adding a preset constant value.
(corresponding to claim 2). In this case, the amount of wear can be estimated with high accuracy by taking into account wear caused by capacitive discharge and wear caused by induced discharge. Further, regarding early ignition, the amount of wear can be estimated easily and accurately by setting the increase in the amount of wear per ignition as a constant value compared to the main ignition. That is, the wear mechanism for early ignition is different from the wear mechanism for main ignition as described above, and the amount of wear changes greatly depending on the gas flow state within the cylinder. Therefore, by examining the amount of wear per early ignition in advance through experiments and adding the increased amount of wear as a constant value, the amount of wear can be estimated easily and accurately. Note that the constant value may be changed depending on the operating state of the engine or the environmental state of the engine.

In order to achieve the second objective, the present invention adopts the following solution method. That is,
A spark plug abnormality determination device comprising the spark plug wear amount estimating device according to claim 1 or 2,
further comprising an abnormality determining means for determining whether or not there is an abnormality in the spark plug based on the value related to the wear amount cumulative value acquired by the wear amount integrating means;
It's like this.

According to the above-mentioned solution method, it is possible to accurately determine whether or not there is an abnormality in the spark plug (that is, whether it is time to replace the spark plug) based on the value related to the integrated value of the amount of wear that is accurately estimated.

A preferred embodiment based on the above solution method is as follows.

The abnormality determination means is configured to determine that the spark plug is abnormal when the cumulative wear amount value is equal to or greater than a predetermined value (corresponding to claim 4). In this case, it is preferable to effectively utilize the integrated value of wear amount itself to determine abnormality using a method as simple as possible.

The abnormality determining means has a gap length determining means for determining a value regarding the gap length of the electrode pair based on the cumulative wear amount value,
The abnormality determining means determines that the spark plug is abnormal when a value related to the gap length determined by the gap length determining means is equal to or greater than a predetermined value.
(corresponding to claim 5). In this case, the abnormality determination is made based on the value related to the gap length, which directly affects the ignitability, which is preferable in terms of accurate abnormality determination.

The abnormality determination means is configured to cause the ignition plug to perform a determination ignition in a state where the ignition performance is worse than normal when the value related to the wear amount cumulative value is equal to or higher than a predetermined value, so that the flammability at that time is determined in advance. The spark plug is determined to be abnormal when it is worse than a set reference value (corresponding to claim 6). In this case, it is possible to more accurately determine whether or not there is an abnormality in the spark plug based on the combustibility at the time of ignition for determination with poor ignition performance.

The main ignition is performed in the latter half of the compression stroke,
the early ignition is performed during the intake stroke;
(corresponding to claim 7). In this case, while the main ignition is at the normal ignition timing, the early ignition is performed in a situation where the pressure in the combustion chamber is extremely low and at a sufficiently earlier stage than the main ignition, so that the activated air-fuel mixture is sufficiently diffused into the combustion chamber. The main ignition can be performed in the state where the

At least in some operating ranges, the engine performs SPCCI combustion, which performs CI combustion (combustion by self-ignition) of unburned components remaining in the combustion chamber after SI combustion (diffusion combustion) is performed by ignition by a spark plug. (corresponding to claim 8). In this case, in an engine that performs SPCCI combustion where ignitability is likely to be a problem, early ignition can be used to sufficiently improve ignitability. In particular, in engines that perform SPCCI combustion, the compression ratio is set extremely high, so wear of the spark plugs tends to be a problem, but since it is possible to accurately determine whether there is an abnormality in the spark plugs, it is recommended to replace the spark plugs. This is preferable in order to avoid unnecessary replacement and reduce the frequency of spark plug replacement.

The early ignition is performed when the SPCCI combustion is performed and the engine is operated at low rotation speed, low load, and an air-fuel ratio leaner than the stoichiometric air-fuel ratio (corresponding to claim 9). In this case, early ignition can sufficiently improve ignitability, especially in situations where ignitability is a problem.

The ignition energy for early ignition is kept constant regardless of the operating state of the engine (corresponding to claim 10). In this case, it is preferable to simplify the ignition control for early ignition. Note that since early ignition is performed in a region where the engine load is extremely small, there is no problem even if the ignition energy for early ignition is constant.

Early ignition is performed only in the region where the SPCCI combustion is performed, in an operating state at low rotation and low load and at an air-fuel ratio leaner than the stoichiometric air-fuel ratio,
The ignition energy of early ignition is assumed to be constant regardless of the engine operating condition.
(corresponding to claim 11). In this case, it is preferable to use early ignition to sufficiently improve ignitability, especially in situations where ignitability is a problem, and to simplify ignition control for early ignition.

When the abnormality determining means determines that the spark plug is abnormal, it is configured to notify the occupant that the spark plug should be replaced (corresponding to claim 12). In this case, the driver can easily know at an appropriate timing that it is time to replace the spark plug.

The engine is a high compression ratio engine with a geometric compression ratio of 16 or more (corresponding to claim 13). In this case, wear of the spark plug is likely to be a problem due to the extremely high compression ratio, but since it is possible to accurately determine whether there is an abnormality in the spark plug, it is possible to avoid replacing the spark plug unnecessarily. This is preferable in terms of reducing the frequency of replacement.

According to the present invention, it is possible to accurately estimate the amount of wear of a spark plug. Furthermore, it is possible to accurately determine whether or not there is an abnormality in the spark plug based on the value related to the integrated value of the amount of wear of the spark plug that is accurately estimated.

FIG. 2 is a diagram illustrating the configuration of an engine. These are diagrams illustrating the configuration of a combustion chamber. The upper diagram is a plan view equivalent view of the combustion chamber, and the lower diagram is a sectional view taken along the line II-II. FIG. 2 is a plan view illustrating the configuration of a combustion chamber and an intake system. FIG. 3 is a diagram illustrating a spark plug and an ignition device. FIG. 2 is a block diagram illustrating the configuration of an engine control device. FIG. 3 is a diagram illustrating an example of classification of engine operating regions. FIG. 7 is a diagram showing details of the operating region A1 shown in FIG. 6; It is a figure which illustrates the waveform of SPCCI combustion. 7 is a time chart showing patterns of fuel injection and spark ignition in the operating range shown in FIG. 6, where (a) to (c) show patterns under conditions where the engine speed and load are different. 10 is a diagram showing an energization signal for spark ignition and its discharge current in pattern (a) shown in FIG. 9; FIG. 10 is a diagram showing an energization signal for spark ignition and its discharge current in pattern (b) shown in FIG. 9. FIG. A diagram showing wear of the center electrode due to premature ignition. The figure which shows the flow velocity in a combustion chamber in an intake stroke. The figure which shows the situation where discharge current changes when additional ignition is performed. FIG. 3 is a diagram showing how the discharge current changes when a spark ignites when the flow velocity in the combustion chamber is low. FIG. 3 is a diagram showing how the discharge current changes when a spark ignites when the flow velocity in the combustion chamber is high. FIG. 4 is a diagram showing the difference in the amount of wear on the ground electrode when the flow velocity in the combustion chamber is high and low. A map showing the relationship between the opening degree of the swirl valve and the swirl ratio. The figure which shows the example of opening degree setting of the swirl valve according to the operating state of an engine. FIG. 3 is a diagram schematically illustrating the amount of wear for each factor that causes wear of the center electrode. FIG. 3 is a diagram showing a situation in which the amount of wear of capacitive discharge, which causes wear of the ground electrode, varies depending on the flow velocity. A flowchart for estimating the amount of electrode wear when performing early ignition. 12 is a flowchart illustrating an example of control for estimating the wear amount of an electrode when performing additional ignition (intermittent ignition). 5 is a flowchart showing an example of control for estimating the amount of wear of an electrode when only main ignition is performed. 5 is a flowchart illustrating an example of control for determining whether a spark plug is abnormal based on the estimated wear amount of the electrode. 5 is a flowchart showing another control example for determining whether a spark plug is abnormal based on the estimated amount of electrode wear.

Hereinafter, embodiments of the present invention will be described in detail based on the drawings. However, the following description is essentially just an example, and does not limit the present invention, its applications, or its uses. The following description is an example of an engine, a wear amount estimating device for a spark plug electrode pair, and an abnormality determining device.

1 to 3 illustrate an engine 1 to which a spark plug wear amount estimating device and an abnormality determining device are 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. Engine 1 is installed in a four-wheeled vehicle. The automobile travels as the engine 1 operates. The fuel for the engine 1 is gasoline in this configuration example. The fuel may be any liquid fuel containing at least gasoline. The fuel may be, for example, gasoline containing bioethanol or the like.

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

A piston 3 is slidably inserted into 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 cylinder head 13 . That is, the combustion chamber 17 is divided into a cylinder so that the volume changes depending on the reciprocating piston. Note that "combustion chamber" may be used in a broad sense. That is, the "combustion chamber" may mean the 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 composed of an inclined surface 1311 and an inclined surface 1312, as shown in the lower diagram of FIG. The inclined surface 1311 slopes upward from the intake side toward the injection axis X2 of the injector 6, which will be described later. The inclined surface 1312 slopes upward 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 is raised toward the ceiling surface of the combustion chamber 17. A cavity 31 is formed in 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 from the center axis X1 of the cylinder 11 toward the exhaust side.

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 typical spark ignition engine. As will be described later, the engine 1 performs SPCCI combustion, which is a combination of SI combustion and CI combustion, in some operating regions. SPCCI combustion uses heat generation and pressure increase due to SI combustion to control CI combustion. Engine 1 is a compression ignition engine.

However, in this engine 1, there is no need to increase the temperature of the combustion chamber 17 (that is, the compression end temperature) when the piston 3 reaches the compression top dead center. The engine 1 can have a relatively low geometric compression ratio. Lowering the geometric compression ratio is advantageous in reducing cooling loss and mechanical loss.

The geometric compression ratio of the engine 1 is 14 to 17 in the regular specification (low octane fuel with a fuel octane number of about 91), and 15 to 17 in the high octane specification (high octane fuel with a fuel octane number of about 96). It is also possible to set it to 18.

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. Intake port 18 communicates with combustion chamber 17 . Although detailed illustration is omitted, 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.

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

The cylinder head 13 is also formed with an exhaust port 19 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. Exhaust port 19 communicates with 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 is opened and closed at predetermined timing by a valve operating mechanism. This valve operating mechanism may be a variable valve mechanism that makes valve timing and/or valve lift variable. In this configuration example, as shown in FIG. 4, the variable valve mechanism includes an exhaust electric SVT 24. The electric exhaust S-VT 24 continuously changes the rotational phase of the exhaust camshaft within a predetermined angular range. The opening timing and closing timing of the exhaust valve 22 change continuously. Note that the exhaust valve mechanism may include 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 in which both the intake valve 21 and the exhaust valve 22 are open. Increasing the length of the overlap period allows residual gas in the combustion chamber 17 to 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 is composed of an intake electric S-VT23 and an exhaust electric S-VT24. Note that the internal EGR system is not necessarily configured by S-VT.

An 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 section. The injector 6 is disposed in the valley of the pent roof where the sloped surface 1311 and the sloped surface 1312 intersect. As shown in FIG. 2, the injection axis X2 of the injector 6 is located closer to the exhaust side than the central 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 and the center of the cavity 31 coincide with each other. The injector 6 faces the cavity 31. Note that the injection axis X2 of the injector 6 may coincide with the central axis X1 of the cylinder 11. In the case of this configuration, the injection axis X2 of the injector 6 and the center of the cavity 31 may coincide.

Although detailed illustration is omitted, the injector 6 is constituted by a multi-nozzle type fuel injection valve having a plurality of nozzles. The injector 6 injects fuel so that the fuel spray spreads radially from the center of the combustion chamber 17, as shown by the two-dot chain line in FIG. In this configuration example, the injector 6 has ten nozzle holes, and the nozzle 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 interposed in the fuel supply path 62 . The fuel pump 65 pumps fuel to the common rail 64. In this configuration example, the fuel pump 65 is a plunger type pump driven by the crankshaft 15. The common rail 64 stores the fuel pumped from the fuel pump 65 at 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 nozzle of the injector 6. The fuel supply system 61 is capable of supplying fuel at a high pressure of 30 MPa or more to the injector 6. The pressure of fuel supplied to the injector 6 may be changed depending on the operating state of the engine 1. Note that the configuration of the fuel supply system 61 is not limited to the above configuration.

A spark plug 25 is attached to the cylinder head 13 for each cylinder 11. The spark plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17. In this configuration example, the spark plug 25 is disposed closer to the intake side than the central axis X1 of the cylinder 11. The spark plug 25 is located between the two intake ports 18. The spark plug 25 is attached to the cylinder head 13 so as to be inclined from above toward the center of the combustion chamber 17 . As shown in FIG. 2, the electrode of the spark plug 25 faces into the combustion chamber 17 and is located near the ceiling surface of the combustion chamber 17. Incidentally, the spark plug 25 may be arranged on the exhaust side with respect to the central 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 spark plug 25 (also simply referred to as connection). The ignition device 251 (an example of an ignition unit) is connected to a battery 252 and supplies power to the spark plug 25 (details of the spark 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. Gas introduced into the combustion chamber 17 flows through the intake passage 40 . An air cleaner 41 is provided at the upstream end of the intake passage 40 . Air cleaner 41 filters fresh air. A surge tank 42 is disposed near the downstream end of the intake passage 40. The intake passage 40 downstream of the surge tank 42 constitutes an independent passage that branches for each cylinder 11. A downstream end of the independent passage is connected to an 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 section" that increases or decreases the amount of air supplied to the inside of each combustion chamber 17 to adjust it.

A supercharger 44 is also disposed in the intake passage 40 downstream of the throttle valve 43. The supercharger 44 supercharges 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 the Roots type, Lysholm type, vane type, or centrifugal type.

An electromagnetic clutch 45 is interposed between the supercharger 44 and the engine 1. The electromagnetic clutch 45 is provided between the supercharger 44 and the engine 1 to transmit driving force from the engine 1 to the supercharger 44 or to interrupt transmission of the driving force. As will be described later, the ECU 10 switches the electromagnetic clutch 45 between disconnection and connection, thereby switching the supercharger 44 between on and off states.

An intercooler 46 is disposed downstream of the supercharger 44 in the intake passage 40 . Intercooler 46 cools the gas compressed in supercharger 44 . The intercooler 46 may be configured to be water-cooled or oil-cooled, for example.

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

When the supercharger 44 is turned on, the engine 1 operates in a supercharged state. The ECU 10 adjusts the opening degree of the air bypass valve 48 when the supercharger 44 is turned on (that is, when the electromagnetic clutch 45 is connected). A portion of the gas that has passed through the supercharger 44 flows back upstream of the supercharger 44 through a bypass passage 47 . When the ECU 10 adjusts the opening degree of the air bypass valve 48, the boost pressure of the gas introduced into the combustion chamber 17 changes. In addition, the term "supercharging" refers to the time when the pressure in the surge tank 42 exceeds atmospheric pressure, and the term "non-supercharging" refers to the time when the pressure in the surge tank 42 falls below atmospheric pressure. Good too.

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

The engine 1 includes a swirl generating section that generates a swirl flow within the combustion chamber 17. The swirl generator includes a swirl valve 56 attached to the intake passage 40, as shown in FIG. The swirl valve 56 is disposed in a secondary passage 402 of a primary passage 401 connected to the first intake port 181 and a secondary passage 402 connected to the second intake port 182. The swirl valve 56 is an opening adjustment valve that can narrow the cross section of the secondary passage 402.

When the opening degree of the swirl valve 56 is small, the amount of intake air flowing into the combustion chamber 17 from the first intake port 181 is relatively large, and the amount of intake air flowing into the combustion chamber 17 from the second intake port 182 is relatively small. As a result, the swirl flow within the combustion chamber 17 becomes stronger. When the degree of opening of the swirl 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 approximately equal, so that the swirl flow in the combustion chamber 17 becomes weaker. . When the swirl valve 56 is fully opened, no swirl flow occurs. Note that the swirl flow circulates in a counterclockwise direction in FIG. 3, as shown 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 exhaust gas discharged from the combustion chamber 17 flows. The upstream portion of the exhaust passage 50 constitutes an independent passage that branches for each cylinder 11, although detailed illustration is omitted. An upstream end of the independent passage is connected to an exhaust port 19 of each cylinder 11.

An exhaust gas purification system having a plurality of catalytic converters is disposed in the exhaust passage 50. Although not shown, the upstream catalytic converter is disposed within the engine room. The upstream catalytic converter includes a three-way catalyst 511 and a GPF (Gasoline Particulate Filter) 512. The downstream catalytic converter is located outside the engine compartment. 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, 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 GPF may be changed as appropriate.

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

A water-cooled EGR cooler 53 is disposed in the EGR passage 52. EGR cooler 53 cools exhaust gas. An EGR valve 54 is also provided in the EGR passage 52. The EGR valve 54 adjusts the flow rate of exhaust gas flowing through the EGR passage 52. By adjusting the opening degree of the EGR valve 54, the amount of recirculation of the cooled exhaust gas, that is, the external EGR gas, can be adjusted.

In this configuration example, the EGR system 55 includes an external EGR system and an internal EGR system. The external EGR system can provide cooler exhaust gas to the combustion chamber 17 than the internal EGR system.

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. These electrode pairs 250 include a ground electrode 250a and a center electrode 250b, which are made of a material such as nickel alloy, platinum, or iridium alloy. The ground electrode 250a and the center electrode 250b face each other across a gap having a predetermined size (gap length G).

When ignition energy is applied to these electrode pairs 250 (specifically, high voltage is instantaneously applied), discharge occurs between the electrode pairs 250. A flame kernel is thereby 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, fuel heat is absorbed by the ground electrode 250a and the center electrode 250b, inhibiting the formation and growth of a flame kernel (so-called cooling loss). Therefore, in this engine 1, the gap length G is set to at least 0.5 mm (initial value of the gap length G≧0.5 mm).

An ignition device 251 is connected to the spark 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, etc., and applies a voltage to the electrode pair 250 corresponding to the energization time (dwell time) to the primary coil 251a1.

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

The other end of the secondary coil 251a2 is connected to a reference potential (earthed) 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 the 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 power from the battery 252 is supplied to the primary coil 251a1 and an off state in which power from 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 formed 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 due to electromagnetic induction and a voltage is generated. Since the number of turns of the secondary coil 251a2 is greater than the number of turns of the primary coil 251a1, a high voltage is generated in the secondary coil 251a2. By applying this high voltage 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 has a correlation with the dwell time. Usually, in order to perform stable ignition, the applied voltage is set higher than the voltage required for discharge (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. Since the gap length G is considered to be a constant value in normal control, 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. to be applied.

Specifically, the ECU 10 determines the voltage to be applied to the electrode pair 250 ( (required voltage). In this engine 1, the required voltage is set to be at least 10 kV or higher.

In contrast, 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. When the required voltage is high, the dwell time is lengthened, and when the required voltage is low, the dwell time is shortened. When the engine 1 is operating, the ignition coil 251a is energized according to a required voltage that is set according to the internal state of the combustion chamber 17, that is, the internal pressure of the combustion chamber 17.

(ECU)
The engine 1 is equipped with an ECU (Engine Control Unit) 10 that controls its operation. The ECU 10 is a controller based on a well-known microcomputer, and as shown in FIG. The device includes a memory 10b configured as a Read Only Memory (Read Only Memory) for storing programs and data, and an input/output bus 10c for inputting and outputting electrical signals. The ECU 10 is an example of a "control unit".

As shown in FIGS. 1 and 5, various sensors SW1 to SW17 are connected to the ECU 10. Sensors SW1 to SW17 output signals to the ECU 10. These sensors SW1 to SW17 are an example of a “measuring unit” that measures various parameters related to the operation of the engine 1. The contents of these sensors SW1 to SW17 are shown below.

Air flow sensor SW1: disposed downstream of the air cleaner 41 in the intake passage 40 and measures the flow rate of fresh air flowing through the intake passage 40.

First intake air temperature sensor SW2: disposed downstream of the air cleaner 41 in the intake passage 40 and measures the temperature of fresh air flowing through the intake passage 40.

First pressure sensor SW3: disposed downstream of the connection position of the EGR passage 52 in the intake passage 40 and upstream of the supercharger 44, and measures the pressure of gas flowing into the supercharger 44.

Second intake air temperature sensor SW4: Disposed downstream of the supercharger 44 in the intake passage 40 and upstream of the connection position of the bypass passage 47, and measures the temperature of the gas flowing out from the supercharger 44.

Second pressure sensor SW5: attached to the surge tank 42 and measures the pressure of the gas downstream of the supercharger 44.

Cylinder pressure sensor SW6: attached to the cylinder head 13 corresponding to each cylinder 11, and measures the pressure within each combustion chamber 17.

Exhaust temperature sensor SW7: disposed in the exhaust passage 50 and measures the temperature of exhaust gas discharged from the combustion chamber 17.

Linear O2 sensor SW8: Disposed upstream of the upstream catalytic converter in the exhaust passage 50, and measures the oxygen concentration in the exhaust gas.

Lambda O2 sensor SW9: Disposed downstream of the three-way catalyst 511 in the upstream catalytic converter, and measures the oxygen concentration in the exhaust gas.

Water temperature sensor SW10: attached to the engine 1 and measures the temperature of the cooling water.

Crank angle sensor SW11: attached to the engine 1 and measures the rotation angle of the crankshaft 15.

Accelerator opening sensor SW12: attached to the accelerator pedal mechanism and measures the accelerator opening corresponding to the operation amount of the accelerator pedal.

Intake cam angle sensor SW13: attached to the engine 1 and measures the rotation angle of the intake camshaft.

Exhaust cam angle sensor SW14: attached to the engine 1 and measures the rotation angle of the exhaust camshaft.

EGR differential pressure sensor SW15: disposed in the EGR passage 52 and measures the differential pressure upstream and downstream of the EGR valve 54.

Fuel pressure sensor SW16: attached to the common rail 64 of the fuel supply system 61 and measures the pressure of fuel supplied to the injector 6.

Third intake air temperature sensor SW17: attached to the surge tank 42 and measures the temperature of the gas in the surge tank 42, in other words, the temperature of the intake air introduced into the combustion chamber 17.

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

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

The ECU 10 sends electrical signals related to the calculated control amounts 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. , air bypass valve 48, swirl valve 56, alarm 57, and ignition device 251. Note that the alarm 57 is a device that notifies the passenger of a warning or the like, and includes, for example, a lamp displayed on an instrument panel.

FIG. 6 is an operation map for explaining differences in combustion control depending on engine speed/load. As shown in this figure, the operating range of the engine is roughly divided into four operating ranges A1 to A4 depending on the combustion form. They are respectively defined as a first operating area A1, a second operating area A2, a third operating area A3, and a fourth operating area A4.

The third operating region A3 is an extremely low speed region in which the engine rotation speed is less than the first speed N1. The fourth operating range A4 is a high speed range where the engine rotational speed is equal to or higher than the third speed N3. The first operating range A1 is a low speed/low load range where the load is relatively low among speed ranges (low/medium speed ranges) other than the third and fourth operating ranges A3 and A4. The second operating range A2 is the remaining range other than the first, third, and fourth operating ranges A1, A3, and A4.

According to the example of FIG. 6, the first operating area A1 is a substantially rectangular area located inside the second operating area A2, and has a first speed N1, which is the lower limit speed of the second operating area A2, and a first speed N1, which is the lower limit speed of the second operating area A2. The engine is surrounded by a second speed N2 that is lower than the upper limit speed (third speed N3) of the second operating region A2, a first load L1 that is higher than the minimum load of the engine, and a second load L2 that is higher than the first load L1. ing. The second load L2, which is the upper limit load of this first operating region A1, is set to a value slightly lower than the third load L3, which is the lower limit load at which the supercharger 33 is driven. That is, the first operating region A1 is set so as not to overlap with the supercharging region where supercharging by the supercharger 33 is performed.

An overview of the combustion control in the first to fourth operating ranges A1 to A4 will be described below.

First operating region A1: In the first operating region A1 of low speed and low load, partial compression ignition combustion (hereinafter referred to as SPCCI combustion), which is a combination of SI combustion and CI combustion, is performed. SI combustion is a type of combustion in which the air-fuel mixture is ignited by a spark generated from the spark plug 16, and the air-fuel mixture is forcibly combusted by flame propagation that spreads the combustion area from the ignition point to the surrounding area. CI combustion is a combustion form in which the air-fuel mixture is combusted by self-ignition in an environment where the temperature and pressure are sufficiently high due to compression of the piston 5, etc. SPCCI combustion, which is a combination of these SI combustion and CI combustion, involves SI combustion of a part of the air-fuel mixture in the combustion chamber 6 by spark ignition performed in an environment on the verge of self-ignition of the air-fuel mixture. This is a combustion form in which, after combustion, other air-fuel mixtures in the combustion chamber 6 are subjected to CI combustion by self-ignition (by further increasing the temperature and pressure associated with SI combustion). Note that "SPCCI" is an abbreviation for "Spark Controlled Compression Ignition".

FIG. 7 is a graph showing a combustion waveform when SPCCI combustion as described above is performed, that is, a change in the heat release rate (J/deg) depending on the crank angle. As shown in this figure, in SPCCI combustion, heat generation due to SI combustion and heat generation due to CI combustion occur successively in this order. At this time, due to the property that CI combustion has a faster combustion rate, the heat generation rises more steeply during CI combustion than during SI combustion. Therefore, the waveform of the heat release rate in SPCCI combustion has an inflection point X that appears at the timing of switching from SI combustion to CI combustion (θci described later).

As a specific form of SPCCI combustion as described above, in the first operating region A1, an A/F lean air-fuel mixture having an air-fuel ratio larger than the stoichiometric air-fuel ratio is formed in the combustion chamber 17, and the air-fuel mixture is converted into SPCCI combustion. Control for combustion, in other words, control for SPCCI combustion of the air-fuel mixture with λ>1 (λ is excess air ratio) is executed. In order to realize such A/F lean SPCCI combustion, in the first operating region A1, each part of the engine is controlled by the PCM 100 as follows.

The opening degree of the throttle valve 32 is set to a relatively large value such that more air than the amount of air corresponding to the stoichiometric air-fuel ratio is introduced into the combustion chamber 6 through the intake passage 30. That is, in the first operating region A1, the air-fuel ratio (A/F ) is set to a value that is sufficiently larger than the stoichiometric air-fuel ratio (14.7). Then, the opening degree of the throttle valve 32 that achieves this target value of the air-fuel ratio (target air-fuel ratio) is determined each time, and the throttle valve 32 is controlled in accordance with that determination.

The supercharger 33 is stopped. That is, since the first operating region A1 is located on the lower load side than the third load L3, which is the lower limit of the load range that requires supercharging, supercharging by the supercharger 44 is not necessary. Therefore, in the first operating region A1, the electromagnetic clutch 45 is released and the connection between the supercharger 44 and the engine body 1 is released, and the bypass valve 48 is fully opened, so that the supercharger 44 generates no overflow. Payment will be stopped.

In SPCCI combustion, which is a combination of SI combustion and CI combustion, it is important to control the ratio of SI combustion and CI combustion according to operating conditions. Therefore, in this embodiment, we focus on the SI rate, which is the ratio of the amount of heat generated by SI combustion to the total amount of heat generated by SPCCI combustion (SI combustion and CI combustion), and set the engine so that this SI rate becomes an appropriate value. control each part of the

The above SI rate will be explained. In FIG. 8, the crank angle θci corresponding to the inflection point X where the combustion mode switches from SI combustion to CI combustion is defined as the start time of CI combustion. In this case, the amount of heat generated by SI combustion corresponds to the area R1 of the waveform of the heat release rate on the advanced side of the θci (start time of CI combustion), and the amount of heat generated by the CI combustion is more than the θci. It can be considered that this corresponds to the area R2 of the waveform of the heat generation rate located on the retarded side. The SI rate can be defined as R1/(R1+R2) using these areas R1 and R2.

In the first operating region A1 in which SPCCI combustion is performed, each part of the engine is controlled so that the above-mentioned SI rate and θci match predetermined target values. That is, in the first operating region A1, a target SI rate that is a target value of the SI rate and a target θci that is a target value of θci are determined for each of various conditions in which the engine load/rotational speed is different. Then, a plurality of control variables such as the fuel injection amount/injection timing from the injector 6, the timing of spark ignition by the spark plug 25 (ignition timing), and the EGR rate (external EGR rate and internal EGR rate) are determined by the target SI rate. and a combination that can realize the target θci. Note that the external EGR rate is the weight percentage of the external EGR gas (exhaust gas recirculated to the combustion chamber 6 through the EGR passage 51) out of all the gas in the combustion chamber 6, and the internal EGR rate is: This refers to the weight ratio of internal EGR gas (burned gas remaining in the combustion chamber 6 due to internal EGR) to all gases in the combustion chamber 6.

For example, the fuel injection amount/injection timing is determined based on a predetermined map in consideration of the target SI rate and target θci. Regarding the external EGR rate and the internal EGR rate, the opening/closing timing (overlap period) of the intake/exhaust valves 21 and 22 and the opening degree of the EGR valve 54, which are the main influencing factors for both EGR rates, are also determined by the above-mentioned factors. It is determined based on a map determined in consideration of the target SI rate and target θci.

Here, in this embodiment, the fuel injection pattern in the first operating region A1 is a pattern in which fuel is injected multiple times during the intake stroke. For example, the injection patterns at driving points P1, P2, and P3 in the driving map shown enlarged in FIG. 7 are each set to a pattern in which three fuel injections are performed during the intake stroke (as shown in FIG. (See fuel injection F1, F2, F3). The fuel injection amount/injection timing in the first operating region A1 is based on the premise that such a split injection pattern is adopted, and the injection amount/injection timing of each fuel injection satisfies the above-mentioned target SI rate and target θci. It is predetermined to a value that is considered.

On the other hand, the timing of spark ignition by the spark plug 25 (ignition timing) is determined by calculation using a predetermined model formula to a timing at which the target SI rate and target θci can be obtained.

As shown in FIG. 9, in this embodiment, depending on the operating conditions, in addition to normal spark ignition (hereinafter referred to as normal ignition Sa or main ignition Sa) for forcibly igniting the air-fuel mixture, Spark ignition (hereinafter referred to as early ignition Sb or advance ignition Sb) that generates a spark at a timing earlier than a predetermined amount may be performed. Specifically, spark ignition in such a special manner (early ignition Sb and normal ignition Sa) is performed in the first divided region A11 including the operating point P1 in FIG. The first divided region A11 is a region of the first operating region A1 in which the rotational speed is equal to or less than the boundary speed Nx and the load is equal to or less than the boundary load Lx.

In FIG. 10, the energization time for the primary coil 251a in the ignition device 251 to perform the early ignition Sb is indicated by the symbol W1, and the discharge current is indicated by the symbol Y1. Similarly, in order to perform the normal ignition Sa, the energization time for the primary coil 251a in the ignition device 251 is indicated by the symbol W2, and the discharge current is indicated by the symbol Y2.

On the other hand, in the other divided areas other than the first divided area A11, that is, the third divided area A13 on the higher side than the boundary speed Nx, and the second divided area A12 on the higher load side than the boundary load Lx, the normal ignition Sa ignition Sb is executed, and early ignition Sb is not executed.

Although details will be described later, in the first divided region A11 where early ignition Sb and normal ignition Sa are performed, the timing of normal ignition Sa is determined using the above model formula. On the other hand, the energy of the normal ignition Sa and the timing/energy of the early ignition Sb are constant regardless of the load/rotational speed. In addition, in the second and third divided regions A12 and A13 where only the normal ignition Sa is executed, the timing of the normal ignition Sa is determined using the above model formula, and the energy of the normal ignition Sa is determined by the load / It is assumed to be constant regardless of rotation speed.

As shown in the pattern (b) of FIG. 9, the normal ignition Sa in the second divided area A12, which is represented by two adjacent arrow lines, temporarily stops the discharge from the spark plug 16 in the middle stage. This indicates that intermittent ignition is performed as normal ignition Sa, and does not mean that early ignition Sb is performed. During this intermittent ignition, the spark ignition that occurs initially becomes the normal ignition or main ignition, and the spark ignition that is ignited later serves as the additional ignition.

In FIG. 11, in order to perform the intermittent ignition Sa, the time period during which current is applied to the primary coil 251a in the ignition device 251 for initial ignition is indicated by the symbol W3a, and the discharge current at that time is indicated by the symbol Y3a. Then, in order to perform subsequent additional ignition, the time during which current is applied to the primary coil 251a in the ignition device 251 is indicated by the symbol W3b, and the discharge current at that time is indicated by the symbol Y3b.

As described above, in the first operating region A1, the ignition timing, fuel injection amount/injection timing, and intake/exhaust valves 21 and 22 are controlled by a method that combines calculations using a predetermined map and a model formula. The opening/closing timing and the opening degree of the EGR valve 54 are controlled to provide a combination that provides a predetermined appropriate SI rate and θci (target SI rate and target θci) for each operating condition.

Next, the second operating region A2 will be explained.

Also in the second operating region A2, control is executed to combust the air-fuel mixture by SPCCI combustion. However, in the second operating region A2, unlike in the first operating region A1, the air-fuel ratio (A/F) in the combustion chamber 17 is set near the stoichiometric air-fuel ratio, and the spark ignition by the spark plug 25 The number of times is limited to once per combustion cycle (only Sa, which is main ignition or normal ignition, and no intermittent ignition).

That is, in the second operating region A2, the opening degree of the throttle valve 43 is such that an amount of air equivalent to the stoichiometric air-fuel ratio is introduced into the combustion chamber 17 through the intake passage 40, that is, the air in the combustion chamber 17 ( The opening degree is set such that the air-fuel ratio (A/F), which is the weight ratio of fresh air (fresh air) to fuel, substantially matches the stoichiometric air-fuel ratio (14.7). In other words, in the second operating region A2, control is performed to perform SPCCI combustion of the air-fuel mixture under a stoichiometric environment in which the air-fuel ratio in the combustion chamber 17 is close to the stoichiometric air-fuel ratio (λ≈1).

Further, spark ignition by the spark plug 25 is performed once per combustion cycle in the vicinity of compression top dead center. That is, in the second operating region A2, only normal spark ignition for forcibly igniting the air-fuel mixture near the compression top dead center is performed, and anything equivalent to the above-mentioned early ignition is not performed.

Here, also in the second operating region A2, the target SI rate and target θci are determined for each load/rotational speed condition, as in the first operating region A1 described above. The fuel injection amount/injection timing, the opening/closing timing of the intake/exhaust valves 21 and 22, and the opening degree of the EGR valve 54 are determined using a map in which values suitable for achieving the above-mentioned target SI rate and target θci are determined in advance. Determined by Regarding the ignition timing by the spark plug 25, the ignition timing that can realize the target SI rate and the target θci is determined by calculation using a predetermined model formula.

The supercharger 44 is driven or stopped depending on whether the engine load is higher or lower than the third load L3. That is, the supercharger 44 is driven in a high-load side region where the engine load is equal to or higher than the third load L3 in the second operating region A2, and when the engine load is less than the third load L3 in the second operating region A2. It is stopped in the low load area. In a high-load region where the supercharger 44 is driven, the electromagnetic clutch 45 is engaged and the supercharger 44 and the engine body 1 are connected, so that supercharging by the supercharger 44 is performed. At this time, the opening of the bypass valve 48 is adjusted so that the pressure (supercharging pressure) in the surge tank 42 detected by the intake pressure sensor matches the target pressure predetermined for each engine load/rotational speed condition. is controlled.

Next, the third operating area A3 and the fourth operating area A4 will be explained.
In the third operating range A3 (extremely low speed range) and the fourth operating range A4 (high speed range), control is performed to combust the air-fuel mixture by SI combustion. For example, the entire amount of fuel to be injected during one combustion cycle is injected from the injector 6 during the intake stroke, and spark ignition is performed by the spark plug 25 near compression top dead center. Then, SI combustion is started in response to this spark ignition, and all of the air-fuel mixture in the combustion chamber 17 is combusted by flame propagation.

Next, estimation of the amount of wear on the center electrode 250b when the spark plug 25 is ignited will be described. First, the wear of the center electrode consists of wear due to capacitive discharge and wear due to inductive discharge. The amount of wear on the center electrode 250b is calculated (estimated) based on the following basic formula (1).

基本式（１）中、Ｄ１～Ｄ４は定数で、それぞれ正の値である（－Ｄ２はマイナスの値となる）。また、δは燃焼室１７内の密度であり、ｉは放電の電流値である。燃焼室１７内の密度δは、燃焼室１７内の全ガス量を点火実行時の燃焼室容積で除した値となる。この密度は、エンジン負荷に対応したものとして把握することができる。したがって、中心電極２５０ａの容量放電に基づく摩耗量は、エンジン負荷が大きくなるほど大きくなると考えられる。

In basic formula (1), D1 to D4 are constants, each of which is a positive value (-D2 is a negative value). Moreover, δ is the density within the combustion chamber 17, and i is the current value of discharge. The density δ in the combustion chamber 17 is a value obtained by dividing the total amount of gas in the combustion chamber 17 by the volume of the combustion chamber at the time of ignition. This density can be understood as corresponding to the engine load. Therefore, it is considered that the amount of wear of the center electrode 250a due to capacitive discharge increases as the engine load increases.

In the basic formula (1), the left term in parentheses corresponds to the amount of wear due to capacitive discharge (the first amount of wear based on the peak value of the discharge current). Furthermore, the term on the right corresponds to the amount of wear due to induced discharge (the second amount of wear based on the integrated value of the discharge current) (i in the formula is the current value). However, the lower limit of the amount of wear based on capacitive discharge is 0 (it does not take a negative value).

The amount of wear calculated using the above basic formula (1) is for the main ignition Sa in pattern P1 or P3 in FIG. The unit of the calculated amount of wear is 10 ⁻¹⁰ (10 to the power of minus 10)×mm ³ (millimeter cubic meter).

Wear of the center electrode 250b due to capacitive discharge can also be understood as a value based on the peak value of the discharge current. The center electrode 250b loses energy due to electron emission due to discharge, and the amount of heat received decreases, which becomes a factor that accelerates wear in areas where the engine load is relatively large.

On the other hand, wear of the center electrode 250b due to induced discharge is caused by collisions of ions in the gas, and is substantially independent of engine load, causing wear of the center electrode 250b over a wide range of engine loads. It becomes a factor.

On the other hand, the wear amount of the center electrode 250b for the early ignition Sb shown in pattern (a) of FIG. 9 is set to be a larger value than the wear amount calculated by basic equation (1). Specifically, the amount of wear is determined by adding a predetermined constant α to the amount of wear calculated using the basic formula (1).

Normally, early ignition Sb is performed in the range from the intake stroke to the early stage of the compression stroke, and is carried out when there is virtually no compression (that is, when the engine load is extremely small), so it is difficult to discharge the capacitance. The accompanying wear on the center electrode 250b was thought to be small.However, in reality, as the early ignition Sb continues to be performed, the center electrode 250b wears out from its sides, as shown in FIG. , the side surface becomes moth-eaten, and the tip is worn so as to become rounded.As the side surface becomes moth-eaten, the wear at the tip of the center electrode 250b is also accelerated.

The above-described wear of the center electrode 250b due to early ignition Sb is caused by the exhaust gas flowing from inside the combustion chamber 17 to the exhaust side (exhaust port side) at high speed at the timing when early ignition Sb is executed. It turned out that. FIG. 13 shows a situation in which the gas flow velocity within the combustion chamber 17 changes from the top dead center of the intake stroke. As is clear from FIG. 13, the gas flow velocity becomes extremely large from around the point slightly beyond the top dead center of the intake stroke, and this large flow velocity causes stagnation on the side of the center electrode 250b on the exhaust port side. This would accelerate wear from the stagnation parts.

For the reasons mentioned above, when performing the early ignition Sb, α, which is a constant value of wear amount, is added to the wear amount based on basic formula (1). Since the engine load is extremely small (virtually 0) from the intake stroke to the early stage of the compression stroke, the additional value α can be set to a constant value. Note that the wear amount α can also be a variable value that is changed depending on, for example, the engine load and the engine rotation speed.

Next, wear of the spark plug 25 due to intermittent ignition in pattern (b) of FIG. 9 will be explained. In the intermittent ignition, after the initial ignition of the main ignition Sa is executed, additional ignition is performed during the induction discharge caused by the initial ignition.

FIG. 14 shows a situation in which the discharge current value changes regarding this intermittent ignition. In FIG. 14, the initial ignition (main ignition) is indicated by the symbol Y3a, and the additional ignition is indicated by the symbol Y3b (see also FIG. 10). At the initial ignition Y3a, the capacitive discharge component is the same as without additional ignition. On the other hand, in the additional ignition Y3b, since capacitive discharge occurs during the inductive discharge of the initial ignition Y3a, the capacitive discharge in the additional ignition Y3b is small and can be virtually ignored. Therefore, for the additional ignition Y3b, the amount of wear on the electrodes 250a and 250b due to capacitive discharge is set to zero.

Next, the influence of the flow velocity (gas flow velocity) in the combustion chamber 17 on the wear of the electrodes 250a, 250b of the spark plug 25 will be explained. First, FIG. 15 shows a discharge situation when the flow velocity in the combustion chamber 17 is low, equal to or less than a predetermined value. When the flow rate is low, the capacitive discharge occurs only once at the beginning.

On the other hand, when the flow velocity in the combustion chamber 17 is so large as to exceed a predetermined value, as shown in FIG. 16, the capacitive discharge is re-formed and the capacitive discharge occurs multiple times. That is, when the discharge is interrupted in the middle of discharge due to a large flow velocity, capacitive discharge will occur again (reformation of the discharge path).

The second and subsequent capacitive discharges for re-forming the discharge path are smaller than the first capacitive discharges. However, even the second and subsequent relatively small capacity discharges cannot be ignored, especially in engines with high compression ratios. The ground electrode 250a is greatly affected by wear due to capacitive discharge.

FIG. 17 shows the difference in the amount of wear of the ground electrode 250a based on the difference in flow velocity. In a conventional engine with a small compression ratio, the difference in the amount of wear on the ground electrode 250a depending on the flow velocity is not a big problem. However, in a high compression ratio engine, the density (engine load) in the combustion chamber 17 after ignition is extremely large, so the amount of wear on the ground electrode 250a varies greatly depending on the flow velocity.

Therefore, when the flow velocity in the combustion chamber 17 is low, the amount of wear on the ground electrode 250a is estimated based on the following equation (2). Further, when the flow velocity in the combustion chamber 17 is so large that it exceeds the specified value, the amount of wear is estimated based on the following equation (3).

式（２）、（３）中、Ｋ１～Ｋ４、Ｌ１～Ｌ４は定数で、それぞれ正の値である（－Ｋ２、－Ｌ２はマイナスの値となる）。また、δは基本式（１）と同様に燃焼室１７内の密度である。ただし、容量放電に基づく摩耗量は、下限値が０とされる（マイナスの値とならない）。式（２）で算出される摩耗量の単位は、１０^-10（１０のマイナス１０乗）×ｍｍ³（ミリ立法メートル）である。

In equations (2) and (3), K1 to K4 and L1 to L4 are constants, each of which is a positive value (-K2 and -L2 are negative values). Further, δ is the density within the combustion chamber 17, as in the basic formula (1). However, the lower limit of the amount of wear based on capacitive discharge is 0 (it does not take a negative value). The unit of the amount of wear calculated using equation (2) is 10 ⁻¹⁰ (10 to the power of minus 10)×mm ³ (millimeter cubic meter).

The amount of wear calculated based on equation (3) is set to be a larger value than the amount of wear calculated based on equation (2). Note that the wear amount of the center electrode 250b is estimated based on the above-mentioned basic formula (1).

FIG. 18 shows the relationship between the opening degree of the swirl valve 56 and the swirl ratio. The smaller the opening degree of the swirl valve 56 is, the larger the swirl ratio becomes, and the flow velocity within the combustion chamber 17 is increased.

FIG. 19 shows an example of setting the opening degree of the swirl valve 56 using the engine load and engine rotation speed, which indicate the operating state of the engine, as parameters. In FIG. 19, V1 to V5 indicate the opening degree of the swirl valve 56. V1<V2<V3<V4<V5. The opening degrees V1 to V5 of the swirl valve 56 are set from the viewpoint of ensuring the amount of intake air and improving the combustion chamber. In the embodiment, V1 is approximately 12 degrees, V2 is approximately 20 degrees, V3 is approximately 30 degrees, V4 is approximately 45 degrees (half open), and V5 is approximately 90 degrees (fully open).

When the opening degree of the swirl valve 56 is a predetermined opening degree, for example, V3 or less (that is, when the flow velocity is high), the amount of wear on the ground electrode 250a is calculated based on equation (3). Further, when the opening degree of the swirl valve 56 exceeds V3 (that is, when the flow velocity is small), the amount of wear on the ground electrode 250a is calculated based on equation (2).

FIG. 20 schematically shows the factors that affect the wear of the center electrode 250b using the engine load as a parameter. The amount of wear due to induced discharge and the amount of wear due to additional ignition is approximately constant over a wide range of engine loads. The amount of wear based on capacitive discharge increases as the engine load increases within a range where the engine load is large. The amount of wear due to early ignition is set to a constant value within a small engine load range.

FIG. 21 schematically shows the factors that affect the wear of the ground electrode 250a, using the engine load as a parameter. The wear amount of the ground electrode 250a increases as the engine load increases within a range where the engine load is high. When the flow velocity in the combustion chamber 17 is high, the amount of wear is greater than when the flow velocity is low.

Next, a control example for estimating the wear amount of the electrodes 250a, 250b of the spark plug 25 will be described with reference to the flowcharts of FIGS. 22 to 24. Further, with reference to the flowchart of FIG. 25, a control example will be described in which it is determined whether or not there is an abnormality in the spark plug 25 (whether or not it should be replaced) based on the estimated amount of wear. Note that this control example is control by the ECU 10 shown in FIG. 10. Further, in the following explanation, Q indicates a step.

First, FIG. 22 shows an example of control for estimating the amount of wear when early ignition is performed. This control is performed, for example, every time the ignition for one cylinder is completed (for example, the control is started in the middle or late stage of the expansion stroke immediately after the ignition is completed). In FIG. 22, first, in Q1, signals necessary for estimating the amount of wear such as engine load, engine speed, and opening degree of the swirl valve 56 are read. In Q2, it is determined whether the operating state of the engine is with early ignition.

When the determination in Q2 is YES, in Q3, the wear amount CM1 of the center electrode 250b for the early ignition is calculated (calculation of the wear amount by adding a constant value to the basic formula (1)). After this, in Q4, the amount of wear CMM of the center electrode 250b for the main ignition is calculated (calculation of the amount of wear based on basic formula (1)).

After Q4, in Q5, it is determined whether the opening degree of the swirl valve 56 is less than or equal to a predetermined opening degree (for example, 30 degrees). When the determination in Q5 is YES, that is, when the flow velocity in the combustion chamber 17 is large, the wear amount EM1 of the ground electrode 250b for the early ignition is calculated in Q6 (the wear amount based on equation (3)). calculation). After this, in Q7,
The amount of wear EMM of the ground electrode 250b for the main ignition is calculated (calculation of the amount of wear based on equation (3)).

When the determination in Q5 is NO, that is, when the flow velocity in the combustion chamber 17 is small, the amount of wear EM1 of the ground electrode 250b for the early ignition is calculated in Q8 (calculation of the amount of wear based on equation (2) ). After that, in Q9, the amount of wear EMM of the ground electrode 250b for the main ignition is calculated (calculation of the amount of wear based on equation (2)). The calculated value of the amount of wear after passing through Q6 and Q7 becomes a larger value than the calculated value of the amount of wear during Q8 and Q9. However, since the engine load is small when early ignition is performed, the wear amount of the ground electrode 250a may be zero.

After Q7 or after Q9, in Q10, CM1, CMM, EM1, and EMM are added to calculate the total wear amount MF due to the current ignition. Q3, Q6, or Q8 corresponds to means for estimating the amount of wear per early ignition. Further, Q4, Q7, or Q9 corresponds to means for estimating the amount of wear per main ignition.

When the determination in Q2 is NO, the process moves to Q21 in FIG. In Q21, it is determined whether the operating state of the engine is with additional ignition (intermittent ignition).

When the determination in Q21 is YES, in Q22, the amount of wear CM2 of the center electrode 250b for the additional ignition is calculated (the amount of wear is calculated based on the basic formula (1), but the amount of wear CM2 is calculated based on the basic formula (1), Calculation of the amount of wear ignoring the amount of wear). After that, in Q23, the amount of wear CMM of the center electrode 250b for the main ignition is calculated (calculation of the amount of wear based on basic formula (1)).

After Q23, the processes of Q24 to Q28 are performed. These Q24 to Q28 correspond to the processes Q5 to Q9 in FIG. 22, so a redundant explanation thereof will be omitted. Note that the wear amount of the ground electrode 250a is EM2 for the additional ignition.

After Q26 or after Q28, in Q29, the referenced wear amounts CM2, CMM, EM2, and EMM are added to calculate the total wear amount MF (corresponding to Q10 in FIG. 22). Q22, Q25, or Q27 corresponds to means for estimating the amount of wear per additional ignition. Furthermore, Q23, Q26, or Q28 corresponds to means for estimating the amount of wear per main ignition.

When the determination in Q21 is NO, the process moves to Q31 in FIG. 24. The process in FIG. 24 is for only main ignition (no intermittent ignition), and corresponds to pattern (c) in FIG. In Q31, the wear amount CMM for main ignition is calculated for the center electrode 250b (calculation based on basic formula (1)).

After Q31, in Q32, it is determined whether the opening degree of the swirl valve 56 is less than or equal to a predetermined opening degree. When the determination in Q32 is YES, that is, when the flow velocity in the combustion chamber 17 is large, the wear amount EMM of the ground electrode 250b for the main ignition component is calculated in Q33 (the wear amount EMM based on equation (3)). calculation).

When the determination in Q32 is NO, that is, when the flow velocity in the combustion chamber 17 is small, the amount of wear EMM of the ground electrode 250b for the main ignition component is calculated in Q34 (calculation of the amount of wear based on equation (2) ).

After Q33 or after Q34, in Q35, the calculated wear amounts CMM and EMM are added to calculate the total wear amount MF (corresponding to Q10 in FIG. 22).
Q31, Q33, or Q34 corresponds to means for estimating the amount of wear per main ignition.

FIG. 25 shows how the spark plug 25 is adjusted based on the calculated wear amount integrated value by calculating the current total wear amount MF calculated by the processes shown in FIGS. 22 to 24. This is a process to determine the presence or absence of an abnormality.

In the control shown in FIG. 25, first, in Q41, the current total wear amount MF calculated in Q10, Q29, or Q35 is added to the previous value of the wear amount integrated value that has been accumulated so far. A wear amount integrated value TMF is calculated. Note that the wear amount integrated value is initialized to 0 when the spark plug 25 is new.

In Q42, based on the wear amount integrated value TMF, it is converted into the amount of wear in the gap length direction, which is the axial distance between the center electrode 250b and the ground electrode 250a. That is, since the wear amount integrated value TMF is acquired as a volume value, the wear amount integrated value TMF that becomes this volume value is converted into the value of the wear amount in the gap length direction between the center electrode 250a and the ground electrode 250b. .

The wear amount integrated value TMF can be converted into a gap length, for example, based on a table created and stored in advance. The relationship between the wear amount integrated value TMF and the wear amount in the gap length direction may be obtained experimentally in advance, and the obtained results may be stored as a table. The converted wear amount in the gap length direction becomes a value in the direction of increasing the original gap length. In other words, the current gap length is obtained by adding the converted wear amount in the gap length direction to the original (when new) gap length.

In Q43, it is determined whether the wear amount GA in the gap length direction converted in Q42 is greater than or equal to a predetermined value. When the determination in Q43 is NO, it is determined in Q44 that the spark plug 25 is normal.

When the determination in Q43 is YES, it is determined in Q45 that the spark plug 25 is abnormal. After that, in Q46, the driver is prompted to replace the spark plug 25. This notification may be made by displaying text on the display, visual notification such as lighting up (or flashing) a display indicating that it is time to replace the spark plug 25, or audio notification (audible notification). For example, a voice notification can be made immediately after the ignition switch is turned on. Q43 to Q46 correspond to an abnormality determining means that determines whether or not there is an abnormality in the spark plug 25 based on the value related to the cumulative amount of wear.

Here, the GA used in the determination in Q43 may be the current gap length obtained by adding the cumulative wear amount in the gap length direction to the initial gap length (when new).

Further, the conversion to the gap length in Q42 can also be performed based on the wear amount integrated value for each electrode 250b, 250a. In this case, by converting the wear amount in the gap length direction for each electrode 250b and 250a and adding the converted wear amounts in the gap length direction, the wear amount GA in the gap length direction can be calculated. You can also. In addition, for the determination in Q42, an appropriate value can be used as long as it is related to the wear amount integrated value, but the wear amount integrated value itself can also be used.

FIG. 26 shows another control example for determining whether or not there is an abnormality in the spark plug 25. In FIG. In this embodiment, when the wear amount in the gap length direction exceeds a predetermined value, ignition is performed in a state with poor ignition performance without immediately determining that the wear amount is abnormal, and if the combustion state is poor at that time (e.g. It is determined that there is an abnormality only when the cylinder pressure is less than a predetermined value.

The flowchart in FIG. 25 shows the control from Q42 in FIG. 15 onwards. That is, in Q51 following Q42, it is determined whether the wear amount GA in the gap length direction converted in Q42 of FIG. 25 is equal to or greater than a predetermined value. When the determination in Q51 is NO, it is determined in Q56 that the spark plug 25 is normal.

When the determination in Q51 is YES, in Q52, the cylinder pressure is detected based on the signal input from the cylinder pressure sensor SW6, and a determination voltage value is calculated from the detected cylinder pressure value. That is, the ECU 10 determines the applied voltage necessary to stably ignite the air-fuel mixture from the detected in-cylinder pressure according to normal control, and obtains the required voltage accordingly. In 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.

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

After Q52, in Q53, a dwell time for determination is calculated based on the calculated voltage for determination. The dwell time for determination is shorter than the dwell time corresponding to the required voltage. Therefore, since the time for energizing the primary coil 251a1 becomes relatively short, the applied voltage also decreases accordingly, and the determination voltage can be applied to the electrode pair 250.

In Q54, a signal is output to the ignition device 251 to activate the spark plug 25 so as to ignite at a predetermined timing. As a result, a determination voltage is applied to the electrode pair 250, and the air-fuel mixture formed inside the combustion chamber 17 is ignited.

In Q55, the ignitability of the air-fuel mixture due to the current ignition is determined based on the signal input from the cylinder pressure sensor SW6. Specifically, it is determined whether the detected value of the cylinder pressure sensor SW6 is less than a predetermined value (ignitability reference value). Note that, instead of the cylinder pressure sensor, a crank angle sensor may be used to determine whether the ignition performance has decreased.

When the determination in Q55 is NO, it is determined in Q56 that the spark plug 25 is normal. It is determined that the current actual gap length has not become large enough to require replacement.

When the determination in Q55 is YES, it is determined in Q57 that the current actual gap length is close to the upper limit value and that the ignitability will soon decrease sharply, that is, the spark plug 25 is abnormal. After this, in Q58, a notification is given to the driver to urge him to replace the spark plug 25. Q51 to Q58 correspond to an abnormality determining means that determines whether or not there is an abnormality in the spark plug 25 based on the value related to the cumulative amount of wear.

Although the embodiments have been described above, the present invention is not limited to the embodiments, and can be modified as appropriate within the scope of the claims. For example, you can do the following: Early ignition can be performed at an appropriate time during the intake stroke, or at the beginning of the compression stroke (for example, when the crank angle of the compression stroke is divided into three or four equal parts, the crank angle closest to the bottom dead center of the compression stroke angular range). The execution (start) timing of additional ignition after the main ignition is carried out in the middle of the induction discharge caused by the main ignition (before the induction discharge caused by the main ignition ends), and when it is carried out after the end of the main ignition ( (after the induction discharge caused by the main ignition has ended). The engine may also be an engine that does not perform intermittent ignition (additional ignition).

The determination of whether or not there is an abnormality in the spark plug 25 is not performed every time the main ignition is performed (every time the main ignition is performed once), but every time the number of ignitions of the main ignition reaches a predetermined number (for example, 100,000 times). (reducing the burden on the control system). The engine may perform only SI combustion without performing SPCCI combustion (particularly suitable for engines with high compression ratios). The estimated amount of wear can be used not only for control of abnormality determination but also for appropriate purposes such as control for determining the voltage applied to the spark plug 25. Of course, the object of the invention is not limited to what is expressly stated, but is also implicitly included to provide any expressed substantial preference or advantage.

The present invention is suitable for application to engines that perform early ignition.

1: Engine body 6: Injector 10: ECU
17: Combustion chamber 25: Spark plug 250: Electrode pair 250a: Ground electrode 250b; Center electrode 251: Ignition device Sa: Main ignition (no additional ignition - pattern (c) in Figure 9)
Sa: Intermittent ignition (main ignition plus additional ignition - pattern (b) in Figure 9)
Sb: Early ignition (pattern (a) in Figure 9)

Claims (13)

It is arranged on the ceiling wall of the combustion chamber in a reciprocating engine, and is used to perform early ignition to activate the air-fuel mixture on the advance side of the main ignition that ignites the air-fuel mixture in the combustion chamber, relative to the engine operating range. A spark plug wear amount estimating device comprising a center electrode and a ground electrode, which is configured to operate in a low speed and low load range,
Wear amount estimating means for estimating the wear amount per early ignition and the wear amount per main ignition of the center electrode of the spark plug in the low speed/low load range, respectively;
Wear amount integration that obtains a wear amount integrated value by integrating the amount of wear of the center electrode per one early ignition of the spark plug estimated by the wear amount estimating means and the amount of wear of the center electrode per one main ignition. means and
Equipped with
The wear amount estimating means calculates the wear amount of the center electrode of the spark plug per main ignition in the low speed/low load range based on a predetermined calculation formula using a constant discharge current value as a parameter. Estimated by
The wear amount estimating means calculates the wear amount per early ignition of the center electrode of the spark plug in the low speed/low load range based on the predetermined calculation formula using the constant discharge current value as a parameter. By adding a predetermined amount to the calculated value, the wear amount of the center electrode is estimated to be larger than the amount of wear of the center electrode during main ignition.
A spark plug wear estimation device characterized by:
In claim 1,
The wear amount estimating means includes a first wear amount estimating means based on capacitive discharge of the spark plug, and a second wear amount estimating means based on the induced discharge of the spark plug,
The wear amount estimating means calculates the amount of wear per early ignition by adding up the amount of wear estimated by the first wear amount estimating means and the amount of wear estimated by the second wear amount estimating means. In contrast, it is estimated as a value obtained by adding a preset constant value.
A spark plug wear estimation device characterized by: A spark plug abnormality determination device comprising the spark plug wear amount estimating device according to claim 1 or 2,
further comprising an abnormality determining means for determining whether or not there is an abnormality in the spark plug based on the value related to the wear amount cumulative value acquired by the wear amount integrating means;
A spark plug abnormality determination device characterized by: In claim 3,
An abnormality determining device for a spark plug, wherein the abnormality determining means determines that the spark plug is abnormal when the integrated value of wear amount is equal to or greater than a predetermined value. In claim 3,
The abnormality determining means has a gap length determining means for determining a value regarding the gap length of the electrode pair based on the cumulative wear amount value,
The abnormality determining means determines that the spark plug is abnormal when a value related to the gap length determined by the gap length determining means is equal to or greater than a predetermined value.
A spark plug abnormality determination device characterized by: In claim 3,
The abnormality determination means is configured to cause the ignition plug to perform a determination ignition in a state where the ignition performance is worse than normal when the value related to the wear amount cumulative value is equal to or higher than a predetermined value, so that the flammability at that time is determined in advance. An abnormality determination device for a spark plug, characterized in that the spark plug is determined to be abnormal when the condition is worse than a set reference value. In any one of claims 3 to 6,
The main ignition is performed in the latter half of the compression stroke,
the early ignition is performed during the intake stroke;
A spark plug abnormality determination device characterized by: In any one of claims 3 to 7,
At least in some operating ranges, the engine performs SPCCI combustion, which performs CI combustion (combustion by self-ignition) of unburned components remaining in the combustion chamber after SI combustion (diffusion combustion) is performed by ignition by a spark plug. A spark plug abnormality determination device characterized in that it is said to be an engine that performs. In claim 8,
An abnormality determination device for a spark plug, characterized in that early ignition is performed when the SPCCI combustion is performed and the operating state is at low rotation speed, low load, and an air-fuel ratio leaner than the stoichiometric air-fuel ratio. . In any one of claims 3 to 9,
A spark plug abnormality determination device characterized in that the ignition energy of early ignition is constant regardless of the operating state of the engine. In claim 8,
Early ignition is performed only in the region where the SPCCI combustion is performed, in an operating state at low rotation and low load and at an air-fuel ratio leaner than the stoichiometric air-fuel ratio,
The ignition energy of early ignition is assumed to be constant regardless of the engine operating condition.
A spark plug abnormality determination device characterized by: In any one of claims 3 to 11,
An apparatus for determining an abnormality in a spark plug, wherein the abnormality determining means, when determining that the spark plug is abnormal, notifies an occupant to prompt replacement of the spark plug. In any one of claims 3 to 12,
An abnormality determination device for a spark plug, characterized in that the engine is a high compression ratio engine having a geometric compression ratio of 16 or more.

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