JP2008303841A - Internal combustion engine and controller of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a controller of an internal combustion engine capable of surely igniting the air-fuel mixture in a cylinder while suppressing the wear of the electrode of an ignition plug by changing over a multi-point ignition and a multiplex ignition to each other. <P>SOLUTION: This internal combustion engine comprises a plurality of ignition plugs for each cylinder. The controller comprises: an ignition control selector means capable of selecting the multi-point ignition control for igniting by using a center ignition plug and side ignition plugs (spark discharge parts) for each cycle or the multiplex ignition control for igniting by boosting to a dielectric breakdown voltage multiple times for each cycle by using the center ignition plug in each cylinder; and an ignitability determination means for determining whether the air-fuel mixture in the cylinder is difficult to ignite or not. When the air-fuel mixture is determined to be difficult to ignite as in the case that the rotational speed of the engine is equal to or higher than a determined rotational speed, an ignition control selector means changes the control from the multi-point ignition control to the multiplex ignition control. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an internal combustion engine having a plurality of spark plugs for each cylinder, and in particular, in many cylinders that perform ignition using a plurality of spark plugs (ignition sources) in each cylinder in accordance with the operating state of the internal combustion engine. The present invention relates to a control technique for an internal combustion engine capable of executing point ignition control and multiple ignition control in which ignition is performed by performing capacity discharge a plurality of times using one ignition plug.

  In an internal combustion engine, in order to rapidly burn an air-fuel mixture formed in a cylinder, each cylinder is provided with a plurality of spark plugs, and a plurality of spark plugs are used to ignite and burn a plurality of portions of the air-fuel mixture. A multi-point ignition internal combustion engine is known (see, for example, Patent Document 1).

  In addition, in order to ensure ignition of the air-fuel mixture formed in the cylinder, so-called multiple ignition, in which ignition is performed by performing capacity discharge a plurality of times in each cycle, using a single spark plug, can be performed. It is known (see, for example, Patent Document 2).

JP 2005-163550 A Japanese Patent Application Laid-Open No. 11-148452

  By the way, in a multi-point ignition type internal combustion engine, even when ignition is performed using one spark plug, such as when the gas flow rate of an air-fuel mixture or the like in a cylinder is fast, the flame propagation after ignition is sufficiently fast. There is a case. In such a case, knocking may occur when multipoint ignition is performed. In addition, since the electric spark generated in the spark discharge portion of the spark plug is caused to flow by the gas flow in the cylinder, the necessary discharge sustaining voltage becomes high, and it may not be possible to maintain the electric spark in the spark discharge portion. There is.

  On the other hand, in an internal combustion engine capable of multiple ignition, the ignition time or number of ignitions of the spark plug increases by the amount of multiple ignition, so that the electrodes constituting the spark discharge part of the spark plug are easily consumed, The problem is that the life of the plug is shortened.

  Therefore, in an internal combustion engine that includes a plurality of ignition plugs for each cylinder and can perform multipoint ignition and multiple ignition, it is necessary to properly use multipoint ignition and multiple ignition depending on the operating state of the internal combustion engine. There is.

  The present invention has been made in view of the above, and by switching between multipoint ignition and multiple ignition, it is possible to more reliably ignite the air-fuel mixture in the cylinder while suppressing the electrode of the spark plug from being consumed. It is an object of the present invention to provide a control device for an internal combustion engine that can be performed in the same manner.

  In order to achieve the above object, a control device for an internal combustion engine having a plurality of spark plugs for each cylinder, the multipoint ignition control for igniting using a plurality of spark plugs for each cycle, and one spark plug Is used to determine whether or not the mixture in the cylinder is difficult to ignite, and the ignition control switching means that can switch between multiple ignition control that performs ignition by performing capacity discharge multiple times for each cycle. Ignitability determining means, and the ignition control switching means switches from multipoint ignition control to multiple ignition control when it is determined that the air-fuel mixture is not easily ignited.

  In the control apparatus for an internal combustion engine according to the present invention, the ignition control switching means may switch from the multiple ignition control to the multipoint ignition control when it is determined that the air-fuel mixture is not difficult to ignite. it can.

  In the control device for an internal combustion engine according to the present invention, the ignitability determining means determines that the air-fuel mixture is difficult to ignite when the engine rotational speed becomes equal to or higher than a predetermined rotational speed. be able to.

  In the control apparatus for an internal combustion engine according to the present invention, the ignitability determining means may determine that the air-fuel mixture is not easily ignited when the engine load becomes equal to or higher than a predetermined determination load. it can.

  In the control device for an internal combustion engine according to the present invention, the internal combustion engine is ignited sequentially from the first spark plug in each cylinder, and further, the secondary current flowing through the first spark plug or the first spark plug is applied. Gas for determining whether or not the gas flow speed in the cylinder is equal to or higher than the determination flow speed based on the secondary discharge detection means for detecting the applied secondary voltage and the detected secondary current or secondary voltage. The ignitability determining means may determine that the air-fuel mixture is not easily ignited when it is determined that the gas flow rate is equal to or higher than the determined flow rate. .

  In the control device for an internal combustion engine according to the present invention, the gas flow determination means is configured to provide a gas flow rate when a discharge sustaining voltage that is a secondary voltage after reaching the breakdown voltage becomes equal to or higher than a predetermined determination voltage. Can be determined to be greater than or equal to the determined flow velocity.

  An internal combustion engine controlled by the control device for an internal combustion engine according to the present invention, wherein each cylinder includes first and second spark plugs, and the multiple ignition control performs ignition using the first spark plug. The first and second ignition coils that apply the secondary voltage to the first and second spark plugs, respectively, and the first that can supply electrical energy to the first and second ignition coils, respectively. And a second capacitor, a first connection state enabling electric energy to be supplied from the first capacitor and the second capacitor to the first ignition coil and the second ignition coil, respectively, and electric energy from the second capacitor to the first ignition coil. When switching to the second connection state enabling supply, the energy distribution means capable of switching, and the multiple ignition control, electric energy is supplied from the first capacitor to the first ignition coil. Later, the energy distribution means is switched from the first connection state to the second connection state, it can be assumed to have a control means for supplying electrical energy from the second capacitor to the first ignition coil.

  In the internal combustion engine according to the present invention, the first spark plug may be a central spark plug in which a spark discharge portion is disposed at the center of the ceiling wall of the combustion chamber, and the second spark plug is a combustion spark The spark plug may be a side spark plug in which a spark discharge portion is disposed at the peripheral edge of the ceiling wall of the chamber.

  According to the present invention, when it is determined that the air-fuel mixture in the cylinder is not difficult to ignite (high ignitability), such as when the gas flow rate in the cylinder is slow or when the gas pressure is low, By performing multi-point ignition, it is possible to improve the output by rapidly burning the air-fuel mixture and to suppress the consumption of the electrode of the spark discharge part of the spark plug. On the other hand, when it is determined that the air-fuel mixture is difficult to ignite, such as when the gas flow rate in the cylinder is high or the gas pressure is high, the ignition of the air-fuel mixture is performed by performing multiple ignition. It can be certain.

  Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or those that are substantially the same.

  First, a schematic configuration of the internal combustion engine according to the present embodiment will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing a schematic configuration around a cylinder of an internal combustion engine. FIG. 2 is a view showing the positional relationship between the first spark plug and the second spark plug and the intake / exhaust valves, and is a view of the ceiling wall of the cylinder head as viewed from the piston side. FIG. 1 and FIG. 2 schematically show only main parts related to the present invention.

  The internal combustion engine according to this embodiment is a gasoline engine in which a fuel injection valve injects fuel into an intake passage, and is a spark ignition engine that ignites an air-fuel mixture formed in a cylinder with an ignition plug. In the present embodiment, the internal combustion engine includes an ignition system that supplies electric energy to the ignition plug, and the ignition system controls the ignition timing and discharge time of the ignition plug according to the operating state of the internal combustion engine. An electronic control device (hereinafter simply referred to as “control device”) is provided as the control means. Hereinafter, one cylinder among the plurality of cylinders of the internal combustion engine will be described.

  As shown in FIG. 1, the internal combustion engine 10 is provided with a cylinder block 12, a cylinder head 20, a piston 30, and a connecting rod and a crankshaft (not shown) as parts of an engine body system in which a cylinder is formed. ing. A cylinder bore 14 is formed in the cylinder block 12, and the piston 30 reciprocates along the axis of the cylinder bore 14 (hereinafter referred to as a bore axis and indicated by a one-dot chain line C).

  The reciprocating motion of the piston 30 is converted into a rotational motion and output from a crankshaft (not shown). The internal combustion engine 10 is provided with a crank angle sensor (not shown) that detects a rotational angle position of the crankshaft (hereinafter referred to as a crank angle), and sends a signal related to the crank angle to the control device. Yes.

  A cylinder head 20 is coupled to the cylinder block 12 so as to face the piston 30 and close the cylinder bore 14. A combustion chamber 40 is formed in the cylinder head 20, and an intake port 24 that leads intake air to the combustion chamber 40 is formed on one side across the bore axis C, and on the other side. Is formed with an exhaust port 26 for exhausting exhaust gas from the combustion chamber 40.

  The cylinder head 20 is provided with an intake valve 25 and an exhaust valve 27 corresponding to the intake port 24 and the exhaust port 26, respectively. The intake valve 25 and the exhaust valve 27 are driven by receiving mechanical power from the crankshaft via a camshaft. The intake valve 25 and the exhaust valve 27 are configured to be openable and closable at a predetermined timing according to the rotation angle position of the crankshaft (hereinafter referred to as the crank angle).

  When the intake valve 25 is opened, the intake port 24 and the combustion chamber 40 communicate with each other, and air from an intake passage (not shown) can be taken into the combustion chamber 40 in the cylinder from the intake port 24. When the exhaust valve 27 is opened, the exhaust port 26 and the combustion chamber 40 communicate with each other, and the exhaust gas in the combustion chamber 40 in the cylinder can be discharged from the exhaust port 26 to an exhaust passage (not shown).

  As shown in FIG. 2, each of the intake port 24 and the exhaust port 26 is provided in two, includes a bore axis C, and the axial direction of the crankshaft (hereinafter simply referred to as “crankshaft direction”). They are arranged so as to face each other across a cylinder row plane (indicated by a one-dot chain line E in the figure) which is a virtual plane extending in the figure as indicated by an arrow S. That is, in an internal combustion engine, a plurality of cylinders are arranged in a row in the crankshaft direction, and in each cylinder, the intake port 24 and the exhaust port 26 are arranged in a so-called “cross flow type”.

  In the following description, the side on which the intake port 24 is provided with respect to the cylinder row plane E including the bore axis C is referred to as “intake side”, and is indicated by the symbol IN in the figure. On the other hand, the side on which the exhaust port 26 is provided with respect to the plane E is referred to as “exhaust side” and is indicated by the symbol EX in the figure.

  The cylinder head 20 is formed with a ceiling wall 22 that is a wall surface that defines the shape of the combustion chamber 40. The ceiling wall 22 is formed so as to smoothly continue to the cylinder wall 15 which is the wall surface of the cylinder bore 14 at the peripheral edge 22e. A spark discharge portion 51 of a central spark plug 50 is disposed at a central portion 22a of the ceiling wall 22 of the combustion chamber 40 formed in the cylinder head 20 (hereinafter referred to as a ceiling wall central portion). The details of the central spark plug will be described later together with the ignition system.

  On the other hand, of the ceiling wall peripheral portion 22 c of the combustion chamber 40 formed in the cylinder head 20, the portion sandwiched between the outer edge 24 e of the intake port 24, the outer edge 26 e of the exhaust port 26 and the peripheral edge 22 e of the ceiling wall 22 A spark discharge portion 55 of the spark plug is provided. The details of the side spark plug will be described later together with the ignition system.

  As shown in FIG. 2, the “ceiling wall central portion” 22 a means the outer edge 24 e of the intake port 24 and the exhaust port 26 in addition to the portion of the ceiling wall 22 of the combustion chamber 40 through which the bore axis C passes. A portion sandwiched between the outer edge 26e is included. On the other hand, the “ceiling wall peripheral portion” 22 c is a portion sandwiched between the peripheral edge 22 e of the ceiling wall 22 and the outer edge 24 e of the intake port 24 or the outer edge 26 e of the exhaust port 26 in addition to the peripheral edge 22 e of the ceiling wall 22. Is included.

  The space surrounded by the cylinder wall 15 of the cylinder block 12, the ceiling wall 22 of the cylinder head 20, and the top surface 32 of the piston 30 described above is a so-called “cylinder”. In the present embodiment, the cylinder includes a combustion chamber 40 formed in the cylinder head 20 in addition to the cylinder bore 14 formed in the cylinder block 12.

  In the following description, of the directions along the bore axis C, the direction in which the piston 30 faces the ceiling wall 22 is indicated as “head side” and is indicated by an arrow U in the figure. Further, the direction opposite to the head side in the direction along the bore axis C is referred to as “crank side” and is indicated by an arrow D in the drawing.

  The direction perpendicular to the bore axis C and perpendicular to the crankshaft direction S, that is, the direction in which the thrust force and the thrust reaction force act between the piston 30 and the cylinder wall 15 is referred to as “thrust "Direction" and indicated by arrow T in the figure. The thrust direction T is a direction orthogonal to the cylinder row plane E.

  Next, the configuration of the ignition system in the internal combustion engine according to the present embodiment will be described with reference to FIGS. FIG. 3 is a schematic diagram showing the configuration of the ignition system of the internal combustion engine. FIG. 4A is a diagram illustrating a relationship between a secondary voltage applied by the ignition coil to the spark plug and time. FIG. 4B is a diagram illustrating a relationship between the secondary current flowing through the spark plug and time. FIG. 5 is an enlarged view of a spark discharge portion of the central spark plug, and is a diagram showing a state of electric spark (arc) in a normal state. FIG. 6 is an enlarged view of a spark discharge portion of the central spark plug, and shows a state in which an electric spark (arc) is caused to flow by gas flow such as air-fuel mixture in the cylinder.

  The ignition system 60 of the internal combustion engine 10 includes two spark plugs for each cylinder as a device for igniting an air-fuel mixture (including fuel spray) formed in the cylinder. Specifically, as shown in FIG. 2, a central spark plug 50 provided in the ceiling wall central portion 22a and a side spark plug (spark discharge portion 55) provided in the ceiling wall peripheral portion 22a are provided. . As shown in FIG. 3, secondary spark voltages are applied to these spark plugs by correspondingly provided first and second ignition coils 61, 62, and spark sparks (electric sparks) are applied to the respective spark discharge portions. Give rise to

  As shown in FIG. 5, the spark discharge portion 51 of the central spark plug 50 is disposed so as to protrude from the ceiling wall central portion 22 a to the combustion chamber 40. The spark discharge part 51 has a center electrode 51a connected to the secondary coil 61c (see FIG. 3) of the first ignition coil 61, and a ground electrode 51c grounded (grounded) to the cylinder head. . When the secondary voltage applied by the secondary coil 61c of the first ignition coil 61 reaches the required dielectric breakdown voltage (capacitance discharge voltage) Vb, as shown in FIG. An electric spark is generated in a gap between the center electrode 51a and the ground electrode 51c, a so-called ignition gap.

  On the other hand, the side spark plug has the same configuration and function as the central spark plug 50, and a spark discharge portion 55 is disposed so as to protrude from the ceiling wall peripheral portion 22c of the cylinder head 20 to the combustion chamber 40. (See FIG. 2). As shown in FIG. 4-1, when the secondary voltage applied by the second ignition coil reaches the required breakdown voltage (capacitance discharge voltage) Vb, the spark discharge unit 55 is connected to the center electrode (not shown) and grounded. An ignition spark is generated between the electrodes.

  Further, as shown in FIG. 3, the ignition system 60 corresponds to the central spark plug 50 and the side spark plug in order to supply the secondary voltage (discharge voltage) to the spark discharge portions 51 and 55 of each spark plug. A first ignition coil 61 and a second ignition coil 62 are provided.

  The first ignition coil 61 has a primary coil 61a, a secondary coil 61c, and an iron core 61b. One end of the primary coil 61 a is connected to an energy distribution device 76 described later, and the other end is connected to the collector of the first transistor 65. On the other hand, one end of the secondary coil 61c is connected to the center electrode 51a of the spark discharge part 51 of the central spark plug 50, and the other end is connected to a control device 80 described later. The secondary voltage generated in the secondary coil 61c of the first ignition coil 61 and the secondary current flowing from the secondary coil 61c to the spark discharge portion 51 of the central spark plug 50 can be detected by the control device 80 described later. Yes.

  Similar to the first ignition coil 61, the second ignition coil 62 has a primary coil 62a, a secondary coil 62c, and an iron core 62b. One end of the primary coil 62a is connected to the energy distribution device 76. The other end is connected to the collector of the second transistor 66. On the other hand, one end of the secondary coil 62 c is connected to the center electrode (not shown) of the spark discharge portion 55 of the side spark plug, and the other end is connected to the control device 80. The secondary voltage generated in the secondary coil 62c of the second ignition coil 62 and the secondary current flowing from the secondary coil 62c to the spark discharge portion 55 of the side ignition plug can be detected by the control device 80 described later. .

  Further, since the primary current flows through the first and second ignition coils 61 and 62 in the ignition system 60, electrical energy of the primary current is stored corresponding to the first and second ignition coils 61 and 62, respectively. The first and second capacitors 67 and 68, the first and second energy generators 71 and 72 for charging the first and second capacitors 67 and 68, and the primary of the first and second ignition coils 61 and 62, respectively. First and second transistors 65 and 66 for interrupting current are provided.

  One end of the first capacitor 67 is connected to an energy distribution device 76 and a first energy generation device 71 described later, and the other end is grounded (earthed). As with the first capacitor 67, one end of the second capacitor 68 is connected to the energy distribution device 76 and the second energy generation device 72, and the other end is grounded.

  The first energy generating device 71 includes a power source, and is configured to be able to supply electric energy to the corresponding first capacitor 67 and store a predetermined charge (charge) under the control of the control device 80. Has been. Similarly to the first energy generation device 71, the second energy generation device 72 is configured to charge the corresponding second capacitor 68. The amounts of power stored in the first and second capacitors 67 and 68 by the first and second energy generators are controlled by the control device 80 in accordance with the discharge maintenance time.

  The first transistor 65 is a so-called “power transistor” that interrupts the primary current of the first ignition coil 61, the collector is connected to the primary coil 61 a of the first ignition coil 61, and the emitter is grounded. Yes. The base of the first transistor 65 is connected to the control device 80. When a signal current flows from the base to the emitter under the control of the control device 80, the first transistor 65 is short-circuited (ON) between the collector and the emitter, and the primary current is supplied to the primary coil 61a of the first ignition coil 61. It is possible to flow.

  Similarly to the first transistor 65, the second transistor 66 has a collector connected to the primary coil 62 a of the second ignition coil 62, an emitter grounded, and a base connected to the control device 80. The second transistor 66 can flow the primary current to the primary coil 62a of the second ignition coil 62 when the signal current flows under the control of the control device 80.

  The ignition system 60 is provided with an energy distribution device 76 that distributes the electric energy (current) of the first and second capacitors 67 and 68 to the first and second ignition coils 61 and 62. The energy distribution device 76 is configured by a changeover switch or the like, and has a function of interrupting current.

  The energy distribution device 76 connects the primary coil 61a of the first ignition coil 61 and the first capacitor 67 so as to be energized, and connects the primary coil 62a and the second capacitor 68 of the second ignition coil 62 to each other. It is configured to be able to be energized in a connected state. In other words, the energy distribution device 76 causes the electric energy (charge) stored in the first capacitor 67 to flow as a primary current to the primary coil 61 a of the first ignition coil 61 and the electric energy stored in the second capacitor 68. It is possible to flow energy as a primary current through the primary coil 62a of the second ignition coil 62.

  In this way, in the energy distribution device 76, the first ignition coil 61 and the first capacitor 67 are electrically connected, and the second ignition coil 62 and the second capacitor 68 are electrically connected, so that the first ignition coil 61 is electrically connected. The coil 61 can be supplied with electric energy from the first capacitor 67, and the second ignition coil 62 can be supplied with electric energy from the second capacitor 68. This connection state is referred to as a “first connection state” of the energy distribution device 76 in the following description.

  The energy distribution device 76 is also configured to be able to be energized by connecting the primary coil 61a of the first ignition coil 61 and the second capacitor 68. That is, the energy distribution device 76 can flow the electrical energy stored in the second capacitor 68 as a primary current to the primary coil 61 a of the first ignition coil 61.

  As described above, in the energy distribution device 76, the first ignition coil 61 can be supplied with electric energy from the second capacitor 68 by electrically connecting the first ignition coil 61 and the second capacitor 68. It becomes. This connection state will be referred to as “second connection state” of the energy distribution device 76 in the following description.

  The energy distribution device 76 includes a first connection state that allows electric energy to be supplied from the first capacitor 67 and the second capacitor 68 to the first ignition coil 61 and the second ignition coil 62, respectively, and a first connection state from the second capacitor 68. The second connection state in which electric energy can be supplied to the ignition coil 61 can be switched. Switching of the energy distribution device 76 between the first connection state and the second connection state is controlled by a control device 80 described later.

  The ignition system 60 includes a control device 80 that controls the first and second energy generation devices 71 and 72, the first and second transistors 65 and 66, and the energy distribution device 76 in accordance with the operating state of the internal combustion engine 10. Have.

  The control device 80 receives signals relating to the rotational speed of the crankshaft (hereinafter referred to as engine rotational speed) from various sensors or other control devices provided in the internal combustion engine 10 and mechanical signals output from the crankshaft by the internal combustion engine. A signal related to power (hereinafter referred to as engine load), a signal related to the discharge time of the central spark plug and the side spark plug, and a signal related to the ignition timing of the central spark plug and the side spark plug are received.

  Based on these signals, the control device 80 can grasp the operating state of the internal combustion engine 10 such as the engine speed and the engine load. In addition, the control device 80 controls the first and second energy generating devices 71 and 72 in accordance with the various signals described above, and the first and second capacitors 67 and 68 are charged with electric energy (electric energy). It is possible to adjust. In addition, the control device 80 controls the energization and shut-off of the first and second transistors 65 and 66 so that the primary current flows through the primary coils 61a and 62a of the first and second ignition coils 61 and 62, respectively. It is possible to adjust the period, that is, the timing and time length at which the secondary voltage is generated in the secondary coils 61c and 62c of the first and second ignition coils 61 and 62.

  As described above, the control device 80 controls the first and second energy generating devices 71 and 72 and the first and second transistors 65 and 66 to thereby control the central spark plug 50 and the side spark plug (spark discharge portion 55). It is possible to control the ignition timing and the discharge time. As a result, the ignition system 60 generates a secondary voltage of several tens of kV in the secondary coils 61c and 62c of the first and second ignition coils 61 and 62, and applies them to the central spark plug 50 and the side spark plug, respectively. Thus, a spark discharge is generated in the spark discharge portions 51 and 55.

  In the present embodiment, the control device 80 performs control so that the central spark plug 50 (first spark plug) is first ignited, and then the side spark plug (only the spark discharge portion 55 is illustrated) is ignited. The control device 80 can also ignite the central spark plug 50 and the side spark plug at the same time.

  Further, since the control device 80 is connected to the secondary coil of the first ignition coil and the secondary coil of the second ignition coil, the secondary coil 61c of the first ignition coil 61 applies to the central spark plug 50. The secondary voltage and the secondary current flowing from the secondary coil 61c to the central spark plug 50 can be detected. In addition, the control device 80 can also detect the secondary voltage applied to the side spark plug by the secondary coil 62c of the second ignition coil 62 and the secondary current flowing from the secondary coil 62c to the side spark plug. . That is, the control device 80 has a function of detecting a secondary voltage applied to the central spark plug 50 (first spark plug) or a secondary current flowing through the central spark plug 50 (secondary discharge detecting means). Yes.

  Further, the control device 80 controls the connection state of the energy distribution device 76 to be switched from the first connection state to the second connection state, and allows a signal current to flow through the first transistor 65, thereby storing the energy in the second capacitor 68. The generated electrical energy can be passed through the primary coil 61a of the first ignition coil 61 as a primary current, a secondary voltage can be generated in the secondary coil 61c, and applied to the central spark plug 50. That is, the control device 80 switches the connection state of the energy distribution device 76 and uses the electric energy of the second capacitor provided corresponding to the side spark plug as the ignition energy of the central spark plug 50 (first spark plug). It can be used.

  Further, based on the detected secondary voltage or current, the control device 80 determines whether or not the gas flow rate in the cylinder, such as the air-fuel mixture (hereinafter simply referred to as “gas flow rate”), is high. The details will be described below with reference to FIGS. The description will be made by taking the central spark plug as an example.

  When the first transistor 65 is controlled by the control device 80 and the primary current flowing through the primary coil 61a of the first ignition coil 61 is cut off, as shown at time T0 in FIG. A secondary voltage begins to be applied to. When the secondary voltage applied to the central spark plug 50 reaches the required dielectric breakdown voltage (capacitance discharge voltage) Vb as shown at time T1 in FIGS. First, arc discharge is started, and an ignition spark (electric spark, arc) extending substantially linearly is generated between the center electrode 51a and the ground electrode 51c as shown in FIG. As a result, as shown in FIG. 4B, a secondary current flows between the center electrode 51a of the spark plug 50 and the ground electrode 51c.

  Thus, once an electric spark is formed between the center electrode 51a and the ground electrode 51c, and arc discharge is started, the gas in the cylinder, such as an air-fuel mixture, is formed along the shape of the electric spark, that is, the discharge path. The molecules to be ionized are reduced, and the electrical resistance between the center electrode 51a and the ground electrode 51c is reduced. Thereby, after time T1, the discharge sustaining voltage Vk (several hundred volts) applied between the center electrode 51a and the ground electrode 51c is compared with the dielectric breakdown voltage (capacitive discharge voltage) Vb (several tens of kilovolts). Small value. Note that arc discharge performed by the discharge sustaining voltage Vk is referred to as “induction discharge” and is distinguished from “capacitive discharge”.

  At this time, when the gas flow speed in the cylinder is not so high, that is, when the engine rotation speed is low, that is, lower than the determination flow speed, the shape of the electric spark that is formed in a substantially straight line at time T1. Is maintained as it is until the end of the arc discharge indicated by time T3 in FIGS. 4-1 and 4-2. In the following description, a state in which a substantially linear electric spark is maintained in the spark discharge portion from the start to the end of the arc discharge is referred to as “normal time”.

  On the other hand, when the gas flow rate is fast, that is, when it is equal to or higher than the judgment flow rate, such as when the engine rotation speed is high, as shown in FIG. May be curved in a convex manner in the gas flow direction F between the center electrode 51a and the ground electrode 51c.

  As described above, when the electric spark is flowed and the shape thereof is curved, the path of the electric spark becomes longer compared to the case where the electric spark is formed in a straight line, and the center electrode 51a and the ground electrode 51c. The electrical resistance between the two will increase. For this reason, the discharge sustaining voltage Vk increases as the gas flow rate in the cylinder increases. That is, the discharge sustaining voltage Vk and the gas flow rate have a substantially proportional relationship, and the gas flow rate in the spark discharge portion in the cylinder can be estimated from the discharge sustaining voltage Vk.

  For this reason, when an electric spark is applied as described above, the discharge sustaining voltage Vkf after the start of the arc discharge at the time T1, that is, after the occurrence of the electric spark, is usually as shown by a broken line in FIG. As compared with the discharge sustaining voltage Vkn at the time, the discharge end timing (time T2) is earlier than the normal discharge end (time T3). That is, the gas flow rate of the air-fuel mixture in the cylinder is substantially proportional to the discharge sustaining voltage Vk. When an electric spark is applied, the discharge sustaining voltage is increased and the time from the generation of the electric spark to the end of the discharge (hereinafter referred to as the discharge sustaining time) is shortened as compared with the normal time.

  Thus, when the gas flow rate of the air-fuel mixture or the like in the cylinder is high, such as when the engine speed is high, the center spark plug is used to perform ignition once for each cycle in each cylinder. Flame propagation may be fast enough. In such a case, if “multi-point ignition” is performed using the center spark plug and the side spark plug for each cycle, knocking or the like may occur. In addition, the spark spark generated in the spark discharge portion of each spark plug is caused to flow by the gas flow in the cylinder, and the electric spark is passed to increase the required discharge sustaining voltage. When the required discharge sustaining voltage becomes high, there is a possibility that the electric spark cannot be maintained in the spark discharge portions 51 and 55 of each spark plug.

  On the other hand, when multiple ignition is performed in each cylinder by performing capacity discharge multiple times per cycle (reaching the capacity discharge voltage) and igniting, the number of ignition times or ignition time of a specific spark plug increases, so that There arises a problem that the wear rate of the center electrode and the ground electrode constituting the discharge part is increased, and the life of the spark plug is shortened.

  Therefore, in the control apparatus for an internal combustion engine according to the present embodiment, it is determined whether or not the air-fuel mixture in the cylinder is in a state that is difficult to ignite, and when it is determined that the air-fuel mixture is not in a state that is difficult to ignite, When multipoint ignition control is performed in which ignition is performed using the center spark plug and the side spark plug for each cycle, and it is determined that the air-fuel mixture is difficult to ignite, a plurality of cycles are performed for each cycle using the center spark plug. And multiple ignition control is performed in which ignition is performed by performing capacity discharge (boost to capacity discharge voltage) once.

  Ignition control executed by the control device for an internal combustion engine according to the present embodiment will be described with reference to FIGS. FIG. 7 is a diagram for explaining the relationship between the operating state of the internal combustion engine and the determined rotational speed. FIG. 8 is a timing chart of the secondary voltage applied to the central spark plug and the side spark plug when it is determined in the control device for the internal combustion engine that the air-fuel mixture is not difficult to ignite. FIG. 9 is a timing chart of the secondary voltage applied to the central spark plug and the side spark plug when it is determined in the internal combustion engine control device that the air-fuel mixture is difficult to ignite.

  First, the control device 80 determines whether or not the air-fuel mixture is difficult to ignite based on the engine speed that is a control variable related to the operating state of the internal combustion engine. Specifically, as shown in FIG. 7, the control device 80 determines whether or not the engine rotational speed is equal to or higher than a predetermined determination rotational speed Nd. That is, the control device 80 determines whether the engine rotational speed is in the low rotational speed range N1 or the high rotational speed range N2.

  The determination rotational speed Nd is obtained in advance by a matching experiment or the like, and is stored in a ROM (not shown) of the control device 80 as a control constant. The determination rotational speed Nd may be set as a control variable according to other control parameters related to the operating state of the internal combustion engine.

  When it is determined that the engine rotation speed is not equal to or higher than the determination rotation speed Nd, that is, when it is determined that the engine rotation speed is in the low rotation speed range N1, the control device 80 has a small flow rate of the air-fuel mixture in the cylinder. In each cycle of the cylinder, even if multiple ignition is not performed with the spark plug, it is determined that the air-fuel mixture ignites satisfactorily, that is, the air-fuel mixture is not difficult to ignite. Select multi-point ignition control that ignites using a plug. If multiple ignition control has been performed until then, the control device 80 switches from multiple ignition control to multipoint ignition control.

  When the multipoint ignition control is selected, as shown in FIG. 3, the control device 80 controls the first energy generating device 71 so that electric energy corresponding to the discharge time of the central spark plug 50 is supplied to the first capacitor 67. At the same time, the second energy generating device 72 is controlled to store the electric energy corresponding to the discharge time of the side spark plug in the second capacitor 68. At the same time, the control device 80 controls the energy distribution device 76 to the first connection state, and sends electric energy from the first capacitor 67 and the second capacitor 68 to the first ignition coil 61 and the second ignition coil 62, respectively. Enable supply.

  And the control apparatus 80 sends a signal current to the 1st transistor 65 and the 2nd transistor 66, respectively according to the ignition timing of the center spark plug 50 and the side spark plug. As a result, the electrical energy stored in the first and second capacitors 67 and 68 flows into the first and second ignition coils 61 and 62 as primary currents, respectively.

  As shown in FIG. 8, the first ignition coil generates a secondary voltage from the time T <b> 0 by the electric energy of the first capacitor 67, and applies this to the central spark plug 50. The central spark plug 50 reaches the dielectric breakdown voltage (capacitive discharge voltage) at the time point T1, and causes the spark discharge portion 51 to generate an electric spark (discharge spark). Similarly, the second ignition coil 62 generates a secondary voltage from the time T2 due to the electric energy of the second capacitor 68, and applies this to the side ignition plug. The side spark plug reaches a dielectric breakdown voltage (capacitive discharge voltage) at time T3, and causes the spark discharge portion 55 to generate an electric spark.

  In this way, the internal combustion engine 10 performs multi-point ignition in which each cylinder performs ignition using both the central spark plug 50 and the side spark plug for each cycle, thereby propagating the flame of the air-fuel mixture after ignition. As a result, the output torque can be improved by completing the combustion at an early stage as compared with the case of performing multiple ignition or single point ignition, and rapidly burning the air-fuel mixture.

  On the other hand, when it is determined that the engine rotation speed is equal to or higher than the determination rotation speed Nd, that is, when it is determined that the engine rotation speed is in the high rotation speed range, the controller 80 has a high flow rate of the air-fuel mixture in the cylinder, In each cylinder, it is determined that the air-fuel mixture cannot be ignited satisfactorily, that is, the air-fuel mixture is not easily ignited, by igniting the center spark plug 50 and the side spark plug once for each cycle. Using the central spark plug 50, multiple ignition control is performed in which ignition is performed by performing capacity discharge (boost to capacity discharge voltage) a plurality of times per cycle. The control device 80 switches from the multipoint ignition control that has been performed so far to the multiple ignition control.

  When multiple ignition control is selected, as shown in FIG. 3, the control device 80 controls the first energy generating device 71 so that the electric energy corresponding to the discharge time of the first ignition of the central spark plug 50 is obtained. The electric energy corresponding to the discharge time of the second ignition of the central spark plug 50 is stored in the second capacitor 68 while being stored in the first capacitor 67 and controlling the second energy generator 72.

  Thereafter, the control device 80 causes a signal current to flow through the first transistor 65 in accordance with the ignition timing of the central spark plug 50. As a result, the electric energy stored in the first capacitor 67 becomes the first primary current in the first ignition coil 61 and flows to the primary coil.

  As shown in FIG. 9, the first ignition coil 61 generates a secondary voltage from the time T <b> 0 by the electric energy of the first capacitor 67 and applies it to the central spark plug 50. The central spark plug 50 reaches the first dielectric breakdown voltage (capacitive discharge voltage) at time T1, and arc discharge is started to cause an electric spark in the spark discharge portion 51.

  Then, the control device 80 controls the energy distribution device 76 to the second connection state so that the primary current can be supplied from the second capacitor 68 to the first ignition coil 61. Then, the control device 80 causes a signal current to flow again through the first transistor 65. The electrical energy stored in the second capacitor 68 becomes the second primary current in the first ignition coil 61 and flows to the primary coil.

  As shown in FIG. 9, the secondary ignition voltage of the first ignition coil 61 rises again immediately after time T2, and at the time T3, the second capacity discharge is started (reaching the capacity discharge voltage). The arc discharge is continued after T3, and the electric spark of the spark discharge unit 51 is continued until time T5.

  In this manner, the internal combustion engine 10 performs multiple ignition to generate a secondary discharge of the secondary voltage applied to the central spark plug 50 twice, and at the spark discharge portion of the central spark plug 50. The length of time that electric spark occurs (time point T1 to time point T5) is made longer than when the spark plug is ignited once (time point T1 to time point T4). As a result, even when the internal combustion engine is operating at a high rotational speed, the gas flow rate in the cylinder is fast, and an electric spark is caused to flow in the spark discharge part 51, so that the mixture is difficult to ignite. Qi ignition can be made more reliable.

  As described above, in the control device 80 for the internal combustion engine according to the present embodiment, the multipoint ignition control in which ignition is performed using both the central spark plug 50 and the side spark plug for each cycle in each cylinder. In the state in which multiple ignition control that performs ignition by performing capacity discharge multiple times per cycle using the central spark plug 50 can be switched, and the air-fuel mixture in the cylinder is difficult to ignite. A function for determining whether or not there is (ignitability determination means), and when it is determined that the air-fuel mixture is difficult to ignite, the ignition control switching means performs multiple ignition from multipoint ignition control. Switch to control.

  When it is determined that the air-fuel mixture in the cylinder is not easily ignited, the control device 80 uses the central spark plug 50 to perform multiple ignition control that performs ignition by performing capacity discharge a plurality of times for each cycle. As a result, the secondary voltage applied to the central spark plug 50 generates a capacitive discharge twice, and the time length during which an electric spark occurs in the spark discharge portion of the central spark plug 50 is determined by the central spark plug 50. It can be longer than when it is ignited once. Thereby, even when the air-fuel mixture in the cylinder is hard to ignite, the air-fuel mixture can be ignited more reliably.

  Further, in the control device 80 for the internal combustion engine according to the present embodiment, the ignition control switching means switches from the multiple ignition control to the multipoint ignition control when it is determined that the air-fuel mixture is not difficult to ignite. Therefore, when the ignitability of the air-fuel mixture is high, such as when the gas flow rate in the cylinder is slow, the control device 80 performs multipoint ignition using both the central spark plug 50 and the side spark plug. The air-fuel mixture in the cylinder can be rapidly burned to improve the output torque of the internal combustion engine. In this case, it is possible to suppress wear of the electrodes of the central spark plug 50 as compared to the case where multiple ignition is performed using the central spark plug 50.

  Further, in the control device 80 for an internal combustion engine according to the present embodiment, the ignitability determining means determines that the air-fuel mixture is not easily ignited when the engine rotation speed becomes equal to or higher than the determination rotation speed. Therefore, in the case where the gas flow rate in the cylinder is increased according to the engine speed and the electric spark generated in the spark discharge portion is caused to flow by the gas flow in the cylinder, multiple ignition can be performed. Thus, ignition of the air-fuel mixture in the cylinder can be made more reliable.

  The internal combustion engine 10 according to the present embodiment is controlled by the control device 80 described above, and includes a central spark plug 50 and side spark plugs (first and second spark plugs) for each cylinder. In the heavy ignition control, ignition is performed using a first ignition plug, and a secondary voltage is applied to each of the central ignition plug 50 (first ignition plug) and the side ignition plug (second ignition plug). The first and second ignition coils 61 and 62, the first and second capacitors 67 and 68 capable of supplying electric energy to the first and second ignition coils 61 and 62, and the first and second capacitors 67 and 68, respectively. A first connection state in which electric energy can be supplied to the first ignition coil 61 and the second ignition coil 62, respectively, and electric energy from the second capacitor 68 to the first ignition coil 61, respectively. When switched to the energy distribution device 76 (energy distribution means) capable of switching between the second connection states to be enabled and the multiple ignition control, electric energy is supplied from the first capacitor 67 to the first ignition coil 61. After that, the energy distribution device 76 is switched from the first connection state to the second connection state, and has a control device 80 (control means) for supplying electric energy from the second capacitor 68 to the first ignition coil 61.

  As a result, the internal combustion engine 10 includes first and second ignition coils 61 and 62 provided corresponding to the center spark plugs and side spark plugs (first and second spark plugs) provided in each cylinder, When the multiple ignition using the first spark plug is performed only by providing two capacitors having the same number of coils, the electric energy stored in the two capacitors is converted to the first primary of the first ignition coil 61, respectively. It can be supplied as a current and a second primary current. An internal combustion engine that includes two ignition plugs for each cylinder and can switch between multi-point ignition control and multiple ignition control can be realized simply by providing two capacitors per cylinder.

  Further, in the internal combustion engine 10 according to the present embodiment, the first spark plug is a central spark plug 50 in which a spark discharge portion 51 is disposed in the center portion 22a of the ceiling wall of the combustion chamber 40, and the second spark plug is The spark plug 55 is a side spark plug in which a spark discharge part 55 is disposed on the ceiling wall peripheral part 22c of the combustion chamber 40. When performing multi-ignition control, multiple ignition is performed using the central spark plug disposed in the center of the ceiling wall. Compared to the case where multiple ignition is used, the air-fuel mixture can be burnt quickly by completing it earlier.

  Ignition control executed by the control apparatus for an internal combustion engine according to the present embodiment will be described with reference to FIGS. 3 to 6 and FIGS. 8 to 10. FIG. 10 is a diagram illustrating the relationship between the operating state of the internal combustion engine and the determination load according to the second embodiment. The ignition control according to the present embodiment differs from the ignition control according to the first embodiment in that it is determined that the air-fuel mixture is difficult to ignite when the engine load becomes equal to or higher than the determination load. In addition, about the structure substantially common with Example 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  First, the control device 80B determines whether or not the air-fuel mixture is difficult to ignite based on the engine load that is a control variable related to the operating state of the internal combustion engine. Specifically, as shown in FIG. 10, control device 80B determines whether or not the engine load is greater than or equal to a predetermined determination load Ld. That is, the control device 80B determines whether the engine load is in the low load range L1 or the high load range L2.

  Note that the determination load Ld is obtained in advance by a matching experiment or the like, and is stored as a control constant in a ROM (not shown) of the control device 80B. The determination load Ld may be set as a control variable in accordance with other control parameters related to the operating state of the internal combustion engine.

  As shown by regions B1 and B3 in FIG. 10, when it is determined that the engine load is not equal to or higher than the determination load Ld, that is, when it is determined that the engine load is in the low load region L1, the control device 80B The gas pressure of the air-fuel mixture in the cylinder is low, and in each cycle of each cylinder, it is determined that the air-fuel mixture ignites satisfactorily, that is, the air-fuel mixture is not difficult to ignite without performing multiple ignition with the spark plug. Multi-point ignition control that performs ignition using the central spark plug 50 and the side spark plug is selected for each cycle. When the multiple ignition control has been performed so far, the control device 80B switches from the multiple ignition control to the multipoint ignition control.

  When the multipoint ignition control is selected, as shown in FIG. 3, the control device 80 </ b> B controls the first energy generating device 71 so that the electric energy corresponding to the discharge time of the central spark plug 50 is supplied to the first capacitor 67. At the same time, the second energy generating device 72 is controlled to store the electric energy corresponding to the discharge time of the side spark plug in the second capacitor 68. At the same time, the control device 80B controls the energy distribution device 76 to the first connection state, and sends electric energy from the first capacitor 67 and the second capacitor 68 to the first ignition coil 61 and the second ignition coil 62, respectively. Enable supply. Then, the control device 80B supplies signal currents to the first transistor 65 and the second transistor 66, respectively, according to the ignition timing of the central spark plug 50 and the side spark plug. As a result, the electric energy stored in the first and second capacitors 67 and 68 becomes a primary current and flows to the first and second ignition coils 61 and 62, respectively.

  As shown in FIG. 8, the first ignition coil 61 generates a secondary voltage from the time T <b> 0 by the electric energy of the first capacitor 67 and applies it to the central spark plug 50. The central spark plug 50 reaches the dielectric breakdown voltage (capacitive discharge voltage) at the time point T1, and causes the spark discharge portion 51 to generate an electric spark (discharge spark). Similarly, the second ignition coil 62 generates a secondary voltage from the time T2 due to the electric energy of the second capacitor 68, and applies this to the side ignition plug. The side spark plug reaches a dielectric breakdown voltage (capacitive discharge voltage) at time T3, and causes the spark discharge portion 55 to generate an electric spark. In this way, the internal combustion engine performs multi-point ignition control in which each cylinder performs ignition using both the central spark plug 50 and the side spark plug for each cycle, thereby propagating the flame of the air-fuel mixture after ignition. The output torque can be improved by completing the combustion earlier and burning the air-fuel mixture rapidly.

  On the other hand, as shown by regions B2 and B4 in FIG. 10, when it is determined that the engine load is equal to or higher than the determination load Ld, that is, when it is determined that the engine load is in the high load region L2, the control device 80B The gas pressure of the air-fuel mixture in the cylinder is high, and the air-fuel mixture cannot be ignited well if it is ignited once by the center spark plug 50 and the side spark plug for each cycle, that is, the air-fuel mixture is difficult to ignite Is determined, and multiple ignition control is performed in which the center spark plug 50 is used to perform ignition by performing capacity discharge a plurality of times per cycle. The control device 80B switches from the multipoint ignition control that has been performed so far to the multiple ignition control.

  When multiple ignition control is selected, as shown in FIG. 3, the control device 80B controls the first energy generating device 71 to generate electric energy corresponding to the discharge time of the first ignition of the central spark plug 50. The electric energy corresponding to the discharge time of the second ignition of the central spark plug 50 is stored in the second capacitor 68 while being stored in the first capacitor 67 and controlling the second energy generator 72. Thereafter, the control device 80B causes a signal current to flow through the first transistor 65 in accordance with the ignition timing of the central spark plug 50. As a result, the electric energy stored in the first capacitor 67 becomes the first primary current in the first ignition coil 61 and flows to the primary coil.

  As shown in FIG. 9, the first ignition coil 61 generates a secondary voltage from the time T <b> 0 by the electric energy of the first capacitor 67 and applies it to the central spark plug 50. The central spark plug 50 reaches a dielectric breakdown voltage (capacity discharge voltage) at time T1, and causes an electric spark in the spark discharge portion 51 where arc discharge is started.

  Then, the control device 80B controls the energy distribution device 76 to the second connection state so that electric energy can be supplied from the second capacitor 68 to the first ignition coil 61. Then, the control device 80B causes a signal current to flow again through the first transistor 65. The electrical energy stored in the second capacitor 68 becomes the second primary current in the first ignition coil 61 and flows to the primary coil.

  As shown in FIG. 9, in the first ignition coil 61, the secondary voltage rises again immediately after time T2, and the second capacity discharge is started at time T3. Arc discharge is continued after time T3, and the electric spark of the spark discharge unit 51 is continued until time T5.

  In this way, the internal combustion engine boosts the secondary voltage applied to the central spark plug 50 to the capacity discharge voltage twice by performing multiple ignition, and at the spark discharge portion of the central spark plug 50. The length of time that electric spark occurs (time point T1 to time point T5) is made longer than when the central spark plug 50 is ignited once (time point T1 to time point T4). Thus, even when the gas pressure in the cylinder is high and the mixture is difficult to ignite, such as when the internal combustion engine is operating in a high load range, the ignition of the mixture can be made more reliable.

  As described above, in the control device 80B for the internal combustion engine according to the present embodiment, the ignitability determining means determines that the air-fuel mixture is not easily ignited when the engine load becomes equal to or higher than the determination load. Therefore, even if the gas pressure in the cylinder increases according to the engine load and the mixture is difficult to ignite, multiple ignition is performed to ensure ignition of the mixture in the cylinder. Can be.

  In the internal combustion engine control apparatus 80B according to the present embodiment, the ignitability determining means determines that the air-fuel mixture is not easily ignited when the engine load becomes equal to or higher than the determination load. The determination of the ignitability of the air-fuel mixture is not limited to this. For example, the ignitability determining means, as shown by a region B4 in FIG. 10, is difficult to ignite the air-fuel mixture when the engine speed is equal to or higher than the determined speed Nd and the engine load is equal to or higher than the determined load Ld. It may be determined that the ignition control switching means switches from the multipoint ignition control to the multiple ignition control.

  In addition, the ignitability determining means, as shown by regions B2, B3, B4 in FIG. 10, when the engine rotational speed is equal to or higher than the determined rotational speed Nd and when the engine load is equal to or higher than the determined load Ld It is also preferable to switch from the multipoint ignition control to the multiple ignition control by determining that the air-fuel mixture is difficult to ignite when one of the conditions is satisfied.

  In the first and second embodiments, when multipoint ignition is performed, the central spark plug 50 is ignited and then the side spark plug is ignited. The firing order of the plugs is not limited to this. For example, when performing multipoint ignition, it is also preferable to ignite the central spark plug 50 and the side spark plug at the same time. Thereby, when multipoint ignition is performed, the air-fuel mixture in the cylinder can be burned more rapidly.

  The ignition control executed by the control device for the internal combustion engine according to the present embodiment will be described with reference to FIGS. 3 to 6, 11, and 12. FIG. 11 is a timing chart of the secondary voltage applied to the central spark plug and the side spark plug when it is determined that the air-fuel mixture is not difficult to ignite in the control device for the internal combustion engine. FIG. 12 is a timing chart of the secondary voltage applied to the central spark plug and the side spark plug when it is determined in the internal combustion engine control device that the air-fuel mixture is difficult to ignite.

  In this embodiment, the internal combustion engine is ignited sequentially from the central spark plug (first spark plug) in each cylinder, and the control device is applied to the secondary current flowing through the central spark plug or the central spark plug. Gas discharge determination means for determining whether or not the gas flow speed in the cylinder is equal to or higher than the determination flow speed based on the detected secondary current or the secondary voltage. And the ignitability determining means determines that the air-fuel mixture is not easily ignited when it is determined that the gas flow rate is equal to or higher than the determined flow rate. In the following, the details will be described. In addition, about the structure substantially common with Example 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  First, the control device 80C determines the ignition timing of the central spark plug 50 and the discharge maintenance time according to the operating state of the internal combustion engine 10, and ignites the central spark plug 50. Specifically, as shown in FIG. 3, the control device 80C controls the first energy generating device 71 to charge the first capacitor 67 with the electrical energy corresponding to the discharge maintaining time, and to change the energy distribution device 76. The first state is controlled. Then, the control device 80C causes a signal current to flow through the base of the first transistor 65 according to the ignition timing, and shuts off after a predetermined time has elapsed. In this way, the control device 80C causes the secondary coil 61c to generate a secondary voltage by causing the primary current to flow through the primary coil 61a of the first ignition coil 61 for a predetermined period.

  Then, as shown at time T0 in FIG. 11, the generated secondary voltage starts to be applied to the central spark plug 50 and rises. When the secondary voltage of the central spark plug 50 reaches the required breakdown voltage (capacity discharge voltage) Vb (time point T1), a substantially linear shape is formed between the center electrode 51a and the ground electrode 51c of the spark discharge portion 51. An electric spark is generated and ignition of the air-fuel mixture in the cylinder is started (see FIG. 5). As shown in FIG. 11, when an electric spark occurs at time T1, the electrical resistance between the center electrode 51a and the ground electrode 51c decreases, and the secondary voltage rapidly drops from the capacitive discharge voltage Vb to the discharge sustaining voltage Vk. To do.

  Then, control device 80C determines whether or not the gas flow rate in the cylinder is equal to or higher than the determination flow rate based on the secondary voltage applied to central spark plug 50. Specifically, control device 80C determines whether or not discharge sustaining voltage Vk, which is a secondary voltage immediately after reaching breakdown voltage Vb (immediately after time T1), is equal to or higher than preset determination voltage Vd. To do.

  The determination voltage Vd is set to a value higher than the sustaining voltage Vkn (see FIG. 4A) when the shape of the linear electric spark is maintained. The determination voltage Vd is obtained in advance by a matching experiment or the like and is stored in the control device 80C as a control constant. Further, the determination voltage Vd may be set as a control variable in accordance with a determination flow speed for determining whether or not the gas flow speed in the cylinder is high.

  As shown in FIG. 11, when the discharge sustaining voltage immediately after dielectric breakdown (time T1) is lower than the determination voltage Vd and it is determined that the discharge sustaining voltage is not equal to or higher than the determination voltage Vd, the control device 80C It is determined that no electric spark is flowing in the 50 spark discharge portions 51 and the gas flow rate in the cylinder is not so fast, and ignition is performed using the central spark plug 50 and the side spark plug for each cycle. Select multipoint ignition control. Until then, when the multiple ignition control has been performed, the control device 80C switches from the multiple ignition control to the multipoint ignition control.

  When the multipoint ignition control is selected, the control device 80C controls the energy distribution device 76 to the first connection state as shown in FIG. 3, and the electric energy is supplied from the second capacitor 68 to the second ignition coil 62. Make it possible to supply. The control device 80C controls the second transistor 66, and causes the electric energy of the second capacitor 68 to flow as a primary current to the primary coil 62a of the second ignition coil 62 for a predetermined time, and 2 to the secondary coil 62c. A next voltage is generated and applied to the side spark plug from time T2. The secondary voltage applied to the side spark plug reaches the dielectric breakdown voltage (capacitive discharge voltage) Vb at time T3, and causes an electrical spark in the spark discharge portion 55.

  In this way, the internal combustion engine performs multi-point ignition control in which each cylinder performs ignition using both the central spark plug 50 and the side spark plug for each cycle, thereby propagating the flame of the air-fuel mixture after ignition. The output torque of the internal combustion engine can be improved by completing the combustion at an early stage and rapidly burning the air-fuel mixture.

  On the other hand, as shown in FIG. 12, when sustaining voltage Vk immediately after dielectric breakdown (time point T1) exceeds determination voltage Vd and it is determined that sustaining voltage Vk is equal to or higher than determination voltage Vd, control device 80C As shown in FIG. 6, it is determined that an electric spark is flowing in the spark discharge portion 51 of the central spark plug 50 and the gas flow rate in the cylinder is high, and the central spark plug 50 is used for each cycle. Multiple ignition control is performed in which ignition is performed by boosting the capacity discharge voltage (capacity discharge) a plurality of times. The control device 80C switches from the multiple ignition control that has been performed so far to the multipoint ignition control.

  When the multiple ignition control is selected, the control device 80C controls the energy distribution device 76 to the second connection state as shown in FIG. 3 so that electric energy is supplied from the second capacitor 68 to the first ignition coil 61. Enable supply. Then, the control device 80C causes the signal current to flow again through the first transistor 65. The electrical energy stored in the second capacitor 68 becomes the second primary current in the first ignition coil 61 and flows to the primary coil. In the first ignition coil 61, as shown in FIG. 12, the secondary voltage rises again immediately after time T2, the second capacity discharge starts at time T3, and arc discharge continues after time T3. Thus, the electric spark of the spark discharge unit 51 is continued until time T5.

  In this manner, the internal combustion engine 10 performs multiple ignition to generate a secondary discharge of the secondary voltage applied to the central spark plug 50 twice, and at the spark discharge portion of the central spark plug 50. The length of time (time T1 to time T5) when the electric spark is generated is longer than that when the central spark plug 50 is ignited once (time T1 to T4). As a result, the gas flow rate in the cylinder is high in each cycle, and even when the electric spark is flown in the spark discharge part 51 and the air-fuel mixture is difficult to ignite as shown in FIG. Can be. In response to a change in the combustion state in the combustion process of the air-fuel mixture, multipoint ignition and multiple ignition can be switched during the combustion process.

  As described above, in the present embodiment, the internal combustion engine 10 is ignited sequentially from the central spark plug 50 (first spark plug), and the control device 80C has the secondary current flowing through the central spark plug 50. Alternatively, based on the function of detecting the secondary voltage applied to the central spark plug (secondary discharge detection means) and the detected secondary current or secondary voltage, whether or not the gas flow speed in the cylinder is fast, That is, it has a function (gas flow determination means) for determining whether or not it is equal to or higher than the determined flow rate. It was determined that it was difficult to perform.

  When the gas flow rate is slow and the ignitability of the air-fuel mixture is high, the control device 80C performs the multi-point ignition control using both the central spark plug 50 and the side spark plug, thereby rapidly increasing the air-fuel mixture in the cylinder. By burning, the output torque of the internal combustion engine can be improved. Compared with the case where multiple ignition is performed by the central spark plug 50, it is possible to suppress the electrodes of the central spark plug 50 from being consumed. On the other hand, when the gas flow rate is fast and the air-fuel mixture is difficult to ignite, the controller 80C uses the central spark plug 50 to reach the capacity discharge voltage Vb a plurality of times per cycle (capacity discharge). By performing multiple ignition control that performs ignition, the secondary voltage applied to the central spark plug 50 is boosted twice to the capacity discharge voltage Vb, and the spark discharge unit 51 of the central spark plug 50 The length of time that the spark is generated can be made longer than when the spark is ignited once by the central spark plug 50. Thereby, even when the air-fuel mixture in the cylinder is hard to ignite, the air-fuel mixture can be ignited more reliably.

  Further, in the control device 80C for the internal combustion engine according to the present embodiment, the gas flow determination means is configured to perform the gas flow when the discharge sustaining voltage, which is the secondary voltage after reaching the breakdown voltage, becomes equal to or higher than the determination voltage. Since the speed is determined to be equal to or higher than the determined flow speed, the gas flow speed is immediately after the secondary voltage applied to the central spark plug 50 (first spark plug) reaches the dielectric breakdown voltage Vb. Whether it is fast or not can be determined. Switching between multipoint ignition control and multiple ignition control can be determined at an early point in time immediately after the insulation breakdown of the central spark plug 50 (first spark plug).

  In this embodiment, whether or not the gas flow rate in the cylinder is equal to or higher than the determination flow rate is determined based on whether or not the discharge sustain voltage Vk is equal to or higher than the determination voltage Vd. The threshold setting method for determining whether or not the speed is high is not limited to this. For example, as shown in FIG. 4B, it is possible to determine whether or not the secondary current is zero, that is, whether or not the spark discharge has ended after a predetermined time has elapsed since the generation of the secondary current. . When the electric spark is caused to flow by the gas flow, the gas flow velocity in the cylinder is increased by utilizing the fact that the discharge ends earlier (refer to FIG. 4-2, time point T2) than the normal time when the electric spark is not flown. It can also be determined whether or not it is equal to or higher than the determination flow speed.

  In each of the above-described embodiments, the side spark plug (spark discharge portion 55) is disposed between the outer edge 24e of the intake port 24 and the outer edge 26e of the exhaust port 26 in the ceiling wall peripheral portion 22c. However, the arrangement of the side spark plugs is not limited to this. The spark discharge part 55 should just be arrange | positioned at the ceiling wall peripheral part 22c of the combustion chamber 40 of the cylinder head 20, for example, between the outer edges 24e of two adjacent intake ports 24 in the ceiling wall peripheral part 22c. It is also preferable to arrange a spark discharge portion 55 of the side spark plug.

  Further, in each of the above-described embodiments, one side spark plug (spark discharge portion 55) is provided at the ceiling wall peripheral portion 22c. However, the number of side spark plugs is not limited to this. . In the side spark plug, the spark discharge portion 55 may be disposed on the peripheral edge portion 22c of the ceiling wall. For example, in the ceiling wall peripheral portion 22c, the spark discharge portion 51 of the central spark plug 50 is centered in the crankshaft direction S. It is also preferable to arrange the spark discharge portions 55 of two side spark plugs on both sides.

  As described above, the present invention is useful for an internal combustion engine including a plurality of spark plugs for each cylinder, and particularly suitable for an internal combustion engine including a supercharger and an internal combustion engine that burns a lean air-fuel mixture in the cylinder. Yes.

1 is a cross-sectional view illustrating a schematic configuration around a cylinder of an internal combustion engine according to a first embodiment. It is a figure which shows the arrangement | positioning relationship of the center spark plug of the internal combustion engine which concerns on Example 1, and a side spark plug, and an intake / exhaust valve, and is the figure which looked at the ceiling wall of the cylinder head from the piston side. 1 is a schematic diagram illustrating a configuration of an ignition system for an internal combustion engine according to a first embodiment. It is a figure which shows the relationship between the secondary voltage which the ignition coil which concerns on Example 1 applies to an ignition plug, and time. It is a figure which shows the relationship between the secondary current which flows into the ignition plug which concerns on Example 1, and time. It is an enlarged view of the spark discharge part of the center spark plug which concerns on Example 1, and is a figure which shows the aspect of the electric spark (arc) in normal time. It is an enlarged view of the spark discharge part of the center spark plug which concerns on Example 1, and is a figure which shows the aspect by which the electric spark was poured by the gas flow in cylinders, such as air-fuel | gaseous mixture. It is a figure explaining the relationship between the driving | running state of the internal combustion engine which concerns on Example 1, and a determination rotational speed. 6 is a timing chart of secondary voltages applied to a central spark plug and a side spark plug when it is determined that the air-fuel mixture is not difficult to ignite in the control device for an internal combustion engine according to the first and second embodiments. 4 is a timing chart of secondary voltages applied to a central spark plug and a side spark plug when it is determined in the control device for an internal combustion engine according to Embodiments 1 and 2 that the air-fuel mixture is difficult to ignite. It is a figure explaining the relationship between the driving | running state of the internal combustion engine which concerns on Example 2, and determination load. FIG. 10 is a timing chart of secondary voltages applied to the central spark plug and the side spark plug when it is determined that the air-fuel mixture is not difficult to ignite in the control apparatus for an internal combustion engine according to the third embodiment. FIG. 6 is a timing chart of secondary voltages applied to a central spark plug and a side spark plug when it is determined in the control device for an internal combustion engine according to Embodiment 3 that the air-fuel mixture is difficult to ignite.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Cylinder block 15 Cylinder wall 20 Cylinder head 22 Combustion chamber ceiling wall 22a Ceiling wall center part 22c Ceiling wall peripheral part 24 Intake port 25 Intake valve 26 Exhaust port 27 Exhaust valve 30 Piston 32 Top surface 40 Combustion chamber 50 Center Spark plug (first spark plug)
51 Spark discharge part of central spark plug 51a Center electrode 51c Ground electrode 55 Spark discharge part of side spark plug 60 Ignition system of internal combustion engine 61 First ignition coil 62 Second ignition coil 65 First transistor 66 Second transistor 67 First capacitor 68 Second capacitor 71 First energy generating device 72 Second energy generating device 76 Energy distribution device (energy distribution means)
80 Control device for internal combustion engine (ignition control switching means, ignitability determination means, secondary discharge detection means, gas flow determination means, control means)
Vb Capacity discharge voltage (secondary voltage, breakdown voltage)
Vk discharge sustaining voltage (secondary voltage)
C Cylinder bore shaft center S Crankshaft direction T Thrust direction IN Intake side EX Exhaust side

Claims (8)

A control device for an internal combustion engine including a plurality of spark plugs for each cylinder,
Ignition capable of switching between multi-point ignition control in which ignition is performed using a plurality of spark plugs per cycle and multiple ignition control in which ignition is performed by capacity discharge multiple times per cycle using one spark plug Control switching means;
Ignitability determination means for determining whether or not the air-fuel mixture in the cylinder is in a state where it is difficult to ignite,
Have
The ignition control switching means is
A control device for an internal combustion engine, characterized in that, when it is determined that the air-fuel mixture is not easily ignited, the multi-point ignition control is switched to the multi-ignition control. The control apparatus for an internal combustion engine according to claim 1,
The ignition control switching means is
A control device for an internal combustion engine, characterized in that, when it is determined that the air-fuel mixture is not difficult to ignite, the multi-ignition control is switched to the multi-point ignition control. The control device for an internal combustion engine according to claim 1 or 2,
The ignitability determination means is
A control apparatus for an internal combustion engine, characterized in that when the engine rotation speed is equal to or higher than a predetermined determination rotation speed, the air-fuel mixture is determined to be difficult to ignite. The control device for an internal combustion engine according to claim 1 or 2,
The ignitability determination means is
A control device for an internal combustion engine, wherein when the engine load becomes equal to or greater than a predetermined determination load, it is determined that the air-fuel mixture is not easily ignited. The control device for an internal combustion engine according to claim 1 or 2,
The internal combustion engine is ignited sequentially from the first spark plug in each cylinder.
further,
Secondary discharge detection means for detecting a secondary current flowing through the first spark plug or a secondary voltage applied to the first spark plug;
Gas flow determination means for determining whether or not the gas flow speed in the cylinder is equal to or higher than the determination flow speed based on the detected secondary current or secondary voltage;
Have
The ignitability determination means is
A control device for an internal combustion engine, wherein when it is determined that the gas flow speed is equal to or higher than the determination flow speed, the air-fuel mixture is determined to be in a state that is difficult to ignite. The control apparatus for an internal combustion engine according to claim 5,
Gas flow judgment means
An internal combustion engine characterized in that a gas flow rate is determined to be equal to or higher than a determination flow rate when a discharge sustaining voltage that is a secondary voltage after reaching a dielectric breakdown voltage is equal to or higher than a predetermined determination voltage. Control device. An internal combustion engine controlled by the control device for an internal combustion engine according to any one of claims 1 to 6,
Each cylinder is provided with first and second spark plugs, and multiple ignition control performs ignition using the first spark plugs.
First and second ignition coils for applying a secondary voltage to the first and second spark plugs, respectively;
First and second capacitors capable of supplying electrical energy to the first and second ignition coils, respectively;
A first connection state in which electric energy can be supplied from the first capacitor and the second capacitor to the first ignition coil and the second ignition coil, respectively, and a second state in which electric energy can be supplied from the second capacitor to the first ignition coil. An energy distribution means capable of switching between connection states;
In the case of switching to the multiple ignition control, after the electric energy is supplied from the first capacitor to the first ignition coil, the energy distribution means is switched from the first connection state to the second connection state, and the first capacitor is switched to the first connection state. Control means for supplying electrical energy to the ignition coil;
An internal combustion engine characterized by comprising: The internal combustion engine according to claim 7,
The first spark plug is a central spark plug in which a spark discharge portion is disposed at the center of the ceiling wall of the combustion chamber,
The second spark plug is a side spark plug in which a spark discharge portion is disposed on the peripheral edge of the ceiling wall of the combustion chamber.
An internal combustion engine characterized by that.

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