Ignition device

Abstract

To provide a technology for converging at an early stage the residual energy that resides in the vicinity of an ignition plug and the like at the end of discharge.SOLUTION: An ignition device 1 for an internal combustion engine using fuel containing hydrogen, includes: an ignition coil 103; a power source device 102; a switching element 70 for switching conduction / breakdown of a primary current; an ignition plug 113 for discharging based on a high voltage induced at one end 822 of a secondary coil L2; a first restriction diode 131; and a first resistance 132. Two first connection lines 121a, 121b are wired in parallel between one end 822 of the secondary coil L2 and the ignition plug 113. The first restriction diode 131 is inserted into the first connection line 121a in a forward direction from one end 822 to another end 821 of the secondary coil L2. A breakdown voltage is a maximum value or more of ON voltage and smaller than a discharge maintaining voltage of the ignition plug 113. The first resistance 132 is inserted into the first connection line 121b with a resistance value of 10 MΩ or more to 50 MΩ or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an ignition device for an internal combustion engine.

Background Art

[0002] Conventionally, an ignition device is mounted on an internal combustion engine including an SI (spark ignition) reciprocating engine used in an automobile or the like. The ignition coil of the ignition device boosts the DC low voltage supplied from the battery to several thousand V to several tens of thousand V under the control of an ECU (Engine Control Unit), supplies it to the spark plug, generates an electric spark, and ignites the fuel. Examples of conventional ignition devices are described in, for example, Patent Document 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent Document 1 discloses an ignition device (1) for an internal combustion engine having the following configuration. First, the primary coil (21) of the ignition coil (2) is connected to a DC power source (VB+), such as an in-vehicle battery, and the energization and interruption of the primary current (I1) flowing through the primary coil (21) are switched by the on / off control of the main switching element (4) (paragraph 0015, Figure 1). One end of the secondary coil (22) magnetically coupled to the primary coil (21) via an iron core is connected to the spark plug (3), and the other end is connected to the DC power supply line via the ON-voltage prevention diode (23). As a result, when the primary current (I1) of the ignition coil (2) is interrupted, a high voltage is generated on the secondary side, dielectric breakdown occurs in the discharge gap of the spark plug (3), and the secondary current (I2) flows in the forward direction of the ON-voltage prevention diode (23). (paragraphs 0016, 0029). On the other hand, the reverse-polarity ON voltage generated in the secondary coil (22) at the start of energization of the primary coil (21) is suppressed by the ON-voltage prevention diode (23) (paragraph 0017).

[0005] In recent years, in SI (spark ignition) reciprocating engines, fuels containing hydrogen have been widely used. Using fuels containing hydrogen is considered to contribute to the realization of a so-called low-carbon society. However, on the other hand, hydrogen has the characteristics of being easily combustible even at relatively low temperatures and having a high combustion speed. For this reason, for example, if a slight discharge occurs at an unexpected timing in the spark plug, the fuel can be ignited and burned. In this case, there is a risk of abnormal combustion such as backfire where the flame blows back from the combustion chamber of the engine to the intake device side, afterfire where the fuel remaining in the exhaust gas of the engine burns in the exhaust passage, etc., or pre-ignition where the ignition timing cannot be controlled.

[0006] In addition, when there is residual energy near the ignition plug or the like at the end of the discharge by the ignition plug in one cycle formed in the combustion chamber of one or more cylinders of the internal combustion engine, there is an increased risk that the fuel may be ignited and burned at an unexpected timing in the next cycle. More specifically, in the intake process of the next cycle, when the pressure in the cylinder decreases and a new air-fuel mixture flows in, there is an even higher risk that discharge may occur due to the residual energy and the fuel may be ignited and burned. In particular, when the rotational speed of each cylinder is high, since the next cycle starts immediately, it is necessary to converge the residual energy to near zero earlier.

[0007] An object of the present invention is to provide a technique capable of suppressing discharge from occurring at an unexpected timing (abnormal timing) in the ignition plug. In particular, it is to provide a technique capable of converging the residual energy remaining near the ignition plug or the like at the end of the discharge by the ignition plug to near zero earlier.

Means for Solving the Problems

[0008] To solve the above problems, the first invention of the present application is an ignition device for an internal combustion engine using a fuel containing at least hydrogen, which includes an ignition coil, a power supply device, a switching element, an ignition plug, a first limiting diode, and a first resistor. The ignition coil is formed by electromagnetic coupling between a primary coil and a secondary coil. The power supply device applies a DC voltage to one end of the primary coil via a power line. The switching element is inserted between the other end of the primary coil and the ground point, and can switch the energization or interruption of the primary current flowing from the power supply device to the primary coil. The ignition plug ignites the fuel by discharging at the gap based on the high voltage induced at one end of the secondary coil. The first limiting diode is inserted in one of the two first connection lines wired in parallel between one end of the secondary coil and the ignition plug, and is a Zener diode or an avalanche diode that is forward-biased in the direction from one end of the secondary coil to the other end. The first resistor is inserted in the other of the two first connection lines. The breakdown voltage of the first limiting diode is equal to or greater than the value calculated by multiplying the voltage value of the DC voltage applied from the power supply device to one end of the primary coil by the ratio of the number of turns of the secondary coil to the number of turns of the primary coil, and is smaller than the discharge maintenance voltage at the gap of the ignition plug. The resistance value of the first resistor is 10 MΩ or more and 50 MΩ or less.

[0009] The second invention of the present application is the ignition device of the first invention, wherein the breakdown voltage is 1 kV or more.

[0010] The third invention of the present application is the ignition device of the first invention or the second invention, wherein the breakdown voltage is 2 kV or less.

[0011] The fourth invention of the present application is an ignition device for an internal combustion engine using a fuel containing at least hydrogen, which has an ignition coil, a power supply device, a switching element, an ignition plug, a second limiting diode, and a second resistor. The ignition coil is formed by electromagnetic coupling between a primary coil and a secondary coil. The power supply device applies a DC voltage to one end of the primary coil via a power line. The switching element is inserted between the other end of the primary coil and the ground point, and can switch the energization or interruption of the primary current flowing from the power supply device to the primary coil. The ignition plug ignites the fuel by discharging at the gap based on the high voltage induced at one end of the secondary coil. The second limiting diode is inserted in one of two second connection lines wired in parallel between the other end of the secondary coil and the power supply device or the ground point, and is a Zener diode or an avalanche diode that is forward-biased in the direction from one end to the other end of the secondary coil. The second resistor is inserted in the other of the two second connection lines. The breakdown voltage of the second limiting diode is equal to or higher than a value calculated by multiplying the voltage value of the DC voltage applied from the power supply device to one end of the primary coil by the ratio of the number of turns of the secondary coil to the number of turns of the primary coil, and is smaller than the discharge maintenance voltage at the gap of the ignition plug. The resistance value of the second resistor is 10 MΩ or more and 50 MΩ or less.

[0012] The fifth invention of the present application is the ignition device of the fourth invention, wherein the breakdown voltage is 1 kV or more.

[0013] The sixth invention of the present application is the ignition device of the fourth invention or the fifth invention, wherein the breakdown voltage is 2 kV or less.

[0014] The seventh invention of the present application is an ignition device of any one of the first to sixth inventions, further comprising a control unit that controls the switching of the switching element. The control unit performs charging control in which a primary current is passed through the primary coil to charge it by closing the switching element, and after performing the charging control, switches the switching element to an open state to induce a high voltage at one end of the secondary coil, thereby performing discharge control to cause discharge in the gap of the spark plug. The absolute value of the voltage induced at one end of the secondary coil at the end point of the discharge control is greater than the absolute value of the voltage induced at one end of the secondary coil at the start point of the discharge control.

[0015] The eighth invention of the present application is an ignition device of any one of the first to seventh inventions, having a stray capacitance formed between one end of the secondary coil and the spark plug.

Advantages of the Invention

[0016] According to the first to eighth inventions of the present application, when a primary current flows through the primary coil (when ON), the current flowing through the secondary coil can be suppressed by the limiting diode and the resistor connected in parallel with each other. Thereby, it is possible to suppress the occurrence of discharge at the spark plug when ON. Further, after the discharge ends, the absolute value of the voltage value due to the residual energy remaining near one end of the secondary coil or near the spark plug can be immediately reduced to the breakdown voltage of the limiting diode. Further, thereafter, by the current flowing through the resistor, it can be quickly reduced toward zero. As a result, it is possible to further suppress the occurrence of discharge at an abnormal timing in the spark plug.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0018] Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. Note that the components described in this embodiment are merely examples and are not intended to limit the scope of the present invention thereto. Also, in the drawings, for ease of understanding, the dimensions and numbers of each part may be exaggerated or simplified as necessary.

[0019] <1. First Embodiment> <1-1. Configuration of Ignition Device> First, the configuration of the ignition device 1 for an internal combustion engine according to the first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram schematically showing the operating environment of the ignition device 1 according to the first embodiment. As will be described later, the primary coil L1 and the secondary coil L2 of the ignition coil 103 included in the ignition device 1 are arranged in a direction where they are laminated on each other. However, in FIG. 1, for ease of understanding, they are shown adjacent to each other.

[0020] The ignition device 1 of this embodiment is, for example, a device that is mounted on an internal combustion engine such as an SI (spark ignition) reciprocating engine used in a vehicle body 100 of an automobile or the like, and applies a high voltage for generating a spark discharge to the spark plug 113. The ignition device 1 is provided for each of one or a plurality of cylinders of the internal combustion engine.

[0021] Also, as shown in FIG. 1, in addition to the ignition device 1, the vehicle body 100 is equipped with the spark plug 113, a power supply device 102 (battery), and an ECU 105 (Engine Control Unit). In a broad sense, the spark plug 113, the power supply device 102, and the ECU 105 can also be regarded as being included in the ignition device 1.

[0022] The spark plug 113 is a device for realizing an ignition operation in the combustion chamber of the internal combustion engine. The spark plug 113 is electrically connected to one end 822 of the secondary coil L2 of the ignition coil 103, which will be described later, via a conducting wire (hereinafter referred to as the "first connection wire 121"). The spark plug 113 is inserted between one end 822 of the secondary coil L2 and a ground point (ground) 151. When a high voltage is induced in the secondary coil L2 of the ignition coil 103 and this high voltage exceeds the breakdown voltage of the insulation in the gap d (see FIG. 1) between the center electrode 161 and the ground electrode 162 of the spark plug 113, a discharge occurs in the gap d and a spark is generated. Thereby, the fuel filled in the internal combustion engine is ignited. That is, the spark plug 113 ignites the fuel by discharging in the gap d based on the high voltage induced at one end 822 of the secondary coil L2.

[0023] In addition, in the present embodiment, hydrogen or a mixture of hydrogen and other substances is used as fuel. That is, at least fuel containing hydrogen is used for the ignition device 1 for the internal combustion engine.

[0024] Also, the first connection line 121 and the spark plug 113 have a capacitance component of about 15 to 20 pF. That is, a capacitance component is formed between one end 822 of the secondary coil L2 and the spark plug 113. Hereinafter, this capacitance component is referred to as a "floating capacitance Cs" defined virtually. As shown in FIG. 1, the floating capacitance Cs can be schematically represented in parallel with the spark plug 113 in the block diagram.

[0025] The power supply device 102 is a power supply device (storage battery) capable of charging and discharging DC power. In the present embodiment, the power supply device 102 is electrically connected to the primary coil L1 of the ignition coil 103 described later via a conducting wire (hereinafter referred to as "power supply line 150"). The power supply device 102 applies a DC voltage to one end 811 of the primary coil L1 of the ignition coil 103 via the power supply line 150.

[0026] The ECU 105 is an existing computer that comprehensively controls the operation of the transmission and airbag of the vehicle body 100.

[0027] The ignition device 1 includes an ignition coil 103, an igniter 104, a first limiting diode 131, and a first resistor 132.

[0028] FIG. 2 is a longitudinal sectional view of the ignition coil 103. As shown in FIG. 2, the ignition coil 103 includes a bobbin 40, a primary coil L1, a secondary coil L2, and an iron core 60. In FIG. 2, the primary coil L1 and the secondary coil L2 are shown with partial simplification. In the following description of the ignition coil 103, the direction parallel to the central axis Bc of the bobbin 40 is referred to as the "axial direction", the direction orthogonal to the central axis Bc of the bobbin 40 is referred to as the "radial direction", and the direction along an arc centered on the central axis Bc of the bobbin 40 is referred to as the "circumferential direction", respectively. Also, the "parallel direction" includes a substantially parallel direction, and the "orthogonal direction" includes a substantially orthogonal direction.

[0029] The bobbin 40 includes a primary bobbin 41 and a secondary bobbin 42 that can be connected to each other. The primary bobbin 41 and the secondary bobbin 42 each extend in a cylindrical shape along the central axis Bc. Also, the secondary bobbin 42 is disposed outside the primary bobbin 41 in the radial direction. For example, resin is used as the material of the primary bobbin 41 and the secondary bobbin 42.

[0030] The primary coil L1 is formed by winding a conducting wire (hereinafter referred to as "primary conducting wire 81") around the outer peripheral surface of the primary bobbin 41 in the circumferential direction centered on the central axis Bc. After the formation of the primary coil L1 is completed, the secondary bobbin 42 is disposed and connected to the primary bobbin 41 so as to cover the outer peripheral surface of the primary coil L1. Then, a conducting wire different from the primary conducting wire 81 (hereinafter referred to as "secondary conducting wire 82") is wound around the outer peripheral surface of the secondary bobbin 42 in the circumferential direction centered on the central axis Bc, thereby forming the secondary coil L2. By arranging the primary coil L1 and the secondary coil L2 so as to be laminated on each other in this way, the entire ignition coil 103 including them can be miniaturized. However, the primary coil L1 and the secondary coil L2 may be arranged adjacent to each other as shown in FIG. 1, not only when they are wound while being laminated on each other in this way.

[0031] The iron core 60 has a structure in which a central iron core 601 and an outer peripheral iron core 602 are combined. The central iron core 601 and the outer peripheral iron core 602 of the iron core 60 are each formed of, for example, a laminated steel sheet in which silicon steel sheets are laminated. The central iron core 601 extends along the central axis Bc of the bobbin 40. Further, the central iron core 601 is inserted into the space 410 inside the primary bobbin 41 in the radial direction. The outer peripheral iron core 602 passes outside the secondary bobbin 42 and the secondary conductor 82 in the radial direction and connects both axial ends of the central iron core 601. Thereby, the iron core 60 forms a closed magnetic circuit structure that electromagnetically couples the primary coil L1 and the secondary coil L2. That is, the ignition coil 103 is formed by electromagnetic coupling between the primary coil L1 and the secondary coil L2.

[0032] As shown in FIG. 1, a power supply line 150, which is a conductor extending from the above-described power supply device 102, is connected to one end 811 of the primary coil L1. The other end 812 of the primary coil L1 is connected to an igniter 104 described later. By being controlled by the igniter 104, a DC low voltage from the power supply device 102 is applied to one end 811 of the primary coil L1, and a primary current that gradually increases begins to flow through the primary coil L1.

[0033] One end 822 of the secondary coil L2 is connected to the spark plug 113 via the first connection line 121. The wire diameter of the secondary conductor 82 is smaller than the wire diameter of the primary conductor 81. Also, the number of turns (for example, 8000 turns) of the secondary conductor 82 in the secondary coil L2 is about 80 times or more the number of turns (for example, 100 turns) of the primary conductor 81 in the primary coil L1. Thereby, as will be described in detail later, the ignition coil 103 boosts the DC low voltage power supplied from the power supply device 102 to several thousand V to several tens of thousand V when the primary current is interrupted. That is, a high voltage is induced in the secondary coil L2. Then, the secondary coil L2 supplies the induced high voltage power to the spark plug 113. Thereby, an electric spark is generated in the spark plug 113 to ignite the fuel.

[0034] The first connection line 121 has two conductors (hereinafter referred to as "first connection line 121a" and "first connection line 121b") that are wired in parallel with each other. That is, the two first connection lines 121a and 121b are wired in parallel between one end 822 of the secondary coil L2 and the ignition plug 113.

[0035] In addition, in the present embodiment, a first limiting diode 131 is inserted in the first connection line 121a, which is one of the two first connection lines 121a and 121b. The first limiting diode 131 is connected in series with the secondary coil L2. A Zener diode is used for the first limiting diode 131 of the present embodiment. However, an avalanche diode may be used for the first limiting diode 131. Also, the first limiting diode 131 is in the forward direction in the direction from one end 822 to the other end 821 of the secondary coil L2.

[0036] In the present invention, as the first limiting diode 131, one having a breakdown voltage equal to or higher than the maximum value of the "ON voltage" described later and smaller than the discharge maintenance voltage at the gap d of the ignition plug 113 (the voltage to be applied to the gap d in order to maintain discharge in the gap d between the center electrode 161 and the ground electrode 162 of the ignition plug 113) is used. The breakdown voltage of the first limiting diode 131 of the present embodiment is 1 kV or higher and 2 kV or lower. The effects of setting the breakdown voltage of the first limiting diode 131 to such a value will be described in detail later.

[0037] In addition, in the present embodiment, a first resistor 132 is inserted in the first connection line 121b, which is the other of the two first connection lines 121a and 121b. The first resistor 132 is connected in series with the secondary coil L2. Also, the resistance value of the first resistor 132 of the present embodiment is 10 MΩ or higher and 50 MΩ or lower. The effects of setting the resistance value of the first resistor 132 to such a value will be described in detail later.

[0038] As shown in FIG. 1, one end 822 of the secondary coil L2, which is opposite to the end 821 to which the ignition plug 113 is connected, is directly or indirectly and electrically connected to the power supply device 102 via a conducting wire (hereinafter referred to as the "second connection wire 122"). In the present embodiment, the other end 821 of the secondary coil L2 is electrically connected to the power supply line 150 via the second connection wire 122.

[0039] As will be described in detail later, when the switching element 70 of the igniter 104 is closed and a primary current is passed through the primary coil L1 for charging (when ON), a potential difference is generated between both ends 821 and 822 of the secondary coil L2. The positive and negative of the voltage induced in both ends 821 and 822 of the secondary coil L2 depend on the winding direction of the secondary coil L2. In the present embodiment, at the time of ON, one end 822 of the secondary coil L2 has a higher voltage than the other end 821. Hereinafter, the potential difference between one end 822 and the other end 821 of the secondary coil L2 will be referred to as the "voltage at the time of ON". The maximum value of the voltage at the time of ON is calculated by multiplying the voltage value of the DC voltage applied from the power supply device 102 to one end 811 of the primary coil L1 via the power supply line 150 by the ratio of the number of turns of the secondary coil L2 to the number of turns of the primary coil L1.

[0040] For example, if the voltage value of the DC voltage applied to one end 811 of the primary coil L1 is 12V, the number of turns of the primary coil L1 is 100 turns, and the number of turns of the secondary coil L2 is 8000 turns, the ratio of the number of turns of the secondary coil L2 to the number of turns of the primary coil L1 is 80. Therefore, the maximum value of the voltage at the time of ON is calculated as 12 × 80 = 960V. For this reason, the maximum value of the voltage applied to one end 822 of the secondary coil L2 is, for example, about +480V, and the minimum value of the voltage applied to the other end 821 of the secondary coil L2 is, for example, about -480V. Also, in some cases, it can be assumed that the maximum value of the voltage applied to one end 822 of the secondary coil L2 is about 0V, and the minimum value of the voltage applied to the other end 821 of the secondary coil L2 is about -960V. On the other hand, at this time, the voltage applied to the power supply line 150 is 12V.

[0041] Therefore, a current flows from the power supply device 102 side to the secondary coil L2 side via the power supply line 150 and the second connection line 122. Here, a first limiting diode 131 is inserted in a first connection line 121a of the first connection line 121 that connects one end 822 of the secondary coil L2 and the ignition plug 113. As described above, the breakdown voltage of the first limiting diode 131 is 1 kV or more. That is, in the present embodiment, the breakdown voltage of the first limiting diode 131 is set so as not to be lower than the maximum value (differential pressure) of the voltage applied to one end 822 of the secondary coil L2 (the cathode side of the first limiting diode 131) with respect to the ground point (ground) 151 (the anode side of the first limiting diode 131) when a primary current flows through the primary coil L1 (at the time of ON). For this reason, no current flows through the first connection line 121a in which the first limiting diode 131 is inserted.

[0042] Also, a first resistor 132 is inserted in a first connection line 121b of the first connection line 121. As described above, the resistance value of the first resistor 132 is 10 MΩ or more. By setting the resistance value of the first resistor 132 to a sufficiently large value in this way, the current flowing through the first connection line 121b can be sufficiently reduced at the time of ON. As a result, the ON-time voltage generated in the secondary coil L2 and the voltage (secondary voltage) generated at one end 822 of the secondary coil L2 can be suppressed at the time of ON. As a result, it is possible to suppress discharge from occurring in the ignition plug 113 at the time of ON, that is, at an abnormal timing. For reference, FIG. 3 shows the results of measuring the relationship between the resistance value of the first resistor 132 and the ON-time voltage when a primary current flows through the primary coil L1 (at the time of ON) while changing the resistance value of the first resistor 132 in a plurality of patterns using the ignition device 1 according to the present embodiment.

[0043] The igniter 104 is a semiconductor device connected to the primary coil L1 and controls the current flowing through the primary coil L1. Also, the igniter 104 is electrically connected to the ECU 105 and receives a signal (hereinafter referred to as the "EST signal") from the ECU 105. The igniter 104 includes a switching element 70 and a drive IC 71. Note that the igniter 104 may be integrated with the electronic circuit of the ECU 105.

[0044] For the switching element 70, for example, an insulated gate bipolar transistor (IGBT) is used. The switching element 70 is inserted between the other end 812 of the primary coil L1 and the ground point (ground) 152. The C (collector) of the switching element 70 is connected to the other end 812 of the primary coil L1. The E (emitter) of the switching element 70 is connected to the ground point (ground) 152. The G (gate) of the switching element 70 is connected to the drive IC 71.

[0045] Thereby, the switching element 70 can switch the energization or interruption of the primary current flowing from the power supply device 102 to the primary coil L1. When the switching element 70 is in the closed state, a primary current flows from the power supply device 102 to the primary coil L1. When the switching element 70 is in the open state, the primary current flowing through the primary coil L1 is interrupted. However, other types of transistors may be used for the switching element 70.

[0046] The drive IC 71 is a control unit that controls the switching of the switching element 70 based on the EST signal received from the ECU 105. The drive IC 71 has a logic device connected to the switching element 70. The logic device includes, for example, a logic circuit, a processor, a CPLD (complex programmable logic device), an FPGA (field-programmable gate array), or an ASIC (application-specific integrated circuit), etc. The logic device performs arithmetic processing for operating the ignition device 1 to ignite the spark plug 113.

[0047] <1-2. Operation of Ignition Device> Subsequently, the operation of the ignition device 1 will be described. FIG. 4 is a graph showing the waveforms of the EST signal, the current flowing through the secondary coil L2 (secondary current), and the voltage generated at one end 822 of the secondary coil L2 (secondary voltage) in time series when operating the ignition device 1. Note that for the secondary current in FIG. 4, the direction from one end 822 to the other end 821 of the secondary coil L2 is negative, and the direction from the other end 821 to one end 822 of the secondary coil L2 is positive as shown. Also, for the secondary voltage in FIG. 4, the value of the voltage applied to one end 822 of the secondary coil L2 with respect to the ground point (ground) is shown.

[0048] As described above, a DC voltage (e.g., 12V) is applied from the power supply device 102 to one end 811 of the primary coil L1 via the power supply line 150. Also, the other end 812 of the primary coil L1 is connected to the switching element 70. Further, the drive IC 71 controls the switching of the switching element 70 based on the EST signal received from the ECU 105. In this embodiment, after a mixture containing fuel is supplied and filled into each combustion chamber of one or more cylinders of the internal combustion engine, each ignition device 1 is operated immediately before TDC (top dead center). As shown in FIG. 4, when operating the ignition device 1, first, at time t0, the signal level of the EST signal transmitted from the ECU 105 to the drive IC 71 is changed from L to H.

[0049] Then, the drive IC 71 switches the switching element 70 from the open state to the closed state based on the EST signal. As a result, a primary current flows through the primary conductor 81 forming the primary coil L1, and the primary coil L1 is charged with electric charge (hereinafter, such a process of flowing a primary current through the primary coil L1 for charging is referred to as "charging control"). Also, an energizing magnetic flux is generated in the primary coil L1, and a magnetic field corresponding to the energizing magnetic flux acts on the iron core 60.

[0050] Also, at both ends 821 and 822 of the secondary coil L2 electromagnetically coupled to the primary coil L1 via the iron core 60, a potential difference, that is, an ON voltage (for example, 960 V) is generated due to the mutual induction effect. As a result, the maximum value of the voltage applied to one end 822 of the secondary coil L2 becomes a positive value (for example, about +480 V), and the minimum value of the voltage applied to the other end 821 of the secondary coil L2 becomes a negative value (for example, about -480 V). At this time, the voltage applied to the power line 150 is, for example, 12 V.

[0051] Therefore, a current flows from the side of the power supply device 102 toward the side of the secondary coil L2 via the power line 150 and the second connection line 122. Here, a first limiting diode 131 is inserted in a first connection line 121a of a first connection line 121 that connects one end 822 of the secondary coil L2 and the ignition plug 113. As described above, the breakdown voltage of the first limiting diode 131 is 1 kV or more. That is, in the present embodiment, the breakdown voltage of the first limiting diode 131 is a value that does not fall below the maximum value (differential pressure) of the voltage applied to one end 822 (the cathode side of the first limiting diode 131) of the secondary coil L2 with respect to the ground point (ground) 151 (the anode side of the first limiting diode 131) when a primary current flows through the primary coil L1 (at the time of ON). For this reason, no current flows through the first connection line 121a in which the first limiting diode 131 is inserted.

[0052] Also, a first resistor 132 is inserted in a first connection line 121b of the first connection line 121. As described above, the resistance value of the first resistor 132 is 10 MΩ or more. In this way, by setting the resistance value of the first resistor 132 to a sufficiently large value, the current flowing through the first connection line 121b can be sufficiently reduced at the time of ON. As a result, at the time of ON, the ON voltage generated in the secondary coil L2 and the voltage (secondary voltage) generated at one end 822 of the secondary coil L2 can be suppressed. As a result, it is possible to suppress the occurrence of discharge in the ignition plug 113 at the time of ON, that is, at an abnormal timing.

[0053] After performing charge control, at time t1, the signal level of the EST signal transmitted from the ECU 105 to the drive IC 71 is changed from H to L. Then, the drive IC 71 switches the switching element 70 from the closed state to the open state to cut off the primary current flowing from the power supply device 102 to the primary coil L1. As a result, an induced electromotive force is induced in the secondary coil L2 magnetically coupled to the primary coil L1 via the iron core 60 by the mutual induction action. In this embodiment, a negative high voltage is induced at one end 822 of the secondary coil L2. At this time, the voltage value (the value of the secondary voltage) applied to one end 822 of the secondary coil L2 ranges from minus several thousand volts to several tens of thousands of volts with respect to the ground point (ground).

[0054] Also, the absolute value of the negative high voltage induced at one end 822 of the secondary coil L2 exceeds the breakdown voltage at the gap d of the spark plug 113. As a result, breakdown occurs at the gap d of the spark plug 113. Then, a current flows from the ground point (ground) 151, through the ground electrode 162 of the spark plug 113 to the center electrode 161 of the spark plug 113 (see FIG. 1), in the forward direction through the first limiting diode 131, or through the first resistor 132, and further through the secondary coil L2. In this embodiment, most of the current flows in the forward direction through the first limiting diode 131, a part flows through the first resistor 132, and further flows to the ground point (ground) 153 via the power supply device 102.

[0055] As a result, due to the occurrence of discharge at the gap d of the spark plug 113, a spark is generated and the fuel filled in the combustion chamber of the internal combustion engine is ignited. When the fuel in the combustion chamber burns, the pressure in the combustion chamber rises and the piston moves from the TDC (top dead center) to the BDC (bottom dead center).

[0056] In the present invention, the process of causing a discharge in the gap d of the ignition plug 113 by switching the switching element 70 to the open state in this way to cut off the primary current flowing through the primary coil L1 and inducing a high voltage at one end 822 of the secondary coil L2 is referred to as "discharge control". When the absolute value of the negative high voltage induced at one end 822 of the secondary coil L2 is lower than the discharge maintenance voltage in the gap d of the ignition plug 113 (at time t2), the discharge in the gap d of the ignition plug 113 once ends.

[0057] Here, the breakdown voltage and the discharge maintenance voltage in the gap d of the ignition plug 113 are greatly affected by the pressure in the combustion chamber. The voltage (the absolute value of the high voltage induced at one end 822 of the secondary coil L2) for causing breakdown and maintaining discharge in the gap d of the ignition plug 113 is substantially proportional to the pressure in the combustion chamber. Also, as described above, when "discharge control" is performed, the fuel in the combustion chamber burns and the pressure rises. Therefore, when the pressure in the combustion chamber becomes high or the fuel burns and the flow becomes intense, the absolute value of the high voltage induced at one end 822 of the secondary coil L2 may become higher.

[0058] As shown in FIG. 4, also in the present embodiment, when "discharge control" is performed, the absolute value of the negative high voltage induced at one end 822 of the secondary coil L2 once approaches zero from the value (Ds) at the start point of "discharge control", but then increases again as the pressure in the combustion chamber rises or the flow becomes stronger. And the value (De) at the end point of "discharge control" has a larger absolute value than the value (Ds) at the start point of "discharge control". That is, in the present embodiment, the absolute value of the voltage induced at one end 822 of the secondary coil L2 at the end point of discharge control is larger than the absolute value of the voltage induced at one end 822 of the secondary coil L2 at the start point of discharge control.

[0059] Also, as described above, a stray capacitance Cs having a capacitance component of about 15 to 20 pF is formed between one end 822 of the secondary coil L2 and the spark plug 113. Therefore, even when the discharge at the gap d of the spark plug 113 has once ended (time t2), charges may still remain in the vicinity of one end 822 of the secondary coil L2, the first connection wire 121, or the vicinity of the center electrode 161 of the spark plug 113. In this embodiment, negative charges remain at these locations. As a result, at time t2, the residual voltage value (value (De) at the end of "discharge control") at one end 822 of the secondary coil L2 becomes a negative value (for example, minus several tens of thousands of volts) with respect to the ground point (ground).

[0060] Note that at time t2, the pressure in the combustion chamber is in a high state, and the absolute value of the above residual voltage value is smaller than the discharge maintenance voltage at the gap d of the spark plug 113. However, if this situation is left unattended, there is a risk that discharge may occur again at the gap d of the spark plug 113 at an unexpected timing (for example, when the pressure in the cylinder decreases and a new air-fuel mixture flows in during the intake process of the next cycle) when a pressure change occurs in the internal combustion engine later.

[0061] Therefore, in the present invention, as the first limiting diode 131, one having a breakdown voltage smaller than the discharge maintenance voltage at the gap d of the spark plug 113 and the absolute value of the above residual voltage value (De) is used. The breakdown voltage of the first limiting diode 131 used in this embodiment is 2 kV or less. On the other hand, in the above example, the residual voltage value (De) at one end 822 (the cathode side of the first limiting diode 131) of the secondary coil L2 is a negative value (for example, minus several tens of thousands of volts), and the absolute value of this value exceeds the breakdown voltage of the first limiting diode 131.

[0062] As a result, after the discharge ends, current flows in the reverse direction through the first limiting diode 131 from the power supply device 102 side all at once without causing discharge again at the ignition plug 113. That is, current (secondary current) flows from the power supply device 102 side through the second connection line 122 to the secondary coil L2 side.

[0063] This cancels the charges remaining near one end 822 of the secondary coil L2, near the first connection line 121, or near the center electrode 161 of the ignition plug 113, etc., and rapidly reduces the absolute value of the voltage (secondary voltage) applied to one end 822 of the secondary coil L2, and the residual energy remaining at these locations can be reduced. As a result, the absolute value of the voltage applied to the center electrode 161 of the ignition plug 113 is rapidly reduced to the breakdown voltage of the first limiting diode 131. Hereinafter, the absolute value of the voltage (secondary voltage) applied to one end 822 of the secondary coil L2 after the reduction will be referred to as the "residual initial voltage Vo". As shown in FIG. 4, at the time (time t2) when the discharge ends, the absolute value of the voltage (secondary voltage) applied to one end 822 of the secondary coil L2 is rapidly reduced and can be regarded as becoming the "residual initial voltage Vo".

[0064] Also, as described above, the first connection line 121b is wired in parallel with the first connection line 121a in which the first limiting diode 131 is inserted, and the first resistor 132 is inserted in the first connection line 121b. After the voltage value applied to the center electrode 161 of the ignition plug 113 is reduced to the breakdown voltage (residual initial voltage Vo) of the first limiting diode 131, current mainly flows through the first connection line 121b. More specifically, current (secondary current) flows from the power supply device 102 side through the second connection line 122 and the secondary coil L2 through the first connection line 121b in which the first resistor 132 is inserted.

[0065] Also, in the present embodiment, the resistance value of the first resistor 132 is 50 MΩ or less. By thus reducing the resistance value of the first resistor 132, after the discharge ends, the current flowing from the power supply device 102 side through the first connection line 121b can be maintained at a certain level or higher. As a result, the residual energy remaining near one end 822 of the secondary coil L2, the first connection line 121, or near the center electrode 161 of the ignition plug 113 can be further reduced and converged to near zero at an early stage.

[0066] In addition, in the ignition device 1 according to the present embodiment, the absolute value of the voltage (secondary voltage) applied to one end 822 of the secondary coil L2, "Vt" at a time t after (after being reduced) when the absolute value of the voltage applied to one end 822 of the secondary coil L2 becomes the breakdown voltage (residual initial voltage Vo) of the first limiting diode 131, can be calculated by the formula "Vt = Vo × exp(-t / (C × R))". In the formula, "C" represents the value of the above-mentioned "floating capacitance Cs", and "R" represents the resistance value of the first resistor 132.

[0067] For reference, using the ignition device 1 according to the present embodiment, while changing the residual initial voltage Vo [kV], the time until the absolute value of the voltage (secondary voltage) applied to one end 822 of the secondary coil L2 converges to 200 V was measured by simulation when the resistance value of the first resistor 132 was "10 MΩ", "22 MΩ", and "33 MΩ". The results are shown in FIG. 5.

[0068] As described above, in the present embodiment, at the time (time t2) when the discharge ends, the "residual initial voltage Vo" is suddenly reduced to the breakdown voltage of the first limiting diode 131, that is, 2 kV or less. Therefore, as shown in FIG. 5, even when the resistance value of the first resistor 132 is "10 MΩ", "22 MΩ", or "33 MΩ", it was confirmed that the absolute value of the voltage (secondary voltage) applied to one end 822 of the secondary coil L2 converges to 200 V within about 3.5 milliseconds.

[0069] Here, as described above, the ignition device 1 of the present embodiment is used for a high-speed internal combustion engine. For example, in an internal combustion engine with a rotational speed of 16,000 rpm, when discharge control is performed near TDC (top dead center), the intake process in the next cycle starts approximately 3.75 ms later. As described above, in the present embodiment, even when the resistance value of the first resistor 132 is "10 MΩ", "22 MΩ", or "33 MΩ", the absolute value of the voltage (secondary voltage) applied to one end 822 of the secondary coil L2 converges to 200 V within about 3.5 milliseconds. As a result, it was confirmed that even in the intake process and the like in the next cycle, it is possible to suppress the occurrence of discharge and ignition of the fuel.

[0070] As described above, in the present embodiment, first, as charge control, when a primary current flows through the primary coil L1 (when ON), the current flowing through the secondary coil L2 can be suppressed by the first limiting diode 131 and the first resistor 132 connected in parallel to each other. Thereby, the ON-time voltage generated in the secondary coil L2 can be reduced. As a result, it is possible to suppress the occurrence of discharge at the ignition plug 113 when ON.

[0071] Also, after the discharge ends, the current (secondary current) flows from the side of the power supply device 102 through the second connection line 122 and the secondary coil L2 in the reverse direction through the first limiting diode 131 all at once. Thereby, the charges remaining near one end 822 of the secondary coil L2, the first connection line 121, or near the center electrode 161 of the ignition plug 113 can be canceled all at once. As a result, the absolute value of the voltage value due to the residual energy remaining in these locations can be immediately reduced to the yield voltage of the first limiting diode 131. Furthermore, thereafter, by the current flowing through the first resistor 132, the absolute value of the voltage value due to the residual energy remaining in these locations can be quickly reduced toward zero.

[0072] As a result, even when a pressure change occurs in the internal combustion engine thereafter, it is possible to suppress the occurrence of discharge at the gap d of the spark plug 113 at an abnormal timing. As a result, even in an internal combustion engine using a fuel containing hydrogen, which is easy to burn even at a relatively low temperature and has a high combustion speed, it is possible to suppress ignition of the fuel at an abnormal timing, leading to suppression of damage to the engine and the like.

[0073] <2. Second Embodiment> Next, a second embodiment of the present invention will be described. In the following, the description will focus on the differences from the first embodiment, and redundant descriptions of the parts equivalent to the first embodiment will be omitted.

[0074] FIG. 6 is a block diagram schematically showing the operating environment of the ignition device 1 according to the second embodiment. As shown in FIG. 6, in the second embodiment, one end 822 of the secondary coil L2 is directly or indirectly and electrically connected to the spark plug 113 via a conducting wire (hereinafter referred to as the "first connection wire 221").

[0075] Also, the other end 821 of the secondary coil L2, which is opposite to the one end 822 to which the spark plug 113 is connected, is directly or indirectly and electrically connected to the power supply device 102 via two conducting wires (hereinafter referred to as the "second connection wire 222a" and the "second connection wire 222b"). The second connection wires 222a and 222b are wired in parallel between the other end 821 of the secondary coil L2 and the power supply device 102. In the present embodiment, the other end 821 of the secondary coil L2 is electrically connected to the power supply line 150 via the second connection wire 222a or the second connection wire 222b.

[0076] Also, in the present embodiment, in the second connection line 222a, which is one of the two second connection lines 222a and 222b, the second limiting diode 231 is inserted. The second limiting diode 231 is connected in series with the secondary coil L2. A Zener diode is used for the second limiting diode 231 of the present embodiment. However, an avalanche diode may be used for the second limiting diode 231. Also, the second limiting diode 231 is in the forward direction in the direction from one end 822 to the other end 821 of the secondary coil L2.

[0077] Also, in the present embodiment, as the second limiting diode 231, one having a breakdown voltage equal to or higher than the maximum value of the ON voltage and lower than the discharge maintenance voltage at the gap d of the spark plug 113 is used. That is, the breakdown voltage of the second limiting diode 231 is a value calculated by multiplying the voltage value of the DC voltage applied from the power supply device 102 to one end 811 of the primary coil L1 via the power supply line 150 by the ratio of the number of turns of the secondary coil L2 to the number of turns of the primary coil L1. Also, the breakdown voltage of the second limiting diode 231 of the present embodiment is 1 kV or higher and 2 kV or lower.

[0078] Also, in the present embodiment, in the second connection line 222b, which is the other of the two second connection lines 222a and 222b, the second resistor 232 is inserted. The second resistor 232 is connected in series with the secondary coil L2. Also, the resistance value of the second resistor 232 of the present embodiment is 10 MΩ or higher and 50 MΩ or lower. Also, a stray capacitance Cs having an electrostatic capacitance component of about 15 to 20 pF is formed between one end 822 of the secondary coil L2 and the spark plug 113.

[0079] In this embodiment, first, as charge control, when a primary current flows through the primary coil L1 (when it is ON), an ON-time voltage (for example, 960 V) is generated at both ends 821 and 822 of the secondary coil L2. The maximum value of the voltage applied to one end 822 of the secondary coil L2 becomes a positive value (for example, about +480 V), and the minimum value of the voltage applied to the other end 821 of the secondary coil L2 becomes a negative value (for example, about -480 V). On the other hand, at this time, the voltage applied to the power supply line 150 is, for example, 12 V.

[0080] Therefore, a current flows from the side of the power supply device 102 through the power supply line 150 toward the side of the secondary coil L2. Here, a second limiting diode 231 is inserted in a second connection line 222a that connects the other end 821 of the secondary coil L2 and the power supply line 150. As described above, the second limiting diode 231 is forward-biased in the direction from one end 822 to the other end 821 of the secondary coil L2. Also, the breakdown voltage of the second limiting diode 231 is 1 kV or more. That is, in this embodiment, the breakdown voltage of the second limiting diode 231 is set so as not to be lower than the differential pressure between the voltage value (for example, +12 V) applied to the power supply line 150 (the cathode side of the second limiting diode 231) and the minimum value (for example, -480 V) of the voltage applied to the other end 821 (the anode side of the second limiting diode 231) of the secondary coil L2 when a primary current flows through the primary coil L1 (when it is ON). For this reason, no current flows through the second connection line 222a in which the second limiting diode 231 is inserted.

[0081] Also, a second resistor 232 is inserted in a second connection line 222b. As described above, the resistance value of the second resistor 232 is 10 MΩ or more. By setting the resistance value of the second resistor 232 to a sufficiently large value in this way, the current flowing through the second connection line 222b during ON-time can be sufficiently reduced. As a result, during ON-time, the ON-time voltage generated in the secondary coil L2 and the voltage (secondary voltage) generated at one end 822 of the secondary coil L2 can be suppressed. As a result, it is possible to suppress discharge from occurring in the ignition plug 113 during ON-time, that is, at an abnormal timing.

[0082] Also, as discharge control, when the switching element 70 is switched from the closed state to the open state to cut off the primary current flowing from the power supply device 102 to the primary coil L1, a negative high voltage ranging from minus several thousand volts to several tens of thousands of volts is induced at one end 822 of the secondary coil L2. As a result, dielectric breakdown occurs at the gap d of the spark plug 113. Then, from the ground point (ground) 151, it goes toward the center electrode 161 of the spark plug 113 through the ground electrode 162 of the spark plug 113 (see FIG. 6), flows through the first connection line 221 and the secondary coil L2, and a current flows in the forward direction through the second limiting diode 231 or through the second resistor 232. In this embodiment, most of the current flows in the forward direction through the second limiting diode 231, a part flows through the second resistor 232, and further flows to the ground point (ground) 153 via the power supply device 102.

[0083] As a result, due to the occurrence of discharge at the gap d of the spark plug 113, a spark is generated and the fuel filled in the combustion chamber of the internal combustion engine is ignited. Note that when the absolute value of the negative high voltage induced at one end 822 of the secondary coil L2 is lower than the discharge maintenance voltage at the gap d of the spark plug 113, the discharge at the gap d of the spark plug 113 once ends.

[0084] Also, similar to the first embodiment, as the second limiting diode 231, one having a breakdown voltage lower than the absolute values of the dielectric breakdown voltage at the gap d of the spark plug 113 and the residual voltage value (De) at one end 822 of the secondary coil L2 at the end of discharge is used. The breakdown voltage of the second limiting diode 231 used in this embodiment is 2 kV or less. At this time, the residual voltage value (De) at one end 822 (the anode side of the second limiting diode 231) of the secondary coil L2 is a negative value (for example, minus several tens of thousands of volts), while the voltage applied to the power supply line 150 (the cathode side of the second limiting diode 231) is, for example, 12 V.

[0085] As a result, after the discharge ends, current flows in the reverse direction through the second limiting diode 231 from the power supply device 102 side all at once without causing discharge to occur again at the ignition plug 113. That is, current (secondary current) flows from the power supply device 102 side toward the secondary coil L2 side via the second connection line 222a.

[0086] This cancels the charges remaining near one end 822 of the secondary coil L2, in the vicinity of the first connection line 221, or near the center electrode 161 of the ignition plug 113, etc., and reduces the absolute value of the voltage (secondary voltage) applied to one end 822 of the secondary coil L2 all at once, and the residual energy remaining in these locations can be reduced. As a result, the absolute value of the voltage (secondary voltage) applied to one end 822 of the secondary coil L2 is reduced all at once to a value approximately equal to the breakdown voltage of the second limiting diode 231.

[0087] Also, as described above, a second connection line 222b is wired in parallel with the second connection line 222a in which the second limiting diode 231 is inserted, and a second resistor 232 is inserted into the second connection line 222b. After the voltage value at one end 822 of the secondary coil L2 is reduced to a value approximately equal to the breakdown voltage of the second limiting diode 231, current flows through the second connection line 222b. More specifically, current (secondary current) flows from the power supply device 102 side toward the secondary coil L2 via the second connection line 222b in which the second resistor 232 is inserted.

[0088] Also, in this embodiment, the resistance value of the second resistor 232 is 50 MΩ or less. In this way, by making the resistance value of the second resistor 232 small, the current flowing from the power supply device 102 side via the second connection line 222b can be maintained at a certain level or more after the discharge ends. As a result, the residual energy remaining near one end 822 of the secondary coil L2, in the vicinity of the first connection line 221, or near the center electrode 161 of the ignition plug 113, etc., can be further reduced and can be converged to near zero earlier.

[0089] As described above, in the present embodiment, first, as charge control, when a primary current is passed through the primary coil L1 (during ON), the current flowing through the secondary coil L2 can be suppressed by the second limiting diode 231 and the second resistor 232 connected in parallel to each other. Thereby, the ON-time voltage generated in the secondary coil L2 can be reduced. As a result, it is possible to suppress the occurrence of discharge at the ignition plug 113 during ON.

[0090] Also, after the discharge ends, the current (secondary current) flows all at once in the reverse direction through the second limiting diode 231 from the side of the power supply device 102 via the second connection line 222a. Thereby, the charges remaining in the vicinity of one end 822 of the secondary coil L2, the first connection line 221, or the vicinity of the center electrode 161 of the ignition plug 113, etc. can be canceled all at once. As a result, the absolute value of the voltage value due to the residual energy remaining in these locations can be immediately reduced to a value approximately equal to the breakdown voltage of the second limiting diode 231. Further thereafter, by the current flowing through the second resistor 232, the absolute value of the voltage value due to the residual energy remaining in these locations can be quickly reduced toward zero.

[0091] As a result, even when a pressure change occurs in the internal combustion engine thereafter, it is possible to suppress the occurrence of discharge at the gap d of the ignition plug 113 at an abnormal timing. As a result, even in an internal combustion engine using a fuel containing hydrogen, which is easy to burn even at a relatively low temperature and has a high combustion speed, it is possible to suppress the ignition of the fuel at an abnormal timing, leading to the suppression of damage to the engine and the like.

[0092] As described above, in the first embodiment, the first limiting diode 131 and the first resistor 132 are provided on the side of one end 822 of the secondary coil L2. In contrast, in this embodiment, the second limiting diode 231 and the second resistor 232 are provided on the side of the other end 821 of the secondary coil L2. However, in many cases, there is also a stray capacitance consisting of a small capacitance component in the secondary coil L2 itself. Therefore, when the second limiting diode 231 and the second resistor 232 are provided on the side of the other end 821 of the secondary coil L2, the capacitance component of about 15 to 20 pF formed between one end 822 of the secondary coil L2 and the spark plug 113 overlaps with the capacitance component of the secondary coil L2 itself.

[0093] As a result, the influence of the overlapping capacitance components becomes greater, the ON voltage described above becomes larger, and there is a risk that the residual energy at the time when the discharge described above has once ended increases. For this reason, it is desirable to provide these limiting diodes and resistors on the side of one end 822 of the secondary coil L2. However, from the viewpoint of ease of securing the mounting space for the second limiting diode 231 and the second resistor 232, there may be cases where it is more preferable to provide them on the other end 821 side of the secondary coil L2 as in the second embodiment.

[0094] <3. Modification Example> As described above, the exemplary embodiments of the present invention have been described, but the present invention is not limited to the above embodiments.

[0095] In the above-described embodiments and modifications, in the charging control, the voltage applied to one end 822 of the secondary coil L2 is configured to be a positive value, and the voltage applied to the other end 821 of the secondary coil L2 is configured to be a negative value. Also, in the discharge control, a negative high voltage ranging from minus several thousand volts to several tens of thousands of volts is induced at one end 822 of the secondary coil L2. However, by changing the winding direction of the primary conductor 81 in the primary coil L1 and the winding direction of the secondary conductor 82 in the secondary coil L2, the positive and negative of the voltage values appearing at both ends 821 and 822 of the secondary coil L2 may be reversed. In this case, the forward and reverse directions of the first limiting diode 131 inserted in the first connection line 121a in the first embodiment and the second limiting diode 231 inserted in the second connection line 222a in the second embodiment may be reversed, respectively.

[0096] In the above-described first embodiment, the cathode side of the first limiting diode 131 and the other end 821 of the secondary coil L2 were each connected to the plus side of the power supply device 102. However, as shown in the first modification of FIG. 7, the cathode side of the first limiting diode 131 and the other end 821 of the secondary coil L2 may be connected to the ground point (ground) 154. Also, in the above-described second embodiment, the cathode side of the second limiting diode 231 and the other end 821 of the secondary coil L2 were connected to the plus side of the power supply device 102. However, as shown in the second modification of FIG. 8, the cathode side of the second limiting diode 231 and the other end 821 of the secondary coil L2 may be connected to the ground point (ground) 154.

[0097] That is, the second limiting diode 231 may be inserted in one of the two second connection lines 222a and 222b wired in parallel between the other end 821 of the secondary coil L2 and the ground point (ground) 154, and may be a Zener diode or an avalanche diode that is forward in the direction from one end 822 to the other end 821 of the secondary coil L2. Also, the second resistor 232 may be inserted in the other of the two second connection lines 222a and 222b.

[0098] In the first and second modified examples, first, as charging control, when a primary current flows through the primary coil L1 (when it is ON), an ON-time voltage (for example, 960 V) is generated at both ends 821 and 822 of the secondary coil L2. The maximum value of the voltage applied to one end 822 of the secondary coil L2 becomes a positive value (for example, about +480 V), and the minimum value of the voltage applied to the other end 821 of the secondary coil L2 becomes a negative value (for example, about -480 V).

[0099] Here, in the first modified example, the first limiting diode 131 and the first resistor 132 are inserted in the first connection lines 121a and 121b. Also, in the second modified example, the second limiting diode 231 and the second resistor 232 are inserted in the second connection lines 222a and 222b. The first limiting diode 131 and the second limiting diode 231 are each in the forward direction in the direction from one end 822 to the other end 821 of the secondary coil L2. For this reason, by the current flowing from one end 822 to the other end 821 of the secondary coil L2 and further to the ground point (ground) 154, the ON-time voltage and the secondary voltage generated in the secondary coil L2 can be reduced. As a result, it is possible to suppress discharge from occurring at the ignition plug 113 at the time of ON, that is, at an abnormal timing.

[0100] Also, as discharge control, when the switching element 70 is switched from the closed state to the open state to cut off the primary current flowing from the power supply device 102 to the primary coil L1, a negative high voltage ranging from minus several thousand volts to several tens of thousands of volts is induced at one end 822 of the secondary coil L2. As a result, dielectric breakdown occurs in the gap d of the ignition plug 113. And in the first modified example, from the ground point (ground) 151, it goes toward the center electrode 161 of the ignition plug 113 through the ground electrode 162 of the ignition plug 113 (see FIG. 7), and a current (secondary current) flows in the forward direction through the first connection line 121a in which the first limiting diode 131 is inserted, or flows through the first connection line 121b in which the first resistor 132 is inserted, flows from one end 822 to the other end 821 of the secondary coil L2, and further flows toward the ground point (ground) 154.

[0101] Also, in the second modification example, a current (secondary current) flows from the ground point (ground) 151, through the ground electrode 162 of the spark plug 113, towards the center electrode 161 of the spark plug 113 (see FIG. 8), from one end 822 to the other end 821 of the secondary coil L2, and in the forward direction through the second connection line 222a in which the second limiting diode 231 is inserted, or through the second connection line 222b in which the second resistor 232 is inserted, and further towards the ground point (ground) 154. As a result, due to discharge occurring at the gap d of the spark plug 113, a spark is generated and the fuel filled in the internal combustion engine is ignited.

[0102] Also, after the discharge ends, in the first modification example, the current (secondary current) flows at once from the ground point (ground) 154, through the secondary coil L2, in the reverse direction through the first limiting diode 131. Thereby, the charges remaining in the vicinity of one end 822 of the secondary coil L2, the first connection line 121, or the vicinity of the center electrode 161 of the spark plug 113, etc., can be canceled at once. As a result, the absolute value of the voltage value due to the residual energy remaining in these locations can be immediately reduced to the yield voltage of the first limiting diode 131. Furthermore, after that, by the current flowing from the ground point (ground) 154 through the first resistor 132, the absolute value of the voltage value due to the residual energy remaining in these locations can be quickly reduced towards zero.

[0103] Also, in the second modification example, after the discharge ends, the current (secondary current) advances from the ground point (ground) 154 in the reverse direction through the second limiting diode 231 and flows at once towards the secondary coil L2. Thereby, the charges remaining in the vicinity of one end 822 of the secondary coil L2, the first connection line 221, or the vicinity of the center electrode 161 of the spark plug 113, etc., can be canceled at once. As a result, the absolute value of the voltage value due to the residual energy remaining in these locations can be immediately reduced to the yield voltage of the second limiting diode 231. Furthermore, after that, by the current flowing from the ground point (ground) 154 through the second resistor 232, the absolute value of the voltage value due to the residual energy remaining in these locations can be quickly reduced towards zero.

[0104] The ignition device of the present invention may be mounted not only on vehicles such as automobiles, but also on various devices such as generators and industrial machines, and may be used to generate an electric spark in the ignition plug of an internal combustion engine to ignite fuel.

[0105] The detailed shape and structure of the above ignition device may be appropriately changed without departing from the gist of the present invention. Also, the respective elements appearing in the above embodiments and modified examples may be appropriately combined within a range where no contradiction occurs.

Explanation of Reference Numerals

[0106] 1 Ignition device 60 Core 70 Switching element 81 Primary conductor 82 Secondary conductor 102 Power supply device 103 Ignition coil 104 Igniter 105 ECU 113 Ignition plug 121, 121a, 121b First connection wire 122 Second connection wire 131 First limiting diode 132 First resistor 150 Power supply line 221 First connection wire 222a, 222b Second connection wire 231 Second limiting diode 232 Second resistor 811 One end of the primary coil 812 The other end of the primary coil 821 The other end of the secondary coil 822 One end of the secondary coil Cs Parasitic capacitance 71 Drive IC (control unit) L1 Primary coil L2 Secondary coil d Gap (of the ignition plug)

Claims

1. An ignition device for an internal combustion engine using a fuel containing at least hydrogen, An ignition coil formed by electromagnetic coupling between a primary coil and a secondary coil, A power supply device that applies a DC voltage to one end of the primary coil via a power line, A switching element inserted between the other end of the primary coil and a ground point, capable of switching the energization or interruption of a primary current flowing from the power supply device to the primary coil, A spark plug that ignites the fuel by discharging at a gap based on a high voltage induced at one end of the secondary coil, A first limiting diode, which is a Zener diode or an avalanche diode, inserted in one of two first connection lines wired in parallel between one end of the secondary coil and the spark plug, and having a forward direction in the direction from one end to the other end of the secondary coil, A first resistor inserted in the other of the two first connection lines, having, The breakdown voltage of the first limiting diode is equal to or greater than a value calculated by multiplying the voltage value of the DC voltage applied from the power supply device to one end of the primary coil by the ratio of the number of turns of the secondary coil to the number of turns of the primary coil, and is smaller than the discharge maintenance voltage at the gap of the spark plug, The resistance value of the first resistor is 10 MΩ or more and 50 MΩ or less. The ignition device.

2. The ignition device according to claim 1, The breakdown voltage is 1 kV or more. The ignition device.

3. The ignition device according to claim 1 or claim 2, The breakdown voltage is 2 kV or less. The ignition device.

4. An ignition device for an internal combustion engine using a fuel containing at least hydrogen, An ignition coil formed by electromagnetic coupling between a primary coil and a secondary coil, A power supply device that applies a DC voltage to one end of the primary coil via a power line, A switching element inserted between the other end of the primary coil and a ground point, capable of switching the energization or interruption of the primary current flowing from the power supply device to the primary coil, An ignition plug that ignites the fuel by discharging in a gap based on a high voltage induced at one end of the secondary coil, A second limiting diode, which is a Zener diode or an avalanche diode, inserted in one of two second connection lines wired in parallel between the other end of the secondary coil and the power supply device or the ground point, and having a forward direction in the direction from one end to the other end of the secondary coil, A second resistor inserted in the other of the two second connection lines, having, The breakdown voltage of the second limiting diode is equal to or greater than a value calculated by multiplying the voltage value of the DC voltage applied from the power supply device to one end of the primary coil by the ratio of the number of turns of the secondary coil to the number of turns of the primary coil, and is less than the discharge maintenance voltage at the gap of the ignition plug, The resistance value of the second resistor is 10 MΩ or more and 50 MΩ or less, an ignition device.

5. The ignition device according to claim 4, wherein the breakdown voltage is 1 kV or more, an ignition device.

6. The ignition device according to claim 4 or claim 5, wherein the breakdown voltage is 2 kV or less, an ignition device.

7. The ignition device according to claim 1 or claim 4, further comprising a control unit that controls the switching of the switching element and, the control unit, By closing the switching element, charging control is performed to charge the primary coil by flowing a primary current through it. After performing the charging control, the switching element is switched to the open state to induce a high voltage at one end of the secondary coil, thereby performing discharge control to cause discharge in the gap of the spark plug. These operations are carried out. An ignition device, wherein the absolute value of the voltage induced at one end of the secondary coil at the end point of the discharge control is greater than the absolute value of the voltage induced at one end of the secondary coil at the start point of the discharge control. Claim 8 An ignition device according to claim 1 or claim 4, having a stray capacitance formed between one end of the secondary coil and the spark plug. An ignition device.

Images