Ignition device

Abstract

To provide a technique which can prevent an electric discharge in an ignition plug at an unexpected timing.SOLUTION: An ignition device 1 for an internal combustion engine using a fuel containing hydrogen has an ignition coil 103 including a primary coil L1 and a secondary coil L2, a power supply device 102, a switching element 70, an ignition plug 113, and a limiting diode 114. The switching element 70 make a switch to carrying or interrupting a primary current flowing to the primary coil L1. The ignition plug 113 discharges electric at a gap d on the basis of a high voltage inducted at one end 822 of the secondary coil L2. The limiting diode 114 is a zener diode or an avalanche diode having a forward direction from the one end 822 of the secondary coil L2 to the other end 821. A breakdown voltage of the limiting diode 114 is larger than a maximum value of a voltage in ON, which is calculated by multiplying a direct current voltage value applied to one end 811 of the primary coil L1 by a ratio of a winding number of the secondary coil L2 to a winding number of the primary coil L1.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 a SI (spark ignition) reciprocating engine used in an automobile or the like. The ignition coil of the ignition device boosts a DC low voltage supplied from a battery to several thousand volts to several tens of thousands of volts under the control of an ECU (Engine Control Unit), supplies it to a spark plug, generates an electric spark, and ignites 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 system (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 onboard battery, and the supply and interruption of the primary current (I1) flowing through the primary coil (21) is switched by the on / off control of the main switching element (4) (paragraph 0015, Figure 1). In addition, one end of the secondary coil (22), which is magnetically coupled to the primary coil (21) via an iron core, is connected to a spark plug (3), and the other end is connected to a DC power supply line via an 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, causing dielectric breakdown in the discharge gap of the spark plug (3), and a 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) when current is first supplied to the primary coil (21) is suppressed by the ON voltage prevention diode (23) (paragraph 0017).

[0005] In recent years, hydrogen-containing fuels have been widely used in SI (spark ignition) reciprocating engines. Using hydrogen-containing fuels is thought to contribute to the realization of a so-called low-carbon society. However, hydrogen has the characteristics of being easily combustible even at relatively low temperatures and having a fast combustion rate. For this reason, for example, if a small discharge occurs at an unexpected timing in the spark plug, the fuel may ignite and burn. In this case, there is a risk of causing abnormal combustion such as backfire, where flames blow back from the engine's combustion chamber to the intake system, afterfire, where residual fuel in the engine's exhaust gas burns in the exhaust passage, or pre-ignition, where the timing of ignition cannot be controlled.

[0006] The objective of the present invention is to provide a technology that can suppress the occurrence of unexpected discharges in a spark plug. [Means for solving the problem]

[0007] To solve the above problems, the first invention of the present application provides an ignition device for an internal combustion engine using a fuel containing at least hydrogen, comprising an ignition coil, a power supply, a switching element, a spark plug, a limiting diode, and , control unit and The ignition coil is formed by the electromagnetic coupling of a primary coil and a secondary coil. The power supply applies a DC voltage to one end of the primary coil via a power line. The switching element is interposed between the other end of the primary coil and a ground point and can switch the flow of primary current from the power supply to the primary coil to either the supply or the interruption of the supply. The spark plug ignites the fuel by discharging in a gap based on a high voltage induced at one end of the secondary coil. The limiting diode is a Zener diode or avalanche diode interposed in a first connecting line that directly or indirectly connects the other end of the secondary coil to the power supply or a ground point, or in a second connecting line that connects one end of the secondary coil to the spark plug, and is forward in the direction from one end to the other end of the secondary coil. The control unit controls the switching of the switching element. The breakdown voltage of the limiting diode is greater than the maximum value of the ON voltage, which is obtained by multiplying the voltage value of the DC voltage applied to one end of the primary coil by the power supply by the ratio of the number of turns of the secondary coil to the number of turns of the primary coil. Furthermore, it is 2kV or less. . Furthermore, the control unit performs charge control, which involves closing the switching element to charge the primary coil by flowing a primary current through it, and, after performing the charge control, switching the switching element to an open state to induce a high voltage at one end of the secondary coil, thereby causing a discharge in the gap of the spark plug. In addition, during the discharge control, once the discharge in the gap of the spark plug has finished, a current flows in the reverse direction through the limiting diode.

[0009] This application 2 The invention was the first Ming An ignition device wherein the breakdown voltage is 1kV or higher.

[0010] This application 3 The invention is an ignition device according to the first or second invention, having a stray capacitance formed between one end of the secondary coil and the spark plug.

[0011] This application 4 The invention is an ignition device according to the first or second invention, wherein the breakdown voltage is smaller than the dielectric breakdown voltage at the gap of the spark plug.

[0013] This application 5 The invention is an ignition device according to the first or second invention, wherein the limiting diode is interposed in the first connecting line.

[0014] This application 6 The invention is an ignition device according to the first or second invention, wherein the limiting diode is interposed in the second connecting line. [Effects of the Invention]

[0015] The first invention of this application 6 According to the invention, when a primary current is passed through the primary coil (ON state), the ON voltage generated in the secondary coil can be reduced. This suppresses the occurrence of discharge in the spark plug when it is ON. Furthermore, after the discharge ends, the residual energy remaining near the spark plug can be reduced by having current flow in the reverse direction through the limiting diode. As a result, it is possible to further suppress the occurrence of subsequent discharges at abnormal timings in the spark plug.

[0016] In particular, the first of the present application 4 According to the invention, after the discharge ends, residual energy remaining near the spark plug can be reduced by allowing current to flow from the power supply side or the ground point side toward one end of the secondary coil and the vicinity of the spark plug without causing another discharge at the spark plug. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic block diagram showing the operating environment of an ignition system for an internal combustion engine according to the first embodiment. [Figure 2] This is a longitudinal cross-sectional view of the ignition coil according to the first embodiment. [Figure 3] This graph shows the waveform of the EST signal, the waveform of the secondary current flowing through the secondary coil, and the voltage generated at one end of the secondary coil (secondary voltage) in time series when operating the ignition device according to the first embodiment. [Figure 4]It is a block diagram schematically showing the operating environment of an ignition device for an internal combustion engine according to a first modification. [Figure 5] It is a block diagram schematically showing the operating environment of an ignition device for an internal combustion engine according to a second modification. [Figure 6] It is a block diagram schematically showing the operating environment of an ignition device for an internal combustion engine according to a third modification.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings.

[0019] <1. First Embodiment> <1-1. Configuration of the Ignition Device> First, the configuration of an 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, but in FIG. 1, for ease of understanding, they are shown adjacent to each other.

[0020] The ignition device 1 of the present embodiment is, for example, a device that is mounted on an internal combustion engine such as a SI (spark ignition) reciprocating engine used in a vehicle body 100 such as an automobile, and applies a high voltage for generating a spark discharge to the spark plug 113. Further, as shown in FIG. 1, in addition to the ignition device 1, the vehicle body 100 is provided 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.

[0021] The spark plug 113 is a device for ignition in the combustion chamber of an 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 conductor (hereinafter referred to as the "second connecting wire 121"). The spark plug 113 is interposed between one end 822 of the secondary coil L2 and the ground point. When a high voltage is induced in the secondary coil L2 of the ignition coil 103, and this high voltage exceeds the dielectric breakdown voltage in the gap d (see Figure 1) between the center electrode 141 and the ground electrode 142 of the spark plug 113, a discharge occurs in the gap d and a spark is generated. This ignites the fuel filled in the internal combustion engine. In other words, the spark plug 113 ignites the fuel by discharging in the gap d based on the high voltage induced in one end 822 of the secondary coil L2.

[0022] In this embodiment, hydrogen or a mixture of hydrogen and other substances is used as fuel. That is, the ignition device 1 for the internal combustion engine uses a fuel containing at least hydrogen.

[0023] Furthermore, the second connecting wire 121 and the spark plug 113 have a capacitance component of approximately 15-20 pF. That is, a capacitance component is formed between one end 822 of the secondary coil L2 and the spark plug 113. Hereafter, this capacitance component will be referred to as the "stray capacitance Cs," which is a hypothetical definition. As shown in Figure 1, the stray capacitance Cs can be schematically represented in parallel with the spark plug 113 in the block diagram.

[0024] The power supply unit 102 is a power supply unit (storage battery) capable of charging and discharging DC power. In this embodiment, the power supply unit 102 is electrically connected to the primary coil L1 of the ignition coil 103, which will be described later, via a conductor (hereinafter referred to as the "power line 150"). The power supply unit 102 applies a DC voltage to one end 811 of the primary coil L1 of the ignition coil 103 via the power line 150.

[0025] The ECU105 is an existing computer that comprehensively controls the vehicle's transmission, airbags, and other functions.

[0026] The ignition device 1 includes an ignition coil 103, an igniter 104, and a limiting diode 114.

[0027] Figure 2 is a longitudinal cross-sectional view of the ignition coil 103. As shown in Figure 2, the ignition coil 103 comprises a bobbin 40, a primary coil L1, a secondary coil L2, and an iron core 60. Note that in Figure 2, the primary coil L1 and secondary coil L2 are shown in a partially simplified manner. Furthermore, in the following description of the ignition coil 103, the direction parallel to the central axis Bc of the bobbin 40 will be referred to as the "axial direction," the direction perpendicular to the central axis Bc of the bobbin 40 will be referred to as the "radial direction," and the direction along the arc centered on the central axis Bc of the bobbin 40 will be referred to as the "circumferential direction." In addition, the "parallel direction" includes a direction that is approximately parallel, and the "perpendicular direction" also includes a direction that is approximately perpendicular.

[0028] 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 cylindrically along the central axis Bc. The secondary bobbin 42 is positioned radially outside the primary bobbin 41. For example, resin is used as the material for the primary bobbin 41 and the secondary bobbin 42.

[0029] The primary coil L1 is formed by winding a conductor (hereinafter referred to as "primary conductor 81") around the outer surface of the primary bobbin 41 in a circumferential direction around the central axis Bc. After the formation of the primary coil L1 is complete, the secondary bobbin 42 is positioned to cover the outer surface of the primary coil L1 and connected to the primary bobbin 41. Then, the secondary coil L2 is formed by winding a conductor (hereinafter referred to as "secondary conductor 82"), different from the primary conductor 81, around the outer surface of the secondary bobbin 42 in a circumferential direction around the central axis Bc. By arranging the primary coil L1 and the secondary coil L2 in this way, stacking them on top of each other, 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 Figure 1, rather than being stacked and wound on top of each other in this way.

[0030] The core 60 has a structure in which a central core 601 and an outer core 602 are combined. The central core 601 and the outer core 602 of the core 60 are each formed from laminated steel sheets, for example, silicon steel sheets. The central core 601 extends along the central axis Bc of the bobbin 40. The central core 601 is also inserted into the radially inner space 410 of the primary bobbin 41. The outer core 602 passes radially outside the secondary bobbin 42 and the secondary conductor 82, connecting the axial ends of the central core 601. As a result, the 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 the electromagnetic coupling of the primary coil L1 and the secondary coil L2 to each other.

[0031] As shown in Figure 1, a power line 150, which is a conductor extending from the 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, which will be described later. Controlled by the igniter 104, a low DC voltage from the power supply device 102 is applied to one end 811 of the primary coil L1, and a gradually increasing primary current begins to flow through the primary coil L1.

[0032] One end 822 of the secondary coil L2 is connected to the spark plug 113. The diameter of the secondary conductor 82 is smaller than the diameter of the primary conductor 81. Also, the number of turns of the secondary conductor 82 in the secondary coil L2 (e.g., 8000 turns) is about 80 times or more than the number of turns of the primary conductor 81 in the primary coil L1 (e.g., 100 turns). As a result, as will be described in detail later, when the primary current is interrupted, the ignition coil 103 boosts the low-voltage DC power supplied from the power supply 102 to several thousand volts to tens of thousands of volts. That is, a high voltage is induced in the secondary coil L2. The secondary coil L2 then supplies the induced high-voltage power to the spark plug 113. This generates an electric spark at the spark plug 113, igniting the fuel.

[0033] As shown in Figure 1, the other end 821 of the secondary coil L2, opposite to the end 822 to which the spark plug 113 is connected, is electrically connected directly or indirectly to the power supply unit 102 via a conductor (hereinafter referred to as the "first connection line 122"). In this embodiment, the other end 821 of the secondary coil L2 is electrically connected to the power line 150. In this embodiment, a limiting diode 114 is interposed in the first connection line 122. The limiting diode 114 is connected in series with the secondary coil L2. The limiting diode 114 is forward in the direction from the one end 822 to the other end 821 of the secondary coil L2. In this embodiment, a Zener diode is used for the limiting diode 114. However, an avalanche diode may also be used for the limiting diode 114.

[0034] As will be described in detail later, when the switching element 70 of the igniter 104 is closed and the primary coil L1 is charged by flowing a primary current (ON state), a potential difference is generated across the ends 821 and 822 of the secondary coil L2. In this embodiment, when 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 "ON state voltage". The maximum value of the ON state voltage 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 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.

[0035] For example, if 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, and the number of turns of the secondary coil L2 is 8000, then the ratio of the number of turns of the secondary coil L2 to the number of turns of the primary coil L1 is 80, and the maximum value of the ON voltage is calculated to be 12 × 80 = 960V. Therefore, the maximum voltage applied to one end 822 of the secondary coil L2 will be, for example, around +480V, and the minimum voltage applied to the other end 821 of the secondary coil L2 will be, for example, around -480V. In some cases, the maximum voltage applied to one end 822 of the secondary coil L2 may be around 0V, and the minimum voltage applied to the other end 821 of the secondary coil L2 may be around -960V. Meanwhile, in this case, the voltage applied to the power line 150 is 12V.

[0036] In this invention, the limiting diode 114 used has a breakdown voltage greater than the maximum value of the ON voltage. The breakdown voltage of the limiting diode 114 used in this embodiment is 1kV or more. On the other hand, in the above example, the minimum voltage applied to the other end 821 of the secondary coil L2 (anode side of the limiting diode 114) is approximately -480V, and the voltage applied to the power line 150 (cathode side of the limiting diode 114) is +12V. This prevents current from flowing in the reverse direction at the limiting diode 114, that is, through the first connecting line 122 to the secondary coil L2 side, when primary current is flowed through the primary coil L1 (ON state). This prevents discharge from occurring at the spark plug 113 when it is ON, i.e., at an abnormal timing.

[0037] Furthermore, in this invention, the limiting diode 114 used has a breakdown voltage lower than the dielectric breakdown voltage at the gap d of the spark plug 113. The breakdown voltage of the limiting diode 114 used in this embodiment is 2kV or less. The effects of setting the breakdown voltage of the limiting diode 114 to 2kV or less will be described in detail later.

[0038] The igniter 104 is a semiconductor device connected to the primary coil L1 and controls the current flowing through the primary coil L1. The igniter 104 is also electrically connected to the ECU 105 and receives signals (hereinafter referred to as "EST signals") from the ECU 105. The igniter 104 includes a switching element 70 and a drive IC 71. The igniter 104 may be integrated with the electronic circuitry of the ECU 105.

[0039] For example, an insulated-gate bipolar transistor (IGBT) is used as the switching element 70. The switching element 70 is interposed between the other end 812 of the primary coil L1 and the ground. The collector (C) of the switching element 70 is connected to the other end 812 of the primary coil L1. The emitter (E) of the switching element 70 is connected to ground. The gate (G) of the switching element 70 is connected to the driver IC 71.

[0040] This allows the switching element 70 to switch between supplying or interrupting the primary current flowing from the power supply 102 to the primary coil L1. When the switching element 70 is closed, primary current flows from the power supply 102 to the primary coil L1. When the switching element 70 is open, the primary current flowing to the primary coil L1 is interrupted. However, other types of transistors may be used for the switching element 70.

[0041] 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). The logic device performs calculations to operate the ignition device 1 and ignite the spark plug 113.

[0042] <1-2. Operation of the ignition system> Next, the operation of the ignition device 1 will be explained. Figure 3 is a graph showing the waveform of the EST signal, the waveform of the secondary current flowing through the secondary coil L2, and the voltage (secondary voltage) generated at one end 822 of the secondary coil L2, in time series, when the ignition device 1 is operated. Note that the secondary current in Figure 3 is shown as negative when it flows in the forward direction of the limiting diode 114, and as positive when it flows in the reverse direction of the limiting diode 114. The secondary voltage in Figure 3 shows the voltage value at one end 822 of the secondary coil L2 relative to the ground point.

[0043] As described above, a DC voltage (for example, 12V) is applied to one end 811 of the primary coil L1 from the power supply unit 102 via the power line 150. The other end 812 of the primary coil L1 is connected to the switching element 70. The drive IC 71 controls the switching of the switching element 70 based on the EST signal received from the ECU 105. As shown in Figure 3, 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. Then, based on the EST signal, the drive IC 71 switches the switching element 70 from the open state to the closed state. As a result, a primary current flows through the primary conductor 81 that forms the primary coil L1, and the primary coil L1 is charged (hereinafter, this process of charging the primary coil L1 by flowing a primary current is referred to as "charging control"). Also, an electromagnetic flux is generated in the primary coil L1, and a magnetic field corresponding to the electromagnetic flux acts on the iron core 60.

[0044] Furthermore, at both ends 821 and 822 of the secondary coil L2, which is electromagnetically coupled to the primary coil L1 via the iron core 60, a potential difference, i.e., an ON voltage (for example, 960V), is generated due to mutual induction. As a result, the maximum voltage applied to one end 822 of the secondary coil L2 is a positive value (for example, about +480V), and the minimum voltage applied to the other end 821 of the secondary coil L2 is a negative value (for example, about -480V). In this embodiment, a limiting diode 114 is interposed in the first connecting line 122. The limiting diode 114 is forward in the direction from one end 822 to the other end 821 of the secondary coil L2. Also, the breakdown voltage of the limiting diode 114 is 1kV or more, which is greater than the maximum ON voltage. Therefore, it is possible to suppress current from flowing in the reverse direction at the limiting diode 114, i.e., through the first connecting line 122 to the secondary coil L2 side. As a result, it is possible to suppress discharge from the spark plug 113 when it is ON, i.e., at an abnormal timing.

[0045] After charging control is performed, at time t1, the signal level of the EST signal transmitted from ECU 105 to drive IC 71 is changed from H to L. The drive IC 71 then switches the switching element 70 from a closed state to an open state, interrupting the primary current flowing from the power supply 102 to the primary coil L1. This induces an induced electromotive force in the secondary coil L2, which is electromagnetically coupled to the primary coil L1 via the iron core 60, due to mutual inductance. In this embodiment, a negative high voltage is induced at one end 822 of the secondary coil L2. At this time, the voltage value at one end 822 of the secondary coil L2 ranges from several thousand volts to tens of thousands of volts relative to the ground point.

[0046] Furthermore, the absolute value of the negative high voltage induced at one end 822 of the secondary coil L2 exceeds the dielectric breakdown voltage at the gap d of the spark plug 113. This causes dielectric breakdown at the gap d of the spark plug 113. Then, a current is generated that flows from the ground point, through the ground electrode 142 of the spark plug 113 to the center electrode 141 of the spark plug 113 (see Figure 1), and further through the secondary coil L2, and is also in the forward direction of the limiting diode 114. As a result, a discharge occurs at the gap d of the spark plug 113, generating a spark and igniting the fuel filled in the internal combustion engine. In this invention, the process of switching the switching element 70 to the open state to interrupt the primary current flowing to the primary coil L1 and inducing a high voltage at one end 822 of the secondary coil L2 to cause a discharge at the gap d of the spark plug 113 is called "discharge control". Furthermore, when the absolute value of the negative high voltage induced at one end 822 of the secondary coil L2 falls below the dielectric breakdown voltage at the gap d of the spark plug 113 (time t2), the discharge at the gap d of the spark plug 113 temporarily ceases.

[0047] As described above, a stray capacitance Cs consisting of a capacitance component of about 15-20 pH is formed between one end 822 of the secondary coil L2 and the spark plug 113. Therefore, even after the discharge at the gap d of the spark plug 113 has ended (time t2), residual charge may still remain near the center electrode 141 of the spark plug 113, the second connecting wire 121, or near one end 822 of the secondary coil L2. In this embodiment, negative charge remains at these locations. As a result, at time t2, the voltage value at one end 822 of the secondary coil L2 (hereinafter referred to as "residual voltage value Rv") is negative (for example, -3kV) relative to the ground point. Note that the absolute value of the residual voltage value Rv is smaller than the dielectric breakdown voltage at the gap d of the spark plug 113. However, if this situation is left untreated, there is a risk that a discharge may occur again at the gap d of the spark plug 113 at an unexpected time, such as when a pressure change occurs within the internal combustion engine.

[0048] Therefore, in this invention, the limiting diode 114 used has a breakdown voltage smaller than the absolute value of the dielectric breakdown voltage and residual voltage Rv at the gap d of the spark plug 113. The breakdown voltage of the limiting diode 114 used in this embodiment is 2kV or less. In the above example, the residual voltage Rv at one end 822 of the secondary coil L2 (anode side of the limiting diode 114) is a negative value (for example, minus 3kV). On the other hand, the voltage applied to the power line 150 (cathode side of the limiting diode 114) is +12V, which is significantly higher than the residual voltage Rv. As a result, in a short time, current flows from the power supply unit 102 in the reverse direction at the limiting diode 114, that is, towards the vicinity of one end 822 of the secondary coil L2 via the first connecting line 122 (time t2 to time t3).

[0049] This cancels out residual charge near the center electrode 141 of the spark plug 113, the second connecting wire 121, or near one end 822 of the secondary coil L2, thereby reducing the absolute value of the voltage (secondary voltage) generated at one end 822 of the secondary coil L2 and reducing residual energy remaining at these locations. As a result, even if a pressure change occurs in the internal combustion engine afterward, it is possible to suppress the recurrence of discharge at the gap d of the spark plug 113 at an unexpected timing. Furthermore, this phenomenon continues until the potential difference between the voltage (secondary voltage) generated at one end 822 of the secondary coil L2 on the anode side of the limiting diode 114 and the voltage applied to the power supply line 150 on the cathode side of the limiting diode 114 becomes equal to the breakdown voltage of the limiting diode 114. Here, the absolute value of the voltage (secondary voltage) generated at one end 822 of the secondary coil L2 is significantly larger than the absolute value of the voltage across the power line 150. Therefore, this phenomenon can be considered to continue until the absolute value of the secondary voltage (indicated as "Vz" in Figure 3) becomes approximately equal to the breakdown voltage of the limiting diode 114. Subsequently, the absolute value of the voltage (secondary voltage) at one end 822 of the secondary coil L2 is further reduced (times t3 to t4) by the flow of ion current through the gap d between the center electrode 141 and the ground electrode 142 of the spark plug 113, and by the flow of leakage current through the limiting diode 114.

[0050] Furthermore, as described above, the breakdown voltage of the limiting diode 114 is smaller than the dielectric breakdown voltage at the gap d of the spark plug 113. Therefore, by allowing current to flow from the power supply 102 in the reverse direction at the limiting diode 114 and towards one end 822 of the secondary coil L2 via the first connecting line 122, residual energy can be reduced, and it is possible to suppress the occurrence of another discharge at the gap d of the spark plug 113 after time t2, i.e., at an abnormal timing.

[0051] As described above, in the present invention, when a primary current is applied to the primary coil L1 (ON), the current is prevented from flowing in the reverse direction through the limiting diode 114 to the secondary coil L2. This prevents discharge from occurring in the spark plug 113 when it is ON, i.e., at an abnormal timing. On the other hand, after the discharge ends, the current flows in the reverse direction through the limiting diode 114 towards the vicinity of one end 822 of the secondary coil L2, thereby reducing residual energy remaining near the center electrode 141 of the spark plug 113, the second connecting wire 121, or the vicinity of one end 822 of the secondary coil L2. This prevents discharge from occurring again in the gap d of the spark plug 113 after the discharge ends, i.e., at an abnormal timing. As a result, even in internal combustion engines using hydrogen-containing fuels that are easily combusted even at relatively low temperatures and have a fast combustion speed, ignition of the fuel at an abnormal timing is suppressed, leading to the suppression of damage to the engine, etc.

[0052] Furthermore, in this embodiment, by inserting a limiting diode 114 in the first connection line 122 of the ignition coil 103, a configuration that solves the problems of the present invention was provided. On the other hand, in conventional ignition coils, a different element than the Zener diode and avalanche diode may be placed in the location corresponding to the first connection line. In other words, in this embodiment, it is only necessary to replace the other element in the conventional ignition coil with the limiting diode 114. Therefore, the workability for manufacturing the ignition device 1 of this embodiment can be improved and manufacturing costs can be reduced.

[0053] <2. Variant> Although exemplary embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above.

[0054] Figure 4 is a schematic block diagram showing the operating environment of the ignition device 1 according to the first modified example. In the above embodiment, the limiting diode 114 was inserted in the first connecting wire 122 that connects the other end 821 of the secondary coil L2 to the power line 150. However, as shown in the first modified example in Figure 4, the limiting diode 114 may be inserted in the second connecting wire 121 that connects one end 822 of the secondary coil L2 to the spark plug 113. In this modified example as well, the limiting diode 114 is forward in the direction from one end 822 to the other end 821 of the secondary coil L2. Furthermore, the limiting diode 114 in this modified example has the same specifications as the limiting diode 114 in the above embodiment. In addition, the configuration of each part of the ignition device 1 in this modified example, excluding the limiting diode 114, is the same as the configuration of each part of the ignition device 1 in the above embodiment, excluding the limiting diode 114.

[0055] In this modified example, as part of the charge control, when the primary coil L1 is charged by flowing a primary current through it (ON), a potential difference, i.e., an ON voltage (for example, 960V), is generated at both ends 821 and 822 of the secondary coil L2 due to mutual inductance. The maximum voltage across one end 822 of the secondary coil L2 is a positive value (for example, around +480V), and the minimum voltage across the other end 821 of the secondary coil L2 is a negative value (for example, around -480V). In this modified example, a limiting diode 114 is interposed in the second connection line 121. The limiting diode 114 is forward in the direction from one end 822 to the other end 821 of the secondary coil L2. Therefore, it is possible to suppress current from flowing in the reverse direction across the limiting diode 114 from the power supply unit 102 to the secondary coil L2 and spark plug 113 via the first connection line 122. As a result, it is possible to suppress discharge from the spark plug 113 when it is ON, i.e., at an abnormal timing.

[0056] Furthermore, after the discharge ends, current flows from the power supply unit 102 in the reverse direction through the limiting diode 114, that is, through the first connecting wire 122 to the secondary coil L2 and the spark plug 113. This reduces residual energy remaining near the center electrode 141 of the spark plug 113, the second connecting wire 121, or near one end 822 of the secondary coil L2. This prevents the discharge from occurring again in the gap d of the spark plug 113 after the discharge ends, i.e., at an abnormal timing.

[0057] In the above embodiment and first modification, the charging control was configured such that the voltage applied to one end 822 of the secondary coil L2 was a positive value, and the voltage applied to the other end 821 of the secondary coil L2 was a negative value. Furthermore, in the discharge control, the configuration was configured such that a negative high voltage ranging from several thousand volts to tens of thousands of volts was induced at one end 822 of the secondary coil L2. However, the positive and negative signs of the voltage values ​​appearing at both ends 821 and 822 of the secondary coil L2 may be reversed by changing the winding direction of the primary wire 81 in the primary coil L1 or the winding direction of the secondary wire 82 in the secondary coil L2. In this case, the forward and reverse directions of the limiting diode 114 inserted in the first connecting wire 122 or the second connecting wire 121 should be reversed.

[0058] In the above embodiment and the first modified example, the cathode side of the limiting diode 114 and the other end 821 of the secondary coil L2 were connected to the positive side of the power supply 102. However, as shown in the second modified example in Figure 5 and the third modified example in Figure 6, the cathode side of the limiting diode 114 and the other end 821 of the secondary coil L2 may be connected to ground. That is, the limiting diode 114 may be a Zener diode or an avalanche diode, interposed in a first connecting line 122 that directly or indirectly connects the other end 821 of the secondary coil L2 to ground, and is forward in the direction from one end 822 to the other end 821 of the secondary coil L2.

[0059] As shown in Figures 5 and 6, in the second and third modified examples, first, as charge control, when a primary current is passed through the primary coil L1 to charge it (ON), a potential difference, i.e., an ON voltage (for example, 960V), is generated at both ends 821 and 822 of the secondary coil L2 due to mutual induction. The maximum voltage across one end 822 of the secondary coil L2 is a positive value (for example, about +480V), and the minimum voltage across the other end 821 of the secondary coil L2 is a negative value (for example, about -480V). In the second modified example, a limiting diode 114 is interposed in the first connecting line 122. In the third modified example, a limiting diode 114 is interposed in the second connecting line 121. The limiting diode 114 is forward in the direction from one end 822 to the other end 821 of the secondary coil L2. Therefore, the current flows from one end 822 of the secondary coil L2 to the other end 821, and then to the ground point, thereby reducing the ON voltage. As a result, it is possible to suppress discharge in the spark plug 113 when it is ON, i.e., at an abnormal timing.

[0060] Furthermore, after the discharge ends, current flows from the ground side in the reverse direction at the limiting diode 114 towards one end 822 of the secondary coil L2 and the vicinity of the center electrode 141 of the spark plug 113. This reduces residual energy remaining near the center electrode 141 of the spark plug 113, the second connecting wire 121, or one end 822 of the secondary coil L2. This prevents further discharge from occurring in the gap d of the spark plug 113 after the discharge ends, i.e., at an abnormal timing.

[0061] The ignition device of the present invention may be installed not only in vehicles such as automobiles, but also in various devices such as generators and industrial machinery, and is used to generate an electric spark at the spark plug of an internal combustion engine to ignite fuel.

[0062] The shape and structure of the ignition device described above may be modified as appropriate without departing from the spirit of the present invention. Furthermore, the elements that appear in the above embodiments and modifications may be combined as appropriate without creating any inconsistencies. [Explanation of Symbols]

[0063] 1 Ignition device 60 Iron Heart 70 switching elements 81 Primary conductor 82 Secondary conductor 102 Power supply 103 Ignition coil 104 Igniter 105 ECU 113 Spark plug 114 Limiting diode 121 Second connection line 122 First connection line 150 Power line 811 One end of the primary coil 812 The other end of the primary coil 821 Other end of secondary coil 822 One end of the secondary coil Cs swimming capacity 71. Drive IC (control unit) L1 Primary coil L2 Secondary Coil Rv residual voltage value d (spark plug) gap

Claims

1. An ignition system for an internal combustion engine using a fuel containing at least hydrogen, An ignition coil is formed by the electromagnetic coupling of 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 supply line, A switching element is interposed between the other end of the primary coil and the ground point, and is capable of switching the supply or interruption of the primary current flowing from the power supply to the primary coil. A spark plug that ignites the fuel by discharging in a gap based on a high voltage induced at one end of the secondary coil, A limiting diode, which is a Zener diode or avalanche diode, is inserted in a first connecting wire that directly or indirectly connects the other end of the secondary coil to the power supply or ground point, or in a second connecting wire that connects one end of the secondary coil to the spark plug, and is oriented forward in the direction from one end to the other end of the secondary coil. A control unit that controls the switching of the switching element, It has, The breakdown voltage of the limiting diode is greater than the maximum ON voltage obtained by multiplying the voltage value of the DC voltage applied to one end of the primary coil by the power supply by the ratio of the number of turns of the secondary coil to the number of turns of the primary coil, and is 2kV or less. The control unit, By closing the switching element, a charging control is performed to charge the primary coil by flowing a primary current through it. After performing the aforementioned charging control, the switching element is switched to an open state to induce a high voltage at one end of the secondary coil, thereby discharging the gap of the spark plug. Perform In the discharge control described above, an ignition device in which, once the discharge in the gap of the spark plug has ended, a current flows in the reverse direction through the limiting diode.

2. An ignition device according to Claim 1, An ignition device in which the breakdown voltage is 1 kV or higher.

3. An ignition device according to claim 1 or claim 2, Stray capacity formed between one end of the secondary coil and the spark plug An ignition device having the following features.

4. An ignition device according to claim 1 or claim 2, An ignition device in which the breakdown voltage is less than the dielectric breakdown voltage at the gap of the spark plug.

5. An ignition device according to claim 1 or claim 2, The limiting diode is an ignition device interposed in the first connecting wire.

6. An ignition device according to claim 1 or claim 2, The limiting diode is an ignition device interposed in the second connecting wire.

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