Ignition device

Abstract

To provide an ignition device capable of early converging residual energy after electric discharge occurs in a spark plug.SOLUTION: An ignition device 1 satisfies a relationship of T / 4≤tt, where T is a resonance period for an LC circuit constituted by an inductance L of a secondary coil 12 and a stray capacitance C existing between the secondary coil 12 and a spark plug 40, and tt is a reverse recovery time for a diode 30. Thus, the residual energy after electric discharge occurs in the spark plug 40 can be reduced by utilizing a resonance phenomenon due to the LC circuit and reverse recovery characteristics of the diode 30. As a result, the residual energy is early converged to suppress abnormal electric discharge due to the residual energy.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Ignition devices used in automotive internal combustion engines are known. The ignition device has a spark plug disposed in a cylinder of the internal combustion engine. When the internal combustion engine is running, the piston compresses fuel gas in the cylinder, and the ignition device generates a spark discharge at the spark plug. This causes the fuel in the cylinder to combust.

[0003] A conventional ignition device is described in, for example, Patent Document 1. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-002818 Summary of the Invention [Problem to be solved by the invention]

[0005] The ignition device has an electromagnetically coupled primary coil and secondary coil. The ignition device energizes the primary coil and then cuts off the power to the primary coil, thereby inducing a high voltage (secondary voltage) in the secondary coil. This causes a discharge to occur in the spark plug connected to the secondary coil.

[0006] However, in this type of ignition device, because there is stray capacitance around the spark plug, charge accumulates in the stray capacitance during discharge, leaving residual energy, which causes the secondary voltage to take a long time to converge.

[0007] Furthermore, the residual energy can cause unintended discharges at the spark plug. In particular, in recent years, fuels containing hydrogen have been used in internal combustion engines in order to reduce greenhouse gas emissions. In such cases, hydrogen is more ignitable than gasoline, so unintended discharges due to residual energy can ignite the fuel.

[0008] The present invention has been made in view of the above circumstances, and has as its object to provide an ignition device that can quickly converge residual energy after a discharge occurs in an ignition plug. [Means for solving the problem]

[0009] In order to solve the above problems, the first invention of the present application is an ignition device for an internal combustion engine, comprising: a primary coil connected to a battery via a power line; a switching element that switches ON / OFF the flow of electricity from the battery to the primary coil; a secondary coil that is electromagnetically coupled to the primary coil; a diode connected in series to the secondary coil; and an ignition plug connected to the other end of the secondary coil, wherein the diode is connected such that the direction from the ignition plug to the secondary coil is the forward direction, and the resonance period of an LC circuit formed by the inductance L of the secondary coil and the stray capacitance C existing between the secondary coil and the spark plug is T, and the reverse recovery time of the diode is tt, satisfying the relationship T / 4≦tt.

[0010] A second aspect of the present invention is the ignition device of the first aspect of the present invention, which satisfies the relationship T / 4≦tt≦T / 2.

[0011] A third aspect of the present invention is the ignition device of the first or second aspect, wherein the inductance of the secondary coil is variable.

[0012] A fourth aspect of the present invention is the ignition device according to any one of the first and second aspects, wherein the internal combustion engine uses a fuel containing hydrogen. [Effects of the Invention]

[0013] According to the first to fourth aspects of the present invention, the residual energy after a discharge occurs in the spark plug can be reduced by utilizing the resonance phenomenon of the LC circuit and the reverse recovery characteristics of the diode. This allows the residual energy to converge quickly and suppresses abnormal discharge due to the residual energy.

[0014] In particular, according to the second aspect of the present invention, after a discharge occurs in the spark plug, a current flows in the reverse direction through the diode due to the resonance phenomenon of the LC circuit, and the reverse recovery time ends before the current flows in the forward direction again through the diode, thereby preventing the current resonance from continuing.

[0015] In particular, according to the third aspect of the present invention, the above relational expression can be easily satisfied by adjusting the inductance of the secondary coil.

[0016] In particular, according to the fourth aspect of the present invention, greenhouse gas emissions can be reduced by using fuel containing hydrogen. However, hydrogen has the problem of being easily ignited, but according to the present invention, ignition of hydrogen due to residual energy can be suppressed. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 2 is a circuit diagram of the ignition device. [Figure 2] 4 is a flowchart showing the flow of the operation of the ignition device. [Figure 3] 6 is a graph showing the ON / OFF state of a switching element, secondary current, and secondary voltage changes over time. [Figure 4] 2 is a graph showing the results of examining changes in secondary voltage over time in the equivalent circuit of the ignition device of FIG. 1. [Figure 5] 2 is a graph showing the results of examining changes in secondary voltage over time in the equivalent circuit of the ignition device of FIG. 1. [Figure 6] 2 is a graph showing the results of examining changes in secondary voltage over time in the equivalent circuit of the ignition device of FIG. 1. [Figure 7]2 is a graph showing the results of examining changes in secondary voltage over time in the equivalent circuit of the ignition device of FIG. 1. [Figure 8] 10 is a graph showing the results of examining the relationship between the reverse recovery time and the residual voltage at the end of the reverse recovery time. [Figure 9] FIG. 4 is a circuit diagram of an ignition device according to a first modified example. [Figure 10] FIG. 10 is a circuit diagram of an ignition device according to a second modified example. [Figure 11] FIG. 10 is a circuit diagram of an ignition device according to a third modified example. DETAILED DESCRIPTION OF THE INVENTION

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

[0019] <1. Ignition device configuration> FIG. 1 is a circuit diagram of an ignition device 1 according to one embodiment of the present invention. This ignition device 1 is mounted on an automobile and ignites fuel supplied to a cylinder of an internal combustion engine. In this embodiment, the internal combustion engine uses fuel containing hydrogen. As shown in FIG. 1, the ignition device 1 includes an ignition coil 10, a switching element 20, a diode 30, an ignition plug 40, and a control unit 50.

[0020] The ignition coil 10 is a unit for inducing a high voltage to the spark plug 40. As shown in FIG. 1, the ignition coil 10 has a primary coil 11, a secondary coil 12, and an iron core 13. The primary coil 11 and the secondary coil 12 are electromagnetically coupled via the iron core 13. The number of turns of the secondary coil 12 is greater than the number of turns of the primary coil 11.

[0021] One end of the primary coil 11 is electrically connected to a battery 70 via a power supply line 61. The battery 70 is a power supply device capable of supplying DC power. The other end of the primary coil 11 is grounded via a ground line 62. A switching element 20, which will be described later, is inserted into the ground line 62.

[0022] One end of the secondary coil 12 is electrically connected to a connection portion 63 located on the path of the power supply line 61 via a first connection line 64. A diode 30 (described later) is inserted in the first connection line 64. The other end of the secondary coil 12 is electrically connected to a center electrode 41 (described later) of the ignition plug 40 via a second connection line 65.

[0023] The switching element 20 is a switch that switches ON / OFF the supply of electricity from the battery 70 to the primary coil 11. For example, an IGBT (Insulated Gate Bipolar Transistor) is used as the switching element 20. The collector of the switching element 20 is electrically connected to the other end of the primary coil 11. The emitter of the switching element 20 is electrically connected to the ground.

[0024] The diode 30 is provided on a first connection line 64 that connects one end of the secondary coil 12 and the connection part 63. The diode 30 is connected in series to the secondary coil 12 with the forward direction being the direction from the secondary coil 12 to the connection part 63 (i.e., the direction from the spark plug 40 to the secondary coil 12).

[0025] The spark plug 40 is disposed in a cylinder of the internal combustion engine. The spark plug 40 has a center electrode 41 and a ground electrode 42. The center electrode 41 is electrically connected to the other end of the secondary coil 12 via a second connection wire 65. The ground electrode 42 is grounded.

[0026] The control unit 50 is a unit for controlling the discharge operation of the spark plug 40 by the ignition coil 10. The control unit 50 is configured by a microcontroller or a computer having a CPU and memory. The control unit 50 is, for example, an ECU (Engine Control Unit) mounted on an automobile. However, the control unit 50 may also be a control board connected downstream of the ECU. The control unit 50 controls the ON / OFF of the switching element 20 by outputting a control signal to the switching element 20.

[0027] <2. Operation of the ignition device> Next, the operation of the above-mentioned ignition device 1 will be described. FIG. 2 is a flowchart showing the flow of the operation of the ignition device 1. The ignition device 1 repeatedly executes the operations of steps S1 to S3 in FIG. 2 in accordance with the operation of the internal combustion engine. FIG. 3 is a graph showing the ON / OFF state of the switching element 20, the secondary current, and the secondary voltage over time. The secondary current is the current flowing through the secondary coil 12. The secondary voltage is the voltage at the other end (the spark plug 40 side) of the secondary coil 12.

[0028] First, at time t1, the ignition device 1 starts energizing the primary coil 11. Specifically, the control unit 50 switches the switching element 20 from OFF (open state) to ON (closed state). This causes a primary current to flow from the battery 70 to the ground via the power supply line 61, the primary coil 11, and the ground line 62. This causes primary energy to be stored in the ignition coil 10 (step S1).

[0029] Thereafter, at time t2, the control unit 50 switches the switching element 20 from ON (closed state) to OFF (open state). This cuts off the current to the primary coil 11. This induces an induced electromotive force in the secondary coil 12 via the iron core 13, and a high voltage corresponding to the primary energy is generated in the secondary coil 12. The positive and negative sides of the induced electromotive force depend on the winding direction of the secondary coil 12, but in this embodiment, a high voltage is generated in the secondary coil 12, with one end (diode 30 side) being positive and the other end (spark plug 40 side) being negative.

[0030] When a high voltage is generated in the secondary coil 12, a high voltage is also generated between the center electrode 41 and the ground electrode 42 of the spark plug 40. Specifically, the voltage value of the center electrode 41 becomes several thousand volts to several tens of thousands volts below the voltage value (ground voltage) of the ground electrode 42. This high voltage causes a dielectric breakdown between the center electrode 41 and the ground electrode 42 of the spark plug 40, resulting in a spark discharge between the electrodes (step S2). This spark ignites the fuel supplied into the cylinder of the internal combustion engine.

[0031] 3, a discharge occurs in the spark plug 40 between times t2 and t3. At this time, a dielectric breakdown occurs between the center electrode 41 and the ground electrode 42, causing a secondary current to flow from the ground to the first connection wire 64 via the ground electrode 42, the center electrode 41, the second connection wire 65, and the secondary coil 12. This secondary current flows through the diode 30 in the forward direction.

[0032] After the discharge ends at time t3, the residual energy E remaining in the vicinity of the spark plug 40 gradually converges (step S3). The details of the residual energy E will be described later.

[0033] <3. ON voltage> In step S1 above, when current begins to flow through the primary coil 11, the primary coil 11 and the secondary coil 12 are electromagnetically coupled, and therefore a slight voltage (hereinafter referred to as "ON voltage") is generated in the secondary coil 12, as shown in Fig. 3. In this embodiment, the ON voltage is generated in the secondary coil 12, with one end (diode 30 side) being negative and the other end (spark plug 40 side) being positive.

[0034] If this ON voltage is high, there is a risk of unintended discharge occurring at the spark plug 40. In particular, when an internal combustion engine uses fuel containing hydrogen, the fuel is more likely to ignite than when gasoline is used. For this reason, it is desirable to keep the ON voltage as low as possible.

[0035] Therefore, in the ignition device 1 of this embodiment, a diode 30 is inserted in the first connection line 64 between the secondary coil 12 and the connection part 63. The diode 30 is connected in a forward direction, that is, from the secondary coil 12 to the connection part 63. Therefore, when current is applied to the primary coil 11, current is prevented from flowing from the battery 70 to the secondary coil 12. This makes it possible to suppress the ON-time voltage. Therefore, it is possible to suppress unintended discharge in the spark plug 40 due to the ON-time voltage.

[0036] <4. Residual energy> 1, there is a capacitance of about 15 to 20 pF (hereinafter referred to as "stray capacitance C") between the secondary coil 12 and the spark plug 40. The stray capacitance C includes, for example, the capacitance between the center electrode 41 and the ground electrode 42, the inter-winding capacitance of the secondary coil 12, and the capacitance parasitic on the second connecting wire 65.

[0037] In step S2 described above, when a discharge occurs in the spark plug 40, charge accumulates in the stray capacitance C. As described above, the diode 30 for suppressing the ON-time voltage is provided in the first connection line 64. Therefore, even after the discharge ends at time t3, residual energy E due to the charge remains near the spark plug 40. Specifically, as shown in FIG. 3, a negative voltage (hereinafter referred to as "residual voltage") remains at the other end of the secondary coil 12 (the spark plug 40 side). This residual voltage can cause an unintended discharge.

[0038] In particular, when an internal combustion engine uses fuel containing hydrogen, the fuel is more likely to ignite than when it uses gasoline, so it is desirable to eliminate the residual voltage as soon as possible.

[0039] Therefore, the ignition device 1 of this embodiment utilizes the resonance phenomenon caused by an LC circuit formed by the inductance L and stray capacitance C of the secondary coil 12 and the reverse recovery characteristics of the diode 30 to quickly converge the residual energy E. This function will be described below.

[0040] During discharge from time t2 to t3, as described above, a secondary current flows from the ground to the first connection wire 64 via the ground electrode 42, the center electrode 41, the second connection wire 65, and the secondary coil 12. This secondary current flows through the diode 30 in the forward direction.

[0041] The current value of the secondary current gradually decreases from time t2 to time t3. However, because an LC circuit is formed on the secondary side of the ignition coil 10 by the inductance L of the secondary coil 12 and the stray capacitance C, a current resonance phenomenon occurs. Therefore, the value of the secondary current does not stop at 0, and a current flows in the reverse direction (from the diode 30 to the secondary coil 12).

[0042] On the other hand, the diode 30 has a reverse recovery characteristic. The reverse recovery characteristic is a characteristic in which, when the current flowing through the diode 30 switches from the forward direction to the reverse direction, the current is not immediately cut off, but the reverse current flows only for the reverse recovery time tt that is specific to the diode 30. Due to this reverse recovery characteristic, the reverse current flows only for the reverse recovery time tt.

[0043] That is, after the discharge at the spark plug 40 is completed, a reverse current generated by the resonance of the LC circuit flows only for the reverse recovery time tt of the diode 30. This reverse current reduces the residual energy E.

[0044] When the reverse recovery time tt of the diode 30 ends, the reverse current is blocked by the diode 30. Therefore, the current resonance caused by the LC circuit does not continue, and the secondary current converges to zero.

[0045] 4 to 7 are graphs showing the results of examining, using analysis software, the change in secondary voltage over time when the reverse recovery time tt of the diode 30 is changed in the equivalent circuit of the ignition device 1 of FIG. 1. In FIG. 4, the reverse recovery time of the diode 30 is set to tt = 0 μs. In FIG. 5, the reverse recovery time of the diode 30 is set to tt = 10.4 μs. In FIG. 6, the reverse recovery time of the diode 30 is set to tt = 12.5 μs. In FIG. 7, the reverse recovery time of the diode 30 is set to tt = 66.6 μs.

[0046] In the results shown in Figure 4, the residual voltage (absolute value) does not suddenly decrease from time t3 onwards, but rather decreases gradually. This is because, under the conditions shown in Figure 4, the reverse recovery time tt is 0, and therefore the effect of reducing the residual energy E due to the reverse current described above cannot be obtained.

[0047] 5, the residual voltage (absolute value) suddenly decreases at time t3, and then the remaining residual voltage (absolute value) gradually decreases. This is because when the discharge ends at time t3, a reverse current generated by the resonance of the LC circuit flows only for the reverse recovery time tt of the diode 30, thereby reducing the residual energy E.

[0048] In the results of Figure 6, the residual voltage (absolute value) drops more rapidly at time t3 than in Figure 5, and then the remaining residual voltage (absolute value) gradually decreases. This is because when the discharge ends at time t3, the reverse current generated by the resonance of the LC circuit flows for only the reverse recovery time tt, which is longer than in Figure 5, and as a result, the residual energy E decreases.

[0049] In the results shown in Figure 7, secondary voltage resonance occurs from time t3. This is because, under the conditions shown in Figure 7, the reverse recovery time tt of diode 30 is too long, causing a second cycle of forward current due to resonance in the LC circuit during the reverse recovery time tt. In this case, the forward current of the next cycle flows through diode 30 before diode 30 can block the reverse current, making it impossible for diode 30 to block the current. This could result in current resonance due to the LC circuit continuing for a long period of time.

[0050] Fig. 8 is a graph showing the results of an analysis similar to that of Figs. 4 to 7, in which the relationship between the reverse recovery time tt and the residual voltage (absolute value) at the end of the reverse recovery time tt was examined. The horizontal axis of Fig. 8 represents the reverse recovery time tt. The vertical axis of Fig. 8 represents the residual voltage (absolute value) at the end of the reverse recovery time tt.

[0051] 8, when the reverse recovery time tt of the diode 30 is 8.3 to 16.7 μs, the residual voltage at the end of the reverse recovery time tt decreases rapidly. When the reverse recovery time tt of the diode 30 is 16.7 μs or longer, the residual voltage at the end of the reverse recovery time tt is kept at a very low value. Therefore, according to the results of FIG. 8, in order to quickly converge the residual energy E, it can be said that it is desirable to set the reverse recovery time tt of the diode 30 to 16.7 μs or longer.

[0052] Here, in the analysis of Figure 8, 16.7 μs corresponds to 1 / 4 of the period of resonance by the LC circuit. In other words, if the period of resonance by the LC circuit is T, then in the analysis of Figure 8, 16.7 μs corresponds to T / 4. Therefore, the condition for quickly converging the residual energy E can be expressed by the following equation (1). T / 4≦tt (1)

[0053] In the results shown in Figure 8, if the reverse recovery time tt of diode 30 is greater than 33.3 μs, the residual voltage at the end of the reverse recovery time tt will be nearly zero. In this case, current resonance will occur due to the LC circuit, as shown in Figure 7 above. To avoid this situation, it is necessary for the reverse recovery time tt to end before the next period of forward current is generated due to resonance. This condition can be expressed by the following equation (2). In the analysis of Figure 8, 33.3 μs corresponds to T / 2. tt≦T / 2 (2)

[0054] Therefore, in order to converge the residual energy E quickly and suppress resonance, it is desirable that the ignition device 1 satisfy the relationship of the following formula (3). T / 4≦tt≦T / 2 (3)

[0055] Here, the frequency f and period T of the resonance due to the LC circuit can be expressed by the following equations (4) and (5). f=1 / 2π√(LC) (4) T=1 / f=2π√(LC) (5)

[0056] By substituting this formula (5) into the above formulas (1) to (3), the following formulas (6) to (8) can be obtained. π√(LC) / 2≦tt (6) tt≦π√(LC) (7) π√(LC) / 2≦tt≦π√(LC) (8)

[0057] That is, to satisfy the condition of formula (1), the inductance L of the secondary coil 12, the stray capacitance C, and the reverse recovery time tt of the diode 30 must satisfy the relationship of formula (6). To satisfy the condition of formula (2), the inductance L of the secondary coil 12, the stray capacitance C, and the reverse recovery time tt of the diode 30 must satisfy the relationship of formula (7). To satisfy the condition of formula (3), the inductance L of the secondary coil 12, the stray capacitance C, and the reverse recovery time tt of the diode 30 must satisfy the relationship of formula (8).

[0058] The following three methods [a] to [c] can be considered as adjustment methods to satisfy the above relationship. [a] The reverse recovery time tt of the diode 30 is adjusted. [b] Adjust the inductance L of the secondary coil 12. [c] Adjust the stray capacitance C.

[0059] When using the above method [a], a diode 30 with a reverse recovery time tt that satisfies the relationship of equation (6), (7), or (8) can be selected. When using the above method [b], a secondary coil 12 with an inductance L that satisfies the relationship of equation (6), (7), or (8) can be selected. If the inductance L of the secondary coil 12 is variable, the relationship of equation (6), (7), or (8) can be easily satisfied by changing the inductance L. When using the above method [c], the capacitance of the spark plug 40 included in the stray capacitance C can be adjusted to satisfy the relationship of equation (6), (7), or (8).

[0060] Alternatively, two or three of the above [a] to [c] may be adjusted to satisfy the relationship of formula (6), (7), or (8). For example, after selecting the diode 30 so as to approximate the relationship of formula (6), (7), or (8), the inductance L of the secondary coil 12 may be fine-tuned to realize the relationship of formula (6), (7), or (8).

[0061] As described above, in the ignition device 1 of this embodiment, the resonance period T of the LC circuit and the reverse recovery time tt of the diode 30 satisfy the relationship of the above formula (1). Therefore, the residual energy E after a discharge occurs in the spark plug 40 can be reduced by utilizing the resonance phenomenon of the LC circuit and the reverse recovery characteristics of the diode 30. This allows the residual energy E to converge quickly, and abnormal discharge due to the residual energy E can be suppressed.

[0062] Furthermore, in the ignition device 1 of this embodiment, the resonance period T of the LC circuit and the reverse recovery time tt of the diode 30 satisfy the relationship of the above formula (3). Therefore, after a discharge occurs in the spark plug 40, a current flows in the reverse direction through the diode 30 due to the resonance phenomenon of the LC circuit, and the reverse recovery time tt ends before a current flows in the forward direction again through the diode 30. This makes it possible to prevent the current resonance caused by the LC circuit from continuing.

[0063] <5. Variations> Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

[0064] <5-1. First modified example> 9 is a circuit diagram of the ignition device 1 according to a first modification. In this first modification, the diode 30 is provided in the second connection line 65, not in the first connection line 64. The diode 30 is connected in series to the secondary coil 12, with the forward direction being the direction from the spark plug 40 to the secondary coil 12.

[0065] 9, the ON voltage can also be suppressed by the diode 30 when current is applied to the primary coil 11. Therefore, it is possible to prevent unintended discharge from occurring in the spark plug 40 due to the ON voltage.

[0066] 9, if the resonance period T of the LC circuit and the reverse recovery time tt of the diode 30 satisfy the relationship of the above formula (1), the residual energy E after a discharge occurs in the spark plug 40 can be reduced by utilizing the resonance phenomenon of the LC circuit and the reverse recovery characteristics of the diode 30, as in the above embodiment. This allows the residual energy E to converge quickly, and abnormal discharge due to the residual energy E can be suppressed.

[0067] <5-2. Second modified example> 10 is a circuit diagram of an ignition device 1 according to a second modified example. In this second modified example, a first connection line 64 is connected to the ground, not to a connection point 63 located on the path of a power line 61. A diode 30 is provided in the first connection line 64. The diode 30 is connected in series to the secondary coil 12, with the forward direction being the direction from the secondary coil 12 to the ground (i.e., the direction from the ignition plug 40 to the secondary coil 12).

[0068] 10, the ON voltage can also be suppressed by the diode 30 when current is applied to the primary coil 11. Therefore, it is possible to prevent unintended discharge from occurring in the spark plug 40 due to the ON voltage.

[0069] 10, if the resonance period T of the LC circuit and the reverse recovery time tt of the diode 30 satisfy the relationship of the above formula (1), the residual energy E after the occurrence of a discharge in the spark plug 40 can be reduced by utilizing the resonance phenomenon of the LC circuit and the reverse recovery characteristics of the diode 30, as in the above embodiment. This allows the residual energy E to converge quickly, and makes it possible to suppress abnormal discharge due to the residual energy E.

[0070] <5-3.Third modified example> 11 is a circuit diagram of an ignition device 1 according to a third modified example. In this third modified example, a first connection line 64 is connected to ground, not to a connection point 63 located on the path of a power supply line 61. Also, in this third modified example, a diode 30 is provided in a second connection line 65, not to the first connection line 64. The diode 30 is connected in series to the secondary coil 12, with the forward direction being the direction from the spark plug 40 to the secondary coil 12.

[0071] 11, the ON voltage can also be suppressed by the diode 30 when current is applied to the primary coil 11. Therefore, it is possible to prevent unintended discharge from occurring in the spark plug 40 due to the ON voltage.

[0072] 11, if the resonance period T of the LC circuit and the reverse recovery time tt of the diode 30 satisfy the relationship of the above formula (1), the residual energy E after a discharge occurs in the spark plug 40 can be reduced by utilizing the resonance phenomenon of the LC circuit and the reverse recovery characteristics of the diode 30, as in the above embodiment. This allows the residual energy E to converge quickly, and abnormal discharge due to the residual energy E can be suppressed.

[0073] <5-4. Other variations>

[0074] In the above embodiment, the ignition device 1 mounted on an automobile has been described. However, the "ignition device" of the present invention may be mounted on transportation equipment other than an automobile. Furthermore, the "ignition device" of the present invention may be mounted on industrial machinery, generators, and the like other than transportation equipment.

[0075] Furthermore, the detailed configuration of the ignition device may be appropriately modified without departing from the spirit of the present invention. Furthermore, the elements appearing in the above-described embodiments and modifications may be appropriately combined without causing any contradiction. [Explanation of symbols]

[0076] 1 Ignition device 10. Ignition coil 11 Primary coil 12 Secondary coil 13 Iron core 20 Switching element 30 Diode 40 Spark plug 41 Center electrode 42 Ground electrode 50 control section 61 Power line 62 Ground wire 63 Wiring section 64 First connecting line 65 Second connecting line 70 Battery C stray capacitance E residual energy L inductance tt Reverse recovery time

Claims

1. An ignition device for an internal combustion engine, a primary coil connected to the battery via a power line; a switching element that switches on / off the power supply from the battery to the primary coil; a secondary coil electromagnetically coupled to the primary coil; a diode connected in series with the secondary coil; a spark plug connected to the other end of the secondary coil; Equipped with The diode is connected in a forward direction from the spark plug to the secondary coil, The resonance period of an LC circuit formed by the inductance L of the secondary coil and the stray capacitance C existing between the secondary coil and the spark plug is defined as T, The reverse recovery time of the diode is tt, As, T / 4≦tt The ignition device satisfies the relationship.

2. 10. The ignition device according to claim 1, T / 4≦tt≦T / 2 The ignition device satisfies the relationship.

3. 3. The ignition device according to claim 1 or 2, An ignition device, wherein the inductance of the secondary coil is variable.

4. 3. The ignition device according to claim 1 or 2, The internal combustion engine uses a fuel containing hydrogen.

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