Ignition devices for internal combustion engines

Abstract

To provide a technology for early convergence of residual energy while reducing ON-time voltage.SOLUTION: An ignition device 1 for an internal combustion engine has a voltage shift circuit 40. In the voltage shift circuit 40, a first diode D1 is connected between a coil connection terminal 41 and a first connection point 51; a first resistance R1 is connected between the coil connection terminal 41 and a second connection point 52; a second diode D2 is connected between the second connection point 52 and an earth terminal 42; a second resistance R2 is connected between the first connection point 51 and the ground; and a capacitor C1 and a Zener diode ZD are connected in parallel between the first connection point 51 and the second connection point 52. The Zener diode ZD sets a direction from the second connection point 52 toward the first connection point 51 as a forward direction. Thus, electric charge corresponding to breakdown voltage of the Zener diode ZD is accumulated in the capacitor. As a result, ON-time voltage can be reduced by that much, and the residual energy by a capacity component around an ignition plug can be rapidly converged.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In an ignition coil for an internal combustion engine, a current is passed through the primary coil of the coil assembly to generate a magnetic field, and then the current is cut off, causing a high voltage to be generated in the secondary coil by self-induction.The high voltage generated in the secondary coil then causes a discharge in the spark plug.

[0003] A conventional ignition coil for an internal combustion engine is described, for example, in Patent Document 1. Fig. 14 shows a simple circuit diagram of such an ignition coil for an internal combustion engine. Fig. 15 shows examples of an ignition signal of such an ignition coil for an internal combustion engine, a current flowing through the secondary coil (secondary current), and a potential difference across the secondary coil (secondary voltage). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-82193 Summary of the Invention [Problem to be solved by the invention]

[0005] In a conventional ignition coil for an internal combustion engine as shown in Figure 14, the igniter Ig is turned on and a voltage Vo is supplied to the primary coil Co1 for a certain period of time, and then the igniter Ig is turned off. Then, a high voltage is generated in the secondary coil Co2 due to self-induction (hereinafter, this voltage will be referred to as the "discharge voltage"). This causes a discharge at the spark plug Pg.

[0006] At this time, as shown in Figure 15, immediately after the igniter Ig is turned ON, a voltage greater than the voltage supplied to the primary coil Co1 is generated in the secondary coil Co2 (hereinafter, this voltage will be referred to as the "ON voltage"). The higher the voltage supplied to the primary coil Co1, the greater the discharge voltage generated in the secondary coil Co2 due to self-induction, making discharge more likely. On the other hand, the higher the voltage supplied to the primary coil Co1, the greater the ON voltage generated in the secondary coil Co2, making it more likely that a discharge will occur due to the ON voltage.

[0007] For example, when using fuel containing hydrogen, hydrogen burns quickly and has a wide flammable range, making it easy to ignite. This increases the likelihood of discharge due to ON voltage. Also, when using a fuel that is difficult to burn, such as ammonia, if the voltage supplied to the primary coil Co1 is increased to increase the discharge voltage, the ON voltage also increases, increasing the likelihood of discharge due to ON voltage.

[0008] Furthermore, in a conventional ignition coil for an internal combustion engine as shown in Fig. 14, charge accumulates in the capacitance component around the spark plug Pg during discharge. As a result, as shown in Fig. 15, this residual energy causes a problem in that it takes time for the secondary voltage to converge after discharge.

[0009] An object of the present invention is to provide a technique for reducing the ON-state voltage while quickly converging the residual energy. [Means for solving the problem]

[0010] In order to solve the above problems, a first invention of the present application is an ignition device for an internal combustion engine, comprising: a transformer having an electromagnetically coupled primary coil and secondary coil; an energization control unit that controls energization of the primary coil; an ignition plug that is electrically connected between a high-voltage side terminal of the secondary coil and ground and performs an ignition operation in a combustion chamber of the internal combustion engine; and a voltage shift circuit that is connected to a low-voltage side terminal of the secondary coil, wherein the voltage shift circuit has a coil connection terminal that is connected to the low-voltage side terminal of the secondary coil; a ground terminal that is grounded to ground; a first connection point and a second connection point that are arranged between the coil connection terminal and the ground terminal; and a voltage shift circuit that has one end connected to the coil connection terminal and the other end connected to the first connection point. a first diode connected to the connection point and having a forward direction extending from the coil connection terminal toward the first connection point; a first resistor having one end connected to the coil connection terminal and the other end connected to the second connection point; a second diode having one end connected to the second connection point and the other end connected to the ground terminal and having a forward direction extending from the second connection point toward the ground terminal; and a second resistor having one end connected to the first connection point and the other end grounded. A first branch and a second branch are connected in parallel between the first connection point and the second connection point, the first branch including a capacitor, and the second branch including a Zener diode having a forward direction extending from the second connection point toward the first connection point.

[0011] A second invention of the present application is the addition device for an internal combustion engine of the first invention, further comprising an ion current detection unit that measures the voltage at the first connection point.

[0012] A third aspect of the present invention is the ignition device for an internal combustion engine according to the first or second aspect of the present invention, further comprising a third branch connected in parallel to the first branch and the second branch between the first connection point and the second connection point, wherein the capacitor is connected in series with a third diode and a third resistor connected in parallel in the first branch, and a fourth resistor, the third connection point, the fourth connection point, and the Zener diode are connected in series in the second branch in this order from the first connection point to the second connection point, and the third branch includes a first MOSFET, a fifth resistor, a sixth resistor, and a second MOSFET, and the first MOSFET is a P a gate terminal of the first MOSFET connected to the third node, a source terminal of the first MOSFET connected to the first node, a drain terminal of the first MOSFET connected to one end of the fifth resistor, a gate terminal of the second MOSFET connected to the other end of the fifth resistor and one end of the sixth resistor, a source terminal of the second MOSFET connected to the second node, a drain terminal of the second MOSFET connected to the fourth node, and the other end of the sixth resistor connected to the second node. [Effects of the Invention]

[0013] According to the first to third aspects of the present invention, a charge equivalent to the breakdown voltage of the Zener diode is stored in the capacitor. This allows the secondary voltage to be kept low by that voltage. As a result, the ON-state voltage is reduced by the shifted voltage without reducing the discharge voltage, thereby suppressing discharge due to the ON-state voltage. Furthermore, a charge greater than the charge stored in the capacitance component around the spark plug during discharge is stored in the capacitor in a direction that cancels out the charge stored in the capacitance component. This allows the residual energy from the capacitance component around the spark plug to be quickly converged.

[0014] In particular, according to the second aspect of the present invention, a constant voltage is applied to the spark plug after the charge stored in the capacitor has finished discharging, making it possible to detect the ionic current flowing through the plug.

[0015] In particular, according to the third aspect of the present invention, the current flowing through the Zener diode after charge is accumulated in the capacitor during discharge of the spark plug can be suppressed, thereby suppressing the consumption of electrical energy in the Zener diode. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a circuit diagram of an ignition device for an internal combustion engine according to a first embodiment. [Figure 2] 3 is a diagram showing an example of a secondary voltage waveform in the internal combustion engine ignition device according to the first embodiment. FIG. [Figure 3] 3 is a diagram showing a current flow immediately after the start of a discharge period in the internal combustion engine ignition device according to the first embodiment. FIG. [Figure 4] 4 is a diagram showing a current flow after a certain time has elapsed since the start of a discharge period in the internal combustion engine ignition device according to the first embodiment. FIG. [Figure 5] 3 is a diagram showing a current flow during a standby period in the ignition device for an internal combustion engine according to the first embodiment. FIG. [Figure 6] FIG. 6 is a circuit diagram of an ignition device for an internal combustion engine according to a second embodiment. [Figure 7] FIG. 10 is a diagram showing an example of a secondary voltage in the ignition device for an internal combustion engine according to the second embodiment. [Figure 8] FIG. 10 is a diagram showing the flow of current in a first stage of a discharge period in an ignition device for an internal combustion engine according to a second embodiment. [Figure 9] FIG. 10 is a diagram showing a current flow in a second stage of a discharge period in an ignition device for an internal combustion engine according to a second embodiment. [Figure 10] FIG. 10 is a diagram showing a current flow in a third stage of a discharge period in the ignition device for an internal combustion engine according to the second embodiment. [Figure 11] FIG. 10 is a diagram showing a current flow in a fourth stage of a discharge period in the ignition device for an internal combustion engine according to the second embodiment. [Figure 12]FIG. 10 is a diagram showing a current flow in a fifth stage of a discharge period in the ignition device for an internal combustion engine according to the second embodiment. [Figure 13] FIG. 10 is a diagram showing a current flow during a standby period in an ignition device for an internal combustion engine according to a second embodiment. [Figure 14] FIG. 1 is a simplified circuit diagram of a conventional ignition device for an internal combustion engine. [Figure 15] 1 is a diagram showing an example of an ignition signal, a secondary current, and a secondary voltage in a conventional ignition device for an internal combustion engine. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings.

[0018] 1. First Embodiment <1-1. Configuration of an ignition device for an internal combustion engine> The configuration of an ignition device 1 for an internal combustion engine according to a first embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a circuit diagram of the ignition device 1 for an internal combustion engine according to the first embodiment. Note that detailed illustration of the primary side circuit is omitted in Fig. 1.

[0019] The internal combustion engine ignition device 1 of this embodiment is mounted on the body of a vehicle such as an automobile, and applies a high voltage to an ignition plug 90 for an internal combustion engine to generate a spark discharge. As shown in FIG. 1, the internal combustion engine ignition device 1 has a transformer 20, an energization control unit 30, the ignition plug 90, and a voltage shift circuit 40.

[0020] The transformer 20 has an electromagnetically coupled primary coil L1 and secondary coil L2. The secondary coil L2 has a larger number of turns than the primary coil L1. The secondary coil L2 has a high-voltage side terminal 21 and a low-voltage side terminal 22 at both ends.

[0021] The current control unit 30 controls the current flow to the primary coil L1. The current control unit 30 includes a battery 31, an ECU (Engine Control Unit) 32, and an igniter 33.

[0022] The battery 31 is a power supply device (storage battery) capable of charging and discharging DC power. In this embodiment, the battery 31 is electrically connected to the primary coil L1 of the transformer 20 and the igniter 33. The battery 31 supplies a DC voltage to the primary coil L1 of the transformer 20 and the igniter 33.

[0023] The ECU 32 is an existing computer that comprehensively controls the vehicle transmission, the operation of airbags, etc. The ECU 32 outputs an ignition signal to an igniter 33 and controls the ON / OFF operation of the igniter 33.

[0024] The igniter 33 controls the energization of the primary coil L1. The igniter 33 is a switching element such as an IGBT (Insulated Gate Biopolar Transistor). The igniter 33 turns on / off in accordance with an ignition signal supplied from the ECU 32, thereby controlling the energization of the primary coil L1.

[0025] The spark plug 90 is a device disposed inside the combustion chamber of an internal combustion engine to realize ignition in the combustion chamber of the internal combustion engine. The spark plug 90 is electrically connected between the high-voltage side terminal 21 of the secondary coil L2 of the transformer 20 and ground. That is, one end of the spark plug 90 is connected to the high-voltage side terminal 21, and the other end of the spark plug 90 is grounded. When a high voltage is induced in the high-voltage side terminal 21 of the secondary coil L2, a discharge occurs in the gap d of the spark plug 90, generating a spark. This ignites the fuel filled in the internal combustion engine.

[0026] The voltage shift circuit 40 is connected to the low-voltage side terminal 22 of the secondary coil L2 of the transformer 20. The voltage shift circuit 40 can maintain the potential of the low-voltage side terminal 22 at a predetermined negative potential by using the charge stored in a capacitor C1, which will be described later.

[0027] The voltage shift circuit 40 has a coil connection terminal 41, a ground terminal 42, a first connection point 51, a second connection point 52, a first branch 61, a second branch 62, a first diode D1, a second diode D2, a first resistor R1, a second resistor R2, a capacitor C1, a Zener diode ZD, and an ion current detection unit 70.

[0028] The coil connection terminal 41 is a terminal connected to the low-voltage side terminal 22 of the secondary coil L2. The ground terminal 42 is a terminal grounded to the ground. The first connection point 51 and the second connection point 52 are connection points disposed between the coil connection terminal 41 and the ground terminal 42. The first branch 61 and the second branch 62 are connected in parallel between the first connection point 51 and the second connection point 52.

[0029] The first diode D1 has one end connected to the coil connection terminal 41 and the other end connected to the first connection point 51. The first diode D1 is a diode whose forward direction is from the coil connection terminal 41 to the first connection point 51.

[0030] The second diode D2 has one end connected to the second connection point 52 and the other end connected to the ground terminal 42. The second diode D2 is a diode whose forward direction is from the second connection point 52 to the ground terminal 42.

[0031] The first resistor R1 has one end connected to the coil connection terminal 41 and the other end connected to the second connection point 52.

[0032] The second resistor R2 has one end connected to the first connection point 51 and the other end grounded.

[0033] The capacitor C1 is disposed in the first branch 61. That is, the first branch 61 includes the capacitor C1. In this embodiment, the capacitor C1 has one end connected to the first connection point 51 and the other end connected to the second connection point 52.

[0034] The Zener diode ZD is a Zener diode whose forward direction is from the second connection point 52 to the first connection point 51. When a reverse voltage exceeding a predetermined breakdown voltage Vz [V] is applied to the Zener diode ZD, a current flows so that the voltage applied to the Zener diode ZD becomes equal to the breakdown voltage Vz [V].

[0035] The Zener diode ZD is disposed in the second branch 62. That is, the second branch 62 includes the Zener diode ZD. In this embodiment, one end of the Zener diode ZD is connected to the first node 51, and the other end is connected to the second node 52.

[0036] The ion current detector 70 measures the voltage at the first connection point 51. This makes it possible to measure the magnitude of the current flowing through the second resistor R2.

[0037] <1-2. Changes in secondary voltage in ignition devices for internal combustion engines> Next, changes in the secondary voltage in the internal combustion engine ignition device 1 of this embodiment will be described with reference to Figures 2 to 5. In the following description, the voltage at the high-voltage side terminal 21 of the secondary coil L2 is referred to as the secondary voltage V2. Figure 2 is a diagram showing an example of the waveform of the secondary voltage V2 in the internal combustion engine ignition device 1. Specifically, Figure 2 shows the results of a simulation of the internal combustion engine ignition device 1. Figures 3 to 5 are diagrams showing the flow of current in the internal combustion engine ignition device 1 at various timings. Specifically, Figure 3 shows the state immediately after the start of the discharge period T2, Figure 4 shows the state after a certain time has elapsed after the start of the discharge period T2, and Figure 5 shows the state during the standby period T3.

[0038] In the internal combustion engine ignition device 1, Current conduction period T1: Current conduction of primary coil L1 Discharge period T2: Discharge at the spark plug 90 Standby period T3: Residual energy recovery / ion current detection By repeating this process in accordance with the movement of the piston, combustion occurs periodically within the combustion chamber, repeating the intake-compression-combustion-exhaust cycle of the internal combustion engine.

[0039] First, changes in the secondary voltage in a conventional ignition device for an internal combustion engine will be described with reference to Fig. 15. Immediately after starting to use the ignition device for an internal combustion engine, that is, before the first current application period T1, the secondary voltage is 0 [V].

[0040] When the current-carrying period T1 begins and current begins to flow to the primary coil, a voltage is supplied to the primary coil, generating a voltage in the secondary coil. Here, the ON voltage generated immediately after current begins is defined as Von [V]. As current continues to flow to the primary coil, the secondary voltage V2 gradually decreases from Von as magnetic flux is formed within the transformer.

[0041] When the current-carrying period T1 ends and the power supply to the primary coil is cut off, a high voltage is generated in the secondary coil in the opposite direction (negative) to the ON voltage. This applies a high voltage to the spark plug, causing a discharge in the spark plug gap (discharge period T2). After that, the magnetic flux formed in the transformer weakens as the discharge occurs, and the absolute value of the secondary current gradually decreases. This ends the discharge in the spark plug.

[0042] Thereafter, during a waiting period T3, the secondary voltage becomes a negative potential for a while due to residual energy stored in the parasitic capacitance around the spark plug 90. As the residual energy converges, the secondary voltage converges to 0 [V].

[0043] In this way, the cycle of periods T1, T2, and T3 is repeated, so the ON voltage is always Von [V].

[0044] Next, changes in the secondary voltage V2 in the internal combustion engine ignition device 1 of this embodiment will be described with reference to Figures 2 to 5. Figure 2 shows the secondary voltage V2 in two cycles immediately after starting use.

[0045] First, immediately after starting use of the internal combustion engine ignition device 1, i.e., before the first current-carrying period T1, no charge is stored in any of the secondary coil L2, the spark plug 90, and the voltage shift circuit 40, and the potentials in all of these circuits are 0 [V]. In other words, the secondary voltage V2 is also 0 [V].

[0046] When the current-carrying period T1 begins and current begins to flow through the primary coil L1, a voltage is supplied to the primary coil L1, and as a result, a voltage is generated in the secondary coil L2. If the voltage generated in the secondary coil L2 immediately after current begins to flow is Von [V], then because the voltage at the low-voltage side terminal 22 is 0 [V], the ON voltage of the secondary voltage V2 is also Von [V]. As current continues to flow through the primary coil L1, the secondary voltage V2 gradually decreases from Von [V] as magnetic flux is formed within the transformer 20.

[0047] When the current-carrying period T1 ends and the power supply to the primary coil L1 is cut off, a high voltage in the opposite direction to the ON voltage is generated in the secondary coil L2. Here, the maximum secondary voltage V2 immediately after the power is cut off is set to -Vd [V]. As a result, a high negative voltage is applied to the spark plug 90, causing a discharge in the gap of the spark plug 90 (discharge period T2).

[0048] During the discharge period T2, current flows from the spark plug 90 through the secondary coil L2 and voltage shift circuit 40 to ground. Immediately after the start of discharge, no charge is stored in the capacitor C1. Therefore, as shown by the dashed arrow in Figure 3, the current that flows from the spark plug 90 through the secondary coil L2 to the voltage shift circuit 40 flows mainly through the coil connection terminal 41, the first diode D1, the first connection point 51, the capacitor C1, the second connection point 52, the second diode D2, and the ground terminal 42 to ground.

[0049] As a result of current flowing through capacitor C1, charge gradually accumulates in capacitor C1. At this time, a positive charge accumulates in the terminal of capacitor C1 on the first node side, and a negative charge accumulates in the terminal on the second node side. When a charge equivalent to the breakdown voltage Vz [V] of Zener diode ZD accumulates in capacitor C1, the potential difference between first node 51 and second node 52 becomes the breakdown voltage Vz [V]. As a result, a voltage of the breakdown voltage Vz [V] is applied across Zener diode ZD, causing Zener diode ZD to break down, and a current flows through Zener diode ZD from first node 51 to second node 52.

[0050] As a result, as shown by the dashed arrow in Figure 4, the current that flows from the spark plug 90 through the secondary coil L2 into the voltage shift circuit 40 mainly flows to ground via the coil connection terminal 41, the first diode D1, the first connection point 51, the Zener diode ZD, the second connection point 52, the second diode D2, and the ground terminal 42.

[0051] After the spark plug 90 has discharged for a while, the magnetic flux formed in the transformer 20 weakens, and the absolute value of the secondary voltage V2 gradually decreases. As a result, the discharge in the spark plug 90 ends.

[0052] During the standby period T3, the charge stored in the capacitor C1 causes the potential difference between the first node 51 and the second node 52 to be equal to a breakdown voltage Vz [V]. Specifically, the potential of the first node 51 is higher than that of the second node 52 by Vz [V]. Because the first node 51 is grounded via the second resistor R2, the potential of the first node 51 is 0 [V] and the potential of the second node 52 is −Vz [V] when no current is flowing. Therefore, when no current is flowing, the secondary voltage V2 at the high-voltage terminal 21, which is connected to the second node 52 via the first resistor R1 and the secondary coil L2, is −Vz [V]. This applies a negative voltage of −Vz [V] to the spark plug 90. If current were to flow through the gap of the spark plug 90, current would flow through the internal combustion engine ignition device 1 in the direction indicated by the dashed arrow in FIG. 5 .

[0053] During discharge period T2, when the spark plug 90 discharges, the fuel supplied to the combustion chamber ignites, and combustion begins within the combustion chamber. Therefore, combustion continues within the combustion chamber at the beginning of standby period T3. During combustion, chemical ions and thermal ions are generated depending on the combustion state, making it easier for current to flow across the gap of the spark plug 90. Therefore, when a constant voltage is applied across the spark plug 90, a current flows across the spark plug 90 depending on the concentration of these ions. This type of current is hereinafter referred to as "ion current."

[0054] As described above, the charge stored in capacitor C1 generates a potential difference across the gap of spark plug 90. When this generates an ionic current, the ionic current flowing through spark plug 90 flows into voltage shift circuit 40 via secondary coil L2, and then flows to ground via coil connection terminal 41, first resistor R1, second connection point 52, capacitor C1, first connection point 51, and second resistor R2, as shown by the dashed arrow in Figure 5.

[0055] During the standby period T3, the ionic current detection unit 70 measures the voltage at the first connection point 51. This allows the ionic current detection unit 70 to measure the magnitude of the ionic current flowing through the second resistor R2. The combustion state inside the combustion chamber can then be estimated from the magnitude of the measured ionic current.

[0056] Furthermore, as shown in FIG. 2, during the standby period T3, the secondary voltage V2 is stabilized at approximately −Vz [V] due to the charge stored in the capacitor C1.

[0057] When the next current-carrying period T1 begins and current begins to flow through the primary coil L1, a voltage is supplied to the primary coil L1, and a voltage is generated in the secondary coil L2. At this time, immediately after current begins to flow, a potential difference Von [V] equal to the first ON voltage is generated across the secondary coil L2.

[0058] Here, in the second and subsequent current-carrying periods T1, the voltage at low-voltage side terminal 22 is approximately -Vz [V], and therefore the ON voltage of secondary voltage V2 is approximately Von-Vz [V], as shown in Fig. 2. That is, in the second and subsequent current-carrying periods T1, the ON voltage of secondary voltage V2 can be reduced by approximately -Vz [V].

[0059] When the current-carrying period T1 ends and the power supply to the primary coil L1 is cut off, a high voltage opposite to the ON voltage is generated in the secondary coil L2, a high negative voltage is applied to the spark plug 90, and a discharge occurs in the gap of the spark plug 90. In the second and subsequent discharge periods T2, the maximum secondary voltage V2 immediately after the power is cut off is -Vd [V], just like in the first discharge period T2. In the second and subsequent standby periods T3, the ion current is detected by the ion current detection unit 70, just like in the first standby period T3.

[0060] In this way, in the second and subsequent cycles, the ON voltage of the secondary voltage V2 can be reduced without reducing the voltage (absolute value of the negative voltage) applied to the spark plug 90 during discharge. This makes it possible to prevent the ON voltage from causing an erroneous discharge at the spark plug 90.

[0061] For example, when starting the engine, fuel may not be introduced into the combustion chamber in the first cycle, but may be introduced into the combustion chamber in the second and subsequent cycles. This prevents combustion due to erroneous discharge in the first cycle, when the ON voltage cannot be reduced.

[0062] Furthermore, during the discharge period T2, a current flows through the spark plug 90, causing charge to accumulate in the capacitance component around the spark plug 90. Specifically, a positive charge accumulates on the ground side of the spark plug 90, and a negative charge accumulates on the secondary coil L2 side. If this residual energy is large, a problem occurs in that it takes time for the secondary voltage V2 to converge during the standby period T3 after discharge, as in the conventional example shown in FIG. 15. In this embodiment, during the discharge period T2, a positive charge accumulates in the terminal of the capacitor C1 on the first connection point side, and a negative charge accumulates in the terminal on the second connection point side. Furthermore, the capacitance of the capacitor C1 (e.g., several tens of μF) is sufficiently large compared to the parasitic capacitance (e.g., several tens of pF) around the spark plug 90. Therefore, immediately after the end of the discharge period T2, the charge accumulated in the parasitic capacitance around the spark plug 90 is absorbed by the capacitor C1. In this way, the charge accumulated in the capacitor C1 can quickly converge the residual energy around the spark plug 90.

[0063] 2. Second Embodiment <2-1. Configuration of an ignition device for an internal combustion engine> Next, the configuration of an ignition device 1A for an internal combustion engine according to a second embodiment of the present invention will be described with reference to the drawings. Fig. 6 is a circuit diagram of the ignition device 1A for an internal combustion engine according to the second embodiment. Note that detailed illustration of the primary side circuit is omitted in Fig. 6. Also, in the following description and Fig. 6, the same reference numerals are used to designate components equivalent to those in the first embodiment.

[0064] 6, the internal combustion engine ignition device 1A has a transformer 20, an energization control unit 30, an ignition plug 90, and a voltage shift circuit 40A. The transformer 20, the energization control unit 30, and the ignition plug 90 are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0065] The voltage shift circuit 40A is connected to the low-voltage side terminal 22 of the secondary coil L2 of the transformer 20. The voltage shift circuit 40A can maintain the potential of the low-voltage side terminal 22 at a predetermined negative potential by using the charge stored in a capacitor C1, which will be described later.

[0066] The voltage shift circuit 40A has a coil connection terminal 41, a ground terminal 42, a first connection point 51, a second connection point 52, a third connection point 53, a fourth connection point 54, a first branch 61, a second branch 62, a third branch 63, a first diode D1, a second diode D2, a third diode D3, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a capacitor C1, a Zener diode ZD, a first MOSFET 81, a second MOSFET 82, and an ion current detection unit 70.

[0067] The coil connection terminal 41 is a terminal connected to the low-voltage side terminal 22 of the secondary coil L2. The ground terminal 42 is a terminal grounded to the ground. The first connection point 51 and the second connection point 52 are connection points disposed between the coil connection terminal 41 and the ground terminal 42. The first branch 61, the second branch 62, and the third branch 63 are connected in parallel between the first connection point 51 and the second connection point 52. The third connection point 53 and the fourth connection point 54 are connection points included in the second branch 62.

[0068] The first diode D1 has one end connected to the coil connection terminal 41 and the other end connected to the first connection point 51. The direction from the coil connection terminal 41 to the first connection point 51 is the forward direction of the first diode D1.

[0069] The second diode D2 has one end connected to the second connection point 52 and the other end connected to the ground terminal 42. The direction from the second connection point 52 to the ground terminal 42 is the forward direction of the second diode D2.

[0070] The first resistor R1 has one end connected to the coil connection terminal 41 and the other end connected to the second connection point 52.

[0071] The second resistor R2 has one end connected to the first connection point 51 and the other end grounded.

[0072] The first branch 61 includes a capacitor C1, a third diode D3, and a third resistor R3. In the first branch 61, the capacitor C1, the third diode D3 connected in parallel, and the third resistor R3 are connected in series. The forward direction of the third diode D3 is from the first node 51 to the second node 52.

[0073] In this embodiment, one end of the capacitor C1 is connected to the first connection point 51, and the other end is connected to one end of the third diode D3 and one end of the third resistor R3. The other ends of the third diode D3 and the third resistor R3 are connected to the second connection point 52. As described above, in this embodiment, the capacitor C1 is disposed closer to the first connection point 51 than the third diode D3 and the third resistor R3, but the capacitor C1 may also be connected closer to the second connection point 52 than the third diode D3 and the third resistor R3.

[0074] The second branch 62 includes a fourth resistor R4, a third node 53, a fourth node 54, and a Zener diode ZD. In the second branch 62, the fourth resistor R4, the third node 53, the fourth node 54, and the Zener diode ZD are connected in series in this order from the first node 51 to the second node 52.

[0075] The Zener diode ZD is a Zener diode whose forward direction is from the second connection point 52 to the first connection point 51. When a reverse voltage exceeding a predetermined breakdown voltage Vz [V] is applied to the Zener diode ZD, a current flows so that the voltage applied to the Zener diode ZD becomes equal to the breakdown voltage Vz [V].

[0076] The third branch 63 includes a first MOSFET 81, a fifth resistor R5, a sixth resistor R6, and a second MOSFET 82. In the third branch 63, the source terminal of the first MOSFET 81, the drain terminal of the first MOSFET 81, the fifth resistor R5, the gate terminal of the second MOSFET 82, and the source terminal of the second MOSFET 82 are connected in series in this order from the first node 51 to the second node 52.

[0077] The first MOSFET 81 is a P-channel MOSFET. The gate terminal of the first MOSFET 81 is connected to the third connection point 53. The source terminal of the first MOSFET 81 is connected to the first connection point 51. The drain terminal of the first MOSFET 81 is connected to one end of the fifth resistor R5.

[0078] The second MOSFET 82 is an N-channel MOSFET. The gate terminal of the second MOSFET 82 is connected to the other end of the fifth resistor R5 and one end of the sixth resistor R6. The source terminal of the second MOSFET 82 is connected to the second connection point 52. The drain terminal of the second MOSFET 82 is connected to the fourth connection point 54.

[0079] The fifth resistor R5 is connected in the third branch 63 between the drain terminal of the first MOSFET 81 and the gate terminal of the second MOSFET 82. That is, one end of the fifth resistor R5 is connected to the drain terminal of the first MOSFET 81. The other end of the fifth resistor R5 is connected to the gate terminal of the second MOSFET 82 and one end of the sixth resistor R6.

[0080] Both ends of the sixth resistor R6 are connected between the gate terminal and the source terminal of the second MOSFET 82. That is, one end of the sixth resistor R6 is connected to the other end of the fifth resistor R5 and the gate terminal of the second MOSFET 82. The other end of the sixth resistor R6 is connected to the second connection point 52.

[0081] When a negative voltage exceeding the threshold voltage is applied to the gate terminal with respect to the source terminal of the first MOSFET 81, a current flows from the source terminal to the drain terminal. Therefore, a current flows through the fourth resistor R4 from the first node 51 to the second node 52, and when the potential difference across the fourth resistor R4 exceeds the threshold voltage of the first MOSFET 81, a current flows through the first MOSFET 81 from the source terminal to the drain terminal.

[0082] When a positive voltage exceeding the threshold voltage is applied to the gate terminal of the second MOSFET 82 with respect to the source terminal, a current flows from the drain terminal to the source terminal. Therefore, a current flows through the sixth resistor R6 from the first node 51 to the second node 52 (i.e., a current flows from one end connected to the fifth resistor R5 to the other end connected to the second node 52), and when the potential difference across the sixth resistor R6 exceeds the threshold voltage of the second MOSFET 82, a current flows through the second MOSFET 82 from the drain terminal to the source terminal.

[0083] The ion current detector 70 measures the voltage at the first connection point 51. This makes it possible to measure the magnitude of the current flowing through the second resistor R2.

[0084] <2-2. Changes in secondary voltage in ignition devices for internal combustion engines> Next, changes in the secondary voltage in the internal combustion engine ignition device 1A of this embodiment will be described with reference to FIGS. 7 to 14. In the following description, the voltage at the high-voltage side terminal 21 of the secondary coil L2 will be referred to as the secondary voltage V2. FIG. 7 is a diagram showing an example of the waveform of the secondary voltage V2 in the internal combustion engine ignition device 1. Specifically, FIG. 7 shows simulation results for the internal combustion engine ignition device 1A. FIGS. 8 to 14 are diagrams showing the current flow in the internal combustion engine ignition device 1 at various timings. Specifically, FIG. 8 shows the first stage of the discharge period T2, FIG. 9 shows the second stage of the discharge period T2, FIG. 10 shows the third stage of the discharge period T2, FIG. 11 shows the fourth stage of the discharge period T2, FIG. 12 shows the fifth stage of the discharge period T2, and FIG. 13 shows the standby period T3.

[0085] In the internal combustion engine ignition device 1A, similarly to the first embodiment, Current conduction period T1: Current conduction of primary coil L1 Discharge period T2: Discharge at the spark plug 90 Standby period T3: Residual energy recovery / ion current detection By repeating this process in accordance with the movement of the piston, combustion occurs periodically within the combustion chamber, repeating the intake-compression-combustion-exhaust cycle of the internal combustion engine.

[0086] Changes in the secondary voltage V2 in the internal combustion engine ignition device 1A of this embodiment will be described with reference to Figures 8 to 14. Figure 8 shows the secondary voltage V2 in two cycles immediately after the start of use.

[0087] First, immediately after starting use of the internal combustion engine ignition device 1A, i.e., before the first current-carrying period T1, no charge is stored in any of the secondary coil L2, the spark plug 90, and the voltage shift circuit 40, and the potentials in all of these circuits are 0 [V]. In other words, the secondary voltage V2 is also 0 [V].

[0088] When the current-carrying period T1 begins and current begins to flow through the primary coil L1, a voltage is supplied to the primary coil L1, and as a result, a voltage is generated in the secondary coil L2. If the voltage generated in the secondary coil L2 immediately after current begins to flow is Von [V], then because the voltage at the low-voltage side terminal 22 is 0 [V], the ON voltage of the secondary voltage V2 is also Von [V]. As current continues to flow through the primary coil L1, the secondary voltage V2 gradually decreases from Von [V] as magnetic flux is formed within the transformer 20.

[0089] When the current-carrying period T1 ends and the power supply to the primary coil L1 is cut off, a high voltage in the opposite direction to the ON voltage is generated in the secondary coil L2. Here, the maximum secondary voltage V2 immediately after the power is cut off is set to -Vd [V]. As a result, a high negative voltage is applied to the spark plug 90, causing a discharge in the gap of the spark plug 90 (discharge period T2).

[0090] During the discharge period T2, a current flows from the spark plug 90 through the secondary coil L2 and the voltage shift circuit 40A to ground. In the first stage of the discharge period T2 shown in FIG. 8, immediately after the start of discharge, a sufficient amount of charge is not stored in the capacitor C1. At this time, the Zener diode ZD is in the reverse direction, so no current flows through the second branch 62 in the direction from the first node 51 to the second node 52. Furthermore, because there is no potential difference between the source and gate of the first MOSFET 81, no current flows through the third branch 63.

[0091] Therefore, as shown by the dashed arrow in Figure 8, the current that flows from the spark plug 90 to the voltage shift circuit 40A via the secondary coil L2 mainly flows to ground via the coil connection terminal 41, the first diode D1, the first connection point 51, the capacitor C1, the third diode D3, the second connection point 52, the second diode D2, and the ground terminal 42.

[0092] As a result of current flowing through capacitor C1, charge gradually accumulates in capacitor C1. At this time, a positive charge accumulates in the terminal of capacitor C1 on the first node side, and a negative charge accumulates in the terminal on the second node side. When a charge equivalent to the breakdown voltage Vz [V] of Zener diode ZD accumulates in capacitor C1, the potential difference between first node 51 and second node 52 becomes the breakdown voltage Vz [V]. This triggers a transition to the second stage of the discharge period T2 shown in FIG. 9.

[0093] In the second stage of the discharge period T2 shown in FIG. 9, a voltage of breakdown voltage Vz [V] is applied across the Zener diode ZD, causing the Zener diode ZD to break down, and a current flows through the Zener diode ZD from the first connection point 51 to the second connection point 52.

[0094] 9, the current flowing from the spark plug 90 to the voltage shift circuit 40A via the secondary coil L2 flows mainly to ground via the coil connection terminal 41, the first diode D1, the first connection point 51, the fourth resistor R4, the Zener diode ZD, the second connection point 52, the second diode D2, and the ground terminal 42. At this time, the current flowing through the fourth resistor R4 causes a transition to the third stage of the discharge period T2 shown in FIG.

[0095] 10 , a current flows through the fourth resistor R4 from the first node 51 to the second node 52, causing the potential difference across the fourth resistor R4 to exceed the threshold voltage of the first MOSFET 81, and causing a current to flow from the source terminal to the drain terminal of the first MOSFET 81. As a result, a current flows not only through the second branch 62 but also through the third branch 63 in the direction from the first node 51 to the second node 52.

[0096] 10, a portion of the current flows from the spark plug 90 through the secondary coil L2 into the voltage shift circuit 40A, passes through the coil connection terminal 41 and the first diode D1, and then flows from the first connection point 51 to the ground via the first MOSFET 81, the fifth resistor R5, the sixth resistor R6, the second connection point 52, the second diode D2, and the ground terminal 42. Here, the current flowing through the sixth resistor R6 causes a transition to the fourth stage of the discharge period T2 shown in FIG.

[0097] 11, a current flows through the sixth resistor R6 from the first node 51 to the second node 52, causing the potential difference across the sixth resistor R6 to exceed the threshold voltage of the second MOSFET 82, and causing a current to flow through the second MOSFET 82 from the drain terminal to the source terminal. As a result, as shown by the dashed arrow in FIG. 11, part of the current that flowed from the first node 51 to the fourth node 54 via the fourth resistor R4 and the third node 53 in the second branch 62 flows to the second node 52 via the second MOSFET 82.

[0098] After the spark plug 90 has been discharging for a while, the magnetic flux formed in the transformer 20 weakens, the absolute value of the secondary voltage V2 gradually decreases, and the current flowing into the voltage shift circuit 40A decreases. This reduces the current flowing through the fourth resistor R4 and the sixth resistor R6, and the source-gate voltages of the first MOSFET 81 and the second MOSFET 82 also decrease. As a result, current no longer flows between the source and drain of the first MOSFET 81 and the second MOSFET 82, and the system transitions to the fifth stage of the discharge period T2 shown in FIG. 12.

[0099] In the fifth stage of the discharge period T2 shown in Fig. 12, similar to the second stage of the discharge period T2 shown in Fig. 9, current flows mainly through the second branch 62. As the discharge continues thereafter, the secondary voltage V2 further decreases, and the discharge at the spark plug 90 ends.

[0100] Subsequently, during the standby period T3, the charge stored in the capacitor C1 causes the potential difference between the first node 51 and the second node 52 to become approximately Vz [V]. As a result, the secondary voltage V2 at the high-voltage side terminal 21 becomes approximately -Vz [V]. As a result, a negative voltage of approximately -Vz [V] is applied to the spark plug 90.

[0101] As in the first embodiment, this negative voltage applied to the spark plug 90 causes an ionic current to flow across the gap of the spark plug 90 during the standby period T3, depending on the combustion state in the combustion chamber. When an ionic current is generated, the ionic current flowing through the spark plug 90 flows into the voltage shift circuit 40A via the secondary coil L2, and then flows to ground via the coil connection terminal 41, the first resistor R1, the second connection point 52, the third resistor R3, the capacitor C1, the first connection point 51, and the second resistor R2, as shown by the dashed arrow in Figure 13.

[0102] During the standby period T3, the ionic current detection unit 70 measures the voltage at the first connection point 51. This allows the ionic current detection unit 70 to measure the magnitude of the ionic current flowing through the second resistor R2. The combustion state inside the combustion chamber can then be estimated from the magnitude of the measured ionic current.

[0103] Furthermore, as shown in FIG. 7, during the waiting period T3, the secondary voltage V2 is stabilized at approximately −Vz [V] due to the charge stored in the capacitor C1.

[0104] When the next current-carrying period T1 begins and current begins to flow through the primary coil L1, a voltage is supplied to the primary coil L1, and a voltage is generated in the secondary coil L2. At this time, immediately after current begins to flow, a potential difference Von [V] equal to the first ON voltage is generated across the secondary coil L2.

[0105] Here, in the second and subsequent current-carrying periods T1, the voltage at low-voltage side terminal 22 is approximately -Vz [V], and therefore the ON voltage of secondary voltage V2 is approximately Von-Vz [V], as shown in Fig. 2. That is, in the second and subsequent current-carrying periods T1, the ON voltage of secondary voltage V2 can be reduced by approximately -Vz [V].

[0106] When the current-carrying period T1 ends and the power supply to the primary coil L1 is cut off, a high voltage opposite to the ON voltage is generated in the secondary coil L2, a high negative voltage is applied to the spark plug 90, and a discharge occurs in the gap of the spark plug 90. In the second and subsequent discharge periods T2, the maximum secondary voltage V2 immediately after the power is cut off is -Vd [V], just like in the first discharge period T2. In the second and subsequent standby periods T3, the ion current is detected by the ion current detection unit 70, just like in the first standby period T3.

[0107] In this way, similar to the first embodiment, in the second and subsequent cycles, the ON voltage of the secondary voltage V2 can be reduced without reducing the voltage (absolute value of the negative voltage) applied to the spark plug 90 during discharge. This makes it possible to prevent the ON voltage from causing an erroneous discharge at the spark plug 90.

[0108] In the first embodiment described above, after the start of the discharge period T2, once the charge in the capacitor C1 reaches the breakdown voltage Vz [V] of the Zener diode ZD, current flows through the Zener diode ZD for the remainder of the discharge period T2. This causes heat generation and electrical energy consumption in the Zener diode ZD. In contrast, in the second embodiment, immediately after the charge in the capacitor C1 reaches the breakdown voltage Vz [V] of the Zener diode ZD, the system transitions to the third and fourth stages of the discharge period T2 shown in FIGS. 10 and 11, thereby reducing the current flowing through the Zener diode ZD. This reduces the electrical energy consumption in the Zener diode ZD.

[0109] 11, when the second MOSFET 82 is turned on, the amount of current flowing from the first node 52 to the second node 52 in the second branch 62 and the third branch 63 increases. This causes the charge accumulated in the capacitor C1 to be released, and a current flows in the first branch 61 from the second node 52 to the first node 51 via the third resistor R3 and the capacitor C1. At this time, the current passing through the third resistor R3 can suppress the release of the charge from the capacitor C1.

[0110] In this embodiment, a third diode D3 is connected in parallel to the third resistor R3. As a result, when storing charge in the capacitor C1 in the first stage of the discharge period T2 shown in Fig. 8, current can flow via the third diode D3 without passing through the third resistor R3. That is, the resistance of the first branch 61 can be reduced in the first stage of the discharge period T2.

[0111] Furthermore, if the charge in the capacitor C1 is released and becomes smaller than Vz [V] in the fourth stage of the discharge period T2 shown in Fig. 11, when the fourth stage of the discharge period T2 shown in Fig. 11 transitions to the fifth stage of the discharge period T2 shown in Fig. 12, a current temporarily flows in the first branch 61 from the first connection point 51 to the second connection point 52, similar to the first stage of the discharge period TA2 shown in Fig. 8, and the charge in the capacitor C1 accumulates. Therefore, in the subsequent standby period T3, the ion current detection unit 70 can stably detect the ion current.

[0112] Furthermore, similar to the first embodiment described above, in this second embodiment, the residual energy stored in the capacitive components around the spark plug 90 during the discharge period T2 can be quickly converged by the charge stored in the capacitor C1.

[0113] <3. Modifications> Although exemplary embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments.

[0114] The ignition device for an internal combustion engine of the present invention may be mounted not only on vehicles such as automobiles, but also on various devices such as generators and industrial machinery, and may be used to generate an electric spark in the spark plug of an internal combustion engine to ignite fuel.

[0115] The detailed shape and structure of the above-described internal combustion engine 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]

[0116] 1,1A Ignition device for internal combustion engines 20 Transformer 21 High voltage terminal 22 Low voltage terminal 30 Power supply control unit 40,40A voltage shift circuit 41 Coil connection terminal 42 Ground terminal 51 First Connection Point 52 Second connection point 53 Third Connection Point 54 Fourth Junction 61 First Branch 62 Second Branch 63 Third Branch 70 Ion current detection unit 81 First MOSFET 82 Second MOSFET 90 Spark plug C1 capacitor D1 First diode D2 Second diode D3 Third diode L1 primary coil L2 secondary coil R1 First resistor R2 2nd resistor R3 3rd resistor R4 4th resistor R5 5th resistor R6 6th resistor ZD Zener diode

Claims

1. An ignition device for an internal combustion engine, a transformer having an electromagnetically coupled primary coil and secondary coil; a current control unit that controls current flow to the primary coil; a spark plug electrically connected between a high-voltage terminal of the secondary coil and ground, and performing an ignition operation in a combustion chamber of the internal combustion engine; a voltage shift circuit connected to the low-voltage side terminal of the secondary coil; and The voltage shift circuit a coil connection terminal connected to the low-voltage side terminal of the secondary coil; a ground terminal connected to ground; a first connection point and a second connection point disposed between the coil connection terminal and the ground terminal; a first diode having one end connected to the coil connection terminal and the other end connected to the first connection point, the forward direction of which is from the coil connection terminal toward the first connection point; a first resistor having one end connected to the coil connection terminal and the other end connected to the second connection point; a second diode having one end connected to the second connection point and the other end connected to the ground terminal, the forward direction of which is from the second connection point to the ground terminal; a second resistor having one end connected to the first connection point and the other end grounded; and a first branch and a second branch are connected in parallel between the first connection point and the second connection point; the first branch includes a capacitor; The second branch includes a Zener diode whose forward direction is from the second connection point to the first connection point.

2. 2. An ignition device for an internal combustion engine according to claim 1, an ion current detection unit that measures the voltage at the first connection point; An ignition device for an internal combustion engine, further comprising:

3. 3. An ignition device for an internal combustion engine according to claim 1 or 2, a third branch connected in parallel to the first branch and the second branch between the first connection point and the second connection point; In the first branch, the capacitor; a third diode and a third resistor connected in parallel; are connected in series, In the second branch, a fourth resistor, a third connection point, a fourth connection point, and the Zener diode are connected in series in this order from the first connection point toward the second connection point, the third branch includes a first MOSFET, a fifth resistor, a sixth resistor, and a second MOSFET; the first MOSFET is a P-channel MOSFET, the second MOSFET is an N-channel MOSFET, a gate terminal of the first MOSFET connected to the third node; a source terminal of the first MOSFET connected to the first node; a drain terminal of the first MOSFET is connected to one end of the fifth resistor; a gate terminal of the second MOSFET is connected to the other end of the fifth resistor and one end of the sixth resistor; The source terminal of the second MOSFET is connected to the second node; a drain terminal of the second MOSFET connected to the fourth node; The other end of the sixth resistor is connected to the second connection point.

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