Internal combustion engine

Abstract

In an internal combustion engine (1), a fuel containing hydrogen is supplied to a combustion chamber. A control unit (4) controls execution of the discharging of a spark plug (2) by controlling eletrification of an ignition coil (3). The control unit (4) performs control so as to execute normal discharging and waste discharging in a discharge gap (G). In normal discharging, the fuel in the combustion chamber is ignited. In waste discharging, energy remaining in the ignition coil (3) is released after normal discharging. The discharge energy in waste discharging is less than the discharge energy in normal discharging. The control unit (4) performs control so as to execute waste discharging from the time after normal discharging has been executed to the time fuel is supplied to the combustion chamber.

Description

Internal combustion engine Cross-reference to related applications

[0001] This application is based on Japanese Application No. 2024-158493 filed on September 12, 2024, the contents of which are incorporated herein by reference.

[0002] This disclosure relates to an internal combustion engine.

[0003] For example, as disclosed in Patent Document 1, an internal combustion engine that uses a gas containing hydrogen as fuel is known. The internal combustion engine described in Patent Document 1 attempts to burn unburned fuel by performing multiple ignition operations in one combustion cycle and suppress damage to the internal combustion engine due to the occurrence of misfires.

[0004] International Publication No. 2023 / 162720

[0005] Regarding the energy remaining in the ignition device after the ignition operation, the internal combustion engine described in Patent Document 1 has not been fully considered. That is, an internal combustion engine that uses a gas containing hydrogen as fuel is more likely to have energy remaining in the ignition device after the ignition operation compared to, for example, an internal combustion engine that uses gasoline as fuel. Therefore, after the ignition operation, there is a possibility that discharge may occur at an unintended timing in the discharge gap of the spark plug, and as a result, there is a possibility that the fuel may burn at an unintended timing. Therefore, it can be said that the internal combustion engine described in Patent Document 1 has room for improvement from the perspective of suppressing the combustion of fuel at an unintended timing.

[0006] This disclosure aims to provide an internal combustion engine capable of suppressing the combustion of fuel at an unintended timing.

[0007] One aspect of the present disclosure is an internal combustion engine comprising: a combustion chamber to which a hydrogen-containing fuel is supplied; a spark plug that ignites the fuel in the combustion chamber by a discharge occurring in a discharge gap; an ignition coil that applies a high voltage to the spark plug; a control unit that controls the execution of the discharge of the spark plug by controlling the supply of current to the ignition coil; and a fuel supply unit that supplies the fuel to the combustion chamber, wherein the control unit controls the discharge gap to perform a normal discharge to ignite the fuel in the combustion chamber and a waste discharge to release the energy remaining in the ignition coil after the normal discharge, the discharge energy in the waste discharge is smaller than the discharge energy in the normal discharge, and the control unit controls the waste discharge to be performed between the time the normal discharge is performed and the time the fuel supply unit supplies the fuel to the combustion chamber.

[0008] In the above-described internal combustion engine, the control unit controls the system to perform a discharge between the time of normal discharge and before fuel is supplied to the combustion chamber. Therefore, it is possible to suppress the occurrence of discharge in the discharge gap at an unintended timing after fuel has been supplied to the combustion chamber. As a result, it is possible to suppress the combustion of fuel at an unintended timing.

[0009] As described above, according to the above embodiment, it is possible to provide an internal combustion engine that can suppress the combustion of fuel at unintended times. The symbols in parentheses in the claims indicate the correspondence with the specific means described in the embodiments described later, and do not limit the technical scope of this disclosure.

[0010] The above-mentioned and other purposes, features, and benefits of this disclosure will be further clarified by the following detailed description with reference to the attached drawings. The drawings are as follows: Figure 1 is a schematic diagram of the internal combustion engine in Embodiment 1; Figure 2 is a cross-sectional view of the vicinity of the combustion chamber of the internal combustion engine in Embodiment 1; Figure 3 is a diagram of the vicinity of the discharge gap of the spark plug in Embodiment 1; Figure 4 is a diagram showing the primary current values ​​during normal discharge and waste discharge in Embodiment 1; Figure 5 is a graph showing the primary current and secondary voltage etc. in the combustion cycle in Experimental Example 1, with the results of 1000 combustion cycles superimposed; Figure 6 is a graph showing the primary current and secondary voltage etc. in the combustion cycle in Experimental Example 1, with the results of a representative combustion cycle; Figure 7 is a graph showing the relationship between crank angle and secondary voltage in Experimental Example 2, with and without waste discharge; Figure 8 is a graph showing the relationship between crank angle and re-discharge frequency in Experimental Example 3, without waste discharge; Figure 9 is a graph showing the relationship between crank angle and re-discharge frequency in Experimental Example 3, with waste discharge. Rough sketch. Figure 10 is a graph showing the relationship between the discard timing and re-discharge during the fuel supply period in Experimental Example 4. Figure 11 is a graph showing the relationship between the crank angle and the re-discharge frequency when the discard timing is BTDC 540°CA in Experimental Example 4. Figure 12 is a graph showing the relationship between the crank angle and the re-discharge frequency when the discard timing is BTDC 530°CA in Experimental Example 4. Figure 13 is a graph showing the relationship between the crank angle and the re-discharge frequency when the discard timing is BTDC 510°CA in Experimental Example 4. Figure 14 is a graph showing the relationship between the crank angle and the re-discharge frequency when the discard timing is BTDC 480°CA in Experimental Example 4, Figure 15 is a graph showing the relationship between the crank angle and the re-discharge frequency when the discard timing is BTDC 420°CA in Experimental Example 4, Figure 16 is a graph showing the relationship between the crank angle and the re-discharge frequency when the discard timing is BTDC 360°CA in Experimental Example 4, Figure 17 is a graph showing the relationship between the crank angle and the re-discharge frequency in Experimental Example 4,Figure 18 shows the relationship between the crank angle and the re-discharge frequency when the discharge timing is set to 340°CA BTDC. Figure 19 shows the relationship between the crank angle and the re-discharge frequency when a discharge is performed with the exhaust valve open in Experimental Example 5. Figure 20 shows the relationship between the primary current value at the discharge timing and the residual energy voltage after the discharge when a discharge is performed with the exhaust valve open in Experimental Example 5. Figure 21 shows the relationship between the crank angle and the re-discharge frequency when a discharge is performed with the intake opening timing 30°CA in Experimental Example 5. Figure 22 shows the relationship between the primary current value during discharge and the coil temperature in Experimental Example 6.

[0011] (Embodiment 1) An embodiment relating to an internal combustion engine will be described with reference to Figures 1 to 4. The internal combustion engine 1 of this embodiment includes a combustion chamber 10, a spark plug 2, an ignition coil 3, a control unit 4, and a fuel supply unit 5, as shown in Figures 1 and 2. The combustion chamber 10 is supplied with fuel containing hydrogen. The spark plug 2 ignites the fuel in the combustion chamber 10 by a discharge generated in the discharge gap G. The ignition coil 3 applies a high voltage to the spark plug 2. The control unit 4 controls the execution of the discharge of the spark plug 2 by controlling the supply of current to the ignition coil 3. The fuel supply unit 5 supplies fuel to the combustion chamber 10.

[0012] The control unit 4 controls the system to perform both a normal discharge and a waste discharge in the discharge gap G. The normal discharge is a discharge to ignite the fuel in the combustion chamber 10. The waste discharge is a discharge to release the energy remaining in the ignition coil 3 after the normal discharge. The discharge energy in the waste discharge is smaller than the discharge energy in the normal discharge. As shown in Figure 4, the control unit 4 controls the system to perform the waste discharge between the time the normal discharge is performed and the time the fuel supply unit 5 supplies fuel to the combustion chamber 10.

[0013] The internal combustion engine 1 of this embodiment can be used, for example, as an engine for an automobile that uses hydrogen gas as fuel. As shown in Figure 2, the internal combustion engine 1 of this embodiment comprises a cylinder head 14, a cylinder block 17, and a piston 15 that reciprocates within a cylinder 150. A combustion chamber 10 is formed surrounded by the cylinder head 14, the cylinder block 17, and the piston 15. The cylinder head 14 has an intake port 610 and an exhaust port 620, each equipped with an intake valve 61 or an exhaust valve 62. A spark plug 2 is installed between the intake port 610 and the exhaust port 620 in the cylinder head 14. The tip of the spark plug 2 is exposed to the combustion chamber 10.

[0014] Furthermore, the cylinder head 14 is provided with a fuel supply unit 5. In this embodiment, the fuel supply unit 5 is a fuel injection valve that injects fuel gas into the combustion chamber 10. In this embodiment, the fuel supply unit 5 injects fuel directly into the combustion chamber 10.

[0015] The volume of the combustion chamber 10 fluctuates as the piston 15 moves back and forth. The internal combustion engine 1 then sequentially repeats a cycle consisting of an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke due to the reciprocating motion of the piston 15. The internal combustion engine 1 in this configuration is a four-stroke engine.

[0016] Specifically, during the intake stroke, as the piston 15 moves down and the intake valve 61 opens, air flows into the combustion chamber 10 from the intake port 610. In this configuration, the fuel supply unit 5 injects hydrogen gas, which is the fuel, into the combustion chamber 10 between a predetermined timing in the intake stroke and a predetermined timing in the compression stroke. Then, as the intake valve 61 closes and the piston 15 moves up to top dead center during the compression stroke, the gas containing hydrogen is compressed. The compressed gas is ignited by a normal discharge from the spark plug 2 and burns, and the expansion of the burned gas pushes the piston 15 down to bottom dead center. Next, during the exhaust stroke, as the pushed-down piston 15 moves up due to inertia, the exhaust valve 62 opens, and the burned gas is pushed out of the combustion chamber 10 through the exhaust port 620. Then, the exhaust valve 62 closes and the intake valve 61 opens, causing the piston 15 to move downward, which initiates the intake stroke, allowing air to flow into the combustion chamber 10. This process is repeated. Using the top dead center (TDC) of the compression stroke as a reference, in this configuration, the expansion stroke period is from before top dead center (BTDC) 720°CA (abbreviation for Crank Angle) to BTDC 540°CA, and the exhaust stroke period is from BTDC 540°CA to BTDC 360°CA. The intake stroke period is from BTDC 360°CA to BTDC 180°CA, and the compression stroke period is from BTDC 180°CA to BTDC 0°CA.

[0017] Furthermore, as shown in Figures 2 and 3, the spark plug 2 comprises a center electrode 21, a ground electrode 22, a cylindrical insulator 23, and a cylindrical housing 24. The housing 24 holds the insulator 23 inside and has a threaded portion 241 on a part of its outer circumference. As shown in Figure 2, the spark plug 2 is attached to the internal combustion engine 1 by screwing the threaded portion 241 of the housing 24 into the female threaded portion of the plug hole 141 of the cylinder head 14. One end of the spark plug 2 in the axial direction Z is positioned in the combustion chamber 10 of the internal combustion engine. In this specification, in the axial direction Z of the spark plug 2, the side positioned in the combustion chamber 10 is referred to as the tip side, and the opposite side is referred to as the base side.

[0018] As shown in Figure 3, the ground electrode 22, which forms a discharge gap G with the central electrode 21, is joined to the tip of the housing 24. The central electrode 21 is held on the inner circumference side of the insulator 23 and is exposed from the insulator 23 toward the tip. In this embodiment, the discharge gap G is formed by the central electrode 21 and the ground electrode 22 facing each other in the axial direction Z of the spark plug 2 and is exposed to the combustion chamber 10. The length L1 of the discharge gap G can be, for example, 0.3 mm or more. In the discharge gap G, the upper limit of the length L1 is preferably 0.5 to 0.6 mm. Furthermore, the length L1 is more preferably 0.55 mm or less. In this embodiment, the length L1 is the axial length Z of the discharge gap G.

[0019] Furthermore, as shown in Figure 1, the internal combustion engine 1 in this embodiment has a battery 11 as a power source that supplies power to the ignition coil 3. The ignition coil 3 also has an igniter 12, a coil section 30, a core section 33, and a diode 13.

[0020] The ignition coil 3 comprises a primary coil 31 and a secondary coil 32 that are magnetically coupled to each other. In other words, the coil section 30 comprises a primary coil 31 and a secondary coil 32. Although not shown in the illustration, in the coil section 30, the winding axis of the primary coil 31 is coaxial with the winding axis of the secondary coil 32. The secondary coil 32 is formed by winding a secondary wire thinner than the primary wire constituting the primary coil 31 on the outer circumference side of the primary coil 31, with a greater number of turns than the primary wire. The number of turns of the secondary wire in the secondary coil 32 can be, for example, 65 to 75 times the number of turns of the primary wire in the primary coil 31. Also, although not shown in the illustration, a core section 33 is inserted on the inner circumference side of the primary coil 31. The core section 33 allows the magnetic flux generated by energizing the primary coil 31 to pass through. In this embodiment, the core section 33 is made by laminating a plurality of magnetic steel plates.

[0021] The igniter 12 energizes and disconnects the primary coil 31 in response to an ignition instruction signal from the control unit 4. In this configuration, the igniter 12 is switched on and off based on the ignition instruction signal from the control unit 4, thereby boosting the voltage of the battery 11 in the coil section 30 and applying a high voltage to the spark plug 2.

[0022] In other words, the control unit 4 applies a high voltage to the spark plug 2 at a predetermined timing by controlling the ignition coil 3. This causes a spark discharge to occur in the discharge gap G of the spark plug 2, either as a normal discharge or a waste discharge. The control unit 4 can, for example, control the transmission of an ignition command signal to the ignition coil 3 based on crank angle information detected by a crank angle sensor (not shown). The control unit 4 also includes a processor and memory.

[0023] The diode 13 of the ignition coil 3 has the role of restricting the direction of the secondary current flowing through the secondary coil 32 to a direction from the spark plug 2 towards the secondary coil 32. The anode side of the diode 13 is connected to the secondary coil 32, and the cathode side is grounded.

[0024] The secondary coil 32 supplies discharge energy to the spark plug 2. The internal combustion engine 1 also has an intake valve 61 and an exhaust valve 62 provided in the combustion chamber 10, as described above. In this embodiment, the control unit 4 controls the system to perform a discharge at least between 30°CA before the intake opening timing and 30°CA after the intake opening timing, or when the exhaust valve 62 is open. The intake opening timing is the timing when the intake valve 61 opens. When performing a discharge between 30°CA before the intake opening timing and 30°CA after the intake opening timing, the control unit 4 controls the system to perform a discharge by cutting off the power supply to the primary coil 31 when the magnitude of the current flowing through the primary coil 31 becomes 1.5A or more, after starting to supply power to the primary coil 31 in order to perform the discharge. Furthermore, when performing a discharge while the exhaust valve 62 is open, the control unit 4 controls the system to perform the discharge by cutting off the power supply to the primary coil 31 when the magnitude of the current flowing through the primary coil 31 becomes 2.0 A or more, after starting to supply power to the primary coil 31.

[0025] Furthermore, when performing a discard discharge, the control unit 4 controls the system to perform the discard discharge by cutting off the power supply to the primary coil 31 after starting to supply power to the primary coil 31, before the magnitude of the current flowing through the primary coil 31 exceeds 2.5 A. It is preferable to perform the discard discharge with the minimum energy required to generate a spark discharge in the discharge gap G.

[0026] In this embodiment, as shown in Figure 4, the control unit 4 controls the system to perform a waste discharge by cutting off the power supply to the primary coil 31 when the magnitude of the primary current flowing through the primary coil 31 reaches 2.0 A. The control unit 4 can also control the system to perform a normal discharge by cutting off the power supply to the primary coil 31 when the magnitude of the primary current reaches, for example, 8 to 10 A. In this embodiment, the control unit 4 controls the system to perform a normal discharge by cutting off the power supply to the primary coil 31 when the magnitude of the primary current reaches 10 A. Furthermore, as shown in Figure 4, the power supply time to the primary coil 31 is shorter when performing a waste discharge than when performing a normal discharge. In this embodiment, a waste discharge is performed once per combustion cycle.

[0027] In this embodiment, the control unit 4 determines the timing of the discharge based on the crank angle information as well as the opening and closing timing information of the intake valve 61 and the exhaust valve 62. The control unit 4 controls the discharge to be performed at least between 30°CA before the intake opening timing and 30°CA after the intake opening timing, or between 70°CA after the exhaust opening timing and 90°CA after the exhaust opening timing. The exhaust opening timing is the timing when the exhaust valve 62 opens.

[0028] Furthermore, the control unit 4 changes the opening and closing timing of the intake valve 61 and the exhaust valve 62 according to the operating conditions of the internal combustion engine 1. Here, the operating conditions of the internal combustion engine 1 can be, for example, the rotational speed and load of the internal combustion engine 1.

[0029] The intake opening timing can be, for example, BTDC 400°CA to BTDC 360°CA, and the intake closing timing, which is the timing when the intake valve 61 closes, can be, for example, BTDC 150°CA to BTDC 110°CA. The exhaust opening timing can be, for example, BTDC 600°CA to BTDC 570°CA, and the exhaust closing timing, which is the timing when the exhaust valve 62 closes, can be, for example, BTDC 360°CA to BTDC 330°CA. It is also possible to adopt a configuration in which a portion of the opening period of the intake valve 61 and a portion of the opening period of the exhaust valve 62 overlap.

[0030] Furthermore, the fuel supply period, which is the period during which fuel is supplied to the combustion chamber 10 by the fuel supply unit 5, can be set, for example, within the period from BTDC 245°CA to BTDC 50°CA.

[0031] Next, the effects of this embodiment will be explained. In the internal combustion engine 1 described above, the control unit 4 controls the system to perform a waste discharge between the time a normal discharge is performed and the time fuel is supplied to the combustion chamber 10. Therefore, it is possible to suppress the occurrence of a discharge in the discharge gap G at an unintended timing after fuel has been supplied to the combustion chamber 10. As a result, it is possible to suppress the combustion of fuel at an unintended timing.

[0032] Generally, internal combustion engines ignite fuel in the combustion chamber by generating a spark discharge as a normal discharge in the discharge gap. Additionally, when a voltage exceeding the required voltage is applied to the discharge gap by an ignition command from the control unit, a spark discharge occurs in the discharge gap due to dielectric breakdown. As long as a voltage exceeding the required voltage is applied to the discharge gap, the spark discharge is maintained, and energy is consumed to generate the spark discharge. When the voltage applied to the discharge gap falls below the required voltage, the formation of the spark discharge stops. However, even after the normal discharge stops, energy for generating a spark discharge may remain in the form of magnetic energy in the core, etc. Furthermore, especially in hydrogen engines, due to the high combustion rate of hydrogen gas, the fuel mixture may be leaned, and a supercharger may be used to supply more air to the combustion chamber during normal discharge. Therefore, the pressure in the combustion chamber during normal discharge tends to be high, and the required voltage of the discharge gap tends to be high. Furthermore, hydrogen gas contained in the fuel is less likely to ionize compared to gasoline, etc., so the energy remaining after a normal discharge (hereinafter referred to as residual energy) is not easily consumed. Here, let's consider an internal combustion engine in a comparative configuration that does not perform a void discharge. In this case, residual energy may not be sufficiently consumed after a normal discharge, and residual energy in the core, etc., may be maintained until the fuel supply period. Also, the pressure in the combustion chamber is lower during the fuel supply period than when a normal discharge is performed. Therefore, during the fuel supply period, as the pressure in the combustion chamber decreases, the required voltage of the discharge gap decreases, which may cause unintended discharge in the discharge gap due to residual energy, potentially leading to abnormal combustion such as pre-ignition. Therefore, the internal combustion engine 1 in this configuration performs a void discharge. This allows residual energy to be consumed along with the energy supplied to the primary coil 31 for the void discharge, thereby reducing the residual energy. Therefore, even when the pressure in the combustion chamber 10 becomes relatively low after the fuel supply period, it is possible to suppress the occurrence of discharge in the discharge gap G. As a result, it is possible to suppress the combustion of fuel at unintended timings.As a result, even under high-load operation, abnormal combustion such as pre-ignition can be sufficiently suppressed, leading to improved fuel efficiency and increased power output.

[0033] Furthermore, the waste discharge is performed by energizing the primary coil 31, just like a normal discharge. Therefore, residual energy can be reduced without the need to provide any new parts to consume residual energy. As a result, abnormal combustion can be suppressed while simplifying the structure of the internal combustion engine 1.

[0034] The control unit 4 controls the system to perform a discharge at least between 30°CA before the intake opening timing and 30°CA after the intake opening timing, or when the exhaust valve 62 is open. When a discharge is performed between 30°CA before the intake opening timing and 30°CA after the intake opening timing, the control unit 4 controls the system to perform the discharge by cutting off the power supply to the primary coil 31 when the magnitude of the current flowing through the primary coil 31 becomes 1.5A or more. Furthermore, when a discharge is performed when the exhaust valve 62 is open, the control unit 4 controls the system to perform the discharge by cutting off the power supply to the primary coil 31 when the magnitude of the current flowing through the primary coil 31 becomes 2.0A or more. As a result, as will be explained in Experimental Example 5 later, the residual energy remaining in the ignition coil 3, etc., can be consumed more sufficiently by performing a discharge. As a result, it is possible to further suppress the occurrence of discharge in the discharge gap G at unintended timings.

[0035] The control unit 4 controls the system to perform a void discharge by cutting off the power supply to the primary coil 31 before the magnitude of the current flowing through the primary coil 31 exceeds 2.5 A. Therefore, as will be explained in Experimental Example 6 later, overheating of the coil section 30 can be sufficiently suppressed. As a result, deterioration of the ignition coil 3 can be prevented, and its lifespan can be extended.

[0036] The control unit 4 controls the system to perform a void discharge at least between 30°CA before the intake opening timing and 30°CA after the intake opening timing, or between 70°CA after the exhaust opening timing and 90°CA after the exhaust opening timing. Therefore, as will be explained in Experimental Example 4 later, a sufficient period for void discharge can be secured, and residual energy can be consumed more easily. As a result, it is possible to further suppress the occurrence of discharge in the discharge gap G at unintended timings.

[0037] In this embodiment, the waste discharge is performed once per combustion cycle. Therefore, overheating of the coil section 30 can be suppressed, while preventing discharge from occurring in the discharge gap G at unintended timings.

[0038] Furthermore, it is preferable to perform the void discharge with the minimum energy required to generate a spark discharge in the discharge gap G. In this case, the residual energy after the normal discharge can be consumed even more, and the temperature rise of the coil section 30 can be further suppressed.

[0039] As described above, this embodiment provides an internal combustion engine 1 that can suppress the combustion of fuel at unintended timings.

[0040] (Experimental Example 1) In this example, as shown in Figures 5 and 6, the relationship between discharge and re-discharge was investigated using an internal combustion engine with the same basic structure as in Embodiment 1. Here, re-discharge refers to a discharge that occurs in the discharge gap at an unintended timing after normal discharge. As experimental conditions, the internal combustion engine used hydrogen gas as fuel, with a rotational speed of 4000 rpm and a torque of 150 Nm. Discharge was performed when the crank angle was BTDC 360°CA. Discharge was also performed by cutting off the power supply to the primary coil when the magnitude of the primary current reached 1.5 A.

[0041] Figure 5 is a graph showing the results of 1000 combustion cycles overlaid on each other, and Figure 6 is a graph showing the results of a typical combustion cycle. As shown in Figures 5 and 6, during period A, after normal discharge and before the execution of a waste discharge, the change in the secondary voltage of the ignition coil is large, indicating that unintended re-discharge occurs frequently. The re-discharge during period A is thought to be caused by residual energy from the ignition coil, etc. On the other hand, during period B after the waste discharge, almost no re-discharge was observed, and in particular, no re-discharge was observed during the fuel supply period. Furthermore, the secondary voltage during period B is significantly lower than the secondary voltage during period A. This is thought to be because residual energy was sufficiently consumed by the execution of the waste discharge. From these results, it can be said that the internal combustion engine of Embodiment 1, which performs a waste discharge, can suppress the occurrence of re-discharge after the fuel supply period and can suppress the combustion of fuel at unintended timings.

[0042] (Experimental Example 2) In this example, as shown in Figure 7, an internal combustion engine with the same basic structure as in Embodiment 1 was used to investigate the relationship between the crank angle and the secondary voltage in the secondary coil, both when a void discharge was performed and when it was not. In the graph in Figure 7, the normal discharge period indicates the period during which normal discharge is maintained. The void discharge was performed when the crank angle was BTDC 510°CA. Other conditions were the same as in Experimental Example 1.

[0043] As shown in the graph in Figure 7, it can be seen that performing a discharge significantly reduces the secondary voltage compared to the case without a discharge. Specifically, performing a discharge reduces the secondary voltage by the amount indicated by arrow R in Figure 7. This is thought to be because the residual energy of the ignition coil, etc., is consumed by performing the discharge. Therefore, it is thought that the internal combustion engine of Embodiment 1, which performs a discharge, can sufficiently reduce the secondary voltage after a normal discharge, thereby suppressing re-discharge during fuel supply periods, etc.

[0044] (Experimental Example 3) In this example, as shown in FIGS. 8 and 9, using an internal combustion engine having the same basic structure as that of Embodiment 1, verification was performed on the presence or absence of re-discharge after the fuel supply period when discard discharge was executed and when it was not executed. As experimental conditions, the internal combustion engine was a V-type 6-cylinder, with a displacement of 3.5 L, a rotational speed of 4000 rpm, a torque of 150 Nm, hydrogen gas as fuel, and the length L1 of the discharge gap was 0.3 mm. Also, the fuel supply period was set from BTDC 200°CA to BTDC 100°CA.

[0045] The graph in FIG. 8 is a graph showing the experimental results of a comparative example in which discard discharge is not executed, and the graph in FIG. 9 is a graph showing the experimental results of an example in which discard discharge is executed. Each of the graphs in FIG. 8 and FIG. 9 is a graph summarizing the results of performing 1000 combustion cycles. Also, in the example shown in FIG. 9, the discard discharge was executed by interrupting the energization when the magnitude of the primary current was 1.5 A, and it was executed at the timing of BTDC 360°CA. Also, in the graph of FIG. 9, in the region indicated by the slanted lines, at a crank angle before BTDC 360°CA, the number of re-discharges was not measured, and only the number of re-discharges after BTDC 360°CA was displayed.

[0046] As shown in the graph of FIG. 8, when discard discharge was not executed, re-discharge was confirmed during the fuel supply period. On the other hand, as shown in the graph of FIG. 9, when discard discharge was executed, compared with the comparative example, the re-discharge frequency after BTDC 360°CA was low, and re-discharge was not confirmed during the fuel supply period. From this result, it can be said that the internal combustion engine of Embodiment 1 that executes discard discharge can suppress the occurrence of re-discharge after the fuel supply period

[0047] (Experimental Example 4) In this example, as shown in FIGS. 10 to 17, using an internal combustion engine having the same basic structure as that of Embodiment 1, the timing of interrupting the energization to the primary coil for the purpose of performing discard discharge and the relationship with the re-discharge during the fuel supply period were investigated. As experimental conditions, the intake opening timing was set to BTDC 390° CA, the intake closing timing was set to BTDC 140° CA, the exhaust opening timing was set to BTDC 600° CA, and the exhaust closing timing was set to BTDC 360° CA. Other experimental conditions were the same as those in Experimental Example 1. Hereinafter, the timing of interrupting the energization to the primary coil for the purpose of performing discard discharge is referred to as the discard timing. Also, in this example, the presence or absence of re-discharge was determined based on the detection of the decrease in the secondary voltage in the ignition coil. Further, the graphs in FIGS. 11 to 17 are graphs summarizing the results when the combustion cycle was performed 1000 times, respectively.

[0048] The graphs in Figures 10 to 17 show that when the discharge timing is BTDC360°CA, BTDC420°CA, BTDC510°CA, and BTDC530°CA, no re-discharge occurs during the fuel supply period. On the other hand, when the discharge timing is BTDC340°CA, BTDC480°CA, and BTDC540°CA, although the probability of occurrence is low at 0.1%, re-discharge does occur during the fuel supply period. From these results, it is thought that re-discharge during the fuel supply period can be sufficiently suppressed by interrupting the power supply to the primary coil for the purpose of performing a discharge, between 30°CA before the intake opening timing and 30°CA after the intake opening timing, and between 70°CA after the exhaust opening timing and 90°CA after the exhaust opening timing. It is presumed that these periods in which no re-discharge occurred during the fuel supply period are periods in which the airflow near the discharge gap in the combustion chamber is relatively weak. Therefore, it is presumed that by performing a discharge during these periods, it is possible to sufficiently suppress the stretching, interruption, or short-circuiting of the discharge due to strong airflow. As a result, it is presumed that the discharge can be maintained for a sufficient period, and residual energy can be fully consumed. Thus, from the results of this example, it is considered that the internal combustion engine of Embodiment 1, which performs a discharge at least between 30°CA before the intake opening timing and 30°CA after the intake opening timing, or between 70°CA after the exhaust opening timing and 90°CA after the exhaust opening timing, can further suppress the occurrence of re-discharge during the fuel supply period.

[0049] (Experimental Example 5) In this example, as shown in Figures 18 to 21, the relationship between the magnitude of the primary current during the discharge and the residual energy voltage was investigated. Here, the residual energy voltage refers to the secondary voltage after the discharge timing, which is an indicator of residual energy. As experimental conditions, the period during which the exhaust valve was open was from BTDC 600°CA to BTDC 360°CA, and the period during which the intake valve was open was from BTDC 390°CA to BTDC 140°CA. The discharge timing was set to when the exhaust valve was open or from 30°CA before the intake opening timing to 30°CA after the intake opening timing. Specifically, the discharge timing was set to BTDC 510°CA when the exhaust valve was open, or BTDC 360°CA 30°CA after the intake opening timing. The magnitude of the primary current at the discharge timing was set to 1.5A, 2.0A, and 2.5A. Other experimental conditions were the same as in Experimental Example 1. Furthermore, the graphs in Figures 18 to 21 summarize the results after 1000 combustion cycles, respectively.

[0050] Figures 18 and 19 are graphs showing the results when the discharge timing is set to when the exhaust valve is open. As shown in the graph in Figure 18, the residual energy voltage is lower when a discharge is performed compared to when no discharge is performed. This is thought to be because residual energy is consumed by the discharge. Furthermore, when the magnitude of the primary current at the discharge timing is 2.0A and 2.5A, the residual energy voltage is lower compared to when the magnitude of the primary current is 1.5A. From these results, it can be said that when a discharge is performed when the exhaust valve is open, setting the magnitude of the primary current at the discharge timing to 2.0A or higher allows the discharge to be maintained for a more sufficient period and residual energy to be consumed more effectively. Also, looking at the graph in Figure 19, it can be seen that performing a discharge sufficiently suppresses the occurrence of re-discharge during the fuel supply period.

[0051] Figures 20 and 21 are graphs showing the results when the discharge timing is set to 30°CA after the intake opening timing. As shown in the graph of Figure 20, it can be seen that the residual energy voltage is significantly lower for all primary current magnitudes at the discharge timing compared to when no discharge is performed. From these results, it can be said that when a discharge is performed 30°CA after the intake opening timing, even more residual energy can be consumed by setting the primary current magnitude at the discharge timing to 1.5A or more. Also, looking at the graph of Figure 21, it can be seen that the occurrence of re-discharge during the fuel supply period is sufficiently suppressed by performing a discharge. In addition, although not shown in the figures, the results were similar to those shown in Figures 20 and 21 when the discharge timing was set from 30°CA before the intake opening timing to the intake opening timing. Therefore, from the results in Figures 18 to 21, it is considered that the internal combustion engine of Embodiment 1, which performs a discharge when the primary current reaches 1.5A or more when a discharge is performed between 30°CA before the intake opening timing and 30°CA after the intake opening timing, and performs a discharge when the primary current reaches 2.0A or more when a discharge is performed while the exhaust valve is open, can sufficiently suppress the occurrence of re-discharge during the fuel supply period.

[0052] (Experimental Example 6) In this example, as shown in Figure 22, an internal combustion engine with the same basic structure as in Embodiment 1 was used to verify the relationship between the magnitude of the primary current in a discharge discharge and the temperature of the coil section of the ignition coil. As experimental conditions, a normal discharge was performed by interrupting the power supply to the primary coil when the magnitude of the primary current reached 10 A. In this example, the magnitude of the primary current in the discharge timing was varied in the range of 1 to 3 A for verification. The normal discharge was performed at BTDC 20°CA, and the discharge timing was set to BTDC 360°CA. The temperature of the coil section was measured one hour after the start of the experiment, and the relationship between the discharge discharge and the temperature of the coil section was verified. Other experimental conditions were the same as in Experimental Example 1. In this example, the criterion for sufficiently suppressing the deterioration of the ignition coil was that the temperature of the coil section one hour after the start of the experiment was below the heat resistance temperature of the coil section. Therefore, the magnitude of the primary current in a discharge discharge that satisfies this criterion was determined from the results of this example.

[0053] In the graph of Figure 22, the circles plot the temperature of the coil section for each primary current value of the discard discharge. The graph of Figure 22 also shows an approximate straight line for these plots. As shown in the graph of Figure 22, it can be seen that the temperature of the coil section decreases as the magnitude of the primary current of the discard discharge decreases. Furthermore, from the approximate straight line, it can be inferred that the above criterion is met when the magnitude of the primary current of the discard discharge is 2.5 A or less. From these results, it can be said that the internal combustion engine of Embodiment 1, in which the magnitude of the primary current is 2.5 A or less when performing a discard discharge, can sufficiently prevent the temperature rise of the coil section and sufficiently suppress the deterioration of the ignition coil.

[0054] In the above embodiment 1, the internal combustion engine 1 is of the direct injection type. However, the internal combustion engine may also be of the port injection type, for example, in which fuel is injected into the intake port. Furthermore, the internal combustion engine may also be equipped with both a fuel supply unit that directly injects fuel into the combustion chamber and a fuel supply unit that injects fuel into the intake port.

[0055] In the above embodiment 1, the magnitude of the primary current for normal discharge is 10A. However, it is also possible to adopt a configuration in which the discharge energy required for the waste discharge is deducted from the discharge energy of the normal discharge in advance. For example, if the magnitude of the primary current at the waste timing is 2A, the magnitude of the primary current at the time of power interruption in normal discharge can be set to 8A. In this case, it is easier to reduce the power supplied to the coil section per combustion cycle. Therefore, overheating of the coil section can be further suppressed, and deterioration of the ignition coil can be further suppressed. Even when such a configuration is adopted, the normal discharge is performed with discharge energy that is sufficient to ignite the fuel, as in embodiment 1.

[0056] Furthermore, normal discharge can also be performed using a primary current value obtained by subtracting the primary current value during a discard discharge from the maximum primary current value in the ignition coil's performance.

[0057] In the above embodiment 1, the waste discharge is performed once during one combustion cycle. However, the waste discharge can be performed multiple times during one combustion cycle, as long as overheating of the coil is suppressed.

[0058] This disclosure is not limited to the embodiments described above, and can be applied to various embodiments without departing from its essence.

[0059] This disclosure is described in accordance with embodiments, but it is understood that this disclosure is not limited to such embodiments or structures. This disclosure also encompasses various variations and variations within the equivalence range. In addition, various combinations and forms, as well as other combinations and forms that include one, more, or fewer of those elements, fall within the scope and concept of this disclosure.

[0060] <Other> The features of this disclosure are as follows: [Item 1] An internal combustion engine (1) comprising: a combustion chamber (10) to which a hydrogen-containing fuel is supplied; a spark plug (2) that ignites the fuel in the combustion chamber by a discharge occurring in a discharge gap (G); an ignition coil (3) that applies a high voltage to the spark plug; a control unit (4) that controls the execution of the discharge of the spark plug by controlling the supply of current to the ignition coil; and a fuel supply unit (5) that supplies the fuel to the combustion chamber, wherein the control unit controls the discharge gap to perform a normal discharge to ignite the fuel in the combustion chamber and a waste discharge to release the energy remaining in the ignition coil after the normal discharge, the discharge energy in the waste discharge is smaller than the discharge energy in the normal discharge, and the control unit controls the waste discharge to be performed between the time after the execution of the normal discharge and before the fuel is supplied to the combustion chamber by the fuel supply unit. [Item 2] The ignition coil comprises a primary coil (31) and a secondary coil (32) that are magnetically coupled to each other, the secondary coil supplies discharge energy to the spark plug, and the combustion chamber has an intake valve (61) and an exhaust valve (62), the control unit controls the execution of the waste discharge at least from 30°CA before the intake opening timing, which is the timing when the intake valve opens, to 30°CA after the intake opening timing, or when the exhaust valve is open, and when the waste discharge is executed between 30°CA before the intake opening timing and 30°CA after the intake opening timing, the control unit controls the execution of the waste discharge by cutting off the power supply to the primary coil when the magnitude of the current flowing through the primary coil becomes 1.5A or more after the power supply to the primary coil has been started in order to execute the waste discharge, The internal combustion engine according to item 1, wherein when the discharge is performed while the exhaust valve is open, the control unit controls the discharge to be performed by cutting off the power supply to the primary coil when the magnitude of the current flowing through the primary coil becomes 2.0 A or more after the power supply to the primary coil has been started to perform the discharge.[Clause 3] The ignition coil comprises a primary coil (31) and a secondary coil (32) that are magnetically coupled to each other, the secondary coil supplies discharge energy to the spark plug, and the control unit controls the execution of the waste discharge by interrupting the power supply to the primary coil after starting to energize the primary coil, before the magnitude of the current flowing through the primary coil exceeds 2.5 A. [Clause 4] The internal combustion engine according to any one of Clauses 1 to 3, further comprising an intake valve (61) and an exhaust valve (62) provided in the combustion chamber, wherein the control unit controls the execution of the waste discharge at least between 30° CA before the intake opening timing, which is the timing when the intake valve opens, and 30° CA after the intake opening timing, or between 70° CA after the exhaust opening timing, which is the timing when the exhaust valve opens, and 90° CA after the exhaust opening timing.

Claims

1. An internal combustion engine (1) comprising: a combustion chamber (10) to which a hydrogen-containing fuel is supplied; a spark plug (2) that ignites the fuel in the combustion chamber by a discharge occurring in a discharge gap (G); an ignition coil (3) that applies a high voltage to the spark plug; a control unit (4) that controls the execution of the discharge of the spark plug by controlling the supply of current to the ignition coil; and a fuel supply unit (5) that supplies the fuel to the combustion chamber, wherein the control unit controls the discharge gap to perform a normal discharge to ignite the fuel in the combustion chamber and a waste discharge to release the energy remaining in the ignition coil after the normal discharge, the discharge energy in the waste discharge is smaller than the discharge energy in the normal discharge, and the control unit controls the waste discharge to be performed between the time after the normal discharge and before the fuel is supplied to the combustion chamber by the fuel supply unit.

2. The ignition coil comprises a primary coil (31) and a secondary coil (32) that are magnetically coupled to each other, the secondary coil supplying discharge energy to the spark plug, and the combustion chamber having an intake valve (61) and an exhaust valve (62), the control unit controls the execution of the discharge at least between 30°CA before the intake opening timing, which is the timing when the intake valve opens, and 30°CA after the intake opening timing, or when the exhaust valve is open, and when the discharge is executed between 30°CA before the intake opening timing and 30°CA after the intake opening timing, the control unit controls the execution of the discharge by cutting off the power supply to the primary coil when the magnitude of the current flowing through the primary coil becomes 1.5A or more after the power supply to the primary coil has been started in order to execute the discharge, The internal combustion engine according to claim 1, in which, when the waste discharge is performed while the exhaust valve is open, the control unit controls the execution of the waste discharge by cutting off the power supply to the primary coil when the magnitude of the current flowing through the primary coil becomes 2.0 A or more after the power supply to the primary coil has been started to execute the waste discharge.

3. The internal combustion engine according to claim 1 or 2, wherein the ignition coil comprises a primary coil (31) and a secondary coil (32) that are magnetically coupled to each other, the secondary coil supplies discharge energy to the spark plug, and the control unit controls the execution of the waste discharge by interrupting the power supply to the primary coil after starting to energize the primary coil, before the magnitude of the current flowing through the primary coil exceeds 2.5 A.

4. An internal combustion engine according to claim 1 or 2, having an intake valve (61) and an exhaust valve (62) provided in the combustion chamber, wherein the control unit controls the execution of the discharge at least between 30°CA before the intake opening timing, which is the timing when the intake valve opens, and 30°CA after the intake opening timing, or between 70°CA after the exhaust opening timing, which is the timing when the exhaust valve opens, and 90°CA after the exhaust opening timing.

Images