Ignition system

Abstract

The ignition system comprises: a spark plug (40) and an ignition control unit (50) for controlling the spark plug. When the engine (90) is in a specified operating state, the ignition control unit (50) performs a post-top dead center ignition control for igniting after compression top dead center (Ta). The ignition system comprises an airflow assist structure (As) for making it easy for airflow to flow to a discharge gap (45) at least after compression top dead center (Ta). The ignition system is configured such that, through the airflow assist structure (As) and the timing (Taf) of ignition, an airflow with a flow rate of 5 m / s or more flows to the discharge gap (45) during a post-top dead center spark period during which a discharge spark (F) of the post-top dead center ignition control is generated.

Description

Technical Field

[0001] The present disclosure relates to an ignition system for igniting fuel within a combustion chamber of an engine. Background Art

[0002] An ignition system generally includes a spark plug. In most cases, the spark plug includes a center electrode and a ground electrode facing the center electrode. The ground electrode includes a vertical portion extending in the length direction of the spark plug and an opposing portion extending inward from the front end of the vertical portion and facing the center electrode. A discharge spark is generated by applying a voltage to a discharge gap between the center electrode and the opposing portion, thereby igniting fuel in the combustion chamber.

[0003] The ignition is described in more detail below. The airflow caused by the tumble or swirl generated in the combustion chamber flows into the discharge gap. Through the airflow, the discharge spark extends to the leeward side, and the ignitability is improved. However, depending on the form of the tumble or swirl, the position of the discharge gap is sometimes just on the leeward side of the upright portion of the ground electrode. In this case, the airflow is blocked by the upright portion, so that the airflow flowing to the discharge gap becomes weaker. As a result, the extension of the discharge spark becomes smaller, and the ignitability caused by the discharge spark decreases. Therefore, in the patent document 1 shown below, wind guide protrusions for guiding the airflow to the discharge gap are arranged on the lateral side of the upright portion of the ground electrode.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 5919214 Summary of the invention

[0007] According to the above technology, even when the position of the discharge gap is just downwind of the upright portion of the ground electrode, the airflow caused by the tumble or vortex is guided to the discharge gap by the air guide protrusion before the compression top dead center, and the airflow flowing to the discharge gap can be strengthened. Therefore, when ignition is performed before the compression top dead center, the discharge spark can be extended to improve the ignitability.

[0008] However, when the engine is in a predetermined operating condition, such as during high-speed idling for catalyst preheating, ignition may be performed after the compression top dead center instead of before the compression top dead center. In this case, the tumble or vortex itself often temporarily collapses when the piston passes the compression top dead center. Therefore, it is difficult to guide the airflow brought by the tumble or vortex to the discharge gap through the air guide protrusion after the compression top dead center. Therefore, when ignition is performed by the discharge spark after the compression top dead center, it is difficult to improve the ignitability brought by the discharge spark.

[0009] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to improve the ignitability by the discharge spark when ignition by the discharge spark is performed after compression top dead center.

[0010] The ignition system disclosed in the present invention comprises: a spark plug that generates a discharge spark by applying a voltage to a discharge gap in a combustion chamber of an engine to ignite fuel; and an ignition control unit that controls the spark plug. The ignition control unit performs a post-top dead center ignition control that performs the ignition after compression top dead center when the engine is in a predetermined operating state.

[0011] The ignition system has an airflow assist structure that makes it easy for the airflow to flow to the discharge gap at least after the compression top dead center. Furthermore, the ignition system is configured so that, through the airflow assist structure and the timing (time point) of the ignition, the airflow with a flow rate of 5 m / s or more flows to the discharge gap during the post-top dead center spark period, which is the period during which the discharge spark occurs in the post-top dead center ignition control.

[0012] According to the present disclosure, the airflow assist structure and the timing (time point) of ignition are configured so that an airflow with a flow rate of 5 m / s or more flows into the discharge gap during the spark period after the top dead center, so that the discharge spark can be extended by the airflow to improve the ignitability. As a result, when ignition is performed by the discharge spark after the compression top dead center, the ignitability based on the discharge spark can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Regarding the above-mentioned object and other objects, features and advantages of the present disclosure, reference is made to the attached Figure 1 This will become clearer through the following detailed description.

[0014] Figure 1 This is a schematic diagram showing an ignition system and its periphery according to the first embodiment.

[0015] Figure 2 This is a cross-sectional view showing a pre-combustion chamber (Japanese: pre-chamber) and its surroundings.

[0016] Figure 3 It is a schematic diagram showing the state of airflow before and after the compression top dead center.

[0017] Figure 4 It is a graph showing how the flow velocity of the airflow changes before and after the compression top dead center.

[0018] Figure 5 This is a cross-sectional view showing a pre-combustion chamber and its surroundings during ignition control before top dead center.

[0019] Figure 6 This is a cross-sectional view showing a pre-combustion chamber and its surroundings during ignition control after top dead center.

[0020] Figure 7 It is a graph showing combustion in a comparative example and the present embodiment.

[0021] Figure 8 This is a cross-sectional view showing a pre-combustion chamber and its surroundings in the second embodiment. DETAILED DESCRIPTION

[0022] Next, refer to the attached Figure 1 However, the present disclosure is not limited to the embodiments, and can be implemented with appropriate changes within the scope of the disclosure.

[0023] [First embodiment]

[0024] Figure 1 1 is a cross-sectional view showing an ignition system 70 and its surroundings according to the first embodiment. The ignition system 70 is provided for an engine 90. The engine 90 is a four-stroke engine having a combustion cycle consisting of four strokes: an intake stroke → a compression stroke → an expansion stroke → an exhaust stroke. Hereinafter, the top dead center between the compression stroke and the expansion stroke is referred to as "compression top dead center Td". The engine 90 has a cylinder 10 and a cylinder head 20 mounted on the cylinder 10.

[0025] Hereinafter, the longitudinal direction of the center line X of the cylinder 10 will be described as the vertical direction with reference to the drawings. However, the engine 90 and the ignition system 70 may be arranged in any direction, for example, by arranging the center line X so as to be inclined relative to the vertical direction, or by arranging the center line X so as to be in the horizontal direction.

[0026] A piston 18 is provided in the cylinder 10. The piston 18 is connected to the crankshaft 11 via the connecting rod 12, and moves up and down with the rotation of the crankshaft 11. A combustion chamber 30 is formed above the piston 18.

[0027] The cylinder head 20 is provided with an intake passage 21 for sucking gas into the combustion chamber 30, and an exhaust passage 29 for exhausting the gas in the combustion chamber 30. In addition, an intake valve 24 is provided in the intake passage 21, and an exhaust valve 26 is provided in the exhaust passage 29. The intake valve 24 is driven by an intake cam 23, and the exhaust valve 26 is driven by an exhaust cam 27. In addition, the cylinder head 20 is provided with a fuel injection device 22 for injecting fuel into the intake passage 21.

[0028] The ignition system 70 includes a spark plug 40 mounted on the cylinder head 20 , an ignition control unit 50 that controls the spark plug 40 , and an airflow assisting structure As that facilitates airflow to the discharge gap 45 of the spark plug 40 .

[0029] The ignition control unit 50 is an ECU (electronic control unit) or the like, and changes the timing (point of time) of ignition according to the operating conditions of the engine 90, such as the rotation speed and load of the engine 90. In addition, the ignition control unit 50 performs a post-top dead center ignition control in which ignition is performed at Ta after the compression top dead center (i.e., the expansion stroke) when the engine 90 is in a specified operating condition, such as during high-speed idling. On the other hand, during other operating conditions, a pre-top dead center ignition control in which ignition is performed at Tb before the compression top dead center (i.e., the compression stroke). In addition, the above-mentioned high-speed idling refers to a period in which the idling speed is higher than usual for catalyst preheating, etc. after the engine 90 is started.

[0030] Figure 2 2 is a cross-sectional view showing a pre-combustion chamber (Japanese: sub-chamber) 38 and its surroundings. The spark plug 40 has a center electrode 44 and an insulator 41 provided on the outer peripheral side thereof. A partition wall 34 is provided around the lower end portion of the insulator 41 so as to surround the lower end portion of the center electrode 44 from below and from the side. The combustion chamber 30 is divided into a main chamber 31 and a pre-combustion chamber 38 by the partition wall 34. Specifically, the pre-combustion chamber 38 is formed inside the partition wall 34, and the main chamber 31 is formed outside the partition wall 34. The partition wall 34 is made of a conductive material and also serves as a ground electrode of the spark plug 40.

[0031] The partition wall 34 is provided with a plurality of communication holes 35, and the pre-combustion chamber 38 and the main chamber 31 are connected through the plurality of communication holes 35. The central communication hole 35c, which is one of the plurality of communication holes 35, is provided on the center line X of the cylinder 10, and penetrates the partition wall 34 in the vertical direction. The lower end of the center electrode 44 is located directly above the central communication hole 35c. That is, the lower part of the center electrode 44 extends downwardly from the lower end of the insulator 41, and the lower end of the center electrode 44 is close to the central communication hole 35c. The gap between the lower end of the center electrode 44 and the upper end peripheral part of the central communication hole 35c of the partition wall 34 constitutes the discharge gap 45. Thus, the discharge gap 45 is provided near the central communication hole 35c in the pre-combustion chamber 38. Thus, the discharge gap 45 is closest to the central communication hole 35c among the plurality of communication holes 35. The spark plug 40 applies a voltage to the discharge gap 45 to generate a discharge spark F, thereby igniting the fuel in the combustion chamber 30.

[0032] Thus, the discharge gap 45 and the central communication hole 35c are close to each other, so that the airflow easily flows into the discharge gap 45. This structure constitutes the airflow assisting structure As. That is, the discharge gap 45 and the central communication hole 35c are close to each other as the airflow assisting structure As.

[0033] Figure 3It is a schematic diagram showing the state of the airflow before and after the compression top dead center Td. Hereinafter, the airflow caused by tumble or vortex is referred to as "general airflow A1", and the airflow flowing into the central communication hole 35c is referred to as "communication airflow A2".

[0034] like Figure 3 As shown in (a), the piston 18 rises Tb before compression top dead center (compression stroke). At this time, in the combustion chamber 30, in addition to the general airflow A1, a communication airflow A2 flows from the main chamber 31 side to the pre-combustion chamber 38 side.

[0035] like Figure 3 As shown in (b), at the compression top dead center Td, the movement of the piston 18 changes from ascending to descending, so it stops instantly. At this time, in the combustion chamber 30, the general airflow A1 collapses or is extremely weakened, and the connecting airflow A2 also stops.

[0036] like Figure 3 As shown in (c), the piston 18 descends after the compression top dead center Ta (expansion stroke). At this time, a communication airflow A2 flows from the pre-combustion chamber 38 to the main chamber 31 in the combustion chamber 30. Then, a general airflow A1 is generated later than this.

[0037] Figure 4 It is a graph showing the changes in the flow rates (absolute values) of the general airflow A1 and the connecting airflow A2 shown above. The flow rate of the general airflow A1 decreases before the compression top dead center Tb as it approaches the compression top dead center Td. In addition, the general airflow A1 collapses or is extremely weakened at the compression top dead center Td or its vicinity. In addition, the general airflow A1 occurs again after a period of time from the compression top dead center Td at Ta after the compression top dead center. This is because, even if the piston 18 begins to descend and the air pressure in the main chamber 31 begins to decrease, the general airflow A1 caused by the tumble or vortex does not occur before a specified start.

[0038] On the other hand, the flow rate of the communication airflow A2 decreases as it approaches the compression top dead center Td before the compression top dead center Tb. And the communication airflow A2 temporarily becomes zero at or near the compression top dead center Td. However, the communication airflow A2 quickly occurs again after the compression top dead center Ta. This is because the communication airflow A2 occurs when the piston 18 starts to descend and a pressure difference occurs between the pre-combustion chamber 38 and the main chamber 31.

[0039] As described above, after compression top dead center Ta, general airflow A1 does not occur immediately, but connected airflow A2 occurs quickly. Therefore, in the present embodiment, during ignition control after top dead center, the connected airflow A2 is actively used instead of general airflow A1 to make the airflow flow toward the discharge gap 45. This is the above-mentioned airflow assist structure As. At the timing Taf when the airflow with a flow velocity Vaf=10 to 240 m / s flows to the discharge gap 45 through the airflow assist structure As, ignition is performed through the spark plug 40.

[0040] Hereinafter, the generation period of the discharge spark F in the ignition control after the top dead center is referred to as the "spark period after the top dead center". As described above, the ignition system 70 is configured so that an airflow with a flow velocity Vaf=10 to 240 m / s flows to the discharge gap 45 during the spark period after the top dead center by means of the airflow assist structure As and the ignition timing Tf. In other words, a structure is formed in which the discharge gap 45 and the central communication hole 35c are close to each other so that an airflow with a flow velocity of 5 m / s or more flows to the discharge gap 45 during the spark period after the top dead center, as the airflow assist structure As.

[0041] Figure 5 1 is a cross-sectional view showing the pre-combustion chamber 38 and its surroundings during the ignition control before the top dead center, such as in normal times. During the ignition control before the top dead center, the upward connecting airflow A2 flowing from the main chamber 31 side to the pre-combustion chamber 38 side flows to the discharge gap 45. Through the connecting airflow A2, the discharge spark F extends upward in the pre-combustion chamber 38. Through the discharge spark F, the spark plug 40 ignites the fuel in the pre-combustion chamber 38. The flame thus generated in the pre-combustion chamber 38 is discharged from each connecting hole 35 toward the main chamber 31. However, regarding the central connecting hole 35c, since the discharge gap 45 is close, the center electrode 44 and the like become obstacles to the discharge of the flame, and therefore the discharge of the flame becomes smaller than that of the other connecting holes 35. Therefore, the flame is mainly discharged from the connecting holes 35 other than the central connecting hole 35c.

[0042] Figure 6 4 is a cross-sectional view showing the pre-combustion chamber 38 and its surroundings during the ignition control after the top dead center, such as during high-speed idling. During the ignition control after the top dead center, the downward communication airflow A2 flowing from the pre-combustion chamber 38 side to the main chamber 31 side flows to the discharge gap 45. Through the communication airflow A2, the discharge spark F extends from the pre-combustion chamber 38 through the central communication hole 35c to the main chamber 31. Through the discharge spark F, the spark plug 40 ignites the fuel in the main chamber 31.

[0043] According to the present embodiment, since the airflow with a flow velocity Vaf=10 to 240 m / s flows into the discharge gap 45 during the spark period after the top dead center, the discharge spark F can be extended by the airflow to improve the ignitability. Therefore, when ignition is performed by the discharge spark F after the compression top dead center Ta, the ignitability of the discharge spark F can be improved. Therefore, the catalyst can be effectively preheated during high-speed idling. For details, please refer to Figure 7 Provide explanation.

[0044] Figure 7 (a) is different from the present embodiment in that it is a time chart of Comparative Example 1 in which the combustion chamber is not divided into a main chamber and a pre-combustion chamber, that is, the entire combustion chamber is the main chamber. In the case of this Comparative Example 1, ignition is performed in the main chamber, and the flame propagates into the main chamber. However, since there is no pre-combustion chamber, there is no flame emitted from the pre-combustion chamber into the main chamber, and the flame propagation in the main chamber is slower than in the case of a pre-combustion chamber. Therefore, the timing (time point) of fuel burnout, that is, Figure 7 The end point of the interval of the main chamber flame propagation shown in FIG. 1 becomes later. Furthermore, the timing of the fuel burnout needs to be earlier than the start of exhaust. This is to prevent unburned fuel from being discharged. Therefore, according to this constraint, in Comparative Example 1 where the burnout timing becomes later, the ignition timing cannot be set so close to the retard angle side. Therefore, during high-speed idling, the catalyst preheating cannot be so effective.

[0045] on the other hand, Figure 7 (b) is a time chart of Comparative Example 2, which has a combustion chamber divided into a main chamber and a pre-combustion chamber, but has no airflow assist structure unlike the present embodiment. In Comparative Example 2, a spark is formed in the pre-combustion chamber, and then the flame is propagated into the pre-combustion chamber, and then the flame is released from the connecting hole into the main chamber, and then the flame propagates into the main chamber. However, since the airflow in the pre-combustion chamber becomes weak after the compression top dead center, the ignition and flame propagation in the pre-combustion chamber become poor in the ignition control after the top dead center, as shown in the figure. Figure 7 As shown in (b), there is a possibility that the fire will not occur.

[0046] For this, Figure 7 In the present embodiment (c), since there is the airflow assist structure As, the ignition and flame propagation in the pre-combustion chamber 38 will not be deteriorated during the ignition control after the top dead center, so that misfire will not occur in the pre-combustion chamber 38. Therefore, during the ignition control after the top dead center, a spark is formed in the pre-combustion chamber 38 as usual, and then the flame propagates into the pre-combustion chamber 38, and then the flame is released from the connecting hole 35 into the main chamber 31, and then the flame propagates into the main chamber 31. As a result, Figure 7 Compared with the comparative example 1 without the pre-combustion chamber shown in (a), Figure 7As shown in the upper side of (c), if the ignition timing is the same, the timing of fuel burnout, i.e. Figure 7 The end point of the interval of flame propagation in the main chamber shown becomes earlier.

[0047] Figure 7 (d) shows the details. Thus, in the present embodiment with the pre-combustion chamber 38, compared with the comparative example 1 without the pre-combustion chamber, the increase of the combustion ratio in the flame propagation in the main chamber due to the flame being released from the pre-combustion chamber 38 becomes faster, and as mentioned above, the timing of fuel burnout becomes earlier. Figure 7 As shown in the upper side of (c), there is enough time from the timing of burnout to the start of exhaust. Therefore, under the constraint of setting the timing of burnout earlier than the start of exhaust, Figure 7 As shown in the lower side of (c), the ignition timing can be set to the retardation side. Therefore, the catalyst can be effectively warmed up during high-speed idling.

[0048] In addition, the following effects can also be obtained. By arranging the discharge gap 45 close to the central communication hole 35c, the airflow assisting structure As can be simply formed. In addition, the airflow assisting structure As strengthens the airflow flowing to the discharge gap 45 by the upward communicating airflow A2 flowing from the main chamber 31 side to the pre-combustion chamber 38 side before the compression top dead center Tb, and strengthens the airflow flowing to the discharge gap 45 by the downward communicating airflow A2 flowing from the pre-combustion chamber 38 side to the main chamber 31 side after the compression top dead center Ta. Therefore, at any time of the ignition control before the top dead center and the ignition control after the top dead center, the airflow flowing to the discharge gap 45 is strengthened during the generation period of the discharge spark F, and the ignitability can be improved.

[0049] In addition, during the ignition control before the top dead center, since the flame is released from the connecting hole 35, the ignitability can also be improved in this regard. In addition, since there are multiple connecting holes 35 at this time, the following effect can also be obtained. That is, regarding the central connecting hole 35c for strengthening the airflow flowing to the discharge gap 45, the release of the flame becomes weaker because the center electrode 44 and the like become obstacles to the release of the flame as described above. Regarding this point, in the present embodiment, as described above, multiple connecting holes 35 are provided, and the flame is released more strongly from the connecting holes 35 other than the central connecting hole 35c. Therefore, the release of the flame in the ignition control before the top dead center can be mainly carried out through the connecting holes 35 other than the central connecting hole 35c, and the strengthening of the airflow flowing to the discharge gap 45 in the ignition control after the top dead center can be carried out through the central connecting hole 35c. As a result, both the release of the flame in the ignition control before the top dead center and the strengthening of the airflow in the ignition control after the top dead center can be fully ensured.

[0050] Furthermore, during the ignition control after the top dead center, since the discharge spark F extends into the main chamber 31 through the central communication hole 35c, ignition can be performed in the main chamber 31. Therefore, the flame can be rapidly extended to the entire main chamber 31. Furthermore, the central communication hole 35c is provided on the center line X of the cylinder 10, and during the ignition control after the top dead center, the discharge spark F extends downward along the center line X of the cylinder 10 through the central communication hole 35c. Therefore, ignition can be performed at the center of the main chamber 31, and in this regard, the flame can be rapidly extended to the entire main chamber 31.

[0051] Furthermore, since the partition wall 34 also serves as the ground electrode of the spark plug 40 , the structure of the spark plug 40 becomes simple, and the discharge gap 45 can be effectively arranged close to the central communication hole 35 c .

[0052] [Second embodiment]

[0053] Next, the second embodiment will be described. In the following embodiments, the same reference numerals are given to the same or corresponding components as those in the previous embodiments. This embodiment will be described mainly on the basis of the first embodiment and the differences therefrom.

[0054] Figure 8 : is a cross-sectional view showing the pre-combustion chamber 38 and its surroundings of the present embodiment. In the present embodiment, a plurality of communication holes 35 are also provided in the partition wall 34, but no central communication hole 35c is provided. Furthermore, the discharge gap 45 is provided in the pre-combustion chamber 38 at a position farther from the communication hole 35 than in the case of the first embodiment. Specifically, the protrusion 36 constituting one electrode is formed in the partition wall 34 so as to protrude toward the center electrode 44 constituting the other electrode. The discharge gap 45 is formed between the protrusion 36 and the center electrode 44. Furthermore, during the after-top dead center ignition control, the discharge spark F extends toward the prescribed communication hole 35 by the airflow flowing from the pre-combustion chamber 38 through the prescribed communication hole 35 into the main chamber 31. Here, the prescribed communication hole 35, i.e., the communication hole 35 that extends the discharge spark F as the airflow assisting structure As, may be configured as the same communication hole 35 each time, or may be configured as a different communication hole 35 depending on the operating condition of the engine 90.

[0055] The ignition control unit 50 controls the spark plug 40 during the after-top dead center ignition control so that the discharge spark F is maintained for a required period longer than the minimum required period from the generation of the discharge spark F until the discharge spark F extends to the above-mentioned predetermined communication hole 35. More preferably, the spark plug 40 is controlled so that the discharge spark F is maintained for a required period longer than the minimum required period from the generation of the discharge spark F until the discharge spark F passes through the above-mentioned predetermined communication hole 35 and extends into the main chamber 31.

[0056] Such control of the spark plug 40 can be performed, for example, as follows: the above-mentioned required period is calculated based on the operating conditions of the engine 90, and the spark plug 40 is controlled so that the discharge spark F is maintained for a period longer than the calculated required period. The operating conditions include, for example, the rotation speed, load, intake air volume, and internal pressure of the engine 90. In addition, such control of the spark plug 40 can also be performed, for example, as follows: the spark plug 40 is controlled during high-speed idling so that the discharge spark F is maintained for a period that is absolutely not less than the above-mentioned required period.

[0057] According to the present embodiment, during the ignition control after the top dead center, the discharge spark F can be extended toward the above-mentioned predetermined communication hole 35 and the ignitability can be improved by the airflow flowing from the pre-combustion chamber 38 into the main chamber 31 through the above-mentioned predetermined communication hole 35. Therefore, in the present embodiment, even when ignition by the discharge spark F is performed after the compression top dead center Ta, the ignitability based on the discharge spark F can be improved.

[0058] Furthermore, as described above, if the required period is calculated based on the operating condition of the engine 90, and the spark plug 40 is controlled so that the discharge spark F is maintained for more than the calculated required period, the required period can be appropriately changed according to the operating condition of the engine 90, and the discharge period can be appropriately changed. Therefore, it is easy to control the discharge period to an optimal period without excess or deficiency.

[0059] [Other embodiments]

[0060] The above embodiments can be implemented by making the following changes. For example, in the first embodiment, the structure in which the discharge gap 45 is close to the central communication hole 35c is adopted as the airflow assisting structure As, but instead of or in addition to it, a blowing device for blowing air or mixed gas into the discharge gap 45 during the spark period after the top dead center can be provided as the airflow assisting structure As. In addition, in this case, the partition wall 34 can also be removed so that the main chamber 31 and the pre-combustion chamber 38 are a continuous combustion chamber 30.

[0061] In addition, for example, in the first embodiment, the fuel is injected into the intake passage 21, but instead of or in addition to this, the fuel or the mixed gas of the fuel and the air may be injected into the main chamber 31 or the pre-combustion chamber 38. In addition, for example, in the first embodiment, a plurality of communication holes 35 are provided in the partition wall 34, but the communication hole 35 may be only the central communication hole 35c. In addition, for example, in the first embodiment, the flame is released more strongly from the communication holes 35 other than the central communication hole 35c close to the discharge gap 45, but instead of this, the flame may be released most strongly from the central communication hole 35c close to the discharge gap 45.

[0062] In addition, for example, in the first embodiment, the partition wall 34 also serves as the ground electrode of the spark plug 40, but the spark plug 40 may have a ground electrode different from the partition wall 34. In addition, the partition wall 34 may be provided outside the ground electrode as the airflow assisting structure As, and the discharge gap 45 between the ground electrode and the center electrode 44 may be close to the communication hole 35.

[0063] In addition, for example, in the first embodiment, an airflow with a flow velocity of Vaf=10 to 240 m / s flows through the discharge gap 45 during the spark period after the top dead center, but instead, an airflow with a flow velocity higher than Vaf=240 m / s or an airflow with a flow velocity lower than Vaf=10 m / s may flow through the discharge gap 45 during the spark period after the top dead center. However, in this case, it is also preferred that an airflow with a flow velocity of Vaf=5 m / s or more flows through the discharge gap 45 during the spark period after the top dead center. This is because, since it is difficult for an airflow with a flow velocity of Vaf=5 m / s or more to flow through the discharge gap 45 during the spark period after the top dead center when there is no airflow assisting structure As, the effect of providing the airflow assisting structure As can be fully exerted as long as the airflow with a flow velocity of Vaf=5 m / s or more flows through the discharge gap 45.

[0064] In addition, for example, in the first embodiment, the lower end of the center electrode 44 is arranged above the upper end of the central communication hole 35c, but it may be arranged inside the central communication hole 35c or below the lower end of the central communication hole 35c. That is, in the first embodiment, the discharge gap 45 is provided near the central communication hole 35c in the pre-combustion chamber 38, but it may be provided inside the central communication hole 35c or near the central communication hole 35c in the main chamber 31.

[0065] In addition, for example, in the first embodiment, the center electrode 44 is arranged on the center line X of the cylinder 10, but it may be arranged at a position other than that. In addition, for example, in the first embodiment, the discharge gap 45 is made close to the central communication hole 35c, but it may be made close to other communication holes 35.

[0066] In addition, for example, in the first embodiment, the discharge spark F is configured to extend downward during the ignition control after the top dead center, but it may be configured to extend in other directions instead. Specifically, it is preferable to configure the ignition system 70 so that the discharge spark F extends, for example, in a direction where the combustion progresses slowly, in accordance with the specifications of the engine 90. Thus, combustion can be promoted in a place where the combustion progresses slowly.

[0067] In addition, for example, in the first embodiment, the engine 90 is a four-stroke engine, but the engine 90 can also be a two-stroke engine in which one combustion cycle is composed only of a compression stroke and an expansion stroke, and intake and exhaust are performed in the second half of the expansion stroke and the first half of the compression stroke.

[0068] The present disclosure is described according to the embodiments, but it should be understood that the present disclosure is not limited to the embodiments and structures. The present disclosure also includes various modifications or modifications within the equivalent range. In addition, various combinations or forms, and further combinations or forms that only include one element, above or below them, also fall within the scope or thought range of the present disclosure.

Claims

1. An ignition system, have: A spark plug applies a voltage to a discharge gap in a combustion chamber of the engine to generate a discharge spark to ignite the fuel; and an ignition control unit, controlling the spark plug, When the engine is in a predetermined operating state, the ignition control unit performs post-top dead center ignition control for performing the ignition after compression top dead center. The combustion chamber is divided into a main chamber and a pre-combustion chamber by a partition wall provided with a communicating hole, so that after the compression top dead center, air flows from the pre-combustion chamber through the communicating hole into the main chamber. The ignition system has an airflow assist structure that makes it easy for the airflow to flow to the discharge gap at least after the compression top dead center. The ignition system is configured such that, through the airflow assist structure and the timing of the ignition, an airflow with a flow rate of 5 m / s or more flows into the discharge gap during the generation period of the discharge spark in the after-top dead center ignition control, i.e., during the after-top dead center spark period, The discharge gap is arranged in the pre-combustion chamber or in the communicating hole, and during the after-top-dead-center ignition control, the discharge spark passes through the communicating hole due to the airflow and extends into the main chamber.

2. The ignition system according to claim 1, As the airflow assisting structure, the discharge gap approaches the communication hole during the after-top dead center spark period so that the airflow at a flow velocity of 5 m / s or more flows into the discharge gap.

3. The ignition system as claimed in claim 2, A plurality of the communicating holes are provided in the partition wall, As the airflow assist structure, during the spark period after the top dead center, the discharge gap approaches a specified communicating hole among the plurality of communicating holes so that the airflow with a flow velocity of 5 m / s or more flows into the discharge gap, and the specified communicating hole is the communicating hole located on the center line of the cylinder.

4. The ignition system as claimed in claim 3, The ignition control unit performs the before top dead center ignition control for performing the ignition before compression top dead center when the engine is not in a predetermined operating state. At least after the ignition in the before top dead center ignition control, the flame is released toward the main chamber from at least the communication holes other than the predetermined communication holes.

5. The ignition system as claimed in claim 4, The flame is released more strongly from the communication holes other than the predetermined communication holes than from the predetermined communication holes.

6. The ignition system according to any one of claims 3 to 5, The discharge gap is arranged in the pre-combustion chamber, During the after-top dead center ignition control, the discharge spark extends toward the predetermined communication hole due to the airflow flowing from the pre-combustion chamber into the main chamber through the predetermined communication hole.

7. The ignition system as claimed in claim 6, During the after-top-dead-center ignition control, the ignition control unit controls the spark plug so that the discharge spark is maintained for a required time or longer, the required time being a minimum required time from when the discharge spark is generated to when the discharge spark passes through the prescribed communication hole and extends into the main chamber.

8. The ignition system as claimed in claim 7, The ignition control unit calculates the required time based on the operating condition of the engine, and controls the spark plug so that the discharge spark is maintained for more than the calculated required time.

9. The ignition system according to claim 1 or 2, The combustion chamber is formed in the cylinder, and the communicating hole is provided on the center line of the cylinder. During the after-top-dead-center ignition control, the discharge spark passes through the communication hole on the center line and extends in the length direction of the center line.

10. The ignition system according to any one of claims 3 to 5, The combustion chamber is formed in the cylinder, During the after-top dead center ignition control, the discharge spark extends in the longitudinal direction of the center line through the predetermined communication hole on the center line.

11. The ignition system according to any one of claims 1 to 5, The discharge gap is formed between two electrodes, and the partition wall also serves as one of the two electrodes.

12. The ignition system according to any one of claims 1 to 5, The discharge gap is formed between two electrodes, and the partition wall has a protrusion constituting one of the electrodes formed so as to protrude toward the other electrode.

13. An ignition system, have: A spark plug applies a voltage to a discharge gap in a combustion chamber of the engine to generate a discharge spark to ignite the fuel; and an ignition control unit, controlling the spark plug, When the engine is in a predetermined operating state, the ignition control unit performs post-top dead center ignition control for performing the ignition after compression top dead center. The combustion chamber is divided into a main chamber and a pre-combustion chamber by a partition wall provided with a plurality of communicating holes, so that after the compression top dead center, air flows from the pre-combustion chamber through the communicating holes into the main chamber. The discharge gap is arranged in the pre-combustion chamber or in the predetermined communication hole in a state of being closest to a predetermined communication hole among the plurality of communication holes, the predetermined communication hole being the communication hole located on the center line of the cylinder, The ignition system is configured such that, through the airflow assist structure and the timing of the ignition, an airflow with a flow rate of 5 m / s or more flows into the discharge gap during the generation period of the discharge spark in the after-top dead center ignition control, i.e., during the after-top dead center spark period, During the after-top-dead-center ignition control, the discharge spark passes through the predetermined communication hole due to airflow and extends into the main chamber.

14. The ignition system of claim 13, The ignition control unit performs the before top dead center ignition control for performing the ignition before compression top dead center when the engine is not in a predetermined operating state. At least after the ignition in the before top dead center ignition control, the flame is released toward the main chamber from at least the communication holes other than the predetermined communication holes.

15. The ignition system of claim 14, The flame is released more strongly from the communication holes other than the predetermined communication holes than from the predetermined communication holes.

16. The ignition system according to any one of claims 13 to 15, The discharge gap is arranged in the pre-combustion chamber, During the after-top dead center ignition control, the discharge spark extends toward the predetermined communication hole due to the airflow flowing from the pre-combustion chamber into the main chamber through the predetermined communication hole.

17. The ignition system of claim 16, During the after-top-dead-center ignition control, the ignition control unit controls the spark plug so that the discharge spark is maintained for a required time or longer, the required time being a minimum required time from when the discharge spark is generated to when the discharge spark passes through the prescribed communication hole and extends into the main chamber.

18. The ignition system of claim 17, The ignition control unit calculates the required time based on the operating condition of the engine, and controls the spark plug so that the discharge spark is maintained for more than the calculated required time.

19. The ignition system according to any one of claims 13 to 15, The combustion chamber is formed in the cylinder, During the after-top dead center ignition control, the discharge spark extends in the longitudinal direction of the center line through the predetermined communication hole on the center line.

20. The ignition system according to any one of claims 13 to 15, The discharge gap is formed between two electrodes, and the partition wall also serves as one of the two electrodes.

21. An ignition system according to any one of claims 13 to 15, The discharge gap is formed between two electrodes, and the partition wall has a protrusion constituting one of the electrodes formed so as to protrude toward the other electrode.

22. An ignition system, have: A spark plug applies a voltage to a discharge gap in a combustion chamber of the engine to generate a discharge spark to ignite the fuel; and an ignition control unit, controlling the spark plug, When the engine is in a predetermined operating state, the ignition control unit performs post-top dead center ignition control for performing the ignition after compression top dead center. The combustion chamber is configured to be divided into a main chamber and a pre-combustion chamber by a partition wall provided with one or more communicating holes, so that after the compression top dead center, airflow flows from the pre-combustion chamber into the main chamber through a prescribed communicating hole, and the prescribed communicating hole is the communicating hole located on the center line of the cylinder. The discharge gap is arranged in the pre-combustion chamber, The ignition system is configured such that, through the airflow assist structure and the timing of the ignition, an airflow with a flow rate of 5 m / s or more flows into the discharge gap during the generation period of the discharge spark in the after-top dead center ignition control, i.e., during the after-top dead center spark period, During the after-top-dead-center ignition control, the discharge spark extends toward the prescribed communication hole due to the airflow from the pre-combustion chamber into the main chamber through the prescribed communication hole. During the after-top-dead-center ignition control, the ignition control unit controls the spark plug so that the discharge spark is maintained for a required time or longer, the required time being a minimum required time from when the discharge spark is generated to when the discharge spark passes through the prescribed communication hole and extends into the main chamber.

23. The ignition system of claim 22, The combustion chamber is formed in the cylinder, During the after-top dead center ignition control, the discharge spark extends in the longitudinal direction of the center line through the predetermined communication hole on the center line.

24. An ignition system as claimed in claim 22 or 23, The discharge gap is formed between two electrodes, and the partition wall also serves as one of the two electrodes.

25. An ignition system as claimed in claim 22 or 23, The discharge gap is formed between two electrodes, and the partition wall has a protrusion constituting one of the electrodes formed so as to protrude toward the other electrode.

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