Ignition system

Abstract

An ignition system has a partition wall (34) that divides a combustion chamber (30) of an engine (90) into a main chamber (31) and a prechamber (38), the partition wall being provided with one or more injection holes (35) that communicate from the main chamber to the prechamber, and a spark plug (40) that generates an electric discharge spark (f) by applying a voltage to an electric discharge gap (45) between a first electrode (44) and a second electrode (46), ignites fuel, the first electrode being disposed in the prechamber, the second electrode being disposed at the partition wall or a portion electrically conducted to the partition wall, the ignition system performs after-top dead center ignition control that ignites after a compression top dead center (Td), in the after-top dead center ignition control, a spark source that is a flame kernel of a size capable of self-growth is disposed in a region (R) within 3 mm from the injection hole center in a region near the injection hole, in the injection hole, or in the main chamber within 20 degrees of crank angle from an ignition start timing (Ts) at which the voltage is started to be applied to the electric discharge gap.

Description

[0001] Cross Reference to Related Applications

[0002] This application is based on Japanese Patent Application No. 2020-134723 filed August 7, 2020, the content of the application is hereby incorporated by reference in its entirety. TECHNICAL FIELD

[0003] The present disclosure relates to an ignition system that ignites fuel in a combustion chamber. BACKGROUND

[0004] In the ignition system, there is a structure having a partition wall and a spark plug. The partition wall divides a combustion chamber of an engine into a main chamber and a prechamber (subchamber). A plurality of injection holes that communicate from the main chamber to the prechamber are provided in the partition wall. The spark plug ignites fuel by generating an electric discharge spark by applying a voltage to a prescribed discharge gap in the prechamber. And, as a document that shows such a technique, there is the following Patent Literature 1.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: Japanese Patent No. 5122367 SUMMARY

[0008] Such an ignition system, at ordinary times or the like, performs pre-top dead center ignition control that is control to ignite before the compression top dead center, that is, during the compression stroke. In this pre-top dead center ignition control, the electric discharge spark generated in the prechamber is elongated by tumble or swirl generated in the combustion chamber. The flame ignited by the elongated electric discharge spark is injected into the main chamber with a strong momentum through the injection hole, and promotes the progress of combustion in the combustion chamber.

[0009] However, the ignition system, under a prescribed condition, performs post-top dead center ignition control that is control to ignite not before but after the compression top dead center, that is, during the expansion stroke. Specifically, for example, at high idle (fast idle) for catalyst warm-up, ignition is performed as late as possible in order to efficiently transfer heat generated by combustion to the catalyst in the exhaust passage. Thus, ignition is performed after the compression top dead center.

[0010] However, after the compression top dead center, tumble or swirl is destroyed when the piston passes the compression top dead center, so the airflow in the prechamber becomes weak. Therefore, the electric discharge spark is difficult to elongate, and the ignitability decreases. Therefore, ignition in the prechamber takes time until the flame propagates to the prechamber and is injected from the injection hole into the main chamber. Therefore, the flame cannot be rapidly propagated to the main chamber.

[0011] The present disclosure was made in view of the above circumstances, and a main object is to rapidly spread a flame into a main chamber in post-top dead center ignition control.

[0012] The ignition system of the present disclosure has a partition wall and a spark plug. The partition wall divides a combustion chamber of an engine into a main chamber and a pre-chamber. One or more injection holes that communicate from the main chamber to the pre-chamber are provided in the partition wall. The spark plug ignites fuel by generating an electric discharge spark by applying a voltage to an electric discharge gap between a first electrode and a second electrode. The first electrode is provided in the pre-chamber. The second electrode is provided in the partition wall or a portion electrically conducted with the partition wall.

[0013] Hereinafter, a timing (a point in time) at which a voltage is started to be applied to the electric discharge gap is referred to as an ignition start timing, a center of an opening of the pre-chamber side of the injection hole is referred to as an injection hole center, and a region within 3 mm from the injection hole center in the pre-chamber is referred to as an injection hole vicinity region.

[0014] The ignition system executes, when the engine is in a prescribed operating condition, post-top dead center ignition control that is control of igniting at a timing after a compression top dead center. In the post-top dead center ignition control, a flame kernel that is an ignition source capable of self-growth is disposed in the injection hole vicinity region, in the injection hole, or in the main chamber within 20 degrees of a crank angle from the ignition start timing.

[0015] According to the present disclosure, the following effects can be obtained. In the post-top dead center ignition control, the ignition source is disposed in the injection hole vicinity region, in the injection hole, or in the main chamber at an early stage within 20 degrees of a crank angle from the ignition start timing. Also, in the case where the ignition source is disposed in the injection hole vicinity region or in the injection hole, the flame that grows from the ignition source is easily ejected into the main chamber. Further, in the case where the ignition source is disposed in the main chamber, the flame that grows from the ignition source is as it is spread into the main chamber. Therefore, in the post-top dead center ignition control, the flame can be rapidly spread into the main chamber. BRIEF DESCRIPTION OF DRAWINGS

[0016] The above objects and other objects, features and advantages of the present disclosure will become more clearly understood from the following detailed description taken in conjunction with the accompanying drawings.

[0017] Figure 1 is a cross-sectional view showing an ignition system of a first embodiment.

[0018] Figure 2 is a cross-sectional view showing a pre-chamber and its periphery.

[0019] Figure 3 is a graph showing a relationship between a distance of an ignition source from an injection hole center and a combustion stability index.

[0020] Figure 4 is a graph showing the growth of a flame kernel.

[0021] Figure 5 is a graph showing the progress of the pressure in the combustion chamber.

[0022] Figure 6 is a graph showing the flow of the manufacturing method of the ignition system.

[0023] Figure 7 is a graph showing the relationship between the jet distance and the jet ratio and the clearance gas flow.

[0024] Figure 8 is a cross-sectional view showing the spark plug and its surroundings of the comparative example and the present embodiment.

[0025] Figure 9 is a time graph showing the progress of the combustion of the comparative example and the present embodiment.

[0026] Figure 10 is a graph showing the ignition start timing of each of the time graphs shown in Figure 9 aligned.

[0027] Figure 11 is a graph showing the progress of the combustion ratio of the comparative example and the present embodiment.

[0028] Figure 12 is a graph showing a part of Figure 9 enlarged.

[0029] Figure 13 is a graph showing the progress of the clearance flow rate of the comparative example and the present embodiment. DETAILED DESCRIPTION

[0030] Next, the embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the present disclosure is not limited to the embodiments, and can be appropriately modified and implemented without departing from the gist of the present disclosure.

[0031] [1st Embodiment]

[0032] Figure 1 is a cross-sectional view showing an engine 90 equipped with the ignition system 70 of the present embodiment. The engine 90 is a four-stroke engine in which one combustion cycle is composed of four strokes (720 degrees of crank angle) of 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 will be referred to as "compression top dead center Td". The engine 90 has a cylinder 10 and a cylinder head 20 installed on the upper portion thereof.

[0033] Hereinafter, the center line X of the cylinder 10 is taken as the vertical direction, and the engine 90 and the ignition system 70 are described with reference to the drawings. However, the engine 90 and the ignition system 70 can be arranged in any direction, for example, the center line X can be taken as a horizontal direction, or the center line X can be taken as a direction inclined with respect to the vertical direction.

[0034] A piston 18 is arranged in the cylinder 10. The piston 18 is connected to the crank shaft 11 via the connecting rod 12, and moves up and down as the crank shaft 11 rotates. A space surrounded by the upper surface of the piston 18, the inner peripheral surface of the cylinder 10, and the lower surface of the cylinder head 20 constitutes a combustion chamber 30.

[0035] An intake passage 21 for taking in gas into the combustion chamber 30, and an exhaust passage 29 for discharging gas from the combustion chamber 30 are provided in the cylinder head 20. 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. A fuel injection device 22 for injecting fuel into the intake passage 21 is provided in the cylinder head 20.

[0036] The ignition system 70 has a partition wall 34, a spark plug 40, and an ignition control section 50. The ignition control section 50 is a part of an ECU (Electronic Control Unit) or the like, and controls the spark plug 40 based on information from prescribed sensors or the like provided in the engine 90. As the prescribed sensors, for example, a crank angle sensor, a knock sensor, an intake pressure sensor, an exhaust pressure sensor, an internal pressure sensor, a catalyst temperature sensor, or the like can be mentioned.

[0037] Figure 2 A sectional view showing the pre-chamber (sub-chamber) 38 and its periphery. The spark plug 40 has a first electrode 44, and an insulator 41 provided on the outer peripheral side thereof. The partition wall 34 is attached to the lower end portion of the insulator 41. The pre-chamber 38 is formed on the inner side of the partition wall 34, and the main chamber 31 is formed on the outer side of the partition wall 34. That is, the partition wall 34 divides the combustion chamber 30 of the engine 90 into the main chamber 31 and the pre-chamber 38. A plurality of injection holes 35 are provided in the partition wall 34, which communicate from the main chamber 31 to the pre-chamber 38. The partition wall 34 is an electrically conductive body, and functions as a second electrode 46 of the spark plug 40. Further, the spark plug 40 generates an electric spark f by applying a voltage to the discharge gap 45 between the first electrode 44 and the second electrode 46, and ignites fuel.

[0038] More specifically, the spark plug 40 has a primary coil and a secondary coil. And, by flowing a current to the primary coil, magnetic energy is accumulated in the primary coil. Then, if the current is stopped, an electromotive force is generated in the secondary coil by the magnetic energy accumulated in the primary coil. By the electromotive force, a voltage is applied to the discharge gap 45 to form the discharge spark f. Therefore, the timing at which the current flowing to the primary coil is stopped becomes the ignition start timing Ts which is the timing at which the voltage starts to be applied to the discharge gap 45 to start ignition.

[0039] Hereinafter, one of the plurality of injection holes 35 is referred to as "central injection hole 35c". The central injection hole 35c is provided on the center line X of the cylinder 10, and the partition wall 34 is penetrated in the up-down direction. The lower end portion of the first electrode 44 is located immediately above the central injection hole 35c. That is, the lower portion of the first electrode 44 protrudes downward from the lower end of the insulator 41, and is closest to the central injection hole 35c among the plurality of injection holes 35. The gap between the lower end portion of the first electrode 44 and the upper end peripheral portion of the central injection hole 35c of the partition wall 34 constitutes the discharge gap 45. Further, other injection holes 35 are provided around the central injection hole 35c of the partition wall 34. The cross-sectional areas and shapes of the central injection hole 35c and the other injection holes 35 can be the same or different.

[0040] The ignition system 70 performs, at normal times and the like, pre-top dead center ignition control which is control to perform ignition before the compression top dead center Td. On the other hand, in a case where the engine 90 is in a prescribed operating condition at high idle for catalyst warm-up and the like, post-top dead center ignition control which is control to perform ignition after the compression top dead center Td is performed.

[0041] Hereinafter, the gas flow in the discharge gap 45 is referred to as "gap gas flow". Further, hereinafter, the direction from the first electrode 44 toward the central injection hole 35c is referred to as "injection hole direction dl", and the opposite direction is referred to as "reverse injection hole direction d2". In the present embodiment, the injection hole direction dl is the downward direction, and the reverse injection hole direction d2 is the upward direction. Further, the direction in which the injection hole direction dl is included in an element (component) is referred to as "injection hole direction dl side", and the direction in which the reverse injection hole direction d2 is included in an element is referred to as "reverse injection hole direction d2 side".

[0042] When the ignition system 70 performs the post-top dead center ignition control, the direction of the gap gas flow is shifted from the reverse injection hole direction d2 side to the injection hole direction dl side before the ignition start timing Ts. Therefore, at the ignition start timing Ts, the direction of the gap gas flow becomes the injection hole direction dl side, and the discharge spark f is elongated in the injection hole direction dl.

[0043] Hereinafter, the center of the opening of the pre-chamber 38 side of the central injection hole 35c is referred to as "injection hole center", and the region within 3 mm from the injection hole center in the pre-chamber 38 is referred to as "injection hole vicinity region R".

[0044] The ignition system 70, when performing the post-top dead center ignition control, configures the igniting source of the size capable of self-growth as the flame kernel in the vicinity of the injection hole region R, in the central injection hole 35c, or in the main chamber 31 at an early stage within 20 degrees of crank angle from the ignition start timing Ts. Hereinafter, the vicinity of the injection hole region R, the central injection hole 35c, or the main chamber 31 is referred to as "the vicinity of the injection hole region R or the like".

[0045] In addition, the size capable of self-growth here means the size of the flame kernel that does not extinguish due to cold loss or lean mixture or the like even if the voltage application to the discharge gap 45 is stopped, but the flame spreads. More specifically, the flame kernel of the size capable of self-growth is a flame kernel of which diameter is approximately 0.5 to 1 mm or more.

[0046] Such a structure that configures the igniting source in the vicinity of the injection hole region R or the like at an early stage is realized by setting the distance from the first electrode 44 to the central injection hole 35c, that is, the injection hole distance D, the volume of the pre-chamber 38, that is, the pre-chamber volume V, the total of the cross-sectional areas of all the injection holes 35 provided to the partition wall 34, that is, the total injection hole area S, the voltage applied to the discharge gap 45, that is, the discharge voltage, and the like. Hereinafter, the details thereof will be described. In addition, in the case where the cross-sectional area of the injection hole 35 is not uniform such as the case where the injection hole 35 is tapered in the middle, the cross-sectional area of the portion where the cross-sectional area is narrowest is set as the cross-sectional area of the injection hole 35.

[0047] First, the injection hole distance D will be described. The smaller the injection hole distance D is, the more easily the gas flow through the central injection hole 35c is affected. Due to this, in addition to the fact that the flame kernel easily grows, the growth easily proceeds in the vicinity of the injection hole region R or the like. Therefore, the smaller the injection hole distance D is, the more easily the igniting source is configured in the vicinity of the injection hole region R or the like at an early stage.

[0048] Next, the pre-chamber volume V and the total injection hole area S will be described. The larger the pre-chamber volume V is, the faster the gas flow through the central injection hole 35c is in the post-top dead center ignition control. This is because, if the flow rate of the gas flowing from the pre-chamber 38 to the main chamber 31 is the same, the larger the pre-chamber volume V is, the more difficult it is for the pressure drop of the pre-chamber 38 to follow the pressure drop of the main chamber 31. Due to this, the pressure difference between the pre-chamber 38 and the main chamber 31 becomes large, and the gas flow through the central injection hole 35c easily becomes fast.

[0049] On the other hand, the smaller the total jet hole area S is, the faster the gas flow through the central jet hole 35c is in the after-top-dead-center ignition control. This is because, if the prechamber volume V is the same, the smaller the total jet hole area S is, the smaller the flow rate of the gas flowing from the prechamber 38 to the main chamber 31 is, and the prechamber 38 is less likely to follow the pressure drop of the main chamber 31. Thus, the pressure difference between the prechamber 38 and the main chamber 31 becomes large, and the gas flow through the central jet hole 35c becomes fast.

[0050] Also, the faster the gas flow through the central jet hole 35c is, the more likely the discharge spark f is to elongate (extend) toward the jet hole direction dl. Thus, in addition to the fact that the flame kernel is likely to grow early, the growth is likely to occur in or near the jet hole vicinity region R. Thus, the smaller the jet hole ratio (S / V) of the total jet hole area S to the prechamber volume V is, the more likely it is to arrange the ignition source in or near the jet hole vicinity region R early.

[0051] Next, the discharge voltage is described. The larger the discharge voltage is, the more likely the flame kernel is to grow. Further, the larger the discharge voltage is, the more difficult it is to blow out, and thus the discharge spark f is likely to elongate (extend) into or near the jet hole vicinity region R by the gas flow. Therefore, the larger the discharge voltage is, the more likely it is to arrange the ignition source in or near the jet hole vicinity region R early.

[0052] As described above, the smaller the jet hole distance D and the jet hole ratio (S / V) are, and the larger the discharge voltage is, the more likely it is to arrange the ignition source in or near the jet hole vicinity region R early. However, in the case where the jet hole distance D or the jet hole ratio (S / V) is too small, or the discharge voltage is too large, disadvantages can occur in other aspects. Therefore, within a range where these disadvantages can be suppressed, the jet hole distance D and the jet hole ratio (S / V) are reduced, and the discharge voltage is increased, thereby realizing the structure described above, in which the ignition source is arranged in or near the jet hole vicinity region R early.

[0053] Also, in the case where the ignition source is arranged in or near the jet hole vicinity region R, or in the jet hole 35, the flame grown from the ignition source is promptly injected into the main chamber 31. Further, in the case where the ignition source is arranged in the main chamber 31, the flame grown from the ignition source is as it is propagated into the main chamber 31. Therefore, in these cases, the flame can be promptly propagated into the main chamber 31.

[0054] Figure 3is a graph showing the relationship between the distance of the ignition source from the center of the injection hole and the Coefficient of Variation. The Coefficient of Variation is an index showing the degree from the worst stability of misfire to the best stability of complete combustion, and the greater the value, the more unstable the combustion. As shown in the graph, if the distance of the ignition source from the center of the injection hole becomes larger, the Coefficient of Variation becomes larger, and in particular, from the vicinity of 3 mm or more from the center of the injection hole, the Coefficient of Variation sharply becomes larger. Therefore, in the present embodiment, as described above, the region within 3 mm from the center of the injection hole is set as the injection hole vicinity region R, and the ignition source is disposed within the injection hole vicinity region R, and the like.

[0055] Figure 4 is a graph showing the growth of the flame kernel. In the case of the present embodiment, the growth of the flame kernel is early, and in addition, the propagation of the flame is early, compared with the cases of Comparative Modes i, ii. In the case where the flame kernel grows to the prescribed ignition threshold value as in the case of the present embodiment or Comparative Mode i, it becomes possible to self-grow, and thus the combustion spreads. On the other hand, in the case where the flame kernel does not grow to the prescribed ignition threshold value as in the case of Comparative Mode ii, it becomes impossible to self-grow and the flame is extinguished.

[0056] Figure 5 is a graph showing the progress of the pressure in the combustion chamber. In each of the present embodiment and Comparative Modes i, ii, before the compression top dead center Td, the pressure rises as the crank angle advances, and from the compression top dead center Td, the pressure falls as the crank angle advances. Also, in the present embodiment and Comparative Mode i, when ignition is performed, the pressure again rises. However, in the present embodiment, compared with the case of Comparative Mode i, the growth of the flame kernel is early, and in addition, the propagation of the flame is early, so the pressure rapidly rises. On the other hand, in the case where the flame is extinguished as in Comparative Mode ii, the pressure does not rise.

[0057] Figure 6 is a graph showing the flow of a manufacturing method of manufacturing the ignition system 70. The manufacturing method has a setting process pi and a manufacturing process p2.

[0058] In the setting process pi, the injection hole ratio (S / V) is calculated, and based on the injection hole ratio (S / V) and the injection hole distance D, the dimensions of the pre-chamber 38 and the injection hole 35 are set. Regarding the details of this setting process pi, refer to Figure 7 which will be described later. Also, in the manufacturing process p2, the ignition system 70 is manufactured so as to be the dimensions set in the setting process pi.

[0059] Figure 7is a graph showing the relationship between the jet hole distance and the jet hole ratio and the clearance gas flow, in which the jet hole distance D is shown on the horizontal axis and the jet hole ratio (S / V) is shown on the vertical axis. Also, the curve a shows the relationship between the jet hole ratio (S / V) and the jet hole distance D in the case where the clearance gas flow to the jet hole direction dl side is 5 m / s in the ignition start timing Ts under the post-TDC ignition control. If this curve a is approximated by a numerical expression, it is the following numerical expression A.

[0060] S / V = -0.025D3+ 0.34D2- 1.4D + 2.1 (Numerical expression A)

[0061] In this numerical expression A, "V" represents the pre-chamber volume V [cc], "S" represents the total jet hole area S [mm2], and "D" represents the jet hole distance D [mm]. Also, "^" represents the power. That is, "^3" represents the 3rd power and "^2" represents the square.

[0062] Therefore, if it is on the upper side than the curve a, the clearance gas flow to the jet hole direction dl side in the ignition start timing Ts under the post-TDC ignition control becomes smaller than 5 m / s. On the other hand, if it is on the lower side than the curve a, the clearance gas flow to the jet hole direction dl side in the ignition start timing Ts under the post-TDC ignition control becomes larger than 5 m / s.

[0063] In the present embodiment, since it is intended that the clearance gas flow to the jet hole direction dl side in the ignition start timing Ts under the post-TDC ignition control be 5 m / s or more, the jet hole ratio (S / V) is selected within a region β including the curve a and on the lower side than it. That is, the jet hole ratio (S / V) is selected so as to satisfy the following numerical expression B in which "=" of the numerical expression A is replaced by "<=".

[0064] S / V < -0.025D3+ 0.34D2- 1.4D + 2.1 (Numerical expression B)

[0065] Thus, the clearance gas flow in the ignition start timing Ts under the post-TDC ignition control is set to be 5 m / s or more to the jet hole direction dl side.

[0066] In addition, this curve a varies in the case of environmental changes. Specifically, for example, in the case where the rotational speed of the engine 90 becomes high, the intake air amount becomes large, or an engine 90 with a larger compression ratio is adopted, and the like, the curve a varies to the right upper side. On the other hand, in the case where the rotational speed of the engine 90 becomes low, the intake air amount becomes small, or an engine 90 with a smaller compression ratio is adopted, and the like, the curve a varies to the left lower side. Therefore, in these cases, it is preferable to appropriately correct the numerical expression B.

[0067] However, even without such correction, when executing the top dead center post-ignition control at high speed idling or the like at a generally normal rotational speed, intake air volume, compression ratio, etc., it can be expected that generally good clearance airflow can be obtained at the ignition start timing Ts.

[0068] However, if the nozzle hole ratio (S / V) is less than 0.3, the airflow through the nozzle hole 35 may become too strong, leading to problems such as extinguishing. Therefore, the nozzle hole ratio (opening ratio, S / V) is preferably 0.3 or greater. Furthermore, in Formula B, when the nozzle hole distance D is 0, the right side is 2.1. Therefore, to satisfy Formula B, the nozzle hole ratio (S / V) must be 2.1 or less. Therefore, the nozzle hole ratio (S / V) is selected so that it satisfies Formula B in addition to the following Formula C.

[0069] 0.3≤S / V≤2.1 (Formula C)

[0070] More specifically, the diameter of each nozzle hole 35 is preferably 0.3 mm or larger to prevent the flame passing through the nozzle hole 35 from being extinguished due to cooling loss. Furthermore, the pre-combustion chamber volume V is preferably 0.2 cc or larger to ensure a sufficient ejection volume (heat) to promote flame propagation within the main chamber 31.

[0071] Furthermore, since the nozzle hole distance D also affects the size of the discharge gap 45, it is preferably set by taking into account the power consumption and blowout of the discharge spark f depending on the size of the discharge gap 45. Furthermore, the cross-sectional area of ​​the central nozzle hole 35c is preferably set by taking into account various factors affecting the discharge gap 45. Furthermore, the nozzle hole ratio (S / V) is preferably adjusted based on the cross-sectional area settings of the nozzle holes 35 other than the central nozzle hole 35c.

[0072] exist Figure 6 In the setting step p1 shown, the nozzle hole ratio (S / V) is set as described above. It is preferable to set other settings related to the nozzle hole ratio (S / V) using conventionally known methods. Furthermore, in the manufacturing step p2, the ignition system 70 is manufactured according to the dimensions set in the setting step p1.

[0073] Next, the function of the ignition system 70 of this embodiment will be described.

[0074] Figure 8 (a) is a cross-sectional view showing an ignition system 70 of Comparative Example 1. Comparative Example 1 does not include the partition wall 34 , and the second electrode 46 (ground electrode) is provided separately from the partition wall 34 , and these points are different from the present embodiment. Figure 8Fig. 6 (b) is a sectional view showing the ignition system 70 of Comparative Example 2. Comparative Example 2 differs from Comparative Example 1 in that it has the partition wall 34 but does not have the central injection hole 35c. Also, the first electrode 44 does not protrude downward as in the case of the present embodiment, but instead the second electrode 46 (ground electrode) protrudes greatly toward the first electrode 44 (center electrode) from the partition wall 34, differing in this respect. Also, in this Comparative Example 2, Formula B described above is not satisfied. In addition, in this Comparative Example 2, there is no central injection hole 35c as described above, but since the center of gravity of the closest multiple injection holes 35 is below the discharge gap 45, in this Comparative Example 2 as well, the downward direction is called the injection hole direction dl and the upward direction is called the counter-injection hole direction d2 in correspondence with the present embodiment.

[0075] Figure 8 Fig. 6 (c) is a sectional view showing the ignition system 70 of Mode 1 of the present embodiment, Figure 8 Fig. 6 (d) is a sectional view showing the ignition system 70 of Mode 2 of the present embodiment. Mode 2 differs from Mode 1 in that the injection hole ratio (S / V) is smaller or the injection hole distance D is smaller. In the figure, the injection hole distance D is smaller. Therefore, in Mode 2, the gap flow to the injection hole direction dl side at the ignition start timing Ts under post-TDC ignition control is larger than in Mode 1. In this connection, in Mode 1, the initial ignition source is formed in the pre-chamber 38 or in the central injection hole 35c, and in contrast, in Mode 2, the initial ignition source is formed not only in the pre-chamber 38 or in the central injection hole 35c but also in the main chamber 31.

[0076] Figure 9 Fig. 7 is a time chart showing the progress of combustion in the post-TDC ignition control in these Comparative Examples 1, 2 and Modes 1, 2. In Comparative Example 1, the combustion proceeds in the order of the spark stage sl→ the main chamber ignition stage s2'→ the main chamber propagation stage s5. The beginning of the spark stage sl is the ignition start timing Ts, and the spark stage sl is a stage in which the application of voltage to the discharge gap 45 has started but a flame kernel has not yet been formed in the combustion chamber 30.

[0077] The main chamber ignition stage s2' is a stage in which a flame kernel grows continuously in the main chamber until it becomes an ignition source that can grow on its own. The end of this main chamber ignition stage s2' indicates the main chamber ignition timing Tj, which is the timing at which an ignition source has been formed in the main chamber 31. The main chamber propagation stage s5 is a stage in which the ignition source propagates continuously into the main chamber 31. Also, the end of the main chamber propagation stage s5 indicates the burnout timing Te, which can be regarded as the timing at which 100% of the fuel has been burned.

[0078] On the other hand, in Comparative Example 2 and Mode 1, the combustion proceeds in the order of the spark stage sl→ the prechamber ignition stage s2→ the prechamber propagation stage s3→ the ejection stage s4→ the main chamber propagation stage s5. The prechamber ignition stage s2 is a stage in which a flame kernel continuously grows in the prechamber 38 until it becomes an ignition source capable of self-growth. The end of this prechamber ignition stage s2 indicates the prechamber ignition timing Ti as the timing at which an ignition source is formed in the prechamber 38.

[0079] The prechamber propagation stage s3 is a stage in which the ignition source continuously propagates into the prechamber 38. The ejection stage s4 is a stage in which the flame, i.e., the ignition source, in the prechamber 38 is ejected from the injection hole 35 into the main chamber 31. The beginning of this ejection stage s4 indicates the main chamber ignition timing Tj as the timing at which an ignition source is disposed in the main chamber 31.

[0080] In Mode 2, the discharge spark f extends from the prechamber 38 through the central injection hole 35c into the main chamber 31. Therefore, in addition to the formation of an ignition source in the prechamber 38 or the central injection hole 35c by the discharge spark f, an ignition source is also formed in the main chamber 31. Therefore, in Mode 2, as in the case of Mode 1, the combustion proceeds in the order of the spark stage sl→ the prechamber ignition stage s2→ the prechamber propagation stage s3→ the ejection stage s4→ the main chamber propagation stage s5, and also proceeds in parallel in the order of the spark stage sl→ the main chamber ignition stage s2'→ the main chamber propagation stage s5. As a result, the main chamber ignition timing Tj becomes earlier than in the case of Mode 1.

[0081] In any of Comparative Examples 1 and 2 and Modes 1 and 2, the burnout timing Te is required to be before the exhaust start timing To, which is the timing at which the exhaust valve 26 starts to open. This is to prevent unburned fuel from being discharged. As a result, in any of the modes, the ignition start timing Ts is first set so that the burnout timing Te comes before the exhaust start timing To, and then the ignition start timing Ts is set so that the fuel actually burns out at this burnout timing Te. That is, the ignition start timing Ts is set from the burnout timing Te. Therefore, in each of Comparative Examples 1 and 2 and Modes 1 and 2, although the burnout timing Te is generally the same, the ignition start timing Ts deviates from each other.

[0082] Figure 10 is for convenience Figure 9The time chart of Comparative Example 1, 2 and Form 1, 2 is shown in the graph in which the ignition start timing Ts is aligned. In the case of Comparative Example 2, since the discharge gap 45 is far from the injection hole 35, the ignition source is disposed in the vicinity of the injection hole region R at the end of the prechamber propagation phase s3. The end of the prechamber propagation phase s3 of this Comparative Example 2 is after 20 degrees of crank angle from the ignition start timing Ts. Therefore, in this Comparative Example 2, the ignition source is disposed in the injection hole region R after 20 degrees of crank angle from the ignition start timing Ts. Thereby, the main chamber ignition timing Tj is late, and the progress of combustion is late compared to Comparative Example 1 without the prechamber 38.

[0083] On the other hand, in the case of Form 1 of the present embodiment, since the discharge gap 45 is close to the central injection hole 35c, the timing at which the ignition source is disposed in the injection hole region R is at the first half or so of the prechamber propagation phase s3. The first half or so of the prechamber propagation phase s3 in this Form 1 is within 20 degrees of crank angle from the ignition start timing Ts. Therefore, in this Form 1, the ignition source is disposed in the injection hole region R within 20 degrees of crank angle from the ignition start timing Ts. Thereby, the delay of the main chamber ignition timing Tj is small compared to Comparative Example 1, and finally the progress of combustion is early compared to Comparative Example 1 without the prechamber 38.

[0084] Further, in the case of Form 2 of the present embodiment, the timing at which the ignition source is formed by the discharge spark f in the main chamber 31 becomes the main chamber ignition timing Tj at the end of the main chamber ignition phase s2'. The main chamber ignition timing Tj of this Form 2 is within 20 degrees of crank angle from the ignition start timing Ts. Therefore, in this Form 2, the ignition source is disposed in the main chamber 31 within 20 degrees of crank angle from the ignition start timing Ts. Thereby, the progress of combustion becomes even earlier compared to Form 1.

[0085] Figure 11 is a graph showing the progress of the combustion ratio of each form of Comparative Examples 1, 2 and Form 1. As described above, in Comparative Example 2, the progress of the combustion ratio is late compared to Comparative Example 1 without the prechamber 38, and in contrast, in Form 1, the progress of the combustion ratio is fast compared to Comparative Example 1.

[0086] Figure 12 is a graph obtained by enlarging a part of Figure 9 . Figure 13 is a graph showing Figure 12the direction of the gap flow is still the backjet direction d2 side. This is because, on the inner side of the prechamber 38, the gap flow, even after the compression top dead center Td, for a while, is directed to the backjet direction d2 side due to inertia and the like. Then, after the intensity of the gap flow temporarily becomes zero, the direction of the gap flow is turned to the jet direction dl side. Therefore, the flow at this time is weak, and the discharge spark f does not effectively elongate, so ignition cannot be effectively performed.

[0087] In this regard, in the modes 1, 2 of the present embodiment, as described above, before the ignition start timing Ts under the post-top dead center ignition control, the direction of the gap flow is already turned from the backjet direction d2 side to the jet direction dl side. Thereby, at the ignition start timing Ts, a certain degree of strong flow, specifically 5 m / s or more, is generated toward the jet direction dl side. Therefore, the discharge spark f easily elongates in the jet direction dl. Therefore, in addition to the fact that the flame kernel easily grows, this growth easily occurs in or near the jet vicinity region R or the like. Therefore, in this regard, in the modes 1, 2 of the present embodiment, it is also easy to arrange the ignition source in the jet vicinity region R or the like at an early stage.

[0088] Reference will again be made to Figure 9 be described. As described above, the burnout timing Te is required to be an earlier timing than the exhaust start timing To. Therefore, because of this constraint, in the comparative examples 1, 2 in which the combustion time, which is the time from the ignition start timing Ts to the burnout timing Te, is long, it is also not possible to set the ignition start timing Ts on the side of the retard angle at the high-speed idle time when the timing of the desired combustion is delayed as much as possible. Therefore, the combustion center of gravity Tc, which is the timing of 50% burnout of the fuel, also cannot be set on the side of the retard angle, and catalyst warm-up cannot be effectively performed in the high-speed idle.

[0089] In this regard, in the modes 1, 2, compared to the comparative examples 1, 2, it is possible to suppress the combustion time, which is the time from the ignition start timing Ts to the burnout timing Te, to be shorter, so it is possible to set the ignition start timing Ts on the side of the retard angle more. Therefore, it is possible to set the combustion center of gravity Tc on the side of the retard angle more, and catalyst warm-up can be effectively performed in the high-speed idle. Therefore, it leads to a reduction in the high-speed idle time, and further to an improvement in fuel consumption and a reduction in emissions.

[0090] According to the present embodiment, the following effects are obtained. In the post-top dead center ignition control, at an early stage within 20 degrees of crank angle from the ignition start timing Ts, the ignition source is arranged in the jet vicinity region R or the like Figure 2the vicinity of the injection hole, in the central injection hole 35c, or in the main chamber 31. Also, in a case where the ignition source is disposed in the vicinity of the injection hole R or in the central injection hole 35c, a flame growing from the ignition source is easily ejected from the central injection hole 35c into the main chamber 31. Further, in a case where the ignition source is disposed in the main chamber 31, a flame growing from the ignition source is propagated as it is into the main chamber 31. Therefore, in the after-top dead center ignition control, the flame can be propagated into the main chamber 31 quickly.

[0091] Further, according to the above-described Mode 2, the following effects can also be obtained. In the after-top dead center ignition control of Mode 2, the discharge spark f is elongated into the main chamber 31. Thereby, in an early stage within 20 degrees of crank angle from the ignition start timing, the ignition source is disposed into the main chamber 31. A flame growing from the ignition source is propagated as it is into the main chamber 31. Therefore, according to the above-described Mode 2, the flame can be propagated into the main chamber 31 more quickly.

[0092] Further, the following effects can also be obtained. The sizes of the prechamber 38 and the injection hole 35 are set so that the injection hole ratio (S / V) is included in Figure 7 The region β, as described above, is a region in which the gap flow at the ignition start timing Ts under the after-top dead center ignition control is 5 m / s or more toward the injection hole direction dl. Also, if the gap flow becomes 5 m / s or more toward the injection hole direction dl, it is easy to dispose the ignition source into the vicinity of the injection hole R or the like in an early stage, as described above.

[0093] Further, the region β, although it slightly varies depending on the environment or the like, in a case where the after-top dead center ignition control is performed generally at a normal rotational speed, an intake air amount, a compression ratio, or the like, it is expected that a generally good gap flow can be obtained at the ignition start timing Ts. Therefore, by setting the injection hole ratio (S / V) so as to be included in the region β, it is easy to realize a structure in which the ignition source is disposed into the vicinity of the injection hole R or the like in an early stage.

[0094] Further, the following effects can also be obtained. As described above, in a case where the injection hole ratio (S / V) is less than 0.3, it is easy to occur a disadvantage or the like in which the gas flow passing through the injection hole 35 becomes too strong and blowout occurs. In this regard, in the present embodiment, since the injection hole ratio (opening ratio, S / V) is 0.3 or more, there is no such concern.

[0095] Further, the following effects can be obtained. In the present embodiment, as Figure 13As shown, before the ignition start timing Ts in the after-top dead center ignition control, the direction of the gap gas flow shifts from the reverse hole direction d2 side to the hole direction dl side. Therefore, at the ignition start timing Ts in the after-top dead center ignition control, the direction of the gap gas flow becomes the hole direction dl side. Therefore, it is possible to effectively elongate the discharge spark f toward the hole direction dl side. Therefore, at this point, it is also easy to arrange the ignition source in the early stage into the hole vicinity region R or the like.

[0096] [Other Embodiments]

[0097] The above-described embodiments can also be implemented by being changed as follows. For example, in the first embodiment, the plurality of holes 35 are provided in the partition wall 34, but the hole 35 can be only one central hole 35c. Further, for example, in the first embodiment, the first electrode 44 is closest to the central hole 35c, but it can be closest to the other hole 35, causing the discharge spark f to elongate toward the other hole 35. Further, for example, in the first embodiment, the partition wall 34 functions as the second electrode 46, and is electrically conducted to the cylinder head 20 by being attached to the cylinder head 20, but it can be that a portion of the partition wall 34, such as a protrusion, which is electrically conducted to the partition wall 34, constitutes the second electrode 46. Further, the second electrode 46 that is electrically conducted to the cylinder head 20 can be constituted by a member different from the partition wall 34.

[0098] Further, for example, in the first embodiment, the partition wall 34 is attached to the insulator 41 of the spark plug 40. Instead, the partition wall 34 can be provided in the cylinder head 20, and the spark plug 40 can be attached in such a manner that the insulator 41 is engaged with the partition wall 34 of the cylinder head 20.

[0099] The present disclosure has been described based on the embodiments, but it should be understood that the present disclosure is not limited to the embodiments or configurations. The present disclosure also includes various modifications or modifications within the equivalent scope. In addition to this, various combinations and modes, and further, only one element, combinations or modes above or below are included in them, fall within the scope or the idea of the present disclosure.

Claims

1. An ignition system, have: a partition wall dividing the combustion chamber of the engine into a main chamber and a pre-combustion chamber, wherein the partition wall is provided with one or more injection holes communicating from the main chamber to the pre-combustion chamber; and The spark plug applies voltage to the discharge gap between the first electrode and the second electrode, thereby generating a discharge spark to ignite the fuel. The first electrode is arranged in the pre-combustion chamber, and the second electrode is arranged on the partition wall or a portion electrically connected to the partition wall. The timing of starting to apply voltage to the discharge gap is defined as the ignition start timing, the center of the opening of the nozzle hole on the pre-combustion chamber side is defined as the nozzle hole center, and the area within 3 mm from the nozzle hole center in the pre-combustion chamber is defined as the nozzle hole vicinity. When the engine is in a predetermined operating state, the ignition system performs post-top dead center ignition control, which is control for performing the ignition after compression top dead center. In the above-mentioned after-top-dead-center ignition control, within a crank angle of 20 degrees from the above-mentioned ignition start timing, an ignition source as a flame kernel of a size capable of self-growth is arranged in the area near the above-mentioned injection hole, in the above-mentioned injection hole, or in the above-mentioned main chamber, Assume that the volume of the pre-combustion chamber is V, in cc, and the sum of the cross-sectional areas of all the nozzle holes provided in the partition wall is S, in mm^2. Assume that the nozzle hole closest to the first electrode among the one or more nozzle holes is a near nozzle hole, and the distance from the first electrode to the near nozzle hole is D, in mm. The above ignition system is configured to meet S / V≤-0.025D^3+0.34D^2-1.4D+2.

1.

2. The ignition system according to claim 1, In the after-top-dead-center ignition control, the discharge spark is extended into the main chamber, and the ignition source is arranged in the main chamber within a crank angle of 20 degrees from the ignition start timing.

3. The ignition system according to claim 1, The configuration is such that an air flow having a flow velocity of 5 m / s or more flows through the discharge gap during the generation period of the discharge spark in the after-top-dead-center ignition control.

4. The ignition system according to claim 2, The configuration is such that an air flow having a flow velocity of 5 m / s or more flows through the discharge gap during the generation period of the discharge spark in the after-top-dead-center ignition control.

5. The ignition system according to any one of claims 1 to 4, The above ignition system is configured to meet 0.3≤S / V≤2.

1.

6. The ignition system according to any one of claims 1 to 4, The direction from the first electrode toward the nozzle-approaching hole is defined as the nozzle direction, the direction opposite to the nozzle direction is defined as the anti-injection direction, the direction including the nozzle direction as an element is defined as the nozzle direction side, the direction including the anti-injection direction as an element is defined as the anti-injection direction side, and the airflow flowing in the discharge gap is defined as the gap airflow. The ignition system is configured such that, before the ignition start timing in the after-top-dead-center ignition control, the direction of the gap airflow is changed from the anti-injection-hole direction side to the injection-hole direction side, thereby changing the direction of the gap airflow to the injection-hole direction side at the ignition start timing.

7. The ignition system according to claim 5, The direction from the first electrode toward the nozzle-approaching hole is defined as the nozzle direction, the direction opposite to the nozzle direction is defined as the anti-injection direction, the direction including the nozzle direction as an element is defined as the nozzle direction side, the direction including the anti-injection direction as an element is defined as the anti-injection direction side, and the airflow flowing in the discharge gap is defined as the gap airflow. The ignition system is configured such that, before the ignition start timing in the after-top-dead-center ignition control, the direction of the gap airflow is changed from the anti-injection-hole direction side to the injection-hole direction side, thereby changing the direction of the gap airflow to the injection-hole direction side at the ignition start timing.

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