WO2021157322A1 - Subsidiary chamber type ignition system - Google Patents

Abstract

A subsidiary chamber type ignition system (70) comprises: a partition wall (34) that partitions a combustion chamber (30) of an engine (90) into a subsidiary chamber (38) and a main chamber (31); and an ignition plug (40) that ignites fuel inside the subsidiary chamber (38). In a high load state, an ignition control unit (60) calculates optimum ignition timing (T1) earlier by a combustion time (t15) than prescribed optimum combustion timing (T5) as shown in Fig. 9(c), and performs optimum ignition control to control ignition timing (t1) at the optimum ignition timing (T1). In a low load state, a jetting control unit (63) performs jetting delay prevention control to prevent a jetting time (t13) from being longer compared with the high load state as shown in Fig. 9(d) to prevent the combustion time (t15) from being long, while the ignition control unit (60) performs the above optimum ignition control.

Description

Sub-chamber ignition system Cross-reference of related applications

This application is based on Japanese Application No. 2020-017879 filed on February 5, 2020, and the contents of the description are incorporated herein by reference.

The present disclosure relates to a sub-chamber ignition system that ignites fuel in the sub-chamber of a combustion chamber divided into a main chamber and a sub-chamber.

The sub-chamber ignition system has a partition wall that divides the combustion chamber of the engine into a sub-chamber and a main chamber, an ignition plug that ignites fuel in the sub-chamber, and an ignition control unit that controls the spark plug. Some partition walls are provided with a communication hole for communicating the sub chamber and the main chamber. Then, as a document showing such a technique, there is the following Patent Document 1.

Japanese Unexamined Patent Publication No. 2009-270541

In the above-mentioned sub-chamber ignition system, the fuel in the sub-chamber is first ignited and the flame spreads in the sub-chamber, and then the flame is ejected from the communication hole into the main chamber and the flame spreads in the main chamber. become. Therefore, the time from ignition to the spread of the flame in the main chamber becomes long. Then, such a problem becomes particularly remarkable in a low load state in which the magnitude of the load applied to the engine is small. That is, in a low load state where the amount of depression of the accelerator is small, the amount of fuel supplied to the combustion chamber is reduced, so that the amount of fuel in the sub-chamber or main chamber is reduced and it becomes difficult to burn. This is because the progress of combustion in the main chamber is slowed down. Therefore, when the load is low in the sub-chamber ignition system, the time from ignition to the spread of the flame in the main chamber becomes long, particularly remarkably.

Therefore, the present discloser has focused on the following problems when the following optimum ignition control is performed in a low load state in the sub-chamber ignition system. In the following, the timing at which the spark plug ignites is referred to as “ignition timing”, and the timing at which a predetermined amount of fuel in the combustion chamber is burned after the ignition timing is referred to as “combustion timing”. Then, the time from the ignition timing to the combustion timing is defined as the "combustion time".

In the optimum ignition control, the optimum ignition timing, which is the timing earlier than the optimum combustion timing as the optimum combustion timing, is calculated. The ignition timing is controlled to the optimum ignition timing. However, in the low load state in the sub-chamber ignition system, as described above, the time from ignition to the spread of the flame in the main chamber becomes long, so that the above-mentioned combustion time becomes long. As a result, the optimum ignition timing, which is earlier than the optimum combustion timing by the amount of the combustion time, becomes too early.

Then, if the calculated optimum ignition timing is too early, it becomes virtually impossible to control the ignition timing to that optimum ignition timing. When actually ignited at the optimum ignition timing, the amount of combustion before the compression top dead point, that is, in the compression stroke becomes too large, and the reverse torque generated by the combustion, that is, the reverse applied in the direction of attenuating the rotation of the engine. This is because the torque in the direction cancels out a part of the torque of the engine and the torque drops.

Therefore, when the load is low in the sub-chamber ignition system, there is no choice but to control the ignition timing later than the optimum ignition timing. However, in that case, since the combustion timing is later than the optimum combustion timing, it becomes impossible to efficiently obtain the torque.

The present disclosure has been made in view of the above circumstances, and its main purpose is to enable the ignition timing to be controlled to the optimum ignition timing even in a low load state in the sub-chamber ignition system.

The sub-chamber type ignition system of the present disclosure uses a partition wall that divides the combustion chamber of an engine into a sub-chamber and a main chamber, and applies a voltage to a predetermined discharge gap to generate a discharge spark to use the fuel in the sub-chamber. It has an ignition plug for igniting and an ignition control unit for controlling the ignition plug. Then, a communication hole for communicating the sub chamber and the main chamber is formed in the partition wall.

In the following, a state in which the load applied to the engine is a predetermined magnitude is defined as a high load state, and a state in which the load applied to the engine is smaller than the predetermined magnitude is defined as a low load state. Further, the timing at which the spark plug starts discharging in the discharge gap is defined as the ignition timing, and the timing at which a predetermined amount of fuel in the combustion chamber is burned after the ignition timing is defined as the combustion timing. Then, the time from the ignition timing to the combustion timing is defined as the combustion time.

The ignition control unit calculates the optimum ignition timing which is the timing earlier than the optimum combustion timing as the optimum combustion timing by the combustion time, and controls the ignition timing to the optimum ignition timing. This is performed in the high load state.

In the following, the timing at which the flame generated in the sub chamber starts to eject from the communication hole into the main chamber between the ignition timing and the combustion timing is defined as the ejection timing. Then, the time from the ignition timing to the ejection timing is defined as the ejection time.

The ignition control unit has an ejection control unit that performs ejection delay suppression control that suppresses the ejection time from becoming longer in the low load state as compared with the high load state. Then, in the low load state, the ejection delay suppression control is performed by the ejection control unit, so that the combustion time is suppressed to be longer than in the high load state, and the ignition control unit performs the ejection delay suppression control. Optimal ignition control is performed.

According to the present disclosure, it is possible to suppress an increase in combustion time as compared with a high load state by performing ejection delay suppression control in a low load state. Therefore, it is possible to prevent the optimum ignition timing, which is earlier than the optimum combustion timing by the amount of the combustion time, from becoming too early. As a result, it becomes possible to control the ignition timing to the optimum ignition timing even in a low load state in the sub-chamber ignition system. Then, by actually performing the optimum ignition control, the ignition timing is controlled to the optimum ignition timing. As a result, the combustion timing is controlled to the optimum combustion timing, and torque can be efficiently generated.

The above objectives and other objectives, features and advantages of the present disclosure will be clarified by the following detailed description with reference to the accompanying drawings. The drawing is
FIG. 1 is a cross-sectional view showing the ignition system of the first embodiment. FIG. 2 is a cross-sectional view showing the sub-chamber and its surroundings. FIG. 3 is a circuit diagram showing a circuit of the spark plug and its surroundings. FIG. 4 is a timing chart showing ignition by a spark plug. FIG. 5 is a graph showing the control of discharge energy. FIG. 6 is a cross-sectional view showing the sub chamber and its surroundings in the ignition control before top dead center. FIG. 7 is a cross-sectional view showing the sub chamber and its surroundings in ignition control after top dead center. FIG. 8 is a graph showing the change in the flow velocity of the continuous airflow. FIG. 9 is a timing chart showing the progress of combustion. FIG. 10 is a flowchart showing control by the ignition control unit.

Next, the embodiment of the present disclosure will be described with reference to the drawings. However, the present disclosure is not limited to the embodiment, and can be appropriately modified and implemented without departing from the spirit of the disclosure.

[First Embodiment]
FIG. 1 is a cross-sectional view showing the sub-chamber ignition system 70 of the first embodiment. The sub-chamber ignition system 70 is installed with respect to the engine 90. The engine 90 is a four-stroke engine in which one combustion cycle consists of four strokes of intake stroke → compression stroke → expansion stroke → exhaust stroke. In the following, the top dead center between the compression stroke and the expansion stroke among them is referred to as "compression top dead center tD". The engine 90 has a cylinder 10 and a head 20 attached to the top of the cylinder 10.

In the following, the length direction of the center line X of the cylinder 10 will be described as the vertical direction according to the drawing. However, for example, the engine 90 and the sub-chamber ignition system 70 may be installed with the center line X oblique to the vertical direction, or the engine 90 and the sub-chamber ignition system 70 may be installed with the center line X horizontal. The engine 90 and the sub-chamber ignition system 70 can be installed in any direction.

A piston 18 is installed in the cylinder 10. The piston 18 is connected to the crankshaft 11 via a link 12, and moves up and down according to the rotation of the crankshaft 11. A combustion chamber 30 is formed above the piston 18.

The head 20 is provided with an intake passage 21 for sucking gas into the combustion chamber 30 and an exhaust passage 29 for discharging the gas in the combustion chamber 30. An intake valve 24 is installed in the intake passage 21, and an exhaust valve 26 is installed in the exhaust passage 29. The intake valve 24 is driven by the intake cam 23, and the exhaust valve 26 is driven by the exhaust cam 27. The head 20 is provided with a fuel injection device 22 for injecting fuel into the intake passage 21.

The sub-chamber ignition system 70 includes an ignition plug 40 attached to the head 20, an air flow support structure As for facilitating the flow of air flow into the discharge gap 45 of the ignition plug 40, sensors 51 to 53, and each sensor. It has an ignition control unit 60 that controls the spark plug 40 based on inputs from 51 to 53.

Each sensor 51 to 53 includes a crank sensor 51, an intake pressure sensor 52, and a water temperature sensor 53. The crank sensor 51 detects the crank angle and the rotational speed of the engine 90. The intake pressure sensor 52 detects the intake pressure, which is the air pressure of the intake passage 21. The water temperature sensor 53 detects the temperature of the cooling water for cooling the engine 90.

The ignition control unit 60 is a part of an ECU (electronic control unit) or the like, and has an ejection control unit 63 and an airflow control unit 64. The ejection control unit 63 controls the ejection time t13, which is the time from when the fuel in the sub chamber 38 is ignited by the spark plug 40 until the flame starts to eject into the main chamber.
Specifically, the ejection control unit 63 includes the load applied to the engine 90, the air-fuel ratio of the engine 90, the EGR amount which is the amount of returning the exhaust gas to the intake air in the engine 90, and the water temperature of the cooling water of the engine 90. Based on each parameter such as, the fluctuation of the ejection time t13 is controlled to be small even by the fluctuation of those parameters. The above load may be calculated from, for example, the amount of depression of the accelerator pedal, the load applied to the engine 90 may be directly detected, or may be calculated from a change in the rotational speed of the engine 90 or the like. .. The airflow control unit 64 controls the spark plug 40 so that the discharge spark F of the spark plug 40 is not interrupted by the airflow caused by the airflow support structure As.

FIG. 2 is a cross-sectional view showing the 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 attached to the lower end of the insulating insulator 41. The combustion chamber 30 is divided into a main chamber 31 and a sub chamber 38 by the partition wall 34. Specifically, the inside of the partition wall 34 constitutes the sub chamber 38, and the outside of the partition wall 34 constitutes the main chamber 31. The partition wall 34 is made of a conductor and also serves as a ground electrode for the spark plug 40.

A plurality of communication holes 35 are formed in the partition wall 34, and the sub chamber 38 and the main chamber 31 communicate with each other 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 just above the central communication hole 35c. That is, the lower portion of the center electrode 44 extends downward from the lower end of the insulating insulator 41 and is close to the central communication hole 35c. The gap between the lower end of the center electrode 44 and the peripheral portion of the upper end of the central communication hole 35c in the partition wall 34 constitutes the discharge gap 45. Therefore, the discharge gap 45 is provided in the sub chamber 38 in the immediate vicinity of the central communication hole 35c, and is closest to the central communication hole 35c among the plurality of communication holes 35.

As described above, since the discharge gap 45 is close to the central communication hole 35c, the airflow can easily flow through the discharge gap 45. This structure constitutes the airflow support structure As. That is, as the airflow support structure As, a structure in which the discharge gap 45 is close to the central communication hole 35c is formed. The spark plug 40 generates a discharge spark F by applying a voltage to the discharge gap 45. The discharge spark F is extended by the airflow due to the airflow support structure As, so that the ignitability to the fuel is improved.

FIG. 3 is a circuit diagram showing the circuit of the spark plug 40 and its surroundings. The spark plug 40 has a primary coil 412 and a secondary coil 421. The primary coil 412 and the secondary coil 421 are wound around the core 401. A battery 411 and a switching element 413 are connected in series to the primary coil 412. On the other hand, the discharge gap 45 and the diode 422 are connected in series to the secondary coil 421. The switching element 413 is controlled by the ignition control unit 60.

In the following, the direction in which current flows in the secondary coil 421 when the switching element 413 is turned from ON to OFF is referred to as "forward direction", and the opposite direction is referred to as "reverse direction". The diode 422 is installed in a direction that allows a forward current to flow and prevents a current from flowing in the reverse direction.

FIG. 4 is a timing chart showing the control of the spark plug 40. As shown in FIG. 4A, when the ignition signal becomes High at a predetermined energization timing t0, the ignition control unit 60 turns on the switching element 413 accordingly. As a result, the primary current shown in FIG. 4B begins to flow in the primary coil 412, and the primary current increases with the passage of time. As a result, as shown in FIG. 4 (e), the discharge energy E is stored in the primary coil 412 in the form of magnetic energy. Then, the ignition signal shown in FIG. 4A becomes Low at the ignition timing t1 after a predetermined charging time t01 from the energization timing t0. As a result, the secondary voltage shown in FIG. 4C is generated in the secondary coil 421, causing dielectric breakdown in the discharge gap 45. As a result, the secondary current shown in FIG. 4D flows through the discharge gap 45, and a discharge spark F is generated in the discharge gap 45. After that, as shown in FIG. 4 (e), the discharge energy E stored as magnetic energy decreases as the secondary current shown in FIG. 4 (d) flows, and the secondary current increases accordingly. The size also decreases.

Next, the control of the discharge energy E applied to the discharge gap 45 will be described with reference to FIG. FIG. 5A is a graph showing the time change of the primary current when the discharge energy E is controlled to be relatively small, and FIG. 5B is a graph showing the time change of the primary current when the discharge energy E is controlled to be relatively large. It is a graph which shows the time change of an electric current. As shown in FIG. 5 (a), when the discharge energy E is controlled to be relatively small, the charging time t01 is set relatively short, and as shown in FIG. 5 (b), the discharge energy E is relatively small. In the case of large control, the charging time t01 is set to be relatively long. By the above control, the ejection control unit 63 and the airflow control unit 64 control the discharge energy E.

FIG. 6 is a cross-sectional view showing the sub-chamber 38 and its surroundings in the pre-dead center ignition control in which ignition is performed before the compression top dead center tD (that is, the compression stroke). Such pre-dead center ignition control is performed at normal times. Hereinafter, the airflow flowing through the central communication hole 35c is referred to as “communication flow A”. At the time of ignition in the ignition control before top dead center, an upward continuous airflow A flowing from the main chamber 31 side to the sub chamber 38 side flows into the discharge gap 45. Due to the continuous airflow A, the discharge spark F extends upward in the sub chamber 38. The extended discharge spark F ignites a flame in the fuel in the sub chamber 38. As a result, the flame generated in the sub chamber 38 propagates into the sub chamber 38 and then is discharged from each communication hole 35 toward the inside of the main chamber 31.

FIG. 7 is a cross-sectional view showing the sub-chamber 38 and its surroundings in the post-top dead center ignition control in which ignition is performed after the compression top dead center tD (that is, the expansion stroke). Such post-dead center ignition control is performed when the engine 90 is in a predetermined operating condition, such as during first idling. During the first idling, after the engine 90 is started, the idle speed is set higher than usual due to catalyst warm-up or the like. At the time of ignition in the ignition control after top dead center, a downward continuous airflow A flowing from the sub chamber 38 side to the main chamber 31 side flows into the discharge gap 45. Due to the communication flow A, the discharge spark F extends from the sub chamber 38 into the main chamber 31 through the central communication hole 35c. The extended discharge spark F ignites the fuel in both the sub chamber 38 and the main chamber 31.

FIG. 8 is a graph showing an image of a change in the flow velocity (absolute value) of the continuous airflow A. The flow velocity flowing through the discharge gap 45 is substantially proportional to the flow velocity of the continuous airflow A. Specifically, in the communication flow A, in the latter half of the compression stroke, the gas in the main chamber 31 flows concentratedly in each communication hole 35 including the central communication hole 35c, so that the main chamber 31 and the sub chamber 38 flow. It becomes stronger than the air flow inside. Therefore, the airflow flowing through the discharge gap 45 close to the central communication hole 35c is also stronger than the airflow in the main chamber 31 and the sub chamber 38. After that, as shown in FIG. 8, the flow velocity of the continuous airflow A decreases as it approaches the compression top dead center tD, and temporarily becomes substantially zero at or near the compression top dead center tD. However, the continuous airflow A occurs rapidly again after the compression top dead center tD. In the communication flow A, when the piston 18 starts descending and a pressure difference begins to occur between the sub chamber 38 and the main chamber 31, the gas in the sub chamber 38 includes the central communication hole 35c. This is because it is generated promptly by concentrating the flow in each communication hole 35.

The sub-chamber ignition system 70 positively utilizes this continuous ventilation flow A to allow an air flow to flow through the discharge gap 45. That is the above-mentioned airflow support structure As. As described above, the continuous airflow A becomes stronger as the distance from the compression top dead center tD increases. Specifically, before the compression top dead center tD, that is, in the latter half of the compression stroke, the airflow flowing through the discharge gap 45 becomes stronger as the crank angle advances from the compression top dead center tD. On the other hand, after the compression top dead center tD, that is, in the first half of the expansion stroke, the more the crank angle is retarded from the compression top dead center tD, the stronger the airflow flowing through the discharge gap 45. Therefore, the farther the ignition timing t1 is from the compression top dead center tD, the easier it is for the discharge spark F to be blown out. Therefore, the anti-airflow control unit 64 controls the discharge energy E so that the discharge spark F is not interrupted by the airflow.

Specifically, the anti-airflow control unit 64 compares with the case where the ignition timing t1 is a predetermined timing at the time of ignition control before top dead center, that is, when ignition is performed in the latter half of the compression stroke. When the ignition timing t1 is earlier than the predetermined timing, the discharge energy E is controlled to be large. More specifically, for example, the discharge energy E is controlled to increase as the ignition timing t1 becomes earlier.

On the other hand, in the airflow control unit 64, when the ignition is controlled after the top dead center, that is, when the ignition is performed in the first half of the expansion stroke, the ignition timing t1 is compared with the case where the ignition timing t1 is a predetermined timing. Is controlled so that the discharge energy E becomes large when the timing is later than the predetermined timing. More specifically, for example, the discharge energy E is controlled to increase as the ignition timing t1 is delayed.

FIG. 9 is a timing chart showing the progress of combustion in the ignition control before top dead center. In the following, the timing at which the spark plug 40 applies a voltage to the discharge gap 45 is referred to as “ignition timing t1”. Further, after the ignition timing t1, the timing at which the flame is ignited by the discharge spark F is defined as the “secondary chamber ignition timing t2”. Further, after the ignition timing t2 of the sub chamber, the timing at which the flame generated in the sub chamber 38 starts to be ejected from the communication hole 35 into the main chamber 31 is defined as “spout timing t3”. Further, after the ejection timing t3, the timing at which the flame starts to ignite in earnest on the fuel in the main chamber 31 due to the ejected flame is defined as the “main chamber ignition timing t4”. Further, the timing at which a predetermined amount of fuel (for example, 50% of the mass) in the combustion chamber 30 is in a burned state after the ignition timing t4 of the main chamber is referred to as “combustion timing t5”.

The period from the ignition timing t1 to the sub-chamber ignition timing t2 is defined as the "spark stage period t12". Further, the period from the ignition timing t2 of the sub-chamber to the ejection timing t3 is defined as the “sub-chamber propagation period t23”. Further, the period from the ejection timing t3 to the main chamber ignition timing t4 is defined as the “flame ejection period t34”. Further, the period from the main chamber ignition timing t4 to the combustion timing t5 is defined as the "main chamber propagation period t45". Further, the time from the ignition timing t1 to the ejection timing t3 is defined as the “spouting time t13”. Further, the time from the ignition timing t1 to the combustion timing t5 is defined as "combustion time t15".

9 (a) and 9 (b) are timing charts showing the progress of combustion in the pre-dead center ignition control in the comparative example. In the comparative example, the same or corresponding members and the like as those of the first embodiment will be described with the same reference numerals. The sub-chamber ignition system 70 of the comparative example is different from that of the present embodiment in that it does not have the airflow support structure As shown in FIG. That is, the sub-chamber ignition system 70 of the comparative example has a shorter center electrode 44 and a ground electrode separate from the partition wall 34 as compared with the present embodiment. Therefore, the discharge gap 45 is not close to the central communication hole 35c. Further, the sub-chamber ignition system 70 of the comparative example is different from the present embodiment in that the ignition control unit 60 shown in FIG. 1 does not have the ejection control unit 63.

FIG. 9A is a timing chart showing the progress of combustion in a high load state in the ignition control before top dead center in the comparative example. Here, the ignition control unit 60 performs the following optimum ignition control. In the optimum ignition control, first, the optimum combustion timing T5 as the optimum combustion timing t5 is acquired. The optimum combustion timing T5 is, for example, the combustion timing t5 at which the obtained torque is substantially maximized, and more specifically, for example, the timing 10 CA (crank angle) after the compression top dead center tD. Next, the burning time t15 is calculated. The details will be described later. Next, the optimum ignition timing T1 which is a timing earlier than the optimum combustion timing T5 by the combustion time t15 is calculated. Next, the ignition timing t1 is controlled at the optimum ignition timing T1. By the above optimum ignition control, the combustion timing t5 is controlled at the optimum combustion timing T5.

FIG. 9B is a timing chart showing the progress of combustion in a low load state in the ignition control before top dead center in the comparative example. Here, if the optimum ignition timing T1 is calculated by the optimum ignition control, which is earlier than the optimum combustion timing T5 by the combustion time t15, the optimum ignition timing T1 becomes too early. Therefore, if ignition is performed at the optimum ignition timing T1, the amount of combustion before the compression top dead center tD, that is, in the compression stroke becomes too large, and the reverse torque generated by the combustion causes the torque of the engine 90 to increase. It is offset and the torque drops. Therefore, in this low load state, the optimum ignition control cannot be performed, and the ignition timing t1 is controlled at a timing later than the optimum ignition timing T1. As a result, the timing later than the optimum combustion timing T5 becomes the combustion timing t5.

FIG. 9C is a timing chart showing the progress of combustion in a high load state in the pre-dead center ignition control in the present embodiment. Also in this embodiment, the same optimum ignition control as in the comparative example is performed. However, since the airflow support structure As is provided in the present embodiment, the discharge spark F is extended as compared with the high load state of the comparative example shown in FIG. 9A. As a result, the ignitability in the sub chamber 38 is improved, and the spark stage period t12 before the sub chamber ignition timing t2 is shortened. Further, the extension of the discharge spark F causes the flame to ignite strongly and firmly to the fuel in the sub chamber 38. As a result, the flame is easily propagated in the sub-chamber 38, and the sub-chamber propagation period t23 is shortened. As a result, the ejection time t13 is shortened. Further, the flame ejection period t34 and the main chamber propagation period t45 are also slightly shortened accordingly. Due to the action of the airflow support structure As described above, the combustion time t15 becomes shorter than that in the high load state of the comparative example shown in FIG. 9A.

At this time, if the ignition timing t1 is the same as in the high load state of the comparative example shown in FIG. 9 (a) as shown by the broken line in FIG. 9 (c), the combustion timing t5 is the optimum combustion. It will be earlier than the timing T5. Therefore, in the present embodiment, the ignition timing t1 is controlled by the optimum ignition control so that the ignition timing t1 is delayed by the shorter the combustion time t15 as compared with the comparative example.

FIG. 9D is a timing chart showing the progress of combustion in a low load state in the ignition control before top dead center in the present embodiment. Since there is an airflow support structure As in this embodiment, the combustion time t15 is shorter than that in the low load state of the comparative example shown in FIG. 9B by itself. Further, in addition to that, the ejection control unit 63 performs ejection delay suppression control for suppressing the ejection time t13 from becoming longer in the low load state as compared with the high load state, so that the combustion time t15 is further increased. It gets shorter.

Specifically, in the low load state, the discharge energy E is increased as compared with the high load state as the ejection delay suppression control. As a result, the ignitability in the sub chamber 38 is improved. As a result, the spark stage period t12 before the sub-chamber ignition timing t2 is shorter than that in the case where the ejection delay suppression control is not performed. Further, as the discharge energy E becomes large, the fuel in the sub chamber 38 is strongly ignited with a strong flame. Therefore, the flame is easily propagated in the sub chamber 38, and the sub chamber propagation period t23 is shortened as compared with the case where the ejection delay suppression control is not performed. As a result, the ejection time t13 is shortened as compared with the case where the ejection delay suppression control is not performed, and the flame ejection period t34 and the main chamber propagation period t45 are also slightly shortened accordingly. Due to the action of the ejection delay suppression control as described above, the combustion time t15 is shortened as compared with the low load state of the comparative example shown in FIG. 9B. That is, due to the actions of both the airflow support structure As and the ejection delay suppression control, the combustion time t15 is remarkably shortened as compared with the low load state of the comparative example shown in FIG. 9B.

Therefore, in the low load state of the present embodiment shown in FIG. 9 (d), unlike the low load state of the comparative example shown in FIG. 9 (b), the optimum ignition control is performed by the amount of the combustion time t15. Even if the optimum ignition timing T1 that is earlier than the optimum combustion timing T5 is calculated, the optimum ignition timing T1 does not become too early. Therefore, even if the ignition timing t1 is controlled at the optimum ignition timing T1, the amount of combustion before the compression top dead center tD, that is, in the expansion stroke, does not become too large and the reverse torque does not become too strong. .. Therefore, in the present embodiment, the optimum ignition control can be performed even in a low load state. Then, by actually performing the optimum ignition control, that is, by controlling the ignition timing t1 at the optimum ignition timing T1, the combustion timing t5 can be controlled at the optimum combustion timing T5.

FIG. 10 is a flowchart showing control by the ignition control unit 60 having the ejection control unit 63 and the airflow control unit 64 shown above. First, each sensor 51 to 53 acquires each parameter indicating the operating status of the engine 90 (S101).

Next, the discharge energy E and the optimum ignition timing T1 are calculated based on those parameters (S102). That is, the ejection control unit 63 calculates the discharge energy E based on the load applied to the engine 90, the air-fuel ratio of the engine 90, the amount of EGR in the engine 90, the temperature of the cooling water of the engine 90, and the like.

Specifically, the ejection control unit 63 calculates so that the discharge energy E becomes larger when the air-fuel ratio is larger than the predetermined air-fuel ratio as compared with the case where the air-fuel ratio is the predetermined air-fuel ratio. More specifically, for example, the larger the air-fuel ratio, the larger the discharge energy E. Further, the ejection control unit 63 controls so that the discharge energy E becomes larger when the EGR amount is larger than the predetermined amount as compared with the case where the EGR amount is the predetermined amount. More specifically, for example, the larger the EGR amount, the larger the discharge energy E. Further, the discharge energy E is controlled to be larger when the water temperature is lower than the predetermined temperature as compared with the case where the water temperature is the predetermined temperature. More specifically, for example, the lower the temperature of the cooling water, the larger the discharge energy E.

On the other hand, the airflow control unit 64 calculates so that the discharge energy E becomes large when the optimum ignition timing T1 is farther than the compression top dead center tD. Therefore, these discharge energies E and the optimum ignition timing T1 are calculated at the same time. This is because the larger the discharge energy E, the shorter the combustion time t15, and the later the optimum ignition timing T1. Therefore, the discharge energy E affects the optimum ignition timing T1. On the other hand, as described above, the airflow control unit 64 increases the discharge energy E when the optimum ignition timing T1 is farther than the compression top dead center tD. Therefore, the optimum ignition timing T1 affects the discharge energy E. In this way, each of the discharge energy E and the optimum ignition timing T1 affects the other. Therefore, both values of the discharge energy E and the optimum ignition timing T1 are calculated at the same time by using, for example, a simultaneous equation or a multidimensional map that can calculate both values at the same time (S102).

Next, the energization timing t0 is calculated from the optimum ignition timing T1 and the discharge energy E (S103). The energization timing t0 is a timing earlier than the optimum ignition timing T1 by the charging time t01. The charging time t01 becomes longer as the discharge energy E is larger, and becomes longer as the voltage of the battery 411 is lower. Further, even if the charging time t01 is the same, the faster the rotation speed of the engine 90, the larger the crank angle occupied by the charging time t01. Based on the above, the ignition control unit 60 calculates the charging time t01, and further calculates the energization timing t0 based on the charging time t01 (S103). This calculation may be calculated based on, for example, a mathematical formula, or may be calculated based on a map.

Next, the switching element 413 is turned on at the calculated energization timing t0 (S104). Next, at the calculated optimum ignition timing T1, the switching element 413 is turned off (S105). That is, the ignition timing t1 is controlled at the optimum ignition timing T1. As a result, ignition by the spark plug 40 is executed, and the above-mentioned predetermined amount (for example, 50% of the mass) of fuel is burned at the optimum combustion timing T5. That is, the combustion timing t5 is controlled at the optimum combustion timing T5.

Although the ignition control before the top dead center during normal operation has been described above, the combustion timing t5 is not the optimum combustion timing T5 but the optimum combustion timing T5 in the ignition control after top dead center during first idling. The ignition timing t1 is controlled so as to be later than the timing. Therefore, the optimum combustion control is not performed in the ignition control after top dead center.

According to this embodiment, the following effects can be obtained. By performing the ejection delay suppression control in addition to the airflow support structure As, it is possible to suppress the combustion time t15 in the low load state in the ignition control before top dead center. Therefore, it is possible to prevent the optimum ignition timing T1, which is earlier than the optimum combustion timing T5 by the amount of the combustion time t15, from becoming too early. As a result, the ignition timing t1 can be controlled to the optimum ignition timing T1 even in a low load state in the sub-chamber ignition system 70. Then, by actually performing the optimum ignition control, the ignition timing t1 is controlled at the optimum ignition timing T1. As a result, the combustion timing t5 is controlled at the optimum combustion timing T5, and torque can be efficiently generated.

Specifically, the ejection control unit 63 controls the ejection delay suppression control so that the discharge energy E becomes larger in the low load state than in the high load state. As a result, when the load is low, the ejection time t13 can be shortened and the combustion time t15 can be shortened.

Further, in the sub-chamber type ignition system 70, the discharge spark F can be extended by facilitating the flow of airflow through the discharge gap 45 by the airflow support structure As. Thereby, the ignitability by the discharge spark F can be improved and the ejection time t13 can be shortened. Thereby, the combustion time t15 can be shortened. Further, by adopting a structure in which the discharge gap 45 is close to the communication hole 35 as the airflow support structure As, the airflow support structure As can be efficiently formed by using the communication hole 35.

Further, the airflow control unit 64 controls the discharge energy E so that the discharge spark F is not interrupted by the airflow caused by the airflow support structure As. Therefore, the stability of the discharge spark F can be ensured even when the airflow support structure As is provided in this way.

Specifically, in the latter half of the compression stroke, the earlier the timing, that is, the farther away from the compression top dead center tD, the stronger the airflow flowing through the discharge gap 45. Therefore, the earlier the ignition timing t1, the easier it is for the discharge spark F to be blown out. In that respect, the airflow control unit 64 controls so that the discharge energy E becomes larger when the ignition timing t1 is in the latter half of the compression stroke and when the ignition timing t1 is earlier than when it is later. As a result, it is possible to efficiently prevent the blowout.

Further, in the first half of the expansion stroke, the later the timing, that is, the farther away from the compression top dead center tD, the stronger the airflow flowing through the discharge gap 45. Therefore, the later the ignition timing t1, the easier it is for the discharge spark F to be blown out. In that respect, the airflow control unit 64 controls so that the discharge energy E becomes larger when the ignition timing t1 is in the first half of the expansion stroke and when the ignition timing t1 is later than when it is earlier. As a result, it is possible to efficiently prevent the blowout.

The partition wall 34 also serves as a ground electrode for the spark plug 40. A communication hole 35 is formed in the partition wall 34. Therefore, the discharge gap 45 can be efficiently arranged close to the communication hole 35.

Further, the ejection control unit 63 controls the discharge energy E based on each parameter indicating the operating state of the engine 90 such as the air-fuel ratio, EGR, and water temperature. Thereby, it is possible to efficiently suppress the lengthening of the ejection time t13 under a predetermined situation.

Specifically, when the air-fuel ratio of the engine 90 is large, the fuel in the combustion chamber 30 becomes lean, which makes it difficult for the fuel to burn and the flame to propagate. In that respect, the ejection control unit 63 controls so that the discharge energy E becomes large when the air-fuel ratio is large as compared with when the air-fuel ratio is small. Therefore, it is possible to prevent the ejection time t13 from becoming longer when the air-fuel ratio is large as compared with when the air-fuel ratio is small.

Further, when the amount of EGR of the engine 90 is large, the amount of exhaust gas returning to the intake air is large, so that the fuel is hard to burn and the flame is hard to propagate. In that respect, the ejection control unit 63 controls so that the discharge energy E becomes larger when the EGR amount is larger than when it is small. Therefore, it is possible to prevent the ejection time t13 from becoming longer when the EGR amount is large as compared with when the EGR amount is small.

Further, when the temperature of the cooling water of the engine 90 is low, the fuel in the combustion chamber 30 is difficult to warm, so that the fuel is hard to burn and the flame is hard to propagate. In that respect, the ejection control unit 63 controls so that the discharge energy E becomes larger when the temperature of the cooling water is lower than when the water temperature is high. Therefore, it is possible to prevent the ejection time t13 from becoming longer when the temperature of the cooling water is lower than when the temperature is high.

In addition, the following effects can be obtained in ignition control after top dead center. That is, in the ignition control after top dead center, the discharge spark F extends into the main chamber 31 through the central communication hole 35c and directly ignites the fuel in the main chamber 31. The burning time t15 can be shortened.

[Other Embodiments]
The embodiment shown above can be modified and implemented as follows. 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 may be injected into the sub chamber 38 or the main chamber 31. Further, for example, in the first embodiment, the discharge energy E is controlled by controlling the charging time t01, but instead of or in addition to this, the discharge energy E is controlled by controlling the current flowing through the primary coil 412. It may be controlled.

Further, for example, the ejection control unit 63 of the first embodiment changes the discharge energy E based on each parameter of the air-fuel ratio, the EGR amount, and the water temperature. It may be eliminated to change the discharge energy E based on this. Further, for example, in the first embodiment, the discharge energy E is controlled by the airflow control unit 64 in both the case of being ignited in the latter half of the compression stroke and the case of being ignited in the first half of the expansion stroke. Instead, the discharge energy E may not be controlled by the airflow control unit 64 in one or both of the case where the ignition is performed in the latter half of the compression stroke and the case where the ignition is performed in the first half of the expansion stroke.

Further, for example, in the first embodiment, the airflow support structure As and the airflow control unit 64 are provided, but the airflow control unit 64 is eliminated, or both the airflow support structure As and the airflow control unit 64 are eliminated. You may do it. Even in such a case, the effect of the ejection delay suppression control by the ejection control unit 63 can be obtained.

Further, for example, in the first embodiment, the ejection control unit 63 performs ejection delay suppression control by controlling the discharge energy E, but instead of this, ejection delay suppression control is performed as follows. You may do so. That is, a spraying device for blowing an airflow is provided in the discharge gap 45, and the spraying device is controlled by the ejection control unit 63 so that the airflow is strongly blown to the discharge gap 45 in a low load state as compared with a high load state. You may. In this case, in the low load state, the discharge spark F extends for a longer time to improve the ignitability, and it is suppressed that the ejection time t13 becomes longer than in the high load state.

Although this disclosure has been described in accordance with the examples, it is understood that the disclosure is not limited to the examples and structures. The present disclosure also includes various modifications and modifications within an equal range. In addition, various combinations and forms, as well as other combinations and forms that include only one element, more, or less, are also within the scope of the present disclosure.

Claims (10)

1. A discharge spark (F) by applying a voltage to a partition wall (34) that divides the combustion chamber (30) of the engine (90) into a sub chamber (38) and a main chamber (31) and a predetermined discharge gap (45). The spark plug (40) that ignites the fuel in the sub chamber and the ignition control unit (60) that controls the spark plug are provided, and the sub chamber and the main chamber are provided in the partition wall. A communication hole (35) for communication is formed, and the communication hole (35) is formed.
   A state in which the load applied to the engine is a predetermined magnitude is defined as a high load state, and a state in which the load applied to the engine is smaller than the predetermined magnitude is defined as a low load state.
   The timing at which the spark plug starts discharging in the discharge gap is defined as the ignition timing (t1), and the timing at which a predetermined amount of the fuel in the combustion chamber is burned after the ignition timing is the combustion timing (t5). The time from the ignition timing to the combustion timing is defined as the combustion time (t15).
   The ignition control unit calculates the optimum ignition timing (T1), which is a timing earlier than the optimum combustion timing (T5) as the optimum combustion timing, and controls the ignition timing to the optimum ignition timing. Optimal ignition control is performed in the high load state.
   In the sub-chamber ignition system (70)
   Between the ignition timing and the combustion timing, the timing at which the flame generated in the sub chamber starts to eject from the communication hole into the main chamber is defined as the ejection timing (t3), and the time from the ignition timing to the ejection timing. As the eruption time (t13)
   It has an ejection control unit (63) that performs ejection delay suppression control that suppresses the ejection time from becoming longer in the low load state as compared with the case of the high load state.
   In the low load state, the ejection delay suppression control is performed by the ejection control unit, so that the combustion time is suppressed to be longer than in the high load state, and the optimum ignition is performed by the ignition control unit. Sub-chamber ignition system for control.
2. The ejection control unit controls the ejection delay suppression control so that the discharge energy (E) applied to the discharge gap becomes larger in the low load state than in the high load state. Sub-chamber ignition system as described in.
3. It has an airflow support structure (As) to facilitate the flow of airflow in the discharge gap, and has an airflow support structure (As).
   The auxiliary chamber according to claim 1 or 2, wherein a plurality of the communication holes are formed in the partition wall, and the discharge gap is close to one of the plurality of communication holes as the airflow support structure. Type ignition system.
4. The sub-chamber ignition system according to claim 3, further comprising an airflow control unit (64) that controls the discharge energy applied to the discharge gap so that the discharge spark is not interrupted by the airflow due to the airflow support structure.
5. The anti-air flow control unit controls the discharge energy based on the ignition timing, and the anti-air flow control unit controls the ignition timing at a predetermined timing when the ignition timing is the latter half of the compression stroke. The sub-chamber ignition system according to claim 4, wherein the discharge energy is controlled to be larger when the ignition timing is earlier than the predetermined timing as compared with a certain case.
6. The anti-air flow control unit controls the discharge energy based on the ignition timing, and the anti-air flow control unit controls the ignition timing at a predetermined timing when the ignition timing is the first half of the expansion stroke. The sub-chamber ignition system according to claim 4 or 5, wherein the discharge energy is controlled to be larger when the ignition timing is later than the predetermined timing as compared with a certain case.
7. Claim that the discharge gap is formed between two electrodes (34, 44), and the partition wall is made of a conductor and also serves as one electrode (34) of the two electrodes. The sub-chamber ignition system according to any one of 3 to 6.
8. The ejection control unit controls the discharge energy applied to the discharge gap based on the air-fuel ratio of the engine, and the air-fuel ratio is the predetermined air-fuel ratio as compared with the case where the air-fuel ratio is the predetermined air-fuel ratio. The sub-chamber ignition system according to any one of claims 1 to 7, wherein the discharge energy is controlled to be large when the fuel ratio is larger than the fuel ratio.
9. The ejection control unit controls the discharge energy applied to the discharge gap based on the EGR amount which is the amount of returning the exhaust gas to the intake air in the engine, as compared with the case where the EGR amount is a predetermined amount. The sub-chamber ignition system according to any one of claims 1 to 8, wherein when the EGR amount is larger than the predetermined amount, the discharge energy is controlled to be large.
10. The ejection control unit controls the discharge energy applied to the discharge gap based on the water temperature of the cooling water of the engine, and the water temperature is higher than the predetermined temperature as compared with the case where the water temperature is the predetermined temperature. The sub-chamber ignition system according to any one of claims 1 to 9, wherein the discharge energy is controlled to be large when the temperature is low.

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