Patent Application
20230184160
The present application claims the benefit of priority of Japanese Patent Application No. 2020-134723 filed on Aug. 7, 2020, the disclosure of which is incorporated in its entirety herein by reference.
This disclosure relates generally to an ignition system which works to ignite fuel in a combustion chamber.
Some ignition systems are equipped with a dividing wall and a spark plug. The dividing wall isolates between a main chamber and a pre-chamber in a combustion chamber of an engine. The dividing wall has formed therein a plurality of spray holes communicating the main chamber with the pre-chamber. The spark plug works to create an electrical spark to ignite fuel upon application of voltage across a spark gap within the pre-chamber. Such a type of spark plug is taught in the following patent literature 1.
Patent Literature 1: Japanese Patent No. 5122367
The above type of ignition system works to perform a before-top-dead-center ignition task to ignite fuel before the top dead center of the compression stroke, in other words, during the compression stroke in the engine in a normal operation mode. The before-top-dead-center ignition task is to elongate a spark, as created in the pre-chamber, by means of tumble or swirl occurring in the combustion chamber. The elongated spark then ignites fuel to produce a flame which, in turn, jets into the main chamber, thereby facilitating the combustion of the fuel within the combustion chamber.
When a given condition is encountered, the ignition system alternatively performs an after-top-dead-center ignition task to ignite fuel in the expansion stroke after the top dead center of the compression stroke, i.e., during the expansion stroke. Specifically, for instance, in a first idling mode of the engine operation to warm up the catalyst installed in an exhaust path of the engine, the ignition system starts the ignition of fuel as late as possible in order to enhance the efficiency in transmitting thermal energy, as generated by the combustion of fuel, to the catalyst. The ignition system, therefore, ignites the fuel after the top dead center of the compression stroke.
After the top dead center of the compression stroke, the flow of the mixture in the pre-chamber is usually reduced in strength due to the breaking of the tumble or swirl when the piston passes through the top dead center of the compression stroke. This will result in a decrease in elongation of the spark, thereby reducing the ease of ignition of the fuel, thereby increasing the length of time in which the fuel is ignited in the pre-chamber, and the flame is jetted from the pre-chamber into the main chamber, in other words, decreasing the speed of propagation of the flame to the main chamber.
This disclosure was made in view of the above problem. It is a principal object to achieve quick propagation of a flame to a main chamber in an after-top-dead-center ignition control mode.
An ignition system in this disclosure comprises a dividing wall and a spark plug. The dividing wall divides a combustion chamber of an engine into a main chamber and a pre-chamber. The has formed therein at least one spray hole which communicates between the main chamber and the pre-chamber. The spark plug works to create a spark by applying voltage across a spark gap between a first electrode and a second electrode to ignite fuel. The pre-chamber has the first electrode. The dividing wall or a member which electrically conducts with the dividing wall has the second electrode.
In the following discussion, the timing when the voltage starts to be applied across the spark gap will be referred to as an ignition timing. The center of an opening of the spray hole which is located close to the pre-chamber will be referred to as a spray hole center. A region which is located 3 mm or less away from the spray hole center within the pre-chamber will be referred to as a spray hole-nearby region.
The ignition system works to execute an after-top-dead-center ignition control mode in which an ignition operation to ignite the fuel is performed after a compression stroke top dead center is reached when a given operating condition of the engine is met. In the after-top-dead-center ignition control mode, an ignition source is provided in the form of a self-growable flame kernel within the spray hole-nearby region, the spray hole, or the main chamber within a crank angle of 20° after the ignition timing is reached.
This disclosure offers the following beneficial advantages. In the after-top-dead-center ignition control mode, the ignition source is provided in the spray hole-nearby region, the spray hole, or the main chamber early, e.g., within a crank angle of 20° following the ignition timing. When the ignition source is provided in the spray hole-nearby region or the spray hole, it facilitates the jetting of a flame, as grown from the ignition source, from the spray hole into the main chamber. Alternatively, when the ignition source is provided in the main chamber, it will cause a flame grown from the ignition source to propagate as it is to the main chamber. It is, therefore, possible to propagate the flame quickly to the main chamber in the after-top-dead-center ignition control mode.
The present disclosure will be understood more fully from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiments of the invention.
In the drawings:
An embodiment in this disclosure will be described below with reference to the drawings. This disclosure is, however, not limited to this embodiment, but may be modified in various ways without departing from the principle of this disclosure.
In the following discussion, a lengthwise direction of the center line X of the cylinder 10 illustrated in the drawings will be referred to as a vertical direction. The engine 90 and/or the ignition system 70 may be optionally oriented in various directions. For instance, the engine 90 and/or the ignition system 70 may be oriented to have the center line X which extends obliquely to the vertical direction or alternatively extends the horizontal direction.
The cylinder 10 has the piston 18 disposed therein. The piston 18 is connected to the crankshaft 11 through the link 12 and reciprocates vertically following rotation of the crankshaft 11. Space surrounded by an upper surface of the piston 18, an inner peripheral surface of the cylinder 10, and a lower surface of the head 20 defines the combustion chamber 30.
The head 20 has formed therein the intake path 21 through which air is inducted into the combustion chamber 30 and the exhaust path 29 from which gas discharged from the combustion chamber 30. The intake path 21 has the intake valve 24 installed therein. The exhaust path 29 has the exhaust valve 26 installed therein. The intake valve 24 is driven by the intake cam 23, while the exhaust valve 26 is driven by the exhaust cam 27. The head 20 has the fuel injector 22 mounted in the intake path 21. The fuel injector 23 works to spray fuel.
The ignition system 70 is equipped with the dividing wall 34, the spark plug 40, and the ignition controller 50. The ignition controller 50 is implemented by a portion of an electronic control unit (ECU) and works to analyze information derived by sensors installed in the engine 90 to control an operation of the spark plug 40. The sensors include, for example, a crank angle sensor, a knock sensor, an intake pressure sensor, an exhaust pressure sensor, an in-cylinder pressure sensor, and a catalyst temperature sensor.
More specifically, the spark plug 40 is equipped with a primary coil and a secondary coil. By applying an electrical current to the primary coil, electromagnetic energy is charged in the primary coil. Subsequently, stopping the application of current will cause the electromagnetic energy stored in the primary coil to induce voltage at the secondary coil. The induced voltage is then applied to the spark gap 45 to create the spark f within the spark gap 45. The time when the application of current to the primary coil is stopped will, therefore, coincide with an ignition timing Ts when the voltage starts to be applied across the spark gap 45 to initiate ignition of fuel.
In the following discussion, one of the spray holes 35 which lies on the center line X of the cylinder 10 will also be referred to as the center spray hole 35c. The center spray hole 35c extends vertically through the thickness of the dividing wall 34. The first electrode 44 has a lower end located just above the center spray hole 35c. In other words, the lower portion of the first electrode 44 protrudes greatly downward from the lower end the porcelain insulator 41, so that it is located closest to the center spray hole 35c among the spray holes 35. The gap between the lower end of the first electrode 44 and an upper periphery of the center spray hole 35c in the dividing wall 34 defines the spark gap 45. The spray holes 35 other than the center spray hole 35c are arranged around the center spray hole 35c in the dividing wall 34. The center spray hole 35c and the other spray holes 35 may be designed to be identical or different in sectional area or configuration with or from each other.
In a normal mode of operation, the ignition system 70 executes a before-top-dead-center ignition control mode to ignite fuel before the compression stroke top dead center Td. Alternatively, when a given operating condition of the engine 90, e.g., a fast idling mode of operation to warm up a catalyst installed in the exhaust path 29, is entered, the ignition system 70 executes an after-top dead center ignition control mode to ignite fuel after the compression stroke top dead center Td.
In the following discussion, a gas flow passing through the spark gap 45 will also be referred to as an in-gap gas flow. A direction from the first electrode 44 toward the center spray hole 35c will also be referred to as a spray hole direction d1. A direction opposite to the spray hole direction d1 will also be referred to as a spray hole opposite direction d2. In this embodiment, the spray hole direction d1 represents a downward direction. The spray hole opposite direction d2 represents an upward direction. A direction including the spray hole direction d1 as a component will also be referred to below as a spray hole direction d1-side or merely referred to as the spray hole direction d1. A direction including the spray hole opposite direction d2 as a component will also be referred to as a spray hole opposite direction d2-side or merely referred to as the spray hole direction d2.
After the after-top-dead-center ignition control mode is entered, in the ignition system 70, the in-gap gas flow is changed from the spray hole opposite direction d2-side to the spray hole direction d1-side until the ignition timing Ts is reached. At the ignition timing Ts, the in-gap gas flow is, therefore, oriented to the spray hole direction d1-side, thereby causing the spark f to be elongated toward the spray hole direction d1-side.
In the following discussion, the center of an opening of the center spray hole 35c which is exposed to the pre-chamber 38 will be also referred to below as a spray hole center. A region located within the pre-chamber 38 at an interval of 3 mm or less away from the spray hole will be referred to below as a spray hole-nearby region R.
When it is required to execute the after-top-dead-center ignition control mode, the ignition system 70 works at an early stage within a crank angle of 20° following the ignition timing Ts to place an ignition source in the form of a flame kernel large in size enough to self-grow in the spray hole-nearby region R, the center spray hole 35c, or the main chamber 31. In the flowing discussion, “in the spray hole-nearby region R, the center spray hole 35c or the main chamber 31” will be generally referred to as “in the spray hole-nearby region R, etc.”.
In this disclosure, “the size of the flame kernel large enough to self-grow” means that the flame kernel which will spread without being extinguished by heat loss or lean mixture in the combustion chamber even when application of voltage to the spark gap 45 is stopped. More specifically, the size of a flame kernel large enough to self-grow refers to a diameter of about 0.5 to 1.0 mm.
The placement of the ignition source within the spray hole-nearby region R, etc. in the early stage is achieved by selecting a spray hole distance D that is a distance between the first electrode 44 and the center spray hole 35c, a prechamber volume V that is a volume of the pre-chamber 38, a total spray hole area S that is the sum of sectional areas of all the spray holes 35 formed in the dividing wall 34, and/or a discharge voltage that is a voltage applied across the spark gap 45. This will be described below in detail. In the case were the spray holes 35 are partially constricted, so that a sectional area of each of the spray holes 35 is ununiform, the smallest sectional area of each of the spray holes 35 will be simply referred to as a sectional area of each of the spray holes 35.
First, the spray hole distance D will be described. The shorter the spray hole distance D, the greater the effects of flows of gas passing through the center spray hole 35c on a flame kernel. This facilitates the growth of the flame kernel, especially, in the spray hole-nearby region R, etc., and its peripheral region. For this reason, the shorter the spray hole distance D, the easier the creation of an ignition source in the spray hole-nearby region R, etc., in the early stage.
Next, the prechamber volume V and the total spray hole area S will be described in detail. The more the prechamber volume V, the faster a flow of gas moving through the center hole 35c in the after-top-dead-center ignition control mode. This is because the larger the prechamber volume V, the more slowly the pressure in the pre-chamber 38 drops following a drop in pressure in the main chamber 31 as long as the flow rate of gas moving out of the pre-chamber 38 into the main chamber 31 is kept constant, thereby resulting in an increased difference in pressure between the pre-chamber 38 and the main chamber 31, which increases the velocity of gas passing through the center spray hole 35c.
The smaller the total spray hole area S, the faster the velocity of gas flowing through the center spray hole 35c will be in the after-top-dead-center ignition control mode. This is because as long as the prechamber volume V remains unchanged, the smaller the total spray hole area S, the smaller the flow rate of gas moving out of the pre-chamber 38 into the main chamber 31 will be, thereby causing a drop in pressure in the pre-chamber 38 to become slow following a drop in pressure in the main chamber 31. This results in an increased difference in pressure between the pre-chamber 38 and the main chamber 31, which increases the velocity of gas passing through the center spray hole 35c.
The increase in velocity of gas passing through the center spray hole 35c will facilitate the elongation of the spark f to the spray hole direction d1-side. This facilitates the growth of a flame kernel in the early stage, especially, in the spray hole-nearby region R, etc. and its peripheral region. When it comes to the prechamber volume V and the total spray hole area S, the smaller a spray hole ratio (S/V) that is a ratio of the total spray hole area S to the prechamber volume V, the more easily the ignition source is created in the spray hole-nearby region R, etc. at the early stage.
Next, the discharge voltage will be described below. The higher the discharge voltage, the easier a flame kernel is to grow. Additionally, the higher the discharge voltage, the higher the stability of the flame kernel, thereby facilitating the ease with which the spark f is elongated by the gas flow into the spray hole-nearby region R, etc. or its peripheral region. Consequently, the higher the discharge voltage, the more easily the ignition source is created in the spray hole-nearby region R, etc. at the early stage.
As apparent from the above discussion, the smaller the spray hole distance D or the spray hole ratio (S/V) or the higher the discharge voltage, the more easily the ignition source is created in the spray hole-nearby region R, etc. at the early stage. Too small the spray hole distance D or the spray hole ratio (S/V) or too high the discharge voltage will, however, result in another adverse effect. In this embodiment, the early creation of the ignition source in the spray hole-nearby region R, etc. is achieved by decreasing the spray hole distance D or the spray hole ratio (S/V) and/or increasing the discharge voltage to an extent that no above adverse effect occurs.
The creation of an ignition source in the spray hole-nearby region R or the spray holes 35 usually causes a flame grown from the ignition source to be quickly jetted into the main chamber 31. The creation of an ignition source within the main chamber 31 causes a flame grown from the ignition source to propagate directly into the main chamber 31. Such cases achieve the quick propagation of a flame into the main chamber 31.
In the setting step p1, a spray hole ratio (S/V) is calculated. The dimensions of the pre-chamber 38 and the spray holes 35 are determined as a function of the spray hole ratio (S/V) and the spray hole distance D. The setting step p1 will also be described below in detail with reference to
S/V=−0.025D{circumflex over ( )}3+0.34D{circumflex over ( )}2−1.4D+2.1 Eq. A
where V denotes the prechamber volume V [cc (cubic centimeter)], S denotes the total spray hole area (i.e., a total sectional area of the spray holes 35) [mm{circumflex over ( )}2], D denotes the spray hole distance D [mm], and “{circumflex over ( )}” represents a power. Note that “{circumflex over ( )}3” is a cube, and “{circumflex over ( )}2” represents a square.
On the upper side above the curve a, the in-gap gas flow at the ignition timing Ts in the after-top-dead-center ignition control mode is lower than 5 m/s in the spray hole direction d1, while on the lower side below the curve a, the in-gap gas flow at the ignition timing Ts in the after-top-dead-center ignition control mode is higher than 5 m/s in the spray hole direction d1.
In this embodiment, in order to have the in-gap gas flow in the spray hole direction d1 which is higher than or equal to 5 m/s at the ignition timing Ts in the after-top-dead-center ignition control mode, the value of the spray hole ratio (S/V) is selected in a region 3 including the curve a and the lower side below the curve a. In other words, the value of the spray hole ratio (S/V) is determined to meet the following Eq. B which is equivalent to Eq. A in which “=” is replaced by “≤”.
S/V≤−0.025D{circumflex over ( )}3+0.34D{circumflex over ( )}2−1.4D+2.1 Eq. B
Eq. B sets the in-gap gas flow in the spray hole direction d1 to be higher than or equal to 5 m/s at the ignition timing Ts in the after-top-dead-center ignition control mode.
The curve a usually changes with a change in environment. For instance, when the speed of rotation of the engine 90 becomes high, the quantity of intake air increases, or the engine 90 is implemented by a high-compression engine, the curve a will be shifted to an upper right-hand side in
However, in the absence of the above correction, the acceptable in-gap gas flow is expected to be obtained at the ignition timing Ts in the after-top-dead-center ignition control mode during the fast idle mode of engine operation in which the speed of the engine, the quantity of intake air, and the compression ratio are normal.
However, when the spray hole ratio (S/V) is lower than 0.3, it causes a risk that too strong a gas flow may pass through the spray holes 35, so that the flame is blown away. It is, therefore, preferable that the spray hole ratio (S/V) be selected to be 0.3 or more. When the spray hole distance D is zero in Eq. B, the right side will be 2.1. Satisfying Eq. B, therefore, requires selecting the value of the spray hole ratio (S/V) to be 2.1 or less. Consequently, the value of the spray hole ratio (S/V) is determined to meet the following Eq. C in addition to Eq. B.
0.3≤S/V≤2.1 Eq. C
More specifically, it is advisable that the diameter of each of the spray holes 35 be selected to be 0.3 mm or more in order to eliminate a risk that a flame passing through each of the spray holes 35 may disappear due to thermal loss thereof. It is also advisable that the prechamber volume V be selected to be 0.2 cc or more in order to ensure an amount of gas jetting from the prechamber 38 (i.e., the quantity of heat) large enough to enhance the propagation of a flame within the main chamber 31.
The spray hole distance D is preferably selected in light of blowing out of the spark f or the amount of electrical power consumed by the spark plug 40 as a function of the size of the spark gap 45 because the spray hole distance D impinges on the size of the spark gap 45. The area of a cross section of the center spray hole 35c is also preferably selected in light of adverse effects thereof on the spark gap 45. The spray hole ratio (S/V) is preferably determined by selecting cross-sectional areas of the spray holes 35 other than the center spray hole 35c.
In the setting step p1 in
The functions of the ignition system 70 in this embodiment will be described below.
The main chamber ignition phase s2′ is a phase in which a flame kernel is growing to a self-growable ignition source within the main chamber. The end of the main chamber ignition phase s2′ coincides with the main chamber ignition timing Tj that is the timing when an ignition source is created within the main chamber 31. The main chamber flame propagation phase s5 is a phase in which the ignition source is propagating to the main chamber 31. The end of the main chamber flame propagation phase s5 coincides with the combustion end timing Te when the fuel is expected to have been burned completely.
In the second comparative example and the first mode, the combustion of fuel proceeds from the spark phase s1 to the pre-chamber ignition phase s2, to the pre-chamber flame propagation phase s3, to the gas jetting phase s4, and then to the main chamber flame propagation phase s5. The pre-chamber ignition phase s2 is a phase in which a flame kernel is growing to a self-growable ignition source in the pre-chamber. The end of the pre-chamber ignition phase s2 coincides with the pre-chamber ignition timing Ti that is the timing when the ignition source is created in the pre-chamber 38.
The pre-chamber flame propagation phase s3 is a phase in which the ignition source is propagating to the pre-chamber 38. The flame jetting phase s4 is a phase in which a flame in the pre-chamber 38, that is, an ignition source is jetting from each of the spray holes 35 into the main chamber 31. The beginning of the flame jetting phase s4 coincides with the main chamber ignition timing Tj that is the timing when the ignition source is placed in the main chamber 31.
In the second mode, the spark f extends from inside the pre-chamber 38 into the main chamber 31 through the center spray hole 35c, thereby causing ignition sources to be created by the spark f within the main chamber 31 as well as the pre-chamber 38 and the center spray hole 35c. Consequently, like in the first mode, the combustion of fuel proceeds from the spark phase s1, to the main chamber ignition phase s2′, and then to the main chamber flame propagation phase s5 in parallel to a series of ignition source development from the spark phase s1, to the pre-chamber ignition phase s2, to the pre-chamber flame propagation phase s3, to the flame jetting phase s4, and then the main chamber flame propagation phase s5. This causes the main chamber ignition timing Tj to appear earlier than in the first mode.
In each of the first and second comparative examples and each of the first and second modes, the combustion end timing Te is required to be earlier than the exhaust start time To that is the time when the exhaust valve 26 starts to open in order to avoid emission of unburned fuel. Accordingly, in any case, the combustion end timing Te is first determined prior to the exhaust start time To. Subsequently, the ignition timing Ts is determined to have fuel completely combusted at the combustion end timing Te. In other words, the ignition timing Ts is calculated back from the combustion end timing Te. Therefore, the combustion end timings Te almost coincide with each other in the first and second comparative examples and the first and second modes, while the ignition timings Ts are different from each other.
In the first mode of this embodiment, the spark gap 45 is located closer to the center spray hole 35c, thereby causing the time when the ignition source appears in the spray hole-nearby region R to lie in the first half of the pre-chamber flame propagation phase s3. The first half of the pre-chamber flame propagation phase s3 in the first mode lies within a crank angle of 20° after the ignition timing Ts. The ignition source, therefore, appears in the spray hole-nearby region R within a crank angle of 20° after the ignition timing Ts. This results in smaller delay in the main chamber ignition timing Tj than in the first comparative example, so that the development of combustion of fuel becomes faster than that in the first comparative example which does not include the pre-chamber 38.
In the second mode of this embodiment, the time when the ignition source is created by the spark f within the main chamber 31 coincides with the main chamber ignition timing Tj corresponding to the end of the main chamber ignition phase s2′. The main chamber ignition timing Tj in the second mode lies within a crank angle of 20° after the ignition timing Ts. This causes the ignition source to appear in the main chamber 31 within a crank angle of 20° after the ignition timing Ts, so that the development of combustion of fuel becomes faster than in the first mode.
In the first and second modes of this embodiment, the in-gap gas flow, as described above, has already turned from the spray hole opposite direction d2 to the spray hole direction d1 before the ignition timing Ts in the after-top-dead-center ignition control mode. This causes a strong flow of gas to be created, for example, at 5 m/s or more in the spray hole direction d1 at the ignition timing Ts, thereby facilitating extension of the spark f in the spray hole direction d1, which enhances the growth of a flame kernel in or around the spray hole-nearby region R. Consequently, the first and second modes of this embodiment are capable of creating the ignition source quickly within the spray hole-nearby region R.
Referring back to
In contrast to the above, the first and second modes of this embodiment are capable of shortening the combustion period of time that is an interval between the ignition timing Ts and the combustion end timing Te as compared with the first and second comparative examples, thereby enabling the ignition timing Ts to be retarded sufficiently. This permits the combustion center-of-gravity Tc to be retarded greatly as compared with the first and second comparative examples, thereby ensuring the stability in warning the catalyst in the fast idling mode, which leads to a decreased duration of the fast idling mode to improve the fuel consumption in the engine 90 and reduce exhaust emissions from the engine 90.
This embodiment offers the following beneficial advantages. In the after-top-dead-center ignition control mode, the ignition source is created in the spray hole-nearby region R, the center spray hole 35c, or the main chamber 31 shown in
The second mode of this embodiment offers the following beneficial advantages. In the after-top-dead-center ignition control mode in the second mode, the spark f is extended to reach the inside of the main chamber 31, thereby creating the ignition source within the main chamber 31 at an early point within a crank angle of 20° after the ignition timing. The flame, as growing from the ignition source, propagates as it is to the main chamber 31. The second mode, therefore, ensures quick propagation of the flame to the main chamber 31.
Additionally, the dimensions of the pre-chamber 38 and the spray holes 35 are selected to meet the above Eq. B in order to have the spray hole ratio (S/V) falling in the region β illustrated in
The region β depends slightly on the circumferences, but however, is expected to produce a required degree of the in-gap gas flow at the ignition timing Ts in the after-top-dead-center ignition control mode when the engine 90 is operated at a usual speed, with a usual quantity of intake air, and at a usual compression ratio. The quick creation of the ignition source in the spray hole-nearby region R is, therefore, achieved easily by selecting the spray hole ratio (S/V) to lie in the region β.
The second mode also has the following beneficial advantage. When the spray hole ratio (S/V) is less than 0.3, it will, as described above, result in too strong a flow of gas passing through the spray holes 35, thereby undesirably blowing away the flame. This embodiment is, as described above, configured to set the spray hole ratio (S/V) to be 0.3 or more, thus eliminating the above problem.
The second mode also has the following beneficial advantage. The in-gap gas flow, as can be seen in
The above described modes of this embodiment may be modified in the following ways. In the first embodiment, the dividing wall 34 has a plurality of spray holes 35 formed therein, but may alternatively be designed to have only the single center spray 35c. The first embodiment has the first electrode 44 located closest to the center spray hole 35c, but however, may alternatively be designed to arrange the first electrode 44 closest to one(s) of the other spray holes 35 to extend the spark f toward it. The dividing wall 34 in the first embodiment also works as the second electrode 46 and is attached to the head 20 in electrical conduction therewith, but however, it may be configured to have a protrusion(s) which is in electrical conduction to the dividing wall 34 and serves as the second electrode 46. Alternatively, the second electrode 46 may be made of a member which is discrete from the dividing wall 34 and electrically connects with the head 20.
The first embodiment has the dividing wall 34 secured to the porcelain insulator 41 of the spark plug 40, but however, the dividing wall 34 may alternatively be attached to the head 20. Additionally, the spark plug 40 may be arranged to have the porcelain insulator 41 arranged in engagement with the dividing wall 34 of the head 20.
While this disclosure has referred to the embodiments, it should be appreciated that the disclosure is not limited to the embodiments. This disclosure may include a variety of combinations of the embodiments, a combination of diverse modifications of the embodiments and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-134723 | Aug 2020 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2021/025838 | Jul 2021 | US |
| Child | 18105561 | US |
