JP5973956B2 - Ignition device for internal combustion engine - Google Patents

Description

  The present invention relates to an ignition device for an internal combustion engine, and more particularly to an ignition device for igniting an air-fuel mixture in a combustion chamber by using electromagnetic waves.

  As an ignition device for an internal combustion engine, an ignition device that ignites an air-fuel mixture in a combustion chamber by using an electromagnetic wave such as a microwave having a frequency of several GHz is known. For example, Non-Patent Document 1 discloses an ignition device that uses microwave resonance generated in a coaxial path through which microwaves are propagated for the purpose of performing ignition in a wider range than existing ignition devices. Patent Document 1 discloses an ignition device that uses microwave resonance generated in a combustion chamber for the purpose of performing ignition in a wide range.

JP 2012-149607 A

A Novel Spark-Plug for Improved Ignition in Engines With Gasoline Direct Injection (GDI), Klaus Linkenheil et. al, IEEE Transactions on Plasma Science, Vol. 33, no. 5, October 2005.

  By the way, in an internal combustion engine, improvement in combustion efficiency is desired. In order to improve the combustion efficiency, it is conceivable to realize a wider range of ignition with lower energy (low power). In the ignition device described in Non-Patent Document 1 above, a high electric field is formed only at the tip of the inner conductor of the coaxial path (the tip of the antenna electrode). The range of the order becomes narrow. For this reason, it has been difficult to realize a wider range of ignition. Further, according to the ignition device described in Patent Document 1, ignition in a wider range is possible, but since a high electric field is formed in a wide region in the combustion chamber, energy (electric power) required for ignition increases. . Therefore, it has been difficult to realize ignition with low energy (low power). As described above, in the conventional technology, it is difficult to realize a wide range of ignition with low energy (low power).

  An object of the present invention is to provide an ignition device capable of performing a wider range of ignition with lower energy (electric power).

  The present invention relates to an ignition device for an internal combustion engine that ignites an air-fuel mixture in a combustion chamber, the electromagnetic wave generating means for generating an electromagnetic wave, and one end portion arranged in a state facing the combustion chamber, and the other end portion Is a ground terminal or an open terminal, and the first electromagnetic wave supplying means for supplying the electromagnetic wave generated by the electromagnetic wave generating means into the combustion chamber from the one end, and the one of the first electromagnetic wave supplying means A second electromagnetic wave supply means connected between the end portion and the other end portion for supplying the electromagnetic wave generated by the electromagnetic wave generation means to the first electromagnetic wave supply means, the electromagnetic wave generation means Generates a first electromagnetic wave that can resonate with the first electromagnetic wave supply means, and starts generating a second electromagnetic wave that can resonate with the combustion chamber while the first electromagnetic wave is being generated. Ignition device for internal combustion engine It is.

  Further, the electromagnetic wave generating means changes the frequency at which the first electromagnetic wave supply means can resonate according to the connection position of the second electromagnetic wave supply means with respect to the first electromagnetic wave supply means, thereby changing the first electromagnetic wave. And the second electromagnetic wave may be generated by changing a frequency capable of resonating in the combustion chamber.

  Further, when the other end of the first electromagnetic wave supply means is a ground termination, the length from the one end to the other end of the first electromagnetic wave supply means is the second end. An odd multiple of one-half of the wavelength of the electromagnetic wave, and the length between the connection position of the second electromagnetic wave supply means to the first electromagnetic wave supply means and the one end of the first electromagnetic wave supply means The electromagnetic wave generating means is configured to be an odd multiple of a quarter of the wavelength of the first electromagnetic wave and an integral multiple of a half of the wavelength of the second electromagnetic wave. One electromagnetic wave and the second electromagnetic wave may be generated.

  Further, when the other end of the first electromagnetic wave supply means is an open terminal, the length from the one end to the other end of the first electromagnetic wave supply means is the second end. An odd multiple of a quarter of the wavelength of the electromagnetic wave, and the length between the connection position of the second electromagnetic wave supply means with respect to the first electromagnetic wave supply means and the one end of the first electromagnetic wave supply means The electromagnetic wave generating means is configured to be an odd multiple of a quarter of the wavelength of the first electromagnetic wave and an integral multiple of a half of the wavelength of the second electromagnetic wave. One electromagnetic wave and the second electromagnetic wave may be generated.

  The first electromagnetic wave supply means includes an inner conductor and an outer conductor provided coaxially on the outer side of the inner conductor, and is disposed with one end facing the combustion chamber, and the other end. Is a grounding termination in which the inner conductor and the outer conductor are short-circuited or an open termination in which the inner conductor and the outer conductor are not connected, and the electromagnetic wave generated by the electromagnetic wave generating means propagates between the inner conductor and the outer conductor. A coaxial path that is supplied from the one end to the combustion chamber may be used.

  According to the present invention, when the first electromagnetic wave is generated by the electromagnetic wave generating means, the first electromagnetic wave resonates in the first electromagnetic wave supplying means, and thereby the electric field at one end of the first electromagnetic wave supplying means. Becomes higher, and plasma is generated at the tip of one end. When the second electromagnetic wave is generated by the electromagnetic wave generating means, the second electromagnetic wave resonates in the combustion chamber, thereby increasing the electric field over a wide range in the combustion chamber. At this time, since the plasma generated by the first electromagnetic wave serves as a trigger, a wider range of plasma is formed in the combustion chamber with lower power than when only the second electromagnetic wave is supplied into the combustion chamber. Is possible. As a result, it is possible to perform ignition over a wider range with lower power.

1 is a diagram showing a schematic configuration of an internal combustion engine according to an embodiment of the present invention. It is a figure which shows schematic structure of the ignition device which concerns on 1st Embodiment of this invention. It is a figure which shows the generation | occurrence | production timing of a microwave. It is a graph which shows the relationship between the electric power feeding position in 1st Embodiment, a resonant frequency, and a reflectance. It is a schematic diagram for demonstrating the conditions of the microwave which induces a resonance. It is a figure which shows the frequency and half wavelength of the microwave used in Example 1. FIG. 6 is a schematic diagram showing an electric field distribution in Example 1. FIG. 6 is a schematic diagram showing an electric field distribution in Example 1. FIG. It is a figure which shows the frequency and half wavelength of the microwave used for the comparative example 1. FIG. 6 is a schematic diagram showing an electric field distribution in Comparative Example 1. FIG. 6 is a schematic diagram showing an electric field distribution in Comparative Example 1. FIG. It is a figure which shows schematic structure of the ignition device which concerns on 2nd Embodiment of this invention. It is a graph which shows the relationship between the electric power feeding position in 2nd Embodiment, a resonant frequency, and a reflectance. It is a schematic diagram for demonstrating the conditions of the microwave which induces a resonance. It is a schematic diagram for demonstrating the conditions of the microwave which induces a resonance. It is a schematic diagram for demonstrating the conditions of the microwave which induces a resonance. It is a figure which shows the frequency and half wavelength of the microwave used in Example 2. FIG. 6 is a schematic diagram showing an electric field distribution in Example 2. FIG. 6 is a schematic diagram showing an electric field distribution in Example 2. FIG. It is a figure which shows the frequency and half wavelength of the microwave used for the comparative example 2. 10 is a schematic diagram showing an electric field distribution in Comparative Example 2. FIG. 10 is a schematic diagram showing an electric field distribution in Comparative Example 2. FIG. 10 is a schematic diagram showing an electric field distribution in Comparative Example 2. FIG.

[First Embodiment]
FIG. 1 shows an example of an internal combustion engine according to an embodiment of the present invention. The internal combustion engine 100 includes a cylinder head 102, a cylinder 104, a combustion chamber 108 formed by the cylinder 104 and the piston 106, an intake valve 112 that opens and closes an intake port 110 provided in the cylinder head 102, and a cylinder head 102. An exhaust valve 116 that opens and closes the provided exhaust port 114 and a fuel injection valve 118 are included. In the intake process, the intake valve 112 is opened and the piston 106 is lowered to introduce intake gas into the combustion chamber 108 from the intake port 110. By disposing the fuel injection valve 118 so as to face the intake port 110, fuel is injected into the intake port 110, so that the air-fuel mixture is introduced into the combustion chamber 108. In the compression process, the intake valve 112 is closed, and the air-fuel mixture is compressed by raising the piston 106. The ignition device 10 ignites the air-fuel mixture in the combustion chamber 108 by radiating electromagnetic waves such as microwaves into the combustion chamber 108. The gas after combustion is discharged to the exhaust port 114 when the exhaust valve 116 is opened in the exhaust process.

  The ignition device 10 includes a microwave radiator 20 as an electromagnetic wave propagation means, an electromagnetic wave generation power source 60, a control device 62, and an electromagnetic wave transmission path 64. The electromagnetic wave generation power source 60 is configured by, for example, a magnetron, a traveling wave amplifier tube, a solid oscillation element, or the like, and generates an electromagnetic wave such as a microwave. The control device 62 controls the output (electric power) by controlling one or more of the height and width of the microwave pulse generated by the electromagnetic wave generation power source 60. The electromagnetic wave generation power source 60 outputs a microwave pulse at the timing of igniting the air-fuel mixture in the combustion chamber 108, and the output microwave pulse propagates through the electromagnetic wave transmission path 64. The electromagnetic wave transmission path 64 is configured by, for example, a coaxial cable or a waveguide. A microwave radiator 20 is provided at the end of the electromagnetic wave transmission path 64 so as to face the combustion chamber 108. As an example, the microwave radiator 20 is disposed at the center of the upper surface of the combustion chamber 108. The microwave radiator 20 radiates the microwave generated by the electromagnetic wave generation power source 60 and propagated through the electromagnetic wave transmission path 64 into the combustion chamber 108. In addition, although the electromagnetic waves used for ignition of the air-fuel mixture are not limited to microwaves, an example using microwaves will be described below as an example.

  FIG. 2 shows a microwave radiator 20 according to the first embodiment. The microwave radiator 20 includes a first coaxial path 30 and a second coaxial path 40 that supplies the microwave transmitted through the electromagnetic wave transmission path 64 to the first coaxial path 30.

  The first coaxial path 30 has a coaxial structure constituted by an outer conductor 32 and an inner conductor 34. The outer conductor 32 has a cylindrical shape. The inner conductor 34 has a columnar shape and is disposed in the outer conductor 32 along the central axis of the outer conductor 32. A dielectric 36 is disposed between the outer conductor 32 and the inner conductor 34. As an example, the dielectric 36 may be air or a solid substance. One end 30 a of the first coaxial path 30 is arranged so as to face the combustion chamber 108. At one end 30 a, the outer conductor 32 is an open end, and the tip end 34 a of the inner conductor 34 protrudes into the combustion chamber 108. Further, the other end 30b of the first coaxial path 30 is a ground terminal that is short-circuited by the outer conductor 32 and the inner conductor 34 being connected. The first coaxial path 30 corresponds to an example of a first electromagnetic wave supply unit.

  A second coaxial path 40 is connected between one end 30 a and the other end 30 b of the first coaxial path 30. One end of the second coaxial path 40 is connected to the first coaxial path 30 at the feeding position 50, and the other end of the second coaxial path 40 is connected to the electromagnetic wave transmission path 64. The second coaxial path 40 has a coaxial structure constituted by an outer conductor 42 and an inner conductor 44. The outer conductor 42 has a cylindrical shape. The inner conductor 44 has a columnar shape and is disposed in the outer conductor 42 along the central axis of the outer conductor 42. A dielectric 46 is disposed between the outer conductor 42 and the inner conductor 44. As an example, the dielectric 46 may be air or a solid substance. For example, the outer conductor 32 of the first coaxial path 30 and the outer conductor 42 of the second coaxial path 40 are connected, and the inner conductor 34 of the first coaxial path 30 and the inner conductor 44 of the second coaxial path 40 are Is connected. The second coaxial path 40 corresponds to an example of a second electromagnetic wave supply unit.

  Here, the entire length of the first coaxial path 30 (the length from one end 30a to the other end 30b) is defined as a length L1, and the feeding position 50 (connection position) from one end 30a. The length from the power feeding position 50 to the other end 30b is defined as a length L3. In the example shown in FIG. 2, the second coaxial path 40 is used as the microwave supply unit, but a waveguide or the like may be used as the microwave supply unit instead of the second coaxial path 40.

  Then, an electromagnetic wave such as a microwave supplied to the microwave radiator 20 via the electromagnetic wave transmission path 64 propagates between the outer conductor 42 and the inner conductor 44 of the second coaxial path 40 and the first coaxial. The first coaxial path 30 is further propagated between the outer conductor 32 and the inner conductor 34, and is radiated into the combustion chamber 108 from one end 30 a of the first coaxial path 30. .

  In the first coaxial path 30, a microwave having a predetermined frequency resonates in a predetermined resonance mode. The electromagnetic wave generating power source 60 generates a microwave having a frequency that resonates in the first coaxial path 30 based on the control of the control device 62. In a state where the microwave is resonating in the first coaxial path 30, there is little energy reflection of the microwave, and most of the microwave energy is stored in the first coaxial path 30. That is, the first coaxial path 30 functions as a resonator that resonates microwaves between one end 30a and the other end 30b. In the following description, the microwave that resonates in the first coaxial path 30 is referred to as “first microwave”, the frequency of the first microwave is referred to as “frequency fa”, and the wavelength of the first microwave. Is referred to as “wavelength λa”.

  In the combustion chamber 108, a microwave having a predetermined frequency resonates in a predetermined resonance mode. The electromagnetic wave generating power source 60 generates a microwave having a frequency that resonates in the combustion chamber 108 based on the control of the control device 62. In a state where the microwave is resonating in the combustion chamber 108, the reflection of the microwave energy is small, and most of the microwave energy is stored in the combustion chamber 108. In the following description, the microwave that resonates in the combustion chamber 108 is referred to as “second microwave”, the frequency of the second microwave is referred to as “frequency fb”, and the wavelength of the second microwave is referred to as “wavelength”. It will be referred to as “λb”.

  Here, the timing for generating the first microwave and the second microwave will be described with reference to FIG. The electromagnetic wave generation power supply 60 supplies the first microwave (fa) under the control of the control device 62, and the second microwave (fb) is simultaneously with or immediately after the start of the supply of the first microwave (fa). Start supplying. For example, as shown in FIG. 3, when the first microwave (fa) is supplied between the times t1 and t2, the supply of the second microwave (fb) is started between the times t1 and t2. That is, the supply of the second microwave (fb) may be started while the first microwave (fa) is being supplied. As an example, the time interval Δt2 for supplying the second microwave (fb) is equal to or longer than the time interval Δt1 for supplying the first microwave (fa). As a specific example, Δt1 is 1 ms. Δt2 is about 1 to 5 ms. Note that “immediately after the start of supply of the first microwave” corresponds to a time period between time t1 and time t2.

  When the first microwave is supplied, the first microwave resonates in the first coaxial path 30, a standing wave is formed in the first coaxial path 30, and the electric field in the first coaxial path 30 is formed. Strength increases. In addition, the electric field strength at the tip 34a of the inner conductor 34 protruding into the combustion chamber 108 is increased, and a relatively small plasma is formed in the vicinity of the tip 34a. When the supply of the second microwave is started simultaneously with or immediately after the supply of the first microwave, the second microwave resonates in the combustion chamber 108 and a standing wave is generated in the combustion chamber 108. It is formed. At this time, starting from one end 30a of the first coaxial path 30, a high electric field is formed in the central portion and a low electric field is formed in the peripheral portion. The small-scale plasma generated in the vicinity of the tip portion 34 a by the supply of the first microwave plays a role of initial electron supply, and the small-scale plasma serves as a trigger, and the plasma is spread over a wide range in the combustion chamber 108. Is formed. The air-fuel mixture in the combustion chamber 108 can be ignited by the plasma generated in the combustion chamber 108. As a result, a flame-retardant mixture (for example, an ultra-lean mixture, a mixture containing a large amount of EGR, a mixture using a flame-retardant fuel, etc.) is stably burned without misfiring or fluctuating combustion. It becomes possible to improve engine fuel consumption.

  Conventionally, after an electric field is formed in the combustion chamber 108, it is necessary to ignite the air-fuel mixture using an assist such as DC discharge or ultraviolet irradiation. On the other hand, according to this embodiment, since the small-scale plasma generated by supplying the first microwave functions as a trigger, the second microwave that resonates in the combustion chamber 108 is supplied alone. Compared to the above, it is possible to ignite the air-fuel mixture by forming plasma in a wide range in the combustion chamber 108 with lower electric power.

  Next, the relationship between the resonance frequencies of the first coaxial path 30 and the combustion chamber 108 and the power feeding position 50 (length L2) will be described. However, the microwave frequency, the dimension of the combustion chamber 108, and the dimension of the first coaxial path 30 described below are examples, and the present invention is not limited to this example.

  As an example, the shape of the combustion chamber 108 is cylindrical, the diameter D of the cylindrical combustion chamber 108 is 90 mm, and the height H is 10 mm. The dielectric 36 of the first coaxial path 30 is air, and the impedance of the first coaxial path 30 is 50Ω. The entire length L1 of the first coaxial path 30 was 90 mm, and the tip end portion 34a of the inner conductor 34 was projected 2 mm into the combustion chamber 108. And the electric power feeding position 50 (length L2) was changed in the range of 20-80 mm, and each resonance frequency and reflectance of the combustion chamber 108 and the 1st coaxial path 30 in each position were calculated by simulation. The reflectance represents an index of the incident energy of the microwaves to the combustion chamber 108 and the first coaxial path 30, and the incidence of the microwaves to the combustion chamber 108 and the first coaxial path 30 becomes lower as the reflectance level is lower. Indicates that energy is large.

  FIG. 4A shows the calculation result for the combustion chamber 108, and FIG. 4B shows the calculation result for the first coaxial path 30. As shown in FIG. 4A, the resonance frequency of the combustion chamber 108 is included in the range of 2.54 to 2.56 GHz, and hardly changes even if the power feeding position 50 (length L2) is changed. Incidentally, the resonance frequency of the combustion chamber 108 depends on the shape and size of the combustion chamber 108, and the Q value of the resonator depends on the conductivity. On the other hand, the reflectance varies greatly depending on the power feeding position 50. The smaller the reflectance, the more energy can be stored in the combustion chamber 108. As an example, the reflectance in the combustion chamber 108 is preferably 0.2 or less, and in the example illustrated in FIG. 4A, the length L2 is preferably included in the range of 40 to 60 mm.

  On the other hand, as shown in FIG. 4B, in the first coaxial path 30, the resonance frequency becomes a value in the vicinity of 2.5 GHz in the range where the power feeding position (length L2) is 20 to 30 mm, and the length L2 is In the case of 50 mm, the resonance frequency is a value in the vicinity of 4 GHz, and in the case where the length L2 is 60 to 80 mm, the resonance frequency is a value in the vicinity of 1 GHz. The reflectivity is about 0.9, and functions to form a relatively small-scale plasma at the tip end 34a of the inner conductor 34.

Here, with reference to FIG. 5, the wavelength (frequency) of the microwave that can induce resonance in each of the first coaxial path 30 and the combustion chamber 108 will be described. FIG. 5 is a diagram schematically showing the first coaxial path 30 and the combustion chamber 108 and also schematically showing the waveforms of the first microwave and the second microwave. A first microwave (frequency fa, wavelength λa) that can induce resonance in the first coaxial path 30 and a second microwave (that can induce resonance in the combustion chamber 108 ( The frequency fb and the wavelength λb) satisfy the following conditions.
(1) The length L1 of the first coaxial path 30 is an odd multiple of (λb / 2).
(2) The feeding position 50 (length L2) is an odd multiple of (λa / 4) and an integral multiple of (λb / 2).
By satisfying the above conditions, the first microwave becomes “antinode of the wave” at the end face (one end 30a) of the combustion chamber 108 when the power feeding position 50 becomes a “wave node”. Will have a wavelength. In addition, the second microwave has a wavelength that becomes a “wave node” at the end face (one end portion 30a) of the combustion chamber 108 when the power supply position 50 becomes a “wave node”. .

  For example, in the example shown in FIG. 5A, the length L1 between the end face (one end 30a) of the combustion chamber 108 and the ground end face (the other end 30b) is equal to (λb / 2). ing. The power feeding position 50 (length L2) is also equal to (λa / 4) and (λb / 2).

  In the example shown in FIG. 5B, the length L1 is equal to (λb / 2), and the length L2 is equal to (3λa / 4) and (λb / 2).

  In the example shown in FIG. 5C, the length L1 is equal to (λb + λb / 2), and the length L2 is equal to (λa / 4) and (λb / 2). Alternatively, the length L2 is equal to (3λa / 4) and (λb + λb / 2).

  In the example shown in FIG. 5D, the length L1 is equal to (λb + λb / 2), and the length L2 is equal to (λa + λa / 4) and (λb + λb / 2). Alternatively, the length L2 is equal to (3λa / 4) and (λb / 2).

  When the first microwave that satisfies the above conditions is supplied, the first microwave resonates in the first coaxial path 30, and a standing wave is formed in the first coaxial path 30. The electric field strength in the path 30 is increased. When the second microwave that satisfies the above condition is supplied, the electric field spreads in the combustion chamber 108 around the one end 30a of the first coaxial path 30, and the second microwave is generated in the combustion chamber 108. And a standing wave is formed, and a high electric field is formed in a wide range in the combustion chamber 108.

Example 1
Next, a specific example of the microwave radiator 20 will be described. First, a preferred embodiment 1 will be described based on the calculation results shown in FIG. FIG. 6 shows the frequency and half wavelength of the microwave used in Example 1. In Example 1, the power feeding position 50 (length L2) was set to 50 mm. When the feeding position 50 is set at this position, as shown in FIGS. 6A and 6B, the resonance frequency of the first coaxial path 30 is 3.986 GHz, the reflectance is 0.67, and the half wavelength ( λa / 2) is 37 mm. The resonance frequency of the combustion chamber 108 is 2.544 GHz, the reflectance is 0.2, and the half wavelength (λb / 2) is 57 mm.

  FIG. 7 schematically shows an electric field distribution when a microwave having a frequency of 3.986 GHz is supplied. In the present application, the intensity of the electric field distribution is indicated by hatching, but this display mode is schematic for convenience of explanation, and the actual electric field is distributed more smoothly. When a microwave having a frequency of 3.986 GHz is supplied to the first coaxial path 30, a standing wave is formed with the other end 30 b (ground termination) and the feeding position 50 as a node of a wave (electric field). As a result, the electric field strength in the first coaxial path 30 is increased, and a high electric field region is formed around the distal end portion 34 a of the inner conductor 34. At this time, the relationship between the length L2, the length L3, and the wavelength λa is as follows. The length L2 (= 50 mm) between one end 30a and the feeding position 50 is equal to {(λa / 4) + (λa / 2)}, and the feeding position 50 and the other end 30b (ground termination) ) Is equal to (λa / 2).

  FIG. 8 shows an electric field distribution when a microwave having a frequency of 2.544 GHz is supplied. When a microwave having a frequency of 2.544 GHz is supplied to the combustion chamber 108 via the first coaxial path 30, no standing wave is formed in the first coaxial path 30 at the resonance frequency of the combustion chamber 108. As a result, most of the microwave energy is supplied into the combustion chamber 108, and a high electric field can be formed over a wide range. Specifically, the electric field in the combustion chamber 108 is highest at the radial center of the combustion chamber 108 (one end 30a of the first coaxial path 30), and the surrounding portion (outside in the radial direction). The lower it gets, the lower it goes. Thus, the electric field distribution in the combustion chamber 108 is formed axially symmetrically about the one end 30 a of the first coaxial path 30. At this time, the relationship between the length L2, the length L3, and the wavelength λb is as follows. The length L2 (= 50 mm) is equal to (λb / 2.4), and the length L3 (= 40 mm) is equal to (λb / 3).

  Then, by supplying the first microwave having a frequency of 3.986 GHz, as shown in FIG. 7, a high electric field is formed around the front end portion 34a of the inner conductor 34, and a relatively small plasma is formed. Then, by supplying the second microwave having a frequency of 2.544 GHz, a high electric field is formed in a wide range in the combustion chamber 108 as shown in FIG. A small-scale plasma generated due to the first microwave serves as a trigger (initial electron supply), and a plasma is formed in a wide range in the combustion chamber 108 to ignite the air-fuel mixture in the combustion chamber 108. It becomes possible. As a result, the air-fuel mixture can be ignited without using assistance such as DC discharge.

  Even if the relationship between the length L2, the length L3, and the wavelength does not satisfy the ideal relationship shown in FIG. 5, if the deviation from the ideal relationship is small, as in the first embodiment, the first Resonance is generated in the coaxial path 30 and the combustion chamber 108, and plasma can be formed in a wide range in the combustion chamber 108.

(Comparative Example 1)
Next, Comparative Example 1 with respect to Example 1 will be described. FIG. 9 shows the frequency and half wavelength of the microwave used in Comparative Example 1. In Comparative Example 1, the power feeding position 50 (length L2) was set to 30 mm. When the feeding position 50 is set at this position, as shown in FIGS. 9A and 9B, the resonance frequency of the first coaxial path 30 is 2.375 GHz, the reflectance is 0.52, and the half wavelength ( λa / 2) is 62 mm. The resonance frequency of the combustion chamber 108 is 2.564 GHz, the reflectance is 0.84, and the half wavelength (λb / 2) is 57 mm.

  FIG. 10 shows an electric field distribution when a microwave having a frequency of 2.375 GHz is supplied. When a microwave having a frequency of 2.375 GHz is supplied to the first coaxial path 30, the other end 30 b (ground termination) and the feeding position 50 serve as a wave (electric field) node, and one end 30 a (combustion chamber). A standing wave having an antinode at the end on the 108 side is formed. As a result, the electric field strength in the first coaxial path 30 is increased, and a high electric field is formed around the distal end portion 34 a of the inner conductor 34. At this time, the relationship between the length L2, the length L3, and the wavelength λa is as follows. The length L2 (= 30 mm) is equal to (λa / 4), and the length L3 (= 60 mm) is equal to (λa / 2).

  FIG. 11 shows an electric field distribution when a microwave having a frequency of 2.564 GHz is supplied. When a microwave having a frequency of 2.564 GHz is supplied to the combustion chamber 108 via the first coaxial path 30, the other end 30 b (ground termination) and the feeding position 50 are used as a wave (electric field) node. A standing wave is formed with the end 30a (end on the combustion chamber 108 side) as the antinode of the wave. As a result, microwave energy is consumed in the first coaxial path 30, and microwave energy supplied to the combustion chamber 108 is reduced, so that a high electric field is formed in a wide range in the combustion chamber 108. I can't do that. At this time, the relationship between the length L2, the length L3, and the wavelength λb is as follows. L2 (= 30 mm) is equal to (λb / 4), and L3 (= 60 mm) is equal to (λb / 2).

  In Comparative Example 1, since a high electric field cannot be formed in a wide range in the combustion chamber 108, plasma cannot be formed in a wide range in the combustion chamber 108 to ignite the air-fuel mixture.

[Second Embodiment]
FIG. 12 shows the configuration of the ignition device 10A and the microwave radiator 20A according to the second embodiment. The ignition device 10A includes a microwave radiator 20A instead of the microwave radiator 20 according to the first embodiment. The microwave radiator 20A includes a first coaxial path 30 and a second coaxial path 40, as in the first embodiment. In the second embodiment, the other end 30b of the first coaxial path 30 is an open end where the outer conductor 32 and the inner conductor 34 are not connected. Note that the end of the inner conductor 34 opposite to the tip 34 a is the other end 30 b (open end) of the first coaxial path 30.

  Similar to the first embodiment, the electromagnetic wave generating power supply 60 supplies the first microwave under the control of the control device 62, and at the same time or immediately after the start of the supply of the first microwave, the second microwave is supplied. Start supplying. As a result, the small-scale plasma generated in the vicinity of the tip portion 34a due to the supply of the first microwave plays a role of supplying initial electrons, so that plasma is formed in a wide range in the combustion chamber 108, and combustion The air-fuel mixture in the chamber 108 can be ignited.

  Next, the relationship between the resonance frequencies of the first coaxial path 30 and the combustion chamber 108 and the power feeding position 50 (length L2) will be described. However, the microwave frequency, the dimension of the combustion chamber 108, and the dimension of the first coaxial path 30 described below are examples, and the present invention is not limited to this example.

  Similar to the first embodiment, as an example, the shape of the combustion chamber 108 is cylindrical, the diameter D of the cylindrical combustion chamber 108 is 90 mm, and the height H is 10 mm. The dielectric 36 of the first coaxial path 30 is air, and the impedance of the first coaxial path 30 is 50Ω. The entire length L1 of the first coaxial path 30 was 90 mm, and the tip end portion 34a of the inner conductor 34 was projected 2 mm into the combustion chamber 108. And the electric power feeding position 50 (length L2) was changed in the range of 10-90 mm, and the resonant frequency and reflectance of each of the combustion chamber 108 and the 1st coaxial path 30 in each position were calculated by simulation.

  FIG. 13A shows the calculation result for the combustion chamber 108, and FIG. 13B shows the calculation result for the first coaxial path 30. As shown in FIG. 13A, the resonance frequency of the combustion chamber 108 is a value in the vicinity of 2.54 GHz, and hardly changes even if the power feeding position 50 (length L2) is changed. On the other hand, the reflectance varies greatly depending on the power feeding position 50. Since the reflectance in the combustion chamber 108 is preferably 0.2 or less, the length L2 is preferably included in the range of 20 to 40 mm and 80 to 90 mm.

  On the other hand, as shown in FIG. 13B, in the first coaxial path 30, the vicinity of 3 GHz (resonance frequency A) and the vicinity of 1.5 GHz (resonance frequency B) according to the feeding position (length L 2). Resonance occurs at frequency. The reflectivity is about 0.9, and functions to form a relatively small-scale plasma at the tip end 34a of the inner conductor 34.

Here, with reference to FIGS. 14 to 16, the wavelength (frequency) of the microwave that can induce resonance in each of the first coaxial path 30 and the combustion chamber 108 will be described. 14 to 16 are diagrams schematically showing the first coaxial path 30 and the combustion chamber 108, and also schematically showing waveforms of the first microwave and the second microwave. A first microwave (frequency fa, wavelength λa) that can induce resonance in the first coaxial path 30 and a second microwave (that can induce resonance in the combustion chamber 108 ( The frequency fb and the wavelength λb) satisfy the following conditions.
(3) The length L1 of the first coaxial path 30 is an odd multiple of (λb / 4).
(4) The feeding position 50 (length L2) is an odd multiple of (λa / 4) and an integral multiple of (λb / 2).
By satisfying the above conditions, the first microwave becomes “antinode of the wave” at the end face (one end 30a) of the combustion chamber 108 when the power feeding position 50 becomes a “wave node”. Will have a wavelength. In addition, the second microwave has a wavelength that becomes a “wave node” at the end face (one end portion 30a) of the combustion chamber 108 when the power supply position 50 becomes a “wave node”. .

  For example, in the example shown in FIG. 14, as shown in FIG. 14A, the length L1 is equal to (3λb / 4), and the feeding position 50 (length L2) is equal to (λb / 2). ing. In an example in which the wavelength relationship is “λb <λa”, the feeding position 50 (length L2) is equal to (λa / 4) as shown in FIG. On the other hand, in an example in which the wavelength relationship is “λb> λa”, the length L2 is equal to (3λa / 4) as shown in FIG.

  In the example shown in FIG. 15, as shown in FIG. 15A, the length L1 is equal to (λb + λb / 4), and the length L2 is equal to (λb / 2). In an example in which the wavelength relationship is “λb <λa”, the length L2 is equal to (λa / 4) as shown in FIG. On the other hand, in an example in which the wavelength relationship is “λb> λa”, the length L2 is equal to (3λa / 4) as shown in FIG.

  In the example shown in FIG. 16, as shown in FIG. 16A, the length L1 is equal to (λb + 3λb / 4), and the length L2 is equal to (λb + λb / 2). In an example in which the wavelength relationship is “λb <λa”, the length L2 is equal to (3λa / 4) as shown in FIG. On the other hand, in an example in which the wavelength relationship is “λb> λa”, the length L2 is equal to (2λa + λa / 4) as shown in FIG.

  When the first microwave that satisfies the above conditions is supplied, the first microwave resonates in the first coaxial path 30, and a standing wave is formed in the first coaxial path 30. The electric field strength in the path 30 is increased. When the second microwave that satisfies the above condition is supplied, the electric field spreads in the combustion chamber 108 around the one end 30a of the first coaxial path 30, and the second microwave is generated in the combustion chamber 108. And a standing wave is formed, and a high electric field is formed in a wide range in the combustion chamber 108.

(Example 2)
Next, a specific example of the microwave radiator 20A will be described. First, a preferred embodiment 2 will be described based on the calculation results shown in FIG. FIG. 17 shows the frequency and half wavelength of the microwave used in Example 2. In Example 2, the power feeding position 50 (length L2) was set to 20 mm. When the feeding position 50 is set at this position, as shown in FIGS. 17A and 17B, the resonance frequency of the first coaxial path 30 is 3.112 GHz, the reflectance is 0.69, and the half wavelength ( λa / 2) is 47 mm. The resonance frequency of the combustion chamber 108 is 2.536 GHz, the reflectance is 0.04, and the half wavelength (λb / 2) is 58 mm.

  FIG. 18 shows an electric field distribution when a microwave having a frequency of 3.112 GHz is supplied. When a microwave having a frequency of 3.112 GHz is supplied to the first coaxial path 30, the other end 30b (open end) is taken as an antinode of the wave (electric field), and L31 (= 23 mm = λa / 4) away from the antinode. The position is a wave node, the power supply position 50 further away from L32 (= 47 mm = λa / 2) is the wave node, and one end 30a (the end on the combustion chamber 108 side) is the antinode of the wave A wave is formed. As a result, the electric field strength in the first coaxial path 30 is increased, and a high electric field region is formed around the distal end portion 34 a of the inner conductor 34. The length L2 (= 20 mm) is equal to (λa / 4).

  FIG. 19 shows an electric field distribution when a microwave having a frequency of 2.536 GHz is supplied. When a microwave having a frequency of 2.536 GHz is supplied to the combustion chamber 108 via the first coaxial path 30, no standing wave is formed in the first coaxial path 30 at the resonance frequency of the combustion chamber 108. As a result, most of the microwave energy is supplied into the combustion chamber 108, and a high electric field can be formed over a wide range. Specifically, the electric field in the combustion chamber 108 is highest at the central portion in the radial direction of the combustion chamber 108 and becomes lower toward the peripheral portion. At this time, the relationship between the length L2, the length L3, and the wavelength λb is as follows. The length L2 (= 20 mm) is equal to (λb / 5.8), and the length L3 (= 70 mm) is equal to (λb / 1.7).

  Then, by supplying the first microwave having a frequency of 3.112 GHz, a high electric field is formed around the tip end portion 34a of the inner conductor 34 to form a relatively small plasma as shown in FIG. Then, by supplying the second microwave having a frequency of 2.536 GHz, a high electric field is formed in a wide range in the combustion chamber 108 as shown in FIG. A small-scale plasma generated due to the first microwave plays a role of a trigger, and a plasma is formed in a wide range in the combustion chamber 108, so that the air-fuel mixture in the combustion chamber 108 can be ignited. .

  If the relationship between the length L2, the length L3, and the wavelength does not satisfy the ideal relationship shown in FIGS. Resonance can be generated in one coaxial path 30 and the combustion chamber 108, and plasma can be formed in a wide range in the combustion chamber 108.

(Comparative Example 2)
Next, Comparative Example 2 with respect to Example 2 will be described. FIG. 20 shows the frequency and half wavelength of the microwave used in Comparative Example 2. In Comparative Example 2, the power feeding position 50 (length L2) was set to 60 mm. When the feeding position 50 is set at this position, as shown in FIGS. 20A and 20B, the first resonance frequency a ₁ of the first coaxial path 30 is 1.563 GHz, and the reflectance is 0.97. next, half-wavelength (λa _1/2) becomes 94 mm. The second resonance frequency _{a 2} is 3.165GHz next to the first coaxial line 30, the reflectivity is 0.94, the half-wavelength ([lambda] a _2/2) becomes 46 mm. The resonance frequency of the combustion chamber 108 is 2.537 GHz, the reflectance is 0.93, and the half wavelength (λb / 2) is 58 mm.

  FIG. 21 shows an electric field distribution when a microwave having a frequency of 1.563 GHz is supplied. When a microwave having a frequency of 1.563 GHz is supplied to the first coaxial path 30, one end 30a (end on the combustion chamber 108 side) and the other end 30b (open end) are connected to the wave (electric field). A standing wave is formed. As a result, a high electric field is formed around the distal end portion 34 a of the inner conductor 34.

  FIG. 22 shows an electric field distribution when a microwave having a frequency of 3.165 GHz is supplied. When a microwave having a frequency of 3.165 GHz is supplied to the first coaxial path 30, the other end 30b (open end) is an antinode of a wave (electric field), the vicinity of the feeding position 50 is a wave node, A standing wave is formed with the end 30a (the end on the side of the combustion chamber 108) of which is an antinode of the wave. As a result, a high electric field is formed around the distal end portion 34 a of the inner conductor 34.

  FIG. 23 shows an electric field distribution when a microwave having a frequency of 2.537 GHz is supplied. When a microwave having a frequency of 2.537 GHz is supplied to the combustion chamber 108 via the first coaxial path 30, the other end 30b (open end) is an antinode of the wave (electric field), and the power feeding position 50 is the wave. A standing wave is formed with a node, and one end 30a (an end on the combustion chamber 108 side) as a wave node. As a result, microwave energy is consumed in the first coaxial path 30, and microwave energy supplied to the combustion chamber 108 is reduced, so that a high electric field is formed in a wide range in the combustion chamber 108. I can't do that. At this time, the relationship between the length L2, the length L3, and the wavelength λb is as follows. The length L2 (= 60 mm) is equal to (λb / 2), and the length L3 (= 30 mm) is equal to (λb / 4).

  In Comparative Example 2, since a high electric field cannot be formed in a wide range in the combustion chamber 108, plasma cannot be ignited by plasma in a wide range in the combustion chamber 108. In Comparative Example 2, the length L1 of the first coaxial path 30 is an odd multiple of (λb / 4), and the feeding position 50 (length L2) is an integral multiple of (λb / 2). However, as shown in FIG. 23, a high electric field is not formed in a wide range in the combustion chamber 108. This is because the feeding position 50 is set so as to be a “wave node” at one end 30 a of the first coaxial path 30 (end surface of the combustion chamber 108). Strong resonance occurs between the intersection (feeding position 50) with the second coaxial path 40 (feeding port) and the other end 30b (open end) of the first coaxial path 30, resulting in combustion. This is because the supply of microwaves to the chamber 108 is hindered and no strong resonance occurs in the combustion chamber 108.

  10, 10A ignition device, 20, 20A microwave radiator, 30 first coaxial path, 32, 42 outer conductor, 34, 44 inner conductor, 36 dielectric, 40 second coaxial path, 50 feeding position, 60 electromagnetic wave Generation power source, 62 control device, 64 electromagnetic wave transmission path, 100 internal combustion engine, 102 cylinder head, 104 cylinder, 106 piston, 108 combustion chamber, 110 intake port, 112 intake valve, 114 exhaust port, 116 exhaust valve, 118 fuel injection valve .

Claims (5)

An internal combustion engine ignition device for igniting an air-fuel mixture in a combustion chamber,
Electromagnetic wave generating means for generating electromagnetic waves;
One end is disposed facing the combustion chamber, the other end is a ground termination or an open termination, and electromagnetic waves generated by the electromagnetic wave generation means are supplied from the one end into the combustion chamber. First electromagnetic wave supply means;
A second electromagnetic wave connected between the one end and the other end of the first electromagnetic wave supply means and supplying the electromagnetic wave generated by the electromagnetic wave generation means to the first electromagnetic wave supply means Supply means;
With
The electromagnetic wave generation means generates a first electromagnetic wave that can resonate by the first electromagnetic wave supply means, and generates a second electromagnetic wave that can resonate in the combustion chamber while the first electromagnetic wave is generated. To start the
An ignition device for an internal combustion engine. An ignition device for an internal combustion engine according to claim 1,
The electromagnetic wave generation unit generates the first electromagnetic wave by changing a frequency at which the first electromagnetic wave supply unit can resonate according to a connection position of the second electromagnetic wave supply unit with respect to the first electromagnetic wave supply unit. And changing the frequency that can resonate in the combustion chamber to generate the second electromagnetic wave,
An ignition device for an internal combustion engine. An ignition device for an internal combustion engine according to claim 1 or 2,
When the other end of the first electromagnetic wave supply means is a ground termination, the length from the one end to the other end of the first electromagnetic wave supply means is the length of the second electromagnetic wave. An odd multiple of one half of the wavelength, and the length between the connection position of the second electromagnetic wave supply means to the first electromagnetic wave supply means and the one end of the first electromagnetic wave supply means is The electromagnetic wave generating means is configured to be an odd multiple of a quarter of the wavelength of the first electromagnetic wave and an integral multiple of a half of the wavelength of the second electromagnetic wave. Generating an electromagnetic wave and the second electromagnetic wave;
An ignition device for an internal combustion engine. An ignition device for an internal combustion engine according to claim 1 or 2,
When the other end of the first electromagnetic wave supply means is an open terminal, the length from the one end to the other end of the first electromagnetic wave supply means is the length of the second electromagnetic wave. An odd multiple of a quarter of the wavelength, and the length between the connection position of the second electromagnetic wave supply means to the first electromagnetic wave supply means and the one end of the first electromagnetic wave supply means is The electromagnetic wave generating means is configured to be an odd multiple of a quarter of the wavelength of the first electromagnetic wave and an integral multiple of a half of the wavelength of the second electromagnetic wave. Generating an electromagnetic wave and the second electromagnetic wave;
An ignition device for an internal combustion engine. An ignition device for an internal combustion engine according to any one of claims 1 to 4,
The first electromagnetic wave supply means includes an inner conductor and an outer conductor provided coaxially on the outer side of the inner conductor, and is disposed with one end facing the combustion chamber, and the other end is It is a ground termination in which the inner conductor and the outer conductor are short-circuited or an open termination in which the inner conductor and the outer conductor are not connected to each other, A coaxial path for supplying the combustion chamber from the one end;
An ignition device for an internal combustion engine.

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