Patent Publication Number: US-10320159-B2

Title: High frequency discharge ignition device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a high frequency discharge ignition device to be used mainly in an internal combustion engine. 
     2. Description of the Related Art 
     In recent years, problems relating to environmental conservation and fuel depletion have been raised, and responding to these problems also represents an urgent task in the automobile industry. As an example of a response thereto, there exists a method in which fuel consumption is improved through engine downsizing using a supercharger. 
     However, when a supercharger is used and a highly supercharged state is reached, pressure in an engine combustion chamber becomes extremely high even in a state where combustion is not occurring, making it difficult to generate a spark discharge for initiating combustion. As a solution to this, a state in which a spark discharge can be generated easily is created by narrowing the gap of a spark plug. However, when the gap of the spark plug is narrowed, quenching effect caused by the electrode part, that is, an effect where energy that allows a just generated spark to grow is depleted by the low-temperature electrode part, becomes more pronounced, which results in a decrease of startability or a combustibility. 
     In order to solve this problem, a method has been considered in which energy that exceeds the thermal energy depleted by the quenching effect is provided by spark discharge. For example, Japanese Patent No. 5250119 describes a high frequency discharge ignition device that enables a high-energy spark discharge to be formed by supplying, to a spark plug, high frequency energy having a high voltage and acquired as a result of coupling high frequency energy boosted by a booster circuit to a spark discharge generated by an ignition coil. 
     SUMMARY OF THE INVENTION 
     However, with the high frequency discharge ignition device described in Japanese Patent No. 5250119, a capacitive component is generated between a coupling circuit and a first metal housing into which the coupling circuit is built. A problem thus exists in that when a potential difference occurs between both ends of the capacitive component such that a capacitive discharge current flows thereacross, the capacitive component emits radiation noise to the outside, causing peripheral devices to malfunction. 
     The present invention has been made to solve the abovementioned problem, and an object thereof is to provide a high frequency discharge ignition device in which the influence of radiation noise on peripheral devices thereof is reduced. 
     A high frequency discharge ignition device according to the present invention is a high frequency discharge ignition device in which high frequency energy supplied from a high frequency energy supply circuit is coupled to a high voltage pulse supplied from an ignition coil and supplied to a spark plug connected to an engine block, the high frequency discharge ignition device including: an output device that includes a coupling circuit supplying the coupled energy to the spark plug; a first housing in which the output device is housed; and a second housing that is connected to the engine block, wherein the output device is directly attached to the spark plug, the first housing and the second housing are respectively formed from metal, the first housing is grounded, the first housing is enclosed in the second housing, and the first housing is separated from the second housing by a gap. 
     With the high frequency discharge ignition device of the present invention, a first housing which houses a coupling circuit is grounded. A second housing is connected to the engine block and thus grounded. The second housing encloses the first housing in a manner so as not to come into contact with the first housing. As a result, the second housing can be formed so as not to allow radiation noise generated by the capacitive discharge current between the coupling circuit and the first housing to escape to the outside of the second housing. 
     As a result, a high frequency discharge ignition device can be provided in which the influence of radiation noise on peripheral devices thereof is reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a circuit configuration of a high frequency discharge ignition device according to a first embodiment of the present invention; 
         FIG. 2  is an exploded perspective view of the high frequency discharge ignition device according to the first embodiment; 
         FIG. 3  is a top view of the high frequency discharge ignition device according to the first embodiment; 
         FIG. 4  is a cross-sectional view taken along the line IV-IV shown in  FIG. 3 ; 
         FIG. 5  is a cross-sectional view showing a modification of  FIG. 4 ; 
         FIG. 6  is provided to explain the effect of the first embodiment, and is a block diagram showing a circuit configuration of a high frequency discharge ignition device in which no second housing to enclose the first housing is provided; 
         FIG. 7  is an exploded perspective view of a first housing in a high frequency discharge ignition device according to a second embodiment of the present invention; 
         FIG. 8  is an exploded perspective view of a first housing in a high frequency discharge ignition device according to a modification of the second embodiment; 
         FIG. 9  is an exploded perspective view of a high frequency discharge ignition device according to a third embodiment of the present invention; and 
         FIG. 10  is a perspective view of a high frequency discharge ignition device according to a fourth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the high frequency discharge ignition device according to the present invention will be described hereinafter with reference to the drawings. Note that identical or corresponding parts will be indicated by identical reference numerals, and redundant description is omitted. 
     Further, in these embodiments, the voltage of a “high voltage pulse” is assumed to be 30 to 40 kV, the voltage of “high frequency energy” is assumed to be 1 to 2 kV, and the frequency of a “high frequency” is assumed to be several hundred kHz to several MHz. 
     First Embodiment 
       FIG. 1  is a block diagram showing a circuit configuration of a high frequency discharge ignition device  101  and peripheral devices thereof according to a first embodiment. The high frequency discharge ignition device  101  is constituted by a coupling circuit  35 , a first housing  1  and a second housing  2 . The coupling circuit  35  is housed in the first housing  1 . The first housing  1  is enclosed in the second housing  2 . 
     The voltage of a power supply  32  is boosted by a booster circuit  33 . Using the boosted voltage, a high frequency energy supply circuit  11  generates and supplies high frequency energy to the coupling circuit  35 . In addition, an ignition coil  10  generates and supplies a high voltage pulse to the coupling circuit  35 . The coupling circuit  35  couples and supplies, to a spark plug  8  connected to an engine block  9 , the high frequency energy and the high voltage pulse. Drive control of the high frequency energy supply circuit  11  and a circuit of the ignition coil  10  is performed by an ECU  34 . 
     Three types of radiation noise, N 1  to N 3 , are dealt with hereinafter in this specification. 
     First radiation noise N 1  is radiation noise generated by the coupling circuit  35 . 
     Second radiation noise N 2  is radiation noise generated due to a capacitive component C 1  between the coupling circuit  35  and the first housing  1 . When a potential difference occurs between both ends of the capacitive component C 1 , a capacitive discharge current flows thereacross, causing radiation of the second radiation noise N 2 . 
     Third radiation noise N 3  is radiation noise generated due to a capacitive component C 2  between the first housing  1  and the second housing  2 . When a potential difference occurs between both ends of the capacitive component C 2 , a capacitive discharge current flows thereacross, causing radiation of the third radiation noise N 3 . 
     The configuration of the high frequency discharge ignition device  101  will be described hereinafter with reference to  FIGS. 2 to 4 . 
       FIG. 2  is an exploded perspective view showing an internal structure of the high frequency discharge ignition device  101 . 
     The spark plug  8  is attached to the engine block  9 . Four female threaded portions  14  are provided around the area in which the spark plug  8  is attached. The four female threaded portions  14  are used when fixing the second housing  2  in place. 
     The first housing  1  is formed by a base  3  and a cover  4 , and houses an output device  5 . The output device  5  is constituted by the coupling circuit  35 , a protector  12 , a connection terminal  50 , and a connection terminal  51 . The coupling circuit  35  is screwed into the first housing  1 . The protector  12  is mounted on the spark plug  8 . In other words, the output device  5  is electrically connected directly to the spark plug  8 . The connection terminal  50  is connected to the ignition coil  10  via a harness  17 . The connection terminal  51  is connected to the high frequency energy supply circuit  11  via a harness  16 . 
     The second housing  2  is provided to the outside of the first housing  1  so as to enclose the first housing  1  with a gap disposed therebetween. The second housing  2  is provided with a hole  40 , a hole  41 , and four flange holes  13 . Bolts  6  pass through each of the four flange holes  13 . The bolts  6  are fastened to each of the female threaded portions  14  in the engine block  9 . In this way, the second housing  2  is connected to the engine block  9 . The harness  17 , which is directed towards the ignition coil  10 , passes through the hole  40 . The harness  16 , which is directed towards the high frequency energy supply circuit  11 , passes through the hole  41 . 
     Note that the first housing  1  and the second housing  2  are formed from metal. Aluminum or stainless steel, for example, may be used as a material therefor. 
       FIG. 3  is a top view of the high frequency discharge ignition device  101 , and  FIG. 4  is a cross-sectional view taken along the line IV-IV shown in  FIG. 3 . 
     As shown in  FIG. 4 , the spark plug  8  is attached to the engine block  9 . The spark plug  8  is directly attached to the coupling circuit  35  by the protector  12 . Further, a connecting member  7  is sandwiched between the spark plug  8  and the first housing  1 . 
     In addition, the second housing  2  is fixed to the female threaded portions  14  in the engine block  9  by the flange holes  13  and the bolts  6 . 
     Next, an electrical pathway of the high frequency discharge ignition device  101  will be described with reference to  FIG. 4 . 
     The first housing  1  is electrically connected to the spark plug  8  via the connecting member  7 . For this reason, the electrical potential of the first housing  1  is equal to 0 V, i.e. ground potential. In other words, the first housing  1  is grounded and, as a result, the first radiation noise N 1  generated from the coupling circuit  35  is shielded by the first housing  1 . 
     The first housing  1  is grounded by being connected to the spark plug  8 , however, as shown in  FIG. 5 , the first housing  1  may also be grounded by a metal lead wire  37  that is fixed to the first housing  1  by a screw  38  and is fixed to the engine block  9  by a screw  39 . 
     The second housing  2  is fixed so as not to come into contact with the first housing  1 , that is, a gap is disposed therebetween. Further, the second housing  2  is connected to the engine block  9 . Accordingly, the second housing  2  is grounded. As a result, the second radiation noise N 2  caused by the capacitive component C 2  between the coupling circuit  35  and the first housing  1  is shielded by the second housing  2 . 
     Here, if the second housing  2  comes into contact with even a part of the first housing  1 , the first housing  1  will be electrically integrated with the second housing  2 . As a result, the capacitive discharge current that flows between the coupling circuit  35  and the first housing  1  passes through this contact point and also flows into the second housing  2  and the engine block  9 . Accordingly, the second radiation noise N 2  is radiated to the outside from the outer surface of the second housing  2  and the surface of the engine block  9 . In other words, if the second housing  2  comes into contact with the first housing  1 , the second housing  2  becomes ineffective at shielding the second radiation noise N 2 . 
     Note that the first housing  1  and the second housing  2  are both grounded and have the same electrical potential. Accordingly, no capacitive discharge current flows through the capacitive component C 2  between the first housing  1  and the second housing  2 , and the third radiation noise N 3  does not occur. 
       FIG. 6  is a block diagram showing a circuit configuration of a high frequency discharge ignition device in which no second housing is provided so as to enclose the first housing. In  FIG. 6 , the coupling circuit  35  is built into the first housing  1 . As the first housing  1  is grounded, the first radiation noise N 1  generated by the coupling circuit  35  is shielded by the first housing  1 . However, as there is no second housing provided so as to enclose the first housing  1 , the second radiation noise N 2  generated due to the capacitive component C 1  between the coupling circuit  35  and the first housing  1  is not shielded, and is radiated to the outside of the first housing  1 . 
     As described above, the high frequency discharge ignition device  101  according to the first embodiment couples and supplies, to the spark plug  8  connected to the engine block  9 , high frequency energy supplied from the high frequency energy supply circuit  11  and a high voltage pulse supplied from the ignition coil  10 . The high frequency discharge ignition device  101  includes the output device  5  which includes the coupling circuit  35  for supplying coupled energy to the spark plug  8 , the first housing  1  in which the output device  5  is housed, and the second housing  2  which is connected to the engine block  9 , the output device  5  being directly attached to the spark plug  8 , the first housing  1  and the second housing  2  being respectively formed from metal, the first housing  1  being grounded, the first housing  1  being enclosed in the second housing  2 , and the first housing  1  being separated from the second housing  2  such that a gap is disposed therebetween. 
     Hence, a high frequency discharge ignition device can be provided in which the influence of radiation noise on peripheral devices thereof is reduced. 
     In addition, the first housing  1  is grounded by being electrically connected to the spark plug  8  or the engine block  9 . As a result, the distance to ground from the first housing  1  is shortened, and the pathway which passes from the coupling circuit  35 , through the spark plug  8 , the engine block  9  (ground), the first housing  1 , and back to the coupling circuit  35  is shortened. For this reason, generation of the second radiation noise N 2  due to a capacitance between the coupling circuit  35  and the first housing  1  can be suppressed. 
     Second Embodiment 
     Next, a high frequency discharge ignition device according to a second embodiment will be described with reference to  FIG. 7 . In the high frequency discharge ignition device according to the second embodiment, a coupling circuit is built into an inner housing. 
       FIG. 7  is a perspective view showing a configuration of a first housing in the high frequency discharge ignition device according to the second embodiment. A coupling circuit  35  is screwed into an interior of a resin inner housing  18 . The interior of the inner housing  18  is then fixed in place by a casting resin  19 . In other words, the inner housing  18  is resin-molded. The inner housing  18 , the interior of which has been fixed in place by the casting resin, is inserted into a metal base  20 . A metal cover  22  provided with hole portions  21  is fixed by screws  24  to flange holes  23  provided on the base  20 . The base  20  and the cover  22  constitute a first housing  61 . 
     At this time, a method is conceivable in which the coupling circuit  35  is fixed directly, i.e. without using the inner housing  18 , into the metal first housing  61  using the casting resin. However, depending on the material used for the casting resin, the casting resin may fail to adhere to the metal and come off. In such a case, the coupling circuit  35  would not be fixed in place. However, when the resin inner housing  18  is used, as in the second embodiment, such a situation, i.e. the casting resin  19  coming off, does not occur, such that the coupling circuit  35  is fixed inside the inner housing  18 . 
     Next, a modification will be described with reference to  FIG. 8 .  FIG. 8  is a perspective view showing the configuration of a first housing of a high frequency discharge ignition device according to a modification of the second embodiment. As shown in  FIG. 8 , the resin inner housing  18  into which the coupling circuit  35  is built is fixed to a metal base  26  using an adhesive  25 . The base  26  constitutes the first housing. 
     As described above, in the high frequency discharge ignition device according to the second embodiment, the coupling circuit  35  is resin-molded into the resin inner housing  18 , and the inner housing  18  is housed in the first housing  61  or  26 . As a result, the insulating properties of the coupling circuit  35 , with which an internal circuit thereof has a high voltage of around 30 to 40 kV, can be improved. 
     Third Embodiment 
     Next, a high frequency discharge ignition device according to the third embodiment will be described with reference to  FIG. 9 . In the first embodiment, the high frequency energy supply circuit is provided separately to the high frequency discharge ignition device, however, in the third embodiment, the high frequency energy supply circuit is incorporated into the high frequency discharge ignition device. 
       FIG. 9  is a perspective view showing the configuration of a high frequency discharge ignition device  103  according to the third embodiment. As shown in  FIG. 9 , a first housing  1  is mounted on a spark plug  8  via a connecting member  7 . A coupling circuit  35  is built into the first housing  1 . The connecting member  7  is formed from metal and has a ring shape. 
     A second housing  70  is provided so as to enclose the first housing  1 . The second housing  70  includes a cover portion  27  and a main body portion  71 , which, when combined, form a box shape. A high frequency energy supply circuit  11  is built into the cover portion  27 . Flange holes  29  are provided at four corners of the cover portion  27 . The main body portion  71  is provided with female threaded portions  28  positioned at four corners thereof which correspond to the flange holes  29 . Bolts  30  pass through the flange holes  29  and are fastened to the female threaded portions  28 , whereby the cover portion  27  is fixed to the main body portion  71 . 
     As described above, in the high frequency discharge ignition device  103  according to the third embodiment, the second housing  70  includes the main body portion  71  and the cover portion  27 , and the high frequency energy supply circuit  11  is built into the cover portion  27 . As a result, a length of wiring through which high frequency energy conducts from the high frequency energy supply circuit  11  to the coupling circuit  35  can be shortened, such that noise generated from the wiring can be reduced. Moreover, as the length of the wiring is shortened, the range over which shielding is applied to the high frequency discharge ignition device  103  can be reduced, with the result that noise becomes easy to deal with. 
     Further, the cover portion  27  is fixed to the main body portion  71 . As a result, vibration resistance of the high frequency energy supply circuit  11 , which is built into the cover portion  27 , can be improved. 
     Fourth Embodiment 
     Next, a high frequency discharge ignition device according to the fourth embodiment will be described with reference to  FIG. 10 . In the high frequency discharge ignition device according to the fourth embodiment, a second housing is provided with opening portions for heat dissipation in addition to harness holes. 
       FIG. 10  is a perspective view showing the configuration of a high frequency discharge ignition device  104  according to the fourth embodiment. As shown in  FIG. 10 , two circular opening portions  31  are provided in addition to holes  40  and  41  through which harnesses  17  and  16  pass, in a second housing  72 . The opening portions  31  allow a space between the first housing  1  and the second housing  72  to communicate with the outside of the second housing  72 . Heat generated inside the second housing  72  can escape to the outside of the second housing  72  through the opening portions  31 . The opening portions  31  form ventilation holes. 
     Note that, as there is concern regarding noise leakage from the opening portions  31 , the permissible size and number of the opening portions  31  are determined by the method described below. 
     First, a permissible noise level is determined in accordance with a standard set by the Japanese Radio Law. A difference between the determined noise level and current noise level is set as a margin S [dB]. Shielding properties are expressed by the following equation (1).
 
 S =20×log {150 /f/l/√n}   (1)
 
     Here, when the wavelength of radio waves of a frequency used f [MHz] is w [m], the diameter l [m] of the opening portions  31  is determined by
 
 l≤w /2.
 
     Accordingly, by substituting the margin S [dB], the frequency f [MHz] and l [m] into equation (1), the permissible number n of opening portions  31  can be calculated. 
     An example is given below. Assuming the frequency of radio waves used for ETC (Electronic Toll Collection) wireless communication f=3000 MHz, the wavelength thereof w is around 0.1 m, so the diameter l of the opening portions  31  will be no more than 0.05 m. If the margin is −3 dB and 1=0.05 m, then, according to equation (1), n will be approximately 2. In other words, it is indicated that, when the permissible noise level is set to −3 dB, up to two opening portions  31  having a diameter of 0.05 m may be provided in the second housing  72 . 
     As described above, in the high frequency discharge ignition device  104  according to the fourth embodiment, the second housing  72  is provided with the opening portions  31 . As a result, heat inside the second housing  72  can escape.