Patent Publication Number: US-2021194220-A1

Title: Igniter

Description:
RELATED APPLICATIONS 
     This application claims the benefit of Japanese Application No. 2019-231552, filed on Dec. 23, 2019, the disclosure of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an igniter that controls a current flowing in a coil unit for supplying a high voltage to a spark plug for use in an internal combustion engine. 
     Description of the Background Art 
     A vehicle body such as that of an automobile is conventionally provided with an ignition device for use in an internal combustion engine. The ignition device increases a DC low voltage supplied from a battery to as high as some thousands of volts at a coil unit under control by an engine control unit (ECU), and supplies the increased voltage to a spark plug. By doing so, an electric spark is generated to ignite fuel. 
     The ignition device is provided with a circuit board with a power element for controlling a current flowing in a primary coil L 1  in a coil unit. For example, an IGBT is used as the power element. The power element has pyrogenic properties. When the ignition device comes into operation, the power element generates heat instantaneously to be placed in a high temperature. Repeating such instantaneous heat generation causes a risk of a break or a crack at a connection between the power element and a peripheral member. Hence, a technique of suppressing temperature increase at the power element has been desired. A conventional configuration of suppressing temperature increase at the power element is disclosed in Japanese Patent No. 4286465, for example. 
     Japanese Patent No. 4286465 discloses a semiconductor device including a power element (1), a lead frame (2a) having a shape like a thin plate, a metal block (5) made of aluminum or copper, and a resin package (6). The power element (1) is fixed to the lead frame (2a) with solder (9). The metal block (5) is arranged on the opposite side of the power element (1) across the lead frame (2a). The metal block (5) has a protrusion of a shape protruding toward the lead frame (2a). The metal block (5) is bonded to the lead frame (2a) at the protrusion with a bonding material (10) (solder, for example). The resin package (6) seals the power element (1), a part of the lead frame (2a), and the metal block (5). An external heat dissipator (11) is attached to a part of the resin package (6) in the vicinity of the metal block (5). Heat generated at the power element (1) passes through the solder (9), the lead frame (2a), the bonding material (10), the metal block (5), and the resin package (6) to be dissipated to the outside from the external heat dissipator (11). 
     In the configuration of Japanese Patent No. 4286465, a plurality of members is present between the power element (1) and the external heat dissipator (11). A plurality of members is also present between the power element (11) and the metal block (5) around the external heat dissipator (11). Further, the power element (1) is bonded only to the protrusion of the metal block (5) through the solder (9), the lead frame (2a), and the bonding material (10). The protrusion mentioned herein is a minor part of the metal block (5). As a result, heat generated during the operation of the power element (1) is hindered from being transferred smoothly to the metal block (5) to cause a risk of raising the power element (1) to a high temperature. 
     SUMMARY OF THE INVENTION 
     The present invention is intended to provide a technique allowing suppression of temperature increase at a power element by transferring heat generated during the operation of the power element to a metal block smoothly in a moment. 
     To solve the foregoing problem, a first aspect of the present invention is intended for an igniter that controls a current flowing in a coil unit for supplying a high voltage to a spark plug for use in an internal combustion engine. The igniter includes: a pyrogenic power element; a metal block; a lead frame electrically connecting the metal block and the coil unit to each other; and a controller that controls the operation of the power element. The power element is fixed to the metal block by soldering at a surface of the power element on one side, and is electrically connected to the controller at a surface of the power element on the other side. 
     According to the first aspect of the present invention, the power element is fixed directly to the metal block by soldering. With this configuration, heat generated during the operation of the power element is transferred smoothly in a moment to the metal block. As a result, temperature increase at the power element is suppressed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram schematically showing an operating environment of an ignition device according to a first preferred embodiment; 
         FIG. 2  is a plan view of a coil unit according to the first preferred embodiment; 
         FIG. 3  is a plan view schematically showing the configuration of an igniter according to the first preferred embodiment; 
         FIG. 4  is a vertical sectional view of the igniter according to the first preferred embodiment; 
         FIG. 5  is a perspective view schematically showing the direction of magnetic flux during charging control according to the first preferred embodiment; and 
         FIG. 6  is a perspective view schematically showing the direction of magnetic flux during interruption control according to the first preferred embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An exemplary preferred embodiment of the present invention will be described below by referring to the drawings. 
     1. First Preferred Embodiment 
     &lt;1-1. Configuration of Ignition Device&gt; 
     The configuration of an ignition device  1  corresponding to a first preferred embodiment of the present invention will be described first by referring to the drawings.  FIG. 1  is a block diagram schematically showing an operating environment of the ignition device  1  according to the first preferred embodiment. As described later, a primary coil L 1  and a secondary coil L 2  in a coil unit  103  in the ignition device  1  are arranged in directions in which these coils are stacked on each other. To facilitate understanding, however, these coils are illustrated in positions adjacent to each other in  FIG. 1 . 
     The ignition device  1  of the first preferred embodiment is a device installed on a vehicle body  100  of a vehicle such as an automobile, for example, and used for applying a high voltage for generating spark discharge at a spark plug  113  for use in an internal combustion engine. As shown in  FIG. 1 , the vehicle body  100  includes the spark plug  113 , a battery  102 , and an engine control unit (ECU)  105 , in addition to the ignition device  1 . The ignition device  1  of the first preferred embodiment includes the coil unit  103  and an igniter  104  described later. 
     The spark plug  113  is connected to one end  821  of the secondary coil L 2  described later in the coil unit  103 . When a high voltage is induced in the secondary coil L 2  in the coil unit  103 , discharge occurs at a gap d in the spark plug  113  to generate a spark. As a result, fuel filling an internal combustion engine is ignited. 
     The battery  102  is a power supply capable of being charged and discharged with DC power. Namely, the battery  102  is a storage battery. In the first preferred embodiment, the battery  102  is electrically connected to the primary coil L 1  described later in the coil unit  103 . The battery  102  supplies a DC voltage to the primary coil L 1  in the coil unit  103 . 
       FIG. 2  is a plan view of the coil unit  103 . As shown in  FIG. 2 , the coil unit  103  includes a bobbin  40 , the primary coil L 1 , the secondary coil L 2 , and an iron core  60 . In the description of the coil unit  103  given below, a direction parallel to the center axis of the bobbin  40 , a direction perpendicular to the center axis of the bobbin  40 , and a direction along an arc centered on the center axis of the bobbin  40  will be called an “axis direction,” a “radial direction,” and a “peripheral direction” respectively. The “parallel direction” mentioned herein includes a substantially parallel direction, and the “perpendicular direction” mentioned herein includes a substantially perpendicular direction. 
     The bobbin  40  includes a primary bobbin  41  and a secondary bobbin  42  connectable to each other. Each of the primary bobbin  41  and the secondary bobbin  42  extends in a tubular shape in the axis direction. The secondary bobbin  42  is arranged external to the primary bobbin  41  in the radial direction. The primary bobbin  41  and the secondary bobbin  42  are made of resin, for example. 
     The primary coil L 1  is formed by winding a conductor in the peripheral direction on the outer peripheral surface of the primary bobbin  41 . This conductor will hereinafter be called a “primary conductor  81 .” After formation of the primary coil L 1  is finished, the secondary bobbin  42  is arranged to cover the outer peripheral surface of the primary coil L 1 . Then, a conductor different from the primary conductor  81  is wound on the outer peripheral surface of the secondary bobbin  42  to form the secondary coil L 2 . This different conductor will hereinafter be called a “secondary conductor  82 .” In this way, the primary coil L 1  and the secondary coil L 2  are arranged to be stacked on each other to achieve size reduction of the coil unit  103  in its entirety including the primary coil L 1  and the secondary coil L 2 . The primary coil L 1  and the secondary coil L 2  are not always required to be formed by winding to be arranged in positions stacked on each other but may alternatively be arranged in positions adjacent to each other as shown in  FIG. 1 . 
     As shown in  FIG. 2 , the iron core  60  has a configuration with a center iron core  601  and an outer iron core  602  combined together. Each of the center iron core  601  and the outer iron core  602  is formed of a stacked steel plate with a stack of silicon steel plates, for example. The center iron core  601  extends in the axis direction. The center iron core  601  is passed through space  410  inside the primary bobbin  41  in the radial direction. The outer iron core  602  is arranged external to the secondary coil L 2  in the radial direction. The outer iron core  602  connects the opposite ends of the center iron core  601  in the axis direction. In this way, the iron core  60  forms a closed magnetic circuit configuration in which the primary coil L 1  and the secondary coil L 2  are electromagnetically coupled to each other. 
     The primary conductor  81  forming the primary coil L 1  has one end  811  to which a conductor extending from the battery  102  is connected. This conductor extending from the battery  102  will hereinafter be called a “power supply line  150 .” The primary conductor  81  has the other end  812  connected to a switch  71  through a lead frame  75  of the igniter  104  described later. In this configuration, when the switch  71  is closed, a DC low voltage from the battery  102  is applied to the one end  811  of the primary coil L 1 . Then, a primary current I 1  starts to flow in the primary coil L 1  in such a manner as to increase gradually. 
     The one end  821  of the secondary conductor  82  forming the secondary coil L 2  is connected to the spark plug  113 . The secondary conductor  82  has a diameter less than that of the primary conductor  81 . The number of turns of the secondary conductor  82  of the secondary coil L 2  (10000 turns, for example) is about 100 times or more the number of turns (100 turns, for example) of the primary conductor  81  of the primary coil L 1 . With this configuration, during interruption of the primary current IL the coil unit  103  increases DC low-voltage power supplied from the battery  102  to as high as some thousands of volts. Namely, a high voltage is induced in the secondary coil L 2 . Then, the secondary coil L 2  supplies the induced high-voltage power to the spark plug  113 . By doing so, an electric spark is generated at the spark plug  113  to ignite fuel. 
     As shown in  FIG. 1 , in the first preferred embodiment, the secondary coil L 2  has the other end  822  to which a diode  114  is connected further in series with the secondary coil L 2  in such a manner that a direction toward the ground is a forward direction. The other end  822  mentioned herein is an end of the secondary coil L 2  on the opposite side of the one end  821  to which the spark plug  113  is connected. This prevents an induced current resulting from the voltage induced in the secondary coil L 2  by the gradually increasing primary current I 1  from flowing in the reverse direction toward the spark plug  113 . 
     The igniter  104  is a semiconductor device connected to the primary coil L 1  and used for controlling a current flowing in the primary coil L 1 . The igniter  104  is electrically connected to the ECU  105  and receives a signal from the ECU  105 . The signal received from the ECU  105  will hereinafter be called an “EST signal.” The igniter  104  may be integrated with an electronic circuit of the ECU  105 . A specific configuration of the igniter  104  and a method of connection between the igniter  104  and each part of the ignition device  1  will be described later. 
     The ECU  105  is an existing computer that controls the motions of a transmission, an air bag, etc. of the vehicle body  100  comprehensively. 
     &lt;1-2. Specific Configuration of Igniter and Method of Connection between Igniter and Each Part of Ignition Device&gt; 
     A specific configuration of the igniter  104  and a method of connection between the igniter  104  and each part of the ignition device  1  will be described next. 
       FIG. 3  is a plan view (top view) schematically showing the configuration of the igniter  104 . As shown in  FIG. 3 , the igniter  104  includes the switch  71 , a metal block  72 , a driving IC  73 , a wire  74  (a gold wire  74  of a diameter from 15 to 50 μm), the lead frame  75 , a plurality of different lead frames  76 , a casing  77 , a wire  78  (an aluminum wire  78  of a diameter from 125 to 500 μm), a plurality of different elements  21  (including a capacitor and a resistor), a plurality of different connection members  22  (including interconnect lines forming parts of the different lead frames  76 ), and a plurality of different wires  23  and  24  (including gold wires  23  of diameters from 15 to 50 μm and an aluminum wire  24  of a diameter from 125 to 500 μm further functioning as a resistor). As the switch  71 , the metal block  72 , the driving IC  73 , the wire  74 , a part of the lead frame  75 , the different lead frames  76 , the wire  78 , the different elements  21 , the different connection members  22 , and the different wires  23  and  24  are covered by molding resin forming the casing  77 , they are visually unrecognizable from outside. To facilitate understanding, however, these elements are indicated by solid lines and the casing  77  is indicated by a line with alternate long and two short dashes in  FIG. 3 . For the convenience of description, the igniter  104  will be described in the subsequent paragraphs in terms of the shape of each part and the positions of parts relative to each other on condition that the switch  71  is on the upper side relative to the metal block  72 , and a “front-back direction” and a “right-left direction” are defined as shown in  FIG. 3 . However, these definitions are not intended to limit the posture of the igniter  104  according to the present invention during manufacture and during use of the igniter  104 . 
     For example, an insulated-gate bipolar transistor (IGBT) is used as the switch  71 . The switch  71  is made of silicon. However, the switch  71  may be made of a different semiconductor material such as silicon carbide. The switch  71  is a pyrogenic power element and generates heat instantaneously to be placed in a high temperature when the ignition device  1  comes into operation. The switch  71  generates heat to be placed in a high temperature within one msec, for example. The switch  71  is arranged on a path of a current flowing in the primary coil L 1 . More specifically, the switch  71  is interposed between the primary coil L 1  and the ground. The switch  71  has a collector (C) connected to the other end  812  of the primary coil L 1  described above. The switch  71  has an emitter (E) connected to the ground. The switch  71  has a gate (G) connected to the driving IC  73 . By doing so, the switch  71  becomes functional to switch between passage and interruption of the primary current I 1  flowing from the battery  102  into the ground through the primary coil L 1 . A different type of transistor may be used for forming the switch  71 . A material different from silicon may be used for forming the switch  71 . In the first preferred embodiment, the switch  71  is required to be made of silicon at least in a part including an area to which an aluminum electrode  90  described later is fixed and its surrounding area. 
       FIG. 4  is a vertical sectional view of the igniter  104  taken at a position I-I in  FIG. 3  from the right direction. As shown in  FIG. 4 , the switch  71  is fixed directly to the metal block  72  at the lower surface of the switch  71  by soldering using solder  50  made of a tin alloy, for example. The volume and mass of the metal block  72  are significantly greater than the volume and mass of the switch  71 . For this reason, the metal block  72  has thermal capacity significantly greater than that of the switch  71 . Thus, heat generated instantaneously when the switch  71  comes into operation is transferred to the metal block  72  and absorbed in the metal block  72 . As a result, temperature increase at the switch  71  is suppressed. 
     The metal block  72  is made of copper, for example. Alternatively, the metal block  72  may be made of metal other than copper (copper alloy, for example). Each of the metals forming the metal block  72  and the solder  50  (copper and tin alloy, for example) has a thermal conductivity that is some hundreds of times or more the thermal conductivity of molding resin used for forming the casing  77  on the upper side of the switch  71 . For this reason, heat generated during the operation of the switch  71  is transferred not toward the upper surface of the switch  71  but toward the metal block  72  smoothly in a moment. As a result, temperature increase at the upper surface of the switch  71  is suppressed to a greater extent. 
     The aluminum electrode  90  is provided on the upper surface of the switch  71 . As shown in  FIG. 3 , one end of the wire  78  is fixed to the electrode  90  on the switch  71 . The wire  78  of the first preferred embodiment is an aluminum wire of a diameter from 125 to 500 μm. The other end of the wire  78  is fixed to the lead frame  76  described later. By doing so, the switch  71  is electrically connected through the wire  78  to the lead frame  76 . Aluminum forming the electrode  90  on the switch  71  and forming the wire  78  has a thermal expansion coefficient that is about ten times or more the thermal expansion coefficient of silicon, meaning that it is significantly greater than that of silicon. For this reason, if the upper surface of the switch  71  made of silicon is placed in a high temperature during the operation of the ignition device  1 , a difference in thermal expansion coefficient causes what is called “thermal stress of power cycle,” and this thermal stress is concentrated on a boundary and its vicinity of the upper surface of the switch  71  with the wire  78  or the electrode  90 . Putting the ignition device  1  into operation repeatedly causes a risk of the occurrence of a break or a crack at the boundary and its vicinity. In this regard, in the first preferred embodiment, the temperature increase is suppressed at the upper surface of the switch  71  as described above to prevent the occurrence of such a break or a crack. 
     As shown in  FIG. 4 , the metal block  72  has protrusions formed near the opposite ends of the metal block  72  in the front-back direction. These protrusions will hereinafter be called a “first protrusion  741 ” and a “second protrusion  742 .” Each of the protrusions  741  and  742  protrudes upward from the upper surface of the metal block  72 . Further, the lead frame  75  made of metal is arranged and a through hole  750  is formed in the lead frame  75 . The through hole  750  penetrates one end  91  of the lead frame  75  in an up-down direction. The first protrusion  741  is inserted into the through hole  750  formed in the lead frame  75  and is fixed by swaging. By doing so, the metal block  72  and the lead frame  75  become electrically connected to each other. Using the swaged configuration allows the metal block  72  to be fixed easily to the lead frame  75  without using a different member, thereby contributing to cost reduction. The other end  92  of the lead frame  75  is connected to the other end  812  of the primary conductor  81  forming the primary coil L 1 . Namely, the lead frame  75  connects the metal block  72  and the coil unit  103  electrically to each other. 
     As shown in  FIG. 4 , the one end  91  of the lead frame  75  has a level difference part  31 . The one end  91  is located closer to the upper side than the other section of the lead frame  75 . The metal block  72  is fixed to the lead frame  75  by swaging at the level difference part  31 . This configuration allows the one end  91  of the lead frame  75  to be arranged more closer to the upper side. Namely, this configuration makes it possible to ensure a greater thickness of the metal block  72 . As a result, the thermal capacity of the metal block  72  is increased further to allow a larger quantity of heat generated during the operation of the switch  71  to be absorbed in the metal block  72 . Thus, temperature increase at the switch  71  is suppressed to a greater extent. 
     In addition to the lead frame  75 , the plurality of different lead frames  76  each having a configuration comparable to that of the lead frame  75  are fixed in a corresponding part in the igniter  104 . These different lead frames  76  are electrically connected through the different connection members  22  or the plurality of different wires  23  and  24 , for example. The driving IC  73  and the electrode  90  on the switch  71  are electrically connected to each other through the wire  74 . Regarding the lead frame  76  to which the second protrusion  742  of the metal block  72  is fixed by swaging (see  FIG. 4 ) and the plurality of different lead frames  76 , these lead frames  76  are used for retaining each part during resin molding of the casing  77  as described later, and are thereafter cut while some parts of the lead frames  76  are reserved. 
     The driving IC  73  is a controller that controls opening and closing of the switch  71  on the basis of an EST signal received from the ECU  105 . The driving IC  73  includes a logical device connected to the switch  71 . Examples of the logical device include a logic circuit, a processor, a complex programmable logic device (CPLD), a field-programmable gate array (FPGA), and an application-specific integrated circuit (ASIC), etc. The logical device performs operation processing for putting the ignition device  1  into operation and igniting the spark plug  113 . 
     For putting the coil unit  103  into operation, the driving IC  73  first closes the switch  71 . At this time, a DC voltage (B+) from the battery  102  is applied to the primary coil L 1  to cause the primary current I 1  to flow in the primary conductor  81  forming the primary coil L 1 .  FIG. 5  is a perspective view schematically showing the direction of the primary current I 1  in the primary conductor  81  flowing at this time and the direction of magnetic flux generated at this time. As indicated by arrows in  FIG. 5 , in the first preferred embodiment, the primary current I 1  flows in the primary conductor  81  in the anticlockwise direction (left-handed screw direction) as viewed from a positive direction. By the flow of the primary current I 1  in the primary coil L 1 , electric charge is stored in the primary coil L 1  (charging control). Further, current passage magnetic flux (pa in the positive direction indicated by a hollow arrow in  FIG. 5  is generated, and a magnetic field responsive to the generated magnetic flux acts on the center iron core  601 . 
     Next, the driving IC  73  changes the switch  71  from the closed state to an open state (interruption control) at the time when a predetermined period of time T has passed from start of the charging control described above.  FIG. 6  is a perspective view schematically showing the direction of a secondary current I 2  in the secondary coil L 2  flowing at this time and the direction of magnetic flux generated at this time. As shown in  FIG. 6 , at this time, the primary current I 1  is interrupted and the current passage magnetic flux (pa in the positive direction generated in the charging control described above changes to be reduced. Then, mutual induction action is generated in the secondary conductor  82  forming the secondary coil L 2  and arranged external to the primary conductor  81  in the radial direction to cause the secondary current I 2  to flow in a direction indicated by an arrow in  FIG. 6 . Then, interruption magnetic flux φs is generated in a direction (a direction indicated by a hollow arrow in  FIG. 6  (positive direction)) in which change in the current passage magnetic flux φa is hindered to generate induced electromotive force Vs in the secondary coil L 2 . 
     As described above, the number of turns of the secondary conductor  82  of the secondary coil L 2  (10000 turns, for example) is about 100 times the number of turns (100 turns, for example) of the primary conductor  81  of the primary coil L 1 . With this configuration, a high voltage is induced in the secondary coil L 2  during the operation of the ignition device  1 . This allows generation of an electric spark at the spark plug  113  to ignite fuel. 
     Referring back to  FIG. 3 , the casing  77  is molding resin accommodating the switch  71 , the metal block  72 , the driving IC  73 , the wire  74 , a part of the lead frame  75 , parts of the plurality of different lead frames  76 , the wire  78 , the plurality of different elements  21 , the plurality of different connection members  22 , and the plurality of different wires  23  and  24 . These different elements  21  include various types of elements such as a capacitor and a resistor for operating the ignition device  1  normally. The switch  71 , the metal block  72 , the driving IC  73 , the lead frame  75 , the different lead frames  76 , and the different elements  21  are connected to each other directly and electrically. Alternatively, these elements may be connected to each other electrically and indirectly through the wire  74 , the wire  78 , the different connection members  22  (such as interconnect lines), or the different wires  23  and  24 . 
     The casing  77  is an insert-molded article obtained by pouring molding resin into a mold retaining the switch  71 , the metal block  72 , the driving IC  73 , the wire  74 , a part of the lead frame  75 , parts of the plurality of different lead frames  76 , the wire  78 , the plurality of different elements  21 , the plurality of different connection members  22 , and the plurality of different wires  23  and  24 . For forming the casing  77  by resin molding, while the other part of the lead frame  75  and the other parts of the different lead frames  76  are retained and suspended in positions, the parts electrically connected to each other in a manner described above are accommodated inside the mold and the molding resin is poured into the mold. After the molding resin is cured, the mold is removed form the casing  77 . Further, the switch  71 , the metal block  72 , the driving IC  73 , the wire  74 , the part of the lead frame  75 , the parts of the different lead frames  76 , and the wire  78  are covered by the single molding resin forming the casing  77  to be retained. The other end  92  of the lead frame  75  is exposed from the molding resin forming the casing  77 . 
     2. Modifications 
     While the exemplary preferred embodiment of the present invention has been described hereinabove, the present invention is not limited to the foregoing preferred embodiment. 
     In the preferred embodiment described above, the switch  71  is fixed to the metal block  72  by soldering at the lower surface of the switch  71 , and is electrically connected to the driving IC  73  at the upper surface of the switch  71 . However, a surface of the switch  71  to be fixed to the metal block  72  is not limited to the lower surface. For example, the switch  71  may be fixed to the metal block  72  at a side surface of the switch  71 . Also, a surface of the switch  71  to be electrically connected to the driving IC  73  is not limited to the upper surface. For example, the switch  71  may be electrically connected to the driving IC  73  at a different side surface of the switch  71 . Namely, the switch  71  is required to be fixed to the metal block  72  by soldering at a surface of the switch  71  on one side, and to be electrically connected to the driving IC  73  at a surface of the switch  71  on the other side. 
     The ignition device including the igniter of the present invention may be any device installable on various types of devices or industrial machines such as power generators in addition to vehicles such as automobiles, and available for use for igniting fuel by generating electric sparks at spark plugs of internal combustion engines. 
     The detailed shape or configuration of the ignition device including the igniter described above can be changed appropriately within a range without deviating from the purport of the present invention. Additionally, the foregoing elements in the embodiment or modifications described above may be combined together, as appropriate, without inconsistencies.