Patent Publication Number: US-8528533-B2

Title: Plughole waterproofing device for engine

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an improvement of a plughole waterproofing device for an engine in which a coil case for covering an ignition coil is fitted onto the ignition coil that is accommodated, together with an ignition plug, in a plughole opened to an upper surface of an engine, and in which a longitudinal air path and a vent hole are provided in a case upper portion, protruding above the engine, of the coil case, the longitudinal air path extending upward from a lower end portion of the case upper portion communicating with the plughole, the vent hole communicating with an upper end portion of the longitudinal air path and being opened to ambient air. 
     2. Description of Related Art 
     Such a plughole waterproofing device for an engine is already known as disclosed, for example, in Japanese Patent Application Laid-open No. 2008-60188. 
     In the plughole waterproofing device for an engine disclosed in Japanese Patent Application Laid-open No. 2008-60188 described above, a vent hole is provided in a lower end portion of an upper portion of a case, and a water holding chamber extending upward from an inner end of the vent hole and communicating with an upper end portion of a longitudinal air path is provided in the upper portion of the case. This allows a plughole to breathe as the engine temperature increases or decreases. In addition, the device prevents the plughole from receiving water by holding, in the water holding chamber, water sucked by a pressure decrease in the plughole involved in the decrease of the engine temperature even when the vent hole sinks in a pool formed on an upper surface of the engine. In this regard, the pool may be formed due to: splashed water entering an engine room during driving on a flooded road or a road having a puddle; rainwater entering the engine room during driving on a rainy day; washing water entering the engine room at the time of washing a vehicle; or the like. 
     In the conventional plughole waterproofing device described above, however, the vent hole is provided in a small size at the lower portion of the water holding chamber. For this reason, when water in the pool drains away, throttle resistance of the vent hole hinders good drainage from the water holding chamber. Accordingly, if the engine repeatedly receives water before water drains away from the water holding chamber completely, the received water enters the vent hole, so that the amount of water in the water holding chamber is increased. If the plughole breathes in such a situation, the plughole might suck water from the water holding chamber. 
     SUMMARY OF THE INVENTION 
     The present invention has been made under these circumstances. An object of the present invention is to provide a simple-structured plughole waterproofing device for an engine, which is capable of effectively preventing water intrusion into a vent hole and thus preventing a plughole from receiving water even when the engine receives water repeatedly. 
     In order to achieve the object, according to a first feature of the present invention, there is provided a plughole waterproofing device for an engine in which a coil case for covering an ignition coil is fitted onto the ignition coil that is accommodated, together with an ignition plug, in a plughole opened to an upper surface of an engine, and in which a longitudinal air path and a vent hole are provided in a case upper portion, protruding above the engine, of the coil case, the longitudinal air path extending upward from a lower end portion of the case upper portion communicating with the plughole, the vent hole communicating with an upper end portion of the longitudinal air path and being opened to ambient air, wherein the vent hole is provided in an upper portion of the case upper portion, a cover wall is continuously provided on the case upper portion, the cover wall hanging toward the upper surface of the engine while surrounding the vent hole, and an air chamber is formed inside the cover wall, the vent hole being opened in an upper portion of the air chamber, an opening face being formed at an entire bottom of the air chamber in such a manner as to open toward the engine. 
     According to the first feature of the present invention, the vent hole is provided in the upper portion of the case upper portion of the coil case, and the cover wall hanging toward the upper surface of the engine and surrounding the vent hole is continuously provided on the case upper portion. Thus, even though the case upper portion receives water, the cover wall prevents the water from entering the vent hole. 
     In addition, the air chamber is formed inside the cover wall. In the air chamber, the vent hole is opened in the upper portion of the air chamber, and the entire bottom forms the opening face which is opened toward the engine. Thus, when a pool is formed on the upper surface of the engine and closes the opening face of the air chamber, air inside the air chamber stops water level from rising. This can prevent the water from entering the vent hole. 
     On top of that, the entire bottom of the air chamber forms the opening face which is opened toward the engine. When the water in the pool drains away, water in the air chamber simultaneously flows through the opening face without any resistance and drains together with the water in the pool. Thereby, the air chamber can be evacuated immediately. Accordingly, even if the plughole takes air with the decrease of the temperature of the engine E, it is possible to prevent the plughole from sucking water through the vent hole. 
     According to a second feature of the present invention, in addition to the first feature, the air chamber is formed in such a manner that a cross-sectional area of the air chamber is gradually increased toward the opening face. 
     According to the second feature of the present invention, the cross-sectional area of the air chamber is gradually increased toward the opening face. This allows water to flow from the air chamber more swiftly. Moreover, mold releasing from the air chamber can be facilitated at the time of forming the coil case. 
     According to a third feature of the present invention, in addition to the first feature, a swelled chamber to which an inner end of the vent hole is opened and a throttle hole through which the swelled chamber communicates with the upper end portion of the longitudinal air path are provided in the upper portion of the case upper portion, so that the vent hole and the longitudinal air path are communicated with each other. 
     According to the third feature of the present invention, even if water drops having momentum and entering the air chamber pass through the vent hole, a pressure decrease effect in the swelled chamber attenuates the momentum of the water drops, thereby reliably preventing the water drops from entering the longitudinal air path through the throttle hole. 
     According to a fourth feature of the present invention, in addition to the third feature, a mold-release hole for forming the swelled chamber is provided in the case upper portion and closed by a closure body. 
     According to the fourth feature of the present invention, when the coil case is formed, the vent hole, the swelled chamber, and the throttle hole can be formed simultaneously with the air chamber and the longitudinal air path. On top of that, the mold-release hole for forming the swelled chamber can be closed with the closure body. 
     According to a fifth feature of the present invention, in addition to the first feature, an annular sealing member placed into close contact with an upper opening portion in the plughole is fitted into the coil case, an outer annular path, an outer longitudinal groove, an inner annular path, and an inner longitudinal groove are formed between the sealing member and the coil case, so that the longitudinal air path and the plughole are communicated with each other, the outer annular path communicating with a lower end of the longitudinal air path, the outer longitudinal groove extending upward from the outer annular path, the inner annular path being connected to an upper end portion of the outer longitudinal groove and arranged inward of the outer annular path, the inner longitudinal groove communicating between the inner annular path and the plughole, at a position different from that of the outer longitudinal groove, on a circumference of the coil case. 
     According to the fifth feature of the present invention, the communicating path between the longitudinal air path and the plug hole forms a complicated maze having many bent portions. Even though moisture is contained in the outside air which is taken by the plughole at the time of breathing, the moisture can be separated from the air because the outside air collides with the many bent walls in the maze. This can prevent the moisture from entering the plughole. 
     In addition, the outer longitudinal groove which is continuous to the plughole side extends upward from the outer annular path communicating with the lower end portion of the longitudinal air path. In the unlikely event that water passing through the air chamber enters the longitudinal air path, the water is held by the outer annular path. Thereby, it is possible to prevent the water from moving to the plughole side. 
     The above description, other objects, characteristics and advantages of the present invention will be clear from detailed descriptions which will be provided for the preferred embodiment referring to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a DOHC type engine for an automobile including a plughole waterproofing device according to an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view taken along a line  2 - 2  in  FIG. 1 ; 
         FIG. 3  is an enlarged cross-sectional view taken along a line  3 - 3  in  FIG. 2 ; 
         FIG. 4  is an enlarged view of a part shown by an arrow  4  in  FIG. 3 ; 
         FIG. 5  is a cross-sectional view taken along a line  5 - 5  in  FIG. 3 ; 
         FIG. 6  is a cross-sectional view taken along a line  6 - 6  in  FIG. 5 ; 
         FIG. 7  is a cross-sectional view taken along a line  7 - 7  in  FIG. 6 ; 
         FIG. 8  is a cross-sectional view taken along a line  8 - 8  in  FIG. 6 ; 
         FIG. 9  is a cross-sectional view taken along a line  9 - 9  in  FIG. 5 ; and 
         FIG. 10  is a cross-sectional view taken along a line  10 - 10  in  FIG. 5 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the present invention will be described below based on a preferred embodiment of the present invention shown in the attached drawings. 
     Firstly, in  FIG. 1 , two protrusions  3 ,  3  and a link protrusion  4  which links one end portions of the respective protrusions  3 ,  3  are formed on an upper surface of a head cover  2  joined to a top surface of a cylinder head  1  in a DOHC type engine E for an automobile. The protrusions  3 ,  3  extend in parallel to each other and respectively correspond to two valve camshafts (unillustrated) in the cylinder head  1 . Multiple ignition coils  7  are attached to the head cover  2 , in a recessed groove  5  defined between the two protrusions  3 ,  3 . 
     As shown in  FIGS. 1 to 3 , an ignition plug  8  standing upright with an electrode thereof facing a combustion chamber in a cylinder is screwed in the cylinder head  1 . The ignition coil  7  is mechanically and electrically connected to an upper end portion of the ignition plug  8 . The ignition coil  7  includes a columnar portion  7   a  connected to the ignition plug  8  and an expanded head portion  7   b  integrally continuous with an upper end of the columnar portion  7   a . A connector  7   c  is integrally provided to the expanded head portion  7   b  so as to protrude from a side surface of the expanded head portion  7   b . A coil case  10  made of a synthetic resin is fitted onto the ignition coil  7 , except for a portion around the connector  7   c . The coil case  10  airtightly and watertightly covers outer peripheral surfaces of the columnar portion  7   a  and the expanded head portion  7   b . A bracket  11  protruding from a side different from the connector  7   c  side is integrally formed on an upper end portion of the coil case  10 . 
     The ignition plug  8  and the columnar portion  7   a  of the ignition coil  7  are accommodated in a corresponding one of a series of cylindrical plugholes  12  which are provided in the cylinder head  1  and the head cover  2  in such a manner as to be opened toward a bottom surface of the recessed groove  5 . The connector  7   c  and the bracket  11  are arranged in the recessed groove  5 . The bracket  11  is fixedly attached to an attachment boss  13  with a bolt  14 , the boss  13  being provided to protrude from the bottom surface of the recessed groove  5 . 
     A plughole waterproofing device of the present invention is configured to allow the plughole  12  to breathe and to prevent intrusion into the plughole  12  of water splashed from a road surface, rainwater, car-washing water or the like entering into an engine room. A description thereof is given below. 
     In  FIGS. 2 to 4 , the coil case  10  made of a synthetic resin is integrally formed with a case lower portion  10   a  covering the columnar portion  7   a  of the ignition coil  7  and a case upper portion  10   b  covering the expanded head portion  7   b . An annular sealing member  15  made of an elastic member such as rubber is fitted to a portion between the case lower portion  10   a  and the case upper portion  10   b . As clearly shown in  FIG. 4 , the sealing member  15  includes an annular first lip portion  15   a  facing upward, an annular second lip portion  15   b  protruding from a base of the first lip portion  15   a  outward around the outer periphery thereof, an annular third lip portion  15   c  protruding downward from a lower portion of the second lip portion  15   b , and an annular fourth lip portion  15   d  protruding downward from a lower portion of the first lip portion  15   a  and arranged inward of the third lip portion  15   c.    
     A large annular groove  17  opened downward and surrounding the case lower portion  10   a  is formed in a lower end surface of the case upper portion  10   b . An upper portion of the large annular groove  17  is divided into a pair of inner and outer small annular grooves  17   a ,  17   b  by an annular separation wall  18  protruding from a ceiling surface of the large annular groove  17 . 
     Accordingly, the sealing member  15  provided to the coil case  10  is designed so that the first lip portion  15   a  is placed into close contact with inner and outer peripheral surfaces of the inner small annular groove  17   a ; the second lip portion  15   b  is placed into close contact with an inner peripheral surface of the large annular groove  17 ; and the fourth lip portion  15   d  is placed into close contact with an outer peripheral surface of the case lower portion  10   a  and an inner peripheral surface of the plughole  12 . In addition, an annular raised wall  19  surrounding an upper opening of the plughole  12  is formed on the bottom surface of the recessed groove  5  of the head cover  2 . The third lip portion  15   c  is designed to come into close contact with an outer peripheral surface of the raised wall  19 . 
     As shown in  FIGS. 5 to 10 , the case upper portion  10   b  is provided with a longitudinal air path  21  extending upward from a portion of the outer small annular groove  17   b . A vent hole  27  communicating with the longitudinal air path  21  is provided in an upper portion of the case upper portion  10   b . A cover wall  22  hanging toward an upper surface of the engine E and surrounding the vent hole  27  is continuously and integrally provided to the case upper portion  10   b . The cover wall  22  defines an air chamber  20  inside thereof. The vent hole  27  is opened in a ceiling surface of the air chamber  20 , and the entire bottom of the air chamber  20  faces the engine E and is opened to ambient air, so that an opening face  20   a  is formed. The cover wall  22  is formed on a side portion which is an opposite side of the case upper portion  10   b  from the bracket  11 . 
     The air chamber  20  and the longitudinal air path  21  adjacent thereto inside are formed by mold releasing from a lower surface side, of the coil case  10 , facing the bottom surface side of the recessed groove  5 , at the time of forming the coil case  10 . In order to facilitate the mold releasing, a draft angle (see  FIG. 6 ) θ is provided to an inner side surface of the air chamber  20 . This means that the air chamber  20  has its cross-sectional area gradually increased toward the opening face  20   a  formed in the lower portion of the air chamber  20 . 
     The air chamber  20  has a larger volume than an amount of air taken one time by the plughole  12  as the temperature of the engine E ordinarily changes. 
     The air chamber  20  and the longitudinal air path  21  have a ceiling wall  23  integral with the case upper portion  10   b  which closes upper surfaces of the air chamber  20  and the longitudinal air path  21 . The ceiling wall  23  is provided with the vent hole  27 , a swelled chamber  26  to which an inner end of the vent hole  27  is opened, and a throttle hole  28  which connects the swelled chamber  26  and the longitudinal air path  21 . The vent hole  27  and the longitudinal air path  21  are communicated with each other via the swelled chamber  26  and the throttle hole  28 . 
     A mold-release hole  29  for forming the swelled chamber  26  is opened to an outer side surface of the ceiling wall  23 . A closure body  30  for closing the mold-release hole  29  is fixedly attached to the mold-release hole  29  by press fitting, adhering, depositing or the like. 
     The vent hole  27  and the throttle hole  28  are formed by mold releasing together with the air chamber  20 , the longitudinal air path  21 , and the swelled chamber  26 . In the mold releasing, multiple reinforcing ribs  31  linking inner walls of the air chamber  20  which face each other are formed on the ceiling surface of the air chamber  20 . 
     Meanwhile, a lower end portion of the longitudinal air path  21  communicates with the plughole  12  via a communicating path  25 . The communicating path  25  is formed of an outer annular path  35 , an outer longitudinal groove  36 , an inner annular path  37 , and an inner longitudinal groove  38 . The outer annular path  35  is defined by the outer small annular groove  17   b  and the sealing member  15 , the outer small annular groove  17   b  being arranged to communicate with the lower end of the longitudinal air path  21 . The outer longitudinal groove  36  is formed in an inner peripheral surface of the annular separation wall  18  with which the first lip portion  15   a  comes in close contact, the outer longitudinal groove  36  communicating with the outer annular path  35 . The inner annular path  37  is defined by the inner small annular groove  17   a  and the first lip portion  15   a , and communicates with the outer longitudinal groove  36 . The inner longitudinal groove  38  is formed in the outer peripheral surface of the case lower portion  10   a , with which the fourth lip portion  15   d  comes in close contact so that the inner annular path  37  communicates with the plughole  12 . The outer longitudinal groove  36  and the inner longitudinal groove  38  are arranged at different positions (see  FIG. 5 ) from each other in the peripheral direction of the coil case  10 . As described above, the communicating path  25  has a maze-shaped structure. In addition, the outer annular path  35  is set to have the largest volume in the communicating path  25 . 
     Next, a description is given of operations of this embodiment. 
     When the engine temperature is increased or decreased as the engine E is operated and stopped repeatedly, the plughole  12  breathes accordingly. The plughole  12  communicates with the vent hole  27  opened to the air chamber  20  via the swelled chamber  26 , the throttle hole  28 , the longitudinal air path  21 , and the communicating path  25  (the outer annular path  35 , the outer longitudinal groove  36 , the inner annular path  37 , and the inner longitudinal groove  38 ), and thus can smoothly take in and out air in the air chamber  20 , that is, the atmospheric air, through the vent hole  27 . 
     Meanwhile, the vent hole  27  is provided in the upper portion of the case upper portion  10   b , and the cover wall  22  hanging toward the upper surface of the engine E and surrounding the vent hole  27  is continuously formed on the case upper portion  10   b . For this reason, the cover wall  22  can prevent water from entering the vent hole  27  when the case upper portion  10   b  receives the water such as splashed water entering the engine room during driving on a flooded road or a road having a puddle, rainwater entering the engine room during driving on a rainy day, washing water entering the engine room at the time of washing a car, or the like. 
     In addition, the air chamber  20  is formed inside the cover wall  22 . In the air chamber  20 , the vent hole  27  is opened in the upper portion of the air chamber  20  and the bottom of the air chamber  20  forms the opening face  20   a  which is opened toward the engine E. Accordingly, even when water entering the engine room forms a pool in the recessed groove  5  in the upper surface of the engine E, and the opening of the air chamber  20  is closed by the pool, air in the air chamber  20  prevents the water level from rising, and thus prevents the water from entering the vent hole  27 . 
     On top of that, the entire bottom of the air chamber  20  is formed into the opening face  20   a  which is opened toward the engine E. When the water in the pool drains, water in the air chamber  20  simultaneously flows away through the opening face  20   a  without any resistance and drains together with the water in the pool. Thereby, the air chamber  20  can be evacuated immediately. This means that even when the engine E receives water repeatedly, water entering the air chamber  20  does not stay therein. Accordingly, even if the plughole  12  takes air with the decrease of the temperature of the engine E, it is possible to prevent the plughole  12  from taking water through the vent hole  27 . 
     In addition, since the air chamber  20  is formed in such a manner that the cross-sectional area thereof is gradually increased toward the opening face  20   a , the air chamber  20  has the largest cross-sectional area in the opening portion thereof. This allows water to flow from the air chamber  20  more swiftly. Moreover, mold releasing from the air chamber  20  can be facilitated at the time of forming the coil case  10 . 
     Further, the vent hole  27  communicates with the longitudinal air path  21  via the throttle hole  28  and the swelled chamber  26  which are formed in the ceiling wall  23  of the longitudinal air path  21  and the air chamber  20 . In the unlikely event that water drops having momentum and entering the air chamber  20  pass through the vent hole  27 , a pressure decrease effect in the swelled chamber  26  attenuates the momentum of the water drops, thereby reliably preventing the water drops from entering the longitudinal air path  21  through the throttle hole  28 . 
     Further, when the coil case  10  is formed, the vent hole  27 , the swelled chamber  26 , and the throttle hole  28  can be formed simultaneously with the air chamber  20  and the longitudinal air path  21 . This facilitates the forming of the coil case  10 . On top of that, the mold-release hole  29  for forming the swelled chamber  26  can be closed with the closure body  30 . 
     Moreover, the annular sealing member  15  for closing the upper opening portion of the plughole  12  is provided between the case lower portion  10   a  and the case upper portion  10   b  of the coil case  10 . Thus, the sealing member  15  prevents water received by the engine E from directly entering the plughole  12 . 
     Furthermore, by utilizing the sealing member  15 , the communicating path  25  communicating between the longitudinal air path  21  and the plughole  12  is formed between the sealing member  15  and the coil case  10 . The communicating path  25  forms a complicated maze which has many bent portions and is formed by the outer annular path  35 , the outer longitudinal groove  36 , the inner annular path  37 , and the inner longitudinal grove  38 . For this reason, even though moisture is contained in the atmospheric air which is taken by the plughole  12  at the time of breathing, the moisture can be separated from the air because the moisture collides with the many bent walls in the maze. This can prevent the moisture from entering the plughole  12 . 
     Besides, the outer longitudinal groove  36  which is continuous to the plughole  12  side extends upward from the outer annular path  35  communicating with the lower end portion of the longitudinal air path  21 . In the unlikely event that water passing through the air chamber  20  enters the longitudinal air path  21 , the water is held by the outer annular path  35 . Thereby, it is possible to prevent the water from moving to the outer longitudinal groove  36  side, that is, to the plughole  12  side. In this case, water remaining in the outer annular path  35  naturally evaporates as the plughole  12  breathes. 
     The present invention is not limited to the above-mentioned embodiment and may be modified in a variety of ways as long as the modifications do not depart from its gist.