Patent Publication Number: US-7584733-B2

Title: Mounting structure of ignition plug tube

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2006-158086, filed in Japan on Jun. 7, 2006, the entirety of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a mounting structure of an ignition plug tube for encircling and protecting an ignition plug in an internal combustion engine. 
   2. Background of the Invention 
   A mounting structure of an ignition plug tube is disclosed in JP-A No. 2004-100651, for example. An ignition plug tube disclosed in this document is a cylindrical member. A lower end of the cylindrical member is inserted into a plughole formed in a cylinder head. A flange is formed in a position slightly lower than an open end face at an upper end thereof. The flange is fitted into a circular hole of a cylinder head cover for positioning. The leakage of oil is prevented by this arrangement. 
   As described above, when the flange is formed on the cylindrical member of the ignition plug tube, the cost of the ignition plug tube itself is greatly increased. When the ignition plug tube is made of a cylindrical member without the flange, the leakage of oil is prevented by press-fitting the sealing member into the cylinder head cover. However, a part for preventing the detachment of the sealing member itself is separately required and the number of parts increases. 
   SUMMARY OF THE INVENTION 
   The invention is made in view of such a problem and the object is to reduce the cost of an ignition plug tube made of a cylindrical member and to provide a simple mounting structure having only a small number of parts of the ignition plug tube. 
   To achieve the above object, the invention is directed to a mounting structure of an ignition plug tube mounted between an ignition plug plughole formed in a cylinder head of an internal combustion engine and a cylinder head cover, wherein the ignition plug tube is made of a cylindrical member, and a sealing member made of a soft member fitted to the cylinder head cover is interposed between the cylinder head cover and the ignition plug tube and the ignition plug tube is fixed and supported by the cylinder head cover. 
   In a further aspect of the invention, the sealing member is made of a hollow disc-like member having a hollow part into which the ignition plug tube is fitted in the center, a groove is formed in a circumferential direction on the periphery of the sealing member, the groove of the sealing member is fitted to an edge of an opening of a circular hole formed in the cylinder head cover, the sealing member is fitted to the cylinder head cover, and is supported by the cylinder head cover. 
   According to the mounting structure of the ignition plug tube according to the invention, since the ignition plug tube is made of a cylindrical member, the ignition plug tube itself can be produced at a low cost. 
   Since the sealing member that is interposed between the cylinder head cover and the ignition plug tube and is made of a soft member that fixes and supports the ignition plug tube, and prevents the leakage of oil, is fitted to the cylinder head cover, no special member for preventing the detachment of the sealing member is required and a simple mounting structure having only a small number of parts of the ignition plug tube is acquired. 
   According to the mounting structure of the ignition plug tube according to the invention, the groove is formed in the circumferential direction on the periphery of the sealing member made of the hollow disc-like member having the hollow part into which the ignition plug tube is inserted, the groove of the sealing member is fitted to the edge of the opening of the circular hole formed in the cylinder head cover, the sealing member is fitted to the cylinder head cover and is supported by the cylinder head cover. Therefore, a structure where the detachment of the sealing member is extremely simply prevented is acquired. 
   Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
       FIG. 1  is a schematic sectional view viewed from the left side and showing the entire internal combustion engine equivalent to one embodiment of the invention; 
       FIG. 2  is a top view showing the internal structure of a cylinder head; 
       FIG. 3  is a top view showing the cylinder head; 
       FIG. 4  is a sectional view viewed along a line IV-IV in  FIG. 2 ; and 
       FIG. 5  is a perspective view showing a sealing member. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will now be described in detail with reference to the accompanying drawings, wherein the same reference numerals will be used to identify the same or similar elements throughout the several views. 
   Referring to  FIGS. 1 to 4 , one embodiment of the invention will be described below. An internal combustion engine  1  for this embodiment is a water-cooled single-cylinder 4-cycle internal combustion engine for a motorcycle.  FIG. 1  is a schematic sectional view viewed from the left side showing the entire internal combustion engine  1  when the engine is mounted on a body. 
   A crankcase  2  is divided into right and left sides. A crank chamber  2   c  is formed on the front side. A transmission case  2   m  is formed on the rear side. A cylinder block  3  is fitted to the crank chamber  2   c  on the front side of the crankcase  2  in a state in which the cylinder block is slightly inclined forward. A cylinder head  4  overlaps the cylinder block  3 . A cylinder head cover  5  is integrated on the cylinder head  4 . 
   A connecting rod  8  couples a crankpin  6   p  of a crankshaft  6  and a piston pin  7   p  of a piston  7 . The crankshaft  6  is directed laterally in the crank chamber  2   c  and is rotatably journalled. The piston  7  reciprocates, sliding in a cylinder bore of the cylinder block  3 . A transmission mechanism  9  is arranged in the transmission case  2   m . A combustion chamber  10  is formed between a top of the piston  7  slid in the cylinder bore and a ceiling to which the top is opposite of the cylinder head  4 . 
   On the ceiling of the combustion chamber  10  of the cylinder head  4 , two right and left intake ports  11 ,  11 , that open on the right and on the left in a rear half, extend backward. Two right and left exhaust ports  12 ,  12 , that open on the right and on the left in a front half, extend forward. 
   An intake valve  21  that opens and closes an opening of the intake port  11  in the combustion chamber  10  is slidably guided by a valve guide  22 . A lifter guide  24  slidably guides a valve lifter  23  that covers an upper end of a valve stem of the intake valve  21 . 
   The intake valve  21  is pressed in a direction in which the valve is closed (upward) by a valve spring  27  interposed between an upper retainer  25  fitted to the upper end of the valve stem and a lower retainer  26  abutting on a top face of the cylinder head  4 . 
   An exhaust valve  31  that opens and closes an opening of the exhaust port  12  in the combustion chamber  10  is slidably guided by a valve guide  32  and is pressed in a direction in which the exhaust valve is closed (upward) by a valve spring  37  interposed between an upper retainer  35  fitted to an upper end of a valve stem and a lower retainer  36  abutting on the top face of the cylinder head  4 . 
   As shown in  FIG. 2 , which is a top view showing internal structure of the cylinder head  4  in a state in which the cylinder head cover  5  is removed, and  FIG. 3 , which is a top view showing the cylinder head, bearing walls  40 ,  40  are provided in parallel with the bearing walls mutually opposite outside right and left lifter guides  24 ,  24  along the right and left lifter guides  24 ,  24  on the top of the cylinder head  4 . 
   Semicircular camshaft supports  40   a ,  40   a  are formed on the respective top faces of the bearing walls  40 ,  40 , and a camshaft  45  is rotatably journalled to the camshaft laid laterally by respective semicircular camshaft supports of camshaft holders  41 ,  41  put on the respective top faces of the bearing walls  40 ,  40  and respectively fastened by bolts  42  with bearings  43 ,  43  that support the camshaft  45  between the camshaft holder and the camshaft. 
   As shown in  FIG. 2 , an exhaust cam lobe  46  protrudes between the right and left camshaft holders  41 ,  41  in the center of the camshaft  45 . Intake cam lobes  47 ,  47  protrude on both sides of the exhaust cam lobe  46 . 
   The right and left intake cam lobes  47 ,  47  are touched to the respective top faces of the valve lifters  23 ,  23  provided at the respective upper ends of the intake valves  21 ,  21  (see  FIG. 1 ). 
   The camshaft  45  protrudes from the left side of the left camshaft holder  41  and a driven sprocket  48  fitted to its left end is arranged in a chain chamber  4   a  formed along a left wall of the cylinder head  4 . 
   As shown in  FIG. 3 , bearing holes  40   b ,  40   b  are coaxially bored in the respective fronts of the right and left bearing walls  40 ,  40 . A rocker arm shaft  50  is installed by fitting both of its ends into the bearing holes  40   b ,  40   b . A rocker arm  51  is pierced by the rocker arm shaft  50 . The rocker arm is journalled to the rocker arm shaft so that the rocker arm can be rocked. 
   The rear of the rocker arm  51  is forked laterally. A roller  53  is rotatably journalled to a spindle  52  installed between right and left forked parts. The roller  53  is touched to the exhaust cam lobe  46  of the camshaft  45 . 
   A front half of the rocker arm  51  is greatly forked laterally and respective ends of both forked parts  51   a ,  51   a  are touched to respective upper end faces of respective valve stems of the right and left exhaust valves  31 ,  31 . Therefore, when the camshaft  45  is rotated, each rotation of the right and left intake cam lobes  47 ,  47  opens and closes the right and left intake valves  21 ,  21 . The exhaust cam lobe  46  in the center rocks the rocker arm  51  via the roller  53 . The rock of the rocker arm  51  opens and closes the exhaust valves  31 ,  31  by the front half forked parts  51   a ,  51   a.    
   As shown in  FIGS. 3 and 4 , an ignition plug plughole  60  is bored opposite to the combustion chamber  10  in the center between the right and left valve guides  32 ,  32  on the top face of the cylinder head  4  of the exhaust valves  31 ,  31  and at the back of the valve guides with the ignition plug plughole slightly inclined forward. 
   The inside diameter of the ignition plug plughole  60  is reduced to be an electrode hole  61 . The electrode hole  61  communicates with the combustion chamber  10 . A lower part of a cylindrical ignition plug tube  62  is inserted and fitted into the ignition plug plughole  60 . 
   An ignition plug  70  is inserted into the ignition plug tube  62 . An electrode  70   a  at the end of the ignition plug  70  is fitted into the electrode hole  61 . The end of the electrode  70   a  is located opposite to the combustion chamber  10  (see  FIG. 1 ). 
   The ignition plug tube  62 , the lower part of which is fitted into the ignition plug plughole  60  of the cylinder head  4 , extends upward with the ignition plug tube inclined forward, passes between the front half forked parts  51   a ,  51   a  of the rocker arm  51 , is fitted to an annular sealing member  65  fitted into a circular hole  5   b  formed in the bottom wall of a recessed portion  5   a  formed in the center of the front side of the cylinder head cover  5 , and an upper end of the ignition plug tube is exposed outside. 
   The sealing member  65  is made of a soft member, as shown in  FIG. 5 . The sealing member  65  is a hollow disc-like member having a hollow part into which the ignition plug tube  62  is inserted. A groove  65   a  is formed in a circumferential direction on the periphery throughout. 
   The inside diameter of the hollow part of the sealing member  65  is substantially equal to the outside diameter of the ignition plug tube  62  and the outside diameter of the bottom of the groove  65   a  on the periphery is substantially equal to the inside diameter of the circular hole  5   b  of the cylinder head cover  5 . 
   The groove  65   a  of the sealing member  65  is fitted to an edge of an opening of the circular hole  5   b  of the cylinder head cover  5  by deforming the sealing member  65 . The sealing member  65  is fitted into the circular hole  5   b  of the cylinder head cover  5 . 
   The lower part of the ignition plug tube  62  is fitted into the ignition plug plughole  60  of the cylinder head  4 . An upper part of the ignition plug tube  62  is fitted to the sealing member  65  attached to the cylinder head cover  5  and is fixed and supported, the opening at the upper end pierces the sealing member  65 , and is protruded outside. 
   Therefore, the sealing member  65  prevents oil in internal space in which a valve mechanism covered by the cylinder head cover  5  on the upside of the cylinder head  4  is housed from leaking outside. 
   Since the sealing member  65  is fitted into the circular hole  5   b  of the cylinder head cover  5 , no special member for preventing the detachment of the sealing member  65  is required and a simple structure having only a small number of parts is acquired. 
   The ignition plug tube  62  is made of a simple cylindrical member without irregularities such as a protrusion including a flange and a groove, the ignition plug tube  62  itself can be produced at a low cost. 
   The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.