Patent Publication Number: US-6338324-B1

Title: Lubricating structure for a four-stroke engine

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a lubricating structure for a four-cycle engine with an enhanced lubrication feature for a cam of a camshaft, a tappet, which is pressed by this cam, and a tappet holder by which the tappet is held. 
     II. Description of the Related Art 
     A direct cast DOHC type four-cycle engine is structured, for example, so that a cam formed on a camshaft directly presses the tappet of an intake-exhaust valve. A plurality of cam journals are formed along with a cam on a camshaft and these cam journals are supported by cam bearings provided on the cylinder head. Generally, a pair of cams is formed adjacent to a cam journal at both ends. 
     The camshaft is a hollow shaft and its interior is used as an oil supply path. A journal path that branches off at a right angle away from this oil supply path opens on the peripheral surface of the cam journal, and oil pumped out through the oil supply path is supplied between the cam journal and the cam bearing to lubricate them. At the same time, excess oil that has overflowed from a gap between the cam journal and the cam bearing causes lubrication between the cam and the tappet and between the tappet and the tappet holder. 
     However in, for example, a vertical four-cycle engine that can be mounted on a outboard motor and whose crankshaft and camshaft are disposed vertically, a cam and a tappet disposed at a higher position than the uppermost cam journal tend to be hardly lubricated, and lubrication conditions for the uppermost cam, the tappet, and the periphery of the tappet holder gets worse, resulting in seizure or uneven wear. 
     In this case, there may be a possibility of providing an exclusive oil path communicating with a periphery of the uppermost cam, the tappet and the tappet holder to lubricate them intensively. However, the structure of the engine becomes more complex by providing the oil path and oil is discharged continuously from the oil path. Therefore, the oil pressure of the entire engine decreases easily and there is concern that problems will occur in other lubricated portions within the engine. Therefore, this alternative design is not desirable. 
     SUMMARY OF THE INVENTION 
     The advantages and purposes of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Moreover, the advantages and purposes of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
     The present invention was made in order to solve the above described exemplary problems. Hence, an exemplary objective is to provide a lubricating structure for a four-cycle engine that is simple, but enables oil to be supplied to cams that are in difficult locations to supply, and in the vicinity of the tappets and the tappet holders, without decreasing oil pressure and improving lubrication conditions to prevent seizure and uneven wear from occurring. 
     In order to achieve these exemplary objectives, the lubricating structure for a four-cycle engine related to the present invention comprises a camshaft having an oil supply path at the axial center thereof and formed with a cam adjacent to a cam journal for pressing a tappet, a journal path branched away from the oil supply path which opens into an opening on the outer peripheral surface of the cam journal so as to supply oil thereto and a cam bearing that supports this cam journal, and wherein an intermittent oil supply means which intermittently discharges some of the oil supplied to the cam bearing and the cam journal from the oil supply path intermittently through the journal path to the cam and the side of the tappet in line with the rotation of the camshaft. 
     Also, in the present invention relating to a lubricating structure for a four-cycle engine the intermittent oil supply means is preferably structured so that an oil groove is formed on the bearing surface of the cam bearing in alignment with the axial direction of the camshaft, and at least one end of this oil groove opens on an end face of the cam side of the cam bearing. 
     Furthermore, in the present invention relating to a lubricating structure for a four-cycle engine, the intermittent oil supply means is further structured so that an oil hole is formed for communicating between the bearing surface of the cam bearing and the end face of the cam side, and the axial direction of the opening of the oil hole on the bearing surface side coincides with the axial direction of the journal path that opens on the outer peripheral surface of the cam journal, and the axial direction of the oil hole is oriented to the cam side. 
     Moreover, in the present invention relating to a lubricating structure for a four-cycle engine, the intermittent oil supply means is still further structured so that a cylindrical tappet pressed by the cam is disposed adjacent to the bearing whereby the bearing surface of the cam bearing is formed with a wide portion and a narrow portion, the position in the axial direction in which the opening on the outer peripheral surface of the cam journal of the journal path is located where the rotational pathway of the journal path is limited to within the widest portion of the bearing surface and, the rotational pathway of the journal path is located outside the range of the narrowest portion of the bearing surface. 
     Furthermore, in the present invention relating to a lubricating structure for a four-cycle engine, the intermittent oil supply means is structured so that a cylindrical tappet pressed by the cam is located adjacent to the cam bearing and the bearing surface of the cam bearing is formed with a wide portion and a narrow portion, then an oil groove that extends in the axial direction of the camshaft is formed on the outer peripheral surface of the cam journal, and the positioning and length of the oil groove in the axial direction is disposed such that the rotational pathway of the entire oil groove is limited to within the range of the widest portion of the bearing surface and, moreover, one end of the oil groove is disposed at a location outside the narrowest portion of the bearing surface on the side of the tappet, and the journal path opens inside this oil groove. 
     It is to be understood that both the foregoing general description and the following detailed description are only exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
     FIG. 1 shows a left side view of an example of an outboard motor wherein the present invention is incorporated; 
     FIG. 2 is a bottom view of an engine viewed from the perspective of arrows II—II in FIG. 1; 
     FIG. 3 is a rear view of the cylinder head viewed from the perspective of arrows III—III in FIG. 2; 
     FIG. 4 is a vertical cross-sectional view of the cylinder head along lines IV—IV in FIG. 3; 
     FIG. 5 is a horizontal cross-sectional view of the cylinder head along lines V—V in FIG. 4; 
     FIG.  6 (A) is an expanded cross-sectional view of the section marked Z in FIG. 4 of a first embodiment of the intermittent oil supply means; 
     FIG.  6 (B) is a cross-sectional view from the perspective of the arrows VIB—VIB in FIG.  6 (A); 
     FIG.  7 (A) is an expanded cross-sectional view of the section marked Z in FIG. 4 of a second embodiment of the intermittent oil supply means; 
     FIG.  7 (B) is a view from the perspective of lines VII B —VII B  in FIG.  7 A: 
     FIG.  8 (A) is an expanded cross-sectional view of the section marked Z in FIG. 4 of a third embodiment of the intermittent oil supply means; 
     FIG.  8 (B) is a cross-sectional view from the perspective of the arrow VIII B  in FIG. 8A; 
     FIG.  9 (A) is an expanded cross-sectional view of the section marked Z in FIG. 4 of a fourth embodiment of the intermittent oil supply means; and 
     FIG.  9 (B) is a cross-sectional view from the perspective of arrow IXB in FIG.  9 A. 
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present preferred embodiments of the invention illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like parts. 
     Hereinafter, a preferred embodiment of the present invention will be described while referring to the drawings. FIG. 1 is a left side view of one example of an outboard motor wherein the invention is applied. The left side viewed from the front represents the front side (the hull side) while the right side represents the back side. 
     Disposed in the uppermost part of this outboard motor  1  is an engine  2  which is, for example, a direct cast DOHC series four cylinder, four-cycle engine and is fixed vertically on a substantially flat engine holder  7  so that crankshaft  3  and two camshafts  4 ,  5  face in the perpendicular direction. Fixed to the bottom surface of the engine holder  7  is an oil pan  8 , and fixed under the oil pan  8  there are a drive housing  9  and a gear housing  10 , in descending order. Further, provided in front of the engine holder  7  and the drive housing  9  is a clamp bracket  11  for attachment to the hull of a boat. 
     As depicted in the lower portion of FIG. 2, the engine  2  comprises, in front to back order, a crankcase  13 , a cylinder block  14 , a cylinder head  15  and a head cover  16 . The crankshaft  3  is supported between the crankcase  13  and the cylinder block  14 , while two camshafts  4 ,  5  are supported within the cylinder head  15 . The camshaft  4  on the right side as viewed from the front is the intake side camshaft, while the camshaft  5  at the left side viewed from the front is the exhaust camshaft. 
     Disposed horizontally and extending in a front-rear direction within the cylinder block  14  are four cylinder bores  18  formed in a single top to bottom row; a piston  19  is inserted within each cylinder bare  18  so as to slide freely and they are connected by a con rod  20  to the crank pin  3   a  for crankshaft  3 . Reciprocating movement of the piston  19 , each cylinder bore  18  rotates the crankshaft  3 . The entire engine  2 , the engine holder  7  and the oil pan  8  are covered over by an engine cover  21  made of a synthetic resin to protect them from water. 
     A drive shaft  23  is supported by being passed vertically through the inside of the engine holder  7 , the oil pan  8 , the drive housing  9  and the gear housing  10 . This drive shaft  23  is offset slightly toward the rear way from the axis line of the crankshaft  3 , and provided on the upper end of the crankshaft  3  is a driven gear  24  that turns integrally therewith. Provided on the lower end of the crankshaft  3  is a drive gear  25  that turns integrally therewith and that engages the driven gear  24 , and so rotation of the crankshaft  3  is transmitted to the drive shaft  23 . 
     Provided horizontally and supported in a front-rear direction within the gear housing  10  is a propeller shaft  27 , and provided at the rear end of the propeller shaft  27  is a screw propeller  28  that rotates integrally therewith. Provided at a point where the propeller shaft  27  and the drive shaft  23  cross each other are a bevel gear mechanism  29  and a clutch shifter  30 . Rotation of the drive shaft  23  is transmitted to the propeller shaft  27  via the bevel gear mechanism  29  and the screw propeller  28  is driven rotationally to generate propulsion. Since the fixed rotation direction of the drive shaft  23  switches between forward and reverse by the clutch shifter  30  and the rotation is transmitted to the propeller shaft  27 , the direction of the outboard motor  1  (the hull of a boat) can be selected between forward and reverse. 
     Provided on the bottom of the driven gear  24  provided on the upper end of the drive shaft  23  is a drive sprocket  31  that rotates integrally therewith, and a timing chain  34  is wound between the drive sprocket  31  and the driven sprockets  32 ,  33  provided integrally at the lower ends of the respective camshafts  4 ,  5  that rotate integrally therewith. Accordingly, the rotation of the drive shaft  23 , namely, the rotation of the crankshaft  3 , is transmitted to the camshafts  4 ,  5 . 
     Provided on the bottom of the engine  2  (cylinder head  15 ) is an oil pump  36 , and provided on the main shaft of the oil pump  36  is a pump driven gear  37  which is engaged with, for example, a pump drive gear  38  provided on the bottom of the driven sprocket  33  on the camshaft  5  on the exhaust side. Accordingly, when the engine  2  operates, the oil pump  36  is driven together therewith and oil stored within the oil pan  8  is pumped up and then pressure fed inside the engine  2  for lubrication. After the inside of the engine  2  has been lubricated, the oil drops through a plurality of oil return holes opened on the bottom of the engine  2  and is returned to the oil pan  8 . 
     FIG. 3 is a rear view of the cylinder head  15  viewed from the direction of arrows III —III in FIG.  2 . FIG. 4 is a vertical cross section of the cylinder head  15  along lines IV—IV in FIG.  3 . FIG. 5 is a horizontal cross section view along lines V—V in FIG.  4 . 
     As shown in FIGS. 4 and 5, in the front surface of the cylinder head  15 , four combustion chambers  41  that integrate with the cylinder bores  18  of cylinder block  14  are formed in concave configuration, and intake ports  42  and exhaust ports  43  that lead to these combustion chambers  41  are formed. For example, intake ports  42  are opened on the right side surface of the cylinder head  15 , and the exhaust ports  43  are opened on the left side surface thereof. 
     The eight respective intake valves  44  and exhaust valves  45  that open and close the intake ports  42  and exhaust ports  43  are housed inside the cylinder head  15 . The intake valves  44  and the exhaust valves  45  are always powered, such that they are in the closed direction, by valve springs  46  and  47 , respectively, and each pulse spring  46  . . . and  47  . . . is sheathed in a cylindrical tappet  48  and  49 , respectively, (refer to FIG.  5 ). Each tappet  48  and  49  is inserted in an airtight manner within a tappet holder  50  and  51  shaped like a cylindrical hole formed on each cylinder head  15  so as to slide freely therein. 
     As shown in FIG. 3, between the two tappet holders  50 ,  51  formed on the intake side and the exhaust side of each cylinder, a total of four cam bearings  53 ,  54  respectively, are provided. Also, cam bearings  55 ,  56  are provided in the lowermost portion of the cylinder head  15  at, respectively, the intake side and the exhaust side. 
     As shown in FIGS. 5-9, each cam bearing  53  ( 55 ),  54  ( 56 ) is structured so that each separate bearing housing  59 ,  60  is fastened by two bolts  61  to the bearing base  57 ,  58  that are each integrally formed in the cylinder head  15  side. The lowermost cam bearings  55 ,  56  are formed larger in width in the axial direction than other cam bearings  53 ,  54 , and a head oil path  62 ,  63  (refer to FIG. 4) that communicates with the outlet of the oil pump  36  is formed within the bearing base. 
     In the camshafts  4 ,  5  are formed five cam journals  65 ,  66 , respectively, in the axial direction, and these cam journals  65 ,  66  are supported so as to freely rotate on the cam bearings  53 ,  55  and the cam bearings  54 ,  56 , respectively. Up to the fourth cam journals  65 ,  66  are formed pairs comprising, respectively, intake cams  68  and exhaust cams  69  at both sides in the axial direction. These intake cams  68  and exhaust cams  69  integrate with the position of the respective tappets  48 ,  49 , the tappets  48 ,  49  are pressed by the rotation of the camshafts  4 ,  5 , and the intake and exhaust valves  44 ,  45  are opened and closed at a predetermined timing against the closing force of the valve springs  46 ,  47 . 
     The camshafts  4 ,  5  are hollow shafts and oil supply paths  71 ,  72  are formed therein. Journal paths  73 ,  74  which branch off at a right angle from the oil supply paths  71 ,  72  at the location of each cam journal  65 ,  66 , opens onto the outer peripheral surface of the cam journal  65 ,  66 , respectively. 
     When the engine  2  starts and the oil pump  36  is driven, some of the oil that is pumped out by the oil pump  36  is supplied to the cam bearings  55 ,  56  at the lowermost point through the head oil paths  62 ,  63 . Furthermore, the oil is supplied to the upper cam bearings  53 ,  54  and the cam journals  65 ,  66  via the journal paths  73 ,  74  at the lowermost point, as well as the oil supply paths  71 ,  72  within the camshafts  4 ,  5  and other journal paths  73 ,  74 . As a result, every cam journal  65 ,  66 , cam bearing  53 ,  54 , and the space between  55  and  56  is lubricated. 
     Excess oil flows down from between each cam journal  65 ,  66  and cam bearing  53 ,  54 , and gaps between every intake and exhaust cam  68 ,  69  and tappet  48 ,  49  located below each cam bearing  53 ,  54  as well as the area between the tappets  48 ,  49  and the tappet holders  50 ,  51  are lubricated. 
     However, as it is not desirable that excess oil from the uppermost cam bearings  53 ,  54  be supplied to the intake and exhaust cams  68 ,  69 , as well as the tappets  48 ,  49  and the tappet holders  50 ,  51 , there is concern that poor lubrication may occur in these locations. Accordingly, an intermittent oil supply means is provided to the uppermost cam bearings  53 ,  54  and the cam journals  65 ,  66  so that some of the oil supplied thereto is discharged intermittently toward the uppermost intake and exhaust cams  68 ,  69 , and the tappets  48 ,  49 , in line with the rotation of the camshafts  4 ,  5 . Hereinafter, four embodiments of the intermittent oil supply means having a camshaft  4  at the intake side and a cam bearing periphery  53  will be described. 
     FIGS. 6 (A) and (B) show the first embodiment of an intermittent oil supply means {circle around (1)}. As shown herein, for example, in the cam bearing  53  that supports the uppermost cam journal  65  of the intake side camshaft  4 , an oil groove  77  is formed that extends in the axial direction of the camshaft  4  in the bearing surface  59   a  of this bearing housing  59  (shown in FIG. 6 (B)) . The upper end of this oil groove  77  opens at the end face  59   b  (shown in FIG. 6 (A)) of the upper side of the bearing housing  59 , while the lower end of the oil groove  77  extends up to the position where the journal path  73  opens on the outer peripheral surface of the cam journal  65 . 
     By providing the oil groove  77  as an intermittent oil supply means {circumflex over (1)}, whenever the camshaft  4  turns, the journal path  73  that opens on the outer peripheral surface of the cam journal  65  coincides with the oil groove  77 . Some of the oil supplied via the journal path  73  is spouted out intermittently in the upward direction indicated by arrow O 1  and splashes over the intake cam  68 , the tappet  48 , and the tappet holder  50  that are located directly above the cam bearing  53 , and lubricates them. Accordingly, lubrication conditions for the uppermost intake cam  68 , tappet  48 , and tappet holder  50  located at what are conventionally hard areas to supply oil are improved. As a result, seizure or uneven wear are prevented from occurring. 
     Also, as described above, by only forming the oil groove  77 , the intermittent oil supply means {circle around (1)}is structured extremely simply and easily. Moreover, if the oil groove  77  is formed by casting at the same time that the bearing housing  59  is die-casted or forged, the oil groove  77  can be formed more easily and inexpensively without machining. 
     FIGS. 7 (A) and (B) show the second embodiment of the intermittent oil supply means {circle around (2)}. Herein, in the cam bearing  53  that supports the uppermost cam journal  65  of the camshaft  4 , an oil hole  78  having an inclined hole configuration and that communicates between the bearing surface  59   a  (shown in FIG. 6 (B)) of this axle housing  59  and the upper side of end face  59   b  (shown in FIG. 6 (A)) on this bearing housing  59 . The position of the opening in the axial direction of the oil hole  78  on the bearing surface  59   a  side coincides with the axial direction of the journal path  73  that opens on the outer peripheral surface of the cam journal  65 , and the axial direction of oil hole  78  is oriented to the uppermost intake cam  68 . 
     By providing the oil hole  78  as an intermittent oil supply means {circle around (2)}, whenever the camshaft  4  turns, the journal path  73  which opens on the outer peripheral surface of the cam journal  65  coincides with the opening of the oil hole  78  at the bearing surface  59   a  side. Some oil that is supplied from the journal path  73  spouts out intermittently toward the uppermost intake cam  68  as indicated with an arrow  02  and lubricates the uppermost intake cam  68 , the tappet  48 , and the tappet holder  50 . In this case, too, because the oil hole  78  can be formed extremely easily, the intermittent oil supply means {circle around (2)} can be structured in a simple manner. 
     FIG. 8 (A) and FIG. 8 (B) show the third embodiment of the intermittent oil supply means {circle around (3)}. As shown herein, the tappets  48  (tappet holders  50 ) are disposed adjacent to both sides of the cam bearing  53  (bearing base  57 ), and the configuration of the bearing surface  57   a  (refer to FIG. 8 (B)) of the bearing base  57  is formed so that the width in the axial direction in the central part in the peripheral direction is narrower than the width in the axial direction at both ends in the peripheral direction so as to look like a cross sectional configuration of a concave lens. 
     In the cam journal  65  at the uppermost point of the camshaft  4 , the position in the axial direction where the journal path  73  opens is structured so that the rotational pathway  73   a  of the journal path  73  is limited to within the widest portion of the bearing surface  57   a  on the bearing base  57 . Moreover, the rotational pathway  73   a  of the journal path  73  is set so as to be positioned outside the narrowest region of the bearing surface  57   a  toward the side of the upper tappets  48  (tappet holders  50 ). This structure constitutes the intermittent oil supply means {circle around (3)}. 
     When structured as described above, whenever the camshaft  4  turns, the journal pathway  73  of the cam journal  65  is displaced from the widest portion to the narrowest portion of the bearing surface  57   a.  At this time, the opening of the journal pathway  73  is released and, once per revolution, oil spouts out intermittently from the journal path  73  as indicated by arrow O 3 . This intermittently spouted oil splashes over the tappet  48  and the tappet holder  50  first, and then splashes over onto the intake cams  68 . As a result, the tappet  48 , the tappet holder  50  and the intake cam  68  are well lubricated. 
     According to this structure, by only displacing the processing position of the journal pathway  73  slightly toward the upper end of the camshaft  4 , the intermittent oil supply means {circle around (3)} is completed. This enables the intermittent oil supply means {circle around (3)} to be made extremely easily and at a small working cost. 
     FIG. 9 (A) and (B) show intermittent oil supply means {circle around (4)} as the fourth embodiment. In this case, too, the tappets  48  (tappet holders  50 ) are disposed adjacent to the cam bearing  53  (bearing base  57 ) at both sides, whereby the configuration of the bearing surface  57   a  of the bearing base  57  is formed so that the width in axial direction in the central part in the peripheral direction is narrower than the width in the axial direction at both ends in the peripheral direction. 
     On the peripheral surface of the cam journal  65  at the uppermost part of the camshaft  4 , a short oil groove  79  is formed extending in the axial direction of the cam shaft  4 . The axial position of this oil groove  79  is structured so that the rotational pathway  79   a  of the oil groove  79  is limited to within the range of the widest portion of the bearing surface  57   a  of the bearing base  57 . Moreover, the rotational pathway  79   a  of the oil groove  79  is set so that one end (the upper end) of the oil groove  79  is positioned outside the range of the narrowest portion of the bearing surface  57   a  on the upper tappets  48  (tappet holders  50 ) side. The journal path  73  opens at the lower end side of the oil groove  79 . In this way, the intermittent oil supply means {circle around (4)} is structured. 
     According to this structure, every time the camshaft  4  turns, the upper end of the oil groove  79  on the cam journal  65  protrudes upwardly from the narrowest portion of the bearing surface  57   a.  Oil supplied from the journal path  73  spouts out intermittently from the upper end of the oil groove  79  once per revolution in the direction indicated by arrow  04 . As in the third embodiment, the tappet  48 , the tappet holder  50 , and the intake cam  68  are well lubricated by oil that is intermittently spouted in this manner. 
     According to the intermittent oil supply means {circle around (1)} through {circle around (4)} as described in the first through the fourth embodiments, by using an extremely simple structure, an appropriate amount of oil is supplied to the tappets  48 , the tappet holders  50 , the intake cams  68 , etc., which are located in places where it is conventionally hard to supply oil, lubrication conditions among these components are improved, and seizure and uneven wear are effectively prevented from occurring. 
     Further, because the intermittent oil supply means {circle around (1)} through {circle around (4)} supplies oil intermittently, rather than continuously, to the necessary locations, there is no need to worry about the oil pressure within the engine  2  dropping or about other portions to be lubricated being adversely affected. Also, excess oil does not splash around, and so the oil does not spout out from the breather outlet (not shown) provided on the head cover  16 . 
     In the above descriptions of the first through the fourth embodiments, descriptions were made by using examples in which the intermittent oil supply means {circle around (1)} through {circle around (4)} are provided in the cam journal  65  and the cam bearing  53  provided in the uppermost camshaft  4  at the intake side. However, it is possible to provide the same intermittent oil supply means to mid-positioned cam bearing  53  and cam journal  65 , as well as to the cam bearing  54  and the cam journal  66  of the exhaust side camshaft  5 . The descriptions of these embodiments were made by using examples whereby the present invention is applied to vertical engines of which crankshaft  3  is disposed vertically. However, the present invention is also applicable to horizontal type engines for which a crankshaft is disposed horizontally (vehicle engine, etc.) 
     As described above, according to the lubricating structure for a four-cycle engine related to the present invention, oil can be supplied to the vicinity of cams and tappets located in positions to which it is conventionally hard to supply oil by using a simple structure and without decreasing oil pressure in the engine, whereby lubrication conditions are improved, and seizure and uneven wear can be prevented. 
     Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only. Thus, it should be understood that the invention is not limited to the illustrative examples in this specification. Rather, the invention is intended to cover all modifications and variations that come within the scope of the following claims and their equivalents.