Abstract:
The lubrication structure of an engine is provided with a crankcase having a crank chamber that houses a crankshaft. A first oil reservoir is in communication with the crank chamber and is formed adjacent a bottom of the crank chamber. A second oil reservoir is in communication with the first oil reservoir and is formed adjacent the side of and on the bottom of the first oil reservoir. A reed valve extends diagonally from the bottom of the first oil reservoir toward the top of the second oil reservoir in an opening where the first oil reservoir and the second oil reservoir communicate with the crankcase. The reed valve includes a valve element that opens and closes according to the variation of pressure in the crank chamber. The valve element of the reed valve is arranged on the side of the second oil reservoir.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2006-120691, filed in Japan on Apr. 25, 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 lubrication structure of an engine that is suitable for a motorcycle, particularly a motorcycle that is used for off-road driving sports. 
   2. Background of the Invention 
   As an agitation loss is caused due to a crankshaft and other things when a motorcycle is run in a state in which lubricating oil accumulates in a crankcase of an engine, a reed valve is provided between a crank chamber and an oil pan to prevent the lubricating oil exhausted into the oil pan from the crank chamber from flowing in a reverse direction into the crank chamber. The reed valve is arranged vertically, that is, so that a valve element is open in a lateral direction of the body (see JP-A No. 2005-61387, for example). 
   However, the lubricating oil exhausted from the crank chamber flows laterally when the reed valve is vertically arranged and the valve element is formed so that it is open in the lateral direction of the body. Therefore, the lubricating oil is apt to stay in a space before and after the reed valve and an efficiency problem occurs, wherein the lubricating oil is not exhausted from the crank chamber sufficiently. On the other hand, a larger space is required for the lubricating oil exhausted from the reed valve on the downstream side of the engine when the reed valve is arranged horizontally so that the valve element of the reed valve is open downward. Therefore, the entire height of the engine is increased as a result and a problem occurs in that it is hard to secure a minimum road clearance (a distance from the ground to the lowest end of the engine). 
   SUMMARY OF THE INVENTION 
   The present invention is made in view of such problems, and an object of the present invention is to provide the lubrication structure of an engine an increase of an entire height that is inhibited by diagonally extending a reed valve. 
   To address these problems, the lubrication structure of the engine according to the present invention is provided with: a crankcase having a crank chamber that houses a crankshaft, having a first oil reservoir in communication with the crank chamber and formed adjacent a bottom of the crank chamber, having a second oil reservoir in communication with the first oil reservoir and formed adjacent a side of and on a bottom of the first oil reservoir, and having a third oil reservoir in communication with the second oil reservoir and formed adjacent a bottom of the second oil reservoir; and a reed valve extending diagonally from the bottom of the first oil reservoir toward the top of the second oil reservoir in a part where the first oil reservoir and the second oil reservoir communicate (for example, the opening  54  in this embodiment) of the crankcase and having a valve element that opens and closes according to the variation of pressure in the crank chamber. The valve element of the reed valve is arranged on the side of the second oil reservoir. 
   As for the lubrication structure of the engine according to the present invention described above, it is desirable that a part where the crank chamber and the first oil reservoir communicate and the valve element of the reed valve are arranged side by side in a tangential direction of the rotational locus of the crankshaft in a side view. 
   In addition, it is desirable that a wall forming the crank chamber and a wall forming the first oil reservoir are continuously formed and the valve element is arranged on an extended line of these walls. 
   The flow of lubricating oil that flows out of the crank chamber is smoothed and the lubricating oil hardly stays in a space before and after the reed valve (in the first oil reservoir and the second oil reservoir) when the lubrication structure of the engine according to the invention is configured as described above. Therefore, the lubricating oil in the crank chamber is promptly exhausted and the agitation loss of the lubricating oil due to the crankshaft and other things can be reduced. In addition, the increase of the entire height of the engine provided with the lubrication structure is inhibited by diagonally arranging the reed valve, the engine can be compacted, and an oil pan (the third oil reservoir) can be arranged on the downside of the reed valve in a state in which minimum road clearance is secured. 
   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 sectional view showing an engine including a crankcase according to the invention viewed from the left side; 
       FIG. 2  is a sectional view viewed from the left side for explaining a cam driving mechanism of the engine; 
       FIG. 3  is a sectional view viewed from the right side for explaining an oil pump of the engine; 
       FIG. 4  is a sectional view viewed from the right side for explaining a balance shaft driving mechanism of the engine; 
       FIG. 5  is a sectional view showing a cylinder block and the crankcase of the engine respectively viewed from the front side; and 
       FIG. 6  is a sectional view showing a main part viewed from the left side for explaining the oil pump of the engine. 
   

   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 the drawings, a preferred embodiment of the invention will be described below. First, referring to  FIG. 1 , an engine  1  to which lubrication structure according to an embodiment of the present invention is applied will be described. The engine  1  is used for a motorcycle, particularly for a motorcycle for off-road driving sports. In the following description, an arrow F shown in  FIG. 1  points to the front of the motorcycle. 
   The engine  1  includes a cylinder head cover  2 , a cylinder head  3 , a cylinder block  4  and a crankcase  5 . A cylinder chamber  6  that extends vertically and cylindrically is formed in the cylinder block  4 . A piston  7  is arranged in the cylinder chamber  6  so that the piston can be vertically slid and is connected to a crankshaft  9  rotatably held in the crankcase  5  via a connecting rod  8 . The connecting rod  8  is connected to the crankshaft  9  by a crankpin  28 . An intake port  13  and an exhaust port  14  communicate with a combustion chamber  10  formed by the cylinder chamber  6 , the cylinder head  3  and the piston  7  via an inlet  11  and an outlet  12  respectively formed in the cylinder head  3 . The respective one ends of an intake poppet valve  15  and an exhaust poppet valve  16  are attached to respective valve stems, are supported by respective retainers, and the respective other ends are pressed in directions in which the inlet  11  and the outlet  12  are ordinarily closed by valve springs  17 ,  18  supported by the cylinder head  3 . 
   Furthermore, a camshaft  19  for opening and closing the intake valve  15  and the exhaust valve  16  is rotatably supported by the cylinder head  3  and a timing chain  22  is wound on a cam driven sprocket  20  arranged on the camshaft  19  and a cam driving sprocket  21  arranged on the crankshaft  9 . Therefore, when the camshaft  19  is rotated in accordance with the rotation of the crankshaft  9  and a cam  23  formed on the camshaft  19  directly pushes down the intake valve  15  or pushes down the exhaust valve  16  via a rocker arm  24 , the inlet  11  and the outlet  12  are opened or closed. 
   A throttle valve  25  and an injector  26  are attached to the intake port  13 . The quantity of air cleaned by an air cleaner (not shown) that flows in is regulated by the throttle valve  25 . The air is mixed with fuel injected from the injector  26 . The air-fuel mixture is supplied to the combustion chamber  10  via the inlet  11  from the intake port  13 . After the air-fuel mixture is compressed by the piston  7 , it is ignited by an ignition plug (not shown) and is combusted to generate energy for rotating the crankshaft  9  via the piston  7 . Afterward, the ignited air-fuel mixture is exhausted outside via the exhaust port  14  from the outlet  12  as exhaust gas. 
   The inside of the crankcase  5  is separated into a crank chamber  51  storing the crankshaft  9  and a transmission chamber  52  storing a transmission mechanism  27  by a wall  50 . The crank chamber  51  is encircled by the front of the crankcase  5  and the wall  50 . The upside of the crank chamber  51  is cylindrically open. A lower end of the cylinder block  4  is attached to the crank chamber. The crank chamber  51  and the cylinder chamber  6  are in communication with each other. 
   A first oil reservoir  53  is formed next to the crank chamber  51  on the downside of the rear side of the crank chamber  51 . The first oil reservoir  53  is in communication with the crank chamber  51  via an opening  54  formed between the upside of the front side and the downside of the crank chamber  51 . A second oil reservoir  56  is formed via a reed valve  55  on the downside of the rear side of the first oil reservoir  53 . Furthermore, a third oil reservoir (an oil pan)  57  in communication with the second oil reservoir  56  is formed on the downside of the second oil reservoir  56  (at the bottom of the crank case  5 ). 
   The reed valve  55  diagonally extends from the downside in front to the rear upside in a space that extends vertically, divides the space into the first oil reservoir  53  and the second oil reservoir  56 , and extends from the bottom of the first oil reservoir  53  to the upside of the second oil reservoir  56 . The reed valve  55  is configured by the body  55   a  of the reed valve which is flat and the substantial center of which is open. A valve element  55   b  like a tongue is attached to the body  55   a  and covers the opening. In this embodiment, the valve element  55   b  is attached to the side of the second oil reservoir  56 , a lower end located on the front side is fixed, and the side of an upper end located on the rear side is open downward. 
   A front side wall W 1  surrounding the crank chamber  51  of the crankcase  5  and a lower side wall W 2  surrounding the first oil reservoir  53  are continuously formed in the shape of an arc. The valve element  55   b  of the reed valve  55  is arranged on an extended line of the wall W 2  extended backward. 
   Therefore, lubricating oil that lubricates the crankshaft  9  and other things accumulates in the first oil reservoir  53  via a lower part of the crank chamber  51  and the opening  54 . When pressure in the crank chamber  51  is increased by the vertical motion of the piston  7 , the valve element  55   b  of the reed valve  55  is opened, the lubricating oil is pushed out into the second oil reservoir  56 , and further, flows into the third oil reservoir  57 . Conversely, as the valve element  55   b  of the reed valve  55  closes even if pressure in the crank chamber  51  decreases, the lubricating oil never flows into the first oil reservoir  53  from the second oil reservoir  56 . 
   In the engine  1 , the crankshaft  9  is rotated counterclockwise in  FIG. 1  (a crankpin  28  fastened to the crankshaft  9  moves the connecting rod  8  from the upside to the downside through the front side and turns the connecting rod to the upside through the rear side). As shown in  FIG. 1 , the front side wall W 1  is formed when pressure in the crank chamber  51  is increased by the piston  7 , that is, along a path that the crankpin  28  is moved from the upside to the downside through the front side and further, the lower side wall W 2  is formed along an extended line of the rotational locus of the crankpin  38  (in a direction of a tangent at a lower end of the circumferential rotational locus in a side view). Therefore, the opening  54  is formed on the extended line of the rotational locus, the lubricating oil in the crank chamber  51  flows along the wall W 2  from the wall W 1  and flows into the first oil reservoir  53 . At this time, the reed valve  55  is diagonally arranged as described above and the valve element  55   b  is located on an extended line in a direction in which the lubricating oil flows from the crank chamber  51  into the first oil reservoir  53  (on the extended line of the walls W 1  and W 2 )(that is, the opening  54  and the valve element  55   b  of the reed valve  55  are arranged side by side in the direction of the tangent of the rotational locus). Therefore, the lubricating oil can also smoothly flow into the second oil reservoir  56  by pushing down the valve element  55   b  of the reed valve  55 . Further, as the third oil reservoir  57  is formed immediately under the second oil reservoir  56 , the lubricating oil in the second oil reservoir  56  also flows into the third oil reservoir  57  soon. 
   As the lubricating oil hardly accumulates in space before and after the reed valve  55  (in the first oil reservoir  53  and the second oil reservoir  56 ) when the first to third oil reservoirs  53 ,  56 ,  57  and the reed valve  55  are arranged as described above, the lubricating oil in the crank chamber  51  is promptly exhausted and the agitation loss of the lubricating oil by the crankshaft  9  and other things can be reduced. As the reed valve  55  is diagonally arranged, the increase of the entire height of the engine  1  is inhibited, the engine can be compacted, and the oil pan (the third oil reservoir  57 ) can be arranged under the reed valve  55  in a state in which minimum road clearance is secured. 
   A balance shaft  80  extended substantially in parallel with the crankshaft  9  is rotatably supported by the crankcase  5  in front of the crankshaft  9 . A balancer driven gear  82  engaged with a balancer driving gear  81  arranged on the crankshaft  9  is attached to the side of a right end of the balance shaft  80  and a balancer  83  is formed at the left end. Therefore, as the balance shaft  80  is rotated via the balancer driving gear  81  and the balancer driven gear  82  when the crankshaft  9  is rotated, the balancer  83  is rotated and the vibration of the piston  7  is negated. 
   An oil pump shaft  85  is rotatably arranged substantially in parallel with the balance shaft  80  on the side of the front end of the crankcase  5  and on the downside of the balance shaft  80 . An oil pump driven gear  86  engaged with an oil pump driving gear  84  arranged at the right end of the balance shaft  80  is arranged at the left end of the oil pump shaft  85  and an oil pump  62  is arranged at the right end of the oil pump shaft  85 . Therefore, when the crankshaft  9  is rotated and the balance shaft  80  is rotated, the oil pump shaft  85  is rotated via the oil pump driving gear  84  and the oil pump driven gear  85  and the oil pump  62  is operated. The lubricating oil that accumulates in the third oil reservoir  53  is pumped up via an oil passage  61  formed in the crankcase  5  by the oil pump  62  after the lubricating oil is cleaned by a strainer  87  and is utilized for lubricating the inside of the engine  1 . 
   As shown in  FIG. 1 , the second oil reservoir  56  and the third oil reservoir  57  are protruded on the lower side of the crankcase  5  in the side view. A drain hose  59  pierced longitudinally and connecting the outside and the third oil reservoir (the oil pan)  57  is formed at the lower end of a side wall  58  on the rear side forming the second oil reservoir  56  and the third oil reservoir  57  in the crankcase  5 . A drain bolt  60  is ordinarily screwed on the drain hose  59 , the drain hose is closed, and the lubricating oil accumulating in the third oil reservoir  57  can be exhausted outside by detaching the drain bolt  60  from the drain hose  59 . The drain bolt  60  is protruded in space under the transmission chamber  52 . 
   As described above, when the drain hose  59  is formed on the side wall  58  on the rear side, a part protruded on the lower side of the engine  1  is not required to be provided, minimum road clearance can be secured, and the engine  1  can be compacted. In addition, as the space under the transmission chamber  52  can be utilized by attaching the drain bolt  60  to the rear side of the crankcase  5  (to a face on the rear side of the side wall  58 ), work for attaching or detaching the drain bolt  60  to/from the drain hose  59  can be also facilitated. 
   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.