Patent Document

PRIORITY INFORMATION  
       [0001]     This application can be based on and claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2004-181932, filed on Jun. 21, 2004, the entire contents of which can be hereby expressly incorporated by reference.  
       BACKGROUND OF THE INVENTIONS  
       [0002]     1. Field of the Inventions  
         [0003]     The present inventions relate to engines, and particularly to engines provided with a crankcase with which a main cylinder body can be integrally formed.  
         [0004]     2. Description of the Related Art  
         [0005]     Conventional motorcycle engines, as well as some other types of engines, include a piston disposed for reciprocating motion inside of a cylinder, and a crankshaft can be connected to the piston via a connecting rod. This allows the reciprocating motion of the piston to be converted into a rotational motion of the crankshaft.  
         [0006]     Japanese Patent JP-A-Hei 4-075364 discloses such a well-known conventional motorcycle engine. This engine can be a V-type, 4-cylinder engine, provided with a crankcase on which a main cylinder body can be integrally formed. In this V-type, 4-cylinder engine, a crankcase can be divided into an upper and a lower crankcase and having a main cylinder body integrally formed on the upper crankcase. A cylinder head can be mounted to the top side of the main cylinder body on the crankcase and tilts forwardly to form a front bank. Another cylinder head can be mounted to the topside of the main cylinder body on the crankcase and tilts rearwardly to form a rear bank.  
         [0007]     An intake and an exhaust camshaft are mounted in each cylinder head. A cam chain transmits a rotary motion of the crankshaft to the intake and exhaust camshafts. A chain guide member guides the loosened-side of the cam chain. Additionally, a cam chain tensioner can be used to maintain tension in the cam chain with the chain guide member.  
         [0008]     The V-type, 4-cylinder engine disclosed in the JP-A-Hei 4-075364 has a chain chamber for accommodating the cam chain provided inside the cylinder head and the crankcase. A housing portion for housing a transmission can be integrally formed at the rear of the main cylinder body of the rear cylinder bank on the crankcase portion thereof.  
       SUMMARY OF THE INVENTIONS  
       [0009]     An aspect of at least one of the embodiments disclosed herein includes the realization that if a cam chain tensioner is mounted so as to extend across a mating face between the cylinder head and the crankcase, the tensioner can achieve better performance. In the conventional V-type, 4-cylinder engine, such as that disclosed in JP-A-Hei 4-075364, it can be difficult to mount the cam chain tensioner (tension applying member). In particularly, a housing portion for housing a transmission can be provided rearward of the main cylinder body on the crankcase on the side of the rear bank, which makes it more difficult to mount the cam chain tensioner (tension applying member) to the main cylinder body.  
         [0010]     For example, the lower part of the chain guide member can be located toward the main cylinder body while the upper part thereof is located toward the cylinder head, such as that in JP-A-Hei 4-075364. If the cam chain tensioner (tension applying member) is disposed completely in the cylinder head, a point where the cam chain tensioner presses against the chain guide member disadvantageously results in being closer to the upper end of the chain guide member inside of the cylinder head. As described above, a portion that can be closer to the upper end of the chain guide member can be pressed by the cam chain tensioner, which results in a shorter length of a vibration-absorbing portion formed between the point where the chain guide member can be pressed and the upper end thereof. This makes the vibration-absorbing portion of the chain guide member less bendable. This creates a problem of difficulty in sufficiently absorbing the vibration of the cam chain in the engine of JP-A-Hei 4-075364.  
         [0011]     Thus, in accordance with an embodiment, an engine comprising a crankcase, a crankshaft disposed within the crankcase, and a main cylinder body disposed on the crankcase. A cylinder head is mounted above the crankcase and a chain chamber is formed inside the cylinder head. A camshaft is provided at the cylinder head and a cam chain is located in the chain chamber and configured to transmit a driving force of the crankshaft to the camshaft. A chain guide member is configured to guide the cam chain, and a tension applying member is configured to apply tension to the cam chain via the chain guide member. The tension applying member is mounted across a mating face between the cylinder head and the crankcase. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The above-mentioned and the other features of the inventions disclosed herein are described below with reference to the drawings of the preferred embodiments. The illustrated embodiments are intended to illustrate, but not to limit the inventions. The drawings contain the following figures:  
         [0013]      FIG. 1  can be a side view of a motorcycle including an engine according to an embodiment.  
         [0014]      FIG. 2  can be an enlarged side elevational view of the engine shown in  FIG. 1 , which can be a V-type, 4-cylinder engine for a motorcycle.  
         [0015]      FIG. 3  can be a partial cut away view of the engine showing a camshaft drive mechanism disposed therein.  
         [0016]      FIG. 4  can be an enlarged top plan view of the rear cylinder bank of the engine, with the valve cover removed, as viewed from the direction indicated by the arrow A.  
         [0017]      FIG. 5  can be a top plan view of the rear cylinder bank of the engine with the camshaft drive mechanism removed from the cylinder head.  
         [0018]      FIG. 6  can be a cross-sectional view of the rear cylinder bank, taken along the line  200 - 200  in  FIG. 5 .  
         [0019]      FIG. 7  can be a perspective view of a cam chain tensioner shown in  FIG. 6 .  
         [0020]      FIG. 8  can be a front elevational view, showing a tightened-side chain guide for the rear cylinder bank of  FIG. 3 .  
         [0021]      FIG. 9  can be a left side elevational view of the tightened-side chain guide for the rear bank of  FIG. 8 .  
         [0022]      FIG. 10  can be a cross-sectional view of a support member, for supporting the tightened-side chain guide member, taken along the line  100 - 100  in  FIG. 3 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]      FIG. 1  can be a left side elevational view of a motorcycle-type two-wheeled vehicle having an engine in accordance with an embodiment. The embodiments disclosed herein are described in the context of a motorcycle-type two-wheel vehicle because these embodiments have particular utility in this context. However, the embodiments and inventions herein can also be applied to other vehicles, such as scooters, all train vehicles and other vehicles with more than two wheels which have limited space for accommodating a propulsion system. It can be to be noted that, as used herein, the terms “front,” “rear,” “left,” “right,” “up” and “down,” correspond to the direction assumed by a driver of the vehicle  1 .  
         [0024]      FIG. 1  can be a side view of a motorcycle  1  according to an embodiment.  FIG. 2  can be a side view of the engine of the motorcycle  1 .  FIGS. 3 through 10  are explanatory views illustrating a structure of a camshaft drive mechanism.  
         [0025]     A motorcycle  1  of this embodiment can be described as follows with reference to  FIGS. 1 through 10 . The arrow F in the drawings indicates the forward direction in which the motorcycle  1  moves.  
         [0026]     The motorcycle  1  of this embodiment can have a head pipe  2  and a main frame  3  connecting its front end to the head pipe  2 . The main frame  3  can be formed to extend rearwardly.  
         [0027]     A front wheel  5  can be rotatably attached to the head pipe  2  via a front fork  4 . Handlebars  6  can be fixed to a top end of the head pipe  2 . A rear wheel  8  can be rotatably attached to the rear of a rear arm  7 . A fuel tank  9  can be installed above the main frame  3 . At the rear of the fuel tank  9 , a driver&#39;s seat  10  can be provided.  
         [0028]     To the head pipe  3  can be attached a down pipe  11  extending downwardly. A water-cooled V-type, 4-cylinder engine  20  can be mounted between the down pipe  11  and the lower end of the main frame  3 . A radiator  12  for cooling a coolant to circulate within the V-type, 4-cylinder engine  20  can be installed in front of the down pipe  11 .  
         [0029]     As shown in  FIG. 2 , the V-type, 4-cylinder engine  20  according to this embodiment can be provided with a crankcase  21  for accommodating a crankshaft  22 , which can be made up of an upper crankcase  21   a  and a lower crankcase  21   b . Four main cylinder bodies (not shown) can be integrally formed with each other on the upper crankcase  21   a  of the crankcase  21 .  
         [0030]     A cylinder head  23  tilts forwardly and thus forms a front bank  51 . Another cylinder head  24  tilts rearwardly and thus forms a rear bank  52 . The cylinder heads  23 ,  24  can be mounted to the topside of the main cylinder body.  
         [0031]     The front bank  51  can be an example of a “first bank” and the rear bank  52  can be an example of a “second bank”. However, as used herein, the identification of any component as “first” or “second” are merely arbitrary labels used solely for purposes of convenience.  
         [0032]     Similarly, the cylinder head  23  can be an example of a “first cylinder head” and the cylinder head  24  can be an example of a “second cylinder head”. Top covers  40   a  and  40   b  can be attached to the topside of the cylinder heads  23  and  24 , respectively. The crankshaft  22  can have two sprockets  22   a  and  22   b  as shown in  FIG. 3 . However, other sprockets can also be used.  
         [0033]      FIG. 2  shows that a balance weight  41 , a crankshaft  22 , a primary shaft  42  and a secondary shaft  43  can be placed, in order from front to back, along a mating face between the upper crankcase  21   a  and the lower crankcase  21   b . The balance weight  41  rotates at the same speed as the crankshaft  22  but in a direction reverse. The main function of the balance weight  41  is to absorb the primary vibrations of the crankshaft  22 .  
         [0034]     The primary shaft  42  and the secondary shaft  43  can be respectively provided with one or pa plurality of speed change gears (not shown). The primary shaft  42 , the secondary shaft  43  and the groups of speed change gears constitute a transmission  44 .  
         [0035]     A housing portion for housing the transmission  44  can be integrally formed with the crankcase  21 , on a rearward side of the main cylinder body (not shown) which is also on the side of the rear bank  52  on the crankcase  21 . In other words, the rear bank  52  can be positioned toward the housing portion for housing the transmission  44  while the front bank  51  can be positioned on the opposite side to the housing portion for housing the transmission  44 .  
         [0036]     As shown in  FIG. 3 , an intake camshaft  25  having a sprocket  25   a  and a gear  25   b , and an exhaust camshaft  26  having a gear  26   a  engaged with the gear  25   b  of the intake camshaft  25  can be rotatably attached to the cylinder head  23  forming the front bank  51 . A cam chain  29  can be wound around between the sprocket  22   a  of the crankshaft  22  and the sprocket  25   a  of the intake camshaft  25  at the cylinder head  23  forming the front bank  51 . The cam chain  29  on the side of the front bank  51  can be located in chain chambers  23   a  and  21   c  which can be located at the axial midsection of the intake camshaft  25  and the exhaust camshaft  26 .  
         [0037]     As shown in  FIG. 3 , a straight chain guide member  31  can be provided on the side where the cam chain  29  for the front bank  51  is tightened, and in turn an arcuate chain guide member  32  can be provided on the side where the cam chain  29  for the front bank  51  is loosened. The side where the cam chain  29  is tightened refers to the side where the cam chain  29  is tightened by the rotation of the crankshaft  22 . The side where the cam chain  29  is loosened refers to the side where the cam chain  29  is loosened by the rotation of the crankshaft  22 .  
         [0038]     The arcuate chain guide member  32  can have a hole portion  32   a  performing as a rotational pivot, a pressed portion  32   b , a vibration-absorbing portion  32   c  located toward the cylinder head  23  above the pressed portion  32   b  for absorbing the vibration of the cam chain  29 , and a guide portion  32   d  for guiding the cam chain  29 . The hole portion  32   a  of the chain guide member  32  for the front bank  51  can be rotatably supported by a support shaft  37   a  of a support member  37  as shown in  FIGS. 3 and 10 . A cam chain tensioner  33  for pressing the loosened-side chain guide member  32  for the front bank  51  against the cam chain  29  can be disposed between the front bank  51  and the rear bank  52 .  
         [0039]     With reference to  FIG. 3 , an intake camshaft  27  having a sprocket  27   a  and a gear  27   b , and an exhaust camshaft  28  having a gear  28   a  engaged with the gear  27   b  of the intake camshaft  27  can be rotatably attached to the cylinder head  24  forming the rear bank  52 . The intake camshaft  27  can be example of a “first camshaft” and the gear  27   b  can be an example of a “first gear”.  
         [0040]     The exhaust camshaft  28  can be an example of a “second camshaft” and the gear  28   a  can be an example of a “second gear”. A cam chain  30  can be wound around between the sprocket  22   b  of the crankshaft  22  and the sprocket  27   a  of the intake camshaft  27  on the cylinder head  24  forming the rear bank  52 .  
         [0041]     The cam chain  30  on the side of the rear bank  52  can be located in the chain chambers  24   a  and  21   d  (see  FIG. 3 ) which can be located at the axial (B direction in  FIG. 4 ) midsection of the intake camshaft  27  and the exhaust camshaft  28 . In short, the embodiment of the present invention employs a center cam chain system.  
         [0042]     In this embodiment, a straight chain guide member  34  can be provided on the side where the cam chain  30  for the rear bank  52  is tightened (during operation), and in turn an arcuate chain guide member  35  can be provided on the side where the cam chain  30  is loosened (during operation). As shown in  FIGS. 8 and 9 , the arcuate chain guide member  35  can have a hole portion  35   a  performing as a rotational pivot, a pressed portion  35   b , a vibration-absorbing portion  35   c  located toward the cylinder head  24  above the pressed portion  35   b  for absorbing the vibration of the cam chain  30 , and a guide portion  35   d  for guiding the cam chain  30 .  
         [0043]     The hole portion  35   a  of the chain guide member  35  on the side of the rear bank  52  can be supported by a support shaft  37   b  of a support member  37  as shown in  FIGS. 3 and 10 . A cam chain tensioner  36  for pressing the loosened-side chain guide member  35  for the rear bank  52  can also be disposed therein. The cam chain tensioner  36  can be an example of a “tension applying member”.  
         [0044]     The cam chain tensioner  36  on the side of the rear bank  52  can be provided below the exhaust camshaft  28  as shown in  FIGS. 2 and 3 . To be more specific, in this embodiment, the cam chain  30  can be wound not around the exhaust camshaft  28  but around the intake camshaft  27 , which results in no cam chain  30  being located below the exhaust camshaft  28 . This allows the cam chain tensioner  36  to be located below the exhaust camshaft  28  on the side of the rear bank  52 , thereby preventing the cam chain tensioner  36  from protruding outward of the exhaust camshaft  28 .  
         [0045]     Engagement of the gear  27   b  of the intake camshaft  27  with the gear  28   a  of the exhaust camshaft  28  enables the rotation of the intake camshaft  27  to be transmitted to the exhaust camshaft  28 . This can reduce a distance between the intake camshaft  27  and the exhaust camshaft  28 , compared to the case where the cam chain  30  is wound around between the intake camshaft  27  and the exhaust camshaft  28  to transmit the rotation from the intake camshaft  27  to the exhaust camshaft  28 . This makes it possible to make a shape of a combustion chamber (not shown) undersurface of the cylinder head  24  flatter, resulting in improved combustion efficiency.  
         [0046]     In the illustrated embodiment, the cam chain tensioner  36  on the side of the rear bank  52  can be located across the mating face  24   b  of the cylinder head  24  and the upper crankcase  21   a , as shown in  FIGS. 2 and 3 . More specifically, as shown in  FIG. 3 , the cam chain tensioner  36  on the side of the rear bank  52  can have a mounting portion  36   a  located inside the cylinder head  24 , and a pressing portion  36   b  located so as to protrude toward the upper crankcase  21   a  for pressing the pressed portion  35   b  of the chain guide member  35 .  
         [0047]     The mounting portion  36   a  of the cam chain tensioner  36  can be provided with mounting holes  36   c  and  36   d  through which mounting screws  60  can be inserted, and an oil supply port  36   e , as shown in  FIG. 7 . The mounting holes  36   c  and  36   d  and the oil supply port  36   e  can be designed to extend substantially in the vertical direction with respect to the mating face  24   b  (See  FIG. 6 ) of the cylinder head  24  and the upper crankcase  21   a.    
         [0048]     The mounting holes  36   c  and  36   d , designed to extend substantially in the vertical direction (as shown by the arrow C in  FIG. 6 ) with respect to the mating face  24   b , allow the screws  60  to be inserted and secured from above the cylinder head  24  in the C direction of  FIG. 6 . This facilitates mounting of the mounting portion  36   a  of the cam chain tensioner  36  to the cylinder head  24 . The oil supply port  36   e  can be designed to connect to an oil passage  36   f  shown in  FIG. 6  through another oil passage (not shown). The top end of the oil passage  36   f  can be sealed by a ball-shaped plug  36   g.    
         [0049]      FIG. 6  also shows that the pressed portion  36   b  of the cam tensioner  36  can be provided with a protrusion  36   i , which can be inserted into an opening  36   h  and can move in a direction shown by the arrow D by given pitch. A compression coil spring  36   j  can be provided for urging the protrusion  36   i  in the direction shown by the arrow D, although other types of springs can also be used.  
         [0050]     In addition, a spring  36   k  for moving the protrusion  36   i  in the direction shown by the arrow D by a given pitch can be located such that the spring  36   k  abuts on the outer periphery of the protrusion  36   i . Inside of the protrusion  36   i , a passage member  361  forming the oil passage can be attached. Also, inside of the protrusion  36   i , a check ball  36   m  which functions as a check valve for sealing the oil passage made of the passage member  361 , and a compression coil spring  36   n  for urging the check ball  36   m  in the direction in which the oil passage made of the passage member  361  can be sealed.  
         [0051]     The protrusion  36   i  can have a pin  36   o  attached to its side surface. A lock  36   p , which can rotate between the engaging position with respect to the pin  36   o  and the disengaging position, can also be provided. The lock  36   p  is configured to engage with the pin  36   o  under the initial condition (at the time when it has just been assembled).  
         [0052]     The protrusion  36   i  can be thus prevented from moving in the D direction of  FIG. 6 . This dispenses with the need for a worker to completely push in and hold the tip end of the protrusion  36   i  so it does not protrude, when the worker assembles the pressing portion  36   b  of the cam chain tensioner  36  so as to press the pressed portion  35   b  of the chain guide member  35 . This allows the worker to easily assemble the cam chain tensioner  36 .  
         [0053]     When the cam chain tensioner  36  has been assembled, the lock  36   p  can be rotated in the E direction of  FIG. 6  due to the vibration created by driving the cam chain  30 . This allows the lock  36   p  to be disengaged from the pin  36   o . Disengagement of the lock  36   p  from the pin  36   o  allows the protrusion  36   i  to move by given pitch in the direction shown by the arrow D, depending on how much slack there can be in the cam chain  30  with time. Therefore, the extent to which the protrusion  36   i  protrudes can be automatically adjusted depending on how much slack there can be in the cam chain  30 , thereby preventing the cam chain  30  from being loosened for a long period of time.  
         [0054]     A passage member  36   q  that forms the oil passage to be connected to the oil passage  36   f  can be fitted into the opening  36   h . The check ball  36   s , which functions as a check valve for sealing the oil passage made of the passage member  36   q , can be placed inside of the opening  36   h . Also, inside of the opening  36   h , a spring retainer  36   r  can be disposed to retain the compression coil spring  36   j  and press the check ball  36   s  using an urging force produced by the compression coil spring  36   j  such that the oil passage made of the passage member  36   q  can be sealed.  
         [0055]     Now, operations of the intake camshaft  25  and exhaust camshaft  26  for the front bank  51  as well as those of the intake camshaft  27  and exhaust camshaft  28  for the rear bank  52  are described with reference to  FIG. 3 . First, the reciprocating motion of the piston (not shown) results in a counterclockwise rotation of the crankshaft  22 , which is transmitted to the intake camshaft  25  for the front bank  51  via the cam chain  29  on the side of the front bank  51 . The rotation of the intake camshaft  25  for the front bank  51  is transmitted to the exhaust camshaft  26  for the front bank  51  through the engagement of the gear  25   b  of the intake camshaft  25  with the gear  26   a  of the exhaust camshaft  26 . Thus, the intake camshaft  25  and exhaust camshaft  26  on the side of the front bank  51  can be driven with the rotation of the crankshaft  22 .  
         [0056]     The counterclockwise rotation (see  FIG. 3 ) of the crankshaft  22  can be also transmitted to the intake camshaft  27  for the rear bank  52  through the cam chain  30  on the side of the rear bank  52 . The rotation of the intake camshaft  27  is transmitted to the exhaust camshaft  28  for the rear bank  52  through the engagement of the gear  27   b  of the intake camshaft  27  with the gear  28   a  of the exhaust camshaft  28 . Thus, the intake camshaft  27  and exhaust camshaft  28  on the side of the rear bank  52  are also driven with the rotation of the crankshaft  22 .  
         [0057]     As described above, in this embodiment, the cam chain tensioner  36  on the side of the rear bank  52  for tensioning the cam chain  30  through the chain guide member  35  can be mounted across the mating face between the cylinder head  24  and the upper crankcase  21   a . Also, the pressing portion  36   b  of the cam chain tensioner  36  can be located on the side of the upper crankcase  21   a , which allows the point where the cam chain tensioner  36  presses against the chain guide member  35  to be located downward of or apart from the upper end of the chain guide member  35 . This can provide a longer length of the vibration-absorbing portion  35   c  formed between the point where the chain guide member  35  can be pressed and the upper end thereof, so that the vibration-absorbing portion  35   c  tends to easily bend. This results in sufficient absorption of the vibration of the cam chain  30 .  
         [0058]     Further, in this embodiment, the mounting portion  36   a  of the cam chain tensioner  36  can be mounted inside of the cylinder head  24 , as described above. Thus, a possible slight oil leakage from the cam chain tensioner  36  does not cause undesirable results because lubricant oil or other oils have already adhered to the inside of the cylinder head  24 . Therefore, a sealing member such as O-ring can be unnecessary, even if a hydraulic cam chain tensioner  36  is employed.  
         [0059]     The above embodiment shows an example of the present inventions to the center cam chain system in which the cam chain can be located in the chain chamber which can be located at the axial midsection of the intake and exhaust camshaft. However, the inventions are not limited to that, but they may also be applied to a side cam chain system in which the cam chain is located in the chain chamber which is located at the axial end of the intake and exhaust camshaft.  
         [0060]     In the above description of the embodiment, an example can be shown in which the tension applying means can be applied to the cam chain tensioner on the side of the rear bank. However, the present inventions are be not limited to that, and may also be applied to the cam chain tensioner on the side of the front bank.  
         [0061]     Furthermore, in the above description of the embodiment, an example is shown in which the inventions are applied to a V-type, 4-cylinder engine for motorcycles. However, the present inventions are not limited to such, and can also be applied to V-type, 4-cylinder engines to be mounted to vehicles other than motorcycles, such as three-wheelers and ATVs (All Terrain Vehicles). Still furthermore, the inventions can also be applied to V-type cylinder engines other than V-type, 4-cylinder engines, or other types of engines.  
         [0062]     Further, although these inventions have been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present inventions extend beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the inventions and obvious modifications and equivalents thereof. In addition, while several variations of the inventions have been shown and described in detail, other modifications, which are within the scope of these inventions, will be readily apparent to those of skill in the art based upon this disclosure. It can be also contemplated that various combination or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the inventions. It should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed inventions. Thus, it can be intended that the scope of at least some of the present inventions herein disclosed should not be limited by the particular disclosed embodiments described above.

Technology Category: f