Patent Publication Number: US-8534257-B2

Title: Engine case

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to an engine case including: a crank chamber of an engine; a clutch chamber having a wet clutch connected to an output shaft protruding from the crank chamber; and a partition wall keeping the crank and clutch chambers separated and connecting the crank and clutch chambers. 
     2. Description of the Related Art 
     For prior art techniques relating to this type of engine case, there can be mentioned Japanese Unexamined Patent Application Publication No. 11-115517 (see paragraphs [0042]-[0044] and FIG. 5). The engine case described in this patent document has a first partition wall at least partially separating a crank chamber from a wet clutch, and a second partition wall separating the wet clutch from a V-belt continuously variable transmission. Engine oil stored in the crank chamber is sent by an oil pump, and supplied to a clutch chamber through a radial oil passage formed inside the second partition wall and an axial oil passage formed in the crankshaft (output shaft), to thereby lubricate various portions of the wet clutch. Through a portion near a lower end of the first partition wall, a communicating passage penetrates that communicates the crank chamber with the clutch chamber, and superfluous engine oil discharged from the wet clutch is allowed to return to the crank chamber through the communicating passage. It should be noted that the above-described patent document does not specifically describe where the oil inlet for engine oil should be located, but from the viewpoint of the general technique, it is presumed that the oil inlet is located in a portion of an outer wall of the crank chamber. 
     However, in the engine case described in the above-described patent document, it is necessary to form oil passages inside the crankshaft that extend in axial and radial directions and to secure an oil passage between an output shaft of the wet clutch and an input shaft of the transmission mechanism. Accordingly, remarkably high processing accuracy has been required. 
     In addition, in the case of the engine case described in the above-described patent document, at an early stage of starting of the engine after feeding the engine oil from the oil inlet, the engine oil is distributed in the crank chamber while the engine oil is not yet distributed over various portions in the clutch chamber. Since the engine is operated under this condition, the clutch should be in an off-state to perform a pre-conditioning interim operation that does not burden the engine, until a sufficient amount of the engine oil is distributed over the various portions in the clutch chamber. 
     SUMMARY OF THE INVENTION 
     In view of the problems of the prior art technique described above, it is desirable to provide an engine case that can smoothly supply the engine oil to the wet clutch, without requiring high processing accuracy. 
     In addition, it is also desirable to provide an engine case which allows the operation of the engine in a loaded state even at the relatively early stage of starting of the engine after feeding a predetermined small amount of the engine oil. 
     Accordingly, in an aspect of the present invention, there is provided an engine case including: a crank chamber of an engine; a clutch chamber having a wet clutch connected to an output shaft protruding from the crank chamber; a partition wall keeping the crank and clutch chambers separated and connecting the crank and clutch chambers; an oil inlet for introducing engine oil; an oil feeding passage which is configured to allow the engine oil introduced from the oil inlet to first enter the clutch chamber separated by the partition wall; and an inflow part which is formed in the partition wall and configured to allow an excess amount of the introduced engine oil over a predetermined amount to flow into the crank chamber. 
     In the engine case described above, it is preferable that a bottom portion of the clutch chamber is provided with a drain hole. 
     In the engine case described above, it is also preferable that a height level of the inflow part is higher than a height level of the output shaft, when the engine is mounted on a vehicle. 
     In the engine case described above, it is preferable that the partition wall serves as a bearing case pivotally supporting the output shaft, and an oil pump configured to suck the engine oil stored in the crank chamber and supply the sucked engine oil to the clutch chamber is provided on a face of the partition wall on a crank chamber side. 
     In the engine case described above, it is preferable that the partition wall is provided with an oil supply pathway configured to distribute the engine oil sent from the oil pump to portions including the clutch chamber and the crank chamber at a predetermined ratio. 
     In the engine case described above, it is preferable that a level gauge insertion opening and the oil inlet for engine oil are disposed on an outer periphery of the partition wall. 
     In the engine case described above, it is preferable that he oil supply pathway is provided with an oil filter. 
     In the engine case described above, it is preferable that the engine oil is distributed at the predetermined ratio by openings provided in the oil supply pathway, the openings being oriented to respective portions. 
     In the engine case described above, it is preferable that a height level of the opening is higher than a height level of the inflow part, when the engine is mounted on a vehicle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various aspects, other advantages and further features of the present invention will become more apparent by describing in detail illustrative, non-limiting embodiments thereof with reference to the accompanying drawings. 
         FIG. 1  is a partially cutaway side view showing an engine case according to the present invention. 
         FIG. 2  is a partially cutaway front view of the engine case of  FIG. 1 . 
         FIG. 3  is a cutaway front view showing a portion around a partition wall (bearing case) and a wet clutch. 
         FIG. 4  is a partially cutaway side view (one side) showing the partition wall (bearing case). 
         FIG. 5  is a cutaway plan view of a fifth oil passage along a line V-V of  FIG. 4 . 
         FIG. 6  is a partially cutaway side view (the other side) showing the partition wall (bearing case). 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinbelow, embodiments of the present invention will be described with reference to the drawings. 
       FIG. 1  shows an OHC type engine  1  having a single cylinder, and a belt-type continuously variable transmission  40  connected to a crankshaft  2  (one example of an output shaft) of the engine  1 . 
     As shown in  FIG. 2 , between the crankshaft  2  of the engine  1  and the belt-type continuously variable transmission  40 , a centrifugal wet clutch  30  is disposed which is configured to transmit a rotary driving force of the crankshaft  2  to a downstream side, based on a centrifugal force increased in accordance with a rotational speed of the crankshaft  2 . It should be noted that a friction multiple disc clutch may be used, instead of the centrifugal wet clutch  30 . 
     A transmission mechanism connected to the centrifugal wet clutch  30  is made up of the belt-type continuously variable transmission  40  connected to an output shaft  31  of the centrifugal wet clutch  30  and an auxiliary transmission mechanism  41  connected to an output shaft  41 A of the belt-type continuously variable transmission  40 . The auxiliary transmission mechanism  41  includes a forward-reverse switching mechanism (not shown) and an auxiliary speed change mechanism (not shown), and from the auxiliary transmission mechanism  41 , an output shaft Si for rear wheel and an output shaft S 2  for front wheel extend. 
     Between the centrifugal wet clutch  30  and the engine  1 , a bearing case  10  (one example of the partition wall) is disposed which is configured to rotatably support an output side of the crankshaft  2 . The bearing case  10  is fastened to a crankcase  2 C of the engine  1  and encloses a crank chamber  2 R, to thereby make up a partition wall configured to separate the crank chamber  2 R from the centrifugal wet clutch  30 . The centrifugal wet clutch  30  is connected to the crankshaft  2  (one example of the output shaft) protruding from the crank chamber  2 R. 
     On an outside of the bearing case  10 , a clutch case  32  into which the output shaft  31  of the centrifugal wet clutch  30  is inserted is hermetically attached, and between the bearing case  10  and the clutch case  32 , a clutch chamber  30 R configured to encase the centrifugal wet clutch  30  is formed. 
     An oil inlet  11  and a level gauge insertion opening  12  for engine oil are disposed on an outer periphery of an upper portion of the bearing case  10 , not on the crankcase  2 C of the engine  1 . 
     With this configuration, the level gauge insertion opening  12  and the oil inlet  11  can be arranged at approximately the same position along the crankshaft  2  (output shaft  31 ), and thus checking of a contamination level of the engine oil, feeding of the engine oil, maintenance of the wet clutch unit, and the like, can be easily performed. 
     The crankcase  2 C, the bearing case  10  (partition wall), and the clutch case  32  collectively make up the engine case according to the present invention. 
     In this case, as shown in  FIGS. 2 and 3 , the bearing case  10  (partition wall) serves as a wall on a right side (in the drawing) of the crank chamber  2 R, and at the same time, serves as a wall on a left side (in the drawing) of the clutch chamber  30 R. With this configuration, when the bearing case  10  (partition wall) is detached from the crankcase  2 C and the bearing case  10  (partition wall) is detached from the clutch case  32 , the right side (in the drawing) of the crank chamber  2 R is opened, and the left side (in the drawing) of the clutch chamber  30 R is opened. 
     A level gauge G inserted from the level gauge insertion opening  12  is guided linearly and obliquely downward toward a bottom area of the crank chamber  2 R. 
     On the other hand, as shown in  FIGS. 2 and 3 , an oil feeding passage  11 R for guiding the engine oil is bent outward of the crank chamber  2 R in a lower portion of the oil inlet  11  so that the engine oil fed from the oil inlet  11  exposed by removing an oil filler cap  11 C first fills the clutch chamber  30 R, instead of going to the crank chamber  2 R. 
     As shown in  FIGS. 2-4 , at a height level slightly above that of the crankshaft  2  in the bearing case  10 , two oil holes  10   h  (one example of the inflow part) are formed. When the engine oil in an amount appropriate for the centrifugal wet clutch  30  is introduced from the oil inlet  11 , a liquid level of the engine oil gradually increases in the clutch chamber  30 R. When the liquid level of the engine oil reaches the oil holes  10   h , it means that the clutch chamber  30 R is filled with an appropriate amount (predetermined amount) of the engine oil. When the introduction of the engine oil is continued, the engine oil overflows from the oil holes  10   h  and begins to flow into the crank chamber  2 R on the left side in  FIG. 3 . In this manner, there is no need to provide an oil passage between, for example, the output shaft  31  of the wet clutch  30  and the input shaft of the transmission mechanism, and thus the engine case can be obtained at a lower cost whose assembly is facilitated. It should be noted that, in the case described above, the oil holes  10   h  are positioned at a height level slightly above that of the crankshaft  2 . However, the height level is not limited to this, and alternatively, the oil holes  10   h  may be formed at a height level approximately the same as that of the crankshaft  2 , or may be formed at a height level slightly below that of the crankshaft  2 . 
     Accordingly, since a sufficient amount of the engine oil is always secured in the clutch chamber  30 R having the wet clutch  30 , even at the early stage of starting of the engine  1  after feeding the engine oil from the oil inlet  11 , such as immediately after the assembling of the engine where no engine oil is present in both the crank chamber  2 R and the clutch chamber  30 R, the immediate operation of the engine  1  in a loaded state becomes possible. 
     As shown in  FIGS. 3 and 4 , on a lower portion of a face of the bearing case  10  on a crank chamber  2 R side, an oil pump  15  of a trochoidal type is mounted. The oil pump  15  is configured to suck in the engine oil stored in the crank chamber  2 R, and spray the engine oil toward an upper area in the crank chamber  2 R, portions of a clutch plate  30 A positioned higher than the oil hole  10   h  in the centrifugal wet clutch  30 , and the like. A rotor  15   a  of the oil pump  15  is driven by a rotary driving force of the crankshaft  2 . In other words, as shown in  FIG. 3 , an output gear  13  is fixed to a portion of the crankshaft  2 , and an input gear  14  which is always engaged with the output gear  13  is configured to be rotated with the rotor  15   a  in a unified manner. 
     With this configuration, as compared with the case where the oil pump  15  is provided on a face of the partition wall on a clutch chamber  30 R side, the wet clutch  30  can be arranged closer to the bearing case  10 , and thus the reduction in the size of the wet clutch unit can be facilitated. In addition, since the oil pump  15  is not present on the clutch chamber  30 R side of the bearing case  10 , which may otherwise be arranged on the clutch chamber  30 R so as not to hinder the wet clutch  30 , the clutch case  32  closing the clutch chamber  30 R can have basically a simple shape, such as a disc enclosing only the wet clutch  30 . 
     In addition, a cartridge type oil filter  20  configured to filter the engine oil may be attached to a portion of an outer periphery of the bearing case  10 . The engine oil sent out from the oil pump  15  is filtered by a filter element in the oil filter  20 , and then sent to the crank chamber  2 R or the clutch chamber  30 R. 
     In the bearing case  10 , there are provided: a first oil passage L 1  extending obliquely upward so as to send the engine oil, sucked from an oil suction hole  2 H (see  FIG. 6 ) formed above the bottom portion of the crank chamber  2 R, to the oil pump  15 ; a second oil passage L 2  extending obliquely downward so as to send the engine oil from the oil pump  15  to an inlet of the oil filter  20 ; a third oil passage L 3  extending obliquely upward from an outlet of the oil filter  20  toward the crankshaft  2 ; a fourth oil passage L 4  extending right above from an end portion of the third oil passage L 3  to above the oil hole  10   h;  and a fifth oil passage L 5  extending horizontally from a portion of the fourth oil passage L 4 . It should be noted that various modifications are possible with respect to the extending directions of the oil passages. For example, the first oil passage L 1  may extend vertically upward, instead of extending obliquely upward. 
     On both sides of the fifth oil passage L 5 , a plurality of small oil discharge holes  24  are formed. As shown in  FIG. 5 , the oil discharge holes  24  include three oil discharge holes  24 A opened toward the crank chamber  2 R, and a single oil discharge hole  24 B opened toward the clutch chamber  30 R (see also  FIG. 6 ). Four oil discharge holes  24  in total have a function of distributing the engine oil to the crank chamber  2 R and the clutch chamber  30 R at a predetermined ratio (e.g., approximately 3 to 1). Of course, the engine oil may be distributed to a camshaft (not shown) of an intake valve (not shown) or an exhaust valve (not shown) of the engine  1 , in addition to the crank chamber  2 R and the clutch chamber  30 R. It should be noted that the number of the oil discharge hole  24  and the oil discharge hole  24 B are not limited to the number described above. 
     To an end portion of the fifth oil passage L 5 , a pressure sensor PS configured to detect a pressure of the engine oil is attached. 
     With the configuration described above, along an inside of the partition wall (bearing case  10 ) having an approximate plate shape, an oil supply pathway can be easily provided. 
     On a lower face of the bearing case  10 , a first drain hole Dl through which the engine oil in the clutch chamber  30 R can be discharged and a second drain hole D 2  through which the engine oil in the crank chamber  2 R can be discharged are separately and adjacently provided along a circumferential direction, in such a manner that they can be closed or opened by attachment or removal of closing plugs P 1  and P 2 , respectively. With this configuration, while retaining the engine oil in the crank chamber  2 R, the engine oil in the clutch chamber  30 R can be drained, so that the checking of the wet clutch  30 , the exchange of the engine oil and the like can be performed. 
     It should be noted that, in the above-described embodiment, two oil holes  10   h  are formed in the bearing case  10 . Alternatively, the inflow part may be, for example, a half-moon-shaped opening, which is defined by a straight line chord connecting the two oil holes  10   h  and an upward extending arc connecting the two oil holes  10   h  with the crankshaft  2  as a center. 
     In addition, the present invention may be applicable to an OHV type engine, whose camshaft (one example of the output shaft, not shown) of the engine  1  is connected to the wet clutch. 
     Accordingly, with respect to an engine case including a crank chamber of an engine, a clutch chamber having a wet clutch connected to an output shaft protruding from the crank chamber, and a partition wall keeping the crank and clutch chambers separated and connecting the crank and clutch chambers, the present invention provides a technique for reasonably arranging an oil inlet for engine oil and oil feeding passages guiding the introduced engine oil.