Patent Publication Number: US-9850791-B2

Title: Oil jet device

Description:
FIELD OF THE INVENTION 
     This application relates to a cooling structure for an internal combustion engine, and more particularly to an oil jet device for cooling an internal combustion engine with oil jets injected from behind a piston. 
     BACKGROUND OF THE INVENTION 
     As a cooling device for a piston of a conventional internal combustion engine, there is known an oil jet device in which a nozzle pipe providing a cooling oil channel held in fluid communication with an oil passageway in the internal combustion engine extends to the back of the piston, and oil is ejected from the nozzle pipe. Japanese Utility Model Laid-Open No. Sho 54-164328 (JP &#39;328) discloses a technology wherein a filter for filtering the oil is disposed in the oil channel to prevent the oil ejection port from being clogged. Japanese Patent Laid-Open No. 2011-94519 (JP &#39;519) reveals a technology wherein a check valve is provided to keep the oil pressure in the oil channel at a level equal to or higher than a predetermined value for thereby achieving the target aiming ability of the ejection (e.g., the ejection of the oil toward an area to be cooled). 
     SUMMARY OF THE INVENTION 
     Heretofore, there has been studied an oil jet device which is provided with the effect of the filter disclosed in JP &#39;328 and the effect of the check valve disclosed in JP &#39;519. However, an arrangement which has both the mounting structure of the filter and the structure of the check valve has caused a pressure loss in the oil channel, making it difficult to obtain a desired response performance with respect to the ejection of oil. 
     One objective of the present invention is to provide an oil jet device which reduces a pressure loss of oil and has an excellent response about the supply of oil. 
     To achieve this objective, there is provided in accordance with a first aspect of the present invention an oil jet device comprising: a main body mounted on an internal combustion engine and having a fluid communication passage held in fluid communication with an oil passageway defined in the internal combustion engine; a nozzle pipe having an oil ejection port configured to eject oil that has passed through the fluid communication passage; a check valve configured to open and close the fluid communication passage when a valve body and a valve seat which are disposed in the main body abut against each other; and a filter having a fluid communication hole configured to pass the oil therethrough and filter the oil, the filter being disposed upstream of the check valve, wherein an inside diameter of the valve seat is smaller than an inside diameter of the filter, and the valve seat has an upstream end wall surface facing at least some of the fluid communication holes, and the upstream end wall surface includes a slanted surface arranged such that a cross-sectional area of an oil channel is progressively smaller in a direction from an upstream region toward a downstream region of the fluid communication passage. 
     According to a second aspect of the present invention, in addition to the arrangement according to the first aspect, the filter includes a bottomed hollow cylinder with an open end at one end of a hollow cylindrical outer circumferential wall thereof and a filter surface with the fluid communication hole at the other end thereof, and the filter is housed in the main body with the outer circumferential wall being held in abutment against the upstream end wall surface. 
     According to a third aspect of the present invention, in addition to the arrangement according to the first aspect, the filter includes a bottomed hollow cylinder with an open end at one end of a hollow cylindrical outer circumferential wall thereof and a filter surface with the thud communication hole at the other end thereof, and the filter is positioned such that an outer circumferential wall of a distal end of the main body is inserted in the outer circumferential wall, and the filter surface is held in abutment against an upstream end of the main body. 
     According to a fourth aspect of the present invention, in addition to the arrangement according to any one of the first, second, and third aspects, the valve seat is integrally formed with the main body the main body includes a valve body housing disposed downstream of the valve seat, the valve body and an elastic body configured to bias the valve body are inserted through an insertion opening of the valve body housing, and a lid member is press-fitted in the insertion opening. 
     According to a fifth aspect of the present invention, in addition to the arrangement according to any one of the first, second, and third aspects, the valve seat includes a member separate from the main body and an elastic body configured to bias the valve body and the valve body are inserted through an upstream end opening of the fluid communication passage, and the valve seat is press-fitted in the upstream end opening. 
     According to a sixth aspect of the present invention, in addition to the arrangement according to the fifth aspect, an inner wall surface that defines the fluid communication passage has a step held in abutment against a downstream end of the valve seat for determining an inserted position of the valve seat. 
     According to a seventh aspect of the present invention, in addition to the arrangement according to any one of the first through sixth aspects, the fluid communication hole includes a plurality of fluid communication holes defined in the filter surface of the filter in each of outer circumferential and central areas thereof, and a diameter of each of the fluid communication holes is smaller than a diameter of the oil ejection port. 
     According to the eighth aspect of the present invention, in addition to the arrangement according to any one of the first seven aspects, the main body has an externally threaded surface on the outer circumference of a tubular portion thereof, the internal combustion engine has an internally threaded surface into which the externally threaded surface is threaded, and the main body is fastened and secured to the internal combustion engine by threaded engagement between the externally threaded surface and the internally threaded surface. 
     According to the first aspect, since the inside diameter of the valve seat is smaller than the inside diameter of the filter, and the upstream end wall surface facing at least some of the fluid communication holes includes the slanted surface arranged such that the cross-sectional area of the oil channel is progressively smaller in the direction from the upstream region toward the downstream region of the oil channel, the cross-sectional area of the channel at the upstream end wall is prevented from being abruptly reduced. As a result, the oil flow that has passed through the fluid communication holes toward the slanted surface gradually joins a straight flow along the slanted surface. Consequently disturbances of the oil flow are avoided immediately below the filter. Therefore, even though the check valve is disposed immediately behind the filter, constricting the fluid communication passage. This stricture is able to reduce the pressure loss caused between the filter and the upstream end wall surface. As a consequence, the oil jet device is of a good response at the time it ejects the oil. 
     According to the second aspect, the filter includes the bottomed hollow cylinder with the open end at one end of the hollow cylindrical outer circumferential wall thereof and the filter surface with the fluid communication hole at the other end thereof, and the filter is housed in the main body with the outer circumferential wall being held in abutment against the upstream end wall surface of the valve seat. Therefore, the filter and the valve seat are disposed adjacent to each other. As a result, the main body is compact in size. As the filter is housed in the main body, the oil jet device is not only small in size but also can be handled and assembled in position with ease. 
     According to the third aspect, since the filter includes the bottomed hollow cylinder with the open end at one end of the hollow cylindrical outer circumferential wall thereof and the filter surface with the fluid communication hole at the other end thereof, the outer circumferential wall of the distal end of the main body is mounted so as to be inserted in the outer circumferential wall of the filter. As the filter surface is positioned in abutment against the upstream end of the main body, the filter and the main body can be assembled together with no clearance left therebetween in a compact fashion. 
     According to the fourth aspect, as the valve seat is integrally formed with the main body, the valve seat is increased in durability and the number of parts of the check valve is reduced, allowing the check valve to be assembled in place with ease. Moreover, since the valve body and the elastic body of the check valve are inserted through the insertion opening of the valve body housing, and the lid member is press-fitted in the insertion opening to close the same, the check valve can be handled as a component assembled in the main body, and hence can be assembled in place with ease. 
     According to the fifth aspect, the valve seat includes a member separate from the main body. Therefore, the valve seat can be press-fitted into the upstream end opening after the elastic body and the valve body have been inserted through the upstream end opening of the fluid communication passage. No special structure is necessary for assembling the components of the check valve and the filter. Consequently, the main body is prevented from being structurally complex, and the oil jet device is excellent in assemblability and good in productivity. 
     According to the sixth aspect, since the inner wall surface that defines the fluid communication passage has the step held in abutment against the downstream end of the valve seat for determining the inserted position of the valve seat, the assembled position of the valve seat can easily be determined simply when the valve seat is press-fitted. Consequently, the assemblability of the oil jet device is increased. As the mounted position of the valve seat is accurately established by the position of the step, the process of setting a threshold value for the pressure for opening the check valve is stabilized. 
     According to the seventh aspect, inasmuch as the plurality of fluid communication holes are defined in the filter surface of the filter in each of outer circumferential and central areas thereof, the entire filter surface is widely used to ensure the flow rate of oil. As the diameter of each of the fluid communication holes is smaller than the diameter of the oil ejection port, the oil ejection port is prevented from being clogged. 
     According to the eighth aspect, the main body has the externally threaded surface on the outer circumference of the tubular portion thereof, and the internal combustion engine has the internally threaded surface into which the externally threaded surface is threaded. The main body can thus directly be threaded into and secured to the internal combustion engine. Therefore, no separate fastening member is required to fasten the oil jet device, which is thus made compact. As the mounting structure for the main body is made compact, when the oil jet device is to be disposed in position, the oil jet device is prevented from interfering with peripheral members of the internal combustion engine, and the degree of freedom about the installed position of the oil jet device is increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a fragmentary cross-sectional view of an internal combustion engine provided with an oil jet device according to a first embodiment, as viewed along an axial direction of a crankshaft. 
         FIG. 2  is a perspective view of the oil jet device shown in  FIG. 1 . 
         FIG. 3  is a fragmentary cross-sectional view of the oil jet device shown in  FIG. 2  which is mounted in place. 
         FIG. 4  is an exploded perspective view of the oil jet device shown in  FIG. 2 . 
         FIG. 5  is an enlarged fragmentary cross-sectional view of the oil jet device shown in  FIG. 3  which is mounted in place. 
         FIG. 6  is a cross-sectional view taken along line A-A of  FIG. 3 . 
         FIG. 7  is a perspective view of a modification of a filter according to the first embodiment. 
         FIG. 8  is a fragmentary cross-sectional view of an oil jet device according to a second embodiment which is mounted in place. 
         FIG. 9  is an enlarged fragmentary cross-sectional view of the oil jet device shown in  FIG. 8 . 
         FIG. 10  is a fragmentary cross-sectional view of an oil jet device according to a third embodiment which is mounted in place. 
         FIG. 11  is a fragmentary cross-sectional view of an oil jet device according to a fourth embodiment which is mounted in place. 
         FIG. 12  is a perspective view of an oil jet device according to a fifth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention will be described below with reference to the accompanying drawings. 
     An oil jet device according to a first embodiment for an internal combustion engine that is applicable to a motorcycle as a saddle-type vehicle will be described in detail below with reference to  FIGS. 1 through 6 . Directions such as upward, downward, leftward, and rightward directions in the present description shall be viewed on the accompanying drawings as they are seen in accordance with the directions of the reference symbols. 
     As shown in  FIG. 1 , an internal combustion engine  1  according to the present embodiment has a cylinder bore  10  defined by a cylinder  3  and a cylinder head  4  which are oriented upwardly from a crankcase  2 . A connecting rod  5  coupled to a crankshaft  9  is coupled to the back side of a piston  6  that is vertically movable in the cylinder bore  10 . 
     The upper surface of the piston  6  and the cylinder bore  10  surround a combustion chamber  10   a  to which there are connected an intake port  7  and an exhaust port  8  through which an air-fuel mixture is introduced and an exhaust gas is discharged at timings corresponding to combustion cycles by opening and closing valves  7   a  and  8   a.    
     As shown in  FIG. 1 , an oil jet device  20  according to the present embodiment is disposed downwardly of the cylinder bore  10 . The oil jet device  20  has a main body  23  held in fluid communication with an oil passageway  12  connected to an oil gallery  11  in the internal combustion engine  1 , and includes various members, to be described later, on the main body  23 . Oil is ejected from the oil jet device  20  through a distal end  22  of a nozzle pipe  21  disposed on a side of a lower end portion of the main body  23  and extending into the cylinder bore  10 . 
     As shown in  FIGS. 2 and 3 , the nozzle pipe  21  has a plurality of oil ejection ports  33  defined in the distal end  22  and a proximal end  21   b  connected in fluid communication with a fluid communication passage  23   d  defined in the main body  23 . The proximal end  21   b  is mounted in a holder  21   g  that is mounted on the lower side of the main body  23 . As shown in  FIG. 3 , the holder  21   g  is of a structure that provides fluid communication between a fluid communication side hole  23   q  that is held in fluid communication with the fluid communication passage  23   d  in the main body  23  and the nozzle pipe  21 . 
     As shown in  FIGS. 2 and 3 , the distal end  22  of the nozzle pipe  21  is of an inverted substantially frustoconical shape. The oil ejection ports  33 , which are defined in a distal end surface  31  of the distal end  22 , include a total of four oil ejection ports  33  including a first oil ejection port  33   a , a second oil ejection port  33   b , a third oil ejection port  33   c  that are positioned along the outer circumferential edge of the distal end surface  31 , and a central fourth oil ejection port  33   d . The oil ejection ports  33  are open upwardly into the cylinder bore  10 . The oil that is supplied from an oil pump (not shown) squirts out from the first oil ejection port  33   a , the second oil ejection port  33   b , the third oil ejection port  33   c , and the fourth oil ejection port  33   d  to aid the back side of the piston  6 . 
     The first oil ejection port  33   a , the second oil ejection port  33   b , and the third oil ejection port  33   c  have their oil ejection angles set to appropriate values. Therefore, as shown in  FIG. 1 , a plurality of oil ejection lines OL 1 , OL 2 , OL 3 , and OL 4  are formed behind the piston  6  that faces the combustion chamber  10   a  for effectively cooling particular areas. 
     According to the present embodiment, the nozzle pipe  21  may be made of metal in the form of a carbon steel pipe of SWCH, STKM, or the like, for example. 
     As shown in  FIG. 2 , the oil jet device  20  according to the present embodiment has an externally threaded surface  23   fm  on the outer circumference of a tubular portion of the main body  23 . As shown in  FIG. 3 , the crankcase  2  of the internal combustion engine  1  has, in a mount portion thereof, an internally threaded surface  2   m  into which the externally threaded surface  23   fm  is threaded. The main body  23  has on its lower end a head  23   he  in the shape of the head of a hexagon head bolt, for example, for an easy threading action. Therefore, the main body  23  can be threaded into and out of the crankcase  2  by the threading action by the main body  23  itself when it is turned about its own axis. The main body  23  and the holder  21   g  are relatively rotatable, so that the orientation of the nozzle pipe  21  will not be affected by the rotation of the main body  23 . 
     As shown in  FIG. 3 , the oil jet device  20  according to the present embodiment has a valve body housing  17  below a valve seat  27  within the main body  23 . The valve body housing  17  houses therein a check ball  25  as the valve body and a compression spring  24  as an elastic body for pressing the check ball  25 . The check ball  25  and a seat surface  27   r  on the lower end of the valve seat  27  jointly provide a check valve  18  for opening and closing the fluid communication passage  23   d . A filter  26  having a number of fluid communication holes  26   h  for filtering oil is disposed immediately upstream of the valve seat  27  of the check valve  18 . 
     In the check valve  18  configured as described above, when the oil pressure of an oil flow f 1  from the oil passageway  12  becomes equal to or greater than a certain level, the check ball  25  is unseated off the seat surface  27   r  of the valve seat  27 , allowing the oil to flow into the valve body housing  17  from which the oil is supplied through the fluid communication side hole  23   q  in the valve body housing  17  into the nozzle pipe  21 . 
     According to the present embodiment, the filter  26  is mounted in an opening  23   de  in the upstream end of the fluid communication passage  23   d . As shown in  FIG. 4 , the filter  26  includes a bottomed hollow cylinder with an open end  26   a  at one end (lower end in  FIG. 4 ) of a hollow cylindrical outer circumferential wall  26   e  thereof and a filter surface  26   b  at the other end thereof (upper end in  FIG. 4 ). The filter surface  26   b  includes a first facet  26   c  near the outer circumferential edge and a second facet  26   d  near the center which lies above the first facet  26   c  (the filter surface  26   b  is projected in the direction of the oil channel at the time the filter  26  is mounted in place). In other words, the filter surface  26   b  is of a two-stepped structure with its central area projecting upwardly. Both the first facet  26   c  and the second facet  26   d  have the plurality of fluid communication holes  26   h.    
     As shown in  FIG. 5 , the filter  26  is mounted in place such that the outer circumferential wall  26   e  is held in abutment against a circumferential edge wall  27   et  of an upstream end wall surface  27   e  of the valve seat  27 . The circumferential edge wall  27   et  positions the filter  26  which is inserted. The width W 7  of the circumferential edge wall  27   et  is equal to or greater than the thickness d 8  of the outer circumferential wall  26   e . The filter  26  is mounted in place when it is pushed into the upstream end opening  23   de , e.g., by being lightly press-fitted, for example. Specifically, the outside diameter D 2  of the outer circumferential wall  26   e  of the filter  26  is substantially the same as the inside diameter D 1  of the upstream end opening  23   de  to make it possible for the filter  26  to be press-fitted into the upstream end opening  23   de . The axial height H 3  of the upstream end opening  23   de  is greater than the height H 2  of the outer circumferential wall  26   e . As a result, the filter  26  is housed in place without projecting from the upstream end opening  23   de  (see  FIG. 2 ). 
     According to the present embodiment, as described above, the filter  26  is mounted in place by being press-fitted. The filter  26  should be press-fitted into position to the extent that the filter  26  can easily be mounted in or removed from the upstream end opening  26   de  manually by the worker, in an engaging state that may be called a “lightly press-fitted” state. The engaging state that allows the filter  26  to be easily mounted in or removed from the upstream end opening  26   de  makes the filter  26  be easily mounted and removed for better maintenance. 
     The diameter d 3  of each of the fluid communication holes  26   h  of the filter  26  is smaller than the minimum diameter d 4  (see  FIG. 6 ) of each of the oil ejection ports  33 . Therefore, the oil ejection ports  33  will not be clogged by minute foreign matter that has passed through the fluid communication holes  26   h.    
     A situation in which relatively large foreign matter that cannot pass through the fluid communication holes  26   h  is trapped by the filter  26  will be described below. In such a situation, the large foreign matter may block a large area of the filter surface  26   b . However, as shown in  FIGS. 4 and 5 , since the filter surface  26   b  is of a two-stepped structure having the first facet  26   c  and the second facet  26   d , a clearance tends to be created between the foreign matter and the filter surface  26   b  (filtration surface), securing the oil channel. As a result, the coil can continuously be supplied to the piston  6 . 
     The filter surface  26   b  which is recessed and projected in shape is increased in rigidity. Though the oil pressure is expected to rise due to the trap of foreign matter, the increased rigidity of the filter surface  26   b  makes the filter  26  higher in mechanical strength against deformation under the oil pressure buildup. 
     The recessed and projected structure of the filter  26  according to the present embodiment may be of a shape shown in  FIG. 7 , for example. The filter  26  shown in  FIG. 7  is of such a structure that the second facet  26   d  in the central area of the filter surface  26   b  is recessed downstream in the oil channel from the first facet  26   c  at the time the oil jet device  20  is mounted in place. This structure offers the same advantages as those of the projected structure described above. 
     As shown in  FIGS. 3 and 5  the inside diameter D 7  of the valve seat  27  according to the present embodiment is smaller than the inside diameter D 6  of the filter  26 . The upstream end wall surface  27   e  of the valve seat  27  faces at least some of the fluid communication holes  26   h . Specifically, the upstream end wall surface  27   e  faces the fluid communication holes  26   h  that are defined in the first facet  26   c  on the outer circumferential area of the filter surface  26   b . The upstream end wall surface  27   e  includes a slanted surface  27   es . The slanted surface  27   es  is arranged such that the cross-sectional area of the oil channel is progressively smaller in a direction from an upstream region toward a downstream region of the fluid communication passage  23   d.    
     As shown in  FIG. 5 , since the slanted surface  27   es  of the upstream end wall surface  27   e  faces a portion nearest the wall (close to an inner wall surface  23   dw ) of an oil flow f 2  that has passed through the fluid communication holes  26   h  (those fluid communication holes  26   h  in the outermost circumferential area on the left in  FIG. 5 ) of the filter  26 , the oil flow near the wall is gradually guided toward the central area as a slanted flow f 3 . 
     In the oil jet device  20  according to the present embodiment, the valve seat  27  is integrally formed with the main body  23 . Therefore, the check ball  25  and the compression spring  24  that are to be placed in the valve body housing  17  disposed downstream of the valve seat  27  are inserted through an insertion opening  17   a  defined in the lower end of the main body  23 . After the check ball  25  and the compression spring  24  have been inserted into the valve body housing  17 , a lid member  29  for closing the insertion opening  17   a  is press-fitted into position. 
     According to the present embodiment which is arranged as described above, the upstream end wall  27   e  of the valve seat  27  which faces the fluid communication holes  26   h  has the slanted surface  27   es  that is arranged such that the cross-sectional area of the oil channel is progressively smaller in the direction from the upstream region toward the downstream region of the oil channel. The cross-sectional area of the oil channel at the upstream end wall  27   e  is thus prevented from being abruptly reduced. With this structure, as the oil flow f 2  that has passed through the fluid communication holes  26   h  toward the slanted surface  27   es  partly forms the slanted flow f 3  gradually oriented toward the central area along the slanted surface  27   es  and gradually joins a straight flow f 4  that flows in the vicinity of the central area, disturbances of the oil flow are avoided immediately below the filter  26 . Consequently, an undisturbed stable flow f 5  is ensured in a portion of the fluid communication passage  23   d  where the cross-sectional area of the oil channel is small. 
     Therefore, even though the check valve  18  is disposed immediately behind the filter  26 , constricting the fluid communication passage  23   d , according to the present embodiment, this structure is able to reduce the pressure loss caused between the filter  26  and the upstream end wall surface  27   e . As a consequence, the oil jet device  20  is of a good response at the time it ejects the oil. 
     According to the present embodiment, the filter  26  is in the form of the bottomed hollow cylinder with the open end  26   a  at one end of the hollow cylindrical outer circumferential wall  26   e  thereof and the filter surface  26   b  with the fluid communication holes  26   h  at the other end thereof. Furthermore, since the filter  26  is disposed such that the outer circumferential wall  26   e  thereof is held in abutment against the upstream end wall surface  27   e  of the valve seat  27 , the filter  26  and the valve at  27  are disposed adjacent to each other. As a result, the main body  23  is compact in size. As the filter  26  is housed in the main body  23 , the oil jet device  20  is not only small in size but also can be handled and assembled in position with ease. 
     According to the present embodiment, because the valve seat  27  is integrally formed with the main body  23 , the valve seat  27  is increased in durability, and the number of parts of the check valve  18  is reduced, allowing the check valve  18  to be assembled in place with ease. The check ball  25  and the compression spring  24  of the check valve  18  are inserted through the insertion opening  17   a  of the valve body housing  17 , and then the lid member  29  is press-fitted into the insertion opening  17   a  to close the same. Therefore, the check valve  18  can be handled as a component assembled in the main body  2  and hence can be assembled in place with ease. 
     According to the present embodiment, since the plurality of fluid communication holes  26   h  are defined in the filter surface  26   b  in each of the outer circumferential and central areas thereof the entire filter surface  26   b  is widely used to ensure the flow rate of oil. As the inside diameter of each of the fluid communication holes  26   h  is smaller than the inside diameter of each of the oil ejection ports  33 , the oil ejection ports  33  are prevented from being clogged. 
     According to the present embodiment, the externally threaded surface  23   fm  is provided on the outer circumference of the tubular portion of the main body  23 , and the internally threaded surface  2   m  into which the externally threaded surface  23   fm  is threaded is provided in the internal combustion engine  1 . The main body  23  can thus directly be threaded into and secured to the internal combustion engine  1 . Therefore, no separate fastening member is required to fasten the oil jet device  20 , which is thus made compact. As the mounting structure for the main body  23  is made compact, when the oil jet device  20  is to be disposed in position, the oil jet device  20  is prevented from interfering with peripheral members of the internal combustion engine  1 , and the degree of freedom about the installed position of the oil jet device  20  is increased. 
     A second embodiment of the present invention will be described below with reference to  FIGS. 8 and 9 . 
     Those parts of an oil jet device  20  according to the second embodiment which are identical to those of the first embodiment will not be described in detail below, and components and peripheral components which are different from those of the first embodiment will be described below.  FIG. 8  is a fragmentary cross-sectional view of the oil jet device according to the second embodiment which is mounted in place. 
     As shown in  FIG. 8 , the oil jet device  20  according to the present embodiment is similar to the oil jet device  20  according to the first embodiment as to the structure wherein the filter  26  is mounted in the main body  23 , but is different therefrom as to the structure of the valve seat  27  and the valve body housing  17 . According to the present embodiment, the valve seat  27  includes a member separate from the main body  23 , and the valve body housing  17  has no insertion opening  17   a . The valve body housing  17  is formed by press-fitting the valve seat  27  through the upstream end opening  23   de  of the fluid communication passage  23   d . Specifically, after the compression spring  24  and the check hall  25  have been inserted through the upstream end opening  23   de , the valve seat  27  is press-fitted into the upstream end opening  23   de , making up the check valve  18 . 
     According to the present embodiment, as shown in  FIG. 9 , the inner wall surface  23   dw  that defines the fluid communication passage  23   d  has a step  23   dr  which reduces the inside diameter of the fluid communication passage  23   d . When the valve seat  27  is inserted, the step  23   dr  engages a downstream end  27   re  of the valve seat  27 , thereby determining an inserted position of the valve seat  27 . 
     According to the present embodiment, therefore, as the valve seat  27  includes a member separate from the main body the valve seat  27  can be press-fitted into the upstream end opening  23   de  of the fluid communication passage  23   d  after the compression spring  24  and the check ball  25  have been inserted through the upstream end opening  23   de . No special structure is necessary for assembling the components of the check valve  18  and the filter  26 . Consequently, the main body  23  is prevented from being structurally complex, and the oil jet device  20  is excellent in assemblability and good in productivity. 
     According to the present embodiment, moreover, since the inner wall surface  23   dw  that defines the fluid communication passage  23   d  has the step  23   dr  held in abutment against the downstream end  27   re  of the valve seat  27  to determine the inserted position of the valve seat  27 , the assembled position of the valve seat  27  can easily be determined simply when the valve seat  27  is press-fitted. Consequently, the assemblability of the oil jet device  20  is increased. As the mounted position of the valve at  27  is accurately established by the position of the step  23   dr , the process of setting a threshold value for the pressure for opening the check valve  18  is stabilized. 
     A third embodiment of the present invention will be described below with reference to  FIG. 10 . 
     Those parts of an oil jet device  20  according to the third embodiment which are identical to those of the second embodiment will not be described in detail below, and components and peripheral components which are different from those of the second embodiment will be described below.  FIG. 10  is a fragmentary cross-sectional view of the oil jet device according to the third embodiment which is mounted in place. 
     The oil jet device  20  shown in  FIG. 10  is of a structure identical to the structure of the second embodiment except for a so-called externally installed filter structure wherein the filter  26  is disposed outside of the main body  23 . 
     The filter  26  according to the present embodiment is of such a structure that an outer circumferential wall  23   f  of the distal end of the main body  23  is inserted in the outer circumferential wall  26   e  of the filter  26 . The filter  26  is positioned when the filter surface  26   b  is held in abutment against an upstream end  23   e  of the main body  21 . 
     According to the present embodiment, the outer circumferential wall  26   e  of the filter  26  is fitted over the outer circumferential wall  23   f  of the distal end of the main body  23 . As the main body  23  is threaded into place, it has the following structure described below. 
     The outside diameter of the outer circumferential wall  26   e  is slightly smaller than the outside diameter of the externally threaded surface  23   fm . When the externally threaded surface  23   fm  is threaded into the internally threaded surface  2   m , therefore, the filter  26  does not interfere with the internally threaded surface  2   m.    
     According to the present embodiment, as is the case with the internally installed filter structure, the filter  26  is press-fitted over the outer circumferential wall  23   f  of the distal end of the main body  23  to the extent that the filter  26  can easily be mounted and removed manually by the worker. 
     Since the filter  26  is fitted over the outer circumferential wall  23   f  of the upstream distal end of the main body  23  through removable engagement to the main body  23 , the oil jet device  20  can easily be mounted on and removed from the internal combustion engine  1  while the filter  26  is being held on the main body  23 . 
     For a maintenance process for replacing the filter  26 , for example, the filter  26  can directly be accessed simply by removing the main body  23  of the oil jet device  20  from the internal combustion engine  1 . Furthermore, as the filter surface  26   h , which is part of the filter  26 , is positionally limited by a wall surface  12   wr  in the oil passageway  12  which is disposed upstream of body  23 , the filter  26  will not be dislodged into a space near the piston. 
     According to the present embodiment, furthermore, the filter  26  is in the form of a bottomed hollow cylinder with the open end  26   a  at one end of the hollow cylindrical outer circumferential wall  26   e  thereof and the filter surface  26   b  with the fluid communication holes  26   h  at the other end thereof. Therefore, the filter  26  is mounted in place such that the outer circumferential wall  23   f  of the distal end of the main body  23  is inserted in the outer circumferential wall  26   e  of the filter  26 . Since the filter  26  is positioned with the filter surface  26   b  being held in abutment against the upstream end  23   e  of the main body  23 , the filter  26  and the main body  23  can be assembled together with no clearance left therebetween in a compact fashion. 
     A fourth embodiment of the present invention will be described below with reference to  FIG. 11 . 
     Those parts of an oil jet device  20  according to the fourth embodiment which are identical to those of the first embodiment will not be described in detail below, and components and peripheral components winch are different from those of the first embodiment will be described below.  FIG. 11  is a fragmentary cross-sectional view of the oil jet device according to the fourth embodiment which is mounted in place. 
     The oil jet device  20  shown in  FIG. 11  is of a structure identical to the structure of the first embodiment except for a so-called externally installed filter structure wherein the filter  26  is disposed outside of the main body  23 . 
     According to the present embodiment, the valve seat  27  is integrally formed with the main body  23 , and as is the case with the third embodiment described above, the filter  26  is of such a structure that the outer circumferential wall  23   f  of the distal end of the main body  23  is inserted in the outer circumferential wall  26   e  of the filter  26 . 
     According to the present embodiment, since the filter  26  is mounted on the outer circumferential wall  23   f  of the distal end of the main body  23 , the circumferential edge wall  27   et  (see  FIG. 5 ) for abutting against the outer circumferential wall  26   e  of the filter  26  may be dispensed with. Therefore, the slanted surface  27   es  may be formed so as to extend directly from the inner wall surface  23   dw  of the fluid communication passage  23   d , resulting in a structure which maximizes the reduction of the pressure loss. 
     A fifth embodiment of the present invention will be described below with reference to  FIG. 12 . 
     An oil jet device  20  according to the fifth embodiment has a basic structure having the filter  26  and the main body  23  which includes the check valve  28 , etc., which may be either one of the structures according to the first through fourth embodiments described above. However, the oil jet device  20  according to the fifth embodiment has two nozzle pipes  21  mounted on the holder  21   g . Such a structure is made possible by constructing the main body  23  and the holder  21   g  as separate members. 
     By thus using the main body  23  of the same structure and modifying the holder  21   g  and the nozzle pipes  21  mounted on the holder  21   g , the shape and number of the nozzle pipes  21  can appropriately be changed. Therefore, the oil jet device  20  which is easily capable of adapting itself to the structure of the internal combustion engine  1  is provided. 
     In the first through fifth embodiments described above, the present invention has been described as a cooling device for a piston in an internal combustion engine for use on a motorcycle. The present invention is not limited to such an application, but can be incorporated in various internal combustion engines for use on ATVs, four-wheeled motor vehicles, etc. 
     In the above embodiments, the slanted surface  27   es  is formed as a flat surface. However, the slanted surface  27   es  may be constructed as a curved surface having a suitable curvature. 
     The filter  26  is mounted in place by a structure in which it is inserted or press-fitted inside or outside of the main body  23 . However, the present invention is not limited to such a structure, but may employ various structures including a structure in which the filter  26  and the main body  23  are secured to each other by threaded engagement, a structure in which the filter  26  and the main body  23  are appropriately fitted together by recessed and projected shapes formed therebetween, or the like, for example. 
     In the above embodiments, the second facet  26   d  of the filter  26  is of a circular shape. However, the second facet  26   d  may be of a polygonal shape, for example, rather than the circular shape. 
     In the fifth embodiment, the oil jet device  20  is of a structure having two nozzle pipes  21 . However, the oil jet device  20  may be of a structure having three or more nozzle pipes  21 .