EP2949888A2 - Engine and vehicle - Google Patents
Engine and vehicle Download PDFInfo
- Publication number
- EP2949888A2 EP2949888A2 EP15163608.1A EP15163608A EP2949888A2 EP 2949888 A2 EP2949888 A2 EP 2949888A2 EP 15163608 A EP15163608 A EP 15163608A EP 2949888 A2 EP2949888 A2 EP 2949888A2
- Authority
- EP
- European Patent Office
- Prior art keywords
- cam shaft
- weight
- cam
- flange
- seen
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
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- 230000006837 decompression Effects 0.000 claims abstract description 75
- 230000005484 gravity Effects 0.000 claims description 15
- 230000002093 peripheral effect Effects 0.000 description 22
- 238000002485 combustion reaction Methods 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 208000004067 Flatfoot Diseases 0.000 description 2
- 230000006835 compression Effects 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- 239000007858 starting material Substances 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 238000005242 forging Methods 0.000 description 1
- 230000012447 hatching Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
Images
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
- F01L13/00—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations
- F01L13/08—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations for decompression, e.g. during starting; for changing compression ratio
Definitions
- the present invention relates to an engine equipped with a decompression mechanism, and to a vehicle.
- the engine When starting an engine, the engine needs to be rotated with an external force until the start is completed. For example, the engine may be rotated using a starter motor or using a kick starter. Conversely, resistance to the rotation increases because the air inside the cylinders is compressed during the compression stroke of the engine. In order to reduce this resistance, a decompression mechanism is known that reduces the pressure inside the cylinders during the compression stroke while the engine is being rotated using the external force.
- the decompression mechanism in an engine disclosed in Japanese Laid-Open Patent Publication No. 2008-128171 includes a decompression cam that alternates between an active state and a release state due to the rotation of a weight.
- This decompression mechanism is supported by a sprocket on a cam chain.
- the cam shaft that includes the decompression mechanism needs to be longer in the axial direction.
- the decompression mechanism described in Japanese Laid-Open Patent Publication No. 2008-64083 is able to effectively use the space between both ends of the cam shaft.
- the cam shaft that includes the decompression mechanism can be made more compact in the axial direction in comparison to a case in which the decompression mechanism is disposed outside of the cam shaft.
- a cam lobe of the exhaust cam has a larger dimension in the radial direction than the base circle portion and thus provides a higher degree of freedom for the attachment location of the support shaft in the radial direction.
- the range of the cam lobe is generally smaller than the range of the base circle portion in the circumferential direction of the exhaust cam. As a result, the attachment location for the support shaft is restricted in the circumferential direction of the exhaust cam.
- the aforementioned restriction of the disposition of the support shaft can be resolved by increasing the size of the exhaust cam.
- the sizes of the cam shaft and the valve mechanism also increase if the size of the exhaust cam is increased.
- the operating ranges of the cam shaft and the valve mechanism also increase if the sizes thereof are increased. As a result, the size of the engine would increase even if the decompression mechanism were disposed between the end portions of the cam shaft.
- An object of the present invention is to improve the degree of freedom for disposing a pivot pin and to make an engine more compact for an engine in which the decompression mechanism is disposed in a location between both end portions of the cam shaft.
- An engine according to the present invention is equipped with a cylinder head, an exhaust valve, a valve mechanism, a cam shaft, a bearing, and a decompression mechanism.
- the exhaust valve is housed inside the cylinder head.
- the valve mechanism opens and closes the exhaust valve.
- the cam shaft drives the valve mechanism by coming into contact with the valve mechanism.
- the bearing supports the cam shaft in a rotatable manner on the cylinder head.
- the decompression mechanism is disposed between both ends of the cam shaft in the axial direction.
- the decompression mechanism includes a flange, a pivot pin, a weight, and a decompression cam.
- the flange is a body separate from the cam shaft and is press-fitted onto the cam shaft.
- the pivot pin is attached to the flange.
- the weight is supported on the flange via the pivot pin in a rotatable manner between a closed state and an open state.
- the decompression cam switches between a state of coming into contact with a valve mechanism and a state of not coming into contact with the valve mechanism in response to a rotation of the weight.
- the flange is press-fitted onto the cam shaft in the engine according to the present invention, the location in the circumferential direction of the flange on the cam shaft during press-fitting can be set freely. Because the flange is a body separate from the cam shaft, increases in the sizes of the cam shaft and the valve mechanism and in the operating ranges thereof can be suppressed even if the size of the flange increases. As a result, the degree of freedom for disposing the pivot pin can be improved while making the engine more compact.
- the decompression cam is preferably supported on the flange.
- the locations of the weight and the decompression cam on the cam shaft can be changed without changing the relative locations of the weight and the decompression cam, by merely changing the location of the flange on the cam shaft because the weight and the decompression cam are both supported on the flange.
- a portion of the weight preferably overlaps the flange as seen from the radial direction of the cam shaft.
- the cam shaft that includes the decompression mechanism can be made more compact in the axial direction.
- the first region is located in the first vertical direction from the horizontal axis and in the first horizontal direction from the vertical axis.
- the weight includes a first portion that is disposed in the first region as seen from the axial direction of the cam shaft. At least a portion of the first portion overlaps the flange as seen from the radial direction of the cam shaft.
- the center of gravity of the weight can be placed further away from the center of rotation of the cam shaft. Therefore, the centrifugal force acting on the weight increases if the rotation speed of the cam shaft is the same. As a result, the spring force can be increased whereby the opening of the weight due to gravitational force can be suppressed without a rise in a set rotation speed.
- the decompression mechanism preferably further includes a return spring that urges the weight to return from the open state to the closed state.
- the weight or the flange includes a housing portion for housing the return spring.
- the cam shaft that includes the decompression mechanism can be made more compact in comparison to when the housing portion is provided on the outside of the weight or of the flange.
- the housing portion preferably has a recessed shape that is recessed from the surface of the weight or of the flange in the axial direction of the cam shaft.
- the cam shaft that includes the decompression mechanism can be made more compact in the axial direction.
- the flange preferably includes a locking portion for locking an end portion of the return spring.
- the locking portion is molded integrally with the flange. In this case, manufacturing of the decompression mechanism can be facilitated in comparison to when a shape for locking the end portion of the return spring is processed into the flange.
- the contour of the flange is preferably larger than the contour of the bearing as seen from the axial direction of the cam shaft. In this case, the degree of freedom for disposing the pivot pin can be improved because the flange is larger.
- the cam shaft preferably includes the exhaust cam that comes into contact with the valve mechanism.
- the exhaust cam includes a cam lobe that protrudes to the outside of a base circle. At least a portion of the pivot pin does not overlap the cam lobe as seen from the axial direction of the cam shaft. In this case, the pivot pin can be disposed in the location that does not overlap the cam lobe because the pivot pin is attached to the flange that is a body separate from the exhaust cam.
- a vehicle according to the present invention includes the above engine.
- the degree of freedom for disposing the pivot pin is improved and the engine can be made more compact in the engine in which the decompression mechanism is disposed in a location between both end portions of the cam shaft.
- FIG. 1 is a side view of the vehicle 1.
- the vehicle 1 is a scooter-type motorcycle.
- the vehicle 1 includes a vehicle body 2, a front wheel 3, a rear wheel 4, a handle 5, and a seat 6.
- the vehicle body 2 includes a flat foot board 2a.
- the vehicle body 2 supports the front wheel 3 and the rear wheel 4.
- the handle 5 and the seat 6 are attached to the vehicle body 2.
- the flat foot board 2a is disposed in front of and under the seat 6.
- the vehicle 1 includes an engine 7 according to the embodiments.
- FIG. 2 is a partial cross-sectional view of the engine 7.
- the engine 7 includes a crankshaft 11, a crankcase 12, a cylinder body 13, a cylinder head 14, and a head cover 19.
- the cylinder body 13 is connected to the crankcase 12.
- the cylinder body 13 may be integrated with the crankcase 12 or may be a separate body.
- the cylinder body 13 houses a piston 15.
- the piston 15 is coupled to the crankshaft 11 via a connecting rod 16.
- the crankshaft 11 is connected to a transmission 8.
- the cylinder head 14 is connected to the cylinder body 13.
- the cylinder head 14 includes a combustion chamber 17.
- a spark plug 18 is attached to the cylinder head 14.
- a distal end portion of the spark plug 18 is disposed so as to face the combustion chamber 17.
- the head cover 19 is attached to the cylinder head 14.
- the engine 7 includes a valve mechanism 25 and a cam shaft 26.
- the valve mechanism 25 and the cam shaft 26 are housed in the cylinder head 14.
- the cam shaft 26 drives the valve mechanism 25 by coming into contact with the valve mechanism 25.
- the cam shaft 26 is supported on the cylinder head 14.
- the cylinder head 14 includes a first supporting wall 141 and a second supporting wall 142.
- the first supporting wall 141 and the second supporting wall 142 are disposed so as to be aligned in the axial direction of the cam shaft 26 (referred to below as "cam shaft direction").
- the first supporting wall 141 supports the cam shaft 26.
- the first supporting wall 141 supports the cam shaft 26 via a first bearing 27.
- the second supporting wall 142 supports the cam shaft 26.
- the second supporting wall 142 supports the cam shaft 26 via a second bearing 28.
- the first bearing 27 and the second bearing 28 are supported in the cylinder head 14 in a manner that allows the cam shaft 26 to rotate.
- the outer diameter of the first bearing 27 is larger than the outer diameter of the second bearing 28.
- the first supporting wall 141 may support the cam shaft 26 without the first bearing 27.
- the second supporting wall 142 may support the cam shaft 26 without the second bearing 28.
- the cam shaft 26 includes a first cam shaft end portion 261 and a second cam shaft end portion 262.
- the first bearing 27 is disposed nearer the first cam shaft end portion 261 in the cam shaft direction than the second cam shaft end portion 262.
- the second bearing 28 is disposed nearer the second cam shaft end portion 262 in the cam shaft direction than the first cam shaft end portion 261.
- a cam chain 29 is wound around the cam shaft 26 and the crankshaft 11. Specifically, a first sprocket 31 is attached to the cam shaft 26. The first sprocket 31 is attached to the first cam shaft end portion 261. A second sprocket 32 is attached to the crankshaft 11. The cam chain 29 is wound around the first sprocket 31 and the second sprocket 32.
- the rotation of the crankshaft 11 is transmitted to the cam shaft 26 via the cam chain 29 whereby the cam shaft 26 rotates.
- the cam shaft 26 includes a suction cam 263 and an exhaust cam 264.
- the suction cam 263 and the exhaust cam 264 are disposed in a line in the cam shaft direction.
- the cam shaft 26 rotates whereby the suction cam 263 and the exhaust cam 264 rotate.
- the suction cam 263 and the exhaust cam 264 come into contact with the valve mechanism 25 and the valve mechanism 25 is driven by the rotation of the suction cam 263 and the exhaust cam 264.
- FIG. 3 is a cross-sectional view of the cylinder head 14 on a plane perpendicular to the cam shaft 26.
- the engine 7 includes an exhaust valve 23 and a suction valve 24.
- the cylinder head 14 includes a suction port 21 and an exhaust port 22 that communicate with the combustion chamber 17.
- the exhaust valve 23 and the suction valve 24 are housed in the cylinder head 14.
- the suction valve 24 opens and closes the suction port 21.
- the exhaust valve 23 opens and closes the exhaust port 22.
- the valve mechanism 25 opens and closes the suction valve 24 and the exhaust valve 23.
- a suction valve spring 241 is attached to the suction valve 24.
- the suction valve spring 241 urges the suction valve 24 in a direction that causes the suction valve 24 to close the suction port 21.
- An exhaust valve spring 231 is attached to the exhaust valve 23. The exhaust valve spring 231 urges the exhaust valve 23 in a direction that causes the exhaust valve 23 to close the exhaust port 22.
- the valve mechanism 25 includes an exhaust rocker shaft 33 and an exhaust rocker arm 34.
- the exhaust rocker shaft 33 is disposed parallel to the cam shaft 26.
- the exhaust rocker shaft 33 is supported on the cylinder head 14.
- the exhaust rocker arm 34 is supported on the exhaust rocker shaft 33 in a manner that enables swinging around the exhaust rocker shaft 33.
- the exhaust rocker arm 34 is provided in a manner that allows the exhaust valve 23 to operate.
- the exhaust rocker arm 34 includes an arm body 341, an exhaust roller 342, and an exhaust valve compressing portion 343.
- the arm body 341 is supported on the exhaust rocker shaft 33 in a manner that enables swinging.
- One end of the arm body 341 supports the exhaust roller 342 in a rotatable manner.
- the other end of the arm body 341 supports the exhaust valve compressing portion 343.
- the exhaust roller 342 comes into contact with the exhaust cam 264 and rotates due to the rotation of the exhaust cam 264.
- a distal end of the exhaust valve compressing portion 343 faces a stem end 232 of the exhaust valve 23.
- the valve mechanism 25 includes a suction rocker shaft 35 and a suction rocker arm 36.
- the suction rocker shaft 35 is disposed parallel to the cam shaft 26.
- the suction rocker shaft 35 is supported on the cylinder head 14.
- the suction rocker arm 36 is supported on the suction rocker shaft 35 in a manner that enables swinging around the suction rocker shaft 35.
- the suction rocker arm 36 is provided in a manner that allows the suction valve 24 to operate.
- the suction rocker arm 36 includes an arm body 361, a suction roller 362, and a suction valve compressing portion363.
- the arm body 361 is supported on the suction rocker shaft 35 in a manner that enables swinging.
- One end of the arm body 361 supports the suction roller 362 in a rotatable manner.
- the other end of the arm body 361 supports the suction valve compressing portion 363.
- the suction roller 362 comes into contact with the suction cam 263 and rotates due to the rotation of the suction cam 263.
- a distal end of the suction valve compressing portion 363 faces a stem end 242 of the suction valve 24.
- the engine 7 includes a decompression mechanism 40.
- FIG. 4 is an enlargement of an assembly (referred to as “cam shaft assembly” below) including the cam shaft 26, the decompression mechanism 40, and the first bearing 27.
- the decompression mechanism 40 is disposed between the first cam shaft end portion 261 and the second cam shaft end portion 262 in the cam shaft direction.
- the decompression mechanism 40 is disposed between the first supporting wall 141 and a second supporting wall 142 of the cylinder head 14.
- FIG. 5 is a perspective view of the cam shaft assembly.
- FIG. 6 is an exploded view of the cam shaft assembly.
- the decompression mechanism 40 includes a flange 41, a weight 42, a decompression cam 43, a decompression pin 44, and a return spring 45.
- the flange 41 is separate from the cam shaft 26 and is fixed to the cam shaft 26.
- the flange 41 includes a hole 411.
- the cam shaft 26 is inserted into the hole 411 of the flange 41 and the flange 41 is fixed to the cam shaft 26 by press-fitting.
- the flange 41 is disposed between the weight 42 and the exhaust cam 264 in the cam shaft direction.
- the flange 41 includes a first convex portion 412 and a second convex portion 413.
- a pivot pin 46 is attached to the first convex portion 412.
- a hole 414 is provided in the second convex portion 413.
- the decompression cam 43 is inserted into the hole 414 of the second convex portion 413.
- the weight 42 is disposed between the first bearing 27 and the flange 41 in the cam shaft direction.
- the weight 42 is supported on the cam shaft 26 in a rotatable manner between a closed state and an open state.
- FIGS. 7 and 8 are cross-sectional views along line A-A in FIG. 4 .
- FIG. 7 illustrates the weight 42 in the closed state.
- FIG. 8 illustrates the weight 42 in the open state.
- the decompression cam 43 is supported in a rotatable manner on the flange 41.
- the weight 42 is supported in a rotatable manner on the flange 41 via the pivot pin 46.
- the weight 42 switches between the closed state and the open state by rotating around the pivot pin 46.
- the decompression cam 43 is connected to the weight 42 via the decompression pin 44. As a result, the decompression cam 43 rotates in response to the rotation of the weight 42.
- the decompression cam 43 includes a head portion 431 and a shaft portion 432.
- the shaft portion 432 is inserted into the hole 414 of the flange 41.
- the head portion 431 is disposed between the flange 41 and the weight 42.
- the outer diameter of the head portion 431 is larger than the inner diameter of the hole 414 of the flange 41.
- the head portion 431 includes a groove portion 433.
- the groove portion 433 has a shape that is recessed from the end surface of the head portion 431.
- the groove portion 433 extends from the external peripheral surface of the head portion 431 toward the inside of the head portion 431.
- An end portion of the decompression pin 44 is disposed inside the groove portion 433.
- inside signifies the inside in the radial direction.
- outside signifies outside in the radial direction.
- the shaft portion 432 includes a cam portion 434.
- the exhaust cam 264 includes a recessed portion 265, and the recessed portion 265 has a shape that is recessed from the external peripheral surface of the exhaust cam 264 toward the inside of the exhaust cam 264.
- FIGS. 9 depicts enlargements of the exhaust cam 264.
- FIG. 10 is side view of the cam shaft assembly.
- the cam portion 434 is disposed inside the recessed portion 265 of the exhaust cam 264.
- a cross-section of the cam portion 434 has a shape that is circular with a portion cut out.
- the decompression cam 43 rotates in response to the rotation of the weight 42.
- FIG. 9(A) illustrates the decompression cam 43 when the weight 42 is in the open state.
- FIG. 9(B) illustrates the decompression cam 43 when the weight 42 is in the closed state.
- the decompression cam 43 switches between a state of coming into contact with the exhaust roller 342 of the valve mechanism 25 and a state of not coming into contact with the exhaust roller 342, in response to the rotation of the weight 42.
- the entire cam portion 434 of the decompression cam 43 is disposed inside the recessed portion 265 when the weight 42 is in the open state. That is, the cam portion 434 is in a state of not protruding to the outside from the external peripheral surface of the exhaust cam 264 when the weight 42 is in the open state. As a result, the decompression cam 43 does not come into contact with the exhaust roller 342 when the weight 42 is in the open state.
- a portion of the cam portion 434 of the decompression cam 43 is disposed outside of the recessed portion 265. That is, a portion of the cam portion 434 is in a state of protruding to the outside from the external peripheral surface of the exhaust cam 264 when the weight 42 is in the closed state. As a result, the decompression cam 43 comes into contact with the exhaust roller 342 when the weight 42 is in the closed state.
- a straight line that passes through the center of rotation C1 of the cam shaft 26 and the center of rotation C2 of the weight 42 is assumed to be a vertical axis Y as seen from the axial direction of the cam shaft.
- a straight line that is orthogonal to the vertical axis Y and passes through the center of rotation C1 of the cam shaft 26 is assumed to be a horizontal axis X.
- the direction that extends from the center of rotation C1 of the cam shaft 26 toward the center of rotation C2 of the weight 42 among directions parallel to the vertical axis Y is assumed to be a first vertical direction y1.
- the direction opposite the first vertical direction y1 is assumed to be a second vertical direction y2.
- One direction among the directions parallel to the horizontal axis X is assumed to be a first horizontal direction x1.
- the direction opposite the first horizontal direction x1 is assumed to be a second horizontal direction x2.
- FIG. 7 illustrates the weight 42 as seen from the first cam shaft end portion 261 side in the cam shaft direction. Therefore, the aforementioned directions x1, x2, y1, and y2 and the regions A1 to A4 are defined when seen from the first cam shaft end portion 261 side in the cam shaft direction, but the aforementioned directions x1, x2, y1, and y2 and the regions A1 to A4 may also be defined when seen from the second cam shaft end portion 262 side in the cam shaft direction.
- the weight 42 has a shape that extends along the circumferential direction of the cam shaft 26.
- the weight 42 is disposed around the cam shaft 26 in the first region A1, the second region A2, and the fourth region A4.
- the weight 42 has a shape that straddles a plurality of regions among the first to fourth regions A1 to A4 in the circumferential direction of the cam shaft 26.
- the weight 42 does not include a portion that is disposed in the third region A3 as seen from the cam shaft direction.
- the weight 42 includes a first weight portion 47 and a second weight portion 48.
- the first weight portion 47 extends from the center of rotation C2 of the weight 42 in the circumferential direction of the cam shaft 26 and in the first horizontal direction x1.
- An end portion 471 in the circumferential direction of the first weight portion 47 is located in the first horizontal direction x1 from the vertical axis Y. That is, the entire first weight portion 47 is located in the first horizontal direction x1 from the vertical axis Y.
- the end portion 471 of the first weight portion 47 is disposed in the second region A2 as seen from the cam shaft direction.
- the second weight portion 48 extends from the center of rotation C2 of the weight 42 in the circumferential direction of the cam shaft 26 and in the second horizontal direction x2.
- An end portion 481 in the circumferential direction of the second weight portion 48 is located in the second horizontal direction x2 from the vertical axis Y. That is, the entire second weight portion 48 is located in the second horizontal direction x2 from the vertical axis Y.
- the end portion 481 of the second weight portion 48 is disposed in the fourth region A4 as seen from the cam shaft direction.
- the first weight portion 47 is longer than the second weight portion 48 in the circumferential direction of the cam shaft 26. That is, an angle from the center of rotation C2 of the weight 42 to the end portion 471 of the first weight portion 47 around the center of rotation C1 of the cam shaft 26 is greater than an angle from the center of rotation C2 of the weight 42 to the end portion 481 of the second weight portion 48.
- the first weight portion 47 includes a first portion 421 and a second portion 422.
- the first portion 421 is disposed in the first region A1 as seen from the cam shaft direction.
- the second portion 422 is disposed in the second region A2 as seen from the cam shaft direction.
- the second weight portion 48 is disposed in the fourth region A4.
- the weight 42 includes a pivot pin support portion 423.
- the pivot pin support portion 423 is disposed across the first portion 421 and the second portion 422.
- the pivot pin 46 is attached to the pivot pin support portion 423.
- the exhaust cam 264 includes a cam lobe 267 that protrudes further to the outside than a base circle 266.
- a portion of the pivot pin 46 does not overlap the cam lobe 267 as seen from the cam shaft direction. That is, a portion of the pivot pin 46 is located to the outside of the external peripheral surface of the exhaust cam 264 as seen from the cam shaft direction.
- the pivot pin 46 further includes a portion located on the inside of the base circle 266 as seen from the cam shaft direction.
- the decompression pin 44 is connected to the first weight portion 47. Specifically, the decompression pin 44 is connected to the second portion 422.
- the decompression pin 44 is disposed in the second region A2 as seen from the cam shaft direction. A distance between the center of rotation C2 of the weight 42 and the decompression pin 44 as seen from the cam shaft direction is equal to or greater than a distance between the center of rotation C2 of the weight 42 and the center of rotation C1 of the cam shaft 26.
- FIG. 11 illustrates the cam shaft assembly as seen from the cam shaft direction.
- the contour of the flange 41 as seen from the cam shaft direction includes a portion larger than the contour of the first bearing 27.
- the first convex portion 412 protrudes to the outside of the external peripheral surface of the first bearing 27.
- the first portion 421 of the weight 42 in the closed state includes a first protruding portion 424.
- the first protruding portion 424 protrudes to the outside of the external peripheral surface of the first bearing 27 as seen from the cam shaft direction.
- the external peripheral surface of the second portion 422 is located on the inside of the external peripheral surface of the first bearing 27 as seen from the cam shaft direction.
- the external peripheral surface of the second weight portion 48 is located on the inside of the external peripheral surface of the first bearing 27 as seen from the cam shaft direction.
- the pivot pin support portion 423 includes a protruding portion 425 that protrudes to the outside of the external peripheral surface of the first bearing 27 as seen from the cam shaft direction.
- the maximum value of the protrusion length of the protruding portion 425 is greater than the maximum value of the protrusion length of the first protruding portion 424. That is, the protruding portion 425 protrudes more than the first protruding portion 424 in the radial direction of the first bearing 27.
- the protrusion length signifies the length of protrusion from the external peripheral surface of the first bearing 27 in the radial direction of the first bearing 27.
- the first bearing 27 includes an inner ring 271 and an outer ring 272.
- the inner ring 271 is in contact with the cam shaft 26.
- the outer ring 272 is in contact with the first supporting wall 141 of the cylinder head 14.
- the weight 42 includes an inner ring contact portion 426.
- the inner ring contact portion 426 is disposed in line with the inner ring 271 in the cam shaft direction.
- the inner ring contact portion 426 protrudes toward the inner ring 271 from the surface of the weight 42 adjacent to the first bearing 27.
- the inner ring contact portion 426 is located further to the inside than the inner peripheral surface of the outer ring 272.
- the inner ring contact portion 426 is located further to the inside than the inner peripheral surface of the outer ring 272 regardless of whether the weight 42 is in the closed state or the open state.
- At least a portion of the inner ring contact portion 426 is disposed nearer the center of rotation C2 of the weight 42 than the center of rotation C1 of the cam shaft 26 as seen from the cam shaft direction.
- the inner ring contact portion 426 is located between the center of rotation C2 of the weight 42 and the cam shaft 26 as seen from the cam shaft direction.
- the other portions of the weight 42 do not come into contact with the outer ring 272 in a state in which the inner ring contact portion 426 is in contact with the inner ring 271.
- the distance between the center of gravity G1 of the weight 42 and the center of rotation C1 of the cam shaft 26 is greater than the distance between the center of gravity G1 of the weight 42 and the center of rotation C2 of the weight 42.
- the first protruding portion 424 includes a near portion 424a and a distant portion 424b that are, as seen from the cam shaft direction, respectively nearer to and further away from the center of rotation C2 of the weight 42 in the circumferential direction of the first bearing 27 than the location of the center of gravity G2 of the weight 42 if there were no first protruding portion 424.
- the amount of protrusion outward from the external peripheral surface of the first bearing 27 is greater in the near portion 424a than in the distant portion 424b.
- a portion of the inner ring contact portion 426 nearer the center of rotation C2 of the weight 42 than the center of gravity G1 of the weight 42 is larger than a portion of the inner ring contact portion 426 further away from the center of rotation C2 of the weight 42 than the center of gravity G1 of the weight 42.
- the maximum width of the first contact portion 426a in the radial direction of the cam shaft 26 is greater than the maximum width of the second contact portion 426b in the radial direction of the cam shaft 26.
- FIG. 13 is a perspective view illustrating the surface on the second cam shaft end portion 262 side of the weight 42.
- FIG. 14 is side view of the cam shaft assembly as seen from the direction of arrow XIV in FIG. 10 .
- the maximum thickness of the first portion 421 in the cam shaft direction is greater than the maximum thickness of the second portion 422 in the cam shaft direction.
- the maximum thickness of the second weight portion 48 in the cam shaft direction is greater than the maximum thickness of the second portion 422 in the cam shaft direction.
- a portion of the weight 42 overlaps the flange 41 as seen from the radial direction of the cam shaft 26.
- the outer diameter portion 421b of the first portion 421 overlaps the flange 41 as seen from the radial direction of the cam shaft 26.
- the surface of the second weight portion 48 and the surface of the inner diameter portion 421a on the second cam shaft end portion 262 side face the surface of the flange 41 on the first cam shaft end portion 261 side.
- the aforementioned head portion 431 of the decompression cam 43 is disposed between the second portion 422 and the flange 41.
- the pivot pin support portion 423 includes a housing portion 423a and a boss portion 423b.
- the boss portion 423b protrudes from the housing portion 423a in the cam shaft direction.
- the thickness of the housing portion 423a in the cam shaft direction is less than the thicknesses of the first portion 421 and the second weight portion 48 in the cam shaft direction. Therefore, the housing portion 423a has a shape that is recessed in the cam shaft direction from the surface of the weight 42.
- FIG. 15 is a view of the flange 41, the weight 42, and the return spring 45 as seen from the second cam shaft end portion 262 side.
- the housing portion 423a houses the return spring 45.
- the boss portion 423b is inserted into the aforementioned return spring 45.
- a hole 423c is provided in the boss portion 423b.
- the pivot pin 46 is inserted into the hole 423c of the boss portion 423b.
- the weight 42 includes a second locking portion 42b.
- the second locking portion 42b locks the second spring end portion 452 of the return spring 45.
- the second locking portion 42b is included in the first portion 421.
- the second locking portion 42b is a stepped portion shaped with regard to the pivot pin support portion 423 in the first portion 421.
- the flange 41 includes a first locking section 42a.
- the first locking section 42a locks the first spring end portion 451 of the return spring 45.
- the first locking section 42a is a portion of the first convex portion 412.
- the first locking section 42a is formed integrally with the flange 41.
- the flange 41 is formed integrally to include the first locking section 42a using a manufacturing method such as sintering, forging, or casting.
- FIG. 16 illustrates the cylinder head 14 in a state in which the head cover 19 is removed.
- the cylinder head 14 includes a first bearing support hole 143.
- the first bearing support hole 143 supports the first bearing 27.
- the first bearing support hole 143 is provided in the first supporting wall 141.
- the first bearing support hole 143 includes a first recessed portion 144, a second recessed portion 145, and a third recessed portion 146.
- the first recessed portion 144, the second recessed portion 145, and the third recessed portion 146 are located on the side opposite the crankshaft 11 from the center of the first bearing support hole 143.
- the first recessed portion 144 has a shape that allows the passage of the first protruding portion 424 and the suction cam 263.
- the second recessed portion 145 has a shape that allows the passage of the exhaust cam 264.
- the third recessed portion 146 has a shape that allows the passage of the pivot pin support portion 423.
- a portion of the first recessed portion 144 may be located on the opposite side of the crankshaft 11 from the center of the first bearing support hole 143, and the other portion of the first recessed portion 144 may be located on the same side as the crankshaft 11 from the center of the first bearing support hole 143.
- a portion of the second recessed portion 145 may be located on the opposite side of the crankshaft 11 from the center of the first bearing support hole 143, and the other portion of the second recessed portion 145 may be located on the same side as the crankshaft 11 from the center of the first bearing support hole 143.
- the location in the circumferential direction of the flange 41 with regard to the cam shaft 26 during press-fitting can be set freely. Further, because the flange 41 is a body separate from the cam shaft 26, increases in the sizes of the cam shaft 26 and the valve mechanism 25 and increases in the operating ranges thereof can be suppressed even if the size of the flange 41 is increased. As a result, the degree of freedom for disposing the pivot pin 46 can be improved while making the engine 7 more compact.
- the decompression cam 43 is supported on the flange 41.
- the locations of the weight 42 and the decompression cam 43 on the cam shaft 26 can be changed without changing the relative locations of the weight 42 and the decompression cam 43, by merely changing the location of the flange 41 on the cam shaft 26 because the weight 42 and the decompression cam 43 are both supported on the flange 41.
- the cam shaft 26 that includes the decompression mechanism 40 can be made more compact in the cam shaft direction.
- the center of gravity G1 of the weight 42 is disposed in the first region A1 as seen from the cam shaft direction.
- the weight 42 includes a first portion 421 that is disposed in the first region A1 as seen from the cam shaft direction. A portion of the first portion 421 overlaps the flange 41 as seen from the radial direction of the cam shaft 26.
- the center of gravity G1 of the weight 42 can be provided further away from the center of rotation C1 of the cam shaft 26. Therefore, the centrifugal force acting on the weight 42 increases if the rotation speed of the cam shaft 26 is the same. As a result, opening of the weight 42 due to gravitational force can be suppressed without raising the set rotation speed because the spring force of the return spring 45 is increased.
- the weight 42 includes the housing portion 423a for housing the return spring 45.
- the cam shaft 26 that includes the decompression mechanism 40 can be made more compact in comparison to when the housing portion 423a is provided on the outside of the weight 42.
- the housing portion 423a has a recessed shape that is recessed in the cam shaft direction from the surface of the weight 42. As a result, the cam shaft 26 that includes the decompression mechanism 40 can be made more compact in the cam shaft direction.
- the flange 41 includes the first locking section 42a that locks the first spring end portion 451 of the return spring 45.
- the first locking section 42a is formed integrally with the flange 41. As a result, the manufacturing of the decompression mechanism 40 can be facilitated in comparison to when a shape for locking the first locking section 42a of the return spring 45 is processed into the flange 41.
- the contour of the flange 41 as seen from the cam shaft direction includes a portion larger than the contour of the first bearing 27. Specifically, the first convex portion 412 of the flange 41 protrudes to the outside of the external peripheral surface of the first bearing 27. In this case, the degree of freedom for disposing the pivot pin 46 can be improved.
- the shape of the weight 42 is not limited to the shape of the above embodiment and may be changed.
- the length in the circumferential direction of the weight can be made shorter than that of the weight 42 of the above embodiment.
- a circumferential direction end portion 471 of the first weight portion 47 may be disposed in the first region A1.
- the length in the circumferential direction of the weight can be made longer than that of the weight 42 of the above embodiment.
- the circumferential direction end portion 471 of the first weight portion 47 may be disposed in the third region A3.
- the first protruding portion 424 of the weight 42 may be omitted. That is, the first portion 421 may be located on the inside of the external peripheral surface of the first bearing 27 as seen from the cam shaft direction.
- the center of gravity G1 of the weight 42 is not limited to the disposition in the first region A1 and may be disposed in another region.
- the center of gravity G1 of the weight 42 may be disposed in the second region A2.
- the location of the pivot pin 46 is not limited to the location of the above embodiment and may be changed.
- the entire pivot pin 46 may be disposed in a location that does not overlap the cam lobe 267. That is, the entire pivot pin 46 may be disposed to the outside of the external peripheral surface of the cam lobe 267.
- the shape of the inner ring contact portion is not limited to the shape of the above embodiment and may be changed. Alternatively, the inner ring contact portion of the weight 42 may be omitted.
- the housing portion for housing the return spring may be provided on the flange instead of the on the weight.
- the housing portion preferably has a recessed shape that is recessed from the surface of the flange in the axial direction of the cam shaft.
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Valve Device For Special Equipments (AREA)
- Valve-Gear Or Valve Arrangements (AREA)
Abstract
Description
- The present invention relates to an engine equipped with a decompression mechanism, and to a vehicle.
- When starting an engine, the engine needs to be rotated with an external force until the start is completed. For example, the engine may be rotated using a starter motor or using a kick starter. Conversely, resistance to the rotation increases because the air inside the cylinders is compressed during the compression stroke of the engine. In order to reduce this resistance, a decompression mechanism is known that reduces the pressure inside the cylinders during the compression stroke while the engine is being rotated using the external force.
- For example, the decompression mechanism in an engine disclosed in Japanese Laid-Open Patent Publication No.
2008-128171 - The engine disclosed in Japanese Laid-Open Patent Publication No.
2008-64083 - The decompression mechanism described in Japanese Laid-Open Patent Publication No.
2008-64083 - A support shaft for a weight is attached to an exhaust cam on the cam shaft in the decompression mechanism in Japanese Laid-Open Patent Publication No.
2008-64083 - Conversely, a cam lobe of the exhaust cam has a larger dimension in the radial direction than the base circle portion and thus provides a higher degree of freedom for the attachment location of the support shaft in the radial direction. However, the range of the cam lobe is generally smaller than the range of the base circle portion in the circumferential direction of the exhaust cam. As a result, the attachment location for the support shaft is restricted in the circumferential direction of the exhaust cam.
- The aforementioned restriction of the disposition of the support shaft can be resolved by increasing the size of the exhaust cam. However, the sizes of the cam shaft and the valve mechanism also increase if the size of the exhaust cam is increased. Moreover, the operating ranges of the cam shaft and the valve mechanism also increase if the sizes thereof are increased. As a result, the size of the engine would increase even if the decompression mechanism were disposed between the end portions of the cam shaft.
- An object of the present invention is to improve the degree of freedom for disposing a pivot pin and to make an engine more compact for an engine in which the decompression mechanism is disposed in a location between both end portions of the cam shaft.
- This object is solved by an engine according to
claim 1 and a vehicle according to claim 10. Advantageous further developments of the invention are specified in the dependent claims and described in the specification. - An engine according to the present invention is equipped with a cylinder head, an exhaust valve, a valve mechanism, a cam shaft, a bearing, and a decompression mechanism. The exhaust valve is housed inside the cylinder head. The valve mechanism opens and closes the exhaust valve. The cam shaft drives the valve mechanism by coming into contact with the valve mechanism. The bearing supports the cam shaft in a rotatable manner on the cylinder head. The decompression mechanism is disposed between both ends of the cam shaft in the axial direction. The decompression mechanism includes a flange, a pivot pin, a weight, and a decompression cam. The flange is a body separate from the cam shaft and is press-fitted onto the cam shaft. The pivot pin is attached to the flange. The weight is supported on the flange via the pivot pin in a rotatable manner between a closed state and an open state. The decompression cam switches between a state of coming into contact with a valve mechanism and a state of not coming into contact with the valve mechanism in response to a rotation of the weight.
- Because the flange is press-fitted onto the cam shaft in the engine according to the present invention, the location in the circumferential direction of the flange on the cam shaft during press-fitting can be set freely. Because the flange is a body separate from the cam shaft, increases in the sizes of the cam shaft and the valve mechanism and in the operating ranges thereof can be suppressed even if the size of the flange increases. As a result, the degree of freedom for disposing the pivot pin can be improved while making the engine more compact.
- The decompression cam is preferably supported on the flange. In this case, the locations of the weight and the decompression cam on the cam shaft can be changed without changing the relative locations of the weight and the decompression cam, by merely changing the location of the flange on the cam shaft because the weight and the decompression cam are both supported on the flange.
- A portion of the weight preferably overlaps the flange as seen from the radial direction of the cam shaft. In this case, the cam shaft that includes the decompression mechanism can be made more compact in the axial direction.
- The center of gravity of the weight is preferably disposed in a first region as seen from the axial direction of the cam shaft. A straight line that passes through the center of rotation of the cam shaft and the center of rotation of the weight is assumed to be a vertical axis as seen from the axial direction of the cam shaft. A straight line that is orthogonal to the vertical axis and that passes through the center of rotation of the cam shaft is assumed to be a horizontal axis. A direction from the center of rotation of the cam shaft toward the center of rotation of the weight among directions parallel to the vertical axis is assumed to be a first vertical direction. One direction among the directions parallel to the horizontal axis is assumed to be a first horizontal direction. The first region is located in the first vertical direction from the horizontal axis and in the first horizontal direction from the vertical axis. The weight includes a first portion that is disposed in the first region as seen from the axial direction of the cam shaft. At least a portion of the first portion overlaps the flange as seen from the radial direction of the cam shaft.
- In this case, the center of gravity of the weight can be placed further away from the center of rotation of the cam shaft. Therefore, the centrifugal force acting on the weight increases if the rotation speed of the cam shaft is the same. As a result, the spring force can be increased whereby the opening of the weight due to gravitational force can be suppressed without a rise in a set rotation speed.
- The decompression mechanism preferably further includes a return spring that urges the weight to return from the open state to the closed state. The weight or the flange includes a housing portion for housing the return spring. In this case, the cam shaft that includes the decompression mechanism can be made more compact in comparison to when the housing portion is provided on the outside of the weight or of the flange.
- The housing portion preferably has a recessed shape that is recessed from the surface of the weight or of the flange in the axial direction of the cam shaft. In this case, the cam shaft that includes the decompression mechanism can be made more compact in the axial direction.
- The flange preferably includes a locking portion for locking an end portion of the return spring. The locking portion is molded integrally with the flange. In this case, manufacturing of the decompression mechanism can be facilitated in comparison to when a shape for locking the end portion of the return spring is processed into the flange.
- The contour of the flange is preferably larger than the contour of the bearing as seen from the axial direction of the cam shaft. In this case, the degree of freedom for disposing the pivot pin can be improved because the flange is larger.
- The cam shaft preferably includes the exhaust cam that comes into contact with the valve mechanism. The exhaust cam includes a cam lobe that protrudes to the outside of a base circle. At least a portion of the pivot pin does not overlap the cam lobe as seen from the axial direction of the cam shaft. In this case, the pivot pin can be disposed in the location that does not overlap the cam lobe because the pivot pin is attached to the flange that is a body separate from the exhaust cam.
- A vehicle according to the present invention includes the above engine.
- According to the present invention, the degree of freedom for disposing the pivot pin is improved and the engine can be made more compact in the engine in which the decompression mechanism is disposed in a location between both end portions of the cam shaft.
-
FIG. 1 is a side view of a vehicle. -
FIG. 2 is a partial cross-sectional view of an engine. -
FIG. 3 is a cross-sectional view of a cylinder head on a plane perpendicular to a cam shaft. -
FIG. 4 is an enlarged cross-sectional view of a cam shaft assembly. -
FIG. 5 is a perspective view of the cam shaft assembly. -
FIG. 6 is an exploded view of the cam shaft assembly. -
FIG. 7 illustrates a weight in a closed state. -
FIG. 8 illustrates a weight in an open state. -
FIGS. 9 depicts enlargements of an exhaust cam. -
FIG. 10 is side view of the cam shaft assembly. -
FIG. 11 illustrates the cam shaft assembly as seen from the axial direction of the cam shaft. -
FIG. 12 illustrates the weight as seen from the axial direction of the cam shaft. -
FIG. 13 is a perspective view of the weight. -
FIG. 14 is side view of the cam shaft assembly as seen from the direction of arrow XIV inFIG. 10 . -
FIG. 15 illustrates a flange, the weight, and a return spring as seen from the axial direction of the cam shaft. -
FIG. 16 illustrates a cylinder head while a head cover is removed. - The following is an explanation of a
vehicle 1 according to the embodiments with reference to the drawings.FIG. 1 is a side view of thevehicle 1. Thevehicle 1 is a scooter-type motorcycle. Thevehicle 1 includes avehicle body 2, afront wheel 3, arear wheel 4, ahandle 5, and a seat 6. Thevehicle body 2 includes aflat foot board 2a. Thevehicle body 2 supports thefront wheel 3 and therear wheel 4. Thehandle 5 and the seat 6 are attached to thevehicle body 2. Theflat foot board 2a is disposed in front of and under the seat 6. - The
vehicle 1 includes an engine 7 according to the embodiments.FIG. 2 is a partial cross-sectional view of the engine 7. As illustrated inFIG. 2 , the engine 7 includes acrankshaft 11, acrankcase 12, acylinder body 13, acylinder head 14, and ahead cover 19. Thecylinder body 13 is connected to thecrankcase 12. Thecylinder body 13 may be integrated with thecrankcase 12 or may be a separate body. Thecylinder body 13 houses apiston 15. Thepiston 15 is coupled to thecrankshaft 11 via a connectingrod 16. Thecrankshaft 11 is connected to atransmission 8. - The
cylinder head 14 is connected to thecylinder body 13. Thecylinder head 14 includes acombustion chamber 17. Aspark plug 18 is attached to thecylinder head 14. A distal end portion of thespark plug 18 is disposed so as to face thecombustion chamber 17. Thehead cover 19 is attached to thecylinder head 14. - The engine 7 includes a
valve mechanism 25 and acam shaft 26. Thevalve mechanism 25 and thecam shaft 26 are housed in thecylinder head 14. Thecam shaft 26 drives thevalve mechanism 25 by coming into contact with thevalve mechanism 25. - The
cam shaft 26 is supported on thecylinder head 14. Thecylinder head 14 includes a first supportingwall 141 and a second supportingwall 142. The first supportingwall 141 and the second supportingwall 142 are disposed so as to be aligned in the axial direction of the cam shaft 26 (referred to below as "cam shaft direction"). The first supportingwall 141 supports thecam shaft 26. The first supportingwall 141 supports thecam shaft 26 via afirst bearing 27. The second supportingwall 142 supports thecam shaft 26. The second supportingwall 142 supports thecam shaft 26 via asecond bearing 28. Thefirst bearing 27 and thesecond bearing 28 are supported in thecylinder head 14 in a manner that allows thecam shaft 26 to rotate. The outer diameter of thefirst bearing 27 is larger than the outer diameter of thesecond bearing 28. The first supportingwall 141 may support thecam shaft 26 without thefirst bearing 27. The second supportingwall 142 may support thecam shaft 26 without thesecond bearing 28. - The
cam shaft 26 includes a first camshaft end portion 261 and a second camshaft end portion 262. Thefirst bearing 27 is disposed nearer the first camshaft end portion 261 in the cam shaft direction than the second camshaft end portion 262. Thesecond bearing 28 is disposed nearer the second camshaft end portion 262 in the cam shaft direction than the first camshaft end portion 261. - A
cam chain 29 is wound around thecam shaft 26 and thecrankshaft 11. Specifically, afirst sprocket 31 is attached to thecam shaft 26. Thefirst sprocket 31 is attached to the first camshaft end portion 261. Asecond sprocket 32 is attached to thecrankshaft 11. Thecam chain 29 is wound around thefirst sprocket 31 and thesecond sprocket 32. - The rotation of the
crankshaft 11 is transmitted to thecam shaft 26 via thecam chain 29 whereby thecam shaft 26 rotates. Thecam shaft 26 includes asuction cam 263 and anexhaust cam 264. Thesuction cam 263 and theexhaust cam 264 are disposed in a line in the cam shaft direction. Thecam shaft 26 rotates whereby thesuction cam 263 and theexhaust cam 264 rotate. Thesuction cam 263 and theexhaust cam 264 come into contact with thevalve mechanism 25 and thevalve mechanism 25 is driven by the rotation of thesuction cam 263 and theexhaust cam 264. -
FIG. 3 is a cross-sectional view of thecylinder head 14 on a plane perpendicular to thecam shaft 26. As illustrated inFIG. 3 , the engine 7 includes anexhaust valve 23 and asuction valve 24. Thecylinder head 14 includes asuction port 21 and anexhaust port 22 that communicate with thecombustion chamber 17. Theexhaust valve 23 and thesuction valve 24 are housed in thecylinder head 14. Thesuction valve 24 opens and closes thesuction port 21. Theexhaust valve 23 opens and closes theexhaust port 22. Thevalve mechanism 25 opens and closes thesuction valve 24 and theexhaust valve 23. - A
suction valve spring 241 is attached to thesuction valve 24. Thesuction valve spring 241 urges thesuction valve 24 in a direction that causes thesuction valve 24 to close thesuction port 21. Anexhaust valve spring 231 is attached to theexhaust valve 23. Theexhaust valve spring 231 urges theexhaust valve 23 in a direction that causes theexhaust valve 23 to close theexhaust port 22. - The
valve mechanism 25 includes anexhaust rocker shaft 33 and anexhaust rocker arm 34. Theexhaust rocker shaft 33 is disposed parallel to thecam shaft 26. Theexhaust rocker shaft 33 is supported on thecylinder head 14. Theexhaust rocker arm 34 is supported on theexhaust rocker shaft 33 in a manner that enables swinging around theexhaust rocker shaft 33. Theexhaust rocker arm 34 is provided in a manner that allows theexhaust valve 23 to operate. Theexhaust rocker arm 34 includes anarm body 341, anexhaust roller 342, and an exhaustvalve compressing portion 343. - The
arm body 341 is supported on theexhaust rocker shaft 33 in a manner that enables swinging. One end of thearm body 341 supports theexhaust roller 342 in a rotatable manner. The other end of thearm body 341 supports the exhaustvalve compressing portion 343. Theexhaust roller 342 comes into contact with theexhaust cam 264 and rotates due to the rotation of theexhaust cam 264. A distal end of the exhaustvalve compressing portion 343 faces astem end 232 of theexhaust valve 23. - When the
exhaust roller 342 is pushed upward due to theexhaust cam 264, the exhaustvalve compressing portion 343 presses down on the stem end 232 of theexhaust valve 23 due to the swinging of theexhaust rocker arm 34. As a result, theexhaust valve 23 is pressed down and theexhaust port 22 is opened. When theexhaust roller 342 is not pushed upward by theexhaust cam 264, theexhaust valve 23 is pressed upward by theexhaust valve spring 231 and theexhaust port 22 is closed. - The
valve mechanism 25 includes asuction rocker shaft 35 and asuction rocker arm 36. Thesuction rocker shaft 35 is disposed parallel to thecam shaft 26. Thesuction rocker shaft 35 is supported on thecylinder head 14. Thesuction rocker arm 36 is supported on thesuction rocker shaft 35 in a manner that enables swinging around thesuction rocker shaft 35. Thesuction rocker arm 36 is provided in a manner that allows thesuction valve 24 to operate. Thesuction rocker arm 36 includes anarm body 361, asuction roller 362, and a suction valve compressing portion363. - The
arm body 361 is supported on thesuction rocker shaft 35 in a manner that enables swinging. One end of thearm body 361 supports thesuction roller 362 in a rotatable manner. The other end of thearm body 361 supports the suctionvalve compressing portion 363. Thesuction roller 362 comes into contact with thesuction cam 263 and rotates due to the rotation of thesuction cam 263. A distal end of the suctionvalve compressing portion 363 faces astem end 242 of thesuction valve 24. - When the
suction roller 362 is pushed upward due to thesuction cam 263, the suctionvalve compressing portion 363 presses down on the stem end 242 of thesuction valve 24 due to the swinging of thesuction rocker arm 36. As a result, thesuction valve 24 is pressed down and thesuction port 21 is opened. When thesuction roller 362 is not pushed upward by thesuction cam 263, thesuction valve 24 is pressed upward by thesuction valve spring 241 and thesuction port 21 is closed. - As illustrated in
FIG. 2 , the engine 7 includes adecompression mechanism 40.FIG. 4 is an enlargement of an assembly (referred to as "cam shaft assembly" below) including thecam shaft 26, thedecompression mechanism 40, and thefirst bearing 27. Thedecompression mechanism 40 is disposed between the first camshaft end portion 261 and the second camshaft end portion 262 in the cam shaft direction. Thedecompression mechanism 40 is disposed between the first supportingwall 141 and a second supportingwall 142 of thecylinder head 14. -
FIG. 5 is a perspective view of the cam shaft assembly.FIG. 6 is an exploded view of the cam shaft assembly. As illustrated inFIGS. 5 and6 , thedecompression mechanism 40 includes aflange 41, aweight 42, adecompression cam 43, adecompression pin 44, and areturn spring 45. - As illustrated in
FIG. 6 , theflange 41 is separate from thecam shaft 26 and is fixed to thecam shaft 26. Specifically, theflange 41 includes ahole 411. Thecam shaft 26 is inserted into thehole 411 of theflange 41 and theflange 41 is fixed to thecam shaft 26 by press-fitting. Theflange 41 is disposed between theweight 42 and theexhaust cam 264 in the cam shaft direction. - The
flange 41 includes a firstconvex portion 412 and a secondconvex portion 413. Apivot pin 46 is attached to the firstconvex portion 412. Ahole 414 is provided in the secondconvex portion 413. Thedecompression cam 43 is inserted into thehole 414 of the secondconvex portion 413. - The
weight 42 is disposed between thefirst bearing 27 and theflange 41 in the cam shaft direction. Theweight 42 is supported on thecam shaft 26 in a rotatable manner between a closed state and an open state. -
FIGS. 7 and8 are cross-sectional views along line A-A inFIG. 4 .FIG. 7 illustrates theweight 42 in the closed state.FIG. 8 illustrates theweight 42 in the open state. - The
decompression cam 43 is supported in a rotatable manner on theflange 41. Specifically, theweight 42 is supported in a rotatable manner on theflange 41 via thepivot pin 46. Theweight 42 switches between the closed state and the open state by rotating around thepivot pin 46. - The
decompression cam 43 is connected to theweight 42 via thedecompression pin 44. As a result, thedecompression cam 43 rotates in response to the rotation of theweight 42. - Specifically as illustrated in
FIGS. 4 and6 , thedecompression cam 43 includes ahead portion 431 and ashaft portion 432. Theshaft portion 432 is inserted into thehole 414 of theflange 41. Thehead portion 431 is disposed between theflange 41 and theweight 42. The outer diameter of thehead portion 431 is larger than the inner diameter of thehole 414 of theflange 41. Thehead portion 431 includes agroove portion 433. Thegroove portion 433 has a shape that is recessed from the end surface of thehead portion 431. Thegroove portion 433 extends from the external peripheral surface of thehead portion 431 toward the inside of thehead portion 431. An end portion of thedecompression pin 44 is disposed inside thegroove portion 433. In the present embodiment, inside signifies the inside in the radial direction. Further, outside signifies outside in the radial direction. - The
shaft portion 432 includes acam portion 434. Theexhaust cam 264 includes a recessedportion 265, and the recessedportion 265 has a shape that is recessed from the external peripheral surface of theexhaust cam 264 toward the inside of theexhaust cam 264.FIGS. 9 depicts enlargements of theexhaust cam 264.FIG. 10 is side view of the cam shaft assembly. - The
cam portion 434 is disposed inside the recessedportion 265 of theexhaust cam 264. A cross-section of thecam portion 434 has a shape that is circular with a portion cut out. As mentioned above, thedecompression cam 43 rotates in response to the rotation of theweight 42.FIG. 9(A) illustrates thedecompression cam 43 when theweight 42 is in the open state.FIG. 9(B) illustrates thedecompression cam 43 when theweight 42 is in the closed state. Thedecompression cam 43 switches between a state of coming into contact with theexhaust roller 342 of thevalve mechanism 25 and a state of not coming into contact with theexhaust roller 342, in response to the rotation of theweight 42. - Specifically as illustrated in
FIG. 9(A) , theentire cam portion 434 of thedecompression cam 43 is disposed inside the recessedportion 265 when theweight 42 is in the open state. That is, thecam portion 434 is in a state of not protruding to the outside from the external peripheral surface of theexhaust cam 264 when theweight 42 is in the open state. As a result, thedecompression cam 43 does not come into contact with theexhaust roller 342 when theweight 42 is in the open state. - When the
weight 42 is in the closed state as illustrated inFIG. 9(B) , a portion of thecam portion 434 of thedecompression cam 43 is disposed outside of the recessedportion 265. That is, a portion of thecam portion 434 is in a state of protruding to the outside from the external peripheral surface of theexhaust cam 264 when theweight 42 is in the closed state. As a result, thedecompression cam 43 comes into contact with theexhaust roller 342 when theweight 42 is in the closed state. - The
return spring 45 urges theweight 42 to return to the closed state from the open state. In the present embodiment, thereturn spring 45 is a coil spring. However, thereturn spring 45 may be another type of spring. As illustrated inFIG. 6 , thereturn spring 45 includes a firstspring end portion 451 and a secondspring end portion 452. The firstspring end portion 451 extends in the cam shaft direction. The secondspring end portion 452 extends in a direction that is orthogonal to the cam shaft direction. The secondspring end portion 452 extends in the circumferential direction of thereturn spring 45. The firstspring end portion 451 is locked to theflange 41. The secondspring end portion 452 is locked to theweight 42. - The following is a detailed description of the structure of the
weight 42. As illustrated inFIG. 7 , a straight line that passes through the center of rotation C1 of thecam shaft 26 and the center of rotation C2 of theweight 42 is assumed to be a vertical axis Y as seen from the axial direction of the cam shaft. A straight line that is orthogonal to the vertical axis Y and passes through the center of rotation C1 of thecam shaft 26 is assumed to be a horizontal axis X. The direction that extends from the center of rotation C1 of thecam shaft 26 toward the center of rotation C2 of theweight 42 among directions parallel to the vertical axis Y is assumed to be a first vertical direction y1. The direction opposite the first vertical direction y1 is assumed to be a second vertical direction y2. One direction among the directions parallel to the horizontal axis X is assumed to be a first horizontal direction x1. The direction opposite the first horizontal direction x1 is assumed to be a second horizontal direction x2. - A region located in the first vertical direction y1 from the horizontal axis X and in the first horizontal direction x1 from the vertical axis Y is assumed to be a first region A1. A region located in the second vertical direction y2 from the horizontal axis X and in the first horizontal direction x1 from the vertical axis Y is assumed to be a second region A2. A region located in the second vertical direction y2 from the horizontal axis X and in the second horizontal direction x2 from the vertical axis Y as seen from the cam shaft direction is assumed to be a third region A3. A region located in the first vertical direction y1 from the horizontal axis X and in the second horizontal direction x2 from the vertical axis Y is assumed to be a fourth region A4.
-
FIG. 7 illustrates theweight 42 as seen from the first camshaft end portion 261 side in the cam shaft direction. Therefore, the aforementioned directions x1, x2, y1, and y2 and the regions A1 to A4 are defined when seen from the first camshaft end portion 261 side in the cam shaft direction, but the aforementioned directions x1, x2, y1, and y2 and the regions A1 to A4 may also be defined when seen from the second camshaft end portion 262 side in the cam shaft direction. - As illustrated in
FIG. 7 , theweight 42 has a shape that extends along the circumferential direction of thecam shaft 26. Theweight 42 is disposed around thecam shaft 26 in the first region A1, the second region A2, and the fourth region A4. Theweight 42 has a shape that straddles a plurality of regions among the first to fourth regions A1 to A4 in the circumferential direction of thecam shaft 26. Theweight 42 does not include a portion that is disposed in the third region A3 as seen from the cam shaft direction. - Specifically, the
weight 42 includes afirst weight portion 47 and asecond weight portion 48. Thefirst weight portion 47 extends from the center of rotation C2 of theweight 42 in the circumferential direction of thecam shaft 26 and in the first horizontal direction x1. Anend portion 471 in the circumferential direction of thefirst weight portion 47 is located in the first horizontal direction x1 from the vertical axis Y. That is, the entirefirst weight portion 47 is located in the first horizontal direction x1 from the vertical axis Y. Theend portion 471 of thefirst weight portion 47 is disposed in the second region A2 as seen from the cam shaft direction. - The
second weight portion 48 extends from the center of rotation C2 of theweight 42 in the circumferential direction of thecam shaft 26 and in the second horizontal direction x2. Anend portion 481 in the circumferential direction of thesecond weight portion 48 is located in the second horizontal direction x2 from the vertical axis Y. That is, the entiresecond weight portion 48 is located in the second horizontal direction x2 from the vertical axis Y. Theend portion 481 of thesecond weight portion 48 is disposed in the fourth region A4 as seen from the cam shaft direction. - The
first weight portion 47 is longer than thesecond weight portion 48 in the circumferential direction of thecam shaft 26. That is, an angle from the center of rotation C2 of theweight 42 to theend portion 471 of thefirst weight portion 47 around the center of rotation C1 of thecam shaft 26 is greater than an angle from the center of rotation C2 of theweight 42 to theend portion 481 of thesecond weight portion 48. - The
first weight portion 47 includes afirst portion 421 and asecond portion 422. Thefirst portion 421 is disposed in the first region A1 as seen from the cam shaft direction. Thesecond portion 422 is disposed in the second region A2 as seen from the cam shaft direction. Thesecond weight portion 48 is disposed in the fourth region A4. - The
weight 42 includes a pivotpin support portion 423. The pivotpin support portion 423 is disposed across thefirst portion 421 and thesecond portion 422. Thepivot pin 46 is attached to the pivotpin support portion 423. - The
exhaust cam 264 includes acam lobe 267 that protrudes further to the outside than abase circle 266. A portion of thepivot pin 46 does not overlap thecam lobe 267 as seen from the cam shaft direction. That is, a portion of thepivot pin 46 is located to the outside of the external peripheral surface of theexhaust cam 264 as seen from the cam shaft direction. Thepivot pin 46 further includes a portion located on the inside of thebase circle 266 as seen from the cam shaft direction. - The
decompression pin 44 is connected to thefirst weight portion 47. Specifically, thedecompression pin 44 is connected to thesecond portion 422. Thedecompression pin 44 is disposed in the second region A2 as seen from the cam shaft direction. A distance between the center of rotation C2 of theweight 42 and thedecompression pin 44 as seen from the cam shaft direction is equal to or greater than a distance between the center of rotation C2 of theweight 42 and the center of rotation C1 of thecam shaft 26. -
FIG. 11 illustrates the cam shaft assembly as seen from the cam shaft direction. As illustrated inFIG. 11 , the contour of theflange 41 as seen from the cam shaft direction includes a portion larger than the contour of thefirst bearing 27. Specifically, the firstconvex portion 412 protrudes to the outside of the external peripheral surface of thefirst bearing 27. - The
first portion 421 of theweight 42 in the closed state includes a first protrudingportion 424. The first protrudingportion 424 protrudes to the outside of the external peripheral surface of thefirst bearing 27 as seen from the cam shaft direction. The external peripheral surface of thesecond portion 422 is located on the inside of the external peripheral surface of thefirst bearing 27 as seen from the cam shaft direction. The external peripheral surface of thesecond weight portion 48 is located on the inside of the external peripheral surface of thefirst bearing 27 as seen from the cam shaft direction. - The pivot
pin support portion 423 includes a protrudingportion 425 that protrudes to the outside of the external peripheral surface of thefirst bearing 27 as seen from the cam shaft direction. The maximum value of the protrusion length of the protrudingportion 425 is greater than the maximum value of the protrusion length of the first protrudingportion 424. That is, the protrudingportion 425 protrudes more than the first protrudingportion 424 in the radial direction of thefirst bearing 27. The protrusion length signifies the length of protrusion from the external peripheral surface of thefirst bearing 27 in the radial direction of thefirst bearing 27. - As illustrated in
FIG. 11 , thefirst bearing 27 includes aninner ring 271 and anouter ring 272. Theinner ring 271 is in contact with thecam shaft 26. Theouter ring 272 is in contact with the first supportingwall 141 of thecylinder head 14. As illustrated inFIG. 7 , theweight 42 includes an innerring contact portion 426. The innerring contact portion 426 is disposed in line with theinner ring 271 in the cam shaft direction. The innerring contact portion 426 protrudes toward theinner ring 271 from the surface of theweight 42 adjacent to thefirst bearing 27. - As illustrated in
FIG. 11 , the innerring contact portion 426 is located further to the inside than the inner peripheral surface of theouter ring 272. The innerring contact portion 426 is located further to the inside than the inner peripheral surface of theouter ring 272 regardless of whether theweight 42 is in the closed state or the open state. At least a portion of the innerring contact portion 426 is disposed nearer the center of rotation C2 of theweight 42 than the center of rotation C1 of thecam shaft 26 as seen from the cam shaft direction. The innerring contact portion 426 is located between the center of rotation C2 of theweight 42 and thecam shaft 26 as seen from the cam shaft direction. As illustrated inFIG. 4 , the other portions of theweight 42 do not come into contact with theouter ring 272 in a state in which the innerring contact portion 426 is in contact with theinner ring 271. - Specifically, the inner
ring contact portion 426 is disposed across the fourth region A4, the first region A1, and the second region A2 when theweight 42 is in the closed state. The innerring contact portion 426 includes afirst contact portion 426a, asecond contact portion 426b, and athird contact portion 426c. Thefirst contact portion 426a is disposed in the first region A1 when theweight 42 is in the closed state. Thesecond contact portion 426b is disposed in the second region A2 when theweight 42 is in the closed state. Thethird contact portion 426c is disposed in the fourth region A4 when theweight 42 is in the closed state. The surface area of thefirst contact portion 426a is larger than the surface area of thesecond contact portion 426b as seen from the cam shaft direction. The surface area of thefirst contact portion 426a is larger than the surface area of thethird contact portion 426c as seen from the cam shaft direction. - G1 in
FIG. 12 indicates the location of the center of gravity of theweight 42. G2 indicates the location of the center of gravity of theweight 42 when there is no first protrudingportion 424. Hatching is provided for the first protrudingportion 424 inFIG. 12 . The phrase "when there is no first protrudingportion 424" signifies a state in which the hatched portions inFIG. 12 are removed. The chain double-dashed line inFIG. 12 indicates the external peripheral surface of thefirst bearing 27. As illustrated inFIG. 12 , the center of gravity G1 of theweight 42 is disposed in the first region A1 as seen from the cam shaft direction. The distance between the center of gravity G1 of theweight 42 and the center of rotation C1 of thecam shaft 26 is greater than the distance between the center of gravity G1 of theweight 42 and the center of rotation C2 of theweight 42. The first protrudingportion 424 includes anear portion 424a and adistant portion 424b that are, as seen from the cam shaft direction, respectively nearer to and further away from the center of rotation C2 of theweight 42 in the circumferential direction of thefirst bearing 27 than the location of the center of gravity G2 of theweight 42 if there were no first protrudingportion 424. The amount of protrusion outward from the external peripheral surface of thefirst bearing 27 is greater in thenear portion 424a than in thedistant portion 424b. - As seen from the cam shaft direction, a portion of the inner
ring contact portion 426 nearer the center of rotation C2 of theweight 42 than the center of gravity G1 of theweight 42 is larger than a portion of the innerring contact portion 426 further away from the center of rotation C2 of theweight 42 than the center of gravity G1 of theweight 42. For example, the maximum width of thefirst contact portion 426a in the radial direction of thecam shaft 26 is greater than the maximum width of thesecond contact portion 426b in the radial direction of thecam shaft 26. -
FIG. 13 is a perspective view illustrating the surface on the second camshaft end portion 262 side of theweight 42.FIG. 14 is side view of the cam shaft assembly as seen from the direction of arrow XIV inFIG. 10 . As illustrated inFIG. 13 , the maximum thickness of thefirst portion 421 in the cam shaft direction is greater than the maximum thickness of thesecond portion 422 in the cam shaft direction. The maximum thickness of thesecond weight portion 48 in the cam shaft direction is greater than the maximum thickness of thesecond portion 422 in the cam shaft direction. - As illustrated in
FIG. 13 , thefirst portion 421 includes aninner diameter portion 421a and anouter diameter portion 421b. Theinner diameter portion 421a is located on the inside of theouter diameter portion 421b. The thickness of theouter diameter portion 421b in the cam shaft direction is greater than the thickness of theinner diameter portion 421a in the cam shaft direction. Theouter diameter portion 421b includes the aforementioned first protrudingportion 424. Therefore, the maximum thickness of the first protrudingportion 424 in the cam shaft direction is greater than the maximum thickness of thesecond portion 422 in the cam shaft direction. The maximum thickness of the first protrudingportion 424 in the cam shaft direction is greater than the maximum thickness of thesecond weight portion 48 in the cam shaft direction. The thickness of the first protrudingportion 424 in the cam shaft direction is greater than the thickness of the pivotpin support portion 423 in the cam shaft direction. - As illustrated in
FIG. 10 , a portion of theweight 42 overlaps theflange 41 as seen from the radial direction of thecam shaft 26. Specifically, theouter diameter portion 421b of thefirst portion 421 overlaps theflange 41 as seen from the radial direction of thecam shaft 26. The surface of thesecond weight portion 48 and the surface of theinner diameter portion 421a on the second camshaft end portion 262 side face the surface of theflange 41 on the first camshaft end portion 261 side. Theaforementioned head portion 431 of thedecompression cam 43 is disposed between thesecond portion 422 and theflange 41. - As illustrated in
FIG. 13 , the pivotpin support portion 423 includes ahousing portion 423a and aboss portion 423b. Theboss portion 423b protrudes from thehousing portion 423a in the cam shaft direction. The thickness of thehousing portion 423a in the cam shaft direction is less than the thicknesses of thefirst portion 421 and thesecond weight portion 48 in the cam shaft direction. Therefore, thehousing portion 423a has a shape that is recessed in the cam shaft direction from the surface of theweight 42. -
FIG. 15 is a view of theflange 41, theweight 42, and thereturn spring 45 as seen from the second camshaft end portion 262 side. As illustrated inFIG. 15 , thehousing portion 423a houses thereturn spring 45. Theboss portion 423b is inserted into theaforementioned return spring 45. Ahole 423c is provided in theboss portion 423b. Thepivot pin 46 is inserted into thehole 423c of theboss portion 423b. - As illustrated in
FIGS. 13 and15 , theweight 42 includes asecond locking portion 42b. Thesecond locking portion 42b locks the secondspring end portion 452 of thereturn spring 45. Thesecond locking portion 42b is included in thefirst portion 421. Specifically, thesecond locking portion 42b is a stepped portion shaped with regard to the pivotpin support portion 423 in thefirst portion 421. - As illustrated in
FIGS. 14 and15 , theflange 41 includes afirst locking section 42a. Thefirst locking section 42a locks the firstspring end portion 451 of thereturn spring 45. Specifically, thefirst locking section 42a is a portion of the firstconvex portion 412. Thefirst locking section 42a is formed integrally with theflange 41. For example, theflange 41 is formed integrally to include thefirst locking section 42a using a manufacturing method such as sintering, forging, or casting. -
FIG. 16 illustrates thecylinder head 14 in a state in which thehead cover 19 is removed. As illustrated inFIG. 16 , thecylinder head 14 includes a firstbearing support hole 143. The firstbearing support hole 143 supports thefirst bearing 27. The firstbearing support hole 143 is provided in the first supportingwall 141. The firstbearing support hole 143 includes a first recessedportion 144, a second recessedportion 145, and a third recessedportion 146. The first recessedportion 144, the second recessedportion 145, and the third recessedportion 146 are located on the side opposite thecrankshaft 11 from the center of the firstbearing support hole 143. The first recessedportion 144 has a shape that allows the passage of the first protrudingportion 424 and thesuction cam 263. The second recessedportion 145 has a shape that allows the passage of theexhaust cam 264. The third recessedportion 146 has a shape that allows the passage of the pivotpin support portion 423. A portion of the first recessedportion 144 may be located on the opposite side of thecrankshaft 11 from the center of the firstbearing support hole 143, and the other portion of the first recessedportion 144 may be located on the same side as thecrankshaft 11 from the center of the firstbearing support hole 143. Alternatively, a portion of the second recessedportion 145 may be located on the opposite side of thecrankshaft 11 from the center of the firstbearing support hole 143, and the other portion of the second recessedportion 145 may be located on the same side as thecrankshaft 11 from the center of the firstbearing support hole 143. - Because the
flange 41 is press-fitted onto thecam shaft 26 in the engine 7 according to the present embodiment, the location in the circumferential direction of theflange 41 with regard to thecam shaft 26 during press-fitting can be set freely. Further, because theflange 41 is a body separate from thecam shaft 26, increases in the sizes of thecam shaft 26 and thevalve mechanism 25 and increases in the operating ranges thereof can be suppressed even if the size of theflange 41 is increased. As a result, the degree of freedom for disposing thepivot pin 46 can be improved while making the engine 7 more compact. - The
decompression cam 43 is supported on theflange 41. As a result, the locations of theweight 42 and thedecompression cam 43 on thecam shaft 26 can be changed without changing the relative locations of theweight 42 and thedecompression cam 43, by merely changing the location of theflange 41 on thecam shaft 26 because theweight 42 and thedecompression cam 43 are both supported on theflange 41. - A portion of the
weight 42 overlaps theflange 41 as seen from the radial direction of thecam shaft 26. As a result, thecam shaft 26 that includes thedecompression mechanism 40 can be made more compact in the cam shaft direction. - The center of gravity G1 of the
weight 42 is disposed in the first region A1 as seen from the cam shaft direction. Theweight 42 includes afirst portion 421 that is disposed in the first region A1 as seen from the cam shaft direction. A portion of thefirst portion 421 overlaps theflange 41 as seen from the radial direction of thecam shaft 26. - As a result, the center of gravity G1 of the
weight 42 can be provided further away from the center of rotation C1 of thecam shaft 26. Therefore, the centrifugal force acting on theweight 42 increases if the rotation speed of thecam shaft 26 is the same. As a result, opening of theweight 42 due to gravitational force can be suppressed without raising the set rotation speed because the spring force of thereturn spring 45 is increased. - The
weight 42 includes thehousing portion 423a for housing thereturn spring 45. In this case, thecam shaft 26 that includes thedecompression mechanism 40 can be made more compact in comparison to when thehousing portion 423a is provided on the outside of theweight 42. - The
housing portion 423a has a recessed shape that is recessed in the cam shaft direction from the surface of theweight 42. As a result, thecam shaft 26 that includes thedecompression mechanism 40 can be made more compact in the cam shaft direction. - The
flange 41 includes thefirst locking section 42a that locks the firstspring end portion 451 of thereturn spring 45. Thefirst locking section 42a is formed integrally with theflange 41. As a result, the manufacturing of thedecompression mechanism 40 can be facilitated in comparison to when a shape for locking thefirst locking section 42a of thereturn spring 45 is processed into theflange 41. - The contour of the
flange 41 as seen from the cam shaft direction includes a portion larger than the contour of thefirst bearing 27. Specifically, the firstconvex portion 412 of theflange 41 protrudes to the outside of the external peripheral surface of thefirst bearing 27. In this case, the degree of freedom for disposing thepivot pin 46 can be improved. - The
pivot pin 46 is attached to theflange 41 that is a body separate from theexhaust cam 264. As a result, thepivot pin 46 can be disposed in a location that does not overlap thecam lobe 267. - Although an embodiment of the present invention has been described so far, the present invention is not limited to the above embodiments and various modifications may be made within the scope of the invention.
- The shape of the
weight 42 is not limited to the shape of the above embodiment and may be changed. Alternatively, the length in the circumferential direction of the weight can be made shorter than that of theweight 42 of the above embodiment. For example, a circumferentialdirection end portion 471 of thefirst weight portion 47 may be disposed in the first region A1. Alternatively, the length in the circumferential direction of the weight can be made longer than that of theweight 42 of the above embodiment. For example, the circumferentialdirection end portion 471 of thefirst weight portion 47 may be disposed in the third region A3. - The first protruding
portion 424 of theweight 42 may be omitted. That is, thefirst portion 421 may be located on the inside of the external peripheral surface of thefirst bearing 27 as seen from the cam shaft direction. - The center of gravity G1 of the
weight 42 is not limited to the disposition in the first region A1 and may be disposed in another region. For example, the center of gravity G1 of theweight 42 may be disposed in the second region A2. - The location of the
pivot pin 46 is not limited to the location of the above embodiment and may be changed. For example, theentire pivot pin 46 may be disposed in a location that does not overlap thecam lobe 267. That is, theentire pivot pin 46 may be disposed to the outside of the external peripheral surface of thecam lobe 267. - The shape of the inner ring contact portion is not limited to the shape of the above embodiment and may be changed. Alternatively, the inner ring contact portion of the
weight 42 may be omitted. - The housing portion for housing the return spring may be provided on the flange instead of the on the weight. The housing portion preferably has a recessed shape that is recessed from the surface of the flange in the axial direction of the cam shaft.
- While a scooter-type motorcycle is mentioned as an example of the vehicle in the above embodiment, the vehicle according to the present invention is not limited to a scooter and may be another type of motorcycle such as a sports type, an off-road type, or a moped. The motorcycle is not limited to two wheels and includes a vehicle with three wheels. Moreover, while the vehicle according to the present invention is preferably a saddle-ridding vehicle such as a motorcycle, an all-terrain vehicle, or a snowmobile, the vehicle may also be a vehicle other than a saddle-ridding vehicle.
Claims (10)
- An engine (7) comprising:a cylinder head (14);an exhaust valve housed inside the cylinder head (14);a valve mechanism (25) for opening and closing the exhaust valve;a cam shaft (26) for driving the valve mechanism (25) by coming into contact with the valve mechanism (25);a bearing (27) supporting the cam shaft (26) in a rotatable manner on the cylinder head (14); anda decompression mechanism (40) disposed between both ends of the cam shaft (26) in an axial direction of the cam shaft (26);wherein the decompression mechanism (40) includes:a flange (41) that is a body separate from the cam shaft (26) and that is press-fitted onto the cam shaft (26);a pivot pin (46) attached to the flange (41);a weight (42) supported on the flange (41) via the pivot pin (46) in a rotatable manner between a closed state and an open state; anda decompression cam (43) configured to switch between a state of coming into contact with the valve mechanism (25) and a state of not coming into contact with the valve mechanism (25) in response to a rotation of the weight (42).
- The engine according to claim 1, wherein:the decompression cam (43) is supported on the flange (41).
- The engine according to claim 1 or 2, wherein:a portion of the weight (42) overlaps the flange (41) as seen from a radial direction of the cam shaft (26).
- The engine according to any one of claims 1 to 3, wherein:when a straight line that passes through a center of rotation (C1) of the cam shaft (26) and through a center of rotation (C2) of the weight (42) is assumed to be a vertical axis (Y), and a straight line that is orthogonal to the vertical axis (Y) and that passes through the center of rotation (C1) of the cam shaft (26) is assumed to be a horizontal axis (X), and when a direction from the center of rotation (C1) of the cam shaft (26) toward the center of rotation (C2) of the weight (42) among directions parallel to the vertical axis (Y) is assumed to be a first vertical direction and a direction parallel to the horizontal axis (X) is assumed to be a first horizontal direction, as seen from the axial direction of the cam shaft (26),the center of gravity (G1) of the weight (42) is disposed in a first region (A1) that is located in the first vertical direction (y1) from the horizontal axis (X) and in the first horizontal direction (x1) from the vertical axis (Y) as seen from the axial direction of the cam shaft (26); andthe weight (42) includes a first portion (421) that is disposed in the first region (A1) as seen from the axial direction of the cam shaft (26); andat least a portion (421b) of the first portion (421) overlaps the flange (41) as seen from the radial direction of the cam shaft (26).
- An engine according to any one of claims 1 to 4, wherein:the decompression mechanism (40) further includes a return spring (45) for urging the weight (42) to return from the open state to the closed state; andthe weight (42) or the flange (41) includes a housing portion (423a) for housing the return spring (45).
- The engine according to claim 5, wherein
the housing portion (423a) has a recessed shape that is recessed in the axial direction of the cam shaft (26) from a surface of the weight (42) or the flange (41). - An engine according to any one of claims 5 to 6, wherein
the flange (41) includes a locking portion (42b) for locking to an end portion (452) of the return spring (45), and
the locking portion (42b) is formed integrally with the flange (41). - An engine according to any one of claims 1 to 7, wherein,
the contour of the flange (41) is larger than the contour of the bearing (27) as seen from the axial direction of the cam shaft (26). - An engine according to any one of claims 1 to 8, wherein
the cam shaft (26) includes an exhaust cam (264) coming into contact with the valve mechanism (25), and
the exhaust cam (264) includes a cam lobe (267) protruding outward from a base circle (266), and
at least a portion of the pivot pin (46) does not overlap the cam lobe (267) as seen from the axial direction of the cam shaft (26). - A vehicle (1) comprising an engine (7) according to any one of the claims 1 to 9.
Applications Claiming Priority (1)
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JP2014108986A JP2015224578A (en) | 2014-05-27 | 2014-05-27 | Engine and vehicle |
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EP2949888A2 true EP2949888A2 (en) | 2015-12-02 |
EP2949888A3 EP2949888A3 (en) | 2016-01-27 |
EP2949888B1 EP2949888B1 (en) | 2017-03-01 |
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EP15163608.1A Active EP2949888B1 (en) | 2014-05-27 | 2015-04-15 | Engine and vehicle |
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JP (1) | JP2015224578A (en) |
CN (1) | CN105317500B (en) |
TW (1) | TWI605188B (en) |
Cited By (2)
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US20200173415A1 (en) * | 2018-11-30 | 2020-06-04 | Kwang Yang Motor Co., Ltd. | Depressurization device of internal combustion engine |
US11384725B2 (en) | 2018-07-05 | 2022-07-12 | Honda Motor Co., Ltd. | Engine decompression device and engine |
Families Citing this family (5)
Publication number | Priority date | Publication date | Assignee | Title |
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TWI655360B (en) * | 2017-06-29 | 2019-04-01 | 三陽工業股份有限公司 | Engine with decompression device |
CN108442989B (en) * | 2018-03-15 | 2019-07-12 | 罗守磊 | A kind of engine exploitation adjustable convex wheel shaft |
TWI675147B (en) * | 2019-04-23 | 2019-10-21 | 宏佳騰動力科技股份有限公司 | Pressure reducing device |
WO2023161950A1 (en) * | 2022-02-28 | 2023-08-31 | Tvs Motor Company Limited | Camshaft assembly for an internal combustion engine and the internal combustion engine thereof |
TWI816429B (en) * | 2022-06-09 | 2023-09-21 | 光陽工業股份有限公司 | Pressure reducing device for internal combustion engines |
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JP2008064083A (en) | 2006-08-08 | 2008-03-21 | Honda Motor Co Ltd | Engine with decompression device |
JP2008128171A (en) | 2006-11-24 | 2008-06-05 | Honda Motor Co Ltd | Internal combustion engine with decompression device |
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US3362390A (en) * | 1966-02-09 | 1968-01-09 | Wisconsin Motor Corp | Automatic compression release |
JP3705726B2 (en) * | 1999-12-15 | 2005-10-12 | 川崎重工業株式会社 | Automatic decompression device |
US20040003791A1 (en) * | 2002-07-08 | 2004-01-08 | Giuseppe Ghelfi | Compression release mechanism |
JP4234653B2 (en) * | 2004-09-03 | 2009-03-04 | ヤマハ発動機株式会社 | Engine decompression device |
JP2006291778A (en) * | 2005-04-07 | 2006-10-26 | Yamaha Motor Co Ltd | Decompression device and vehicle |
JP5171521B2 (en) * | 2008-09-30 | 2013-03-27 | 本田技研工業株式会社 | Variable valve gear for engine |
-
2014
- 2014-05-27 JP JP2014108986A patent/JP2015224578A/en active Pending
-
2015
- 2015-04-15 EP EP15163608.1A patent/EP2949888B1/en active Active
- 2015-05-20 TW TW104116118A patent/TWI605188B/en active
- 2015-05-26 CN CN201510276226.9A patent/CN105317500B/en active Active
Patent Citations (2)
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JP2008064083A (en) | 2006-08-08 | 2008-03-21 | Honda Motor Co Ltd | Engine with decompression device |
JP2008128171A (en) | 2006-11-24 | 2008-06-05 | Honda Motor Co Ltd | Internal combustion engine with decompression device |
Cited By (2)
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US11384725B2 (en) | 2018-07-05 | 2022-07-12 | Honda Motor Co., Ltd. | Engine decompression device and engine |
US20200173415A1 (en) * | 2018-11-30 | 2020-06-04 | Kwang Yang Motor Co., Ltd. | Depressurization device of internal combustion engine |
Also Published As
Publication number | Publication date |
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TW201604384A (en) | 2016-02-01 |
TWI605188B (en) | 2017-11-11 |
CN105317500B (en) | 2017-11-03 |
JP2015224578A (en) | 2015-12-14 |
CN105317500A (en) | 2016-02-10 |
EP2949888B1 (en) | 2017-03-01 |
EP2949888A3 (en) | 2016-01-27 |
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