JP2015224579A - Engine and vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine and a vehicle capable of improving the startability of a decompression mechanism.SOLUTION: When viewed from an axial direction of a cam shaft, a straight line passing through a rotation center of the cam shaft and a rotation center of a weight is made to be a vertical axis. A straight line orthogonal to the vertical axis and passing through the rotation center of the cam shaft is made to be a lateral axis. Of directions parallel with the vertical axis, a direction extending from the rotation center of the cam shaft toward the rotation center of the weight is made to be a first vertical direction. One of directions parallel with the lateral shaft is made to be a first lateral direction. The gravity center of the weight is disposed in a first area, when viewed from the axial direction of the cam shaft. The first area is positioned in the first vertical direction to the lateral axis, and the first lateral direction to the vertical axis. The weight includes a first part disposed in the first area, when viewed from the axial direction of the cam shaft. In a close state, the first part includes a first projecting portion projecting outward from an outer peripheral surface of a bearing, when viewed from the axial direction of the cam shaft.

Description

  The present invention relates to an engine and a vehicle including a decompression mechanism (hereinafter referred to as “decompression mechanism”).

  When starting the engine, it is necessary to rotate the engine by external force until the start is completed. For example, there are those that are rotated by a cell motor and those that are rotated by a kick starter. On the other hand, in the compression process of the engine, since the air in the cylinder is compressed, the resistance to rotation increases. In order to reduce such resistance, there is known a decompression mechanism for reducing the pressure in the cylinder in the compression process when the engine is rotated by an external force.

  For example, the decompression mechanism disclosed in Patent Document 1 has a decompression cam that switches between an activated state and a released state by rotation of a weight. This decompression mechanism is supported by the sprocket of the cam chain. For this reason, there exists a problem that the cam shaft containing a decompression mechanism becomes large in an axial direction.

  In the engine disclosed in Patent Document 2, the decompression mechanism is disposed at a position between both ends of the cam shaft. The decompression mechanism has a weight and a decompression cam, and the weight is supported by a support shaft so as to be rotatable with respect to the cam shaft. The decompression cam and the weight are connected by a pin, and the pin rotates the decompression cam as the weight rotates about the support shaft.

  In the decompression mechanism of Patent Document 2, when the camshaft is not rotating, the weight is held in a closed state by the action of the return spring. In a state where the weight is closed, the decompression cam is operable to the exhaust valve. Therefore, when the engine is started, the decompression cam acts on the exhaust valve to open the exhaust valve, thereby reducing the pressure in the cylinder.

  When the cam shaft rotates, the weight rotates around the support shaft by receiving centrifugal force. When the rotational speed of the cam shaft rises above a certain set rotational speed, the centrifugal force exceeds the spring force of the return spring, so that the weight is opened. When the weight is open, the decompression cam does not act on the exhaust valve.

JP 2008-128171 A JP 2008-64083 A

  In the decompression mechanism of Patent Document 2, the space between both ends of the cam shaft can be used effectively. For this reason, compared with the case where a decompression mechanism is arrange | positioned outside a cam shaft, the cam shaft containing a decompression mechanism may be made compact in an axial direction. However, when the inventor of the present application examined, it has been found that the engine according to the related art as described in Patent Document 2 may not be sufficiently improved in startability because the decompression mechanism does not operate when starting. It was.

  The subject of this invention is providing the engine and vehicle which can improve the startability of a decompression mechanism.

  The inventor of the present application has verified the cause of the decompression not being activated at the time of starting in the engine according to the prior art. As a result, it has been found that when the engine is started, the weight may already be open. In other words, it was found that when the engine is stopped, the weight may be kept open without closing.

  According to the study of the inventors of the present application, this is considered to be caused by the weak spring force of the return spring. The reason why the spring force becomes weak is that the weight is reduced by arranging the decompression mechanism between both ends of the cam shaft. That is, in the decompression mechanism of Patent Document 2, since the decompression mechanism is disposed between both ends of the camshaft, the arrangement restriction is larger than that of the decompression mechanism of Patent Document 1. Therefore, in the decompression mechanism of Patent Document 2, it is necessary to make the weight smaller than the weight in the decompression mechanism of Patent Document 1.

  As the weight decreases, the weight mass decreases. The magnitude of the centrifugal force acting on the weight decreases as the mass of the weight decreases as the rotational speed is the same. For this reason, the centrifugal force acting on the weight is reduced at the set rotational speed for opening the weight. Therefore, it is necessary to reduce the spring force.

  However, the weight position changes depending on the rotation phase of the camshaft. The camshaft may stop when the weight opening direction coincides with the direction of gravity. At this time, by reducing the spring force, the inventor of the present application has found that the moment due to gravity acting on the weight is greater than the spring force, and as a result, the weight is in an open state. .

  In order to prevent the above phenomenon, it is conceivable to increase the spring force. However, if the spring force is increased, the set rotational speed at which the weight opens is increased. An increase in the set rotational speed is undesirable because it causes noise.

  An engine according to an aspect of the present invention includes a cylinder head, an exhaust valve, a valve operating mechanism, a cam shaft, a bearing, and a decompression mechanism. The exhaust valve is accommodated in the cylinder head. The valve mechanism opens and closes the exhaust valve. The cam shaft drives the valve mechanism by contacting the valve mechanism. The bearing supports the camshaft rotatably on the cylinder head. The decompression mechanism is disposed between both ends in the axial direction of the cam shaft.

  The decompression mechanism includes a weight, a return spring, and a decompression cam. The weight is supported so as to be rotatable between a closed state and an open state with respect to the cam shaft. The return spring biases the weight to return from the open state to the closed state. The decompression cam is provided so as to come into contact with the valve mechanism when the weight is in a closed state and not to come into contact with the valve mechanism when the weight is in an open state.

  A straight line passing through the rotation center of the cam shaft and the rotation center of the weight as viewed from the axial direction of the cam shaft is taken as the vertical axis. A horizontal axis is a straight line perpendicular to the vertical axis and passing through the rotation center of the cam shaft. A direction from the rotation center of the cam shaft toward the rotation center of the weight among the directions parallel to the vertical axis is defined as a first vertical direction. One of the directions parallel to the horizontal axis is defined as a first horizontal direction.

  The center of gravity of the weight is disposed in the first region when viewed from the axial direction of the cam shaft. The first region is located in the first vertical direction with respect to the horizontal axis and in the first horizontal direction with respect to the vertical axis. The weight includes a first portion disposed in the first region when viewed from the axial direction of the cam shaft. In the closed state, the first portion includes a first protrusion that protrudes outward from the outer peripheral surface of the bearing when viewed from the axial direction of the cam shaft.

  In the engine according to this aspect, the first protruding portion of the first portion located in the first region of the weight protrudes outward from the outer peripheral surface of the bearing. Thereby, compared with the case where the 1st part does not protrude, the gravity center of a weight can be kept away from the rotation center of a cam shaft. Therefore, if the rotational speed of the cam shaft is the same, the centrifugal force applied to the weight increases. As a result, the spring force can be increased, so that the opening of the weight due to gravity can be suppressed without increasing the set rotational speed.

  Preferably, the weight further includes a second portion. The second portion is disposed in the second region when viewed from the axial direction of the cam shaft. The second region is located in the second vertical direction with respect to the horizontal axis and in the first horizontal direction with respect to the vertical axis. The second vertical direction is a direction opposite to the first vertical direction. The outer peripheral surface of the second portion is located inward of the outer peripheral surface of the bearing when viewed from the axial direction of the cam shaft.

  In this case, the center of gravity of the weight can be further away from the rotation center of the cam shaft. In addition, the center of gravity of the weight can be brought closer to the center of rotation of the weight as compared with the case where the outer peripheral surface of the second portion is positioned outward from the outer peripheral surface of the bearing. Therefore, the moment due to gravity acting on the weight can be reduced. For this reason, the opening of the weight by gravity can be suppressed. This makes it easier to avoid a state in which the weight is open when the engine is started, so that the startability of the engine can be improved.

  The second portion may include a second protrusion that protrudes outward from the outer peripheral surface of the bearing when viewed from the axial direction of the cam shaft. The volume of the first protrusion is larger than the volume of the second protrusion.

  In this case, the center of gravity of the weight can be further away from the rotation center of the cam shaft. In addition, the center of gravity of the weight can be brought closer to the center of rotation of the weight than in the case where the volume of the second protrusion is larger than the volume of the first protrusion. Therefore, the moment due to gravity acting on the weight can be reduced. For this reason, the opening of the weight by gravity can be suppressed. This makes it easier to avoid a state in which the weight is open when the engine is started, so that the startability of the engine can be improved.

  Preferably, the maximum thickness of the first protrusion in the axial direction of the cam shaft is greater than the maximum thickness of the second portion in the axial direction of the cam shaft. In this case, the center of gravity of the weight can be further away from the rotation center of the cam shaft.

  Preferably, the weight further includes a third portion. The third portion is disposed in the third region when viewed from the axial direction of the cam shaft. The third region is located in the second vertical direction with respect to the horizontal axis and in the second horizontal direction with respect to the vertical axis. The second lateral direction is a direction opposite to the first lateral direction. The outer peripheral surface of the third portion is located inward of the outer peripheral surface of the bearing when viewed from the axial direction of the cam shaft. In this case, the center of gravity of the weight is further away from the center of rotation of the cam shaft than when the outer peripheral surface of the third portion is located outward from the outer peripheral surface of the bearing when viewed from the axial direction of the cam shaft. be able to.

  The third portion may include a third protrusion that protrudes outward from the outer peripheral surface of the bearing when viewed from the axial direction of the cam shaft. The volume of the first protrusion is larger than the volume of the third protrusion. In this case, the center of gravity of the weight can be further away from the center of rotation of the camshaft as compared with the case where the volume of the third protrusion is larger than the volume of the first protrusion.

  Preferably, the maximum thickness of the first protrusion in the axial direction of the cam shaft is greater than the maximum thickness of the third portion in the axial direction of the cam shaft. In this case, the center of gravity of the weight can be further away from the center of rotation of the camshaft as compared with the case where the maximum thickness of the first protrusion is smaller than the maximum thickness of the third portion.

  Preferably, when viewed from the axial direction of the camshaft, the first projecting portion includes a portion closer to the center of rotation of the weight and a portion farther from the center of gravity of the weight when there is no first projecting portion. The near part is larger than the far part. In this case, the center of gravity of the weight can be made closer to the center of rotation of the weight than when the far portion is larger than the closer portion.

  Preferably, the weight includes a pivot pin support. The decompression mechanism further includes a pivot pin attached to the pivot pin support. The weight is rotatably supported with respect to the camshaft via the pivot pin. The thickness of the first protrusion in the axial direction of the cam shaft is greater than the thickness of the pivot pin support portion in the axial direction of the cam shaft.

  In this case, the center of gravity of the weight can be moved away from the rotation center of the camshaft as compared with the case where the thickness of the first protrusion is smaller than the thickness of the pivot pin support.

  Preferably, the engine further includes a crankshaft and a cam chain. The cylinder head includes a bearing support hole that supports the bearing. The bearing support hole includes a recess through which the first protrusion can pass. At least a part of the recess is located on the side opposite to the crankshaft with respect to the center of the bearing support hole.

  In this case, when the camshaft, the decompression mechanism, and the bearing are integrally attached to the cylinder head, the first protrusion can pass through the recess. Thereby, it can avoid that a 1st protrusion part interferes with a bearing support hole. On the other hand, if the concave portion is provided in the bearing support hole, the bearing is not supported by the concave portion, so there is a concern that the bearing support strength may be reduced. However, at least a part of the recess is located on the opposite side of the crankshaft with respect to the center of the bearing support hole. For this reason, it is possible to suppress a decrease in the support strength of the portion on the crankshaft side of the bearing support hole that receives a large load from the crankshaft.

  A vehicle according to another aspect of the present invention includes the engine described above.

  ADVANTAGE OF THE INVENTION According to this invention, the engine and vehicle which can improve the startability of a decompression mechanism can be provided.

It is a side view of a vehicle. It is a sectional view of a part of an engine. Sectional drawing of the cylinder head in a plane perpendicular | vertical to a cam shaft. It is an expanded sectional view of a cam shaft assembly. It is a perspective view of a cam shaft assembly. It is an exploded view of a cam shaft assembly. It is a figure which shows the weight of a closed state. It is a figure which shows the weight of an open state. It is an enlarged view of an exhaust cam. It is a side view of a cam shaft assembly. It is a figure which shows the camshaft assembly seen from the camshaft direction. The figure which shows the weight seen from the cam axis direction. It is a perspective view of a weight. FIG. 11 is a side view of the camshaft assembly as seen from the direction of arrow XIV in FIG. 10. It is a figure which shows the flange, weight, and return spring which were seen from the cam axis direction. It is a figure which shows the cylinder head of the state from which the head cover was removed. It is a figure which shows the weight which concerns on a 1st modification. It is a figure which shows the weight which concerns on a 2nd modification. It is a figure which shows the weight which concerns on a 3rd modification. It is a figure which shows the weight which concerns on a 4th modification. It is a figure which shows the weight which concerns on a 5th modification. It is a figure which shows the weight which concerns on a 6th modification.

  Hereinafter, a vehicle 1 according to an embodiment will be described with reference to the drawings. FIG. 1 is a side view of the vehicle 1. The vehicle 1 is a scooter type motorcycle. The vehicle 1 includes a vehicle main 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 wheels 3 and the rear wheels 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 below the seat 6.

  The vehicle 1 includes the engine 7 according to the embodiment. FIG. 2 is a cross-sectional view of a part of the engine 7. As shown in FIG. 2, 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 accommodates the piston 15. The piston 15 is connected to the crankshaft 11 via a connecting rod 16. The crankshaft 11 is connected to the 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. The tip of the spark plug 18 is disposed facing 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 accommodated in the cylinder head 14. The cam shaft 26 drives the valve mechanism 25 by contacting the valve mechanism 25.

  The cam shaft 26 is supported by the cylinder head 14. The cylinder head 14 includes a first support wall 141 and a second support wall 142. The first support wall 141 and the second support wall 142 are arranged side by side in the axial direction of the cam shaft 26 (hereinafter referred to as “cam axial direction”). The first support wall 141 supports the cam shaft 26. The first support wall 141 supports the cam shaft 26 via the first bearing 27. The second support wall 142 supports the cam shaft 26. The second support wall 142 supports the cam shaft 26 via the second bearing 28. The first bearing 27 and the second bearing 28 support the cam shaft 26 on the cylinder head 14 so as to be rotatable. The outer diameter of the first bearing 27 is larger than the outer diameter of the second bearing 28. Note that the first support wall 141 may support the camshaft 26 without the first bearing 27 interposed therebetween. The second support wall 142 may support the camshaft 26 without using the second bearing 28.

  The cam shaft 26 includes a first cam shaft end 261 and a second cam shaft end 262. The first bearing 27 is disposed closer to the first cam shaft end portion 261 than the second cam shaft end portion 262 in the cam axis direction. The second bearing 28 is disposed closer to the second cam shaft end portion 262 than the first cam shaft end portion 261 in the cam shaft direction.

  A cam chain 29 is wound around the cam shaft 26 and the crank shaft 11. Specifically, the first sprocket 31 is attached to the camshaft 26. The first sprocket 31 is attached to the first camshaft end 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 camshaft 26 via the cam chain 29, whereby the camshaft 26 rotates. The cam shaft 26 includes an intake cam 263 and an exhaust cam 264. The intake cam 263 and the exhaust cam 264 are arranged side by side in the cam axis direction. As the cam shaft 26 rotates, the intake cam 263 and the exhaust cam 264 rotate. The intake cam 263 and the exhaust cam 264 are in contact with the valve mechanism 25, and the valve mechanism 25 is driven by the rotation of the intake cam 263 and the exhaust cam 264.

  FIG. 3 is a cross-sectional view of the cylinder head 14 in a plane perpendicular to the cam shaft 26. As shown in FIG. 3, the engine 7 includes an exhaust valve 23 and an intake valve 24. The cylinder head 14 includes an intake port 21 and an exhaust port 22 that communicate with the combustion chamber 17. The exhaust valve 23 and the intake valve 24 are accommodated in the cylinder head 14. The intake valve 24 opens and closes the intake port 21. The exhaust valve 23 opens and closes the exhaust port 22. The valve mechanism 25 opens and closes the intake valve 24 and the exhaust valve 23.

  An intake valve spring 241 is attached to the intake valve 24. The intake valve spring 241 biases the intake valve 24 in a direction in which the intake valve 24 closes the intake port 21. An exhaust valve spring 231 is attached to the exhaust valve 23. The exhaust valve spring 231 biases the exhaust valve 23 in a direction in which the exhaust valve 23 closes 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 in parallel with the cam shaft 26. The exhaust rocker shaft 33 is supported by the cylinder head 14. The exhaust rocker arm 34 is supported by the exhaust rocker shaft 33 so as to be swingable about the exhaust rocker shaft 33. The exhaust rocker arm 34 is provided so that the exhaust valve 23 can operate. The exhaust rocker arm 34 includes an arm main body 341, an exhaust roller 342, and an exhaust valve pressing portion 343.

  The arm body 341 is swingably supported by the exhaust rocker shaft 33. One end of the arm main body 341 supports the exhaust roller 342 in a rotatable manner. The other end of the arm body 341 supports the exhaust valve pressing portion 343. The exhaust roller 342 is in contact with the exhaust cam 264 and is rotated by the rotation of the exhaust cam 264. The tip of the exhaust valve pressing portion 343 faces the stem end 232 of the exhaust valve 23.

  When the exhaust roller 342 is pushed up by the exhaust cam 264, the exhaust rocker arm 34 swings and the exhaust valve pressing portion 343 presses down the stem end 232 of the exhaust valve 23. Thereby, the exhaust valve 23 is pushed down and the exhaust port 22 is opened. When the exhaust roller 342 is not pushed up by the exhaust cam 264, the exhaust valve 23 is pushed up by the exhaust valve spring 231 and the exhaust port 22 is closed.

  The valve mechanism 25 includes an intake rocker shaft 35 and an intake rocker arm 36. The intake rocker shaft 35 is disposed in parallel with the cam shaft 26. The intake rocker shaft 35 is supported by the cylinder head 14. The intake rocker arm 36 is supported by the intake rocker shaft 35 so as to be swingable about the intake rocker shaft 35. The intake rocker arm 36 is provided so that the intake valve 24 can operate. The intake rocker arm 36 includes an arm main body 361, an intake roller 362, and an intake valve pressing portion 363.

  The arm body 361 is swingably supported by the intake rocker shaft 35. One end of the arm main body 361 supports the intake roller 362 in a rotatable manner. The other end of the arm body 361 supports the intake valve pressing portion 363. The intake roller 362 is in contact with the intake cam 263 and rotates by the rotation of the intake cam 263. The leading end of the intake valve pressing portion 363 faces the stem end 242 of the intake valve 24.

  When the intake roller 362 is pushed up by the intake cam 263, the intake rocker arm 36 swings and the intake valve pressing portion 363 pushes down the stem end of the intake valve 24. As a result, the intake valve 24 is pushed down to open the intake port 21. When the intake roller 362 is not pushed up by the intake cam 263, the intake valve 24 is pushed up by the intake valve spring 241 to close the intake port 21.

  As shown in FIG. 2, the engine 7 includes a decompression mechanism 40. FIG. 4 is an enlarged view of an assembly of the cam shaft 26, the decompression mechanism 40, and the first bearing 27 (hereinafter referred to as “cam shaft assembly”). 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 axis direction. The decompression mechanism 40 is disposed between the first support wall 141 and the second support wall 142 of the cylinder head 14.

  FIG. 5 is a perspective view of the camshaft assembly. FIG. 6 is an exploded view of the camshaft assembly. As shown in FIGS. 5 and 6, the decompression mechanism 40 includes a flange 41, a weight 42, a decompression cam 43, a decompression pin 44, and a return spring 45.

  As shown in FIG. 6, the flange 41 is separate from the cam shaft 26 and is fixed to the cam shaft 26. Specifically, 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 axis direction.

  The flange 41 includes a first protrusion 412 and a second protrusion 413. A pivot pin 46 is attached to the first convex portion 412. The second convex portion 413 is provided with a hole 414. 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 axis direction. The weight 42 is supported so as to be rotatable with respect to the cam shaft 26 between a closed state and an open state.

  7 and 8 are cross-sectional views taken along line AA in FIG. FIG. 7 shows the weight 42 in the closed state. FIG. 8 shows the weight 42 in the open state.

  The decompression cam 43 is rotatably supported by the flange 41. Specifically, the weight 42 is rotatably supported by the flange 41 via the pivot pin 46. The weight 42 is switched between a closed state and an 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 according to the rotation of the weight 42.

  Specifically, as shown in FIGS. 4 and 6, 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 part 431 includes a groove part 433. The groove portion 433 has a shape recessed from the end surface of the head portion 431. The groove portion 433 extends from the outer 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 in the groove portion 433. In the present embodiment, “inward” means inward in the radial direction. Further, outward means outward in the radial direction.

  The shaft portion 432 includes a cam portion 434. The exhaust cam 264 includes a recess 265, and the recess 265 has a shape recessed from the outer peripheral surface of the exhaust cam 264 inward of the exhaust cam 264. FIG. 9 is an enlarged view of the exhaust cam 264. FIG. 10 is a side view of the camshaft assembly.

  The cam portion 434 is disposed in the recess 265 of the exhaust cam 264. The cross section of the cam portion 434 has a circular shape with a part cut away. As described above, the decompression cam 43 rotates in accordance with the rotation of the weight 42. FIG. 9A shows the decompression cam 43 when the weight 42 is in the open state. FIG. 9B shows the decompression cam 43 when the weight 42 is in the closed state. The decompression cam 43 switches between a state in contact with the exhaust roller 342 of the valve operating mechanism 25 and a state in which the decompression cam 43 does not contact the exhaust roller 342 in accordance with the rotation of the weight 42.

  Specifically, when the weight 42 is in the open state, the entire cam portion 434 of the decompression cam 43 is disposed in the recess 265 as shown in FIG. That is, when the weight 42 is in the open state, the cam portion 434 does not protrude outward from the outer peripheral surface of the exhaust cam 264. Thereby, when the weight 42 is in the open state, the decompression cam 43 does not contact the exhaust roller 342.

  When the weight 42 is in the closed state, a part of the cam portion 434 of the decompression cam 43 is disposed outside the recess 265 as shown in FIG. That is, when the weight 42 is in the closed state, a part of the cam portion 434 protrudes outward from the outer peripheral surface of the exhaust cam 264. Thereby, when the weight 42 is in the closed state, the decompression cam 43 comes into contact with the exhaust roller 342.

  The return spring 45 urges the weight 42 to return from the open state to the closed state. In the present embodiment, the return spring 45 is a coil spring. However, the return spring 45 may be another type of spring. As shown in FIG. 6, the return spring 45 includes a first spring end 451 and a second spring end 452. The first spring end 451 extends in the cam axis direction. The second spring end 452 extends in a direction intersecting the cam axis direction. The second spring end 452 extends in the circumferential direction of the return spring 45. The first spring end 451 is engaged with the flange 41. The second spring end 452 is engaged with the weight 42.

  Next, the structure of the weight 42 will be described in detail. As shown in FIG. 7, a straight line passing through the rotation center c <b> 1 of the cam shaft 26 and the rotation center c <b> 2 of the weight 42 as viewed from the cam axis direction is defined as a vertical axis Y. A horizontal axis X is a straight line that is orthogonal to the vertical axis Y and passes through the rotation center c1 of the cam shaft 26. A direction from the rotation center c1 of the cam shaft 26 toward the rotation center c2 of the weight 42 in a direction parallel to the vertical axis Y is defined as a first vertical direction y1. A direction opposite to the first vertical direction y1 is defined as a second vertical direction y2. One of the directions parallel to the horizontal axis X is defined as a first horizontal direction x1. A direction opposite to the first lateral direction x1 is defined as a second lateral direction x2.

  An area located in the first vertical direction y1 with respect to the horizontal axis X and in the first horizontal direction x1 with respect to the vertical axis Y is defined as a first area A1. A region located in the second vertical direction y2 with respect to the horizontal axis X and in the first horizontal direction x1 with respect to the vertical axis Y is defined as a second region A2. A region located in the second vertical direction y2 with respect to the horizontal axis X and in the second horizontal direction x2 with respect to the vertical axis Y when viewed from the cam axis direction is defined as a third region A3. A region located in the first vertical direction y1 with respect to the horizontal axis X and in the second horizontal direction x2 with respect to the vertical axis Y is defined as a fourth region A4.

  FIG. 7 shows the weight 42 as seen from the first cam shaft end 261 side in the cam shaft direction. Therefore, the above-mentioned directions x1, x2, y1, y2 and the region A1-A4 are defined when viewed from the first cam shaft end 261 side in the cam axis direction, but the second cam shaft in the cam axis direction. When viewed from the end 262 side, the above-described directions x1, x2, y1, y2 and the region A1-A4 may be defined.

  As shown in FIG. 7, the weight 42 has a shape extending along the circumferential direction of the cam shaft 26. The weight 42 is disposed around the cam shaft 26 in the first area A1, the second area A2, and the fourth area A4. The weight 42 has a shape straddling a plurality of regions in the first to fourth regions A1 to A4 in the circumferential direction of the cam shaft 26. The weight 42 does not have a portion arranged in the third region A3 when viewed from the cam axis direction.

  Specifically, the weight 42 includes a first weight portion 47 and a second weight portion 48. The first weight portion 47 extends from the rotation center c2 of the weight 42 in the circumferential direction of the cam shaft 26 and in the first lateral direction x1. An end portion 471 in the circumferential direction of the first weight portion 47 is located in the first lateral direction x1 with respect to the vertical axis Y. That is, the entire first weight portion 47 is located in the first lateral direction x1 with respect to the vertical axis Y. The end portion 471 of the first weight portion 47 is disposed in the second region A2 when viewed from the cam axis direction.

  The second weight portion 48 extends from the rotation center c2 of the weight 42 in the circumferential direction of the cam shaft 26 and in the second lateral direction x2. An end portion 481 in the circumferential direction of the second weight portion 48 is located in the second lateral direction x2 with respect to the vertical axis Y. That is, the entire second weight portion 48 is located in the second lateral direction x2 with respect to the vertical axis Y. The end portion 481 of the second weight portion 48 is disposed in the fourth region A4 when viewed from the cam axis 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, the angle from the rotation center c2 of the weight 42 around the rotation center c1 of the cam shaft 26 to the end portion 471 of the first weight portion 47 is from the rotation center c2 of the weight 42 to the end portion 481 of the second weight portion 48. Greater than angle.

  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 when viewed from the cam axis direction. The second portion 422 is disposed in the second region A2 when viewed from the cam axis 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 peak 267 (cam lobe) that projects outward from the base circle 266. A part of the pivot pin 46 does not overlap with the cam nose 267 when viewed from the cam axis direction. That is, a part of the pivot pin 46 is located outward from the outer peripheral surface of the exhaust cam 264 when viewed from the cam axis direction. The pivot pin 46 includes a portion located inward of the base circle 266 when viewed from the cam axis 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 when viewed from the cam axis direction. When viewed from the cam axis direction, the distance between the rotation center c2 of the weight 42 and the decompression pin 44 is equal to or greater than the distance between the rotation center c2 of the weight 42 and the rotation center c1 of the cam shaft 26.

  FIG. 11 is a view showing the camshaft assembly as seen from the camshaft direction. As shown in FIG. 11, the outer shape of the flange 41 includes a larger portion than the outer shape of the first bearing 27 when viewed from the cam axis direction. Specifically, the first convex portion 412 protrudes outward from the outer peripheral surface of the first bearing 27.

  In the closed state, the first portion 421 of the weight 42 includes a first protrusion 424. The first protrusion 424 protrudes outward from the outer peripheral surface of the first bearing 27 when viewed from the cam axis direction. The outer peripheral surface of the second portion 422 is located inward of the outer peripheral surface of the first bearing 27 when viewed from the cam axis direction. The outer peripheral surface of the second weight portion 48 is located inward of the outer peripheral surface of the first bearing 27 when viewed from the cam axis direction.

  The pivot pin support portion 423 includes a protruding portion 425 that protrudes outward from the outer peripheral surface of the first bearing 27 when viewed from the cam axis direction. The maximum value of the protrusion length of the protrusion 425 is larger than the maximum value of the protrusion length of the first protrusion 424. That is, the protruding portion 425 is larger than the first protruding portion 424 and protrudes in the radial direction of the first bearing 27. The protruding length means a protruding length from the outer peripheral surface of the first bearing 27 in the radial direction of the first bearing 27.

  As shown in FIG. 11, 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 support wall 141 of the cylinder head 14. As shown in FIG. 7, the weight 42 includes an inner ring contact portion 426. The inner ring contact portion 426 is arranged side by side with the inner ring 271 in the cam axis direction. The inner ring contact portion 426 protrudes from the surface of the weight 42 adjacent to the first bearing 27 toward the inner ring 271.

  As shown in FIG. 11, the inner ring contact portion 426 is located inward of the inner peripheral surface of the outer ring 272. Note that, regardless of whether the weight 42 is in the closed state or the open state, the inner ring contact portion 426 is located inward of the inner peripheral surface of the outer ring 272. When viewed from the cam axis direction, at least a part of the inner ring contact portion 426 is disposed closer to the rotation center c2 of the weight 42 than the rotation center c1 of the cam shaft 26. The inner ring contact portion 426 is positioned between the rotation center c2 of the weight 42 and the cam shaft 26 when viewed from the cam axis direction. As shown in FIG. 4, when the inner ring contact portion 426 is in contact with the inner ring 271, the other part of the weight 42 does not contact the outer ring 272.

  Specifically, with the weight 42 closed, the inner ring contact portion 426 is disposed across the fourth region A4, the first region A1, and the second region A2. The inner ring contact portion 426 includes a first contact portion 426a, a second contact portion 426b, and a third contact portion 426c. When the weight 42 is closed, the first contact portion 426a is disposed in the first region A1. When the weight 42 is in the closed state, the second contact portion 426b is disposed in the second region A2. With the weight 42 closed, the third contact portion 426c is disposed in the fourth region A4. When viewed from the cam axis direction, the area of the first contact portion 426a is larger than the area of the second contact portion 426b. As viewed from the cam axis direction, the area of the first contact portion 426a is larger than the area of the third contact portion 426c.

  In FIG. 12, G <b> 1 indicates the position of the center of gravity of the weight 42. G2 indicates the position of the center of gravity of the weight 42 when the first protrusion 424 is not provided. In FIG. 12, the first protrusion 424 is hatched. “When there is no first protrusion 424” means a state in which the hatched portion in FIG. 12 is removed. Moreover, in FIG. 12, the outer peripheral surface of the 1st bearing 27 is shown with the dashed-two dotted line. As shown in FIG. 12, the center of gravity G1 of the weight 42 is disposed in the first region A1 when viewed from the cam axis direction. The distance between the gravity center G1 of the weight 42 and the rotation center c1 of the cam shaft 26 is larger than the distance between the gravity center G1 of the weight 42 and the rotation center c2 of the weight 42. When viewed from the cam axis direction, the first protrusion 424 is a portion 424a closer to the rotation center c2 of the weight 42 in the circumferential direction of the first bearing 27 than the position of the center of gravity G2 of the weight 42 when there is no first protrusion 424. And a distant portion 424b. Regarding the amount of outward protrusion from the outer peripheral surface of the first bearing 27, the near portion 424a is larger than the far portion 424b.

  In addition, when viewed from the cam axis direction, a portion of the inner ring contact portion 426 that is closer to the center of rotation c2 of the weight 42 than the center of gravity G1 of the weight 42 is a center of rotation c2 of the weight 42 that is closer to the center of gravity G1 of the weight 42 at the inner ring contact portion 426 It is bigger than the part far from. For example, the maximum width of the first contact portion 426 a in the radial direction of the cam shaft 26 is larger than the maximum width of the second contact portion 426 b in the radial direction of the cam shaft 26.

  FIG. 13 is a perspective view showing the surface of the weight 42 on the second camshaft end 262 side. FIG. 14 is a side view of the camshaft assembly as viewed from the direction of arrow XIV in FIG. As shown in FIG. 13, the maximum thickness of the first portion 421 in the cam axis direction is larger than the maximum thickness of the second portion 422 in the cam axis direction. The maximum thickness of the second weight portion 48 in the cam axis direction is larger than the maximum thickness of the second portion 422 in the cam axis direction.

  As shown in FIG. 13, the first portion 421 includes an inner diameter portion 421a and an outer diameter portion 421b. The inner diameter part 421a is located inside the outer diameter part 421b. The thickness of the outer diameter portion 421b in the cam axis direction is larger than the thickness of the inner diameter portion 421a in the cam axis direction. The outer diameter part 421b includes the first protrusion 424 described above. Therefore, the maximum thickness of the first protrusion 424 in the cam axis direction is larger than the maximum thickness of the second portion 422 in the cam axis direction. The maximum thickness of the first protrusion 424 in the cam axis direction is larger than the maximum thickness of the second weight portion 48 in the cam axis direction. The thickness of the first protrusion 424 in the cam axis direction is larger than the thickness of the pivot pin support portion 423 in the cam axis direction.

  As shown in FIG. 10, a part of the weight 42 overlaps the flange 41 when viewed from the radial direction of the cam shaft 26. Specifically, the outer diameter portion 421 b of the first portion 421 overlaps with the flange 41 when viewed from the radial direction of the cam shaft 26. The surface of the second weight portion 48 on the second cam shaft end portion 262 side and the surface of the inner diameter portion 421a face the surface of the flange 41 on the first cam shaft end portion 261 side. Between the second portion 422 and the flange 41, the head portion 431 of the decompression cam 43 described above is disposed.

  As shown in FIG. 13, the pivot pin support portion 423 includes a housing portion 423a and a boss portion 423b. The boss portion 423b protrudes from the accommodating portion 423a in the cam axis direction. The thickness of the accommodating portion 423a in the cam axis direction is smaller than the thickness of the first portion 421 and the second weight portion 48 in the cam axis direction. Therefore, the accommodating portion 423a has a shape that is recessed from the surface of the weight 42 in the cam axis direction.

  FIG. 15 is a view of the flange 41, the weight 42, and the return spring 45 as viewed from the second camshaft end 262 side. As shown in FIG. 15, the accommodating portion 423 a accommodates the return spring 45. The boss portion 423b is inserted into the return spring 45 described above. A hole 423c is provided in the boss portion 423b. A pivot pin 46 is inserted into the hole 423c of the boss portion 423b.

  As shown in FIGS. 13 and 15, the weight 42 includes a second locking portion 42 b. The second locking portion 42 b is locked to the second spring end 452 of the return spring 45. The second locking portion 42b is included in the first portion 421. Specifically, the second locking portion 42 b is a step portion formed with respect to the pivot pin support portion 423 in the first portion 421.

  As shown in FIGS. 14 and 15, the flange 41 includes a first locking portion 42 a. The first locking portion 42 a is locked to the first spring end 451 of the return spring 45. Specifically, the first locking portion 42 a is a part of the first convex portion 412. The first locking portion 42a is formed integrally with the flange 41. For example, the flange 41 includes the first locking portion 42a and is integrally formed by a manufacturing method such as sintering, forging, or casting.

  FIG. 16 is a view showing the cylinder head 14 with the head cover 19 removed. As shown in FIG. 16, 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 support wall 141. The first bearing support hole 143 includes a first recess 144, a second recess 145, and a third recess 146. The first recess 144, the second recess 145, and the third recess 146 are located on the opposite side of the crankshaft 11 with respect to the center of the first bearing support hole 143. The first recess 144 has a shape through which the first protrusion 424 and the intake cam 263 can pass. The second recess 145 has a shape through which the exhaust cam 264 can pass. The third recess 146 has a shape through which the pivot pin support 423 can pass. A part of the first recess 144 is located on the opposite side of the crankshaft 11 with respect to the center of the first bearing support hole 143, and the other part is connected to the crankshaft 11 with respect to the center of the first bearing support hole 143. It may be located on the same side. Alternatively, a part of the second recess 145 is located on the opposite side of the crankshaft 11 with respect to the center of the first bearing support hole 143, and the other part is connected to the crankshaft 11 with respect to the center of the first bearing support hole 143. It may be located on the same side.

  In the engine 7 according to the present embodiment, the first protrusion 424 of the first portion 421 located in the first region A <b> 1 of the weight 42 protrudes outward from the outer peripheral surface of the first bearing 27. As a result, the center of gravity G1 of the weight 42 can be moved away from the rotation center c1 of the cam shaft 26 as compared with the case where the first portion 421 does not protrude (see the center of gravity G2 in FIG. 12). Therefore, if the rotational speed of the cam shaft 26 is the same, the centrifugal force applied to the weight 42 increases. Thereby, since the spring force of the return spring 45 can be increased, the opening of the weight 42 due to gravity can be suppressed without increasing the set rotational speed.

  The outer peripheral surface of the second portion 422 of the weight 42 is located inward of the outer peripheral surface of the first bearing 27 when viewed from the axial direction of the cam shaft 26. Therefore, the center of gravity G1 of the weight 42 can be further away from the rotation center c1 of the cam shaft 26. Further, the position of the center of gravity G1 of the weight 42 can be made closer to the rotation center c2 of the weight 42 as compared with the case where the outer peripheral surface of the second portion 422 is located outward from the outer peripheral surface of the first bearing 27. . Thereby, the moment by the gravity which acts on the weight 42 can be made small. For this reason, the opening of the weight 42 by gravity can be suppressed. This makes it easier to avoid the state in which the weight 42 is open when the engine 7 is started, so that the startability of the engine 7 can be improved.

  The maximum thickness of the first protrusion 424 in the axial direction of the cam shaft 26 is larger than the maximum thickness of the second portion 422 in the axial direction of the cam shaft 26. Therefore, the center of gravity G1 of the weight 42 can be further away from the rotation center c1 of the cam shaft 26.

  When viewed from the axial direction of the camshaft 26, the first protrusion 424 is located closer to the rotation center c2 of the weight 42 in the circumferential direction of the first bearing 27 than the position of the center of gravity G2 of the weight 42 when there is no first protrusion 424. The near portion 424a is larger than the far portion 424b. For this reason, the center of gravity G1 of the weight 42 can be made closer to the rotation center c2 of the weight 42 than in the case where the far portion 424b is larger than the near portion 424a.

  The thickness of the first protrusion 424 in the axial direction of the cam shaft 26 is larger than the thickness of the pivot pin support portion 423 in the axial direction of the cam shaft 26. For this reason, the center of gravity G1 of the weight 42 can be moved away from the rotation center c1 of the cam shaft 26 as compared with the case where the thickness of the first protrusion 424 is smaller than the thickness of the pivot pin support 423.

  The first bearing support hole 143 of the cylinder head 14 has a first recess 144, a second recess 145, and a third recess 146. Therefore, when the cam shaft 26, the decompression mechanism 40, and the first bearing 27 are integrally attached to the cylinder head 14, the first protrusion 424 and the intake cam 263 pass through the first recess 144, and the exhaust cam 264 The pivot pin support 423 can pass through the third recess 146 through the second recess 145. For this reason, it can avoid that the 1st protrusion part 424, the intake cam 263, the exhaust cam 264, and the pivot pin support part 423 interfere with the 1st bearing support hole 143.

  The first recess 144, the second recess 145, and the third recess 146 are located on the opposite side of the crankshaft 11 with respect to the center of the first bearing support hole 143. For this reason, it is possible to suppress a decrease in the support strength of the portion on the crankshaft 11 side of the first bearing support hole 143 that receives a large load from the crankshaft 11.

  As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the summary of invention.

  The shape of the weight is not limited to the shape of the above embodiment, and may be changed. For example, FIG. 17 is a diagram showing a weight 42 according to the first modification. As shown in FIG. 17, the second portion 422 may include a second protrusion 427. The second protrusion 427 protrudes outward from the outer peripheral surface of the first bearing 27 when viewed from the axial direction of the cam shaft 26. The volume of the first protrusion 424 is larger than the volume of the second protrusion 427. In this case, similarly to the above embodiment, the center of gravity G1 of the weight 42 can be further away from the rotation center c1 of the cam shaft 26. Further, the position of the center of gravity G1 of the weight 42 can be brought closer to the rotation center c2 of the weight 42 than in the case where the volume of the second protrusion 427 is larger than the volume of the first protrusion 424.

  FIG. 18 is a view showing a weight 42 according to a second modification. As shown in FIG. 18, the weight 42 may include a third portion 428 disposed in the third region A3. The outer peripheral surface of the third portion 428 is located inward of the outer peripheral surface of the first bearing 27 when viewed from the axial direction of the cam shaft 26. The maximum thickness of the first protrusion 424 in the axial direction of the cam shaft 26 is larger than the maximum thickness of the second weight portion 48 in the axial direction of the cam shaft 26. In this case, the outer peripheral surface of the third portion 428 has the center of gravity G1 of the weight 42 as compared with the case where the outer peripheral surface of the third bearing 428 is positioned outward from the outer peripheral surface of the first bearing 27 as viewed from the axial direction of the cam shaft 26. 26 away from the center of rotation c1.

  Alternatively, the circumferential length of the weight may be shorter than the weight 42 of the above embodiment. For example, the circumferential end portion 471 of the first weight portion 47 may be disposed in the first region A1.

  FIG. 19 is a view showing a weight 42 according to a third modification. As shown in FIG. 19, the third portion 428 may include a third protrusion 429. The third protrusion 429 protrudes outward from the outer peripheral surface of the first bearing 27 when viewed from the axial direction of the cam shaft 26. The volume of the first protrusion 424 is larger than the volume of the third protrusion 429. In this case, the center of gravity G1 of the weight 42 can be moved away from the rotation center c1 of the cam shaft 26 as compared with the case where the volume of the third protrusion 429 is larger than the volume of the first protrusion 424.

  FIG. 20 is a view showing a weight 42 according to a fourth modification. As shown in FIG. 20, the pivot pin support portion 423 may be located inward of the outer peripheral surface of the first bearing 27 when viewed from the cam axis direction.

  FIG. 21 is a view showing a weight 42 according to a fifth modification. As shown in FIG. 21, the pivot pin 46 may be located inward of the basic circle 266 of the exhaust cam 264 when viewed from the cam axis direction. That is, the rotation center c <b> 2 of the weight 42 may be located inward of the basic circle 266 of the exhaust cam 264 when viewed from the cam axis direction.

  FIG. 22 is a view showing a weight 42 according to a sixth modification. As shown in FIG. 22, the rotation center c <b> 2 of the weight 42 may be located outward from the cam crest 267 of the exhaust cam 264 when viewed from the cam axis direction. Further, the entire pivot pin 46 may be located outward from the outer peripheral surface of the exhaust cam 264.

  In the above embodiment, the weight 42 is supported by the cam shaft 26 via the flange 41, but the weight may be directly supported by the cam shaft. In the above embodiment, the flange 41 is separate from the cam shaft and is fixed to the cam shaft by press-fitting, but may be fixed by a fixing means other than press-fitting. Alternatively, the flange may be formed integrally with the cam shaft.

  The inner ring contact portion of the weight may be omitted. The weight accommodating portion may be omitted. That is, the return spring may be arranged at a position other than the weight.

  In the above embodiment, a scooter type motorcycle is cited as an example of a vehicle. However, the vehicle according to the present invention is not limited to a scooter, but other types of motorcycles such as a sports type, an off-road type, and a moped. There may be. Here, the motorcycle is not limited to two wheels, but includes a three-wheeled vehicle. The vehicle according to the present invention is preferably a straddle-type vehicle such as a motorcycle, a rough terrain vehicle (ALL-TERRAIN VEHICLE), or a snowmobile, but is a vehicle other than a straddle-type vehicle. Also good.

  The terms and expressions used herein are used for explanation and are not used for limited interpretation. It should be recognized that any equivalents of the features shown and described herein are not excluded and that various modifications within the claimed scope of the invention are permitted. The present invention can be embodied in many different forms. This disclosure should be regarded as providing embodiments of the principles of the invention. The embodiments are described herein with the understanding that the embodiments are not intended to limit the invention to the preferred embodiments described and / or illustrated herein. It is not limited to the embodiment described here. The present invention also encompasses any embodiment that includes equivalent elements, modifications, deletions, combinations, improvements and / or changes that may be recognized by those skilled in the art based on this disclosure. Claim limitations should be construed broadly based on the terms used in the claims and should not be limited to the embodiments described herein or in the process of this application.

  ADVANTAGE OF THE INVENTION According to this invention, the engine and vehicle which can improve the startability of a decompression mechanism can be provided.

7 Engine 14 Cylinder head 23 Exhaust valve 25 Valve mechanism 26 Cam shaft 27 First bearing 40 Decompression mechanism 42 Weight 45 Return spring 43 Decompression cam A1 First region A2 Second region A3 Third region 424 First protrusion 421 First part 422 Second portion 427 Second protrusion 48 Second weight 429 Third protrusion 423 Pivot pin support 46 Pivot pin 11 Crank shaft 29 Cam chain 143 First bearing support hole 144 First recess

Claims (11)

A cylinder head;
An exhaust valve accommodated in the cylinder head;
A valve mechanism for opening and closing the exhaust valve;
A camshaft that drives the valve mechanism by contacting the valve mechanism;
A bearing that rotatably supports the camshaft on the cylinder head;
A decompression mechanism disposed between both ends of the cam shaft in the axial direction;
With
The decompression mechanism is
A weight that is rotatably supported between the closed state and the open state with respect to the camshaft;
A return spring that urges the weight to return from the open state to the closed state;
A decompression cam provided so as to come into contact with the valve mechanism when the weight is in the closed state and not to come into contact with the valve mechanism when the weight is in the open state;
Including
A straight line passing through the rotation center of the cam shaft and the rotation center of the weight is a vertical axis when viewed from the axial direction of the cam shaft, and a straight line passing through the rotation center of the cam shaft is orthogonal to the vertical axis. The direction from the rotation center of the cam shaft toward the rotation center of the weight among the directions parallel to the vertical axis is a first vertical direction, and one of the directions parallel to the horizontal axis is a first horizontal direction,
The center of gravity of the weight is disposed in a first region located in the first vertical direction with respect to the horizontal axis and in the first horizontal direction with respect to the vertical axis when viewed from the axial direction of the cam shaft. ,
The weight includes a first portion arranged in the first region when viewed from the axial direction of the cam shaft,
In the closed state, the first portion includes a first protrusion that protrudes outward from the outer peripheral surface of the bearing when viewed from the axial direction of the camshaft.
engine. The direction opposite to the first vertical direction is the second vertical direction,
The weight further includes a second portion;
The second portion is disposed in a second region located in the second vertical direction with respect to the horizontal axis and in the first horizontal direction with respect to the vertical axis when viewed from the axial direction of the cam shaft. ,
The outer peripheral surface of the second portion is located inward of the outer peripheral surface of the bearing as viewed from the axial direction of the cam shaft.
The engine according to claim 1. The direction opposite to the first vertical direction is the second vertical direction,
The weight further includes a second portion;
The second portion is disposed in a second region located in the second vertical direction with respect to the horizontal axis and in the first horizontal direction with respect to the vertical axis when viewed from the axial direction of the cam shaft. ,
The second portion includes a second projecting portion that projects outward from the outer peripheral surface of the bearing when viewed from the axial direction of the cam shaft,
The volume of the first protrusion is larger than the volume of the second protrusion,
The engine according to claim 1. The maximum thickness of the first protrusion in the axial direction of the cam shaft is greater than the maximum thickness of the second portion in the axial direction of the cam shaft;
The engine according to claim 2 or 3. The direction opposite to the first vertical direction is the second vertical direction,
The direction opposite to the first lateral direction is the second lateral direction,
The weight further includes a third portion,
The third portion is disposed in a third region located in the second vertical direction with respect to the horizontal axis and in the second horizontal direction with respect to the vertical axis when viewed from the axial direction of the cam shaft. ,
The outer peripheral surface of the third portion is located inward of the outer peripheral surface of the bearing as viewed from the axial direction of the cam shaft.
The engine according to any one of claims 1 to 4. The direction opposite to the first vertical direction is the second vertical direction,
The direction opposite to the first lateral direction is the second lateral direction,
The weight further includes a third portion,
The third portion is disposed in a third region located in the second vertical direction with respect to the horizontal axis and in the second horizontal direction with respect to the vertical axis when viewed from the axial direction of the cam shaft. ,
The third portion includes a third protruding portion that protrudes outward from the outer peripheral surface of the bearing when viewed from the axial direction of the cam shaft,
The volume of the first protrusion is larger than the volume of the third protrusion,
The engine according to any one of claims 1 to 4. The maximum thickness of the first protrusion in the axial direction of the cam shaft is greater than the maximum thickness of the third portion in the axial direction of the cam shaft;
The engine according to claim 5 or 6. When viewed from the axial direction of the cam shaft, the first protrusion is farther from the portion near the rotation center of the weight in the circumferential direction of the bearing than the position of the center of gravity of the weight when there is no first protrusion. The near portion is larger than the far portion,
The engine according to any one of claims 1 to 7. The weight includes a pivot pin support;
The decompression mechanism further includes a pivot pin attached to the pivot pin support.
The weight is rotatably supported with respect to the camshaft via the pivot pin,
The thickness of the first projecting portion in the axial direction of the cam shaft is greater than the thickness of the pivot pin support portion in the axial direction of the cam shaft.
The engine according to any one of claims 1 to 8. A crankshaft,
A cam chain wound around the crankshaft and the camshaft;
Further comprising
The cylinder head includes a bearing support hole that supports the bearing,
The bearing support hole includes a recess through which the first protrusion can pass,
At least a part of the recess is located on the opposite side of the crankshaft with respect to the center of the bearing support hole.
The engine according to any one of claims 1 to 9.   A vehicle comprising the engine according to claim 1.

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