TW201604382A - Engine and vehicle - Google Patents

Abstract

A straight line that passes through the center of rotation of a cam shaft and the center of rotation of a 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 and 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 direction opposite the first horizontal direction is assumed to be a second horizontal direction. The center of gravity of the weight is disposed in a first region as seen from the axial direction of the cam shaft. The first region is located in the first vertical direction from the horizontal axis and in the first horizontal direction from the vertical axis. A circumferential direction end portion of a first weight portion is located in the first horizontal direction from the vertical axis. A circumferential direction end portion of a second weight portion is located in the second horizontal direction from the vertical axis. The first weight portion is longer than the second weight portion in the circumferential direction of the cam shaft. The decompression pin is connected to the first weight portion.

Description

Engine and vehicle

The present invention relates to an engine and a vehicle including a decompression mechanism (hereinafter referred to as a "pressure reducing mechanism").

When the engine is started, the engine needs to be rotated by an external force until the start is completed. For example, there is a person who rotates with a starter motor or a person who rotates with a foot starter. On the other hand, in the compression step of the engine, the air in the cylinder is compressed, so the resistance to rotation increases. In order to reduce such resistance, a pressure reducing mechanism for reducing the pressure in the cylinder during the compression step when the engine is rotated by an external force is known.

For example, the pressure reducing mechanism of the engine disclosed in Japanese Laid-Open Patent Publication No. 2008-128171 has a pressure reducing cam that is switched to an actuated state and a released state by the rotation of the weight body. The pressure reducing mechanism supports the sprocket of the cam chain. Therefore, there is a problem that the cam shaft including the pressure reducing mechanism becomes larger in the axial direction.

In the engine disclosed in Japanese Laid-Open Patent Publication No. 2008-64083, the pressure reducing mechanism is disposed at a position between both end portions of the cam shaft. The pressure reducing mechanism has a weight body and a pressure reducing cam, and the weight body is rotatably supported by the support shaft with respect to the cam shaft. The decompression cam and the weight body are connected by a pin, and the weight body rotates around the support shaft, whereby the pin rotates the decompression cam.

In the pressure reducing mechanism of Japanese Laid-Open Patent Publication No. 2008-64083, when the cam shaft does not rotate, the weight body is held in a closed state by the action of the return spring. For weight closure In this state, the decompression cam is in a state in which the exhaust valve can be acted upon. 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 body rotates around the support shaft due to centrifugal force. When the rotational speed of the camshaft rises above a certain set rotational speed, the centrifugal force exceeds the elastic force of the return spring, thereby bringing the weight body into an open state. When the weight body is opened, the pressure reducing cam does not act on the exhaust valve.

In the pressure reducing mechanism of Japanese Patent Laid-Open No. 2008-64083, the space between the both ends of the cam shaft can be effectively utilized. Therefore, the cam shaft including the pressure reducing mechanism can be simplified in the axial direction as compared with the case where the pressure reducing mechanism is disposed outside the cam shaft. However, the inventors of the present invention have found that in the engine of the prior art as described in Japanese Patent Laid-Open No. 2008-64083, there is a case where the pressure reducing mechanism is not actuated at the time of starting, and the improvement of the startability is insufficient.

An object of the present invention is to provide an engine and a vehicle that can improve the startability of a pressure reducing mechanism.

The inventor of the present invention verified the reason why the decompression was not activated at the time of starting in the engine of the prior art. As a result, it can be seen that there is a case where the weight body has been opened when the engine is started. That is, it can be seen that there is a case where the weight body is rotated to the open state when the cam shaft is not rotated.

According to the research of the inventor of the present case, the reason is that the spring force of the return spring is weak. Further, the reason why the elastic force is weakened is that the weight body is made small by disposing the pressure reducing mechanism between both ends of the cam shaft. In other words, in the pressure reducing mechanism of Patent Document 2, since the pressure reducing mechanism is disposed between both ends of the cam shaft, compared with the pressure reducing mechanism of Patent Document 1, The configuration is more restrictive. Therefore, in the pressure reducing mechanism of Patent Document 2, it is necessary to make the weight body smaller than the weight body in the pressure reducing mechanism of Patent Document 1.

If the weight body becomes smaller, the mass of the weight body becomes smaller. If the rotation speed is the same, the smaller the mass of the weight body, the smaller the centrifugal force acting on the weight body. Therefore, the centrifugal force acting on the weight body becomes small at the set rotation speed for setting the weight body to the open state. Therefore, it is also necessary to reduce the elasticity.

However, the position of the weight body varies depending on the phase of the rotation of the cam shaft. There is also a case where the cam shaft is stopped in a state in which the opening direction of the weight body coincides with the direction of gravity. The inventors of the present invention have found that at this time, the moment caused by the gravity acting on the weight body becomes larger than the elastic force due to the reduction in the elastic force, and as a result, the weight body is opened.

It is considered that in order to prevent the phenomenon as described above, the elastic force is increased, but if the elastic force is increased, the set rotational speed of the opening weight body is increased. Setting the increase in the rotational speed becomes a cause of noise, which is not preferable.

An engine of one aspect of the present invention includes a cylinder head, an exhaust valve, a valve operating mechanism, a camshaft, a bearing, and a pressure reducing mechanism. The exhaust valve is housed in the cylinder head. The valve mechanism opens and closes the exhaust valve. The camshaft drives the valve actuation mechanism by contact with the valve actuation mechanism. The bearing rotatably supports the camshaft to the cylinder head. The pressure reducing mechanism is disposed between both end portions in the axial direction of the cam shaft. The pressure reducing mechanism includes a weight body, a return spring, a pressure reducing cam, and a pressure reducing pin. The weight body is rotatably supported between the closed state and the open state relative to the camshaft. The return spring biases the weight body in such a manner that the weight body returns from the open state to the closed state. The decompression cam is disposed in such a manner as to be in contact with the valve actuation mechanism when the weight body is in the closed state, and not in contact with the valve actuation mechanism when the weight body is in the open state. The decompression pin connects the weight body and the decompression cam.

The straight line passing through the center of rotation of the cam shaft and the center of rotation of the weight body is set as the vertical axis as viewed in the axial direction of the cam shaft. A straight line orthogonal to the vertical axis and passing through the center of rotation of the cam shaft is set as the horizontal axis. Orienting from the center of rotation of the camshaft in a direction parallel to the longitudinal axis The direction of the center of rotation of the weight body is set to the first longitudinal direction. One of the directions parallel to the horizontal axis is set to the first horizontal direction. The direction opposite to the first lateral direction is referred to as the second lateral direction.

The center of gravity of the weight body is disposed in the first region as viewed in the axial direction of the cam shaft. The first region is located in the first longitudinal direction with respect to the horizontal axis and is located in the first lateral direction with respect to the vertical axis. The weight body includes a first weight body portion and a second weight portion. The first weight body extends from the center of rotation of the weight body along the circumferential direction of the cam shaft. The circumferential end portion of the first weight body portion is located in the first lateral direction with respect to the vertical axis. The second weight body extends from the center of rotation of the weight body along the circumferential direction of the cam shaft. The circumferential end portion of the second weight portion is located in the second lateral direction with respect to the vertical axis. In the circumferential direction of the camshaft, the first weight body portion is longer than the second weight body. The decompression pin is connected to the first weight body.

In the engine of the aspect, the circumferential end portion of the first weight body portion is located in the first lateral direction with respect to the vertical axis. That is, the first weight body portion extends so as not to straddle the vertical axis in the second lateral direction. Therefore, the center of gravity of the weight body can be rotated away from the cam shaft as compared with the case where the first weight body portion extends from the region in the first lateral direction with respect to the longitudinal axis to the position in the second lateral direction across the vertical axis. center. Therefore, if the rotational speed of the cam shaft is the same, the centrifugal force applied to the weight body becomes large. Thereby, the elastic force can be increased, so that it is possible to suppress the opening of the weight body caused by the gravity without increasing the set number of revolutions.

Moreover, the center of gravity of the weight body can be brought close to the center of rotation of the weight body, so that the moment caused by the gravity acting on the weight body can be reduced. Therefore, the opening of the weight body caused by gravity can be suppressed.

Further, the decompression pin is connected to the first weight body portion of the second weight body. Therefore, the distance between the decompression pin and the center of rotation of the weight body can be increased as compared with the case where the decompression pin is connected to the second weight body. Thereby, the amount of movement of the decompression pin with respect to the rotation angle of the weight body is increased. In other words, the rotation angle of the weight body for switching the weight body from the closed state to the open state can be reduced. Thereby, the displacement of the center of gravity of the weight body when the weight body is in the closed state and in the open state can be reduced. Further, by making the rotation angle of the weight body small, it is possible to easily avoid interference between the weight body and the surrounding members. Thereby, the shape of the weight body The degree of freedom is higher.

Here, the distance between the center of gravity of the weight body and the center of rotation of the cam shaft when the weight body is in the open state is greater than the distance between the center of gravity of the weight body and the center of rotation of the cam shaft when the weight body is in the closed state. . Therefore, the greater the displacement of the center of gravity of the weight body when the weight body is in the closed state and the open state, the more difficult it is for the weight body to return to the closed state.

However, in the engine of the present aspect, as described above, the displacement of the center of gravity of the weight body when the weight body is in the closed state and in the open state can be reduced, so that the weight body is easily restored to the closed state.

As described above, in the engine of the present aspect, it is easy to avoid the state in which the weight body is opened when starting, so that the startability of the engine can be improved.

Preferably, the first weight body portion includes the first portion and the second portion. The first portion is disposed in the first region as viewed in the axial direction of the cam shaft. The second portion is disposed in the second region as viewed in the axial direction of the cam shaft. The second region is located in the second longitudinal direction with respect to the horizontal axis and is located in the first lateral direction with respect to the vertical axis. The second longitudinal direction is opposite to the first longitudinal direction. The end portion of the first weight portion is disposed in the second region as viewed in the axial direction of the cam shaft. In this case, the center of gravity of the weight body can be moved away from the cam as compared with the case where the first weight body portion extends from the region in the first lateral direction with respect to the vertical axis to the position in the second lateral direction across the vertical axis. The center of rotation of the shaft. Further, it is easier to arrange the decompression pin away from the center of rotation of the weight body than when the end portion of the first weight portion is disposed in the first region.

Preferably, the decompression pin is disposed in the second region as viewed in the axial direction of the cam shaft. In this case, the end portion of the first weight portion can be disposed in the second region as viewed in the axial direction of the cam shaft.

Preferably, the distance between the center of rotation of the weight body and the decompression pin is greater than the distance between the center of rotation of the weight body and the center of rotation of the cam shaft as viewed in the axial direction of the camshaft. In this case, the distance between the decompression pin and the center of rotation of the weight body can be increased.

Preferably, the camshaft includes an exhaust cam that is in contact with the valve actuation mechanism. Exhaust cam package A cam projection that protrudes more outward than the base circle. Viewed from the axial direction of the camshaft, the center of rotation of the weight body is located radially inward of the camshaft from the base circle of the exhaust cam. In this case, the center of rotation of the weight body can be brought close to the center of gravity of the weight body.

It is also possible to observe from the axial direction of the cam shaft such that the center of rotation of the weight body is located radially outward of the cam shaft from the outer peripheral surface of the cam lobe. In this case, the distance between the decompression pin and the center of rotation of the weight body can be increased.

Preferably, the weight body does not have a portion disposed in the third region as viewed from the axial direction of the cam shaft. The third region is located in the second longitudinal direction with respect to the horizontal axis and in the second lateral direction with respect to the vertical axis. In this case, the center of gravity of the weight body can be further moved away from the center of rotation of the camshaft. Moreover, the center of rotation of the weight body can be brought closer to the center of gravity of the weight body.

Preferably, the end portion of the second weight portion is disposed in the fourth region as viewed in the axial direction of the cam shaft. The fourth region is located in the first longitudinal direction with respect to the horizontal axis and in the second lateral direction with respect to the vertical axis. In this case, the center of rotation of the weight body can be brought close to the center of gravity of the weight body.

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

According to the present invention, an engine and a vehicle capable of improving the startability of a pressure reducing mechanism can be provided.

1‧‧‧ Vehicles

2‧‧‧ Vehicle body

2a‧‧‧flat pedals

3‧‧‧ Front wheel

4‧‧‧ Rear wheel

5‧‧‧Hands

6‧‧‧s

7‧‧‧ engine

8‧‧‧Transmission

11‧‧‧ crankshaft

12‧‧‧ crankcase

13‧‧‧Cylinder block

14‧‧‧Cylinder head

15‧‧‧Piston

16‧‧‧ Connecting rod

17‧‧‧ combustion chamber

18‧‧‧Mars plug

19‧‧‧ head cover

21‧‧‧Intake 埠

22‧‧‧Exhaust gas

23‧‧‧Exhaust valve

24‧‧‧Intake valve

25‧‧‧Valve mechanism

26‧‧‧Camshaft

27‧‧‧1st bearing

28‧‧‧2nd bearing

29‧‧‧Cam chain

31‧‧‧1st sprocket

32‧‧‧2nd sprocket

33‧‧‧Exhaust rocking shaft

34‧‧‧Exhaust rocker arm

35‧‧‧Intake shaft

36‧‧‧Intake swing arm

40‧‧‧Relief mechanism

41‧‧‧Flange

42‧‧‧weights

42a‧‧‧1st stop

42b‧‧‧2nd stop

43‧‧‧Decompression cam

44‧‧‧Demolition pin

45‧‧‧Return spring

46‧‧‧ pivot

47‧‧‧1st weight body

48‧‧‧2nd weight body

141‧‧‧1st support wall

142‧‧‧2nd support wall

143‧‧‧1st bearing support hole

144‧‧‧1st recess

145‧‧‧2nd recess

146‧‧‧3rd recess

231‧‧‧Exhaust valve spring

232‧‧‧ rod end

241‧‧‧Intake valve spring

242‧‧‧ rod end

261‧‧‧1st camshaft end

262‧‧‧2nd camshaft end

263‧‧‧Intake cam

264‧‧‧Exhaust cam

265‧‧‧ recess

266‧‧‧Ke Yuan

267‧‧‧ cam convex

271‧‧‧ Inner wheel

272‧‧‧Outside

341‧‧‧arm body

342‧‧‧Exhaust roller

343‧‧‧Exhaust valve pusher

361‧‧‧arm body

362‧‧‧Intake roller

363‧‧‧Intake valve pusher

411‧‧‧ hole

412‧‧‧1st convex

413‧‧‧2nd convex

414‧‧‧ hole

421‧‧‧Part 1

421a‧‧‧Down section

421b‧‧‧ OD

422‧‧‧Part 2

423‧‧‧ pivot support department

423a‧‧‧Storage Department

423b‧‧‧seat

423c‧‧ hole

424‧‧‧1st protrusion

Closer part of 424a‧‧

424b‧‧‧ farther part

425‧‧‧Protruding

426‧‧‧Internal wheel contact

426a‧‧1st contact

426b‧‧‧2nd contact

426c‧‧3rd contact

427‧‧‧2nd protrusion

431‧‧‧ head

432‧‧‧Axis

433‧‧‧ slot department

434‧‧‧Cam Department

451‧‧‧1st spring end

452‧‧‧2nd spring end

471‧‧‧ end

481‧‧‧End

A1‧‧‧1st area

A2‧‧‧2nd area

A3‧‧‧3rd area

A4‧‧‧4th area

C1‧‧‧Rotation center of camshaft 26

C2‧‧‧The center of rotation of the counterweight 42

G1‧‧‧Center of gravity 42

G2‧‧‧ Center of gravity of the weight body 42 in the absence of the first protrusion 424

X‧‧‧ horizontal axis

X1‧‧‧1st horizontal direction

X2‧‧‧2nd horizontal direction

Y‧‧‧ vertical axis

Y1‧‧‧1st longitudinal direction

Y2‧‧‧2nd longitudinal direction

Figure 1 is a side view of the vehicle.

Figure 2 is a cross-sectional view of a portion of the engine.

Figure 3 is a cross-sectional view of the cylinder head in a plane perpendicular to the camshaft.

4 is an enlarged cross-sectional view of the camshaft assembly.

Figure 5 is a perspective view of a camshaft assembly.

Figure 6 is an exploded view of the camshaft assembly.

Fig. 7 is a view showing a weight body in a closed state.

Fig. 8 is a view showing a weight body in an open state.

9(A) and (B) are enlarged views of the exhaust cam.

Figure 10 is a side view of the camshaft assembly.

Fig. 11 is a view showing the cam shaft assembly viewed from the cam axis direction.

Fig. 12 is a view showing the weight body viewed from the direction of the cam axis.

Figure 13 is a perspective view of the weight body.

Fig. 14 is a side view of the camshaft assembly viewed from the direction of the arrow XIV of Fig. 10.

Fig. 15 is a view showing the flange, the weight body, and the return spring viewed from the direction of the cam axis.

Fig. 16 is a view showing a cylinder head in a state in which the head cover is removed.

Fig. 17 is a view showing a weight body of a first modification.

Fig. 18 is a view showing a weight body of a second modification.

Fig. 19 is a view showing a weight body of a third modification.

Fig. 20 is a view showing a weight body of a fourth modification.

Hereinafter, the vehicle 1 of the embodiment will be described with reference to the drawings. 1 is a side view of the vehicle 1. The vehicle 1 is a scooter type locomotive. The vehicle 1 includes a vehicle body 2, a front wheel 3, a rear wheel 4, a handle 5, and a seat portion 6. The vehicle body 2 includes a flat footboard 2a. The vehicle body 2 supports the front wheel 3 and the rear wheel 4. The handle 5 and the seat portion 6 are attached to the vehicle body 2. The flat footboard 2a is disposed in front of and below the seat portion 6.

The vehicle 1 includes an engine 7 of an embodiment. 2 is a cross-sectional view of a portion of the engine 7. As shown in FIG. 2, the engine 7 includes a crankshaft 11, a crankcase 12, a cylinder block 13, a cylinder head 14, and a head cover 19. The cylinder block 13 is coupled to the crankcase 12. The cylinder block 13 may be integral with the crankcase 12 or may be separate from the crankcase 12. The cylinder block 13 houses the piston 15. The piston 15 is coupled to the crankshaft 11 via a connecting rod 16 . The crankshaft 11 is connected to the gearbox 8.

The cylinder head 14 is coupled to the cylinder block 13. The cylinder head 14 includes a combustion chamber 17. On the cylinder head 14 installed with Mars plug 18. The front end of the Mars plug 18 is disposed facing the combustion chamber 17. The head cover 19 is mounted to the cylinder head 14.

The engine 7 includes a valve mechanism 25 and a camshaft 26. The valve mechanism 25 and the cam shaft 26 are housed in the cylinder head 14. The camshaft 26 drives the valve actuation mechanism 25 by contact with the valve actuation mechanism 25.

The camshaft 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 axis 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 rotatably support the cam shaft 26 to the cylinder head 14. The outer diameter of the first bearing 27 is larger than the outer diameter of the second bearing 28. Further, the first support wall 141 can support the cam shaft 26 without passing through the first bearing 27 . The second support wall 142 can also support the cam shaft 26 without passing through the second bearing 28 .

The camshaft 26 includes a first camshaft end 261 and a second camshaft 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 axis direction.

A cam chain 29 is wound around the cam shaft 26 and the crankshaft 11. Specifically, the first sprocket 31 is attached to the cam shaft 26 . The first sprocket 31 is attached to the first camshaft 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 camshaft 26 via the cam chain 29, whereby the camshaft 26 is rotated. The camshaft 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. The intake cam 263 and the exhaust cam 264 are rotated by the rotation of the cam shaft 26. The intake cam 263 and the exhaust cam 264 are in contact with the valve mechanism 25, and the intake cam 263 and the exhaust cam 264 are rotated to drive the valve mechanism 25.

3 is a cross-sectional view of the cylinder head 14 in a plane perpendicular to the camshaft 26. As shown in Figure 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 housed 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 actuation 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 toward the intake valve 24 in the direction of closing 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 the direction in which the exhaust valve 23 closes the exhaust port 22.

The valve actuation mechanism 25 includes an exhaust swing shaft 33 and an exhaust swing arm 34. The exhaust rocking 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 swing arm 34 is slidably supported by the exhaust swing shaft 33 around the exhaust swing shaft 33. The exhaust swing arm 34 is provided to operate the exhaust valve 23. The exhaust swing arm 34 includes an arm body 341, an exhaust roller 342, and an exhaust valve pressing portion 343.

The arm body 341 is rockably supported by the exhaust rocking shaft 33. One end of the arm body 341 rotatably supports the exhaust roller 342. 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 front end of the exhaust valve pressing portion 343 faces the rod end 232 of the exhaust valve 23.

When the exhaust roller 342 is pushed up by the exhaust cam 264, the exhaust swing arm 34 is rocked, whereby the exhaust valve pressing portion 343 presses the rod end 232 of the exhaust valve 23. Thereby, the exhaust valve 23 is depressed to open the exhaust port 22. When the exhaust roller 342 is not pushed up by the exhaust cam 264, the exhaust valve 22 is closed by the exhaust valve spring 231 pushing up the exhaust valve 23.

The valve actuation mechanism 25 includes an intake swing shaft 35 and an intake swing arm 36. The intake rocking shaft 35 is disposed in parallel with the cam shaft 26. The intake rocking shaft 35 is supported by the cylinder head 14. The intake swing arm 36 is slidably supported by the intake swing shaft 35 about the intake swing shaft 35. The intake swing arm 36 is arranged to operate the intake valve 24. The intake swing arm 36 includes an arm body 361, an intake roller 362, and an intake valve pressing portion 363.

The arm body 361 is rockably supported by the intake rocking shaft 35. One end of the arm body 361 rotatably supports the intake roller 362. 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 is rotated by the rotation of the intake cam 263. The front end of the intake valve pressing portion 363 is opposed to the rod end 242 of the intake valve 24.

When the air roller 362 is pushed up on the intake cam 263, the intake swing arm 36 is rocked, whereby the intake valve pressing portion 363 presses down the rod end of the intake valve 24. Thereby, the intake valve 24 is depressed to open the intake port 21. When the air roller 362 is not propelled by the intake cam 263, the intake valve 21 is closed by pushing the air valve 24 on the intake valve spring 241.

As shown in FIG. 2, the engine 7 includes a pressure reducing mechanism 40. 4 is an enlarged view of an assembly of the camshaft 26, the pressure reducing mechanism 40, and the first bearing 27 (hereinafter referred to as a "camshaft assembly"). The pressure reducing 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 pressure reducing mechanism 40 is disposed between the first support wall 141 of the cylinder head 14 and the second support wall 142.

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

As shown in FIG. 6, the flange 41 is separated from the cam shaft 26 and is fixed to the cam shaft 26. In detail, the flange 41 includes a hole 411. A 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 body 42 and the exhaust cam 264 in the cam axis 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. A pressure reducing cam 43 is inserted into the hole 414 of the second convex portion 413.

The weight body 42 is disposed between the first bearing 27 and the flange 41 in the cam axis direction. The weight body 42 is rotatably supported relative to the camshaft 26 between a closed state and an open state.

7 and 8 are cross-sectional views taken along line A-A of Fig. 4. Fig. 7 shows the weight body 42 in a closed state. Fig. 8 shows the weight body 42 in an open state.

The pressure reducing cam 43 is rotatably supported by the flange 41. In detail, the weight body 42 is rotatably supported by the flange 41 via the pivot pin 46. The weight body 42 is switched to a closed state and an open state by being rotated about the pivot pin 46.

The pressure reducing cam 43 is connected to the weight body 42 via a pressure reducing pin 44. Thereby, the decompression cam 43 rotates as the weight body 42 rotates.

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 body 42. The outer diameter of the head 431 is larger than the inner diameter of the bore 414 of the flange 41. The head 431 includes a groove portion 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 inner side of the head portion 431. The end of the decompression pin 44 is disposed in the groove portion 433. Further, in the present embodiment, the inner side refers to the inner side in the radial direction. Further, the outer side means the outer side in the radial direction.

The shaft portion 432 includes a cam portion 434. The exhaust cam 264 includes a recess 265. The recess 265 has a shape recessed from the outer peripheral surface of the exhaust cam 264 toward the inner side of the exhaust cam 264. FIG. 9 is an enlarged view of the exhaust cam 264. Figure 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 partially rounded shape. As described above, the decompression cam 43 rotates as the weight body 42 rotates. Fig. 9(A) shows the decompression cam 43 when the weight body 42 is in an open state. Fig. 9(B) shows the decompression cam 43 when the weight body 42 is in the closed state. The decompression cam 43 is switched to a state of being in contact with the exhaust roller 342 of the valve actuation mechanism 25 and not in contact with the exhaust roller 342 as the weight body 42 rotates.

Specifically, when the weight body 42 is in the open state, as shown in FIG. 9(A), the entire cam portion 434 of the pressure reducing cam 43 is disposed in the concave portion 265. In other words, when the weight body 42 is in the open state, the cam portion 434 does not protrude outward from the outer peripheral surface of the exhaust cam 264. borrow Thus, when the weight body 42 is in the open state, the pressure reducing cam 43 is not in contact with the exhaust roller 342.

When the weight body 42 is in the closed state, as shown in FIG. 9(B), one of the cam portions 434 of the pressure reducing cam 43 is disposed outside the concave portion 265. In other words, when the weight body 42 is in the closed state, one of the cam portions 434 is in a state of protruding outward from the outer circumferential surface of the exhaust cam 264. Thereby, when the weight body 42 is in a closed state, the pressure reducing cam 43 comes into contact with the exhaust roller 342.

The return spring 45 biases the weight body 42 in such a manner that the weight body 42 is restored 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 can also be other types of springs. As shown in FIG. 6, the return spring 45 includes a first spring end portion 451 and a second spring end portion 452. The first spring end portion 451 extends in the cam axis direction. The second spring end portion 452 extends in a direction crossing the cam axis direction. The second spring end portion 452 extends in the circumferential direction of the return spring 45. The first spring end portion 451 is locked to the flange 41. The second spring end portion 452 is locked to the weight body 42.

Next, the configuration of the weight body 42 will be described in detail. As shown in Fig. 7, the straight line passing through the center of rotation C1 of the cam shaft 26 and the center of rotation C2 of the weight body 42 is defined as the vertical axis Y as viewed in the direction of the cam axis. A straight line orthogonal to the vertical axis Y and passing through the rotation center C1 of the cam shaft 26 is referred to as a horizontal axis X. The direction from the rotation center C1 of the cam shaft 26 toward the rotation center C2 of the weight body 42 in the direction parallel to the longitudinal axis Y is referred to as the first longitudinal direction y1. The direction opposite to the first longitudinal direction y1 is referred to as the second longitudinal direction y2. One of the directions parallel to the horizontal axis X is set to the first horizontal direction x1. The direction opposite to the first lateral direction x1 is referred to as the second lateral direction x2.

Further, a region located in the first longitudinal direction y1 with respect to the horizontal axis X and located in the first lateral direction x1 with respect to the vertical axis Y is referred to as a first region A1. A region located in the second longitudinal direction y2 with respect to the horizontal axis X and located in the first lateral direction x1 with respect to the vertical axis Y is referred to as a second region A2. The region located in the second longitudinal direction y2 with respect to the horizontal axis X and in the second lateral direction x2 with respect to the vertical axis Y is referred to as the third region A3 as viewed in the cam axis direction. A region located in the first longitudinal direction y1 with respect to the horizontal axis X and located in the second lateral direction x2 with respect to the vertical axis Y is referred to as a fourth region. A4.

Further, Fig. 7 shows the weight body 42 viewed from the side of the first cam shaft end portion 261 in the cam axis direction. Therefore, the above-described directions x1, x2, y1, y2 and the regions A1 to A4 are defined when viewed from the side of the first camshaft end portion 261 in the cam axis direction, but may be in the direction of the cam axis. When the camshaft end 262 side is viewed, the directions x1, x2, y1, and y2 and the areas A1 to A4 are defined.

As shown in FIG. 7, the weight body 42 has a shape that extends in the circumferential direction of the cam shaft 26. The weight body 42 is disposed around the cam shaft 26 in the first area A1, the second area A2, and the fourth area A4. The weight body 42 has a shape that straddles the circumferential direction of the cam shaft 26 and a plurality of regions in the first to fourth regions A1 to A4. The weight body 42 does not have a portion disposed in the third region A3 as viewed in the cam axis direction.

Specifically, the weight body 42 includes the first weight body portion 47 and the second weight body portion 48 . The first weight body portion 47 extends from the rotation center C2 of the weight body 42 in the circumferential direction of the cam shaft 26 and in the first lateral direction x1. The circumferential end portion 471 of the first weight portion 47 is located in the first lateral direction x1 with respect to the vertical axis Y. In other words, the entire first weight body 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 body portion 47 is disposed in the second region A2 as viewed in the cam axis direction.

The second weight body portion 48 extends from the rotation center C2 of the weight body 42 in the circumferential direction of the cam shaft 26 and in the second lateral direction x2. The circumferential end portion 481 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 body 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 body portion 48 is disposed in the fourth region A4 as viewed in the cam axis direction.

The first weight body portion 47 is longer than the second weight body portion 48 in the circumferential direction of the cam shaft 26. That is, the angle from the rotation center C2 of the weight body 42 around the rotation center C1 of the cam shaft 26 to the end portion 471 of the first weight body portion 47 is larger than the rotation center C2 to the second weight body portion 48 of the weight body 42. The angle of the end 481.

The first weight body portion 47 includes a first portion 421 and a second portion 422. From the cam axis direction It is observed that the first portion 421 is disposed in the first area A1. The second portion 422 is disposed in the second region A2 as viewed in the cam axis direction. The second weight body portion 48 is disposed in the fourth region A4.

The weight body 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 mounted to the pivot pin support portion 423.

The exhaust cam 264 includes a cam lobe 267 that protrudes further outward than the base circle 266. One portion of the pivot pin 46 does not overlap the cam projection 267 as viewed in the direction of the cam axis. That is, one portion of the pivot pin 46 is located further outward than the outer peripheral surface of the exhaust cam 264 as viewed in the direction of the cam axis. Further, the pivot pin 46 includes a portion located further inside than the base circle 266 as viewed from the direction of the cam axis.

The decompression pin 44 is connected to the first weight body 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 viewed in the cam axis direction. The distance between the rotation center C2 of the weight body 42 and the decompression pin 44 is greater than the distance between the rotation center C2 of the weight body 42 and the rotation center C1 of the cam shaft 26 as viewed in the cam axis direction.

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

In the closed state, the first portion 421 of the weight body 42 includes the first protruding portion 424. The first protruding portion 424 protrudes outward from the outer peripheral surface of the first bearing 27 as viewed in the cam axis direction. The outer peripheral surface of the second portion 422 is located further inward than the outer peripheral surface of the first bearing 27 as viewed in the cam axis direction. The outer peripheral surface of the second weight body portion 48 is located further inward than the outer peripheral surface of the first bearing 27 as viewed in 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 as viewed in the cam axis direction. The maximum value of the protruding length of the protruding portion 425 is larger than the maximum value of the protruding length of the first protruding portion 424. In other words, the protruding portion 425 protrudes more strongly in the radial direction of the first bearing 27 than the first protruding portion 424. Furthermore, the length is The length from the outer circumferential surface of the first bearing 27 in the radial direction of the first bearing 27 is referred to.

As shown in FIG. 11, the first bearing 27 includes an inner ring 271 and an outer ring 272. The inner wheel 271 is in contact with the camshaft 26. The outer wheel 272 is in contact with the first support wall 141 of the cylinder head 14. As shown in FIG. 7, the weight body 42 includes an inner wheel contact portion 426. The inner wheel contact portion 426 is arranged side by side with the inner wheel 271 in the cam axis direction. The inner wheel contact portion 426 protrudes toward the inner ring 271 from the surface of the weight body 42 adjacent to the first bearing 27.

As shown in FIG. 11, the inner wheel contact portion 426 is located further inside than the inner circumferential surface of the outer wheel 272. Furthermore, regardless of the state in which the weight body 42 is in the closed state and the open state, the inner wheel contact portion 426 is located further inward than the inner circumferential surface of the outer wheel 272. At least a portion of the inner wheel contact portion 426 is disposed closer to the rotation center C2 of the weight body 42 than the rotation center C1 of the cam shaft 26 as viewed in the cam axis direction. The inner wheel contact portion 426 is located between the center of rotation C2 of the weight body 42 and the cam shaft 26 as viewed in the direction of the cam axis. As shown in FIG. 4, in a state where the inner wheel contact portion 426 is in contact with the inner ring 271, the other portion of the weight body 42 does not contact the outer wheel 272.

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

G1 in Fig. 12 indicates the position of the center of gravity of the weight body 42. G2 indicates the position of the center of gravity of the weight body 42 when the first protruding portion 424 is absent. Further, in FIG. 12, the first protruding portion 424 is hatched. "When there is no first protruding portion 424" means a state after the portion marked with hatching in Fig. 12 is removed. In addition, in FIG. 12, the two-point chain line indicates 1 bearing 27 outside the circumference. As shown in FIG. 12, the center of gravity G1 of the weight body 42 is disposed in the first area A1 as viewed in the cam axis direction. The distance between the center of gravity G1 of the weight body 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 body 42 and the center of rotation C2 of the weight body 42. The first protruding portion 424 includes a relatively proximal portion 424a which is closer to the center of gravity G2 of the weight body 42 than the first protruding portion 424 when viewed from the cam axis direction. The rotation center C2 of the weight 42 and the farther portion 424b are located farther from the weight body 42 in the circumferential direction of the first bearing 27 than the center of gravity G2 of the weight body 42 when the first protrusion 424 is absent. Rotate center C2. Regarding the amount of protrusion from the outer peripheral surface of the first bearing 27 toward the outer side, the closer portion 424a is larger than the farther portion 424b.

Further, as seen from the direction of the cam axis, the portion of the inner wheel contact portion 426 that is closer to the center of rotation C2 of the weight body 42 than the center of gravity G1 of the weight body 42 is larger than the center of gravity of the weight portion 42 of the inner wheel contact portion 426. G1 is further away from the portion of the center of rotation C2 of the weight body 42. For example, the maximum width of the first contact portion 426a in the radial direction of the cam shaft 26 is larger 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 showing the surface of the second cam shaft end portion 262 side of the weight body 42. Figure 14 is a side elevational view of the camshaft assembly viewed from the direction of arrow XIV in Figure 10; 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 greater 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 portion 421a is located inside the outer diameter portion 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 portion 421b includes the first protruding portion 424 described above. Therefore, the maximum thickness of the first protruding portion 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 protruding portion 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 direction of the cam axis is larger than the pivot pin in the direction of the cam axis The thickness of the holding portion 423.

As shown in FIG. 10, one portion of the weight body 42 overlaps the flange 41 as viewed in the radial direction of the cam shaft 26. Specifically, the outer diameter portion 421b of the first portion 421 is overlapped with the flange 41 as viewed in 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. A head portion 431 of the decompression cam 43 is disposed between the second portion 422 and the flange 41.

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 housing 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 body 42 in the cam axis direction.

Fig. 15 is a view of the flange 41, the weight body 42, and the return spring 45 as seen from the second cam shaft end portion 262 side. As shown in FIG. 15, the accommodating part 423a accommodates the return spring 45. The boss portion 423b is inserted into the above-described return spring 45. 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 body 42 includes a second locking portion 42b. The second locking portion 42b is locked to the second spring end portion 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 formed in the first portion 421 with respect to the pivot pin supporting portion 423 .

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

Fig. 16 is a view showing the cylinder head 14 in a state in which the head cover 19 is 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 shaft Cheng 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 recessed portion 144 , the second recessed portion 145 , and the third recessed portion 146 are located on the opposite side of the crankshaft 11 from the center of the first bearing support hole 143 . The first recess 144 has a shape in which the first protrusion 424 and the intake cam 263 can pass. The second recess 145 has a shape that allows the exhaust cam 264 to pass therethrough. The third recess 146 has a shape that allows the pivot pin support portion 423 to pass therethrough. Further, one of the first recessed portions 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 may be located at the same center as the crankshaft 11 with respect to the center of the first bearing support hole 143. One side. Alternatively, one of the second recesses 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 may be located at the same center as the crankshaft 11 with respect to the center of the first bearing support hole 143. One side.

In the engine of the present embodiment, the circumferential end portion 471 of the first weight body portion 47 is located in the first lateral direction x1 with respect to the vertical axis Y. That is, the first weight body portion 47 extends so as not to straddle the vertical axis Y in the second lateral direction x2. Therefore, compared with the case where the first weight body portion 47 extends from the region in the first lateral direction x1 with respect to the vertical axis Y to the position in the second lateral direction x2 across the vertical axis Y, the weight body 42 can be made. The center of gravity G1 is away from the center of rotation C1 of the camshaft 26. Therefore, if the rotational speed of the cam shaft 26 is the same, the centrifugal force applied to the weight body 42 becomes large. Thereby, the elastic force of the return spring 45 can be increased, so that the opening of the weight body 42 due to gravity can be suppressed without increasing the set number of revolutions.

Further, the center of gravity G1 of the weight body 42 can be brought closer to the rotation center C2 of the weight body 42, so that the moment caused by the gravity acting on the weight body 42 can be reduced. Therefore, the opening of the weight body 42 caused by gravity can be suppressed.

Further, the decompression pin 44 is connected to the first weight portion 47 which is smaller than the second weight body 42. Therefore, the distance between the decompression pin 44 and the rotation center C2 of the weight body 42 can be increased as compared with the case where the decompression pin 44 is connected to the second weight body 42. Thereby, the amount of movement of the decompression pin 44 with respect to the rotation angle of the weight body 42 is increased. In other words, it can be reduced to use the weight body 42 The angle of rotation of the weight body 42 is switched from the closed state to the open state. Thereby, the displacement of the center of gravity G1 of the weight body 42 when the weight body 42 is in the closed state and in the open state can be reduced. Further, by making the rotation angle of the weight body 42 small, it is easy to avoid interference between the weight body 42 and the surrounding members. Thereby, the degree of freedom of the shape of the weight body 42 is high.

Here, the distance between the center of gravity G1 of the weight body 42 and the center of rotation C1 of the cam shaft 26 when the weight body 42 is in the open state becomes larger than the center of gravity G1 of the weight body 42 when the weight body 42 is in the closed state. The distance from the center of rotation C1 of the camshaft 26. Therefore, the greater the displacement of the position of the center of gravity G1 of the weight body 42 when the weight body 42 is in the closed state and the open state, the more difficult it is for the weight body 42 to return to the closed state.

However, in the engine of the present embodiment, as described above, the displacement of the position of the center of gravity G1 of the weight body 42 when the weight body 42 is in the closed state and in the open state can be reduced, so that the weight body 42 is easy. Return to the closed state.

As described above, in the engine of the present aspect, it is easy to avoid the state in which the weight body 42 is opened at the time of starting, so that the startability of the engine 7 can be improved.

The end portion 471 of the first weight body portion 47 is disposed in the second region A2 as viewed in the cam axis direction. Therefore, compared with the case where the first weight body portion 47 extends from the region in the first lateral direction x1 with respect to the vertical axis Y to the position in the second lateral direction x2 across the vertical axis Y, the weight body 42 can be made. The center of gravity G1 is away from the center of rotation C1 of the camshaft 26. Further, it is easier to arrange the decompression pin 44 away from the rotation center C2 of the weight body 42 than when the end portion 471 of the first weight body portion 47 is disposed in the first region A1.

The decompression pin 44 is disposed in the second region A2 as viewed in the cam axis direction. Therefore, the end portion 471 of the first weight body portion 47 can be disposed in the second region A2 as viewed in the cam axis direction.

The distance between the rotation center C2 of the weight body 42 and the decompression pin 44 is greater than the distance between the rotation center C2 of the weight body 42 and the rotation center C1 of the cam shaft 26 as viewed in the cam axis direction. Therefore, the distance between the decompression pin 44 and the center of rotation C2 of the weight body 42 can be increased.

The weight body 42 does not have a portion disposed in the third region A3 as viewed from the cam axis direction. Therefore, the center of gravity G1 of the weight body 42 can be further moved away from the rotation center C1 of the cam shaft 26. Further, the center of rotation C2 of the weight body 42 and the center of gravity G1 of the weight body 42 can be further brought closer.

The end portion 481 of the second weight 42 portion is disposed in the fourth region A4 as viewed in the cam axis direction. Therefore, the center of rotation C2 of the weight body 42 can be brought closer to the center of gravity G1 of the weight body 42.

The embodiment of the present invention has been described above, but the present invention is not limited to the embodiment described above, and various modifications can be made without departing from the spirit and scope of the invention.

The shape of the weight body 42 is not limited to the shape of the above embodiment, and may be changed. For example, Fig. 17 is a view showing the weight body 42 of the first modification. As shown in FIG. 17, the second portion 422 may be included in the second portion 427. The second protruding portion 427 protrudes outward from the outer peripheral surface of the first bearing 27 as viewed in the axial direction of the cam shaft 26. The volume of the first protruding portion 424 is larger than the volume of the second protruding portion 427. In this case, as in the above embodiment, the center of gravity G1 of the weight body 42 can be further moved away from the rotation center C1 of the cam shaft 26. Further, the position of the center of gravity G1 of the weight body 42 can be made closer to the rotation center C2 of the weight body 42 than when the volume of the second protrusion portion 427 is larger than the volume of the first protrusion portion 424.

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

Alternatively, the first protruding portion 424 of the weight body 42 may be omitted. That is, the first portion 421 may be located further inward than the outer peripheral surface of the first bearing 27 as viewed in the cam axis direction.

Fig. 18 is a view showing the weight body 42 of the second modification. As shown in FIG. 18, the pivot pin support portion 423 may be located further inward than the outer peripheral surface of the first bearing 27 as viewed in the cam axis direction.

Fig. 19 is a view showing the weight body 42 of the third modification. As seen in Fig. 19, the pivot pin 46 can also be located more inward than the base circle 266 of the exhaust cam 264 as viewed in the direction of the cam axis. That is, it can also be viewed from the direction of the cam axis so that the center of rotation C2 of the weight body 42 is located. It is closer to the inner side than the base circle 266 of the exhaust cam 264.

Fig. 20 is a view showing the weight body 42 of the fourth modification. As shown in FIG. 20, the center of rotation C2 of the weight body 42 may be located further outward than the cam protrusion 267 of the exhaust cam 264 as viewed in the direction of the cam axis. Further, the entire pivot pin 46 may be located further outward than the outer peripheral surface of the exhaust cam 264.

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

The inner wheel contact portion of the weight body 42 may also be omitted. The housing portion of the weight body 42 may also be omitted. That is, the return spring may be disposed at a position other than the weight body 42.

In the above embodiment, a quick-speed locomotive is used as an example of a vehicle. However, the vehicle of the present invention is not limited to a quick-acting type, and may be other types of locomotives such as a sporty type, an off-road type, and a light type. Here, the locomotive is not limited to the second round, including three-wheeled vehicles. Further, the vehicle of the present invention is preferably a straddle type vehicle such as a locomotive, an all-terrain vehicle (ALL-TERRAIN VEHICLE), or a snowmobile, but may be a vehicle other than a straddle type vehicle.

The terms and expressions used herein are for the purpose of description and are not intended to be construed as limiting. It is to be understood that the invention is not to be construed as a The invention can be implemented in many different forms. This disclosure should be considered as an embodiment of the principles of the invention. The embodiments are not intended to limit the invention to the preferred embodiments described herein and/or illustrated in the drawings. It is not limited to the embodiment described herein. The present invention also includes all embodiments in which the elements, modifications, deletions, combinations, improvements, and/or changes are included in the embodiments. The limitation of the scope of application for patent application shall be interpreted broadly based on the terms used in the scope of patent application, and shall not be limited to the description of this specification or the case. The embodiment described.

27‧‧‧1st bearing

42‧‧‧weights

47‧‧‧1st weight body

48‧‧‧2nd weight body

272‧‧‧Outside

421‧‧‧Part 1

422‧‧‧Part 2

423‧‧‧ pivot support department

424‧‧‧1st protrusion

Closer part of 424a‧‧

424b‧‧‧ farther part

426‧‧‧Internal wheel contact

A1‧‧‧1st area

A2‧‧‧2nd area

A3‧‧‧3rd area

A4‧‧‧4th area

C1‧‧‧Rotation center of camshaft 26

C2‧‧‧The center of rotation of the counterweight 42

G1‧‧‧Center of gravity 42

G2‧‧‧ Center of gravity of the weight body 42 in the absence of the first protrusion 424

X‧‧‧ horizontal axis

Y‧‧‧ vertical axis

Claims (9)

An engine comprising: a cylinder head; an exhaust valve housed in the cylinder head; a valve moving mechanism that opens and closes the exhaust valve; and a cam shaft that drives the above by contacting the valve mechanism a valve mechanism that rotatably supports the cam shaft to the cylinder head; and a pressure reducing mechanism disposed between both end portions of the cam shaft in the axial direction; the pressure reducing mechanism includes: a weight a body that is rotatably supported between the closed state and the open state with respect to the cam shaft; and a return spring that biases the weight body in a manner to restore the weight body from the open state to the closed state; a pressure reducing cam that is disposed in contact with the valve actuation mechanism when the weight body is in the closed state, and is not in contact with the valve actuation mechanism when the weight body is in the open state; And a decompression pin connected to the weight body and the decompression cam; viewed from an axial direction of the cam shaft, passing through a center of rotation of the cam shaft and a rotation center of the weight body a straight line is a vertical axis, and a straight line orthogonal to the vertical axis and passing through a center of rotation of the cam shaft is a horizontal axis, and a center of rotation from the cam shaft in a direction parallel to the longitudinal axis is directed toward the weight body The direction of the center of rotation is the first longitudinal direction, one of the directions parallel to the horizontal axis is the first lateral direction, and the direction opposite to the first lateral direction is the second horizontal direction. a direction in which the center of gravity of the weight body is disposed in the first region, the first region is located in the first longitudinal direction with respect to the horizontal axis, and is located at the first horizontal direction with respect to the vertical axis as viewed in the axial direction of the cam shaft In the direction, the weight body includes: a first weight body extending from a rotation center of the weight body along a circumferential direction of the cam shaft, wherein a circumferential end portion is located in the first lateral direction with respect to the vertical axis; and a weight body extending from a rotation center of the weight body in a circumferential direction of the cam shaft, wherein a circumferential end portion is located in the second lateral direction with respect to the vertical axis; and the first direction is in a circumferential direction of the cam shaft The weight body portion is longer than the second weight body, and the pressure reducing pin is connected to the first weight body portion. The engine of claim 1, wherein the direction opposite to the first longitudinal direction is the second longitudinal direction, and the first weight portion includes the first portion and the second portion, and is viewed from an axial direction of the cam shaft. The first portion is disposed in the first region, and the second portion is disposed in the second region as viewed in the axial direction of the cam shaft, and the second region is located in the second longitudinal direction with respect to the horizontal axis, and is opposite to the first region The vertical axis is located in the first lateral direction, and an end portion of the first weight portion is disposed in the second region as viewed in the axial direction of the cam shaft. The engine of claim 2, wherein the decompression pin is disposed in the second region as viewed in the axial direction of the cam shaft. Such as the engine of claim 1, wherein The distance between the center of rotation of the weight body and the decompression pin is greater than or equal to the distance between the center of rotation of the weight body and the center of rotation of the cam shaft as viewed in the axial direction of the cam shaft. The engine of any one of claims 1 to 4, wherein the camshaft includes an exhaust cam that is in contact with the valve actuation mechanism, and the exhaust cam includes a cam lobe that protrudes outward from the base circle, The center of rotation of the weight body is located radially inward of the camshaft from the base circle of the exhaust cam as viewed in the axial direction of the camshaft. The engine of any one of claims 1 to 4, wherein the camshaft includes an exhaust cam that is in contact with the valve actuation mechanism, and the exhaust cam includes a cam lobe that protrudes outward from the base circle, The center of rotation of the weight body is located radially outward of the cam shaft from the outer circumferential surface of the cam lobe as viewed in the axial direction of the cam shaft. The engine of claim 1, wherein the weight body does not include a portion disposed in the third region as viewed from an axial direction of the cam shaft, and the third region is located in the second longitudinal direction with respect to the horizontal axis, and is opposite to the above The vertical axis is located in the second lateral direction described above. The engine of claim 1, wherein the end portion of the second weight portion is disposed in the fourth region as viewed in the axial direction of the cam shaft, and the fourth region is located in the first longitudinal direction with respect to the horizontal axis, and Located in the second lateral direction with respect to the vertical axis. A vehicle comprising an engine as in claim 1.