TW201814146A - Engine - Google Patents

Abstract

A first rocker arm includes a roller and a pressing member. The pressing member presses a valve. A second rocker arm includes a slipper. When the engine rotation speed is in a predetermined low-speed region, the pressing member presses the valve according to the rotation of the first rocker arm. When the engine rotation speed is in a predetermined high-speed region, the pressing member presses the valve according to the rotation of the second rocker arm. The roller comes into rolling contact with the camshaft. The slipper comes into sliding contact with the camshaft. The tip end of the slipper is closer to the axis of the rocker shaft than the tip end of the roller as seen from the axial direction of the rocker shaft. The maximum width of the slipper is greater than the width of the roller in the axial direction of the rocker shaft.

Description

engine

The present invention relates to an engine.

There is a variable valve mechanism in the engine. The variable valve mechanism includes a low speed rocker arm used in a low speed region of the engine rotational speed and a high speed rocker arm used in a high speed region of the engine rotational speed. For example, in Patent Document 1, the low speed rocker arm and the high speed rocker arm are mounted side by side on the rocking shaft in the axial direction of the rocking shaft. The low speed rocker arm has a first roller that rolls in contact with the low speed cam of the camshaft. The high speed rocker arm has a second roller that rolls in contact with the high speed cam of the camshaft. In the low speed region of the engine rotational speed, the valve is opened and closed by driving the low speed rocker arm with a cam for low speed. The low speed rocker arm is coupled to the high speed rocker arm in a high speed region of the engine's rotational speed. Specifically, the coupling pin inserted into the hole of the low speed rocker arm is moved by the actuator and inserted into the hole of the high speed rocker arm. Thereby, the low speed rocker arm is coupled to the high speed rocker arm. In this state, the low speed rocker arm is not driven by the cam for low speed, and the high speed rocker arm is driven by the cam for high speed, thereby opening and closing the valve. [Prior Art Document] [Patent Document] [Patent Document 1] Japanese Patent Laid-Open No. 2015-010554

[Problem to be Solved by the Invention] In the above engine, the low-speed rocker arm and the high-speed rocker arm respectively employ rollers, and thus the weight is high. Therefore, when the engine rotation speed is a high speed region, the influence of the equivalent weight of the rocker arm increases. For example, if the equivalent weight of the rocker arm is large, it will affect the behavior of the rocker arm under the high speed area. Therefore, there is a problem that the upper limit of the engine rotation speed must be limited to be small in order to suppress the disorder of the swing arm. Therefore, in order to suppress the equivalent weight to be small, the inventors of the present invention considered that the roller of both the low speed rocker arm and the high speed rocker arm was changed to the sliding portion. By using the sliding portion, the rocker arm can be made lighter than in the case of using a roller, whereby the equivalent weight can be reduced. However, in the low speed region of the engine rotation speed, the sliding speed of the sliding portion with respect to the cam is small, so that the oil film generated by the contact surface of the sliding portion is thin and becomes the boundary lubrication. Therefore, if the sliding portion is used in the low-speed rocker arm, there is a problem in that the frictional resistance between the sliding portion and the cam is increased to cause an increase in mechanical loss in the engine. On the other hand, in the high speed region of the engine rotational speed, the sliding speed for the sliding portion of the cam is large, and thus the mechanical loss is relatively reduced. However, the sliding portion has a problem that the surface pressure is allowed to be lowered as compared with the roller. In particular, since the two rocker arms are connected in a high-speed region of the engine rotation speed as described above, it is difficult to increase the rigidity. Therefore, there is a case where the sliding portion is partially in contact with the cam due to the deformation of the rocker arm. If local contact occurs, the surface pressure on the sliding portion is locally increased. Such local contact is easier to produce in a high speed region than in the low speed region of the engine's rotational speed. That is, in the high speed region of the engine rotation speed, there is a problem that the partial contact pressure is required in addition to the lower allowable surface pressure of the sliding portion. Here, as one method of reducing the surface pressure, it is considered to increase the radius of curvature of the contact surface of the sliding portion. However, if the radius of curvature is increased, the sliding portion is increased. Further, if the sliding portion is increased, there is a tendency that the arm portion supporting the sliding portion also grows. Due to these factors, the equivalent weight of the rocker arm is increased, so that even if a sliding portion is used instead of the roller, the effect of lowering the equivalent weight is suppressed. The object of the present invention is to reduce the mechanical loss in the low speed region of the engine rotational speed and increase the upper limit of the engine rotational speed. [Technical means for solving the problem] The engine of the first aspect includes a cylinder head, a valve, a rocking unit, a cam shaft, and a point changing portion at the time of opening and closing. The valve is mounted to the cylinder head. The shaking unit presses the valve to open and close the valve. The camshaft drives the rocking unit. When opening and closing, the point change unit changes the opening and closing timing of the valve. The rocking unit includes a rocking shaft, a first rocker arm, a second rocker arm, and a joint pin. The rocking shaft is supported by the cylinder head. The first rocker arm includes a roller and a pressing member. The roller can be placed in contact with the camshaft. The pressing member presses the valve. The first rocker arm rotates about the axis of the rocking shaft by the roller contacting the camshaft. The second rocker arm includes a sliding portion. The sliding portion can be disposed in contact with the cam shaft. The second rocker arm is arranged side by side with the first rocker arm in the axial direction of the rocking shaft. The second rocker arm rotates about the axis of the rocking shaft by the sliding portion contacting the cam shaft. The connecting pin is provided to be movable to the connecting position and the releasing position by the opening/closing point changing unit. The connecting pin connects the second rocker arm to the pressing member at the connecting position. The connecting pin releases the second rocker arm with respect to the pressing member at the release position. When the engine rotation speed is in a specific low speed region, the opening/closing point changing unit positions the coupling pin at the release position, whereby the pressing member presses the valve in accordance with the rotation of the first rocker arm. When the engine rotation speed is a specific high speed region, the opening/closing point changing unit positions the coupling pin at the coupling position, whereby the pressing member presses the valve in accordance with the rotation of the second rocker arm. The roller is in rolling contact with the camshaft. The sliding portion is in sliding contact with the cam shaft. When viewed from the axial direction of the rocking shaft, the front end of the sliding portion is closer to the axis of the rocking shaft than the front end of the roller. In the direction of the axis of the rocking shaft, the maximum width of the sliding portion is greater than the width of the roller. In the engine of this aspect, the first rocker arm for low speed uses a roller. Therefore, in the low speed region of the engine rotation speed, the frictional resistance between the roller and the camshaft can be reduced. Thereby, the mechanical loss in the low speed region can be reduced. Further, the second rocker arm for high speed uses a sliding portion. Therefore, the equivalent weight of the second rocker arm can be reduced. Further, in the high speed region of the engine rotation speed, the sliding speed of the sliding portion with respect to the cam shaft is large, so that the contact surface of the sliding portion can produce a thick oil film. Therefore, even if the sliding portion is used for the second rocker arm for high speed, the mechanical loss can be suppressed to be small. In this way, by using the roller for the first rocker arm for low speed and the sliding portion for the second rocker arm for high speed, the mechanical loss can be suppressed to be small in the entire region of the engine rotation speed, and the equivalent weight can be reduced. Further, in the direction of the axis of the rocking shaft, the maximum width of the sliding portion is larger than the width of the roller. Thereby, the surface pressure of the sliding portion can be suppressed to be small, and the occurrence of local contact can be suppressed. Further, when viewed from the axial direction of the rocking shaft, the front end of the sliding portion is closer to the axis of the rocking shaft than the front end of the roller. That is, by making the maximum width of the sliding portion larger than the width of the roller, the surface pressure of the sliding portion can be suppressed to be small, so that the necessity of increasing the radius of curvature and reducing the surface pressure is lowered. Therefore, the sliding portion can be made shorter. Thereby, the increase in the equivalent weight can be suppressed as compared with the case where the sliding portion is extended to increase the radius of curvature of the sliding portion. Thereby, the upper limit of the engine rotation speed can be increased. The sliding portion may also include a curved contact surface in contact with the cam shaft. The radius of curvature of the contact surface may also be greater than the radius of curvature of the roller. In this case, the surface pressure of the sliding portion can be suppressed to be small. The center of gravity of the second rocker arm may also be closer to the axis of the rocking axis than the center of gravity of the first rocker arm. In this case, the equivalent weight of the second rocker arm can be further reduced. The weight of the portion of the second rocker arm that is located closer to the end side of the sliding portion than the imaginary plane extending in the cylinder axis direction of the axis of the cylinder head may be smaller than the imaginary plane of the first rocker arm. The weight of the portion on the end side. In this case, the equivalent weight of the second rocker arm can be further reduced. The second rocker arm may also include a boss portion and an arm portion. The boss portion may also have a hole through which the rocking shaft passes. The arm portion may also extend from the boss portion to the sliding portion. The sliding portion may also include a contact surface that contacts the camshaft. In the direction of the axis of the rocking shaft, the maximum width of the contact surface of the sliding portion may be smaller than the width of the boss portion. In this case, the sliding portion can be made lighter while suppressing the surface pressure of the sliding portion to be small, whereby the equivalent weight of the second rocker arm can be further reduced. The arm portion may also include a recess between the contact surface and the boss portion. In this case, it is possible to reduce the weight of the contact portion to the boss portion, thereby further reducing the equivalent mass of the second rocker arm. Moreover, during the processing of the contact surface, interference with the jig for processing can be avoided by the concave portion. The arm portion includes a convex portion that extends from the sliding portion to the boss portion and protrudes from the sliding portion from a surface opposite to the contact surface. In this case, the arm portion can be made lighter, and the rigidity of the arm portion can be ensured by the convex portion. In the direction of the axis of the rocking shaft, the width of the convex portion may also be smaller than the width of the contact surface. In this case, the arm portion can be made lighter, whereby the equivalent weight of the second rocker arm can be further reduced. When viewed from the axial direction of the rocking shaft, the surface of the arm opposite to the contact surface may have a shape that is recessed toward the contact surface side. In this case, the arm portion can be made lighter, whereby the equivalent weight of the second rocker arm can be further reduced. The sliding portion may also include a hardened layer. The hardened layer may also be in contact with the camshaft and have a coefficient of friction of the substrate below the sliding portion and a hardness of the substrate above the sliding portion. In this case, the wear resistance of the sliding portion can be improved. [Effect of the Invention] According to the present invention, the mechanical loss in the low speed region of the engine rotation speed can be reduced, and the upper limit of the engine rotation speed can be increased.

Hereinafter, an engine for a straddle type vehicle and a straddle type vehicle according to an embodiment will be described with reference to the drawings. FIG. 1 is a side view of a straddle type vehicle 100. The straddle type vehicle 100 is a so-called speed skating type motorcycle. As shown in FIG. 1, the straddle type vehicle 100 includes a front wheel 101, a seat portion 102, a rear wheel 103, a power unit 104, a steering device 105, and a vehicle body casing 106. The front wheel 101 is rotatably supported by the steering device 105. A handle 113 is attached to the upper end of the steering device 105. The seat portion 102 is disposed behind the steering device 105. The power unit 104 is disposed below the seat portion 102. The power unit 104 includes an engine 1 and a gearbox 107. The power unit 104 supports the rear wheel 103 and is rotatable. The body casing 106 includes a rear casing 108, a bottom casing 109, and a front casing 110. The rear outer casing 108 is disposed below the seat portion 102. The front outer casing 110 covers the periphery of the steering device 105. The bottom case 109 is disposed between the front case 110 and the rear case 108. The upper surface of the bottom case 109 includes a leg portion 111 and a channel portion 112. The channel portion 112 is provided at a central portion in the vehicle width direction of the upper surface of the bottom case 109. The channel portion 112 protrudes upward from the leg portion 111. The leg portion 111 is disposed on the left and right of the channel portion 112. The footrest portion 111 is provided in such a manner that the rider places the foot. Furthermore, the channel portion 112 can also be omitted. That is, the upper surface of the bottom case 109 may have a flat leg portion extending in the left-right direction. Fig. 2 is a cross-sectional view showing a part of the engine 1 for a straddle type vehicle according to the embodiment. In the present embodiment, the engine 1 is a water-cooled single-cylinder engine. As shown in FIG. 2, the engine 1 includes a crankcase 2, a cylinder block 3, a cylinder head 4, and a head cover 5. The crankcase 2 houses the crankshaft 6. The cylinder block 3 is connected to the crankcase 2. The cylinder block 3 and the crankcase 2 may be integral or may be independent individuals. The cylinder block 3 houses the piston 7. The piston 7 is coupled to the crankshaft 6 via a connecting rod 8. In the present embodiment, the direction from the cylinder head 4 toward the head cover 5 in the cylinder axis Ax1 direction of the cylinder block 3 is referred to as "head cover side". Further, the direction from the cylinder head 4 toward the cylinder block 3 in the cylinder axis Ax1 direction is referred to as "cylinder block side". The cylinder head 4 is disposed on the head cover side of the cylinder block 3. The cylinder head 4 is mounted to the cylinder block 3. The head cover 5 is disposed on the head cover side of the cylinder head 4. The head cover 5 is mounted to the cylinder head 4. 3 is a cross-sectional view of the cylinder head 4 and the head cover 5 as viewed from a direction perpendicular to the cylinder axis Ax1 and the cam axis Ax3. As shown in Fig. 3, the cylinder head 4 includes a side wall 4a extending in the cylinder axis Ax1 direction. The head cover 5 includes a side wall 5a extending in the direction of the cylinder axis Ax1. The end portion 4b of the side wall 4a of the cylinder head 4 (hereinafter referred to as "side wall end 4b") abuts against the end portion 5b of the side wall 5a of the head cover 5 (hereinafter referred to as "side wall end 5b"). In detail, the side wall end 4b of the cylinder head 4 is butted to the side wall end 5b of the head cover 5 via the seal member 9. Furthermore, the cylinder head 4 and the cylinder block 3 may be independent bodies or may be integrated. As shown in FIG. 2, the cylinder axis Ax1 is perpendicular to the center axis Ax2 of the crankshaft 6 (hereinafter referred to as "crank axis Ax2"). The cylinder head 4 contains a combustion chamber 11. A spark plug 12 is mounted to the cylinder head 4. The front end of the spark plug 12 is disposed facing the combustion chamber 11. The base end of the Mars plug 12 is disposed outside of the engine 1. A valve actuation mechanism 13 is housed in the cylinder head 4 and the head cover 5. The valve actuation mechanism 13 is a mechanism for opening and closing the following exhaust valves 25 and 26 and the intake valves 27 and 28. The valve actuation mechanism 13 employs a SOHC (Single Over Head Camshaft) type mechanism. The valve actuation mechanism 13 employs a so-called variable valve mechanism that switches the timing of opening and closing of the intake valves 27 and 28. The valve actuation mechanism 13 includes a camshaft 14. The camshaft 14 is supported by the cylinder head 4. The central axis Ax3 of the camshaft 14 (hereinafter referred to as "cam axis Ax3") is perpendicular to the cylinder axis Ax1. The cam axis Ax3 is parallel to the crankshaft axis Ax2. As shown in FIG. 3, the camshaft 14 includes a first camshaft end portion 141 and a second camshaft end portion 142. A sprocket 29 is attached to the first camshaft end portion 141. The cam chain 15 shown in Fig. 2 is wound around the sprocket 29. As shown in FIG. 2, a cam chain chamber 16 is provided in the cylinder head 4 and the cylinder block 3. The cam chain 15 is disposed in the cam chain chamber 16. The camshaft 14 is coupled to the crankshaft 6 via a cam chain 15 . The rotation of the crankshaft 6 is transmitted to the camshaft 14 via the cam chain 15, whereby the camshaft 14 rotates. A water pump 17 is coupled to the first camshaft end portion 141. The water pump 17 is connected to a coolant passage (not shown) and a radiator 19 in the engine 1 via a coolant hose 18. The water pump 17 is driven by the rotation of the cam shaft 14, thereby circulating the coolant of the engine 1. As shown in FIG. 3, the camshaft 14 includes a rod portion 143, a first intake cam portion 144, a second intake cam portion 145, and an exhaust cam 146. The rod portion 143 is rotatably supported by the first shaft support portion 21 and the second shaft support portion 22 of the cylinder head 4. The first intake cam portion 144 , the second intake cam portion 145 , and the exhaust cam 146 are disposed on the outer circumference of the rod portion 143 . The first intake cam portion 144, the second intake cam portion 145, and the exhaust cam 146 are arranged side by side in the cam axis Ax3 direction. 4 and 5 are perspective views of the inside of the cylinder head 4. Fig. 6 is a view of the inside of the cylinder head 4 as viewed from the cylinder axis Ax1 direction. As shown in FIGS. 3 to 6 , the cylinder head 4 includes a first shaft support portion 21 and a second shaft support portion 22 . The first shaft support portion 21 and the second shaft support portion 22 are integrally formed with the cylinder head 4 . The first shaft support portion 21 and the second shaft support portion 22 are arranged side by side in the cam axis Ax3 direction. The first shaft support portion 21 and the second shaft support portion 22 support the cam shaft 14 and are rotatable. As shown in FIG. 3, the first shaft support portion 21 includes a first cam shaft hole 211 into which the cam shaft 14 is inserted. The first bearing 23 is attached to the first camshaft hole 211. The first shaft support portion 21 supports the cam shaft 14 via the first bearing 23 . The second shaft support portion 22 includes a second cam shaft hole 221 into which the cam shaft 14 is inserted. The second bearing 24 is attached to the second camshaft hole 221. The second shaft support portion 22 supports the cam shaft 14 via the second bearing 24 . The end portion 21a on the head cover side of the first shaft support portion 21 is located closer to the head cover than the side wall end 4b of the cylinder head 4. In other words, the first shaft support portion 21 protrudes toward the head cover side from the side wall end 4b of the cylinder head. The end portion 22a on the head cover side of the second shaft support portion 22 is located closer to the head cover than the side wall end 4b of the cylinder head 4. In other words, the second shaft support portion 22 protrudes toward the head cover side from the side wall end 4b of the cylinder head 4. As shown in FIG. 6, the intake valves 27 and 28 and the exhaust valves 25 and 26 are attached to the cylinder head 4. Figure 7 is a cross-sectional view of the inside of the cylinder head 4 as seen from the direction of the cam axis Ax3. As shown in FIG. 7, the cylinder head 4 includes an intake port 31 and an exhaust port 32 that communicate with the combustion chamber 11. The intake valves 27 and 28 open and close the intake port 31. As shown in FIG. 6, the intake valves 27 and 28 include a first intake valve 27 and a second intake valve 28. The first intake valve 27 and the second intake valve 28 are arranged side by side in the direction of the cam axis Ax3. As shown in FIG. 4, an intake valve spring 271 is attached to the first intake valve 27. The intake valve spring 271 pushes the first intake valve 27 in a direction in which the first intake valve 27 closes the intake port 31. Similarly to the second intake valve 28, the intake valve spring 281 is attached, and the second intake valve 28 is pushed in the direction in which the second intake valve 28 closes the intake port 31. The exhaust valves 25 and 26 open and close the exhaust port 32. The exhaust valves 25 and 26 include a first exhaust valve 25 and a second exhaust valve 26. The first exhaust valve 25 and the second exhaust valve 26 are arranged side by side in the direction of the cam axis Ax3. As shown in FIG. 5, an exhaust valve spring 251 is attached to the first exhaust valve 25. The exhaust valve spring 251 pushes the first exhaust valve 25 in a direction in which the first exhaust valve 25 closes the exhaust port 32. The exhaust valve spring 261 is attached to the second exhaust valve 26, and the second exhaust valve 26 is pushed in the direction in which the second exhaust valve 26 closes the exhaust port 32. As shown in FIG. 7, the valve actuation mechanism 13 includes an exhaust swing unit 33 and an intake swing unit 34. The exhaust swaying unit 33 presses the exhaust valves 25 and 26 to open and close the exhaust valves 25 and 26. The intake swing unit 34 presses the intake valves 27 and 28 to open and close the intake valves 27 and 28. The exhaust rocking unit 33 and the intake rocking unit 34 are driven by a camshaft 14. The exhaust swing unit 33 includes an exhaust swing shaft 35, an exhaust rocker arm 36, and a pressing member 38. The exhaust rocking shaft 35 is disposed in parallel with the cam shaft 14. The exhaust rocker shaft 35 is supported by the cylinder head 4. Specifically, the exhaust rocking shaft 35 is supported by the first shaft support portion 21 and the second shaft support portion 22 . The exhaust rocker arm 36 is swingably supported by the exhaust rocking shaft 35 around the exhaust rocking shaft 35. The exhaust rocker arm 36 is configured to operate the exhaust valves 25 and 26. The exhaust rocker arm 36 includes a roller 37 and an arm portion 39. The arm portion 39 includes a through hole 364 through which the exhaust rocker shaft 35 passes. As shown in Figure 6, the arm 39 supports the roller 37 and is rotatable. The central axis of rotation of the roller 37 is parallel to the cam axis Ax3. The roller 37 is in contact with the exhaust cam 146 and is rotated by the rotation of the exhaust cam 146. The pressing member 38 is formed integrally with the arm portion 39. As shown in FIGS. 5 and 6, the first adjustment screw 365 and the second adjustment screw 366 are provided at the front end of the pressing member 38. The front end of the first adjustment screw 365 faces the base end of the first exhaust valve 25. As shown in FIG. 7, the front end of the second adjustment screw 366 is opposed to the base end of the second exhaust valve 26. When the roller 37 is pushed up by the exhaust cam 146, the exhaust rocker arm 36 swings, whereby the pressing member 38 presses the first exhaust valve 25 and the second exhaust valve 26. Thereby, the exhaust port 32 is opened. When the roller 37 is not pushed up by the exhaust cam 146, the first exhaust valve 25 and the second exhaust valve 26 are pushed up by the exhaust valve springs 251 and 261, thereby closing the exhaust port 32. . FIG. 8 is a perspective view of the intake rocking unit 34. Figure 9 is a view of the intake rocking unit as viewed from a direction perpendicular to the cam axis. Fig. 10 is a view of the intake rocking unit viewed from the cam axis direction. As shown in FIGS. 8 to 10, the intake rocking unit 34 includes an intake rocking shaft 41, a first rocker arm 42, a second rocker arm 43, a pressing member 44 (see FIG. 6), and a coupling pin 45. Further, the intake rocking shaft 41 is omitted in Fig. 10, but the position of the axis of the intake rocking shaft 41 is indicated by the symbol Ax4. The intake rocking shaft 41 is disposed in parallel with the cam shaft 14. The intake rocking shaft 41 is supported by the cylinder head 4. Specifically, the intake rocking shaft 41 is supported by the first shaft support portion 21 and the second shaft support portion 22 . The first rocker arm 42 is swingably supported by the intake rocking shaft 41 around the intake rocking shaft 41. The first rocker arm 42 is configured to operate the intake valves 27 and 28. As shown in FIG. 3, the first rocker arm 42 includes a first mounting portion 421. The first attachment portion 421 is provided in a hole of the first rocker arm 42. The intake rocking shaft 41 passes through the first mounting portion 421. The first rocker arm 42 includes a first connection hole 422. The first coupling hole 422 is located closer to the head cover than the intake rocking shaft 41. The first coupling hole 422 extends in the direction of the cam axis Ax3. The coupling pin 45 is inserted into the first coupling hole 422. As shown in FIG. 8, the first rocker arm 42 includes a first arm portion 420 and a roller 423. The roller 423 is provided in contact with the first intake cam portion 144. The roller 423 is rotatably supported by the first arm portion 420. The roller 423 is in rolling contact with the first intake cam portion 144. The roller 423 is rotated by the rotation of the first intake cam portion 144. The central axis of rotation of the roller 423 is parallel to the cam axis Ax3. The first rocker arm 42 is rotated about the axis Ax4 of the intake rocking shaft 41 by bringing the roller 423 into contact with the first intake cam portion 144. As shown in FIG. 7, the second rocker arm 43 is swingably supported around the intake rocking shaft 41. The second rocker arm 43 is arranged side by side with the first rocker arm 42 in the direction of the cam axis Ax3. The second rocker arm 43 is disposed on the cam chain chamber 16 side of the first rocker arm 42. As shown in FIG. 3, the second rocker arm 43 includes a second attachment portion 431. The second attachment portion 431 is provided in a hole of the second rocker arm 43. The intake rocking shaft 41 passes through the second attachment portion 431. The second rocker arm 43 includes a second coupling hole 432. The second coupling hole 432 is located closer to the head cover than the intake rocking shaft 41. The second coupling hole 432 extends in the direction of the cam axis Ax3. The second connection hole 432 is disposed so as to overlap the first connection hole 422 in the direction of the cam axis Ax3. Therefore, the coupling pin 45 can be inserted into the second coupling hole 432 of the second rocker arm 43. As shown in FIGS. 8 and 10 , the second rocker arm 43 includes a boss portion 430 , a sliding portion 433 , and a second arm portion 434 . The boss portion 430 includes the second mounting portion 431 described above. The second arm portion 434 extends from the boss portion 430 to the sliding portion 433. The second arm portion 434 supports the sliding portion 433. The sliding portion 433 is in contact with the second intake cam portion 145 and is slidably provided to the second intake cam portion 145. The boss portion 430, the second arm portion 434, and the sliding portion 433 are integrally formed. The second rocker arm 43 is rotated about the axis Ax4 of the intake rocking shaft 41 by sliding the sliding portion 433 against the second intake cam portion 145. As shown in FIG. 9, in the axial direction of the intake rocking shaft 41, the maximum width of the sliding portion 433 is larger than the width of the roller 423. Fig. 11 is a view of the second rocker arm 43 as viewed from below in Fig. 10. As shown in FIGS. 10 and 11, the sliding portion 433 includes a contact surface 435 that is in contact with the second intake cam portion 145. In the axial direction of the intake rocking shaft 41, the maximum width of the contact surface 435 of the sliding portion 433 is smaller than the width of the boss portion 430. The second arm portion 434 includes a convex portion 439 that protrudes from the sliding portion 433 from a surface opposite to the contact surface 435. The convex portion 439 extends from the sliding portion 433 to the boss portion 430 via the second arm portion 434. In the axial direction of the intake rocking shaft 41, the width of the convex portion 439 is smaller than the width of the contact surface 435. As shown in FIG. 10, the second arm portion 434 includes a concave portion 436. The recess 436 is located between the contact surface 435 and the boss portion 430. More specifically, it has a shape in which the imaginary plane Q from which the contact surface 435 is extended to the boss portion 430 is recessed toward the head cover side. When the concave portion 436 is viewed in the axial direction of the intake rocking shaft 41, the concave portion 436 has a shape recessed from the contact surface 435 toward the head cover side. The recess 436 has a shape curved in an arc shape. The recess 436 extends in the axial direction of the intake rocking shaft 41. The front end of the sliding portion 433 is closer to the axis Ax4 of the intake rocking shaft 41 than the front end of the roller 423 as viewed in the axial direction of the intake rocking shaft 41. The contact surface 435 has a curved shape. The radius of curvature of the contact surface 435 is greater than the radius of curvature of the roller 423. As shown in FIG. 10, the contact surface 435 has a shape curved around the bending center C1. The bending center C1 extends in the axial direction of the intake rocking shaft 41. The bending center C1 is located on the head cover side with respect to the contact surface 435. The bending center C1 is located at a position that does not overlap the intake rocking shaft 41 when viewed in the axial direction of the intake rocking shaft 41. The bending center C1 is located closer to the head cover side than the axis Ax4 of the intake rocking shaft 41 when viewed in the axial direction of the intake rocking shaft 41. When viewed from the axial direction of the intake rocking shaft 41, the surface 438 of the second arm portion 434 opposite to the contact surface 435 has a shape that is recessed toward the contact surface 435 side. Specifically, the opposite surface 438 includes a first surface 438a and a second surface 438b. The first face 438a extends in a direction generally along the contact face 435. The second surface 438b extends from the first surface 438a toward the head cover side. The opposite surface 438 has a shape that is curved between the first surface 438a and the second surface 438b. The weight of the portion of the second rocker arm 43 which is located closer to the end side of the sliding portion 433 than the imaginary plane P1 is smaller than the weight of the portion of the first rocker arm 42 which is located closer to the end side of the roller 423 than the imaginary plane P1. The imaginary plane P1 includes the axis Ax4 of the intake rocking shaft 41 and extends in the cylinder axis direction. Fig. 12 is a view of the second rocker arm 43 as seen from the cam axis direction. In Fig. 12, G1 indicates the position of the center of gravity of the first rocker arm 42. G2 indicates the position of the center of gravity of the second rocker arm 43. As shown in FIG. 12, the center of gravity G2 of the second rocker arm 43 is closer to the axis Ax4 of the intake rocking shaft 41 than the center of gravity G1 of the first rocker arm 42. The contact surface 435 of the sliding portion 433 includes a hardened layer 437 formed by surface treatment. The hardened layer 437 has a coefficient of friction lower than that of the substrate of the sliding portion 433 and a hardness of the substrate higher than the sliding portion 433. The coefficient of friction of the hardened layer 437 is lower than the coefficient of friction of the surface of the chromium nitride coating or the sintered material. In other words, the hardened layer 437 has a high ablation resistance. Specifically, the hardened layer 437 is preferably a carbon-based hard film, and more specifically, DLC (Diamond Like Carbon). DLC has self-lubricating properties as a graphite structure, so the friction coefficient is low and the ablation resistance is high. Moreover, the DLC has a diamond structure, so that the highest hardness is higher and the wear resistance is higher than that of the coating formed of the chromium nitride coating. The substrate is, for example, chromium molybdenum steel. As shown in FIG. 6, the pressing member 44 is connected to the first rocker arm 42. The pressing member 44 is formed integrally with the first rocker arm 42. The first adjustment screw 441 and the second adjustment screw 442 are provided at the front end of the pressing member 44. The front end of the first adjustment screw 441 is opposed to the base end of the first intake valve 27. The front end of the second adjustment screw 442 is opposed to the base end of the second intake valve 28. The pressing member 44 rotates in the axial direction of the intake rocking shaft 41 to press the first intake valve 27 and the second intake valve 28 . The intake swing unit 34 includes an arm spring member 46, a first support member 47, and a second support member 48. The arm spring pushing member 46 pushes the second rocker arm 43 in a direction in which the sliding portion 433 is pressed toward the cam shaft 14. In the present embodiment, the arm spring pushing member 46 is a coil spring, and the intake rocking shaft 41 passes through the arm spring pushing member 46. The first support member 47 supports one end of the arm spring member 46. The first support member 47 has a pin shape and protrudes from the second rocker arm 43 in the cam axis Ax3 direction. The second support member 48 supports the other end of the arm spring member 46. The second support member 48 is composed of a bent plate material. FIG. 13 is a cross-sectional view of the vicinity of the second shaft support portion 22 and the arm spring pushing member 46. As shown in FIG. 13, the step portion 222 is provided in the second shaft support portion 22, and the second support member 48 is supported by the step portion 222. As shown in FIG. 3, the coupling pin 45 is provided to be movable in the axial direction of the cam shaft 14 and is movable to the coupling position and the release position. The coupling pin 45 is disposed at the connection position over the first connection hole 422 and the second connection hole 432. Thereby, the coupling pin 45 connects the first rocker arm 42 and the second rocker arm 43. In other words, the connecting pin 45 connects the pressing member 44 to the second rocker arm 43 via the first rocker arm 42 at the connecting position. Thereby, the pressing member 44 swings integrally with the first rocker arm 42 and the second rocker arm 43. The coupling pin 45 is disposed in the first coupling hole 422 at the release position, and is not disposed in the second coupling hole 432 of the second rocker arm 43. Thereby, the first rocker arm 42 and the second rocker arm 43 are non-connected at the release position by the joint pin 45. In other words, the connecting pin 45 releases the second rocker arm 43 from the pressing member 44 at the release position. Thereby, the pressing member 44 and the first rocker arm 42 swing independently of the second rocker arm 43. The valve actuation mechanism 13 includes an opening/closing point changing unit 49. The opening/closing timing changing unit 49 changes the opening and closing timing of the first intake valve 27 and the second intake valve 28. The opening/closing point changing unit 49 is attached to the head cover 5. The opening/closing point changing unit 49 is an electromagnetic solenoid, and when the coupling pin 45 is pressed in the axial direction of the cam shaft 14 by energization, the position of the coupling pin 45 is switched from the release position to the connection position. When the energization of the opening/closing timing changing unit 49 is stopped, the position of the coupling pin 45 is returned from the connection position to the release position by the elastic force of the pin pushing member 59 described below. The opening/closing point changing unit 49 includes a rod 491 that presses the coupling pin 45 and a body portion 492 that drives the rod 491. The central axis of the rod 491 is parallel to the cam axis Ax3. The rod 491 is disposed so as to overlap the joint pin 45 when viewed in the direction of the cam axis Ax3 in the swing range of the joint pin 45. The lever 491 is driven by the body portion 492, thereby pressing the coupling pin 45. As shown in FIG. 3, the intake rocking unit 34 includes a pin pushing member 59. The pin spring pushing member 59 is disposed in the first coupling hole 422. The pin pushing member 59 pushes the coupling pin 45 in a direction from the connection position toward the release position. Therefore, when the joint pin 45 is not pressed by the opening/closing point changing unit 49, the joint pin 45 is held at the release position by the pin spring pushing member 59. When the joint pin 45 is pressed by the opening/closing point changing unit 49, the joint pin 45 moves from the release position to the joint position against the elastic thrust of the pin spring pushing member 59. FIG. 14 shows a state in which the sliding portion 433 is pushed up by the second intake cam portion 145 when the coupling pin 45 is at the coupling position. When the joint pin 45 is at the joint position, the first rocker arm 42 is coupled to the second rocker arm 43 and swings integrally with the second rocker arm 43. Therefore, when the sliding portion 433 is pushed up by the second intake cam portion 145, the second rocker arm 43 swings around the intake rocking shaft 41, whereby the first rocker arm 42 also swings in the direction in which the pressing member 44 is lowered. Thereby, the first intake valve 27 is pressed down at the front end of the first adjustment screw 441, and the second intake valve 28 is pressed down at the front end of the second adjustment screw 442. Thereby, the first intake valve 27 and the second intake valve 28 open the intake port 31. As described above, when the connecting pin 45 is at the connecting position, the pressing member 44 presses the first intake valve 27 and the second intake valve 28 in accordance with the rotation of the second rocker arm 43. When the sliding portion 433 is not pushed up by the second intake cam portion 145, the first intake valve 27 and the second intake valve 28 are pushed up by the intake valve springs 271 and 281 to close the intake port 31. . When the joint pin 45 is at the release position, the first rocker arm 42 and the second rocker arm 43 swing independently. Therefore, when the roller 423 is pushed up by the first intake cam portion 144, the first rocker arm 42 swings in the direction in which the pressing member 44 is lowered around the intake rocking shaft 41. Thereby, the first intake valve 27 is pressed down at the front end of the first adjustment screw 441, and the second intake valve 28 is pressed down at the front end of the second adjustment screw 442. Thereby, the first intake valve 27 and the second intake valve 28 open the intake port 31. As described above, when the coupling pin 45 is at the release position, the pressing member 44 presses the first intake valve 27 and the second intake valve 28 in accordance with the rotation of the first rocker arm 42. When the roller 423 is not pushed up by the first intake cam portion 144, the first intake valve 27 and the second intake valve 28 are pushed up by the intake valve springs 271 and 281 to close the intake port 31. Further, the shape of the first intake cam portion 144 and the second intake cam portion 145 is such that the second intake cam portion 145 pushes up the sliding portion 433 before the front end of the first intake cam portion 144 reaches the roller 423. The way to set. Therefore, when the coupling pin 45 is at the coupling position, the first rocker arm 42 is operated by the rotation of the second intake cam portion 145, whereby the rotation of the first intake cam portion 144 is not transmitted to the first rocker arm. 42. Therefore, when the coupling pin 45 is at the connection position, the first intake valve 27 and the second intake valve 28 are opened and closed in response to the rotation of the second intake cam portion 145. On the other hand, when the joint pin 45 is at the release position, the rotation of the second intake cam portion 145 is not transmitted to the first rocker arm 42. Therefore, when the joint pin 45 is at the release position, the first intake valve 27 and the second intake valve 28 are opened and closed in response to the rotation of the first intake cam portion 144. When the engine rotation speed is in a specific low speed region, the opening/closing timing changing unit 49 causes the coupling pin 45 to be at the release position. For example, when the engine rotation speed is less than a specific switching threshold, the opening/closing timing changing unit 49 sets the coupling pin 45 to the release position. Thereby, the pressing member 44 presses the first intake valve 27 and the second intake valve 28 in accordance with the rotation of the first rocker arm 42. As a result, the first intake valve 27 and the second intake valve 28 are opened and closed in response to the rotation of the first intake cam portion 144. When the engine rotation speed is a specific high speed region, the opening/closing timing changing unit 49 causes the coupling pin 45 to be at the coupling position. For example, when the engine rotation speed is equal to or higher than a specific switching threshold, the opening/closing timing changing unit 49 causes the coupling pin 45 to be at the coupling position. Thereby, the pressing member 44 presses the first intake valve 27 and the second intake valve 28 in accordance with the rotation of the second rocker arm 43. As a result, the first intake valve 27 and the second intake valve 28 are opened and closed in response to the rotation of the second intake cam portion 145. Next, the configuration of the intake rocking shaft 41 will be described in detail. Figure 15 is a perspective view of the intake rocker shaft 41. As shown in FIG. 15, the intake rocking shaft 41 includes a shaft member 51 and a collar member 52. The shaft member 51 and the collar member 52 are independent of each other. The collar member 52 has a tubular shape. The shaft member 51 is inserted into the hole 521 of the collar member 52. The shaft member 51 is not fixed to the collar member 52. Therefore, the collar member 52 is rotatable relative to the shaft member 51. The shaft member 51 includes a first end portion 511 and a second end portion 512. The first end portion 511 is one end portion of the intake rocking shaft 41 in the axial direction. The second end portion 512 is the other end portion of the intake rocking shaft 41 in the axial direction. The first end portion 511 protrudes from the collar member 52 in one of the axial directions of the intake rocking shaft 41. The second end portion 512 protrudes from the collar member 52 toward the other of the axial direction of the intake rocking shaft 41. As shown in FIG. 3, the first end portion 511 is supported by the first shaft support portion 21. The first shaft support portion 21 includes a first rocking shaft hole 212. The first rocking shaft hole 212 is disposed adjacent to the first camshaft hole 211. The first rocking shaft hole 212 penetrates the first shaft support portion 21 in the direction of the cam axis Ax3. The first end portion 511 is inserted into the first rocking shaft hole 212. The end surface of the first end portion 511 faces the cam chain chamber 16 and is disposed. The second end portion 512 is supported by the second shaft support portion 22 . The second shaft support portion 22 includes a second rocking shaft hole 223. The second rocking shaft hole 223 is disposed adjacent to the second cam shaft hole 221. The second rocking shaft hole 223 does not penetrate the second shaft support portion 22 . Further, the second rocking shaft hole 223 may also pass through the second shaft support portion 22. The second end portion 512 is inserted into the second rocking shaft hole 223. As shown in FIG. 8, the boundary B between the first connection hole 422 of the first rocker arm 42 and the second connection hole 432 of the second rocker arm 43 is intermediate to the interval L between the first end portion 511 and the second end portion 512. M is closer to the second end 512. More specifically, the distance L2 from the boundary B to the second end portion 512 is smaller than the distance L1 (L2 < L1) from the boundary B to the first end portion 511. As shown in FIG. 15, the locking groove 513 is provided in the end surface of the 1st edge part 511. The shaft member 51 can be attached to and detached from the first rocking shaft hole 212 by locking the tool to the locking groove 513. A locking hole 514 is formed in the second end portion 512. The locking hole 514 penetrates the second end portion 512 in a direction perpendicular to the axis of the shaft member 51. As shown in FIG. 5, the second shaft support portion 22 is provided with a hole 224 extending perpendicularly to the axial direction of the second rocking shaft hole 223. The hole 224 is open to the upper surface of the second shaft support portion 22. By inserting the fastening member 53 shown in FIG. 6 into the hole 224 of the second shaft support portion 22 and the locking hole 514 of the second end portion 512, the shaft member 51 is prevented from coming off the second shaft support portion 22. The collar member 52 and the shaft member 51 are separate bodies. The collar member 52 is disposed between the first end portion 511 and the second end portion 512 in the axial direction of the intake rocking shaft 41. The collar member 52 is disposed between the first shaft support portion 21 and the second shaft support portion 22 . The first rocker arm 42 and the second rocker arm 43 are attached to the collar member 52. In other words, the collar member 52 is inserted into the first mounting portion 421 of the first rocker arm 42 and the second mounting portion 431 of the second rocker arm 43. The arm spring pushing member 46 and the second support member 48 are also attached to the collar member 52. The outer diameter of the collar member 52 is larger than the outer diameter of the shaft member 51. The outer diameter of the collar member 52 is larger than the outer diameter of the exhaust rocker shaft 35. The outer diameter of the collar member 52 is larger than the outer diameter of the first end portion 511 and larger than the outer diameter of the second end portion 512. The inner diameter of the first rocking shaft hole 212 is smaller than the outer diameter of the collar member 52. The inner diameter of the second rocking shaft hole 223 is smaller than the outer diameter of the collar member 52. In the engine 1 of the present embodiment described above, the roller 423 is used for the first rocker arm 42 for low speed. Further, the second rocker arm 43 for high speed uses the sliding portion 433. The weight of the sliding portion 433 and the portion supporting the sliding portion 433 is smaller than the weight of the portion of the roller 423 and the supporting roller 423. Thereby, the equivalent weight of the second rocker arm 43 can be reduced. Therefore, by using the sliding portion 433 for the second rocker arm 43 for high speed, the second rocker arm when the engine rotation speed is the high speed region can be reduced as compared with the case where the roller is used for the second rocker arm 43 for high speed. The effect of the equivalent weight of 43. Thereby, the upper limit of the engine rotation speed can be increased. Fig. 16 is a view showing a change in the loss torque with respect to the rotational speed of the engine when the rocker arm uses the roller 423 and when the sliding portion 433 is used. The lost torque represents the magnitude of the output torque of the engine 1 lost by the rocker arm. In Fig. 16, L_roller indicates the case where the rocker arm uses the roller 423. L_slipper indicates the case where the rocker arm uses the sliding portion 433. As shown in FIG. 16, the loss torque when the sliding portion 433 is used is larger than the loss torque when the roller 423 is used. However, in the high speed region of the engine rotational speed, the sliding speed of the sliding portion 433 with respect to the cam shaft 14 is large, so that the contact surface 435 of the sliding portion 433 produces a thick oil film. Therefore, the frictional resistance between the sliding portion 433 and the cam shaft 14 in the high speed region becomes small. Thereby, as shown in FIG. 16, the larger the engine rotation speed, the smaller the difference in loss torque. Therefore, by using the sliding portion 433 for the second rocker arm 43 for high speed, the mechanical loss in the high speed region can be suppressed to be small while reducing the equivalent weight. On the other hand, in the low speed region of the engine rotation speed, the difference in loss torque increases. Therefore, by using the roller 423 for the first rocker arm 42 for low speed, the frictional resistance between the roller 423 and the camshaft 14 can be reduced. Thereby, the mechanical loss in the low speed region can be suppressed to be small. Further, in the low speed region, the influence of the equivalent weight is reduced as compared with the high speed region. Therefore, even if the roller 423 is used, the influence of the equivalent weight of the second rocker arm 43 can be reduced. As described above, the roller 423 is used by the first rocker arm 42 for low speed, and the sliding portion 433 is used for the second rocker arm 43 for high speed, so that the mechanical loss can be suppressed to be small in the entire region of the engine rotation speed, and can be reduced. Small equivalent weight. Further, in the axial direction of the intake rocking shaft 41, the maximum width of the sliding portion 433 is larger than the width of the roller 423. Thereby, the surface pressure of the sliding portion 433 can be suppressed to be small, and the occurrence of local contact can be suppressed. Further, when viewed from the axial direction of the exhaust rocking shaft 35, the front end of the sliding portion 433 is closer to the axis of the exhaust rocking shaft 35 than the front end of the roller 423. That is, the surface pressure of the sliding portion 433 can be suppressed to be small by making the maximum width of the sliding portion 433 larger than the width of the roller 423, so that the necessity of increasing the radius of curvature and reducing the surface pressure is lowered. Therefore, the sliding portion 433 can be configured to be short. Thereby, the increase in the equivalent weight can be suppressed as compared with the case where the sliding portion is extended to increase the radius of curvature of the sliding portion 433. Thereby, the upper limit of the engine rotation speed can be increased. Further, the sliding portion 433 includes a hardened layer 437. Thereby, the wear resistance of the sliding portion 433 can be improved. In the axial direction of the exhaust rocker shaft 35, the maximum width of the contact surface 435 of the sliding portion 433 is smaller than the width of the boss portion 430. Therefore, the sliding portion 433 can be made lighter while suppressing the surface pressure of the sliding portion 433 to be small, whereby the equivalent weight of the second rocker arm 43 can be further reduced. The weight of the portion of the second rocker arm 43 which is located closer to the end side of the sliding portion 433 than the imaginary plane P1 is smaller than the weight of the portion of the first rocker arm 42 which is located closer to the end side of the roller 423 than the imaginary plane P1. In the axial direction of the exhaust rocker shaft 35, the maximum width of the contact surface 435 of the sliding portion 433 is smaller than the width of the boss portion 430. In the axial direction of the exhaust rocker shaft 35, the width of the convex portion 439 is smaller than the width of the contact surface 435. Further, when viewed from the axial direction of the exhaust rocking shaft 35, the surface of the arm portion 434 opposite to the contact surface 435 has a shape that is recessed toward the contact surface 435 side. The sliding portion 433 and the second arm portion 434 are further reduced in weight by the shapes of the sliding portion 433 and the second arm portion 434. Thereby, the weight of the sliding portion 433 side of the second rocker arm 43 is reduced. As a result, the equivalent weight of the second rocker arm 43 can be further reduced. The second arm portion 434 includes a recess 436 between the contact surface 435 and the boss portion 430. It is possible to reduce the weight of the contact surface 435 to the boss portion 430, thereby further reducing the equivalent mass of the second rocker arm 43. Thereby, interference with the jig for processing can be avoided by the recess 436 during the processing of the contact surface 435. As described above, the sliding portion 433 is brought closer to the boss portion 430 by bringing the front end of the sliding portion 433 closer to the axis Ax4 of the intake rocking shaft 41 than the front end of the roller 423. Even in such a configuration, by forming the concave portion 436, the curved contact surface 435 can be processed (for example, polished) without causing the processing jig to interfere with the convex portion 430. The second arm portion 434 includes a convex portion 439. Thereby, the second arm portion 434 can be made lighter and the rigidity of the second arm portion 434 can be ensured. Further, the center of gravity G2 of the second rocker arm 43 is closer to the axis of the rocking shaft 41 than the center of gravity G1 of the first rocker arm 42. Therefore, the equivalent weight of the second rocker arm 43 can be further reduced. Thereby, the spring load (elastic thrust) of the arm spring pushing member 46 can be reduced, so that the abrasion of the arm spring pushing member 46 can be suppressed to be small. Further, the mechanical loss generated by the arm spring pushing member 46 can be suppressed to be small. 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 engine is not limited to a water-cooled single-cylinder engine. For example, the engine can also be air cooled. The engine can also be a multi-cylinder engine. The number of valves for exhaust is not limited to two, and may be one or three or more. The number of intake valves is not limited to two, and may be one or three or more. In the above-described embodiment, the intake valve is a mechanism for switching the opening and closing timing of the valve by the opening/closing point changing unit 49. However, this mechanism may be employed for the exhaust valve. The configuration including the rocking shaft of the shaft member 51 and the collar member 52 can also be applied to the exhaust rocking shaft. The collar member 52 can also be mounted to the shaft member 51 in a non-rotatable manner. The collar member 52 can also be omitted. As in the first modification shown in FIG. 17, the pressing member 44 and the first rocker arm 42 and the second rocker arm 43 may be independent members. For example, when the connecting pin 45 is at the connecting position, the second rocker arm 43 and the pressing member 44 may be coupled by the connecting pin 45. When the connecting pin 45 is at the releasing position, the first rocking is performed by the connecting pin 45. The arm 42 is coupled to the pressing member 44. The joint pin 45 can also be driven by a hydraulic pump (a point change portion at the time of opening and closing). For example, in the second modification shown in FIG. 18, the first oil chamber 42r and the oil passage 42m are formed in the first rocker arm 42. The oil of the first oil chamber 42r can be pressurized and depressurized via the oil passage 42m. Similarly, the second oil chamber 43r and the oil passage 43m are formed in the second rocker arm 43. The oil of the second oil chamber 43r can be pressurized and depressurized via the oil passage 43m. A pin hole 45r is formed in the pressing member 44. The pin hole 45r communicates with the first oil chamber 42r and the second oil chamber 43r. A coupling pin 45 is housed in the pin hole 45r. In this configuration, the connecting pin 45 is displaced by the hydraulic pressure, whereby the pressing member 44 can be selectively coupled to the first rocker arm 42 and the second rocker arm 43. As in the third modification shown in FIG. 19, the first rocker arm 42 and the second rocker arm 43 may be provided with pressing members 44a and 44b, respectively. In other words, the first rocker arm 42 may be provided with the first pressing member 44a, and the second rocker arm 43 may be provided with the second pressing member 44b. In this case, when the coupling pin 45 is at the release position, the first pressing member 44a provided in the first rocker arm 42 presses the first intake valve 27 in accordance with the rotation of the first rocker arm 42. Further, when the coupling pin 45 is at the coupling position, the second pressing member 44b provided in the second rocker arm 43 presses the second intake valve 28 in accordance with the rotation of the second rocker arm 43. [Industrial Applicability] According to the present invention, mechanical loss in a low speed region of the engine rotation speed can be reduced, and an upper limit of the engine rotation speed can be increased.

1‧‧‧ engine

2‧‧‧Crankcase

3‧‧‧Cylinder block

4‧‧‧ cylinder head

4a‧‧‧ side wall

4b‧‧‧ sidewall end

5‧‧‧ head cover

5a‧‧‧ side wall

5b‧‧‧ sidewall end

6‧‧‧ crankshaft

7‧‧‧Piston

8‧‧‧ Connecting rod

9‧‧‧Seal components

11‧‧‧ combustion chamber

12‧‧‧Mars plug

13‧‧‧Valve mechanism

14‧‧‧Camshaft

15‧‧‧Cam chain

16‧‧‧Cam chain room

17‧‧‧Water pump

18‧‧‧ coolant hose

19‧‧‧ radiator

21‧‧‧1st shaft support

21a‧‧‧End

22‧‧‧2nd axis support

22a‧‧‧End

23‧‧‧1st bearing

24‧‧‧2nd bearing

25‧‧‧1st exhaust valve

26‧‧‧Intake valve

27‧‧‧1st intake valve

28‧‧‧2nd intake valve

29‧‧‧Sprocket

31‧‧‧Intake 埠

32‧‧‧Exhaust gas

33‧‧‧Exhaust shake unit

34‧‧‧Intake Shake Unit

35‧‧‧Exhaust rocking shaft

36‧‧‧Exhaust rocker arm

37‧‧‧ Roll

38‧‧‧ Pressing members

39‧‧‧ Arms

41‧‧‧Intake shaft

42‧‧‧1st rocker

42m‧‧‧ oil road

42r‧‧‧1st oil room

43‧‧‧2nd rocker

43m‧‧‧ oil road

43r‧‧‧2nd oil room

44‧‧‧ Pressing members

44a‧‧‧1st pressing member

44b‧‧‧2nd pressing member

45‧‧‧Links

45r‧‧ pin hole

46‧‧‧arm push member

47‧‧‧1st support member

48‧‧‧2nd support member

49‧‧‧Change Department when opening and closing

51‧‧‧Axis components

52‧‧‧ collar components

53‧‧‧ fastening members

100‧‧‧Sitting vehicle

101‧‧‧ front wheel

102‧‧‧Site

103‧‧‧ Rear wheel

104‧‧‧Power unit

105‧‧‧Steering device

106‧‧‧ body shell

107‧‧‧Transmission

108‧‧‧ rear casing

109‧‧‧ bottom shell

110‧‧‧ front casing

111‧‧‧Foot

112‧‧‧Channel Department

113‧‧‧Handles

141‧‧‧1st camshaft end

142‧‧‧2nd camshaft end

143‧‧‧ Rod

144‧‧‧1st intake cam section

145‧‧‧2nd intake cam section

146‧‧‧Exhaust cam

211‧‧‧1st camshaft hole

212‧‧‧1st rocking shaft hole

221‧‧‧2nd camshaft hole

222‧‧‧

223‧‧‧2nd shaking shaft hole

224‧‧‧ holes

251‧‧‧Exhaust valve spring

261‧‧‧Exhaust valve spring

271‧‧‧Intake valve spring

281‧‧‧Intake valve spring

364‧‧‧through holes

365‧‧‧1st adjustment screw

366‧‧‧2nd adjustment screw

420‧‧‧1st arm

421‧‧‧1st installation department

422‧‧‧1st link

423‧‧‧roll

430‧‧‧Seat

431‧‧‧Second Installation Department

432‧‧‧2nd link

433‧‧‧Sliding section

434‧‧‧2nd arm

435‧‧‧Contact surface

436‧‧‧ recess

437‧‧‧ hardened layer

438‧‧‧ the opposite

438a‧‧‧1st

438b‧‧‧2nd

439‧‧‧ convex

441‧‧‧1st adjustment screw

442‧‧‧2nd adjustment screw

491‧‧‧ drive rod

492‧‧‧ Body Department

511‧‧‧1st end

512‧‧‧2nd end

513‧‧‧ card slot

514‧‧‧Clock hole

521‧‧‧ hole

Ax1‧‧‧Cylinder axis

Ax2‧‧‧ crankshaft axis

Ax3‧‧‧ cam axis

Ax4‧‧‧ axis of the intake rocking shaft 41

B‧‧‧ Junction

C1‧‧‧Bending Center

G1‧‧‧ Position of the center of gravity of the first rocker arm 42

G2‧‧‧ Position of the center of gravity of the second rocker arm 43

L‧‧‧ interval

L1‧‧‧ distance

L2‧‧‧ distance

M‧‧‧ intermediate position

P1‧‧‧imaginal plane

Q‧‧‧ imaginary face

Fig. 1 is a side view of a straddle type vehicle of an embodiment. Fig. 2 is a cross-sectional view showing a part of an engine for a straddle type vehicle according to an embodiment. Figure 3 is a cross-sectional view of the cylinder head and the head cover viewed from a direction perpendicular to the cylinder axis and the cam axis. Figure 4 is a perspective view of the interior of the cylinder head. Figure 5 is a perspective view of the interior of the cylinder head. Fig. 6 is a view of the inside of the cylinder head viewed from the cylinder axis direction. Figure 7 is a cross-sectional view of the inside of the cylinder head viewed from the direction of the cam axis. Figure 8 is a perspective view of the intake rocking unit. Figure 9 is a view of the intake rocking unit as viewed from a direction perpendicular to the cam axis. Fig. 10 is a view of the intake rocking unit viewed from the cam axis direction. Fig. 11 is a view of the second rocker arm viewed from below. Fig. 12 is a view of the second rocker arm viewed from the cam axis direction. Fig. 13 is a cross-sectional view showing the vicinity of the second shaft support portion and the arm spring pushing member. Figure 14 is a cross-sectional view showing the inside of the cylinder head from the direction of the cam axis. Figure 15 is a perspective view of the intake rocking shaft. Fig. 16 is a view showing changes in the loss torque with respect to the rotational speed of the engine when the rocker uses the roller and when the sliding portion is used. Fig. 17 is a view of the intake swing unit of the first modification as seen from the cylinder axis direction. Fig. 18 is a view showing the intake swing unit of the second modification viewed from the cylinder axis direction. Fig. 19 is a view showing the inside of the cylinder head of the third modification from the cylinder axis direction.

Claims (11)

An engine comprising: a cylinder head; a valve mounted to the cylinder head; a rocking unit that presses the valve to open and close the valve; a cam shaft that drives the rocking unit; and an opening and closing point change unit for changing The swinging unit includes: a rocking shaft that supports the cylinder head; and a first rocker arm that includes a roller that is rotatable in contact with the camshaft and a pressing member that presses the valve, and The roller rotates about the axis of the rocking shaft by the roller shaft; the second rocker arm includes a sliding portion that can be disposed in contact with the cam shaft, and the first rocker arm in the axial direction of the rocking shaft Arranging side by side, the sliding portion is in contact with the cam shaft to rotate about the axis of the rocking shaft; and the connecting pin is provided to be movable to the connecting position and the releasing position by the opening and closing point changing portion. The connection position connects the second rocker arm to the pressing member, and the second rocker arm is released relative to the pressing member at the release position When the engine rotation speed is a specific low speed region, the opening/closing timing changing unit positions the coupling pin at the release position, and the pressing member presses the valve in accordance with the rotation of the first rocker arm at the engine rotation speed. In the case of the specific high-speed region, the opening/closing timing changing unit positions the connecting pin at the connecting position, and the pressing member presses the valve in accordance with the rotation of the second rocker arm, and the roller performs rolling contact with the cam shaft. The sliding portion is in sliding contact with the cam shaft. When viewed from the axial direction of the rocking shaft, the front end of the sliding portion is closer to the axis of the rocking shaft than the front end of the roller, and the sliding is in the axial direction of the rocking shaft. The maximum width of the portion is greater than the width of the roller. The engine of claim 1, wherein the sliding portion comprises a curved contact surface in contact with the cam shaft, and a radius of curvature of the contact surface is greater than a radius of curvature of the roller. The engine of claim 1, wherein the center of gravity of the second rocker arm is closer to the axis of the rocking axis than the center of gravity of the first rocker arm. The engine of claim 1, wherein a weight of a portion of the second rocker arm that is located closer to an end surface of the sliding portion than an imaginary plane extending in an axial direction of the cylinder head of the cylinder head is smaller than the first portion 1 The weight of a portion of the rocker arm that is located closer to the end side of the roller than the imaginary plane. The engine of any one of claims 1 to 4, wherein the second rocker arm comprises: a boss portion having a hole through which the rocking shaft passes; and an arm portion extending from the boss portion to the sliding portion And the sliding portion includes a contact surface in contact with the cam shaft. The engine of claim 5, wherein the maximum width of the contact surface of the sliding portion is smaller than the width of the protruding portion in the axial direction of the rocking shaft. The engine of claim 5, wherein the arm portion includes a recess between the contact surface and the boss portion. The engine of claim 5, wherein the arm portion includes a convex portion that extends from the sliding portion to the convex portion and protrudes from a surface opposite to the contact surface from the sliding portion. The engine of claim 5, wherein the width of the convex portion is smaller than the width of the contact surface in the axial direction of the rocking shaft. The engine of claim 5, wherein the surface of the arm portion opposite to the contact surface has a shape that is recessed toward the contact surface side when viewed from the axial direction of the rocking shaft. The engine of claim 1, wherein the sliding portion comprises a hardened layer in contact with the cam shaft, and the hardened layer has a friction coefficient lower than a base of the sliding portion and a hardness of a substrate higher than the sliding portion.