JP5197526B2 - Cylinder head structure of internal combustion engine for vehicle - Google Patents

Description

  The present invention relates to a cylinder head structure of a single-cylinder four-stroke cycle internal combustion engine for a vehicle such as a motorcycle.

  A stopper mechanism for a decompression cam (hereinafter referred to as “decompression cam”) having a decompression device (hereinafter referred to as “decompression device”) in a cylinder head of a single cylinder four-stroke cycle internal combustion engine for a vehicle such as a motorcycle. For example, Patent Document 1 discloses a structure in which a locking member to be embedded is embedded in a camshaft holder portion of a cylinder head and secured with a bolt.

  However, in the case of the cylinder head structure as shown in Patent Document 1, a dedicated part such as a bolt for preventing the locking member from being detached is required, and the camshaft holder part needs to be internally threaded. There was a problem that man-hours increased.

Japanese Patent No. 4260841 (FIG. 4)

  An object of the present invention is to provide a cylinder head structure for an internal combustion engine for a vehicle that reduces the number of parts and the number of processing steps, and further improves lubrication of an air supply / exhaust cam, etc. in a cylinder head structure provided with a variable cam such as a decompression cam. And

In order to achieve the above object, the invention described in claim 1 is a pair of camshaft holders that support a camshaft, a variable cam that is rotatably supported by the camshaft, and an engagement with the variable cam. In the cylinder head structure of the internal combustion engine for a vehicle that includes a locking member that restricts the rotation of the variable cam, the cylinder head structure includes a reinforcing member that is fixed to the cylinder head and connects the camshaft holders. The locking member, which is provided with a through hole, is accommodated in the through hole and protrudes from one end thereof and is urged to engage with the variable cam, and the other end of the through hole is closed by the reinforcing member. Rutotomoni held in the through hole, said cylinder head, when the vehicle engine is mounted on the vehicle, substantially horizontally cylinder axes, said camshaft are oriented in the vehicle width direction, under the same cam shaft In Are arranged such contact portion is located between the gas valve or the exhaust valve and the rocker arm, said reinforcing member, as adhered lubricating oil is dropped supplied to the contact portion, that lower is curved It is the cylinder head structure of the internal combustion engine for vehicles characterized.

  According to a second aspect of the present invention, in the cylinder head structure for an internal combustion engine for a vehicle according to the first aspect, the camshaft holder portion extends in the camshaft direction on the outer periphery of the camshaft, and the variable cam and its It has an extending portion that faces in the radial direction, and the through hole is formed perpendicular to the cam shaft direction in the extending portion.

According to a third aspect of the present invention, in the cylinder head structure for an internal combustion engine for a vehicle according to the first or second aspect , the variable cam is a decompression cam disposed adjacent to the exhaust cam, and the exhaust cam An oil reservoir is formed between the compressor and the decompression cam.

According to a fourth aspect of the present invention, in the cylinder head structure of the internal combustion engine for a vehicle according to the third aspect , the oil sump is formed on the cam shaft, and the outer diameter of the exhaust cam and the outer diameter of the decompression cam. It is a smaller diameter part.

According to a fifth aspect of the present invention, in the cylinder head structure for an internal combustion engine for a vehicle according to any one of the first to fourth aspects, the reinforcing member is an annular plate member, A plurality of fastening bolts for fastening the cylinder block and fixing the reinforcing member to the cylinder head are provided, and the reinforcing member, the cylinder head, and the cylinder block are fastened together.

According to the cylinder head structure of the internal combustion engine for a vehicle of the first aspect of the invention, since the reinforcing member also serves as a retaining member for the retaining member, the retaining bolt and the internal thread processing for screwing thereof become unnecessary, and the number of parts is reduced. The number of processing steps is reduced , and the contact portion between the intake valve or the exhaust valve and the rocker arm can be lubricated satisfactorily with a simple structure .

  According to the invention of claim 2, in addition to the effect of the invention of claim 1, the through hole serving as the locking member accommodating portion is provided with an extending portion extending in the cam shaft direction in the cam shaft holder portion. Since it is provided integrally, the strength of the camshaft holder portion can be increased.

According to the invention of claim 3 , the effect of the invention of claim 1 or claim 2 is achieved in the structure of the decompression cam device, and the decompression cam can be lubricated well with a simple configuration.

According to the invention of claim 4 , in addition to the effect of the invention of claim 3 , an oil sump can be formed with a simple structure while reducing the weight of the camshaft.

According to the invention of claim 5 , in addition to the effect of the invention of any one of claims 1 to 4 , by using the annular reinforcing member as a washer corresponding to a plurality of fastening bolts, The number of points can be further reduced, and the fastening bolt can be easily assembled.

1 is a left side view of a motorcycle equipped with a power unit having a cylinder head structure of a vehicle internal combustion engine according to an embodiment of the present invention. It is a left side sectional view of the power unit concerning this embodiment. FIG. 3 is a developed sectional view taken along the line III-III in FIG. 2. FIG. 4 is an enlarged view of the vicinity of a cylinder head in FIG. 3. (A) is sectional drawing in alignment with the axis of a cam shaft, a decompression cam, and a cam bearing in FIG. 4, (b) is a front view of the decompression cam by VV arrow in (a). FIG. 6 is a top cross-sectional view of the vicinity of a cylinder head as viewed in the direction of arrows VI-VI in FIG. 4. (A) is a cylinder head vicinity right side sectional drawing by the VII-VII arrow in FIG. 4, (b) is an enlarged view of a locking member vicinity in (a). It is a typical operation explanatory view of the decompression device concerning this embodiment. It is a typical operation explanatory view of the decompression device concerning this embodiment. It is a typical operation explanatory view of the decompression device concerning this embodiment. It is a typical operation explanatory view of the decompression device concerning this embodiment. It is a typical operation explanatory view of the decompression device concerning this embodiment.

  A cylinder head structure for an internal combustion engine for a vehicle according to an embodiment of the present invention will be described with reference to FIGS. In the following description, the directions such as front, rear, left, right, up, down, and the like follow the direction of the vehicle when the power unit including the cylinder head structure of the internal combustion engine for a vehicle according to this embodiment is mounted on a vehicle such as a motorcycle. Further, unless otherwise specified, arrow FR in the figure indicates the front of the vehicle, LH indicates the left side of the vehicle, RH indicates the right side of the vehicle, UP indicates the upper side of the vehicle, and DN indicates the lower side of the vehicle.

  FIG. 1 shows a left side surface of a motorcycle 1 according to an embodiment of the present invention. A body frame 2 of the motorcycle 1 is inclined obliquely downward and rearward from a head pipe 3 at the front of the vehicle body, and one main frame 4 extends, and a pair of left and right pivot brackets 5 are disposed at the rear of the main frame 4. 5 extends downward and is fixed. A pair of left and right seat rails 6, 6 extend rearward and obliquely upward from the vicinity of the fixing position of the pivot brackets 5, 5 at the rear portion of the main frame 4, and bend in the middle to reach the rear end. Middle frames 7 and 7 are interposed between the center portions of the seat rails 6 and 6 and the pivot brackets 5 and 5.

  A storage box 8 and a fuel tank (not shown) are installed between the pair of left and right seat rails 6 of the vehicle body frame 2, and a seat 9 covers the storage box 8 and the like so as to be freely opened and closed. A front fork 10 pivotally supported by the head pipe 3 extends below the front of the vehicle body, a front wheel 11 is pivotally supported at the lower end thereof, and a steering handle 12 is provided above the front fork 10. A pivot shaft 13 provided in pivot brackets 5 and 5 at the center of the vehicle body supports a rear fork 14 that is pivotally supported at the front end and extends rearward. A rear wheel 15 is pivotally supported at the rear end. Rear cushions 16, 16 are interposed between the rear portion of the rear fork 14 that swings up and down about the pivot shaft 13 and the seat rails 6, 6.

  A power unit 17 is mounted below the main frame 4 and in front of the pivot brackets 5 and 5. The power unit 17 is suspended from a support bracket 29 provided on the main frame 4 via a support shaft 30 and is supported by support shafts 31 at the upper and lower portions of the pivot brackets 5 and 5. The body frame 2 is covered with a synthetic resin cover member 32 divided into various parts. 150 is a side stand.

  The power unit 17 includes a front internal combustion engine 18 and a rear power transmission device 19. The internal combustion engine 18 is a single-cylinder four-stroke cycle internal combustion engine, and when mounted on the motorcycle 1, the crankshaft 35 (see FIGS. 2 and 3) is oriented in the vehicle width direction and serves as a power unit case (also serves as a crankcase). ) The cylinder block 21, the cylinder head 22, and the cylinder head cover 23 that constitute the cylinder part 210 are stacked from the front surface of 20, and protruded and attached in a posture that is largely inclined forward to a substantially horizontal state. A throttle body 25 and an air cleaner 26 are connected to an intake pipe 24 extending above the cylinder head 22. Further, an exhaust pipe 27 that extends below the cylinder head 22 and bends backward is extended rearward and connected to a muffler 28 on the right side of the rear wheel 15.

  As shown in the left side cross-section of the power unit 17 in FIG. 2, the cylinder portion 210 of the power unit 17 has its axis X (cylinder axis) substantially horizontal (in detail, slightly raised in front), and the front end of the power unit case 20. It protrudes forward (vehicle traveling direction) from the part. The cylinder head 22 and the cylinder block 21 are integrally coupled to the power unit case 20 by a plurality of fastening bolts 60 penetrating from the front of the vehicle (see FIGS. 6 and 7), and the cylinder head cover 23 is inserted from the front of the vehicle. It is fixed to the cylinder head 22 by bolts 61 (see FIG. 7).

  Hereinafter, the front-rear direction parallel to the axis X in the cylinder part 210 may be referred to as the front and rear of the cylinder, and the upper and lower directions orthogonal to the axis X may be referred to as the cylinder upper and lower directions.

  Although the shell of the power transmission device 19 will be described later with reference to FIG. 3, the power unit case 20 includes a left power unit case 20L and a right power unit case 20R which are divided into left and right parts. As shown in FIG. And the right power unit case 20R are integrally coupled at the mating surface Y to form the power unit 17. The outer shell of the power transmission device 19 shown in FIG. 2 is the left side surface of the right power unit case 20R. The power transmission device 19 includes a V-belt type continuously variable transmission 33 and a reduction gear mechanism 34.

  The power unit 17 includes a motor start mechanism 47 and a kick start mechanism 51. The motor start mechanism 47 is provided on a drive pinion 48a of the starter motor 48, a motor start mechanism intermediate shaft 49, large and small gears provided on the intermediate shaft 49, and a left side portion 35L of the crankshaft 35 (see also FIG. 3). The motor starting mechanism is driven by a driven gear 50. The motor start mechanism 47 is a speed reduction mechanism. The starter motor 48 is disposed in front of a vertical line C passing through the center of the crankshaft 35 as shown in the figure.

  The kick starting mechanism 51 includes a kick shaft 52, a kick arm 52a, a kick pedal 52b (FIG. 1), a first intermediate shaft 53a, a second intermediate shaft 53b, a gear group provided on these shafts, and a right side of the crank shaft 35. And a kick start mechanism driven gear 54 provided in the section. The kick start mechanism 51 is a speed increasing mechanism. The kick shaft 52 is disposed between the crank shaft 35 and the output shaft 43 and below the two shafts.

  As shown in FIG. 3, the cylinder block 21 is formed with a cylinder bore 55 along the cylinder axis X, and a piston 56 is fitted in the cylinder bore 55 so as to be able to reciprocate. A small end portion of a connecting rod 59 is swingably connected to the piston 56 via a piston pin 57 along the left-right direction, and a large end portion of the connecting rod 59 is connected to the crankshaft 35 via a crank pin 58 along the left-right direction. It is connected rotatably. The crankshaft 35 rotates counterclockwise in FIG. 2 showing the left side as the piston 56 reciprocates during normal operation of the power unit 17 (rotates clockwise in the right side view).

  A drive pulley shaft 36 of a V-belt type continuously variable transmission 33 is coaxially disposed at the right end portion of the crankshaft 35, and a driven pulley shaft 37 of the V-belt type continuously variable transmission 33 is provided at the rear portion of the power unit case 20. . A V-belt 40 is wound around a drive pulley 38 provided on the drive pulley shaft 36 and a driven pulley 39 provided on the driven pulley shaft 37 to constitute a V-belt continuously variable transmission 33. 33a is a transmission case, and 33b is a transmission cover. An AC generator 68 is provided on the left extension 35L of the crankshaft 35. 68a is a generator cover. 69 is a spark plug.

  A wet centrifugal clutch 41 having substantially the same diameter is provided coaxially with the driven pulley 39 of the driven pulley shaft 37 of the V-belt type continuously variable transmission 33, and the left side portion of the driven pulley shaft 37. 37L is an input shaft of the reduction gear mechanism 34. The rotation shaft of the reduction gear mechanism 34 includes a left portion 37L of the driven pulley shaft 37, a reduction gear mechanism intermediate shaft 42, and an output shaft 43. The reduction gear mechanism 34 is configured by a gear group provided on these shafts. Yes. The output shaft 43 protrudes leftward from the rear part of the left power unit case 20L. The rotational driving force of the power unit 17 is output via the output shaft 43. As shown in FIG. 1, a power transmission chain 46 is bridged between a rear wheel drive sprocket 44 fitted to the output shaft 43 and a rear wheel driven sprocket 45 provided integrally with the rear wheel 15, The rotational driving force of the power unit 17 is transmitted to the rear wheel 15. 44a is a rear cover that covers the left side surface of the power unit case 20 from the generator cover 68a to the rear wheel drive sprocket 44.

  As shown in FIG. 2, the cylinder head 22 closes the front end opening of the cylinder bore 55 and forms a so-called pent roof type combustion chamber 66 together with the piston 56. The internal combustion engine 18 in the present embodiment is an OHC 2 valve, and two combustion chamber side openings of an intake port 70 and an exhaust port 71 are formed on two inclined upper surfaces 67 in the roof forming portion of the combustion chamber 66, respectively. The chamber side openings are opened and closed by an intake valve 72 and an exhaust valve 73, respectively.

  Each port 70, 71 is a flow passage that communicates the combustion chamber 66 with the intake pipe mounting portion 62 at the top of the cylinder head 22 and the exhaust pipe mounting portion 63 at the bottom of the cylinder head 22. After obliquely extending in the forward direction of the cylinder so as to be substantially orthogonal to 67, it is curved upward and downward in the cylinder to reach the intake pipe attachment part 62 and the exhaust pipe attachment part 63. The intake pipe attachment portion 62 and the exhaust pipe attachment portion 63 form a plane that is substantially orthogonal to the cylinder vertical direction, and the intake pipe 24 and the exhaust pipe 27 are fastened to the respective planes (see FIG. 1).

  The stems 74 and 75 of the valves 72 and 73 are V-shaped in a side view so as to be substantially orthogonal to the inclined upper surfaces 66 and 67 and extend in the forward direction of the oblique cylinder, and these penetrate the inner walls of the intake and exhaust ports 70 and 71. After that, retainers 76 (shown only on the exhaust valve 73 side in FIG. 8 are shown in FIG. 8 is a schematic view of the decompression device in the right side cross section in the same direction as FIG. 7). The spring force of the corresponding valve spring 77 (shown only on the exhaust valve 73 side in FIG. 8) is input to each valve 72, 73 via each retainer 76, so that these are the combustion chambers of each port 70, 71. It is biased to the side that closes the side opening.

A single camshaft 64 that is parallel to the crankshaft 35 and oriented in the vehicle width direction is disposed between the stems 74 and 75 of the valves 72 and 73. As shown in FIGS. 3 and 4, the camshaft 64 is integrally provided with an intake cam 64a and an exhaust cam 64b in the middle in the longitudinal direction thereof, and both ends are an intake cam side bearing 65L on the left side and an exhaust cam side bearing on the right side. It is rotatably supported by a pair of left and right left camshaft holder portions 80L and right camshaft holder portion 80R of cylinder head 22 via 65R. A cam chain driven sprocket 81 is coaxially fixed to the left end portion of the cam shaft 64, and an endless cam chain 83 is wound around the cam chain driven sprocket 81 and a cam chain drive sprocket 82 coaxially fixed to the left end portion of the crankshaft 35. It is hung. As a result, the camshaft 64 is linked to the crankshaft 35 and rotates in the same direction at half the rotational speed.

  Between the camshaft 64 and the distal ends of the stems 74 and 75 of the valves 72 and 73, intake side and exhaust side rocker shafts 84 and 85, which are parallel to the camshaft 64, are respectively arranged (FIG. 2, FIG. 7, see FIG. The rocker shafts 84 and 85 are supported by both camshaft holder portions 80L and 80R, respectively. On the rocker shafts 84 and 85, intermediate portions of the intake side and exhaust side rocker arms 86 and 87 are swingably supported. Cam rollers 87a (shown only on the exhaust valve 73 side in FIG. 8) that are in contact with the outer peripheral surfaces of the intake cam 64a and the exhaust cam 64b are rotatably supported at the ends of the rocker arms 86 and 87 on the cam shaft 64 side, respectively. The On the other hand, tappet bolts 87b (shown only on the exhaust valve 73 side in FIG. 8) are screwed to the other end portions of the rocker arms 86 and 87, and are fixed integrally with a lock nut.

  Each rocker arm 86, 87 abuts on the tip end of the stem 74, 75 of each valve 72, 73 via a tappet bolt 87b, and when the cam shaft 64 rotates, the outer peripheral pattern of each cam 64a, 64b It swings accordingly. As a result, the contact portions 74a and 75a of the rocker arms 86 and 87 and the stems 74 and 75 of the valves 72 and 73 are swung, and the corresponding valves 72 and 73 reciprocate according to the stems 74 and 75. It moves to open and close the combustion chamber side opening of each port 70,71. The stems 74 and 75 of the valves 72 and 73, the rocker arms 86 and 87, the camshaft 64, and the like are supported on the inside of the front part of the cylinder head 22, and these are the front part of the cylinder head 22 and a cup for closing it. Is accommodated in a valve operating chamber 88 formed by a cylindrical cylinder head cover 23.

  The left and right pair of left and right camshaft holder portions 80L and 80R are formed integrally with the cylinder head 22b. However, in order to resist the load and the bending that are received from the camshaft 64 and the rocker shafts 84 and 85. 4, 6, and 7, a reinforcing member 89 that connects the front end surfaces (top surfaces) of the camshaft holder portions 80 </ b> L and 80 </ b> R is attached.

The reinforcing member 89 is an annular plate member fixed to both the camshaft holder portions 80L and 80R of the cylinder head 22 by a fastening bolt 60 for fastening the cylinder head 22 and the cylinder block 21 to the power unit case 20. The fastening bolt 60 includes a plurality of bolts, and fastens the reinforcing member 89, the cylinder head 2, and the cylinder block 21 together.
Therefore, the annular and integral reinforcing member 89 also functions as a washer for the fastening bolt 60, the number of parts of the washer for the plurality of fastening bolts 60 is reduced, and the assembling property of the fastening bolt 60 is improved. .

  Further, as described with reference to FIG. 2, the cylinder portion 210 of the present embodiment projects forward (vehicle traveling direction) from the front end portion of the power unit case 20 with its axis X substantially horizontal to the ground. The head 22, the cylinder block 21, and the reinforcing member 89 are fastened together by a plurality of fastening bolts 60 penetrating them from the front of the vehicle, and are integrally coupled to the power unit case 20. Therefore, the reinforcing member 89 is attached so as to be oriented substantially in the vertical direction of the cylinder. The camshaft 64 is parallel to the crankshaft 35 and is horizontally oriented in the vehicle body width direction, and a contact portion 74a between the stem 74 of the intake valve 72 and the intake-side rocker arm 86 in the upper direction of the cylinder, A contact portion 75a between the stem 75 of the exhaust valve 73 and the exhaust-side rocker arm 87 is positioned in the direction.

  In such a cylinder head structure, as shown in FIG. 2, the cylinder head cover 23 communicates with a lubricating oil supply mechanism (not shown) in the cylinder upward direction of the contact portion 74a between the intake valve 72 and the intake side rocker arm 86. A lubricating oil supply hole 78 for supplying the lubricating oil a to the valve operating chamber 88 is provided. The lubricating oil a supplied from the lubricating oil supply hole 78 is dropped on the contact portion 74a between the intake valve 72 and the intake side rocker arm 86 in the cylinder downward direction, and lubricates the contact portion 74a. Along with the movement of the abutting portion 74a, a part thereof is dropped and supplied to the cam shaft 64 in the cylinder downward direction, and the cam shaft 64, the intake cam 64a, and the exhaust cam 64b are lubricated. Further, a part of the gas flows down the cylinder through the reinforcing member 89 and is supplied dropwise to a contact portion 75a between the exhaust valve 73 and the exhaust-side rocker arm 87 in the cylinder downward direction, thereby lubricating the contact portion 75a. To do.

For this purpose, as shown in FIG. 6, the annular reinforcing member 89 has a lower side 89a on the abutting portion 75a side between the exhaust valve 73 and the exhaust side rocker arm 87 in the cylinder downward direction. Direction). Since the lubricating oil a is accurately dropped according to the curved portion, the contact portion 75a between the exhaust valve 73 and the exhaust-side rocker arm 87 can be lubricated satisfactorily with a simple structure.
In the case where the arrangement of the intake side and the exhaust side in the present embodiment is reversed in the cylinder vertical direction, the contact portion 74a between the intake valve 72 and the intake side rocker arm 86 can be lubricated similarly.

  As shown in FIG. 5, a decompression cam 91 having a one-way clutch (one-way clutch) 90 is supported at the right end of the cam shaft 64 so as to be relatively rotatable. In FIG. 5 (b), which shows a front view of the decompression cam 91 as viewed in the direction of arrows V-V in FIG. 5 (a), the cam shaft 64 rotates clockwise (forward rotation, rotation in the direction of arrow N. The N direction indicates the internal combustion engine. 18 (the rotational direction of the cam shaft 64 in the normal operation state), the forward rotation torque of the cam shaft 64 is hardly transmitted to the decompression cam 91 by the action of the one-way clutch 90, and the cam shaft 64 is shown in FIG. When rotating counterclockwise (reverse rotation, rotation in the direction of arrow R), the reverse rotation torque of the camshaft 64 is transmitted. As shown in FIG. 4, the decompression cam 91 is disposed adjacent to the outside (right side) of the cam roller 87 a support portion of the exhaust side rocker arm 87. A cam abutting portion 87 c that can abut on the outer peripheral surface of the decompression cam 91 is formed outside the cam roller 87 a support portion of the exhaust side rocker arm 87.

  The outer peripheral portion 91a having a substantially circular shape when viewed from the front (FIG. 5B) in the decompression cam 91 is formed with a cutout portion 92 formed by cutting out a portion of the outer peripheral portion 91a in a flat shape. A cam crest 93 is formed adjacent to the forward direction leading side, and a locking projection 94 is formed adjacent to the approximate center of the notch 92 on the trailing direction trailing side. The cam crest 93 is formed on the outer peripheral portion of the decompression cam 91 at a substantially constant height over a predetermined range, and the exhaust side rocker arm 87 is in contact with the cam contact portion 87c of the exhaust side rocker arm 87. Swing a predetermined amount (see FIG. 9). Further, the locking protrusion 94 can be engaged with a locking member 100 described later in a state where the notch 92 is in contact with the cam contact portion 87c of the exhaust side rocker arm 87 (see FIG. 8). A second notch portion 95 may be provided in order to reduce the weight of the member within a range where the notch portion 92 is spaced away from the trailing direction trailing side of the notch portion 92 and does not reach the cam peak portion 93.

Further, as shown in FIG. 5, a decompression cam 91 is disposed adjacent to the exhaust cam 87, but the outer diameter of the exhaust cam 64b and the decompression cam 91 are connected to the cam shaft 64 between the exhaust cam 64b and the decompression cam 91. A small diameter portion 64c smaller than the outer diameter is formed. Therefore, as described above with reference to FIG. 2, the lubricating oil a supplied to the valve operating chamber 88 and adhering to the camshaft 64 stays in the small diameter portion 64c sandwiched between the exhaust cam 64b and the decompression cam 91, and becomes a small diameter portion. 64c forms an oil reservoir 79.
Therefore, since the oil reservoir 79 is formed between the exhaust cam 64b and the decompression cam 91, the decompression cam 91 can be lubricated well, and the oil reservoir 79 is formed by forming the small diameter portion 64c. While reducing the weight of 64, the oil reservoir 79 can be formed with a simple structure.

  As shown in FIGS. 4 and 7, the right camshaft holder portion 80R extends in the camshaft direction Z on the outer periphery of the camshaft 64, and is positioned in front of the decompression cam 91 (shown above), the decompression cam 91 and its radius. An overhanging portion (an “extending portion” in the present invention) 101 (FIG. 4) facing each other in the direction is provided. The overhang portion 101 is formed with a through hole 102 that passes through the cylinder axis X direction and intersects the cam axis direction Z perpendicularly. In the through hole 102, a locking member 100 protruding downward from the one end (rear end, lower end in the figure) toward the decompression cam 91 is inserted and accommodated so as to be able to reciprocate. Note that the locking member 100 is restricted by the stepped portion 102a in the through hole 102 so that the protruding range does not contact the decompression cam 91 except for the locking protrusion 94 and the inclined surface 94a.

  As shown in FIG. 7, a coil spring 103 is loosely fitted in the through hole 102 so as to contact the front side (the upper side in the figure) of the locking member, and the other end (front end, The upper end in the figure is closed by a reinforcing member 89 screwed to the front end face (top face; upper end face in the figure) of the right camshaft holder portion 80R. Therefore, the coil spring 103 is held in the through-hole 102 to generate a spring force, and the latch member 100 is urged toward the decompression cam 91 by the spring force so as to be engaged with the locking protrusion 94. It protrudes downward in the figure. That is, the through hole 102 constitutes a locking member attaching portion together with the coil spring 103 and the reinforcing member 89.

  When the decompression cam 91 rotates N with the locking member 100 protruding (clockwise in FIG. 8), the locking projection 94 engages with the locking member 100 and stops the forward rotation N of the decompression cam 91. Let In addition, an inclined surface 94a is formed on the forward rotation N direction trailing side of the locking projection 94, and when the decompression cam 91 rotates in the reverse direction R (counterclockwise in FIG. 8), the locking projection 94 The locking member 100 rides on the inclined surface 94a and is pushed into the through hole 102 against the spring force of the coil spring 103, so that the locking projection 94 gets over the locking member 100 and allows the decompression cam 91 to be reversed. .

Next, the operation of the decompression device in the internal combustion engine 18 of the power unit 17 described above will be described.
First, when the operation of the internal combustion engine 18 is stopped from the normal operation state, the rotation of the crankshaft 35 stops before the top dead center of the compression stroke due to the pressure increase in the combustion chamber 66. The positions of the intake cam 64a, the exhaust cam 64b, and the decompression cam 91 of the cam shaft 64 at this time are shown in FIG.

  As shown in FIG. 8, after the crankshaft 35 (FIGS. 2 and 3) is stopped, the piston 56 (FIGS. 2 to 4) is pushed down by the pressure in the combustion chamber 66, and the crankshaft 35 is slightly moved accordingly. Reverse. At this time, as shown in FIG. 9, the camshaft 64 also reverses R in the same direction, and the decompression cam 91 also reverses R due to the action of the one-way clutch 90, both of which are half the rotation angle of the crankshaft 35. Reverse R by the angle. As a result, the cam contact portion 87c of the exhaust side rocker arm 87 rides on the cam crest portion 93 of the decompression cam 91, the exhaust side rocker arm 87 swings to operate the exhaust valve 73, and the exhaust port is in the compression stroke. The combustion chamber 66 side opening of 71 opens. For this reason, the pressure in the combustion chamber 66 decreases, and the camshaft 64 stops the reverse rotation R together with the crankshaft 35 and enters the operation stop state.

  When the camshaft 64 is rotated forward N in conjunction with the crankshaft 35 rotated by the motor start mechanism 47 or the kick start mechanism 51 from the operation stop state shown in FIG. 9, the exhaust cam 64b is moved as shown in FIG. While approaching the cam roller 87a of the exhaust side rocker arm 87, the cam contact portion 87c of the exhaust side rocker arm 87 abuts against the cam crest portion 93 of the decompression cam 91, so that the decompression cam 91 has a force to stop its rotation. Therefore, the decompression cam 91 remains stationary regardless of the forward rotation N of the cam shaft 64.

  When the cam shaft 64 further rotates forward from the state shown in FIG. 10 and the cam roller 87a of the exhaust side rocker arm 87 rides on the exhaust cam 64b as shown in FIG. 11, the cam contact portion 87c separates from the cam peak portion 93. The decompression cam 91 is completely unrestrained, and is rotated along with the cam shaft 64 in the forward rotation N direction by a slight forward rotation torque of the one-way clutch 90, but the engagement protrusion 94 is engaged with the engagement member 100. The rotation of the decompression cam 91 stops at that position.

  The cam shaft 64 further rotates forward from the state shown in FIG. 11, and after the exhaust cam 64b passes through the cam roller 87a of the exhaust side rocker arm 87 as shown in FIG. 12, the cam contact portion 97c is notched in the decompression cam 91. The state in contact with 92, that is, the same state as that in FIG. 8, the decompression function by the decompression cam 91 is automatically released, and the internal combustion engine 18 smoothly shifts to the normal operating state.

As described above, the crankshaft 35 rotates twice while the camshaft 64 rotates once, and the piston 56 reciprocates twice within the cylinder bore 55 to perform four strokes. At this time, the combustion chamber 66 communicates with the atmosphere in the combustion chamber 66 from the state near the top dead center of the compression stroke shown in FIG. 8 to the end of the intake stroke via the expansion stroke and the exhaust stroke. Therefore, the forward rotation suppression force of the internal combustion engine 18 due to the pressure increase is eliminated, so that the forward rotation of the crankshaft 35 is smoothly and sufficiently accelerated, and the internal combustion engine 18 can be started reliably.

  As described above, the cylinder head structure of the internal combustion engine 18 of the above embodiment has the cylinder head 210 having the cylinder portion 210 arranged with the axis X substantially horizontal and having the intake port 70 and the exhaust port 71 in the cylinder portion 210. Further, the decompression cam 91 is applied to the internal combustion engine 18 that supports the camshaft 64 that opens and closes the intake and exhaust valves 72 and 73, and includes a one-way clutch 90 that can transmit torque only when the camshaft 64 is reversely rotated. The cylinder head 22 is provided with a locking member 100 that is attached to one side of the camshaft 64 and that engages with the decompression cam 61 when the camshaft 64 is rotated forward N to restrict and stop the operation of the decompression cam 91. It is attached to the through hole 102 of the camshaft holder portion 80R.

The cylinder head 22 and the cylinder block 21 are fastened to the cylinder head 22 by fastening bolts 60, and a reinforcing member 89 for connecting the pair of camshaft holder portions 80L and 80R is provided. The locking member 100 is held in the through hole 102 by the reinforcing member 89 closing the other end of the through hole 102 and is accommodated in the cylinder head 22. When the internal combustion engine 18 is mounted on the motorcycle 1, the cylinder axis X is substantially horizontal, the cam shaft 64 is oriented in the vehicle width direction, and the exhaust valve 73 and the exhaust rocker arm 87 are disposed below the cam shaft 64. The reinforcing member 89 is disposed so that the contact portion 75a is positioned, and the lower side 89a of the reinforcing member 89 is curved so that the adhered lubricating oil a is supplied to the contact portion 75a .
The right camshaft holder portion 80R includes an overhang portion 101 extending in the camshaft direction Z on the outer periphery of the camshaft 64, and the through hole 102 is formed in the overhang portion 101 perpendicular to the camshaft direction Z. ing.

According to the cylinder head structure of the internal combustion engine 18 of the present embodiment, the reinforcing member 89 also serves as a retaining member for the retaining member 100, so that a retaining bolt and a female thread for screwing are not required, and the number of parts and processing are reduced. The man-hour is reduced , and the reinforcing member 89 is simple because the lower side 89a is curved so that the adhered lubricating oil a is supplied dropwise to the contact portion 75a between the exhaust valve 73 and the exhaust rocker arm 87. With the structure, the contact portion 75a between the exhaust valve 73 and the exhaust rocker arm 87 can be well lubricated .
Further, since the through hole 102 serving as the locking member 100 accommodating portion is provided integrally with the right camshaft holder portion 80R with the overhang portion 101 extending in the cam shaft direction Z, the right camshaft holder portion 80R Strength can be increased.

The present invention is not limited to the configuration of the above-described embodiment. For example, the above-described embodiment describes the case of the decompression cam 91 provided on the cam shaft 64, but the decompression cam limits the forward rotation and the reverse rotation. However, the present invention is not limited to the decompression cam, and the cylinder head structure of the internal combustion engine for a vehicle of the present invention can be effectively employed and implemented even in the case of various variable cams as a variable cam. In the embodiment, the camshaft holder portions 80L and 80R are formed integrally with the cylinder head 22. However, the camshaft holder portions 80L and 80R are partially formed separately from the cylinder head 22 and are integrally formed. It can also be applied to what is assembled. Further, the present invention may be applied to an engine having a plurality of intake / exhaust valves, a multi-cylinder engine, or a water-cooled engine.
The above embodiment is an example of the present invention, and is not limited to a motorcycle, and is applied as a cylinder head structure of a vehicle internal combustion engine for various vehicles such as a vehicle equipped with a similar power unit, for example, a three-wheel or a four-wheel buggy. It goes without saying that it is possible.

DESCRIPTION OF SYMBOLS 1 ... Motorcycle, 2 ... Body frame, 11 ... Front wheel, 15 ... Rear wheel, 17 ... Power unit, 18 ... Internal combustion engine, 19 ... Power transmission device, 20 ... Power unit case, 20L ... Left power unit case, 20R ... Right power unit case , 21 ... Cylinder block, 22 ... Cylinder head, 35 ... Crankshaft, 44 ... Rear wheel drive sprocket, 47 ... Motor start mechanism, 51 ... Kick start mechanism, 56 ... Piston, 60 ... Fastening bolt, 64 ... Camshaft, 64a ... intake cam, 64b ... exhaust cam, 64c ... small diameter part, 66 ... combustion chamber, 72 ... intake valve, 73 ... exhaust valve, 74a ... contact part, 75a ... contact part, 78 ... lubricating oil supply hole, 79 ... Oil reservoir, 80L ... Left camshaft holder, 80R ... Right camshaft holder, 86 ... Intake side rocker arm, 87 ... Exhaust side rocker arm, 87a ... Cam roller, 87c ... Cam contact part, 89 ... Reinforcing member, 89a ... bottom, 90: One-way clutch, 91: Decompression cam, 92 ... Notch, 93 ... Cam crest, 94 ... Locking protrusion, 100 ... Locking member, 101 ... Overhang (extension), 102 ... Through hole, 103 ... Coil spring, 210 ... Cylinder part

Claims (5)

A pair of camshaft holders (80L, 80R) that support the camshaft (64), a variable cam (91) that is rotatably supported by the camshaft (64), and the variable cam (91) are engaged. In the cylinder head structure of the vehicle internal combustion engine (18) provided with the locking member (100) for restricting the rotation of the variable cam (91),
A reinforcing member (89) fixed to the cylinder head (22) and connecting the camshaft holder portions (80L, 80R);
The camshaft holder (80R) includes a through hole (102), is received in the through hole (102), protrudes from one end thereof, and is urged to engage with the variable cam (91). member (100) is, the through hole is held the other end of (102) to said reinforcing member (89) same through hole by the closing (102) the Rutotomoni,
When the vehicle internal combustion engine (18) is mounted on the vehicle (1), the cylinder head (22) has a cylinder axis (X) oriented substantially horizontally and the cam shaft (64) oriented in the vehicle width direction. The abutting portion (74a, 75a) between the intake valve (72) or the exhaust valve (73) and the rocker arm (86, 87) is positioned below the camshaft (64),
The cylinder head of the internal combustion engine for a vehicle, wherein the reinforcing member (89) has a lower side (89a) curved so that the adhering lubricating oil is supplied dropwise to the contact portions (74a, 75a). Construction. The camshaft holder portion (80R) includes an extending portion (101) extending in the camshaft direction on the outer periphery of the camshaft (64) and facing the variable cam (91) in the radial direction thereof,
The cylinder head structure for an internal combustion engine for a vehicle according to claim 1, wherein the through hole (102) is formed in the extending portion (101) perpendicular to the cam shaft direction . The variable cam (91) is a decompression cam disposed adjacent to the exhaust cam (64b), and an oil reservoir (79) is formed between the exhaust cam (64b) and the decompression cam (91). A cylinder head structure for an internal combustion engine for a vehicle according to claim 1 or 2 . The oil reservoir (79) is a portion formed on the cam shaft (64) and having a smaller diameter than the outer diameter of the exhaust cam (64b) and the outer diameter of the decompression cam (91). Item 4. A cylinder head structure for an internal combustion engine for a vehicle according to Item 3 . The reinforcing member (89) is an annular plate member,
A plurality of fastening bolts (60) for fastening the cylinder head (22) and the cylinder block (21) and fixing the reinforcing member (89) to the cylinder head (22) include the reinforcing member (89). The cylinder head structure for an internal combustion engine for a vehicle according to any one of claims 1 to 4, wherein the cylinder head (22) and the cylinder block (21) are fastened together.

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