JP4933463B2 - Single cylinder 4-stroke internal combustion engine - Google Patents

Abstract

The invention claims a valve structure of an internal combustion engine which can compactly arrange a water pump in a camshaft having a decompressing device in order to realize the miniaturization of cylinder cover. The valve structure includes a camshaft (53), an engine valve (56e) that opens or closes by a valve cam arranged in the camshaft, and a decompressing device (100), a decompressing counterweight (101) of the decompressing cam (105) coming in and going out a cam surface of the valve cam (53e) can be shaft-supported in an end portion or in the vicinity of an end portion of the camshaft (53) in an oscillating way; a water pump (120) is arranged in an end portion of the camshaft (53) in the opposite side of the decompressing counterweight (101) in the axial direction.

Description

  The present invention relates to a valve operating structure including a decompression device for an internal combustion engine.

  A decompression device is attached to the camshaft that opens and closes the intake and exhaust valves, and the water pump that circulates cooling water to the required part of the internal combustion engine rotates with its pump drive shaft coaxial with the camshaft. There exists an example arrange | positioned (for example, refer patent document 1).

JP 2005-307840 A

In the valve operating structure disclosed in Patent Document 1, a cam chain sprocket is fixed to an end portion of a cam shaft, and the rotation of the crankshaft is transmitted to the cam chain sprocket via the cam chain to rotate the cam shaft. .
The decompression weight of the decompression device and the water pump are sequentially arranged at a position where the camshaft is extended to the axial cam chain sprocket side.

  In this way, since the decompression weight and the water pump are arranged in order on the same side with respect to the cam chain sprocket in the axial direction of the camshaft, the swinging decompression weight and the water pump are adjacent to each other, so that mutual interference is avoided. Therefore, it is necessary to make a space between each other in the axial direction as much as possible. Therefore, the width in the axial direction of the cylinder head accommodating the camshaft is widened, and the cylinder head is enlarged.

  The present invention has been made in view of the above points, and an object of the present invention is an internal combustion engine in which a water pump can be compactly arranged on a camshaft equipped with a decompression device to reduce the size of a cylinder head. The point is to provide a valve operating structure.

In order to achieve the above object, according to the first aspect of the present invention, there is provided a camshaft (53) in which the rotation of the crankshaft (40) is transmitted through a cam chain (51) and driven to rotate, and the camshaft ( An engine valve (56i, 56e) that is opened and closed by a valve cam (53i, 53e) provided in 53), and a decompression device (100) that opens the engine valve (56e) during the compression stroke at the time of start-up A valve case for an internal combustion engine comprising a crankcase (31) for accommodating a crankshaft (40), a cylinder block (32), a cylinder head (33), and a cylinder head cover (34) connected in order , A decompression weight (101) that operates a decompression cam (105) that can freely move in and out of the cam surface of the valve cam (53e) is a shaft that can be swung by centrifugal force at one end portion or near one end portion of the camshaft (53). It is supported on the end portion of the cam shaft of said decompression weight (101) axially opposite side (53) Otaponpu shaft (121) coupled coaxially integrally the water pump (120) is arranged, said cam shaft (53) and the rocker shaft (57, 59) is, in the said cylinder head cover (34), wherein The camshaft holder (53hl) on the decompression weight (101) side in the axial direction of the camshaft (53) is supported by a pair of camshaft holders (53hl, 53hr) provided on the cylinder head (33). A single cylinder 4 provided with a holder recess recessed in the axial direction around the camshaft (53), wherein the decompression weight (101) is disposed in the holder recess and directly below the camshaft holder (53hl). Stroke internal combustion engine .

According to a fifth aspect of the present invention, in the single-cylinder four-stroke internal combustion engine according to any one of the first to fourth aspects, the decompression weight (101) includes the valve cam (53i, 53e). The washer is supported by a cantilever shaft (102) so as to be swingable along the side surface of the exhaust cam (53e), and the decompression weight (101) contacts the support bearing (53b) of the camshaft (53). (108) and the exhaust cam (53e).

A sixth aspect of the present invention is the single-cylinder four-stroke internal combustion engine according to any one of the first to fifth aspects, wherein the decompression weight (101) is in the axial direction of the camshaft (53). It is characterized by being disposed within the width of the cylinder bore.

Invention of claim 7, in single-cylinder 4 engine strokes according to any one of claims 1 to 5, wherein the decompression weight (101), the cam chain across the cylinder axis line (Lc) The camshaft (53) is disposed on the opposite side of the sprocket (54) and at the tip in the insertion direction of the camshaft (53).

  According to the valve operating structure of the internal combustion engine according to claim 1, since the water pump is disposed at the end of the camshaft opposite to the decompression weight in the axial direction, the swinging decompression weight and the water pump are axially mutually connected. It is not necessary to provide an interval in consideration of mutual interference by being positioned on the opposite side, so that the water pump can be arranged compactly on the camshaft, and the cylinder head can be downsized.

In the single-cylinder four-stroke internal combustion engine according to claim 5 , the decompression weight is cantilevered by the support shaft so as to be swingable along the side surface of the exhaust cam. No shaft support member is required, the axial width can be reduced, and the decompression weight is sandwiched between the exhaust cam and the washer that contacts the support bearing of the camshaft. The play of the decompression device can be maintained satisfactorily by preventing rattling.

According to the single-cylinder four-stroke internal combustion engine of the sixth aspect , since the decompression weight is disposed within the width of the cylinder bore in the axial direction of the camshaft, the size of the cylinder head can be reduced.

According to the single-cylinder four-stroke internal combustion engine according to claim 7 , since the decompression weight is disposed on the opposite side of the cam chain sprocket across the cylinder axis and at the tip in the insertion direction of the cam shaft, Assembling property can be improved.

Hereinafter, an embodiment according to the present invention will be described with reference to FIGS.
FIG. 1 is a side view of a scooter type motorcycle 1 according to an embodiment to which the present invention is applied.

The vehicle body front portion 1f and the vehicle body rear portion 1r are connected via a low floor portion 1c, and the vehicle body frame forming the skeleton of the vehicle body is generally composed of the down tube 3 and the main pipe 4.
That is, the down tube 3 extends downward from the head pipe 2 at the front part 1f of the vehicle body, the down tube 3 is bent horizontally at the lower end and extends rearward under the floor 1c, and a pair of left and right main pipes 4 at the rear end. The main pipe 4 rises obliquely rearward from the connecting portion, bends horizontally at a predetermined height, and extends rearward.

A fuel tank 5 and the like are supported by the main pipe 4, and a seat 6 is disposed above the fuel tank 5 and the like.
On the other hand, at the vehicle body front portion 1f, a handle 11 is provided above and supported by the head pipe 2, a front fork 12 extends downward, and a front wheel 13 is supported at the lower end thereof.

A bracket 15 projects from the center of the inclined portion of the main pipe 4, and the power unit 20 is swingably connected to the bracket 15 via a link member 16.
The power unit 20 is a single-cylinder four-stroke water-cooled internal combustion engine 30 at the front, and the cylinder block 32 is in a position that is largely inclined forward to a substantially horizontal state, and forward from the upper end of the crankcase 31. The protruding end portion of the hanger bracket 18 is connected to the link member 16 via a pivot shaft 19.

The power unit 20 includes a belt-type continuously variable transmission 46 extending rearward from the internal combustion engine 30, and a rear wheel 21 is provided on a rear axle 21a that is an output shaft of a speed reduction mechanism 38 provided at a rear portion thereof.
A rear cushion 22 is interposed between a bracket 39 erected at the rear portion of the power unit 20 having the speed reduction mechanism 38 and the rear portion of the main pipe 4.

  Referring to FIG. 2 which is a side view of the power unit 20 and FIG. 3 which is a top view of the power unit 20, an intake pipe 23 extends from the upper part of the cylinder head 33 which is largely inclined forward of the internal combustion engine 30 in the upper part of the power unit 20. The air cleaner 26 connected to the throttle body 25 via the connecting pipe 23c is connected to the throttle body 25 via the connecting pipe 23c. Arranged above.

The intake pipe 23 is provided with an injector 24 that injects fuel toward the intake port.
On the other hand, the exhaust pipe 27 extending downward from the lower portion of the cylinder head 33 is bent rearward, is biased to the right and extends rearward, and is connected to a muffler (not shown) on the right side of the rear wheel 21.

The front part 1f of the vehicle body is covered from the front and the back by the front cover 9a and the leg shield 9b, and the lower part is covered from the front to the left and right by the front lower cover 9c, and the center part of the handle 11 is covered by the handle cover 9d.
The floor portion 1c is covered with a side cover 9e, and the vehicle body rear portion 1r is covered with a body cover 10 from the left and right sides.

4 is a sectional view of the internal combustion engine 30 (a sectional view taken along the line IV-IV in FIG. 3), and FIG. 5 is a sectional view of the power unit 20 (a sectional view taken along the line VV in FIG. 2).
In the internal combustion engine 30, a connecting rod 43 connects a piston 42 that reciprocates in a cylinder liner 44 of a cylinder block 32 and a crank pin 40 a of a crankshaft 40.
The crankcase 31 is configured by combining a left crankcase 31L and a right crankcase 31R which are divided into left and right parts. The right crankcase 31R forms a half of a crankcase portion, and the left crankcase 31L is a front crankcase 31L. The portion forms a half of the crankcase portion, and also serves as a transmission case that swells rearward and accommodates a long belt-type continuously variable transmission 46 in the front and rear.

  The left and right open front surfaces of the left crankcase (transmission case) 31L are covered with a transmission case cover 36 to form a transmission chamber 46C in which a belt-type continuously variable transmission 46 is housed. The open surface is covered with a speed reducer case 37, and a speed reduction mechanism 38 is accommodated therein.

  5 and 6, a crankshaft 40 is rotatably supported by the left and right main bearings 41 and 41 in a so-called crankcase formed by combining the front portion of the left crankcase 31L and the right crankcase 31R. Of the extending portions extending in the horizontal direction, the right extending portion is provided with a cam chain driving sprocket 55a, an oil pump driving gear 55b, and an AC generator 72, and the left extending portion is provided with a belt type continuously variable transmission. 46 centrifugal weights 47 and drive pulleys 48a are provided.

  The belt-type continuously variable transmission 46 is configured such that a V-belt 49 is stretched between a driving pulley 48a and a driven pulley 48b provided on an input shaft 38a of the speed reduction mechanism 38, and power is transmitted. The winding weight of the V belt 49 in the driving pulley 48a is changed by the centrifugal weight 47 that moves in response to the change, and at the same time, the winding diameter in the driven pulley 48b is automatically changed to change continuously.

The rotation of the driven pulley 48b is transmitted to the input shaft 38a of the speed reduction mechanism 38 via the centrifugal clutch 35.
The speed reduction mechanism 38 is a gear mechanism, and a gear mesh is formed between the input shaft 38a and the intermediate shaft 38b and between the intermediate shaft 38b and the rear axle 21a, and the rotation of the input shaft 38a is reduced to reduce the rear axle 21a. The rear wheel 21 is driven to rotate.

  Referring to FIGS. 5 and 6, the front portion of transmission case cover 36 forms a front flat portion 36af that is recessed inward, and the portion of front flat portion 36af that faces drive pulley 48a introduces cooling air. An opening 36i is formed, and air can be introduced into the transmission chamber 46C from the cooling air introduction port 36i by the rotation of the cooling fan 48F provided on the left side surface of the fixed pulley half on the left side of the drive pulley 48a.

A duct cover 91 is fitted into the recessed front flat portion 36af of the transmission case cover 36, and a side cover 92 is attached so as to cover the duct cover 91 from the outside.
The duct cover 91 is formed with a cooling air introduction port 91i connected to the cooling air introduction port 36i of the transmission case cover 36, and a louver 91L is formed at the upper part.

  A gap 96 is formed between the louver 91L on the upper rear side of the duct cover 91 and the front flat portion 36af of the transmission case cover 36 as shown in FIG. 6, and the upper side of the gap 96 is a top view of FIG. As shown in FIG. 2, the end surface of the peripheral wall 92b of the side cover 92 is communicated with the outside as an outside air introduction port 95 formed so as to be cut into a long rectangle.

  When the internal combustion engine 30 is operated and the cooling fan 48F provided on the drive pulley 48a rotates together with the crankshaft 40, first, the cooling air flows into the gap from the outside air inlet 95 as shown by the broken line arrows in FIG. 96, is passed through the louver 91L of the duct cover 91 from the air gap 96, flows into the outside air introduction space 97 between the duct cover 91 and the side cover 92, and is led to the air guide wall 91d to be supplied with the cooling air inlet 36i, The belt type continuously variable transmission 46 is cooled by being smoothly introduced into the transmission chamber 46C from 91i.

  Referring to FIGS. 5 and 6, the side wall constituting the cam chain chamber 52 of the right crankcase 31R has a large opening, and the opening is closed by a partition wall 70 attached from the right side by a bolt 71. The crankshaft 40 passes through the cylindrical portion 70a.

  In the AC generator 72, a bowl-shaped outer rotor 74 is fixed to the right end portion of the crankshaft 40 passing through the cylindrical portion 70a of the partition wall 70 via an ACG boss 73, and is disposed on the inner peripheral surface thereof in the circumferential direction. An inner stator 76 around which a stator coil 77 is wound is fixed to the cylindrical portion 70 a of the partition wall 70 inside the magnet 75.

  A fan substrate 78a having a disk shape with a center bulging is attached to the right side surface of the outer rotor 74, and a plurality of radiator fans 78 are formed on the fan substrate 78a so as to protrude rightward.

  The outer periphery of the outer rotor 74 of the AC generator 72 is generally surrounded by a peripheral wall 31Rs extending rightward from the side wall of the right crankcase 31R. The outer periphery of the radiator fan 78 is surrounded by a shroud 90, and on the right side of the radiator fan 78 A radiator 80 is provided in the vicinity, and the radiator 80 is covered with a radiator cover 81 with a louver.

  Referring to FIG. 6, an oil pump 61 is provided by rotatably installing a pump drive shaft 62 between the right crankcase 31 </ b> R and the partition wall 70, and a driven gear 63 fitted to the pump drive shaft 62. Is meshed with an oil pump drive gear 55b formed integrally with the cam chain drive sprocket 55a.

An oil passage 64a extends downward from the oil pump 61 to the right crankcase 31R, and a horizontal oil passage 64b extends horizontally from the middle of the oil passage 64a to the left crankcase 31L so that an oil filter 65 is provided. The insertion hole 64c has an enlarged diameter to be inserted.
The oil filter 65 is a bottomed cylindrical mesh filter that is inserted into a fitting insertion hole 64c opened in the left outer surface of the left crankcase 31L, and covers the left end of the horizontal oil passage 64b oriented in the horizontal direction. Thus, the horizontal oil passage 64b is partitioned from the outside.

Below the horizontal oil passage 64b is an oil reservoir 64e, and a notch 64d communicating with the insertion hole 64c is formed in the ceiling wall of the oil reservoir 64e.
An oil supply cylinder 66 is provided at the opening of the insertion hole 64c by connecting its end openings.
The oil supply cylinder 66 includes a horizontal cylinder part 66a in which an oil supply passage 67 having an inner diameter smaller than the outer diameter of the bottomed cylindrical oil filter 65 is formed, and an inclined cylinder part 66b that is bent from the horizontal cylinder part 66a and extends obliquely upward. Thus, the end portion is fitted into the fitting insertion hole 64c at the end portion of the oil passage 64b with the horizontal cylinder portion 66a oriented in the left-right direction.

  When the horizontal cylinder portion 66a of the oil supply cylinder 66 is fitted into the opening of the fitting insertion hole 64c, one end of the coil spring 65s provided around the outer periphery of the oil filter 65 is regulated and the other end is the opening of the oil filter 65. The end flange is pressed against and fixed to the open end face of the horizontal oil passage 64b to prevent a gap from occurring.

An upper end opening 66c having a slightly larger diameter of the inclined cylinder portion 66b of the oil supply cylinder 66 serves as an oil supply port, and an oil filler cap 68 is screwed into the upper end opening 66c to make the oil supply passage 67 liquid-tight. Can be occluded.
The oil filler cap 68 is provided with a dipstick gauge 69 extending into the oil supply passage 67, and the gauge portion at the tip of the dipstick gauge 69 is submerged under the oil surface to mark the oil amount on the gauge portion. The

When the oil filler cap 68 is removed, the lubricating oil can be supplied into the crankcase 31 from the oil supply port of the oil supply cylinder 66.
When the oil pump 61 is driven by the rotation of the crankshaft 40 through the meshing of the drive gear 55b and the driven gear 63, the oil accumulated in the oil reservoir 65e is purified through the oil filter 65 and pumped up. Supplied from 61 to a required portion of the internal combustion engine 30.

  The four-cycle internal combustion engine 30 employs an SOHC type valve system. A valve mechanism 50 is provided in the cylinder head cover 34, and a cam chain 51 that transmits power to the valve mechanism 50 includes a camshaft 53. The cam chain chamber 52 is provided between the right crankcase 31R, the cylinder block 32, and the cylinder head 33 (see FIG. 5).

  That is, the cam chain 51 is connected to the cam chain chamber 52 between the driven cam chain sprocket 54 fitted to the right end of the cam shaft 53 oriented in the horizontal direction and the drive cam chain sprocket 55a fitted to the crankshaft 40. It is passed through the inside.

On the other hand, a spark plug 45 is inserted into the cylinder head 33 from the side opposite to the cam chain chamber 52 (left side) toward the combustion chamber 33a (see FIGS. 2 and 5).
An ignition coil 29 is attached to the same left side surface of the cylinder block 32 via a support bracket 28 (see FIGS. 2 and 3).

  Referring to FIG. 4, the intake port 33i extends upwardly from the combustion chamber 33a of the cylinder head 33 tilted greatly forward and is connected to the intake pipe 23, and the exhaust port 33e curves downward from the combustion chamber 33a. And is connected to the exhaust pipe 26.

  As shown in FIG. 4, the valve mechanism 50 in the cylinder head cover 34 is greatly inclined forward to a state in which the cylinder is almost horizontal, so that the intake valve 56i that opens and closes the opening of the intake port 33i to the combustion chamber 33a Is disposed above the camshaft 53, and an exhaust valve 56e for opening and closing the opening of the exhaust port 33e to the combustion chamber 33a is disposed below the camshaft 53.

  The camshaft 53 is rotatably supported by being sandwiched between camshaft holders 53hl and 53hr via bearings 53b and 53b on the left side wall of the cylinder head 33 and the inner side wall 33c constituting the cam chain chamber 52, and the right side bearing. A driven cam chain sprocket 54 is fitted to the right end protruding from 53b.

As shown in FIG. 4, the intake rocker shaft 57 and the exhaust rocker shaft 59, which are respectively arranged at obliquely upper and lower positions in front of the camshaft 53, have left and right camshaft holders 53hl, It is erected between 53hrs.
The camshaft holders 53hl and 53hr are fastened together with the cylinder head 33 and the cylinder block 32 to the crankcase 31 by screwing the nuts 111 to the four stud bolts 110 (see FIG. 7).

  The intake rocker shaft 57 and the exhaust rocker shaft 59 are in a vertical position with respect to each other, and a roller 58r pivotally supported on one end of an intake rocker arm 58 pivotally attached to the upper intake rocker shaft 57 is a camshaft. An adjustment screw 58s that contacts the intake cam 53i of 53 and is screwed to the other end contacts the end of the valve stem of the intake valve 56i (see FIG. 4).

Similarly, a roller 60r pivotally supported at one end of an exhaust rocker arm 60 pivotably attached to the lower exhaust rocker shaft 59 is in contact with the exhaust cam 53e of the camshaft 53 and screwed to the other end. The adjusting screw 60s contacts the end of the valve stem of the exhaust valve 56e (see FIG. 4).
Accordingly, the rotation of the camshaft 53 causes the intake cam 53i and the exhaust cam 53e to swing the intake rocker arm 58 and the exhaust rocker arm 60, respectively, so that the intake valve 56i and the exhaust valve 56e are opened and closed at a predetermined timing.

In such a valve operating mechanism 50, the decompression device 100 is provided on the camshaft 53.
Referring to FIG. 8, decompression device 100 abuts the side surface of exhaust cam 53e and left bearing 53b between left bearing 53b that supports the left end of cam shaft 53 and exhaust cam 53e of cam shaft 53. A decompression weight 101 positioned between the washer 108 and the washer 108 is cantilevered on a support shaft 102 projecting from the exhaust cam 53e so as to be swingable along the side surface of the exhaust cam 53e. The decompression cam 105 that pivots freely on the cam surface of the exhaust cam 53e is actuated by an actuation pin 104 that projects from the decompression weight 101.

FIG. 9 and FIG. 10 are left side views showing extracted main parts for explaining the operation of the decompression device 100, and FIG. 9 shows the camshaft 53 stopped or rotating at a low speed. FIG. 10 shows a state when the camshaft 53 exceeds a predetermined rotational speed.
The decompression weight 101 has a C shape and surrounds the camshaft 53. The base end of the decompression weight 101 is pivotally supported by a support shaft 102 protruding from the side surface of the exhaust cam 53e, and can swing along the side surface of the exhaust cam 53e. is there.

  The decompression weight 101 has an extending portion 101a that extends slightly to the opposite side of the tip from the support shaft 102, and biases a pressing member 107a that is detachably fitted to the camshaft 53 in a protruding direction by a spring 107s. The urging means 107 is provided, and the pressing member 107 a of the urging means 107 abuts against the extending portion 101 a of the decompression weight 101 and presses it to urge the decompression weight 101 in a direction to approach the camshaft 53.

An operating pin 104 protrudes toward the exhaust cam 53e at a predetermined position on the distal end side of the decompression weight 101.
Further, a circular hole is excavated at a predetermined position of the small cam portion on the side surface of the exhaust cam 53e, and a cylindrical decompression cam 105 is rotatably fitted, and a part of the decompression cam 105 is also part of the exhaust cam 53e. It is fitted so that it can protrude from the cam surface of the small-diameter portion of the cam.

  The decompression cam 105 has a long groove 105 formed in the radial direction on the left side surface on the decompression weight 101 side, and an operating pin 104 protruding from the decompression weight 101 is inserted into the long groove 105 and engaged therewith. Therefore, when the decompression weight 101 is swung, the operation pin 104 integral with the decompression weight 101 rotates the decompression cam 105 through the engagement with the long groove 105.

  Further, a notch 105b is formed on the right side surface of the decompression cam 105, and when the notch 105b does not face the cam surface due to the rotation of the decompression cam 105, the decompression cam 105 projects from the cam surface of the exhaust cam 53e. When the notch 105b faces the cam surface, the decompression cam 105 does not protrude from the cam surface due to the notch 105b (see FIG. 10).

  Now, when the engine speed at the start of the internal combustion engine 30 is low, the camshaft 53 also rotates at a low speed, and the oscillation of the decompression weight 101 due to the centrifugal force is small as shown in FIG. The biased decompression weight 101 is near the camshaft 53, and the operation pin 104 projecting from the decompression weight 101 has the decompression cam 105 cut out so that the notch 105b does not face the cam surface. The decompression cam 105 projecting from the cam surface of the exhaust cam 53e pushes up the roller 60r of the exhaust rocker arm 60 during the compression stroke (the state shown in FIG. 9), and opens the exhaust valve 56e to compress the compression pressure. This makes it possible to make the start easier.

  When the engine speed increases after the internal combustion engine 30 is started, the camshaft 53 also exceeds a predetermined rotational speed, and the swing of the decompression weight 101 due to the centrifugal force is large as shown in FIG. Then, the decompression weight 101 swings away from the camshaft 53, the operating pin 104 rotates the decompression cam 105 to a position where the notch 105b faces the cam surface, and the decompression cam 105 is moved to the exhaust cam 53e by the notch 105b. Thus, the exhaust valve 56e can be closed and the decompressed state is released without pushing up the roller 60r of the exhaust rocker arm 60 even during the compression stroke (the state shown in FIG. 10).

  In this decompression device, since the decompression weight 101 is cantilevered by the support shaft 102 so as to be swingable along the side surface of the exhaust cam 53e, there is no need for one shaft support member when pivotally supported by both ends. The axial width can be reduced, and the decompression weight 101 is positioned between the washer 108 that contacts the support bearing 53b of the camshaft 53 and the exhaust cam 53e. Thus, the operability of the decompression device 100 can be maintained satisfactorily.

Referring to FIG. 8, decompression weight 100 is disposed immediately below left camshaft holder 53hl, and is disposed within the left-right width of the cylinder bore in the left-right direction that is the axial direction of camshaft 53.
Therefore, the left and right width of the cylinder head 33 can be suppressed and the size can be reduced.

  While the decompression device 100 described above is provided near the left end of the camshaft 53, a driven cam chain sprocket 54 is fixed to the right end of the camshaft 53 by a bolt 109, and further to the right side of the camshaft 53. A water pump 120 is provided at the extension (see FIGS. 7 and 8).

Referring to FIG. 8, the camshaft 53 is inserted from the right side to the left side as indicated by an arrow, and the decompression weight 100, the exhaust cam 53e, and the intake cam 53i are inserted from the front end side in the camshaft insertion direction. , Driven cam chain sprockets 54 are arranged in this order.
Since the decompression weight 100 is disposed on the opposite side of the cam chain sprocket 54 across the cylinder axis Lc and at the front end in the insertion direction of the cam shaft 53, the assemblability of the cam shaft 53 can be improved.

  A circular opening is formed on the right side surface of the cylinder head 33, and an annular seal ring member 128 is fitted into the circular opening. A water pump body 121 having a cylindrical shape of the water pump 120 is attached to the seal ring member 128. It is watertightly inserted and supported.

  8, 11, and 12, the water pump body 121 of the water pump 120 has a long cylindrical portion 121 a that is long in the axial direction for rotatably supporting the pump drive shaft 123 via a bearing 125. And a short cylindrical portion 121b that extends in the radial direction and extends in the radial direction to partially accommodate the impeller 124 fitted to the water pump drive shaft 123 by extending one open end thereof in the radial direction. A cylindrical portion 121a is fitted and fixed to the right side wall of the cylinder head 33 via a seal ring member 128 so that the water pump drive shaft 123 is coaxial with the cam shaft 53, and the left end of the pump drive shaft 123 is fixed to the cam shaft 53. It is configured to be fitted directly into a fitting hole drilled in the right end surface and directly connected to rotate coaxially.

A water pump cover 122 that covers the right opening of the short cylindrical portion 121b of the water pump body 121 and accommodates the impeller 124 together with the short cylindrical portion 121b is superimposed on the opening end surface of the short cylindrical portion 121b.
Four bolt holes 121h are formed on the outer periphery of the short cylindrical portion 121b of the water pump body 121, and four bolt holes 122h are formed in the water pump cover 122 corresponding to the bolt holes 121h of the water pump body 121. Yes.

As shown in FIG. 8, the bolt hole 121h of the water pump body 121 located near the upper part of the cylinder head cover 34 is engraved with a female screw, and the bolt 129a penetrating the bolt hole 122h of the corresponding water pump cover 122 is a bolt. They are screwed into the holes 121h and fastened together.
As shown in FIG. 7, the other three bolt holes 121h and 122h are overlapped with mounting boss portions 33b formed corresponding to the cylinder head 33, and the bolt 129b penetrates the bolt holes 122h and 121h. Then, the water pump 120 is attached to the cylinder head 33 by screwing into the female screw hole of the mounting boss portion 33 b and fastening the water pump body 121 and the water pump cover 122 together to the cylinder head 33.

In the water pump cover 122, a water suction tube portion 122b extends from the suction port portion 122a bulging rightward of the water pump drive shaft 123 along the right side surface of the cylinder head 33 in the direction of the crankshaft 40. The discharge port portion 122c extends obliquely downward and downward in the tangential direction from the lower part of the outer periphery of the impeller 124. As shown in FIGS. 11 and 12, a discharge connection pipe 126 is further projected from the discharge port portion 122c. .
An air vent 122d is formed in the upper part of the outer periphery of the impeller 124, and an air vent connecting pipe 127 protrudes obliquely rearward and upward from the air vent 122d.

As described above, the decompression device 100 and the water pump 120 are provided in the cylinder head 33.
With respect to the cam chain sprocket 54 fixed to the camshaft 53, the pump shaft 123 is connected to the end of the camshaft 53 opposite to the decompression weight 101 in the axial direction, and the water pump 120 is disposed. The weight 101 and the water pump 120 are positioned opposite to each other in the axial direction with respect to the cam chain sprocket 54, so that it is not necessary to provide a space in consideration of mutual interference. Therefore, the water pump 120 is arranged on the camshaft 53 in a compact manner. The cylinder head 33 can be reduced in size.

  In the decompression device 100, the decompression weight 101 is cantilevered by a support shaft so as to be swingable along the side surface of the exhaust cam 53e. The axial width can be reduced, and the decompression weight 101 is positioned between the washer 108 that contacts the support bearing 53b of the camshaft 53 and the exhaust cam 53e. Thus, the operability of the decompression device 100 can be maintained satisfactorily.

  The water pump 120 can be miniaturized by making the pump body 121 into a cylindrical shape so that the pump drive shaft 123 is rotatably supported via a bearing 125, and the cylindrical pump body 121 can be downsized. Since the water pump 120 is supported by being inserted into the side wall of the cylinder head 33, the water pump 120 can be compactly attached to the cylinder head 33.

1 is an overall side view of a scooter type motorcycle according to an embodiment of the present invention. It is a whole side view of a power unit. It is a whole top view of the same power unit. It is sectional drawing (IV-IV sectional view taken on the line of FIG. 3) of an internal combustion engine. It is sectional drawing (VV sectional view taken on the line of FIG. 2) of a power unit. It is sectional drawing (VI-VI sectional view taken on the line of FIG. 2) of the power unit. It is a top view of the valve mechanism and water pump in a cylinder head. FIG. It is a side view of a decompression device. It is a left view of the decompression device in another state. It is a left view of a water pump. It is a right view of the water pump.

Explanation of symbols

20 ... Power unit, 30 ... Internal combustion engine, 31 ... Crank case, 32 ... Cylinder block, 33 ... Cylinder head, 34 ... Cylinder head cover, 40 ... Crankshaft,
50 ... Valve mechanism, 51 ... Cam chain, 52 ... Cam chain chamber, 53 ... Cam shaft, 54 ... Driven cam chain sprocket, 55a ... Cam chain drive sprocket, 56e ... Exhaust valve, 56i ... Intake valve, 58 ... Intake rocker arm , 58r ... roller, 60 ... exhaust rocker arm, 60r ... roller,
100 ... Decompression device, 101 ... Decompression weight, 102 ... Support shaft, 104 ... Actuation pin, 105 ... Decompression cam, 107 ... Biasing means, 108 ... Washer,
120 ... Water pump, 121 ... Water pump body, 121a ... Long cylindrical part, 121b ... Short cylindrical part, 122 ... Water pump cover, 123 ... Water pump drive shaft, 124 ... Impeller, 125 ... Bearing, 128 ... Seal ring member .

Claims (7)

Rotation of the crankshaft (40) is transmitted through the cam chain (51) and rotated and driven by a camshaft (53) and a valve operating cam (53i, 53e) provided on the camshaft (53) A crankcase (31) that includes an operated engine valve (56i, 56e) and a decompression device (100) that opens the engine valve (56e) during a compression stroke at the start, and houses a crankshaft (40) , A valve structure for an internal combustion engine in which a cylinder block (32), a cylinder head (33), and a cylinder head cover (34) are sequentially connected ,
A decompression weight (101) that operates a decompression cam (105) that can freely move in and out of the cam surface of the valve cam (53e) is a shaft that can be swung by centrifugal force at one end portion or near one end portion of the camshaft (53). Supported,
The water pump shaft (121) is coaxially connected integrally to the end of the camshaft (53) opposite to the decompression weight (101) in the axial direction , and a water pump (120) is disposed.
The camshaft (53) and the rocker shaft (57, 59) are in the cylinder head cover (34) and supported by a pair of camshaft holders (53hl, 53hr) provided in the cylinder head (33),
The camshaft holder (53hl) on the decompression weight (101) side in the axial direction of the camshaft (53) includes a holder recess recessed in the axial direction around the camshaft (53). The single-cylinder four-stroke internal combustion engine is characterized in that the decompression weight (101) is disposed directly under the camshaft holder (53hl) . A cam chain sprocket (54) is attached to the end of the camshaft (53) on the opposite side of the decompression weight (101) in the axial direction,
  A sprocket recess is formed in the center of the cam chain sprocket (54),
  A cylindrical pump body (121) that rotatably supports the water pump drive shaft (123) via a bearing (125) is supported on the side wall of the cylinder head (33),
  The single-cylinder four-stroke internal combustion engine according to claim 1, wherein an end of the pump body (121) on the cam chain sprocket (54) side faces the recessed portion of the sprocket. A cylindrical pump body (121) that rotatably supports the water pump drive shaft (123) via a bearing (125) includes an outer peripheral surface of the pump body (121) and the cylinder head (33). The single cylinder four-stroke according to claim 1, wherein the cylinder head (33) is supported via an annular seal ring member (128) between the inner peripheral surface of the opening formed on the side surface of the cylinder). Internal combustion engine. The decompression weight (101) is C-shaped to surround the camshaft (53), and one end side of the C-shape is pivotally supported on a support shaft (102) provided on a side surface of the valve cam (53e). And an operating pin (104) for operating the decompression cam (105) is provided on the other end side, and the support shaft (102) and the operating pin (104) are generally in relation to the axis of the camshaft (53). 2. The single-cylinder four-stroke internal combustion engine according to claim 1, wherein the single-cylinder four-stroke internal combustion engine is provided at positions opposite to each other. The decompression weight (101) is cantilevered by a support shaft (102) so as to be swingable along the side surface of the exhaust cam (53e) of the valve cams (53i, 53e),
Claims, characterized in that said decompression weight (101) is positioned pinched between said exhaust cam (53e) and the washer (108) abutting the supporting bearing (53b) of the camshaft (53) The valve operating structure for an internal combustion engine according to any one of claims 1 to 4 . The operation of the internal combustion engine according to any one of claims 1 to 5, wherein the decompression weight (101) is disposed within a width of a cylinder bore in an axial direction of the camshaft (53). Valve structure. The decompression weight is on the opposite side of the cam chain sprocket across the cylinder axis, and of any one Kouki mounting of an internal combustion engine of claims 1 disposed in the insertion direction of the distal end of the cam shaft to claim 6 Valve train structure.

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