JP4382621B2 - Cam mechanism with decompression device - Google Patents

Description

  The present invention relates to a cam mechanism with a decompression device that facilitates starting by reducing the compression pressure in a combustion chamber when starting a reciprocating internal combustion engine.

  In a reciprocating internal combustion engine (engine), an intake valve is opened, and a mixture of air and fuel introduced into the combustion chamber is compressed by a cylinder and burned, and the cylinder is reciprocated by the energy of this combustion. Although power is obtained, it may be difficult to start if the pressure of the air-fuel mixture in the combustion chamber is high when the engine is started. For this reason, apart from the cam that opens and closes the exhaust valve in normal operation, when the engine speed is slower than a predetermined speed, such as when the engine is started, a small amount of the air-fuel mixture is compressed by opening the exhaust valve slightly. A decompression device is used that lowers the pressure in the combustion chamber by exhausting the part. As such a decompression device, a centrifugal weight portion is provided outside the cam sprocket for rotating the cam, and a decompression cam mount for opening and closing the exhaust valve by swinging the centrifugal weight portion by the centrifugal force generated by the rotation of the cam sprocket. What is comprised so that it may make it protrude is known (for example, refer patent document 1).

JP 2003-254025 A

  However, the centrifugal weight portion becomes large because it requires a certain amount of weight, and in the case of the configuration as described above, the width of the cylinder head of the engine increases by the thickness of the centrifugal weight portion. Therefore, it is a problem to provide a decompression device in which the width of the cylinder head does not increase even when the centrifugal weight portion is disposed outside the cam sprocket.

  The present invention has been made in view of such problems, and a cam with a decompression device in which a part of a centrifugal weight portion is positioned in an opening formed in a cam sprocket so that the width of a cylinder head is not widened. The purpose is to provide a mechanism.

In order to solve the above-described problems, a cam mechanism with a decompression device according to the present invention includes a camshaft having at least one cam (for example, the exhaust cam 71 in the embodiment), and is coupled to the camshaft and interlocked with the crankshaft. A cam sprocket that is rotationally driven (for example, the cam driven sprocket 67 in the embodiment), a cylindrical shaft portion, a decompression cam crest formed on a circumferential surface side of one end side of the shaft portion, and a shaft portion A decompression cam having a centrifugal weight portion extending in a direction orthogonal to the axis of the shaft portion on the other end side, the centrifugal weight portion is close to the cam sprocket, the shaft portion extends in parallel to the camshaft, and the camshaft The centrifugal weight is swung outward by the centrifugal force by the rotation of the cam sprocket. Rotates the shaft portion by being, the decompression cam mountains is intended to enter projecting from the cam shaft, the space extending through the cam sprocket portion facing the centrifugal weight part of the decompression cam in the cam sprocket (e.g., weights in the embodiment configured to have an opening 169).

Then, the centrifugal weight part is inserted into the space from the surface opposite the cam of the cam sprocket, cam side end of the centrifugal weight part is the cam sprocket least a portion of the centrifugal weight part is positioned in the space portion It is comprised so that it may be located on the substantially same plane as this surface.

  Further, it is preferable that the center of gravity of the centrifugal weight portion is configured to be located outward from the center of the cam sprocket and half the radius of the cam sprocket.

Further, it is preferable that a stopper portion for restricting the swing of the centrifugal weight portion is provided at the opening end of the space portion in the cam sprocket.

  Further, the shaft portion of the decompression cam is composed of a first shaft portion that extends to the centrifugal weight portion side with the decompression cam mountain interposed therebetween and is supported by the camshaft, and a second shaft portion that extends to the cam side and is supported by the camshaft. It is preferable that a notch is formed on the circumferential surface in the direction in which the decompression cam crest of the second shaft portion is formed.

If the cam mechanism with a decompression device according to the present invention is configured as described above, the axial width of the camshaft can be reduced while securing the weight of the centrifugal weight necessary for the swinging of the decompression cam, so the cylinder head is compact. Can be. Moreover, since it is possible space is formed so as to penetrate the cam sprocket, which the thickness of the centrifugal weight part is positioned in the space in the thickness of the cam sprocket is substantially the same size, the centrifugal weight part It becomes easy to secure the weight of the. In addition, the centrifugal weight portion can function effectively by configuring the centrifugal weight portion so that the center of gravity of the centrifugal weight portion is located outside the half of the radius of the cam sprocket from the center of the cam sprocket. Further, by providing the stopper portion in the space portion, a dedicated stopper member becomes unnecessary, and the manufacturing cost of the cam mechanism with a decompression device according to the present invention can be reduced.

  Furthermore, the shaft portion of the decompression cam is composed of the first shaft portion and the second shaft portion, and the decompression cam is supported by the first shaft portion and the second shaft portion, thereby supporting both ends and suppressing the shake of the shaft portion. Can do. At the same time, by providing a notch in the second shaft portion, a space for tilting the shaft of the shaft portion is formed, so that the shaft portion and the portion that receives the shaft portion are twisted, and the decompression device is released. Unnecessary vibration of the centrifugal weight portion at the rotation speed or less can be suppressed.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. First, a scooter type vehicle 1 on which a secondary air supply device according to the present invention is mounted will be described with reference to FIG. The scooter-type vehicle 1 has a body frame 2, which is positioned at the front portion thereof, and has a head pipe 3 extending in the vertical direction, a down frame 4 extending downward from the head pipe 3, and a down frame. The frame 4 includes a pair of left and right side frames 5 extending downward and rearward and further rearward and obliquely upward from a substantially central portion of the frame 4, and an arcuate curved frame 7 attached to the side frames 5 via side plates 6. .

  A steering shaft (not shown) is rotatably attached to the head pipe 3, and a front fork 8 is attached to the lower end of the steering shaft. A front wheel 9 is supported at the lower end of the front fork 8. On the other hand, a handle post 10 is attached to the upper end of the steering shaft. Further, a handle 11 is attached to the upper end of the handle post 10, and the front wheel 9 can be steered by operating the handle 11. An upper stay 12 and a lower stay 13 are attached to extend forward from the head pipe 3, and a front car 14 is attached to the front ends of these upper and lower stays 12, 13.

  A fuel tank 15 is attached between the pair of side frames 5 below the pair of side frames 5. The front end of the power unit 16 is attached to the rear end of the curved frame 7 located behind the fuel tank 15 so as to swing up and down, and the rear end of the power unit 16 is connected to the rear end of one side frame 5 via the rear cushion unit 17. The end is attached. Here, the fuel tank 15 is provided with a fuel pump 18 having an overturn sensor inside, and is configured to be able to supply fuel from a fuel filler port (cap) 19 provided at the top. The power unit 16 includes an engine 50, a transmission 90, a throttle body 21, an air cleaner 22, an exhaust pipe 23 extending rearward from the engine 50, and a muffler 24 connected to the rear end of the exhaust pipe 23. Is done. A rear wheel 25 is attached to the rear end of the power unit 16, and the rear wheel 25 is driven by the power unit 16 so that the scooter type vehicle 1 can travel with power.

  A luggage box 26 and a grab rail 20 are attached to the rear portion of the side frame 5. The luggage box 26 is supported at the front by a front cross pipe 27 attached to the side frame 5 via the front plate 28, and supported at the rear by a portal frame 29 attached to the side frame 5. The grab rail 20 is supported by a rear stay 30 extending upward from the side frame 5. The helmets 31 and 32 represent a state of being stored in the luggage box 26. A rear storage box 33 is attached to the rear part of the grab rail 20.

  In the scooter type vehicle 1 configured as described above, the front upper portion of the vehicle body is covered with the front cover 34, and the left and right front side covers 35 are attached to the lower side of the front cover 34. A turn signal lamp (not shown) is attached to the front side cover 35. A front inner cover 36 is attached to the rear portion of the front cover 34, and a side portion of the step floor 37 on which the driver and the passenger rest his / her feet is covered with a side cover and an under cover 38. Further, a seat 39 is attached to the upper portion of the luggage box 26, and the lower periphery of the seat 39 is covered with the body cover and the body side cover 40. Further, a handle cover 42 that covers the handle 11 is attached to the upper portion of the front cover 34, and a head lamp 43 is attached to the handle cover 42. A front fender 44 is attached so as to cover the upper part of the front wheel 9, and a rear fender 45 is attached so as to cover the upper part of the rear wheel 25.

  A tail lamp 46 is disposed below the grab rail 27, and a battery 41 is stored between the front cover 34 and the front inner cover 36.

  Next, details of the power unit 16 will be described with reference to FIGS. In the present embodiment, the direction of the arrow F in FIG. 2 is the front, and the direction of the arrow U in FIG. The engine 50 configuring the power unit 16 includes a cylinder head cover 51, a cylinder head 52, a cylinder block 53, and a crankcase 54. In a cylinder chamber 55a formed by being surrounded by a cylinder sleeve 55 fitted in the cylinder block 53, a piston 56 is disposed so as to be slidable in the vertical direction. The piston 56 is connected to a crankcase via a connecting rod 57. It is connected to a crankshaft 58 that is rotatably held in 54. An intake port 60 and an exhaust port 61 communicate with the combustion chamber 59 formed by the cylinder block 53 (cylinder sleeve 55), the cylinder head 52, and the piston 56 via an intake port and an exhaust port, respectively. The saddle-shaped intake valve 62 and the saddle-shaped exhaust valve 63 are each provided with an intake port by valve springs 64 and 65, one end of which is attached to the valve shaft and supported by the retainer, and the other end is supported by the cylinder head 52. And the exhaust port is normally biased in the direction of closing.

  Further, a camshaft 66 for opening and closing the intake valve 62 and the exhaust valve 63 is rotatably disposed in the cylinder head 52. The camshaft 66 is arranged on a cam driven sprocket 67 and a crankshaft 58. A timing chain 69 is wound around the cam drive sprocket 68 provided. Therefore, the camshaft 66 rotates in accordance with the rotation of the crankshaft 58, and the cams 70 and 71 formed on the camshaft 66 push down the intake valve 62 and the exhaust valve 63 via the rocker arms 72 and 73. Open and close intake and exhaust ports. The intake port 60 is provided with an injector 74, and fuel is atomized into the intake port 60 and injected by the injector 74. Further, a spark plug 75 is attached to the cylinder head 52.

  A cam chain tensioner 84 for adjusting the timing of opening and closing the intake valve 62 and the exhaust valve 63 by the cams 70 and 71 by adjusting the tension of the timing chain 69 is attached to the side of the cylinder block 53. .

  In the engine 50 configured as described above, a mixture of the air cleaned by the air cleaner 22 and the fuel injected by the injector 74 is supplied from the intake port 60 to the combustion chamber 59 and compressed by the piston 56 and then ignited. It is ignited by the plug 75 and combusted to become energy for rotating the crankshaft 58 through the piston 56, and then exhausted as exhaust gas from the exhaust port 61 to the outside.

  The crankshaft 58 includes a right crankshaft half body 58a and a left crankshaft half body 58b, and a connecting rod 57 is connected to the crankshaft 57 via a crank pin 76 that is connected to both the crankshaft half bodies 58a and 58b. It is connected. The crankcase 54 that houses the crankshaft 58 includes a right case half 54a and a left case half 54b, and one end of the crankshaft 58 (the journal portion of the right crankshaft half 58a) is provided with a bearing 77. The other end (the journal portion of the left crankshaft half 58b) is supported by the left case half 54b via a bearing 78. Further, an ACG 79 and a cooling fan 85 are disposed at the tip of the journal portion of the right crankshaft half 58a.

  A left side portion of the left case half 54b extends rearward to form a part of the transmission case 80, and a transmission chamber 82 surrounded by a transmission cover 81 attached to the left side surface of the left case half 54b. A transmission 90 is stored. The transmission 90 is attached to the front end of the journal portion of the left crankshaft half 58b extending into the transmission chamber 82 and rotates integrally with the drive pulley 91. The transmission 90 is positioned behind the transmission chamber 80 and the crankshaft 58. A countershaft 92 that extends in parallel and is rotatably mounted, a driven pulley 93 that is mounted so as to be relatively rotatable with respect to the countershaft 92 at a substantially central portion of the countershaft 92, and is mounted and driven at the left end of the countershaft 92. A clutch 94 that engages and disengages the pulley 93 and the counter shaft 92 and a transmission belt (not shown) that is wound around the drive pulley 91 and the driven pulley 93 and transmits the rotation of the drive pulley 91 to the driven pulley 93.

  The drive pulley 91 is fixedly attached to the crankshaft 58 so as to be integrally rotatable. The drive pulley 91 is relatively movable in the axial direction with respect to the fixed pulley half 91a and rotates integrally with the crankshaft 58. The transmission belt is sandwiched between the fixed pulley half 91a and the movable pulley half 91b. On the other hand, the driven pulley 93 is fixed to the countershaft 92 so as to be rotatable relative to the countershaft 92. The driven pulley 93 can move relative to the stationary pulley half 93a in the axial direction and can rotate relative to the countershaft 92. The movable pulley half 93b, and the transmission belt is sandwiched between the fixed pulley half 93a and the movable pulley half 93b. Therefore, by variably setting the pulley widths of the drive pulley 91 and the driven pulley 93, the wrapping radius of the transmission belt around the pulleys 91 and 93 is continuously changed, so that the gear ratio is continuously variable (continuously). Can be controlled.

  In parallel with the counter shaft 92, a rear wheel shaft 96 to which the idle shaft 95 and the rear wheel 25 are attached is rotatably attached, and a gear train attached to the counter shaft 92, the idle shaft 95 and the rear wheel shaft 96 is arranged. The rotational driving force of the countershaft 92 is transmitted to the rear wheel 25 via this. As described above, the output of the engine 50 is transmitted to the crankshaft 58, and after being shifted by the transmission 90, is transmitted to the rear wheel 25.

  In addition, when such a power unit 16 is operated, since it generates heat | fever, it is necessary to cool each part. Therefore, a water jacket 122 that cools the cylinder head 52 by flowing cooling water therein is formed and cooled by the cooling water. The cylinder block 53 protrudes outward at the side. A plurality of cooling fins 86 are formed to release heat generated in the cylinder block 53 from the cooling fins 86, and the transmission case 80 extends forward at the front portion of the transmission case 80. A cooling air introduction passage 83 for taking outside air into the transmission chamber 82 is provided for cooling.

  Now, a cam mechanism 160 with a decompression device used in the scooter type vehicle 1 will be described with reference to FIGS. 6 and 7. The cam mechanism 160 with a decompression device is supported on the cylinder head 52 by bearings 87 and 88 and is rotatably mounted. The cam shaft 66 includes an intake cam 70 and an exhaust cam 71, and the cam shaft 66 is attached to the cam shaft 66. The cam driven sprocket 67 and the decompression cam 161 are configured.

  The camshaft 66 is formed with an intake cam 70, an exhaust cam 71, and a guide portion 66b arranged in this order so as to protrude from the outer peripheral surface of the cylindrical shaft portion 66a, and the cam driven sprocket 67 is attached to the guide portion 66b. It is formed at the end on the end face 66c side. The intake cam 70 and the exhaust cam 71 are formed with cam peaks 70a and 71a that push up the intake rocker arm 72 and the exhaust rocker arm 73, respectively, in order to push down the intake valve 62 and the exhaust valve 63.

  The camshaft 66 is formed with a decompression holding hole 170 having an opening 170a on the end surface 66c side and extending inward. The decompression holding hole 170 is formed in parallel to the axial line at a position shifted from the axial line of the shaft part 66a toward the end part of the exhaust cam 71 facing the cam crest 71a. The decompression holding hole 170 is opened outwardly on the outer peripheral surface of the shaft portion 66a between the guide portion 66b and the exhaust cam 71 to form a cam opening portion 170b. The decompression holding hole 170 reaches the position where the exhaust cam 71 is formed, and a groove 71b is formed in a portion of the exhaust cam 71 facing the cam crest 71a with the shaft 66a interposed therebetween. The groove 71b This opening is formed integrally with the cam opening 170b.

  Next, the decompression cam 161 attached to the decompression holding hole 170 will be described. In the decompression cam 161, a centrifugal weight portion 163 extending in a direction orthogonal to the axis of the shaft portion 162 is formed at one end of a cylindrical shaft portion 162, and a decompression cam crest 164 and a decompression groove 165 are formed in the vicinity of the other end of the shaft portion 162. Is formed. The shaft portion 162 includes a first shaft portion 162a formed between the centrifugal weight portion 163 and the decompression cam peak 164, a decompression portion 162b in which the decompression cam peak 164 and the decompression groove 165 are formed, and the other end. The second shaft portion 162c is formed, and the circumferential surface of the second shaft portion 162c in the same direction as the direction in which the decompression cam crest is formed is notched to form a notch portion 162d. . The decompression cam crest 164 and the decompression groove 165 formed in the decompression part 162 b are formed at positions facing each other across the axis of the shaft part 162. Further, the centrifugal weight portion 163 is formed in a fan shape that spreads around the shaft portion 162 in a side view, and a protruding portion 166 that protrudes outward is formed on the surface on which the shaft portion 162 extends.

  On the other hand, a disc-shaped cam-driven sprocket 67 attached to the camshaft 66 is formed with a weight opening 169 that extends in an arc shape outwardly from a position slightly shifted from the center, and this weight opening. The part 169 penetrates in the plate thickness direction. The weight opening 169 has a stopper portion 169a formed on one end side of a portion corresponding to the arc string, and an urging portion 169b formed on the other end side. The cam driven sprocket 67 is attached to the end surface 66 c of the camshaft 66 by inserting bolts 172 into attachment holes 173 and 173 that penetrate in the plate thickness direction. At this time, the cam driven sprocket 67 is attached to the camshaft 66 so that the opening 170 a of the decompression holding hole 170 formed in the camshaft 66 is in a position visible from the outside through the weight opening 169.

  The decompression cam 161 is attached in such a manner that the shaft 162 is inserted into the decompression holding hole 170 from the opening 170a formed in the end surface 66c of the camshaft 66 in a state where the cam driven sprocket 67 is attached to the camshaft 66. The first shaft portion 162a is rotatably held in a decompression holding hole 170 formed in the guide portion 66b, and the second shaft portion 162c is rotatably held in the groove portion 71b. At this time, the decompression cam crest 164 and the decompression groove 165 are at the position of the cam opening 170b. The protruding portion 166 of the centrifugal weight portion 163 is positioned in the weight opening 169 of the cam driven sprocket 67, and the end of the protruding portion 166 is substantially flush with the surface of the cam driven sprocket 67 on the cam 71 side or the weight. It is located in the vicinity of the plane in the opening 169. With the above configuration, the decompression cam 161 can rotate around the shaft portion 162, the centrifugal weight portion 161 swings along the surface of the cam driven sprocket 67, and accordingly, the protruding portion 166 always has a weight opening 169. Swing inside. The decompression cam 161 is configured so that the movement of the camshaft 66 in the axial direction is restricted by a restriction member 171 attached to the camshaft 66 together with the cam driven sprocket 67 by a bolt 172 and does not come out of the decompression holding hole 170. ing. That is, the bolt 172 can be shared for coupling the cam driven sprocket 67 and the restricting member 171.

  A cylindrical spring mounting portion 167 extending on the axis of the shaft portion 162 is formed at a connection portion between the centrifugal weight portion 161 and the shaft portion 162, and a return spring 168 is wound around the spring mounting portion 167. ing. The return spring 168 is attached to the decompression cam 161 in a direction in which the centrifugal weight portion 163 approaches the camshaft 66, that is, a direction in which the protruding portion 166 is biased to the biasing portion 169b of the weight opening 169 (FIG. 6). Position L in (a)). Thus, when the decompression cam 161 is in the position L, the decompression cam crest 164 is located in the cam opening 170b, and the decompression groove 165 is located in the decompression holding hole 170.

  On the other hand, when the engine 50 is started and the cam driven sprocket 67 rotates, a centrifugal force acts on the centrifugal weight portion 163 according to the rotation speed, and the centrifugal weight portion 163 is swung out around the shaft portion 162. Rocks. At this time, since the decompression cam 161 swings against the urging force of the return spring 168, the centrifugal weight portion 163 is not swung out unless the cam sprocket 67 reaches a predetermined rotational speed or more. When the centrifugal weight portion 163 is swung out by centrifugal force, the protrusion 166 contacts the stopper portion 169a of the weight opening 169 and does not swing any more (position H in FIG. 6B). Thus, when the decompression cam 161 is in the position H, the decompression groove 165 is located in the cam opening 170b, and the decompression cam mountain 164 is located in the decompression holding hole 170 (FIG. 6A). ) State). A groove 170 c is formed in a portion of the decompression holding hole 170 facing the decompression cam peak 164 so as not to interfere with the decompression cam peak 164.

  With respect to the cam mechanism 160 with the decompression device configured in this way, the end portion of the exhaust rocker arm 73 provided is formed so as to protrude downward from the side portion, and the cam crest 71a of the exhaust cam 71 is formed. Thus, a pressing portion 73a that is pushed upward is formed. The pressing portion 73a is located in the decompression holding hole 170 from the cam opening 170b. The pressing portion 73a is configured to be positioned in the decompression groove 165 formed in the decompression cam 161 when the decompression cam 161 is at the position H.

  For this reason, when the engine 50 starts, when the rotation speed of the crankshaft 58 of the engine 50 is slow, that is, when the decompression cam 161 is at the position L, the decompression cam crest 164 is located at the cam opening 170b. . For this reason, immediately before the air-fuel mixture compressed in the combustion chamber 59 is ignited, the decompression cam crest 164 pushes up the pressing portion 73a of the exhaust rocker arm 73 and opens the exhaust valve 63 by a small amount. The pressure of the mixture decreases. On the other hand, when the engine 50 starts to start and the rotation speed of the crankshaft 58 becomes equal to or higher than a predetermined value, the centrifugal weight portion 163 of the decompression cam 161 swings outward and swings and moves to the position H. Then, since the shaft 162 rotates and the decompression groove 165 is located in the cam opening 170b, and the pressing portion 73a is located in the decompression groove 165, the exhaust valve 63 is not opened immediately before ignition. The engine 50 is operated normally.

  Since the decompression cam 161 has a return spring 168, the decompression cam 161 is configured to return to the position L when the rotational speed of the crankshaft 58 becomes a predetermined value or less.

  By configuring the cam mechanism 160 with the decompression device as described above, a part of the centrifugal weight portion 163 (projection portion 166) constituting the decompression cam 161 is positioned in the weight opening 169 formed in the cam driven sprocket 67. Therefore, the width of the cam shaft 66 in the axial direction can be narrowed while securing the weight necessary for the swing of the decompression cam 161, so that the cylinder head 52 can be made compact. Since the weight opening 169 is configured to penetrate the cam driven sprocket 67 in the plate thickness direction, the thickness of the projection 166 can be made substantially the same as the plate thickness of the driven sprocket 67. The weight of the centrifugal weight portion 163 can be easily secured.

  In this cam mechanism 160 with a decompression device, the centrifugal weight portion 163 is configured such that the center of gravity of the centrifugal weight portion 163 is located outside the half of the radius of the cam driven sprocket 67 from the center of the cam driven sprocket 67. The part 163 can function effectively. Further, when the centrifugal weight part 163 is swung out and swung outward, the protrusion 166 is in contact with the stopper part 169a of the weight opening 169 so that the rotation is restricted. This stopper member becomes unnecessary, and the manufacturing cost of the cam mechanism 160 with the decompression device can be reduced.

  When the decompression cam 161 is attached to the camshaft 66, the first shaft portion 162a of the shaft portion 162 is rotatably held by the decompression holding hole 170 formed in the guide portion 66b, and the second shaft portion 162c is rotated. Since it is rotatably held in the groove portion 71b, the shaft portion 162 is supported at both ends, and the shaft portion 162 can be prevented from swinging. Further, when the rotation speed of the cam driven sprocket 67 is slow and the exhaust rocker arm 73 is pushed up by the decompression cam crest 164 (below the decompression speed of the decompression device), if the decompression cam 161 vibrates, the second shaft portion Since the notch portion 162d is formed in the 162c, the second shaft portion 162c is not supported by the groove portion 71b and the shaft portion 162 is in the axial direction of the decompression holding hole 170 as schematically shown in FIG. It can be tilted by a small angle. Therefore, the first shaft portion 162a contacts the end portion (position X, Y in FIG. 8) of the decompression holding groove 170 in the guide portion 66b, and unnecessary vibration of the decompression cam 161 can be suppressed.

It is a side view of a scooter type vehicle to which a cam mechanism with a decompression device according to the present invention is attached. It is a top view of a power unit. It is a left view of a power unit. It is a right view of a power unit. It is sectional drawing of a cylinder head. It is a figure which shows the cam mechanism with a decompression apparatus which concerns on this invention, (a) is the side view seen from the cam driven sprocket side, (b) is side sectional drawing containing a cylinder head. It is a front view of a cam sprocket. It is explanatory drawing which shows the operation | movement at the time of vibration of a decompression cam.

Explanation of symbols

58 Crankshaft 66 Camshaft 67 Cam-driven sprocket (cam sprocket)
71 Exhaust cam (cam)
160 Cam mechanism 161 with decompression device Decompression cam 162 Shaft portion 162a First shaft portion 162c Second shaft portion 162d Notch portion 163 Centrifugal weight portion 164 Decompression cam crest 169 Weight opening portion (opening portion)
169a Stopper part

Claims (4)

A camshaft having at least one cam;
A cam sprocket connected to the camshaft and driven to rotate in conjunction with the crankshaft;
A cylindrical shaft portion; a decompression cam crest formed on a circumferential surface side of one end side of the shaft portion; and a centrifugal weight portion extending in a direction orthogonal to the axis of the shaft portion on the other end side of the shaft portion. With decompression cam,
The centrifugal weight portion is close to the cam sprocket, the shaft portion extends in parallel with the cam shaft and is rotatably supported with respect to the cam shaft, and the centrifugal weight portion is subjected to centrifugal force by rotation of the cam sprocket. And a cam mechanism with a decompression device that pivots the shaft portion by being swung outwardly and swinging, and projects the decompression cam mountain from the camshaft.
A space portion penetrating the cam sprocket at a portion of the cam sprocket facing the centrifugal weight portion of the decompression cam;
The centrifugal weight part, the inserted from the cam on the opposite side of the surface of the cam sprocket in the space portion, the end portion of the centrifugal weight part at least partially located within the space portion of the centrifugal weight part is the the decompression device with a cam mechanism, characterized in that it is configured to be positioned on the cam side face and substantially on the same plane in the cam sprocket.   2. The cam mechanism with a decompression device according to claim 1, wherein the center of gravity of the centrifugal weight portion is configured to be located outward from a center of the cam sprocket and half a radius of the cam sprocket.   3. The cam mechanism with a decompression device according to claim 1, wherein the cam sprocket includes a stopper portion that restricts swinging of the centrifugal weight portion at an opening end of the space portion. The shaft portion of the decompression cam is
A first shaft portion that extends toward the centrifugal weight portion and is supported by the camshaft across the decompression cam mountain, and a second shaft portion that extends toward the cam side and is supported by the camshaft,
The cam mechanism with a decompression device according to any one of claims 1 to 3, wherein a notch portion is formed on a circumferential surface of the second shaft portion in a direction in which the decompression cam mountain is formed. .

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