JP4540655B2 - Internal combustion engine with decompression device - Google Patents

Description

  The present invention relates to an internal combustion engine including a decompression device that reduces a compression pressure at the time of starting and facilitates starting.

A decompression device of an internal combustion engine includes a centrifugal weight that is swingably supported by a camshaft of a valve gear that opens and closes an intake valve and an exhaust valve, and a decompression cam that is driven by a centrifugal weight that is swung by the action of centrifugal force. It is known that the engine valve opened and closed by the decompression cam is driven and opened by the decompression cam during the compression stroke, thereby reducing the compression pressure in the combustion space and reducing the load on the starter. (For example, see Patent Document 1)
JP 2004-360538 A

By the way, the centrifugal weight of the decompression device is arranged so as to have a center of gravity at a position deviated from the rotation center line of the cam shaft with respect to the cam shaft as the rotation shaft, thereby causing rotational unbalance of the cam shaft. . This rotational imbalance increases as the engine rotational speed increases, causing the camshaft to sway and vibrate and affect the opening / closing accuracy of the engine valve by the valve cam.
If the camshaft is provided with a centrifugal weight and decompression cam, the camshaft itself must be enlarged in the radial direction or a space for the centrifugal weight to swing must be secured. May increase in size.
Furthermore, when the decompression device is installed in different types of internal combustion engines as a common part, the compression pressure may differ from model to model, so the opening of the engine valve, which is the decompression valve that is opened by the decompression cam, can be simplified. It is preferable that adjustment is possible with an adjustment member having a simple structure.
In addition, it is preferable if the cam contact portion that contacts the decompression cam can be arranged to reduce the size of the cam shaft and the size of the cylinder head in the radial direction.

  The present invention has been made in view of such circumstances, and the inventions of claims 1 to 6 reduce rotation unbalance of the camshaft by the decompression device, and open / close accuracy of the engine valve by the valve cam. The purpose is to improve. The inventions of claims 2 to 4 further reduce the size of the cam shaft provided with the balancer weight or the size of the cylinder head in the radial direction by downsizing the weight portion constituting the balance weight. The object of the present invention is to make it possible to adjust the amount of reduction of the compression pressure and to simplify the structure of the decompression device including an adjusting member for adjusting the amount of reduction. The invention described in Item 6 further aims to reduce the size of the cam shaft or the cylinder head in the radial direction by arranging the cam contact portion that contacts the decompression cam.

According to a first aspect of the present invention, there is provided a valve operating apparatus including a cam shaft having a valve operating cam that opens and closes an engine valve, a centrifugal weight that is swingably supported by the cam shaft, and a rotational speed of the cam shaft. And a decompression cam driven by the centrifugal weight that oscillates under the action of centrifugal force generated by the centrifugal force, and the decompression cam is compressed to reduce the compression pressure in the combustion space when starting the engine in which the centrifugal weight occupies a low speed side position. An internal combustion engine having a decompression position that occupies a decompression position that opens the engine valve during a stroke, and that occupies a decompression release position that does not open the engine valve after the engine is started in which the centrifugal weight occupies a high speed side position; the shaft, the balance weight to reduce the rotational imbalance of the cam shaft by the centrifugal weight occupying the high speed side position is provided, said balance U Site is an internal combustion engine including a plurality of weight portions spaced apart from each other in the axial direction of the camshaft.
The invention according to claim 2 is the internal combustion engine according to claim 1, further comprising a cylinder head provided with a plurality of bearing portions for rotatably supporting the camshaft , and a pair of bearings adjacent in the axial direction. Each part is integrally formed with the cylinder head and forms a bearing hole into which the journal part of the cam shaft is inserted. At least one weight part integrally formed with the cam shaft is 1 in the axial direction. It is arrange | positioned between the said journal part of a pair .
According to a third aspect of the present invention, in the internal combustion engine according to the second aspect, the weight portion is disposed between the valve cam and the journal portion adjacent in the axial direction.
According to a fourth aspect of the present invention, in the internal combustion engine according to the second or third aspect, the decompression device includes a restriction member that is provided on the camshaft and restricts movement of the centrifugal weight in the axial direction. A member has one said weight part.
According to a fifth aspect of the present invention, in the internal combustion engine according to the first aspect, the valve operating device includes a cam follower that is driven by the valve operating cam to open and close the engine valve, and the decompression device adjusts the position of the cam follower. An adjusting member that is provided so as to be in contact with the decompression cam is provided, and an opening amount of the engine valve by the decompression cam is adjusted by a position of the adjusting member.
According to a sixth aspect of the present invention, in the internal combustion engine according to the first aspect, the valve operating device includes a cam follower that is driven by the valve operating cam to open and close the engine valve, and the decompression device is provided in the cam follower. And a cam contact portion that contacts the decompression cam, and the contact surface of the cam contact portion with the decompression cam is inward of the cam surface of the base circle portion of the valve cam in the radial direction of the cam shaft. It is located in the direction.

According to the first aspect of the present invention, the camshaft unbalance caused by the centrifugal weight of the decompression device after the internal combustion engine is started to be reduced by the balance weight. As a result, the opening / closing accuracy of the engine valve by the valve operating cam is improved.
According to the second aspect of the present invention, the plurality of balance portions constituting the balance weight are arranged in the axial direction so that each weight is downsized in the radial direction, and the cam shaft is provided with the balance weight. Is reduced in the radial direction.
According to the third aspect of the present invention, the camshaft provided with the weight portion integrally formed with the camshaft is inserted into the pair of bearing portions integrally formed with the cylinder head using the bearing holes, and the cylinder Since it is supported by the head, the camshaft provided with the balance weight is reduced in size in the radial direction, and since there is no need to use a split type bearing portion, the bearing portion is reduced in size in the radial direction of the camshaft, As a result, the cylinder head is reduced in size in the radial direction. In addition, since the weight part formed integrally with the camshaft is arranged using the space in the axial direction formed between the valve cam and the journal part, the camshaft provided with the balancer weight is in the axial direction. Miniaturized.
According to the fourth aspect of the present invention, since the weight portion is formed by using the regulating member that is a constituent member of the decompression device, it is not necessary to provide a new member for constituting the balance weight. In addition, since the other weight portions provided on the cam shaft can be further downsized in the radial direction, it contributes to downsizing of the cam shaft or cylinder head in the radial direction.
According to the fifth aspect of the present invention, since the amount of reduction of the compression pressure can be adjusted by adjusting the position of the adjusting member with respect to the cam follower, the decompression device can be made common to different types of internal combustion engines. This contributes to cost reduction. In addition, since the adjustment member abuts on the decompression cam, there is no need to interpose another member between the decompression cam and the adjustment member, so that the structure of the decompression device including the adjustment member is simplified.
According to the sixth aspect of the present invention, the contact surface of the cam contact portion is positioned radially inward from the cam surface of the base circle portion of the valve operating cam that opens and closes the engine valve opened by the decompression cam. Therefore, the position of the decompression cam can be arranged closer to the rotation center line of the cam shaft in the radial direction than when the contact surface is at the same position as the cam surface of the base circle portion. This contributes to downsizing of the camshaft or cylinder head.

Embodiments of the present invention will be described below with reference to FIGS.
Referring to FIGS. 1 and 2, an internal combustion engine E to which the present invention is applied is a single-cylinder reciprocating four-stroke internal combustion engine mounted on a motorcycle as a vehicle. The air-cooled internal combustion engine E includes a cylinder 1 that forms a cylinder bore 1a into which a piston 5 is reciprocally fitted, a cylinder head 2 that is coupled to the upper end of the cylinder 1, and a head cover that is coupled to the upper end of the cylinder head 2. 3 and a crankcase (not shown) coupled to the lower end of the cylinder 1 and rotatably supporting a crankshaft (hereinafter simply referred to as “crankshaft”). The cylinder head 2 and the head cover 3 form a valve operating chamber 4 in which an overhead camshaft type valve operating device 20 provided in the internal combustion engine E is accommodated.

  In this embodiment, for convenience of explanation, it is assumed that the vertical direction is the cylinder axis direction, that is, the direction parallel to the cylinder axis Ly. Further, unless otherwise specified, the axial direction, the radial direction, and the circumferential direction are respectively a direction parallel to the rotation center line Lc of the cam shaft C of the valve gear 20, a radial direction about the rotation center line Lc, and a rotation center. It is assumed that the circumferential direction is centered on the line Lc.

  The cylinder head 2 is formed with a combustion chamber 6 provided at a position facing the piston 5 in the cylinder axial direction, and an intake port 7 and an exhaust port 8 that open to the combustion chamber 6, respectively. An intake valve 9 and an exhaust valve 10 composed of poppet valves for opening and closing the ports 8 respectively, and an ignition plug 11 facing the combustion chamber 6 are provided. The intake valve 9 and the exhaust valve 10 which are engine valves are each slidably guided by a valve guide 12 press-fitted into the cylinder head 2. The combustion chamber 6 and the cylinder bore 1a between the piston 5 and the cylinder head 2 constitute a combustion space in which the air-fuel mixture burns.

  3 and 4, the valve operating device 20 has an intake cam 22 and an exhaust cam 23 as valve operating cams and is rotatably supported by the cylinder head 2 via bearings 15a and 15b. The intake rocker arm 24 and the exhaust rocker arm 25 as cam followers that are driven by the shaft C, the intake cam 22 and the exhaust cam 23, respectively, to open and close the intake valve 9 and the exhaust valve 10, and the intake valve 9 and the exhaust valve 10 by elastic force. And a valve spring 26 that is constantly urged in the valve closing direction.

The camshaft C is supported by a pair of bearings 15a and 15b comprising rolling bearings respectively held by a pair of bearing portions 13a and 13b provided integrally with the cylinder head 2. The respective bearings 15a and 15b are inserted into bearing holes 14a and 14b formed of through holes formed by the respective bearing portions 13a and 13b. Bolts 16 for connecting the cylinder head 2 to the cylinder 1 are inserted into the bearing portions 13a and 13b.
The bearing hole 14a has an outer diameter of the bearing 15a having the largest outer diameter among the bearings 15a and 15b respectively held by the bearing parts 13a and 13b, which are a pair of adjacent bearing parts adjacent in the axial direction, and both The cams 22 and 23 have a hole diameter larger than twice the maximum radius Ri and Re (see FIG. 6). Therefore, the cam shaft C is inserted between the bearing holes 13a and 13b from the bearing hole 14a in the axial direction and is mounted on the bearings 13a and 13b.

  The cam shaft C includes a shaft main body 21, and an intake cam 22 and an exhaust cam 23 provided integrally with the shaft main body 21. The shaft main body 21 has a pair of journal portions 21c and 21d at shaft end portions 21a and 21b, which are portions inserted into the bearing holes 14a and 14b and supported by the bearings 15a and 15b. The intake cam 22 and the exhaust cam 23 are disposed between the journal portions 21c and 21d in the axial direction, that is, inside the journal portions 21c and 21d or the bearing portions 13a and 13b in the axial direction.

  The exhaust cam 23 includes a base circle portion 23a that keeps the exhaust valve 10 closed, a cam peak portion 23b that opens the exhaust valve 10, and an exhaust cam 23 that extends across the base circle portion 23a and the cam peak portion 23b. And a cam surface S that is slidably contacted with a slipper described later.

  The camshaft C has a rotation center line Lc parallel to the rotation center line of the crankshaft that is rotationally driven by the piston 5 via a connecting rod (not shown), and is transmitted via the valve gear transmission mechanism 30. The crankshaft is driven to rotate at half the rotational speed of the crankshaft by the power of the crankshaft. The valve train transmission mechanism 30 includes a drive sprocket coupled to the crankshaft, a cam sprocket 32 as a rotating body attached to the shaft end 21a, and an endless transmission belt spanned over the drive sprocket and the cam sprocket 32. And the timing chain 31.

  The cam sprocket 32 disposed outside the pair of bearing portions 13a, 13b or the pair of bearing holes 14a, 14b in the axial direction has a pair of holes 28a (see FIG. 6A) provided in the shaft end portion 21a. Are positioned with respect to the camshaft C by a pair of positioning pins 28b that are press-fitted to each other, and are coupled to the shaft end 21a by a pair of bolts 29. Further, the cam sprocket 32 is provided with an opening 33 as an accommodation space in which a later-described centrifugal weight 41 and a part of the decompression shaft 42 are inserted and accommodated.

  Both rocker arms 24 and 25 are swingably supported by a pair of rocker shafts 27 held by the bearing portions 13a and 13b and prevented by bolts 16, respectively. The intake rocker arm 24 has a slipper 24 a as a cam contact portion that contacts the intake cam 22 and a pair of valve pressing portions 24 b that press the intake valve 9. The exhaust rocker arm 25 includes a slipper 25 a as a cam contact portion that contacts the exhaust cam 23 and a pair of valve pressing portions 25 b that press the exhaust valve 10.

  The valve operating device 20 allows the intake cam 22 to open and close the intake valve 9 via the intake rocker arm 24 and the exhaust cam 23 opens and closes the exhaust valve 10 via the exhaust rocker arm 25 in synchronization with the rotation of the crankshaft. Opens and closes according to time and lift.

  Then, air sucked through an intake device (not shown) having an intake pipe attached to the side portion 2i of the cylinder head 2 where the inlet of the intake port 7 opens is supplied from a fuel supply device such as a carburetor. The fuel is mixed with the fuel to form an air-fuel mixture, which is sucked into the combustion chamber 6 through the intake port 7 through the intake valve 9 opened in the intake stroke. The mixture of intake air and fuel is compressed during the compression stroke in which the piston 5 is raised, burned by being ignited by the spark plug 11 at the end of the compression stroke, and driven by the pressure of the combustion gas in the expansion stroke in which the piston 5 is lowered. The piston 5 is driven to rotate the crankshaft. The combustion gas passes through an exhaust valve 10 opened in the exhaust stroke in which the piston 5 moves up, passes through the exhaust port 8 from the combustion chamber 6 as exhaust gas, and then the side of the cylinder head 2 where the outlet of the exhaust port 8 opens. 2e is exhausted to the outside of the internal combustion engine E through an exhaust device (not shown) having an exhaust pipe attached to 2e.

1 to 4, when the internal combustion engine E is started, the decompression device D for reducing the load of the manual starter such as a kick starter and a recoil starter or the starter consisting of a starter motor is controlled at the engine speed. A driving mechanism provided on a cam shaft C as a rotating shaft that rotates synchronously and rotated together with the cam shaft C, and driven by the driving mechanism that operates in accordance with the engine rotational speed, reduces the compression pressure of the combustion space to the outside. And a valve mechanism for escaping.
The drive mechanism includes a decompression body 40 that is attached to the camshaft C so as to be relatively movable, and a control spring 51 as a control member that controls the operation of the decompression body 40 that occupies the decompression position and the decompression release position according to the engine rotational speed. In order to hold the decompression body 40 on the shaft body 21, a restriction plate 52 is provided as a restriction member for restricting movement of the decompression body 40 in the axial direction. Here, the decompression position is a position where a decompression cam 43, which will be described later, opens the exhaust valve 10 during the compression stroke, that is, a decompression operation is performed in order to reduce the compression pressure in the combustion space when the engine is started. The decompression release position is a position where the decompression cam 43 does not open the exhaust valve 10 after the engine is started, that is, no decompression operation is performed.

  The decompression body 40 is supported by the shaft body 21 so as to be able to swing, and the centrifugal weight 41 swings by the action of a centrifugal force generated according to the rotational speed of the cam shaft C, and the cam shaft C driven by the centrifugal weight 41. And a decompression cam 43 driven by the driving force of the centrifugal weight 41 transmitted through the decompression shaft 42. In this embodiment, the decompression body 40 is formed by integrally forming a centrifugal weight 41, a decompression shaft 42, and a decompression cam 43, but at least one of the centrifugal weight 41, the decompression shaft 42, and the decompression cam 43 is formed by a separate member. It may be configured and assembled so as to interlock with each other.

The centrifugal weight 41 is swingably supported by the shaft body 21 with the rotation center line Ld of the decompression shaft 42 as the swing center line Lw and thus with the decompression shaft 42 as the center axis. Referring also to FIG. 4B, the centrifugal weight 41 has an arm portion 41a extending in the radial direction of the decompression shaft 42 and a weight main body portion 41b thicker than the arm portion 41a.
The arm portion 41a, which is a part of the centrifugal weight 41, extends along the swing center line Lw from the first radial direction portion 41c extending outward in the radial direction of the swing center line Lw and the tip of the first radial direction portion 41c. The axial direction part 41d and the 2nd radial direction part 41e extended in the radial direction outward of the rocking | swiveling centerline Lw from the front-end | tip of the axial direction part 41d are included. The first radial direction portion 41c is disposed in the opening 33, and is equal to or lower than a set rotational speed (hereinafter simply referred to as “set rotational speed”) that is an engine rotational speed when the internal combustion engine E leaves the cranking state. Sometimes it contacts the low speed side stopper 34a, and after the internal combustion engine E starts, it contacts the high speed side stopper 34b when the engine speed exceeds the set speed. Each of the stoppers 34 a and 34 b is constituted by a part of the peripheral edge 34 that defines the opening 33. Therefore, the cam sprocket 32 provided integrally with the camshaft C is also a stopper member in which both stoppers 34a and 34b for defining the swinging amount of the centrifugal weight 41 are formed.

Moreover, the axial direction part 41d is extended in the direction opposite to the position of both the bearing parts 13a and 13b from the 1st radial direction part 41c in the axial direction. For this reason, the second radial direction portion 41e and the weight main body portion 41b are arranged on the opposite side of the bearing portion 13a from the cams 22 and 23 in the axial direction, and accordingly, a pair of bearing portions 13a in the axial direction. , 13b.
When the centrifugal weight 41 occupies the low speed side position described later, most of the weight main body 41b is positioned radially outward of the cam shaft C from the arm 41a, and the centrifugal weight 41 has a high speed side position described below. When occupied, the whole or almost the whole is located radially outward of the cam shaft C with respect to the arm portion 41a.

  The decompression shaft 42 is slidably inserted into and held in a holding hole Ce provided in the cam shaft C, and held at a position eccentric from the rotation center line Lc by a predetermined distance. Has a rotation center line Ld parallel to the rotation center line Ld. Therefore, the decompression shaft 42 is slidably supported by the pair of support portions Ca and Cb of the cam shaft C in a pair of supported portions 42a and 42b that are separated in the axial direction. The pair of support portions Ca and Cb are respectively provided at positions overlapping the journal portions 21c and 21d and the exhaust cam 23 in the axial direction.

  1, 2, and 5, the decompression cam 43 is exposed to the shaft main body 21 in a space 45 formed by a notch portion 21 e provided between the journal portion 21 c and the exhaust cam 23 in the axial direction. The decompression shaft 42 is provided at an exposed portion. The decompression cam 43 disposed in the vicinity of the exhaust cam 23 in the axial direction includes an operation portion 43a that operates the valve mechanism to perform decompression operation when the decompression cam 43 occupies the decompression operation position, and a release portion 43b that does not perform decompression operation. Have The operating portion 43a abuts on an adjusting screw 56, which will be described later, in a state where it does not protrude radially outward from the cam surface Sa of the base circular portion 23a of the exhaust cam 23 during decompression operation, and opens the exhaust valve 10 slightly. To do. On the other hand, the release portion 43 b formed by cutting out the decompression shaft 42 does not contact the adjustment screw 56.

  Both the locking end portions 51 a and 51 b of the control spring 51 are locked to the axial direction portion 41 d of the centrifugal weight 41 and the axial direction portion 52 b of the regulating plate 52, respectively. The locking end portion 51b is locked in a state of passing through the slit 54 provided in the axial direction portion 52b. The shaft end portion 42c of the decompression shaft 42 disposed outside the pair of bearing portions 13a and 13b in the axial direction is supported by the centrifugal weight 41 and the control spring 51 in order from the bearing portions 13a and 13b in the axial direction. A portion 42d and an engaging portion 42e that engages with the regulating plate 52 are provided.

  The centrifugal weight 41 is biased by the control spring 51 as shown by the solid line in FIG. 4A when the internal combustion engine E is in a stopped state and when the engine rotational speed is equal to or lower than the set rotational speed. When the engine rotational speed exceeds the set rotational speed by contacting the first stopper 34a and the engine rotational speed exceeds the set rotational speed, the elastic force of the control spring 51 is increased as shown by the two-dot chain line in FIG. In contrast, it rotates away from the low-speed side stopper 34a and abuts on the high-speed side stopper 34b to occupy the high-speed side position.

2 to 4, the regulating plate 52 coupled to the shaft end portion 21 a together with the cam sprocket 32 by the bolt 29 is paired on the opposite side of the cam sprocket 32 with respect to the cam sprocket 32 in the axial direction. Are disposed outside the bearing portions 13a and 13b. The restricting plate 52 includes a flat plate-like mounting portion 52a through which the bolt 29 is inserted and in surface contact with the cam sprocket 32, and an axial portion connected to the mounting portion 52a and sandwiching the shaft end portion 42c in the radial direction of the decompression shaft 42. An axial direction portion 52b extending along the rotation center line Ld at a position facing 41d, a restriction portion 52c extending in the radial direction of the decompression shaft 42 from the tip of the axial direction portion 52b toward the axial end portion 42c, and an attachment portion And a weight part 52e extending radially outward in a fan shape or semicircular shape, and a mounting member 52a, an axial direction part 52b, a restricting part 52c, and a weight part 52e formed as a single member. is there.
The restricting portion 52c is engaged with the retaining ring 53 and the engaging portion 42e disposed on both sides of the restricting portion 52c in the axial direction in a state where the tip end portion of the shaft end portion 42c penetrates the hole provided in the restricting portion 52c. As a result, the movement of the decompression body 42 including the decompression shaft 42 and the centrifugal weight 41 in the axial direction is restricted, and the decompression body 40 is prevented from being detached from the camshaft C.

Referring to FIGS. 4 and 6, the weight portion 52e is located at a position overlapping the weight main body portion 41b at the low speed side position with respect to the centrifugal weight 41, and at the high speed side position. The entire portion 41b and further the entire centrifugal weight 41 are arranged at positions that do not overlap at all.
Furthermore, when the centrifugal weight 41 occupies the high speed side position with respect to the centrifugal weight 41, the weight portion 52e is a plane H1 including the rotation center line Lc, and the weight main body on one side with the plane H1 as a boundary. The entire portion 41b and the entire or almost entire centrifugal weight 41 are positioned, and the entire weight portion 52e is positioned on the other side. The centrifugal weight 41 and the weight portion 52e occupying the high speed side position are arranged at positions facing each other across the rotation center line Lc in the radial direction.

  The weight portion 52e has a part of the outer peripheral portion thereof in a range that does not interfere with the swinging weight main body portion 41b, and is axially extended farther than the weight main body portion 41b relative to the cam sprocket 32 or the bearing portion 13a in the axial direction. It has a partial cylindrical additional weight portion 52f extending along the direction. The additional weight portion 52f is located closer to the rotation center line Lc radially inward than the outermost peripheral portion of the centrifugal weight 41 occupying the high speed side position in the radial direction, and the weight main body portion 41b. On the other hand, in the radial direction, they are arranged at positions facing each other across the rotation center line Lc.

  Referring to FIGS. 1 to 3, the valve mechanism communicates with the combustion space to the outside, and an exhaust valve 10 serving as a decompression valve for releasing the pressure in the combustion space, and an exhaust valve 10 ( A decompression cam follower for opening and closing a decompression valve) or an exhaust rocker arm 25 as a decompression rocker arm. The exhaust rocker arm 25 (decompressor arm) is provided with a support portion 55 formed of a protruding portion that protrudes from the slipper 25a toward the bearing portion 13a in the axial direction in the vicinity of the slipper 25a. An adjustment screw 56 that is an adjustment member as a cam contact portion that contacts the decompression cam 43 is screwed to the support portion 55 that is in a position overlapping the space 45 in the axial direction (see FIG. 2), and the position can be adjusted. Provided. The adjustment screw 56 adjusts its position to adjust the amount of reduction of the compression pressure, so that the opening of the exhaust valve 10 during decompression operation is optimally adjusted from the viewpoint of reducing the load on the starter. The lift amount of the exhaust valve 10 is adjusted, and after the adjustment, the lock nut 57 is held at the optimum position.

  Referring also to FIG. 5, in the adjustment screw 56 that faces the decompression cam 43 in the radial direction, the contact surface 56 a that is formed at the tip of the adjustment screw 56 and that abuts the decompression cam 43 is the cam of the base circle portion 23 a of the exhaust cam 23. It is located radially inward from the surface Sa. As a result, the decompression cam 43 and the decompression shaft 42 can be arranged radially inward on the cam shaft C, and the oscillation center line Lw of the centrifugal weight 41 can be brought close to the rotation center line Lc. Within the chamber 4, the centrifugal weight 41 attached to the camshaft C can be compactly arranged in the radial direction.

Further, the internal combustion engine E is provided with a balance weight 60 that reduces unbalanced rotation of the camshaft C caused by an unbalance force generated due to the decompression body 40 having the centrifugal weight 41.
Referring to FIGS. 1, 2, and 6, a balance weight 60 that reduces rotational unbalance of the cam shaft C due to the centrifugal weight 41 occupying the high speed side position is provided on the cam shaft C. The balance weight 60 includes a plurality of divided weight portions 61, 62, 63, and 52e, that is, first to third weight portions 61 to 63 provided integrally with the shaft body 21 of the cam shaft C, and a cam shaft. It is comprised from the weight part 52e as a 4th weight part provided in the control plate 52 which is a member different from C. As shown in FIG. Therefore, the weight portion 52e is attached to the camshaft C and is a balance weight.

The first to third weight portions 61 to 63 are disposed between a pair of journal portions 21c and 21d or a pair of bearing portions 13a and 13b adjacent in the axial direction in the same manner as the intake cam 22 and the exhaust cam 23. The weight portion 52e is an inner weight portion, and is an outer weight portion disposed on the opposite side of the cams 22 and 23 with the journal portion 21c or the bearing portion 13a interposed therebetween in the axial direction.
The first and second weight portions 61 and 62 and the weight portion 52e are separated from each other in the axial direction, and the second and third weight portions 62 and 63 and the weight portion 52e are separated from each other in the axial direction. Yes. On the other hand, the first and third weight portions 61 and 63 are arranged so as to have overlapping portions in the axial direction.

  The first and second weight portions 61 and 62 disposed adjacent to each other in the vicinity of the journal portions 21c and 21d in the axial direction are in the same or substantially the same range in the circumferential direction and in the radial direction. The range not exceeding the maximum radius Ri, Re of the cam 22 and the exhaust cam 23 and the outer diameter of each journal portion 21c, 21d. In this embodiment, the maximum radius Ri, Re and the outer diameter of each journal portion 21c, 21d. In a small range, it is provided to project radially outward from the shaft body 21. Further, the plane H2 includes the rotation center line Lc, and the first and second weight portions 61 and 62 are arranged on one side with the plane H2 as a boundary, and the centrifugal weight 41 occupies the high speed side position on the other side. The decompression body 40 including the whole is disposed so as to be positioned. Accordingly, each of the first and second weight portions 61 and 62 and the centrifugal weight 41 occupying the high speed side position are arranged at positions facing each other across the rotation center line Lc in the radial direction.

  The entire third weight portion 63 has a smaller diameter than both the cams 22 and 23, and is arranged at a position overlapping the notch portion 21e and the decompression shaft 42 in the exhaust cam shaft direction. Then, the third weight portion 63 and the decompression shaft 42, which is a portion where the unbalanced force is exerted by the centrifugal weight 41 on the camshaft C, are arranged at positions facing each other across the rotation center line Lc in the radial direction. As a result, the bending rigidity of the cam shaft C where the notch 21e is provided is increased.

The first and third weight portions 61 and 63 are disposed between the exhaust cam 23 and the journal portion 21c adjacent in the axial direction, and the second weight portion 62 is the intake cam 22 and the journal portion 21d adjacent in the axial direction. Between. Therefore, at least one weight portion 61 to 63 integrally formed with the cam shaft C is disposed between the pair of journal portions 21c and 21d in the axial direction and adjacent to the exhaust cam 23 and the journal portion 21c in the axial direction. Or between the intake cam 22 and the journal portion 21d. The first and third weight portions 61 and 63 and the second weight portion 62 are arranged so as to be distributed on both sides of the cams 22 and 23 with the cams 22 and 23 interposed therebetween in the axial direction.
Further, since the first and third weight portions 61 and 63 are provided at positions that overlap with at least one of the decompression body 40, that is, the centrifugal weight 41, the decompression shaft 42, and the decompression cam 43 in the axial direction, the bending rigidity of the cam shaft C is improved. Contribute to.

The operation of the decompression device D will be described with reference to FIGS.
As indicated by the solid line in FIG. 4, when the internal combustion engine E is stopped, the centrifugal weight 41 occupies the low speed side position that is urged by the control spring 51 and contacts the low speed side stopper 34a. When the internal combustion engine E is started by the starter and enters a cranking state in which the crankshaft is rotationally driven, the centrifugal weight 41 rotates together with the camshaft C. At this time, when the engine rotational speed is equal to or lower than the set rotational speed, the centrifugal force generated in the centrifugal weight 41 is small, and the centrifugal weight 41 is urged by the control spring 51 to occupy the low speed side position, Including the decompression body 40 occupies the decompression position.

  In this state, during the compression stroke of the internal combustion engine E, as shown in FIG. 5A, the operating portion 43a of the decompression cam 43 at the decompression position contacts the adjustment screw 56 to drive the exhaust rocker arm 25 and swing. A decompression operation is performed in which the exhaust valve 10 (see FIG. 1) driven by the exhaust rocker arm 25 is opened with a decompression lift amount. Thereby, the compression pressure in the combustion space escapes to the outside during the compression stroke and is reduced. In FIG. 5A, the exhaust rocker arm 25 that is in contact with the base circle portion 23a of the exhaust cam 23 is indicated by a two-dot chain line.

  When the engine rotation speed exceeds the set rotation speed, the centrifugal force generated in the centrifugal weight 41 overcomes the elastic force of the control spring 51, and the centrifugal weight 41 rotates counterclockwise in FIG. 4, as shown by the two-dot chain line in FIG. 5 (b), the rotation stops in contact with the high speed side stopper 34b and occupies the high speed side position. In the process until the centrifugal weight 41 moves from the low speed side position to the high speed side position, the decompression shaft 42 driven by the driving force of the centrifugal weight 41 and the driving force of the centrifugal weight 41 transmitted through the decompression shaft 42 The decompression cam 43 to be driven rotates integrally with the centrifugal weight 41, and the decompression main body 40 including the decompression cam 43 occupies the decompression release position shown in FIG. In this state, the exhaust rocker arm 25 is not driven by the decompression cam 43 during the compression stroke, and therefore the exhaust valve 10 is not opened.

  Further, when the internal combustion engine E stops after the engine rotational speed reaches the set rotational speed at the end of the operation of the internal combustion engine E, an operation reverse to the above is performed, and the centrifugal weight 41 is moved from the high speed side position to the low speed side position. The decompression body 40 including the decompression cam 43 occupies the decompression position.

Next, operations and effects of the embodiment configured as described above will be described.
The decompression device D of the internal combustion engine E includes a centrifugal weight 41 that is swingably supported by the cam shaft C of the valve gear 20 and a centrifugal swing that is swung by the action of a centrifugal force generated according to the rotational speed of the cam shaft C. A decompression shaft 42 and a decompression cam 43 driven by a weight 41 are provided, and the cam shaft C has a balance weight 60 that reduces rotational unbalance of the cam shaft C due to the centrifugal weight 41 occupying a high speed side position after the internal combustion engine E is started. Since the balance weight 60 reduces the rotational imbalance of the camshaft C caused by the centrifugal weight 41 of the decompression device D after the internal combustion engine E is started. Occurrence is suppressed, and the opening / closing accuracy of the intake valve 9 and the exhaust valve 10 by the intake cam 22 and the exhaust cam 23 is improved.

  The balance weight 60 is composed of a plurality of weight portions 61 to 63, 52e that are separated from each other in the axial direction of the camshaft C, so that the plurality of weight portions constituting the balance weight 60 are dispersed in the axial direction. Therefore, each of the weight portions 61 to 63, 52e is reduced in size in the radial direction, and the cam shaft C provided with the balance weight 60 is reduced in size in the radial direction.

  A pair of bearing portions 13a and 13b for rotatably supporting the camshaft C are formed integrally with the cylinder head 2 and form bearing holes 14a and 14b into which the journal portions 21c and 21d of the camshaft C are inserted. All the weight portions 61 to 63 formed integrally with the cam shaft C are disposed between the pair of journal portions 21c and 21d in the axial direction and adjacent to the exhaust cam 23 in the axial direction and the journal portion 21c or in the axial direction. The cam shaft C provided with the weight portions 61 to 63 formed integrally with the cam shaft C by being arranged between the adjacent intake cam 22 and the journal portion 21d is integrally formed with the cylinder head 2. Since it is inserted into the pair of bearing portions 13a and 13b using the bearing hole 14a and supported by the cylinder head 2, the camshaft C provided with the balance weight 60 is reduced in size in the radial direction, and further by bolts. Since it is not necessary to use a split-type bearing unit to be coupled, the bearing units 13a and 13b are downsized in the radial direction, and as a result, the cylinder head 2 and the head cover forming the cylinder head 2 or the valve operating chamber 4 in the radial direction. 3 is reduced in size in the radial direction. In addition, each of the weight portions 61 to 63 formed integrally with the cam shaft C is formed between the exhaust cam 23 and the journal portion 21c in the axial direction or between the intake cam 22 and the journal portion 21d. Therefore, the cam shaft C provided with the balance weight 60 is reduced in size in the axial direction.

  The decompression device D includes a regulation plate 52 that is provided on the camshaft C and regulates the movement of the centrifugal weight 41 in the axial direction. The regulation plate 52 has a weight portion 52e that constitutes the balance weight 60, whereby the decompression device D Since the weight portion 52e is formed by using the restriction plate 52, which is a constituent member, there is no need to provide a new member for configuring the balance weight 60. In addition, since the first to third weight portions 61 to 63, which are other weight portions than the weight portion 52e provided on the cam shaft C, can be further downsized in the radial direction, the cam shaft C or the cylinder head 2 in the radial direction can be reduced. Contributes to downsizing. Further, since the weight portion 52e has the additional weight portion 52f integrally formed with the weight portion 52e, the first to third weight portions 61 to 63 can be further reduced in size, and the weight portion 52e itself has a diameter. Can be miniaturized in the direction.

  The decompression device D is provided on the exhaust rocker arm 25 so that the position can be adjusted, and includes an adjustment screw 56 that contacts the decompression cam 43, and the lift amount for decompression of the exhaust valve 10 by the decompression cam 43 is adjusted by the position of the adjustment screw 56. By adjusting the position of the adjustment screw 56 with respect to the exhaust rocker arm 25 in the radial direction, the amount of reduction of the compression pressure can be adjusted, so that the decompression device D can be made common to different types of internal combustion engines E This contributes to cost reduction. In addition, since the adjustment screw 56 contacts the decompression cam 43, there is no need to interpose another member between the decompression cam 43 and the adjustment screw 56, so that the structure of the decompression device D including the adjustment screw 56 is simplified.

  The contact surface 56a of the adjustment screw 56 with the decompression cam 43 is positioned inward of the cam surface of the base circle portion 23a of the exhaust cam 23 in the radial direction of the cam shaft C. The position of the decompression cam 43 and the decompression shaft 42 (or the rotation center line Ld), and further the position of the swing center line Lw of the centrifugal weight 41, compared with the case where the cam surface Sa is located at the same position as the base circle 23a of the cam 23. Since the position can be arranged close to the rotation center line Lc of the camshaft C in the radial direction, the camshaft C or the cylinder head 2 in the radial direction can be downsized or the cylinder head 2 and the head cover forming the valve operating chamber 4 3 contributes to downsizing.

Hereinafter, an embodiment in which a part of the configuration of the above-described embodiment is changed will be described with respect to the changed configuration.
The internal combustion engine may be a multi-cylinder internal combustion engine having two or more cylinders. When three or more bearing portions of the cam shaft C are provided, a pair of adjacent bearing portions adjacent in the axial direction may be configured by all the bearing portions or a part of the bearing portions.
Although the plurality of weight portions 61 to 63 are all integrally formed with the cam shaft C, at least one of the weight portions 61 to 63 may be formed of a member separate from the cam shaft C.
The decompression cam may be constituted by a plunger or a pin.
In addition to the adjustment screw 56, the cam contact portion with which the decompression cam contacts may be configured by an adjustment member that can change the position of the contact surface of the cam contact portion with the decompression cam. May be configured by a member whose position cannot be adjusted, for example, a protrusion formed integrally with the exhaust rocker arm 25.

3 is a cross-sectional view of an internal combustion engine including a decompression device to which the present invention is applied, in a plane perpendicular to the rotation center line of the cam shaft, and is a schematic II line in FIG. 3 and a schematic I-- in FIG. It is sectional drawing in I line. FIG. 5 is a schematic cross-sectional view taken along the line IIa-IIa of FIG. 4 with respect to the cam shaft of the internal combustion engine of FIG. 1, and a schematic cross-sectional view taken along the line IIb-IIb of FIG. FIG. 3 is a view taken in the direction of arrow III in FIG. 1 with the head cover of the internal combustion engine removed, and a part thereof is shown in cross section. (A) is a figure of the principal part by the IVa arrow of FIG. 2, (b) is the IVb arrow arrow of FIG. 2 of a decompression main body. FIG. 2 is a diagram of a main part similar to FIG. 1 during a compression stroke, where (a) shows a state when the decompression cam is in the decompression position and the rocker arm is driven to swing, and (b) shows the decompression cam being decompressed. The state when in the release position is shown. (A) is a side view of the camshaft as seen from the arrow VIa in FIG. 2, and (b) is a side view of the camshaft as seen from the arrow VIb in FIG. The decompression body is shown.

Explanation of symbols

2 ... Cylinder head, 10 ... Exhaust valve, 13a, 13b ... Bearing part, 20 ... Valve operating device, 23 ... Exhaust cam, 25 ... Exhaust rocker arm, 40 ... Decompression body, 41 ... Centrifuge weight, 42 ... Decompression shaft, 43 ... Decompression cam, 52e ... Weight part, 56 ... Adjustment screw, 60 ... Balance weight, 61-63 ... Weight part,
E: Internal combustion engine, C: Cam shaft, Lc: Rotation center line, D: Decompression device.

Claims (6)

A valve gear including a camshaft having a valve cam for opening and closing the engine valve;
A centrifugal weight supported by the cam shaft so as to be swingable; and a decompression cam driven by the centrifugal weight that is swung by the action of a centrifugal force generated according to a rotational speed of the cam shaft, The centrifugal weight occupies a decompression position that opens the engine valve during a compression stroke to reduce the compression pressure in the combustion space when the engine occupies a low speed side position, and the centrifugal weight occupies a high speed side position after the engine starts. A decompression device occupying a decompression release position that does not open the engine valve;
An internal combustion engine comprising:
The camshaft is provided with a balance weight that reduces rotational unbalance of the camshaft due to the centrifugal weight occupying the high speed side position ,
The internal combustion engine according to claim 1, wherein the balance weight includes a plurality of weight portions that are separated from each other in the axial direction of the cam shaft . A cylinder head provided with a plurality of bearing portions that rotatably support the cam shaft is provided, and the pair of bearing portions adjacent in the axial direction are respectively integrally formed with the cylinder head and the cam shaft A bearing hole into which a journal part is inserted is formed, and at least one of the weight parts integrally formed with the cam shaft is disposed between the pair of journal parts in the axial direction. Item 6. An internal combustion engine according to Item 1. The internal combustion engine according to claim 2 , wherein the weight portion is disposed between the valve cam and the journal portion adjacent in the axial direction.   The decompression device includes a restriction member provided on the camshaft to restrict the movement of the centrifugal weight in the axial direction, and the restriction member has one of the weight portions. The internal combustion engine described.   The valve operating device includes a cam follower that is driven by the valve operating cam to open and close the engine valve, and the decompression device includes an adjustment member that is provided in the cam follower so as to be adjustable in position and abuts against the decompression cam. 2. The internal combustion engine according to claim 1, wherein an opening amount of the engine valve by the decompression cam is adjusted by a position of a member.   The valve operating device includes a cam follower that is driven by the valve operating cam to open and close the engine valve, and the decompression device includes a cam contact portion that is provided on the cam follower and contacts the decompression cam. 2. The internal combustion engine according to claim 1, wherein a contact surface of the portion with the decompression cam is located inward of a cam surface of a base circle portion of the valve cam in the radial direction of the cam shaft.

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