JPH0213122B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a single-cylinder single-overhead camshaft engine having one overhead camshaft that traverses near the upper center of a combustion chamber.

(Background of the Invention) Some engines of this type have one spark plug disposed between two exhaust valves (for example, Japanese Patent Laid-Open No. 55-43228). However, in this conventional type, both ends of the camshaft for one cylinder are supported by bearings, and the cam is formed near the center of the camshaft. For this reason, when the ignition plug is arranged so as to face near the center of the combustion chamber, there is a problem in that the cam in the center narrows the installation/removal hole for the ignition plug.
That is, since the cam diameter of the central cam is relatively large, the ignition plug attachment/removal hole must be formed to avoid interference with this cam.

As a result, the ignition plug attachment/detachment hole becomes narrow, or the attachment/detachment hole has to be tilted significantly, making it difficult to arrange the ignition part of the ignition plug in an ideal position.

Therefore, it is conceivable to provide a bearing that supports the camshaft near the upper center of the combustion chamber. However, in this case, heat from the combustion chamber is transferred to this bearing, and the temperature of the inner rocker arm closer to the bearing becomes higher than the temperature of the outer rocker arm farther from the bearing.

On the other hand, the tappets of the rocker arm are adjusted to have a predetermined tappet distance when the rocker arm is cold, taking into account deformation due to temperature changes.However, if there is a temperature difference in the rocker arm, the tappet distance is adjusted to be constant when the rocker arm is cold. Also, when warming up, the tappets become uneven,
A problem arises in that the tappet noise increases.

(Purpose of the Invention) The present invention was made in view of the above circumstances, and when a single camshaft is provided that crosses the upper part of the center of the combustion chamber, it is possible to make a relatively large spark plug attachment/removal hole close to the camshaft. This not only improves the workability of attaching and removing the spark plug, but also allows the ignition part of the spark plug to be placed in the ideal position.Furthermore, it is possible to reduce the gap between the tappets when the tappet is cold and to improve the ease of attaching and removing the spark plug. To provide a single overhead camshaft engine capable of reducing tappet noise by aligning the tappets.

(Structure of the Invention) According to the present invention, this object is achieved by providing one overhead camshaft that crosses near the upper part of the center of the combustion chamber, two intake valves located on one side of the camshaft, and two intake valves located on the other side. In a single overhead camshaft engine equipped with two exhaust valves, four rocker arms that open and close these intake and exhaust valves, and a spark plug whose ignition part faces near the center of the combustion chamber, the camshaft is positioned above the center of the combustion chamber. The camshaft is provided with one intake valve cam and one exhaust valve cam on each side of the bearing, and the camshaft is driven by two outer cams farther from the bearing. This is achieved by a single overhead camshaft engine characterized in that the two outer rocker arms are longer than the inner rocker arms, and the spark plug is disposed between these two longer rocker arms.

(Embodiment) Fig. 1 is a partially sectional side view of an embodiment of the present invention applied to a motorcycle, Fig. 2 is a central vertical sectional view showing the main parts of the engine, and Fig. 3 is the same as Fig. 2. FIG. 4 is a plan view showing the valve operating mechanism with the cylinder head cover removed, and FIG. 4 is a partially sectional plan view of the cylinder head cover to show how each rocker arm is attached.

In FIG. 1, numeral 10 is the main frame, 1
2 is a front fork supporting the front wheel 14; 16;
is the rear wheel. 18 is 4 valves 1 overhead camshaft type 1
The engine is a cylinder engine and is mounted on a main frame 10 so that its intake passage 20 and exhaust passage 22 point toward the rear of the vehicle body and toward the front of the vehicle body, respectively. 24 is a carburetor that supplies air-fuel mixture to the intake passage 20; 26 is an exhaust pipe;
6 is bent so as to guide the exhaust gas discharged from the exhaust passage 22 from the front of the engine 10 to the rear through the lower part of the engine 10.

28 is a crankcase, 30 is a cylinder, 32
34 is a cylinder head, and 34 is a cylinder head cover (hereinafter referred to as a head cover). A camshaft 36 is laterally supported between the joint surfaces of the cylinder head 32 and the head cover 34, and a sprocket 38 fixed to one end of the camshaft 36 is connected to the crankshaft 4.
The timing chain 42 that runs between
The crankshaft 40 is rotated at half the speed of the crankshaft 40. This camshaft 36 crosses the vicinity above the center of the combustion chamber 44 .

Two intake ports 46, 46 (FIGS. 2 and 3) that open into the combustion chamber 44 and two exhaust ports 48, 48 are formed in the cylinder head 32, and each intake port 46,
46 communicates with the two intake passages 20, 20, and each exhaust port 48, 48 communicates with the two exhaust passages 22, 22. In this embodiment, two exhaust pipes 26 (only one of which is shown in FIG. 1) are provided, and exhaust gas from each exhaust passage 22, 22 is separately discharged through these two exhaust pipes 26. .

Reference numerals 50 and 50 indicate intake valves, and as is clear from FIG. The ports 46, 46 are biased closed. In FIG. 3, reference numerals 58, 58 indicate the axes of the intake valves 50, 50, and as is clear from this figure, the axes 58, 58 are perpendicular to the camshaft 36.

Reference numerals 60 and 60 are exhaust valves, and as is clear from FIG. The exhaust ports 48, 48 are biased to close. 68,6 in Figure 3
Reference numeral 8 indicates the axes of the exhaust valves 60, 60, and as is clear from this figure, the exhaust valves 60, 60 are supported such that their upper portions are gradually separated from each other.

The cylinder head 32 has each valve 50, 50, 60,
After assembling 60 and each valve spring 54, 54, 64, 64, it is fixed to the cylinder 30 (FIG. 1) by four bottles 70 shown in FIG.

As shown in FIG. 3, the camshaft 36 is formed with two intake-side cams 72, 72 located on the inside and two exhaust-side cams 74, 74 located on the outside. and 74 are close to each other, while the inner cams 72 and 72 are spaced apart. The camshaft 36 is pivotally supported at both ends and the center by three slide bearings 76, 78, and 80 formed between the joint surfaces of the cylinder head 32 and the head cover 34. That is, the inner cam 72,
72 is pivotally supported by a central bearing 80 located above the center of the combustion chamber 44. The bearing surface of this bearing 80 has a diameter smaller than the maximum diameter of each cam 72, 74, and in this embodiment, the diameter is even smaller than the minimum diameter portion of each cam 72, 74. This camshaft 36
At one end (upper side in Fig. 3) is the sprocket 3.
8 is fixed, and a rotational speed detection gear mechanism (not shown) is connected to the other end (lower side in FIG. 3). Cylinder head 32 and head cover 34
As shown in FIGS. 2 and 3, a cooling air passage 82 is formed therein. That is, a vertically elongated gap is formed between the exhaust valves 60, 60 that opens forward and upward of the engine 18, and in this embodiment, this gap extends from below the central bearing 80 to between the intake valves 50, 50. It opens rearward through. The cooling air passage 82 has a substantially cylindrical space between the two exhaust valves 60 and 60 near the bearing 80, and this space serves as a spark plug attachment/removal hole 84. That is, the wall forming the attachment/detachment hole 84 is integrated with the bearing 80. In FIGS. 2 and 3, reference numeral 86 denotes an ignition plug disposed close to the bearing 80, and the ignition portion of the ignition plug 86 is located near the center of the combustion chamber 44.

Since the bearing surface of the bearing 80 has a smaller diameter than the maximum diameter of the cams 72 and 74, the spark plug 86 is even closer to the cam shaft 36.
It can be placed close to the In other words, if there is a cam near the center of the camshaft 36, that is, above the center of the combustion chamber 44, the wall of the valve chamber that houses the valve mechanism (this wall is the ignition plug It is necessary to provide a hole (which also serves as the attachment/detachment hole 84),
While this wall is far from the center of the camshaft 36, according to the present application there is no cam at this position and the bearing 8
0, and its bearing surface has a diameter smaller than the maximum diameter of the cams 72 and 74, so that the wall of the valve chamber can be brought closer to the center of the camshaft 36. Therefore, the ignition plug 86 can be disposed at an angle closest to vertical without greatly tilting the engine while keeping the overall height of the engine low, which is a preferable position for obtaining good combustion.

The cylinder head 32 and head cover 34 are provided with auxiliary ribs 88 and 90 on the cooling air inflow side. In particular, the rib 88 of the cylinder head 32
An oil passage 922 (FIG. 2) is formed inside, and this oil passage 92 supplies lubricating oil after lubricating the exhaust valve 60 located below in FIG. 3 to the exhaust valve 60 located above in the figure. The sprocket 38 is guided through the loading chamber of the valve spring 64 into the sprocket receiving chamber 94 (FIG. 3). On the other hand, since both exhaust valves 60, 60 are expanded so that their upper parts are separated from each other, a large area can be secured on the inflow side of the cooling air passage 80 and the ignition plug attachment/detachment hole 84, and the cooling performance and attachment/detachment of the ignition plug 86 are improved. Improve further.

Note that the cylinder head 32 and head cover 3
The wall of the spark plug attachment/removal hole 84 formed in the cylinder head 4 functions as a kind of pillar, and since the bearing 80 is formed integrally with this wall, the rigidity of the cylinder head 32 and the head cover 34 is also improved.

As shown in FIG.
It is fixed at 2. That is, bearings 76, 78 are connected to bolts 96, 96, 98, 98, and central bearing 8 is connected to bolts 96, 96, 98, 98.
0 is tightened with three bolts 100, and the outer periphery of the joint surface is further tightened with a large number of bolts 102, respectively.

Reference numerals 104 and 104 designate inner rocker arms that slide and swing from above on the inner cams 72 and 72, respectively. The inner rocker arms 104, 104 are pivotally supported by a rocker arm shaft 106 inserted into the inner surface of the head cover 34 so as to be parallel to the cam shaft 36 (FIG. 4). This Rotsuka arm 104,
104, each one arm 108, 108 is the inner cam 7
2,72 sliding contact from above, local arm 110,1
10 presses the shaft end of each intake valve 50, 50. In FIG. 4, reference numeral 112 denotes a positioning bolt screwed into the head cover 34 from the inner surface so as to pass through the rocker arm shaft 106. That is, two bolts 98, 100 of the large number of bolts 96 to 102 are attached to this rocker arm shaft 106.
(Fig. 4) Recesses 114, 114
are formed, and in order to fix the positions of these recesses 114, 114 and make it easier to insert the bolts 98, 100 when attaching the head cover 34 to the cylinder head 32, a positioning bolt 112 is required. .

Reference numerals 116 and 116 designate outer rocker arms that slide into contact with the outer cams 74 and 74 from above. These rocker arms 116, 116 are longer than the inner rocker arm 104, and are pivotally supported by two rocker arm shafts 118, 118 held by the head cover 34 so as to be parallel to the cam shaft. This rocker arm 116, 116 has one arm 120, 1
20 slides into contact with the outer cams 74, 74 from above,
The other arm 122, 122 is connected to each of the exhaust valves 60, 6.
Press the shaft end of 0. Note that 124 and 124 are positioning bolts that pass through each rocker arm shaft 118 and 118, and 126 and 126 are recessed portions to avoid interference with the bolt 100. Note that the camshaft 3
6 is disposed at a position lower than each rocker arm shaft 106, 118. In this embodiment, the rocker arms 116, 116 on the exhaust side are not only disposed on the outside with respect to the combustion chamber 44, but also the outer rocker arms 116, 116 are disposed outside the arms 120, 120 as shown in FIGS. Arms 122, 12 on the side
2, the distance between the two rocker arm shafts 118, 118 can be increased, and as a result, the ignition plug attachment/removal hole 84 can be sufficiently enlarged. Here is the exhaust valve 60,
As described above, the point where the upper part of the 60 is inclined so that the interval gradually widens also makes the ignition plug attachment/removal hole 8
Of course, it is contributing to the expansion of 4.

The rocker arm 104,1 is attached to the head cover 34.
04, 116, 116, Rocker arm shaft 106,
118, 118 are assembled in advance, and each recess 1 is further assembled with positioning bolts 112, 124, 124
14, 126, and 126 are positioned as shown in FIG. 4, they are mounted on the cylinder head 32 and tightened with the respective bolts 96 to 102.

During operation of the engine 18, the camshaft 26 rotates, and the cams 72, 72, 74, 74 swing the rocker arms 104, 104, 116, 116 to move the intake valves 50, 50 and exhaust valves 60, 60 to predetermined positions. Opens and closes according to intake and exhaust timing. While the vehicle is running, running air flows into the cooling air passage 82 formed between the exhaust valves 60, 60, and particularly sufficiently cools the area around the threaded portion of the ignition plug 86. A portion of the cooling air flows out to the rear of the engine 18 through the space between the intake valves 50 and 50, and another portion flows out to the upper side of the engine 18 through the ignition plug attachment/removal hole 84.

According to the above embodiment, since the upper portions of both exhaust valves are widened, the ignition plug attachment/removal hole can be made even larger.

(Effects of the Invention) As described above, the present invention provides a cam when two intake and exhaust valves are driven to open and close via rocker arms by one overhead camshaft that crosses the upper part of the center of the combustion chamber. Since a bearing is provided near the center of the shaft without providing a cam, the diameter of this bearing can also be reduced by making the diameter of this bearing surface of the camshaft smaller than the maximum diameter of the cam. Therefore, the ignition plug disposed between the outer rocker arms at a position far from the bearing can be brought closer to the camshaft. In other words, it is possible to ensure a large mounting/removal hole for the ignition plug and to place the ignition part at an ideal position near the center of the combustion chamber.

Furthermore, in this case, the inner rocker arm located closer to the center of the combustion chamber receives heat from the combustion chamber through the central bearing, and tends to reach a higher temperature than the outer rocker arm. For this reason, the temperature change range between cold and warm up is larger for the inner rocker arm, but since the inner rocker arm is shorter than the outer rocker arm, its deformation can be made equal to the deformation of the outer rocker arm. . That is, if the temperature is the same, the amount of deformation of the larger outer rocker arm is greater, but the outer rocker arm has a smaller temperature change range. Therefore, it is possible to equalize the distance between the tappets of each rocker arm and reduce tappet noise.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view of a motorcycle to which an embodiment of the present invention is applied, FIG. 2 is a central longitudinal sectional side view of the main parts thereof, and FIG. 3 is a plan view showing the state in which the head cover is removed in FIG. 2. FIG. 4 is a partially sectional plan view of the head cover. 18...Engine, 36...Camshaft, 50...
Intake valve, 60... Exhaust valve, 72, 74... Cam,
76, 78...Bearing, 80...Central bearing, 82
...Cooling air passage, 84...Ignition plug attachment/removal hole, 86...
...Spark plug, 104...Inner lock arm, 116
...Outer rotuka arm.

Claims (1)

[Scope of Claims] 1. One overhead camshaft that crosses near the upper part of the center of the combustion chamber, two intake valves located on one side of the camshaft, two exhaust valves located on the other side, and these intake valves.・Four lock arms that open and close the exhaust valve,
In a single overhead camshaft engine equipped with a spark plug whose ignition part faces near the center of the combustion chamber, the camshaft is provided with a bearing that supports the camshaft near the top of the center of the combustion chamber, and the camshaft is provided with a bearing that supports each of the camshafts with the bearing in between. One intake valve cam and one exhaust valve cam on each side.
Two outer rocker arms driven by two outer cams farther from the bearing are longer than the inner rocker arm, and the spark plug is disposed between these two longer rocker arms. 1 Overhead camshaft engine. 2. The two exhaust valve cams are both located far from the bearing, the exhaust side rocker arm located on the outside is made longer than the intake side rocker arm, and the spark plug is disposed between the two exhaust side rocker arms. A single overhead camshaft engine according to claim 1.