JPH11166449A - Four-cycle engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a four-cycle engine of four-valve SOHC type which is constituted in a multi-cylinder structure and whose part operating together with the valves is light. SOLUTION: In a four-valve SOHC engine comprising two or more cylinders, a) an ignition plug 50 is installed in such an arrangement that an electrode 51 protrudes to the center of the upper part in a combustion chamber 5 and a core passes between a cam shaft 11 and two exhaust valves 42, b) rocker arm 22/23 for an exhaust valve 42 is installed on each side of the ignition plug 50 and they are contacted with cams 13 and 14 for the exhaust valve 42, while a rocker arm 21 for a suction valve 41 is contacted with a cam 12 for suction valve 41 formed between the cams 13 and 14 for the exhaust valve 42, and c) a shim 47 is installed between the rocker arms 21, 22, 23 and valves 41 and 42 for adjustment of the valve clearance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-valve, SOHC, multi-cylinder, four-stroke engine suitable for use in motorcycles and the like.

[0002]

2. Description of the Related Art A four-valve four-stroke engine having four valves per cylinder has a small inertial weight of each valve and a large total opening area of the valves to increase the intake and exhaust efficiency. For this reason, in recent years, the engine is often mounted on a motorcycle or the like as a high-output engine. When using a four-valve model, the DOHC that makes it easy to simultaneously set the valve mechanism and the combustion chamber in the direction of high-speed rotation
Although a type (double overhead camshaft; two camshafts for driving a valve on a cylinder head) are often used, the cost-effective SO
An HC type (having only one camshaft on the cylinder head) is often used.

FIG. 8 shows a valve and a valve train 10 'of a conventional four-valve SOHC type four-cycle engine.
FIG. 1 is a perspective view showing an outline of the present invention, which is described in Japanese Patent Publication No. 8-33144. Cylinder head (not shown)
There is one camshaft 11 'above the camshaft 11', and cams 12 'and 13' provided on the camshaft 11 'drive two intake valves 41' and two exhaust valves 42 'on both sides. These four valves 41 'and 42' are arranged obliquely from the left and right (that is, the intake side and the exhaust side) as shown in the figure, and cover the upper part of the combustion chamber (not shown) at the lower end, and provide intake and exhaust gas. Each port (not shown) is opened and closed. The ignition plug 50 'has its upper end directed toward the end of the camshaft 11' (that is, toward the front of the drawing), and a core (insulating) between the left and right intake valves 41 'and exhaust valves 42'. The electrode at the lower end is mounted so as to be located at the center of the upper part of the combustion chamber while the insulator and the terminal pass through the portion (the portion where the insulator and the terminal extend axially) 52 '.

[0004]

Since a four-cycle engine as shown in FIG. 8 is of a four-valve SOHC type, it is likely to be configured as a low-cost one that exhibits high output as described above. However, the following problems still exist in the four-cycle engine as shown in the figure.
8) Although the engine of FIG. 8 may be a single cylinder engine, when the spark plug 50 'is arranged as shown in the figure, a multi-cylinder engine, that is, a four-cycle engine having two or more cylinders is constituted. Not easy to do. If the illustrated engine is a multi-cylinder engine, a new cylinder will be provided on the near side or the far side of the drawing adjacent to the cylinder (not shown) below the spark plug 50 '. This is because even if it is provided on the side, the ignition plug 50 'and the like cannot be properly arranged. When a cylinder is added to the front side of the drawing, the space for mounting the currently illustrated spark plug 50 'cannot be secured due to the valve operating mechanism on the new cylinder. On the other hand, when a cylinder is added on the back side of the drawing, it is difficult to provide a spark plug on the new cylinder. Illustrated spark plug 50 '
When the upper end is directed toward the front of the drawing in the same manner as above, there is not enough space for mounting a new spark plug because of the valve operating mechanism shown, and conversely, the upper end is directed toward the back of the drawing. Then, it is difficult to secure the location of the ignition plug in relation to the power transmission mechanism (transmission chain and gears, not shown) between the crankshaft and the camshaft, which should be on that side. Even if it is a 4-valve SOHC type engine, if the number of cylinders cannot be increased to two or more, it is difficult to make a high-power engine with smooth rotation.

B) Among the operating parts of the valve train 10 ',
There is still a mass that can be reduced. That is, the rocker arm 2 in contact with the upper end of each valve 41 ', 42'
An adjusting screw 47 'is provided at the tip of 1' / 22 'for adjusting the valve clearance, which is not preferable. Adjustment screw 47 'is a part not involved in the adjustment of the valve clearance (a part protruding upward)
And a nut 48 'for preventing loosening is attached, so that it has a considerable mass. Due to this point, when the mass of the tip of the rocker arms 21 ′ and 22 ′ is large, similar to the case where the mass of the valves 41 ′ and 42 ′ is large,
This is disadvantageous in terms of mechanical loss and noise.

The present invention has been made in view of the above points, and is a four-valve / SOHC type four-cycle type four-cycle SOHC engine having a multi-cylinder structure, capable of smoothly rotating, and having a small mass operating together with the valve. It does not provide an engine.

[0007]

According to a first aspect of the present invention, there is provided a four-stroke engine, wherein one camshaft on a cylinder head drives two intake and exhaust valves per cylinder on both sides thereof. In a four-stroke cylinder engine (ie, a four-valve SOHC engine with two or more cylinders), a) a spark plug is used to protrude the electrode into the center of the upper part of the combustion chamber and the core (that is, the insulator and the terminal) is a camshaft. And b) rocker arms for the exhaust valves, one on each side of the spark plug (ie, a total of two per cylinder), each with a rocker arm for the exhaust valve. (A cam portion formed on the cam shaft), and a rocker arm for the intake valve is formed between the cams for the exhaust valve. Is brought into contact with a cam for gas valve, between c) rocker arm and the valve, shims were attached to the adjustment of the valve clearance - and wherein the.

The four-cycle engine according to the first aspect is a so-called four-valve SOHC engine. As described above, there are two intake / exhaust valves per cylinder, and each valve has a small inertial weight and intake / exhaust. Since the efficiency can be increased, a high output can be efficiently exhibited. Since the SOHC, that is, the type having only one camshaft, is advantageous in terms of cost as compared with the DOHC type.

In particular, in this four-stroke engine, it is easy to increase the number of cylinders, that is, to increase the number of cylinders to two or more, and in that case, it is not difficult to attach / detach a spark plug. This is because the core body of the spark plug is arranged not to pass between the intake valve and the exhaust valve as shown in FIG. 8 but to pass between the camshaft and the two exhaust valves as described in a) above. Since the space between two exhaust valves provided in a multi-cylinder engine is a portion located in a direction perpendicular (or substantially perpendicular) to the direction in which the cylinders are arranged, a multi-cylinder engine requires more than a spark plug. The arrangement of the spark plug does not make space difficult in the cylinder. Since the electrode at the tip of the spark plug protrudes toward the upper center of the combustion chamber, flame propagation is excellent and knocking does not easily occur even if the number of spark plugs is not plural.

[0010] In determining the mounting position of the spark plug, as described in a) above, it is necessary not only to avoid contact with the camshaft and the exhaust valve, but also to use the spark plug and the intake valve.
It is also necessary to consider the positional relationship with each rocker arm for the exhaust valve. In this regard, in this four-cycle engine, the respective rocker arms are arranged as described in b) above, and the positional relationship with the spark plug and the like is made appropriate to ensure smooth mutual operation. That is, first, rocker arms for the exhaust valves are arranged one by one on both sides of the ignition plug so as to provide an ignition plug between the two exhaust valves and the camshaft. Similarly, two cams for driving the rocker arm for the exhaust valve are formed on the camshaft so as to be separated from each other. Therefore, the spark plug is appropriately arranged between the rocker arm and the cam. On the other hand, as for the intake valve rocker arm on the opposite side of the camshaft, a cam for driving the intake valve rocker arm is formed between the two exhaust valve cams spaced apart as described above. As a result, the cam for the intake valve and the cam for the exhaust valve are formed on the cam shaft in a well-divided manner, and the rocker arm for each valve also operates smoothly at a position away from the intake side and the exhaust side. Will be.

[0011] Further, in this four-cycle engine,
Adjust the valve clearance with the shim to be mounted as in c). That is, by selecting a shim having an appropriate thickness from several types of shims having different thicknesses and mounting the shim between the rocker arm and the valve, the valve clearance is made appropriate. Since the thickness of the shim is involved in the adjustment of the valve clearance and does not include a useless portion and does not require the attachment of a nut, the shim has a larger mass than the adjusting screw 47 'shown in FIG. Is much smaller. Since the mass of the valve and the mass of the tip of the rocker arm are thereby reduced, mechanical loss can be reduced and noise can be reduced by making the valve spring soft.

It is also possible to arrange the core of the ignition plug so as to pass between the camshaft and the two intake valves. In this case, by replacing "exhaust valve" with "intake valve" and reading "intake valve" with "exhaust valve" in the above a) and b), a four-stroke engine having the same function can be configured. .

[0013] In the four-stroke engine according to the second aspect of the present invention, d) each rocker arm for the exhaust valve has an arm portion in contact with the cam for the exhaust valve and an arm portion in contact with the exhaust valve in one plane. E) a rocker arm for the intake valve, one (common) arm portion in contact with the cam for the intake valve, and a bifurcated arm extending from both sides to contact the two intake valves. It is formed integrally with the arm part of the book.

In this four-stroke engine, each rocker arm can be simplified and lightened. In other words, the rocker arm for the exhaust valve is
Since it has a planar shape as shown in d), it is obviously easy to construct and light. The rocker arm for the intake valve, as described in e) above, has one arm part in contact with the cam and two arm parts that branch off to both sides and extend so as to be in contact with the two intake valves. It is a thing. According to b), the cam for the intake valve can be integrally formed between the two cams for the exhaust valve, so that only one arm portion of the rocker arm for the intake valve is in contact with the cam. is there. Since the rocker arms for the two intake valves are made into one part, the number of parts is small, and the configuration is simple by that much. Moreover, since the two arm portions on the side in contact with the intake valve are branched to both sides from the one arm portion on the cam, it can be said that the rocker arm does not have a particularly complicated shape and is not unnecessarily large. Since the two arm portions on the valve side with respect to the one arm portion are formed not on only one side but on both sides, the dimension in the direction along the rocker shaft for support is determined by the distance between the intake valves. This is because it can be suppressed to the extent. All rocker arms are excellent in motion characteristics if they are lightweight, so that the performance of the engine in a high-speed range can be improved. When the spark plug core is arranged on the intake valve side in the above a), the "exhaust valve" in the above d) and e) is read as "intake valve", and the "intake valve" is replaced with the "exhaust valve". Can be configured as a four-stroke engine having a similar function.

The four-stroke engine according to claim 3 is characterized in that: f) the rocker arms for the intake valve and the exhaust valve are arranged so as to be slidable along a rocker shaft for supporting the same. And

In this four-stroke engine, adjustment of the valve clearance, that is, the operation of exchanging the shim c) mounted between the rocker arm and the valve can be easily performed. This is because, based on the configuration of the above f), by sliding each rocker arm to a position away from each valve, the shim is easily exchanged. It is of course possible to replace the shim after removing the rocker arm or rocker shaft from the cylinder head, but it is time-consuming to remove (and re-attach) such a part, so this engine according to claim 3 The benefits are great. In order to arrange the rocker arm so that it can slide along the rocker shaft, the two are fitted together with a clearance fit, and the position of the rocker arm on the rocker shaft can be moved by means such as set screws or springs. It is good to fix to.

The four-stroke engine according to claim 4 is further characterized in that: g) a plug hole formed by a pipe is closely assembled between the cylinder head and the cylinder head cover.

In this four-cycle engine, the manufacture of the cylinder head cover is easy. Above the cylinder head in the four-cycle engine, there is a valve operating mechanism including a camshaft, a rocker arm, intake / exhaust valves, and the like, and a cylinder head cover is generally attached to cover them. However, the spark plug, which is also mounted on the cylinder head, must allow the electrode at its tip to protrude into the lower combustion chamber while being removable from the outside. Therefore, when the spark plug is mounted on the top of the cylinder head, the cylinder head cover must have a shape that covers the valve mechanism but does not confine the spark plug alone. It is formed in part and separates the valve operating mechanism and the spark plug by the hole. In this four-cycle engine, the manufacture of the cylinder head cover including such plug holes is easy.

The reason why the cylinder head cover can be easily manufactured with this engine is that the plug hole is formed by a pipe separately from the other parts of the cover as described in g) above. In that case, the shape of the cover (excluding the plug hole) becomes extremely simple, and it is easy to form the hole with a pipe, and it is not difficult to tightly assemble both. The manufacture of the head cover becomes extremely easy. In this engine, since the spark plug is disposed so as to pass between the camshaft and the exhaust valve as described in a), the hole is inclined with respect to the axis of the cylinder. If it is to be integrally molded, the construction of the mold and the core becomes extremely complicated, and its production should not be easy. Considering that point, the merit of the engine of claim 4 is great.

[0020]

1 to 7 show an embodiment of the present invention. FIG. 1 shows a 4-valve SO for a motorcycle.
FIG. 2 is a longitudinal sectional view showing a cylinder head 3, a valve mechanism 10, and the like for an HC type two-cylinder four-cycle engine.
FIG. 2 is a plan view showing the valve train 10 of the engine, and is a II-II sectional view in FIG. FIG. 3 is a drawing of the same engine when the rocker arms 21, 22, 23 and the like are viewed from below, and is a view taken along the line III-III in FIG. FIG. 4 is a view taken in the direction of arrows IV-IV in FIG.
42, excluding the spark plug 50, etc.). FIGS. 3 and 4 are drawn in such a direction that the lower part of FIG. 3 overlaps the upper part of FIG. FIGS. 5 and 6 are cross-sectional views of the components and the like in FIGS. 3 and 4 which are superimposed as described above, taken along line V-V in FIGS. 3 and 4.
FIG. 6 is a cross-sectional view as viewed in FIG. And FIG.
4 is a graph showing the torque acting on the camshaft 11 in the engine of FIG. In addition,
FIGS. 1, 2, 5, and 6 show the first cylinder of the two-cylinder engine. The other second cylinder is shown in FIG. 3 and FIG. 4 with the same reference numeral as the same part in the first cylinder (however, “A” is added at the end), and the description is omitted below.

The schematic structure of this engine will be described below with reference to FIG. First, a cylinder head 3 is mounted on an upper portion of a cylinder 1 having a piston 2 therein.
A combustion chamber 5 and an exhaust port 6 are formed. The head 3 is provided with two intake valves 41 and two exhaust valves 42 for each cylinder, and the inlets of the intake port 4 and the exhaust port 6, which are also two each, are opened and closed by them. The upper portions of the valves 41 and 42 protrude above the cylinder head 3 through the mounting holes 45 and 46, respectively.
Is receiving force in the closing direction (upward). An ignition plug 50 is further attached to the cylinder head 3, and an electrode 51 at the tip of the ignition plug 50 projects into the upper center of the combustion chamber 5.

A valve mechanism 10 for driving the above-described valves 41 and 42 is disposed above the cylinder head 3. Referring to FIG. 1, the outline is as follows.
The camshaft 11 is bridged so as to pass right above both of the two cylinders (see FIG. 4), and the rocker arms 21, 22. 23 are attached. Cam bracket 31 as a part for supporting rocker shafts 24 and 25
Is mounted on the cylinder head 3 and the camshaft 11 is
It is rotatably supported by a bearing formed between the cam bracket 31 and the cylinder head 3.
When rocked by the cam 12, the rocker arm 21 pivotally mounted via the rocker shaft 24 pushes down (ie, opens) the intake valve 41 against the force of the coil spring 43. On the other hand, rocker shaft 25
Arm 22.2 arranged to be swingable through the
3 is swung by the cams 13 and 14 and pushes down and opens the exhaust valve 42 against the force of the coil spring 44.
These valve operating mechanisms 10 are covered by a cylinder head cover 8 that covers the upper part of the cylinder head 3.

This engine is configured so that the number of cylinders is increased and the output characteristics are improved. In connection with this, the following configuration is employed.

1) As described above, with respect to the ignition plug 50 in which the electrode 51 is projected to the upper center of the combustion chamber 5, as shown in FIGS. 1, 4 and 6, the core 52 and the plug hole 55 surrounding the core 52. With the camshaft 11 and the two exhaust valves 4
2 were arranged in a direction passing therethrough. That is, as shown in FIG. 4, the ignition plug 50 is inserted between the mounting holes 46 for the exhaust valve 42.
6, and the core 52 of the plug 50 is inclined to avoid contact with the camshaft 11 as shown in FIG. In a first cylinder of this engine having two cylinders, a second cylinder is provided on the left side as shown in FIG. 4 and a power transmission mechanism to the camshaft 11 (a driving force of a crankshaft (not shown) is transmitted to the camshaft 11 on the right side). 8, the core body 52 of the plug 50 cannot be directed toward the end of the camshaft 11 unlike the example of FIG. However, the direction of the exhaust valve 42 is a direction perpendicular to the arrangement direction between the cylinders, and furthermore, it is forward in a general motorcycle engine. Therefore, by inclining the core 52 and the like in the direction as described in 1) above, The ignition plug 50 can be arranged regardless of the number of cylinders. There may be no other members in the vicinity of the spark plug 50, so that maintenance can be performed smoothly.

2) Connect the ignition plug 50 to the two exhaust valves 4
2 and the rocker arm 21
・ 22 and 23 were configured and arranged as shown in FIG. First, as the rocker arms 22 and 23 for exhaust, linear ones (as viewed from above, which are I-shaped as shown in FIG. 2) are arranged one by one on both sides of the spark plug 50. I have. For the rocker arm 21 for intake, the camshaft 11
The arm part on the side in contact with
A shape extending in the middle of 23 and the other arm portion extending over the two intake valves 41, that is, a so-called Y-shaped shape (see FIG. 3) (one that can drive the two intake valves 41 integrally) Are arranged. And the camshaft 11
The cams 13 and 14 which contact the arm portions of the rocker arms 22 and 23 and the cam 12 which contacts the arm portion of the rocker arm 21 are formed between them. With such a configuration, the exhaust rocker arms 22 and 23 are provided so as to be in contact with the cams 13 and 14 on both sides of the spark plug 50, and the intake rocker arm 21 is provided between them so as to be in contact with the cam 12. Each rocker arm 21
22 and 23 and the valves 41 and 42 can function smoothly.

3) In order to adjust the valve clearance, as shown in FIG. 5, the distal ends of the rocker arms 21, 22 and 23 (the distal ends opposite to the side in contact with the cams 12, 13 and 14) and the intake air A shim 47 was mounted between the upper ends of the exhaust valves 41 and 42. A plurality of types of shims 47 having different thicknesses are prepared, an appropriate thickness is selected from the shims 47, and the shims 47 are exchangeably mounted in concave portions provided at the upper end portions of the respective valves 41 and 42 to thereby provide a valve clearance. To adjust. Compared with the adjusting screw 47 'used in the example of FIG. 8 for the same adjustment, the shim 47 is considerably small, and is extremely lightweight because it does not need to include a nut 48' or the like. Therefore, it is suitable for high-speed rotation of the engine.

4) Each rocker arm 21 shown in FIG.
22 and 23 are provided with rocker shafts 24.2 for supporting them.
5 and a rocker arm 21, 22, 23 on each rocker shaft 24, 25 so as to be slidable in the axial direction by fitting a gap to the rocker arm 5, and a cam bracket. The coil springs 26, 27, and 28 were compressed and mounted between them. That is, the rocker arm 21 slidable on the shaft 24 is kept in a proper position for operation by being pressed against a part of the cam bracket 31 by the spring 26 as shown in FIG. For the arms 22 and 23, the springs 27 and 28 respectively control the central support portions 36 of the cam bracket 31.
Keep in place for driving by pressing against. The reason for arranging the rocker arms 21, 22, and 23 in this manner is to simplify the adjustment of the valve clearance described above. That is, by adopting such a configuration, when the shim 47 (FIG. 5) is replaced, the rocker arms 21, 22, and 23 are connected to the springs 26, 27, respectively.
This can be done by sliding the rocker shafts 24 and 25 along the rocker shafts 24 and 25 away from the valves 41 and 42 against the rocker arms 21 and 22.
It is no longer necessary to remove 23 and move it upward.

5) As shown in FIG. 6, the core 5 of the spark plug 50
The plug hole 55 surrounding the cylinder head 2 is formed by a cylindrical aluminum pipe, and is closely assembled between the cylinder head 3 and the cylinder head cover 8. The cylinder head cover 8 covers the valve operating mechanism 10 that is an operating part and also uses a lubricating oil so as to isolate the valve operating mechanism 10 from the outside. The plug hole 55 exposes the spark plug 50 that requires maintenance and replacement to the outside. And the plug 50
And the valve mechanism 10. It is preferable that the cylinder head cover 8 and the plug hole 55 can be integrally formed because the number of parts can be reduced. However, in this engine, since the ignition plug 50 is arranged to be inclined from the cylinder axis as described above, the two are integrally formed by casting. It is extremely difficult to mold due to the configuration of the mold. Therefore, as described above, the plug hole 55 is formed separately from the cylinder head cover 8 by a pipe to facilitate the manufacture. The plug hole 55 thus formed is connected to the cylinder head cover 8 as shown in FIG. 6, and the connection between the plug hole 55 and the cylinder head 3 is also made when the cylinder head cover 8 is put on the cylinder head 3. I decided that. As shown in the figure, a seal member 5 is provided between the plug hole 55 and the cylinder head cover 8 and between the plug hole 55 and the cylinder head 3.
The lubricating oil used for the valve train 10 does not enter the plug hole 55 because the 6.57 is mounted.

6) In this engine having two cylinders, the phase difference of the crankshaft (not shown) between the cylinders is set to 36.
By setting it to 0 °, the fluctuation of the cam driving torque is reduced. The fact that the phase difference of the crankshaft is 360 ° means that the difference in the explosion timing between the cylinders is 360 ° in terms of the rotation angle difference of the crankshaft.
It means that both cylinders move up and down in the same phase. The reason why the fluctuation of the driving torque of the cam is reduced in such an engine can be explained as follows with reference to FIG. That is, FIG. 7 shows that the load torque (vertical axis) required to rotate the camshaft 11 (FIG. 1) is the rotation angle of the crankshaft (horizontal axis).
It is a figure showing how it changes with time. Intake ・
In each exhaust stroke, the positive load torque (crank) as shown in FIG. 7 is determined by the relationship between the shapes of the cams 12, 13, and 14 of the valve mechanism 10 and the springs 43 and 44 of the valves 41 and 42 shown in FIG. The output of the shaft drives the camshaft 11) and the negative load torque (torque when the camshaft 11 is turned from the valve mechanism 10) acts continuously. As a characteristic of the four-stroke engine, there is a phase difference of about 180 ° between the exhaust and intake in the same cylinder. In this engine in which the phase difference of the crankshaft is set to 360 °, the intake air in the first cylinder (“No. 1” in FIG.
360 ° between the intake air in the cylinder ("No. 2" in the figure)
There is also a phase difference of 360 ° between the exhaust in the first cylinder and the exhaust in the second cylinder. Therefore, in the two-cylinder SOHC four-cycle engine in which the phase difference of the crankshaft between the cylinders is set to 360 °, the positive load torque and the negative load torque simultaneously act on the camshaft 11 as shown in the figure. And the two act simultaneously in an angle range where the absolute value of the torque is large. At the same time, the positive and negative
Since the negative load torques cancel each other out on the shaft, the camshaft 1
Thus, the fluctuation of the torque occurring in No. 1 is reduced.

7) As shown in FIG. 1 and FIG.
As shown in FIG. 6, a notch (not shown) is provided in a part of the rocker shaft 25 in relation to the fact that the zero core 52 and the like are provided between the camshaft 11 and the two exhaust valves 42 ((1) above). (A thinned portion) 25a and the notch 25a
Near the center support portion 36 of the cam bracket 31.
I decided to support it. First, rocker shaft 2
5 is formed with a cutout portion 25a in FIG.
-As can be seen from FIG. 6 and the like, the camshaft 11 and the exhaust valve 4
This is because it is difficult to provide the spark plug 50 between the two valves 41 and 42 and the camshaft 11 while arranging the rocker shaft 25 as close as possible to the middle between the two. That is, in order to avoid contact with the valves 41 and 42, the plug holes 55
When the plug hole 55 is arranged slightly above, the plug hole 55 comes very close to the rocker shaft 25, so that the rocker shaft 25 and the plug hole 55 come into contact with each other unless the cutout portion 25a is partially formed. If the rocker shaft 25 is moved closer to the camshaft 11, the notch 25a may be unnecessary, but in this case, the lengths of the rocker arms 22 and 23 tend to be unbalanced. Further, if the position of the camshaft 11 is largely moved from directly above the center line of the cylinder 1 to the intake side, the arm of the rocker arm 25 on the exhaust side becomes longer as a whole, and the motion characteristics are also lowered. Next, the cam bracket 31 is provided with a center support portion 36 so that the rocker shaft 25 is provided.
The notch 25a is supported in the vicinity of the notch 25a.
This is because the strength of the rocker shaft 25 is reduced due to the formation of “a”. And near that,
By the two rocker arms 22 and 23, a greater force acts on the rocker shaft 25 than in the other parts. Therefore, as shown in FIG. 3, the cam bracket 31 is formed in a rectangular frame shape, and a support portion 36 is provided near the center.
The shaft 25 is supported by passing the rocker shaft 25 through the inner boss hole. The support portion 36 is located between the two rocker arms 22 and 23 and is close to the plug hole 55 of the ignition plug 50, and thus includes a cutout portion 36a as shown in the drawing.
5 (notch portion 25a) is exposed, but the notch portion 36a does not reach the entire length of the support portion 36 (the entire length in the axial direction), so that the rocker shaft 25 is held with sufficient strength. And reduces its deflection and stress.

Although one embodiment of the present invention has been described above, it goes without saying that the present invention is not limited to this example. For example, the above-described engine is a two-cylinder engine. However, as long as the arrangement of the ignition plug 50 and the like is appropriately determined according to the above 1) and 2), an engine having three or more cylinders can be configured.

[0032]

The four-stroke engine according to the first aspect has the following effects. That is, a) a so-called four-valve SOHC engine, in which the inertial weight of each valve is small and the intake / exhaust efficiency can be increased, so that high efficiency and high output can be achieved. Also DOH
It is lighter and more cost effective than the C type.

B) Since the core of the spark plug is disposed so as to pass between the camshaft and the two exhaust valves, the number of cylinders is increased.
That is, it is easy to increase the number of cylinders to two or more. 4
If the valve / SOHC engine can be made multi-cylinder, the engine can have a high output and smooth rotation. Even in the case where the engine is multi-cylinder, it is not difficult to attach / detach a spark plug in this engine, and the smooth operation of the rocker arm for each valve is ensured.

C) In order to adjust the valve clearance with a shim that is lighter than an adjusting screw,
The mechanical loss is small and noise can be reduced.

In the four-stroke engine according to the second aspect, d) each rocker arm can be configured to be simple and lightweight. This is because the rocker arm for the exhaust valve is formed in a planar shape, and the rocker arm for the intake valve is also formed as an integral unit with the dimension along the rocker shaft as short as possible. If the rocker arm is lightweight, the engine will perform better at high speeds.

In the four-cycle engine according to the third aspect, e) since each rocker arm is slidably disposed along the rocker shaft, the replacement of the shim in the above item c), that is, the operation of adjusting the valve clearance can be easily performed. it can.

In the four-cycle engine according to the fourth aspect, f) since the plug hole is formed by the pipe, it is easy to manufacture the cylinder head cover by casting or the like.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of the present invention, and is a longitudinal sectional view showing a main part near a cylinder head 3 of a two-valve SOHC two-cylinder four-cycle engine for a motorcycle.

FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1, and is a plan view showing the valve train 10 of the engine.

FIG. 3 is a view taken in the direction of arrows III-III in FIG. 1, and is a view of the engine when the rocker arms 21, 22, 23, etc. are viewed from below. Note that the lower part in FIG. 3 overlaps the upper part in FIG.

FIG. 4 is a view taken in the direction of arrows IV-IV in FIG.
It is a top view which shows the cylinder 3 grade | etc. Except the 1 * 42 and the spark plug 50 grade | etc.,. Note that the lower part in FIG. 3 overlaps the upper part in FIG.

FIG. 5 is a cross-sectional view of the parts and the like in FIGS. 3 and 4 that are superimposed as described above, as viewed along VV in FIGS. 3 and 4.

FIG. 6 is a cross-sectional view of the parts and the like in FIGS. 3 and 4 which are superimposed as described above, as viewed along VI-VI in FIGS. 3 and 4.

7 is a graph showing the relationship between the engine shown in FIG. 1 with the torque acting on the camshaft 11 on the vertical axis and the rotation angle of the crankshaft on the horizontal axis.

FIG. 8 is a perspective view showing an outline of a valve operating mechanism 10 ′ and the like for a conventional four-valve SOHC type four-stroke engine.

[Description of Signs] 3 Cylinder head 8 Cylinder head cover 10 Valve operating mechanism 11 Camshaft 12.13.14 Cam 21.22.23 Rocker arm 24.25 Rocker shaft 41 Intake valve 42 Exhaust valve 47 Shim 50 Spark plug 51 Electrode 52 Core 55 Plug hole

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02B 23/08 F02B 23/08 S 75/18 75/18 Z

Claims (4)

[Claims] 1. A single camshaft on the cylinder head allows two intakes per cylinder on each side of the cylinder.
In a multi-cylinder four-stroke engine that drives an exhaust valve, an ignition plug is arranged such that an electrode protrudes into the upper center of a combustion chamber and a core body passes between a camshaft and two exhaust valves. Rocker arms for the exhaust valve were formed between the cams for the exhaust valve, while the rocker arms for the exhaust valve were arranged one by one on both sides of the spark plug to make contact with the respective cams for the exhaust valve. A four-stroke engine in which a shim is mounted between a rocker arm and a valve to contact a cam for an intake valve and adjust a valve clearance. 2. A rocker arm for an exhaust valve, wherein an arm portion in contact with the cam for the exhaust valve and an arm portion in contact with the exhaust valve are formed in one plane. A single arm portion in contact with the cam for an intake valve and two arm portions branched to both sides and extending so as to contact two intake valves are formed integrally. Item 4. The four-stroke engine according to item 1. 3. A rocker arm for an intake valve and an exhaust valve is slidably arranged along a rocker shaft for supporting the same.
Or a four-stroke engine according to 2. 4. The four-stroke engine according to claim 1, wherein a plug hole formed by a pipe is closely assembled between the cylinder head and the cylinder head cover.