JPH01301908A - Valve system for four-cycle engine - Google Patents

Abstract

PURPOSE:To make a valve system more light-weight by mounting a cam shaft so as to cross the nearly central upper side of a combustion chamber, and supporting the nearly center of the cam shaft by a central bearing. CONSTITUTION:A cam shaft 36 for driving suction valves 23 to 25 and exhaust valves 26, 27 via a rocker arm, is mounted so as to cross the nearly central upper side of a combustion chamber 15. The nearly center of the cam shaft 36 is supported by a central bearing 39. An ignition plug inserting hole 29 is formed between two-exhaust valves 26, 27 and at the position being opposite to the central bearing 39, then the lower half-part 39a of the central bearing 39 is connected to the head side inserting hole circumference wall of the ignition plug inserting hole 29. Thereby, it is unnecessary to make the cam shaft of a large diameter, so that a valve system can be more light-weight.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a valve train adopted for example in a water-cooled four-stroke single-cylinder engine for motorcycles, and in particular, the present invention relates to a valve train that is used for example in a water-cooled four-stroke single-cylinder engine for motorcycles, and in particular, the present invention relates to a valve train that is used in a water-cooled four-stroke single-cylinder engine for motorcycles. The present invention relates to a structure in which the rigidity of a central bearing portion formed in a cylinder head can be improved when the central portion of a camshaft is also pivotally supported in an OHC engine in which an exhaust valve is driven to open and close.

[Conventional technology]

Generally, the valve train of an OHC engine is configured such that a single camshaft is placed across the upper center of the combustion chamber, and the camshaft opens and closes both the intake valve and the exhaust valve via a rocker arm. has been done. In this case, as the displacement increases and the combustion chamber diameter increases, the camshaft becomes longer, and in order to ensure the necessary rigidity, the shaft diameter increases, which tends to cause the problem of increased weight. left of axis.

There are examples of reducing the diameter of the camshaft by supporting not only the right end but also the center (for example, Japanese Patent Laid-Open No. 57-1
(See Publication No. 02506).

[Problem that the invention seeks to solve]

By the way, when supporting the central part of the camshaft mentioned above, it is of course necessary to form a lower half of the central bearing part in the cylinder head, but this lower half is simply formed by bulging a part of the cylinder head. In this case, the rigidity of this part may be insufficient, or the weight of the cylinder head itself increases due to the reinforcement wall for improving the rigidity of this part, which tends to cancel out the effect of reducing the diameter of the camshaft.

SUMMARY OF THE INVENTION In view of these conventional circumstances, the present invention aims to provide a valve train for a four-stroke engine that can significantly improve the rigidity of the central bearing portion of the camshaft while suppressing an increase in the weight of the cylinder head. There is.

[Means for solving problems]

The present invention provides a liquid-cooled four-stroke engine in which at least the vicinity of the combustion chamber of the cylinder head is cooled with liquid.
In a valve train in which an intake valve and two exhaust valves are driven to open and close by a single camshaft via a rocker arm, the camshaft is disposed so as to cross above the center of the combustion chamber, and The approximate center of the camshaft is supported by a central bearing, and a cylindrical spark plug insertion hole is formed between the two exhaust valves and at a position facing the central bearing, and the lower half of the central bearing is provided with a cylindrical spark plug insertion hole. is connected to the peripheral wall of the head-side insertion hole of the plug insertion hole, which is integrally formed with the cylinder head.

The reason why the present invention is applicable to liquid-cooled engines that are cooled with water or oil is that generally, in the case of liquid-cooled engines, the spark plug is inserted into the plug hole formed in the ceiling wall of the combustion chamber, and the spark plug is inserted into the cylinder head. A cylindrical plug insertion hole is formed for insertion from the outside, and the purpose is to improve the rigidity of the central bearing portion by using the peripheral wall of this insertion hole.

[Effect]

According to the valve train according to the present invention, since the center portion of the camshaft is supported by the central bearing portion, the camshaft does not need to have a large diameter, and the weight of the camshaft can be reduced. Since the lower half of the central bearing is connected to the peripheral walls of the four plug insertion holes located between the exhaust valves, the rigidity of the central bearing can be greatly improved. Moreover, this increase in rigidity can be achieved simply by connecting the lower half of the central bearing to the peripheral wall of the plug insertion hole adjacent to and facing the central bearing, and there is no need to form an extra wall surface on the cylinder head. There is no problem of weight increase due to the wall portion for reinforcing the bearing portion of the cylinder head.

In addition, in the present invention, the central bearing portion is located in the center surrounded by multiple valves and does not interfere with these valves, so the height of the camshaft can be lowered, and the cylinder head can be made more compact. .

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1 to 4 are diagrams for explaining a valve train for a four-stroke engine according to an embodiment of the present invention.

In the figure, reference numeral 1 denotes a motorcycle equipped with a four-stroke engine to which the device of the present invention is applied, and a front fork 4 whose lower end pivotally supports a front end 3 is pivotally supported at the front end of a body frame 2 of the motorcycle. At the lower center end, a rear arm 6 that pivotally supports the rear wheel 5 at the rear end is pivoted so as to be able to swing up and down.Furthermore, at the rear is a large fuel tank 7, and above it is a seat 8.
are installed in each. Note that 62 to 64.58 are an oil tank, a radiator, an air cleaner, and a carburetor, respectively.

A water-cooled four-stroke single-cylinder engine unit 9 is mounted on the front portion of the vehicle body frame 2. This engine unit 9 includes a cylinder 10, a cylinder head 1
1. and a head cover 12 are stacked on a crankcase 14.

The cylinder 10 is constructed by press-fitting a cylindrical cylinder liner 10c into a cylinder body 10b having a water cooling jacket 10a, and a piston 14 is slidably inserted into the cylinder liner loc.

Further, a combustion chamber recess 16 is formed substantially in the center of the lower surface of the cylinder head 11 and forms a combustion chamber 15 with the upper surface of the piston 14 . Three intake valve openings 17 to 19 and two exhaust valve openings 20.degree. 21 are formed approximately on the circumference along the periphery of the combustion chamber recess 16. Further, a plug hole 22 is formed in the center of the four combustion chamber parts 16, and this plug hole 22 is led out to the outside by a plug insertion hole 29 for inserting a spark plug from the outside. This plug insertion hole 29 has a cylindrical shape surrounded by a peripheral wall, and has a cylindrical shape surrounded by a peripheral wall. Direct vA to head cover 12
It is composed of a head-side insertion hole 29a and a cover-side insertion hole 29b formed in the cane.

Further, a spark plug 30 is installed in the plug hole 22.

The three intake valve openings 17 to 19 merge into one common intake passage 31 formed in the cylinder head 11, and then lead out to the rear side in the longitudinal direction of the vehicle, and the two exhaust valve openings 20.21 are each separate exhaust passage 32.3
3 leads to the front side. Each exhaust passage 32, 33° intake passage 31. and the combustion chamber recess 16
A head-side water-cooling jacket 19 is formed around the cylinder-side water-cooling jacket 10a, and the jacket 19 communicates with the cylinder-side water-cooling jacket 10a.

The intake valve openings 17 to 19 and the exhaust valve openings 20 and 21 have intake valves 23 to 25 and an exhaust valve 26 that open and close them.
27 valve plates are arranged. Each intake and exhaust valve 23~
27 valve stems 23a to 27a are the intake and exhaust passages 31 to 27.
It penetrates the ceiling wall portion of 33 and projects above this cylinder head 11. In this case, the valve stem 24a is 23a
, 25a, and the plug insertion hole 29 is located between the exhaust valves 26.27 and parallel to both exhaust valves 26.27. Also, the intake valve stem 23
As shown in FIG.
It is located above. Further, a biasing spring 35 is provided between a spring stopper 34 attached to the upper end of each valve stem 23a to 27a and a spring seat 11a attached to the cylinder head 11.
are arranged, thereby urging the multiple valves 23 to 27 to close the respective valve openings 17 to 21.

Between the straight lines A and B, one camshaft 36 is parallel to these lines and is located at a distance D from the center C of the combustion chamber 15 in plan view.
It is arranged so as to cross a position shifted by 2 to the rear of the vehicle. The left and right ends and the center of this camshaft 36 when viewed from the front of the vehicle (right side in Figure 1) are left and right bearing portions 37.3, respectively.
8, and a central bearing portion 39, which is offset from the center C by an amount DI to the right.

The central bearing portion 39 is located between the central intake valve 24° and the plug insertion hole 29, and faces both.

Further, a driving sprocket 40 is attached to a protruding portion of the camshaft 36 from the left bearing portion 37, and this is connected to the crankshaft by a cam chain 41.

Further, a first
A second intake and exhaust cam 36C236d is integrally formed between the exhaust and intake cams 36a and 36b, and the bearing portion 39.38, and this first intake cam 36b is connected to the intake valve 24.25.
Both valves 24, 25
It is located approximately in the middle. And each of these cams 36a to 3
Sliding portions 423 to 45a of first exhaust and intake rocker arms 42 and 43, and second intake and exhaust rocker arms 44 and 45 are in sliding contact with 6d, respectively. Both intake rocker arms 43, 44. and exhaust rocker arm 42.45
are swingably supported by intake and exhaust rocker arm shafts 46 and 47, respectively, which are arranged parallel to the camshaft 36. The other end side of the first intake rocker arm 43 is branched into two operating parts 43b, 43c, and the operating parts 42 of the two operating parts 43b, 43e and other rocker arms.
Adjustment bolts 4B are screwed onto the valve stems 23a to 23b, 44b, and 45b, and each adjustment bolt 48 is attached to each of the valve stems 23a to 23a.
It is in contact with the upper end of 7a.

The left and right bearing portions 37, 38 and the center bearing portion 39 have a two-part structure consisting of a lower half formed on the cylinder head 11 side and an upper half formed on the head cover 12 side. In front of the lower half 39a of the central bearing part 39,
The rear portion includes a peripheral wall of the head side insertion hole 29a, and
It is integrally connected to the ceiling wall 31a of the shared intake passage 31.

Furthermore, a fastening bolt 12b for tightening and fixing the rad cover 12 to the cylinder head 11 is inserted into this connecting portion. This bolt 12b serves as a suspension flange integrally formed with the head cover 12 and is suspended from a tension run pipe 2a of the vehicle body frame 2.

Next, the effects of this embodiment will be explained.

In the valve train of this embodiment, when the camshaft 36 is rotationally driven by the crankshaft via the cam chain 41, each cam 3
6a to 36d, each rocker arm 42 to 45 swings, and each intake and exhaust valve 23 to 27 is driven to open and close.

In a valve train that operates in this way, when the number of valves per cylinder is large, for example five, the total length of the camshaft becomes longer, and the camshaft diameter becomes larger to ensure the rigidity of the camshaft. However, in this embodiment, the camshaft 36 is supported not only by the left and right bearing parts 37 and 38 but also by the center bearing part 39.
The camshaft diameter can be made smaller and weight increase can be prevented.

On the other hand, if the camshaft is also supported at the center, depending on the design, a reinforcing wall may be required to ensure the rigidity of the center bearing, which tends to increase the weight of the cylinder head itself. In the embodiment, the central bearing portion 39
are arranged between the central intake valve 24 and the plug insertion hole 29, and the front and rear portions of the lower half 39a of the central bearing portion 39 are respectively connected to the peripheral wall of the plug insertion hole 29 and the shared intake passage 3.
1, the rigidity of the center bearing portion 39 can be greatly improved compared to, for example, a case where the lower half portion is formed in an overhang shape. Moreover, in this improvement in rigidity, since this engine is water-cooled, the plug insertion hole 29 is formed in a cylindrical shape with a peripheral wall.
And as mentioned above, the central bearing part 39 is inserted into this plug insertion hole 2.
9 and the common intake passage 31, and because it is close to and facing the common intake passage 31, the lower half 39a of the central bearing part 39 can be easily connected to the peripheral wall of the head side insertion hole 29a and the ceiling wall 31a of the @airway 31. Since there is no need to form an extra bearing wall on the cylinder head 11, there is no problem of increased weight of the cylinder head 11.

In addition, in this embodiment, five valves are arranged separately, three on the left side and two on the right side of the central bearing part 39, and when the central bearing part 39 is viewed from the plane of the combustion chamber 15. With respect to the center C, it is eccentric by Dl to the right side where the number of valves is small and there is a relatively large amount of space, so the free space can be used effectively, and the valve train, and by extension the cylinder head 1, can be used effectively.
181 can be made more compact. In addition, in this embodiment, the camshaft 3G remains between the five valves, and the central bearing 39 does not interfere with them, so the camshaft 36 can be placed low, and from this point as well, the camshaft 36 can be placed between the five valves. can be made compact.

In addition, in this embodiment, the camshaft 36 is eccentric to the rear side by D2 with respect to the center C of the combustion chamber, and the plug insertion hole 29 is located at the front side, which is advantageous in terms of space due to this eccentricity.
is formed toward the center C of the combustion chamber, and a notch 47a is formed in the exhaust rocker arm shaft 47 to prevent interference when the spark plug is inserted, so the verticality of the spark plug 30 can be greatly increased without complicating the structure. can be improved. By the way,
Conventionally, in order to improve this perpendicularity, the rocker arm shaft has been divided into two or a through hole has been formed in the shaft, resulting in problems such as an increase in the number of parts and a complicated structure.

In addition, in this embodiment, the notch 4 of the rocker arm shaft 47
The surface 7a constitutes a part of the inner circumferential wall of the cover-side insertion hole 29b, which allows for effective use of space and weight reduction.

Furthermore, in this embodiment, since the vicinity of the insertion portion of the fastening bolt 12b between the cylinder head 11 and the head cover 12 is suspended on the vehicle body frame 2, the strength can be improved accordingly.

In addition, although the above-mentioned embodiment explained an engine for a two-wheeled motor vehicle, the present invention can of course be applied to engines other than this.

〔Effect of the invention〕

As described above, according to the valve train for a liquid-cooled four-stroke engine according to the present invention, the plug insertion hole is formed between the two exhaust valves and at a position facing the center bearing of the camshaft. Since the lower half of the cylinder head is connected to the peripheral wall of the plug insertion hole, the rigidity of the central bearing part can be improved while preventing an increase in the weight of the cylinder head.

[Brief explanation of the drawing]

1 to 4 are diagrams for explaining a valve train according to an embodiment of the present invention. FIG. 1 is a plan view of the valve train with its head cover removed, and FIG. n, -
n, &I sectional side view, Fig. 2 (hl is a sectional view showing the suspended state, Fig. 3 is a bottom view of the cylinder head, Fig. 4 is a left side view of the motorcycle to which the device of this embodiment is applied) In the figure, 9 is an engine unit, 15 is a combustion chamber, 2
3 to 25 are intake valves, 26 and 27 are exhaust valves, 29 is a plug insertion hole, 36 is a camshaft, 39 is a central bearing portion, and 39a is a lower half portion. Patent applicant: Yamaha Motor Co., Ltd. Figure 2 (vC02) Figure 3

Claims (1)

[Claims] (1) The intake valve and two exhaust valves of a liquid-cooled four-stroke engine that uses liquid to cool at least the vicinity of the combustion chamber of the cylinder head are connected to one another via a rocker arm.
In a valve train which is driven to open and close by a real camshaft, the camshaft is disposed so as to cross substantially above the center of the combustion chamber, and the substantially center of the camshaft is pivotally supported by a central bearing. A cylindrical spark plug insertion hole is formed between the two exhaust valves and at a position facing the central bearing, and the lower half of the central bearing is formed integrally with the cylinder head of the spark plug insertion hole. A valve gear for a four-cycle engine, characterized in that the valve gear is connected to a peripheral wall of a head-side insertion hole.