JPH0445645B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an engine equipped with a plurality of valves having the same function per cylinder,
In particular, the present invention relates to an improvement in the bearing structure of an overhead camshaft that is applied to small engines such as motorcycles that are driven at high speeds.

(Prior art and its problems) In recent years, small engines installed in motorcycles, etc. have become faster and faster, and the responsiveness of valve opening and closing must be improved accordingly. There is a need to increase the elastic force of the springs used to open and close the valves, which in turn requires improvements in the rigidity of the camshafts equipped with cams for opening and closing the valves, as well as improvements in the strength of the bearings that support the camshafts.

By the way, FIG. 4 shows a partially cutaway plan view of the bearing structure of an overhead camshaft in a conventional engine, and FIG. 5 shows a longitudinal sectional view thereof. This engine has a plurality of cylinders 9, and each cylinder 9 is provided with a plurality of, for example, two intake valves 1 and two exhaust valves 2, and these valves are arranged in the cylinder head 3. The opening and closing operations are performed according to the cam ridge positions of the cams 5 of the two camshafts 4 (only one camshaft is shown in FIG. 4).

In this case, as shown in FIG.
In the two valves (either intake valve 1 or exhaust valve 2) related to the cylinder 9 located at the outermost position in the axial direction, the elastic force of both valves is the same as that of the one located at the outermost position. Although the cam 5a is supported by the cam ridge, it is supported in a cantilevered state, and the distance L from the center of the bearing 7 to the center of the cam 5 becomes longer, so the camshaft 4 becomes easily bent. As mentioned above, in order to improve the strength of the bearing 7, it is necessary to make the bearing 7 wide in the axial direction. There was a problem in that the gap 8 between the two increases in proportion to the distance L, which adversely affects the opening and closing operations of the valves 1 and 2.

Further, in other conventional structures shown in FIGS. 7 and 8, the shaft end of the camshaft 14 is supported by a bearing 17, and therefore, as shown in FIGS. However, as shown in FIG. 9, the length l of the camshaft 14 in the axial direction of the cylinder head 13 increases, and the entire engine becomes larger, and there is a particular demand for downsizing. This creates a new problem that makes it difficult to apply to engines installed in motorcycles, etc.

In FIGS. 7 to 9, 11 is an intake valve, 12 is an exhaust valve, 15 is a cam, and 16 is a rocker arm.

(Means for Solving the Problems) The present invention has been made to solve the above-mentioned problems of the conventional art.
2 or the exhaust side passage 33 is provided with a plurality of valves 21 having the same function,
Cams 25 having cam ridges for opening and closing these valves are provided at appropriate intervals, and
In an engine in which a camshaft 24 driven by the engine is provided in a cylinder head 23 above the cylinder head, at least the outermost cylinder 20
A plurality of valves 21 having the same function in a
cam 25 for a, 21b, 22a, 22b
The bearings located between a and 25b and their cams 25
a, 25b closer to the center of the camshaft 24,
Each lower bearing 27'b, 27b is formed integrally with the cylinder head 23, and the lower bearing 27'b, 27
Each upper bearing 27' corresponding to b and forming the holding member 37
a, 27a, and each upper and lower bearing 27'a,
27a, 27'b, 27b with bolts 35', 35,
35, and the outermost cam 25a of the cam shaft 24 is supported in a cantilevered manner.

(Function) When the camshaft 24 rotates and the valves 21 open and close according to the cam ridge positions of the cams 25, the cams 25 receive the elastic force of the springs 29 of both valves 21. Both valves 21a located at
The camshaft portion 24a located between the bearings 21a and 21a is
7'a, the camshaft 24 is effectively supported without bending.Moreover, the outermost cam 25a is cantilevered, and there are no bearings other than the bearing 27'a. does not require.

(Example) Hereinafter, an example of the present invention will be described based on FIGS. 1 to 3.

1 to 3 show one embodiment of the present invention, and the bearing structure and other parts of the engine of this embodiment except for the camshaft are shown in FIGS. 4 to 9.
Since there is no difference from the conventional structure shown in the figure, redundant explanation will be omitted. Note that in the description of this specification, the subscripts a or b will not be attached to items that are not particularly specified as being located at the shaft end of the camshaft.

Above each cylinder 20 is an intake passage 32.
and an exhaust side passage 33 are formed, and both passages 32 and 33 can communicate with the cylinder 20 via the intake valve 21 and the exhaust valve 22, respectively. The intake valve 21 and the exhaust valve 22 are vertically movably fitted into a sleeve 36 fitted into a guide hole 34 formed in the upper part of the intake passage 32 or the exhaust passage 33, respectively; A return spring 29 is fitted into each of the portions projecting upward from the sleeve 36. For example, each of the two intake valves 21 and the two exhaust valves 22 are connected to the cams 25 of the corresponding camshafts 224. Therefore, they are respectively opened and closed.

In the following explanation, the exhaust valve side can be explained in the same way as the intake valve 21 side, so the intake valve 21 side can be explained in the same way as the intake valve 21 side.
Only the first side will be explained.

Two intake valves 21a, 21b shown in FIG.
These intake valves 21a and 21b are provided on the outermost cylinder 20a located at one shaft end position of the camshaft 24, and these intake valves 21a and 21b are provided on the camshaft 24 in correspondence with the intake valves 21a and 21b. Locker arms 26a, 26 are attached to the provided cams 25a, 25b.
They are connected to each other via b.

On the other hand, a lower bearing 27'b as an auxiliary bearing integrally formed with the cylinder head 23 is provided on the camshaft portion 24a between the cams 25a and 25b.
One bolt 3 placed on the lower bearing 27'b
An upper bearing part 27'a of the holding member 37 is provided, which is tightened and fixed at the lower bearing part 27'a.
7'b has a width W' that is approximately the same length as the axial length of the camshaft portion 24a. Note that, as shown in FIG. 3, the lower bearing 27'b is a portion between the axial direction of the stem of the valve 21a inclined with respect to the axis of the cylinder 20 and the direction perpendicular to the axis of the cylinder 20. The part facing the head side of the valve 21a (the part indicated by the symbol α in FIG. 3) is missing, and therefore the sliding surface (inner periphery) of the lower bearing 27'b relative to the camshaft part 24a is missing. The surface) is a substantially quarter-cylindrical concave surface. In addition, a lower bearing 27b as a main bearing is disposed adjacent to the lower bearing 27'b closer to the center of the camshaft 24 than the lower bearing 27'b.
This lower bearing 27b is formed integrally with the cylinder head 23 (FIG. 1).
An upper bearing 27a is placed on top and is fastened and fixed with two bolts 35. In other words, the lower bearing 27'b and the lower bearing 27b are the upper bearing 27'a of the holding member 37, the rib portion 28, and the upper bearing 27a.
bolts 35', 35,
They are integrally connected and fixed at 35.

Next, the operation of this embodiment will be explained.

When the intake valves 21a and 21b of the outermost cylinder 20a in the axial direction of the camshaft 24 open and close in response to the rotation of the cam 25 of the camshaft 24, the camshaft 24 rotates the respective arrangement of the cams 25a and 25b. Intake valves 21a, 21 that act in a direction substantially perpendicular to the axial direction of the camshaft 24 at the installation location.
It receives the elastic force of return springs 29a and 29b of b. At this time, this camshaft 24 is attached to a lower bearing 27b having a predetermined sufficient width W in the axial direction.
Moreover, since the camshaft portion 24a between the cams 25a, 25b near the shaft ends of the camshaft 24 is supported by the lower bearing 27'b, that is, the return springs 29a, 2
Since the elastic force of the camshaft 9b is received closest to the cam ridges of the camshaft portion 24a, the slight deflection at the shaft end of the camshaft 24 that tends to occur in a normal cantilevered state is prevented.

In particular, when the engine according to the present invention is mounted on a motorcycle that requires high speed rotation, the overall length of the top of the engine can be shortened by omitting the outermost bearing. When installed as a multi-cylinder engine, for example, there is no need to unnaturally widen the distance between the knees of an occupant in a seated position.

(Effects of the Invention) As explained above, according to the present invention, a plurality of valves 2 having the same function are provided in at least one of the intake side passage 32 and the exhaust side passage 33 per cylinder.
1, and cams 25 having cam ridges for opening and closing these valves are provided at appropriate intervals, and a camshaft 24 driven by the engine is connected to the cylinder head 2 above the cylinder head.
3, the bearings located between the cams 25a, 25b for the plurality of valves 21a, 21b, 22a, 22b having the same function in at least the outermost cylinder 20a, and the camshaft from the cams 25a, 25b. 24, the central bearing 24, lower bearings 27'b, 27b formed integrally with the cylinder head 23, and upper bearings 27'a forming the holding member 37 corresponding to the lower bearings 27'b, 27b. , 27a, and the upper and lower bearings 27'a, 27a, 27'b, 27b are integrally fixed with bolts 35', 35, 35, and the cam 25a located at the outermost side of the camshaft 24 is fixed together with bolts 35', 35, 35. Since it is supported in a cantilevered state, the plurality of valves 21a, 21b,
22a, 22b is applied to the valves 21a, 21.
cams 25a, 2 for opening/closing operation of b, 22a, 22b
5b is received near the shaft end of the camshaft 24 where the camshaft 24 is disposed, it is possible to prevent the camshaft from deflecting. Valve 21 by b
a, 21b, 22a, 22b, and can effectively support the load. Furthermore, the width of the bearings 27'a and 27'b in the axial direction becomes narrower, and as a result, the weight of the bearings can be reduced, which in turn makes it possible to reduce the weight of the entire engine. Cam 2 located outward
5a is supported in a firm cantilevered state by the holding member 37 or the like without requiring any special bearing. Furthermore, two adjacent upper bearings 27
a, 27'a are integrated as a holding member 37, so each upper bearing 27a, 27'a straddles the adjacent lower bearing 27b, 27'b, and the bolt 35,
35, 35', one end of the camshaft 24 does not bend, and the cams 25a,
The width of the bearings 27'a and 27'b between the bearings 25b can be narrowed. And each upper bearing 27a, 2
Since 7'a constitutes the integral holding member 37, the number of parts of the upper bearing is reduced, and assembly is not only easy by using bolts, etc., but also the mounting accuracy is improved.

These effects combine to make it possible to downsize the engine, and it is extremely effective to install the engine in a motorcycle or the like.

[Brief explanation of drawings]

FIG. 1 is a cutaway plan view showing an embodiment of the present invention;
2 is a longitudinal sectional view of FIG. 1, FIG. 3 is a sectional view taken along the - line in FIG. 1, and FIG. 4 is a partially cutaway plan view showing the bearing structure of a camshaft in a conventional engine.
5 is a vertical sectional view of FIG. 4, FIG. 6 is a conceptual explanatory diagram for explaining the bearing structure of FIGS. 4 and 5, and FIG. 7 is a part showing another conventional bearing structure. 8 is a longitudinal sectional view of FIG. 7, and FIG. 9 is a conceptual explanatory diagram for explaining the bearing structure of FIGS. 7 and 8. 20...Cylinder, 21...Intake valve, 22...Exhaust valve, 23...Cylinder head, 21a, 21b...
Valve, 24...camshaft, 25a, 25b...cam,
27'b...lower bearing, 32...intake side passage, 33...
Exhaust passage.

Claims (1)

[Claims] 1. A plurality of valves 21 having the same function are provided in at least one of the intake side passage 32 or the exhaust side passage 33 per cylinder, and cams 25 having cam ridges for opening and closing these valves are arranged at appropriate intervals. In an engine in which a camshaft 24 driven by the engine is provided in the cylinder head 23 above the cylinder, a plurality of valves 21a, 21b, having the same function at least in the outermost cylinder 20a, 22
The bearings located between the cams 25a, 25b for the cylinder heads 22b and the bearings closer to the center of the camshaft 24 than the cams 25a, 25b are connected to the lower bearings 27'b, 27b integrally formed in the cylinder head 23,
The holding member 3 corresponds to the lower bearings 27'b, 27b.
7, each upper bearing 27'a, 27a,
Upper and lower bearings 27'a, 27a, 27'b, 27b
are fixed together with bolts 35', 35, 35, and the outermost cam 25a of the camshaft 24 is supported in a cantilevered state. Bearing structure.