JPH0141807B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a camshaft drive device for a double overhead cam type engine.

The double overhead cam type engine is the first
As shown in the figure, a first camshaft 2 on the intake valve side is provided directly above the intake valve 1, and a second camshaft 4 on the exhaust valve side is provided directly above the exhaust valve 3. A chain 9 is wound around the sprocket 5, the sprocket 6 of the second camshaft 4, and the sprocket 8 of the crankshaft 7, and the crankshaft 7 drives them. However, the first camshaft 2 and the second camshaft 4 are 1/2 of the crankshaft 7.
It is necessary to have a rotation ratio of
The sprockets 5 and 6 have large diameters, and the first camshaft 2 and second camshaft 4 must be spaced apart from each other.
Sprocket 5 and sprocket 6 will be in contact. This increases the size of the cylinder head, requires more materials and processing, and increases manufacturing costs. Double overhead cam type engines can directly open and close the intake and exhaust valves with the cams on the two camshafts, providing high performance, but as mentioned above, the cylinder head is large and manufacturing costs are high, so some Used only by high-performance request engines.

In view of these points, the present invention has been improved so that the cylinder head can be made smaller, more compact, and less expensive.Hereinafter, an embodiment of the present invention shown in FIGS. 2 to 4 will be described.

The distance between the first camshaft 2 on the intake valve 1 side and the second camshaft 4 on the exhaust valve 3 side is narrowed, and the sprockets 5 and 6 are shifted in the axial direction and arranged so that they partially overlap side by side. The sprocket 5 is fixed to the first camshaft 2, and the sprocket 6 is fixed to the second camshaft 4. On the other hand, a double sprocket 8 is fixed to the crankshaft 7, and a double chain 9 is wound around it. The double chain 9 is configured such that one chain line is wound around the sprocket 5 and the other chain line is wound around the sprocket 6, and the first camshaft 2 and the second camshaft 4 are driven by the crankshaft 7. do.

Thus, the sprocket 5 of the first camshaft 2 and the sprocket 6 of the second camshaft 4 are connected to the crankshaft 7.
is driven by a double sprocket 8 through a double chain 9. In this case, since the two sprockets 5 and 6 are offset in the axial direction, the first camshaft 2 and the second camshaft 4 can be arranged with a narrower distance between them, and the cylinder head can be made smaller and less expensive. In addition, since the two sprockets 5 and 6 are driven by one double chain 9, even if the double chain 9 stretches slightly, the first camshaft 2 and the second camshaft 4 will not be affected. There is no rotational phase difference, and no deviation in the opening/closing timing of the intake valve 1 and the exhaust valve 3 occurs.

As explained above, this invention narrows the gap between the first camshaft on the intake valve side and the second camshaft on the exhaust valve side, and aligns the sprocket of the first camshaft and the sprocket of the second camshaft in the axial direction. The two chains are arranged so that they partially overlap and are wound around the two sprockets of the crankshaft, and are driven by being wound around the sprockets of the first camshaft and the second camshaft. The first camshaft and the second camshaft can be arranged with a narrower interval, and the cylinder head can be made smaller and manufactured at a lower cost. Since the first camshaft and the second camshaft are driven by one double chain, there is no difference in the opening/closing timing of the intake valve and the exhaust valve.

[Brief explanation of drawings]

Figure 1 is a front view showing a conventional example, Figures 2 to 4
The figure shows one embodiment of the present invention, and FIG. 2 is a front view;
FIG. 3 is a side view, and FIG. 4 is an enlarged view of the section viewed from the X arrow in FIG. 1...Intake valve, 2...First camshaft, 3...Exhaust valve, 4
...second camshaft, 5...sprocket, 6...sprocket, 7...crankshaft, 8...double sprocket,
9...Double chain.

Claims (1)

[Claims] 1. Narrow the gap between the first camshaft on the intake valve side and the second camshaft on the exhaust valve side, and arrange the sprockets on the first camshaft and the second camshaft so that they partially overlap in the axial direction. A double overhead cam type engine characterized in that a double chain wrapped around a double sprocket of a crankshaft is driven by being wound around a sprocket of a first camshaft and a sprocket of a second camshaft. .