JPH04116207A - Valve-operating device of two-cycle internal combustion engine - Google Patents

Abstract

PURPOSE:To improve durability of a camshaft and a camshaft bearing by shifting a contacting part of each locker arm in a circunmferential direction of the camshaft to each other, thereby counterbalancing each horizontal component of a driving reaction force of an intake valve and that of a discharge valve. CONSTITUTION:When a camshaft 8 revolves, a locker arm 6 for an intake valve and a locker arms 7 for a discharge valve rotate, and an intake valve 2 and a discharge valve 4 are driven to open. A contacting part between a cam 8a for the intake valve and a roller 11 is shifted in a circumferential direction against a contacting part between a cam 8b for the discharge valve and a roller 14. As a result, the direction of the drive reaction force F1 for the intake valve and the direction of the drive reaction force F2 for the discharge valve 4 are different to each other. The resultant force of the drive reaction forces F1, F2 exerting on the camshaft 8 and its bearing respectively becomes smaller by the portion which the horizontal components f1, f2 of the drive reaction forces F1, F2 counterbalance. The durability of the camshaft and its bearing can be improved accordingly.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a valve train for a two-stroke internal combustion engine.

[Conventional technology]

A two-stroke internal combustion engine is known in which an intake valve and an exhaust valve are driven by a single camshaft (see West German Publication No. OH 3143402Al).

In this two-stroke internal combustion engine, the contact portion of the intake valve and the contact portion of the exhaust valve with respect to the cam formed on the camshaft are located at approximately the same position in the circumferential direction of the camshaft. The direction of the drive reaction force of the exhaust valve and the direction of the drive reaction force of the exhaust valve acting on the camshaft are substantially the same direction.

[Problem to be solved by the invention]

However, in a two-stroke internal combustion engine, the intake valve and exhaust valve open almost simultaneously, so if the direction of the driving reaction force of the intake valve and exhaust valve is almost the same as described above, the camshaft and its bearings will be affected. There is a problem in that a large force is applied to the camshaft and the durability of the camshaft and its bearing is impaired.

[Means to solve the problem]

In order to solve the above problems, according to the present invention, the intake valve rocker arm and the exhaust valve rocker arm are driven by - camshafts, and the contact portion of each rocker arm with the cam formed on the camshaft is controlled. The rocker arms are formed in an arc shape in the cross section of the camshaft, and the contact portions of the rocker arms are offset from each other in the circumferential direction of the camshaft.

[For production]

By shifting the contact portions of the rocker arms from each other in the circumferential direction of the camshaft, the directions of the drive reaction forces of the intake valve and the exhaust valve are different, and the horizontal components of the respective drive reaction forces cancel each other out.

〔Example〕

FIG. 1 shows a valve train for a two-stroke internal combustion engine.

Referring to Figure 1, 1 is the cylinder head, 2 is the intake valve, 3 is the intake port, 4 is the exhaust valve, 5 is the exhaust boat, 6 is the rocker arm for the intake valve, and 7 is the rocker arm for the exhaust valve. , 8 indicate camshafts, respectively. One end of the air supply valve rocker arm 6 is supported by the cylinder head 1 via a pivot 9, the other end of the rocker arm 6 is seated on the top of the air intake valve 2, and the middle part of the rocker arm 6 is supported by the cylinder head 1 via a pivot 9. A roller 11 is rotatably attached via a roller pin 10. On the other hand, one end of the exhaust valve rocker arm 7 is supported by the cylinder head 1 via a pivot 12.
The other end of the rocker arm 7 is seated on the top of the exhaust valve 4, and a roller pin 13 is provided in the middle of the rocker arm 7.
A roller 14 is rotatably attached via the . An intake valve cam 8a and an exhaust valve cam 8b are formed on the camshaft 8 and are slightly out of phase with each other. The roller 11 rotates while contacting the cam surface of the air supply valve cam 8a, and the roller 14 rotates while contacting the cam surface of the exhaust valve cam 8b. When the camshaft 8 rotates, each rocker arm 6.7 rotates about the pivot 9.12, thereby driving the intake valve 2 and the exhaust valve 4 to open.

Since the air supply valve cam 8a and the roller 11 are in contact with each other on the line connecting the center axis of the camshaft 8 and the center axis of the roller 11, the reaction force of the driving force acting on the roller 11 by the camshaft 8 is expressed as shown in FIG. It passes through the central axis of the camshaft 8 as shown by the arrow F1. Similarly, the exhaust valve cam 8b and the roller 14 contact each other on the line connecting the center axis of the camshaft 8 and the center axis of the roller 14, so the reaction force of the driving force acting on the roller 14 by the camshaft 8 is shown in FIG. It passes through the central axis of the camshaft 8 as shown by the arrow F2.

By the way, in the embodiment shown in FIG. 1, the roller pin 10 and the roller pin 13 are offset from each other in the circumferential direction of the camshaft 8, so that the contact portion between the intake valve cam 8a and the roller 11 is the same as the exhaust valve cam 8b. It is offset in the circumferential direction of the camshaft 8 with respect to the contact portion with the roller 14. As a result, as shown in FIG. 1, the driving reaction force F against the intake valve 2,
The direction of the drive reaction force F2 against the exhaust valve 4 is different from the direction of the drive reaction force F2. These drive reaction forces F1. The resultant force of F2 will act, but these drive reaction forces F;, F2 are almost equal, so the drive reaction forces Fl, horizontal components of F2, , f2 are in opposite directions and are almost equal in magnitude. Become. Therefore, these horizontal component elements, f2 cancel each other out, and the drive reaction forces Fl and F2 acting on the camshaft 8 and its bearings increase by the amount by which these horizontal component elements, f2 are canceled. The resultant force becomes smaller.

As shown in FIG. 2, the air supply valve 2 and the exhaust valve 4 are open at the same time for a long period of time. Even if the valve is closed, the resultant force of the driving reaction forces F, F2 acting on the camshaft 8 and its bearing portion can be reduced during this time, so that the durability of the camshaft 8 and its bearing portion can be improved.

Incidentally, instead of the rollers 11 and 14, fixed projections having an arcuate cross section may be formed on each rocker arm 6.7, and these fixed projections may be brought into contact with each of the cams 8a and 8b.

[Effects of the Invention] The durability of the camshaft and the bearing portion of the camshaft can be improved.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of the cylinder head, and FIG. 2 is a diagram showing the opening timings of the intake valve and the exhaust valve. 2...Air supply valve, 4...Exhaust valve, 6.7.
...Rocker arm, butt...Camshaft, 8a, 8b...Cam, 1
1.14... Laura.

Claims (1)

[Claims] The intake valve rocker arm and the exhaust valve rocker arm are driven by one camshaft, and the contact portion of each rocker arm with the cam formed on the camshaft is formed in an arc shape within the cross section of the camshaft. A valve train for a two-stroke internal combustion engine in which the contact parts of the rocker arms are offset from each other in the circumferential direction of the camshaft.