JPH01193433A - One cylinder internal combustion engine - Google Patents

Abstract

PURPOSE:To produce an engine which is miniature and light, and less in vibration by forming a flywheel mounted on a crankshaft protruding out of a crank case with balance weights which are distributed at plural positions across the center line of the flywheel and provided in a body with the flywheel. CONSTITUTION:A flywheel 12 fixed onto an extension 5c of a crankshaft 5 protruding out of a crank case 1 is provided with an arc-shaped thick wall part on the side opposite to a pin 5b to form a balance weight 13, and on the other hand, with a balance weight 14 on its another side face. Thus the position of the lower end 2a of a cylinder 2 and the length of a connecting rod 4 can be determined without considering the height of an end face of a crank arm 5a to make the height of an engine lower.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a single-cylinder internal combustion engine that is required to have little vibration and be small and lightweight.

(Prior Art) Providing balance weights on a pair of crank arms of a crankshaft in order to cancel the inertial force of reciprocating members such as pistons is the most common method in single-cylinder internal combustion engines, but In order to make the engine more compact, it is also known to provide this balance weight on a rotating body outside the crankcase.

For example, in Utility Model Publication No. 51-50892, there are two types: ■ A balance weight is provided only on the output boom at one end of the crankshaft, but not on the crank arm, ■ A balance weight is provided only on one end of the crank arm, and the other side is omitted. A flywheel has been disclosed in which a weight for supplementing the action of a balance weight and a weight for canceling a couple caused by an unbalance of centrifugal force are provided on the flywheel.

(Problems to be solved by the invention) In the technique disclosed in the above-mentioned Japanese Utility Model Publication No. 51-50892,
A type in which a balance weight is installed only on the output pulley has the advantage of making the crankshaft more compact and making the crank chamber smaller, but since the output pulley usually has a small diameter, it is practically difficult to install a large balance ff1ffi. , and a couple due to centrifugal force occurs, causing vibration.

In addition, in the above-mentioned (2), where a balance weight is provided only on one side of the crank arm, the compacting force of the crankshaft (') is insufficient and the crank chamber cannot be made very compact.

(Means for Solving the Problems) The present invention solves the problems of the prior art, and makes it possible to downsize the crankshaft and the crank chamber, and prevent vibrations. The means is a single-cylinder internal combustion engine in which a crankshaft without a balance weight is mounted in a crank chamber, and a flywheel is attached to one of the extensions of the crankshaft that protrudes outside the crank chamber. The flywheel is characterized by being integrally provided at multiple locations with the center line distanced from the flywheel.

(Function) With the above means, the inertial force of the piston, etc. is canceled out by the balance weights distributed at a plurality of locations on the flywheel, and no couple is generated.

(Example) Examples of the present invention will be described below based on the drawings. In Figures 1 and 2, 1 is the crank chamber, 2 is the cylinder, and 2a
is its lower end, 3 is a piston, 4 is a connecting rod, 5 is a crankshaft, and the crankshaft 5 is a crank arm 5a,
5a and a crank pin 5b, but usually does not include a balance weight which is provided integrally with the crank arm 5a as shown by the imaginary line. One crank arm 5
A cam drive gear 6 is fixed in contact with a, and a cam shaft 7
The cam gear 8 is driven to open and close the intake/exhaust valves 11 via the cam 7a, tappet 9, and rocker arm 10.

A flywheel 12 is attached to an extension 5c of the crankshaft 5 that protrudes from the crank chamber 1 to the outside. On the opposite side of the flywheel 12 from the crank bin 5b, an arc-shaped thick portion is provided, and a balance weight 13 is provided.
A balance weight 14 is provided which projects outward in the axial direction from the side surface of the flywheel.

And the centers of gravity 13a, 14 of these weights 13.14
If the mass at a is ffl, , m2, then Fig. 3 (
The vibration system is as shown in a), and if the inertial force to be balanced corresponding to the inertial force of the piston, etc. is F, then m, r, ω2
J! When 1-m2r2ω212, the couple is canceled and F =
(ml rl m2r2) 612 is the inertial force generated by the flywheel.

On the other hand, in a conventional crank arm in which two weights mSm are provided at positions of radius r, the vibration system becomes as shown in FIG. 3(b), resulting in an inertial force F -2mtω2.

Therefore, ml rl 4-111z I'2 j!
By determining the mass and position of the weight 13.14 so that 2It11 r, -m2 r2 - 2mr, the same balance as the conventional one can be obtained.

As described above, by removing the balance weight from the crank arm 5a, when the piston 3 descends and the crank pin 5b comes to the lower position, the end surface of the crank arm 5a opposite to the crank pin 5b is Even when it comes to the lower end or just below the lower end 2a of the cylinder 2, a considerable gap remains between them.

Therefore, the position of the lower end 2a of the cylinder 2 and the length of the connecting rod 4 can be determined without considering the height of the end surface of the crank arm 5a, and by lowering the cylinder, the height of the crank chamber 1 can be lowered. , the height of the engine can also be lowered. Furthermore, since it is not necessary to provide a balance weight to the crank arm 5a, the crank arm 5a
By making it thinner, the distance between bearings and the length of the crankcase can be shortened.

(Effects of the Invention) As described above, the present invention has no balance weight located inside the crankcase, so the crank chamber can be made smaller, and thereby the entire internal combustion engine can be made smaller and lighter. . In addition to the inertial force of pistons,
The couple between the weights can also be eliminated, and an engine with less vibration can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional front view of an embodiment of the present invention, FIG. 2 is a longitudinal sectional side view, and FIGS. 3(a) and 3(b) are explanatory diagrams of the operation of the present invention and the prior art. 1...Crank chamber 5. ,, crank 5a...
・Crank arm 12...flywheel 13.14
...Balanced weight patent applicant Honda Motor Co., Ltd. Figure 1

Claims (1)

[Claims] 1. In a single-cylinder internal combustion engine in which a crankshaft without a balance weight is mounted in a crank chamber, and a flywheel is attached to one of the extensions of the crankshaft that protrudes outside the crank chamber, A single cylinder internal combustion engine characterized in that balance weights are integrally provided at a plurality of locations with their center lines distanced from the flywheel. 2. The single-cylinder internal combustion engine according to claim 1, wherein the balance weights distributed at a plurality of locations are arranged on opposite sides in the diametrical direction so as to intersect at right angles to the crankshaft center. institution.