JP2002181133A - Engine crankshaft structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide engine crankshaft structure capable of securing inertia mass as large as possible and at the same time securing its weight lightened. SOLUTION: The aperture 5a of a disk shaped balance weight 5 is fitted to the crank web 2 of a crank shaft 1 comprising the crank web 2 and a crank pin 3 molded in a body. With the balance weight 5 fitted to the crank web 2, the crank shaft 1 and the balance weight 5 become a coaxial state. The center O2 of the balance weight 5 and the center O3 of the aperture 5a are offset. A positioning key 6 is provided between the crank web 2 and the balance weight 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a crankshaft structure for an engine.

[0002]

2. Description of the Related Art Conventionally, for example, Japanese Patent Application Laid-Open No. 8-93746
As described in Japanese Patent Application Laid-Open Publication No. H10-209, as a crankshaft structure of a multi-cylinder engine, a crankpin connected to a large end of a connecting rod of each cylinder, and a pair of crank webs holding the crankpin from both ends are forged or cast. Is integrally formed. In such a structure, a balance weight is provided on the side opposite to the crankpin of the crank web, and the inertial force of the reciprocating mass of the piston and the like of each cylinder, and the rotational motion mass around the large end of the connecting rod. The centrifugal force is
The balance weights are balanced by the inertia.

[0003]

However, with such a structure, the inertia mass of the crankshaft increases as the mass of the outer periphery increases, but only the balance weight is provided on the crank web on the side opposite to the crankpin. Therefore, the inertial mass cannot be made sufficiently large.

In order to sufficiently increase the inertial mass, it is conceivable to increase the diameter of the crank web and provide a balance weight on the outer periphery thereof. In addition, in addition to the difficulty of manufacturing by forging, the weight is increased, and the assembling property is poor.

It is an object of the present invention to provide a crankshaft structure of an engine that secures as large an inertial mass as possible and reduces the weight.

[0006]

According to a first aspect of the present invention, in a crankshaft structure of an engine provided with a crank web and a crank pin for a crankshaft, an annular balance weight is provided on the crank web. It is fitted externally coaxially with the crankshaft.

According to the first aspect of the present invention, a simple structure in which an annular balance weight is externally fitted to the crank web so as to be coaxial with the crankshaft, and the outer peripheral portion having a large influence on the inertial mass is provided. It is possible to distribute the weight uniformly over the whole, and to increase the mass of the outer peripheral portion without increasing the total weight much. Therefore, the structure is advantageous in increasing the inertial mass.

In this case, although the structure is advantageous in increasing the inertial mass, S in FIG.
Since it is not possible to add mass to the part of 1, S2,
Constrained by an increase in inertial mass. In addition, the portion near the center of rotation of the crankshaft is a portion where the inertial mass does not increase relatively, but the mass of that portion increases and the mass of the entire crankshaft increases, so there is still room for improvement. Have been.

Therefore, the present invention is further improved, and in a crankshaft structure of an engine in which a crank web and a crank pin are provided for the crankshaft, a circular shape is provided for the crank web. The opening of the disc-shaped balance weight having an opening may be fitted so that the crankshaft and the balance weight are coaxial.

According to the second aspect of the present invention, the weight of the portion near the rotation center of the crankshaft, which does not significantly affect the increase of the inertial mass, is reduced, and the outer peripheral portion can be reduced without increasing the overall weight. By increasing the mass, the inertial mass can be increased. In particular, since the balance weight has a disk shape and the openings formed in the balance weight are also circular, it is easy to manufacture the balance weight, which is advantageous in terms of mass productivity.

According to a third aspect of the present invention, the center of the balance weight may be offset from the center of the aperture.

According to a third aspect of the present invention, there is provided a simple structure in which the center of the balance weight and the center of the opening of the balance weight are offset from each other. Reduce the weight of
The mass of the outer peripheral portion can be increased without increasing the overall weight, thereby increasing the inertial mass.

[0013] As described in claim 4, a positioning key is provided between the balance weight and the crank web.

According to the fourth aspect of the present invention, the positional relationship between the balance weight and the crank web is uniquely determined by the positioning key, and the balance with the reciprocating portion mass of the piston, the connecting rod and the like is not impaired.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a longitudinal sectional view showing a crankshaft structure of a four-cylinder engine according to the present invention, FIG. 2 is an enlarged view of the same part, FIG.
FIG. 3 is a sectional view taken along line AA in FIG. 2.

As shown in FIGS. 1 to 3, a crank web 2 and a crank pin 3 are integrally formed with a crank shaft 1 by forging or casting. here,
Both ends of the crank pin 3 are held by a pair of crank webs 2. Journal portions 1a are provided at both ends of the crankshaft 1 and at portions corresponding to between the cylinders. Each journal portion 1a is rotatably supported by a crankcase (not shown).

The opening 5a of the disc-shaped balance weight 5 having the circular opening 5a is fitted to the crank web 2 having a substantially constant width integrally formed with the crankshaft 1. Balance weight 5
Are fixed to the crank web 2 by welding.
In the fitted and fixed state, the center O1 of the crankshaft 1 and the center O2 of the balance weight 5 match. Therefore, the balance weight 5 is fitted to the crank web 2 so as to be coaxial with the crankshaft 1, and is fixed by welding.

The balance weight 5 has a center O2
And the center O3 of the opening 5a is offset by a certain amount in the diameter direction of the balance weight 5. As a result, as shown in FIG. 4, the balance weight 5 is formed so that the thickness on one side is large and the thickness on the other side is small in the diameter direction. While reducing the mass in the vicinity and reducing the weight, the mass of the outer peripheral portion is increased to increase the inertial mass.

On one side of the balance weight 5, a weight-side key groove 5b facing the opening 5a is formed, and the crank web 2 corresponding to the weight-side key groove 5b is also shown in FIG. As shown, the web side keyway 2
a is formed. And, between the balance weight 5 and the crank web 2, the key grooves 5b and 2a are provided.
The positioning key 6 is inserted into the
And the crank web 2 is positioned. This is because the end faces 2b and 2c of the crank web 2 are curved surfaces having a curvature corresponding to the shape of the peripheral surface of the opening 5a because the crank web 2 is inserted into the opening 5a of the balance weight 5. If the positioning key 6 is not used, the relative position between the crank web 2 and the balance weight 5 cannot be determined.

An outer peripheral concave portion 2d is formed on the outer peripheral portion side of the crank web 2 to secure rotational balance, while a central concave portion 2e is formed on the central portion side to reduce weight. .

The crankpin 3 of the crankshaft 1 thus formed is connected to the large end 11a of the connecting rod 11 of each cylinder (not shown) as shown in FIG. The piston 12 is connected to the small end portion 11b of the first through a piston pin 13.
The inertial force of the reciprocating motion mass of the piston 12 and the like of each cylinder and the centrifugal force of the rotating motion mass around the large end of the connecting rod 11 are the inertia force of the balance weight 5,
It will be effectively balanced.

According to the above construction, an opening 5a of a disk-shaped balance weight 5 is formed in the crank web 2 having a substantially constant width integrally formed with the crankshaft 1 by using the crankshaft 1 and the crankshaft 1. Since the balance weight 5 is fitted so as to be coaxial, the weight of the portion near the rotation center O1 of the crankshaft 1, which is a portion that does not significantly affect the increase in inertial mass, is reduced, and the overall weight is increased. By increasing the weight of the outer peripheral portion without increasing the weight, it is possible to increase the inertial mass. In particular, since the disc-shaped balance weight 5 having the opening 5a is used, it is possible to realize that the weight of the outer peripheral portion can be increased without difficulty.

In order to increase the inertial mass, it is effective to increase the mass at a position where the distance from the center of the crankshaft 1 is large. To reduce the weight without reducing the inertial mass, it is effective to increase the inertial mass. This is because it is necessary to reduce the weight near the center of the crankshaft, which does not significantly affect the increase.

In the balance weight 5, the center O2 is coaxial with the center O2 of the crankshaft 1, and the center O2 and the center O3 of the opening 5a are offset in the diameter direction. Center O1 of crankshaft 1
This is because it is possible to reduce the mass of the portion close to, and increase the mass of the portion far away. Thus, the center O2 of the balance weight 5 and the center O3 of the opening 5a thereof
The weight of the outer periphery is reduced without increasing the overall weight by reducing the weight of the portion near the rotation center of the crankshaft 1, which is a portion that does not significantly affect the increase in the inertial mass, with a simple structure of offsetting Can be increased to increase the inertial mass.

Moreover, since the balance weight 5 has a disk shape and the opening 5a formed in the balance weight 5 has a circular shape, processing is easy, and manufacture of the balance weight 5 is also easy.

Further, since the positioning key 6 is provided between the balance weight 5 and the crank web 2, even if the balance weight 5 is provided separately, the balance key 5 and the crank web 2 can be moved by the positioning key 6. Is uniquely determined, and the inertial force of the reciprocating portion weight of the piston 12, the connecting rod 11, etc., and the centrifugal force of the rotational motion mass around the large end of the connecting rod 11 are determined by the inertial force of the balance weight 5. It is balanced and their power balance is not compromised.

In the above embodiment, the crankshaft 1
As the balance weight 5 provided on the crank web 2 integrally formed with the shaft, a center weight O2 of the balance weight 5 and a center O3 of the opening 5a thereof are offset, but the present invention is not limited thereto. Instead, for example, as shown in FIG. 7, it is also possible to use an annular balance weight 21 having a uniform thickness and a constant thickness over the entire circumference. That is, as shown in FIG.
The crank web 22 of the crank shaft 24 formed integrally with the crank web 22 and the crank pin 23
On the other hand, an annular balance weight 21 is externally fitted,
It is fixed to the crankshaft 24 by welding. By being externally fitted in this way, the center of the crankshaft 24 and the center of the balance weight 21 coincide with each other. The structure has been. Therefore, with a simple structure in which the annular balance weight 21 is externally fitted to the crank web 22, it is possible to increase the weight of the outer peripheral portion without increasing the overall weight much.

In this case, since mass cannot be added to the portions S1 and S2 in FIG. 7, the increase in the inertial mass is restricted.
Compared with the one described in JP-A-93746, it is possible to increase the inertial mass without increasing the outer diameter.

Further, in the above embodiment, the balance weight is fixed to the crank web by welding, but it is also possible to employ fastening by bolting or press fitting.

Further, notches or projections may be provided on the crank web, or notches or gaps (voids) may be provided on the balance weight. In addition, the crank web may be provided so as to be inserted (press-fit) into the gap of the balance weight.

Further, the crankshaft structure of the engine according to the present invention can be applied not only to the number of cylinders of the engine but also to single cylinders or multiple cylinders.
Either a stroke engine or a four-stroke engine can be used.

[0033]

The present invention is embodied as described above, and has the following effects.

The invention according to claim 1 has a simple structure in which an annular balance weight is externally fitted to a crank web provided on a crankshaft, and increases the weight of the outer peripheral portion without increasing the overall weight much. Can be done.

According to a second aspect of the present invention, the opening of the disc-shaped balance weight having an opening is formed coaxially with the crank web provided on the crankshaft. So that the weight of the part near the center of rotation of the crankshaft, which does not significantly affect the increase in inertial mass, is reduced, and the weight of the outer peripheral part is increased without increasing the overall weight By doing so, the inertial mass can be increased.

According to a third aspect of the present invention, if the center of the balance weight is offset from the center of the opening of the balance weight, the inertia mass can be increased with a simple structure without increasing the overall weight. Can be planned.

According to a fourth aspect of the present invention, if a positioning key is provided between the balance weight and the crank web, the positional relationship between the balance weight and the crank web is uniquely determined by the positioning key. Once determined, the balance with the weight of the reciprocating part of the piston, connecting rod, etc. is not impaired.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a crankshaft structure of a four-cylinder engine according to the present invention.

FIG. 2 is an enlarged view of the same part.

FIG. 3 is a cross-sectional view taken along line AA of FIG.

FIG. 4 is a front view of a balance weight according to the present invention.

FIG. 5 is a front view of the crank web according to the present invention.

FIG. 6 is a diagram showing a relationship between a crankshaft and a piston according to the present invention.

FIG. 7 is a view similar to FIG. 3, showing another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Crankshaft 1a Journal part 2 Crank web 2a Keyway 3 Crankpin 5 Balance weight 5a Opening 5b Keyway 6 Positioning key 11 Connecting rod 12 Piston 13 Piston pin O1 Center of crankshaft 1 O2 Center of balance weight 5 O3 Opening Center of 5a

Claims (4)

[Claims] 1. A crankshaft structure for an engine, wherein a crank web and a crank pin are provided on a crankshaft, wherein an annular balance weight is fitted around the crank web coaxially with the crankshaft. The crankshaft structure of the engine, characterized in that: 2. A crankshaft structure of an engine in which a crank web and a crank pin are provided on a crankshaft, wherein the opening of a disc-shaped balance weight having a circular opening is provided on the crank web. The crankshaft structure of the engine, wherein the crankshaft and the balance weight are fitted so as to be coaxial. 3. The engine crankshaft structure according to claim 2, wherein the balance weight has a center offset from the center of the opening. 4. The engine crankshaft structure according to claim 2, wherein a positioning key is provided between said balance weight and said crank web.