JPS5822409Y2 - Crankshaft of a two-cylinder model engine - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a crankshaft applied to a two-cylinder engine for models.

A conventional crankshaft used in a two-cylinder model engine has a structure in which a crank arm 3 having two crank pins 2 is integrally connected and fixed to a shaft 1, as shown in Fig. 1. Connecting rod 4 for each pin 2
are connected by a connecting part 5 provided at the tip thereof.

Furthermore, as shown in Fig. 2, in order to make it possible to remove the connecting rod from the crankshaft when disassembling the engine, the connecting portion 5 of the connecting rod 4 has a structure in which a cylindrical body is cut along a plane that includes its axis. The members 6 separated thereby are removably attached by attachment screws 7.

However, model engines are extremely small, and the diameter of the connecting rod 4 is generally only a few millimeters, so the mounting screws that can be applied to the mounting portion 5 have a diameter of 1 mm or less, which poses many problems in terms of processing and strength.

In particular, for small engines of 0.2 in 3 type or smaller, the internal volume of the crankcase is small, so it is actually extremely difficult to adopt the structure shown in Figures 1 and 2. It is difficult to

This invention provides a crankshaft for a two-cylinder model engine that can be made compact while maintaining sufficient strength, and that allows connecting rods to be easily attached and detached without impairing the positional accuracy of each crank pin. The purpose is to

The gist of this invention to achieve the above object is as described in the claims for utility model registration above.

A preferred embodiment of this invention will be described below with reference to the drawings.

A shaft indicated by reference numeral 11 in FIG. 3 is supported via a bearing (not shown) on a crank kennis 12 of a two-cylinder horizontally opposed model engine, and a crank arm 13 is removably attached to one end of this shaft 11. installed.

As shown in FIGS. 4 and 5, this crank arm 13 has a pair of crank pins located symmetrically across the axis of a disc-shaped disc portion 14 with a through hole 14a in the center. 15 and 16 are provided.

One crank pin 16 has a stepped cylindrical shape, and its small diameter stepped portion 16 a engages with an engagement groove 17 a of a rotary valve shaft 17 supported by the crank case 12 .

The rotary valve shaft 17 is a known rotary valve shaft that sucks a mixture from a carburetor (not shown) at a predetermined timing through a port 18 thereof.

The other crank pin 15 has a retaining portion 15a formed by cutting off a portion of the tip of a cylinder.

And each crank pin 15 and 16 connects the connecting rod 1
The connecting rod 19 and the crankshaft are connected to each other by passing through a through hole in a mounting portion 19 a at the tip of the connecting rod 19 .

Also, in this state, the small diameter stepped portion 16 a of the crank pin 16
is engaged and held in the engagement groove 17a of the rotary valve shaft 17, and the outer peripheral end surface of the crank pin 16 is held in a position close to or in contact with the inner wall surface 17b of the rotary valve shaft 17.
This serves to prevent the connecting rod 19 connected to the connecting rod 19 from being pulled out.

On the other hand, the shaft 11 has a cylindrical connecting portion 20 at one end thereof,
As shown in FIGS. 7 and 8, the center hole of the connecting portion 20 has an outer circumferential surface 21a having an outer diameter slightly smaller than the inner diameter of the center hole of the connecting portion 20, and an outer circumferential surface 21a having a tapered cross section. A conical inner circumferential surface 21b and a slotted groove 2
A C ring 21 having a diameter of 1 C is housed coaxially.

Further, as shown in FIG. 6, the connecting portion 20 is formed with a mounting hole 22 extending in the axial direction from the end surface thereof.

The mounting hole 22 is circular and has the same diameter as the crank pin 15, and a portion of its circumference overlaps with the circumference of the center hole of the connecting portion 20.

That is, the mounting hole 22 has a shape in which a part of a cylinder is cut out along the circumferential surface of a cylinder having a larger diameter than this, and the C-ring accommodated in the center hole of the connecting part 20 is inserted into the cutout surface. It is in contact with the outer circumferential surface 21a of 21.

The crank pin 15 is inserted into this mounting hole 22.
The engaging portion 15a has a cross section similar to this attachment hole 22.

Further, in order to press the C-ring 21 toward the mounting hole 22, a fixing screw 23 is provided with a screw head having a conical outer circumferential surface 23a that joins the conical inner circumferential surface 21b of the C-ring. , a screw hole 2 provided on the connecting portion 20 side of the shaft 11
It is screwed into 4.

In the crankshaft configured in this way, the shaft 1
To fix the crank arm 13 to the crank arm 1, insert the retaining part 15a formed on one crank pin 15 into the mounting hole 22, and insert the center of the crank arm 13 into the hexagonal hole provided in the head of the fixing screw 23. A special tool is inserted through the through hole 14a of the shaft 11, and the fixing screw 23 is screwed into the threaded hole 24 of the shaft 11. ring 21
This is done by pressing the engaging portion 15a toward the inner circumferential surface of the mounting hole 22 by expanding in the radial direction.

The retaining part 15a has a shape obtained by cutting out a part of a cylinder,
Since the outer circumferential surface 21a of the C-ring 21 is pressed against this cut surface, it is pressed against the inner circumferential surface of the mounting hole 22, is accurately positioned with respect to the mounting hole 22, and is attached to the other crank pin 16. The connecting rod 19 is inserted and connected, and the small diameter stepped portion 16a is inserted into the retaining groove 17 of the rotary valve shaft 17.
All you have to do is engage with a.

Also, during disassembly, the crankcase 12 is moved and the retaining groove 17a of the rotary valve shaft 17 and the crank pin 1 are connected to each other.
By releasing the small diameter stepped portion 16 a of No. 6 and loosening the fixing screw 23 using a special tool, the engaging portion 15 a of the crank pin 15 can be removed from the mounting hole 22 and the crank can be removed from the shaft 11. The arm 13 can be easily separated, and therefore the connecting rod 19 can be easily removed from the crank pins 15, 16.

Therefore, the mounting portion 19a of the connecting rod 19 only needs to have a through hole through which the crank pin 15 or 16 is inserted, and its wall thickness can be reduced.

This is not only advantageous for a small engine with a small internal volume of the crankcase 12, but also allows the diameters of the crank pins 15 and 16 to be increased, resulting in an improvement in overall strength.

[Brief explanation of the drawing]

Fig. 1 is a side view showing a conventional crankshaft and a connecting rod connected thereto, Fig. 2 is an enlarged sectional view taken along line A-A in Fig. 1, and Fig. 3 is a crankshaft according to an embodiment of this invention. FIG. 4 is a side view showing the crank arm of the same crankshaft, and FIG.
The figure is a front view, Figure 6 is a sectional view taken along line B-B in Figure 3, Figure 7 is an enlarged front view of the C ring shown in Figure 3, and Figure 8 is taken along line C-C in Figure 7. FIG. 11... shaft, 12... crank case, 13... crank arm, 14...
Disc part, 14a...Through hole, 15°16...
...Crank pin, 15a...Engagement part, 1
6 a...Small diameter step part, 19...Connecting rod, 19a...Mounting part, 20...Connecting part, 21...CIJ song 21b...
...Conical inner peripheral surface, 22...Mounting hole, 23...
...Fixing screw, 23a...Conical outer peripheral surface.

Claims (1)

[Scope of utility model registration request] It has a shaft with a cylindrical connecting part at one end, and a pair of crank pins installed at symmetrical positions across the axis of a disc part with a through hole in the center, and a crank arm connected to the shaft by engaging an engaging portion with the connecting portion, the connecting portion comprising:
a mounting hole extending in the axial direction and arranged so as to partially overlap the circumferential surface of the center hole; a fixing C ring having a conical inner circumferential surface inserted coaxially into the center hole; a fixing screw having a conical outer circumferential surface that engages with the conical inner circumferential surface of the C-ring to press the C-ring toward the mounting hole; A crankshaft for a two-cylinder model engine, characterized in that the crankshaft has a cross section similar to a hole, and is held in a predetermined position by the C-ring when inserted into the mounting hole.