JPH1078025A - Assembly type crank shaft - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain material and processing cost from increasing and improve fatigue strength of a fitting part by forming a protrusion part axially at an outer periphery continuous to the shrinkage fit part of a journal, protruding a crank web end surface axially to the end surface of the protrusion part, and forming an overhung part. SOLUTION: A protrusion part 12 protruding by an amount (a) axially from an axial surface 1c is formed on the shrinkage fit surface 11 side of the outer periphery of a journal 1, and the inner periphery of the protrusion part 12 is jointed smoothly to the round part 1d of a radius ρ, and the round part 1d is ground by an amount (e) from a bearing sliding surface 1b. The end surface 2a of a crank web 2 is protruded by an amount (b) axially to the end surface 1a of the protrusion part 12 to eliminate a fitted part at an overhung part (b). During running, the line of force 20 of repetitive stress moves to the interior side of the journal 1, and in a sliding range near the protrusion part 12, repetitive stress becomes lower, so that safety factor against fatigue failure rises. It is possible to provide material and processing cost reduction by reducing the diameter of the journal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an assembled crankshaft used for an internal combustion engine, a reciprocating compressor and the like.

[0002]

FIGS. 3A and 3B show a main part of an assembled crankshaft for an internal combustion engine.
In the drawing, reference numeral 1 denotes a journal, 2 denotes a crank web, and 3 denotes a crank pin. The journal 1 and the crank web 2 and the crank web 2 and the crank pin 3 are connected by shrink fitting.

FIG. 4 shows a conventional example of a shrink fit connection between the journal 1 and the crank web 2 in the crankshaft.
As shown in FIG. 4 and 5, reference numeral 20 denotes a stress line. In such a crankshaft, the diameter D ₁ of the shrink fit surface 11 between the journal 1 and the crank web 2 is
Is formed by shaving from the shrink-fitting surface 11 and is set in consideration of the material and processing cost and the stress of the shrink-fitting surface.

In the crankshaft shown in FIG. 4, since the diameter D ₁ of the shrink fit fitting surface 11 is large,
Stress is lower, it is necessary to mold the journal 1 scraped up journal diameter D ₂ from the rod-like body to the diameter D ₁ of the shrink fit fitting surface and an outer diameter, the greater the scraping allowance, Material costs and processing costs increase.

In the crankshaft shown in FIG.
It is smaller than that of FIG. 4 the diameter D ₁ of the shrink fit mating face 11. In this case, the material cost and processing cost associated with the above-mentioned shaving are reduced as compared with those in FIG. 4, but the stress of the shrink fit fitting surface 11 increases and
One end may be locally slippery, and the occurrence of fretting fatigue cracks 12 due to the local slip may be observed.

When the journal 1 and the crank web 2 partially (especially at the end) slip relative to each other on the shrink fit surface 11, the crankshaft is incorporated. Since the surface stress due to the frictional force caused by the slip is added to the repetitive stress caused by the operation of the engine, the stress becomes abnormally high.

FIG. 6 shows the distribution of shear force and slip resistance in the vicinity of the shrink fit surface 11 in the conventional assembled crankshaft shown in FIGS. In FIG. 6, τ is the shearing force of the shrink-fit fitting surface 11 that generates slip, and μp is the slip resistance of the fitting surface 11.

The above-mentioned shearing force τ is proportional to the repetitive stress caused by the operation of the engine, and becomes maximum near the end of the shrink fit surface 11. Therefore, the shrink fit is used to reduce the material cost and the processing cost. The diameter D _{1 of the} mating surface 11 is set to the journal diameter D.
_As it approaches ₂ , the stress will increase.

On the other hand, the slip resistance μp decreases at the end of the shrink fit surface 11, but in the relative slip region S where the shear force τ is larger than the slip resistance μp, the journal 1 and the crank web 2 and a relative slip occurs. Due to the relative slip, fretting fatigue cracks occur in the relative slip region S even if the fatigue strength of the base material of the crankshaft is 1/3 to 1/4 and the stress is extremely small.

Therefore, in the above crankshaft, it is required that the diameter D ₁ of the shrink fit surface 11 be kept small to reduce the stress near the fit surface 11.

An object of the present invention is to reduce the material cost and the processing cost by keeping the diameter of the shrink fit portion small,
An object of the present invention is to provide an assembled crankshaft in which the stress at the fitting portion is reduced to improve the fatigue strength.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the gist thereof is to provide an assembling type crankshaft in which a crank web is shrink-fitted around the outer periphery of a journal. A journal is formed with an axially protruding portion at an outer peripheral portion connected to the shrink fit portion, and the end surface of the crank web is protruded in the axial direction with respect to the end surface of the protruding portion so that the journal is formed. This is because an overhang portion that does not fit with the crank web is formed.

According to the above-mentioned means, since the axially projecting portion is provided at the outer peripheral portion connected to the shrink fit fitting surface of the journal with the crank web, the line of force of the repeated stress caused by the operation of the engine or the like is reduced. It moves to the inner side from the protruding portion, and the repetitive stress in the slip region near this portion decreases. Therefore, even if the diameter of the shrink fit surface, that is, the outer diameter of the journal, is reduced, a safety factor against repeated stress can be secured, and the journal diameter is reduced while the repeated stress is kept below the fretting fatigue limit. Can be.
Thereby, reduction of material cost and processing cost can be realized.

Further, the surface pressure in the vicinity of the slip region is increased by overhanging the end surface of the crank web with respect to the outer peripheral end surface of the journal to shorten the fitting portion.
The slip area can be reduced. By the above, it is possible to isolate the slip region and the point of maximum stress application,
Fretting fatigue strength can be increased.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS. FIG. 1 is a sectional view showing the vicinity of a shrink fit portion between a journal 1 and a crank web 2 of an assembled crankshaft for an internal combustion engine according to a first embodiment of the present invention, and FIG. FIG. 1 is a diagram showing a second embodiment of the present invention.

1 and 2, reference numeral 1 denotes a journal, 2 denotes a crank web, and both are shrink fit on a shrink fit surface 11.

Shrink fit surface 1 on the outer periphery of journal 1
On one side, a protruding portion 12 protruding from the axial surface 1c by a in the axial direction is formed. And the protrusion 1
The inner peripheral side of 2 is smoothly coupled to a rounded portion 1d having a radius ρ via an inclined portion 1f. Further, the rounded portion 1d is formed by shaving e from the bearing sliding surface 1b.

The end surface 2a of the crank web 2
Are the protrusions 12 located inside the shrink fit surface 11.
Is protruded (overhang) by b in the axial direction with respect to the end surface 1a, and the overhang portion b has no fitting portion.

Here, the relationship between the protruding amount a of the protruding portion 12 and the overhang amount b of the crank web 2 is b = (1/2 to 1) in consideration of a shearing force and a slip deformation described later.
/ 3) a is preferred.

The rounded portion 1d formed on the inner peripheral side of the protruding portion 12 has a large radius of curvature ρ ₂ on the inner peripheral side and a small radius of curvature ρ ₂ as shown in the second embodiment of FIG. _It may be formed as a curved surface having _two radii of curvature ρ ₁ and ρ ₂ such that _one curved surface is smoothly connected.

Here, the large and small radii of curvature ρ ₁ and ρ ₂
Is preferably about ρ ₁ ≒ (１ ／) ρ ₂ .

During operation of the engine incorporating the assembled crankshaft constructed as described above, as shown in FIGS. 1 and 2, the force lines 20 indicating the transmission of the repetitive stress are:
Since the projection 12 is formed, the projection 12 moves to a position deeper than the end surface 1a of the projection 12 (inside the journal 1).

Therefore, in the slip region near the protruding portion 12, as shown in FIG. 2, the repetitive stress (shear force τ) decreases, and the safety factor against fretting fatigue failure increases. Therefore, even by reducing the diameter D ₁ of the above shrink-fit mating face 11 will have a sufficient safety factor against the fretting fatigue fracture.

The overhang portion b is provided so that the end surface 2a of the crank web 2 and the end surface 1a of the protruding portion 12 are provided.
By forming a part that is not fitted between the
The surface pressure in the slip region S of the shrink fit surface 11 is kept high, and the slip region S is reduced.

Therefore, by reducing the slip region S, it is possible to increase the fretting fatigue limit for repeated stress.

[0026]

The present invention is configured as described above.
According to the present invention, by providing a projection in the axial direction near the shrink fit fitting portion on the outer periphery of the journal, the maximum stress application point on the outer circumference of the journal moves inward, and the end of the shrink fit fitting portion By providing an overhang portion where the journal and the crank web do not fit together, the slip region is reduced, and as a result, the maximum stress action point and the slip region are isolated, and the fretting fatigue strength can be improved.

Further, since the safety factor of fretting fatigue is increased, if the safety factor is suppressed to a required value, the outer diameter of the journal can be reduced to realize a reduction in material cost and processing cost associated with the reduction in the diameter of the journal. Can be.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of an assembled crankshaft according to a first embodiment of the present invention.

FIG. 2 is an equivalent view of FIG. 1 showing a second embodiment of the present invention.

3A and 3B show a schematic structure of an assembled crankshaft, in which FIG. 3A is a longitudinal sectional view, and FIG.

FIG. 4 is a structural view of a conventional assembled crankshaft showing a case of a large diameter journal.

FIG. 5 is a view showing a small-diameter journal corresponding to FIG. 4;

FIG. 6 is a stress and slip resistance diagram of a conventional crankshaft.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Journal 2 Crank web 11 Shrink fit fitting surface 12 Projection

Claims (1)

[Claims] 1. An assembling type crankshaft in which a crank web is shrink-fitted onto the outer periphery of a journal, wherein a projecting portion projecting in the axial direction is formed on an outer circumferential portion of the journal connected to the shrink-fitting portion. An assembling type crankshaft, characterized in that an end face of the crank web is axially protruded from an end face of the protruding portion to form an overhang portion where the journal and the crank web are not fitted. .