JP2017053441A - Method for manufacturing crank shaft - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a crank shaft that can decide a depth of a quench hardening layer based on strength required for a crank shaft and prevent a shaft center from being bent.SOLUTION: In the method for manufacturing a crank shaft, a crank fillet 6 positioned at a boundary point between a crank journal 2 and a crank arm 4 is quenched before quenching of a pin fillet 7 positioned at a boundary point between a crank pin 3 and the crank arm 4.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for manufacturing a crankshaft, and more particularly, to a method for manufacturing a crankshaft that can achieve both improvement in strength and wear resistance and prevention of axial center bending.

  A crankshaft that converts a reciprocating motion of a piston into a rotational motion is used in an internal combustion engine (hereinafter sometimes referred to as an engine). The crankshaft rotates while receiving a large force, and is required to be excellent in strength and rigidity and to rotate smoothly in a balanced manner.

  The crankshaft has a crankpin and a crank journal connected via a crank arm. Crankshaft crankpins and crank journals require bending and torsional stresses generated by rotational movement, as well as sliding surfaces that can withstand wear, and heat treatment such as quenching is required to improve strength and wear resistance. Done.

  For example, a steel material mainly composed of a ferrite / pearlite structure can be hardened by being changed to a hard and wear-resistant martensite structure by heating and cooling above the austenitizing temperature.

  However, the quenched and hardened portion of the crankshaft that has been quenched undergoes a volume change due to expansion due to phase transformation. When the fillet portion located at the boundary point between the crank journal or the crank pin and the crank arm is quenched, the volume change tends to be unbalanced, and the crankshaft axis is bent.

  Therefore, after quenching, not only the process of correcting the bending is necessary, but also the residual stress distribution is changed by the correction, and the compressive residual stress in the vicinity of the surface of the fillet portion is reduced, and the fatigue strength is reduced. Sometimes. On the contrary, in order to make correction possible, it is not possible to sufficiently harden when quenching to such an extent that plastic deformation is possible in advance.

  In particular, the crank pin is connected to the piston via the connecting rod and receives a large stress directly from the piston, and the pin fillet portion located at the boundary point between the crank pin and the crank arm becomes a neck of fatigue strength.

  Therefore, it is necessary to sufficiently harden the pin fillet portion. After sufficiently hardening the pin fillet portion located at the boundary point between the crank pin and the crank arm, the journal fillet side located at the boundary point between the crank journal and the crank arm is used. Curvature correction is performed.

  Japanese Patent Application Laid-Open No. 2003-286520 of Patent Document 1 is located at the boundary point between the crank journal and the crank arm, based on the quench hardened layer depth of the pin fillet portion located at the boundary point between the crank pin and the crank arm. It has been disclosed to reduce the bending of the crankshaft by adjusting the depth of the quench hardened layer of the journal fillet.

JP-A-10-214640

However, in the thing of patent document 1, since the depth of the hardening hardening layer of a journal fillet is adjusted based on the hardening hardening layer depth of a pin fillet part, the bending of a crankshaft is corrected. For this reason, the depth of the hardened hardening layer such as the journal fillet portion is restricted.
Therefore, it is difficult to achieve both improvement in the strength and wear resistance of the crankshaft and prevention of occurrence of axial center bending.

  The present invention has been made in view of such problems of the prior art, and the object of the present invention is to determine the depth of the hardened hardened layer according to the strength required by the crankshaft, and Another object of the present invention is to provide a method for manufacturing a crankshaft that can prevent the occurrence of axial center bending.

  As a result of intensive studies to achieve the above-mentioned object, the present inventors have changed the journal fillet portion in contrast to the conventional method of adjusting the bending caused when the pin fillet portion is cured by the journal fillet portion. By hardening before the pin fillet part, it is possible to suppress the deformation in the vicinity of the crank pin caused by the hardening of the pin fillet part, to suppress the bending when hardening the pin fillet part, and to prevent the axial center bending. The headline and the present invention were completed.

  That is, the crankshaft manufacturing method of the present invention includes a pin fillet portion positioned at a boundary point between the crank pin and the crank arm after quenching a journal fillet portion positioned at a boundary point between the crank journal and the crank arm. It is characterized by quenching.

  According to the present invention, the journal fillet portion is hardened before the pin fillet portion, and the deformation in the vicinity of the crank pin that occurs when the pin fillet portion is hardened is suppressed. It is possible to provide a method of manufacturing a crankshaft that can achieve both improvement in strength and wear resistance and prevention of axial center bending without being restricted.

It is an external view which shows an example of the crankshaft of this invention. It is a figure which shows the position of each crankpin (P1-P6) when the crankshaft of FIG. 1 is seen from an axial direction. It is sectional drawing which shows the hardening hardening layer of a crankshaft. It is the schematic which shows the arrangement | positioning state of the heating coil at the time of induction-quenching a crank journal and a crank fillet. It is the schematic which shows the arrangement | positioning state of a heating coil when it sees from the axial direction of a crankshaft.

The manufacturing method of the crankshaft of this invention is demonstrated in detail.
In the crankshaft manufacturing method of the present invention, the crankpin, the crank journal, and the surfaces in the vicinity thereof are quenched to improve the strength and wear resistance of the crankshaft.

First, the crankshaft will be described.
The crankshaft is integrally formed by forging a carbon steel for mechanical structure (for example, S53C, S48C, etc.). As shown in FIG. 1, the crankshaft 1 is connected to a crank journal 2 (J1 to J4) and a crankpin 3 (P1 to P6) via a crank arm 4 having a balance weight 5. FIG. 2 shows the positions of the crankpins 3 (P1 to P6) when viewed from the axial direction.

  The crank arm 4 that connects the crank journal 2 and the crank pin 3 has a balance weight 5 extending to the opposite side of the crank pin 3.

As shown in FIG. 3, at the end of the crank journal 2, the crank journal 2 is cranked at the corner between the peripheral surface of the crank journal 2 and the crank arm 4, that is, at the boundary point between the crank arm 4 on the peripheral surface of the crank journal 2. A fillet 6 is formed.
A pin fillet 7 is formed at the end of the crankpin 3 at the corner between the peripheral surface of the crankpin 3 and the crank arm 4, that is, at the boundary point between the peripheral surface of the crankpin 3 and the crank arm 4.

Since the crankshaft 1 rotates at a high speed, an oil hole 8 is formed in the radial direction of the crank journal 2 so that oil circulates through the crank journal 2 and the crankpin 3 in order to prevent seizure due to long-time operation. .
The oil hole 8 is formed so as to communicate with the crank pin 3, the surface of the crank journal 2 and the surface of the crank pin 3 are lubricated with oil to reduce the friction coefficient, and the generated heat is transferred to the crankshaft 1. Release outside.

  The crank journal 2 is rotatably supported on the cylinder block by a main bearing (not shown). The crank pin 3 is rotatably connected to one end of a connecting rod by a connecting rod bearing (not shown).

  The crankshaft 1 in the engine converts linear thrust obtained by exploding fuel in a cylinder (not shown) into rotational movement of the crankpin 3 by a connecting rod (not shown).

  When this linear motion is converted into rotational motion, a strong bending load is applied to the crankshaft 1, particularly the crankpin 3. The stress due to this bending load most acts on the pin fillet.

  Further, the crank pin 3 and the crank journal 2 must withstand wear due to rotational movement, and the surfaces of the crank journal 2 and the journal fillet portion 6 and the crank pin 3 and the pin fillet portion 7 are hardened by quenching. A layer is formed.

  In the present invention, the pin fillet portion 7 is quenched after the journal fillet portion 6 of the crankshaft 1 is quenched.

  The crankpin 3 is provided offset from the central axis of the crankshaft 1, and it can be seen from FIG. 3 on the central axis side (bottom side) of the crankshaft and the side far from the central axis (top side). The adjoining crank arm is different. Therefore, when the pin fillet portion 7 is quenched, bending occurs.

  That is, the carbon steel generally has a large mass effect and has a large difference in hardening depending on the size and thickness of the steel material. Therefore, the amount of expansion associated with martensite formation differs between the bottom side and the top side. Therefore, quenching the pin fillet portion 7 causes a large bend due to the shape of the crankshaft 1.

  On the other hand, since the center of the crank journal 2 is the same as the center axis of the crankshaft 1 and the manner of attaching adjacent crank arms is substantially uniform, the pin fillet portion 7 is quenched even if the journal fillet portion 6 is quenched. A big bend like when it was done is unlikely to occur.

  The yield stress of the hardened layer martensified by quenching is about four times the yield stress of the ferrite / pearlite structure before hardening.

  Therefore, when the journal fillet portion 6 is quenched first, the journal fillet portion 6 does not bend even when subjected to stress due to volume expansion accompanying quenching of the crank pin and the pin fillet portion 7. In addition, since the pin fillet portion 7 is pressed by the hardened layer, bending of the pin fillet portion 7 is suppressed.

  In the present invention, the bend may be corrected after quenching the journal fillet portion 6 of the crankshaft 1 and before quenching the pin fillet portion 7. By correcting the bending caused by quenching of the journal fillet portion 6 with the pin fillet portion 7 and quenching the pin fillet portion 7, the occurrence of bending can be further prevented.

  The depth of the hardened layer of the journal fret portion is preferably 1 mm or more, and more preferably 2 mm or more and 5 mm or less, although it depends on the required strength and the shape of the crankshaft. If the depth of the hardened layer of the journal fret portion is 1 mm or more, it is possible to prevent the bending caused by quenching of the pin fillet portion 7.

  Although the said hardening can employ | adopt conventionally well-known hardening methods, such as induction hardening and laser hardening, it is preferable that it is induction hardening. In laser quenching, the heating range is narrow and shallow, so that the quenching time is very long. On the other hand, in the induction hardening, the heating range is wide and deep, so that quenching can be performed efficiently.

  In the present invention, it is preferable to quench the journal fillet portion and the crank journal at the same time, and to quench the pin fillet portion and the crank pin at the same time. By performing the burning simultaneously, not only the production efficiency is improved, but also the structure of the hardened layer of the crank journal and the journal fillet portion or the crank pin and the pin fillet portion is continuous, and the strength can be improved.

  The induction hardening can be performed by an induction hardening apparatus. The induction hardening apparatus, for example, by connecting a heating coil to an AC power source, generating an eddy current in the metal by a magnetic field generated by flowing an alternating current having a high frequency to the heating coil, applying heat treatment by Joule heat, and cooling, This is done by changing the phase to a hard and wear-resistant martensite structure.

The induction hardening apparatus 10 includes a rotating device 11, a heating coil 12, and a cooling device 13.
FIG. 4 is a diagram showing the arrangement of the heating coils when the crank journal and the crank fillet are induction-hardened, and FIG. 5 is a diagram showing the arrangement of the heating coils when viewed from the axial direction of the crankshaft. In FIG. 5, the portion of the crankpin is indicated by a dotted line.

  The rotating device 11 includes a rotation driving device such as a motor and a chuck 14 for gripping the crankshaft 1 and is configured to be rotatable while the crankshaft 1 is gripped. As shown in FIG. 3, the chuck grips and fixes both the left and right ends of the crankshaft 1 so that the rotation axis is horizontal.

  The heating coil 12 includes a semi-circular coil body and a plurality of substantially spherical insulating chips 15 provided on the lower end surface of the curved portion of the coil body.

  As shown in FIG. 5, the lower end surface of the curved portion of the coil body is formed corresponding to a partial region of the outer peripheral surface of the crank journal or the crank pin, and by supplying a high frequency current, the crank journal and the journal fret portion. Alternatively, the crankpin and the pin fillet are configured to be heatable.

  The insulating chip 15 is in contact with the peripheral surface of the crank journal or the peripheral surface of the crank pin, and when a high frequency current is applied, between the lower end surface of the curved portion of the coil body and the surface of the crank journal or the surface of the crank pin. Is maintained at regular intervals.

  The heating coil 12 is held by a tension member 16 such as a chain so that the heating coil 12 can be moved vertically and horizontally corresponding to the position of a crank journal or a crank pin that forms a hardened hardening layer.

  The cooling device 13 includes a coolant nozzle that can supply coolant, and supplies coolant to the surfaces of the crank journal and the journal fret part or the crank pin and pin fillet part that are heated to a substantially uniform temperature as a whole. It is configured to be available. The cooling device 13 supplies the coolant in a state where the crankshaft 1 is rotated after the heating energization is completed.

  When a high frequency current is supplied to the coil body of the induction hardening apparatus 10, an eddy current is generated in the crank journal and the journal fret part or the crank pin and the pin fillet part by a magnetic field generated by the coil body by electromagnetic induction. The surface of the crank journal and the journal fret part or the crank pin and the pin fillet part is heated by the Joule heat.

  The said heating temperature is more than an austenitizing temperature, for example, it heats to 930-950 degreeC. And after energization heating, the cooling water from a coolant nozzle is injected and cooled, and the ferrite pearlite structure before induction hardening changes into a martensite structure, and a hardened layer is formed.

According to the present invention, after the induction hardening is performed on the peripheral surface of the crank journal 2 and the journal fillet portion, the peripheral surface of the crank pin 3 and the pin fillet portion are induction-hardened to form the journal fillet portion. The formed hardened layer suppresses deformation caused by hardening of the pin fillet portion.
Therefore, in order to prevent the crankshaft from being bent, there is no restriction on the formation of the hardened layer such as the depth of the hardened layer, and the strength and wear resistance can be improved.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to the following Example.

[Example 1]
Induction hardening was performed on the crankshaft for the V6 engine shown in FIG.
Quenching is performed in the order shown in Table 1, that is, the journal part is quenched one by one in the order of J ₄ → J ₂ , and then quenched one by one in the order of the pin part P ₆ → P _3. The bending of the axis was measured.

The axial center bend was measured by chucking and rotating the axial center holes at both ends of the crankshaft and applying a dial gauge to the groove bottom of each journal (J ₁ , J ₂ , J ₃ , J ₄ ).
Table 1 shows the X and Y components when the axis center is the origin, and the amount of bending change in each process.

[Comparative Example 1]
The order of quenching is shown in Table 2, that is, after quenching one by one in the order of pin portions P ₁ → P ₄ , the journal portion is quenched one by one in the order of J ₄ → J ₃ . The bending of the axial center was measured at the end of quenching. The measurement results are shown in Table 2.

From the results of Tables 1 and 2, Example 1 in which the journal part was first hardened had a maximum change of 0.336 (P2, P4), whereas the pin part was hardened first. 1, the maximum change amount is as large as 0.528 (P5).
Further, in Example 1, the final bending was smaller than that in Comparative Example 1.
From the above results, by quenching from the journal part,
It can be seen that the occurrence of bending when quenching the pin portion is suppressed, and the bending amount of the entire crankshaft can be reduced.

1 Crankshaft 2 Crank Journal 3 Crankpin 4 Crank Arm 5 Balance Weight 6 Crank Fillet 7 Pin Fillet 8 Oil Hole 9 Hardened Layer

DESCRIPTION OF SYMBOLS 10 Induction hardening apparatus 11 Rotating apparatus 12 Heating coil 13 Cooling apparatus 14 Chuck 15 Insulating chip 16 Tension member 17 AC power supply

Claims (3)

A crankshaft manufacturing method in which a crankpin and a crank journal are connected via a crank arm,
The crankshaft has a journal fillet portion located at a boundary point between the crank journal and the crank arm, and a pin fillet portion located at a boundary point between the crank pin and the crank arm,
A crankshaft manufacturing method comprising quenching the pin fillet portion after quenching the journal fillet portion.   The crankshaft manufacturing method according to claim 1, wherein quenching of the journal fillet is performed simultaneously with quenching of the crank journal, and quenching of the pin fillet is performed simultaneously with quenching of the crankpin.   The method for manufacturing a crankshaft according to claim 1, wherein the quenching is induction quenching.

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