JP2000337345A - Manufacture of crankshaft - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the output of an engine and to make it lightweight by highfrequency-heating and quenching fillet R sections at connection portions of a crankpin, journals and crank webs, tempering the whole at a low temperature, and applying roll machining to the fillet R sections. SOLUTION: A crankpin 12, bearing metal slide sections of journals 14 and fillet R sections 20, 22 are quenched to form hard layers 24. The bending of the whole crankshaft 10 is corrected by tempering and high-frequency-quenching, and the occurrence of a grinding crack at the time of final grinding can be effectively prevented. The fillet R sections 20, 22 are pressed by rollers 26 for roller machining with the crankshaft 10 rotated. The bending fatigue strength of the fillet R sections 20, 22 can be sharply improved than before, and the crankshaft 10 can effectively cope with a recent request for the high output of an engine and the lightweight engine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a crankshaft suitable for use in a crankshaft of a diesel engine for a truck.

[0002]

2. Description of the Related Art Crankshafts for diesel engines for trucks and the like operate under the action of large bending stress, torsional stress and the like, and therefore must have strength and rigidity to withstand these. FIG. 4 shows a main part of a normal crankshaft, which is formed by forging a steel material by a conventional method, and the crankshaft generally denoted by reference numeral 10 is connected to a connecting rod (not shown). A crank pin 12 connected to a piston via a shaft, a journal 14 supported on a shaft and a receiving portion of a crank case, and a crank web 16 connecting the crank pin 12 and the journal 14; A balance weight 18 is formed integrally with the portion 16.

In the forged crankshaft 10, a fillet R portion 20 at a joint between the crank pin 12 and the crank web 16 and a fillet R at a joint between the journal 14 and the crank web 16 are provided.
As is well known in the art, the portion 22 forms the weakest point in strength and has a weakest cross section passing through the fillet R portion 20 and the fillet R portion 22 as shown by the dotted line E in the figure. Along with cracks and fractures. In particular, in recent years, further improvement in the bending fatigue strength of the crankshaft has been demanded from demands for improvement in engine output and weight reduction, and enhancement of the fatigue strength of the fillet R portions 20 and 22, which are the weakest points, is an important issue. It has become.

[0004] As a method of enhancing the bending fatigue strength of the fillet R portions 20 and 22 in the crankshaft 10, a method of performing induction hardening on the fillet R portions 20 and 22 and a method of performing roll processing on the fillet R portions 20 and 22 are available. Has been proposed. The above induction hardening method,
Conventionally, the roll processing method is independently performed, and a method of further performing a roll processing on a quenched surface having a sufficiently high hardness by induction hardening has not been performed at all. This is because the more skilled the person skilled in the art, the higher the hardness of the quenched surface, which has already reached a high hardness by induction quenching, is to perform further roll processing to generate plastic deformation, thereby improving the fatigue strength. It is out of common sense, and adverse effects such as peeling of the hardened surface layer and cracking of the surface are expected.Therefore, performing the roll processing after induction hardening is rather contrary to the conventional technical knowledge. It is supposed to be.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and is a joint between a crank pin and a journal, which is the weakest point of a crankshaft made by forging a steel material, and a crank web. Fillet R at
The bending fatigue strength of the part can be improved more effectively than in the case of the induction hardening method and the roll processing method, each of which has been conventionally performed independently. An object of the present invention is to provide a crankshaft capable of responding to the demands for conversion.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a fillet at a joint between a crankpin and a journal and a crank web of a crankshaft of a crankshaft formed by forging a steel material whose hardenability is guaranteed. After high-frequency heating and rapid cooling and quenching in the R part, low-temperature tempering of the entire crankshaft is performed.
Thereafter, a method of manufacturing a crankshaft, characterized in that a roll processing is further performed on a fillet R portion, is proposed.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.
This will be specifically described with reference to FIG. Members and portions that are the same as or correspond to the configuration of the general crankshaft described with reference to FIG. 4 are denoted by the same reference numerals, and redundant description is omitted. First, the crankshaft 10 according to the present invention is made of a steel material whose hardenability is guaranteed, for example, SM
manganese steel such as n443H, manganese chrome steel such as SMnC443H, chromium steel such as SCr440H, SCM8
An appropriate steel material selected from chromium molybdenum steel such as 22H, nickel chrome steel such as SNC815, and nickel chromium molybdenum steel such as SNCM420H is formed by hot forging. Crankpin 12 of forged crankshaft, fillet R portion 20 thereof, and journal 1
4 and its fillet R portion 22 are heated to a temperature slightly higher than a predetermined quenching temperature according to the type of steel used by a high-frequency heating device by a conventional method, and then a coolant containing water as a main component is radiated and heated. The quenched surface is quenched. Thereafter, low-temperature tempering of about 1 to 3 hours is performed at a temperature of about 180 ° C. The above-mentioned induction hardening and low-temperature tempering are carried out after forging, during an appropriate cutting step prior to final grinding of the crank pin 12, the journal portion 14, and the fillet R portions and 20, 22 thereof.

As a result of the induction hardening, as shown in a cross section in FIG. 1, the bearing metal sliding portion of the crank pin 12 and the journal 14 and the fillet R portion 2
At 0.22, a hardened hard layer 24 of 0.3 mm to several mm is formed depending on the hardening conditions such as the output of the high-frequency heating device, the energizing time, and the dimensions of the crank pin 12 and the journal portion 14 as the work. Further, the subsequent tempering can correct the bending of the entire crankshaft caused by the induction hardening, and can effectively prevent the occurrence of polishing cracks during the final polishing. For example, in the case of SMn443H, the surface hardness after tempering is around 60 in Rockwell C hardness (HRC), although it depends on the type of steel used.

After performing the above induction hardening and tempering, as shown in FIG. 1, rollers 26 are used for the fillet R portions 20 and 22 while applying pressure as indicated by an arrow P in the drawing. By rotating the crankshaft 10, roller processing is performed. HRC6 already after low temperature tempering
Fillet R portions 20 and 22 having high hardness of about 0
The roller 26 has a hardness exceeding HRC 60, and
For example, JIS G4403 having a hardness of HRC 65 or more
, Or a high-hardness sintered metal having a hardness equal to or higher than that specified in the above.
In addition, roll processing is performed using a normal processing apparatus, for example,
A hydraulic pressurizing device or the like shown in FIG. 7 of the specification attached to the specification of Japanese Patent Application Laid-Open No. 47960 can be appropriately employed. As an example, the roller 26 and the fillet R portions 20 and 2 are used.
2, the contact surface pressure (Hertz surface pressure) is 450 to 550 kg
f / mm ² . In addition, as shown in FIG.
On the surface of the crank pin 12 substantially opposite to the roller 26,
One or more flat rollers 28 that bear the pressure reaction force of the rollers 26 are in contact with each other.

As described above, induction hardening is performed on the outer peripheral surfaces of the crank pin 12, the journal 14, and the fillet R portions 20 and 22 to form a hardened hardened layer indicated by reference numeral 24 in FIG. At the same time, compressive residual stress is generated. Further, in the next step, the above-mentioned fillet R portions 20 and 22 are subjected to roll processing by the rollers 26, whereby the fillet R portions 20 and 22 are plastically deformed and work hardened, and at the same time, additional compressive residual stress is generated. appear. In addition, regarding low-temperature tempering after induction hardening, it is considered that there is a slight decrease in surface hardness and compressive residual stress, but it is only a level that can be ignored in practical use.

FIG. 2 shows, as an example, the fillet R portions 20 and 22 when only normal induction hardening is performed on the crankpin 12, the journal 14, and the fillet R portions 20 and 22 of the crankshaft 10 made of SMn443H steel. A bar graph A shows the compressive residual stress, and a bar graph B shows the fillet R portion compressive residual stress when the fillet R portions 20 and 22 are rolled after induction hardening. As is apparent from the figure, in the case of only induction hardening, the fillet R portions 20 and 2
2, the compressive residual stress of the fillet R portions 20 and 22 subjected to roll processing after induction hardening was 1400 (MPa).
It became clear that a compressive residual stress was generated about 2.6 times. No harmful surface peeling or cracking was observed in the fillet R portions 20 and 22 that were subjected to roll processing after induction hardening.

Next, FIG. 3 shows that the crankpin 12, the journal 14, and the fillet R portions 20 and 22 of the crankshaft made by forging the same steel material as described above are not subjected to any induction hardening and no roll processing. In the bar graph C, the bending fatigue strength of the crankshaft in the case of the above is shown by a bar graph C, and the bending fatigue strength of the crankshaft when only the induction hardening is performed on the crankpin 12, the journal 14, and the fillet R portions 20 and 22 is shown by a bar graph A '. After quenching, low temperature tempering is performed, and then fillet R part 2
The bar graph B 'shows the bending fatigue strength of the crankshaft when the roll processing is performed on Nos. 0 and 22. As is clear from the figure, the bending fatigue strength is less than 300 (MPa) in the case of no treatment, and
About 600 (MPa) and about 800 (MPa) when subjected to roll processing after induction hardening, it is clear that remarkable improvement in bending fatigue strength can be achieved by the present invention, and a recent increase in engine output has been achieved. It has been confirmed that the demand for weight reduction can be sufficiently satisfied. The method of the present invention is not necessarily applied to all the fillet R portions 2 of the crankshaft 10.
0 and 22 are not limited to induction hardening and rolling. For example, the fillet R portion 22 of the journal 14 at the front and rear ends of the crankshaft having a small bending load may be either induction hardening or rolling. May be applied only.

[0013]

As described above, the method for manufacturing a crankshaft according to the present invention relates to a joint portion between a crankpin and a journal of a crankshaft and a journal of a crankshaft formed by forging a steel material whose quenching property is guaranteed. After high-frequency heating and rapid cooling and quenching, the fillet R part was subjected to low-temperature tempering of the entire crankshaft, and then roll processing was performed on the fillet R part. The bending fatigue strength of the fillet R at the joint between the crankpin and the journal and the crank web to be formed can be greatly improved compared to the conventional art, and it can effectively respond to recent demands for higher output and lighter engines. A crankshaft can be formed.

[Brief description of the drawings]

FIG. 1 is a side view of a main part of a crankshaft showing a part of the embodiment of the method of the present invention in cross section.

FIG. 2 is a diagram showing a comparison of compressive residual stress between a case where only induction hardening is performed on a crankpin and a journal of a crankshaft and a case where roll processing is performed on a fillet R portion after induction hardening.

FIG. 3 shows a case in which neither induction hardening nor roll processing is performed on the crank pin, journal, and fillet R after forging, a case where only induction hardening is performed on each of the above-described portions, and a case in which the above-described fillet R is subjected to induction hardening. It is the diagram which showed bending fatigue strength in the case where roll processing was given in comparison.

FIG. 4 is a side view of a main part of a general crankshaft.

[Explanation of symbols]

10 ... crankshaft, 12 ... crankpin, 14 ...
Journal, 16: crank web, 20 and 22, fillet R, 24: hardened hardened layer, 26: roll, 2
8. Flat roller.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3J033 AA02 AC01 BA15 4E087 AA10 BA02 CA11 CA21 CA31 CB01 DB03 DB14 DB15 DB16 EC12 EC17 EC22 EC37 FA21 FB06 GA09 HA32 HB17 4K042 AA16 DA01 DA02 DB01 DE02

Claims (1)

[Claims] 1. A high-frequency heating, rapid cooling, and quenching of a fillet R at a joint between a crankpin and a journal and a crank web of a crankshaft of a crankshaft formed by forging using a steel material whose hardenability is guaranteed, and then quenching is performed. , Low temperature tempering of the entire crankshaft,
A method for manufacturing a crankshaft, characterized in that a roll process is further performed on a fillet R portion thereafter.