【発明の詳細な説明】[Detailed description of the invention]
（産業上の利用分野）
本発明は自動車等用エンジンの重要な構成部品
であるクランクシヤフトの製造法に関し、特には
曲げ強度及びねじり強度に優れたクランクシヤフ
トの製造法に関する。
（従来の技術）
クランクシヤフトは高い燃焼ガス圧を軸回転力
に転換する一方、高重量の車両からも反力を受け
ており、爆発圧力や慣性力による曲げ応力、駆動
トルクによるねじり応力のほか、曲げ振動、ねじ
り振動、縦振動による付加応力に耐える強度と剛
性が要求される。したがつて一般的には構造用炭
素鋼を用いて鍛造されたものを焼入れ、焼戻し、
焼ならし等の調質処理を施して供されてきた。そ
して最近ではエンジンの高出力化に伴い、より高
強度なクランクシヤフトが要求されてきている。
クランクシヤフトにかかる応力としては曲げ応
力が、次いでねじり応力が他に比べ大きい為それ
らが重要視され、その応力集中部位は第３図及び
第４図の付号２で示したピンフイレツト部であ
る。なお第３図（断面図）及び第４図（ａは正面
図、ｂはその−線断面図）は各異なる一般的
なクランクシヤフト１のピン部を示したもので、
３はピン、４はジヤーナル、５はコンロツドベア
リングに潤滑油を供給するための油孔、６はジヤ
ーナルフイレツト部である。
従来、クランクシヤフトの曲げ強度やねじり強
度を向上させるために、一般的にロール加工、高
周波焼入れ、軟窒化処理等の表面加工処理が施さ
れてきた。他方では構造用炭素鋼の代わりに、母
材自体の疲労強度が高いクロムモリブデン鋼、ニ
ツケルモリブテン鋼、窒化用鋼等の特殊合金鋼が
採用されることもあつた。
（発明が解決しようとする問題点）
しかしながら、上記従来の高強度化方法には以
下のような問題がある。
まずロール加工は第５図に示すようにクランク
シヤフト１の応力集中部であるフイレツト部２を
ローラ７により塑性加工を施して、即ちこの部位
に圧縮残留応力を与え強化するものであるが、一
般にはフイレツト部２に幅ｍの溝が形成されるた
め、その切欠による逆効果も生じ、実質的に大幅
な強度高上は望めないという問題がある。
また高周波焼入れによつてフイレツト部２の曲
げ強度やねじり強度を向上させようとする場合に
はコンロツドベアリングとの耐摩耗性も考慮し第
６図に示すようにピン３の全周にも焼入れが施さ
れるがその際、油孔５。加工部の焼入硬化層８と
母材の境界には引張残留応力が発生する。また特
に油孔５がピン３軸に直交方向に貫通する形状で
ねじり応力が作用した場合には油孔表面付近がフ
イレツト部２と並んで応力集中部となり、その結
果焼入境界部の引張応力発生が悪影響し、ねじり
疲労破壊時の最弱部位となる。即ち高周波焼入れ
を施しても、ねじり強度の向上が計れないため、
総体的に強度水準が非高周波処理品に比べ高くな
らないという問題が残されている。
また、上記のような焼入境界部における問題を
生じない点でねじり強度の向上が期待できる軟窒
化処理では、高周波焼入れに比べ曲げ強度を殆ど
向上することができない。軟窒化処理の強度向上
効果は母材強度（硬さ）に左右され、一般的に引
張強さ60〜80Kgｆ／mm2（硬さHv180〜280）程度
のクランクシヤフト材料に軟窒化処理を施しても
引張り強さ100Kgｆ／mm2以上（硬さHv300以上）
のものは望めず、そのためには高価なクロムモリ
ブデン鋼、ニツケルクロムモリブデン鋼、窒化用
鋼等の合金鋼の調質したものを用いる必要があ
る。
一方、そのような合金鋼は高価という問題の他
に被削性が著しく劣るため、該合金鋼を母材とし
て採用する場合は生産性も問題となる。
本発明は上記問題点を解決するためになされた
ものであり、その目的とするところは曲げ強度と
ねじり強度を同時に向上させ且つ経済性にも優れ
た高強度クランクシヤフトの製造法を提供するこ
とである。
（問題点を解決するための手段）
上記目的を達成するための本発明の高強度クラ
ンクシヤフトの製造法は、炭素量0.45〜0.6重量
％の構造用炭素鋼を熱間鍛造して粗形材を得、続
く機械加工工程内でピン軸及びフイレツト部に高
周波焼入れを施し、研削加工後に軟窒化処理を行
なうことを特徴とする。
使用することのできる上記鋼の例をJIS規格品
で挙げるならS45C〜S58Cであり、炭素量が0.45
％以下のものは所望の強度が得られず、0.6％以
上のものは切削性が悪くかつ脆い。
上記鋼は熱間鍛造された後、調質することなく
機械加工に付されるが該鍛造粗材は引張り強さ60
〜80Kg／mm2あるいは硬さHv180〜280の強度水準
にあるのが好ましい。機械加工工程内においてピ
ンフイレツト部を含めてピン軸の半周以上から全
周にわたり高周波焼入れを行ない、必要に応じて
歪修正や研削加工を行い、その後に軟窒化処理を
施すことになる。
上記の熱間鍛造、高周波焼入れ及び軟窒化処理
の各工程は従来と同様の条件、方法に従い行なつ
てよい。
（作用）
クランクシヤフトの製造に上記構成からなる製
造法を採用することにより、強い曲げ及びねじり
作用（外力）に対して従来以上に耐えることので
きる性質をクランクシヤフトに付与することがで
きる。
（実施例）
以下に本発明のクランクシヤフトの製造法につ
いて、実施例を掲げ更に詳しく説明する。なお、
本発明はこれにより何ら限定されるものではな
い。
JIS構造用炭素鋼S55Cを素材とするクランクシ
ヤフトを1200℃で熱間鍛造後、室温まで空冷し、
硬さHv215の粗形材を得、ついでピン軸直交方向
への油孔穿設加工も含め機械加工によりピン径
φ45、ジヤーナル径φ55、貫通油孔径φ6、フイレ
ツトR2.5の４気筒クランクシヤフトを製作した。
その後ピンフイレツト及び軸部全周に高周波焼入
を行い焼入深さ1.7mmの半製品を得、特に580℃×
1hr電気炉中で焼戻しを行い硬化層の硬さを
Hv310とした。その後研削加工をおこない所要の
精度を確保した後580℃×90分塩浴中で軟窒化処
理を行い、こうして得た最終製品を後記試験に供
した。
比較例 １〜４
本発明方法の効果を確認するため、４種の比較
用クランクシヤフト材を製造した。すなわち、上
記実施例の製造法を準用しつつ、表面処理とし
て、高周波焼入れのみを施したもの（比較材１）、
軟窒化処理のみを施したもの（比較材２）、全く
表面処理を施さなかつたもの（比較材３）及び母
材としてJIS構造用炭素鋼S55Cの代わりに合金鋼
SNCM440を用い焼入れ、焼戻しを行い硬さ
Hv325としたのち580℃×90分塩浴中で軟窒化処
理を施したもの（比較材４）を製造した。
曲げ強度試験
前記の実施例で得られたもの（以下「本発明
品」という）及び上記の比較材１〜４について共
振式疲労試験機を用いてピンフイレツト部に繰り
返し曲げ荷重を加え、両振り曲げ疲れ限度を調べ
た。即ち各荷重ごとの試験品破断に至るまでの負
荷繰り返し数を求め、第１図に示すような結果を
得た。第１図から、本発明品は合金鋼製のもの
（比較材４）と比べ同等ないしやや優る強度を、
そして比較材１〜３に比べ明らかに優る強度を有
していることが判る。そして本発明方法によれば
疲れ限度3.8tの非調質品を疲れ限度9.5tの製品へ
と変えることができ大幅な曲げ強度の向上を計る
ことができることを示している。
ねじり強度試験
本発明品、比較材１及び４について油圧式ねじ
り疲労試験機を用い、１×107回の繰り返しねじ
り荷重負荷で変形を来たさない最大トルク振幅を
求めた。その結果を下表に示す。該表から本発明
品は、表面処理として高周波焼入のみを施したも
のに比べ約30％高の、そして合金鋼製のものとほ
ぼ同等のねじり強度を示すことが判る。
(Industrial Application Field) The present invention relates to a method for manufacturing a crankshaft, which is an important component of an engine for an automobile, and more particularly to a method for manufacturing a crankshaft that has excellent bending strength and torsional strength. (Prior technology) While the crankshaft converts high combustion gas pressure into shaft rotational force, it also receives reaction forces from heavy vehicles, and in addition to bending stress due to explosion pressure and inertial force, and torsional stress due to drive torque. , strength and rigidity are required to withstand added stress due to bending vibration, torsional vibration, and longitudinal vibration. Therefore, in general, products forged using structural carbon steel are quenched, tempered,
It has been provided after undergoing tempering treatments such as normalizing. Recently, as engines have become more powerful, crankshafts with higher strength have been required. The stresses applied to the crankshaft include bending stress, followed by torsional stress because they are larger than others, and the stress concentration area is the pin fillet portion shown by number 2 in FIGS. 3 and 4. Note that FIG. 3 (cross-sectional view) and FIG. 4 (a is a front view, b is a cross-sectional view taken along the line), which show the pin portions of different general crankshafts 1.
3 is a pin, 4 is a journal, 5 is an oil hole for supplying lubricating oil to the connecting rod bearing, and 6 is a journal fillet. Conventionally, in order to improve the bending strength and torsional strength of crankshafts, surface treatments such as roll processing, induction hardening, and nitrocarburizing treatments have generally been performed. On the other hand, instead of structural carbon steel, special alloy steels such as chromium molybdenum steel, nickel molybdenum steel, and nitriding steel, which have high fatigue strength as a base material, were sometimes used. (Problems to be Solved by the Invention) However, the above conventional method for increasing strength has the following problems. First, in roll processing, as shown in Fig. 5, the fillet section 2, which is the stress concentration section of the crankshaft 1, is plastically worked using rollers 7, that is, compressive residual stress is applied to this section to strengthen it. Since a groove having a width m is formed in the fillet portion 2, the notch also produces an adverse effect, and there is a problem in that a substantial increase in strength cannot be expected. In addition, when attempting to improve the bending strength and torsional strength of the fillet portion 2 by induction hardening, the entire circumference of the pin 3 is also hardened as shown in Figure 6, taking into consideration the wear resistance with the conrod bearing. is applied, but at that time, the oil hole 5. Tensile residual stress is generated at the boundary between the quenched hardened layer 8 and the base material in the processed portion. In addition, especially when the oil hole 5 is shaped to penetrate in a direction perpendicular to the pin 3 axis and torsional stress is applied, the vicinity of the oil hole surface becomes a stress concentration area along with the fillet portion 2, resulting in tensile stress at the quenching boundary. This occurrence has a negative effect, and it becomes the weakest part during torsional fatigue failure. In other words, even if induction hardening is applied, the torsional strength cannot be improved.
Overall, the problem remains that the strength level is not higher than that of non-high frequency treated products. In addition, soft nitriding treatment, which is expected to improve torsional strength because it does not cause the above-mentioned problem at the hardening boundary, cannot improve bending strength nearly as much as induction hardening. The strength improvement effect of soft-nitriding depends on the strength (hardness) of the base material, and generally, soft-nitriding is applied to crankshaft materials with a tensile strength of about 60 to 80 Kgf/mm 2 (hardness Hv180 to 280). Tensile strength 100Kgf/ mm2 or more (hardness Hv300 or more)
For this purpose, it is necessary to use tempered alloy steels such as expensive chromium molybdenum steel, nickel chrome molybdenum steel, and nitriding steel. On the other hand, in addition to being expensive, such alloy steels have extremely poor machinability, so when such alloy steels are used as a base material, productivity also becomes an issue. The present invention has been made to solve the above problems, and its purpose is to provide a method for manufacturing a high-strength crankshaft that simultaneously improves bending strength and torsional strength and is also economically efficient. It is. (Means for Solving the Problems) A method for manufacturing a high-strength crankshaft of the present invention to achieve the above object is to hot forge structural carbon steel with a carbon content of 0.45 to 0.6% by weight to produce a rough shape. The pin shaft and fillet portion are subjected to induction hardening in the subsequent machining process, and soft nitriding treatment is performed after the grinding process. Examples of the above steels that can be used are JIS standard products, S45C to S58C, with a carbon content of 0.45
If it is less than 0.6%, the desired strength cannot be obtained, and if it is more than 0.6%, it has poor machinability and is brittle. After the above steel is hot forged, it is machined without refining, but the forged raw material has a tensile strength of 60
It is preferable that the strength level is ~80Kg/ mm2 or hardness Hv180~280. During the machining process, induction hardening is performed from more than half the circumference to the entire circumference of the pin shaft, including the pin fillet, and distortion correction and grinding are performed as necessary, followed by nitrocarburizing. Each of the steps of hot forging, induction hardening, and nitrocarburizing treatment described above may be performed under the same conditions and methods as conventional ones. (Function) By employing the manufacturing method having the above configuration for manufacturing a crankshaft, it is possible to impart properties to the crankshaft that can withstand strong bending and twisting actions (external forces) more than ever before. (Example) The method for manufacturing the crankshaft of the present invention will be described in more detail below with reference to Examples. In addition,
The present invention is not limited to this in any way. A crankshaft made of JIS structural carbon steel S55C is hot forged at 1200℃, then air cooled to room temperature.
A rough profile with a hardness of Hv215 was obtained, and then a 4-cylinder crankshaft with a pin diameter of φ45, journal diameter of φ55, through oil hole diameter of φ6, and fillet R2.5 was created by machining, including drilling an oil hole in the direction perpendicular to the pin axis. Manufactured.
After that, the pin fillet and the entire circumference of the shaft were induction hardened to obtain a semi-finished product with a hardening depth of 1.7mm.
Tempering is performed in an electric furnace for 1 hour to increase the hardness of the hardened layer.
It was set to Hv310. After that, grinding was performed to ensure the required accuracy, and then nitrocarburizing treatment was performed in a salt bath at 580°C for 90 minutes, and the final product thus obtained was subjected to the tests described below. Comparative Examples 1 to 4 In order to confirm the effects of the method of the present invention, four types of comparative crankshaft materials were manufactured. That is, the manufacturing method of the above example was applied mutatis mutandis, but only induction hardening was applied as surface treatment (comparative material 1);
One subjected to soft nitriding treatment only (Comparison material 2), one without surface treatment at all (Comparison material 3), and alloy steel instead of JIS structural carbon steel S55C as the base material.
Hardness achieved by quenching and tempering using SNCM440
After adjusting the temperature to Hv325, a material (comparative material 4) was produced by performing soft nitriding treatment in a salt bath at 580°C for 90 minutes. Bending strength test For the products obtained in the above examples (hereinafter referred to as "products of the present invention") and the comparative materials 1 to 4 above, repeated bending loads were applied to the pin fillet using a resonance fatigue tester, and double-sided bending was performed. I checked my fatigue limit. That is, the number of load repetitions until the test sample breaks for each load was determined, and the results shown in FIG. 1 were obtained. From Figure 1, the product of the present invention has the same or slightly superior strength compared to the product made of alloy steel (comparative material 4).
It can be seen that the strength is clearly superior to that of Comparative Materials 1 to 3. It is also shown that according to the method of the present invention, it is possible to change a non-tempered product with a fatigue limit of 3.8 tons to a product with a fatigue limit of 9.5 tons, and to significantly improve the bending strength. Torsional strength test For the products of the present invention and comparative materials 1 and 4, a hydraulic torsional fatigue tester was used to determine the maximum torque amplitude that would not cause deformation under repeated torsional loading of 1×10 7 times. The results are shown in the table below. It can be seen from the table that the products of the present invention exhibit torsional strength approximately 30% higher than those subjected to only induction hardening as surface treatment, and approximately equivalent to those made of alloy steel.
【表】
硬さ試験
本発明品、比較材２及び４について、ビツカー
ス硬さ試験機を用い、油孔近傍表面部の表面から
の深さごとの硬さを調べた。その結果を第２図に
示す。この図から本発明品は高周波焼入れ深さ
（1.7mm）に相当する深さまで合金鋼なみのHv320
の硬さを維持していることが判る。
（発明の効果）
本発明方法によれば、高強度の調質合金鋼を用
いることなく、曲げ強度及びねじり強度ともに該
合金鋼に匹敵する程の強度を持つたクランクシヤ
フトを提供することができる。
また本発明方法は、合金鋼に比べ安価で且つ加
工性の良い構造用鋼を用い、しかも非調質のまま
機械加工を施す工程を含むため、生産性や経済性
の面でも優れている。
従つて別の見地に立てば、本発明方法により製
造コストや強度を犠性にすることなくクランクシ
ヤフトの幅縮小、細径化ができ、エンジンの小型
軽量化に寄与することができる。[Table] Hardness Test The hardness of the inventive product and Comparative Materials 2 and 4 was examined at each depth from the surface of the surface near the oil hole using a Bitkers hardness tester. The results are shown in FIG. From this figure, the product of the present invention has Hv320, which is equivalent to alloy steel, to a depth equivalent to the induction hardening depth (1.7 mm).
It can be seen that the hardness is maintained. (Effects of the Invention) According to the method of the present invention, it is possible to provide a crankshaft that has bending strength and torsional strength comparable to that of alloy steel without using high-strength tempered alloy steel. . Furthermore, the method of the present invention uses structural steel, which is cheaper and has better workability than alloy steel, and also includes a step of performing machining without heat refining, so it is excellent in terms of productivity and economy. Therefore, from another point of view, the method of the present invention allows the width and diameter of the crankshaft to be reduced without sacrificing manufacturing cost or strength, contributing to the reduction in size and weight of the engine.
【図面の簡単な説明】[Brief explanation of the drawing]
第１図はクランクシヤフトの曲げ強度試験にお
ける荷重と破断に至るまでの負荷回数の関係を示
す図、第２図はクランクシヤフト表面部の深さと
硬さの関係を示す図、第３図はクランクシヤフト
のピン部の一例を示す断面図、第４図は他の例を
示すものでａは正面図、ｂはその−線断面
図、第５図はフイレツト部の加工法を示す部分拡
大図、第６図は高周波焼入状態を示すものでａは
断面図、ｂはその−線断面図である。
図中、１…クランクシヤフト、２…ピンフイレ
ツト部、３…クランクピン、５…油孔、８…高周
波焼入れ層。
Figure 1 shows the relationship between the load and the number of loads until fracture in a crankshaft bending strength test, Figure 2 shows the relationship between the depth and hardness of the crankshaft surface, and Figure 3 shows the relationship between the crankshaft surface depth and hardness. A sectional view showing an example of the pin part of the shaft, FIG. 4 shows another example, in which a is a front view, b is a sectional view taken along the line B, and FIG. 5 is a partially enlarged view showing a processing method for the fillet part. FIG. 6 shows the state of induction hardening, in which a is a cross-sectional view and b is a cross-sectional view taken along the - line. In the figure, 1...crankshaft, 2...pin fillet portion, 3...crank pin, 5...oil hole, 8...induction hardening layer.