JP5967920B2 - Manufacturing method of light alloy wheel for vehicle and light alloy wheel for vehicle - Google Patents
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本発明は、既存のホイールリムフランジ形状を変更することなくリムフランジ部の割れを抑制することが可能な車両用軽合金ホイールの製造方法及び車両用軽合金ホイールに関する。 The present invention relates to a method for manufacturing a light alloy wheel for a vehicle and a light alloy wheel for a vehicle that can suppress cracking of a rim flange portion without changing an existing wheel rim flange shape.
近年、自動車は、装備の充実や安全面からその重量増の傾向にあるが、環境面などからも燃費向上のために細部に渡る軽量化が試みられている。車両用ホイールについても同様に意匠と機能の両立を求めるニーズが高まる一方で、軽量化が求められている。その一方でタイヤ性能向上、車両大型化や重量増に伴いタイヤサイズが大型化するとともに、ブレーキも大型化する傾向にあるため、車両用ホイールは大口径化し、タイヤは低扁平なものが増えてきているのも事実である。このような経緯から、車両用ホイールは、軽量かつ高剛性のアルミニウム合金やマグネシウム合金等の軽合金ホイールが主となり、意匠面と機能面の両立の研究が日々行われている。車両用軽合金ホイールは大別して鋳造と鍛造の２つの製法があり、鋳造にはＡＣ４ＣＨなどの鋳造用合金を、鍛造には６０００系などの展伸用合金といった形でそれぞれ製法に適した材料が用いられている。一般に鋳造組織に比べ、鍛造組織は緻密かつ微細であり、機械的性質にも優れているため軽量化が行い易い。しかし、いくら機械性質に優れる材料を用いた車両用軽合金ホイールであっても、車量重量・組み合わされるタイヤや車両性能・特性といった因子の影響を受けやすく、鍛造、さらにはスピニング加工といった一般的に用いられている塑性加工だけでは軽量化にも限度がある。また、車両用ホイールは、重要保安部品という特性上、過酷な耐久性能が求められ、軽量化とともに耐久性を無視することができない。 In recent years, automobiles have tended to increase in weight due to the enhancement of equipment and safety, but from the viewpoint of environment and the like, attempts have been made to reduce the weight in detail to improve fuel efficiency. Similarly, there is a growing need for reducing the weight of vehicle wheels, while increasing the need for both design and function. On the other hand, as the tire performance increases, the size of the vehicle increases and the weight increases, the size of the tire increases and the brake tends to increase in size. It is also true. For this reason, light-weight and high-rigidity light alloy wheels such as aluminum alloy and magnesium alloy are mainly used for vehicle wheels, and researches on both design and function are being conducted every day. Light alloy wheels for vehicles can be broadly divided into two methods: casting and forging. Casting alloys such as AC4CH are used for casting, and 6000 series and other wrought alloys are used for forging. It is used. Generally, compared to a cast structure, a forged structure is dense and fine, and is excellent in mechanical properties, so that it is easy to reduce the weight. However, even light alloy wheels for vehicles using materials with excellent mechanical properties are easily affected by factors such as vehicle weight, tires to be combined, vehicle performance and characteristics, and are generally used for forging and spinning. There is a limit to the weight reduction only by the plastic working used in the manufacturing process. In addition, the vehicle wheel is required to have severe durability performance due to the characteristic of being an important safety part, and the durability cannot be ignored as the weight is reduced.
車両用ホイールの設計段階において回転曲げ試験を想定した応力解析、実際の回転曲げ疲労試験や半径方向負荷耐久試験、衝撃試験などＪＩＳＤ ４１０３に基づき評価が行われている。衝撃試験はホイールディスク面側へ衝撃を与えることでホイールディスクやディスク側のアウターリムの変形・破損、またはエア漏れがないかの評価が行われるが、ホイールディスクと反対面側のインナーリムの変形・破損、またはエア漏れの評価について定められたものはなく、事業者独自の評価がなされているにすぎない。しかし、サスペンション構造上タイヤと車両用ホイールは地面と常に垂直が保たれている訳ではなく、車体が沈み込むと左右でハの字型に角度がつくため、タイヤ・ホイールの内側（車体内側）が外側よりも早く接地する傾向となり、この部位は車両走行時、最も負荷がかかりやすい。そのため、車両用ホイールメーカーにおいてはインナーリムの評価をより重要視し、強度面の強化がなされる傾向にある。 Evaluation is performed based on JISD 4103, such as stress analysis assuming a rotational bending test, an actual rotational bending fatigue test, a radial load endurance test, and an impact test at the vehicle wheel design stage. In the impact test, it is evaluated whether there is deformation or damage of the wheel disc or the outer rim on the disc side or air leakage by giving an impact to the wheel disc surface side, but the inner rim on the opposite side of the wheel disc is deformed.・ There are no rules for evaluating damage or air leaks, but only an independent evaluation by the operator. However, because of the suspension structure, the tire and the vehicle wheel are not always kept perpendicular to the ground. When the car body sinks, the left and right sides are angled, so the inside of the tire / wheel (inside the car body) Tends to touch the ground earlier than the outside, and this part is most likely to be loaded when the vehicle is running. For this reason, vehicle wheel manufacturers place more emphasis on the evaluation of the inner rim and tend to strengthen the strength.
ところで、車両用ホイールが大径化し、タイヤは低扁平化し、車重増加する傾向の中で、車両走行時にタイヤと車両用ホイールが衝撃を受けた場合、高扁平のタイヤであればタイヤの弾性変形で衝撃吸収していたような衝撃であっても、低扁平タイヤであれば車両用ホイールそのものにまで衝撃が至りやすい。さらに、車両用ホイールは、軽量化によってホイールリムの肉厚が薄くなれば材質に関係なく、当然変形し易くなる。 By the way, when a vehicle wheel is enlarged, a tire is flattened, and a vehicle weight is increased. Even if the impact is absorbed by deformation, the impact is likely to reach the vehicle wheel itself if it is a low flat tire. Furthermore, the vehicle wheel is naturally easily deformed regardless of the material if the wheel rim is thinned by weight reduction.
例えば、車両走行時において、道路上のはみ出し防止のためセンターライン上に設けられた突起や縁石等を踏んだり、凹凸のある路面状況の悪路やポットホールと呼ばれる穴の生じた路面を通過した場合、タイヤとホイールが衝撃を受けることになる。その衝撃により、車両用ホイールのリムフランジ部が変形し、割れの原因となる場合がある。この場合、目視で容易に確認できる大きな変形や割れであったり、割れがリムフランジ部からビードシート部に至ってタイヤのエア漏れを生じさせると、車両使用者はホイール損傷に容易に気付いて直ちに修理の対策を講じることができる。ところが、リムフランジ部の凹み等の変形が約３ｍｍ以下の目視では判別し難い微小変形の場合、エア漏れすることが一般になく、即座に走行不能となることはないため、車両使用者が気付かず車両走行を続けてしまうことが考えられる。また、この微小変形が車体内側となるインナーリムフランジ部であれば、通常確認しにくい部位であるため、ほとんど変形に気付かない。リムフランジ部にこのような微小変形が生じたまま車両走行を続けると、微小変形部位には車両走行により繰り返し応力がかかるため、運転者等の車両使用者の知らない間にこの微小変形部位から破断が生じ、タイヤがエア漏れを起こすなどの不具合を生じさせる。 For example, when a vehicle is running, it has stepped on a protrusion or curb provided on the center line to prevent it from protruding on the road, or has passed through a rough road surface or a road surface with a hole called a pothole. In that case, the tires and wheels will be impacted. Due to the impact, the rim flange portion of the vehicle wheel may be deformed and cause a crack. In this case, if there is a large deformation or crack that can be easily confirmed by visual inspection, or if the crack reaches the bead seat from the rim flange to cause tire air leakage, the vehicle user will easily notice wheel damage and immediately repair it. Measures can be taken. However, in the case of minute deformation that is difficult to discern visually by deformation of the rim flange portion or the like of about 3 mm or less, air leakage generally does not occur, and the vehicle user does not immediately become unable to travel, so the vehicle user does not notice. It is conceivable that the vehicle will continue to travel. In addition, if the minute deformation is an inner rim flange portion on the inner side of the vehicle body, it is a part that is usually difficult to confirm, and therefore hardly notices the deformation. If the vehicle travels with such a minute deformation in the rim flange, the stress is repeatedly applied to the minute deformation part due to the vehicle running. Breaking occurs, causing problems such as tires leaking air.
従来、リムフランジ部を強化する方法として、リムフランジ部の肉厚を厚くすることや、リムフランジ部の内径部を塊状に張り出し形成することが行われていた（特許文献１、特許文献２）。しかし、これらの方法では、リムフランジ部での肉厚増に伴う材料増により当然ながら重量が増え、さらにはリムフランジ部の形状変更に伴って一般に用いられる打ち込みタイプのバランスウエイトが使用できなくなるなどの弊害があった。しかも、分厚くしたリムフランジ部は、厚みにより剛性は増すものの、許容できる応力以上の外的荷重が加わると、弾性・塑性変形域が少ないため、変形するよりも先にその剛性故に即時破断が生じ易くなるという弊害もある。 Conventionally, as a method for reinforcing the rim flange portion, the rim flange portion is thickened or the inner diameter portion of the rim flange portion is formed in a lump shape (Patent Documents 1 and 2). . However, in these methods, the weight increases due to the material increase accompanying the increase in the thickness at the rim flange portion, and furthermore, a generally used driving type balance weight cannot be used in accordance with the shape change of the rim flange portion. There was a negative effect. In addition, the thickened rim flange part increases in rigidity depending on the thickness, but if an external load exceeding the allowable stress is applied, the elastic / plastic deformation area is small, so that it immediately breaks before it deforms due to its rigidity. There is also a harmful effect that it becomes easy.
本発明は、ホイールリムフランジ形状を変えることなく、リムフランジ部の割れを長期間抑制することを可能とする車両用軽合金ホイールの製造方法及び車両用軽合金ホイールを提供することを目的とする。 An object of the present invention is to provide a method for manufacturing a light alloy wheel for a vehicle and a light alloy wheel for a vehicle that can suppress cracking of the rim flange portion for a long period of time without changing the shape of the wheel rim flange. .
本発明は、冷間での塑性加工の中でも圧縮残留応力に着目し、解析・実試験で破断起点となりやすいリムフランジ部へ局所的に押圧工具を用いて加圧し圧縮残留応力を付与することで実現される。 The present invention focuses on compressive residual stress even during cold plastic working, and applies a compressive residual stress by locally applying pressure using a pressing tool to the rim flange, which tends to be the starting point of fracture in analysis and actual tests. Realized.
すなわち、本発明に係る車両用軽合金ホイールの製造方法は、
車両用軽合金ホイールの製造方法において、ホイールリムにおける筒状リム胴部の端縁部に突設するリムフランジ部を加工する工程を含むホイールリムの加工工程にあって、
前記ホイールリムの加工工程は、車両走行中に突発的に受けた衝撃でホイール内径方向へ微小変形しエア漏れなく走行可能な場合であって前記微小変形部位へ車両走行によって受ける繰り返し応力を原因とする割れの起点となるリムフランジ部に対して、回転式のボール又はローラからなる押圧工具をタイヤと接触するリムフランジ部の外側表面部に押し当て加圧することで前記リムフランジ部の外側表面部には前記微小変形による引っ張り応力を緩和させるための圧縮残留応力が付与された組織構造の緩和層となる表層部と、意図的な前記圧縮残留応力が付与されず変形可能な組織構造の内層部との２層構造が形成される押圧工程を含み、
前記押圧工程により、前記表層部には表面から１５０μｍの深さで３００ＭＰａ〜３５０ＭＰａの圧縮残留応力値を有し、当該圧縮残留応力値が表面から３００μｍの深さにおける前記内層部の圧縮残留応力値よりも高い緩和層が形成されるものである。
That is, the method for manufacturing a light alloy wheel for a vehicle according to the present invention includes:
In a method for manufacturing a light alloy wheel for a vehicle, in a wheel rim processing step including a step of processing a rim flange portion protruding from an end edge portion of a cylindrical rim body portion in a wheel rim,
The processing process of the wheel rim is caused by the repeated stress received by the vehicle traveling to the minute deformation portion when the vehicle can travel without air leakage by minute deformation in the inner diameter direction of the wheel due to an impact received suddenly while traveling the vehicle. for the rim flange portion serving as a starting point for cracks to the outer surface portion of the rim flange by pressurizing pressing the press tool consisting of balls or rollers rotating on the outer surface of the rim flange contacting the tire Includes a surface layer portion serving as a relaxation layer of a tissue structure to which a compressive residual stress is applied to relieve a tensile stress due to microdeformation, and an inner layer portion of a tissue structure that is deformable without intentionally applying the compressive residual stress. And a pressing step in which a two-layer structure is formed,
By the pressing step, have a residual compressive stress value 300MPa~350MPa at a depth of 150μm from the surface on the surface layer portion, the compressive residual stress value of the inner portion at a depth of 300μm the compressive residual stress value is from the surface Higher relaxation layer is formed.
上記構成より、リムフランジ部表面へ局所的に回転式ボール又はローラからなる押圧工具を用いて加圧し圧縮残留応力を付与することで、加圧表面の表層部のみに意図的に引っ張り応力を緩和させる圧縮残留応力が付与された組織構造とすることができ、一方、内層部は圧縮されず弾性・塑性変形が比較的大きく許容される変形可能域とすることができる。これにより、車両走行時に突起物を踏む等した場合に、その衝撃によりリムフランジ部が径方向に微小変形（例えば、約３ｍｍ程度までの内径方向への凹み）しても、その引っ張り応力は圧縮残留応力によって相殺されると同時に内層部の変形可能域で変形許容されて破断に至らないようにできる。従って、リムフランジ部が微小変形する程度の外的衝撃を受けても即時の割れを生じ難くするとともに、その微小変形の存在下で車両走行を続行し変形部位に繰り返し応力がかかっても割れの起点となり難い性能を具備した車両用ホイールが提供できる。しかも、リムフランジ部は、既存のホイールリムフランジ形状から形状変更されないから、既存の打ち込みタイプのバランスウエイトを支障なく使用することができ、且つ重量増にもならない。
ところで、車両走行中の衝撃によってリムフランジ部に約３ｍｍ程度の微小変形を生じた場合、目視では判別し難い微小変形と言え、即座に走行不能となることはないため、車両使用者が気付かず車両走行を続けてしまうことが考えられる。
そこで、前記表層部には表面から１５０μｍの深さで３００ＭＰａ〜３５０ＭＰａの圧
縮残留応力値を有し、当該圧縮残留応力値が表面から３００μｍの深さにおける前記内層部の圧縮残留応力値よりも高い緩和層が形成され、この場合、前記のような状況下で車両走行を続けて変形部位に繰り返し応力がかかっても、この変形部位が起点となって割れ発生することを抑制することができる。
From the above configuration, the tensile stress is intentionally reduced only on the surface layer of the pressure surface by applying a compressive residual stress to the surface of the rim flange using a pressing tool consisting of a rotating ball or roller. Thus, the inner layer portion is not compressed, and a deformable region in which elastic and plastic deformation is allowed to be relatively large can be obtained. As a result, when a protrusion is stepped on while the vehicle is running, even if the rim flange is slightly deformed in the radial direction due to the impact (for example, a recess in the inner diameter direction of about 3 mm), the tensile stress is compressed. At the same time, it is canceled by the residual stress, and at the same time, it is allowed to be deformed in the deformable region of the inner layer portion so as not to break. Therefore, even if the rim flange part receives external impacts that cause microdeformation, it is difficult to cause immediate cracking, and even if the vehicle continues to run in the presence of the microdeformation and repeated stress is applied to the deformed part, cracking does not occur. It is possible to provide a vehicle wheel having performance that is difficult to be a starting point. Moreover, since the shape of the rim flange portion is not changed from the shape of the existing wheel rim flange, the existing driving type balance weight can be used without hindrance and the weight is not increased.
By the way, when a minute deformation of about 3 mm is generated in the rim flange portion due to an impact during traveling of the vehicle, it can be said that it is a minute deformation that is difficult to distinguish visually, and the vehicle user does not notice immediately because it does not become impossible to travel immediately. It is conceivable that the vehicle will continue to travel.
Therefore, to have a compressive residual stress value 300MPa~350MPa at a depth of 150μm from the surface on the surface layer portion is higher than the compressive residual stress value of the inner portion at a depth of 300μm the compressive residual stress value is from the surface A relaxation layer is formed. In this case, even if the vehicle is continuously traveled under the above-described conditions and a stress is repeatedly applied to the deformed portion, it is possible to suppress the occurrence of cracks starting from the deformed portion.
前記押圧工程は、少なくともタイヤとの接触面側に対して行う必要があるが、リムフランジ部におけるタイヤと接触しない側の面を含めてリムフランジ部全域に対して行われることが望ましい。
これにより、リムフランジ部全域を強化することができる。
The pressing step needs to be performed on at least the contact surface side with the tire, but is desirably performed on the entire rim flange portion including the surface of the rim flange portion that does not contact the tire.
Thereby, the whole rim flange part can be strengthened.
前記押圧工程は、リムフランジ部の切削加工を行った旋盤加工工程において引き続いて切削工具を前記押圧工具に交換して行われることが望ましい。
これにより、押圧工具としての回転式ボール又はローラのツールの追加のみで、旋盤でのホイールリムの切削加工完了後そのままツール交換して加圧することで前記押圧工程を行うことができる。従って、特別な設備を導入することなく既存設備を活用して短時間で効率よくリムフランジ部の強化構造形成を行うことができる。
It is desirable that the pressing step be performed by replacing the cutting tool with the pressing tool in the lathe processing step in which the rim flange portion has been cut.
Thereby, only the addition of a rotary ball or roller tool as a pressing tool can be performed by exchanging and pressing the tool as it is after the wheel rim has been cut by a lathe. Therefore, it is possible to efficiently form the rim flange portion in a short time using existing equipment without introducing special equipment.
前記押圧工程は、少なくともインナーリムフランジ部に対して行われることが望ましい。
車両走行時、タイヤと車両用ホイールは左右でハの字型に角度がつくため、インナーリムフランジ部に最も負荷がかかりやすい。しかも、インナーリムフランジ部は、車体内側に位置しているから車体外側からは通常確認しにくいため、インナーリムフランジ部に微小変形が生じても運転者等の車両使用者は気付かず車両走行を続けてしまうことが考えられる。従って、インナーリムフランジ部に対して前記押圧工程を行うことで、インナーリムフランジ部に微小変形が生じた場合であっても、車両走行を続けて変形部位に繰り返し応力がかかっても、この変形部位が起点となって割れ発生するのを抑制することができる。
The pressing step is preferably performed at least on the inner rim flange portion.
When the vehicle is running, the tire and the vehicle wheel are angled in a U-shape on the left and right, so the load is most likely to be applied to the inner rim flange. In addition, since the inner rim flange portion is located on the inner side of the vehicle body, it is usually difficult to confirm from the outside of the vehicle body, so even if a slight deformation occurs in the inner rim flange portion, a vehicle user such as a driver does not notice the vehicle running. It is possible to continue. Therefore, by performing the pressing process on the inner rim flange portion, even if a minute deformation occurs in the inner rim flange portion, even if the vehicle is continuously driven and the deformation site is repeatedly stressed, this deformation It can suppress that a site | part becomes a starting point and a crack generate | occur | produces.
また、本発明に係る車両用軽合金ホイールは、
筒状のリム胴部の端縁部にリムフランジ部を連設するホイールリムを備える車両用軽合金ホイールにおいて、
前記リムフランジ部には、車両走行中の衝撃で微小変形し割れの起点となるリムフランジ部におけるタイヤと接触するリムフランジ部外側表面部に対して前記微小変形による引っ張り応力を緩和させるための圧縮残留応力が付与された組織構造の緩和層となる表層部と、意図的な圧縮残留応力が付与されず変形可能な組織構造の内層部との２層構造が形成され、
前記表層部には表面から１５０μｍの深さで３００ＭＰａ〜３５０ＭＰａの圧縮残留応力値を有し、当該圧縮残留応力値が表面から３００μｍの深さにおける前記内層部の圧縮残留応力値よりも高い緩和層が形成されているものである。
この車両用軽合金ホイールによれば、前記製造方法での説明と同様に、リムフランジ部が微小変形する程度の外的衝撃を受けても割れを生じ難くするとともに、その微小変形の存在下で車両走行を続行し変形部位に繰り返し応力がかかっても割れの起点とり難い性能を具備した車両用ホイールが提供できる。しかも、リムフランジ部は、既存のホイールリムフランジ形状から形状変更されないから、既存の打ち込みタイプのバランスウエイトを支障なく使用することができ、且つ重量増にもならない。
Moreover, the light alloy wheel for vehicles according to the present invention is:
In a light alloy wheel for a vehicle including a wheel rim that continuously connects a rim flange portion to an end edge portion of a tubular rim body portion,
The said rim flange, to mitigate the tensile stress due to the small deformation against the rim flange outer surface portion for contacting a tire definitive the rim flange portion serving as a starting point for small deformation cracks caused by impact of the vehicle is traveling A two-layer structure is formed of a surface layer portion serving as a relaxation layer of a tissue structure to which compressive residual stress is applied, and an inner layer portion of a tissue structure that is deformable without intentional compressive residual stress being applied,
Have a compressive residual stress value 300MPa~350MPa at a depth of 150μm from the surface on the surface layer portion, high relaxivity layer than the residual compressive stress value of the inner portion at a depth of 300μm the compressive residual stress value is from the surface Is formed.
According to this vehicle light alloy wheel, as described in the above manufacturing method, even if the rim flange portion is subjected to an external impact to the extent that the rim flange is slightly deformed, cracks are less likely to occur, and in the presence of the minute deformation. Even if the vehicle travels continuously and a stress is repeatedly applied to the deformed portion, a vehicle wheel having a performance that makes it difficult to start a crack can be provided. Moreover, since the shape of the rim flange portion is not changed from the shape of the existing wheel rim flange, the existing driving type balance weight can be used without hindrance and the weight is not increased.
本発明によれば、ホイールリムフランジ形状を変えることなく、リムフランジ部の割れを長期間抑制することができる。そして、例えば、以下の効果もある。
リムフランジ部の肉厚を厚くする場合に比べて、軽量化され、打込みタイプのバランスウエイトが使用可能であるといったメリットがある。
リムフランジ部の肉厚を厚くすると変形域が少なくなり、外的衝撃を受けると伸びて変形するよりも剛性によって即時に破断が生じやすいが、本発明によれば、外的衝撃に対してリムフランジ部の変形による引っ張り応力を緩和して割れの発生を抑制することができる。
リムフランジ部に微小変形が生じても割れを防いで走行可能となるから、ランフラットタイヤのように非常・応急時の使用もより安全に使用可能となる。
According to the present invention, cracking of the rim flange portion can be suppressed for a long time without changing the wheel rim flange shape. For example, there are the following effects.
Compared with the case where the thickness of the rim flange portion is increased, there is an advantage that the weight is reduced and a balance weight of a driving type can be used.
When the thickness of the rim flange portion is increased, the deformation area decreases, and when subjected to an external impact, the rim flange is more likely to break immediately due to rigidity than to stretch and deform. The tensile stress due to the deformation of the flange portion can be relaxed and the occurrence of cracks can be suppressed.
Even if a minute deformation occurs in the rim flange portion, it is possible to run while preventing cracking, so that it can be used more safely during emergency and emergency like a run flat tire.
以下に、本発明の実施形態を説明する。
図１に示す車両用軽合金ホイール１は、自動車の車軸に取り付けられるホイールディスク２と、タイヤが装着される円筒状のホイールリム３とを備える。この車両用軽合金ホイール１は、アルミニウム合金、マグネシウム合金、チタン合金等の軽合金製の鋳造品又は鍛造品により形成され、また、ホイール構成は、１ピースタイプ、２ピースタイプ、３ピースタイプ等の各種の構成が採用可能である。ホイールディスク２は、中央に設けられて自動車の車軸が連結されるハブ取付部２１と、ハブ取付部２１の外周に形成された複数のスポーク部２２と、各スポーク部２２の間に形成された飾り孔２３とを備える。ホイールリム３は、タイヤのビードを着座させるビードシート部３２を両端部に形成する円筒状のリム胴部３１と、リム胴部３１の両側の端縁部においてビードシート部３２からＬ形に湾曲して突設されてタイヤのビート側面を支持するリムフランジ部３３とを備える。ホイールディスク２は、ホイールリム３の内径部に設けられ、車体外側に向く表面が意匠面を構成する。リムフランジ部３３は、車両用軽合金ホイール１を車体に取り付けた際、車体外側に向く方をアウターリムフランジ部３３ｆとし、車体内側に向く方をインナーリムフランジ部３３ｒとする。
Hereinafter, embodiments of the present invention will be described.
The light alloy wheel 1 for vehicles shown in FIG. 1 is equipped with the wheel disc 2 attached to the axle of a motor vehicle, and the cylindrical wheel rim 3 with which a tire is mounted | worn. The light alloy wheel 1 for a vehicle is formed of a cast or forged product made of a light alloy such as an aluminum alloy, a magnesium alloy, or a titanium alloy, and the wheel configuration is a one-piece type, a two-piece type, a three-piece type, or the like. Various configurations can be adopted. The wheel disk 2 is formed between a hub mounting portion 21 provided at the center and connected to the axle of the automobile, a plurality of spoke portions 22 formed on the outer periphery of the hub mounting portion 21, and the spoke portions 22. A decorative hole 23 is provided. The wheel rim 3 is curved in an L shape from the bead seat portion 32 at the edge portions on both sides of the rim barrel portion 31 and a cylindrical rim barrel portion 31 that forms bead seat portions 32 on both ends of which the tire bead is seated. And a rim flange portion 33 that protrudes and supports the beat side surface of the tire. The wheel disc 2 is provided on the inner diameter portion of the wheel rim 3, and the surface facing the outer side of the vehicle body constitutes a design surface. When the light alloy wheel 1 for a vehicle is attached to the vehicle body, the rim flange portion 33 is an outer rim flange portion 33f that faces the outside of the vehicle body and an inner rim flange portion 33r that faces the inside of the vehicle body.
ところで、車両用軽合金ホイール１は、車両走行中に路上の各種の突起物等を踏んだ場合にその衝撃をタイヤの弾性変形のみでは吸収できずリムフランジ部３３に微小変形が生じ、運転者等の車両使用者がこのような微小変形に気付かずそのまま車両走行を続けると、車両使用者の知らない間にこの微小変形部位から割れが生じ、タイヤのエア漏れを起こすなどの不具合を生じさせる場合がある。このような割れは、変形による引っ張り応力が一定の限界値を超えることで発生する。そして、リムフランジ部３３において車両走行中に最も応力集中する部位は、リムフランジ部３３の表層部である。従って、割れは、最も応力集中するリムフランジ部３３表層部が起点となる。このことを検証するため、リムフランジ部３３に変形の無い適正な車両用軽合金ホイール１を用いて、半径方向負荷耐久試験（ＪＩＳ Ｄ４１０３）におけるホイールリム３の応力解析を行ったところ、図２に示すように、タイヤと接触するリムフランジ部３３の外側（外径側）表面部が最大応力部であることが確認された。 By the way, the light alloy wheel 1 for vehicles cannot absorb the impact only by elastic deformation of the tire when stepping on various projections on the road while the vehicle is running, and the rim flange portion 33 is slightly deformed. If the vehicle user does not notice such minute deformation and continues to drive the vehicle as it is, cracks will occur from this minute deformation part without the vehicle user's knowledge, causing problems such as tire air leakage. There is a case. Such cracks occur when the tensile stress due to deformation exceeds a certain limit value. The portion of the rim flange portion 33 where stress is concentrated most during vehicle travel is the surface layer portion of the rim flange portion 33. Therefore, the crack starts from the surface layer portion of the rim flange portion 33 where stress is most concentrated. In order to verify this, a stress analysis of the wheel rim 3 in a radial load endurance test (JIS D4103) was performed using an appropriate vehicle light alloy wheel 1 in which the rim flange portion 33 is not deformed. As shown in FIG. 5, it was confirmed that the outer (outer diameter side) surface portion of the rim flange portion 33 that contacts the tire is the maximum stress portion.
そこで、本実施形態においてリムフランジ部３３は、割れの起点となるリムフランジ部３３表層部に対して意図的に圧縮残留応力を付与することにより変形による引っ張り応力を緩和させる組織構造の緩和層を形成する一方、内層部はこのような意図的な圧縮残留応力が付与されず変形可能な組織構造とするようにした。すなわち、リムフランジ部３３表層部を硬い層で覆うと、硬い層は変形自体を防止できても割れ易くなり得る。これに対して、本実施形態のリムフランジ部３３表層部の緩和層は、変形阻止目的の層ではなく変形を許容して変形による引っ張り応力を打ち消すように作用し、繰り返し引っ張り応力が加わっても割れに至る限界値に達するのを抑制させる。その結果、リムフランジ部３３が微小変形しても割れの起点となるリムフランジ部３３表層部において割れの発生を抑制することができる。これにより、本実施形態の車両用軽合金ホイール１は、路上の突起物等からの衝撃荷重が最も集中し得るホイールリム３のリムフランジ部３３に対してその形状や寸法を既存のホイールリムフランジ形状から変更することなく耐久性を向上させる構造となる。 Therefore, in the present embodiment, the rim flange portion 33 is provided with a relaxation layer having a tissue structure that relieves tensile stress due to deformation by intentionally applying compressive residual stress to the surface layer portion of the rim flange portion 33 that is a starting point of cracking. On the other hand, the inner layer portion was made to have a deformable structure without being given such intentional compressive residual stress. That is, when the surface layer portion of the rim flange portion 33 is covered with a hard layer, the hard layer can be easily broken even if the deformation itself can be prevented. On the other hand, the relaxation layer of the surface layer portion of the rim flange portion 33 according to the present embodiment is not a layer for preventing deformation but acts to allow deformation and counteract tensile stress due to deformation, even if repeated tensile stress is applied. Suppressing reaching the limit value leading to cracking. As a result, even if the rim flange portion 33 is slightly deformed, it is possible to suppress the occurrence of cracks in the surface layer portion of the rim flange portion 33 that is the starting point of the crack. Thereby, the light alloy wheel 1 for vehicles of this embodiment changes the shape and dimension with respect to the rim flange part 33 of the wheel rim 3 in which the impact load from the projections etc. on the road can concentrate most. It becomes a structure which improves durability without changing the shape.
このようなリムフランジ部３３の構造は、以下の押圧工程により形成される。
リムフランジ部３３を所定の最終形状に加工した後のホイールリム３に対して、回転式のボール又はローラからなる押圧工具（ボール又はローラを回転可能に取り付けた工具）をリムフランジ部３３表面に押し当て加圧する押圧工程を行う。このとき、図３に示すように、ホイールリム３は回転軸線を中心に押圧工具６に対して相対回転させ、押圧工具６はリムフランジ部３３表面を押し込みつつリムフランジ部３３の表面に沿ってホイールリム３の軸線方向へ移動させる。なお、図３は、インナーリムフランジ部３３ｒとアウターリムフランジ部３３ｆとを同時に押圧工具６を押し当てている様子を図示するが、前記押圧工程は、インナーリムフランジ部３３ｒとアウターリムフランジ部３３ｆとを別々に押圧工具６を押し当てる場合も含む。また、前記押圧工程は、ホイールディスク２を装備していない状態のホイールリム３に対して行う場合も含む。
Such a structure of the rim flange portion 33 is formed by the following pressing process.
On the surface of the rim flange 33, a pressing tool (a tool with a ball or roller rotatably attached) is formed on the wheel rim 3 after the rim flange 33 is processed into a predetermined final shape. A pressing step of pressing and pressing is performed. At this time, as shown in FIG. 3, the wheel rim 3 rotates relative to the pressing tool 6 around the rotation axis, and the pressing tool 6 pushes the surface of the rim flange portion 33 along the surface of the rim flange portion 33. The wheel rim 3 is moved in the axial direction. FIG. 3 illustrates a state in which the inner rim flange portion 33r and the outer rim flange portion 33f are simultaneously pressed against the pressing tool 6, but the pressing step includes the inner rim flange portion 33r and the outer rim flange portion 33f. And the case where the pressing tool 6 is pressed separately. In addition, the pressing step includes a case where the pressing step is performed on the wheel rim 3 not equipped with the wheel disc 2.
一般に、車両用軽合金ホイール１は、鋳造又は鍛造により製造されるが、いずれの場合も製造工程の最終過程では最終形状となる所定の外形に仕上げる切削加工が行われる。そこで、前記押圧工程は、車両用軽合金ホイール１の製造工程において旋盤でホイールリム３を所定の外形形状に仕上げる切削加工の完了後に、この切削加工を行った旋盤で引き続いて、切削工具を回転式ボール又はローラからなる押圧工具６に交換し、切削加工時にリムフランジ部３３表面を切削するときと同じ要領で、押圧工具６をリムフランジ部３３表面に押し当て加圧することより行うことができる。具体的に、旋盤にはＮＣ旋盤が用いられるので、押圧工具６による加圧は、押し込み寸法を数値制御して行われ、この場合、例えば、押圧工具６をリムフランジ部３３表面から０．５ｍｍ以内の範囲で押し込むように数値設定される。 In general, the light alloy wheel 1 for a vehicle is manufactured by casting or forging, and in any case, in the final process of the manufacturing process, a cutting process is performed to finish a predetermined outer shape as a final shape. Therefore, in the pressing process, after the cutting process for finishing the wheel rim 3 to a predetermined outer shape with a lathe in the manufacturing process of the light alloy wheel 1 for a vehicle, the cutting tool is continuously rotated by the lathe that performed the cutting process. It is possible to replace the pressing tool 6 made of a ball or roller and press the pressing tool 6 against the surface of the rim flange 33 in the same manner as when cutting the surface of the rim flange 33 during cutting. . Specifically, since an NC lathe is used as the lathe, pressurization by the pressing tool 6 is performed by numerically controlling the indentation dimension. In this case, for example, the pressing tool 6 is 0.5 mm from the surface of the rim flange portion 33. The numerical value is set so as to push in within the range.
以上の押圧工程によって、リムフランジ部３３は、意図的に圧縮残留応力が付与された組織構造の緩和層で形成する表層部と、意図的な圧縮残留応力が付与されない組織構造（変形可能域）を有する内層部との２層構造に形成される。このリムフランジ部３３表層部の緩和層は、例えば、表面から１５０μｍの深さであって１７０ＭＰａ〜３５０ＭＰａの圧縮残留応力が付与された組織構造を有する。この２層構造により、リムフランジ部３３は、車両走行時の衝撃で微小変形（例えば、目視困難な約３ｍｍ以内の凹み）を許容しつつ車両走行で繰り返し応力がかかってもこの微小変形を起点とする割れの発生が抑制される。すなわち、車両走行時に突起物を踏む等した場合にその衝撃によってリムフランジ部３３が径方向に微小変形（例えば、約３ｍｍ程度までの内径方向への凹み）しても、その微小変形に伴う引っ張り応力は表層部の緩和層の圧縮残留応力によって相殺されると同時に内層部の変形可能域で変形許容されて即時に破断に至らないようにすることができる。従って、リムフランジ部３３が微小変形する程度の外的衝撃を受けても割れを生じ難くするとともに、その微小変形の存在下で車両走行を続行し変形部位に繰り返し応力がかかっても割れの起点になり難い性能を具備した車両用軽合金ホイール１が得られる。しかも、このリムフランジ部３３は、従来品のように肉厚を厚くしたり塊状の張り出しを形成したもの（特許文献１、特許文献２）とは異なり、既存のホイールリムフランジ形状から形状変更されないから、既存の打ち込みタイプのバランスウエイトを支障なく使用することができ、且つ重量増にもならない利点を有する。 By the above pressing step, the rim flange portion 33 has a surface layer portion formed by a relaxed layer of a tissue structure to which compressive residual stress is intentionally applied, and a tissue structure (deformable region) to which no intentional compressive residual stress is applied. It is formed in a two-layer structure with an inner layer portion having The relaxing layer of the surface layer portion of the rim flange portion 33 has, for example, a structure having a depth of 150 μm from the surface and a compressive residual stress of 170 MPa to 350 MPa. Due to this two-layer structure, the rim flange portion 33 starts with this minute deformation even when repeated stress is applied during vehicle running while allowing minute deformation (for example, a dent within about 3 mm that is difficult to see) due to impact during vehicle running. The occurrence of cracks is suppressed. That is, even when the rim flange portion 33 is slightly deformed in the radial direction (for example, a recess in the inner diameter direction of about 3 mm) due to the impact when the projection is stepped on while the vehicle is running, the tensile force accompanying the micro deformation is The stress is canceled by the compressive residual stress of the relaxation layer in the surface layer portion, and at the same time, the deformation is allowed in the deformable region of the inner layer portion so as not to break immediately. Therefore, even if the rim flange portion 33 is subjected to an external impact to the extent that the rim flange portion is subjected to minute deformation, it is difficult to generate a crack, and even if the vehicle travels in the presence of the minute deformation and a repeated stress is applied to the deformation portion, Thus, the light alloy wheel 1 for a vehicle having performance that is difficult to be obtained is obtained. In addition, the rim flange portion 33 is not changed in shape from the existing wheel rim flange shape unlike the conventional rim flange portion 33 which is thickened or has a lump-like overhang (Patent Literature 1, Patent Literature 2). Therefore, there is an advantage that an existing driving type balance weight can be used without hindrance and the weight is not increased.
そして、リムフランジ部３３表層部の緩和層は、表面から１５０μｍの深さであって１７０ＭＰａ〜３５０ＭＰａの圧縮残留応力値を有することで、車両走行中の衝撃によってリムフランジ部３３に約３ｍｍ程度の微小変形が形成されてもこの微小変形を起点とする繰り返し応力による割れ発生を抑制することができる。しかも、リムフランジ部３３の凹み等の変形が約３ｍｍ以下の目視では判別し難い微小変形の場合は即座に走行不能となることはないため、車両使用者が気付かず車両走行を続けてしまうことが考えられるが、そのような状況下で車両走行を続けて変形部位に繰り返し応力がかかっても、この変形部位が起点となって割れ発生することを抑制することができる。この割れ抑制効果（耐久性）は、意図的に圧縮残留応力が付与された緩和層で形成する表層部を有さず且つ未変形のリムフランジ部３３を備える車両用軽合金ホイール１の耐久性と同等又はそれ以上の効果が得られる。 And the relaxation layer of the surface layer part of the rim flange part 33 has a depth of 150 μm from the surface and a compressive residual stress value of 170 MPa to 350 MPa, so that about 3 mm is applied to the rim flange part 33 due to an impact during traveling of the vehicle. Even if a minute deformation is formed, it is possible to suppress the occurrence of cracking due to repeated stress starting from the minute deformation. In addition, when the deformation of the rim flange portion 33 such as a dent or the like is a minute deformation that is difficult to visually discern, it is not immediately impossible to travel, so that the vehicle user does not notice and continues to travel the vehicle. However, even if the vehicle travels continuously in such a situation and stress is repeatedly applied to the deformed portion, it is possible to suppress the occurrence of cracks starting from the deformed portion. This crack suppression effect (durability) is the durability of the light alloy wheel 1 for a vehicle that does not have a surface layer portion formed by a relaxation layer intentionally applied with compressive residual stress and includes an undeformed rim flange portion 33. The effect equivalent to or better than is obtained.
また、前記押圧工程は、切削加工を行った旋盤加工工程において引き続いて切削工具を回転式ボール又はローラの押圧工具６に交換して実行されることで、ツール（押圧工具６）の追加のみで、旋盤でのホイールリム３の切削加工完了後にそのままツール交換して行うことができ、特別な設備を導入することなく既存設備を活用して短時間で効率よくリムフランジ部３３の強化構造を形成することができる。 Further, the pressing step is executed by replacing the cutting tool with a rotary ball or roller pressing tool 6 in the lathe processing step in which cutting is performed, so that only a tool (pressing tool 6) is added. After the cutting of the wheel rim 3 on the lathe, the tool can be replaced as it is, and the rim flange 33 can be efficiently formed in a short time using existing equipment without introducing special equipment. can do.
なお、本発明は、上記実施形態のみに限定されず、本発明の要旨の範囲内で適宜に変更することが可能である。
例えば、半径方向負荷耐久試験時におけるホイールリム３の応力解析の結果、最大応力部はタイヤと接触するリムフランジ部３３の外側（外径側）表面部であった（図２参照）。従って、前記押圧工程として、リムフランジ部３３表層部に対して圧縮残留応力を付与した緩和層の形成は、リムフランジ部３３全域に施工するのが望ましいが、少なくともタイヤと接触する外側面（車両走行時に最も応力を受ける部位）のみに施工することにより、衝撃による微小変形部位が起点となって割れ発生するのを抑制することができる。この場合、前記押圧工程をリムフランジ部３３全域に行う場合に比べて簡易に且つ短時間で済ませることができる。
In addition, this invention is not limited only to the said embodiment, It can change suitably within the range of the summary of this invention.
For example, as a result of the stress analysis of the wheel rim 3 during the radial load endurance test, the maximum stress portion was the outer (outer diameter side) surface portion of the rim flange portion 33 in contact with the tire (see FIG. 2). Accordingly, as the pressing step, the formation of the relaxation layer that imparts compressive residual stress to the surface layer portion of the rim flange portion 33 is preferably performed over the entire area of the rim flange portion 33, but at least the outer surface (vehicle) that contacts the tire By carrying out the construction only on the part that receives the most stress during traveling, it is possible to suppress the occurrence of cracks starting from the minutely deformed part due to impact. In this case, it is possible to simply and in a short time compared to the case where the pressing step is performed on the entire rim flange portion 33.
また、前記押圧工程により、リムフランジ部３３表層部に対する圧縮残留応力を付与した緩和層の形成は、インナーリムフランジ部３３ｒのみに行うことでもよい。すなわち、車両走行時にタイヤと車両用ホイール１は左右でハの字型に角度がつくため、インナーリムフランジ部３３ｒに最も負荷がかかりやすく、しかも、インナーリムフランジ部３３ｒは、車体内側に位置しているから車体外側からは通常確認しにくいため、車両使用者はインナーリムフランジ部３３ｒに微小変形が生じても気付かず車両走行を続けてしまうことが考えられる。従って、インナーリムフランジ部３３ｒに対して前記押圧工程を行うことで、インナーリムフランジ部３３ｒに微小変形が生じたにもかかわらず、車両走行を続けて変形部位に繰り返し応力がかかっても、この変形部位が起点となって割れ発生するのを抑制することができる。 Moreover, the formation of the relaxation layer imparted with compressive residual stress to the surface layer portion of the rim flange portion 33 by the pressing step may be performed only on the inner rim flange portion 33r. That is, since the tire and the vehicle wheel 1 are angled in a U-shape on the left and right when the vehicle is running, the load is most easily applied to the inner rim flange portion 33r, and the inner rim flange portion 33r is located inside the vehicle body. Therefore, since it is difficult to confirm from the outside of the vehicle body, it is conceivable that the vehicle user does not notice even if the inner rim flange portion 33r is slightly deformed and continues to travel the vehicle. Therefore, by performing the pressing step on the inner rim flange portion 33r, even if the inner rim flange portion 33r is slightly deformed, even if the vehicle is continuously driven and stress is repeatedly applied to the deformed portion, It is possible to suppress the occurrence of cracks starting from the deformed portion.
次に、実施例を説明する。
所定の鍛造によりアルミニウム合金（Ａ６０６１）の鍛造品からなる車両用軽合金ホイール１を成形し、その後、旋盤により切削加工する切削工程を行って最終のホイールの形状及び寸法と略等しい外形に形成した。この車両用軽合金ホイール１は、リム径１９インチとし、リム胴部３１の肉厚約２．５ｍｍ、リムフランジ部３３の肉厚約７ｍｍとする。
Next, examples will be described.
A light alloy wheel 1 for a vehicle made of a forged product of an aluminum alloy (A6061) is formed by a predetermined forging, and then a cutting process is performed by a lathe to form an outer shape substantially equal to the shape and dimensions of the final wheel. . The vehicle light alloy wheel 1 has a rim diameter of 19 inches, a rim body portion 31 having a thickness of about 2.5 mm, and a rim flange portion 33 having a thickness of about 7 mm.
そして、切削工程に引き続いて、切削加工を行った旋盤において切削工具を回転式ボールからなる押圧工具６にツール交換して、この押圧工具６をリムフランジ部３３表面に押し当て加圧するリムフランジ部３３の押圧工程を行った（図３参照）。すなわち、切削後の車両用軽合金ホイール１を旋盤の回転プレートにより回転軸線を中心に回転させるとともに、押圧工具６をリムフランジ部３３表面に押し付け加圧しつつリムフランジ部３３の回転軸線方向に移動させることによって、リムフランジ部３３におけるタイヤとの接触表面（外側面）のみに対して押圧工具６を押し当てて加圧し、リムフランジ部３３外径表面全体に圧縮残留応力を付与した緩和層を形成した。このときの条件として、旋盤による車両用軽合金ホイール１の回転数５０ｒｐｍ、押圧工具６の移動速度０．１ｍｍ／ｓｅｃ、押圧工具６のリムフランジ部３３表面への押し込み量０．５ｍｍとした。 Then, following the cutting process, the cutting tool is replaced with a pressing tool 6 made of a rotary ball in the lathe that has been subjected to cutting, and the pressing tool 6 is pressed against the surface of the rim flange 33 to pressurize the rim flange. 33 pressing steps were performed (see FIG. 3). That is, the light alloy wheel 1 for a vehicle after cutting is rotated around a rotation axis by a rotating plate of a lathe and the pressing tool 6 is pressed against the surface of the rim flange 33 and moved in the direction of the rotation axis of the rim flange 33. By pressing the pressure tool 6 against only the contact surface (outer side surface) of the rim flange portion 33 with the tire, the relaxation layer is applied with a compressive residual stress applied to the entire outer diameter surface of the rim flange portion 33. Formed. The conditions at this time were: the rotational speed of the light alloy wheel 1 for a vehicle using a lathe was 50 rpm, the moving speed of the pressing tool 6 was 0.1 mm / sec, and the pressing amount of the pressing tool 6 onto the surface of the rim flange portion 33 was 0.5 mm.
以上の押圧工程により、リムフランジ部３３には、意図的に圧縮残留応力が付与された組織構造の緩和層が形成された表層部と、意図的な圧縮残留応力が付与されない組織構造のままの内層部（変形可能域）との２層構造が形成された車両用軽合金ホイール１を製造した。 By the above pressing process, the rim flange portion 33 remains as a surface layer portion formed with a relaxed layer of a tissue structure to which compressive residual stress is intentionally applied and a tissue structure to which no intentional compressive residual stress is applied. The light alloy wheel 1 for vehicles in which the two-layer structure with the inner layer part (deformable region) was formed was manufactured.
上述した実施例との比較のため、前記押圧工程を行わなかった車両用軽合金ホイール（比較例：旋盤加工品）を準備した。また、参考例として、前記押圧工程に代えてリムフランジ部３３表面にショットブラスト処理を施した車両用軽合金ホイール（参考例：ショットブラスト品）を準備した。なお、これら比較例及び参考例の車両用軽合金ホイールは、上記のこと以外は実施例と同様に製作した。 For comparison with the above-described embodiment, a light alloy wheel for vehicle that did not perform the pressing step (comparative example: lathe processed product) was prepared. In addition, as a reference example, a light alloy wheel for a vehicle (reference example: shot blast product) in which the surface of the rim flange portion 33 was subjected to shot blasting instead of the pressing step was prepared. In addition, the light alloy wheel for vehicles of these comparative examples and reference examples was manufactured similarly to the Example except the above.
以上の実施例、比較例及び参考例の車両用軽合金ホイールに対して耐久性能を比較検証するために、半径方向負荷耐久試験を行った。なお、いずれの車両用軽合金ホイールにも、同じタイヤを装着してタイヤエア圧１５０ｋＰａとした。ここで、半径方向負荷耐久試験は、ＪＩＳ Ｄ４１０３に従って、一定速度で回転するドラムに対して、タイヤを装着した車両用軽合金ホイールを押し付けて半径方向に負荷を加えながら回転させた。以上の半径方向負荷耐久試験の結果、実施例、比較例及び参考例の車両用軽合金ホイールでは、いずれも規定の５０万回転に対して２００万回転させても亀裂や割れは発生しなかった。 In order to compare and verify the durability performance of the light alloy wheels for vehicles of the above examples, comparative examples, and reference examples, a radial load durability test was performed. Note that the same tire was attached to each vehicle light alloy wheel, and the tire air pressure was set to 150 kPa. Here, the radial load endurance test was performed in accordance with JIS D4103 by rotating a light alloy wheel for vehicles equipped with a tire against a drum rotating at a constant speed while applying a load in the radial direction. As a result of the above-described radial load endurance test, in the light alloy wheels for vehicles of the examples, comparative examples, and reference examples, no cracks or cracks were generated even after 2 million rotations against the prescribed 500,000 rotations. .
次に、図４に示すように、実施例、比較例及び参考例の車両用軽合金ホイールに対して、上述したタイヤ４を装着しタイヤ外形方向からの衝撃を想定して、突起物５に対して車軸から３４．１ｋＮの荷重Ｆを加えてタイヤ４及びホイール１を押し付けた。なお、実際の車両走行時ではタイヤ及びホイールが左右でハの字型となってインナーリムへの負荷大となることを想定して、突起物５の高さは、インナーリム側をアウターリム側よりも少し高く設置した。すると、実施例、比較例及び参考例のいずれのホイールも、インナーリム側のリムフランジ部３３ｒには、タイヤ４の弾性変形のみでは衝撃を吸収することができず、内径方向に約３ｍｍの変形が生じた（図５の矢印部分を参照）。アウターリム側のリムフランジ部３３ｆには、変形は生じていなかった。 Next, as shown in FIG. 4, the above-described tire 4 is mounted on the light alloy wheels for vehicles of the examples, comparative examples, and reference examples, and the projections 5 are formed assuming an impact from the tire outer direction. The tire 4 and the wheel 1 were pressed against the axle by applying a load F of 34.1 kN from the axle. Note that the height of the protrusion 5 is set so that the inner rim side is closer to the outer rim side, assuming that the tires and wheels are square-shaped on the left and right during actual vehicle travel, and the load on the inner rim is large. Installed a little higher than. Then, in any of the wheels of the example, comparative example, and reference example, the rim flange portion 33r on the inner rim side cannot absorb the impact only by elastic deformation of the tire 4, and is deformed by about 3 mm in the inner diameter direction. (See the arrow in FIG. 5). The rim flange portion 33f on the outer rim side was not deformed.
そして、この変形後の車両用軽合金ホイールについて、上記未変形状態のときにクリアした５０万回転の半径方向負荷耐久試験を行ったところ、比較例及び参考例の車両用軽合金ホイールは、いずれも、アウターリムフランジ部３３ｆでのクラックは生じなかったが、インナーリムフランジ部３３ｒには、上記変形部位からビードシート部３２付近まで達してリムフランジ部３３ｒを貫通した割れｋが生じていた（図６参照）。図７の写真は、比較例の車両用軽合金ホイールにおけるインナーリムフランジ部の割れｋを示し、図７（ａ）はホイール外径側（外周側）の写真であり、図７（ｂ）はホイール内径側（内周側）の写真であり、割れｋがリムフランジ部３３ｒの内外に貫通していることがわかる。なお、参考例の車両用軽合金ホイールにおけるインナーリムフランジ部３３ｒの割れも同様のものであった。 And about the light alloy wheel for vehicles after this deformation | transformation, when the radial load endurance test of 500,000 rotations cleared in the said undeformed state was performed, the light alloy wheel for vehicles of a comparative example and a reference example was However, cracks did not occur in the outer rim flange portion 33f, but cracks k occurred in the inner rim flange portion 33r from the deformed portion to the vicinity of the bead seat portion 32 and penetrating the rim flange portion 33r ( (See FIG. 6). The photograph of FIG. 7 shows the crack k of the inner rim flange part in the light alloy wheel for vehicles of a comparative example, FIG. 7 (a) is a photograph of the wheel outer diameter side (outer peripheral side), and FIG. It is a photograph of the wheel inner diameter side (inner peripheral side), and it can be seen that the crack k penetrates the inside and outside of the rim flange portion 33r. In addition, the crack of the inner rim flange portion 33r in the light alloy wheel for a vehicle of the reference example was the same.
これに対して、実施例の車両用軽合金ホイール１では、アウターリムフランジ部３３ｆはもちろんのこと、インナーリムフランジ部３３ｒの変形部位から亀裂や割れは発生していなかった。なお、このリムフランジ部３３ｒを変形させた実施例の車両用軽合金ホイール１では、半径方向負荷耐久試験により、１５０万回転させても、リムフランジ部３３ｒの変形部位から割れは生じなかった。 On the other hand, in the light alloy wheel 1 for a vehicle according to the example, not only the outer rim flange portion 33f but also the cracks and cracks were not generated from the deformed portion of the inner rim flange portion 33r. In the light alloy wheel 1 for a vehicle according to the example in which the rim flange portion 33r was deformed, cracks did not occur from the deformed portion of the rim flange portion 33r even when the rim flange portion 33r was rotated 1.5 million times in the radial load durability test.
以上の結果より、実施例のようにリムフランジ部３３の形状変更を行うことなく割れの発生起点となるリムフランジ部３３表層部に圧縮残留応力を付与した緩和層を形成することで、万一リムフランジ部３３が変形しても、タイヤがホイールから外れたりエア漏れするような大きな変形でなく、目視困難な約３ｍｍ程度の変形が生じた状況では、車両走行によって変形部位に繰り返し応力が加わっても、この変形部位から割れが発生することなく、通常どおり走行することが可能となることが実際に確認された。なお、以上の試験では、インナーリムフランジ部３３ｒを変形させた場合であるが、アウターリムフランジ部３３ｒを変形させた場合も同様の結果となる。 From the above results, by forming a relaxation layer imparting compressive residual stress to the surface layer portion of the rim flange portion 33 that is the starting point of cracking without changing the shape of the rim flange portion 33 as in the embodiment, Even if the rim flange portion 33 is deformed, in a situation where the deformation is about 3 mm, which is difficult to visually observe, rather than a large deformation in which the tire comes off the wheel or air leaks, a repeated stress is applied to the deformed portion by running the vehicle. However, it was actually confirmed that it is possible to travel as usual without cracking from the deformed portion. In the above test, the inner rim flange portion 33r is deformed, but the same result is obtained when the outer rim flange portion 33r is deformed.
次に、実施例、比較例及び参考例の車両用軽合金ホイールについて、リムフランジ部３３の未変形状態と変形後の圧縮残留応力値を測定した。圧縮残留応力の測定方法は、非破壊的方法として、ＪＩＳ Ｂ２７１１に規定されているＸ線応力回折を利用したＸ線応力測定法を用いた。この圧縮残留応力値の測定値を、図８のグラフに示す。なお、図８のグラフ中、マイナス側が圧縮応力が加わっていることを示し、プラス側が引っ張り応力が加わっていることを示す。 Next, the undeformed state of the rim flange portion 33 and the compressive residual stress value after deformation were measured for the light alloy wheels for vehicles of Examples, Comparative Examples, and Reference Examples. As a method for measuring the compressive residual stress, an X-ray stress measurement method using X-ray stress diffraction defined in JIS B2711 was used as a non-destructive method. The measured value of the compressive residual stress value is shown in the graph of FIG. In the graph of FIG. 8, the minus side indicates that compressive stress is applied, and the plus side indicates that tensile stress is applied.
図８のグラフに示したとおり、リムフランジ部３３の表面から深さ１５０μｍまでの表層部において、比較例（旋盤加工品）では、変形前に６０〜７２ＭＰａであった圧縮残留応力が、変形後には、この圧縮残留応力が引っ張り応力によって打ち消され、さらに０以上のプラス側に３〜５ＭＰａの引っ張り応力が加わった状態になっていた。参考例（ショットブラスト品）では、変形前に９９〜１６６ＭＰａであった圧縮残留応力が、変形後には、３〜１５ＭＰａの圧縮残留応力となり、ショットブラストによる圧縮残留応力が変形による引っ張り応力によってほとんど打ち消された。 As shown in the graph of FIG. 8, in the surface layer portion from the surface of the rim flange portion 33 to a depth of 150 μm, in the comparative example (turned product), the compression residual stress that was 60 to 72 MPa before the deformation was In this case, the compressive residual stress was canceled by the tensile stress, and a tensile stress of 3 to 5 MPa was applied to the positive side of 0 or more. In the reference example (shot blast product), the compressive residual stress that was 99 to 166 MPa before deformation becomes 3 to 15 MPa compressive residual stress after deformation, and the compressive residual stress due to shot blast is almost canceled by the tensile stress due to deformation. It was.
これに対して、実施例では、変形前に３０５〜３３４ＭＰａであった圧縮残留応力は、変形後においても５０〜６４ＭＰａの圧縮残留応力が残っていた。すなわち、実施例では、変形後においても比較例（旋盤加工品）の未変形状態と同等程度の圧縮残留応力が確保されることが確認された。以上の結果、リムフランジ部３３表層部（深さ約１５０μｍの範囲）において、１７０ＭＰａ〜３５０ＭＰａ、好ましくは３００ＭＰａ〜３５０ＭＰａの圧縮残留応力を付与する必要があることがわかった。 On the other hand, in the examples, the compressive residual stress that was 305 to 334 MPa before the deformation remained after the deformation was 50 to 64 MPa. That is, in the example, it was confirmed that a compressive residual stress equivalent to the undeformed state of the comparative example (turned product) was secured even after deformation. As a result, it has been found that it is necessary to apply a compressive residual stress of 170 MPa to 350 MPa, preferably 300 MPa to 350 MPa, in the surface layer portion of the rim flange portion 33 (with a depth of about 150 μm).
１ 車両用軽合金ホイール
２ ホイールディスク
３ ホイールリム
４ タイヤ
５ 突起物
２１ ハブ取付部
２２ スポーク部
２３ 飾り孔
３１ リム胴部
３２ ビードシート部
３２ｆ アウタービードシート部
３２ｒ インナービードシート部
３３ リムフランジ部
３３ｆ アウターリムフランジ部
３３ｒ インナーリムフランジ部
６ 押圧工具
ｋ 割れ
DESCRIPTION OF SYMBOLS 1 Vehicle light alloy wheel 2 Wheel disk 3 Wheel rim 4 Tire 5 Protrusion 21 Hub attachment part 22 Spoke part 23 Decoration hole 31 Rim trunk | drum 32 Bead sheet | seat part 32f Outer bead seat part 32r Inner bead seat part 33 Rim flange part 33f Outer rim flange part 33r Inner rim flange part 6 Press tool k Crack
Claims (5)
前記ホイールリムの加工工程は、車両走行中に突発的に受けた衝撃でホイール内径方向へ微小変形しエア漏れなく走行可能な場合であって前記微小変形部位へ車両走行によって受ける繰り返し応力を原因とする割れの起点となるリムフランジ部に対して、回転式のボール又はローラからなる押圧工具をタイヤと接触するリムフランジ部の外側表面部に押し当て加圧することで前記リムフランジ部の外側表面部には前記微小変形による引っ張り応力を緩和させるための圧縮残留応力が付与された組織構造の緩和層となる表層部と、意図的な前記圧縮残留応力が付与されず変形可能な組織構造の内層部との２層構造が形成される押圧工程を含み、
前記押圧工程により、前記表層部には表面から１５０μｍの深さで３００ＭＰａ〜３５０ＭＰａの圧縮残留応力値を有し、当該圧縮残留応力値が表面から３００μｍの深さにおける前記内層部の圧縮残留応力値よりも高い緩和層が形成される車両用軽合金ホイールの製造方法。 In a method for manufacturing a light alloy wheel for a vehicle, in a wheel rim processing step including a step of processing a rim flange portion protruding from an end edge portion of a cylindrical rim body portion in a wheel rim,
The processing process of the wheel rim is caused by the repeated stress received by the vehicle traveling to the minute deformation portion when the vehicle can travel without air leakage by minute deformation in the inner diameter direction of the wheel due to an impact received suddenly while traveling the vehicle. for the rim flange portion serving as a starting point for cracks to the outer surface portion of the rim flange by pressurizing pressing the press tool consisting of balls or rollers rotating on the outer surface of the rim flange contacting the tire Includes a surface layer portion serving as a relaxation layer of a tissue structure to which a compressive residual stress is applied to relieve a tensile stress due to microdeformation, and an inner layer portion of a tissue structure that is deformable without intentionally applying the compressive residual stress. And a pressing step in which a two-layer structure is formed,
By the pressing step, have a residual compressive stress value 300MPa~350MPa at a depth of 150μm from the surface on the surface layer portion, the compressive residual stress value of the inner portion at a depth of 300μm the compressive residual stress value is from the surface The manufacturing method of the light alloy wheel for vehicles in which a higher relaxation layer is formed.
前記押圧工程は、リムフランジ部におけるタイヤと接触しない側の面を含めてリムフランジ部全域に対して行われる車両用軽合金ホイールの製造方法。 In the manufacturing method of the light alloy wheel for vehicles according to claim 1,
The said press process is a manufacturing method of the light alloy wheel for vehicles performed with respect to the rim flange part whole region including the surface of the side which does not contact a tire in a rim flange part.
前記押圧工程は、リムフランジ部の切削加工を行った旋盤加工工程において引き続いて切削工具を前記押圧工具に交換して行われる車両用軽合金ホイールの製造方法。 In the manufacturing method of the light alloy wheel for vehicles according to claim 1 or 2,
The said press process is a manufacturing method of the light alloy wheel for vehicles performed by exchanging a cutting tool for the said press tool succeedingly in the lathe processing process which performed the cutting process of the rim flange part.
前記押圧工程は、少なくともインナーリムフランジ部に対して行われる車両用軽合金ホイールの製造方法。 In the manufacturing method of the light alloy wheel for vehicles given in any 1 paragraph of Claims 1-3,
The said press process is a manufacturing method of the light alloy wheel for vehicles performed with respect to an inner rim flange part at least.
前記リムフランジ部には、車両走行中の衝撃で微小変形し割れの起点となるリムフランジ部におけるタイヤと接触するリムフランジ部外側表面部に対して前記微小変形による引っ張り応力を緩和させるための圧縮残留応力が付与された組織構造の緩和層となる表層部と、意図的な圧縮残留応力が付与されず変形可能な組織構造の内層部との２層構造が形成され、
前記表層部には表面から１５０μｍの深さで３００ＭＰａ〜３５０ＭＰａの圧縮残留応力値を有し、当該圧縮残留応力値が表面から３００μｍの深さにおける前記内層部の圧縮残留応力値よりも高い緩和層が形成されている車両用軽合金ホイール。 In a light alloy wheel for a vehicle including a wheel rim that continuously connects a rim flange portion to an end edge portion of a tubular rim body portion,
The said rim flange, to mitigate the tensile stress due to the small deformation against the rim flange outer surface portion for contacting a tire definitive the rim flange portion serving as a starting point for small deformation cracks caused by impact of the vehicle is traveling A two-layer structure is formed of a surface layer portion serving as a relaxation layer of a tissue structure to which compressive residual stress is applied, and an inner layer portion of a tissue structure that is deformable without intentional compressive residual stress being applied,
Have a compressive residual stress value 300MPa~350MPa at a depth of 150μm from the surface on the surface layer portion, high relaxivity layer than the residual compressive stress value of the inner portion at a depth of 300μm the compressive residual stress value is from the surface A light alloy wheel for vehicles in which is formed.
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