JP2011137555A - Roller type ball screw - Google Patents

Roller type ball screw Download PDF

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JP2011137555A
JP2011137555A JP2011087931A JP2011087931A JP2011137555A JP 2011137555 A JP2011137555 A JP 2011137555A JP 2011087931 A JP2011087931 A JP 2011087931A JP 2011087931 A JP2011087931 A JP 2011087931A JP 2011137555 A JP2011137555 A JP 2011137555A
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screw
ball
groove
nut
ball screw
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JP5004312B2 (en
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Kiyotake Shibata
清武 柴田
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NTN Corp
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NTN Corp
NTN Toyo Bearing Co Ltd
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a roller type ball screw which improves operating efficiency both in positive action and reverse action, and reduces mechanical loss. <P>SOLUTION: A ball screw which is equipped with a screw shaft 1 in which a spiral screw groove 2 is formed in periphery, a nut 3 which is externally interfit into this screw shaft 1 and forms a spiral screw groove 4 in inner circumferential surface, a plurality of ball 5 housed in a rolling passage formed by both mutually faced screw grooves, and a piece member 7 which is mounted in a periphery of the nut 3 and has a connecting groove 8 connecting the screw groove 4 of this nut 3, wherein a ratio of depth t of the screw groove 2 of the screw shaft 1 with respect to a ball diameter d is set in a range of t/d=0.20-0.30 and an initial contact angle α between the ball 5 and screw groove 2 is set in a range of 25-40°. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

本発明は、放電加工機やタッピングセンター等の各種工作機械、あるいは自動車の電動パワーステアリングやアクチュエータ等に使用されるボールねじに関し、特に、作動時の摩擦効率向上を図ったボールねじに関する。   The present invention relates to a ball screw used for various machine tools such as an electric discharge machine and a tapping center, or an electric power steering or an actuator of an automobile, and more particularly to a ball screw that improves friction efficiency during operation.

ボールねじは、外周面に螺旋状のねじ溝が形成されたねじ軸と、このねじ軸に外嵌され、内周面に螺旋状のねじ溝が形成されたナットと、対向する両ねじ溝により形成された転動路に収容された複数のボールと、転動路を周回経路とする循環機構とを備え、例えば、ナットを回転運動させることでねじ軸を直線運動させる運動変換機構として使用されている。   The ball screw is composed of a screw shaft having a helical thread groove formed on the outer peripheral surface, a nut externally fitted to the screw shaft, and a spiral screw groove formed on the inner peripheral surface, and both opposing screw grooves. A plurality of balls accommodated in the formed rolling path and a circulation mechanism having the rolling path as a circulation path are used as, for example, a motion conversion mechanism that linearly moves the screw shaft by rotating the nut. ing.

一般的にボールねじは、ボールの循環機構が異なる種々の形式のものがあり、その一つに駒式と呼ばれるものがある。この駒式ボールねじは、ねじ溝の連結路を有し、転動路を周回経路とする循環用の駒部材がナットに装着されている。駒式ボールねじは構成が比較的簡素で、かつコンパクトに構成できる利点がある。   Generally, there are various types of ball screws having different ball circulation mechanisms, one of which is called a piece type. This piece-type ball screw has a threaded groove connection path, and a circulation piece member having a rolling path as a circulation path is mounted on a nut. The piece-type ball screw has an advantage that the configuration is relatively simple and the configuration can be made compact.

この種のボールねじは、精度良く造られた場合には、ナットに負荷されるねじ軸に沿った荷重やねじ軸に負荷されるトルクに対して安定した作動特性を有する。然しながら、実際には、ボールねじの各溝を形成する円弧状の曲率半径や螺旋状に形成されたねじ溝のリード等々の誤差が組み合わさることで、ボールねじの転がり摩擦抵抗が変動する。そのため、ボールねじの位置決め精度や制御性の低下、あるいは摩擦による発熱等が生じ、ボールねじの寿命を低下させることがある。   When this type of ball screw is manufactured with high accuracy, it has stable operating characteristics with respect to the load along the screw shaft loaded on the nut and the torque loaded on the screw shaft. However, in reality, the rolling frictional resistance of the ball screw varies due to a combination of errors such as the arc-shaped radius of curvature forming each groove of the ball screw and the lead of the screw groove formed in a spiral shape. As a result, the positioning accuracy and controllability of the ball screw are reduced, or heat is generated due to friction, which may reduce the life of the ball screw.

こうした問題を解決したものとして、図４に示すようなボールねじが知られている。このボールねじ５１は、ねじ軸ＳとナットＮと多数のボール５２とを備えている。ねじ軸Ｓの外周面５３とナットＮの内周面５４には、対向する螺旋状のねじ軸溝５５とナット溝５６が形成されている。ボール５２は、これらねじ軸溝５５とナット溝５６にそれぞれ転接している。   As a solution to these problems, a ball screw as shown in FIG. 4 is known. The ball screw 51 includes a screw shaft S, a nut N, and a large number of balls 52. Opposed helical screw shaft grooves 55 and nut grooves 56 are formed on the outer peripheral surface 53 of the screw shaft S and the inner peripheral surface 54 of the nut N. The ball 52 is in rolling contact with the screw shaft groove 55 and the nut groove 56, respectively.

ねじ軸溝５５とナット溝５６は、断面がゴシックアーク形状に形成されている。ボールの半径をｒ、ねじ軸溝５５の断面を形成する第１の円弧５５ａ、５５ｂの曲率半径をＲｓ１、Ｒｓ２、これら第１の円弧５５ａ、５５ｂの曲率半径の中心Ｃｓ１、Ｃｓ２からボール５２の中心Ａを通るねじ軸Ｓに垂直な線Ｂまでのねじ軸Ｓの軸方向に沿う方向の距離をＸｃｓ１、Ｘｃｓ２、ナット溝５６の断面を形成する第２の円弧５６ａ、５６ｂの曲率半径をＲｎ１、Ｒｎ２、これら第２の円弧５６ａ、５６ｂの曲率半径の中心Ｃｎ１、Ｃｎ２からボール５２の中心Ａまでのねじ軸Ｓの軸方向に沿う方向の距離をＸｃｎ１、Ｘｃｎ２、ボール５２の中心Ａを通るねじ軸Ｓに垂直な線Ｂに対してねじ軸溝５５とボール５２の接点５２ｓａ、５２ｓｂがなす中心Ａの角度（接触角）をαｒｓ１、αｒｓ２、ナット溝５６とボール５２の接点５２ｎａ、５２ｎｂの接触角をαｒｎ１、αｒｎ２とすると、
ｓｉｎαｒｓ１＝Ｘｃｓ１／（Ｒｓ１−ｒ）
ｓｉｎαｒｓ２＝Ｘｃｓ２／（Ｒｓ２−ｒ）
ｓｉｎαｒｎ１＝Ｘｃｎ１／（Ｒｎ１−ｒ）
ｓｉｎαｒｎ２＝Ｘｃｎ２／（Ｒｎ２−ｒ）
この時、Ｒｓ１＝Ｒｓ２＝Ｒｓ、Ｘｃｓ１＝Ｘｃｓ２＝ＸｃｓＲｎ１＝Ｒｎ２＝Ｒｎ、Ｘｃｎ１＝Ｘｃｎ２＝Ｘｃｎなので、αｒｓ１＝αｒｓ２、αｒｎ１＝αｒｎ２である。そして、−０．１≦｛Ｘｃｓ／(Ｒｓ−ｒ)−Ｘｃｎ／(Ｒｎ−ｒ)｝＜０を満たすようにねじ軸溝５５とナット溝５６とが形成されている。 The screw shaft groove 55 and the nut groove 56 are formed in a gothic arc shape in cross section. The radius of the ball is r, the radii of curvature of the first arcs 55a and 55b forming the cross section of the screw shaft groove 55 are Rs1 and Rs2, and the centers of curvature radii Cs1 and Cs2 of the first arcs 55a and 55b The distance along the axial direction of the screw shaft S to the line B perpendicular to the screw shaft S passing through the center A is Xcs1, Xcs2, and the radius of curvature of the second arcs 56a, 56b forming the cross section of the nut groove 56 is Rn1. , Rn2, the distance along the axial direction of the screw shaft S from the centers Cn1 and Cn2 of the radius of curvature of these second arcs 56a and 56b to the center A of the ball 52 passes through Xcn1, Xcn2 and the center A of the ball 52. The angle (contact angle) of the center A formed by the contact 52sa, 52sb of the screw shaft groove 55 and the ball 52 with respect to the line B perpendicular to the screw shaft S is αrs1, αrs2, the contact between the nut groove 56 and the ball 52. When the contact angles of 52na and 52nb are αrn1 and αrn2,
sinαrs1 = Xcs1 / (Rs1-r)
sinαrs2 = Xcs2 / (Rs2-r)
sinαrn1 = Xcn1 / (Rn1-r)
sinαrn2 = Xcn2 / (Rn2-r)
At this time, since Rs1 = Rs2 = Rs, Xcs1 = Xcs2 = XcsRn1 = Rn2 = Rn, and Xcn1 = Xcn2 = Xcn, αrs1 = αrs2 and αrn1 = αrn2. The screw shaft groove 55 and the nut groove 56 are formed so as to satisfy −0.1 ≦ {Xcs / (Rs−r) −Xcn / (Rn−r)} <0.

以上のように形成されたボールねじ５１の接触角、すなわち、運動方向の変換過程において、ねじ軸溝５５とナット溝５６にそれぞれ転接しているボール５２の接触角を変えることでその転がり摩擦が軽減され、作動効率が向上して耐久性に優れたボールねじ５１を提供することができる。   When the contact angle of the ball screw 51 formed as described above, that is, in the process of changing the direction of movement, the contact angle of the ball 52 that is in rolling contact with the screw shaft groove 55 and the nut groove 56 is changed to thereby reduce the rolling friction. It is possible to provide a ball screw 51 that is reduced, has improved operating efficiency, and has excellent durability.

特開２００３−１７２４２５号公報JP 2003-172425 A

然しながら、この従来のボールねじ５１において、直線運動を回転運動に変換する場合（以下、逆作動という）、また回転運動を直線運動に変換する場合（以下、正作動という）とで、ねじ軸ＳとナットＮの接触角の組み合わせを変更する必要があり、両条件で作動効率を向上させることはできない。一般的に、ねじ軸とナットとでその接触角を変えた場合、正作動または逆作動のどちらか一方の作動効率が向上するが、他方の作動効率が逆に低下する。   However, in this conventional ball screw 51, when converting linear motion into rotational motion (hereinafter referred to as reverse operation) and when converting rotational motion into linear motion (hereinafter referred to as forward operation), the screw shaft S It is necessary to change the combination of the contact angles of the nut N and the operating efficiency cannot be improved under both conditions. Generally, when the contact angle is changed between the screw shaft and the nut, the operation efficiency of either the normal operation or the reverse operation is improved, but the other operation efficiency is decreased.

例えば、電動パワーステアリング用ボールねじの場合、ボールねじにはピニオンからの力とタイヤからの力が作用し、力の大きさや方向は路面状況やハンドル（ステアリングホイール）操作で常に異なっている。それに対し、ハンドルをどちらに切るかは運転手の判断による。すなわち、ねじ軸Ｓに作用する力の方向に対し、ナットＮはどちらの方向にも回転する可能性があり、ボールねじ５１には正作動と逆作動のどちらも作用することになる。したがって、こうした従来のボールねじ５１において、ねじ軸ＳとナットＮとでその接触角を変えることにより、正作動時、逆作動時において総合的な作動効率の向上を図ることは難しい。   For example, in the case of an electric power steering ball screw, a force from a pinion and a force from a tire act on the ball screw, and the magnitude and direction of the force are always different depending on the road surface condition and steering wheel (steering wheel) operation. On the other hand, it is up to the driver to turn the steering wheel. That is, there is a possibility that the nut N rotates in either direction with respect to the direction of the force acting on the screw shaft S, and both the normal operation and the reverse operation act on the ball screw 51. Therefore, in such a conventional ball screw 51, it is difficult to improve the overall operation efficiency during normal operation and reverse operation by changing the contact angle between the screw shaft S and the nut N.

本発明は、このような事情に鑑みてなされたもので、正作動、逆作動共に作動効率を向上させ、かつ機械損失を低減させたボールねじを提供することを目的としている。   The present invention has been made in view of such circumstances, and an object of the present invention is to provide a ball screw in which the operating efficiency is improved in both the forward operation and the reverse operation, and the mechanical loss is reduced.

係る目的を達成すべく、本発明のうち請求項１に記載の発明は、外周面に螺旋状のねじ溝が形成されたねじ軸と、このねじ軸に外嵌され、内周面に螺旋状のねじ溝が形成されたナットと、対向する両ねじ溝により形成される転動路に収容された複数のボールと、前記ナットに装着され、前記転動路を周回経路とする循環部材とを備えたボールねじにおいて、前記ボール径ｄに対する前記ねじ軸のねじ溝の深さｔの比率が、ｔ／ｄ＝０．２０〜０．３０の範囲に設定された構成を採用した。   In order to achieve such an object, the invention according to claim 1 of the present invention includes a screw shaft having a spiral thread groove formed on the outer peripheral surface thereof, and is externally fitted to the screw shaft and spirally formed on the inner peripheral surface. A nut formed with a screw groove, a plurality of balls accommodated in a rolling path formed by opposing screw grooves, and a circulation member mounted on the nut and having the rolling path as a circulation path In the provided ball screw, a configuration was adopted in which the ratio of the thread groove depth t of the screw shaft to the ball diameter d was set in the range of t / d = 0.20-0.30.

このように、ボールねじにおいて、ボール径ｄに対するねじ軸のねじ溝の深さｔの比率が、ｔ／ｄ＝０．２０〜０．３０の範囲に設定されているので、ボールねじ全体の機械損失が低減でき、正作動時、逆作動時に係らず高効率のボールねじを提供することができる。また、それに伴いボールねじの位置決め精度や制御性の向上、さらに摩擦による発熱等の抑制を図ることができ、ボールねじの寿命を向上させることができる。   Thus, in the ball screw, since the ratio of the thread groove depth t of the screw shaft to the ball diameter d is set in the range of t / d = 0.20-0.30, Loss can be reduced, and a high-efficiency ball screw can be provided regardless of whether the operation is normal or reverse. Accordingly, it is possible to improve the positioning accuracy and controllability of the ball screw, and to suppress heat generation due to friction, thereby improving the life of the ball screw.

また、請求項２に記載の発明は、前記循環部材が、前記ねじ軸におけるねじ溝の隣合う１周分同士を連結する連結溝を有する駒部材からなるので、例えば、ボールがねじ軸のねじ山を乗り越えて駒部材に移行する時の摩擦抵抗が低減し、ボールねじとしての機械損失が低減する。   In the invention according to claim 2, since the circulation member is composed of a piece member having a connection groove for connecting adjacent ones of the screw grooves in the screw shaft, for example, the ball is a screw of the screw shaft. The frictional resistance when moving over the mountain to the piece member is reduced, and the mechanical loss as a ball screw is reduced.

また、請求項３に記載の発明は、前記ボールとねじ溝との初期接触角が２５〜４０°に設定されているので、ボールの接触楕円が肩部を乗り上げるのを防止し、負荷容量の低下を防止する。   In the invention according to claim 3, since the initial contact angle between the ball and the thread groove is set to 25 to 40 °, the contact ellipse of the ball is prevented from climbing over the shoulder, and the load capacity is reduced. Prevent decline.

また、請求項４に記載の発明は、前記ボール径ｄと前記ねじ溝のリードＬとの関係が、ｄ＝０．７５〜１．１０Ｌに設定されているので、ボールの接触楕円の肩部乗り上げを防止すると共に、ボールねじの作動効率の向上および摩擦係数の低減を図ることができる。   According to a fourth aspect of the present invention, since the relationship between the ball diameter d and the lead L of the thread groove is set to d = 0.75 to 1.10 L, the shoulder portion of the contact ellipse of the ball It is possible to prevent the ride and improve the ball screw operating efficiency and reduce the friction coefficient.

また、請求項５に記載の発明のように、前記ねじ軸のねじ溝が転造加工によって形成されていても良い。本発明に係るボールねじにおいては、従来のねじ溝よりも浅く設定されているので、ボールねじの生産性が一層向上し、低コスト化が図れる。   Further, as in the invention described in claim 5, the thread groove of the screw shaft may be formed by rolling. Since the ball screw according to the present invention is set shallower than the conventional screw groove, the productivity of the ball screw can be further improved and the cost can be reduced.

好ましくは、請求項６に記載の発明のように、前記ねじ溝の表面に超仕上げ加工が施され、その表面粗さがＲａ０．１以下、または転走方向のうねりが２μｍ以下に規制されていれば、単に良好な表面粗さが得られるだけでなく、ねじ溝のボールとの接触点における真円度、また、そのうねり成分が改善され、ボールねじの作動効率向上と摩擦係数を一層低減させることができる。   Preferably, as in the invention described in claim 6, the surface of the thread groove is subjected to super finishing, and the surface roughness is restricted to Ra 0.1 or less, or the rolling direction undulation is restricted to 2 μm or less. As a result, not only a good surface roughness can be obtained, but also the roundness at the contact point of the thread groove with the ball and the waviness component are improved, and the operation efficiency of the ball screw and the friction coefficient are further reduced. Can be made.

本発明に係るボールねじは、外周面に螺旋状のねじ溝が形成されたねじ軸と、このねじ軸に外嵌され、内周面に螺旋状のねじ溝が形成されたナットと、対向する両ねじ溝により形成される転動路に収容された複数のボールと、前記ナットに装着され、前記転動路を周回経路とする循環部材とを備えたボールねじにおいて、前記ボール径ｄに対する前記ねじ軸のねじ溝の深さｔの比率が、ｔ／ｄ＝０．２０〜０．３０の範囲に設定されているので、ボールねじ全体の機械損失が低減でき、正作動時、逆作動時に係らず高効率のボールねじを提供することができる。また、それに伴いボールねじの位置決め精度や制御性の向上、さらに摩擦による発熱等の抑制を図ることができ、ボールねじの寿命を向上させることができる。   The ball screw according to the present invention is opposed to a screw shaft having a helical thread groove formed on the outer peripheral surface, and a nut externally fitted to the screw shaft and having a helical thread groove formed on the inner peripheral surface. In a ball screw comprising a plurality of balls accommodated in a rolling path formed by both screw grooves, and a circulating member attached to the nut and having the rolling path as a circuit path, the ball diameter d with respect to the ball diameter d Since the ratio of the thread groove depth t in the screw shaft is set in the range of t / d = 0.20-0.30, the overall mechanical loss of the ball screw can be reduced, during normal operation and reverse operation. Regardless, a highly efficient ball screw can be provided. Accordingly, it is possible to improve the positioning accuracy and controllability of the ball screw, and to suppress heat generation due to friction, thereby improving the life of the ball screw.

（ａ）は、本発明に係るボールねじの実施形態を示す平面図である。 （ｂ）は、同上、縦断面図である。 （ｃ）は、同上、駒部材を示す斜視図である。(A) is a top view which shows embodiment of the ball screw which concerns on this invention. (B) is a longitudinal cross-sectional view same as the above. (C) is a perspective view which shows a piece member same as the above. （ａ）は、ねじ溝とボールとの関係を示した説明図である。 （ｂ）は、同上、ねじ溝の深さを小さくした場合を示す説明図である。 （ｃ）は、同上、ボール径を大きくした場合を示す説明図である。(A) is explanatory drawing which showed the relationship between a thread groove and a ball | bowl. (B) is an explanatory view showing a case where the depth of the thread groove is reduced, as in the above. (C) is an explanatory view showing the case where the ball diameter is increased. （ａ）は、初期接触角と肩部乗り上げとの関係を示す説明図である。 （ｂ）は、同上、初期接触角を小さくした場合を示す説明図である。(A) is explanatory drawing which shows the relationship between an initial contact angle and shoulder part riding. (B) is explanatory drawing which shows the case where an initial contact angle is made small similarly. 従来のボールねじを示す横断面図である。It is a cross-sectional view showing a conventional ball screw.

外周面に螺旋状のねじ溝が形成されたねじ軸と、このねじ軸に外嵌され、内周面に螺旋状のねじ溝が形成されたナットと、対向する両ねじ溝により形成される転動路に収容された複数のボールと、前記ナットに装着され、このナットのねじ溝を連結する連結溝を有する駒部材とを備えたボールねじにおいて、前記ボール径ｄに対する前記ねじ軸のねじ溝の深さｔの比率が、ｔ／ｄ＝０．２０〜０．３０の範囲に設定されていると共に、前記ボールとねじ溝との初期接触角が２５〜４０°の範囲に設定されている。   A screw shaft having a spiral thread groove formed on the outer peripheral surface, a nut externally fitted to the screw shaft and having a spiral thread groove formed on the inner peripheral surface, and a roller formed by both opposing screw grooves. A ball screw comprising a plurality of balls accommodated in a moving path and a piece member having a connecting groove that is attached to the nut and connects a screw groove of the nut, wherein the screw groove of the screw shaft with respect to the ball diameter d The ratio of the depth t is set in the range of t / d = 0.20 to 0.30, and the initial contact angle between the ball and the thread groove is set in the range of 25 to 40 °. .

以下、本発明の実施の形態を図面に基いて詳細に説明する。
図１は、本発明に係るボールねじの実施形態を示し、（ａ）は平面図、（ｂ）は縦断面図、そして（ｃ）は循環部材となる駒部材の斜視図である。
ねじ軸１は螺旋状のねじ溝２が外周に形成され、このねじ軸１に外嵌されるナット３の内周には、ねじ溝２に対応する螺旋状のねじ溝４が形成されている。そして、両ねじ溝２、４の間に多数のボール５が収容されている。 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows an embodiment of a ball screw according to the present invention, wherein (a) is a plan view, (b) is a longitudinal sectional view, and (c) is a perspective view of a piece member serving as a circulation member.
The screw shaft 1 has a spiral thread groove 2 formed on the outer periphery, and a spiral thread groove 4 corresponding to the screw groove 2 is formed on the inner periphery of a nut 3 fitted on the screw shaft 1. . A large number of balls 5 are accommodated between the screw grooves 2 and 4.

円筒状のナット３の胴部には、内外の周面に貫通してねじ溝４の一部を切欠く楕円状の駒窓６が穿設され、この駒窓６に楕円状の駒部材７が嵌合されている。駒部材７の内方には、ねじ溝４の隣合う１周分同士を連結する連結溝８が形成され、この連結溝８とねじ溝４の略１周の部分とでボール５の転動路を構成している。転動路内の内外のねじ溝２、４間に介在された多数のボール５はねじ溝２、４に沿って転動し、駒部材７の連結溝８に案内され、ねじ軸１のねじ山を乗り越えて隣接するねじ溝４に戻り、再びねじ溝２、４に沿って転動する。   An elliptical piece window 6 penetrating the inner and outer peripheral surfaces and notching a part of the thread groove 4 is formed in the barrel portion of the cylindrical nut 3, and an elliptical piece member 7 is formed in the piece window 6. Is fitted. A connecting groove 8 is formed on the inner side of the piece member 7 so as to connect adjacent ones of the screw grooves 4, and the ball 5 rolls between the connecting groove 8 and the substantially one part of the screw groove 4. Constitutes the road. A large number of balls 5 interposed between the inner and outer screw grooves 2 and 4 in the rolling path roll along the screw grooves 2 and 4, and are guided by the connecting grooves 8 of the piece members 7. The mountain passes over the mountain and returns to the adjacent screw groove 4 and rolls along the screw grooves 2 and 4 again.

駒部材７の連結溝８は、ナット３の隣接するねじ溝４間を滑らかに接続するように、Ｓ字状に湾曲して形成されているため、その両端開口縁８ａを、ナット３の隣接するねじ溝４の窓開口縁部６ａに合致するようにして、駒部材７の連結溝８がねじ溝４に接続されている。   Since the connecting groove 8 of the piece member 7 is formed to be curved in an S shape so as to smoothly connect the adjacent thread grooves 4 of the nut 3, both end opening edges 8 a are adjacent to the nut 3. The connecting groove 8 of the piece member 7 is connected to the screw groove 4 so as to match the window opening edge portion 6 a of the screw groove 4 to be performed.

ボールねじの効率は一般的に以下の式で表わされるが、リード角βあるいは初期接触角αを大きくすることで作動効率が向上するとされている。正作動時の作動効率（以下、正効率という）をＥｐ、逆作動時の作動効率（以下、逆効率という）をＥｎ、初期接触角をα、正作動時の機械損失をμｐ、逆作動時の機械損失をμｎとした時、
Ｅｐ＝（ｓｉｎα−μｐ×ｔａｎβ）／（ｓｉｎα＋μｐ／ｔａｎβ）
Ｅｎ＝（ｓｉｎα−μｎ／ｔａｎβ）／（ｓｉｎα＋μｎ×ｔａｎβ）
しかし、これら作動効率の式内には機械損失μｐ、μｎが含まれる。実際にはこの機械損失μｐ、μｎは、ねじ溝２、４とボール５同士の摩擦のような単純な摩擦係数だけでなく、例えば、駒式のボールねじにおいては、駒部材７内の無負荷領域でボール５が前のボール５を押す時に生じる力のロスやボール５がねじ溝２を乗り越える時のロスも含めた、所謂ボールねじ全体としての機械損失となる。そこで本出願人は、ボール径ｄに対するねじ溝の深さｔの比率に着目し、これを小さくすることによりボール５がねじ溝２を乗り越える時のロスを低減させることを検証した。 The efficiency of the ball screw is generally expressed by the following equation, and it is said that the operation efficiency is improved by increasing the lead angle β or the initial contact angle α. Ep is the operating efficiency during normal operation (hereinafter referred to as positive efficiency), En is the operating efficiency during reverse operation (hereinafter referred to as reverse efficiency), α is the initial contact angle, μp is mechanical loss during normal operation, and reverse operation When the mechanical loss is μn,
Ep = (sin α−μp × tan β) / (sin α + μp / tan β)
En = (sin α−μn / tan β) / (sin α + μn × tan β)
However, these operational efficiency formulas include mechanical losses μp and μn. Actually, this mechanical loss μp, μn is not only a simple friction coefficient such as the friction between the screw grooves 2, 4 and the ball 5, but, for example, in a piece type ball screw, there is no load in the piece member 7. This is a so-called mechanical loss of the entire ball screw including a loss of force generated when the ball 5 pushes the previous ball 5 in the region and a loss when the ball 5 gets over the screw groove 2. Therefore, the present applicant has focused on the ratio of the thread groove depth t to the ball diameter d, and verified that reducing the loss when the ball 5 gets over the thread groove 2 is reduced.

本発明に係るボールねじにおいては、ボール５が駒部材７内を通過して循環するが、この時ボール５は、図２に示すように、ねじ溝２、２間のランド部２ａを乗り越える。従来のボールねじでは、作動効率や負荷容量等を考慮し、ボール５の直径ｄに対するねじ溝２の深さｔの比率ｔ／ｄが、０．３６〜０．３８になっている。これに対し、本実施形態では、このボール５の直径ｄに対するねじ溝２の深さｔの比率を、ｔ／ｄ＝０．２０〜０．３０の範囲に設定して種々検証を行った。   In the ball screw according to the present invention, the ball 5 passes through the piece member 7 and circulates. At this time, the ball 5 gets over the land portion 2a between the screw grooves 2 and 2, as shown in FIG. In the conventional ball screw, the ratio t / d of the depth t of the thread groove 2 to the diameter d of the ball 5 is 0.36 to 0.38 in consideration of operation efficiency, load capacity, and the like. On the other hand, in this embodiment, various verifications were performed by setting the ratio of the depth t of the thread groove 2 to the diameter d of the ball 5 within a range of t / d = 0.20 to 0.30.

ボール５の直径ｄに対するねじ溝２の深さｔの比率を従来よりも小さく、ｔ／ｄ＝０．２０〜０．３０にするには、ねじ溝２の深さｔを浅くするか、ボール５の直径ｄを大きくする。または、ねじ溝２の深さｔを浅く、かつボール５の直径ｄを大きくすることが考えられる。ここで、ねじ溝２の深さｔを単に小さくすると、ボール５の接触楕円が肩部を乗り上げ、負荷容量が低下する恐れがあるため、ねじ溝２の深さｔとの関係において、ボール５の直径ｄを大きくすることで負荷容量の低下を防止することができる。   In order to make the ratio of the depth t of the thread groove 2 to the diameter d of the ball 5 smaller than that of the prior art, and t / d = 0.20 to 0.30, the depth t of the thread groove 2 is reduced, or the ball The diameter d of 5 is increased. Alternatively, it is conceivable that the depth t of the thread groove 2 is shallow and the diameter d of the ball 5 is increased. Here, if the depth t of the thread groove 2 is simply reduced, the contact ellipse of the ball 5 may ride on the shoulder portion and the load capacity may be reduced. Therefore, in relation to the depth t of the thread groove 2, the ball 5 By increasing the diameter d of the load, it is possible to prevent a decrease in load capacity.

また、ねじ溝２の深さｔとボール径ｄとの関係において、ボール５とねじ溝２との初期接触角αを小さく設定することによりボール５の接触楕円が肩部を乗り上げるのを防止することができる（図３参照）。すなわち、初期接触角αを従来の４５°に変え、α＝２５〜４０°の範囲に設定することにより、ボール５の接触楕円が肩部を乗り上げるのを防止する。   Further, in the relationship between the depth t of the thread groove 2 and the ball diameter d, the contact ellipse of the ball 5 is prevented from climbing over the shoulder by setting the initial contact angle α between the ball 5 and the thread groove 2 to be small. (See FIG. 3). That is, by changing the initial contact angle α to the conventional 45 ° and setting it to a range of α = 25-40 °, the contact ellipse of the ball 5 is prevented from riding on the shoulder.

実際に本出願人は、ボール径ｄに対するねじ溝２の深さｔの比率ｔ／ｄを小さく設定したサンプルと従来品との作動効率を比較検証し、表１、表２の結果を得た。なお、測定は、スラスト荷重５．５ｋＮ、ナットの回転数３６０ｒｐｍで実施し、その結果の代表的なものを示す。また、表１は正効率の測定結果、表２は逆効率の測定結果をそれぞれ示している。   Actually, the applicant of the present invention compared and verified the operation efficiency of a sample in which the ratio t / d of the depth t of the thread groove 2 with respect to the ball diameter d was set to be small, and obtained the results shown in Tables 1 and 2. . The measurement was performed at a thrust load of 5.5 kN and a nut rotation speed of 360 rpm, and representative results are shown. Table 1 shows the measurement result of the positive efficiency, and Table 2 shows the measurement result of the reverse efficiency.

Figure 2011137555
Figure 2011137555

Figure 2011137555
Figure 2011137555

作動効率の一般式より、従来は初期接触角αおよびリード角βを変更することにより効率向上を図っていたが、例えば、初期接触角αを４５°から本実施形態のように２５〜４０°の範囲に変更すると作動効率は逆に低下してしまう。本実施形態は、リード角βを変更せずに、初期接触角αおよびボール径ｄに対するねじ溝２の深さｔの比率ｔ／ｄを小さくすることにより、作動効率向上だけでなく摩擦係数、すなわちボールねじの機械損失が低減することが判った。   Conventionally, the efficiency is improved by changing the initial contact angle α and the lead angle β from the general formula of the operating efficiency. For example, the initial contact angle α is changed from 45 ° to 25 to 40 ° as in the present embodiment. If it is changed to the range, the operating efficiency is reduced. In the present embodiment, the ratio t / d of the depth t of the thread groove 2 with respect to the initial contact angle α and the ball diameter d is reduced without changing the lead angle β. That is, it was found that the mechanical loss of the ball screw is reduced.

また、本実施形態では、ボール５の直径ｄとねじ溝２のリードＬとの関係が、ｄ＝０．７５〜１．１０Ｌになるように設定されている。ｄ＜０．７５Ｌの場合、作動効率の向上および摩擦係数の顕著な低減が認められず、一方、ｄ＞１．１０Ｌの場合、ボール５の接触楕円の肩部乗り上げの危険性が増大するので好ましくない。   In the present embodiment, the relationship between the diameter d of the ball 5 and the lead L of the screw groove 2 is set so that d = 0.75 to 1.10L. When d <0.75L, no improvement in operating efficiency and no significant reduction in the friction coefficient is observed, whereas when d> 1.10L, the risk of riding on the shoulder of the contact ellipse of the ball 5 increases. It is not preferable.

また、本実施形態では、ねじ軸１の外周に転造加工によってねじ溝２が形成されているが、従来のボールねじに比べねじ溝２の深さｔがボール径ｄに対して小さく設定されているので、一層生産性が向上し、低コスト化が達成でできる。さらにこのねじ溝２の表面に超仕上げ加工を施すことにより、ボールねじの摩擦係数が低減できることが判った。これは、従来の転造品の表面粗さＲａ１．５〜２．０μｍに比べ、超仕上げ加工によりその表面粗さがＲａ１．０μｍ以下の良好な表面粗さが単に得られるだけでなく、ねじ溝２のボール５との接触点における真円度、また、そのうねり成分も改善されたためと考えられる。なお、ねじ溝２は、ゴシックアーチ形状であってもボール５とサーキュラコンタクトする円弧状の形状であっても良い。   In this embodiment, the thread groove 2 is formed on the outer periphery of the screw shaft 1 by rolling. However, the depth t of the thread groove 2 is set smaller than the ball diameter d as compared with the conventional ball screw. Therefore, productivity can be further improved and cost reduction can be achieved. Furthermore, it has been found that the friction coefficient of the ball screw can be reduced by superfinishing the surface of the thread groove 2. This is because not only the surface roughness Ra of 1.5 to 2.0 μm of the conventional rolled product is obtained, but the surface roughness Ra of 1.0 μm or less is simply obtained by superfinishing. This is probably because the roundness at the contact point of the groove 2 with the ball 5 and the swell component thereof were improved. The thread groove 2 may be a Gothic arch shape or an arc shape that makes a circular contact with the ball 5.

このように、本発明に係るボールねじは、従来よりもボール径ｄに対するねじ溝２の深さｔの比率ｔ／ｄを小さく設定することにより、ボールねじ全体の機械損失が低減でき、正効率、逆効率に係らず高効率のボールねじを提供することができる。また、それに伴いボールねじの位置決め精度や制御性の向上、さらに摩擦による発熱等の抑制を図ることができ、ボールねじの寿命を向上させることができる。   Thus, in the ball screw according to the present invention, the mechanical loss of the entire ball screw can be reduced by setting the ratio t / d of the depth t of the thread groove 2 to the ball diameter d to be smaller than the conventional one, and the positive efficiency. Thus, a highly efficient ball screw can be provided regardless of the reverse efficiency. Accordingly, it is possible to improve the positioning accuracy and controllability of the ball screw, and to suppress heat generation due to friction, thereby improving the life of the ball screw.

以上、本発明の実施の形態について説明を行ったが、本発明はこうした実施の形態に何等限定されるものではなく、あくまで例示であって、本発明の要旨を逸脱しない範囲内において、さらに種々なる形態で実施し得ることは勿論のことであり、本発明の範囲は、特許請求の範囲の記載によって示され、さらに特許請求の範囲に記載の均等の意味、および範囲内のすべての変更を含む。   The embodiment of the present invention has been described above, but the present invention is not limited to such an embodiment, and is merely an example, and various modifications can be made without departing from the scope of the present invention. Of course, the scope of the present invention is indicated by the description of the scope of claims, and further, the equivalent meanings described in the scope of claims and all modifications within the scope of the scope of the present invention are included. Including.

本発明に係るボールねじは、自動車の電動パワーステアリング等、使用中に正作動と逆作動ともに発生する用途に用いられるボールねじに適用できる。また、循環部材は駒部材に限らず、リターンチューブやエンドプレート等、あらゆるボール循環方式のボールねじに適用することができる。   The ball screw according to the present invention can be applied to a ball screw used for an application in which both normal operation and reverse operation occur during use, such as an electric power steering of an automobile. Further, the circulation member is not limited to the piece member, and can be applied to any ball circulation type ball screw such as a return tube or an end plate.

１・・・・・・・・・・ねじ軸
２、４・・・・・・・・ねじ溝
２ａ・・・・・・・・・ランド部
３・・・・・・・・・・ナット
５・・・・・・・・・・ボール
６・・・・・・・・・・駒窓
６ａ・・・・・・・・・窓開口縁部
７・・・・・・・・・・駒部材
８・・・・・・・・・・連結溝
８ａ・・・・・・・・・開口縁部
５１・・・・・・・・・ボールねじ
５２・・・・・・・・・ボール
５２ｓａ、５２ｓｂ・・ねじ軸溝とボールとの接点
５２ｎａ、５２ｎｂ・・ナット溝とボールとの接点
５３・・・・・・・・・ねじ軸の外周面
５４・・・・・・・・・ナットの内周面
５５・・・・・・・・・ねじ軸溝
５６・・・・・・・・・ナット溝
５５ａ、５５ｂ・・・・ねじ軸溝のゴシックアークを形成する円弧
５６ａ、５６ｂ・・・・ナット溝のゴシックアークを形成する円弧
Ａ・・・・・・・・・・ボールの中心
Ｂ・・・・・・・・・・ボール中心Ａを通るねじ軸に垂直な線
Ｌ・・・・・・・・・・リード
Ｎ・・・・・・・・・・ナット
Ｓ・・・・・・・・・・ねじ軸
ｄ・・・・・・・・・・ボールの直径
ｒ・・・・・・・・・・ボールの半径
ｔ・・・・・・・・・・ねじ溝の深さ
Ｅｐ・・・・・・・・・正効率
Ｅｎ・・・・・・・・・逆効率
Ｒｓ１・・・・・・・・円弧５５ａの曲率半径
Ｒｓ２・・・・・・・・円弧５５ｂの曲率半径
Ｒｎ１・・・・・・・・円弧５６ａの曲率半径
Ｒｎ２・・・・・・・・円弧５６ｂの曲率半径
Ｃｓ１・・・・・・・・曲率半径Ｒｓ１の中心
Ｃｓ２・・・・・・・・曲率半径Ｒｓ２の中心
Ｃｎ１・・・・・・・・曲率半径Ｒｎ１の中心
Ｃｎ２・・・・・・・・曲率半径Ｒｎ２の中心
Ｘｃｓ１・・・・・・・Ｃｓ１とＢ間の距離
Ｘｃｓ２・・・・・・・Ｃｓ２とＢ間の距離
Ｘｃｎ１・・・・・・・Ｃｎ１とＢ間の距離
Ｘｃｎ２・・・・・・・Ｃｎ２とＢ間の距離
αｒｓ１・・・・・・・ねじ軸溝とボール接点５２ｓａとの接触角
αｒｓ２・・・・・・・ねじ軸溝とボール接点５２ｓｂとの接触角
αｒｎ１・・・・・・・ナット溝とボール接点５２ｎａとの接触角
αｒｎ２・・・・・・・ナット溝とボール接点５２ｎｂとの接触角
α・・・・・・・・・・初期接触角
β・・・・・・・・・・リード角
μｐ・・・・・・・・・正作動時の機械損失
μｎ・・・・・・・・・逆作動時の機械損失 1 ... Screw shaft 2, 4 ... Screw groove 2a ... Land 3 ... Nut 5 ... Ball 6 ... Frame window 6a ... Window opening edge 7 ... Piece member 8 ... Connection groove 8a ... Opening edge 51 ... Ball screw 52 ... Balls 52sa, 52sb .... Contact 52na, 52nb between screw shaft groove and ball .... Contact 53 between nut groove and ball .... Outer peripheral surface 54 of screw shaft ... Nut inner peripheral surface 55... Screw shaft groove 56... Nut groove 55 a, 55 b... Arc 56 a that forms a gothic arc of the screw shaft groove, 56b ··· nut groove Arc A that forms a quark ... Ball center B ... Line L perpendicular to the screw axis passing through ball center A ... ····················································· Ball diameter r・ ・ ・ Ball radius t ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Thread groove depth Ep ・ ・ ・ ・ ・ ・ ・ ・ Effective efficiency En ・ ・ ・ ・ ・ ・ ・ ・ Reverse efficiency Rs1 ・ ・ ・... curvature radius Rs2 of arc 55a ... curvature radius Rn1 of arc 55b ... curvature radius Rn2 of arc 56a ... Curvature radius Cs1... Center Cs2 of curvature radius Rs1... Center Cn1 of curvature radius Rs2... Center Cn2 of curvature radius Rn1. ··· Center Xcs1 of radius of curvature Rn2 ········· Distance Xcs2 between Cs1 and B ·········· Distance Xcn1 between Cs2 and B ········· Distance Xcn2 between Cn1 and B ········ Distance αrs1 between Cn2 and B ········· Contact angle αrs2 between screw shaft groove and ball contact 52sa ······· Contact between screw shaft groove and ball contact 52sb Angle αrn1 ········· Contact angle between nut groove and ball contact 52na αrn2 ····· Contact angle between nut groove and ball contact 52nb α ··· Initial contact Angle β ······ Lead angle µp · · · · · Mechanical loss during normal operation µn · · · · · · Mechanical loss during reverse operation

Claims (6)

外周面に螺旋状のねじ溝が形成されたねじ軸と、このねじ軸に外嵌され、内周面に螺旋状のねじ溝が形成されたナットと、対向する両ねじ溝により形成される転動路に収容された複数のボールと、前記ナットに装着され、前記転動路を周回経路とする循環部材とを備えたボールねじにおいて、
前記ボール径ｄに対する前記ねじ軸のねじ溝の深さｔの比率が、ｔ／ｄ＝０．２０〜０．３０の範囲に設定されていることを特徴とするボールねじ。 A screw shaft having a spiral thread groove formed on the outer peripheral surface, a nut externally fitted to the screw shaft and having a spiral thread groove formed on the inner peripheral surface, and a roller formed by both opposing screw grooves. In a ball screw provided with a plurality of balls accommodated in a movement path, and a circulation member attached to the nut and having the rolling path as a circulation path,
The ratio of the depth t of the thread groove of the said screw shaft with respect to the said ball diameter d is set to the range of t / d = 0.20-0.30, The ball screw characterized by the above-mentioned. 前記循環部材が、前記ねじ軸におけるねじ溝の隣合う１周分同士を連結する連結溝を有する駒部材からなる請求項１に記載のボールねじ。   2. The ball screw according to claim 1, wherein the circulation member is a piece member having a connection groove for connecting adjacent ones of the screw grooves on the screw shaft. 前記ボールとねじ溝との初期接触角が２５〜４０°に設定されている請求項１または２に記載のボールねじ。   The ball screw according to claim 1 or 2, wherein an initial contact angle between the ball and the screw groove is set to 25 to 40 °. 前記ボール径ｄと前記ねじ溝のリードＬとの関係が、ｄ＝０．７５〜１．１０Ｌに設定されている請求項１乃至３いずれかに記載のボールねじ。   The ball screw according to any one of claims 1 to 3, wherein a relationship between the ball diameter d and the lead L of the screw groove is set to d = 0.75 to 1.10L. 前記ねじ軸のねじ溝が転造加工によって形成されている請求項１乃至４いずれかに記載のボールねじ。   The ball screw according to claim 1, wherein a thread groove of the screw shaft is formed by rolling. 前記ねじ溝の表面に超仕上げ処理が施され、その表面粗さがＲａ０．１以下、または転走方向のうねりが２μｍ以下に規制されている請求項１乃至５いずれかに記載のボールねじ。   The ball screw according to any one of claims 1 to 5, wherein the surface of the thread groove is subjected to a superfinishing process, and the surface roughness is restricted to Ra 0.1 or less, or the rolling direction undulation is controlled to 2 µm or less.
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2016120606A (en) * 2014-12-24 2016-07-07 三菱重工プラスチックテクノロジー株式会社 Mold clamping device
JP2017064876A (en) * 2015-10-02 2017-04-06 日立オートモティブシステムズ株式会社 Manufacturing method for ball screw shaft

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JPS5252071A (en) * 1975-10-07 1977-04-26 Buiruke Rihiaruto Spindleenut apparatus
JP2001248708A (en) * 2000-03-03 2001-09-14 Nsk Ltd Rolling device
JP2003137112A (en) * 2001-11-02 2003-05-14 Ntn Corp Wheel steering gear
JP2003301917A (en) * 2002-04-10 2003-10-24 Toyoda Mach Works Ltd Ball screw
JP2004036831A (en) * 2002-07-05 2004-02-05 Nsk Ltd Ball screw device

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Publication number Priority date Publication date Assignee Title
JPS5252071A (en) * 1975-10-07 1977-04-26 Buiruke Rihiaruto Spindleenut apparatus
JP2001248708A (en) * 2000-03-03 2001-09-14 Nsk Ltd Rolling device
JP2003137112A (en) * 2001-11-02 2003-05-14 Ntn Corp Wheel steering gear
JP2003301917A (en) * 2002-04-10 2003-10-24 Toyoda Mach Works Ltd Ball screw
JP2004036831A (en) * 2002-07-05 2004-02-05 Nsk Ltd Ball screw device

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2016120606A (en) * 2014-12-24 2016-07-07 三菱重工プラスチックテクノロジー株式会社 Mold clamping device
JP2017064876A (en) * 2015-10-02 2017-04-06 日立オートモティブシステムズ株式会社 Manufacturing method for ball screw shaft

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