M428920 五、新型說明： 【新型所屬之技術領域】 本新型是關於曲柄組裝體，尤其是關於僅由四支鏈輪 安裝臂部所構成的自行車用曲柄組裝體。 【先前技術】 在已知的自行車的曲柄組裝體，具有四支鏈輪安裝臂 φ 部（例如，日本實開昭5 7-3 98 93號公報）。習知的曲柄組 裝體，是維持曲柄組裝體的強度來達到輕量化的技術。具 體來說，在安裝有踏板的棒狀的曲柄主體越過死點而在扭 矩變大的區域，以位於死點的方式，將相同形狀的各兩支 鏈輪安裝臂部設置成夾著曲柄主體。藉此，即使鏈輪安裝 臂部爲四支，也能有效地提升曲柄組裝體的剛性。 【新型內容】 φ 〔新型欲解決的課題〕 • 在具有四支鏈輪安裝臂的曲柄組裝體，作用於：配置 ' 成夾著曲柄主體的各兩支鏈輪安裝臂的力量，並不相同。 也就是說，在驅動自行車時的自行車用曲柄組裝體的旋轉 方向，作用於旋轉方向上游側的鏈輪安裝臂的力量小於： 作用於旋轉方向下游側的鏈輪安裝臂的力量。可是’在習 知的曲柄組裝體，四支鏈輪安裝臂的形狀相同，所以變得 要配合藉由踩踏動作而較大負荷作用的臂部，來設計曲柄 臂的剛性，而很難有效率地達到曲柄組裝體的輕量化。 -3- M428920 本新型的課題，在具有四支鏈輪安裝臂的曲柄組裝H ’要具備有所需要的剛性，且有效地達成曲柄組裝體的輕 量化。 〔用以解決課題的手段〕 本新型的自行車用曲柄組裝體，是僅由四支鏈輪安裝 臂部所構成的自行車用曲柄組裝體。自行車用曲柄組裝體 ’具備有：曲柄主體、第一鏈輪的安裝臂部、第二鏈輪的 安裝臂部、第三鏈輪的安裝臂部、以及第四鏈輪的安裝臂 部。曲柄主體’具有：在其中一端形成有曲柄軸安裝孔的 曲柄軸安裝部、以及在另一端具有踏板軸安裝孔的踏板軸 安裝部。第一鏈輪安裝臂部，從曲柄軸安裝部延伸，且具 有第一鏈輪安裝孔。第二鏈輪安裝臂部，從曲柄軸安裝部 延伸’且具有第二鏈輪安裝孔。第三鏈輪安裝臂部，從曲 柄軸安裝部延伸’且具有第三鏈輪安裝孔。第四鏈輪安裝 臂部’從曲柄軸安裝部延伸，且具有第四鏈輪安裝孔。 第一鏈輪安裝臂部、第二鏈輪安裝臂部、第三鏈輪安 裝臂部、及第四鏈輪安裝臂部，沿著當驅動自行車時的自 行車用曲柄組裝體的旋轉方向，從曲柄主體起，配置成： 第一鏈輪安裝臂部、第二鏈輪安裝臂部、第三鏈輪安裝臂 部、及第四鏈輪安裝臂部的順序。 本新型的自行車用曲柄組裝體，具有：第一假想線與 第一假想線所構成的第一中心角；上述第二假想線與第三 假想線所構成的第二中心角：上述第三假想線與第四假想 • 4 · M428920 線所構成的第三中心角；以及上述第四假想線與 假想線所構成的第四中心角； 上述第一假想線是將曲柄軸安裝孔的中心與 安裝孔的中心連結而成；上述第二假想線是將上 安裝孔的中心與第二鏈輪安裝孔的中心連結而成 三假想線是將上述曲柄軸安裝孔的中心與第三鏈 的中心連結而成；上述第四假想線是將曲柄軸安 φ 心與第四鏈輪安裝孔的中心連結而成； 第一及第三中心角爲較第二及第四中心角更 ’第二鏈輪安裝臂部與第四鏈輪安裝臂部的剛性 第一鏈輪安裝臂部與第三鏈輪安裝臂部的剛性。 在該曲柄組裝體，第一中心角及第三中心角 一中心角及第四中心角。因此，在藉由踩踏動作 負荷的部位’鏈輪安裝臂之間的間隔變窄，而能 升曲柄組裝體的剛性。 ^ 第二鏈輪安裝臂部與第四鏈輪安裝臂部的剛 •第一鏈輪安裝臂部與第三鏈輪安裝臂部的剛性 所需要的剛性更小的第一鏈輪安裝臂部與第三鏈 部，可成爲更特別輕量化的構造。 〔新型效果〕 藉由本新型’第一中心角及第三中心角小於 角及第四中心角，第二鏈輪安裝臂部與第四鏈輪 的剛性，高於：第一鏈輪安裝臂部與第三鏈輪安 上述第一 第一鏈輪 述曲柄軸 ;上述第 輪安裝孔 裝孔的中 小的關係 ，高於： ，小於第 施加較大 有效地提 性，高於 。藉此， 輪安裝臂 第二中心 安裝臂部 裝臂部的 -5- M428920 剛性，所以具備有所需要的剛性，且能有效地達成曲柄組 裝體的輕量化。 【實施方式】 <第一實施方式> 於第1圖、第2圖、第3圖、及第4圖，本新型的一種實 施方式的自行車用曲柄組裝體10具備：曲柄主體12、從曲 柄主體12的其中一端以放射狀延伸的鏈輪安裝部14。在第 1圖〜第3圖，顯示安裝了第一鏈輪30及第二鏈輪32的狀態 〇 曲柄主體12及鏈輪安裝部14是一體成形。在本實施例 ，曲柄主體12及鏈輪安裝部14分割成第一曲柄部16和第二 曲柄部18。 第一曲柄部16及第二曲柄部18是例如鋁合金等的金屬 製的。第一曲柄部16是主要負責曲柄主體12及鏈輪安裝部 14的強度的部分。第二曲柄部18，是以覆蓋第一曲柄部16 的方式被固定於第一曲柄部16。第二曲柄部18負責曲柄主 體〗2及鏈輪安裝部14剩下的剛性以及襞飾。因此，較佳是 將第一曲柄部16形成爲厚度較第二曲柄部18更厚。 曲柄主體12是如第4圖及第5圖所示，是從曲柄軸20朝 直徑方向延伸的中空棒狀的部分。曲柄主體I2的第一曲柄 部16，具有：具有在其中一端形成的曲柄軸安裝孔12a的 曲柄軸安裝部12b、以及具有在另一端形成的踏板軸安裝 孔12c的踏板軸安裝部1 2d。 -6 - M428920 曲柄軸安裝部12b具有筒狀的第一轂部16a。曲柄軸安 裝孔12a，形成於第一轂部16a的內周面。在曲柄軸安裝孔 12a的內周面’形成有：在周方向隔著間隔形成有多數凹 部的鋸齒部12f。踏板安裝部12d，具有厚度較厚的第二轂 部16b。在第二轂部16b形成有踏板軸安裝孔12c。 在曲柄軸安裝孔12a，可固定曲柄軸20。在該實施方 式，是將中空的曲柄軸20壓入固定於曲柄軸安裝孔12a。 φ 曲柄軸20，隔介著軸亲而可自由旋轉地被支承於沒有圖示 的自行車的底托架β曲柄軸20的曲柄主體12的固定部分， 是較其他部分更大直徑，在大直徑部分的外周面，形成有 :與曲柄軸安裝孔12a的鋸齒部12f卡合的鋸齒部20a。曲 柄軸20，如第4圖所示，藉由從曲柄主體12的第一曲柄部 16的外側面，貫穿曲柄軸安裝孔12a，將鋸齒部20a壓入到 曲柄軸安裝孔12a，而將曲柄軸20固定於曲柄主體12。 曲柄軸20的鋸齒部20a形成側的端面，如第6圖所示， φ 藉由蓋構件19所封閉。蓋構件19，是例如合成樹脂製或金 • 屬製的構件。蓋構件19，具有：大直徑的頭部19a、以及 與曲柄軸20的內周面嵌合的筒部19b。頭部19a的外側面 19c，接觸於：曲柄主體12的第二曲柄部18的後述的第二 底部1 8a的內側面18c。在該接觸部分塗佈黏接劑，來固定 第二曲柄部18。而藉由以曲柄軸20的配置部分接觸於第二 曲柄部18的第二底部18a，而補強讓第二曲柄部18不容易 凹陷。 在踏板軸安裝孔12c ’如第4圖及第5圖所示’形成有 M428920 :與沒有圖示的踏板的踏板軸螺合的母螺紋部12e。 在曲柄主體12’第一曲柄部16’具有：朝曲柄軸20的 軸方向延伸，較第二轂部16b更薄的第一底部16c、以及形 成於第一底部16c的外緣部的第一壁部16d。第一壁部I6d ，是與第一底部16 c爲相同厚度或較第一底部16c更薄。 在曲柄主體12，第二曲柄部18’具有：與第一曲柄部 16的第一底部16c相對向配置的第二底部18a、以及在第二 底部18a的外緣部形成的第二壁部18b。藉此，則在第一曲 柄部1 6與第二曲柄部1 8之間形成空間。在第二曲柄部1 8的 與踏板軸安裝孔12c相對向的部分，形成有可讓踏板軸貫 穿的貫穿孔18d。第二曲柄部18的與曲柄軸安裝孔12a相對 向的部分，則將曲柄軸安裝孔12a覆蓋而從外部不會看到 曲柄軸安裝孔1 2a »第二壁部1 8b形成爲可緊貼於第一壁部 1 6d的外側面。第二壁部1 8b，是例如藉由黏接劑而黏接於 第一壁部16h 鏈輪安裝部14具有：自曲柄軸安裝部12b延伸的第一 〜第四鏈輪安裝臂部21〜24。第一鏈輪安裝臂部21具有第 一鏈輪安裝孔21a。第二鏈輪安裝臂部22具有第二鏈輪安 裝孔22a。第三鏈輪安裝臂部23具有第三鏈輪安裝孔23ae 第四鏈輪安裝臂部24具有第四鏈輪安裝孔24a。第——^第 四鏈輪安裝孔21a〜24a被形成於第--第四鏈輪安裝臂部 21〜24的目ij端部附近，第--第四鏈輪安裝孔21a〜24a的 周圍的兩面被機械加工爲厚度較其他部分更薄。將第一鏈 輪30固定於此第--第四外側面21b〜24b，藉由未圖示的 M428920 固定螺栓，與第一鏈輪30同時地將第二鏈輪32固定於相反 側的內側面》 第一鏈輪安裝臂部21、第二鏈輪安裝臂部22、第三鏈 輪安裝臂部23、及第四鏈輪安裝臂部24，是沿著驅動自行 車時的自行車用曲柄組裝體10的旋轉方向（在第1圖由箭 頭A所表示的順時鐘旋轉方向），自曲柄主體12起，依第 • 一鏈輪安裝臂部21、第二鏈輪安裝臂部22、第三鏈輪安裝 φ 臂部23、第四鏈輪安裝臂部24的順序加以配置。在第二曲 柄部18上也設有第一〜第四鏈輪安裝臂部21’、22，、23，、 24’。第二曲柄部18的第--第四鏈輪安裝臂部21’〜24’設 爲：將除了第一〜第四鏈輪安裝孔21a〜24a的周圍之外的 部分加以覆蓋。因此，於本實施例，由第一曲柄部16的第 —〜第四鏈輪安裝臂部21、22、23、24和第二曲柄部18的 第--第四鏈輪安裝臂部21’、22，、23，、24’來構成曲柄 組裝體10的4支鏈輪安裝臂部。 # 如第5圖所示’本新型的自行車用曲柄組裝體1 〇，具 有：第一中心角α 1、第二中心角α 2、第三中心角α 3、 第四中心角α: 4。第一中心角α丨，是以第一假想線L丨與第 二假想線L2構成的角度；第一假想線L1，是將曲柄軸安裝 孔12a的中心C與第一鏈輪安裝孔2la的中心C1連結而成； 第二假想線L2 ’是將曲柄軸安裝孔的中心c與第二鏈輪 安裝孔22a的中心C2連結而成。第二中心角α2，是以上述 桌一假想線L2與弟二假想線L3構成的角度；第二假想線L3 ’是將曲柄軸安裝孔12a的中心C與第三鏈輪安裝孔233的 M428920 中心C3連結而成。第三中心角α 3，是以上述第三假想線 L3與第四假想線L4構成的角度；第四假想線L4，是將曲柄 軸安裝孔l2a的中心C與第四鏈輪安裝孔24a的中心C4連結 而成。第四中心角Q：4，是以上述第四假想線L4與上述第 —假想線L1構成的角度。並且，第—中心角αι、第二中 心角α 2、第三中心角α 3、第四中心角α 4，其第—中心 角αΐ及第三中心角α3’形成爲小於：第二中心角“2及 第四中心角α 4。 在該實施方式，第一中心角αΐ與第三中心角α3相等 。第二中心角α 2與第四中心角α 4相等。第一中心角α 1 及第三中心角α3’較佳爲60度〜80度的範圍，在該實施 方式爲度。 第二鏈輪安裝臂部22以及第四鏈輪安裝臂部24的剛性 ’是高於：第~鏈輪安裝臂部21及第三鏈輪安裝臂部23的 剛性。具體來說，在該實施方式，第二鏈輪安裝臂部22及 第四鏈輪安裝臂部24的與第二假想線L2及第四假想線“正 交的方向的寬度W2’是大於：上述第一鏈輪安裝臂部21 及第三鏈輪安裝臂部23的與第一假想線L1及第三假想線L3 正交的方向的寬度W1。藉此，則第二鏈輪安裝臂部22及 第四鏈輪安裝臂部24的彎曲剛性較第一鏈輪安裝臂部21及 第三鏈輪安裝臂部23更高。關於第二曲柄部18的第--第 四鏈輪安裝臂部21’、22’、23’、24，，作成與第一曲柄部 16的第一〜第四鏈輪安裝臂部21、22、23、24相同較佳。 在第一〜第四鏈輪安裝臂部21〜24的外緣部，在第— -10 - M428920 曲柄部16，形成有第一底部16c與第一壁部16d。第一壁部 16d，也形成在第--第四外側面21b〜24b的交界部分。 於是，第一〜第四鏈輪安裝臂部21〜24，除了第一〜第四 外側面2 lb〜24b之外，被第一壁部1 6d包圍。 在本實施方式，在曲柄主體12與第一鏈輪安裝臂部21 之間、第二鏈輪安裝臂部22與第三鏈輪安裝臂部23之間、 以及第四鏈輪安裝臂部24與曲柄主體12之間，形成有補強 φ 用的肋部25。肋部25，放射狀地從第一轂部16a朝向第一 壁部16d形成。 在第一〜第四鏈輪安裝臂部21〜24，將第二曲柄部18 的第二壁部18b，配置成緊貼於第一壁部I6d的外側面。而 沒有配置在：於與第--第四外側面21b〜24b的交界部分 形成的第一壁部16d。 在以該方式構成的自行車用曲柄組裝體10，在踩踏動 作中施加較大負荷的，第一鏈輪安裝臂部21與第二鏈輪安 • 裝臂部22之間、以及第三鏈輪安裝臂部23與第四鏈輪安裝 臂部24之間，鏈輪安裝臂部之間的間隔變窄，能有效地提 升曲柄組裝體的剛性。而第二鏈輪安裝臂部與第四鏈輪安 裝臂部的剛性，是高於：第一鏈輪安裝臂部與第三鏈輪安 裝臂部的剛性。藉此，所需要的剛性更小的第一鏈輪安裝 臂部與第三鏈輪安裝臂部，則可成爲更特別輕量化的構造 〇 如第7圖所示，當曲柄主體1 2配置在：作用於曲柄組 裝體10的扭矩變大的預定的角度區域（例如，曲柄主體12 -11 - M428920 在，從朝曲柄驅動旋轉方向旋轉到距離上死點UD約70度 的位置F起，直到從上死點UD旋轉大約90度的位置G爲止 之角度点爲大約20度的區域）時，具體來說，當將曲柄主 體12的曲柄軸安裝孔12a的中心C、與踏板軸安裝孔12c的 中心C5連結的假想曲柄主體中心線L5，配置在預定的角度 區域時，第三中心角α3藉由鏈條CN朝向負荷作用的上死 點UD。在該狀態，雖然較大的負荷作用於第一鏈輪30或 第二鏈輪32，而由於以較窄間隔配置的第三鏈輪安裝臂部 23與第四鏈輪安裝臂部24位於上死點UD附近，所以第一 鏈輪30及第二鏈輪32能具備有抵抗負荷的必須的充分剛性M428920 V. New description: [Technical field to which the new type belongs] The present invention relates to a crank assembly, and more particularly to a bicycle crank assembly comprising only four sprocket mounting arms. [Prior Art] In the known crank assembly of a bicycle, there are four sprocket mounting arms φ (for example, Japanese Laid-Open Patent Publication No. SHO-5-7-98 93). The conventional crank assembly is a technique for maintaining the strength of the crank assembly to achieve weight reduction. Specifically, in a region where the rod-shaped crank main body to which the pedal is attached passes over the dead point and the torque is increased, the two sprocket mounting arms of the same shape are placed to sandwich the crank main body so as to be located at a dead point. . Thereby, even if the sprocket mounting arm portion is four, the rigidity of the crank assembly can be effectively increased. [New content] φ [New problem to be solved] • The crank assembly with four sprocket mounting arms acts as: "The force of the two sprocket mounting arms that sandwich the crank body is not the same. . In other words, in the rotation direction of the bicycle crank assembly when the bicycle is driven, the force of the sprocket attachment arm acting on the upstream side in the rotation direction is smaller than the force of the sprocket attachment arm acting on the downstream side in the rotation direction. However, in the conventional crank assembly, the shape of the four sprocket mounting arms is the same, so that the rigidity of the crank arm is designed to match the arm portion that is subjected to a large load by the pedaling operation, and it is difficult to be efficient. The weight of the crank assembly is achieved. -3- M428920 The problem of the present invention is to provide the required rigidity in the crank assembly H' having four sprocket mounting arms, and to effectively reduce the weight of the crank assembly. [Means for Solving the Problem] The bicycle crank assembly of the present invention is a bicycle crank assembly including only four sprocket attachment arm portions. The bicycle crank assembly ‘ includes a crank main body, a mounting arm portion of the first sprocket, an attachment arm portion of the second sprocket, a mounting arm portion of the third sprocket, and a mounting arm portion of the fourth sprocket. The crank main body ' has a crank shaft mounting portion in which a crank shaft mounting hole is formed at one end thereof, and a pedal shaft mounting portion having a pedal shaft mounting hole at the other end. The first sprocket mounting arm extends from the crankshaft mounting portion and has a first sprocket mounting hole. The second sprocket mounting arm portion extends from the crank shaft mounting portion and has a second sprocket mounting hole. The third sprocket mounting arm portion extends from the crank shaft mounting portion and has a third sprocket mounting hole. The fourth sprocket mounting arm portion ' extends from the crank shaft mounting portion and has a fourth sprocket mounting hole. a first sprocket mounting arm portion, a second sprocket mounting arm portion, a third sprocket mounting arm portion, and a fourth sprocket mounting arm portion along a rotation direction of the bicycle crank assembly when the bicycle is driven The crank main body is arranged in the order of the first sprocket mounting arm portion, the second sprocket mounting arm portion, the third sprocket mounting arm portion, and the fourth sprocket mounting arm portion. The bicycle crank assembly of the present invention has a first central angle formed by a first imaginary line and a first imaginary line, and a second central angle formed by the second imaginary line and the third imaginary line: the third imaginary The fourth central angle formed by the line and the fourth hypothesis • 4 · M428920 line; and the fourth central angle formed by the fourth imaginary line and the imaginary line; the first imaginary line is the center and installation of the crank shaft mounting hole The center of the hole is connected; the second imaginary line connects the center of the upper mounting hole and the center of the second sprocket mounting hole. The three imaginary lines connect the center of the crank shaft mounting hole to the center of the third chain. The fourth imaginary line is formed by connecting the center of the crankshaft and the center of the fourth sprocket mounting hole; the first and third central angles are more than the second and fourth central angles. The rigidity of the rigid first sprocket mounting arm portion and the third sprocket mounting arm portion of the mounting arm portion and the fourth sprocket mounting arm portion. In the crank assembly, the first central angle and the third central angle have a central angle and a fourth central angle. Therefore, the interval between the sprocket mounting arms by the stepping action load is narrowed, and the rigidity of the crank assembly can be raised. ^ The first sprocket mounting arm portion of the second sprocket mounting arm portion and the first sprocket mounting arm portion of the fourth sprocket mounting arm portion and the rigidity required for the rigidity of the third sprocket mounting arm portion is smaller The third chain portion can be a more particularly lightweight structure. [New effect] With the first central angle and the third central angle being smaller than the angle and the fourth central angle, the rigidity of the second sprocket mounting arm portion and the fourth sprocket is higher than: the first sprocket mounting arm portion And the third sprocket is mounted on the first first sprocket wheel; the small relationship between the first wheel mounting hole and the first wheel mounting hole is higher than: less than the first effective larger extraction, higher than the first sprocket. As a result, the -5-M428920 of the arm mounting arm of the second center mounting arm portion is rigid, so that it has the required rigidity and can effectively reduce the weight of the crank assembly. [Embodiment] <First Embodiment> In the first, second, third, and fourth drawings, a bicycle crank assembly 10 according to an embodiment of the present invention includes a crank main body 12 and a slave body. One end of the crank main body 12 has a sprocket mounting portion 14 that extends radially. In the first to third figures, the state in which the first sprocket 30 and the second sprocket 32 are attached is shown. 曲 The crank main body 12 and the sprocket attachment portion 14 are integrally formed. In the present embodiment, the crank main body 12 and the sprocket mounting portion 14 are divided into a first crank portion 16 and a second crank portion 18. The first crank portion 16 and the second crank portion 18 are made of metal such as aluminum alloy. The first crank portion 16 is a portion mainly responsible for the strength of the crank main body 12 and the sprocket mounting portion 14. The second crank portion 18 is fixed to the first crank portion 16 so as to cover the first crank portion 16. The second crank portion 18 is responsible for the remaining rigidity of the crank main body 2 and the sprocket mounting portion 14, as well as the enamel. Therefore, it is preferable to form the first crank portion 16 to be thicker than the second crank portion 18. The crank main body 12 is a hollow rod-shaped portion extending in the radial direction from the crank shaft 20 as shown in Figs. 4 and 5. The first crank portion 16 of the crank main body I2 has a crank shaft mounting portion 12b having a crank shaft mounting hole 12a formed at one end thereof, and a pedal shaft mounting portion 12d having a pedal shaft mounting hole 12c formed at the other end. -6 - M428920 The crankshaft mounting portion 12b has a cylindrical first boss portion 16a. The crankshaft mounting hole 12a is formed on the inner peripheral surface of the first boss portion 16a. The inner peripheral surface ' of the crankshaft mounting hole 12a is formed with a serration portion 12f in which a plurality of recesses are formed at intervals in the circumferential direction. The pedal mounting portion 12d has a second hub portion 16b having a relatively large thickness. A pedal shaft mounting hole 12c is formed in the second boss portion 16b. The crankshaft 20 can be fixed to the crankshaft mounting hole 12a. In this embodiment, the hollow crankshaft 20 is press-fitted and fixed to the crankshaft mounting hole 12a. The φ crankshaft 20 is rotatably supported by a fixed portion of the crank main body 12 of the bottom bracket β crankshaft 20 of the bicycle (not shown), and is larger in diameter than the other portions, and has a large diameter. A part of the outer peripheral surface is formed with a serration portion 20a that engages with the serration portion 12f of the crank shaft mounting hole 12a. As shown in FIG. 4, the crank shaft 20 is inserted into the crank shaft mounting hole 12a from the outer side surface of the first crank portion 16 of the crank main body 12, and the crank portion 20a is pressed into the crank shaft mounting hole 12a. The shaft 20 is fixed to the crank main body 12. The serration portion 20a of the crank shaft 20 forms a side end surface, and as shown in Fig. 6, φ is closed by the cover member 19. The cover member 19 is, for example, a member made of synthetic resin or metal. The cover member 19 has a large-diameter head portion 19a and a tubular portion 19b fitted to the inner circumferential surface of the crankshaft 20. The outer side surface 19c of the head portion 19a is in contact with the inner side surface 18c of the second bottom portion 18a of the second crank portion 18 of the crank main body 12, which will be described later. An adhesive is applied to the contact portion to fix the second crank portion 18. Further, by the arrangement of the crank shaft 20 in contact with the second bottom portion 18a of the second crank portion 18, the second crank portion 18 is not easily recessed. As shown in Figs. 4 and 5, the pedal shaft mounting hole 12c' is formed with a M428920: a female screw portion 12e that is screwed to a pedal shaft of a pedal (not shown). The first crank portion 16' of the crank main body 12' has a first bottom portion 16c extending toward the axial direction of the crank shaft 20, being thinner than the second hub portion 16b, and a first portion formed at the outer edge portion of the first bottom portion 16c. Wall portion 16d. The first wall portion I6d is the same thickness as the first bottom portion 16c or thinner than the first bottom portion 16c. In the crank main body 12, the second crank portion 18' has a second bottom portion 18a disposed opposite to the first bottom portion 16c of the first crank portion 16, and a second bottom portion 18b formed at an outer edge portion of the second bottom portion 18a. . Thereby, a space is formed between the first crank portion 16 and the second crank portion 18. A through hole 18d through which the pedal shaft can pass is formed in a portion of the second crank portion 18 opposed to the pedal shaft mounting hole 12c. The portion of the second crank portion 18 opposed to the crank shaft mounting hole 12a covers the crank shaft mounting hole 12a and does not see the crank shaft mounting hole 1 2a from the outside. The second wall portion 18b is formed to be snugly attached. On the outer side of the first wall portion 16d. The second wall portion 18b is bonded to the first wall portion 16h by, for example, an adhesive. The sprocket mounting portion 14 has first to fourth sprocket mounting arm portions 21 extending from the crank shaft mounting portion 12b. twenty four. The first sprocket mounting arm portion 21 has a first sprocket mounting hole 21a. The second sprocket mounting arm portion 22 has a second sprocket mounting hole 22a. The third sprocket mounting arm portion 23 has a third sprocket mounting hole 23ae. The fourth sprocket mounting arm portion 24 has a fourth sprocket mounting hole 24a. The fourth-segment sprocket mounting holes 21a to 24a are formed in the vicinity of the ij-end of the fourth-sprocket mounting arm portions 21 to 24, and around the first-fourth sprocket mounting holes 21a to 24a. Both sides are machined to a thinner thickness than the other parts. The first sprocket 30 is fixed to the first to fourth outer side surfaces 21b to 24b, and the second sprocket 32 is fixed to the opposite side simultaneously with the first sprocket 30 by a fixing bolt of M428920 (not shown). Side sill The first sprocket mounting arm portion 21, the second sprocket mounting arm portion 22, the third sprocket mounting arm portion 23, and the fourth sprocket mounting arm portion 24 are assembled along the bicycle crank when the bicycle is driven. The direction of rotation of the body 10 (in the clockwise direction indicated by the arrow A in Fig. 1), from the crank main body 12, the first sprocket mounting arm portion 21, the second sprocket mounting arm portion 22, and the third The sprocket mounting φ arm portion 23 and the fourth sprocket mounting arm portion 24 are arranged in this order. The first to fourth sprocket mounting arm portions 21', 22, 23, 24' are also provided on the second crank portion 18. The first-fourth sprocket mounting arm portions 21' to 24' of the second crank portion 18 are provided to cover portions other than the circumferences of the first to fourth sprocket mounting holes 21a to 24a. Therefore, in the present embodiment, the first to fourth sprocket mounting arm portions 21' of the arm portions 21, 22, 23, 24 and the second crank portion 18 of the first crank portion 16 are attached. 22, 23, and 24' constitute four sprocket mounting arm portions of the crank assembly 10. As shown in Fig. 5, the bicycle crank assembly 1 of the present invention has a first central angle α 1 , a second central angle α 2 , a third central angle α 3 , and a fourth central angle α: 4. The first central angle α丨 is an angle formed by the first imaginary line L丨 and the second imaginary line L2; the first imaginary line L1 is the center C of the crankshaft mounting hole 12a and the first sprocket mounting hole 2la The center C1 is connected; the second imaginary line L2' is formed by joining the center c of the crankshaft mounting hole and the center C2 of the second sprocket mounting hole 22a. The second central angle α2 is an angle formed by the above-described table imaginary line L2 and the second imaginary line L3; the second imaginary line L3 ′ is the center C of the crankshaft mounting hole 12a and the third sprocket mounting hole 233 of M428920 The center C3 is connected. The third central angle α 3 is an angle formed by the third imaginary line L3 and the fourth imaginary line L4; and the fourth imaginary line L4 is the center C of the crank shaft mounting hole l2a and the fourth sprocket mounting hole 24a. The center C4 is connected. The fourth central angle Q: 4 is an angle formed by the fourth imaginary line L4 and the first imaginary line L1. And, the first central angle αι, the second central angle α 2, the third central angle α 3, and the fourth central angle α 4, the first central angle αΐ and the third central angle α3′ are formed to be smaller than: the second central angle "2 and the fourth central angle α 4. In this embodiment, the first central angle α 相等 is equal to the third central angle α 3 . The second central angle α 2 is equal to the fourth central angle α 4 . The first central angle α 1 and The third central angle α3' is preferably in the range of 60 to 80 degrees, and is in this embodiment. The rigidity of the second sprocket mounting arm portion 22 and the fourth sprocket mounting arm portion 24 is higher than: The rigidity of the sprocket mounting arm portion 21 and the third sprocket mounting arm portion 23. Specifically, in this embodiment, the second sprocket mounting arm portion 22 and the fourth sprocket mounting arm portion 24 and the second imaginary line The width W2 of the orthogonal direction in the L2 and the fourth imaginary line is larger than the first imaginary line L1 and the third imaginary line L3 of the first sprocket attachment arm portion 21 and the third sprocket attachment arm portion 23 The width W1 of the direction of intersection. Thereby, the bending rigidity of the second sprocket mounting arm portion 22 and the fourth sprocket mounting arm portion 24 is higher than that of the first sprocket mounting arm portion 21 and the third sprocket mounting arm portion 23. Regarding the first to fourth sprocket mounting arm portions 21', 22', 23', and 24 of the second crank portion 18, the first to fourth sprocket mounting arm portions 21, 22 of the first crank portion 16 are formed. 23, 24 are equally preferred. The first bottom portion 16c and the first wall portion 16d are formed on the outer edge portion of the first to fourth sprocket attachment arm portions 21 to 24 in the first -10 - M428920 crank portion 16. The first wall portion 16d is also formed at a boundary portion of the first-fourth outer side surfaces 21b to 24b. Then, the first to fourth sprocket attachment arm portions 21 to 24 are surrounded by the first wall portion 16d except for the first to fourth outer side faces 2 lb to 24b. In the present embodiment, between the crank main body 12 and the first sprocket mounting arm portion 21, between the second sprocket mounting arm portion 22 and the third sprocket mounting arm portion 23, and the fourth sprocket mounting arm portion 24 A rib 25 for reinforcing φ is formed between the crank main body 12. The rib 25 is formed radially from the first hub portion 16a toward the first wall portion 16d. The arm portions 21 to 24 are attached to the first to fourth sprocket wheels, and the second wall portion 18b of the second crank portion 18 is placed in close contact with the outer surface of the first wall portion I6d. The first wall portion 16d formed at a boundary portion with the fourth-outer side surface 21b to 24b is not disposed. In the bicycle crank assembly 10 configured as described above, a large load is applied during the stepping operation, and between the first sprocket attachment arm portion 21 and the second sprocket mounting arm portion 22, and the third sprocket Between the mounting arm portion 23 and the fourth sprocket mounting arm portion 24, the interval between the sprocket mounting arm portions is narrowed, and the rigidity of the crank assembly can be effectively increased. Further, the rigidity of the second sprocket mounting arm portion and the fourth sprocket mounting arm portion is higher than the rigidity of the first sprocket mounting arm portion and the third sprocket mounting arm portion. Thereby, the required smaller sprocket mounting arm portion and the third sprocket mounting arm portion can be made more particularly lightweight, as shown in Fig. 7, when the crank main body 12 is disposed at : a predetermined angular region in which the torque acting on the crank assembly 10 becomes large (for example, the crank main body 12 -11 - M428920 is rotated from the crank driving rotation direction to the position F from the top dead center UD by about 70 degrees until When the angle point from the position G at which the top dead center UD is rotated by about 90 degrees is an area of about 20 degrees), specifically, the center C of the crank shaft mounting hole 12a of the crank main body 12 and the pedal shaft mounting hole 12c The center C5 of the imaginary crank main body center line L5 is disposed at a predetermined angle region, and the third center angle α3 is directed toward the top dead center UD of the load by the chain CN. In this state, although a large load acts on the first sprocket 30 or the second sprocket 32, the third sprocket mounting arm portion 23 and the fourth sprocket mounting arm portion 24 are disposed at a narrow interval. Near the dead point UD, the first sprocket 30 and the second sprocket 32 can have sufficient rigidity to withstand the load.
Q 接近上死點UD且位於曲柄驅動旋轉方向的下游側的 第四鏈輪安裝臂部24，雖然承受鏈條CN造成的較大負荷， 而由於第四鏈輪安裝臂部24的寬幅較寬而剛性較高，所以 第四鏈輪安裝臂部24能具備有抵抗踩踏動作中的負荷的必 須的充分剛性。 另一方面，如第8圖所示，當左曲柄LC也配置於上述 預定的角度區域時，作用於曲柄組裝體10的扭矩變大。在 該情況，第一中心角αΐ朝向藉由鏈條CN而力量作用的上 死點UD。即使在該狀態，雖然較大的負荷作用於第—鏈 輪3 0或第二鏈輪32，而由於以較窄間隔配置的第一鏈輪安 裝臂部21與第二鏈輪安裝臂部22位於上死點UD附近，所 以第一鏈輪30及第二鏈輪32能具備有抵抗負荷的必須的充 分剛性。 -12- M428920 接近上死點UD且位於曲柄驅動旋轉方向的下游側的 承受鏈條CN造成的較大負荷的第二鏈輪安裝臂部22的寬幅 較寬而剛性較高，所以第二鏈輪安裝臂部22能具備有抵抗 踩踏動作中的負荷的必須的充分剛性。 藉此，所需要的剛性更小的第一鏈輪安裝臂部21與第 兰鏈輪安裝臂部23，可作成更特別輕量化的構造。 <其他實施方式> 以上雖然針對本新型的一種實施方式來說明，而本新 型並不限定於上述實施方式，在不脫離新型的主旨的範圍 可進行各種變更。 (a) 在上述實施方式，雖然是將曲柄軸20壓入固定 於曲柄主體12，而也取代壓入固定方式，而藉由黏接劑將 曲柄軸20與曲柄主體12固定。或者，藉由螺栓或螺母將自 行車用曲柄組裝體可一體旋轉地且可裝卸地固定於曲柄軸 〇 (b) 在上述實施方式，雖然第二曲柄部18爲金屬製 ’而例如以碳纖維強化樹脂等的合成樹脂製也可以。 (c )在上述實施方式，雖然爲了將自行車用曲柄組 裝體輕量化而作成以第一曲柄部與第二曲柄部構成的中空 構造’而本新型並不限於此。例如，也可作成未以第一曲 柄部與第二曲柄部分割的一體中空構造。而自行車用曲柄 組裝體全體作成實心也可以。 (d)在上述實施方式，由於將自行車用曲柄組裝體 -13- M428920 10的第一及第三鏈輪安裝臂部21、23、與第二及第四鏈輪 安裝臂部22、24的剛性改變，使其與第--第四假想線正 交的方向的寬度變化，而本新型並不限於此。例如如第9 圖所示在鏈輪安裝部114的第一曲柄部116，第--第四鏈 輪安裝臂部121〜124的寬度作成相同，第二鏈輪安裝臂部 122與第四鏈輪安裝臂部124作成實心，第一鏈輪安裝臂部 121及第三鏈輪安裝臂部123作成中空，來使剛性變化也可 以。 例如如第10圖所示，在中空的鏈輪安裝部214的第一 曲柄部216’只在第二鏈輪安裝臂部222與第四鏈輪安裝臂 部2 24形成有作爲補強部的肋部226，將剛性提高也可以。 肋部226，與第二鏈輪安裝臂部222及第四鏈輪安裝臂部 224—體形成。可是，肋部，是與第二鏈輪安裝臂部222及 第四鏈輪安裝臂部224爲不同構件也可以。也可取代肋部 ’藉由在第二鏈輪安裝臂部222及第四鏈輪安裝臂部224的 中空部配置塡充物，來使剛性變化。 並且，在鏈輪安裝部的第一曲柄部，也可使第二及第 四鏈輪安裝臂部的剖面積，大於第一及第三鏈輪安裝臂部 ’來使剛性變化。 【圖式簡單說明】 第1圖是本新型的一種實施方式的自行車用曲柄組裝 體的正視圖。 第2圖是自行車用曲柄組裝體的後視圖。 -14- M428920 第3圖是自行車用曲柄組裝體的左側視圖。 第4圖是自行車用曲柄組裝體的分解立體圖。 第5圖是曲柄主體的正視圖。 第6圖是自行車用曲柄組裝體的曲柄軸固定部分的局 部剖面圖。 第7圖是用來說明較大扭矩作用於曲柄主體的範圍的 自行車用曲柄的正視圖。 第8圖是用來說明在左曲柄有較大扭矩作用於曲柄主 體的範圍的自行車用曲柄的正視圖。 第9圖是其他實施方式的曲柄主體的與第5圖相當的圖 〇 第10圖是另外其他實施方式的曲柄主體的與第5圖相 當的圖。 【主要元件符號說明】 1 0 :自行車用曲柄組裝體 1 2 :曲柄主體 12a :曲柄軸安裝孔 12b :踏板軸安裝孔 14 :鏈輪安裝部 2〇 :曲柄軸 21、 21’ ：第一鏈輪安裝臂部 22、 22’：第二鏈輪安裝臂部 23、 23’：第三鏈輪安裝臂部 -15 - M428920 24、24’ ：第四鏈輪安裝臂部 121 :第一鏈輪安裝臂部 122:第二鏈輪安裝臂部 123 :第三鏈輪安裝臂部 124:第四鏈輪安裝臂部 222:第二鏈輪安裝臂部 224:第四鏈輪安裝臂部 226 :肋部 α 1 :第一中心角 α 2 :第二中心角 α 3 :第三中心角 <2 4 :第四中心角 C :曲柄軸安裝孔的中心 C 1 :第一鏈輪安裝孔的中心 C2:第二鏈輪安裝孔的中心 C3 :第三鏈輪安裝孔的中心 C4 :第四鏈輪安裝孔的中心 L 1 :第一假想線 L2 :第二假想線 L3 :第三假想線 L4 :第四假想線Q. The fourth sprocket mounting arm portion 24 near the top dead center UD and located on the downstream side in the crank drive rotation direction receives a large load due to the chain CN, and the wider width of the fourth sprocket mounting arm portion 24 is wide. Since the rigidity is high, the fourth sprocket mounting arm portion 24 can have sufficient rigidity necessary for resisting the load during the pedaling operation. On the other hand, as shown in Fig. 8, when the left crank LC is also disposed in the predetermined angular region, the torque acting on the crank assembly 10 becomes large. In this case, the first central angle α ΐ faces the top dead center UD which is forced by the chain CN. Even in this state, although a large load acts on the first sprocket 30 or the second sprocket 32, the first sprocket mounting arm portion 21 and the second sprocket mounting arm portion 22 are disposed at narrow intervals. Located near the top dead center UD, the first sprocket 30 and the second sprocket 32 can have sufficient rigidity necessary to withstand the load. -12- M428920 The second sprocket mounting arm portion 22, which is close to the top dead center UD and is subjected to a large load on the downstream side of the crank drive rotation direction, has a wide width and a high rigidity, so the second chain The wheel mounting arm portion 22 can have sufficient rigidity necessary to resist the load during the pedaling operation. Thereby, the required first sprocket mounting arm portion 21 and the third sprocket mounting arm portion 23 having a smaller rigidity can be made more particularly lightweight. <Other Embodiments> The above description of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the novel features. (a) In the above embodiment, the crankshaft 20 is press-fitted to the crank main body 12, and the crankshaft 20 and the crank main body 12 are fixed by an adhesive instead of the press-fitting method. Alternatively, the bicycle crank assembly can be integrally and rotatably fixed to the crank axle (b) by bolts or nuts. In the above embodiment, the second crank portion 18 is made of metal, for example, carbon fiber reinforced resin. It can also be made of synthetic resin. (c) In the above embodiment, the hollow structure constituting the first crank portion and the second crank portion is formed in order to reduce the weight of the bicycle crank assembly, and the present invention is not limited thereto. For example, an integral hollow structure that is not divided by the first crank portion and the second crank portion may be formed. It is also possible to make the whole of the bicycle crank assembly. (d) In the above embodiment, the first and third sprocket mounting arms 21, 23 of the bicycle crank assembly-13-M428920 10 and the second and fourth sprocket mounting arms 22, 24 are The rigidity is changed so as to vary the width in the direction orthogonal to the first-fourth imaginary line, and the present invention is not limited thereto. For example, as shown in Fig. 9, in the first crank portion 116 of the sprocket mounting portion 114, the widths of the fourth to fourth sprocket mounting arm portions 121 to 124 are made the same, and the second sprocket mounting arm portion 122 and the fourth chain are formed. The wheel mounting arm portion 124 is made solid, and the first sprocket mounting arm portion 121 and the third sprocket mounting arm portion 123 are made hollow to change the rigidity. For example, as shown in Fig. 10, in the first crank portion 216' of the hollow sprocket mounting portion 214, only the second sprocket mounting arm portion 222 and the fourth sprocket mounting arm portion 24 are formed with ribs as reinforcing portions. The portion 226 can also increase the rigidity. The rib 226 is formed integrally with the second sprocket mounting arm portion 222 and the fourth sprocket mounting arm portion 224. However, the ribs may be different from the second sprocket mounting arm portion 222 and the fourth sprocket mounting arm portion 224. Instead of the ribs, the ridges may be disposed in the hollow portions of the second sprocket attachment arm portion 222 and the fourth sprocket attachment arm portion 224 to change the rigidity. Further, in the first crank portion of the sprocket attachment portion, the cross-sectional area of the second and fourth sprocket attachment arm portions can be made larger than the first and third sprocket attachment arm portions to change the rigidity. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a front elevational view showing a bicycle crank assembly according to an embodiment of the present invention. Fig. 2 is a rear view of the bicycle crank assembly. -14- M428920 Figure 3 is a left side view of the bicycle crank assembly. Fig. 4 is an exploded perspective view of the bicycle crank assembly. Figure 5 is a front view of the crank body. Fig. 6 is a partial sectional view showing a crank shaft fixing portion of a bicycle crank assembly. Fig. 7 is a front view of a bicycle crank for explaining a range in which a large torque acts on the crank main body. Fig. 8 is a front elevational view showing a bicycle crank in a range in which a large crank has a large torque acting on the crank main body. Fig. 9 is a view corresponding to Fig. 5 of the crank main body of another embodiment. Fig. 10 is a view corresponding to Fig. 5 of the crank main body of still another embodiment. [Description of main component symbols] 1 0 : Crank assembly for bicycle 1 2 : Crank main body 12a : Crankshaft mounting hole 12b : Pedestrian shaft mounting hole 14 : Sprocket mounting portion 2 : Crankshaft 21 , 21 ' : First chain Wheel mounting arm portions 22, 22': second sprocket mounting arm portion 23, 23': third sprocket mounting arm portion -15 - M428920 24, 24': fourth sprocket mounting arm portion 121: first sprocket Mounting arm portion 122: second sprocket mounting arm portion 123: third sprocket mounting arm portion 124: fourth sprocket mounting arm portion 222: second sprocket mounting arm portion 224: fourth sprocket mounting arm portion 226: Rib α 1 : first central angle α 2 : second central angle α 3 : third central angle < 2 4 : fourth central angle C : center C 1 of the crankshaft mounting hole: first sprocket mounting hole Center C2: Center C3 of the second sprocket mounting hole: Center C4 of the third sprocket mounting hole: Center of the fourth sprocket mounting hole L1: First imaginary line L2: Second imaginary line L3: Third imaginary line L4: fourth imaginary line