US20080005905A1 - Hollow crank arm for a bicycle and process for manufacturing the same - Google Patents
Hollow crank arm for a bicycle and process for manufacturing the same Download PDFInfo
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- US20080005905A1 US20080005905A1 US11/837,209 US83720907A US2008005905A1 US 20080005905 A1 US20080005905 A1 US 20080005905A1 US 83720907 A US83720907 A US 83720907A US 2008005905 A1 US2008005905 A1 US 2008005905A1
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- process according
- cavity
- crank arm
- opening
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62M—RIDER PROPULSION OF WHEELED VEHICLES OR SLEDGES; POWERED PROPULSION OF SLEDGES OR SINGLE-TRACK CYCLES; TRANSMISSIONS SPECIALLY ADAPTED FOR SUCH VEHICLES
- B62M3/00—Construction of cranks operated by hand or foot
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49616—Structural member making
- Y10T29/49622—Vehicular structural member making
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T74/00—Machine element or mechanism
- Y10T74/21—Elements
- Y10T74/2164—Cranks and pedals
Definitions
- the present invention relates to a hollow crank arm for a bicycle and a process for its fabrication.
- Crank arms for bicycles traditionally consist of a monolithic body made of metal material (typically aluminium or its alloys) provided at its ends with holes for attachment of the pedal and of the bottom bracket spindle.
- metal material typically aluminium or its alloys
- the Japanese document No. 5116670 describes a process for forming an inner cavity in the solid body of a crank arm by extrusion. According to this proposal, the cavity extends up to one end of the crank arm. Consequently, in order to obtain the threaded hole for fixing of the pedal it is necessary to provide an insert fixed in an end area of the crank arm.
- This solution presents structural strength problems in so far as it gives rise to a basically tubular structure opened at one end. This presents poor resistance to torsional and bending stresses, in particular owing to the fact that the point of application of a load, represented by the area of connection to the pedal, is provided in a hollow part.
- 6,058,803 describes a process for producing a hollow crank arm by casting, in which a sand core is positioned in a die and the molten metal is poured into the die and solidified in order to form a crank arm body with an elongated cavity having a blind bottom and an end that opens to the outside of the hole which is provided for fixing the pedal. Also this solution presents strength problems because the cavity opens into the hole for connection of the pedal and thus weakens that area.
- the purpose of the present invention is to provide a hallow crank arm for a bicycle and a process for its fabrication which will overcome the problems of the prior art.
- the invention provides a forged hollow crank arm for a bicycle comprising a first end area for connection to a bottom bracket spindle, a second end area for connection of a pedal and an intermediate area having a defined longitudinal cavity that extends between the ends along a longitudinal axis with an opening that faces to the outside of the crank arm and is offset with respect to the longitudinal axis.
- FIGS. 1 and 2 illustrate a billet of metal material designed to undergo a series of operations of plastic deformation to obtain a crank arm according to the present invention
- FIG. 3 illustrates the billet of FIGS. 1 and 2 at the end of a first drawing step
- FIGS. 4, 5 and 6 are, respectively, a front view, a sectional view, and a top-plan view of a preform or intermediate form of a pedal at the end of a second drawing step;
- FIGS. 7, 8 and 9 are, respectively, a front view, a sectional view, and a top-plan view of a preform or intermediate form of a pedal at the end of a third drawing step;
- FIGS. 10 and 11 are, respectively, an elevation and a sectional view of a preform or intermediate form of a pedal at the end of a fourth drawing step;
- FIGS. 12, 13 and 14 are, respectively, a front elevation, a side elevation, and a sectional view of a finished crank according to a first embodiment of the present invention
- FIG. 15 is a sectional view illustrating another embodiment of the present invention.
- FIGS. 16 and 17 are cross sections illustrating two additional embodiments of the present invention.
- FIGS. 18 to 23 illustrate another embodiment of the invention which is formed by folding over flaps or extensions to form an internal cavity
- FIGS. 24 to 26 illustrated the embodiment of FIGS. 18 to 23 with the further addition of a weld bead along the folds forming the internal cavity.
- FIGS. 1 and 2 Designated by 20 in FIGS. 1 and 2 is a billet made of light metal material such as aluminium, its alloys, or similar light alloys, which constitutes the starting element for obtaining a hollow crank arm according to the present invention.
- the billet 20 preferably has the shape of a solid cylinder with a circular cross section, preferably obtained starting from a cylindrical bar by making a cut in the direction orthogonal to the longitudinal axis of the bar.
- the billet 20 undergoes a first operation of hot plastic deformation, preferably a forging in a press, which draws the billet and results in the formation of a cylindrical cavity having a blind end or bottom, designated by 22 in FIG. 3 .
- the cylindrical cavity opens out onto an end 24 of the billet.
- FIG. 3 illustrates the billet 20 at the end of the first drawing step.
- This billet is subjected to a second drawing step, at the end of which a preform or intermediate form of the crank arm 26 is obtained, with basically the shape illustrated in FIGS. 4, 5 and 6 .
- the crank arm preform 26 has a cavity with a blind bottom 22 having an open end 24 .
- a solid portion 28 is set between the bottom 30 of the cavity 22 and a first end 32 of the crank arm preform 26 .
- a projecting portion 34 extends laterally with respect to the cavity 22 and projects beyond the open end 24 of the cavity 22 on the opposite side with respect to the cavity 22 .
- the crank arm preform 26 undergoes a third forging step, at the end of which the semi-finished product illustrated in FIGS. 7, 8 and 9 is obtained.
- This semi-finished product has a projecting portion 34 that extends laterally with respect to the cavity 22 and is set on the opposite side of said cavity.
- This drawing step elongates the cavity 22 and renders the thickness of the wall surrounding the cavity 22 uniform.
- the semi-finished product 26 assumes the shape illustrated in FIGS. 10 and 11 .
- the cavity 22 is elongated and restricted, whilst the solid portion 28 is shaped so as to form an area of connection to the bottom bracket spindle.
- the projecting portion 34 is always set laterally with respect to the cavity 22 and, at the end of this fourth forging step, is slightly inclined outwards. It may be noted that in all the foregoing forging steps the projecting portion 34 is positioned in relation to the cavity 22 in such a way as not to obstruct the insertion and extraction of a drawing punch, as will be known to those skilled in the art that is inserted inside the cavity 22 during each forging step. That is, the cavity 22 has a longitudinal axis that extends between portions 28 and 34 and the centre of the opening of the opening 24 is on the longitudinal axis.
- the semi-finished product 26 then undergoes a fifth and final fabrication step of hot plastic deformation, which results in a crank arm body 36 having the final shape illustrated in FIGS. 12, 13 and 14 .
- a crank arm body 36 having the final shape illustrated in FIGS. 12, 13 and 14 .
- the opening 24 of the cavity 22 is biased toward the side 54 and opening 24 becomes offset with respect to the longitudinal axis of the cavity 22 .
- the finished crank arm body 36 comprises a solid area 28 for connection to the bottom bracket spindle and a solid area 40 for connection of the pedal, in which respective holes 42 , 44 are formed by machining away material.
- the hole 44 for connection of the pedal 44 is usually threaded, whereas the hole 42 for connection to the bottom bracket spindle has a shape, for example square, designed to transmit torque when coupled with a complementary part of the bottom bracket spindle.
- the crank arm body has a hollow section 50 and a solid section 52 which extend between the aforesaid areas 28 and 40 for connection to the bottom bracket spindle and connection of the pedal.
- the solid section 52 includes the solid area 40 for connection of the pedal.
- the hollow section is adjacent to the solid area 28 for connection to the bottom bracket spindle. In said hollow section, the walls are thin and the cavity has a predominant dimension with respect to the thickness of the walls.
- the projecting portion 34 is bent and shaped so that the hollow section 50 and the solid section 52 are substantially aligned on the longitudinal axis 60 of the crank arm body.
- the solid section 52 may be slightly inclined towards the inner side of the crank arm, as illustrated in the variants of FIGS. 16 and 17 in order to exploit in an optimal way the space available when the crank arm is mounted on a bicycle. In this way, in fact, a shorter bottom bracket spindle can be made, which leads to a better transmission of motion.
- temperatures can range between 260 and 480 degrees Celsius.
- temperatures between 390 and 400 degrees Celsius render the metal plastically deformable in all steps.
- the actual temperatures and formation pressures will depend on the selected material, tooling and equipment used in the process.
- the crank arm body 36 has a wide inner side 54 , a wide outer side 56 and two narrow sides 58 .
- the hollow section 50 has a cavity 22 that communicates with the outside through the opening 24 located on one of the aforesaid sides in an area comprised between the aforesaid areas 28 , 40 for connection to the bottom bracket spindle and for connection with the pedal.
- the opening 24 is located on the wide inner side 54 .
- the cavity 22 has an elongated shape with an axis that substantially coincides with the longitudinal axis 60 of the crank arm body. From the point of view of the structural strength of the crank arm, it is particularly important that the areas for connection of the bottom bracket spindle and of the pedal should be made in solid areas that do not communicate with the cavity 22 . This provides a greater structural strength in the connection areas.
- the cavity 22 is substantially closed, except for the opening 24 , and this provides high stiffness and high resistance to torsional and flexural stresses to be obtained.
- the opening 24 may be closed, to prevent any penetration of dust, water or dirt into the cavity 22 , with a closing element that need not make any contribution to the structural strength of the crank arm.
- the opening 24 may be closed with the purpose of improving the structural strength of the crank arm.
- a way of so closing the opening 24 is illustrated in FIG. 15 and consists in forming an integral flap 62 that is closed and fixed against the open edge of the opening 24 . Fixing is performed in the area indicated by 64 , for instance by welding or bonding. Closing the cavity 22 is believed to be advantageous from the standpoint of the structural strength, since it is known that a closed structure has a higher moment of inertia and is able to distribute the stresses more evenly.
- FIG. 16 illustrates a crank arm with a cavity 22 that is completely closed, the said crank arm being obtainable with a process of casting of molten metal material, such as aluminium or its alloys or titanium, into a die.
- molten metal material such as aluminium or its alloys or titanium
- the said core having a shape corresponding to the shape of the cavity 22 .
- the core may consist of a vitreous material with a density and specific weight smaller than that of the material constituting the crank arm body, and may remain englobed in the crank arm body.
- the core could be made from a granular material which is extracted at the end of solidification of the molten material, for example through an opening that can be closed, as indicated previously.
- FIG. 17 illustrates a further alternative for producing a crank arm according to the invention. This consists in forming a crank arm body with an open lowered area 66 that is closed by a closing element 68 , which covers the entire lowered area 66 in order to form a closed cavity.
- the crank arm body 36 may be obtained by plastic deformation, casting or by machining-away of material, and the closing element 68 may be fixed by welding or bonding.
- a crank arm having the shape illustrated in FIGS. 12 to 17 may be obtained by crosslinking, in a die, of a structural-fibre-based fabric embedded in a matrix of plastic material.
- the fibres may be chosen in the group comprising carbon fibres, glass fibres, aramidic fibres, boron fibres, ceramic fibres, or any combination thereof.
- the cavity 22 may be formed by providing an expandable core on which the fabric englobed in a non-crosslinked matrix is wound. During crosslinking of the material, the core applies a forming pressure on the inner surfaces of the cavity and is extracted from the crank arm body at the end of crosslinking of the material.
- the expandable core may consist of a thermally dilatable material such as Teflon or the like.
- the cavity may be formed by providing an inflatable element for forming the inner surfaces of the cavity.
- the crank arm according to the present invention irrespective of the process and of the material used for its fabrication, is characterized by certain dimensional ratios that enable optimal results to be obtained in terms of mechanical strength and lightness.
- the letter l indicates the useful length of the crank arm, defined as the distance between the centres of the holes 42 and 44 ;
- the letter l 1 indicates the distance between the outer end of the opening 24 and the centre of the hole 42 ;
- l 2 indicates the distance between the outer end of the opening 24 and the hole 44 ;
- l 3 indicates the distance between the inner edge of the opening 24 and the centre of the hole 42 ;
- l 4 indicates the distance between the outer edge and the inner edge of the opening 24 , all these distances being measured in the direction of the longitudinal axis 60 of the crank arm.
- the ratio l 2 /l (which expresses the length of the solid section in proportion to the useful length of the crank arm) is comprised between 0.2 and 0.5, and preferably between 0.3 and 0.4;
- the ratio l 3 /l (i.e. the ratio between the length in the “closed” hollow section and the useful length of the crank arm) is comprised between 0.3 and 0.8, and preferably between 0.5 and 0.7;
- the ratio l 4 /l i.e. the length of the opening in proportion to the useful length) is comprised between 0.1 and 0.25, and preferably between 0.15 and 0.22;
- the ratio l 1 /l (i.e. the ratio between the overall length of the hollow section and the useful length of the crank arm) is comprised between 0.3 and 0.8, and preferably between 0.6 and 0.7.
- the areas 28 and 40 for connection to the bottom bracket spindle and for connection of the pedal, and the area bearing the opening 24 have a width, designated by b 2 , greater than the width of the hollow section 50 and of the solid section 52 designated by b 1 .
- the ratio b 2 /b 1 is comprised between 1.1 and 1.5, and preferably between 1.2 and 1.3.
- a further particularly important ratio of dimensions is that of the thicknesses, s c (thickness of the hollow section 50 ), s p (thickness of the solid section 52 ) and s l (thickness of the wall surrounding the cavity 22 ), indicated in FIGS. 13, 14 and 17 .
- the ratio s c /s p is comprised between 1.2 and 3.0, and preferably between 1.5 and 1.7, whilst the ratio s l /s p is comprised between 0.1 and 0.3, and is preferably 0.2.
- the variation in the wall thickness from s l to s p must preferably be gradual with smooth curves without any sharp edges, in order to prevent stress concentrations from forming at the opening 24 , this being one of the most critical areas from the point of view of the risk of failure since it has an open section.
- crank arm according to the present invention and the process for its fabrication may be varied.
- the cavity 22 could open onto the outside in two different points, for instance on both of the wide sides, 54 and 56 , of the crank arm.
- the crank arm 136 may also be obtained from a U-shaped forging as illustrated in FIGS. 18-26 .
- the intermediate portion between the end portions 128 and 134 is formed with the flaps or extensions 129 spaced on either side of the longitudinal axis through the crank arm perform 126 .
- the flaps 129 are formed over toward the longitudinal axis and produce the cavity 122 in the crank arm 136 , see FIGS. 21-23 .
- the resulting structure 136 is then closed or fixed by welding bead 138 along the edges of the formed over flaps or extensions 129 as illustrated in FIGS. 24-26 .
- This formation technique yields a crank arm having the features of the previously described embodiments.
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- Shafts, Cranks, Connecting Bars, And Related Bearings (AREA)
Abstract
A hollow crank arm for a bicycle comprising a body of elongated shape, at the ends of which are formed, respectively, an area for connection of the bottom bracket spindle and an area for connection of the pedal. The body includes a cavity of elongated shape and two solid end portions which are the aforesaid connection areas for the bottom bracket spindle and for the pedal. The crank arm is preferably formed through a forging process.
Description
- This application is a division of U.S. patent application Ser. No. 10/391,705, filed Mar. 19, 2003, which is incorporated by reference as if fully set forth.
- The present invention relates to a hollow crank arm for a bicycle and a process for its fabrication.
- Crank arms for bicycles traditionally consist of a monolithic body made of metal material (typically aluminium or its alloys) provided at its ends with holes for attachment of the pedal and of the bottom bracket spindle.
- Various solutions have already been proposed which have the purpose of creating a cavity inside the body of the crank arm in order to reduce its weight.
- The Japanese document No. 5116670 describes a process for forming an inner cavity in the solid body of a crank arm by extrusion. According to this proposal, the cavity extends up to one end of the crank arm. Consequently, in order to obtain the threaded hole for fixing of the pedal it is necessary to provide an insert fixed in an end area of the crank arm. This solution presents structural strength problems in so far as it gives rise to a basically tubular structure opened at one end. This presents poor resistance to torsional and bending stresses, in particular owing to the fact that the point of application of a load, represented by the area of connection to the pedal, is provided in a hollow part. The U.S. Pat. No. 6,058,803 describes a process for producing a hollow crank arm by casting, in which a sand core is positioned in a die and the molten metal is poured into the die and solidified in order to form a crank arm body with an elongated cavity having a blind bottom and an end that opens to the outside of the hole which is provided for fixing the pedal. Also this solution presents strength problems because the cavity opens into the hole for connection of the pedal and thus weakens that area.
- The purpose of the present invention is to provide a hallow crank arm for a bicycle and a process for its fabrication which will overcome the problems of the prior art.
- The invention provides a forged hollow crank arm for a bicycle comprising a first end area for connection to a bottom bracket spindle, a second end area for connection of a pedal and an intermediate area having a defined longitudinal cavity that extends between the ends along a longitudinal axis with an opening that faces to the outside of the crank arm and is offset with respect to the longitudinal axis.
- The characteristics and advantages of the present invention will emerge clearly in the course of the ensuing detailed description with reference to the annexed drawings, in which:
-
FIGS. 1 and 2 illustrate a billet of metal material designed to undergo a series of operations of plastic deformation to obtain a crank arm according to the present invention; -
FIG. 3 illustrates the billet ofFIGS. 1 and 2 at the end of a first drawing step; -
FIGS. 4, 5 and 6 are, respectively, a front view, a sectional view, and a top-plan view of a preform or intermediate form of a pedal at the end of a second drawing step; -
FIGS. 7, 8 and 9 are, respectively, a front view, a sectional view, and a top-plan view of a preform or intermediate form of a pedal at the end of a third drawing step; -
FIGS. 10 and 11 are, respectively, an elevation and a sectional view of a preform or intermediate form of a pedal at the end of a fourth drawing step; -
FIGS. 12, 13 and 14 are, respectively, a front elevation, a side elevation, and a sectional view of a finished crank according to a first embodiment of the present invention; -
FIG. 15 is a sectional view illustrating another embodiment of the present invention; -
FIGS. 16 and 17 are cross sections illustrating two additional embodiments of the present invention; - FIGS. 18 to 23 illustrate another embodiment of the invention which is formed by folding over flaps or extensions to form an internal cavity; and
- FIGS. 24 to 26 illustrated the embodiment of FIGS. 18 to 23 with the further addition of a weld bead along the folds forming the internal cavity.
- Designated by 20 in
FIGS. 1 and 2 is a billet made of light metal material such as aluminium, its alloys, or similar light alloys, which constitutes the starting element for obtaining a hollow crank arm according to the present invention. Thebillet 20 preferably has the shape of a solid cylinder with a circular cross section, preferably obtained starting from a cylindrical bar by making a cut in the direction orthogonal to the longitudinal axis of the bar. Thebillet 20 undergoes a first operation of hot plastic deformation, preferably a forging in a press, which draws the billet and results in the formation of a cylindrical cavity having a blind end or bottom, designated by 22 inFIG. 3 . The cylindrical cavity opens out onto anend 24 of the billet.FIG. 3 illustrates thebillet 20 at the end of the first drawing step. This billet is subjected to a second drawing step, at the end of which a preform or intermediate form of thecrank arm 26 is obtained, with basically the shape illustrated inFIGS. 4, 5 and 6. The crank arm preform 26 has a cavity with ablind bottom 22 having anopen end 24. Asolid portion 28 is set between thebottom 30 of thecavity 22 and afirst end 32 of the crank arm preform 26. A projectingportion 34 extends laterally with respect to thecavity 22 and projects beyond theopen end 24 of thecavity 22 on the opposite side with respect to thecavity 22. - The crank arm preform 26 undergoes a third forging step, at the end of which the semi-finished product illustrated in
FIGS. 7, 8 and 9 is obtained. This semi-finished product has a projectingportion 34 that extends laterally with respect to thecavity 22 and is set on the opposite side of said cavity. This drawing step elongates thecavity 22 and renders the thickness of the wall surrounding thecavity 22 uniform. - By means of a further forging step the
semi-finished product 26 assumes the shape illustrated inFIGS. 10 and 11 . In this further forging step, thecavity 22 is elongated and restricted, whilst thesolid portion 28 is shaped so as to form an area of connection to the bottom bracket spindle. The projectingportion 34 is always set laterally with respect to thecavity 22 and, at the end of this fourth forging step, is slightly inclined outwards. It may be noted that in all the foregoing forging steps the projectingportion 34 is positioned in relation to thecavity 22 in such a way as not to obstruct the insertion and extraction of a drawing punch, as will be known to those skilled in the art that is inserted inside thecavity 22 during each forging step. That is, thecavity 22 has a longitudinal axis that extends betweenportions opening 24 is on the longitudinal axis. - The
semi-finished product 26 then undergoes a fifth and final fabrication step of hot plastic deformation, which results in acrank arm body 36 having the final shape illustrated inFIGS. 12, 13 and 14. As a result of this deformation, theopening 24 of thecavity 22 is biased toward theside 54 and opening 24 becomes offset with respect to the longitudinal axis of thecavity 22. - The finished
crank arm body 36 comprises asolid area 28 for connection to the bottom bracket spindle and asolid area 40 for connection of the pedal, in whichrespective holes hole 44 for connection of thepedal 44 is usually threaded, whereas thehole 42 for connection to the bottom bracket spindle has a shape, for example square, designed to transmit torque when coupled with a complementary part of the bottom bracket spindle. The crank arm body has ahollow section 50 and asolid section 52 which extend between theaforesaid areas solid section 52 includes thesolid area 40 for connection of the pedal. The hollow section is adjacent to thesolid area 28 for connection to the bottom bracket spindle. In said hollow section, the walls are thin and the cavity has a predominant dimension with respect to the thickness of the walls. - During the last formation step, the projecting
portion 34 is bent and shaped so that thehollow section 50 and thesolid section 52 are substantially aligned on thelongitudinal axis 60 of the crank arm body. Alternatively, thesolid section 52 may be slightly inclined towards the inner side of the crank arm, as illustrated in the variants ofFIGS. 16 and 17 in order to exploit in an optimal way the space available when the crank arm is mounted on a bicycle. In this way, in fact, a shorter bottom bracket spindle can be made, which leads to a better transmission of motion. - With respect to the forging process the temperatures can range between 260 and 480 degrees Celsius. For the aluminium alloy of the present embodiments, temperatures between 390 and 400 degrees Celsius render the metal plastically deformable in all steps. As will be recognized by those skilled in the art, the actual temperatures and formation pressures will depend on the selected material, tooling and equipment used in the process.
- Again with reference to
FIGS. 12, 13 and 14, thecrank arm body 36 has a wideinner side 54, a wideouter side 56 and twonarrow sides 58. Thehollow section 50 has acavity 22 that communicates with the outside through the opening 24 located on one of the aforesaid sides in an area comprised between theaforesaid areas opening 24 is located on the wideinner side 54. - The
cavity 22 has an elongated shape with an axis that substantially coincides with thelongitudinal axis 60 of the crank arm body. From the point of view of the structural strength of the crank arm, it is particularly important that the areas for connection of the bottom bracket spindle and of the pedal should be made in solid areas that do not communicate with thecavity 22. This provides a greater structural strength in the connection areas. Thecavity 22 is substantially closed, except for theopening 24, and this provides high stiffness and high resistance to torsional and flexural stresses to be obtained. - The
opening 24 may be closed, to prevent any penetration of dust, water or dirt into thecavity 22, with a closing element that need not make any contribution to the structural strength of the crank arm. - If desired the
opening 24 may be closed with the purpose of improving the structural strength of the crank arm. A way of so closing theopening 24 is illustrated inFIG. 15 and consists in forming anintegral flap 62 that is closed and fixed against the open edge of theopening 24. Fixing is performed in the area indicated by 64, for instance by welding or bonding. Closing thecavity 22 is believed to be advantageous from the standpoint of the structural strength, since it is known that a closed structure has a higher moment of inertia and is able to distribute the stresses more evenly. - The crank arm according to the present invention can be produced with processes different from the one described previously. For example,
FIG. 16 illustrates a crank arm with acavity 22 that is completely closed, the said crank arm being obtainable with a process of casting of molten metal material, such as aluminium or its alloys or titanium, into a die. To form theclosed cavity 22 the use of a core (not illustrated) is envisaged, the said core having a shape corresponding to the shape of thecavity 22. The core may consist of a vitreous material with a density and specific weight smaller than that of the material constituting the crank arm body, and may remain englobed in the crank arm body. Alternatively, the core could be made from a granular material which is extracted at the end of solidification of the molten material, for example through an opening that can be closed, as indicated previously. -
FIG. 17 illustrates a further alternative for producing a crank arm according to the invention. This consists in forming a crank arm body with an open loweredarea 66 that is closed by a closing element 68, which covers the entire loweredarea 66 in order to form a closed cavity. In the above variant thecrank arm body 36 may be obtained by plastic deformation, casting or by machining-away of material, and the closing element 68 may be fixed by welding or bonding. - A crank arm having the shape illustrated in FIGS. 12 to 17 may be obtained by crosslinking, in a die, of a structural-fibre-based fabric embedded in a matrix of plastic material. The fibres may be chosen in the group comprising carbon fibres, glass fibres, aramidic fibres, boron fibres, ceramic fibres, or any combination thereof. In this case, the
cavity 22 may be formed by providing an expandable core on which the fabric englobed in a non-crosslinked matrix is wound. During crosslinking of the material, the core applies a forming pressure on the inner surfaces of the cavity and is extracted from the crank arm body at the end of crosslinking of the material. The expandable core may consist of a thermally dilatable material such as Teflon or the like. Alternatively, the cavity may be formed by providing an inflatable element for forming the inner surfaces of the cavity. - With reference to FIGS. 12 to 17, the crank arm according to the present invention, irrespective of the process and of the material used for its fabrication, is characterized by certain dimensional ratios that enable optimal results to be obtained in terms of mechanical strength and lightness. In the figures, the letter l indicates the useful length of the crank arm, defined as the distance between the centres of the
holes opening 24 and the centre of thehole 42; l2 indicates the distance between the outer end of theopening 24 and thehole 44; l3 indicates the distance between the inner edge of theopening 24 and the centre of thehole 42; and l4 indicates the distance between the outer edge and the inner edge of theopening 24, all these distances being measured in the direction of thelongitudinal axis 60 of the crank arm. According to the present invention, the ratio l2/l (which expresses the length of the solid section in proportion to the useful length of the crank arm) is comprised between 0.2 and 0.5, and preferably between 0.3 and 0.4; the ratio l3/l (i.e. the ratio between the length in the “closed” hollow section and the useful length of the crank arm) is comprised between 0.3 and 0.8, and preferably between 0.5 and 0.7; the ratio l4/l (i.e. the length of the opening in proportion to the useful length) is comprised between 0.1 and 0.25, and preferably between 0.15 and 0.22; and the ratio l1/l (i.e. the ratio between the overall length of the hollow section and the useful length of the crank arm) is comprised between 0.3 and 0.8, and preferably between 0.6 and 0.7. - As is illustrated in
FIG. 12 , according to a preferred aspect of the present invention, theareas opening 24 have a width, designated by b2, greater than the width of thehollow section 50 and of thesolid section 52 designated by b1. In particular, the ratio b2/b1 is comprised between 1.1 and 1.5, and preferably between 1.2 and 1.3. - A further particularly important ratio of dimensions is that of the thicknesses, sc (thickness of the hollow section 50), sp (thickness of the solid section 52) and sl (thickness of the wall surrounding the cavity 22), indicated in
FIGS. 13, 14 and 17. According to a preferred aspect of the present invention, the ratio sc/sp is comprised between 1.2 and 3.0, and preferably between 1.5 and 1.7, whilst the ratio sl/sp is comprised between 0.1 and 0.3, and is preferably 0.2. In addition, the variation in the wall thickness from sl to sp must preferably be gradual with smooth curves without any sharp edges, in order to prevent stress concentrations from forming at theopening 24, this being one of the most critical areas from the point of view of the risk of failure since it has an open section. - The foregoing description refers to a process for the production of what is commonly recognized as a left-hand crank arm. It will understood that the process applies equally to a right-hand crank arm.
- The crank arm according to the present invention and the process for its fabrication may be varied. For example, the
cavity 22 could open onto the outside in two different points, for instance on both of the wide sides, 54 and 56, of the crank arm. Furthermore, thecrank arm 136 may also be obtained from a U-shaped forging as illustrated inFIGS. 18-26 . In the initial forging 126 for thecrank arm 136, the intermediate portion between theend portions extensions 129 spaced on either side of the longitudinal axis through the crank arm perform 126. Subsequently, theflaps 129 are formed over toward the longitudinal axis and produce thecavity 122 in thecrank arm 136, seeFIGS. 21-23 . Preferably, the resultingstructure 136 is then closed or fixed by weldingbead 138 along the edges of the formed over flaps orextensions 129 as illustrated inFIGS. 24-26 . This formation technique yields a crank arm having the features of the previously described embodiments.
Claims (18)
1. A process for the production of a hollow crank arm for a bicycle having an area for connection to the bottom bracket spindle and an area for connection of the pedal, wherein it forms a cavity and two solid end portions containing said areas located on opposite sides of said cavity.
2. A process according to claim 1 , wherein it comprises the step of forming the cavity with an opening that opens onto the area between the solid portions.
3. A process according to claim 1 , wherein it comprises the steps of forming holes for fixing the bottom bracket spindle and the pedal which do not communicate with the cavity.
4. A process according to claim 2 , wherein it comprises the step of closing the opening.
5. A process according to claim 4 , wherein it comprises the steps of forming a flap for integral closing which extends in the proximity of said opening and of fixing said flap along at least one part of an edge of the opening.
6. A process according to claim 5 , wherein the fixing of said flap is carried out by welding or bonding.
7. A process according to claim 6 , wherein it comprises the steps of: providing a separate closing element having a shape suited for fitting to the opening and fixing said closing element to the body.
8. A process according to claim 1 , wherein the cavity is obtained by means of hot drawing with a punch.
9. A process according to claim 1 , wherein the cavity is formed by fixing a closing element to a body in which a lowered area has been formed.
10. A process according to claim 9 , wherein the closing element is fixed to the crank arm body by means of welding or bonding.
11. A process according to claim 9 , wherein the lowered area is formed by machining with removal of material or plastic deformation.
12. A process according to claim 1 , wherein the body is formed by casting in a die and in that the cavity is formed by a filling element positioned in the die prior to casting of the molten material.
13. A process according to claim 12 , wherein the filling element is a core of porous material which remains inserted in the crank arm body.
14. A process according to claim 12 , wherein the filling element is extracted from the body of the crank arm after solidification of the molten material.
15. A process according to claim 1 , wherein the body is formed by the crosslinking, in a die, of a structural-fibre-based fabric embedded in a matrix of plastic material, in which the fibres are chosen in the group comprising carbon fibres, glass fibres, aramidic fibres, boron fibres, ceramic fibres, or any combination thereof.
16. A process according to claim 15 , wherein the cavity is formed by providing an extractable expandable core.
17. A process according to claim 16 , wherein the expandable core is made of thermally dilatable material.
18. A process according to claim 16 , wherein the cavity is formed by providing an inflatable element.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US11/837,209 US20080005905A1 (en) | 2002-03-19 | 2007-08-10 | Hollow crank arm for a bicycle and process for manufacturing the same |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP02425171.2 | 2002-03-19 | ||
EP02425171A EP1350714A1 (en) | 2002-03-19 | 2002-03-19 | Hollow crank arm for a bicycle, and process for manufacturing the same |
US10/391,705 US7258040B2 (en) | 2002-03-19 | 2003-03-19 | Hollow crank arm for a bicycle and process for manufacturing the same |
US11/837,209 US20080005905A1 (en) | 2002-03-19 | 2007-08-10 | Hollow crank arm for a bicycle and process for manufacturing the same |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US10/391,705 Division US7258040B2 (en) | 2002-03-19 | 2003-03-19 | Hollow crank arm for a bicycle and process for manufacturing the same |
Publications (1)
Publication Number | Publication Date |
---|---|
US20080005905A1 true US20080005905A1 (en) | 2008-01-10 |
Family
ID=27838217
Family Applications (3)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US10/391,705 Expired - Fee Related US7258040B2 (en) | 2002-03-19 | 2003-03-19 | Hollow crank arm for a bicycle and process for manufacturing the same |
US11/837,209 Abandoned US20080005905A1 (en) | 2002-03-19 | 2007-08-10 | Hollow crank arm for a bicycle and process for manufacturing the same |
US11/837,102 Abandoned US20080034919A1 (en) | 2002-03-19 | 2007-08-10 | Hollow crank arm for a bicycle and process for manufacturing the same |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US10/391,705 Expired - Fee Related US7258040B2 (en) | 2002-03-19 | 2003-03-19 | Hollow crank arm for a bicycle and process for manufacturing the same |
Family Applications After (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/837,102 Abandoned US20080034919A1 (en) | 2002-03-19 | 2007-08-10 | Hollow crank arm for a bicycle and process for manufacturing the same |
Country Status (5)
Country | Link |
---|---|
US (3) | US7258040B2 (en) |
EP (1) | EP1350714A1 (en) |
JP (1) | JP2003276671A (en) |
CN (3) | CN100333964C (en) |
TW (1) | TWI238138B (en) |
Cited By (6)
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US20180259345A1 (en) * | 2016-04-18 | 2018-09-13 | Beijing Didi Infinity Technology And Development C O., Ltd. | Systems and methods for recommending an estimated time of arrival |
US10363989B2 (en) * | 2016-11-04 | 2019-07-30 | Cherub Cycle Enterprise Co., Ltd. | Dual purpose cycle |
US11142280B2 (en) | 2016-03-24 | 2021-10-12 | The Hive Global, Inc. | Bicycle crank with spindle attachment structure |
US11351815B2 (en) | 2017-08-21 | 2022-06-07 | The Hive Global, Inc. | Bicycle cassette with clamping connection |
US11485449B2 (en) | 2015-09-01 | 2022-11-01 | The Hive Global, Inc. | Bicycle cassette with locking connection |
US11932351B2 (en) | 2020-07-17 | 2024-03-19 | The Hive Global, Inc. | Conical bicycle cassette sprocket structure |
Families Citing this family (16)
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EP1350714A1 (en) * | 2002-03-19 | 2003-10-08 | Campagnolo Srl | Hollow crank arm for a bicycle, and process for manufacturing the same |
EP1486412B1 (en) | 2003-06-10 | 2014-05-07 | Campagnolo S.R.L. | Bicycle pedal crank |
EP2130756B1 (en) | 2003-06-11 | 2012-10-03 | CAMPAGNOLO S.r.l. | Bicycle component and method for manufacturing such a component |
US7181823B2 (en) * | 2003-09-09 | 2007-02-27 | Jie Dong Zeng | Method for manufacturing integrated bicycle crank arm and spider assembly and the crank arm and spider assembly made thereby |
JP2005289166A (en) * | 2004-03-31 | 2005-10-20 | Sumitomo Metal Ind Ltd | Crank for bicycle, and its manufacturing method |
EP1818252B1 (en) * | 2006-02-14 | 2011-09-07 | CAMPAGNOLO S.r.l. | Bicycle pedal crank and method for manufactoring such a pedal crank |
US7530291B2 (en) * | 2006-07-13 | 2009-05-12 | Chang Hui Lin | Crank device for bicycle |
EP2230166B1 (en) * | 2009-03-16 | 2016-09-28 | Cycling Sports Group, Inc. | Unitary crank spindle assembly and method of fabrication |
FR2958193B1 (en) * | 2010-04-06 | 2012-06-29 | Saint Jean Ind | PROCESS FOR MANUFACTURING LIGHT ALLOY FORGED PARTS INCORPORATING FULL OR DRAWN THICKNESS SECTIONS |
US8616085B2 (en) * | 2010-08-18 | 2013-12-31 | Shimano Inc. | Bicycle crank assembly |
JP5860214B2 (en) * | 2011-02-18 | 2016-02-16 | 株式会社スギノエンジニアリング | Bicycle crank arm and method of manufacturing the same |
US9651138B2 (en) | 2011-09-30 | 2017-05-16 | Mtd Products Inc. | Speed control assembly for a self-propelled walk-behind lawn mower |
JP2019034686A (en) * | 2017-08-21 | 2019-03-07 | 株式会社シマノ | Crank arm |
FR3077751B1 (en) * | 2018-02-13 | 2020-01-24 | Saint Jean Industries | METHOD FOR MANUFACTURING A BICYCLE COMPONENT, BICYCLE COMPONENT AND BICYCLE CRANKSET |
TWI804619B (en) | 2018-05-11 | 2023-06-11 | 義大利商坎帕克諾羅公司 | Bicycle crankarm provided with electric/electronic system |
IT201800005299A1 (en) * | 2018-05-11 | 2019-11-11 | BICYCLE COMPONENT EQUIPPED WITH STRESS / DEFORMATION SENSOR COMPENSATED FOR TEMPERATURE |
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- 2003-03-19 US US10/391,705 patent/US7258040B2/en not_active Expired - Fee Related
- 2003-03-19 CN CNB031204899A patent/CN100333964C/en not_active Expired - Fee Related
- 2003-03-19 CN CNA2007101278071A patent/CN101108646A/en active Pending
- 2003-03-19 CN CNA200610091824XA patent/CN1876478A/en active Pending
- 2003-03-19 JP JP2003075358A patent/JP2003276671A/en active Pending
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2007
- 2007-08-10 US US11/837,209 patent/US20080005905A1/en not_active Abandoned
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Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US11485449B2 (en) | 2015-09-01 | 2022-11-01 | The Hive Global, Inc. | Bicycle cassette with locking connection |
US11142280B2 (en) | 2016-03-24 | 2021-10-12 | The Hive Global, Inc. | Bicycle crank with spindle attachment structure |
US20180259345A1 (en) * | 2016-04-18 | 2018-09-13 | Beijing Didi Infinity Technology And Development C O., Ltd. | Systems and methods for recommending an estimated time of arrival |
US10363989B2 (en) * | 2016-11-04 | 2019-07-30 | Cherub Cycle Enterprise Co., Ltd. | Dual purpose cycle |
US11351815B2 (en) | 2017-08-21 | 2022-06-07 | The Hive Global, Inc. | Bicycle cassette with clamping connection |
US11932351B2 (en) | 2020-07-17 | 2024-03-19 | The Hive Global, Inc. | Conical bicycle cassette sprocket structure |
Also Published As
Publication number | Publication date |
---|---|
TWI238138B (en) | 2005-08-21 |
US7258040B2 (en) | 2007-08-21 |
CN1445134A (en) | 2003-10-01 |
JP2003276671A (en) | 2003-10-02 |
CN100333964C (en) | 2007-08-29 |
CN1876478A (en) | 2006-12-13 |
TW200305526A (en) | 2003-11-01 |
US20080034919A1 (en) | 2008-02-14 |
EP1350714A1 (en) | 2003-10-08 |
CN101108646A (en) | 2008-01-23 |
US20030226422A1 (en) | 2003-12-11 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: CAMPAGNOLO S.R.L., ITALY Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:VALLE, MAURIZIO;PASQUA, PAOLO;REEL/FRAME:019680/0629;SIGNING DATES FROM 20030716 TO 20030806 |
|
STCB | Information on status: application discontinuation |
Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION |