A method for manufacturing a bicycle crank is revealed. After being extended, bent and forged, an aluminum alloy pipe becomes an L-shaped part formed by a cylindrical crankshaft portion and an oval crank portion integrally connected to each other. A plug is inserted into an outer end of the crank portion while a periphery of an outer end of the crankshaft portion is punched to form a shaft-connecting portion. An assembling hole is arranged at the outer end of the crank portion, corresponding to the plug. Thus a bicycle crank is produced. Thereby not only the assembly of the bicycle crank is easier and more convenient, the structural strength of the bicycle crank is increased effectively to against vibrations and impacts. The bicycle is lightweight and the bicycle crank is more streamlined so that consumers are attracted. Thereby the market competitiveness is increased.

Disclosed is a method for producing a forged crankshaft. This production method includes: a pressing step of pressing a part in a longitudinal direction (first region) of a bar-like member with a pair of first dies, thereby decreasing a cross sectional area of the first region; and a decentering step of decentering a second region of the bar-like member with a second die with the first region being held. The second region is at least a part of the region of the bar-like member excepting the first region. The decentering direction by the second die is a direction perpendicular to each of the pressing direction by the first dies and the longitudinal direction of the bar-like member.

Disclosed is a method for producing a forged crankshaft. This production method includes: a pressing step of pressing a part in a longitudinal direction (first region) of a bar-like member with a pair of first dies, thereby decreasing a cross sectional area of the first region; and a decentering step of decentering a second region of the bar-like member with a second die with the first region being held. The second region is at least a part of the region of the bar-like member excepting the first region. The decentering direction by the second die is a direction perpendicular to each of the pressing direction by the first dies and the longitudinal direction of the bar-like member.

A method of manufacturing a crankshaft includes the steps of: (1) forming a crankshaft blank via a first half and a second half; (2) measuring a plurality of surface variations between a predetermined surface in a first region and a corresponding predetermined surface in a second region of the crankshaft blank; (3) calculating centering offset data based on the plurality of surface variations; (4) machining a pair center holes based on the centering offset data; (5) machining a counterweight and a journal relative to the pair of center holes to produce a partially machined crankshaft; (5) milling and grinding the partially machined crankshaft to produce a finished machined crankshaft; and (6) rotating the finished machined crankshaft typically on the outermost main journals in a final balancing machine and then modifying the counterweights to eliminate undesirable vibration generated during the rotation and engine operation.

A method of manufacturing a crankshaft includes the steps of: (1) forming a crankshaft blank via a first half and a second half; (2) measuring a plurality of surface variations between a predetermined surface in a first region and a corresponding predetermined surface in a second region of the crankshaft blank; (3) calculating centering offset data based on the plurality of surface variations; (4) machining a pair center holes based on the centering offset data; (5) machining a counterweight and a journal relative to the pair of center holes to produce a partially machined crankshaft; (5) milling and grinding the partially machined crankshaft to produce a finished machined crankshaft; and (6) rotating the finished machined crankshaft typically on the outermost main journals in a final balancing machine and then modifying the counterweights to eliminate undesirable vibration generated during the rotation and engine operation.

A method for producing a forged crankshaft includes: a clumping step of holding a first region by clumping a first region of a bar-like material by a pair of first dies, and a decentering step of decentering a second region of the bar-like material with second dies while the first region is held. The second region is a pin-corresponding part which is to be the pin. The first region is a crank arm-corresponding part which is to be the crank arm. The decentering direction by the second die is a direction perpendicular to each of the clumping direction of the first dies and the longitudinal direction of the bar-like material, and is the same direction as the decentering direction of the corresponding pin. This improves material yield while suppressing increase in the facility cost.

A method for producing a forged crankshaft includes: a clumping step of holding a first region by clumping a first region of a bar-like material by a pair of first dies, and a decentering step of decentering a second region of the bar-like material with second dies while the first region is held. The second region is a pin-corresponding part which is to be the pin. The first region is a crank arm-corresponding part which is to be the crank arm. The decentering direction by the second die is a direction perpendicular to each of the clumping direction of the first dies and the longitudinal direction of the bar-like material, and is the same direction as the decentering direction of the corresponding pin. This improves material yield while suppressing increase in the facility cost.

A crankshaft (4) with a first central axis (A), has at least two main bearing journals (12), through which the first central axis (A) extends. At least one crankshaft web (10) is arranged between the main bearing journals (12), wherein the at least one crankshaft web (10) comprises two crank discs (14) connected with each other via a crankpin (16) with a second central axis (B). At least one crank disc (14) has a recess (26) with a planar bottom surface (28), wherein the recess (26) is adapted in the at least one crank disc (14) in such a way that the second central axis (B) of the crankpin (16) cuts the planar bottom surface (28). That planar bottom surface (28) is oriented at a right angle in relation to the direction of the second central axis (B) of the crankpin (16). A bore (30) with a third central axis (C) extend through the planar bottom surface (28) of the recess (26), through the at least one crank disc (14), and into the at least one crankpin (16). Also, a combustion engine (2), a vehicle (1) and a method for manufacture of a crankshaft (4) are disclosed.

A crankshaft (4) with a first central axis (A), has at least two main bearing journals (12), through which the first central axis (A) extends. At least one crankshaft web (10) is arranged between the main bearing journals (12), wherein the at least one crankshaft web (10) comprises two crank discs (14) connected with each other via a crankpin (16) with a second central axis (B). At least one crank disc (14) has a recess (26) with a planar bottom surface (28), wherein the recess (26) is adapted in the at least one crank disc (14) in such a way that the second central axis (B) of the crankpin (16) cuts the planar bottom surface (28). That planar bottom surface (28) is oriented at a right angle in relation to the direction of the second central axis (B) of the crankpin (16). A bore (30) with a third central axis (C) extend through the planar bottom surface (28) of the recess (26), through the at least one crank disc (14), and into the at least one crankpin (16). Also, a combustion engine (2), a vehicle (1) and a method for manufacture of a crankshaft (4) are disclosed.

A production method includes a forging step, a flash-trimming step, and a pressing step. In the forging step, a finish-forged product with flash is formed by an upper forging, die and a lower forging die. In the forging step, an excess portion is formed on at least one crankarm which is connected to a first or third pin, in a portion near the first or third pin, on an outer periphery of a lateral part near the upper forging die, such that the excess portion protrudes from the outer periphery. In the pressing step, the excess portion is pressed by an upper die such that the excess portion bulges toward a journal. This method allows production of a forged crankshaft with a reduced weight and a sufficient rigidity in a simple facility.