Machine element or mechanism – Gearing – Rotary bodies
Reexamination Certificate
2000-03-30
2001-12-18
Herrmann, Allan D. (Department: 3682)
Machine element or mechanism
Gearing
Rotary bodies
C029S893320, C029S893340, C029S893370, C148S586000, C420S008000
Reexamination Certificate
active
06330836
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to steel for a gear that is the best suited for molding cogs by component rolling, a gear that is made of the steel for the gear and is a drive plate gear used in starting of an engine, and a method for producing the gear.
2. Description of the Related Art
As steel for a gear of this type, there is S35C material defined in the Japanese Industrial Standard (JIS),for example. The S35C material includes C: 0.32 to 0.38%, Si: 0.15 to 0.35, Mn: 0.60 to 0.90%, P: 0.03% or less, S: 0.035% or less, and the balance of Fe and unavoidable impurity, by weight.
The drive plate gear transmits rotation of an engine to a transmission side and transmits rotation of a starter motor to the engine by a gear provided to an outer periphery of the drive plate gear.
Such a drive plate gear is usually produced by cold working by using the above S35C material. In other words, in producing the drive plate gear, a thick portion is molded on an outer periphery portion of the S35C material provided in a shape of a disc, and then, the gear is molded on an outer periphery of the thick portion by component rolling.
However, because hardness increases in molding the thick portion when the above S35C material is used, end portions of a cog (end portions in a width direction of the cog) are likely to crack in molding the gear. There is also a disadvantage of extremely short life of a gear-molding tool because of high hardness of the thick portion.
SUMMARY OF THE INVENTION
The present invention has been accomplished with the above circumstances in view and it is an object of the invention to provide steel for a gear, a drive plate gear, and a process for producing the drive plate gear for preventing cracking of end portions of a cog in molding a gear and for increasing life of the gear molding tool.
To achieve the above object, an invention according to a first aspect is steel for a gear formed of steel comprising C: 0.32 to 0.38%, Si: 0.1% or less, Mn: 0.60 to 0.90%, P:
0.03% or less, and S: 0.035% or less.
In the invention according to the first aspect with the above structure, percentages of the respective components are based on weight and the balance includes Fe (iron) and unavoidable impurity. The components other than Si correspond to S35C material In JIS. By setting Si at 0.1% or less, increase in hardness of the thick portion is smaller and elongation is improved as compared with the S35C material when cold working for increasing a thickness of the disc-shaped peripheral edge portion in an axial direction is applied. Therefore, it is possible to prevent cracking of end portions of the cog in molding the gear on the thick portion and to increase life of a gear molding tool. Moreover, by setting Si at 0.1% or less, a yield point rises to improve durability of the disc.
An invention according to a second aspect is a drive plate gear molded of the steel for the gear according to the first aspect, comprising: an arm (
1
); a rim (
2
) formed in an annular shape on an outer periphery portion of then arm (
1
), the rim (
2
) having a predetermined thickness in an axial direction; and a plurality of cogs (
3
) molded on an outer peripheral surface of the rim (
2
) by component rolling, wherein the rim (
2
) is retained by a molding support die (
6
) which has an inner periphery support surface (
61
a
) for supporting an inner peripheral surface of the rim (
2
) and which includes resistance means for providing resistance to a flow of the rim (
2
) in the component rolling; and the cogs (
3
) are molded on the rim(
2
) by the component rolling from an outer peripheral surface side while the rim (
2
) is retained by the molding support die (
6
).
In the invention according to the second aspect, because the cogs (
3
) are formed by component rolling on the outer peripheral surface of the rim (
2
) while supporting the inner peripheral surface of the rim (
2
) by the inner periphery support surface (
61
a
) and the resistance means for providing resistance to the flow of the rim (
2
) in the component rolling is provided to the inner periphery support surface (
61
a
), it is possible to suppress escaping of the rim pressed in the component rolling to end surface sides of the rim (
2
). Therefore, the rim (
2
) escapes only slightly in the component rolling, and thus, the accurate cogs (
3
) can be molded by component rolling without providing much extra material to the rim (
2
).
Although the resistance means suppresses the flow of the rim (
2
) in component rolling, the resistance means does not forcibly and firmly restrain the flow of the rim (
2
). Therefore, it is possible to suppress or reduce hardening and residual stress of material generated in the rim (
2
). Thus, molding cracking of bottom portions of the cogs (
3
) molded by component rolling can be prevented and accuracy of the cogs (
3
) can be improved.
Furthermore, by using the steel for the gear including the components of the present application, it is possible to improve durability of the arm (
1
) (a plate portion between the rim and the through holes (
11
), (
12
) for connection with the crankshaft side).
An invention according to a third aspect is a method for producing a drive plate gear molded of the steel for the gear according to the first aspect, comprising the step of: molding a plurality of cogs (
3
) by component rolling on an outer peripheral surface of a rim (
2
) which is formed in an annular shape on an outer periphery portion of an arm (
1
) and which has a predetermined thickness in an axial direction, wherein while the rim (
2
) is retained from an inner peripheral surface (
61
a
) side by a molding support die (
6
) which has an inner periphery support surface (
61
a
) for supporting an inner peripheral surface of the rim (
2
) and which includes resistance means for providing resistance to a flow of the rim (
2
) in the component rolling, the cogs (
3
) are molded on the outer peripheral surface of the rim (
2
) by the component rolling.
The invention according to the third aspect exhibits similar operations to the invention according to the second aspect.
Moreover, because the rim (
2
) is not restrained in a recessed manner in a restraining recessed portion, it is possible to maintain a large gap between a tool for component rolling and the inner periphery support surface (
61
a
) of the molding support die (
6
). Therefore, even when the material escapes to an end surface side in component rolling, the material is retained between the molding tool, for example, for component rolling and the molding support die (
6
), and therefore, force (F) for pushing the molding tool against the rim (
2
) does not increase. Thus, life of a component rolling tool such as the molding support die (
6
) can be increased.
Furthermore, because increase in hardness is small and elongation is improved in the steel for the gear including the components of the present application, it is possible to prevent cracking of end portions of the cog in molding the gear on the thick portion and to increase life of the gear molding tool.
An invention according to a fourth aspect is a drive plate gear molded of the steel for the gear according to the first aspect, comprising: a disc (
111
); amounting portion (
111
a
) for mounting the drive plate gear to a crankshaft (
120
) of an engine at a center portion of the disc (
111
); a mounting portion (
111
d
) for mounting the drive plate gear to a torque converter (
140
) at an outer periphery portion of the disc(
111
); and a cylindrical portion (
112
) formed with cogs (
113
) and provide on an outer peripheral edge of the disc (
111
), wherein an intermediate portion between the cylindrical portion (
112
) and the mounting portion (
111
a
) for mounting the drive plate gear to the crankshaft (
120
) is formed to be thin so as to absorb vibration of the torque converter (
140
) mounted to the drive plate gear and has flexibility; the cylindrical portion (
112
) is formed to be thick by increasing thicknesses of opposite end p
Ohya Masakiyo
Shibata Masato
Watanabe Hiroshi
Fujikiko Kabushiki Kaisha
Herrmann Allan D.
Kilpatrick & Stockton LLP
LandOfFree
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