Vehicle fenders – Buffer or bumper type
Reexamination Certificate
2000-04-24
2001-12-04
Pape, Joseph D. (Department: 3612)
Vehicle fenders
Buffer or bumper type
C293S120000, C293S121000, C293S122000, C052S749100, C052S749100, C052S749100
Reexamination Certificate
active
06325431
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a roll-formed product and a vehicle bumper using the same.
2. Prior Art
A roll-formed product which is in the form of a steel-made tubular configuration is widely used, in various fields, due to the fact that such a roll-formed product is very low in production cost. Today, there is a social request for producing the roll-formed product from much thinner steel sheet, which will contribute energy-saving. Meeting such a request, forming the roll-formed product can be achieved with the usage of a device which is produced at a low cost, with the result that together with a low cost of the raw material the provision of the roll-formed product at much lower cost becomes possible. However, sometimes employing the thinner steel sheet as the raw material of the roll-formed product may raise a problem in strength.
In the field of an automotive vehicle, roll-forming is used for manufacturing various components. In this field, each component is requested to be lightweight from a view point of improving fuel economy which leads to energy-saving. To comply with such a request, using thinner steel sheet is now on demand. However, each of the automotive vehicle components or parts must have a sufficient strength against an outer force applied thereto such as a collision impact or shock, which compels to use a steel sheet having an enough strength and a considerable thickness.
Typical roll-formed products used in automotive vehicles are vehicle bumpers. The vehicle bumper is secured to frontward and rearward sides of a vehicle body for the protection thereof upon collision. To absorb the shock upon collision, the vehicle bumper is requested to have a sufficient strength, while for improving the fuel economy the vehicle bumper has to be lightweight.
In the foregoing circumstances, Japanese Patent Laid-open Print No.Hei.07(1996)-246894 provides an end-closed tubular shaped vehicle bumper which is formed from a continually fed steel sheet having a tensile strength of not less than 6OKSI (413.7 MPa) and a thickness of not greater than 0.1 inches (2.54 mm).
However, using such a high tensile strength steel sheet brings restrictions with respect to roll-forming and cost when producing the roll -formed product. In detail, as the strength of the high tensile strength steel sheet increases, the formability becomes bad, thereby failing to constitute a designed outer profile of the roll-formed product and causing production problems such as lowering rolling speed and shortening the life of the rolling device. In addition, using the highly tensile steel sheet results in that the vehicle bumper becomes poor in shock absorbing ability.
SUMMARY OF THE INVENTION
In order to overcome the aforementioned problems or drawbacks, an object of the present invention is to provide a roll-formed product and a vehicle bumper using the same which are excellent in formability, which are of high strength causing an excellent shock absorbing ability, and which are produced at a low cost.
A first aspect of the present invention is to provide a roll-formed product which comprises:
a main body formed from a steel sheet having a tensile strength of not greater than 400 MPa; and
one or more locally reinforced portions provided to the main body.
In accordance with the first aspect of the present invention, the following effects or results are produced:
The low strength steel sheet having a tensile strength of not greater than 400 MPa is excellent in formability, which makes it possible to design an outer profile of the roll-formed product free. In addition, the excellent formability improves the productivity when the roll-formed product is in production and an at-a-low-cost availability of the low strength steel sheet per se makes it possible to produce the roll-formed product at a lower cost. Moreover, the reinforced portions retain the strength of the roll-formed product, while otherwise portions absorb the shock, whereby the roll-formed product becomes excellent in strength and shock-absorbing ability.
A second aspect of the present invention is to modify the roll-formed product of the first aspect in such a manner that the main body is made up of a first high strength portion extending in a lengthwise direction and strengthened, a first low strength portion extending in the lengthwise direction in continuous with the first high strength portion such that a strength of the first low strength portion remains unchanged, a second high strength portion extending in the lengthwise direction in continuous with the first low strength portion and strengthened, and a second low strength portion extending in the lengthwise direction in continuous with such that a strength of the second low strength portion remains unchanged, the main body being characterized in that a summation of a projection area of the first high strength portion and a projection area of the second high strength portion occupies 20% or above of a projection region whose one end portion perpendicular to the lengthwise direction, a central portion, and the other end portion perpendicular to the lengthwise direction are in coincidence with the first high strength portion, either of the first low strength portion and the second low strength portion, and the second high strength portion, respectively.
In accordance with the second aspect of the present invention, the following effects or results are produced: Due to the fact that the roll-formed product is strengthened along its lengthwise direction, such strengthening can be made successively or continually, thereby producing the roll-formed product in good productivity and at a lower cost. In addition, the summation of the projected areas of the first high strength portion and the second strength portion occupies 20% and above of the projection region, the roll-formed product from the low strength steel sheet can be made to equivalent with one which is produced from a high strength steel sheet.
A third aspect of the present invention is to modify the roll-formed product of the first aspect in such a manner that at least one of the first high strength portion and the second high strength portion is in the form of either of a concave configuration and a convex configuration.
In accordance with the third aspect of the present invention, the following effects or results are produced: providing such a concave or convex portion can be made without adding any element to the roll-formed product, thereby making the roll-formed product in much easier way, with the result that strengthening the roll-formed product can be established at a lower cost such that the weight of the product remains unchanged. In addition, concave configuration strengthening makes it possible to reinforce or strengthen the roll-formed product without changing its outer profile.
A fourth aspect of the present invention is to modify the roll-formed product of the first aspect in such a manner that the first high strength portion and the second strength portion are reinforced by means of heat treatment of the main body.
In accordance with the fourth aspect of the present invention, employing the heat treatment for locally reinforcing the roll-formed product brings that the reinforcing per se is made to be easier.
A fifth aspect of the present invention is to modify the roll-formed product of the fourth aspect in such a manner that the heat treatment is high-frequency quenching hardening.
In accordance with the fifth aspect of the present invention, applying high-frequency energy makes it possible to reinforce desired portions of the roll-formed product, thereby lowering the production cost thereof.
A sixth aspect of the present invention is to modify the roll-forming product of any one of the first, second, third, fourth, and fifth aspects in such a manner that the main body is used as a bumper beam of a vehicle bumper.
In accordance with the sixth aspect of the present invention, the bumper beam is of high strength, is excellent in shock-absorbing ability, and is pro
Aisin Seiki Kabushiki Kaisha
Blankenship Greg
Burns Doane , Swecker, Mathis LLP
Pape Joseph D.
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