SHIFTING SYSTEM FOR CHAIR TECHNICAL FIELD The present invention relates to a shifting system for chair, and more particularly to a shifting device that is attached to chair legs. In the shifting device with a wheel, when an occupant seats in the chair, the wheel ascends and is inserted into a storage cavity by the pressure of an occupant weight, thereby fixing the chair, while when the occupant rises up from the chair, the wheel descends and is protruded from the storage cavity, thereby enabling free movement of the chair.

BACKGROUND ART Conventionally, seating articles such as chairs are classified into two types, i. e., a stationary type without wheels and a mobile type with wheels.

The stationary type of the chair is fixed and immovable. Therefore, with this type of the chair, the occupant feels very stable and comfortable. But it is inconvenient to move this type of chair.

On the other hand, the mobile type of the chair is easily and freely moved anywhere. However, the mobile type of the chair is unstable, thereby the occupant feels uncomfortable. Moreover, since the mobile type of the chair

is considerably big in size and is non-elegant in design, this type of the chair has limits in using it in high-grade and/or luxury articles.

DISCLOSURE OF THE INVENTION In order to solve the above-described problems, the present invention provides provide a shifting device for chair. The shifting device comprises a base body with a storage cavity formed in a designated shape on the lower surface, a shaft formed on the bottom surface of the storage cavity, a driving plate engaged with the shaft to freely change a rotating direction of a wheel, a connection cylinder with a threshold formed on an edge of the bottom surface of the driving plate, a spring formed within the connection cylinder, and a wheel holder with the wheel attached to the end of the spring.

Preferably, a leaf spring in a cone shape is used as the spring to minimize the. spring size when pressed.

In another aspect of the present invention, a shifting device for chair comprises a threshold formed on the end of the storage cavity of the base body, an elevating plate attached to the end of the spring, a shaft formed on the lower surface of the elevating plate, a driving plate engaged with the shaft, and a wheel holder with a wheel formed on an edge of the bottom surface of the driving

plate..

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects, features and advantages of the present invention will be readily understood with reference to the following detailed description thereof provided in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and, in which: FIG. 1 is a perspective view of. a chair provided with a shifting device in accordance with the present invention; FIGs. 2A and 2B are cross-sectional views of a shifting device for, chair in accordance with a preferred embodiment of the present invention, respectively, in an insertion and a protrusion condition of a wheel; FIGs. 3A and 3B are cross-sectional views of a shifting device for chair in accordance with another preferred embodiment of the present invention, respectively, in an insertion and a protrusion condition of a wheel; and FIGs. 4A and 4B are diagrammatic front views of a chair leg provided with a shifting device of the present invention, respectively, in an insertion and a protrusion condition of a wheel.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a perspective view of a chair provided with a shifting device in accordance with the present invention.

FIGs. 2A and 2B are cross-sectional views of a shifting system for chair in accordance with a preferred embodiment of the present invention, respectively, in an insertion and a protrusion condition of a wheel. As shown in FIGs. 1,2A, and 2B, a base body 10 of a shifting device is prepared.

Herein, since the shifting device is attached to chair legs, the base body 10 needs to maintain the load of the chair. The base body 10 comprises a storage cavity 11 formed in a designated shape on the lower surface of the base body 10. A shaft 12 is formed on the bottom surface of the storage cavity 11. A driving plate 20 is engaged with the shaft 12 to freely change a rotating direction of a wheel 40. Ball bearings 13 are interposed between the bottom surface of the storage cavity 11 and the top surface of the driving plate 20, thereby enabling the more smooth rotating movement of the driving plate 20. A connection cylinder 21 with a threshold 21a is formed on an edge of the bottom surface of the driving plate 20. A spring 30 with elasticity is formed within the connection cylinder 21 and a wheel holder 41 with the wheel 40 is attached to the end of the spring 30.

Herein, a leaf spring in a cone shape is preferably

used as the spring 30 to minimize the spring size when pressed.

FIGs. 3A and 3B are cross-sectional views of a shifting system for chair in accordance with another preferred embodiment of the present invention, respectively, in an insertion and a protrusion condition of a wheel. In this embodiment, threshold 10a is formed on the end of the storage cavity 11 of the base body 10. A spring 30 with elasticity is attached to the bottom surface of the storage cavity 11 and an elevating plate 14 is attached to the end of the spring 30. A shaft 12 is formed on the lower surface of the elevating plate 14 and the driving plate 20 is engaged with the shaft 12t. The wheel holder 41 with the wheel 40 is formed on an edge of the bottom surface of the. driving plate 20. An auxiliary leg 22 is formed on an opposite edge of the bottom surface of the driving plate 20. The auxiliary leg 22 is distant from the ground in a protrusion condition of the wheel 40 but contacts the ground in an insertion condition of the wheel 40, thereby serving to prevent the incline of the elevating plate 14 when ascending.

FIGs. 4A and 4B are diagrammatic front views of a chair leg provided with the shifting device of the present invention, respectively, in an insertion and a protrusion condition of a wheel. The shape of the base body 10 of the shifting device may be variously modified correspondingly to

the shape of the chair leg A. Further, the base body 10 of the shifting device is attached to the chair leg A by a connection means such as a screw B or other means.

In accordance with the preferred embodiments of the present invention, the base body 10 of the shifting device is attached to the end of the chair leg Ai Therefore, when the chair is unoccupied, the wheel 40 descends and is protruded from the storage cavity 11 of the base body 10 by the elasticity of the spring 30, then the lower surface of the base body 10 is separated from the ground, thereby enabling free movement of the chair.

When an occupant seats in the chair, the spring 30 is pressed by the occupant weight, and the wheel 40 ascends and is inserted into the storage cavity 11 of the base body 10, then the lower surface of the base body 10 contacts the ground, thereby fixing the chair.

And, the base body 10 of the shifting device of the present invention may easily be attached to any easy chairs such as sofas as well as the conventional chairs.

Furthermore, since the wheel 40 is stored within the storage cavity 11 of the base body 10, the shifting device of the present invention simplifies and beautifies the exterior of the chair In the drawings and specification, there have been disclosed typical preferred embodiments of this invention

and although specific terms are employed, they are used in a generic and descriptive sense only not for purpose of limitation, the scope of this invention being set forth in the following claims.

INDUSTRIAL APPLICABILITY In the shifting system for chair of the present invention, when an occupant seats in the chair, the wheel ascends and is inserted into a storage cavity by the pressure of an occupant weight, thereby fixing the chair, while when the chair is vacant, the wheel descends and is protruded from the storage cavity, thereby enabling free movement of the chair. Further, the shifting system for chair of the present invention is easily attached to the conventional chairs and beautifies the exterior of the chair.