Technical Field The present invention relates to a flat type vibration motor, and more particularly, to a brush of a flat type vibration motor. •■■ ■• Still-• more particularly, the present invention relates to a brush of a flat type vibration motor capable of retaining its shape over a long duration of use in order to improve the reliability of the motor itself.

Background Art A conventional vibration motor includes an upper and a lower case that are joined together, a rotor shaft running from the upper case to the lower case, a stator with magnets mounted thereon, a rotor portion for emitting vibrations, and a plurality of brushes to electrically connect the stator and the rotor portion. In further detail, on the inside of the stator's lower case is a lower board, through which an outside electrical current can pass, and on which several magnets are sequentially and circularly stacked. Also, the rotor portion, which • is eccentrically weighted to cause vibration when it spins, is radially positioned, to spin around the rotor shaft. Fixed to the eccentrically weighted rotor are coils; and fixed to the lower area of the rotor is a lower board, whose lower portion contains a plurality of brushes that make contact with a commutator. The lower portions of the brushes are fixed to the lower board, and the upper portions make contact with the commutator, thereby electrically connecting the stator to the rotor portion. As explained above, the brush, being fixed to the lower board, is abutted on the commutator. Since the commutator is fixed to the rotor portion, its movements follow those of the rotor portion, which is connected to the rotor shaft in a manner that allows its axial movement along the shaft. Thus, axial movement of the rotor portion along the shaft can occur if the rotor portion is subject to an external shock or during the operation of the motor. When such rotor movement along the shaft occurs, the 5 displacement of the rotor portion exerts a load upon the brushes. When the brushes are subject to this load, their shapes can be permanently altered, which can lead to the severing of the electrical contacts between the brushes and the commutator. Moreover, in order to maintain a firm 10 contact between the brushes and the commutator, the upper portions of conventional brushes are pressed down on by the rotor portion, whereby the brushes' shapes are altered ipso facto. Under these circumstances, if a force is continually exerted upon the brushes, the brushes will deform at a faster •15 rate. . . A detailed explanation of the permanent deformation of such brushes will now be given. Because the width of conventional brush in flat type vibration motors is uniform along its length, a compression 20 load on the brush cannot be' evenly distributed,, and the brush's elasticity is weak. Furthermore, though the upper portion of the brush installed between the lower and upper boards is pressed upon by the upper board, the shape of the brush is not suitable to 25 evenly distribute the compression load at it bent portion, so that stress on the brush is concentrated in a localized area. Thus, the permanent deformation of the brush quickens and the product's durability diminishes. Additionally, when devices that require flat vibration 30 motors, such as cellular phones are dropped, the resulting substantial shock can permanently change the shape of the brushes- The deformed brushes can cause a disruption of electrical current flow between the stator and 'the rotor. Hence, the vibration motor and the cellular phone will not 35 function properly. Additionally, because the brush's curved upper portion is deformed and pressure on the brush is concentrated in a small area, the brush can be damaged. When a brush is permanently deformed, the entire vibration motor must be replaced.

Disclosure Technical Paroblem Accordingly, the present invention, is directed to a flat type vibration motor and brush of the same that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. An object of the present invention is to provide a flat type vibration motor capable of increased operational reliability. Another object of the present invention is to provide a flat type vibration motor capable of preventing the deformation of its brush and extending its operating life by increasing the elasticity and durability of its brush. .

Technical Solution To ach±eve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, there is provided a flat type vibration motor including: a case; a rotor shaft extending from one end to the other end of the case; a stator attached to the inside of the lower portion of the case; a rotor portion installed a predetermined distance from the stator and radially to spin around the rotor shaft; and a brush whose lower contact portion contacts the stator and whose upper contact port±on contacts the rotor portion. A bent portion of the brush bends and extends from the lower contact portion; and an upper contact portion bends and extends further from the bent portion to contact the rotor portion. The width of the brush becomes narrower from the lower contact port±on to the upper contact portion. According to another aspect of the present invention, there is provided a flat type vibration motor including: a case, a rotor shaft running from one end of the case to the other, a stator attached to the inside of a lower portion of the case; a rotor portion installed a predetermined distance from the stator and radially to spin around the rotor shaft; and a brush whose upper contact portion contacts the rotor portion and whose lower contact portion contacts the stator, thereby electrically connecting the stator to the rotor portion. The width of the brush becomes narrower from the lower contact portion to the upper contact portion. According to a further aspect of the present invention, there is provided a flat type vibration motor having a stator and an eccentrically rotating rotor portion spinning against the stator and a plurality of brushes, each brush including: a lower contact portion contacting the stator; a bent portion bending and extending from the lower contact portion; and an upper contact portion further extending from the bent portion to contact the rotor portion. The width of the brush becomes narrower from the lower contact portion to the upper contact portion.

Advantageous Effects According to the present invention, a flat type vibration motor and its brush can assume a new level of reliability and have a longer operating life. Also, by preventing the deformation of the brush, the motor can operate stably, and the motor's operating life and reliability increase.

Description of Drawings The accompanying drawings are included to provide a further understanding of the invention. In the drawings: Fig. 1 is a side-sectional view of a flat type vibration motor according to an embodiment of the present invention; Fig. 2 is a perspective view of a brush according to an embodiment of the present invention; Fig. 3 is a plan view of the brush in Fig. 2; Fig. 4 is a frontal view of the brush in Fig. 2; Fig. 5 is a perspective view of a brush according to another embodiment of trie present invention; Fig. 6 is a plan view of the brush in Fig. 5; and Fig. 7 is a frontal of the brush in Fig. 5.

Best Mode for Carrying out the Invention Hereinafter, preferred embodiments of the present invention will be described in detail with reference to accompanying drawings. Fig. 1 is a side-sectional view of a flat type vibration motor according to an embodiment of the present invention. Referring to Fig. 1, a flat type vibration motor 100 according to the present invention includes a case 110, a rotor shaft 120, a stator 130, a rotor portion 140, and a brush 150. More specifically, the case 110 has an upper case 111 and a lower case 115, and the upper and lower ends of the rotor shaft 120 respectively attach to the upper case 111 and lower case 115. The stator 130 has a lower board 131 attached to the inside of the lower case 115 and a plurality of magnets 135 that are circularly arranged on top of the lower board 131. A rotor portion 140 has an eccentric rotor 141 axially installed to spin around the upper portion of the rotor shaft 120 with a predetermined axial gap from magnets 135.* Attached to the rotor 141 are coils 143 of wound wire that spin with the rotor, a weight (not shown) , an upper board 145 on the lower portion of the rotor 141, and a commutator 147 formed on the lower portion of the upper board 145 and connected to the coils 143. Between the stator 130 and the rotor portion 140, and more specifically, in the space between the lower board 131 and the upper board 145 are a pair of brushes 150 that electrically connect the stator 130 with the rotor portion 140, allowing the flow of current therebetween. The brushes 150 are symmetrically centered around the rotor shaft 120. In embodiments of the present invention a brush is formed in a ladder shape for the sake of durability and elasticity, which will be explained while referring to -Figs. 2 through 4. Fig. 2 is a perspective view of a brush according to an embodiment of the present invention, Fig. 3 is a plan view of the brush in Fig. 2, and Fig. 4 is a frontal view of the brush in Fig. 2. Referring to Figs. 2 through 4, the brush 150 has a lower contact portion 151, a first bent portion 153, a second bent portion 155, a first extended portion 156, a second extended portion 157, and an upper contact portion 159. In further detail, the lower contact portion 151 is flat and rectangular and fixed to the lower board 131, and the first bent portion 153 bends and extends from one end of the lower contact portion 151 in a substantially perpendicular direction. The second bent portion 155 is bent from the top end of the first bent portion 153, and gradually rises from a horizontal plane as it moves away from the first bent portion 153. Also, the width of the second bent portion 155 gradually narrows as it moves away from the first bent portion 153, and its contour arcs in a curve. The first extended portion 156 extends from the narrower end of the second bent portion 155, and gradually narrows as it extends. The second extended portion 157 bends and extends upward from the narrower end of the first extended section 156 toward the upper board 145, and gradually becomes narrower as it extends upward. Finally, the upper contact portion 159 bends and extends from the narrower end of the second extended portion 157 in an upwardly convex flex to contact the commutator 147, and gradually becomes narrower towards its free end. Here, the first extended portion 156, second extended portion 157, and upper contact portion 159 are formed as a sequentially connected pair of prongs with a predetermined space between the two prongs. Because the first extended portion 156, second extended portion 157, and upper contact portion 159 are formed as a pair of prongs, the contact between the brush 150 and commutator 147 can be more reliable. The brush 150 according to an embodiment of the present invention is characterized by its second bent portion 155 having a gradually varying width. To elaborate, the width Wl of the end of the second bent portion 155 extending from first bent portion 153 and the width W2 of the end of the second bent portion 155 meeting the first extended portion 156 are of the following relative dimensions: Wl : W2 = 1.2-1.5 : 1. The brush 150 according to the present invention is also characterized by the respective end widths of extended portions 156 and 157 and upper contact portion 159 being different. To expatiate, the width W3. of the free end of the upper contact portion 159 and the width W2 at the juncture of the second bent portion 155 and the first extended portion 156 are of the following relative dimensions: W2 : W3 = 1 : 0.71-0.83. Also, because the width along the first 156 and second 157 extended portions, through to the upper contact portion 159 gradually decreases, the brush's elasticity can increase. The following relation of the respective widths is obtained: Wl : W2 : W3 = 1.2-1.5 : 1 : 0.71-0.83. According to an embodiment of a brush 150 of the present invention, the brush width gradually decreases when going from the lower board 131 to the upper board 145. Thus, an outside load, vibration, or shock transmitted to the brush 150 will be evenly distributed to its entirety, thereby increasing its reliability. 'Due to the structure of the brush 150, a load on the brush 150 (caused by the upper board 145 pressing on the brush 150) can be distributed evenly to the entirety of the second bent portion 155, thus preventing further brush deformation. In this way, permanent deformation of the brush 150 can be avoided, increasing the reliability of the brush and the vibration motor.

Mode for Invention Fig. 5 is a perspective view off a brush according to another embodiment of the present invention, Fig. 6 is a plan view of the brush in Fig. 5, and Fig. 7 is a frontal view of the brush in Fig. 5. Referring to Figs. 5 through 7, a brush 170 includes a lower contact portion 171, a first bent portion 173, a second bent portion 175, and an upper contact portion 178. In more detail, the lower contact portion 171 is flat and rectangular and fixed to the lower board 131. The first bent portion 173 bends and extends from one end of the lower, contact portion 171 in a substantially perpendicμlar direction. The second bent portion 175 bends and extends horizontally from the top end of the first bent portion 173, and gradually narrows in width as it moves away from the first bent portion 173. Also, the contour of the second bent portion 175 arcs in a curve. The upper contact portion 178 bends and extends from the narrower end of the second bent portion 175 towards the upper board 145, its width gradually narrowing towards its open end. The upper contact portion 178 is a pair of prongs with a predetermined space between the prongs, and its short portion 179 flexes convexly upward to contact the commutator (see 147 in F±g. 1) . To elaborate on the ladder-shaped brush 170, the width Wl where the first bent portion 173 and the second bent portion 175 meet, the width W2 where the second bent portion 175 and the upper contact portion 178, and the width W3 of the short portion's 179 free end have the following relative dimensions: Wl : W2 : W3 = 1.2-1.5 : 1 : 0.71-0.83. While the present invention has been described and illustrated herein with reference to the preferred embodiments thereof, it will be apparent to those skilled in the art that various modifications and variations can be made therein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention that come within the scope of the appended claims and their equivalents.

Industrial Applicability The ladder-shaped brush of the flat type vibration motor of the present invention gradually becomes narrower in width from the stator to the rotor. Due to this characteristic, the brush's durability and elasticity when subjected to outside shocks and loads increase. In addition, because loads, vibrat±ons, and shocks inflicted on the brush are softly dissipated over the entire brush, permanent deformation of the brush does not occur, and the reliability of the vibration motor is ameliorated.