Technical Field

[1] The present invention relates, in general, to continuously variable transmissions and, more particularly, to a continuously variable transmission which functions as a clutch to control speed and has an integrated structure, so that the continuously variable transmission can be used in various fields, for example, in a machining device, a vehicle, etc. Background Art

[2] Generally, in the case of apparatuses using power, for example, in vehicles, machining devices, etc., a transmission changes the speed and torque of power transmitted from a power source before it is output, rather than the power being directly used.

[3] Hitherto, as mechanical continuously variable transmissions having the above functions, belt or chain mechanical continuously variable transmissions have been mainly used.

[4] However, the belt or chain type mechanical continuously variable transmissions have the following problems.

[5] In the case of the belt transmission, if the belt tension is relatively low, a slipping phenomenon is probable. If the tension of the belt is excessively high, overload is induced, and contact surfaces between pulleys and the belt become worn. Furthermore, a foreign substance may be undesirably interposed between the pulley and the belt, with the result that power loss is caused by slipping therebetween.

[6] In the case of the chain transmission, although the gearshift thereof is continuous, because the connection between a chain and pulleys is discontinuous, impulsive sound attributable to contact between the chain and the pulleys is induced. In addition, due to the weight of the chain, centrifugal force increases when the chain rotates. Thus, there is a limit when it comes to increasing the speed or the size thereof.

[7] Meanwhile, as mechanical continuously variable transmissions, there is also a method involving changing speed using a rotating conical plate and a ring which come into contact with each other, in addition to a method involving changing the speed using the viscosity of oil between disks. However, in these cases, an apparatus is excessively enlarged and a separate body is required, so that the installation space thereof is also increased. As well, the efficiency of power transmission is relatively low. Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a continuously variable transmission in which elements for restraining or controlling speed to be transmitted have an integrated structure, thus reducing the volume and weight of the transmission, and preventing a drive unit from being damaged by overload.

[9] Another object of the present invention is to provide a continuously variable transmission which has a reduced installation space in an electric motor, thus reducing the entire size of the electric motor, and enhancing the efficiency of power transmission.

[10] A further object of the present invention is to provide a continuously variable transmission which further includes a torque control unit for controlling torque, so that depending on manipulation of the torque control unit, the continuously variable transmission can be used for controlling the speed of a device of large capacity, and output which is precisely changed in relation to the speed can be obtained. Technical Solution

[11] In order to accomplish the above objects, the present invention provides a continuously variable transmission, including: a housing having a space therein; a gearshift control unit installed in the space of the housing to control speed; an input unit transmitting an external power to the gearshift control unit, the input unit comprising: an input shaft protruding outside of the housing; and a connection part integrated with the input shaft and disposed in the housing; and an output unit outputting the power changed in speed by the gearshift control unit, the output unit having an output shaft coaxially provided with the input unit, such that a first end of the output shaft protrudes outside of the housing and a second end thereof is rotatably coupled to the input unit, and a flange provided on the second end of the output shaft, the flange having power transmission arms receiving the power changed in speed, with a roller provided on each of the power transmission arms.

[12] In order to accomplish the above objects, the present invention provides a continuously variable transmission, including: a housing; a gearshift control unit connected to an input unit supported by one end of the housing, the gearshift control unit controlling speed; and an output unit outputting power changed in speed by the gearshift control unit, the output unit having an output shaft coaxially provided with the input unit, such that a first end of the output shaft protrudes outside of the housing and a second end thereof is rotatably coupled to the input unit, and a flange provided on the second end of the output shaft, the flange having power transmission arms receiving the power changed in speed, with a roller provided on each of the power transmission arms.

[13] The input unit may be coaxially provided with the output unit to transmit the power changed in speed in one direction.

[14] Furthermore, the gearshift control unit may include: a cylindrical rotary body coupled to the input unit; a speed change unit provided in the cylindrical rotary body to control the speed; a compression unit coupled to an inner surface of the cylindrical rotary body and disposed in front of the speed change unit; and a speed control unit provided in front of the compression unit, the speed control unit being coupled at a portion thereof to the speed change unit.

[15] The speed change unit may include: a pair of outer raceways coupled to the cylindrical rotary body such that the outer raceways rotate along with the cylindrical rotary body, each of the pair of outer raceways having an annular shape, with an arc- shaped recessed surface formed in a circumferential inner surface of each of the pair of outer raceways; a pair of inner raceways having outer diameters less than inner diameters of the pair of outer raceways, the pair of inner raceways provided around a circumferential outer surface of the output unit, wherein the pair of inner raceways are threaded to each other, and each of the pair of inner raceways has an annular shape, with an arc-shaped recessed surface formed in a circumferential outer surface of each of the pair of inner raceways; a plurality of gearshift balls provided between the recessed surfaces of the inner and outer raceways, the gearshift balls being in contact with the recessed surfaces of the inner and outer raceways depending on adjustment of a distance between the inner and outer raceways, thus conducting planetary motion.

[16] The compression unit may include a support member fastened to the cylindrical rotary body and the speed control unit, and an elastic member provided between the support member and the speed change unit.

[17] The support member may be coupled to a circumferential inner surface of the cylindrical rotary body by one of screw coupling or forcibly fitting, and an extension pipe extends a predetermined length from a first end of the support member, with a worm wheel provided on a circumferential outer surface of the extension pipe. A torque control ring may be provided on a circumferential outer surface of the speed control unit. The torque control ring may be disposed on the first end of the support member and threaded over the circumferential outer surface of the speed control unit. A worm wheel may be provided on a circumferential outer surface of the torque control ring. A rotation drive unit may be provided on the worm wheel to operate the support member.

[18] The rotation drive unit may include: a pair of friction control shafts having worm gears engaging with the worm wheel of the support member, each of the pair of friction control shafts extending at both ends thereof outside of the cylindrical rotary body; friction control wheels disposed outside the cylindrical rotary body, the friction control wheels being coupled to the friction control shafts; and a friction ring provided in a circumferential inner surface of the housing, the friction ring having an annular shape, with a friction depression formed in a circumferential inner surface of the friction ring so that the friction control wheels are coupled to the friction depression.

[19] Furthermore, first gears may be respectively provided on both ends of each friction control shaft. The first gears may be disposed in the friction depression of the friction ring of the housing. A second gear may be provided on each of the friction control wheels. A third gear may be provided between each of the first gears and the corresponding second gear. A fourth gear may be provided between the second gear which is disposed on one of both ends of each of the friction control shafts and the corresponding third gear to couple the second and third gears to each other.

[20] The rotation drive unit may include: a friction control shaft having a worm gear engaging with the worm wheel, the friction control shaft extending at both ends thereof outside of the housing; and a motor coupled to one end of the friction control shaft.

[21] The speed control unit may include: a mounting pipe coupled to the output unit, wherein the inner raceways are provided on one end of the mounting pipe; a rotating pipe provided on a circumferential outer surface of the mounting pipe, with a worm wheel provided on one end of the rotating pipe; a worm gear engaging with the worm wheel of the rotating pipe; a gearshift shaft provided on both ends of the worm gear, the gearshift shaft protruding outside of the housing; and a motor coupled to one end of the gearshift shaft.

Advantageous Effects

[22] In the continuously variable transmission according to the present invention, power transmission between gearshift balls and raceways using frictional force therebetween can be precisely adjusted by appropriately controlling a worm wheel and a worm gear. Therefore, output rotating force (the change in speed) can be precisely controlled.

[23] Furthermore, even when shifting gears, rotating speed and revolution speed of the rotary members which conduct planetary motion can be precisely controlled by adjusting the distance between the raceways using the worm wheel and the worm gear.

[24] In addition, even when the speed is controlled, an elastic member maintains elastic force constant, so that torque can be maintained constant. As well, the present invention has the function as a clutch. Hence, the present invention does not require a separate clutch, thereby reducing the volume and weight of the transmission. Moreover, the continuously variable transmission of the present invention can be easily connected to various types of input or output units, so that the transmission can be used for a variety of purposes. [25] As well, the continuously variable transmission of the present invention further includes a speed control unit for controlling speed. Therefore, the continuously variable transmission can be used for controlling the speed of a device of large capacity, and output which is precisely changed in speed can be obtained.

Brief Description of Drawings [26] FIG. 1 is a side sectional view illustrating a continuously variable transmission, according to a first embodiment of the present invention; [27] FIG. 2 is an enlarged sectional view taken along line A-A of FIG. 1;

[28] FIG. 3 is a plan view illustrating the continuously variable transmission according to the first embodiment of the present invention; [29] FIGS. 4a and 4b are enlarged views showing a method for controlling the gearshift of the continuously variable transmission according to the first embodiment of the present invention; [30] FIG. 5 is a side sectional view illustrating a continuously variable transmission, according to a second embodiment of the present invention; [31] FIG. 6 is an enlarged sectional view taken along line B-B of FIG. 5;

[32] FIG. 7 is a plan view illustrating the continuously variable transmission according to the second embodiment of the present invention; [33] FIGS. 8A and 8B are enlarged views showing the operation of a frictional control wheel according to the second embodiment; [34] FIG. 9 is a side sectional view illustrating a continuously variable transmission, according to a third embodiment of the present invention; and [35] FIG. 10 is a plan view illustrating the continuously variable transmission according to the third embodiment of the present invention.

Best Mode for Carrying out the Invention [36] Hereinafter, a continuously variable transmission according to the present invention will be described in detail with reference to the attached drawings. [37] FIG. 1 is a side sectional view illustrating a continuously variable transmission, according to a first embodiment of the present invention. FIG. 2 is an enlarged sectional view taken along the line A-A of FIG. 1. FIG. 3 is a plan view illustrating the continuously variable transmission according to the first embodiment of the present invention. [38] As shown in FIGS. 1 through 3, the continuously variable transmission 10 according to the present invention includes a housing 100 which has a cylindrical structure which has an internal space 102 therein and is open on both ends thereof. The open ends of the cylindrical housing 100 are covered with covers 110. [39] The continuously variable transmission 10 further includes a gearshift control unit 200 which is installed in the internal space 102 of the housing 100 to receive external power and control the speed of output.

[40] The gearshift control unit 200 includes a cylindrical rotary body 210 which is open on both ends thereof. Furthermore, a stop protrusion 212 is provided on a first end of the circumferential inner surface of the rotary body 210. A depression 214 is formed in the circumferential inner surface of the rotary body 210 at a position adjacent to the stop protrusion 212. In addition, an internal threaded part 216 having a predetermined depth is formed on a second end of the circumferential inner surface of the rotary body 210 which is opposite to the first end on which the stop protrusion 212 is formed.

[41] Furthermore, a speed change unit 220 is installed in the cylindrical body 210. The speed change unit 220 functions to change the speed of the output.

[42] In detail, the speed change unit 220 includes first and second outer annular raceways

221 and 221a which respectively have on the circumferential inner surfaces thereof recessed surfaces 222 and 222a having arc-shaped cross-sections. The first and second outer raceways 221 and 221a are installed in the depression 214 using a retaining bar 218 such that the first and second outer raceways 221 and 221a can be rotated along with the cylindrical rotary body 210.

[43] Here, the first outer raceway 221 is closely fastened to the stop protrusion 212 of the cylindrical rotary body 210 and is thus prevented from moving. The second outer raceway 221a is provided such that it is movable on the depression 214 of the cylindrical rotary body 210 in the longitudinal direction of the cylindrical rotary body 210 under the guidance of the retaining bar 218.

[44] The speed change unit 220 further includes first and second inner annular raceways

223 and 223a which respectively have outer diameters less than the inner diameters of the first and second outer raceways 221 and 221a. Furthermore, recessed surfaces 224 and 224a are respectively formed in the circumferential outer surfaces of the first and second inner raceways 223 and 223a. In addition, the first and second inner raceways

223 and 223a are threaded to each other such that they can approach and move away from each other.

[45] In detail, the recessed surfaces 224 and 224a are respectively formed in the first and second inner raceways 223 and 223a at positions adjacent to each other. The recessed surfaces 224 and 224a respectively correspond to the recessed surfaces 222 and 222a of the first and second outer raceways 221 and 221a. Therefore, when the first and second outer raceways 221 and 221a and the first and second inner raceways 223 and 223a are installed in the cylindrical rotary body 210, the recessed surfaces 222, 222a,

224 and 224a form an annular doughnut shape. When one of the first and second inner raceways 223 and 223a rotates, the first and second inner raceways 223 and 223a approach or move away from each other because of the threaded coupling structure. [46] A plurality of protrusions 223b is provided on one surface of one of the first and second inner raceways 223 and 223a. It is preferable that the protrusions 223b be provided on the first inner raceway 223a.

[47] Furthermore, a plurality of gearshift balls 226, which have high hardness and stiffness, is installed in an annular space that is formed by the recessed surfaces 222, 222a, 224 and 224a of the first and second outer raceways 221 and 221a and the first and second inner raceways 223 and 223 a.

[48] The circumferential outer surfaces of the gearshift balls 226 come into frictional contact with the surfaces of the recessed surfaces 222, 222a, 224 and 224a, so that when the first and second outer raceways 221 and 221a rotate, the gearshift balls 226 perform planetary motion along the recessed surfaces 224 and 224a of the first and second inner raceways 223 and 223a.

[49] Meanwhile, a compression unit 230 is installed in the cylindrical rotary body 210 and disposed in front of the speed change unit 220.

[50] The compression unit 230 includes an elastic member 232 which is in contact with the sidewall of the second outer raceway 221a and elastically compresses the second outer raceway 221a towards the first outer raceway 221. The compression unit 230 further includes a support member 234 which has an external thread 235 on the circumferential outer surface thereof and is threaded to the circumferential inner surface of the cylindrical rotary body 210 to support the elastic member 232.

[51] It is preferable that the elastic member 232 be formed by overlapping several disk- shaped springs (disk springs), the central portions of which protrude in one direction, in order to ensure high elasticity. However, the elastic member 232 is not limited to the disk springs, and any spring can be used as the elastic member 232, so long as it has relatively high elasticity.

[52] Furthermore, a speed control unit 240 which is coupled at a portion thereof to the speed change unit 220 is provided in front of the compression unit 230.

[53] The speed control unit 240 includes a mounting pipe 242 and a rotating pipe 244.

The first and second inner raceways 223 and 223 a are seated onto the circumferential outer surface of a first end of the mounting pipe 242. The rotating pipe 244 surrounds the circumferential outer surface of the mounting pipe 242. To movably couple the rotating pipe 244 to the mounting pipe 242, the support member 234 is coupled to the circumferential outer surface of the rotating pipe 244. Protrusions 244a which alternate with the protrusions 223b of the second inner raceway 223a are provided on the rotating pipe 244. Furthermore, a worm wheel 245 is provided on the circumferential outer surface of a second end of the rotating pipe 244.

[54] As well, a worm gear 246 engages with the worm wheel 245 of the rotating pipe 244.

A gearshift shaft 247 which protrudes outside of the housing 100 is provided on both ends of the worm gear 246. A motor 248 for rotating the rotating pipe 244 is coupled to one end of the gearshift shaft 247.

[55] Furthermore, an input unit 300 is provided on a longitudinal center axis of the housing 100, so that external power is input to the gearshift control unit 200 through the input unit 300 to rotate the cylindrical rotary body 210.

[56] The input unit 300 includes an input shaft 310, which is supported by the corresponding cover 110 of the housing 100. A first end of the input shaft 310 extends outside and is coupled to a drive unit (not shown) which is separately provided outside of the transmission. The input unit 300 further includes a connection part 320 which is disposed in the housing 100 and coupled to the cylindrical rotary body 210 using a coupling means.

[57] In addition, an output unit 400 is coaxially provided at a position opposite to the input unit 300. Therefore, power is input from the input unit 300 into the gearshift control unit 200, is changed in speed through the gearshift control unit 200, and then is output through the output unit 400.

[58] The output unit 400 comprises an output shaft 410 which is fitted into the mounting pipe 242. A first end of the output shaft 410 extends outside of the housing 100, and a second end thereof is rotatably coupled to the input unit 300.

[59] Furthermore, a flange 420 is provided on the second end of the output shaft 410 at a predetermined position adjacent to the input 300. The output shaft 410 is connected to the speed change unit 220 through the flange 420.

[60] The flange 420 includes a plurality of power transmission arms 422 which extend into spaces defined between the gearshift balls 226 that are installed in the recessed surfaces 222, 222a, 224 and 224a of the first and second outer raceways 221 and 221a and the first and second inner raceways 223 and 223a of the speed change unit 220. A roller 424 which is in rolling contact with the surfaces of the corresponding gearshift balls 226 is provided on the end of each power transmission arm 422.

[61] Therefore, when the cylindrical rotary body 210 and the first and second outer raceways 221 and 221a are rotated by power input from the input unit 300, the gearshift balls 226 planetarily move along the recessed surfaces 224 and 224a of the first and second inner raceways 223 and 223a. Thus, power is changed in speed by contact between the gearshift balls 226 and recessed surfaces 222, 222a, 224 and 224a and then output through the flange 420 and the output shaft 410.

[62] Meanwhile, the internal space of the cylindrical rotary body 210 is filled with oil. For this, oil passages 243 are formed between the mounting pipe 242 and the rotating pipe 244. Preferably, the oil passages 243 are formed in the outer surface of the mounting pipe 242.

[63] The operation of the continuously variable transmission according to the present invention having the above-mentioned construction will be explained below. [64] First, the input shaft 310 is connected to the external drive unit (not shown). The input shaft 310 is rotated by the drive unit. [65] Thus, the cylindrical rotary body 210 and the first and second outer raceways 221 and 221a which are connected to the input shaft 310 are rotated together by the rotation of the input shaft 310. [66] The gearshift balls 226, which are disposed between the recessed surfaces 222 and

222a of the first and second outer raceways 221 and 221a and the recessed surfaces

224 and 224a of the first and second inner raceways 223 and 223a, are planetarily moved along the recessed surfaces 222, 222a, 224 and 224a. Power, which is changed in speed by the planetary movement of the gearshift balls 226, is output through the output shaft 410. [67] In detail, the planetary movement of the gearshift balls 226 is transmitted to the flange 420 through the power transmission arms 422, thus rotating the flange 420.

Then, the output shaft 410 is rotated by the rotation of the flange 420. As a result, power changed in speed is output to outside of the transmission. [68] The continuously variable transmission of the present invention is operated by the above-mentioned motion of the elements thereof. [69] The gear shifting operation of the continuously variable transmission of the present invention will be explained below. [70] FIGS. 4a and 4b are enlarged views showing a method for controlling the gearshift of the continuously variable transmission according to the first embodiment of the present invention. [71] As shown in FIG. 4a, in the state in which the gearshift balls 226 come into frictional contact with and planetarily move between the first and second outer raceways 221 and

221a and the first and second inner raceways 223 and 223a, the gearshift shaft 247 is rotated by the operation of the motor 248 of the speed control unit 240. Then, the rotating pipe 244 rotates in one direction along the circumferential outer surface of the mounting pipe 242 because of the engagement between the worm gear 246 and the worm wheel 245. [72] At this time, the second inner raceway 223a rotates, because the protrusions 223b provided on the second inner raceway 223a are alternately coupled to the protrusions

224a provided on the rotating pipe 244. [73] As such, when the second inner raceway 223a rotates, the second inner raceway 223a moves towards the first inner raceway 223, because they are threaded to each other.

Hence, a distance between the first and second inner raceways 223 and 223a reduces. [74] Furthermore, as shown in FIG. 4b, when a distance between the first and second outer raceways 221 and 221a is increased by adjusting the compression unit 230, contact positions between the gearshift balls 226 and the outer and inner raceways 221, 221a, 223 and 223a are changed from Pl and P2 to P3 and P4. Thereby, the radius of the revolution trajectory of the gearshift balls 226, each of which performs planetary motion, that is, revolves around the center axis of the transmission and rotates on its own axis, is increased, so that the rotating speed of the gearshift balls 226 is reduced. The rotation of the gearshift balls 226 which was reduced in speed is transmitted to the output shaft 410 through the power transmission arms 422. As a result, the speed of the output shaft 410 is reduced. Meanwhile, the gearshift operation for increasing speed can be implemented by adjusting the positions of the gearshift balls 226 in the direction opposite to that of the above-mentioned gearshift operation for reducing speed.

[75] Meanwhile, the internal space of the cylindrical rotary body 210 is filled with oil.

The oil is applied to the contact surfaces between the gearshift balls 226 and the outer and inner raceways 221, 221a, 223 and 223a. Therefore, sufficient frictional force is provided between the elements, so that power transmission can be reliably ensured. Furthermore, oil is injected into the cylindrical rotary body 210 through one of the two oil passages 243 which are formed in the outer surface of the mounting pipe 242, and the oil is discharged from the cylindrical rotary body 210 through the remaining one of the two oil passages 243. Hence, replacement of oil and the operation of cooling the gearshift balls 226 and the outer and inner raceways 221, 221a, 223 and 223a can be conducted at the same time. Thus, power loss is prevented from occurring due to variation in the physical properties of the oil. As well, the gearshift balls 226 and the outer and inner raceways 221, 221a, 223 and 223a can be cooled despite not using a separate cooling device.

[76] FIG. 5 is a side sectional view illustrating a continuously variable transmission, according to a second embodiment of the present invention. FIG. 6 is an enlarged sectional view taken along line B-B of FIG. 5. FIG. 7 is a plan view illustrating the continuously variable transmission according to the second embodiment of the present invention.

[77] As shown in FIGS. 5 and 7, a compression unit 230 is installed in a cylindrical rotary body 210 which is provided in a housing 100. The compression unit 230 includes an elastic member 232 which is in contact with a sidewall of a second outer raceway 221a and elastically compresses the second outer raceway 221a towards the first outer raceway 221. The compression unit 230 further includes a support member 234 which has an external thread 235 on the circumferential outer surface thereof. The support member 234 is threaded to the circumferential inner surface of the cylindrical rotary body 210 to support the elastic member 232. The compression unit 230 further includes a rotation drive unit 250 which rotates the support member 234. [78] Preferably, the elastic member 232 is formed by overlapping several disk-shaped springs (disk springs), the central portions of which protrude in one direction, in order to ensure high elasticity. However, the elastic member 232 is not limited to the disk springs, and any spring can be used as the elastic member 232, so long as it has relatively high elasticity.

[79] The rotation drive unit 250 includes an extension pipe 236 which extends from the support member 234, and a worm wheel 251 which is provided on the circumferential outer surface of the extension pipe 236. The rotation drive unit 250 further includes a pair of friction control shafts 254 which have worm gears 252 which engage with the worm wheel 251. Both ends of each friction control shaft 254 extend from the worm gear 252 to the outside of the cylindrical rotary body 210.

[80] Furthermore, first gears 264 are respectively provided on both ends of each friction control shaft 254. The first gears 264 are disposed in a friction depression 262 of the housing. A second gear 265 is provided on each friction control wheel 258. A third gear 266 is provided between each first gear 264 and the second gear 265. In addition, a fourth gear 267 is provided between the second gear 265 which is disposed on one of both ends of each friction control shaft 254 and the corresponding third gear 266.

[81] In the embodiment, the rotation drive unit 250 comprises a pair of rotation drive units

250 which engage with the worm wheel 251 at positions corresponding to each other. As shown in FIG. 6, in the rotation drive units 250, the fourth gear 267 is provided on only one end of each friction control shaft 254 such that the friction control shaft 254 can smoothly rotate.

[82] Therefore, when a friction ring 260 moves forwards or backwards, the friction control wheels 258 are rotated by friction with the friction ring 260. Then, the second gears 265 which are integrally provided on the friction control wheels 258 also rotate along with the friction control wheels 258. The rotating force of the friction control wheels 258 rotates the first gears 264 through the third gears 266 which engage with the second gears 265. Thereby, the friction control shafts 254 rotate, thus moving the support member 234 forwards or backwards. As a result, the elastic force of the elastic member 232 is changed, thus controlling the torque of the continuously variable transmission.

[83] In addition, the friction control wheels 258 are disposed outside the cylindrical rotary body 210 and connected to the friction control shafts 254.

[84] The friction ring 260 is provided on the circumferential inner surface of the housing

100 and has on the circumferential inner surface thereof a friction depression 262 to which the friction control wheels 258 are coupled.

[85] Here, the friction ring 260 can move only forwards and backwards on the circumferential inner surface of the housing 100 but cannot rotate. Various structures can be used as a control means for moving the friction ring 260 forwards or backwards. Preferably, the control means is constructed such that an actuating arm (not shown) extends from a portion of the friction ring 260 to the outside of the housing 100, and the friction ring 260 is moved forwards or backwards by operating the actuating arm in a manual manner or using a motor.

[86] The general operation, in other words, the method of controlling the gearshift, of the continuously variable transmission of the second embodiment having the above- mentioned construction is almost the same as that of the prior embodiment, therefore further explanation is deemed unnecessary.

[87] Only, the operation of the friction control wheel according to the second embodiment of the present invention will be explained below.

[88] As shown in FIG. 8, in the state in which the friction control wheels 258 rotate along with the cylindrical rotary body 210, when the friction ring 260 is moved forwards or backwards, the friction control wheels 258 come into contact with one of the sidewalls 264 of the friction depression 262 of the friction ring 260. Then, the friction control wheels 258 are rotated in a forward or reverse direction.

[89] Hence, when the friction control wheels 258 are rotated after the friction ring 260 is moved forwards or backwards, the support member 234 is also rotated by the worm wheel 251 which engages with the worm gears 252 of the friction control shafts 254 connected to the friction control shafts 254. Thus, the support member 234 which rotates moves forwards or backwards with respect to the cylindrical rotary body 210 because of the engagement between the threaded part 216 of the cylindrical rotary body 210 and the threaded part 235 of the support member 234.

[90] Depending on the forward or backward movement of the support member 234, the compression force with which the elastic member 232 supported by the support member 234 compresses the second outer raceway 221a is controlled.

[91] In other words, when the support member 234 moves forwards and pushes the elastic member 232, the elastic member 232 compresses the second outer raceway 221a towards the first outer raceway 221.

[92] Then, the first and second outer raceways 221 and 221a push the gearshift balls 226 which are in the recessed surfaces 222 and 222a towards the first and second inner raceways 223 and 223a, thus increasing friction therebetween. Thus, the gearshift balls 226 are brought into closer contact with the recessed surfaces 222, 222a, 224 and 224a of the outer and inner raceways 221, 221a, 223 and 223a, so that a torque transmission rate between the gearshift balls 226 and the outer and inner raceways 221, 221a, 223 and 223a is increased.

[93] Conversely, when the support member 234 is moved backwards, the compression force of the elastic member 232 is reduced. Thus, friction between the gearshift balls 226 and the outer and inner raceways 221, 221a, 223 and 223a is reduced. Thereby, the torque transmission rate is also reduced.

[94] When the support member 234 is further moved backwards, the gearshift balls 226 are completely removed from the outer and inner raceways 221, 221a, 223 and 223 a. Then, friction between the gearshift balls 226 and the outer and inner raceways 221, 221a, 223 and 223a becomes zero. In this case, torque can no longer be transmitted between the elements, in other words, the clutching operation is implemented.

[95] Therefore, in the present invention, power interruption can be conducted only by the internal construction of the continuously variable transmission without using a separate clutch mechanism. Thus, compared to the conventional continuously variable transmission using a clutch, the size and weight of the transmission are reduced. In addition, power loss attributable to the clutch can be prevented.

[96] FIG. 9 is a side sectional view illustrating a continuously variable transmission, according to a third embodiment of the present invention. FIG. 10 is a plan view illustrating the continuously variable transmission according to the third embodiment of the present invention.

[97] As shown in FIGS. 9 and 10, a support member 234 is forcibly fitted into a cylindrical rotary body 210 which is installed in an internal space 102 of the housing 100. The support member 234 supports an elastic member 232 which compresses a second outer raceway 221a. An external threaded part 244a is formed on a circumferential outer surface of a rotating pipe 244. A torque control ring 500 is threaded over the circumferential outer surface of the rotating pipe 244. A worm wheel 510 is provided on the circumferential outer surface of the torque control ring 500.

[98] Furthermore, a rotation drive unit 520 engages with the worm wheel 510 of the torque control ring 500. The rotation drive unit 520 includes a rotary shaft 524 which protrudes to the outside of the housing 100. The rotary shaft 524 has thereon a worm gear 522 which engages with the worm wheel 510. One end of the rotary shaft 524 which protrudes to the outside of the housing 100 is connected to a motor 526.

[99] The general operation, in other words, the method of controlling the gearshift, of the continuously variable transmission of the third embodiment having the above- mentioned construction is almost the same as that of the prior embodiments, therefore further explanation will be omitted.

[100] Only, in this embodiment, when the motor 526 of the rotation drive unit 520 is operated, the rotary shaft 524 rotates, thus rotating the worm wheel 510 which engages with the worm gear 522 of the rotary shaft 524. Thereby, the torque control ring 500 which is threaded over the rotating pipe 244 moves in the axial direction along the rotating pipe 244, thus moving the support member 234 in the axial direction.

[101] That is, when the torque control ring 500 moves forwards, it pushes the support member 234. Then, the support member 234 slides forwards and maintains the state in which it is in close contact with the circumferential inner surface of the cylindrical rotary body 210.

[102] Here, depending on displacement of the support member 234, the compression force of the elastic member 232 is adjusted. For example, when the support member 234 pushes the elastic member 232, the second outer raceway 221a is compressed towards the first outer raceway 221 by the elastic member 232.

[103] In this case, the gearshift balls 226 which are in the recessed surfaces 222 and 222a of the first and second outer raceways 221 and 221a are pushed towards the first and second inner races 223 and 223a. Thus, the gearshift balls 226 are brought into closer contact with the recessed surfaces 222, 222a, 224 and 224a, so that friction therebetween increases.

[104] Conversely, when the motor 526 is operated such that the rotation drive unit 520 reversely rotates, the torque control ring 500 moves backwards through the external threaded part 244a of the rotating pipe 244. When the torque control ring 500 moves backwards, the support member 234 which compresses the elastic member 232 also slides backwards along the circumferential inner surface of the cylindrical rotary body 210.

[105] Then, the force with which the elastic member 232 compresses the second outer raceway 221a is reduced. Hence, friction between the gearshift balls 226 and the outer and inner raceways 221, 221a, 223 and 223a is reduced, so that a torque transmission rate therebetween is reduced.

[106] When the support member 234 is moved further backwards, the gearshift balls 226 are completely removed from the outer and inner raceways 221, 221a, 223 and 223 a. Then, friction between the gearshift balls 226 and the outer and inner raceways 221, 221a, 223 and 223a becomes zero. In this case, torque can be no longer transmitted between the elements, in other words, the clutching operation is implemented.

[107] Meanwhile, the gear shifting operation of the continuously variable transmission 10 according to the third embodiment remains the same as that of the prior embodiment, therefore further explanation will be omitted.

[108] Only, in this embodiment, while the elastic member 232 compresses the first outer raceway 221, the distance between the first and second inner raceways 223 and 223a can be reduced or increased by rotating the rotating pipe 244.

[109] In detail, when the rotating pipe 244 rotates in one direction, the distance between the first and second inner raceways 223 and 223a which engage with each other through the threaded parts is reduced. Simultaneously, the torque control ring 500 which is threaded over the rotating pipe 244 is moved in the reverse direction, that is, backwards. Thus, the distance between the first and second outer raceways 221 and 221a is increased.

[110] Here, even though the second outer raceway 221a is moved backwards in the direction away from the gearshift ball 226 and the elastic member 232 is moved backwards, the support member 234 is also moved backwards along with the torque control ring 500 which is threaded over the rotating pipe 244. Hence, the elastic force of the elastic member 232 can be maintained constant despite the second outer raceway 221a being moved backwards. As a result, the torque of the transmission can be maintained constant even when implementing the gear shifting operation.

[I l l] Although the preferred embodiments of the continuously variable transmission according to the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. Industrial Applicability

[112] As described above, the present invention provides a continuously variable transmission which can function as a clutch to control speed and has an integrated structure, so that the continuously variable transmission can be used in various fields, for example, in a machining device, a vehicle, etc.