Patent Publication Number: US-6901778-B2

Title: Clutch apparatus for washing machine

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a clutch apparatus for a washing machine, and more particularly, to a clutch apparatus for a washing machine for controlling rotary power transmitted from a driving motor to a basket shaft using electromagnetic force. 
   2. Description of the Background Art 
     FIG. 1  is a vertical sectional view for a washing machine with a clutch apparatus according to a conventional technology. 
   In general, a washing machine, as shown in  FIG. 1 , includes a case  111  for forming a housing space inside, a tub  113  installed in the case  111 , the tub  113  for storing water inside, a spin basket  115  rotatably positioned in the tub  113 , the spin basket  115  for washing laundry, a pulsator  119  positioned in the spin basket  115  to be in a relative rotary motion with respect to the spin basket  115 , the pulsator  119  for forming a water current, and a driving motor  125  formed in the lower portion of the tub  113 , the driving motor  125  for providing driving power to the spin basket  115  and the pulsator  119 . 
     FIG. 2  is a vertical sectional view showing the clutch apparatus according to the conventional technology, which is included in the above washing machine. 
   A basket shaft  117  formed of a hollow member on the bottom of the spin basket  115  is combined with the spin basket  115 . The basket shaft  117  is rotatably supported to the tub  113  and a bearing housing  130  by bearings  114 . 
   A pulsator shaft  121  that rotates while being directly coupled with the driving motor  125  so as to rotate the pulsator  119  is inserted into the basket shaft  117 . The pulsator shaft  121  is supported to the basket shaft  117  by bearings  120  so as to be in the relative rotary motion. 
   The driving motor  125  includes a stator  129  fixed to the lower portion of the bearing housing  130  fixed to the tub  113  and a rotor  127  connected from the outer circumference of the stator  129  to the center of the stator  129  and combined with the pulsator shaft  121 . 
   In particular, a clutch device  131  is included between the bearing housing  130  and the rotor  127  so as to selectively transmit the rotary power generated by the driving motor  125  to the basket shaft  117 . 
   The clutch device  131  includes a solenoid actuator  137  fixed to the lower portion of the bearing housing  130 , the solenoid actuator  137  for generating electromagnetic force, a coupling member  133  combined with around the basket shaft  117 , the coupling member  133  for transmitting or intercepting the rotary power while being in an up and down motion due to the electromagnetic force of the solenoid actuator  137 , thus being combined with or being separated from a serration member  122  fixed to the rotor  127 , a spring member  141  installed between the coupling member  133  and the bearing housing  130 , the spring member  141  for providing elasticity to the coupling member  133  so that the coupling member  133  moves due to the electromagnetic force and then, is returned to an original position. 
   The solenoid actuator  137  includes a solenoid coil  138  positioned on the outer circumference of the coupling member  133 , the solenoid coil  138  for forming an electric field, and a solenoid case  139  fixed to the bearing housing  130 , the solenoid case  139  for supporting the solenoid coil  138 . 
   The coupling member  133  includes a serration coupling  134   a  combined with around the basket shaft  117  by a serration method, the serration coupling  134   a  combined with or separated from the serration member  122  and a magnetic coupling  134   b  integrally fixed to around the serration coupling  134 , the magnetic coupling  134   b  for generating force corresponding to the solenoid coil  138 . 
   That is, a shaft tooth  118  and a rotor tooth  123  are respectively formed on the outer circumference of the basket shaft  117  and the outer circumference of the serration member  122 . A coupling tooth  135  is formed on the inner circumference of the serration coupling  134   a . The coupling tooth  135  transmits the rotary power of the driving motor  125  to the basket shaft  117  or intercepts the rotary power of the driving motor  125  from the basket shaft  117  while being in the up and down motion along the shaft tooth  118 , thus combined with or separated from the rotor tooth  123 . 
   The operation of the washing machine with the clutch apparatus according to the conventional technology will now be described. 
   When the laundry is washed or is dried after finishing washing the laundry while integrally rotating the spin basket  115  and the pulsator  119 , the laundry is washed/dried by driving the driving motor  125  in a state where power is not supplied to the solenoid actuator  137 , that is, the solenoid actuator  137  is turned off. 
   At this time, the coupling tooth  135  simultaneously gears with and is combined with the shaft tooth  118  and the rotor tooth  123  in a state where the coupling member  133  moves downward due to the elasticity of the spring member  141 . Therefore, the spin basket  115  integrally rotates together with the pulsator  119 . 
   When the laundry is washed while rotating only the pulsator  119  in a state where the spin basket  115  is stopped, the power is applied to the solenoid actuator  137 . The electromagnetic force generated by the solenoid coil  138  forms a magnetic path for connecting the magnetic coupling  134   b  of the coupling member  133 , the central region of the rotor  127 , and the basket shaft  117  to each other via the bearing housing  130  positioned in the upper portion of the solenoid case  139  and the solenoid case  139 . At this time, the magnetic force operates as attraction in the direction, where magnetic reactance is minimized, that is, the direction, where the magnetic coupling  134   b  of the coupling member  133  approaches to the bottom of the solenoid case  139 . 
   Accordingly, the coupling tooth  135  of the coupling member  133  is separated from the rotor tooth  123  and is combined with only the shaft tooth  118 , the rotary power transmitted from the driving motor  125  is not transmitted to the spin basket  115  and is transmitted to only the pulsator  119 . 
   When the power supplied to the solenoid actuator  137  is intercepted in such a state, the coupling member  133  falls due to the elasticity of the spring member  141  and self-weight. Accordingly, the coupling tooth  135  simultaneously gears with the shaft tooth  118  and the rotor tooth  123 . 
   However, in the clutch apparatus of the washing machine according to the conventional technology, since the solenoid actuator  137  is formed to use direct current (DC) power, an additional DC power supply circuit for supplying the DC must be included. Also, flux leaks since many parts that can be magnetized are arranged around the solenoid actuator  137 . In particular, since the thickness of the bearing housing  130  and the thickness of the solenoid case  139  are about 2 mm, respectively, thus the degree of self-saturation is high, the leakage of the flux deteriorates. 
   Also, the magnetic force becomes larger than motive power for raising the coupling member  133  at an initial stage as the coupling member  133  rises, thus the distance between the coupling member and the solenoid coil becomes narrower. Accordingly, when the coupling member  133  rises, excessive magnetic force is generated. Also, when the coupling member  133  rises and reaches the final position, the magnetic force becomes stronger. Accordingly, the coupling member  133  collides with the bearing housing  130 , thus causing collision noise. 
   When the elasticity of the spring member  141  increases so as to rapidly fall the coupling member  133  against the magnetic force caused by residual flux, a holding voltage applied to the solenoid coil  138  must be increased in order to maintain the state where the coupling member  133  rises. Accordingly, consumption of power increases. 
   SUMMARY OF THE INVENTION 
   Therefore, an object of the present invention is to provide a clutch apparatus of a washing machine, which is capable of preventing the generation of collision noise that can be caused when a coupling member rises by letting a clutching operation occurs using repulsive force that pushes the coupling member upward and of reducing the amount of consumption of power for maintaining a state where the coupling member rises by preventing the increase of the compression force of a spring and the increase of a holding voltage according to residual flux after the coupling member rises. 
   Another object of the present invention is to provide a clutch apparatus of a washing machine, which is capable of simplifying the structure of the clutch apparatus and of reducing the consumption of the power by including a trans in order to supply another voltage to a solenoid coil according to the position of the coupling member. 
   To achieve these and other advantages and in accordance with the purposes of the present invention, as embodied and broadly described herein, there is provided a washing machine, comprising a spin basket rotatably installed in a tub, a pulsator positioned in the spin basket to be in a relative rotary motion, a driving motor installed in the lower portion of the tub, a pulsator shaft directly connected from the driving motor to the pulsator, the pulsator shaft for transmitting rotary power, a basket shaft connected from the outside of the shaft to the spin basket so as to form a dual shaft structure together with the pulsator shaft, and a clutch means for transmitting power of the driving motor to the basket shaft or intercepting the power of the driving motor from the basket shaft. The clutch means comprises a coupling member comprising a magnetic member at least in one part, combined around the basket shaft, and combined with a rotor of the driving motor in a state where the coupling member moves downward, the coupling member for transmitting the rotary power of the driving motor to the basket shaft and a solenoid actuator comprising a solenoid coil and fixed to the lower portion of the tub, the solenoid actuator for supplying electromagnetic repulsive force between the solenoid actuator and the coupling member so that the coupling member is separated from the rotor of the driving motor, to thus push the coupling member upward. 
   The coupling member is combined with the basket shaft and the rotor of the driving motor in a serration method, to thus be in an up and down motion. 
   A bearing housing for supporting the basket shaft is fixed on the bottom of the tub and the solenoid actuator is supported to the bearing housing. 
   An elastic means for supplying elasticity so that the coupling member rapidly moves downward when electromagnetic repulsive force is cancelled is comprised between the coupling member and the bearing housing. 
   The coupling member comprises a cylindrical non-magnetic coupling combined with the basket shaft, the non-magnetic coupling combined with or separated from the rotor of the driving motor, while being in an up and down motion, a ring-shaped conductive coupling corresponding to the solenoid actuator in an up and down direction and fixed to the upper end of the non-magnetic coupling, a ring-shaped magnetic coupling formed of a magnetic member and fixed to the upper end of the non-magnetic coupling, which is the center of the conductive coupling. 
   The non-magnetic coupling is formed of synthetic resin. A coupling tooth axially and longitudinally formed in the inner circumference of the non-magnetic coupling so that the coupling tooth is combined with the basket shaft by a serration method. 
   The conductive coupling is formed of a metal having conductivity. A uniform opening is formed between the conductive coupling and the magnetic coupling in a radius direction. 
   The lower end of an elastic means supported by the lower portion of the tub, the lower end of the elastic means for supplying elasticity to the coupling member is inserted into the opening between the conductive coupling and the magnetic coupling. 
   The solenoid actuator comprises a solenoid coil positioned around the coupling member and a solenoid case fixed to the lower portion of the tub, the solenoid case for supporting the solenoid coil. 
   A bearing housing for supporting the basket shaft is installed in the lower portion of the tub and the solenoid case is fixed to the bearing housing. 
   The solenoid case is formed of a magnetic member. A plurality of axial slits are formed in the solenoid case. The slits are uniformly formed in the solenoid case to be separated from each other by a predetermined distance in the direction of a circumference. 
   The solenoid case comprises a coil fixing portion having a cylindrical portion and a bottom portion and having the solenoid coil  53  inside and a flange portion extended from the upper end of the coil fixing portion in the direction of a radius and fixed to the lower portion of the tub. 
   The washing machine further comprises a transformation operating means for applying voltages of different levels to the solenoid coil according to the position of the coupling member. The transformation operating means can supply the voltages of the different levels to the solenoid coil during an initial operation for generating electromagnetic force so as to move the coupling member  41  upward and during a maintaining operation for maintaining a state where the coupling member is completely moved upward. 
   The transformation operating means comprises a position sensor for sensing the position of the coupling member, a trans installed on a line for supplying power to the solenoid coil, the trans for supplying the voltages of different levels, and a switch means installed on a line between the trans and the solenoid coil, the switch means for selecting one among the voltages of the different levels, which are provided by the trans, according to a signal of the position sensor. 
   The switch means is a relay switch operated according to a signal of a control unit receiving the signal of the position sensor. 
   The clutch apparatus of the washing machine according to the present invention is repulsive type unlike a conventional attractive type clutch apparatus. Accordingly, it is possible to prevent the collision noise that can be generated when the coupling member rises. Also, it is possible to reduce the amount of power consumption for maintaining the state where the coupling member rises. 
   The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
     In the drawings: 
       FIG. 1  is a vertical sectional view of a washing machine with a clutch apparatus according to a conventional technology; 
       FIG. 2  is a vertical sectional view showing the clutch apparatus shown in  FIG. 1  in detail; 
       FIG. 3  is a vertical sectional view showing a clutch apparatus according to an embodiment of the present invention; 
       FIG. 4  is an enlarged view showing the clutch apparatus shown in  FIG. 3 ; 
       FIG. 5  is a perspective view showing a coupling member according to the present invention; 
       FIG. 6  is a perspective view showing a solenoid case according to the present invention; 
       FIG. 7  shows a control circuit of a clutch apparatus according to the present invention; 
       FIGS. 8A and 8B  show the distribution of a magnetic field and the distribution of eddy current abandoned to the inside of conductive coupling in the position where the coupling member according to the present invention initially operates; 
       FIGS. 9A and 9B  show the distribution of a magnetic field and the distribution of eddy current abandoned to the inside of conductive coupling in the position where the coupling member according to the present invention completely rises; and 
       FIG. 10  is a graph comparing the magnetic force according to the displacement of the coupling member of an attractive type clutch apparatus according to a conventional technology with the magnetic force according to the displacement of the coupling member of a repulsive type clutch apparatus according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An embodiment of a clutch apparatus of a washing machine according to the present invention will now be described with reference to the attached drawings. 
   A plurality of embodiments of the clutch apparatus of the washing machine according to the present invention can exist. However, a preferred embodiment will now be described. 
     FIG. 3  is a vertical sectional view showing a washing machine with a clutch apparatus according to an embodiment of the present invention.  FIG. 4  is an enlarged view of main portions of FIG.  3 . 
   Referring to  FIG. 3 , a washing machine using the clutch apparatus according to the present invention includes a case  11 , a tub  13  supported to the inside of the case  11 , the tub  13  for storing water, a spin basket  15  rotatably installed inside the tub  13 , the spin basket  15  for washing laundry, a pulsator  29  installed inside the spin basket  15  to be in a relative motion with respect to the spin basket  15 , and a driving motor  35  fixed to the lower portion of the tub  13 , the driving motor  35  for rotatively driving the spin basket  15  and the pulsator  29 . 
   Referring to  FIG. 4 , the spin basket  15  is combined with a basket shaft  17  formed of a hollow member on the bottom of the spin basket  15 . The basket shaft  17  is rotatably supported to bearing housings  21  and  23  fixed to the tub  13  by bearings  19  and  25 . 
   A shaft tooth  17   a  in the form of a spline or a serration is axially formed over a predetermined length section on the lower outer circumference in the lower portion of the basket shaft  17 . 
   A pulsator shaft  31  that rotates while being directly coupled with the driving motor  35  so as to form a dual axial structure and to rotate the pulsator  29  passes through the inside of the basket shaft  17 . The pulsator shaft  31  is supported to the basket shaft  17  by bearings  12  so as to be in a relative motion. 
   The driving motor  35  includes a stator  39  fixed in the lower portion of the lower bearing housing  23  and a rotor  37  connected from the outer circumference of the stator  39  to the center of the stator  39  and combined with the pulsator shaft  31 . 
   A bushing  38  combined with the pulsator shaft  31  is installed in the center of the rotor  37 . A serration member  32  integrally combined with the pulsator shaft  31  is fixed in the upper center portion of the bushing  38 . 
   A rotor tooth  32   a  in the form of the spline or the serration is formed in the same direction as the direction of the shaft tooth  17   a  on the outer circumference of the serration member  32 . 
   A repulsive type clutch device  40  is included between the bearing housing  23  and the bushing  38  so that the rotary power generated by the driving motor is selectively transmitted to the basket shaft  17 . 
   The clutch device  40  includes a solenoid actuator  51  fixed to the lower portion of the bearing housing, the solenoid actuator  51  for generating electromagnetic force, a coupling member  41  combined around the basket shaft  17 , the coupling member  41  for transmitting or interpreting the rotary power while moving up and down by the electromagnetic force of the solenoid actuator  51 , thus combined with or separated from the serration member  32 , and a spring member  60  installed between the coupling member  41  and the bearing housing  23 , the spring member  60  for providing elasticity so that the coupling member  41  moves due to the electromagnetic force and is returned to an original position. 
   As shown in  FIG. 5 , the coupling member  41  includes a cylindrical non-magnetic coupling  42 , in which a coupling tooth  42   a  formed by engaging the shaft tooth  17   a  with the rotor tooth  32   a  is formed, a cylindrical magnetic coupling  43  axially and extendedly formed in the upper portion of the non-magnetic coupling  42 , and a ring-shaped conductive coupling  44  fixed on the upper outside of the magnetic coupling. 
   The non-magnetic coupling  42  is formed of synthetic resin and is formed to have a length such that the coupling tooth  42   a  of the non-magnetic coupling  42  simultaneously gears with the shaft tooth  17   a  and the rotor tooth  32   a  in a state where the non-magnetic coupling  42  completely falls along the basket shaft  17 . 
   The magnetic coupling  43  is formed of a magnetic member so as to form a magnetic field corresponding to the solenoid actuator  51 . 
   The conductive coupling  44  is formed of a metal having excellent conductivity such as aluminum (Al) and is formed to have an internal diameter larger than the external diameter of the magnetic coupling  43  so that the inner circumference of the conductive coupling  44  is separated from the external diameter of the magnetic coupling  43  by a predetermined distance. 
   The spring member  60  for supplying elasticity to the coupling member  41  so that the coupling member  41  does not reside in the upper portion due to residual flux and rapidly falls is positioned in an opening region  41   a  between the magnetic coupling  43  and the conductive coupling  44 . 
   Since the coupling member  41  can reduce the self-weight since the non-magnetic coupling  42  is formed of the synthetic resin lighter than the metal. Accordingly, the coupling member  41  can reduce the electromagnetic force of the solenoid actuator  51  required for an initial operation. 
   The solenoid actuator  51  is ring-shaped so as to house the coupling member  41  inside. The solenoid actuator  51  includes a solenoid coil  53  for forming the electromagnetic force when power is applied and a solenoid case  54  formed of a magnetic material so as to form the main path of an alternating current (AC) magnetic field and fixed to the lower bearing hosing  23  so as to support the solenoid coil  53 . 
   As shown in  FIG. 6 , the solenoid case  54  includes a coil fixing portion  55 , which has a cylindrical portion  55   a  and a bottom portion  55   b  and the solenoid coil  53  is installed inside and a flange portion  56  extended from the upper end of the coil fixing portion  55  in a radius direction and fixed to the lower bearing housing  23 . 
   In particular, a plurality of slits  55   c  connected from the cylindrical portion  55   a  to the bottom are formed in the coil fixing portion  55  so as to reduce the eddy current. The slits  55   c  are uniformly formed to be separated from each other by a predetermined distance in a direction of the circumference of the cylindrical portion  55   a.    
   The slits  55   c  prevent the eddy current from being abandoned to the solenoid case  54  and cools the solenoid coil  53  by forming a channel, through which air is flown. 
   The clutch device according to the present invention includes a transformation operating unit so as to apply voltages of different levels to the solenoid coil  53  according to the position of the coupling member  41 . 
   The transformation operating unit can supply the voltages of the different levels to the solenoid coil  53  during an initial operation for generating the electromagnetic force so as to move the coupling member  41  upward and a maintaining operation for maintaining a state where the coupling member  41  is completely moved upward. 
   The transformation operating unit includes a position sensor  75  installed in the solenoid case  54 , the position sensor  75  for sensing the position of the coupling member  41 , a trans  57  installed on a line for supplying the power to the solenoid coil  53 , the trans  57  for providing the voltages of the different levels, and a relay switch  59  installed on a line between the trans  57  and the solenoid coil  53 , the relay switch  59  for selecting one among the voltages of different levels, which are provided by the trans, according to a signal of the position sensor  75 . 
   Output terminals  58   a  and  58   b  are formed in the trans  57  so as to output the voltages of the different levels. A relay switch  59  including a plurality of contact points A and B connected to the output terminals  58   a  and  58   b  of the trans  57  is included between the solenoid coil  53  and the trans  57  so that the voltages of the different levels can be applied. 
   The relay switch  59  is preferably operated according to the signal of a control unit  70  that received the signal of the position sensor  75 . 
   The operation and the effect of the clutch apparatus according to the present invention will now be described. 
   When the laundry is washed while integrally rotating the spin basket  15  and the pulsator  29  or the laundry is to be dried after completing the washing of the laundry, the driving motor  35  is operated in a state where the power is not supplied to the solenoid actuator  51 , that is, a state where the solenoid actuator  51  is turned off. 
   At this time, the coupling member  41  falls while contacting the upper surface of the rotor  37 . Accordingly, the coupling tooth  42   a  is combined with the shaft tooth  17   a  and the rotor tooth  32   a  in a state where the coupling tooth  42   a  simultaneously gears with the shaft tooth  17  and the rotor tooth  32   a . Therefore, the rotary power of the rotor  37  is transmitted to the basket shaft  17  through the coupling member  41  according to the operation of the driving motor  35 . Accordingly, the spin basket  15  integrally rotates together with the pulsator  29 . 
   When the laundry is washed while rotating the pulsator  29  in a state where the spin basket  15  is stopped, the coupling member  41  is moved upward by applying the power to the solenoid coil  53  of the solenoid actuator  51 . At this time, the coupling tooth  42   a  of the coupling member  41  is separated from the rotor tooth  32   a  and is combined with only the shaft tooth  17   a , the rotary power generated by the driving motor  35  is transmitted to only the pulsator  29 . 
   During the initial operation where the power starts to be applied to the solenoid coil  53  in order to raise the coupling member  41 , the relay switch  59  contacts the contact point A so that a higher level of voltage is applied as shown in FIG.  7 . 
   When a high level of voltage is applied to the solenoid coil  53 , the eddy current is abandoned to the conductive coupling  44  due to the AC magnetic field formed by the solenoid coil  53  between the solenoid case  54  and the lower bearing housing  23 . At this time, electromagnetic repulsive force corresponding to Lorenz force operates to the conductive coupling  44 . Accordingly, the coupling member  41  is separated from the rotor tooth  32   a  and moves upward. 
     FIGS. 8A and 8B  the distribution of the magnetic field and the distribution of the eddy current abandoned to the inside of the conductive coupling  44  in the position where the coupling member  41  initially operates.  FIGS. 9A and 9B  show the distribution of the magnetic field and the distribution of the eddy current abandoned to the inside of conductive coupling in the position where the coupling member completely rises. 
   As the coupling member  41  rises, the magnitude of the eddy current abandoned to the conductive coupling  44  becomes smaller. The elasticity of the spring member  60  arranged in the upper portion of the coupling member  41  becomes larger, the coupling member  41  stops in a state where the coupling member  41  does not collide with the lower bearing housing  23 . Accordingly, the collision noise is not generated. 
   When the coupling member  41  rises, to thus reach the position where the coupling member  41  finally rises, the relay switch  59  contacts the contact point B and operates so that a relatively low level of voltage can be applied to the solenoid coil  53 . At this time, the coupling member  41  is maintained raised. 
     FIG. 10  is a graph comparing the magnetic force according to the displacement of the coupling member of an attractive type clutch apparatus according to a conventional technology with the magnetic force according to the displacement of the coupling member of a repulsive type clutch apparatus according to the present invention. While the electromagnetic force becomes gradually larger as the displacement of the coupling member becomes larger in the conventional attractive type clutch apparatus, the electromagnetic force becomes smaller than the initial electromagnetic force as the displacement of the coupling member becomes larger in the repulsive type clutch apparatus according to the present invention. 
   When the power applied to the solenoid coil  53  of the solenoid actuator  51  is intercepted, the coupling member  41  rapidly falls due to the elasticity and the self-weight of the spring member  60 . At this time, the coupling tooth  42   a  is combined with the shaft tooth  17   a  and the rotor tooth  32   a  in a state where the coupling tooth  42   a  simultaneously gears with the shaft tooth  17   a  and the rotor tooth  32   a . Accordingly, it is possible to integrally drive the spin basket  15  and the pulsator  29 . 
   Since the clutch apparatus of the washing machine according to the present invention is repulsive type where the solenoid actuator pushes the coupling member upward in the lower portion unlike the attractive type clutch apparatus, it is possible to prevent the collision noise that can be generated while the coupling member rises. 
   Also, in the clutch apparatus of the washing machine according to the present invention, since almost parts that form the coupling member such as the non-magnetic coupling and the conductive coupling are formed of the non-magnetic material, it is possible to prevent the compressive force and the holding voltage from rising due to the residual flux after the coupling member rises. Accordingly, it is possible to reduce the amount of the consumption of the power for maintaining the coupling member raised. 
   Also, in the clutch apparatus of the washing machine according to the present invention, the trans for providing the different voltages to the solenoid coil is included. Accordingly, it is possible not to use the conventionally used parts for DC power supply and to reduce the amount of the consumption of the power.