Patent Publication Number: US-6903520-B2

Title: Deflection york and CRT device using the deflection york

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a deflection yoke and a cathode ray tube (CRT) device using the deflection yoke. 
   2. Description of the Related Art 
   In recent years, energy-conservation measures are being taken in various fields and industries to prevent environmental destruction. The filed of CRT devices is no exception, and various attempts have been made to reduce power requirements of CRTs. 
   One attempt to reduce power consumption is to change the shape of deflection yokes. 
     FIGS. 1A ,  1 B,  1 C, and  1 D show, as one example, a color CRT device  100  resulted from such an attempt. The CRT device  100  has a 4:3 aspect ratio, a deflection angle of 100°, and a diagonal size of 19 inches. 
     FIG. 1A  is a schematic side view showing the color CRT device  100 . 
   The color CRT device  100  is composed of a CRT  102  and a deflection yoke  104 . 
   The CRT  102  includes a glass bulb  112  composed of: a glass panel  106  having a rectangular front face; a glass funnel  108 ; and a cylindrical glass neck  110  that are joined together in the stated order. Formed inside the panel  106  is a phosphor screen (not illustrated), and installed inside the neck  110  is an in-line type electron gun (not illustrated). The in-line type electron gun is composed of three electron guns respectively corresponding to B (blue), G (green), and R (red) arranged in a horizontal direction (X axis direction) in the stated order when seen from the side of the panel  106 . 
   The deflection yoke  104  is mounted along the outer surface of the glass bulb  112  in a manner to cover the boundary between the neck  110  and the funnel  108 . That is, the deflection yoke  104  is mounted on the glass bulb  112  to cover a particular part. At the particular part, the outer surface of the glass bulb  112  has such a shape that cross sections taken along lines perpendicular to the tube axis (Z axis) of the CRT gradually change from circular to substantially rectangular as the section lines shift closer from the neck  110  to the panel  106 . In this specification, the ouster surface of the glass bulb where the deflection yoke is mounted is referred to as a “yoke-mounting part”. 
   In the color CRT device  100 , the in-line type electron gun emits electron beams along the tube axis (Z axis) direction of the CRT  102 . The electron beams are then deflected by the action of deflection magnetic field that is generated inside the deflection yoke  104  so as to accomplish scanning over the phosphor screen provided inside the panel  106 . 
     FIGS. 1B ,  1 C, and  1 D are sectional views showing the deflection yoke  104  taken along the lines K—K, L—L, and M—M in  FIG. 1A , respectively. The distances from the front face of the panel to the section lines K—K, L—L, and M—M in the axial direction (Z axis direction) are 56.9 [mm], 31.9 [mm], and 21.9 [mm], respectively. 
   As shown in  FIGS. 1B ,  1 C, and  1 D, the cross sections of the deflection yoke  104 , roughly speaking, change from circular to substantially rectangular as the section lines shift closer from the neck  110  to the panel  106 , so that the deflection yoke  104  conforms to the outer shape of the yoke-mounting part of the glass bulb  112 . 
   To be more specific, the deflection yoke  104  is composed of: a funnel-shaped plastic separator  114  having a part of which cross section is substantially rectangular conforming to the outer shape of the yoke-mounting part of the glass bulb  112 ; a horizontal deflection coil  116  deposed along the inner surface of the separator  114 ; a vertical deflection coil  118  disposed along the outer surface of the separator  114 ; and a ferrite core  120  disposed externally to the vertical deflection coil  118  and having a part of which cross section is substantially rectangular. 
   A conventionally common deflection yoke (not illustrated) is normally composed of a substantially conical separator, a horizontal deflection coil disposed along the inner surface of the separator, a vertical deflection coil disposed along the outer surface of the separator, and a substantially conical ferrite core disposed externally to the vertical deflection coil. Due to its shape, such a conventionally common deflection yoke inevitably has gaps of a considerable size formed between the horizontal deflection coil and the outer surface of the glass bulb. 
   Unlike such a conventionally common deflection yoke, the deflection yoke  104  has the above-described construction. With this construction, it is intended to position the horizontal deflection coil  116  as close as possible to the outer surface of the glass bulb  112 , so that the horizontal deflection coil  116  is positioned as close as possible to the path area of electron beams. This arrangement improves deflection efficiency and consequently reduces power consumption. In addition, in the deflection yoke  104 , the vertical deflection coil  118  is also positioned closer to the path area of electron beams than in a conventionally common deflection yoke. This arrangement also contributes to power consumption reduction. Yet, the horizontal deflection coil  116  consumes much greater power than vertical deflection coil  118  does. Thus, the advantageous effect of the deflection yoke  104  is achieved primary by the horizontal deflection coil  116  being arranged close to the glass bulb  112 . 
   As described above, though improvement in the shapes of the separator  114  and other components, the deflection yoke  104  has achieved improved deflection efficiency and, as a consequence, lower power consumption. 
   It should be noted, however, that the color CRT devices  100  composed of the deflection yoke  104  involve a problem that the convergence performance fluctuates to a greater extent than CRT devices composed of such a conventionally common deflection yoke as above. 
   SUMMARY OF THE INVENTION 
   A first object of the present invention is to provide a deflection yoke capable of reducing power consumption without sacrifice of convergence performance as much as possible. 
   A second object of the present invention is to provide a CRT device composed of a deflection yoke achieving the first object. 
   (1) The first object of the present invention is achieved by a deflection yoke mounted around a glass bulb of a CRT so as to cover a predetermined area of the glass bulb. The predetermined area is where an outer shape of the glass bulb smoothly goes from circular to substantially rectangular along a tube axis of the CRT. The deflection yoke includes a horizontal deflection coil disposed in a shape to fit with the outer shape of the glass bulb, and a funnel-shaped ferrite core disposed to surround the horizontal deflection coil. An inner shape of the ferrite core is circular throughout a length of the ferrite core. 
   (2) Alternatively, the first object of the present invention is achieved by a deflection yoke mounted around a glass bulb of a CRT so as to cover a predetermined area of the glass bulb. The predetermined area is where an outer shape of the glass bulb smoothly goes from circular to substantially rectangular along a tube axis of the CRT. The deflection yoke includes a horizontal deflection coil disposed in a shape to fit with the outer shape of the glass bulb; and a funnel-shaped ferrite core disposed to surround the horizontal deflection coil. An inner surface of the ferrite core has been ground with a grinding machine. 
   (3) The second object of the present invention is achieved by a CRT device including a CRT having a glass bulb; and a deflection yoke of (1). The deflection yoke is mounted around the glass bulb so as to cover a predetermined area of the glass bulb. The predetermined area is where an outer shape of the glass bulb smoothly goes from circular to substantially rectangular along a tube axis of the CRT. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and the other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate a specific embodiment of the invention. 
     In the drawings: 
       FIGS. 1A ,  1 B,  1 C, and  1 D are views for illustrating a conventional CRT device and a conventional deflection yoke; 
       FIG. 2  is a schematic view showing a color CRT device according to an embodiment of the present invention; 
       FIG. 3  is an oblique view showing a separator and a ferrite core, which are the components of the deflection yoke according to the embodiment; 
       FIG. 4A  is a side view showing the deflection yoke according to the embodiment; 
       FIGS. 4B ,  4 C, and  4 D are sectional views showing the deflection yoke taken along lines shown in  FIG. 4A ; 
       FIG. 5  is an enlarged view of  FIG. 4C ; 
       FIG. 6  is a view showing test results conducted on the deflection yoke according to the embodiment and the deflection yoke according to the prior art to compare respective deflection power; 
       FIG. 7  is a view showing test results conducted on the deflection yoke according to the embodiment and the deflection yoke according to the prior art to compare respective convergence performance; 
       FIGS. 8A and 8B  are views showing a ferrite core used in the deflection yoke according to the prior art; 
       FIGS. 8C and 8D  are views showing a ferrite core used in the deflection yoke according to the embodiment; 
       FIG. 9  is partly enlarged view of  FIG. 3 ; 
       FIG. 10  is a view showing measurement results of tests conducted on the deflection yoke according to the embodiment and the deflection yoke according to the prior art to measure temperature-rise in respective horizontal deflection coils; 
       FIG. 11  is a view showing dimensions of each part of the ferrite core and the separator shown in  FIGS. 4B ,  4 C, and  4 D; 
       FIG. 12  is a view showing dimensions of each part of a ferrite core and a separator shown in  FIGS. 1B ,  1 C, and  1 D; and 
       FIG. 13  is a view showing one exemplary modification of a resilient mechanism in the deflection yoke according to the embodiment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The following describes one preferred embodiment of the present invention with reference to the accompanying drawings. 
     FIG. 2  is a schematic view showing a color CRT device  10  according to this embodiment. 
   The color CRT device  10  has a 4:3 aspect ratio, a deflection angle of 100°, and a diagonal size of 19 inches. 
   The color CRT device  10  includes a glass bulb  20  that is composed of: a glass panel  14  having a substantially rectangular display  12  at the front; a glass funnel  16  joined to the panel  14 ; and a cylindrical glass neck  18  joined to the funnel  16 . The funnel  16  literally has a funnel shape, and the tube end of the funnel shape is circular conforming to the shape of the neck  18  joined thereto. On the other hand, the flare part of the funnel shape is substantially in a shape of pyramid. 
   Mounted around a yoke-mounting part  22  of the glass bulb  20  is a deflection yoke  24 . That is, the deflection yoke  24  is disposed around the outer surface of the glass bulb  20  in a manner to cover the boundary between the neck  18  and the funnel  16 . 
   Provided inside the panel  14  is a phosphor screen  26  composed of a three-color phosphor layer that is composed of phosphors each emitting blue, green, or red light and are arranged in dots or stripes. Opposing to and inside the phosphor screen  26 , there is provided a shadow mask  28  having a plurality of apertures for electron beams to pass through. 
   Disposed within the neck  18  is an in-line type electron gun  32  that emits three electron beams  30 . The in-line type electron gun is composed of three electron guns that correspond to B (blue), G (green), and R (red), respectively and that are horizontally arranged in the stated order from left to right when seen from the panel  14 . The electron beams  30  are deflected in the horizontal and vertical directions by virtue of horizontal and vertical deflection magnetic fields that are generated by the deflection yoke  24 , and pass through the apertures of the shadow mask  28  to be scanned horizontally and vertically over the phosphor screen  26 . As a result, visible color images are produced on the display  12 . 
   Note that the glass bulb  20  that includes the electron gun  32  and the other components described above is hereinafter referred to as a CRT  34 . That is, the color CRT device  10  is composed of the CRT  34  and the deflection yoke  24 . 
     FIG. 3  is an oblique view showing components of the deflection yoke  24 , namely a separator  36  and a ferrite core  38 . 
     FIG. 4A  is a side view of the deflection yoke  24 .  FIGS. 4B-4D  are sectional views showing the deflection yoke  24  taken along the lines B—B, C—C, and D—D shown in  FIG. 4A , respectively. Similarly to the deflection yoke  104  shown in  FIGS. 1B-1D , the distances from the front face of the panel  14  to the section lines B—B, C—C, and D—D in the axial direction (Z axis direction) are 56.9 [mm], 31.9 [mm], and 21.9 [mm], respectively. 
   As shown in FIGS.  3  and  4 B- 4 D, the shape of the separator  36  gradually changes in cross section from circular at the part closer to the neck  18  of the CRT  34  to substantially rectangular at the part closer to the panel  14 . That is, the separator  36  has a funnel shape conforming to the shape of the yoke-mounting part  22  of the glass bulb  20 . On the other hand, the ferrite core  38  is always circular in cross section taking along any of the section lines. Yet, the diameter of the circular cross section is smaller as the section line is closer to the neck  18 . As shown in  FIG. 4A , the part P where the separator  36  is non-circular in the inner periphery of the cross section is referred to as a non-circular part, while the part Q where the separator  36  is circular in the inner periphery of the cross section is referred to as a circular part. 
   Next, the construction of the deflection yoke  24  is described in detail with reference additionally to FIG.  5 .  FIG. 5  is an enlarged view of FIG.  4 C. 
   As shown in  FIG. 5 , the separator  36  having the non-circular part is an insulating frame that insulates a horizontal deflection coil  40  and a vertical deflection coil  42 . The separator  36  is made of a plastic material (electric non-conductance resin). 
   The horizontal deflection coil  40  is composed of a pair of coil segments that are wound into a so-called saddle-shape and that are arranged inside the separator  36  symmetrically to the X axis (major axis) of the separator. The horizontal deflection coil  40  is disposed along the inner surface of the separator  36 . That is, when the deflection yoke  24  is mounted to the glass bulb  20 , the horizontal deflection coil  40  is located along the outer surface of the glass bulb  20  at the yoke-mounting part  22 . 
   Similarly, the vertical deflection coil  42  is composed of a pair of coil segments that are wound into a saddle-shape and that are arranged outside the separator  36  symmetrically to the Y axis (minor axis) of the separator. From a macroscopic viewpoint, the horizontal deflection coil  40  and the vertical deflection coil  42  substantially define a rectangle in cross section so that both the coils conform to the shape of the separator  36 . 
   Additionally, the ferrite core  38  is mounted in a manner to cover the separator  36 , the horizontal deflection coil  40 , and the vertical deflection coil  42 . The ferrite core  38  has a funnel shape, and is circular in cross section. 
   As described above, the deflection yoke  24  according to the embodiment of the present invention has the non-circular part P (see  FIG. 4A ) where the separator  36 , the horizontal deflection coil  40 , and the vertical deflection coil  42  are non-circular in cross section, thereby conforming to the shape of the yoke-mounting part  22  of the glass bulb  20 . In the non-circular part P, the horizontal deflection coil  40  and the vertical deflection coil  42  (especially the horizontal deflection coil  40 ) are closer to the path area of the electron beams  30  in comparison with a conventionally common deflection yoke composed of a substantially conical separator and a substantially conical ferrite core. As a consequence, power required to deflect the electron beams  30  (i.e., deflection power) is reduced. 
   Note that the deflection yoke  24  according to the embodiment of the present invention has the construction that, in the non-circular part P, the ferrite core  38  is farther away from the path area of the electron beams  30  in comparison with the deflection yoke  104  described with reference to  FIGS. 1A-1D . For this reason, there was a concern that the deflection yoke  24  would require greater deflection power than the deflection yoke  104  did. However, computer simulations performed by the inventors of the present invention has made it clear, although the details of the simulations are omitted here, that the important factor to reduce deflection power lies not in the ferrite core but in the horizontal deflection coil and the vertical deflection coil (especially, the horizontal deflection coil). Thus, similarly to the deflection yoke  104 , the deflection yoke  24  according to this embodiment of the present invention sufficiently realizes the effect to reduce deflection power. 
   To confirm the above effect, tests were actually conducted and the results are shown in FIG.  6 . 
   The tests were conducted on the deflection yoke  24  according to the embodiment of the present invention and the deflection yoke  104  according to the prior art. In the tests, the electron beams  30  were deflected to a corner of the respective display and various measurements were made, and deflection power of each deflection yoke was calculated from the respective measurements. 
   In  FIG. 6 , LH is an inductance of the horizontal deflection coil, LV is an inductance of the vertical deflection coil, RH is a resistance of the horizontal deflection coil, RV is a resistance of the vertical deflection coil, IH is a current passing through the horizontal deflection coil, and IV is a current passing through the vertical deflection coil. Note that all these values are actually measured values. 
   In addition, PH is a deflection power required by the horizontal deflection coil, and PV is a deflection power required by the vertical deflection coil. Note that values of PH and PV are calculated from the following expressions.
 
 PH=LH×IH   2 
 
 PV=RV×IV   2 
 
   As apparent from the test results shown in  FIG. 6 , there was no difference in PH between the deflection yoke  24  according to the present embodiment and the deflection yoke  104  according to the prior art. In addition, with respect of PV, the deflection yoke  24  was greater only slightly than the deflection yoke  104  by 0.5 [ΩA 2 ], and thus there was no substantial difference. The test results support that an important factor determining the deflection power lies not in the ferrite core but in the horizontal deflection coil and the vertical deflection coil. 
   Further, the inventors of the present invention conducted tests to confirm that the deflection yoke  24  according to the present embodiment is better than the deflection yoke  104  in the convergence performance. (Note that hereinafter the deflection yoke  24  is also referred to as a “rectangular coil-circular core type deflection yoke”, and the deflection yoke  104  is also referred to as a “rectangular coil-rectangular core type deflection yoke.”) 
   The inventors of the present invention conducted measurements on the rectangular coil-circular core type deflection yoke  24  and the rectangular coil-rectangular core type deflection yoke  104  under the standard of EIAJ (Electronic Industries Association of Japan) to obtain “Xh” and “Xhs”, the indices showing the state of convergence. The measurements were also conducted on the conventionally common deflection yoke mentioned in the “Description of the Related Art”, i.e. a deflection yoke composed of a substantially conical separator, a horizontal deflection coil mounted along the inner surface of the separator, a vertical deflection coil mounted along the outer surface of the separator, and a substantially conical ferrite core disposed externally to the vertical deflection coil (hereinafter such a conventionally common deflection yoke is also referred to as “circular coil-circular core type deflection yoke). 
   Ten deflection yokes were manufactured for each of the three types, and measurements were preformed on each deflection yoke to obtain “Xh” and “Xhs”. Then, a standard deviation a for each type of the deflection yokes was calculated from the respective measurement values. The variations in the convergence performance were evaluated using the values obtained by multiplying the above standard deviations σ by three. The results are shown in FIG.  7 . 
   As apparent from  FIG. 7 , the rectangular coil-circular core type deflection yokes  24  according to the present embodiment exhibited the convergence performance of which variations (3σ) were smaller than the variations of the rectangular coil-rectangular core type deflection yokes  104 , and almost equal to the variations of the circular coil-circular core type deflection yokes. 
   Factors contributing the above differences in the variations of the convergence performance may be ascribable to degrees of dimensional accuracy of each ferrite core, i.e., dimensional deviation of each ferrite core from the designed dimensions. Generally, ferrite cores are manufactured by press-molding magnetic powder into a metal mold, followed by sintering the press-molded body. At the time of sintering, the press-molded body inevitably undergoes volume contraction, which results in dimensional variations. 
   Among the dimensional variations, it is assumed that the internal diameter of the ferrite core is especially influential in determining the convergence performance. This is because distribution of magnetic flux that the deflection coil generates varies depending on the internal shape of the ferrite core. 
   In the case of the substantially conical ferrite core used in the deflection yoke  24  according to the present embodiment, the dimensional accuracy is such that the internal diameter of the ferrite core is held to vary within ±1% from the designed value. In contrast, the substantially pyramid-shaped ferrite core used in the deflection yoke  104  according to the prior art, the dimensional accuracy is such that the internal rectangle varies within ±2.5% in the length of the major side, ±1.6% in the length of the minor side, and ±3.3% in the diagonal length. The difference in the dimensional accuracy among each type of ferrite cores maybe ascribable to the uniformity in the ferrite core thickness and the axial symmetry to the tube axis. 
   As described above, by improving the dimensional accuracy in the internal dimensions of the ferrite core, the convergence performance is expected to improve. 
   In view of the above, the deflection yoke  24  according to the present invention having the substantially conical ferrite core  38  has the following advantage over the conventional deflection yoke  104  having the substantially pyramid-shaped ferrite core  120 . That is, the substantially conical ferrite core has a smooth internal shape without corners, so that the internal surface may be finished with grinding. On the contrary, such grinding is not possibly applied to the generally pyramid-shaped ferrite core, so that there is no choice but to use the ferrite core as sintered. 
   In general, metal-molded products are poor in the dimensional accuracy in comparison with ground products. With grinding, the internal diameter of the ferrite core may be held to vary within ±0.2 mm or so regardless of the size of the designed internal diameter. With metal-molding, however, accuracy of the metal molding directly counts for the dimensional accuracy of the finished ferrite core, and thus the internal diameter of such a ferrite core varies from the designed internal diameter to the extent of ±1% or so. 
   As described above, the greater the dimensional variations of the ferrite cores are, the greater the variations of the convergence performance of the deflection yokes are. This results in degradation of the image quality. 
   Now, description is given to the dimensional accuracy of the pyramid-shaped ferrite core and the conical ferrite core with reference to  FIGS. 8A-8D .  FIG. 8A  is a sectional view of a pyramid-shaped ferrite core taken along the line E—E shown in FIG.  8 B.  FIG. 8C  is a sectional view of a conical ferrite core taken along the line F—F shown in FIG.  8 D. 
   As shown in  FIGS. 8A and 8B , when manufacturing by metal molding pyramid-shaped ferrite cores in the designed dimensions: the minimum internal diameter φ 1  min of which half value is 22.90 mm and the maximum internal diameter φ 1  max of which half value is 39.75 mm, the finished dimensions vary within the range of 0.79 mm. On the other hand, as shown in  FIGS. 8C and 8D , when manufacturing with grinding the conical ferrite cores in the designed dimensions: the minimum internal diameter φ 2  min of which half value is 23.00 mm and the maximum internal diameter φ 2  max of which half value is 39.85 mm, the finished dimensions vary within the range of 0.2 mm. In short, the conic ferrite core shown in  FIGS. 8C and 8D  is better in the dimensional accuracy. 
   That is to say, a substantially conical ferrite core produced merely by sintering is still capable of improving the convergence performance in comparison with a substantially pyramid-shaped ferrite core. Yet, by grinding the internal surface of the ferrite core, the convergence performance is further improved. The grinding of the internal surface is done using a conventional grinding machine. 
   Now, referring back to  FIGS. 3 and 5 , there are provided resilient mechanisms  44  in the vicinity of a Y axis of the separator  36 .  FIG. 9  is an enlarged oblique view showing one of the resilient mechanisms  44 . The resilient mechanisms  44  resiliently support the ferrite core, and prevent misalignment of the ferrite core  38  that possibly occurs at the time of assembling the deflection yoke  24 . Since the misalignment of the ferrite core  38  is prevented, the deflection yoke exhibits stable magnetic field characteristics and convergence performance, whereby enabling to provide a color CRT device having good image quality. 
   Further, there are provided sandwiching mechanisms  46  in adjacent to each resilient mechanism  44 . With the sandwiching mechanisms  46 , it is possible to dispose the vertical deflection coil at any intended position. Thus, the deflection yoke exhibits stable magnetic field characteristics and convergence performance. Note that the horizontal deflection coil  40  is disposed along the inner surface of the separator  36 . 
   As shown in  FIGS. 3 and 5 , in the vicinity of the X axis of the separator  36 , there are provided holding mechanisms  48  for holding the ferrite core  38  in place. Note that the holding mechanisms  48  are integrally formed with the separator  36  at the time of molding resin. In order to secure a mold drawing direction, each holding mechanism is in U-shape in cross section with an opening in the mold drawing direction as shown in FIG.  5 . Alternatively, however, the holding mechanisms may have the similar shape and function to the resilient mechanisms  44 . 
   In addition, there are provided hollows  50  between the ferrite core  38  and the horizontal deflection coil  40  via the separator  36 , and hollows  52  between the ferrite core  38  and the vertical deflection coil  42 . As described above, in the deflection yoke  24  according to the embodiment of the present invention, the separator  36 , the horizontal deflection coil  40 , and the vertical deflection coil  42  are all non-circular in cross sections, while the ferrite core  38  is circular in cross section. With this construction, the deflection yoke  24  of the present invention secures the hollows that the conventional deflection yoke  104  shown in  FIGS. 1B-1D  does not have. 
   The hollows  50  and  52  serve to improve cooling effect of the horizontal deflection coil  40  and the vertical deflection coil  42 . Thus, the horizontal deflection coil  40  and the vertical deflection coil  42  generate less heat in comparison with conventional deflection coils included in a deflection yoke having no such hollows, thus temperature rise in the entire deflection yoke  24  is suppressed. 
   For further enhancing cooling effect, the diameter of the ferrite core  38  may be enlarged while the dimensions of the separator  36  are left unchanged, thereby enlarging the hollows  50  and  52 . Being larger in diameter, however, the ferrite core  38  exhibits less effect on increasing magnetic flux density, which as a result requiring greater deflection power. In addition, if the diameter of the ferrite core  38  is larger without changing the dimensions of the other components, it is increasingly difficult to securely hold the ferrite core  38 . As a consequence, the problem of misalignment is likely to arise. In view of the above, it is preferable to dispose the ferrite core  38  close to the horizontal deflection coil  40  and the vertical deflection coil  42 . In other words, it is preferable that the inner diameter of the ferrite core  38  be as small as possible. 
   For the reasons stated above, it is preferable that the inner diameter of the ferrite core  38  at the non-circular part P be made to generally equal to the diagonal distance of the substantially rectangular cross section of the separator  36 , or of the substantial rectangle defined by the horizontal deflection coil  40  and the vertical deflection coil  42 . To be more specific, it is preferable that the inner diameter of the ferrite core  38  be made generally equal to the diagonal distance between the outermost corners of the vertical deflection coil  42 . The vertical deflection coil  42  is provided with an adhesive member  54  such as an adhesive sheet along each corner of the substantial rectangle, which is in contact with the separator  36 , so that the vertical deflection coil  42  is protected and fixed to the separator  36 . 
   Next, with reference to  FIG. 10 , description is given to the temperature-rise tests conducted on the deflection yoke  24  according to the embodiment of the present invention and on the deflection yoke  104  according to the prior art to measure temperature rise in the respective horizontal deflection yokes. In this test, both the deflection yoke  24  according to the present embodiment and the conventional deflection yoke  104  were deflection yokes (diameter φ of the wire forming the horizontal deflection coil: 0.10 mm) for a color CRT (diagonal size: 19 inches, deflection angle: 100°, and neck diameter φ: 29.1 mm) to be used as a computer display monitor. Further, the tests were conducted in the environmental temperature of 40° C. and with horizontal deflection frequency of 95 kHz.  FIGS. 11 and 12  show the dimensions of each part of respective ferrite cores and separators of the deflection yoke  24  according to the present invention and the deflection yoke  104  according to the prior art, respectively. The dimensions were measured in the cross sections shown in  FIGS. 4B-4D  and in  FIGS. 1B-1D , respectively. The horizontal deflection coil and the vertical deflection coil were disposed along the inner and outer surface of each separator, respectively. 
   According to the tests, as shown in  FIG. 10 , the temperature of the horizontal deflection coil in the conventional deflection yoke  104  rose to 110° C., whereas the temperature of the horizontal deflection coil in the deflection yoke  24  of the present embodiment rose only to 103° C. That is to say, the deflection yoke  24  according to the present embodiment successfully reduces the temperature rise of the horizontal deflection coil by 7° C. in comparison with that in the conventional deflection yoke  104 . Note that the reason for measuring the temperature of the horizontal deflection coil is because the horizontal deflection coil is where the temperature apt to rise most in the deflection yoke. 
   Here, the separator of the deflection yoke is made of a plastic material, such as PPE (polyphenylene ether) resin, and the long-term thermal deformation resistance of the resin is guaranteed at temperatures up to 110° C. Thus, there is a risk if the temperature of the horizontal deflection coil reaches 110° C., the separator is thermally deformed so that the insulation between the horizontal deflection coil and the vertical deflection coil may not be maintained. However, with the deflection yoke  24  according to the present invention, the above risk is eliminated, thereby improving thermal reliability of the deflection yoke. 
   Up to this point, description has been given to the embodiment of the present invention. Yet, it should be understood that the present invention is not limited to the specific embodiment disclosed above, and various modifications as provided below are applicable.
     (1) In the above embodiment, the present invention is described by way of the color CRT device. Yet, the present invention may be applied to a monochrome CRT device constituting a projection tube type projector as well as to a deflection yoke used in such a monochrome CRT device.   (2) In the above embodiment, the ferrite core employed is substantially conical having circular cross section.
 
Alternatively, a ferrite core having a funnel shape with a flare part having elliptic cross section may be applicable. With such a shape having elliptic cross section, the inner surface of the ferrite core maybe ground, thereby assuring dimensional accuracy required for good convergence performance.
   

   In addition, using with a funnel shaped separator having a pyramid-shaped flare part, gaps are provided between the ferrite core that is elliptic in cross section and a vertical deflection coil that is disposed along the outer surface of the separator. The gaps serve to provide cooling effect on the deflection coil similarly to the above embodiment.
     (3) Aside from the resilient mechanisms disclosed in the above embodiment, resilient mechanisms as shown in  FIG. 13 , for example, may be applicable.  FIG. 13  is an enlarged oblique view showing a modified resilient mechanism and in correspondence with FIG.  9 . As shown in  FIG. 13 , there is provided a rib  62  along the outer surface of the separator  36  in the longitudinal direction, and the resilient mechanism is composed of a projection  60  diagonally extending from the top face of the rib  62 . The projection  60  is integrally formed with the separator  36  by injection molding. Thus, the projection  60  is made of the same synthetic resin as the material of the separator  36 , and has a certain degree of flexibility owing to its shape.   

   The projections  60  are to be disposed generally at the same locations where the resilient mechanisms  44  are located. That is to say, at least two projections  60  are provided as a pair blow and above the Y axis (see FIG.  5 ). 
   Upon assembling the deflection yoke according to this modification, the ferrite core  38  is inserted in the direction shown by an arrow G in FIG.  13 . As a consequence, the projection  60  is pressed by the inner surface of the ferrite core  38  to flex in the direction shown by an arrow J. The restoring force produced by the projection  60  resiliently supports the ferrite core  38  from inside against the separator  36 . 
   In addition, a stopper  64  for preventing breakage of the projection  60  is provided in an extended condition from the top face of each rib  62 . In case where the ferrite core  38  is inserted in the state somehow deviated in the direction of Y axis, it is inevitable that one of the pair of the projections  60  flexes excessively. The stopper  64  is provided in order to prevent the projection  60  from damage that possibly occurs in such a case. Each stopper  64  is located in the direction that the projection  60  flexes so as to engage against the projection  60  before the projection  60  flexes beyond the flexible limit. As a consequence, the projection  60  does not flex any further. In other words, the stopper  64  restricts the flexible amount of the projection  60  so as to prevent breakage of the projection  60  due to the excessive flexing.
     (4) The deflection yoke according to the above preferred embodiment is composed of the saddle-shaped horizontal deflection coil and the saddle-shaped vertical deflection coil that are disposed along the inner surface and the outer surface of the separator, respectively. Yet, a deflection yoke consistent with the present invention is not limited to such a deflection yoke and, for example, the following modification is possible.   

   That is, the horizontal deflection coil may be a similar one to the above horizontal deflection coil, i.e., a saddle-shaped horizontal deflection coil disposed along the inner surface of the ferrite core. Here, the vertical deflection coil may be a toroidal coil that is wound around the ferrite core. 
   Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Therefore, unless such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.