Flywheel device having metal disk and resin portion and method of producing the flywheel device

A flywheel device for use in a magnetic recording/reproducing unit or the like which device is simple in construction, and can be produced at low costs, and a method of making it. A capstan shaft is press-fitted in a hole formed in a central portion of a metal disk, and then a resin is filled on an outer peripheral portion and a central portion of the disk by outsert molding to form an outer peripheral resin portion and a central resin portion. The outer peripheral resin portion has a groove formed in an outer periphery thereof, and the central resin portion has gear portions.

BACKGROUND OF THE INVENTION 
This invention relates to a flywheel device used in a magnetic 
recording/reproducing unit for smoothly driving a magnetic tape, and also 
relates to a method of producing such a flywheel device. 
FIG. 5 shows an audio cassette used, for example, in a magnetic 
recording/reproducing unit (including a reproduction-only unit) for 
mounting on a car. In FIG. 5, reels 2A and 2B are rotatably supported 
within a cassette body 1, and a magnetic tape 3 is wound on the reels 2A 
and 2B. Cassette-positioning holes 4A and 4B are formed adjacent to a 
front side of the body 1, and holes 5A and 5B for respectively receiving 
capstan shafts are also formed adjacent to the front side of the body 1. 
FIG. 6 shows an important portion of the magnetic recording/reproducing 
unit for mounting on a car. In FIG. 6, cassette guide members 7A and 7B 
are supported respectively on opposite side walls of a base plate 6 for 
upward and downward movement. The cassette shown in FIG. 5 is horizontally 
inserted while being guided by the cassette guide members 7A and 7B. When 
the cassette is inserted into a predetermined position while being guided 
by the cassette guide members 7A and 7B, a plunger 8 is operated to drive 
the cassette guide members 7A and 7B to move them downward toward the base 
plate 6, thereby moving the cassette into a recording/reproducing 
position. Cassette-positioning pins 9A and 9B are fixedly secured to the 
base plate 6. The capstan shafts 10A and 10B are rotatably supported 
respectively by bearings fixedly mounted on the base plate 6. A flywheel 
is fixedly secured to a lower end of each of the capstan shafts 10A and 
10B. A slide plate 11 is slidably supported on the base plate 6, and a 
magnetic head 12 is supported on the slide plate 11. Reel drive shafts 13A 
and 13B are engaged respectively with the reels 2A and 2B in the cassette, 
and drive the reels 2A and 2B for rotation by a rotational drive force 
applied by a motor 14. 
In FIG. 6, when the cassette, inserted into the cassette guide members 7A 
and 7B, reaches the predetermined position, the plunger 8 is operated to 
drive the cassette guide members 7A and 7B to move them downward. As a 
result, the cassette-positioning pins 9A and 9B are inserted into the 
cassette-positioning holes 4A and 4B, respectively, and the capstan shafts 
10A and 10B are inserted respectively into the holes 5A and 5B in the 
cassette, and also the reel drive shafts 13A and 13B are engaged with the 
reels 2A and 2B of the cassette, respectively. When the cassette is thus 
transferred to the recording/reproducing position by the cassette loading 
mechanism, the slide plate 11 slides to bring the magnetic head 12 into 
contact with the magnetic tape, and also the reel drive shafts 13A and 13B 
are rotated by the rotational drive force of the motor 14, so that the 
reels 2A and 2B, engaged respectively with the reel drive shafts 13A and 
13B, are rotated, thereby effecting a reproducing operation or a recording 
operation. The rotational drive force of the motor 14 is transmitted to 
the flywheels through respective belts to rotate the flywheels, and the 
capstan shafts 10A and 10B, fixedly secured respectively to these 
flywheels, are also rotated, and the magnetic tape is caused to travel by 
the rotating capstan shafts 10A and 10B and pinch rollers. 
FIG. 7 shows the above flywheel. The flywheel 15 shown in FIG. 7 is molded 
of a resin containing metal powder. The metal powder is included in the 
molding resin so as to provide a required inertia moment during the 
rotation of the flywheel 15. A groove 16 of a V-shaped cross-section is 
formed in a peripheral surface (edge) of the flywheel 15, and the belt is 
engaged in this groove 16. Gear portions 17 and 18 are formed integrally 
on an upper surface of the flywheel 15. A rotational drive force of the 
gear portion 17 is transmitted to the reel drive shaft 13, (13B) via other 
gears to rotate the same. At the time of a fast-forward operation and a 
rewind operation, a rotational drive force of the gear portion 18 is 
transmitted to the reel drive shaft 13A, (13B) via other gears to rotate 
the same. The capstan shaft 10A, (10B) is press-fitted in a central 
portion of the flywheel 15. FIGS. 8A, 8B and 8C show a process of 
producing the flywheel 15. First, the resin, containing metal powder, is 
molded to form the flywheel 15 having the integral gear portions 17 and 
18, as shown in FIG. 8A. Then, a cylindrical bushing 20 of metal is 
press-fitted in a hole 19 formed in a central portion of a lower surface 
of the flywheel 15, as shown in FIG. 8B. Then, the capstan shaft 10A, 10B 
is press-fitted in a central hole 21 of the flywheel 15 and the bushing 
20, thereby completing the flywheel, as shown in FIG. 8C. In the above 
conventional flywheel device, the special resin containing the metal 
powder for obtaining the required inertia moment is used, and the metal 
bushing 20 is used for firmly fastening the capstan shaft 10A, (10B) to 
the flywheel 15, and therefore there has been encountered a problem that 
the conventional flywheel device is expensive. 
SUMMARY OF THE INVENTION 
This invention has been made in order to overcome the above problem of the 
prior art, and an object of the invention is to provide a flywheel device 
which is simple in construction and can be produced at low costs. 
Another object of the invention is to provide a method of producing such a 
flywheel device. 
According to a first aspect of the present invention, there is provided a 
flywheel device comprising a disk of metal, a capstan shaft press-fitted 
in a hole formed in a central portion of the disk, and a resin portion 
formed at an outer peripheral portion of the disk by filling a resin on 
the outer peripheral portion, the resin portion having a groove formed in 
an outer peripheral surface thereof. 
According to a second aspect of the invention, there is provided a flywheel 
device comprising a disk of metal having a hole formed in a central 
portion of the disk, a hollow cylindrical portion formed on the disk 
around a peripheral edge of the hole, a capstan shaft press-fitted in the 
hole in the disk, and a resin portion formed at an outer peripheral 
portion of the disk by filling a resin on the outer peripheral portion, 
the resin portion having a groove formed in an outer peripheral surface 
thereof. 
According to a third aspect of the invention, there is provided a method of 
producing a flywheel, comprising the steps of press-fitting a capstan 
shaft in a hole formed in a central portion of a disk of metal; and 
filling a resin on an outer peripheral portion of the disk to form a resin 
portion, the resin portion having a groove formed in an outer peripheral 
surface thereof. 
With the above construction of the first aspect of the invention, the metal 
disk is used as a core material, and therefore a required inertia moment 
can be obtained without the use of a resin-molded product containing metal 
powder as in the conventional construction. Moreover, since the capstan 
shaft is press-fitted in the central hole in the metal disk, the capstan 
shaft can be firmly fixed without the use of a bushing as in the 
conventional construction. 
In the second aspect of the invention, the hole is formed in the central 
portion of the metal disk, and the hollow cylindrical portion is formed 
around the peripheral edge of this hole. Therefore, the area of contact 
between the capstan shaft (press-fitted in this central hole) and the disk 
is larger, so that the capstan shaft can be more firmly fixed to the disk. 
In the third aspect of the invention, the flywheel device can be produced 
merely by filling the resin after the capstan shaft is press-fitted in the 
metal disk serving as a core material, and the step of press-fitting the 
bushing in the conventional process is unnecessary.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
One preferred embodiment of the present invention will now be described 
with reference to FIGS. 1 to 3. FIG. 1 shows one preferred embodiment of a 
flywheel device of the present invention, FIGS. 2A to 2C shows a process 
of producing the flywheel device, and FIG. 3 is shows a lower surface of 
the finished flywheel device. In FIG. 2A, a projected portion 23 is formed 
at a central portion of a disk 22 of metal, and a hole 24 is formed 
through this projected portion 23. A plurality of small holes 25 are 
formed through the disk 22. As shown in FIG. 2B, a capstan shaft 10A, 
(10B) is press-fitted in the central hole 24 in the disk 22 processed or 
worked as shown in FIG. 2A. Then, a resin is filled or applied by outsert 
molding onto upper and lower surfaces of an outer peripheral portion of 
the disk 22 and upper and lower surfaces of the central portion of the 
disk 22, thereby forming an outer peripheral resin portion 26 and a 
central resin portion 27, as shown in FIG. 2C. In this outsert molding 
operation, the disk 22, having the capstan shaft 10A (10B) press-fitted 
therein (as shown in FIG. 2B), is set in a mold for the resin, and then 
the resin is poured into this mold. At a result of carrying out this 
outsert molding, a groove 28 of a V-shaped cross-section is formed in an 
outer peripheral surface of the outer peripheral resin portion 26, and 
also gear portions 29 and 30 are formed on the central resin portion 27. 
During this outsert molding, the resins filled respectively on the upper 
and lower surfaces of the disk 22 are joined together through the small 
holes 25 formed through the disk 22. As shown in FIG. 3, interconnecting 
resin portions 31 interconnect the outer peripheral resin portion 26 and 
the central resin portion 27 at the lower surface of the disk 22. 
The flywheel device shown in FIG. 1 is rotatably supported on a base plate 
(as at 6 in FIG. 6) by a bearing fixedly mounted on the base plate, and a 
rotational drive force of a motor is transmitted via a belt to the 
flywheel to rotate the same. 
As described above, in this embodiment, the disk 22 of metal is used as a 
core material of the flywheel, and therefore a required inertia moment can 
be obtained without the use of the special resin containing the metal 
powder as in the conventional flywheel. Moreover, since the capstan shaft 
10A, (10B) is press-fitted in the metal disk 22 serving as the core 
material, the capstan shaft 10A, (10B) can be firmly fixed without the use 
of the bushing 20 as in the conventional flywheel. Furthermore, since any 
metal powder does not need to be contained in the resin to be used for the 
outsert molding shown in FIG. 2C, the flywheel of this embodiment can be 
produced at lower costs. 
FIGS. 4A to 4C show another preferred embodiment of the invention. This 
embodiment is characterized in that a hole 44 is formed through a central 
portion of a disk 42, and that a hollow cylindrical portion 42A, 
projecting upwardly, is formed by drawing (beading) on an upper surface of 
the disk 42 around a peripheral edge of the hole 44. The capstan shaft 
10A, (10B) is press-fitted in the central hole 44 as shown in FIG. 4B, and 
then as shown in FIG. 4C, an outer peripheral resin portion 46, a central 
resin portion 27 and interconnecting resin portions not shown are formed 
by outsert molding as in the preceding embodiment shown in FIG. 2. Holes 
45, groove 48 and gear portions 49, 50 are similar to holes 25, groove 28 
and gear portions 29, 30 of the preceding embodiment. In this embodiment, 
the area of contact between the capstan shaft 10A, (10B) (press-fitted in 
the central hole 44) and the disk 42 is larger, and therefore there is 
achieved an advantage that the capstan shaft 10A (10B) is fixed more 
firmly. In both embodiments, the central resin portion is in contact with 
the capstan shaft. 
In the above construction of the present invention, the metal disk is used 
as the core material, and therefore there is achieved an advantage that 
the required inertia moment can be obtained without the use of a metal 
power-containing resin as in the conventional construction. Moreover, 
since the capstan shaft is press-fitted in the metal disk serving as the 
core material, the capstan shaft can be firmly fixed without the use of a 
bushing as in the conventional construction. In the second aspect of the 
invention, the hollow cylindrical portion is formed around the peripheral 
edge of the central hole in the disk, and therefore the area of contact 
between the capstan shaft (press-fitted in this central hole) and the disk 
is larger, thereby achieving an advantage that the capstan shaft can be 
more firmly fixed to the central portion of the disk. In the third aspect 
of the invention, the step of press-fitting a bushing in a resin-molded 
flywheel as in the conventional construction, as well as the step of 
press-fitting the capstan shaft in this bushing, is unnecessary, and the 
flywheel device of the invention can be produced easily at lower costs.