Cooling apparatus of a gear transmission having an electromagnetic clutch

A cooling structure of a power transmission apparatus is provided. The power transmission apparatus has an electromagnetic clutch including a fixed outer member with an exciting coil and a rotary inner member adapted to be fixed to the outer member by controlling electric energy provided to the exciting coil, and a gear device connected to the inner member of the electromagnetic clutch. A cooling apparatus is positioned between the outer member and a gear case member housing the gear device, for cooling both of the electromagnetic clutch and the gear device concurrently.

BACKGROUND OF THE INVENTION 
The present invention relates to a power transmission apparatus used for a 
clutch or a brake, and particularly to a cooling structure thereof. 
In an magnetic particle type electromagnetic clutch having an outer member 
forming an annular space, an inner member arranged inside of the outer 
member and electromagnetic powder of magnetic particles interposed between 
the outer and inner members, when an exciting coil supported by the outer 
member is charged with electricity to produce a magnetic field, magnetic 
particles in the electromagnetic powder are magnetized and a linkage of 
the magnetic particles is formed for connecting the outer and inner 
members. When the exciting coil is not charged with electricity, the outer 
and inner members are disconnected so as to freely rotate mutually. 
In such a magnetic particle type electromagnetic clutch, a large amount of 
heat is generated by the exciting coil and slipping of the clutch on 
connecting and disconnecting to deteriorate stable 
connection-disconnection function and durability, therefore a forced 
cooling is necessary in general. 
Accordingly, in a magnetic particle type electromagnetic clutch disclosed 
in Japanese Laid-Open Utility Model Publication No. Sho 63-64938 (1988), 
within an inner member is formed a cooling water passage from a core 
portion to an outer peripheral portion opposed to an outer member and at 
the outer peripheral portion is provided a special annular chamber to 
improve cooling effect. 
There is also another example wherein a cooling water passage is formed in 
an outer member to cool mainly an exciting coil side. 
In these examples, the cooling water passage is formed within an inner 
member or an outer member, so that it is advantageous spatially and the 
electromagnetic clutch itself does not become large. 
However, since the cooling water passage is formed in the inner or outer 
member, construction of the member becomes complicated and the working is 
very troublesome. In case of a clutch which is connected and disconnected 
while both inner and outer members rotate, formation of the cooling water 
passage at a boundary between a fixed part and a rotating part is 
difficult. When the cooling water passage is formed in the inner member, 
cooling effect against heat generation of the exciting coil is small. 
Further, the inner and outer members must be worked with high accuracy or 
sealed surely so that the cooling water passage is blocked surely from the 
electromagnetic powder and the exciting coil, which are apt to be 
influenced by liquid, and no leak of the cooling water occurs. This is 
difficult technically and results in a high cost, sometimes. 
When the cooling water passage is formed within the inner or outer member, 
it is difficult to form fins within a limited interior space resulting in 
a small heat transmitting area, therefore a large quantity of water must 
be flowed in order to obtain a high cooling effect. If the cooling water 
passage is made of iron or steel material apt to rust, there is the 
possibility that the passage is stopped up by the rust, therefore 
complications on use such as rust prevention, administration of the 
cooling liquid, periodical maintenance are accompanied. 
Further, when the magnetic particle type electromagnetic clutch is combined 
with a gear device to constitute a power transmission apparatus and the 
gear device is also necessitated to be cooled, another cooling apparatus 
for the gear device has to be provided, that is uneconomical in view of 
space and cost. 
SUMMARY OF THE INVENTION 
The present invention has been accomplished in view of the foregoing and an 
object of the invention is to provide a cooling structure of a power 
transmission apparatus in which the construction is simple and easily 
worked, it is easy to provide fins for improving cooling effect, there is 
no complication on use and both a clutch side and a gear device side can 
be cooled concurrently. 
In order to attain the above object, the present invention provides a 
cooling structure of a power transmission apparatus having an 
electromagnetic clutch including a fixed outer member with an exciting 
coil and a rotary inner member adapted to be fixed to the outer member by 
controlling electric energy provided to the exciting coil, and a gear 
device connected to the inner member, comprising a cooling apparatus 
positioned between the outer member and a gear case member housing the 
gear device. 
According to the present invention, since the cooling apparatus is provided 
utilizing a dead space between the fixed outer member of the 
electromagnetic clutch and the gear case member, it can be avoided that 
the power transmission apparatus becomes large owing to the cooling 
apparatus. Since the cooling apparatus is provided outside of the outer 
member, the construction can be simplified, the working is easy, the 
cooling medium can be sealed simply and surely, and the maintenance is 
also easy without accompanying complications on use. 
Both slipping portion between the outer and inner members and the exciting 
coil, which are the heat sources, can be cooled by the cooling apparatus 
with a high cooling efficiency. In addition, the cooling apparatus 
concurrently cools the gear device side too, so that another cooling 
apparatus is unnecessary. 
The above-mentioned gear device may be a planetary gear device having a 
first gear element connected to an input member for inputting a rotational 
driving force, a second gear element connected to an output member and a 
third gear element connected to the inner member of the electromagnetic 
clutch. According to this configuration, a power transmission apparatus 
with a variable-speed mechanism can be constituted easily. 
The above-mentioned cooling apparatus may have a passage for cooling medium 
formed by fins projected from the outer member toward the gear case 
member. According to this configuration, a large heat transmitting area is 
ensured within a narrow space to improve the cooling effect and therefore 
it is unnecessary to let a large quantity of cooling medium flow. Since 
the fins are formed outside of the outer member, the work is easy. 
The above-mentioned passage for cooling medium may have an outlet port at 
an uppermost portion of the passage and an inlet port at a portion lower 
than the outlet port. In this configuration, air within the cooling 
apparatus is discharged from the outlet port at the uppermost position and 
never stay in the cooling medium passage so that an efficient cooling can 
be maintained. 
A second passage for cooling medium constituting a heat exchange portion to 
an interior of the gear case member may be formed between the outer member 
and the gear case member in addition to the above-mentioned first passage 
for cooling medium. According to this configuration, both the 
electromagnetic clutch and the gear device can be cooled efficiently by 
only one cooling apparatus. 
The first and second passages may be connected with each other positioning 
the second passage at an upper stream side of flow of the cooling medium 
and the first passage at a lower stream side of flow of the cooling 
medium. In this configuration, the cooling medium flows firstly through 
the second passage constituting the heat exchange portion to the interior 
of the gear case member in which heat generation and temperature are lower 
than those in the electromagnetic clutch, and then flows through the first 
passage of higher temperature, so that an efficient cooling can be 
obtained. 
A lubricating oil introducing port may be provided at the heat exchange 
portion. Since the lubricating oil is cooled at the heat exchange portion 
by the cooling medium then supplied to the gear device, the gear device is 
cooled very effectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Hereinafter, an embodiment of the present invention will be described with 
reference to FIGS. 1 to 3. This embodiment is a two-stage variable-speed 
apparatus 1 of which a rough constitutional view is shown in FIG. 1. The 
two-stage variable-speed apparatus 1 is constituted by combining a 
magnetic particle type electromagnetic clutch 10, a planetary gear device 
20 and a hydraulic clutch 30, on the whole, and a cooling apparatus 40 is 
provided between the electromagnetic clutch 10 and the planetary gear 
device 20. 
The magnetic particle type electromagnetic clutch 10 comprises a fixed 
stationary outer member 11 and an inner member 12 arranged rotationally 
inside of the outer member fitted to a rotary cylindrical member 13. An 
exciting coil 14 wound in a circumferential direction is housed in a 
circumferential wall 18 of the outer member 11 and electromagnetic powder 
15 is interposed between the outer member 11 and the inner member 12. The 
exciting coil 14 on the stationary side is supplied with electric power 
from an electric source 16 through electric lines 17. 
The planetary gear device 20 and the hydraulic clutch 30 are accommodated 
in a gear case member 35. The planetary gear device 20 has a ring gear 21 
integrally connected to an input shaft 2 as well as a rotary member 31 of 
the hydraulic clutch 30, a sun gear 22 connected to the rotary cylindrical 
member 13 of the electromagnetic clutch 10 through an one-way clutch 5, 
and a planetary gear 23 connected to another rotary member 32 of the 
hydraulic clutch 30 through a carrier 24. The rotary member 32 is 
integrally connected to an output shaft 3. 
Between the gear case member 35 covering the planetary gear device 20 and 
the hydraulic clutch 30 and the rotary cylindrical member 13 projecting 
from the gear case member is interposed a seal member 36, between the gear 
case member 35 and the output shaft 3 is interposed a seal member 37 and 
also between the input shaft 2 and the rotary cylindrical member 13 is 
interposed a seal member 38. These seal members prevent lubricating oil in 
the gear case member 35 from leaking out. 
When both of the magnetic particle type electromagnetic clutch 10 and the 
hydraulic clutch 30 are in clutch-out states, the inner member 12 of the 
electromagnetic clutch 10 can rotate freely and the sun gear 22 connected 
to the inner member 12 also can rotate freely. Rotation of the ring gear 
21 caused by rotational power of the input shaft 2 is transmitted to the 
freely rotatable sun gear 22 through the planetary gear 23 with no load, 
and the sun gear 22 runs idle in reverse together with the rotary 
cylindrical member 13 connected to it through the one-way clutch 5. 
Since the planetary gear 23 rotates on its axis but does not revolve round 
the sun gear, no power is transmitted to the carrier 24, the rotary member 
32 of the hydraulic clutch 30 and the output shaft 3, therefore the 
apparatus is in a neutral state. 
At this time, if the exciting coil 14 of the electromagnetic clutch 10 is 
electrified, a magnetic field takes place and the magnetic particles of 
the electromagnetic powder 15 are magnetized to form a linkage for 
connecting the inner member 12 with the stationary outer member 11. As the 
result, the inner member 12 is fixed together with the rotary cylindrical 
member 13 to prohibit the reverse rotation of the sun gear 22 through the 
one-way clutch 5. And between the sun gear prohibited from the reverse 
rotation and the ring gear 21 rotated by the rotational power of the input 
shaft 2, the planetary gear 23 revolves round the sun gear 22 while 
rotating on its own axis to rotate the carrier 24, the rotary member 32 of 
the hydraulic clutch 30 and the output shaft 3 at a low speed. 
Hereupon, if also the hydraulic clutch 30 is let in, the ring gear 21 and 
the carrier 24 are integrally connected and the whole planetary gear 
device 20 can rotate as one body, because the normal rotation of the sun 
gear is not prohibited by the one-way clutch 5. Namely, the input shaft 2 
is directly connected to the output shaft 3 for rotating the output shaft 
3 at a high speed. 
As mentioned above, according to the variable-speed apparatus 1, two stages 
of variable-speed states, high and low, can be obtained besides the 
neutral state. Shifting from the neutral state to the low or high speed 
rotation state can be carried out quickly and smoothly using the magnetic 
particle type electromagnetic clutch 10. 
Now, the cooling apparatus provided in the annular space between the gear 
case member 35 and the circumferential wall 18 of the magnetic particle 
type electromagnetic clutch 10 will be described. FIG. 3 shows a more 
concrete construction of a part of the electromagnetic clutch 10 and the 
gear case member 35 relating to the cooling apparatus 40. 
The input shaft 2 is rotationally supported by a bearing 6 within the 
rotary cylindrical member 13. The member 13 is rotationally supported by a 
bearing 7 within a cylindrical opening 35a at the input side of the gear 
case member 35 and extruded outside. A radially extending disk-like flange 
13a is formed at the extruded outer end of the rotary cylindrical member 
13. An inner circumferential portion of the annular inner member 12 is 
fixed to the flange 13a. 
The inner member made of iron material has an outer circumferential 
enlarged portion 12a surrounded by the annular circumferential wall 18 of 
the outer member 11. The wall 18 is made of aluminum which is nonferrous 
material having a good thermal conductivity and formed in a U-shaped 
section by an outer wall portion 18a, an outer peripheral wall portion 18b 
and an inner wall portion 18c. The wall portions 18b and 18c are formed in 
one body. The wall portions 18a, 18b, 18c cover an annular interior space 
and at a radially outer portion in the annular interior space is provided 
the exciting coil 14 supported by a field core 19 made of iron. 
The enlarged portion 12a of the inner member 12 is positioned in the space 
at an inner circumference side of the exciting coil 14. At an inner 
circumference side of the enlarged portion 12a, on surfaces of the both 
sides of the inner member and each inner surface of the outer wall portion 
18a and the inner wall portion 18c are fixed tapering ring-shaped 
obstruction plates 8 being opened toward radially outward direction to 
prevent the magnetic particles from falling toward radially inner side and 
let them remain in the neighborhood of the exciting coil 14 always. Thus, 
biasing of the electromagnetic powder 15 can be prevented and a smooth 
operation of the clutch is obtainable. 
At a radially outer circumference on an outer face of the inner wall 
portion 18c of the outer member 11 are formed and projected a plurality of 
arcuate cooling fins 41 coaxially. Each cooling fin 41 has inner and outer 
circumferential surfaces slightly inclined to each other so as to be 
tapered and a slope .theta. for mold drawing is formed. 
A side wall 35b of the gear case member 35 facing the electromagnetic 
clutch 10 and having the cylindrical opening portion 35a has a cylindrical 
portion 35c projecting at the radially outer circumference thereof. The 
inner diameter of the cylindrical portion 35c is equal to the outer 
diameter of the outer peripheral wall portion 18b of the circumferential 
wall 18 of the outer member 11 and in the cylindrical portion 35c is 
fixedly fitted the outer member 11 with intermediation of O-ring 39. A 
space between the inner wall portion 18c of the outer member 11 and the 
side wall 35b of the gear case member 35 forms a cooling water passage 42 
through which cooling water of the cooling apparatus 40 flows. 
The cooling fins 41 provided at the radially outer circumference in the 
passage 42 have tip ends close to the side wall 35b of the gear case 
member 35 with some clearance C. Cooling water passages 42a are formed 
between adjacent cooling fins 41. 
As shown in FIG. 2, the cooling fins 41 are shaped in semicircular arcs and 
arranged separated in right and left at appropriate intervals. A cooling 
water inlet port 44 is provided at a lower separation space 43 and a 
cooling water outlet port 46 is provided at an upper separation space 45. 
In the cooling apparatus 40 formed between the electromagnetic clutch 10 
and the gear case member 35, cooling water is introduced into the lower 
separation space 43 through the cooling water inlet port 44, branches off 
into right and left from the space 43 and flows upward through the cooling 
water passages 42a formed by the arcuate cooling fins 41. The right and 
left flows join at the upper separation space 45 to be discharged through 
the cooling water outlet port 46 at the uppermost position of the cooling 
water passage 42. 
As described above, the cooling apparatus 40 is provided utilizing a dead 
space between the outer member 11 of the magnetic particle type 
electromagnetic clutch 10 and the gear case member 35 of the planetary 
gear device 20, so that the variable-speed apparatus 1 does not become 
large owing to the cooling apparatus 40. In addition, since the cooling 
apparatus 40 is capable of cooling the planetary gear device side too, 
another apparatus for cooling the planetary gear device 20 is unnecessary. 
The cooling apparatus 40 is provided outside of the outer member 11 instead 
of being provided within the outer member 11 or the inner member 12, so 
that the construction of the magnetic particle type electromagnetic clutch 
10 itself can be simplified and working and manufacturing of the clutch is 
easy. 
Since the cooling fins 41 are formed on the outer side of the inner wall 
portion 18c of the circumferential wall 18 of the outer member 11 and have 
the slopes .theta., mold drawing is easy. Further, the circumferential 
wall 18 is made of aluminum having plasticity, so that the outer member 
can be worked very easily and produced in large quantities cheaply. 
The inner wall portion 18c and the cooling fins made of aluminum are 
corrosion-resistant and rustless, so that there is no possibility that the 
cooling water passage is stooped up by the rust to lower cooling effect 
and complications on use such as rust prevention, administration of the 
cooling liquid and periodical maintenance are not accompanied. 
The electromagnetic powder 15 and the exciting coil 14 housed within the 
circumferential wall 18 of the outer member 11 are apt to be influenced by 
liquid, but since the cooling water flows outside of the circumferential 
wall 18, a reliable seal is ensured without adopting a special 
construction for sealing. Therefore, an improvement of performance 
reliability can be expected. 
The cooling water passage 42 of the cooling apparatus 40 extends over 
nearly whole surface of a side of the outer member 11 and the cooling fins 
41 are provided on the circumferential wall 18 covering heat sources such 
as the exciting coil 14 and the sliding portion between the outer and 
inner members 11, 12, so that the heat sources are cooled efficiently. 
The circumferential wall 18 with the cooling fins 41 formed integrally is 
made of aluminum having a good heat conductivity and the iron core 19 
supporting the exciting coil 14 is wrapped in the circumferential wall 18 
for effective cooling of the exciting coil 14. 
Cooling water introduced from the lower inlet port 44 flows upward through 
the passage 42a formed by the cooling fins 41 and discharges out of the 
outlet port 46 positioned at an uppermost portion of the cooling water 
passage 42. There is some clearance formed between the cooling fin 41 
projecting from the circumferential wall 18 and the side wall 35b of the 
gear case member 35. Therefore, air within the cooling water passage 42 is 
discharged without remaining in the passage to obstruct the cooling. 
Needless to say, as for the cooling medium, it is better to use liquid 
such as water which has far superior heat transfer rate compared with gas. 
FIGS. 4 to 6 show another embodiment of the present invention. The 
variable-speed apparatus 50 according to this embodiment has the same 
construction as the above-mentioned variable-speed apparatus 1 excepting 
that a heat exchange portion 60 to an interior of the gear case member is 
provided in the cooling apparatus 51. Therefore, in FIGS. 4 to 6, parts 
similar to those of the above-mentioned embodiment are denoted by the same 
reference numerals. 
As shown in FIG. 6, at a central part of the side wall 35b of the gear case 
member 35 are provided a heat exchange portion 60 having arcuate cooling 
fins 61, 62 formed on the both surfaces. The fins 61 project into the 
cooling water passage 42 of the cooling apparatus while the fins 62 
project into an interior of the gear case member 35. 
The cooling fins 61 comprises a cooling fin 61a of maximum diameter having 
a circular shape opened at a lower part only and the other fins 61 having 
semicircular shape arranged right and left separately. These cooling fins 
61 form a second cooling water passage 64 communicating with the 
aforementioned first cooling water passage 42a formed by the cooling fins 
41. Among the cooling fins 61, fins 61b of an intermediate diameter are 
connected with a connecting passage 63 extending radially downward. The 
connecting passage 63 passes through the lower separation space 43 of the 
cooling fins 41 to communicate with the cooling water inlet port 44. 
As shown in FIG. 5, the cooling water introduced from the cooling water 
inlet port 44 provided at the lower side of the cooling apparatus 51 
passes through the connecting passage 63 toward the center side, enters 
radially inner portion of the cooling water passage 64 of the heat 
exchange portion 60, separates right and left to flow upward and again 
joins together at the upper space. Then, the cooling water flows down 
through right and left radially outer portions of the cooling water 
passage 64 to the lower separation space 43, enters right and left cooling 
water passage 42a, joins together at the upper separation space 45 and 
discharges from the cooling water outlet port 46 at the uppermost position 
of the cooling water passage. 
As described above, in the cooling apparatus 51, the second cooling water 
passage 64 for cooling the gear case member 35 side is arranged at the 
upper stream side of flow of the cooling water and the first cooling water 
passage 42a for cooling the magnetic particle type electromagnetic clutch 
10 side is arranged at the lower stream side of flow of the cooling water 
so that the cooling water flows from the gear case member 35 side to the 
electromagnetic clutch 10 side. 
As the heat exchange portion 60 is provided, the planetary gear device 20 
is cooled efficiently concurrently with cooling of the electromagnetic 
clutch 10. In addition, since the cooling water firstly flows through the 
second cooling water passage 64 on the side of the planetary gear device 
20 in which heat generation is smaller and temperature is lower compared 
with the electromagnetic clutch, then flows through the first cooling 
water passage 42a in which temperature is higher, more efficiently cooling 
can be carried out. 
Another heat exchange portion 70 shown in FIG. 7 is formed by transforming 
its side wall 71 into a wave-like sectional shape in place of providing 
the above-mentioned cooling fins 61, 62. There is no substantial 
difference in heat exchange effect between the heat exchange portions 51, 
71, but the heat exchange portion 71 can be worked more easily. 
FIGS. 8 and 9 show the other embodiment. The variable-speed apparatus 80 of 
this embodiment has the same construction as the above-mentioned 
variable-speed apparatus 1, 50 and the cooling apparatus 81 is provided 
with a heat exchange portion 90 to the interior of the gear case member 
similarly to the above-mentioned cooling apparatus 51, however the heat 
exchange portion 90 has a lubricating oil introducing passage 96. 
Therefore, in FIGS. 8 and 9, parts similar to those of the above-mentioned 
embodiments are denoted by the same reference numerals. 
The heat exchange portion 90 has arcuate cooling fins 91, 92 on both sides 
similarly to the aforementioned heat exchange portion 60, and the cooling 
water passage formed by the cooling fins 91 projecting into the cooling 
apparatus 81 and the cooling fins 41 of the electromagnetic clutch 10 side 
has the same construction as that of FIG. 5. 
The cooling fins 92 on the side of the planetary gear device 20 are 
semicircular and arranged apart right and left within an outermost 
circumferential wall 92a which is perfectly circular. These fins 92 are 
separated from interior of the gear case by a partition wall 95 and form a 
lubricating oil introducing passage 96. 
Lubricating oil is introduced into the lubricating oil introducing passage 
96 from an introducing port 96a provided on a lower side of the central 
cylindrical opening portion 35a of the gear case member 35, and discharged 
from a discharging port 96b provided in the partition wall 95 at a 
position corresponding to an outer circumferential and upper portion of 
the cooling fins 92 to be supplied into the gear case. 
Since the lubricating oil is cooled just before it is supplied into the 
gear case, the planetary gear device 20 can be cooled efficiently. 
In the above-mentioned embodiments, the present invention is applied to the 
power transmission apparatus using the magnetic particle type 
electromagnetic clutch, however, the cooling structure of the present 
invention is also applicable to an electromagnetic clutch of hysteresis 
type or friction plate type, a mechanical type clutch using a friction 
plate or a oil-air type clutch. 
In the cooling apparatuses 40, 51, 70, the cooling fins 41 project from the 
side of the electromagnetic clutch 10, but cooling fins projecting from 
the side of the gear case member 35 may be formed additionally. Further, 
in the heat exchange portions 60, 90, additional cooling fins facing to 
the cooling fins 61, 91 may be projected from the side of the 
circumferential wall 18 of the electromagnetic clutch 19.