US20060196575A1

US20060196575A1 - Overflow tube

Info

Publication number: US20060196575A1
Application number: US11/295,550
Authority: US
Inventors: Kazuaki Nakamura; Hiromichi Kimura; Kazuyuki Watanabe; Terufumi Miyazaki; Daisuke Kusamoto
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2005-03-07
Filing date: 2005-12-07
Publication date: 2006-09-07
Also published as: JP2006242365A; CN1831382A; DE102006000018A1; CN100449179C; CN101245847A; DE102006000018B4

Abstract

An overflow tube is provided at an oil pan and when the oil pan receives an amount of a working fluid exceeding a prescribed amount the overflow tube causes the fluid to overflow to allow the fluid to have a level set at a prescribed level. The overflow tube has an end portion positioned in the oil pan and defining an opening of a drain hole receiving and passing the fluid overflowing. The end portion has a curved surface facing vertically upward and extending to surround the opening of the drain hole, and curving in a direction in contact with a generally horizontal direction. The overflow tube can thus help to set the fluid's level at a prescribed level precisely.

Description

This nonprovisional application is based on Japanese Patent Application No. 2005-062770 filed with the Japan Patent Office on Mar. 7, 2005, the entire content of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates generally to overflow tubes and particularly to overflow tubes used to control oil level oil in a casing.
2. Description of the Background Art
For a conventional oil level control scheme, for example Japanese Patent Laying-open No. 10-213210 discloses an automatic transmission intended to provide increased workability in storing a prescribed amount of working fluid. The disclosed automatic transmission is provided with an oil introduction port for introducing the working fluid into an oil chamber and an oil adjustment port allowing the working fluid to overflow from the oil chamber. Thus the working fluid can be replenished while the working fluid can overflow allowing one to confirm that the prescribed amount of the working fluid has been stored.
Furthermore Japanese Utility Model Laying-open No. 05-017336 discloses an oil supply tank for a petroleum combustion instrument that can help to break fuel's surface tension to prevent the fuel from being replenished in a large amount at a time. The disclosed tank has a plurality of recesses in a surface thereof located at a topmost end of the tank and defining a fixed oil level in contact with an oil level. The surface faces a vertically downward direction.
As disclosed in Japanese Patent Laying-open No. 10-213210, when more than the prescribed mount of oil is introduced the oil level control scheme that exploits overflow externally discharges the oil through an overflow tube to set an oil level at the position of an end of the tube.
However, oil has surface tension and in reality the oil level is set at a level several millimeters higher than the end of the tube. The oil level thus set is unstable because of a condition in introducing the oil, the oil's waving, and the like, and may have an error introduced therein. Furthermore, it also causes the tube to have difficulty in stopping the oil flowing out the tube and one cannot determine when to apply a drain plug to close the tube, resulting in poor workability in exchanging the oil.

SUMMARY OF THE INVENTION

The present invention has been made to overcome the above disadvantage, and it contemplates an overflow tube that can help to set an oil level precisely at a prescribed level.
The present invention in one aspect provides an overflow tube provided at a case body and causing an amount of a working fluid exceeding a prescribed amount received by the case body to overflow to set a level of the working fluid at a prescribed level. The overflow tube includes an end portion positioned in the case body and defining an opening receiving and passing the working fluid overflowing. The end portion has a curved surface facing vertically upward and extending to surround the opening, and curving in a direction in contact with a generally horizontal direction. It should be noted that “facing vertically upward” means facing away from the ground with respect to the horizon (or a straight line perpendicular to a vertical direction) and corresponds to a range from a vertically upward direction to a horizontal direction.
The overflow tube thus structured has the curved surface curved in a direction that is in contact with a generally horizontal direction. The working fluid having a level raised around the end portion by surface tension can be guided along the curved surface into the opening. Thus the working fluid's surface tension can be broken and the working fluid can have a level readily set at a prescribed level as intended.
The present invention in another aspect provides an overflow tube provided at a case body and causing an amount of a working fluid exceeding a prescribed amount received by the case body to overflow to set a level of the working fluid at a prescribed level. The overflow tube includes an end portion positioned in the case body and defining an opening receiving and passing the working fluid overflowing. The end portion has an inclined surface facing vertically upward and extending to surround the opening, and inclining from a circumference of the end portion toward the opening vertically downward.
The overflow tube thus structured has the inclined surface inclined from the end portion, which is filled with the working fluid, toward the opening vertically downward. The working fluid having a level raised around the end portion by surface tension can be guided along the inclined surface into the opening. Thus the working fluid's surface tension can be broken and the working fluid can have a level readily set at a prescribed level as intended.
The present invention in still another aspect provides an overflow tube provided at a case body and causing an amount of a working fluid exceeding a prescribed amount received by the case body to overflow to set a level of the working fluid at a prescribed level. The overflow tube includes an end portion positioned in the case body and defining an opening receiving and passing the working fluid overflowing. The end portion has a surface facing vertically upward and extending to surround the opening, and formed to be uneven.
The overflow tube that has the end portion with an uneven surface can contact the working fluid over a surface having an increased area. This can promote a fluid guiding effect attributed to capillarity (i.e., the action by which the surface of a liquid where it is in contact with a solid is attracted to the solid) to more positively guide to the opening the working fluid contacting the surface. Thus the working fluid's surface tension can be broken and the working fluid can have a level readily set at a prescribed level as intended.
Preferably the surface is satin finished. Furthermore, preferably the surface is serrated to have a plurality of teeth arranged along a circumference of the opening. Furthermore, preferably the surface has a groove extending from a circumference of the end portion toward the opening. The overflow tube thus structured allows a capillary fluid guiding effect to more effectively be utilized.
The present invention in still another aspect provides an overflow tube provided at a case body and causing an amount of a working fluid exceeding a prescribed amount received by the case body to overflow to set a level of the working fluid at a prescribed level. The overflow tube includes: an end portion positioned in the case body and defining an opening receiving and passing the working fluid overflowing; and a guiding member provided at the end portion in a form of a string extending from a circumference of the end portion toward the opening.
The overflow tube thus structured allows the working fluid having a level raised around the end portion by surface tension to be guided through capillarity along the guide member into the opening. Thus the working fluid's surface tension can be broken and the working fluid can have a level readily set at a prescribed level as intended.
The present invention in still another aspect provides an overflow tube provided at a case body and causing an amount of a working fluid exceeding a prescribed amount received by the case body to overflow to set a level of the working fluid at a prescribed level. The overflow tube includes an end portion positioned in the case body and defining an opening receiving and passing the working fluid overflowing. The end portion has a surface facing vertically upward and extending to surround the opening, and lipophilically coated.
The overflow tube that has the end portion with a surface coated with a lipophilic coating allows the working fluid to have a surface contacting that of the end portion at a reduced contact angle. Thus the working fluid's surface tension can be broken and the working fluid can have a level readily set at a prescribed level as intended. Note that the “contact angle” as referred to herein indicates an angle formed by a surface of a solid contacting a liquid and a gas and a surface of the liquid at a boundary interface at which the three phases contact each other, as represented on the liquid's side.
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

FIG. 1 is an exploded view of an automatic transmission employing the present overflow tube in a first embodiment.
FIG. 2 is a cross section of the automatic transmission of FIG. 1, as enlarged at a portion encircled by a chained line II.
FIG. 3 is a top view of the overflow tube as seen in a direction indicated in FIG. 2 by an arrow III.
FIG. 4 is a cross section for illustrating an oil level set by the overflow tube of FIG. 2.
FIG. 5 is a cross section of the overflow tube of FIG. 2 in an exemplary variation.
FIGS. 6 and 7 are cross sections of the present overflow tube in second and third embodiments, respectively.
FIG. 8 is a cross section of the overflow tube of FIG. 7 in a first exemplary variation.
FIGS. 9A and 9B are a perspective view and a cross section, respectively, of the overflow tube of FIG. 7 in a second exemplary variation.
FIGS. 10A and 10B are a perspective view and a cross section, respectively, of the present overflow tube in a fourth embodiment.
FIG. 11 is a perspective view of the present overflow tube in a fifth embodiment.
FIG. 12 is a cross section of the overflow tube of FIG. 11 at a portion encircled by a chained line XII indicated in FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention in embodiments will now be described with reference to the drawings. In the figures, identical or like components are identically denoted.

First Embodiment

With reference to FIG. 1 an automatic transmission 10 has a casing formed of a transmission case 11 opened in a vertically downward direction and an oil pan 12 in the form of a saucer attached to transmission case 11 to close the position of the opening. In transmission case 11 is housed a gear, a shaft, a bearing and the like shifting force output from an engine for output toward a drive shaft.
The casing of automatic transmission 10 has a prescribed amount of working fluid sealed therein and oil pan 12 receives the working fluid. The working fluid serves for example as a lubricant oil referred to as automatic transmission fluid (ATF) and serving to allow a shifting clutch to be operated and a torque converter's force to be transmitted, and prevent gears and other similar mechanical elements from seizing up. Oil pan 12 has a bottom 12 m having a mechanism located at a position indicated in a circle II for controlling the working fluid in level.
With reference to FIGS. 1 and 2, oil pan 12 is provided at bottom 12 m with an overflow tube 21 having a cylindrical portion 26 extending from bottom 12 m vertically upward toward an internal space 13 of oil pan 12, and an end portion 23 formed at an end of cylindrical portion 26 opposite to bottom 12 m.
Cylindrical portion 26 has external and internal walls 28 and 27, respectively, and is formed to extend cylindrically around a vertically extending center axis 101. Surrounded by internal wall 22 is a drain hole 22 communicating external to oil pan 12. Note that overflow tube 21 may be integrated with oil pan 12 or attached to a side portion of oil pan 12. Furthermore oil pan 12 may not necessarily be provided at oil pan 12. For example it may be provided at transmission case 11. Furthermore, cylindrical portion 26 may by bent between bottom 12 m and end portion 23.
With reference to FIGS. 1-3, end portion 23 is formed to flare from cylindrical portion 26. At a location surrounded by end portion 23 is defined an opening of drain hole 22, and at that location drain hole 22 communicates with internal space 13. End portion 23 is formed in a body of revolution around center axis 101. More specifically, end portion 23 has an identical cross section in a circumferential direction with center axis 101 serving as a center. Working fluid 31 contacts external wall 28 and fills a circumference of end portion 23 (i.e., a side opposite drain hole 22 with end portion 23 posed therebetween).
End portion 23 has a curved surface 23 a. Curved surface 23 a faces vertically upward and extends annularly to surround the opening of drain hole 22. Curved surface 23 a is formed to curve to contact in a generally horizontal direction. Curved surface 23 a is formed to directly adjacent to internal wall 27. Curved surface 23 a has a portion 23 q extending from a portion 23 p, which is in contact with a generally horizontal direction, toward internal wall 27 in a direction varying from the generally horizontal direction to a vertically downward direction.
FIG. 4 illustrates an oil level set by the overflow tube of FIG. 2. More specifically, FIG. 4 shows a portion indicated in FIG. 2 that is surrounded by a chained circle IV. With reference to FIGS. 1-4, working fluid 31 is introduced into the casing of automatic transmission 10 through a port (not shown) formed through transmission case 11. When working fluid 31 introduced exceeds a prescribed amount the excessive amount of working fluid 31 is externally discharged through the overflow tube 21 drain hole 22.
In doing so, surface tension acts to causes working fluid 31 to have a level, higher than the position of the opening of overflow tube 21. In the present embodiment, however, curved surface 23 a is provided at a position spacing working fluid 31 and drain hole 22. As such, working fluid 31 having a level raised by surface tension is guided along the curved surface 23 a portion 23 q toward drain hole 22. Working fluid 31 can thus have a raised level 31 a′ reduced to a level 31 a having substantially the same level as portion 23 p of curved surface 23 a, and set at that level. Furthermore working fluid 31 located at the raised level will not gradually flow out drain hole 22, and the tube can thus have reduced difficulty in stopping working fluid 31 discharged therethrough. This can provide increased workability in controlling the level.
With reference to FIG. 2, to further reduce difficulty in stopping working fluid 31 discharged through drain hole 22, overflow tube 21 may have internal wall 27 with a groove formed therein along center axis 101. The working fluid can flow along the groove and thus be externally discharged through drain hole 22 rapidly. Note that the embodiments described hereinafter can all have internal wall 27 provided with a groove.
Once a level has completely been set an oil plug (not shown) is attached to overflow tube 21 to close drain hole 22.
In the present invention as described in the first embodiment overflow tube 21 is provided at oil pan 12 serving as a case body and when oil pan 12 receives more than a prescribed amount of working fluid 31 overflow tube 21 causes the excessive amount of working fluid 31 to overflow to set level 3 la at a prescribed level. Overflow tube 21 has end portion 23 positioned internal to oil pan 12 and defining an opening of drain hole 22 serving as an opening receiving and passing the working fluid that overflows. End portion 23 has curved surface 23 a facing vertically upward and extending to surround the opening of drain hole 22, and also curving in a direction contacting a generally horizontal direction.
The present overflow tube 21 in the first embodiment thus configured allows end portion 23 that has curved surface 23 to break surface tension. As such, when automatic transmission 10 is assembled or repaired or working fluid 31 is exchanged or the like, working fluid 31 can have level 31 a readily set at a prescribed level previously assumed within oil pan 12. This can for example prevent level 31 a from attaining too high a level resulting in increased agitation resistance between a gear housed in transmission case 11 and working fluid 31. This can contribute to reduced energy loss in automatic transmission 10 and also prevent the working fluid from increasing in temperature and thus degrading. Furthermore, level 31 a will not be too low, and a pump that sucks working fluid 31 from oil pan 12 will not suck air. Automatic transmission 10 can thus be enhanced in reliability and durability.
Furthermore, as an appropriate amount of working fluid 31 can be supplied to oil pan 12, working fluid 31 is not wastefully consumed, which can contribute to reduced cost. Furthermore automatic transmission 10 can be prevented from having a weight larger than assumed.
With reference to FIG. 5, an overflow tube 41 presented as an exemplary variation has cylindrical portion 26 and an end portion 42 formed at an end of cylindrical portion 26. End portion 42 is directly adjacent to cylindrical portion 26 and extends therefrom along center axis 101 cylindrically. End portion 42 has a curved surface 42 a located at its extending end. Curved surface 42 a faces vertically upward and extends to surround the opening of drain hole 22 and curves in a direction contacting a generally horizontal direction. Overflow tube 41 thus configured can be as effective as overflow tube 21.
Note that while in the present embodiment overflow tube 21 is applied to automatic transmission 10, it is also applicable to a manual transmission, a continuously variable transmission (CTV), and the like. Furthermore the present invention is similarly applicable to engines, power shovels, working robots and other wet sump machines that require controlling a fluid in amount and level.

Second Embodiment

In the present embodiment the arrangement that overlaps that of overflow tube 21 in the first embodiment will not be described repeatedly.
With reference to FIG. 6 an overflow tube 46 has cylindrical portion 26 and an end portion 47 formed at an end of cylindrical portion 26. End portion 47 is directly adjacent to cylindrical portion 26 and extends therefrom along center axis 101 cylindrically. End portion 47 has an inclined surface 47 a located at its extending end. Inclined surface 47 a faces vertically upward and extends annularly to surround the opening of drain hole 22.
Inclined surface 47 a has an outer circumferential edge 47 p directly adjacent to external wall 28 and located relatively distant from center axis 101 and an inner circumferential edge 47 q directly adjacent to internal wall 27 and located relatively close to center axis 101. Inclined surface 47 a as seen from outer circumferential edge 47 p toward inner circumferential edge 47 q is formed to extend vertically downward. Inclined surface 47 a may be adapted to have an inclination varying between outer circumferential edge 47 p and inner circumferential edge 47 q.
Thus working fluid 31 having a level raised around overflow tube 46 by surface tension is guided along inclined surface 47 a into drain hole 22. Working fluid 31 can thus have level 31 a set substantially at the same level as outer circumferential edge 47 p of inclined surface 47 a.
The present invention in the second embodiment provides overflow tube 46 including an end portion 47 positioned internal to oil pan 12 and defining an opening of drain hole 22 receiving and passing a working fluid that overflows. End portion 47 has an inclined surface 47 a facing vertically upward and extending to surround the opening of drain hole 22, and also inclining from a circumference of end portion 47 toward the opening of drain hole 22 vertically downward.
Overflow tube 46 thus configured can achieve an effect similar to that described in the first embodiment.

Third Embodiment

In the present embodiment the arrangement that overlaps that of overflow tube 21 in the first embodiment will not be described repeatedly.
With reference to FIG. 7 an overflow tube 51 has cylindrical portion 26 and an end portion 52 formed at an end of cylindrical portion 26. End portion 52 is directly adjacent to cylindrical portion 26 and extends therefrom along center axis 101 cylindrically. End portion 52 has an uneven surface 52 a located at its extending end. Uneven surface 52 a faces vertically upward and extends annularly to surround the opening of drain hole 22.
Uneven surface 52 a is formed of surfaces of a protrusion 53 and a depression 54, respectively, alternately arranged around center axis 101 circumferentially. Protrusion 53 and depression 54 are formed to have a top surface 53 a and a bottom surface 54 a, respectively, having a step in a direction along center axis 101. Depression 54 is formed to extend around center axis 101 radially.
Uneven surface 52 thus formed enables working fluid 31 filling around the opening of drain hole 22 to contact surface 52 a over an area larger than when surface 52 a is formed flat. This can promote a capillary fluid guiding effect to guide working fluid 31 into drain hole 22 more positively. Working fluid 31 can thus have level 31 a set substantially at the same level of top surface 53 a of protrusion 53. It should be noted that for a different height of protrusion 53, a different width of depression 54 and some other conditions, level 31 a may be set at bottom surface 54 a of depression 54.
The present invention in the third embodiment provides overflow tube 51 including an end portion 52 positioned internal to oil pan 12 and defining an opening of drain hole 22 receiving and passing a working fluid that overflows. End portion 52 has an uneven surface 52 a facing vertically upward and extending to surround the opening of drain hole 22.
Overflow tube 51 thus configured can achieve an effect similar to that described in the first embodiment.
With reference to FIG. 8, an overflow tube 56 as an exemplary variation has cylindrical portion 26 and an end portion 57 formed at an end of cylindrical portion 26. End portion 57 has a serrated surface 57 a facing vertically upward and, as seen at a circumference of end portion 57, zigzagging around center axis 101 circumferentially. This arrangement allows working fluid 31 to have level 31 a set substantially at the same level as an apex of serrated surface 57 a. An effect similar to that of overflow tube 51 can be achieved.
FIG. 9 shows the overflow tube of FIG. 7 in a second exemplary variation, or an overflow tube 61, having cylindrical portion 26 and an end portion 62 formed at an end of cylindrical portion 26 and having an uneven surface 62 a formed of a surface of a protrusion 63 provided around center axis 101 for every 90° and a surface of a groove 64 formed between adjacent protrusions 63. Protrusion 63 and groove 64 are formed to have a top surface 63 a and a bottom surface 64 a, respectively, together forming a step in a direction along center axis 101, with top surface 63 a smaller in area than bottom surface 64 a. This arrangement allows working fluid 31 to have level 31 a set substantially at the same level as bottom surface 64 a of groove 64. An effect similar to that of overflow tube 51 can be achieved.
Furthermore, as a still another exemplary variation, the end portion may have an end surface satin finished and thus uneven. In that case, the end portion preferably has the end surface with maximum and minimum heights having a difference of 0.1 mm or larger, more preferably 0.3 mm or larger, most preferably 0.5 mm or larger.

Fourth Embodiment

In the present embodiment the arrangement that overlaps that of overflow tube 21 in the first embodiment will not be described repeatedly.
With reference to FIG. 10, an overflow tube 66 is formed of cylindrical portion 26, an end portion 67 formed at an end of cylindrical portion 26, and a guiding string 68 provided at end portion 67. End portion 67 is directly adjacent to cylindrical portion 26 and extends therefrom along center axis 101 cylindrically. End portion 67 has an end surface 67 a located at its extending end. End surface 67 a is formed in a plane extending in a generally horizontal direction. Guiding string 68 is located on end surface 67 a and also extends from external wall 28 to internal wall 27. Note that while the figure shows only a single guiding string 68, more than one guiding string 68 may be provided.
Working fluid 31 contacting guiding string 68 around a circumference of overflow tube 66 is drawn by capillarity to guiding string 68 and guided along guiding string 68 into drain hole 22. Working fluid 31 can thus have level 31 a set substantially at the same level as end surface 67 a.
In the present invention as described in the fourth embodiment overflow tube 66 includes end portion 67 positioned internal to oil pan 12 and defining an opening of drain hole 22 receiving and passing a working fluid that overflows, and guiding string 68 provided at end portion 67 and serving as a guiding member in the form of a string extending from a circumference of end portion 67 into the opening of drain hole 22.
Overflow tube 66 thus configured can achieve an effect similar to that described in the first embodiment.

Fifth Embodiment

In the present embodiment the arrangement that overlaps that of overflow tube 21 in the first embodiment will not be described repeatedly.
With reference to FIGS. 11 and 12 an overflow tube 71 has cylindrical portion 26 and an end portion 72 formed at an end of cylindrical portion 26. End portion 72 is directly adjacent to cylindrical portion 26 and extends therefrom along center axis 101 cylindrically. End portion 72 has an end surface 72 a located at its extending end. End surface 72 a is formed in a plane extending substantially in a generally horizontal direction. End surface 72 a is directly adjacent to both external wall 28 and internal wall 27. End surface 72 a for example has applied thereto a lipophilic coating 73 formed of titanium oxide.
Working fluid 31 having a level raised by surface tension around overflow tube 66 contacts a surface 73 a of lipophilic coating 73 at a reduced angle α. Working fluid 31 can thus have a raised level 31 a′ reduced to level 31 a located substantially at the same level as surface 73 a. Working fluid 31 can thus have a level set at that level.
The present invention in the fifth embodiment provides overflow tube 71 including an end portion 72 positioned internal to oil pan 12 and defining an opening of drain hole 22 receiving and passing a working fluid that overflows. End portion 72 has an end surface 72 a facing vertically upward and extending to surround the opening of drain hole 22, and lipophilically coated.
Overflow tube 71 thus configured can achieve an effect similar to that described in the first embodiment.
The overflow tubes of the first to fifth embodiments may structurally be combined as appropriate to form a different overflow tube. For example, overflow tube 21 of the first embodiment may have curved surface 23 a satin finished, and overflow tube 66 of the fourth embodiment may have end surface 67 a lipophilically coated.
Thus the present invention can provide an overflow tube that can help to set a level at a prescribed level precisely.
Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being limited only by the terms of the appended claims.

Claims

1. An overflow tube provided at a case body and causing an amount of a working fluid exceeding a prescribed amount received by said case body to overflow to set a level of said working fluid at a prescribed level, the overflow tube comprising an end portion positioned in said case body and defining an opening receiving and passing said working fluid overflowing, said end portion having a curved surface facing vertically upward and extending to surround said opening, and curving in a direction in contact with a generally horizontal direction.

2. An overflow tube provided at a case body and causing an amount of a working fluid exceeding a prescribed amount received by said case body to overflow to set a level of said working fluid at a prescribed level, the overflow tube comprising an end portion positioned in said case body and defining an opening receiving and passing said working fluid overflowing, said end portion having an inclined surface facing vertically upward and extending to surround said opening, and inclining from a circumference of said end portion toward said opening vertically downward.

3. An overflow tube provided at a case body and causing an amount of a working fluid exceeding a prescribed amount received by said case body to overflow to set a level of said working fluid at a prescribed level, the overflow tube comprising an end portion positioned in said case body and defining an opening receiving and passing said working fluid overflowing, said end portion having a surface facing vertically upward and extending to surround said opening, and formed to be uneven.

4. The overflow tube according to claim 3, wherein said surface is satin finished.

5. The overflow tube according to claim 3, wherein said surface is serrated to have a plurality of teeth arranged along a circumference of said opening.

6. The overflow tube according to claim 3, wherein said surface has a groove extending from a circumference of said end portion toward said opening.

7. An overflow tube provided at a case body and causing an amount of a working fluid exceeding a prescribed amount received by said case body to overflow to set a level of said working fluid at a prescribed level, the overflow tube comprising:

an end portion positioned in said case body and defining an opening receiving and passing said working fluid overflowing; and

a guiding member provided at said end portion in a form of a string extending from a circumference of said end portion toward said opening.

8. An overflow tube provided at a case body and causing an amount of a working fluid exceeding a prescribed amount received by said case body to overflow to set a level of said working fluid at a prescribed level, the overflow tube comprising an end portion positioned in said case body and defining an opening receiving and passing said working fluid overflowing, said end portion having a surface facing vertically upward and extending to surround said opening, and lipophilically coated.