Drainage pump

A drainage pump includes a pump casing having an inlet and an outlet, and an impeller accommodated in the casing and rotated by a driving motor. The impeller has a plate-like vane. A liquid flows from the inlet toward a front end portion of the vane along the axis of the vane, and is discharged from the outlet in a direction substantially perpendicular to the axis of the vane. The front end portion of the vane has a convex shape, and therefore has an inclined portion which extends from a portion located on the axis of the vane to an outer peripheral edge thereof.

BACKGROUND OF THE INVENTION 
The present invention relates to a drainage pump for use in an electric 
washing machine, and more particularly, to a drainage pump which is 
suitable for use in draining a liquid containing elongated fibers such as 
thread waste or cloth waste. 
Conventional drainage pumps have been disclosed in the specifications of, 
for example, Japanese Patent Laid-Open Publication No. 54-131101, Japanese 
Patent Publication No. 47-43241, Japanese Utility Model Publication No. 
53-47204, Japanese Utility Model Laid-Open Publication No. 59-19994 and 
U.S. Pat. No. 3,130,679. 
However, in each of the drainage pumps of the above-described type, when a 
liquid containing elongated fibers such as thread waste, which have a 
small specific gravity is drained, the fibers tend to attach onto vanes of 
an impeller or to gather at a center of the vanes. It is difficult to 
remove the fibers from the vanes and to discharge them from the pump. 
Furthermore, such thread waste gathers in a clearance between the impeller 
and a casing of the pump thereby disabling the rotation of the vanes. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a drainage pump which is 
suitable for use in draining a liquid containing elongated fibers such as 
thread waste having a small specific gravity, which has a simple 
structure, and which facilitates maintenance. 
To this end, the present invention provides a drainage pump which includes 
a pump casing having an inlet and an outlet, and an impeller accommodated 
in the casing and rotated by a driving motor. The impeller has a first 
plate-like vane. The liquid flows from the inlet toward the front end 
portion of the first vane along an axis of first vane of the impeller, and 
is discharged from the outlet in a direction substantially perpendicular 
to the axis of the first vane. The front end portion of the first vane has 
a convex shape, and has an inclined portion which extends from the axis of 
the vane to an outer peripheral edge thereof. 
In the present invention, the cloth waste or the like, which has a small 
specific gravity and which would gather at the center of the vane due to 
the vortex of the liquid located between the casing and the vane, is 
forcibly diffused toward the peripheral portion of the vane from the 
central portion thereof. 
Also, when the cloth waste having a small specific gravity may attach onto 
the front end portion of the vane of the drainage pump, such cloth waste 
or the like is moved toward the peripheral of the vane (in the direction 
perpendicular to the rotation axis of the impeller) due to the centrifugal 
force generated by the rotation of the vane. More specifically, since the 
front end portion of the vane is formed so as to be inclined such that the 
vane is highest at the central portion thereof and that the height thereof 
gradually decreases toward the outer periphery thereof, the cloth waste 
which attaches the front end portion of the vane moves toward the outer 
peripheral portion of the vane and readily leaves therefrom. 
Furthermore, since the vane accommodated in the pump casing consists of 
only one vane, no elongated thread waste is caught across one vane member 
and an adjacent one. 
More specifically, no elongated thread waste is caught across the adjacent 
vane members which are disposed crosswise, and accordingly the thread 
waste can be therefore moved toward the outer periphery of the vanes 
readily.

DETAILED DESCRIPTION OF THE INVENTION 
Referring first to FIG. 1, a drainage pump has an impeller 1 having a first 
vane 1a. The vane 1a has an inclined portion 2 which is the highest at the 
end portion thereof located on the axis of the impeller and which 
gradually becomes lower toward the outer periphery thereof, and the vane 
1a is thereby formed in a convex shape. The impeller 1 also has a second 
vane 1b which has a smaller height than the first vane 1a and which is 
disposed such that it intersects the first vane 1a at right angle. The 
impeller 1 also has a boss portion 1c having a threaded portion 1d through 
which the impeller 1 is fixed to a driving shaft 4 of a motor 3. That is, 
the first vane incorporates the threaded portion for fixing the first vane 
to the impeller. A seal retaining portion 5 has a rising portion 5b and a 
projecting portion 5a. The seal retaining portion 5, together with a 
projection le formed on the impeller 1, forms a labyrinth packing. Part of 
the seal retaining portion 5 is gripped by a collar 3a of the motor 3 and 
a flange portion 6a of the pump casing 6, and is fixed by means of a screw 
8 through a packing 7. A first chamber 9 is formed between the front end 
surface of the impeller 1 and the inner wall of the pump casing 6. A 
length of the first chamber formed by a front end portion of the first 
vane and the casing in an axial direction thereof increases as it 
separates from the axis. A swirling stream of water containing cloth waste 
or the like is generated in the first chamber 9 during the operation of 
the pump. The water is discharged from a fluid discharging pipe 11. The 
fluid (water) containing foreign matter is sucked into the pump from a 
fluid sucking pipe 10 connected to a pipe (not shown). A fluid sucking 
passage 12 has an inclined opened portion 12a at the end thereof. A second 
chamber 13 is formed between the outer wall of the fluid sucking passage 
12 and the inner wall of the pump casing 6. The pump is closed by a lid 
14. The second chamber 13, the inclined opened portion 12a of the fluid 
sucking passage 12, and the lid 14 of the pump in combination form a trap 
which catches the foreign matter which enters the casing 6. In FIG. 2, an 
inner edge portion of a connecting portion which connects the pump casing 
to the outlet is arcuate. That is, the arcuate portion 11a is formed at 
the portion which connects the fluid discharge pipe 11 to the casing 6 to 
allow cloth waste or the like to be prevented from being caught. 
In the drainage pump arranged in the above-described manner, once the motor 
3 is started and the impeller 1 is thereby rotated after the pump casing 6 
has been filled with water, the water containing the foreign matter such 
as cloth waste or the like enters the second chamber 13 of the casing 6 
from the fluid sucking pipe 10, and large foreign matter is caught. The 
water containing cloth waste or the like having a small specific gravity 
in turn flows into the fluid sucking passageway 12 then reaches the vane 
1a, by means of which it is subjected to pumping action, i.e., a 
centrifugal force, and is thereby directed toward the first chamber 9 so 
that it is discharged from the fluid discharge pipe 11. 
In embodiment FIGS. 1 and 2, the first vane (main vane) 1a and the second 
vane (auxiliary vane) 1b, which are disposed adjacent to each other, have 
different heights. That is, the first vane has a second vane mounted 
coaxially to the first vane, and the second vane is shorter in an axial 
direction thereof than the first vane. Furthermore, at least the front end 
portion of the first vane 1a having a larger height has an inclined 
portion which is the highest at the end located on the axis of the 
impeller and which gradually becomes lower toward the periphery of the 
vane. The first vane 1a therefore has a convex form. Consequently, the top 
of the front end portion of the first vane is located substantially at the 
center of the vortex generated in the pump, causing the cloth waste or the 
like having a small specific gravity to gather in the vicinity of the top 
of the front end portion. However, such cloth waste or the like is 
forcibly diffused toward the periphery of the vane due to the stirring 
action generated by the inclined portion of the first vane, and therefore 
prevented from staying and gathering at the center of the vortex so as to 
prevent clogging, which would occur after a long use in a conventional 
drainage pump in which the center of a vane is recessed. 
Furthermore, the cloth waste or the like having a small specific gravity, 
which are attached to the main vane 1a of the impeller 1, moves toward the 
outer end of the vane due to the centrifugal force generated by the 
rotation of the main vane 1a. As stated above, since the main vane 1a has 
the inclined portion 2, such cloth waste or the like attached peels off 
from the main vane smoothly and moves toward the periphery thereof into 
the first chamber 9. Moreover, since the main vane 1a and the auxiliary 
vane 1b have different heights, as stated above, elongated thread waste or 
the like is prevented from being caught across one of the vane members and 
the adjacent another vane member. In the conventional drainage pump, 
however, the vanes readily are problematical because they are not given 
the above-described consideration. The thread waste which is caught across 
the adjacent vanes would not be readily moved toward the periphery of the 
vane. Furthermore, thread waste would gather in a pile in the gap between 
the vanes and the pump casing, thereby causing locking of the impeller in 
a long run. However, in this embodiment, since the main vane 1a and the 
auxiliary vane 1b have different heights, as stated above, elongated 
thread waste or the like can be prevented from being caught across one of 
the vane members and the adjacent another vane member, and locking of the 
impeller due to the cloth waste or the like caught between the vane and 
the pump casing can be thus prevented. Consequently, maintenance of the 
drainage pump can be eliminated. 
In FIG. 1, when a clearance G between the outer periphery of the main vane 
1a and the pump casing 6 is small, the water, which would be forced toward 
the casing 6 by means of the centrifugal force of the main vane 1a, is 
directed toward the first chamber 9, allowing the cloth waste or the like 
attached on the main vane 1a to readily peel off and to move into the 
first chamber 9. It has been experimentally determined, when the clearance 
G was set to a value which was 0.2 times the diameter of the main vane 1a 
or less, the cloth waste or the like attached on the main vane 1a peeled 
off excellently. Furthermore, since the first chamber 9 is formed such 
that the length thereof in the axial direction increases as it separates 
away from the axis of the impeller, the water which flows into the first 
chamber 9 can be effectively prevented from flowing back. 
In the embodiment of FIGS. 3A and 3B, the vane of an impeller 31 has a form 
which consists of two curves exhibiting a point symmetry, as viewed in the 
direction in which a fluid flows in the pump casing. In this case, the 
impeller 31 does not have an auxiliary vane 1b, unlike the case of the 
embodiment of FIGS. 1 and 2, and the pumping effect is therefore slightly 
degraded when compared with the first embodiment. However, the degree of 
degradation is small, and smooth removal of the cloth waste or the like is 
assured, as in the case of the embodiment of FIGS. 1 and 2. A threaded 
portion 31C with an internal thread 31d is provided for fixing the 
impeller 31. 
In the embodiment of FIGS. 4A and 4B, a threaded portion 41d for fixing the 
impeller is incorporated in the vane of an impeller 41. In this way, the 
overall size of the pump can be made small. 
In the embodiment of FIG. 5, a fluid discharge pipe 51 is connected to a 
pump casing 56 in such a manner that the axis of the discharge pipe 
intersects the axis of the main vane 1a at right angle. This allows 
connecting portions 51a between the fluid discharge pipe 51 and the casing 
56 to have a large angle, resulting in a reduction in the attached cloth 
waste or the like on these connecting portions 51a. Furthermore, the same 
pumping action and the same cloth waste removal effect are assured when 
the impeller 1 is rotated in opposite directions. 
In the embodiment of FIG. 6, a first vane 61 differs from that of the first 
embodiment in that a front end portion 62 thereof has at its periphery a 
vertical portion 65 which extends perpendicular to the axis of the first 
vane 61. In the embodiment of FIG. 6, the cloth waste or the like, which 
slips down along an inclined portion 62 toward the periphery of the vane, 
can also be pushed by inertia toward the pump casing in spite of the 
presence of the vertical portion 65, and the same cloth waste removal 
effect can be thus assured. 
In the embodiment of FIG. 7, a main vane 71 differs from that of the first 
embodiment in that an inclined portion 72 thereof has a plurality of 
stages 75. The embodiment of FIG. 7 also assures the same effect as that 
achieved by either of the aforementioned embodiments. 
In FIG. 8, the abscissa represents the amount of thread waste contained in 
55 l of water, and the ordinate represents the rate of attachment of 
thread cloth or the like on the drainage pump. For example, 10% of this 
rate was obtained when there was attached thread waste in one of the tests 
which were conducted 10 times in total.