Title of Invention

A WATER PUMP

Abstract

Abstract (817/MAS/2001) A WATER PUMP A water pump 1 comprises: a housing 2, having a bearing unit 4 in which is fixed a ball bearing 13 that supports a rotary shaft 12 with which an impeller 11 is coupled; and a steam passage 17 and a drain passage 19, which are linearly extended in the radial direction and communicate with an inner space 16 defined between the ball bearing 13 and a mechanical seal 15. Since the drain passage 19 passes through a passage rib 8, extending outward in the radial direction from the outer surface of the bearing unit 4, the air-flow resistance of the drain passage 19 is increased and is greater than that of the steam passage 17 and prevents the entry of dust. Further, positioned above the steam passage 17, to prevent the entry of dust, is a circumferential rib 7 that is provided only along part of the circumference.

Full Text

BACKGROUND OF THE INVENTION The present invention relates to a water pump for transferring under pressure, for example, cooling water in a water cooled combustion engine, and relates in particular to a structure for preventing the entry of dust via a steam passage and a drain passage that are provided in a housing of a water pump including a mechanical seal. Conventionally, this type of the water pump is disclosed in JP-A-2000-213349 . The water pump disclosed therein comprises : a steam discharge port and a water discharge port, both of which communicate with an inner space defined between a mechanical seal and a bearing that rotatably supports a rotary shaft on which an impeller is fitted; a drain trap; and a lid for covering the exit of the drain trap. The steam discharge port and the water discharge port pass through the pressurized portion, in which the bearing is seated under pressure, and machining for them is performed by a drill that is moved up from the bottom of the water trap perpendicular to the axial line of the rotary shaft. The steam discharge port communicates with an outer through hole that is formed in the pressurized portion outwardly in the radial direction, while the water discharge port communicates with a drain trap provided outside the pressurized portion in the radial direction. For this water pump, the entry of dust from the surrounding space via the water discharge port is suppressed comparing with a structure wherein the water discharge port communicates directly with the surrounding space, since the water discharge port communicates with the space surrounding the body through the drain trap. Further, the entry of dust into the inner space via the steam discharge port is suppressed by a cover member, which covers the upper portion of the steam discharge port. Thus, a reduction of the durability of the bearing and of the mechanical seal, which results in the attachment of dust entering the inner space, can be prevented. However, the number of required parts is increased, since a lid is required for the dust entry prevention structure at the water discharge port. A process for closing the hole is additionally performed, since a hole formed in the bottom of the drain trap must be covered. Therefore, the manufacturing costs and the time required for assembly are increased for the dust entry prevention structure of the water pump. From the viewpoint of productivity, the structure of this water pump must be improved because of the inclusion of the dust entry prevention features. SUMMARY OF THE INVENTION To resolve this problem, it is an objective of the present invention to provide a water pump structured for the prevention of the entry of dust for which superior productivity can be realized at a low cost. A water pump of the present invention required only a small number and having a hole, which is formed to provide a drain passage, need not be closed. According to a first aspect of the invention, a water pump comprises: a rotary shaft for driving an impeller; a housing in which a pump chamber unit is provided that includes a bearing unit, for supporting the rotary shaft, via a bearing, and a pump chamber, in which the impeller is arranged; a mechanical seal provided between the rotary shaft and the housing in order to completely close the bearing and the pump chamber; an inner space formed between the bearing and the mechanical seal; and a steam passage and a drain passage, one end of each of which opens into the inner space while the other end of each of which opens to the space surrounding the housing, wherein the steam passage and the drain passage are holes that are extended linearly in the radial direction, wherein the drain passage at one end passes through a passage rib that is extended from the outer face of the bearing unit outward in the radial direction while the other end of the drain passage opens at the bottom of the outer face of the housing, and wherein by passing the drain passage through the passage rib the air-flow resistance of the drain passage is increased and is greater than the air-flow resistance of the steam passage. According to the first aspect of the invention, the steam flows into the inner space, when water for lubricating and for cooling the sealing friction face of the mechanical seal is changed to steam at the sealing friction face by frictional heat. Then the steam flows through the steam passage to the surrounding space, water generated by condensing the leaking steam flows out through the drain passage to the surrounding space. The steam passage and the drain passage are easily formed by machining from the outer face of the housing in the diameter direction, since the steam passage and the drain passage are straight or linear holes. Further, since the drain passage that passes through the rib extending outwardly in the radial direction opens at the outer lower face of the housing, the holes formed in the outer face of the housing constitute a part of the drain passage. Thus, unlike the related art, the holes need not be sealed even when the steam passage and the drain passage are formed by machining the outer surface of the housing outwardly in the radial direction . In addition, since the drain passage is extended by being passed through the passage rib and is thus comparatively long, the air-flow resistance of the drain passage is greater than that of the steam passage. As a result, it is difficult for dust floating in the surrounding space to enter the inner space through the drain passage, and it is possible to prevent the reduction of the durability of the bearing and the mechanical seal that occurs when dust enters the inner space and is attached to the bearing and the mechanical seal. On the other hand, the steam easily flows out through the steam passage, because the air-flow resistance is small . As a result, the following effects are obtained. Since the steam passage and the drain passage are constituted by linear holes, they can easily be formed by machining from the outer surface of the housing in the direction of the diameter. Since the drain passage is formed by machining from the outer surface of the housing in the radial direction, the hole, which passes through the passage rib extending across the diameter of the hole, opens at the outer lower wall of the housing. Further, since the drain passage passes through the passage rib extending in the radial direction, the air-flow resistance of the drain passage is greater than that of the steam passage, even though a separate member is not added. Thus, the number of required parts and the manufacturing costs are reduced, and the productivity of the water pump having the dust entry prevention structure is improved. According to a second aspect of the invention, a circumferential rib, which is provided in one circumferential part of the bearing, extends along the circumferential direction of the rotary shaft in the water pump. The circumferential rib constitutes a dust prevention cover which is positioned only at the upper portion of the steam passage. The dust prevention covers the upper portion of the other end of the steam passage that opens at the upper portion of the outer face of the bearing. According to the second aspect of the invention, since the upper portion of the other end only of the stream passage is covered by the dust prevention cover constituted by the circumferential rib, it is difficult for dust in the surrounding space to enter the inner space through the steam passage. As a result, the following effects can be obtained. Since the upper portion of the other end of the steam passage is covered by the circumferential rib that constitutes the dust prevention cover, dust in the surrounding space seldom enters the inner passage. Further, since the circumferential rib is only partially extended along the circumferential direction of the rotary shaft, the water pump is lighter when compared with one for which the rib is provided around the entire circumference. Accordingly, the present invention provides a water pump comprising: a rotary shaft for driving an impeller; a housing having a pump chamber unit having a pump chamber on which said impeller is disposed and a bearing unit for supporting said rotary shaft through a bearing and a passage rib extending from the outer face of said bearing unit outwardly in the radial direction of said rotary shaft; a mechanical seal provided between said rotary shaft and said housing so as to closely seal said bearing and said pump chamber; characterized in that said housing has an inner space formed between said bearing and said mechanical seal, and said housing has a steam passage having a hole extending linearly in a radial direction of said rotary shaft, and one end of said steam passage opens into said inner space, and the other end of said steam passage opens to a space surrounding said housing, and said housing has a drain passage having a hole extending linearly in the radial direction of said rotary shaft along a center line passing through said steam passage, and one end of said drain passage opens into said inner space, and the other end of said drain passage passes through said passage rib. With reference to the accompanying drawings, in which The present invention is now described in detail with reference to the accompanying drawings. Fig. 1 is a front view showing the housing of a water pump in an internal combustion engine according to an embodiment of the present invention. Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1, showing a housing in which a rotary shaft, a bearing and a mechanical seal are assembled. One embodiment of the present invention is described while referring to Figs, 1 and 2. In Figs. 1 and 2, a water pump according to the present invention is applied for use as a water pump for water cooled internal combustion engine. A water pump 1, which is an assembly that is part of the cooling system of an internal combustion engine [not shown}, sucks in cooling water cooled by passing through a radiator. The water pump 1 transfers the water under pressure to the cylinder block and the cooling water jacket of a cylinder head (none of them shown), which constitutes the main body of the engine. Further, the water pump 1 feeds the water, which is heated to a high temperature by the heat of the individual sections of the engine, back to the radiator. The water pump 1 sucks in and circulates cooling water that is cooled by a heat exchange process at the radiator again. While referring to Figs. 2 and 3, a housing 2 of the water pump 1, which is secured by bolts to the end face of the cylinder block, comprises: a pump chamber unit 3, which is formed at the end face of the cylinder block, constitutes a pump chamber 10 having a recessed portion that is connected to the path along which cooling water flows from the radiator; a bearing unit 4 is fixed in place by inserting a ball bearing 13 under the pressure. The ball bearing 13 arranged in the pump chamber 10 rotatably supports a rotary shaft 12. The ball bearing 13 couples to one end of an impeller 11 so that they rotate together, a discharge unit 5 extends from the pump chamber unit 3 outwardly in the radial direction of the rotary shaft 12. By interacting with a groove formed in the end face of the cylinder block, the discharge unit 5 constitutes a flow path communicating with the pump chamber 10 for the transfer of cooling water driven by the impeller 11 . The pump chamber unit 3 and the bearing unit 4, which have a substantially cylindrical shape, are formed along the same axis as that of the rotation axial line LI of the rotary shaft 12. The bearing unit 4 has a smaller diameter than that of the pump chamber unit 3. The bearing unit 4 outwardly projects at the other side end of the rotary shaft 12, which is in the opposite direction along the rotation axial line LI of the rotary shaft 12 (hereinafter referred to simply as the axial direction) . As is shown in Fig. 1, multiple attachment bosses Bl to B5 are formed outwardly in the radial direction of the bearing unit 4. Each of the multiple attachment bosses Bl to B5 passes through a bolt hole A in order to secure the housing 2 to the cylinder block. The base of the discharge unit 5 extends from the pump chamber unit 3 outwardly in the radial direction. First and second attachment bosses Bl and B2 are positioned on either side in the circumferential direction to sandwich the discharge path. Third and fourth attachment bosses B3 and B4 are respectively positioned substantially symmetrical to Bl and 82 with respect to the axial rotation line LI. A fifth attachment boss B5 for the discharge unit 5 is positioned at a location opposite to the circumferential edge of the port of the cylinder block into which the cooling water is introduced in the direction of an axis. First to fourth reinforcing ribs CI to C4 are provided between the outer face of the bearing unit 4 and the first to the fourth attachment bosses Bl to B4. The first to fourth reinforcing ribs CI to C4 are extended in the axial direction from the outer face of the pump chamber unit 3. Further, the first to fourth reinforcing ribs CI to C4 are extended from the outer face of the bearing unit 4 to the individual attachment bosses. At this time, an acute angle is set as the angle that is formed by the first plane and second plane. The first plane includes the center line and the rotational axial line LI of the bolt hole A of the attachment boss Bl. The second plane includes the center line and the rotational axial line LI of the bolt hole A of the attachment boss B2. The acute angle formed by the first plane and second plane is an angle al sandwiched by the first and the second reinforcing ribs CI and C2. An angle a2 is sandwiched by the third and the fourth reinforcing ribs C3 and C4. The angle a2 is also an acute angle. An obtuse angle is set as angle a3 sandwiched by the first and fourth reinforcing ribs CI and C4. An angle c(4 sandwiched by the second and third reinforcing ribs C2 and C3 is also an obtuse angle. While referring to Fig. 2, a pump pulley (not shown) is fixed to an attachment plate 14, which is coupled with one end of the rotary shaft 12. The other end of the rotary shaft 12 is coupled with the impeller 11. The attachment plate rotates with the rotary shaft 12. A drive pulley rotates with the crankshaft of the internal combustion engine. An endless belt extends between the pump pulley and the drive pulley. The endless belt transmits the driving power produced by the crankshaft to the rotary shaft 12 in order to rotate the rotary shaft 12. The radial ball bearing 13 includes: an outer race 13a, which is inserted into the inner wall of the bearing unit 4 under pressure; multiple balls 13c engage two annular guide grooves 13b, which are formed at a distance in the inner wall of the outer lace 13a and the outer surface of the rotary shaft 12; and a sealing member 13d for closing both ends in the axial direction. In the axial direction between the ball bearing 13 and the impeller 11, a mechanical seal 15 is provided between the rotary shaft 12 and the housing 2 in order to closely seal between the ball bearing 13 and the pump chamber 10, The mechanical seal 15 includes; a rotary ring l5a, which is closely coupled with the rotary shaft 12 at the rear of the impeller 11 in liquid-tight. The rotary ring 15a is integrally rotated with the rotary shaft 12; a fixed ring 15i3, which is liquid-tightly fixed to a seal attachment portion 6 of the housing 2 nearer the ball bearing 13 than the rotational ring 15a; and a coil spring 15c, which drives the fixed ring 15b against the rotary ring 15a. A sealing friction face 15d, which is formed by the axial end faces of the rings 15a and 15b that contact each other, is located in the pump chamber 10 behind the impeller 11 so that water for lubricating and cooling enters the sealing friction face 15d. While also referring to Fig. 1, the ball bearing 13 and the mechanical seal 15 are arranged at a distance in the axial direction, and an annular inner space 16 is defined between them. One steam passage 17 is formed in the portion of the bearing unit 4 that is adjacent to the seal attachment portion 6. The steam passage 17 communicates with the upper portion of the inner space 16 at one end at an inner opening 17a and communicates with the space S surrounding the housing 2 at the other end at an outer opening 17b that opens in the outer surface of the bearing unit 4. Therefore, the cooling water flowing into the sealing friction face 15d is changed to steam by friction produced heat, and the steam flowing through the inner space 16 passes through the steam passage 17. The cooling water is discharged to the surrounding space S. A circumferential rib 7 having a partially cylindrical shape is connected at both circumferential ends to the first and the fourth reinforcing ribs CI and C4 outwardly in the radial direction of the bearing unit 4. Between the first and the fourth reinforcing ribs CI and C4, the circumferential rib 1 is extended, from the outer surface of the pump chamber unit 3, in the axial direction and in the circumferential direction. The circumferential rib 7 is coaxially provided with the bearing unit 4, and serves as a part of a cylinder having a smaller diameter than an outer circumferential edge 3a of the pump chamber unit 3, which is the portion that has the largest diameter. With this arrangement, an annular partial space 18 is defined between the circumferential rib 7 and the bearing unit 4 and communicates with the surrounding space S, while the pump chamber 10 side is closed and the ball bearing 13 side is opened. The circumferential rib 7 intersects the center line L2 of the steampassage 17, constituting a dust cover that covers the entire outer opening 17b from above. With this circumferential rib 7, dust floating in the surrounding space S can be prevented from entering into the inner space 16 through the steam passage 17. Therefore, by using the circumferential rib 7, the structure of the entry prevention mechanism on the steam passage 17 side can be formed. In addition, since the circumferential rib 7 is located between the first and the fourth reinforcing ribs CI and C4, which form an obtuse angle o;3, it also serves as a reinforcing rib by providing increased rigidity for the housing 2 at the interval between the first and the fourth reinforcing ribs CI and C4, which are circumferentially located at a distance. The position of the circumferential rib 7 in the radial direction is appropriately determined, while taking into account ventilation for steam and the entry of dust. The position of a distal end 7a of the circumferential rib 7 is determined so as to be slightly nearer the pump pulley than the axial position of an end face 13e of the ball bearing 13 on the inner space 16 side- A passage rib 8 includes an axial end face 8a that is located substantially at the same axial position as the distal end 7a of the circumferential rib 7. This passage rib 8 extends from the outer surface of the bearing unit 4 downwardly and outwardly in the radial direction to the outer surface of the outer circumferential edge 3a of the pump chamber unit 3, and also extends outward axially from the outer lower wall of the pump chamber unit 3. One drain passage 19 formed in the passage rib 8 communicates with the lower portion of the inner space 16 at one end. One end of the drain passage 19 is an inner opening 19a, while communicating with the surrounding space S at the other end, at which is an outer opening 19b that opens at the outer lower wall of the housing 2. the outer opening 19b is located at a position whose distance from the rotation axial line LI is substantially the same as that for the outer lower wall of the pump chamber unit 3. Therefore, the cooling water entering the sealing friction face 15d is changed to steam by friction produced heat, and when the steam flows into the inner space 16 and is condensed, the water that the steam is condensed passes through the drain passage 19. The water is discharged to the surrounding space S. VJhile the steam passage 11 and the drain passage 19 have substantially the same diameter, the drain passage 19 is longer than the steam passage 17 because it connects with the inner space 16 and the surrounding space S only at the openings 19a and 19b. Therefore, the air-flow resistance of the drain passage 19 is greater than that of the steam passage 17. It is difficult for dust floating in the surrounding space S to enter the inner space 16 through the drain passage 19, since the drain passage 19 opens downward. Therefore, the dust entry prevention structure on the drain passage 19 side is provided by using the drain passage 19, which has a large air-flow resistance. Since the passage rib 9 is located between the second and third reinforcing ribs C2 and C3, which form an obtuse angle a4, it also serves as a reinforcing rib that provides increased rigidity for the housing 2 between the second and third reinforcing ribs C2 and C3, which are located at a distance in the circumferential direction. The steam passage 17 and the drain passage 19 are formed at one drilling step in the housing 2 obtained by integrally forming the pump chamber unit 3, the bearing unit 4, the discharge unit 5, the seal attachment portion 6 and the ribs CI to C4, 7 and 8. The one drilling step is operated from the outer surface of the passage rib 8 in the direction substantially perpendicular to the rotation axial line LI. As a result, these passages 17 and 19 are holes that have substantially the same diameter and that pass through the inner space 16. Thus, the passages 17 and 19 have the common center line L2 along the virtual plane that is substantially perpendicular to the rotation axial line LI, and are linearly extended in the radial direction without any bends. The operation and effects of the thus structured embodiment is described. When the internal combustion engine is operated and the impeller 11 is rotated at the rotary shaft 12, the cooling water that flows from the inflow port is supplied under pressure produced by the impeller 11 in the pump chamber 10, and passes through the discharge port to the input port of the cylinder block. Thus, the cooling water is supplied to the cooling system of the internal combustion engine including the cooling jacket of the cylinder block. The cooling water is circulated in this manner. A tiny amount of cooling water in the pump chamber 10 behind the impeller 11 flows into the sealing friction face 15dof the mechanical seal 15 for use for lubricating and cooling the sealing friction face 15d. The cooling water is changed to steam by friction produced heat at the sealing friction face 15d, and flows into the inner space 16. Then, the steam is passes through the steam passage 17 and is discharged to the surrounding space S, while the water that is generated by the condensation of the leaking steam is discharged through the drainpassage 19 to the surrounding space S . Therefore, the ball bearing 13 can be prevented frorii being adversely affected by the steam and water that are present in the inner space 16. Since the steam passage 17 and the drain passage 19 are linear holes, they can be easily manufactured by machining performed from the outer surface of the housing 2 outwardly in the radial direction. And since the drain passage 19 passes through the passage rib 8 that is extended outwardly in the radial direction and opens at the outer lower wall of the housing 2, the hole opened in the outer surface of the housing 2 constitutes a part of the drain passage 19. Therefore, unlike the related art, the hole need not be closed when the drain passage 19 is formed by machining from the outer surface of the housing 2 outwardly in the radial direction. Further, the drain passage 19 penetrates the passage rib 8 that extends in the radial direction. Since the drain passage 19 is longer than the steam passage 17,the air-flow resistance of the drainpassage 19 is greater than that of the steam passage 17, Thus, dust floating in the surrounding space S seldom enters the inner space 16 through the drain passage 19. Therefore, it is possible to prevent a reduction in the durabilityof theball bearing 13 and themechanical seal 15 that occurs when dust enters the inner spacer 16 and is attached to the ball bearing 13 and the mechanical seal 15. Further, the steam is easily discharged to the surrounding space S through the steam passage 17, which has only a small air-flow resistance. As a result, the following effects can be obtained. Since the steam passage 17 and the drain passage 19 are linear holes, they can be easily manufactured by machining performed from the outer surface of the housing 2 outwardly in the radial direction. Further, since the drain passage 19 passes through the passage rib 8 and opens at the outer lower wall of the housing 2, the hole opened in the outer surface need not be closed when the drain passage 19 is formed by the machining from the outer surface of the housing 2 outwardly in the radial direction. Further, since the length of the drain passage 19 is increased because it passes through the passage rib 8 extended in the radial direction, the air-flow resistance of the drain passage 19 is increased without an additional member being required. Therefore, the air-flow resistance of the drain passage 19 is greater than that of the steam passage 17. Thus, the number of required parts and the manufacturing costs are reduced, and productivity can be increased for the water pump 1 having the dust entry prevention structure. Since the outer opening 17b of the steam passage 17 is covered from above by the dust cover constitutes by the circumferential rib 1, which has a partially cylindrical shape, it is difficult for the dust in the surrounding space S to enter the inner space 16 through the steam passage 17. Further, it is possible to prevent a reduction in the durability of the ball bearing 13 and the mechanical seal 15 by the dust to enter the inner space 15,which is attached to the ball bearing 13 and the mechanical seal 15. The following effects are thus obtained. Since the outer opening 17b of the steam passage 17 is covered from above with the circumferential rib 7 that constitutes the dust cover, the dust in the surrounding space S seldom enters the inner space 16. In addition, since only a partial circumferential rib 7 is provided, the water pump 1 is lighter when compared with one for which the rib 7 is extended around the entire circumference. Since the steam passage 27 and the drain passage 19 have the same center line L2 on the virtual plane substantially perpendicular to the rotation axial line L1 and are linearly extended in the radial direction, the center of the outer opening 17b of the steam passage 17 is not axially positioned closer to the ball bearing 13 than is the center of the inner opening 17a. As a result, the following effects are obtained. Since the axial length of the circumferential rib 7, which covers the outer opening 17b of the steam passage 17, can be shortened, the portion of the circumferential rib 7 that covers the outside of the ball bearing 13 can be minimized, and the axial distance between the ball bearing 13 and the mechanical seal 15 can also be reduced. Therefore, the axial length of the housing 2 can be reduced, and not only the housing 2, but also the water pump 1 can be made compact. The circumferential rib 7 is located between the first and the fourth reinforcing ribs C1 and C4 that form the obtuse angle a3, and provides increased rigidity for the housing 2 at the interval between the first and fourth reinforcing ribs C1 and C4, which are circumferentially located at a distance. The passage rib 8 is located between the second and the third reinforcing ribs C2 and C3 that form the obtuse angle a4, and provides increased rigidity for the housing 2 at the interval between the second and third reinforcing ribs C2 and C3, which are circumferential1y located at a distance. As a result, the following effects are obtained. Since the circumferential rib 7 and the passage rib 8 serve as reinforcing ribs that provide increased rigidity for the housing 2, the thus provided increased rigidity suppresses the vibration of the housing 2 and permits the housing 2 to be made thinner. The axial position of the distal end 7a of the circumferential rib 7 is slightly nearer the pump pulley than the axial position of the end face 13e of the ball bearing 13 on the inner space 16 side. Thus, the outer surface of the bearing unit 4 , which is positioned outward of the ball bearing 13 in the radial direction, is only partially covered by the circumferential rib 7. In the inner space S, almost all of the outer surface is directly exposed so that the heat generated at the ball bearing 13 is efficiently discharged to the inner space S through the bearing unit 4. Since the heat generated at the ball bearing 13 is efficiently discharged to the inner space S, the functioning of the cooling process for the ball bearing 13 is improved, thereby increasing its durability. A modification obtained by changing one part of the structure of the embodiment is described. While the steam passage 17 and the drain passage 19 share the center line L2 on the virtual plane, the center line may be located on the plane tilted relative to the rotation axial line L1. While the rotary shaft 12 is rotated by the power produced by an internal combustion engine, it may be driven by another drive means, such as an electromotor. Further, the water pump 1 can be applied for an apparatus other than an internal combustion engine WE CLAIM: 1. A water pump comprising: a rotary shaft for driving an impeller; a housing having a pump chamber unit having a pump chamber on which said impeller is disposed and a bearing unit for supporting said rotary shaft through a bearing and a passage rib extending from the outer face of said bearing unit outwardly in the radial direction of said rotary shaft; a mechanical seal provided between said rotary shaft and said housing so as to closely seal said bearing and said pump chamber; characterized in that said housing has an inner space formed between said bearing and said mechanical seal, and said housing has a steam passage having a hole extending linearly in a radial direction of said rotary shaft, and one end of said steam passage opens into said inner space, and the other end of said steam passage opens to a space surrounding said housing, and said housing has a drain passage having a hole extending linearly in the radial direction of said rotary shaft along a center line passing through said steam passage, and one end of said drain passage opens into said inner space, and the other end of said drain passage passes through said passage rib. 2. The water pump as claimed in claim 1, wherein an air-flow resistance of said drain passage passing through said passage rib is greater than that of said steam passage. 3. The water pump as claimed in claim 1, wherein a circumferential rib extends partially along the circumferential direction of said rotary shaft and apart from said rotary shaft, and said circumferential rib constitutes a dust prevention cover positioned at the upper portion of said steam passage, and said dust prevention cover covers the upper portion of the other end of said steam passage that opens at the upper portion of the outer face of said bearing. 4. The water pump as claimed in claim 1, wherein said drain passage and said steam passage are positioned on an imaginary tilted plane having an axis of the said rotary shaft. 5, A water pump substantially as herein described with reference to the accompanying drawings.

Documents:

0817-mas-2001 abstract-duplicate.pdf

0817-mas-2001 abstract.pdf

0817-mas-2001 claims-duplicate.pdf

0817-mas-2001 claims.pdf

0817-mas-2001 correspondence-others.pdf

0817-mas-2001 correspondence-po.pdf

0817-mas-2001 description (complete)-duplicate.pdf

0817-mas-2001 description (complete).pdf

0817-mas-2001 drawings-duplicate.pdf

0817-mas-2001 drawings.pdf

0817-mas-2001 form-1.pdf

0817-mas-2001 form-19.pdf

0817-mas-2001 form-26.pdf

0817-mas-2001 form-3.pdf

0817-mas-2001 form-5.pdf

0817-mas-2001 others.pdf

0817-mas-2001 petition.pdf