Patent Publication Number: US-6984158-B2

Title: Cooling water pump device for outboard motor

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a cooling water pump device for pumping cooling water toward an engine of an outboard motor that includes a hollow driveshaft housing under the engine and a driving shaft vertically mounted in the driveshaft housing for transmitting the drive force of the crankshaft of the engine to a screw. 
     (2) Description of the Prior Art 
     The outboard motor engine is cooled by taking in seawater or river water through, for example, a water filter in the lower case (or gear case) and forwarding the intake seawater or river water to the water jacket of the engine as cooling water. 
     In general, an outboard motor is equipped with a cooling water pump device for sending (pumping up) cooling water for engine cooling. 
     Specifically, an outboard motor is provided under its engine with a driveshaft housing that incorporates a driving shaft mounted vertically for transmitting the drive force of the crankshaft of the engine to a screw. The outboard motor has a cooling water pump device (water pump) which by using an impeller made of elastic material, accommodated eccentrically in the pump case, at a position partway through the length of the driveshaft, pushes cooling water forwards to the engine by rotation of the impeller inside the pump case as the driveshaft is driven (see Japanese Patent Application Laid-open Hei 5 No. 306687 and Japanese Utility Model Application Laid-open Hei 2 No. 126992). 
     As stated above, the cooling water pump device of an outboard motor employs a so-called water cooling type which draws cooling water and pushes it forward to the engine side so as to cool the engine with the thus pumped cooling water. In general, almost all models of outboard motors, from compact models (low horsepower models) as low as 2 horsepower (2 hp) to large-scale models (high horsepower models) as high as 250 horsepower employ water cooled engines that use a cooling water pump device. 
     The material of the pump case used for cooling water pump devices can be classified roughly into stainless steel and resin. As specific configurations,  FIG. 15  shows a cooling water pump device with a pump case “b” formed of stainless steel and  FIG. 16  shows a cooling water pump device with a pump case “b” of resin. 
     Either of these cooling water pump devices shown in  FIGS. 15 and 16  is assembled around a driveshaft “a” of the outboard motor, and an impeller “c” of elastic material is arranged eccentrically inside the pump case “b” and is fixed to driveshaft “a” by a key “d” with respect to the direction of rotation. 
     As the impeller “c” is rotationally driven as driveshaft “a” turns, water for cooling is drawn in from the outside of the outboard motor through an inlet port (not shown) of a lower case “e” (also called a gear case: accommodating gears and a screw shaft) located at the bottom of driveshaft “a” and pumped toward the engine. Concerning each pump case “b”, in order to secure watertightness at the contact face with lower case “e”, the pump case “b” is mounted by interposing an under-panel “f” and a gasket “g” between the underside of pump case “b” and the top side of lower case “e”. 
     In the case of a cooling water pump device of the type shown in  FIG. 15 , using a stainless pump case “b”, it can present a high enough strength against sliding of impeller “c”. On the other hand, in the case of a cooling water pump device of the type shown in  FIG. 16 , using a resin pump case “b”, a sleeve “h” made of metal such as stainless steel, is fitted to the pump case “b” side which impeller “c” comes into sliding contact with so as to prevent abrasion of pump case “b” due to rotation of impeller “c”. Further, an O-ring “i” is held between the abutment faces of resin pump case “b” and under-panel “f” and fixed by bolts. 
     In contrast with this, in the stainless pump case of the type shown in  FIG. 15 , the fitting surface of the pump case to the under-panel “f” is flattened so that no O-ring is used at the interface. 
     The advantage of using a stainless pump case for the cooling water pump device of an outboard motor is that when the engine is started in the dry for maintenance of the outboard motor, no deficiency such as the onset of case fusing will occur if the impeller “c” rotates and generates heat at its sliding surface with the pump case due to lack of cooling water. Therefore, it is possible to use the outboard motor in an ordinary manner after checkup with the engine started. Further, as will be described later, no metal sleeve is used as used for resin pump cases, hence there is no possibility of salt building up between the pump case and the metal sleeve and producing cracks that might cause the sleeve to move toward the case. 
     Because of these advantages, conventional pump cases, in general, have been made of stainless steel. 
     However, a pump case made of stainless steel suffers from various drawbacks: it is heavier than the that made of resin, causing a hindrance to lightening of the engine; and it is usually produced using the lost wax process, which is poor in mass productivity and needs high material cost and processing cost, resulting increase in cost. 
     For the above reasons, recently there has been a trend toward using resin pump cases. There are various advantages of using a resin pump case: it can be configured of a reduced number of parts because its parts can be integrally formed within limits and hence it is preferable for mass production; the weight of the pump case is lighter than that made of stainless steel or other metal, so that the pump, hence the outboard motor can be readily lightened; and the cost is low because the materials are inexpensive and the processing cost is low. 
     However, the resin pump case tends to deform due to heat during the operation in the dry. Further, for the case where outboard motors are used in seawater, saltwater may enter the interface between the pump case and the metal sleeve, forming salt buildup which may cause cracks in the case and deformation of the metal sleeve. 
     As a measure to prevent infiltration of salt water into the interface between the pump case and metal sleeve, a sealant for water protection may be applied between the metal sleeve and the pump case. 
     However, the applied amount of sealant may vary depending on the worker. Use of an automatic sealant coater to deal with this results in cost increase. And also, the sealant effectiveness will become lower due to heat and aging. Further, when the metal sleeve is to be replaced, adhesion of sealant is hard to peel off, increasing the workload. Moreover, when a new part is to be assembled, sealant is to be applied at a site in the local dealer, resulting in increase the number of steps and yet lack of reliability. 
     SUMMARY OF THE INVENTION 
     The present invention has been devised to solve the above problems it is therefore an object of the present invention to provide a cooling water pump device for an outboard motor, which, even with the use of a pump case made of resin and a metal sleeve fitted therein, can reliably prevent infiltration of water such as seawater into the interface between the pump case and the sleeve without the need of sealant application, prevent the pump case from cracking due to salt buildup, can reduce the work load and cost by omitting the step of sealant application, and can positively prevent deformation due to heat during the operation in the dry. 
     In order to achieve the above object, the present invention is configured as follows: 
     In accordance with to the first aspect, the cooling water pump device for an outboard motor, for pumping cooling water toward an engine of an outboard motor that includes a hollow driveshaft housing under an engine and a driving shaft vertically mounted in the driveshaft housing for transmitting the drive force of the crankshaft of the engine to a screw, comprising: a pump case made of resin disposed at a position partway, with respect to the axial direction of the driveshaft, inside the driveshaft housing; a sleeve made of metal fitted in the pump case; an impeller made of elastic material mounted eccentrically in the pump case with the metal sleeve interposed therebetween, the impeller being rotated by rotational drive of the driveshaft to draw cooling water from the bottom of the pump case and pump the cooling water toward the engine located above; and a plurality of annular seal elements for keeping the interface between the inner peripheral surface of the resin pump case and the metal sleeve watertight, arranged between the inner peripheral surface of the resin pump case and the metal sleeve, surrounding the driveshaft, and disposed at plural positions vertically apart with respect to the axial direction of the driveshaft. 
     The cooling water pump device for an outboard motor defined in the second aspect is characterized in that the pump case having the above first feature has an approximately bowl-like configuration having a bottom opening which is covered with an under-panel forming a pump chamber that accommodates the impeller, and at least the annular seal elements are arranged at an upper end of an ejection port of the pump chamber and at a place surrounding the driveshaft insert hole at an upper position of the pump case. 
     The cooling water pump device for an outboard motor defined in the third aspect is characterized in that, in the invention of the first aspect, a plurality of joint seal elements that extend in the axial direction or radial direction of the driveshaft and connect the annular seal elements one to another, are provided so as to produce a unified structure of the annular seal elements made up of elastic resin material to keep the interface between the inner peripheral surface of the resin pump case and the metal sleeve watertight. 
     The cooling water pump device for an outboard motor defined in the fourth aspect is characterized in that, in the invention of the third aspect, the lower annular seal element disposed between the bottom opening rim of the pump case and the under-panel and the upper annular seal element disposed at a place surrounding the driveshaft insert hole at an upper position of the pump case are connected by the joint seal elements, and at least the joint seal elements are arranged at both sides of the ejection port of the pump chamber. 
     The cooling water pump device for an outboard motor defined in the fifth aspect is characterized in that, in the invention of the first aspect, grooves for receiving seal elements are formed in the inner peripheral surface of the pump case. 
     The cooling water pump device for an outboard motor defined in the sixth aspect is characterized in that, in the invention of the first aspect, ribs are formed in the interior surface of the pump case so as to create an air layer between the pump interior surface and the metal sleeve. 
     According to the inventions of the first to sixth aspects, in the cooling water pump device of an outboard motor, a plurality of annular seal elements that surround the driveshaft for creating watertightness at the interface between the inner peripheral surface of the resin pump case and the metal sleeve are disposed vertically apart, one from another, with respect to the axial direction of drive shaft, between the inner peripheral surface of the resin pump case and the metal sleeve. Therefore it is possible to reliably prevent water such as seawater from infiltrating into the interface between the pump case and the sleeve by virtue of the water-protective function of the annular seal elements even when the outboard motor is used in the sea. 
     Accordingly, it is possible to positively prevent the salt buildup problem which would occur when water, especially seawater infiltrates into and between the resin pump case and the metal sleeve as in the conventional cooling water pump device and the possible initiation of cracks in the metal sleeve due to salt buildup. 
     The invention having each of the above features presents the following effect in addition to the above effect. 
     In the invention according to the above second feature, the pump case has an approximate bowl-shape having a bottom opening which is enclosed by an under-panel, forming a pump chamber that accommodates an impeller therein. At least the aforementioned annular seal elements are disposed at the upper end of the ejection port of the pump chamber and at a place surrounding the driveshaft insert hole at the upper position of the pump case, so that the pump case can be constructed so as to have a bottom opening which permits easy assembly of the sleeve and impeller. Also, provision of the annular seal elements at the upper end of the ejection port of the pump chamber and at a place surrounding the driveshaft insert hole at the upper position of the pump case produces sufficient watertight performance. Further, since the portion that would cause drawback in a conventional pump case when a trial operation is carried out in the dry without cooling water is positioned in the top side area of the pump case and the place surrounding the driveshaft insert hole at the upper position of the pump case and the ejection port of the pump chamber are sealed with the annular seal elements, it is possible to secure watertightness and solve the inconvenience of operation in the dry. As to the matter with salt buildup between the pump case and the sleeve, water is unlikely to stagnate across the upright side wall portion of the sleeve extending along the driveshaft, the provision of a seal at the ejection port and the place surrounding the driveshaft insert hole only also establishes effective watertightness. 
     According to the invention of the above third feature, a plurality of joint seal elements that extend in the axial direction or radial direction of the driveshaft to connect the annular seal elements to each other are provided so as to produce a unified structure of the annular seal elements made up of elastic resin material to create watertightness between the inner peripheral surface of the resin pump case and the metal sleeve. Therefore, watertightness against infiltration of water such as seawater into the interface between the pump case and the sleeve can be achieved in a more reliable manner by the integrated water protecting function of the joined elements. Moreover, handling at manufacturing and assembly is simple compared to that when the seal elements are provided piece by piece. Moreover, the seal can be formed of resin material of a uniform composition and the strength at the joints can be enhanced in terms of design. 
     According to the invention of the above fourth feature, the joint seal elements are used to connect the lower annular seal element interposed between the bottom opening rim of the pump case and the under-panel, with the upper annular seal element arranged at a place surrounding the driveshaft insert hole at the upper position of the pump case and the joint seal elements are disposed at least at both sides of the ejection port of the pump chamber. Therefore, infiltration of water such as seawater into the interface between the pump case and the sleeve through the surrounding of the ejection port of the pump chamber can be more reliably prevented by these joint seal elements. 
     According to the invention of the above fifth feature, since grooves for receiving seal elements are formed in the inner peripheral surface of the pump case, only the fitting of the sealing elements into these grooves makes it possible to attach the seal elements simply and reliably when the sealing structure is fitted into the pump case. 
     According to the invention of the above sixth feature, since ribs are formed in the interior surface of the pump case so as to create an air layer between the pump interior surface and the metal sleeve, frictional heat arising when the impeller frictionally rotates inside the sleeve can be prevented from transferring to the pump case by insulation and reduction of heat conduction owing to presence of the air layer. As a result it possible to reliably prevent the resin pump case from being heated by the frictional heat and hence prevent the resin pump case from melting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an external side illustration showing an outboard motor according to one embodiment of the present invention; 
         FIG. 2  is a vertical sectional illustration showing a drive mechanism under an engine of the outboard motor shown in  FIG. 1  and the arrangement of a cooling water pump device and others; 
         FIG. 3  is a detailed vertical sectional illustration showing a cooling water pump device of an outboard motor and its lower portion according to one embodiment; 
         FIG. 4  is a vertical sectional view for illustrating the configuration of a cooling water pump device; 
         FIG. 5A  is a bottom view for illustrating the configuration of a pump case of the cooling water pump device,  FIG. 5B  is a vertical sectional view cut along a line B—B in  FIG. 5A ; 
         FIGS. 6A and 6B  are constructional illustrations of an integrally formed sealing structure to be fitted to the cooling water pump device; 
         FIG. 7  is a vertical sectional view for illustrating the configuration of a cooling water pump device according to another embodiment of the present invention; 
         FIGS. 8A and 8B  are illustrative views of example 1 of a sealing structure constructed by combination of annular seal elements, provided for a cooling water pump device according to the embodiment shown in  FIG. 7 ,  FIG. 8A  a top view,  FIG. 8B  a perspective illustration; 
         FIGS. 9A and 9B  are illustrative views of example 2 of a sealing structure constructed by combination of annular seal elements,  FIG. 9A  a top view,  FIG. 9B  a perspective illustration; 
         FIGS. 10A and 10B  are illustrative views of example 3 of a sealing structure constructed by combination of annular seal elements and joint seal elements,  FIG. 10A  a top view,  FIG. 10B  a perspective illustration; 
         FIGS. 11A and 11B  are illustrative views of example 4 of a sealing structure constructed by combination of annular seal elements and joint seal elements,  FIG. 11A  a top view,  FIG. 11B  a perspective illustration; 
         FIGS. 12A and 12B  are illustrative views of example 5 of a sealing structure constructed by combination of annular seal elements and joint seal elements,  FIG. 12A  a top view,  FIG. 12B  a perspective illustration; 
         FIGS. 13A and 13B  are illustrative views of example 6 of a sealing structure constructed by combination of annular seal elements and joint seal elements,  FIG. 13A  a top view,  FIG. 13B  a perspective illustration; 
         FIGS. 14A and 14B  are illustrative views of example 7 of a sealing structure constructed by combination of annular seal elements and joint seal elements,  FIG. 14A  a top view,  FIG. 14B  a perspective illustration; 
         FIG. 15  is a structural illustration showing a conventional cooling water pump device with a pump case made of stainless steel; and 
         FIG. 16  is a structural illustration showing a conventional cooling water pump device with a pump case made of resin and a stainless sleeve fitted therein. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments of the present invention will hereinafter be described in detail with reference to the accompanying drawings. 
     As shown in  FIGS. 1 and 2 , the outboard motor  1  is fixed and mounted on the top of a transom  3  at the rear part of a boat  2  by means of a clamp bracket  4  that grips the top of the transom  3 . The clamp bracket  4  pivotally supports a swivel bracket  5  that can sway up and down. 
     This swivel bracket  5  is axially supported at its upper and lower ends (of a cylinder portion  5   b  on the driveshaft housing  8  side) by the top  1   a  and bottom  1   b  on the front side of driveshaft housing  8  of outboard motor  1 . With this arrangement, outboard motor  1  can swivel left and right within a certain range of angle with respect to clamp bracket  4  by control of a handle  1   c.    
     Swivel bracket  5  is adapted to be driven by an actuator  5   a  of a hydraulic type (Power Tilt and Trim, abbreviated as ‘PTT’) or the like so that it sways up and down with respect to clamp bracket  4  (see  FIG. 2 ). 
     In outboard motor  1 , as shown in  FIGS. 1 and 2 , driveshaft housing  8 , which is an hollow body extending vertically and has a horizontal section of a spindle shape, is joined to the swivel bracket  5  while an engine holder  7  on which an engine  6  (roughly depicted by its outline in  FIG. 2 ) is mounted and fixed with bolts is provided on top of driveshaft housing  8 . 
     Arranged vertically inside the driveshaft housing  8  is a driveshaft  10  which transmits the driving force from crankshaft  6   a  (the central axis is shown in  FIG. 2 ) of the engine to a screw  9 . Further, driveshaft housing  8  is constituted of engine holder  7  and vertically separable upper and lower cases  8   a  and  8   b  which are joined to the underside of engine holder  7 . 
     The engine  6  located on top of the outboard motor and fixed to engine holder  7  with bolts is enclosed by a helmet-like upper cover  6   b . Further, a lower cover  8   d  is provided so as to cover the range from engine holder  7  of driveshaft t housing  8  to the upper edge of upper case  8   a  so as to produce a unified appearance of the outboard motor. 
     A box-like oil pan  7   a  for receiving and temporarily storing lubricant flowed from engine  6  is provided under the engine holder  7 . 
     In the driveshaft t housing  8 , driveshaft  10  is rotatably accommodated inside a hollow  11  that extends vertically across engine holder  7 , upper case  8   a  and lower case  8   b.    
     The upper end of the driveshaft  10  projects out above the engine holder  7  and is inserted into and coupled with the lower end of crankshaft  6   a  of engine  6 . A drive gear  13   a  of a bevel gear set  13  inside lower case  8   b  is fixed at the lower end of the driveshaft  10  with respect to the direction of rotation. 
     Housed in lower case  8   b  are a screw shaft  12  which rotates on a rotational axis that is perpendicular to the rotational axis of driveshaft  10  and bevel gear set  13  which transmits the driving force from driveshaft  10  to screw shaft  12  (screw  9 ). 
     The rotational rate of the engine is varied (preferably reduced) by the setting of the gear ratio of the bevel gear set  13  (preferably, the number of teeth of the drive gear&lt;the number of teeth of the driven gear) and transmitted to screw shaft  12 . 
     A pair of driven gears  13   b , in bevel gear set  13 , are provided so as to mesh drive gear  13   a  from the front and rear. In this arrangement, the control movement of an aftermentioned shift lever  14  is transmitted via a shift rod  14   a  to a clutch mechanism arranged between screw shaft  12  and paired driven gears  13   b , whereby one of the driven gears  13   b  is selectively engaged with or disengaged from screw shaft  12  (by shift control), so that the action of screw shaft  12  can be switched between normal rotation, reverse rotation and neutral. 
     Specifically, for example, shift lever  14  is provided for steering handle  1   c  so that the user (operator) is able to make shift operations during maneuvering while grasping the handle  1   c . The aforementioned shift rod  14   a  is arranged from its top to bottom passing through cylinder portion  5   b  of swivel bracket  5  that is axially supported by the top  1   a  and bottom  1   b  on the front side of driveshaft housing  8  located in front of the driveshaft  10 , and the lower end is positioned at the front end of screw shaft  12 , whereby the clutch mechanism between driven gears  13   b  of the bevel gear set  13  and screw shaft  12  can be selectively engaged or disengaged. 
     In the present embodiment, as shown in  FIG. 3 , a cooling water pump device  17  that uses the driveshaft  10  as a driveshaft therefor is arranged at a position partway through the length of the driveshaft  10  in the driveshaft housing  8 . 
     In this cooling water pump device  17 , an impeller  16  of elastic material such as rubber, is arranged eccentrically inside the pump case  15  made of resin such as Nylons® resin, with a sleeve  25  made of metal such as stainless steel disposed therebetween. As the driveshaft  10  is driven, the impeller  16  rotates, whereby cooling water is drawn in from an aftermentioned inlet  17   b  to push the cooling water out to the engine  6  located above. 
     In the aforementioned hollow  11  of lower case  8   b  of the driveshaft housing  8 , a wall portion  8   c  that surrounds driveshaft  10  and has a watertight seal  10   b  for sealing between the lower part of driveshaft  10  and the intake side of cooling water pump device  17 , inserted at the upper end thereof, is formed upright. Inside this wall portion  8   c  a cooling water conduit  8   e  is extended upwards to the bottom of cooling water pump device  17 . Because of this cooling water conduit  8   e  the upper portion of wall portion  8   c  presents a double cylindrical configuration of outer and inner walls, and this inner cylindrical wall serves as the cylinder that surrounds driveshaft  10 . 
     An inlet port  8   f  for taking water (seawater, river water) from the outside of the outboard motor is opened with a filter on the side portion of the lower case  8   b , and the interior of inlet port  8   f  is connected to the cooling water passage  8   e.    
     In the cooling water pump device  17 , as shown in  FIGS. 3 and 4 , pump case  15  is formed of a large-diametric approximate cylinder (large-diametric cylinder)  15   a  and a small-diametric approximate cylinder (small-diametric cylinder)  15   b , arranged below and above, respectively, and joined to each other continuously. The wall separating large-diametric cylinder  15   a  and small-diametric cylinder  15   b  is formed with an opening, i.e. , insert hole  15   c  through which driveshaft  10  penetrates. Further, a plate-like under-panel  19  (having an inlet  17   b  opened as a cooling water inlet port, as indicated by the broken line in  FIG. 4 ) is provided to cover the bottom opening, designated at  15   d , of the large-diametric cylinder  15   a  that opens downward, thus forming a pump chamber  17   c  inside pump case  15 . This under-panel  19  has a gasket  19   a  on its undersurface so as to establish watertightness with the contact portion of lower case  8   b.    
     In the pump device  17 , as shown in  FIGS. 3 and 4 , impeller  16  is constructed of plural, radially extended vanes  20  and an approximately cylindrical boss portion  21 , these elements being integrally formed of an elastic material such as rubber. Further, a tubular core  22  made of a material that has a higher rigidity than the elastic material (e.g. , hard resin or metal) is embedded to this boss portion  21 . This tubular core  22  is fixed to the inner periphery of boss portion  21  with its end faces, with respect to the axial direction, covered with inner flanges  23  formed in boss portion  21 . 
     Formed in the inner peripheral surface of tubular core  22  is a key slot  22   a  extending axially. A key  16   a  having a semicircular form, viewed from side, is inserted into both the key slot  22   a  and another key slot  10   a  formed in driveshaft  10 , whereby impeller  16  is integrally fixed to driveshaft  10  with respect to the direction of rotation. Upon-assembly of cooling water pump device  17 , key  16   a  is adapted to be fitted into key slot  22   a  of tubular core  22  of impeller  16  after key  16   a  is fitted to key slot  10   a  of driveshaft  10 . 
     The cooling water pump device  17  is mounted in driveshaft housing  8  in such a manner that the under-panel  19  is positioned in correspondence with the joint portion, designated at  18 , of the upper case  8   a  to lower case  8   b  and the approximate cylindrical cap-like pump case  15  is projected upward into the upper case  8   a  side. Other than small-diametric cylinder  15   b , an outlet  17   d  that opens upward as a cooling water outlet port is formed at a side upper part of pump case  15 . The lower end of a cooling water pipe  17   e  extending upward is connected to this outlet  17   d . The upper end of this cooling water pipe  17   e  is connected to the water jacket (not shown) of engine  6 . 
     As the aforementioned inlet port  8   f , cooling water conduit  8   e , inlet  17   b , pump case  15  (pump chamber  17   c ), outlet  17   d , cooling water pipe  17   e  and the like constitute a cooling water path, a negative pressure arises as shown in  FIG. 3  to  FIGS. 5A and 5B  when cooling water pump device  17  is actuated. By this negative pressure, water is taken in from the outside of outboard motor  1  from the inlet port  8   f , passing through cooling water conduit  8   e  and inlet  17   b  opened in under-panel  19  under cooling water pump device  17  into pump chamber  17   c.    
     Then, cooling water is positively pressurized in pump chamber  17   c  of the cooling water pump device  17 , is supplied to the water jacket of engine  6  through outlet  17   d  and cooling water pipe  17   e , to cool down the engine  6 . 
     Designated at  17   a  is a guide wall portion for leading cooling water from pump chamber  17   c  to outlet  17   d . This guide wall portion  17   a  constitutes part of the wall that surrounds the pump chamber  17   c  and is located on the positive pressure side forming an ejection port  17   f . This ejection port  17   f  establishes communication between pump chamber  17   c  and outlet  17   d  and is provided in the form of a cutout window located at the lower part of the guide wall portion  17   a.    
     The cooling water pump device  17  here is formed of resin pump case  15 , which is low in manufacturing costs such as material cost and processing cost, and metal sleeve  25  inside the pump case  15 , so as to prevent melting and deformation due to frictional heat arising when impeller  16  frictionally rotates. As shown in  FIG. 4  to  FIGS. 6A and 6B , in cooling water pump device  17 , annular seal elements  26  (upper annular seal element  26   a  and lower annular seal element  26   b ) are arranged vertically apart and interposed between pump case  15  and metal sleeve  25  in order to secure and improve watertightness therebetween. These elements are joined by joint seal elements  27 , thus forming a one-piece continuously formed, sealing structure  28 . 
     More specifically, as shown in the vertical sectional view of cooling water pump device  17  in  FIG. 4 , the seal structure  28  is formed of a multiple number of (two, above and below in this embodiment) annular seal elements  26  ( 26   a ,  26   b ) which encircle the driveshaft  10  and are arranged apart vertically with respect to the axial direction of driveshaft  10  so as to be interposed between the inner peripheral surface of the resin pump case  15  and metal sleeve  25 , and a multiple number of joint seal elements  27  which extend in the axial direction to join each annular seal element  26  ( 26   a ,  26   b ) to the other, so that the annular seal elements  26  ( 26   a ,  26   b ) retain watertightness between the inner peripheral surface of pump case  15  and metal sleeve  25 . 
     The pump case  15  has an approximate bowl-shape formed of large-diametric cylinder  15   a  with bottom opening  15   d  as stated above, and is constructed such that the pump case  15  accommodates impeller  16  with sleeve  25  interposed there around and the bottom opening  15   d  is enclosed with under-panel  19 , forming the pump chamber  17   c . As shown in  FIG. 4  and  FIGS. 5A and 5B , pump case  15  has driveshaft  10  vertically penetrated therethrough. The top part of small-diametric cylinder  15   b  located on the upper side is folded closer to the outer peripheral surface of driveshaft  10  so as to prevent water leakage from pump chamber  17   c  as strongly as possible. Further, a multiple number of reinforcing ribs  15   e  (provided at four places, equi-angularly apart along the circumference, in the embodiment) that project close to driveshaft  10  are formed parallel to the driveshaft  10  axis, from the top end of small-diametric cylinder  15   b  to the driveshaft insert hole  15   c.    
     The sleeve  25  consists of a bottom  25   a  and a side wall portion  25   b  and has an approximately cylindrical cap-like configuration with its bottom  25   a  positioned up, and is fitted to the interior of large-diametric cylinder  15   a  of pump case  15 , in a close contact manner. The interior of sleeve  25  substantially constitutes the pump chamber  17   c  with which impeller  16  comes into frictional contact. Formed at a place in the upper part of sleeve  25 , i.e. , bottom  25   a , corresponding to the driveshaft insert hole  15   c  is an insert hole  25   c  similar to insert hole  15   c  for allowing insertion of driveshaft  10 . In the sleeve side wall portion  25   b , a cutout  25   d  that allows communication between pump chamber  17   c  and outlet  17   d  is formed at a place corresponding to the ejection port  17   f , i.e. , the cutout window located in the lower part of guide wall portion  17   a  of pump case  15 . 
     Here, sleeve  25  is made of metal, preferably stainless steel, and may be formed by diverse methods such as press-forming, casting and forging, and also may be formed with uniform thickness or varying thickness. 
     The lower side of seal is established by the lower annular seal element  26   b  interposed between the periphery of the bottom opening  15   d  of pump case  15  and under-panel  19 . In this embodiment, this seal element is provided in an approximately circular, partly angled, irregular shape, as shown in  FIGS. 5A and 5B  and  FIGS. 6A and 6B , surrounding the periphery of pump chamber  17   c  and the periphery of outlet  17   d.    
     Further, the upper annular seal element  26   a  is formed of an approximately circular shaped part arranged around the driveshaft insert hole  15   c  located at an upper position of the inner peripheral side of resin pump case  15  and a rectangular portion having two parallel sides enclosing an air discharge opening (air discharge hole)  15   f  extended from the insert hole  15   c  that is connected to small-diametric cylinder  15   b . Therefore, the upper annular seal element  26   a  has an approximate circular, partly irregular form having projections for covering air discharge opening  15   f.    
     Provided between the lower annular seal element  26   b  and the upper annular seal element  26   a  are joint seal elements  27 , which are formed at positions adjoining the guide wall portion  17   a  where ejection port  17   f  of pump chamber  17   c  is cut out and at the wall opposite to the guide wall portion  17   a.    
     Here, the annular seal elements  26   a  and  26   b  and joint seal elements  27  have circular cross-sections or so-called O-ring configurations. However, they can be formed to have various cross-sections to obtain appropriate sealing performance: they may be formed to have partly rectangular cross-sections at necessary positions, for example. 
     On the other hand, in order to fit annular seal elements  26   a  and  26   b  and joint seal elements  27 , grooves  29   a  to  29   d  are formed at necessary sites in the inner peripheral surface of the resin pump case  15 . Specifically, a groove  29   a  for receiving the lower annular seal element  26   b  is undercut formed in the interior side (other than guide wall portion  17   a ) surrounding pump chamber  17   c  at the bottom opening  15   d  while a groove  29   b  for receiving the lower annular seal element  26   b  is recessed so as to surround outlet  17   d  (other than guide wall portion  17   a ) continuously from the groove  29   a.    
     Further, a groove  29   c  for receiving the upper annular seal element  26   a  is formed in a recessed configuration, around the driveshaft insert hole  15   c  and towards the upper proximal part of guide wall portion  17   a  along air discharge opening  15   f.    
     Further, in the interior wall surface of pump case  15 , grooves  29   d  for receiving joint seal elements  27  that connect the upper annular seal element  26   a  and lower annular seal element  26   b  are formed vertically in the inserted direction of driveshaft  10  at both sides of guide wall portion  17   a  and at a position on its opposite side. 
     As shown in  FIGS. 5A and 5B , the interior surface of pump case  15 , specifically, the top peripheral part (the peripheral area that faces the bottom  25   a  of sleeve  25 ) of large-diametric cylinder  15   a , is hollowed out leaving the contour of the groove  29   c  for receiving the upper annular seal element  26   a , forming ridge-like ribs  30  that project downwards (downwards in the axis direction of driveshaft  10 ). The lower endface of the thus formed ribs  30 , or the lowermost part with respect to the axial direction of driveshaft  10 , abuts the bottom  25   a  of sleeve  25 , creating clearance between the interior surface of pump case  15  and metal sleeve  25 , hence forming an air layer  31 . 
     Thus, the spaces are created between ribs  30  and  30 , so that air layer  31  can be formed between the peripheral area of the ceiling surface of pump case  15  and the bottom  25   a  of sleeve  25  when sleeve  25  is fitted into pump case  15 . 
     As described above, the annular seal elements  26   a  and  26   b  establish watertightness between the inner peripheral surface of resin pump case  15  and metal sleeve  25 , so that it is possible to prevent seawater from infiltrating into the interface between pump case  15  and sleeve  25  by virtue of the water-protective function of the annular seal elements  26   a  and  26   b  even when the outboard motor is used in the sea. 
     Further, since lower annular seal element  26   b  is interposed between the rim of bottom opening  15   d  of resin pump case  15  and under-panel  19 , it is possible to provide a bottom-open pump case configuration made up of pump case  15  and bottom opening  15   d , which facilitates easy assembly of sleeve  25  and impeller  16 , and it is also possible to prevent cooling water in the pump chamber  17   c  from infiltrating into the interface between pump case  15  and sleeve  25 , by keeping watertightness (water preventive function) between the rim of bottom opening  15   d  and under-panel  19  that closes the bottom opening  15   d , with the provision of reliable lower annular seal element  26   b.    
     Of the seal elements, joint seal elements  27  are formed at such positions as to enclose the ejection port of pump chamber  17   c , so it possible to prevent water such as seawater from infiltrating into the interface between pump case  15  and sleeve  25  through the surrounding of ejection port  17   f  of pump chamber  17   c , in a more reliable manner. Further, since grooves  29   a  to  29   d  for receiving seal elements  26  and  27  are also formed on the inner peripheral surface of the resin pump case  15 , fitting of seal elements  26  and  27  into these grooves  29   a  to  29   d  for assembly of seal elements  26  and  27  into pump case  15  can be achieved in a simple and reliable manner. 
     Further, sealing is performed by continuous sealing structure  28  made of elastic resin, constituted of upper annular seal element  26   a , lower annular seal element  26   b  and joint seal elements  27 , watertightness against infiltration of water such as seawater into the interface between pump case  15  and sleeve  25  can be achieved in a more reliable manner by the integrated water protecting function of the joined elements. Moreover, handling at manufacturing and assembly can be simplified compared to that when seal elements  26  and  27  are provided piece by piece. Further, the seal can be formed of resin material of a uniform composition and the strength at the joints can be enhanced in terms of design. 
     Since ribs  30  are formed on the interior surface of pump case  15 , which produces air layer  31  between the interior surface of pump case  15  and sleeve  25 , frictional heat arising when impeller  16  frictionally rotates inside sleeve  25  can be prevented from transferring to pump case  15  by insulation and reduction of heat conduction owing to presence of air layer  31 . As a result it is possible to reliably prevent resin pump case  15  from being heated by the frictional heat. 
     Accordingly, it is possible to prevent resin pump case  15  from melting. 
     The present invention is not limited to the above embodiment, but various modifications can be added. 
       FIG. 7  is a vertical sectional view of a cooling water pump device  17 A of an outboard motor according to another embodiment of the present invention.  FIG. 7  corresponds to  FIG. 4  of the above embodiment. This second embodiment has almost the same configuration except in that the configurations and arrangement of seal elements  40  and  42  are different from those of the embodiment shown in  FIG. 1  to  FIGS. 6A and 6B , so the same components are allotted with the same reference numerals. 
     Cooling water pump device  17 A of an outboard motor of the second embodiment, similarly to the embodiment shown in  FIGS. 1 to 3 , is provided for an outboard motor including an engine  6 , a hollow driveshaft housing  8  under the engine; and a driveshaft  10  arranged vertically in the driveshaft housing  8  for transmitting the drive force of a crankshaft  6   a  of engine  6  to a screw  9 . In this outboard motor, the cooling water pump device functions in the following manner. That is, a pump case  15  made of resin is arranged at a position partway through the length of the driveshaft  10  in the drive housing  8 ; an impeller  16  made of elastic material is accommodated eccentrically in the pump case with a metal sleeve  25  interposed therebetween; and the impeller  16  is rotated by driving of the driveshaft  10 , whereby cooling water is drawn in from an inlet  17   b  at the bottom of pump case  15  and pumped up toward the engine  6  located above. 
     In this pump device  17 A according to the second embodiment, annular seal elements  40 [ a ] to  40 [ d ] that surround the driveshaft  10  for keeping watertightness at the interface between the inner peripheral surface of the resin pump case  15  and metal sleeve  25  are disposed between the inner peripheral surface of the resin pump case  15  and metal sleeve  25 , at multiple sites vertically apart with respect to the axial direction of driveshaft  10  while joint seal elements  42 [ a ] to  42 [ o ] that join annular seal elements  40 [ a ] to  40 [ d ] to each other are provided. 
     Pump case  15  has an approximate bowl-shape with a bottom opening  15   d  (for example, a bowl placed upside down) and is constructed such that the pump case  15  accommodates impeller  16  and the bottom opening  15   d  is enclosed with an under-panel  19 , forming a pump chamber  17   c.    
     For the cooling water pump device  17 A of the second embodiment, there are variational examples 1 to 7 as shown in  FIGS. 8A and 8B  to  FIGS. 14A and 14B , where different types of sealing structures are configured by combinations of annular seal elements  40 [ a ] to  40 [ d ] and joint seal elements  42 [ a ] to  42 [ o].    
       FIGS. 8A and 8B  to  FIGS. 14A and 14B  show the arrangements of annular seal elements  40 [ a ] to  40 [ d ] and joint seal elements  42 [ a ] to  42 [ d ] of sealing structures of examples 1 to 7, indicated with reference numerals. 
     In  FIGS. 8A and 8B  to  FIGS. 14A and 14B , diagrams A are schematic expansion plans showing respective sealing structures made up of seal elements in examples 1 to 7, by pressing each sealing structure from above. In  FIGS. 8A and 8B  to  FIGS. 14A and 14B , diagrams B are schematic perspective views showing each sealing structure made up of seal elements. 
     Any of annular seal elements  40 [ a ] to  40 [ d ] is composed of an annular so-called O-ring that surrounds driveshaft  10  uninterrupted. 
     As shown in  FIG. 7 , these annular seal elements  40 [ a ] and  40 [ b ] are fitted in grooves  44 [ a ] and grooves  44 [ b ], respectively, both of which are in the ceiling surface of the interior surface of large-diametric cylinder  15   a  of pump case  15 , the former being formed at a position closest to driveshaft  10  and the latter being formed at a position away from the groove  44 [ a ]. Annular seal element  40 [ c ] and  40 [ d ] are fitted in grooves  44 [ c ] and grooves  44 [ d ], respectively, the former being formed at a position higher than the upper end of ejection port  17   f  on the side wall of large-diametric cylinder  15   a , the latter being formed on the undersurface of large-diametric cylinder  15   a.    
     These grooves  44 [ a ] to  44 [ d ] are to be formed in conformity with the arrangement of the seal elements, and can be formed as appropriate in accordance with the disposition of the annular seal elements. 
     Joint seal elements  42 [ e ] to  42 [ g ] extend substantially in the radial direction or axial direction of driveshaft  10 , and are formed, as will be described hereinbelow, at two places ( 42 [ e ],  42 [ f ]) adjoining ejection port  17   f  and at a place ( 42 [ g ]) on the side opposite to ejection port  17   f . With this arrangement, the joint seal elements provide watertight function, i.e. , the function of preventing water such as seawater from infiltrating into the interface between pump case  15  and sleeve  25  and the function of joining the annular seal elements and forming an integrated sealing structure. In other examples, joint seal elements, designated at  42 [ h ] to  42 [ o ], which extend along annular seal elements  40 [ a ] to  40 [ d ] are also provided. 
     These joint seal elements  42 [ e ] to  42 [ g ] have an O-shaped section as the aforementioned annular seal elements do, and the positions of their attachment are formed with grooves (not shown) which extend in the radial direction or axial direction of driveshaft  10 , in order to prevent their displacement. 
     As shown in  FIGS. 8A and 8B , the annular seal element indicated at  40 [ a ] is arranged at a position, inside the large-diametric cylinder  15   a  of pump case  15 , opposing the bottom  25   a  of sleeve  25 , adjacent to and surrounding driveshaft  10 , or adjoining and surrounding insert hole  15   c , and closest, among the annular seal elements, to driveshaft  10 . 
     The annular seal element indicated at  40 [ b ] is arranged at a position, inside the large-diametric cylinder  15   a  of pump case  15 , opposing the bottom  25   a  of sleeve  25  at the vicinity of side wall portion  25   b , in other words, at a position surrounding insert hole  15   c  through which driveshaft  10  is inserted and away from the insert hole, or near the circumference of the sleeve. 
     Further, the annular seal element indicated at  40 [ c ] is arranged surrounding driveshaft  10  at a position on the interior side of the side wall portion of large-diametric cylinder  15   a , opposing the side wall portion  25   b  of sleeve  25 , and formed annularly passing along the upper edge of the cutout  25   d  of sleeve  25  and above ejection port  17   f . This annular seal element  40 [ c ] in cooperation with an annular seal element designated at  40 [ d ] encloses the upper end of ejection port  17   f  of pump chamber  17   c.    
     The annular seal element designated at  40 [ d ] is interposed between the rim of bottom opening  15   d  of pump case  15  and under-panel  19 . This seal element roughly has a circular and partly angled, irregular shape, in correspondence with the bottom opening  15   d  of pump case  15 . In this respect, this seal element has the same configuration as that of lower annular seal element  26   b  described in the foregoing embodiment. 
     First, sealing structures of examples 1 and 2 will be described with reference to  FIGS. 8A and 8B  and  FIGS. 9A and 9B . 
     The sealing structures in examples 1 and 2 are made up of the aforementioned annular seal elements only, which are arranged at the upper end of ejection port  17   f  of the pump chamber and at places surrounding driveshaft insert hole  15   c  of the upper part of pump case  15 , so as to provide watertightness between pump case  15  and sleeve  25 . 
     EXAMPLE 1 
     The sealing structure of example 1 is given in combination of annular seal elements denoted by  40 [ a ],  40 [ b ] and  40 [ d ], as shown in  FIGS. 8A and 8B . Specifically, this sealing structure is composed of an annular seal element  40 [ a ] located close to insert hole  15   c  of driveshaft  10  in large-diametric cylinder  15   a , an annular seal element  40  [ b ] located at a place away from the above element and close to the periphery of large-diametric cylinder  15   a  and an annular seal element  40 [ d ] interposed between the rim of bottom opening  15   d  of pump case  15  and under-panel  19 . 
     In  FIGS. 8A and 8B , the sealed area (watertight area) from the annular seal elements is indicated by hatching  46 . In  FIGS. 8A and 8B , the broken line denotes the position of annular seal element  40 [ c].    
     With the above sealing structure of example 1, sealed area  46  is set up to extend between ceiling area of large-diametric cylinder  15   a  and the bottom  25   a  of sleeve  25 , as shown in  FIGS. 8A and 8B . In the conventional pump case  15 , this ceiling area of large-diametric cylinder  15   a  is most likely to cause drawbacks when the engine is operated in the dry without cooling water. Therefore, sealing only this area works well to fix the drawback. Water such as seawater having infiltrated between pump case  15  and sleeve  25  drains off and is unlikely to stagnate across the side wall portion of pump case  15  and sleeve  25 , no cracks of sleeve  25  due to salt buildup will occur. 
     EXAMPLE 2 
     The sealing structure of example 2 is given in combination of annular seal elements denoted by  40 [ a ],  40 [ c ] and  40 [ d ], as shown in  FIGS. 9A and 9B . Specifically, this sealing structure is composed of an annular seal element  40 [ a ] located close to insert hole  15   c  of driveshaft  10  in large-diametric cylinder  15   a , an annular seal element  40  [ c ] arranged opposing the side wall portion  25   b  of sleeve  25  and annularly passing along the upper edge of the cutout  25   d  of sleeve  25  and near and above ejection port  17   f , and an annular seal element  40 [ d ] interposed between the rim of bottom opening  15   d  of pump case  15  and under-panel  19 . 
     In the above sealing structure of example 2, sealed area  46  shown in  FIGS. 9A and 9B  is made to extend up to the side wall portion of large-diametric cylinder  15   a , though only the ceiling portion of large-diametric cylinder  15   a  can be sealed in the sealing structure of example 1. Thus the sealed area is enlarged. 
     Next, sealing structures of examples 3 to 7 will be described with reference to  FIGS. 10A and 10B  to  FIGS. 14A and 14B . 
     As shown in  FIGS. 10A and 10B  to  FIGS. 14A and 14B , the sealing structures of examples 3 to 7 employ joint seal elements  42 [ e ] to  42 [ m ] which extend in the radial direction or axial direction of driveshaft  10  to connect any one of the annular seal elements  40 [ a ] to  40 [ d ] to another or a plurality of joint seal elements  42 [ n ],  42 [ o ] along annular seal elements  40 [ a ] to  40 [ d ], so as to construct unified parts formed of the annular seal elements made of elastic resin material for providing watertightness at the interface between the inner peripheral surface of the resin pump case  15  and metal sleeve  25 . 
     EXAMPLE 3 
     The sealing structure of example 3 is configured, as shown in  FIGS. 10A and 10B , so that the aforementioned annular seal elements are arranged at a place ( 40 [ a ]) adjacent to insert hole  15   c  and at another place ( 40 [ b ]) away from the former, both surrounding driveshaft insert hole  15   c  at the upper position of the pump case  15 , and three joint seal elements ( 42 [ e ] to  42 [ g ]) extending in the radial direction of driveshaft  10  are provided to join the annular seal elements one to another. Further, an annular seal element  40 [ d ] is interposed at the position between the rim of bottom opening  15   d  of pump case  15  and under-panel  19 . 
     This sealing structure is given in combination of an annular seal element  40 [ a ] located close to insert hole  15   c  of driveshaft  10  in large-diametric cylinder  15   a , an annular seal element  40 [ b ] located at a place more distant from insert hole  15   c  and close to the periphery of large-diametric cylinder  15   a , joint seal elements  42 [ e ] to  42 [ g ] arranged radially therebetween for joining these annular seal elements  40 [ a ] and  40 [ b ], and an annular seal element  40 [ d ] interposed between the rim of bottom opening  15   d  of pump case  15  and under-panel  19 . 
     With this sealing structure of example 3, as shown in  FIGS. 10A and 10B , a sealed area  46  extending between ceiling area of large-diametric cylinder  15   a  and the bottom  25   a  of sleeve  25  are created in the same manner as the sealed area of the sealing structure of example 1 shown in  FIGS. 8A and 8B . In addition, since annular seal elements  40 [ a ] and  40 [ b ] are connected by joint seal elements  42 [ e ] to  42 [ g ], the annular seal elements  40 [ a ] and  40 [ b ] are unlikely to separate compared to the sealing structure of example 1, hence this configuration brings about higher watertightness and improvement in assembly. 
     EXAMPLE 4 
     The sealing structure of example 4 is configured such that, as shown in  FIGS. 11A and 11B , the annular seal elements are disposed at the upper end ( 40 [ c ]) of ejection port  17   f  of the pump chamber  17   c  and at a place ( 40 [ a ]) surrounding the driveshaft insert hole at the upper position of the pump case, and three joint seal elements ( 42 [ h ] to  42 [ j ]) that extend in the radial direction of driveshaft  10  and connect between the above annular seal elements are provided. Further, an annular seal element  40 [ d ] is interposed at the position between the rim of bottom opening  15   d  of pump case  15  and under-panel  19 . 
     Specifically, this sealing structure of example 4 is composed of annular seal element  40 [ a ] located close to insert hole  15   c  of driveshaft  10  in large-diametric cylinder  15   a , annular seal element  40 [ c ] arranged opposing the side wall portion  25   b  of sleeve  25  and passing along the upper edge of the cutout  25   d  of sleeve  25  and near and above ejection port  17   f , and joint seal elements  42 [ h ] to  42 [ j ] having an inverted L-shape or a hook-shape, viewed from a circumferential direction of driveshaft  10 , arranged radially for joining these annular seal elements  40 [ a ] and  40 [ c ], and annular seal element  40 [ d ] interposed between the rim of bottom opening  15   d  of pump case  15  and under-panel  19 . 
     This sealing structure of example 4 is configured, as shown in  FIGS. 11A and 11B , so that a sealed area  46  covers the ceiling area of large-diametric cylinder  15   a  and extends from it to cutout  25   d  of side wall portion  25   b  of sleeve  25  or the upper end of ejection hole  17   f . In addition, since annular seal elements  40 [ a ] and  40 [ c ] are connected by joint seal elements  42 [ h ] to  42 [ j ], the annular seal elements  40 [ a ] and  40 [ c ] are unlikely to separate compared to the sealing structure of example 2, hence this configuration brings about higher watertightness and improvement in assembly. 
     EXAMPLE 5 
     The sealing structure of example 5 is configured such that, as shown in  FIGS. 12A and 12B , an annular seal element is disposed at a place ( 40 [ a ]) surrounding the driveshaft insert hole  15   c  at the upper position of pump case  15 , and an annular seal element is interposed at the position ( 40 [ d ]) between the rim of bottom opening  15   d  of pump case  15  and under-panel  19 . In addition, three joint seal elements ( 42 [ k ] to  42 [ m ]) that extend in the radial direction of driveshaft  10  and then in the axial direction are provided to connect between the above annular seal elements. 
     Specifically, this sealing structure of example 5 is composed of annular seal element  40 [ a ] located close to insert hole  15   c  of driveshaft  10  in large-diametric cylinder  15   a , annular seal element  40 [ d ] interposed between the rim of bottom opening  15   d  of pump case  15  and under-panel  19 , and joint seal elements  42 [ k ] to  42 [ m ] having an inverted L-shape or a hook-shape, viewed from a position perpendicular to the axis, arranged radially from the axis of driveshaft  10  for joining these annular seal elements  40 [ a ] and  40 [ d].    
     With this sealing structure of example 5, as shown in  FIGS. 12A and 12B , a sealed area  46  covers the ceiling area of large-diametric cylinder  15   a  and seals the surrounding of cutout  25   d  of the side wall portion  25   b  of sleeve  25  or the surrounding of the ejection port. That is, the ceiling area and two thirds of the side wall portion can be sealed. In addition, since annular seal elements  40 [ a ] and  40 [ d ] are connected by joint seal elements  42 [ k ] to  42 [ m ], improvement in assembly can be obtained. 
     EXAMPLE 6 
     The sealing structure of example 6 is made up of, as shown in  FIGS. 13A and 13B , the sealing structure of example 5 (annular sealing elements  40 [ a ],  40 [ d ] and joint sealing elements  42 [ k ] to  42 [ m ]) and a joint seal element  42 [ n ] located at the ceiling of large-diametric cylinder  15   a  over ejection port  17   f  for connecting joint seal elements  42 [ k ] and  42 [ l ]. This joint seal element  42 [ n ] lies at the same position as the aforementioned annular seal element  40 [ b ] with respect to the axial direction of driveshaft  10 , but formed only within the section over the ejection port  17   f . Other configurations are the same as the sealing structure of example 5, so the same reference numerals are allotted to the same components. 
     This sealing structure of example 6 provides a more efficient water preventing function than that of example 5 to prevent water such as seawater from infiltrating into the interface between pump case  15  and sleeve  25  through ejection port  17   f.    
     Here, the joint seal element  42 [ n ] may be formed like the annular seal element  40 [ b ], so as to be located between pump case  15  and sleeve  25  in a fully encircled configuration (the same configuration as annular seal element  40 [ b ]). This further enhances watertightness. 
     This sealing structure of example 6 is similar to the seal structure of the embodiment shown in  FIGS. 6A and 6B , differing in that annular seal element  26  in the first embodiment is formed with projected portions to detour air discharge hole  15   f.    
     EXAMPLE 7 
     The sealing structure of example 7 is made up of, as shown in  FIGS. 14A and 14B , the sealing structure of example 5 (annular sealing elements  40 [ a ],  40 [ d ] and joint sealing elements  42 [ k ] to  42 [ m ]) and a joint seal element  42 [ o ] located adjacent to the upper portion of ejection port  17   f  for connecting joint seal elements  42 [ k ] and  42 [ l ]. This joint seal element  42 [ o ] lies at the same position as the aforementioned annular seal element  40 [ c ] with respect to the axial direction of driveshaft  10 , but formed only within the section along the ejection port  17   f . Other configurations are the same as the sealing structure of example 5, so the same reference numerals are allotted to the same components. 
     This sealing structure of example 7 provides a more efficient water preventing function than that of example 5 to prevent water such as seawater from infiltrating into the interface between pump case  15  and sleeve  25  through ejection port  17   f . Here, the joint seal element  42 [ o ] may be formed so as to be located between pump case  15  and sleeve  25  in a fully encircled configuration (the same configuration as annular seal element  40 [ c ]). This further enhances watertightness. 
     According to the above embodiment, as seen in the sealing structures of the above examples 1 to 7 in the cooling water pump device  17 A of an outboard motor, a plurality of annular seal elements  40 [ a ] to  40 [ d ] that surround the driveshaft  10  for creating watertightness at the interface between the inner peripheral surface of the resin pump case  15  and metal sleeve  25  are disposed vertically apart, one from another, with respect to the axial direction of driveshaft  10 , between the inner peripheral surface of the resin pump case  15  and metal sleeve  25 . Therefore it is possible to reliably prevent water such as seawater from infiltrating into the interface between pump case  15  and sleeve  25  by virtue of the water-preventive function of the annular seal elements even when the outboard motor is used in the sea. 
     Accordingly, it is possible to positively prevent the salt build up problem which would be caused when water, especially seawater infiltrates into and between the resin pump case and the metal sleeve as in the conventional cooling water pump device, and the drawback of cracks of the metal sleeve due to salt buildup. 
     Pump case  15  has an approximate bowl-shape having bottom opening which is enclosed by under-panel  19 , forming pump chamber  17   c  that accommodates impeller  16  therein. As the sealing structure of example 2 shown in  FIGS. 9A and 9B  and that of example 4 shown in  FIGS. 11A and 11B , at least the above-described annular seal elements  40  are disposed at the upper end of ejection port  17   f  of the pump chamber  17   c  and at a place surrounding driveshaft insert hole  15   c  at the upper position of the pump case  15 , so that pump case  15  can be constructed so as to have a bottom opening which permits easy assembly of sleeve  25  and impeller  16 . Also, provision of the annular seal elements at the upper end of ejection port  17   f  of the pump chamber  17   c  and at a place surrounding driveshaft insert hole  15   c  at the upper position of the pump case  15  produces sufficient watertightness performance. Further, since the portion that would cause inconveniences in a conventional pump case when a trial operation is carried out in the dry without cooling water is positioned in the top side area of the pump case and the place surrounding the driveshaft insert hole  15   c  at the upper position of pump case  15  and ejection port  17   f  of pump chamber  17   c  are sealed with the annular seal elements, it is possible to secure watertightness and solve the drawback during operation in the dry. As to the salt buildup inconvenience between pump case  15  and sleeve  25 , water is unlikely to stagnate across the upright side wall portion of the sleeve  25  extending along the driveshaft, the provision of a seal at ejection port  17   f  and the place surrounding driveshaft insert hole  15   c  only also establishes effective watertightness. 
     As the sealing structures shown from examples 3 of  FIGS. 10A and 10B  through example 7 of  FIGS. 14A and 14B , a plurality of joint seal elements  42  that extend in the axial direction or radial direction of driveshaft  10  to connect the annular seal elements  40  to each other are provided so as to produce a unified structure of the annular seal elements made up of elastic resin material to create watertightness between the inner peripheral surface of the resin pump case and the metal sleeve. Therefore, watertightness against infiltration of water such as seawater into the interface between the pump case and sleeve can be achieved in a more reliable manner by the integrated water protecting function of the joined elements. Moreover, handling at manufacturing and assembly is simple compared to that when the seal elements are provided piece by piece. Moreover, the seal can be formed of resin material of a uniform composition and the strength at the joints can be enhanced in terms of design. 
     As in example 7 shown in  FIGS. 14A and 14B , the joint seal elements  42 [ k ] to  42 [ m ] are used to connect the lower annular seal element  40 [ d ] interposed between the bottom opening rim of the pump case  15  and the under-panel  19 , with the upper annular seal element  40 [ a ] arranged at a place surrounding driveshaft insert hole  15   c  at the upper position of pump case  15  and the seal elements  42 [ k ] and  42 [ l ] are disposed at both sides of the ejection port of the pump chamber. Therefore, infiltration of water such as seawater into the interface between pump case  15  and sleeve  25  through the surrounding of the ejection port of the pump chamber can be more reliably prevented by these joint seal elements.