Abstract:
An electric propulsion pod for a ship having a electric propulsion pod heat rejection member. The electric propulsion pod is attached below the ship by a hollow ship access shaft. The electric propulsion pod contains an electric motor for producing a water propulsion. The electric motor generates an amount of heat that is conducted and subsequently released into the water through the electric propulsion pod and ship access shaft surfaces. The heat rejection member is fitted for increasing the conduction and subsequent release of the electric motor heat.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an electric propulsion pod for a ship, which pod has an electric motor fitted into a design of propulsion pod which ensures favorable flow of the water around the pod, the propulsion pod being located on the bottom of the ship by means of a hollow -access shaft and the heat generated by the electric motor being rejected via the surface of the propulsion pod to the water flowing around it. 
     2. Description of the Prior Art 
     An electric propulsion pod for a ship corresponding to the above can be seen in the applicant&#39;s publication with the title: Siemens-Schottel-Propulsor (SSP) “The Podded Electric Drive with Permanently Excited Motor”, presented to the AES 97—All Electric Ship 13-14.03.97, Paris. The publication on the Siemens-Schottel-Propulsor (SSP) shows an electric propulsion pod for a ship with a motor surface-cooled which is in a simple manner and is in the form of a permanently excited synchronous motor. 
     This motor, whose more precise details can be seen from FIG. 2 of the publication, is completely encapsulated and maintenance-free. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide a solution which permits reliable cooling of the motor even when the electric propulsion pod is employed at overload in tropical waters with high water temperatures. In addition, the working temperature of the electric motor is to be lowered and a more uniform temperature of the individual components of the motor, for example the coil winding heads, is to be achieved. 
     The object is, in principle, achieved in that the heat is rejected, by heat rejection areas in the water both from the propulsion pod ( 17 ,  23 ) and from the access shaft ( 16 ,  18 ), that are employed to improve the heat conduction and rejection. The inclusion of the access shaft in the heat rejection from the motor very advantageously achieves the effect that the cooling of the motor is not limited to the surface of the propulsion pod only. This can advantageously occur, in accordance with the invention, without departure from the simple surface cooling as the cooling principle. 
     An embodiment of the invention provides for improving the heat rejection to be an increase in the effective heat rejection area. In the electric propulsion pod known from the prior art, only the outer wall of the propulsion pod, in the winding region of the electric motor, is provided as the effective heat rejection area. In this case direct heat rejection from the shrunk-in inner part takes place at the outer wall. This effective heat rejection area is substantially increased according to the present invention. The result is an advantageously improved thermal behavior of the propulsion pod. 
     A further embodiment of the invention provides for improving the heat rejection to be an increase in the temperature of the effective heat rejection area. Increasing the temperature of the effective heat rejection area advantageously increases the temperature difference relative to the surrounding sea water and satisfactory cooling of the propulsion system is ensured even in the case where the propulsion system is employed in tropical waters with water temperatures of between 30° C. and 35° C. This is important, particularly for cruise ships which pass through the Red Sea, for example. 
     In order to improve the heat conduction, in particular to improve the heat conduction from the winding region of the electric motor, provision is made for a material with higher thermal conductivity than steel to be used. For this purpose, a material made of non-ferrous alloy with good thermal conductivity is particularly advantageous. Copper-containing non-errous alloys, in particular, have a higher thermal conductivity than steel. When special copper bronzes are used, there is a further essential advantage that no growth occurs on the surface. It is therefore possible to dispense with the use of an anti-fouling paint on the surface of the pod and that of the transition between the pod and the access shaft. Dispensing with a coat of paint, in this way, leads to a not insubstantial increase in the surface temperature of the heat rejection area because anti-fouling paint coats have a thermal conductivity which is lower than that of metal by a power of 10. They act as an insulating layer and impair the heat rejection. An unexpected advantage is achieved by the use of a special copper bronze, the so-called propeller bronze G-CU Al 10 Ni being recommended in this case; not only is the thermal conductivity improved because such materials are better heat conductors than steel but a substantially increased heat rejection temperature is also achieved. 
     Provision is also made in the electric propulsion pod for the propulsion pod to have a reduced wall thickness, in the part directed into the access shaft, as compared with the wall thickness present in the part with the favorable flow configuration. This advantageously provides particularly good heat rejection into the access shaft from the part of the pod surface not directly cooled by the sea water. The wall thickness in the part of the propulsion pod directed into the shaft can be reduced as much as is permitted by the casting technique. There is, therefore, an essentially higher surface temperature in this region as compared with the rest of the central region of the motor pod, which has to have a favorable flow configuration and therefore has a relatively large wall thickness in the center. 
     Provision is also made for the propulsion pod to have an enlarged surface on the part directed into the access shaft, an enlarged surface due to ribs, beads or honeycomb sheet, for example. This advantageously achieves the effect that the heat rejecting surface is essentially enlarged so that, in this region, increased heat rejection can occur. The heat rejected is convectively distributed by the air located in the hollow access shaft and, in this way, passes via the large surface of the access shaft into the sea water. 
     An embodiment of the invention provides for components of the enlarged surface to have heat conduction devices (heat ducts) which are in connection with the inside of the electric motor. In this way, the surface temperature of the enlarged surface can be raised and, therefore, the heat rejection to the air circulating within the access shaft can be still further increased. This does not depart from the simple cooling which is a principle of the invention. 
     Additionally, or as an alternative, the access shaft can have a lower part which has, at least in part, a double-walled configuration, the inside of the double-walled part having heat conducting media such as air or water. Devices, for example fans, are also, if appropriate, provided in the access shaft for circulating the access shaft air, these devices being used to maintain a stable circulation. By this way, the heat rejected by the pod into the access shaft can be satisfactorily rejected to the access shaft wall and be led along the latter and through it to the sea water in a satisfactory manner. 
     The above devices are advantageously located in the lower part only of the access shaft, around which sea water always washes. The transition between the access shaft and the ship is located above the water line and thus sea water only washes around parts of the upper part of the access shaft. Reliable heat removal is achieved by the arrangement of the devices for increasing the heat removal in the lower part of the access shaft. If the propulsion pod is arranged on a short access shaft whose transition to the ship occurs below the water line, for which provision is likewise made, the corresponding devices are of course located in the whole of the access shaft. Because, in principle, no provision is made for the arrangement of the transition between the access shaft and the ship at the water line, only these two alternatives need to be considered for the arrangement of the heat rejection components in the access shaft. 
     As a supplement, or likewise as an alternative, provision is made for the propulsion pod to have devices which contain heat transfer media (heat ducts); such that, the heat can be advantageously led away directly, so that a particularly effective, low-cost and simple solution results. Pursuing this principle, furthermore, provision is made for the electric motor to have a hollow shaft, which is open at both ends, through which sea water can flow and which has, if required, a conical configuration. In consequence, cooling of the electric motor also takes place from the inside. 
     In another embodiment, provision is made for a convective cooling circuit to be arranged in the shaft of the electric motor, which circuit transports heat from the center of the electric motor to the cool ends. Thus, the area of the hub and, in fact, a part of the propeller surface can be advantageously used for conducting away the heat. 
     Provision is also made for the coil winding heads of the electric motor to have convectively operating heat ducts, which lead to the cool outer ends, to side fins or into the lower part of the access shaft. The coil winding heads are not in direct contact with the outer wall of the propulsion pod but they develop a substantial quantity of heat because of the currents flowing within them. In some cases, therefore, additional cooling of the coil winding heads is necessary and this can take place in a particularly simple manner by the heat ducts described above. The surface of the cool outer ends, the side fins or the lower part of the access shaft is utilized particularly favorably for this purpose. 
     In order to conduct away the heat developed by the coil winding heads directly the latter are also advantageously provided with heat bridges to the outer wall of the propulsion pod. In the case of smaller propulsion systems, it is then even possible to dispense with heat ducts and further cooling components. The cooling of the propulsion pod at the outer wall is then sufficient. 
     These heat conducting bridges advantageously consist of heat conducting plastic with a filler material of a material which conducts heat particularly well. Epoxy resin can, for example, be considered as the plastic, while minerals can be used as the filler material. In this arrangement, the heat conducting bridges can be larger than the coil winding head dimensions and can, for example, be configured as heat conducting rings, which advantageously have parting lines between the individual coil winding head sections. The result is a particularly large-volume configuration of the heat conducting bridges with good thermal conduction from the coil winding heads to the outer wall of the propulsion pod. 
     Provision is also made for the propulsion pod and/or the lower part of the access shaft to have surface enlarging elements, for example external ribs or external beads, to improve the cooling. This likewise achieves improved heat removal from the motor into the sea water, it being possible, in a particularly advantageous manner, for these external ribs or external beads also to undertake flow guidance functions which support the action of fins. 
     Cooling ducts, through which water flows and which have a conical configuration to avoid blocking due to flotsam, are likewise provided at the transition between the access shaft and the propulsion pod; this provides particularly good cooling for this region. Heat ducts, which are led out from the inside of the propulsion motor, can advantageously end at the cooling ducts. 
     Provision is also made, if appropriate, for the external region of the motor and/or the motor/access shaft transition region to have an at least partially double-walled configuration, the space between the two walls being configured so that a coolant, in particular water, can flow through it. In such double-walled spaces, a circulation occurs due to the one-sided supply of heat so that these double-walled regions can be used as good heat rejection regions. In addition, they have the advantage that they can, for example, reinforce the lower part of the access shaft or that they can contribute to the formation of a shape which is particularly favorable to flow. This therefore makes it possible to achieve a combined effect. 
     The heat conducting devices, like the electric motor, are of maintenance-free design. This is readily possible because they operate without circulating pumps. They can therefore be configured as a unit forming a block with the propulsion pod motor, for which no provision is made for maintenance, or even for repair, in service operation. Because the heat conducting and rejection devices are completely located in the lower part of the access shaft, they do not interfere with the dismantling of the lower part of the access shaft. This dismantling work takes place by divers when the propulsion pod is exchanged for repair, the ship remaining in the water. As compared with the known heat-exchanger solutions with heat exchangers in the ship or on deck, there are therefore substantial handling and cost advantages. 
    
    
     FIG. 1 shows a sectional view of a propulsion pod corresponding to the prior art (publication AES 97). 
     FIG. 2 shows a sectional view of a propulsion pod cooled in accordance with the present invention. 
     FIG. 3 shows a sectional view of a cooling surface arrangement in accordance with FIG.  2 . 
     FIG. 4 shows sectional view of a cooling ducts, through which water flows, at the transition between the propulsion pod and the access shaft. 
     FIG. 5 shows a sectional view of the arrangement of an inner double wall in the lower part of the access shaft; 
     FIG. 6 shows a detailed section through one end of the propulsion pod with heat bridges in the region of the coil winding heads. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1, which shows the prior art on which the invention is based,  1  designates the electric propulsion motor,  2  designates the propeller driven by the propulsion motor  1 ,  3  designates the pod outer wall, whose contour is also retained in the part directed into the access shaft,  4  designates the flange transition between the propulsion pod and the lower part of the access shaft and  5  designates a flange in the middle of the access shaft. The cable harness  6  passes down through the access shaft to supply current to the electric motor  1 . A ladder  7 , by means of which an inspector  8  has easy access to the lower part of the access shaft, is located in the access shaft itself. Because the propulsion pod is maintenance-free and is not configured to be accessible, the inspector  8  only has to monitor the flange connections  4  and  5 . Because these are designed for a long life, the lower part of the ladder  7  is dispensed with in more recent embodiments, and therefore also in the case of the embodiment according to the invention. The lower part of the access shaft is therefore free for installation features, even for installation features which make access to the outer wall of the electric motor impossible. 
     Auxiliary equipment (not drawn in any more detail), for example bilge pumps, the compressed air supply for the seal at the transition of the access shaft to the ship etc., are fitted in the upper part of the access shaft. 
     FIG. 2 shows a diagrammatic representation of a propulsion pod with the electric motor  10 , which is connected by heat ducts (not represented) to one or a number of cooling elements  11  in the lower part of the access shaft, in particular on the walls of the lower part of the access shaft. For further cooling, the propulsion pod shown has a hollow shaft through which water flows. The flow duct in the hollow shaft is designated by  12  and the arrows indicate the direction in which the water flows through the shaft. The heat ducts (not shown) are, like the flow duct, advantageously configured without installation features. 
     FIG. 3 shows, again diagrammatically, cooling elements  13  and  14  located in the lower part of the access shaft. Like the embodiment of a cooling element shown diagrammatically in FIG. 2, all the cooling elements known from cooling technology can be employed here. The arrangement of the cooling elements is arbitrary and additional cooling elements are also possible in the free space of the hollow access shaft. The electric motor does not, in fact, need to be accessible. 
     Coolant tubes  15  at the transition from the access shaft  16  to the propulsion pod  17  are shown in FIG.  4 . Like the hollow shaft shown in FIG. 2, flow takes place through them in the longitudinal direction. The outer surfaces of the coolant tubes  15  can also be connected to the inside of the propulsion motor by means of heat ducts. The coolant tubes  15  can, however, also be used for particularly intensive cooling of the part of the pod outer wall facing them. 
     FIG. 5 shows a double-walled embodiment of the lower part of the access shaft with the outer wall  18  and an inserted inner wall  19 , with heat ducts  20 , which are here configured in an embodiment in which water flows through them, entering into the intermediate space between the outer wall  18  and the inner part  19 . In the case where water is used, the flow cross section for the coolant is preferably round; if heat ducts for air are used, inlet flow slots are preferably provided. 
     In FIG. 6, which shows a detailed section through one end of the body of the propulsion pod,  21  designates a heat bridge for the coil winding heads  22  of the stator windings  24 . The stator windings  24  are located centrally in the actual pod body  23 , which is preferably made from the same material as the propeller  29 , i.e. from propeller bronze. The air gap  30  is located between the rotor winding  25  and the stator winding  24 . The rotor  25  is arranged on an inner tube  26 , which is in turn fastened to the shaft  27 . The fastening takes place by means of a coupling  31 . At the access shaft end, the pod housing  23  also has cooling chambers  28 , which can be used as the outlet for heat ducts into the access shaft. In this case, it is then possible to dispense with enlarging the surface by ribs or the like. The coupling, the shaft bearing system etc. are not part of the invention and are therefore not shown in any more detail. 
     In the hub, there is also a hollow space  33  which, if appropriate, is connected to the central part of the propulsion pod, which is subject to heat, by a large central bore  32  (shown by interrupted lines) in the shaft  27 . This permits good thermal utilization of the cool ends of the propulsion pod. 
     The invention&#39;s cooling elements in accordance with the invention permit a multiplicity of cooling combinations. The individual measures are selected to suit the area in which the ship is traveling and the size of the motor. A common feature is that they dispense with long coolant paths and coolant circulating units. This results in a substantial improvement even when compared with the prior art shown in U.S. Pat. No. 5,403,216 and U.S. Pat. No. 2,714,866. 
     Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the Scope of their contribution to the art.