Patent Publication Number: US-2022224190-A1

Title: Fluid cooled electric machine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent application claims the benefit and priority of European Patent Application No. 21150939.3 filed on Jan. 11, 2021, the disclosure of which is incorporated by reference herein in its entirety as part of the present application. 
     BACKGROUND 
     The present disclosure relates to a fluid cooled electric machine, and a method for producing the same. More specifically, the present disclosure relates to a fluid cooled electric machine including a shaft extending along an axis of the machine, a rotor rotationally coupled to the shaft, a stator radially surrounding the rotor and having a stator core, first and second end shields mounted at axially opposite ends of the machine, and a cooling system, and to a method for producing the same. 
     Air cooled electric machines generally include a shaft extending along an axis of the machine, a rotor rotationally coupled to the shaft, a stator radially surrounding the rotor and having a stator core, first and second end shields mounted at axially opposite ends of the machine. Air cooled machines are generally less complex and less expensive to produce than fluid cooled machines. 
     In contrast, fluid cooled electric machines, which use a cooling fluid such as water, can more effectively remove heat from the machine, and thereby provide increased performance, such as higher output power, speed, torque, and durability, with a smaller layout than air cooled machines. 
     One type of fluid cooled electric machine is a water cooled electric motor which includes a single welded and rounded pipe wrapped around the stator core, through which water flows to cool the motor. However, such a design requires the production of a suitably shaped pipe, which gives rise to increased production steps and increased costs. 
     Fluid cooled electric machines which are based on existing designs of an air cooled electric machines, are also known. 
     One example of such a fluid cooled electric machine is a water cooled electric motor which includes specialized end shields having dedicated water chambers, and several pipes connected at their ends to the end shields, to form a path for the flow of water. However, this design has the disadvantage that specially engineered end shields are required, which are more complex than the end shields of an existing air cooled design. This design has the further drawback that it becomes necessary to use a special material, such as a cast iron material used for hydraulic applications, which does not leak fluid under pressure, to form the end shields, thus increasing costs. Accordingly, such an end-shield lacks modularity, because it is specific to water cooled motors and cannot be applied to air cooled motors. 
     BRIEF DESCRIPTION 
     In view of the above, embodiments of the present disclosure provide a fluid cooled electric machine according to claim  1  and a method of producing the same according to claim  14 . 
     According to an aspect of the present disclosure, a fluid cooled electric machine includes a shaft extending along an axis of the machine, a rotor rotationally coupled to the shaft, a stator radially surrounding the rotor and having a stator core, first and second end shields mounted at opposite ends of the machine in the axial direction, and a fluid cooling system for cooling the electric machine, the stator core having a plurality of axial cavities. The cooling system includes first and second collector bodies, each including a plurality of collector chambers for the fluid, and a plurality of pipes, wherein the first collector body is mounted, as a separate piece, between a first end of the stator core and the first end shield, the second collector body is mounted, as a separate piece, between a second end of the stator core and the second end shield, each pipe is mounted in the axial cavities of the stator core, and interconnects a collector chamber of the first collector body and a collector chamber of the second collector body. 
     According to a further aspect of the disclosure, the fluid cooled electric machine is produced by a method including the steps of mounting the pipes in the axial cavities of the stator core, mounting the first collector body to a first end of the stator core, and mounting the second collector body to a second end of the stator core, so that the pipes interconnect the connecting chambers of the first and the second collector bodies, and mounting the first end shield to the first collector body, and mounting the second end shield to the second collector. 
     The fluid cooled electric machine may reduce at least some of the drawbacks of the background art described above. In particular, the fluid cooled electric machine may be produced in a modular manner using a limited number of components. Particularly advantageously, the fluid cooled electric machine may be produced using common components with an air cooled electric machine, and/or can be retrofitted from an existing air cooled electric machine. In particular, the fluid cooled electric machine may be readily produced by adding simple components to an existing design of an air cooled electric machine. Thereby, a minimum of specialized components or specialized tools, and only simple production steps may be required. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter of the disclosure will be explained in more detail in the following text with reference to exemplary embodiments which are illustrated in the attached drawings. 
         FIG. 1  is a cross sectional view of components of a fluid cooled electric motor of an embodiment of the present disclosure, cut along the axis of the electric motor. 
         FIG. 2  is a cross sectional view of a stator core of an embodiment of the present disclosure, cut perpendicular to the axis. 
         FIG. 3  is an oblique view of components of an embodiment of the present disclosure. 
         FIG. 4  is a partially cut-out, oblique view of components of an embodiment of the present disclosure. 
         FIGS. 5A and 5B  is an oblique view of the cooling system of an embodiment of the present disclosure. 
         FIG. 6  is a partially cut-out, oblique view showing a portion of an embodiment of the present disclosure. 
         FIG. 7  is a cooling system according to an aspect of the present disclosure. 
         FIG. 8  is an exterior view of the electric motor of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of an electric machine  1  including a fluid cooling system  10  according to the present disclosure is described in the following with reference to the figures. 
     As shown in  FIG. 1 , the electric machine  1  of the present embodiment is a water-cooled motor, which is produced from an existing design of an air cooled motor, by adding simple components to the existing design, without requiring modification or replacement of the rotor, stator, or end shields of the existing design. Hence, the rotor, stator, and end shields of the present embodiment are the same ones used for the existing air-cooled motor. 
     An oblique view of the exterior of an electric motor is shown in  FIG. 8 . 
     The electric machine  1  of the present embodiment includes a shaft  3 , a rotor  4 , a stator core  5 , a drive-end end shield  6 , and a non-drive-end end shield  7 . The shaft  3  is supported by bearings in the end shields  6 , 7  and protrudes from an opening of the drive-end end shield  6 . 
       FIG. 2  is a cross sectional view of the  13  stator core  5  cut perpendicular to the axis of the machine. As shown in  FIG. 2 , the stator core  5  of the present embodiment has an inner opening which accommodates the shaft  3  (not shown) and rotor  4  (not shown), and projections which project towards the axis, and support the windings (not shown) of the stator. The outer periphery of the stator core  5  has the shape of a square with truncated corners. The stator core  5  includes through-holes  8  which extend parallel to the axis of the machine. These through-holes  8  are arranged in the vicinity of the truncated corners of the square cross section. In the present embodiment, there are three through-holes  8  provided near each corner. 
     In the water-cooled motor of the present embodiment, pipes  12 , which are part of the cooling system  10 , are provided in the through-holes  8 . These pipes  12  provide a fluid-sealed path for flow of the cooling water. In the present embodiment, pipes  12  are included in all three of the through-holes  8  near each corner. 
       FIG. 3  is an oblique view showing components of the present embodiment, including the stator core  5 , and collector bodies  13 , 14 .  FIG. 4  shows the same view as  FIG. 3 , but in  FIG. 4  part of the stator core  5  is cut away to reveal the pipes  12  inside the stator core. Also, in  FIG. 4 , parts of the pipes are cut away to reveal the through-holes  8 . 
       FIGS. 5A and 5B  are oblique views showing the cooling system  10  of the present embodiment.  FIG. 5A  shows the cooling system  10  with the collector body  13  closest to the viewer;  FIG. 5B  shows the cooling system  10  with the collector body  14  closest to the viewer. In  FIGS. 5A and 5B , the portions of the collector chambers  20  and fluid channels  21  are cut open to illustrate the fluid flow. Fluid is input under pressure into the fluid inlet  22  of the collector body  14 . The means for supplying pressurized cooling fluid to the fluid inlet  22  are provided by the user of the motor, and are not shown. The arrows illustrate the flow of fluid. As shown by the arrows, the cooling fluid flows into fluid inlet  22 , and sequentially flows through collector chambers  20 A,  20 B,  20 C . . .  20 H via the pipes  12  and fluid channels  21 , and out of the fluid outlet  23 . 
     More specifically, the cooling fluid flows through the fluid inlet  22  into the first collector chamber  20 A of the collector body  14 . From the first collector chamber  20 A, the fluid flows through pipes  12 , into a second collector chamber  20 B of the collector body  13 . From the collector chamber  20 B, the fluid flows through the fluid channel  21  into a third collector chamber  20 C of collector body  13 , and from there flows through the pipes  12  into a fourth collector chamber  20 D of collector body  14 . The fluid then continues to flow through other fluid channels, collector chambers, and pipes as illustrated by the arrows, until it reaches the fluid outlet  23 . Along this path, the cooling fluid absorbs heat from the stator core  5  (not shown). The warmer fluid emerging from the fluid outlet  23  can be cooled and recirculated to the fluid inlet  22  by a circulating system (not shown) provided by the user of the electric machine. 
     Thus, the cooling fluid flows axially from collector chamber  20 A of collector body  14  to collector chamber  20 B of collector body  13  in a first axial direction through pipes  12 . Then the cooling fluid flows through fluid channel  21  of collector body  13 , to collector chamber  20 C of collector body  13 . From collector chamber  20 C, the cooling fluid flows through pipes  12  to collector chamber  20 D of collector body  14 , in a second axial direction which is opposite to the first axial direction, as shown by the arrows in  FIGS. 5A and 5B . Then, the cooling fluid flows through fluid channel  21  to collector chamber  20 E, and then flows through pipes  12  to collector chamber  20 F of collector body  13 , in the first axial direction. Then, the cooling fluid flows through fluid channel  21  of collector body  13  to collector chamber  20 G of collector body  13 . Then, the cooling fluid flows from collector chamber  20 G to collector chamber  20 H of collector body  14  in the second axial direction. 
       FIG. 6  is an oblique view showing a portion of the collector body  13  and pipes  12 , with a cutout showing the collector chamber  20  and connecting hole  16  inside the collector body  13 . As shown in  FIG. 6 , the connecting hole  16  includes a groove  17  for accommodating the seal ring  18 . The seal ring  18  provides a fluid-sealed connection between the pipe  12  and the connecting hole  16 . As shown in  FIG. 6 , one side of the connecting hole  16  opens to the face of the collector body  13  to allow insertion of the pipes  12 , while the other side of the connecting hole  16  opens to the collector chamber  20 , thereby connecting the pipe  12  and the collector chamber  20  to allow the flow of fluid. 
     In the following, general aspects of the present disclosure are described in detail. The description uses reference signs found in the figures, but these reference signs are only used for illustration and the aspects are not limited to the embodiments shown in the figures. 
     According to an aspect of the present disclosure, the fluid cooled electric machine can be readily produced based on existing designs of air cooled electric machines. Such existing air-cooled electric machines generally include a shaft extending along an axis of the machine, a rotor rotationally coupled to the shaft, a stator radially surrounding the rotor and having a stator core, and first and second end shields mounted at axially opposite ends of the machine, and the electric machine of the present disclosure can utilize these components of an air-cooled electric machine without modification. 
     One example of such an electric machine of the present disclosure is an electric motor. Another example is a generator. 
     According to an aspect of the present disclosure, the shaft  3  of the fluid cooled electric machine  1  protrudes from the drive end of the electric machine, and rotates about an axis. In the present description, the axis of rotation of the shaft is referred to as the axis of the electric machine, and “axial” or “axially” generally refers to a line which is parallel to the axis of the electric machine. 
     According to an aspect of the present disclosure, the rotor  4  is rotationally coupled to the shaft, so that the shaft and rotor rotate as a unit. 
     According to an aspect of the present disclosure, the stator radially surrounds the rotor, and includes a stator core  5 . The stator core  5  includes cavities  8  extending axially. Such cavities are generally present in existing designs of air cooled machines, for air cooling. One example of such cavities are through-holes extending axially through the stator core  5 . Another example of such cavities are spaces such as axial channels formed between adjacent cooling fins. 
     According to an aspect of the present disclosure, pipes  12  are inserted into these cavities  8  for cooling the electric machine. Cooling fluid runs inside the pipes  12  to cool the electric machine. The pipes  12  are closely in contact with the cavities  8  of the stator core  5 , in order to transfer heat from metallic parts, such as lamination sheets of the stator core  5  and the pipes  12 , to the cooling fluid. Because the cavities  8  extend axially, it is possible to insert straight pipes. In this way, the present disclosure does not require cooling pipes having a complicated shape which wrap around the electric machine. 
     According to an aspect of the present disclosure, the shape of the cross section of the outer periphery of the stator core  5  is not particularly limited, and for example, may be may be round, square, or approximately square, such as a square with rounded corners, or truncated corners as shown in  FIG. 2 . In this case, the cavities may be arranged near the corners of the square, as shown in  FIG. 2 , in order to take advantage of the larger available cross-sectional space in this part of the stator. 
     According to an aspect of the present disclosure, the end shields  6 , 7  of the electric machine are provided at both axial ends of the electric machine. The end shields  6 , 7  provide a cover for the axial ends of the stator&#39;s inner space in which the rotor is provided, while leaving an opening for the shaft, at least at the drive-end end shield  6 , and also strengthen the structure the electrical machine. The drive-end end shield  6  is mounted to the drive end of the electric machine. The non-drive-end end shield  7  is mounted to the non-drive-end of the electric machine. 
     According to an aspect of the present disclosure, the end shields  6 , 7  generally include bearing seats which rotationally support the rotor. The end shields  6 , 7  may also have integrated feet, to support the electric machine, and/or a flange for fixing the electric machine to a base plate. 
     According to an aspect of the present disclosure, in the fluid cooled electric machine of the present disclosure, the rotor  4 , stator and stator core  5 , and end shields  6 , 7  are the same as the rotor, stator and stator core, and end shields used in an already existing design of an air cooled electric machine. In this way, the fluid cooled electric machine of the present disclosure requires a minimum of new components, and can be readily produced based on an existing design of an air cooled electric machine. 
     The fluid cooling system  10  includes pipes  12 , and first and second collector bodies  13 , 14  each including collector chambers  20  for the fluid. 
     According to an aspect of the present disclosure, the fluid cooling system  10  is a stand-alone system. This means that the first and second collector bodies  13 , 14  and pipes  12  are made of separate parts, separate from the other components of the electric machine, to provide a path for fluid flow. Because the fluid cooling system is a stand-alone system, it can be easily added to the components of an existing (e.g., air-cooled) electric machine, without specialized tools. 
     According to an aspect of the present disclosure, the pipes  12  of the cooling system have a size and shape which allows insertion into the axial cavities  8 , such as through-holes, of the stator core  5 . The pipes  12  may have sufficient length so that both ends of each pipe  12  protrude from the stator core  5  when the pipes  12  are positioned in the axial cavities (through-holes)  8 . 
     In an example aspect of the disclosure, the pipes  12  are cylindrical. This has the advantage that specially shaped pipes are not required. 
     According to an aspect of the present disclosure, the material for the pipes  12  is a mainly a material having suitable thermal conductivity. Examples of a suitable material are aluminum alloy, stainless steel or copper and copper nickel alloys. 
     The number of pipes  12  used for the fluid cooled electric machine is not particularly limited. For example, the fluid cooling system may include four pipes  12 . If the shape of the cross section of the outer periphery of the stator core  5  is square or approximately square, as shown in  FIG. 2 , one pipe  12  can be located near each corner of the square. However, to provide higher cooling capacity, two, three or more pipes  12  could be provided near each corner of the square. Alternatively, the pipe diameter can be increased to provide higher cooling capacity. The shape of the cross section of the outer periphery of the stator core  5  is not limited to a square or approximately square shape, and for example, a round shape may be employed. Other arrangements of the pipes  12  are also possible, such as an even distribution of the pipes around the periphery of the stator core. 
     The present disclosure includes two collector bodies  13 , 14 . One collector body  13  is mounted, as a separate piece, between one end of the stator core  5  and one end shield  6 . The other collector body  14  is mounted, as a separate piece, between the other end of the stator core  5  and the other end shield  7 . 
     Because the collector bodies  13 , 14  of the present disclosure are separate pieces from the end shields  6 , 7 , the cooling fluid does not have to flow through the end shields. Therefore, the end shields do not require dedicated chambers or holes for fluid flow. Also, the end shields do not have to be made of a special material such as cast iron for hydraulic applications. Instead, the end shields can be made of a material such as aluminum alloy, which is lighter, and easier to manufacture. As a result, the fluid cooled electric machine of the present disclosure can use the same end shields as existing designs of air cooled electric machines. 
     According to an aspect of the present disclosure, the material of the collector body is a material having suitable thermal conductivity. Examples of a suitable material are aluminum alloy or stainless steel. 
     The shape of the collector bodies  13 , 14  is not particularly limited, and may be selected in view of the shape of the stator core  5 , end shields  6 , 7 , and pipes  12 . For example, if the outer periphery of the stator core has an approximately square cross-sectional shape, the collector bodies may also have an outer periphery with a corresponding approximately square cross-sectional shape. However, other shapes such as a round or oval cross-sectional shape may also be selected. 
     Each collector body  13 , 14  includes collector chambers  20 . Each pipe  12  is mounted in an axial cavity  8  of the stator core  5 , and interconnects a collector chamber  20  of the first collector body  13  and a collector chamber  20  of the second collector body  14 . 
     In this way, a path can be formed for the cooling fluid to flow from one collector chamber  20  of one collector body  13 , 14 , though the pipe  12 , to the other collector chamber  20  of the other collector body  13 , 14 . 
     The number of collector chambers  20  is not particularly limited. For example, if the stator core  5  has an approximately square cross-sectional shape, and the pipes are arranged near the corners of the square, each collector body may have one collector chamber  20  near each corner of the square. In this case, each collector body will have a total of 4 collector chambers. 
     According to an aspect of the present disclosure, the first end  6  shield is mountable to the first end of the stator core  5 , and the second end shield  7  is mountable to the second end of the stator core  5 . In a previously existing design of an air cooled electric machine, which has no fluid cooling system, the end shields are mounted onto the ends of the stator core. In this aspect, the collector bodies  13 , 14  are configured to be mounted between the stator core and end shields of an existing air cooled design, so that each end shield is mountable to its respective collector body, or to its respective end of the stator core. 
     In this way, the fluid cooled electric machine of the present disclosure can use the same end shields and the same stator of an existing design of an air cooled electric machine, without modification. This allows a manufacturer of electric machines to flexibly offer both air cooled and fluid cooled electric machines, based on the same air cooled design, at low cost. 
     According to an aspect of the present disclosure, the first and second collector bodies  13 , 14  include connecting holes  16  which connect one end of a pipe  12  to the collector chamber  20  of the first collector body  13 , and the other end of the pipe  12  to the collector chamber  20  of the second collector body  14 . These connecting holes  16  allow for easy connection between the pipes  12  and the collector chambers  20 . 
     According to an aspect of the present disclosure, the pipes and collector bodies are connected in a fluid-sealed state. In the present application, “fluid-sealed” means that cooling fluid can be made to flow under pressure through the cooling system, without leaking to the outside of the cooling system. 
     According to an aspect of the present disclosure, each connecting hole  16  includes a seal ring  18 . The seal rings are one means of providing a fluid-sealed connection between the collector chambers  20  and the pipes  12 . A soft material of a seal ring  18  allows and ensures the proper self-alignment between the pipes  12 , at their outer diameter, and the connecting holes  16 . 
     According to an aspect of the present disclosure, the seal rings are disposed in an inner groove  17  of the connecting holes  16 . The grooves  17  hold the seal rings  18  in place. By providing the grooves  17  in the connecting holes  16 , instead of on the pipe  12 , it is possible to use pipes having a thinner wall. Thinner pipe walls allow for more efficient heat transfer and better cooling. 
     The material of the seal rings  18  is not particularly limited, provided that it can form a suitable seal between the connecting holes  16  and the pipes  12 . Examples of suitable materials are synthetic rubbers with good proprieties of compression and heat resistance. 
     According to an aspect of the present disclosure, the connecting holes  16  are connection openings extending from the collector chamber  20  to the stator-facing side of the respective collector body  13 , 14 , wherein the pipe  12  is inserted into the connection opening and is thereby connected to the collector chamber  20 . 
     The number of connecting holes  16  is not particularly limited. For example, there may be one, two, three or more connecting holes  16  provided for one collector chamber  20 . In this way, it is possible to connect more than one pipe  12  to each collector chamber  20 , which can provide increased flow of cooling fluid. 
     According to an aspect of the present disclosure, the first and second collector bodies  13 , 14  each include a fluid channel  21  which forms a fluid path interconnecting a pair of collector chambers  20  of the respective collector body  13 , 14 . The number of fluid channels  21  for each collector body  13 , 14  is not particularly limited, and may be appropriately set depending on the desired fluid flow path. Also, each collector body  13 , 14  may have a different number of fluid channels  21 . 
     According to an aspect of the present disclosure, at least one of the collector bodies  13 , 14  includes a fluid inlet  22  and a fluid outlet  23 . The fluid inlet  22  and the fluid outlet  23  may include a plug-in nipple. The fluid inlet  22  and fluid outlet  23  may be provided on either of the collector bodies  13 , 14 . 
     According to another aspect of the present disclosure, the fluid inlet  22  may be provided on one of the collector bodies  13 , 14 , and the fluid outlet  23  may be provided on the other of the collector bodies  13 , 14 . 
     According to an aspect of the present disclosure, the position of the fluid inlet  22  and the fluid outlet  23  can be changed by changing the orientation at which the collector body is mounted to the stator. For example, the fluid inlet  22  and the fluid outlet  23  can be positioned at the upper side of the electric machine, or at the lower side of the electric machine. Also, by reversing the collector bodies  13  and  14 , the fluid inlet  22  and the fluid outlet  23  can be positioned at the non-drive end or drive end of the electric machine. This allows a flexible positioning of fluid inlet  22  and a fluid outlet  23 , in accordance with pipes provided for cooling fluid at the user&#39;s location. 
     According to an aspect of the present disclosure, the cooling fluid is water. Other cooling fluids which can be used are coolant fluids for industrial applications. 
     According to an aspect of the present disclosure, the collector bodies  13 , 14  and pipes  12  form a closed fluid-sealed path extending from the fluid inlet  22 , through the collector bodies  13 , 14  and pipes  12 , to the fluid outlet  23 . The number and arrangement of pipes  12 , and collector chambers  20 , connecting holes  16 , fluid channels  21  and the like may be suitably set to provide a flow of cooling fluid as required to achieve acceptable cooling performance. 
     According to an aspect of the present disclosure, the fluid flows axially from a collector chamber  20  of one collector body  13 , 14 , to a collector chamber  20  of the other collector body  13 , 14 , through one or more pipes  12 . Because the pipes  12  are mounted in the axial cavities  8  of the stator core  5 , the fluid flowing through the pipes  12  can cool the stator core  5 . 
     According to an aspect of the present disclosure, the fluid flows from one collector chamber  20  of one collector body  13 , 14 , to another collector chamber  20  of the same collector body  13 , 14 , through a fluid channel  21 . In this way the fluid channel  21  can connect collector chambers  20  of the same collector body  13 , 14 . Such a flow of fluid within the collector bodies  13 , 14  can cool the ends of the stator core  5 , and also cool the end shields  6 , 7 . 
     According to an aspect of the present disclosure, the flow of cooling fluid follows a zigzag path from the fluid inlet  22  to the fluid outlet  23 . This means that the fluid flow in the pipe(s)  12  connected to one collector chamber  20  of one collector body  13 , 14 , will be in the opposite direction to the fluid flow in the pipe(s)  12  connected to adjacent collector chambers  20  of the same collector body  13 , 14 . 
     For example, the fluid may flow axially from a first collector chamber  20  of a first collector body  13  to second collector chamber  20  of a second collector body  14  in a first axial direction (for example, from a drive end to a non-drive end of the electric machine), through one or more pipe(s)  12  connecting the first and second collector chambers  20 . Then, the fluid flows from the second collector chamber  20 , through a fluid channel  21 , to a third collector chamber  20  of the same collector body  14 . Then, the fluid flows axially from the third collector chamber  20  of the second collector body  14  to a fourth collector chamber  20  of the first collector body  13  in a second axial direction (for example, from a non-drive end to a drive end of the machine) through pipe(s)  12  connecting the third and fourth collector chambers  20 . The fourth collector chamber  20  is adjacent to the first collector chamber  20  of the first collector body  13 , and the second axial direction of fluid flow in the pipes  12  connected to the fourth collector body  20 , is opposite to the first axial direction of fluid flow, through the pipes  12  connected to the adjacent first collector chamber  20 . 
     By such a flow of cooling fluid, it is possible to efficiently circulate fluid through a large portion of the stator core  5 , and efficiently cool the electric machine. 
     However, the fluid flow is not limited to the path described above, and the stand-alone cooling system  10  for cooling fluid flow can flexibly provide other options for cooling fluid flow. For example, as shown in  FIG. 7 , in another aspect, two collector bodies  13 , 13   a  can have the same arrangement of collector chambers  20  and fluid channels  21  as shown for the collector body  13  in  FIG. 5A . In this case, the fluid inlet  22  and fluid outlet  23  are positioned on the collector body  13   a . Then, by appropriately arranging the orientations of the collector bodies  13 , 13   a , it is possible to provide a flow of cooling fluid on the upper side of the electric machine, left and right, from non-drive end to drive end, and on the lower side of the electric machine, from drive end to non-drive end, left and right. 
     Namely, as shown by the arrows in  FIG. 7 , cooling fluid flows through the fluid inlet  22  at the upper side of the electric machine, into a first collector chamber  20 I. The cooling fluid will also flow from the collector chamber  20 I to the second collector chamber  20 J of collector body  13   a  via the fluid channel  21 . Collector chambers  20 I and  20 J are in the collector body  13   a  at the upper side of the electric machine. From collector chambers  20 I and  20 J, the cooling fluid flows, in the same direction, as shown by the arrows, to two respective collector chambers at the upper side of the collector body  13 , via pipes  12 . The fluid then flows via fluid channels  21  to two collector chambers at the lower side of the collector body  13 . Then, the fluid flows via pipes  12  into collector chambers  20 K and  20 L at the lower side of the collector body  13   a , and flows out of the fluid outlet  23  at the lower side of the collector body  13   a.    
     A method of producing a fluid cooled electric machine according to the present disclosure includes the steps of mounting the pipes  12  in the axial cavities  8  of the stator core  5 , mounting the first collector body  13  to a first end of the stator core  5 , and mounting the second collector body  14  to a second end of the stator core  5 , so that the pipes  12  interconnect the collector chambers  20  of the first and the second collector bodies  13 , 14 , and mounting the first end shield  6  to the first collector body  13 , and mounting the second end shield  7  to the second collector body  14 . In this manner, the cooling system can also be included in an existing (e.g., air-cooled) electric machine. 
     The present disclosure provides a fluid cooled electric machine which can be readily manufactured by adding simple components to an existing air cooled design, with a minimum of specialized components or specialized tools, and with simple production steps. 
     While the disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The disclosure is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art and practicing the claimed disclosure, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. Any reference signs in the claims should not be construed as limiting the scope.