Field of the disclosure

The disclosure relates generally to rotating electric machines. More particularly, the invention relates to an end-shield for an electric machine. Furthermore, the invention relates to an electric machine.

Background

In a rotating electric machine, such as an electric motor or a generator, a magnetic flux is developed between the electromagnetically active parts of the rotor and the stator of the electric machine. In a radial flux electric machine, the maximum torque is proportional to the product of the air-gap radius, the area of the air-gap surface, the magnetic flux density in the air-gap, and the linear current density in the air-gap surface of the stator. Hence, without increasing the mechanical size of the electric machine, the maximum torque can be increased by increasing the lin- ear current density because the magnetic flux density cannot be practically increased any more when the saturation point of iron has been exceeded. Increasing the linear current density increases, however, the resistive losses in the windings of the electric machine. Therefore, the cooling plays a significant role in the operation of the electric machine. Various cooling arrangements have been used and are used in conjunction with electric machines. One possible cooling arrangement of an electric machine comprises one or more cooling tubes connected to electromagnetically active parts of the electric machine so that cooling fluid is arranged to be in close vicinity of the electrical conductors of the windings and/or other parts of the electric machine where the heat is generated. The cooling fluid can be liquid such as for example water, or gas such as for example air or hydrogen. An inconvenience related to a cooling arrangement of the kind described above is that the manufacture and assembly of the cooling arrangement is more complex and expensive than manufacturing and assembling a cooling arrangement where there are no cooling tubes and where substantially all heat is removed through the end-windings and through the outer surfaces of the stator and the rotor including the air-gap surfaces.

Summary

The following presents a simplified summary in order to provide basic understand- ing of some aspects of various invention embodiments. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying embodiments of the inven- tion.

In accordance with the invention, there is provided a new end-shield for an electric machine. An end-shield according to the invention comprises:

- a bearing housing for mechanically supporting one or more bearings of the electric machine, - apertures for receiving ends of one or more cooling tubes connected to electromagnetically active parts of a stator of the electric machine,

- sealing structures for sealing outer surfaces of the ends of the one or more cooling tubes into the apertures, and

- an inlet pipe connection for receiving cooling fluid from an external system and an outlet pipe connection for purging the cooling fluid to the external system.

The end-shield is shaped to constitute a manifold for conducting the cooling fluid from the inlet pipe connection to flow through first one or more of the apertures and for conducting the cooling fluid flowed through second one or more of the ap- ertures to the outlet pipe connection. The cooling fluid can be liquid such as for example water, or gas such as for example air or hydrogen.

The above-described end-shield constitutes not only the mechanical support for the one or more bearings of the electric machine but also the manifold for connect- ing the cooling tubes of the electric machine to the external system for circulating the cooling fluid. Thus, there is no need for a separate manifold arrangement for connecting the cooling tubes of the electric machine to the external system for circulating the cooling fluid. In accordance with the invention, there is provided also a new electric machine. An electric machine according to the invention comprises:

- a stator comprising electromagnetically active parts and one or more cooling tubes,

- a rotor rotatably supported with respect to the stator with bearings, and - at least one end-shield according to the invention and arranged to mechanically support at least one of the bearings and connected to ends of the one or more cooling tubes.

An electric machine according to the invention may comprise an end-shield according to the invention at only one end of the electric machine or at both ends of the electric machine.

A number of exemplifying and non-limiting embodiments of the invention are described in accompanied dependent claims.

Various exemplifying and non-limiting embodiments of the invention both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying and non-limiting embodiments when read in connection with the accompanying drawings.

The verbs "to comprise" and "to include" are used in this document as open limitations that neither exclude nor require the existence of unrecited features. The fea- tures recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e. a singular form, throughout this document does not exclude a plurality. Brief description of the figures

Exemplifying and non-limiting embodiments of the invention and their advantages are explained in greater detail below in the sense of examples and with reference to the accompanying drawings, in which: figure 1 a shows a section view of a part of an electric machine comprising an end- shield according to an exemplifying and non-limiting embodiment of the invention, figure 1 b shows a view of a section taken along the line A-A shown in figure 1 a, figure 1 c shows a detail of the section view shown in figure 1 a, and figures 2a and 2b illustrate an end-shield according to another exemplifying and non-limiting embodiment of the invention.

Description of the exemplifying embodiments

The specific examples provided in the description given below should not be construed as limiting the scope and/or the applicability of the appended claims. Lists and groups of examples provided in the description given below are not exhaus- tive unless otherwise explicitly stated.

Figure 1 a shows a section view of a part of an electric machine comprising an end-shield 101 according to an exemplifying and non-limiting embodiment of the invention. The section plane is parallel with the yz-plane of a coordinate system 199. The electric machine comprises a stator 1 16 and a rotor 121 . The rotational axis of the rotor is parallel with the z-axis of the coordinate system 199. The electric machine can be for example an induction machine, a permanent magnet machine, or an electrically excited synchronous machine. The stator 1 16 of the electric machine comprises a core structure 1 19 made of, or at least comprising, ferromagnetic material. The core structure 1 19 comprises a yoke and stator teeth connected to the yoke. The core structure 1 19 may comprise a stack of ferromagnetic sheets that are electrically insulated from each other and stacked in the axial direction, i.e. in the z-direction of the coordinate system 199. The stator 1 16 comprises windings 120 whose coil sides are located in the stator slots between the stator teeth. The core structure 1 19 and the windings 120 represent electromag- netically active parts of the stator 1 16. In this exemplifying case, the stator 1 16 further comprises a frame 126 that constitutes an outer casing of the stator. The stator 1 16 further comprises cooling tubes for conducting cooling fluid that can be liq- uid such as for example water, or gas such as for example air or hydrogen. The cooling tubes are advantageously located in the stator slots and thus the cooling tubes can be among the electrical conductors of the stator windings. Therefore, the cooling fluid can be arranged to be in close vicinity of the electrical conductors where heat is generated. It is also possible that the electric machine comprises cooling tubes each of which is located in an axial channel extending axially through the yoke of the core structure 1 19. In figure 1 a, two of the cooling tubes are shown and denoted with reference numbers 1 17 and 1 18. The rotor 121 comprises an electromagnetically active part 127 and a shaft 123. The electromagneti- cally active part 127 may comprise for example a squirrel cage winding, an excita- tion winding, and/or permanent magnets.

The end-shield 101 comprises a bearing housing 102 for mechanically supporting bearings of the electric machine. In figure 1 a, one of the bearings is denoted with a reference number 122. The end-shield 101 comprises apertures for receiving ends of the above-mentioned cooling tubes of the stator 1 16. Figure 1 b shows a view of a section taken along the line A-A shown in figure 1 a. The section plane related to figure 1 b is parallel with the xy-plane of the coordinate system 199. In figure 1 b, the apertures are denoted with reference numbers 103a, 103b, 104a, and 104b. The end-shield 101 comprises sealing structures for sealing the outer surfaces of the ends of the cooling tubes into the apertures. In figure 1 b, the sealing structures are denoted with reference numbers 105a, 105b, 105c, and 105d. The sealing structures 105a and 105c are shown in figure 1 a too. The end-shield 101 comprises an inlet pipe connection 106 for receiving the cooling fluid from an external system and an outlet pipe connection 107 for purging the cooling fluid to the external system. As illustrated in figures 1 a and 1 b, the end-shield 101 is shaped to consti- tute a manifold for conducting the cooling fluid from the inlet pipe connection 106 to flow through the apertures 103a and 103b and for conducting the cooling fluid flowed through the apertures 104a and 104b to the outlet pipe connection 107. The end-shield 101 has a modular construction so that the end-shield comprises first and second sections 108 and 109 that the stacked axially on each other as illustrated in figure 1 a. The first section 108 comprises the above-mentioned apertures for the ends of the cooling tubes and the above-mentioned seal structures for sealing the outer surfaces of the ends of the cooling tubes into the apertures. The first and second sections 108 and 109 constitute the above-mentioned manifold when the first and second sections are stacked axially on each other. The end- shield comprises seals for sealing a joint between the first and second sections. In figure 1 a, one of the seals is denoted with a reference number 1 10. Each of the seals can be for example a rubber O-ring that is coaxial with the shaft 123 or otherwise surrounds the shaft 123. The modular construction that comprises the axially stacked first and second sections 108 and 109 makes it easier to arrange the sealing between the cooling tubes and the apertures of the end-shield because, when installing the end-shield, one has access to the sealing structures 105a- 105d.

In the exemplifying end-shield 101 illustrated in figures 1 a and 1 b, the first and second sections 108 and 109 comprise mutually aligned first holes for first bolts for fastening the end-shield 101 to the stator 1 16 of the electric machine so that the first bolts are through the first and second sections. One of the first bolts is denot- ed with a reference number 124 in figure 1 a, and one of the first holes is denoted with a reference number 1 1 1 in figure 1 b. The first section 108 comprises second holes for second bolts for fastening the first section to the stator 1 16 so that the heads of the second bolts are between the first and second sections. In figure 1 a, one of the second bolts is denoted with a reference number 125. The fastening ar- rangement of the kind described above makes it possible to first install the first section 108 on the stator 1 16, then install the sealing arrangements 105a-105d, and thereafter install the second section 109. As illustrated in figure 1 a, the first section 108 constitutes a part of the bearing housing 102 and the second section 109 constitutes another part of the bearing housing. Therefore, the rotor 121 can be mechanically supported during the installation also in a phase where only the first section 108 has been installed. It is also possible that an end-shield according to an embodiment of the invention has a non-modular, i.e. a single piece, con- struction and the sealing structures are such that the sealing is achieved when the ends of the cooling tubes are inserted in the apertures. It is, however, easier to arrange a reliable sealing when the end-shield has a modular construction of the kind illustrated in figure 1 a. Figure 1 c shows a section view of the sealing structure 105a. The aperture for receiving the end of the cooling tube 1 17 comprises a first portion 1 12 having a first diameter and second portion 1 13 having threads and a second diameter greater than the first diameter. The sealing structure 105a comprises a toroidal flexible seal element 1 14 that can be for example a rubber O-ring. The seal structure 105a comprises a tubular part 1 15 that surrounds the cooling tube 1 17 and has external threads suitable for the threads of the second portion of the aperture. The tubular part 1 15 can be tightened with the aid of the threads so that the toroidal flexible seal element 1 14 is axially pressed and thereby squeezed against the outer surface of the cooling tube 117 and against the wall of the aperture. In the exemplifying end-shield illustrated in figures 1 a and 1 b, the second section 109 comprises the inlet and outlet pipe connections 106 and 107. Figures 2a and 2b show section views which illustrate an end-shield according to another exemplifying and non-limiting embodiment of the invention. The section shown in figure 2a is taken along a line A-A shown in figure 2b and the section plane related to figure 2a is parallel with the xy-plane of a coordinate system 299. The section shown in figure 2b is taken along a line B-B shown in figure 2a and the section plane related to figure 2b is parallel with the yz-plane of the coordinate system 299. The section view shown in figure 2a corresponds to the section view shown in figure 1 b. The end-shield illustrated in figures 2a and 2b comprises axially stacked first and sec- ond sections 208 and 209 in the same way as the end-shield illustrated in figures 1 a and 1 b comprises the axially stacked first and second sections 108 and 109 but, in the end-shield illustrated in figures 2a and 2b, the first section 208 that comprises the apertures 203a, 203b, 204a, 204b for the cooling tubes comprises also the inlet and outlet pipe connections 206 and 207 for connecting to an exter- nal system for circulating cooling fluid. The specific examples provided in the description given above should not be construed as limiting the applicability and/or the interpretation of the appended claims. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated.