Patent Application
20240120781
The present application claims the benefit of U.K. Patent Application No. 2214729.2, filed Oct. 7, 2022, the disclosure of which is incorporated herein in its entirety for all purposes.
The present disclosure relates to a stator for an electrical machine, and in particular a stator which can facilitate cooling while maintaining ease of manufacture. The present disclosure has particular application with stators having an open slot design with concentrated windings. The stator may be, for example, the stator of a motor/generator for automotive applications.
Rotating electrical machines, such as motors and generators, comprise a rotor and a stator separated by an airgap. Typically, the stator comprises a stator core with a plurality of teeth extending radially inwards. The teeth define a plurality of slots for accommodating stator windings. The rotor is typically arranged to rotate inside the stator, with rotor poles facing the stator windings.
In known electrical machines, the stator windings may be either distributed or concentrated. In the case of distributed windings, each coil of the windings is distributed over two or more stator teeth. In the case of concentrated windings, each coil is wound on one tooth. Concentrated windings may provide various advantages in terms of ease of manufacture, as well as power/torque density and fault tolerance. For example, it may be possible to slide pre-formed coils onto the stator teeth rather than winding them in situ. However, this requires the stator to have an open slot design, with sufficient clearance between the teeth to allow the coils to be inserted.
Efforts have been made to operate electrical machines, particularly those for automotive applications, at increasing high speeds and electrical frequencies, in pursuit of weight and volume reduction. However, this may lead to increased AC losses in the stator windings. The AC losses are due amongst other things to phenomena known as the skin effect and the proximity effect. The AC losses may reduce the efficiency of the machine and create challenges in terms of heat dissipation, potentially leading to overheating of the machine.
It has been proposed to replace the conventional random wires in stator windings with flat rectangular conductors. The flat rectangular conductors have a cross section with a relatively high aspect ratio. This may help to reduce AC losses, by reducing the influence of the skin effect.
Electrical machines with an open-slot stator design using pre-formed coils of flat rectangular wire may therefore provide various advantages in terms of ease of manufacture and reduction in AC losses, as well as a high power/torque density and good fault tolerance. However, further improvements in heat dissipation would be desirable.
According to one aspect of the present disclosure there is provided a stator for an electrical machine, the stator comprising:
The present disclosure may provide the advantage that, by providing auxiliary teeth which extend radially inwards into a stator slot between the coils of two adjacent stator teeth, a heat transfer path can be provided from the windings, which may allow a better heat dissipation to be achieved, while maintaining ease of manufacture.
The auxiliary teeth in some examples are arranged to be in thermal contact with the coils. For example, the auxiliary teeth may be in direct contact with the coils, or may be in contact with the coils via a thermally conductive medium such as thermally conductive paper or a thermally conductive former. This may help to achieve a heat transfer path from the coils through the auxiliary teeth, for example, to the stator yoke.
The auxiliary teeth may have sides which run parallel to the sides of the coils. For example, the auxiliary teeth may have sides which run alongside (for example, in contact with or in close proximity to) the sides of the coils. This may help to maximise the area of contact between the coils and the auxiliary teeth, thereby helping to ensure a good transfer of heat between the coils and the auxiliary teeth.
The auxiliary teeth may have a width (in a circumferential direction) which decreases with increasing distance into the stator slot from the stator yoke. For example, the auxiliary teeth may have a triangular or trapezoidal shape in axial cross-section. In this case, the teeth may have a base at the point where they meet the stator yoke, and may narrow to an apex at a point inside the slot. This may help to ensure that the sides of the auxiliary teeth run parallel to the sides of the coils.
The auxiliary teeth may extend at least 20%, 30%, 40% or 50% into a stator slot in a radial direction (from the stator yoke to the slot opening). For example, in one embodiment, the auxiliary teeth may extend approximately 60% in a stator slot, although other values may be used instead. The auxiliary teeth may extend along at least 30%, 40%, 50% or 60% of a coil in a radial direction. For example, in one embodiment, the auxiliary teeth may extend along approximately 70% of a coil, although other values may be used instead.
In some examples, each auxiliary tooth substantially fills a (circumferential) gap between the coils of two adjacent teeth, for example over a distance extending at least part way into a stator slot. This may help to ensure a good transfer of heat between the coils and the auxiliary teeth.
In some examples, the stator slots have an open slot design. For example, the stator teeth may have a width at the slot opening which is substantially the same as the width of the teeth elsewhere. In some examples, each stator tooth has parallel sides.
This may allow the pre-formed coils of stator windings to be slid onto the stator teeth.
In some examples, the pre-formed coils form concentrated stator windings, such that each coil is wound on one tooth. This may provide advantages in terms of ease of manufacture, power/torque density, heat dissipation and/or fault tolerance.
In general, the pre-formed coils may comprise any suitable electrical conductor, such as electrical wire, which may have any appropriate cross-section, such as round or any other shape. However, in a preferred embodiment, the pre-formed coils comprise coils of rectangular wire, that is, wire having a rectangular cross-section. In this case, the wire may have a depth (in a radial direction relative to the axis of the machine) which is less than its width (in a circumferential direction). This may help to reduce skin effect losses for a wire with a given cross-sectional area. Furthermore, rectangular wires may facilitate assembly and may help with the slot fill factor.
In some examples, the wire is flat rectangular wire, that is, wire with a relatively high aspect ratio (ratio of width to depth). For example, the wire may have an aspect ratio of at least 1.4:1, 2:1, 3:1, 4:1 or 5:1, or any other appropriate ratio.
In some examples, each coil comprises a plurality of turns of rectangular wire. In one embodiment, each turn comprises a single width of rectangular wire. In this case, the thickness of the coil (from an inside surface to an outside surface) may be equivalent to the width of the rectangular wire. This may help to maximize the cross-sectional area of the wire, thereby helping to minimize current density, while at the same time helping to reduce skin effect losses. However, the preformed coils can allow each turn to comprise multiple rectangular wires. In this case, a plurality of strands of rectangular wire could be used in each turn.
In some examples, each of the coils comprises an input terminal and an output terminal. In this case, an output terminal on one coil may be connected to an input terminal on another coil using a connector. The connector may be, for example, a wire, a jump lead, or a strip of metal, or a connection ring, or any other suitable type of connector. This may facilitate connection of the coils in an appropriate winding configuration.
The stator yoke in some examples may be an annular yoke, and may be part of a stator core, which may also comprise the stator teeth and the auxiliary teeth.
The auxiliary teeth in some examples may be arranged to conduct heat from the coils to the stator yoke. In this case, the stator yoke may be arranged to dissipate heat. For example, the stator may comprise a cooling jacket arranged to cool the stator yoke. The cooling jacket may be provided around the outside of the stator yoke and may for example convey a liquid coolant in order to remove heat from the stator yoke. Alternatively, or in addition, the stator yoke itself may comprise cooling channels and/or cooling fins. Heat may also be conducted through the stator teeth to the stator yoke.
It has been found pursuant to the present disclosure that the auxiliary teeth themselves can be provided with cooling channels. Thus, in a preferred embodiment, at least some of the auxiliary teeth comprise cooling channels.
By providing cooling channels in the auxiliary teeth, it may be possible to locate the cooling channels in areas which are close to the coils, and which thus minimise the heat transfer paths, thereby helping with cooling. Furthermore, the cooling channels may be provided in areas which are not overlapped by the coils, thereby facilitating the transfer of coolant into and out of the cooling channels (for example using fluid conduits). In addition, by providing the cooling channels in the auxiliary teeth, it may be possible to locate the cooling channels in areas which are not substantially in the stator's magnetic flux paths (which typically are primarily through the stator yoke and the stator teeth where the coils are wound), thereby helping to minimize flux leakage. Thus, providing cooling channels in the auxiliary teeth may allow additional cooling to be achieved, without significantly impacting other parts of the stator.
This aspect of the disclosure may also be provided independently. Thus, according to another aspect of the disclosure, there is provided a stator for an electrical machine, the stator comprising:
The stator yoke, stator teeth, auxiliary teeth and/or stator windings may be in any of the forms described above.
The cooling channels in some examples may run axially through the auxiliary teeth. This may allow a coolant to flow through the stator from one side to the other, or from the middle of the stator core to the two sides. The cooling channels may be arranged to convey a liquid coolant, although other types of coolant could be used instead.
The stator may further comprise means for conveying coolant into and/or out of the cooling channels. For example, the stator may comprise a conduit for introducing coolant to the cooling channels and/or a conduit for receiving coolant from the cooling channels. Each conduit may comprise, for example, a pipe and a plurality of ports. In this case, the ports may be arranged to introduce coolant into and/or receive coolant from the cooling channels. The conduits may be connected to a cooling circuit for circulating coolant through the machine.
In another embodiment, the stator yoke may comprise a cooling passage for introducing coolant into the cooling channels. The cooling passage may be provided at the centre of the stator yoke axially, or elsewhere, and may run circumferentially around the outside of the stator yoke. The cooling passage in some examples may be in fluid communication with the cooling channels in the auxiliary teeth. This may provide a convenient and space efficient way of introducing coolant into the cooling channels. Furthermore, if the cooling passage is provided at the centre of the stator yoke axially, it may be possible to introduce the coolant into the stator yoke in an area where temperatures are likely to be the highest.
The cooling passage may be in the form of an annular trough in the outside of the stator yoke. For example, a group of laminations at the centre (axially) of the stator core may be provided, in which group the outside diameter of the stator yoke is less than that of the other laminations. Alternatively, a separate ring made from an electrically and/or magnetically non-conductive material could be provided at the centre of the stator core, between groups of laminations. In this case the ring may have an outside diameter which is less than that of the laminations, in order to form the cooling passage.
Coolant may be introduced into the cooling passage using a conduit such as a hose or pipe. Coolant flowing into the cooling channels from the cooling passage may flow axially through the stator core towards each end of the stator. Coolant exiting the cooling channels may flow through the interior of the stator and be collected in a sump. Alternatively, coolant exiting the cooling channels may be collected by a conduit such as a pipe and/or ports.
If desired, it would be possible for the stator to comprise a cooling jacket and/or cooling channels in the stator yoke. However, in some circumstances, it may be possible for sufficient cooling to be achieved using cooling channels in the auxiliary teeth. In this case, cooling may be achieved without the additional size and complexity of a cooling jacket or a stator yoke with cooling channels (or with a smaller sized cooling jacket and/or stator yoke). Thus, this arrangement may allow cooling to be achieved with a compact machine design.
In a preferred embodiment, the stator comprises a stator core formed from a plurality of stacked laminations. In this case, the auxiliary teeth may be formed from the same laminations as the stator yoke and/or the stator teeth. For example, the auxiliary teeth may be produced from the same sheet of raw material as the stator yoke and/or as part of the same stamping process. This may facilitate manufacture and may allow the auxiliary teeth to be formed from part of the raw material that would otherwise be scrap.
Where cooling channels are provided in the auxiliary teeth, these may also be produced as part of the same process. For example, the cooling channels may be stamped in the teeth as part of the process of stamping the laminations. This may allow the cooling channels to be formed without requiring a separate step of forming the cooling channels. However, it would also be possible for the cooling channels to be formed in the auxiliary teeth after the laminations have been stamped, for example by drilling or machining.
Alternatively or in addition it would be possible for at least some of the auxiliary teeth to be a separate component. For example, separate auxiliary teeth could be added to a stator slot after the stator core has been formed and/or after the stator coils have been inserted. The separate auxiliary teeth in some examples may be arranged to be in thermal contact with the stator yoke and the coils. The separate auxiliary teeth could be made from the same material as the stator core, or from a different material. For example, it would be possible for the separate auxiliary teeth to be made from a material with a high thermal conductivity, such as a ceramic material.
Where cooling channels are provided in the auxiliary teeth, the cooling channels may be provided with fins extending into the cooling channels. The fins may be formed as part of the process of stamping laminations, or they may be added later. The fins may help to improve the transfer of heat from the auxiliary teeth to a cooling fluid flowing through the cooling channels.
According to another aspect of the disclosure there is provided a rotating electrical machine comprising a rotor and a stator in any of the forms described above.
The machine may further comprise a cooling circuit for circulating coolant through the machine. For example, where the auxiliary teeth comprise cooling channels, the machine may further comprise a cooling circuit for circulating coolant through the cooling channels.
Corresponding methods may also be provided. Thus, according to another aspect of the disclosure there is provided a method of manufacturing a stator for an electrical machine, the method comprising:
The method may comprise forming cooling channels in the auxiliary teeth.
In some examples, the stator core is formed from a plurality of stacked laminations. The laminations may be stamped from a sheet of raw material. In this case, the auxiliary teeth may be produced as part of the same stamping process. Furthermore, where the auxiliary teeth comprise cooling channels, the cooling channels may be produced as part of the stamping process.
According to another aspect of the disclosure there is provided a stator for an electrical machine, the stator comprising:
This aspect of the disclosure may allow coolant can be conveyed around the stator and then introduced into the cooling channels in areas which are not overlapped by the stator windings. This may provide a convenient and space efficient way of introducing coolant into the cooling channels. Furthermore, if the cooling passage is provided at the centre of the stator yoke axially, it may be possible to introduce the coolant into the stator yoke in an area where temperatures are likely to be the highest. In addition, the cooling channels may be located in areas which are not substantially in the stator's magnetic flux paths, which may help to avoid any negative impact on the machine's electromagnetic performance.
The cooling passage in some examples may be in fluid communication with the cooling channels in the auxiliary teeth. The stator yoke, stator teeth, auxiliary teeth, stator windings and/or other parts of the stator or electrical machine may be in any of the forms described above.
The stator windings may comprise a plurality of pre-formed coils, and each coil may be arranged to be slid onto one of the stator teeth. Alternatively, coils may be wound on the stator teeth in situ. In either case, each auxiliary tooth may extend radially inwards from the stator yoke into a stator slot between the coils of two adjacent stator teeth.
In one embodiment, the conduit may comprise a pipe and a plurality of ports. For example, the pipe may be arranged to carry coolant circumferentially around the stator, and the ports may be arranged to carry coolant from the pipe into the cooling channels in the auxiliary teeth.
In another embodiment, the conduit may comprise a cooling passage in the stator yoke. In this case, the cooling passage may run circumferentially around the outside of the stator yoke. For example, the cooling passage may be an annular trough in the outside of the stator yoke.
In one embodiment, the cooling passage is located at or towards the centre, axially, of the stator yoke. For example, the cooling passage may be located at greater than 25%, 30%, 35%, 40% or 45% and/or less than 75%, 70%, 65%, 60% or 55% of the way through the stator yoke axially, although other values may be used instead. In general, the centre of the stator yoke is likely to experience the greatest rise in temperature. Thus, by providing the cooling passage at or towards the centre of the stator yoke, it may be possible to introduce coolant into an area of the stator yoke which is likely to experience the highest temperatures. This in turn may help to ensure effective cooling of the stator.
The stator may comprise a plurality of stacked stator laminations, in which case the cooling passage may be formed by providing a group of stator laminations with an outside diameter which is less than that of other stator laminations. Alternatively or in addition, the cooling passage may be formed by providing a ring of material between two groups of stator laminations, the ring of material having an outside diameter which is less than that of the laminations. The ring of material may comprise an electrically and magnetically non-conductive material. For example, in one embodiment the ring of material may be at least partially made from a thermoplastic polymer, such as a polyether ether ketone (PEEK) material, although any other suitable material or materials could be used instead.
The cooling passage may be arranged to carry coolant circumferentially around the stator yoke and the cooling channels may be arranged to carry coolant axially through the auxiliary teeth. For example, coolant may flow circumferentially around the stator yoke through the cooling passage, then radially inwards towards a cooling channel in an auxiliary tooth, then axially through the cooling channel. When in a cooling channel, the coolant may flow axially outwards in both directions (for example, from the centre of a cooling channel, axially outwards in both directions). The coolant may exit the cooling channel at both ends, axially, of the stator. Coolant exiting a cooling channel may be collected using for example a sump and/or a pipe and a plurality of ports.
According to another aspect of the disclosure there is provided a rotating electrical machine comprising a stator in any of the forms described above and a cooling circuit for circulating coolant through the cooling channels.
According to another aspect of the disclosure there is provided a method of manufacturing a stator for an electrical machine, the method comprising:
Features of one aspect of the disclosure may be provided with any other aspect. Apparatus features may be provided with method aspects and vice versa.
In the present disclosure, terms such as “radially”, “axially”, “tangentially” and “circumferentially” are generally defined with reference to the axis of rotation of the electrical machine, unless the context implies otherwise.
Preferred embodiments of the present disclosure will now be described, purely by way of example, with reference to the accompanying drawings, in which:
In operation, the rotor 10 rotates inside the stator 12 about a central axis of rotation. A magnetic flux developed by the permanent magnets 15 crosses the airgap and combines with the stator windings 22. In the case of motor operation, a varying electrical current is supplied to the stator windings 22 and the thus generated magnetic field causes the rotor to rotate. In the case of generator operation, the rotor is rotated by a prime mover and the rotating magnetic field developed by the permanent magnets 15 causes an electrical current to flow in the stator windings. The stator windings may be, for example, connected to a three-phase inverter. The rotor may be, for example, connected to a vehicle drivetrain. A cooling jacket (not shown) may be provided around the stator for circulating coolant in order to cool the machine.
Attempts have been made to operate electrical machines for automotive applications at higher speeds and higher electrical frequencies in order to achieve weight and volume reductions. However, this may lead to increased AC losses in the stator windings. The AC losses are at least partially caused by phenomena known as the skin effect and the proximity effect. The skin effect loss is associated with the non-uniform current distribution of the AC current flowing in the conductor, while the proximity effect loss is caused by the effect of the alternating field of other nearby conductors. Both loss components exist at the same time, and both affect the machine's efficiency and create localized high conductor temperature, especially at the slot opening area.
In order to reduce AC losses, it has been proposed to use flat rectangular wire to replace the traditional random windings with multiple stranded round wires. The flat rectangular wire has a cross section with a relatively high aspect ratio (ratio of width to depth), in order to reduce skin effect losses for a given cross-sectional area. The flat rectangular wire may be pre-formed into coils for insertion onto the stator teeth, in order to help with ease of manufacture. The flat rectangular wire may be, for example, as disclosed in the article “Application of Flat Rectangular Wire Concentrated Winding for AC loss Reduction in Electrical Machines”, Zhu et al, 2021 IEEE Energy Conversion Congress and Exposition, 10-14 Oct. 2021, Vancouver, Canada, the subject matter of which is incorporated herein by reference.
The coil 24 also comprises an input terminal 28 and an output terminal 29. In this example, the input terminal 28 is located at one side of the coil and the output terminal 29 is located at the other side, circumferentially. The input terminal 28 extends in an axial direction (parallel to the axis of the machine) at the radially outwards end of the coil, while the output terminal 29 extends in an axial direction at the radially inwards end of the coil. if desired, it would also be possible for either or both of the input terminal and the output terminal to be bent forwards or backwards before extending axially outwards, to facilitate interconnectivity.
The coil 24 is pre-formed for insertion onto a stator tooth. If desired, the coil 24 may be provided on a bobbin or a former which is also slid onto the tooth. Alternatively, the coil 24 may be slid directly onto the tooth, or a barrier such as electrically insulating paper may be provided between the tooth and the coil.
In the arrangement of
In conventional machines, gaps between the coils are filled with a potting compound such as epoxy. However, in embodiments of the disclosure, the gap 32 is used to help dissipate heat from the coils.
In the embodiment of
In the arrangement of
Each auxiliary tooth 34 is arranged to be in thermal contact with the coils 24 on either side of the tooth 34. For example, the auxiliary tooth 34 may be in physical contact with the coils 24, or in close proximity to the coils. If desired, a thermally conducting material, such as a thermally conducting (and electrically insulating) sheet or former, may be provided between the auxiliary teeth 34 and the coils 24. As a consequence, heat produced by the coils 24 is conducted by the auxiliary teeth 34 to the stator yoke 18. Heat may be removed from the stator yoke 18 by a cooling jacket and/or other heat dissipating means such as cooling channels through the stator yoke and/or cooling fins.
In the arrangement of
In the arrangement of
In the assembled stator, the coils 24 are connected in an appropriate winding arrangement, such as a star or delta winding arrangement. The coils may be connected using, for example, a connection ring or wires or jump leads. In general, any appropriate winding arrangement may be used. For example, if desired, the winding arrangement described in co-pending United Kingdom patent application number 2207742.4, the subject matter of which is incorporated herein by reference, could be used, although other arrangements could be used instead.
The arrangement of
In the arrangement of
In an alternative arrangement, rather than providing a separate cooling jacket, cooling channels could be provided in the stator core itself. For example, a plurality of cooling channels could be provided in a radially outwards part of the stator yoke. In this case, the location and spacing of the cooling channels is chosen to minimize any impact on the magnetic properties of the stator core. For example, the size of the stator yoke may be increased to accommodate the cooling channels without increasing flux leakage. If desired, other heat dissipation means such as cooling fins could be used instead or as well.
In the arrangement of
As can be seen from
If desired, a separate cooling jacket could be provided around the stator yoke, in a similar way to that shown in
In the arrangement of
In operation, a coolant is pumped into the pipe 42 and circulates through the pipe to the inlet ports 44. The coolant passes through the inlet ports 44 and into the cooling channels 40. Coolant which has passed through the cooling channels 40 is collected by the outlet ports 48, and fed to the pipe 46. The pipe 46 collects the coolant from the ports 48 and feeds it back to the cooling circuit.
In operation, coolant from the sump 50 is pumped by the pump 52 through the filter 54 to the heat exchanger 56. The filter 54 is used to filter particles from the coolant. The heat exchanger 56 is used to remove heat from the coolant. The coolant is then introduced into the pipe 42 via hose 58. The pipe 42 distributes coolant around the stator and into the inlet ports 44 (see
In this embodiment the coolant is a heat transfer fluid in the liquid phase. If desired, the coolant may be a lubricating coolant such as engine oil (i.e., oils which are used for lubrication of internal combustion engines) or any other lubricating oil. Alternatively, in some circumstances, a water-based coolant may be used instead. For example, an organic chemical such as glycol (e.g., ethylene glycol, diethylene glycol, or propylene glycol) in water, or any other type of coolant, could be used. In general, any suitable coolant in the liquid and/or gaseous phase could be used.
In this embodiment, the pump 52 is an external pump which is driven electrically by a separate motor. The speed of the pump 52 is controlled by the control unit 62 to ensure that an appropriate amount of coolant is injected into the cooling channels. The control unit 62 may receive inputs from various sensors 64, such as sensors which monitor the speed, load and/or temperature of the electrical machine and/or the level of coolant in the sump 50 or the flow of coolant, and may control the speed of the pump 52 in dependence thereon.
In alternative embodiments, it would be possible for the pump to be driven mechanically, for example by the electrical machine itself. It would also be possible for the sump, pump and/or filter to be located internally within the machine enclosure. Furthermore, if desired, the sump, filter and/or heat exchanger could be dispensed with or replaced with other components.
If desired, the pipes 42, 46 and ports 44, 48 shown in
In an alternative arrangement, rather than using pipes and ports to feed coolant to and from the cooling channels in the auxiliary teeth, other types of conduit could be used as instead or as well. For example, an annular cap could be provided on each side of the stator core to take coolant to and from the cooling channels. Alternatively, a flooded stator arrangement could be used in which the stator housing was used to contain the coolant. If desired, coolant exiting the cooling channels could be collected by a sump at the bottom of the housing.
Where cooling channels are provided in the auxiliary teeth, these may also be produced as part of the stamping process. However, it would also be possible for the cooling channels to be formed in the auxiliary teeth after the laminations have been stamped.
In step 102, the laminations are stacked together to form the stator core. Once stacked, the laminations may be held together using a suitable stacking method, such as welding, interlocking, bonding, clamping, riveting, or any other appropriate technique.
In step 104, the stator coils are formed. In one embodiment, each coil is formed by winding a flat rectangular wire into a coil, with each turn of the coil comprising a single width of the wire. The coils may be for example as described above with reference to
In step 106, the coils are inserted onto the stator teeth. This is achieved by sliding the pre-formed coils radially onto the teeth. If the coils are on formers, then the formers may be slid onto the teeth together with the coils. Alternatively, the coils may be slid directly onto the teeth, or a barrier such as a former or electrically insulating paper may be inserted on the teeth prior to inserting the coils.
Where the auxiliary teeth have cooling channels, then in step 108 suitable conduits are provided to feed coolant into and out of the cooling channels. For example, the pipes 42, 46 and ports 44, 48 described above with reference to
In step 110, the coils are connected in an appropriate winding arrangement. In one embodiment, this is achieved using a connection ring. The connection ring is positioned adjacent to the stator yoke in an axial direction. The connection ring has a body which is moulded from an electrically non-conductive material such as a plastic resin. Inside the body are three electrically conductive rings. Each of the conductive rings provides one of the three phases of the electrical machine. The terminals of the coils are then connected to the appropriate conductive ring, in order to achieve the desired winding arrangement. The conductive rings are connected to terminals in a terminal block. The terminal block provides the electrical connections for the stator (which may be high voltage or low voltage).
If desired, one of the pipes 42, 46 show in
Alternatively, rather than using a connection ring, it would also be possible to connect the coils using any other appropriate electrical connectors such as wires or jump leads.
In step 112, the stator is impregnated. For example, the stator may be impregnated with a suitable potting compound such as epoxy resin. This helps to ensure the stability of the assembled stator. Furthermore, the potting compound may help to ensure that there are no leaks in the coolant flow paths, for example, between the ports and the cooling channels.
If desired, the steps shown in
In the arrangement of
In the arrangement of
The cooling passage 70 of
In practice, laminations with the shape shown in
The solid ring 74 shown in
In operation, coolant is introduced into the cooling passage 70 through the port 86. Coolant then flows circumferentially around the stator yoke through the cooling passage 70. When the coolant encounters a cooling channel 40 in an auxiliary tooth 34, some of the coolant flows axially inwards into the cooling channel 40. Coolant in the cooling channel 40 then flows from the centre of the cooling channel, axially outwards in both directions. The coolant exits the cooling channels at both ends, axially, of the stator. Coolant exiting the cooling channels is collected in a sump and re-introduced into the cooling circuit. Alternatively, a pipe and a plurality of ports could be used to collect the coolant, in a similar way to that shown in
In operation, coolant is introduced into the pipe 88 through the port 90. Coolant then flows circumferentially around the stator yoke through the pipe 88. When the coolant encounters a cooling channel 40 in an auxiliary tooth 34, some of the coolant flows radially inwards into the cooling channel 40. Coolant in the cooling channel 40 then flows from the centre of the cooling channel, axially outwards in both directions. The coolant exits the cooling channels at both ends, axially, of the stator, and may be collected using for example a sump or a pipe and a plurality of ports.
It will therefore be appreciated that embodiments of the disclosure provide a stator core integrated in-slot cooling design for electrical machines with concentrated windings. The stator has small auxiliary teeth in the middle of the slots. Cooling channels may be provided in the auxiliary teeth. Typically, most of heat is generated in the windings and the stator teeth. With a shorter heat transfer path from the windings to cooling channels, a better heat dissipation capability can be achieved, which in turn can improve the torque/power density of the machine. This is particularly suitable for electric machines with flat rectangular wire concentrated windings where the middle of slot is normally left empty, and thus the proposed design need not sacrifice the slot fill factor.
While the above embodiments relate to a rotating electrical machine, the same concepts could be applied to a linear machine. A linear machine may be achieved for example by splitting the stator along radial direction and unfolding it along the circumferential direction.
Embodiments of the disclosure have been described above by way of example only, and variations in detail are possible. For example, rather than using a single coil on each stator tooth, a plurality of coils could be provided on each tooth. Rather than using coils with a single wire, each coil could comprise a plurality of wires (for example, a plurality of flat rectangular wires). Rather than using coils with a uniform thickness, the coils may have a variable thickness. Rather than using teeth with parallel sides, it would be possible for the teeth to be tapered. In this case, the internal diameter of the coils may have a corresponding taper. The stator may have any appropriate number of stator teeth and auxiliary teeth, and may have any appropriate number of poles and phases. Various other modifications will be apparent to the skilled person within the scope of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2214729.2 | Oct 2022 | GB | national |
