Field of the Disclosure The present disclosure relates to stators for electrical machines such as motors and more particularly to the cooling of stators.

Background to the Disclosure Electrical machines have stators which are generally formed of laminated magnetically permeable material such as ferritic steel. The stator laminations are usually thin flat sheets which are stacked and form multiple teeth, which are wound with wire to form the stator poles. Heat is generated in electrical machines primarily by resistive losses in the wire windings and inductive losses in the stator laminations. The need to avoid overheating may limit the power rating of the machine.

Summary of the Disclosure

The present disclosure provides a stator assembly for receiving a rotor rotatable about a longitudinal axis of the stator assembly, the assembly including a stator core comprising: a peripheral portion extending around the longitudinal axis of the stator assembly; and teeth extending inwardly towards the axis from the peripheral portion, for receiving wire windings, wherein at least one channel is defined internally within the stator core for carrying coolant fluid.

Such an arrangement facilitates cooling of the stator in a compact manner as the coolant channel may be defined within the volume occupied by the stator core itself, that is, within the body of the stator core, as opposed to providing coolant paths around the outside of the stator core. Provision of the channel within the stator core also ensures that the coolant fluid passes in close proximity to (or in contact with) the stator core, facilitating the transfer of heat from the stator core to the coolant fluid. Increasing the effectiveness of the stator cooling allows higher current densities to be reliably used, resulting in a smaller electrical machine for a given performance.

Preferably, the stator core itself defines at least one wall or part of the channel. In further implementations, the whole of the wall of the channel within the stator core may be defined or formed by the stator core itself. Using the stator core itself to form part or all of each channel reduces the need for additional components to provide coolant pathways adjacent to the stator core.

The at least one channel may extend in the axial direction between one outer transverse face of the stator core and another, opposite transverse face of the stator core. These two transverse faces may be parallel or substantially parallel to each other.

The stator assembly may comprise at least one elongate fastening element, such as a bolt, which extends through a respective at least one channel, with a coolant path being defined between the fastener and the stator core through the channel.

The stator assembly may comprise a plurality of discrete channels for carrying coolant fluid which extend axially through its peripheral portion. The at least one channel may extend radially inwardly into a tooth of the stator core. For example, a channel having an elongate fastening element extending therethrough may extend radially inwardly within an adjacent tooth of the stator core.

A discrete channel which extends through a peripheral portion of the stator core may also extend radially inwardly from the peripheral portion within an adjacent tooth of the stator core. The peripheral portion of the stator core may extend entirely around the longitudinal axis of the stator assembly. The stator core may be divided through its peripheral portion between each pair of adjacent teeth to form stator segments. The at least one channel may be defined wholly within a single stator segment. The at least one channel may be defined by two or more adjoining stator segments.

The stator assembly may include a first structure adjacent to one transverse outer face for supplying coolant to the at least one channel. The first structure may define grooves in a surface facing the stator core for carrying coolant fluid.

The stator assembly may include a second structure for mounting in engagement with the other, opposing transverse face of the stator core which is configured to allow fluid to flow out of the at least one channel. The second structure may engage with this transverse face at (preferably four) circumferentially evenly spaced apart discrete regions of the peripheral portion of the stator core. A plurality of axially extending elongate fastening elements may extend through the second structure and the stator core.

In some implementations, the stator assembly may comprise at least two individual stators each having a stator core for receiving a respective rotor. The individual stator cores may be arranged with their longitudinal axes mutually parallel and laterally spaced apart. Each stator may be formed of stator segments. At least one segment may be a shared segment which forms part of at least two adjacent individual stators. The present disclosure further provides an electrical machine including a stator assembly as disclosed herein. More particularly, the present disclosure may provide an electromagnetic valve actuator including a stator assembly as described herein.

Brief Description of the Drawings

Figure 1 shows a perspective view of a stator core of a stator assembly according to an example of the present disclosure; Figure 2 is a rear perspective view of a stator assembly according to an example of the present disclosure which includes the stator core of Figure 1;

Figures 3 and 4 are perspective views of first and second structures of the assembly shown in Figure 2;

Figures 5 and 6 are front and rear perspective views of the stator assembly shown in Figure 2; and Figure 7 shows a perspective view of a stator core of a stator assembly according to another example of the present disclosure

Detailed Description of the Drawings Figure 1 shows an individual stator core 2. It is formed by eight stator segments 4, 6. Stator segments 6 are shared segments, which also form part of an adjacent individual stator. The other segments of the adjacent stator are not shown in the drawing. The stator 2 has a longitudinal axis 8, which passes through the centre of a cylindrical opening 10 defined by inner surfaces of the segments 4, 6. Eight stator teeth 18 extend radially inwardly from respective stator segments.

A plurality of axially extending channels 20, 22, 24 are defined internally within the stator core for carrying coolant fluid. Channels 20 are cylindrical and able to accommodate respective elongate fasteners 26 of the stator assembly.

Channels 22 are in the form of axially elongated slots formed in the peripheral portion of the stator core.

Channels 24 are in the form of axially elongated slots which are in fluid communication with cylindrical passages through the stator core similar to the channels 20. Each of the channels 20 and 22 is formed by a single respective stator segment. The channels 24 are formed by two adjacent shared stator segments. The channels 24 also serve to cool the adjacent individual stator of which the shared segments form a part.

Figure 7 shows an individual stator core T which is similar to that shown in Figure 1. The channels 20’ and 22’ defined by stator segments 4’ and 6’ have been modified so that they also extend radially inwardly, towards the central longitudinal axis 8, into an adjacent tooth 18’. The channels are in fluid communication with radially orientated passages 90 which are defined by seven of the teeth. The provision of a radially extending passage for receiving coolant within a stator tooth allows a coolant fluid to penetrate into the tooth and thereby enhance extraction of heat energy from the stator core. Each passage within a stator tooth may be closed at axially opposite ends by a lamination at each end which covers the passage where it would otherwise be exposed (and therefore allow coolant to escape) in the assembled stator.

Figure 2 shows a stator assembly including a stator core 2 of the form shown in Figure 1. A first support structure 30 is shown in engagement with a front transverse face 32 of the stator core. A second support structure 34 is shown in engagement with a rear transverse face 36 of the stator core. The front support structure 30 supplies coolant to the channels of the stator core as will be described in more detail below. The rear support structure 34 is configured so as to allow coolant fluid to flow out of the channels at the rear surface 36 of the stator core.

In the example shown in Figure 2, a PCB 40 is located adjacent to the rear face 36 of the stator core. An opening 42 is defined by the rear support structure 34 which facilitates access to the PCB and also allows coolant to flow out of an adjacent channel 22. As illustrated in Figure 3, the front support structure 30 defines a distribution channel, groove or gallery 50 in its face 52 which is brought into engagement with the front face 32 of the stator core in the assembled device. In the assembled device, the distribution channel is in fluid communication with the channels of the stator core. It therefore enables coolant fluid to be supplied to the channels. The front support structure could be integrally formed, by die casting, for example.

The rear support structure 34 of Figure 2 is shown in Figure 4. In addition to the opening 42 discussed above, it also defines further cut-outs 60, 62 which allow fluid to flow out of respective channels 22 of the stator core. It also includes fingers 64 which extend partway over respective channels 24 of the stator core in the assembled device. The rear support structure could be integrally formed, by die casting, for example. The rear support structure 34 defines four cylindrical openings 66 for receiving fasteners 26, 28.

When the stator assembly shown in Figure 2 is mounted on a supporting substrate (not shown) using fasteners 26, 28, the open ends of the cylindrical portions 66 at the rear face 68 (see Figure 2) of the second support structure are closed off by the supporting substrate. Accordingly, as shown in Figure 4, the rear support structure defines slots 70 in fluid communication with two of the cylindrical portions 66 to allow coolant fluid to flow out of the cylindrical portions. The fingers 64 together with the adjacent cylindrical portions 66 block off part of the channels 24 when the stator assembly is fastened to a supporting substrate. This forces coolant fluid flowing in the channels 24 to flow towards the inner ends of the slots before exiting the stator core.

Figure 5 shows a front perspective view of the stator assembly of Figure 2. The front support structure 30 is shown in ghost-form to show its distribution channel 50 which is highlighted with darker shading. The windings 80 of the stator assembly are visible in this view. Figure 6 shows a rear perspective view of the stator assembly of Figure 2. The PCB 40 is shown in ghost-form so that the windings and teeth of the stator are visible. A plurality of holes or slots 82 are formed in the PCB to allow coolant fluid to flow to the windings 80. It can be seen in Figure 6 how the fingers 64 expose part of each channel 24 to allow coolant fluid to flow away therefrom.