The first circumferential flow channel 46 is closed to flow at a first circumferential location (in the example shown, at a plurality of first circumferential locations) and the second circumferential flow channel 48 is closed to flow at a second circumferential location (in the example shown, at a plurality of second circumferential locations). Each second circumferential location is circumferentially spaced or removed from each first circumferential location so as to form a plurality of first sets of passages connected in parallel and a plurality of second, separate sets of passages connected in parallel, each first set of passages being circumferentially adjacent to a second set of passages. It will be understood that each first set of passages will extend between a first circumferential location and a second circumferential location. Each second set of passages will extend between a second circumferential location and a first circumferential location. Thus, when fluid or coolant flows into the first circumferential flow channel 46, the fluid will flow along the first circumferential flow channel 46 to a first circumferential location at which the first circumferential flow channel 46 is closed to flow. The fluid will therefore flow through each passage of a first set of passages from the first circumferential flow channel to the second circumferential flow channel. The fluid will then flow along the second circumferential flow channel to a second circumferential location at which the second circumferential flow channel 48 is closed to flow and the fluid will flow through each passage of the second set of passages, from the second circumferential flow channel 48 to the first circumferential flow channel 46.

A possible example flow arrangement according to the disclosure is shown in FIG. 5. As seen, fluid or coolant may flow into the first circumferential flow channel 46 through an inlet I (corresponding to an inlet aperture in the first radial wall 30 for example). In the example of FIG. 5, the first circumferential flow channel 46 is closed to flow at a first circumferential location located between the third 50c and fourth 50d cooling passages in the direction of circumferential flow from the inlet. Thus, a first set S1 of 3 passages connected in parallel is formed such that fluid will therefore flow through each of the three passages (50a-50c) of the first set of three passages S1 in a first axial direction D1 from the first circumferential flow channel (not seen in FIG. 5) to the second circumferential flow channel (not seen in FIG. 5).

As seen in FIG. 5, the second circumferential flow channel 48 is closed to flow at a second circumferential location located between the sixth 50f and seventh 50g passages in the direction of circumferential flow from the inlet I. Thus, a second set S2 of three passages connected in parallel is formed adjacent to the first set of passages S1 such that fluid will therefore flow through each of the three passages 50d-50f (the fourth, fifth and sixth passages shown) of the second set of three passages S2 from the second circumferential flow channel (not seen in FIG. 5) to the first circumferential flow channel (not seen in FIG. 5) in a second axial direction D2.

In the example of FIG. 5, the pattern repeats itself such that sets of three passages 50 are provided for parallel flow of fluid in alternating directions. This is achieved by closing the first circumferential flow channel 46 to flow at a number of first circumferential locations located between the third and fourth passages, the ninth and tenth passages and so on in the direction of circumferential flow from the inlet. The second circumferential flow channel 48 is also closed to flow at a number of second circumferential locations located between the sixth and seventh passages, the twelfth and thirteenth passages and so on in the direction of circumferential flow from the inlet I. In the example of FIG. 5, the stator is configured to include three first sets S1 of passages for flow in the first axial direction D1 which alternate with two second sets S2 of passages for flow in the second axial direction D2. An outlet O for fluid to flow out of the second circumferential flow channel 48 can be provided adjacent the final passage 50 final of the third first set S1 of passages comprising the thirteenth, fourteenth and fifteenth passages.

It will be appreciated that the arrangement shown in FIG. 5 is only one possible configuration and that the number of passages in each of the first and second sets of passages can be varied as required. Thus, each set of passages could include any number of passages from two to a much higher number such as for example, ten. Further, each set of passages could contain a different number of passages from the other sets if required.

In some examples of the disclosure, the first and second circumferential flow channels 46, 48 may be closed to flow by permanent structures which are put into place when the stator 2 is manufactured and which cannot subsequently be moved or altered. In one such example, the housing 22 may be formed to include structure such as walls which act to close the first and second circumferential flow channels 46, 48 to flow at the relevant circumferential locations.

In other examples of the disclosure, the first and second circumferential flow channels 46, 48 may be closed to flow by inserts which can be used to close the first and second circumferential flow channels 46, 48 to flow at any desired circumferential location and which may be removed or moved to different circumferential locations so as to change the flow pattern of coolant within the stator as desired.

An insert 60 is shown in situ in the first circumferential flow channel 46 in FIGS. 3 and 4. The insert 60 comprises a sheet made of a non-electrically conductive material such as a ceramic. The ceramic material will act to absorb heat from the winding 8, thus improving the cooling of the winding 8. However, in other examples, the insert 60 could be made of plastic. The sheet is sufficiently rigid to maintain its shape in use and is shaped to provide a fluid-tight fit or a close fit when inserted between the first radial wall 30 of the housing 22 and the core 4. The insert 60, as shown in FIG. 8, further comprises a cut-out portion 62 configured to extend around and over the winding 8. In some examples, the insert 60 could be configured to extend to the annular base 24 of the housing 22. In the example of FIG. 3 however, a protrusion 64 is formed on the annular base 24 of the housing 22 extending radially outwardly therefrom and the insert 60 is configured to extend to and engage with the protrusion 64.

In some examples, the protrusion 64 may be a part of the housing, for example having been formed by being machined into the housing. In other examples, the protrusion