Stator cooling

The present invention relates to cooling of an electric motor driving a shaft in an arbitrary application, for example spindles for milling, grinding, drilling and so forth.

Many applications require both very efficient cooling of the stator of the electric motor and cost-effective and simple design, the requirements for the unit moreover being low weight and small volume. This is achieved in part by using an efficient and low-volume cooling method. This has been achieved by the invention having been provided with the feature indicated in Patent Claim 1.

The invention will be described in greater detail in the form of examples with reference to the drawing, in which Figure 1 shows diagrammatically an embodiment of the invention, Figure 2 shows another variation of the invention and Figure 3 shows a section along the line A-A in Figure 2.

In Figure 1 and Figure 2, Ia and Ib designate an essentially cylindrical housing, which has centrally the stator iron 3 of an electric motor connected to the housing Ia, and a shaft 4. The shaft 4, bearing the tool or the parts it is desired to rotate, can be mounted relative to the housing by any bearing method, for example fluid bearings, magnetic bearings, ball bearings or roller bearings.

In the drawing, 7 designates the rotor of an electric motor, which rotor is fastened to the shaft 4. The stator winding 2 of the electric motor is, together with its stator iron 3, received in a space 10 in the housing Ia, Ib. The parts 2,

3 of the electric motor, sealing sleeves 5 and the housing Ia, Ib are cooled by a coolant which is introduced through an inlet 11 (lateral side of the housing in Fig. 1; end wall side of the housing in Fig. 2), flows through the stator winding 2 and the stator iron 3 via channels 8 (winding slots) and leaves the space 10 through an outlet 12 (lateral side of the housing in Fig. 1 ; end wall side of the housing in Fig. 2). The space 10 is thus sealed completely in relation to the rotating parts, the rotor 7 and the shaft 4, with the aid of the cylindrical sealing sleeves 5 arranged between the stator winding 2 and the rotor 7 with the shaft 4, which on the one hand seal in relation to the stator iron, the winding slots 8 of which are sealed in the region 9 between the stator winding and the rotor, and on the other hand are sealed by O rings for example in relation to the housing Ia and Ib. The design of the cooling system as described contributes considerably to the compact design of the unit. 15 indicates diagrammatically electric cables and other connections to the stator of the rotor.

The active tool, which is fixed to the shaft 4, is not illustrated in the drawing, but it is to be understood that such a tool functions in a known manner.

As mentioned, the space 10 is flowed through by a coolant (inlet 11, outlet 12) which cools the stator iron, the stator winding and the housing Ia, Ib. In order to make cooling of the stator winding and the stator iron possible, these must be insulated against direct contact with the coolant because the coolant can be electrically conductive or corrosive. This can suitably be effected by means of a thin, heat-conducting film made of a material which is not electrically conductive and is not affected by the coolant. In order to make it possible to machine a close tolerance on the outside diameter of the stator without the stator iron being exposed, a machinable material 14 which tolerates the coolant has been applied firmly to the outside diameter of the stator iron before the

protective film is applied, whereupon the outside diameter of the stator can be machined exactly.

In Figure 3, 16 designates barriers which are arranged axially, extending from the inside of the housing end wall (on the right in Figure 3) to the stator iron 3

(its right end in the figure), and bring about reduced direct communication between the volumes at the inlet 11 and the outlet 12. This forces the bulk of the coolant to pass via the inlet 11 through the stator to its left side in the figure and back through the stator to the outlet 12. The purpose of this arrangement of the inlet and the outlet is that the coolant can be connected to the unit on only one side of the stator.