An electric machine has a stator and a rotor and a so-called air gap between them.

Solid rotors, which are usually manufactured of one piece, are commonly used in motors in which rotation speeds are substantially higher than the ones in conventional motors, typically over 6,000 rpm, but the rotation speed may be as high as 200,000 rpm and even more. In these high-speed drives, a solid rotor is used because of its mechanical strength. Compared to a squirrel-cage rotor, the solid rotor increases, however, the resistance of the rotor and thus increases the slip of the rotor. In addition, compared to a so-called squirrel-cage short-circuited rotor, the solid rotor decreases significantly the displacement factor of an inductor machine which factor ordinarily varies between 0.6-0. 7 in the case the solid rotor.

In known solid-rotor electric motors based on the induction principle, the solid rotor of the motor is often slotted with axial slots in order to increase efficiency, torque production capacity and power ratio. An example of a solid rotor is described in patent specification F192114. This specification describes a solid rotor of an induction-based electric motor in which the rotor is slotted.

The slotting of a solid rotor may often-depending on peripheral speed-be useful from the viewpoint of cooling of the rotor, as the slotting of the rotor increases the cooling area, and thus the cooling of an air-cooled machine working in ambient pressure is enhanced because of slotting. However, the use of solid rotors does not limit only to items in which the air-gap pressure corresponds the ambient pressure.

The solid rotors may be used in items in which the air-gap pressure may be considerably higher than the ambient pressure, and the air-gap pressure may be, for example, as high as 8 MPa. In such applications of the solid rotor, the friction characteristics of the rotor become a relatively important factor. The flow of fluid filling the air gap causes friction in the air gap of the electric machine. Especially high friction is caused if the flow in the air gap is turbulent. The friction may grow, depending on the characteristics of the fluid in the air gap, detrimentally high because of the slotting of the rotor. Detrimentally high friction may occur in the case of the slotted solid rotor also when the peripheral speed of the rotor is sufficiently high, or if there is high-viscosity fluid in the machine air gap, even though the machine works in the atmospheric pressure. In order to decrease the friction of the air gap, the surface of the rotor should be smooth.

One has not been able to solve the problems involving solid-rotor machines in question in known solutions with a satisfactory and economically sensible manner.

An object of this invention is to eliminate the disadvantages of known prior art and to achieve such a solution which maximises the electric characteristics and minimises the friction of the solid rotor, and because of these, the efficiency of the motor rises to a good level. In addition, an object of the invention is to achieve such a rotor the resistance of which is sufficiently low, and which rotor has no significant overheating problems caused by friction. A further object is to accomplish good strength characteristics for the rotor. Slotting the rotor surface weakens the rotor mechanically. Closing the surface of the rotor with a mechanically strong method reinforces the rotor mechanically almost or even totally to the level of an unslotted rotor.

The rotor according to the invention should also be suited for a wide rotation speed range, and one should be able to manufacture it in an economically competitive manner.

A manner to achieve this with a rotor according to the invention is closing the slot holes opening to the outer periphery of the slotted solid rotor completely or partially with a blocking member, such as a wedge, and where the wedge is welded to the basic material of the rotor.

Another advantageous embodiment of the invention is closing the wedge slot or slots completely or partially with a collar fastened partly upon the rotor, which collar closes the holes of the rotor slots opening to the air gap. The collar is manufactured from a suitable material, based on its strength-theoretical and electrotechnical characteristics.

To be precise, the slotted rotor according to the invention is characterised by what is said in the accompanying claims.

With a rotor according to the invention and by closing its slotting, one achieves good electric characteristics and advantageous friction characteristics of the rotor, in which case also the efficiency of the whole electric machine (electric motor) is increased significantly, to a good level. In addition, one achieves with the invention such a rotor in which the resistance of the rotor is on a sufficiently low level and overheating

problems caused by friction do not become a significant factor in the operation of the rotor.

Next, the invention is described in more detail by referring to the accompanying drawings 1-3.

Figure 1 is a perspective view of an electric-machine rotor according to the invention.

Figure 2 describes a detail of the electric-machine rotor as an end view of the rotor.

Figure 3 describes an alternative solution of an electric-machine rotor according to the invention as an end view of the rotor.

Figure 1 describes a solid rotor according to the invention. A collar 2 is fitted upon the rotor 1 which collar covers the rotor 1 completely or a part of it. The rotor is slotted with axial slots 3 formed in the rotor part 1. According to the inventive idea, the collar 2 covers the slot holes opening to the air gap completely or a part of them, and the collar is fastened by welding or with a tight adapter to the rotor part 1.

In the detail of figure 2, which is an end view of the rotor, the collar 2 is fastened by welding it to the rotor part 1, in which case the collar covers the slot 3.

Electrotechnically suitable, advantageous materials of the collar 2 are, for example, rustproof ferritic materials (and in some cases, acid-proof or so-called Dublex steels) which have high resistivity and reasonably high saturation current density, because these materials have a positive effect to decreasing eddy current losses from the rotor surface. The collar 2 should, in certain cases and/or applications, be of corrosion-resistant material. The collar material may also be rotor-temperature- enduring plastics or composite materials, such as carbon fibre.

The collar 2 which is fastened upon the rotor 1 may be manufactured from a sheet, and it can be rolled upon the rotor 1, the fastening to each rotor teeth being performed with a suitable welding method, such as seam or projection welding, electric-arc welding or some other welding method. By leaving the rotor slots 3 partially uncovered from their ends when collaring the rotor, that is, the collaring does not cover the whole length of the rotor part (axially), and by leaving then an exit opening to the middle of the collar, the rotor may also operate as a fan, that is, the rotor slots 3 and thus especially the uncovered points of the slots then form a cooling fan of the electric machine.

Figure 3 describes another rotor according to the invention seen as an end view of the rotor. According to the inventive idea, the rotor slot 3 is closed with a wedge 4 from the hole opening to the outer periphery of the slots, and the wedge is placed to a wedge slot 6 which is formed either by routing or other rnachining method to the rotor part 1. The depth of the wedge slot 3 may be greater than the thickness of the wedge, in which case the wedge lies somewhat deeper in the slot in the longitudinal direction of the slot, and the upper part of the wedge is not thus in the same level with the outer periphery of the rotor 1. The width of the wedge slot is chosen advantageous from the viewpoint of manufacturing, the wedge slot being little wider than the other part of the wedge slot, and widening of the wedge slot facilitating manufacture. However, a wedge slot wider than the other slot is not essential.

The wedge 4 is fastened to the rotor part 1 with a suitable welding method. The wedge 4 may be made of the same or different material as the rotor part 1.

Mechanically, the wedge is most advantageously of the same material as the rotor part 1, and electrotechnically, the most advantageous solution is the use of low- conducting, non-magnetic stainless steel.

The welding methods for fastening the wedge may be electric-arc welding, laser welding, electron beam welding, seam or projection welding or some other most advantageously applicable welding method. The strength of the welded joint should be such that the joint endures forces caused by high rotation speed.

From the viewpoint of mechanical characteristics, the material of the wedge 4 is most advantageously the same material as the frame material of the rotor 1. When choosing the material of the wedge 4 as the same as the frame material of the rotor 1, the amount of stresses is as small as possible. The width of the wedge 4 is chosen as such that its width is sufficient from the viewpoint of manufacturing. The wedge slot 3 is done by routing or other machining method, and the upper part of the wedge slot, into which the wedge is fitted, is most advantageously wider than the other part of the slot 3. From the viewpoint of electromagnetism, the material of the wedge 4 may, in some cases, differ from the basic material of the rotor.

It is well known by those skilled in the art that the different embodiments of the invention are not solely limited to the examples described above, and thus they may vary within the scope of the appended patent claims.