Technical Field The invention relates to a homopolar machine for generating an electromotive force with low voltage and high strength of current comprising a stator and a rotor, the stator being formed as the outer surface of at least one cylindrical chamber whose upper and lower walls are formed of two circular magnets between which a rotary, plate-shaped paddle wheel is arranged, the space between the paddle wheel and the stator being filled with a fluid material, such as a fluid metal, having relatively high conductivity.

Background Art Swedish published specification No. 372.151 discloses a homopolar machine in which the rotor is formed of a plurality of metallic plates. Radially extending paddles are arranged on said plates and force fluid metal to move between the plate rotor and the stator. The use of paddle wheels prevents large pressure differences from occurring in the fluid metal. However the fluid metal only serves to establish an electric con- nection between the stator and the rotor, whereby two contacts contribute to the internal resistance.

Brief Description of the Invention The object of the invention is to provide a homopolar machine having a lower internal resistance than hitherto known.

A homopolar machine of the above type is according to the invention characterised in that the rotor preferably is exclusively formed of the fluid material with high con- ductivity and made to rotate by the rotatable paddle wheel to generate an electromo-

tive force between the periphery of the paddle wheel and the central portion of paddle wheel. The fact that the rotor is formed of the fluid material per se entails that no contact resistance exists between the rotor and the fluid material.

Moreover according to the invention the fluid material may be a fluid metal, such as mercury.

In a particularly advantageous embodiment according to the invention the cylindrical chamber is made of copper with an iron lining.

The paddle wheel may for instance be of plastics.

Furthermore according to the invention the body of the paddle wheel may be of varying thickness, whereby it is possible to vary the strength of current slightly.

Brief Description of the Drawings The invention is explained in greater detail below with reference to the accompanying drawings, in which Fig. 1 is a perspective view of a homopolar machine according to the invention, Fig. 2 is a cross-sectional view through the homopolar machine shown in Fig. 1, Fig. 3 is a top view of a paddle wheel forming part of the homopolar machine, Fig. 4 illustrates another embodiment of a homopolar machine, in which the thickness of the rotary paddle wheel varies, Fig. 5 is a top view of the homopolar machine shown in Fig. 4

Fig. 6 illustrates a particularly advantageous embodiment of the homopolar machine, in which the thickness of the paddle wheel varies in a more advantageous manner, Fig. 7 is a top view of the homopolar machine shown in Fig. 6, Fig. 8 illustrates yet another embodiment of a homopolar machine, in which the circular permanent magnets are divided into sectors in form of sectors of a circle of alternating orientation, Fig. 9 illustrates the paddle wheel of the homopolar machine shown in Fig. 8, Fig. 10 is a top view of the permanent magnets which are divided into sectors, Fig. 11 illustrates yet another embodiment of a homopolar machine, in which the magnetic field has a different direction and Fig. 12 illustrates the paddle wheel of the homopolar machine shown in Fig. 11.

Best Mode for Carrying Out the Invention The homopolar or acyclic machine illustrated in Fig. 1 for generating an electromo- tive force with low voltage and high strength of current comprises a stator and a rotor.

The stator is shaped as a cylindrical chamber whose upper and lower walls are formed of cylindrical permanent magnets 2. A plate- and/or star-shaped paddle wheel 4 is arranged between the permanent magnets 2, said paddle wheel being rotatable around a shaft 6 whose ends are attached to the permanent magnets 2. The paddle wheel 4 is provided with radially extending paddles 5 and is formed of a non-magnetic mate- rial, such as plastic or another material which tolerates contact with fluid metal, loads and a certain generation of heat. The space between the paddle wheel 4 and the stator is filled with mercury or another fluid material having relatively high conductivity.

Fig. 2 is a sectional view through the homopolar machine shown in Fig. 1. The tubular, peripheral stator 1 comprises an outer copper pipe with an inner iron lining which is not corroded by fluid metal. The copper pipe serves to increase conductivity.

A bottom section 10 is mounted at one end of the copper pipe 1, whereby no conduc- tive connection exists between the copper pipe 1 and the bottom section 10. A bearing for the shaft 6 of the rotary paddle wheel 4 is provided in the middle of the bottom section 10. The lowermost permanent magnet 2a is mounted on the bottom section 10 with the north pole oriented toward the bottom section 10. One end of shaft 6 of the paddle wheel 4 is mounted in a bearing 11 in the bottom section 10. A top section 12 is provided in the other end of the copper pipe 1. The second permanent magnet 2b is mounted on the top section 12 with the south pole oriented toward the top section 12. A central stator 9 is also mounted on the top section with a bearing 13 for the shaft 6. The top section with the central stator 9 and the bearing 12 is mounted on the shaft arrangement and the peripheral stator 1 such that no conductive connection exists between the top section 12 and the peripheral stator 1. Subsequent hereto fluid metal, such as mercury, can be filled into the top section 12 through a filler hole 14.

The mercury thus takes up the portion of the space between the permanent magnets which is not occupied by the paddle wheel 4. Furthermore the space between the permanent magnets 2a,2b and the shaft 6 of the paddle wheel is filled. When the mercury is made to rotate by the paddles 5 of the paddle wheel 4, an electromotive potential difference between the periphery 7 of the rotor and the central portion 8 of the rotor is induced.

The idea is to have the rotor only be formed of mercury which is made to rotate by the paddle wheel 8 so as to generate an electromotive force between the areas at the periphery 7 of the paddle wheel 4 and at the central portion 8 of the paddle wheel 4.

This embodiment involves smaller commutation losses and the fluid conducting mate- rial between the stator and the rotor is mixed with the fluid conducting material of the rotor into one mixture. Thus, two potential drops are eliminated.

The known commutator parts in form of slide rings at the periphery and at the centre are thus superfluous. As a result the structure of the generator is advantageously considerably simplified at the same time as the simplified structure ensures that cool- ing takes place from a larger surface through the contact of the fluid metal to the permanent magnets, the shaft, the rotor paddle wheel and the stator. Moreover the structure according to the invention prevents the fluid metal from having a long contact with the atmosphere in a simple manner, the fluid metal being quickly filled into the hole 14 which is sealed thereafter.

When the rotor is in motion a potential difference is induced between the periphery 7 of the rotor and the central portion, said difference depending on the rpm, the radius of the rotor and the strength of the magnetic field. The potential difference is transmit- ted through direct, continuous contact with central and peripheral stators 1 of the generator. The current is tapped at the terminals 15 and 16.

When an outer circuit is formed by a complete or partial short-circuit of the central and peripheral stator, a current flows, the force of which varying in relation to the following: (the induced potential difference divided by (the ohmic resistance in the outer circuit plus the resistance in the central and peripheral stator plus the resistance in the rotor)) multiplied by the degree of short-circuit), where the degree of short- -circuit is the fraction of the peripheral stator of the rotor which is short-circuited by the central stator. The ohmic resistance in the rotor is proportional to the radius of the rotor and inversely proportional to the thickness of the rotor. Typically, the thickness is of a few millimetres. However the thickness also be of several centimetres, so as to reduce the internal resistance correspondingly.

In a test model the paddle wheel 4 had a thickness of 5.5. mm, an outer diameter of 110.0 mm and an internal diameter of 27.0 mm. The iron lining had a thickness of 12.0 mm, an outer diameter of 43.0 mm and an inner diameter of 25 mm. The top section 12 had a thickness of 14.0 mm, an outer diameter of 140.0 mm and an inner

diameter of 25 mm. The inner rotor had a thickness of 2.3 mm, an outer diameter of 43.0 and an inner diameter of 20.0 mm. The mercury rotor had a thickness of 5.8 mm, an outer diameter of 120.0 mm and an inner diameter of 110 mm.

Some of the measurements of the test model are shown in table 1 below.

Table 1 Millivolts Millivolts Revolutions/sec unloaded in operation Amperes copper (5x30x530) 2 1.8 2.8 3 2.9 1.0 3.5 4 ~ 3.9 1.4 4.5 5 4.9 1.8 5.4 6 5.9 2.1 6.4 7 7.0 2.6 7.3 8 8.1 3.0 8.4 9 9.0 3.4 9.3 10 1 9.9 3.8 10.6 11 10.7 4.1 11.6 12 4.7 12.7 13 13.3 14 Fig. 4 illustrates a particularly advantageous embodiment of the homopolar machine, in which the thickness of the paddle wheel varies. Initially the body of the paddle wheel is thin. The thickness increases with the angle counter-clockwise up to 360°.

In other words the thickness of the body increases, while the paddle wheels merely fill in the remaining thickness. Mercury used to be distributed evenly on 360°, whereas now the mercury thickness is higher at the points where the body is thin.

The mercury thickness determines the inner resistance and thus the strength of cur- rent. The thicker the body, the higher the inner resistance. However the thickness is the same from centre to the periphery. When the body is turned clockwise, the mer- cury thickness decreases until it at a specific point increases steeply again. The mer- cury and thus the strength of current is maintained by the paddles 5 during the rotation of the paddle wheel 4. The current at each current tap terminal will thus vary at each revolution. More specifically a ramp-shaped current is provided. The currents to the conductor being short-circuited is changed synchronously therewith. As a result a current is generated which optionally can be transformed. The paddle wheel having varying thickness is preferably made of plastic, but may also be made of an electri- cally conducting material.

The embodiment shown in Fig. 6 is a variety of the embodiment of Fig. 4 wherein the body furthermore is symmetrical shaped. One side of the body is thin, while the other side is thick, ie. the mercury is disproportionate, as the mercury content is highest in one side (the left side) and practically non-existent in the other side (the right side). A more soft current curve is thus obtained.

The current may essentially be formed as desired by varying the design level of the body, optionally with several cycles per revolution. This is one of the advantages of the invention.

In the embodiment of Fig. 8 each of the circular permanent magnets is divided into sectors in form of sectors of a circle, the north/south direction of the individual partial magnets having alternating orientation. In the embodiment shown each permanent magnet is divided into eight sectors of alternating excitation direction. As a result a homopolar machine is obtained which is able to generate an alternating current being

easily transformed.

Fig. 11 shows an embodiment of a homopolar machine in which the magnetic field is horizontal, the permanent magnets 2c, 2d being annular and one of the permanent magnets 2c being arranged inside the other magnet such that a space between the magnets 2c and 2d is provided.

The permanent magnet 2d (the outermost) is secured to the bottom section slightly interspaced from the top section, while the innermost permanent magnet 2c is secured to the top section slightly interspaced from the bottom section. The rotor paddle wheel, which is pivotal around the central axis, is arranged below the innermost permanent magnet 2c, the paddle wheel 5a extending in the cavity between the mag- nets 2c and 2d. Fig. 12 is a top view of the paddle wheel 5a.The strength of current is unlimited, the height should merely be increased correspondingly, as the inner resistance is substantially inversely proportional to the height.

The mercury may be substituted by sodium or gallium melting at 98"C and 30"C respectively. Sodium alloyed with 77 % by weight potassium has a melting point of -12,5°C and may also be used.

The homopolar machine according to the invention is particularly advantageous in that it has an unusually low inner resistence, a low generation of heat due to the low inner resistance and effective cooling possibilities. In addition the structure is very simple.

The invention may used in connection with supra conductors for providing particu- larly powerful magnetic fields, for instance on particle accelerators and devices utiliz- ing core magnetic resonance. The invention may also be used in connection with chemical processes, in which a very low voltage and a high strength of current are required. In such an instance the homopolar machine is particularly advantageous in that it has low losses contrary to all other current generators. The invention is thought to be of particularly vital importance within the chemical industry, in which the power consumption must be reduced as much as possible for instance due to government energy duties.

The machine may optionally be used as an engine, in which case the paddle wheels may be formed in a more advantageous manner.