Rotatable electrical machine.

The invention relates to a rotary, electrical machine with a first functional part and a second functional part, one of the two functional parts being rotatable relative to the other functional part and an air gap between the two facing surfaces of the two functional parts, in combination with the following features:<ul id="ul0001" list-style="none"><li>(a) one of the two functional parts has, on its side facing the air gap, a plurality of permanent magnet poles in alternating polarity, distributed in a ring shape;</li><li>(b) the permanent magnet poles are of permanent magnets with a permeability number that is in the order of the permeability of air (µ_r = 1) is formed;</li><li>(c) the other of the two functional parts has a plurality of electromagnetic poles with switchable electromagnetic pole windings distributed in a ring shape on its side facing the air gap;</li><li>(d) the number of permanent magnetic poles is equal to or different from the number of electromagnetic poles by a small integer;</li><li>(e) the electromagnetic poles are provided with individually assigned electromagnetic pole windings;</li><li>(f) for switching the electromagnetic pole windings in the appropriate current direction for the duration of a functionally suitable relative position to permanent magnet poles, several electronic switching devices are provided, each of which switches a partial number of electromagnetic pole windings and by detecting the rotational relative position of the two functional parts of at least one, on the one with the Electromagnetic poles provided functional part arranged sensor are controlled;</li><li>(g) an electronic switching device is provided in each case<ul id="ul0002" list-style="none"><li>(g1) for switching the electromagnetic pole winding of a single electromagnetic pole, or</li><li>(g2) for jointly switching the electromagnetic pole windings of several, but not all of those electromagnetic poles which, in the case of a difference between the number of permanent magnetic poles and the number of electromagnetic poles of the machine, are in the same relative position to permanent magnetic poles;</li></ul></li><li>(h) the electronic switching devices are constructed with four controllable semiconductor switching elements arranged in a bridge circuit.</li></ul>

In particular, it is an electric motor or an electric generator. Functionally, the machine according to the invention can best be assigned to the class of direct current electric motors.

An electric motor with the above features (a), (c), (d) 2. alternative, (f) and (h) is known from document DE-A1-31 32 483. This electric motor has 10 permanent magnetic poles and 4 electromagnetic poles, the windings of 2 electromagnetic poles each, which have the same relative position to permanent magnetic poles, are connected in series and are switched in the correct direction in their current direction by a switching device with four controllable semiconductor switching elements arranged in a bridge circuit.

Rotary electric motors with permanent magnetic poles on an external rotor and sensor-controlled electronically switchable electromagnetic pole windings on the stator are known (FR-A-2 099 961, DE-A 2 245 557), also with the electromagnetic pole windings individually assigned to the electromagnetic poles (FR-A-2 099 961). Permanent magnets made of samarium cobalt, which meet the condition µ_r in the region of 1 are also known per se in electric motors (FR-A-2 267 650).

The electrical machine according to the invention also differs from the entirety of the features known from the cited documents by the special design of the electronic control specified under (g) above, in which an electronic switching device is provided for a single electromagnetic pole winding or for a specific number of parts of the electromagnetic pole windings a four quadrant is provided.

The combination of features of the invention achieves a number of advantages which are very valuable for practical use:<ul id="ul0003" list-style="none"><li>1. In the case of electric motors, the electromagnetic fields have a weakening effect on the excitation part of the motor against the rotation of the motor. The magnitude of this reaction depends on the magnetic resistance in the individual magnetic circuits between the rotor and the stator, this magnetic resistance being previously small due to the small thickness of the air gap, which is usually sought for other reasons. In the machine according to the invention, however, the individual magnetic circuits, even with a small thickness of the air gap, have a high magnetic resistance due to the permeability number of the permanent magnets that is several orders of magnitude lower than that of iron. As a result, the described weakening retroactivity is reduced significantly. In addition, the inductance of the electromagnets to be reversed drops significantly, so that at high speeds of reversing or the circuit of the electromagnetic poles can work. This results in the inexpensive possibility of equipping the machine according to the invention with many poles and / or of working at a high peripheral speed on the active surface or on the air gap surface of the machine.</li><li>2nd Since each of the electronic switching devices only switches a single or only a specific number of electromagnetic poles together, only smaller powers have to be switched by each electronic switching device. As a result, disproportionately cheaper switching devices can be used, the cooling effort for the switching devices can be reduced and the reliability of the machine increased considerably, since the failure of individual switching devices does not significantly impair the overall function. The maintenance of the machine is also easier because comparatively cheap switching devices can be replaced individually.</li></ul>

Preferred embodiments of the invention emerge from claims 2 to 15. The subject matter of claim 1 and some of these configurations are explained below.

In principle, it is immaterial whether the functional part provided with the permanent magnet poles is stationary and the functional part provided with the electromagnetic poles rotates or vice versa. In principle, it is irrelevant whether the two functional parts are opposite each other in the axial direction or in the radial direction, so that one functional part is arranged within the other functional part. In the latter case of the radial interlacing of the two functional parts, it is also in principle irrelevant whether the permanent magnet poles are arranged on the radially inner functional part and the electromagnetic poles on the radially outer functional part or vice versa. However, a design is particularly preferred in which the rotating part of the machine is arranged radially outside around the stationary part of the machine and in which the permanent magnetic poles are arranged on the inner circumference of this rotating machine part. The particular advantages of this design will be explained in more detail below.

The machine according to the invention can be constructed so that the number of permanent magnet poles corresponds exactly to the number of electromagnet poles. However, a slight difference between the number of permanent magnetic poles and the number of electromagnetic poles is preferred, in particular a difference of less than 10% of the number of permanent magnetic poles. It is particularly favorable to provide some, for example 1, 2, 3 or 4, electromagnetic poles less than permanent magnet poles. This leads to a safe motor start-up, an even motor run and an even network load.

Permanent magnets made from a material based on rare earths with cobalt, in particular samarium-cobalt permanent magnets, are particularly preferred.

In the electrical machine according to the invention, a plurality of electronic switching devices are provided, each of which is coupled to at least one sensor, and each of the electronic switching devices only switches a small number of electromagnetic poles which are in at least substantially the same relative position to the permanent magnet poles. It is also possible to implement the lower limit of the design, that one electronic switching device is provided for each electromagnetic pole.

Hall generators are particularly preferred as sensors because they are robust and can be arranged in a structurally convenient manner in response to the magnetic fields of the permanent magnets. However, other sensors can also be used, for example read contacts, photocells, induction sensors or permeability sensors.

Before installation, electromagnetic pole components that are wound and exchangeably fastened to the functional part in question can be provided. These components can be identical to one another, which makes manufacture cheaper and simplifies interchangeability.

The electromagnets are preferably provided with their feet abutting one another. In this case, one can do without a magnetic back made of laminated iron to create a magnetic flux path behind adjacent electromagnets, because the abutting electromagnet feet create the required magnetic connection.

The permanent magnets are preferably provided in the circumferential direction directly or by abutting thin plastic intermediate layers, which optimally accommodates a large volume of permanent magnets. A magnetically conductive back is usually arranged behind the permanent magnets.

The division of the arrangement of the permanent magnetic poles and / or the length of the permanent magnetic poles in the circumferential direction of rotation essentially corresponds to the length of the electromagnetic poles in the circumferential direction of rotation. In this way, optimal volume utilization is achieved and the circumferential angle ranges that do not contribute to the flow change are reduced.

It is particularly preferred to use the machine according to the invention as a wheel drive motor in motor vehicles.

A schematically illustrated electric motor is described in more detail below. This electric motor does not realize the feature (g) of claim 1 and is therefore not designed according to the patent; its description nevertheless facilitates understanding of the invention. Show it:<ul id="ul0004" list-style="none"><li>1 shows a cross section of an electric motor perpendicular to its axis of rotation.</li><li>Figure 2 shows a detail with regard to the construction and attachment of two adjacent electromagnets.</li><li>Fig. 3 shows the basic structure of an electronic switching device for switching the electromagnetic poles.</li></ul>

1, 30 electromagnets 4 are arranged in a uniform division on the outer circumference of a stationary functional part 2 in the circumferential direction schematically indicated winding 6, the wires of which run perpendicular to the plane of the drawing. On the outer circumference, each electromagnet 4 has an electromagnet pole 8, which is a north pole or a south pole depending on the direction of current through the winding 6.

Arranged around the stationary functional part 2 is a rotatable functional part 10, which overall has essentially the shape of a hollow cylinder closed in a pot shape on one side, which is fastened on the closed side axially next to the stationary functional part 2 on a shaft, not shown. On the inner circumference of the rotatable functional part 10, permanent magnets 12 are attached in an annular distribution with uniform division, namely 32 permanent magnets in the illustrated embodiment. The permanent magnets 12 provide permanent magnetic poles 14 on their inner circumference, namely alternately north poles and south poles in the circumferential direction. The permanent magnets 12 and the permanent magnet poles 14 are each substantially as long as the electromagnetic poles 8 in the circumferential direction. The individual permanent magnets 12 abut each other directly in the circumferential direction and can, for. B. be glued.

To facilitate understanding, the case is first considered that the number of electromagnetic poles 8 and the number of permanent magnet poles 14 are the same. Then, with each relative position of the two functional parts 2, 10, in which each permanent magnet pole 14 is exactly opposite to an electromagnetic pole 8, all electromagnets 4 would have to be switched over simultaneously.

In the illustrated embodiment, two permanent magnet poles 14 are provided more than electromagnetic poles 8. Not all of the electromagnets 4 are switched over at the same time, but with the aid of 5 electronic switching devices (cf. following description of FIG. 3) 6 electromagnets 4 each at the same time, namely two diametrically opposed groups of three of electromagnets 4. The two groups of three are in exactly the same relative position to permanent magnet poles 14, while within each group of three the relative position to permanent magnetic poles 14 varies slightly from electromagnetic pole 8 to electromagnetic pole 8. An electronic switching device 16 for the 6 electromagnets 4 described is shown schematically. 4 further such electronic switching devices 16 are provided analogously to the switching of the remaining electromagnets 4.

On the front edge in the circumferential direction and on the rear edge of the middle electromagnetic pole 8 of each group of three in the circumferential direction, a Hall probe is attached as a sensor S which detects the change from the rotating permanent magnet north pole to the permanent magnet south pole and vice versa. This information about the relative position of stationary functional part 2 and rotatable functional part 10 is passed on to the respective switching device 16.

The following formula applies:<maths id="math0001" num=""><math display="block"><mrow><msub><mrow><mtext>n</mtext></mrow><mrow><mtext>s</mtext></mrow></msub><msub><mrow><mtext> · N</mtext></mrow><mrow><mtext>v</mtext></mrow></msub><mtext> = </mtext><mfrac><mrow><msub><mrow><mtext>n</mtext></mrow><mrow><mtext>E</mtext></mrow></msub></mrow><mrow><msub><mrow><mtext>n</mtext></mrow><mrow><mtext>M</mtext></mrow></msub><msub><mrow><mtext> - n</mtext></mrow><mrow><mtext>E</mtext></mrow></msub></mrow></mfrac></mrow></math><img file="EP0094978B2_D0001.tif" /></maths>    n_s = 5 Number of electronic switching devices 16    n_v = 3 Number of neighboring, simultaneously switched electromagnetic poles    n_E = 30 Number of electromagnetic poles    n_M = 32 Number of permanent magnet poles.

At each point in time considered, all of the electromagnetic poles 8 are switched on, each with a suitable current direction in relation to the respectively interacting permanent magnet pole 14. The switching devices 16 cause the individual electromagnetic poles 8 to be switched over in the other current direction in the correct time.

It is pointed out that designs of the machine according to the invention are also possible in which, due to the number of permanent magnetic poles and electromagnetic poles and due to the dimensions of the permanent magnetic poles and the electromagnetic poles, the switching of the electromagnetic poles is not a switching practically without a pause in the current application, but rather more Switch on for a certain period of time, switch off for a certain period of time, switch on again with reverse current direction, etc

2 shows on a larger scale how the individual electromagnets 4 are arranged and fixed on the stationary functional part 2. Each electromagnet 4 has a double T-shaped core 18 in the sectional view shown. The core 18 can be designed as a stack of iron lamellae layered perpendicular to the plane of the drawing. Another possibility is to construct the core 18 from iron powder particles embedded as densely as possible in plastic, the core 18 being particularly easy to produce by injection molding.

Radially on the inside, each core 18 has an axially extending, undercut groove 20. With the aid of a strip 22 inserted into this groove 20 and provided with threaded bores, each core 18 is screwed from the inside to the stationary functional part 2 by means of screws 24. The technique described for the production of the cores 18 and the simple attachment of the cores 18 to the stationary functional part 2 described is possible in particular because the stationary functional part 2 does not rotate, so that the electromagnets 4 are not subject to centrifugal force.

Adjacent electromagnets 4 are provided with their feet 26, that is the radially inner leg of the double-T-shaped cross section, abutting one another in the circumferential direction. The foot contact surfaces 28 ensure a magnetic flux path between adjacent electromagnets 4, so that no magnetically conductive back has to be provided radially inside the electromagnets 4 on the stationary functional part 2.

The electromagnetic cores 18 can also be manufactured without a radially inner leg and screwed onto the stationary functional part 2. In this case, however, a laminated back or a backing built up with iron powder particles embedded in plastic must be provided radially inside the individual electromagnets 4.

3 shows an electronic switching device in more detail. Of the electrical machine, only the stationary functional part 2 with two diametrically opposed electromagnets 4, namely in each case the middle electromagnet 4 from the respective group of three, is shown. The windings designated here with E1 and E2 are connected in series; however, they could also be connected in parallel.

The series connection with the windings E1 and E2 is connected to the two center points M1 and M2 of a switching bridge which, in the embodiment shown, is constructed with 4 controllable semiconductor switching elements T1, T2, T3 and T4. The switching bridge is connected at one end to the negative pole and at the other end to the positive pole of an operating voltage source. The control electrodes of the diagonally opposite semiconductor switching elements T1 and T4 in the bridge circuit are connected to the output of a first control circuit A1, while the control electrodes of the remaining semiconductor switching elements T2 and T3 are connected to the output of a second control circuit A2. Control connections on the input side of the control circuits A1 and A2 are connected to separate outputs of a control circuit SS.

At least one sensor S is assigned to one of the two functionally related electromagnetic poles P1 and P2, with which the rotational relative position between this electromagnetic pole and the permanent magnet pole of the rotating embodiment is assumed. that the permanent magnet poles are arranged on a ring. which rotates around the outside of the electromagnetic poles P1 and P2. With the help of the sensor, the windings E1 and E2 are switched over when a permanent magnetic pole change is detected. For this purpose, the control circuit SS is acted upon by an output signal from the sensor S and the control circuit SS then uses the two control circuits A1 and A2 to switch on two diagonally opposite semiconductor switching elements of the switching bridge in such a way that current flows in either one or the other direction the windings E1 and E2 connected in series flow.

In the embodiment shown, two sensors S are provided on both sides of the electromagnetic pole P1, the switching of the current direction in the windings E1 and E2 being controlled in one direction of rotation of the electrical machine by one sensor S and in the other direction by the other sensor S.

The control circuit SS is further connected to a command circuit B, with which control commands such as start / stop, speed and direction of rotation can be entered. The control circuit SS is preferably a microprocessor. which gives its switching signals via the control circuits A1 and A2 to the SSwitching bridge T1 to T4 with a fixed or changeable program depending on the command signals from the command circuit B and the output signals from the sensors S.

Electrical machines constructed according to the principles of the invention provide a whole series of advantages which are important in practice: the electronic switching of the individual electromagnets prevents wear-prone and manufacturing-intensive sliding contacts and a commutator. The electronic control opens up control options that were only possible with great effort in conventional electrical machines, e.g. B. large usable speed range with high efficiency, control to specific torque, speed change and the like. The electronic control enables a design with a difference between the number of permanent magnet poles and the number of electromagnet poles, which results in a safe motor start, a smooth motor run and a uniform network load. The permanent magnets are low-maintenance and energy-efficient. If you use permanent magnets with a permeability number in the vicinity of air, you can work with much higher currents in the electromagnets and with a high reversal speed of the electromagnets due to the reduced reaction of the electromagnetic fields. The winding of the electromagnetic functional part of the machine can take place according to the principle of single-phase, ie that the windings of the individual electromagnets are not connected to one another by bulky, so-called winding heads. This results in the possibility of prefabricating the electromagnets as mutually identical components outside the machine and assembling them as components, with all the advantages for replacement and maintenance. The electronic control can be designed as required so that each electronic switching device switches only one or more electromagnets which are in an at least substantially analogous relative position to permanent magnet poles. As a result, one can choose electronic switching devices with the switching capacity that is just right, in particular a small switching capacity that is favorable in terms of price, cooling and maintenance. The arrangement of the electromagnets radially outside on an inner, stationary functional part as well as the attachment of the permanent magnets radially inside on a radially outer, rotatable, functional part simplifies the magnet fastening as a whole, since the electromagnets are not subject to centrifugal force and since the permanent magnets are pressed against their fastening surface by the centrifugal force . If the permanent magnets are arranged radially outside the air gap, the so-called active surface of the machine moves radially outwards because the permanent magnets take up less radial space than the electromagnets. Because the machine's active surface is further out, there is more space available for the electromagnets. The greater distance between the active surface and the axis of rotation of the machine results in an increase in the active surface and an enlarged lever arm of the magnetic forces to the axis of rotation of the machine.

The cup-shaped rotor can be accommodated in a conventional motor vehicle wheel with the tire mounted on the outside. In this case, the electromagnets are fastened to the outer circumference of a stationary, additional component in such a way that the air gap remains between their outer pole faces and the inner pole faces of the permanent magnets.