WO2012028992A1

WO2012028992A1 - Brush-slip ring system for electrical rotary machines, in particular current-energized synchronous motor

Info

Publication number: WO2012028992A1
Application number: PCT/IB2011/053674
Authority: WO
Inventors: Andreas Holzner; Arno Mathoy
Original assignee: Brusa Elektronik Ag
Priority date: 2010-09-01
Filing date: 2011-08-22
Publication date: 2012-03-08
Also published as: EP2426793A1

Abstract

The invention relates to a brush-slip ring system (2) for electrical rotary machines, in particular current-energized synchronous motors (1) having a rotor (4) and a fixed part, e.g. stator (3) associated with said rotor. Said brush- slip ring system (2) comprises slip rings (18, 19) fastened to the rotor (4) and brushes (15) arranged in said fixed part of the machine. Each of the brushes (15) is connected to each of the slip rings (18, 19) in a sliding frictional connection so as to transmit energizing current to windings of the rotor (4). The slip rings (18, 19) are connected on a printed circuit board (17) and are arranged coaxially and radially spaced apart from one another. The brushes (15) are oriented in axial direction of the rotor (4). The slip rings (18, 19) and the printed circuit board (17) of said brush-slip ring system (2) are integrated by an insulating casing (20) to form an integrated slip ring unit (14), and this integrated slip ring unit (14) is co-rotatably fastened to a face of the rotor (4).

Description

BRUSH-SLIP RING SYSTEM FOR ELECTRICAL ROTARY MACHINES, IN PARTICULAR CURRENT-ENERGIZED

SYNCHRONOUS MOTOR [0001] This application claims benefit of priority to prior U.S. provisional application no.61/378,985 filed on September 1, 2010 and as a non-provisional thereof; this application also claims benefit of priority to prior European application no. EP10174941 filed on September 1, 2010; the entirety of European application no. EP10174941 and of U.S. application no.61/378,985 are expressly incorporated herein by reference in their entirety, for all intents and purposes, as if identically set forth herein.

FIELD OF THE INVENTION

[0002] The present invention relates to a brush-slip ring system, which is preferably suitable for transmitting energizing current to rotor windings of current-energized synchronous motors for main drives of electric vehicles.

[0003] As is known, the extent of the transmission of energizing current from the fixed motor housing to the rotating shaft of the rotor in current-energized electric motors, in particular in current-energized synchronous motors plays an important role. Without this external supply of current, said motor - apart from slight magnetization by possibly present permanent magnets - acts like a reluctance motor. The uninterrupted supply of current from the rotor windings is thus a basic requirement in order to make the advantages of the current- energized synchronous motor useable in practice. As a result of the current energizing, high quality magnets consisting of rare earths may be dispensed with. The increasing global requirement for rare earths, combined with the restricted capacity for supply, increases the importance of developing a current- energized electric motor and associated therewith the requirement for cost- effective, conductive rotor current transmission using brushes and slip rings. PRIOR ART

[0004] In electrical rotary machines with high output and high efficiency it is intended to reduce the electrical losses of the brushes as far as possible, as the electrical losses in the brushes considerably impair the overall efficiency of the electrical rotary machine. A known possibility for reducing the electrical losses uses brushes which are produced from graphite and a conductive metal, in particular copper.

[0005] The field of application of carbon brushes and slip rings is very wide and may be divided into two areas:

■ Carbon brushes for DC motors (starter motors, fan motors, windscreen wiper motors, servo-motors and fuel pump motors);

^■ Carbon brushes for AC motors (primarily in domestic appliances: vacuum cleaners, electric whisks and electric mixers).

However, in the design of brushes and slip rings in current-energized synchronous motors, reference may only be partially made to the current prior art, as the boundary conditions differ from the previous fields of application.

[0006] At the present time, in current-energized synchronous motors, radial brush arrangements are exclusively used relative to the slip ring. In the radial brush arrangement of conventional generators or electric motors, generally the entire motor power is passed over the brushes, which requires the brushes to be of a particularly large size.

[0007] Occasionally, axially arranged carbon brushes are used in practice, for example in a wet fuel pump, or as the earth contact of a railroad and for lightning protection in wind energy rotors. Typically, carbon brushes are arranged radially on the rotor shaft.

[0008] A typical electrical rotary machine, namely a starter motor, is disclosed in DE-102008059994, in which radial acting brushes are pressed onto slip rings which are fastened to the rotor shaft in order to conduct an energizing current electrically for the energizer winding on the rotor. [0009] A drawback with the above brush-slip ring system comprising radial brushes is that, on the one hand, a large installation space is required in the machine housing for the use of the brushes and the slip rings and, on the other hand, the replacement and/or repair of the brushes is too complicated and labor-intensive. This is slightly significant in a starter motor, as its operating time is relatively short and thus generally the service life without replacing the brushes corresponds to the service life of the motor vehicle. The size is accepted, nevertheless, as the starter motor in comparison with the remaining engine is relatively small overall.

[0010] EP-0695662 discloses a brush-slip ring system for supplying an electric current to the winding coils on the rotor driving a motor wheel, wherein a rotary annular board type conductive plate is fastened onto an insulated surface plate on a lateral side of the wheel frame. The printed-circuit board having a group of radially distributed conductive sheets in an inner area thereof interconnected with a group of radially distributed conductive sheets in an outer area thereof, wherein the former is provided for contact with a plurality of conductive elements such as carbon brushes attached onto a securing element on the rotor shaft, whereas the latter is connected respectively to each winding coil on the rotor so that the electric current passes through the carbon brushes and the printed-circuit board to supply power to each winding coil on the rotor.

[001 1 ] This brush-slip ring system has a relatively complicated arrangement and the replacement and/or repair of the axial brushes is too labor-intensive.

[0012] However, the situation in the field of electric rotor machines for driving electric vehicles is basically different. Here the above mentioned drawbacks cannot be accepted. In particular for the use of current-energized synchronous motors in electric vehicles, a small space requirement for the electrical transmission system and a low service requirement and/or easy accessibility for a possible replacement of the brushes are required. SUMMARY OF INVENTION

[0013] The object of the invention is to provide an improved brush-slip ring system for transmitting electrical energizing current to a rotor of electrical rotary machines, for example electric motors, in particular current-energized synchronous motors for driving electric vehicles, by which the above-mentioned drawbacks of the prior art can be reduced and/or eliminated. Basically, a more perfect electric current transmission between the brushes and the slip rings is to be provided, even at high speed ranges of the motor.

[0014] Additionally, special requirements for the construction of the electric vehicle should be taken into account without appreciably increasing the costs of the brush system.

[0015] By means of the system according to the invention, therefore, the followings are to be implemented:

^■ A continuous and problem-free transmission of current between elements which rotate relative to one another of electrical rotary machines;

^■ Compact arrangement of the brush elements with easy accessibility of the brushes, which are intended to be easily replaceable as wearing parts;

^■ To enable a short overall axial length of the rotary machine.

The objects set forth are achieved by the features of the attached independent claim 1 . Advantageous developments of the solution according to the invention are disclosed in the dependent claims.

[0016] The invention provides a "substance-to-substance bond" or "material integrated bond" between the circuit board and the slip rings, which is much better against the high centrifugal loads at high speeds than the known solutions, and on the other hand, an improved and freely adaptable electrical insulation.

[0017] In the field of application, proposed by way of example, of an axial brush arrangement, however, only approximately 2% of the nominal power - as energizing power - is passed over the brushes. For reliable operation of this electric motor, a continuous contact of the brushes with the slip ring is particularly important.

[0018] The following inventive recognitions particularly influenced the inventive concept and the development of the invention based thereon of the brush-slip ring system according to the invention, as follows:

^■ Constructional space neutrality: This means a compatibility with all conventional electric motors comprising a permanent magnet drive (for example: IPM), wherein the external geometry of the electric motor being kept unaltered but the internal geometry of the bearing shields may be adapted;

^■ Minimum constructional space for the brush-slip ring system - in spite of the axial brush position - (till now persons skilled in the art have taken as a starting point an increase in the overall length of the motor by using axial brushes);

■ Brushes are intended to be able to be replaced as easily as possible: the invention, therefore, provides a brush unit with a plug connection which may be replaced as a unit, so that with easy accessibility the brushes may be replaced rapidly;

^■ Special winding connection is provided by means of a printed circuit board enclosed by plastic injection-molding. On the one hand, this results in the freedom to vary the pole arrangement with identical rotor windings, but on the other hand, this also results in an improved and more economical basis for the slip rings;

^■ According to the invention, the slip rings are integrated but, sufficiently separated from one another in order to maintain air gaps and creepage distances;

^■ As a result of the invention, there is the possibility of reliably fastening the slip rings to the front face of the rotor;

^■ First, at the high rotational speeds of main drives (up to 12000 r/min), a brush fire can be prevented by means of the invention. Similar to skimming the slip rings in a radial arrangement, the printed circuit board provides the possibility of subsequent machining in order to achieve the required linear movement thereby. On the other hand, the printed circuit boards are produced and mounted easily in a planar manner, so that in this regard an advantage results relative to the slip rings which have to be pulled on in the form of a sleeve;

^■ The configuration of the slip rings according to the invention increases the circumferential speed of at least one slip ring relative to a radial arrangement on the shaft, but this also has the positive side effect in that by the increased centrifugal force carbon dust is more effectively cleaned out of the insulating parts of the slip rings.

[0019] The invention was thus based on the brush-slip ring system for transmitting electrical signals and/or energizing current to a rotor of electrical rotary machines, in particular current-energized synchronous motors which are provided with slip rings fastened to the rotor and fixedly arranged brushes. Each of the brushes is frictionally connected to each of the slip rings so as to transmit current.

[0020] The essence of the invention lies in that the slip rings are combined with at least one printed circuit board and at least one insulating casing to form an integrated slip ring unit. In this integrated slip ring unit, the slip rings are arranged coaxially and spaced apart from one another at a radial distance and cooperate with the brushes for the transmission of electrical current. The integrated slip ring unit is centered on the front face of the rotor and rigidly fastened thereto so that it rotates at the same time. The brushes are oriented and arranged in the axial direction of the rotor.

[0021 ] As this brush-slip ring system may be similarly used for transmitting signal currents (for example for evaluating a temperature sensor on the rotor), it is not restricted to the transmission of energizing current but is generally also able to be used for the transmission of signals between the rotor and the non- rotating parts of the motor. [0022] In a preferred exemplary embodiment, the integrated and axially impinged slip ring unit is fastened to the front face of the rotor by a support ring protecting the winding heads of the rotor against axial and radial loads. The integrated slip ring unit has preferably of annular ring-shaped configuration. [0023] In a further embodiment of the invention, an additional electrical breakdown-insulator is fitted in the radial space between the slip rings of the integrated slip ring unit located coaxially and, in the installed state, preferably in the same vertical plane. As a result, the breakdown resistance for higher voltages may be increased further. [0024] In terms of the technological process, it is advantageous if the insulating casing of the integrated slip ring unit is prepared by a plastic injection-molding.

[0025] In a preferred embodiment of the invention the axial brushes are combined in a common insulating housing to form an integrated brush unit. As a result, the integrated brush unit may be easily and rapidly replaced as a whole. To this end, it is also expedient if the integrated brush unit is provided with an electrical plug connection which is preferably disconnected solely by removing the brush unit and is connected by attaching the brush unit.

[0026] Preferably, the brushes of the integrated brush unit are produced from electrographite Έ43" and the slip rings of the integrated slip ring unit from CuSnI O (copper-tin), in order to limit the wear in the slip ring brush system according to the invention as far as possible exclusively to the wear of the brushes, and to minimize the electrical contact resistance and to keep the wear of the brushes as low as possible. The choice of brush material is closely linked with the choice of material for the slip ring. In this regard, other material combinations may also be optionally selected.

[0027] The compact brush-slip ring system according to the invention may be installed in a relatively small installation space of a current-energized synchronous motor, which is defined axially by a support ring of the rotor and a bearing shield of the synchronous motor, and in radial direction by the bearing shield and stator winding. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The invention is described in more detail hereinafter with reference to the accompanying drawings which illustrate a preferred exemplary embodiment of the solution according to the invention, in which:

· Figure 1 shows a partial sectional view of a current-energized synchronous motor with an exemplary embodiment of the brush-slip ring system according to the invention;

• Figures 2A-2C show views of the parts of the integrated slip ring unit according to the invention of the brush-slip ring system according to Figure 1 in enlarged scale;

• Figure 3 shows a perspective view of the integrated slip ring unit according to Fig. 2C with two axially arranged brushes;

• Figure 4 shows a perspective view of the exemplary embodiment of the integrated brush unit according to the invention of the brush-slip ring system according to Fig. 1 ;

• Figures 5 - 6 show exploded perspective views of the integrated brush unit according to Fig. 4;

• Figure 7 shows a perspective view of the exemplary embodiment of the integrated brush unit according to the invention according to Figures 5 and 6 in an assembled state;

• Figure 8 shows a sectional view of the integrated slip ring unit along the lines VIM-VIM in Figure 3.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT OF THE INVENTION

[0029] Fig. 1 shows a partial sectional view of a current-energized synchronous motor 1 particularly for main drives of electric vehicles, with a first exemplary embodiment of a brush-slip ring system 2 according to the invention which has the purpose of reliably transmitting an electrical energizing current to a rotor 4 of the current-energized synchronous motor 1 . A stator of the synchronous motor 1 was designated by 3. [0030] It is to be noted that the brush-slip ring system 2 according to the invention may expediently be used in all other applications of electrical rotary devices, in which electric signals and/or electric current, in particular energizing current, is intended to be transmitted between units of the electrical rotary devices which rotate relative to one another.

[0031 ] In this embodiment (Fig. 1 ), the rotor 4 is provide with a protective device (so-called "retaining system") in order to support winding heads 7 protruding from a laminated rotor core 6 in the axial direction on both front faces, against loads on both sides by means of one respective support ring 5, even at greater rotational speeds of the rotor 4. The two support rings 5 are preferably connected by axial screws 9 at a predetermined pretension; as a result a compact and rigid rotor unit is provided. In Fig. 1 , a laminated stator core is designated by 8, a stator winding by 10, a bearing shield by 1 1 , a rotor shaft by 12 and a rotational axis of the rotor 4 by 13. [0032] With the transmission of energizing current by means of brushes and slip rings - similar to permanently energized motors - the high dynamic response of the motor is a basic requirement for the transmission of energizing current. In electric motors for electric vehicles the rotational speed may be above 12000 r/min and the output should be above 100 kW. [0033] Thus - in addition to avoiding the drawbacks of expensive magnetic materials - because of a high dynamic response of the motor the drawbacks of known brush-slip ring systems are to be taken into consideration. The prior art is, however, not yet sufficiently advanced in this regard, in order to fulfill the complex requirements of such a current-energized synchronous motor. Thus an additional electro-technical development cost was required in order to improve the transmission of energizing current between the brushes and slip rings. This is achieved by the present invention.

[0034] As regards the possible positioning of the brush-slip ring system 2 in the synchronous motor 1 , initially the requirements were specifically defined which are set for the installation position and the transmission system. The requirement for constructional space neutrality which permits a compatibility with all previous applications and thus at any time a replacement of already installed electric motors, may be regarded as an important prerequisite on the part of the present Applicant.

[0035] According to the invention, the following concept for the transmission of energizing current is achieved:

^■ The minimum possible constructional space for the brush-slip ring system; the brush-slip ring system substantially uses the space inside the upright stator winding heads of the energizer winding and may be maintained or replaced from the axial side. In other words, the brushes may be accessed from the front face and do not require the machine housing to be accessible radially. This simplifies the maintenance and assists the motor vehicle servicing personnel trained as mechanics;

^■ The integrated slip ring unit: easy to mount, it has low weight, exceptionally smooth running, minimum axial constructional space;

■ Replaceable integrated brush unit with plug connection;

^■ Freedom to vary the winding arrangement using a printed circuit board of the integrated slip ring unit enclosed preferably by plastic injection-molding.

[0036] Based on the installation situation illustrated in Fig .1 , therefore, within the meaning of the invention a new concept was able to be developed for main drives of electric vehicles for transmitting current from the stator 3 to the rotor 4. In contrast to the traditional arrangement of carbon brushes in the radial direction, as is disclosed in the prior art, according to the invention an axial arrangement of the brushes and a new brush-slip ring system has been implemented.

[0037] Both the slip ring construction and the brushes may be installed in the available constructional space of the motor. Additionally, the direct current connection from a rotor current converter or regulator to the electric motor and optionally several electronic components (not shown) are integrated in the constructional space for improved operation. This is possible because the brushes are arranged on the one side of the motor shaft. [0038] Within the meaning of the present invention, the proposed brush-slip ring system 2 in the second detailed exemplary embodiment (see Fig. 3) consists of an integrated slip ring unit 14 and two axially positioned brushes 15 associated with the integrated slip ring unit 14. [0039] The brushes 15 according to the invention are preferably assembled together as a completely replaceable integrated brush unit 16 (this is described in more detail hereinafter in connection with Figures 4-7).

[0040] Of course, a variant is also within the scope of the invention, in which the brushes may be individually replaced, by being able to be removed individually from the brush housing, as in the case of conventional carbon brushes. In the context of a short servicing time and simple assembly, however, the integrated and pluggable solution is preferred.

[0041 ] The details of the integrated slip ring unit 14 according to the invention are illustrated in Figures 2A-2C and 8. The preferred embodiment of the slip ring unit 14 consists of a printed circuit board 17 as initial material (illustrated separately in Fig. 2A), slip rings 18 and 19 and an insulating casing 20 preferably designed as a plastic covering. In Fig. 2B, the printed circuit board 17 may be seen with the associated two slip rings 18 and 19, and in Fig. 2C, the completely integrated slip ring unit 14 can be seen, together with the printed circuit board 17, the two slip rings 18-19 and the casing 20 (see also Fig. 2B). As illustrated in Fig. 2C, the integrated slip ring unit 14 is configured in this case to be annular ring-shaped.

[0042] In Figures 2C and 8, coaxial circular grooves 21 and 22 are also provided in the casing 20, in order to make the two slip rings 18 and 19 of the integrated slip ring unit 14 accessible to the brushes. The axially arranged brushes (not shown here) cooperate by a spring-loaded sliding-frictional connection with the slip surfaces of the slip rings 18 and 19. On the other hand, the slip ring unit 14 is provided along its circumference with bores or recesses 23 (Fig. 3) through which screws (not shown) are passed in order, on the one hand, to fasten the slip ring unit 14 on the front face of the support ring 5 of the rotor unit coaxially (Fig. 1 ), on the other hand, to connect the printed circuit board 17 to the windings in a suitable manner.

[0043] According to the invention, the integrated slip ring unit 14 is thus reliably fastened rigidly to the rotor 4 on the front face so that it is able to co-rotate at the same time, in order always to produce and/or maintain a stabilized and perfect frictional contact with the axial brushes 15.

[0044] This integrated slip ring unit 14 in the embodiment according to Fig. 1 is directly mounted on the support ring 5, which is supported via axial feet (not shown) directly on the laminated rotor core 6. As a result, the slip rings 1 8 and 19, the integrated slip ring unit 14 and a front face of the support ring 5 of the rotor unit are substantially located in a common vertical plane which is arranged perpendicular to the rotational axis 13.

[0045] Details of the construction and mounting of the support ring 5 may be derived from patent application EP10169565 and U.S. application serial no. 61 /364,439 of the same Applicant which is thus entirely incorporated by reference, in all respects and for all purposes, within the disclosure of the present application, for subsequently combining the teaching of this cited application with the present application.

[0046] By means of this improved fastening of the integrated slip ring unit 14, there are no such problems with the brushes 15 when rotating the rotor 4 - even at higher rotational speeds of 12000 1 /min - as in the prior art. By the high number of revolutions, centrifugal forces act on the slip rings 18 and 19. As said slip rings are radially further outside the rotor shaft 12, due to the greater centrifugal forces said slip rings are more effectively cleaned of possible abraded matter or dust.

[0047] As illustrated in Fig. 1 , a relatively small installation space for the integrated slip ring unit 14 is available, which is defined axially between the laminated rotor core 6 and the integrated brush unit 16 and the bearing shield 1 1 , and in the radial direction by the bearing shield 1 1 and the stator windings 10. [0048] Within the sense of the invention, therefore, in this installation space the following functions are intentionally incorporated:

a) Integration of the slip rings, i.e. the integrated slip ring unit 14; this measure is associated with the advantage that each slip ring may be produced as a separate structural element which at any time may be easily adapted in the future, depending on the respective workshop tests, by altering the material; b) Freedom when arranging the individual pole windings, i.e. connection of the ends of the wire:

In a six pole (3-pole pair) lamination thus the following possibilities of the winding arrangement result: 3 x 2 in parallel or 6 x in series. This is advantageous as the same production process with the freedom to vary the winding arrangement permits a separation of the winding process and the connection of the twelve ends of the wire from one another.

The invention, however, may also be used in other constructions with more than two energizing current poles, by more concentric slip rings being accordingly formed on the printed circuit board. It is thus also conceivable that the design according to the invention of the slip ring unit is exclusive to the winding arrangement. The winding arrangement may thus be

implemented by the wire guide, the functionality and/or the advantages of the disclosed slip ring unit being nevertheless maintained. In this case, a minimum of two ends of the wire would be brought into contact with the slip ring unit;

c) Insulating partition 30 of the slip rings 18 and 19 for separation from one another in the integrated slip ring unit 14 for cooperation with the brush unit 16. This measure is preferred as due to the high voltages - for increased dynamic requirements - the air gaps and creepage distances have to be maintained in this manner, in order both to be able to prevent both sparkover and short circuit to earth.

[0049] According to the invention, on the one hand, the printed circuit board 17 of the integrated slip ring unit 14 (Fig. 2A) into which the copper ends of the wire (not shown) are soldered and may be connected together by a corresponding layout, forms a basis for implementing the above three functions. This printed circuit board 17 is then provided with two copper rings, i.e. the slip rings 18 and 19 (Fig. 2B) and thus electrically connected correspondingly. This means that contacts and/or conductor tracks (not shown) of the printed circuit board 17 are arranged with the poles aligned, on the one hand, with rotor windings 7 and, on the other hand, with the slip rings 18 and 19.

[0050] As the radial constructional space and the air gaps and creepage distances to be maintained act in opposite directions, the printed circuit board 17 provided with the slip rings 18 and 19 - as already mentioned - is provided with the additional casing 20 for increasing the air gaps and creepage distances. The casing 20 is the third element of the slip ring unit 14 (Fig. 2C) made preferably by plastic injection-molding. This casing 20 of the integrated slip ring unit 14 (Fig. 2C) is used for:

^■ It serves, on the one hand, as a material connection ("substance-to- substance bond" or "material integrated bond") between the components used, namely the printed circuit board 17 and the slip rings 18 and 19, because the basic connection - for example, by soldering - is not always physically sufficient, due to the high centrifugal force loads;

^■ On the other hand, it serves as electrical insulation of the integrated slip ring unit 16 which may be easily adapted by the free geometric form to the respective functional requirements.

[0051 ] In Figure 2C, the integrated slip ring unit 14 is configured as an annular unit. Between the slip rings 18 and 19 which are arranged coaxially and at a radial distance A from one another, the integrated slip ring unit 14 may be provided with an additional insulating partition 30 (see also Fig. 8).

[0052] An insulating system designed in this manner actually has at least two positive effects: Firstly it permits improved insulation by extended spark gaps and/or air gaps and creepage distances, and secondly possible carbon dust deposits in the groove are respectively "loosened" by the brushes and then removed by the centrifugal forces from the slip ring. As a result, a long-term stability of the insulating body is possible.

[0053] By means of this brush-slip ring concept, all necessary functions are implemented in the constructional space which is present, and thus the constructional space neutrality is maintained. Moreover, a flexibility regarding the motor design and adaptation, for example, in the choice of material of the slip rings or the arrangement of the motor windings, is maintained. This freedom of variation permits a rapid reaction to new circumstances in the practice and is thus regarded as a significant advantage.

[0054] The slip rings may be configured as already integrated with the printed circuit board, by the slip rings themselves forming the conductor tracks of the printed circuit board. The printed circuit board and slip rings are in any case integrated by being enclosed by an electrically insulating plastic injection- molding which additionally increases the spark gap and/or air gap and creepage distance and improves the rigidity of the slip ring unit 14.

[0055] In a particular embodiment of the invention, the plastics partition 30 may be constructed between the slip rings 18 and 19 (Fig. 8) to be sufficiently high that it cooperates with a corresponding groove (visible in Fig. 6) of the integrated brush unit 16 and thus effects full screening of the two brushes 15 relative to one another in the event of contact with the slip ring 18 or 19. In a technical reversal, the brush body could have a corresponding projection, which runs with an annular groove in the insulating partition 30 between the slip rings 18 and 19 without any friction. Optionally, additional material preventing breakdown may be filled into the material of the insulating partition 30.

[0056] The operating principle of the axial brushes 15 and the slip rings 18 and 19 is based on minimizing the wear by enhanced sliding properties, and by the choice of a proper material pairing to restrict the wear which may possibly arise on the brushes 15, as the brushes, in contrast to the slip ring unit, are designed to be easily replaceable and thus consciously "sacrificed" as wearing components of the system. [0057] According to the present invention, however, an axial arrangement of the brushes 15 is proposed (Figures 1 and 3). According to Figure 3, each of the two axial and fixed brushes 15 parallel to one another is held non-positively in frictional contact with each of the slip rings 18 and 19 of the rotating integrated slip ring unit 14 through each of the grooves 21 and 22. In Fig. 3 it is also illustrated that in this arrangement carbon dust from the integrated slip ring unit 14 is always flung away radially by the high number of revolutions.

[0058] The carbon brushes are currently available in very different designs. By the use of a standard / industrialized unit, the brush is already pre-dimensioned with the tension spring and (paper) insulation (not shown) and is available in a cylindrical construction. It is necessary to position the individual brushes correctly on the slip ring in the axial direction (tangentially to the slip ring) and to carry out as easily as possible their electrical connection to an energizer voltage source. On the other hand, after a long period of operation it is possibly necessary to undertake a replacement of the brushes due to wear.

[0059] In Figures 4-7 a preferred embodiment of the integrated brush unit 16 according to the invention may be seen. This integrated brush unit 16 is configured as a replaceable unit. It consists of an insulating housing 24, preferably made of plastics, which is provided with two brushes 15, for example carbon brushes. The housing 24 (Fig. 4) is provided with a removable cover 25 which is fixed by screws 26 to the housing 24 after inserting or changing at least one of the brushes 15. The integrated brush unit 16 is provided with further screws 27 which are used for fastening the brush unit 16 in its axially set and/or oriented position relative to the slip ring unit 14, for example in a recess (not shown) of the bearing shield 1 1 . The integrated brush unit 16 may thus as a whole be easily and rapidly replaced when the brushes 15 are worn.

[0060] For connection and replace-ability of the integrated brush unit 16 a plug connection is provided by which the integrated brush unit 16 may be easily connected electrically to the energizing current supply. As shown in Figures 5- 7, for this plug connection two plug contacts 31 are provided on the housing 24 and, on the other hand, on a contact element 32. The housing 24 may be easily removed from the contact element 32 in order to disconnect the plug contacts 31 .

[0061 ] For the different applications, various brush materials are available. The brushes 15 are optionally made of precious (noble) metals (and the alloys thereof) only where there are higher requirements for contact materials. If, however, high temperatures and increased mechanical loads are to be expected relative to the brush speed, such as for example in electric motors for main drives of electric vehicles, then carbon materials (for example hard carbon, carbon graphite, special graphite, electro-graphite, metal graphite, etc.) are used.

[0062] The choice of brush material is, however, closely linked to the choice of material for the slip rings 18-19. For example the carbon of the brush 15 - with a copper graphite pairing - diffuses into the oxidized surface of the copper slip rings and both harden and lubricate at that point, which also has to be taken into account as a positive effect.

[0063] In order to restrict wear of the brush-slip ring system 2 according to the invention, as far as possible exclusively to the wear of the brushes, materials are available for the slip rings 18-19, namely for example a slip ring can be made of Cu or Cu alloys, CuZn, CuSn, Ag or Ag alloys, Au or Au alloys, steel and/or a coating of Ni or Co or galvanized Au layer.

[0064] By bench testing-cyclic testing it has been shown, that the material pairings proposed for the rotor current transmission with the axial brush 15 and slip ring 18-19 are excellent. Thus two material pairings are preferred:

^• The preferred electrical material pairing is: C72/CuAg0.1 (brush/slip ring); · The preferred mechanical material pairing is regarded as E43/CuSn10, i.e. the brushes 15 are made from electro-graphite Έ43" and the slip rings 18- 19 from CuSnI O (Copper-Tin).

[0065] Both the choice of materials and the dimensioning of the brushes 15 and the slip rings 18-19 require great experience in this field. Due to the critical, generally contradictory influence of many parameters, primarily often only estimation thereof is possible. Due to our longstanding experience, however, several parameters have been combined by means of which an inventive design was able to be implemented.

[0066] One of these parameters is the current density in the brush 15. In the known manner, in addition to the limitation by electrical overload, also a lower limit of the current density has to be maintained in order to keep the wear of the brush 15 to a minimum. In an electro-graphite brush 15, the current density in our tests was between 4.0 - 16.0 [A/cm²], with brief overload at 30.0 [A cm²] . This brush 15 provided very good results specifically at high slip ring speeds (at about 88.0 - 96.0 m/s).

[0067] A second, but also important criterion for the dimensioning is the temperature. Due to the mechanical friction between the brush and slip ring and the loss of electrical power due to the resistance in the brush, increased temperatures are produced directly on the brush. The effects of the temperature on the wear behavior are very complex. It may be established that - after our test results - a temperature range of 60 - 90°C is a preferred range. Thus a suitable formation of the oxidized layer is ensured which in turn may be seen as important feature for the relatively low wear of the brushes 15.

[0068] Heat is introduced over the brush surface into the slip ring, which has to be discharged again over the remaining annular surface, in order to remain in thermal balance. Thus our goal was also to keep the brush surface as small as possible in comparison with the remaining slip ring surface. Due to the low energizing power, the cross-sectional surface of the axial brushes 15 (see Fig. 1 ) may be kept very small. [0069] In Fig. 1 , a junction box 28 for electrical safety components and external power supply and an electrical connection element 29 between the integrated brush unit 16 and the junction box 28 are only shown schematically by dotted lines. [0070] In summary, it should be noted that by means of the brush-slip ring system 2 according to the invention at least the following advantages may be achieved:

• Continuous and fault-free signal or current transmission with high dynamic response even with current-energized synchronous motors at high rotational speed;

• Constructional space neutrality, i.e. compatibility with regard to external motor geometry for different types of electric motors;

• Compact construction and minimal overall length with an axial brush position (see e.g. the use of the hollow space below and/or inside the stator winding heads 10 in Fig. 1 );

• Possibility of reliably fastening the integrated slip ring unit 14 on the front face of the rotor;

• Compact and easily replaceable integrated brush unit 16 with electrical plug connection;

• Flexibility with regard to the motor design and adaptation in the choice of material of the slip rings 18 and 19 and the brushes 15, and the arrangement of the motor windings;

• Continuous and direct current transmission, in particular in vehicle drives; · Possibility to reduce the diameter of the motor and the brush speed which leads to reduced wear.

[0071 ] This invention is naturally not limited to the disclosed exemplary embodiment. Further embodiments and combinations are also conceivable within the claimed scope of the invention according to the attached claims on the basis of the present disclosure.

[0072] LIST OF REFERENCE CHARACTERS:

1 Current-energized synchronous motor / electric rotary machine

2 Brush-slip ring system

3 Stator Rotor

Support ring

Laminated rotor core

Winding head

Laminated stator core

Screw

Stator winding

Bearing shield

Rotor shaft

Rotational axis

Integrated slip ring unit

Brush

Integrated brush unit

Printed circuit board

Slip ring

Casing / plastic injection-molding

Groove

Bore

Housing

Cover

Screw

Junction box

Connection element

Insulating partition

Plug contact

Contact element

Claims

C L A I M S

A brush-slip ring system for electrical rotary machines, in particular current- energized synchronous motors having a rotor (4) and a fixed part, e.g. stator

(3) associated with said rotor; said brush-slip ring system (2) comprising slip rings (18, 19) fastened to the rotor (4) and brushes (15) arranged in said fixed part of the machine; wherein each of said brushes (15) is connected to each of the slip rings (18, 19) in a sliding frictional connection so as to transmit energizing current to windings of the rotor (4); said slip rings (18, 19) are disposed on a printed circuit board (17) and are arranged coaxially and radially spaced apart from one another; and said brushes (15) are oriented in axial direction of the rotor (4), characterized in that the slip rings (18, 19) and the printed circuit board (17) of said brush- slip ring system (2) are integrated by an insulating casing (20) to form an integrated slip ring unit (14), and in that the integrated slip ring unit (14) is co-rotatably fastened to a face of the rotor (4).

The brush-slip ring system as claimed in claim 1 , wherein the printed circuit board (17) of the integrated slip ring unit (14) comprises contacts and/or conductor tracks being connected with poles aligned, on the one hand, to rotor windings and, on the other hand, to the slip rings (18, 19).

The brush-slip ring system as claimed in claim 1 or 2, wherein the integrated slip ring unit (14) is fastened to the front face of the rotor

(4) by means of a support ring

(5) protecting the winding heads (7) of the rotor (4).

The brush-slip ring system as claimed in any one of claims 1 to 3, wherein the integrated slip ring unit (14) has an annular disc-shaped configuration.

The brush-slip ring system as claimed in any one of claims 1 to 4, wherein a radial spacing (A) between the coaxial slip rings (18, 19) of the integrated slip ring unit (14) is provided, into which an additional electrical insulating partition (30) is located.

6. The bush-slip ring system as claimed in any one of claims 1 to 5, wherein the insulating casing (20) of the integrated slip ring unit (14) is formed by plastic injection-molding.

7. The brush-slip ring system as claimed in any one of claims 1 to 6, wherein the axial oriented brushes (15) are integrated into a common housing (24) to form an integrated brush unit (16).

8. The brush-slip ring system as claimed in claim 7, wherein the integrated brush unit (16) is formed to be replaceable as a single module.

9. The brush-slip ring system as claimed in claim 7 or 8, wherein the integrated brush unit (16) is provided with an electrical plug connection (31 , 32) for connection to an energizing current source.

10. The brush-slip ring system as claimed in any one of claims 1 to 9, wherein the axial brushes (15) consist of electro-graphite Έ43".

1 1 . The brush-slip ring system as claimed in any one of claims 1 to 10, wherein the slip rings (18, 19) of the integrated slip ring unit (14) consist of CuSnI O (copper-tin-alloy).

12. The brush-slip ring system as claimed in any one of claims 1 to 1 1 , wherein the brush-slip ring system (2) is formed to be installed into an installation space of the current-energized synchronous motor (1 ), which is defined axially by a support ring (5) of the rotor (4) and a bearing shield (1 1 ) of the synchronous motor (1 ), and radially by said bearing shield (1 1 ) and heads of stator windings (10).

13. An electric motor brush and slip ring system comprising:

a rotor, said rotor having windings thereon, said rotor having an end face;

said windings having winding heads;

a support ring connected to said rotor end face, said support ring configured to protect said winding heads; an integrated slip ring unit connected to said support ring, said

integrated slip ring unit having an insulating casing, said insulating casing having an annular disc-shaped configuration;

a circuit board arrangement located in said insulating casing, said circuit board arrangement having electrical connections to said windings;

a first slip ring electrically connected to said circuit board arrangement, said first slip ring forming the bottom of a first annular radial track in said insulating casing;

a second slip ring electrically connected to said circuit board

arrangement, said second slip ring forming the bottom of a second annular radial track in said insulating casing;

said first annular radial track being concentric with and radially spaced from said second annular radial track by a radial spacing;

a bearing shield, said bearing shield being operationally associated with a rotor shaft;

an installation space defined between said bearing shield and said support ring, said installation space being further delineated by stator winding heads;

a modular integrated brush assembly mounted in said installation space; said modular integrated brush assembly including a housing, said housing having a forward end wall, said forward end wall having two holes, and said housing having two holes therethrough, each of said two housing holes respectively terminating at an associated respective one of said two end wall holes;

a rear end wall on said modular integrated brush assembly, said rear end wall situated opposite to said forward end wall;

an intermediate wall extending from said housing, said intermediate wall located between said forward and rear end walls; an electrical plug connection configured to connect to an energizing current source, said electrical plug connection including plural plug contacts extending from said intermediate wall;

a first cylindrical brush unit located in a first one of said housing holes, said first cylindrical brush unit's end extending through and beyond the associated respective end wall hole of said first housing hole;

a second cylindrical brush unit located in a second one of said housing holes, said second cylindrical brush unit's end extending through and beyond the associated respective end wall hole of said second housing hole;

said first cylindrical brush unit end having a first brush shoe, said first brush shoe riding in said first annular radial track in spring-loaded frictional contact with said first slip ring;

said second cylindrical brush unit end having a second brush shoe, said second brush shoe riding in said second annular radial track in spring-loaded frictional contact with said second slip ring;

a groove in said forward end wall of said modular integrated brush assembly; and,

an insulating radial partition located on said insulated casing in said radial spacing between said first annular radial track and said second annular radial track, said insulating radial partition situated as a rail riding in said groove and separating said first cylindrical brush unit from said second cylindrical brush unit.

14. An electric motor brush and slip ring system comprising:

a rotor, said rotor having windings thereon, said rotor having an end face;

said windings having winding heads;

a second slip ring electrically connected to said circuit board

an insulating radial partition located on said insulated casing in said radial spacing between said first annular radial track and said second annular radial track;

a bearing shield, said bearing shield being operationally associated with a rotor shaft; an installation space defined between said bearing shield and said support ring;

a first cylindrical brush unit located in a first one of said housing holes, said first cylindrical brush unit's end extending through and beyond the associated respective end wall hole of said first housing hole; a second cylindrical brush unit located in a second one of said housing holes, said second cylindrical brush unit's end extending through and beyond the associated respective end wall hole of said second housing hole;

said first cylindrical brush unit end having a first brush shoe, said first brush shoe riding in said first annular radial track in spring-loaded frictional contact with said first slip ring; and,

said second cylindrical brush unit end having a second brush shoe, said second brush shoe riding in said second annular radial track in spring-loaded frictional contact with said first slip ring.

15. An electric motor brush and slip ring system as claimed in claim 14, further comprising:

an electrical plug connection configured to connect to an energizing current source, said electrical plug connection located on said modular integrated brush assembly.

16. An electric motor brush and slip ring system as claimed in claim 15, further comprising: a rear end wall on said modular integrated brush assembly, said rear end wall situated opposite to said forward end wall;

an intermediate wall extending from said housing, said intermediate wall located between said forward and rear end walls; and,

said electrical plug connection includes plural plug contacts extending from said intermediate wall.

17. An electric motor brush and slip ring system as claimed in claim 14, further comprising: a groove-rail interfitting between said forward end wall of said modular integrated brush assembly and said insulating radial partition.

18. An electric motor brush and slip ring system as claimed in claim 17, further comprising: a groove in said forward end wall of said modular integrated brush assembly; and,

said insulating radial partition situated as a rail riding in said groove to separate said first cylindrical brush unit from said second cylindrical brush unit.

19. An electric motor brush and slip ring system as claimed in claim 14, further comprising:

stator winding heads further delineating said installation space.

20. The electric motor brush and slip ring system as claimed in claim 14, wherein:

said slip-rings are made of material selected from the group consisting of Cu, Cu alloys, CuZn, CuSn, Ag, Ag alloys, Au, Au alloys, and steel.

21 . The electric motor brush and slip ring system as claimed in claim 14, wherein:

said slip rings have a coating layer made of material selected from the group consisting of Ni, Co, and galvanized Au.

22. The electric motor brush and slip-ring system as claimed in claim 14, wherein: said brush shoes are made of electro-graphite.

23. The electric motor brush and slip ring system as claimed in claim 14, wherein:

said brush shoes and slip rings are made of C72 and CuAgO.1 , respectively.

24. The electric motor brush and slip ring system as claimed in claim 14, wherein:

said brush shoes and slip rings are made of E43 and CuSnI O, respectively.

25. The electric motor brush and slip ring system as claimed in claim 14, wherein:

said insulating casing is made of injection-molded plastic.

26. An electric motor brush and slip ring system comprising:

a rotor;

a stator operationally associated with said rotor;

slip rings, said slip rings being electrically connected to a circuit board, said slip rings being mutually coaxial and radially spaced apart from one another;

a plurality of brushes mounted to said motor, said plurality of brushes mounted on at least one fixed part of the motor, each one of said plurality of brushes being in electrical connection with and sliding frictional contact with a respective slip ring to conduct energizing current to windings of said rotor, said brushes being oriented in an axial direction of said rotor; and,

an insulating casing, said insulating casing integrating said slip rings and said circuit board in mechanical assembly to form an integrated slip ring unit, said integrated slip ring unit being fastened to a rotor face so as to rotate with said rotor.

27. An electric motor brush and slip ring system as claimed in claim 26, further comprising: said integrated slip ring unit including electrical conductors between said windings of said rotor and said slip rings.

28. An electric motor brush and slip ring system as claimed in claim 26, further comprising:

a support ring, said support ring configured to protect winding heads of said rotor, and said integrated slip ring unit being fastened to a front face of said rotor by said support ring.

29. An electric motor brush and slip ring system as claimed in claim 28, further comprising:

an installation space in said electric motor, said installation space receiving said brushes and said slip rings, said installation space being delineated by said support ring and by a bearing shield of said motor, said installation space being additionally delineated by stator winding heads.

30. The electric motor brush and slip ring system as claimed in claim 26, wherein:

said integrated slip ring unit has an annular disc-shaped configuration.

31 . An electric motor brush and slip ring system as claimed in claim 26, further comprising: an insulating partition situated at a radial spacing between said coaxial slip rings.

32. An electric motor brush and slip ring system as claimed in claim 26, further comprising: a modular integrated brush assembly, said modular integrated brush assembly having a common housing that integrates said plurality of brushes.