Abstract
An electrical device comprises a stack of electric elements, each comprising: an electrically insulating substrate, for instance of plastic, and at least one electrically conductive track connected to said substrate; the end zones of each of which tracks have terminals either for connection to a source of electrical energy, whereby electric current is conducted through each track during operation, or connection to a device for taking off electric current generated by magnetic induction in the track; which electric elements are connected mechanically to each other such that the device is unitary.
Claims
1. An electrical device comprising a stack of electric elements, each comprising: an electrically insulating substrate and at least one electrically conductive track connected to said substrate; the end zones of each of which tracks have terminals either for connection to a source of electrical energy, whereby electric current is conducted through each track during operation, or connection to a device for taking off electric current generated by magnetic induction in the track; which electric elements are connected mechanically to each other such that the device is unitary; wherein: the terminals of each of the at least one electrically conductive track are arranged to be connected selectively in parallel or in series by an external switching device; the device comprises a coil assembled from winding having electrically the same orientation, and the tracks comprise electrically conductive material and each winding extends in loop-form between two end zones; wherein each element has a registered and uniform through-hole present inside the or each loop, these registered and uniform through-holes forming a channel in which a fixed or longitudinally movable ferromagnetic core is present which co-acts with the windings; the core comprises grains of ferromagnetic material embedded in a plastic; and the grains are substantially spherical and a number of classes of grains of different grain size are premixed in accordance with a Gaussian distribution during production in a manner such that the interstitial spaces between relatively large grains are filled for a major part with relatively small grains such that the available space is occupied to a minimum of 90% by grains of ferromagnetic material.
2. The device as claimed in claim 1, wherein each substrate consists of a thermoplastic and the electrical elements are adhered to each other by welding the substrates of mutually adjacent electrical elements to each other by fusion through temperature increase to the softening temperature of the plastic.
3. The device as claimed in claim 1, wherein each substrate consists of a thermoplastic and the electrical elements are adhered to each other by evaporating solvent in which the plastic was present prior to the manufacture of the device by increasing temperature.
4. The device as claimed in claim 1, wherein the core forms part of a closed ferromagnetic circuit, wherein the end zones of the core outside the area of the coil are connected to each other by a ferromagnetic bridge.
5. The device as claimed in claim 4, wherein the core with the bridge is embodied divided into at least two parts, and during assembly of the device the whole core or at least the first part of the core with the part of the bridge connected thereto or forming a whole therewith is first inserted into the channel and the remaining part of the bridge with optionally the second part of the core is then connected tightly thereto.
6. An electric motor, comprising: an electrical device comprising a stack of electric elements, each comprising: an electrically insulating substrate and at least one electrically conductive track connected to said substrate; the end zones of each of which tracks have terminals either for connection to a source of electrical energy, whereby electric current is conducted through each track during operation, or connection to a device for taking off electric current generated by magnetic induction in the track; which electric elements are connected mechanically to each other such that the device is unitary; wherein: the terminals of each of the at least one electrically conductive track are arranged to be connected selectively in parallel or in series by an external switching device; the device comprises a coil assembled from winding having electrically the same orientation, and the tracks comprise electrically conductive material and each winding extends in loop-form between two end zones; and each element has a registered and uniform through-hole present inside the or each loop, these registered and uniform through-holes forming a channel in which a fixed or longitudinally movable ferromagnetic core is present which co-acts with the windings; a stator with an annular collar of electromagnets; an electronic power supply and control unit for conducting electric currents through the electromagnets such that they together effectively generate a rotating magnetic field; and a rotor with at least one ferromagnetic element which co-acts magnetically with the magnetic fields generated by the electromagnets; such that the rotor is driven rotatingly by the rotating magnetic field, wherein under the control of the power supply and control unit the starting torque of the rotor is temporarily increased during starting thereof by temporarily connecting in parallel the coils of two or more adjacent devices.
7. The electric motor as claimed in claim 6 operatively associated with one of a rotary actuator, a motor, a clutch between two axially aligned rotatable shafts, an adjustable transmission, a stirring device.
8. An adjustable clutch between two shafts which are disposed axially aligned for rotation relative to a frame, the clutch comprising: a first clutch disc carried by the one shaft with: an annular collar of electromagnets comprising a stack of electric elements, each comprising: an electrically insulating substrate and at least one electrically conductive track connected to said substrate; the end zones of each of which tracks have terminals either for connection to a source of electrical energy, whereby electric current is conducted through each track during operation, or connection to a device for taking off electric current generated by magnetic induction in the track; which electric elements are connected mechanically to each other such that the device is unitary; wherein: the terminals of each of the at least one electrically conductive track are arranged to be connected selectively in parallel or in series by an external switching device; the device comprises a coil assembled from winding having electrically the same orientation, and the tracks comprise electrically conductive material and each winding extends in loop-form between two end zones; and each element has a registered and uniform through-hole present inside the or each loop, these registered and uniform through-holes forming a channel in which a fixed or longitudinally movable ferromagnetic core is present which co-acts with the windings; a stator with an annular collar of electromagnets; an electronic power supply and control unit for conducting electric currents through the electromagnets such that they together effectively generate a rotating magnetic field; a rotor with at least one ferromagnetic element which co-acts magnetically with the magnetic fields generated by the electromagnets; such that the rotor is driven rotatingly by the rotating magnetic field; the electromagnets being carried on the free end surface of the clutch disc; and a secondary section of a rotary transformer, a primary section of which is disposed fixedly relative to the frame, which secondary section is connected to the electromagnets for actuation thereof; and a second clutch disc which is carried by the other shaft and the free end surface of which carries a number of ferromagnetic elements corresponding to the number of electromagnets of the first clutch disc for magnetic co-action with said electromagnets when these are actuated via the rotary transformer by an adjustable, at least on and off switchable, external source of alternating current.
9. The clutch as claimed in claim 8, wherein: cores of the electromagnets are embodied as permanent magnets; coils of the electromagnets are connected via rectifier means to the secondary section of the rotary transformer; such that: when the electromagnets are not actuated, these electromagnets co-act with the ferromagnetic elements and the shafts are forced to rotate together; and when the electromagnets are actuated by the external source of alternating current the magnetization of the cores is reduced to a value of at least approximately zero and the magnetic coaction between the electromagnets and the ferromagnetic elements is disabled and the shafts can rotate independently of each other.
10. The clutch as claimed in claim 8, wherein the number of active electromagnets can be adjusted under the control of the electronic unit in a manner such that the active electromagnets are distributed individually or in groups angularly equidistant over the collar such that the clutch also operates as transmission with adjustable transmission ratio.
Description
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
(1) The invention will now be elucidated with reference to the accompanying drawings. In the drawings:
(2) FIG. 1 shows a ferromagnetic core of an electromagnet;
(3) FIG. 2 shows a coil assembled from stacked electrically insulating substrates with electrically conductive tracks for co-action with the ferromagnetic core according to FIG. 1;
(4) FIG. 3 shows a view corresponding to FIG. 2 of the assembly of the core according to FIG. 1 with the coil according to FIG. 2;
(5) FIG. 4 shows an end view of an embodiment in which the terminals of the conductive tracks are connected in parallel;
(6) FIG. 5 shows a view corresponding to FIG. 4 of a variant in which the terminals of the tracks are all connected in series;
(7) FIG. 6 shows a schematic representation of the statistical grain size distribution when three grain size classes of ferromagnetic grains are used for the assembly of for instance the core according to FIG. 1;
(8) FIG. 7 shows a view corresponding to FIG. 1 of a ferromagnetic core of an electromagnet which comprises through-holes intended for passage of medium for cooling purposes;
(9) FIG. 8 shows a view corresponding to FIG. 2 of a coil assembled from stacked electrically insulating substrates with electrically conductive tracks and likewise provided with continuous cooling channels;
(10) FIG. 9 shows a view corresponding to FIGS. 2 and 8 of a variant in which the conductive tracks extend over the whole of the relevant surfaces of the substrates and the number of cooling channels is increased relative to the embodiment according to FIG. 8;
(11) FIG. 10 shows a structure of substrates with conductors zigzag foldable in concertina manner and thus stackable for the purpose of manufacturing a stack of windings;
(12) FIG. 11 shows a view corresponding to FIGS. 2, 8 and 9 of an embodiment obtained with the structure according to FIG. 10;
(13) FIG. 12 shows a top view of an elongate plastic substrate embodied as foil on which a number of electrically conductive tracks are arranged, the end zones of which are connected to each other and to two terminals;
(14) FIG. 13 shows a perspective view of a coil obtained by wrapping of the substrate with conductors according to FIG. 12;
(15) FIG. 14 shows a top view of a substrate with two windings which are connected to each other in series;
(16) FIG. 15 shows a structure of substrates with conductors zigzag foldable in concertina manner and thus stackable for the purpose of manufacturing a stack of windings;
(17) FIG. 16 shows an end view of an embodiment of a coil with a through-hole obtained with the structure according to FIG. 15;
(18) FIG. 17 shows a stack of foil-like substrates on which tracks of resistance material are present which are provided with perforations, in addition to a heat pipe construction for discharging the heat from the tracks of resistance material;
(19) FIG. 18 shows the detail XVIII on larger scale;
(20) FIG. 19 shows a schematic view of a transformer with a largely oval-shaped magnetic circuit and two coils;
(21) FIG. 20 shows the cross-section XX-XX according to FIG. 19;
(22) FIG. 21 shows the cross-section XXI-XXI according to FIG. 22 of a more less apple-shaped transformer according to the invention with a heat pipe system for discharging heat;
(23) FIG. 22 shows the section XXII-XXII according to FIG. 21;
(24) FIG. 23 shows a cross-section through a loudspeaker according to the invention;
(25) FIG. 24 shows the view XXIV-XXIV according to FIG. 23 of the motor system of the loudspeaker according to FIG. 23;
(26) FIG. 25 shows a cross-section through a stirring device in a first embodiment;
(27) FIG. 26 shows a cross-section corresponding to FIG. 25 through a stirring device in a second exemplary embodiment;
(28) FIG. 27 shows a cross-section through an adjustable electromagnetic clutch according to the invention in a first embodiment;
(29) FIG. 28 shows a cross-section corresponding to FIG. 27 through an adjustable clutch in a second embodiment.
DETAILED DESCRIPTION
(30) FIG. 1 shows a core 69 as component of an electromagnet 26, 27. The core is for instance embodied as a granular and/or powder-form ferromagnetic material, for instance niobium, iron, ferrite or the like, embedded in polyetherimide.
(31) FIG. 2 shows a coil 29 comprising a stack of thin printed circuit boards or foils 72, for instance with a thickness in the order of a maximum of 0.1 mm, in which is present a through-hole 70 around which extends a loop-like copper track 71. Printed circuit boards 72 are stacked onto each other in the manner shown in FIG. 2 such that the free terminals 73, 74 of copper track 71 can all come into contact with two electrical conductors 75, 76. Core 69 fits into the through-hole in the stack of printed circuit boards 72. An electromagnet 26, 27 is in this way realized.
(32) FIG. 3 shows an electromagnet assembled from coil 29 according to FIG. 2 and core 69 according to FIG. 1. Reference numeral 24 designates the upper pole. Reference numeral 1 designates the lower pole which takes a plate-like form.
(33) FIG. 4 shows that in this embodiment terminals 73, 74 are all connected in parallel and are connected to the respective electrical conductors 75 and 76.
(34) In the embodiment according to FIG. 5 terminals 73, 74 of the adjacent winding elements are connected alternately to each other, whereby the copper tracks 71 forming the windings are connected to each other in series.
(35) FIG. 6 is a graph showing the relative number of particles in three types of commercially available ferromagnetic powders, the grains of which are spherical. As discussed above, for the purpose of the best possible utilization of the available space in a mould the powders are added, by way of example in the proportions shown in FIG. 6, to polyetherimide absorbed in a solvent and mixed intimately therein. A ferromagnetic dough is hereby obtained which is introduced into a mould of the desired form in order to manufacture for instance a core 69 as according to FIG. 1. In the example according to FIG. 6 three types of powder are used having respectively an average grain size of 100 m, one of 50 m in a smaller proportion and one of 25 m in an even smaller proportion. The main constituent is formed by the portion of the powder with a grain size of an average of 100 m, while the rest of the grains are distributed statistically in accordance with the shown Gaussian curves. Stacking of the grains of 100 m type leaves interstitial spaces which are then filled as far as possible by the grains of 50 m category. The then still remaining interstitial cavities are then further filled, i.e. with the grains in the 25 m category. Through this mixing an aggregate is obtained with a filling varying little from 100%. Filling ratios of a minimum of 95% can in this way be realized. The ferromagnetic core obtained in this way thus has the properties of the solid ferromagnetic material. However, because it is incorporated as grains in the insulated plastic, the occurrence of eddy currents is precluded.
(36) FIG. 7 shows a ferromagnetic core 96 with the same general form as core 69 according to FIG. 1. Core 96 differs from core 69 in the presence of continuous channels 97. Cooling medium can be guided through channels 97. The increase in temperature of core 96 during operation can hereby remain limited to a chosen maximum value.
(37) FIG. 8 shows a coil 98 which, like coil 29 (FIG. 2), comprises a stack of winding elements which each consist of an electrically insulating substrate and a loop-like conductor, for instance of copper, aluminium or other suitable material, present thereon. Situated in the four corner zones of each winding element 100 is a through-hole 99. These holes 99 are registered in coil 98, which comprises a stack of winding elements 100, and thus form four continuous cooling channels through which cooling medium can be guided for the purpose of cooling coil 98.
(38) The conductive loop-like tracks 71 are situated around the registered through-holes 70 into which, as in the embodiment according to FIGS. 1, 2, the ferromagnetic core 96 fits.
(39) FIG. 9 shows a coil 102 which differs from coils 29 according to FIGS. 2 and 98 as according to FIG. 8 in the sense that the whole surface on one side of the electrically insulating substrate is provided with an electrically conductive layer, for instance of copper. Extending in this embodiment through both layers are ten cooling channels, all designated 101 here for the sake of convenience. The degree of cooling can hereby be substantially improved. It will be apparent that it is necessary to ensure in both the embodiment according to FIG. 8 and the embodiment according to FIG. 9 that the medium flowing through the cooling channels may only be in thermally conductive contact with the winding elements and that the cooling medium must be electrically separated therefrom. The cooling medium can optionally be guided via tubes through channels 97, which are formed by the registered holes 99, and the channels 101. It is for instance possible to envisage thermally conductive tubes, for instance of copper, provided on their outer side with an electrically insulating coating, for instance of polyetherimide.
(40) FIG. 10 shows schematically a strip of winding elements, all designated 7 and mutually connected via hinge zones 103. These elements can be laid on each other pivoting zigzag-wise in the manner indicated schematically with arrows 105. A stack 106 according to FIG. 11 can hereby be formed which corresponds functionally to coil 29 according to FIG. 2.
(41) FIG. 12 shows a strip of foil material 2 on which a number of copper tracks 3 extend. At their end zones these tracks are mutually interconnected and also connected to external terminals 4, 5. The foil material can advantageously be polyetherimide, just as the printed circuit boards or substrates 72 according to FIGS. 2, 3, 4 and 5. Strip 2 need only have a thickness such that its mechanical integrity is ensured during the production process, while it is also necessary to ensure that during winding up of strip 2 to form the coil 6 shown in FIG. 13 the electric voltage between adjacent conductive tracks remains below the breakdown voltage of the polyetherimide foil.
(42) FIG. 14 shows a polyetherimide substrate 7 which, just as substrates 72 according to FIGS. 2, 3, 4 and 5, has a rectangular form. Other than substrates 72, substrate 7 carries two more or less concentrically placed, generally oval or loop-like copper tracks 8, 9, and tracks 8, 9 are connected in series between terminals 11, 12 by means of an external interconnection 10.
(43) FIG. 15 shows schematically a strip of winding elements, all designated 7 and mutually connected via hinge zones 103. These elements 7 can be laid on each other pivoting zigzag-wise in the manner indicated schematically with arrows 105. A stack 13 of substrates 7 according to FIG. 16 can hereby be formed. A coil is then hereby realized wherein each coil element 7, 8, 9 comprises two windings.
(44) FIG. 17 shows a stack 14 of rectangular polyimide substrates 15 with tracks 16 of resistance material extending in zigzag manner. The tracks are widened locally and provided at the position of each widening with a through-hole 17 which is clearly shown particularly in FIG. 18. All substrates 15 with tracks 16 and holes 17 are given an identical form and placed in register with each other such that channels (not shown) extend through stack 14. Tubes 18, which are closed on the underside, of a grid-like arrangement with manifolds 18 are inserted as according to an arrow 20 into these channels. Tubes 18 fit tightly into holes 17 and have on their surface a very thin coating of polyetherimide. Tubes 18, which take a very thin-walled form and consist of copper, are hereby only in thermal contact with the tracks of resistance material 16 and are electrically insulated therefrom. During passage of electric current via terminals 21, 22 through the tracks 16 connected in parallel the tracks 16 are heated, and tubes 18 are hereby heated. Tubes 18 are filled with a two-phase medium consisting partially of liquid and partially of vapour. Tubes 18 thus operate as heat pipes. These are able to transport heat with a very high coefficient of thermal conduction to the central manifold 23 which transports the heat, in a manner which is per se known and therefore not drawn and elucidated, to a location where it has to be used.
(45) Attention is duly drawn to the fact that all through-holes in the stacks of substrates according to FIGS. 2, 3, 4, 5, 8, 14, 15, 16 are exactly in register with each other, whereby a core, a heat discharge element or the like can be inserted into the thus continuous holes or channels.
(46) FIG. 19 shows a transformer 32 with a primary coil 30 and a secondary coil 31, which coils are of the type according to FIG. 2, FIG. 8, a type with coils consisting of winding elements as according to FIG. 14, or the like, wherein as in all shown exemplary embodiments the through-hole is prismatic, i.e. has the same cross-section throughout. In this embodiment the hole is round as shown in FIG. 20. A ferromagnetic core 32 extends in the prismatic holes of primary coil 30 and secondary coil 31 and a ferromagnetic core 33 extends in the through-hole of secondary coil 31. Outside the area of windings 30, 31 the cores are mutually interconnected by means of two semi-toroidal bridges 34, 35, likewise of ferromagnetic material, which for instance form part of two respective ferromagnetic units comprising both a part of the cores and a bridge.
(47) Cores 32, 33 and bridges 34, 35 consist of ferromagnetic material of the type described above, i.e. on the basis of an aggregate of three types of ferromagnetic powders of differing grain sizes embedded in plastic.
(48) The terminals of coils 30, 31 are designated respectively 36, 37 and 38, 39.
(49) FIGS. 21 and 22 show a highly advanced transformer 40 with a primary coil 30 and a secondary coil 31 which in this embodiment form part of one stack 41 of substrates 42.
(50) The prismatic core 43 with bridge 45 is embodied divided into two parts. During assembly of the transformer the first part of core 43 with the part of bridge 45 forming a whole therewith is first inserted into the continuous prismatic channel in stack 41, and the remaining part of core 43 with the second part of bridge 45 connecting tightly thereto is then connected.
(51) As shown clearly in FIGS. 21 and 22, bridge 45 is rotation-symmetrical and the transformer 40 has a generally spherical shape.
(52) As will however be apparent from FIG. 21, transformer 40 does not have an ideal spherical shape externally. It is to some extent elongate, while having slight recesses at the poles. There is a technical reason for this shape. In this advanced transformer 40 the overall effective cross-sectional area of bridge 45 through which the magnetic flux flows is substantially equal at each angular position +/90 relative to the equator plane 44 to the cross-sectional area of core 43, whereby the magnetic flux density is substantially equal in each said cross-sectional area.
(53) This structure achieves that the magnetic saturation, should this already be reached, is reached substantially simultaneously at each location. Transformer 40 thereby has the greatest possible magnetic efficiency with a minimum quantity of ferromagnetic material.
(54) During use of the transformer, and certainly when it is loaded close to its limit, it is not possible to avoid some heating taking place. In this respect seven heat pipes 46, which are connected to a manifold 47, extend through the upper pole of bridge 45.
(55) FIG. 23 shows a cross-section through an electrodynamic loudspeaker 48 according to the invention. The loudspeaker comprises a frame 49, a cone 50 suspended in elastically reciprocating manner relative to said frame 49, a voice coil unit 51 which is coupled to cone 50 and which comprises a coil which corresponds functionally to coil 98 according to FIG. 8, and a magnet unit with an annual permanent magnet 52, and a ferromagnetic yoke 53, 54, 55 which defines a cylindrical gap 56 in which a magnetic field prevails under the influence of permanent magnet 52 and in which the voice coil unit 51 is movable reciprocally in axial direction under the influence of the electric alternating currents carried by the coil of the voice coil unit. All yoke parts 53, 54, 55 are embodied in grains of ferromagnetic material embedded in polyetherimide.
(56) Voice coil unit 51 comprises a stack of elements, for instance similar to stack 98 according to FIG. 8, which stack comprises a collar of, in this embodiment, twelve continuous channels 57 for passage of a reciprocating airflow 58 during operation of loudspeaker 48. This airflow has a cooling effect on voice coil unit 51. The ferromagnetic yoke plate 54 likewise has a collar of continuous cooling channels 59 for passage of a reciprocating airflow during operation of loudspeaker 48.
(57) FIG. 24 shows yoke plate 53 and voice coil unit 5 with cooling channels 57.
(58) FIG. 25 shows a stirring device 60. This comprises a support frame 61 carrying an operating unit 62. Connected to operating unit 60 is a central control unit 63 which controls an annular electromagnetic unit 64. This unit 64 comprises a number of electromagnets 65 which are disposed in a collar formation and which all comprise a generally U-shaped core 66 and a coil 67 co-acting therewith. The core is of the type discussed above and is manufactured on the basis of ferromagnetic spherical grains embedded in polyetherimide. Coil 67 is of the above described type according to the invention comprising a stack of substrates with one or more windings thereon. With appropriate control by control unit 63 a rotating magnetic field is generated by electromagnets 65. An elongate ferromagnetic element 77, likewise on the basis of the magnet material according to the invention embedded in a disc 78 of inert material, is hereby set into rotation. Stirring bracket 79 is connected to the disc.
(59) The stirring gear consists of disc 78 with stirring bracket 79. In the presence of the rotating magnetic field the elongate ferromagnetic element 77, and thereby disc 78, will follow this rotation and the stirring bracket is driven in rotation. Stirring gear 77, 78, 79 is situated in a holder 80 in which the substance 81 for stirring is situated. The holder can in principle be of any size.
(60) FIG. 26 shows a stirring device 82 which differs from stirring device 60 according to FIG. 25 in the sense that the electromagnets 65 are smaller and connect at a smaller angular distance to each other.
(61) In this embodiment the stirring gear comprises only a twisted ferromagnetic ribbon 83 modelled in the shape of a ring. The diameter of the ring and the diameter of the collar of electromagnets are roughly equal. The wavelength of the twisted ribbon in this embodiment is about 4 to 5 times greater than the pitch distance of electromagnets 65. The electronic control unit 63 conducts currents through electromagnets 65 during operation such that all lowest zones 84 of ribbon 83 which lie closest to electromagnets 65 all co-act magnetically with electromagnets 65. In the present embodiment the ribbon comprises twelve wavelengths. With a 48-pole stator, i.e. the collar of electromagnets 65, a powerful rotating magnetic field can thus be generated, whereby the ferromagnetic ribbon is rotated effectively and with force through driving via all twelve lowest zones.
(62) FIG. 27 shows an adjustable clutch 85 between two shafts 86, 87 which are disposed axially aligned to each other for rotation relative to a frame (not shown).
(63) The clutch comprises a first clutch disc supported by shaft 86 and having on the free end surface thereof an annular collar of electromagnets 89 according to the invention carried and the secondary section of a rotary transformer, the primary section of which is disposed fixedly relative to the frame, which secondary section is connected to electromagnets 89 for actuation thereof.
(64) The primary section of the rotary transformer comprises an annular collar of electromagnets 90 which are connected to the second clutch disc 93 supported by second shaft 87. In the case where electromagnets 89 are thus actuated, clutch discs 88 and 93, and thereby shafts 86 and 87, are forced to rotate together. When actuation of electromagnets 89 is terminated, this clutch is released and shafts 86 and 87 can rotate independently of each other.
(65) In an alternative embodiment the cores of electromagnets 89 are embodied as powerful permanent magnets, for instance of neodymium. The coils of these electromagnets 89 are connected via rectifiers (not shown) to the secondary electromagnets of rotary transformer 90, 91. The amperage and the strength of the permanent magnets is selected such that, when electromagnets 89 are not actuated, these electromagnets co-act with ferromagnetic elements 92 and the shafts are forced to rotate together and, when electromagnets 89 are actuated by the external source of alternating current, the magnetization of the cores of electromagnets 89 are reduced to a value of substantially zero and the magnetic co-action between electromagnets 89 and ferromagnetic elements 92 is disabled, whereby the shafts can rotate independently of each other.
(66) The number of active electromagnets 89 can be set under the control of an electronic unit, this such that, individually or in groups, the active magnets are distributed angularly equidistant over the collar. The clutch according to FIG. 27 can thus operate as transmission with adjustable transmission ratio.
(67) FIG. 28 shows an embodiment in which clutch 107 is constructed wholly symmetrically from two identical discs 88, 88. Such an embodiment provides a greater degree of freedom of electronic control.
