GB2358523A

GB2358523A - Electronically commutated electrical machine

Info

Publication number: GB2358523A
Application number: GB9930173A
Authority: GB
Inventors: Richard Fletcher
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-12-21
Filing date: 1999-12-21
Publication date: 2001-07-25
Also published as: WO2001047089A3; WO2001047089A2; GB9930173D0; AU2200901A

Abstract

An electronically commutated electrical machine having a rotor 3 interacting with a stator (2) in the form of an armature(s) comprising insulated stip conductors sections 11 interleaved with cores of ferromagnetic material 7 passing between the conductors, the whole bonded together with resin to form a disc(s), magnetic forces between rotor and stator being balanced, the stator being held at edge parts by the housing. Rotor driven air cooling or liquid cooling chambers are disclosed. The clips 10 securing the outer ends of adjacent winding sections act as heat dissipaters. Various arrangements are disclose including cantilevered rotors and anti burst structures. The rotor may comprised permanent magnets or a cage winding.. An alternative embodiment has a single rotor/dual stators.

Description

1 2358523 ELECTRONICALLY COMMUTATED ELECTRICAL MACHINE

This invention relates to electrical machines which convert mechanical energy into electrical energy, or vice versa, by interaction between a magnetic field and an electric current without the use of carbon brushes. Examples of such machines are electric motors, dynamos and alternators.

1. PRIOR ART

Known brushless electrical machines generally have a cylindrical rotor having either permanent magnets in the synchronous form, or conductors and magnetic material in the asynchronous or induction form of the machine.

Machines with a cylindrical rotor generally have a cylindrical stator generating a rotating magnetic flux around the rotor by means of alternating or electronically commutated direct current.

Synchronous machines have some means of sensing the phase angle between: rotor and stator which may entail use of sensors.

Asynchronous machines rely on the induced current in the rotor interacting with the stator's magnetic field.

Such cylindrical machines have the disadvantage that the magnetic flux can enter the rotor only from the outside of the cylinder; there is thus a single air gap between rotor and stator, and the magnetic flux lines into the rotor are curved, indirect and imprecisely located with the result that there may be considerable stray fields and the available magnetic flux may not be used to its best advantagein relation to the active elements in the rotor - whether magnets or conductors.

Further, there are additional losses in the iron of the armature which provides a rotating return path for the magnetic flux through the air gap. Such an arrangement is typically shown in the vacuum cleaner motor of Oberdorfer-Bogel US 5,394,041.

Some of these disadvantages can be overcome by use of a disc rotor with a flat radial airgap and axial flux passing transversely into the disc which provides the magnetic return path and rotates about its principal axis.

This configuration - which may be of the synchronous or asynchronous type - is generally asymmetrical, with the stator coils on one side of the disc as shown by Wang US 5,789,841. This has the following disadvantages.

(1) The very substantial unbalanced magnetic forces on one side of the--. disc require heavy bearings and supporting structure to keep the air gap rea.96n4bly constant throughout the motor's life; also, bearing wear will alter the air gap:

(2) There is only a single air gap and there is some loss of magneticflux density due to leakage from and losses in the magnetic return path in the stator which is usually a: backing plate of ferromagnetic material.

2 In brushed motors with a disc rotor, these disadvantages are overcome in so-called pancake motors in which a thin iron-less conducting armature usually of copper foil runs In a relatively narrow magnetic air gap between two sets of magnets. Because there is no iron in the armature, it must be relatively slender to keep the airgap small, and thus avoid attenuating the magnetic flux, with the result that pancake or ironless motors are viable only in sizes up to about IKW at the most because of the thinness of the conductors.

This limitation in brushed disc motors was overcome commercially in the Lynch disc armature motor GB 2,184,613 and GB 9,326,353 which showed ferromagnetic material passing axially through the armature disc, This has brushes commutating on the edges of the conductor strips. This was a successful new departure in brushed DC motor design which has been licensed, manufactured and used on the world market in C, some quantities since its invention in 1985.

Attempts have also been made to design 'double-sided' cylindrical armatures - eg as in the ironless armature manufactured by Portescap that is, using a hollow cylindrical armature of woven and bonded copper wire, with magnets on both theinside and outside of the cylinder. This is more difficult to construct than a disc and such motors tend to be costly and of low power - a few hundred watts - but, like the pancake motors, have advantages where, for example, low inertia is required.

Pavlovich et al US 5,892,307 (Pr. 7/3/95) show a brusWess motor having as rotor three discs of magnets with two sets of armature coils inserted between them. As there is no iron in the armature this design has the disadvantages of relatively low power output found in pancake motors, referred to above. Also there is no indication as to how the motor is assembled, bearing in mind the potentially large forces between the magnet discs and other magnets or ferromagnetic material.

2. SUMMARY OF THE INVENTION

To overcome the above-stated disadvantages, according to the present invention, the stator acts equally in both axial directions on the rotor in the form of one or more discs, and/or one or more annular rings with the result that there are two, or a multiple of two, air gaps, thus doubling the total available flux as compared with a conventional cylindrical motor and thereby doubling the torque on the rotor and also ensuring that magnetic forces on the rotor are balanced when it is in the central plane of the stator.

The stator comprises conducting windings of one or more turns preferably wave wound with their active elements extending axially from a radially inner region to a radially outer region in more than one plane, interleaved with ferromagnetic material in a form which minin-iises hysteresis losses, such as laminations, compacted or bonded powder. The windings form a fiamework into which the ferromagnetic cores are bonded, eg with resin, to make a rigid assembly which is supported by mounting pads, bonded mounting inserts or brackets, rebates or other means which hold it firmly in relation to the case.

3 In the disc stator the ferromagnetic cores are wedge-shaped and it is important that they have sufficient strength in shear, as is the case with stacks of iron or steel laminations, to hold the two planes of conductors together against the operating forces of the motors. Where powder metal is used in the cores it can be pressed into wedgeshaped pieces of iron lamination in which a single lamination is bent into a V with the powder filling the inner part of the V, to give a composite structure with greater strength than that of powder metal alone which can be quite brittle. This arrangement is cheaper and simpler to make than the alternative comprising stacks of laminations of different lengths made up into wedge-shaped bundles.

Stiffhess of the stator, including the windings which can be of hard copper strips of substantial section in a plane resisting lateral bending forces, is essential to prevent deflection of the armature - of which the strips form a part, under attraction from strong magnetic forces generated by the rotor. As the armature forms the stator in the brushless motor, its construction differs from that of a brushed disc motor in that it is not required to resist centrifugal forces.

The rotor is held accurately in place in the case - eg by use of a laterally locating double angular contact bearing or other suitable means - and the stator is also firmly held so that it is positioned centrally between the two parts of the rotor, thus providing substantially equal air gaps.

Means are provided to cool the stator, by blowing air through the air gap by means of centrifugal forces developed by viscous air drag and/or fins on the rotor or by a separate fan or blower, or by liquid cooling of the stator conductor end-windings.

Where heat transfer by natural air ventilation is inadequate or not possible (eg when totally enclosed), liquid cooling is preferred because of the higher heat transfer than with air or other gases and the avoidance of a separate blower. One advantage of the present invention is that it offers simple and efficient means of liquid cooling.

The rotor discs or annuli are separated by spacers or shoulders which maintain the correct air gap. Where the motor is air cooled, circumferential gaps between the spacers allow cooling air to flow between the discs, the air entering.and exiting through suitably aligned vents in the case. The spacers will be in one of two positions, according to the design chosen to suit the particular application. In the first case the rotor spacers are radially inside the stator, in which case the stator is held in the case by its radially outer part; in the second case the rotor spacers are radially outside the stator, in which case the stator is held in the case by its radially inner part.

Where the stator is to be air cooled, the rate of cooling can be increased by allowing the air to flow over and/or through the inner or outer or both end windings which may both be spaced apart and/or extended to form fins over and between which the air is constrained to flow.

Where the stator is liquid cooled, an enclosing chamber is formed about the inner or outer or both end windings which may or not have projecting fins or have apertures over or through which the liquid is caused to flow by a pump or other means.

4 These cooling arrangements can be made using standard wire coils, but can be made even more effective if the coils are made of single or a small number of turns of conducting strip. Under these conditions it can be secured that every turn of the conductor is in contact with the cooling liquid.

3. ILLUSTRATIONS Fig I shows the simplest version of the motor having a rotor made up of two discs, and a stator made up of radial conductors with iron laminations interleaved between them. The stator is gripped at its outer edge and the airflow is taken through outer fins as shown in Fig IE.

Fig I A shows one of identical conductors making up the rotor.

Figs IB, C & D show cross-sections and shaft end view in Figl.

Fig 1E shows airflow through the end windings and their connections.

Fig IF shows a rotor for an asynchronous motor.

Fig 2 shows a main rotor as it might be attached to a pump or engine with a second rotor plate in the form of an annulus mounted on spacers at its inner circumference. The stator is held in rebates in the case at its outer part.

Fig 2A shows optional fins in the gaps between the spacers, which serve to increase the width of the gaps and thus the radial airflow.

Fig 2B shows a similar system with conductors adjacent to a liquidcooling chamber.

Fig 2C shows a larger liquid-cooling chamber surrounding the end windings.

Fig 3 shows a single-disc motor with air-cooled stator held at its inside. It is similar in arrangement to Fig 2 except that the stator (7) is held at its inner part by spacers and screws which attach it to the inner part of the back cover of the case (1).

Fig 3 A shows a motor similar to Fig 3, but with stator liquid-cooled.

Fig 4 shows a centrifugal fan motor as might be used in a vacuum cleaner.

Fig 5 shows a motor for a hybrid vehicle drive, having two clutches to connect it to the 1C engine or transmission or both.

Fig 6 shows a single disc motor in which two armatures form stators on either side of the disc Fig 7 shows a stator core as used in Fig 6 and means of making it.

Fig 8 shows possible configurations with single stator or single rotor.

Fig 9 shows possible configurations with multiple stators and rotors.

Fig 10 shows composite ferromagnetic core made of folded lamination material filled with compacted ferromagnetic powder.

In Figs 1, 2, 2A, 2B, 2C, 3, 4, 5 and 6, the conductors are shown schematically only in that the cross section of the end windings is not shown. The true shape of the conductors is as shown in Figs IA and IB and IE. An approximation to the true cross-section is shown in the Section at A in Fig 1E.

6 4. KEY TO MLUSTRATIONS 1. Case 2. Stator 3. Rotor 4. Magnets 5. Bearing 6. Shaft 7. Ferromagnetic material - transformer steel laminations or compacted powder, metal or ceramic.

8. Tie bars 9. Insulating supports for stator.

10. Clips 11. Conductors 12. Cooling air inlet to case 13. Air passage through rotor 14. Air flow 15. Air outlet from case 16. Fins in rotor.

17. Electrical connections to stator 18. Power supply cable.

19. Suction inlet to fan 20. Fan 21. Pressure outlet from fan 22. Liquid cooling chamber 23. Inner boundary of liquid cooling chamber 7 24. Spacers separating two halves of case 25. Extended clips 26. Liquid cooling chamber 27. Closure to cooling chamber 28. Insulator extended to close cooling chamber 29. Cooling chamber extended to laminations 30. Second, annular disc 3 1. Dovetail ends of conductors 32. Spacer 33. Axis of rotation 34. Clutch to engine 3 5. Clutch to transmission 36. Magnetic return path 37. Slots.

38. First part of conductor 39. Second part of conductor 40. Joining member 41. First end of conductor 42. Second end of conductor 43. Flap on end of conductor 44. Solder or other joint 45. Fins at edge of rotor 46. Enlargements at base of slots 47. Grille or mesh over air inlet 48. Clamping ring 8 49. Conducting material 50. Ferromagnetic material 5 1. Case retaining screws 52. Axis of rotation 53. Ferromagnetic powder, pressed and bonded 54. V-shaped ferromagnetic lamination 9 5. EXAMPLES OF THE INVENTION In one embodiment of the invention (shown in Fig 1) the objectives set out above are achieved by splitting the rotor into two disc-shaped elements (3) which rotate on each side of the armature which acts as the stator (2). The magnetically active surfaces of the discs point towards the faces of the stator. The rotor may be fitted either with conductors embedded in ferromagnetic material or with permanent magnets (4) but in either case these are mounted on or are part of ferromagnetic backing plates (3) whose purpose is to complete the magnetic circuit through a medium which rotates with the rotor, thus avoiding hysteresis and eddy current losses in the return path. The discs may have ridges or recesses against which the radially outer parts of the magnets make contact, thus helping to resist centrifugal forces on the magnets as the discs rotate.

The stator is made up of radial conductors (I I - Figs I & I A) built up into an annular ring (Fig IB) with two faces both in planes at right angles to the rotor axis directed towards and spaced from the abovementioned two rotor faces in order to give the desired air gap which may typically, but without limit, be in the range 0. 1 to 3 mm. depending on the size of the machine. An important factor is the ratio of the airgap to the active face area of the rotor - whether made up of magnets (synchronous case) or conductors (asynchronous case). This ratio should be as small as is practicable within cost-effective tolerances of construction.

The stator comprises overlapping single- or multiple-turn conducting coils of strip or wire running radially with ferromagnetic material (7) passing axially between them to conduct the magnetic flux through the stator. One advantage of this arrangement is that a single coil element, whether of one turn or multiple turns, energises both magnetic pole faces, thus reducing resistive losses and also manufacturing costs as against having two separate coils, one for each disc. Also there is no need for a return path within the stator as both ends of the magnetic circuit are closed by the rotor faces.

One form of the conductor is shown in Fig I A, formed from flat strip or sheet as in view (c) and possibly having a dovetail as shown in view (d), or other form of indent, particularly when the armature is to be held at its radially inner part, in order to provide greater rigidity.

The conductors (11) are joined by clips (10) or tabs as shown in Fig IA (e), which may be butt-joined or be folded to overlap as shown. Connections can then be made by soldering, welding or other means. Fig la (f) and (g) show an alternative form of the conductor bent out of a single strip.

The side of the rotor away from the magnets may be provided with fins (16) as shown in Fig I C which increase the radial flow of cooling air which enters at inner holes in the case (12), passes around and through the open endwindings; and clips, as shown in Fig IE, leaving the case at the apertures (15), which run round the circumference of the case, and are separated by spacers (24) through which pass fixings holding the two halves of the case together.

Air also flows through holes in the discs (13), providing additional cooling of the stator and magnets. The air passes between the magnets and through the air gap, exiting through the apertures (15).

Care is needed in assembling machines using permanent magnets because of the large forces generated between the magnets and ferromagnetic material which can cause damage and injury to workers. A possible but not the only procedure for assembling the machine shown in Fig I is as follows:

I. Bearing, shaft and first disc are assembled into the right hand half case.

2. Magnets, which may be pre-magnetised or magnetised in situ, are bonded to first disc using a non-magnetic jig to place them accurately.

3. Armature is gripped at its centre on a screw or hydraulicallycontrolled mounting jig acting on the free end of the shaft so that the armature can be lowered in a controlled way into the rebates in the case first half thus creating the correct air gap. The shaft is firmly held in the right hand bearing so that the disc cannot move towards the armature.

4. Magnets are attached to the second disc as to the first disc. 5. The second disc is lowered onto the free end of the shaft using a controlling jig as for the armature until it engages with the shoulder on the shaft which will hold it at the correct distance from the armature.

6. The second half of the case and bearing are slid over the shaft into place so that the rebate in the case firmly grips the armature when the two halves of the case are tightened together by means of holding screws.

Fig IF shows schematically an alternative asynchronous rotor which can be used in most embodiments of the invention in place of permanent magnets. Conducting material (49) runs radially like the spokes of -a wheel being joined at inner and outer parts to form closed circuits in which currents circulate under the influence of magnetic fields generated by the stator. Spaces between the conducting spokes are filled with ferromagnetic material (50) - powder, ceramic or laminations - running axially and providing a continuous return path extending on one side of the disc as shown in Fig I Fa, except in the case shown in Fig 6 where the conductors occupy the full width of the disc as shown in Fig lFb.

While 8 radial conductors are shown in Fig 6 to illustrate the principle of construction, the actual number of conductors may be greater or smaller to suit particular circumstances.

The conductors may be formed by casting, fabrication or any other method which gives a strong assembly with electrical continuity.

6. SECOND EMBODIMENT In an alternative embodiment of the invention shown in Fig 2, a single disc is used, connected to a second annular disc (30) by spacers (32). Cooling air enters between the tie bars, is entrained by the spinning rotor and is forced out between the end windings as in Fig IE.

The space between the tie bars may have fins running parallel to the motor's axis in a cylindrical plane at an angle to the air stream, forming a cylindrical fan which further helps to drive the cooling air towards the outlets (15) as shown in Figs 2, Details A-A, and 2A. The main rotor can be optionally extended as shown in Figs 2 and 2A to encourage the flow of cooling air through the outlet in the case.

Where greater cooling is required the clips can be extended (25) as shown in Fig 2A, providing increased surface area for cooling and a larger aperture allowing greater airflow.

A possible but not the only procedure for assembling the machine shown in Fig 2 is similar to that for the first embodiment except that in step (5) the second disc is lowered with or without fins onto the spacers (32) whose screws are tightened up by means of a key or screwdriver through aligning hole or holes in the case.

Fig 2B shows an alternative version with liquid cooling by means of a closed chamber (26) formed round the ends of the conductors. The bottom and sides of the chamber are closed by resin (27) which may be reinforced as necessary by glass or other filaments. Fig 2C shows how the liquid cooling chamber (26) can be extended as far as the ferromagnetic laminations (7), the chamber being closed by resin; which may be fibrereinforced and/or injected in place, at (28) and (29).

7. FURTHER EMBODIMENTS Fig 3 shows an alternative embodiment in which the stator is held to the case at its inner part. The annular magnet plate (30) is held to the main disc (3) by spacers (3 1) at its periphery, where fins may also be provided as shown in Detail A-A, Fig 2. The air flow and cooling are similar to those shown in Fig 2. The outer edges of one or more disc may be extended as shown in Fig 2A to improve or direct the airflow. Alternatively, liquid cooling can be provided as in Figs 2B and 2C, except that the cooling chamber is at the inner part of the rotor where it is connected to the case..

While Fig 3 shows dovetail mounting of the conductors, (3 1) they can alte, matively be held by parallel insulation as shown in Figs 2B and 2C (28) or other shaped indents.

Fig 3A shows an alternative liquid-cooled arrangement of the motor with the stator held at its inside parL The holding ring and insulation form a closed chamber (26) in which cooling fluid circulates as in Figs 2B and 2C where the stator is held at its outside edge.

The principle of liquid cooling the conductors is the same whether the stator - with armature built up of conductors and laminations - is held at its inner or outer edges. In each case the liquid flows in close proximity to the inner or outer ends of the conductors.

The machine shown in Fig 3 can be assembled as for those of Figs I and 2 except that the stator is lowered onto removable spacing pads of plastic or non-magnetic metal 12 about the thickness of the air gap, serving to separate the stator (2) from the main rotor (3) during assembly.

After the case (1) has been assembled, the inner clamping rings (48) are tightened and the spacing pads are removed through the outer apertures in the case.

8. CENTRIFUGAL FAN Fig 4 shows a motor of the type shown in Fig 3 built into a centrifugal fan as might be used in a vacuum cleaner. The stator (2), in the form of an armature, is mounted on a hub (9) which is attached to the case (1).

The outer part of the annulus (3A) is turned over to form a cylindrical flange by which it is separated from and attached to the main rotor (3) and having passages (13) through which cooling air can pass.

The main rotor disc (3), and rotor annulus (3A) are thus joined at their outside edges and the stator (2) is held at its centre. The centrifugal fan (20) is attached,to the far side of the main drive plate which is mounted on a single double angular contact bearing (5). The stator and annular rotor plate have their own inlet (12) and exhaust ( 15) apertures for cooling air which is kept quite separate from the dust-laden air (19) entering the centrifugal fan (20), which discharges into the outlet manifold (21). The fan (20) is attached to the rotor (3) to form a single unit mounted on one double angular contact or other bearings giving positive axial and radial location.

Cooling air enters the case at holes (12) and passes through holes in the rotor, circulating through the end windings, out through holes (13) in the rotor, emerging through the aperture (15) in the outer part of the case. Extended clips may be used as shown in Fig 2A.

In the alternative asynchronous version the rotor is without magnets and comprises a set of radial conductors cross connected at their inner and outer circumferences interleaved with ferromagnetic material which also forms a solid backing ring to provide a magnetic return path. The conductor assembly can be made in one piece by casting, pressing, stamping or moulding A motor of this type is capable of high rotational speed as this is limited only by the bursting strength of the rotor. While rare earth magnets will give more power, it is possible to use lower cost ferrite magnets in appropriate circumstances. Ferromagnetic material in the core can be low cost powder metal or ceramic, or rnild steel in place of transformer steel where some reduction of efficiency can be tolerated.

The fan motor can be assembled as follows with reference to Fig 4:

(1) Magnets (4) are bonded to the rotor (3) abutting against circumferential upstanding ridges.

(2) The rotor (3), bearing (5) and shaft (6) are attached to the stator (2) by means of the central socket head screw whose head is constrained by a circlip (1) such that the screw holds the rotor and stator apart resisting the magnetic 13 forces between them when they are allowed to come together as the screw is tightened up.

(3) The cup-shaped disc (3A) complete with magnets is then lowered over the rotor under the control of a central screw or hydraulic jig resting on the hub of the stator.

(4) The fan (20) is then attached to the rotor and the whole mounted in the case (1) by means of suitable fasteners such as screws attaching the hub to the case as shown in Fig 4.

Fig 5 shows the motor design adapted to a hybrid electric vehicle drive. The stator (2) and rotor (3) are of relatively large diameter. The case (1) is flanged and bolted to the vehicle's internal combustion engine on one side, and to the transmission on the other side.

The case thickness can be as little as 50-75mm depending on the power output required. The rotor is built into a double clutch assembly (34, 35) supported on the engine drive shaft, A, and transmission layshaft, B, whose axes of rotation (33) coincide with that of the motor. The clutches are not shown, as their construction is well known to one versed in the art of automobile engineering.

The electric motor acts as an engine starter with clutch A (34) engaged and B (35) disengaged. With B only engaged, the motor alone drives the vehicle. With both A and B engaged both the IC engine and the electric motor drive the vehicle - that is, as a parallel hybrid system. If series hybrid running is required then a second motor acting as generator can be mounted on the IC engine. There are some applications in which it is advantageous for vehicles to operate either in series or in parallel hybrid modes - eg if they alternate between extended periods of congested urban and high-speed motorway running.

The vehicle drive is assembled substantially as for the earlier embodiments, the two annular magnet plates being separated by shoulders on the clutch housing, equivalent to the shoulders shown on the shaft in Fig 1.

The mounting jigs may be such that the magnets may be magnetised in situ while the discs are held in the assembly jigs, so that said disc assemblies, which may be relatively large and thus generate large magnetic forces, are fully constrained once they have been magnetised.

The magnet discs may be provided with at least 3 tapped holes at right angles to the disc into which screws may be inserted which serve to lower the discs into position against magnet forces, or to move them apart when dismantling the machine.

9. EMBODIMENT WITH SINGLE DISC In an alternative embodiment of the invention (Fig 6), a single rotor disc (4) of nonmagnetic material, such as a strong plastic composite holds a ring of magnets (4) equally spaced and at a fixed radius in a plane at right angles to the axis of the disc. This disc is placed between two single-sided armatures. The magnets pass through the 14 disc so that both faces are exposed. They are firn-dy bonded into the disc by their edges.

Air gaps are formed between opposite faces of the magnets and the two stator armatures whose construction is similar to that shown in Fig I B except that the outside face of each half of the stator is provided with aferromagnetic return path of laminated steel or powder iron, as shown in Fig 6A (36), According to the present invention, one way of making the backing plate is by coiling ferromagnetic material in the form of a strip with gradually expanding spaces between cut-outs such that the cut-outs form radial slots (37) in an annular disc of laminated ferromagnetic material; the windings are then put into these slots.

Fig 7 shows schematically how strip is punched continuously so that the cut-outs line up to form radial slots. If N slots are required in the face of the annulus then the punch must be triggered in time with the rotation of the annulus as the annulus former rotates every 360/N degrees. Under these circumstances the cut-outs in the strip will automatically line up with each other along a radial centre-line regardless of the diameter at which they are laid down.

An alternative way of making the core and backing plate assembly is to cut or press it from powder or ceramic ferromagnetic material.

10. ALTERNATIVE METHOD OF MAKING FERROMAGNETIC CORES The coiled method of making ferromagnetic cores can also be used if through laminations are required without a backing plate as in the first and second embodiments of this invention. The coiled configuration, after resin impregnation to make it solid, can be cut in a plane outside and parallel to the conductors as shown in Fig 7A at X-X. So that there is less metal to cut through, the slots can be cut wider at their base, the cut being made level with the resulting shoulder (Fig 7B), so that the residual metal neck is narrower than the lamination core which is to be inserted into the armature.

The advantage of this arrangement is that the stator can be built in the manner of a conventional motor in which the iron core is first set up and the windings are then inserted into it. With suitable jigs it is then possible to insert the iron laterally into the assembled matrix of copper strip, in one piece, rather than loading it up one segment at a time.

To aid assembly, the strip may be mounted on projecting fingers on which it can slide, these fingers being held in line with the iron cores so that the armature assembly can be slid off the fingers onto the cores in one piece. In an alternative method, the cores are mounted in slots in a circular plate, which line up with the apertures in the armature and are then slid simultaneously or sequentially into the armature of copper. The above methods can also apply to wound coils as well as strip conductors provided the coils are wound and impregnated as single units, being built up onto non-adhering mandrels from which they can be slideably removed and built up into an armature ready to receive the cores as described above.

Where powder or ceramic core assemblies are used the extensions (46) at the bottoms of the slots may be given a triangular shape (47) to form a narrow neck so that after assembly and impregnation the backing plate can be broken away at the narrow part without cutting. The broken surfaces can then be dressed flat and the waste material in the backing plate can then be processed and recycled.

11. ALTERNATIVE LAYOUTS While the preferred arrangement for maximum efficiency and magnetic field strength uses two magnet plates and one armature, or two armatures and one magnet plate, it is possible to use a single magnet plate for the rotor and a single stator as shown in Figs 6 & 7 with a backing plate of larninated or powder ferromagnetic material. In this case the rotor will be attracted strongly to the magnets and it must therefore be made stronger than in the case shown in Fig 6 where the magnet forces are approximately balanced out by the attraction on both sides. However where lower performance is acceptable this method can be adopted in order to reduce costs.

There may be circumstances in which the rotor (3) or stator (2) elements are required to be laid out other than with radial geometry. While the principles of construction will be the same as described in this specification the geometrical configurations will be adapted as shown schematically in Fig 8. This shows the radial layouts for single armature configurations in details (a) to (d) as described earlier in this specification, and inclined and cup-shaped orientations in details (e) and (f). Single disc arrangements are shown in radial form as described in this specification (g) and (h), and with inclined and cup-shaped orientations in (i) and 0).

In the various configurations set out in this specification the arrangement of components can be repeated to provide multiple stator and rotor elements on the same axis where this is required to increase the power density - eg in automotive applications where space is at a premium. Examples of multiple arrangements in which such rotor (3) and stator (2) elements have the same basic construction as set out in this specification are shown schematically in Fig 9.

In Figs 8 and 9 the basic stator elements with a rotor on each side are as shown, for example, in Fig I and drawings following therefrom, and the basic single-rotor elements with double-sided magnets are as in Fig 6. Figs 8 and 9 are intended to show schematically how these basic elements are transformed in different geometrical orientations. As well as the rotor (3) and stator (2) elements, these drawings show magnets (4) and insulating stator supports (9). They also show magnetic backplates (36) in end positions where magnets are not found on both sides of the stator elements. The axis of rotation is shown as 52. These numerals are not repeated where it is obvious that certain elements already referenced are repeated in the drawing..

C1716W (0362.2) 04/10/99 16 While the present invention applies to electronically commutated machines, many of the inventive features particularly those relating to cooling or mechanical construction - can apply to electrical machines in general whether commutated by brushes or other means, or having stators or rotors of solid cylindrical or hollow cylindrical geometry.

17

Claims

12. CLAIMS

What is claimed is:

1. An electronically commutated electrical machine having a rotor interacting with a stator in the form of an armature or armatures comprising insulated conductors interleaved with cores of ferromagnetic material passing between the conductors, the whole bonded together to form a disc or discs or annular structure in one or more planes such that to a first approximation magnetic forces between rotor and stator are equal and opposite and therefore balance out, the stator being held at one or more of its side or edge parts which are not surrounded by, nor connected by a bearing to, parts of the rotor, with sufficient strength to resist magnetic and mechanical forces when in operation and having provision for cooling by means of conduction, convection or fluid flow and having connections for an alternating current electrical supply, said current being generated by means of a commutating circuit comprising an electronic inverter or other known means.

2. A machine as described in Claim I in which the rotor comprises one or more complete or annular disc-shaped members, to the surface of which are attached permanent magnets presenting alternating North and South poles in a given direction symmetrically spaced about the centre of rotation of the disc-shaped members such that the magnets face the active areas of the stator where the conductors are interleaved with cores of ferromagnetic material and said conductors cut the magnetic flux substantially at right angles, there being a fixed air gap between said magnets and magnetic cores, and having a sensor fixed in relation to the stator capable of determining the position of the rotor and thereby controlling the said commutating circuit so that the machine is operable in the synchronous mode.

3. A machine as described in Claim I in which the rotor comprises a set of substantially radial conductors connected in one or more closed circuits crossconnected at the radially inner and outer parts and set in a ferromagnetic matrix, the whole forming one or more disc-shaped elements providing cores between the conductors and a continuous return path behind the cores such that the conductors face the active areas of the stator with which they have a constant air gap so that the machine is operable in the asynchronous mode..

4. A machine as described in any one of Claims 1, 2 or 3 in which the armature or armatures forming the stator comprise conductors of one or more turns running substantially radially in more than one plane crossconnected either at the radially outer part or at the radially inner part by means of clips or by joining the conductors directly.

5. A machine as described in any one of the previous claims in which the stator conductors are each in the form of a strip divided in two along its length apart from a short bridging piece, the two halves of the strip being bent away from each other to form an inner end winding, two radial conductors in different adjacent planes and two halves of outer end windings being joined to adjacent conductors as described in Claim 4.

18 6. A macliine as described in any one of Claims I to 4 in which the conductors are each single strips twisted through 180 degrees where they form the inner end winding such that their two outer parts form two radial conductors in different adjacent planes and two halves of outer end windings are joined to adjacent conductors as described in Claim 4, thus enabling the strips to fit together to form a complete armature.

7. A machine as described in Claims 5 or 6 in which the cross-connections between the conductors are made at the radially inner part of the armature rather than at the radially outer part.

8. A machine as described in any of the previous claims in which the stator is wave wound and to which electrical connections are made as far as possible electrically symmetrically to the or each armature comprising the stator at a number of points corresponding to the number of phases in the current supply or a multiple thereof 9. A machine as described in any one of Claims 5 - 8 in which the inner or outer parts of the conductor strips are bonded to each other and to the ferromagnetic material in the armature, one or more of which comprises the stator, to form a rigid structure so that by virtue of the stiffness of the material of the strip being on edge, the projecting parts of all the strips are able collectively to support the armature in rebates in the case with sufficient strength to overcome mechanical and magnetic forces on the armature, said projecting parts being electrically insulated from the rebates in which they are held.

10. A machine as described in any one of the previous claims having means for cooling the stator by air or other gas coolant comprising any combination of the following:

Apertures in the case to admit coolant to the stator and rotor.

Apertures in the rotor angled radially and axially so as to direct coolant on to the stator.

Gaps between the projecting parts of the conductors or clips whereby the stator is held in rebates in the case at either its radially inner or outer parts through which coolant can flow.

Spacing between the radially outer parts of the conductors in the 'radially outer end windings such that coolant can flow between them.

Spacing between the radially inner parts of the conductors in the radially inner end winding such that coolant can flow between them.

Extensions to the conductors or clips by which said conductors are held in rebates in the case such that both the apertures through which coolant can flow and the surface area of conductors and/or clips in contact with coolant are increased, thereby increasing heat transfer to the coolant.

11. A machine as described in Claim 10 in which coolant enters the case at a radially inner region, makes contact with the rotor by which said coolant is constrained to rotate by means of viscous drag and variations of surface contour such as vanes, magnets or other projections, thereby creating centrifugal forces which cause the coolant to pass through the stator, exiting by means of outlets at a radially outer part of the case.

19 12. A machine as described in any one of Claims I to 9 having means for cooling the stator by liquid coolant comprising any combination of the following including passages in the case for entry and exit of coolant:

Channels to convey coolant to the stator and round the radially inner or outer ends or clips of the radially inner or outer end windings respectively or to both such ends.

Channels to convey coolant round substantial parts of the inner and/or outer end windings, such that coolant flows close to or in contact with the conductors.

Channels to convey coolant between substantial parts of the end-winding conductors where they are spread apart from adjacent conductors.

13. A machine as described in any one of Claims I to I I comprising:

A rotor having on a common shaft two concentric ferromagnetic discs on which are mounted symmetrically permanent magnets at a fixed radius on either side of a stator held at its radially outer part in insulated rebates in a case, such that the magnets face the stator opposite the radial parts of the conductors in the stator.

A stator as described in any one of Claims 4 to 9.

Means of cooling as described in any one of Claims 10 and 11, comprising apertures in the radially inner parts of the case, holes in and fins on the rotor and apertures for the exit of air in radially outer parts of the case such that cooling air passes over the stator conductors before leaving the case.

A case provided with bearings to support the rotor, apertures as described for inlet and exit of cooling air and further apertures through which pass electric cables supplying the stator with power.

14. A machine as described in claim 13 having provisions for liquid cooling as described in Claim 12 in place of those described for air cooling.

15. A machine as described in any one of Claims I to I I comprising:

A rotor in the form of a disc on which is mounted an annular disc by means of spacers at a radially inner part.

A stator as described in any one of the above claims mounted at its radially outer part.

A case having inner and outer inlet and outlet apertures and a shaft supporting the disc rotating in double angular contact or other bearing arrangements and apertures for the passage of electric power cables to the stator.

16. A machine as described in Claim 15 having vanes at the radially inner part of the rotor substantially on the same radius as the spacers, said vanes positioned so as to increase airflow on rotation of the rotor.

17. A machine as described in Claims 15 or 16 in which the conductors in the stator armature have clips or extensions by which the stator is held in the case, such clips or extensions serving to increase both the radially outer apertures in the case and the active cooling area of the stator by conduction through the clips.

18. A machine as described in any one of Claims I to 9 and 12 comprising:

A disc rotor on which is mounted an annular disc by means of spacers at a radially inner part.

A stator as described in any of the above claims held at its radially outer part having a liquid cooling chamber at its radially outer part with inlet and outlet apertures for the flow of coolant through the case, into said cooling chamber.

19. A machine as described in any one of Claims I to I I comprising:

A disc rotor on which is mounted an annular disc by means of spacers at a radially outer part.

A stator as described in any of the above claims held by its radially inner part.

Casing, shaft, bearing means and apertures as described in Claim 15.

20. A machine as described in Claim 19 in which the stator is held by a dovetail or T section at one of its ends, with insulated means for clamping it to the case by means of the dovetail.

21. A machine as described in Claim 19 and 20 in which the stator is provided with extensions or clips as described in Claim 10 at its inner part to increase the airflow.

22. A machine as described in Claims 19 to 21 having vanes in the spaces between the disc and annulus at their radially outer part serving to increase the airflow.

23. A machine as described in any one of Claims I to 9 and 12 comprising:

A disc rotor on which is mounted an annular disc by means of spacers at its radially outer part.

A stator as described in any of the above claims held at its radially inner part and having a liquid cooling chamber at its radially inner part with inlet and outlet apertures for the flow of coolant through the case to said cooling chamber.

24. A machine substantially as described in Claim 19 comprising:

A rotor in two parts with separating members with apertures between them to allow for airflow having the annular part mounted concentrically on the disc.

A case with inlet apertures at its radially inner part and outlet apertures at its radially outer part on which the stator is mounted.

A stator rigidly attached to the case having a hub on which is mounted a double angular contact or other bearing having stiffhess in both axial and radial directions which supports the rotor and provided with seals to keep out contamination.

A centrifugal fan attached to or forming an integral part of the rotor '%kith a separate casing attached to the motor case such that the dustladen inlet and exhaust air from the fan does not mix with the inlet air cooling the motor eg by means of a labyrinth seal or other similar device.

25. A machine as described in any one of Claims I to 9 and 12 comprising:

A rotor made of two annular discs with a large diameter aperture surrounding a clutch member forming spacers at the radially inner part of said discs.

21 A liquid cooled stator held at its radially outer part with provision for liquid cooling as described in Claim 18.

Means for mounting the said machine with two clutches in relation to the said clutch member between engine and drive train in a vehicle transmission such that the machine can (a) drive the engine as a starter when declutched from the transmission (b) operate as a generator when connected by clutch to the engine operate as a motor to drive the vehicle when connected by clutch to the transmission either in parallel hybrid mode when both engine and said machine are connected to the transmission and in pure electric mode when the machine is connected to the transmission only 26. A machine as described in Claims 1, having a single disc rotor rotating between two single-sided armatures making up the stator as described in any one of Claims 4 to 9 and cooled by means set out in any of Claims 10 to 12, 14, 16 to 18, the disc having magnets passing through its width presenting- alternating North and South poles on opposite sides of the disc, the machine being operable in the synchronous mode.

27. A machine as described in Claim 26 in which the armature cores have ferromagnetic backing members made of laminations or powder metal to provide magnetic return paths.

28. A machine as described in Claim 27 in which the armature cores are formed from ferromagnetic strip punched with equal slots and then wound up on a suitable former or mandrel into a circular ring such that the slots are punched in phase with equal angular rotations of the said circular ring and thereby line up along equally spaced radii of the ring to form an armature core with circumferential laminations and radial slots into which the conductors can be inserted.

29. A machine as described in any one of Claims 26 to 28 in which the armature cores are bonded in place by resin.

30. A machine as described in any of Claims 26 to 29 in which the armature is assembled by inserting the conductors into the slots in the armature core., 3 1. A machine as described in any of Claims 26 to 29 in which the armature is assembled by inserting the armature core assembly into a preformed conductor assembly, the leading edges of the core segments being rounded off or tapered as necessary to ease insertion.

32. A method of assembly as described in Claim 30 in which removable spacers between the two or more planes of the armature winding conductors prevent the layers of windings being crushed together on insertion of the core, thus maintaining the initial spacing between said planes of conductors.

33. A machine as described in any of Claims 1 to 26 in which the ferromagnetic cores are inserted as a single assembly as in Claims 28 to 32 and the ferromagnetic backing 22 forming a return path is then sliced off between the plane of the conductors and that of the backing ring by means of a suitable saw or cutting disc leaving individual cores between the conductors, thus enabling all the placing of the cores to be completed in two operations only, the first being their simultaneous insertion and the second being cutting off the backing ring.

34. A method of inserting the cores described in Claim 33 in which the slots described in Claim 28 have short widened sections at the bottom of each slot so that there is less metal to cut away when the individual core members are cut from the backing plate, or so as to enable the cores to be broken off if made of brittle material.

35. A machine or method as described in Claim 26 operating in the asynchronous mode in which the rotor has linked conductors passing through the disc from face to face set in a ferromagnetic matrix substantially as described in Claim 3 but having no return path, the conductors being flush with both surfaces of the disc.

36. A machine as described in Claims 25 to 27 and 32 to 34, in which the armature is wound with wire into the slots in the armature core.

37. A machine as referred to in any of Claims I to 27 in which the ferromagnetic material is compacted powder, ceramic or metal laminate with surface coatings of sufficient resistance to reduce eddy currents in the cores to an acceptable level.

38. A machine as described in Claim 2 and dependent claims in which each disc has rebates or an upstanding rim or projections radially outside of the magnets to assist in resisting centrifugal forces acting radially outwards on the magnets.

39. A machine substantially as described in any one of Claims 13, 15, 18 19, 23, 24 or 25 but operating in the asynchronous mode without permanent magnets substantially as described in Claim 3.

40. A machine as described in Claim 26, operating in the asynchronous mode having a disc rotor without magnets substantially as described in Claim 3 except that the conductors pass through the rotor from one face to the other without any magnetic return path on one or other side of the disc.

41. A machine as described in Claim 9 in which the ferromagnetic material inserted between the conductors in the stator comprises single pieces of steel lamination bent into a V shape with powder ferromagnetic material pressed and bonded into the inner part of the V, the whole forming a solid wedge-shaped composite ferromagnetic core of high strength.

42. A machine in configurations as substantially described herein with reference to Figures I to IF, Figures 2 to 2C, Figures 3 and 3A, Figure 4, Figure 5, Figure 6 and Figure 7.

43. Alternative configurations of machines based on those described herein as set out in figures 8 and 9.