GB1587440A

GB1587440A - Dynamo-electric machine

Info

Publication number: GB1587440A
Application number: GB43016/77A
Authority: GB
Original assignee: Kgel Ltd
Current assignee: Kgel Ltd
Priority date: 1977-10-17
Filing date: 1977-10-17
Publication date: 1981-04-01
Also published as: BE871322A; ZA785592B

Description

(54) A DYNAMO-ELECTRIC MACHINE (71) We, KGEL LIMITED, a British Company of Kennedy Tower, St. Chads Queensway, Birmingham B4 6EL, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to a dynamoelectric machine with an axial air gap; such a machine has a stator separated by an axial gap from a rotor.

According to this invention there is provided an axial air gap dynamo-electric machine comprising a stator from which teeth project axially, a central boss projecting in the same direction as the teeth, a rotor having a central aperture and mounted for rotation so that the boss passes through the central aperture and so that there is an axial gap between the rotor and the teeth, an AC winding wound through the slots between the teeth, and a DC winding surrounding the central boss.

By an AC winding is meant a winding intended to be energised with AC and by DC winding is meant a winding which is intended to be energised with DC.

The DC winding produces a magnetic field which energises the rotor which therefore does not need a winding energised with DC through slip rings.

The machine in accordance with this invention may be one sided, that is to say, it has a rotor only on one side of the stator and consequently there is an axial force produced on the rotor as a result of the magnetic flux in the air gap.

In this case the magnetic flux between the boss and the rotor passes in a radial direction and creates no axial force. However, the force created by the magnetic flux passing between the teeth and the rotor will still produce an axial force.

Preferably, the stator is built up from laminations onto which the said AC winding is wound; this gives a relatively cheap stator construction.

The stator of an axial air gap dynamoelectric machine (whether motor or generator) is conventionally constructed by rolling a strip of laminations into an annular core and then machining slots in that annular core to form teeth as is illustrated in .Figure 1 of the drawings accompanying the Provisional Specification of Application No.

43017/77 in which the core is denoted at 1, the teeth at 2 and the slots at 3. This construction is exepensive because of a number of expensive machining operations.

The stator may comprise a circular stack of laminations to which a plurality of cores forming teeth are secured, said cores being laminated.

Preferably, the cores are L-shaped, corresponding limbs being clamped between clamping plates extending on opposite sides of the circular stack.

In this embodiment the circular stack is preferably cylindrical.

Alternatively, the stator is built-up of L-shaped laminated cores, the ends of corresponding limbs of the cores being mitred to fit together around the central boss.

With this construction the said corresponding limbs appear as spokes from a central point.

Embodiments of this invention will now be described, by way of example only, with reference to Figure 2 of the drawings accompanying the Provisional Specification of Application No. 43016/77 and Figures 1 to 3 and 6 of the drawings accompanying the Provisional Specification of Application No.

43017/77. In the drawings accompanying the Provisional Specification of Application No.

43016/77: Figure 2 is a schematic sectional elevation of an axial air gap motor in accordance with this invention.

In the drawings accompanying the Provisional Specification of Application No.

43017/77: Figure 1 is a perspective view of the stator of a conventional axial air gap machine and has been described earlier; Figure 2 is a perspective view of a stator of an axial air gap machine in accordance with this invention; Figure 3 is a perspective view of an alternative stator of an axial air gap machine in accordance with this invention; and Figure 6 is a perspective view of yet another stator of an axial air gap machine in accordance with this invention.

Referring to Figure 2 of the drawings accompanying the Provisional Specification of Application No. 43016/77, a homopolar axial air gap motor has a stator consisting of an annulus or cylinder 1 from which teeth 2 project axially; a central boss 3 projects axially beyond the teeth 2. An AC winding 4 is wound using the slots between the teeth 2 whereas a DC winding 5 is wound around the boss 3. A bar-like rotor 6 with similar poles at its ends has a central aperture by means of which it is rotatably mounted on the boss 3 and is positioned adjacent to the stator with an axial gap 7 therebetween.

The rotor 6 is magnetised by the DC winding 5 with two similar poles at its ends and consequently the motor is a homopolar machine.

No axial force generated as a result of the flux passing between the boss 3 and the rotor 6 but there will be an axial force produced by the flux passing between the teeth 2 and the rotor 6.

Referring to Figure 2 of the drawings accompanying the Provisional Specification of Application No. 43017/77, the stator comprises a central cylindrical stack 4 of laminations to which there are secured axially extending cores 5 constituting teeth, each of which consists of a stack of laminations laminated along radial paths. The teeth 5 arc arranged around the periphery of the cylindrical stack 4.

This construction is somewhat idealised and, in practice, will not be used. The machine winding is wound onto the teeth in the normal way using the spaces between the cores 5 as the machine slots.

Figure 3 of the drawings accompanying the Provisional Specification of Application No. 43017/77 shows a more practical arrangement in which the central cylindrical stack 4 is present but the cores 5 constituting the teeth are L-shaped and are built-up from L-shaped laminations. Corresponding limbs 6 of the cores 5 are clamped between two clamping plates 7 and 8 which also clamp opposite sides of the central cylindrical stack 4.

The stator illustrated in Figure 6 of the drawings accompanying the Provisional Specification of Application No.43017/77 consists of laminated L-shaped cores 15 in which corresponding limbs 16 are extended and are mitred to fit together. The cores are laminated but not radially in contrast to the cores of Figure 3. The particular type of lamination in Figure 6 is preferred to that of Figure 3. Although not shown in any of Figures 2, 3 and 6 of the drawngs accompanying the Provisional Specification of Application No. 43017/77, there is provided a central boss corresponding to the boss 3 shown in Figure 2 of the drawings accompanying the Provisional Specification of Application No. 43016/77.

In the drawings, radial slots are illustrated although they could be modified to provide skewed slots.

The axial air gap machines in accordance with this invention are suitable for use as the drive motor of a battery powered vehicle. In this case the axial air gap motor may be a synchronous machine energised from the battery through an inverter. In the illustrated embodiments the rotor is a passive steel member with primary side excitation so that the wound primary section, that is to say the stator, could be replaced quickly in case of failure leaving the robust rotor still in place with its own bearing system.

The use of a synchronous motor has advantages in relation to the use of an induction motor as is disclosed in our Patent Specification No. 1 402 321 in that when a synchronous motor is used, the inverter could be frequency locked to the rotor speed for which purpose rotor position sensors would be located on the stator and would control the inverter.

In this case, the switching can be controlled to give a torque angle of 90 electrical degrees between the stator poles and the rotor poles; this will result in reduced axial force and maximum torque.

The inverter could be relatively simple and moreover since a synchronous machine can be arranged to operate at a relatively satisfactory power factor in relation to an induction machine the current switched by the power switching devices of the inverter may be arranged to be relatively low which is highly advantageous.

WHAT WE CLAIM IS: 1. An axial air gap dynamo-electric machine comprising a stator from which teeth project axially, a central boss projecting in the same direction as the teeth, a rotor having a central aperture and mounted for rotation so that the boss passes through the central aperture and so that there is an axial gap between the rotor and the teeth, an AC winding wound through the slots between the teeth, and a DC winding surrounding the central boss.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

In the drawings accompanying the Provisional Specification of Application No.

43017/77: Figure 1 is a perspective view of the stator of a conventional axial air gap machine and has been described earlier; Figure 2 is a perspective view of a stator of an axial air gap machine in accordance with this invention; Figure 3 is a perspective view of an alternative stator of an axial air gap machine in accordance with this invention; and Figure 6 is a perspective view of yet another stator of an axial air gap machine in accordance with this invention.

Referring to Figure 2 of the drawings accompanying the Provisional Specification of Application No. 43016/77, a homopolar axial air gap motor has a stator consisting of an annulus or cylinder 1 from which teeth 2 project axially; a central boss 3 projects axially beyond the teeth 2. An AC winding 4 is wound using the slots between the teeth 2 whereas a DC winding 5 is wound around the boss 3. A bar-like rotor 6 with similar poles at its ends has a central aperture by means of which it is rotatably mounted on the boss 3 and is positioned adjacent to the stator with an axial gap 7 therebetween.

The rotor 6 is magnetised by the DC winding 5 with two similar poles at its ends and consequently the motor is a homopolar machine.

No axial force generated as a result of the flux passing between the boss 3 and the rotor 6 but there will be an axial force produced by the flux passing between the teeth 2 and the rotor 6.

Referring to Figure 2 of the drawings accompanying the Provisional Specification of Application No. 43017/77, the stator comprises a central cylindrical stack 4 of laminations to which there are secured axially extending cores 5 constituting teeth, each of which consists of a stack of laminations laminated along radial paths. The teeth 5 arc arranged around the periphery of the cylindrical stack 4.

This construction is somewhat idealised and, in practice, will not be used. The machine winding is wound onto the teeth in the normal way using the spaces between the cores 5 as the machine slots.

Figure 3 of the drawings accompanying the Provisional Specification of Application No. 43017/77 shows a more practical arrangement in which the central cylindrical stack 4 is present but the cores 5 constituting the teeth are L-shaped and are built-up from L-shaped laminations. Corresponding limbs 6 of the cores 5 are clamped between two clamping plates 7 and 8 which also clamp opposite sides of the central cylindrical stack 4.

The stator illustrated in Figure 6 of the drawings accompanying the Provisional Specification of Application No.43017/77 consists of laminated L-shaped cores 15 in which corresponding limbs 16 are extended and are mitred to fit together. The cores are laminated but not radially in contrast to the cores of Figure 3. The particular type of lamination in Figure 6 is preferred to that of Figure 3. Although not shown in any of Figures 2, 3 and 6 of the drawngs accompanying the Provisional Specification of Application No. 43017/77, there is provided a central boss corresponding to the boss 3 shown in Figure 2 of the drawings accompanying the Provisional Specification of Application No. 43016/77.

In the drawings, radial slots are illustrated although they could be modified to provide skewed slots.

The axial air gap machines in accordance with this invention are suitable for use as the drive motor of a battery powered vehicle. In this case the axial air gap motor may be a synchronous machine energised from the battery through an inverter. In the illustrated embodiments the rotor is a passive steel member with primary side excitation so that the wound primary section, that is to say the stator, could be replaced quickly in case of failure leaving the robust rotor still in place with its own bearing system.

The use of a synchronous motor has advantages in relation to the use of an induction motor as is disclosed in our Patent Specification No. 1 402 321 in that when a synchronous motor is used, the inverter could be frequency locked to the rotor speed for which purpose rotor position sensors would be located on the stator and would control the inverter.

In this case, the switching can be controlled to give a torque angle of 90 electrical degrees between the stator poles and the rotor poles; this will result in reduced axial force and maximum torque.

The inverter could be relatively simple and moreover since a synchronous machine can be arranged to operate at a relatively satisfactory power factor in relation to an induction machine the current switched by the power switching devices of the inverter may be arranged to be relatively low which is highly advantageous.

WHAT WE CLAIM IS: 1. An axial air gap dynamo-electric machine comprising a stator from which teeth project axially, a central boss projecting in the same direction as the teeth, a rotor having a central aperture and mounted for rotation so that the boss passes through the central aperture and so that there is an axial gap between the rotor and the teeth, an AC winding wound through the slots between the teeth, and a DC winding surrounding the central boss.
2. A machine as claimed in claim 1,

wherein the stator is built up from laminations on to which the said AC winding is wound.
3. A machine as claimed in claim 2, wherein the stator comprises a circular stack of laminations to which a plurality of cores forming said teeth are secured, said cores being laminated.
4. A machine as claimed in claim 3, wherein the cores are L-shaped, corresponding limbs being clamped between clamping plates extending on opposite sides of the circular stack.
5. A machine as claimed in claim 3 or claim 4 wherein the circular stack is cylindrical.
6. A machine as claimed in claim 2, wherein the stator is built-up of L-shaped laminated cores, the ends of corresponding limbs of the cores being mitred to fit together around the central boss.
7. A machine as claimed in any of claims 1 to 6 wherein the rotor is bar-like.
8. An axial air gap dynamo-electric machine substantially as hereinbefore described with reference to Figure 2 of the drawings accompanying the provisional Specification of Application No. 43016/77 and Figures 1 to 3 and 6 of the drawings accompanying the Provisional Specification of Application No. 43017/77.