GB2202685A - Printed circuit stator for a brushless D.C. electric motor - Google Patents

Abstract

The motor has a stator comprising an electrically insulating support and at least two current carrying circuits (11) printed on the support. The support is formed from one or more fold able blanks (10) having a plurality of interconnected blank parts (10a-i) folded about lines 12 on top of one another. Each circuit (11) comprises a wave-shaped conductive path extending about two or more parts of a blank, the conductive parts (11c) of the path which produce the driving magnetic field of the motor being arranged on each of said two parts to supplement one another. A circuit may be provided on the reverse side of the blank. <IMAGE>

Description

Brushless D.C. Electric Motor This invention relates to a brushless direct current electric motor.

Brushless direct current electric motors are well known in the art and generally comprise a stator winding and a rotor designed to provide the working flux. The stator field is advanced by electronically switching the current in the stator winding in response to rotor position sensors to maintain uni-directional torque.

The use of brushless electronic commutation avoids sparking and consequent radio interference, eliminates brush wear and does not suffer from the problems caused by dirt and moisture in conventional commutators. It is particularly applicable to small, i.e. fractional horsepower, motors, which employ permanent magnet rotors.

The present invention seeks to provide a brushless motor having a novel stator which is simple to manufacture.

According to the invention there is provided a brushless direct current electric motor having a stator comprising an electrically insulating support and at least two current carrying circuits printed on the support, the support being formed from one or more foldable blanks having a plurality of interconnected blank parts folded on top of one another Preferably, each circuit comprises a wave-shaped conductive path extending arcuately around two or more parts of a blank, the conductive parts of the path which produce the driving magnetic field of the motor being arranged on each of said at least two parts to supplement one another.In this case, advantageously, each wave-shaped conductive path includes a plurality of regularly spaced radially extending path sections, the radially extending path sections on each of said two or more blank parts being in register and arranged such that in use current flows through in register sections in the same direction so as to supplement one another.

Preferably, the support comprises a single blank, a first continuous circuit being provided on one side of said blank to extend around the one side of each of said blank parts and a second continuous circuit being provided on the other side of said blank to extend around the other side of each of said blank parts, the two circuits being out of phase with one another.

The invention will now be more particularly described by way of example with reference to the accompanying drawing which is a plan view of a blank from which a stator of a motor, embodying the invention, may be made.

Referring now to the drawing, the blank 10 shown therein comprises nine interconnected blank parts lOa-i of foldable electrically insulating, e.g.

plastics, material with a current carrying circuit 11 printed thereon by a conventional etching process.

The nine blank parts lOa-l are arranged in a regular 3x3 array. The central blank part 10e is joined to blank parts lOb, lOd, lOf, and 10h. Blank part lOb is also joined to blank parts 10a and lOc and blank part 10h is also joined to blank parts lOg and lOi.

The blank parts 10a-10i are foldable one on top of the other about fold lines 12 to form a stator of a brushless direct current electric motor; insulating material being provided between each blank part or being painted or otherwise deposited over the printed circuit.

The circuit 11 comprises a continuous wave-shaped electrically conductive (e.g. copper) path which extends circumferentially around each of the blank parts lOa-lOi. Circuit terminations lla and llb are printed on a tab 13 joined to the blank part lOb.

Starting from termination lla the circuit takes the following path to termination llb.

900 around blank part lOb 3600 around blank part lOa 90" around blank part lOb 900 around blank part lOe 3600 around blank part lOd 900 around blank part lOe 900 around blank part lOh 3600 around blank part lOg 1800 around blank part lOh 3600 around blank part lOi 900 around blank part lOh 90" around blank part lOe 3600 around blank part lOf 90 around blank part lOe 900 around blank part lOb 360" around blank part lOc 900 around blank part lOb The conductive path defining the circuit 11 has a plurality of regularly spaced radially extending path sections llc joined to one another by radially outer and radially inner generally circumferentially extending path sections lld and lle, respectively.

The radially extending sections llc are arranged so that when the parts lOa to lOi have been folded one on top of one another about fold lines 12 the sections llc on each blank part are in register, i.e.

in axial alignment with one another, and so that current will flow through in register sections in the same direction to supplement one another in generating the driving magnetic field of the motor.

By way of example, assuming current enters the circuit at termination lla, the direction of current flow in some of the path Sections llc on blank parts lOa and lOb is illustrated by arrows in the accompanying drawing. It will be appreciated that when blank parts lOa and lOb are folded one on top of the other about line 12 path sections llc' and lIc" will be in register and in each case the current flow will be radially inwards.

The circuit 11 described above will produce alternating North and South poles around the stator.

By reversing the direction of current in the circuit using electronic switching devices, such as thyristors, triggered in response to a rotor position sensor, such as a Hall-effect device, the magnetic field will be caused to advance circumferentially by a single circuit pitch for each current reversal, or in the example shown, by about 6 mechanical degrees.

This will therefore require 60 switching operations for each revolution of the rotor.

Ideally, the other side of the blank has a second current carrying circuit printed thereon. This second circuit is similar to the first-mentioned circuit but is preferably arranged half a circuit pitch (i.e. 90 electrical degrees) out of phase with the first-mentioned circuit. Terminations of the second circuit can be printed on tab 14 joined to the blank part lOh. By alternately reversing the current in the two circuits the magnetic field will be advanced in steps of 3 mechanical degrees at a time ensuring smoother operation of the motor.

The blank parts lOa-lOi can be appropriately bonded together to form the stator.

The motor further comprises a rotor, typically a permanent magnet rotor, rotor position sensors and an electronic switching circuit responsive to the rotor position sensors as is conventional in the art.

The above embodiment is given by way of example only and various modifications will be apparent to persons skilled in the art without departing from the scope of the invention defined by the appended claims. For instance, the blank could be provided with more than one circuit on one or each side thereof. These would be isolated from one another and each circuit would extend over only some of the annular blank parts.

Alternatively, there may be, for example, two or more blanks each bearing its own. In this latter case the blanks could be interleaved for even distrubution of flux.

Claims (6)

1. A brushless direct current electric motor having a stator comprising an electrically insulating support and at least two current carrying circuits printed on the support, the support being formed from one or more foldable blanks having a plurality of interconnected blank parts folded on top of one another

2. A motor according to claim 1, wherein each circuit comprises a wave-shaped conductive path extending arcuately around about two or more parts of a blank, the conductive parts of the path which produce the driving magnetic field of the motor being arranged on each of said at least two parts to supplement one another.

3. A motor according to claim 2, wherein each wave-shaped conductive path includes a plurality of regularly spaced radially extending path sections, the radially extending path sections on each of said two or more blank parts being in register and arranged such that in use current flows through in register sections in the same direction so as to supplement one another.

4. A motor according to anyone of the preceding claims, wherein the support comprises a single blank, a first continuous circuit being provided on one side of said blank to extend around the one side of each of said blank parts and a second continuous circuit being provided on the other side of said blank to extend around the other side of each of said blank parts, the two circuits being out of phase with one another.

5. A motor according to claim 4, wherein the two circuits are 90 electrical degrees out of phase.

6. A stator of a brushless direct current electric motor substantially as hereinbefore described with reference to the accompanying drawings.