EP0219497A1 - Pulsating current electromotor without commutator - Google Patents

Abstract

A pulsating electric motor without collector comprises a rotor (11) of the permanent magnet type or of the electromagnetic type keyed to a rotary shaft (12) and having two poles (14-18) diametrically opposite with respect to the shaft (12 ) and extending over most of its circumference. These poles (15, 16) have opposite polarities and face a stator element (10) formed by a substantially cylindrical hollow body where the rotor (11) is arranged. Uniformly spaced cavities (13) in the stator body (10) contain two-layer stator windings (41) of which half is oriented in one direction and the other half is oriented in opposite directions, at the outlet of each cavity (13). Optical detection systems which detect the angular position of the shaft (12) are connected to electronic pilot circuits which drive power distribution members to the windings (41) of the stator according to the angular displacements of the shaft ( 12). The machine components are supplied by an alternating or direct current network.

Description

Pulsating current electromotor without commutator

DESCRIPTION

The invention relates to a pulsating current electric

machine with a permanent magnet type or electromagnetic type

rotor. More particularly, the subject of the invention is an electric motor supplied with direct or alternate, current, in which the rotor is formed by permanent magnets having no winding

or by a rotor with poles having a winding; either of the rotors

employed is mounted on a rotating shaft, -and arranged around the rotor is a hollow cylindrical stator provided with windings.

The permanent magnet type or electromagnetic type rotor formed

in this manner is not provided with the commutator usually connected to the armature with which it^* forms the rotor, whilst,

in the case of the rotor being of the type with permanent magnet's ,it does not even possess the so-called brushes of

the conventional commutator.

Schematically, the conventional direct current electric machines are formed by a stator and a rotor, both of which are

made of iron; generally, the stator supports the inducto windings, whilst the rotor supports the induced windings.

The stator costitutes almost always the outer part of

the machine and generally it is formed by a ring (or core) ,

towards the inside of which the poles, each provided with

excitation windings made of copper^are projecting.

-___ *S The rotor, usually of massive structure owing to the

excitation by direct current, is a rolled iron cylinder keyed

on a shaft resting on supports. Formed in the peripheral zone of the rotor, near the air gap, are cavities in which* the induced winding is housed; this latter is connected, by means of conductors, to a cylinder-shaped commutator, with segments insulated with respect to each other, also inserted onto the

shaft. Resting on the outer surface of the cylinder are the brushes having^ extending therefrom.the conductors leading to

the terminals of the machine. The operation of this conventional

machine being well-known to those skilled in the art, will not be described herein.

As can be- seen, this machine requires various components,

the structurally most delicate of which are the rotor provided

with a winding, the commutator with segment's made of copper and insulated from each other, and the brushes formed by blocks

of conductive material. All this implies a"^'careful working of

the various components, a quite higher cost thereof and a constant maintenance of the machine to always keep each componen

thereof in a perfectly efficient condition so as not to reduce the efficiency of the machine itself.

The invention proposes now the provision of an electric

machine based on a new concept and which allows first of all the omission of the commutator and in one embodiment will

allow providing a rotor type wh±-drhwill not require any kind

of windings thereon, the whole affording a consequent undoubted

saving in the consumption of materials, in the assembly of the

components and in the maintenance which in thus reduced to simple checks on an extremely reliable machine.

Another object of the invention is to provide an electric

machine having, the characteristics being equal, much higher

efficiency than that of the prior art electric machines, thereby avoiding any danger of overheating during its operation, even at

peak r.p. . For attaining these and other objects which will be

better understood from the following ^'description, the invention

proposes the provision of a pulsating current electric motor

having no commutator, characterized in comprising a rotor, keyed

on a rotating shaft, provided with poles diametrically opposite

to one another relative to the shaft itself on which they extend

for the greater part of its circumference, the poles having an opposite polarity with respect to one another disposed in face of a stator member formed by a substantially cylindrical hollow

body, within which the rotor is arranged; in the stator body there being formed cavities uniformly spaced from one another, each of which is arranged to contain stator double layer windings

which, at the outlet from each cavity, are directed half in a direction and half in the opposite direction; detector means

being provided for detecting the angular position of the shaft,

connected to electronic means piloting the distribution of the power to the stator windings as a function of said angular displacement of the shaft; the components of the machine receivin

their supply from a network.

Two preferred embodiments of the machine according to the invention will now be described by way of non limiting examples

with reference to the annexed drawings, in which:

Figure 1 is a sectional view taken along the line I-I of Fig.2,._. showing the electric machine according to a first embodime

of the invention,

Figure 2 is a sectional view taken along the line II-II of

Fig. 1,

Figure 3 is a sectional view taken along the line III-III

of Fig. 4, showing a second embodiment of the electric machine according to the invention,

Figure 4 is a sectional view taken along the line IV-IV of Fig. 3,

Figure 5 is a block diagram of the machine with the respect feeding, distribution and power circuits.

Figure ^β is a diagrammatic view of the machine control circuit, Figure 7 is an electric scheme of the machine control logic

Figures 8 and 9 are two alternative embodiments of the elec

Dower circuit of the machine,

Figures 10a, 10b and 11a, 11b are diagrams showing the stat

windings in two different embodiments, respectively,

Figures from 12 to 15 are diagrams showing the different

positions of the rotor relative to the stator windings during the

operation of the machine,

Figures 16a, 16b and 17a, 17b are diagrams showing the stat

windings in two further embodiments, respectively,

Figures from 18 to 21 are diagrams of the different positio

of the rotor relative to the stator windings in their embodiment

shown in Figures 16a, 16b, 17a, and 17b.

Figures 22, 23 are, respectively, the block diagram and

the time chart of the electric machine in the embodiment shown

in Figures 17a, 17b.

The pulsating current motor proposed by the invention is ^•

provided substantially with a hollow cylindrical fixed member or

stator 10 and a rotating member or rotor 11 mounted on a shaft 12

within and coaxially to the stator 10 (see Figures from 1

to 4) . Stator 10 is formed by a cylindrical ring,which may be of

a rolled structure, i.e. formed by the superposition of a plurali

BAD O of plate sectors or discs insulated from one another by means of

paper or varnish, in order to reduce the losses by eddy currents.

Within the inner part of the stator near the air gap there are

formed, parallel to the axis of the machine (hence along the generatrixes of the inner cylindrical surface of the stator) , the cavities (or channel) 13 intended to contain the conductors or windings forming the induced circuit. Rotor 11 may instead be

of two types: the first, shown in Figures 1 and 2, is formed by two permanent magnet open rings 14, keyed on the shaft 12, in such a way that on their outer surfaces 15 and 16 there will

appear a "north" and a "south", respectively, and the opposite, i.e. a "south" and a "north" will appear on the corresponding

inner surfaces 17 and 18 contacting the shaft 12.

In the second embodiment shown in Figures 3 and 4, instead, the rotor 11 is of the type with electromagnet formed by a boss * 19, keyed on the shaft 12_A extending from which are poles 20 whi

are widening towards the air gap with pole pieces or shoes 21 , a. on which there are wound inductor windings 22. The poles 20 are

magnetized by direct current and may have.a massive structure or

be made of a bundle of stampings. The windings 22 are insulated electrically from the poles 20 and are supplied through a system

of sliding contacts formed by two continuous rings 23 fixed on t shaft 14 and insulated electrically therefrom; resting on the

rings 23 are the brushes 24 to which there arrive the feeding

conductors 25 (Fig. 4) .

From the electric point of view, the motor may be considered

as being formed essentially by three parts: an electronic control

circuit 26, a distribution circuit 27 for distributing the power,

and the stator windings (as can be seen also in Fig. 5) .

For the motor with electromagnetic rotor, in addition td th

parts mentioned hereinabove should be considered .also a direct

current excitation circuit provided on the rotor.

In Fig. 5, reference numeral 39 indicates the supply from

a network, while reference numeral 40.identifies the flow of powe

As can be seen from Fig. 6, the control_, circuit 26 is forme

by a mechanical portion 29 and an electronic portion 30. The

mechanical portion is formed by one or more opaque segments 31

keyed on the shaft 14 and therefore rigidly connected to it.

The segments 31 are mounted eccentrically (as can be seen

also in Fig. 2) so as to alternately traverse a beam of light 32

directed from a transmitter 33 to a receiver 34, both of them

being mounted on the stator body 38..

The electronic portion 30 of the control circuit (Fig. 7)

is formed by a pilot circuit 27 for the distribution of power,

comprising the phototransistor receiver 34 which receives the bea

of light from the emitter diode 33 when the segment 31 does not interrupt it during the rotation θ of the shaft 14. From the

phototransistor 34,through the pre-amplifier 37, the control

logic pilots the power distributor 27. This latter is shown in two possible embodiments thereof identified in Fig. 8 as circuit SCR, and in Fig. 5 as transistor circuit.

In both cases, the power distributor 27 is substantially

a static switch which must allow the arrival of current to the

stator winding when the segment 31 keyed on the shaft 13 interru the optical circuit 32.

In the circuit illustrated in Fig. 8 there are shown essentially two signal amplifiers 42 and 43, a power SCR 44, a tripping SCR 45, a tripping capacitor 46 and a diode 47 for

discharging the coils.

Instead, in Fig. 9, in addition to an amplifier 48, there

is shown a power transistor 49 and the diode 47 for discharging

the coils, in parallel with the stator winding 41, as in the case of Fig. 8.

It is obvious that both- circuits shown in Figures 8 and 9

are given by way of a non limiting example only, 'inasmuch as the power electronics may be provided in various manners without

departing from the scope of the invention.

As shown in Figures 1, 2 and 3, the stator windings 41 are imbricated or of the spiral type and contained in each of the twentyfour cavities formed in the body 10. Obviously, the cavities may be more or less tha 24, and hereinafter reference

will be made to this latter embodiment only by way of example.

The coils forming the windings 41 are of the double layer type, i.e. the conductors contained in each cavity 13 form two

separate elements.

Figures 10a and 10b show a winding with 2 channels for a

stator with 24 cavities; to be noted is the winding having a double layer, one for each channel.

Instead, Figures 11a and 1 b show 3 double layer windings

for 6 channels, still for a stator with 24 cavities.

Figures 16a and 16b show, as a variant with respect to Figures 10a and 10b, not more than two channels with inlets and

outlets spaced by 180 from one another, but only the inlets being spaced by 180 from one another and the -outlets being

disposed at an angle between 180 and 270 relative to the respective inlet, which,- as results from tests- which have been

carried out, allows to further improve the efficiency of the motor as compared with the solution shown in Figures 10a and 10b.

Figures 17a and 17b show a variant with respect to Figures 16a and 16b, with 3 double layer windings for 6 channels, still for a stator with 24 cavities. .

The operation of the motor is as follows.

The position sensor 29 detects the angular position (angle

in Fig. 6) of the rotor relative to a suitable mark.

This information is transmitted to the control logic 30

which generates a pulse signal which pilots the power electronics

27. This latter>^• in its turn, supplies energy to the winding 41

of the stator 10. The active conductors (in the cavities 13) of the respective winding are traversed by a current which interacts with the magnetic field generated by the rotor 11, and therefor

a torque is originated which is adapted to rotate the driving shaft 12.

For a more detailed explanation, le.t us suppose that the

motor has a stator 10 formed by only one double layer winding (i.e. two windings), as shown in Figures 10a, 10b or 16a, 16b.

In this case, the angular position detector 29 will be formed by a segment 31 and two optical switches.

Each optical switch is coupled to the respective stator

winding, so that each switch pilots the inflow of current for

each winding. For this reason, two "channels" are mentioned.

Let us suppose that the segment 31 has initiated the

interruption of the optical circuit of the first switch. In this situation, the current is enabled to pass into the first winding

which generates a magnetic field having the polarities indicated

in Figures 12 or 18, respectively. This situation is maintained till the segment 31 interrupts the optical circuit of the first

switch. Let us suppose also that the rotor 11 is positioned as shown in Figures 12 or 18, respectively, (the rotor being of

either a permanent magnet type or of an electromagnetic type) .

The rotor 11 will then rotate to assume the position shown in

Figures 13 or 19, respectively. It will be noted that during

this period the winding 2 is not traversed by the current.

When the rotor will have reached the position shown in Fig.14

or 20, respectively, the segment 31 will permit the passage

of light into the first optical switch, and therefore the current in the winding 1 will be interrupted. Segment 31 interrupts now the optical circuit in the second switch and therefore in the winding 2 will begin the passage of current

which generates a magnetic field as in Figures 14 or 20, respectively. The current I will persist till -the rotor 11 reaches the position shown in Figures 15 or 21, respectively. be At this point the current I will/equal to zero whilst the

winding 1 will be traversed again by the current I . This

will take place till the rotor will have reached again the position shown in Figures 13 or 19, respectively.

Thus, the rotation is ensured because the types of windings and the manner of feeding them permit a continuous commutation of the magnetic field. It should be noted that the stator windings 41 are

traversed by the current always in the same direction (the

current I flows in the winding 1 always in the same direction, and this happens also for the winding 2), i.e. there is no inversion of current in the same winding during the operation of the motor.(Fig.22) .

In the case of 6 channels the situation is analogous,

except that during a turn of the rotor each winding is fed for

a period of time equal to about 1/6 of the time employed by

the rotor for accomplishing a turn.(Fig.23) •

Finally, it should be noted that the number of channels

may vary from 1 to 2, 3, 4 or more.

Claims

1.- A pulsating current electric motor having no commutator characterized in comprising a rotor keyed on a rotating shaft,

provided with poles diametrically opposite to one another relativ to the shaft itself on which they extend for the greater part of its circumference, the poles having an opposite polarity

with respect to one 'another disposed in face of a stator member formed by a substantially cylindrical hollow body within which

the rotor in arranged; in the stator body there being formed cavities uniformly spaced from one another, each of which is arranged tσ contain stator double layer windings which, at the

outlet from each cavity, are fed always in the same direction;

detector means being provided for detecting the angular position of the shaft, connected to electronic means piloting the members

distributing the power to the stator windings as a function

of said angular displacement of the shaft; the machine components

receiving their supply from a network.

2.- A motor according to Claim 1, characterizes in that

the stator windings contained in each cavity are two, each being fed in an opposite direction with respect to the other.

3.- A motor according to Claims 1 or 2, characterized in that the windings of the stator are such that each active conductor of each winding has its symmetrical at 180 and the

conductors are traversed by the current in opposite directions with respect to one another; the active conductors traversed by the current in the same direction forming an arc of circumference of less than 180 .