Multiphase motor with magnetized rotor having N pairs of poles with axial magnetization

This invention relates to multiphase motors, the rotor of which has N pairs of poles with axial magnetization.

Different types of motors with magnetized rotors exist. According to the present invention the magnetization axes of the rotor is parallel to the rotation axis of the rotor.

A principal object of the invention is to create a multiphase motor with a high efficiency by using existing materials, and which is easily manufactured by industrial processes and the phase number of which, as well as the range of powers, can be very extensive without modifying the motor conception. Subsidiarily, the invention also has as its object to create a multiphase motor which can easily be adapted to the stepping mode.

The field of applications of the motor according to the invention is thus very large. This motor can particularly be used with driving systems for office automation, robots, aeronautical and space industry, photographic installations and time-keepers. More generally, the motor according to the present invention is suitable to all the systems using digital techniques, and, more particularly, to all those with which size output power and speed constitute critical criteria.

One embodiment of the motor according to the invention and two variants are represented schematically and simply by way of example in the drawings in which:

FIG. 1 is a view of that embodiment in the direction of the rotation axis of the rotor;

FIG. 2 is a plan view of its stator;

FIG. 3 is a plan view of its rotor;

FIG. 4 is a perspective view of this rotor;

FIG. 5 is a view similar to that of FIG. 4, but relating to the first variant;

FIG. 6 is a plan view of a piece of the second variant;

FIGS. 7 and 8 are linear unrollings of the motor which illustrate its mode of operation.

The motor represented in FIGS. 1 to 4 has a rotor 1 provided with a number N of pairs of poles equal to eight. The number m of the phases of this motor is equal to two. Moreover, the shifting between these two phases is equal to 2τ/(N·m).

The rotor 1 is of ferromagnetic material such as samarium-cobalt, the coercive force of which is high and the specific mass small. It has eight pairs of poles, the magnetization axes of which are parallel to the rotation axis of the rotor, but alternately in opposite directions, and they are regularly arranged around that axis.

The rotor 1 is mounted opposite a stator 2 which forms two phases r and s. Each phase r, s comprises two polar pieces 3, 4 coplanar, interpositional in one another, piece 3 being within piece 4. The two polar pieces 3, 4 are separated from one another by a sinuous air-gap 5 in each phase.

The polar pieces 3, 4 are of ferromagnetic material having a small coercive force and a high saturation induction. They have poles 6 (FIG. 1) which are designated by p₁, p₂, . . . , p₉ in FIG. 2 to facilitate the explanation.

FIG. 2 shows that the poles p₁, p₃ of polar piece 4 of phase r, the poles p₂, p₄ of polar piece 3 of this same phase r, poles p₆, p₈ of polar piece 4 of phase s and pole p₇ of this same phase s have, each one, the same arc. These different poles are called full poles, whereas poles p₅ and p₉ of polar piece 3 of phase s are fractional poles. The sum of the angular extensions of these two fractional poles is at least approximately equal to the angular extension of a full pole.

In the general case of a motor with m phases, the rotor of which has N pairs of poles, the poles of the polar pieces of m-1 phases and those of one polar piece of the mth phase are full; they are 1/2 N/m in number per polar piece and they are arranged at an angular interval at least approximately equal to twice that between the pairs of adjacent poles of the rotor. Regarding the poles of the remaining polar piece, there are (1/2 N/m)-1 which are full, whereas the m remaining poles are fractional, the sum of their arcs being at least approximately equal to the arc of a full pole.

With the embodiment represented, one of the phases r, s is displaced with respect to the other one through an angle α.sub.γ of 22.5°. In the general case of a motor with m phases, the rotor of which has N pole pairs, α.sub.γ =2π/Nm. The arc of every fractional pole is at least approximately equal to 1/m times that of a full pole.

The displacement α.sub.γ can be made different from 2π/Nm. In this case, the sum of the arcs of the fractional poles remains at least approximately equal to the arc of a full pole, but all these fractional poles no longer have the same arc.

The two polar pieces of each phase of stator 2 are magnetically connected to one another by a core 7 of ferromagnetic material having a small coercive force and a high saturation induction. A coil 8 is wound around the core of each phase.

The polar pieces 3, 4 of each phase can be positioned each one by a pin and a threaded foot (not shown). Regarding mounting the rotor 1, it is conventional. It can be journaled in bearings having a small sliding friction. Its shaft (not shown) can carry a pinion meshing with a first wheel of a wheel gear to transmit the rotor rotations to the gear.

In the first variant (FIG. 5), a disk 9 of soft ferromagnetic material is secured to the face of the rotor opposed to that facing the stator.

In the variant of FIG. 6, the motor comprises a fixed soft ferromagnetic disk which is mounted so that the rotor will be located between that disk and the stator. That disk is provided with openings 10 which are judiciously located in order to produce a positioning torque.

FIGS. 7 and 8 illustrate the operation of the motor. They are linear developed views thereof. More particularly, they are diagrammatic sections linearly unrolled. The shift of the phases r, s is 22.5°.

FIG. 8 shows the state of the motor when the rotor has moved through 22.5° with respect to that represented in FIG. 7, i.e., in the general case, through an angle α.sub.γ =2π/Nm.

In order to facilitate understanding the operation of the motor represented, the manner to determine the characteristic curve called mutual torque is first disclosed. The mutual torque is that due to the interaction between the magnetic fluxes of the rotor and those of the coils.

In the position of FIG. 7, poles of the rotor 1 are exactly opposite poles p₁, p₂, p₃ and p₄ of phase r. That Figure shows that the rotor fluxes directed toward the stator are received by poles p₂ and p₄ of polar piece 3, from which they are directed to core 7 of phase r, through which they flow from B to A. They are then closed by passing through poles p₁ and p₃ of polar piece 4 of the stator. Regarding the rotor fluxes directed in the opposed directon, they are also received by polar piece 3 of phase r and are consequently directed along the same path as that of the first ones considered. Thus, they flow through core 7 also from B to A before they get closed. In the considered rotor position, the rotor flux through core 7 of phase r is thus maximum.

Upon moving the rotor from that position through an angle α.sub.ρ equal to 2π/N, it is easy to see that the flux through core 7 of phase r is maximum too, but in the opposite direction, i.e., it flows through this core from A to B. There is thus a reversal of the rotor flux in core 7 of phase r, every time the rotor turns through an angle equal to 2π/N, of 45° in the example represented.

When the coil of phase r is driven, an interaction torque results between the coil and the magnetized rotor, the mutual torque, the period of which is equal to 4π/N, and the neutral positions of which correspond to the rotor positions in which the poles of the rotor are exactly opposite the poles of the polar pieces of this phase r.

Regarding poles p₅, p₆, p₇, p₈ and p₉ of phase s, between which are the poles of the rotor in FIG. 7, it is easy to see that this phase s also has a mutual torque with a period of 4π/N, but displaced with respect to the mutual torque of phase r through an angle α.sub.γ =2π/Nm, of 22.5° in the example represented.

The rotor position in which its flux through core 7 of phase s is maximum in that of FIG. 8. The two fractional poles p₅ and p₉ each receive a flux equal to 1/m times the flux received by a full pole, thus 1/2 times that of a full pole in the presented example.

The remarks made here above with respect to an angular displacement of the phases different from 2π/Nm are applicable here too.

The motor behavior with the indicated mutual torques, when the coils are driven, is known and will not be disclosed.

The two-phase motor represented with a rotor having eight pairs of poles is obviously not the only possible embodiment of the motor according to the invention. The relation m=N/2n between the number N of pole pairs of the rotor and that m of the phases, n being an integer, need only be satisfied. The following table indicates the possible configurations of the motor according to the invention.

______________________________________m                  n     N______________________________________2                  1      4two-phase          2      8              3     12              4     16              . . . . . .              . . . . . .3                  1      6three-phase        2     12              3     18              4     24              . . . . . .              . . . . . .4                  1      8four-phase         2     16              3     24              4     32              . . . . . .              . . . . . .. . .              . . . . . .              . . . . . .______________________________________

With the first variant represented in FIG. 5, the presence of the soft ferromagnetic disk 9 on the rotor has an effect to increase the flux of every pair of rotor poles by increasing the permeance from the view point of the rotor.

The fixed ferromagnetic disk of the second variant represented in FIG. 6 has an analogous effect. Moreover, it overbalances the attraction between the rotor and the stator. The openings 10 of this disk have as effect to generate a positioning torque. The openings are equal in number to that of the pole pairs of the rotor and they are regularly distributed to form a circular row concentric to the rotor. In this case, the period of the positioning torque is equal to 2π/N. However, it would also be possible to generate a positioning torque with a period of 4π/N by suppressing every other opening 10.

Regarding the efficiency of the motor according to the invention and without going into the details of the theory, those skilled in the art will note that it is high.

At first, the fluxes of all the pole pairs of the rotor flow in the same direction through each coil core, because of the disclosed interpositioning of polar pieces 3, 4, of the magnetic connection provided between the two polar pieces and of the provision of full and fractional poles. There is, indeed, no pole pair of the rotor, the flux of which would be lost, i.e. would not be closed through the cores and would not contribute in additive manner to the mutual flux.

Moreover, when the motor operates stepwise, the fact that the rotor is plain, i.e. has no angular gap between the magnetization axes which would not be equal to 2π/N, optimizes, from the view point of the efficiency, the relation between the total flux of the pole pairs of the rotor and the inertia of the rotor. That is due to the fact that the efficiency is a function increasing with the flux and decreasing with the inertia, but that the power to which that function increases with the flux is higher than that to which it decreases with the inertia.

The phase number of the motor according to the invention can be very great without modifying the motor concept, since it suffices that the relation m=N/2n be satisfied for n being an integer. In other words, it suffices to increase the number N of pole pairs of the rotor in order to increase the number m of phases.

The motor according to the invention also has the advantage of offering a very large range of powers, without having to modify the motor concept. Without going into the details of theory, it is, indeed, intuitive to observe that the mechanical power of a motor of this type is a function increasing with the number of pole pairs of the rotor as well as with the diameter of the rotor.

The manufacture of the motor according to the invention is easy, since its stator is wholly determined in a plane.

Finally, the motor according to the invention has the advantage of being suitable to the stepping mode of operation, since the disk of FIG. 6 permits the entry of the positioning torque required by that operation mode.