Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1997-10-02
2000-03-28
Dougherty, Thomas M.
Electrical generator or motor structure
Dynamoelectric
Rotary
310254, 310156, H02K 3700, H02K 2112, H02K 112
Patent
active
060435747
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a two-phase electric motor, especially a motor for a counter mechanism or a motor for driving an indicator pointer.
SUMMARY OF THE INVENTION
Such motors are described, for example, in European Patent EP 587,685 of the Applicant. The object of the invention is to improve such motors so as to increase the torque and eliminate the magnetic shunt without losing the advantage of simplicity of manufacture and the possibilities of integrating associated mechanisms such as step-down gears.
To this end the invention relates to a two-phase motor formed by a stator part excited by electric coils and by a magnetized rotor provided with N pairs of poles magnetized radially in alternate directions, N being equal to 3 or to 5. The stator part is provided with at least two W-shaped circuits, each having an electric coil surrounding the central leg. The W circuits are disposed such that when one of the central legs is facing a magnetic transition, the other central leg is facing a magnetic pole. The pole shoes of the legs of a W circuit being spaced angularly by .pi./4 and the pole shoes of the central legs of two W circuits belonging to different phases being spaced angularly by an angle substantially equal to .pi./2.+-.k. .pi./N, where N is the number of pairs of magnetic poles, in this case 3 or 5, and k is equal to 0, 1 or 2.
Such a motor meets the objectives of the invention by virtue of an increased number of active teeth (6 instead of 4) and by virtue of a shorter path of the lines of flux in air. The "W" shape of the stator circuit ensures closing of the lines of flux between the central pole accommodating the coil and the two adjacent poles.
Advantageously, the two "W" circuits have a common leg. The stator can therefore be constructed as a single piece, thus eliminating any problem of angular positioning that is found with stators formed from a plurality of pieces fixed on one support.
In a preferred embodiment, the invention relates to a motor of low assembly cost and very small thickness.
According to a first embodiment, the outer legs of the two "W" circuits are connected by a yoke shaped like the arc of a circle, the yoke advantageously being provided with stator teeth having a spacing of .pi./4 degrees. This embodiment permits construction of a motor with a smaller number of components, namely a rotor, a stator formed by a single piece supporting only two electric coils.
The prior-art step motors also exhibit jerky displacement, due to the fact that a magnetized pole of the rotor assumes a preferential equilibrium position when it is placed facing a stator tooth or when a transition between two magnetic poles is facing a stator tooth. Consequently the relaxing torque constitutes a periodic function of the angular position, with frequency depending on the number of magnetic poles and on the number of stator poles. Attempts have been made in the prior art to "smooth" this function by increasing the number of poles. However, this entails greater mechanical complexity and high manufacturing and assembly cost.
A second object of the present invention is to remedy this drawback by proposing a construction that permits substantial limitation of the relaxing torque with a reasonable number of magnetic and stator poles.
To this end, the invention relates to a preferred embodiment using four "W" circuits, the adjacent legs of which are common, thus forming an 8-pole stator. The central legs of the diametrically opposite "W" circuits support coils of like phase.
This structure permits considerable reduction of the relaxing torque by canceling out harmonics 2 and 4 of the function (relaxing torque, angular position). The motor according to the invention therefore exhibits smooth displacement despite the reduced number of magnetic or stator poles.
Advantageously, the stator comprises a single piece cut such that it has two pairs of diametrically opposite "W" circuits, the pole ends of which are angularly equidistant. Advantageously, t
REFERENCES:
patent: 4475051 (1984-10-01), Chai et al.
patent: 5521451 (1996-05-01), Oudet et al.
patent: 5710474 (1998-01-01), Mulgrave
patent: 5780944 (1998-07-01), Sakamoto
patent: 5880551 (1999-03-01), Prudham
Dinh Le Dang
Dougherty Thomas M.
Sonceboz S.A.
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