Electrical generator or motor structure – Dynamoelectric – Linear
Reexamination Certificate
1998-01-12
2001-06-05
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Linear
Reexamination Certificate
active
06242822
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to an electric machine with a separately excited rotor order for the generation of magnetic fields which follow one another in the movement direction of the rotor, each magnetic field corresponding to a whole magnetic period, and with stator poles which are arranged so as to follow one another along the rotor arrangement.
2. Description of the Related Art
In known electric machines of this type with a separately excited rotor (or stator, the two terms rotor and stator being interchangeable for present purposes), the magnetic fields corresponding to the whole magnetic periods are formed by individual poles, a north pole and a south pole (for each magnetic period), which are separated from one another. Stator pole sets which correspond with respect to the arrangement and quantity of stator poles are provided in accordance with the quantity of magnetic fields formed by the pairs of rotor poles, so that corresponding arrangements of stator poles are located under every pair of rotor poles. Permanent magnets can be used, for example, for the rotor poles.
As a result of stray flux and especially owing to the gaps between the rotor poles, a rotor field is formed in machines of this type such that a movement of the rotor relative to the stator results in a nonlinear variation of the forces present at the rotor poles, which forces are dependent on the sum of the prevailing field amounts at the poles. This results finally in a self-locking behavior, i.e., a self-holding torque occurs (also known as cogging torque or cogging). This self-locking behavior is especially pronounced during slow idling. This effect occurs especially because the nonlinearly changing forces add up over the entire length of the stator or rotor due to the constantly identical ratios within the individual magnetic periods of the rotor field. In connection with the self-locking behavior, such machines have other disadvantages such as rough running, vibrations, the need to operate the machines as minimum speeds, etc.
Since narrow limits are imposed on variations in the shape of the stator and rotor poles, a reduction of the self-holding torque is possible only by means of offsetting the pole stack or laminated core, increasing the air gap, or by means of a specially developed pole head shape. However, these steps impair the operating parameters of the machine, so that a machine with a self-locking behavior which is improved as a result of these steps represents an unfavorable compromise.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide an electric machine of the type mentioned in the beginning, whose self-holding torque is eliminated or at least reduced.
In accordance with a first solution according to the invention, this object is met in an electric machine which is characterized in that a number of stator poles which is not a whole number is allotted to a magnetic period.
In accordance with this solution of the invention, there result different arrangements of stator poles relative to the individual magnetic fields corresponding to whole magnetic periods, so that nonlinearly changing forces present at the rotor poles which could lead to a self-holding torque do not add up along the length of the stator or rotor leading to a multiplying of these forces, but rather cancel one another by reducing or eliminating the self-holding torque. In accordance with the number of stator poles allotted to a magnetic period, which number differs from a whole number, there results a varying offset between the individual magnetic fields corresponding to the whole magnetic periods and the stator poles arranged opposite thereto, so that differently oriented forces act on the different rotor poles, which forces can average out along the length of or circumference of the stator or rotor.
In accordance with the divergence from the whole number, a periodicity in the spatial arrangement of the stator poles relative to the magnetic field periods within the rotor or stator length is avoided. Accordingly, there are no repetitions in the spatial relationships between the magnetic fields and stator poles, so that there is no addition effect which magnifies cogging torques.
The construction of the electric machine according to the invention can advantageously make use exclusively of standard materials and standard structural component parts.
In an advantageous embodiment form of the invention, the stator poles are supplied in a time-delayed manner to compensate for the varying spatial offset between the magnetic fields and the stator poles which is caused by the divergence of the number of stator poles to be allotted to a magnetic field period from a whole number. As a result of this step, impairment of the motor output is compensated in that the time-delayed supply which takes into account the offset provides that the contribution of the stator poles to the total force generating the motor torque is substantially independent from their offset.
Another electric machine according to the invention in which the above-stated object is met is characterized in that the magnetic fields which follow one another, each of which corresponds to a whole magnetic period, are formed by permanent magnet portions having alternately a magnetic north pole and a magnetic south pole, wherein separating gaps which extend diagonally to the movement direction of the rotor with alternately opposite angles of inclination are provided between the permanent magnet portions.
Also, an averaging effect can be achieved by the solution according to the invention, in which amounts of force by means of which a holding torque could be formed cancel one another at least partially as a result of the configuration of the separating gaps.
In an advantageous construction of this additional solution according to the invention, the separating gaps are parts of an individual, continuous separating gap by which, extending continuously in the movement direction, the magnet bodies containing the permanent magnet portions are separated from one another, wherein one of the magnet bodies comprises the magnet elements for the north poles and the other magnet body comprises the magnet elements for the south poles. In particular, the continuous separating gap can be configured in the shape of a sine curve. Discontinuities in the field pattern between the opposite poles are suitably compensated by means of this continuous separating gap, which contributes to a further reduction of the self-holding torque.
Further advantageous possibilities for configuring the invention follow from the subclaims.
The invention will now be explained and described more fully with reference to embodiment examples and with reference to the accompanying drawings referring to these embodiment examples.
REFERENCES:
patent: 4315171 (1982-02-01), Schaeffer
patent: 4847526 (1989-07-01), Takahara et al.
patent: 4978895 (1990-12-01), Schwarz
patent: 5206567 (1993-04-01), Sakurai et al.
patent: 5298827 (1994-03-01), Sugiyama
patent: 5672944 (1997-09-01), Gokhale et al.
patent: 5821725 (1998-10-01), Wang et al.
patent: 2386181 (1978-10-01), None
patent: 2434505 (1980-03-01), None
patent: 2057778 (1981-04-01), None
I.E.E.E., vol. MAG 23, NO 5, Sep. 1987, New York, pp. 2578-2580, K. Hayafune; E. Masada; Dynamics of the PM Type Linear Synchronous Motor Magnetically Levitated Carrier Vehicle Sep. 1987.
Patent Abstracts of Japan, vol. 014, No. 268 (E-0939), Jun. 11, 1990 & JP 2083903 (Asahi Chem Co Ltd), Mar. 26, 1990.
Strothmann Rolf
Strothmann Thomas
Friedrich Kueffner
Jones Judson H.
Ramirez Nestor
LandOfFree
Electric machine does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electric machine, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electric machine will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2459514