Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1983-04-04
1984-11-06
Miller, J. D.
Electrical generator or motor structure
Dynamoelectric
Rotary
310156, 310168, 318254, H02K 304
Patent
active
044814402
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a brushless d-c motor with a permanent magnet rotor, in which the poles, when viewed in the direction of rotation, have an approximately rectangular or trapezoidal magnetization curves.
BACKGROUND
It is known to obtain pulses from the main winding of a brushless d-c motor when the motor operates. The frequency of the pulses is proportional to the instantaneous rotor speed and can therefore be used for measuring or controlling the motor speed. However, the frequency is relatively low, to wit, p.times..omega..sub.mech, wherein p is the number of pole pairs and .omega..sub.mech is the angular velocity of the rotor per second. The main, or power current flowing in the winding of the motor affects the pulses in their relative phase position with respect to each other and relative to the position of the rotor. A speed control employing these pulses for comparing nominal or command values and actual values is undesirably affected and continuous oscillations of the rotor may result.
THE INVENTION
It is an object to provide a brushless d-c motor which generates pulses having a sufficiently high frequency proportional to the motor speed, that are, preferably, uninfluenced by the power currents flowing in the main winding of the motor, and which has low equipment requirements.
Briefly, in accordance with the invention, the stator of the motor has a sensor winding thereon for picking up and coupling-out at least one harmonic wave of the voltage induced in the stator by the rotor poles; the sensor winding is matched to the number of rotor poles which is equal to the product (2p .times.L), wherein 2p is the actual number of poles of the rotor, and L is the ordinal number of the harmonic wave to be picked up. The special harmonic fields included in the nonsinusoidally magnetized poles induce voltages in the sensor winding in this manner corresponding to that harmonic wave for which the sensor winding is dimensioned. The fundamental wave is substantially or completely suppressed. Advantageously the sensor winding is located such that transformer coupling between it and the main winding is avoided. This is achieved by a special selection of the spacial phase position between the main winding and the sensor winding, or by omission of several winding steps and/or spacial phase shifting of part of the sensor winding with respect to another part thereof.
A particularly simple arrangement of the sensor winding results when separate slots are provided for the same having a position exactly defined relative to the main winding. For economic reasons it is advantageous to place the sensor winding directly into the slots of the main winding, since then no additional slots are required for the sensor winding. Transformer coupling with the main winding can still be avoided by forming the sensor winding with two simple wave windings shifted relative to each other by a predetermined angle. In certain cases individual winding steps have to be omitted.
DRAWINGS
FIG. 1 is a sectional view through a cylindrical air gap motor illustrating a first embodiment of the invention,
FIG. 2 is a sectional view through the stator of a second embodiment,
FIGS. 3A-3C are diagrams explaining FIGS. 1 and 2,
FIG. 4 is a circuit diagram explaining the invention,
FIG. 5 is a diagram of a variant of FIG. 3B showing main windings employed with the sheet metal stamping of FIG. 2, which windings can be advantageously employed even independently of the sensor winding,
FIG. 6 is a plan view of the stator winding of a four pole motor with flat, or axial air gap and a sensor winding suitable for decoupling of the second harmonic wave,
FIG. 7 is an alternative type of the sensor winding of FIG. 6, which is particularly suitable for flat motors having an axial stray field,
FIG. 8 is a second alternative type of the sensor winding of FIG. 6, which is also particularly suitable for flat motors having an axial stray field,
FIG. 9 is an enlarged representation of the developed magnetization represented in FIG. 3A of a rotor for a cylindri
REFERENCES:
patent: 3045197 (1962-07-01), Vanslette
patent: 4093897 (1978-06-01), Fujita et al.
patent: 4109170 (1978-08-01), Fujita et al.
patent: 4125792 (1978-11-01), Schmider
patent: 4211963 (1980-07-01), Mueller
Miller J. D.
Papst-Motoren KG
Rebsch D. S.
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