US 4,398,134 AGranted

Two-pulse permanent magnet brushless D-C motor

AssigneePapst-Motoren GmbH & Co. KG

InventorRolf Muller

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Abstract

To reduce even instantaneous torque variations when pole gaps of a rotor pass stator pole gaps, the stator pole shoes, adjacent the tip, are shaped to provide an air gap (19) which, behind a projecting tip (FIG. 4: 61) first increases to an intermediate value (53) and then decreases to a minimum (50, 50B) over a zone (54) adjacent the pole gap (44A, 44B) which extends, preferably, over about 7.degree. to 20.degree.-el. Preferably, the opposite pole tip (51A) likewise has a projecting end (61A) with an air gap increasing to a maximum (52) and then decreasing essentially monotonically over the major portion of the pole shoe (41) to the minimum (50) close to the other pole tip (51), the maximum air gap (52) being offset about 10.degree.-20.degree.-el from the actual end of the pole tip (51A). Preferably, the pole gaps (17) on the permanent magnet rotor are narrow and skewed over an extent at least as wide as the stator pole gaps (44), for example between 20.degree. to 45.degree..

Claims24

Dependent claims

Two-pulse brushless direct current (d-c) motor having

an essentially cylindrical permanent magnet rotor element (11, 16) having approximately trapezoidal magnetization with narrow gaps (17) between the poles thereof;
a stator element having a core (18), salient poles terminating in pole shoes (41-44) extending from the core, the tips of adjacent pole shoes being separated by pole gaps (44;
44A, 44B), and winding means (23, 25) on the poles positioned beneath the pole shoes;
an essentially cylindrical air gap (19) separating said rotor element and said stator element;
means (37) controlling current flow, in pulses, through respective winding means on the poles to produce, in operation, an alternating magnetic field to generate an electromagnetic driving torque in the rotor elements,
said stator element pole shoes (41-44) being shaped, in the direction of rotation of the rotor element, to define magnetically effective air gap dimensions which increase and decrease over the angular range of the pole shoes and further to provide, in the region of the pole gaps (44),
compensating means to compensate for torque variations due to the presence of the pole gaps, the pulsed current flow through said winding means being controlled by said current flow control means (37) to energize a winding means when a rotor pole gap passes through a zone of magnetically effective decreasing air gap, while a pulse gap is controlled to occur when the rotor pole gap passes through a zone of magnetically effective increasing air gap;
and wherein, in accordance with the invention,
starting from a region (51A) just inwardly of a first pole tip (61A) adjacent a pole gap (44B)--with respect to the angular circumference of the pole shoe (41)--the air gap (19) is a maximum (52) and said air gap then decreases over a major portion of the pole shoe to a minimum (50) located inwardly of, and close to the other pole tip (61), and then increases again throughout a zone (54) towards said other pole tip (61) to an intermediate value (53).

6 more elements

Two-pulse brushless direct current (d-c) motor having an essentially cylindrical permanent magnet rotor element (11, 16) having approximately trapezoidal magnetization with narrow gaps (17) between the poles thereof;

a stator element having a core (18), salient poles terminating in pole shoes (41-44) extending from the core, the tips of adjacent pole shoes being separated by pole gaps (44;
44A, 44B), and winding means (23, 25) on the poles positioned beneath the pole shoes;
an essentially cylindrical air gap (19) separating said rotor element and said stator element;
means (37) controlling current flow, in pulses, through respective winding means on the poles to produce, in operation, an alternating magnetic field to generate an electromagnetic driving torque in the rotor elements,
said stator element pole shoes (41-44) being shaped, in the direction of rotation of the rotor element, to define magnetically effective air gap dimensions which increase and decrease over the angular range of the pole shoes and further to provide, in the region of the pole gaps (44),
compensation means to compensate for torque variations due to the presence of the pole gaps, the pulsed current flow through said winding means being controlled by said current flow control means (37) to energize a winding means when a rotor pole gap passes through a zone of magnetically effective decreasing air gap, while a pulse gap is controlled to occur when the rotor pole gap passes through a zone of magnetically effective increasing air gap;
wherein, as seen in the direction of rotation (26) of said rotor element (16), each stator element pole shoe (41-44) comprises a portion of strongly increasing magnetically effective air gap including the stator pole tips (61, 61A) adjacent to the respective stator pole gap (44, 44A, 44B) and a stator pole portion contiguous to said gap and extending to a position of maximum air gap (52) located approximately 10.degree. to 20.degree.-el away from the end (61A) of the adjacent pole tip (51A), and a portion of decreasing magnetically effective air gap comprising at least the majority of the remainder of the respective stator element pole shoe (41-44).

4 more elements

Dependencies are inferred from the claim text.