Two-pulse permanent magnet brushless D-C motor

Claim 2

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).

Claim 3

Motor according to claim 1, wherein the course of the air gap (19) in said zone (54) leading towards said other pole tip--with respect to a cylindrical envelope (49)--has, in cross section, the approximate form of a biconvex lens.

Claim 4

Motor according to claim 2, wherein said zone (54) extends over a range of from between 7° to 20°-el from said other pole tip.

Claim 5

Motor according to claim 1, wherein the terminal ends (51, 51A) of the pole tips are formed with extensions (61, 61A) projecting towards the air gap.

Claim 6

Motor according to claim 1, wherein the air gap starting from said first pole tip (61A) first increases from an intermediate level to the position of maximum air gap (52), said position of maximum air gap being located inwardly of and close to said adjacent first pole tip (61A), said maximum air gap having a width which is greater than said intermediate value (53) of the air gap adjacent the other pole tip (61).

Claim 7

Motor according to claim 5, wherein the position of said maximum air gap (52) is approximately 10° to 20°-el away from the adjacent first pole tip (61A).

Claim 8

Motor according to claim 1, wherein the pole gaps (17) of the rotor element are inclined or skewed with respect to the pole gaps (44) of the stator element.

Claim 9

Motor according to claim 7, wherein said angle of inclination or skew is in the order of between 20° to 45°.

Claim 10

Motor according to claim 1, wherein the terminal ends (51, 51A) of the pole shoe tips have pointed projections (61, 61A) directed towards the rotor.

Claim 11

Motor according to claim 1, wherein the terminal zones (51, 51A) of the pole tips immediately adjacent the pole gaps (44) comprise zones of increased iron volume magnetically effective to decrease the magnetic effect of said pole gaps; said zones of increased iron volume being concentrated within an angular range of between about 5° to 10°-el from the limit of the stator pole gap.

Claim 12

Motor according to claim 1, wherein the width (N) of the stator pole gaps is more than 5% of one pole pitch (180°-el).

Claim 13

Motor according to claim 11, wherein said motor is an external rotor motor.

Claim 14

Motor according to claim 6, wherein the pole gaps (17) of the rotor element are inclined or skewed with respect to the pole gaps (44) of the stator element.

Claim 15

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° to 20°-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).

Claim 16

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° to 20°-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).

Claim 17

Motor according to claim 14, wherein the air gap (19) adjacent to the pole tip (61) pointing in the direction of rotation (26) has a portion (54) which, with respect to a cylindrical envelope (49) of said stator, in cross section has the approximate form of a biconvex lens and forms part of said portion of increasing magnetically

Claim 18

Motor according to claim 14, further including a portion of increasing magnetically effective air gap at a zone (54) adjacent the region of the pole at said minimum air gap (50), in which the effective air gap (53) has an intermediate value, said zone (54) extending over a range of from between 7° to 20°-el from the contiguous pole tip (61).

Claim 19

Motor according to claim 15, wherein said maximum air gap (52) has a width greater than the greatest value of the air gap at its portion (54) having the approximate form of a biconvex lens.

Claim 20

Motor according to claim 14, wherein the terminal ends (51, 51A) of the pole shoe tips are formed with extensions (61, 61A) projecting towards the rotor.

Claim 21

Motor according to claim 18, wherein said extensions are pointed projections.

Claim 22

Motor according to claim 14, wherein the pole gaps (17) of the rotor element are inclined or skewed with respect to the pole gaps (44) of the stator element.

Claim 23

Motor according to claim 20, wherein said angle of inclination or skew is in the order of between 20° to 45°.

Claim 24

Motor according to claim 14, wherein the terminal zones (51A, 52) of the pole tips immediately adjacent the pole gaps (44) comprise zones of increased iron volume magnetically effective to decrease the magnetic effect of said pole gaps; said zones of increased iron volume being concentrated within an angular range of between about 5° to 10°-el from the limit of the stator pole gap.

Claim 25

Motor according to claim 14, wherein the width (N) of the stator pole gaps is more than 5% of one pole pitch (180°-el).

Claim 26

Motor according to claim 23, wherein said motor is an external rotor motor.