Enclosed miniature motor

• US 4,755,699 A
• Filed: 09/24/1984
• Issued: 07/05/1988
• Est. Priority Date: 09/22/1983
• Status: Expired due to Term

• Current Assignee: Papst Licensing GmbH & Company Kg
• Original Assignee: Papst-Motoren GmbH & Company KG (Ebm-Papst Mulfingen GmbH & Company KG)
• Inventors: Schmider, Fritz
• Primary Examiner(s): Skudy, R.
• Application Number:
  US06/653,970
• Time in Patent Office: 1,380 Days
• Field of Search: 310/40 MM, 310/46, 310/68 R, 310/68 B, 310/156, 310/43, 310/90, 310/179, 310/180, 310/184, 310/254, 310/258, 310/259, 310/DIG. 3, 310/DIG. 6, 318/138, 318/154, 318/254 A, 318/439
• US Class Current: 310/68.00R
• CPC Class Codes: H02K 29/08 using magnetic effect devices, e.g. Hall-plates, magneto-resistors H02K29/12 takes precedence

Abstract

Designed especially for hand-held dictation devices the motor has a three-phase external stator and two-pole permanent-magnet internal rotor, the two enclosed by an external housing from one axial end of which the rotor shaft projects out, its other axial end provided with a thrust bearing for the rotor shaft'"'"'s other end. At least one Hall element, although more typically three, is provided, located at the peripheral edge of one of the axial ends of the rotor to sense axially emanating stray rotor flux. The rotor is directly secured to the rotor shaft, the shaft being ferromagnetic and near its outwardly projecting end provided with a ferromagnetic bearing mounted in a ferromagnetic end plate, so that stray flux sensed by the Hall element can travel from the rotor to the Hall element along a magnetic circuit for such sensed stray flux, but with the magnetic circuit being made up of motor components and structural parts that are required anyway. At least the radially outer part of the stator iron, serving as yoke for conducting motor flux circumferentially along the stator, is constituted by a stack of sheet-metal sheets. The stator iron may be a hollow cylinder at whose inner periphery is provided an annular, cylindrical winding constituted by a continuously wound conductor of uniform conductor-density but provided with angularly spaced taps to form the three phases, or the stator iron may have three radially inwardly extending T-shaped salient poles each carrying a stator-winding coil, with the radially innermost part of the T-shaped salient pole being a pole-shoe plate having circumferentially extending, axially spaced, comb-like slits, with all pole-shoe plates being mounted on a plastic carrier for simultaneous installation of all of them as a single unit. Each phase is energized twice per rotor rotation, with current of a first direction during a respective first half-rotation and then with current of opposite direction during the next half-rotation, to maximize the power-to-weight ratio, this being done using a full-bridge energizing circuit for the three phases.

Claims

1. An enclosed, miniature, brushless, cylindrical-air-gap d.c. motor, comprising

a generally cylindrical external housing having two axial ends,

interiorly of the external housing a stator,

internally of the stator a permanent-magnet rotor having a total of one north and one south pole,

a rotor shaft,

means mounting the rotor coaxially with the rotor shaft for joint rotation of the two, with the rotor shaft projecting outwardly from one axial end of the external housing and furthermore mounting the stator coaxially with the permanent-magnet rotor, said means including an axial bearing mounted at one of said ends of the external housing, the rotor shaft having an axial end which axially bears against said axial bearing,

a three-phase stator winding mounted to cooperate with the stator, the three-phase stator winding consisting of three phases which comprise a plurality of stator coils provided with feed lines for connecting the three phases to a circuit for energizing the three phases, the stator further comprising radially extending pole portions, which include coil carrying portions and circumferentially extending pole shoe portions,

the stator, except for the circumferentially extending pole shoe portions, being substantially entirely constituted by a stack of sheet-metal sheets,

the stator for the circumferentially extending pole shoe portions being in the form of pole-shoe plates provided at the radially inner end of each coil-carrying portion and extending in the axial direction of the rotor shaft in a first axial direction beyond the stator'"'"'s sheet-metal stack and also extending in the opposite second axial direction beyond the stator'"'"'s sheet-metal stack, the permanent-magnet rotor having two axial ends, and

at least one magnetic-field responsive rotor position sensor and means mounting the latter in the region of one of the axial ends of the rotor at a location which is in the region of the axially travelling stray flux emanating from the rotating permanent-magnet rotor,

each pole-shoe plate being provided with comb-like parallel slits which extend parallel to the rotation direction and are spaced one from the next in the axial direction of the motor.

2. A miniature motor as defined in claim 1, including a circuit for energizing the three phases of the three phase stator winding, the energizing circuit comprising full-bridge energizing circuit means operative for energizing each of three phases twice per rotor rotation by driving current in a first direction through each phase during a respective first half of a rotor rotation but then in the opposite direction during the next-following half of the rotor rotation.

3. A miniature motor as defined claim 1,

the rotor having a periphery and a peripheral edge at one axial end thereof,

the means mounting the at least one magnetic-field-responsive rotor position sensor comprising means mounting the latter in the region of the rotor'"'"'s aforementioned peripheral edge.

4. A miniature motor as defined in claim 1,

the external housing of the motor having at the one of its two axial ends that is nearer to the at least one rotor position sensor a ferro magnetic housing end wall, the latter being provided at the portion thereof near the at least one rotor position sensor with an axially inwards depression serving to locate the said end wall, at said portion thereof, axially close to the sensor to form, together with the sensor and the rotor, part of a magnetic circuit for the stray rotor flux sensed by the sensor.

5. A miniature motor as defined in claim 1,

the number of pole shoe plates being three in correspondence to the number of the stator pole shoe portions, said stator including a generally star-shaped plastic carrier means which mounts the three pole-shoe plates.

6. A miniature motor as defined in claim 1,

the permanent-magnet rotor comprising a tubular permanent-magnet part provided with said one north and one south pole and furthermore comprising a disk of ferromagnetic material located at the same end face of the rotor at which the sensor is located and directly connecting the tubular part to the rotor shaft.

7. A miniature motor as defined in claim 1,

the rotor comprising a cylindrical permanent magnet secured directly on the rotor shaft,

the external housing of the motor having at each axial end thereof a generally flat end wall,

first and second bearings provided in respective ones of the flat end walls of the external housing mounting the rotor shaft for rotation.

8. A miniature motor as defined in claim 1,

furthermore, comprising a conductor plate and means mounting the conductor plate on the stator of the motor at the other of said axial ends of the external housing, said axial bearing being a thrust bearing directly secured on said conductor plate.

9. A miniature motor as defined in claim 1, the stack of sheet-metal sheets being secured to the interior of the external housing.

10. A miniature motor as defined in claim 4,

the permanent-magnet rotor comprising a tubular permanent-magnet part provided with said one north and one south pole and furthermore comprising a disk of ferro-magnetic material directly connecting the tubular part to the rotor shaft, the disk of ferromagnetic material being located at the same axial end of the rotor at which the sensor is located so as to form, together with said tubular part, said ferromagnetic housing end wall and said sensor, part of said magnetic circuit for the stray rotor flux sensed by the sensor.

11. An enclosed, miniature, brushless, cylindrical-air-gap d.c. motor, comprising

a generally cylindrical external housing having two axial ends,

interiorly of the external housing a stator,

internally of the stator a permanent-magnet rotor having a total of one north and one south pole,

a rotor shaft,

means mounting the rotor coaxially with the rotor shaft for joint rotation of the two, with the rotor shaft projecting outwardly from one axial end of the external housing and furthermore, mounting the stator coaxially with the permanent-magnet rotor, said means including an axial bearing mounted at the other end of the external housing, the rotor shaft having an axial end which axially bears against said axial bearing,

a three-phase stator winding mounted to cooperate with the stator,

the stator being formed by a stack of sheet-metal sheets,

the permanent-magnet rotor having two axial ends,

and at least one magnetic-field-responsive rotor position sensor and means mounting the latter in the region of one of the axial ends of the rotor at a location which is in the region of the axially travelling stray flux emanating from the rotating permanent-magnet rotor,

the stator having a radially inner peripheral surface which is generally cylindrical,

the three-phase stator winding comprising a winding of annular cylindrical shape made up of continuously wound conductor exhibiting a uniform conductor-density and encircling the rotor, said annular cylindrical winding being mounted coaxial with, in proximity to and in electromagnetically cooperating relationship to the generally cylindrical inner peripheral surface of the stator,

the permanent-magnet rotor comprising a tubular permanent-magnet part provided with said one north and one south pole and furthermore comprising a cylindrical carrier member of ferromagnetic material directly connecting said tubular part to the rotor shaft at the axial end of the rotor at which the at least one sensor is located,

the external housing being made of plastic material and comprising a peripheral wall portion, a generally flat end wall portion of one piece with the peripheral wall portion and located at that axial end of the rotor which is opposite to the axial end of the rotor at which the sensor is located, and furthermore, comprising an axially projecting extension which is of one piece with said generally flat end wall portion, said axially projecting extension projecting axially into the interior of the motor,

and furthermore, including two bearings for the rotor shaft, both encircling the rotor shaft and being mounted on said axially projecting extension of said external housing,

the cylindrical carrier member comprising a first tubular portion which is located radially outwards of and encircles said axially projecting extension of said external housing, and

the cylindrical carrier member furthermore, comprising a second tubular portion having an internal peripheral surface secured to the rotor shaft.

12. A miniature motor as defined in claim 11,

furthermore including a circuit for energizing the three phases of the three-phase stator winding,

the energizing circuit comprising full-bridge energizing circuit means operative for energizing each of the three phases twice per rotor rotation by driving current in a first direction through each phase during a respective first half of a rotor rotation but then in the opposite direction during the next-following half of the rotor rotation.

13. A miniature motor as defined in claim 11,

the rotor having a periphery and a peripheral edge at one axial end thereof,

the means mounting the at least one magnetic-field-responsive rotor position sensor comprising means mounting the latter in the region of the rotor'"'"'s aforementioned peripheral edge.

14. A miniature motor as defined in claim 11,

said stack of sheet-metal sheets having the shape of a hollow cylinder, said radially inner peripheral surface of the stator being the inner peripheral surface of said hollow cylinder, said winding of annular cylindrical shape being secured to the inner peripheral surface of the stack of sheet-metal sheets.