Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K1/00—Details of the magnetic circuit
  • H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
  • H02K1/22—Rotating parts of the magnetic circuit
  • H02K1/27—Rotor cores with permanent magnets
  • H02K1/2786—Outer rotors
  • H02K1/2787—Outer rotors the magnetisation axis of the magnets being perpendicular to the rotor axis
  • H02K1/2789—Outer rotors the magnetisation axis of the magnets being perpendicular to the rotor axis the rotor consisting of two or more circumferentially positioned magnets
  • H02K1/2791—Surface mounted magnets; Inset magnets
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K29/00—Motors or generators having non-mechanical commutating devices, e.g. discharge tubes or semiconductor devices
  • H02K29/06—Motors or generators having non-mechanical commutating devices, e.g. discharge tubes or semiconductor devices with position sensing devices
  • H02K29/08—Motors or generators having non-mechanical commutating devices, e.g. discharge tubes or semiconductor devices with position sensing devices using magnetic effect devices, e.g. Hall-plates, magneto-resistors

Definitions

• This invention is concerned with the design of a D.C. Motor which is particularly, but not exclusively, suited for use in fans which are of relatively small size and are intended for use within housings of computers or other electronic equipment for cooling purposes.
• this invention provides a brushless D.C. Motor incorporating an electronic commutation system incorporating a sensor for sensing the angular position of the rotor magnet and circuitry for controlling switching of the current to the stator windings, the electronic components being mounted on a printed circuit which is integrally moulded with a body providing a bearing housing for the rotor shaft.
• the integral formation of the printed circuit with the bearing housing for the rotor shaft enables the rotor to be mounted with very great accuracy (both linear and angular) with respect to components carried by the printed circuit.
• the body shouldprovide locating portions for predetermined positioning of the stator and the sensor, since the relationship of the rotor to the stator, and particularly to the sensor, is critical for optimum operation of the motor.
• the locating portions include upstanding posts which limit axial movement of the 'stator and locate within interpole slots in the stator to determine rotational position thereof.
• the locating portions will incorporate a mount for receipt of the sensor in one of two alternative positions. This enables the sensor to be mounted in the correct position for either rotation of the rotor, as required.
• the bearing housing will incorporate a bearing assembly for the rotor shaft.
• the body can incorporate locating means for retaining an end cap which is positioned over the end of the body to cover the electronic components.
• This end cap can locate over and seal the end of the bearing housing and thus, for example, retain lubricant.
• the printed circuit will ideally be embedded within a body formed from moulded plastics.
• the preferred form of sensor comprises a Hall effect device.
• the invention also extends to a stator and rotor assembly for a D.C. motor wherein the rotor incorporates an annular magnet surrounding the stator and one or more thin steel arcuate strips are positioned around the magnet to act as flux return paths between poles of adjacent magnetic portions of the magnet.
• each steel strip will be stressed to provide frictional location of the magnet within the rotor housing.
• the magnet will then ideally be shaped to provide for the accurate positioning and location of each steel strip.
• the invention provides a stator and rotor assembly for a D.C. motor wherein the rotor incorporates a magnet which surrounds the stator and embodies castellations or other shape modifications to create a desirable offset of the magnetic field.
• the preferred embodiment incorporates a moulded magnet.
• a magnetising process may be used that reduces the stray magnetic flux on the surfaces not adjacent to the stator. This in turn reduces the need for a heavy flux return circuit, in order to reduce the stray flux on the outer surfaces of the motor.
• stator and rotor assemblies defined above it is desirable for the rotor housing to " incorporate a flexible retaining rim enabling the magnet to be installed within the rotor housing as a snap fit.
• the brushless D.C. motor of this invention as hereinbefore defined will ideally incorporate the forms of stator and rotor assembly of this invention as defined above. Since all rotating components may be produced as 'balanced' injection mouldings, the resultant light weight rotor assembly requires far less correction to achieve a given balance standard.
• Figure 1 is an exploded perspective view from ⁇ one side of parts of an assembly for a brushless D.C. motor of this invention
• Figure 2 is an exploded view from the other side of the same assembly
• Figure 3 is a vertical cross-section through the assembly illustrated in Figures 1 and 2.
• the motor assembly illustrated in the drawings incorporates a stator 1 and a rotor 2 together with a support body 3.
• the support body 3 incorporates a printed circuit on which is mounted various electronic components 4, including, a Hall effect device 5.
• the body 3 is integrally moulded about the printed circuit and part of the moulding defines a bearing housing 6 which receives a bearing system and a rotor shaft 7 projecting from the outer housing 8 of the rotor 2.
• Installed within the housing 8 is an annular magnet 9 provided with flux return segments in the form of arcuate steel strips 10.
• the insulated stator, carrying coils 11 is precisely located onto the support body 3 by upstanding lugs 12.
• Mounting arms 15 provide for precise location (both linear and angular) of the Hall effect device 5.
• An alternative mounting arm 15A allows for the Hall effect device to be located in a different position which will apply when the stator is mounted in an inverted position to cause rotation of the rotor in the opposite direction.
• the Hall effect device 5 senses a change in magnetic state during rotation of the rotor magnet 9 and controls switching of the current to the coils 11 by means of the electronic circuitry mounted on the printed circuit. Because the stator 1 and the Hall effect device 5 are precisely located with respect to the bearing housing 6 by means of the integrally moulded body 3, the motor can be operated to optimum efficiency, since the rotor magnet 9 is also precisely located through its connection to the rotor " shaft 7 which is located within the bearing housing 6. This particular motor is intended for driving a fan and the rotor housing 8 will therefore carry impeller blades (not shown) .
• the impeller will then rotate within an outer housing (not shown) to which the body 3 will be secured by screws 16 (or rivets or the like) passing through holes 17 to a central ring 18 of the outer housing.
• This arrangement will also provide a degree of -7-
• the design of the magnet 9 is such that it will occupy minimal space and be of low weight.
• the conventional fairly thick steel surrounding cage has been replaced by the arcuate steel strips 10 which provide little bulk but achieve an adequate flux return path.
• the strips 10 are located within grooves defined by ribs 19 on the outer surface of the magnet 9.
• the magnet 9 also carries downwardly projecting castellations 20 which provide a dual effect. Firstly the castellations 20 are the parts of the magnet which are sensed by the Hall effect device 5. Also, because part of the magnet is effectively absent between the castellations, the magnetic field is axially offset above the central plane of the stator 1 , thus creating a degree ?f down ⁇ ward thrust of the rotor 2.
• the end of the rotor shaft 7 will then press against a thrust bearing 21.
• the symmetrical positioning of the rotor with respect to the stator by means of the precise location of the parts on the body 3, and the downward thrust produced, results in a "floating effect" for the rotor 2 so that there is very low force applied to the main bearing system 22 ( Figure 3) by the rotor shaft 7, and thus low frictional losses.
• the magnet 9 is held within the housing 8 as a snap fit within a flexible retaining rim 23 near the open end of the housing 8.
• the steel strips 10 (which may be lightly sprung outwardly) act as a radial tolerance ring to hold the magnet concentric with the housing 8 so that there is no relative rotation between the magnet 9 and the housing 8.
• the end of the assembly is closed by an end cap 24 having arms 25 which are secured as a snap fit over ledges26 after passing through openings27 in the moulded body 3.
• the end cap 24 will then also close off the bearing housing 6 and provide a support surface for the thrust, bearing 21.
• the closed region 28 may be filled with a lubricant if desired.
• the sensor will comprise a bipolar Hall effect device, since this reduces or eiiminates the need to build up selective magnetic reluctance areas on the stator magnet for starting purposes.
• the bipolar device senses both poles with similar sensitivity and thus achieves a correct mark/space ratio for each full revolution. Also if, on starting the rotor is caused to rotate initially in the wrong direction, it will be reversed almost immediately to rotate con- tinuously thereafter in the correct direction once the sensor senses the next change.
• the printed circuit which is formed integrally with the body 3, can be of various forms. Thus it could be a separate printed circuit board about which the body 3 is sub ⁇ sequently moulded or it could, for example, be formed by deposition onto a previously moulded body 3.
• the D.C. motor of this invention can be used for a variety of purposes. Thus, for example, it may be used in connection with paper feeds on photocopiers as well as within computers for cooling purposes.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Brushless Motors (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=10613691

Family Applications (1)

Country Status (4)

Cited By (15)

Citations (9)

• 1987
  • 1987-03-10 GB GB878705656A patent/GB8705656D0/en active Pending
• 1988
  • 1988-03-01 EP EP88901898A patent/EP0305431A1/en not_active Withdrawn
  • 1988-03-01 WO PCT/GB1988/000145 patent/WO1988007285A1/en not_active Application Discontinuation
  • 1988-03-01 JP JP63502030A patent/JPH01502552A/ja active Pending

Patent Citations (9)

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