WO2005091469A1

WO2005091469A1 - Miniature electrical motor and blower

Info

Publication number: WO2005091469A1
Application number: PCT/HU2004/000119
Authority: WO
Inventors: Leslie Hoffman; Ákos Ottó PETRIK
Original assignee: Lc Hoffman International Corp
Current assignee: Lc Hoffman International Corp
Priority date: 2004-03-22
Filing date: 2004-12-16
Publication date: 2005-09-29
Anticipated expiration: 2006-09-22
Also published as: HU2836U; HU0400068V0

Abstract

The invention relates a miniature motor comprising a permanent magnet rotor (6) arranged rotatably inside of a stator, magnetic fields of said stator being generated by energizing windings of the stator by an electronic commutator unit connected to the coils (4) of the stator, made as a one-piece stator/housing molding, in which thermoplastic material of the housing (1) is injected around the iron core (5) and coils (4). The invention relates further a miniature blower having an impeller being fixed on the shaft (7) of the rotor (6), said housing (1) of motor comprising a half of a two parts blower housing having at least an air-outlet canal (15) near to its perimeter, while the other part (3) of the blower housing has a coaxial inlet air-opening and covers said impeller (11) of the blower, where the two parts of the blower housing are fixed to each other at their perimeters.

Description

MINIATURE ELECTRICAL MOTOR AND BLOWER

Background of the Invention The invention generally relates to electronically commutated motors and miniature blowers for moving air, having such a motor. Motors of miniature blowers comprise a mostly outer rotor, having permanent magnet elements, and a stator having windings on iron core poles. The rotor may rotate relative to the stator as a result of the magnetic interaction of the magnetic elements and the magnetic fields generated by energizing windings of the stator. The outputs of a DC powered electronically commutating unit of the motor are connected to the ends of the windings. Miniature electrical motors may have built for above 20000 rpm. The rotors of known miniature motors are rotatably mounted in bearings arranged in the housing of the rotor and the stator, and this arrangement restricts the possibility of miniaturization. Such a direct current brushless motor is described in the Patent Application published as US 2003/00901 Al . The motor includes housing having a base body with a receiving chamber for the cylindrical rotor and a cover plate for the bearing of the rotor shaft. A film printed circuit is mounted on the periphery of the base, the film printed coil sets are distributed on the periphery of the base in equally angular manner, with the receiving chamber serving as a center. There are some drawbacks of this construction, which make it difficult and costly the manufacturing of the motor. Such drawback is that the printed film comprises a set of Hall-elements, therefore it is complicated to produce. The positioning and fixing of the printed coils in equally angular manner is a questionable manipulation.

Miniature motors are used in most cases as miniature blowers, which miniature blowers have to occupy a very narrow place e.g. on a plate of a computer. There is a need for a miniature motor, which is smaller than the known motors of similar moment.

Summary of the Invention:

Aim of the invention is to provide a miniature motor and blower, which can be of smaller outer perimeter than the known motors of similar moment, and which can be produced in a few and more automated steps.

In one form the invention comprises a miniature electrical motor comprising a permanent magnet rotor arranged rotatably inside of a stator, magnetic fields of said stator being generated by energizing windings of the stator by an electronic commutator unit connected to the coils of the stator, made as a one-piece stator/housing molding, in which thermoplastic material of the housing is injected around the iron core and coils wound on the iron core. Preferably the thermoplastic material of the housing is polycarbonate. Preferably the housing has a hole at its frontal side for a bearing of the shaft and has a rim on its backside receiving a cover in which the second bearing of the shaft of the rotor has been arranged. In an other form the housing has coaxial holes for both bearings of the shaft of the rotor and preferably the stator inside diameter is slightly larger than the outside diameter of the smallest bearing to be used, and slightly smaller than the backside bearing of larger outside diameter. In a possible form the housing comprises also a sensor of the position of the poles of the rotor. Preferably coil wires of the stator end in contacts arranged along a coaxial circle on the backside of the housing, which contacts are connected to appropriate contacts of commutator circles of an electronic commutator unit. The cylindrical rotor comprises preferably one or more "n" pair of permanent magnetic poles. Said housing of motor may comprise a half of a two parts blower housing having air-outlet canal in it, near to its perimeter, the other part of the blower housing having a coaxial inlet air-opening and covering an impeller of the blower, said impeller being fixed on the shaft of the rotor of the electric miniature motor, where the two parts of the blower housing are fixed to each other at their perimeters.

The motor has optimized motor efficiency achieved by reducing amount of iron and increasing motor resistance to get an optimum size where further reduction would cause the copper-losses to increase faster than iron losses are decreasing.

In another form, the invention comprises a miniature blower having a motor comprising a permanent magnet rotor arranged rotatably inside of a stator and an impeller being fixed on the shaft of the rotor, characterized in a one-piece stator/housing molding, in which thermoplastic material of the housing is injected around the iron core and coils, said housing of motor comprising a half of a two parts blower housing having an air-outlet canal in it near to its perimeter, while the other part of the blower housing has a coaxial inlet air-opening and covers said impeller of the blower, where the two parts of the blower housing are fixed to each other at their perimeters. Preferably the impeller has full-length vanes and partial length vanes arranged at the outer section of the impeller. Preferably said impeller's hub (14) has a special shape described by the following equation: y = V (R_s - 2R_sZ) ; (for O < Z < b) where y = radius of hub surface at Z Z = height of radius y above base of impeller R_s = radius of inlet opening b = vane height. For some application the miniature blower housing has two tangential air- outlet canals. Brief Description of the Drawings: Fig. 1 is a cross sectional view of a miniature blower integrated with an electric miniature motor Fig. 2 is a cross sectional view of a modified version of the blower . Fig. 3 is a cross sectional view of an other modified version of the blower Fig. 4 is a front view of an impeller Fig. 5 is a view of an one-piece stator/housing molding of a blower having two outlets. Detailed Description of the Preferred Embodiments: Referring to Fig. 1 a housing 1 of the electric miniature motor comprises a half of a two parts blower housing having an air-outlet canal in it, near to its perimeter, while the other part 3 of the blower housing has a coaxial inlet air-opening and covers an impeller 11 of he blower, said impeller 11 being fixed on the shaft 7 of the rotor 6 of the electric miniature motor. The two parts of the blower housing are fixed to each other at their perimeters.

There is no separate housing of the motor; the housing 1 of polymeric material comprises a one-piece stator/housing molding. The preferably polycarbonate thermoplastic material of the housing is injected around the iron core 5 and coils 4 wound on the iron core 5. The injected housing 1 has a with opening of the stator coaxial hole at its frontal side for a bearing 8 of the shaft 7 of the rotor 6 and has a rim on its backside receiving a cover 2 in which the second bearing 9 of the shaft 7 has been arranged. The second bearing 9 is propped by a springy washer 10. The cylindrical rotor 6 has preferably one or more "n" pair of permanent magnetic poles; the stator has at least one pair of electrical induced magnetic poles surrounding the rotor 6. Preferably the one-piece stator/housing molding comprises a Hall-device or other sensor of the relative position of the poles of the rotor 6 to the poles of the stator (not shown) but in case arranging an electronic commutator unit in appropriate position relative to the poles of the stator, it is not a necessity. The coils 4 are of insulated wire. The wires of coils 4 (and sensor) end in contacts arranged along a coaxial circle on the backside of the housing 1, which contacts are connected to appropriate contacts of commutator circles of an electronic commutator unit (not shown). This arrangement makes it simple the changing or mounting the electronic commutator unit according to different demands. The electronic commutator unit can be arranged in the cover 2 or is integrated in the cover 2 having DC connector in the outer side (not shown). We refer to the Patent Application published as US 2003/00901 Al where details of the electronic commutator unit and working such motors are described. An advantage of the above motor and blower is that there is no separate housing of the motor, which would add to the diameter of the motor, therefore the motor can be of smaller outer perimeter than the known motors of similar moment. A further advantage of the invention is that the production of one-piece stator/housing moldings in one step is really productive without any drawback, the geometrical and dimensional accuracy is secured with no further measure. Normally the inlet air-flow to the blower tends to concentrate near the base of the impeller 11 before entering vanes 12 of the 11 impeller (see Fig. 4). To encourage more of the air to enter the vanes 12 on the impeller 11 a hub 14 having a special shape (see Fig. 2) can be used. This shape is described by the following equation: y = V (R_s ² - 2R_SZ) ; (for 0 < Z < b) where y = radius of hub surface at Z Z = height of radius y above base of impeller R_s = radius of inlet opening b = vane height.

This shape results in the annular area between the hub 14 and the vanes 12 at Z to be equal to the cylindrical area remaining below Z at vane entrance. Small blowers have pressure pulsation at the outlet caused by a small vane count. The (blade) vane count is limited by the vane thickness at the inlet closing off area through which the air must pass. To increase the frequency and decrease the amplitude of the pulsation, between full-length 12 vanes partial-length vanes 13 can be used arranged at the outer section of the impeller 11 thus increasing the vane count at the outlet while maintaining a low vane count at the inlet. In some applications the output of the blower is used in two different locations. To facilitate this without lossy and noisy Y coupling, the miniature blower is constructed to have two air-outlet canals 15, 16 (Fig. 5). In applications where the output flow is restricted to a small fraction of the amount that could be generated by a blower of the size determined by the pressure required, parasitic eddies are present between vanes of the impeller. Eddies cause acoustic noise and reduce the blower efficiency. In this cases the vane height b (Fig. 2) can be reduced to an optimum.

A typical small blower with an output of 100 liters/minute at a pressure of 12 centimeters of water and an efficiency of approximately 50 % requires only 4 watts of power to drive it. At 23000 rpm this represents only 1 ,77 x 10^" Newton-meters of torque. The motors normally used to drive a blower of this size have iron-losses two or three times this load. The usual technique to increase motor efficiency is to lower the motor resistance by making the motor larger. This is the wrong approach for driving a load that is this mall. The proper technique is to reduce the size of the motor thus reducing the amount of iron and increasing the resistance. There is an optimum size where further reduction causes the copper-losses (i R) to increase faster than the iron losses are decreasing.

It is possible to arrange both bearings 8, 9 in the one-piece stator/housing molding (Figs. 2 and 3). This allows the rear end cap 2 of the original configuration (Fig. 1) to be eliminated. When sizing the stator inside diameter slightly larger than the outside diameter of the smallest bearing 8 to be used, and applying a backside bearing 9 of a larger outside diameter than the rotor 6 has, it is possible to mount both bearing 8, 9 on the shaft 7 of the stator 6 and than to mount this subassembly in one step into the stator opening (Fig. 3).

Claims

1. A miniature electrical motor comprising a permanent magnet rotor arranged rotatably inside of a stator, magnetic fields of said stator being generated by energizing windings of the stator by an electronic commutator unit connected to the coils of the stator, characterized in a one-piece stator/housing molding, in which thermoplastic material of the housing (1) is injected around the iron core (5) and coils (4) wound on the iron core (5).

2. A miniature motor according to claim 1 characterized in that the thermoplastic material of the housing (1) is polycarbonate.

3. A miniature motor according to claims 1 or 2 characterized in that the housing (1) has a hole at its frontal side for a bearing (8) of the shaft (7) and has a rim on its backside receiving a cover (2) in which the second bearing (9) of the shaft (7) of the rotor (6) has been arranged.

4. A miniature motor according to claims 1 or 2 characterized in that the housing (1) has coaxial holes for both bearings (8, 9) of the shaft (7) of the rotor (6).

5. A miniature motor according to claim 4 characterized in that the stator inside diameter is slightly larger than the outside diameter of the smallest bearing (8) to be used, and slightly smaller than the backside bearing (9) of larger outside diameter.

6. A miniature motor according to one of claims 1 - 5 characterized in that the housing (1) comprises a sensor of the position of the poles of the rotor (6).

7. A miniature motor according to one of claims 1 - 6 characterized in that coil (4) wires of the stator (6) end in contacts arranged along a coaxial circle on the backside of the housing (1), which contacts are connected to appropriate contacts of commutator circles of an electronic commutator unit.

8. A miniature motor according to one of claims 1 - 7 characterized in that the cylindrical rotor (6) comprises one or more "n" pair of permanent magnetic poles.

9. A miniature motor according to one of claims 1 - 8 characterized in that said housing (1) of motor comprises a half of a two parts blower housing having an air-outlet canal (15) in it, near to its perimeter, the other part (3) of the blower housing has a coaxial inlet air-opening and covers an impeller (11) of the blower, said impeller (11) being fixed on the shaft (7) of the rotor (6) of the electric miniature motor, where the two parts of the blower housing are fixed to each other at their perimeters.

10. A miniature motor according to one of claims 1 - 9 characterized in having optimized motor efficiency achieved by reducing amount of iron and increasing motor resistance to get an optimum size where further reduction would cause the copper-losses to increase faster than iron losses are decreasing.

11 A miniature blower having a motor comprising a permanent magnet rotor arranged rotatably inside of a stator and an impeller being fixed on the shaft of the rotor, characterized in a one-piece stator/housing molding, in which thermoplastic material of the housing (1) is injected around the iron core (5) and coils (4), said housing (1) of motor comprising a half of a two parts blower housing having an air-outlet canal (15) in it near to its perimeter, while the other part (3) of the blower housing has a coaxial inlet air-opening and covers said impeller (11) of the blower, where the two parts of the blower housing are fixed to each other at their perimeters.

12. A miniature blower according to claim 11 characterized in that the blower housing has two tangential air-outlet canals (15, 16).

13. A miniature blower according to claim 11 or 12 characterized in that the impeller (11) has full-length vanes (12) and partial length vanes (13) arranged at the outer section of the impeller (11).

14. A miniature blower according to one of claims 11-13 characterized in said impeller's hub (14) having a special shape described by the following equation: y = V (R_s ² - 2R_SZ) ; (for 0 < Z < b) where y = radius of hub surface at Z Z = height of radius y above base of impeller R_s = radius of inlet opening b = vane height.