FAN COMPRISING AN ELECTRONICALLY COMMUTATED DRIVE MOTOR

Abstract

A fan having an electronically commutated drive motor (27) has a bearing tube (62) having an inner side and an outer side. The internal stator of the drive motor (27) is arranged in the region of the outer side. An external rotor (28) of said motor interacts during operation with the internal stator (72). Fan blades (26) of the fan (22) are arranged on the outer periphery of the external rotor (28). Bearing elements (52, 54), by means of which a shaft (46) connected to the external rotor (28) is journaled, are arranged on the inner side of the bearing tube (62). Conduits (90), which enable coolant to flow through the bearing tube (62) during operation of the fan (22), are provided in the bearing tube (62).

Description

FIELD OF THE INVENTION

The invention relates to a fan having an electronically commutated drive motor.

BACKGROUND

Such fans are used principally as so-called “equipment fans” for cooling electronic devices, for example for cooling computers, servers, circuit boards, etc. Such fans must be extremely inexpensive, but, on the other hand, are expected to be highly reliable and to have a service life at least as long as the service life of the device cooled by the fan.

Such fans contain a variety of elements, for example Hall sensors, ICs, transistors, capacitors, etc., as well as bearings, for example plain bearings, rolling bearings, etc.

That element which is most greatly jeopardized by high operating temperatures is referred to as the “performance-determining element.” Depending on the construction of the fan, this can therefore be an electronic or a mechanical element.

Higher temperatures occur in particular in fans having a plastic housing, since the heat created during operation can be dissipated only very poorly by the plastic, so that hot regions, which can also be referred to as “hot spots,” can be produced in the interior of such a fan.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to make a novel heat-dissipating fan structure available.

This object is achieved, according to the invention, by a fan having an internal stator, an external rotor coupled to a central shaft, rotatably journaled inside a bearing tube containing a plurality of bearings, wherein, to facilitate cooling and avoid “hot spots,” the cylindrical wall of bearing tube is formed with a plurality of conduits through which a coolant, for example air, can pass, thereby dissipating heat. Preferably, the conduits are longitudinal and mutually parallel.

Coolant (i.e. generally air) can flow through the conduits, provided in the wall of the bearing tube between the internal stator and the bearing elements, so that the waste heat created in the lamination stack cannot be transferred directly to the bearing elements in the bearing tube. This is the case, in particular, for the bearing element adjacent the rotor shaft base, the temperature of which bearing element is lowered by the coolant, so that the temperature at this sensitive location can be reduced, thereby correspondingly extending the service life of the bearing element there, and thus the service life of the fan as a whole.

With an appropriate design, a bearing tube of this kind can be implemented to be very light and very economical of material, but still sufficiently rigid and functionally suitable, for example in terms of cooling at critical locations.

BRIEF FIGURE DESCRIPTION

Further details and advantageous refinements of the invention are evident from the exemplifying embodiment, in no way to be understood as a limitation of the invention, that is described below and depicted in the drawings.

FIG. 1 is a perspective depiction of the housing of an axial fan prior to installation of the drive motor and the fan wheel, the bearing tube being visible at the center;

FIG. 2 is a depiction analogous to FIG. 1, from a slightly different angle of view and at greatly enlarged scale;

FIG. 3 is a depiction viewed from the underside of the depiction of FIG. 2, i.e. in the direction of arrow III of FIG. 1;

FIG. 4 depicts a rotor on which a fan wheel is arranged;

FIG. 5 is a perspective depiction of housing, drive motor, and fan wheel, viewed approximately in the direction of arrow III of FIG. 1;

FIG. 6 is a perspective depiction of housing, drive motor, and fan wheel, viewed from a perspective similar to that of FIG. 1;

FIG. 7 is a longitudinal section through the assembled fan, similar to the depiction of FIG. 5;

FIG. 8 depicts measurement curves; this figure shows the measurements for a fan not having conduits in the bearing tube and for use of a standard rotor not having a radial fan wheel;

FIG. 9 is a depiction analogous to FIG. 8 for a fan of the same size as in FIG. 8 but having a radial fan wheel in the rotor and having conduits in the bearing tube, although here they are closed off so that air cannot flow through them; and

FIG. 10 is a depiction analogous to FIGS. 8 and 9 for a fan of the same size as in those figures, but having a radial fan wheel in the rotor and having conduits in the wall of the bearing tube which are open, so that air can flow through them during operation, as indicated schematically in FIG. 7.

DETAILED DESCRIPTION

FIG. 1 shows housing 20 of a typical equipment fan 22 that is depicted in the assembled state in FIG. 6. Fan 22 here has a fan wheel 24 having seven fan blades 26, which are mounted on the central rotor 28 of a drive motor 27 and, in FIG. 6, rotate in the direction of an arrow 30, i.e. counter-clockwise, so that in FIG. 6 air is transported through fan 22 in the direction of an arrow 34, i.e. from top to bottom. The result is to produce a corresponding pressure difference at fan 22, i.e. in FIG. 6 the pressure is greater at the bottom than at the top. Flow-through direction 34 of the transported air is also schematically depicted in FIG. 7 for the right half of that Figure.

Fan wheel 24 is depicted in FIG. 4 from the lower (in FIG. 6) side. Rotor 28 has on its outer side a pot- or bell-shaped housing 29 that is made of plastic and is integral with blades 26, as clearly shown in FIG. 5.

A magnetic yoke 40, whose shape is best gathered from FIG. 7, is mounted in housing 29 by molding. The upper (in FIG. 4) end 44 of a rotor shaft 46 is cast, by means of a suitable metal alloy 42 (e.g. ZAMAK) in a collar 41 in the center of yoke 40. Also preferably produced in the casting operation is a small radial fan wheel 48 that keeps air moving there during operation and that improves cooling, particularly in the region of the winding ends. In some cases, such a fan wheel is not necessary, this being ascertained by experiment. Upper end 44 of shaft 46 has an annular groove 45 into which metal alloy 42 engages (see FIG. 7). A multi-pole, radially magnetized ring magnet 47 is mounted in yoke 40.

Shaft 46 is journaled in two bearings 52, 54, in this case in ball bearings, whose inner rings are slid onto shaft 46. The inner ring of the lower (in FIG. 7) bearing 54 is additionally retained by a snap ring 56.

The outer ring of upper bearing 52 is pressed from above into an opening 60 of a bearing tube 62 as far as a stop 64, and the outer ring of lower bearing 54 is likewise pressed from below into an opening 66 of bearing tube 62 to the same stop 64. The latter holds the two outer rings at a predefined spacing.

Bearing tube 62 has a wall 59, whose inner surface is designated 61 and whose outer surface is designated 63. It is manufactured from a suitable plastic that has the requisite mechanical stability and heat resistance. It is, in this case, integral with a flange 70 whose function is to support internal stator 72 of drive motor 27 and the associated circuit board 76 for the motor electronics. This flange 70 is held by spokes 78 in outer ring 80 of housing 20.

Internal stator 72 has a lamination stack 84 equipped with a stator winding 82 (see FIG. 7), which stack is pressed onto ribs 81 on the outer side 63 of bearing tube 62 as far as a stop 86 (FIG. 2) so that waste heat from lamination stack 84 is transferred to wall 59 of bearing tube 62 and, via the latter, in particular to upper bearing 52 (FIG. 7).

Wall 59 of bearing tube 62 is equipped with, for example, ten continuous conduits 90 (FIG. 2) whose angular extent alpha can be equal to, for example 25°. Extending between them are radial ribs 92 having an angular extent of, for example, 11°, i.e. the angular extent of conduits 90 is approximately 1.5 to three times the angular extent of ribs 92. Ribs 81 are located radially outside conduits 90.

As FIGS. 3 and 5 show, conduits 90 extend through flange 70 so that cooling air can flow, in FIG. 7, from the discharge (lower) side of fan 22 upward through conduits 90, as indicated by arrows 94 schematically and only for the right side of FIG. 7. This air 94 cools wall 59 of bearing tube 62 and transports, upward in FIG. 7, the heat that travels from lamination stack 84 into bearing tube 62.

This air flows there, along arrows 96, over the winding ends of stator winding 82, downward between the stator poles, and then from there along arrows 98 to a gap 100 between rotor 28 and flange 70; there it is entrained (Venturi effect) by the air flowing past in the direction of arrows 34, so that a continuous and powerful air circulation takes place in internal stator 72 during operation, cooling principally the upper bearing 52 and stator winding 82 and thereby lengthening the service life of fan 22 (see FIG. 10).

Bearing tube 62 thus has a honeycomb structure in cross section, making it possible to lengthen the service life of the fan without additional outlay. Radial fan wheel 48 (if present) causes a distribution of the circulating air in the upper (in FIG. 7) part of internal stator 72, and thereby produces uniform cooling.

FIG. 8 shows measurement curves for a standard fan in which a radial fan wheel is not provided in rotor 28, and in which a solid bearing tube, not having a honeycomb structure, is used.

The symbol P designates the electrical power level, plotted on the right-hand scale in FIG. 8.

The measured room temperature is labeled 102, and in this case is equal to 24° C.

Curve 104 is the temperature difference of stator winding 82 (FIG. 7) relative to room temperature 102, i.e. for a volumetric flow rate of zero, this temperature difference is equal to 38° K, and at 380 m³/h, it decreases to 22° K.

Curve 106 is the temperature difference of upper ball bearing 52, and 108 is the temperature of lower ball bearing 54, both relative to room temperature. It is evident that the upper (in FIG. 7) ball bearing 52 is hotter than lower ball bearing 54 because the upper ball bearing is being cooled less effectively.

FIG. 9 shows measurement curves for a bearing tube 62 that has a honeycomb structure, but in which conduits 90 are closed off.

Once again, P designates the electrical power level, the curve for which is similar to that in FIG. 8 and is likewise plotted on the right-hand scale in FIG. 9.

Room temperature is labeled 112 and in this case is equal to 23° C.

Curve 114 is the temperature difference of stator winding 82 with respect to room temperature.

Curve 116 is the temperature difference of upper ball bearing 52 with respect to room temperature. Curve 118 shows the temperature difference of lower ball bearing 54 with respect to room temperature. It is evident that upper ball bearing 52 is approximately 5° K hotter than lower ball bearing 54.

FIG. 10 shows measurement curves for a bearing tube 62 having a honeycomb structure as depicted in FIG. 2, conduits 90 being open, so that air flows through conduits 90 and through motor 27 as indicated schematically in FIG. 7 by flow arrows 94, 96, 98. Radial fan wheel 48 (FIG. 4) is also provided. Once again, P designates the electrical power level.

A comparison of FIGS. 9 and 10 shows the considerable difference.

Room temperature is labeled 122 in FIG. 10, and is equal here to 23° C.

The difference between the winding temperature and room temperature is labeled 124, and is somewhat lower than in FIG. 9 because winding 82 is being cooled better.

The temperature difference between upper ball bearing 52 and room temperature is labeled 126, and is 10° K lower here than in FIG. 9, i.e. upper ball bearing 52 is being cooled substantially better in FIG. 10 than in FIG. 9.

The temperature difference between lower ball bearing 54 and room temperature 122 is labeled 128. That difference is approximately 7° K less than in FIG. 9, i.e. bearing 54 is also being cooled substantially better, so that what results as a whole, from the measures and features according to FIGS. 1 to 7, is a substantially longer service life for fan 22, without the need for additional costs for that purpose.

Numerous variants and modifications are, of course, possible within the scope of the invention.

Claims

1. A fan comprising

an electronically commutated drive motor (27) having an internal stator (72) and an external rotor (28) cooperating therewith, said external rotor being supported by a central shaft (46) connected therewith;

a plurality of fan blades (26) being arranged on an outer periphery of said external rotor (28); and

a bearing tube (62) having an outer side (63) and an inner side (61), a plurality of bearings (52,54) being arranged on said inner side (61), journaling said central shaft (46) for rotation therein;

wherein

the bearing tube (62) includes, between said outer side (63) and said inner side (61), a wall formed with cooling conduits (90), enabling streaming of coolant through the wall,

said inner side (60, 66) of said bearing tube separating said cooling conduits (90) from said bearings (52, 54) arranged within said bearing tube (62).

2. (canceled)

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12. (canceled)

13. The fan according to claim 1, wherein

the bearing tube (62) is formed, at least in part, of plastic material.

14. The fan according to claim 1, wherein

said cooling conduits (90) in said bearing tube wall (59) are arranged in a pattern whose cross-section resembles a honeycomb.

15. The fan according to claim 1, wherein said bearing tube (62) is arranged on a flange (70) oriented generally perpendicular to an axis of said bearing tube, and at least some of said cooling conduits (90) extend axially through said flange (70).

16. The fan according to claim 1, wherein, in said wall (59) of said bearing tube (62), a plurality of carrier segments or ribs (92) are provided, each extending radially from said inner side (61) to said outer side (63).

17. The fan according to claim 16, wherein, measured in a circumferential direction, an average angular extent of said cooling conduits (90) exceeds an average angular extent of said carrier segments (92) by a factor of 1.5 to 3.

18. The fan according to claim 1, wherein

bearing seats (64) for said bearings (52, 54) are formed on said inner side (61) of said bearing tube (62).

19. The fan according to claim 1, wherein

said fan, when operating, creates a pressure differential between a first longitudinal end of said cooling conduits (90) and a second longitudinal end thereof, thereby causing cooling air to stream (94) through said cooling conduits (90).

20. The fan according to claim 1, wherein said external rotor (28) has a bell configuration, with an internal center, to which said central shaft (46) is attached.

21. The fan according to claim 20, wherein the shaft (46) is cast into a recess formed on the inside of the rotor bell.

22. The fan according to claim 21, wherein

a radial fan wheel (48) is implemented from the material with which the shaft (46) is cast into the recess at the base of the bell, which fan wheel has the function of distributing, in the region of the base of the bell, coolant flowing out of the conduits (90) provided in the bearing tube (62).

23. The fan according to claim 20, wherein, to facilitate the discharge of coolant from the fan (22), a gap (100) is provided, past which air moved (34) by said fan blades (26) passes, thereby creating an underpressure adjacent this gap (100).

24. The fan according to claim 23, wherein said gap (100) is defined by a spacing between said flange (70) and a circumferential rim of said bell-shaped rotor (28), and passage of air from said fan blades (34) causes a Venturi effect, entraining coolant exiting (98) via said gap (100).