For many applications, it is desirable to use fans which weigh less than 30 grams and are driven by electric motors not more than a few centimeters in size. Mass-producing products this small, which nevertheless must be extremely reliable, poses unique manufacturing challenges, which are best overcome by an improved structure which is susceptible to automation. Preferably, the fan motor is electronically commutated and has an internal stator (50) and an external rotor (22) supported on a central rotor shaft (34). The shaft is journaled within a bearing tube (70) supporting first and second rotor bearings (72, 76). By injection-molding the bearing tube (70) with first and second axial extensions (90′, 90″), the extensions can hold the bearings in place and insure uniform manufacturing quality and a desirably long service life. One of the extensions can also be shaped to abut against a circuit board (46) which supports components which control commutation.

This application claims priority of German application DE 20 2006 002 068.3, filed 3 Feb. 2006, the entire content of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to an electronically commutated motor, in particular to a miniature or subminiature motor. Such motors are preferably used in miniature or subminiature fans.

BACKGROUND

Miniature and subminiature fans usually have very small dimensions and correspondingly weigh very little. Fans of the EBM-PAPST 250 series, for example, have dimensions of 8×25×25 mm and weigh approx. 5 g. For fans of the ebm-papst 400 series, the dimensions are 20×40×40 mm and the weight is less than 30 grams. The motors are correspondingly even smaller and weigh even less than the fans of which they are a part.

With such motors, assembly must be simple and uncomplicated, in order to allow cost-effective manufacture by means of a high level of automation. Uniform quality, which is a prerequisite for a long average service life, can moreover be achieved by extensive automation.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to make available a novel miniature or subminiature motor.

According to the invention, this object is achieved by an electronically commutated motor having an external rotor supported on a rotor shaft, an internal stator including a stator lamination stack defining a plurality of axial slots, and a plastic layer which extends through the slots and also forms a bearing tube for receiving the rotor shaft, the bearing tube being formed with at least one recess which holds in place a respective rolling bearing for journaling the rotor shaft. According to a method aspect of the invention, this plastic element can be injection-molded. A motor of this kind can, in particular, be made very compact, and enables operation at high rotation speeds, i.e. high output. The manufacturing steps can be automated, thereby assuring consistent results and a desirably long service life.

DETAILED DESCRIPTION

In the description that follows, the terms “left,” “right,” “top,” and “bottom” refer to the respective figure of the drawings and can vary from one figure to the next, depending on the orientation (portrait or landscape) selected in each case. Identical or identically functioning parts are labeled with the same reference characters in the various figures, and are usually described only once.

FIG. 1is a longitudinal section through an axial fan20having a motor21according to a preferred embodiment of the invention, at greatly enlarged scale (enlarged approximately five times). To illustrate the small dimensions necessary for miniature and subminiature fans, fan20is shown inFIG. 13, by way of example, at a scale of approximately 1:1.

Motor21is arranged in an air-directing tube80and has an external rotor22and an internal stator50. External rotor22has a rotor cup24on whose outer periphery is provided a fan wheel23having fan blades26. Mounted on the inner periphery of rotor cup24, on a soft-ferromagnetic yoke element27, is a rotor magnet28that can be magnetized, for example, with four poles. Rotor cup24has a base30in which an upper shaft end32of a rotor shaft34is mounted, which shaft has a lower, free shaft end35. Shaft34is preferably made of steel, and rotor cup24of plastic. Rotor cup34is mounted on upper shaft end32by plastic injection molding.

Internal stator50, which is described in detail inFIGS. 2 to 11, has a stator lamination stack52having a plastic coating77, which together form a bearing tube70for journaling of rotor shaft34. Arranged for this purpose at one end71′ of stator lamination stack52is a plastic part90′ therein, in the form of a first axial extension of plastic coating77, having a bearing72. Arranged at the other end71″ of stator lamination stack52is a plastic part90″ in the form of a second axial extension in which a bearing76is present.

According to a preferred embodiment of the invention, plastic coating77and extensions90′ and90″ are formed integrally, bearing72being held in extension90′ by plastic injection molding, the shape of the molded element form-lockingly defining the alignment of the bearing with respect to the rotor shaft which it journals. As an alternative thereto, extension90′ can be formed as a separate component, in such a way that bearing72can be anchored in it by being pressed in. Extension90′ can, in this case, be manufactured independently of plastic coating77and, in a simple working step, e.g. press-fitted thereon. Extension90′ can comprise, for this purpose, one or more guidance elements that facilitate such a press-fitting operation. Bearing76can likewise optionally be injection-embedded into extension90″ or pressed into it.

Bearings72and76are preferably implemented as rolling bearings, but are not limited to a specific bearing type. A variety of bearing types can instead be used, for example, plain bearings. Rolling bearing72has an inner ring72′ and an outer ring72″, and rolling bearing76has an inner ring76′ and an outer ring76″. Rotor shaft34, rotatably journaled in rolling bearings72and76, is held therein by means of an abutment or retaining element92and a compression spring94. Abutment92, for example a snap washer or other latching member, is snapped into an annular slot at lower end35of shaft34. Tensioned spring94is held between inner ring72′ of rolling bearing72and latching member92. A conical extension of base30of rotor cup24is pressed by said spring against inner ring76′ of rolling bearing76, so that shaft34is held with dynamic tension in rolling bearings72and76of internal stator50. This action of spring94is assisted by the fact that rotor magnet28is offset downward, with respect to stator lamination stack52, thereby creating a magnetic pull on external rotor22which pulls the latter upward with reference toFIG. 1.

Arranged on outer periphery74of extension90′ is a circuit board46having a relatively large electronic component48, e.g. a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), that is provided to control the current in a stator winding97of motor21. Further electronic components, e.g. a Hall IC (Integrated Circuit), can likewise be arranged on circuit board46, onto which connector elements96for stator winding97are soldered. These connector elements96are supported in a shoulder95of extension90′ by plastic injection molding.

The lower end of extension90′ is secured to a hub85by being pressed in, and can additionally be adhesively bonded and/or welding thereonto. Struts86′ and86″, which support air-directing tube80, extend from this hub85.613

FIG. 2is a top view of hub85of fan20ofFIG. 1.FIG. 2illustrates struts86′,86″, and86″′ arranged between hub85and air-directing tube80, as well as extension90′ whose exposed end is connected to hub85.

FIG. 3is a perspective longitudinal section through air-directing tube80of fan20, with a perspective depiction of internal stator50.FIG. 3illustrates the assembly of fan20according to a preferred embodiment, in which, in a first step, circuit board46having component48thereon is arranged on internal stator50, and the latter is then mounted on hub85in a further step. As is apparent fromFIG. 3, internal stator50comprises, for example, four spacers59′,59″,59″′,59″″. These serve to prevent damage to stator winding97when internal stator50is pressed into hub85.

FIG. 4is a three-dimensional view of internal stator50(FIG. 3) enlarged approximately ten times. Internal stator50is shown for illustrative purposes inFIG. 12, by way of example, at a scale of approximately 1:1.

FIG. 4shows circuit board46, abutting against shoulder95of extension90′, onto which board connector element96′ is soldered, and also shows rolling bearing76mounted in extension90″. To facilitate the pressing of rolling bearing76into extension90″, the latter has two recesses75′ and75″ at its upper end.

Stator lamination stack52contains laminations, three of which are labeled55′,55″, and55″′. Stator lamination stack52is “packeted,” i.e. its plates or laminations have small holes that are stamped with mating bosses, so that they form an aligned, unitary block. The plastic of plastic coating77, which plastic is injected into stator lamination stack52and, together therewith, forms bearing tube70, can also stabilize and contribute to the strength of this block. As shown inFIG. 4, this plastic constitutes strip-shaped plastic facings79(two plastic facings being labeled79′ and79″ by way of example) at locations on the outer side of lamination stack52, which facings further enhance strength.

As shown inFIG. 9, stator lamination stack52has salient stator poles52′,52″,52″′,52″″ that are separated from one another by slots54′,54″,54″′,54″″ through which plastic coating77extends. Stator winding97is arranged on stator poles52′,52″,52″′,52″″ (cf.FIG. 4).

FIG. 5is a side view of internal stator50ofFIG. 4, but without winding97, and illustrates shoulder95of extension90′, in which shoulder connector element96′ is mounted. In the region of extension90′ in which component48is arranged on circuit board46, said extension has a recess99.

FIG. 6is a longitudinal section through internal stator50, and illustrates recess99as well as bearing tube70formed by plastic coating77and stator lamination stack52.

Plastic coating77forms, at lower end71′ of stator lamination stack52, an end layer73′ on which axial extension90′ is arranged. The latter has a recess or compartment91in which first rolling bearing72is arranged. Recess91is formed with a first shoulder91′ and a second, opposing shoulder91″. As mentioned with reference toFIG. 1, at least outer ring72″ of this rolling bearing72is injection-embedded into the plastic of extension90′. For this purpose, prior to plastic injection molding, a first tool is guided from above through stator lamination stack52and immobilizes the upper rim of said outer ring72″. The latter's lower rim is immobilized by a second tool coming from below. The two tools seal off rolling bearing72, in such a way that no plastic can penetrate into bearing72during plastic injection.

At upper end71″ of stator lamination stack52, plastic coating77forms an end layer or terminal disk73″ on which axial extension90″ is arranged. As is apparent fromFIG. 6, plastic coating77and extensions90′ and90″ are preferably formed integrally. Extension90″ has an opening93for the reception of rolling bearing76. The latter is preferably pressed into opening93(cf.FIG. 7).

FIG. 7is a sectioned view of internal stator50with both rolling bearings72and76.

FIG. 8is another side view, analogous toFIG. 5, of internal stator50. In contrast to the side view ofFIG. 5, internal stator50is rotated 45° to the right inFIG. 8, and is depicted without circuit board46and component48. Slot54″″ located between stator poles52′ and52″″, and connector elements96″″ and96″′ injection-embedded into shoulder95, are thus visible inFIG. 8. Said connector elements are preferably implemented as bronze pins.

FIG. 9is a top view of internal stator50.FIG. 9shows a preferred embodiment of stator lamination stack52equipped with plastic coating77, and illustrates slots54′,54″,54″′, and54″″ provided between poles52′,52″,52″′, and52″″.

As is apparent fromFIG. 9, end layer73′ of plastic coating77has cutouts56′,56″,56″′, and56″″ at the axial ends of slots54′,54″,54″′, and54″″. End layer73″ located opposite end layer73′ analogously has cutouts58′,58″,58″′, and58″″. These cutouts at both ends allow stator winding97(not shown inFIG. 9) to be arranged on stator lamination stack52.

All the poles52″,52″,52″′, and52″″ have an identical configuration. To simplify matters, only the configuration of pole52′ will therefore be described. The latter has a pole core12and a pole shoe having pole ends or pole horns14,16. Pole horn16, onto which plastic facing79′ is applied, has a smaller diameter than pole horn14. This conformation is usually referred to as a “reluctance lamination form,” and serves to generate a so-called “reluctance torque.” For interaction with this stator shape, rotor magnet28has a trapezoidal magnetization.

FIG. 10is a sectioned view of internal stator50along section line X-X ofFIG. 9, andFIG. 11is a sectioned view of internal stator50along section line XI-XI ofFIG. 9.FIG. 11illustrates cutouts56′,56″′ in end layer73′ at end71′ of lamination stack52, as well as cutouts58′,58″′ in end layer73″ at its end71″.

It has been found that, as a result of the type of journaling described, the fan depicted inFIG. 13can be operated at a rotation speed of 15,000 rpm. Many variants and modifications are of course possible within the scope of the present invention.