Stator for a polyphase electric machine and method for manufacturing same

A stator (16) is proposed for a polyphase electric machine, having a core body (17), which is provided with slots (114), which are situated in the radial direction with respect to an axis of rotation of the electric machine on one side of the core body (17) parallel to the longitudinal axis of the core body (17), having a slot width (bn1, bn2) and a stator yoke (122) being provided on the opposite side, with two slots (114) each being separated from one another by a tooth (116) having a tooth width (bz1, bz2) and extending from a slot base (120) to a tooth head (118), these slots (114) being provided to receive at least one coil winding having a plurality of coils that is electrically connected in series and are manufactured from at least one continuous wire (124) without interruption, the ratio (bz2/hj) of the tooth width (bz2) to the yoke height (hj) at the tooth head (118) being between 0.3 and 0.8 and/or the ratio (bz2/bn2) of the tooth width (bz2) at the tooth head (118) to the slot width (bn2) at the tooth head (118) being between 0.3 and 3, and/or the ratio (mCu(slot)/mCu(total)) of the copper mass of the wire (124) in the slot (114) to the total copper mass of the wire (124) being between 0.43 and 0.55.

BACKGROUND INFORMATION

The present invention relates to a polyphase electric machine, in particular a polyphase generator for motor vehicles, having a stator according to the definition of the species of Claim1and a method for manufacturing a stator as recited in Claim17.

Various methods and configurations for achieving a high slot filling factor in generators have already been proposed, in which more than 60% of the slot is filled with copper wire, e.g., in DE 103 029 47 A1, DE 103 061 47 A1 or EP1372242A2. U-shaped connector pieces may be inserted axially from one end through the stator slots, bent on the opposite side, and then welded together. This method is very complex and expensive due to the large number of spot welds. Coils may also be inserted into the open slots of a flat metal laminate and then the laminated core together with the coils may be bent into a round shape. This method is also complex and also entails tolerance problems.

An attempt is made with the present invention to eliminate or at least greatly reduce the aforementioned disadvantages through a suitable design of the stator.

SUMMARY OF THE INVENTION

It is assumed that windings are inserted into the slots of a round laminated core with the aid of a winding mandrel, a winding being held by a mandrel, and then inserted radially into the open slots of the laminated core, the wire width corresponding essentially to the slot width minus the slot insulation.

The stator according to the present invention has a ratio of tooth width at the head of the tooth to yoke height between 0.3 and 0.8 and/or a ratio of tooth width at the head of the tooth to slot width at the head of the tooth between 0.3 and 3 and/or a ratio of copper mass of the wire in the slot to the total copper mass of the wire being between 0.43 and 0.55, the slot width being essentially equal to the slot width at the tooth head. The total copper mass includes the terminal wiring. Therefore, alternatively or in combination, an optimized design of tooth width to yoke height, of tooth width to slot width and/or of the cooling effect of the stator is achieved. It is advantageous if the laminated core of the stator does not have pronounced tooth heads, each winding has continuous wires, and the slot width corresponds approximately to the wire width. Expediently in the design of the stator, the slot is designed to have parallel sides. At smaller values of the aforementioned tooth width to yoke height of less than 0.3 and/or the aforementioned tooth width to slot width of less than 0.3, when a current is applied to it, the core circuit of the stator is so weak that it reaches saturation before the maximum power of the polyphase electric machine is deliverable. At values of more than 0.8 (tooth width to yoke height) and/or more than 3 (tooth width to slot width) the core circuit is dimensioned well but the winding resistance increases due to smaller and smaller slot areas. From the ranges according to the present invention, preferred slot numbers between 60 and 120 are obtained in the stator. If fewer slots are provided, the wire diameter increases due to the increasing slot area and results in a marked skin effect in the wire. The aforementioned ratio of copper masses according to the present invention allows advantageous cooling of the stator, even if the slot area is reduced in comparison with trapezoidal slots due to the parallel sides of the slots and therefore less copper may be introduced into the slot. The total mass of the copper in the stator is composed of the mass of the copper in the slots forming the electromagnetically active part and the mass of the copper in the winding heads, which provides cooling but at the same time is also responsible for the winding resistance and thus for the copper losses. Adequate cooling may be achieved despite the reduced copper mass. For generators having a smaller iron length in the rotor, the optimum mass ratio is shifted toward higher values; for generators having a greater iron length, the optimum is shifted toward lower values.

A particularly favorable range for the ratio of tooth width at the tooth head to yoke height is between 0.4 and 0.6, preferably between 0.4 and 0.5.

A particularly favorable range for the ratio of tooth width at the tooth head to slot width at the tooth head is between 0.5 and 2.5, preferably between 0.7 and 1.6.

A particularly favorable range for the ratio of copper mass of the wire in the slots to the total copper mass of the wire in the stator is between 0.45 and 0.53, preferably between 0.47 and 0.51.

The slots in the area of the tooth head and in the area of the slot base preferably have a comparable approximately equal width.

In a favorable embodiment, a good attachment of the windings is achievable despite the lack of a pronounced tooth head, if their wires have a winding head which protrudes axially beyond the slots and if the winding head is impregnated in such a way that the impregnation of a wire of one phase in the winding head has at least one point of contact with all other phases due to the impregnation, this contact point being reinforced by impregnation.

The method according to the present invention for manufacturing a stator for a polyphase electric machine provides that the core body is formed from a laminated core which is shaped from a strip having slots and teeth, in such a way that the strips are situated in parallel and intermeshed and are cut in pairs out of sheet metal. There is very little waste in cutting, thus allowing inexpensive production.

Of such strips and/or strip-shaped lamellae, a flat core body may also be formed from one of the toothed parallel strips by cutting it to a predetermined length and stacking and/or bundling the strip lamellae thereby produced one on top of the other. In a subsequent method step, the flat laminated core may be bent to form a round stator.

Alternatively, a round, i.e., hollow cylindrical core body may also be wound from a toothed parallel strip in a helical pattern and the winding may then be inserted into the round laminated core. Then with each revolution of the strip about the axis of the cylinder, one layer of the laminated core is formed on the preceding layer.

In a favorable method step, the wires are secured in the slots by impregnation of their winding heads.

In a favorable method step, the round wires of the winding are impressed onto the slot shape of the round stator and are then introduced into the stator.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 5shows a polyphase electric machine10designed as a generator such as that used in motor vehicles, for example. Electric machine10has a stator16having a core body17and a winding system18. Stator16is carried by two bearing shields, a drive bearing shield13.1facing a pulley6and a slip ring beating shield13.2. Stator16radially encompasses a rotor20mounted on a shaft27and designed as a claw pole rotor. Rotor20has two claw pole boards22,23, claw fingers24,25designed essentially in a trapezoidal shape extending axially on the outside circumference thereof. Shaft27carries the two oppositely polarized claw pole boards, which are situated in the rotor in such a way that their claw fingers extending axially are intermeshed and alternate with one another as north and south poles in the circumferential direction. This results in the claw pole interspaces that are required magnetically between the oppositely magnetized claw fingers situated opposite one another in the circumferential direction. The claw finger tips of claw fingers24,25situated opposite one another in the circumferential direction are spaced axially apart from one another. Rotor20is designed to be essentially cylindrical, having a pole core26which holds the two claw pole boards22,23at a distance and is surrounded by excitation winding21. The excitation winding has a single ring coil having a pole pair. Claw pole boards22,23of pole core26, and excitation winding21together form the magnetically active part of rotor20. Shaft27is supported in a roller bearing28on each end, each bearing being situated in one of two bearing shields13.1,13.2. Behind the slip ring bearing shield13.2—outside of the bearing shield—in this exemplary embodiment there is a 6-pulse bridge circuit (not shown in detail) and an electric field regulator which regulates the electromagnetic excitation of rotor20and contacts excitation winding21, but as an alternative, both the 6-pulse bridge circuit and the field regulator may be located inside slip ring bearing shield13.2. The 6-pulse bridge circuit is designed as bridge rectifier19. A fan30is connected axially to each of the two end faces of rotor20. Fans30cool electric machine10, in particular stator16, via its winding heads45,46. To do so, fresh air is drawn in axially through intake openings40, deflected radially and directed to at least one part of winding heads45,46to thereby cool them. Fans30are preferably designed as radial fans, but may also be designed in such a way that either individually or the two together they have at least one axial component.

This yields the following function of electric machine10, which is designed as a generator: if shaft27is driven to rotate by a drive, e.g., the internal combustion engine of a motor vehicle, via pulley6, then rotor20rotates and induces a polyphase alternating current in winding system18of stator16—with current flow through excitation winding21—this alternating voltage being rectified via bridge rectifier19by connecting a winding system18of stator16. Alternatively, winding system18may also be connected to or in the vicinity of a winding head. The size of the output voltage is regulated by excitation current regulation at a constant voltage, which is independent of rotational speed and load. The dc current supplies power to the consumers and charges a battery in the vehicle electric system.

FIG. 1ashows a top view of a preferred stator16, which does not include winding system18for reasons of simplicity.FIG. 1bshows a detail of preferred stator16for a polyphase electric machine as a detail. Stator16has a core body17which, as seen in the radial direction from an axis of rotation of the electric machine, has slots114on one side parallel to the longitudinal axis of core body17, which coincides with the axis of rotation (not shown), one slot114of which may be seen in the detail, and is provided with a stator yoke122on the opposite side. Slot114has a first slot width bn1at slot base120and a second slot width bn2in the area of tooth head118. Two slots114are separated from one another by tooth116, extending from slot base120to tooth head118.

Teeth116have a first tooth width bz1at the slot base and second tooth width bz2at tooth head118and are spaced a distance apart by a slot width sn at tooth width118. “Tooth width bz1at the slot base” is the distance at which the imaginary continuation of the flanks of the teeth would intersect with the imaginary continuation of the slot base. Such a method of ascertaining tooth width bz1is indicated, for example, when the transition between the side and the slot base is rounded out. Stator16may be designed for an external rotor or an internal rotor. In the case of an external rotor, slots114protrude radially outward and yoke122protrudes inward; for an internal rotor, slots114protrude radially inward and the yoke protrudes outward. Teeth116have a comparable width in the area of tooth head118and in the area of slot base120, i.e., tooth head118is not designed in a pronounced manner and therefore essentially does not protrude beyond the slot. Slot width sn is essentially equal to slot width bn2at tooth head118. The diagram inFIG. 1bis only exemplary in this regard.

Slots114are provided with a plurality of coils connected in series electrically to accommodate at least one coil winding, which is manufactured from at least one continuous wire124without interruption.

Ratio bz2/hj of tooth width bz2at tooth head118to yoke height hj, the yoke height being the radial distance between slot base120in core body17and the opposite outside diameter of core body17, is between 0.3 and 0.8 according to the present invention, preferably between 0.4 and 0.6, in particular preferably between 0.4 and 0.5. For the case when there is also an exterior tooth at the location where the outside diameter is situated, its radial extent is not taken into account beyond a continuous arc-shaped yoke part. Ratio bz2/bn2of tooth width bz2at tooth head118to slot width bn2at tooth head118is thus between 0.3 and 3 according to the present invention, preferably between 0.5 and 2.5, in particular preferably between 0.7 and 1.6.

On installation of stator16into a generator housing (not shown) of the polyphase electric machine, it is expedient to mount stator16between bearing shields13.1,13.2of the type conventionally found in a generator, in such a way that the mounting faces are embodied as the attachment faces for bearing shields13.1,13.2in a ring shape on the end faces of stator16, so they are both parallel to one another and at a certain installation distance from one another and extend radially over the part of stator yoke122that is required magnetically because the winding protrudes radially to the outside only slightly beyond slot base120. In addition, it is favorable to additionally provide slots that are not depicted in greater detail here in three to four locations on the outside circumference of stator16, allowing housing screws to be installed in an even smaller radius around the generator, e.g., at the slot base of these slots provided on the outside circumference of stator16.

FIG. 2shows a top view of two toothed parallel strips126,128, where the strips having slots and teeth are situated so that the strips are parallel to one another and mesh with one another to thereby allow them to be cut in pairs without waste from sheet metal (see also WO 01/54254).

To manufacture stator16, core body17is formed from a laminated core which is shaped from toothed parallel strips126,128. This is made possible by the fact that tooth head118is not stamped, i.e., does not protrude with respect to the tooth in the circumferential direction. Strips126,128may be cut to a predetermined length, stacked one above the other as strip lamellae to form a flat laminated core108and rolled about an axis parallel to the direction of stacking of the laminated core by bending deformation to form a round laminated core112and thereby create core body17. Wires124of the winding may next be introduced.

Alternatively, the winding may be inserted together with wires124into a flat laminated core108and then bent to form stator16. In a laminated core, slot114is opened wider in the flat state than in the round state. The winding may be mounted in the laminated core more easily.

FIG. 6shows an example of a core body17formed as a flat laminated core108having two core ends109,110. By bending laminated core108into a round shape and then joining the two adjacent core ends109,110, round laminated core112shown inFIG. 6is obtained with an impact point111. In one of the methods according to the present invention, winding system18is introduced into flat laminated core108before bending, although this is not shown inFIG. 7.

Wires124may be secured in slots114by impregnating their winding head. This is favorable with teeth116having tooth heads118, which are not pronounced, i.e., essentially do not protrude in the circumferential direction with respect to the teeth because for installation of the winding in slots114, the width of the slot must be greater than the width of the wire. For this purpose, it is advantageous if the impregnation of a wire124in the winding head has at least one point of contact through impregnation with all other phases reinforced by impregnation.

It is advantageous to manufacture the winding of round wires124and then to stamp it onto the slot shape of round stator16. All wires filling a slot114may be stamped jointly for this purpose. It is also conceivable to stamp each wire individually.FIG. 3ashows round wires124in a mold130having the slot shape of round stator16before stamping wire124. An arrow shows the force acting on wires124in stamping.FIG. 3bshows wires124after stamping in mold130. Slightly trapezoidal mold130facilitates unmolding of wires124. Stamping allows a higher filling factor of the winding and/or wires124in slot114at a low cost. It is particularly favorable if the width of the mold for stamping the winding and/or the internal end contour of mold130is between 1× and 1.49× the original wire diameter. Wire crossings may then be largely avoided. Stamping of individual wires124as well as all wires124together is thus possible.

FIG. 4shows a curve of temperature Ts of stator16as a function of the mCu(slot)/mCu(total) ratio of copper mass mCu(slot) (or metal mass) of wire124in slot114to total copper mass mCu(total) (or total metal mass) of wire124. Wire124is preferably made of copper. The mCu(slot)/mCu(total) ratio according to the present invention is between 0.43 and 0.55, preferably between 0.45 and 0.53, in particular preferably between 0.47 and 0.51. At lower mass ratios, temperature Ts is high, e.g., 170° C., and drops to a minimum of 150° C., for example, whereas it then rises at higher mass ratios.