GB2461914A - Stator of an electric machine, electric machine and electric power tool - Google Patents

Abstract

The stator 50 of an electric machine 30, e.g, a universal motor, has stator poles 36,38 receiving field windings 32, 34, at least one pole (winding holder) 36 having a larger winding width X3 than width X1 of the other pole 38. Pole 36 has its circumference flattened so as to define an increased gap 66 between the stator and the housing 18, which gap may accommodate the switch actuator 20 and/or electrical/electronic components, fluid/signal lines, and electrical conductors. The stator may comprise two parts 76,78 divided along line 68 at 70. The present stator allows for the hand grip section of a power tool e.g. a grinder, to be of reduced cross section.

Description

Description Title

Stator of an electric machine, electric machine and electric power tool

Prior art

The invention starts from a stator of an electric machine, an electric machine and an electric power tool according to the precharacterising clauses of the independent claims.

Electric machines which comprise a stator and rotor and can Ua opaated with cltorrioti ng ss 11 as dirent rllrrRnt also known as universal motors. Such electric motors are frequently employed in domestic appliances and electric power tools and can be supplied by an alternating-current network, it also being possible for a rectifier to be used where appropriate.

Particularly in the case of electric power tools, such as, for example, angle grinders, increasingly higher power densities are required, since ever-smaller appliances are desired. The reduction of the appliance size should not, however, be accompanied by a reduction of its power, but rather should even enable an increase in power. This frequently comes up against geometrical constraints.

For instance, in the case of small angle grinders, the electric motor is located directly in the grip region of the user, which is why particular importance is attached to the diameter of the electric motor here, since it has a direct influence on the grip diameter. However, angle grinders generally also possess a further feature which influences the grip shape or the grip diameter. The appliance is put into operation by actuation of a switching button, and the switching-on movement is effected via a switching slide moving past the electric motor into the rear region of the appliance, in order to actuate an electric switch there inside the appliance housing. For this purpose, the field assembly of the electric motor has a flattened area in the axial direction on both sides of the fie'd assembly. The housing in the grip region accordingly surrounds the electric motor, a switching slide and, where appropriate, an air gap between electric motor and housing in order to enable sufficient cooling.

If the switching slide is routed too close to the field assembly, i.e. the laminated iron core, there is a risk of the switching slide jamming in the event of dirt accumulation or deformation due to an excess temperature of the field windings and impairing or even preventing the switching-on and especially the switching-off of the appliance.

For this reason, so-called two-part fields, i.e. a

longitudinally divided field assembly with two assembly halves, in which the field assembly is separated at the pole separation, have already been proposed. The field winding of the coil can be placed in the assembly halves very easily and precisely, both as a prefabricated coil and by direct winding-in of the coil. The assembly halves are placed on top of one another prior to assembly and assembled together with the motor housing. The two-part field is generally flattened at the sides and allows a significantly greater spacing of the switching slide from the field assembly than a one-part configuration. In the case of the one-part configuration, the field assembly comprises merely one laminated core. However, the width of the field winding is greater than in the case of a one-part field, with the disadvantage of higher losses in the field winding compared with the one-part configuration.

Disclosure of the invention

The invention starts from a stator of an electric machine, in particular of a universal motor, having a cross-section, a longitudinal extent and a lateral surface.

It is proposed that at least one winding holder for receiving a field winding has a larger winding width than another winding holder.

In principle, the stator is usable both in electric motors and in generators. Particularly advantageous is the use in universal motors for domestic appliances and electric power tools. The stator may be designed in a one-part configuration with one field assembly, which is formed from a single laminated core, or in a configuration with two or more parts, where the field assembly is accordingly formed from two or more laminated cores. In principle, the field assembly may even be composed of solid material or else of sintered material instead of laminated iron.

Advantageously, the winding holder with the larger winding width may be provided on one side of the cross-section and a winding holder of smaller winding width on an opposite side of the cross-section.

Advantageously, the asymmetrical arrangement of the winding widths of the field windings on the one hand results in a favourable geometry in one of the halves of the stator corresponding to a one-part configuration of a field assembly, which results in a relatively small winding length owing to a relatively small winding width of the field winding, from which there follows a low ohmic resistance and consequently low electric losses in the field winding, which is generally formed from copper. This results in a favourable efficiency with correspondingly favourable high power density in the case of an electric machine, especially as no unnecessary clearance has to be formed on installation into a motor housing. Rather, on this side, the stator can optimally fill a motor housing and optimally utilise the structural space of the latter, so that a relatively large amount of iron is available on this side for the electromagnetic effects of the electric machine or electric motor. On the other hand, the asymmetrical arrangement of the winding widths results in a desired clearance on the opposite side of the stator cross-section with the larger winding width on installation into a housing, which clearance can be utilised for components of any type, for instance for receiving a switching slide, for leading lines etc. therethrough. The inside diameter of the stator into which a rotor can be received remains unchanged in this case. A large flattened area of the lateral surface of the field assembly on this stator side results in an advantageous synergy in relation to the structural space in a housing. Despite the enlarged winding width on this stator side, overall a favourable power density is obtained for the electric machine in which the stator according to the invention is used.

A flattened area may be formed in the lateral surface parallel to the longitudinal extent on that side of the cross-section on which the winding holder with the larger winding width is arranged. The flattened area makes it possible to provide a large clearance when the stator is received in a housing, in particular a cylindrical or at least almost cylindrical housing, such as, for instance, in a grip part of an angle grinder.

Advantageously, a smaller wall thickness of the stator may be provided in the region of the larger winding width than in the region of the smaller winding width. As a result, structural space outside the stator may be gained on this stator side when the stator is inserted into a housing.

A favourable mounting of field windings is possible if an axial division of the stator into two halves may be provided, the at least one flattened area being arranged completely in one half. The windings may be prefabricated and inserted into the freely accessible interior of the stator halves, or directly wound into the winding holders.

According to a further aspect of the invention, an electric machine, in particular a universal motor, having a stator, which has a cross-section, a longitudinal extent and a lateral surface, and a rotor cooperating with the stator is proposed, in which at least one winding holder for receiving a field winding has a larger winding width than another winding holder. The electric machine offers a high power density while at the same time providing a relatively large structural space between stator and housing. Only in one part of the stator are large winding widths and large winding overhangs of corresponding large winding length necessary, while in another part of the stator a small winding length enables lower ohmic losses.

A flattened area may be formed in the lateral surface parallel to the longitudinal extent on that side of the cross-section on which the winding holder with the larger winding width is arranged. A large structural space for components, for instance sliding switches, electric lines, capacitors, coils, circuit boards, resistors, signal lines, optical waveguides, coolant lines and the like is available between the flattened area and a housing surrounding the státor.

Advantageously, for this purpose, the lateral surface may be able to be fitted into a cylindrical motor housing.

According to a further aspect of the invention, an electric power tool, in particular angle grinder, having an electric motor arranged inside a housing, having a stator, which has a cross-section, a longitudinal extent and a lateral surface, and a rotor is proposed, in which at least one winding holder for receiving a field winding has a larger winding width than another winding holder.

Advantageously, a flattened area may be formed in the lateral surface parallel to the longitudinal extent on that side of the cross-section on which the winding holder with the larger winding width is arranged. A large clearance is available in the region of the flattened area.

A recess may be formed on the flattened area for guiding a sliding element and/or an electric supply line and/or a signal line and/or fluid line. :i.o

Brief description of the drawings

Drawing Further advantages will become clear from the following description of the drawing. Exemplary embodiments of the invention are illustrated in the drawing. A person skilled in the art will consider the features disclosed in

combination in the drawing, description and claims

expediently also individually and combine them to form appropriate further combinations.

In the drawing: Fig. 1 shows a preferred electric power tool in the form of an angle grinder; Fig. 2 shows a cut-open grip part of the angle grinder from Fig. 1; and Fig. 3 shows a plan view of a cross-section of the grip part from Figs. 1 and 2.

Embodiment of the invention Identical elements or elements of the same kind are denoted by the same reference symbols in the figures.

Fig. 1 shows a preferred electric power tool 10, embodied as an angle grinder, for the purpose of explaining the invention. The electric power tool 10 embodied as an angle grinder has a grip part 14, in whose front section, directed towards an insertion tool 16, a motor housing 18 is arranged. A handle 12 projects away transversely with respect to the grip part 14. On handling by a user, the latter holds the handle 12 with one hand and the grip part 14 with the other hand, and guides the electric power tool 10, embodied as an angle grinder, with the insertion tool 16 over a workpiece to be worked on. The grip part 14 is therefore expediently limited in its diameter to a dimension which enables the handling by the user, who should be able to grip the grip part 14 with one hand and securely guide it.

Fig. 2 shows a cut-open grip part 14 of the angle grinder from Fig. 1. Inserted in the motor housing 18 is an electric motor 30, embodied as a universal motor, the longitudinal axis of which lies in the longitudinal orientation of the grip part 14. There can be seen an upper and a lower winding overhang of a field winding 32, which project axially out of a stator 50 of the electric motor 30. A flattened area 60 can be seen on a lateral surface 58 of the stator 50.

Arranged above the flattened area 60 is a switching slide 20, which is actuated by a switching button 22 accessible to the user from outside, and which is pushed rearwards to a switch 24 arranged inside the grip part 14.

The diameter of the stator 50 and the distance of the switching slide 20 from the stator 50 substantially determine the diameter of the grip part 14.

Details of the preferred stator 50 and of the preferred electric motor 30 embodied as a universal motor can be seen in Fig. 3 in a plan view of a cross-section 54 of the grip part 14 from Figs. 1 and 2. The stator 50 has, by way of example, two pole shoes, which serve as winding holders 36, 38.

A rotor 40 is arranged inside the stator 50 as an internal rotor. Stator 50 and rotor 40 are arranged inside a preferably cylindrical or virtually cylindrical motor housing 18 which surrounds a lateral surface 58 of the stator 50 largely as closely as possible. The air gap between motor housing 18 and lateral surface 58 serves for the air cooling of the electric motor 30. The axial extent of rotor 40, stator 50 and motor housing 18 is indicated by the longitudinal extent 56 marked as an axis in plan view.

The stator 50 is of asymmetrical design in cross-section.

The cross-section of the stator 50 is divided into two sides 62 and 64 in relation to a separating line 68 marked by broken lines. The right-hand side 64 in the figure has a winding holder 38 with pole horns 38a, 38b, around which a field winding 34 is arranged and which has a relatively small winding width Xl. The field winding 34 is in this case arranged in customary fashion in one groove each between the respective pole horn 38a and 38b and the inner side of the stator 50. The lateral surface 58 of the stator 50 is slightly flattened symmetrically with respect to the winding holder 38.

If the stator 50 were designed, in its configuration with the shown pole horns 38a, 38b on the side 64, mirror-symmetrically with respect to the separating line 68, this would correspond to a customary one-part configuration of a stator with a single laminated core as the field assembly.

The asymmetrical construction of the stator 50 can be seen from the fact that a winding holder 36 with pole horns 36a, 36b on the opposite side 62 of the cross-section 54 requires a considerably larger winding width X3 than on the opposite side 64. The pole horns 36a, 36b project closer to the separating line 68 than the pole horns 38a, 38b, so that the field winding 32 likewise comes closer to the separating line 68 than the pole horns 38a, 38b of the field winding 34. The windings 32, 34 are electrically connected to one another in customary fashion in order to enable a rotation of the rotor 40 when the windings 32, 34 are energised. Despite the asymmetrical construction of the stator 50, the pole axes, which form the centre of the winding holders 36, 38, are symmetrical with respect to one another, and the mutual circuit angle, measured between each of the pole axes at the centre of the winding holders 36, 38, is 180°.

The lateral surface 58 of the stator 50 has on the side 62 a flattened area 60 which provides a clearance 66 between lateral surface 58 and motor housing 18, in which clearance the switching slide 20 can be moved with sufficient spacing from the stator 50. A dimension across flats X2, which denotes the distance between the flattened area 60 and the small flattened area on the side 64, is designed asymmetrically with respect to the separating line 68. The pole horns 36a, 36b of the pole half (winding holder 36) with the larger winding width X3 are designed shorter than the pole horns 38a, 38b of the pole half (winding holder 38) with the smaller winding width Xl.

If the stator 50 were symmetrical with respect to the separating line 68 in this configuration on the side 62, the configuration would correspond to that of a two-part field assembly with highly flattened lateral areas and a large winding width.

The stator 50 has a small wall thickness 72 in the region of the flattened area 60 and hence in the region of the larger winding width X3 at the pole axis at the centre of the winding holder 36, while in the region of the smaller winding width Xl a larger wall thickness 74 is formed at the pole axis of the winding holder 38.

The stator 50 may optionally be axially divided into two halves 76, 78, which is indicated by dotted lines at diametrically opposite points of separation 70, the flattened area 60 being arranged completely in one half 76.

In this case, the field windings 32, 34 may be inserted in each half 76, 78 and the halves 76, 78 joined together.

Subsequently, the halves 76, 78 provided with the field windings 32, 34 are inserted into the motor housing 18. The windings 32, 34 may be electrically connected to one another before or after insertion into the motor housing 18.

The preferred configuration of the stator 50 in combination with a cylindrical or approximately cylindrical housing 18 in conjunction with a switching slide 20 enables optimum utilisation of the structural space of the housing 18 and an advantageously small diameter of the grip part 14 with a high power output, in particular in the case of a universal motor in a hand-held electric power tool 10.