The invention is directed to an electromagnetic coil for an electric motor, in particular to an electromagnetic coil for a high power electric motor operated with high drive currents. Typically, such electromagnetic coils are provided with a wound coil wire providing a helical drive current flow. For high power electric motors, the coil wire must be provided with a large cross section to allow high electric drive currents of typically up to 100 A or even more. However, the large wire cross section limits the minimal bending radius of the coil wire. As a result, the filling factor of the electromagnetic coil, i.e. the ratio of the total coil wire volume to the volume being available for the electromagnetic coil, is generally limited to a value of about 60% which limits the efficiency of the electric motor. Furthermore, the tolerances of the electromagnetic coil increase with increasing coil wire cross section.

WO 91/12619 A1 discloses an electromagnetic coil for an electric motor being helical and composed of a stack of substantially annular metal sheet bodies being interrupted in circumferential direction. The metal sheet bodies are electrically isolated from each other except for connection sections at both circumferential ends of every metal sheet body. The metal sheet bodies are electrically connected in series with each other by axially welding or soldering together the connection sections of adjacent metal sheet bodies so that a helical drive current flow is provided within the metal sheet stack. The stacked electromagnetic coil is provided with several axially extending positioning holes, in which corresponding positioning elements are arranged to radially align and position the metal sheet bodies of the metal sheet stack with respect to each other. Because the metal sheet bodies can be manufactured very accurate even for large metal sheet thicknesses, for example by punching, the stacked electromagnetic coil allows a high coil filling factor and, as a result, a high motor efficiency even if high drive currents are required. However, the welded or soldered axial connections require additional manufacturing steps and are liable to wear, in particular if being exposed to vibrations. Furthermore, separate positioning elements are required to reliably align and position the metal sheet bodies with respect to each other.

It is an object of the invention to provide a reliable and cost-efficient electromagnetic coil for an electric motor, which allows a high motor efficiency at high motor powers. This object is achieved with an electromagnetic coil for an electric motor with the features of claim 1.

The electromagnetic coil according to the invention is helical and is composed of a stack of substantially spiral-shaped metal sheets bodies. The metal sheet bodies can be accurately manufactured, for example by punching. The spiral shape of the metal sheet bodies provides a circumferential drive current flow in the metal sheet body plane. The metal sheet bodies are electrically isolated from each other except for connection sections at both spiral ends of every metal sheet body and are electrically connected in series with each other via the connection means so that a helical drive current flow is provided within the metal sheet stack.

According to the invention, the connection sections of the metal sheet bodies are provided with integral axial connection means which provide an electrical connection between adjacent metal sheet bodies of the metal sheet stack in axial direction. The axial connection means furthermore provide a positive locking in a radial plane between adjacent metal sheet bodies which exactly radially aligns and positions the adjacent metal sheet bodies with respect to each other. Since the axial connection means are provided integrally with the metal sheet bodies, no additional components and/or manufacturing steps are required neither for providing the electrical connection in axial direction nor for providing the radial alignment and positioning of adjacent metal sheet bodies of the metal sheet stack. This allows a very reliable and cost-efficient electromagnetic coil for an electric motor, which can provide a high motor efficiency at high motor powers.

In a preferred embodiment of the invention, the connection sections of adjacent metal sheet bodies within the metal sheet stack are positioned on top of each, i.e. the connection sections of the adjacent metal sheet bodies are radially aligned with respect to each other. This allows a simple and reliable electrical connection between the connection sections of axially adjacent metal sheets.

Preferably, either the radial outsides or the radial insides of the two connection sections of the metal sheet body are provided with a tooth structure defining the axial connection means, wherein the teeth of the tooth structures are bent in axial direction so that the teeth of adjacent metal sheet bodies mesh. The tooth structure can be simply manufactured integrally with the metal sheet bodies, for example by punching. The tooth structures of adjacent metal sheet bodies are provided corresponding to each other so that the teeth of the adjacent metal sheet bodies mesh if bent in axial direction during the manufacturing process of the electromagnetic coil. The meshing teeth provide a very reliable electrical connection in axial direction as well as a reliable alignment and positioning of adjacent metal sheet bodies with respect to each other. More preferably, the tooth structure of every connection section is complementary symmetric with respect to a radially extending bisector of the connection sections, i.e. every tooth on one side of the bisector corresponds with an equally positioned recess on the opposite of the bisector. As a result, the tooth structures of a first metal sheet body and a second metal sheet body being arranged upside-down on top of the first metal sheet body mesh. This allows composing the electromagnetic coil from a stack of identically shaped metal sheet bodies, wherein every second metal sheet body is arranged upside-down.

In an alternative preferred embodiment of the invention, the connection means are defined by punch protrusions and corresponding punch holes, wherein the punch protrusions and the punch holes of adjacent metal sheet bodies mesh. The punch protrusions and corresponding punch holes are provided integrally with the metal sheet bodies and can be simply manufactured within the punching process of the metal sheet bodies. The meshing punch protrusions and punch holes allow a reliable electrical connection between adjacent metal sheet bodies and an exact alignment and positioning of adjacent metal sheet bodies with respect to each other.

Preferably, each of the two connection sections of a metals sheet body is provided with an equal number of punch protrusions and punch holes, wherein the punch protrusions and the punch holes of each connection section are arranged complementary symmetric with respect to a radially extending bisector of the connection sections. As described above, the complementary symmetry of the connection sections allows composing the electromagnetic coil of identically shaped metal sheets being stacked in alternating orientation.

In a preferred embodiment of the invention, all metal sheet bodies of the metal sheet stack are identically shaped, wherein every second metal sheet body of the metal sheet stack is arranged upside-down. As a result, all metal sheet bodies can be manufactured by a single manufacturing tool, for example by a punching tool with a single stamp. This allows a very cost-efficient realization of the electromagnetic coil.

Preferably, the punch protrusions and/or punch holes are provided with a substantially circular cross section in a metal sheet body plane. This allows a homogeneous distribution of the electric drive current within the punch protrusions and, as a result, within the axial connection means providing the electric connection between adjacent metal sheet bodies. Alternatively, the punch protrusions and/or punch holes are provided with a substantially rectangular cross section in the metal sheet body plane. The simple cross section geometries (circular/rectangular) can be manufactured with a very high accuracy allowing a very exact radial alignment and positioning of the metal sheet bodies with respect to each other and, as a result, allowing very low tolerances of the electromagnetic coil.

In a preferred embodiment of the invention, one of the two connection sections of a metal sheet body is provided with rectangular punch holes and the other connection section is provided with corresponding connection stripes being defined by two parallel punch slits extending substantially in circumferential direction. The connection stripes define the punch protrusions which are axially pressed into the corresponding punch holes of the adjacent metal sheet body to provide the electrical contact between the adjacent metal sheet bodies and to provide a positive locking in a radial plane between the adjacent metal sheet bodies. The meshing punch stripes and punch holes allow a very simple and reliable connection between adjacent metal sheet bodies.

Preferably, an axial clamping means is provided, which axially presses together the connection sections of adjacent metal sheet bodies within the metal sheet stack to ensure a reliable electrical connection between adjacent metal sheet bodies and a stable alignment of all metal sheet bodies within the metal sheet stack. More preferably, the axial clamping means is a pressure die casting body being cast around the assembled electromagnetic coil to fix the metal sheet bodies of the metal sheet stack and to press them together.

Alternatively, an axial screw hole is provided in the electromagnetic coil by substantially circular recesses in the metals sheet bodies, wherein the connection sections of adjacent metal sheet bodies within the metal sheet stack are pressed together in axial direction by a screw being arranged in the screw hole and defining the axial clamping means. The screw allows providing a very high press force and thus a very reliable connection between the metal sheet bodies.

Different embodiments of the invention are described with reference to the enclosed drawings, wherein

figure 1 shows a schematic side view of a first embodiment of an electromagnetic coil according to the invention being provided with a pressure die casting body,

figure 2 shows a schematic top view of a metal sheet body of the electromagnetic coil of figure 1,

figure 3 shows a schematic cross section of connection sections of two axially stacked metal sheet bodies of figure 2, wherein tooth structures of the connection sections mesh with each other,

figure 4 shows a schematic top view of alternative metal sheet bodies of the electromagnetic coil of figure 1,

figure 5 shows a schematic cross section of connection sections of two axially stacked metal sheet bodies of figure 4, wherein a punch protrusion being defined by a connection stripe of the first metal sheet body is axially pressed into a corresponding punch hole of the second metal sheet body, figure 6 shows a schematic side view of a second embodiment of an electromagnetic coil according to the invention, wherein the connection sections of the metal sheet bodies are axially pressed together by a screw, figure 7 shows a schematic top view of a metal sheet body of the electromagnetic coil of figure 6, and

figure 8 shows a schematic cross section of connection sections of two axially stacked metal sheet bodies of figure 7, wherein punch protrusions and punch holes of the metal sheet bodies mesh with each other. Figure 1 shows an electromagnetic coil 10 for an electric motor (not shown). The electromagnetic coil 10 is composed of a metal sheet stack 12 comprising numerous metal sheet bodies 14 being stacked on top of each other in axial direction. The electromagnetic coil 10 is provided with a pressure die casting body 15 cast around the metal sheet stack 12 to fix the metal sheet bodies 14 with respect to each other. The pressure die casting body 15 defines an axial clamping means 42 which axially presses together connection sections 16a, b of the metal sheet bodies 14.

Figure 2 shows a schematic top view of a metal sheet body 14 of the metal sheet stack 12 before the assembly of the electromagnetic coil 10. The metal sheet body 14 is provided with a substantially spiral shape with the connection sections 16a, b at both of its spiral ends. Each of the connection sections 16a, b is provided with a tooth structure 18a, b at its radial outside. The tooth structures 18a, b are each provided complementary symmetric with respect to a radially extending bisector B of the connection sections 16a, b, i.e. every tooth 20 at one side of the bisector B corresponds with a tooth recess 22 at the opposite of the bisector B. The metal sheet bodies 14 are stacked on top of each other in alternating orientation, i.e. every second metal sheet body 14 is arranged upside- down. The metal sheet bodies 14 are radially positioned so that the connection sections 16a, b of adjacent metal sheet bodies 14 are arranged on top of each other. The metal sheet bodies 14 are electrically isolated from each other except for the connection sections 16a, b, for example, by introducing suitable isolation sheets between the metal sheet bodies 14 in the metal sheet stack 12.

The teeth 20 of the tooth structures 18a, b are bent in axial direction during the assembly of the electromagnetic coil 10 so that each tooth structure 18a, b meshes with the respective tooth structure 18a, b of an axially adjacent metal sheet body 14 as schematically depicted in figure 3. The meshing tooth structures 18a, b define axial connection means 40. The metal sheet bodies 14 are provided so that one of the connection sections 16a, b provides a connection to the overlying metal sheet body 14 and the other connection section 16a, b provides a connection to the underlying metal sheet body 14. As a result, the metal sheet stack 12 provides a helical drive current flow. The axial connection means 40 provide a reliable electrical connection between axially adjacent metal sheet bodies 14, in particular between the connection sections 16a, b of the adjacent metal sheet bodies 14. Furthermore, the axial connection means 40 provide a positive locking in a radial plane between the adjacent metal sheet bodies 14 which reliably aligns and positions the metal sheet bodies 14 of the metal sheet stack 12 with respect to each other. As a result, no additional positioning elements are required. Figure 4 shows a schematic top view of alternative metal sheet bodies 14"a,b of the electromagnetic coil 10. The metal sheet bodies 14"a,b are each provided with a spiral shape but with inverse circumferential orientations. Starting at the radial inside, the metal sheet body 14"a extends in clockwise circumferential direction and the metal sheet body 14"b extends in counterclockwise circumferential direction. The radially inner connection section 16"a of the metal sheet body 14"a and the radially outer connection section 16"d of the metal sheet body 14"b are each provided with four rectangular connection stripes 34 defining four punch protrusions 30, wherein each connection stripe 34 is defined by two parallel punch slits 36 extending substantially in circumferential direction. The radially outer connection section 16"b of the metal sheet body 14"a and the radially inner connection section 16"c of the metal sheet body 14"b are each provided with four rectangular punch holes 28. The punch protrusions 30 and the punch holes 28 of the radially inner connection sections 16"a,c are provided corresponding with each other and the punch protrusions 30 and the punch holes 28 of the radially outer connection sections 16"b,d are provided corresponding with each other. The metal sheet bodies 14"a and the metal sheet bodies 14"b are alternately stacked on top of each other and are radially positioned so that the punch protrusions 30 and punch holes 28 of the metal sheet bodies 14"b are aligned with the respective punch holes 28 and punch protrusions 30 of the metal sheet bodies 14"a. The metal sheet bodies 14"a,b are electrically isolated from each other except for the connection sections 16"a,b. The connection stripes 34 define the punch protrusion 30 which are axially pressed into the corresponding punch holes 28 of the axially adjacent metal sheet body 14"a,b as schematically depicted in figure 5. The meshing punch protrusions 30 and punch holes 28 define axial connection means 40" which provide a reliable electrical connection between the axially adjacent metal sheet bodies 14"a,b. Furthermore, the axial connections means 40" provide a positive locking in a radial plane which reliably aligns and positions the metal sheet bodies 14"a,b with respect to each other.

Figure 6 shows an alternative electromagnetic coil 10' according to the invention, wherein the connection sections 16'a,b of the metal sheet bodies 14' are axially pressed together by an axial clamping means 42' being defined by a screw 24. The screw 24 is arranged in a screw hole 26 and is electrically isolated with respect to the metal sheet bodies 14'. Figure 7 shows a schematic top view of a metal sheet body 14' of the metal sheet stack 12'. The connection sections 16'a,b at the spiral ends are provided with punch holes 28' and with punch protrusions 30' axially protruding from the metal sheet body 14' as depicted in figure 8. The punch holes 28' and the punch protrusions 30' are provided with a substantially circular cross section in the metal sheet body plane. Each connection section 16'a,b is provided with one punch hole 28' and with one punch protrusion 30' which are provided complementary symmetric with respect to the bisector B'. The connection sections 16'a,b are also provided with connection section recesses 32a, b with the shape of circle sectors. The connection section recess 32a is provided at the radial outside of the connection section 16'a and the connection section recess 32b is provided at the radial inside of the connection section 16'b. Both connection section recesses 32a, b together define a substantially circular screw recess 33.

The metal sheet bodies 14' are stacked with alternating orientation, i.e. every second metal sheet body 14' is arranged upside-down. The metal sheet bodies 14' are radially positioned so that the punch holes 28' and the punch protrusion 30' of axially adjacent metal sheet bodies 14' mesh with each other as schematically depicted in figure 8. The meshing punch holes 28' and punch protrusion 30' define axial connection means 40' providing a reliable electrical connection of axially adjacent metal sheet bodies 14'. Furthermore, the axial connection means 40' provide a positive locking in a radial plane which reliably aligns and positions the metal sheet bodies 14' with respect to each other. The screw recesses 33 of all metal sheet bodies 14' are positioned on top of each other and define the screw hole 26. Reference list

10 electromagnetic coil

12 metal sheet stack

14 metal sheet bodies

15 pressure die casting body

16 connection sections

18 tooth structures

20 teeth

22 tooth recesses

24 screw

26 screw hole

28 punch holes

30 punch protrusions

32 connection section recesses

33 screw recesses

34 connection stripes

36 punch slits

40 axial connection means

42 axial clamping means

B bisector