GB2373643A

GB2373643A - Method of manufacturing a stator for a linear-motion electrical machine

Info

Publication number: GB2373643A
Application number: GB0126791A
Authority: GB
Inventors: Bernulf Goesling; Datong Wu; Hans-Werner Zimmermann; Barry Penswick
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2000-11-07
Filing date: 2001-11-07
Publication date: 2002-09-25
Anticipated expiration: 2021-11-07
Also published as: GB0126791D0; GB2373643B; NL1019319A1; DE10055079C1; NL1019319C2

Abstract

The disclosed method of manufacturing a stator (10) for a linear-motion electrical machine allows inexpensive mass production of the stator. The stator comprises a plurality of stator units (101 - 104). Each stator unit (101 - 104) comprises a plurality of stator poles (21) equally angularly spaced around the circumference of the unit, and an identical number of permanent magnets (22) which are fastened on successive stator poles (21) and magnetised with alternating polarity. The stator units (101 - 104) are joined axially to one another in such a way that permanent magnets (22) of alternating polarity lie adjacent to one another on axially mutually aligned stator poles (21) of the stator units. The stator units (101 - 104) are prefabricated separately from one another, including the fitting and magnetization of the permanent magnets, and are then put together to form the stator (10). The magnetization of the individual stator units before assembly avoids the neutral zones (dead zones) that might arise in the prior art magnetisation of a complete stator. Un-magnetised permanent magnets (blanks) may be brought into position more easily than highly magnetized magnets, with the result that finishing of the blanks may be reduced to a minimum.

Description

1 2373643

Method of manufacturing a stator for a linear-motion electrical machine Background art

The invention proceeds from a method of manufacturing a stator for a linear-motion electrical machine of the type defined in the preamble of claim 1.

In a known linear-motion electrical machine of said type (US 5 654 596, Figs. 1A to 3A) the stator, which is constructed in a laminated manner from sheet-metal punched sections, has four stator units disposed axially adjacent to one another, each having four stator poles offset by identical angles in peripheral direction. In each stator unit a shellsegment-shaped permanent magnet is disposed on the free end face of the stator poles.

The permanent magnets of the, in peripheral direction, successive stator poles in each stator unit are of alternating polarity, i.e. north-southnorth-south polarity. The permanent magnets lying adjacent to one another on axially aligned poles of the four stator units are likewise of a polarity which alternates successively in axial direction. On each four axially aligned stator poles a coil of the stator winding is wound. In the stator the shell-segment-shaped permanent magnets are glued onto the end faces, which are likewise shell-shaped or in the shape of a cylinder envelope segment, of the stator poles projecting radially from the return yoke.

During manufacture, however, bringing the highly

magnetized permanent magnets into the correct tolerance zone position is a very elaborate process.

A crucial factor for the quality of the linear generator is the formation of the air gap between the permanent magnets and the oscillator, also known as the mover, which moves axially back and forth in the interior of the stator. After assembly of the linear generator said air gap, which is typically 300 m, has to be constant at every point of the circumference of the oscillator because otherwise undesirable lateral forces arise. The subsequent machining of the permanent magnets needed for said purpose requires special tools, with the result that additional manufacturing costs arise.

Advantages of the invention The method according to the invention has the advantage that the stator of the linear generator may be inexpensively mass-produced with greater precision. On the one hand, by virtue of prefabrication of the stator units, including the fitting and magnetization of the permanent magnets, machining of the permanent magnets in the stator units before the magnetization process is simplified so that the air gap width may be kept very precisely constant. Thus, after assembly the undesirable lateral forces on the oscillator are minimized.

Furthermore, by virtue of the magnetization of the individual stator units before they are put together to form the stator, neutral zones between the north and south poles lying adjacent to one another in the direction of the stator axis, also known as dead zones,

are avoided. with magnetization of the complete stator, however, said dead zones might arise because during magnetization of the permanent magnets of alternating polarization, which lie closely adjacent to one another in the stator, only an incomplete magnetization is possible in the border area of said permanent magnets.

With magnetization of the individual stator units, on the other hand, the permanent magnets are fully magnetized, with the result that the material and power losses of the linear-motion machine, which are caused by the dead zones, are also avoided.

Advantageous developments and improvements of the method indicated in claim 1 are possible by virtue of the measures outlined in the further claims.

According to a preferred form of implementation of the method according to the invention, the as yet unmagnetized permanent magnets are fastened, preferably glued, on the end faces of the stator poles and then magnetized with the appropriate polarization. This has the advantage that the unmagnetized permanent magnets, so-called blanks, may be brought much more easily into the correct tolerance zone position on the stator pole than highly magnetized permanent magnets, with the result that finishing of the blanks may be reduced to a minimum.

According to an advantageous form of implementation of the invention, each permanent magnet is composed of a plurality of small, preferably rectangular segments.

Particularly in the case of permanent magnets of higher energy density, such as e.g. Nd-Fe-B magnets, this offers

a manufacturing advantage because said permanent magnets may be advantageously compressed into a suitable shape, then sintered and cut to size from a wintered block. The rectangular shape is particularly simple and inexpensive for automatic production. Said rectangular magnet segments are glued onto the end faces of the stator poles, and by suitably machining the upper side of the permanent magnets remote from the stator poles the necessary air gap relative to the oscillator is produced.

Magnetization is then effected after machining is complete. The magnetization process is advantageously preceded by a cleaning process, which removes all machining residues.

A linear-motion electrical machine having a stator manufactured by the method according to the invention is indicated in claim 9.

Drawings There now follows a detailed description of an embodiment

of the invention, which is illustrated in the drawings.

The drawings show in partially schematic representation: Fig. 1 a front view of a linear generator, Fig. 2 a section along the line II-II in Fig. 1, Fig. 3 a perspective view of the four mutually separate stator units of the linear generator in Fig. 2 without stator winding.

Description of the embodiment

The linear generator, which is shown in front view in Fig. 1 and in section in Fig. 2 and serves as an embodiment of a general linear-motion electrical machine, in a known manner comprises a hollow-cylindrical stator 10 and an oscillator 11, also called mover, which is disposed in the interior of the stator 10, executes an oscillating linear motion in axial direction 12 of the stator 10 and for said purpose is drivable e.g. by a Stirling engine. The oscillator 11 comprises two cylindrical iron core stacks 13, 14, which are held apart from one another by bolts 15 and fastened in an axially displaceable manner on a push or drive rod 16. The two iron core stacks 13, 14 are covered at their end face by end caps 17, 18, which are also used for the non-

illustrated guidance of the oscillator 11 in the stator 10. The hollowcylindrical stator 10 comprises a plurality of identically constructed stator units, in the embodiment four stator units 101, 102, 103, 104, which are disposed adjacent to one another along the stator axis 12 and, after being rotated through 90 relative to one another, are connected to one another. Each stator unit 101 has a stator body 19 with a return ring 20 made of ferromagnetic material and integral, radially inward projecting, salient stator poles 21. The stator poles 21 are arranged offset by identical angles at circumference relative to one another on the return ring 20, i.e. in the embodiment by 90 . The stator bodies 19 with return ring 20 and stator poles 21 are of an integral laminated

construction and are formed in each case by a stack of mutually joined sheet-metal punched sections, which are firmly connected to one another, e.g. by pressure punching, and form in each case a basic unit which may be handled separately. In each stator unit 101 - 104 permanent magnets 22 are fastened on the free end faces of the stator poles 21 directed towards the oscillator 11 and, together with the periphery of the iron core stacks 13, 14 of the oscillator 11, delimit a defined air gap of e.g. 300 m. The permanent magnets 22 on the successive stator poles 21 in each stator unit 101 - 104 are of alternating polarity, i.e. in the sequence of the stator poles 21 north-south-north-south. The stator bodies 19, for their axial arrangement, are rotated in each case through 90 about the stator axis relative to one another and axially firmly connected to one another by bolts 25.

Thus, on axially mutually aligned stator poles 21 of the stator units 101 - 104 permanent magnets 22 of alternating polarity lie adjacent to one another. Thus, as is illustrated in Fig. 2 by N and S for north and south polarization, the polarity of the permanent magnets 22 on the mutually aligned top stator poles 21 is north in the stator unit 101, south in the stator unit 102, north in the stator unit 103 and south in the stator unit 104, whereas the polarity of the permanent magnets 22 on the adjacent mutually aligned stator poles 21 is S-N-S-N.

A coil 23 of a stator winding 24 is wound in each case over all mutually aligned stator poles 21 of the stator units 101 and 104 so that the single-phase stator winding 24 has a total of four coils 23.

The stator 10 constructed in the previously described manner is massproduced in that the stator units 101 -

104 are prefabricated separately from one another, including the fitting and magnetization of the permanent magnets 22, and are then put together to form the stator 10. A perspective view of the four completely prefabricated stator units 101 - 104 is shown in Fig. 3.

Each stator body 19 is composed of an appropriate number of sheet-metal punched sections, wherein the sheet-metal punched sections are firmly connected to one another, e.g. by pressure punching, to form the stator body 19.

To achieve a high efficiency, permanent magnets 22 of higher energy density are used. For example, for manufacture of the permanent magnets 22 magnetic powder (Nd-Fe-B) is compressed and then sintered. In said case, either the shape of the individual permanent magnets 22 may be already defined or the permanent magnets 22 may be cut off a sintered block. For the manufacture of such non-magnetized blanks from magnetic material, the rectangular shape is simple and inexpensive. The individual permanent magnets 22 are therefore preferably composed of a plurality of small, rectangular segments 221, as is illustrated in Figs. 1 and 3. Said segments 221 are glued onto the free end face of the individual stator poles 21. Alternatively, it is possible for each permanent magnet 22 on the stator poles 21 to be manufactured in a shape adapted to the dimensions of the end face of the stator poles 21 and to be glued whole onto the stator poles 21. As the blanks are not yet magnetized, an exact positioning of the permanent magnets 22 on the stator poles 21 is possible without difficulty.

After the blanks have been glued onto the stator poles 21, the inside diameter of the stator units 101 - 104 is machined in order to guarantee a constant air gap width for the moving oscillator 11. After a cleaning process, the individual stator units 101 - 104 are then magnetized separately from one another, wherein the permanent magnets 22 on successive stator poles 21 experience an alternate magnetization so that they have the polarity indicated by N and S in Fig. 3. The four stator units 101 - 104 are then rotated in each case through 90 relative to the adjacent stator unit and placed against one another. The axially adjacent permanent magnets 22 on the mutually aligned stator poles 21 of all stator units 101 - 104 therefore have an alternating polarizing direction. The stator units 101 - 104 aligned in said manner are firmly connected to one another by the bolts 25, which pass through the stator bodies 19 in the region of the return rings 20, and in their entirety form the stator lO, which is then additionally wound with the stator winding 24, wherein the individual coils 23 are wound in each case onto the mutually aligned stator poles 21, as may be seen in Fig, 2.

The invention is not restricted to the described embodiment. For example, the number of stator poles 21 may be higher or lower than four. If m is the number of stator poles 21, wherein m is a whole number greater than 1, then when the stator units 101 - 104 are put together the next stator unit is always rotated through 360 /m relative to the preceding stator unit. Also, the stator units placed against one another in axial direction may be provided in any desired, but always even number. The

oscillator 11 then has to be suitably adapted and is designed, e.g. in the case of six stator units, with three iron core stacks and, in the case of two stator units, with one iron core stack.

Claims

1. Method of manufacturing a stator (10) for a linear-motion electrical machine comprising a plurality of stator units (101 - 104), which comprise in each case a plurality of stator poles (21) arranged offset by identical angles at circumference relative to one another and an identical number of permanent magnets (22), which are fastened with alternating polarity on successive stator poles (21), and are joined axially to one another in such a way that permanent magnets (22) of alternating polarity lie adjacent to one another on axially mutually aligned stator poles (21) of the stator units (101 - 104), characterized in that the stator units (101 - 104) are prefabricated, including the fitting and magnetization of the permanent magnets (22), separately from one another and put together to form the stator (10).

2. Method according to claim 1, characterized in that for each stator unit (101 - 104) a stator body (19) composed of sheet-metal sections is manufactured, which comprises a return ring (20) and the stator poles (21) , which are integral with and project radially inwards from the return ring (20).

3. Method according to claim 2, characterized in that the nonmagnetized permanent magnets (22) are

fastened, preferably glued, on the end faces of the stator poles (21) and then magnetized with alternating polarization at successive stator poles (21).

4. Method according to claim 3, characterized in that prior to their magnetization the permanent magnets (22) fastened on the stator poles (21) are treated, preferably machined, in order to keep within dimensional tolerances.

5. Method according to one of claims 1 - 4, characterized in that the permanent magnets (22) are composed of a plurality of small, preferably rectangular segments (221).

6. Method according to claim 5, characterized in that the composing of the permanent magnets (22) is effected during fastening on the stator poles (21).

7. Method according to one of claims 2 - 6, characterized in that the stator bodies (19) fitted with permanent magnets (22) are subjected, prior to the magnetization of the permanent magnets (22), to a cleaning process.

8. Method according to one of claims 1 - 7, characterized in that, after the stator units (101 - 104) have been put together, a coil (23) of a single-phase stator winding (24) is wound in each case onto the axially mutually aligned stator

poles (21) of the various stator units (101 104).

9. Linear-motion electrical machine having a stator (10), which comprises a plurality of stator units (101 - 104), which comprise in each case a plurality of stator poles (21) arranged offset by identical angles at circumference relative to one another and an identical number of permanent magnets (22), which are fastened with alternating polarity on successive stator poles (21), and are joined axially to one another in such a way that permanent magnets (22) of alternating polarity lie adjacent to one another on axially mutually aligned stator poles (21) of the stator units (101 - 104) , characterized in that each stator unit (101 - 104) comprises an independent stator body (19) fitted with the permanent magnets (22) and that the stator bodies (19) are rotated through 360 /m relative to one another and firmly connected to one another, wherein m corresponds to the number of stator poles (21) per stator unit (101 - 104).

10. Linear-motion machine according to claim 9, characterized in that each stator body (19) is formed by a core stack comprising a plurality of sheet-metal sections, which are firmly connected to one another.

11. Linear-motion machine according to claim 9 or 10, characterized in that the permanent magnets (22)

are composed of a plurality of small, preferably rectangular segments (221).

12. Linear-motion machine according to one of claims 9 - 11, characterized in that the firm connection of the stator bodies (19) is effected by means of the axially penetrating bolts (25).

13. Method of manufacturing a stator substantially as herein before with reference to the accompanying drawings.

14. Linear-motion machine substantially as herein before described with reference to the accompanying drawings.