GB2302215A

GB2302215A - Hand machine tool electric motor

Info

Publication number: GB2302215A
Application number: GB9611267A
Authority: GB
Inventors: Wilfried Kabatnik
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1995-06-14
Filing date: 1996-05-30
Publication date: 1997-01-08
Anticipated expiration: 2016-05-30
Also published as: GB9611267D0; GB2302215B; DE19521425A1; DE19521425B4

Description

1 I- 1 2302215 Hand machine tool with electric motor, as well as its

electric motor

Background art

The invention proceeds from a hand machine tool with electric motor according to the preamble of claim 1 and from an electric motor according to the preamble of claim 10. A hand machine tool with electric motor is already known (DE 33 11 557 Al), the electric motor of which comprises a stator, which is provided with an end shield and in which a rotor is rotatably supported. Supporting of the rotor relative to the stator in end shields has the advantage of enabling good centring so that contact between rotor and stator is substantially avoidable while the hand machine tool is in operation. On the other hand, said type of support takes up more room and entails a higher manufacturing outlay.

From DE 35 02 449 Al, a hand machine tool with electric motor is known, the rotor of the electric motor being supported at bearing points directly relative to the machine housing and the stator of the electric motor being fixed likewise relative to the machine housing. In order for the rotor and stator axes to be aligned as well as possible, the rotor and the stator have to be disposed precisely in the machine housing. Since the stator outer periphery, which is usually formed by a pole tube, is generally not subject to high dimensional tolerances, its mounting in the machine housing is effected by means of a sleeve-like, radially elastic packing. The resultant effect promoted by the pot-type style of construction of the housing is a satisfactory centring of the stator although, on account of the radially elastic packing, 2 M - in the event of impact loads an undesired displacement of the stator and in extreme cases even contact between the rotor and stator may occur.

Advantages of the invention In contrast, the hand machine tool according to the invention having the characterizing features of claim 1 or t-he electric motor according to the invention having the characterizing features of claim 10 has the advantage that an accurately positioned mounting of the stator is guaranteed, even in the case of a machine housing comprising two shells, without creating high tolerance requirements with regard to the outer periphery of the stator. In particular, the nature of the mounting also enables the use of mass-produced electric motors which, for a different application, may also be provided with an end shield.

By virtue of the measures described in the sub-claims, advantageous developments and improvements of the electric motor indicated in claim 1 are possible.

Drawings An embodiment of the invention is illustrated in the drawings and explained in greater detail in the following description. Of the drawings, Figure 1 is a longitudinal section through an electric motor constructed according to the invention, Figure 2 a view of a stator of the electric motor, Figure 3 and Figure 4 views of a centring ring and Figure 5 a partial view of a housing shell of a hand machine tool.

Description of the embodiment

In Figure 1, 10 denotes an electric motor which, in a known manner, comprises a stator 11 and a rotor 12. The rotor 12 has a rotor shaft 12a, which carries an armature 13 with 3 winding 13a. By means of bearings 14, 15, the rotor shaft 12a is supportable relative to a housing 52 (Figure 5) of a hand machine tool. A driving pinion 18 is provided at one end of the rotor shaft 12a, while a collector 19 is seated on the rotor shaft 12a close to its other end.

The stator 11 surrounds the rotor 12 in the region of its armature 13 between driving pinion 18 and collector 19. The stator 11 comprises a hollow cylindrical pole tube 20, to the inner wall 21 of which magnets 22 are fixed. The pole tube 20 at its two end faces 23, 24 is provided with recesses 25 which, in another application of the electric motor, are used to fasten end brackets or end shields to the pole tube 20. Lugs 26 of a centring ring 27 engage in each case into the recesses 25, which are repeated in pairs offset by 1800. Such a centring ring 27 is fitted on each end face 23, 24 of the pole tube 20. The task of the centring rings 27 is to fix the stator 11 relative to the housing 52 of the hand machine tool and ensure a precise alignment of stator 11 and rotor 12.

The pole tube 20 comprises a steel tube, the inside diameter 30 (Figure 2) of which is closely toleranced since the magnets 22 inserted into the pole tube 20 require a defined external contact surface. Because of a relatively coarse thickness tolerance of the wall of the pole tube 20 combined with the close tolerance of the inside diameter 30, the pole tube 20 has a relatively imprecise outside diameter 31 which is unsuitable for mounting of the stator 11 in the housing of the hand machine tool. Especially when said housing is of a shell-type construction, a precisely toleranced outside diameter 31 is required to enable the stator 11 to be accommodated in the housing 52 with minimum play and centrically relative to the rotor shaft 12a.

Such an exact accommodation of the stator 11 in the housing 52 of the hand machine tool is guaranteed by means of the two identical-type centring rings 27, which are preferably made of 4 plastic material. The centring rings 27, which are shown in greater detail in Figures 3 and 4, engage with two diametrically opposed projections 34 having a closely toleranced outside diameter 33 axially into the pole tube 20 and are therefore centred relative to the likewise closely toleranced inside diameter 30 of the pole tube 20. The centring rings 27 themselves have an outside diameter 35, which is manufactured precisely with regard to the dimensional and positional tolerance, so that they are fixable with their outer periphery 36 accurately positioned in the housing of the hand machine tool, the overall result being a high positional accuracy of the stator 11 in the housing 52 of the hand machine tool.

In Figure 2, the stator 11 is shown viewed from the side. Said view shows an end face 23 of the pole tube 20 which is provided with the diametrically opposed, end-face recesses 25, into which the lugs 26 may engage to form a twistlock connection. Further provided in the end faces 23, 24 of the pole tube 20 are additional recesses 40 of differing size and position, with the aid of which, for example, a correct poling of the stator is guaranteed in the event of magnetization in a magnetizing device. Corresponding lugs 41 (see Figure 4) on the centring ring 27 engage into said asymmetrically disposed recesses 40. As a result of said recesses 40, the centring rings 27 may be fitted only in a specific position relative to the pole tube 20 and hence non-interchangeably onto the pole tube. The recesses 40 in the end faces 23, 24 may also be used to fix the position of the stator 11 in the housing 52 of the hand machine tool.

Figure 5 shows, by way of examnle, the interior of a housing shell 52a of a two-shell housing 52 of a hand machine tool. Dashes indicate the stator 19 inserted into the housing shell 52a and having the two centring rings 27 fitted onto the end faces of the pole tube 20. Provided in the housing 52 are housing ribs 53 which project inwards from the housing wall and, when the stator 11 is inserted into the housing 52, engage radially into corresponding recesses 40 in the end faces 23, 24 of the pole tube 20 and prevent insertion of the stator 11 in the event of an incorrectly fitting position.

Projections 42a, b (see also Figure 3) on the side of the centring rings 27 remote from the pole tube 20 also serve to position the stator 11 correctly in the housing 52 of the hand machine tool. The projections 42a, b differ in terms of their width and are provided for engagement into corresponding gaps 54a, b (Figure 5) between radially inward-projecting webs 55, 56 in the housing shells 52a, b. In the present case, a narrow projection 42a corresponds with a correspondingly narrow gap 54a and a wide projection 42b is intended for engagement into a correspondingly wide gap 54b. Thus, the stator 11 may be inserted only in a quite specific position into the housing 52. If the stator 11 is incorrectly inserted, the housing shells 52a, b are unable to be joined together. Figure 5 also shows a bearing block 57 for the bearing 15 of the rotor shaft 12a.

As Figure 2 reveals, the magnets 22 are pressed out towards the inner wall 21 of the pole tube 20 by means of leaf springs 45, which are fixed by means of rivets 47, 48 to the inner wall 21 of the pole tube 20. The magnets 22 are prevented from sliding out in an axial direction by the centring rings 27 fitted laterally onto the pole tube 20.

As may be seen in Figure 1, it is additionally possible at at least one centring ring 27 for an air housing 51 to be attached to an inner edge 50 of the centring rings 27. For assembly reasons, the air housing 51 may be provided with a bezel 52 which is centred on the air housing 51. In another form of construction, the air housing 51 may be injectionmoulded on one of the centring rings 27, thereby dispensing with one injectionmoulded part and also enabling better utilization of the installation space.

6 p -

Claims

1. Hand machine tool with electric motor (10), which has a rotor (12) with a rotor shaft (12a), which is supported at bearing points (14, 15) in a housing (52) of the hand machine tool, and having a stator (11) which surrounds the rotor shaft (12a) in the region of an armature (13), the stator (11) in turn being separately supported in the housing (52) of the hand machine tool and having a hollow cylindrical pole tube (20), to the inner wall (21) of which magnets (22) are fastened, characterized in that, for supporting the stator (11) in a precisely positioned manner in the housing (52) of the hand machine tool, centring rings (27) are disposed on each of the end faces (23, 24) of the pole tube (20), which centring rings on the one hand are centred on the pole tube (20) and on the other hand with their outside diameter (36) support the stator (11) in the housing (52).

Hand machine tool according to claim 1, characterized in that provided on the centring rings (27) are axial projections (34) which engage axially into the pole tube (20), rest against the inner wall (21) and hence centre the centring rings (27) relative to the inner wall (21) of the pole tube (20).

3.

Hand machine tool according to claim 2, characterized in that lead-in bevels (37) are provided at free ends of the projections (34).

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4. Hand machine tool according to one of the preceding claims, characterized in that provided in the end faces (23, 24) of the pole tube (20) are recesses (25), into which lugs (26) disposed on the centring rings (27) axially engage.

5. Hand machine tool according to claim 4, characterized in that provided in the end faces (23, 24) are 5dditional recesses (40), which differ in terms of their position and size in such a way that the centring rings (27) are fitted only in a specific rotational position noninterchangeably on the pole tube (20).

6. Hand machine tool according to one of the preceding claims. characterized in that the magnets (22) are held by means of radially prestressed leaf springs (45, 46) against the inner wall (21) of the pole tube (20), the magnets (22) being secured in an axial direction by the centring rings (27) fitted onto the pole tube (20).

7 Hand machine tool according to claim 1, characterized in that formed in a diametrically offset manner on each of the centring rings (27) at their side remote from the pole tube (20) are projections (42a, b) of differing width, which engage into corresponding gaps (54a, b) of differing width, which are formed in housing shells (52a, 52b) of the housing (52) of the hand machine tool between radially inward-projecting webs (55, 56).

8. Hand machine tool according to claim 1, characterized in that fitted on at least one of the centring rings (27) is an air housing (51), which is centred by an inner edge (50) of the centring ring (27).

9. Hand machine tool according to claim 1, characterized in that an air housing (51) is integrally formed on at least one of the centring rings (27).

8 1..

1 Electric motor for a hand machine tool according to claim 1, which has a rotor (12) with rotor shaft (12a) and is provided with a stator (11), which surrounds the rotor shaft (12a) in the region of an armature (13) and has a hollow cylindrical pole tube (20), to the inner wall (21) of which magnets (22) are fastened, characterized in that disposed on each of the end faces (23, 24) of the pole tube (20) are centring rings (27), which on the one hand are centred on the pole tube (20) and on the other hand serve with their outside diameter (36) to support the stator (11) in a housing (52) of the hand machine tool.

A hand machine tool substantially as herein described with reference to the accompanying drawings.

12. An electric motor substantially as hereinbefore described with reference to the accompanying drawings.