GB1585325A

GB1585325A - Brush holders for electric machines

Info

Publication number: GB1585325A
Application number: GB17953/78A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1977-07-22
Filing date: 1978-05-05
Publication date: 1981-02-25
Also published as: DE2733130A1; IT1097824B; FR2398397A1; IT7825750A0

Description

(54) IMPROVEMENTS IN BRUSH HOLDERS FOR ELECTRIC MACHINES (71) We, ROBERT BOSCH GMBH, a German company of Postfach 50, 7 Stuttgart 1, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a brush holder for an electrical machine having a commutator or at least one slipring.

A known brush holder comprising a brush carrier for the spatial co-ordination of the brush with respect to the commutator or slipring, a brush guide contained in the brush carrier for the displaceable accommodation of the brush, and a spring for holding the brush against the commutator or slipring.

In particular in machines of miniature construction, such brush holders make assembly more complicated, since the compact construction of such machines does not allow the installation of the brush holders also after completion of the assembly. Thus it becomes necessary to fix the brush holders on the machine and also to mount brushes and brush spring during some favourable stage of the assembly work, for example prior to the insertion of the rotor or the placement of the bearing cover at the brush side. Thus the brushes in the brush guide have to be additionally retained against the force of the brush spring, up to the fitting into the correct position of the commutator or the sliprings.

All this and the presence of the bulky brush lead-wire considerably complicate the further assembly of the electric miniature machine.

It is therefore an object of the invention to provide a brush holder which does not complicate the assembly of the electrical machine, such as a miniature d.c. motor, and which can be manufactured simply and cheaply and fixed to the machine, ready for operation, by a few manipulations.

The present invention resides in a brush holder for an electrical machine having a commutator or slipring, said brush holder comprising at least one receptacle formed in a single piece, injection moulded plastics bearing cover for the machine and a brush guide bent out of sheet metal and received in said receptacle for slidably retaining a brush and brush spring captive therein for resilient abutment of said brush against the commutator or slipring, and in which the brush guide has at least one projection and the receptacle in the bearing cover has at least one detent which engages behind the corresponding projection when the brush guide has been inserted into the receptacle.

By these measures on the one hand a saving is achieved, in that a separate brush carrier is no longer required, since its function is assumed by the bearing cover. Secondly it is made possible completely to pre-assemble the brush guide, including the brush spring and the brush, as a sub-assembly, and to insert it after completion of the assembly of the electrical machine into the receptacle in the bearing cover, with the result that the brush is positioned correctly for its operation. Thanks to the measures in accordance with the invention the brush holder can therefore be assembled as the last part on the electrical machine, and brushes and brush lead-wires do not interfere in any way with the assembly of the electrical machine.

The assembling of the brush holder is performed by simple insertion of the completely pre-assembled sub-assembly: brush guide, brush spring and brush, into the receptacle in the bearing cover, which does not require a special assembling tool or any assembling space within the machine for engagement by an assembling tool. The brush holder in accordance with the invention thus also promotes a compact mode of construction of the electrical miniature machine.

In a preferred embodiment of the invention the receptacle is provided with guide slots, and lugs are arranged on the brush guide which can be inserted into the guide slots. In this way a secure and correct positioning of the brush guide in the receptacle in the bearing cover is achieved in a simple manner.

Advantageously, the brush guide is provided with at least one projection, and the receptacle in the bearing cover with at least one detent which engages behind the corresponding projection, when the brush guide has been inserted into the receptacle. In this manner a locking of the brush guide in the receptacle is provided which retains the brush guide and hence the brush invariably in its correct position and also prevents a possible drop-out of the brush guides from their seat in the bearing cover during the transport of the machine.

A further preferred feature of the invention is that the guide slots are formed by two angular section ribs extending at a distance from and parallel to one another perpendicularly to the axis of the machine, which ribs are fixed to the bearing cover and engage over the lugs of the brush guide when the same has been inserted into the receptacle. An insertion opening for the lugs is provided at one end of the ribs and at least one stop is provided at the other end to limit the insertion movement of the brush guide. The detent is conveniently arranged at the insertion opening between the ribs and is made so that it is resilient. In this way a particularly simple practical realisation of the receptacle for the brush guide, including the detent, is achieved.

In accordance with a further preferred feature of the invention, the bearing cover is made as a single-piece plastics injection moulding. In this way, in a single stage of operation, the ribs, the stops and the detent, including the resilient realisation of the latter, can be moulded in a simple manner onto the bearing cover.

In accordance with another preferred feature of the invention, the brush guide comprises a base plate with sideways projecting lugs and a sleeve of rectangular cross-section open on one longitudinal side, which with its open longitudinal side rests on the base plate and is fixed to the same by means of tabs bent from the sleeve. The lugs of the plate conveniently have recesses through which pass the tabs of the sleeve, the bent-over tabs then resting against the back of the base plate.

By these measures altogether a form of the brush guide is achieved which is easy to manufacture and for the finishing of which no welding or soldering operations are required.

In accordance with a further preferred feature of the invention, the bent-over tabs on the sleeve resting against the back of the base plate form the projection co-operating with the detent in the receptacle of the bearing cover. This simplifies the tool for the manufacture of the brush guide and saves the need for a further stage of operation for producing such a separate latch projection.

One end of the sleeve can have a cover so that the brush spring arranged inside the sleeve abuts on this cover. The sleeve thus serves at the same time for the guiding and accommodation of the brush spring, and the spring need not be held or fixed separately.

In accordance with a preferred feature of the invention, the brush guide is made as a single piece, the base plate, the lugs, the sleeve, the tabs and the cover being stamped all in one piece from a flat piece of sheet-metal and the brush guide is formed by bending of the sleeve walls, the tabs and the cover off from the base plate. By this procedure the entire brush guide can be made complete from one part with the help of one progressive tool.

Only one stamping, and several minor bending operations are necessary. The inside dimensions of the sleeve accommodating the brush are maintained with a relatively high degree of consistency.

The brush lead-wire can be attached to the sleeve cover and the length of the lead-wire from the brush to this point of attachment is dimensioned so that the brush is prevented from sliding out of the brush guide. By this measure it is made possible to insert the brush spring and the brush into the brush guide be fore fixing the brush guide to the bearing cover. In other words, the brush guide includ ing the brush spring and the brush can be pre-assembled as a complete sub-assembly, without any additional measures being required for retaining the brush under spring pressure in the brush guide. When the so pre assembled brush guide is inserted into the receptacle in the bearing cover, the brush will automatically strike the commutator or the slipring and slide, against the spring force, to the required extent into the brush guide.

in accordance with a further embodiment of the invention the bearing cover is provided with a clamping device for the connection cable. In this way a secure stress relief of the point of contact of the connection cable and brush lead-wire or litz is achieved.

Such a clamping device is preferably provided with a lug and a rib which are arranged at one opening of channel accommodating the brush cable and which are located near the point of attachment of the cable on the sleeve cover when the brush guide has been inserted into the bearing cover receptacle. One opening of the channel points in the direction of the rotary axis, and the other opening of the -channel, carrying the lug and the rib, is arranged perpendicularly thereto. By this arrangement the brush cable in the channel is turned through nearly 90 degrees, which ensures an additional clamping of the cable in the channel.

The invention is further described, by way of example, with reference to the accompanying drawings, wherein:- Figure 1 is a longitudinal section of a d.c.

miniature motor having a brush holder in accordance with the invention; Figure 2 is a front elevation of the preassembled sub-assembly of brush guide, brush spring and brush; Figure 3 is a side elevation of the preassembled sub-assembly in Fig. 2, partly in section; Figure 4 is a plan view of th sheet-metal blank of the brush guide; Figure 5 is a plan view of the bearing cover with two receptacles each intended for a brush guide, and Figure 6 is a side elevation of the bearing cover in Fig. 5.

The d.c. motor of Fig. 1 comprises a housing 1 carrying magnets 2. The housing 1 is closed at both ends by bearing covers 3 and 4, each of which is provided in a central recess 5 or in a central bore 6 respectively with a sintered bearing 7 and 8 for a rotor shaft 9. On the rotor shaft 9 are rigidly fixed a rotor 10, and close by the bearing cover 3, a commutator 11.

The motor has a brush holder 12 comprising a brush carrier whose function is assumed by the bearing cover 3, a brush guide 13 for the displaceable accommodation of a brush 14 perpendicularly to the rotor shaft 9 and a brush spring 15 for pressing the brush against the commutator 11. It is customary for the d.c. motor to have two brushes offset by 1800 with respect to each other and hence also two brush holders. For the sake of clarity, however, only one brush holder 12 has been depicted in Fig. 1.

As can be seen from Figs. 2 and 3, the brush guide 13 is in the form of a structural element accommodating the brush spring 15.

Two identical receptacles, offset by 1800 are provided in the bearing cover 3 for the insertion of a respective brush guide 13. For the sake of clarity only one of the receptacles 16 has been shown in Fig. 1.

As can be seen in particular from Figs. 5 and 6, the receptacle 16 is provided with guide slots 17, and on the brush guide 13 there are lugs 18 which can be inserted into the guide slots 17. Moreover, the brush guide 13 is provided with at least one projection 19 (Fig. 3) and the bearing cover 3 has per receptacle 16 at least one detent 20, which engages behind the corresponding projection 19, when the brush guide 13 has been inserted into the receptacle 16 of the bearing cover 3 (see Fig. 1). The guide slots 17 for each receptacle 16 is formed in the bearing cover 3 by two parallel spaced apart angular ribs 21 and 22 extending perpendicularly to the rotor shaft 9. The ribs 21 and 22 are fixed to the bearing cover 3 and engage over the lugs 18 of the brush guide 13 when the latter is inserted into the receptacle 16. An insertion opening 23 (Fig. 6) for the lugs is provided at one end of the ribs 21, 22 and at least one stop 24 (Fig. 5) is provided at the other end face to limit the insertion movement of the brush guide. The detent 20 is resilient, and is located between the ribs 21 and 22 at the insertion opening 23. The bearing cover 3 is in the form of a single-piece plastics injection moulding, so that the ribs 21 and 22, the stop 24 and the detent 20 can be moulded onto the bearing cover 3 in a simple manner. Moreover, further spacers 25 are moulded onto the bearing cover 3 and serve for the axial fixing of the magnets 2 in the housing 1 of the d.c.

motor.

The brush guide 13 comprises a base plate 26 with the laterally projecting lugs 18 and a sleeve 27 of rectangular cross-section, which is open on one longitudinal side and which with its open longitudinal side rests on the base plate 26, and is fixed to the same by means of tabs 28 bent off the sleeve. The lugs 18 of the base plate 26 have recesses 40 extending as far as the base plate 26, through which pass the tabs 28. The bent-over tabs 28 rest against the back of the base plate 26 and form the projection 19 co-operating with the detent 20 in the bearing cover 3. One end of the sleeve 27 is provided with a cover 29, on which abuts the brush spring 15 arranged inside the sleeve 27. The longitudinal side of the sleeve 27 opposite the base plate 26 has a longitudinal slot 30 which extends from the open end of the sleeve and which accommodates a brush litz 31 pressed laterally into the brush 14 to allow the displacement of the brush 14 within the brush guide 13.

The brush guide 13 is made of a single piece, with the base plate 26, the lugs 18, the sleeve 27, the tabs 28 and the cover 29 being stamped out of a flat piece of sheet-metal. The blank of this piece of sheet metal is represented in figure 4. The brush guide 13 is formed by simple bending of the walls of the sleeve 27,' the cover 29 and the tabs 28 off the base plate 26. The blank and the complete manufacture of the brush guide 13 can be performed by means of a single progressive tool.

The brush lead-wire or litz 31 pressed into the brush 14 is fixed to the sleeve cover 29, the length of the cable end from the point of attachment 32 on the cover 29 to the point of contact between the litz 31 and the brush 14 being dimensioned so that the brush 14 is prevented from sliding out of the brush guide 13, that is from the sleeve 27, under the effect of the brush spring 15. This litz or braid is preferably made without insulation, whilst the connection cable 33, which is also fixed to the same point of attachment 32, is insulated. The bearing cover 3 accommodating the brush guide 13 is provided additionally with a clamping device 34 (Fig. 6) for the connection cable 33. This clamping device comprises a lug 35 and a rib 36 which are arranged at an opening 37 of a channel 38 carrying the connection cable 33, and which are located close to the point of attachment 32 of the cable 33 on the cover 29 when the brush guide 13 has been inserted into the receptacle 16. The other opening 39 of the channel 38 points in the direction of the rotor shaft 9, whilst the opening 37 of the channel 38 carrying the lug 35 and rib 36 are arranged perpendicularly thereto. As a result the connection cable 33 is turned through approximately 90 , so that in association with the lug 35 and the rib 36 a clamping effect on the cable 33 in the channel 38 is produced. By means of this clamping device 34 a secure stress relief of the point of contact at the point of attachment 32 and on the point of connection of the brush cable 31 on the brush 14 is achieved. The brush guide 13 bent from a sheet-metal stamping is preassembled completely to a sub-assembly by the insertion of the spring 15 and of the brush 14 into the sleeve 27 and attachment of the cables 31 and 33 on the cover 29. After the complete assembly of the d.c. motor this completely pre-assembled brush guide 13 is inserted into the receptacle 16 of the bearing cover 3, the lugs 18 sliding into the guide slots 17. The ribs 21 and 22 of the guide slots 17, engaging over the lugs 18, provide a safe hold for the brush guide. The stop 24 on the ribs 21 and 22 determines the depth of insertion of the brush guide in the receptacle 16. When the brush guide is inserted, the resilient detent 20 will be pushed back in the first place by the projecting tabs 28 on the back of the base plate 26, and after complete insertion of the brush guide 13 into the receptacle 16 the detent 20 springs back again and engages behind the projection 19 formed by the tabs 28. Thus the brush guide 13 is locked in the receptacle 16 of the bearing cover 3, and the brush 14 assumes its operationally correct position within the motor. When the brush guide 13 is inserted into the receptacle 16, the brush 14 rests against the commutator 11 and is pushed by the commutator 11 into the sleeve 27, with compression of the brush spring 15, until the brush guide 13 is locked in the receptacle 16.

WHAT WE CLAIM IS: 1. A brush holder for an electric machine having a commutator or slipring, said brush holder comprising at least one receptacle formed in a single piece, injection moulded plastics bearing cover fcr the machine and a brush guide bent out of sheet-metal and received in said receptacle for slidably retaining a brush and brush spring captive therein for resilient abutment of said brush against the commutator or slipring, and in which the brush guide has at least one projection and the receptacle in the bearing cover has at least one detent which engages behind the corresponding projection when the brush guide has been inserted into the receptacle.

2. A brush holder in accordance with claim 1, in which the receptacle is provided with guide slots, and the brush guide has lugs which are inserted into the guide slots.

3. A brush holder in accordance with claim 2, in which the guide slots are formed by two parallel angular section ribs extending per pendicularly to the rotary axis, which ribs are fixed to the bearing cover and engage over the lugs of the brush guide when the same has been inserted into the receptacle, an insertion opening for the lugs being provided at one end of the ribs, and at least one stop being pro vided at the other end for limiting insertion movement of the brush guide.

4. A brush holder in accordance with claim 3, in which the detent is arranged at the in sertion opening between the ribs and is resilient.

5. A brush holder in accordance with any of claims 1 to 4, in which the brush guide comprises a base plate with sideways project ing lugs and a sleeve of rectangular cross-sec tion open on one longitudinal side, which with its open longitudinal side rests on the base plate and is fixed to the same by means of bent over tabs on the sleeve.

6. A brush holder in accordance with claim 5, in which the lugs of the base plate have recesses through which pass the tabs on the sleeve and the bent-over tabs rest against the back of the base plate.

7. A brush holder in accordance with claim 1 and claim 5 or 6 in which the bent-over tabs form the projection co-operating with the detent of the receptacle.

x. A brush holder in accordance with any of claims 5 to 7 in which one end of the sleeve has a cover and the brush spring arranged inside the sleeve abuts this cover.

9. A brush holder in accordance with any of claim 1 to 8, in which the brush guide is made as a single piece.

10. A brush holder in accordance with claims 8 and 9, in which the base plate, the lugs, the sleeve, the tabs and the cover are stamped all in one piece from a flat piece of sheet metal and the brush guide is formed by bending of the sleeve walls, the tabs and the cover from the baseplate.

11. A brush holder in accordance with any of claims 8 to 10, in which the brush lead wire is situated externally of the brush spring and is attached to the cover of the sleeve and the length of the brush lead-wire from the brush to this point of attachment is dimen sioned so as to prevent the brush from sliding out of the brush guide.

12. A brush holder in accordance with any of claims 1 to 11, in which the bearing cover is provided with a clamping device for a connection cable.

13. A brush holder in accordance with any of claims 8 to 11 and claim 12, in which the clamping device is provided with a lug and a rib, which are arranged at an opening of a channel accommodating connection cable and which are located near the point of attach ment of the brush lead-wire to the cover when the brush guide has been inserted into

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. shaft 9, whilst the opening 37 of the channel 38 carrying the lug 35 and rib 36 are arranged perpendicularly thereto. As a result the connection cable 33 is turned through approximately 90 , so that in association with the lug 35 and the rib 36 a clamping effect on the cable 33 in the channel 38 is produced. By means of this clamping device 34 a secure stress relief of the point of contact at the point of attachment 32 and on the point of connection of the brush cable 31 on the brush 14 is achieved. The brush guide 13 bent from a sheet-metal stamping is preassembled completely to a sub-assembly by the insertion of the spring 15 and of the brush 14 into the sleeve 27 and attachment of the cables 31 and 33 on the cover 29. After the complete assembly of the d.c. motor this completely pre-assembled brush guide 13 is inserted into the receptacle 16 of the bearing cover 3, the lugs 18 sliding into the guide slots 17. The ribs 21 and 22 of the guide slots 17, engaging over the lugs 18, provide a safe hold for the brush guide. The stop 24 on the ribs 21 and 22 determines the depth of insertion of the brush guide in the receptacle 16. When the brush guide is inserted, the resilient detent 20 will be pushed back in the first place by the projecting tabs 28 on the back of the base plate 26, and after complete insertion of the brush guide 13 into the receptacle 16 the detent 20 springs back again and engages behind the projection 19 formed by the tabs 28. Thus the brush guide 13 is locked in the receptacle 16 of the bearing cover 3, and the brush 14 assumes its operationally correct position within the motor. When the brush guide 13 is inserted into the receptacle 16, the brush 14 rests against the commutator 11 and is pushed by the commutator 11 into the sleeve 27, with compression of the brush spring 15, until the brush guide 13 is locked in the receptacle 16. WHAT WE CLAIM IS:

1. A brush holder for an electric machine having a commutator or slipring, said brush holder comprising at least one receptacle formed in a single piece, injection moulded plastics bearing cover fcr the machine and a brush guide bent out of sheet-metal and received in said receptacle for slidably retaining a brush and brush spring captive therein for resilient abutment of said brush against the commutator or slipring, and in which the brush guide has at least one projection and the receptacle in the bearing cover has at least one detent which engages behind the corresponding projection when the brush guide has been inserted into the receptacle.

the receptacle in the bearing cover.

14. A brush holder in accordance with claim 13, in which one opening of the channel points in the direction of the rotary axis and the other opening of the channel carrying the lug and the rib is arranged perpendicularly thereto.

15. A brush holder for an electrical machine, constructed substantially as herein described with reference to and as illustrated in the accompanying drawings.