GB2433651A

GB2433651A - Vibration decoupling mounting of brushes or brush holders

Info

Publication number: GB2433651A
Application number: GB0624486A
Authority: GB
Inventors: Bernhard Rupp; Gerald Kuenzel; Christof Bernauer; Christian Bauer; Ruediger Schroth
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2005-12-09
Filing date: 2006-12-07
Publication date: 2007-06-27
Also published as: GB0624486D0; DE102005058833A1

Abstract

A hand machine tool with a commutated electric motor comprises a brush holder 24,72 with at least one brush 28,80 and a decoupling means 36,66,78a,78b,82,90, which is provided to counteract transmission of a vibration, resulting from the rotation of the commutator. Springs 40 and friction dampers 38.1,38.2 may mount brush unit 24 to a shell which supports the brush unit (24). Alternatively, the decoupling means may be present between the brush and the brush holder, being formed for example by integral elements 78a,78b on the brush holder, by elements 84 partially embedded in the brush, or an inserted resilient liner (fig 5). In a further embodiments the brush holder may comprise guide walls 88, decoupler 90 having a double wall. Two brush holders may be supported on a ring which is resiliently attached by elastic fins to a circumferential two part shell.

Description

Hand machine tool

Prior art

Hand machine tools with an electric motor are known. The latter has a commutator which can rotate around an armature axis to change the polarity of an armature winding, and which includes several conducting segments arranged around the circumference. In operation of the hand machine tool, these are contacted by a carbon brush, which is arranged in a tubular brush-holder so that it can be moved in the radial direction, said tubular brush-holder being rigidly joined to a motor housing. When the commutator rotates, vibrations are transmitted to the carbon brush and further to the tubular brush-holder and motor housing, because of the segment structure of the commutator surface and because of component tolerances and imbalances.

Advantages of the invention A hand machine tool with an electric motor, which includes a commutator which can rotate around an axis of rotation, a brush unit with at least one brush, a shell to carry the brush unit and a decoupling means, which is provided to counteract transmission of a vibration, resulting from the rotation of the commutator, of at least a part of the brush unit, transversely to the radial direction onto the shell, is proposed. In this way, a reduction of vibration which occurs during operation of the electric motor, and its transmission onto the shell, can be advantageously achieved. In particular, emission of running noise can be reduced. The brush is preferably movable in the radial direction and guided by a guiding means. The decoupling means can be in the form of a joining component to join the guiding means to the shell directly. A "decoupling means" should be understood as, in particular, a means of vibration insulation and/or a means of vibration damping. A "part" of the brush unit should be understood as, in particular, the brush and/or another component of the brush unit, e.g. a guiding means to guide the brush.

It is also proposed that the decoupling means and at least part of the brush unit form a unit which has an inherent vibration mode, and that the decoupling means is provided to prevent stimulation of the inherent vibration mode when the electric motor is operated. In this way, vibration of at least the part of the brush unit with large amplitudes can be prevented. In particular, vibration of the brush and/or of a guiding means to guide the brush can be reduced. In this way, wear of the brush because of friction between the brush and the commutator, and because of brush sparking caused by loss of contact between brush and commutator, can be reduced, and the lifetime of the brush can be increased. The decoupling means is preferably adapted, e.g. by its shape and/or the choice of material, so that the inherent vibration mode has one or more resonance frequencies, which are different from the stimulation frequencies of the commutator.

It is also proposed that the brush unit has a guiding means to guide the brush, and that a decoupling means is provided to counteract transmission of vibration of the brush to the guiding means. Vibration of the guiding means during operation can be advantageously reduced, so that contact time of the brush with the commutator during a revolution of the commutator in the temporal medium can be increased.

In this way, contact losses between the brush and the commutator and the occurrence of brush sparking can be reduced, so that a further reduction of the wear of the brush can be achieved. Also, because of increased contact time, effective commutation during operation can be achieved.

In a further embodiment of the invention, it is proposed that the brush unit has a guiding means to guide the brush, and that the decoupling means is at least partly arranged in a receiving area, which is provided to receive the brush, of the guiding means. In this way, close contact of the decoupling means with the brush can be achieved, in which case compact construction and effective decoupling can be achieved.

Advantageously, the brush unit has a guiding means to guide the brush, and the decoupling means is rnoulded onto the guiding means in one piece. In this way, compact form and simple assembly can be achieved.

In relation to this, it is proposed that the decoupling means is in the form of a springy elastic fin, which is moulded onto the guiding means in one piece. In this way, transmission of vibrations of large amplitude onto the guiding means can be advantageously reduced, and material for constructing the guiding means can be saved.

Preferably, the springy elastic fin is in such a form that a progressive spring characteristic is achieved.

In a further embodiment of the invention, it is proposed that the decoupling means is formed from a partial wall area of the guiding means, which in particular is in doubled-walled form. In this way, a robust decoupling means can be achieved.

If the decoupling means is in the form of a springy elastic sheet metal part, a low production cost can be achieved.

The sheet metal part is usefully in such a form that a progressive spring characteristic is achieved.

Advantageously, the decoupling means is fixed to the brush.

In this way, the brush can easily be used in existing electric motors. For instance, replacing a traditional brush with a brush according to the invention is conceivable.

In relation to this, it is proposed that the decoupling means should be partly embedded in the brush, so that robust fixing of the decoupling means can be achieved.

Drawings Other advantages are given in the following description of the drawings. In the drawings, embodiments of the invention are shown. The drawings, description and claims contain numerous features in combination. The person skilled in the art will usefully also consider the features individually, and combine them into useful further combinations.

Fig. 1 shows a hand machine tool with an electric motor, Fig. 2 shows a commutator, a tubular brush-holder, a brush and decoupling means of the electric motor from Fig. 1, Fig. 3 shows a tubular brush-holder with joining components, Fig. 4 shows two tubular brush-holders mounted on a joining ring arid a supporting plate which is joined to the joining ring by fins, Fig. 5 shows a tubular brush-holder, a damping sheet metal part which is integrated with the tubular brush-holder, and a brush, Fig. 6a shows a tubular brush-holder with fins, Fig. 6b shows the tubular brush-holder from Fig. La in another embodiment, Fig. 7 shows the tubular brush-holder from Fig. 2 and an alternative brush with an embedded decoupling means, and Fig. 8 shows a tubular brush-holder with a double-walled section and a brush.

Description of the embodiments

Fig. 1 shows, in a side view, a hand machine tool in the form of a drill 10 with a machine housing 12. This has an electric motor 14, which comprises a motor housing 16, an armature 20 which can rotate around an axis of rotation 18 and is surrounded by a stator (not shown), a commutator 22 which is permanently joined to the armature 20, a brush unit 24 and a shell 26, which is supported on the motor housing 16, to carry the brush unit 24. The brush unit 24 has a brush 28 of a conducting material, and a guiding means 30 in the form of a tubular brush-holder to guide the brush 28, which is carried in the guiding means 30 so that it can move relative to the axis of rotation 18 in the radial direction 32. The brush 28 is provided to transmit an electric current from a power supply unit (not shown) of the drill 10 to the commutator 22. For this purpose, the brush 28 is in contact with conducting segments 34 of the commutator 22, which are arranged around the circumference of the commutator 22 and connected electrically to an armature winding (not shown) of the armature 20.

Because of the segmented structure of the commutator surface, and because of friction between the brush 28 and the segments 34, during operation of the electric motor 14 and/or rotation of the commutator 22 vibration of the brush 28 and guiding means 30 occurs. The electric motor 14 is provided with decoupling means 36 to decouple the brush unit 24 from the shell 26. Said decoupling means 36 are provided to counteract transmission of this vibration onto the shell 36.

In Fig. 2, the arrangement of the brush unit 24, the decoupling means 36 and the commutator 22 is shown in a perspective view. For clarity, the shell 26 is not shown in the figure. The brush 28, which is received in a receiving area 37 (see Fig. 7) of the guiding means 30, is pressed onto the commutator 22 in the radial direction 32 by means of a brush pressure spring (not shown), which is arranged within the guiding means 30. The decoupling means 36 each comprise a damping component 38, which is provided to damp vibration of the brush unit 24, and a spring component 40.

The damping component 38 has a first shaft 38.1, which is fixed to the guiding means 30, and a second shaft 38.2, which is fixed to the shell 26 and arranged movably on the first shaft 38.1. Vibration damping is achieved by a frictional force when the shaft 38.2 moves on the shaft 38.1. The damping component 38 is surrounded by the spring component 40, which is supported on the guiding means 30 on the one hand and the shell 26 on the other hand. The decoupling means 36 allow vibration of the brush unit 24 transversely to the radial direction 32. The brush unit 24 with the brush 28 and guiding means 30, together with the decoupling means 36, forms a unit 44 which is provided for vibration, and has inherent vibration modes. These inherent vibration modes are each characterized by a resonance frequency, and the resonance frequencies can be adapted by the shape and the choice of material of the decoupling means 36. These resonance frequencies are greater than the rotational frequencies of the commutator 22, which correspond to the various rotational speed settings of the drill 10, and for each rotational speed setting are less than the corresponding frequency of the vibration stimulation which occurs because of the segmented structure of the commutator 22. Also, by suitable adaptation of the resonance frequencies, vibration of the brush unit 24 transversely to the radial direction 32 with low amplitude can be achieved, so that wear of the brush 28 by friction and brush sparking can be kept low.

Fig. 3 shows another embodiment of a guiding means 46 of the brush unit 24, in the form of a tubular brush-holder, to guide the brush 28 (not shown in the figure) . Said guiding means 46 is fixed directly to the shell 26 by four connecting components, each of which is in the form of a decoupling means 48. The decoupling means 48 are moulded onto the guiding means 46 in one piece. The decoupling means 48 allow vibration of the brush unit 24 both transversely to the radial direction 32 and in the radial direction 32.

Another embodiment of the brush unit 24 is shown in Fig. 4.

This shows two guiding means 50 in the form of tubular brush-holders, each to guide a brush 28 and an annular supporting component 52, on which the guiding means 50 are mounted. The supporting component 52 fixes the position of the guiding means 50 relative to each other. The supporting component 52 is arranged around the axis of rotation 18 of the commutator 22 (not shown for clarity) . It is also joined by four decoupling means 56 to a shell 54 in the form of a supporting plate. The shell 54 includes two bearing components 54.1, 54.2, which are joined to each other by two joining components 57. These joining components 57 are not in contact with the guiding means 50.

The bearing component 54.1 is rigidly joined to a part of the motor housing 16. The decoupling means 56 are each in the form of a springy elastic bridge-shaped fin. The supporting component 52 can be rotated around the axis of rotation 18, so that vibration of the brush unit 24 with the supporting component 52 and the guiding means 50 in the direction of rotation 58 is allowed. The brush unit 24, together with the decoupling means 56, forms a unit 60 which is intended to vibrate, and which has a resonance frequency which depends on the material and shape of the decoupling means 56, particularly the width and height of the bridge-shaped fins. In an alternative embodiment, the guiding means 50 can each be joined by a decoupling means 56 to the shell 54, independently of each other.

In Fig. 5, another embodiment of the brush unit 24 and of a shell 62 to carry the brush unit 24 is shown. The shell 62 is in the form of a tubular brush-holder with a receiving area 64 to receive the brush unit 24. The brush unit 24 surrounds the brush 28, and is provided with a guiding means to guide the brush 28, which is in the form of a decoupling means 66. This decoupling means 66 is formed from a springy elastic sheet metal part, which is arranged in the receiving area 64 of the shell 62. The sheet metal part fits closely on a surface 68 of the receiving area 64.

The sheet metal part also has four sections 70, which are formed with a trapezoidal profile, so that the decoupling means 66 has a progressive spring characteristic.

Alternatively, other forms of the sheet metal part by which a progressive spring characteristic can be achieved are possible, e.g. a sinusoidal profile. The decoupling means 66 allows vibration of the brush 28, which is arranged in the receiving area 64, perpendicularly to the radial direction 32.

Fig. 6a shows another embodiment of a guiding means 72 of the brush unit 24. The guiding means 72 includes a receiving area 74 to receive the brush 28. On a wall area 76a of the guiding means 72, two decoupling means 78a in the form of springy elastic fins are formed in one piece.

The decoupling means 78a each protrude in their longitudinal direction into a recess of the wall area 76a, and extend in the longitudinal direction of the guiding means 72. The decoupling means 78a allow vibration of the brush 28 in the direction of the axis of rotation 18. The decoupling means 78a each have a section 79 which is formed with a trapezoidal profile and protrudes into the receiving area 74.

Fig. 6b shows the guiding means 72 in an alternative version. In this embodiment, the guiding means 72 is provided with two decoupling means 78b. These each extend in the longitudinal direction of the guiding means 72 in a recess of a wall area 76b, on which they are formed in one piece and supported on both sides. The decoupling means 78b also each have the trapezoidal section 79 (see Fig. 6a), which protrudes into the receiving area 74. Because of the trapezoidal profile and the fixing of the decoupling means 78b on the wall area 76b on both sides of the section 79, the decoupling means 78b each have a progressive spring characteristic. For this purpose, other versions of the section 79 are also conceivable.

In Fig. 7, a further embodiment of the brush unit 24 with the guiding means 30 and a brush 80 is shown. A decoupling means 82 in the form of a spring component is embedded in the brush 80. This has a sub-area 84, which protrudes out of a surface 86 of the brush 80 and extends in the longitudinal direction of the brush 80, or in the mounted state in the radial direction 32. The brush 80 with the decoupling means 82 can be used in combination with an existing guiding means. For instance, it can be inserted into the receiving area 37 of the guiding means 30. The decoupling means 82 can allow vibration of the brush 80 within the guiding means 30 in a transverse direction to the radial direction 32. It is also conceivable that one or more further decoupling means 82 are embedded in the brush 80.

Another embodiment of the brush unit 24, which comprises the brush 28 and a guiding means 88, is shown in Fig. 8.

This has a double-walled partial wall area in the form of a decoupling means 90. The decoupling means 90 allows vibration of the brush 28 in a transverse direction to the radial direction 32. In the case of the layout, shown in the figure, of the brush unit 24 relative to the axis of rotation 18, vibration of the brush 28 in the direction of the axis of rotation 18 is allowed.

01. 12. 05 ROBERT BOSCH GMBH; D-70442 Stuttgart Reference symbols drill 12 machine housing 14 electric motor 16 motor housing 18 axis of rotation armature 22 commutator 24 brush unit 26 shell 28 brush guiding means 32 radial direction 34 segment 36 decoupling means 37 receiving area 38 damping component 38.1 shaft 38.2 shaft spring component 44 unit 46 guiding means 48 decoupling means 50 guiding means 52 supporting component 54 shell 54.1 bearing component 54.2 bearing component 56 decoupling means 57 connecting component 58 direction of rotation unit 62 shell 64 receiving area 66 decoupling means 68 surface section 72 guiding means 74 receiving area 76a wall area 76b wall area 78a decoupling means 78b decoupling means 79 section brush 82 decoupling means 84 sub-area 86 surface 88 guiding means decoupling means

Claims

Claims 1. Hand machine tool with an electric motor (14), which includes

a commutator (22) which can rotate around an axis of rotation (18), a brush unit (24) with at least one brush (28, 80), a shell (26, 54, 62) to carry the brush unit (24) and a decoupling means (36, 48, 56, 66, 78a, 78b, 82, 90), which is provided to counteract transmission of a vibration, resulting from the rotation of the commutator (22), of at least a part of the brush unit (24), transversely to the radial direction (32) onto the shell (26, 54, 62)
2. Hand machine tool according to Claim 1, characterized in that the decoupling means (36, 56) and at least part of the brush unit (24) form a unit (44, 60) which has an inherent vibration mode, and that the decoupling means (36, 56) is provided to prevent stimulation of the inherent vibration mode when the electric motor (14) is operated.

3. Hand machine tool according to Claim 1 or 2, characterized in that the brush unit (24) has a guiding means (30) to guide the brush (80), and that a decoupling means (82) is provided to counteract transmission of vibration of the brush (80) to the guiding means (30) 4. Hand machine tool according to one of the preceding claims, characterized in that the brush unit (24) has a guiding means (72, 30) to guide the brush (28, 80) and that the decoupling means (78a, 7Gb, 82) is at least partly arranged in a receiving area (74, 37), which is provided to receive the brush (28, 80), of the guiding means (72, 30) 5. Hand machine tool according to one of the preceding claims, characterized in that the brush unit (24) has a guiding means (72, 88) to guide the brush (28), and the decoupling means (66, 78a, 7Gb, 90) is moulded onto the guiding means (72, 88) in one piece.

6. Hand machine tool according to Claim 5, characterized in that the decoupling means (78a) is in the form of a springy elastic fin, which is moulded onto the guiding means (72) in one piece.

7. Hand machine tool according to Claim 5, characterized in that the decoupling means (90) is formed from a partial wall area of the guiding means (88), which in particular is in doubled-walled form.

8. Hand machine tool according to one of the preceding claims, characterized in that the decoupling means (66) is in the form of a springy elastic sheet metal part.

9. Hand machine tool according to one of the preceding claims, characterized in that the decoupling means (82) is fixed to the brush (80) 10. Hand machine tool according to Claim 9, characterized in that that the decoupling means (82) is partly embedded in the brush (80).

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