GB2416926A

GB2416926A - Mounting a switching actuator onto a brush holder assembly for rotating the assembly

Info

Publication number: GB2416926A
Application number: GB0515992A
Authority: GB
Inventors: Manfred Buck; Siegfried Fehrle; Uwe Engelfried; Michael Weiss
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2004-08-05
Filing date: 2005-08-03
Publication date: 2006-02-08
Anticipated expiration: 2025-08-03
Also published as: GB2416926B; CN1773816A; DE102004037899A1; GB0515992D0

Abstract

A rotatable brush holder for switching between a clockwise rotation and an anti-clockwise rotation of the electric motor of an electrical machine eg an electric drill or screwdriver has an a brush element 24, comprises a brush boxes 26 supported in a holder ring 46, and a separately formed switching means 36, which is connected via resilient latching members 48 to the holder 46 and has an actuating element 14 for actuation by an operator. The switching means 36 is pushed in the axial direction 34 to engage the brush element 24 so that the latches engage into ventilation slots 50 The actuator member 14 has a blocking element 58 which cooperages with to a locking assembly 66,68 formed with the motor power switch 16 so as to prevent the application of power when the actuator element is in a central position and to prevent movement of the actuator element from either of its positions of maximum rotation when power is applied (fig 4). Projections 56 and 84 formed on housing member 4 respectively prevent the switching means 66,68 from being withdrawn by the action of the locking assembly or the locking assembly being deflected radially. Chamfers 74 (fig 4) of part 68 ensure that the actuator is fully urged to its correct position during operation.

Description

24 1 6926 R.307757 23.07.04 ROBERT BOSCH GMBH; D-70442 Stuttgart

Electrical Machine

Prior art

The invention takes as its starting point an electrical machine according to the precharacterising clause of Claim DE 102 27 782 A2 discloses an electrical machine having an electric motor and a rotatable brush plate, the rotation of which enables the electric motor to switch between a clockwise rotation and an anti-clockwise rotation. To actuate the brush plate, the brush plate comprises an actuating element which is arranged on its radial outer face, is guided outwards through a housing of the electrical machine and can be actuated by an operator.

Advantages of the invention The invention takes as its starting point an electrical machine having an electric motor, a brush element, which is rotatably mounted for switching between a clockwise rotation and an anticlockwise rotation of the electric motor, and a brush holder, and having a switching means, which is constructed separately from the brush element, is connected with positive fit to the brush element and has an actuating element for actuation by an operator.

It is proposed that the switching means be pushed in the axial direction onto the brush element arranged on the electric motor and be connected in the axial direction to the brush element. It is possible to produce a modular system which comprises the brush element and the switching means and which, with the same brush element and different switching means, enables the position of the actuating element in relation to the brush element and the electric motor to be freely selected within certain limits depending on the machine type. The actuating element can be positioned in the vicinity of a switch button. The switching means can be connected with friction fit to the brush element in the axial direction. The switching means is advantageously connected with positive fit to the brush element in the axial direction, in which case it is possible to produce the positive connection particularly simply and economically by a positive connection between an element of the switching means and an element of the brush element.

Because the switching means can be pushed in the axial direction onto the brush element arranged on the electric motor, it is easy to assemble the electrical machine since the brush element can firstly be mounted on the electric motor and the switching means can then be pushed onto the brush element. As a result of the positive connection between the switching means and the brush element in the axial direction, it is not necessary to mount the switching means separately, for example on a housing of the electrical machine. Both mutually connected components can be mounted together at a suitable point. The axial direction refers to the axial direction of the electric motor and therefore the direction of the axis of the electric motor. The switching means can be expediently pushed onto the brush element in the axial direction and in the direction of the electric motor.

In an advantageous construction of the invention, the brush element comprises a holding ring which supports the brush holder, and the switching means can be pushed onto the holding ring in the axial direction. It is possible to achieve a tilt-resistant stable mounting of the switching means on the brush element.

With respect to the switching means tilting, it is possible to further increase the stability if the brush element comprises a holding ring supporting the brush holder, and the switching means is connected with positive fit to the holding ring in the axial direction.

By means of a latching means for a latching connection of the switching means on the brush element, the switching means can be easily assembled on the brush element and connected with positive fit to this latter. The latching means can be arranged on the brush element, and can particularly be connected in one piece to the brush element. The latching means is expediently connected to the switching element and is particularly constructed in one piece therewith. A stable connection between the switching means and the brush element can be achieved if the latching means reaches behind an element of a holding ring supporting the brush holder. At least two, particularly at least four, latching means are expediently provided. Here, the latching means advantageously reaches radially inwards through the holding ring, at least partially, and latches behind the element as a result of a radially outwardly directed movement. A radially outer lateral surface of the brush element can remain free so that it is possible to arrange the brush element independently of the switching means, in different houses of different machine types.

A further advantage is achieved if the brush element includes ventilation slots. The electric motor can be cooled in simple manner. The latching element engages expediently in these ventilation slots, which means that it is possible to dispense with an additional holding element for reaching behind the latching element. The latching element expediently reaches only partially through the ventilation slots, which means that a radially outer lateral surface is not influenced by the latching element.

In a further construction of the invention, the brush element has a holding ring supporting the brush holder and the switching means comprises a ring element, the ring element abutting against the holding ring in the axial direction. It is possible to achieve a particularly tilt- resistant stable mounting of the switching means on the brush element.

The ring element advantageously engages in the holding ring. It is possible to achieve a stable mounting of the switching means on the brush element, particularly in the radial direction. To greater advantage, the ring element, and particularly the entire switching means, is arranged outside a space directly adjoining the brush element in the radial direction. A lateral surface of the brush element, which is directed outwards in the radial direction, remains free from the ring element and the switching means so that the brush element can be positioned in different, and even narrow, housings.

In relatively large electrical machines, for example a hammer drill having a front and a rear handle, the brush element is arranged relatively far away from a switch button for actuating the electrical machine. The actuating element can be positioned near to a switch button if the actuating element is arranged at least predominantly on that side of the brush element which is remote from the electric motor in the axial direction. The actuating element can be operated comfortably, for example by the operator's hand grasping the switch button. In an equivalent construction, the actuating element is arranged at least predominantly behind the brush element in the axial direction, with the direction being defined in that the electric motor is arranged predominantly in front of the brush element.

It is moreover proposed that the electrical machine comprise a centring means and the brush element comprise a holding ring supporting the brush holder, the centring means being provided for centring the switching means radially on the holding ring during assembly of the actuating means. The switching means can be mounted particularly simply on the brush element. The centring means can be arranged on the holding ring. The centring means is expediently arranged on the switching means and is particularly connected to the switching means in one piece for simple manufacture of the electrical machine. The centring means engages expediently in the holding ring, as a result of which a radially outer lateral surface of the brush element remains free. If a latching means is present, the centring element advantageously projects over the latching means in the axial direction, as a result of which, when assembling the switching means on the brush element, the centring element firstly has a centring effect and then the latching element is brought into play for latching in the respectively opposing element. It is possible to achieve simple assembly of the switching means on the brush element.

In a further construction of the invention, it is proposed that the electrical machine comprise a switch button having a switching-on position for switching on the electric motor and a switching-off position for switching off the electric motor, in which case a securing means is connected to the switch button and the switching means comprises a blocking element for abutting against the securing means and, when the switch button is in the switching-on position, the securing means blocks a rotation of the actuating element for switching over the brush element by abutting against the blocking element. It is possible to effectively prevent the brush element from rotating when the switch button is actuated and consequently avoid wear on the electrical machine caused by faulty operation.

To the same advantage, the electrical machine comprises a switch button having a switching-on position for switching on the electric motor and a switching-off position for switching off the electric motor, a securing means being connected to the switch button and the switching means comprising a blocking element for abutting against the securing means and, when the brush element is rotated into an intermediate position between a clockwise rotation and an anti-clockwise rotation, the blocking element blocking the switch button from switching from the switching-off position to the switching-on position by abutting against the securing means. When the brush element is switched over from a clockwise rotation to an anticlockwise rotation, or vice versa, the actuation of the switch button, and a resulting increase in the wear on the collector, the carbon brushes and contacts, is effectively prevented.

A further advantage is achieved if the electrical machine comprises a housing with a housing wall which at least partially delimits a housing interior from a housing exterior, the actuating element being arranged at least partially outside the housing and being held by at least two holding elements projecting separately through the housing wall. The actuating element is thus mounted at at least two points and therefore in stable manner, which means that the actuating element can be constructed on a large scale and still be mounted in stable manner.

Moreover, the holding elements can be guided through ventilation slots in the housing and can, for example, be of a narrow construction.

The invention is particularly suitable for an electrical machine which is constructed as a hand-held machine tool, particularly as a mains-operated or battery-operated screwdriver, drill or hammer drill. Hand-held machine tools are manufactured in many different models, so that the variability of the switching means and the position of the actuating element combined with low assembly costs is particularly advantageous. It is also particularly advantageous for the actuating element to be arranged near to a switch button, particularly in hand-held machine tools.

Drawing Further advantages are revealed in the following description of the drawing. The drawing shows an exemplary embodiment of the invention. The drawing, the description and the claims contain numerous features combined. The person skilled in the art will also expediently consider the features individually and combine them in further useful ways.

The drawing shows: Fig. 1 a schematically illustrated hammer drill in a side view; Fig. 2 a longitudinal section through a detail II in Figure 1; Fig. 3 a brush element with a switching means in an exploded illustration; and Fig. 4 a section along the line IV in Figure 2.

Description of the exemplary embodiment

Figure 1 shows an electrical machine 2 which is constructed as a hammer drill and has an electric motor 6 which is assembled in a housing 4 and whereof the direction of rotation 8 for a tool 12 clamped in a tool holder 10 can be selected by way of an actuating element 14. The direction of rotation 8 thus also includes a first direction of rotation 8 for a clockwise rotation and a second direction of rotation 8 for an anti-clockwise rotation, which is opposed to the first direction of rotation 8. The actuating element 14 is arranged in the vicinity of a switch button 16 so that the operator of the electrical machine 2 can operate both the switch button 16 and the actuating element 14 with one hand.

Figure 2 shows a detail II of the electrical machine 2 of Figure 1 in a longitudinal section. The electric motor 6, which is not shown in Figure 2 for the sake of clarity, is arranged in a front part 18 of the housing 4. A rotor of the electric motor 6 projects with a commutator through a housing opening 20 into a rear part 22 of the housing 4. It is surrounded there by a brush element 24 which comprises two opposing brush holders 26 constructed as tubular carbon-brush holders. A carbon brush 28 is inserted into each of the brush holders 26 and is pressed radially inwards onto the commutator (not shown) by spring elements (one of the two spring elements 30 is shown in Figure 3). From a neutral, unstable central position, the brush element 24 is loaded in the circumferential direction in each case towards an end position by way of two leg springs 32 which have a bistable position. Depending on the end position, the commutator is supplied with current for a clockwise rotation or an anti- clockwise rotation.

A switching means 36 is pushed onto the brush element 24 arranged on the electric motor (not illustrated in Figure 2) in the axial direction 34, i.e. parallel to the tool 12 and towards the tool 12 and the electric motor 6. The actuating element 14 is a one piece component of this switching means 36.

The switching means 36 and the brush element 24 are shown in perspective and in an exploded illustration in Figure 3.

To push the switching means 36 onto the brush element 24, the switching means 36 comprises four centring means 38 in the form of projections which surround two holding elements on both sides when the switching means 36 is pushed onto the brush element 24. A different number of centring means is also conceivable. To centre the switching means 36 on the brush element 24 without difficulty, the centring means 38 comprise chamfers 42 which enable them to be guided more easily along both sides of the holding elements 40 and into a holding ring 44. The holding ring 44 is part of the brush element 24 and surrounds the commutator (not illustrated) in the form of a ring. It supports the brush holders 26 and has a radially outwardly facing lateral surface 46. The centring means 38 engage radially from within in this holding ring 44 and hold the switching means 36 in the radial direction and the tangential direction such that it is clearly defined with respect to the brush element 24.

When the switching means 36 is pushed further onto the brush element 24, latching means 48 constructed as latching hooks come into contact with the holding ring 44 (by way of example, there are four latching hooks in the Figure). As the switching means 36 is pushed on further, they are pressed radially inwards by the holding ring 44 and slide along an inside face of the holding ring 44 until they latch radially outwards in ventilation slots 50 in the brush element 24. The latching means 48 produce a positive connection between the switching means 36 and the brush element 24 in the axial direction 34.

An additional latching element 48 is shown in section in a dashed circle in Figure 2 to illustrate the position of the four latching elements 48. The latching element 48 engages in one of the ventilation slots 50 and reaches only partially through it. The centring means 38 project somewhat beyond the latching means 48 in the axial direction 34 so that, when the switching means 36 is pushed onto the brush element 24, the centring means 38 firstly position the switching means 36 in centred manner and only then do the latching means 48 come into contact with the holding ring 44.

When the latching elements 48 have latched in, the switching means 36 abuts with a ring element 52 against the holding ring 44 of the brush element 24 in the axial direction 34 and is connected thereto in tiltresistant manner. To hold the switching means 36 more securely on the brush element 24, the ring element 52 has two further centring means 54 which abut against the inside face of the holding ring 44 and hold the ring element 52 on the holding ring 44 in defined manner in the radial direction. The ring element 52 engages with both the centring means 38 and the latching means 48 and the further centring means 54 in the holding ring 44. During operation of the electrical machine 2, webs 56 of the housing 4 hold the ring element 52 in the axial direction 34 on the brush element 24 for further security.

If an operator actuates the actuating element 14, the switching means 36 can now be moved in a direction of rotation 8 from one end position into the other end position and this sets a clockwise rotation or an anticlockwise rotation of the electric motor 6. To prevent an adjustment to the switching means 36 when the switch button 16 is simultaneously pressed, the switching means 36 has a blocking element 58 which is connected in one piece to the actuating element 14 and the ring element 52. The blocking element 58 is shown in plan view in Figure 4.

Figure 4 shows the switching means 36 in a plan view, looking forwards in the direction of the electric motor and the tool 12 from the switch button 16. Three positions of the actuating element 14 are shown: an outer end position for an anti-clockwise rotation and, in dashed lines, a second outer end position 62 for a clockwise rotation and an unstable central intermediate position 64 arranged between the two positions 60, 62. From the central intermediate position 64, the actuating element 14 is pressed by the leg springs 32 into one of the two end positions 60, 62. Figure 2 shows the actuating element 14 in the intermediate position 64.

Shown in section in Figure 4 is a securing means 66 which is integrally formed in one piece on the switch button 16 and comprises a securing head 68. If the actuating element 14 is located with the blocking element 58 in an intermediate position 64 between the end positions 60, 62, the blocking element 58 is arranged behind the securing head 68 in the axial direction 34. As shown in Figure 2, upon actuation of the switch button 16, the securing head 68 is pulled backwards, offset at a slight angle to the axial direction 34, and comes into contact with a blocking face 72 of the blocking element 58 by means of a securing face 70. The blocking element 58 thus prevents the switch button 16 from being pressed further into a position for switching on the electric motor 6, which is illustrated by dashed lines in Figure 2. The webs 56 secure the switching means 36 against being pulled out in the axial direction 34 when the switch button 16 is pressed. Supporting ribs 84 support the securing means 66 against bending downwards.

To enable the switch button 16 to be moved from a switching-off position into a switching-on position, the actuating element 14 with the blocking element 58 firstly has to be brought into one of the two end positions 60, 62.

The securing means 66 can then be guided with its securing head 68 past the blocking element 58 and the switch button 16 can be brought into a switching-on position.

If the actuating element 14 is in one of the two end positions 60, 62 and the switch button 16 is in a switching-on position, the securing means 66 is arranged in the position shown by dashed lines in Figure 2. As shown in Figure 4, one of the two lateral blocking faces 74 comes into contact with one of two securing faces 76 of the securing head 68 when the actuating element 14 is rotated from one of the end positions 60, 62 in the direction of an intermediate position 64. Further rotation of the actuating element 14 from the end positions 60, 62 in the direction of an intermediate position 64 is blocked. Thus, the electric motor 6 cannot be switched from a clockwise rotation to an anti-clockwise rotation, or vice versa, when the switch button 16 is pressed. If the actuating element 14 is not fully in one of the end positions 60, 62, the blocking element 58, and with it the actuating element 14, is pressed into the respective end position 60, 62 by one of the lateral sloping faces 78 of the securing head 68 when the switch button 16 is actuated.

The actuating element 14 is connected in stable manner to both the blocking element 58 and the ring element 52 of the switching means 36 by two web-shaped holding elements 80 (see Figure 2). Even with strong pressure on the actuating element 14, the actuating element 14 is prevented from buckling by the two holding elements 80. The holding elements 80 are each constructed as an elongated web which is aligned perpendicularly to the plane of the paper in Figure 2 and is shown in a perspective illustration in Figure 3. The holding elements 80 are of a thin construction and reach through ventilation slots in the housing 4.

The switching means 36 has a connecting element 82 between the actuating element 14 and the ring element 52. Depending on the construction of this connecting element 82, the actuating element can be positioned further forwards towards the electric motor 6 or further backwards towards the switch button 16 in terms of its position relative to the brush element 24. This enables the switching means 36 to be adapted very flexibly to different geometries of the housing. In the embodiment of the switching means 36 shown in Figure 2, the actuating element 14 is arranged predominantly behind the brush element 24 in the axial direction and therefore relatively near to the switch button 16.

R.307757 23.07.04 ROBERT BOSCH GMBH; 70442 Stuttgart Reference Numerals 2 Electrical machine 4 Housing 6 Electric motor 8 Direction of rotation Tool holder 12 Tool 14 Actuating element 16 Switch button 18 Part 12 Housing opening 22 Part 24 Brush element 26 Brush holder 28 Carbon brush Spring element 32 Leg spring 34 Axial direction 36 Switching means 38 Centring means Holding element 42 Chamfer 44 Holding ring 46 Lateral surface 48 Latching means Ventilation slot 52 Ring element 54 Centring means 56 Web 58 Blocking element End position 62 End position 64 Intermediate position 66 Securing means 68 Securing head Securing face 72 Blocking face 74 Blocking face 76 Securing face 78 Sloping face Holding element 82 Connecting element 84 Supporting rib

Claims

R.307757 23.07.04 ROBERT BOSCH GMBH; D-70442 Stuttgart Claims 1. An

electrical machine (2) having an electric motor (6), a brush element (24), which is rotatably mounted for switching between a clockwise rotation and an anti clockwise rotation of the electric motor (6) and comprises at least one brush holder (26), and having a switching means (36) which is constructed separately from the brush element (24), is connected with positive fit to the brush element (24) and has an actuating element (14) for actuation by an operator, characterized in that the switching means (36) can be pushed in the axial direction (34) onto the brush element (24) arranged on the electric motor (6) and is connected in the axial direction (34) to the brush element (24).
2. An electrical machine (2) according to Claim 1, characterized in that the brush element (24) comprises a holding ring (44) supporting the brush holder (26) and the switching means (36) is connected with positive fit to the holding ring (44) in the axial direction (34) of the electric motor (6).
3. An electrical machine (2) according to Claim 1 or 2, characterized by a latching means (48) for the latching connection of the switching means (36) on the brush element (24).
4. An electrical machine (2) according to one of the preceding claims, characterized in that the brush element (24) comprises a holding ring (44) supporting the brush holder (26) and the switching means (36) comprises a ring element (52) and the ring element (52) abuts against the holding ring (44) in the axial direction.
5. An electrical machine (2) according to Claim 4, characterized in that the ring element (52) engages in the holding ring (44).
6. An electrical machine (2) according to one of the preceding claims, characterized in that the actuating element (14) is arranged at least predominantly on that side of the brush element (24) which is remote from the electric motor (6) in the axial direction (34).
7. An electrical machine (2) according to one of the preceding claims, characterized by a centring means (38), the brush element (24) comprising a holding ring (44) supporting the brush holder (26) and the centring means (38) being provided for centring the switching means (36) radially on the holding ring (44) during assembly of the actuating means (14).
8. An electrical machine (2) according to one of the preceding claims, characterized by a switch button (16) having a switching-on position for switching on the electric motor (6) and a switching-off position for switching off the electric motor (6), the switch button (16) being connected to a securing means (66) and the switching means (36) comprising a blocking element (58) for abutting against the securing means (66) and, when the switch button (16) is in the switching-on position, the securing means (66) blocking a rotation of the actuating element (14) for switching over the brush element (24) by abutting against the blocking element (58).
9. An electrical machine (2) according to one of the preceding claims, characterized by a switch button (16) having a switching-on position for switching on the electric motor (6) and a switching-off position for switching off the electric motor (6), the switch button (16) being connected to a securing means (66) and the switching means (36) comprising a blocking element (58) for abutting against the securing means (66) and, when the brush element (24) is rotated into an intermediate position (64) between a clockwise rotation and an anti clockwise rotation, the blocking element (58) blocking the switch button (16) from switching from the switching-off position to the switching-on position by abutting against the securing means (66).

lO.An electrical machine (2) according to one of the preceding claims, characterized by a housing (4) having a housing wall which at least partially delimits a housing interior from a housing exterior, the actuating element (14) being arranged at least partially outside the housing (4) and being held by at least two holding elements (80) projecting separately through the housing wall.

ll.An electrical machine substantially as here described with reference to the accompanying drawings.