GB2449970A

GB2449970A - Pivoted cover for brush plate

Info

Publication number: GB2449970A
Application number: GB0809924A
Authority: GB
Inventors: Axel Kuhnle; Willy Braun
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2007-06-05
Filing date: 2008-05-30
Publication date: 2008-12-10
Anticipated expiration: 2028-05-30
Also published as: GB2449970B; GB0809924D0

Abstract

An electric hand tool comprises an electric motor (58), a housing (60) receiving the motor (58) and a brush plate (100) rotatable for changing the rotational direction of the motor. The brush plate (100) is covered in its cross-section by a pivotable cover (30), which when open allows access to the brush plate for servicing, for example exchange of carbon brushes. The cover includes an actuating element (36) for rotating the brush plate via the assembly 50,52,54 mounted in the cover. Spring loaded carbon brushes mount in brush boxes 102 and electric links 68,70 connect to and from the brush plate assembly.

Description

ELECTRIC HANDTOOL

The present invention relates to an electric handtool with a rotatable brush plate and to subassemblies for such an electric handtool.

In electric handtool machines use is usually made of universal motors in order to drive utility tools rotationally and/or with hammering action. A brush plate holding carbon brushes which are in electrical contact with a commutator of such a motor is used as electrical tap at the commutator. The brush plate is rotatable for switching over the motor rotational direction. When the brush plate is rotated not only is the motor power feed repoled, but also the rotational position of the carbon brushes with respect to the field windings is changed, so that satisfactory commutation can be achieved for both directions of rotation.

There remains scope for improvement of electric handtools of the kind with an electric machine such as a motor, a housing receiving the machine and a rotatable brush plate for switching over a rotational direction of the machine.

According to a first aspect of the present invention there is provided an electric handtool machine with an electric machine, a motor housing receiving the electric machine and a rotatable brush plate for switching over a rotational direction of the electric machine, wherein the brush plate is covered in its cross-section by a pivotable cover.

The cover can with particular advantage be captively retained at the housing of the electric handtool. The cover can be closed by simple and easily releasable means, for example a fastening screw and/or a detent or the like. Advantageously, these means are captively connected with the brush plate. The arrangement is robust relative to shock, dust and vibrational loads and operable easily and safely. In addition, an improvement in the operability of the electric handtool can be achieved in the case of tight space.

A particularly simple manipulation of the cover is possible if the cover is mounted to be pivotable perpendicularly to its axis of rotation. The cover can be pivoted away in simple manner and thus enable free access to the brush plate. By virtue of the easy access to the brush plate, ease of servicing of the handtool is improved. A change of carbon brushes of the brush plate can be carried out easily and quickly.

The compact and robust mode of construction is improved if an actuating element for rotation of the brush plate can be integrated in the cover. An economic and tolerance-insensitive arrangement of cover, brush plate and rotation actuating element is thereby possible.

If the rotation actuating element can engage with at least one entraining element in the brush plate, which enables a rotationally secure connection between actuating element and brush plate, insensitivity to tolerances and operating ease can be further improved. A rotation of the brush plate, i.e. changeover of the rotational direction of the handtool, is significantly simplified.

Advantageously the brush plate can be mounted on a mounting dome of the motor housing. This allows a compact mode of construction of the electric machine, which can preferably be constructed as a universal motor.

If the brush plate can be stably retained in each of two end positions, defined end points for the changeover of direction of rotation can be achieved. In a neutral position between the end positions the brush plate may be able to be removed in simple manner from its mount, for example the mounting dome of the housing. In the end positions, for example, restraintng means can be provided under which the brush plate moves on rotation thereof and which axially and optionally also radially secure the brush plate in each end position.

A first contact element, which is associated with the brush plate, for electrical contact-making with a second contact element associated with the electric machine, and the second contact element can advantageously be so arranged that on rotation of the brush plate an electrical contact can be made only near the respective end position. The electrical contact is preferably produced at the earliest in the last 20%, preferably at the earliest in the last 10%, of the range of rotation. Commutaton of the electric machine is thereby possible in particularly advantageous manner. The service life of the carbon brushes can be improved and maintenance of radio anti-interference limit values made possible without additional effort.

An economic embodiment is achieved if a premounted brush cover subassembly and/or a premounted brush plate subassembly and/or a premounted motor housing subassembly can be provided. In assembly of the handtool, this embodiment is compact, economic and insensitive to tolerances. During the main assembly time of the handtool the working steps and parts stocking are advantageously reduced. The throughput time can thus be reduced and production costs and assembly costs lowered.

With particular advantage the proposed handtool can be constructed as an impact drill or hammer drill, particularly for higher levels of performance.

In another aspect of the invention there is provided a brush cover subassembly for an electric handtool with an electric machine with a rotatable brush plate in which, by premounting, a cover is combined with a first actuating element for rotation of such a brush plate and with a second actuating element for actuation of the first actuating element.

In yet another aspect of the invention there is provided a brush plate subassembly for an electric handtool machine with an electric machine with a rotatable brush plate, in which.

by premounting, the brush plate is combined with one or more holders for reception of carbon brushes, spring elements for loading the carbon brushes with pressure force, and contact elements for electrical contact-making with contact elements, which are external to the subassembly, of such an electric machine.

In a further aspect of the invention there is provided a motor housing subassembly for an electric handtool with an electric machine, which is receivable in a housing, with a rotatable brush plate, in which, by premounting, the housing is combined with at least one contact element for contact-making with a contact element external to the subassembly, at least one stator part, for example a pole piece, of the electric machine and at least one plug element for electrical contact-making.

Through the provision of premounted subassemblies the main assembly of the electric handtool machine can be simplified and made Inexpensive In the case of repair the respective subassembly, for example the brush plate subassembly, can be exchanged in simple manner without large expenditure of time or costs.

The electric handtool is preferably of L form of construction, but can in principle be any other form of machine construction in which a rotatable brush plate is used.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, noting that the skilled addressee may also consider the features, which are disclosed in combination in the drawing, description and claims, individually and combine them to form feasible further combinations. In the drawings: Fig. 1 is a schematic perspective view of an electric handtool machine, in the form of a hammer drill, embodying the invention; Fig. 2 is a cross-sectional detail view, to enlarged scale, of part of the electric handtool machine of Fig. 1, with pivoted-open cover; Fig. 3 is an inverted plan view, to enlarged scale, of a mounting flange with fitted brush plate of the electric handtool machine of Fig. 1; and Fig. 4 is an exploded perspective view, to enlarged scale, of components of the electric handtoo? machine of Fig. 1.

Referring now to the drawings there is shown in Fig. 1, for explanation of the invention, an electric handtool machine or power tool 10 which is constructed, by way of example, as a hammer drill of L form. The handtool 10 can be held by a user at a first handle 14 and a second handle 20 Arranged at the second handle 20 is a switch latch 22 by which the power supply to an electric machine (not visible), which is arranged in a housing shell 18 and operates as a motor, can be provided and a utility tool bit 12, which is arranged in longitudinal direction of the handtool 10, can be set into rotational and/or hammering operation. The handles 14 and 20 protrude laterally with respect to the longitudinal direction. The electric machine, which is not visible, is accommodated between the two handles 14 and 20 in a limb 16 which protrudes in a lateral direction 55 from the longitudinal direction, and the machine extends in that lateral direction Arranged at the base 26 of the limb 16 is a cover 30 which is fastened to the apparatus limb 16 by a screw 32 arranged in an opening 34. An actuating element 36 in an opening 38 can be seen diametrically opposite the screw 32. The opening 38 allows pivotation of the actuating element 36 out of the plane of the drawing A detail view of the base region of the limb 16 is illustrated in Fig. 2, in which the cover 30 depicted in Fig. 1 is opened and allows a view of a commutator 62 of the electric machine 58 arranged in the limb 16, the pole pieces 64 of which can be seen. A thread 28 which is at the housing and corresponds with the screw 32 can be seen near a brush plate 100 mounted on a mounting dome 66 of a motor housing 60. Respective receptacles 102 of the brush plate 100 can be seen on both sides of the commutator 62 perpendicularly to a motor rotational axis, which extends parallel to the lateral or transverse direction 55, of the electric machine 58. Carbon brushes (not visible), which n the switched-on state of the handtool transfer the electric current to the commutator 62, are retained in the receptacles.

The motor rotational axis corresponds with a rotational axis 56 of the brush plate 100.

Depending on the respective setting of the brush plate 100 the electric machine rotates in clockwise or anticlockwise sense. The mounting of the rotational brush plate 100 with radial contacting directly on the mounting dome 66 enables precise running of the carbon brushes on the commutator 62 and constantly good contact-making between the electrical contacts (contact element 68 and contact element 120 in Fig. 4).

The cover 30, which is shown swung away from the base 26 of the limb 16 is pivotable about a mounting dome 24, which acts as fulcrum pin, of the housing shell 18.

The brush plate 100 is covered in its entire cross-section by the cover 30 pivotable perpendicularly to the axis 56 of rotation. The screw 32 is captively inserted, for example clipped in place, in the opening 34.

A basket-shaped actuating element 50 for rotation of the brush plate 100 is integrated in the cover 30 and is inserted by a basket part 54 thereof into a depression 40 of the cover 30. The actuating element 50 is captively retained by a lateral transversely protruding lug 52 in the actuating element 36, which is constructed as a trigger. The lug 52 of the actuating element 50 is on insertion into the actuating element 36 introduced into a slot 42 of the cover 30 and clipped together with the actuating element 36 Entraining elements 46, which are constructed as entraining lugs, of the actuating element 50 are provided for the purpose of engaging in corresponding recesses (not visible) in the brush plate 100.

The entraining elements 46 are so arranged that the cover 30 can be closed only if the rotational setting of the brush plate 100 and the actuating element 36 correspond. The elements 46 enable a rotationally secure connection between the actuating element 50, which is rigidly connected with the actuating element 36, and the brush plate 100.

Rotation of the brush plate 100 is carried out in the manner that with the cover 30 closed the trigger-like actuating element 36 is pivoted in the opening 38 of the limb 16 from one end position into a opposite end position. Each end position corresponds with a respective current direction and thus rotational direction of the electric machine 58.

Advantageously the cover 30 forms a premounted subassembly, namely a brush cover subassembly which on main assembly of the handtool can be inserted in prefitted state.

The brush plate 100 is freely accessible by release of the screw 32 and pivoting away of the cover 30 and can be demounted, for example for servicing purposes, from the limb 16.

Details of the brush plate 100 can be inferred from Fig. 3, which shows an inverted plan view of a mounting flange 72 with the brush plate 100 mounted on the mounting dome 62.

The view allows the compact mode of construction of the brush plate 100 to be seen.

Two diametrally arranged receptacles 102 each hold a respective carbon brush 104, which brushes are pressed against the commutator 62 of the electric machine 58 by means of limbs 114 of spring elements 106 constructed as spiral springs. The receptacles 102 are peened over on the brush plate 100 together with radially acting spring elements 118 and constructed as contact elements or contact springs. The spring elements 118, 120 are arranged symmetrically about each receptacle 102 and are each disposed in radial contact with a respective one of two diametrically opposite contact plates 68, which are in turn electrically connected with a respective pole piece 64 (Fig. 2). The term pole piece 64 is here synonymous with the stator of the electric machine. Depending on the respective rotational setting of the brush plate 100, one or other of the contact plates 68 is contacted by the spring elements 118, 120. Of each contact plate 68, only a limb 68a can be seen in the inverted plan view.

The brush plate 100 is shown in a first end position 108 (indicated by the orientation of the receptacles 102). If the brush plate 100 is pivoted to the other end position, indicated generally by 1101 the rotational direction of the electric machine changes. Provided between the end positions 108 and 110 is a free space 112 allowing pivotation of the brush plate 100. The specific angle of the pivot range a depends on the actually employed winding arrangements of the respective electric machine 58. In a neutral position between the end positions 108 and 110, the brush plate 100 can be withdrawn in simple manner from the mounting dome 66.

The contact element 120 associated with the brush plate 100 is provided for electrical contact-making with the contact element 70 (Fig. 4) which is associated with the electric machine 58 and which is largely covered in Fig. 3. Both are designed so that on rotation of the brush plate 100 an electrical contact can be made only near the respective end position 108 or 110. It can thereby he ensured that the brush plate 100 can be operated only in one of its defined end positions 108 and 110, which contributes to a high quality commutation.

In order to ensure the mobility of the brush plate 100 in conditions of use, for example high dust loading, this is guided not only radially, but also axially only on narrow strips. The brush plate is stably retained in each of its end positions 108, 110 by means of two diametrically opposite leg springs 122. The brush plate is axially fixed in each instance by four holding-down or restraining devices 124 which are diametrically opposite in pairs and which are integrated in the housing 60. In the end positions 108, 110 a part of the brush plate 100 moves under the respective device 124 so as to be axially fixed, whilst in the neutral position between the end positions 108, 110 there is no axial fixing.

For clarification of the arrangement, Fig. 4 shows an exploded illustration of the components depicted in Figs. 1 to 3. The cover 30, the brush plate 100 and the motor housing 60 are preferably constituents of respective premounted subassemblies 130, 140, It is advantageous to use these subassemblies 130, 140 and 150 in the main assembly of the electric handtool machine.

The brush cover subassembly 130 preferably comprises the cover 30 with the actuating element 36, the screw 32 and the actuating element 50, which are captively connected together.

The brush plate subassembly 140 preferably comprises the brush plate 100 with one or more receptacles 102 provided for reception of carbon brushes, spring elements 106 provided for loading the carbon brushes 104 with pressure force and contact elements 120 (Fig. 3) for electrical contact-making of contact elements 68, which are external to the subassembly, of the electric machine.

The motor housing subassembly 150 preferably comprises the motor housing 60, which is inserted into the housing shell 18, with at least one contact element 68 for electrical contact-making with a contact element 120 (Fig. 3) external to the subassembly, at least one pole piece 64, and at least one plug element 70 for contact-making with power connections 80. The limb 68a of each contact element 68 projects, in the mounted state, into the brush plate 100 (Fig. 3). The pole shoe 64, the two contact elements 68 constructed as contact plates and two plug contact plates 70 can be press-fitted into the housing 60 in one working step in timesaving and cost-saving manner. The contact plates 68 and the plug plates 70 have small barbs by which they can firmly hook into the material, in particular plastics material, of the housing 60. The plug plates 70 are yoke-shaped, wherein a plug spade extends away to one side of the yoke of each plate. The plug spades project, in the mounted state, laterally out of the housing 60 so that prior to insertion of the motor pot of the electric machine 58 into the housing shell 18 (Fig. 3) the two power connecting lines 80 can be plugged on.

Claims

1. An electric handtool comprises an electric machine, a housing receiving the machine, a brush plate rotatable to change a rotational direction of the machine and a pivotable cover covering the brush plate in its cross-section.

2. A handtool as claimed in claim 2, wherein the cover is pivotable substantially perpendicularly to an axis of rotation of the machine.

3. A handtool as claimed in claim 1 or claim 2, comprising an actuating element integrated in the cover and actuable to rotate the brush plate.

4. A handtool as claimed in claim 3, wherein the actuating element comprises an entraining element engageable in the brush plate to connect the actuating element with the brush plate to be secure against relative rotation.

5. A handtool as claimed in any one of the preceding claims, wherein the brush plate is mounted on a mounting dome of the housing

6. A handtool as claimed in any one of the preceding claims, comprising means for holding the brush plate in each of two end positions of rotation of the brush plate.

7. A handtool as claimed in any one of the preceding claims, comprising two contact elements respectively associated with the brush plate and the machine and arranged to come into contact only on approach to either one of two end positions of rotation of the brush plate.

8. A handtool as claimed in any one of the preceding claims, wherein the brush cover is part of a brush cover subassembly.

9. A handtool as claimed in claim 8, wherein the brush cover subassembly includes a first actuating element to rotate the brush plate and a second actuating element to actuate the first actuating element.

10. A handtool as claimed in any one of the preceding claims, wherein the brush plate is part of a brush plate subassembly.

11. A handtool as claimed in claim 10, wherein the brush plate subassembly includes at least one holder holding a carbon brush, spring means pressurably loading the or each carbon brush and contact means for electrical contact-making with further contact means external to the brush plate subassembly

12 A handtool as claimed in any one of the preceding claims, wherein the housing is part of a housing subassembly.

13. A handtool as claimed in claim 11, wherein the housing subassembly includes contact means for electrical contact-making with further contact means external to the housing subassembly, at least one pole piece, and at least one electrical connector for connection with electrical power feed means.

14. A brush cover subassembly for an electric handtool which comprises an electric machine with a rotatable brush plate, the subassembly comprising a brush cover combined with a first actuating element to rotate the brush plate and a second actuating element to actuate the first actuating element.

A brush plate subassembly for an electric handtool which comprises an electric machine with a rotatable brush plate, the subassembly comprising a brush plate combined with at least one holder holding a carbon brush, spring means pressurably loading the or each carbon brush and contact means for electrical contact-making with further contact means external to the brush plate subassembly.

16. A housing subassembly for an electric handtool which comprises an electric machine received in the housing and a rotatable brush plate, the subassembly comprising a housing combined with contact means for electrical contact-making with further contact means external to the housing subassembly, at least one pole piece, and at least one electrical connector for connection with electrical power feed means.