GB2480137A

GB2480137A - Suppression of commutator-sourced interference in an electric tool

Info

Publication number: GB2480137A
Application number: GB1107088A
Authority: GB
Inventors: Joachim Hecht; Moosa Ali Khan
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2010-04-28
Filing date: 2011-04-27
Publication date: 2011-11-09
Anticipated expiration: 2031-04-27
Also published as: DE102010028299A1; GB2480137B; GB201107088D0

Abstract

A handheld electric tool 100 comprises a tool casing 105 forming an interior space 107 in which a drive motor 180 with an associated commutator 182 is arranged. A screening housing 160, which surrounds at least the commutator 182 and comprises conductive plastics, metal coated plastics or metal for screening electromagnetic interference radiation, is provided in the interior space 107 of the casing 105. The housing may be of grid construction so as not to impede cooling air flow and may shield the commutator terminals and a portion of the lead wires 193. Alternatively the housing may be of solid construction with apertures formed therein for coolant flow. The shield may be electrically bonded to the motor housing 185.

Description

SUPPRESSION OF COMMUTATOR-SOURCED INTERFERENCE IN AN ELECTRIC

TOOL

The present invention relates to a handheld electric tool and has particular reference to suppression of commutator-sourced interference in the tool.

Handheld electric tools of known kind include those comprising a drive motor provided with a commutator and arranged in the interior space of a tool casing, the power required for motor operation being fed to the motor by way of the commutator. It is disadvantageous that the commutator in operation of the tool generates electromagnetic interference at the time of commutation changes, particularly wide-band interference emitted by the * ** commutator. * * * * ** S. S

It is therefore an object of the invention to provide a handheld electric tool in which at least a reduction of the electromagnetic interference generated during tool operation thereof is made possible.

According to the present invention there is provided a handheld electric tool with a tool casing forming an interior space in which a drive motor with an associated commutator is arranged, a screening housing, which surrounds at least the commutator and comprises metal, for screening electromagnetic interference radiation being provided in the interior :.: space of the casing.

* *. Such a tool thus includes a simple and economic measure, namely the screening housing, for reduction in the electromagnetic interference emitted by the tool at the time of * commutation changes by the commutator.

Terminals by way of which the commutator is electrically conductively connected with associated connecting lines for power supply can be provided at the commutator, in which case the screening housing preferably surrounds the terminals and, at least partially, the connecting lines. A further reduction of the electromagnetic interference emission of the tool can thus be achieved.

The drive motor is preferably arranged in an associated motor housing fastened in the tool casing, in which case the screening housing surrounds the motor housing at least regionally. It is thus possible to achieve a reduction in the electromagnetic interference emission of the tool not only in the case of tools with an open-frame' mode of construction, but also in the case of tools with a can' mode of construction.

For preference, an electrically conductive connection is formed between the screening housing and the motor housing. The screening effect of the screening housing can thus S.....

* be guaranteed in simple mode and manner.

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The screening housing is preferably of grid-shaped construction, which thus makes it possible in simple mode and manner to avoid impairing a cooling air flow flowing through the drive motor during operation of the tool. * ** * S S

In one embodiment, the screening housing is constructed from electrically conductive * plastics material, whereby a compact screening housing with comparatively low weight can be provided. Alternatively, the screening housing can be made of plastics material and have a metallic coating, which also achieves an effective and economic screening housing. In yet another embodiment the screening housing can be made of metal, which again results in a simple and effective housing.

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The screening housing is preferably of substantially pot-shaped or bag-like construction, whereby a secure and reliable screening of at least the commutator is provided.

The screening housing is preferably constructed for the purpose of enabling at least a * S. reduction of electromagnetic wide-band interferences which are radiated in operation of the tool and which arise at the time of changes in commutation of the commutator.

Embodiments of the present invention will now be described in more detail by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic view of a handheld electric tool embodying the invention; Fig. 2 is a side view of a drive motor of the tool of Fig. I with a first form of a screening housing; Fig. 3 is an end view of a commutator, which is surrounded by the screening housing of Fig. 2, of the drive motor of Fig. 2; Fig. 4 is a side view of the drive motor of the tool of Fig. 1 with a second form of a screening housing; Fig. 5 is a side view of the drive motor of the tool of Fig. 1 with a third form of a screening * housing; * *. ***

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Fig. 6 is a side view of the drive motor of the tool of Fig. 1 with a fourth form of a ** S. *..: screening housing; and *:::* Fig. 7 is a side view of the drive motor of the tool of Fig. 1 with a fifth form of a screening housing.

Referring now to the drawings Fig. 1 shows a handheld electric tool 100 embodying the invention. This comprises a tool casing 105 with a handle 115, the casing forming a housing interior space 107.

*:" The tool 100 is, for power supply independently of the mains, mechanically and electrically connectible with a battery pack 190. In Fig. 1 the tool 100 is constructed, by way of example, as a battery-operated drill/screwdriver. However, there is no restriction to battery drill/screwdrivers and the tool can be of any kind, particularly battery-operated, in which, for example, a tool bit is set in rotation, for example an impact drill, etc. Moreover, the tool can equally well be operated by mains power.

. .: An electric drive motor 180, which is supplied with power by a battery pack 190, and a transmission 170 are arranged in the casing 105, which in accordance with one embodiment is constructed at least in part from plastics material. The drive motor is, for example, connected by way of a motor shaft 189 with the transmission 170, which in turn is connected with a drive shaft 120. The drive shaft 120 is rotatably mounted in the casing by way of bearing arrangement 130 and is provided with a tool bit mount 140, which is arranged in the region of an end face 112 of the casing 105 and comprises, for example, a drill chuck 145. The bearing arrangement 130 is held in the casing.

The mount 140 serves for reception of a tool bit 150 and can be formed on the drive shaft or connected therewith in the manner of an attachment. In Fig. 1 the mount 140 is constructed, by way of example, as an attachment and attached to the drive shaft 120 by way of a fastening device 122 provided at the drive shaft.

The bearing arrangement 130 comprises a first bearing 132 and a second bearing 134, which is spaced therefrom and constructed as, for example, a ball bearing. However, other bearing types are also usable, for example plain bearings, needle sleeves, roller *:" bearings and other rollable bearing types. S...

According to one form of embodiment the drive motor 180 is constructed in a can' mode of construction. Correspondingly, at least the drive motor 180 is arranged in an associated * .. motor housing 185, which is arranged or fastened in the casing interior space 107.

:.:; However, the motor is not restricted to the can mode of construction, but can equally be * as realised in an open-frame' mode of construction in which the casing 105 serves directly as motor housing. In the open-frame mode of construction, stator and rotor components of the drive motor 180 are supported and fastened, for example, directly at the tool casing 105.

The transmission 170 is, by way of illustration, arranged in a transmission housing 110 and is, for example, a planetary transmission, which is constructed with different gear or planet stages and with which an optional torque coupling 172 is associated. In operation of the tool 100 the planetary transmission 170 is rotationally driven by the drive motor 180.

However, the use of a planetary transmission is merely by way of example and is not to be understood as restrictive. Rather, any desired suitable transmission type can be used.

The drive motor 180, which, by way of example, is activatable by a manual switch 195, is, for example, a direct current motor. This has, for commutation, a commutator 182 by way of which a suitable motor current can be fed to the motor 180 in operation of the tool 100.

In this regard the drive motor 180 can be controllable or regulable in such a manner that not only a reversing operation, but also presets with respect to a desired rotational speed can be realised. The function and the construction of a suitable commutator as well as a suitable drive motor are well-known from the prior art, so that a detailed description is dispensed with for the purpose of conciseness of the description.

The manual switch 195 is, by way of example, connected with a switching element 192, which on the one hand is connected by way of electrical lines 191 with the battery pack and on the other hand by way of connecting lines 193, as shown in Fig. 3, with the commutator 182. The switching element 192 is actuable by way of the manual switch 195 in order, for switching-on of the drive motor 180, to electrically conductively connect the lines 191 with the connecting lines 193 and thus the battery pack 190 with the motor 180 by way of the commutator 182. This connection can be interrupted by actuation of the *:: switching element 192 by way of the manual switch 195 for switching off the drive motor 180.

A screening housing 160, which is constructed of metal or at least comprises metal, is provided in the interior space 107 of the casing 105. The screening housing 160 is ::; preferably constructed in the manner of a pot or beaker.

* The screening housing 160 is constructed and arranged to screen emitted electromagnetic interference, particularly for screening electromagnetic wide-band noise which arises in operation of the tool 100 in the case of commutation changes at the commutator 182 and is emitted by the electric tool 100. For this purpose the screening housing 160 is arranged in the region of the commutator 182 and surrounds at least the commutator 182. An electrically conductive connection can be formed between the screening housing 160 and metallic components of the drive motor 180 or the motor housing 185, as shown in Figs. 4 and 5. * ** * * * *** *

Fig. 2 shows the drive motor 180, which is arranged in the motor housing 185, of Fig. 1 with the motor shaft 189 and the commutator 182, which is electrically conductively * ** connected with the connecting lines 193 of Fig. 1, as illustrated in Fig. 3. As apparent from * Fig. 2, the screening housing 160, which by way of example is of grid-shaped construction, is arranged at least in the region of the commutator 182 and encloses the connecting lines 193 at least in part (see Fig. 3).

Air outlet openings 220, through which an air flow conducted in the direction of arrows 210 and 230 through the motor housing 185 can issue, are provided in the motor housing 185.

This air flow serves for cooling rotor and stator components of the drive motor as well as the commutator 182 in operation of the tool 100.

Fig. 3 shows the switching element 192 of Fig. 1, by which the lines 191 are electrically conductively connectible with the connecting lines 193, and thus the battery pack 190 of Fig. 1 electrically conductively connectible by way of the commutator 182 with the drive motor 180. The connecting lines 193 are connected by way of example with terminals 312, 314, for example soldered or clamped in place, the terminals being provided at the commutator 182. The grid-shaped screening housing 160 encloses the connecting lines 193 at least in the region of the commutator 182.

*S.*** * . In one embodiment, air inlet openings 392, 394, 396, through which the air flow is *: conducted in the direction of the arrow 230 of Fig. 2 in operation of the tool 100 in order to pass through the commutator 182 to the air outlet openings, are provided at the commutator 182. An undesired heat output at the commutator 182 can thus be *:*::* prevented. ** *

* * Fig. 4 shows a second form of the screening housing 160, at which by way of example an axial enlargement 460 of grid-shaped construction, which encloses the air outlet openings 220 of the motor housing 185, is provided. Through this form of axial enlargement 460 it is possible to prevent obstruction of the cooling air flow conducted through the motor housing in the direction of arrows 210, 230 as shown in Fig. 2. An electrically conductive connection 462 can optionally be provided between the grid-shaped screening housing and the motor housing 185.

Fig. 5 shows a third form of screening housing 560, which is provided with a metallic coating 570 and constructed from plastics material and which for the purpose of clarity of the illustration is illustrated in sectional form. This is pot-shaped and has an interior space * ** 568 bounded by an annular side wall 562 and a grid-shaped base or closure wall 566.

The metallic coating 570, for example in the form of a metal grid, is formed in the interior space 568. Alternatively thereto, the metallic coating 570 can also be provided on the outer circumference of the housing 560. The metallic coating 570 forms, for example, an electrically conductive connection 580 with the motor housing 185.

Fig. 6 shows a fourth form of screening housing 660, which is provided with a metallic coating 665 and made of plastics material and which for the purpose of clarity of the illustration is illustrated in sectional form. This, by way of example, is similarly pot-shaped and has an interior space 668 which is bounded by an annular side wall 662 with an axial enlargement 666 and a base or closure wall 663. The metallic coating 665 is again constructed in the manner of a metal grid in the interior space 668 and the axial enlargement 66 encloses the air outlet openings 220 of the motor housing 185.

By contrast to the screening housing 560 of Fig. 5 the screening housing 680 of Fig. 6 has openings 680 in the annular side wall 662 as well as openings 667, 669 in the axial enlargement 666. Moreover, the base or closure wall 663 is grid-shaped only in part and * * has a grid section 664.

S * *

Fig. 7 shows a fifth form of pot-shaped screening housing 760 which is constructed from an electrically conductive plastics material and which for the purpose of clarity of illustration is again shown in sectioned form. This has a base or closure wall 761 with * *. mutually axially offset wall sections 762, 764, which form an opening 765 in the manner of a labyrinth, but is otherwise constructed similarly to the screening housing 660 of Fig. 6. *

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****** * * * S. * * * *** . * S. * S * * SI * S * . S S.

Claims

CLAIMS1. A handheld electric tool comprising a casing defining an interior space, a motor, a commutator associated with the motor and a screening housing for screening electromagnetic interference, the motor, commutator and screening housing being arranged in the casing and the screening housing comprising metal and surrounding the * * commutator.

* ***** * *
2. A tool according to claim 1, wherein the commutator comprises terminals electrically conductively connected with power feed lines, the screening housing surrounding the terminals and at least part of the lines. * **
3. A tool according to claim 1 or claim 2, comprising a motor housing mounted in the * casing and receiving the motor, the screening housing surrounding at least part of the motor housing.
4. A tool according to claim 3, wherein the screening housing and the motor housing are electrically conductively connected.

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5. A tool according to any one of the preceding claims, wherein the screening housing is of grid-shaped construction. * ** * * * *** S
6. A tool according to any one of claims 1 to 4, wherein the screening housing is *: ::* made of electrically conductive plastics material.
7. A tool according to any one of claims 1 to 4, wherein the screening housing is made of plastics material and is provided with a metallic coating.
8. A tool according to any one of claims 1 to 4, wherein the screening housing is made of metal
9. A tool according to any one of the preceding claims, wherein the screening housing is of substantially pot-shaped form.
10. A tool according to any one of the preceding claims, wherein the screening housing is constructed and arranged to at least reduce wide-band electromagnetic noise emitted by the commutator at the line of commutation changes during operation of the tool.S * SS* S.... * S S. .* * *5** * *5 * S * * .* *. S * S S * S.S S.�S * S*****S * * * .* * S S S.. * * *. * . * * S. ** *S S * S.