GB2209885A

GB2209885A - Reversible motor for an electric hand tool

Info

Publication number: GB2209885A
Application number: GB8821783A
Authority: GB
Inventors: Heinz Deuschle; Hermann Kieser
Original assignee: Metabowerke GmbH and Co
Current assignee: Metabowerke GmbH and Co
Priority date: 1987-09-16
Filing date: 1988-09-16
Publication date: 1989-05-24
Anticipated expiration: 2008-09-16
Also published as: DE3731079C2; DE3731079A1; GB2209885B; FR2620582B1; FR2620582A1; GB8821783D0

Description

29E 52 912(2) "Motor for an electric hand tooP W-9 b b This invention

relates to a motor for an electric hand tool, and in particular to a motor adapted for forward and reverse operation.

Such a motor is known from EP-A2-0 208 137, in which a support ring is combined with an additional contact holder so that, by rotating the support ring in relation to the contact holder a changing contact is made at the connecting point between these two parts, thereby to effect a reversal of the rotational direction of the rotor or armature of the motor. When the support ring is rotated to supply current to the armature, the motor brushes are displaced at the same time, thereby avoiding a loss of Power due to wrong positioning in the rotational direction of the brushes in relation to the commutator of the armature. In the known construction both the connections for the mains as well as the connections for the field coil are located on the contact holder requiring a complicated arrangement and design of the contacts both on the contact holder and on the support ring, in order to secure in the two rotational end positions of the support ring a different polarisation of the field coil as opposed to that of the armature coil. Furthermore, the contact holder is an additional part requiring separate manufacture and more costly assembly together with the support ring on the commutator side of the motor.

Furthermore, a reversing device for an electric motor is known from the US-A-3,440,465, said reversing device also having a support ring for the brush holders which can be roatated in the peripheral direction, thus resulting not only in a displacement of the brushes but also in a changing polarity of the two brush holders. An additional contact ring is also necessary here which, by changing contact. secures the different polarity of the two brushholders in the rotational end positions of the support ring. The contact ring and the support ring, together with a-supporting body, are assembled here to a Dreassembled sub-component and when assembling the sub-component on the commutator side of the respective motor a connection not fully explained has to be made with the field coil.

According to the present invention there is provided a motor for an electric hand tool, said motor being adapted for forward and reverse operation, and comprising a support ring surrounding the commutator and diametrically disposed brush holders, the support ring being rotatable about the axis of the commutator by a limited angle, and two contact springs peripherally disposed about the support ring and each being electrically connected with one of the brush holders, each said contact springs having at one end a supply contact point and at the other end a field contact point, said respective supply contact points being disposed adjacent each other and angularly spaced by said angle of rotation, and said field contact points being disposed adjacent each other and angularly spaced by sai,d angle, whereby when said support ring is in a first rotational end position a field contact connected with the first end of a field coil makes contact with one of the two field contact points of said springs and a fixed supply contact connected with a first mains connection makes contact with the supply contact point of the contact spring which is not in contact with the field contact in the same rotational end position, the second mains connection being at the second end of the r 3 field coil, each of said field and supply contacts making contact with the other of said respective pairs of contact points when said ring is in a second rotational end position to differently polarise the motor.

By means of this arrangement there is provided a motor, in which the manufacturing cost for the reversing switch are further reduced and whose electrical connection with the field coil and the main connections is simplified. In particular contact change for the reversal of the rotational direction of the motor only result from the specific arrangement and design of the contact springs of the support ring, while only one fixed contact tongue is necessary for on the one hand connecting the contacts of the support ring with one of the two mains connections and on the other side with the field coil. So, basically, only the support ring serves as a contact carrier, on which moreover the brush holders are provided.

In a particularly preferred embodiment the two contact springs of the support ring may be identically formed, each of these springs having at their one end the supply contact point and at their other end the field contact point and in addition a further contact for the electrical connection with the respective brush holder. The springs are offset axially-symmetrically to each other, preferably on the inside of the support ring, whilst the two supply contact points and the two field contact points of the two different springs are adjacent to each other, however, being spaced from each other by the arc of the angle of rotation of the support ring respectively.

Furthermore, a locking device is advantageously provided between the motor housing and the support ring in order to achieve a fixing of the support 4 - ring in its two rotational end positions. Moreover, a safety device may advantageously be provided to prevent the support ring from being operated intentionally or unintentionally as an actuating member of the reversing switch, when the motor is switched on. For this purpose on the switch button normally provided with the electric hand tool a locking tongue is provided which cooperates with corresponding recesses on the support ring in such a way that the engagement of the switch button is not possible if the support ring is positioned in the intermediate positions between its two rotational end positions. Additionally, the locking tongue on the switch button can cooperate with a projecting supporting arm on the support ring in such a way, that a displacement of the support ring during operation away from the respective rotational end position is blocked. The arm projecting from the support ring can also be used for blocking the switch button in the intermediate positions between the two rota- tional end positions of the support ring. An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which:25 Figure 1 is a schematic, perspective illustration of a universal motor without armature for an electric tool with an exploded view of a support ring and retaining ring, Figure 2 is a sectional part side view of an electric hand tool with a universal motor having a reversing switch corresponding substantially to that of Figure 1, Figure 3 is a kear view according to the direction of the arrow III in Figure 2, the handle of the hand tool being sectioned along the line I-I, 1 Figure 4 is a part section along the line IV-IV in Figure 3, Figure 5 is a view of the support ring of the reversing switch, Figure 6 is a part section through the border region between the support ring of the reversing switch and the retaining ring thereof along the line VI-VI in Figure 2 in the mid-position of the support ring, and Figure 7 is an illustration as in Figure 6, but in one of the rotational end positions of the support ring.

Figure 1 shows a motor housing 1 for a universal motor made of an insulating material, a field pack 2, a field coil former 3 and a field coil 4. The rotor armature of the motor is not illustrated here. In position, the rotor armature with its commutator protrudes axially on the right hand side of field pack 2 in Figure 1. The space occupied by the commutator of the rotor armature is surrounded by a collar 5 formed on the motor housing 1 coaxially with the motor axis. The transition part to collar 5 adjacent to housing 1 is formed as a flange 6 with a slightly larger diameter disposed coaxially with the motor axis and serving as a bearing surface for a support ring 7 which can be axially mounted over collar 5 on flange 6 on housing 1.

The support ring 7 is the actuator of the reversing switch which can be rotated in its circum- ferential direction between two rotational end positions. The contact reversal in the electrical supply of the rotor armature and the field coil 4 is thereby such that in the two end positions the rotor armature and the field coil are differently polarised, resulting in a universal motor with different rotational directions of the rotor armature.

- 6 Brush holders 8, in which usually carbon brushes are mounted. which slide on the commutator of the rotor armature, are provided on the support ring 7. In order to improve commutation, the brushes can be displaced out of the neutral position according to the rotational direction, to which the rotational angle a of the support ring 7 is adapted. The collar 5 on the motor housing 1 has respective cut-outs 9 in the radial direction so that the carbon brushes guided in the brush holders 8 can reach the commutator of the rotor armature without hindrance. The rotation of the support ring 7 occurs via radially formed wings 10 which will be explained more fully hereinafter.

The locking in position of the support ring 7, which is radially spaced from the collar 5, occurs axially relative to the housing flange 6 by means of a retaining ring 11 which can abut on the outer end face of the support ring 7, engage in the support ring 7 or engage over it.

The support ring 7 has on its inside 12 circumferentially arranged a pair of contact springs 13, which are offset to each other axiallysymmetrically by 180'. The contact springs 13 are identically formed, which is apparent in detail from Figure 5. The respective adjacent, opposite ends of the contact springs 13 have a distance from each other corresponding substantially to the arc of the angle of rotation a of the support ring 7. At the ends of the contact springs 13 contact points 14 and 15 are formed, which could also be contact surfaces or other forms of contacts. The two contact points facing each other in the support ring 7 at the bottom Figure 1 are supply contact points 14 which are spaced from each other by the angle of rotation a. At the other end of the contact snrinas 13 the two field contact points 15 are also spaced from

1 each other by this angle, so that in each rotational position of the support ring 7 connection is made with the power supply via one of the two supply contact points 14 and in same rotational position via the respective contact point 15 of the other contact spring 13 electrical connection is made with the field coil 4.

Parallel to the axis of the support ring 7 a projecting field tongue 16 is positioned on the field coil form 3, projecting into the inside of the support ring 7 and in the two rotational end positions thereof being in contact with one of the two field contact points 15 of the respective leaf spring 13. On the retaining ring 11, parallel to the axis of the support ring 7, a supply contact tongue 18 is positioned projecting in the reverse axial direction into the support ring 7 and in the two rotational end positions of the support ring 7 in electrical contact with one of the supply contact points 14 of the leaf springs 13. The field contact tongue and the supply contact tongue 18 are in the assembled arrangement positioned diametrically to each other inside the support ring. In the same way the field contact point 14 of one leaf spring 13 lies diametrically opposite one supply contact point 15 of the other leaf spring 13. Thus the supply tongue and the field tongue are only able at the same time to be in contact with the respective opposite leaf spring 13 in the support ring 7, and by rotating the support ring 7 from one of its rotational end positions to the other by the rotation angle a contact reversal for the reversal of the rotational direction of the universal motor may be effected. That is to say, upon rotation of ring 7 the supply and field tongues are both switched to contact the other leaf spring. On the retaining ring 11 the supply

8 - contact tongue 18 is in electrical contact with a first mains connection 19, whereas the second mains connection 17 is positioned at the second end of the field coil 4. It goes without saying that in an electric hand tool the mains connections 17 and 19 do not directly lead to the mains but to a mains switch and if required a speed controller.

Whilst for the field coil 4 the polarity in the two rotational end positions of the support ring 7 does not change, a change of polarity on the rotor armature does take place when the support ring 7 rotates from one of its rotational end positions to the other, because the supply contact tongue 18 changes its connection from one leaf spring contact 13 to the other leaf spring 13 and thus its electrical connection to the two brush holders 8. This results not only in a change of polarity on the rotor armature, but at the same time in a displacement of the brush holder 8 due to the rotation of the support ring 7. so that commutation at the commutator of the rotor armature for the respective rotational direction is improved.

An embodiment is shown in Figure 2, in which the retaining ring 11, the support ring 7 and the bearing of the support ring 7 on the motor housing 1 are only diagrammatically illustrated. In this illustration a locking device positioned between the motor housing 1 and the support ring 7 is instru mental in preventing an unintended rotation of the support ring 7 from one of its two rotational end positions. In addition, Figure 2 also shows the rotor armature 29 with its commutator 30, on which the brush holders 8 on the support ring 7 are radially aligned.

The locking device mentioned comprises a blind hole 22 which extends parallel to the axis of the support ring 7 and opens toward the support It ring. A compression spring 23 is positioned therein acting upon a ball 24, which clicks into two spherical recesses 25 on the support ring 7, which in the rotational end positions of the support ring 7 align with the displacement direction of the ball 24. Consequently it is only possible to rotate the support ring 7 away from its two rotational end positions, once the locking resistance of the ball 24 has been overcome.

Figure 2 also shows a safety device which prevents the switching on of the universal motor so long as the support ring 7 is not in one of its two rotational end positions. To that end, an arm 28, in the form of a radial extension is positioned on the support ring cooperating with a locking tongue 27 disposed on the switch button 26 of a mains switch 31 for the universal motor. The arm 28 is formed sufficiently broad in circumferential direction, that it blocks an engagement of the switch button 26 by stopping of the locking tongue 27, whilst the support ring 7 is in a position between its two rotational end positions. In these intermediate positions of the support ring 7 the field contact points 15 of the leaf springs 13 have no electrical connection with the field contact tongue 16, neither is the supply contact tongue 18 in contact with one of the two supply contact points 14 of the leaf spring 13. Consequently, with supply voltage applied to the supply contact points 17 and 19, switching on and off of the motor would be possible by rotating the support ring 7; furthermore, the rotational direction could be changed during operation. This is prevented in order to protect the contact springs 13 and the motor itself by the aforementioned locking device in that it is only possible to activate the mains switch 31 via the switch button 26 if there is a closed connection between the supply contact tongue 18 and one of the two leaf springs 13 and the field contact tongue 16 with the other of the two contact springs 13.

In cooperation with the arm 28 on the support ring 7 the locking tongue 27 can at the same time act as a safeguard against rotation of the support ring 7. In the engaged position of the switch button 26 the locking tongue 27 is positioned in the rotational plane of the arm 28 on the support ring 7 and can, therefore, be used as a stop for the arm 28 in its rotational direction. As shown in Figures 1 and 3, this arm 28 is positioned axially in front of one of the two brush holders 8.

The operation of the support ring 7, i.e. how it can be rotated from one of its rotational end positions into the other, can be seen from Fig. 3. In radial direction to the wings 10 of. the support ring 7 longitudinal slits are provided in the surrounding machine housing 20, through which the wings 10 of the support ring 7 project outwardly. As can be deduced from Figure 2 the electric hand tool could be, for example, a drilling machine with a pistol grip. In this case the two ends of the wing 10 of the support ring 7 are so easily accessible that the thumb and forefinger of the operating hand can easily reach them. It is thus possible to activate the reversing switch without having to let go of the machine.

Furthermore, it is clear from Figures 3 and 4 that the supply contact tongue 18 on the retaining ring 11 is connected to the mains connection 19.

A conductor plate 32 runs externally of the support ring, the conductor plate being fixed by one of the assembly screws 33 for the retaining ring 11. On one end of this conductor plate 32 the mains connection 19 is made by a plug contact, at the 1 2!' same time the conductor plate 32 is at its other end formed integrally with the projecting supply contact tongue 18.

Finally, Figure 5 shows details of the support ring 7 and of the two contact springs 13 fitted therein, which, as already mentioned, are identical and are arranged in the circumferential direction axially-symmetrically offset to each other by 180. The contact springs 13 are attached in the support ring 7 in such a way that in the region of the supply contact points 14 and the field contact points 15 they are formed as resilient wiper contacts so that with the support ring 7 the contact points 14, 15 can thus easily run up onto the field contact tongue 16 or the supply contact tongue 18 respectively, in order thereupon to make a secure electrical connection with the said contact tongues 16, 18. In order to fix the contact springs 13 in such a way that they are prevented from rotating especially in the circumferential direction, they are provided with fastening legs 34, having one or more angles, by which they are inserted in a direction parallel to the axis of the support ring 7 into respective mounting slits in the support ring 7. The contact springs 13 are held in part by axially projecting tabs 35 on the inside of the support ring 7 which have opposite them respective counter tabs 36 which are radially spaced outwardly, said tabs 35 and 36 forming a locating slit for the respective contact spring 13 which is open to one of the two end faces of the support ring 7. A plurality of such tabs 35 and 36 along the inner periphery of the support ring 7 can be provided, the tabs 35 positioned inside with their cylindrically curved inner sides help to form the guide surface of the support ring 7, by which the supr)ort ring is supported on the housing flange 6 as shown in Figure 1.

Figures 6 and 7 illustrate an axial support free from play of the support ring 7 on the retaining ring 11. For this purpose the support ring 7 has on its rear face one or more axially projecting protuberances 37, the retaining ring 11 having on the opposed front face corresponding recesses 38 into which the protuberances 37 of the support ring 7 can extend. This extension of the protuberance 37 is illustrated in Figure 6, the support ring 7 being here in an intermediate position between its two rotational end positions. Figure 7 shows the relative position of the support ring and the retaining ring 11 in one of the two rotational end positions of the support ring 7, whereby, when pushing the protuberance or protuberances 37 onto the end frontal surface of the retaining ring 11, an axial bracing of the support ring 7 occurs, which is supported on the opposed face of the motor housing 1 not illustrated in Figure 6 and 7. The unavoidable axial play of the support ring in the two rotational end positions has thus been more or less eliminated, in that the support ring 7 cannot vibrate when the machine is in operation, which is a positive feature as far as the reduced risk of a brush fire and the life of the carbon brushes is concerned. The clamping of the support ring 7 in its two rotational end positions is such that it can easily be overcome when activating the reversing switch.

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Claims

1. A motor for an electric hand tool, said motor being adapted for forward and reverse operation, and comprising a support ring surrounding the commutator and diametrically disposed brush holders, the support ring being rotatable about the axis of the commutator by a limited angle, and two contact springs peripherally disposed about the support ring and each being electrically connected with one of the brush holders, each said contact springs having at one end a supply contact point and at the other end a field contact point, said respective supply contact points being disposed adjacent each other and angularly spaced by said angle of rotation, and said field contact points being disposed adjacent each other and angularly spaced by said angle, whereby when said support ring is in a first rotational end position a field contact connected with the first end of a field coil makes contact with one of the two field contact points of said springs and a fixed supply contact connected with a first mains'connection makes contact with the supply contact point of the contact spring which is not in contact with the field contact in the same rotational end position, the second mains connection being at the second end of the field coil, each of said field and supply contacts making contact with the other of said respective pairs of contact points when said ring is in a second rotational end position to differently polarise the motor.

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2. A motor according to claim 1 wherein said field contact comprises a tongue extending into the arc of rotation of said field contact points, and said supply contact comprises a tongue extending into the arc of rotation of said supply contact points.

3. A motor according to claim 2, wherein the contact springs are disposed on the inside of the support ring and the field contact tongue and the supply contact tongue project.into the support ring.

4. A motor according to claim 1, 2 or 3, wherein the contact springs are identically formed and are disposed on the support ring axially symmetrically to each other.

5. A motor according to any preceding claim wherein the support ring is supported on a flange on the motor housing projecting coaxially to the armature axis.

6. A motor according to claim 4, wherein on the inside of the support ring are provided tabs spaced radially thereto which abut on the housing flange and behind which the contact springs are inserted. 25

7. A motor according to any preceding claim wherein a collar fixed to the motor housing projects through the support ring and that at the end of the collar a retaining ring for the support ring is attached, on which the supply contact and the first mains connection are disposed.

8. A motor according to claim 7, wherein on the support ring and/or on the retaining ring axial supporting means are provided, which at least in the rotational end positions brace the support Jr - is - ring with respect to the retaining ring free from play.

9. A motor according to any preceding claim wherein on the motor housing a locking device is provided fixing the support ring in its two rotational end positions.-

10. A motor according to claim 9, wherein the locking device has at least one spring loaded ball, engaging in spherical recesses on the support ring in the two rotational end positions.

11. A motor substantially as hereinbefore described with reference to the accompanying drawings.

12. An electric hand tool including a motor according to any preceding claim.

13. An electric hand tool according to claim 12, wherein said support ring comprises at least one radially projecting actuating wing, and said tool comprises a housing surrounding the support ring and in which through slits are provided for said at least one radially projecting actuating wing.

14. An electric hand tool according to claim 12 or 13, wherein the support ring is disposed adjacent to a switch button on which a projecting locking tongue positively cooperates with the support ring, locking the support ring when the switch is in the on-position.

15. An electric hand tool according to claim 14, wherein the support ring has a projecting arm and when the suDT)ort rinq is positioned between the two rotational end positions, the arm is located lk t - 16 in the displacement position of the locking tongue, thus blocking an engagement of the switch button.

Y1 4

16. An electric hand tool substantially as herein- before described with reference to the accompanying drawings.

z Pub'W- C 1988 a n-.e Fazen Office. State House. 667. H.: H7,.-crrLondon WC1R 4TP. F'arther copies maybe obtained from The Patent Office. Sales Branch. St Mary Cray. Orpington. Kent BR5 3RD. Printed by Multiplex techmques ltd, St Mary Cr&V. Kent. Con. 1'87. bales zrancn, bt mary Cray. Orpington. Kent BR5 3RD. Printed by Multiplex techmaues ltd. St Marv CrFv T(Pnt. r.r. 1'R7