GB2200501A - Electric motor with protective switch insensitive to vibration - Google Patents

Abstract

An electric motor comprises two salient stator poles (1) which carry a winding and the gap between which is closed off by an inserted cover member (6). A protective switch (3) associated with the field winding is inserted between reinforcing ribs (7) of the cover member, such ribs extending in axial direction of the motor, and is fixed therein by means of a wedging element (9) in a predetermined position orienting the direction of movement of the switch contacts radially to the axial direction of the motor so as to render the contacts insensitive to stator oscillations about the stator axis. <IMAGE>

Description

ELECTRIC MOTOR WITH PROTECTIVE SWITCH The present invention relates to an electric motor, especially a collector motor in which a gap between the stator poles is closed off by a cover as described in, for example, DE-OS 30 08 937.

It is usual to provide an electric motor with a protective switch (protector) which is arranged near to or within the field winding and switches the field off in the case of excess current or overheating.

However, due to their construction the switches used for this purpose are sensitive to vibration, especially in respect of their installed position relative to the axis of oscillation of the motor. In the case of a collector motor, for example, relatively large pendulum moments result from the reaction forces between stator and rotor in operation, in particular in case of stopping of the rotor, so that the stator oscillates about its axis at twice the mains frequency.

These vibrations are transmitted to the protective switch mounted on the stator so that co-oscillation of the contacts of the switch relative to the axis of oscillation of the stator takes place at least in certain installed positions of these contacts. This occurs particularly when the direction of movement of the switch contacts is tangential to the direction of the stator axis, thus in the direction of oscillation. The transmitted oscillations of the stator have the effect that the switch contacts carry out switching movements in the rhythm of the oscillation, whereby the life of the switch is significantly reduced.

It would thus be desirable to fix such a protective switch in an oriented position relative to the motor axis so that oscillation of the motor stator does not excite the switch contacts into co-oscillation in the switching direction. This fixing should preferably be able to be carried out within the scope of the usual assembly steps, including by manipulators.

According to the present invention there is provided an electric motor comprising a stator provided with a winding and two spaced apart salient poles, a cover member disposed between the poles and provided with reinforcing ribs extending substantially parallel to the axis of the motor, a protective switch disposed between two such ribs and comprising relatively movable contacts electrically connected to the winding, and a fixing element fixing the switch in a position in which the direction of relative movement of the contacts is substantially radial to the motor axis.

A motor embodying the present invention may have the advantage that the installed position of the protective switch is securely and permanently fixed, wherein the installation takes place in such a manner that the direction of movement of the switch contacts extends radially of the axial direction of the motor. Thereby, the switch contacts are fixed ina position in which, in the case of oscillation of the stator, they are not excited into rhythmic opening and closing. In advantageous manner, the fixing element, for example a wedging piece, is fastenable at the side of the stator packet to be secure against rotation and displacement by means of wedging or detent connections at the longitudinally and/or transversely extending reinforcing ribs of the cover member.

Preferably, the wedging piece comprises two projections which are connected with each other by a connecting portion, such as a cross-piece, a first one of the projections being inserted between two connecting wires of the switch nearly as far as their exit point from the switch and the second projection being inserted and detented between two further ribs of the cover member. Expediently, the thickness of the first projection substantially corresponds to the spacing of the connecting wires and a free end portion of the first projection is constructed to be narrowing in cross-section, the length of the first projection being substantially equal to the spacing between the cross-piece and the switch.For preference, the width of the first projection is substantially equal to the spacing between the ribs between which the protective switch is inserted, while the width of the second projection is substantially equal to the spacing between the ribs between which it is inserted, the free end portion of the second projection being provided with a longitudinal slot. Preferably, also, the length of the second projection is such that it extends across at least two transverse ribs at the cover member and a detent hook, which is detentable with one of the transverse ribs, is arranged at at least one of its free end parts formed by the longitudinal slot.

A detent hook, which is detentable at the tangentially outward longitudinal rib of the cover member, may be arranged at an end of the cross-piece remote from the second projection.

Means for retentive guidance of the connecting wires may be arranged at the cover member and/or at the wedging piece.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic end view of an electric motor, illustrating alternative installations of a protective switch; Fig. 2 is an end view of part of an electric motor embodying the invention, showing a protective switch arranged in a stator pole gap cover member; Fig. 3a is a view of a wedging piece in the cover member, in the direction A of Fig. 3b; Fig. 3b is an elevation of the wedging piece; Fig. 3c is a view of the wedging piece in the direction B of Fig. 3b; Fig. 3d is a view of the wedging piece in the direction X of Fig. 3b; Fig. 4 is a sectional view of the cover member with a protective switch, considered tangentially of the motor; and Fig. 5 is a sectional viewof the cover member with installed protective switch, considered radially of the motor.

Referring now to the drawings, there is shown in Fig. 1 a twopole stator lamination packet 1 of an electric motor. In certain operational states of the motor, the stator oscillates about its axis so that pendulum moments according to the arrows -2 occur. Protective switches or protectors 3a or 3b serve for protection of the field winding. In the case of arrangement of the switch in the position 3a, the direction of movement of the two switch contacts 4 extends tangentially of a circle concentric with the axis of the stator.

Pendulum moments in the directions of the arrows 2 thus cause continuous opening and closing of the switch contacts 4 by reason of their mass inertia. Thereagainst, in the case of an arrangemient of the switch in position 3b, the switch contacts 5 are so oriented that their switching movement extends radially of the stator axis; thus transversely to the directions of arrow 2. Switching movements caused by oscillation are thus excluded.

The arrangement of the switch 3 in a cover member 6, which is inserted into the gap between salient poles of the stator lamination packet 1, is evident from Fig. 2. The cover member 6, which is matched at its rotor side to the curvature of the interior space of the stator, is provided at its outer side with several reinforcing ribs, some of which are constructed as longitudinal ribs 7 in axial direction of the motor and some as transverse ribs 8 extending transversely of the ribs 7. The switch 3 is inserted between two longitudinal ribs 7, as is recognisable from Fig. 5.

Fixing of the switch 3 in the illustrated position is effected by means of a wedging element 9, which is illustrated in detail in Figs. 3a to 3d and the use of which is evident from Figs. 4 and 5.

The member 9 comprises a projection 10 and a projection 11, which are so arranged at a common cross-piece 12 that their spacings from each other correspond with those of the longitudinal ribs 7 of the cover member 6. The switch 3 is, as is apparent from Figs. 4 and 5, constructed as cylindrical component which possesses two connecting wires 13 and 14, which extend out from its head part and between which the projection 10 engages. The end of the projection 10 connected with the cross-piece 12 has a width which approximately corresponds to the spacing between two longitudinal ribs 7 and can narrow towards the free end. Its thickness corresponds at its free end to the spacing of the connecting wires 13 and 14 where they emerge from the head part of the switch and can increase continuously towards the cross-piece 12.The axial length of the projection 10 is so chosen that its free end nearly touches the head part of the switch 3.

The projection 11 engages between two adjacent ribs 7 of the cover member 6 and serves to fix the element 9 in position. For this purpose the projection 11 can be provided with a longitudinal slot 15 to enable resilient wedging of the projection 11 between the two ribs 7. Provided at the free end of the projection 11 is at least one detent hook 16, which for the axial latching of the element 9 engages behind a transverse rib 8 of the cover member 6. The length of the projection 11 is preferably such that the projection 11, for reasons of stability, engages over at least two of the transverse ribs 8.

A detent hook 17 can be provided to fix or detent the element 9 at a longitudinal rib 7 in a direction tangential to the motor.

The projection 10 disposed between the wires 13 and 14 prevents the switch 3 from rotating relative to its axial direction during operation of the motor. Moreover, it is ensured that installation of the switch 3 is confined to the predetermined position, namely the position corresponding to position 3b according to Fig. 1. It is in that case presumed that the position of the connecting wires relative to the setting of the switch contacts corresponds to the examples illustrated in the figures.

Means for the guidance and/or mounting of the connecting wires 13 and 14 can be arranged at the cover member 6 and/or at the wedging piece 9, as shown by way of example in Fig. 5.

The wedging member 9 is, during the manufacture of the stator, installed simply by plugging into the cover member 6, in which the detent hooks 16 and 17 effect automatic latching in the installed position. Installation by means of manipulators is also possible.

Claims (9)

1. An electric motor comprising a stator provided with a winding and two spaced apart salient poles, a cover member disposed between the poles and provided with reinforcing ribs extending substantially parallel to the axis of the motor, a protective switch disposed between two such ribs and comprising relatively movable contacts electrically connected to the winding, and a fixing element fixing the switch in a position in which the direction of relative movement of the contacts is substantially radial to the motor axis.

2. A motor as claimed in claim 1, wherein the fixing element comprises a first projection so inserted between two electrical connection wires of the switch as to extend into the region of the switch and a second projection connected to the first projection by a connecting portion and inserted and retained between two ribs of the cover member, at least one of those ribs being different from the ribs between which the switch is disposed.

3. A motor as claimed in claim 2, wherein the first projection tapers inwardly at a free end portion thereof in direction towards the switch and has a thickness substantially equal to a spacing between the connecting wires and a length substantially equal to a spacing between the switch and the connecting portion.

4. A motor as claimed in either claim 2 or claim 3, wherein the first projection has a width-substantially equal to the spacing between the ribs between which the switch is disposed.

5. A motor as claimed in any one of claims 2 to 3, wherein the second projection has a width substantially equal to the spacing between the ribs between which the second projection is inserted and is provided in a free end portion thereof with a slot extending in the longitudinal direction of the projection.

6. A motor as claimed in claim 5, wherein the cover member is provided with further reinforcing ribs extending transversely to the firstmentioned reinforcing ribs and the second projection extends across at least two of the further ribs and is provided at its free end portion with a detent hook engaging one of the further ribs.

7. A motor as claimed in any one of claims 2 to 6, wherein the connecting portion is provided in a region thereof remote from the second projection with a detent hook engaged with an outermost one of the ribs extending substantially parallel to the motor axis.

8. A motor as claimed in any one of claims 2 to 7, wherein at least one of the fixing element and cover member comprises means for holding and guiding the connecting wires.

9. An electric motor substantially as hereinbefore described with reference to the accompanying drawings.