GB2265762A

GB2265762A - Plastics cap for the slip-ring chamber of electric machines

Info

Publication number: GB2265762A
Application number: GB9306387A
Authority: GB
Inventors: Henning Stilke; Dominique Eynius
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1992-04-02
Filing date: 1993-03-26
Publication date: 1993-10-06
Anticipated expiration: 2013-03-26
Also published as: ES1024410Y; GB2265762B; ITMI930241U1; IT229757Y1; GB9306387D0; FR2689701B3; ES1024410U; FR2689701A3; DE9204517U1; ITMI930241V0

Abstract

A plastics cap (10) for a slip-ring chamber of a three- phase generator for motor vehicles, has a force-fit ring section (13) for a bearing installed in the bearing shield of the generator. In order to prevent gases, fluids or bodies from penetrating at a longitudinal slot (16), which is provided in the force-fit ring section, and to compensate the tolerances and expansion caused by temperature variations, the longitudinal slot is sealed by a resilient skin (18) of the plastics cap. Ventilation channels (19) are present. <IMAGE>

Description

DESCRIPTION PLASTICS CAP FOR THE SLIP-RING CHAMBER OF ELECTRIC MACHINES The invention relates to a plastics cap for the slip-ring chamber of an electric machine, and in particular, but not exclusively, the slip ring chamber of a three-phase generator for motor vehicles.

In a known plastics cap for the slip-ring chamber of a three-phase generator for motor vehicles, disclosed in DE-GM 89 11 295, it is known to encapsulate the slip-ring chamber of the machine by a plastics sleeve, which is inserted with an end section formed as a force-fit ring between the bearing at the slip-ring side and the bearing bore in the housing flange of the machine. This solution has the disadvantage, that the plastics material in the forcefit ring section is compressed during the differing thermal expansions of the bearing and of the bearing bore and can remain deformed, so that on subsequent cooling, the bearing seat is relaxed.

Moreover, it is known from DE-OS 35 09 604 to use a longitudinally slotted plastics force-fit ring at the bearing shield at the brush side between the bearing bore and the bearing. This does, however, have the disadvantage that when using this solution in the case of a plastics cap for the slip-ring chamber of the machine, moisture, saline mist or other various foreign bodies, such as fluids and gases, can penetrate the slip-ring chamber through the expansion slot in the force-fit ring section, so that the desired protection of the slip-ring chamber by means of an encapsulation becomes ineffective.

With the present solution, it is endeavoured to encapsulate the slip-ring chamber behind the bearing of the machine at the brush side, in such a way that the plastics cap on the one hand comprises an expansion slot in the region of the force-fit ring and on the other hand, gases, fluids or bodies are prevented from penetrating the slip-ring chamber through the expansion slot.

In accordance with the present invention there is provided a plastics cap for the slip-ring chamber of an electric machine, having a claw-pole rotor, whose excitation winding is supplied by way of a slip-ring arrangement of carbon brushes, wherein the plastics cap envelops in the shape of a cup the slip-ring chamber at the end section of the rotor shaft behind the bearing at the brush side of the machine and by means of an expanded force-fit ring section forms a force-fit for the external ring of the bearing, which is provided with a longitudinal slot for the purpose of compensating for the tolerance and the expansion caused by temperature variations, which longitudinal slot is sealed by a resilient skin of the plastics cap.

This has the advantage, that without additional expenditure when manufacturing the plastics cap by injection moulding, the resilient skin and/or the film is formed at the same time, this resilient skin and/or film seals the longitudinal slot in the force-fit ring section of the plastics cap. The resilience of this skin enables the longitudinal slot to be expanded or compressed to compensate for the tolerance between the bearing bore and the outer ring of the bearing.

Moreover, the skin as a resilient closure yields in the region of the bearing force-fit ring, when the temperature causes the plastics cap to expand.

Advantageously, the longitudinal slot extends over the bearing width radially outwardly as far as the annular wall of the plastics cap disposed in advance of the bearing and is sealed over its entire length by means of the skin. As the longitudinal groove can also be used for ventilating the slip-ring chamber, it is particularly expedient, if the skin covers the longitudinal groove at the outer periphery of the bearing force-fit ring and is used, in this way, at the same time to form a ventilation channel for the slip-ring chamber. On the other hand, it can be advantageous when manufacturing the plastics cap by injection moulding, if the longitudinal groove is covered by the skin at the internal periphery of the bearing force-fit ring.

By way of example only, specific embodiments of the present invention will now be described, with reference to the accompanying drawings, in which: Fig. 1 illustrates an enlarged longitudinal view of a plastics cap for the slip-ring chamber of a three-phase generator constructed in accordance with one embodiment of the present invention; Fig. 2 illustrates a greatly enlarged partial section of the force-fit ring section of the plastics cap of Fig.1, as seen from the front; Fig. 3 is a sectional view along the line III-III of Fig. 2; Fig. 4 illustrates a longitudinal view of a second embodiment of the plastics cap; and Fig. 5 illustrates a front view of the plastics cap with partial sections at two ventilation channels in the cutting plane according to x and y of Fig. 4.

The plastics cap 10 shown in Fig.1 is for the slip-ring chamber of a three-phase generator for motor vehicles. The three-phase generator (not illustrated) is provided in a manner known per se (see DE-GM 89 11 295) with a claw-pole rotor, whose excitation winding is supplied by way of a slip-ring arrangement using carbon brushes. The cup-shaped plastics cap 10 for the slip-ring chamber lies in this case at the end section of the rotor shaft behind the bearing at the brush side. In the assembled condition, as shown in Fig.4, the plastics cap 10 is inserted into the bearing bore of an bearing shield 21 at the brush side of the machine and a brush holder is inserted in a corresponding opening 11 of the plastics cap 10 by means of a sealing ring and the carbon brushes of the brush holder press against the slip rings rotating in the slip-ring chamber.At the same time, the plastics cap is sealed at the end at the slip-ring side by means of a front wall 12 and expands at its end open at the bearing side to form a force-fit ring section 13 for the outer ring of a bearing 22. The force-fit ring section 13 is connected in this case by means of an annular wall 14 to the slip-ring chamber section 15 of the plastics cap 10.

The force-fit ring section 13 is provided at its periphery with a longitudinal slot 16 which extends over the bearing width and which is able to compensate both the manufacturing tolerances of the bearing, of the bearing bore and of the force-fit ring sections 13. Moreover, the material of the force-fit ring section can resiliently deform into the longitudinal slot 16 upon the thermal expansion of the bearing. A radially outwardly directed annular collar 17, which is injection moulded as one piece at the end of the force-fit ring section 13, seals the longitudinal slot 16 towards the front.

It is evident from the greatly enlarged illustration of the partial sectional view at the force-fit ring section 13 as shown in Figs. 2 and 3, that the longitudinal slot 16 is covered at the internal periphery of the force-fit ring section 13 by a resilient skin 18 of the plastics cap 10. When the longitudinal slot 16 is compressed, the resilient skin 18 can arch in the longitudinal section 16 or can extend when expanding the longitudinal slot 16, so that the resilient skin 18 constantly seals the longitudinal slot 17. In order on the one hand to prevent the penetration of gases, moisture or foreign bodies through the longitudinal slot 16, but on the other hand to be sufficiently resiliently mouldable, the skin 18 in the embodiment is produced in a thickness of 0.3 mm from PBT = Polybutylenterephthalte when injection moulding the plastics cap 10. In addition to this, the longitudinal slot 16 extends radially outwards over the bearing width as far as the annular wall 14 of the plastics cap 10 disposed in advance of the bearing, wherein it is sealed over the entire length by means of the skin 18.

In order to be able to ventilate sufficiently this slip-ring chamber, three ventilation channels 19 are formed evenly distributed over the periphery at the force-fit ring section 13 and the longitudinal slot 16 as shown in Fig. 2 is disposed adjacent to one of the ventilation channels 19.

In the second embodiment as shown in Figs. 4 and 5 the parts which correspond with those of the first embodiment are provided with identical designations.

In so doing, it is evident from Fig. 4, that the plastics cap 20 with its force-fit ring section 13 is inserted into the bearing bore of a bearing shield 21 in such a manner as to prevent relative rotation and receives a ball bearing 22 for the machine shaft. The longitudinal slot 16 in the force-fit ring section 13 of the plastics cap 20 is covered here at the external periphery of the force-fit ring section 13 by the skin 18 of the plastics cap 20. In this way, the longitudinal slot 16 simultaneously forms one of the three ventilation channels 19 which are evident from Fig. 5.

It is also possible to attach at the longitudinal slot 16 a skin which is injection moulded as one and/or a material film at an optional height in the longitudinal slot 16, provided that it is ensured, that nothing can penetrate the slip-ring chamber through the longitudinal slot. Moreover, it is possible to dimension the skin 18 at the longitudinal slot 16 in such a way, that in the case of the forcefit ring section 13 expanding excessively, the skin 18 serves as an intended braking point. For this purpose, it is expedient, if the longitudinal slot 16 is continued as far as the front annular collar 17 and is sealed there at the front by the skin 18.

Claims

1. A plastics cap for the slip-ring chamber of an electric machine, having a claw-pole rotor, whose excitation winding is supplied by way of a slip-ring arrangement of carbon brushes, wherein the plastics cap envelops in the shape of a cup the slip-ring chamber at the end section of the rotor shaft behind the bearing at the brush side of the machine and by means of an expanded force-fit ring section forms a force-fit for the external ring of the bearing, which is provided with a longitudinal slot for the purpose of compensating for the tolerance and the expansion caused by temperature variations, which longitudinal slot is sealed by a resilient skin of the plastics cap.

2. A plastics cap according to claim 1, wherein the longitudinal slot extends over the width of the force-fit ring section radially outwards as far as an annular wall of the plastics cap disposed in advance of the bearing and is sealed over its entire length by means of the skin.

3. A plastics cap according to claim 1 or 2, wherein for the purpose of forming a ventilation channel for the slip-ring chamber, the skin covers the longitudinal slot at the outer periphery of the forcefit ring section.

4. A plastics cap according to claim 1 or 2, wherein the longitudinal slot is disposed adjacent to a ventilation channel of the force-fit ring section and is covered at the internal periphery by the skin.

5. A plastics cap constructed and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.