A commutator

Abstract: The commutator comprises a commutator base (10) and a plurality of commutator segments (11). The base (10) is in two parts. One part is a pre-formed base part (12) and the other part (13) is moulded to the base part (12) after the segments (11) have been located on the base part (12) to firmly secure the segments (11) thereto. The commutator is of the barrel-type and the base part (12) is tubular and has castellated ends. The segments (11) have apertured lugs (14 and 15) which engage with the castellated ends of the base part (12) and extend inside opposite ends of the base part (12) to locate the segments (11) relative to the base part (12). The part (13) forms a sleeve inside the base part (12) and firmly secures the lugs (14 and 15) and hence the segments (11) to the base part (12).

Description: This invention relates to a commutator, to an electric motor equipped with such a commutator, and to a method of manufacturing a commutator. Commutators for small fractional horsepower motors are most commonly made by insert moulding. In barrel commutators, the commutator segments are commonly formed as an integral sleeve and the commutator base is moulded to this sleeve. Slits are subsequently made through the sleeve to form the individual commutator segments. A moulded commutator can also be formed such as disclosed in Patents Abstract of Japan, volume 9, no.208 (E-338) 1931, 24th August 1985 JP-A-6070950. The manufacturing processes are complicated and in recent years some manufacturers have been turning to assembled commutators in which individual segments are mechanically secured to a pre-formed base such as described in USA 1410914. It is, however, desirable to machine these commutators to perfect roundness after assembly and it has proven difficult to mechanically secure the segments to a pre-formed base in a manner which prevents circumferential displacement of the segments during a machining operation. According to the present invention there is provided a commutator comprising a plurality of commutator segments mounted on a pre-formed tubular electrically insulating commutator base part in equi-angularly spaced relationship, each segment having a hook-shaped lug at each of two opposite ends, the hook-shaped lugs extending inside opposite ends of the pre-formed base part and the commutator segments being firmly secured to the pre-formed base part by plastics material moulded to the pre-formed base part and the lugs of the commutator segments after the segments have been mounted on the base part. The segments are thus firmly secured to the base part so that machining, and if necessary welding, can be carried out without displacing the segments relative to the base part. Preferably, each lug also engages with a respective end of the pre-formed base part so as to locate the lug angularly with respect to the base part. This may be achieved, for example, by providing the ends of the base part with castellations and engaging the lugs with the castellations. Advantageously, the moulded plastics material forms a sleeve within the pre-formed base part so that this sleeve can be mounted fast on a shaft. The invention will now be more particularly described by way of example with reference to the accompanying drawings, wherein Figure 1 is a longitudinal section through one embodiment of a commutator according to the invention, Figure 2 is an end view taken in the direction of arrow A of Figure 1, and Figure 3 is a plan view of one of the commutator segments shown partially formed. Referring to the drawings, the barrel commutator shown in Figures 1 and 2 comprises a base 10 and a plurality of commutator segments 11 secured to the base 10 in equi-angularly spaced relationship. The base 10 comprises an electrically insulating pre-formed tubular base part 12, typically of plastics material, and a sleeve 13 of moulded material within the base part 12 securing the segments 11 firmly to the base part 12. Each segment 11 has hook-shaped lugs 14 and 15 at opposite ends to locate the segments 11 on the base part 12. The base part 12 has castellated ends and apertures 16 and 17 in the lugs 14 and 15, respectively, engage with the castellations to locate the segments 11 angularly with respect to the base part 12. Each segment 11 has an integral tang 18 at one end. The tang 18 is cut out from the lug 14 leaving the aperture 16 and is used to connect a wire of a wound armature to the segment 11. The inner surface of the base part 12 is uneven to create cavities between the lugs 14 and 15 and the base part 12 so that the moulded material forming the sleeve 13 gets into these cavities to better clamp the segments 11 to the base part 12. In the embodiment shown, longitudinally extending ribs 19 are provided on the inside of the base part 12. These ribs 19 extend beyond the free ends of the hook-shaped lugs 14 and 15 but not to the ends of the base part 12 and support the lugs 14 and 15 away from the inside surface of the base part 12 to create the aforesaid cavities. The commutator is made as follows: Each segment 11 is blanked out (see Figure 3) and formed into its final shape shown in Figures 1 and 2 with the exception of the lug 15. The segments 11 are then mounted on the pre-formed base part 12 by sliding them along the base part 12 from the left hand end thereof as viewed in Figure 1 until the apertures 16 in radial limbs of the lugs 14 engage with the castellations at the left hand end of the base part 12 and the free ends of the longitudinally extending limbs of the lugs 14 contact respective ribs 19. The lugs 15 are then bent over the right hand end of the base part 12 so that the apertures 17 in the radial limbs of the lugs 15 engage with the castellations at the right hand end of the base part 12 and the free ends of the longitudinally extending limbs of the lugs 15 contact respective ribs 19. The base part 12 together with the commutator segments 11 is then placed in a mould. Thermoplastics material or injection grade thermosetting plastics material is then introduced into the inside of the base part 12 filling all cavities between the lugs 14 and 15 and the inner surface of the base part 12 and forming the sleeve 13. This moulded sleeve 13 firmly locks the segments 11 to the base part 12 allowing the segments 11 to be machined without risk of displacing the segments 11 with respect to the base part 12. The finished commutators can then be mounted fast on an armature shaft of an electric motor, typically a small fractional horsepower p.m.d.c. motor, and the armature winding is welded or otherwise secured to the tangs 18.

Claims: A commutator comprising a plurality of commutator segments (11) mounted on a pre-formed tubular electrically insulating commutator base part (12) in equi-angularly spaced relationship, each segment having a hook-shaped lug (14, 15) at each of two opposite ends, the hook-shaped lugs extending inside opposite ends of the pre-formed base part (12), characterised in that the commutator segments (11) are firmly secured to the pre-formed base part (12) by plastics material (13) moulded to the pre-formed base part (12) and the lugs (14, 15) of the commutator segments (11) after the segments have been mounted on the base part (12). A commutator as claimed in claim 1, characterised in that an end of the pre-formed base part (12) is castellated and the lugs (15) engage over the castellations. A commutator as claimed in claim 1 or claim 2, characterised in that the moulded plastics material forms a sleeve (13) within the pre-formed base part (12). A commutator as claimed in any one of claims 1 to 3, characterised in that the inner surface of the pre-formed base part is uneven to create cavities between the lugs (14, 15) and the pre-formed base part (12), which cavities are filled with the moulded plastics material. A commutator as claimed in any one of the preceding claims, characterised in that each segment (12) has an integral tang (18) for connection to a wire of a wound armature. A fractional horsepower electric motor equipped with a commutator according to any one of the preceding claims. A method of manufacturing the commutator of any one of claims 1 to 5, characterised by placing the commutator segments (11) on the pre-formed base part (12) with their hook-shaped lugs (14, 15) extending inside opposite ends of the base part (12), and moulding plastics material (13) to the pre-formed base part and the commutator segments (12) to firmly secure the commutator segments (11) and lugs (14, 15) to the pre-formed base part (12).

Inventors: STROBL GEORG, STROBL, GEORG
Applicants: JOHNSON ELECTRIC SA, JOHNSON ELECTRIC S.A.
Application year: 1989
Main classification: H01R39
IPC codes: H02K13, H01R39, H01R43