US 3617785 A
Description (OCR text may contain errors)
United States Patent Inventor llenry Kristiansen Sarnen, Switzerland Appi. No. 57,964
Filed July 24, 1970 Patented Nov. 2, 1971 Assignee lnterelectrle Seehseln A.G.
Switzerland CURRENT-COLLECTING DEVICE FOR SMALL  References Cited UNITED STATES PATENTS 3,191,084 6/1965 Ooka et al. 310/252X 3,171,997 3/1965 Hammer..... 310/233 3,310,718 3/1967 Lupfer 252/514 X Primary Examiner-Milton O. l-lirshfield Assistant Examiner-B. A. Reynolds Attorney-Arthur Schwartz ABSTRACT: A current-collecting device for small commutating machines having a commutator of 85 to 95 percent silver and 15 to 5 percent copper; and having brushes of 50 to 70 percent silver, 25 to 40 percent palladium, and 3 to 10 percent copper.
PATENTEDuuv 2 l97l INVENTOR HENRY KRISTIANSEN 'iATTORNEY CURRENT-COLLECTING DEVICE FOR SMALL COMMUTATING MACHINES BACKGROUND AND OBJECTS The invention relates to a current-collecting device for small or midget commutating machines comprising a commutator mounted on the rotor shaft and stationary brushes brushing on the commutator.
in small commutating machines the problem arises that under a high-current load of the current-collecting device the commutator and the brushes burn away rapidly. The life of high-performance small motors has thus been very limited hitherto.
Especially in small commutating machines having an ironless armature, which may be constructed for high speeds, an excessively high current arises during starting in motor operation and this current makes the life of the machine several times shorter than the life in continuous operation. It is already known to increase the life by using relatively thick brushes. This has, however, the disadvantage of producing relatively high frictional losses, thus reducing the efficiency of the micromotor. Moreover, the use of thick brushes results in only a relatively small increase in the life because the thick brushes must be applied with a relatively high contact pressure, particularly at high speeds, and this in turn increases the frictional wear of the brushes.
The problem underlying the invention is to produce a current-collecting device of the type mentioned at the beginning for small or midget commutating machines which has a long life even under a high-current load.
SUMMARY The solution of this problem resides in that the commutator consists of a silver-copper alloy comprising 85 to 95 percent silver and 15 to percent copper and that the brushes consist of a silver-palladium-copper alloy comprising 50 to 70 percent silver, 25 to 40 percent palladium and 3 to percent copper.
It is admittedly already known to increase the life of a current-collecting device by a specific choice of alloys. However, for this purpose relatively expensive alloys have been used, consisting of silver and palladium for the brushes and platinum, iridium or gold, platinum and copper for the commutators.
Preferably, the material of the brushes consists of an alloy of 63 percent silver, 32 percent palladium and 5 percent copper and the material of the commutator of an alloy of 90 percent silver and 10 percent copper. Such a current-collecting device is relatively insensitive to high-current loads of the type which can occur more particularly in commutating machines having an ironless armature.
To improve the commutating in high-speed machines the brush may be coated at least on its contact surface with a softmetal layer having a thickness of 2 to 40 microns. It is advantag'eous for the surface roughness of the commutator to be 0.3 to 6 microns and preferably 0.3 to 2 microns. Such a current-collecting device may be used with advantage in highspeed machines with a high-current load of the commutator, ensuring long life of the current-collecting device.
DETAILED DESCRIPTION The invention will be described in detail hereafter with reference to an example of embodiment.
The FIGURE shows a current-collecting or takeoff device comprising a commutator 1 having five segments 2 mounted on an insulating hub 3 which is fixedly mounted on a shaft 4 carrying the armature. Two brushes 5 engage the commutator, only one of these brushes being illustrated. The brush is provided with a thin tin coating 6.
The material used for the commutator segments 2 was an alloy of 90 percent silver and 10 percent copper and the material used for the brushes a silver-palladium-copper alloy comprising 63 percent silver, 32 percent palladium and 5 percent co er.
The rameter of the commutator was of the order 2 mm.
and each brush consisted of three individual brush leaves having a width of0.5 mm. and a thickness of 0.1 mm.
For comparison purposes a current-collecting device was made having the same dimensions as the device according to the invention but having commutator segments which consisted in known manner of an alloy of 97 percent silver and 3 percent copper and brushes of a gold-silver-copper alloy comprising 70 percent gold, 20 percent silver and 10 percent copper.
Comparative tests showed that at currents over 0.2 A. the life of the current-collecting device according to the invention was 5 to 10 times greater than the life of the known device used for comparison.
The surface of the brushes and/or the commutator segments may be coated with a thin soft-metal layer, preferably tin. This considerably reduces commutation faults of the type which arise at high speed, even over long operating times.
The current-collecting devices according to the invention may be used both for direct current and for alternating current machines.
1. In a current-collecting device for small commutating machines including a commutator member mounted on a rotor shaft and stationary brush members contacting the commutator, the improvement comprising:
a. said commutator member being formed of segments of an alloy comprising approximately to 95 percent silver and 15 to 5 percent copper, and
b. said brush members formed of an alloy comprising 50 to 70 percent silver, 25 to 40 percent palladium, and 3 to 10 percent copper.
2. A collecting device as defined in claim 1 wherein said brush alloy being approximately 63 percent silver, 32 percent palladium and 5 percent copper.
3. A collecting device as defined in claim 1 wherein said commutator segments being of approximately percent silver and 10 percent copper.
4. A collecting device as defined in claim 1 wherein the surface of at least one of said members having a coating of a layer of soft metal thereon.
5. A collecting device as defined in claim 4 wherein said metal is tin.
6. A collecting device as defined in claim 4 wherein the layer on said brush members has a thickness of approximately 2 to 4 microns.
7. A collecting device as defined in claim 1 wherein said commutator member has a surface roughness of 0.3 to 6 microns.
8. A brush for a motor comprising an alloy of approximately 50 to 70 percent silver, 25 to 40 percent palladium and 3 to 10 percent copper.
9. A brush as defined in claim 8 wherein said alloy is approximately 63 percent silver, 32 percent palladium, and 5 percent copper.
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