ES2299017T3 - BRUSHES FOR ELECTRIC MOTORS THAT OPERATE AT HIGH TEMPERATURE. - Google Patents

Abstract

The unit has copper particles obtained from a mixture of electrolytic copper, atomized copper and crushed copper, and a mixture of natural graphite, organic binder e.g. bakelite resin, and molybdenum disulphide. The weight percent of the copper particles is comprised between 20 and 60 percentage. Additional metal e.g. zinc carbonate, is added with material in the form of metallic particles. Independent claims are also included for the following: (A) a fabricating method of a sliding contact unit (B) a fabricating method of an electric motor operating under low voltage.

Description

Brushes for electric motors that work at high temperature

Technical scope

The invention relates to brushes for electric motors, more particularly those that are used to operate the equipment mounted on board cars (motor fans (autonomous fans fixed directly on the radiator) and other fans, alternators, auxiliary engines, etc.), for which it is intended to achieve performance high.

State of the art

Electric motors of this type work at Low voltage with high current. Due to this current high, the brushes that equip these motors must ensure a high temperature electrical friction contact, typically higher than 100ºC, even higher than 200ºC, with a current density greater than 15 A / cm2. The conditions of operation of the electric motors referred to in the Inventions are totally different from those of starters.

The starters, which are not subject to this invention, are intended to work about a hundred thousand times during a few milliseconds with current densities greater than 500 A / cm2. The application US2003 / 0135993 describes brushes adapted for conditions of operation of this type. They are certainly subject to some violent solicitations but they work very little in accumulated time and because of this they get very hot during the short period in which they work.

On the contrary, engines such as can be the motor fans, placed under the engine covers of the vehicles, subjected to increasingly high temperatures, they work continuously, that is, while the thermal engine They work with lower current densities, typically below 50 A / cm2, but are subject to a warming by Joule effect and should work at about high temperatures, above 100ºC, even higher than 200ºC during the operating time of a motor vehicle, this is a few thousand hours, typically more than 2,000 hours

The operating conditions more and more severe imposed on these brushes require an adaptation of these latest not only to resist new solicitations but also to increase their life time.

Brushes for electric motors from equipment mounted on board cars (motor fans,  alternators, fans, etc.) are usually constituted by a mixture of copper particles and particles of graphoid

Copper particles can come from diverse origins: electrolytic copper (copper obtained by electrolytic deposit in a cathode, the anode being pure copper, the electrolyte being typically a mixture of copper sulfate, of sulfuric acid and additives), atomized copper (molten copper dispersed in the form of fine drops under the effect of a jet violent gaseous or liquid) or crushed copper (atomized copper crushed which comes in the form of thin sheets).

Graphoids include various graphites, so general natural graphites, and organic binders. Mix like this constituted is hot treated and then crushed to obtain grafoid particles.

To these bases (copper particles + graphoid), abrasive conductors are usually added, typically carbides - for example silicon carbide, or cokes, and lubricants solids, typically molybdenum bisulfide (MoS2). The nature and weight content of each of these constituents are adjusted based on the application pursued. The material resulting from the mixture generally has a electrical resistivity that should not degrade over time with the so that the expected performance of the engines is not lost electrical devices of this type (see document US-A-2003/0135993).

However, when the engine is running at high temperatures, for example in motor fans, in which the ambient temperature is often higher than 100 ° C in the course of its operation, the brush is brought to temperatures that can reach, even exceed 200 ° C, and there is a strong increase in the resistivity of the material and a pronounced oxidation of copper. These probably interdependent phenomena can cause accelerated brush wear and loss of performance or speed of the brush.
engine.

Posed problem

Therefore, the applicant has developed a method to obtain an electric motor brush material that has improved wear resistance when the motor runs at a temperature above 100ºC, typically close to 150ºC, while allowing the provision of said engine is substantially constant throughout its lifetime. The accumulated operating time of the motors involved can range from a few hours (window lifters, windshield wipers) and more than 2,000 hours (motoventila-
dores).

Object of the invention

A first object of the invention is a piece of sliding contact that transmits an electric current of high density, typically greater than 15 A / cm2 e less than 50 A / cm2, which comprises copper particles, graphoid particles, coming from the crushing of a mixture of graphite particles, preferably natural graphite, and of organic binders, characterized in that, to transmit said current for at least 2,000 hours at a temperature above 100 ° C, typically close to 150 ° C, said part of contact includes copper particles whose percentage by weight it is between 20% and 60% and also some particles comprising, in the form of metal or compound of said metal, a additional metal belonging to the group consisting of the elements following: zinc, manganese and tin.

The sliding contact piece suitable for transmitting an electric current is a friction element current conductor, such as a motor brush electric. The current density transmitted through the contact may be greater than 15 A / cm2. The application contemplated corresponds to small electric motors mounted on a car such as motor fans, fans, alternators, etc. that work with a current whose intensity, typically less than 50 A / cm2, it is less than it is necessary to operate a starter, typically superior at 100 A / cm2. However, the average density value of the current that feeds these motors constantly increases to meet the increasing demands of power, having been this less than the kilowatt so far. Motors of this type they must be fed without interruption, which is translated by a increasingly high operating temperature.

Typically, the conditions used for test the strength capacity of materials constitutive of the brushes for electric motors are the following: the brush must transmit for 2,000 hours a current density of 25 A / cm2, the temperature being engine environment close to 150ºC.

According to the invention, preferably a quite high copper weight content, typically of the order 30%, between 20% and 60%, preferably between 20% and 30%. The resulting material of the mixture has therefore general low electrical resistivity (AG resistivity or "against grain", that is in the direction perpendicular to the larger grain size), greater than 200 µm \ Omegacm (2 10-6 \ Omegam) but that should typically be less than 10,000 Ome \ Omegacm (10-4 \ Omegam), preferably less than 5,000 µm \ Omegacm (5 10-5 \ Omegam), after 2,000 hours of use at 150ºC.

Copper particles can be obtained by mixing particles of various origins (electrolytic copper, atomized copper, crushed copper) and that have an apparent density typically between 0.3 g / cm 3 and 4 g / cm 3. Preferably, copper is used electrolytic, with an apparent density between 0.6 and 0.9 g / cm3 or a mixture of electrolytic copper particles (from 65% to 100% weight) and crushed copper (bulk density) between 0.9 and 1.2 g / cm3) (from 0% to 35% by weight).

The graphoids preferably include graphites natural and organic binders, preferably of type phenolic or based on polyamides or polyethylene Terephthalate Solid lubricant can be included, typically molybdenum bisulfide in the composition of the graphoid.

A copper + grafoid mixture is added to the conductive abrasive, preferably a mixture of coke and carbide  of silicon and an additional metal belonging to the group constituted by metals and alloys based on zinc, manganese or tin.

Said additional metal is added in the material in form of metallic particles or in the form of a compound of said metal, preferably unstable at the cooking temperature of the mixture. Thus, an oxide, an carbonate or sulfate. The weight content of said metal additionally it is advantageously between 0.1% and 20%, preferably between 0.5 and 10%. The applicant has been able to observe in effect that, by its presence, said additional metal allowed, by limiting the oxidation of copper, to delay the degradation of the brush.

Another object of the invention is a process. of manufacturing a sliding contact piece suitable for transmit an electric current of a high density, typically greater than 15 A / cm2 and less than 50 A / cm2, comprising copper particles and graphoid particles, coming from the crushing of a mixture of particles of graphites and organic binders, characterized in that:

a) a mixture of copper particles is made, of graphoid particles and particles comprising, in the form of metal or compound of said metal, an additional metal that belongs to the group consisting of the following elements: zinc, manganese and tin, the percentage of particle weight being of copper between 20% and 60%, the percentage being weight of grafoid particles between 45% and a 75%, and the percentage of weight of the additional metal or its compound between 0.5% and 20%.

b) the particles thus mixed are brought to a cooking temperature between 250ºC and 700ºC, preferably between 250 ° C and 450 ° C, typically at a temperature close to 400 ° C, for a time between 0.5 and 10 hours, typically close to 4 hours, in a gaseous atmosphere reducing, which comprises between 5% and 50% hydrogen, being the nitrogen complement or a neutral gas, typically a mixture that It comprises 40% hydrogen and 60% nitrogen.

The graphoid results in turn from the mixture of graphite, preferably natural, of organic binder, preferably phenolic, typically a bakelite resin, and of solid lubricant, typically molybdenum bisulfide, having mixing the assembly preferably by kneading in the middle wet, then the solvent evaporated and crushed and sifting the powder to obtain a particle size corresponding to a sieve less than 630 µm, preferably between 90 and 355 µm.

It can also be added to the mixture before firing a conductive abrasive such as a carbide mixture of silicon and coke, in a proportion of weight included typically between 0.05% and 1%.

The mixture thus obtained is brought to a cooking temperature between 250ºC and 700ºC, preferably between 250 ° C and 450 ° C, typically, with a range of a dozen degrees in more or less, at a temperature close to 400 ° C, for a time between 0.5 and 10 hours, typically close to 4 hours, in a gaseous reducing atmosphere, comprising between 5% and 50% hydrogen and as a complement nitrogen or neutral gas, typically a mixture of 40% of hydrogen and 60% nitrogen.

Another object of the invention is the use of a sliding contact piece comprising copper particles, graphoid particles, the weight percentage of the copper particles between 20% and 60%, including also said contact piece particles comprising, in the form of metal or compound of said metal, an additional metal that belongs to the group consisting of the following elements: zinc, manganese and tin, characterized in that said piece is used as brush of a direct current electric motor to equip a motor vehicle - such as a motor fan, a motor window lifter, a windshield wiper motor or an alternator- and that operates at a lower electrical voltage or equal to 60 volts, said piece transmitting a current electrical density greater than 15 A / cm2 and less than 50 A / cm2 and being adapted to transmit said current for 2,000 hours at an ambient temperature exceeding 100 ° C, typically close to 150 ° C.

Another object of the invention is a process. of manufacturing a collector electric motor, typically a DC motor, which includes

a) the realization of a housing in which it is fixed an inductor,

b) the realization of an armature coupled to a collector that rotates around an axis, including the induced ones conductive wires attached to the thinner of said collector

c) the inductor and armature assembly Y

d) fixing on an element coupled to the housing of sliding electrical contacts, suitable for being connected to a power supply at a voltage less than or equal to 60 volts, the electrical contacts being sliders, to electrically connect the windings of the induced, applied against the surface of the collector, so that, during rotor rotation, they are successively contacted with each of the collector's thinner,

characterized in that, for said engine to run for at least 2,000 hours with an ambient temperature exceeding 100 ° C, typically close to 150 ° C, and with a current density between 15 A / cm 2 and 50 A / cm 2, sliding electrical contacts comprising copper particles are used, whose weight ratio is between 20% and 60%, graphoid particles, coming from the crushing of a mixture of graphite particles and organic binders , and particles comprising, in the form of metal or compound of said metal, a metal belonging to the group consisting of the following elements: zinc, manganese and
tin.

The examples provided below they present some nuances elaborated within the framework of the invention and illustrate the suitability of brushes obtained from these nuances to better resist wear and oxidation.

Figures

Figure 1a illustrates a micrograph of a brush made with a material outside the scope of the invention that It has operated at 150 ° C for 620 hours: the copper particles They appear considerably oxidized. Figure 1b represents a scheme of the areas observed in the micrograph of the figure 1st.

Figure 2a illustrates a micrograph of a brush made with a material similar to the material of figure 1 but to which some additional metal particles have been added according to the invention. Figure 2b represents an outline of the zones observed in the micrograph of figure 2a. The brush has also operated at 150 ° C for 620 hours: the particles of Copper does not appear particularly oxidized.

Figure 3 illustrates, by grouping in the same graph of the measurement results, the evolution in the course of time of the electrical resistivity AG of Various brush materials.

Examples Example 1 Observation of the oxidation of copper with two shades, one without zinc, the other with 2% zinc carbonate (Figures 1 and 2)

We have produced a powder (hue X1) that contains

?

34% copper weight (mixture of electrolytic copper with low bulk density and copper crushed),

?

2% carbonate zinc,

?

2% molybdenum bisulfide MoS2,

?

0.4% abrasive (mixture of coke and silicon carbide)

?

and 61.6% of graphoid.

The graphoid constitutes a pre-mixed. It comprises 86% natural graphite, 5% MoS2 and 9% of bakelite resin After kneading in wet medium, the solvent is evaporated and the powder crushed and sifted in order to have a particle size between 90 and 355 µm.

To be able to compare with a nuance outside the frame of the invention, we have developed the X2 hue with the same components as mentioned above, present with the same amounts in the mixture, except for zinc carbonate. This Hue X2 corresponds to the hue usually proposed by the Applicant for motor motors before this invention.

Afterwards, brushes were made with the two shades X1 and X2, cooked at 400 ° C with 40% H2 and 60% N2

A test of resistance at 150 ° C, with 25 A / cm 2, for 620 hours with two series of brushes (hue X1 and hue X2). Two micrographs Representatives have been extracted in each of the games. They are illustrated in Figures 1a and 2a. You can see some areas 10 and 10 'occupied by more or less oxidized copper particles and some zones 20 occupied by graphoid particles, which comprise their once graphite particles and binders. When it's not rusty, copper comes in the form of much lighter 10 'zones that zones 20 of graphoid, while zones 10 of copper oxidized have little contrast with respect to zones 20 of graphoid Therefore you can clearly see the difference between the high  degree of oxidation of copper of hue X2 (zones 10 - figure 1a) and the low degree of oxidation of copper of hue X1 (zones 10 '- figure 2a).

Example 2 Measurement of the resistivity of brushes with different shades kept in the drying chamber at 155 ° C and 25 A / cm 2 (Figure 3)

Hue Y1 contains 48% copper and 0% of zinc.

Hue Y2 contains 52% copper and 3% of zinc carbonate

Hue Y3 contains 48% copper and 1% of zinc carbonate

Several samples related to each nuance have been subject of resistivity measurements in the course of weather.

You can see in figure 3 the influence of the addition of zinc in its carbonate form in the maintenance of a constant resistivity during the lifetime of the brush.

The resistivity AG of hue Y1, which does not contain zinc, increases very quickly over time: exceeds 10,000 µ \ Omegacm after 500 hours of operation at 155 ° C.

According to the samples, the resistivity of the hue Y3, which contains 1% zinc carbonate, does not evolve so quickly. We are at the limit of the characteristics that they are intended to be achieved within the framework of the invention since the resistivity of some samples (Y3.1 for example) results evolve too quickly, so that it is not possible ensure that the resistivity of this hue will not exceed 10,000 µm \ Omegacm after 2,000 hours at 150 ° C.

The resistivity of hue Y2, which contains 3% of zinc carbonate, is much more stable over time, which allows you not to exceed 10,000 \ mu \ Omegacm after 2,000 hours at 150 ° C.

We have then developed a Y4 hue, which it contains 50% copper and 2% zinc carbonate and we have made Some measurements on brushes made with this hue. The results obtained from the trials have responded to the expectations.

Claims (13)

1. Sliding contact piece that transmits an electric current of density between 15 A / cm2 and 50 A / cm2, which comprises copper particles, graphoid particles, from the crushing of a mixture of graphite particles, preferably natural graphite, and organic binders, characterized in that, to transmit said stream for at least 2,000 hours at a temperature greater than 100 ° C, typically close to 150 ° C, said contact piece includes copper particles whose Weight percentage is between 20% and 60% and particles comprising manganese in the form of metal or compound. 2. Sliding contact piece according to the claim 1 in which the percentage of particle weight Copper is between 20% and 30%. 3. Sliding contact piece according to claims 1 or 2 in which the copper particles are electrolytic copper particles or a mixture of copper electrolytic (from 100% to 65% by weight) and crushed copper (from 0% to 35% weight). 4. Sliding contact piece according to a any one of claims 1 to 3 in which the particles of graphoid come from the mixture of natural graphites and organic binders, typically phenolic or based on polyamides or also polyethylene terephthalate. 5. Sliding contact piece according to a any one of claims 1 to 4 comprising particles of conductive abrasive, typically a mixture of coke and carbide of silicon. 6. Sliding contact piece according to a any one of claims 1 to 5 wherein said manganese It is present in the composition with a weight concentration between 0.5% and 20%, preferably between 1% and 10% 7. Sliding contact part according to any one of claims 1 to 6 characterized in that it is an electric motor brush that operates at a voltage of less than or equal to 60 volts for at least 2,000 hours with an ambient temperature of more than 100 ° C, typically close to at 150 ° C, its electrical resistivity AG being between 200 [mu] Omegacm and 10,000 [mu] Omegacm (between 2-10-6 [Omegam] and 10-4 [Omegam]) for 2,000 hours at a temperature of 150 ° C . 8. Method of manufacturing a sliding contact piece adapted to transmit an electric current of high density, typically greater than 15 A / cm 2 and less than 50 A / cm 2, comprising copper particles and graphoid particles, coming from the crushing of a mixture of graphite particles and organic binders, characterized in that:

to)

be effect a mixture of copper particles, grafoid particles and of particles comprising manganese, in the form of metal or compound of said metal, the weight percentage of the copper particles between 20% and 60%, the weight percentage of graphoid particles between 45% and 75%, and the weight percentage of manganese or its compound between 0.5% and 20%.

b)

the particles so mixed are brought to a cooking temperature between 250 ° C and 450 ° C, typically close to 400 ° C, for a time between 0.5 and 10 hours, typically next to 4 hours, in a gaseous reducing atmosphere, which It comprises between 5% and 50% hydrogen, being the complement nitrogen or a neutral gas, typically a mixture comprising a 40% hydrogen and 60% nitrogen.

9. Procedure for manufacturing a piece of sliding contact according to claim 8, in which is added said manganese in the material in the form of metal particles or in form of a compound of said metal, preferably unstable at the cooking temperature of the mixture. 10. Procedure for manufacturing a piece of sliding contact according to claims 8 or 9, in which said graphoid results from the mixture of graphites, preferably natural, organic binder, preferably phenolic, typically a bakelite resin, and solid lubricant, typically molybdenum bisulfide, the whole having mixed preferably by kneading in a moist environment, the evaporated solvent and the powder crushed and sieved so that a sifting of less than 630 µm is obtained, preferably between 90 and 355 µm. 11. Procedure for manufacturing a piece of sliding contact according to any one of claims 8 to 10, in which a mixture is added to the mixture before cooking conductive abrasive such as a mixture of silicon carbide and coke, in a proportion of weight typically between 0.05% and 1%. 12. Engine manufacturing procedure electric collector, typically a DC motor, what includes:

to)

the realization of a housing in which a inductor,

b)

the realization of an armature coupled to a rotating manifold around an axis, including the induced some conductive wires attached to the delgas of said collector

C)

he inductor and armature assembly and

d)

the fixing, in an element coupled to the housing, of some contacts electric sliders, adapted to be connected to a source power supply at a voltage less than or equal to 60 volts, keeping the electrical contacts sliding applied on the surface of the collector, so that, during Rotation of the rotor, are successively contacted with each of the collector's delgas,

characterized in that, for said motor to run for at least 2,000 hours with an ambient temperature exceeding 100 ° C, typically close to 150 ° C, and with a current density between 15 A / cm 2 and 50 A / cm 2 2}, sliding electrical contacts comprising copper particles are used, whose weight ratio is between 20% and 60%, graphoid particles, coming from the crushing of a mixture of graphite particles and organic binders, and particles comprising manganese in the form of metal or compound. 13. Use of a sliding contact piece comprising copper particles, graphoid particles, the percentage of weight of the copper particles being between 20% and 60%, said contact piece including particles comprising, in form of metal or compound of said metal, an additional metal which is manganese, characterized in that said piece is used as a brush of a direct current electric motor that operates at an electrical voltage of less than or equal to 60 volts, said piece transmitting a current electrical of a density greater than 15 A / cm 2 and less than 50 A / cm 2 and being adapted to transmit said current for 2,000 hours at an ambient temperature greater than 100 ° C, typically close to 150 ° C.