Koichiro Sawa

The Effect of Various Atmospheric Temperature on the Contact Resistance of Sliding Contact on Silver Coating Slip Ring and Silver Graphite Brush

The performance and reliability of electric motors, electric devices and electrical connections depend on the quality of their materials. One suitable material that is used in the electrical field is silver, because of its high electrical and thermal conductivities. Laboratory studies were made of the effect of temperature changes on a silver coated slip ring and silver graphite brushes. Over the past months, a study have been made on sliding contact using copper ring and natural graphite brush, as compare the copper ring and natural graphite brush, and silver coating ring and silver graphite brush. The contact voltage drop of the copper ring and natural graphite brush increased with the sliding time. However, the contact voltage drop of the silver coated ring and silver graphite brush had little change. In this study we focused on the contact voltage drop, surface film and brush wear at low temperature range -15 to 0 ¿Z under using silver material. The main rule of low current sliding contact should combine high wear resistance, low friction with stable contact voltage drop. To meet this requirement we realized that at 70 wt% silver brush, we could reach to this requirement.

Influence of nickel content on various characteristics of AgNi contacts for electromagnetic contactors

The silver nickel contact material is widely used as contacts of the electromagnetic contactor. Experiments have been carried out to clarify the influence of nickel content on various characteristics, such as arc duration, contact resistance, arc energy and electrode mass change. There are six kinds of contacts used, that is, Ag, AgNi5%, AgNi0% AgNi15% AgNi20% and AgNi30% The source voltages are DC-100V, load current is set to 5A constant, and an electromagnetic contactor is operated continuously up to 100,000 times by generating only break arc. Consequently, it can be made clear that arc duration is almost the same, about 3.2ms at all nickel content. However, the contact resistance becomes larger as the nickel content increased. Further, the relation between electrode mass change and arc energy is experimentally obtained. The cathode loss per unit arc energy is minimized when the content of nickel is 20%, it is about 0.08μg/J. On the other hand, the maximum of the cathode loss per arc energy is 0.14μg/J at the nickel content of 5%.

Influence of Arc Discharge on Carbon Commutator and Brush Wear in DC Motor Driving Fuel Pump

A small DC motor is used to drive an automotive fuel pump. In the DC motor the commutation arc causes a high rate of wear of brush and commutator. Therefore, it is important how the commutation arc influences the erosion and wear of commutator and brush in various fuels. The wear of commutator and brush is caused by both mechanical sliding action and arc discharge. To evaluate the wear of commutator and brush, mechanical wear and arc erosion have to be separated respectively. In this paper, to examine the erosion only by arc a switching device system is developed and the arc discharge almost equivalent to the commutation arc is realized by it. Using this system the mass change of carbon contacts is examined in air, gasoline, ethanol and methanol to evaluate the arc erosion of commutator and brush. Tests with switching operation of 30,000 times are carried out in various fuels, and after the tests the mass loss is evaluated by a 3D laser microscope. Consequently, it can be made clear that mass loss per unit arc energy is a little bit larger in ethanol and methanol than in air and gasoline, but it is around 0.92 μm3/μJ for the cathode. In addition the mass change of the anode is also loss and the loss per arc energy is smaller than that of the cathode. Further, the mass loss per arc energy is somewhat dependent on the circuit inductance.

Fluctuation components of contact voltage at AgPd brush and Au-plated slip-ring system with lubricant

The authors have investigated the deterioration process of the system of Au-plated slip-rings mating with AgPd brushes, which is used mainly in chip-mounters. Past tests have shown that the lubricant is very important for obtaining long lifetime. The lubricant can not only decrease ring wear but also protect the ring from oxidation. In operation the contact voltage drop is generally low and stable at the beginnings of tests and increases with the operation time. In this paper the fluctuation characteristics are observed in detail and the following characteristics are observed. The contact voltage fluctuation increases with the operation time while the fluctuation pattern is different at each ring. The minimum value of the contact voltage waveform stays almost constant around 20mV. The maximum value can become as high as 180mV on some rings. However, the surface morphology of rings with high peak values is almost the same as those with low peak value. Further, the peak value is greatly dependent on rotational speed. The peak value approaches the minimum value at low speeds. From these results it is deduced that the contact voltage increase is controlled by the lubricant thickness between brush and ring and not from ring surface itself. This indicates that tunnel effect resistance is important. The relationship between peak value and lifetime is discussed.

Influence of opening velocity on various characteristics in DC high voltage Ag break arc

Recently, the demand to interrupt high DC voltage and current with electrical contacts has risen because of photovoltaic and electric vehicles (EV) applications. We produced the separating device that is able to open electrical contacts by the constant speed (1~200mm/s). The experiments had set the closed contact current to 10A constant under the source voltage DC200, 300, and 500V respectively. The arc voltage and current waveforms were observed. In addition, the video of the arc discharge light was recorded. To evaluate various characteristics of Ag break arc, arc duration time, contacts gap length, arc length and arc energy etc. were measured. As a result, it has been understood that the arc duration is in inverse proportion to opening velocity. This was similar to past research results. Further, arc energy is inversely proportional to opening velocity.

Effect of lubricant on sliding conditions in Au-plated slip-ring system for small electric power transfer

The authors have been investigating the sliding quality and the deterioration process of the system of Au plated slip-ring and Ag-Pd brush, which is used mainly in the chip-mounter, to realize stable long life time. Through the past tests, it can be made clear that lubricant is very important for long lifetime, because it can not only make ring wear decrease, but also protect the ring from oxidation. In this paper deterioration process of ring and brush is examined in details, and the followings can be obtained. Usually contact voltage drops have fluctuation. The fluctuation is found to be two types; one is a component which is dependent on rotation speed and the other comes from surface deterioration, such as oxidation. The details are investigated by using Fourier analysis of contact voltage waveforms. Generally, during the test the contact resistance of a ring increases suddenly and the ring reaches end of life, mainly because the lubricant disappears from the contact surface. In this test a temporary decrease of the contact resistance is observed just before the sudden increase of resistance. Further, a supply of lubricant to the ring which became high in resistance, is found to be useful to decrease its resistance. In addition Fourier transform is carried out on the contact voltage waveforms.

Erosion by Arc Discharge at Carbon Contacts in Various Automotive Fuels

A small DC motor is used to drive an automotive fuel pump. It is one of its features that brush and commutator work in gasoline or other fuels. In the DC motor the commutation arc causes a high rate of wear of brush and commutator. Therefore, it is important how the commutation arc influences the erosion and wear of commutator and brush in various fuels. The wear of commutator and brush is caused by both mechanical sliding action and arc discharge. In the previous paper, a switching device system was developed to realize the arc discharge almost equivalent to the commutation arc. Using this system the mass change of carbon contacts was examined in air, gasoline, ethanol and methanol to evaluate the arc erosion of commutator and brush. In this paper the arc erosion is examined in Butanol and MTBE besides fuels of the previous paper by the switching device. Further, based on the previous and present results the lifetime is predicted and compared with the experimental results of the commutation tests. Consequently, the predicted lifetimes are generally shorter than the experimental ones. The reason is guessed as follows; mechanical wear takes place together with arc erosion. Then, arc-eroded part is sometimes changed again to sliding surface. A model is discussed.

Effects of lubricant oil on sliding contact phenomena in carbon brush-slip ring system

Sliding contact systems are widely used as a method of exchanging electrical power and/or signal between static and moving components. Considerable challenges remain regarding the need for improving the service life and reliability of these systems. The sliding characteristics of C-brushes and Cu-rings have been thoroughly investigated; however, lubricated C-brush and Cu- sliding contact systems have received comparatively little attention. In this work lubricants are shown to influence contact resistance of slip ring-brush system.

Commutation characteristics and brush wear of DC motor at high rotation speed

Many small-size DC commutator motors are still widely used in automobiles and other applications. In recent years, DC motors have been driven at high speed to realize small size and high-power. However, as is well-known, the commutation becomes difficult at higher speed and brush wear/erosion increases due to the commutation arc. Therefore, it is important to understand how the motor speed influences commutation phenomena, including arc duration and residual current, so the correct motor can be selected for the particular application to achieve the required reliability. In this paper as the rotation speed is changed from 1000 to 5000min−1, the influence of the speed on commutation characteristics is investigated, such as effective commutation period, arc duration and others. In addition, it is also examined how the rotation speed affects brush wear/erosion. Consequently the followings can be made clear. The effective commutation period decreases in inverse proportion to the rotation speed, while the arc duration and residual current are almost constant, around 42μsec and 0.55A respectively up to 3000min−1. When the rotation speed increased to 3000 and 5000min−1, brush wear/erosion is found to increase rapidly. This indicates that as arc erosion increases the mechanical wear also becomes larger due to the effect of arc discharge. Based on experimental results, a model including the effect of the rotation speed is proposed for brush wear/erosion.

Influence of contact materials and opening velocity on various characteristics of DC high voltage arc

In this study, we use a apparatus that can be opened at constant speed. The voltage is set to DC 200, 300, and 500 V. The closed contact current is set to constant at 10 A at each voltage. The opening velocity is varied in the range of 1 to 200 mm/s. The contact material is Pd and Pt with low thermal conductivity. The arc duration is obtained from the voltage· current waveforms of the arc discharge, and the arc energy is obtained from the electric power waveform. In addition, arc length and contacts gap length at the time of arc extinction is obtained from the video analysis of the arc discharge light. As a result, it became clear that the arc duration and the arc energy are inversely proportional to the opening speed. These results were similar to that of Ag, W, Ni, and Cu, and the difference due to the contact material was small. The arc length immediately before the arc extinguishment became a constant value determined by the source voltage independent of the contact material and opening velocity. The value was about 30 mm at 200 V, about 60 mm at 300 V and about 110 mm at 500 V.