Ryoichi Honbo

Development of the lead-free brush material for the high-load starter

Carbon brushes for automotive starters are used under severe conditions of high electrical current density, high contact pressure and high sliding velocity. Lead has traditionally been added to carbon brushes to improve their performance and durability. Because lead is an environmental hazardous substance, after January 2005 the EU has prohibited adding lead to carbon brushes for electric motors installed in new vehicles. This paper reports the development of the lead-free brush material for the high-load starter. Those brushes are used in much more extreme conditions - at a PV-value (the product of brush contact pressure and sliding velocity) approximately three times that of other starter brushes, and double the electrical current density. The major technical requirement of this development was to decrease the electrical wear in brushes caused by commutation sparking. We developed the brush material that reduces electrical wear by adding a phosphorous compound. Because the phosphorous compound can improve the lubricity at high-temperature and the contact stability of brushes, the developed brush reduces commutation sparks. The life of the developed brush is about 1.5 times longer than that of conventional brushes containing lead.

Characteristics of arc-reducing effect by capacitor in commutation circuit

DC motors are indispensable to improve the automotive functions. Recently, 70-100 motors are installed on luxury cars and this number is increasing year by year. With the recent demand for improved fuel economy and better equipment layout, the improvement of the motors efficiency and the minimization of the motor size are the key to enhancing the competitive edge of the products. Adopting the high-density coil is an effective method for that, but it is accompanied by the commutation inductance rise which causes the commutation arc increase. The increase of commutation arc decreases motor life, because it causes the rise of brush/commutator wear. This report describes an arc-reducing effect obtained when capacitors are built into a commutation circuit for the purpose of reducing arcing under high commutation inductance conditions. The results of an evaluation using a equivalent commutation circuit and carbon brush/carbon flat-commutator showed that although a commutation circuit with built-in capacitor generated the same arc energy as a commutation circuit without a capacitor above a certain value of residual current, it displayed an excellent arc-reducing effect below that value of residual current.

The Development of the Lead Free Carbon Brush for Starters

Carbon brushes for automotive starters are used under severe conditions of high electric current density, high contact pressure and high sliding velocity. Therefore lead has traditionally been added to brushes to improve performance and durability. Lead is an environmental hazardous substance. In the EU, the law prohibits adding lead to brushes for electric motors which is installed on new automobiles in and after January 2005. In order to develop the lead free carbon brush for starters, we analyzed the effect and selected substitutive substance of lead. Adding lead to the brush reduces the electric resistance increase of the brush in high-temperature and high-humidity atmosphere and in high-temperature atmosphere. Furthermore lead reduces the wear amount of brush. We developed the lead free brush surpassing the lead addition brush in performance and durability by addition of lead alternatives silver and zinc.

Development of the Lead-Free Carbon Brush Material for Starters

Carbon brushes for starters are used under severe conditions of high electric current density, high contact pressure and high sliding velocity. Lead has traditionally been added to carbon brushes to improve their performance and durability. Because lead is an environmentally hazardous substance, after January 2005 the EU will prohibit adding lead to carbon brushes for electric motors installed in vehicles. The purpose of our current study is to develop materials of lead-free carbon brushes for starters. Analyzing the effects of adding lead has shown that lead inhibits the brush resistance from increasing under high temperatures, or a combination of both high temperature and high humidity. This is because corrosion of lead precedes that of copper, which is one of the materials comprising the brush, and this prevents the copper from corroding. Moreover, lead functions as a solid lubricant and reduces brush wear. We developed the leadfree brush material, by adding soft metallic substances that corrode prior to copper and are also oxidation-resistant, as well as possessing low hardness and solid lubricant properties. The developed lead-free brush surpasses the conventional lead-added brush in durability and permanence. key words: carbon brush, lead free, starter, wear, corrosion