汽车启动机电刷的特性

Characteristics of Automotive Starter Brush

汽车启动机电刷具有短时工作制、电流密度大及接触压降小的特点。适合启动机用的电刷是金属石墨电刷,由于其含铜量为75％～85％,电阻小,允许的电流密度大,故适用于低电压、大电流的汽车启动机。启动机电刷的动态特性包括电刷的接触压降、换向器与电刷间的摩擦系数、电刷的磨损情况以及施加于电刷上的压力;启动机电刷的静态特性包括密度、电气特性、机械特性、热膨胀系数、化学特性,其中影响运行效果的主要指标有电刷的电阻系数、硬度、刷体与刷辫间的接触电阻及电刷刷辫脱开刷体的拉力等。

Describing the specialities of the starting motor brushes are of short-time duty system , big current density and the contact voltage drop must be as small as possible. They are made of metallic carbon. The copper content is 75%~ 85%. Due to low resistance and the current density allowable is so big that they are used for starters of low voltage and big current. This paper has also analyzed the brush dynamic and static characteristics. The former includes contact voltage drop, the frictonal coefficient between the commutator and the brush, brush wear as well as the pressure applied on the brush, etc. The static includes the specific gravity, electrical, mechanical and chemical properties, thermal expansion coefficient. Among these,the following items are critical-electrical resistancce coefficient,hardness contact resistance coefficient between the brush body and the tail, and the pull strength of the tail apart from the body.