Introduction
In order to meet the continuous development of automobiles in the direction of energy saving and lightening, there are increasing examples of the electronicization of various parts. Therefore, not only traditional equipment such as wipers, but also power steering, fuel pumps, etc. have gradually been motorized. DC motors generally use brushes for rectification. Due to the friction between the brush and the commutator, a sharp current change results, resulting in noise and sparks. (Picture 2) This noise is transmitted to each part through the power cord, which will affect peripheral equipment. This noise has a wide frequency range depending on the number of revolutions of the motor, from hundreds of kHz to hundreds of MHz, so noise suppression measures are very necessary.
Figure 2 shows the mode of noise generated by the brush motor and the main points of countermeasures against noise. Basically, the noise includes two modes, which are the differential mode noise in the same path as the power supply current, and the common mode noise generated by the parallel conduction of the two power lines. Therefore, effective noise suppression measures must be taken for each mode. Among them, the simpler and more cost-effective countermeasures are those for capacitors. For countermeasures against differential mode noise, use a jumper capacitor (X-type capacitor) that is connected between the two lines of the power line, and for countermeasures against common mode noise, use a bypass capacitor that is connected between the two lines of the power line and ground (Y type capacitor). When only capacitors are used, if the noise cannot be completely and effectively eliminated, a common mode choke coil can be added to this, which can effectively remove the common mode noise that is difficult to solve, and can also achieve a noise suppression effect in the high-frequency field.
<Countermeasures against noise caused by motor brushes>
Sparks and noise due to friction between the brush and commutator,
The generated differential mode noise and common mode noise are characterized by a wide frequency band.
Noise countermeasures
â‘ The measures against the inside of the motor (near the source of noise) are effective.
â‘¡In addition to the use of X capacitors and Y capacitors, countermeasures against both differential mode common mode noise are effective.
Figure 2 The countermeasures for the cause of noise on the motor brush
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