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原理结构
直流电动机是依靠直流工作电压运行的电动机,广泛应用于收录机、录像机、影碟机、电动剃须刀、电吹风、电子表、玩具等。   1.电磁式直流电动机 电磁式直流电动机由定子磁极、转子(电枢)、换向器(俗称整流子)、电刷、机壳、轴承等构成,   电磁式直流电动机的定子磁极(主磁极)由铁心和励磁绕组构成。根据其励磁(旧标准称为激磁)方式的不同又可分为串励直流电动机、并励直流电动机、他励直流电动机和复励直流电动机。因励磁方式不同,定子磁极磁通(由定子磁极的励磁线圈通电后产生)的规律也不同。   串励直流电动机的励磁绕组与转子绕组之间通过电刷和换向器相串联,励磁电流与电枢电流成正比,定子的磁通量随着励磁电流的增大而增大,转矩近似与电枢电流的平方成正比,转速随转矩或电流的增加而迅速下降。其起动转矩可达额定转矩的5倍以上,短时间过载转矩可达额定转矩的4倍以上,转速变化率较大,空载转速甚高(一般不允许其在空载下运行)。可通过用外用电阻器与串励绕组串联(或并联)、或将串励绕组并联换接来实现调速。   并励直流电动机的励磁绕组与转子绕组相并联,其励磁电流较恒定,起动转矩与电枢电流成正比,起动电流约为额定电流的2.5倍左右。转速则随电流及转矩的增大而略有下降,短时过载转矩为额定转矩的1.5倍。转速变化率较小,为5%~15%。可通过消弱磁场的恒功率来调速。   他励直流电动机的励磁绕组接到独立的励磁电源供电,其励磁电流也较恒定,起动转矩与电枢电流成正比。转速变化也为5%~15%。可以通过消弱磁场恒功率来提高转速或通过降低转子绕组的电压来使转速降低。   复励直流电动机的定子磁极上除有并励绕组外,还装有与转子绕组串联的串励绕组(其匝数较少)。串联绕组产生磁通的方向与主绕组的磁通方向相同,起动转矩约为额定转矩的4倍左右,短时间过载转矩为额定转矩的3.5倍左右。转速变化率为25%~30%(与串联绕组有关)。转速可通过消弱磁场强度来调整。   换向器的换向片使用银铜、镉铜等合金材料,用高强度塑料模压成。电刷与换向器滑动接触,为转子绕组提供电枢电流。电磁式直流电动机的电刷一般采用金属石墨电刷或电化石墨电刷。转子的铁心采用硅钢片叠压而成,一般为12槽,内嵌12组电枢绕组,各绕组间串联接后,再分别与12片换向片连接。The DC motor is to rely on the DC working voltage to run the motor, widely used in tape recorders, VCRs, DVD players, electric shavers, hair dryer, electronic watches, toys. A. Electromagnetic DC motor electromagnetic DC motor stator poles, rotor (armature), the commutator (commonly called the commutator), brush, chassis, bearings, etc., and electromagnetic DC motor stator poles (poles) from the core and of the field winding. According to their mode of excitation (the old standard called excitation) can be divided into a series excited DC motor, and excited DC motor, excited DC motor and re-excited DC motor. Excitation mode, the stator pole flux (generated by the stator magnetic poles of the exciter coil is energized), the law is also different. Series excited DC motor field winding and rotor winding in series between brushes and commutator, the excitation current and the armature current is proportional to the stator flux is increasing with the increase of the excitation current, torque approximation and the electric proportional to the square of the armature current, speed rapidly decreased with the increase in torque or current. More than four times the short time overload torque up to more than five times its starting torque up to rated torque, rated torque, the speed rate of change of the high-load speed (usually not allowed to run under no-load ). Can be achieved by topical resistor and series excited winding in series (or parallel), or the series excited windings in parallel for access to the governor. Shunt DC motor field winding and rotor winding connected in parallel, the excitation current is relatively constant, the starting torque is proportional to the armature current, starting current is approximately 2.5 times the rated current. Speed ​​with increasing current and torque, while a slight decrease, 1.5 times the short-time overload torque is rated torque. Speed ​​the rate of change is small, 5% to 15%. May weaken the magnetic field of constant power speed. Excited DC motor field winding received independent of the excitation power supply, the excitation current is relatively constant, the starting torque is proportional to the armature current. The speed changes from 5% to 15%. Can weaken the magnetic field of constant power to increase the speed or the speed is reduced by reducing the voltage of the rotor winding. Compound excited DC motor on the stator magnetic pole shunt winding, but also equipped with a winding up petition (the number of turns less) in series with the rotor winding. The series winding produces magnetic flux direction of the main winding flux in the same direction, the starting torque is approximately four times the rated torque, the short time overload torque is about 3.5 times the rated torque. Speed ​​change rate of 25% to 30% (series winding). Speed ​​can be adjusted by weakening the magnetic field strength. Commutator commutator segment using silver copper, cadmium, copper and other alloys, molded high-strength plastic. Brush and commutator sliding contact with the rotor windings of the armature current. Electromagnetic DC motor brushes commonly used metal graphite brush or electric graphite brush. Silicon steel laminated from the rotor core, usually a 12-slot, embedded 12 armature windings, each winding connected in series, and then with 12 commutator segment connection.
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