【導讀】1．外文文獻翻譯的內(nèi)容應與畢業(yè)設計/論文課題相關。業(yè)學生應完成不少于2021漢字的二外文獻翻譯任務。中）并注明出處。本附件為封面，封面上不得出現(xiàn)頁碼。直流電機的特點是他們的多功用性。依靠不同的并勵、串勵和他勵勵磁繞組。伏安特性或速度轉矩特性。范圍發(fā)動機轉速或精確控制發(fā)動機的輸出量的場合。直流電機的總貌如圖所示。定子上有凸極，而且由一個或幾個勵磁線圈勵磁。氣隙磁通量以磁極中心線為軸線對稱分布。這條軸線叫做磁場軸線或直軸。旋轉的換向器和靜止的電刷，在電樞線圈出線端轉換成直流電壓。電刷的位置應使換向線圈也處于磁極中性區(qū)，即兩磁極之間。90度，這是因為元件的末端形狀構成圖示結果與換向器相連）?；プ饔玫慕Y果來表示。壓的總和，在圖中標以ae的文波表示。面有必要重新檢驗這一假設，飽和效應會深入研究。會有所下降，但在許多應用場合，這并不妨礙使用。中的變阻器在適度的范圍內(nèi)得到調(diào)節(jié)。所有勵磁的方法在電動機上同樣適用。

　　

【正文】 niformly spaced slots into which the armature winding is fitted. A mutator, and often a fan, is also located on the machine shaft. The frame is fixed to the floor by means of a bedplate and bolts. On low power machines the frame and yoke are one and the same ponents, through which the magic flux produced by the excitation poles closes. The frame and yoke are built of cast iron or cast steel or sometimes from welded steel plates. In lowpower and controlled rectifiersupplied machines the yoke is built up of thin (～ 1mm) laminated iron sheets. The yoke is usually mounted inside a nonferromagic frame (usually made of aluminum alloys, to keep down the weight). To either side of the frame there are bolted two end shields, which contain the ball or sliding bearings. The (main)excitation poles are built from ～ 1mm iron sheets held together by riveted bolts. The poles are fixed into the frame by means of bolts. They support the windings carrying the excitation current. On the rotor side, at the end of the pole core is the socalled poleshoe that is meant to facilitate a given distribution of the magic flux through the air gap. The winding is placed inside an insulated frame mounted on the core, and secured by the poleshoe. The excitation windings are made of insulated round or rectangular conductors, and are connected either in series or in parallel. The windings are liked in such a way that the magic flux of one pole crossing the air gap is directed from the poleshoe towards the armature (North Pole), which the flux of the next pole is directed from the armature to the poleshoe (South Pole). The mutating poles, like the main poles, consist of a core ending in the poleshoe and a winding wound round the core. They are located on the symmetry (neutral) axis between two main poles, and bolted on the yoke. Commutating poles are built either of castiron or iron sheets. The windings of the mutating poles are also made from insulated round or rectangular conductors. They are connected either in series or in parallel and carry the machine39。s main current. The rotor core is built of ～ 1mm siliconalloy sheets. The sheets are insulated from one another by a thin film of varnish or by an oxide coating. Both some ～ thick. The purpose is to ensure a reduction of the eddy currents that arise in the core when it rotates inside the magic field. These currents cause energy losses that turn into heat. In solid cores, these losses could bee very high, reducing machine efficiency and producing intense heating. The rotor core consists of a few packets of metal sheet. Redial or axial cooling ducts (8～ 10mm inside) are inserted between the packets to give better cooling. Pressure is exerted to both side of the core by pressing devices foxed on to the shaft. The length of the rotor usually exceeds that of the poles by 2～ 5mm on either side－the effect being to minimize the variations in magic permeability caused by axial armature displacement. The periphery of the rotor is provided with teeth and slots into which the armature winding is inserted. The rotor winding consists either of coils wound directly in the rotor slots by means of specially designed machines or coils already formed. The winding is carefully insulated, and it secured within the slots by means of wedges made of wood or other insulating material. The winding overcharge are bent over and tied to one another with steel wire in order to resist the deformation that could be caused by the centrifugal force. The coiljunctions of the rotor winding are connected to the mutator mounted on the armature shaft. The mutator is cylinder made of small copper. Segments insulated from one another, and also from the clamping elements by a layer of minacity. The ends of the rotor coil are soldered to each segment. On lowpower machines, the mutator segments form a single unit, insulated from one another by means of a synthetic resin such as Bakelite. To link the armature winding to fixed machine terminals, a set of carbon brushes slide on the mutator surface by means of brush holders. The brushes contact the mutator segments with a constant pressure ensured by a spring and lever. Clamps mounted on the end shields support the brush holders. The brushes are connected electrically － with the oddnumbered brushes connected to one terminal of the machine and the evennumbered brushes to the other. The brushes are equally spaced round the periphery of the mutator－ the number of rows of brushes being equal to the number of excitation poles.