Lesson 15

I. Read and memorize the following words and word-combinations:

II. Read and translate the following text: Direct current generators and their applicatios

The essential difference between a d. c. generator and a. c. generator is that the former has a commutator by means of which the generated e. m. f. is made continuous, i. e., the com­mutator mechanically rectifies the alternating e. m. f. so that it is always of the same polarity. This is not, however, the only difference between them. A d. c. generator as well as a motor of conventional type is made up of the following parts: outer frame, or yoke, pole cores, pole coils, armature core, armature windings, commu­tator, brushes, and bearings. Of these, the yoke, pole cores, ar­mature core and the air gap between armature and pole core form the magnetic circuit while the pole coils, armature win­ dings, commutator, and brushes form the electric circuit. Generator fields may be either of two main types — sepa­rately excited or self-excited. The self-excited type is further, classfied as series-wound, shunt-wound and compound-wound. In general practice compound-wound machines are used.

Industrial application of d. C. Generators

D. C. generators are used for electrolytic processes such as electroplating. We know that large d. c. generators art employed in certain manufacturing processes, such as steel making. The d. c. generator of small capacities is used for various special purposes such as arc welding, automobile generators, train lighting systems, etc. It also finds rather extensive use in connection with communication systems. For supplying direct-current power networks, the supply comes first from an alternating-current source and is convert­ed to direct current by synchronous converters or motor-ge­nerator sets.

The compound motor

The features of the shunt and series type of motors may be combined in one machine by providing both series and shunt-windings for the field. This arrangement gives the compound motor. There are two windings on each field pole; a heavy or series winding for carrying the armature current, and a shunt winding connected to the supply. Each winding is formed by the series connection of the corresponding coils, and the fields due to the respective windings aid each other. Speed control of a compound motor may be obtained by means of resistance in the field or armature circuit, as in the case of the shunt motor. The compound motor may be regarded as having a higher starting torque than a shunt motor and a more constant speed under changing load conditions than the series motor. Either feature may be emphasized by varying the proportion of the total field strength due to each winding.

Lesson 16

I. Read and memorize the following words and word-combinations:

II. Read and translate the following text: c arburettor Engine- карбюраторний двигун

1 — fan belt ремінь вентилятора; 2 — generator генератор; 3 — fan вентилятор; 4 — piston pin поршневий палець; 5 — small end of connecting rod верхня головка шатуна; 6 — water jacket водяна рубашка; 7 — spark plug свічка запалювання; 8 — cylinder циліндр; 9 — piston поршень; 10 — poppet-valve тарільчатий клапан; 11 — exhaust manifold вихлопний збірник; 12 — inlet manifold всмоктуючий коллектор; 13 — flywheel маховик; 14 — main bearing ко­рінний підшипник; 15 — oil pan піддон картера; 16 — crankshaft колінчатий вал; 17 — camshaft розпредільний вал; 18 — cam кулачок; 19 — tappet толкатель; 20 — big end of connecting rod нижня головка шатуна; 21 — main bearing корінний підшипник; 22 — journal корінна шийка (вала)

The small end of the connecting rod is rotatably con­nected to the piston by the piston pin. The big end of the connecting rod is also rotatably connected with the crank­shaft. The flywheel is located on the rear end of the crank­shaft. It is equipped with a toothed rim for meshing with the starter pinion. Piston with piston pin, connecting rod and crankshaft with flywheel are called crank-drive as­sembly.

Inlet of the fuel-air mixture into the cylinder and out­let of the burned gases are controlled by valves. The valves are actuated by the camshaft generally supported in the crankcase. Valves, camshaft and camshaft drive are forming the control mechanism of the engine.

The crankcase bottom is closed by the oil pan holding the oil required for lubrication. The oil pan is connected to the crankcase.

The liquid fuel is mixed with air and vaporized in the carburettor. This fuel-air mixture enters cylinder and com­bustion chamber. Inside the combustion chamber, the fuel-air mixture is ignited and burned by a spark jumping at the electrodes of a spark plug.

The generator is located at and driven by the engine. When the engine is running at sufficient speed, the gene­rator supplies the ignition current and charges the sto­rage battery.

The starting motor is a small electric motor. When it is actuated, a driving pinion is shifted and meshes with the toothed rim of the flywheel. Thus the crank-drive as­sembly begins cranking (working).