Читать практическое задание по английскому: "Строение и работа двигателя" Страница 2

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Thus for initial starting with a cold engine a very rich mixture of about 9 pounds of air to 1 pound of gasoline is needed. After the engine has warmed up, it will run satisfactorily on a leaner mixture of about 15 pounds of air for each pound of gasoline. For acceleration and full-load, the mixture must again be enriched.

The fuel system consists of a tank in which the liquid gasoline is stored, a fuel line, or tube, through which the gasoline can be brought from the tank to the engine, a pump, which pulls the gasoline through the fuel line, and a carburetor, which mixes the gasoline with air.

Fuel Pump. The fuel pump consists of a rocker arm, a flexible diaphragm, and two valves. The rocker arm rests against a cam on the camshaft so that rotation of the shaft makes the arm rock. This rocking motion causes the diaphragm to fluctuate up and down, alternately creating pressure and vacuum in the pump chamber. When vacuum is created, the inlet valve is lifted off its seat, allowing gasoline to be drawn from the fuel tank, through the fuel line, and into the pump chamber. On the return stroke the diaphragm creates pressure in the pump chamber. This causes the inlet valve to close and the outlet valve to open, forcing gasoline from the pump chamber through a fuel line to the carburetor.

Fuel Tank. The fuel tank, normally located at the rear of the vehicle and attached to the frame, is merely a storage tank made of sheet metal. It often contains a number of metal plates, which are attached to the inner surface of the tank parallel to the ends. These have openings through which the gasoline can pass, and their main purpose is to prevent sudden surging of the gasoline from one to the other end of the tank, when the car rounds a corner.

Power Train. The power that the engine develops must be transmitted to the car wheels, so that the wheels will rotate and cause the car to move. The power train performs this job, providing in the process several different gear ratios between the engine crankshaft and wheels, so that the engine crankshaft may rotate approximately four, eight, or twelve times to cause the wheels to rotate once. The power train consists of a series of gears and shafts, which mechanically connect the engine shaft with the car wheels, and contains a clutch, a transmission or change gears, a propeller shaft, and the final drive.

Clutch. The clutch permits the driver to connect the crankshaft to or disconnect it from the power train. A clutch is necessary since the automobile engine must be started without load. In order for the engine to deliver power, the crankshaft must be rotating at a reasonable speed of several hundred revolutions per minute or more. The engine will start at speeds below 100 r.p.m. (revolutions per minute), but it would not continue to operate at this low speed if a load were immediately thrown on it. Consequently, a clutch is placed in the power train between the crankshaft and transmission. The clutch permits the engine to run freely without delivering power to the power train. It also permits operation of the transmission so that the various gear ratios between the engine crankshaft and wheels may be obtained. Двигатель. Двигатель - источник мощности, который заставляет колеса вращаться и автомобиль двигаться. Он обычно упоминается как двигатель внутреннего сгорания, потому, что бензин сжигается внутри цилиндров или камер сгорания. Это горение или воспламенение происходит с такой высокой скоростью, что может быть названо "взрывом"; высокое давление созданное таким образом вызывает поворот или вращение вала. Это вращательное движение передается на колеса автомобиля силовой передачей.

Большинство автомобильных двигателей имеют шесть или восемь цилиндров, хотя некоторые четырех-, двенадцати- и шестнадцати цилиндровые двигатели также эксплуатируются.

Работа двигателя. Действия, которые имеют место в цилиндре двигателя, могут быть разделены на четыре стадии или такта. "Такт" относится к движению поршня. Верхний предел движения поршня называется верхней мертвой точкой или ВМТ. Нижний предел движения поршня называется нижней мертвой точкой основания или НМТ. Такт включает движение поршня от ВМТ до НМТ, или от НМТ до ВМТ. Другими словами, поршень, завершая такт, каждый раз изменяет направление движения. Поскольку полный цикл событий в цилиндре требует четырех тактов

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