ТОП 10 на сайтеПриготовление дезинфицирующих растворов различной концентрации
Техника нижней прямой подачи мяча.
Франко-прусская война (причины и последствия)
Организация работы процедурного кабинета
Смысловое и механическое запоминание, их место и роль в усвоении знаний
Коммуникативные барьеры и пути их преодоления
Обработка изделий медицинского назначения многократного применения
Образцы текста публицистического стиля
Четыре типа изменения баланса
Задачи с ответами для Всероссийской олимпиады по праву
ЗНАЕТЕ ЛИ ВЫ?
Влияние общества на человека
Приготовление дезинфицирующих растворов различной концентрации
Практические работы по географии для 6 класса
Организация работы процедурного кабинета
Изменения в неживой природе осенью
Уборка процедурного кабинета
Сольфеджио. Все правила по сольфеджио
Балочные системы. Определение реакций опор и моментов защемления
NOMENCLATURE OF ENGINE PARTS
While different types and makes of engines vary as to size, horsepower developed, and design, they are all alike in that they have certain parts that perform similar functions. The various parts of the engine and their functions are as follows:
Cylinder Block. The cylinder block, together with the crankcase, forms the main body of the engine. On automotive engines the two are usually cast together forming a single casting. Some engines have separate cylinder block and crankcase castings bolted together to give a rigid form of construction. Individually mounted cylinders are employed on some types of engines. The cylinder block provides the smooth cylindrical bores which guide the pistons. The number of cylinders in an engine varies according to the engine size and design. The crankcase supports the crankshaft and camshaft by means of bearings, as well as numerous other engine parts. An oil pan bolted to the bottom of the crankcase provides a tight enclosure for, the crankshaft and a reservoir for a supply of lubricating oil.
Cylinder Head. The cylinder head is usually a one-piece gray iron or aluminium casting that is bolted to the top of the cylinder block. The cylinders, together with the cylinder head, form the combustion chambers in which the burning and expansion of gases takes place. A gasket between the cylinder block and cylinder head maintains a pressure-tight joint.
Pistons. Pistons receive the energy or force resulting from the combustion of fuel within the cylinders. As the pistons move downward, they transmit this energy through a connecting rod to the crankshaft.
Piston Rings. Piston rings are used to maintain a pressure-tight seal between the moving piston and the cylinder wall. Piston rings also provide a means of conducting heat away from the head of the piston, and they are designed to prevent oil from entering the combustion chamber. They generally are made of cast gray iron, although steel is sometimes used. Most piston rings are classified as either “compression” or “oil-control” rings. The number and type of piston rings used is determined by the requirements of a particular engine.
Piston Pins. A piston pin, sometimes called the wrist pin, connects the piston to the upper end of a connecting rod. The piston pin is fitted into accurately bored holes located in the piston bosses. The upper end of the connecting rod rides on the central portion of the pin between the two piston bosses. The piston pin rides on bearing surfaces located either in the piston bosses, the connecting rod, or both. Several types of retaining devices are employed to prevent endwise movement of the piston pin.
Connecting Rod.A connecting rod, attached to the piston by means of the piston pin, converts the reciprocating (up and down) motion of the piston to a rotary motion of the crankshaft. Connecting rods are usually drop-forged from alloy steels and are made with an I-beam cross section. The upper or small end of the connecting rod usually contains a bushing or clamp or the piston pin. The lower end of the connecting rod is split to permit assembly to the crankshaft and contains a journal bearing.
Crankshaft. The crankshaft transforms the power it receives from the pistons and connecting rods into a rotary motion, returning the piston to the top of the cylinder. The crankshaft is provided with journals which rotate in bearings located in the engine crankcase. The crankshaft has one or more crank arms along its length, the number depending upon the design of the engine and the number of cylinders. The journals, between the crank arms provide bearing surfaces for the large, split end of the connecting rod. Crankshafts are either forged or cast from alloy steels and often have counterbalances located opposite the crank arms to assist in reducing main-bearing loads and to improve engine smoothness. A flywheel bolted to a flange on the crankshaft serves to smooth out the flow of power from the engine.
Engine bearings. The rotating parts of an engine generally are supported in plain bearings, the journals turning within a bearing of antifriction metal. The antifriction metal employed in engine bearings is an alloy such as babbitt, copper-lead, cadmium-silver, and others. Bearing metals are selected for their low coefficient of friction and their ability to withstand heavy bearing loads, high surface speeds, and high temperatures without seizure and excessive wear of the crankshaft. Engine bearings are either replaceable or cast directly in the crankcase or connecting rods. Replaceable bearings usually are composed of thin steel shells lined with a thin layer of bearing metal. To provide ease in assembly and replacement, the main and connecting rod bearings are usually the “split” or two-piece type. On some types of engines, ball or roller bearings are employed for main and connecting rod bearings.
Valves. In most engines, intake and exhaust valves of the poppet type are employed to open and close openings or ports through which the gases enter and leave the cylinders. Each cylinder in the four-stroke-cycle engine has at least one intake and one exhaust valve. The valves are located either in the cylinder block or in the cylinder head and are supported in valve guides. A camshaft opens each valve at the proper time and a valve spring closes the valve.
In two-stroke-cycle gasoline engines, the fuel mixture is admitted and the exhaust gases expelled through ports in each side of -the cylinder, the ports being opened and closed by the action of the piston. Two-stroke-cycle diesel engines generally have one port opening in the cylinder and one cam-actuated poppet valve through which the air is admitted into the cylinder and the exhaust gases expelled.
Camshaft. A camshaft opens the valves against the tension of the valve springs at the proper time and holds them open for the required interval. A separate cam is provided on the camshaft for the operation of each valve. Some opposed engines have each intake cam operate two intake valves. The camshaft is driven from the crankshaft through timing gears, or a timing chain and sprockets.
In four stroke-cycle engines, the camshaft revolves at one-half crankshaft speed, and each valve opens and closes once every two, revolutions of the crankshaft. In a two-stroke-cycle diesel engine, the camshaft revolves at crankshaft speed, and each valve opens and closes with each revolution of the crankshaft,
Valve Lifters.Valve lifters or tappets are employed between the camshaft and the valve stem to open the valves. Valve stems expand when they become heated; and in most, engines a definite clearance must be provided between the valve stem and the valve lifter. In some engines, valve lifters are provided with adjusting screws to regulate the clearance. Some engines are equipped with self-adjusting hydraulic, valve lifters which operate with no clearance between the valve stem and valve lifter.
Manifolds. Manifolds are employed to conduct the gases into and out of the cylinders. An intake manifold is connected between the carburetor and the intake valve ports leading into the cylinders. The exhaust manifold connects the exhaust ports to the exhaust system. The intake and exhaust manifolds may be separate castings bolted together, or both may be cast together. Exhaust gas usually is utilized to heat the intake manifold, thus assisting in vaporizing the incoming fuel charge.
In diesel engines, the intake manifold conducts air to the cylinders, the fuel oil being sprayed directly into the cylinder at the proper time by a fuel injector. Two-stroke-cycle gasoline engines have no intake manifold. The crankcase is utilized as a receiver for the fuel mixture.
Transport for Tomorrow
One thing is certain about the public transport of the future: it must be more efficient than it is today. The time is coming when it will be quicker to fly across the Atlantic to New York than to travel from home to office. The two main problems are: what vehicle shall we use and how can we plan our use of it?
There are already some modern vehicles which are not yet in common use, but which may become a usual means of transport in the future. One of these is the small electric car: we go out into the street, find an empty car, get into it, drive to our destination, get out and leave the car for the next person who comes along. In fact, there may be no need to drive these cars. With an automatic guidance system for cars being developed, it will be possible for us to select our destination just as today we select a telephone number, and our car will move automatically to the address we want.
For long journeys in private cars one can also use an automatic guidance system. Arriving at the motorway, a driver will select the lane he wishes to use, switch over to automatic driving, and then relax — dream, read a newspaper, have a meal, flirt with his passenger — while the car does the work for him. Unbelievable? It is already possible. Just as in many ships and aircraft today we are piloted automatically for the greater part of the journey, so in the future we can also have this luxury in our own cars.
A decade ago, the only thing electronic on most automobiles was the radio. But at present sophisticated electronics is playing a big part in current automotive research. For example, in every gasoline-powered car that General Motors Corporation makes there is a small computer continuously monitoring the exhaust. The device, about the size of a pack of cigarettes, adjusts the vehicle carburetor fuel intake to get the best fuel economy. Ford cars are equipped with an electronic instrument panel that, among otherthings, will calculate how far one can drive on the fuel left in the tank. It will also estimate the time of arrival at destination and tell the driver what speed he hasaveraged since turning on the ignition.
According to specialists these features made possible by microelectronics are only the beginning. Radar may control the brakes to avoid collisions, and a display screen may show the car's position on the road. Recently a radar to be mounted on lorries and cars has been designed in the USA. The radar aerial looks like a third headlight placed directly above the bumper. Having summed up the information about the speed and distance of various objects ahead, the computer detects all possible dangers and their nature. A third component in the system is a monitor on the instrument panel. The radar only observes objects ahead of the vehicle. It is automatically turned on when the speed exceeds ten miles an hour. The green light on the panel indicates that the system is on. The yellow light warns of stationary objects ahead, or something moving slower than the car. The red light and buzzer warn that the speed should go down. Another red light and sound signal make the driver apply the brakes.
A Japanese company is designing a car of a new generation. When completed, the new model will have a lot of unusual characteristics. The car's four-wheel control system will ensure movement diagonally and even sideways, like a crab, at right angles to the longitudinal axis. This is especially important when leaving the car in parking places. To help the driver get information while concentrating on the road, the most important data will be projected on the wind screen. A tourist travelling in such a car will not lose his way even in Sahara with its impassable roads: a navigation Earth satellite will indicate the route.
A new ceramic engine has been developed in Japan. Many important parts as pistons, pressure rings, valves and some others have been made of various ceramic materials, piston rings made of silicon materials being in many respects better than those of steel. They withstand temperatures up to 1,000 °C. Therefore, the engine does not need a cooling system.
The Running Gear
The running gear of the car includes the wheel-suspension system, the stabilizers, and the wheels and tyres. The frame of the car may be considered the integrating member of the running gear. It is attached to the rear axle and to the front wheels by springs. These springs, along with the axles, the control and support arms, and the shock absorbers, constitute the wheel-suspension system. In modern cars the front wheels are independently suspended from the frame in a manner that permits either wheel to change its plane without appreciably affecting the other. This type of front-wheel suspension is known popularly as independent suspension. The stabilizers consist of spring-steel bars, connected between the shock-absorber arms by levers, to decrease body roll and improve steerability.
The Control System
Steering is controlled by a hand wheel, mounted on an inclined column and attached to a steering tube inside the column. The other end of the tube is connected to the steering gear, which is designed to provide maximum ease of operation. Power steering, adapted for passenger cars in the early 1950s, is generally a hydraulic mechanism used as a booster to reduce the effort of steering.
A car has two sets of brakes: the hand or emergency brake and the foot brake. The emergency brake generally operates on the rear wheels only. The foot brake in modern cars is always of the four-wheel type, operating on all wheels. Hydraulic brakes on cars and hydraulic vacuum, air, or power brakes on lorries apply the braking force to the wheels with much less force on the brake pedal than is required with ordinary mechanical brakes. The wheel brakes are generally of the internally expanding type, in which a convex strip of material is forced against a concave steel brake drum.
Последнее изменение этой страницы: 2016-12-12; Нарушение авторского права страницы
infopedia.su Все материалы представленные на сайте исключительно с целью ознакомления читателями и не преследуют коммерческих целей или нарушение авторских прав. Обратная связь - 188.8.131.52 (0.016 с.)