Wednesday, July 15, 2009

Automobile Engine

Automobile Engine


The body of an automobile is categorized according to the number of doors, the arrangement of seats, and the roof structure. Their roofs are conventionally supported by pillars on each side of the body in recent times, there are convertible models with retractable fabric tops that rely on the pillar at the side of the windshield for upper body strength, as convertible mechanisms and glass areas are essentially nonstructural. The glass areas have been increased for improved visibility and for aesthetic reasons. New designs are usually programmed on three- to six-year cycles with generally minor refinements appearing during the cycle.

Redesigning was a tough job in the past, when as much as four years of planning and new tool purchasing was needed for a completely new design. Computer-aided design (CAD) and computer-aided manufacturing (CAM) techniques may now be used to reduce this time requirement by 50 percent or more.

Sheet steel is generally used to make automotive bodies. Elements are added to the alloy to improve its ability to be formed into deeper depressions without wrinkling or tearing in manufacturing presses. Steel is used because of its general availability, low cost, and good workability. Other materials for certain other materials are also used. Other materials, such as aluminum, fiberglass, and carbon fiber reinforced plastic are used because of their special properties.

For more toughness and resistance to brittle deformation, Polyamide, polyester, polystyrene, polypropylene, and ethylene plastics have been formulated. Tooling for plastic components generally costs less and requires less time to develop than that for steel components.

Painting and priming processes are used to protect bodies from corrosive elements and to maintain their strength and appearance. Bodies are first dipped in cleaning baths to remove oil and other foreign matter and then they go through a succession of dip and spray cycles. Enamel and acrylic lacquer are both in common use.

Electro deposition of the sprayed paint, a process in which the paint spray is given an electrostatic charge and then attracted to the surface by a high voltage, helps assure that an even coat is applied and that hard-to-reach areas are covered. To speed up the drying process in the factories, ovens with conveyer lines are used. In those body areas that are more susceptible to corrode, galvanized steel with a protective zinc coating and corrosion-resistant stainless steel are used

Cooling System

Liquid cooling systems are employed by most engines today. A typical automotive cooling system comprises

(1) a series of channels cast into the engine block and cylinder head, surrounding the combustion chambers with circulating water or other coolant to carry away excessive heat,
(2) a radiator, consisting of many small tubes equipped with a honeycomb of fins to radiate heat rapidly, that receives and cools hot liquid from the engine,
(3) a centrifugal-type water pump with which to circulate coolant,
(4) a thermostat, which maintains constant temperature by automatically varying the amount of coolant passing into the radiator, and
(5) a fan, which draws fresh air through the radiator.

For operation at temperatures below 32º F (0º C), it is necessary to prevent the coolant from freezing. This is usually done by adding some compound to depress the freezing point of the coolant. Alcohol formerly was commonly used, but it has a relatively low boiling point and evaporates quite easily, making it less desirable than organic compounds with a high boiling point, such as ethylene glycol. By varying the amount of additive, it is possible to protect against freezing of the coolant down to any minimum temperature normally encountered. Coolants contain corrosion inhibitors designed to make it necessary to drain and refill the cooling system only once a year.

Air-cooled cylinders operate at higher, more efficient temperatures, and air cooling offers the important advantage of eliminating not only freezing and boiling of the coolant at temperature extremes but also corrosion damage to the cooling system. Control of engine temperature is more difficult, however, and high-temperature-resistant ceramic parts are required when design operating temperatures are significantly increased.

Pressurized cooling systems with operating pressures up to 14 pounds per square inch (100 kilopascals) have been used to increase effective operating temperatures. Partially sealed systems using coolant reservoirs for coolant expansion if the engine overheats were introduced in 1970.

Electrical System

The electrical system of the automobile was, at first limited to the ignition equipment. However, electric lights and horns began to replace the kerosene and acetylene lights and the bulb horns with the advent of the electric starter on a 1912 model. Electrification was rapid and complete, and, by 1930, six-volt systems were standard everywhere. The electrical system consists of a storage battery, generator, starting (cranking) motor, lighting system, ignition system, and various accessories and controls.

It was difficult to meet high ignition voltage requirements with the increased engine speeds and higher cylinder pressures of the post-World War II cars. The larger engines required higher cranking torque. Additional electrically operated features, such as radios, window regulators, and multispeed windshield wipers, also added to system requirements. 12-volt systems generally replaced the 6-volt systems in 1956 production to meet these needs.

The ignition system consists of the spark plugs, coil, distributor, and battery, and provides the spark to ignite the air-fuel mixture in the cylinders of the engine. In order to jump the gap between the electrodes of the spark plugs, the 12-volt potential of the electrical system must be stepped up to about 20,000 volts. This happens with the aid of a circuit that starts with the battery, one side of which is grounded on the chasis and leads through the ignition switch to the primary winding of the ignition coil and back to the ground through an interrupter switch. A high voltage id induced across the secondary of the coil by interrupting the primary circuit. The high-voltage secondary terminal of the coil leads to a distributor that acts as a rotary switch, alternately connecting the coil to each of the wires leading to the spark plugs.

It was in the 1970s that solid-state or transistorized ignition systems were introduced. Increased durability by eliminating the frictional contacts between breaker points and distributor cams was provided by these distributor systems. A revolving magnetic pulse generator in which alternating-current pulses trigger the high voltage needed for ignition by means of an amplifier electronic circuit replaced the breaker point. Changes in engine ignition timing are made by vacuum or electronic control unit (microprocessor) connections to the distributor.

The generator is the basic source of energy for the various electrical devices of the automobile. An alternator that is belt-driven from the engine crankshaft is also used at times. The design is usually an alternating-current type with built-in rectifiers and a voltage regulator to match the generator output to the electric load and also to the charging requirements of the battery, regardless of engine speed.

To store excess output of the generator, a lead-acid battery is used which serves as a reservoir. Energy for the starting motor is thus made available along with power for operating other electric devices when the engine is not running or when the generator speed is not sufficiently high to carry the load.

The starting motor then drives a small spur gear, which is so arranged that it automatically moves into mesh with gear teeth on the rim of the flywheel as the starting-motor armature begins to turn. As soon as the engine starts, the gear is disengaged, which prevents the starting motor from getting damaged due to overspeeding. The starting motor is designed for high current consumption and delivers considerable power for its size for a limited time.


Night driving has long been dangerous due to the glare of headlights that blind drivers approaching from the opposite direction. Therefore, headlights that satisfactorily illuminate the highway ahead of the automobile for night driving without temporarily blinding approaching drivers have long been sought. To correct this problem resistance-type dimming circuits, which decreased the brightness of the headlights when meeting another car, were first introduced. This gave way to mechanical tilting reflectors and later to double-filament bulbs with a high and a low beam, called sealed-beam units.

There was only one filament at the focal point of the reflector in the double-filament headlight unit of necessity. Greater illumination required for high-speed driving with the high beam, consequently, the lower beam filament was placed off center, with a resulting decrease in lighting effectiveness. From the 1950s, manufacturers equipped their models with four headlights to improve illumination.

In some cars, dimming is automatically achieved. This happens by means of a photocell-controlled switch in the lamp circuit that is triggered by the lights of an oncoming car. Larger double-filament lamps and halogen-filled lamp bulbs with improved photometrics permitted a return to two-headlight systems on some cars. At many places the law limits the total intensity of forward lighting systems to 75,000 candlepower (800,000 lux).

In most new automobiles, lowering front hood heights for improved aerodynamic drag and driver visibility reduces the vertical height available for headlights. Due to this, lower-profile rectangular sealed-beam units and higher-intensity bulbs, in conjunction with partial parabolic reflectors with reduced vertical axis, were adopted in the 1970s. In some cases, models featured full-size concealed headlights that were not visible until turned on. An electric motor linkage was used to rotate the lamp housing or a housing cover into proper position to supply lighting. Aerodynamic benefits were provided by this system only when the headlights were concealed.

In the 1960s, signal lamps and other special-purpose lights were increased in usage. Amber-colored front and red rear signal lights are flashed as a turn indication; all these lights are flashed simultaneously in the "flasher" system for use when a car is parked along a roadway or is traveling at a low speed on a high-speed highway. The law requires that marker lights that are visible from the front, side and rear be also present. Red-colored rear signals are used to denote braking, and, on some models, cornering lamps to provide extra illumination in the direction of an intended turn are available. These are actuated in conjunction with the turn signals. To provide illumination to the rear when backing up, backup lights are required.


The chassis forms the main structure of the modern automobile. A large number of designs in pressed-steel frame form a skeleton on which the engine, wheels, axle assemblies, transmission, steering mechanism, brakes, and suspension members are mounted. During the manufacturing process the body is flexibly bolted to the chasis.

This combination of the body and frame performs a variety of functions. It absorbs the reactions from the movements of the engine and axle, receives the reaction forces of the wheels in acceleration and braking, absorbs aerodynamic wind forces and road shocks through the suspension, and absorbs the major energy of impact in the event of an accident.

There has been a gradual shift in modern small car designs. There has been a trend toward combining the chasis frame and the body into a single structural element. In this grouping, the steel body shell is reinforced with braces that make it rigid enough to resist the forces that are applied to it. To achieve better noise-isolation characteristics, separate frames are used for other cars. The presence of heavier-gauge steel components in modern separate frame designs also tends to limit intrusion in accidents.

Fuel and lubrication

The only fuel used for automobile operation is specially formulated gasoline, even though diesel fuels are used for many trucks and buses and a few automobiles. The things in a good fuel for automobile are proper volatility, sufficient antiknock quality, and freedom from polluting by-products of combustion.

The volatility is reformulated seasonally by refiners so that sufficient gasoline vaporizes, even in extreme cold weather, to permit easy engine starting. Antiknock compounds, principally tetraethyl lead, were added to most gasolines to prevent knocking, a rapid, uncontrolled burning in the final stages of combustion that results in a characteristic "knock," or pinging noise, and may damage an engine or reduce its performance.

Small lead deposits on such places as engine-valve seats improve valve life. Antiknock quality is rated by the octane number of the gasoline and depends primarily on the compression ratio of the engine. However it is also affected by combustion-chamber design and chamber-wall deposits. In the early 1990s regular gasoline carried an octane rating of 87 and high-test in the neighborhood of 93.

Lubrication is an essential requirement for all vehicles. In its absence, friction would increase power consumption and damage the parts. The lubricant also serves as a coolant, a noise-reducing cushion, and a sealant between engine piston rings and cylinder walls. The engine lubrication system includes a gear-type pump that delivers filtered oil under pressure to a system of drilled passages leading to various bearings. Oil spray also lubricates the cams and valve lifters.

Fairly stiff grease is required by wheel bearings and universal joints. The other chasis joints require soft grease that can be injected by pressure guns. A special grade of light hydraulic fluid is required by hydraulic transmissions. Manually shifted transmissions use heavier gear oil similar to that for rear axles to resist heavy loads on the gear teeth. Gears and bearings in lightly loaded components, such as generators and window regulators, are fabricated from self-lubricating plastic materials.

Fuel injection

In an internal combustion engine, the fuel injection system is that which delivers fuel or a fuel-air mixture to the cylinders by means of pressure from a pump. It was originally used in diesel engines because of diesel fuel's greater viscosity and the need to overcome the high pressure of the compressed air in the cylinders. A diesel fuel injector sprays an intermittent, timed, metered quantity of fuel into a cylinder, distributing the fuel throughout the air within. Fuel injection is also now used in gasoline engines in place of a carburetor. In gasoline engines the fuel is first mixed with air, and the resulting mixture is delivered to the cylinder. Computers are used in modern fuel injection systems to regulate the process. The positive effects of fuel injection are that there is more efficient fuel combustion, better fuel economy and engine performance and reduced polluting exhaust emissions.


This is a device in a gasoline engine. It vaporizes the gas and mixes it with a regulated amount of air that aids in efficient combustion in the engine cylinders. Land vehicles, boats, and light aircraft have a float carburetor, in which a float regulates the fuel level in a reservoir from which the fuel is continuously sucked into the intake manifold at a restriction called a venturi. The carburetor has been replaced by the fuel injection system in many modern vehicles.