汽车专业英语电子课件Unit 2

Main Components
• The engine consists of several different mechanisms and systems including cylinder block, crankshaft and connecting rod mechanism, valve mechanism, fuel supply system, lubrication system, cooling system, ignition system and starting system.
Compression Stroke
• With both intake and exhaust valves (open,close), the piston returns to the top of the cylinder compressing the fuelair mixture into the combustion chamber of the cylinder head.
9
1 2
8 3 4
7
6
5
• 1—the cap of the cylinder head 2—valve • 3—engine block 4—flywheel 5—crankshaft • 6—oil pan 7—pulley 8—cylinder 9—timing gear
Classification of Engine
Intake Stroke
• On the intake stroke of the piston, the piston descends from (TDC,BDC) to (TDC, BDC), reducing the pressure inside the cylinder. A mixture of fuel and air, or just air in a diesel engine, is forced by atmospheric pressure into the cylinder through the intake port. The intake valve(s) then (open,close).
Fuel Supply System
• The fuel system supplies fuel to the engine. It also has the functions to regulate the volume['vɔlju:m] of fuel supply. • The fuel systems in diesel and gasoline engines are different.
Cooling System
• The cooling system regulates the engine temperature to an optimal level (80℃ to 90℃ at coolant temperature) by circulating the coolant throughout the engine under all operating conditions and during all seasons of the year. • The cooling fan cools the coolant in the radiator and water pump circulates the coolant through the cylinder head and the cylinder block.
• The engine can be classified in following ways:
By Fuel System
• Gasoline engine and diesel engine are used. In a gasoline engine, the air-fuel mixture is exploded in the engine. • A diesel engine uses diesel fuel. • It generates high power at low speeds. The fuel efficiency is better than that of a gasoline engine.
• They draw in an air-fuel mixture to the cylinders, compress it, ignite and combust it, then discharge it. Repeating these four actions gives gasoline engines their power. The cycle begins at Top Dead Centre (TDC), when the piston is farthest away from the crankshaft. A cycle refers to the full travel of the piston from TDC to Bottom Dead Centre (BDC).
Cylinder Block
• The core[kɔ:] of the engine is the cylinder, with the piston moving up and down inside the cylinder.
Crankshaft and Connecting Rod Mechanism • The crankshaft changes the linear['liniə] movement of the piston into a rotational movement via a connecting rod. • The connecting rod connects the piston to the crankshaft. • It can rotate at both ends so that its angle['æŋɡl] can change as the piston moves and the crankshaft rotates.
Lubrication System
• The lubrication system uses an oil pump to continuously supply engine oil throughout the inside of the engine. • This system reduces friction between parts with a film of oil. If the engine is run without oil, the friction can cause poor running, or cause even meltdown. In addition to lubrication, engine oil cools and cleans the engine.
• 1—intake valve 2—spark plug 3—exhaust valve 4—combustion cha源自文库ber 5—piston head
• As their name implies, four-stroke internal combustion engines have four basic steps that repeat with every two revolutions of the crankshaft:① Intake stroke ② Compression stroke, ③ Power stroke, ④ Exhaust stroke. The four strokes will be illustrated in Fig.2.4.
Ignition System
• Internal combustion engines require ignition of the mixture, either by spark ignition (SI) or compression ignition (CI).
Starting System
• The starting system forces the engine to crank with an electric motor, and starts the engine.
Engine Operating Principles
• A four-stroke engine, also known as fourcycle, is an internal combustion engine in which the piston completes four separate strokes： • intake, compression, power and exhaust— during two separate revolutions of the engine’s crankshaft, and one single thermodynamic[ˈθ :məudaiˈnæmik] ə cycle. • The main parts in four stroke engine are shown in Fig.2.3.
By Cylinder Arrangement
• Most cars have more than one cylinder. Four, six and eight cylinders are common used. • In a multi-cylinder engine, the cylinders are usually arranged in one of three ways: inline, V-type, or flat (Fig.2.2). • Today the number of cylinders is growing, the cylinders also can be arranged as Wtype.
Unit2
Classification and Main Components of Engine
• The internal combustion engine is an engine in which the combustion of fuel occurs with oxygen(usually air) in a combustion chamber, as shown in Fig.2.1.
By Cooling System
• Liquid-cooled engines and air-cooled engines are being used. Liquid-cooled engines are the most common in the engine industry. • There are also other ways to classify the engines. Despite of these classifications, the structure of the engine is basically the same.
Valve Mechanism
• A valve mechanism is a group of components that opens and closes the intake and exhaust valves in the cylinder head at the appropriate[ə'prəupriit] time. • The main functions['fʌŋkʃən] of the valve gear are to provide timely admission of the fresh charge into the cylinders and exhaust of spent gases from them.