July 26 2023
The heart of car! Introduce you to basic structure and classification of engine
The car engine is device that powers car and is heart of car, determining power, efficiency and environmental protection of car. According to different energy sources, automobile engines can be divided into diesel engines, gasoline engines, electric vehicle engines and hybrids.
Conventional gasoline and diesel engines are reciprocating internal combustion engines that convert chemical energy of fuel into mechanical energy of piston movement and output power to outside. The gasoline engine has high speed, light weight, low noise, easy start and low cost; diesel engine has a higher compression ratio, high thermal efficiency and better economic and emission performance than a gasoline engine.
According to way intake system works, it can be divided into four types: naturally aspirated, turbocharged, supercharged and dual-charged.
According to way piston moves, it can be divided into two types: a piston internal combustion engine and a rotary piston engine.
According to arrangement of cylinders, in-line, V-shaped, W-shaped and boxer engines are distinguished.
According to number of cylinders, they can be divided into single-cylinder and multi-cylinder engines. Modern cars mainly use three-cylinder, four-cylinder, six-cylinder and eight-cylinder engines.
According to different cooling methods, it can be divided into water-cooled engine and air-cooled engine. The water-cooled engine has uniform cooling, reliable performance and good cooling effect, and is widely used in modern car engines.
According to number of strokes, it can be divided into a four-stroke internal combustion engine and a two-stroke internal combustion engine. Four-stroke internal combustion engines are widely used in automobile engines.
Classification by fuel delivery method: carbureted engine, electronic injection engine and direct injection engine.
The engine consists of two main mechanisms: a crank mechanism and a gas distribution mechanism, as well as five main systems, including cooling, lubrication, ignition, fuel supply and starting systems. The main components are cylinder block, cylinder head, piston, piston pin, connecting rod, crankshaft, flywheel, etc. The working cavity of a piston internal combustion engine is called a cylinder, and inner surface of cylinder is cylindrical. The reciprocating piston in cylinder is pivotally connected to one end of connecting rod through piston pin, and other end of connecting rod is connected to crankshaft, which rests on a bearing on cylinder block and can rotate into a bearing forming a crank mechanism. When piston reciprocates in cylinder, connecting rod drives crankshaft. In contrast, as crankshaft rotates, crankpin makes a circular motion in crankcase and causes piston to move up and down in cylinder through connecting rod. Each time crankshaft makes one revolution, piston moves up and down once, and volume of cylinder constantly changes from small to large, and then from large to small, so that cycle is endless. The top of cylinder is closed by cylinder head. The cylinder head is equipped with intake and exhaust valves. Through opening and closing of intake and exhaust valves, air is forced into cylinder, and exhaust is thrown out of cylinder. The intake and exhaust valves are opened and closed by camshaft. The camshaft is driven by crankshaft through a toothed belt or gears.
Crank mechanism
During power cycle, crank mechanism converts gas pressure formed after combustion of fuel into torque of crankshaft through piston and connecting rod; auxiliary shutdown. The crank mechanism consists of three parts: crankcase group of cylinder block, piston connecting rod group and cranked flywheel group.
Air distribution mechanism
The role of valve train is to open and close intake and exhaust valves in time, according to engine sequence and duty cycle requirements of each cylinder, so that combustible mixture (gasoline engine) or fresh air (diesel engine) enters cylinder and exhaust gases are released into atmosphere.
Fuel supply system
The role of gasoline engine fuel system is to prepare combustible mixture of clean air and gasoline in appropriate proportion according to needs of different engine operating conditions and send it to each cylinder for combustion, and exhaust gas generated is released into atmosphere.
Ignition system
In a gasoline engine, ignition of combustible mixture in cylinder occurs from an electric spark, so a spark plug is installed on cylinder head of a gasoline engine, and spark plug head goes into combustion chamber. . All equipment capable of generating an electrical spark between electrodes of a spark plug in time is called an ignition system. The traditional ignition system consists of batteries, alternators, ignition coils, distributors, spark plugs, etc. The original and conventional ignition systems are similar except that distributor has been replaced with electronic components. The electronic ignition type is an all-electronic ignition system that completely overrides mechanical device, and ignition timing is controlled by electronic system, including battery, alternator, ignition coil, spark plug and electronic control system.
Cooling system
The cooling system dissipates some of heat absorbed by hot parts in a timely manner to keep engine running at most suitable temperature. The water-cooled cooling system is composed of water jacket, water pump, radiator, fan, thermostat and so on. The air-cooled type consists of a fan and a heatsink.
Lubrication system
The function of lubrication system is to supply a certain amount of pure lubricating oil to surface of parts in relative motion to achieve fluid friction, reduce frictional resistance and reduce wear on parts. And clean and cool surface of parts. The lubrication system consists of oil pump, filter, pressure limiting valve, oil passage,oil filter, etc.
Start system
To bring engine from static to running, engine's crankshaft must first be rotated by an external force to cause piston to reciprocate. The combustible mixture in cylinder burns and expands, doing work, pushing piston down to rotate crankshaft. The engine can run independently and work cycle can be carried out automatically. Therefore, whole process from start of rotation of crankshaft under action of an external force to start of engine at idle is automatically called engine start. The device necessary to complete starting process is called engine starting system. It consists of a starter and its accessories.
Engine performance ratings are used to characterize performance of an engine and serve as a basis for evaluating performance of various engines. Engine performance indicators mainly include: power indicators, economic indicators, environmental indicators, reliability indicators and durability indicators.
Dynamics index. Power index is a measure of engine performance. Typically, engine effective torque, engine effective power and engine speed are used as evaluation metrics.
Economy index. The engine efficiency index is usually expressed as effective fuel consumption. The amount of fuel consumed by engine per 1 kWh of useful work (in g) is called effective fuel consumption.
Environmental performance: vehicle emission standards and vehicle noise levels. According to Chinese Motor Vehicle Noise Standard (GB/T 18697-2002), vehicle noise must not exceed 79 dB(A).
Reliability index and durability index: The reliability index is an index that indicates ability of an engine to operate normally and continuously for a certain period of time under certain operating conditions. There are many methods for evaluating reliability, such as first failure mileage, average failure mileage, etc. The durability index refers to limit of time when main parts of an engine wear to point where they cannot continue to function normally.
Universal Engine Specifications: Automotive engine operating conditions can vary widely. As engine operating conditions (i.e. power and speed) change, so will engine performance (including power, economy, emissions and noise, etc.). The relationship between engine efficiency and operating conditions is called universal characteristic of engine.
Variable Valve Timing (VVT-i) is a unique Toyota engine technology that adjusts angle of camshaft to obtain best valve timing.
The continuously variable valve timing (CVVT) system was developed in South Korea based on VVT-i and i-VTEC, which allows more complete combustion of fuel by controlling opening and closing of valves.
Variable Valve Timing and Lift Electronic (VTEC) The VTEC system developed by Honda Motor has now been converted to i-VTEC. At low, medium and high speeds, two sets of different valves are used to drive cams, and opening time and valve lift can be controlled, that is, intake air volume and exhaust air volume can be changed. .
Flex direct injection (FSI) combustion injects fuel directly into combustion chamber at optimum time. Due to design of internal shape of combustion chamber, there will be a richer mixture around spark plug, while there will be a leaner mixture in other areas, ensuring that lean combustion can be achieved as far as possible under condition of smooth ignition. .
The Variable Displacement (MDS) engine can automatically switch between 4-cylinder and 8-cylinder modes.
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