The engine is composed of two major mechanisms: crank connecting rod mechanism and valve mechanism, as well as five major systems including cooling, lubrication, ignition, fuel supply, and starting system. The main components are cylinder block, cylinder head, piston, piston pin, connecting rod, crankshaft, flywheel, etc. The working chamber of a reciprocating piston internal combustion engine is called a cylinder, and the inner surface of the cylinder is cylindrical. The reciprocating piston in the cylinder is hinged with one end of the connecting rod through a piston pin, and the other end of the connecting rod is connected with the crankshaft. The crankshaft is supported by a bearing on the cylinder block and can rotate in the bearing to form a crank connecting rod mechanism. When the piston reciprocates in the cylinder, the connecting rod pushes the crankshaft to rotate. Conversely, when the crankshaft rotates, the connecting rod journal makes a circular motion in the crankcase, and the connecting rod drives the piston to move up and down in the cylinder. Each revolution of the crankshaft, the piston moves up and down once, and the volume of the cylinder is constantly changing from small to large, and then from large to small, and so on. The top of the cylinder is closed with a cylinder head. The cylinder head is equipped with intake and exhaust valves. Through the opening and closing of the intake and exhaust valves, charging into the cylinder and exhausting to the outside of the cylinder are realized. The opening and closing of the intake and exhaust valves are driven by the camshaft. The camshaft is driven by the crankshaft through a toothed belt or gear.
During the power stroke, the crank connecting rod mechanism converts the gas pressure generated after fuel combustion into the torque of the crankshaft rotation through the piston and connecting rod; then, the inertia of the flywheel is used to complete the three auxiliary strokes of intake, compression and exhaust. The crank connecting rod mechanism is composed of a cylinder block crankcase group, a piston connecting rod group and a crankshaft flywheel group.
Cylinder block and crankcase are usually cast into one body, collectively called cylinder block, which is the outer shell and assembly basis of the engine, and is generally made of high-quality alloy cast iron or aluminum alloy. The cylindrical space in the cylinder is called the cylinder, and the surface of the cylinder is called the cylinder wall. Cylinder is the place for gas exchange and combustion, and it is also the orbit of piston movement. In order to ensure the seal between the piston and the cylinder and reduce wear, the cylinder wall should have effective higher machining accuracy and lower surface roughness. In order to dissipate the heat of the cylinder when it is working, a sandwich cavity that can contain the coolant is made between the cylinder block and the cylinder liner block, which is called a water jacket.
There is a main bearing seat at the lower part of the cylinder block, which is used to install the crankshaft flywheel assembly. A tappet chamber is provided on the side of the cylinder block for installing valve drive components. A cylinder head is installed on the upper surface of the cylinder block, an oil pan is installed on the lower surface, and a timing gear cover is installed on the front end, all of which are lined and tightened and sealed with bolts. A flywheel housing is installed on the rear end of the cylinder block.
In order to enhance the wear resistance of the cylinder block and prolong the service life of the cylinder block, most of the cylinder block is inlaid with a cylinder liner. Cylinder liners are divided into dry type and wet type. The dry cylinder liner is not in contact with the coolant. In order to prevent the cylinder liner from moving downward, it can be limited at the upper/lower stop. The outer surface of the wet cylinder liner is in direct contact with the coolant. In order to prevent the coolant from leaking, 1 to 3 rubber sealing rings are installed at the bottom stop of the cylinder liner.
The function of the oil pan is to store lubricating oil, so it is commonly called the oil pan. It is generally stamped from thin-walled steel plate, with an oil stabilizing baffle inside to prevent excessive turbulence of the lubricating oil, and an oil drain plug at the bottom to replace the lubricating oil.
The main function of the cylinder head is to close the upper part of the cylinder and form a combustion chamber with the piston top. There are combustion chambers, water jackets, spark plug seat holes (diesel engines have injector mounting holes), intake and exhaust ducts, valve seats, valve guide seat holes, etc. on the cylinder head. The upper part is equipped with a rocker shaft assembly, which is closed with a cylinder head cover, and a sealing point gasket is installed between the joint surfaces. Gasoline engine cylinder heads are generally integral, but there are exceptions. For example, the EQ6100-1 engine has two cylinder heads. Diesel engines with larger cylinder diameters use one cylinder and one head or two cylinders and one head, with no more than three cylinders and one head at most to prevent the cylinder head from deforming.
Cylinder head gasket, commonly known as cylinder bed, is installed between the cylinder head and the cylinder block. Its function is to seal the joint plane of the cylinder block and the cylinder head to prevent air leakage, coolant leakage and oil leakage. Cylinder head gaskets are mostly made of asbestos board materials, some are made of asbestos boards with two copper sheets or iron sheets, and some are made of middle steel sheets pasted on both sides of suitable latex asbestos sheets. The holes of the combustion chamber are covered with double-layer or single-layer metal to prevent the burning gas from damaging the asbestos layer.
The function of the valve mechanism is to open and close the intake and exhaust valves in time according to the working sequence of the engine and the requirements of the working cycle of each cylinder, so that the combustible mixture (gasoline engine) or fresh air (diesel engine) enters the cylinder, and The exhaust gas is discharged into the atmosphere.
Four-stroke engines widely use valve cam type valve trains, which are composed of a valve group and a valve drive group. According to its different transmission modes, it can be divided into two types: timing gear transmission and chain transmission; according to the position of the camshaft, it can be divided into lower camshaft, middle camshaft and upper camshaft. When the lower camshaft valve mechanism works, the crankshaft drives the camshaft to rotate through a pair of intermeshing timing gears. When the cam’s protruding tip rises to the highest position, the valve opening is maximized. When the protruding tip of the cam moves downwards, the valve and its transmission parts return to the original position due to the elastic force of the valve spring, closing the airway. Compared with the lower camshaft type valve mechanism, the middle and upper camshaft type valve mechanisms are mostly driven by a timing chain or a timing belt due to the greater distance between the crankshaft and the camshaft. The center camshaft type eliminates the push rod; the upper camshaft type eliminates the tappet and push rod.
1. Valve group
The valve group is generally composed of valves, valve seats, valve guides, valve oil seals, valve springs, and valve lock plates. 
The valve is divided into two types: intake valve and exhaust valve, and its function is to close the intake and exhaust passages respectively. The valve is composed of a head and a rod, and the head is made into a cone to match the cone of the valve seat. The cone angle of the head is generally 45°. The diameter of the intake valve head of the same engine is larger than that of the exhaust valve head to increase the engine’s charge. The valve stem is cylindrical and fits with the inner hole of the valve guide. The end of the stem is made with a ring groove for installing the valve spring seat lock plate.
The valve seat is used to ensure the sealing of the valve and transfer the heat from the valve head to the cylinder head. The valve seat is generally made of a special alloy in a ring shape, which is tightly inlaid on the cylinder head.
The valve guide is used to guide the valve to make a reciprocating linear motion to ensure the correct closing position of the valve and the valve seat. In order to prevent the lubricating oil on the cylinder head from entering the combustion chamber from the gap between the valve and the valve guide, a valve oil seal is installed at the upper end of the valve guide.
The valve spring is a cylindrical spiral spring, which can close the valve quickly and press the valve head and the valve seat against each other to ensure sealing.
2. Valve drive group
The function of the valve drive group is to open and close the valves in a timely manner according to the working sequence of the engine, and to ensure that the valves have sufficient opening. 
The camshaft is used to control the opening and closing of the valve, and to drive the gasoline pump, oil pump and distributor to work. The camshaft is equipped with intake cams, exhaust cams, journals, gears that drive the oil pump and distributor, and eccentric wheels that drive the rocker arm of the gasoline pump. The intake and exhaust cams are an important part of the camshaft. The arrangement order on the camshaft is determined by the arrangement of the intake and exhaust ducts.
The timing gear and timing chain or timing belt realize the transmission between the crankshaft and the camshaft. For example, the CA6102, BJ492Q engine is a timing gear transmission; the Beijing Cherokee car engine is a timing chain transmission; the Shanghai Santana car engine is a timing belt transmission. The crankshaft of a four-stroke engine rotates for two cycles, and the camshaft should rotate once, so that the intake and exhaust valves are opened and closed once, and the timing of the valve opening and closing must be adapted to the needs of the working cycle of each cylinder. Therefore, whether it is a gear drive or a chain drive, it must be assembled in accordance with the prescribed signs, which are generally pits in the gear teeth.
The function of the valve lifter is to transmit the thrust of the cam to the push rod or valve. The types of tappets include bacteria type, cylindrical non-hydraulic type, cylindrical hydraulic type, etc., cylindrical hydraulic type, etc. The cylindrical hydraulic tappet has no valve clearance, which can reduce the noise of the engine, but it requires strict precision and high cost. Mostly used in high-end car engines.
The function of the valve push rod is to transmit the thrust of the tappet to the rocker arm to drive the valve to open. The upper and lower ends of the putter are heat treated and polished to improve wear resistance; the shaft is available in solid and hollow shafts.
The function of the rocker arm and rocker shaft assembly is to change the thrust direction of the push rod (lower camshaft type), tappet (middle camshaft type) or cam (upper camshaft type) to open the valve. The rocker shaft assembly is fixed on the upper part of the cylinder head. It is mainly composed of rocker arm and rocker shaft support. The rocker arm is made of two arms with unequal lengths, so that the tappet and push rod can be obtained with a smaller lift. Large valve opening. One end of the long arm of the rocker arm corresponds to the valve stem, and one end of the short arm is equipped with adjusting screws and nuts to adjust the valve foot gap. The rocker shaft is a hollow shaft, and there is a lubricating oil passage through the rocker shaft support and the rocker arm to lubricate the friction surface of the air distribution mechanism.
The function of the gasoline engine fuel system is to formulate pure air and gasoline into a combustible mixture in an appropriate proportion according to the needs of the engine’s different working conditions, and send the exhaust gas generated after combustion into each cylinder to be discharged into the atmosphere.
In a gasoline engine, the combustible mixture in the cylinder is ignited by electric sparks. For this reason, a spark plug is installed on the cylinder head of the gasoline engine, and the head of the spark plug extends into the combustion chamber. All equipment that can generate sparks between the spark plug electrodes on time is called the ignition system. The traditional ignition system consists of batteries, generators, ignition coils, distributors, spark plugs, etc. The ordinary ignition system is similar to the traditional ignition system, except that the distributor is replaced by electronic components. All electronic ignition systems are fully electronic ignition systems, which completely eliminate mechanical devices, and the ignition timing is controlled by an electronic system, including batteries, generators, ignition coils, spark plugs, and electronic control systems.
The cooling system radiates part of the heat absorbed by the heated parts in time to ensure that the engine works at the 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 is composed of fans and heat sinks.
The function of the lubrication system is to deliver a certain amount of clean lubricating oil to the surface of the relative moving parts to achieve liquid friction, reduce frictional resistance, and reduce the wear of mechanical parts. And clean and cool the surface of the parts. The lubrication system consists of an oil pump, a filter, a pressure limiting valve, an oil passage, and an oil filter.
To make the engine transition from a stationary state to a working state, the crankshaft of the engine must first be rotated by an external force to make the piston move back and forth. The combustible mixture in the cylinder burns and expands to work, pushing the piston down to rotate the crankshaft. The engine can run on its own, and the work cycle can proceed automatically. Therefore, the whole process from the crankshaft starting to rotate under the action of external force to the engine starting to idle automatically is called engine starting. The device required to complete the starting process is called the engine’s starting system. It consists of a starter and its accessories.
Engine performance indicators are used to characterize the performance characteristics of the engine and serve as a basis for evaluating the performance of various engines. Engine performance indicators mainly include: power indicators, economic indicators, environmental indicators, reliability indicators and durability indicators.
Power index: The power index is an index that characterizes the power of the engine. Generally, the effective torque, effective power, and engine speed of the engine are used as evaluation indicators.
Economic index: The engine economic index is generally expressed by the effective fuel consumption rate. The amount of fuel (in g) consumed by the engine for every 1kW·h of effective power output is called the effective fuel consumption rate.
Environmental indicators: vehicle emission standards and vehicle noise levels. According to the Chinese Motor Vehicle Noise Standard (GB/T 18697-2002), the noise of cars shall not exceed 79dB(A).
Reliability index and durability index: Reliability index is an index that indicates the ability of the engine to work normally and continuously within a specified time under specified conditions of use. There are multiple evaluation methods for reliability, such as mileage for first failure, mileage between average failures, etc. The durability index refers to the limit time for the main parts of the engine to wear to the point where it cannot continue to work normally.
The universal characteristics of the engine: the working conditions of the car engine can be changed in a wide range. When the engine’s operating conditions (that is, power and speed) change, its performance (including power, economy, emissions, noise, etc.) also changes. The relationship between engine performance indicators and operating conditions is called the universal characteristics of the engine.
The Intelligent Variable Valve Timing System (VVT-i) is Toyota’s unique engine technology, which adjusts the camshaft angle to obtain the best valve timing.
The continuously variable valve timing system (CVVT) is developed in South Korea on the basis of VVT-i and i-VTEC, which controls the opening and closing of the valve to make fuel burn more fully.
Variable valve valve valve phase and valve lift electronic control system (VTEC) VTEC developed by Honda Motor has now evolved into i-VTEC. Two sets of different valves are used to drive the cams at medium and low speeds and high speeds, and the opening time and lifting degree of the valves can also be controlled, that is, the intake and exhaust volumes can be changed.
In-cylinder direct injection stratified combustion (FSI) injects fuel directly into the combustion chamber at the most appropriate time. Through the design of the internal shape of the combustion chamber, there will be a thicker mixture around the spark plug, and a leaner mixture in other areas, which ensures that the lean combustion is achieved as much as possible under the condition of smooth ignition.
The variable displacement engine (MDS) can automatically switch between 4-cylinder and 8-cylinder modes.
Post time: Jun-09-2021