汽车英文文章

张小浩

The summary of automobile engine and chassis

The engine which is called the “heart” of a vehicle is used to supply power for an automobile. It includes the fuel, lubricating, cooling, ignition and starting systems. Generally, an automobile is operated by internal combustion engine. The internal combustion engine burns fuel within the cylinders and converts the expanding force of the combustion or “explosion” into rotary force used to people the vehicle.
Four-stage-engine Operation
The actions taking place in the engine cylinder can be classified into four stages or strokes. “Stroke” refers to piston movement. A stroke occurs when the piston moves from one limiting piston to the other. The upper limit of piston movement is called TDC (top dead center). The lower limit of piston movement is called BDC (bottom dead center). A stroke is piston movement from TDC or from BDC.
Where the entire cycle of events in the cylinder requires four stroke (or two crankshaft revolutions), the engine is called a four- stroke-cycle engine. The four piston strokes are intake stroke, compression stroke, power stroke and exhaust stroke.
Intake Stroke
On the intake stroke, the intake valve has opened, the piston is moving downward, a mixture of air and vaporized gasoline is entering the cylinder through the valve port.
Compression Stroke
After the piston reaches BDC, it begins to move upward. As this happens, the intake valve closes. The exhaust valve also closes, so the cylinder is sealed. As the piston moves upward, the air-fuel mixture is compression.
Power Stroke
As the piston reaches TDC on the compression stroke, an electric spark is produced at the spark plug. The spark ignites the air-fuel mixture. It now begins to burn very rapidly, the cylinder pressure increases to as much as 3MPa-5MPa or even more. This terrific push against the piston forces it downward, and a power impulse is transmitted through the connecting rod to the crankpin on the crankshaft. The crankshaft is rotated as the piston is pushed down by the pressure above it.
Exhaust Stroke
As the piston reaches BDC again, the exhaust valve opens. Now, the piston moves up on the exhaust stroke, it forces the burned gases out of the cylinder through the exhaust-valve port. When the piston reaches TDC, the exhaust valve closes, the intake valve opens. A fresh charge of air-fuel mixture will be drawn into the cylinder as the piston moves down again toward BDC.
This four-stroke-cycle of piston within the cylinder is repeated time and again to put the vehicle forward.
The Power Mechanism of the Engine
In a reciprocating engine, the power mechanism is called the crankshaft and connecting rod assembly. In this assembly, all of the major units such as the engine crankcase and cylinder block, the piston and connecting rod, the crankshaft and flywheel work together to convert thermal energy into mechanical energy used to drive the vehicle.
The engine crankcase and block are usually cast into one piece and therefore can be seemed as the largest and most intricate piece of metal in an automobile. They are usually made of high-grade cast alloy iron to improve wear characteristics of the cylinder.
The piston converts the potential engine of the fuel into the kinetic energy that turns the crankshaft. The piston is composed of piston head, piston ring, piston lands, piston skirt and piston pin hole. The piston rings carried in the ring groove are of two basic types: compression rings and oil-control ring. The upper ring or compression rings are to prevent compression leakage; the lower ring or oil-control rings the amount of oil being deposited on the cylinder wall.
The piston pinhole in the piston also serves as a bearing for the piston pin, which is used to connect the connecting rod. The connecting rod is attached to the crankshaft at one end and to the piston at the other end. The connecting rod is in form of a bar with ring shaped heads at its end. They are composed of connecting rod small end, connecting rod shank, connecting rod big end, connecting rod cap, and connecting rod bearing half shells. Shank of the connecting rod is provided with an I-cross section to give the rod maximum rigidity with the minimum of weight. The big end of the rod is split so that it can be connected to the crankshaft. To avoid misplacing the rod caps during assembly, the connecting rods and their mating caps are marked on one side with serial numbers, starting with the first rod from the radiator to identify their location in the engine.
The crankshaft serves to change the reciprocating motion of the piston into rotary motion and handles the entire power output. The crankshaft is made up of various parts such as main bearing journals, rod journal, crank arm bearing, counter-balanced weight and flywheel end. The crankshaft revolves in bearings located in the engine crankcase, but the number of bearing used usually depends on the number of cylinders in the engine and the design of the engine. In order to reduce or eliminate such vibration, it must be provided with counter balanced weights that extend radially from the crankshaft centerline in the opposite direction of the crank arms. In that way, the forces acting on the crankshaft are balanced and vibration is reduced.
The flywheel is a relatively heavy metal wheel, which is firmly attached to the crankshaft. Its function is to help the engine to run smoothly by absorbing energy during the power stroke and releasing energy during the other strokes.
Valves and valve Train
The valve gear of an internal combustion engine provides timely admission of the fresh charge into the cylinders and exhaust of spent gases from them. For this purpose the valves at definite moments open and close the intake and exhaust ports in the cylinder head, through which the cylinder communicate with the intake and exhaust manifold.
The valve gear is composed of timing gears, a camshaft, tappets, valves, spring with fasteners and valve guides.
These are necessary to transmit rotation from the crankshaft to the camshaft, fuel injection pump shaft, and to oil pump and other mechanisms.
Camshaft’s function is to open the engine valves positively and timely, in a definite sequence, and to control their closing against the return action of the valve spring.
A valve consists of a head and stem. The valve head has a narrow chamfer of 45 or 30 referred to as valve face. The valve face fits tightly against the seat, which is achieved by grinding.
The valve spring provides the force necessary to close the valve and hold it tightly against its seat.
Engine fuel System
The fuel system is critical to operation. The system consists of the fuel tank, line, pump, filter and injectors.
For an electric fuel-injected engine, the fuel is pressurized and sent to the fuel feed pipe, through a fuel filter, and into the fuel injectors.
The fuel tank is used to store the fuel of engine needed. As the float position changes with different levels of fuel, the needle position on the dashboard gauge changes.
Fuel filers are used to stop any contamination from getting into the fuel system of both gasoline and diesel engine. The gasoline may have one or two filters in the fuel system. The first filter is usually placed inside the fuel tank to prevent large pieces of contaminant from damaging the fuel pump. The second one is an in-line type used to filter out small dirt particles.
Engine Cooling System
The purpose of the cooling system is to keep the engine at its most efficient operating temperature at all speeds under all driving conditions.
Water-cooling system is common. The cooling medium or coolant in it is either water or some low-freezing liquid, called antifreeze. A water-cooling system consists of the engine water jacket, thermostat, water pump, radiator, radiator cap, fan, fan drive belt and necessary hoses.
A water-cooling system means that water is used as a cooling agent to circulate through the engine to absorb the hot and carry it to the radiator for disposal. The engine is cooled mainly through heat transfer and heat dissipation. The heat generated by the mixture burned in engine must be transferred from the iron or aluminum cylinder to the water in the water in the water jacket. The outside of the water jacket dissipates some of the heat to the air surrounding it, but most of the heat is carried by the cooling water to the radiator for dissipation. When the coolant temperature in the system reaches 90, the thermostat valve open fully, its slanted edge shutting off the shorter circuit so that the coolant circulates through the longer one: water-pump, cooling jacket, thermostat, radiator top-tank, radiator core, bottom tank, pump.
Engine Lubrication System
The engine lubrication is mainly conducted by the lubrication oil. Engine lubricating systems are divided into two types: splash, pressure feed.
Pressure or forced lubrication is practically used in all engines apart from simple lubrication and splash lubrication, and is characterized by the oil being fed under pressure from a pump to the majority of engine parts, especially to main bearing and connecting rod bearings.
In modern engine designs, these two methods are often combined. Pressure is developed by the oil pump, which delivers oil to the filter for cleaning before it is sent to the camshaft and valve train components at the top of the engine. Other components are lubricated by splashing oil and by a network of passages, or galleries.
The oil filter can filter dirt and solids out of the oil in lubrication system. As these particles of foreign matter are prevented from entering the engine by oil filter, the rate of wear of engine parts is reduced. Engines of more recent designs use a full-flow centrifugal oil filter. That is, all oil passes through the filter before it reaches the bearings. This is a reaction-type centrifugal filter with which all oil delivered by the oil pump is cleaned in the filter rotor. This filter has an oil outlet pipe fitted inside the hollow spindle of the filter rotor and connected to the oil line that distributes the oil to the various parts of the lubrication system.
The chassis is a framework used to assemble auto components on it. The chassis itself is divided into transmission system is to apply to the components needed to transfer the drive from the engine to the road wheels. The main components are clutch, gearbox, drive shaft, final drive and differential.
Clutch
The clutch is a device used to provide smooth engagement and disengagement of the engine and manual transmission. Most cars equipped with a manual transmission use a single plate, dry clutch disc, a diaphragm type pressure plate and cover assembly, a clutch release bearing, and a clutch release fork.
In its operating position in the engine \transmission linkup, the clutch disc is sandwiched between the engine flywheel and clutch pressure plate. The clutch fork and linkage provide the means of converting the up-and-down movement of the clutch pedal to the back-and-forth movement of the clutch release bearing assembly. The clutch release bearing, in most cases, is a ball bearing assembly with a machined face on one side that is designed to contact the pressure plate diaphragm release fingers during disengagement. Engagement and disengagement of the clutch assembly are controlled by a foot pedal and linkage that must be properly adjusted and relatively easy to apply.

张小浩

不错，不错的

张小浩

可以可以，，好的的

张小浩

哈哈哈哈哈，，，，好的

927235448

just introduce  the power system

小何不帅

这是极好的