Many people want to learn more about cars to deepen their understanding of cars, but due to the complexity of car structures, they all give up. Below we have prepared a set of illustrated car articles for you, which analyze the internal structure of the car with pictures, making complex principles easy to understand.
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Analysis of engine structure types
The engine is the power source of the car, just like the human heart. However, the size and structure of different people's hearts are not much different, but the internal structures of the engines of different cars are very different. So what are the differences in the structures of different engines? Let's find out together below.
● Source of automobile power
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The power source of a car is the engine, and the power of the engine comes from inside the cylinder. The engine cylinder is a place where the internal energy of the fuel is converted into kinetic energy. It can be simply understood that the fuel is burned in the cylinder, generating huge pressure to push the piston up and down, and the force is transmitted to the crankshaft through the connecting rod, and finally converted into rotational motion, and then Through the transmission and drive shaft, the power is transmitted to the drive wheels to propel the car forward.
●The number of cylinders cannot be too many
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Most cars in general have four-cylinder and six-cylinder engines. Since the power of the engine mainly comes from the cylinders, does it mean that the more cylinders the better? In fact, as the number of cylinders increases, the parts of the engine also increase. With the corresponding increase, the structure of the engine will be more complex, which will also reduce the reliability of the engine. In addition, it will also increase the engine manufacturing cost and subsequent maintenance costs. Therefore, the number of cylinders in a car engine is selected after a comprehensive trade-off based on the engine's use and performance requirements. Engines like V12, W12 and W16 are only used in a few high-performance cars.
● V-type engine structure
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In fact, a simple understanding of a V-shaped engine is that adjacent cylinders are grouped together at a certain angle. When viewed from the side, it looks like a V shape, which is a V-shaped engine. Compared with the in-line engine, the height and length of the V-type engine are reduced, which can make the engine cover lower and meet aerodynamic requirements. The cylinders of the V-type engine are arranged in opposite directions at an angle, which can offset part of the vibration. However, the disadvantage is that two cylinder heads must be used, and the structure is relatively complicated. Although the height of the engine has been reduced, its width has also increased accordingly, making it difficult to install other devices in a fixed-space engine compartment.
●W type engine structure
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The cylinders on both sides of the V-shaped engine are staggered at a small angle to form a W-shaped engine. Compared with V-type engines, the advantage of W-type engines is that the crankshaft can be shorter and the weight can be lighter, but the width also increases accordingly, and the engine compartment will be filled more fully. The disadvantage is that the W-type engine is structurally divided into two parts, the structure is more complex, and it will produce a lot of vibration during operation, so it is only used in a few vehicles.
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● Horizontally opposed engine structure
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The adjacent cylinders of a horizontally opposed engine are arranged opposite each other (the bottom of the piston faces outward). The angle between the two cylinders is 180°, but it is essentially different from the 180° V-type engine. Horizontally opposed engines are similar to inline engines in that they do not share a crank pin (that is, one piston is only connected to one crank pin), and the direction of movement of the opposing pistons is opposite, but the 180° V-type engine is just the opposite. The advantages of the horizontally opposed engine are that it can well offset vibrations and make the engine run more smoothly; the center of gravity is low, and the front of the car can be designed lower to meet aerodynamic requirements; the direction of the power output shaft is consistent with the direction of the transmission shaft, and the power transmission is Higher efficiency. Disadvantages: The structure is complex and maintenance is inconvenient; the production process is demanding and the production cost is high. Among well-known brand cars, only Porsche and Subaru still insist on using horizontally opposed engines.
● Why does the engine continuously provide power?
The reason why the engine can continuously provide power is due to the orderly cyclic operation of the four strokes of intake, compression, power and exhaust in the cylinder.
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During the intake stroke, when the piston moves from top dead center to bottom dead center in the cylinder, the intake valve opens, the exhaust valve closes, and fresh air and gasoline mixture are sucked into the cylinder.
During the compression stroke, the intake and exhaust valves are closed, and the piston moves from bottom dead center to top dead center, compressing the mixed gas to the top of the cylinder to increase the temperature of the mixed gas and prepare for the power stroke.
During the power stroke, the spark plug ignites the compressed gas, and the mixed gas "explodes" in the cylinder to generate huge pressure, pushing the piston from top dead center to bottom dead center, and pushing the crankshaft to rotate through the connecting rod.
During the exhaust stroke, the piston moves from bottom dead center to top dead center. At this time, the intake valve closes and the exhaust valve opens, and the burned exhaust gas is discharged out of the cylinder through the exhaust manifold.
● Engine power comes from explosions
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The power the engine can generate actually comes from the "explosive force" in the cylinder. In the sealed cylinder combustion chamber, the spark plug ignites a certain proportion of gasoline and air mixture instantly at the right moment, which will produce a huge explosive force. The top of the combustion chamber is fixed, and the huge pressure forces the piston to move downward. , pushing the crankshaft through the connecting rod, and then transmits the power to the driving wheels through a series of mechanisms, and finally drives the car.
● Spark plugs are masters of "detonation"
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If you want the "explosion" in the cylinder to be more powerful, timely ignition is very important, and the spark plug in the cylinder plays the role of "detonation". In fact, the principle of spark plug ignition is somewhat similar to that of lightning. The head of the spark plug has a center electrode and a side electrode (relative to two clouds with opposite polarity ions). There is a small gap (called the ignition gap) between the two electrodes. When energized, it can produce electric sparks of up to more than 10,000 volts, which can instantly "detonate" the mixed gas in the cylinder.
●The intake valve is larger than the exhaust valve
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In order to continuously "explode" in the cylinder, new fuel must be continuously input and exhaust gas must be discharged in time. The intake and exhaust valves play an important role in this process. The intake and exhaust valves are controlled by cams to perform the two actions of "opening" and "closing" in a timely manner. Why do the intake valves you see always be larger than the exhaust valves? Because the intake air is generally sucked in by vacuum, and the exhaust is squeezed to push out the exhaust gas, so exhaust is relatively easier than intake. In order to get more fresh air to participate in combustion, the intake valve needs to be larger to get more air intake.
● The number of valves should not be too many
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If the engine has multiple valves, the air intake volume is large at high speeds, the exhaust is clean, and the engine performance is better (similar to a movie theater, if there are many doorways, it will be much easier to get in and out). However, multi-valve design is more complicated, especially the valve driving method, combustion chamber structure and spark plug position, which all need to be carefully arranged. This requires high production process, high manufacturing cost, and difficult later maintenance. Therefore, the number of valves should not be too many. Common engines have 4 valves per cylinder (2 in and 2 out).
Analysis of engine variable valve principle
We have already learned about the basic structure and power source of the engine. In fact, the actual running speed of the engine is not static, but like a person running, sometimes fast and sometimes gentle, so it is especially important to adjust your own breathing rhythm. Let's take a look at how the engine "breathes".
● Function of camshaft
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Simply put, a camshaft is a metal rod with multiple disc-shaped cams. What role does this metal rod play in engine operation? It is mainly responsible for opening and closing the intake and exhaust valves. The camshaft continues to rotate driven by the crankshaft, and the cam continuously presses the valve (rocker arm or push rod), thereby controlling the opening and closing of the intake valve and exhaust valve.
●What do OHV, OHC, SOHC and DOHC mean?
The letters SOHC and DOHC are often seen on the engine casing. What do these letters mean? OHV refers to overhead valve and bottom camshaft, which means that the camshaft is arranged at the bottom of the cylinder and the valves are arranged at the top of the cylinder. OHC refers to overhead camshaft, that is, the camshaft is arranged on the top of the cylinder.
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If there is only one camshaft at the top of the cylinder that is responsible for opening and closing the intake and exhaust valves at the same time, it is called a single overhead camshaft (SOHC). If there are two camshafts on the top of the cylinder responsible for opening and closing the intake and exhaust valves, it is called a double overhead camshaft (DOHC).
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The cam of the bottom camshaft and the valve rocker arm need to be connected by a metal connecting rod. The cam lifts the connecting rod and pushes the rocker arm to open and close the valve. However, excessively high rotational speed can easily cause the ejector rod to break, so this design is mostly used in engines with large displacement, low rotational speed, and pursuit of large torque output. The overhead camshaft can omit the push rod, which simplifies the transmission mechanism from the camshaft to the valve, and is more suitable for the power performance of the engine at high speed. The overhead camshaft is widely used.
● The role of the gas distribution mechanism
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The valvetrain mainly includes timing gear train, camshaft, valve transmission components (valves, push rods, rocker arms, etc.). Its main function is to timely open and close the intake and exhaust valves of each cylinder according to the working conditions of the engine. , so that the fresh mixed gas can fill the cylinder in time, and the exhaust gas can be discharged out of the cylinder in time.
● What is valve timing? Why is timing needed?
The so-called valve timing can be simply understood as the moment when the valve opens and closes. Theoretically, during the intake stroke, when the piston moves from top dead center to bottom dead center, the intake valve opens and the exhaust valve closes; during the exhaust stroke, when the piston moves from bottom dead center to top dead center, the intake valve Close and exhaust valve open.
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So why do we need to be on time? In fact, in actual engine operation, in order to increase the amount of air intake in the cylinder, the intake valve needs to be opened in advance and closed later; similarly, in order to discharge the exhaust gas in the cylinder cleaner, the exhaust valve also needs to be opened in advance and closed later. Delay shutdown to ensure efficient engine operation.
●What are variable valve timing and variable valve lift?
When the engine rotates at high speed, the suction and exhaust time of each cylinder in one working cycle is very short. To achieve high charging efficiency, the suction and exhaust time of the cylinder must be extended, which is the requirement. Increase the valve overlap angle; when the engine is at low speed, an excessive valve overlap angle will easily cause exhaust gas to flow backwards, and the intake volume will decrease instead, resulting in unstable engine idling and low low-speed torque.
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It is difficult for fixed valve timing to meet the needs of both high and low engine speeds at the same time, so variable valve timing came into being. Variable valve timing can be adjusted according to different engine speeds and working conditions, so that the engine can achieve ideal intake and exhaust efficiency at high and low speeds.
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The essence that affects engine power is actually related to the amount of oxygen entering the cylinder per unit time. The variable valve timing system can only change the opening and closing time of the valve, but cannot change the amount of air intake per unit time. Variable valve timing Lift can meet this demand. If the engine valve is regarded as a "door" of the house, the valve timing can be understood as the time when the "door" opens, and the valve lift is equivalent to the size of the "door" opening.
● Toyota VVT-i variable valve timing system
Toyota's variable valve timing system has been widely used. The main principle is to install a hydraulic mechanism on the camshaft, and through the control of the ECU, adjust the opening and closing time of the valve within a certain angle range, or Advance, delay, or remain the same.
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The outer rotor of the timing gear of the camshaft is connected to the timing chain (belt), and the inner rotor is connected to the camshaft. The outer rotor can indirectly drive the inner rotor through hydraulic oil, thereby achieving angle advance or delay within a certain range.
● Honda i-VTEC variable valve lift system
The structure and working principle of Honda's i-VTEC variable valve lift system are not complicated. It can be seen as adding a third rocker arm and a third camshaft to the original one. How does it change the valve lift? It can be simply understood that through the separation and integration of three rocker arms, the switching of high and low angle camshafts is achieved, thereby changing the valve lift.
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When the engine is under low load, the three rocker arms are in a separated state. The rocker arms on both sides of the low-angle cam control the opening and closing of the valve, and the valve lift is small. When the engine is under high load, the three rocker arms are combined into one, and the valve lift is small. The angle cam drives the intermediate rocker arm and has a large valve lift.
● BMW Valvetronic variable valve lift system
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BMW's Valvetronic variable valve lift system mainly changes the valve lift by adding components such as eccentric shafts, servo motors and intermediate push rods to its valve mechanism. When the motor works, the worm gear mechanism drives the eccentric shaft to rotate, and then pushes the valve through the intermediate push rod and rocker arm. The eccentric rotates at different angles, and the camshaft pushes the valve through the intermediate push rod and rocker arm to produce different lifts, thereby controlling the valve lift.
● Audi AVS variable valve lift system
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Audi's AVS variable valve lift system mainly changes the valve lift by switching two sets of cams with different heights on the camshaft. Its principle is very similar to Honda's i-VTEC, except that the AVS system is installed on the camshaft. The spiral groove sleeve on the camshaft is used to move the camshaft left and right, thereby switching the high and low cams on the camshaft.
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When the engine is under high load, the electromagnetic driver moves the camshaft to the right and switches to the high-angle cam, thereby increasing the valve lift; when the engine is under low load, the electromagnetic driver moves the camshaft to the left and switches to the low-angle cam. , to reduce the valve lift.
Analysis of the principle of direct injection in the engine cylinder
As the requirements for energy and environmental protection become increasingly stringent, engines must continue to be upgraded and evolved to meet people's needs. I believe everyone is familiar with terms such as "in-cylinder direct injection", "stratified combustion" and "variable displacement". How do they work? Let's find out together below.
● Are the piston and crankshaft the most "tiring"?
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Once it is started and running, the "head" of the piston will be subjected to high temperature and high pressure, and it will continue to move up and down at high speed. The working environment is very harsh. It can be said that the piston is the "heart" of the engine, so the material production accuracy of the piston has very high requirements.
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The crankshaft being stepped on by the piston is also uncomfortable, as it has to continuously rotate at high speed. The crankshaft rotates thousands of times per minute and shoulders the arduous task of driving the oil pump, generator, air conditioning compressor, camshaft and other mechanisms. It is the intermediate shaft of engine power, so it is also relatively "strong".
● How to change linear motion into rotational motion?
We all know that the piston in the cylinder moves up and down in a linear motion, but in order to output the rotational force that drives the wheels forward, how does the linear motion be converted into rotational motion? In fact, this has a lot to do with the structure of the crankshaft. The connecting rod shaft of the crankshaft and the main shaft are not in the same straight line, but are arranged oppositely.
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This principle of movement actually follows me
