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17
2020
-
09
Why does the engine have a flywheel? What does it do? What is the dual-mass flywheel?
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Let me ask you a question, why can a car engine run smoothly and continuously? I think everyone will say that the engine is well tuned, the crankshaft is balanced, the fuel system and ignition system are working properly, the multi-cylinder engine does work overlapping, and so on. But many people will ignore a very important factor, that is, the role of the engine flywheel.
Many people may not know what the engine flywheel is and where it is. If I tell you that it is installed at the end of the crankshaft, you may not understand it easily. But I'll tell you one thing, and you should know where the flywheel is. When our car starts, it needs a starter to drive the engine to run before it can start. This starter directly drives the flywheel. As long as you find the starter, you find the flywheel. When the car is started, the starter is energized to run, the drive gear meshes with the ring gear on the flywheel, and then the starter rotates to drive the flywheel to rotate, the flywheel drives the crankshaft to rotate, and the engine starts to run. Therefore, the flywheel is one of the components of the engine. It is assembled with the crankshaft and is the power output element of the engine.
The structure of the flywheel is very simple, it is a cast iron disc with a large moment of inertia. In order to increase the moment of inertia under the same mass, the edge of the flywheel is generally made thicker. The edge of the flywheel is generally inlaid with a ring gear, which meshes with the starter gear when the engine is started to drive the crankshaft to rotate. There are several screw holes in the center of the flywheel, which are combined with the crankshaft through bolts. One side of the flywheel is a flat surface, which is in contact with the clutch plate, and the other side is a special shape, which is connected with the crankshaft.
So what is the role of the flywheel? As mentioned earlier, the flywheel is needed when the engine is started, but the start is only one of the functions of the flywheel. Now some engines equipped with a 48V light hybrid system directly drive the front end of the crankshaft when starting, and there is no need to drive the flywheel. In fact, the flywheel has a more important role, that is, to improve the uniformity of engine operation by storing and releasing energy, and to improve the ability of the engine to overcome short-term overload. At the same time, the flywheel is also the power output element of the engine, through which the engine The power is transmitted to the clutch or torque converter. In addition, the flywheel is also engraved with a top dead center mark to calibrate the ignition timing or fuel injection timing and adjust the valve clearance.
So why does the engine have a flywheel? This starts with the working principle of the engine. Nowadays, reciprocating piston four-stroke engines are commonly used in automobiles. This type of engine performs work once every four piston strokes, but in the entire working cycle, only the power stroke generates power, and other intake, compression and exhaust strokes are all It consumes power. If there is no flywheel, all the power generated by the engine's power stroke is output to the outside, and there is no excess power to overcome the work consumed by the intake, compression and exhaust strokes, and the engine cannot continue to run. Even if a multi-cylinder engine does work at intervals, the crankshaft will run extremely unevenly, the speed will fluctuate from high to low, and the engine will stall if there is a slight resistance, making it difficult to continue running.
The flywheel is a disk-shaped part with a large moment of inertia, which acts as an energy storage. In the power stroke, in addition to the external output, part of the energy emitted by the engine is absorbed by the flywheel, and then released in the intake, compression and exhaust strokes to compensate for the work consumed in these three strokes, so that the crankshaft can overcome Resistance to continue running. In this way, the engine can run continuously without stalling due to the energy consumption of the other three strokes. In addition, when the piston is at the top dead center or bottom dead center, the connecting rod is completely perpendicular to the crankshaft. At this time, the power of the connecting rod cannot be transmitted to the crankshaft, which means it is "stuck. The huge moment of inertia of the flywheel can help the piston smoothly cross the top and bottom dead centers, re-form the angle between the connecting rod and the crankshaft, continue to transmit power, and avoid engine "stuck".
In addition, because the four-stroke engine does work at intervals, the crankshaft will be subjected to periodically changing torque. The crankshaft runs fast and slow, and the speed is high and low. The fewer the number of cylinders, the more obvious this phenomenon is. It will make the car extremely difficult to drive. Due to the large moment of inertia of the flywheel, it can absorb part of the energy when the crankshaft is increasing, and it can also release energy when the crankshaft is decelerating to increase the power of the crankshaft and hinder its deceleration, thus improving the operation of the crankshaft. Uniformity. Even if the engine encounters a short-term overload condition, the flywheel can release power to avoid the engine stalling and improve the engine's ability to overcome the short-term overload.
Therefore, the flywheel must exist for the engine, but the size and shape of different types of engine flywheels are different. Generally speaking, the fewer the number of engine cylinders, the greater the size and mass of the flywheel, and the more the number of engine cylinders, the smaller the size and mass of the flywheel. In addition, the form of the gearbox will also affect the size and quality of the flywheel. For example, for manual transmission models, because the flywheel needs to be combined and rubbed with the clutch plate, the flywheel size and mass are larger, and at the same time, it must have the ability to overcome thermal degradation; and Automatic transmission models can absorb engine vibration and balance the speed of the crankshaft to a large extent, so the size and mass of the flywheel are small, even some models use a flexible flywheel with a very small mass.
So is the weight of the flywheel related to the power of the engine? The weight of the flywheel will not increase or decrease the power output of the engine, but it can change the power output characteristics of the engine. If the flywheel mass is too large, it will cause the engine to speed up slowly, but the ability to overcome overload will be stronger, and the power viscosity effect will be stronger; if the flywheel mass is small, the engine will speed up faster, but the overload capacity will be slightly worse, and the car will accelerate and decelerate. More smoothly. In fact, the mass and size of the flywheel of all engines are the result of comprehensive consideration of various factors, after precise calculation, and strict dynamic balance test, the overall performance is very balanced.
The traditional flywheel is an integral part that can help the engine run smoothly, but it does not have a shock absorption function. The vibration of the engine will be directly transmitted to the transmission system, and the vibration of the transmission system will also be fed back to the engine, thereby affecting the stability of the engine and the transmission system. Run. Therefore, automotive engineers invented the dual-mass flywheel. The so-called dual-mass flywheel refers to the division of the original flywheel into two parts, one part is retained on the side of the original engine, and acts as the original flywheel for starting and transmitting the torque of the engine; the other part is placed On the transmission side of the drive train, it is used to increase the moment of inertia of the transmission. There is an annular oil chamber between the two parts of the flywheel, and a spring damper is installed in the chamber. The spring damper connects the two parts of the flywheel into a whole.
The biggest advantage of the dual-mass flywheel is that it can effectively reduce the uneven rotation of the engine and cause the torsional vibration of the drive train. In the traditional clutch structure, there is a torsion damper on the clutch plate to reduce the torsional vibration when the clutch is engaged and the speed changes, but it cannot perfectly balance the vibration of the engine and the gearbox. The dual-mass flywheel is divided into two, one is to reduce the impact of the clutch when it is engaged or disengaged, and the other is to reduce the vibration of the engine. In addition, the dual-mass flywheel itself has a shock absorption function, so the clutch plate matched with it does not need to be equipped with a torsion damper, which reduces the mass and size of the clutch plate.
Therefore, dual-mass flywheels are now being used more and more. In traditional dual-clutch gearboxes, dual-mass flywheels are generally used instead of hydraulic torque converters; in some manual gearboxes, dual-mass flywheels can be used to subtract clutch plates. The torsion damper on the disc reduces the moment of inertia of the clutch disc, makes the gearbox shift smoother, and can also reduce the burden on the synchronizer; in addition, there are many diesel vehicles in Europe, due to the large diesel engines, the use of dual-mass flywheels can effectively reduce engine vibration.
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2020-09-17
Why does the engine have a flywheel? What does it do? What is the dual-mass flywheel?
Let me ask you a question, why can a car engine run smoothly and continuously? I think everyone will say that the engine is well tuned, the crankshaft is balanced, the fuel system and ignition system are working properly, the multi-cylinder engine does work overlapping, and so on. But many people will ignore a very important factor, that is, the role of the engine flywheel. Many people may not know what the engine flywheel is and where it is. If I tell you that it is installed at the end of the crankshaft, you may not understand it easily. But I'll tell you one thing, and you should know where the flywheel is. When our car starts, it needs a starter to drive the engine