Crankshaft, as its name implies, is a curved shaft. However, its bending is not random, but has a certain shape and regularity. A complete crankshaft consists of front axle, main journal, connecting rod journal, crank, counterweight and rear axle. A crank with two journals, and the crank and the main journals at both ends form a crank. Each cylinder of an in-line engine corresponds to a crankshaft, and every two cylinders of a V-type multi-cylinder engine correspond to a crankshaft. For example, a single-cylinder engine has one crank, a two-cylinder engine has two cranks, a four-cylinder engine has four cranks, an in-line six-cylinder engine has six cranks, but a V-type six-cylinder engine has only three cranks, a V-type eight-cylinder engine has four cranks, and so on.
The so-called crank arrangement is the included angle between cranks of multi-cylinder engines. The common three included angles are 90,120 and180, where 90 and120 are called spatial cranks and180 is called plane cranks. The arrangement position of cranks is closely related to the number of cylinders of the engine, the arrangement type of cylinders, the balance of the engine and the working order of each cylinder, and has certain rules. Generally speaking, the principles should be followed, such as balanced work interval angle of each cylinder, large distance between two cylinders for continuous work, alternating work between left and right cylinders of V-type engine as far as possible, symmetrical and even crankshaft arrangement, and good balance of engine work.
Let's analyze the crankshaft layout of different types of engines and their influence on engine performance. ? 1, single cylinder engine? The single-cylinder engine has only one crank, so it is not arranged. Because the single-cylinder engine can't achieve self-balance in work, its vibration is very large, so a balance shaft must be designed to cushion the vibration.
2. Two-cylinder engine? There are three types of two-cylinder engines, namely, in-line, V-type and horizontally opposed. Either way, it has two cranks, and the two cranks form an included angle of180, which belongs to a plane crank arrangement. The working interval angle is 360, and the working sequence is 1-2. Theoretically, this kind of engine can achieve self-balance, and the vibration of the engine is relatively small, especially when the pistons are arranged horizontally opposite, and the vibration is smaller. For example, a long time ago, the Yangtze River 750 motorcycle was equipped with a horizontally opposed two-cylinder engine, which ran very smoothly.
3. Three-cylinder engine? Three-cylinder engines can only be arranged in a straight line It has three cranks, and the included angle between them is 120, which belongs to the spatial crank arrangement. The working range angle is 240 and the working sequence is 1-3-2. Three engines are widely used now, and many cars and SUVs are equipped with them. Everyone's biggest concern about the three-cylinder machine is vibration. Because each cylinder does work at intervals, there is a gap period, and the up-and-down movement of the piston in each cylinder interferes with each other, so its vibration is natural. Although the balance shaft is installed, its vibration can still be felt.
4. Four-cylinder engine? There are three types of four-cylinder engines: in-line, V-type and horizontally opposed. In ordinary cars, inline four-cylinder is the most common. It has four cranks, most of which form an angle of180, belonging to a plane crank arrangement. But there are also spatial cranks arranged at 90 degrees to each other. This kind of engine is generally used on motorcycles. V-type and horizontally opposed engine also have four cranks, which are also arranged in the plane crank angle of180. In order to shorten the length of the engine, a semi-supported crankshaft is generally used. Four-cylinder engines can balance the first-order vibration in operation, but the second-order vibration cannot be balanced, so most four-cylinder engines still have a balance shaft. The working range angle of the four-cylinder engine is 180, and the working sequence is 1-3-4-2 and 1-2-4-3.
5. Five-cylinder engine? Five-cylinder engines are rare, and only some Audi models are still in use. Five-cylinder engines are generally arranged in a straight line, with five cranks, which form an angle of 72 degrees with each other, belonging to the spatial crank arrangement. The working range angle is 144 and the working sequence is 1-2-4-5-3. The five-cylinder engine has overlapping work, so it runs smoothly, but its type is special and not easy to be accepted. It is rare in family cars and only used in some performance cars.
6. Six-cylinder engine? There are three types of six-cylinder engines: inline, V-shaped and horizontally opposed, of which inline six-cylinder is the most common. It has six cranks, which form 120 with each other, and belongs to the spatial crank arrangement. The working range angle is 120, and the working sequence is 1-5-3-2-4 (right type) or 1-4-2-6-3-5 (left type). The six cranks of an in-line six-cylinder engine are evenly arranged in the three planes of 120, so that the first-order vibration and the second-order vibration generated when the piston moves up and down cancel each other out, and the cylinders work perfectly, so that self-balance can be perfectly realized. Among all engines, the inline six-cylinder engine is the only one that can run smoothly without any balancing device.
V-type six-cylinder engines are also common, and there are many kinds. The included angles of the two cylinders are 60, 90, 15 respectively, and the number of cranks is also different. Generally, a V6 engine with an included angle of 60 and 90 has three cranks, which are arranged at an angle of120, and belong to a spatial crank arrangement. The VR6 engine with an included angle of 15 belongs to Volkswagen's patent. Similar to an in-line six-cylinder engine, it has six cranks and is also arranged in space. The working range angle is 120 and the working sequence is 1-6-3-5-2-4.
7. Eight-cylinder engine? An eight-cylinder engine can only be V-shaped, and generally the included angle between two rows of cylinders is 90 degrees. The working range angle of the engine is 90, and the working sequence varies with different engines, generally 1-5-4-8-6-3-7-2 and 1-5-4-2-6-3-7-8. The V8 engine has four cranks, which can be arranged in two ways. One is the plane layout with an included angle of180, and the other is the spatial layout with an included angle of 90. What's the difference between these two arrangements?
Cranks are arranged at 90 degrees to each other, which is commonly used in American V8 engines. The biggest advantages of this arrangement are smooth operation, better mute effect and longer engine service life. However, in this arrangement, the crankshaft is heavier, the engine is heavier, and the acceleration performance of the car is slightly worse. In addition, because the cylinder on the same side will continue to do work, there will be exhaust interference, and the engine will emit a unique boiling water exhaust sound.
(arc space layout)? Cranks are arranged in the plane of 180, which is generally adopted by V8 engines in Europe. The biggest advantages of this arrangement are light weight of crankshaft, small moment of inertia, rapid increase of engine speed and good acceleration performance of automobile. The disadvantage is that the engine vibration is relatively large, so it is necessary to install a balance shaft to balance the moment of inertia of the crankshaft. Therefore, the large-displacement V8 sports car produced in Europe has superior driving performance, but the noise and vibration are relatively large; The large-displacement V8 sports car made in America runs very quietly and elegantly, with good linear acceleration performance, but the track performance is poor.
(Crank plane layout)? The above is the crank arrangement of common engines and its influence on engine performance. There are also some unusual engines, such as V 10, V 12 and W 12 engines. They have many cylinders and can only use the spatial layout of cranks. In fact, this problem should be more considered by automotive engineers. As consumers of the terminal, we can't choose and don't have to struggle.