What brand of bus engine do you have?

The main engines used by Yutong and Jinlong buses are domestic Yuchai, Chaochai, Xichai, Dachai and Shangchai engines, but Yuchai is the best and most used engine among these engines.

Because the engine has strong power, good quality and low fuel consumption, it is an advanced engine. Yuchai's engine sales and output rank second in the world. Other domestic engines cannot be compared with Yuchai. Also exported to many countries, buses with Yuchai engines are more expensive than buses without Yuchai engines.

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engine parts

Piston is the "heart" of the engine, which bears alternating mechanical load and thermal load, and is one of the key components in the engine with the worst working conditions. The function of the piston is to bear the gas pressure and transmit it to the connecting rod through the piston pin to drive the crankshaft to rotate. The piston top is also an integral part of the combustion chamber.

Conditions of use

The piston works at high temperature, high pressure, high speed and poor lubrication. The piston is in direct contact with high-temperature gas, and the instantaneous temperature can reach more than 2500K, so the heat generation is serious and the heat dissipation condition is poor. Therefore, the temperature of the piston is very high, up to 600 ~ 700 K, and the temperature distribution is very uneven. The top of the piston bears great gas pressure, especially the power stroke pressure, which is as high as 3 ~ 5 MPa for gasoline engine and 6 ~ 9 MPa for diesel engine, which makes the piston impact and bear lateral pressure.

The piston reciprocates in the cylinder at a high speed (8 ~ 12m/s), and the speed is constantly changing, resulting in a great inertia force, which makes the piston bear a great additional load. When the piston works in this harsh condition, it will deform, accelerate wear, generate additional load and thermal stress, and be chemically corroded by gas.

Piston structure

Usually, the piston is cylindrical. According to the working conditions and requirements of different engines, the structure of the piston itself is varied. Generally, the piston is divided into three parts: head, skirt and piston pin seat. The head refers to the piston top and the ring groove part. The top of the piston depends entirely on the requirements of the combustion chamber. The flat top or near flat top design is beneficial to reduce the contact area between the piston and high temperature gas and make the stress distribution uniform.

Most gasoline engines use flat-topped pistons. Some engines (such as direct injection diesel engine and new in-cylinder injection gasoline engine) need to have a pit with complex shape and certain depth at the top of the piston as a part of the combustion chamber in order to improve combustion efficiency and minimize deflagration. The groove of the piston is called the ring groove, which is used to install the piston ring. The function of piston ring is to seal, prevent air leakage and prevent oil from entering the combustion chamber.

Piston skirt refers to the lower part of the piston, and its function is to keep the vertical posture of the piston in reciprocating motion as much as possible, that is, the guiding part of the piston. The piston pin seat is the supporting part of the piston connected with the connecting rod through the piston pin, which is located above the piston skirt. The special feature of high-speed engine piston pin seat is that the pin seat hole is not necessarily on the same centerline plane as the piston, but can be slightly offset to one side, that is, to the side where the piston contacts the cylinder wall during the power stroke.

In this way, when the piston changes direction to the top dead center, the degree of the piston knocking on the cylinder wall will be reduced, thus reducing the engine noise. The shape of the piston skirt is very particular, especially for light passenger cars like cars. Designers often use their brains on the piston skirt to make the engine compact and run smoothly from the perspective of engine structure and performance.

Piston influence

With the more and more strict requirements of the whole vehicle on the power, economy, environmental protection and reliability of the engine, the piston has developed into a high-tech product integrating new technologies such as lightweight and high-strength new materials, special-shaped cylindrical composite surfaces and special-shaped pin holes, so as to ensure the heat resistance, wear resistance, guiding smoothness and good sealing function of the piston, reduce the friction loss of the engine and reduce oil consumption, noise and emissions.

In order to meet the above functional requirements, the outer circle of the piston is usually designed as a special-shaped outer circle (convex ellipse), that is, the section perpendicular to the piston axis is an ellipse or a modified ellipse, and the ellipticity changes along the axis direction according to certain rules, and the ellipticity accuracy reaches 0.005mm；; The outer contour of the piston longitudinal section is a fitting curve of higher-order function, and the contour accuracy is 0.005 ~ 0.01mm; In order to improve the bearing capacity of piston and engine power, the pin hole of high-load piston is usually designed as a micro-inner conical surface or a normal stress curved surface (special pin hole). The pin hole dimension accuracy reaches IT4 level, and the contour accuracy is 0.003 mm ..

Piston, as a typical key part of automobile, its cutting process has strong manufacturability. Domestic piston manufacturing industry is usually composed of general machine tools and special equipment combined with piston process characteristics. Therefore, special equipment has become the key equipment for piston cutting, and its function and accuracy will directly affect the quality index of the key characteristics of the final product.

Baidu encyclopedia-Yuchai heavy-duty engine