Views: 2 Author: Site Editor Publish Time: 2022-07-15 Origin: Site
In order to reduce fuel consumption and carbon dioxide emissions, vehicle lightweight has become one of the focuses of public attention. The research shows that the fuel consumption per 100 kilometers can be reduced by 0.3~0.6 L for every 100 kg reduction in vehicle curb weight. In addition, vehicle lightweight can also improve vehicle power, save materials and reduce costs. It is estimated that by 2010, the average curb weight of vehicles will be reduced by 17%, that is, 250 kg; The curb weight of the car will be reduced from the current average of about 1300 kg to 1000 kg.
In addition to the above purposes, the lightweight of the engine also involves the mass distribution of the whole vehicle (vehicle driving dynamics). When replacing a gasoline engine with a diesel engine, it often makes the engine heavier (solid structure, turbocharger, charge air cooler, fuel injection device, etc.), resulting in an increase in the axle load of the front axle, which destroys the balance of the whole vehicle. Therefore, the light weight of the car engine has become a problem that can not be ignored in the development of the whole vehicle.
The first way to lighten the engine is to increase the lift power to reduce the mass of the engine per unit power. The most advanced power density index has approached 1 kg/kw. Take the car diesel engine as an example. If the rising power was only around 20-30 kw/l in the early 1990s, its rising trend can be described as "rapid progress" since the end of the 20th century. Nowadays, the maximum burst pressure of diesel engine has reached 20 MPa and the power rise has reached 60 kW / L.
In principle, the casting process of aluminum alloy body can be divided into multiple use mold (metal mold) and one-time use mold (sand mold). The manufacturing methods of sand cores are also different. Nowadays, sand mold gravity casting and die casting are the most commonly used in mass production. Sand gravity casting provides the greatest degree of freedom in molding, and closed cylinder head connection surface (closed top plate) can be used. If the number of pieces produced is high (more than 200000 pieces per year), die casting is an economic solution. Die casting can realize the thin-walled structure of castings with very short beat, fine surface quality and precise size. However, due to the high filling pressure of molten metal, sand cores cannot be used, and the water jacket must usually be opened upward (open top plate). This means that the cylinder barrel lacks radial support. However, even so, it may not cause serious deformation of the cylinder barrel. Now, even direct injection diesel engines can be made into open roof structures. In addition, the rapid filling process of die casting is easy to lead to the formation of bubbles, so that the mechanical properties cannot be improved by thermal aging hardening. This disadvantage can be avoided by squeeze casting, because the pressure used in this process is low, which significantly slows down the filling process and may make feeding possible. In addition, die casting has an indirect effect on the length of the water jacket. Due to the cylinder diameter, the position of the pull rod bolt, the minimum width of the sealing flange and the necessary, usually 0.5 ° mold withdrawal angle, the water jacket of the actually made die-casting body usually only covers 70% of the piston stroke at most. This will reduce the heat flow through the piston ring and increase the heat load of the oil. Die casting has some limitations in the body structure. However, these can be controlled by technical means. Whether the machine body adopts the die-casting process depends on the production batch first.
For high load engine, sand casting can produce reliable and durable engine body through appropriate molding process, alloy optimization and heat treatment. From the perspective of part cost, making full use of the large degree of freedom of sand casting in molding can also integrate various functions into the cylinder block, so as to reduce the quality and improve economic benefits on the whole.
If the gray cast iron cylinder body is converted to aluminum alloy casting, some additional requirements must be met, which are described below
1 ensure that the sliding surface of the cylinder barrel is wear-resistant and not easy to deform
2 meet the requirements of transmitting force flow
3. Control the expansion of main bearing clearance
4 Effect of low elastic modulus of aluminum alloy on acoustics and vibration
1. Measures for the sliding surface of cylinder barrel
2 measures to ensure force flow transmission and control main bearing clearance
3. Measures to ensure the dynamic characteristics of the structure
Cost performance analysis
The cost performance analysis of 2.0L 4-cylinder engine made of gray cast iron, vermicular cast iron and aluminum alloy is carried out. The results are shown in Table 1.
According to the annual output of 400000 pieces, when vermicular cast iron is used, the cost is increased by 38%, and the blank cost and machining cost are increased to the same extent; When using aluminum alloy body, the cost increases by 62%, mainly due to the high material price. The cost advantage of aluminum alloy in machining is greatly weakened by a variety of mixed processing.
Cost performance analysis shows that aluminum alloy structure has great potential. Only when the overall arrangement is very compact (the center distance of the cylinder is small), the material properties of vermicular cast iron will be highlighted.