Lightweight technology for automotive turbochargers[Copy link]
The turbocharger can improve the power performance of the engine without changing the displacement of the engine, but there is a turbo lag phenomenon. In order to improve its acceleration performance and reduce turbo lag, the inertia moment of the rotating body must be reduced, and the most effective way is to reduce the mass of the rotating body. Therefore, many countries have carried out research and development of new lightweight materials. 1 Ceramicization of turbine rotors Ceramic materials have good high temperature strength, high corrosion resistance, high wear resistance, low expansion coefficient and low density (about 1/2 of steel). Using it to replace heat-resistant alloys can greatly improve the efficiency of thermal engines, reduce energy consumption, save precious metals, and achieve lightweight effects. At present, ceramic materials have been widely used to replace Ni-based heat-resistant alloys to manufacture turbocharger rotors, and good results have been achieved. 1.1 Material selection Ceramic materials are light in weight and have good heat resistance, but they have the disadvantage of brittleness. According to the use environment and conditions of automotive superchargers, especially in the temperature range below 100 ℃, various ceramic materials were selected. It was found that Si3N4 ceramics have the advantages of light weight, high strength, heat shock resistance and good toughness, and are ideal materials for manufacturing turbine rotors. Using Si3N4 instead of Ni-based heat-resistant alloys to manufacture turbine rotors can reduce the inertia moment of the rotor monomer by 45% and the inertia moment of the rotating body by 34%. The acceleration time of the supercharger from starting to 100,000 r/min is shortened by about 36%. 1.2 Forming technology There are generally three types of ceramic forming methods: spray forming, slurry casting and hydrostatic (hydraulic) forming. Spray forming is to inject ceramic slurry into a high-pressure spray gun and spray it into the prefabricated cavity through the spray gun; slurry casting is the most common ceramic forming method, which is to directly inject ceramic slurry into a prepared model and blow it dry; hydrostatic (hydraulic) forming is to inject ceramic slurry into the mold, apply a certain pressure and blow it dry, which is an improvement on the slurry casting method. Table 1 lists the characteristics of ceramic forming methods. As a forming method for ceramic turbine rotors, the injection molding method should be selected because it has high productivity and is easy to obtain complex shapes (because the slurry casting method is limited by shape). The specific process is to first use hydrostatic pressure (hydraulic) forming to make the shaft part and injection molding to make the thin-walled blade part, and then use stamping to form the shaft and blade as a whole.
1.3 Sintering technology Si3N4 is a difficult-to-sinter material with strong covalent bonding, but it can become a relatively easy-to-sinter material by using oxide-based sintering aids. Its commonly used sintering methods include reaction sintering, pressureless sintering, hot pressing sintering and gas pressure sintering. Pressureless sintering: It is the most common ceramic manufacturing method. For example, pressureless sintering Si3N4 is made by adding sintering catalysts (such as Be, Mg, Al) to Si3N4 powder and sintering it under normal pressure. Reaction sintering: It uses the synthetic reaction of ceramics at high temperatures for sintering. For example, reaction sintering Si3N4 is to mix the crushed metal Si powder with a binder, process it or spray it, and sinter it once at 1180℃～1200℃. After processing, it is nitrided at 1350℃～1450℃ to become the finished Si3N4. Hot-pressing sintering method: It is to heat and pressurize the carbon model to carry out high-temperature sintering of ceramics. For example, hot-pressing sintering of Si3N4 is to add MgO, Y2O3, etc. to Si3N4 powder, pressurize to 20 MPa~30 MPa, and heat to 1700℃ to obtain a sintered body. Gas pressure sintering method: When gas-pressure sintering Si3N4, a sealed box containing Si3N4 powder is placed in a pressure-resistant container equipped with a heating wire, and heated and sintered in argon at 1700℃~1800℃ and 100 MPa pressure.
The performance of Si3N4 ceramic sintered bodies is related to the sintering method. Table 2 lists the characteristics of various Si3N4 sintering methods. From the perspective of manufacturing supercharger turbine rotors, the rotor strength is insufficient when the reaction sintering method is used; and it is difficult to meet the requirements of complex shapes using the hot pressing method. Therefore, the atmospheric pressure sintering method and the gas pressure sintering method are currently commonly used to manufacture Si3N4 rotors. Table 3 lists the characteristic values of Si3N4 obtained by these two sintering methods. The former is characterized by the ability to obtain microscopic crystals of complex polymers; the latter is characterized by suppressing sintering aids and sintering under high pressure to increase high-temperature strength, etc. As a high-speed rotating body, it shows sufficient advantages.
The joint surface between ceramic and metal shaft is close to the rotor to prevent lubricating oil from flowing to the exhaust side when ceramic is damaged. The temperature of this joint surface is quite high. Therefore, as a high-temperature resistant joining technology, the press-in method and active brazing method are generally used. When using the active brazing method, the surface of Si3N4 is brazed with silver containing Ti, but a stress relief layer composed of Ni and W is configured. In this structure, since the linear expansion coefficient and Young's modulus of Si3N4 and the metal shaft are quite different during brazing, the stress relief layer is set to reduce the residual stress. In addition, the combination of Ni and W is selected based on comprehensive considerations such as the temperature distribution of the joint part, the linear expansion coefficient and Young's modulus of each material, and the reaction of the brazing material. 2 Resinization of compressor impeller Since the strength of fiber-reinforced resin is higher than that of high-strength steel, its density is only 1.5 g/cm3~2.0 g/cm3, which is lower than that of aluminum alloy. The use of fiber-reinforced resin to manufacture compressor impellers can achieve the purpose of reducing the mass of the turbocharger. 2.1 Characteristics of carbon fiber reinforced resin PKU The newly developed polymer material is based on polyether ketone resin, with a mass percentage of 30% carbon fiber reinforced plastic PKU, which is used to manufacture compressor impellers to replace the aluminum alloy materials used in the past. Table 4 lists the comparison of the characteristics of the two. It has good creep resistance, corrosion resistance, wear resistance and small thermal expansion (no expansion between -65 ℃ and 105 ℃). Compared with other carbon fiber composite materials, PKU/CF30, a carbon fiber reinforced material with PKU 30% (mass), has a higher glass transition temperature (about 30 ℃ higher than polyether ketone resin), which is suitable for the use environment of compressor impellers.
2.2 Application effect of resin compressor impellers After the compressor impeller material is replaced by carbon fiber reinforced resin instead of aluminum alloy, the inertia moment of the rotating body can be reduced by 27%, and the time from stepping on the accelerator pedal to setting the boost pressure can be shortened by 8% to 9%. Figure 1 shows the comparison of acceleration performance when the turbocharger is fully opened. 3 Conclusion The use of ceramic materials and fiber reinforced resins instead of heat-resistant alloys and aluminum alloys in turbochargers can achieve the purpose of lightweighting. In the future, with the development of related technologies such as material joining technology and part design technology, lightweight materials will be widely used in automobiles.
600)this.width=600" border=0>
600)this.width=600" border=0>
600)this.width=600" border=0>
600)this.width=600" border=0>
600)this.width=600" border=0>
提升卡
变色卡
千斤顶
京公网安备 11010802033920号
