Research on surface strengthening technology of high strength automobile gear

Gear is an important part to transmit power in mechanical devices. The Japanese mechanical society has carried out systematic investigation and Research on the failure cases of gear transmission in various industries. About 74% of the failure of gear transmission pairs is caused by the fatigue failure of gear surface, which fully shows that the strength and service life of gear are closely related to the quality of mechanical devices. In recent years, with the development of modern automobiles and new energy vehicles, military vehicles, warships, aerospace vehicles, high-speed railway facilities and other technologies, its power transmission mechanism further requires that the gears have the characteristics of high strength, high speed, high efficiency, high life, lightweight and small type (four high, one light and small). This not only puts forward new tasks for the design of gears, but also brings new research and development tasks for the development of new materials and innovative material processing technology. Among them, the surface strengthening technology is the key to ensure the realization of four high and one light gears. At present, there is a considerable gap between China and Europe, the United States, Japan and other countries in the design and manufacturing technology of high-strength gears, especially in the strength and service life of high-end automobile and mechanical parts and foreign products, which restricts the development of China’s auto transmission and other high-end mechanical and electrical equipment, so we should comprehensively improve the high-end gear It is imperative to turn the wheel into a wheel with high strength. As we all know, according to the research practice, to improve the fatigue strength life limit of gear, not only the alloy composition, carburizing and carbonitriding heat treatment technology of optimized materials need to be improved, but also the research and development of the surface strengthening treatment technology of gear must be combined, that is, to achieve the integrated surface integrity of gear to get better fatigue resistance, so as to achieve the high-strength gear High performance requirements for wheel contact fatigue limit, bending fatigue limit, fatigue endurance life and optimum friction factor.

In recent years, in order to develop new markets, various automobile companies are constantly improving the guaranteed driving mileage. Many internationally famous automobile companies have increased the guaranteed driving mileage to more than 340000 km. In order to achieve this performance index, the United States, Japan, Europe and other automotive companies have put forward stricter market specifications, increased the research efforts to improve the fatigue strength life of gears, and carried out in-depth research and development from the perspective of multi-element comprehensive index. This mainly includes the analysis and optimization of gear alloy materials, gear optimal heat treatment technology, gear surface strengthening technology, such as chemical treatment of manganese phosphate conversion coating, gear surface composite shot peening, molybdenum disulfide plus particle shot peening and other gear surface strengthening technology, and has achieved good practical results in the application of car automatic and manual transmission.

Module is an important parameter of gear. When selecting the module of automobile gear, the factors such as strength, noise, lightweight and processing technology should be considered. The range of common module and diameter process parameters of gears for passenger cars and commercial vehicles. In the process of transmitting torque and changing speed, automobile gears are usually in the working environment of high speed, high load and alternating impact load. Automobile gear materials not only need good machining performance and heat treatment carburizing and quenching performance, but also must meet the reasonable cost demand. In order to ensure the stability of the quenching depth of the tooth surface and the tooth top, the carburizing alloy steel with carbon content of about 0.2% and alloy elements such as Ni, Cr, Mn and Mo added alone or in combination is usually selected. Japan and Germany have carried out long-term research and development in the field of automobile high strength gear low carbon alloy steel materials. The composition of commonly used automobile gear materials is as follows: at present, the domestic and foreign automobile gear steels are mainly 20CrMnTi (domestic), 20mncrs (German) and 20CrMoH (Japanese). The steel grades A, B and C in the table are high fatigue steels.