Face gear drive is a kind of transmission mechanism that the involute cylindrical gear (small wheel) and the bevel gear mesh, in which the angle γ between the axis of the small wheel and the face gear can be arbitrary in the range of 0 ° ~ 180 °. When γ = 90 °, the pitch cone of face gear will be a plane on which the teeth are distributed. In order to be different from the cylindrical (when γ = 0 ° or 180 °, it is two cylindrical gears) or the bevel gear transmission, the transmission mechanism that the involute cylindrical gears and the bevel gears whose teeth are distributed on the circular plane mesh with each other and whose tooth profiles and surfaces are conjugate is generally called the face gear transmission, and the bevel gear is called the face gear.
Although face gear drive was introduced before 1945, its application was generally limited to low-speed, light load transmission occasions, limited to the technical level at that time. With the development of manufacturing, testing, materials, especially computing technology, it is possible to accurately calculate, test and evaluate the tooth surface coordinates of face gears, and its transmission characteristics are gradually recognized by people. Since the axes of the face gears of the small wheels can be intersected or staggered (offset), and the angle between the axes can be arbitrarily selected within the range of 0 ° ~ 180 °, the arrangement of the face gear transmission is very flexible, which enriches the optional types of angle transmission. In the application of bevel gear, worm gear, cross axis helical cylindrical gear and other existing angular transmission occasions, face gear transmission can be selected. For example, bevel gear transmission needs high axial installation accuracy to obtain a reasonable tooth surface contact area, while for face gear transmission, the contact area is not very sensitive to the axial installation accuracy of the small wheel, so the small wheel does not need accurate axial positioning and adjustment; because the transmission error amplitude is small, the noise level of the face gear transmission is low, and the transmission smoothness is good; The influence of installation error and support deformation on meshing is small, especially conducive to the thinning of gearbox shell. In addition, the external gear transmission has many advantages, such as high angle accuracy, single-stage transmission ratio up to 1:20, and high transmission efficiency.
In view of the many characteristics of face gear drive itself, foreign countries have increased the research of face gear drive since the 1990s, and have successfully applied examples, and achieved good economic benefits. For example, in the military neighborhood: NASA has applied the face gear drive in the shunting confluence drive system after many years of experimental research, and has played a unique advantage, showing obvious advantages in the application of the aviation field. Surface gear drive is used instead of the original spiral bevel gear drive in Albuquerque helicopter produced by Boeing company, which greatly reduces the weight of gearbox, saves space and improves its bearing capacity [6]. In the 21st century military helicopter drive system plan (rds-21), Boeing will continue to adopt face gear drive and further develop its application technology. In the civil field, crown gear, assag and other institutions are committed to promoting the application of face gear transmission in such fields as automobile differential, radar antenna, renewable energy, printing and dyeing, wind power, multi branch transmission, robot and so on. As shown in Figure 2, the center differential based on face gear design in the full-time four-wheel drive system of Audi high performance sports car RS5 is used to distribute torque to the front and rear axles, which has the characteristics of wide torque distribution range, high efficiency and light weight.
Although face gear drive has many excellent performance indexes, the application of face gear drive is mainly limited to the key transmission systems in the fields of helicopters, high-performance vehicles and so on. There are many reasons for the low popularity of gear transmission at home and abroad. The high manufacturing cost and complex manufacturing equipment and technology are the main obstacles to its wide application. The purpose of this paper is to summarize the research progress of current gear manufacturing technology, summarize the characteristics and application occasions of existing manufacturing methods, and discuss the future research trend.