Face gear drive is a transmission mechanism in which involute cylindrical gear (small wheel) meshes with bevel gear, as shown in Figure 1, in which the included angle between the axis of small wheel and face gear γ It can take any value in the range of 0 ° ~ 180 °. When γ = The pitch cone surface of the 90 ° face gear will be a plane on which the teeth are distributed. To distinguish it from a cylinder (when γ= At 0 ° or 180 °, it is two cylindrical gears) or bevel gears, which will be driven under specific conditions γ = At 90 °, the transmission mechanism of involute cylindrical gear with bevel gear teeth distributed on the circular plane meshing with bevel gear and their tooth profile surfaces conjugate with each other is generally called face gear transmission, and the bevel gear is called face gear.
Although face gear transmission appeared as early as 1945, limited to the technical level at that time, its application is generally limited to low-speed and light load transmission. With the development of manufacturing, testing, materials, especially computing technology, it is possible to accurately calculate, detect and evaluate the tooth surface coordinates of face gear, and its transmission characteristics are gradually recognized by people. As the small wheels are opposite to the face gear, their axes can be intersected or staggered (offset), and the included angle of the shaft can be arbitrarily selected in the range of 0 ° ~ 180 °. Therefore, the arrangement of face gear transmission is very flexible, enriching the optional types of angle transmission. In the application of bevel gear, worm gear, staggered shaft helical cylindrical gear and other existing angular transmission occasions, face gear transmission can be selected.
For example, bevel gear transmission requires 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 face gear transmission is low and the transmission smoothness is good; Installation error and support deformation have little influence on meshing, which is especially conducive to the lightness and thinness of gearbox shell. In addition, the external gear transmission has many advantages: high angle accuracy, single-stage transmission ratio of 1:20, high transmission efficiency and so on.
In view of the many characteristics of face gear transmission, foreign countries have increased the research of face gear transmission since the 1990s, and there have been successful application examples, and achieved good economic benefits. For example, in the military neighborhood: after years of experimental research, NASA has applied face gear transmission in shunt confluence transmission system, and has played a unique advantage, showing obvious advantages in the application of aviation. In the Apache helicopter produced by Boeing, the face gear transmission replaces the original spiral bevel gear transmission, which greatly reduces the weight of the gearbox, saves space and greatly improves its bearing capacity. In the 21st century military helicopter transmission system plan (rds-21), Boeing will continue to adopt face gear transmission and further develop its application technology. In the civil field, crowngear, assag and other institutions are committed to promoting the application of face gear transmission in fields such 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 vehicle RS5 is used to distribute torque to the front and rear axles. It has the characteristics of wide torque distribution range, high efficiency and light weight.