The load sharing of the cogwheel of a helicopter

The coaxial gear split torque drive is a new type of helicopter main reducer. The enhanced rotorcraft drive system program (ERDs) was first proposed by the United States Army Aviation Application Technology Agency and Boeing company. Compared with the traditional gear split torque transmission, the transmission ratio is larger and the structure is more compact. In the 21st century, a large number of invention patents have emerged in foreign countries. The research on this configuration is being carried out gradually in China. The research content of this paper is based on the research plan of a certain helicopter coaxial gear split torque transmission main reducer during the 13th five year plan.

Although the structure of the cogwheel is symmetrical in geometry, the force is not symmetrical, and the power transmission path is complex, which makes the load transmitted by each branch not equal. The uneven load of each branch in the system will greatly reduce the fatigue life of the gear and increase the maintenance cost of the main reducer. In engineering, the input gear floating method is usually used to balance the load between the branches. The research on the load sharing of the gear split torque drive is mainly seen in the planetary gear drive and the cylindrical gear split torque parallel drive. The configuration of the cogwheel is different from the above-mentioned type of split torque transmission, and the research literature related to load sharing is very limited. There is no relevant research report in China, and only Chun and heath are reported in foreign literature.

Chun et al. Used analytical method and finite element method to calculate the load distribution at the meshing position of each gear, and the error of the calculation results of the two methods was within 10%; heath et al. Built a complex testing platform for the load distribution of the cogwheel in the meshing position, and the test results obtained by adjusting the system parameters were as follows: both gears at the input gear The load factor is 1.083, and the average load factor between the two idlers is 1.33. However, the cost of test method is huge, and the whole test cycle is long. In order to analyze the load sharing characteristics of the cogwheel system, this paper uses the method of equivalent transformation to study the causes of the uneven load and the key parameters of the uneven load. Through a large number of numerical simulation, the influence of input gear support stiffness and backlash on system load sharing is analyzed, which provides theoretical guidance for system parameter design and selection.

This paper analyzes the application of the cogwheel in a helicopter, and reveals the mechanism of uneven load. An analytical model for calculating the load sharing of the cogwheel split torsional transmission is established, and the influence of input gear support stiffness and backlash on the load sharing performance of the system is studied by numerical simulation. The conclusions are as follows:

(1) Because of the difference between the backlash parameters and the stiffness parameters of each branch, the system is generally uneven load.

(2) The smaller the support stiffness of the input gear is, the better the load sharing of the two gears at the input gear is.

(3) The increase of backlash can reduce the load transmitted by the branch. When the input gear support stiffness can not meet the load balancing requirements, the backlash of the branch with larger load can be increased to achieve load balancing.

(4) In order to achieve the load sharing between the two idlers, it is necessary to ensure that the backlash between the idler 3 and the idler 4 is the same during manufacturing and installation.

(5) When the support stiffness of input gear is very small, the load distributed by each branch is low sensitive to the backlash of input gear.

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