With the rapid development of the automobile industry, automobile users have higher and higher requirements for the comfort of automobile ride, and the quality of NVH (noise, vibration and harshness) has been paid more and more attention. The performance of NVH has become an important index to measure the quality of automobile manufacturing. As the heart of automobile, powertrain system not only affects the dynamic performance of automobile, As an important part of automobile power transmission system, transmission is one of the main sources of vibration and noise of powertrain

Automobile transmission noise is divided into five categories, including transmission squeal noise, transmission gear knock noise, gear shift noise, bearing noise and close noise. For gear system, according to different vibration states, the vibration noise is mainly divided into gear knock and squeal noise [1]. Among them, gear knock noise occurs in the constant meshing non bearing gear pair, When the transmission is put into a certain gear, the non load-bearing gear which is not put into gear is sleeved on the transmission shaft. Because there is backlash between the gear pairs, if the amplitude of the circumferential movement displacement difference of the non load-bearing gear pair exceeds the magnitude of backlash between the teeth, there will be knocking phenomenon. The strong knocking vibration between the non load-bearing gear pairs is mainly transmitted to the transmission housing through the transmission shaft and bearings, The transmission case radiates noise when it is excited. The knocking phenomenon of transmission gear has obvious wide-band noise characteristics and noise level jumping phenomenon [2], which makes it different from other transmission system noises, easily makes the passengers fidgety and uneasy, and seriously affects the ride comfort of the vehicle. Therefore, it is very important to study the knocking phenomenon of transmission gear

The research on gear knocking first appeared in the 1970s, when it was aimed at the research on the classical model of “vibration impact”. The research focuses on the solution method and dynamic characteristic analysis. With the deepening of research, the research focus is no longer a single “vibration impact” model, Li Runfang and Wang Jianjun [3] discussed the theoretical system, research trends and development trends of gear system dynamics as a whole earlier, with emphasis on the research content and methods of parameter vibration of gear system, However, the problem of gear knocking (slapping) in automobile transmission system is only discussed preliminarily [4], Domestic and foreign researchers and institutions have made a lot of achievements in the study of this problem

This paper discusses the present situation and development trend of the research on the knock dynamics of automobile transmission gears at home and abroad, focusing on the mechanism of knock noise of automobile transmission gears, the solution method of theoretical analysis model, the objective evaluation method of knock of transmission gears, the knock test of gears and the solutions to knock problems, This paper analyzes the research results and shortcomings of the current research on the problem of gear knock in transmission. Finally, it makes a summary and prospect from the perspectives of refinement and accuracy of the simulation model of gear knock, effectiveness of the test scheme, objective evaluation index and rationalization of the knock method, so as to clarify the direction of the research on the dynamic problem of gear knock in transmission.

This paper summarizes the present situation of the research on the dynamics of gear knock in automobile transmission, and focuses on the analysis of the research results and shortcomings in the aspects of gear knock modeling and test analysis. It is suggested that the future research should focus on the following aspects:

(1) The research on the refinement and accuracy of the simulation model of gear knock mainly includes: 1. For the knock model of automobile transmission gear, based on the overall consideration of the structural parameters, geometric parameters and manufacturing parameters of the gear system, the factors such as the time-varying meshing stiffness and static transmission error of the gear system, the friction of the meshing tooth surface, the squeeze effect of the oil film, etc. should be taken into account, and the theory of friction and lubrication should be combined, Study the complex and strong nonlinear system of transmission gear knocking; 2. The modeling method of the model should not rely solely on the system dynamics model based on the concentrated mass, but should establish the transmission gear knocking model based on the continuous distributed parameters such as the gear pair model considering the spatial displacement, the nonlinear stiffness bearing model and the transmission shaft treated by the finite element method, The simulation model parameters are continuously improved by using the corresponding transmission bench test results; 3. The research on the knock phenomenon of automobile transmission gears is no longer limited to the single establishment of transmission model, but also the whole power train model including transient engine model, clutch model, main reducer and differential, half axle and tire model, It can simulate the gear knocking phenomenon that may occur in the whole vehicle under various working conditions, and perfect the model parameters through the real vehicle test data

(2) Reasonable and effective test plan. Pay attention to the following methods to study the problem of gear knocking: 1. The transmission gear system is a complex and strong nonlinear system. First, the nonlinear dynamic characteristics of other components of the whole vehicle power transmission system should be excluded, and the characteristics of each component in the transmission should be studied by bench test sheet 1, It includes gear meshing characteristics, gear surface lubrication characteristics, bearing movement and friction characteristics, etc., which provide the test basis for improving the refinement model of transmission; 2. The knock noise of automobile transmission gear occurs in the specific working condition of the real vehicle, which is the result of the comprehensive action of the automobile transmission system, so the knock test (road test and drum test) of automobile transmission gear should be carried out, By arranging reasonable speed sensor, vibration acceleration sensor and microphone, and post-processing the collected effective data, it is used to guide and perfect the analysis model of transmission gear knock based on the whole power transmission system

(3) More reasonable evaluation indexes and methods. For the existing objective evaluation methods of gear knocking, all have their limitations. In the future research, we should pay more attention to the combination with the test data analysis results and subjective evaluation results, put forward more reasonable and effective objective evaluation indexes, and use regression method to establish the quantitative relationship between the subjective and objective evaluation indexes

(4) In the active design, the problem of transmission gear knock is considered. In the engineering practice, the phenomenon of transmission gear knock is often found in the sample vehicle, so the enterprise should pay enough attention to it. In the future, the possible problem of gear knock should be considered in the early development of automobile transmission, power train matching and other automobile active design, so as to reduce the cost of vehicle research and development