Gear transmission refers to the transmission of motion and power by the gear pair device, it is the most widely used modern equipment in a variety of mechanical transmission. Its transmission is more accurate, high efficiency, compact structure, reliable work and long life. Its function is to change the speed ratio and direction of the motion mechanism. In particular, automotive system is mainly used to transfer the motion and power between the two axes,which help to achieve the effect of variable torque. If the gear train transmission is adopted, some specific functions such as commutation can also be realized, and the circular speed applicable to the work has a wide range of its application. Therefore, the shadow of gear transmission can be seen everywhere in the composition of the automobile.

In order to improve the intensity of gear transmission and to reduce the production cost at the same time, it is necessary to strength the treatment of the transmission gear, Variety of strengthening treatment methods are available but finally we choose the simple operation, low price, good strengthening effect of peening strengthening treatment. Shot blast also calls the shot peening, is to reduce fatigue,which improve the life of gears is one of effective methods. Shot peening treatment is high-speed projectile flow injection to the surface of gear parts. Due to plastic deformation in the surface layers of components, we form a certain thickness of reinforcement layer, which strengthened layer formed in high residual stress, The existence of the surface compressive stress when the load bearing parts can offset some of the stress, to improve the fatigue strength of gear parts.

However, the strengthening effect of different projectile medium on the gear is different in the process of shot peening. The main focus of this paper is to establish the gear model and the projectile model, then realize the process of shot peening,along with analyzing the strengthening effect of different projectile medium of shot peening method. In this way, the projectile medium with the best strengthening effect along with low cost can be determined to meet the demand for the use of auto parts. Besides it improves the quality of auto products and reduce the production cost of automobiles,which upgrade the interests of enterprises.

The realistic significance of the study is still very vast, because on one hand, the application of shot peening treatment range is suitable for all kinds of metal materials of reinforcement, on another hand, different hard medium and process parameters caused by shot peening effect still have very big difference. So both in colleges or universities and scientific research department of enterprise technology making deep research in this subject matter. For example, zhang yuanyuan wrote in "experimental study on the shot peening process of carburized gear steel" ^[1] : by changing the type, size and other process parameters of the used cast steel shot and performing shot peening process test on the carburized steel of a certain helicopter reducer, the type of cast steel shot with the best strengthening effect is obtained. Similarly, Harbin HuiLong auto box bridge co., LTD Jin Rongzhi engineer in his article "the application of shot peening technology in auto manufacturing, is discussed in the ^[3]: nowadays, the application of shot peening technology in automotive manufacturing is becoming more and more wide, different projectile materials such as cast steel shot, cast iron pills, steel cut pill, glass balls, ceramic balls, etc. There are big differences, so the reasonable choice of the projectile medium is particularly important.

2. 研究的基本内容与方案

2.1 Design basics and objectives

(1) Select appropriate gear design parameters and establish gear model amp; projectile model.

(2) The finite element method for analysis with software abaqus will be used to realize the shot peening simulation process; and the enhancement effect was viewed through post-processing.After that, the projectile material was replaced and the simulation analysis was repeated.

(3) Compare the effect of various projectile media on gear strengthening treatment, and select the projectile material with the best strengthening effect with low cost.

2.2 The technical scheme and measures to be adopted

(1) technical scheme flow chart is shown as follows: