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Served as a transmission method, chain transmission has its virtue. Now it is playing an irreplaceable role in the field of Mechanic Engineering. Above all, with the moving forward of the high-speed drive method, silent chains have been widely used in industry. Straight tooth profile are used in conventional silent chains wheel, whose impact, crosscut vibration and noise are very big, The antithesis of which is the coordination of involutes tooth profile and silent chains, and this kind of drive is more stable and the performance was improved in to certain degree. In this paper, the silent chain wheel with involutes tooth profile was discussed, and the relevant parts are as follows:1. The history of chain drive was introduced briefly, and compared with gear and belt drive, chain drive’s strength and weakness were analyzed. That chain has been a kind of important component was pointed out. At the same time, this paper’s aim and underlying meaning were given a sketch.As well as above, the present situation and some kinds of silent chains’characteristics was introduced, virtue of Hy—Vo chain and a new complex engaged silent chains were mentioned briefly.2. This paper placed much emphasis on the chain wheel with involutes of the external meshing silent chain. So the gear teeth outline equation is the theoretical basis of the chain wheel teeth outline equation. Therefore, the meshing point coordinate used to fix on the position of the plate and the wheel is elicited according to the characters of involute, the teeth outline equation and the shape of plate.3. According to the formula hereinbefore, the modification coefficient of silent chain wheel with involute teeth outline can be elicited. When design the silent chain, if Pitch p (r the distance between the center of roller and the plate working side f) and z (the wheel teeth number) are determined, we may make use of the relationship of chain board and chain wheel and teeth chain board, the equation of the plate shape will be elicited. The steps are as follows. Firstly, the sprocket outline equation can be elicited by supposing a modified coefficient.4. When changing the center distance of silent chain transmission mechanism, increasing or decreasing chain links was used as a general way. Obviously, when speed ratio is 1:1, center distance was increase or decrease half or an exact multiple of half(np/2), n chain links are increased or decreased is workable. Or when speed ratio is not 1:1, and the change ofcenter distance satisfies the formula ,n chain links are increased or decreased is workable too. But if the change of center distance is too little, application of above is not functional. In this situation, the theory of modified gear transmission can be used to solve this kind of problem. If the center distance increase and keep the links number, the length of chain is not enough and can not be assembled whit chain wheel. But at the same time, if the modified coefficient of the chain wheel decrease, the teeth of wheel will become thin and the pitch circle will become small, so the chain can be assembled with the chain wheel. Similarly, if the modified coefficient of wheel increase to decrease the center distance, the teeth of wheel will become thick and the pitch circle will become big, so the chain is not too long relative to the chain wheel and the transmission mechanism can work normally. In this paper, the range of wheel modified coefficient is elicited approximately when the center distance change and the new way to deal with the center distance of silent chain with involute tooth outline change.5. A kind of Multi-body dynamics emulation software is applied to analyze the theoretical research result. The model of plate and the model of wheel with involute tooth outline can be got more easily by using this software and the dynamics model of silent chain transmission mechanism with determinate center distance also can be founded. By simulation computation, speed, directional acceleration of x and y coordinate axis, angular velocity and acceleration of driven wheel, and strain are obtained. Comparing between the emulation result and the theoretical analysis result, the former can fits the real situation. When varying the center distance, change the modification coefficient of chain wheel, compared with standard chain wheel mechanism, there is no marked change in kinematical and dynamical result. As a result, when the center distance of silent chain transmission mechanism is non-standard, it is workable to change the modified coefficient of the wheel.6. The primary merit of silent chain is low yawp. So, the numerical value of the yawp is an important standard to evaluate how to change the modified coefficient of chain wheel. The yawp contrast experiments of silent chain, which has different center distance, and different modified coefficient has been done and the experiment results demonstrate the numerical value of yawp doesn’t increase obviously.
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