HYPOID GEAR DESIGN BEYOND CONVENTIONAL APPROACH

摘要

Conventional hypoid gear design approach utilizes specific commercial programs provided by gear machine providers. Those programs typically have a set of assumptions as the starting point for the hypoid gear design. That type of approach works well when the overall system performance matches the assumptions. The gearing systems have been evolving significantly to reach ever-higher customer demands. The condition challenges the engineering community to go beyond the conventional wisdom. As the breakthrough ideas come into the system concept, the conventional hypoid gear design assumptions might not be sufficient to represent the actual performance. Unexpected failure modes and reliability of the products could cause serious consequences. Hypoid gear design based on system concept becomes a more effective approach under such conditions. This paper presents examples of how system approach helped analyzing and designing hypoid gears for modern powertrain systems in heavy vehicle applications. The effectiveness of such approach makes those systems realistic and reliable to meet extremely strict customer demands. Conventional hypoid gear design tools require the system to be sufficiently rigid to duplicate the actual gear tooth contacts as observed on the gear tester. Typical relationship between the gear set is represented by E, P, G, and α, which represents three linear displacements and one angle displacement as shown in Figure 1 [1]. This approach works well if the system performance meets all the assumptions defined by the tools. As the complexity of the system increases, more considerations for hypoid gear design become critical. Analytical tools that take into consideration other components beyond the gear set provide an effective way to understand the hypoid gear performance in different conditions closer to the reality. Figure 2 is an example analytical model of a heavy vehicle carrier [2]. Gear performance could be predicted in advanced engineering stage and compared to experimental results at a later stage of the product development. This approach provides insight into potential risks earlier in a product development cycle and cuts the product development cycle time significantly. Another advantage of this type of approach is the possibility to understand the gear set performance under different operating conditions. Conventional hypoid gear design tools focus primarily on vehicle driving condition. The heavy vehicle industry faces more diversified operating conditions based on customer needs. Figure 3 is one example showing the analysis results of one testing condition where ring gear concave side drives pinion convex side (coast mode).