A new Method for Selecting High Ratio Coaxial Gear Drives for Specific Applications

摘要

In the automotive industry, electric actuators are used for many applications. The gear drives in these actuators usually consist of a worm paired with a helical gear which is usually an ideal solution for brushed DC-motors. In some applications, these DC-motors are being replaced by electronically commutated motors (EC-motors) because they offer a significant reduction in axial length compared to DC-motors. For EC-motors, coaxial gear drives could therefore be the ideal choice as they require less axial space. Today, many different coaxial gear drive principles are known. The goal of this investigation was to develop a method allowing the selection of the best-suited coaxial gear drive for a given application. First, a matrix containing the most appropriate coaxial gears was generated. Second, a 'selection' table based on criteria such as efficiency, acoustic behaviour, costs, size, etc. was derived. Finally, by selecting the decisive criteria for a specific application, the designer is able to select the best-suited gear principle from the matrix for his specific application. This method was verified by applying it to a coaxial gear drive for a backrest actuator. For this specific application, a Wolfram-gear with three continuous planets was selected. A prototype was built and will be extensively tested. The predicted efficiency should be verified and different measurements to optimise the gear noise and the sensitivity to tolerances of the design such as symmetrical and non-syrnmetrical tooth engagement and variations of the carrier shall be carried out. From these experimental results more detailed design rules should be adopted; these can be applied to other principles and applications. In the future, this will help the designer to select the best-suited gear drive for his application and to reduce the time for the development for an actuator. In summary, this investigation shows that this new method is ideal for selecting the best-suited coaxial gear drive principle for a specific application.