A New System for Testing Gears Under Variable Torque and Speed

In many applications, the transmitted power by a gearbox is fluctuating strongly. For example, in wind energy converters the rotor torque depends on the wind velocity and therefore varyies over a wide range, whereas the rotor speed is constant. In automotive applications, both torque and speed vary according to the driving conditions. It is evident, that in order to test such gearboxes, test rigs are needed that enable torque and speed to vary during the test according to the testing requirements and simulate the actual loading conditions as accurately as possible. The first part of this paper is a review of the many known mechanical devices developed to load gears. Their advantages and disadvantages are commented and presented. The second part describes a novel system designed and built by the authors (patent pending), which makes it possible to apply the test torque and speed according to a given load pattern during the test of the gears. It can further be implemented in close power loop test rigs (known also as back-to-back test rigs) such as the FZG test rig. The gearboxes of the test rig may be similar enabling thus the measurements of the power loss and efficiency of the gear pairs. It can also be used in the research of fatigue related surface failures, such as pittings and micro-pittings. The system consists mainly of a self-locking planetary Wolfrom gear train. Its sun gear is connected to a high starting torque electric motor, while its two ring gears are connected to the shafts ends of the two gearboxes. The operation of the motor is controlled by a computer. The software compares the actually applied torque, which is measured by a contactless torque meter, with the required torque, which has been already prescribed.