Test Bench for Static Transmission Error Evaluation in Gears

In this paper a test bench for measuring the Static Transmission Error of two mating gears is presented and a comparison with the results obtained with the commercial software GeDy TrAss is shown. Static Transmission Error is considered as the main source of overloads and Noise, Vibration and Harshness issues in mechanical transmissions. It is defined as the difference between the theoretical angular position of two gears under load in quasi-static conditions and the real one. This parameter strictly depends on the applied torque and the tooth macro and micro-geometry. The test bench illustrated in this work is designed to evaluate the actual Static Transmission Error of two gears under load in quasi-static conditions. In particular, this testbed can be divided in two macro elements: The first one is the mechanism composed by weights and pulleys that generates a driving and a braking torque up to 500 Nm. The second element is composed by two structures called "supports": One fixed to the floor and the other movable in order to be as much as possible flexible to set tests for every kind of gears (spur, helical, bevel, hypoid, etc.). Above these two supports the kinematic chain (shafts, bearings, gears), the torque-meter to measure the instantaneous torque and two high precision angular encoders to detect angular differences as small as 10-6 rad are mounted. The Static Transmission Error experimental results obtained by the test bench for a pair of standard spur gears are then described and compared with virtual results of the numerical-analytical code GeDy TrAss. Finally, conclusions are drawn, and future developments are discussed.