Measurement of the friction forces between piston and cylinder in reciprocating machines using the connecting rod strain behavior

The design of slider-crank mechanisms is usually done using numerical simulation supported by experiments to validate the results of both the individual parts and whole assembly. The largest challenge in this process is to establish parameters to evaluate the simulation using experimental results. The dynamic measurement of the connecting rod strain can provide important information about the forces which act on the piston, such as the ones caused by friction and pressure. However, this measurement is challenging, since it is done in an adverse environment where oil, high temperature variation and vibration are present. This work aims to solve this problem by proposing a concept of connecting rod instrumented with a strain gauge tee-rosette bridge and the proper signal conditioning method to measure the friction forces between the piston and the cylinder. To work with the worst-case scenario, a small-sized sintered connecting rod was used to verify if the proposed method is applicable to a wide range of equipment. The obtained results are at least equivalent to the ones presented in the literature, but the proposed method uses a simpler setup and allows the test to be done using the motor in its application condition. In addition, the proposed method allows the observation of high-frequency phenomena, such as impacts during a cycle, which cannot be characterized using the methods proposed in the literature. (C) 2019 Elsevier Ltd. All rights reserved.