Torsional vibration is defined as the angular vibration ofan object, often represented by a shaft along its axis of rotation. This effect can become a serious concern in power transmission systems, comprising of shafts and couplings, where failures may occur as a result of increasing or uncontrolled torsional vibration.In this article, David Proud General Manager of Reich Drive Systems UK highlights the critical part that torsional vibration calculations play in ensuring that the coupling specified has the correct design characteristics for the application.
Torsional vibration, induced by torque pulses from the combustion process, occurs naturally as part of the operation of a diesel engine and can vary dependent upon the number of cylinders, the firing order and the speed of the engine. In addition, in other applications, there are also driven components such as piston compressors, plunger pumps, propellers etc. that can induce torque pulses in a torsional system. Irrespective of the application, if left unchecked, the resulting torsional vibration can lead to significant failure of one or more parts of the drive train.
The only way to avoid the potentially damaging effects of torsional vibration within a drive train is to ensure that all parties, including the coupling supplier perform appropriate torsional vibration calculations and, where required, torsional vibration analysis, based upon the engine, alternator and the coupling proposed for the application.
Torsional vibration calculations are a core competence of Reich, where for example as standard, in depth analysis of both engine and alternator data contributes to a number of factors including: operational safety, space requirements for the design, the choice of coupling recommended and of course cost. Reich also offers as an option a further and more detailed torsional vibration analysis of the proposed application, for events such as engine mis-fires.
The choice of conducting a torsional vibration calculation or a torsional vibration analysis will be determined largely by the complexity of the application. The standard torsional vibration calculation, for a 2-mass system, has been developed in-house by Reich and conforms to DIN 740 Part 2. The relevant coupling values used in this calculation include: nominal torque, maximum torque, fatigue torque and torsional stiffness. For more complex applications, and in instances where information other than coupling loads is required, Reich uses the more comprehensive n-mass system, which is widely recognised by industry bodies.
David Proud comments: ”It is essential that designers and engineers selecting couplings to be used in powertrain applications draw on the resources and expertise of a trusted coupling supplier such as Reich. In addition to torsional calculations and analysis, Reich is recognised for its ability to provide application and customer specific solutions through the company’s D2C (Design to Customer) philosophy. Together, these factors will ensure that the final installation will meet the specified criteria, and crucially, mitigate the potential effects from torsional vibration.”
Reich offers a comprehensive range of different coupling types, including the ARCUSAFLEX coupling, which has been designed to absorb high levels of torsional vibration and shock loading, protecting drive trains against overload conditions. This highly flexible flywheel coupling provides a torsionally soft connection between the internal combustion engine and a driven machine. Other highly flexible couplings in this range include the ARCUSAFLEX-VSK, TOK, MULTI CROSS FORTE and MULTI CROSS RILLO.
(Reich’s Arcusaflex coupling provides a torsionally soft connection between the internal combustion engine and the driven machine)