Ringfeder Power Transmission recently introduced the Tschan TNR, a new model for highly elastic couplings. Unlike commonly used torsionally elastic shaft couplings, the TNR is adjustable and therefore allows for a smoother start-up of power transmissions. It also optimizes torsional vibration during operation. If it is mounted between the combustion engine and the transfer box, for example, this novel, non-shiftable coupling is not just suitedfor mobile construction machines such as excavators, cranes and wheel loaders, but also for power generation wherever combustion engines such as emergency power units or mobile generator are used. 

When internal combustion engines are employed, as is frequently the case with Diesel engines, the power train is subject to dynamic stimuli. These manifest in torsional-vibration behavior and are caused periodically as gas and mass forces are excited. The actual dynamic behavior of the power train can be plotted mathematically by joining mass moments of inertia, damping and rigidity. It is, however, the stiffness and the mass moments of inertia of the entire power train that determine at which frequencies, i.e. rotations, the disruptions occur. The position of the lowest natural frequency is defined by the distribution of the mass moments of inertia of the rotating components and the smallest rigidity; it thus depends on what kind of coupling is being used. When the excitation frequency and the natural frequency coincide, resonance is inevitable. By adjusting the mass moments of inertia and the rigidity of the coupling, both can be moved from service speed into the non-critical range.  

An example of the aforementioned behavior is the flywheel in diesel engines. Thanks to the additional mass moments of inertia, it homogenizes the torque curve. However, since the dimensions of flywheels are made with the fuel consumption and operating characteristics in mind, i.e. they are designed for the combustion process, it would be unwise to try to do anything at the vibration points on the drive side by using an additional mass moment of inertia. In practice, elastic couplings with a relatively low stiffness have stood their ground as the “problem solvers”. 

This is where the new Tschan TNR comes in. Due to its low stiffness, the shaft coupling influences the above-mentioned vibration points the most. The key figures of the coupling can now be adjusted on a larger scale and with little effort, while the out dimensions remain the same. The coupling becomes “adjustable” because the elastic buffers are separated one from another and, as a result, are ordered in series. This requires a smart combination of available elastomers on one inner and one outer buffer plane. Thus, the rigidity can be optimized for each power train. 

Frequently, there is a limited range of mechanical transmission elements available for the various coupling types and sizes. In addition, they are often fixed on a hub. In the past, it was therefore necessary to make compromises as far as the torsional vibration behavior was concerned. Now, however, with the Tschan TNR, the characteristics of the couplings can be adjusted.

 

“While I was working in the research and development department at Ringfeder Power Transmission, I always had the challenge of having to find the right coupling for the right power transmission that would match the torsional-vibration behavior of a given plant,” said engineer Simon Graf.