Mayr shaft couplings selected for industrial test stands

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Kistler is the world market leader in dynamic measurement technology for measuring pressure, force, torque and acceleration. Numerous cooperations with partners from both the industry and science characterise the company philosophy. In the area of compensating couplings for torque measurement flanges, Kistler has for many years trusted in the cooperation with the renowned family company mayr power transmission.

Whether e-mobility or emission reductions for combustion engines – the current trends and the rapid progress lead to the industry’s increasing demand for dynamic and highly precise products in torque measurement. That is why Kistler has developed KiTorq, an innovative torque measurement flange system for industrial test stands. This device is able to reliably determine, for example, the performance during the efficiency measurement of e-motors, gearboxes and pumps. It is characterised by a high dynamic with a limit frequency of 10kHz and an accuracy class of 0.05 per cent.

To make sure that the high-precision torque measurement flange system also provides exact and reliable data even for high-performance applications at all times, it is used together with a shaft compensating coupling. This coupling is a decisive accessory to minimise the disturbance variables having an effect on the measurement flange. Based on the proven backlash-free and torsionally rigid ROBA-DS construction series, mayr power transmission therefore provides a design based on their compensating coupling which is specially adapted for measurement flanges, and which creates the prerequisites for accurate measurement results.

Disturbance variables or so-called parasitic loads acting on the measurement flange often occur due to alignment errors in the drive line. As a result, misalignments between the input and output side occur in almost all applications. Due to existing radial, angular and axial shaft misalignments, bending torques and radial and axial forces occur on the measurement flange. Normally, all these misalignments occur simultaneously. Here, even as accurate an alignment of the shaft train as possible using the ultra-modern laser alignment equipment available today can only partly provide a remedy. Furthermore, misalignments cannot be completely eliminated due to the existing tolerances in size accuracy of the components used and due to external influences such as the temperature. Therefore, torsionally rigid shaft misalignment compensating couplings such as the ROBA-DS disk pack coupling are used together with the measurement flange. These couplings transmit the torque backlash-free and with extreme torsional rigidity.

Berk Buharali, Product Manager Torque Sensors at Kistler Instrumente GmbH explains: “The couplings compensate for transverse and axial forces as well as bending torques. This allows us to realise even the smallest measurement uncertainties. Therefore, the couplings do not only guarantee precise measurement results, but also provide the best possible protection for the measurement flange, the mechanically weakest link in the drive line. So they guarantee a long service lifetime.” In addition to high running smoothness and a low mass moment of inertia, the couplings are distinguished by high balance quality and are particularly robust and resistant.

No limitations at nominal torque

Ralf Epple, Product Manager at mayr power transmission explains: “For the ROBA-DS disk pack coupling, the nominal torques specified in the catalogue are exploitable without any limitations. A reduction in this nominal torque due to misalignment, overall load configuration or balancing requirements is not necessary.” The couplings are compact, and simultaneously combine high performance density with absolutely backlash-free operation. Design details such as sand-blasting of the disks and the use of specially formed collar bushings ensure a backlash-free flow of force with an outstanding force flow density between the input and output. The ROBA-DS disk pack couplings transmit torques up to the nominal torque absolutely backlash-free and with a consistently high torsional rigidity. The specified shaft misalignments can be used to 100 per cent in total without influencing the transmitted torque.

Ralf Epple adds: “The connection of the ROBA-DS couplings and the measurement flanges to the shaft train is normally executed backlash-free via high-quality shrink disk hubs. Moreover, different coupling designs and flexible combination possibilities especially tailored to the requirements of the test stand enable the integration of measurement flanges in almost every test stand and drive constellation.” For this purpose, depending on the construction size, standard designs of the ROBA-DS coupling cover a speed range of 8000 to 18,000 rpm and are balanced to a balance quality of G 2.5 (reference speed 3000 rpm).

With high-speed designs, in which the individual parts are machined to an extremely high accuracy (quality IT5) and narrowed concentricity and axial run-out tolerances, speeds of up to 30,000 rpm are permissible. Here the balance quality of the coupling is G 2.5 at a reference speed of 5000 rpm.

Reliable protection against overload

In many test stand applications, torque limiters are often used in a combined design with shaft couplings. With the correct dimensioning, they not only protect the measurement flange, but also the frequently expensive test pieces against overload damage. Should the torque exceed the set limit value on the torque limiter, then the clutch disengages and disconnects the input and output within a fraction of a second. Following an overload occurrence, the measurement shaft may in worst cases have to be re-calibrated, but any expensive damage to the drive line or the test piece is reliably prevented by the torque limiter. With the EAS-HSC and EAS-HSE construction series, mayr power transmission has developed torque limiters which are tailored to the extreme requirements of test stand technology. For the combination of a shaft coupling and a torque limiter, mayr power transmission provides complete solutions from a single source. For this purpose, the tradition-steeped family business can call on comprehensive expertise and many years of experience in development and design. All products are extensively tested on calibrated test stands and accurately adjusted to the required values of the respective application.

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