Modified precision couplings key to oil viscosity measuring instrument

Modern automotive engines run at increasingly higher speeds and temperatures, placing ever greater demands on lubricant performance. With lubricant formulators aware of the limitations of existing viscometry technologies, a tribology test equipment specialist set out to design a new breed of instrument. And when it needed a high-performance coupling as part of the design that could reach speeds of 20,000 rpm, it turned to Huco.

In the development of engine oils and lubricant additive packages, researchers look to characterise a candidate lubricant with measurements of viscosity at different temperatures and shear rates – the rate at which fluid layers move past each other, measured in reciprocal seconds. For lubricant formulators developing products for today’s high-performance engines, the ability in testing to recreate accurately the increased shear rates encountered is critical.

Not so long ago, a typical shear rate for an engine oil might have been expected in the order of 1,000,000 reciprocal seconds, and this represented the state-of-the-art in viscosity measurement. Today, though, developments in engine technology and lubricants mean that shear rates have risen sharply, and in-service conditions are more like 10,000,000 reciprocal seconds.

This creates difficulties with existing viscometry instruments. It is difficult to simply extend their range due to problems caused by shear heating of the lubricant. Further complications would be created for the user, due to the calibration procedures that would have to be carried out manually every time the instrument was used.

A global leader in the tribology test equipment industry, sought to address this issue, developing a new breed of ultra shear viscometer (USV). The company patented a novel measurement technique that avoids the problems of shear heating found in conventional steady-state viscometers by only subjecting the test lubricant to the high shear rate for a short time – short enough that the oil film temperature does not change significantly. A second benefit of this technique is that it allows a once-and-for-all calibration to be made at the start of operation, with this calibration then used for all subsequent measurements.

Combining high performance with high reliability

The fully automated, microprocessor-controlled USV utilises proprietary software to perform ultra shear rate measurements in less than an hour. In its development, a key challenge was sourcing a precision coupling to connect the machine’s rotary head, with the requirement to reach speeds up to 20,000 rpm in extremely short bursts. With the highest levels of both performance and reliability a priority, and with a standard coupling unavailable to meet the demands of the application, the company contacted Huco.

With over 40 years’ experience to call on, Huco offers machine builders access to a convenient and responsive customisation service that encompasses its complete range of standard couplings. A brand of Altra Industrial Motion Corp., a leading global supplier of power transmission equipment, Huco is able to offer cost-effective modification and customisation on any of the products in its extensive range, even when only relatively small batches are required.

Offering an in-house design and manufacturing capability, Huco has built a reputation for being able to provide customised couplings with a wide range of specifications on short lead times. The company can complete the design process in days, with average sized orders manufactured and delivered in a couple of weeks.

After a careful review of the application requirements, Huco recommended modified versions of its Flex-M membrane-type couplings, with a torque rating of 11.3Nm. Flex M precision couplings feature thin pressed steel membranes – torque is resolved to simple tensile stresses in opposing segments of the membranes. The couplings have near-infinite life and a dynamically balanced construction which makes them suitable for applications requiring high rotational speed and motion integrity. A double-stage version of the coupling was selected to provide greater misalignment capacity.

The new instrument is already proving its worth to lubricant researchers and manufacturers, playing a key role in the development and test of new formulations, and Huco is pleased to have contributed to the project. At the heart of the USV, the Flex-M couplings have demonstrated not only their performance but also their reliability, with the instrument manufacturer reporting no field issues despite the highly demanding nature of the application.

About Huco

With more than 50 years of innovation, Huco Dynatork is recognised as a world leader in precision coupling and piston air motor technologies. Backed by extensive application experience, utilising the most advanced materials, Huco Dynatork designs and manufactures innovative power transmission solutions that meet the most demanding customer requirements.
Huco Dynatork manufactures a comprehensive range of precision coupling types including beam, Oldham, Uni-Lat, bellows, rigid, flex membrane, jaw and double loop. A full line of highly efficient piston air motors and air motor/worm gearbox assemblies is also offered.
Reliable Huco Dynatork products can be found in a variety of key markets including food processing, energy, textiles, medical, packaging, metals, machine tools and material handling on applications such as stepper & servo drives, dynamometers, scanners, pumps, fans & blowers, mixers, conveyors and compressors.