Direct integration of an HBM Torque Sensor in transmission systems for high speed applications

Direct integration of an HBM Torque Sensor in transmission systems for high speed applications
HBM - Hottinger Baldwin Messtechnik GmbH (France) - The specialist T40HS sensor allows the precise measurement of a torque of 1000 N with 0.05% accuracy in difficult mechanical and thermal environments with very high torques.

If there is any project that deserves to be called "innovative", it is the one recently completed by BCSA and HBM. BCSA specializes in mechanical force introduction systems for sophisticated applications with regard to torque, rotational speed, precision, resilience and longevity.

A little over a year ago, the French company with about 30 employees participated in a call for tender for the implementation of a mechanical transmission system for an F&E test bench in the area of aeronautics. The biggest names in test bench manufacture applied for the project for a Chinese end customer. Should BCSA be successful with their bid, then it will be down to the fact that the company offers an entirely new technical solution, which entails the integration of a torque sensor inside the transmission.

A bold solution:
This is a bold solution, as there has never been an integrated solution for torque flanges with 0.05% accuracy class in this combination of torque and rotational speed (1000 Nm and 45.000 rpm) available on the market to date. Nicolas Di Pol, in charge of torque applications at HBM France explains: "The torque sensors are among our core products and we need to continuously expand our product range to ensure that our company stays ahead of the competition in this segment. This is why we were able to quickly respond to BCSA’s request by developing a new, innovative product."

Easing the workload for system integrators:
BCSA has positioned itself as a flexible, innovative company with a focus mainly on export - a segment in which BCSA excels with up to 80% of turnover attributed to exports. The technical development of the BCSA transmission system has far surpassed standard specifications to on the one hand stay ahead of the competition and on the other - most importantly - to ease the workload of the customer.

Such a statement requires some explanation. It is important to remember that power test benches (e.g. for airplane or race car motors) require a physical simulation of real conditions and specifically of the actual loads a motor will be subjected to in order to correctly test the motor during its acceleration and deceleration processes at all speeds and depending on the simulation profile (ascends and descends, curves, type of road surface).

Loads are generally simulated using an electric motor in generator and/or brake mode. In most cases, a mechanical transmission is implemented between the motor under test (running at very high speed) and the load running at a lower speed.

The test benches are equipped with test and measurement equipment including at least one torque sensor to measure motor performance. The torque sensor will usually be positioned at the side that rotates at high speed, located between the turbo transmission and the test specimen. In terms of the invitation to tender in the area of aeronautics, BSCA of course applied in the segment in which the company excels, i.e. in the field of test bench systems for applications with high rotational speed.

Turbo transmissions by BCSA with instrument cabinet

nother bonus: The torque sensor is fully integrated in the turbo transmission:
The company, however, has another ace up the sleeve, which set it apart from its competitors and ensured the project win. David Montillet, Managing Director, offers some insights: "Usually, the test bench integrator will implement the integration of the torque transducer in the drive train at the input of the transmission. Prerequisite here is that two additional mechanical couplings plus a torque flange have to be installed in the shaft. That means that a lot more space is needed. Aligning the shafts requires specific expertise, since otherwise vibrations and mechanical loads might develop that could result in damage to the test bench.

In our case there is another challenge to overcome: rotational speed! At high rotational speeds, adding mechanical masses and components will increase the risk of vibrations which, in the worst case, may result in destruction of the test bench.

Our customer was well aware of these issues, which is why our ready to use solution with its turbo transmission-integrated torque sensor closed the deal ..."

"Promising strategy for the future"
"When BCSA contacted us, we had not even developed a sensor matching their requirements as yet. The request we received, however, was of great interest to us as it reflected a market trend. In my experience, the integration of test benches focuses mainly on monitoring and all the electronics involved, while the mechanical portion is left out. In effect, the higher the rotational speeds tested, the more the integration becomes a task for specialists. BCSA's suggestion to integrate the 1 kNm T40HS torque sensor inside the transmission is a very promising strategy for the future", explains Nicolas Di Pol.

This implementation is particularly suited to high speeds and HBM feels that it will increase the demand for high rotational speed torque sensors, specifically for airplane engine test benches. Motors run with ever increasing speeds to reduce weight - and therefore fuel consumption.

Turbo transmissions by BCSA with T40HS/1 kNm torque sensor by HBM

Technical challenges overcome:
BCSA was searching for a high performance and precise torque sensor, which would take up very little installation space and would be able to cope with difficult ambient conditions. BCSA's interest focused specifically on measurement flanges that would be much easier to install than the measurement shafts, while requiring only a minimum of installation space. HBM offers a wide range of products in this area, which is why BCSA looked for their assistance.

Precision was not an issue, as HBM’s strain gauge technology perfectly meets the requirements (an accuracy of 0.05% is more than sufficient). HBM’s range of torque sensors up to 45,000 rpm also satisfies the high rotational speed requirements.

The only remaining challenge is that of the ambient conditions. The transmission system developed by BCSA is oil-cooled - an environment that had to be taken into account. And then there was the issue of temperature.

The main challenge will therefore have been keeping the sensor within its operating temperature range.

Relevant studies and tests have proven that BCSA has developed technical solutions in which the sensor temperature will not surpass 75°C, which is more than sufficient.

The bespoke sensor developed for BCSA will of course be added to the HBM portfolio as well.

"This development represents a new technological breakthrough.”

“It puts us ahead of the competition in the current market - and in order to stay one step ahead, we will take the time we need to protect our innovations", explains Nicolas Di Pol.

Torque sensor by HBM

Instrument cabinet with PMX industry system for the measurement of torque, rotational speed and therefore performance, and all of that including realtime correction by way of active temperature measurements

About BCSA:
BCSA has been specializing in mechanical force introduction systems for 50 years. The implementation of reduction/turbo transmissions for test benches like the ones introduced in application introduced here, represents one of the core activities of the French company.
  • In addition to their application in test benches, the force introduction systems by BCSA are used primarily in the oil and gas sector and in cement factories and in the steel and paper industries.
  • The company designs, develops and delivers tailor-made systems for each individual application to match the exact customer requirements. These can be entirely new applications but will - for the most part - replace outdated systems. Their offering has always been characterized by the high performance and great resilience of their products.
  • A new development can now be seen in the development of systems for high rotational speed applications (30,000 rpm and higher - currently up to 125,000 rpm).
  • BCSA offers service and maintenance options for the installation and commissioning of their systems.
  • Also worth mentioning is the fact that BCSA additionally represents products by FLSmidt Maag Gear in France and in the Maghreb states, and that 80% of the company's turnover stems from exports (specifically in Asia (China), Europe (Germany, Austria, England, Italy), the Maghreb states, Eastern Europe (Russia), Brazil, etc.

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