Developing an Advanced Testing System for Variable Speed Hydraulic Motors

It all started with the T40B torque transducer from HBM. InTest were developing a new test bench for hydraulic motors, which needed more versatility than its existing system. The T40B is well-known for its outstanding precision, reproducibility and robustness. This device is particularly well suited for the static and dynamic torque measurements required in hydraulic applications. InTest were developing the test rig for Hydro Leduc (HL), a specialist hydraulic manufacturer, who have now adopted the T40B as its standard torque transducer and decided to equip all existing testing machines in their inventory to simplify maintenance management …

InTest manufactures industrial production test rigs and facilities for technologies such as hydraulics, pneumatics, electrics that are used in industries including automotive, aerospace, electronics and telecommunications.

Alexis Sanchis has been a project manager at InTest since 2007 and stressed that HBM has been one of InTest's preferred suppliers for more than five years. Sanchis said, "For difficult metrological applications, HBM is simply unrivalled, for example, when unsurpassed accuracy is required or when first-class transducers and modules for measuring data acquisition are need”. He continued, “HBM is a hugely professional company the sales department is highly cooperative; the employees have an excellent vision of the work we undertake in the various sectors and have detailed familiarity with their own products.”

Alexis Sanchis believes that HBM is more than just a supplier, and that they are real partners. Sanchis recalled a collaboration between HBM and InTest in the recent past to develop a Quantum module (acquisition/processing), which is now part of HBM's inventory of products. He explained, "Based upon a customer's request, HBM developed this product as part of a joint arrangement with InTest… both companies worked well together and a long-term association was born.”

Designing an Innovative and Powerful Test Bench

The test bench was designed for the customer Hydro Leduc, to test new variable displacement hydraulic adjusting motors for large agricultural and construction machinery. The test bench is 6 m long, 3.1 m wide, 3.5 m high, weighs 17 tonnes and is designed for 24 hours 6 days per week operation.

But the requirements do not stop there. In contrast to classic constant-velocity hydraulic motors, variable-speed motors work with large speed and power dynamics. This means that engines have to be tested at a higher number of operating points. Consequently, the new test bench is far more demanding than the constant-speed test bench provided by InTest for Hydro Leduc ten years ago.

The test rig is required to measure the horsepower developed by the engines and determine the torque and speed. The power can then be calculated by multiplying the torque by the speed. The InTest bench delivered to Hydro Leduc has a flexibility and adaptability allowing it to be used by all engines manufactured by the company.

The exacting demands of manufacturing this new equipment meant that both the knowledge and torque transducers of HBM were required again by InTest.

The Torque Transducer T40B at the Heart of the Test Bench

In order to meet the requirements of metrological performance and robustness InTest equipped its test bench with the cost-effective and highly accurate T40B torque transducer from HBM. The T40B features 0.03% accuracy in terms of linearity including hysteresis, as well as high temperature stability.

Coupled with the integrated magnetic rotational speed measuring system, it allows for power measurement in the drive train. In addition, the non-contact power supply and digital signal transmission guarantee fail-safe and maintenance-free operation. There is no contact between the transducer and the measuring electronics, which makes it easier to implement. The measured speeds set out by HL were up to 2,000 rpm but the T40B is actually capable of handling speeds of up to 24,000 rpm allowing it to be used for additional high-duty applications.

Also, the torque measurement requirements for HL were only up to 1,300 Nm and far below the performance of the T40B, which allows measurements of up to 2,000 Nm and direct measurement (with neither a transducer nor a multiplier, which might affect accuracy).

Alexis Sanchis explained about the transmission of the torque measurement to the detection electronics via the frequency output of the transducer, which was an ‘issue’ in the project. He said, "We chose frequency and not voltage output because of electromagnetic interference due to some large electric motors around the transducer."

Software is Key to Management and Measurement

The InNova software for the data processing and the control of the test bench were written in the .NET (by Microsoft) language and is constantly being improved by InTest. This open source software is completely customizable, and can be tailored by the user to develop the test bench according to their requirements.

The Hydro Leduc test bench for example, was originally designed to test variable displacement engines, but can now be used on all HL's engines, some 350 different models. Hydro Leduc can collect data for statistical evaluations to identify divergent production trends at an early stage and ensure full product traceability.

Why the T40B was the Best Option

Because of the flexibility, reliability, and precision of the T40B torque transducer in the new test bench it has been adopted across the board at Hydro Leduc on all of their test rigs. This means that not only has the T40B increased productivity, it has also allowed the HL maintenance department to reduce the number of items in their inventory and simplify parts management. To summarize the T40B torque transducer has the following benefits:

  • High accuracy: 1024 pulses/revolution
  • Angular accuracy of up to 212 steps
  • Integrated sensor optimized for magnetic fields
  • High signal quality and signal-to-noise ratio
  • No additional adjustment between pulse wheel and sensor required
  • Air gap of up to 2.5 mm between pulse wheel and sensor
  • Protected against environmental influences

This information has been sourced, reviewed and adapted from materials provided by HBM, Inc.

For more information on this source, please visit HBM, Inc.

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