New application possibilities for innovative torque measurement in test benches – with PMX

Main target of politics and economics is to develop standards for the next phase of more fuel efficient vehicles, particularly directed towards medium to heavy duty fleets. This will help with bolstering energy security & cut carbon pollution, thereby saving money and supporting the manufacturing innovation. As such, engine manufacturers and drivetrain engineers have a challenge - to enhance the performance of current and future engines with fuel efficiencies so as to be compliant with the standards, as well as lead over their competition & satisfy customer expectations.

Today's essential success factors include lightning-fast response to market needs with new products, which are nevertheless mature. Manufacturers must respond to this with shorter development times and test methods that are both efficient and flexible. This in turn requires separation organizationally and in terms of time when preparing and conducting test tasks. Efficiency improvement by a factor of 10 can be achieved here. Energy efficiency is an important issue in the automotive and aviation industries. Focus is shifting increasingly to engine development, rolling resistance and energy conversion efficiency.

First, it must be possible to implement the test structures quickly. This can be achieved with intelligent sensors and measuring amplifier systems that communicate with each other and exchange configuration data, for example by using TEDS sensor data detection. Essential preconditions for this are high quality of measured values and accuracy. HBM's torque flanges of series T10, T12 and T40 meet both these preconditions – high accuracy combined with high dynamics and rotational speed.

In addition, the measuring amplifier and control system must be capable of further processing the measurement data in real time, so that the test bench can then be regulated. It is also essential to make measurement data available at high resolution for analysis and to save it. To achieve real efficiency gains, all these functions must be combined in a single device. The PMX^® measuring amplifier system was developed by HBM based on these requirements. It allows for use in testing and proving grounds and can also be used as a measurement and automation system in the production area. This is made possible by flexibly fitting it with measurement and output channels. Depending on the level of automation, analog or Ethernet-based fieldbus interfaces can be used in real time.

It is exactly this flexibility of hardware combined with the possibility of data recording at the highest data rate and resolution that brings users a further efficiency gain by a factor of up to 30.

3. What can be done to further enhance the performance of torque measurements?

Measurement signals from torque sensors are acquired with the PMX plug-in module for frequency measurements, the PX460. It works with an accuracy of 0.01% and up to four torque sensors of series T10, T12 or T40 can be operated. Mixed operation is also possible. To further optimize the measurement data, the PMX^® measuring amplifier system includes a whole series of internal computing channels specially designed for operation and use of torque transducers. They work exactly like measurement channels in real time at a calculation rate of 50 microseconds.

This includes for example a 21-point linearization of the characteristic curve of the transducer for the torque sensor. The result is an improvement in the raw signal of the sensor in PMX^® – beyond the accuracy specified in the data sheet. The improved measurement signal can then be further processed, which increases the measurement quality of the test bench.

Other ways of scaling is the use of polynomials and straight pitches. Especially with the use of polynom-scaling, an increase by a factor of 10 can be achieved since these represent the sensor characteristic again significantly more accurate. The coefficients of the polynomial of the sensor is determined already are in production and subsequent calibration of the sensors during the calibration. Since only 3rd order polynomials are needed here, later parameterization of the PMX measurement channels is very simple and avoids incorrect entries.

To rise the accessible accuracy of torque sensors, calibration equipment can be used to capture the behavior of the sensor under various load cases. These load case include on one hand the dynamic right- and left rotation, on the other hand beside the 100% measuring range also a high accurate measurement in partial ranges are needed. This is necessary e.g. to capture the residual breaking torque. For this purpose, these different applications are measured during the calibration of the sensor and determines the corresponding characteristic curves according to DIN51309 or VDI / VDE 2646 and held firmly in the calibration protocol. These characteristics can then be stored in PMX^® and then be used in the test depending on the application. PMX^® recognizes from the current measured parameters which application is present and then automatically share-fourth the predefined sensor characteristics.

Another important function is parallel, independent processing of raw measurement values, for example filtering. This makes it possible to adapt the signals for regulation and automation of the test bench. It is this combination of analog outputs and/or PMX® real-time Ethernet fieldbuses that makes it possible to implement efficient test bench automation.

Special filter for testing combustion engines: Due to the work cycle with compression and expansion in the individual cylinders and the corresponding fluctuations in combustion, the torque generated by an engine exhibits highly dynamic behavior. In many measurement systems it appears as "noise" (or rapid changes). This can be eliminated by using a CASMA filter (a filter that works angle-synchronously).

5. Which automation task concept should be selected?

6. What are the features of the service concept?

Service requirements may be categorized as either "on-site service" or "remote service." Measurement and control systems must actively support personnel "on site" during startup and maintenance. This means it must be possible query the status of measured values and the device and to obtain the desired information directly as an LED display on the device or by using a menu in the web browser. Log files also make it easy to record and query all errors and details of device operation. This is especially helpful when searching for sporadic errors or effects. Another possibility is to make "monitoring signals" available. These are voltage signals to which the measurement signals or the computing channels as well can be interconnected for monitoring purposes. Then a simple measurement can be conducted on site by any service engineer. The log files are stored power failsafe in the device and can also be downloaded and archived via web browser for documentation purposes.