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Inside powertrain: a harsh environment for shakers

Siemens Visionary Siemens Visionary
Siemens Visionary

Q-HSH installed.jpgHigh Frequency Shaker installed in bearing mounting locationA question that often arises about the high frequency shakers is their immunity against Automatic Transmission Fluid(ATF)? During the installation of the shaker, ATF or similar fluids sometimes remain in the vicinity. What would happen with the shaker if it gets in contact with a drop of Q-HSH in gearbox fluid_2 - Copy.jpgFully submerged shakerfluid? Will the shaker loose its integrity?

 

Transmission oils contain many different additives for anti-wear and extreme pressures. This has been taken into account during the design of the shaker. But let’s see what happens when we submerge the shaker in ATF-3 fluid; a fluid commonly used in passenger cars and light commercial vehicles, for the duration of a whole weekend. We took a glass, mounted a shaker at the bottom, filled the glass with ATF-3 fluid and simply enjoyed the weekend…

 

Our smallest variant of inertia shakers is often used to excite components and driveline assemblies. The shaker enables the measurement of structural and vibro-acoustic FRFs, from about 500Hz to over 10kHz. This wide band can be obtained using signals ranging from classic band-limited  white noise to pseudo-random signals.

 

The High Frequency Shaker is so compact, it fits inside the recess where the shaft bearings are located. It is connected to the structure by a glue bond. The shaker is self-aligning, a feature that ends up saving precious time. A short application video can be found here. In addition, the integrated IEPE force cell measures the shaker force in real-time.

 

Below, you can find a bode diagram containing typical FRF results, followed by a coherence function. The FRF data, whether directly or in the form of a modal model, can be used for correlation and updating CAE models both at component and assembly levels.bode_coh_gearbox.jpgA combined Bode and coherence diagram shows a complex structural transfer function from an automotive transmission housing

The comparison between before and after the experiment did not show any difference in the force generation performance of the shaker! Though we do not recommend submerging the shaker in fluid, a drop on the housing won’t matter. Just wipe it off with a towel and do your thing.

 

When attaching the shaker onto a transmission, make sure the area is free of fluid and that the surface has been degreased in order to ensure optimal adhesion. In the end, you really don’t have to worry if a drop of ATF fluid gets on the shaker during installation. The  Qsources webpage contains information on the portfolio of structural exciters.

 

>> LMS Qsources website

 

Comments
Siemens Experimenter

With the electric motor becoming more frequently used in automotive and other fields, concerns about their NVH performance are also rising. In the case brought up by one of our customers, the stator of the electric motor contains internal liquid coolant. To assess the effect of the coolant on the dynamic behavior of the assembled electric motor and housing, the question arises whether a high frequency shaker can be used while it is submerged in the liquid. A straightforward measurement set-up can provide an initial answer to this. A generic electric motor housing is hung in free condition and two locations are selected on its structure: One that can be covered in oil on one side and one that will remain dry. Capture1.PNGMeasurement Set Up

 

On both locations, a force cup for the high frequency shaker is placed and on the other side of the structure, at the same locations, a 1D “droplet” accelerometer is fixed. These two locations provide the opportunity to measure two driving point FRFs and two reciprocal FRFs. The aluminum housing structure is assumed to be linear and therefor a reciprocity check can validate the measured FRFs. 

Capture2.PNGSubmerged Location 

Capture3.PNGDry Location

Two conditions are studied: Without and with oil. The measurements without oil can be used as “dry” reference and also to validate that the assumption of reciprocity. After they are finished, the oil (ATF – Automatic Transmission Fluid) is poured into the housing and the measurement run with the shaker in the dry location is performed. Then the shaker is placed on the force cup inside the oil to measure the submerged shaker condition. The results show that the oil has the expected mass and damping effect on the FRF; furthermore the reciprocity check on the condition with oil indicate that the submerged shaker also provides reliable data. The “submerged shaker” measurements are repeated with a (10dB) lower load level and after a time lapse (1hr, 1 night) and these don’t seem to negatively affect the quality either. 

 

Capture4.PNGReciprocity of Measured FRFs

 

Capture5.PNGAutopowers for all conditions

To conclude, this quick study demonstrates that a high frequency shaker that is submerged in oil remains reliable for at least 12 hours. However it doesn’t guarantee that the shaker will work with other fluids. This use of the shaker is not recommended, but for this specific case, it was the only resolution.