Truck & Off-Highway Engineering - October 2021 - 28

Developing a NEXT-GEN VGT
POWERTRAIN FEATURE
inflow temperature. To confirm the endurance
of the rotor, deformation was measured
at each blade during tip-timing test.
The maximum deformation was measured
for each blade and was confirmed to be
within the safety-factor limits (calculated
from the fatigue limit and ultimate tensile
strength). None of the blades showed any
degradation after the test, proving the
reliability of the new VGT turbine.
The researchers observed that with an
increase in the vane opening angle from
TOHE Eberspacher Ad 0819.qxp_1/2 Page Island 7/25/19 3:16 PM Page 1
10% to 100%, the dominant vibration
mode shifted from Mode 3 to Mode 2.
The stress values were calculated from
the deformation measured in tip-timing
test. These values agree with the values
obtained from unsteady CFD simulations;
slight deviation can be considered
due to the limitation of positioning the
tip-timing sensor only at the trailing
edge tip and not being able to slide it
upstream towards the leading edge.
Conclusion
The efficiency improvement obtained in
the experiment is a combined effect of
the non-scallop rotor and new 3D vanes.
The steady-state CFD simulations
showed 5% improvement at low mass
flow region and the experiment showed
about 7%, which indicates that the contribution
of the new rotor is roughly
1-2%. The combined improvement of
nozzle vane and rotor was measured to
be 2% at higher mass flow, corresponding
to engine LET and HEP, respectively.
The experiment results show that the
maximum flow capacity of the new VGT
is reduced compared to the base design,
which is a consequence of increasing the
rotor blade number and the limitation of
maximum nozzle opening due to the
position of the stopper, which was fixed
in accordance to engine operability.
The new design can operate at rotation
speeds higher than mode 2 and 3
resonance, which has overcome the conventional
design approach of keeping
the higher vibration modes out of operation
range. Higher vibration modes include
the deformation at regions upstream
of the trailing edge; hence it is
necessary to validate the simulations by
measuring those deformations, too. In
the future, Mode 2 and 3 will be measured
precisely by keeping the sensors
at the rotor leading edge, which is a difficult
task given the small size of the turbocharger
and the complexity of components
around the rotor.
This feature is based on SAE Technical
Paper 2021-01-0643 written by Bipin
Gupta, Toru Hoshi, Shinji Ogawa, Masaki
Osako, Hiroaki Yoshizawa and Noriyuki
Inoue of Mitsubishi Heavy Industries Ltd.
28 October 2021
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Truck & Off-Highway Engineering - October 2021

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