The trend in passenger vehicle internal combustion (IC) engines is to produce
smaller, more fuel-efficient engines with power outputs comparable to those of large
displacement engines. One way to accomplish this goal is through using turbochargers
(TCs) supported on semi-floating ring bearings (SFRBs). The thesis presents progress
on the nonlinear modeling of rotor-bearing systems (RBSs) by including engine-induced
TC housing excitations. Test data collected from an engine-mounted TC unit operating
to a top speed of 160 krpm (engine speed = 3,600 rpm) validates the nonlinear
predictions of shaft motion. Engine-induced housing excitations are input into the
nonlinear time transient rotor model as Fourier coefficients (and corresponding phase
angles) derived from measured TC center housing accelerations.
Analysis of recorded housing accelerations shows the IC engine induces TC
motions with a broad range of subsynchronous frequencies, rich in engine (e) superharmonics.
In particular, 2e and 4e vibration frequencies contribute greatly to housing
motion. Most importantly, the analysis reveals TC center and compressor housings do
not vibrate as a rigid body.
Eigenvalue analysis of the TC system evidences four damped natural frequencies
within the TC operating speed range. However, only the highest damped natural
frequency (first elastic mode, f = 2,025 Hz, ΞΎ = 0.14) is lightly-damped (critical speed =
150 krpm). Predicted linear and nonlinear imbalance response amplitudes increase with
TC shaft speed, with linear predictions agreeing with test data at high shaft speeds. The
differences between predictions and test data are attributed to an inaccurate knowledge
of the actual TC rotor imbalance distribution. For the nonlinear analysis, predicted shaft motions not accounting for housing
accelerations show the TC is stable (i.e. no subsynchronous whirl) at all but the lowest
shaft speeds (<70 krpm). However, predicted shaft motions accounting for housing
accelerations, as well as the test data, reveal TC motions rich in subsynchronous activity.
Clearly, engine-induced housing accelerations have a significant impact on TC shaft
motions. Predicted total shaft motions show good agreement with test data. Predicted
nonlinear subsynchronous amplitudes as well as peak shaft amplitudes also agree well
with test data. However, nonlinear predictions only show TC shaft vibrations attributed
to engine order frequencies below 6e, whereas test data evidences TC vibrations are due
to order frequencies greater than 6e. Overall, nonlinear predictions and test data
illustrate the importance of accounting for engine-induced housing vibrations in the
design and operation of TC systems. The good agreement between predictions and test
data serve to validate the rotor model. The tools developed will aid a TC manufacturer
in reducing development time and expenditures.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2546 |
| Date | 15 May 2009 |
| Creators | Maruyama, Ashley Katsumi |
| Contributors | San Andres, Luis A. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, application/pdf, born digital |
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