16_Strchler_de 14.10.

2008 13:00 Uhr Seite 1

Experimental modal and operational

vibration analysis in practice

Optimized vibration control

of diesel-electric power
units in rail vehicles
RUDOLF STRCHLER Diesel-electric vehicles are frequently used
SULZER INNOTEC in public rail transit systems. Diesel motors
inherently pose vibration-related problems.
Consequently, vibration testing and vibration
control modifications are necessary to
address each individual application. In close
collaboration with Stadler Bussnang AG,
the vibration engineering experts at Sulzer
Innotec have successfully reduced the
vibration produced in the drive units of
articulated railcars. After conducting modal
and vibration analyses, the specialists
determined the complex dynamic behavior
involved and developed measures for
optimization.

Commuter rail traffic in Stadler Bussnang AG equips its

densely populated metropoli- model GTW articulated railcars
tan areas is growing significantly with standard diesel motors of
throughout the world. Diesel-elec- commercial vehicles. These motors
tric vehicles are frequently em- are inexpensive to operate due to
ployed since many lines are not elec- their standard design, easy pro-
trified. In contrast to vehicles pow- curement, and low maintenance
ered by overhead lines, diesel mo- costs. However, since vibration
tors pose vibration control problems. behavior is specific to a particular

16 SULZER TECHNICAL REVIEW 3/2008 4244

16_Strchler_de 14.10.2008 13:00 Uhr Seite 2

application, the standard motor in both stationary testing as well

has to be specially verified for use as testing in actual operation (up 160
in the railcar power unit and its to 56 measurement channels are

Velocity (mm/s)
design modified as needed. available). The measured signals 120

Time (s)
In the context of a successful of the structural accelerations were
long-term collaboration, Stadler then analyzed using time func- 80
Bussnang AG commissioned the tions, frequency spectra, waterfall
vibration engineering specialists diagrams, transfer functions (Bode 40
20
of the Sulzer Innotec research and plots) and spectrograms. Apart 10
0
development unit to conduct stud- from showing vibration ampli- 0 40 80 120 160
ies of the various GTW models. tudes and associated frequencies, Frequency (Hz)

The experts analyzed the dynamic these representations allow the 2 Operational vibration analysis:
behavior via modal and opera- relation of vibration maximums to example of a waterfall diagram.
tional vibration analyses and a specific rotational speed or oper-
developed measures for optimiz- ating condition, respectively. The Using operational vibration
ing the design and operational waterfall diagram (Fig. 2) showed measurements, it was shown
characteristics of the power unit in clear-cut excitation frequency that in some mounted compo-
cooperation with the motor sup- bands. When they encounter natu- nents the wideband RMS
plier and vehicle manufacturer. ral frequencies, resonances result values (101000 Hz) would reach
that are clearly recognizable at the vibration velocities of up to
Vibration characteristics of the vibration maxima. Four-stroke 95 mm/srms during operation at
power unit during operation piston engines create a wide spec- the resonance points. Consequent-
As a starting point, the specialists trum of vibrations, beginning with ly, targeted measures are required
of Sulzer Innotec assessed the dy- a first order of f = 0.5fn (fn = rota- in order not to exceed the guide-
namic behavior of the power unit tional frequency [r.p.s.]) and their line values prescribed by relevant
and its components (Fig. 1). They higher harmonics, i.e., 1, 1.5, 2, 2.5 standards. In order to develop
used 3-dimensional operational times the rotational frequency. The these measures, the vibration en-
vibration measurements with a speed range lies between 800 and gineering experts of Sulzer Innotec
wide variety of structure points 1900 r.p.m. analyzed the modal parameters
(mode shapes, natural frequencies,
and damping) of the power unit
1 Power unit with components and measurement points:
instrumentation applied. using modal analysis.

1 Hydraulic unit Modal analysis

2 Turbocharger
3 Generator
During modal analysis, the struc-
4 Motor ture undergoing testing is sepa-
5 Flywheel housing
rately excited employing a suitable
method in order to determine the
1
2 modal parameters of the structure
on the basis of the free decay
3
responses. In the case at hand, the
structure was struck using an
4
impulse hammer, featuring a load
5 cell, on the motor block at the
driving point. Figure 3 shows the
modal analysis model. The loca-
tion of the points and the corre-
sponding number depends on the
complexity of the mode shape. The

SULZER TECHNICAL REVIEW 3/2008 17

16_Strchler_de 14.10.2008 13:00 Uhr Seite 3

3 Modal analysis Figure 5 shows one of the critical Location of maximum

vibration amplitudes
model (wireframe mode shapes (torsional vibration
model).
of the power unit). If no measures Non-deformed
Deformed
are taken, the power unit could be
Motor
Hydraulic unit run to its natural frequency mode
Turbocharger in the higher speed range and thus
Frame
Generator lead to pronounced vibration am-
Driving point plitudes at the structure points lo- 5 Shape of the torsional vibration of
cated furthest from the center of the power unit (Mode 5) coupled with
torsion due to their kinematics. A bending of the hydraulic unit.

portion of this torsion would

occur in the flywheel housing.
installation frame in the vehicle This vibration would also be cou- ing, which became the torsionally
was also included in the analysis pled with the vibration of the hy- elastic element since it was the
for the purpose of obtaining com- draulic unit, which is supported weakest link in the chain. The fly-
prehensive information and as- on the generator and linked to the wheel housing represented only
sessing the elastic bedding. motor block via the power take- part of the power units overall
As expected, a sizable number of off. Vertical and horizontal bend- rigidity matrix. The increase in
natural frequencies occurred ing modes of the power unit also the torsional natural frequency
rigid body modes and elastic lie in the possible excitation fre- amounted to only 11%. However,
modes. This can be seen on the quency range. The turbocharger the basic rigidity of the system was
basis of the so-called global trans- also exhibits local resonances. increased, thus enabling a reduc-
fer matrix, which in simplified tion in the vibration amplitudes to
terms reflects the mean square of Modifications and measures be achieved.
all measured transfer functions Following from the results of the A second focus of the specialists
(Fig. 4). Regardless of their ampli- operational vibration and modal was the hydraulic unit, whose
tude, the peaks in this diagram analyses, the experts of Sulzer In- pronounced deflection occurred
correspond to the natural frequen- notec increased the basic rigidity outwardly in a horizontal direc-
cies (resonances). level of the power unit. This was tion, so that the strongest vibra-
done by replacing the cast-alu- tions occurred there (Fig. 5), which
minum flywheel housing with one was due to a linked local torsional
made of nodular cast iron. Since resonance in the same frequency
the nodular cast-iron housing pos- range. This can be clearly noted on
4 Modal analysis: global transfer matrix with
marked key resonant frequencies. sesses a modulus of elasticity 2.3 the basis of the deformation of the
times higher, this results in stiffen- hydraulic unit, which exhibited
106 Rigid body modes Elastic modes
6 ing of the link between the motor far greater vibration amplitudes at
and generator. Being primarily the outer points than would have
related to this stiffness, the modes been the case considering the
(horizontal and vertical torsion of angle of torsion alone. Conse-
4 the power unit) consequently quently, the mounting of the
(m/s2/N)2

exhibited increases in frequency hydraulic unit support member

between 17.6% and 19%. The situ- on the generator was shifted out-
ation was less clear with regard to ward (Fig. 6).
2 the torsion of the power unit since The impact of the 2 measures on
the motor block was also substan- the horizontal vibration of the
tially involved in this vibration outer hydraulic unit is shown in
shape (Fig. 5). By stiffening the fly- figure 7. The vibration reductions
0
0 40 80 120 160 200 wheel housing, the torsion was and frequency shifts of the 2 vari-
Frequency (Hz)
largely shifted to the engine cas- ants are clearly visible. However,

18 SULZER TECHNICAL REVIEW 3/2008

16_Strchler_de 15.10.2008 16:23 Uhr Seite 4

6 Modification of Transfer functions at measurement

7 Comparison of the
the hydraulic unit 10 -2 point 32 (outer hydraulic unit) transfer functions for
9
support member. various versions of
the hydraulic support

(mm/s/N)
2
6
1 member.
3 3
4
1 Hydraulic unit Cast-aluminum flywheel housing
(support member: original)
2 Power takeoff 0 Nodular cast-iron flywheel housing
0 40 80 120 160 200 (support member: original)
3 Position of the original support member
Frequency (Hz) Nodular cast-iron flywheel housing
4 New support member (support member: new)

this change has an unfavorable Absorption of the relative tion control optimization, that
impact on the vertical vibration radial movements in the area resulted in high operational relia-
since the support member can not of the power takeoff resulting bility of the power unit coupled
be affixed directly to the genera- from this concept by an elastic with low maintenance costs.
tor, but rather requires a connect- coupling
ing plate between the 2 ends of As a result of the new concept
the generator. Therefore, the ver- (Fig. 8) the remaining residual
tical rigidity of the support mem- vibration of the hydraulic unit
ber is reduced significantly, and during resonant operation was
8 New design of the affixation of the hydraulic unit
the vibration in the vertical direc- reduced by more than half. with measurement point 32.
tion increases. As a consequence, A further reduction in vibration
damage to the support member was attempted by restricting the
could not be ruled out in this ver- speed range, i.e., by avoiding
sion. It was suspected that, due to resonant operation altogether.
the vibration shape, the outer part Resonance-free operation can not
of the hydraulic unit and the be realized in any other manner
power takeoff linked to it at the owing to the numerous excitation 1
2
motor moved in phase opposition orders of the 4-stroke piston en-
as a result of the torsion of the gine. The motor characteristic of 3

power unit. Another disadvan- the power units makes it possible

tage is that a high degree of to take this step without any per-
mounting accuracy is required in formance loss.
order to prevent stress loading of
the pump assembly due to the Summary 1 Hydraulic unit rigidly mounted to generator using a mounting frame
fabrication tolerances of the sup- By conducting vibration measure- 2 Elastic coupling
3 Power take-off
port member. ments during operation and
Measurement point 32
After Sulzer Innotec completed the experimental modal analysis, the
analysis of the proposed measures, experts at Sulzer Innotec were able
the design engineers at Stadler to determine the complex dynam- Contact
Bussnang AG developed a new ic behavior of the power unit. Sulzer Innotec
concept with the following main Understanding the dynamic Frank May
features: behavior is necessary in order to Sulzer-Allee 25
Disconnection of the hydraulic develop suitable measures for 8404 Winterthur
unit from the power takeoff cas- reducing operation-induced vibra- Switzerland
ing tion. Through close collaboration Phone +41 52 262 21 56
Rigid mounting of the hydraulic with Stadler Bussnang AG, Sulzer Fax +41 52 262 00 15
unit on the generator Innotec was able to achieve vibra- frank.may@sulzer.com

SULZER TECHNICAL REVIEW 3/2008 19