Gearbox Noise & Vibration Prediction and Control

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 04 Issue: 11 | Nov -2017 www.irjet.net p-ISSN: 2395-0072
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Gearbox Noise & Vibration Prediction and Control
Chetan Ramesh Patil1, Prasad Prabhakar Kulkarni2, Nitin Narayan Sarode3 Kunal Uday Shinde4
1,2,3,4 Assistant Professor, Dept of Mechanical Engg,SIEM Nashik, Maharastra,India
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Abstract - This paper will review practical techniques and
procedures employed to quiet gearboxes and transmission
units. The author prefers solving the gear noise problem at
the very source to introduce an enclosure as a means to
reduce radiated noise, which seems to be easy but its effect
on the sound pressure level is small. The gearbox noise
problem solution is focused on the improvement of gear
design; on the verification of its effect on the radiated noise
and the determination of the gears’ contribution to the
truck’s or car’s overall noise levels and on the analytical
and/or numerical computer-based tools needed to perform
the signal processing and diagnostics ofgearedaxissystems.
All of the analytical methods are based on the time and
frequency domain approach. Special care is addressedtothe
smoothness of the drive resulting from the transmission
error variation during a mesh cycle. This paper will review
the progress in technique of the gear angular vibration
analysis and its effect on gear noise due to the self excited
vibration. This presentation will include some examples of
the use of such approaches in practical engineering
problems
Key Words: Gear Noise, GearboxVibration,TaguchiMethod,
Tools for Gearbox vibration analysis, etc .
1.INTRODUCTION
The general performance of laser beam printers can be
expressed in terms of the printing speed, resolution, image
quality with regard to the vibration, First-Print-Out-Time
(FPOT), and printing noise [1]. As the printing speed of laser
beam printers becomes faster, reducing the printingnoise is
a prerequisite for research of laserbeamprinter.Laserbeam
printers feature less noise and vibration than the impact
type (e.g., dot-matrix printers) printers. However, theyhave
many rotating parts such as OPC, belts, rollers, and gears,
and their power is delivered mostly from a brushless DC
(BLDC) motor by gears, whicharethemainmachine element
of power transmission. Although the speed of revolution of
the gears varies with the printing speed, most gears in low-
end laser beam printers (printing speed of 20 ppm)rotateat
100~300 rpm. The pinion on the BLDC motor revolves at
more than 1000 rpm. However, a high-speed printer
(printing speed of 40~60 ppm) has power transmission
gears that rotate at 500rpm.In this research, plastic gears
have been optimized through Taguchi’s analysis to reduce
the printing noise. Further more, the sound qualityresulting
from the optimization of the gears has been evaluated. The
sources of printer noise can be classified into three
categories: driving noise, paper noise, and mechanical noise.
Driving noise is produced by the operation of rotating parts
such as motors, gears, the laser scanning unit (LSU), and
fans. Paper noise is caused by friction and the impact of
paper through the paper path of the laser beam printer.
Finally, mechanical noise is produced in the pick-up,
actuator, clutch, cam, etc., which all control the rotating
parts. A dominant source of driving noise is the vibrations
due to transmission error (TE) of the gears. TE of the gears
has been studied extensively in attempts to reduce printer
noise and vibration. Usually, the gear noise that resultsfrom
the meshing of gear teeth is transmitted via forces and
motions to the shafting, bearing, and transmission housing
where it is then radiated to the surroundings, as depicted in
Fig. 1 [2, 3]. Non-measurable factors for gear design such as
temperature and material humidity are not major
contributors to TE. However, both TE and noise are
influenced by the load on the gears [4]. In this sense, Houser
designed optimal gears that gave minimum noise and stress
by using a unique method such as Run-Many-Cases[5].Also,
an attempt was made to reduce the gear noise by either
reducing the excitations at the mesh via minimizing the
dynamic forces due to TE or by reducing the force
transmissibility from the meshtothenoise-radiationsurface
[6].
Fig.1.Path of Gear noise transmission

Fig.2 Factors related to Gear noise
2. Gear noise
The gear noise generated from the meshing of gear teeth is
externally emitted through the gear-noise transmission
path.(See Fig. 1) The main gear noise is produced at a
specific frequency that corresponds to the natural mode of
vibration of the gear’s main frame under flexure. The gear
noise also results from the noise at the mesh frequency,
which is produce from each tooth of the gear pairs. In
addition, the aerodynamics of rotating gears may be the
reason for the gear noise. However, the noise at the mesh
frequency and the noise due to sliding friction and wear
arise mainly because a lubricant is normally not used forthe
plastic gears in laser beam printers. Usually,plastic gearsare
more advantageous than metal gears in terms of material
cost, noise, and design flexibility. However, in light of the
increasing requests from consumers with regard to product
noise, there has been much effort to reduce noise in plastic
gears. The gears that are used in office automation
appliances, such as laser beam printers, fax, and copier
should yield only low noise at low-torque conditions of
operation. In general, the noise can be reduced greatly by
greasing the gears in polyacetal or poly-amide gear driving.
Also, provided that there is no problem of gear strength in
the high-speed domain of operation, the application of
pinions made of soft material wouldconsiderablyreducethe
noise. In addition, the noise level tends to be low when the
accuracy of the gear is getting higher.
However, if the accuracy of the gear exceeds JGMA 6, noise
cannot be reduced markedly. In this case, improving the
surface roughness of gearteethwouldbemore effectivethan
improving the accuracy of gear for the noise-reduction. The
noise-reduction methods that are described above have
limited applicability in high-volume mass production
because of the resulting increase in production cost. Hence,
considering cost, it is the most desirable to employa method
that changes the design of the gear teeth to reduce noise.
Several gear-design factors among others are the module,
number of teeth, pressure angle, profile shift, face width,
temperature, torque, speed of revolution, and helix angle
shown in Fig. 2.
TE is the most dominant characteristic in gear noise. It is
definedas “the difference between the actual position of the
output gear and the position it would occupy if the gears
were perfectly conjugate” and can be expressed either in
angular units or as a linear displacement along the line of
action. TE is illustrated graphically in Fig. 3.
θ denotes the angular position of pinion, 2
θ denotes the angular position of gear, 1 Z denotes the
number of teeth of pinion, 2 Z denotes the numberofteethof
gear, 1 R denotes the radius of pitch circle of pinion, and 2 R
denotes the radius of pitch circle of gear.
Methods to Reduce Gear Noise and vibration:
Gearbox noise can be attributed to 3 general phenomena:
Whining, Rattle, and Hammering. Vibrates is an expert in
researching and understandingthemechanismsbehindeach
of these phenomena and has developed a complete
methodology for understanding the excitationsanddynamic
response of the gearbox casing responsible for gearbox
whine. Gearbox whine is the resultofvibrationgenerated by
the meshing process itself, which depends on Material
properties, plus the Macro and Micro Geometry of the
pinions reacting to the speed and torque placed upon them.
This vibrational energy is then transmitted to the gearbox
casing and, depending on its dynamic behavior, radiated as
airborne noise via the casing or via structure borne
transmission to other components (vehicle interior,
equipment skid etc.). The following presents a general step
by step method for understanding the relevant mechanisms
involved in unwanted gearbox whine.
1. TRANSMISSION ERROR
Typically it is necessary to determine the Transmission
Error of the gears and the fluctuation of the gear stiffness.
Simplistically the transmission error corresponds to the
difference between the actual positionofthedrivengearand
its theoretical position. This difference is governed by the
bending of the gear teeth from the torque placed uponthem,
defects and the dynamic behavior of the gearbox at the
rotational speeds considered. Typically, the lower the
transmission error, the lower the whining noise generated
by the gearbox. Calculations for this element of the process
are relatively straightforward for engineers involved in
gearbox design. Vibratec has developed specific algorithms
to optimize the tooth profile modifications for a range of
torque.

2. GEAR (MESH) STIFFNESS
The fluctuation of the gear stiffness (mesh stiffness) is a
primary excitation mechanism and is a function of the
Transmission Error (and the number of active teeth), which
varies with time. This calculation is again relatively
straightforward but necessary to couple properly the gears
involved in the dynamic model.
3. CALCULATE DYNAMIC RESPONSE
Using the Mesh Stiffness, it is possible to determine the
Dynamic Response of the full gear system based upon the
inputs from the Static Transmission Error and the Gear
(Mesh) Stiffness fluctuations. Typically it is not possible to
use standard Finite Element Models to accurately predict
such a response using these input parameters, however,
Vibratec has developed specific solverstoallowsuchmodels
to be created. By analyzing the dynamic response of the
system it is then possible to correlatestructural modesof the
gearbox casing with specific modes generated by the geared
system. In such cases this re-enforcement of modes will
often result in unwanted (whining) noise.
By understanding the dynamicresponseofa Gearboxsystem
in this manner, it is possible to investigate the optimization
of the gear tooth profiles and the geometry of the system to
best reduce the degree of excitation generated by the
system. This can be done for a range of torques. Similarly
for any of the modes of the system that generate unwanted
noise, structural modifications of the casing design can be
incorporated. This overall approach allows potential
modifications to be made in an efficient manner to allow the
optimum solution to reduce unwanted gearbox whining
noise problem, though it has not yet led to a resolution.
Comparative analysis of trace files is clearly not a manual
activity. SvPablo and TAU can also be used for the iterative
process of (f) detailed performance debugging, i.e.,
identifying and tracking performance problems down to
individual routines and lines of code. When performed by
hand, detailed performance debugging is time consuming
and fraught with problems due to instrumentation
perturbation and global effects (e.g., load imbalances)
masquerading as local performance problems.
4. SOURCES OF GEARBOX NOISE AND VIBRATION
Gearbox noise is tonal. This means that the noise frequency
spectrum consists of sinusoidal components at discrete
frequencies with low-level random background noise. The
frequency that is the product of the gear rotational speed in
Hz International Journal of Acoustics and Vibration, Vol. 14,
No. 2, 2009 3 Tuma, J.: GEARBOX NOISE AND VIBRATION
PREDICTION AND CONTROL Figure 3. TATRA truck (T815-
2) gearbox arrangement and the number of teeth are
referred to as the base tooth meshing frequency or gear
meshing frequency GMF . A simple gear train (a pair of
meshing gears extended optionally by idler gears) is
characterized by only one tooth meshing frequency. All the
basic spectrum components are usually broken down into a
combination of the following effects7: low harmonics of the
shaft speed originating from unbalance, misalignments, a
bent shaft, and resulting in low frequency vibration,
therefore, without influence on the gearbox noise level;
harmonics of the base tooth meshing frequency and their
sidebands due to the modulation effects that are well
audible; the noise and vibration of the geared axis systems
originated from parametric, self-excitation due to the time
variation of tooth-contact stiffness in the mesh cycle, the
inaccuracy of gears in mesh, and non-uniform load and

rotational speed;_ ghost (or strange) components due to
errors in the teeth of the index wheel of the gear cutting
machine, especially gear grinding machines employing the
continuous shift grinding method that results in high
frequency noise due to the large number of index-wheel
teeth, these ghost components disappear after running-in;
components originating from faults in rolling-element
bearings usually of the low level noise except for fatal
bearing faults as the cracking or pitting of the inner or outer
race or of the rolling element itself.
5. GEARBOX NOISE AND VIBRATION PREDICTION AND
CONTROL
Figure3 . Running noise autospectra of the gearbox noise in
RMS. harmonics of all the gear trains under load on the
input-shaft rotational speed forthe3N gearareshowninFig.
5. Except for the 5R gear, only three pairs of the engaged
gears, whichare designated by N, 3, and SG (Secondary
Gearbox), are under load. The panels of the diagram in Fig. 5
titled Gear N, 3, and SG, corresponds to the mentioned gear
pairs. The curve in these panels marked by ’Sum’ is a sum of
the power contributionsof5harmonic componentsresulting
in the noise level excited only by the appropriate pair of the
gears. As the pass by vehicle noise test is based on the
maximum of the overall SPL, the maximum of the gearbox
overall SPL (Max Tot) and a maximum of the 5 tonal
components SPL (Max Sum) can be chosen as a gear quality
criterion. Optionally, the maximum isevaluatedfortheinput
shaft rotational speed range either from 1000 to 2200 RPM
or for an interval corresponding to the engine rotational
speed during the pass-by tests. Due to the low rotational
speed of the secondary gearboxgeartrain,itscontribution to
the overall (Total) SPL is negligible. The right lower panel in
the diagram in Fig. 5 compares the contribution of all the
gear train under load to the overall SPL of the gearbox. The
minimum of the difference between the overall SPL and the
contributions of the N, 3, and SG gears for the mentioned
RPM range is designated by MinDiff. As was noted in the
introduction section, the main sources of the gearbox noise
are gears under load.7 Figure 5. Overall (Total)SPL andlevel
of the of 5 toothmeshing harmonics of all the gear trains
under load for the 3N gear vs.input-shaftrotational speed.to
the time interval of one tooth pitch rotation. In this way,
filtered signals are called average tooth mesh signals.12The
average tooth mesh acceleration measured on the gearbox
housing close to the shaft bearing is proportional to the
dynamic forces acting between the teeth in mesh. The
average tooth mesh is a tool to represent the average mesh
cycle. It can be observed that both the average tooth mesh
signals corresponding to meshinggearshavethesameshape
(see Fig. 6).This fact follows from Newton’s third law. To
assess a uniformity of tooth meshing duringa completegear
rotation, an International Journal of AcousticsandVibration,
Vol. 14, No. 2, 2009 5 Tuma, J.
Conclusion:
The paper reviews the effect of the most efficient
improvements reducing noise excited by gears, as well.
Concerning the gearbox noise problem, one can conclude
that a low noise gearbox requires sufficiently rigid housing,
shafts and gears, and the HCR gears and the tooth surface
modification for design load. The positive effect of
introducing the HCR gears depends on the gear qualityclass.
Gears finished by grinding are needed. All these
improvements introducedbytheTATRAcompany result ina
decrease of the gearbox noise, which was measured on the
test stand at the distance of 1 m by 8 dB at minimum. The
TATRA truck gearboxes do not require an enclosure to fulfil
the requirements given bythevehicle noiselegislation.Noise
and vibration measurement and signal analysis are
important tools when experimentally investigating gear
noise because gears create noise at specific frequencies,
related to number of teeth and the rotational speed of the
gear.
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control methods, Handbook of noise and vibration control,
M. Crocker Ed., Wiley, New York, (2007), Chapter 69, 847–
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