PROCEEDINGS of the23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Investigation on Abnormal Gear Rattle Noise in Automated ManualTransmission (AMT) after Gear Upshifting
Abhishek Lakhanlal VAISHYA1; Archan Sunilbhai PUJARA2; Devendra Kumar KHARE3; Kingshuk
SATPATHY4; Vivek SINGH5
Maruti Suzuki India Ltd, India

ABSTRACT
Customers are getting delighted after receiving best in class vehicle NVH performance. In order to enhancecustomer NVH comfort, a specific abnormal gear rattle noise phenomenon during product development wasinvestigated. The transmission produces gear rattling noise by impacting gears, oscillating through the gear
backlash. Similar noise was observed in one of the prototype vehicle with AMT, immediately after gear
upshifting which sustained for some time and then became inaudible. In this case, the noise frequency band
was found to be higher than the usual gear rattling frequency band. In this paper, along with the assessment
methodology, root causes of this abnormal gear rattle noise will be elaborated.
Keywords: Torsional vibration, Engine knocking

1. INTRODUCTION
In vehicle transmission, sound is generated by excitation in gear teeth meshes and in rolling
bearings. Impacts, sliding, rolling, etc. absorb disturbance energy in the elastic structure of systemparts and transmit it through the whole structure. Interior surfaces emit a part of this energy into thesurroundings in the form of noise (1). Gear rattle noise has little contribution to the overall soundpressure level; however, it significantly impacts the sound quality because it can easily be recognizedfrom the other sounds produced by the automobile. It is for this reason that many researchers havedone a great quantity of work in this area to reduce the gear rattle noise. Some of them studied thetransmission gear rattle behavior produced by torsional vibrations of the complete driveline (2). Elasis
S.C.p.A. used a Virtual Engine Simulator to replace the internal combustion engines in reproducing themean value of both speed and combustion forces. The experimental results revealed that the gear rattle
noise increases with the increase of gearbox input shaft rotational fluctuation ( 3). The application of aclutch with lower stiffness and a drive shaft with higher stiffness can improve the rotational fluctuation,
hence, the gear rattle noise can be reduced significantly (4).
In this paper, all the above probable root causes were investigated namely gear backlash, clutch
damper behavior and engine behavior in order to eliminate the abnormal rattle noise phenomenon. A
parallel investigation approach was taken where both engine and transmission abnormalities wereconsidered.

2. ABNORMAL GEAR RATTLE NOISE
2.1

Introduction of Vehicle Parameters
Table 1 – Testing vehicle specifications
NameVehicle kerb weight1

abvauto@gmail.comarchan.pujara@gmail.com
3DevendraKumar.Khare@maruti.co.in
4Kingshuk.satpathy@maruti.co.in
5Vivek.Singh2@maruti.co.in
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Parameter values or type825 kgDrive mode

Front – engine, Front wheeled drive

Engine type

3 cylinder; 4 stroke

Transmission type5 – speed; Automated Manual Transmission (AMT)

Fuel type

Gasoline

2.2 Problem Description
During vehicle development phase, gear rattling type of noise was observed from engine cabin
while accelerating the vehicle with 10-15% throttle pedal position. The noise was observed inside
passenger cabin, immediately after gear upshifting to 2nd, 3 rd, 4 th and 5 th gear, which sustained forsome time and then became inaudible in both MT and AMT mode. The noise event which was observed
inside passenger cabin is shown in figure 1 where engine speed is plotted w.r.t. time during vehicle
running on road in AMT mode.
In order to understand the phenomenon in depth, the vehicle was also driven in WOT condition for~20 km and this noise was also observed initiating. During further investigation, vehicle was tested on
different road gradient and it was found that road gradient plays no role in this noise phenomenon.
2.3 Abnormal Gear Rattle Type of Noise Investigation
Abnormal gear rattle type of noise was investigated with objective data measurement for which
different sensors were used. Sensor types and their location in the vehicle are shown in Table 2.
Table 2 – Sensor types and location
No.

Sensor type

Sensor location

1

Single – axis accelerometer

Top surface of transmission housing

2

Microphone

Near top surface of transmission housing3

Microphone

NFC inside passenger cabin

4Magnetic pick up sensor for rotational

Flywheel

5speed measurement
Magnetic pick up sensor for rotational

Transmission - Input shaft

speed measurement
The objective data was measured, immediately after 3 rd gear upshift in AMT mode. Time –frequency analysis results of SPL inside passenger cabin in the frequency band of 500 Hz – 5kHz and
5kHz – 10kHz, SPL near transmission housing top surface and vibration level in Z – direction (referfigure 13) on top surface of the transmission housing are shown in figure 2, figure 3, figure 4 andfigure 5 respectively (the magnitude scale of each graph is different).
The SPL was found higher in the frequency band from 1 kHz to 4 kHz inside passenger cabin andadditional abnormality was identified at a higher frequency band of 6.3 kHz to 8.7 kHz. It was also
found that the magnitude of noise and vibration signature near transmission housing top surface washigh between above frequency bands. The noise near transmission housing in the higher frequency
band was non-continuous as shown in figure 5, which indicates that some other abnormal noise is also
involved from another source apart from gear rattle noise.

Figure 1– Engine speed w.r.t. time during vehicle running on road in AMT mode7201

Figure 2 – SPL inside passenger cabin in dBA

Figure 3 – SPL inside passenger cabin in dBA(500 Hz to 5 kHz)

(5 kHz to 10kHz)

Figure 4 – Vibration on transmission housing top

Figure 5 – SPL near transmission housing top surface

surface in dBin dBA

3. INFLUENCE OF MODIFIED GEARS OF TRANSMISSION ON ABNORMALGEAR RATTLE NOISE
Gear backlash reduction beyond a certain limit will result in improper lubrication during low speed
operation. Increment of drag torque or inertia of gears will affect transmission efficiency adversely.
Therefore, limits of any subsystem cannot be extended as there is always an undesirable trade -off.
Gear backlash design was checked and scope of improvement in final gear backlash was identified
among all gear pairs considering manufacturability and assembly constraints. Final gear backlash wasreduced by 38%. The objective data was measured, immediately after 3 rd gear upshift in AMT modewith optimized final gear pair. Although the overall noise was subjectively reduced, still a different
type of rattle noise of higher frequency was clearly audible. Time – frequency analysis results of SPL
inside passenger cabin, SPL near transmission housing top surface and vibration on top surface of thetransmission housing are shown in Figure 6, Figure 7, Figure 8 and Figure 9 respectively (themagnitude scale of each graph is different)
Subjectively, the gear rattle noise was reduced to substantial level. SPL inside passenger cabin wasreduced by ~5 dBA in the frequency band of 1000 Hz - 2000 Hz and ~3 dBA in the frequency band of2000 Hz - 5000 Hz. The abnormality in gear rattle noise was clearly audible and it was found higher by~7 dBA in the frequency band of 6 kHz – 9 kHz as compare to its background noise inside passenger
cabin as shown in Figure 7. SPL near transmission housing and vibration on top surface of thetransmission housing were also found higher in the same frequency band as shown in figure 8 and 9.

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Figure 6 – SPL inside passenger cabin in dBA

Figure 7 – SPL inside passenger cabin in dBA(500 Hz to 5 kHz)

(5 kHz to 10 kHz)

Figure 8 – Vibration on transmission housing top

Figure 9 – SPL near transmission housing top

surface in dB

surface in dBA

4. Influence of Clutch Damper on Abnormal Gear Rattle Noise
The torsional vibrations produced by the engine are transmitted to the transmission system throughclutch damper. There is always lash between the transmission gears, so the torsional vibrations cause
rattle noises due to the gear teeth impacting with one another. Flywheel and inputshaft rotational speed
was measured w.r.t. time and observations are as follows:1. A lag was observed between engine rotational speed and inputshaft rotational speed in each cycle
as shown in figure 10.
2. The rotational speed fluctuation of inputshaft was found higher by ~30 % than that of engine
speed fluctuation and behavior was abnormal as shown in figure 11. Preferably, inputshaft speed
fluctuations must be equal or less than engine speed fluctuations.
It was hypothesized that the above behavior was inducing excitations in free gears and causing
drive rattle.

Figure 10 – Rotational speed of flywheel and inputshaft in RPM; with standard clutch in 3rd gear; AMT mode

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One of the most important tasks for the clutch is to reduce the torsional vibration of the flywheel.
With the popularity and development of high-powered engines, higher demand is required for clutch toreduce the flywheel torsional vibration. Among the parameters to reduce the torsional vibration, thespring stiffness and hysteretic damping of clutch are the most important factors . Based on theparametric sensitivity analysis, some control strategies, including increase of the clutch damping
hysteresis and decrease of clutch spring stiffness (5). This led us to investigate the clutch damper
further and upon measurement, it was observed that the clutch damper hysteresis was manufactured
lower than what it was designed for. The speed fluctuations of inputshaft speed were reduced toslightly less than engine speed fluctuations as shown in figure 12.

Figure 11 – With standard clutch; 1.5th order -Figure 12 – With modified clutch; 1.5th order -Torsional fluctuations (RPM) 3rd gear; AMT mode

Torsional fluctuations (RPM) 3rd gear; AMT mode

5. ROOT CAUSE ANALYSIS OF ABNORMALITY IN GEAR RATTLE NOISE
5.1 Time – lag Analysis
With modified (improved) clutch and gears, the gear rattle noise was significantly reduced.
However, the abnormality in gear rattle noise was still perceivable. The vibration signal was measured
on engine cylinder 1 head and top surface of transmission housing with the help of accelerometer fixedon positions as shown in figure 13. It was natural that the vibration level of engine cylinder 1 head top
surface and transmission housing top surface will not be same due to different dynamic behavior ofcomponents inside respective systems.

Figure 13 – Acceleration sensor position on cylinder 1 head top surface and transmission housing top surface
Mittal, V., Revier, B., and Heywood determined knock intensities for each cycle by using Fast
Fourier transforms (FFT) and bandpass filtering techniques. Primarily two ranges of frequencies canbe excited during engine knocking phenomenon: the lower frequency is just above 6 kHz andcorresponds to the first circumferential frequency of the combustion chamber. The microphone data7204

shows that the audible knock signal has the same 6 kHz peak. The second range of peaks in the 15 -22
kHz frequency band (6). The wave signal of 7362 Hz – 7362.5 Hz was filtered and plotted w.r.t. time
as shown in figure 14. The data was acquired in every 39.0625 μs. The magnitude of signal is rising
w.r.t. time and the signal from accelerometer near cylinder 1 head was found ahead by ~ 191.5999 μs
than transmission housing. This time is sufficient to travel ~1074 mm from accelerometer located nearcylinder 1 head to transmission housing through metallic medium. This indicates that this wave wasoriginated from engine and propagated towards transmission.

Figure 14 – Vibration signal; Filtered: 7362 Hz – 7362.5 Hz frequency w.r.t. time; 3rd gear; AMT mode
5.2 Engine Knocking Phenomenon
Vibration level through accelerometer near engine cylinder 1 head is plotted w.r.t. engine
combustion cycles and time as shown in figure 15. The vibrations were found to be cyclic in nature.
Further investigation of engine was done by instrumenting a pressure sensor in place of spark plug
which can provide spark as well as can measure cylinder pressure simultaneously. The main reason ofoccurrence of these vibrations was found to be uncontrolled combustion inside all three cylinders.

Figure 15 – Vibration on cylinder 1 head top surface in m/s2; 3rd gear; AMT mode

6. Influence of Modified Gears, Clutch and Engine Calibration on Abnormal
Type of Gear Rattle Noise
Retarded spark supports to decrease the engine knock because comparatively lo wer maximum
engine pressures are produced. The maximum pressure occurs late in the cycle during the power stroke
and is not as high as that of the normal case. The engine knocking noise and shock vibrations weresignificantly reduced after engine calibration optimization. Vibration level through accelerometer nearcylinder 1 head is plotted w.r.t. engine combustion cycles and time as shown in figure 16.

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Figure 16 – With modified engine calibration; Vibration on cylinder 1 head top surface in m/s2; 3rd gear;
AMT modeWith modified condition (modified clutch, gears and engine calibration), inputshaft speed wasfound completely synchronized with the engine speed as shown in Figure 17.

Figure 17 – Rotational speed of flywheel and inputshaft in RPM; with modified gears, clutch and engine
calibration in 3rd gear in WOT condition; AMT mode
Time – frequency analysis results of noise inside passenger cabin and vibration on top surface oftransmission housing are shown in figure 18, figure 19, figure 20 and figure 21 respectively (themagnitude scale of each graph is different). Improvement can be easily seen as compare to standard
condition.

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Figure 18 – With modified condition; SPL inside

Figure 19 – With modified condition; SPL inside

passenger cabin in dBA

passenger cabin in dBA(500 Hz to 5 kHz)

(5 kHz to 10 kHz)Figure 20 – With modified condition; Vibration on

Figure 21 – With modified condition; SPL neartransmission housing top surface in dB

transmission housing top surface in dBA

7. SUMMARY/CONCLUSIONS
Experimental approach is established for understanding abnormal gear rattle noise and torsional
vibration behavior. Gear rattle noise along with engine knocking noise was studied and eliminatedsuccessfully.

REFERENCES
1. Jadhav, S., "Powertrain NVH Analysis Including Clutch and Gear Dynamics," SAE Technical Paper
2014-01- 1680, 2014, doi:10.4271/2014-01-1680
2. Robinette, D., Beikmann, R., Piorkowski, P., and Powell, M., "Characterizing the Onset of ManualTransmission Gear Rattle Part II: Analytical Results," SAE Int. J. Passeng. Cars - Mech. Syst.
2(1):1365-1376, 2009, doi:10.4271/2009-01-2069
3. Forcelli, A., Grasso, C., and Pappalardo, T., "The Transmission Gear Rattle Noise:Parametric Sensitivity
Study," SAE Technical Paper 2004-01-1225, 2004, doi:10.4271/2004-01-1225
4. Chae, C., Won, K., Kang, K., and Schulz, I., "Measurement of Transmission Rattle Sensitivity andCalculation of Driveline Torsional Vibration for Gear Rattle Analysis," SAE Technical Paper
2005-01-1785, 2005, doi:10.4271/2005-01-1785
5. Yang, X., Pang, J., Wang, L., Tian, X. et al., "A Study on Reducing Gear Rattle Noise Based on
Sensitivity Analysis of Drivetrain Torsional Model," SAE Technical Paper 2017-01-1779, 2017,
doi:10.4271/2017-01-1779
6. Mittal, V., Revier, B., and Heywood, J., "Phenomena that Determine Knock Onset in Spark-Ignition
Engines," SAE Technical Paper 2007-01-0007, 2007, https://doi.org/10.4271/2007-01-0007

CONTACT INFORMATION
Abhishek Vaishya currently holds the position of Manager - NVH, Transmission system at theResearch and Development department of Maruti Suzuki India Ltd. in Rohtak, India. His educational
background includes a Bachelor's Degree in Automobile Engineering from the A.D. Patel Institute ofTechnology, India and Master's Degree in Automotive Engineering from the Vellore Institute ofTechnology collaborated with Automotive Research Association of India (ARAI), India. He can becontacted via e-mail at Abhishek.vaishya@maruti.co.in ; abvauto@gmail.com

Abbreviations / Units
MTv/s
RPM
w.r.t.
SPLdBA

Manual transmission
versusRotation per minutewith respect toSound Pressure level
Decibel (A - weighted)

WOTTM
NFC

Wide open throttle
Transmission
Noise front row center

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