© Jiri Tuma, 2004 1

VŠB Technical University of Ostrava Faculty of Mechanical Engineering 17. listopadu 15, Ostrava Poruba

Czech Republic

Gearbox Noise ReducingCase Study

Jiri TumaDepartment of Control Systems and Instrumentation

© Jiri Tuma, 2004 2

Content

• Test stand instrumentation• Gearbox under test• Problem to be solved• Analysis Methods• Results

© Jiri Tuma, 2004 3

Dominating Spectrum Components

• low harmonics of the shaft speed

• harmonics of the base toothmeshing frequency and their sidebands

• ghost component• components resulting

from fault in rolling bearings

n1

n2 n3

n4

© Jiri Tuma, 2004 4

Test Stand and Instrumentation

Accelerometer

Tacho

Auxiliary gearboxLoad

Drive

Semi-unechoic room

Torque

Gearbox under test

Microphone

Signal AnalyserBK 3550

Back-to-back test rig

© Jiri Tuma, 2004 5

Gearbox under Test

© Jiri Tuma, 2004 6

Problem to Be Solved

• Gearbox is noisy

• No uniform toothmeshing

© Jiri Tuma, 2004 7

Analysis Methods

• Frequency domain analysis– Total noise level– Separate noise level

• Time domain analysis– Average toothmesh– Envelope analysis

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Noise Measurement during Run-up Test

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Slice Analysis

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Time Domain Analysis

Acceleration signal

Tacho signal

TimeInstrumentation

•BK 2034/2032 + 5050•BK 3550•BK LabShop PULSE

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Synchronized averagingAcceleration signal

1st revolution

2nd revolution

3rd revolution

Enhanced Time Signal Gear RevolutionAveraging in Time Domain

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Average Toothmesh

-6

-4

-2

0

2

4

6

0,000 0,025 0,050 0,075 0,100 0,125 0,150 0,175 0,200 0,225 0,250

m/s

2

00,20,40,60,8

11,21,41,61,8

0 40 80 120

m/s

2

00,20,40,60,8

11,21,41,61,8

0 40 80 120

m/s

2

-3

-2

-1

0

1

2

3

4

0,000 0,025 0,050 0,075 0,100 0,125 0,150 0,175 0,200 0,225 0,250

m/s

2

-3

-2

-1

0

1

2

3

4

0 0,5 1

m/s

˛

IFFT

FFT

CombFilter

Enhanced Time Signal Enhanced Spectrum

Time Domain Frequency Domain

Average Toothmesh

Tooth Pitch Rotation

Gear Revolution Orders

© Jiri Tuma, 2004 13

Amplitude and Phase DemodulationEnhanced Time Signal

-15

-10

-5

0

5

10

0,0 0,2 0,4 0,6 0,8 1,0Revolution

m/s

2

Envelope

02468

0,0 0,2 0,4 0,6 0,8 1,0Revolution

m/s

2

Angular Vibration in deg

-1

-0,5

0

0,5

1

0,0 0,2 0,4 0,6 0,8 1,0Revolution

deg

Enhanced Time Signal

Envelope

Phase Modulation Signal

Frequency spectrumEnhanced Spectrum

0123456

20 30 40 50 60 70 80 90 100Orders

m/s

2

Carrying Component

Sidebands

Gear Revolution

© Jiri Tuma, 2004 14

Average Toothmesh and EnvelopeAcceleration Signal

Average Toothmesh

Envelope

Tooth PitchRotation

Gear Revolution

Gear TrainGear Revolution

Gear Revolution

Order

Order

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Effect of RPM on the Average Toothmesh

1100 RPM

1200 RPM

1900 RPM

© Jiri Tuma, 2004 16

Results of Improvements

LCR HCR HCR

© Jiri Tuma, 2004 17

Effect of Contact Ratio on the Average Toothmesh

total contact ratio = profile contact ratio + face contact ratioγε αε βε

( )0.1≈εβ

Truck Gearbox

LCR HCR

© Jiri Tuma, 2004 18

Effect of Contact Ratio on the Noise Level in dB

Truck gearbox noise level at the distance of 1m

86,0

88,0

90,0

92,0

94,0

96,0

98,0

100,0

Speed

dB(A

)

LCR 92,0 92,9 95,0 95,4 95,0 96,5HCR 90,0 91,8 90,4 89,7 88,2 90,3

3R 3N 4R 4N 5R 5N

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Effect of Load on the Average Toothmesh

Gear A Gear B Gear A

Gear B

3.5 dB

Gear A: Without Modification

Gear B: Tooth Surface Modified

© Jiri Tuma, 2004 20

Effect of Pitting of Teeth on the Enhanced Time Signal

Under load of 2350 Nm

Under load of 500 Nm

Pitting

© Jiri Tuma, 2004 21

Bibliography– McFadden P.D.: Detecting Fatigue Cracks in Gears by Amplitude and Phase

Demodulation of the Meshing Vibration. ASME J. of Vib. Acous. Stress and Rel. in Des., April 1986, Vol. 108, pp. 165-170.

– Angelo M.: Vibration Monitoring of Machines. Brel & Kjaer Technical Review, No. 1, 1987.

– Tůma, J. Analysis of Periodic and Quasi-Periodic Signals in Time Domain. In Proceedings of the Noise ‘93, St. Petersburg (Russia). 1st. ed. Auburn (USA) : Auburn University, 1993. Volume 6, pp. 245-250.

– Tůma J., Kuběna R. Nykl V: Assessment of Gear Quality Considering the Time Domain Analysis of Noise and Vibration Signals. In: Proceedings of 1994 Gear International Conference. Newcastle 1994, pp.463-468.

– Tůma, J.: Zpracování signálů získaných z mechanických systémů. Sdělovací technika, Praha 1997. ISBN 80-901936-1-7.

– Tůma, J. & Růna, B. Order analysis and averaging in the time domain of gearboxnoise and vibration signals. In Proceedings of the 6th International Congress on Sound and Vibration, Lyngby, 5. - 8. 6. 1999. Lyngby (Denmark) : Technical University of Denmark, 1999. vol. 1, pp. 2367-2374. ISBN 87-987457-9-4.