00 - 14 - ho - power train nvh topics

3439-EME 6383 – Automotive Powertrain II

Session # 14: Powertrain NVH Issues and Trouble

Shooting

This teaching material is developed by Shan Shih, 2012

1

January - May 2012

Professor: Shan Shih, Ph.D.

LTU, Automotive Research Institute

Master Degree Program

Session Summary

• NVH issues and their trouble shooting is a very important subject in auto component and system design and product development. It is related to product quality, customary satisfaction and product durability. In powertrain the most important NVH issues are (1) the torsional vibration, (2) bending vibration, (3) prop shaft critical speed, (4) gear box noise, etc. They will be introduced here. (5) Half shaft and (6) sub-frame resonances will be discussed as well

• In product design there are 3 major category of performance considerations: functionality, durability and quality. NVH belongs to quality. NVH problems usually is being addressed the last in the product development cycle. This is because most NVH problems are system related and are difficult to address up front. However, in modern engineering more and more NVH issues are considered in the design stage instead of trouble shooting stage. The methodology will be introduced in this session.

This teaching material is developed by Shan

Shih, 2012 2

Outline (1/2)

• Powertrain Torsional Vibration – Symptoms – Required techniques in Problem Solving – Solutions

• Powertrain Bending Vibration – Symptoms – Required techniques in Problem Solving – Solutions

• Powertrain Shaft Critical Speed – Symptoms – Required techniques in Problem Solving – Solutions


3

Outline (2/2)

• Gearbox Noise NVH Issues

– Symptoms

– Required techniques in Problem Solving

– Solutions

• Powertrain NVH Trouble Shooting Methodology

– Basics

– Approaches


4

Powertrain NVH Issues - Classification


5

ADAMS Powertrain Dynamic Models


6

ADAMS Powertrain & Suspension Interaction Models

Outline (1/2)





7

Simple Analysis

• Do a quick calculation: 3000/60*2=100, therefore we know this 2nd order engine excitation hits the natural frequency of the powertrain which is 99 Hz.


8

Engine excitation frequency Powertrain Natural Frequency

Matching or not Matching

?

第9页

4 Cylinder Longitudinal Mounted Powertrain:

Engine excitation can be in the (1) around x, (2)around

y and (3) z directions


X

Y

Z

Torsional Vibration is in the “around x” direction.

Front vehicle

第10页

4 Cylinder Transversely Mounted FWD Powertrain: Engine excitation can be in the (1) around x, (2)around

y and (3) z directions

In this case: Torsional Vibration is in the “around y” direction.


第11页

后置后驱


Engine rear mount RWD


12


13

Powertrain Torsional Vibration Symptoms

• Torsional Resonance due to engine firing pulses and/or driveline U-joint 2nd order excitations

• Vibration, noise, and premature parts failure


14

Powertrain Torsional Vibration Required Techniques in Problem Solving

• Test Measurement – Resonance in vehicle acceleration

– Rotating speed or torque fluctuation at various powertrain locations

• Simulation Analysis – Lumped moment of inertia, torsional stiffness and

damping

– Engine harmonic torque input at each crank throw, U-joint motion input

– Mode shape and frequency response analysis


15

Powertrain Torsional Vibration Root Causes

• High amplitude engine firing pulses

• Large or unequal driveline U-joint angles

• Unequal Phasing, high driveline speed

• Inadequate clutch damper design


16

Powertrain Torsional Vibration Solutions

• Clutch damper stiffness and damping design

• Driveline U-joint angles/phasing

• Driveline inertial damper, viscous damper, dual mass flywheel damper


17

Outline (1/2)





18

第19页

Bending Vibration


Powertrain Bending Vibration Symptoms

• Bending mode resonance of powertrain

• Cracked transmission/clutch housing, noise and vibration


20

Transmission Housing Crack


21

Powertrain Bending Vibration Required Techniques

• Test Measurement

– Modal analysis, lateral and vertical bending

• Simulation Analysis

– ADAMS linear eigen and dynamic analysis

– Mode tuning via test Modal analysis

– Vibration modes characterization

– Dynamic operation loads and deflections


22

Powertrain Bending Vibration Root Causes

• First order excitation of unbalance from engine, Torque converter, or U-joint

• High speed driveline

• Unbalanced driveline


23

Powertrain Bending Vibration Solutions

• Structural stiffening

• Damping

• Lower driveline speed

• Driveline/U-joint balance

• Add center bearing for shaft support


24

Outline (1/2)





25

Use 2 Hooke Joints


26

第27页

Double Cardan U-joints for main

prop shaft

Bearing supports are required

to avoid critical speed issue.

3 U-joints

4 U-joints

2 U-joints


28 Shan Shih, 2001, #12

4.349.678.264.405.505.20

5.405.206.006.00

Can you count how many u-joints are used in this 8x8 vehicle?


第29页

5.0

412

87.9

L

EIgf

73EE

64

44

io DDI

g=386 22

4io RR

Avoid shaft’s

flextural natural

frequency

Assumed rigid

simply supported

shaft

To design, make f1 as

high as possible.


第30页

Drive shaft Bending resonance due to engine excitation：

0.00 400.00Linear

Hz

0.00

0.14

Am

plit

ude

(g/N

)

80.91

FRF shaft:-RZ/force:+RZ

FRF shaft:-RZ/force:+RZ

0.00 400.00Linear

Hz

0.00 400.00Hz

-180.00

180.00

Phase

°

80.91

Calculate the corresponding shaft speed from the engine speed：

4th gear ratio=1: 4800（engine rpm）÷60÷1（4th

gear ratio）=80Hz 5th gear ratio: 4100（engine rpm）÷60÷0.838（5th gear

ratio）=81.5Hz

81 HZ

It is determined as 81 Hz

Based on the above analysis it is concluded that the vibration is 1st order shaft bending.

Step2 –from test to determine the shaft natural frequency

Step1 – check the waterfall plot

Step3 This teaching material is developed by Shan Shih, 2012

Powertrain Shaft Critical Speed

• Symptoms – Booming noise and vibration at certain engine speed and

transmission gear ratio

• Required techniques in Problem Solving – Test Measurement

• Modal analysis

• Simple test on driveline natural frequencies

– Analysis • CAE modeling

• Solutions – 2-segment shaft with center bearing

– Add shaft damper

This teaching material is developed by Shan

Shih, 2012 31

Outline (2/2)

• Gearbox Noise NVH Issues

– Symptoms

– Required techniques in Problem Solving

– Solutions

• Powertrain NVH Trouble Shooting Methodology

– Basics

– Approaches


32

第33页

ENGINE RPM & TORQUE

DATA

SPUR & HELICAL GEAR

GEOMETRY

SHAFT STIFFNESS &

MISALIGNMENT

BEARING STIFFNESS

DATA

GEAR STATIC TRANSMISSION

ERROR

LOADED GEAR TOOTH PROFILE SIMULATION , [6]

(LDP)

GEAR-SHAFT-BEARING SIMULATION (ADAMS)

BEARING DYNAMIC LOADS TIME DOMAIN

FFT (MATLAB)

DYNAMIC BEARING LOADS; FREQUENCY DOMAIN

STRUCTURAL DYNAMIC MODEL (ANSYS)

ACOUSTIC MODEL (COMET)

SURFACE VELOCITIES IN FREQUENCY RANGE

SOUND PRESSURE LEVEL (dB) IN

FREQUENCY RANGE. POWER.

CORRELATE WITH TEST

CORRELATE WITH TEST


第34页

ENGINE RPM & TORQUE

DATA

SPUR & HELICAL GEAR

GEOMETRY

SHAFT STIFFNESS &

MISALIGNMENT

BEARING STIFFNESS

DATA

GEAR STATIC TRANSMISSION

ERROR

LOADED GEAR TOOTH PROFILE SIMULATION , [6]

(LDP)

GEAR-SHAFT-BEARING SIMULATION (ADAMS)

BEARING DYNAMIC LOADS TIME DOMAIN

FFT (MATLAB)

DYNAMIC BEARING LOADS; FREQUENCY DOMAIN

STRUCTURAL DYNAMIC MODEL (ANSYS)

ACOUSTIC MODEL (COMET)

SURFACE VELOCITIES IN FREQUENCY RANGE

SOUND PRESSURE LEVEL (dB) IN

FREQUENCY RANGE. POWER.

CORRELATE WITH TEST

CORRELATE WITH TEST


Gearbox Noise

• Symptoms – Transmission, Transfer Gearbox and Axle Gear Noise and

Gearbox Housing Resonance – Engine idling, acceleration, cruise, and coasting – High frequency booming noise or low frequency rattle

• Required Techniques – Test Measurement – Analysis

• Root Causes – Gear profile precision – Gearbox stiffness – System design consideration

• Solutions – Design and manufacturing improvements


35

Engine and Chassis Components NVH Problem Solving Example

• Half Shaft Resonance

• Sub-frame Resonance


36

Suspension Components NVH Demo #1: Half Shaft Resonance


37

Procedures in Excitation-Resonance Type NVH Problem Diagnosis

• This method uses the waterfall plot as a starting point

• It is most suitable in powertrain NVH problem solving because the excitation frequencies are well defined

• Focus on the locations of red spots in the waterfall plot

• Conduct a CAE analysis to check the system’s various natural frequencies

• Comparison the analysis results with the test measurement generated plots

• Check the correlation with the database for conclusions


38

Powertrain NVH Trouble Shooting Root cause Identification

• Information Gathering – interviewing

– observing

– test measurement

– Simple analytical model can help if dynamic properties are available.

• Diagnostic and Analysis – To identify the frequency at which the problem occurred

– To identify the source of excitation,

– To identify the subsystem or component whose natural frequency coincides with the problem frequency


39

Powertrain NVH Trouble Shooting Make Design Change Recommendations.

• To eliminate the NVH source by changes in design or control at the source component, such as an engine, U-joint, tire, brake, pump, gear, shaft, etc.

• To isolate the NVH source from the rest of the system, such as the increase of shaft spline backlash

• To change system's stiffness or inertia, or supporting condition so that to shift the system's natural frequency

• To add damping to the system


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