Vibration Diagnostics

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# Vibration Diagnostics - PowerPoint PPT Presentation

Vibration Diagnostics. Vibration Diagnostics. Vibration Diagnostics. Vibration Diagnostics. Why Wheel Balancing?. What is . Vibration?. Vibration?. Vibration?. Vibration?. In order to Diagnose a Vibration we must understand some... . Basic Principles. 1st cycle. 2nd cycle.

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Presentation Transcript

Vibration Diagnostics

Vibration Diagnostics

Vibration Diagnostics

Vibration Diagnostics

Why Wheel Balancing?

What is

Vibration?

Vibration?

Vibration?

Vibration?

1st cycle

2nd cycle

What is a cycle?

1 second in time

2 cycles per second or 2 Hz

Frequency

1 second in time

1st cycle

2nd cycle

Frequency is 2 CPS or 2 Hz

1 second

Tire Imbalance

With a Frequency of 4 Hz

Imbalance

4 Revolutions = Frequency of 4 CPS/Hz

Amplitude of Force

1 second

6 Hz

Tire Imbalance

If the Frequency increases...

so does the amplitude of force

Imbalance

Reed Tachometer

can identify Frequency

500 250 100 25

Hz

"Steering Wheel Shake"

Wobble

Shimmy

What is Static Balance?

Static Balance is when the weight of the wheel and tire assembly is distributed equally around the axis of the wheel rotation.

If static Balance exists the wheel will have no tendency to rotate.

If rotated it rotates with Equal Force

How do we Balance this Wheel?

Heavy Area Rotates to Bottom

.25 oz Imbalance

Is this wheel in static balance?

.25 oz imbalance

If this wheel is in perfect balance at a

speed of 40 mph,

will it remain in balance at all speeds?

.25 oz imbalance

Yes,

the

is the word

“Perfectly”

.86 lbs

.86 lbs

At 20 MPH

.25 ounces of imbalance generates

.86 pounds of force

Imbalance in Tire

Balance Weight Applied

10.5 lbs.

10.5 lbs.

At 70 MPH

.25 ounces of imbalance generates

10.5 pounds of force

At 70 mph the force is 10.53 pounds

It\'s still in perfect balance!

10.53 lbs.

NOTE: Speed rated Tires Utilize a Nylon Over-lay to prevent tire distortion at high speeds.

10.53 lbs.

Common Problems:

• Round Off vs. Fine Mode
• Mounting
• Clean Mounting Surface
• Excessive Runout
• Tolerance stack up

Consider this...

Most Computer Wheel Balancers Round off to the nearest .25 oz.

1 oz. Balance Weight

1.12 oz. Imbalance

Is this a Problem?

1.12 ounces Imbalance

.25 Round Off = .12 Error

1 oz. Balance Weight

1.12 oz. Imbalance

Is this a Problem?

On most cars,

this Slight Imbalance would not be felt, however

"My Car Vibrates at 55 MPH"

Why Does it Vibrate at

One Speed?

RESONANCE

To Understand Resonance,

you must understand an objects

Natural Frequency

Mechanical Objects have there own

Natural Frequency

1 second

Tire Imbalance

With a Frequency of 4 Hz

Imbalance

4 Revolutions = Frequency of 4 CPS/HZ

Amplitude of Force

1 second

6 Hz

Tire and Wheel Frequency increases...

with Speed

Imbalance

Suspension Natural Frequency

Range from 10 - 15 Hz/CPS

14 Hz

12 Hz

Suspension Frequency

Tire & Wheel Frequency

Sum of Tire & Wheel

Beating - & - Phasing

Vibration at One Speed

1st order harmonic

15

10

5

0 10 20 30 40 50 60

"...But I balanced the tires in

the fine mode and...

... it still vibrates at 55 MPH"

If a Tire and Wheel assembly is square,

can it be balanced to Zero?

Yes, balance only refers to force

Are Tires and Wheels

Perfectly Round?

Center Hole

-or-

Lug Circle...

can be off-center as much as .010”

95% of O.E.M wheels are Hub-centric

& *100% through 1 Ton

*(as of 1/1/00)

Mounting Error

Duplicate O.E.M. Mounting

Hub-centric

Are wheels centered by the center hole?

Are wheels centered by the lug nuts?

Lug-centric

Mounting Error

Corvette Wheel

Hub-centric

Tire High Spot

Wheel High Spot

Max assembly radial and lateral runout is .050” measured off the vehicle and .060” on the vehicle

Note: Rule of thumb for passenger cars and light trucks

Would this tire and wheel mismatch

cause a problem?

One Revolution

15

10

5

0 10 20 30 40 50 60

Runout Problem

1st order harmonics

Match Mounting

Mis-Matched Matched

Lateral Runout .045” Steel Wheel*

.030” Aluminum*

.030” Aluminum*

* Reference GM

.030” Aluminum*

Measure runout at bead seat area

* Reference GM

Lateral Runout .045” Steel Wheel*

.030” Aluminum*

Measure lateral runout at inside rim lip

* Reference GM

Lateral Runout

.050” Off Vehicle*

.060” On Vehicle*

.060” On Vehicle*

* Reference GM

.060” On Vehicle*

Tape

* Reference GM

Lateral Runout

.050” Off Vehicle*

.060” On Vehicle*

* Reference GM

Dynamic Imbalance

1 oz. Imbalance

Dynamic Imbalance

Is normally not a problem

under 30MPH

Dynamic Imbalance

Under 30MPH Excessive

Lateral Runout of Tire/Wheel

can cause

Look for Bulges

Bulges indicate weak areas and indention\'s are strong areas

Sidewall Stiffness

Sidewall Stiffness

Manufacturers Test for Radial Force Variations at the Factory

…and it is not a common problem

Mounting Errors

.011” Can Results in 1oz. Dynamic Imbalance Error

Mounting Errors

.011” Can Results in 1oz. Dynamic Imbalance Error

Mounting Errors

Duplicate O.E.M. Mounting

Back Cone

-or-

Front Cone

Hub Centric

-or-

Lug Centric

Mounting Errors

Check Cones for Damage or Wear

2.000”

2.001”

Mounting Errors

On a 36 lb. Tire and Wheel, .006” cone wear can result in 1/2 ounce imbalance

2.000”

2.006”

Off center .006” creates more mass on one side