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Vibration 101 -excitation modes and countermeasures.pdf

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VIBRATION 101 EXCITATION MODES AND COUNTERMEASURES
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Vibration 101 Page 1 Vibration 101: Excitations, Modes, and Countermeasures Vibration 101 Page 2 Agenda ? Excitations, Modes, and Countermeasures for: – Shake and Nibble (0 to 20 Hz) – Roughness (0 to 40 Hz) – Brake Roughness Vibration 101 Page 3 0 – 20 Hz (Nibble and Shake) ? Typical inputs in frequency domain – Static Imbalance – Couple Imbalance – Radial 1 stHarmonic (R1H) – Tangential 1 stHarmonic (T1H) – Flat Spot Impact on Forces – Road Impact Vibration 101 Page 4 0 – 20 Hz (Nibble and Shake) Static Imbalance F/A Vertical F = 2mrω 2 m r Force Force Frequency Frequency Vibration 101 Page 5 0 – 20 Hz (Nibble and Shake) Couple Imbalance Caster m F = mdrω 2 Force Frequency d r Vibration 101 Page 6 0 – 20 Hz (Nibble and Shake) Radial 1 stHarmonic (R1H) Vertical F = kx ? One part of tire dominates stiffness ? Wheel radial runout helps provide displacement for force ? R1H is usually symmetric CW and CCW with approximately 1.4 amplification with speed f – CW f – CCW Force Vibration 101 Page 7 0 – 20 Hz (Nibble and Shake) Tangential 1 stHarmonic (T1H) Fore-aft F = m (r ω + ω r) ground unground f – CW f – CCW Force ? Tire speeds up and slows down due to change in radius (shape dependent) ? Increases approximately with ω 2 ? Grinding causes asymmetry Vibration 101 Page 8 Vertical Uniformity and Imbalance vs. Speed 0 20 40 60 80 100 120 140 160 180 200 0 10 20 30 40 50 60 70 80 Speed (MPH) Force (lbs) Imbalance Force (lb): Initial Imbalance: 60 g Rate of Increase: 0 g/MPH Initial R1H: 40 lbs Rate of Incease: 0.005 lbs/MPH Vertical Uniformity and Imbalance vs. Speed 0 20 40 60 80 100 120 140 160 180 200 0 10 20 30 40 50 60 70 80 Speed (MPH) Force (lbs) Uniformity (lbs): Initial Imbalance: 60 g Rate of Increase: 0 g/MPH Initial R1H: 40 lbs Rate of Incease: 0.005 lbs/MPH Vertical Uniformity and Imbalance vs. Speed 0 20 40 60 80 100 120 140 160 180 200 0 10 20 30 40 50 60 70 80 Speed (MPH) Force (lbs) Uniformity (lbs): Imbalance Force (lb): Combined Force (lb): Initial Imbalance: 60 g Rate of Increase: 0 g/MPH Initial R1H: 40 lbs Rate of Incease: 0.005 lbs/MPH 0 – 20 Hz (Nibble and Shake) ? Flat Spot Impact on Forces Flat spot T1H Flat spot Imbalance Flat spot R1H Resultant Vertical Force is believed to increase then decay with speed T1H Uniformity and Imbalance vs. Speed 0 50 100 150 200 250 0 10 20 30 40 50 60 70 80 Speed (MPH) Force (lbs) T1H (lbs): Imbalance Force (lb): Combined Force (lb): Initial Imbalance: 60 g Rate of Increase: 2 g/MPH T1H at 80 MPH: 80 lbs Rate of Incease: 0.0001 lbs/ ω 2Vibration 101 Page 9 0 – 20 Hz (Nibble and Shake) ? Road Impact ? Road input is much broader in frequency with a decay at higher frequency ? The shorter the event in time domain, the broader in frequency domain ? Broader inputs could excite many more modes Impact Strip Frequency Response Vibration 101 Page 10 Waterfall Representation of Vibration Vehicle Speed / Frequency Vehicle or system frequency Vibration 101 Page 11 Waterfall Representation of Vibration Tire orders are diagonal on plot Road inputs are swept across frequency range Vibration 101 Page 12 0 - 20 Hz (Nibble and Shake) ? Typical Modes and Countermeasures – Suspension fore-aft modes ? Out-of-phase ? In-phase – Suspension vertical modes ? Tramp ? Hop ? Steering Sensitivity ? Modal Alignment Vibration 101 Page 13 0 – 20 Hz (Nibble and Shake) ? Suspension fore-aft modes ? Out-of-phase ? Right and left suspension move fore-aft out-of-phase with or with some vertical motion causing tierod “push/pull” ? Dominant springs are lower control arm bushings ? Nibble and brake roughness can be different frequencies due to preload of bushings ? Hydrobushing damps mode ? Modal mass is made up of suspension, wheel-end mass, steering mass ? Modal mass for isolated subframe vehicles can include subframe and engine mass significantly dropping resonant frequency ? Most common suspension countermeasures: stiffer pt. 4 bushings, hyrdrobushings Vibration 101 Page 14 0 – 20 Hz (Nibble and Shake) ? Suspension fore-aft modes ? In-phase ? Right and left suspension move fore-aft in- phase with tierods in tension and compression at the same time ? Dominant springs are lower control arm bushings ? Occurs higher in frequency suggesting stiffness is higher likely due to rack forcing condition ? Hydrobushing can damp mode ? Modal mass is made up of suspension, wheel- end mass, steering mass ? Modal mass for isolated subframe vehicles can include subframe and engine mass significantly dropping resonant frequency ? Most common suspension countermeasures: stiffer pt. 4 bushings, hydrobushings Vibration 101 Page 15 0 – 20 Hz (Nibble and Shake) ? Suspension vertical modes ? Tramp ? Right and left suspension move vertically out-of-phase ? Dominant spring is the tire ? Stabilizer bar differentiates hop from tramp ? Struts / shocks can damp mode ? Modal mass is made up of wheel-end mass ? Mode can be nonlinear – higher excitation can shift mode lower in frequency Vibration 101 Page 16 0 – 20 Hz (Nibble and Shake) ? Suspension vertical modes ? Hop ? Right and left suspension move vertically in-phase ? Dominant spring is tire ? Will only have one frequency for hop and tramp without stabilizer bar ? Struts / shocks can damp mode ? Modal mass is made up of wheel-end mass Vibration 101 Page 17 0 – 20 Hz (Nibble and Shake) ? Typical frequency ranges – Fore-aft out-of-phase ? Can vary from 10 to 20 Hz – Isolated subframe vehicles can be as low as 10 or 11 Hz – Bolt-on crossmembers can have high frequencies – Trucks commonly are in 14 Hz range – Fore-aft in-phase ? Typically in the 16 to 20+ Hz range – Tramp / Hop ? Typically in 10 to 15 Hz range Vibration 101 Page 18 0 – 20 Hz (Nibble) – Steering HPAS torsional modes are typically in the 5 to 8 Hz range – The tail of mode can cause increased sensitivity but rarely is there an alignment issue – EPAS modes are much higher in frequency than HPAS modes which causes issues and added new modes in this frequency range – Critical tunable elements ? Tbar (lower is better) ? Rack damping (higher is better) ? MOI of steering wheel (higher is better) ? Geometry (reduce KPO and wheel load lever arm) ? Yoke spring (higher friction better) ? Rack speed (faster is better) ? Steering Sensitivity Vibration 101 Page 19 0 – 20 Hz (Shake) ? Modal Alignment – Framed vehicles can have full-vehicle modes in this frequency range – Be especially concerned about alignment of “sympathetic ” modes like torsion and tramp or fore- aft out-of-phase and bending with hop or fore-aft in- phase – Steering column modes should not ever be in this frequency range Vibration 101 Page 20 0 - 40 Hz (Roughness) ? Typical inputs in frequency domain – Radial 2 ndHarmonic (R2H) – Tangential 2 ndHarmonic (T2H) – Flat Spot Impact on Forces ? Example Vibration 101 Page 21 0 - 40 Hz (Roughness) ? Typical inputs in frequency domain – Radial 2 ndHarmonic (R2H) ? Tire modes are approximately related by the inverse of the order so R2H is approximately ? R1H ? Tire has 2 locations of the tire that are stiffer than others ? Wheel can create second order effect ? Offset bead wheels with one flange offset 180 degrees from the other could introduce 2 ndorder effect ? R2H is relatively constant vs. frequency or speed Vibration 101 Page 22 0 - 40 Hz (Roughness) ? Typical inputs in frequency domain – Tangential 2 ndHarmonic (T2H) F2H 16“ & 17“ 0 10 20 30 40 50 60 70 80 0 10 20 30 40 50 60 70 80 90 Speed (MPH) Magnitude (LBS.) F2H 16“ F2H 17“ ? T2H is both speed squared and resonant dependent ? First mode of tire is torsional mode of tire on rim mode which tangential forces aggravate Tire can be oval shaped Vibration 101 Page 23 0 - 40 Hz (Roughness) ? Typical inputs in frequency domain – Flat Spot Impact on Forces General BFG 275 BFG 265 Michelin Hankook (U152) Michelin 40 30 20 10 0 90 80 70 60 50 40 30 20 10 0 R2H R1H Hunter R1H vs. R2H Similar to “green” tire, R2H approaches half of flat spot R1H Vibration 101 Page 24 0 - 40 Hz (Roughness) ? Typical modes and countermeasures – Full Vehicle Modes ? Torsion ? Bending – Steering Column Modes ? Vertical ? Lateral Vibration 101 Page 25 0 - 40 Hz (Roughness) ? Full Vehicle Modes ? Torsion – Torsion modes are determined by the section of the main beams (rockers), the body joints, and the shear panels (front and rear glass, panel dash, package tray) – Most common countermeasures: boxed rails, good joints Vibration 101 Page 26 0 - 40 Hz (Roughness) ? Full Vehicle Modes ? Bending – Bending modes are determined by the section of the main beams (rockers) and the body joints. – Most common countermeasures: high section height on rails, tuned absorbers Vibration 101 Page 27 0 - 40 Hz (Roughness) ? Steering Column Modes ? Steering Wheel Vertical – Column on bedplate, column and crosscar beam on bedplate, and column and crosscar beam in vehicle are tested – Modal mass is dominated by steering wheel and column – Crosscar beam and braces can play big role in frequency – Trade-off to increased MOI Vibration 101 Page 28 0 - 40 Hz (Roughness) ? Steering Column Modes – Steering Lateral – Similar to vertical mode except system moves laterally – Typically slightly higher in frequency than vertical mode – Modal mass is wheel and column – Trade-off to increased MOI Vibration 101 Page 29 0 - 40 Hz (Roughness) ? Modal Alignment – Framed and unibody vehicles can have full-vehicle modes in this frequency range – Again, be especially concerned about alignment of “sympathetic ” modes like torsion and tramp or fore- aft out-of-phase and bending with hop or fore-aft in- phase – Steering column modes will be in this range and must be considered Vibration 101 Page 30 0 - 40 Hz (Roughness) ? Example – V29 Vibration 101 Page 31 Brake Roughness ? Typical brake inputs in frequency domain – Overview of Disc Thickness Variation (DTV) and Brake Torque Variation (BTV) ? Traditional 1 stOrder DTV (Nibble and Shake) ? Traditional 2 ndOrder DTV (Roughness) ? Rotor Bump (Audible and Tactile) ? Corrosion (Audible and Tactile) Vibration 101 Page 32 Brake Roughness ? Overview of DTV and BTV ? Lateral runout (LRO) is caused from the axis of rotation being off-axis from the brake plates ? DTV is permanent wear of the rotor frequently due to incidental contact on one or both sides of the rotor at runout high spots ? BTV is the AC torque response caused by DTV or other causal factors Vibration 101 Page 33 Brake Roughness 0 – 20 Hz (Nibble and Shake) ? Traditional 1 storder DTV 1st Order Runout vs. Rotor Angle -10 -5 0 5 10 0 30 60 90 120 150 180 210 240 270 300 330 360 Rotor Angle (Degrees) Runout(microns) ? Most common ? Caused by wear out of inboard or outboard surface only Vibration 101 Page 34 Brake Roughness 20 – 40 Hz (2 ndOrder) ? Traditional 2nd Order DTV 2nd Order Runout vs. Rotor Angle -5 0 5 0 30 60 90 120 150 180 210 240 270 300 330 360 Rotor Angle (Degrees) Runout (microns) ? Less common ? Either wear out of one side of 2 ndorder runout or inner and outer wear of 1 storder runout Vibration 101 Page 35 Brake Roughness 0 – 80 Hz (Audible and Tactile) ? Rotor Bump ? Recent failure mode (P22) ? Localized bulge in LRO plots due to casting ? Repeatable position relative to risers and in-gates ? Acts more as impact exciting higher orders ? May cause “beating” issue with integer axle orders 1st 2nd 5th 3rd 4th Bul ged rotor -0. 035 -0. 025 -0. 015 -0. 005 0. 005 0. 015 1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 DTV BTV Vibration 101 Page 36 Brake Roughness 0 – 80 Hz (Audible and Tactile) ? Corrosion – Common failure mode when vehicles sit on lot – Corrosion typical forms in location where pad was or in area around rotor where pad wasn ’t – Believed to aggravate higher orders – Some lining are more susceptible to corrosion than others and some are better at cleaning up rust than others – Looking at “Jag Bags ” in some situations to mitigate rust Vibration 101 Page 37 Summary ? Frequency of response must be considered ? Excitations must be understood and controlled when possible ? Vehicle sensitivity is influenced by modes, must understand what modes are causing issues to understand what countermeasures will work and why
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