Lecture_01-23-08 - 1 MECH 668 Vehicle Noise, Vibration and...

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1 MECH 668 Vehicle Noise, Vibration and Harshness (NVH) Gear Vibrations and Noise Winter 2008
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2 Description of automotive gear vibration and noise problem Transmission Error Excitation Dynamic Mesh Force System Dynamics Sensitivity Vibration Transmissibility Gear Noise Gear Noise In vehicle In vehicle Gear vibrations & noise generation . Source Path Receiver
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3 Gear Whine Generation & Transmission TE excitation Dynamic mesh force generation Vibration transmissibility Dynamic interactions Structural-acoustic transfer functions
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4 ± Transmission error (TE) arising from deviation of gear rotations from the ideal motion defined by the gear ratio. This deviation is caused by profile errors , elastic deformation and misalignment . N = number of teeth (p=pinion, g=gear) θ = gear angular displacement (rotational motion) Δ = deviation from ideal gear ratio ± Other possible excitation sources: Mesh stiffness variations Shuttling forces and bearing forces Friction forces Air and lubricant entrainment Gear Excitation Sources pg gp N (TE) N θ =+ Δ θ g p k mp k mg TE Li n e - of a c t i on D r o n ( L O A )
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5 How do we define a mesh model ? ± Mesh model comprises of TE, mesh stiffness, mesh point and LOA ± For spur and helical gears, mesh point (intersection of base circle) and LOA (pressure angle) are usually determined from gear geometry. TE and mesh stiffness are obtained from tooth contact analysis (may be finite element-based) ± For more complex gears like hypoid and bevel gears, typically we can use quasi-static tooth contact analysis to derive mesh stiffness, mesh point, line-of-action and transmission error Pinion Load distribution and contact stress
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6 Pure Torsion Lumped Parameter System K m C m θ p g Torsional Vibration Model r g r p Pinion Gear Damped mesh stiffness ± Typically rigid body rotation is ignored. Only interested in perturbation about the mean speed as that relates to gear noise ± In pure torsion vibration model, hypoid gear system basically behaves like a parallel axis gear pair J g J p
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7 2-DOF Linear Torsional Vibration Model Equations of motion (Semi-definite system) Derivation using the Lagrange’s method
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8 1-DOF Definite System Out-of-phase gear pair torsion mode Damped natural frequency
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9 Example Modal Calculation Results Rigid body mode Flexible mode Eigenvalue problem (modal analysis)
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10 Rear Axle Hypoid Gear Torsional Mode Out-of -phase gear pair rotation = m m n m K ω Rigid body (in-phase) gear pair rotation Pinion Gear Gear Pinion g e a r s h f t p i n o () 0 = n
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11 Modal Analysis Results ω r (Hz) Mode descriptions 229 Out-of-phase torsion, pinion and gear axial motion 441 Out-of-phase torsion, gear transverse motion 589 Out-of-phase torsion, pinion yaw and pitch motion 770 Pinion torsion and pitch motion, gear pitch 880 Out-of-phase torsion, gear yaw and pitch motion 1210 Pinion torsion and pitch motion 1960 Out-of-phase torsion, pinion bounce 2490 Out-of-phase torsion, pinion yaw motion 3670 Out-of-phase torsion, pinion pitch motion
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12 ±
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This note was uploaded on 10/13/2010 for the course MECH 668 taught by Professor Lim during the Winter '08 term at University of Cincinnati.

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Lecture_01-23-08 - 1 MECH 668 Vehicle Noise, Vibration and...

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