Automotive NVH Research Instrumentation and Infrastructure at UC-SDRL Teik C. Lim, Jay Kim, Randall Allemang Structural Dynamics Research Laboratory Mechanical, Industrial & Nuclear Engineering University of Cincinnati
Long-term Objectives Integrated experimental, analytical & computational research laboratories y Drivetrain and propulsion noise & vibrations y Vehicle system dynamics and control y NVH and acoustic noise quality Discovery, research and education-centered facility y Training of next generation engineers y Partnerships with industry and government y Conception & deployment of new technologies (new challenges: wider use of alternative fuels/systems)
Research Focus Study of forces/motions FEM/modal analysis Spectral techniques Noise path analysis Drivetrain Systems (Gears, Bearings, Trans., Engines) Nonlinear response/stability Active control / smart systems Noise/Vib Control Vehicle Structures (Body, Chassis, Interior Acoustics) Structure-borne contributions Hybrid models Vibro-acoustic design/analysis NVH & Sound Quality (Actuators, Brakes, Rotating Machines) Audio-visual simulations Jury Evaluation / statistical models Signal analysis Target setting
Major Research Infrastructure 4-axis nonlinear road simulator Advanced modal/spectral analysis Gear dynamics/acoustics Clutch Coupling Test Gearbox Torque & Speed Transducers Isolating Belt/Pulleys Test Foundation Drive Motor Slave Gearbox for Torque Application 1 in. Anechoic chamber Acoustic noise quality studio Computational Vibro-acoustics
4-Axis Road Simulator MTS Series 3 Data Acquisition Equipment: HP-36X Modules 4-ch (1. khz) & 4-ch ( khz) HP-VXI Modules 96-ch ( khz) Larsen Davis Network System 64-ch ( Hz) Application Areas: Squeak & Rattle Nonlinear Response Ride quality Software: MTS Ideas LMS Matlab Computers: HP-UX workstations Windows NT/
4-Axis Road Simulator (Results)
Inverse Sub-structuring (Spectral Domain) {x o(a) } {x c(a) } [K] {x c(b) } {x o(b) } Free sub-structure structure A {f c }=[D A ]{x c } {R c(a) } {R c(b) } Free sub-structure structure B {f c }=[D B ]{x c } {f i(a) } {f c(a) } Inversion {f c(b) } {f i(b) } {x c }=[H c ]{f c } Frequency-dependent Nonlinear Algebraic Solutions (express free sub-structure FRFs in term of system response) One-dimensional case H o(a)c(a) = K ( H H H ) = s,c(a)c(a) H ( H H ) s,c(b)c(b) s,c(a)c(a) s,c(b)c(b) H H s,c(a)c(b) s,c(b)c(b) s,c(a)c(b) H s,c(a)c(b) H s,c(a)c(b) H s,c(a)c(a) s,o(a)c(a)
Vehicle Structure (Chassis Force Transmissibility) Data Acquisition System Spindle excitation test Accelerometer Test vehicle Road Noise/Vib VXI frontend Air mount support Modal Hammer Impact hammer sub-structure A mic, o(a) Body structural-acoustic Sensitivity response Frame/suspension dynamics (Transmissibility and Resonance Effects) Chassis force input to body Spindle Loads Tire patch excitation c(b) c(a) i(b) accel o(a) sub-structure B mount
Vehicle Structure (Validation Results) Stiffness (kn/mm) 1 1 Rear left mount stiffness Measured (Elastomeric test) Predicted 1 1 3 3 4 Frequency (Hz) Sound Pressure (db) 8 6 4 Driver's ear SPL due to spindle force Predicted Measured 1 1 3 3 4 Frequency (Hz) Method to dissect system response into free sub-structure characteristics Modular viewpoint to study dynamic response of complex structures Readily provides force transmissibility and path contribution functions
Crank Rumble (Nature of Problem) Transient, rough sound due to combustion-induced crankshaft vibration Most severe in 4-cylinder, manual transmission powertrains Correlation between the annoyance level and main journal clearance Ramp-up Ramp-down Neutral no-load snap test Rumble contains several modulated, constant, narrow-band signals Spectrogram Function (time-frequency analysis)
Periodicity of Rumble (Engine speed effect) Specific loudness & moving average filters SPL rumble period Modulation Frequency band: 87 9 Hz slope = p/6 p=. (half-order effect) Time scale 1 1 3 4 6 7 8 Engine rpm Half-order effect implies sensitivity to a specific cyl. or main journal brg. Speed-invariant frequencies suggest effects of structural modes.
Rumble Transmission (Simulated Air-borne) Sound Quality Playback System Baffled Speaker DAT Recorder TL Input Signals No-load snap nd gear ramp Random noise Mic Specific Loudness Reduction Operating Data Simulated Data Bark 1 18-17 Hz Air-borne dominance Simulated Data Same effect for Barks thru 7 (4-1, 1-63, 63-77 Hz) Bark 8 77-9 Hz Operating Data Structure-borne dominance
Damping Identification (Hybrid Modeling) Direct damping identification from measured dynamic stiffness matrix Imaginary([H(ω)] -1 ) = [C(ω)] Represent true loss mechanism & spatial distribution in freq. domain Use with analytical mass and stiffness matrices to form a hybrid model - x 1 9-1 1 1 Real x 1 9 Imag - x 1 9-1 1 1 x 1 9 - x 1 9-1 1 1 x 1 9 - -1 1 1 x 1 9 x 1 9 - -1 1 1 x 1 9 x 1 9 - -1 1 1 x 1 9 x 1 9 Typical results: Diagonal elements of experimentally identified damping matrix -1-1 -1-1 -1-1 - - - - - - 1 1 1 1 1 1
Sound Transmission (Anechoic Facility) 4 Calculated Me a s ure d 3 TL (db) 1 Cylindrical structure -1 1 1 1 1 3 1 4 Fre quency (Hz) 4 3 W/ S tiffe ne r W/O S tiffener Flat-stiffened 1 9 Cylindrical-stiffened W/O stiffener W/ s tiffe ne r 3 8 7 TL (db) TL (db) 6 1 1 4 3 1 1 1 1 3 1 4 Fre quency (Hz) 1 1 1 1 3 1 4 Frequency (Hz)
Concluding Remarks New challenges requiring integrated test & analysis facility for research, education and services y Nonlinear & time-varying problems y More stringent NVH requirements y Combined design & NVH analysis/testing approach y Alternative vehicle, propulsion and fuel systems Center for discovery, research and education y Repository for basic and applied NVH technologies y Partnerships between academia, industry and govt. y Combined research & education activities