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Part 5_NVH training Physics and Strategy_B_handout.pdf

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PART _NVH TRAINING PHYSICS AND STRATEGY_B_HANDOUT
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1 NVH Course pg 1 NVH Physics and Strategies for P/T NVH NVH Course pg 2 0.1 1 10 100 1,000 10,000 Hz idle Powertrain Road blocks highway wheel unbalance fore aft shuffle 2nd order engine auxiliaries powertrain bending gear rattle & whine whole vehicle Vehicle Human motion sickness visual disturbance hearing disturbance chassis & subframe drive shaft acoustic cavity modes wheel hop Design Attributes fatigue vibration comfort acoustic comfort Lateral & longitudinal motion engine rigid body organ resonances body The Automotive Frequency Spectrum Response Response Excitation Excitation System System Resonances Resonances2 NVH Course pg 3 NVH Phenomena: A System Approach Excitation Sources Excitation Sources Road Road P/T P/T Interface Systems Interface Systems Chassis Chassis P/T Mounting P/T Mounting Vibrations Vibrations Ride Shake Harshness Ride Ride Shake Shake Harshness Harshness Idle Shake P/T Shake Harshness Idle Shake Idle Shake P/T Shake P/T Shake Harshness Harshness Noise Noise Road Noise Road Noise Road Noise Idle Boom P/T Boom P/T Noise Idle Boom Idle Boom P/T Boom P/T Boom P/T Noise P/T Noise Structure Structure- -borne borne Air Air- -borne borne Vibration Excitation of Body Vibration Excitation of Body NVH Course pg 4 Basic Powertrain NVH Design Objectives Powertrains should meet the following general NVH objectives consistent with other functional requirements: ! At low frequencies: ! Minimal resonant amplification within the operating speed range by either the basic structure or any attachments ! Major order dominance up to 10E to meet sound quality objectives ! At higher frequencies: ! Minimal direct noise radiation from the basic structure and its attachments ! Smooth 1/3 octave spectral characteristics and adequate control of gear rattle and whine to meet sound quality objectives3 NVH Course pg 5 The Source-Transmitter-Receiver Chain Interior Noise Road Noise Wind Noise Powertrain Noise Structure borne Air borne Air borne Chassis dynamics Transmis- sion loss Forcing Functions Resonances Mount Positions Point mobility Cavity dynamics Powertrain vibration Mount isolation Transfer mobility Powertrain forces Structure borne ? Engine block stiffness & mass ? Transmission ribbing ? Structural oilpan ?Et c… ? Cross sections ? Joint stiffness ? Sheet metal thickness ?Et c… Body Noise TF NVH Course pg 6 Powertrain-related NVH Air Borne Air Borne Structure Borne Structure Borne Excitation Excitation Isolation Isolation Transfer Transfer Vehicle Vehicle Interior Noise Interior Noise ΣΣ 2nd order excitation accel accel spectrum shape SPL SPL discrete frequencies SPL SPL 2nd order excitation accel accel harmonic pattern accel accel mount character- istics dyn dyn stiffness stiffness Body Noise TF dB/N dB/N level & linearity dB dB discrete frequencies SPL SPL spectrum shape SPL SPL harmonic pattern Accel Accel chassis dynamics transfer transfer function function Trans- mission Loss dB/dB dB/dB4 NVH Course pg 7 Hierarchy of P/T Structure-borne Noise Targets Forcing Functions Component Resonances Dyn. Stiffness of Mounts SYSTEM SYSTEM COMPONENT COMPONENT SUBSYSTEM SUBSYSTEM Forces at P/T Mounts Vibrations at P/T Mounts Vibrations at P/T Mounts NVH Course pg 8 Axes for Power-Train Displacement pitch roll Transversal axis Longitudinal axis Conrod- Crank Assembly yaw axis5 NVH Course pg 9 The reciprocating-piston Engine Vertical Forces applied to bloc Tranversal Forces applied to bloc NVH Course pg 10 Gas-force components Connecting-rod Force F S = F G / cos β Piston side Force F N = F G . tan β Radial Force F R = F G . cos(α +β )/cos β Tangential Force F T = F G . sin(α +β )/cos β λ = r / l r = ? stroke l = conrod length sin β = λ sin α cosβ = √ 1-λ 2 . sin 2 α α : crankshaft angle ω = dα / dt engine rotation speed6 NVH Course pg 11 Pressure vs Time Time Expansion Exhaust Pressure Admission Compression Explosion NVH Course pg 12 Inertial Forces Oscillating Mass m o = 1/3 m connecting rod + m piston Rotating Mass m r = 2/3 m connecting rod + m crankshaft Rotating inertial Force F r = m r . r . ω 2 Oscillating inertial Force F o = m o . r . ω 2 . (cosα + λ cos 2α + …) F y = r . ω 2 . m r . sin α F z = r . ω 2 . [m r . cosα + m o . (cosα + λ cos 2α )] 1 st order 2 nd order7 NVH Course pg 13 Inertial Moments NVH Course pg 14 Torsional Force Diagram 1. Gas and Inertial forces 2. Gas forces 3. Inertial forces single-cylinder, four-stroke engine8 NVH Course pg 15 Cyclic Variation at Partial and Full Load Coefficient of cyclic variation δ s = (ω max - ω min ) / ω min NVH Course pg 16 1 5 4 3 2 6 10 9 8 7 1 2 3 4 5 6 7 8 9 10 Equal firing intervals through crank offset V10 engine, 4 stroke Firing interval = 2 . 360° / 10 = 72° V-angle : 90o Offset: 18°9 NVH Course pg 17 Crankshaft with offsets 90° V6 engine NVH Course pg 18 Firing Orders in multi-cylinder engines10 NVH Course pg 19 Vibrational Schematic of 6-cylinder crankshaft NVH Course pg 20 Crankshaft Order Analysis with differing firing orders11 NVH Course pg 21 NVH Course pg 22 Forces and Moments in Multi-Cylinder Engines H3, H6, … H3, H6, H2.5, H5, H7.5,… H2, H4,… H1.5, H3, H4.5,… Mc H3 (roll) H1, H2, H4 (pitch) H6 (small) 6 cylinder V H3, H6 (roll) H6 (small) 6 cylinder line H5 (roll) H1, H2, H4 (pitch) H10 (very small) 5 cylinder H2, H4, …(roll) H3 (roll) H1, H2, H4 (pitch) Mi H2, H4, H6 4 cylinder H6 (small) 3 cylinder Fi12 NVH Course pg 23 Technical solutions Weight, friction, cost, packaging Reduction of inertial forces Balancing shafts Weight, cost, packaging Reduction of cyclic variation for ancillaries Filtering pulley Increase of cyclic variation on engine side, weight, cost, packaging Reduction of cyclic varation on driveline side Dual mass flywheel (DMFW) cons pros NVH Course pg 24 Dual-mass flywheel Engine Flywheel Gearbox Wheel Gain Gearbox/Engine Amplification Range Idle Engine Speed Engine Speed Idle Clutch Drives Tire Vehicle operating range Inertia Classical Solution “Double Flywheel” Solution Inertia Stiffness second Flywheel13 NVH Course pg 25 Dual-mass flywheel Flywheel with Clutch Clutchdisc with Torsiondamper Engine Gearbox Engine Gearbox Engine Gearbox Engine Gearbox Dual-Mass Flywheel Gearbox-side Flywheel with Clutch Engine-side Flywheel Torsiondamper Time Time Rotational Non-uniformity [min -1 ] Rotational Non-uniformity [min -1 ] Clutchdisc Conventional Flywheel NVH Course pg 26 DMFW by Sachs14 NVH Course pg 27 Force flow in Sachs DMFW Primary Flywheel Ring Gear NVH Course pg 28 Load-dependent damping Twist Angle Calculation Measurement High Damping on Load Switching Partial Loops under Pull Load with low Damping15 NVH Course pg 29 Filtering pulley Torsion Spring Engine Torsional Vibrations Driving Belt Vibrations Engine Torsional Vibrations Torsional Vibrations transmitted to Peripherals Torsional Vibrations filtered by pulley Directly coupled Decoupled By Pulley NVH Course pg 30 Belt pulley damper Bearing Bushing Flyring 2 Hub Flyring 1 Damper rubber Damper rubber Coupling rubber Bushing Hub Belt Disc16 NVH Course pg 31 Belt pulley damper NVH Course pg 32 Balancing for rotating and oscillating masses17 NVH Course pg 33 4 Cylinder Crankshaft NVH Course pg 34 Balancing rates18 NVH Course pg 35 Star Diagram of 1 st and 2 nd order for in-line engines NVH Course pg 36 The 2nd order issue of the four-cylinder engine Engine Gearbox CoG d F i In reality : ! F inertia is not applied at the gravity center of the powertrain block (incl. gear box), which generates a pitch moment ! The crankshaft, the engine block and the auxiliaries are not perfectly rigid, which generates vibration amplifications around eigen frequencies19 NVH Course pg 37 2 nd order balancing with two countershafts Without Balancing Shafts Balancing Shafts without Level Offset Balancing Shafts with Level Offset NVH Course pg 38 Balancing 2 nd order inertial forces and moments with two offset countershafts20 NVH Course pg 39 Application in BMW 318i NVH Course pg 40 Application in BMW 318i21 NVH Course pg 41 Application in BMW 318i NVH Course pg 42 Application in BMW 318i22 NVH Course pg 43 Application in BMW 318i Sound Pressure Level dB[A] Engine Speed rpm overall level 318i with Balancing Shafts overall level 316i without Balancing Shafts Comparison overall noise level NVH Course pg 44 Application in FORD Zetec23 NVH Course pg 45 Crankshaft stresses and deformations NVH Course pg 46 Crankshaft Bending24 NVH Course pg 47 Basic Excitation Mechanisms of structure-borne noise EVEN ORDERS EVEN ORDERS [2E, 4E, 6E, [2E, 4E, 6E, … …] ] Unbalanced inertia forces HALF ORDERS HALF ORDERS [0.5E, 1.5E, 2.5E, ] [0.5E, 1.5E, 2.5E, ] Cylinder to Cilinder variation of combustion ODD ORDERS ODD ORDERS [1E, 3E, 5E, [1E, 3E, 5E, … …] ] Bending of rotating Crankshaft ΣΣ e.g. I4 NVH Course pg 48 Basic P/T Structure-borne NVH Targets LEVEL QUALITY Smooth second order vibration/force Major order Dominance, Avoidance of roughness25 NVH Course pg 49 Design Requirements for minimal structure-borne noise transmission to the body from second order excitation “ Excitation ! Reduce secondary shaking forces “ Amplification ! Resonance frequencies of the lowest basic structure bending mode and the localized modes of P/T mounted accessories should be greater than 2E+30% at maximum engine speed 303 7000 282 6500 216 5000 Frequency Hz Speed Rev/min NVH Course pg 50 Design Requirements for minimal structure-borne noise transmission to the body from second order excitation “ Important features ! Light weight pistons, long conrod (max. l/r) ! Balance shafts ! Integrated engine-transmission with close-coupled brackets and accessories (for low inertia) ! Funnel shape design at engine-transmission interface (for high stiffness) ! High attachment point stiffness at bracket and accessory mounting points ! Weight optimization26 NVH Course pg 51 Design Requirements for minimal structure-borne noise transmission to the body from higher order excitations “ Excitation ! Minimize minor order forces at the crankshaft-main bearing interfaces “ Amplification ! P/T mounting bracket resonance frequencies should be at least 500 Hz to minimize resonance amplification of sound quality- critical higher orders “ Important features ! Stiff bottom end design (e.g. by use of ladder frame) ! Correspondingly stiff crankshaft design ! Stiff, rigidly coupled P/T mounting brackets ! P/T mounts with broad frequency independent stiffness characteristics NVH Course pg 52 Basic Powertrain NVH Design Objectives Powertrains should meet the following general NVH objectives consistent with other functional requirements: ! At low frequencies: ! Minimal resonant amplification within the operating speed range by either the basic structure or any attachments ! Major order dominance up to 10E to meet sound quality objectives ! At higher frequencies: ! Minimal direct noise radiation from the basic structure and its attachments ! Smooth 1/3 octave spectral characteristics and adequate control of gear rattle and whine to meet sound quality objectives27 NVH Course pg 53 Hierarchy of P/T Airborne Noise Targets Forcing Forcing Functions Functions Component Component Resonances Resonances Damping Damping SYSTEM SYSTEM COMPONENT COMPONENT SUBSYSTEM SUBSYSTEM Powertrain radiated noise Engine radiated noise Transmission radiated noise 100 % 61 % 39 % Forcing Forcing Functions Functions Component Component Resonances Resonances Damping Damping NVH Course pg 54 State-of-the-Art Car Engines28 NVH Course pg 55 Engine radiated noise sources and paths Inner Path Outer Path Cylinder Pressure Gas Pressure Valve Train Impacts Piston Impacts NVH Course pg 56 Important control measures for engine radiated noise ? Minimize impulsive forces (piston/cylinder and valve train) ? Stiffening of bottom end structure ? Stiffening of external surfaces by ‘internal’ ribbing (minimize radiating surface area) ? Stiffening/damping of c
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