EnginemountsNVH专业资料1

– Engine - inertia/ gas forces, torques, abuse
starts, hill starts
• Isolation
– Ride Comfort 2- 20Hz – Noise and Vibration 20Hz+
• Engine Location
– Compression set – Power unit / engine bay positioning – Torque control -tip in/ tip out , gear shift
Lotus experience of engine mounts
• Design of mounting concept for engine
– NTA 3 point , NTA 4 point, 3 point , 4 point mounting – Location of engine mounts relative to engine torque axis (CAE)
• First strategy is far more common approach.
• If the bodystructure was infinitely stiff then no structural
noise would be generated. (bedplate).
• Body sensitivity is measured by INPUT POINT MOBILITY
Powertrain bending mode 138Hz
Practical engine mount design
• There is no single right location for an engine mount system. • Idealised mounting positions may not be achievable due to
• Engine solid body modes are shifted to either
coincide or avoid vehicle system modes.
• Decouple / avoid modes - example
– Engine roll
8Hz
– Engine Bounce – Engine pitch
• Engine side mounting design
– Refinement, durability (FEA)
• Engine mount detailed design • Body structural design of engine mounts (FEA) • NVH development of engine mount rates , brackets • Ride / shake development of engine mounts • Transient engine load reaction (shunt reaction) • Modal testing of powertrain modes in vehicle
engine torque.
• In some mounting concepts static load and torque reaction are
done by separate mounts in other concepts mounts provide reaction to both kinds of load.
Bodyside bracket front reinforced
Bodyside bracket rear reinforced
Engine block pick up - improved casting
Improved noise at 4800rpm
Engine relation to vehicle modes
Engine Bounce mode - 10.8Hz
Engine fore aft mode 11.8Hz
Engine roll mode 14.3Hz
Engine pitch mode 14.8Hz
Engine yaw mode 16.8Hz
Engine Flexural modes
Engine mounting concepts
• The generally used engine mounting concepts use either 3 or 4
main mounts.
• At least 2 mounts must bear the static weight of the engine. The
geometry and package.
• Locating mounts with minimal offsets from structural members
or the main block leads to good refinement - this can be far better than an idealised position that requires long brackets or high offsets.
Engine mount example
Engine mount response measured
• Strong vibration found
on engine RH engine mount.
Engine side - overall level Body side - overall level Engine side 2nd order Body side 2nd order
• Overall good mount
attenuation Engine side to Body sideElastomer rates are therefore OK.
Structural changes to engine mounts
Reinforced engine side mount
Engine rigid body behaviour
• Modes are influenced by powertrain
– Mass , C of G, directions of inertia axis
• Modes are influenced by mounting system
– Number and location of mounts, mount orientation, mount stiffness
• Generally more
problematic on RWD installations
– Bending mode usually sub
200Hz
– System mass higher
• Ideal mount position is
on nodal points of bending mode to prevent energy transfer into body structure
Engine mount functions
• Static Load acceptance
– Hold the mass of the engine
• Dynamic load acceptance
– Vehicle- braking, cornering, kerb strike,
bumps, crash
and damping
• Six Natural modes can be expected
Fore aft (x) Lateral (y)
Bounce (z)
Roll (Rx) Pitch (Ry)
Yaw (Rz)
Some of these modes are often difficult to identify especially if 2 modes are virtually co-incident - e.g. lateral (Y) in following example
• For a force acting on a mount generating vibration
– Sound power (Structural noise) Mechanical power transfer – Mechanical Power transfer Force x velocity – Body mount mobility m/s/N provides correlation to noise path seor different engine derivatives may
determine a compromise location is selected.
• Other vehicle requirements such as crash performance can
influence location and stiffness of engine mounts.
• Manufacturing requirements for engine installation can also
influence engine mount location ( e.g. assembly access)
3 point mount - milking stool
All 3 mounts carry the mass of the engine and react engine torque
4 point platform
All 4 mounts carry the mass of the engine and react engine torque Distribution of forces varies with geometry tolerances