Noise, Vibration and Harshness
Noise, coming from the vehicle and which can be
heard inside and outside the vehicle.
Vibrations, oscillations that are felt and noticeable
inside the vehicle.
Harshness, noises which come from the vehicle
and which can be heard, felt and noticed inside
and outside the vehicle.
These terms are grouped together under the title
Noise, Vibration, Harshness, or NVH for short.
The task of vehicle development and production
is to ensure that noises caused by the vehicle do
not disturb the driver and passengers. Moreover,
the the external noises emitted by the vehicle must
not exceed the thresholds set by law.
NOTE: Basic and advanced training courses are
offered for the following contents. For an overview
of all courses offered, please refer to the Ford
Service Organisation's training course brochure.
Noise types and causes
Noises in and around the vehicle are assigned
specific descriptions:
• Humming and droning are perceived as low
tones.
• Buzzing and whirring are middle tones.
• Howling, whistling, squeaking are assigned to
the high tones.
Low to middle tones are considered to be
unpleasant. They are palpable and noticeable as
oscillations and vibrations throughout the body.
Loud howling and whistling is painful to the ears.
A noise usually consists of a superimposition of
different tones which spread as oscillations.
Each of these oscillations has a specific oscillating
time and can be measured in frequencies. The
frequency describes the number of oscillations per
second. The frequency unit is specified in Hertz
(Hz).
The human ear can perceive frequencies between
20 and 20000 Hz.
Where the different notes come from in a
vehicle:
• Low notes are mostly produced by the engine.
• Low tones can also be produced by the
roadbed, particularly on rough surfaces. This is
a form of droning which can be felt by the
vehicle occupants as vibration or roughness.
• High tones however, which are experienced as
howling or whistling noises, are often air
currents (wind noises) or come from ancillary
components such as the generator, power
steering pump or drivebelt.
• There are also clattering noises which can occur
when driving over an uneven road. These
jerking noises are produced by, for example,
the shock absorbers, chassis components or
loose articles inside the vehicle.
Noises can already be contained where they occur
or, if this is not possible, can be confined with
suitable measures.
The basic procedures here are the damping of
oscillating parts, the insulation of components or
the absorption of the noises through appropriate
materials.
Damping
If a damper is installed next to an oscillating mass,
the characteristic of the damper will reduce the
movement of this mass accordingly (e.g. bumper
on chassis).
Damping affects the resonance of an object or
system.
Isolation
In oscillation technology, the term isolation means
decoupling (separation) of components and
systems. An engine is mounted in sprung elements,
so that as little oscillation as possible is passed to
the vehicle.
In automotive technology, the isolation technique
used is nearly always rubber mounting. Rubber
has a large internal damping capacity. The
elasticity of the rubber acts like a spring.
Absorption
Sound waves are reflected from hard surfaces
Through the use of absorption material, sound
waves hit soft surfaces and are absorbed by them.
The composition and thickness of the material used
plays an important role here. A soft surface,
depending on its composition, absorbs the sound
waves and reduces their energy.
NVH elements
NVH elements are installed to prevent airborne
sound transfers to the passenger compartment in
different body cavities.
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Body Repairs - General Information
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DESCRIPTION AND OPERATION
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