FIELD OF INVENTION
This invention relates to a harmonic damper for booming noise reduction in a
vehicle. The harmonic damper absorbs the excitation energy at problem
frequency and dampens the amplitude of resonating panel.
BACKGROUND/PRIOR ART
Iu; thc passenger cars, low frequency (30Hz-100Hz) booming noise is a common
problem. The reason for the same is usually the resonance of a plurality of
structural panels owing to the forces entering the vehicle in dynamic condition.
The vibration path is as follows:-
During the vehicle running condition, combustion forces from the engine will
be transferred to the engine mount which are in turn transferred to the body
panels. This causes the vibration of body panels which displaces the air cavity
and creates pressure differences resulting in booming noise inside vehicle
cabin.
I11 order to avoid resonance of the structural panels, damper is introduced in
the vehicle. Damper can be classified into various types of dampers namely
mass damper, harmonic damper and dynamic damper.
Dynamic damper involves phenomena of phase cancellation. This is usually
made of rubber, which is expensive.
Mass dampers of heavy weight (lkg, 2kg, etc) can also be employed. When
excitation frequency of combustion forces coming from engine and natural
frequency of body panel of vehicle matches, noise is generated inside the car
cabin due to resonance of body panels.
Therefore, to avoid resonance at excitation frequencies, heavy mass is added to
the body panel by means of mass damper to change the natural frequency of
.body panel.
Some known mass dampers are discussed hereinbelow:
Reinforcement and rod type mass damper (fig I):.-
It comprises of a bigger bracket (BI) which is spot welded to a smaller bracket
(B2) with a rod (R) therebetween, wherein said rod is arc welded to the bigger
bracket. Finally the mass damper is spot welded to body panel.
Bracket and plate type mass damper (fig. 2):-
This damper comprises a bracket (B) spot welded to a plate (P), which is
rnounted on the body panel.
Solid block mass damper (Fig.3):-
It constitutes a metallic solid block (S) as' shawn to be fixed onto a resonating
panel (R).
The aforesaid mass dampers involve the phenomena of addition of mass, which
shifts the natural frequency to a lower value. It relies on the following relation:
Increase in mass leads to reduction of natural frequency (fn). This decouples
the excitation frequency of the combustion forces coming from engine with the
mode frequency alongwith amplitude reduction (i.e. Excitation Frequency of
engine is decoupled with natural frequency of body panel of vehicle] and thus
reduces the sound pressure level inside the cabin of car.
I However, the disadvantage is that heavy weight of the mass damper leads to
additional cost and reduced fuel efficiency. Further, there are chances of
increase of Sound pressure levels inside vehlzle cabin at other frequencies due
to shift in natural frequencies of the body panel after the addition of heavy
mass. It also involves high cost of tool/die to make the set-up for damper
which is bulky.
' j I
Now, reference may be made to the following Patents/Publications:
CE f 028343 11 11 A: Disclosed is a windshield glass pane support structure
provided with a windshield glass pane; a lower end support member which
extends in the vehicle width direction, and supports the lower end of the
windshield glass pane; and a dynamic damper which is provided at a location
that constitutes a resonant vibration antinode, in the vehicle width direction, of
the .lower end support member in a state where both of the vehicle-widthwise
ends of the windshield glass pane constitute resonant vibration nodes. The
dynamic damper is an additional vibration system having an additional spring
and an additional mass, whereas a main vibration system is such that the
glass support stiffness based on the end support member forms the basis of a
main spring, and that the windshield glass pane constitutes a main mass.
Furthermore, a'resonant vibration frequency of the dynamic damper is set in a
frequency band where the additional mass vibrates in a phase reverse to the
vibration phase wherein the lower end of the windshield glass pane vibrates in
a vehicle longitudinal resonant vibration mode generated by a vibration
excitation input.
Thus, it comprises plate/bracket attached to cowl upper to simulate an
overhanging mass, which is used for windshield.
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JP2006137327A: To provide windshield glass supporting structure capable of
effectively reducing booming noise. In this - windshield glass -supporting
structure, a cowl part supports a lower end of a front windshield glass, I and a
roof header part supports an upper end of the front windshield glass. In the
cowl part and the roof header part, secondary resonance frequency of them is
respectively set to generate the vibration with a secondary mode in an opposite
phase to each other and to vibrate with an opposite angle mode in the
predetermined frequency zone.
It is used for windshield upper and lower connection.
Another prior art directing to upper strUCtLiie of the vehicle body including a
cowl panel to be joined with a lower end of a windshield, a front member to be
joined with an upper end of the windshield and a front end of a roof panel, and
a rear member to be joined with a rear end of the roof panel and a front end of i
a rear window. The natural frequencies of the cowl panel, the front member of
' , the roof panel, and the rear member are'higher in the order of the cowl panel,
the .front member, and the .rear member.
Thus, it consists of closed section for cowl and roof front. It is used for upper
body of vehicle.
Still another known art is related to a wi:ld shield glass for reducing car
booming to reduce the booming of a vehicle interior by isolating excitation
frequency and resonant frequency generated between the wind shield glass and
a roof panel. A wind shield glass for reducing car booming is constituted as
follows. A side part and a center part are formed to have different curvature.
Excitation frequency and resonant frequency generated between the wind
shield glass and a roof panel are isolated from each other. The thickness of thc
side part is thicker than the thickness of the center part.
I-Iere, variable thickness of windshield isolates the excitation frequency with the
resonance frequency of roof and windshield. Thus, windshield is designed with
different curvature and variable thickness at center and side parts.
All the above discussed ~atents/~ublicationfso llow phase cancellation
phenomena to avoid resonance.
In accordance with another existing mass damper, there is provision of a
simple rod with a mass block at the end, connected to the vibration isolation
system. The buffer rod and mass 'resonates at the problem frequencies to
dampen the vibrations.
This is connected in parallel to engine vibration isolation unit to dampen
cnginc vibration.
The instant invention proposes a harmonic damper for booming noise
reduction in a vehicle, which can efficiently reduce booming noise in vehicle in
comparison to the currently available prior arts.
OBJECTS OF THE INVENTION
Primary object of the present invention is to provide a harmonic damper for
booming noise reduction in a vehicle which overcomes drawbacks associated
with the prior art.
Another object' of the present invention is, to provide a harmonic damper for
booming noise reduction in a vehicle which is lesser in weight to serve the
pu.rposc efficiently.
Further object of the present invention is to provide a harmonic damper for
booming noise reduction in a vehicle which reduces the sound pressure level in
the car by reducing the peak value (Amplitude) of resonance.
Yet another object of the present invention is to provide a harmonic damper for
booming noise reduction in a vehicle which is simple in construction and cost
effective.
SUMMARY OF THE INVENTION
Acco'rding to this invention, there is provided a harmonic damper for booming
noisc reduction in a vehicle comprising of a longitudinal member connected to
a bracket at one end thereof, other end of which is' mounted on body panel of
vehicle to allow vibration of the longitudinal ,member locally in dynamic
condition of vehic'le.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
-Further objects and advantages of this invention will. be more apparent from
the ,ensuing description when read in conjunction with the accompanying
drawings of exemplary embodiments of invention and wherein:
Pig. 1-3 shows: Conventional mass damper.
Fig. 4 shows: Harmonic damper of present invention.
Fig. 5 shows: Vibration results.
Fig. 6A shows: Back door of vehicle without harmonic damper.
Fig. 6B shows: Back door of vehicle with harmonic damper.
Fig. 7A shows: Graph between frequency and sound pressure level
according to prior art.
izig. 713 shows: Graph between frequency and sound pressure level in
accordance with present invention.
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DIETAIL DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING DRAWINGS
The invention discloses a harmonic damper for booming noise reduction in a
vchiclc, which is based on the principle of energy absorption to dampen the
amplitude of vibration.
In order to create a path for vibration, a structure is required having less
stiffness (K) than the body panel of vehicle in contact on which it is mounted.
So that, the excitation forces coming during running condition of vehicle won't
transmit to the body panel instead it dissipates through the less stiffened
structure. This in turn reduces expansion/compression of air cavity in the
vehicle.
Now, reference may be made to fig. 4, 'in which a rod (1) is connected to a
bracket (2) at one end on peripheral circumference of the rod.
The rod is solid or hollow, which can be for example arc welded to sheet'metal
bracket. The rod is free at one end to vibrate. The rod is pi-eferably cylindrical
and the bracket is optionally integrated with a bead (3) provided longitudinally
along the centre line thereof. In the exeklplary embodiment, the bracket
constitutes a L-section without restricting scope of the invention to the same.
The bracket is mounted on the required body panel at other end (4).
As the bracket is in contact with the panel, the rod is free to vibrate locally to
relieve the vibration. Thus the harmonic damper comprises a rod with a
bracket which is mounted on the resonating panel of vehicle wherein the rod is
integrated to the bracket forming a single structure.. The mounting of bracket
on the panel can be done by spot welding/bolting/adhesives.
Stiffness of harmonic damper is much lesser than the stiffness (K) of resonating
panel of vehicle
Tn addition to the above, it is required to tune the frequency of harmonic
damper with excitation frequency of forces from engine at problem frequency by
attaching harmonic damper to the resonating panel which cause the booming
noise inside cabin.
For the same onelany combination of foll~wing parameters is subjected to
variation, which depends on feasibility.
X- Length of rod
Y-Thickness of bracket
Z-Inner diameter of hollow rodldiameter of solid rod.
Ti-lus, the harmonic damper is first tuned to vibrate at the'~rob1emfr equency.
This is accomplished by changing the size (length, diameter, thickness) of the
cylindrical rod and bracket and carrying out. the vibration performance analysis
of the same to find the resonance frequency. Drive point vibration analysis
iterations are carried out until the resonance frequency matches the problem
frequency. An example is given hereinbelow:
Iterations by varying rod length:
I
I
v1- (Y) Rod diameter ' ~1
Resonance Frequency
(Hz) r
Iteration
1
I ) (2) are kept constant
Rod
9
Length, X.
(mm)
50
Parameters "Y" &
"2"
Bracket thickness 39
-10-
I
In this regard, reference may be made to fig. 5 illustrating vibration I
results using a graph between frequency (Hz) in X-axis and mobility (dB)
in Y-axis.
Once the harmonic clainper is tuned at the prohl.em frequency, it is
assembled to the resonating panel which causes the booming noise
inside cabin. Now both, panel and the harmonic damper resonate'at the
problem frequency.
Phenomena: I The excitation energy available zt the problem frequency is now
distributed between the panel and the harmonic damper. But since
the harmonic damper is having very less stiffness as compared to
the panel, most of the excitation energy is absorbed by the harmonic
damper, thereby, reducing the amplitude of vibration 6f the panel.
Since the amplitude of vibration of the panel is reduced, the volume
of air cavity inside vehicle cabin displaced by the panel is also
reduced. Thus, lesser pressure differences are generated inside
vehicle cabin which results in reduction' of booming noise at the
problem frequency.
Now referring to fig. 6A, which is reflecting high amplitude of resonance of back
door (A) without harmonic damper and fig. 6B which is reflecting reduced
amplitude of resonance of back door (8) with the help of harmonic damper of
the invention.
The known mass damper can be replaced by the novel harmonic damper
having lesser weight (max 250 g).The size (length, diameter) of the rod and
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bracket (thickness) is optimized to tu.ne the harmonic damper for different
problem frequencies. The harmonic damper resonates at the problem frequency
and absorbs more energy (due to lesser stiffness compared to structural panel)
and results in reduction of vibration of structural panel. Subsequently,
perceivable reduction in booming noise inside vehicle cabin is achieved with
less weight and cost as compared to conventional mass dampers.
Attachment .Location:
The resonating panel needs to be identified with the root cause analysis.
Thereafter the region where the maximum displacement occurs is identified
and the harmonic damper needs to be fitted at that location or preferably* 100
mm from that location depending on the feasibility without restricting scope of
t:hl invention to the same.
To appreciate the difference between the existing mass damper and harmonic
damper, reference may be made to fig.' 7A and.7B.
In accordance with the existing mass damper as in fig. 7A, the natural
frequency of body panel decreases by the addition of mass, whereas from fig.
7B with the .help of harmonic damper of lesser weight, the amplitude of
vibration of body panel reduces which decreases the level of noise inside I
vehicle cabin at the problem frequency. Thus, the invention serves the purpose
more efficiently than the prior art.
~ivantageousF eatures:
- Perceivable reduction in booming noise.
- Enhanced customer comfort level.
- . Up to 80% weight saving (- lkg to -1.5kg) as compared to conventional
mass'damper giving rise the same effect.
- .
- Simplification of design facilitating manufacturing.
I - Feasibility of scrap utilization due to .design simplicity.
- Cost effective.
I I t is to be noted that the present invention ib susceptible to modifications,
I adaptations and changes by those skilled in the art. Such variant embodiments
1 employing the concepts and features of this invention are intended to be within . I
I
1 the scope of the present invention, ,which .is further. set forth under the
following claims: -

We Claim: ,
1. A harmonic damper for booming rioise reduction in a vehicle comprises a
longitudinal member connected to a .bracket at one- end which is
mounted on body panel and other end of the longitudinal member is free
to vibrate in vehicle running condition.
2. A harmonic damper for booming noise reduction in a vehicle as claimed
in claim 1 wherein the longitudinal member constitutes a rod, which is
preferably cylindrical.
3. A harmonic damper for booming noise reduction in a vehicle as claimed
in claim 1 or 2 wherein the rod is a hollow rod, alternatively which can
be a solid rod.
4. A harmonic damper for booming noise reduction in a vehicle as claimed
in any of the preceding claims wherein the bracket forms a sheet, which
can be provided with a bead longitudinally preferably at the middle.
5. A harmonic damper for booming noise 'reduction in a vehicle as claimed
in any of the. preceding, claims wherein the rod is connected to the
bracket on its peripheral circumference.
6. A harmonic damper for booming noise reduction in a vehicle as claimed
in any of the preceding claims wherein the ;od and bracket can be
integrated to constitute a single structure.
7. A harmonic damper for booming noise reduction in a vehicle as claimed
in any of the preceding claims wherein to tune the frequency of the
harmonic damper with the excitation frequency of forces from engine at
problem frequency, parameter(s) of the rod and bracket undergo
variation.
8. A harmonic damper for booming noise reduction' in a vehicle as claimed
in claim 7 wherein said parameters include diameter of solid rod/inner
diameter of hollow rod, length of the rod and thickness of the bracket.
9. A harmonic damper for booming noise reduction in a vehicle as claimed
in any of the preceding claims wherein the harmonic damper can be
attached to the body panel by welding or bolting or by adhesives.
10. A harmonic damper for booming noise reduction in a vehicle as
claimed in any of, the preceding claims wherein the damper is less
stiffened than the body panel i.e. K of damper <<