AU2002341726A1 - Engine intake manifold made of noise barrier composit material - Google Patents

Description

ENGINE INTAKE MANIFOLD MADE OF NOISE BARRIER COMPOSIT MATERIAL

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to sound attenuation systems that restrict airborne and

structural-borne sound wave transmission; and more particularly, to an air intake manifold

shell having a combination of compositional and structural features that significantly reduce

engine induced noise.

2. Description of the Prior Art

Continued efforts to reduce vehicle weight and cost have led automobile

manufactures to replace metal components with alternative materials. Plastic air intake

manifolds represent one example of this trend. These air intake manifolds cost and weigh

less thus reducing manufacturing costs while increasing fuel efficiency. Air intake

manifolds currently sold to original equipment manufacturers are segregated into several

feature categories. Significant feature categories- typiea-Hy- considered inclu e- cost,

temperature performance, aesthetics, recycling aspects and noise abatement performance.

While materials such as nylons have been used in air intake manifold applications,

such attempts to meet automotive needs have encountered manufacturing and performance

issues; there remains significant room for improvement in low cost noise abatement air intake manifolds. Because of the imminent noise radiation increase with plastic

components, most engine systems require air intake manifolds or shields as a separate

component. Typical materials used for acoustic shields are polyurethanes, foam and fiber

pads, usually treated onto the plastic shell. These all require post injection molding

operations and are therefore costly. In addition, the noise attenuation provided by such

shields has been unsatisfactory.

Conventionally, noise has been reduced using air intake manifolds of the type

described by increasing the surface density of the air intake manifold shell. In cases where

a noise source is identified, stiffening ribs have been added, or the mass of the air intake

manifold shell has been increased.

No one has taken the approach of incorporating the noise shielding function into the

plastic component itself, such as utilizing co-injection technology, and vibration welding to

improve noise abatement performance at a lower cost. Nor have superior sound transmission

loss materials been used in air intake manifold shell fabrication.

Accordingly, there remains a need in the art for an air intake manifold having a

compact, light-weight construction, improved noise absorption and attenuation

characteristics, which operate collectively to reduce engine noise economically, in a highly

reliable manner.

SUMMARY OF THE INVENTION

The present invention provides an improved air intake manifold shell that provides

significantly improved noise reduction at low cost. Materials having superior sound transmission loss properties are combined with a barrier construction especially suited to

provide increased absorption, and superior sound transmission loss properties.

In one embodiment, the invention provides a co-injection molded air intake manifold

shell comprising an inner and outer layer separated by a sound-absorbing core. Each of the

outer layers is composed of a polyamide resin. Preferably, the polyamide resin contains

glass-fiber reinforcement and mineral filler such as barium sulfate. The inner layer is

composed of a low-density, high damping material having a foam structure, and or

dispersed high-density material such as a glass-fiber reinforced and mineral filled

polyamide resin.

Optionally, the layers are provided with a plurality of blisters to distribute localized

increased core thickness (pockets) at predetermined locations across the air intake manifold

shell surface, the locations being selected to increase noise transmission losses. The noise

transmission loss is further improved by introducing higher density materials into the

localized pockets. In an alternative embodiment, a double layer air intake manifold shell comprises an

inner and outer layer separated by an air core.

In yet another embodiment, a single layer air intake manifold shell is comprised of a

polyamide resin containing glass and mineral fillers such as barium sulfate or high

damping carbon ^"nano-tubes. Optionally, the single layer air intake manifold shell has non-

uniform thickness. The thickness is preferably greatest over preselected areas from which

emanate noise transmissions having larger amplitude, to increase noise transmission losses. The present invention incorporates barrier and absorption technologies in plastic

constructions thereby reducing overall noise transmittance while at the same time reducing

space, weight and cost requirements of existing technologies.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be more fully understood and further advantages will become

apparent when reference is had to the following detailed description and the accompanying

drawings, in which:

Fig. 1 is a perspective view illustrating a typical air intake manifold shell

construction;

Fig. 2 is a cross sectional view depicting a co-injected air intake manifold shell;

Fig. 3 is a cross sectional view of a co-injected air intake manifold shell provided

with a blister; and

Fig. 4. is a cross sectional view depicting a two-layer air intake manifold shell

having an air core.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Sound attenuating thermoplastic materials designed for use as barrier systems in the

automotive and consumer industries have certain acoustical characteristics that vary as

functions of the stiffness and density of the barrier material. An important acoustic property

for a barrier material is its sound transmission loss (STL). The STL determines the

effectiveness of the material in attenuating unwanted noises. Accordingly, a barrier is a

material that causes the sound wave to lose energy as the wave is transmitted through it. The sound transmission loss is the proportion of energy lost as a result of sound being

transmitted through the material/ In general, a higher STL means the barrier exhibits better

noise attenuation performance.

While not being bound by any specific theory, the transmission loss coefficient is

defined as:

Where :P_t = Transmitted sound power

P_;= Incident sound power

And the sound transmission loss in a specified frequency band is ten times the common

logarithm of the ratio of the airborne incident sound power to the transmitted sound power,

expressed in decibels:

(2) m = 101ogl/τ

Conventional methods for reducing noise, as applied to a plate for example,

comprise either increasing the surface density of the plate or, for cases wherein the noise

source is identified, adding stiffening ribs or mass uniformly over substantially the entire

surface area of the plate. In order to raise the sound transmission loss capability of a single

panel or barrier made from such material and used as a partition barrier, its surface mass

must be increased.

This is achieved according to the empirical mass-law equation:

(3) m = 201og_I0 7, + 201og/ - C p_s = surface density of barrier in kg I m²

Where: = frequency in Hz

C = constant (in above units 47.2) STL = Sound transmission Loss in dB

A typical single panel STL curve defines various frequency ranges and their effects on

transmission Toss. The STL performance can be grouped into three controlling regions.

These are:

1. Stiffness and resonance controlled region - less than 200Ηz;

2. Mass controlled region (Mass Law) - between 200 and the critical frequency,

which ranges from about 5000Hz to 20,000Hz, depending on the parameters set

forth in equation 4 hereinafter;

3. Wave coincidence (at the critical frequency) and stiffness controlled region -

above the critical frequency.

The increase in surface mass tends to shift the critical frequency down. At this

frequency, the incident sound wave couples with the bending wave in the panel, thus

increasing the motion of the barrier, which is then transmitted, to the other side. This

phenomenon causes a decrease in the sound transmission loss and hence is the dip in the

STL curve as shown above. Having a lower critical frequency reduces the effective range of

application of the material.

The critical frequency of a homogenous barrier is given by:

c 2 ps _ c 2 ' p ™ „m^« Λ ^λ

(4) /_ please change the subscripts to match later text

2π B 1.8t \ E f

Where: c = Speed of sound in the propagating medium, m/sec p_s = Surface density of the barrier, Kg I m²

B - Bending stiffness of the barrier per unit width N - m = Et³ 1\2

E = Youngs Modulus of the barrier, N/m² p_m = Volume density of the barrier, Kg I m³

One way to improve the STL performance significantly without necessarily

increasing the "mass" is to have a double wall barrier construction. Recent developments in

the Noise, Vibration and Harshness (NVH) technology field, indicate that double layer

systems separated by air gaps offer exceptionally high noise barrier characteristics

compared to a single panel.

The present invention provides an air intake manifold shell having superior noise

abatement properties. It has been discovered that these superior noise abatement properties

are afforded by air intake manifold shell constructions, which comprise:

a) a single layer of uniform thickness with optimized density and mass/thickness

distribution;

b) a double layer separated by a sound absorbing core (sandwiched) layer;

c) a single or sandwich structure with optimally distributed lumped masses "local

bumps" or " pocket blisters;" and

dj a s ngϊe-layer-sfrucϊure with optimally distributed rib -structures

Engine air intake manifold shell structures a) and b) afford noise reduction according to

the "mass law" theory, and the "double layer" theory, respectively. Core layers in case b)

are air pockets, foam structure, high damping elastomer, and/or high-density materials. The

core material that can be an absorption type material acts as a decoupler, since it decouples or isolates the two barrier walls from each other, and thereby aids in enhancing the STL

performance. Case c) reduces noise by shifting the local natural frequencies away from the

input driving frequency domain; lowering the frequency by adding lumped mass. Case d)

reduces noise by shifting the frequency through stiffening the local area. The location and

the number of the distributed masses and pockets can be optimized based on the nature of

noise to filter out.

Use of a single layer structure having optimally distributed rib structures reduces noise by

shifting the local natural frequencies away from preselected frequency components that are

identified as undesirable sounds, such as rumbling, hissing and air rush noise. They lower

the frequency by adding local ribs; increase the frequency by stiffening the local area.

The sound transmission loss (STL) behavior was tested on extruded sheets of

Capron® 8233 nylon 6 from Honeywell sandwiched with a 6-mm air gap. Structures having

this construction exhibited a substantial increase in sound barrier attenuation properties.

The high performance of a double wall system takes place only after the system experiences

double wall resonance. This phenomenon takes place due to the mass-air-mass resonance of

the double wall, produced when the panels act as two masses connected by a spring or

spacer. Double wall resonance frequency is given by:

(5 ,; = * =-Hz^~

Iwd

Where: w = Equivalent surface density = ,w₂ /(w, + w₂ ) w_λw₂ = Surface density of individual barrier walls d = Thickness of the spacer material between the two barriers (assumption : the weight of the spacer material is negligible) k₃ = Constant

= 42, if wis in Kg I sq. m, and d is in m = 120, if wis in lb/sq.ft, and <fis in inch

At frequencies lower than the f_dw, the double wall system behaves like a single wall

having a mass equivalent to the sum of the masses of the two barriers. Therefore, in this

region, the performance of the double wall and single wall systems is the same, provided the

5 mass is the same. However, right at that frequency, sound transmission loss is decreased

below that of a single barrier. For frequencies above the f_dw, the two walls decouple from

each other, and the sound transmission loss increases significantly (18 dB/Octave

theoretically) until it is limited by the critical frequency of either of the two panels. Thus,

the double wall resonant frequency in the low frequency region, and the critical frequency

10 of the individual walls at the high frequency limit the effectiveness of the double wall

system.

At the f_dw and cavity resonance (which is due to the physical size and shape of the air

gap or cavity separating the two layers), a core layer with sound absorption properties can

serve as a coupling material. This coupling material can significantly increase sound

V5- transmission loss, and^' introduce & damping effect to: the mass- atamass. 1^ and^" cavity

resonances. The sound absorbing property of the coupling material causes the sound wave

amplitude to decay with distance. A general solution for the ratio of transmitted to incident

sound pressure is then: (according to F.J. Fahy, Sound and Structural Vibration: Radiation,

Transmission and Response - Academic, New York, 1987).

Where:

= jω(z₂ + p₀c) z, = m, (jω + η_λω )- js lω z₂ = m₂ (jω + η₂ }₂ )- js₂ 1 ω γ = propagation constant of coupler η_{l 2} = mechanical loss factors of the barrier

For large attenuation constants of the coupling material, the layers become

decoupled. The low frequency mass-air-mass resonance becomes less pronounced.

Similarly the sound absorption of the coupler suppresses cavity resonance. According to

Fahy, the maximum pressure transmission ratio is:

Which gives

STL = TL(o_im, )+ TL(o,m₂)+ S.6ad + 2 log ₀ - (l) ^KJ

The component 8.6ad (dB/m) corresponds to the transmission loss of the sound absorbing

coupler.

As previously noted, one of the options for improving the performance of a barrier

material is to increase the "mass" (or surface density) of the barrier. As has been

demonstrated by previous studies, doubling the surface density of a barrier improves the

STL performance by 6 dB. Further, doubling the surface density again improves the STL

performance by 12 dB. This approach, may not be practical from manufacturing

consideration as a significant weight and cost increase occurs. In addition to the increase in mass, the critical frequency of the material is lowered, which is not desirable. To establish a

baseline, a program was written in Matlab release 11 to calculate theoretically and plot the

STL curve based on varying thickness and property parameters. Next, newly developed

grades of Nylon 6, having added thereto different levels of barium sulfate filler, were

selected to calculate, and plot the NVH performance at the single and double the mass

configurations and against aluminum.

Capron® 8267 nylon 6 (15% glass fiber and 25% mineral) and Capron® 8233 nylon

6 (33% glass fiber) from Honeywell were selected, and compared against each other and

aluminum in order to understand the specific gravity and density effects on the performance.

The results showed that the performance of the two materials was equivalent (not a

significant change in the specific gravity), but below that of aluminum due to the density

effects.

The results show a significant improvement in the STL performance due to the

composition of the new material. The STL were calculated for 24"x24" sheets using SAE

J1400 formulae. The SAE J1400 based calculations were found to substantially agree with

the theoretical field incidence calculated curve.. For correlation purposes, the field

incidence theoretical calculated TL's are interspersed with the experimental results.

STL tests were conducted on 3mm thick panels. The samples tested are distributed

according to the following:

A thin lead panel of 4.9 Kg/m² (1.0 lb/ft²) surface weight was used to compute the

correlation factor as referenced in SAE J1400. The lowest usable frequency band of

measurement for this test (in a 508 mm by 508 mm, or 20 inch by 20 inch opening) is 125

Hz (based on the 0.72 m or 2.36 ft) diagonal of the opening between the source room and

the receiving room.

Measurements were made at six microphone locations in the source room and at one

location 100 mm (4 inches) away from the sample, six times in the receiving room.

STL data obtained from the samples clearly show the increase in performance

obtained using the new material over the existing Capron® 8233 resin material, for

STL data was obtained for a single sheet of Capron® 8233 resin vs. the double

wall design. The results clearly show the superior performance of the double wall system

over the single wall structure. The critical frequency dips in the lower frequency region of

the double wall system can be eliminated using an absorbing core layer. The high specific gravity of Capron® XA2935 resin has proven to exhibit high STL performance, and the

double sheet configuration having 6 mm air gap proved to offer superior STL performance.

Co-injection molding is a process that creates a skin and core material arrangement

in a molded part. The skin material is injected first into the mold cavity, and is immediately

followed by a core material. As the skin material flows into the cavity, the material next to

the cavity walls freezes and material flows down a center channel. When the core material

enters it displaces the skin material in the center of the channel by pushing the skin ahead.

As it flows ahead of the core material, the skin material continues to freeze on the walls

producing the skin layer.

Fig. 1 shows a perspective view of a typical air intake manifold 10. Air intake

manifold 10 comprises a plurality of shells welded into one assembly; air intake manifold

10 is constructed of multiple runners 12 and plenum 14. Air enters plenum 14 through the

throttle body neck 16, to be distributed into runners 12, which feed the air into the engine

cylinders (not shown). Fig. 2 shows a cross sectional view of a co-injection molded multi-layer air intake

manifold shell 20. Air intake manifold shell 20 comprises outer layer 22; sound absorbing

core 24; and inner layer 26. Preferably, inner layer 26 and/or outer layer 24 comprises a

polyamide resin comprising a nylon resin, a high specific gravity filler, optionally a

reinforcement fiber and optionally an elastomer. The polyamide preferably comprises at

least one of nylon 6, nylon 616 and nylon 6/66. The high specific gravity filler preferably

comprises a mineral and/or a metal filler, more preferably at least one of barium sulfate and

tungsten. The elastomer, if present, preferably comprises at least one of functionalized

ethylene-propylene copolymer, functionalized styrene-ethylene butadiene-styrene copolymer and metal salt neutralized ethyl ene methylacrylic acid di- and ter-polymers. The

reinforcement fiber, if present, preferably comprises at least one of glass fibers, carbon

fibers and steel fibers. Preferably, the polyamide is present in an amount of from about 20

to about 45 wt. % and the high specific gravity filler ranges from about 40 to about 70 wt.

%. The reinforcement fiber may be present in amounts up to about 30 wt. % and the

elastomer ranges up to about 10 wt. %. One polyamide resin found especially well suited

for use as inner layer 26 and/or outer layer 24 is Capron® XA2935 resin containing glass

fibers and mineral filler. Preferably, the mineral filler has a specific gravity in the range of

4 - 20, such as barium sulfate or tungsten. In the Capron® XA2935 resin, barium sulfate is

present in an amount substantially equal to about 53 % by weight, and the amount of the

glass fiber reinforcement is substantially equal to about 15% by weight. Core 24 is

alternatively comprised of a low-density material, such as a polyamide resin, having a foam

structure. The foam structure can be either open- or closed-cell in nature, and produced by

either chemical or physical blowing agent(s), known in the art, introduced into the

polyamide resin either in the pellet or melt state. The foam cell structure would have an

average diameter range of from the order of one micron (i.e. via MuCell process) to as large

as one centimeter. The range in reduction of density of the polyamide resin as a result of the

foaming process would be 10 to 70%.

Preferably, core 24 is comprised of a high damping elastomer, such as specific types

of thermoplastic elastomers and thermoplastic polyurethanes available commercially, which

are capable of being co-injection molded with the polyamide resin. One high damping

elastomer found to be especially well suited for use as core layer is a polyamide-based

Santoprene, used alone or in-combination with high damping 'carbon nanotubes'. Optionally the section of the air intake manifold shell, shown generally at 30 in

Figure 3, is provided with a plurality of blisters 38 to distribute localized increased core

thickness at predetermined locations over air intake manifold shell 30. Such an arrangement

of blisters 38 on air intake manifold shell 30 increases the mass effect. The locations are

selected to increase noise transmission losses. Noise is reduced by shifting the local natural

frequencies away from the input driving frequency domain and lowering the frequency by

adding lumped mass. The location and the number of the distributed masses or blisters can

be optimized based on the locus and amplitude of noise appointed to be filtered out.

In Fig. 4 there is shown another embodiment of the invention. A cross-section of an

air intake manifold shell is shown in the figure. Double layer air intake manifold shell,

shown generally at 40, comprises inner layer 46 and outer layer 42 of polyamide resin

separated by air core 44. Preferably the air gap has a thickness ranging from about 1 about

25 mm, and the polyamide resin layers contain glass fiber reinforcement and mineral filler.

The mineral filler is preferably barium sulfate, present in an amount of about from 40 to

about 70 % by weight of the polyamide resin composition. The amount of the glass fiber

reinforcement present ranges from about 0 to about 30% by weight of the composition.

In yet another embodiment of the invention, the air intake manifold shell comprises

a single layer of Capron® XA2935 resin to achieve superior noise abatement. Optionally,

thfl_airJntake_manifold shell thickness is not uniform. Air intake manifold shell portions

having increased thickness are positioned over predetermined areas to increase noise

transmission losses by increasing the mass effect. Each of the locations is selected to

maximize noise attenuation over larger amplitude transmission points, thereby providing

increased noise transmission losses over substantially the entire surface area of the air intake manifold shell. This arrangement of the thicker air intake manifold shell portions reduces

noise by shifting the local natural frequencies away from the input driving frequency

domain and lowering the frequency by adding lumped mass. Tailoring the location and the

number of the distributed masses permits optimum noise attenuation for a given air intake

manifold weight, size and thickness. The air intake manifold can be constructed

economically using a minimum of material, and is small, light, efficient, and highly reliable

in operation.

Having thus described the invention in rather full detail, it will be understood that

such detail need not be strictly adhered to, but that additional changes and modifications

may suggest themselves to one skilled in the art, all falling within the scope of the invention

as defined by the subjoined claims.

Claims (25)

CLAIMSWe claim:

1. A multi-layer engine air intake manifold shell, comprising:

a. an outer layer for providing structural rigidity to said air intake

manifold shell;

b. a sound absorbing core for dissipating sound energy; and

c. an inner layer for providing structural rigidity and heat resistance to

said air intake manifold shell.

2. An air intake manifold shell as recited by claim 1, wherein at least one of

said inner and said outer layers comprises a polyamide resin.

3. An air intake manifold shell as recited by claim 2, wherein said polyamide

resin comprises a high specific gravity filler and, optionally, glass fibers for

reinforcement.

4. An air intake manifold shell as recited by claim 3, wherein said filler has

comprises a mineral and/or a metal filler.

5. An air intake manifold shell as recited in claim 4, wherein said filler

comprises at least one of barium sulfate and tungsten.

6. An air intake manifold shell as recited by claim 5, wherein the amount of

said high specific gravity filler comprises from about 40 to about 70 % by

weight of said polyamide resin.

7. An air intake manifold shell as recited by claim 3, wherein said

reinforcement comprise glass fiber present in an amount ranging up to about

30% by weight of said polyamide resin.

8. An air intake manifold shell as recited in claim 3, wherein said polyamide

resin further comprise an elastomer.

9. An air intake manifold shell as recited in claim 8, wherein said elastomer

comprises at least one of one of functionalized ethylene-propylene

copolymer, functionalized styrene-ethylene butadiene-styrene copolymer and

metal salt neutralized ethylene methylacrylic acid di- and ter-polymers.

10. An air intake manifold shell as recited in claim 9, wherein said elastomer is

present in an amount up to about 10 wt. % of said polyamide resin.

11. An air intake manifold shell as recited in claim 2, wherein at least one of said

inner and said outer layers is formed from composition comprising a

polyamide resin comprised of at least one of nylon 6, nylon 6/6 and nylon

6/66; a high specific gravity filler comprising at least one of barium sulfate

and tungsten; glass fiber reinforcement; and an elastomer comprising at least

one of functionalized ethylene-propylene copolymer, functionalized styrene-

ethylene butadiene-styrene copolymer and metal salt neutralized ethylene

methylacrylic acid di- and ter-polymers.

12. An air intake manifold shell as recited by claim 1, wherein said core is

comprised of a high specific gravity material.

13. An air intake manifold shell as recited by claim 1, wherein said core is

comprised of a foam structure.

14. An air intake manifold shell as recited by claim 12, wherein said foam

structure is comprised of a foamed polyamide resin.

15. An air intake manifold shell as recited by claim 1 , wherein said core is

comprised of a high damping elastomer.

16. An air intake manifold shell as recited by claim 1, wherein said layers are

provided with a plurality of pockets that permit distribution of localized

lumped masses at predetermined locations over said air intake manifold

shell, said locations being selected to increase noise transmission losses, and

to shift resonance frequencies away from preselected regions of undesirable

frequencies identified as rumbling, hissing and air rush noises.

17. A double layer air intake manifold shell comprising an inner and outer layer

of polyamide resin separated by an air core.

18. A single layer air intake manifold shell comprised of polyamide resin

containing reinforcement fiber and a high specific gravity filler.

19. An air intake manifold shell as recited by claim 18, wherein said high

specific gravity filler comprises barium sulfate.

20. An air intake manifold shell as recited by claim 19, wherein the amount of

said barium sulfate filler ranges from about 40 to about 70 % by weight of

said polyamide resin.

21. An air intake manifold shell as recited by claim 18, wherein the amount of

said reinforcement fiber ranges up to about 30 % by weight of said

polyamide resin.

22. An air intake manifold shell as recited by claim 18, wherein the thickness of

said layer ranges from about 1 to about 25 mm, said thickness being greater over predetermined areas associated with noise having higher amplitude, to

increase noise transmission losses.

23. An air intake manifold shell as recited by claim 18, wherein said shell is

formed from a composition comprising a polyamide resin comprised of at

least one of nylon 6, nylon 6/6 and nylon 6/66; a high specific gravity filler

comprising at least one of barium sulfate and tungsten; glass fiber

reinforcement; and an elastomer comprising at least one of functionalized

ethylene-propylene copolymer, functionalized styrene-ethylene butadiene-

styrene copolymer and metal salt neutralized ethylene methylacrylic acid di-

and ter-polymers.

24. An air intake manifold shell as recited by claim 23, wherein said layer has a

non-uniform thickness ranging from about 1 about 25 mm, said thickness

being larger over predetermined areas to maximize noise transmission losses

for a given nominal air intake manifold shell thickness.

25. An air intake manifold shell as recited by claim 24, wherein said layers are

provided with a plurality of pockets that permit distribution of localized

lumped masses at predetermined locations over said air intake manifold

shell, said locations being selected to increase noise transmission losses, and

to shift resonance frequencies away from preselected regions of undesirable

frequencies identified as rumbling, hissing and air rush noises.