CA2209244A1 - Noise abating components - Google Patents

Abstract

The invention relates to a material which comprises a metal matrix composite reinforced with an appropriate amount and type of reinforcement. The matrix metal can be any metal which is capable of desirably interacting with the reinforcement. The metal matrix composite material has applications in environments which experience resonant vibrations. This material ameliorates undesirable resonant vibrations.

Description

Wo 96/26371 PCrlUS96102474 DESCRIPTION
NOISE ABATING COMPONENTS

Technical Field The invention relates to a material which comprises a metal matrix composite 10 reinforced with an ~~ liate amount and type of reinforcement. The matrix metal can be any metal which is capable of desirably interacting with the reinforcement. The metal matrix composite material has applications in environments which experience resonant vibrations. Ihis material ameliorates undesirable resonant vibrations.

5 Back~round Art Many devices currently exist which em~n~te undesirable noise thelerloll1. Such undesirable noise may be due to some type of frictional or rubbing contact between two members or two separate structures. This frictional or rubbing contact can be coll~ micate1l by, for example, vibrations tr~n~mitt~l to one or more other members 2 o which are in c ontact with the noise generating members which can result in said one or more other members also em~n~tin~ undesirable noise.
For e~ample, in the case of disc brake rotors, it is well known that disc brakesgenerate undesirable noises during braking. These undesirable noises are typically referred to as squeals, chirps, grunts, and moans. The noises in disc brakes are generated 2 5 by the frictional contact between the brake linings or pads and the rotor surface. The brake linings contact the rotor by various pressurizing means, all of which, typically, result in the ~eneration of noise. The noise is thought to occur due to a resonance which develops at tke interface between the brake pad or lining and the rotor. This resonance can then be tr~n~mittçd through the brake shoe assembly to other brake portions such as 3 0 brake mounting hal.lw~l~, as well as into the suspension of the vehicle. The transfer of this resonance or noise to other vehicle parts can actually result in an amplification of objectionable sound.
A sim.lar situation exists for drum-type brake rotors wherein a friction material contacts a brake drum. The interface between the friction material and brake drum also 3 5 may cause un1iesirable resonance to develop and thus, in a similar manner, result in a tr~n~mi.~sion of undesirable noise.

W O96/26371 PCTrUS96/02474 Similarly, undesirable resonant vibrations can occur in virtually any environment where moving parts are contacted with each other. Additional examples of automotive applications would include tr~ncmiccions, drive shafts, gears, alternators, generators, engines, wheels, hubs, etc. Each of these areas are also subjects of the present invention.
- 5 Likewise, other a~aldlus that have moving parts that are also the subject of the present invention include electric motors, railway engines and railway cars, hydraulic motors, bearing assemblies, etc.
- In general, the larger the masses associated with each other and/or the larger the frictional forces, the more excessive the undesirable noise which emanates from such - 10 contact. Thus, whether the contact is rotational, sliding, or otherwise, the present : invention can provide desirable noise dampening effects.
With specific regard to brake rotor assemblies, a~Le~ L~ have been made to - ameliorate undesirable noise ~lu~ ti~g from the assemblies by including, for example, a disc brake shoe dampener. An example of a disc brake shoe dampener is set forth in - 15 U.S. Patent No. 3,937,305 which issued on February 10, 1976 in the name of Vanden - Bossche. Other ~lelllpLs to dampen noise from either brake discs or brake drums can be . found in the following U.S. Patents: 5,139,117, which issued on August 18, 1992, in the name of Melinant; 5,083,643 which issued on January 28, 1992, in the names of ~llmmPl et. al.; 4,738,338 which issued on April 19, 1988, in the names of Schandelmeier, et. al.;

4,513,844 which issued on April 30, 1985, in the name of Hoffman; and 4,445,594 which issued on May 1, 1984, in the name of Hoffman.
It is clear that the prior art is searching for reliable, cost efficient techniques to reduce noise in various apparatuses, including automotive braking a~al~Luses.

2 5 Definitions As used herein, it should be understood that the following terms should have consistent mPaningc throughout the application:

"All~ .lll", as used herein, means and includes essentially pure metal (e.g., a 3 o relatively pure, commercially available unalloyed ~lumimlm) or other grades of metal and metal alloys such as the commercially available metals having i~nl~uliLies and/or alloying conctitlnPntc such as iron, silicon, copper, m~gnPsillm, m~ng~n~se, chromium, zinc, etc., therein. An alllmimlm alloy for purposes of this definition is an alloy or interm~t~llic compound in which alnmin-lm is the major con.ctit lent 3 5 "Bronze", as used herein, means and includes a copper rich alloy, which may include iron, tin, zinc, al -minllm, silicon, beryllium, m~n~nPse and/or lead. Specific bronze alloys include those alloys in which the proportion of copper is about 90% by .

Wo 96/2637L PCTIUS~6102474 weight, the proportion of silicon is about 6% by weight, and the proportion of iron is about 3 % by weight.
,c "Cast Iron", as used herein, refers to the family of cast ferrous alloys wherein the proportion of carbon is at least about 2% by weight.
"Ceramic", as used herein, should not be unduly construed as being limited to a ceramic body in the classical sense, that is, in the sense that it consists entirely of non-mPt~llic arld inorganic materials, but rather refers to a body which is predo.,.i.~.-11y ceramic with respect to either composition or dolllillc-llL properties, although the body may contain m nor or substantial amounts of one or more m~t~ constituents (isolated and/or o interconnected, depending on the proces~ing conditions used to form the body) derived from a parent metal, or reduced from an oxidant or a dopant, most typically within a range of fLom about 1-40 percent by volume, but may include still more metal.
"Copper", as used herein, refers to the commercial grades of the substantially pure metal, e.g., 99% by weight copper with varying amounts of illl~uliLies contained therein.
Moreover it also refers to metals which are alloys or int~rmetallics which do not fall within the definition of bronze, and which contain copper as the major constituent therein.
"F~ller", as used herein is intended to include either single constituents or mixtures of con~tit~ nt~ which are subst~nti~lly non-reactive with and/or of limited solubility in the matrix or parent metal and may be single or multi-phase. Fillers may be provided in a 2 0 wide variety of forms, such as powders, flakes, platelets, microspheres, whiskers, bubbles, f~bers, particulates, fiber mats, chopped fibers, spheres, pellets, tubules, refractory cloths, etc., and may be either dense or porous. "Filler" may also include ceramic fi~lers, such as ~ min~ or silicon carbide, as fibers, chopped fibers, partirlll~t~s, whiskers, bubbles, spheres, fiber mats, or the like, and coated fillers such as carbon fibers coaled with ~lllmin~ or silicon carbide to protect the carbon from attack, for example, by a molten ~lnminllm matrix metal. Fillers may also include metals.
"Matrix Metal" or "Matrix Metal Alloy"; as used herein means that metal which isutilized to form a metal matrix composite (e.g., before infiltration) and/or that metal which is i1lLcllllillgled with a filler material to form a metal matrix composite body (e.g., 3 o after infilt~ation). When a specified metal is mentioned as the matrix metal, it should be understood that such matrix metal includes that metal as an essentially pure metal, a commercially available metal having hll~uliLies and/or alloying constituents therein, an intermetall.ic compound or an alloy in which that metal is the major or predominant constitllenr .
"Metal Matrix Composite" or "MMC", as used herein, means a material comprisinlJ a two- or three-dimensionally interconn~ctecl alloy or matrix metal which has embedded a ~lcrOllll or filler material. The matrix metal may include various alloying elements to provide specifically c~esired mechanical and physical ~1ope1~ies in the resulting composite.
"Spo~ltaneous Infiltration'~, as used here*l, means that the infiltration of matrix metal into the permeable mass of filler or preform occurs without requirement for the application clf ~ll'eS~iUlc or vacuum (whether Pxtern~lly applied or internally created).

Summary of the Invention The present invention provides a material which desirably abates noise which is caused from the frictional contac~ of two or more members. Specifically the present o invention co~prises a metal matrix composite wherein the matrix metal is any desirable metal which can be made to infiltrate any desirable reinforcement material. Typically, matrix meta]s include ~ mimlm, bronze, copper, m~gn~sium, cast iron, etc (and alloys thereof~. Typical filler materials include various particulate materials such as oxides, nitrides, carl~ides, oxynitrides, clays, etc. Fillers may also include various shapes inrlllrling diiferent fibers, platelets, whiskers, etc.
An important aspect of the invention is the unexpected discovery of a peculiar behavior in certain composite materials. Specifically, it has been unexpectedly discovered that the inte~nal friction or dampening behavior of composites having a matrix of metal and various reinforcements behave in a manner which causes composites, when constructed n an a~1op1iate manner, to function as a noise dampener. For example, when a particulate reinforcement is combined with a matrix metal in an amount of about 50% by volume, or even more preferably in an amount of at least about 60% by volume, or greater, t le amount of damping behavior experienced in the composite signifir~ntly increases.
2 5 Partirularly ~1erc11cd 1ci1lro1cement materials of the present invention include particulate alnmim~m oxide and particulate silicon carbide in an ~lllmin~lm alloy matrix metal.

Brief Description of the Drawin~s 3 0 Figu~e 1 shows the damping behavior of silicon carbide reinforced ~lllmimlm metal matrix composite as a function of reinforcement content.

Detailed Description of the Invention ~.
The present invention provides a material which desirably abates noise which is 3 5 caused froni the frictional contact of two or more members. Specifically the present invention comprises a metal matrix composite wherein the matrix metal is any desirable metal which can be made to ir~lltrate any des*able 1chlrolcement material. Typically, wo 96/26371 PCTIUS96102474 matrix metaLs include ~ .", bronze, copper, m~gnPsillm~ cast iron, etc (and alloys thereof). T~!pical filler materials include various particulate materials such as oxides, nitrides, car1~ides, oxynitrides, clays, etc. Fillers may also include various shapes including different fibers, platelets, whiskers, etc.
An important aspect of the invention is the unexpected discovery of a peculiar behavior in certain composite materials. Specifically, it has been unexpectedly discovered that the intemal friction or dampeI~ing behavior of composites having a matrix of metal and various ~h~l-;etn~ntc behave in a manner which causes composites, when constructed in an applo~liate manner, to function as a noise dam~ellel. For example, when a parti~ulate reinforcement is combined with a matrix metal in an amount of about 50% by volume, or even more preferably in an amount of at least about 60% by volume, or greater, the amount of damping behavior experienced in the composite ~ignifi(~nt1y increases.
Particularly ~rert:lled m~feri~1~ of the present invention include particulate ~ min1lm o~!ide and particulate silicon carbide as l~einror~ements in an ~ alloymatrix metal.
Particularly plcrt;llcd materials of the present invention include particulate mimlm o~ide and particulate silicon carbide as lci,~ol~;ements in an alll~ alloymatrix metal However, various combinations of other materials will also behave in a 2 o manner which results in desirable noise dalll~cml1g.
There are numerous techniques which ~;ullelllly exist for forming metal matrix composite bcdies. It is expected that many of these techniques can result in a desirable volume percent of particulate lei-,rolcement being present in the matrix metal of a composite bc~dy. However, it should be understood that lesser volume percents of other reinforcements such as, for example, platelets, fibers or whiskers, when combined with a desirable matrix metal, could also produce desirable noise dampening effects. However, the two particularly preferred methods for forming metal matrix composites include the process kno~n as the PRIMEXT~ Pressureless Metal Infiltration Process, which is set forth in numc--rous patents ~sign~l to T.~nxitl~ Technology Company, LP, as well as the 3 0 self-generatec'1 vacuum process, which is also set forth in numerous patents ~signP~ to T ~nxi(le Tecbnology C~ pa-ly, LP. These various p~tent~ processes permit the simple and economical fabrication of highly loaded metal matrix composite components having ~, desirable mechanical pl~,pellies.
It has been unexpectedly discovered that the damping behavior of various metal 3 5 matrix compc sites changes dramatically as the volume percent of reinforcement increases.
Specific lcfel~nce to Figure 1 shows the damping behavior of a metal matrix composite wherein the reinforcement is a particulate silicon carbide and the matrix metal comprises ~ll.. i.... The technique utilized to measure the damping behavior of the composites measured in Figure 1 was d~l~l "~i"~rl using tihe flexural resonant frequency Zener Band Width Method. This method is well known and can be found in the publication by G. ' Zener, Elaslicity and An Elastic~ty of Metals, (University of Chicago Press, 1948). The 5 particulate silicon carbide in the composite of Figure 1 was comprised of 500 grit in some cases and a ~nixture of 220 grit and 500 grit in other cases . Moreover the ~ mimlm matrix metal comprised an alnmim~m-silicon-m~gn~sillm alloy. It is clear from reviewing Figure 1 that a .signifir~nt increase in intern~l friction, or damping, begins to occur when the volume percent of particulate silicon carbide l~hlrul~;ement reaches about 50 volume 10 percent, an~ even greater effects are achieved at loadings of about 60 volume percent and more. It is clear from Figure 1 that with increasing lc~inrol~:ement content, the internal friction initially increases, then decreases slightly until achieving loading of about 50 volume percent silicon carbide, and then rapidly increases with further increases in loading. The cause of this behavior is not fully understood, but without hlL~lldi,,g to be 5 bound by a~y particular theory or explanation, the behavior is perhaps attributable to two com..peting e.ffects. First, because r..ost of t.he d~mpin.g is provided by th.e deforml.ahle matrix, it m~y be expected that the damping could decrease steadily as the volume fraction of tne deformable metal matrix is decreased. It is known that many ceramics such as silic~n carbide are low damping materials relative to metals. Accordingly, this 2 o effect could cause a reduction in damping as the content of silicon carbide is increased from about ~0 volume percent to about 50 volume percent. However, the addition of ,~hlf(Jlcemeflt will lead to .~i~nifii- ~nt disruption of the microstructure. It is possible that the addition of ceramic rei"rorcement can increase damping of a metal in different ways such as (1) the formation of particle to matrix interfaces which may lead to interfacial 2 5 damping, (2) the formation of dislocations due to a coefficient of thermal expansion mi~m~tch m~y cause dissipation of vibrational energy, and/or (3) grain size refinement of the matrix nlay lead to enh~nre(l damping by grain boundary sliding. While these effects are not parti~ularly understood, it is clear that an overall increase in damping does occur.
Thus, it is clear from the data in Figure 1 that a metal matrix composite made 3 o according to the PRIMEXTM Pressureless Metal Infiltration Process (discussed above) which utilizes an ~ll""i""", matrix metal and a silicon carbide particulate ,~hlfol~:ement, results in a material having desirable damping effects.
It ha~s been determined that this material can be useful in various applications ,~
including au~omotive applications. Two particular applications which have shown very 3 5 desirable results include brake pad backing plates for disc brakes and brake caliper pistons for disc brakes. The materials of the present invention are particularly desirable because of the combination of mechanical properties and damping effects. For example, it has Wo 96/26371 PCTIUS96102474 been determined that when this material is forrned into a brake pad backing plate, the prior art techniques for a~L~ ling to damp undesirable noise caused from the frictional ,~ contact between a brake pad and a brake rotor are no longer required to achieve the same, or greater, noise level reductioll. It is, of course, possible to combine the te~rlling.c of the 5 present inv~ntion with those of the prior art to achieve even greater noise reduction.
Additionally, when this material is formed into a brake caliper piston, the overall damping effects are increased. Specifically, in a brake caliper assembly, a brake caliper piston and ~ brake pad backing plate, typically come into contact with each other at least during the portion of the braking phrase where the brake pad contacts the brake rotor.
0 Many of the undesirable resonant frequencies which are tr~n~mi~ l from the rotor or into the rotor, cue the to contact of the rotor with the brake pad, can be damped by the pad backing plate and/or the brake caliper piston.
It should be understood that desirable damping effects are achieved by lltili7ing either of the brake pad backing plate or the brake caliper piston alone, however, the 15 combination of the two components may result in even further noise dampening effects.
Wit~ specific reference ~o the brake caliper piston, a particularly desirable combinatio~ of materials include a highly corrosion resistant all-min--m alloy and an al--min--m oxide particulate lch~olcclllcllL. This particular combination of materials results in a very high elastic modulus and a very low thermal conductivity material, as 2 o well as ach~eving very desirable sound dampening effects in the same material. It is important f~r the alnmim-m alloy to be corrosion resistant due to the environment within which it op~rates.
While the present invention has been described in specific detail, various alternatives to this inventive dampening material should occur to an artisan of ordinary 2 5 skill. It is ntended that all such applications should be covered by the scope of the appended c..aiims.

Claims (14)

What is Claimed is:

1. A brake pad backing plate comprising:
a matrix metal; and at least one reinforcement present in said matrix metal in an amount greater than 50 volume percent.

2. The brake pad backing plate of Claim 1, wherein said matrix metal comprises aluminum.

3. The brake pad backing plate of Claim 1, wherein said at least one reinforcement comprises at least one of silicon carbide and aluminum oxide.

4. The brake pad backing plate of Claim 3, wherein said silicon carbide and aluminum oxide comprise at least one particulate material selected from the group consisting of a substantially uniform particle size distribution and a bimodal particle size distribution.

5. The brake pad backing plate of Claim 4, wherein said at least one reinforcement is present in an amount of at least 60 percent by volume.

6. The brake pad backing plate of Claim 1, wherein said at least one reinforcement is present in an amount of at least 70 percent by volume.

7. A brake caliper piston comprising:
a matrix metal comprising a corrosion resistant aluminum alloy; and a particulate aluminum oxide reinforcement present in amount of at least about 50 percent by volume.

8. The brake caliper piston of Claim 7, wherein said aluminum oxide reinforcement comprises at least one particulate aluminum oxide reinforcement.

9. The brake caliper piston of Claim 8, comprising aluminum oxide reinforcement with at least a bimodal particle size distribution.

10. The brake pad backing plate of Claim 1, wherein said brake pad backing plateis formed by a spontaneous infiltration process.

11. The brake caliper piston of Claim 7, wherein said brake caliper piston is formed by a spontaneous infiltration process.

12. The brake pad backing plate of Claim 1, wherein said brake pad backing plateis formed by a self-generated vacuum process.

13. The brake caliper piston of Claim 7, wherein said brake caliper piston is formed by a self-generated vacuum process.

14. The brake caliper piston of claim 7, wherein said particulate aluminum oxidereinforcement is present in an amount of at least about 60 percent by volume.