WO1996026371A2

WO1996026371A2 - Noise abating components

Info

Publication number: WO1996026371A2
Application number: PCT/US1996/002474
Authority: WO
Inventors: Virgil Jr. Irick; Michael John Hollins
Original assignee: Lanxide Technology Company, L.P.
Priority date: 1995-02-24
Filing date: 1996-02-23
Publication date: 1996-08-29
Also published as: JPH11500813A; CA2209244A1; EP0811124A2; WO1996026371A3

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

DESCRIPTION NOISE ABATING COMPONENTS

Technical Field

Background Art

Many devices currently exist which emanate undesirable noise therefrom. 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 communicated by, for example, vibrations transmitted to one or more other members which are in contact with the noise generating members which can result in said one or more other members also emanating undesirable noise.

For example, in the case of disc brake rotors, it is well known that disc brakes generate undesirable noises during braking. These undesirable noises are typically referred to as squeals, chirps, grunts, and moans. The noises in disc brakes are generated 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 generation of noise. The noise is thought to occur due to a resonance which develops at the interface between the brake pad or lining and the rotor. This resonance can then be transmitted through the brake shoe assembly to other brake portions such as brake mounting hardware, 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 similar 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 may cause undesirable resonance to develop and thus, in a similar manner, result in a transmission of undesirable noise. 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 transmissions, drive shafts, gears, alternators, generators, engines, wheels, hubs, etc. Each of these areas are also subjects of the present invention. Likewise, other apparatus 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 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, attempts have been made to ameliorate undesirable noise emanating from the assemblies by including, for example, a disc brake shoe dampener. An example of a disc brake shoe dampener is set forth in U.S. Patent No. 3,937,305 which issued on February 10, 1976 in the name of Vanden

Bossche. Other attempts 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 Hummel 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 apparatuses.

Definitions

As used herein, it should be understood that the following terms should have consistent meanings throughout the application:

"Aluminum", as used herein, means and includes essentially pure metal (e.g., a relatively pure, commercially available unalloyed aluminum) or other grades of metal and metal alloys such as the commercially available metals having impurities and/or alloying constituents such as iron, silicon, copper, magnesium, manganese, chromium, zinc, etc. , therein. An aluminum alloy for purposes of this definition is an alloy or intermetallic compound in which aluminum is the major constituent. "Bronze", as used herein, means and includes a copper rich alloy, which may include iron, tin, zinc, aluminum, silicon, beryllium, manganese and/or lead. Specific bronze alloys include those alloys in which the proportion of copper is about 90% by weight, the proportion of silicon is about 6% by weight, and the proportion of iron is about 3% by weight.

"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- metallic and inorganic materials, but rather refers to a body which is predominantly ceramic with respect to either composition or dominant properties, although the body may contain minor or substantial amounts of one or more metallic constituents (isolated and/or interconnected, depending on the processing 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 from 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 impurities contained therein. Moreover, it also refers to metals which are alloys or intermetallics which do not fall within the definition of bronze, and which contain copper as the major constituent therein.

"Filler", as used herein is intended to include either single constituents or mixtures of constituents which are substantially 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 wide variety of forms, such as powders, flakes, platelets, microspheres, whiskers, bubbles, fibers, particulates, fiber mats, chopped fibers, spheres, pellets, tubules, refractory cloths, etc. , and may be either dense or porous. "Filler" may also include ceramic fillers, such as alumina or silicon carbide, as fibers, chopped fibers, particulates, whiskers, bubbles, spheres, fiber mats, or the like, and coated fillers such as carbon fibers coated with alumina or silicon carbide to protect the carbon from attack, for example, by a molten aluminum matrix metal. Fillers may also include metals.

"Matrix Metal" or "Matrix Metal Alloy "'. as used herein means that metal which is utilized to form a metal matrix composite (e.g. , before infiltration) and/or that metal which is intermingled with a filler material to form a metal matrix composite body (e.g. , after infiltration). 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 impurities and/or alloying constituents therein, an intermetallic compound or an alloy in which that metal is the major or predominant constituent. "Metal Matrix Composite" or "MMC". as used herein, means a material comprising a two- or three-dimensionally interconnected alloy or matrix metal which has embedded a preform or filler material. The matrix metal may include various alloying elements to provide specifically desired mechanical and physical properties in the resulting composite.

"Spontaneous Infiltration", as used herein, means that the infiltration of matrix metal into the permeable mass of filler or preform occurs without requirement for the application of pressure or vacuum (whether externally applied or internally created).

Summary of the Invention

The present invention provides a material which desirably abates noise which is caused from 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 infiltrate any desirable reinforcement material. Typically, matrix metals include aluminum, bronze, copper, magnesium, cast iron, etc (and alloys thereof). Typical filler materials include various particulate materials such as oxides, nitrides, carbides, 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 internal friction or dampening behavior of composites having a matrix of metal and various reinforcements behave in a manner which causes composites, when constructed in an appropriate 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, the amount of damping behavior experienced in the composite significantly increases. Particularly preferred reinforcement materials of the present invention include particulate aluminum oxide and particulate silicon carbide in an aluminum alloy matrix metal.

Brief Description of the Drawings Figure 1 shows the damping behavior of silicon carbide reinforced aluminum 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 caused from 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 infiltrate any desirable reinforcement material. Typically, matrix metals include aluminum, bronze, copper, magnesium, cast iron, etc (and alloys thereof)- Typical filler materials include various particulate materials such as oxides, nitrides, carbides, 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 internal friction or dampening behavior of composites having a matrix of metal and various reinforcements behave in a manner which causes composites, when constructed in an appropriate 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, the amount of damping behavior experienced in the composite significantly increases.

Particularly preferred materials of the present invention include particulate aluminum oxide and particulate silicon carbide as reinforcements in an aluminum alloy matrix metal.

Particularly preferred materials of the present invention include particulate aluminum oxide and particulate silicon carbide as reinforcements in an aluminum alloy matrix metal. However, various combinations of other materials will also behave in a manner which results in desirable noise dampening.

There are numerous techniques which currently exist for forming metal matrix composite bodies. It is expected that many of these techniques can result in a desirable volume percent of particulate reinforcement being present in the matrix metal of a composite body. 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 known as the PRIMEX*^M Pressureless Metal Infiltration Process, which is set forth in numerous patents assigned to Lanxide Technology Company, LP, as well as the self-generated vacuum process, which is also set forth in numerous patents assigned to

Lanxide Technology Company, LP. These various patented processes permit the simple and economical fabrication of highly loaded metal matrix composite components having desirable mechanical properties.

It has been unexpectedly discovered that the damping behavior of various metal matrix composites changes dramatically as the volume percent of reinforcement increases.

Specific reference 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 aluminum. The technique utilized to measure the damping behavior of the composites measured in Figure 1 was determined using the flexural resonant frequency Zener Band Width Method. This method is well known and can be found in the publication by G. Zener, Elasticity and An Elasticity of Metals. (University of Chicago Press, 1948). The particulate silicon carbide in the composite of Figure 1 was comprised of 500 grit in some cases and a mixture of 220 grit and 500 grit in other cases . Moreover the aluminum matrix metal comprised an aluminum-silicon-magnesium alloy. It is clear from reviewing Figure 1 that a significant increase in internal friction, or damping, begins to occur when the volume percent of particulate silicon carbide reinforcement reaches about 50 volume percent, and even greater effects are achieved at loadings of about 60 volume percent and more. It is clear from Figure 1 that with increasing reinforcement 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 intending to be bound by any particular theory or explanation, the behavior is perhaps attributable to two competing effects. First, because most of the damping is provided by the deformable matrix, it may be expected that the damping could decrease steadily as the volume fraction of the deformable metal matrix is decreased. It is known that many ceramics such as silicon carbide are low damping materials relative to metals. Accordingly, this effect could cause a reduction in damping as the content of silicon carbide is increased from about 10 volume percent to about 50 volume percent. However, the addition of reinforcement will lead to significant disruption of the microstructure. It is possible that the addition of ceramic reinforcement can increase damping of a metal in different ways such as (1) the formation of particle to matrix interfaces which may lead to interfacial damping, (2) the formation of dislocations due to a coefficient of thermal expansion mismatch may cause dissipation of vibrational energy, and/ or (3) grain size refinement of the matrix may lead to enhanced damping by grain boundary sliding. While these effects are not particularly 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 according to the PRIMEX™ Pressureless Metal Infiltration Process (discussed above) which utilizes an aluminum matrix metal and a silicon carbide particulate reinforcement, results in a material having desirable damping effects.

It has been determined that this material can be useful in various applications including automotive applications. Two particular applications which have shown very 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 been determined that when this material is formed into a brake pad backing plate, the prior art techniques for attempting 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 reduction. It is, of course, possible to combine the teachings of the present invention 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 a 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. Many of the undesirable resonant frequencies which are transmitted from the rotor or into the rotor, due 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 utilizing either of the brake pad backing plate or the brake caliper piston alone, however, the combination of the two components may result in even further noise dampening effects. With specific reference to the brake caliper piston, a particularly desirable combination of materials include a highly corrosion resistant aluminum alloy and an aluminum oxide particulate reinforcement. This particular combination of materials results in a very high elastic modulus and a very low thermal conductivity material, as well as achieving very desirable sound dampening effects in the same material. It is important for the aluminum alloy to be corrosion resistant due to the environment within which it operates.

While the present invention has been described in specific detail, various alternatives to this inventive dampening material should occur to an artisan of ordinary skill. It is intended that all such applications should be covered by the scope of the appended claims.

Claims

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 plate is 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 plate is 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 oxide reinforcement is present in an amount of at least about 60 percent by volume.