FRICTION MATERIAL FOR DRUM-IN-HAT DISC BRAKE ASSEMBLY

Abstract: A drum-in-hat disc brake assembly is disclosed having a drum brake shoe with a friction material comprising a phenolic polymer resin having incorporated into the polymer chain one or more inorganic atom-containing groups selected from the group consisting of a boron-containing group, a phosphorous-containing group, a nitrogen-containing group, a silicon-containing group, and a sulfur-containing group.

Description: FRICTION MATERIAL FOR DRUM-IN-HAT DISC BRAKE ASSEMBLY Field of the Invention This invention relates generally tc friction materials, and more specifically tc friction materials for use in the drum brake shoe of a dru -in-hat disc brake assembly. Background of the Invention For many years, drum brakes were the most predominant type of brakes used in automotive and other motor vehicle applications. In recent years, however, disc brakes have become more and more widely used. In some cases, disc brakes have been used on only the front wheels cf the vehicle and drum brakes used on the rear wheels, but disc brakes are now being used on both front and rear brakes with increasing frequency. Although disc brakes provide many advantages over drum brakes, one limitation they have relates to parking brake or emergency brake applications. Unlike drum brakes, which can readily double as parking brakes, disc brakes require special modifications in order to perform that function. This limitation of disc brakes is not typically a problem on a vehicle with front disc brakes and rear drum brakes because the rear drum brakes can double as the parking brake. when both front and rear brakes are disc brakes, however, the disc brakes must be modified in order tc perform the parking brake function. One such disc brake configuration involves adapting the disc brake caiiper to include components that will compress the piston and brake pads against the brake disk when the parking brake s actuated. This approach increases the complexity cf the caiiper mechanism and can have problems with reliability. Also, the use cf disc brakes fcr parking can change the static/dynamic friction ratio cf the disc friction material, v.-hicr. ca lead tc undesirable noise generation. alternative modification of disc brakes tc function as carkir.c crakes is known as the drum-in-hat approach. Witn this approach, a small ora e drum is incorporated into the hat secticn of the disc brake rotor. Drum-in-hat brake assemblies are well-known in the art and are described, for example in U . S . Patents 5,180,037, 5,385,216 and 5,529,145, the disclosures of which are incorporated herein by reference. When the parking brake is actuated, a small brake shoe is applied to engage the drum and prevent the wheel from moving. The drum-in-hat approach for parking brakes with disc brake assemblies has become a popular approach due to its reliability and low cost. One problem experienced by drum-in-hat disc brake assemblies has been degradation cf the drum brake shoe friction material due to heat buildup ir. the brake assembly. This problem is particularly severe in heavy duty brakes used on vehicles with gross vehicle weights in excess of 4000 pounds, and is quite surprising as it can occur from repeated application of the disc brakes without the parking brake even being actuated. Traditional drum brake shoe friction materials are typically rolled into a sheet cf friction material that can be cured and cut into brake segments. While this is an efficient way of manufacturing friction material and provides satisfactory friction materials fcr conventional drum brakes, the liquid resins required for this process have been found to be insufficient to meet the stringent heat-resistance demands of drum-in-hat brake shoes. Moreover, even many conventional solid phenolic resins typically used for compression-molded disc brake pads are unable to withstand sustained temperatures in excess of 450 c~ , resistance to which has new beer, found to be necessary in order tc meet tr.e cemandi g standards fcr these severe drum-in-hat bra ice shoe applications. Summary of the Invention It has now beer, found according tc tne present invention that effective fricticr. materials fcr t e drum orake snoes cf drum-in-hat disc brake assemblies are provided by incorporating into the resin matrix of the friction material at least one phenolic polymer resin having incorporated into the polymer chain one or more inorganic atom-containing groups selected from the group consisting of a boron-containing group, a phosphorous-containing group, a nitrogen-containing group, a silicon-containing group, and a sulfur-containing group. Such disc brake assemblies can provide effective parking brake friction even after repeated application of the parking and/or the disc brakes. Description of the Preferred Embodiments Inorganic-modified phenolic resins are well-known in the polymer arts and are described, for example, in A. Knop and W. Scheib, Chemistry and Application of Phenolic Resins, Springer-Verlag, New York, the disclosure of which is incorporated by reference in its entirety. The phenolic resin is preferably a phenol formaldehyde resin such such as resole, novolac or phenolic-triazine, but may also include amounts of other types of resins, such as bismaleimide- triazine. Phenolic resins typically consist of a number of phenolic ring structures linked together by methylene linking groups to form a polymer chain. The above-described inorganic moieties are incorporated into the phenolic polymer chain (as opposed to being incorporated as a pendant side group on the chain) . This is preferably accomplished by replacing one or more of the methylene linking groups with a boron-containing group, a phosphorous-containing group, a nitrogen-containing group, a silicon-containing group, or a sulfur-containing group. The resin may contain combinations cf these groups by replacing various methylene linking groups throughout the polymer chain with different moieties. Modified phenolic resins naving boron moieties, phosphorous moieties, nitrogen moieties, silicon moieties, or sulfur moieties at the methylene iinkinc σrouo positions in the resin are well-Known in the polymer industry, and include Durite© RD-4545 from Border. Chemicals (boron- modified phenolic resin,, F-4109 from FERS Resins S.A. (Spain) (boron-modified cr.enolic resin) , HRJ217A or HRJ-381 from Schenectady Chemicals Inc. (phosphorous-modified phenolic resin), F-4514 c: F-453C from FERS Resins S.A. (Spain) (phosphorous-modified phenolic resin) , and 9587RP from Bakelite (Germany) (boron-phcsphorous-nitrogen-modified phenolic resin) . Incorporation cf silicon moieties at the methylene linking group position cf phenolic resins is well- known in the art and is described, for example, in U.S. 2,258,218, 2,836,740, and 2,842,522, as well as DE OS 1,694,974 and DE ?Ξ 937,555. As used herein, the term "silicon-containing group" is distinguished from and does not include silicone (i.e., organopolysiloxane) groups. Techniques for incorporation of sulfur-containing group at the methylene linking group position of phenolic resins are described by J. Scheiber, Chemie und Technologie der kϋnstlichen Harze, Stuttgart, Wissenschaftl, Verlagsges, 1943, and M. Cherubim, Kunststoff Rundscha u 13, 235 (1966) . A phenolic resin may be modified with nitrogen by reacting the resin with a compound having at least one, and preferably at least two reactive nitrogen groups capable of reacting with the pnenoiic hydroxy groups en the resin. Such reactive nitrogen compounds include, but are not limited to, dicyandiamide, urea, melamine, guanidine, and thiourea, as described in U.S. Patents 3,223,668 and 5,473,012. Alternatively, mixtures cf resins modified with different inorganic moieties cr combinations cf different inorganic moieties may also be used. One such preferred combination utilizes a resin containing boron modification (e.g., a boron-modifieα or B-F-H-mcdifiec resin) and a phosphorus-mo ifiec phenolic resin. In th s preferred combination, tne weigr.t ratio cf coron-ccntaming resin tc phosphorus-modified resin preferably ranges from 5 : I tc 0.2:1, and more preferably from 2:1 to 1:1. The friction material used in the practice cf the present invention preferably comprises at least 3 weight percent and more preferably at least 6 weight percent of inorganic-modified phenolic resin, and can comprise up to 20 weight percent and more preferably up to 10 weight percent of inorganic-modified resin. The friction material used in the practice of the invention can also contain other resinous binders in addition to the above-described inorganic modified phenolic resins. Resins for use as the binder cf the composition of this invention include non-heterocyclic aromatic polymers such as phenolics and phenolic derivatives, aromatic polyamides, aromatic polyesters, and other aromatic polymers such as polyphenylene and mesophase pitch, modified phenolic resins as for example, phenolic resins in which the hydroxyl group has been derivatized as for example, with a crosslinkable group such as cyanate, epoxy and alkyl groups, phenolic triazine resins, and copolymers and mixtures thereof. The friction material used in the practice of the present invention may contain, based upon the total weight of the composition, from about C.5 percent to about 99 percent, preferably from about 3 percent to about 60 percent, more preferably from about 6 percent to about 55 percent and most preferably from about 6 percent to about 45 percent by weight, of the above-mentioned binders, including the inorganic modified phenolic resins. The friction material used in the practice cf the invention can also contain various reinforcing fibers (e.g., aramid, steel, acrylic, and, although no longer widely used, asbestos), metal powders (e.g., iron, copper, brass, zinc, aluminum, antimony, and the like), solid lubricants (e.g., tin sulfide, iron sulfide, molybdenum disulfide, graphite, coke, antimony trisuifide,, abrasives (e.g., magnesia, silica, iron oxide, alumina, zirccnia, tin oxide, chrome oxide, iron chromite, rutilε, and the like), organic fillers (e.g., rubber particles, cashew nut shell particles, nitrile rubber particles), and inorganic fillers (e.g., barytes, gypsum, mica, titanates, and the like) . Other materials and additives may be added as well, as is known in the art. The relative amounts cf these materials will vary widely depending on the desired characteristics of the particular application, and can be readily determined by one skilled in the art. In one preferred embodiment cf the invention, the fricticn material contains from 3 to 55 weight percent bauxite and/or from 2 to 30 weight percent reinforcing whiskers, preferably attapulgite clay whiskers, but also other reinforcing whiskers like potassium titanate, gypsum, calcium silicate, or alumina silicate. The friction material used in the practice of the present invention can be prepared by pressing the friction composition into the desired shape and curing. The material is generally pressed at pressures of 500 to 15,000 psi and preferably 1000 to 10,000 psi. Pressing temperatures can range from ambient temperatures to 400°F. After pressing, the friction material is preferably pest cured by convectivε, conductive, radiant, cr microwave heating. Generally, the lower the degree cf curing that takes place during the pressing operation (usually because the pressing takes place at a low temperature and/or for a short duration) , the greater is the need for some sort of post- press cure. After curing, the fricticn material is subjected to finishing operations, such as trimming, drilling mounting holes or ether openings if needed, painting if desired, and other typical finishing operations as s known in the art. Then the friction material is mounted onto a drum crake shoe bv conventional means such as screws, bolts, rivets, and/or adhesive, along with a packing plate if desired, and incorporated into the drum-in-hat brake assembly. Alternatively, the friction material can be integrally molded onto tne brake snoe in conjunction with adhesive and/or mechanical attachment-enhancing means. The invention is further described in the following examples . Preparation 1 A friction material composition was prepared with the following ingredients: Component Weiσht (α * Abrasives 430 Steel fiber 200 Kevlar and other reinforcing 130 materials Solid and depolymerized 50 rubbers Phosphorus-modified resin 40 Phosphorus-Boron-Nitrogen- 40 modified resin Liquid resole resin 40 Lubricants 40 All dry ingredients were "weighed into containers using a scale with 0.1 gram accuracy, and the depolymerized rubber was added tc a separate container using the same scale. The total combined weight cf solid and liquid components was 1.0 kg. The solid rubber, acrasives, lubricants, and reinforcing materials were mixed fcr five minutes using a paddle mixer with rotating cncppers; all other dry ingredients except for tne steel fiber were then added and mixed for an additional tnree minutes. With the mixer plow and cnoppers still running, t e αepolymerized rubcer was added over a four minute pericα, after which the steel fiber was introduced into tne mixer . Mixing then continued for another six minutes to rive total mixmc time cf eicnteer. minutes. The contents of the mixer were then emptied into a suitable container and formed into drum-in-hat linings as described below in Examples 1 - 2. Example 1 The friction material described in Preparation 1 was weighed and compression molded at 8,000 psi and 320°F for 200 seconds, with adequate time for degassing. Linings were then either bonded or riveted to drum shoes according to the part specifications. Examp -le 2 The friction material described in Preparation 1 was weighed and compression molded at 10,000 psi and 340°F for 180 seconds, with adequate time for degassing. Linings were then either bonded or riveted to drum shoes according to the part specifications. Preparation 2 A friction material composition was prepared with the following ingredients: Component Weight (q) Abrasives 440 Steel fiber 200 Glass fiber 100 Phosphorus-modified resin 80 Solid and depolymerized 50 rubbers Liquid resole resin 40 Lubricants 40 Curing agents and resin 30 reinforcers Kevlar® aramid fiber 20 All dry ingredients were weighed into containers using a scale with 0.1 gram accuracy, and the depolymerized rubber was added to a separate container using the same scale. The total combined weight cf solid and liquid components was 1.0 kg. The solid rubber, abrasives, lubricants, and reinforcing materials were mixed for five minutes using a paddle mixer with rotating choppers; all other dry ingredients except for the steel fiber were then added and mixed for an additional three minutes. With the mixer plow and choppers still running, the depolymerized rubber was added over a four minute period, after which the steel fiber was introduced into the mixer. Mixing then continued for another six minutes to give a total mixing time of eighteen minutes. The contents of the mixer were then emptied into a suitable container and formed into drum-in-hat linings as described below in Examples 3 - 4. Example 3 The friction material described in Preparation 2 was weighed and compression molded at 8,000 psi and 320°F for 200 seconds, with adequate time for degassing. Linings were then either bonded or riveted to drum shoes according to the part specifications. Example 4 The friction material described in Preparation 2 was weighed and compression molded at 10,000 psi and 340°F for 180 seconds, with adequate time fcr degassing. Linings were then either bonded or riveted to drum shoes according to the part specifications. Preparation 3 A friction material composition was prepared with the following ingredients: Component Weight (q) Abrasives 440 Steel fiber 200 Glass fiber 100 Phosphorus-Boron-Nitrogen- 80 modified resin Solid and depolymerized 50 rubbers Liσuic resole resin 40 Lubricants 40 Curing agents 30 Kevlar© aramid fiber 20 All dry ingredients were weighed into containers using a scale with 0.1 gram accuracy, and the depciymerizec rubber was added to a separate container using the same scale. The total combined weight of solid and liquid components was l.C kg. The solid rubber, abrasives, lubricants, and reinforcing materials were mixed for five minutes using a paddle mixer with rotating choppers; all other dry ingredients except for the steel fiber were then added and mixed for an additional three minutes. With the mixer plow and cnoppers still running, t e depolymerized rubber was added over a four minute period, after which the steel fiber was introduced into the mixer. Mixing then continued for another six minutes to give a total mixing time of eighteen minutes. The contents cf the mixer were then emptied into a suitable container and formed into drum-in-hat linings as described below in Examples 5 - 6. Example 5 The friction material described in Preparation 3 was weighed and compression molded at 8,000 psi and 320°F for 200 seconds, with adequate time for degassing. Linings were then either bonded or riveted to drum shoes according to the part specifications. Example 6 The friction material described in Preparation 3 was weighed and compression molded at 10,000 ps and Ξ C°F fcr 180 seconds, with adequate time fcr degassing. linings were then either ponded or rivetec to drum snoeε according tc t e part specifications. Comparative Preparation 1 A conventional drum oraκe fricticn material composition for roll processing was prepared with the following ingredients : Component Weiσht (c Abrasives 270 Steel fiber 200 Liquid cashew resin 160 Glass fiber 100 Fillers 100 Oil-modified phenolic resin 80 Lubricants 60 Curing agents 30 All dry ingredients were weighed into containers using a scale with 0.1 gram accuracy, and the liquid cashew rubber was added to a separate container using the same scale. The total combined weight of solid and liquid components was 1.0 kg. The abrasives, lubricants, and reinforcing materials were mixed for five minutes using a paddle mixer with rotating choppers; all other dry ingredients except for the steel fiber were then added and mixed for an additional three minutes. With the mixer plow and choppers still running, the liquid cashew rubber was added over a four minute period, after which the steel fiber was introduced into the mixer. Mixing then continued for another six minutes to give a total mixing time of eighteen minutes. The contents of the mixer were then emptied into a suitable container and formed into drum-in-hat linings as described below in Example 7. Comparative Example 1 The friction material described in Comparative Preparation i was fed into a standard rcll line in order to produce rolled linings approximately 25 feet long. The thickness and width cf the rolled strips were part-specific. Linings were then subjected to an oven curing cycle and bonded or riveted onto drum snoes . Comparative Preparation 2 A conventional friction material composition for compression melding was prepared with the following ingredients : Component Weight (g ) Liquid cashew resin 250 Abrasives 240 Steel fiber 100 Liquid rubber 100 Lubricants 100 Glass fiber 80 Fillers 80 All dry ingredients were weighed into containers using a scale with 0.1 gram accuracy, and the depolymerized rubber was added to a separate container using the same scale. The total combined weight of solid and liquid components was 1.0 kg. The solid rubber, abrasives, lubricants, and reinforcing materials were mixed for five minutes using a paddle mixer with rotating choppers; all other dry ingredients except for the steel fiber were then added and mixed for an additional three minutes. With the mixer plow and choppers still running, the depolymerized rubber was added over a four minute period, after which the steel fiber was introduced into the mixer. Mixing then continued for another six minutes to give a total mixing time of eighteen minutes. The contents of the mixer were then emptied into a suitable container and formed into drum-in-hat linings as described below in Comparative Examples 3 - 4. Comparative Example 2 The fricticn material described in Preparation I was weighed and compression molded at 8,000 psi and 320°F for 200 seconds, with adequate time for degassing. Linings were then either bonded cr riveted to drum shoes according to the part specifications. Comparative Example 3 The friction material described in Preparation 2 was weighed and compression molded at 10,000 psi and 340°F for 180 seconds, with adequate time fcr degassing. Linings were then either bonded or riveted to drum shoes according to the part specifications. Description cf Test Results To test the high temperature stability and green static friction of the linings described above in Examples 1 - 6 and Comparative Examples 1 - 2, samples were placed in an oven for an extended period of time at an elevated temperature designed tc simulate the severe conditions the material would experience during severe drum-in-hat application. The linings were weighed both before and after the cure, and the weight loss due to the oven cure was recorded. In the typical rolled lining for which an example is detailed in Comparative Preparation 1, there was a weight loss of approximately 25%. In the material which used both the phosphorus-modified and phosphorus-boron-nitrogen- modified resin (Preparation 1) , however, the weight loss was only 8.5%. The high weight loss in the rolled material was accompanied by excessive softness and crumbling of the lining, making the linings unusable in any application. The linings made using the modified resin according to the invention, however, remained solid and had very little chipping. In addition to the weight loss measurements, green static friction was measured fcr linings that were heat- soaked at an elevated temperature for 72 hours, 120 hours, and 168 hours and for linings that were net heat-soaked. As mentioned before, the rolled linings crumbled at elevated temperatures, so meaningful fricticn data was unavailable for the 120 hour and 168 hour rolled linings. Tables i and 2 below gives the coefficient of static friction at the various heat soak times: Table 1 Averaσe Torσue Friction (Forward) Heat Inorαanic Inorσanic Inorαanic Rolled Lining Soak Modified resin Modified Modified resin (Comparative lining resin lining lining Example 1 ) (Example 1) (Example 3) (Example 5) None 10.96 13.45 11.92 7 . 53 72h @ 11.57 12.85 12.05 6. 91 550°F 120h @ 11.17 11.92 11.51 Not testable 550°F 168h @ 9.44 10.58 10.31 Not testable 550°F Table 2 Average Torσue Friction (Reverse) Heat Inorganic Inorganic Inorganic Rolled Lining Soak Modified resin Modified Modified resin (Comparative lining resin lining lining Example 1) (Example 1) (Example 3) (Example 5) None 9.86 9.82 9.15 6.62 72h @ 10.12 10.12 11.11 5.63 550°F 120h @ 10.08 10.87 10.54 Not testable 550°F 168h @ 11.02 11.02 10.54 Not testable 550°F Both the thermal stability of the structural properties and the good static friction performance of the linings made with the inorganic-modified resins according to the invention make for a safer and more practical lining material for drum-in-hat applications than the conventional drum brake shoe friction material.

Claims: WO 01/33099 !5 PCT/USOO/29778 Claims : 1. A drum-in-hat disc brake assembly including a drum brake shoe that comprises a friction material comprising a phenolic polymer resin including one or more inorganic atom-containing groups selected from the group consisting of a boron-containing group, a phosphorous- containing group, a nitrogen-containing group, a silicon-containing group, and a sulfur-containing group incorporated into its polymer chain. 2. A drum-in-hat disc brake assembly according to claim 1 wherein said phenolic polymer resin has incorporated into its polymer chain one or more inorganic atom- containg groups selected from the group consisting of a boron-containing group, a phosphorous-containing group, and a nitrogen-containing group. 3. A drum-in-hat disc brake assembly according to claim 1 wherein said phenolic polymer resin includes a boron- containing group incorporated into its polymer chain. 4. A drum-in-hat disc brake assembly according to claim 1 wherein said phenolic polymer resin includes a phosphorous-containing group incorporated into its polymer chain. 5. A drum-in-hat disc brake assembly according to claim 1 wherein said phenolic polymer resin includes a nitrogen- containing group incorporated into its polymer chain. 6. A drum-in-hat disc brake assembly according to claim 1 wherein said phenolic polymer resin includes phosphorous and nitrogen-containing groups incorporated into its polymer chain. 7. A drum-in-hat disc Drake assembly according to claim 1 wherein said phenolic resin includes boron and nitrogen- containing groups incorporated into its polymer chain. 8. A drum-in-hat disc brake assembly according to claim 1 wherein said phenolic polymer resin includes boron, phosphorous, and nitrogen-containing groups incorporated into its polymer chain. 9. A drum-in-hat disc brake assembly according to claim 1 comprising a first phenolic polymer resin including a phosphorous-containing group incorporated into its polymer chain, and a second phenolic resin including a boron-containing group incorporated into its polymer chain. 10. A drum-in-hat disc brake assembly according to claim 1 comprising a first phenolic polymer resin including a phosphorous-containing group incorporated into its polymer chain, and a second phenolic resin including boron-, phosphorous-, and nitrogen-containing groups incorporated into its polymer chain. 11. A drum-in-hat disc brake assembly according to claims 1- 10 wherein said one or more inorganic atom-containing groups are incorporated into said polymer chain in place of methylene linking groups. 12. A drum-in-hat disc brake assembly according to claims 1- 11 wherein said friction material further comprises bauxite. 13. A drum-in-hat disc brake assembly according to claims 1- 12 wherein said friction material further comprises attapulgite clay. 14. A drum-in-hat disc brake assembly according to claims 1- 13 that is adapted for use on a motor vehicle having a gross vehicle weight of at least 1816 kg. 15. A drum-in-hat disc brake assembly according tc claims 1- 14 that is adapted for use on a rear wheel of said motor vehicle.

Inventors: KESAVAN SUNIL, RUSSIK JOSEPH B, STAKLIS ANDRIS A, TSANG PETER H S, KESAVAN, SUNIL, RUSSIK, JOSEPH, B., STAKLIS, ANDRIS, A., TSANG, PETER, H., S.
Applicants: HONEYWELL INT INC, HONEYWELL INTERNATIONAL INC.
Application year: 2000
Main classification: F16D69
IPC codes: C09K3, F16D69