Patent ID: 12253133

DETAILED DESCRIPTION

Next generation wet friction materials for electric and hybrid applications need to provide higher torque which requires a higher friction coefficient. To achieve this the friction material will need to reach and maintain the desired friction coefficient.

The present disclosure provides a friction material with cellulose fibers, calcined kaolin clay, graphite, and diatomaceous earth saturated in tung modified phenolic resin that achieves higher friction coefficients. The inventors discovered that while friction materials including tung oil usually had acceptable durability but insufficient friction performance, adding clay to friction materials with tung oil surprisingly result in a friction material with a higher friction coefficient that may be useful for in drive trains of electric and hybrid vehicles. The inventors discovered that using the calcined kaolin and the tung modified phenolic resin together has a synergistic effect of increasing both the dynamic and static friction coefficients.

The graphite and diatomaceous earth aid in durability and friction stability. Exemplary formulations showed a 5-40% increase in friction coefficient compared to the friction material disclosed in U.S. Pub. No. 2018/0149222 A1.

FIG.1schematically illustrates a wet friction material layer in accordance with an embodiment of the present disclosure in a clutch assembly.

A wet friction material layer12may be formed of fibers, filler material and a binder. The fibers may be cellulose fibers. The filler material may be particles of both diatomaceous earth and calcined kaolin clay. The binder may be a tung modified phenolic resin. A friction modifier in the form of graphite may also be included in wet friction material layer12.

In one preferred embodiment, wet friction material layer12may include, before being saturated by tung modified phenolic resin, by percentage weight, 20-60% fibers, which in one example are advantageously cellulose, 5-60% calcined kaolin clay, 1-20% graphite, 5-40% diatomaceous earth. The tung modified phenolic resin is added on in weight percent that is 31-35% of the weight of the resulting friction material. Thus, the dried and cured friction material would be 13-41% cellulose, 3-41% calcined kaolin clay, 1-14% graphite, 3-21% diatomaceous earth, and 31-35% tung modified phenolic resin.

In a further preferred embodiment, wet friction material layer12may include, before being saturated by tung modified phenolic resin, by percentage weight, 30-60% fibers, which in one example are advantageously cellulose, 10-40% calcined kaolin clay, 5-20% graphite, 10-40% diatomaceous earth. The tung modified phenolic resin is added on in weight percent that is 31-35% of the weight of the resulting friction material. Thus, the dried and cured friction material would be 20-41% cellulose, 7-28% calcined kaolin clay, 3-14% graphite, 7-21% diatomaceous earth, and 31-35% tung modified phenolic resin.

In a further preferred embodiment, wet friction material layer12may include, before being saturated by tung modified phenolic resin, by percentage weight, 45-55% fibers, which in one example are advantageously cellulose, 15-25% calcined kaolin clay, 5-15% graphite, 25-35% diatomaceous earth. The tung modified phenolic resin is added on in weight percent that is 31-35% of the weight of the resulting friction material. Thus, the dried and cured friction material would be 29-38% cellulose, 10-17% calcined kaolin clay, 3-10% graphite, 16-24% diatomaceous earth, and 31-35% tung modified phenolic resin.

In each of the above-mentioned embodiments, the calcined kaolin clay, graphite and diatomaceous earth may advantageously form 45-55%, by percentage weight, of the wet frictional material layer before being saturated by tung modified phenolic resin.

As disclosed in U.S. Pub. No. 2018/0149222 A1, the calcined kaolin clay has the chemical formulation of MAl2O3NSiO2, wherein M and N are integers. The exact values for M and N depend on a number of factors including the source of the raw material for the kaolin clay. In an example embodiment, the chemical composition of the calcined kaolin clay may be represented at having an alumina content of at least 35 wt % and at most 55 wt % and a silica content of at least 45 wt % and at most 65 wt %.

The calcined kaolin clay may advantageously have particle sizes 0.5 to 2 microns.

The tung modified phenolic resin may advantageously have a solid percent of 30-60%, a viscosity of 200-600 cps and a pH of 6-9.

The fibers of layer12may have a length of 0.5-3.0 mm, a diameter of 5-25 micron.

The graphite may have a surface area of 6.35 m2/g.

Wet friction material layer12is placed on top of a metal part14and layer12and part14are joined together to form a friction assembly. Prior to joining of layer and part14, the binder is subject to initial curing to a level called B-stage, where the layer12is somewhat flexible. The joining of layer12and part14together includes pressing wet friction material layer12against metal part14with a heat plate to complete curing of the binder in wet friction material layer12, fixing wet friction material layer12and metal part14together. The force of pressing of heat plate against outer surface12aof wet friction material layer12, while inner surface12bof wet friction material layer12rests on an outer layer14aof metal part14, causes the binder to accumulate at an interface of inner surface12bof wet friction material layer12and outer surface14aof metal part14, while the curing of the binder by the heat of heat plate creates a permanent connection between metal part14and wet friction material layer12. The binder solidifies and hardens in wet friction material layer12in contact with filler and fibers. In one preferred embodiment, the heat at a surface of plate that contacts outer surface12aof outer layer is 375 to 425 degrees F.

FIG.2shows a friction versus speed graph illustrating a friction material50(illustrated by dashes) including calcined kaolin clay with a standard phenolic resin and a friction material52(illustrated by circles) including calcined kaolin clay with a tung modified phenolic resin at different pressures. Both of the examples inFIG.2consist of a material matrix that is, by weight percentage, 50% cellulose fiber, 30% diatomaceous earth and 20% calcined kaolin clay, with the phenolic resin being added on in weight percent that is 33% of the of the weight of the material matrix. Thus, the dried friction material includes, by weight percentage, 34% cellulose fiber, 20% diatomaceous earth, 13% calcined kaolin clay and 33% phenolic resin.

As shown inFIG.2, friction material52has a surprisingly greater dynamic friction coefficient than friction material50over a variety of speed ranges, solely due to tung modified phenolic resin being used with calcined kaolin clay instead of standard phenolic resin, across a number of different speeds and application pressures. All of the tests were performed using FORD ultra low viscosity (ULV) automatic transmission fluid, which has a viscosity of 19.2 cSt at 40° C. and 4.5 cSt at 100° C., having a temperature of 120° C. for the results shown below in Table 1, which are illustrated inFIG.2.

Tung Modified Phenolic ResinStandard Modified Phenolic ResinAppliedRotationalFrictionAppliedRotationalFrictionPressureSpeedCoefficientPressureSpeedCoefficient1.050.211.050.15100.23100.16300.24300.16400.24400.17500.24500.171.550.201.550.14100.22100.15300.23300.16400.22400.16500.21500.162.050.192.050.14100.20100.15300.21300.16400.20400.16500.19500.162.550.172.550.13100.19100.14300.19300.15400.19400.15500.18500.15

Accordingly,FIG.2shows that for a range of 5 RPM to 50 RPM and a range of 1.0 MPa to 2.5 MPa, the friction material52including calcined kaolin clay with a tung modified phenolic resin surprisingly performs substantially better than the friction material50including calcined kaolin clay with a standard phenolic resin. In particular, the friction material50has a frictional coefficient range of 0.17 to 0.24 for a range of 5 RPM to 50 RPM and a range of 1.0 MPa to 2.5 MPa. In contrast, friction material52has a frictional coefficient range of 0.13 to 0.17 for a range of 5 RPM to 50 RPM and a range of 1.0 MPa to 2.5 MPa.

With an applied pressure of 1.0 MPa, the friction material52has a frictional coefficient range of 0.21 to 0.24 for a range of 5 RPM to 50 RPM.

With an applied pressure of 1.5 MPa, the friction material52has a frictional coefficient range of 0.20 to 0.23 for a range of 5 RPM to 50 RPM.

With an applied pressure of 2.0 MPa, the friction material52has a frictional coefficient range of 0.19 to 0.21 for a range of 5 RPM to 50 RPM.

With an applied pressure of 2.5 MPa, the friction material52has a frictional coefficient range of 0.17 to 0.19 for a range of 5 RPM to 50 RPM.

With a rotational speed of 5 RPM, the friction material52has a frictional coefficient range of 0.17 to 0.21 for a range of 1.0 MPa to 2.5 MPa.

With a rotational speed of 10 RPM, the friction material52has a frictional coefficient range of 0.19 to 0.23 for a range of 1.0 MPa to 2.5 MPa.

With a rotational speed of 30 RPM, the friction material52has a frictional coefficient range of 0.19 to 0.24 for a range of 1.0 MPa to 2.5 MPa.

With a rotational speed of 40 RPM, the friction material52has a frictional coefficient range of 0.19 to 0.24 for a range of 1.0 MPa to 2.5 MPa.

With a rotational speed of 50 RPM, the friction material52has a frictional coefficient range of 0.18 to 0.24 for a range of 1.0 MPa to 2.5 MPa.

It is notable that for applied pressures of 1.0 to 1.5 MPa, the friction material52has a frictional coefficient range of 0.20 to 0.24 for a range of 5 RPM to 50 RPM.

Tests have also been conducted that show friction material52reaches a static friction coefficient of 0.23 while friction material50reaches a static friction coefficient of 0.16. The tests were performed by a performing a 5 second breakaway cycle ramping up to 5 RPMs at a pressure of 1.0 MPa and a temperature of 120° C., as shown inFIG.3.

FIG.4shows wet friction material layer12bonded to a plurality of clutch plates60in a clutch pack62. A piston64forces to clutch plates60together to couple parts66,68together such that parts66,68rotate together when the clutch pack62is engaged.

In the preceding specification, the disclosure has been described with reference to specific exemplary embodiments and examples thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of disclosure as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative manner rather than a restrictive sense.

LIST OF REFERENCE NUMERALS

12wet friction material layer12aouter surface12binner surface14metal part14aouter surface50friction material with calcined kaolin clay and standard phenolic resin52friction material with calcined kaolin clay and tung modified phenolic resin60clutch plates62clutch pack64piston66,68rotating parts