WET FRICTION MATERIAL WITH ORIFICES

A method of making a wet friction material includes providing an outer layer on a base layer to form the wet friction material. The base layer includes a proportion of first fiber material and a proportion of first filler material and the outer layer includes a proportion of second fiber material and a proportion of second filler material. The proportion of second fiber material is less than the proportion of first fiber material and the proportion of second filler material is greater than the proportion of first filler material. The method also includes forming a plurality of orifices passing through the outer layer.

The present disclosure relates generally to friction clutches and plates used in torque converters and motor vehicle transmissions and more specifically to wet friction material.

BACKGROUND

The friction material in wet-type friction clutches generally operates in an oil submerged environment and is often paper-based material used to form friction material rings. It is known to spray or sprinkle diatomaceous earth sold under the trade name CELITE on top of the base materials directly during the paper making process in a Fourdrinier machine at the wet end of the machine when the paper base material is being moved along a conveyor. This process is good for very high volume papers, but there is large waste during initial set up, so it is not practical for smaller volume production.

U.S. Pat. No. 6,013,696 discloses using a laser to form pores in a cured, resin-impregnated friction material.

U.S. Pub. 2017/0089415 discloses friction material including a bottom layer and a top layer forming a paper composite, with pores being created by a laser in the top surface.

SUMMARY OF THE INVENTION

A method of making a wet friction material is provided. The method includes providing an outer layer on a base layer to form the wet friction material. The base layer includes a proportion of first fiber material and a proportion of first filler material and the outer layer includes a proportion of second fiber material and a proportion of second filler material. The proportion of second fiber material is less than the proportion of first fiber material and the proportion of second filler material is greater than the proportion of first filler material. The method also includes forming a plurality of orifices passing through the outer layer.

According to embodiments of the method, the base layer has a first thickness, the outer layer has a second thickness, the wet friction material may have a total thickness equaling the first thickness plus the second thickness and the second thickness may be 10% to 30% of the total thickness. The orifices may have a maximum diameter of 50 μm to 200 μm. The orifices may represent 10% to 30% of a total surface area of an outer surface of the outer layer. The first filler material and the second filler material may be each formed by one or more fillers from a group consisting of diatomaceous earth and/or clay. The first fiber material and the second fiber material may be each formed by one or more fibers from a group consisting of aramid fibers, organic fibers and/or carbon fibers. The proportion of first fiber material may be between 35 to 60% of the base layer and the proportion of second fiber material may between of 5 to 25% of the outer layer. The proportion of first filler material may be between 15 to 50% by percentage weight of the base layer and the proportion of second filler may be between of 45 to 75% by percentage weight of the outer layer. The providing of the outer layer on the base layer to form the wet friction material may include laminating the outer layer on the base layer. At least one of the base layer and the outer layer may include a binder. The laminating of the outer layer on the base layer may include applying heat and pressure to the outer layer to fix the outer layer and the base layer together via the binder.

A clutch assembly is also provided including a metal part and the wet friction material fixed on the metal part.

A wet friction material is also provided. The wet friction material includes a base layer; and an outer layer on the base layer. The base layer includes a proportion of first fiber material and a proportion of first filler material and the outer layer includes a proportion of second fiber material and a proportion of second filler material. The proportion of second fiber material is less than the proportion of first fiber material and the proportion of second filler material is greater than the proportion of first filler material. The outer layer includes a plurality of orifices passing through the outer layer.

According to embodiments of the wet friction material, the base layer has a first thickness, the outer layer has a second thickness, the wet friction material may have a total thickness equaling the first thickness plus the second thickness and the second thickness may be 10% to 30% of the total thickness. The orifices may have a maximum diameter of 50 μm to 200 μm. The orifices may represent 10% to 30% of a total surface area of an outer surface of the outer layer. The first filler material and the second filler material may be each formed by one or more fillers from a group consisting of diatomaceous earth and/or clay. The first fiber material and the second fiber material may be each formed by one or more fibers from a group consisting of aramid fibers, organic fibers and/or carbon fibers. The proportion of first fiber material may be between 50 to 80% of the base layer and the proportion of second fiber material may be between of 5 to 30% of the outer layer. The proportion of first filler material may be between 15 to 50% by percentage weight of the base layer and the proportion of second filler may be between of 45 to 75% by percentage weight of the outer layer.

DETAILED DESCRIPTION

The present disclosure provides embodiments of wet friction material that are able to provide a sufficient friction at high slip speed while also maintaining porosity. Adding a friction modifier layer to the top surface improves the friction performance, but clogs the pores of the underlying wet friction material. The present disclosure provides small orifices in the friction modifier layer increase the porosity and the performance in high slip speed.

FIGS. 1 to 4schematically illustrate a method of forming a wet friction material and a clutch assembly in accordance with an embodiment of the present disclosure. A base wet friction material layer10is manufactured separately from or as a single piece with an outer layer12.FIG. 1shows base layer10and outer layer12as separate pieces.

Base layer10is a wet friction material formed of fibers, filler material and a binder. The fibers can be aramid fibers, organic fibers, carbon fibers and/or fiberglass. The organics fibers include cellulose fibers or cotton fibers. The fillers can be diatomaceous earth and/or clay. The binder can be a phenolic resin, a latex or a silane. Optionally a friction modifier such as graphite may also be included in base layer10.

Outer layer12includes fibers, filler material and a binder. The fibers can be aramid fibers, organic fibers, carbon fibers and/or fiberglass. The organic fibers include cellulose fibers or cotton fibers. The fillers can be diatomaceous earth and/or clay. The binder can be a phenolic resin, a latex or a silane. Optionally a friction modifier such as graphite may also be included in outer layer12. The composition of outer layer12includes a higher ratio of filler material and a lower ratio of fibers than base layer10, such that outer layer12is less porous and more dense than base layer10, has a higher coefficient of friction than base layer10and a higher wear resistance than base layer10. The fibers of layers10and12have a mean diameter of 45 to 55 microns and a mean length of 1 to 2 millimeters.

In one preferred embodiment, base layer10includes, by percentage weight, 35 to 60% fibers, 15 to 40% filler material and 20 to 30% binder. In another preferred embodiment, base layer10, by percentage weight, 35 to 55% fibers, 15 to 40% filler material and 20 to 30% binder. More specifically, in one preferred embodiment, base layer10includes, by percentage weight, 30 to 55% aramid and organic fibers and 5 to 10% carbon fibers, 15 to 40% filler material and 20 to 30% binder. In another preferred embodiment, base layer10includes, by percentage weight, 40 to 60% aramid and organic fibers and 5 to 10% carbon fibers, 15 to 40% filler material and 20 to 30% binder.

In one preferred embodiment, outer layer12includes, by percentage weight, 5 to 25% fibers, 45 to 75% filler material and 20 to 30% binder.

FIG. 2shows the two separate layers10,12being joined together via lamination. The lamination includes pressing outer layer12against base layer10with a heat plate14to cure the binder in at least one of layers10,12, fixing outer layer12and base layer10together. The binder is provided into the pores of a matrix formed by the fibers and the filler material of layers10,12. The force of pressing of heat plate14against an outer surface12aof outer layer12, while a lower surface12bof outer layer12rests on a support surface, causes the binder to accumulate at an interface of an inner surface12bof outer layer12and an outer surface10aof base layer10, while the curing of the binder by the heat of heat plate14creates a permanent connection between base layer10and outer layer12. In one preferred embodiment, the heat at a surface14aof plate14that contacts outer surface12aof outer layer is 375 to 425 degrees F.

FIG. 3shows a wet friction material16formed by the joining of base layer10and outer layer12as described with respect toFIG. 2. Wet friction material16is formed such that outer layer12has a thickness T1between outer surface12aand inner surface12b, base layer14has a thickness T2between outer surface10aand lower surface10b,and wet friction material16has a total thickness T3between outer surface10aand lower surface10b.In one preferred embodiment, the thickness T2of outer layer12is equal 10 to 30% of the total thickness T3, with thickness T1of base layer10thus being 70 to 90% of the total thickness T3.

After the forming of wet friction material16, a plurality of orifices18are formed in outer layer12by a laser20. Orifices18extend from outer surface12ato inner surface12bsuch that orifices18extend through outer layer12to undercover the porous matrix of base layer10. Orifices18thus allow fluid at outer surface12aof outer layer12to access the porous matrix of base layer10. Laser20is moved in a controlled manner over surface12aof outer layer12and repetitively pulsed to form orifices18. In one preferred embodiment, orifices18are formed in outer layer12each have a maximum diameter of 50 μm to 200 μm and represent 10% to 30% of the total surface area of outer surface12aof outer layer. Maximum diameter is defined as the greatest distance between two edge points of an orifice as measured from outer surface12a.Total surface area means the surface area of outer surface12abefore orifices18are added, i.e., the surface area of outer surface12aafter orifices18are added, plus the surface area removed by the formation of orifices18.

FIG. 4shows wet friction material16bonded to a metal part22. More specifically, adhesive is applied to lower surface10bof base layer10or to a surface22aof metal part22and wet friction material16is bonded to metal part22with surface12aand orifices18facing away from metal part22.

FIG. 5shows wet friction material16bonded to both sides of a metal part in the form of a clutch plate30of lockup clutch assembly32of a torque converter34. A piston36of lockup clutch assembly32forces clutch plate30against an inside surface38aof a front cover38of torque converter34. Piston36contacts the surface12aprovided with orifices18(FIG. 4) of the rear piece of wet friction material16to force the surface12aprovided with orifices18on the front piece of wet friction material16against inside surface38aof front cover38. The forcing of clutch plate30against front cover38by piston36locks the lockup clutch assembly32such that a torque path in torque converter34to a transmission input shaft bypasses an impeller40and a turbine42of torque converter34, and instead flows from front cover38to clutch plate30and through a damper assembly44to a transmission input shaft that is connected to an output hub46of torque converter34.

FIG. 6shows a top plan view of an exemplary embodiment of outer surface12a. Outer surface12aincludes a plurality of orifices18spaced apart from each other. Orifices18are each elliptically shaped and have a maximum diameter D1and a minimum diameter D2at outer surface12a.

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.

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