Clutch plate member having layer of high durability, self-conforming friction facing

A clutch plate member for operating in a fluid medium to transmit torque to a metal mating surface situated on an opposing clutch plate member in a wide range of slip speeds. The clutch plate member is constructed of a friction facing layer consisting of thermoset resin bonded carbon particles bonded to a compliant carrier sheet which is in turn bonded to a metal support plate. The compliant carrier sheet improves the conformability of the friction facing layer to the metal mating surface resulting in a reduction in the maximum operating temperature of the friction facing layer.

FIELD OF THE INVENTION 
The present invention relates to a clutch plate member used in an 
automotive transmission and, more particularly, is concerned with a clutch 
plate member used in an automotive transmission which has a high 
durability, self-conforming friction material layer consisting of carbon 
and phenolic particles bonded to a compliant carrier sheet. 
BACKGROUND OF THE INVENTION 
Clutch plate members of the type described in the present invention are 
used extensively in automotive transmissions utilizing a fluid medium. 
When used in an automotive transmission as the driving member, a clutch 
plate member compresses and engages a driven member to drive the vehicle 
when pressure is applied to it. To increase the fuel economy of a vehicle, 
it is desirable to have the clutch plate members engaged over a wide range 
of slip speed (engine and transmission speed differential). It is 
therefore an important consideration when designing a clutch plate member 
to use a friction material which can be efficiently operated at a lower 
operating temperature over a wide range of slip speed. This lower 
operating temperature leads to a more durable clutch plate member having a 
longer service life. 
Another important consideration in the design of a clutch plate member is 
that the frictional property of the material should remain approximately 
constant over the wide range of slip speed that the clutch plate member 
operates in order to minimize the transmission shudder phenomenon. 
Transmission shudder usually occurs at the friction interface where the 
static or low speed coefficient of friction is higher than the dynamic or 
high speed coefficient of friction. This condition causes the clutch to 
operate in a so-called stick slip mode which in turn translates into the 
transmission shudder phenomenon. 
A variety of friction materials have been used to construct the friction 
facing layer of an automotive clutch plate member. Most of these 
traditional friction materials can be categorized into two types. The 
first type is a highly porous fibrous material made first by traditional 
paper making technology and then saturated with a thermoset plastic binder 
such as phenolic or epoxy. This type of material provides good 
conformability with a rigid mating surface due to its high 
compressibility. However, they typically have only a medium internal 
strength and a medium heat resistance therefore limiting their use to 
medium duty transmission applications. Materials of this type are 
described in U.S. Pat. No. 3,316,138 to Taylor and Almen et al U.S. Pat. 
No. 2,733,797, both assigned to the assignee of the present invention. 
The second traditional type of friction material is a highly rigid material 
composed of grannular or fibrous carbon or other similar materials bonded 
together by a thermoset type of plastic resin or a metallic brazing 
material. These materials have very high internal strength and high energy 
absorbing capacity. However, they have the inherent drawback of poor 
conformability to a mating surface due to their rigidity. This poor 
conformability leads to hot spot formation in the friction material which 
in turn causes higher overall operating temperature of the clutch plate 
member. It is believed that higher operating temperatures cause premature 
failure of the friction facing layer and consequently a short service 
life. Materials of this type are disclosed in Yamamoto et al U.S. Pat. No. 
4,146,527 and German Patent Application No. 1-525-334. 
It is therefore an object of the present invention to provide a clutch 
plate member having a friction facing layer that offers both the 
conformability of a porous fibrous material and the strength and energy 
absorbing capacity of a hard grannular material. 
It is another object of the present invention to provide a clutch plate 
member having a friction facing layer of high conformability, high 
strength, and energy absorbing capacity, and can be manufactured in a 
continuous process at low cost. 
SUMMARY OF THE INVENTION 
Our novel invention is a new clutch plate member design consisting of a 
friction facing layer bonded to a rigid metal plate by a layer of 
adhesive. Our invention offers the conformability of a traditional porous 
fibrous material and yet the strength and energy absorbing capability of a 
rigid grannular material. Our novel clutch plate member is constructed in 
the following manner. A compliant carrier sheet of porous fibrous nature 
having high conformability and compressive strength is coated with a 
grannular mixture of carbon and a phenolic thermoset binder to form a 
friction facing layer. This friction facing layer may be produced in a 
continuous process at low manufacturing cost. The surface of the compliant 
carrier sheet opposite to the friction material coating is then fastened 
to a rigid metal plate by adhesive means to form a clutch plate member.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring initially to FIG. 1, a cross-sectional view of a clutch plate 
member embodying the present invention is shown. Layer A composed of 
carbon particles 10 and phenolic powder 12 compression molded together 
onto layer C, a compliant carrier sheet with a layer B of adhesive in 
between. Layers A, B and C form the friction facing layer when compression 
molded together. The carbon particles 10 used in this invention is a 
petroleum-coke based carbon generally of spherical shape. The diameters of 
the particles are approximately within the 0.002 to 0.006 inch range. This 
type of carbon particles is commercially available from suppliers such as 
Asbury Graphite Mills, Inc. The phenolic powder used in the present 
invention is an epoxy modified phenolic obtained from Schenectady 
Chemicals Co., grade HRJ 1797. The powder was characterized by screen 
analysis to be zero percent of +40 mesh and 96 percent minimum of -200 
mesh. It has a cure temperature of 135 degrees centigrade and contains 
11/2 percent maximum ash content. The carbon particles and the phenolic 
powder are mixed together in a suitable container at a weight percent 
ratio of 60 to 85 percent carbon and 15 to 40 percent phenolic. 
The compliant carrier sheet used in the present invention is a friction 
paper composed primarily of cellulose fibers saturated with a liquid 
phenolic resin. The friction paper also contains small amounts of 
diatomaceous earth particles and other friction modifiers. It has a 
compressive modulus in the range of 5,000 to 10,000 psi. It typically 
contains 35-65 percent porosity which provides high compliance and 
absorption of oil to keep the paper cool and lubricated during operation 
of the clutch plate member. A commercial source for this type of friction 
paper is Fabricon Automotive Products. We have found a suitable thickness 
to be used is 0.035 inch. Other suitable materials having similar 
properties may also be used as the compliant carrier sheet. For instance, 
we have successfully used sheets of epichlorohydrin rubber having a Shore 
A durometer hardness of 35. 
The friction facing layer which consists of the friction material layer A, 
an adhesive layer B, and a compliant carrier sheet C (FIG. 1) is assembled 
to a metal substrate plate, layer E, by using a second solid film adhesive 
layer D. We have found a suitable solid film adhesive to be used in this 
invention is a nitrile phenolic based adhesive film supplied by Morgan 
Adhesive Company. We have also found that a suitable thickness of the 
solid adhesive film to be used is between 0.001 to 0.002 inch. This solid 
adhesive film becomes tacky when heated to 200 degrees fahrenheit. 
Although solid film adhesive was used in the present invention, anyone 
skilled in the art should be able to use other fastening means equally 
well to practice the current invention. For instance, various kinds of 
sprayed-on adhesive or even some mechanical means may be utilized to 
assemble the friction facing layer to the metal substrate plate. 
The clutch plate member embodying the present invention may be assembled 
by, but not limited to, the following two examples. 
EXAMPLE 1 
Carbon particles are first blended with 15 to 40 weight percent epoxy 
modified phenolic resin powder. A layer of solid film adhesive is placed 
on top of a carrier paper situated in a fixture for level fill of powder 
mixture. The blended carbon particles/epoxy modified phenolic powder is 
then level filled on top of the carrier paper to a depth of 0.030 inch. 
The fixture is first transferred to an oven set at 275 degrees fahrenheit 
for 20 seconds to heat set the powder mixture. It is then transferred to a 
hot platen press heated to 450 degrees fahrenheit and pressed under 300 
psi pressure for 15 seconds to bond the friction material layer to the 
carrier paper. 
A second layer of solid film adhesive is then tacked to the surface of the 
carrier paper opposite to the surface containing the friction material. A 
friction facing layer of desirable shape can now be blanked out of the 
laminated sheet and bonded to a metal substrate plate. We have found a 
pressure of approximately 500 pounds per square inch is adequate for this 
bonding operation. 
This method is suitable for either making samples in the laboratory or for 
a production process. 
EXAMPLE 2 
A slurry process is utilized in this method. First, carbon particles 
between 40 to 50 weight percent are blended with 50 to 60 weight percent 
liquid phenolic resin obtained from Ashland Chemical Company, AROFENE.RTM. 
295-E15. This slurry is then spread out by rollers on a continuous roll of 
adhesive film coated friction paper to a thickness of approximately 0.030 
inch. The coated friction paper is then fed into a series of ovens set at 
250 degrees fahrenheit on a conveyor belt for a total heating time of 15 
minutes. It is then pressed in a series of pressure rollers at 1000 pounds 
per square inch pressure at 450 degrees fahrenheit for a total time of 1 
minute. Desirable shapes of the friction facing layer are then punched out 
from the roll and bonded to metal substrate plates to make clutch plate 
members. This slurry process is a continuous process and can be completely 
automated to produce low cost clutch plate members. 
The advantages of the present invention over the prior art are shown in 
FIGS. 2 and 3. FIG. 2 is a graph of coefficient of friction data plotted 
against a range of slip speed between 0 to 175 rounds per minute. Curve G 
represents data obtained on a friction facing layer made by bonding carbon 
particles/phenolic powder to a compliant carrier sheet. Curve F represents 
data obtained on a prior art porous fibrous sheet without the carbon 
particles/phenolic powder layer. It is seen that for the friction facing 
layer embodying the present invention, curve G, the coefficient of 
friction remains essentially constant throughout a wide range of slip 
speed between 10 to 175 rounds per minute. In contrast, the coefficient of 
friction of the prior art friction facing layer decreases by approximately 
35 percent within the same range of slip speed. 
The essentially constant coefficient of friction of the clutch plate member 
embodying the present invention over the wide range of slip speed 
eliminates the transmission shudder phenomenon almost completely. The 
drivability of the automobile is greatly improved because of the 
elimination of shudder. 
FIG. 3 shows the benefit obtained when a compliant carrier sheet is used 
between the carbon particles/phenolic resin layer and the metal substrate 
plate. The temperature at the interface between friction material on a 
driving clutch plate member and the mating metal surface on a driven 
clutch plate member is recorded against time in FIG. 3. Curves L and M 
represent data obtained on the clutch plate member embodying the present 
invention, L and M denote data obtained at the high spot and low spot of 
the interface respectively. Curves N and O represent data obtained on a 
prior art clutch plate member where no compliant carrier sheet was used, N 
and 0 denote data obtained at the high spot and low spot of the interface 
respectively. The high spot temperature at the interface is also referred 
to as the maximum operating temperature of the friction facing layer. 
It is seen when curves L and N are compared that the high spot temperature 
of a clutch plate member having a compliant carrier sheet are 
approximately 25 degrees fahrenheit lower than that obtained on a clutch 
plate member without the carrier sheet. A reduction in the high spot 
temperature, or the maximum operating temperature, of approximately 7% is 
achieved. It should be noted here that it is desirable in the design of 
transmission clutch plate members to have the lowest possible high spot 
temperature. This is to avoid the degradation of the fluid medium 
contained in the transmission and the phenolic resin contained in the 
friction material. It is advantageous to have a lower high spot 
temperature in order to provide a clutch plate member of high durability 
and long service life. 
The low spot temperatures, represented by curves M and O in FIG. 3, also 
show the advantages achieved by the present invention. The low spot 
temperature data obtained on the clutch plate member embodying the present 
invention is approximately 25 degrees higher than that obtained on the 
prior art clutch plate member. This is a desirable result since it 
indicates that in the clutch plate member embodying the present invention 
the temperature gradient on the friction facing surface is smaller than 
that on the prior art clutch plate member. It is believed that a more 
uniform temperature distribution on the friction facing surface helps to 
eliminate the formation of hot spots. Since hot spots reduce the 
durability of the friction facing layer, an overall lower operating 
temperature resulting from a lower and more uniform temperature profile 
across the friction facing surface improves the service life of the clutch 
plate member. 
The achievement of lower operating temperature in the friction facing layer 
by the present invention can be explained as follows. First, it is 
recognized that the two mating surfaces, i.e., the metal surface on a 
driven clutch plate member and the surface of the friction material layer, 
are both very rigid. It is further recognized that the two rigid mating 
surfaces are never perfectly flat, i.e., there is always waviness or taper 
present. A highly compressible compliant carrier sheet paper placed in 
between the metal substrate plate and the friction material layer on the 
driving clutch plate member improves the conformance between the two 
mating surfaces, i.e., surface on the driven clutch plate member and the 
surface of the friction material layer, when they are pressed against each 
other. Data (not shown here) indicated that contact area between the two 
mating surfaces achieved without the compliant carrier sheet is only 
approximately 30 percent of the total available area. The addition of a 
compliant carrier sheet in between the metal substrate plate and the 
friction material layer increases the contact area to approximately 70 
percent. The contact between the two rigid mating surfaces when they are 
pressed against each other is significantly improved. This in turn enables 
an overall lower operating temperature in the friction material layer 
leading to a clutch plate member having improved durability and service 
life. 
While our invention has been described in terms of a preferred embodiment 
thereof, it is to be appreciated that those skilled in the art will 
readily apply these teachings to other possible variations of the 
invention.