Annular friction disc with radial grooving

An annular friction disc has a flat friction surface on each side of a flat steel plate with each friction surface having a plurality of radially extending grooves formed therein. Each groove has a flat bottom portion which extends between the inner and outer circumference of the friction surface and is displaced axially from the friction surface at the inner circumference and is contiguous with the friction surface at the outer circumference. Each groove also has a pair of tapered side walls extending between the bottom portion and the adjacent flat friction surface.

This invention relates to friction discs and more particularly to grooved 
friction discs. 
It is an object of this invention to provide an improved grooved friction 
disc wherein oil flow channeled by the groove will assist in causing 
separation of the discs when used in a clutch or brake pack. 
It is another object of this invention to provide an improved friction disc 
wherein the grooves are tapered from the inside diameter to the outside 
diameter of the disc and the side walls are slanted so that oil flow in 
the groove will create a separating force in a "free running" clutch or 
brake pack.

Referring to the drawings, wherein like characters represent the same or 
corresponding parts throughout the several views, there is seen a friction 
disc, generally designated 10, having a flat steel annular plate or disc 
12 bounded on each side by friction discs 14 and 16. The friction discs 14 
and 16 are identical and are preferably made in accordance with the 
present acceptable manufacturing techniques wherein impregnated paper can 
be utilized as a friction disc. After the paper is treated, it is then 
bonded to the annular steel disc member 12, which has formed at the inner 
diameter a plurality of spline teeth 18 which are operable to provide a 
mechanical connection in a well-known manner. 
Since the friction disc 14 and 16 are identical, the following discussion 
will be limited to the friction disc 16. However, the same numerical 
designations will be given to corresponding structures formed on friction 
disc 14. The friction disc 16 has a generally flat outer surface 20, an 
inner circumference 22 and an outer circumference 24. The flat surface 20 
is interrupted by a plurality of radially extending grooves 25 each having 
a flat bottom 26 which extends from the inner circumference 22, at a 
distance displaced from the flat surface 20 to a line contiguous with the 
flat surface 20 at the outer circumference 24. Each groove 25 has side 
walls 28 and 30 which intersect the flat bottom 26 and extend upward and 
outward to intersect the flat surface of disc 20. 
A plurality of friction discs 10 are used in a clutch or brake pack to 
provide a friction drive establishing connection in power transmissions. 
These friction drive connections take the form of either a clutch which 
transmits torque between rotating components or a brake which provides a 
connection with a stationary housing. Such a structure is shown in FIG. 5 
and is generally designated 32 and will be referred to as a brake, 
however, as is well-known, a clutch structure would be substantially 
identical. In the brake 32, the friction discs 10 are separated by steel 
plates or discs 34 which have a splined portion 36 at the outer diameter. 
The spline 36 is adapted to be fitted in a mating spline portion formed in 
a stationary housing 38 in which is slidably disposed a fluid actuated 
piston 40. The piston 40 forms one side of the brake 32 while the other 
side is defined by a back-up plate 42 which is splined on the housing 38 
and maintained in position by an annular snap ring 44. The spline 18 of 
the friction discs 10 mate with a spline 46 formed on a hub 48. The hub 48 
is adapted to be connected with a conventional gear member, such as a sun 
gear in a planetary gear system. When fluid pressure is admitted to the 
chamber 50, formed between piston 40 and housing 38, the piston 40 will be 
pressed into engagement with one of the plates 34 which will result in the 
alternate plates 34 and friction discs 10 being forced into a friction 
engaging relationship as is well-known. When the chamber 50 is thus 
pressurized, the hub 48 is held stationary and there is no relative motion 
between discs 10 and 34. However, when the chamber 50 is not pressurized, 
there will generally be relative rotation between friction discs 10 and 
plate 34. 
There is a drag torque between discs 10 and 34 when the brake pack is in 
the "free running" condition. This drag torque is a parasitic loss, and 
should be eliminated to the extent possible. The grooves 25 reduce the 
drag torque considerably by creating a flow pattern between the discs 10 
and 34 which assist in causing separation between the discs. 
When the chamber 50 is unpressurized, lubricating fluid within the system 
flows through openings 52 formed in the hub 48 and accordingly toward the 
grooves 25. Once the fluid reaches the grooves 25, it flows both radially 
outward and also circumferentially across the slanted surfaces 30 and 28, 
depending upon the direction of rotation, to create a separating force 
between the discs 10 and 34. This effectively creates a fluid bearing 
between adjacent surfaces considerably reducing the drag friction normally 
present in such devices. 
As previously mentioned, the grooved friction disc will operate equally 
well in either a clutch structure or a brake structure. However, it will 
be found most useful in brake structures, because, generally in power 
transmissions for use in motor vehicles, clutches are engaged for most 
operation while brakes are engaged during lower gear ratios used for 
acceleration or deceleration.