Porous sintered metal and nonporous friction material for clutches

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Today's automotive transmission friction clutches are typically designed with synchronization rings having an inner cone and opposing shifting gear friction surfaces having an outer cone.
However, designs are known, and can be implemented according to the present invention wherein either the synchronization ring has an outer cone and the shifting gear has an inner cone, or wherein the individual parts of the clutch have one friction surface formed as an outer cone and another, additional friction surface formed as an inner cone (double cone synchronization).
The increased friction surface area offered by the latter design substantially increases the frictional power which can be transmitted.
Depending on the required design and dimensional characteristics of a friction clutch, it may be advantageous to either manufacture a clutch part as a single solid sintered part, or to mount the sintered portion which is the friction surface on a base part not made from sintered metal.
Until now it has been important that sintered parts used as stress-bearing components in friction clutches be manufactured having the lowest porosity possible, uniform density, and as high a mechanical strength as possible.
In contrast, the present invention uses known sintered-metal technology processes to manufacture a solid sintered part having the desired degree of porosity in the region of the friction surface.
For example, a solid sintered part can be designed having a completely compact base area and a porous friction surface region simply by adding a pore-forming substance to the powdered-metal blank in the region of the friction surface, which substance evaporates during the sintering process (DE-PS 16 08 128).
If the metal powder used for the sintered part has the appropriate form and size, an open-pored skeleton can be formed in the region of the friction surface; it is also possible to create individual pores, most of which are not interconnected, extending into the friction surface down to a depth of 0