Abstract:
One embodiment includes a friction plate and method of manufacture thereof wherein the friction plate is fabricated from a thixomolded magnesium or titanium material or alloy thereof, which is lighter than comparable steel friction plates.

Description:
This application claims benefit of priority to U.S. Provisional Application Ser. No. 61/340,491 filed Mar. 18, 2010. 
    
    
     TECHNICAL FIELD 
     The technical field relates to friction plates, including, but not limited to friction plates used in wet or dry friction clutch modules in automotive transmissions, such as, but not limited to passenger vehicles, motor cycles, rough terrain vehicles, and truck vehicles. 
     BACKGROUND 
     Currently, most if not all friction plates used in automotive transmissions are fabricated from steel stampings. 
     SUMMARY OF SELECT ILLUSTRATIVE EMBODIMENTS 
     A friction plate and a method of manufacture thereof wherein the friction plate is fabricated from a thixomolded magnesium or titanium, which is lighter than comparable steel friction plates. 
     Other illustrative embodiments of the invention will become more apparent to those skilled in the art in view of accompanying drawings and detailed description of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 and 1A  are front elevational views of one embodiment of friction plates; 
         FIG. 2  is a side elevational view of a core plate utilized in the friction plate shown in  FIG. 1 ; 
         FIG. 3  is an enlargement of the core plate shown in  FIG. 2  and is a partial sectional view of a friction disc shown in  FIG. 1 ; 
         FIGS. 4A-4C  are partial side elevational views of a portion of a friction pack module utilizing various embodiments of friction plates of the present invention; 
         FIG. 5  is a view similar to  FIG. 1  of an alternative embodiment of a friction plate; 
         FIG. 6  is an enlarged partial sectional view showing an interface between a core plate and a backing; and 
         FIG. 7  is a partial sectional view of an injector and mold cavity. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A friction plate  7  is provided in  FIG. 1 . The friction plate  7  has an annular core plate  10 . Preferably, the core plate  10  is fabricated from a thixomolded light but strong material including at least one of titanium or magnesium. Select embodiments may include magnesium alloys AZ91D, AM50 and AM60. 
     The core plate  10  may have an integral reduced thickness rim portion  14 . Typical core plates  10  may have a thickness ranging from 0.76-1.20 mm with an outer diameter of 75 to 225 mm depending upon the application. Core plates outside of this size range are also contemplated. 
     The inner diameter of the typical core plate may have a series of radially inward facing spline teeth  16  ( FIG. 1A ). Some core plate applications may have radially outward facing spline teeth instead of inward facing spline teeth. The spline teeth  16  provide a torsional interface for the friction plate  7  with a rotating member (not shown). Further, some applications may not have any spline teeth at all. 
     Connected with the rim  14  is a friction facing  18 . The friction facing may be on both sides of the core plate, or only on one side. The friction facing  18  may be a cellulosic fiber base friction material, although other friction materials such as, but not limited to, sintered metals, ceramics, or foam may also be used. As shown, the friction facing  18  may be a paper fiber based friction material. The friction facing may be a continuous ring or may be fabricated from individual arcuate segments arranged radially. In select embodiments the number of segments may be 3-5. The segmenting of the facing  18  provides significant savings in friction material cost. The individual arcuate segments  22  may have interlocking tab  24  and slot  26  end portions. Another segmented facing design provides for independent or non-interlocking facing segment arcs and can provide an oil flow path between facing segments. The friction base facing  18  may be connected with the rim  14  by adhesives or by other means as described herein. 
     In one embodiment, the facing (full ring or segments) may be first placed in open halves of an injection mold ( FIG. 7 ). The mold halves  29 ,  31  are closed. In one embodiment, the mold is then pressurized to hold one or both facings in position against a surface of the mold half. In an alternate embodiment, the facing(s) may be held by fixtures and or by a vacuum. Chips  33  including at least one of Magnesium or titanium are dropped into an injection hopper  35  in an inert gas atmosphere. An injector reciprocating screw  37  is encircled by a barrel which in turn is encircled by heater bands  39 . In select embodiments, when magnesium is used, the magnesium may be AS91D, AM50 or AM60 or combinations thereof. The magnesium may be brought to a temperature of 1040 to 1080° F. while it is being mixed by reciprocating screw  37  of the injector  41 . The magnesium becomes a semi-solid and may have globular dendrites within the melt. Additionally, the flow through the injector nozzle into the mold may be laminar rather than turbulent. In one embodiment, care is taken to keep the temperature of the magnesium beneath 1300° F. wherein magnesium would form a liquid melt and passage through the nozzle of the die could become turbulent. By keeping the molding process thixotropic, porosity is virtually eliminated and additionally, there is less warpage than in a conventional die casting process. The mold temperature may be between 350-480° F. so that as the thixomolded material exits the nozzle, it will be in a consistency of a slurry. As the thixomolded material solidifies and forms the core plate geometry, the fibers  108  of the facing  18  are at least partially encapsulated by the material  112  of the core plate  10 , creating a boundary layer  110  and a mechanical bond between facing and core plate. 
     Referring to  FIG. 4A , a partial view of a clutch pack module  27  is provided having two separator plates  34 . When the separator plates  34  engage with the friction plate facings, the separator plates  34  are separated by a first distance  36 . The thickness of the spline teeth  16  is greater than the thickness of the rim  14 , but equal to the final design thickness  36  of the finished friction plate, to provide more strength to the spline teeth  16 . Referring to  FIG. 4B  a clutch module  40  having a friction plate  47  has spline teeth  46  that have a thickness less than the first distance  36 . Referring to  FIG. 4C  a clutch module  50  has a friction plate  57  having spline teeth  56  that are greater width than the first distance  36 . 
     Referring to  FIG. 5  a friction plate  67  is provided wherein the friction facing  71  have a plurality of radially extending oil grooves  74 . The oil grooves  74  can be formed on the facing  71  before connection with the core plate. In another embodiment, the oil grooves  74  can be cut after connection of the friction facing  71  with the underlying core plate. The cut oil grooves  74  can also extend into the core plate. 
     In another embodiment, the oil grooves  74  can be formed in the facing  71  and optionally in the core plate in an injection molding operation. The mold cavity is machined with a rib to impart a slightly oversized oil groove to compensate for any spring back in the material. 
     In another embodiment, the oil grooves can be formed in alternative geometries, such as single direction parallel, double direction parallel (criss-crossed), non-standard linear or non-linear pattern. Oil grooves may extend fully through facing, allowing a through oil passage, or may terminate short of outer diameter to create a dead-end groove. 
     In another embodiment, the oil grooves may be formed through the use of the injection molding process, whereas the individual, non-connected arcuate segments are positioned with a defined gap between segments into mold, with the molding process forming the core plate and achieving the required bond between friction material and core plate. 
     IN SELECT EMBODIMENTS 
     While Illustrative embodiments have been disclosed, it is to be understood it has been described by way of example only, and various modifications can be made.