Abstract:
A clutch piston amplifier assembly is provided for applying pressure to a clutch pack for engaging a first member and second member of an automatic transmission. The clutch piston amplifier assembly utilizes an amplifier piston which applies a secondary force to an apply piston for increasing the amount of apply force that can be obtained from the clutch assembly without increasing the diameter of the apply piston or the line pressure supplied to the piston assembly.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a clutch assembly, and more particularly, to a clutch having a piston amplifier assembly.  
       BACKGROUND OF THE INVENTION  
       [0002]     Clutch assemblies have been used in automatic transmissions for vehicles for many years. As illustrated in  FIG. 6 , the typical clutch design  110  includes a first member  112  and a second member  114  rotatable relative to the first member. A clutch pack  116  including at least one first clutch disk  118  attached to the first member  112  and at least one second clutch disk  120  attached to the second member  114  is provided for selectively, frictionally engaging the first and second members  112 ,  114 . In an automotive transmission, the first and second members  112 ,  114  can be any one of a rotating shaft, gears, and planetary gearing system components, or a fixed non-rotatable member, such as a housing. In a typical friction clutch assembly, an apply piston  122  is disposed in a fluid chamber  124  for selectively applying axial pressure on the clutch pack  116 . A return spring mechanism  126  typically in the form of a spring pack, wave spring, or Bellville spring is used to apply a biasing force against the apply piston to bias the apply piston to a disengaged position. The input into the system is hydraulic pressure delivered to the piston chamber  124  and acting directly on the apply piston  122 . The apply piston  122  translates toward the friction plates  118 ,  120  coming into contact with the plates and applying pressure thereto. The pressure applied to the friction plates  118 ,  120  increases and eventually causes the rotation of the component for which the system is design to engage.  
         [0003]     The apply piston pressure must overcome the force of the return spring  126  in order to apply pressure to the clutch pack. The return spring&#39;s main function is to return the apply piston into the disengaged position from which it came after the apply pressure has dissipated in order to disengage the clutch.  
         [0004]     The apply pressure applied to the clutch pack is dependent upon the fluid line pressure generated by the pump of a hydraulically controlled transmission and the surface area of the apply piston. Because of the space constraints on the design of a transmission, the size of the apply piston is greatly limited. Similarly, the pump of the hydraulically controlled transmission may also be limited due to size and weight requirements. Accordingly, it is desirable to provide a clutch design that increases the apply forces achievable with the clutch without greatly affecting the size of the system or requiring increased line pressure.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention provides a clutch assembly having a clutch piston amplifier assembly for applying pressure to the clutch pack. The clutch piston amplifier assembly is disposed in a piston chamber and includes an apply piston operable for applying axial pressure to the clutch pack and an amplifier piston operable for applying axial pressure to the apply piston for amplifying the amount of pressure applied to the clutch pack.  
         [0006]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0008]      FIG. 1  is a partial cross-sectional view of a clutch piston amplifier assembly according to the principles of the present invention;  
         [0009]      FIG. 2  is a plan view of an amplifier plate piston according to the principles of the present invention;  
         [0010]      FIG. 3  is a plan view of a separator plate according to the principles of the present invention;  
         [0011]      FIG. 4  is a partial cross-sectional view of a second embodiment of a clutch piston amplifier assembly according to the principles of the present invention;  
         [0012]      FIG. 5  is a partial cross-sectional view of a third embodiment of the clutch piston amplifier assembly according to the principles of the present invention; and  
         [0013]      FIG. 6  is a cross-sectional view of a prior art clutch design. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0015]     With reference to  FIG. 1 , the clutch assembly  10 , according to the principles of the present invention, will now be described. The clutch assembly  10  includes a first member  12  and a second member  14  rotatable relative to the first member  12 . A clutch pack  16  includes a plurality of clutch plates  18  having external splines which engage internal splines of the first member  12  and a plurality of clutch plates  20  having internal splines connected to external splines of rotational second member  14 . The first member  12  defines a piston chamber  22  having a first chamber portion  22   a  and a second chamber portion  22   b . A stage separator plate  24  is provided between the first chamber portion  22   a  and the second chamber portion  22   b . An apply piston  26  is disposed in the first chamber portion  22   a  of the piston chamber  22  and includes an inner diameter seal  28  engaging an inner diameter surface of the piston chamber  22 . An outer diameter seal  30  is provided on an outer diameter portion of the piston  26  and engages an outer diameter surface of the piston chamber  22 . The apply piston  26  includes an axially extending arm portion  32  which engages the clutch pack  16  for applying axial pressure thereto, as will be described in greater detail herein.  
         [0016]     An amplifier piston  34  is provided in the second chamber portion  22   b  of the piston chamber  22  and includes an outer diameter seal  36  which engages an outer diameter surface of the piston chamber  22  and an inner diameter seal  38  which engages an inner diameter surface of the piston chamber  22 . A plurality of amplifier drive pins  40  are provided in engagement with the apply piston  26  and the amplifier piston  34 . As shown in  FIG. 2 , preferably, three or more amplifier drive pins  40  are provided equally spaced around the annular shaped piston chamber so as to have a first end  42  engaging the first piston  26  and having a second end with a reduced diameter portion  44  slidably received in respective apertures  46  provided in the amplifier piston  34 . The reduced diameter portion  44  of the amplifier drive pins  40  is slidable relative to the amplifier piston  34  with the amplifier piston  34  abutting against a shoulder  48  of the amplifier drive pin  40 .  
         [0017]     The stage separator plate  24  includes an inner diameter seal  50  engaging an inner diameter surface of the piston chamber  22  and an outer diameter seal  52  engaging an outer diameter surface of the piston chamber  22 . An inner diameter shoulder  54  and an outer diameter shoulder  56  are provided between the first chamber portion  22   a  and second chamber portion  22   b  with the stage separator plate  24  abutting against the inner diameter shoulder  54  and outer diameter shoulder  56 . The amplifier drive pins  40  extend through respective apertures  60  (best shown in  FIG. 3 ) provided through the stage separator plate  24  and include a drive pin seal  62  providing a sealed relationship between the stage separator plates  24  and movable amplifier drive pins  40 .  
         [0018]     A spring retainer plate  66  is provided between the first piston  26  and the clutch pack  16  and is secured in place by a retaining ring  68  which is received in a groove  70  provided in the first rotatable member  12 . A return spring assembly  72  is disposed between the first piston  26  and retainer plate  66  for applying a return force to the first piston  26 . The piston chamber  22  is provided with a first pressurized fluid inlet port  72  which communicates with an apply piston volume A and a second pressurized fluid supply inlet  74  in communication with a second amplifier plate piston volume B.  
         [0019]     During operation, pressurized fluid is applied to the apply piston volume A for applying pressure within the first chamber portion  24   a  against the apply piston  26 . Pressure is also introduced through the second inlet  74  to the amplifier plate piston volume B within the second chamber portion  22   b  for applying axial pressure on the amplifier piston  34 . The amplifier piston  34  acts against the shoulder  48  of the amplifier drive pins  40  which impart an additional axial force against the apply piston  26  for amplifying the apply pressure that is applied to the clutch pack  16  by the apply piston  26 .  
         [0020]     It should be understood by one of ordinary skill in the art that the supply of pressurized fluid to the first and second inlet ports  72 ,  74  can be selective so that hydraulic pressure can be applied to either apply chamber A, B, individually, or in combination to apply a range of apply pressures to the clutch pack  16 .  
         [0021]     It should be understood that the amplifier drive pins  40  can be provided as separate members or affixed to the first piston  26  so as to be movable therewith.  
         [0022]     With reference to  FIG. 4 , an alternative arrangement of the clutch piston amplifier assembly  80  will now be disclosed. As illustrated in  FIG. 4 , the piston amplifier assembly  80  is utilized for engaging a clutch pack  16  for engaging a first member  12  and a second member  14  in the same manner as described with reference to  FIG. 1 . Furthermore, the piston amplifier assembly  80  includes an apply piston chamber portion  82  and an amplifier piston chamber portion  84 . A stage separator plate  86  is provided between the apply chamber portion  82  and the amplifier chamber portion  84 . An apply piston  88  is disposed in the apply chamber portion  82  and includes an inner diameter seal  90  that engages a first axially extending portion  86   a  of the stage separator plate  86 . An outer diameter seal  92  is provided on an outer diameter portion of the piston  88  and engages an outer diameter surface of a second axially extending portion  86   b  of the stage separator plate  86 . The apply piston  88  includes an axially extending arm portion  88   a  which engages the clutch pack  16  for applying axial pressure thereto, in the same manner as apply piston  26  described with reference to  FIG. 1 .  
         [0023]     An amplifier piston  94  is provided in the amplifier chamber portion  84  and includes an outer diameter seal  96  which engages an outer diameter surface of the piston chamber  84  and an inner diameter seal  98  which engages an inner diameter surface of the amplifier piston chamber  84 . A plurality of amplifier drive pins  100  are provided in engagement with the apply piston  88  and the amplifier piston  94 . Similar to the embodiment in  FIG. 1 , preferably three or more amplifier drive pins  100  are provided equally spaced around the annular shaped piston chamber so as to have a first end  102  engaging the apply piston  88  and having a second end  104  engaging apertures  106  provided in the amplifier piston  94 . The amplifier drive pins  100  are provided with a through passage  108  extending therethrough so as to communicate pressurized fluid between the apply side of the amplifier piston  94  and the apply side of the apply piston  88  as illustrated by the force arrows therein. The first end  102  of the drive pins  100  are provided with grooves to allow radial flow of pressurized fluid from passage  108  into the apply chamber. The second end  104  of the drive pins  100  may be provided with similar grooves. With the communication passage  108  provided in the amplifier drive pins  100 , only a single fluid inlet port  110  is necessary for supplying pressurized fluid to both the piston chambers  82 ,  86 . In other words, by supplying pressurized fluid to the amplifier piston chamber  84 , the pressurized fluid travels through passage  108  of the amplifier pins  100  and enters the apply piston chamber  82 . The pressurized fluid acts on both the apply piston  88  and amplifier piston  94  with the stage separator plate  86  serving to isolate the pressurized fluid acting on the apply piston  88  from the amplifier piston chamber  84 .  
         [0024]     Additional seals  112  are provided between the amplifier drive pins  100  and the apertures in the stage separator plate  86 . A fluid return chamber is defined between the stage separator plate  86  and the amplifier piston  94 . The return chamber  114  is supplied with pressurized fluid via inlet passage  116  which can be provided with hydraulic fluid or pressurized gas for returning the amplifier piston  94  and apply piston  88  to a disengaged position. As an alternative as shown in  FIG. 5 , a return spring  118  can be utilized in place of the fluid return configuration shown in  FIG. 4  in order to return the apply piston  88  and amplifier piston  94  to the disengaged position.  
         [0025]     The clutch piston amplifier assembly of the present invention increases the apply forces that can be achieved with the clutch pack. This is done by increasing the working surface area of the piston assembly by stacking the piston stages. There is no need to increase the piston diameters or line pressure in order to achieve the increased apply forces. The system of the present invention allows use of higher apply forces with the same or lower hydraulic pressures. The present invention also allows the ability to tune the booster piston for desired apply forces. The use of the present invention also allows the possibility of smaller diameter pistons which would potentially increase the ground clearance of the transmission unit.  
         [0026]     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.