Abstract:
A case cover for a continuously variable transmission includes a wall having a plurality of fastening elements thereon and at which a sheave assembly is rotatably mountable. The wall forms at least a portion of a cavity for containing at least a portion of the sheave assembly. Two surfaces define a slot that is configured to position and positively locate a portion of the bearing retainer to result in coarse alignment of bearing retainer fastening elements with the case cover fastening elements. The bearing retainer fastening elements are preferably protruding nuts, and the case cover fastening elements are preferably tapered holes configured to further align the nuts for engagement with threaded fasteners.

Description:
TECHNICAL FIELD  
       [0001]     This invention relates to continuously variable transmissions having a case cover defining a concavity in which a sheave assembly is rotatably mounted to the case cover, and a locating feature to provide alignment between fastening elements on the sheave assembly and fastening elements on the case cover.  
       BACKGROUND OF THE INVENTION  
       [0002]     Continuously variable transmissions (CVT) of the variable pulley or sheave type include an input sheave assembly and an output sheave assembly operatively interconnected by a flexible transmitter, such as a belt or chain. Each of the sheave assemblies has a piston in fluid communication with a pressurized fluid source, and is configured such that the distance from the sheave assembly&#39;s axis of rotation to where the flexible transmitter engages the sheave assembly is responsive to fluid pressure acting on the piston. Thus, the transmission ratio is varied by selectively changing the fluid pressure acting on each sheave assembly&#39;s piston.  
         [0003]     Each sheave assembly is rotatable about an axis; thus, fluid is supplied to each sheave assembly axially, i.e., along the sheave assembly&#39;s axis of rotation, from a fluid passageway connected to the pressurized fluid source. The sheave assemblies are at least partially contained in a transmission housing, or case, which is closed by a case cover.  
       SUMMARY OF THE INVENTION  
       [0004]     A case cover for a continuously variable transmission is provided. The continuously variable transmission includes a sheave assembly having a bearing retainer with a plurality of bearing retainer fastening elements thereon. The case cover includes a wall that at least partially defines a cavity sufficiently sized and shaped to contain a portion of the sheave assembly. A plurality of case cover fastening elements on the wall are engageable with the bearing retainer fastening elements to rotatably mount the sheave assembly to the case cover. The case cover also includes two surfaces defining a slot configured to contain a portion of the bearing retainer.  
         [0005]     The cavity has an open end for receiving the portion of the sheave assembly, and the slot has an open end for receiving the portion of the bearing retainer. The slot is sufficiently positioned and shaped such that the plurality of bearing retainer fastening elements substantially align with the plurality of case cover fastening elements when the portion of the bearing retainer is inserted sufficiently into the slot.  
         [0006]     In a preferred embodiment, the slot is tapered to facilitate the insertion of the portion of the bearing retainer into the slot. Preferably, the case cover fastening elements are holes formed in the wall, and the bearing retainer fastening elements are integral nuts that protrude from the surface of the bearing retainer. The holes are tapered such that they are widest in the direction of the cavity and thus further guide the integral nuts into position for engagement with threaded fasteners such as bolts.  
         [0007]     In a preferred embodiment, the case cover member is sufficiently sized and shaped so that the bearing retainer deforms when the nuts sufficiently engage the bolts, thereby resulting in a lateral force exerted by the nuts to lock the threads of the bolts.  
         [0008]     The invention facilitates one-piece construction of the case cover member because a transmission assembler can align the fastening elements of the bearing retainer and the case cover with ease when mounting the case cover to a transmission case, even if the cavity is deep and the fastening elements are inaccessible to the assembler&#39;s fingers. The one-piece construction facilitated by the present invention may result in reduced cost, a simpler design, improved durability, reduced mass, reduced transmission length, simpler manufacturing and assembly, increased cover member stiffness, and better belt and sheave alignment compared to the prior art. Furthermore, the invention may enable the elimination of some external pressurized seals found in prior art case covers. Improved bearing life may also be achieved compared to the prior art because a one-piece case cover member flexes in similar fashion at the input sheave bearing and the output sheave bearing.  
         [0009]     The above features and advantages, and other features and advantages, of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a schematic, partially exploded perspective view of a drive sheave assembly, a driven sheave assembly, and a case cover for a vehicular continuously variable transmission;  
         [0011]      FIG. 2  is a schematic perspective view of a portion of the case cover of  FIG. 1  that defines a cavity for containing at least a portion of the drive sheave assembly of  FIG. 1 ;  
         [0012]      FIG. 3  is a schematic perspective view of the case cover with the bearing and bearing retainer of the drive sheave assembly attached thereto; and  
         [0013]      FIG. 4  is another schematic perspective view of the case cover with the bearing and bearing retainer attached thereto. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]     Referring to  FIG. 1 , a drive sheave assembly  14  and a driven sheave assembly  18  of a continuously variable transmission (CVT)  20  are schematically depicted. The drive sheave assembly  14  is driven by an engine crankshaft (not shown) for rotation about axis A 1  via a transmission input shaft and clutch or torque converter. The driven sheave assembly  18  is rotatable about axis A 2  and is drivingly connected with vehicle drive wheels (not shown). The drive sheave assembly  14  and the driven sheave assembly  18  are interconnected by a flexible transmitter  22  such as a belt. The drive sheave assembly  14  is adjustable so that the distance from axis A 1  to where the flexible transmitter  22  engages the drive sheave assembly  14  is selectively adjustable. More specifically, the drive sheave assembly  14  is in fluid communication with a pressurized fluid source, such as a pump  26 . The drive sheave assembly  14  includes a first portion  30  and a second portion  32 . The first portion  30  is axially movable with respect to the second portion  32  in response to pressurized fluid  33  from the pump  26  thereby to alter the distance from the axis A 1  to where the flexible transmitter  22  engages the drive sheave assembly  14 .  
         [0015]     In a similar manner, the driven sheave assembly  18  is in fluid communication with the pump  26 . A first portion  34  of the driven sheave assembly  18  is axially movable with respect to a second portion  36  of the driven sheave assembly  18  in response to pressurized fluid  33  from the pump. Exemplary CVTs with adjustable pulleys are described in U.S. Pat. No. 4,539,866, issued Sep. 10, 1985 to Koivunen, and U.S. Pat. No. 6,287,227, issued Sep. 11, 2001 to Vahabzadeh et al, both of which are hereby incorporated by reference in their entireties.  
         [0016]     The drive sheave assembly  14  and the driven sheave assembly  18  are primarily contained within a transmission housing, or case (not shown). The case is closed off by a one-piece case cover member  40 . The case cover member  40  is preferably cast aluminum, and includes an attachment flange  42  with holes  43  therein at which the case cover member  40  is mountable to the transmission case with threaded fasteners (not shown). The case cover member  40  also includes conduits  44 ,  46  formed therein for supplying pressurized fluid from the pump  26  to the sheave assemblies  14 ,  18 . The conduits  44 ,  46  each include an inlet port (not shown) adjacent to the flange  42  for attachment to a corresponding outlet port on the transmission case to provide fluid communication between the pump  26  and the sheave assemblies  14 ,  18 . Routing of pressurized fluid from the pump to drive sheave assembly  14  is more fully described in a commonly assigned, concurrently filed U.S. patent application Ser. No. ______ entitled “Transmission Case Cover with Radial Inflow Channel” and having attorney docket number GP-303614, which is hereby incorporated by reference in its entirety.  
         [0017]     The sheave assemblies  14 ,  18  each include a bearing  50 A,  50 B and a stamped bearing retainer  54 A,  54 B for attachment to the case cover member  40  so that the case cover member rotatably supports the sheave assemblies  14 ,  18 . The bearing retainers  54 A,  54 B include bearing retainer fastening elements thereon, such as integral flange nuts  58 . The integral nuts  58  on each bearing retainer  54 A,  54 B have a predetermined spatial relationship with one another. The case cover member has case cover fastening elements thereon in the form of holes  66  in end wall  70 . One set of holes  66  is arranged in the same predetermined spatial relationship with one another as the nuts  58  on bearing retainer  54 A, and another set of holes  66  is arranged in the same predetermined spatial relationship with one another as the nuts  58  on bearing retainer  54 B. The nuts  58  are engageable with threaded fasteners  62  through the holes  66  to fasten the bearing retainers  54 A,  54 B to the case cover member  40 . Thus, the nuts  58  must align with the holes  66  during attachment of the case cover member  40  to the transmission housing. To achieve proper alignment, bearing retainers  54 A,  54 B are rotatable prior to being fastened to the case cover member  40 . The bearing retainers  54 A,  54 B are generally ring-shaped and are each characterized by a respective protrusion  74 A,  74 B that extends radially outward. Threaded fasteners  62  are preferably sealed bolts.  
         [0018]     When the case cover member  40  is operatively attached to the sheave assemblies  14 ,  18  and the transmission housing, the drive sheave assembly  14  is at least partially contained in a cavity  78  formed in the case cover member  40 . In the embodiment depicted, the cavity  78  is sufficiently deep and narrow such that a transmission assembler cannot view or access the nuts  58  when the sheave assembly  14  is inserted into the cavity  78  during attachment of case cover member  40  to the transmission case.  
         [0019]     Referring to  FIG. 2 , wherein like reference numbers refer to like components from  FIG. 1 , the cavity  78  is formed by end wall  70  and a generally cylindrical wall  80 . The case cover member  40  includes two surfaces  82  that are spaced a distance apart from one another and that form a slot  84  therebetween. The slot  84  is adjacent to the cavity  78 . The cavity  78  is open at one end  88  to receive the drive sheave. The slot  84  is open at one end  90  to receive at least a portion of the protrusion on the drive sheave&#39;s bearing retainer. The slot  84  is tapered so that its width is larger at the open end  90  than at a closed end  92 . The slot  84  is an as-cast feature of the case cover member  40 .  
         [0020]     End wall  70  includes a formation  94  with an annular case cover shoulder  96  for supporting the bearing of the drive sheave assembly and a generally annular surface  98  that partially defines and surrounds holes  66 . The formation  94  also partially defines a fluid chamber  100  into which conduit  46  supplies pressurized fluid through opening  102 .  
         [0021]     Referring to  FIG. 3 , wherein like reference numbers refer to like components from  FIGS. 1 and 2 , end portion  104  of the slot  84  is positioned and shaped so that when the bearing retainer protrusion  74 B is located therein, each nut  58  on bearing retainer  54 B is aligned with, and adjacent to, a corresponding hole  66 . More specifically, the width of the slot  84  is sufficiently small at the end portion  104  to prevent any rotation of the bearing retainer  54 B that results in misalignment of the nuts  58  and the holes  66 .  
         [0022]     Furthermore, the surfaces  82  act on the protrusion  74 B as the sheave assembly enters and travels through the cavity  78  during assembly of the case cover member to the case, thereby rotating the bearing retainer  54 B as necessary to ensure proper alignment of the holes and nuts. The slot  84  thus functions as a coarse alignment feature. The width of the slot  84  at end portion  104  is sufficiently wide to permit fine adjustment of the alignment of nuts  58  and holes  66  as described below in conjunction with  FIG. 4 .  
         [0023]     Only the bearing  50 B and the bearing retainer  54 B of drive sheave assembly  14  are shown in  FIG. 3 . An insert  108  is provided in the formation  94  between the sheave assembly  14  and the case cover member  40  for directing fluid from the conduit  46  and the chamber  100  to the sheave assembly.  
         [0024]     Referring to  FIG. 4 , wherein like reference numbers refer to like components from  FIGS. 1-3 , the race  112  of bearing  50 B contacts the case cover shoulder  96 . The race  112  includes a notch  116 , partially formed by race shoulder  120 , in which the inner diameter  124  of the bearing retainer  54 B is located. Surface  126  of the bearing retainer  54 B contacts race shoulder  120 . The race  112  and formation  94 , including shoulder  96  and surface  98 , are sufficiently dimensioned such that surface  120  of notch  116  is protuberant with respect to surface  98  when the race  112  contacts the shoulder  96 . Thus, race shoulder  120  maintains the bearing retainer  54 B, and more specifically bearing retainer surface  126 , a distance D from surface  98  such that there is a gap  130  between the bearing retainer  54 B and surface  98  prior to the bolts  62  being sufficiently tightened.  
         [0025]     Each of the holes  66  includes a tapered portion  128  wherein the hole diameter is largest at surface  98 . The tapered portion  128  is an as-cast feature of the case cover member  40 . A non-tapered portion  132  of each hole  66  is formed in a subsequent drilling operation.  
         [0026]     Each nut  58  has a segment  136  that protrudes from surface  126  of the bearing retainer  54 B. The diameter of each hole  66  at surface  98  is greater than the diameter of each segment  136 . Tapered portions  128  guide the nuts  58  for alignment with non-tapered portions  132  and for engagement with threaded fasteners  62  as the segments  136  are inserted into holes  66 . Tapered portions  128  thus function as fine alignment features.  
         [0027]     The bearing retainer  54 B includes a self-locking feature. More specifically, as the bolts  62  engage nuts  58  and are tightened, each bolt  62  exerts a force F B  on one of the nuts  58  and, correspondingly, the bearing retainer  54 B. The gap  130  allows the bearing retainer  54 B to deform as a result of force F B  such that the outer diameter  140  of the bearing retainer is drawn toward surface  98 , and as a result each nut  58  exerts a lateral force F N  against one of the bolts  62 . The deformed bearing retainer is shown schematically in phantom at  54 B′. In the context of the present invention, a “lateral force” exerted against a bolt is generally perpendicular to the bolt&#39;s axis. Preferably, the bearing retainer  54 B is sufficiently deformed during bolt engagement such that the outer diameter  140  contacts surface  98  and the bearing retainer  54 B is locked against the case cover member  40 . The nuts  58  are designed to provide two diameters of thread engagement.  
         [0028]     While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.