Abstract:
A pump drive shaft for an automatic transaxle wherein the cross-sectional profile of the internal flow tube has been modified to a non-cylindrical configuration to increase the flow of transmission fluid through the pump drive shaft from the torque converter. A selected surface of the non-cylindrical tube is positioned at a predetermined angular orientation within the pump drive shaft to provide increased radial clearance between the flow tube and the fluid inlets/outlets to increase the flow of transmission fluid from the torque converter. In various embodiments the flow tube is elliptical, rectangular, bi-lobular in cross-section or a variation thereof, which produces an axially extending fluid passage between the flow tube and the fluid inlets/outlets having an increased cross-sectional and flow capacity from the torque converter. The present disclosure also sets forth a method of installing the present internal flow tube within the pump drive shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 60/391,956 filed Jun. 27, 2002, entitled Pump Drive Shaft With Internal Flow Tube. 

   BACKGROUND OF INVENTION 
   The present invention relates generally to the field of automatic transmission hydraulic systems and, more particularly, to an improved pump shaft for the Ford AX4S, AXODE, and AXOD transaxles and other similar transmissions. 
   The Ford AX4S transaxle has a variable displacement pump that supplies fluid under pressure to the hydraulic system. In the Ford transaxle the torque converter cover assembly drives the impeller blades and rotates a pump drive shaft that operates the pump. It contains hydraulic fluid and provides a mating surface for the Torque Converter Clutch (TCC) piston and damper assembly. The turbine is driven by fluid from the impeller and transmits power to the chain drive and planetary gear sets. The reactor or stator component redirects fluid flow returned from the turbine to the impeller so that it rotates in the same direction as the impeller, which assists in torque multiplication. 
   The original equipment manufacture (hereinafter “OEM”) pump drive shaft includes fluid passages extending through the shaft and through an internal flow tube installed therein, which transmit automatic transmission fluid (hereinafter “ATF”) to the TCC piston to release the torque converter clutch. The internal ATF flow tube installed within the pump drive shaft defines an axial fluid passage between the flow tube and the pump shaft bore, which forms part of the turbine fluid circuit and carries ATF flow from the torque converter. 
   A problem in the Ford AX4S transaxle arises when this axial fluid passage becomes even partially restricted with particulate debris upsetting the balance of ATF flow through the torque converter. The lack of adequate ATF flow may cause delayed engagement, converter shudder, overheating, and lock up problems. Thus, the present invention has been developed to resolve this problem and other shortcomings of the prior art. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is a pump drive shaft wherein the cross-sectional profile of the internal flow tube has been modified to a non-cylindrical configuration to increase the flow of ATF through the pump drive shaft from the torque converter. In alternative embodiments the present flow tube is either elliptical, rectangular, or bi-lobular in cross-section (or variations thereof), which provides increased radial clearance between the outer diameter of the flow tube and the shaft bore. The flow tube is positioned at a predetermined angular orientation to the ATF inlets/outlets formed in the shaft to increase the cross-sectional area of the axial fluid passage. The present invention also discloses a method of installing the modified ATF flow tube within the pump drive shaft. 
   Further, dimensional changes to the annular seal grooves formed on the exterior of the shaft have been implemented to provide improved sealing of the Teflon® seals installed therein with the mating turbine shaft, which is radially disposed about the pump drive shaft. The seal grooves have been modified in both width and depth to provide better lift and sealing characteristics. 
   There has thus been outlined, rather broadly, the important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto. 
   Other features and technical advantages of the present invention will become apparent from a study of the following description and the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features of the present invention are set forth in the appended claims. The invention itself, however, as well as other features and advantages thereof will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures, wherein: 
       FIG. 1  is an exploded perspective view of the components of the torque converter assembly of the Ford AX4S transaxle showing the location of the pump drive shaft and is labeled Prior Art; 
       FIG. 2A  is a longitudinal cross-section of the internal flow tube that is installed within the pump drive shaft and is labeled Prior Art; 
       FIG. 2B  is a cross-sectional view taken along the section line  2 B— 2 B of  FIG. 1  showing the flow tube within the pump drive shaft and is labeled Prior Art; 
       FIG. 3A  is a longitudinal cross-section of the pump drive shaft of the present invention showing the orientation of the modified flow tube to the ATF inlet/outlet ports; 
       FIG. 3B  is a longitudinal cross-section of the pump drive shaft of  FIG. 3A  shown rotated 90 degrees axially from the position shown in  FIG. 3A ; 
       FIG. 4A  is a cross-sectional view of one embodiment of the present pump drive shaft showing the orientation of an elliptical flow tube; 
       FIG. 4B  is a cross-sectional view of another embodiment of the present pump drive shaft showing the orientation of a rectangular flow tube; 
       FIG. 4C  is a cross-sectional view of yet another embodiment of the present pump drive shaft showing the orientation of a bi-lobular flow tube; and 
       FIG. 5  is an enlarged partial cross-section of the present pump drive shaft. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With further reference to the drawings, there is shown therein an exploded view of the Ford AX4S transaxle torque converter wherein the present invention is utilized, indicated generally at  100  and illustrated in  FIG. 1 . The AX4S torque converter is a multi-element assembly containing an impeller and cover assembly, indicated generally at  105 , a turbine, indicated generally at  110 , a reactor assembly, indicated generally at  115  including a reactor thrust washer  116  and a one-way clutch assembly  117 , a Torque Converter Clutch (TCC) piston and damper assembly, indicated generally at  120 , and a front cover including TCC friction material, indicated generally at  125 . 
   The pump drive shaft, indicated generally at  150 , is disposed within the turbine shaft, indicated generally at  140 , in coaxial relation thereto. A forward end of pump shaft  150  engages the front cover  125 , which turns at engine speed. The rearward end of the shaft  150  engages and drives the hydraulic pump (not shown). 
   As shown in  FIG. 2A , the OEM pump shaft  150  is provided with an elongated, cylindrical flow tube, indicated generally at  160 , which is installed within the inside diameter (hereinafter “I.D.”) of the pump shaft  150  at a predetermined axial location. The flow tube  160  is a thin-walled, cylindrical construction, which is flared at a distal end  160   a  thereof and dimensioned at an opposite end  160   b  to provide an interference fit with the I.D. of the pump shaft  150 . Once installed, the flow tube  160  functions to transmit fluid pressure axially through the I.D.  162  ( FIG. 2B ) of the flow tube to release the TCC piston from the front cover  125  when converter lock up is not required. 
   In addition, the flow tube  160  also carries ATF away from the turbine  110  within the axially extending fluid passage as at  164  between the outside diameter (hereinafter “O.D.”) of the flow tube  160  and the inside diameter of the pump shaft  150  via ATF ports as at  152 . 
   A chronic problem in the Ford AXODE transaxle results from a partial restriction and/or blockage of ATF flow within the aforementioned passage  164 . In the OEM design this passage  164  is only 1 mm in depth when measured radially and is prone to the accumulation of particulate debris and ATF residue, which is a by-product of normal operation. Further, because the flow tube  150  is relatively difficult to remove and clean, it is often neglected by service technicians even during major transaxle service and overhaul. Thus, the present invention has been developed to resolve this problem and will now be described. 
   Referring to  FIGS. 3A and 3B  there is shown therein an improved pump drive shaft in accordance with the present invention, indicated generally at  10 . The pump shaft  10  is an elongated, cylindrical construction having a central bore  15  formed along the longitudinal axis thereof. The central bore  15  is formed in fluid communication with a plurality of ATF inlet/outlet ports  16 ,  17 ,  18 , and  19  extending through the shaft  10 , which deliver ATF to and carry ATF away from the torque converter. It will be appreciated that in the present shaft assembly  10 , the ATF ports  16 – 19  are machined to predetermined dimensions to accurately meter the flow of ATF based on the lubrication requirements of the assembled components. At its forward end the pump shaft  10  includes an external spline  20  for mating engagement with an internal spline formed in the front cover  125  of the torque converter. 
   A rearward end of the shaft  10  includes a crowned external spline  30  for mating engagement with an internal spline formed in the hydraulic pump (not shown). The crowned spline  30  is advantageous in that it allows limited radial movement of the shaft  10  during operation and reduces wear on the internal surfaces of the pump in comparison to the standard spline provided on the OEM shaft  150 . The rearward end of the shaft  10  also includes an end plug  35 , which is installed in the rearward end of the pump shaft  150  to maintain fluid pressure and to divert ATF flow to the release side of TCC piston via port  19 . 
   In one embodiment of the present shaft  10 , a non-cylindrical flow tube, indicated generally at  25 , is provided in which the body member  27  is elliptical in cross-section as most clearly shown in  FIG. 4A . The flow tube  25  is formed from steel tubing material and is formed into the generally elliptical shape illustrated using conventional sheet metal working equipment and techniques. Both the forward end  25   a  and the rearward end  25   b  of the flow tube  25  are flared to predetermined dimensions to provide an interference fit with the mating I.D. surfaces of the bore  15  to prevent leakage between the TCC release circuit as at  40  and that part of the turbine return circuit defined by the axial passage as at  45 . The direction of flow within these hydraulic circuits is indicated by directional arrows  29  ( FIG. 3B ). 
   Referring to  FIG. 4A  the flow tube  25  is angularly oriented within the shaft assembly  10  such that the greater longitudinal plane  26  (denoted by broken line) of the ellipse is positioned in perpendicular relation to the ATF inlet/outlet ports  17 ,  18  to provide increased radial clearance between the O.D. of the flow tube  25  and the bore  15  of the shaft as indicated by dimension “X” in  FIG. 4A . Thus, an increase in ATF flow between ATF ports  17 ,  18  is achieved on either side of the elliptical flow tube  25  corresponding to the increased radial clearance denoted by dimension “X”. 
   Still referring to  FIG. 4A  it will be noted that the radial clearance between the O.D. of the flow tube  25  and the ends of the ellipse (i.e. portions defined by the smallest radius) have been slightly decreased. However, flow testing of the present pump drive shaft  10  has demonstrated an overall increase in ATF flow between ATF inlet/outlet ports  17 ,  18  with no detrimental effects in the turbine return circuit  45  resulting from modification of the flow tube  25 . Further, the change in the cross-section of the present flow tube  25  to an elliptical shape has no appreciable effect on the flow of ATF through the interior of the flow tube  25 . 
   In an alternative embodiment shown in  FIG. 4B , a modified flow tube  25 ′, is provided in which the body  27  thereof is generally rectangular in cross-section defining a generally rectangular interior passage or circuit  40 ′. As in the embodiment shown in  FIG. 4A , the flow tube  25 ′ is angularly oriented within the shaft assembly  10 ′ such that the greater longitudinal plane  26 ′ (denoted by broken line) of the rectangle is positioned in perpendicular relation to the axis of the ATF inlet/outlet ports  17 ,  18  to provide increased radial clearance between the external sides of the rectangular flow tube  25 ′ and the bore  15  of the shaft as indicated by dimension “X” in  FIG. 4B . Thus, an increase in ATF flow between ATF ports  17 ,  18  is similarly achieved on either side of the rectangular flow tube  25 ′ corresponding with the increased radial clearance denoted by dimension “X”′. 
   In yet another alternative embodiment shown in  FIG. 4C , a modified flow tube  25 ″, is provided in which the body  27  thereof is a symmetrical, bi-lobular construction. More particularly, the body portion is configured (i.e. in cross-section) of vertically opposed, concave surfaces on the lateral sides and horizontally opposed, convex surfaces on the ends defining a bi-lobular passage or circuit  40 ″. As shown in the previous embodiments ( FIGS. 4A–4B ) the flow tube  25 ″ is angularly oriented within the shaft assembly  10 ″ such that the greater longitudinal plane  26 ″ (denoted by broken line) of the bi-lobular flow tube  25 ″ is positioned in perpendicular relation to the axes of the ATF inlet/outlet ports  17 ,  18  to provide increased radial clearance between the external surface of the flow tube  25 ″ and the bore  15  of the shaft as indicated by dimension “X”″ in  FIG. 4C . Thus, an increase in ATF flow between ATF ports  17 ,  18  is similarly achieved on either concave side of the bi-lobular flow tube  25 ″ corresponding with the increased radial clearance denoted by dimension “X”″. 
   It will be understood that other alternative constructions of the internal flow tube may be devised with minor variation of the aforementioned examples. Such alternative constructions are considered to be within the scope of the present invention. 
   In addition to the aforementioned improvements, the present pump drive shaft  10  also includes modifications to the annular seal grooves  41 ,  42 ,  43 ,  44  ( FIG. 5 ). More particularly, the present seal grooves  41 – 44  have been modified in both width and depth to provide better lift to the Teflon® seals  50  installed therein. The OEM seal grooves (not illustrated) have 0.035″ clearance between the sidewalls of the grooves and the Teflon® seals. Further, in the OEM design the O.D. of the shaft  10  on either side of the grooves  155  (i.e. groove lands) shown in  FIG. 1  can cause damage (i.e. galling) to the mating bores of the turbine shaft  140  in operation if the Teflon® seals do not lift properly or after the seals wear during operation. 
   In the present invention the clearance between the groove lands  55  ( FIG. 5 ) and the mating bores (not shown) of the turbine shaft  140  is designed to be greater than the clearance between the seal I.D. and the groove diameters. Thus, if the shaft  10  is forced to an eccentric position in relation to the turbine shaft  140 , the groove lands  55  are prevented from contacting and/or galling the bore. 
   In order to install or retrofit the present flow tube  25  or  25 ′ within the pump drive shaft, the end plug  35  and OEM flow tube  160  are initially removed. Next, a flow tube  25 ,  25 ′ or  25 ″ is rotated into position to obtain the desired angular orientation of the profile of the tube ( FIGS. 4A–4C ) to the fluid ports  17 ,  18 . It can be seen that the greater longitudinal plane (denoted by broken line) of the flow tube  25 ,  25 ′ or  25 ″ is preferably perpendicular to the axis of ports  17 ,  18 . A sealant such as Loctite® or other sealant may be applied to the flared ends of the flow tube  25  to ensure against leakage. Next, the replacement flow tube  25  or  25 ′ is pressed into the bore  15  from the rearward end of the pump shaft  10  to the position shown in  FIGS. 3A and 3B  using a suitable tool. Thereafter, the end plug  35  is installed in the forward end of the shaft  10  to complete the installation. 
   Although not specifically illustrated in the drawings, it should be understood that additional equipment and structural components will be provided as necessary and that all of the components described above are arranged and supported in an appropriate fashion to form a complete and operative Pump Drive Shaft with Internal Flow Tube incorporating features of the present invention. 
   Moreover, although illustrative embodiments of the invention have been described, a latitude of modification, change, and substitution is intended in the foregoing disclosure, and in certain instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of invention.