Abstract:
A replacement forward clutch control valve assembly including a primary control land, which is designed to properly align the valve piston within its mating bore in the valve body of an automatic translate is disclosed. The primary control land has a substantially increased axial length in comparison to the original equipment manufacture valve piston without exceeding the overall length of the original valve piston. The present forward clutch control valve assembly provides a substantially improved control land-to-bore surface contact ratio and also provides a more durable end surface area for contact with the retaining clip during operation. As a result the present forward clutch control valve assembly is substantially less prone to bending and/or seizure within its mating bore during operation.

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. 60/350,067 filed Jan. 23, 2002 entitled, Forward Clutch Control Valve. 
    
    
     BACKGROUND OF INVENTION 
     The present invention relates generally to the field of automatic transmission systems and, more particularly, to an improved forward clutch control valve assembly for use in Ford AX4N transmissions and other similar transmissions. 
     Automatic transmission systems of the prior art have a hydraulic circuit subsystem which includes at least a hydraulic pump, a valve body having fluid conducting passages or circuits, input and exhaust ports formed within the fluid circuits, and a plurality of spool valves so-called because of their resemblance to sewing-thread type spools. Such valves are comprised of generally cylindrical pistons having control diameters or lands formed thereon, which alternately open and close the ports to the fluid circuits to regulate the flow and pressure of automatic transmission fluid (hereinafter “ATF”) in order to charge the fluid circuits and actuate the hydraulic components of the transmission. It will be understood that in describing hydraulic circuits, ATF usually changes names when it passes through an orifice or control valve in a specific fluid circuit. 
     In the Ford AX4N automatic translate (hereinafter “Ford translate”), the forward clutch control valve regulates the flow of ATF from the pump to operate the forward clutch via the  1 - 2  shift valve circuit and the  3 - 4  shift valve circuit. The original equipment manufacture (hereinafter “OEM”) forward clutch control valve is an aluminum spool valve, which is configured with a pair of control lands interconnected by a valve stem and terminates in a narrow front valve stem whereon a compression spring resides. During operation the front valve stem typically strikes against a steel retaining clip that secures the valve within the valve body when the forward control valve is stroked. This striking action between the front valve stem and retaining clip causes the OEM valve to bend and eventually the valve can become seized in the bore causing a malfunction of the forward clutch. 
     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 forward clutch control valve assembly for the Ford AX4N translate and similar transaxles including a primary control land having an increased outside diameter and axial length, which replaces the narrow forward stem of the OEM valve piston. The increased axial length of the primary control land on the present valve piston is based on the limits of axial travel of the piston within the cylindrical bore wherein the valve piston resides during operation. 
     The present forward clutch control valve assembly provides a substantially increased control land-to-bore surface contact ratio and also provides an increased end face surface area for contact with the aforementioned steel retaining clip. As a result the present forward clutch control valve assembly is substantially less prone to bending and/or seizure within its mating bore during operation. 
     The present forward clutch control valve assembly is provided in kit form including a replacement compression spring, which is substituted for the OEM spring when the present forward clutch control valve assembly is installed. A bore-sizing tool is also provided to resize the mating bore in the valve body to retrofit the present valve to the Ford AX4N translate. 
     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 a perspective view of the OEM valve body component of a Ford AX4N translate labeled Prior Art and illustrating the components of the forward clutch control valve shown in exploded view; 
     FIG. 2 is a schematic representation of the forward clutch control valve being labeled Prior Art and showing the associated hydraulic circuits thereof; 
     FIG. 3 is a composite elevational view of the OEM forward clutch control valve being labeled Prior Art and showing an enlarged view of a damaged front valve stem thereof; 
     FIG. 4 is a perspective view of the OEM retaining clip labeled Prior Art shown in a damaged condition; 
     FIG. 5A is a cross-sectional view of the valve piston of the present Forward Clutch Control Valve Assembly; 
     FIG. 5B is a front elevational view of the retaining clip of the present valve assembly showing the relative contact positions (in phantom outline) of the OEM valve stem and the modified primary control land in relation to the retaining clip; 
     FIG. 6 is a cross-sectional view of the present Forward Clutch Control Valve Assembly shown in its functional position within the valve body; and 
     FIG. 7 is a bore-sizing tool in accordance with the present invention shown in its functional position within the valve body. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Prior to describing the present invention in detail it may be beneficial to briefly review the structure and function of the prior art forward clutch control valve of the Ford AX4N translate. With reference to the drawings there is shown therein a forward clutch control valve of the prior art, indicated generally at  100  and illustrated in FIG.  1 . The OEM valve  100  is shown in exploded view and removed from its functional position within a mating bore as at  105 , which is machined into the valve body, indicated generally at  110 , of the Ford AX4N translate. 
     In the prior art the forward clutch control valve  100  comprises a spool valve including a generally cylindrical valve piston, indicated generally at  102 , having a pair of control diameters  101  and  103 , a compression spring  104 , and a retaining clip  106 , which retains the forward clutch control valve within its mating bore  105  in the valve body  110 . 
     As shown in FIG. 2 fluid under line pressure in the pump circuit as at  112  passes through the forward clutch control valve  100  and enters the forward clutch control valve circuit (hereinafter “FCC circuit”) as at  115 . ATF under line pressure in the FCC circuit  115  applies the forward clutch as at  120 . This is accomplished when S 3  circuit pressure as at  125  is delivered to valve  100  through Shift Solenoid  3  (SS 3 ) as at  126  when the Power Control Module (PCM) (not shown) turns (SS 3 ) OFF, which opens the forward clutch control valve  100 . During the forward clutch apply ATF passes through the  3 - 4  shift valve, indicated generally at  130 , and also through the  1 - 2  shift valve, indicated generally at  140 , to the forward clutch  120 . 
     During each clutch apply cycle the forward clutch control valve  100  is stroked against the force of spring  104  (FIG. 1) by the flow of ATF from the S 3  circuit and the outwardly facing valve stem  102   a  typically strikes against the vertically disposed retaining clip  106  that secures the valve  102  and spring  104  within the valve body  110 . The aluminum OEM valve  100  striking against the steel retaining clip  106  eventually damages the valve stem  102   a  as most clearly shown in FIG.  3  and also the retaining clip  106  shown in FIG.  4 . This causes the position of the valve  102  to deviate from its normal axis of movement in the bore  105  and the stem  102   a  to be deflected laterally as it contacts the damaged clip  106  causing bending and/or seizure of the OEM valve  102  within the valve body. Thus, the present invention has been developed to provide a direct replacement for the OEM forward clutch control valve (hereinafter “FCC” valve assembly) and will now be described. 
     Referring to FIG. 5 there is shown therein a replacement FCC valve assembly in accordance with the present invention, indicated generally at  10 . The present FCC valve assembly  10  is also a spool valve comprised of a valve piston  12 , and a compression spring  14 , arranged coaxially for installation within the bore  105 . The valve piston  12  and the spring  14  are secured in position by an OEM retaining clip  106  (FIG. 1) in new condition. 
     In one embodiment the present valve piston  12  is fabricated from 6262-T8/T9 aluminum or 6061-T6 aluminum material. The valve piston  12  is coated with a hard anodized finish in accordance with MIL-A-8625, Type III, Class 2 to yield 0.02+/−0.01 (metric) build up per surface, which significantly reduces wear and increases service longevity. 
     The valve piston  12  also includes control diameters or lands, which function to regulate the flow of ATF within the FCC valve assembly  10  as shown in FIG.  5 . More particularly, valve piston  12  includes an S 3  land  16 , which is acted upon by fluid from the S 3  circuit as at  125  (FIG. 2) to control the position of the valve piston  12 . The S 3  land  16  is integrally connected by relief diameter  18  to the adjacent RL 12  land  20 , which controls line pressure in the RL 12  circuit as at  127  (FIG.  2 ). The RL 12  land  20  is integrally connected by valve stem  22  to the primary control land  24 , which has been substantially lengthened and further modified in comparison to the corresponding land  103  (FIG. 1) of the OEM valve piston  102 . 
     More particularly, it can be seen that the primary control land  24  of the present piston  12  has been increased in axial length as at dimension “X” (FIG. 5) to provide more than twice the control land-to-bore contact area previously achieved by the land  103  of the OEM valve piston  102  while maintaining the overall length of the OEM piston. The increased axial length of control land  24  is accommodated without modification of the OEM valve body  110  and is calculated based on the limits of axial travel of the piston  12  within the bore. 
     The increased outside diameter of the land  24  also provides a corresponding increase in the surface area of end face  24   a  for contact with the retaining clip  106  (as at  24   a ′ in FIG. 5B) in comparison with the OEM valve stem  102   a  (as at  102   a ′ in FIG.  5 B). This virtually eliminates the mechanical damage, which commonly occurs in the prior art valve piston  102  and retaining clip  106  illustrated in FIGS. 3-4. 
     The present valve piston  12  also provides structures comprising centering means including, but not limited to, the following structures. The increased axial length of the primary control land  24  permits the machining of a plurality of annular grooves  25  about the circumference of land  24 :as shown in FIG.  5 . In the embodiment shown three of such grooves  25  are formed to a predetermined depth at regular intervals. Annular grooves  25  function to distribute pressure across the surface of land  24  by filling with ATF during operation. ATF retained within the grooves  25  forms is distributed about the adjacent outer surface of the valve piston  12  thereby centering and supporting the valve piston  12  within the valve body  110  and virtually eliminating side loading (i.e. lateral movement) of the valve piston  12 , which substantially reduces friction and wear. Annular grooves  25  also f unction to collect dirt and other contaminants in the fluid, which are subsequently flushed from the valve chamber by the flow of ATF to prevent interference with the operation of the valve assembly  10 . 
     The present valve piston  12  also includes a counterbore  27  formed in coaxial relation to the lengthened control land  24  as shown in FIG.  5 . The counterbore  27  functions as a receptacle for compression spring  14  when installation is complete. 
     Compression spring  14  replaces the OEM spring  104 . In view of the dimensional changes to the valve piston  12 , the compression spring  14  is also modified to a shorter axial length and smaller outside diameter to fit within the counterbore  27 . Compression spring  14  is manufactured from a suitable material in accordance with commercial specifications to provide a predetermined spring rate and desired performance characteristics for this application. 
     In the at rest condition, the present FCC Valve  10  is spring-biased to the position illustrated in FIG.  6 A. In operation ATF is delivered to the present valve  10  through Shift Solenoid (SS 3 ) as at  126  via the S 3  circuit when the Power Control Module (PCM) turns the solenoid OFF initiating the clutch apply cycle. Shift Solenoid (SS 3 )  126  controls the position of the FCC valve  10  with one exception. This exception is when the SS 3  solenoid is ON and line pressure in the RL 12  circuit as at  127  moves the FCC valve  10  against spring pressure. 
     During each clutch apply cycle the FCC valve  10  is stroked against the force of spring  14  to the position shown in FIG. 6B by the flow of ATF via solenoid SS 3   126  to feed line pressure from the pump as at  112  into the FCC circuit as at  115 . During the forward clutch apply, ATF passes via the FCC circuit  115  through the  3 - 4  shift valve, indicated generally at  130 , and also through the  1 - 2  shift valve, indicated generally at  140  (FIG.  2 ). ATF under line pressure in the FCC circuit  115  applies the forward clutch. 
     In an installation procedure for the present FCC valve  10 , the OEM retaining clip  106  is initially removed and the OEM valve  100  and spring  104  are withdrawn from the valve body  110 . Next, to ensure that the present replacement valve  10  will function properly, the use of a bore-sizing tool  35  is recommended to remove any burrs and/or ridges in the bore  105  caused by a bent or seized OEM valve piston  102 . The bore-sizing tool  35  is reciprocated within the bore  105  mimicking the stroking action of the valve piston  12  in preparation for installation of the valve piston  12 . Next, the present valve piston  12  is lubricated and installed within the bore with spring  14  seated in counterbore  27 . Thereafter, the OEM retaining clip  106  is inserted into the valve body  110  (FIGS. 6A-6B) to secure the present FCC valve  10  in position. 
     It will be noted that using the present installation method to replace a worn OEM valve piston not only provides an increased spool-to-bore surface contact ratio as previously described, but also realigns the present valve piston  12  by positioning the primary control land  24  in an unused portion of the bore as at  107 , which retains its original surface. Thus, the present invention restores the forward clutch control valve in the Ford AX4N and other similar transmissions to factory performance standards and costly replacement of a damaged valve body is avoided. 
     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 forward clutch control valve assembly 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.