Abstract:
A replacement 1-2 shift valve for an automatic transmission, which restores a smooth shift from first to second gear thereby correcting a shudder shift or a complete failure to shift from first to second gear is disclosed. The present 1-2 shift valve comprises a valve piston including at least one bi-directionally tapered valve stem that changes the direction of transmission fluid flow within the valve such that a rebound force is generated which acts to propel the valve piston in an axial direction toward the second gear position of the valve. The piston lands which comprise the valve piston are provided with a plurality of annular grooves that function to retain transmission fluid and to center the valve piston in its mating bore to resist to side loading during operation. In addition, the present valve piston is provided with an anodized surface finish, which increases service longevity.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Patent Application No. 60/329,492 filed Oct. 5, 2001, entitled Improved 1-2 Shift Valve. 
    
    
     BACKGROUND OF INVENTION 
     The present invention relates generally to the field of hydraulic circuits utilized in automatic transmission systems and, more particularly, to a direct replacement valve mechanism for a 1-2 Shift Valve that regulates hydraulic fluid pressure within the valve body to affect proper shifting of the transmission from first to second gear. 
     Automatic transmission systems of the prior art have a hydraulic circuit sub-system 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 cylindrical pistons having a plurality of piston lands formed thereon, which alternately open and close the ports to regulate the flow and pressure of automatic transmission fluid (hereinafter “ATF”) within the hydraulic circuits to actuate different components of the transmission. It will be understood that in describing such hydraulic circuits, ATF usually changes names when it passes through an orifice or control valve in a specific circuit. 
     The so-called 1-2 Shift Valve regulates proper gear shifting from first to second gear in automatic transmissions such as the General Motors 4T60E transmission and other similar automatic transmissions made available on General Motors vehicles. The original equipment manufacture (hereinafter “OEM”) 1-2 Shift Valve on such transmissions is fabricated from a low grade aluminum material, which is subject to premature wear and scoring. Further, the OEM valve also has a large reaction area and is highly affected by side loading (i.e. vertical movement) caused by ATF entering the valve under pressure, which wears the mating bore prematurely. 
     As the wear increases the OEM valve tends to stick and/or eventually seize in the bore during its reciprocating movement from the first gear to the second gear position due to mechanical friction between the worn surfaces of the valve piston and the mating bore. This produces a characteristic shift problem in the General Motors 4T60E transmission wherein the second gear clutch slips or “shudders” and may completely prevent a shift to second gear. 
     Thus, the present invention has been developed to resolve this problem and other shortcomings of the prior art. 
     DESCRIPTION OF RELATED PRIOR ART 
     The theory of forces exerted upon a hydraulic piston by fluid flowing past it has been the subject of considerable scholarly study, which has been applied to practical valve piston construction in the prior art. One example of such a study appears in the article, “Contributions to Hydraulic Control” by Lee and Blackburn,  Transactions of the ASME , August, 1952, in which a theory is given of the origin of the steady-state force exerted upon a piston by fluid flowing past its corner. In this article reference is made to a considerable body of experimental evidence in support of that theory. 
     Another such example is disclosed in the article, “CFD Simulation of Steady-State Flow Forces on Spool-Type Hydraulic Valves” by Miller et al.,  Society of Automotive Engineers , 1999, which describes a new methodology for determining the steady-state flow force on a hydraulic flow valve. 
     However, these prior art references do not teach or suggest the combination of structural features and functional aspects of the present invention. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is a direct replacement 1-2 Shift Valve for the GM 4T60E transmission, which restores a smooth 1-2 gear shift thereby correcting the “shudder” shift or complete failure to shift from first to second gear, which is a common service complaint among owners of a vehicle with this transmission. 
     The present 1-2 Shift Valve includes at least one bi-directionally tapered valve stem having fluid deflecting and/or redirecting surfaces that change the direction of transmission fluid flow upon ingress of fluid into the valve such that a rebound force is generated by the fluid&#39;s impact with the defelecting surfaces, which acts to propel the valve piston in an axial direction to facilitate the shift from first to second gear. 
     In addition, the so-called spools or piston lands, which comprise the valve piston are provided with a plurality of annular grooves that function to retain a layer of ATF bout the circumference of the valve piston to buffer it against side loading (i.e. lateral movement) within the mating bore during operation. Further, the present valve piston is provided in an anodized aluminum finish, which reduces surface friction and increases service longevity. 
     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 of a General Motors 4T60E transmission labeled Prior Art showing the location of the 1-2 shift valve shown in exploded view; 
     FIG. 2 is a schematic diagram of the hydraulic fluid circuits within the valve body of the General Motors 4T60E transmission labeled Prior Art; 
     FIG. 3A is a partial section view of the OEM valve body labeled Prior Art showing the position of the OEM 1-2 shift valve in 1 st  gear with the Solenoid “A” in the ON state; 
     FIG. 3B is a partial section view of the OEM valve body labeled Prior Art showing the position of the OEM 1-2 shift valve in 2 nd  gear with the Solenoid “A” in the OFF state; 
     FIG. 4 is an elevational view of the 1-2 Shift Valve of the present invention showing details of the construction thereof; 
     FIG. 5 is an enlarged elevational view of the contoured valve stem showing further details thereof; 
     FIG. 6A is a partial section view of the OEM valve body showing the position of the present 1-2 Shift Valve in 1 st  gear with the Solenoid “A” in the ON state; and 
     FIG. 6B is a partial section of the OEM valve body showing the position of the present 1-2 Shift Valve in 2 nd  gear with the Solenoid “A” in the OFF state. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With further reference to the drawings there is shown therein a 1-2 shift valve of the Prior Art, indicated generally at  100 . The OEM 1-2 shift valve  100  is shown in exploded view and removed from its functional position within mating bore  105 , which is machined into the valve body, indicated generally at  110  of the General Motors 4T60E transmission (hereinafter “GM transmission”). 
     In the GM transmission 1-2 shift valve  100  is a spool-type valve including a generally cylindrical piston  102  having a plurality of concentric control diameters or spools and a compression spring  104  arranged coaxially for installation with the bore  105  as shown. The shift solenoid “A”  106 , a mating O-ring seal  108 , and retaining clip  109  are included in the 1-2 shift valve circuit and illustrated for reference purposes 
     More particularly, the shift solenoid “A”  106  is an ON/OFF type solenoid that receives its voltage supply through the ignition switch (not shown). The Powertrain Control Module (hereinafter “PCM”) controls the shift solenoid “A”  106  by providing a ground to energize it in: Park, Neutral, Overdrive Range, First gear, Fourth gear, and also Manual First gear. When energized, its corresponding exhaust port closes actuating the 1-2 shift valve  100  and allowing filtered line pressure to enter the solenoid “A” fluid circuit  222  (FIG.  2 ). When the PCM (not shown) removes the ground, the shift solenoid “A” is turned OFF allowing line pressure to exhaust through the solenoid “A” and the valve piston  102  returns to the rest position shown in FIG.  2 . 
     FIG. 2 shows the ATF circuits in the valve body  110  of the GM transmission schematically. It will be appreciated that the 1-2 shift valve  100  responds to solenoid “A”  106  ON-fluid pressure, to force from the compression spring  104 , and also to solenoid “B”  220  OFF-fluid pressure. Depending on the position of the 1-2 shift valve  100 , it will route Lo circuit fluid as at  216  into the Lo-1 st  fluid circuit at  218  or D-4 circuit fluid as at  112  into the 2 nd  gear fluid circuit at  214 . 
     As more clearly shown in FIG. 3A, solenoid “A” is in the ON state in 1 st  gear and the 1-2 shift valve  100  is stroked against the force of spring  104  blocking D-4 circuit pressure from entering the 2 nd gear clutch circuit at  214 . In second gear solenoid “A” is turned OFF and the valve  100  returns to the rest position shown in FIG. 3B allowing D-4 fluid pressure to apply the 2 nd  gear clutch. 
     This reciprocating movement of the valve  100  and its susceptibility to side loading causes characteristic wear spots on the O.D. surfaces of the spools as at  125  (FIG. 3A) and on the mating surfaces of the bore  105 . This results in scoring and/or eventual seizing of the valve piston  102  in the bore  105  on the return stroke to the rest position producing the socalled “shudder” shift problem and/or a complete failure to shift to second gear as described hereinabove. Thus, the present replacement 1-2 Shift Valve has been developed to solve this problem and will now be described. 
     Referring now to FIG. 4, there is shown therein a direct replacement 1-2 Shift Valve Assembly in accordance with the present invention, indicated generally at  10 . The present 1-2 Shift Valve Assembly  10  is also a spool-type valve mechanism comprised of a valve piston, indicated generally at  12 , and a compression spring  14  arranged as shown. In one embodiment the valve piston  12  is constructed of a high grade 6262-T8/T9 or 6061-T6 aluminum or other suitable material for this application. 
     The valve piston  12  is also provided with a hard anodized coating to yield 0.0008 +/−0.0004 inches build up per surface in accordance with MIL-A-8625, Type III, Class 2, for improved wear resistance and increased service longevity. 
     The present valve piston  12  is constructed with a plurality of so-called spools or piston lands, namely a primary spool  16 , a secondary spool  18 , and a tertiary spool  20  which function to regulate the flow of ATF within the fluid circuits of the valve body  110  (FIG.  2 ). The valve piston  12  also includes a spring guide diameter  22  of sufficient size to support the compression spring  14  in the position shown in FIG.  4 . The terminal end  22   a  of spring guide diameter  22  is chamfered to avoid entanglement with spring  14  during installation. An opposite end of spring guide diameter  22  is integrally connected to spool  20 , which functions as a seating surface for spring  14  on a first end face thereof. 
     Compression spring  14  is manufactured from a suitable material such as spring wire in accordance with commercial specifications to provide a specific spring rate and desired operating characteristics for this application. 
     Still referring to FIG. 4 it can be seen that primary and secondary spools  16 ,  18  respectively are provided with a plurality of annular grooves  30  formed about the circumference thereof to a predetermined depth. In one embodiment, among others, primary spool  16  includes a set of six grooves  30  formed thereon and secondary spool  18  includes a set of three grooves. The annular grooves  30  function to distribute fluid pressure across the circumference of spools  16 ,  18  by filling with ATF during operation thereby centering the valve piston  12  within the bore  105  and buffering it against side loading (i.e. lateral movement). The axial length of primary and secondary spools  16 ,  18  has also been increased in comparison to the OEM design to maximize the axial spacing of the grooves  30  to further stabilize the valve piston  12  during operation. 
     The present 1-2 Shift Valve  10  also incorporates features comprising fluid deflecting and/or redirecting means including, but not limited to, the following structures. As most clearly shown in FIG. 5, the valve piston  12  includes at least one bi-directionally tapered stem  32 , which integrally connects the secondary spool  18  to the adjacent tertiary spool  20 . Stem  32  includes a radius “R” formed at a predetermined axial distance “X” from an adjacent end face of tertiary spool  20  as shown. In one embodiment radius “R” is in the range of 0.090-0.100 inches. The radius “R” is blended with angled ramp segments  32   a ,  32   b , which are formed at predetermined angles “A” and “B” respectively to the longitudinal axis of the valve piston  12  as shown. In one embodiment, among others, angle “A” is in the range of 65-75 degrees and angle “B” is in the range of 20-30 degrees. 
     Stem  32  is configured in this manner to take advantage of the force of ATF under line pressure (105-125 psi) as it enters the valve chamber  50  from the D-4 fluid circuit  112  as illustrated in FIGS. 6A and 6B. More particularly, in first gear solenoid “A” is ON and the piston  12  is stroked to the position shown in FIG. 6A against the force of the spring  14  such that spool  18  is blocking the D-4 circuit  112 . When the shift to 2 nd  gear is commanded by the PCM, the solenoid “A” is turned OFF and the piston  12  begins the return stroke to the rest position shown in FIG.  6 B. 
     ATF entering the valve chamber  50  flows under line pressure over the ramp segment  32   a  and is deflected off the radius “R” of the stem  32  and changes direction flowing over the ramp segment  32   b  and relief diameter  32   c  into the 2 nd  gear circuit  214 . It will be appreciated that the rebound effect created by the impact of ATF being deflected off of the radius “R” and into the 2 nd  gear circuit  214  generates a reaction force “F” resultant from the change in ATF flow direction as indicated by directional arrow “F”, which is exerted on the valve piston  12 . This force “F” in combination with force of the released spring  14  propels the valve piston  12  axially toward the rest position as shown by directional arrow  55  in FIG.  6 B. 
     It will also be noted that relief diameter  32   c  provides less resistance to the flow of fluid into the 2 nd  gear circuit  214  by eliminating the end face of tertiary spool  20  at the juncture of the angled ramp segment  32   b  as most clearly shown in FIG.  5 . This improves the efficiency of the valve  10  during the shift to 2 nd  gear. 
     Thus, it can be seen that the present invention provides a direct replacement 1-2 Shift Valve  10  that is resistant to side loading and substantially reduces wear. Further, the bi-directional, tapered geometry of the contoured stem  32  takes advantage of the force of ATF flowing within the present valve  10  to provide a smoother, more efficient shift from first to second gear thereby eliminating the 1-2 “shudder” shift problem common to the 4T60E transmission. 
     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 1-2 Shift Valve 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.