Abstract:
A reverse boost valve assembly for installation within the hydraulic pump of an automatic transmission is disclosed. The present invention includes valve pistons that oscillate within close-tolerance mating valve sleeves to minimize hydraulic leakage. The present valve pistons are manufactured from aluminum material and are provided with a hard anodize coating, which produces a low coefficient of friction between the mating surfaces. The valve sleeves are provided with a compatible anodize coating or, in the alternative, are fabricated from highly wear-resistant aluminum material. The reverse boost valve assembly is provided in both standard volume and oversize embodiments, which are interchangeable to permit a predetermined rate of line pressure rise to be selected for a given transmission. The reverse boost valve assembly is also supplied with or without external O-ring seals, which function to prevent line pressure leakage at the interface of the valve sleeve and the hydraulic pump body.

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. 60/315,180 filed Aug. 27, 2001, entitled Reverse Boost Valve Assembly. 
    
    
     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 reverse boost valve assembly for a General Motors 4L60E (hereinafter “GM”) transmission that acts to increase hydraulic pump output as engine torque increases and to increase the operating range of line pressure in reverse gear. 
     Automatic transmission systems of the prior art have a hydraulic circuit subsystem which includes a hydraulic pump having fluid conducting passages or circuits, a valve body having fluid conducting circuits, input and exhaust ports formed within such fluid circuits, and a plurality of spool valves so-called because of their general resemblance to sewing-thread type spools. Such valves are comprised of 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”) within the fluid circuits to actuate different 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. 
     The reverse boost valve is a spool-type valve, which is disposed within a mating sleeve and is installed within the hydraulic pump of the transmission. The reverse boost valve functions in combination with the pressure regulator valve to increase line pressure as engine torque increases. It also functions to increase the operating range of line pressure when the transmission is in reverse gear. Torque signal fluid pressure (this fluid pressure is proportional to engine torque) moves the reverse boost valve piston against the isolator spring located in the hydraulic pump assembly. The isolator spring then transfers the force of the torque signal fluid pressure to the pressure regulator valve, which in turn raises line pressure. Thus, line pressure increases as throttle position and engine torque increase. Reverse input fluid pressure acting on the reverse boost valve also increases the operating range of line pressure when the transmission is in reverse gear. 
     Line pressure leakage can eventually develop due to the constant oscillation and mechanical wear of the original equipment manufacture (hereinafter “OEM”) reverse boost valve piston within its mating sleeve. When this occurs ATF that enters the torque signal orifice in the valve sleeve leaks past the valve piston and exhausts through the reverse input orifice resulting in poor line pressure rise causing clutch/band failure and/or poor shift quality. Similarly, fluid may leak past the valve piston in the opposite direction when fluid enters the valve chamber through the reverse input orifice in reverse gear and escapes via the torque signal orifice. 
     Thus, the present replacement reverse boost valve has been developed to provide a solution to these problems and other shortcomings of the prior art valve assembly. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides a replacement reverse boost valve assembly wherein the valve piston and mating valve sleeve are manufactured from a high quality aluminum material specifically designed to resist wear. In addition, a wear resistant, hard anodize coating is applied to the valve piston to provide a low coefficient of friction between the mating valve surfaces. The present reverse boost valve assembly is provided in both standard OEM (0.470″ spool diameters) and oversize (0.490″ spool diameters) with or without O-ring seals. The O-ring seals provide additional protection against leakage through the pump body and maintain pressure in the hydraulic circuits that supply the valve. The variable size spool diameters and optional seal configurations provide for interchangeability of these alternative embodiments in the hydraulic pump to provide an increased rate of line pressure rise for a particular transmission or vehicle use. 
    
    
     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 hydraulic pump wherein the present reverse boost valve assembly is utilized and being labeled Prior Art; 
     FIG. 2 is a schematic diagram of the hydraulic pump shown in FIG. 1 showing the internal components and circuits thereof and being labeled Prior Art; 
     FIG. 3A is a schematic diagram showing the hydraulic pump in a minimum output condition; 
     FIG. 3B is a schematic diagram showing the hydraulic pump in a maximum output condition; 
     FIG. 4 is a longitudinal cross-section of the reverse boost valve assembly of the present invention; 
     FIG. 5 is an elevational view of the valve piston of the present invention; and 
     FIG. 6 is a longitudinal cross-section of the one embodiment of the valve sleeve of the present invention including external O-ring grooves. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With further reference to the drawings there is shown therein a reverse boost valve of the prior art, indicated generally at  200 , and illustrated in FIG.  1 . The reverse boost valve  200  is shown in exploded view and removed from its functional position within a mating bore as at  205  which is machined into the hydraulic pump, indicated generally at  250 , of the GM transmission. It will be understood that the OEM reverse boost valve  200  operates in combination with the pressure regulator valve  216  and isolator spring  217  shown in FIG. 1, which do not form a part of the reverse boost valve assembly  200  for purposes of this application. 
     In the prior art the reverse boost valve assembly  200  comprises a spool valve including a modified, cylindrical piston  219  having a plurality of concentric diameters or spools, a compression spring  218 , and a valve sleeve  220 . The reverse boost valve assembly  200 , the pressure regulator valve  216 , and the isolator spring  217  are arranged coaxially and secured within the bore  205  of the pump assembly  250  by retaining ring  221 . 
     Referring to FIG. 2 there is shown a diagrammatic view of the hydraulic pump  250  wherein the OEM reverse boost valve  200  is located. In operation torque signal fluid pressure within the torque signal circuit as at  222  moves the reverse boost valve piston  219  against the isolator spring  217  located in the hydraulic pump assembly  250 . The isolator spring  217  then exerts the force received from the torque signal fluid circuit  222  onto the pressure regulator valve  216 . Thus, line pressure increases as throttle position and engine torque increase. When the transmission is in reverse gear, reverse input fluid pressure acting on the boost valve  200  via the reverse input circuit as at  224  increases the operating range of line pressure in reverse gear. 
     As shown in FIGS. 3A and 3B, the pressure regulator valve  216  routes pressure into both the converter feed circuit as at  230  and the decrease fluid circuit  235 . Converter feed fluid is routed to both the torque converter and cooler fluid circuits (not shown). Decrease fluid pressure as at  235  moves the pump slide  203  against the force of the pump slide springs (outer,  206  and inner,  207 ). Decrease fluid pressure and the position of the pump slide  203  constantly vary in relation to torque signal fluid pressure as at  222  and engine torque as controlled by the pressure regulator valve  216 . 
     Vehicles with the GM transmission frequently have poor line rise (i.e. insufficient increase in line pressure), which can result in 3-4 clutch failure, 2-4 band failure, and poor shift quality. These problems can be caused by the oscillating action of the boost valve piston  219 , which causes abrasion and mechanical wear on the inside diameter of the sleeve  220 . When this occurs, ATF that enters the OEM boost valve  200  via the torque signal circuit  222  leaks past the boost valve piston  219  and exhausts through the reverse input circuit  224  resulting in poor line rise. In addition, reverse input pressure at  224  can leak around the boost valve piston  219  and exhaust through the torque signal circuit  222  in the opposite direction when operating in reverse gear. 
     Further, in the OEM boost valve  200  leakage of line pressure occurs at the interface of the outside diameter of the metallic sleeve  220  and the mating bore  205  in the aluminum pump body (FIG.  1 ), which contributes to aforementioned insufficient line rise and shift quality problems. Thus, the present invention has been developed to provide a replacement reverse boost valve assembly to correct these problems and will now be described. 
     Referring to FIG. 4 there is shown therein a reverse boost valve assembly in accordance with the present invention, indicated generally at  10 . The present invention is designed as a direct replacement for the OEM reverse boost valve  200  that is standard equipment installed in the hydraulic pump  250  of the GM transmission provided on many General Motors vehicles. 
     The present reverse boost valve assembly  10  is a spool-type valve comprised of a valve piston, indicated generally at  12 , a cylindrical valve sleeve, indicated generally at  14 , and a compression spring  16 . In the embodiment shown the present reverse boost valve assembly  10  also includes O-ring seals  18 ,  20 , which function to prevent ATF leakage and line pressure depletion at the interface of sleeve  14  and bore  205  (FIG.  1 ). 
     FIG. 5 illustrates the valve piston  12  showing the structural features thereof in further detail. In the preferred embodiment the valve piston  12  is constructed of Aluminum Association (hereinafter “AA”) 6262-T8/T9, AA 6061-T6 aluminum, or other suitable material for this application. The valve piston  12  includes control diameters or spools  22 ,  24 , which function to regulate the flow of ATF within the valve. 
     More particularly, valve piston  12  includes a spring guide diameter  26  of sufficient size to support the compression spring  16  in the position shown. The terminal end  26   a  of the spring guide diameter  26  is chamfered to avoid entanglement with spring  16  during installation. An opposite end of spring guide diameter  26  is integrally connected to relief diameter  28  that, in turn, connects the spring guide diameter  26  with an adjacent first end face of spool  24 , which functions as a seating surface for spring  16 . A contoured stem  32  including the annular identification groove  30  formed thereon integrally connects the spool  24  to the adjacent EPC spool  22  on a first end face thereof. On the opposite end face the EPC spool  22  is integrally connected to a smaller stop diameter  34 , which limits the travel of the valve piston  12  within the sleeve  14 . 
     Compression spring  16  is manufactured from a suitable material such as steel wire in accordance with commercial specifications and calibrated to provide a specific spring rate and desired operating characteristics for a given valve application. 
     The valve piston  12  is coated with a hard anodized finish in accordance with MIL-A-8625, Type III, Class 2, to produce 0.02+/−0.01 millimeters build up per surface providing improved wear characteristics. 
     FIG. 6 illustrates the valve sleeve  14  showing its structural features in further detail. In one embodiment, among others, the valve sleeve  14  is constructed of AA 4032-T6/T651/T86 aluminum sold under the trademark, Deltalloy®, which includes a high percentage of silicon to provide exceptional resistance to abrasion and mechanical wear. In an alternative embodiment, the sleeve  14  is fabricated from AA 6061-T6 aluminum, which is subsequently hard anodized per MIL-A-8625, Type III, Class 2 to yield a build up of 0.02+/−0.01 millimeters per surface. Valve piston  12  and sleeve  14  are matched during the manufacturing process to provide a close-tolerance fit to facilitate rapid oscillation of the valve piston within the sleeve during operation. 
     The combination of either the hard anodize finish on both piston  12  and sleeve  14  or, in the alternative, the hard anodize finish on the piston  12  and the AA 4032-T6/T651/T86 (Deltalloy®) aluminum sleeve  14  (without anodization) provides a low coefficient of friction between the mating surfaces and, thus, increased lubricity and service longevity for the present valve. 
     Still referring to FIG. 6 sleeve  14  is comprised of a cylindrical body  40  including a primary bore  46  and a coaxial counterbore  48 . At least one torque signal orifice  44  is formed at the inner end  14 a of sleeve  14  in fluid communication with the torque signal circuit  222 . In one embodiment, among others, the torque signal orifice  44  is calibrated within the range of Ø0.037-0.041 inches to regulate ATF within the valve chamber  50  to the desired operating pressure. Similarly, at least one reverse input orifice  47  is formed at the juncture of bore  46  and counterbore  48  in fluid communication with the reverse input circuit  224 . In one embodiment, among others, the reverse input orifice  47  is calibrated within the range of Ø0.059-0.063 inches to regulate ATF pressure in reverse gear. If increased reaction time (i.e. faster line rise) is desired the orifices  44 ,  47  may be enlarged. 
     In the embodiment shown in FIG. 6, a pair of annular grooves  42 ,  43  are formed about the circumference of sleeve  14 , which receive O-ring seals  18 ,  20  respectively or other sealing rings that serve to prevent leakage of line pressure at the interface of sleeve  14  and the bore  205  within the pump. 
     Referring again to FIG. 4, the function of the replacement reverse boost valve assembly  10  will now be described. The present reverse boost valve assembly  10  is normally biased to the position shown in FIG. 4 by spring  16 , which permits the flow of ATF into the valve chamber  50  at line pressure through the torque signal orifice  44  as shown by directional arrows  60 . Torque signal fluid pressure moves the boost valve piston  12  (i.e. to the right in FIG. 4) against the OEM pressure regulator isolator spring  217 , which acts against the pressure regulator valve (FIG. 1) to generate a higher line pressure as described hereinabove in relation to FIGS. 3A and 3B. When the vehicle is in reverse gear, ATF also enters the valve chamber  50  through reverse input orifice  47  as shown by directional arrows  65  via the reverse input circuit  224  and strokes the valve piston  12  (i.e. to the right in FIG. 4) to boost line pressure. 
     The present reverse boost valve assembly  10  is provided in alternative embodiments in a kit format wherein the EPC spool  22  of valve piston  12  and mating bore  46  of sleeve  14  are available in both the OEM standard (0.470″ spool diameter) and also an oversize (0.490″ spool diameter). In addition, these alternative embodiments are available either with or without O-ring seals  18 ,  20  and their corresponding annular grooves  42 ,  43 . The variable size spool diameter and optional O-ring seal configuration provides a system for selective use of such alternative embodiments of the present reverse boost valve assembly  10  in a transmission to provide firmer shifts and/or faster line pressure rise to match a given vehicle use and/or driving application. 
     In an installation procedure for the present reverse boost valve  10 , the OEM valve assembly  200  is initially removed from the pump assembly  250  and discarded. Next, a valve kit of the desired standard or oversize configuration is selected for reassembly. Thereafter, the O-rings  18  and  20  are lubricated and installed in the annular grooves  42 ,  43  on the sleeve  14 , if applicable. Next, the valve piston  12  and spring  16  are carefully inserted into the mating sleeve  14 , which is lubricated and placed in engagement with the pressure regulator valve within the bore  205 , and secured with the OEM retaining clip  221  (FIG.  1 ). 
     Thus, it can be seen that the present invention provides a direct replacement reverse boost valve assembly  10  that is resistant to wear and reduces torque signal circuit leakage, which can result in clutch/band failure and poor shift quality. In addition, the close-tolerance fit within the mating valve sleeve  14  and the hard anodize finish applied to valve piston  12  increases service longevity. 
     The present reverse boost valve assembly  10  is provided in alternative embodiments in a kit format wherein the valve piston and mating sleeve are available in both the OEM standard (0.470″ spool diameter) and also an oversize (0.490″ spool diameter). Such alternative embodiments are available either with or without O-ring seals and their corresponding annular grooves. The variable size spool diameter and optional O-ring seal configuration provides for selective use and interchangeability of the present valve assembly in a given transmission to provide firmer shifts and/or faster line pressure rise to match a specific driving application. 
     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 AFL valve mechanism 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.