Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a method for fabricating a regulator valve controlled by a direct acting solenoid located in a machined main control casting for an automatic transmission. 
     2. Description of the Prior Art 
     An automatic transmission includes a hydraulic system for regulating fluid pressure and hydraulic fluid flow in various lines connected to components of the transmission. The system includes a regulator spool valve packaged in a main control casting, which is machined at a transmission production plant. The casting, preferably of an aluminum alloy, is usually referred to as a valve body. The components of the system are assembled in the valve body. 
     A solenoid-actuated shift valve controls pressure communicated from the valve to a clutch or brake whose state of engagement and disengagement determines the gear in which the transmission operates. But the dimensional tolerance stack-up in most valve body castings is too large to permit use of a practical integrated electromagnet and achieve required flow and pressure regulation accuracy. 
     Transmissions with direct acting solenoids require a method to provide hydraulic pressure to clutches and brakes for high torque operating conditions such that the pressure can be delivered independently of the control pressure range suitable for shift control. 
     A need exists in the industry for a method for machining a valve in a valve body, such that the dimensions of certain features of the valve and the related tolerances are ultra-precise. Preferably the critical features, such as a groove and a face surface, are machined concurrently in a single operation with processing equipment that employs a minimum quantity lubrication machining process. 
     SUMMARY OF THE INVENTION 
     A method for forming a valve includes forming a valve body, machining a bore by passing a tool having cutting edges along an axis into the valve body, machining a groove and face in the bore at axially spaced locations by revolving the tool about a circular circumference whose center is aligned with the bore, and supplying lubricant in a pneumatic stream through the tool to the cutting edges. 
     The method machines several critical functional features simultaneously using a circular interpolation machining process. 
     All edges that requiring precise relative positions are cut in a single operation for improved tolerances and manufacturing efficiency. The metering edges  48 ,  49  are precision machined rather than cast for improved edge quality, location accuracy, and zero draft. High precision tolerances enable close control of hydraulic fluid leakage and pressure regulation accuracy. 
     The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
         FIG. 1  is a cross section through a diametric plane of a casting-integrated direct acting solenoid valve formed in a valve body; 
         FIG. 2  are schematic top and end views of a tool for machining valve of  FIG. 1 ; and 
         FIG. 3  is top view of the tool of  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The casting-integrated, direct acting solenoid hydraulic valve  10  shown in  FIG. 1  is formed in a valve body  12  formed of cast metal, preferably an aluminum alloy. The valve  10  includes a valve spool  14 , formed with lands  16 - 19 ; an adapter  22 ; an armature pin  24  extending through the adapter and contacting the spool  14 ; an electromagnetic solenoid  26 , which actuates the pin  24  to move leftward when the solenoid is energized and allows the spool to be axially displaced when the solenoid is deenergized. 
     The valve body  12  is formed with control ports  30 ,  42  through which control pressure communicates with the chamber  32  containing the spool  14 ; a line pressure port  34 , through which line pressure communicates with the chamber; sump port  36 , through which hydraulic fluid flows from the chamber to a low pressure sump; and an exhaust ports  38 ,  40 , through which the chamber  32  communicates with a low pressure source. 
     Adapter  22  is continually held in contact with an installation datum, i.e., a reference face surface  46  formed in sump port  36 . An elastic force produced by a resilient clip, secured to the outer surface of a housing that encloses the solenoid  26 , maintains adapter  22  in contact with the face surface  46  and establishes the correct axial position of the solenoid module  50 . The solenoid module  50  includes adapter  22 , solenoid  26 , housing  45  and spring  28 . 
       FIG. 1  shows that the diameters of control lands  17 ,  18 ,  19  are substantially identical yet larger than the diameter of land  16 . The lands  16 - 19  are machined in the bore  70 . The diameter of land  16  defines a large diameter spool end damper  60  for enhancing stability, permitting use of a relatively large diameter, contamination resistant damper port. Damper  60  is formed outside of the feedback path  64  for minimum feedback lag and improved stability. The diameter of damper  60  is large relative to the difference in diameter of the lands  16  and  17 . 
     The axial surface  64  of adapter  22  is located in chamber  32  due to contact with reference face surface  46  such that, when solenoid  26  is deenergized and spool  14  moves rightward in the chamber, land  19  contacts surface  64  before the armature pin  24  contacts a stop surface in the solenoid module. In this way, the spool end feature provides positive stop for forced over travel protection of the solenoid module  50 . 
     A single cutting tool  68 , shown in  FIGS. 2 and 3 , machines in the valve body  12  a groove  72  in bore  70 , which is concentric with the axis of bore  70 . Tool  68  concurrently machines in the valve body  12  (i) both of the metering edges  48 ,  49  at control port  30 , (ii) the radial groove  72  that connects edges  48 ,  49 , and (iii) the installation datum or reference face surface  46  at sump port  36 . Surfaces  74  are located at the radial outer side of the groove base  72   
     All edges that requiring precise relative positions are cut in a single operation for improved tolerances and manufacturing efficiency. The metering edges  48 ,  49  are precision machined rather than cast for improved edge quality, location accuracy, and zero draft. High precision tolerances enable close control of hydraulic fluid leakage and pressure regulation accuracy. Close tolerances enable flow control with a short stroke magnetic section  50 . 
     The cutting tool  68  is formed with a precision axially-directed shank  76 . A first supported cutting edge  78  extends radially from shank  76  and includes a cutting edge  80  for forming the groove  72  in valve body  12 , the groove being defined by the inner metering edge  48  and outer metering edge  49  at control port  30 . A second supported cutting edge  82  spaced axially from supported cutting edge  78  and extending radially from shank  76  includes a cutting edge  84  for forming the reference face surface  46  formed at sump port  34 . 
     All diameters and chamfers of the precision bore and other features of valve  10  are semi-finished with an existing standard cutting tool before using cutting tool  68 , or can be finished after the completed bore  70  has been finished machined. 
     The radial ports  30 ,  34 ,  36 ,  38 ,  40  and  42  are subsequently formed with another cutting tool. 
     Cutting tool  68  functions with lubricant carried in an axial passage  86  along the shank  76  and in radial passages  88 ,  90  along the supported cutting edges  78 ,  82  to the cutting edges  80 ,  84 , A pneumatic stream, preferably compressed air, carries the lubricant through the passages  86 ,  88 ,  90  to the cutting edges  80 ,  84  at a preferred flow rate in the range 10-200 ml per hour. The passages  88 , 90  shall be sized to achieve steady and equal amounts of flow from each outlet location. 
     Preferably the lubricant is CareCut™ ES 1 NA, a chlorine and heavy metal-free neat cutting oil commercially available from Castrol. 
     After the bore  70  is semi-finished or finished machined, the radial groove  72  that establishes edges  48 ,  49  and the installation datum or reference face surface  46  are machined in the bore by revolving the axis  92  of cutting tool  68  along a circular circumference  94 , whose center is aligned with the axis of bore  70  and whose radius is substantially equal to the radial distance between the radius of metering edges  48 ,  48  and the outer radius of supported cutting edge  80 . 
     In a previous or subsequent processing step the precision diameters and surfaces of the control body casting are finish machined using industry standard reamers. 
     In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.

Technology Category: 4