Abstract:
A solenoid valve is provided which includes a valve member, an armature for moving the valve member, an electro-magnetic coil for inducing movement of the armature. A coil spring is provided for engagement with the armature, the coil spring has at least a first end being generally cylindrical and a second end contacting the armature. A plug is provided threadably engaged with the spring first end along an adjustable length of the spring.

Description:
FIELD OF THE INVENTION 
     The present invention relates to solenoid valves, especially proportional solenoid valves and methods of adjustment thereof. 
     BACKGROUND OF THE INVENTION 
     When utilizing proportional hydraulic solenoid valves, especially when utilizing them in the environment of control of an automatic transmission, it is desirable that a spring rate of the compression spring, which positionally biases an armature of a control valve, be matched with the “spring rate” of the solenoid magnetic force such that the combination of the two spring rates cancel one another resulting in a uniform net force across a stroke range of a solenoid valve. The cancelling out of the spring rates provides a hydraulic solenoid valve design that regulates a control pressure independent of a supply pressure and temperature. The freedom of utilizing a solenoid valve as described above, in most applications is denied due to the manufacturing tolerances of the spring and the solenoid magnetic components. Matching of the spring rates is not precise enough to achieve the desired performance. It is desirable to provide an apparatus and a method supplying an ability to calibrate the rate of the compression spring. 
     Prior to the present invention, a compression spring load was often calibrated by pressing or screwing an adjustment component into another solenoid component to achieve a load upon the armature of the solenoid at a specific height. However, the adjustment components that adjusted the spring provided no means to adjust the rate of the compression spring. It is desirable to provide an apparatus and method of utilization thereof of adjusting the spring rate of a compression spring utilized in a proportional hydraulic control valve. 
     SUMMARY OF THE INVENTION 
     To make manifest the above noted and other desires, a revelation of the present invention is brought forth. In a preferred embodiment of the present invention, an adjustment plug is provided. The plug has a helical groove or thread. The groove is designed to have a pitch that closely matches that of the compression spring. The compression spring has at least one end that is left open (rather than “closed”) such that it can be threaded onto the helix of the adjustment plug. By twisting more of the coils into the helix, the number of the active coils is reduced and thus the spring rate of the adjusted spring is lowered. The adjustment sub assembly consisting of the adjustment plug and compression spring can be measured and adjusted so that the spring rate is precisely set prior to incorporation into a solenoid assembly. Once the above noted subassembly is added to the solenoid assembly, the plug can be pressed into a solenoid component (in most cases a pole piece) until the desired load and related performance (in most cases a “zero amp pressure”) is achieved. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of a preferred embodiment solenoid valve of the present invention; 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     Referring to  FIG. 1 , a normally high version of a control valve  7  of the present invention is presented. The control valve  7  has a solenoid portion  10 . The control valve  7  also has a hydraulic portion  12 . The hydraulic portion  12  has a valve sleeve  14 . The valve sleeve  14  can be fabricated from a number of suitable metals or polymeric materials, but in most instances, it is typically preferable to be fabricated from a die cast and machined aluminum. The valve sleeve  14  has a central spool bore  16 : The spool bore  16  has a central axis  18  which is co-terminus with an axis of a stem bore  20 . The valve stem  14  has a series of radial passages which intercept the spool bore  16 . Passage  22  is connected with a control pressure passage in a valve housing (not shown) encircling the valve spool  14 . The control pressure (Pc) is typically that of a clutch (not shown) in an automatic transmission. Radial inlet passage  24  via a housing passage (not shown) connects the spool bore  14  with a pressure supply source typically provided by a hydraulic pump (not shown). Passages  26  and  22  are juxtaposed by radial passage  24 . Radial passage  26  is connected with the control pressure via a housing passage (not shown). Radial passage  26  typically acts as an inlet for control pressure. Radial passage  22  typically acts as an outlet for control pressure. Radial outlet passage  28  via a housing passage  9  (not shown) is typically utilized to connect a hydraulic exhaust or sump  13  with the spool bore  16 . Adjacent to the control and exhaust pressure passages  22  and  28 , the bore  16  has two annular enlargements  30  and  32 . 
     Valve sleeve  14  at its extreme end has an axial opening which is plugged by a cap  34  which fits into an annular enlargement  36 . The annular enlargement  36  connected with an annular enlargement  38 . The annular enlargement  36 ,  38  along with the cap  34  form a lower feedback chamber  40 . The annular enlargement  38  is radially intersected by a radial orifice  42 . The ratio of the area of the orifice  42  to the volume of the feedback chamber  40  is small enough that the feedback chamber  40  provides a dampening function to movement of the valve spool  60 . 
     Towards an upper end of the spool bore  16 , the valve sleeve has an annular enlargement  44 . The annular enlargement  44  forms an upper feedback chamber. The upper feedback chamber  46  has a radial orifice  48 . The orifice  48  is typically larger than the orifice  42 . The radial orifice  48  is fluidly connected with a longitudinal slot  50  that extends along an outer radial surface of the valve sleeve  14 . Longitudinal slot  50  along its outer radial edge  52  contacts the housing  15 . The longitudinal slot  50  fluidly connects the lower feedback chamber  40  with the upper feedback chamber  46 . The longitudinal slot  50  is also fluidly connected with the valve spool bore  16  by a radial orifice  54 . 
     Slidably mounted within the valve spool bore  16  is valve member or spool  60 . Valve spool  60  has a lower landing  62 , a middle landing  64  and an upper landing  66 . Separating the landings  62  and  64  is a reduced diameter portion or shank  68 . Separating the landings  66  and  64  is a shank  70  which is additionally exposed to the radial orifice  54 . At the top of the spool  60  is a stem  72 . The spool  60  also has a series of balancing annular grooves  73 . The spool  60  in the configuration shown has a metered out configuration for supply pressure to control pressure and a metered out configuration for control pressure to exhaust. Movement of the valve spool  60  downward from the position shown in  FIG. 1  causes fluid adjacent the spool shank  68  to be metered out from the supply pressure to the control pressure and thereafter exit the control pressure outlet passage  22 . A top portion of the valve sleeve  14  spreads out into an annular yolk  76 . The annular yolk  76  is intersected by a radial side bore  78 . The solenoid portion  10  has a can or housing  80 . The housing  80  has a central top aperture  82 . The housing  80  is crimped to the yolk  76  of the valve sleeve and also has a side opening  84  to allow for a connection within an electrical connector  86 . Positioned within the housing  80  is an annular bobbin  88 . The bobbin  88  supports a coil bundle  90 . Inside the bobbin  88  is a flux tube  92 . The flux tube  92  along its upper portion has on its outer radial surface a longitudinal annular groove  94 . Supported on the groove  94  by an interferance fit is an alignment tube  96 . The alignment tube  96  is typically fabricated from a non-magnetic material like brass or stainless steel. The alignment tube positions an interference fitted pole piece  98 . The pole piece  98  has an annular groove for acceptance of the alignment tube  96 . The pole piece  98  has a central bore  100  that has its extreme end closed by a plug  102 . The plug  102  acts as a retainer for a biasing spring  104 . The biasing spring  104  positionally biases an armature  120  against the valve stem  72 . Positioned under the flux tube  92  is a ferro-magnetic flux washer  106 . When a housing peripheral portion  108  is crimped to the yolk  76  of the valve sleeve, the yolk  76  is in compression with the flux washer  106 , flux tube  92 , alignment tube  96 , pole piece  98  and the top cover portion  112  of the housing. When the coil  90  is energized, the flux loop includes the pole piece  98 , flux tube  92 , and flux washer  106  and the housing  80 . 
     The alignment tube  96  precisely locates the flux tube  92  to the pole piece  98 . Slidably mounted within the flux tube  92  is an armature  120 . The armature  120  outside diameter is plated or coated with a hard, low-friction, non-magnetic or semi-magnetic material such as nickel phosphorous or chrome in a thickness in approximately 50 micron. The plating or coating later serves a dual purpose of providing a hard, low friction bearing surface and maintaining a non-magnetic (or semi-magnetic) “air-gap”. The plated or coated armature outside diameter slides directly on the flux tube  92  inside diameter. The clearance between the armature  120  OD and the flux tube  92  ID is minimized to thus minimize the relative eccentricity of the tube components. By minimizing the relative eccentricity, magnetic slide-loading is also minimized which in turn minimizes friction and hysteresis. At the same time the magnetic return gap is also held to a very small distance (equal to the layer thickness; approximately 50 micron) so that solenoid efficiency is maximized. A non-magnetic washer  105  prevents the armature  120  from “locking” with the pole piece  98 . 
     A diaphragm  130  is located between the yolk  76  of the valve sleeve  14  and the solenoid portion  10  to prevent contaminated oil, typically found in automatic transmission fluid, from being transferred into the solenoid portion  10 . Typically the diaphragm  130  will be shaped such that volume displacement in the solenoid portion of the solenoid valve  7  will be minimized regardless of the position of the valve spool  60 . 
     As mentioned previously, the solenoid valve  7  is biased to be normally high. Therefore, in most situations, the spring  104  positions the armature  120  to position the valve spool  60  so that oil surrounding the annular groove  68  of the valve spool is being metered out from the supply inlet passage  24  to the control pressure outlet  22 . In a normal position, fluid exiting orifice  54  travels through slot  50  and then through orifice  42  to pressurize the feedback chamber  40 . The feedback chamber  40  acts against the full cross-sectional surface area of the valve spool along the surface  132  which is greater than the surface acted upon within the upper feedback chamber  46  due to the diameter of the stem  20 . Accordingly, there is upward biasing force acting upon the spool  60  which keeps the spool  60  in contact with the armature  120 . In an embodiment (not shown) the biasing force can be supplemented by a spring positioned within the chamber  40  pushing against the valve spool  60 . To reverse the position of the valve, the solenoid coil  90  is energized causing the armature  120  to be attracted against the force of the biasing of spring  104  to be attracted to the pole piece  98  thereby causing the fluid about the reduced diameter portion  70  to be metered out to the exhaust  28  when the fluid from the control pressure inlet  26  is connected therewith. When the fluid is flowing to the exhaust, the transient flow factors act upon the valve spool  60  in a direction to close, thus having a stability effect. 
     By using two feedback chambers  40  and  46  that act opposite of one another, the total volume of oil that is pumped in and out of the feedback chambers  40  and  46  is maximized. The larger feedback chamber  46  has an orifice  42  sized to balance damping for stability and cold response of the spool valve  60 . The size of orifice  42  can be customized for a given clutch or transmission. 
     The spring  104  has a first end  136 . The end  136  is generally cylindrical and is open. A second bottom end  138  of the spring  138  engagingly contacts the armature  120  to positionally bias the armature  120  against the valve spool  60 . The plug  102  on an outer diameter has a helical groove or thread  140 . The groove  140  is designed to have a pitch that closely matches that of the spring  104 . Accordingly, a bottom end  142  of the plug can be threaded into the first end  136  of the spring. By twisting more of the coils of spring  104  upon the plug  102 , the number of active coils is reduced with infinite variation within a specific range and thus, the spring rate is lowered. A sub-assembly of the plug  102  and spring  104  can be measured and adjusted so that the spring rate for the spring  104  is precisely set prior to assembling into the solenoid assembly through the central bore  100  of the pole piece  98 . 
     The plug  102  can be a polymeric or metal material or other suitable alternative. The axial location of the plug  102  within the central bore  100  of the pole piece also serves to set the preload of the spring  104  upon the armature  120 . The plug  102  is typically press fitted within the central bore  100  to set the aforementioned preload of the spring  104  upon the armature  120 . Additionally, since the plug  102  is deformable, its deformation properties can be utilized to deform about or crimp in place the spring  104  with respect to the plug  102  to prevent the spring from rotating over its operational life and therefore modifying the final adjusted spring rate by changing the amount of active coils that are in the spring. The crimping function can be accomplished as a result of the press fitting operation. It is desirable that the preload upon spring  104  and the setting of the spring load of the spring  104  be such that a specific “zero amp pressure state” is achieved. In the embodiment shown the solenoid valve is a normally “high pressure or on” type solenoid valve, however the present invention can be utilized in a normally “low pressure or off” type solenoid valve application. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.