Abstract:
A solenoid operated pressure control valve of the type using a spool valve member for controlling flow from a source inlet to a control outlet port and to an exhaust port. The solenoid has a reduced area portion of the flux collector in magnetic loop forming an annular air gap remote from the working air gap. The reduced flux across the annular air gap compensates for the rapid flux increase as the working air gap closes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     MICROFICHE APPENDIX 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     The present invention relates to solenoid operated valves employed for controlling flow of pressurized hydraulic fluid to actuators in an hydraulic system in response to an electrical control signal, such as provided by a microcomputer. Solenoid operated pressure control valves are employed in a variety of applications; one such application being for the control of shifting clutch actuators in an automatic transmissions for motor vehicles. 
     Heretofore, electrically operated pressure control valves for controlling the shifting in an automatic transmission for a motor vehicle have employed a valving member configured as a spool with cylindrical valving lands provided thereon for controlling flow of hydraulic fluid between an inlet and a control or signal outlet port with pressure control provided by bleeding fluid through an exhaust outlet port which returns the flow to the source or sump. 
     In providing such an electrically operated pressure control valve for motor vehicle automatic transmission shift control, problems have been encountered in obtaining adequate pressure control over a wide range of flow required to provide the necessary shift actuator movement because of the magnetic characteristics of the actuating solenoid. 
     For a given level of solenoid electrical energization, the magnetic force on a typical solenoid armature varies non-linearly with respect to armature movement. As the armature reduces the working air gap with the stationary pole piece or flux collector, the magnetic force tends to increase exponentially thereby giving the resultant response of the valve spool connected to the armature undesirable valving characteristics. The exponential increase in the magnetic force causes prohibitively rapid opening and closing of the respective ports for given port and spool land configurations and thus renders proper control of the hydraulic pressure in the actuating circuit extremely difficult. 
     Accordingly, it has long been desired to provide a solenoid operated pressure control valve for controlling the flow of hydraulic fluid in an actuating circuit which provides a relatively long armature stroke with substantially linear response for a given level of solenoid energization and provides generally linear or proportional pressure control over the operating range of coil energization. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention addresses the above described problem and provides a solenoid operated pressure control valve of the type having a spool moveable in a valve body for controlling flow from an inlet to an control or signal outlet port and to a bleed port for maintaining pressure control. The spool of the valving member in the present invention has a pair of spaced lands for controlling flow respectively to the control and exhaust port in response to spool movement by the solenoid armature. The solenoid is constructed to provide reduced magnetic flux at one end of the armature as the working air gap on a remote end of the armature is closed by a given level at coil energization. The flux is decreased at the one end of the armature by a reduced area portion of the flux collector which surrounds the distal end of the armature forming an annular air gap therebetween. The decrease in flux at the remote end of the armature results in a substantially linear force versus stroke characteristics for the solenoid upon coil energization at a given level. The resultant pressure at the control pressure outlet is thus generally proportionally changed with respect to changing coil energization. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the valve assembly of the present invention taken from the solenoid end; 
     FIG. 2 is a view similar to FIG. 1 taken from the valve body end; 
     FIG. 3 is a cross-section of the valve assembly of FIG. 1; 
     FIG. 4 is an exploded view of valve assembly of FIG. 1; 
     FIG. 5 is a portion of a cross-section similar to FIG. 3 showing the valve spool in a low flow position; 
     FIG. 6 is a view similar to FIG. 5 showing the valve spool in a high flow position; 
     FIG. 7 is a graph of flow pressure at the control outlet plotted as a function of coil currents; and, 
     FIG. 8 is a graph plotted of magnetic force on the armature as a function of armature stroke for a given level of coil current. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 through 4, the valve assembly of the present invention is indicated generally at  10  and includes a valve body  12  attached to a base or mounting flux collector  14  which has received thereover and attached thereto one end of an outer flux member configured as cylindrical shell  16  and which is registered against shoulder  18  provided on the flux collector  14 . Flux collector  14  has a reduced diameter annular portion  20  provided thereon and extending axially therefrom, the magnetic function of which will be hereinafter described. 
     Valve body  12  has a valving bore  22  formed therein into which is slidably received in closely fitting arrangement a spool member  24  having a pair of spaced cylindrical valving lands  26 ,  28  formed thereon which may be lapped into bore  22 , if desired to provide the desired close fit. 
     Outer shell  16  has its opposite end connected to a second flux collector member  30  and registered against a shoulder  32  provided thereon. A coiled bobbin  34  is disposed within shell  16  and between the flux collectors  14 ,  30  and has an electrical coil  36  wound thereon as shown in FIG.  3 . 
     Each of the flux collectors  14 ,  30  has a bearing respectively  38 ,  40  disposed therein; and, an operating rod  42  is slidably disposed in the bearings  38 ,  40 . Operating rod  42  has an armature  44  received thereover. Stop washer  46  acts as a magnetic spacer between armature  44  and pole piece  30 . A spring retainer  48  is received over the end of rod  42  and a spring  50  has one end registered against the retainer  48  with the opposite end registered against the undersurface of an adjustment plug  52  which is threadedly engaged in the flux collector  30 . 
     Armature  44  has the end adjacent flux collector  30  tapered as indicated by reference numeral  54 ; and, flux collector  30  has a correspondingly configured tapered recess  56  formed therein which tapers  54 ,  56  define a working air gap between armature  44  and flux collector  30 , a portion of which has an annular configuration. 
     In the present practice of the invention, it has been found satisfactory to taper the end  54  of the armature at an angle of twenty-two degrees (22°) to the coil axis. 
     Similarly, the inner periphery  54  of the reduced diameter portion  20  of flux collector  14  defines an annular air gap with the end of armature  44  distal the tapered end  54 . 
     In the embodiment of FIGS. 1 through 4, the valve body  12  has an inlet port comprising apertures  60  formed adjacent the free end thereof in a collector ring  62 ; and, spaced along bore  22  is a control or signal pressure outlet comprising apertures  64  formed in a collector ring  66 . Spaced further along bore  22  is an exhaust outlet comprising apertures  68 . The inlet apertures  60  are located at a station along bore  22  such that valve land  28  is operable upon movement to control the flow through apertures  60  entering the valving bore  22  in the region intermediate lands  28 ,  26 . 
     Valving land  26  is operative to control the bleed flow through exhaust apertures  68  from bore  22 . 
     As shown in dashed outline in FIG. 3, the exhaust port apertures  68  include a feathering notch denoted by reference numeral  72  to permit a small amount of hydraulic fluid to be exhausted upon initial opening of the exhaust port; and, conversely to prevent a sudden rapid close off of the exhaust port upon closing. 
     The valve spool  24  is retained in bore  22  by a spring  74  registering on one end thereof against a recess  76  formed in the end of land  28 ; and, at its opposite end the spring is retained by a cap  76  pressed in the end of valve body  12 . 
     A groove  78  is provided near the end of valve body  12  and has received therein a snap ring  80  which it will be understood is employed for retaining the valve body in a bore (not shown) in the hydraulic circuit of the device to be controlled. 
     Referring to FIG. 5, the spool  24  is shown in a low flow position where valving land  26  has only opened the feathering notch portion  72  of port  68 ; and, land  28  is positioned to permit only a small amount of flow through inlet port  60  to the bore  22 ; and, therefore the pressure in control port  64  is maintained at a low level. 
     Referring to FIG. 6, spool  24  is shown moved to a position where land  26  has closed the exhaust port  60 ; and, valving land  28  has substantially opened inlet port  60  allowing full flow to the control port  64 . 
     Referring to FIG. 7, the pressure piece P c  at the control outlet port  64  is plotted as a function of the coil excitation current I c ; and, it will be seen from FIG. 7 that the control pressure in port  64  increases generally proportional with respect to increasing coil current. 
     Referring to FIGS. 1,  2  and  4 , the flux collector  30  is shown has having a plurality of peripherally spaced cut-out formed therein which are disposed opposite corresponding cutouts  84  provided in cylindrical shell  16 . Flux collector  30  is adjustably rotatable in shell  16  to vary the location of the slots  82 ,  84  with respect to each other for adjusting the flux nodes created thereby for calibrating armature movement with respect to a given level of coil energization. 
     It will be understood, that as the armature is attracted to flux collector  30 , and the tapered portion  54  of armature  44  closes against the recess  56 , the magnetic flux across the tapered air gap increases generally exponentially. However, the reduced area portion  20  of flux collector  14  decreases the flux across the annular air gap at the end of armature  44  opposite taper  54  so as to compensate for the rapid increase in flux at the tapered end of the armature. 
     It will be understood that if so desired the tapered end of the armature may be alternatively reversed and attracted to the flux collector  14 ; and, if this alternate arrangement is employed, the tapered recess  56  will be provided in collector  14  if it is desired to reverse the movement of the armature with respect to coil energization for reverse valving movement of spool  24 . 
     Referring to FIG. 8, the effect of the decreased area of portion  20  of flux collector  14  is illustrated. The force characteristics of the solenoid as a function of armature stroke as shown in graphical representation; and, as illustrated are quite linear and have a sufficiently low slope as to be considered generally constant. The present invention thus permits a longer stroke of the armature for a given coil current and thereby provides for greater flexibility or higher resolution in controlling flow through the valve ports. 
     Although the invention has hereinabove been described with respect to the illustrated embodiments, it will be understood that the invention is capable of modification and variation and is limited only by the following claims.