Abstract:
A direct acting solenoid actuator includes an armature and associated push pin that are suspended from certain fixed solenoid components, such as a pole piece and/or flux sleeve, by a fully floating cage of rolling elements. The fixed solenoid component may comprise a pole piece and/or a flux sleeve. The pole piece may include stops to limit movement of the cage of rolling elements in the axial direction.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of U.S. Patent Application No. 61/741,054 filed on Jul. 11, 2012, which is incorporated by reference as if fully set forth. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a direct acting electromagnetic solenoid actuator having an armature mechanism that drives a fluid control element. 
     BACKGROUND OF THE INVENTION 
     Direct acting solenoid actuators are often used to control fluid pressure in a variety of systems, including clutch mechanisms and other devices in an automobile. Direct acting solenoid actuators employ an armature mechanism that drives a fluid control element, such as a spool, a spring-biased four-way proportional flow control valve, a poppet valve and the like in various hydraulic control applications. Typically, the armature is connected to, and drives, a push pin that engages the fluid control element to this end. 
     A change in the electrical current supplied to the solenoid results in a change in fluid pressure. Ideally, a given input current corresponds to a single pressure, independent of whether the input current is increasing or decreasing. For example, consider a solenoid that is initially at high pressure (20 bars) at zero current. When a 0.5 Amp current is applied, the pressure drops to 12 bars. Ideally, if the current is increased to 1 Amp, and then decreased back down to 0.5 Amps, the pressure will again be 12 bars. Thus, a pressure value can be determined for each value of the current, independent of whether the current is increasing or decreasing. 
     In reality, a number of factors contribute to hysteresis in solenoid actuators. Hysteresis describes the difference in output for a given input when the input is increasing versus decreasing. In a direct acting solenoid actuator, friction between the armature and the armature sleeve, as well as debris in the hydraulic fluid surrounding the armature, may prevent the armature from sliding smoothly in response to the induced magnetic field. This may result in different values of pressure for a given current, depending on whether the current is increasing or decreasing. As such, the reliability of the actuator decreases, and the direction of the current (increasing or decreasing) must be taken into account when selecting a current for achieving a desired pressure. 
     Thus, there is a need for direct acting solenoid actuators that reduce or minimize hysteresis during operation while improving robustness to contamination in the form of foreign matter in the hydraulic fluid. 
     SUMMARY OF THE INVENTION 
     A direct acting solenoid actuator includes an armature and associated push pin member that are suspended from certain fixed solenoid components by a fully floating and independent cage of rolling elements, such as ball or radial bearings. The fixed solenoid component may comprise a pole piece and/or a flux sleeve. The pole piece may include stops to limit movement of the cage of rolling elements in the axial direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevation view of a fluid control valve having a direct acting solenoid actuator for driving a spool having a floating feedback piston in linear fashion pursuant to an illustrative embodiment of the invention. 
         FIG. 2  is a longitudinal cross-sectional view taken along line A-A of  FIG. 1 . 
         FIG. 3  shows a sectional view of the cage of rolling elements pursuant to an illustrative embodiment. 
         FIG. 4  shows a perspective view of the cage of rolling elements of  FIG. 3 . 
         FIG. 5  shows a sectional view of the cage of rolling elements having different radial bearing diameters pursuant to another illustrative embodiment. 
         FIG. 6  shows a perspective view of the cage of  FIG. 5  for the radial bearings. 
         FIG. 7  is an elevation view of a fluid control valve having a direct acting solenoid actuator for driving a spool having a floating feedback piston in linear fashion pursuant to another embodiment of the invention. 
         FIG. 8  is a longitudinal cross-sectional view taken along line A-A of  FIG. 7 . 
         FIG. 9  is an elevation view of a fluid control valve having a direct acting solenoid actuator for driving a spring biased fourway proportional flow control spool valve in linear fashion pursuant to another embodiment of the invention. 
         FIG. 10  is a longitudinal cross-sectional view taken along line A-A of  FIG. 9 . 
         FIG. 11  is an elevation view of a direct acting solenoid actuator for driving a spool (not shown), a threeway poppet valve (not shown), or other fluid control valve in relation to a commanded variable control pressure. 
         FIG. 12  is a longitudinal cross-section view taken along line A-A of  FIG. 11 . 
         FIG. 13  shows normally high pressure versus current achievable by the fluid control valve of  FIGS. 1 ,  2 ;  3 ,  4 ; and  5 ,  6 . 
         FIG. 14  shows normal low pressure versus current for the fluid control valve of  FIGS. 7 ,  8 ;  3 ,  4 ; and  5 ,  6 . 
         FIG. 15  shows flow versus current for the four-way fluid control valve of  FIGS. 9 ,  10 ;  3 ,  4 ; and  5 ,  6 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a direct acting solenoid actuator  100  is shown having electrical terminals  102  and a calibration cap  104 . A longitudinal cross-sectional view taken along line A-A of  FIG. 1  is shown in  FIG. 2 . 
     A fluid control valve  264  has a direct acting solenoid actuator  200  pursuant to an illustrative embodiment of the invention. The direct acting solenoid actuator  200  drives a spool  228  within a nozzle body  226  of the fluid control valve  264 . In one embodiment of the invention, the spool  228  includes a spool cap (floating feedback piston)  258 . The direct acting solenoid actuator  200  comprises a housing  206  containing a bobbin  210 , a coil  212  of wire wound on the bobbin  210  and connected to electrical terminals  202 . In one embodiment, the housing  206  comprises steel and the bobbin  210  is a synthetic material such as plastic, although those in the art would realize that other materials may be used. The coil  212  is contained between the outer part of the housing  206  and a flux sleeve  208 . A pole piece  214  is fixedly mounted on the end of the housing  206  with an armature stop  224  fixedly disposed in the inner bore of the pole piece  214 . A spacer  246  is provided on the end wall of the housing  206  to position the fluid control valve  264 . 
     As will be described hereinafter, a fully floating cage  220  of radial bearings  222  is disposed in the inner bore of the pole piece  214 , with the radial bearings  222  riding on the inner surface of the pole piece  214  and also riding on the outer surface of the push pin  218  (armature push member) associated with the armature  216 . The cage  220  is fully floating in the annular space between the pole piece  214  and the push pin  218  in that the cage  220  is not fixed in any plane and can move freely axially and radially in the annular space between the illustrated integral shoulder on the inner bore of the pole piece  214  and the armature stop  224 . This permits the movement of the armature  216  to be axially aligned relative to the pole piece  214  and the flux sleeve  208 . The push pin  218  is press fit or otherwise connected to the armature  216 , which is received in the flux sleeve  208  of the housing  206  such that the armature  216  and push pin  218  together move axially in response to current applied to the coil  212 . 
     Referring to  FIG. 3 , a cage  302  of radial bearings  304  is shown. The cage  302  may have a variety of shapes, not limited to that shown. The ratio of the diameter of the cage  302  with respect to the diameter of the radial bearings  304  may also be varied. The diameter of the cage  302  may be determined based on a particular direct acting solenoid actuator. For example, the cage  302  may be sized such that the radial bearings  304  ride on the inner surface of the pole piece  214  in  FIG. 2  and also ride on the outer surface of the push pin  218 . The cage  302  may be “thin” with respect to the diameter of the radial bearings  304 , thereby exposing a greater portion of the radial bearings  304 , or may surround the radial bearings  304  almost completely. In either case, a portion of the radial bearings  304  may be exposed, and may extend beyond the inner and outer diameter of the cage  302 . The cage  302  may house six radial bearings  304 , as shown  FIG. 3 , or may have greater or fewer radial bearings  304 . 
       FIG. 4  shows a perspective view of the cage  302  of radial bearings  304  shown in  FIG. 3 . Referring to  FIG. 4 , the cage  402  may comprise a top piece  406  and a bottom piece  408 . The top piece  406  and bottom piece  408  may be solid, covering the top and bottom of each radial bearing  404 , or may be open, such that a portion of the top and bottom of the radial bearings  404 , as well as the sides, are exposed. Alternatively, the cage  402  may comprise a single piece. The radial bearings  404  may be free to rotate in all directions within the cage  402 . Of course, those of skill in the art would realize that the function of the top and bottom pieces  406 ,  408  is to hold the radial bearings  404  in position relative to each other, although some amount of flexibility in the top and bottom pieces  406 ,  408  may be permitted. 
       FIG. 5  shows another embodiment of a cage  502  of radial bearings  504 . The cage  502  in this embodiment has a larger diameter with respect to the diameter of the radial bearings  504 .  FIG. 6  shows a side view of the cage  602  of radial bearings  604 . 
     In a conventional solenoid actuator, the armature push member is received with a tight fit into the pole piece. Referring back to  FIG. 2 , this would correspond to the push pin  218  being in full contact with the pole piece  214 , or in sliding contact with a bushing (not shown) which is received with a tight fit into the pole piece  214 . Changes in current applied to the coil  212  result in movement of the armature  216  and push pin  218 , causing the outer surface of the push pin  218  to slide against the inner surface of the pole piece  214  or bushing. If fluid carrying contaminants were to enter the area between the push pin  218  and the pole piece  214  or bushing, the contaminants may become lodged between the push pin  218  and the pole piece  214  or bushing, greatly increasing the friction between them, and altering the response of the fluid control valve  264  to a given applied current. This altered response contributes to hysteresis, reducing the reliability and/or repeatability of the fluid control valve  264  response to a particular current. Depending on the size and quantity of the contaminants, the performance of the fluid control valve  264  may degrade to the point of failure. If the area between the push pin  218  and the pole piece  214  were increased, the armature  216  and push pin  218  may become misaligned with the flux sleeve  208  and pole piece  214 , increasing the friction between the surfaces, and degrading the fluid control valve response. 
     In contrast, referring back to  FIG. 2 , the present invention comprises a cage  220  of radial bearings  222  that is positioned between the push pin  218  and the pole piece  214 . The cage  220  of radial bearings  222  allows for a space between the pole piece  214  and the push pin  218 . In the event that fluid carrying contaminants enters the space between the pole piece  214  and the push pin  218 , the likelihood that contaminants will become lodged between the push pin  218  and the pole piece  214  is greatly reduced due to the larger space. The solenoid is thus less susceptible to damage caused by contaminants in the fluid. The cage  220  of radial bearings  222  also serves to guide the axial motion of the push pin  218 , meanwhile reducing friction between the pole piece  214  and the push pin  218 . Instead of the pole piece  214  being in full contact with the push pin  218 , the pole piece  214  and push pin  218  are each now only in contact with the radial bearings  222 . These radial bearings  222  are free to move within the cage  220 , and thus allow the push pin  218  to move within the pole piece  214  with minimal resistance. It should be noted that although only one cage  220  is shown the particular location, several cages  220  may be utilized, and in different locations. 
     The reduced diameter end of the armature  216  is received with tight supporting fit on the adjacent end of the spool  228 . The nozzle body  226  includes supply port  234  defined between O-ring seals  238  and  240  and protected by filter  260 ; control port  232  defined between O-ring seals  236  and  238  and protected by filter  262 ; exhaust port  230 ; and end exhaust opening  256  in the nozzle cap  254 . The spool  228  is moved in response to movement of the armature  216  to regulate pressure at the control port  232 . 
     The outer end of the push pin  218 , and thus the armature  216 , is biased by a spring mechanism  244 .  FIG. 2  shows a conical coil spring, though other types of spring mechanisms may be used. The spring mechanism  244  is confined between a spring cap  242  and a calibration cap  204  that may be deformed to adjust spring preload that establishes the high pressure state of the control valve (shown in  FIG. 2  at 0 Amps; no current to coil  212 ). Thus, at 0 Amps, the supply port  234  is open to the control port  232 , defining the high pressure state. As the current applied to the coil  212  increases, the armature  216  and thus the spool  228  are displaced toward the spring mechanism  244 , resulting in a narrowing of the hydraulic pathway between the supply port  234  and the control port  232 . This causes the control pressure and thereby the hydraulic force to drop accordingly. 
     In one embodiment of the invention, the spool  228  includes a spool cap (floating feedback piston)  258  that communicates to a longitudinal spool bore  248  and radial spool bore  250  that is open to the control port  232  as shown in  FIG. 2 . The exterior of the spool cap  258  is exposed to exhaust or zero pressure in chamber  252 , while the interior of the spool cap  258  is exposed to control pressure as just described so that the spool cap  258  is axially and independently movable relative to the spool  228  and so that the pressure contained in the spool cap  258  acts on the spool  228  with a force that is directly proportional to the control pressure and the fluid-contacting area inside the spool cap  258 . The spool cap  258  in effect acts as a vessel to retain this pressure. This hydraulic force balances out the magnetic force on the armature  216 . 
     The spool cap  258  will be forced or moved axially against or abutting the nozzle cap  254  due to the hydraulic control pressure therein and will remain stationary, while the spool  228  moves to regulate control pressure as commanded. The spool cap  258  eliminates the need for the spool  228  and nozzle body  226  to have stepped diameters between each other to achieve equivalent differential feedback area as the spool cap  258  provides. 
     Referring to  FIG. 7 , a direct acting solenoid actuator  700  is shown having electrical terminals  702  and an armature end cap  704 . A longitudinal cross-sectional view taken along line A-A of  FIG. 7  is shown in  FIG. 8 . A fluid control valve  864  has a direct acting solenoid actuator  800  pursuant to another illustrative embodiment of the invention. The direct acting solenoid actuator  800  drives a spool  828  within a nozzle body  826  of the fluid control valve  864 . In one embodiment of the invention, the spool  828  includes a spool cap (floating feedback piston)  858 . The direct acting solenoid actuator  800  comprises a housing  806  containing a bobbin  810 , a coil  812  of wire wound on the bobbin  810  and connected to electrical terminals  802 . The coil  812  is contained between the outer part of the housing  806  and a flux sleeve  808 . A pole piece  814  is fixedly mounted on the end of the housing  806  with an armature stop  824  fixedly disposed in the inner bore of the pole piece  814 . A spacer  846  is provided on the end wall of the housing  806  to position the fluid control valve  864 . 
     A first fully floating cage  820  of radial bearings  822  is disposed in the inner bore of the pole piece  814 , with the radial bearings  822  riding on the inner surface of the pole piece  814  and also riding on an outer surface of the push pin  818  associated with the armature  816 . The cage  820  is fully floating in the annular space between the pole piece  814  and the push pin  818  in that the cage  820  is not fixed in any plane and can move freely axially and radially in the annular space between the illustrated integral shoulder on the inner bore of the pole piece  814  and the armature stop  824 . The push pin  818  is press fit or otherwise connected to armature  816 , which is received in the flux sleeve  808  of the housing  806 , such that the armature  816  and push pin  818  move axially in response to current applied to the coil  812 . 
     The outer end surface of the armature  816  is also received in a second fully floating cage  844  of radial bearings  842  residing in armature end cap  804 , which is fixed to the housing  806  with the radial bearings  842  riding on the outer end surface of the armature  816 . The second cage  844  is fully floating as described above in the annular space between the end of the housing  806  and the armature end cap  804 . 
     The normally low and normally high pressure states of the control valve shown in  FIG. 8  are established by externally commanded control current signals provided to the coil  812 . An optional spring (not shown) may be disposed between the nozzle cap  854  and the spool cap  858  if a calibration feature is desired. 
     The inner end of the push pin  818  engages the adjacent end of the spool  828 . The nozzle body  826  includes a supply port  834  between O-ring seals  838  and  840  and protected by filter  860 ; control port  832  between O-ring seals  836  and  838  and protected by filter  862 ; exhaust port  830 ; and exhaust opening  856  in nozzle cap  854 . The spool  828  is moved in response to movement of the armature  816  to regulate pressure at the control port  832 . 
     In one embodiment of the invention, the spool  828  includes a spool cap (floating feedback piston)  858  that communicates to a longitudinal spool bore  848  and radial spool bores  850  to the control port  832  as shown in  FIG. 8 . The exterior of the spool cap  858  is exposed to exhaust or zero pressure in chamber  852 , while the interior of the spool cap  858  is communicated to control pressure as described via bores  848 ,  850  so that the pressure contained in the spool cap  858  acts on the spool  828  with a force that is directly proportional to the pressure and area inside the spool cap  858 . This hydraulic force balances out the magnetic force on the armature  816 . The spool cap  858  will be forced or moved axially against and abutting the nozzle cap  854  due to the hydraulic control pressure therein and will remain stationary, while the spool  828  moves to regulate control pressure as commanded. 
     Referring to  FIG. 9 , a direct acting solenoid actuator  900  is shown having electrical terminals  902  and an armature end cap  904 . A longitudinal cross-sectional view taken along line A-A of  FIG. 9  is shown in  FIG. 10 . A fluid control valve  1056  is shown having a direct acting solenoid actuator  1000  pursuant to an embodiment of the invention. The direct acting solenoid actuator  100  drives a spring biased four-way proportional flow control spool  1028  in linear fashion. 
     The direct acting solenoid actuator  1000  comprises a housing  1006  containing a bobbin  1010 , and a coil  1012  of wire wound on the bobbin  1010  and connected to electrical terminals  1002 . The coil  1012  is contained between the outer part of the housing  1006  and a flux sleeve  1008 . A pole piece  1014  is fixedly mounted on the end of the housing  1006  with an armature stop  1024  fixedly disposed in the inner bore of the pole piece  1014 . A spacer  1054  is provided on the end wall of the housing  1006  to position the fluid control valve  1056 . 
     A first fully floating cage  1020  of radial bearings  1022  is disposed in the inner bore of the pole piece  1014 , with the radial bearings  1022  riding on the inner surface of the pole piece  1014  and also riding on an outer surface of the push pin  1018  associated with the armature  1016 . The cage  1020  is fully floating in the annular space between the pole piece  1014  and the push pin  1018  in that the cage  1020  is not fixed in any plane and can move freely axially and radially in the annular space between the illustrated integral shoulder on the inner bore of the pole piece  1014  and the armature stop  1024 . The push pin  1018  is press fit or otherwise connected to armature  1016 , which is received in the flux sleeve  1008  of the housing  1006 , such that the armature  1016  and push pin  1018  move axially in response to the current applied to the coil  1012 . 
     The outer end surface of the armature  1016  is also received in a second fully floating cage  1046  of radial bearings  1044  residing in the armature end cap  1004 , which is fixed to the housing  1006  with the radial bearings  1022  riding on the outer end surface of the armature  1016 . The second cage  1046  is fully floating as described above in the annular space between the end of the housing  1006  and the armature end cap  1004 . The push pin  1018  is press fit or otherwise connected to the armature  1016 . 
     The outer end of the spool  1028  is biased by a spring mechanism  1052 .  FIG. 10  shows a conical coil spring, though other types of spring mechanisms may be used. The spring mechanism  1052  is confined in an outermost end chamber of the nozzle body  1026 . The inner end of the push pin  1018  engages the adjacent end of the spool  1028 . The nozzle body  1026  includes first and second control ports  1032  defined between O-ring seals  1036  and  1038  and between O-ring seals  1040  and  1042  protected by filters  1050  and exhaust ports  1030  outboard of O-ring seals  1036  and  1042 , and a central supply port  1034  between O-ring seals  1038  and  1040  and protected by a filter  1050  as well. The spool  1028  is moved in response to armature  1016  movement to regulate pressure at the control ports  1032 . The spool  1028  is pressure balanced hydraulically so that the solenoid force is opposed by the spring mechanism  1052 . 
     Referring to  FIG. 11 , a direct acting solenoid actuator  1100  is shown having electrical terminals  1102  and a calibration cap  1104 . A longitudinal cross-sectional view taken along line A-A of  FIG. 1  is shown in  FIG. 12 . A direct acting solenoid actuator (motor)  1200  sans valve nozzle body may be used for driving a spool (not shown), a three-way poppet valve (not shown), or other fluid control valve in relation to a commanded variable control pressure. 
     The actuator  1200  of  FIG. 12  is similar to that shown in  FIG. 10 , with like numbers 00-24 corresponding to like elements. For example, the armature  1016  in  FIG. 10  is labeled  1216  in  FIG. 12 . A first fully floating cage  1220  of radial bearings  1222  is disposed in the inner bore of the pole piece  1214 , with the radial bearings  1222  riding on the inner surface of the pole piece  1214  and also riding on an outer surface of the push pin  1218  associated with the armature  1216 . The outer end surface of the armature  1216  is also received in a second fully floating cage  1226  of radial bearings  1228  residing in the armature end cap  1204 , which is fixed to the housing  1206  with the radial bearings  1228  riding on the outer end surface of the armature  1216 . The second cage  1226  is fully floating as described above in the annular space between the end of the housing  1206  and the armature end cap  1204 . This actuator  1200  would be supplied to a customer for integrating into the customer&#39;s valve or nozzle body for a particular fluid control valve. 
     The normally low and normally high pressure states of the control valve shown in  FIG. 12  are established by externally commanded control current signals provided to the wire coil  1202 . 
       FIG. 13  shows a hysteresis plot achievable by a normally high pressure at zero (0) coil current fluid control valve in  FIGS. 1 and 2 , described above. The two curves represent two current sweeps, in one case increasing current from 0 Amps to about 1 Amp (current in Amps on the horizontal axis), and in the other case decreasing current from about 1 Amp to 0 Amps. The minimal difference in pressure for a given current reflects the device&#39;s reduced friction and robustness to contaminants. 
       FIG. 14  shows a hysteresis plot achievable by a normally low pressure at zero (0) coil current fluid control valve such as the valve in  FIGS. 7 and 8 , described above. Like the previous plot, this plot reflects two current sweeps, one in which current in increasing, and one in which it is decreasing. In this case the hysteresis is sufficiently minimized that the two curves are indistinguishable. 
       FIG. 15  shows flow versus current for a four-way fluid control valve similar to that shown in  FIGS. 9 and 10 . As the current is increased from 0 Amps to about 0.8 Amps, the flow at one control port drops from 8 liters/minute to 0 liters/minute. As the current continues to increase from 0.8 Amps to 1.4 Amps, the flow at the other control port increases from 0 liters/min to 8 liters/min. The process then is reversed, creating the curves displayed in  FIG. 15 . 
     Although certain illustrative and/or preferred embodiments of the direct acting solenoid actuator and associated fluid control valves have been shown and described in detail, it should be understood that variations or modifications may be made without departing from the spirit or scope of the present invention.