Abstract:
A solenoid operated valve has a valve body with a plurality of ports and a spool slideable within the valve body to interconnect the ports in different combinations. An actuator drives the spool into several operating positions. The actuator has a solenoid assembly with an armature that moves within a bore in response to an electromagnetic field. A push member projects from the armature and has a bearing secured thereto. The bearing has a cage that retains a plurality of rollable elements in slots separated by walls that are resilient enabling the rollable elements to be forced into the slots during assembly and thereafter be captured in the cage when the walls return to their original positions. A latch on the cage engages the push member to affix the bearing in place.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to electrically operated spool valves that control flow of a fluid, and more particularly to electrical actuators, such as solenoids, for operating those valves. 
     2. Description of the Related Art 
     A wide variety of machines have moveable members that are operated by an hydraulic actuator. For example an internal combustion engine has a camshaft which is mechanically coupled to rotate with the crankshaft and which opens and closed cylinder intake and exhaust valves. Traditionally the camshaft timing was fixed at a setting that produced the best operation at all engine operating speeds. However, it has been recognized that engine performance can be improved if the valve timing varies section as a function of engine speed, engine load, and other factors. Thus a hydraulic actuator is being used on some engines to vary the coupling relationship of the camshaft to the crankshaft and a solenoid operated valve is employed to control the application of pressurized fluid to operate the hydraulic actuator. 
     U.S. Pat. No. 7,007,925 discloses one type of solenoid operated valve that has been used to vary the timing of an internal combustion engine. A unique feature of this valve is that the armature assembly of the solenoid has a ball bearing which reduces resistance to movement of the armature. The armature assembly included the metal armature from which a push pin projected to engage and move a flow control spool of the valve. The ball bearing comprised a cylindrical cage that held a plurality of balls inserted through openings in one end of the cage. The cage was slid over the push pin until the openings were against the armature to retain the balls and then the cage was secured to the push member by a push-on nut. When the solenoid is assembled the armature assembly moved within a bore and the balls rolled along the surface of the bore. Although the ball bearing worked very well, it added complexity to the valve assembly process. 
     Therefore, it is desirable to refine the design of this type of solenoid operated valve to facilitate manufacturing. 
     SUMMARY OF THE INVENTION 
     An electrohydraulic valve comprises a body with a longitudinal bore into which an inlet port, an outlet port, and one or more workports communicate. A spool is slideably received within the bore and has passages that selectively connect the inlet port and the outlet port to the workports in different positions of the spool in the bore. 
     The spool is moved within the bore by an electrically operated actuator, that includes a solenoid coil assembly which has a coil aperture in which an armature is slideably located. A push member extends from the armature and abuts the spool. A bearing is secured to push member to minimize resistance of the armature to motion. The bearing includes a cage that holds a plurality of rollable elements, such as spheres for example. The cage is a single piece that comprises a plurality of walls extending between spaced apart first and second rings and forming a plurality of slots between adjacent walls. It is preferred that the walls are resilient enabling the rollable elements to be forced there between and into the plurality of slots during assembly of the actuator and thereafter the walls return to their original position to capture the plurality of rollable elements in the cage. 
     In a preferred embodiment the cage includes a latch that engages at least one of the push member and the armature to fasten the cage in a fixed position along the push member. For example, the latch comprises an L-shaped finger that projects outward from the main part of the cage and a leg of the L is received in a groove in the push member. 
     In that preferred embodiment, the actuator has a first pole piece with a tubular section extending into one end of the coil aperture. A second pole piece has a tubular section that extends into another end of the coil aperture. The armature slides within the first and second pole pieces in response to a magnetic field produced by the solenoid coil. A housing, which encloses the first and second pole pieces and the coil, is staked to retain the solenoid coil assembly and is secured to the valve body by a crimped connection. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal cross section view through an electrohydraulic valve according the present invention; 
         FIG. 2  is an isometric view of an actuator plunger in the valve; 
         FIG. 3  shows one end of a cage that is part of the actuator plunger; 
         FIG. 4  is an isometric view of the cage; 
         FIG. 5  is a plan view of another end of the cage; 
         FIG. 6  is a cross sectional view taken along line  6 - 6  in  FIG. 2 ; 
         FIG. 7  illustrates a filter used in the electrohydraulic valve; 
         FIG. 8  shows the filter bent into a closed band as occurs upon being mounted on the electrohydraulic valve; and 
         FIG. 9  illustrates another embodiment of a filter. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , an electrohydraulic control valve  20  has a tubular valve body  21  that during use is inserted into an aperture  22  in a manifold  24 . The tubular valve body  21  has a longitudinal bore  42  into which a plurality of ports open. A supply passage  26  in the manifold  24  conveys pressurized fluid from a pump and a return passage  25  conveys fluid back to a tank of the hydraulic system in which the valve is incorporated. The supply passage  26  opens into an inlet port  28  of the control valve  20  and the return passage  25  at the end of the manifold aperture  22  communicates with an outlet port  27  of the valve. The inlet port  28  includes a first annular recesses  29  which is formed in an exterior curve surface  23  of the valve body  21 . First and second workports  30  and  32  in the tubular valve body  21  communicate with passages  34  and  36  that lead to a hydraulic actuator being controlled. The first and second workports  30  and  32  include annular recesses  31  and  33  respectively which are formed in the exterior curve surface of the valve body  21 . 
     A spool  44  is slideably received within the bore  42  of the valve body  21  and has an exterior annular notch  46  which, in selective positions of the spool, provides a fluid passage between the inlet port  28  and one of the two workports  30  and  32  and thus between the associated manifold passages. In a middle, or intermediate, position of the spool travel as depicted in  FIG. 1 , the inlet port  28  is closed from both workports  30  and  32 . A central passage  48  extends between the opposite ends  47  and  49  of the spool  44 . A head  54  projects from the outward end  49  of the valve spool  44  and has an aperture  53  there through. A spring  50  biases the spool  44  away from a nose piece  52  at the end of the valve body  21  at which the outlet port  27  is located. 
     Three filters  100  are wrapped around the valve body  21  to form cylindrical bands that cover the inlet port  28  and the two workports  30  and  32 . With specific reference to  FIG. 7 , each filter  100  is formed from a thin, flat rectangular plate  102  with a plurality of perforations  104  between the two major surfaces of the plate. For example, a standard photolithographic etching process can be employed to form perforations of a size small enough to prevent undesirable particles from entering and adversely affecting operation of the valve. A rectangular slot  106  is formed in a first end section  105  of the plate  102  and a pair of opposing U-shaped apertures are produced at the second end section  107  to form two tabs  108 . Although the exemplary slot  106  is spaced from the edge of the plate  102 , as an alternative the slot could be formed as a notch in the end edge of the plate. 
     To install a band-shaped filter  100 , the two tabs  108  are first bent perpendicular to the plate  102 . Then the second end section  107  of the plate  102  is placed against the valve body  21  with the tabs  108  projecting outward. The rectangular plate  102  is wrapped around the valve body  21  in a recess  29 ,  31  or  33  associated with one of the ports  28 ,  30  or  32 . The first end section  105  of the plate  102  overlaps the second end section  107  with the tabs extending through the rectangular slot  106 . The tabs  108  are then bent against the surface of the first end section  105  to secure the plate in an annular band as illustrated in  FIG. 8 . 
       FIG. 9  shows an alternative plate  110  for the band-shaped filter  100 . This plate  110  has a similar pattern of perforations  112 . A rectangular slot  114  is formed near one end section of this plate and a single U-shaped aperture is produced in the other end section with the opening of the U facing that end of the plate  110 . This U-shaped aperture defines a relatively large rectangular tab  116 . When the plate  110  is wrapped around the valve body  21  with overlapping end section, the tab  116  is bent to project through the rectangular slot  114  and is bent further against the surface of the plate  110  to secure the plate in an annular band. 
     Referring again to  FIG. 1 , the valve  20  also includes a linear actuator  51  with a metal outer housing  55  that surrounds a solenoid coil  58  in a non-magnetic bobbin  60 , preferably made of plastic molded around the coil. As used herein, “non-magnetic” designates an object as being neither attracted to or repelled by a magnetic field. The solenoid coil  58  is driven by a pulse width modulated (PWM) electrical signal having a duty cycle that is varied in a conventional manner to move the spool  44  to different desired positions in the valve body  21 . The PWM signal is applied to the linear actuator  51  via a connector  57  formed in a lateral projection of the bobbin  60  and connected by wires to the solenoid coil  58 . 
     The linear actuator  51  further includes two magnetically conductive pole pieces  64  and  66 . The first pole piece  64  has a interior, tubular section  65  that extends into one end of the bobbin  60 . An O-ring  67  provides a hermetic seal between the first pole piece  64  and the bobbin  60 . The first pole piece  64  has a first flange  68  which projects outwardly from the tubular section  65  across the outer end of the valve body  21 . The second pole piece  66  has a second tubular section extending into the opposite end of the bobbin  60  and has an interior end that is spaced from the first pole piece  64 . An inwardly projecting annular rib  63  of the bobbin magnetically separates the first and second pole pieces  64  and  66 . The outer end of the second pole piece  66  has a second flange  71  projecting outwardly and another O-ring  75  provides a hermetic seal between this flange and the bobbin  60 . The solenoid coil  58 , the bobbin  60 , and the first and second pole pieces  64  and  66  the form a solenoid coil assembly  56 . 
     The primary components of the solenoid coil assembly  56  are inserted through the wider open end  69  of the outer housing  55  until abutting an inwardly projecting flange  74  at the opposite end of the housing and secured in that position by stakes  61  that then are formed in the housing. The solenoid coil assembly  56  also comprises a liner tube  62 , preferably of stainless steel, is inserted through the opposite housing end into the first and second pole pieces  64  and  66 . The liner tube  62  provides a magnetic barrier between the pole pieces, as well as acting as a guide for a sliding actuator plunger  70 . An open end of the liner tube  62  faces the valve body  21  and a closed end is adjacent the outwardly projecting flange  71  of the second pole piece  66 . 
     A disk  72  is inserted into the wider open end  69  of the outer housing  55 , which is crimped against the disk  72  to close that opening. The inwardly projecting flange  74  at the opposite end of the outer housing  55  is crimped into an annular groove  76  in the exterior surface of the valve body  21 , thereby securing those components together. An O-ring  78  provides a fluid tight seal between a flange on the liner tube  62  and the valve body  21 . Thus the closed liner tube  62  creates an actuator bore within the linear actuator  51  that contains the fluid passing through the valve body  21 . 
     Referring to  FIGS. 1 and 2 , the actuator plunger  70  of the linear actuator  51  is slideably located within the aperture of the liner tube  62  and includes an armature  80  of ferromagnetic material. A region  81  at the outer end portion of the armature  80  has a slightly larger diameter than the remainder of the armature so that only a relatively small surface area engages the actuator bore formed by the curved inside surface of the liner tube  62 . Therefore, a gap  82  exists between most of the armature and the liner tube. By reducing this surface area of contact, resistance to the armature  80  sliding in the liner tube  62  is minimized. However, enlarging that gap  82  in this manner increases the magnetic impedance, which tends to diminish the magnetic force acting on the armature. In response, the inner end of the armature  80  has a tapered recess  83 , which forms a knife edge  84  around the outer perimeter of that end. The magnetic flux flowing between the armature and the first pole piece  64  is concentrated through the region of the knife edge  84 , thereby counteracting the adverse effect of the gap  82  on the electromagnetic performance of the linear actuator  51 . 
     A tubular push member  86  is received within an aperture that extends longitudinally through the armature  80  and both ends of the armature are “ring staked” to the push member. Ring staking involves forming indentations  85  in the armature end surfaces which push armature material into the aperture and tightly against the push member  86 . The push member  86  projects outward from the open end of the liner tube  62  and abuts the head  54  of the valve spool  44 . 
     The actuator plunger  70  further includes a bearing  88  mounted on the push member  86  against the armature  80 . An axial force is applied to the actuator plunger  70  by the magnetic flux at the end of the first pole piece  64  and bearing  88  at this location prevents binding of the armature due to that axial force. With additional reference to  FIGS. 3-5 , the bearing  88  comprises a cage  90  fabricated of a non-magnetic material, preferably a resilient plastic. The cage  90  is a single piece with two spaced-apart end rings  91  and  92  between which five walls  94  extend, equidistantly spaced around the cage. Each wall  94  has a somewhat Y-shaped cross section, as seen in the cross section of  FIG. 6 , so as to be wider at the outer curved surface of the cage  90  than toward the center of the cage. Five longitudinal slots  96  are formed between adjacent ones of the five walls  94 . The outer surfaces of the walls  94  are concave forming longitudinal channels  93  that extend the entire length of the walls. These channels  93  allow fluid to flow around the cage  90  which reduces resistance to the sliding motion of the actuator plunger  70  that would otherwise occur due to restricted fluid flow. 
     As show in  FIGS. 1 ,  2  and  6 , a separate chromium plated sphere  98  provides a rollable element in each slot  96 . The top of each generally Y-shaped wall  94  spreads into each slot  96  thereby narrowing the slot opening in the exterior curved surface of the cage so that the spheres  98  are captured and cannot freely exit the slot. The plastic material of the cage  90  is resilient allowing adjacent walls  94  to be spread apart enough to allow insertion of a sphere  98  into the associated slots  96  and then return to their original positions to retain the sphere. The rings  91  and  92  at each end of the cage prevent the spheres  98  from traveling out the ends of the slots. The term “captured” as used herein means that the spheres  98  are retained by the walls  94  and rings  91  and  92  of the cage without requiring other components as in prior actuator plunger designs. As seen in  FIG. 1 , each sphere  98  projects from the respective slot into contact with the liner tube  62  and is able to roll within the respective slot  96 . Other forms of rollable elements, such as cylinders, may be used in place of the spheres  98 . 
     With particular reference to  FIG. 2 , the cage  90  has a latch that comprises five L-shaped fingers  95  project outwardly from the second ring  92  with tabs  97  that protrude into an annular groove  99  around the push member  86 . Engagement of the finger tabs  97  with the push member&#39;s annular groove  99  retains the cage  90  against the armature  80 . Alternatively, the cage  90  and the push member  86  can be fabricated as a single plastic part. 
     Referring again to  FIG. 1 , the control valve  20  is fabricated by placing the solenoid coil  58  in a mold into which molten plastic for the bobbin  60  is injected to encapsulate the solenoid coil. After that molded assembly has hardened, the first pole piece  64  along with the inner O-ring  67  and the second pole piece  66  with the outer O-ring  75  are placed into opposite ends of the bobbin. That combination then is inserted into the outer housing  55 . A tool is driven against the exterior surface of the outer housing  55  which creates dimples  59  in that surface and forces some of the metal of the housing into the bobbin  60  in the form of stakes  61  than hold the first pole piece  64  within the outer housing. The disk  72  is positioned in the open end of the outer housing  55  and crimped in place. The liner tube  62  is inserted into the other end of the first pole piece  64  and the actuator plunger  70  is slid into the liner tube  62 , thereby completing assembly of the linear actuator  51 . 
     The valve components then are assembled into the valve body  21  and the nose piece  52  is pressed into the valve body to provide a spring preload. The linear actuator  51  is placed on the end of the valve body  21  with O-ring  78  between the valve body  21  and the flange of the liner tube  62  to provide a hydraulic seal. Then, the flange  74  is crimped into an annular groove  76  in the valve body  21  securing the linear actuator  51  to the valve body  21 . 
     When the electrohydraulic valve  20  in  FIG. 1  is not activated by electric current applied to the solenoid coil  58 , the spring  50  forces the spool  44  into a position at which the annular notch  46  provides a fluid passage between the inlet port  28  and the first workport  30  leading to the first manifold passage  34 . In this de-energized state, the inner end  47  of the spool  44  is positioned to the right which opens a path between the outlet port  27  and the second workport  32  communicating with the second manifold passage  36 . Pressurized fluid now is fed through the supply passage  26  to first workport  30  and fluid is drained from second workport  32  to the return passage  25 . 
     From the de-energized state, application of a relatively small magnitude electric current to the solenoid coil  58  produces movement of the armature  80  and push member  86  toward the nose piece  52 . This motion also moves the spool  44  to the left in  FIG. 1 , thereby reducing the size of the fluid paths described immediately above. This decreases the flow of fluid between the various valve ports. 
     Application of a greater magnitude electric current to the solenoid coil  58  eventually moves the spool  44  farther leftward into an intermediate position depicted in  FIG. 1 , closing the previous paths between the inlet port  28  and the first workport  30  and between the outlet port  27  and the second workport  32 . This terminates all fluid flow through the control valve  20 . 
     Alternatively, the annular spool notch  46  in the valve body  21  can be configured so that in this intermediate position the first and second workports  30  and  32  both communicate with the inlet port  28 . This applies equal pressure to both the first workport  30  and the second workport  32 . 
     Referring still to  FIG. 1 , applying a still greater magnitude electric current to the solenoid coil  58  causes the spool  44  to move farther to the left into a position where the first workport  30  communicates with the central passage  48  through the spool  44 . This opens a fluid path between the first workport  30  and the outlet port  27 . In this position, the annular notch  46  around the spool  44  provides a passage between the inlet port  28  and only the second workport  32 . This applies pressurized fluid from supply passage  26  to the second workport  32  and drains the fluid from the first workport  30  to the return passage  25 . The size of the openings between these passages is varied by controlling magnitude of the electric current applied to the solenoid coil  58  to meter the flow of fluid and thus control the rate at which valve timing changes. 
     The foregoing description was primarily directed to preferred embodiments of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.