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 includes a solenoid coil assembly and an armature slideably received in the solenoid coil assembly. A bushing has a cylindrical body from which a push member projects into engagement with the spool and from which a coupling shaft extends into an aperture in the armature. A passage is provided in the bushing to allow fluid to flow between opposites sides as the bushing slides in the solenoid coil assembly. The cylindrical body rides in the solenoid coil assembly and has a plurality of external grooves that enable fluid to pass around the body.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable 
       STATEMENT REGARDING FEDERALLY 
     SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    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. 
         [0005]    2. Description of the Related Art 
         [0006]    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. 
         [0007]    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. 
         [0008]    Therefore, it is desirable to refine the design of this type of solenoid operated valve to facilitate manufacturing. 
       SUMMARY OF THE INVENTION 
       [0009]    An electrohydraulic valve includes a body with a valve bore into which an first port and a second port communicate. A spool slides within the valve bore to connect and disconnect selectively the first and second ports in different positions of the spool. 
         [0010]    The spool is moved within the valve bore by an electrically operated actuator, that includes a solenoid coil assembly having an actuator bore in which an armature and a bushing are slideably located. The bushing is attached to a first end of the armature and is in contact with the spool. In a preferred embodiment, the bushing comprises a cylindrical body from one side of which a push member projects into engagement with the spool and from another side of which a coupling shaft extends into an aperture in the armature. 
         [0011]    A region at a second end of the armature is in contact with a surface of the actuator bore and a gap exists between the actuator bore and a portion of the armature extending from the region to a second end of the armature. The cylindrical body of the bushing contacts the surface of the actuator bore and maintains the gap at the first end of the armature. Preferably, a passage is provided for fluid to flow between opposite sides of the bushing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a longitudinal cross section view through an electrohydraulic valve according the present invention; 
           [0013]      FIG. 2  is an isometric view of an actuator plunger in the valve; 
           [0014]      FIG. 3  is a side view of a bushing that is part of the actuator plunger; and 
           [0015]      FIG. 4  is an end view of the bushing. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    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 . 
         [0017]    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  is at 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. 
         [0018]    Referring again to  FIG. 1 , the valve  20  also includes an electromagnetic linear actuator  51  which comprises 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 produce a magnetic field that moves 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 . 
         [0019]    The linear actuator  51  further includes two magnetically conductive pole pieces  64  and  66 . The first pole piece  64  has an 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  61  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  form a solenoid coil assembly  56 . 
         [0020]    The solenoid coil assembly  56  also comprises a liner tube  62 , preferably of a non-magnetic material such as stainless steel, inserted through the inner 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 . 
         [0021]    A disk  72  is inserted into the outer 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  63  within the linear actuator  51  that contains the fluid passing through the valve body  21 . 
         [0022]    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 contacts the actuator bore  63  formed by the inside curved surface of the liner tube  62 . Therefore, a gap  82  exists between most of the armature and the liner tube surface. By reducing this area of contact, resistance to the armature  80  sliding in the actuator bore  63  is minimized. However, creating that gap  82  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 knife edge  84 , thereby counteracting the adverse effect of the gap  82  on the electromagnetic performance of the actuator  51 . 
         [0023]    The actuator plunger  70  further includes a bushing  88  that interfaces the armature  80  to the spool  44  and maintains the gap  83  between the armature and the liner tube  62 . Thus, the only part of the armature  80  that contacts actuator bore  63  in the liner tube  62  is the region  81  at the outer end. An axial force is applied to the actuator plunger  70  by the magnetic flux at the end of the first pole piece  64  and the bushing  88  at this location prevents binding of the armature in the actuator bore  63  due to this axial force. The bushing  88  has a cylindrical body  86  with a push member  90  projecting from one side and a coupling shaft  92  projecting from the other side. The bushing is fabricated of a non-magnetic material, preferably a polymer, such as Ultem® 2300 glass reinforced polyetherimide (Ultem is a registered trademark of the General Electric Company). 
         [0024]    Both the push member  90  and the coupling shaft  92  have cross sections in the shape of a cross, particularly one resembling a plus sign. The push member  90  abuts the head  54  of the valve spool  44  and the coupling shaft  92  is pressed into an aperture  87  through the armature  80 . A annular flanges  93  extend outward from the cylindrical body  86  and a portion of the coupling shaft  92 . The flanges  93  are received in the tapered recess  83  of the armature  80  and space the cylindrical body  86  from the armature&#39;s knife edge  84 . A passage  94  extends completely through the bushing  88  between ends of the push member  90  and the coupling shaft  92  that are remote from the cylindrical body  86 , thereby enabling fluid to flow through the actuator plunger  70 . 
         [0025]    As shown particularly in  FIGS. 3 and 4 , the cylindrical body  86  is formed by a plurality of fins  96  which define grooves  97  between the ends of the body. The grooves allow fluid to flow between opposite sides of the cylindrical body  86  upon movement of the actuator plunger  70  within the liner tube  62  due to the magnetic field produced by the solenoid coil  58 . Enabling this free flow of fluid through the actuator plunger  70  and around the cylindrical body  86  minimizes resistance to motion of the actuator plunger that otherwise could the result if those flows were more restricted. 
         [0026]    The outer curved surface of the cylindrical body  86  contacts the interior surface of the liner tube  62 . The grooves  97  in cylindrical body  86  result in only the longitudinal edges of the fins  96  contacting the liner tube  62 , thereby reducing the area of that contact and the friction there between. The feature further reduces resistance to the motion of the actuator plunger  70 . 
         [0027]    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 oil is drained from second workport  32  to the return passage  25 . 
         [0028]    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  90  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. 
         [0029]    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. 2 , 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 . 
         [0030]    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 . 
         [0031]    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. 
         [0032]    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.