Abstract:
An hydraulic valve has a body with an exterior surface, a longitudinal bore, and first and second fluid ports in communication with the bore wherein the first fluid port opens through the exterior surface. A band is wrapped in first and second layers around the exterior surface which layers extend over the opening of the first fluid port. The first layer has a plurality of apertures there through and overlaying the opening to provide a filter. The second layer has a flap that flexes in response to pressure to open and close the plurality of apertures thereby acting as a check valve. An actuator slides a spool within the bore thereby selectively connecting and disconnecting the first and second fluid ports.

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 such valves that have an integral filter and check valve for fluid flowing through the valve. 
         [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 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]    Over time the hydraulic fluid flowing through a machine carry small particles, such as pieces of metal from the engine components. Those particles can block orifices in the valve or become lodged so as to impede motion of valve components. The particles also may adversely affect operation of other elements of the hydraulic system. Some prior valves incorporated filters to prevent the small particles from entering the valve. 
         [0008]    Hydraulic systems for controlling engine operation included check valves that allowed fluid to flow in only one direction. For example, a separate check valve connected in a conduit coupled to an inlet or an outlet of solenoid operated valve permitted fluid to flow only to or from that latter valve. However, providing the solenoid operated valve and check valve as separate components increased the number of parts to connect together in the hydraulic system. 
       SUMMARY OF THE INVENTION 
       [0009]    An electrohydraulic valve comprises a body with a longitudinal bore into which a first port and a second port communicate. A spool is slideably received within the bore and has a passage that selectively connects and disconnects the first and second ports in different positions of the spool in the bore. The spool is moved within the bore by an actuator, that preferably is electrically operated. 
         [0010]    The first port opens through an exterior surface of the valve body. A band is wrapped around the exterior surface, thereby forming first and second layers of the band extending over the opening of the first port. The first layer has a plurality of apertures there through and overlaying the first port opening, thereby forming a filter. The second layer has a flap that in response to pressure flexes to open and close the plurality of apertures, thereby acting as a check valve to allow fluid flow in only one direction through the plurality of apertures. 
         [0011]    In one version of the electrohydraulic valve, the first layer is against the exterior surface of the valve body and the second layer is against a side of the first layer that is remote from the valve body. In this version, the flap forms a check valve that prevents fluid from entering the valve through the plurality of apertures. 
         [0012]    In another version of the electrohydraulic valve, the second layer is against the exterior surface of the valve body and the first layer is against a side of the second layer that is remote from the valve body. In this latter version, the flap forms a check valve that prevents fluid from exiting the valve through the plurality of apertures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a longitudinal cross sectional view through an electrohydraulic valve according the present invention; 
           [0014]      FIG. 2  illustrates a filter plate used in the electrohydraulic valve; 
           [0015]      FIG. 3  shows the filter plate bent into a tube as occurs upon being mounted around the electrohydraulic valve; 
           [0016]      FIG. 4  is a cross sectional view along line  4 - 4  in  FIG. 1  showing a band that provides filters and check valves at inlet ports of the electrohydraulic valve; 
           [0017]      FIG. 5  is a plan view of the filter and check valve band; 
           [0018]      FIG. 6  is an enlarged plan view of a section of the filter and check valve band showing details of a check valve; and 
           [0019]      FIG. 7  is a cross sectional view through the electrohydraulic valve showing use of the filter and check valve band at an outlet port. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    Referring to  FIG. 1 , an electrohydraulic control valve  18  has a tubular valve body  20  that during use is inserted into an aperture  22  in a manifold  24 . The tubular valve body  20  has a longitudinal bore  21  into which a plurality of ports open. A supply passage  26  in the manifold  24  conveys pressurized fluid from a pump or other source and opens into an inlet port  28  of the control valve  18 . The inlet port  28  opens into a first annular recess  29  formed in an exterior curved surface  23  of the valve body  20 . At the inner end of the manifold aperture  22 , a return passage  25  communicates with an outlet port  27  of the valve to convey fluid back to a tank of the hydraulic system. First and second workports  30  and  32  in the tubular valve body  20  communicate with manifold passages  34  and  36  that lead to a hydraulic actuator being controlled. The first and second workports  30  and  32  open into annular recesses  31  and  33 , respectively, formed in the exterior curved surface of the valve body  20 . 
         [0021]    A spool  44  is slideably received within the bore  21  of the valve body  20  and has an exterior annular notch  46  which, in selected positions of the spool, provides fluid paths between the inlet port  28  and the two workports  30  and  32  and thus between the associated manifold passages. In a middle, or intermediate, position of the spool travel, 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  20  at which the outlet port  27  is located. 
         [0022]    The valve  18  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  20 . 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 . 
         [0023]    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 . 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  20 . The second pole piece  66  has a second tubular section  67  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  69  projecting outwardly. A liner tube  62 , preferably of stainless steel, is inserted through the first and second pole pieces  64  and  66  and has an open end facing the valve body  20 . The opposite end of the liner tube  62  is closed. 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 . The solenoid coil  58 , the bobbin  60 , the first and second pole pieces  64  and  66 , and the liner tube  62  form a solenoid coil assembly  56 . 
         [0024]    The actuator plunger  70  is slideably located within the aperture of the liner tube  62  and includes an armature  72  of ferromagnetic material. A tubular push member  74  is received within an aperture that extends longitudinally through the armature  72  and both ends of the armature are “ring staked” to the push member. The push member  74  projects outward from the open end of the liner tube  62  and abuts the head  54  of the valve spool  44 . 
         [0025]    Two filters  80  are wrapped around the valve body  20  to form tubes that cover the two workports  30  and  32 . With specific reference to  FIGS. 2 and 3 , each filter  80  is formed from a thin, flat rectangular plate  82  with a plurality of apertures  84  between its two major surfaces. For example, a standard photolithographic etching process can be employed to form apertures of a size small enough to prevent undesirable particles from entering and adversely affecting operation of the valve. A rectangular aperture  86  is formed in a first end section  85  of the plate  82  and a single U-shaped slot is cut through the plate at the opposite second end section  87  with the opening of the U facing that end. This U-shaped slot defines a rectangular tab  88 . 
         [0026]    To install a filter  80 , its tab  88  is bent perpendicular to the plate  82 . Then the second end section  87  of the plate  82  is placed against the valve body  20  with the tab  88  projecting outward. The rectangular plate  82  is wrapped around the valve body  20  in a recess  31  or  33  associated with one of the workports  30  or  32 . The first end section  85  of the plate  82  overlaps the second end section  87  with the tab  88  extending through the rectangular aperture  86 . The tab  88  then is bent against the surface of the first end section  85 , as illustrated in  FIG. 3 , to secure the plate in tubular shape. 
         [0027]    Although the present filter and check valve band is being describe in the context of use on an electrohydraulic spool valve, it should be understood that the band can be used on other types of valves. 
         [0028]    With reference again to  FIGS. 1 and 4 , a filter and check valve band  90  is wound around the valve body within the recess  29  located at the inlet ports  28 . As will be described, this band  90  serves both as a filter, similar to the filters  80 , and also as a check valve that allows fluid to flow only in a direction from the supply passage  26  into the valve body bore  21 . Unlike the filters  80  that are wrapped once around the valve body  20  to form a tube, the filter and check valve band  90  is wrapped substantially twice around the valve body in two convolutions (see  FIG. 4 ), thereby forming first and second layers that overlay the openings of the inlet ports  28 . 
         [0029]    With reference to  FIG. 5 , the band  90  is illustrated laid flat prior to installation condition. The band is an elongated strip of metal 0.1 mm thick, for example. A pair of ears  92  project outwardly from each longitudinal side  93  at one end of the band  90 . The band has two check valves  94  and two filter areas  96  formed at spaced locations along its length. Those locations correspond to places where the band overlaps the two inlet ports  28  in the valve body  20 . Other valves may have a greater or lesser number of inlet ports, in which case the appropriate band has a corresponding different number of check valves  94  and filter areas  96 . To understand the physical relationship between the inlet ports  28  and each of the check valves and filter areas, the inlet port positions when the band is wound around the valve body have been indicated by phantom rectangles designated by numeral  28  in  FIG. 5 . 
         [0030]    Each of the filter areas  96  is formed by a pattern of apertures  97  perforating through the band  90  that are sufficient for fluid to flow adequately between the supply passage  26  and the inlet port  28 . A standard photolithographic etching process, for example, can be used to form apertures of a size small enough to prevent undesirable particles from entering the valve. With additional reference to  FIG. 6 , each check valve  94  is defined by a U-shaped slot  98  cut through the band  90  thereby forming a flap  100 . As will be described, the flap  100  is able to flex about a line  99  that is transverse to the longitudinal axis of the band and parallel to the longitudinal axis  35  of the valve body bore  21 . 
         [0031]    A rectangular aperture  102  is formed approximate to the opposite end of the band  90  from the ears  92 . Near the midpoint of the band  90 , a rectangular tab  104  is created by a U-shaped slot through the band. As will be explained hereinafter, the tab  104  and the aperture  102  are used to hold the band on the valve body  20 . 
         [0032]    With reference to  FIG. 6 , the filter and check valve band  90  is attached to the valve body  20  by placing the end of the band with ears  92  into the first annular recess  29 . This annular recess  29  has two notches  108  projecting transversely into the side walls  105  of that recess. The two ears  92  of the band are received in those notches  108  to secure the band from sliding in the first annular recess  29  around the valve body as the band is wrapped about the valve body  20 . The notches  108  also ensure alignment of the check valves  94  and the filter areas  96  with the inlet ports  28  as that wrapping occurs, see  FIG. 4 . Prior to the wrapping the band, the tab  104  is bent perpendicular to the band&#39;s major surface. At the completion of wrapping the tab  104  is inserted through the rectangular aperture  102  and bent over the remote end of the band to secure that end in place. As an alternative to an aperture  102  and a tab  104 , the remote end of the band  90  from the ears  92  can be welded to hold the band tightly wound around the valve body  20 . Other techniques for securing the band in place also can be employed. 
         [0033]    Assume that the linear actuator  51  has positioned the spool  44  so that the annular notch  46  provides a path between the inlet port  28  and one of the workports  30  or  32  in  FIG. 1  and that the pressure in the supply passage  26  is greater than pressure at that one workport. Thus as depicted in  FIG. 4 , pressurized fluid introduced from the supply passage  26  flows through the apertures of the associated filter area  96  and is applied against the surface of the flap  100  of the check valve  94 . The greater pressure from the supply passage  26  forces the flap  100  of the check valve to flex inward toward the center of the valve, thereby providing an opening between the filter apertures and the inlet port  28 . This allows fluid to flow through the corresponding filter area  96 , into the inlet port  28 , and then through the spool to the connected workport. 
         [0034]    At other times, a very large load applied to the actuator, that is connected to the associated workport  30  or  32 , produces pressure at that workport which is greater than pressure in the supply passage  26 . In this situation, when the spool  44  connects that workport to the inlet port  28 , the higher workport pressure causes the flap  100  of the check valve  94  to close against the filter area  96  preventing the flow of fluid there through, as depicted for the inlet port  28  at the lower half of  FIG. 4 . Thus the check valve  94  prevents fluid flow out of the valve through the inlet port  28  into the supply passage  26 . It should be appreciated that the opening of one check valve  94  and the closure of the other check valve in  FIG. 4  is shown for explanation purposes only, whereas in actuality both check valves will be in the same state simultaneously because they are acted on by the same pressures. 
         [0035]    Referring to  FIG. 7 , a filter and check valve band  110  can be used at a workport  30  or  32  of the valve body or in a similar transverse outlet port to allow fluid to flow only out of the valve  18  and not into the valve through that port. For example, if the workport feeds fluid to a hydraulic motor, it might be undesirable to inhibit fluid to flow backwards from the hydraulic motor into the valve. In this case, a band  110  has a similar configuration to the one in  FIG. 5 , except that the two check valves  94  and the two filter areas  96  are interchanged in positions. Thus, when the band  110  is wrapped around the valve body  20 , the two filter areas  96  are in the inner layer, or convolution, that abuts the curved surface of the valve body as shown in  FIG. 7  and the check valves  94  in the outer layer. 
         [0036]    Now when pressure within a port  112  of the valve is greater than pressure in the passage  114  of the manifold  24 , the check valve flap  100  flexes open allowing fluid to flow through the filter area  96 . On the other hand, when pressure in the manifold passage  114  is greater than pressure in the valve port  112 , the net force from that pressure differential closes the check valve flap  100  against the filter area  96  blocking the flow of fluid through the filter apertures in the band  110 . 
         [0037]    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.