Abstract:
A solenoid operated valve has a valve body with a plurality of ports and a spool slidable within the body to interconnect the ports in different combinations. A solenoid, which is coupled to drive the spool, has a coil wound on an annular bobbin with a tube of an electrically conductive, non-magnetic metal within the bobbin. A first pole piece extends into one end of the tube and a second pole piece extends into another end of the tube. A separate bushing is located in an aperture in each pole piece. Each bushing has a tubular body with a first end section that has a larger outer diameter than a second end section and the second end section that has a smaller inner diameter than the first end section. The solenoid further includes an armature that is slidably received in the bushings and engaging the spool.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Pot Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OF DEVELOPMENT 
     Not Applicable 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to hydraulic control valves for controlling flow of a fluid in an internal combustion engines, and more particularly to electrohydraulic valves for operating a mechanism which varies the phase relationship between a cam shaft and a crankshaft of the engine. 
     2. Description of the Related Art 
     Internal combustion engines have a plurality of cylinders containing pistons that are connected to a crankshaft. Each cylinder has two or more valves to control the flow of a fuel mixture into the cylinder and the flow of exhaust gases there from. Traditionally the valves were controlled by a cam shaft which in turn was mechanically connected to rotate with the rotation of the crankshaft. Gears, chains, or belts were used to couple the crankshaft to the cam shaft so that the two would rotate in unison. It is important that the valves open and close at the proper times during the combustion cycle within each cylinder. Heretofore, that timing relationship was fixed by the mechanical coupling between the crankshaft and the cam shaft. 
     The setting of the cam shaft timing often was a compromise which produced the best overall operation at all engine operating speeds. However, it was recognized that optimum engine performance could be obtained if the valve timing was varied as a function of engine speed, engine load and other factors. With the advent of computerized engine control, it became possible to determine the optimum engine valve timing based on the operating conditions occurring at any given point and time. With reference to FIG. 1, the engine computer determines the optimum valve timing and issues a signal to an electrohydraulic valve  10  which controls the flow of pressurized engine oil from a pump to a cam phase adjustment mechanism  12 . The adjustment mechanism  12  couples the cam shaft  14  to a pulley or other mechanism that is connected to the engine crankshaft. By controlling the application of engine oil to either of two ports  18  or  19  of the adjustment mechanism, the phase relationship between the rotating pulley  16  and the cam shaft  14  can be varied. For example, application of engine oil from the pump to the first port  18  and exhausting engine oil from the second port  19  to the tank advances the valve timing. Whereas connecting the second port  19  of the adjustment mechanism  12  to the pump and coupling the first port  18  to the tank retards the valve timing. The hydraulic valve  10  is a proportional type valve which allows the amount that the cylinder valves are advanced or retarded to be proportionally varied by metering the flow of engine oil to and from the adjustment mechanism  12 . A sensor  15  provides an electrical signal indicating the angular phase of the cam shaft. 
     Key to the operation of the variable cam shaft is the proper control of engine oil to the two port  18  and  19  and accurately metering that engine oil. Thus the control valve  10  becomes a critical element in the proper operation of the engine. 
     SUMMARY OF THE INVENTION 
     An electrohydraulic control valve includes a tubular valve body that has a longitudinal bore there through forming an outlet port at one end of the valve body. A first port, a second port and an inlet port extend transversely through the body and communicate with the longitudinal bore. A spool is slidably received within the bore of the valve body and has an aperture extending from an end of the spool that is proximate to the one end of the valve body to a point proximate an opposite end of the spool. The spool includes an notch in an exterior surface. A spring biases the spool away from the one end of the valve body. 
     An actuator comprises a solenoid coil wound on an annular bobbin with a tube of an electrically conductive, non-magnetic metal within the bobbin. A first pole piece of the actuator extends into one end of the tube and a second pole piece extends into another end of the tube. A first bushing is located in an aperture in the first pole piece and a second bushing is in another aperture in the second pole piece. Each of the first and second bushings has a tubular body with a first end section with a larger outer diameter than a second end section. The outer diameter of the first end section engages the respective pole piece. The second end section of each bushing has a smaller inner diameter than the first end section. The actuator also includes an armature is slidably received in the first and second bushings and engaging the spool. 
     The spool moves to several positions within the valve body depending upon the net force resulting from interaction of forces from the spring and the armature. In a first position the spool notch provides a first fluid path between the first port and the inlet port, and a second fluid path is provided between the second port and the outlet port. When the spool is at a second position, the notch provides a fourth fluid path between the inlet port and the second port and the aperture provides a fifth between the first port and the outlet port. 
     In an intermediate position of the spool, between the first and second positions, the outlet port is disconnected from the first and second ports. The notch can be manufactured to have one of several sizes to alter the connection provided in the intermediate position. A relatively short notch while being located adjacent to the inlet port does not extend to either the first or second ports. Therefore the first and second port are closed in the intermediate position. A relatively long notch forms a third fluid path that simultaneously connects the first port, the second port and the inlet port when the spool is in the intermediate position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a variable cam adjustment system in which the present hydraulic valve may be employed; 
     FIG. 2 is a longitudinal cross section view through an electrohydraulic valve according the present invention; 
     FIG. 3 is a cross section view through the electrohydraulic valve along line  3 — 3  in FIG. 2; 
     FIG. 4 is a cross section view of a bushing in the electrohydraulic valve; 
     FIG. 5 is a top view of the bushing; 
     FIG. 6 is a cross section view of an alternative bushing; 
     FIG. 7 is an isometric view of a housing and actuator subassembly of the electrohydraulic valve; and 
     FIG. 8 is a cross section view of an alternative valve spool for the electrohydraulic valve. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to FIG. 2, an electrohydraulic control valve  30  is illustrated inserted into an aperture  32  in a manifold  34  of a variable cam phase adjustment mechanism. The ports  18  and  19  of the cam phasing mechanism  12  illustrated in FIG. 1 are connected respectively to two passages  20  and  21  that extend through the manifold  34  with those passages communicating with the aperture  32 . A supply passage  22  extends between the oil pump and the manifold aperture  32 , while a return passage  23  at the interior end of the aperture  32  leads to the oil pan of the engine. 
     The electrohydraulic valve  30  has a tubular valve body  40  with a longitudinal bore  42  and transverse openings which provide ports between the manifold passages and the longitudinal bore. Specifically a first port  24  connects to the first passage  18  and a second port  25  communicates with the second passage  21 . An inlet port  26  in the valve body is associated with the supply passage  22  and an outlet port  27  opens into the return passage  23 . 
     A spool  44  is slidably received within the bore  42  of the valve body  40  and has an exterior annular notch  46  which, in selective positions of the spool, provides a fluid path between different ones of the ports and thus between the manifold passages. A central aperture  48  extends between the opposite ends of the spool  44 . A spring  50  biases the inward end of the spool  44  away from the interior end  52  of the valve body  40 . The outward end of the valve spool  44  has a head  54 . 
     The valve  30  further includes an electrical actuator  56  comprising a solenoid coil  58  wound on a non-magnetic bobbin  60 , preferably formed of a plastic. The coil is driven by a pulse width modulated (PWM) signal having a duty cycle that is varied to position the spool  44  in the valve body  40 . A copper or brass liner tube  62  extends within and along substantially the entire length of the bobbin  60 . The liner tube  62  acts as a shading coil, thereby changing the input impedance characteristic of the solenoid coil  58  to be more like a resistor and less like an inductor. As a result when a clamping type suppression diode in used in the electronic circuit that drives the solenoid coil  58 , the liner tube  62  linearizes the relationship between the duty cycle of the PWM driving signal and the RMS current of that signal. This improves the controllability of the solenoid current and thus the position of the armature  72  and valve spool  44 . A magnetically conductive C-pole piece  64  has a cylindrical section  66  which extends into one end of the bobbin and the copper tube. An O-ring  65  provides a fluid tight seal between the C-pole piece  64  and the liner tube  62 . The C-pole piece  64  has a flange  68  which projects outwardly from the cylindrical section  66 , extending across the outward end of the valve body  40 . An end-pole piece  70  extends into the opposite end of the bobbin  60  and has an interior end within the bobbin that is spaced from the C-pole piece  66 . A spacer  69  of non-magnetic material is between the two pole pieces  68  and  70 . Another O-ring  71  provides a fluid tight seal between the end-pole piece.  70  and the liner tube  62  within the bobbin. 
     A moveable armature  72  of the actuator  56  is within the bobbin and includes an armature cylinder  74  of magnetic material with an aperture through which a push pin  76  pressed fitted. The push pin  76  projects through a central aperture in the C-pole piece  64  and is slidably supported therein by a first bushing  78 . The head  54  of the valve spool  44  abuts the inner end of the push pin  76 . The push pin  76  also extends into an aperture in the end-pole piece  70  in which the push pin is supported by a second bushing  79 . 
     The first and second bushings  78  and  79  are fabricated of aluminum bronze and have similar tubular constructions with the detail of the second bushing being illustrated in FIGS. 4 and 5. Specifically, the second bushing  79  has a tubular body  80  extending from a flange  81  which prevents the armature cylinder  74  from striking the end-pole piece  70 . A pair of slots  77  extend along the outer surface of the body  80  to provide paths for fluid displaced by movement of the armature  72  to vent between both side of the bushing  79 . The tubular body  80  has an enlarged outer diameter first end section  82  which engages the inner surface of the aperture in the end-pole piece  70 . The inner diameter of the first end section  82  is substantially larger than the outer diameter of the push pin  76  so that contact does not occur between those components. The opposite end of the bushing&#39;s tubular body  80  has a smaller inner diameter second end section  83  which engages the outer surface of the push pin  76 . The two different diameter end sections  82  and  83  are spaced apart longitudinally on the second bushing  79 , i.e. the firs. end section  82  does not extend into the second end&#39;section  83 . Therefore, radially directed forces applied to the bushing upon being pressed into the aperture in the end-pole piece  70  do not deform the bushing to an extent that contact is made with the push pin  76 . Such compression forces are limited to the larger diameter first end section  82  and are not be transmitted to the second end section  83  which is in contact with the push pin  76 . This facilitates assembly of the valve without concern that deformation of the bushing may adversely affect subsequent movement of the push pin  76 . This force isolation function also is provided by the alternative design of the second bushing shown in FIG.  6 . In this alternative, the first end section  84  has a smaller inner diameter that engages the outer surface of the push pin  76  and the second end section  85  of the tubular body  80  has the larger outer diameter that engages the inner surface of the pole piece aperture. 
     A plastic enclosure  86  is molded around the electric actuator  56  and projects outwardly there from. An electrical connector  88  is formed at the remote end of the projecting section of the enclosure. The electrical connector  88  has a pair of terminals  87  projecting through a resilient gasket  89  and connected to the solenoid coil  58  by wires  59 . The resilient gasket  89  provides seal that prevent water from entering the valve between the terminals  87  and the plastic body  86  and also prevents pressurized oil that may travel along the wires  59  from exiting the valve. 
     With reference to FIGS. 2 and 3, a metal outer housing  90  extends around that portion of the plastic enclosure  86  which encapsulates the electrical actuator  56 . The lower end of the outer housing  90  in the orientation of the valve in FIG. 2 tightly engages the outer diameter of the flange  68  on the C-pole piece  64  and is crimped at  91  around the upper edge of the tubular valve body  40 . The upper end of the outer housing  90  has a central aperture  92  through which the end-pole piece  70  extends as seen in FIG.  7 . The edge of that central aperture  92  is has a plurality of indentations  94  at which the material of the enclosure is force against the end-pole piece  70  to stake those two components together. The tight engagement of the C-pole piece  64  with the outer housing  90  provides a highly conductive flux path for the solenoid actuator, as well as holding those components together during subsequent assembly operations. 
     References herein to directional relationships and movement, such as upper and lower or up and down, refer to the relationship and movement of the components in the orientation illustrated in the drawings, which may not be the orientation of the components as attached to machinery. 
     Referring again to FIG. 2, during fabrication of the valve  30 , the assembled actuator  56  is placed in a mold into which molten plastic for the enclosure  86  is injected. That molten plastic is forced into the gap between the outer housing  90  and the bobbin/solenoid coil subassembly where that plastic bonds to the bobbin  60  to encapsulate the solenoid coil  58 . Thus the molded enclosure  86  upon hardening provides a hermetic seal that prevents water from penetrating to the solenoid coil  58  and producing a short circuit to the exposed outer housing  90 . 
     When the electrohydraulic control valve  30  is not being 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 path between the inlet port  26  and the first port  24  leading to the first manifold passage  18 . In this de-energized state, the inner end of the spool  44  is retracted upward which opens a path between the outlet port  27  and the second port  21  communicating with the second manifold passage  19 . Pressurized engine oil now is fed through to port  18  of the cam phasing mechanism  12  and oil is drained from that mechanism&#39;s second port  20  to the oil pan, thereby advancing the valve timing. 
     From the de-energized state, application of a relatively small magnitude electric current to the solenoid coil  58  produces movement of the armature cylinder  74  and push pin  76  toward the valve body  40 . That motion also moves the spool  44  thereby reducing the size of the fluid paths described immediately above. This decreases the flow of engine oil to the cam phasing mechanism  12  which reduces the rate at which the valve timing is being changed. 
     Application of a greater magnitude electric current to the solenoid coil  58  eventually moves the spool  44  downward in FIG. 2 into an intermediate position at which the path between the second port  25  and the outlet port  27 , via the spool&#39;s central aperture  48 , is closed. The annular spool notch  46  now extends between the first port  24  and the second port  25 , thereby applying pressurized engine oil received at the inlet port  26  to both the first and second ports  24  and  25  connected to the cam phasing mechanism  12 . This stops movement of the cam phasing mechanism  12  fixing the relationship between the crankshaft and the cam shaft on the engine. 
     An alternative spool  45  is shown in FIG. 8 in which the notch  47  in the exterior surface is shorter than the notch  46  in the spool  44  in FIG.  2 . Thus when the spool is moved to the intermediate position in the bore  32 , neither the first or second ports  24  or  25  the is connected to the inlet port  26 . In the intermediate position the short notch  47  is centered over the inlet port  26  and the two ends fall on the lands between the inlet port and the first and second ports. Furthermore the outlet port  27  also is closed off from the first and second ports  24  and  25 . This alternative spool  45  provides a center off position in which fluid can not flow to or from the cam phasing mechanism  12 . Otherwise the alternative spool  45  spool provides the same fluid path connections as the first embodiment of a spool  44 . 
     Referring again to FIG. 2, applying a still greater magnitude electric current to the solenoid coil  58  eventually moves the spool  44  farther downward into a position where the first port  24  communicates with the central aperture  48  through the spool  44 . This opens a fluid path between the first port  24  and the outlet port  27 . In this position the annular notch  46  of the spool provides a path between the inlet port  26  and only the second port  25  that leads to the second port  19  of the cam phasing mechanism  12 . This applies pressurized engine oil to the mechanism&#39;s second port  19  and drains the oil from the mechanism&#39;s first port  18  to the oil pan, thereby retarding the phase relationship between the cam and crank shafts. The size of the openings between these passages is varied by controlling the magnitude of the electric current applied to the solenoid coil  58  to meter the flow of engine oil 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.