Abstract:
A solenoid operated valve has a valve body with a plurality of ports and a spool slidable 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 aperture within which first and second tubular pole pieces are received. An armature is able to slide within the two pole pieces and a push member projects from the armature abutting the spool. The push member is secured to a rolling bearing which has a plurality of rolling elements that roll against the pole pieces to reduce resistance to movement of the armature.

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 for controlling flow of a fluid, and more particularly to such electrohydraulic valves that operate a mechanism which alters timing of an internal combustion engine by varying the phase relationship between a cam shaft and a crankshaft.  
         [0005]     2. Description of the Related Art  
         [0006]     Internal combustion engines used in motor vehicles have a plurality of cylinders containing pistons that are connected to a crankshaft. Each cylinder has two or more valves that control the flow of a fuel mixture into the cylinder and the flow of post-combustion gases therefrom. Traditionally the cylinder valves were controlled by a camshaft which was mechanically coupled to rotate with the crankshaft. Gears, chains or belts have been used to couple the crankshaft to the camshaft so that the two 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 camshaft.  
         [0007]     The setting of the camshaft timing often was a compromise that produced the best overall operation at all engine operating speeds. However, it has been recognized that more optimum engine performance could be obtained if the valve timing varies 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.  
         [0008]     With reference to  FIG. 1 , the engine computer  11  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 cam phase adjustment mechanism  12  couples the camshaft  14  to a pulley  16 , gear or other device that is driven by the engine crankshaft. The phase relationship between the rotating pulley  16  and the camshaft  14  can be dynamically varied by selectively applying pressurized engine oil to one of two ports  18  or  19  of the adjustment mechanism. 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 varied proportionally 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 camshaft.  
         [0009]     Key to the operation of the variable cylinder valve timing is the proper control of engine oil flow to the two port  18  and  19  and the accurate metering of that flow. Thus the control valve  10  becomes a critical element in the proper operation of the engine.  
       SUMMARY OF THE INVENTION  
       [0010]     An electrohydraulic valve comprises a body with a longitudinal bore into which an inlet port, an outlet port, a first workport, and a second workport communicate. A spool is slidably received within the bore and has passages therein that selectively connect the inlet port and the outlet port to the first workport and the second workport in different positions of the spool in the bore.  
         [0011]     The spool is moved within the bore by an electrically operated actuator, that includes a solenoid coil assembly with an coil aperture therein. An armature is slidably located in the coil aperture. A push member is attached to the armature and abuts the spool. A cage is secured to at least one of the armature and the push member and has an outer surface with a plurality of slots. A plurality of elements, such as spheres for example, are rollably received in the plurality of slots and contact with the actuator aperture. The cage and the plurality of elements form a rolling bearing that reduces resistance of the armature to motion.  
         [0012]     In a preferred embodiment of the electrohydraulic valve, the actuator has a first pole piece with a tubular interior section that extends 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 tubular interior section of the first pole piece and the tubular section second pole piece 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 secured to the valve body by crimped connection.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a schematic diagram of a variable camshaft adjustment system for an internal combustion engine in which the adjustment system is operated by an electrohydraulic valve;  
         [0014]      FIG. 2  is a longitudinal cross section view through an electrohydraulic valve according the present invention;  
         [0015]      FIG. 3  is an isometric view of an actuator plunger in the electrohydraulic valve;  
         [0016]      FIG. 4  is an isometric view illustrating an armature of the actuator plunger ring staked to a push member; and  
         [0017]      FIG. 5  illustrates an alternative embodiment for a bearing cage and a push member of the actuator plunger. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     Referring to  FIG. 2 , an electrohydraulic control valve  30  is illustrated inserted into an aperture  32  in a manifold  34  of a conventional variable cam phase adjustment mechanism. The ports  18  and  19  of the cam phasing mechanism  12  shown in  FIG. 1  are connected respectively to two passages  20  and  21  that extend through the manifold  34  and those passages open into the aperture  32 . A supply passage  22  extends between the engine&#39;s oil pump and the manifold aperture  32 , while a return passage  23  at the interior end of the aperture leads to the oil pan (or tank) of the engine.  
         [0019]     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 workport  24  connects to the first passage  20  and a second workport  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 .  
         [0020]     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 the inlet port  26  and one of the two workports  24  and  25  and thus between the associated manifold passages. In a middle, or intermediate, position of the spool travel, the inlet port  26  is closed from both workports  24  and  25 . A central aperture  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  55  there through. A spring  50  biases the spool  44  away from a nose piece  52  of the valve body  40 .  
         [0021]     The valve  30  further includes an electromagnetic actuator  56  comprising a solenoid coil  58  in a non-magnetic bobbin  60 , preferably made of plastic molded around the coil to form a solenoid assembly. The solenoid coil  58  is driven by a pulse width modulated (PWM) signal having a duty cycle that is varied in a conventional manner to position the spool  44  in the valve body  40 . The PWM signal is applied to the electromagnetic actuator  56  via a connector  57  formed in a lateral projection of the bobbin  60  and connected by wires to the solenoid coil  58 .  
         [0022]     The electromagnetic actuator  56  further includes two magnetically conductive pole pieces  64  and  66 . The first pole piece  64  has a cylindrical tubular interior 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 flange  68  which projects outwardly from the interior section  65  across the outer end of the valve body  40 . The second pole piece  66  has a second tubular section that extending into the opposite end of the bobbin  60  and has an interior end that is spaced from the first pole piece  64 . An 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 an outwardly projecting flange  71  and another O-ring  75  provides a hermetic seal between this flange and the bobbin  60 .  
         [0023]     A liner tube  62 , preferably of stainless steel, extends through 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 plunger  73 . An open end of the liner tube  62  faces the valve body  40  and a closed end is adjacent the outwardly projecting flange  71  of the second pole piece  66 .  
         [0024]     The electromagnetic actuator  56  is enclosed by a metal outer housing  69  that extends around the first and second pole pieces  64  and  66  and the bobbin  60 . The open end of the outer housing  69 , adjacent the second pole piece  66 , is crimped to a disk  72  to close that opening. At the opposite end, the outer housing  69  has an inwardly projecting flange  70  which is crimped into a depression, such as an annular groove  61 , in the exterior surface of the valve body  40 , thereby securing those components together. An O-ring  59  provides a fluid tight seal between a flange on the liner tube  62  and the valve body  40 . Thus the closed liner tube  62  provides a sealed inner cavity within the electromagnetic actuator  56  that contains the fluid passing through the valve body  40 .  
         [0025]     With reference to  FIGS. 2 and 3 , the plunger  73  of the electromagnetic actuator  56  is slidably located within the liner tube  62  and includes an armature  74  of ferromagnetic material. A region  77  at the outer end of the armature  74  has a larger diameter than the remainder of the armature so that only a relatively small surface area engages the inside diameter of the liner tube  62  and a gap  79  exists between most of the armature and the liner tube. By minimizing this surface area of engagement, resistance to the armature  74  sliding in the liner tube  62  is minimized. However, enlarging that gap  79  increases the magnetic impedance which tends to diminish the magnetic force acting on the armature. In response, the inner end of the armature  74  has a tapered recess  81 , which forms a knife edge  82  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  82 . Concentrating the magnetic flux in this manner, counteracts the adverse effect of the gap  79  on the electromagnetic performance of the actuator  56 .  
         [0026]     The armature  74  has a longitudinal aperture in which a tubular push member  76  is received. Both ends of the armature are “ring staked” to the push member  76 . As shown in  FIG. 4 , ring staking involves forming indentations of the armature end surfaces at locations  85  which pushes that armature material around the aperture tightly against the push member  76 . Referring again to  FIGS. 2 and 3 , the push member  76  projects outward from the open end of the liner tube  62  and abuts the head  54  of the valve spool  44 .  
         [0027]     The plunger  73  further includes a rolling bearing  80  mounted on the push member  76  between the armature  74  and the valve spool head  54 . An axial force is applied to the plunger  73  by the magnetic flux at the end of the first pole piece  64  and rolling bearing  80  at this location prevents binding of the armature due to that axial force. The rolling bearing  80  comprises a plastic cage  83  with five longitudinal slots  84  equidistantly spaced around its outer surface. A separate chromium plated sphere  86  is located in each slot  84 . Each sphere  86  projects from the respective slot into contact with the liner tube  62  and the push member  76  and is able to roll within the respective slot  84 . Other forms of rollable elements, such as cylinders, may be used in place of the spheres  86 . The cage  83  is held in place on the push member  76  by a retaining ring  88 . Alternatively the cage  83  and the push member  76  can be fabricated as a single plastic part  90  as shown in  FIG. 5 .  
         [0028]     Referring specifically to  FIG. 2 , the valve  30  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 the bobbin. The assembly then is inserted into the outer housing  69 . Next the disk  72  is positioned in the open end of the outer housing  69  and crimped in place. The liner tube  62  is inserted into the other end of the first pole piece  64  and the plunger  73  is slid into the liner tube  62 , thereby completing assembly of the electromagnetic actuator  56 .  
         [0029]     The valve components then are assembled into the valve body  40  and the nose piece  52  is pressed into the valve body to provide a spring preload. The electromagnetic actuator  56  is placed on the end of the valve body  40  with O-ring  59  between the valve body  40  and the flange of the liner tube  62  to provide a hydraulic seal. Then, the flange  70  is crimped into an annular groove  61  in the valve body  40  securing the components together.  
         [0030]     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.  
         [0031]     When the electrohydraulic valve  30  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 path between the inlet port  26  and the first workport  24  leading to the first manifold passage  20 . In this de-energized state, the inner end of the spool  44  is positioned to the right which opens a path between the outlet port  27  and the second workport  25  communicating with the second manifold passage  21 . Pressurized engine oil now is fed through the first manifold passage  20  to port  18  of the cam phasing mechanism  12  and oil is drained from that mechanism&#39;s second port  19  through the second manifold passage  21  to the oil pan, thereby advancing the valve timing.  
         [0032]     From the de-energized state, application of a relatively small magnitude electric current to the solenoid coil  58  produces movement of the armature  74  and push member  76  toward the valve body  40 . This 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.  
         [0033]     Application of a greater magnitude electric current to the solenoid coil  58  eventually moves the spool  44  leftward in  FIG. 2  into an intermediate position closing the previous path between the second workport  25  and the outlet port  27 , via the spool&#39;s central aperture  48 . The annular spool notch  46  now opens only into the inlet port  26  and both the first and second workports  24  and  25  are closed. This stops movement of the cam phasing mechanism  12  fixing the relationship between the crankshaft and the camshaft on the engine. Alternatively, the annular spool notch  46  in the valve body  40  can be configured so that in this intermediate position the first and second workports  24  and  25  both communicate with the inlet port  26 . This applies equal pressure to both the first workport  24  and the second workport  25 .  
         [0034]     Referring still to  FIG. 2 , applying a still greater magnitude electric current to the solenoid coil  58  eventually moves the spool  44  farther to the left into a position where the first workport  24  communicates with the central aperture  48  through the spool  44 . This opens a fluid path between the first workport  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 workport  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.  
         [0035]     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.