Patent Publication Number: US-8534639-B1

Title: Solenoid valve with a digressively damped armature

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 solenoid operated hydraulic valves and in particular to techniques for damping the operation of such valves. 
     2. Description of the Related Art 
     Solenoid operated valves have been developed for a variety of equipment to selectively apply and exhaust pressurized fluid to and from a component, the operation of which is controlled by that valve. One type of such valve has a spool that slides within a bore. In one position, the spool provides a path between a supply conduit containing pressurized fluid to a workport that is connected to the component being operated by the valve. In another position, the spool provides a path between the workport and an exhaust port to relieve pressure at the workport. In a third position of the spool, the workport is disconnected from both the supply and the exhaust ports. 
     In many applications relatively high pressure acts on the spool and other components of the valve which can produce large forces that adversely affect the operation of the valve and the longevity of those components. As a consequence, these valves often include a damping mechanism to restrict the rate at which the spool and solenoid components operate, thereby reducing the adverse affects that high pressure forces have on the valve components. Such damping devices also provide stability to the valve operation under a range of pressure levels. 
     In a typical valve, the armature moves within a central bore of the solenoid. In order for that motion to occur, fluid in a chamber on one side of the armature must flow to a chamber on the opposite side of the armature in order to provide space for the armature motion. In the most simplistic form of damping, a fixed orifice is provided between the chambers, thereby restricting the rate of flow and thus the velocity of the armature. However, satisfactory damping control with a fixed orifice is often difficult to achieve for systems, such as in outdoor equipment, in which the viscosity of the fluid varies with respect to temperature. In other words, the fluid at relatively high temperatures has a low viscosity and thus can flow more freely through the fixed orifice, as compared to when the fluid has a lower temperature and a higher viscosity. 
     Therefore, it is desirable to provide a damping mechanism that yields a more uniform damping over a wide range of operating temperatures and fluid viscosities. 
     SUMMARY OF THE INVENTION 
     An electrohydraulic control valve has a valve body with a fluid passage therein and a first port, a second port, and a workport open into the fluid passage. A valve element is moveably received within the fluid passage for selectively controlling the flow of fluid between the workport and each of the first and second ports. A solenoid actuator includes a moveable armature that is operatively coupled to move the valve element. A first chamber is defined on one side of the armature and a second chamber is defined on another side of the armature. The armature has an armature bore extending between the first chamber and the second chamber. 
     A digressive damping element is operatively coupled to control bidirectional fluid flow through the armature bore. The digressive damping element opens and closes the armature bore to fluid flow in response to a difference in pressure between the first chamber and the second chamber. The digressive damping element maintains the armature bore closed as the difference in pressure increases from zero, and opens the armature bore when the difference in pressure exceeds a given level. 
     In one aspect of the present invention, the digressive damping element comprises a body with passages in an exterior surface and a spring that bidirectionally biases the body into a closed state. 
     In another aspect of the present invention, the digressive damping element comprises a disk secured in the armature bore, wherein the disk has a flap that bends in response to the difference in pressure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view through a first electrohydraulic control valve according to the present invention in which a workport is normally connected to an exhaust port in a deactivated state of the valve; 
         FIG. 2  is a graph depicting the relationship between the velocity at which the armature and valve element move and damping force provided by a damping element in the control valve; 
         FIG. 3  is a cross sectional view through a valve element which incorporates an alternative damping element to the one shown in  FIG. 1 ; 
         FIG. 4  is a plane view of the alternative damping device; and 
         FIG. 5  is a cross sectional view through a second electrohydraulic control valve that normally connects the workport to a pressurized fluid supply port. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     References herein to directional movement, such as left or right, refer to the motion of the components in the orientation illustrated in the drawings, which may not be the orientation of the components or the present control valve when attached to a machine 
     With initial reference to  FIG. 1 , an electrohydraulic first control valve  30  is illustrated inserted into an aperture  22  in a manifold  20 . The manifold  20  has a supply passage  23  that conveys pressurized fluid from a source such as a pump (not shown) and a return passage  24  that conveys fluid back to a tank (not shown). The manifold  20  also has a device passage  26  to which is connected a hydraulic component that is controlled by the first control valve  30 . 
     The first control valve  30  has a tubular valve body  32  with a longitudinal bore  34  and transverse openings which provide ports between the manifold passages and the longitudinal bore. Specifically, the longitudinal bore  34  is connected by a supply port  36  to the supply passage  23  and by an exhaust port  38  to the return passage  24 . A workport  40  at the nose of the tubular valve body  32  opens into the manifold device passage  26 . 
     A spool-like, tubular valve element  44  is slideably received within the bore  34  of the valve body  32  and is moved therein by a solenoid actuator  60 . A central bore  48  extends between the opposite ends of the valve element. A plurality of radial apertures  46  communicate with the valve element bore  48  which forms a fluid passage, so that in selective positions of the valve element fluid paths are provided between the workport  40  and either the supply port  36  or the exhaust port  38 . In this type of proportional control valve, the flow to and from the workport goes through the center of the valve element. The first control valve  30 , is referred to as having a “normally low pressure state” because in the deactivated state the workport  40  is connected to the exhaust port  38 . 
     The workport pressure acts on the adjacent end surface of the valve element and for previous valve elements this was the entire circular end surface area. This also applies when the valve element bore is a blind aperture opening only at the end of the valve element facing the workport. In this case, the pressure also acts on the interior end surface of that bore. Even in designs in which that bore extends completely through the valve element, the workport pressure reaching the opposite end often acts on the solenoid actuator that operates the valve, thereby having the same effect on valve operation as with a blind valve element bore. In all these designs, the solenoid actuator has to overcome the feedback force that results from the workport pressure acting on that valve element surface area. 
     A drawback of these designs is that in order to control a greater amount of fluid flow, a larger valve element is required which results in a larger feedback force from the workport pressure acting on the valve element. The larger feedback force in turn requires greater counter force from the solenoid to move the valve element, thus requiring a larger solenoid. The present valve element arrangement eliminates the need for a significantly larger solenoid in order to design a valve with a larger flow capability. This is accomplished by designing a tubular valve element  44  wherein the force from the workport pressure acts only on an annular end surface  49  of the valve element. By judiciously designing the inner and outer diameters of the valve element  44 , the area of that annular end surface  49  does not increase significantly as the size of the valve element is increased to handle greater flow. Thus the surface area on which the workport pressure acts remains relatively unchanged. Therefore, the size of the solenoid actuator can remain the same or at least does not have to increase as significantly to operate a larger flow capacity valve element. 
     This is accomplished by placing a slug  54  of solid material within the valve element  44  and transferring the pressure force acting on the slug to a stationary part of the valve structure and not to the valve element. In particular, the slug  54  is located within the valve element bore  48  and has an outer diameter slightly less than the diameter of that valve element bore, so as to allow the valve element  44  to slide over the slug. A tab  56  extends from one end of the slug  54  and has an aperture there through. A cross pin  52  extends through that aperture and through elongated slots  50  near the end of the valve element  44  that is remote from the workport  40 . The length of the slots  50  allows the valve element  44  to slide unobstructed within the valve body bore  34 , as will be described. End sections of the cross pin  52  are held between the valve body  32  and the solenoid actuator  60  which thereby holds the slug  54  in a fixed position relative to the valve body. In other words, as the valve element  44  slides within the valve body bore  34 , the slug  54  remains stationary. With this arrangement, the force exerted on the slug  54  of solid material, due to the workport pressure in the valve body bore  34 , is transferred directly to the stationary part of the valve structure, i.e. the valve body  32  and the solenoid actuator  60 , and is not applied to the valve element  44 . As a consequence that force does not affect the motion of the valve element. 
     The slug  54  reduces the surface area on which pressure acts on the valve element  44  to the area between the outer diameter of the valve element and the outer diameter of the slug. This results in an annular surface area at the end  49  of the valve element  44  that faces the workport. Thus the surface area on which the pressure at the workport  40  acts on the valve element  44  has been reduced from the entire circular cross sectional surface area to just this annular surface area. The force exerted on the valve element  44  due to the pressure is directly related to the surface area on which the pressure acts and that force must be overcome by the solenoid actuator  60  to move the valve element. Heretofore with previous valve element arrangements, in which the pressure acted on the entire cross sectional surface area of the valve element, as the size of the valve element was increased in order to control a larger fluid flow, the force due to the pressure increased proportionally. Thus a larger solenoid actuator was required to overcome that greater force and move the valve element. With the present valve element arrangement, as the size of the valve element  44  is increased for a higher flow capacity valve, so too is the size of the slug  54  increased. Therefore, the size of the annular end surface  49  of the valve element  44  does not increase as significantly, and may remain relatively the same by increasing the size of the slug  54  disproportionally to the valve element size increase. As a result, the present valve element arrangement enables the valve element size to be increased without any or at least without a significant increase in the size of the solenoid actuator  60 . 
     The solenoid actuator  60  includes a can-like metal case  61  that contains an electromagnetic coil  62  which is wound on a non-magnetic bobbin  63 , preferably formed of a plastic. A magnetically conductive first pole piece  64  has a cylindrical, tubular section  66  which extends into one end of the bobbin  63 . A magnetically conductive, second pole piece  68  extends into the opposite end of the bobbin  63  and has an interior end that is spaced from the first pole piece  64 . The second pole piece  68  has an outwardly projecting flange  70  that extends across the open end of the metal case  61  which is crimped around part of the valve body  32 . The metal case  61  and the second pole piece  68  form a housing of the solenoid actuator  60 . The engagement of the metal case  61  with the first and second pole pieces  64  and  68  provides a highly conductive magnetic flux path within the electromagnetic coil  62 . 
     An armature  72  within the solenoid actuator  60  is slideably received within the first and second pole pieces  64  and  68 . One end of the armature  72  defines a first chamber  81  within the second pole piece  68  and the opposite end of the armature defines a second chamber  82  within the first pole piece  64 . These chambers fill with the fluid that flows through the control valve. The armature  72  slides within the first and second pole pieces  64  and  68  in response to a magnetic field that is produced by applying electric current to the electromagnetic coil  62  via a connector  65 . For example, the electromagnetic coil  62  may be driven by a pulse width modulated (PWM) signal having a duty cycle that is varied in order to position the valve element  44  within the pole pieces. The armature  72  engages a driver tube  73  that is formed of a non-magnetic material and that abuts the interior end of the valve element  44 . Therefore, application of the electric current to the electromagnetic coil  62  moves the armature  72  to the right in  FIG. 1 , thereby pushing the valve element  44  to the right. 
     The armature  72  has a bore  74  extending between opposite ends, thereby forming a fluid passageway between the first and second chambers  81  and  82 . The armature bore  74  has a section adjacent the end that faces the valve element  44  which has a reduced diameter thereby forming an armature aperture  75 . A digressive damping element  76  is located within that armature aperture  75  and is able to slide longitudinally therein. A spring  80  is within the armature bore  74  and has a first end affixed to the damping element  76 . For example, at one end of the spring  80  is a first section  84  of coil turns with a smaller diameter than a second section  85  of coil turns in the center of the spring. The coil turns in the first section  84  are wrapped around a tab with a head that projects from the main body of the digressive damping element  76 . A third section  86  of coil turns at an opposite end of the spring  80  has larger diameter than the center second section  85 . The coil turns of the third section  86  are press fitted into the armature bore  74  and thereby are held stationary in the bore at that position. When equal fluid pressure levels act on both sides of the damping element  76 , the spring  80  centers the damping element within the armature aperture  75 . The spring  80  exerts both tension and compression forces, which allow the damping element  76  to move bidirectionally in response to a pressure differential across the damping element. 
     A first flute  77  extends partway along the exterior surface of the digressive damping element  76  from the end facing the valve element  44 . When the damping element  76  is centered longitudinally within the armature aperture  75 , the first flute  77  only communicates with the first chamber  81  and does not open into the armature bore  74 . A second flute  78  extends partway along the exterior surface of the damping element  76  from the end that is in the armature bore  74 . When the damping element  76  is centered longitudinally within the armature aperture  75 , the second flute  78  only communicates with the armature bore  74  and does not open into the first chamber  81 . Thus when centered in the armature aperture, the damping element  76  does not provide a significant fluid path between the two armature chambers  81  and  82 . Alternatively the flutes may be replaced by flat regions on the exterior surface of the damping element. With either version, the flutes or flats form passageways in the exterior surface of the damping element  76 . 
     A conical coil spring  45  is located adjacent the workport  40 . A small diameter end of the conical coil spring  45  engages the end of the valve element  44  and the larger end of the spring is held within the bore  34  of the valve body  32  by a retaining ring  47 . The conical coil spring  45  biases the valve element into the illustrated normal position when current is not being applied to the solenoid actuator  60 . In that illustrated position, the apertures  46  in the valve element open into the exhaust port  38 , thereby providing a path between the exhaust port and the workport  40  when the valve is in the de-energized state. 
     When electric current is applied to the electromagnetic coil  62 , a magnetic field is produced within the solenoid actuator  60  that causes the armature  72  to move to the right in the drawing, thereby pushing the valve element  44  to the right as well. By applying a first level of electric current to the electromagnetic coil  62 , the armature  72  is moved so that the valve element apertures  46  align with a land  88  in the valve body bore  34  between the supply port  36  and the exhaust port  38 . In this position, the valve element apertures  46  are closed so that the bore  48  of the valve element  44  is not in communication with either the supply or the exhaust port  36  or  38 . As a consequence, the workport  40  is closed off from the other two ports. Increasing the magnitude of electric current applied to the electromagnetic coil  62  moves the armature  72  and the valve element  44  farther to the right in  FIG. 1  aligning the apertures  46  with the supply port  36 . This enables fluid from the supply port to flow through the apertures  46  and the valve element bore  48  toward the workport  40 . Thereafter, when the application of electric current to the electromagnetic coil  62  is terminated, a magnetic field no longer acts on the armature  72 . At that time, the conical coil spring  45  pushes the valve element  44  and thus the armature  72  leftward in  FIG. 1  and into the illustrated normal position where the valve element apertures  46  communicate with the exhaust port  38 . 
     When the armature  72  moves within the pole pieces  64  and  68 , the volume of one of the chambers  81  or  82  is expanding while the volume of the other chamber is correspondingly decreasing. For that motion to continue, fluid within the chamber that is decreasing in volume must flow into the expanding chamber. For example, if the armature is moving to the right in  FIG. 1 , that motion will increase the pressure of the fluid within the first chamber  81  and decrease the pressure in the second chamber  82 , producing a difference in pressure that acts on the damping element  76 . As the armature initially moves, the fluid in the first chamber  81  can only flow into the second chamber  82  around the closed damping element  76  and between the armature  72  and the two pole pieces  64  and  68 . These are small paths thereby causing the pressure in the first chamber  81  to increase rapidly as the velocity of the armature  72  increases. This pressure increase exerts a relatively rapidly increasing the motion damping force on the armature  72  as depicted by the graph in  FIG. 2 . 
     If the magnitude of electric current applied to the solenoid actuator  60  causes the armature  72  to move at a sufficiently high velocity, then a significantly higher pressure will be produced in the first chamber  81  than in the second chamber  82 . This difference in pressure causes the damping element  76  to be pushed far enough into the bore aperture  75  that the first flute  77  opens into the armature bore  74 . That event occurs at point  89  on the damping curve in  FIG. 2 . This exposure of the first flute  77  provides a sizeable path for additional fluid to flow past the damping element  76  from the first chamber  81  into the second chamber  82 . Thereafter as the velocity of the armature continues to increase, the damping force exerted thereon by the pressure within the first chamber  81  increases very gradually. This results in the first control valve  30  having relatively high damping rates at low armature velocities and significantly lower damping rates at higher armature velocities, which is referred to as “digressive damping.” As used herein a “digressive damping element” is a component of a valve than damps the motion of the valve element according to that velocity-force relationship. 
     A similar digressive damping operation occurs when the electric current is removed from the electromagnetic coil  62  and the valve element  44  and armature  72  move to the left due to the force of the conical coil spring  45  and the workport pressure. At that time, fluid is forced out of the second chamber  82  into the first chamber  81 . If the armature moves rapidly enough, the pressure in the second chamber  82  reaches a point at which the damping element  76  moves sufficiently far to the right where the second flute  78  opens a path from the armature bore  74  into the first chamber  81 . This operation produces a similar damping curve as illustrated in  FIG. 2 . Therefore the first control valve  30  exhibits digressive damping in both directions of operation. 
       FIG. 3  illustrates a second type of an armature  90  which has an alternative digressive damping element  92 . This armature  90  has a longitudinal bore  91  extending between both ends of the armature. One end of the longitudinal bore  91  has an enlarged opening in which a flat, disk-shaped damping element  92  is held by a snap-type retaining ring  93 . With additional reference to  FIG. 4 , the disk-shaped damping element  92  has a U-shaped slot  94  extending there through and centrally located therein. The slot  94  forms a flap  96 . When the armature  90  moves within the solenoid actuator  60 , the pressure differential between the chambers  81  or  82  on opposite sides of the armature causes the flap  96  to bend away from the plane of the disk. This produces an opening through that disk. That opening increases the size of the passage through which fluid flows between the two chambers  81  and  82 . The flap  96  is able to bend in either direction from the plane of the disk to accommodate the bidirectional motion of the armature  90 . This disk-shaped digressive damping element  92  functions in a similar manner to the cylindrical damping element  76  and its spring  80  shown in  FIG. 1 . 
       FIG. 5  illustrates a second control valve  100  in which components that are the same as those in the first control valve  30  have been assigned identical reference numerals. To simplify the description herein, those components will not be described in detail again. The second control valve  100  has a normally high pressure state, meaning that when electric current is not being applied to the electromagnetic coil  62 , the valve element  102  is biased into a position in which a path is formed between the pressurized fluid supply port  36  and the workport  40 . As a consequence, the valve element  102  is slightly different so that the apertures  104  that extend outward from the central bore  106  are located to communicate with the supply port  36  in that de-energized state. The valve element  102  directly abuts the armature  110 . 
     The armature  110  also is slightly different in that the armature aperture  114  is located in the midsection of the armature bore  112 . The cylindrical digressive damping element  116 , located in the armature aperture  114 , is biased by a damping spring  118  connected to the side of the damping element that faces the valve element  102 . The damping spring  118  is identical to the previously described damping spring  80  for the first control valve  30  and is secured to the damping element and in the armature bore  112  in the same ways. 
     An armature spring  120  biases the armature  110  away from the exterior end of the solenoid actuator  60  so as to push the armature and the valve element  102  into the normally high pressure state of the valve that is illustrated. A spring adjustment cup  122  is press fitted into an aperture in the first pole piece  124  by an amount that sets the force which the armature spring  120  exerts on the armature  110 . A second pole piece  126  provides an interior cylindrical surface against which the armature  110  slides. 
     When electric current is applied to the electromagnetic coil  62  of the second control valve  100 , a magnetic field is produced within the solenoid actuator  60  that pulls the armature  110  father into the electromagnetic coil, i.e., to the left in the orientation of the drawing. This action compresses the armature spring  120 . The bias force applied to the valve element  102  by the conical coil spring  45  pushes the valve element against the end of the armature  110  thereby causing the valve element to follow the motion of the armature. Therefore, the valve element  102  initially moves into a position in which the transverse apertures  104  are covered by a land  105  within the valve body bore  34 . In this position, the fluid communication which previously existed between the supply port  36  and the workport  40  is terminated. Thus, fluid is not allowed to flow between those ports. It should be understood that by applying the proper level of electric current to the electromagnetic coil  62 , the valve element  102  may be maintained in this closed position. Application of a greater level of electric current to the electromagnetic coil  62  enables the armature  110  and the valve element  102  to move farther leftward into a position at which the apertures  104  in the valve element open into the exhaust port  38 . Fluid communication now is established between the workport  40  and the exhaust port  38  through the valve element bore  106  and the apertures  104 . 
     As the armature  110  of the second control valve  100  moves, fluid is forced to flow between the first and second solenoid chambers  81  and  82 . The direction of that flow depends upon the direction in which the armature  110  is moving. For example, when the armature  110  moves to the left in  FIG. 5 , fluid is forced from the second chamber  82  into the first chamber  81 . Initially the fluid flows only around the outside of the armature  110  and through its bore  112  past the closed digressive damping element  116 . As the pressure within the second solenoid chamber  82  increases due to greater velocity of the armature  110 , the force exerted on the end of the damping element  116  that faces the second chamber  82  increases. Eventually the force pushes the damping element  116  into a position in which the first flute  126  provides a path between both sides of the armature aperture  114 . This increases the amount of fluid flow from the second chamber  82  into the first chamber  81 . This operation provides digressive damping of the motion of the armature  110  and the valve element  102 , as depicted in  FIG. 2 . 
     Thereafter, when the electric current is removed from being applied to the electromagnetic coil  62 , the force of the armature spring  120  returns the armature  110  and the abutting valve element  102  to the normal position illustrated in  FIG. 3 . The pressure differentials produced in chamber  81  and  82  by the armature motion are similar to but reversed from those produced when the electromagnetic coil was energized. In response, the digressive damping element  116  operates in a reverse manner, damping the fluid flow from the first chamber  81  into the second chamber  82 . Therefore the damping element  116  provides digressive damping of the bidirectional movement of the armature  110  and valve element  102  in the second control valve  100 . 
     It should also be appreciated that the disk-type digressive damping element  92  shown in  FIG. 4  could be substituted for the cylindrical damping element  116  in the second control valve  100 . 
     The foregoing description was primarily directed to one or more embodiments of the invention. Although some attention has been 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.