Abstract:
A solenoid valve and method has a simplified structure that integrates the fluid metering functions of the spool in the armature, thereby eliminating the need for a separate spool, bearings, and pin in the valve. The armature has a aperture that communicates with at least one port in a valve body. The position of the differential in the armature with respect to the ports in the valve body controls the pressure of fluid exiting the outputs of the valve body. In one embodiment, the same overall valve structure can be modified to form both inversely proportional valves and directly proportional valves. By integrating the fluid metering functions of the spool into a single ported armature, the inventive valve assembly reduces the number of parts in the valve, simplifying construction.

Description:
TECHNICAL FIELD 
   The present invention relates to electrically operated valves, and more particularly to electrically operated solenoid valves that control fluid pressure based on the amount of current through the solenoid. 
   BACKGROUND OF THE INVENTION 
   Solenoid operated valves have found widespread usage in on-board vehicle applications for controlling hydraulic pressure and fluid flow in automatic shifting power transmissions on the vehicle. Conventional solenoid valve structures include a solenoid that receives an electrical current signal, an armature that moves in response to the signal via magnetic force, and a spool that operates in response to the armature movement to change a pressure output of the valve. A pin acts as a mechanical interface between the armature and the spool. A spring force acts on the armature as well; as a result, the position of the armature and spool, and therefore the valve pressure, depends on the counterbalance of forces in the spring, the magnetic forces on the armature, and the hydraulic pressure. Normally, the spool is continually engaged with the armature via any pressure imbalances on the spool, the spring force, or both. The spool therefore meters fluid out of the valve based on the armature position. 
   Occasionally, contaminants may enter the valve. To loosen the contaminants so that they can be flushed out of the valve, a dithered signal is applied to the armature to continually oscillate the armature, and therefore the spool. However, proper valve operation requires the armature and spool to be in constant contact. Low operating pressures within the valve may cause the spool to lose contact with the armature, preventing dither in the armature from being transferred to the spool. As a result, any future movement by the spool must first overcome static friction, causing the spool to unstick itself in an uncontrolled fashion, creating undesirably rapid pressure change at the valve output. 
   Also, currently known valve structures require tight manufacturing tolerances. The alignment of the pin, armature and spool are particularly delicate and must be perfectly linear and centered to ensure proper valve operation. If any one of these components is even slightly out of alignment, the valve will fail. The pin, in particular, must be perfectly aligned with the spool; however, the length of the pin and the spool causes any misalignments in the pin to be magnified at the spool. The many components in current valve assemblies makes it challenging to manufacture and introduces greater opportunities for potential valve malfunctions. 
   There is a desire for a solenoid valve assembly that operates more reliably and also has a simpler construction than currently known valve assemblies. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is directed to a solenoid valve and method having a simplified structure that integrates the fluid metering functions of the spool in the armature, thereby eliminating the need for a separate spool, bearings and pin in the armature. The valve assembly includes an armature that is responsive to a spring force, a magnetic force generated by the solenoid, and fluid pressure in the valve. The armature has an aperture that communicates with at least one port in a valve body. The position of the differential in the armature with respect to the ports in the valve body controls the pressure of fluid exiting the outputs of the valve body. In one embodiment, the same overall valve structure can be modified by changing the position of a pole piece and the porting in the valve body to form both inversely proportional valves and directly proportional valves. 
   By integrating the fluid metering functions of the spool into a single ported armature, the inventive valve assembly reduces the number of parts in the valve and simplifies the alignment of parts within the valve. Moreover, the simplified valve structure allows the same overall structure be used for different types of valves with only minor modifications. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a representative solenoid valve assembly; 
       FIG. 2  is a representative section view of the valve taken along line  2 - 2  in  FIG. 1 ; 
       FIGS. 3A through 3C  are schematic diagrams of a relationship between a aperture in the armature and the ports at various stages of operation in the valve of  FIG. 1 . 
       FIG. 4  is a section view taken along line  2 - 2  of  FIG. 1  of an alternative embodiment of the invention; and 
       FIGS. 5A through 5C  are schematic diagrams of a relationship between the aperture in the armature and the ports at various stages of operation in the valve of  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , a valve  10  having an inventive integrated structure includes a housing  12  and a valve body  14 . The housing  12  encases other valve components and includes a casing portion  16  and a cover portion  18 . As will be described in greater detail below, either the casing  16  or the cover  18  can act as a magnetic pole for the valve  10 , depending on the desired operation of the valve  10 . An exposed portion  20  of the valve body  14  is configured to fit in a manifold (not shown) and has one or more openings  36   b  through which fluid can flow at various pressures. 
     FIG. 2  is a section view of the valve  10  taken along line  2 - 2  of  FIG. 1 . In this embodiment, the cover portion  16  of the housing  12  acts as the magnetic pole for the valve  10  to create an inversely proportional valve. The housing  12  encases an armature  30  that surrounds a hidden portion  32  of the valve body  14 . The armature  30  has an aperture  34  that communicates with one or more ports  36  of the valve body  14  to meter fluid flow in response to changes in fluid pressure at the ports  36 . The ports  36  each have a first opening  36   a  within the housing  12  and a second opening  36   b  outside the housing  12 , allowing fluid to freely communicate through the ports  36  to and from a fluid supply (not shown), a fluid exhaust (not shown) and a manifold (not shown). The fluid pressure within the aperture  34  pushes the armature  30  toward the casing  16  (toward the left in the orientation shown in  FIG. 2 ). A spring  38  also applies a biasing force on the armature  30  to push the armature  30  toward the cover  18  (toward the right in  FIG. 2 ), in the opposite direction of the force from the fluid pressure in the aperture  34 . 
   The armature  30  is disposed inside a non-magnetic bobbin  40 , which supports a conductive winding forming a solenoid  42 . As is known in the art, current flow through the solenoid  42  generates a magnetic force having a strength that is proportional to the amount of current, and this magnetic force is applied to the armature  30  to pull the armature toward the casing  16  of the housing  12  (toward the left in the orientation shown in  FIG. 2 ). As a result, the position of the armature  30  is dependent on the interacting forces applied to the armature  30  by the spring  38 , the magnetic force, and the hydraulic force generated by the fluid flowing through the aperture  34 . The armature  30  will change position until these forces counterbalance each other into an equilibrium state. In this inversely proportional valve example, the spring force is equal to the sum of the magnetic force and the fluid force applied to the armature  30 , or F magnet +F fluid =F spring . In this example, the output pressure of the valve  10  decreases as the current to the valve  10  increases. 
   As a result, the fluid pressure at the outputs  36  can be controlled by changing the amount of current through the solenoid  42 , which in turn changes the magnetic force on the armature  30 ; the movement of the armature&#39;s position will then change which internal openings  36   a  are covered or exposed, changing the control pressure inside the ports  36  through the valve body  14  and therefore changing the output pressure of the valve  10 . 
   A calibration assembly  50  is connected to the housing  12  to allow control of the tension in the spring  38  and/or the size of an air gap  52  between the casing  16 , which acts as the magnetic pole in this embodiment, and the armature  30  The calibration assembly  50  can have any desired structure and is not critical to the claimed invention. In one embodiment, the calibration assembly  50  includes a first threaded portion  54  that engages with the valve body  14  to set the size of the air gap  52  and a second threaded portion  58  that engages with the first threaded portion  54  to set the spring  38  tension. In one embodiment, the first and second threaded portions  54 ,  58  are threaded in opposite directions (i.e., one has a left-hand thread and the other has a right-hand thread), and a calibration support  56  locks the first threaded portion  54  and the second threaded portion  58  together. 
   Near the cover portion  18  of the housing  12 , a spring washer  60  creates physical resistance against movement of the first threaded portion  54  to set the size of the air gap  52 . A clip  62  is attached to the valve body  14  to hold the valve  10  assembly together. 
     FIGS. 3A through 3C  show the armature  30  in various operating states. Because the valve  10  in this embodiment is an inversely proportional valve, the fluid pressure at the valve output  36  decreases as the current applied to the solenoid  42  increases. 
   The port openings  36   a  in the hidden portion  32  of the valve body  14  include a supply port P 1 , a control port P 2 , and an exhaust port P 3 . The control port P 2  is always fluidically coupled to the armature  30  via the aperture  34  and controls the output pressure of the valve  10 . As can be seen in the figures, the aperture  34  is configured so that the control port P 2  is connectable primarily to either the supply port P 1  or the exhaust port P 3 . To change the output pressure, the magnetic force F magnet  applied to the armature  30  is changed, causing the armature  30  to move along the valve body  14 . This, in turn, causes the aperture  34  to connect the control port P 2  to either the supply port P 1  or exhaust port P 3 , depending on whether the fluid pressure is to be increased or decreased at the output  36   b  of the control port P 2 . The changing fluid pressure brings the armature  30  back to an equilibrium state. 
     FIG. 3A  shows the armature in a steady state position. At this point, F magnet +F fluid =F spring  and therefore the aperture  34  only exposes the control port P 2 , substantially covering the supply port P 1  and the exhaust port P 3  so that only leakage fluid can enter or exit the aperture  34 , allowing the armature  30  to maintain its steady state position. If there is no current being sent through the solenoids, the magnetic force F magnet  is zero, and the fluid force F fluid  is equal to the spring force F spring . During manufacturing, the spring force is calibrated via the calibration assembly  50  based on the desired fluid force that will be considered “steady state” when the solenoid is de-energized. 
   Referring to  FIG. 3B , increasing the current through the solenoid  42  decreases the fluid pressure at the control port P 2  and therefore its corresponding output  36   b . More particularly, the increasing current will increase the magnetic force F magnet  acting on the armature  30 , causing the armature to move toward the casing portion  16  of the housing  12  (toward the left) acting as the magnetic pole. This creates a pressure imbalance because the increased magnetic force F magnet  causes the sum of the magnetic force F magnet  and the fluid force F fluid  to be greater than the counteracting spring force F spring . The new position of the armature  30 , as shown in  FIG. 3B , causes the aperture  34  to be fluidically coupled to both the control port P 2  and the exhaust port P 3 . This allows fluid contributing to the excess fluid pressure F fluid  to flow from the control port P 2  into the aperture  34  and out the exhaust port P 3 , decreasing the fluid pressure F fluid  in the control port P 2  and causing the armature  30  to move and meter (i.e., cover/uncover the supply port P 1  and/or the exhaust port P 3  to varying degrees) in response to the changing fluid pressure. The fluid pressure F fluid  continues to decrease until it compensates for the increased magnetic force F magnet  to equalize the spring force F spring . At this point, the armature has metered so that the armature  30  covers the exhaust port P 3  nearly completely and is at the steady state ( FIG. 3A ) at the new fluid pressure. 
   When the current is reduced or shut off, the magnetic force F magnet  will go down as well. As a result, the imbalance between the fluid force F fluid  and the spring force F spring  will cause the fluid force within the aperture  34  to initially push the armature  30  toward the cover portion  18  of the housing  12  (because the spring force F spring  at this point will be greater than the sum of the magnetic force F magnet  and the fluid pressure F fluid ). This causes the aperture  34  in the armature to fluidically couple the control port P 2  with the supply port P 1 , as shown in  FIG. 3C . Additional fluid flows from the supply port P 1  into the aperture  34  and increase the fluid pressure F fluid  at the control port P 2 , causing the armature  30  to move and meter the fluid flow until the fluid pressure in the aperture compensates for the decreased magnetic force F magnet  to equalize the spring force F spring . Once this occurs, the armature  30  will again reach the steady state position in  FIG. 3A , substantially closing off the supply port P 1  to maintain the fluid pressure corresponding to the amount of current through the solenoid  42 . 
   The examples described above focus on an inversely proportional valve assembly, but the same inventive concept can be used in a proportional valve.  FIGS. 4 and 5A  through  5 C show the structure and operation of a proportional valve  10  according to one embodiment of the invention. In this embodiment, the cover portion  18  of the housing  12  serves as the magnetic pole. In this embodiment, the valve  10  operates according to the equation F magnet =F spring +F fluid . The pole orientation and the spring tension causes the valve  10  to operate so that when the output pressure of the valve  10  increases as the current to the valve  10  increases. 
   The steady state position of the armature  30  relative to the inputs  36   a  of the ports  36  as shown in  FIG. 5A  is conceptually the same as the position shown in  FIG. 3A , with the aperture  34  in the armature fluidically coupled to the control port P 2 , with possible leakage coming through the supply port P 1  and the exhaust port P 3  to maintain the selected fluid pressure. To increase the fluid pressure, the current through the solenoid  42  is increased, thereby increasing the magnetic force F magnet  on the armature  30 . As a result, the combined spring force F spring  and increased magnetic force F magnet  is initially greater than the fluid force F fluid , pushing the armature  30  toward the cover  18  (i.e., toward the right in  FIG. 4 ). As a result, the aperture  34  exposes the supply port P 1  and couples it with the control port P 2  ( FIG. 5C ). Fluid then flows through the supply port P 1  into the control port P 2  and is metered by the armature  30  until the increased fluid pressure F fluid  compensates for the increase in the magnetic force F magnet . 
   Decreasing the current through the solenoid  42  decreases the magnetic force F magnet , thereby decreasing the fluid pressure F fluid  at the output  36   b  corresponding to the output port P 2 . More particularly, the reduction in the magnetic force F magnet  causes the combined forces applied on the armature  30  by the magnet F magnet  and the spring F spring  to be less than the force applied in the opposite direction by the fluid F fluid , forcing the armature  30  toward the calibration assembly  50  (toward the left in  FIG. 4 ). This causes the aperture  34  to uncover the exhaust port P 3  and couple it to the control port P 2 , which in turn allows fluid to drain out of the control port P 2  through the aperture  34  and out the exhaust port P 3  to reduce fluid pressure. The position of the aperture adjusts and meters until the fluid pressure F fluid  has been reduced sufficiently to compensate for the drop in magnetic force F magnet . 
   By configuring the armature  30  with an aperture  34  that meters fluid flow through the inputs  36   a  of the ports in the valve body  14 , the inventive structure eliminates the need for a separate spool, bearings, and armature pin, thereby reducing the number of components in the valve  10  compared to currently known assemblies. Also, aligning the various components in the inventive valve  10  is simpler because the armature  30  is tube-shaped and fits around the valve body  14 ; as a result, if the armature  30  is properly aligned with the hidden portion  32  of the valve body  14  the valve  10  will work properly. This structure makes it difficult to misalign the armature  30  with the valve body  14  and also ensures that any misalignments that do occur are not magnified along the entire length of the valve body  14 . 
   Also, the lack of a separate spool in the inventive valve  10  makes it impossible for any disconnection between the armature  30  and pressure control. As a result, dithering of the armature can be reliably conducted by simply varying the current applied to the valve; proper dithering is not dependent on the fluid pressure in the valve  10 . These factors improve the valve&#39;s reliability and robustness. The simple configuration also makes it possible to use the same overall configuration for different valve types (i.e., proportional, inversely proportional) through minor machining modifications, reducing manufacturing complexity. 
   Although the invention has hereinabove been described with respect to the illustrated embodiments, it will be understood that the invention is capable of modification and variation and is limited only by the following claims.