Abstract:
A solenoid assembly for providing control over fluid pressure distribution in a transmission, where the solenoid assembly includes a solenoid portion and a valve portion, and the movement of the valve portion is controlled by the solenoid portion. There is a valve which is part of the valve portion, and the valve controls the distribution of fluid between a supply port, a control port, and an exhaust port. The distribution of fluid between the ports may include providing a pressure balance between the supply port and the control port, and allowing any excess fluid to pass through the exhaust port, or controlling the flow of fluid between the supply port and the control port, with any excess fluid exiting the exhaust port.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/891,007 filed Oct. 15, 2013. The disclosure of the above application is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates generally to a solenoid assembly which ensures stable force balance and pressure control with magnetic and hydraulic forces. 
       BACKGROUND OF THE INVENTION 
       [0003]    Solenoids are generally known, and some solenoids are used to control fluid pressure in different types of hydraulic systems. Some transmissions use open-loop systems to control the actuation of different components, and control pressure in different locations in the transmission. Some types of highly precise solenoids have been incorporated into these open-loop applications. However, many different types of solenoids have issues with contamination, and disproportionate magnetic and hydraulic forces during operation. Additionally, despite these solenoids having high levels of precision, the control units for these solenoids need to be individually calibrated in production. Accordingly, there exists a need for a solenoid assembly which overcomes the aforementioned drawbacks, and may be used as part of a closed-loop feedback control system in a transmission to eliminate the need for calibration of the controller. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention is a normally low solenoid assembly for a transmission, where the normally low solenoid assembly has a low, or zero, output when inactivated. The normally low solenoid assembly of the present invention is used for providing control over fluid pressure distribution in a transmission, where the solenoid assembly includes a solenoid portion and a valve portion, and the movement of the valve portion is controlled by the solenoid portion. There is a valve which is part of the valve portion, and a magnet core and armature which are part of the solenoid portion such that the armature moves toward and away from the magnet core. 
         [0005]    A plunger is connected to the armature, and in contact with the valve. A sleeve surrounds the armature and the valve portion, such that the valve portion is substantially contained within the sleeve. A valve seat is part of the valve portion and surrounded by the sleeve, and the valve is selectively in contact with the valve seat. A supply port, a control port, and an exhaust port are formed as part of the sleeve such that all three ports are in fluid communication with the valve portion. 
         [0006]    A return spring is located between the magnet core and the armature, the return spring biasing the armature away from the magnet core, such that the return spring biases the valve toward a closed position. A coil at least partially surrounds the sleeve, the coil being part of the solenoid portion. The armature and plunger move towards the coil when the coil is energized, allowing fluid flowing into the supply port to move the valve away from the valve seat, such that at least a portion of the fluid flows through the control port. When the coil de-energized, the valve moves towards the valve seat, and at least a portion of the fluid flows through the exhaust port. 
         [0007]    The sleeve includes a small diameter portion and a large diameter portion which are integrally formed together. The armature is substantially surrounded by the large diameter portion, and the valve portion is substantially surrounded by the small diameter portion. The supply port, the control port, and the exhaust port are all integrally formed as part of the small diameter portion of the sleeve. A separation plate is located within the large diameter portion of the sleeve, the separation plate separates the valve portion from the solenoid portion, and the plunger extends through the separation plate. 
         [0008]    The valve seat includes a first insert disposed in the small diameter portion of the sleeve, and a second insert disposed in the small diameter portion of the sleeve. The valve in one embodiment is a ball, and the ball is disposed between the first insert and the second insert. The ball is in contact with the second insert when the valve is in the closed position, and the ball moves away from the second insert and towards the first insert when the valve changes to the open position. 
         [0009]    Different types of manufacturing methods may be used to create the solenoid assembly. In one embodiment, the sleeve and the separation plate are deep drawn parts, but it is within the scope of the invention that other types of manufacturing methods may be used. 
         [0010]    In one embodiment, the solenoid assembly of the present invention is used in a closed-loop feedback control system in a hydraulic system for a transmission. 
         [0011]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a sectional side view of a solenoid assembly, according to embodiments of the present invention; 
           [0014]      FIG. 2  is a force balance diagram of a solenoid assembly, according to embodiments of the present invention; 
           [0015]      FIG. 3  is a diagram depicting pressure versus current characteristics of a solenoid assembly, according to embodiments of the present invention; 
           [0016]      FIG. 4  is a sectional side view of an alternate embodiment of a solenoid assembly, according to embodiments of the present invention; 
           [0017]      FIG. 5  is a perspective view of a cap connected to a yoke, which is part an alternate embodiment of a solenoid assembly, according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
         [0019]    A solenoid assembly according to the present invention is shown in  FIG. 1  generally at  10 . The solenoid assembly  10  includes a solenoid portion, shown generally at  12 , and a valve portion, shown generally at  14 . The solenoid portion  12  includes a magnet core  16  connected to a plate  18 . The plate  18  is connected to a yoke ring  20  by a press-fit connection, but it is within the scope of the invention that other types of connections may be used. 
         [0020]    The yoke ring  20  partially surrounds an outer surface of a coil  22 , and the coil  22  at least partially surrounds a bobbin  24 . Surrounded by the bobbin  24  is a sleeve  26 , and the sleeve  26  at least partially surrounds the magnet core  16 , and also at least partially surrounds an outer wall  28  formed as part of a housing  30 . The sleeve  26  is connected to the magnet core  16  and the outer wall  28  through a laser welding process. The housing  30  also includes an inner wall  32 , and a recess, shown generally at  34 , located between the outer wall  28  and inner wall  32 . Partially located in the recess  34  is an armature  36 , which is able to move relative to the magnet core  16  and the housing  30 . 
         [0021]    The armature  36  also includes a stepped portion, shown generally at  38 , which is shaped to correspond to a stepped portion, shown generally at  40 , formed as part of the magnet core  16 . 
         [0022]    A spring  42  is disposed between the magnet core  16  and the armature  36 . More specifically, the spring  42  is partially disposed in a recess, shown generally at  44 , formed as part of the magnet core  16 , and the spring  42  is also partially disposed in another recess, shown generally at  46 , formed as part of the armature  36 . The spring  42  biases the armature  36  away from the magnet core  16 , the function of which will be described later. In one embodiment, the spring  42  is a hot preset spring  42 , which helps to ensure a constant spring preload over the lifetime use of the spring  42 , and have stable force balancing between the magnetic and hydraulic forces in the solenoid assembly  10 . 
         [0023]    The armature  36  also has an aperture  48 , and a plunger  50  is press-fit into the aperture  36 . However, it is within the scope of the invention that plunger  50  may be held in place in the aperture  48  in other ways. The plunger  50  extends through another aperture  52  formed as part of the inner wall  32  of the housing  30 , such that the plunger  50  is at least partially surrounded by the inner wall  32 . The plunger  50  and armature  36  are also movable relative to the housing  30 , such that a portion of the plunger  50  slides within the aperture  52  formed as part of the inner wall  32 , and the inner wall  32  also functions as a guide to the movement of the plunger  50 , and prevents the armature  36  from moving relative to the sleeve  26  in an undesirable manner. 
         [0024]    The housing  30  also includes an exhaust port  54 , which is in fluid communication with an intermediary port  56 , the intermediary port  56  is in fluid communication with a control port  58 , and the control port  58  is in fluid communication with a supply port  60 . Disposed in the intermediary port  56  is a first insert  62 , and the first insert  62  includes an exhaust seat  64 . Disposed in the supply port  60  is a second insert  66 , and the second insert  66  includes a supply seat  68 . The first insert  62  is press-fit into the intermediary port  56 , and the second insert  66  is press-fit into the supply port  60 . The plunger  50  also includes a reduced diameter portion  70  which extends through the intermediary port  56  and partially into the control port  58 . The reduced diameter portion  70  contacts a valve, which in this embodiment is a ball  72 , but it is within the scope of the invention that other types of valves may be used. The reduced diameter portion  70  and the ball  72  are part of the valve portion  14 . 
         [0025]    In operation, pressurized fluid flows into the supply port  60  and is prevented from entering into the control port  58  because the spring  42  biases the valve portion  14  to a closed position when no current is applied to the coil  22  (the ball  72  is in contact with the supply seat  68  when the valve portion  14  is in the closed position, as shown in  FIG. 1 ). When current is applied to the coil  22 , magnetic force is generated to overcome the force of the spring  42  applied to the armature  36 , such that the armature  36  moves toward the magnet core  16 , and therefore the plunger  50  also is moved away from the ball  72 , allowing the ball  72  to lift off of the supply seat  68 , and fluid to pass from the supply port  60  to the control port  58 . 
         [0026]    When the ball  72  is in the closed position, as shown in  FIG. 1 , there is an air gap between the armature  36  and the magnet core  16 , and the stepped portions  38 , 40  of the armature  36  and magnet core  16  create a larger air gap between the armature  36  and the magnet core  16 , as compared to an armature and magnet core not having stepped portions  38 , 40 . This increased air gap allows for an increased force output between the armature  36  and the magnet core  16  when the coil  22  is energized, and provides for better control over movement of the armature  36  when the coil  22  is energized to place the armature  36  in intermediate positions between the magnet core  16  and the housing  30 . 
         [0027]    If enough current is applied to the coil  22 , the armature  36  and plunger  50  move close enough to the magnet core  16  to allow the ball  72  to contact the exhaust seat  64 , such that all of the fluid from the supply port  60  flows into the control port  58 . However, when the solenoid assembly  10  is used in certain applications, current is applied to the coil  22  to move the armature  36  and allow the ball  72  to move away from the supply seat  68 , and provide a pressure balance between the supply port  60  and the control port  58 . Additionally, the current applied to the coil  22  may be varied to control the fluid passing between the supply port  60  and control port  58 , and therefore control the fluid pressure in the supply port  60  and control port  58 . 
         [0028]    Once the current is no longer applied to the coil  22 , there is no longer a magnetic attraction between the armature  36  and the magnet core  16 , and the spring  42  moves the plunger  50  and armature  36  away from the magnet core  16 , and therefore moves the ball  72  toward the supply seat  68  to place the valve portion  14  in the closed position. As this occurs, fluid in the control port  58  flows through the intermediary port  56  and through the exhaust port  54 . The amount of current applied to the coil  22  may be varied to vary the position of the armature  36 , plunger  50 , and therefore the ball  72 , to vary the amount of fluid passing from the supply port  60  to the control port  58  and exhaust port  54 . A chart depicting the force balance relationship between the current applied to the coil  22 , the force applied to the armature  36  by the spring  42 , and the position of the armature  36  is shown in  FIG. 2 . The current shown as part of the chart in  FIG. 2  includes several curves depicting current verses force at multiple currents. The curve for the hydraulic force is shown at  96 , the curve for the spring force is shown at  98 , and curve for the summation of the hydraulic force  96  and spring force  98  is shown at  100 . 
         [0029]    A chart depicting the pressure in the control port  58  versus the current applied to the coil  22  is shown in  FIG. 3 . The solenoid assembly  10  of the present invention is referred to as a “normally low” solenoid assembly, in reference to the state of the output. When no current is applied to the coil  22  (the solenoid assembly  10  is inactive), the ball  72  is in contact with the supply seat  68 , and the pressure in the control port  58  is very low or substantially zero. The pressure in the ports  54 , 58 , 60  may be detected using one or more pressure sensors. As the current is applied to the coil  22  and then increased, the ball  72  moves away from the supply seat  68  and closer to the exhaust seat  64 , increasing the pressure in the control port  58 . This relationship of increase in current applied to the coil  22  and increase in pressure in the control port  58  is shown in  FIG. 3 . When the ball  72  is in contact with the exhaust seat  64 , the pressure in the supply port  60  and the pressure in the control port  58  are substantially equal. In one embodiment, the solenoid assembly  10  is used as part of a closed-loop feedback control system in a transmission. 
         [0030]    The solenoid assembly  10  also has several features to prevent debris from flowing into the area around the armature  36 . The plunger  50  includes several ribs  74  which create a tortuous path for the flow of the fluid, and therefore limits or prevents debris from flowing past the plunger  50  and around the armature  36 . The ribs  74  also reduce friction between the plunger  50  and the aperture  52 , and the fluid in the ribs  74  also provides lubrication to reduce wear. In one embodiment, the armature  36  is also coated with a Teflon coating to reduce friction between the armature  36  and the outer wall  28 . 
         [0031]    Formed as part of the sleeve  26  are exit apertures  76 , and fluid around the armature  36  is able to flow out of the exit apertures  76  and around the sleeve  26 , and out one or more grooves  78  formed as part of the housing  30 . The exit apertures  76  and the grooves  78  provide pressure equilibrium around the armature  36 , such that any fluid that flows into the area around the armature  36  has little to no effect on the movement of the armature  36 . Additionally, the flow path through the exit apertures  76  and the grooves  78  creates a tortuous path to prevent dirt migration into the air gap between the armature  36  and magnet core  16  from outside of the assembly  10 . 
         [0032]    To facilitate optimal contact between the ball  72  and the supply seat  68  and contact between the ball  72  and the exhaust seat  64 , both the supply seat  68  and exhaust seat  64  have a tapered edge, or sharp edge  68 A and  64 A, respectively, to balance forces under flow conditions. The seats  64 , 68  also ensure stable functionality over various temperature ranges, and control leakage over the lifetime of the assembly. The shape of the edges  64 A, 68 A minimizes the hydraulic force variations at constant supply pressure during positioning of the ball  72 , and ensure a stable sealing diameter and hydraulic force on the ball  72  over the lifetime of the assembly  10 . 
         [0033]    Another embodiment of the present invention is shown in  FIGS. 4-5 , with like numbers referring to like elements. However, in this embodiment, the housing  30  is not used, and the sleeve  26  is larger such that the sleeve  26  contains the valve portion  14 . In one embodiment, the sleeve  26  is a deep drawn part, containing all the parts of the valve portion  14 . The sleeve  26  shown in  FIG. 3  is magnetic conductive to optimize the magnetic forces between the armature  36  and the magnet core  16 . In one embodiment, the armature  36  shown in  FIG. 3  has a Teflon coating to reduce friction between the armature  36  and the sleeve  26 , and reduce the magnetic eccentric forces. The sleeve  26  in this embodiment has two portions, a large diameter portion  26 A and a small diameter portion  26 B. The armature  36  is located in the large diameter portion  26 A, and the valve portion  14  is located in the small diameter portion  26 B. More specifically, both of the inserts  62 , 66  and the ball  72  are located in the small diameter portion  26 B of the sleeve  26 . The ball  72  in this embodiment has a larger diameter than the ball  72  shown in  FIG. 1 , which reduces hydraulic force variations in the valve portion  14 . 
         [0034]    Additionally, the exhaust port  54  is formed as part of the large diameter portion  26 A, the control port  58  is formed as part of the small diameter portion  26 B, and the supply port  60  is formed as part of the small diameter portion  26 B. The supply port  60  shown in  FIG. 3  extends outwardly away from the second insert  66 , and has a diameter that is smaller than the diameter of the small diameter portion  26 B. 
         [0035]    Also, in this embodiment, there is a separation plate  80  located within the sleeve  26 , and the plate  80  has an aperture  82  which the plunger  50  extends through. The separation plate  80  is located in the large diameter portion  26 A of the sleeve  26  in an area between the armature  36  and the exhaust port  54 . The separation plate  80  separates the valve portion  14  from the solenoid portion  12 , preventing the solenoid portion  12  from being exposed to the fluid in the valve portion  14 . In one embodiment, the separation plate  80  is a deep drawn part, but it is within the scope of the invention that other methods may be used to form the separation plate  80 . 
         [0036]    The yoke ring  20  shown in  FIG. 3  is larger than the yoke ring  20  shown in  FIG. 1 , and includes several retention features shown generally at  86 . The retentions features  86  are integrally formed with the yoke ring  20 , and the yoke ring  20  in this embodiment is formed as a single piece, and as a deep drawn part, but it is within the scope of the invention that other methods may be used to form the yoke ring  20 . The sleeve  26  is connected to the yoke ring  20  through the use of a first weld connection  90 , and the sleeve  26  is also connected to the magnet core  16  through the use of a second weld connection  92 . 
         [0037]    The embodiment shown in  FIG. 3  also includes a cap, shown generally at  88 , which connects with and is surrounded by part of the yoke ring  20 . The cap  88  is connected to the yoke ring  20  through a snap-fit connection, shown generally at  94 , in  FIG. 5 . The snap fit connection  94  also functions to properly position the cap  88  relative to the yoke ring  20 , such that any data marking on the cap  88  is correctly positioned as well. Furthermore, the cap  88  also protects electrical terminals  102  from becoming exposed and contaminated by the fluid. 
         [0038]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.