Patent Publication Number: US-2005139273-A1

Title: Electromechanically controlled proportional valve

Description:
BACKGROUND of the INVENTION  
      The invention relates to an electromechanically controlled proportional valve. In particular a preferred use of the valve is for clutch activation in transmissions for vehicles having motors that develop high-intensity torque. The valve is of a cartridge type which is insertable in a support element and connectable thereto. A mobile obturator located internally of a hollow body selectively places in communication some openings, from which a pressurized operating fluid flows, with some outlets predisposed to send the pressurized fluid to an actuator, typically a hydraulic cylinder predisposed to close the clutch which, in the absence of commands, is kept open by springs or like elements.  
      In known-type valves the mobile obturator exhibits a substantially axial conduit which connects the inlet openings with a pilot conduit, placing the valve in communication with a storage reservoir for the operator fluid. The outlet of the pilot conduit can be closed by means of a spherical control bearing on which an electromechanical actuator operates. The actuator, on command, presses the bearing against the pilot conduit outlet. The action of the electromechanical actuator on the control bearing leads to an increase of pressure in an internal chamber of the valve which induces a movement of the obturator towards a position in which the pressurized fluid reaches the hydraulic actuator.  
      In known-type valves the axial conduit of the obturator sends the pressurized oil directly onto the control bearing. The dynamic action of the oil flow makes an equilibrium position difficult to reach, in which the bearing maintains a certain position with respect to the pilot conduit outlet. Turbulence in the oil flow can lead to vibrations which compromise the precision of the valve operation.  
      The electromechanical actuator acts on the control bearing by means of a stem, a length of which must correspond with extreme precision to a defined value, in order to guarantee that the valve will function correctly. In known-type valves correct operation is guaranteed during a testing stage of the valves by substituting the stems with stems having different lengths, until the correct-length stem is identified. This operation is very slow and laborious, as it requires a valve which is already full of oil to be dismounted in order for the stem to be changed. This operation may need repeating several times until the correct-length stem is found.  
      Known-type valves also require additional components in order that they can be fixed to support elements therefor.  
      The main aim of the present invention is to provide an electromechanically controlled proportional valve which enables the drawbacks in the prior art to be obviated.  
      An advantage of the present invention is that a relatively stable pressure acts on the bearing, i.e. a pressure which is not subject to sharp fluctuations due to turbulence in the fluid; as a result the valve is extremely stable.  
      A further advantage of the invention is that the regulation of the stem length by which the electromechanical actuator acts on the bearing is extremely simple and rapid and does not require the valve to be dismounted.  
      A further advantage of the invention is that the valve can be fixed to the relative support element without additional components or mechanisms.  
     SUMMARY of the INVENTION  
      The proportional valve is insertable in a support element and comprises a hollow body having a plurality of inlet openings, a plurality of outlet openings and a plurality of discharge openings. The hollow body further comprises a pilot channel afforded in a base surface, an end of which pilot channel can be closed by a bearing. The valve comprises an obturator which is predisposed to place in communication the inlet, outlet and discharge openings selectively. The obturator exhibits an internal channel which transmits a pressure in the inlet openings to the bearing. The hollow body is screwed to a container which houses an electromechanical actuator that acts on the bearing. The valve can be connected to the support element by means of a screw. 
    
    
     BRIEF DESCRIPTION of the DRAWINGS  
      Further characteristics and advantages of the present invention will better emerge from the detailed description that follows of an electromechanically controlled proportional valve, illustrated purely by way of a non-limiting example in the accompanying figures of the drawings, in which:  
       FIG. 1  is an overall view in section of a valve according to the invention;  
       FIG. 2  is an exploded view of a part of the valve of  FIG. 1 ;  
       FIG. 3  is a detail of the valve of  FIG. 1 , installed and connected to a support element. 
    
    
     DESCRIPTION of the PREFERRED EMBODIMENTS  
      With reference to the figures of the drawings, the valve of the present invention comprises a hollow body  2 , cylindrical in shape and having a longitudinal axis x which comprises a lateral surface  2   a , and a first and a second base surface  2   b ,  2   c . The hollow body exhibits a cylindrical internal cavity  3  and is radially provided, on the lateral surface  2   a , which a plurality of inlet openings  4 , a plurality of outlet openings  5  and a plurality of discharge openings  6 . The inlet openings  4  are predisposed for connecting the internal cavity  3  with a pressurized operator fluid source, for example a positive displacement pump. The outlet openings  5  are predisposed for connecting the internal cavity  3  with an actuator, for example a cylinder for closing the clutch. The discharge outlets  6  are predisposed for connecting the internal cavity  3  with a reservoir from which the operator fluid is taken by the positive displacement pump. The inlet openings  4  can be protected by a filter surface  25  enveloping the hollow body  2 .  
      The hollow body  2  further comprises a pilot channel  7  afforded in the first base surface  2   b  and coaxial to the longitudinal axis x. The exit of the pilot channel  7  can be occluded by a bearing  8  which is mobile in a parallel direction to the longitudinal axis. The pilot channel  7  is predisposed to place the internal cavity  3  in communication with a discharge chamber  40 , the function of which will be better clarified herein below, which discharge chamber  40  is annular and arranged coaxially to the hollow body  2 . The discharge chamber  40  exhibits secondary outlet openings  6   a  connected to the reservoir of operator fluid.  
      The valve of the invention further comprises a container  50 , preferably cylindrical, internally of which an electromechanical actuator  9  and a cylindrical element  18  which is coaxial to the longitudinal axis x are arranged. At an end thereof the cylindrical element  18  exhibits a cylindrical seating  19 , coaxial to the longitudinal axis x, internally of which the bearing  8  can slide. The cylindrical element  18  also exhibits a through-hole, coaxial to the longitudinal axis x, along which a stem runs  10 . The electromechanical actuator  9  is predisposed on command to exert on the stem  10  a force directed along the longitudinal axis x. Following the application of this force, the stem  10  pushes the bearing  8  towards the exit of the pilot channel  7 .  
      The cylindrical seating  19  is provided with radial through-holes  19   a  which place the seating in communication with the discharge chamber  40 . At least two of the through-holes  19   a  open into shaped portions  18   a  of the cylindrical element  18  located in a diametrically opposite position with respect to the cylindrical element  18 . The shaped portions  18   b  are flattened areas of the lateral surface of the cylindrical element  18 . The arrangement of the radial through-holes  19   a  induces a fluid circulation, about parallel to the longitudinal axis x, about the cylindrical element  18 . From the radial through-holes  19   a  which open onto the shaped portions  18   b  the fluid tends to move in a distancing direction from the discharge chamber  40 , while from the other radial through-holes  19   a  the fluid is directed towards the discharge chamber  40 . Thanks to the fluid circulation the internal chamber in the container  50 , in which the cylindrical element  18  and the cursor of the electromechanical actuator  9  are located, fills rapidly and is kept constantly full of fluid; this is a factor which increases the precision and the stability of the valve operation. The hollow body  2  is connected to the container  50  in such a way that it projects, at least for a tract thereof, internally of the container  50 . The discharge chamber  40  is defined between the above-mentioned tract of the hollow body  2  and a projecting cylindrical portion  50   a  of the container  50 . In greater detail, the hollow element  2  is screwed to the container  50 , projecting inwardly of the projecting cylindrical portion  50   a , which internally exhibits a threading having a mean diameter which is smaller than the internal diameter of the cylindrical portion  50   a . In this way, a hollow space is created between the hollow body  2  and the cylindrical portion  50   a ; this hollow space defines the discharge chamber  40 .  
      The cylindrical element  18  comprises an annular expansion  18   a  predisposed to rest against a striker surface  40   a  of the discharge chamber  40  and prevent distancing displacements of the cylindrical element  18  from the hollow body  2 . Elastic means  20  are interpositioned between the cylindrical element  18  and the hollow body  2  to keep the annular expansion  18   a  in contact with the striker surface  40   a.    
      The threaded connection between the hollow body  2  and the container  50 , and the contact between the annular surface  18   a  and the striker surface  40   a  enable the length of the stem  10  to be adapted to the desired operating characteristics of the valve. The elastic means, for example Belleville washers, keep the cylindrical element  18  in striking position against the discharge chamber  40 , so by unscrewing or screwing the hollow element  2  it is possible to vary the force the stem  10  exerts on the bearing  8  both in the presence of a command to the electromechanical actuator and in absence thereof. Once the relative positioning between the hollow element  2  and the container  50  have been defined, the two parts can be fixed by slightly deforming the edge of the projecting portion  50   a  at a slightly weakened point which can be afforded on the external surface of the hollow element  2 .  
      The valve of the present invention further comprises a cylindrical obturator  11  which is sealingly slidable internally of the internal cavity  3  along the longitudinal axis x. The obturator  11  exhibits an annular channel  13  which defines, with the surface of the internal cavity  3 , a communication chamber  30 . The obturator  11  is mobile between a first position, in which through the communication chamber  30  it places in communication the outlet openings  5  with the discharge openings  6 , and a second position, in which it places in communication, once more through the communication chamber  30 , the outlet openings with the inlet openings  4 .  
      The obturator  11  is provided with an internal channel  14  for placing the inlet openings  4  and the pilot channel  7  in communication when the obturator  11  is in the first position. A terminal tract  15  of the internal channel  14 , which ends close to an inlet of the pilot channel  7 , exhibits a different longitudinal axis x′ to the longitudinal axis x, so that the outlet of the terminal tract  15  does not face the inlet of the pilot channel  7 .  
      The terminal tract  15  of the internal channel  14  is afforded internally of an end element  16  which is inserted in an end of the obturator  11  which is located by the pilot channel  7 . The end element  16  comprises an inlet tract  17  which opens, through a nozzle, into the terminal tract  15 . Preferably the terminal tract  15  is perpendicular to the longitudinal axis x. The inlet tract  17  of the internal channel  14  can be protected by a sleeve filter  26  connected to the end element  16 .  
      The obturator  11  is provided at ends thereof with sealed surfaces  12 , arranged in contact with the surfaces of the internal cavities  3 , between which the annular channel  13  is comprised. At the position of the sealing surfaces the external diameter of the obturator  11  is close to that of the internal cavity  3  in order to prevent oil leakage along the walls of the internal cavity  3 .  
      The obturator  11  comprises a first end surface  11   a , perpendicular to the longitudinal axis x, which defines within the internal cavity  3  a first pilot chamber  31  in communication with the pilot channel  7 . The first pilot channel  31  is defined by the first end surface  11   a  of the obturator  11 , the first base surface  2   b  and the lateral surface  2   a  of the hollow element  2 . In the illustrated embodiment in the figure, the first end surface  11   a  comprises an annular crown which surrounds a central portion  16   a  defined by a base surface of the end element  16 . The central portion  16   a  is arranged in a recessed position with respect to the annular crown, so that when the obturator  11  is in the first position, the annular crown is in contact with the first base surface  2   b  of the hollow element  2 , forming a hollow jacket between the central portion  16   a  and the first base surface  2   b.    
      The obturator  11  further comprises a second end surface  11   b , perpendicular to the longitudinal axis x, which inside the internal cavity  3  defines a second pilot chamber  32 , arranged on an opposite side of the obturator  11  to the first pilot chamber  31 . The second pilot chamber  32  is defined by the second end surface  11   b  of the obturator  11 , the second base surface  2   c  and the lateral surface  2   a  of the hollow element  2 . The second pilot chamber  32  is in fluid communication with the communication chamber  30  through a small-diameter conduit  21 . Elastic means  24  are arranged internally of the second pilot chamber  32 , for example a helix spring arranged between the second end surface  11   b  of the obturator  11  and the second base surface  2   c  of the hollow element  2 , which keep the obturator  11  in the first position thereof.  
      The valve operates as follows.  
      In the absence of commands to the electromechanical actuator  9 , the stem  10  does not exert any force of the bearing  8  which is free to move from the outlet of the pilot channel  7 . Internally of the pilot channel  7  and the first pilot chamber  31 , therefore, the operator fluid pressure is the reservoir pressure, i.e. a “low” pressure. The obturator  11  is kept in the first position by the action of elastic means  24 . In this condition the fluid coming from the positive-displacement pump passes through the inlet opening  4 , penetrates into the internal channel  14  of the obturator  11 , reaches the first pilot chamber  31 , runs along the pilot channel  7 , moves the bearing  8  from the outlet of the pilot channel  7 , reaches the discharge chamber  40  and from there, passing through the secondary outlet openings  6   a , reaches the reservoir.  
      In the presence of a command on the electromechanical actuator  9 , the stem  10  exerts a force on the bearing  8 , which bearing opposes passage of fluid by increasing the pressure in the pilot channel  7 , in the first pilot chamber  31  and in the internal channel  14 . The increase of pressure in the first pilot chamber  31  causes a force which overcomes the elastic means  24  and the pressure in the second pilot chamber  32  and pushes the obturator  11  towards the second position. During the displacement the obturator  11  closes the discharge openings  6  and, through the communication chamber  30 , places the inlet openings  4  in communication with the outlet openings  5 . The pressurized fluid thus reaches the hydraulic actuator. The obturator is kept in this position by the equilibrium between the pressure in the first pilot chamber  31  and the pressure in the second pilot chamber  32  plus the action of the force exerted by the elastic means  24 . The pressure in the second pilot chamber  32 , by dint of the small diameter conduit  21 , is the same as the pressure in the communication chamber  40 , i.e. the pressure in the hydraulic actuator. The small-diameter conduit  21  softens the pressure peaks which can occur internally of the communication chamber  40 . The position of the obturator  11  can be regulated by modulating the signal sent to the electromechanical actuator  9 . This has an influence on the force which is exerted on the bearing  8 , and therefore on the pressure in the first pilot chamber  31 . The regulation of the position of the obturator  11  enables the degree of aperture of the inlet opening  4  to be varied, i.e. the pressure in the communication chamber  30  can be varied, and thus so can the pressure of the fluid sent to the hydraulic actuator.  
      The valve of the present invention can be connected to a support element  100  by a screw  22  passing through a portion of the support element  100 . The support element  100  can be for example a part of a machine on which the valve is mounted. The screw  22  inserts, at least at a terminal portion thereof, into an annular channel  23  afforded externally of the projecting cylindrical portion  50   a  of the container  50 . Preferably the screw  22  is arranged radially of the projecting cylindrical portion  50   a . The screw  22  must be tightened extremely precisely in order to avoid any kind of radial stress on the projecting cylindrical portion  50   a  which might be transmitted to the hollow body  2 . Deformations in the hollow body  2 , even of a small entity, might compromise optimum valve operation.  
      The valve of the present invention offers important advantages. Firstly, it is extremely stable and precise as, thanks to the conformation of the internal channel of the obturator, only a static pressure acts on the control bearing. A further advantage is that the valve is extremely simple and rapid to calibrate, as it is not necessary to dismount the valve in order to replace the stem acting on the control bearing. A further advantage is that fastening the valve to the support element does not require the use of special fastening elements, but only a screw.