Abstract:
A solenoid valve which regulates the pressure in a pressurized fuel injection system includes a body containing a needle that is pressed by an electromagnet including a coil and a magnetic core. The core has a cavity that is in fluid communication via an internal channel with a counterbore in the body into which the needle protrudes and into which fuel flows during use. The core also has a restriction which restricts the fluid communication and which attenuates pressure waves propagating in the fuel to prevent the waves from moving the core.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a national stage application under 35 USC 371 of PCT Application No. PCT/EP2015/063355 having an international filing date of Jun. 15, 2015, which is designated in the United States and which claimed the benefit of FR Patent Application No. 1456266 filed on Jul. 1, 2014 the entire disclosures of each are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL DOMAIN 
       [0002]    The invention relates to a pressure regulating solenoid valve in a common rail of an injection system, notably for an internal-combustion engine. 
       TECHNOLOGICAL BACKGROUND TO THE INVENTION 
       [0003]    Diesel injection systems need to be operational over a wide pressure range covering several thousand bars and a wide temperature range covering the northern winter and the southern summer. The system is provided with a controlled solenoid valve that adjusts the pressure in the common rail of the system to within a few bars. However, pressure waves propagate in the fuel and can disturb the correct operation of said solenoid valve. Said solenoid valve is provided with means for attenuating such waves, notably channels for recirculating some of the fuel between the output of the common rail and the magnetic core of the solenoid valve. 
         [0004]    Unfortunately, such attenuation only works on a limited portion of the pressure range and disturbances may appear outside of this portion, preventing the optimal operation of the solenoid valve and of the system. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention is intended to at least partially address these problems by proposing a solenoid valve that is designed to regulate the pressure in a pressurized fuel injection system. The solenoid valve includes a body containing a needle sliding between a closed position and an open position, the needle being pressed by an electromagnet including a coil rigidly connected to the body and a magnetic core that is movable axially between a first position in which the magnetic core presses the needle into the closed position and a second position in which the needle is free to move to the open position. The core is provided with a cavity that is in fluid communication via an internal channel with a counterbore in the body into which the needle protrudes and into which fuel flows during use. 
         [0006]    The core is also provided with means for restricting said fluid communication that are designed, during use, to attenuate the pressure wave propagating in the fuel and to prevent said waves from moving the core. 
         [0007]    The restriction means are a device designed to naturally block the fluid communication, said device, when in use, closing said communication if a pressure wave propagating in the fuel attempts to move the core to the second position. 
         [0008]    According to one embodiment, the device is a check valve including a ball placed in the channel and a valve seat against which the ball can be positioned to block the channel. 
         [0009]    According to another embodiment, the device includes an elastic member that, when in use, blocks the channel if the core is pushed by a pressure wave towards the second position, thereby preventing said movement, the elastic member opening the channel by bending under the influence of the movement of the core when this latter moves towards the first position. 
         [0010]    More specifically, the elastic member is a membrane attached to the bottom of the cavity. 
         [0011]    According to another embodiment, the elastic member is a diaphragm including flexible arms, one end of which is attached to the bottom of the cavity, while the other movable end is positioned at the output of the channel. According to an alternative, the movable end of the diaphragm only partially obstructs the channel so that the fuel retained in the cavity can exit same via a limited fuel flow. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0012]    An embodiment of the invention is described below using the following figures. 
           [0013]      FIG. 1  is an axial cross section of a pressure regulating solenoid valve known in the prior art. 
           [0014]      FIGS. 2, 3, 4 and 5  are details of a solenoid valve according to three embodiments of the invention. 
           [0015]      FIGS. 6 and 7  show a check diaphragm such as the one used in the solenoid valve in  FIG. 5 . 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0016]    In a diesel injection system  10 , it is known to arrange a solenoid valve  14  at the end of a common rail  12  with a plurality of injectors, said solenoid valve  14  being used to regulate the pressure of the fuel in the rail  12 . The application chosen to illustrate the invention is part of the diesel system. However, the subject matter of the invention is not dependent on fuel type and may be used as part of an injection system for petrol or any other fuel. 
         [0017]    A solenoid valve  14  known in the prior art is described below with reference to  FIG. 1 , using the top-down orientation shown in the figure for the sake of clarity of the description, without thereby limiting same. 
         [0018]    The solenoid valve  14  extends along a main axis A and includes a body  16  designed to fit the end of the rail  12 . There are multiple alternatives to this arrangement that are not detailed here. 
         [0019]    The body  16  has an axial borehole  18  opening out at the ends of the body into a lower counterbore  20  and into an upper counterbore  22 , said borehole  18  containing a sliding needle  24 , the tip  26  of which protrudes into the lower counterbore  20  and, conversely, the head  28  protrudes into the upper counterbore  22 . The needle has a helical groove  30  running from the tip  26  to the head  28 . 
         [0020]    Thus arranged, the needle  24  can move in the borehole  18  between a closed position PF and an entirely open position PO. In the closed position PF, the tip  26  of the needle  24  butts against a valve seat  32  and blocks an output orifice  34  keeping the fuel inside the common rail  12  and, in the open position PO, the tip  26  is withdrawn from the seat  32 , the orifice  34  is opened and the pressurized fuel can exit the rail  12  to flow into a return channel  36 . 
         [0021]    The solenoid valve in  FIG. 1  includes a specific arrangement of the seat  32  positioned in another counterbore of the body  16  with a small ball placed between the seat  32  and the tip  26  of the needle  24 , and a return channel  36  arranged laterally. There are very many alternatives to this arrangement that are also not detailed above. 
         [0022]    At the end opposite the seat  32 , at the top of the figure, the solenoid valve  14  has an electromagnet  38  attached to the top of the body  18 . The electromagnet includes a coil  40  connected to an electronic controller (not shown) and a movable magnetic core  42  that cooperates with the head  28  of the needle  24 . The coil  40  is rigidly connected to the body  16 , is ring shaped and surrounds the top of the body  16 . At the center of the coil there is an axial seat  44  in which the magnetic core  42  is arranged in line with the body  16  and the needle  24 . The magnetic core  42  is cylindrical, extending axially A between an upper face  46  and a lower face  48 , and has a cavity  50  in the form of a cylindrical counterbore opening out onto the upper face  46 , and a channel  52  linking the bottom  54  of the cavity  50  to the lower face  48  of the core  42 . A single channel  52  is described and illustrated here. Nonetheless, alternatives including a plurality of channels  52  also exist. 
         [0023]    Inside the seat  44 , the magnetic core  42  can slide between a low position PB, adopted when the coil  40  is powered electrically, and a high position PH, adopted when the coil  40  is not powered. A spring  56  is compressed between the bottom of the upper counterbore  22  and the lower face  48  of the core  42 , said spring  56  permanently pressing the core  42  towards the high position PH. 
         [0024]    Operation of the solenoid valve  14  is described below. 
         [0025]    If the pressure of the fuel in the common rail  12  is below a predetermined limit stored in the electronic controller, the coil  40  is powered and presses the core  42  into the low position PB. The lower face  48  of the core bears against the head  28  of the needle  24  and holds same in the closed position PF. If the pressure in the common rail  12  reaches said predetermined limit, the power to the coil  40  is stopped and the core  42  moves to the high position PH, pressed simultaneously by the spring  56  and also by the needle  24 , which is pushed into the open position PO by the pressurized fuel coming out of the output orifice  34 . Most of the fuel is then discharged via the return channel  36 , while a lesser portion passes between the needle  24  and the borehole  18 , notably following the helical groove  30 . This fuel moves upwards towards the upper counterbore  22 , then the channel  52  inside the core  42 , and finally the cavity  50 . When the coil  40  is being powered again, the core  42  returns to the low position PB and the portion of the fuel that had moved up towards the core can flow in the opposite direction towards the return channel  36 . 
         [0026]    When in use, the pressure of the fuel must be kept within a range of ±15 bars, while the nominal pressure varies between approximately 200 bars and approximately 2500 bars, the fuel flow rate varies between approximately 5 L/h and approximately 120 L/h and the temperature of the fuel varies between −30° C. and +110° C. The channel  52  is the mentioned such that, at low temperatures, the response time of the solenoid valve is less than one half second. However, the portion of the fuel flowing towards the core carries pressure waves that disturb the movements commanded by the core  42 . 
         [0027]    A check valve is arranged in the core to mitigate the effects of these waves. 
         [0028]    A first embodiment is described below with reference to  FIGS. 2 and 3 . 
         [0029]    An elastic membrane  58  is arranged at the bottom  54  of the cavity  50 , said elastic membrane  58  fitting the bottom  54  of the cavity  50  and obstructing the channel  52  when idle. The example chosen shows a membrane  58  attached at the center of same to the bottom  54  of the cavity  50  by a pin  60 . However, the attachment method may be replaced by a screw or any other alternative attachment method, including adhesive, as required. Furthermore, the attachment shown here is central, but may be moved towards one side of the cavity. When a pressure wave rises and reaches the upper counterbore  22  beneath the magnetic core  42 , said pressure wave presses the core towards the high position PH. In response to this movement, the membrane  58  is pressed against the bottom  54  of the cavity  50  and blocks the channel  52 . Since the cavity  50  and all of this top space of the valve in general is full of incompressible liquid, blocking the channel  52  results in a sudden increase in the pressure inside the cavity  50 , which prevents the core  42  from moving upwards. 
         [0030]    A second embodiment is described below with reference to  FIG. 4 . 
         [0031]    The channel  52  includes a check valve  62  formed as follows: the channel  52  includes a first “lower” portion  64  of smaller section and a second “upper” portion  66  of larger section. The lower portion  64  extends towards the cavity  50  from the lower face  48  of the core, while the upper portion  66  extends towards the lower face  48  from the bottom  54  of the cavity  50 . The intersection of the lower portion  64  and the upper portion  66  forms a conical section defining a valve seat  68 . A ball  70  arranged in the upper portion  66  is free to move therein and, as shown in the figure, the ball  70  rests when idle against the valve seat  68  and blocks the lower portion  64  of the channel  52 . A spring (not shown) may be placed in the upper portion  66  to permanently press the ball  70  against the seat  68 . 
         [0032]    Operation is similar to operation of the membrane  58  in the first embodiment. When a pressure wave rises and reaches the upper counterbore  22  beneath the magnetic core  42 , said pressure wave presses the core towards the high position PH. In response to this movement, the ball  70  is pressed against the valve seat  68  and closes the channel  52 , which prevents the core  42  from moving upwards for the same reasons as specified above. 
         [0033]    A third embodiment is described below with reference to  FIGS. 5, 6 and 7 . 
         [0034]    An elastic diaphragm  72  known as a reed valve is placed at the bottom  54  of the cavity  50 . The diaphragm  72  is formed in a thin metal sheet and includes an outer disk  74  from which arms  76  extend inwards. In order to increase the flexibility of the arms  76 , the arms  76  are both narrow and relatively long. Thus, as shown in  FIGS. 6 and 7 , the arms  76  are curved, extend nearly tangentially to the disk  74  and coil round to a circular distal end  78  that is perforated at the center  80  of same. According to the figures, the disk  74  is arranged at the periphery of the bottom  54  of the cavity  50  and the arm  76 , when idle, extends such that the circular extremity  78  is positioned at the opening of the channel  52  and partially obstructs same, in consideration of the central hole  80 . 
         [0035]    Thus far, the description has disclosed a magnetic core  42  having a single channel  52  joining the lower face  48  to the bottom  54  of the cavity  50 . Regardless of the embodiment selected (elastic membrane  58 , check valve  62  or reed diaphragm  72 ), the core may have a plurality of channels  52  and a person skilled in the art would be able to adapt each of the embodiments with one or more channels  52  without difficulty. Thus, the diaphragm  72  shown is clearly provided to block a plurality of channels  52  (six in the figure). 
         [0036]    Operation of the diaphragm  72  is explained below. When a pressure wave rises and reaches the upper counterbore  22  beneath the magnetic core  42 , said pressure wave presses the core towards the high position PH. In response to this movement, the circular end  78  is moved against the inlet of the channel  52  and blocks the channel  52 , which prevents the core  42  from moving upwards for the same reasons as specified above. 
         [0037]    In the alternative disclosed, the circular end  78  has a small central hole  80  such that the channel  52  is never completely blocked and a limited flow of fluid can always flow through the channel  52 . This mitigates the effect of the pressure wave and reduces movement of the core. 
         [0038]    The following reference signs have been used in the description: 
         [0039]      10  Injection system 
         [0040]      12  Common rail 
         [0041]      14  Solenoid valve 
         [0042]      16  Body of the solenoid valve 
         [0043]      18  Borehole 
         [0044]      20  Lower counterbore 
         [0045]      22  Upper counterbore 
         [0046]      24  Needle 
         [0047]      26  Tip of the needle 
         [0048]      28  Head of the needle 
         [0049]      30  Helical groove 
         [0050]      32  Valve seat 
         [0051]      34  Output orifice 
         [0052]      36  Return channel 
         [0053]      38  Electromagnet 
         [0054]      40  Coil 
         [0055]      42  Magnetic core 
         [0056]      44  Coil seat 
         [0057]      46  Upper face of the core 
         [0058]      48  Lower face of the core 
         [0059]      50  Cavity in the core 
         [0060]      52  Channel 
         [0061]      54  Bottom of the cavity 
         [0062]      56  Spring 
         [0063]      58  Elastic membrane 
         [0064]      60  Attachment pin 
         [0065]      62  Check valve 
         [0066]      64  Lower portion of the channel 
         [0067]      66  Upper portion of the channel 
         [0068]      68  Valve seat 
         [0069]      70  Ball 
         [0070]      72  Elastic reed diaphragm 
         [0071]      74  Outer disk 
         [0072]      76  Ann 
         [0073]      78  Circular end 
         [0074]      80  Central hole 
         [0075]    A Main axis 
         [0076]    PF Closed position 
         [0077]    PO Open position 
         [0078]    PB Low position of the core 
         [0079]    PH High position of the core