Abstract:
A flow limiting valve, comprising a valve body adjustable between a closed position and an open position, wherein in the open position a flow channel for a conveying fluid is opened in the flow limiting valve and in the closed position the flow channel is closed, whereby the adjustment of the valve body is subject to conveying fluid pressure; wherein a control valve is integrated into a housing of the flow limiting valve through which the valve body is adjustable between open and closed positions, regardless of the conveying fluid.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation of PCT application No. PCT/EP2015/000638, entitled “FLOW LIMITING VALVE, IN PARTICULAR FOR A DUAL FUEL INJECTION SYSTEM”, filed Mar. 25, 2015, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a flow limiting valve, in particular to a dual fuel injection system. 
         [0004]    2. Description of the Related Art 
         [0005]    In EP 2 423 498 A1 a flow limiting valve for a large diesel engine is described that includes an axially adjustable valve body in a valve chamber that is pre-tensioned by a spring element against a valve seat on the inlet side. The pressure on the outlet side at the flow limiting valve reduces at the beginning of a fuel injection process, as a result of which the valve body is lifted off the valve seat and fuel can pass through the flow limiting valve. As soon as the injection process is ended, the pressure on the outlet side is again built up, causing the valve body to again move into the closed position. 
         [0006]    What is needed in the art a compact flow limiting valve that offers variable adjustment possibilities by applying simple constructive measures. 
       SUMMARY OF THE INVENTION 
       [0007]    The flow limiting valve according to the present invention is used to control the flow of a conveying fluid that is directed through the flow limiting valve. The conveying fluid is for example a gaseous medium, whereby in principle also liquid media are considered. It is in particular possible to use the flow limiting valve for a fuel injection system in an internal combustion engine, preferably for a dual-fuel injection system wherein the internal combustion engine can be driven with burnable gas in particular in the pilot injection method, as well as with liquid fuel, in particular with diesel fuel, bio fuel or heavy fuel oil. In a dual fuel injection system of this type, the flow limiting valve is allocated preferably to a burnable gas injector. It is however also possible to additionally or alternatively allocate the flow limiting valve to a liquid fuel injector. 
         [0008]    The flow limiting valve includes a valve body that is adjustable between a closed and an open position, wherein in the open position a flow channel for the conveying fluid is opened and in the closed position is closed. The adjustment movement of the valve body is controlled by the pressure of the conveying fluid. 
         [0009]    In addition, a control valve is integrated into the housing of the flow limiting valve, in order to be able to adjust the valve body between open and closed position, regardless of the pressure of the conveying fluid. This allows for closure of the flow limiting valve also in situations—and thereby interrupting the through-flow of the conveying fluid—wherein the conveying fluid assumes a value at which the valve body remains in the open position. The control valve actuates the valve body that is in the open position and moves the same into the closed position. The control valve thus permits closure of the flow limiting valve in additional situations, regardless of the pressure of the conveying fluid. It is in particular possible to close the flow limiting valve via the control valve if the valve body is in the open position due to the actual pressure of the conveying fluid. 
         [0010]    The control valve is integrated into the housing of the flow limiting valve, so that no additional space requirement arises for the control valve; and overall, a compact flow limiting valve can be provided. The flow limiting valve can possibly be integrated into the injector unit. 
         [0011]    According to one advantageous embodiment, the control valve is designed as a passive unit without its own energy supply, so that no electric, pneumatic or hydraulic actuator is necessary in the control valve for implementation of the adjusting motion. According to an alternative embodiment it can, however, also be useful to design the control valve as an active unit and to equip it with an electric, pneumatic or hydraulic actuator, for example an electromagnetic control element that, when operated, moves the valve body. The actuator of the control valve that is designed as an active unit is preferably controlled via control signals that originate from a sensor in the fuel injection system, for example a pressure sensor. 
         [0012]    According to one embodiment, a control element of the control valve that forms the valve element of the control valve and that actuates the valve body of the flow limiting valve is adjusted via a control fluid. In particular, when using the flow limiting valve in a fuel injection system, a liquid fuel that is under pressure in the fuel injection system can be used as the control fluid and fed to an injector unit. It is for example possible to divert part of the liquid fuel that is under pressure via a control line and to supply it to the control valve for activation of the control element. This embodiment offers the advantage that the control element is of a passive design and an active activation of the control element through its own energy supply is not necessary. Rather, activation occurs via the liquid fuel, whereby pressure changes in the supplied liquid fuel lead to an adjusting motion of the control element of the control valve. 
         [0013]    According to another embodiment, the flow limiting valve is utilized in a dual fuel injection system that includes a burnable gas injector unit and a liquid fuel injector unit. The flow limiting valve is preferably allocated to the burnable gas injection unit. In principle it can, however, also be assigned to the liquid fuel injector unit. The flow limiting valve is located in the flow path to the injector unit and is in a position to interrupt the supply flow of fluid to the injector unit. Herein, blocking of the flow limiting valve occurs; on the one hand subject to the conveying fluid pressure, in that the valve body of the flow limiting valve is moved from the open into the closed position when the average pressure during an injection process falls below a pressure threshold value. On the other hand, during a malfunction of the injection system—for example when the valve body is not moved automatically into the closed position—the valve body can be moved into the closed position through activation of the integrated control valve. This occurs through a change in pressure in the control fluid which—in the case of the dual-fuel injection system—is a liquid fuel. At an accordingly significant change in pressure in the control fluid, the control element of the control valve is moved from the non-functional into the functional position in which the control element moves the valve body into the closed position. 
         [0014]    The valve body of the flow limiting valve is advantageously force-actuated into its open position by a spring element. According to an additional advantageous embodiment, the control element of the control valve is force-actuated by a spring element into its non-functional position where the valve body is unaffected by the control element. Through activation of the control element—for example via the control fluid—the control element is moved from the non-functional position into the functional position, against the force exerted upon it by the spring element and can move the valve body from the open into the closed position, against the force exerted upon it by the spring element. 
         [0015]    The control element of the control valve is again moved into the non-functional position through the force of the spring element, as soon as the pressure conditions in the control fluid readjust accordingly. This is the case during proper function of a dual fuel injection system. 
         [0016]    According to an additional embodiment, a throttle is integrated into a control line of the control fluid where a drop in pressure in the control fluid occurs that can be used for activation the control valve. For example, the higher pressure upstream from the throttle is supplied to the control element, so that the increased pressure moves the control element into the non-functional position and holds it in same. If the pressure in the control line drops, the control element moves into its functional position due to the spring force effect and moves the valve body into the closed position. 
         [0017]    The adjustment of the control element of the control valve occurs when a minimum pressure is exceeded. An adjustable pilot valve can be arranged in a control line that, in the case of a dual fuel injection system, is connected with the liquid fuel injector unit, whereby the control line runs into a fuel tank downstream of the pilot valve and the pressure of the control fluid is tapped for the adjustment motion of the control valve. The throttle is located expediently downstream from the pilot valve whereby the pressure immediately upstream of the throttle is tapped for activation of the control valve. The pilot valve—for example a 2/2-way valve—switches with the cycle of the injection in the liquid fuel injector unit, whereby in the case of a closed pilot valve the pressure downstream of the pilot valve is decreased and in the case of an open pilot valve it is increased. A medium pressure is thereby adjusted that is greater than the minimum pressure that is necessary to hold the control valve in the non-functional position. In contrast, the minimum pressure is no longer attained if the pilot valve remains closed in the case of a malfunction, whereupon the control valve is moved into the functional position for closing of the valve body. 
         [0018]    According to an additional embodiment, the control element of the control valve is designed as an adjusting piston that is adjustable in a piston housing space in the flow limiting valve. At least one side of the adjusting piston or of a component that is connected with the adjusting piston is supplied with the control fluid in order to hold the adjusting piston in the non-functional position, against the force of the spring element. According to an additional embodiment, both opposite end faces of the adjusting piston or of components connected with the adjusting piston are supplied with the control fluid, however at different pressures, in particular with the pressure in the control line upstream and downstream of the throttle. This embodiment offers the advantage that the volume displacement that occurs in the piston housing space during a movement of the adjusting piston can be removed via the connection with the control line. Moreover, possible erroneous flows are immediately discharged between the two chambers of the piston housing space on opposite sides of the adjusting piston or the component that is connected with the adjusting piston, without impairing the operational function. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0020]      FIG. 1  is a schematic illustration of a dual fuel injection system for an internal combustion engine according to the invention; and 
           [0021]      FIG. 2  is a longitudinal sectional view of a flow limiting valve according to the invention. 
       
    
    
       [0022]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one embodiments of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    The dual fuel injection system  1  illustrated in  FIG. 1  is equipped for operation in the pilot injection method with liquid fuel, for example diesel fuel or heavy oil or bio-oil, as well as for operation with burnable gas, for example natural gas or bio-gas. Dual fuel injection system  1  includes a dual fuel injector system  2 , a high-pressure gas tank  3  for storage of pressurized burnable gas, a burnable gas flow limiting valve  4  that is supplied by the high-pressure gas storage tank  3 , two pumps  5  and  6  that are located in series in the fuel section, and a liquid fuel tank  7 . Dual fuel injector system  2  includes a liquid fuel injector unit  8 , as well as a burnable gas injector unit  9  through which the liquid fuel or burnable gas can be injected into the combustion chamber of an internal combustion engine. 
         [0024]    High pressure tank  10  for the liquid fuel is associated with dual fuel injector system  2 ; said tank being supplied via in-series connected pumps  5  and  6  with the liquid fuel that is under high pressure. High pressure tank  10  is located either in the injector unit or is arranged as a common-rail high pressure tank outside the injector unit. Following high pressure tank  10 , a liquid fuel flow limiting valve  11  is located in a high pressure line  12  that leads to liquid fuel injector unit  8 . From this high pressure line  12 , supply control lines  13  and  14  each branch to a throttle for activation of liquid fuel injector unit  8  or burnable gas injector unit  9 . The fuel supplied via supply control lines  13 ,  14  represents the control fluid for activation of injector units  8 , 9 . 
         [0025]    The control fluid supplied to liquid fuel injector unit  8  flows via a return control line  15  in which a pilot valve  16  is located, to liquid fuel tank  7 . Pilot valve  16  is designed for example as a 2/2-way valve. A throttle  17  is located in the control line segment between pilot valve  16  and fuel tank  7 ; throttles are also located in supply control lines  13  and  14  to the injector units  8 ,  9  and in return control line  15  upstream of pilot valve  16 . 
         [0026]    On the gas side, the burnable gas flows from high-pressure fuel tank  3  to burnable gas flow limiting valve  4  and onward via line  18  to burnable gas injector unit  9 . Activation of injector unit  9  occurs via the liquid fuel that is supplied via supply control line  14 . On the outlet side, the control fluid is discharged from supply control line  14  via return line  19  into which a throttle and downstream a control or pilot valve  20  is integrated. Downstream of valve  20 , return control line  19  runs into return control line  15  of liquid fuel injector unit  8 , upstream of throttle  17 . 
         [0027]    During the starting procedure of the internal combustion engine, the dual fuel injection system  1  operates preferably exclusively with fuel injection via liquid fuel injector unit  8 . At higher speeds, changeover to gas operation in the pilot injection method can occur, whereby a pilot injection occurs via liquid injector unit  8 . 
         [0028]    Now referring to  FIG. 2  with continued reference to  FIG. 1 , a longitudinal section of burnable gas flow limiting valve  4  is illustrated. Flow limiting valve  4  includes a housing  21 , as well as flange piece  22  facing the injector inlet and which is connected with housing  21  by way of a cap nut  23 . 
         [0029]    In housing  21  a gas chamber  24  is established into which gas flows from the high pressure gas tank  3 , through a connecting element  25  located on the opposite side of flange piece  22  as indicated by the arrow. In gas chamber  24  a piston shaped valve body  26  can move axially, whereby into its wall an axially progressing overflow channel  27  is incorporated through which the gas travels from gas chamber  24  to an outlet channel  28  in flange piece  22 , from where the gas—as indicated by the arrow—is diverted out of the burnable fuel flow limiting valve  4  and is moved along in the direction of the injector unit. 
         [0030]    Valve body  26  is force-actuated into its open position by a spring element  29 . Valve body  26  is located in a housing space  30  and can be axially moved inside housing space  30 . As a result of the force of spring element  29 , valve body  26  is held in its open position where valve body  26  protrudes partially into gas chamber  24  and whereby gas from gas chamber  24  gets into outlet channel  28  via overflow channel  27 . In the event that valve body  26  is completely or almost completely pushed into housing space  30 , overflow channel  27  will be located outside the flow connection with gas chamber  24 , so that the flow connection is interrupted; the valve body is thus in a closed position wherein the flow through flow limiting valve  4  is interrupted. 
         [0031]    The pressure of the introduced burnable gas prevailing in gas chamber  24  acts upon the face side of valve body  26  and actuates same against the force of spring element  29  into the closed position. At the same time, a gas pressure that force-actuates valve body  26  into the open position also prevails in housing space  30  where valve body  26  can move. Provided that the gas pressure is approximately equal at both end faces of valve body  26 , valve body  26  is held in the open position by the force of the spring element acting upon it. However, if the gas pressure drops on the side facing away from gas chamber  24 , then valve body  26  is moved into the closed position by the pressure in gas chamber  24 . 
         [0032]    A control valve  31  is integrated into housing  21  of flow limiting valve  4 , whose control element  32  is in the embodiment of an adjusting piston that is arranged coaxially as well as coaxially offset relative to valve body  26 . The adjusting piston is accommodated axially adjustable in an enclosed piston housing space  33  and is force actuated by a spring element  34  in a direction of a functional position, where adjusting piston  32  moves valve body  26  axially into the closed position. Adjusting piston  32  is connected with a head  35  that divides piston housing space  33  into two chambers, whereby spring element  34  engages on head  35  on the side opposite adjusting piston  32 . 
         [0033]    Piston housing space  33  is connected on both sides of head  35  via control channels  36  and  37  with control lines  38  and  39  ( FIG. 1 ) that branch immediately upstream and downstream of throttle  17  in return control line  15  that leads to liquid fuel tank  7 . Control channels  36  and  37  are provided in flange plate  22  or respectively housing  21 . Sealing rings  40 ,  41  and  42  that seal control channels  36  and  37  radially are located between flange plate  22  and housing  21 . 
         [0034]    Via first control channel  36  that is connected with control line  38 , liquid fuel is supplied as the control fluid under relatively high pressure into the chamber of piston housing space  33  with adjusting piston  32 . The opposite chamber of piston housing space  33  in which spring element  34  is arranged is connected via second control channel  37  with control line  39  downstream from throttle  17  where a lower pressure prevails. This pressure differential actuates the control element with the adjusting piston and the head against the force of spring element  34  into the retracted non-functional position. If the pressure difference drops below a threshold value, the resulting force of the hydraulic differential pressure upon head  35  drops below the spring force of spring element  34 , and adjusting piston  32  is moved axially from the non-functional position into the functional position in which the front face of the adjusting piston presses against valve body  26  and moves valve body  26  into its closed position. 
         [0035]    During the fuel injection operation, pilot valve  16  opens and closes in sequence with the injection. An average pressure results hereby in return control line  15 , downstream of pilot valve  16  that is conveyed via control line  38  and control channel  36  into the chamber of piston housing space  33  with adjusting piston  32 . In regular operation, the average pressure exceeds the threshold value that is relevant for maintaining the non-function position, so that the control element of control valve  31  is held in the non-functional position. 
         [0036]    If on the other hand, for example due to a malfunction, the average pressure immediately upstream of throttle  17  drops below the threshold value—which is the case for example during permanent closing of pilot valve  16 —the pressure in the chamber of piston housing space  33  with the adjusting piston drops accordingly, so that spring element  34  presses the adjusting piston into the functional position and said piston closes valve body  26 . 
         [0037]    If pilot valve  20  that is allocated to burnable fuel injector unit  9  remains open due to a malfunction and at the same time, pilot valve  16  that is allocated to liquid fuel injector unit  8  is closed due to a malfunction, valve body  26  of flow limiting valve  4  is also moved into the closed position, whereas control valve  31  remains in its non-functional position. 
         [0038]    If pilot valve  20  that is allocated to burnable fuel injector unit  9  remains open, then liquid fuel flow limiting valve  11  closes advantageously, so that flow limiting valve  4  closes subsequently. 
         [0039]    While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.