Patent Publication Number: US-6712296-B1

Title: Fuel injection valve for internal combustion engines

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 U.S.C. 371 application of PCT/DE 00/03269 filed on Sep. 20, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is directed to a fuel injection valve and particularly to such a valve for internal combustion engines. 
     2. Description of the Prior Art 
     One known fuel injection valve, known from German Published, Nonexamined Patent Application DE 195 08 636 A1, employs a pistonlike valve member disposed in the bore of the valve body and is axially movable counter to the closing force of a spring. On its end toward the combustion chamber, the valve member has a valve sealing face, which cooperates with a valve seat embodied in the valve body, and as a result at least one injection opening is controlled. The inward- or outward-oriented opening stroke motion of the valve member is defined by a stroke stop. In the closing motion of the valve member away from the stroke stop, the valve member is accelerated in the direction toward the valve seat by the force of the spring. The fuel, which is located between the valve sealing face and the valve seat, has to be expelled in the process. Although this fuel does provide a certain damping of the impact of the valve member on the valve seat, nevertheless the force on the valve member upon impact with the valve seat is still so great that relatively loud engine noise results. Furthermore, in long-term operation, wear can occur in the region of the valve seat, along with incomplete sealing of the injection openings from the combustion chamber. 
     SUMMARY OF THE INVENTION 
     The fuel injection valve of the invention for internal combustion engines has the advantage over the prior art that the seating of the valve member on the valve seat in the closing motion is additionally damped. Between the portion of the valve member guided in the bore and the oil leakage chamber, a control chamber is provided, which surrounds the valve member over its entire circumference. By means of a pressure face embodied on the valve member, upon the closing motion of the valve member, fuel is expelled from the control chamber through the control bore into the oil leakage chamber, which takes place unthrottled at the onset of the closing motion. In a partial stroke of the valve member, a cylindrical portion of the valve member plunges into the control bore, thus forming an annular throttle gap between the control bore and the cylindrical part of the valve member, through which throttle gap the fuel can now flow out of the control chamber only in throttled fashion. As a result, the seating of the valve member on the valve seat is damped, and the maximum impact forces are reduced. The noise caused by the closure of the valve member is thus lessened, leading to quieter engine operation. Furthermore, the damping leads to reduced wear of the valve sealing face and the valve seat. 
     Another advantage of the invention is that it can be employed in both fuel injection valves that open inward, away from the combustion chamber, and in fuel injection valves that open outward. All that is needed is to transpose the disposition of the control piston and the control bore. 
     The outflow of fuel from the control chamber need not take place exclusively via the annular throttle gap. In a further version, it can also be provided that additional throttling conduits are embodied in the valve body or in the valve member that connect the control chamber to the oil leakage chamber. This also makes it possible for the throttling action of the control chamber to be regulatable via adjustable throttle connections. 
     In both versions, the spring loading the valve member is disposed in the oil leakage chamber, which has an outflow conduit through which the fuel is carried back into the tank via an outflow line. The outflow rate of the fuel from the control chamber depends not only the flow resistance of the throttle connection to the oil leakage chamber but also on the pressure difference between the oil leakage chamber and the pressure chamber. If the pressure of the fuel in the oil leakage chamber is relatively high, then the outflow of fuel from the control chamber will proceed more slowly than at low pressure. As a result, a higher pressure can build up in the control chamber, which via the higher pressure on the pressure face damps the seating motion of the valve member more markedly. By the provision of a pressure holding valve in the outflow conduit of the oil leakage chamber or in the outflow line, a previously determined pressure can be maintained in the oil leakage chamber. The outflow rate from the control chamber and thus the damping action of the control chamber can thus be varied by way of the holding pressure. If the pressure holding valve is embodied in regulatable form, then the damping action can be adapted to given requirements as a function of the engine operating state. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages and features of the invention will be apparent from the description contained herein below, taken with the drawings, in which: 
     FIG. 1 is a longitudinal section through the first exemplary embodiment of an inward-opening fuel injection valve; 
     FIG. 2 is an enlargement of FIG. 1 in the region of the control chamber; 
     FIG. 3 is a longitudinal section through the second exemplary embodiment of an outward-opening fuel injection valve; and, 
     FIGS. 4 a  and  4   b  show two features of the fuel outflow system with a pressure holding valve. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, in detail, a fuel injection valve of the invention for internal combustion engines is shown in longitudinal section in FIG. 1, and first the construction will be described, then the mode of operation of the fuel injection valve will be explained. 
     A valve body  1 , which can be constructed in multiple parts, is disposed in a receiving bore of the housing of an internal combustion engine, not shown in the drawing; the upper end, remote from the combustion chamber, of the valve body  1  is fixed in the receiving bore, while the lower end, toward the combustion chamber, protrudes into the combustion chamber of the engine. A bore  5  is embodied in the valve body  1  and is subdivided into an upper portion  5   a  and a lower portion  5   b . The bore  5  ends, on its end toward the combustion chamber, inside the valve body  1 , and the part of the valve body  1  that closes the bore  5  toward the combustion chamber is embodied as an essentially conical valve seat  7 . The valve seat  7  is adjoined toward the combustion chamber by a blind bore  19 , in which at least one injection opening  8  is disposed that connects the blind bore  19  to the combustion chamber. Disposed in the bore  5  is a pistonlike, axially movable valve member  4 , which on its end toward the combustion chamber has a substantially conical valve sealing face  6 , which cooperates with the valve seat  7  embodied in the valve body. The valve member  4  is embodied with a graduated diameter, which subdivides it into an upper portion  4   a  and a lower portion  4   b . The valve member  4  is guided in the bore  5  by its upper portion  4   a . The lower portion  4   b  of the valve member  4  is embodied with a smaller diameter than the upper portion  4   a , so that a pressure face  9  is formed at the transition between the two portions  4   a ,  4   b . Between the wall of the bore  5  and the lower portion  4   b  of the valve member  4 , an annular conduit  18  is formed, which in the region of the pressure face  9  forms a pressure chamber  3  by means of a radial widening in cross section. An inlet conduit  2  extending within the valve body  1  discharges into the pressure chamber  3  and can be made to communicate on its other end, via a high-pressure inlet line, not shown in the drawing, with a high-pressure fuel pump or some other high-pressure source. The inlet conduit  2  communicates with the valve seat  7  via the pressure chamber  3  and the annular conduit  18 . In the inward-oriented opening stroke motion of the valve member  4 , the valve sealing face  6  opens the communication from the annular conduit  18  to the blind bore  19 , effecting communication of the inlet conduit  2  with the injection opening  8 . 
     The upper portion  4   a  of the valve member  4  is adjoined by a substantially cylindrical, larger-diameter control piston  11 , and as a result a pressure face  12  is disposed at the transition from the valve member  4  to the control piston  11 . In the region of the upper portion  4   a  of the valve member  4 , a control chamber  10  is formed by means of a radial cross-sectional widening of the bore  5 . The jacket face of the control piston  11 , on the end of the jacket face toward the combustion chamber, has a damping edge  13 , which cooperates with a control edge that is embodied by a portion of the bore  5  embodied as a control bore  40 . The control piston  11  is adjoined by an intermediate pin  17 , disposed coaxially to the valve member  4  in an intermediate bore  26 , and the intermediate pin is connected in turn to a spring plate  22  that protrudes into an oil leakage chamber  20  embodied on the end of the valve body  1  remote from the combustion chamber. Via this intermediate bore  26 , the upper portion  5   a  of the bore  5  communicates with the oil leakage chamber  20 , which in turn communicates with an outflow system  35  via an outflow conduit  30  embodied in the valve body  1 . Between the spring plate  22  and the end of the oil leakage chamber  20  remote from the combustion chamber, a spring  21  is disposed with initial tension; it presses the valve member  4  with the valve sealing face  6  against the valve seat  7 , via the spring plate  22 , the intermediate pin  17 , and the control piston  11 . 
     The intermediate pin  17  is embodied with a smaller diameter than the control piston  11 , and thus a stop shoulder  24  is formed at the transition from the control piston  11  to the intermediate pin  17 . At the transition from the bore  5  to the intermediate bore  26 , a stop ring  23  is disposed coaxially to the axis of the valve member  4 . The stop ring  23  is fixed in the intermediate bore  26 , and the side of the stop ring  23  toward the combustion chamber is embodied as a stroke stop  25 ; the axial spacing of the stroke stop  25  from the stop shoulder  24  in the closed state of the fuel injection valve defines the opening stroke h of the valve member  4 . The overlap s of the damping edge  13  and the control edge  14  in the closing position of the valve member  4  is always dimensioned such that it is less than the opening stroke h of the valve member  4 . Preferably, the overlap s amounts to from 10-50% of the opening stroke h. 
     In FIG. 2, the region of the control chamber  11  of the fuel injection valve is shown again, enlarged. In the closed state of the fuel injection valve, the damping edge  13  and the control edge  14  overlap, so that the control chamber  10  communicates with the oil leakage chamber  20  only via an annular throttle gap  15 . The second opening of the control chamber  10  is defined via the throttling annular gap  16  embodied between the upper portion  4   a  of the valve member and the bore  5 ; the flow resistance of the fuel through the throttling conduit or gap  15  is less than that of the annular gap  16 . The control chamber  10  is embodied in FIG. 2 as radial widening of the upper portion of the bore  5 , so that the volume of the control chamber  10  decreases in the closing motion of the valve member  4  when the control piston  11  plunges into it. 
     The mode of operation of the first exemplary embodiment of the fuel injection valve of FIG. 1 is as follows: Through a high-pressure fuel pump, via a fuel inlet line, fuel is introduced at high pressure into the inlet conduit  2 . As a result, the fuel pressure also increases in the pressure chamber  3  and the annular conduit chamber  18 . Because of the pressure face  9  disposed in the region of the pressure chamber  13 , there is a resultant force acting on the valve member  4 , oriented in the axial direction away from the combustion chamber, that counteracts the closing force of the spring  21 . If this resultant force exceeds the closing force of the spring  21 , then the valve member  4  moves axially away from the combustion chamber, and the valve sealing face  6  lifts from the valve seat  7 . As a result, the injection opening  8  is made to communicate with the pressure chamber  3  via the blind bore  19  and the annular conduit  18 , and fuel is injected into the combustion chamber. 
     At the onset of the opening stroke motion of the valve member  4 , the control edge  14  overlaps the damping edge  13 , and the control chamber  10  communicates with the oil leakage chamber  20  via the throttle gap  15 . In the course of the opening stroke motion, the throttling edge  13  overtakes the control edge  14  and moves past it, until the valve member  4  with its stop shoulder  24  contacts the stroke stop  25 . Because of the high fuel pressure in the pressure chamber  3 , some of the fuel is also expelled through the annular gap  16  into the control chamber  10 . 
     The closing motion of the valve member  4  is initiated when the fuel pressure in the inlet conduit  2  and thus also in the pressure chamber  3  drops. As soon as the resultant force on the pressure face  9  becomes less than the closing force of the spring  21 , the valve member  4  is accelerated in the direction of the valve seat  7 . When the pressure face  12  plunges into the control chamber  10 , the fuel located in that chamber is positively displaced and expelled out of the control chamber  10  into the oil leakage chamber  20 . As long as the damping edge  13  has not yet reached the control edge  14 , this takes place with a comparatively slight flow resistance of the fuel, so that the pressure in the control chamber  10  is largely equal to that in the oil leakage chamber  20 . As soon as the damping edge  13  reaches the control edge  14 , the control chamber  10  is closed toward the oil leakage chamber  20 , except for the throttle gap  15 . The fuel pressure in the control chamber  10  thereupon rises and is decreased only slowly by the outflow of the fuel via the throttle gap  15 . Because of the increased fuel pressure in the control chamber  10 , a force on the pressure face  12  and thus on the valve member  4  results which force is counter to the closing force of the spring  21 . The motion of the valve member  4  in the direction of the valve seat  7  is slowed down as a result; the valve sealing face  6  does not sit down as hard on the valve seat  7 , and the high-frequency oscillations in the injection pressure and of the valve member  4  that occur upon impact are damped. A marked calming of the pressure course occurs at the fuel injection valve, and because of the softer seating of the valve member  4  on the valve seat  7 , the maximum forces on the valve member  4  are reduced sharply, which in turn contributes to reduced engine noise. The wear of the valve member  4  caused by the valve seat  7  and of the valve sealing face  6  is reduced markedly as a result, and thus the service life of the fuel injection valve is prolonged. 
     In FIG. 3, as a second exemplary embodiment, a longitudinal section through an outward-opening fuel injection valve is shown. The valve member  4  is again subdivided into an upper portion  4   a , guided in the bore  5 , and a lower portion  4   b , which protrudes freely into the bore  5 . The lower portion  4   b  of the valve member  4  is embodied with a smaller diameter than the upper portion  4   a , so that an upper pressure face  50  is formed at the transition between the two portions  4   a ,  4   b . A closing head  53  is disposed on the lower end of the valve member  4 , and in this closing head at least one injection conduit  52  with an injection opening  108  is formed. The closing head  53  is embodied with a larger diameter than the upper portion  4   a , so that a lower pressure face  51  is formed on the side of the closing head  53  remote from the combustion chamber. On the end toward the combustion chamber, the closing head  53  has a closing plate  54 , whose annular end face toward the valve body  1  is embodied as a valve sealing face  106 . The end face of the valve body  1  toward the combustion chamber is embodied as a valve seat  107  and cooperates with the valve sealing face  106 . In the closed state of the valve member  4 , the opening of the injection conduit  52  is closed by the valve body  1 , and the valve sealing face  106  and the valve seat  107  assure secure sealing off of the injection opening  108  from the combustion chamber. 
     The bore  5  is adjoined, on the end of the valve member  4  remote from the combustion chamber, by a control bore  40 , which is adjoined in turn by an oil leakage chamber  20 . On the end toward the combustion chamber, the valve member  4  changes over into a control piston  111 , which is embodied with a smaller diameter than the guided portion  4   a  of the valve member  4 . As a result, a pressure face  112  is formed at the transition from the valve member  4  to the control piston  111 , and the tapered embodiment of the control piston  111  forms a control chamber  10  between the control piston and the bore  5 . The control piston  111  is adjoined by a spring tappet  44 , which protrudes into the inside of the oil leakage chamber  20 , and the spring tappet is adjoined by a valve plate  122 . The spring tappet  44  is embodied with a smaller diameter than the control piston  111 . In the control bore  40 , a stroke stop  125  embodied as an annular shoulder is formed, which cooperates with a stop ring  123  shaped like an annular collar and disposed on the spring pin. The axial spacing of the lower face of the stop ring  123  and the upper face of the stroke stop  125  determines the opening stroke h of the valve member  4 . A spring  21 , preferably embodied as a helical compression spring, is disposed between the spring plate  122  and the end of the oil leakage chamber  20  toward the combustion chamber. This spring braces the spring plate  122  away from the combustion chamber, so that via the spring tappet  44  and the control piston  111 , the valve member  4  is pressed with its valve sealing face  106  against the valve seat  107 . 
     On the end remote from the combustion chamber of the jacket face of the control piston  111 , a damping edge  113  is formed, which cooperates with a control edge  114  formed by the transition from the control bore  40  to the bore  5 . In the closed state of the fuel injection valve, the control piston  111  plunges with the overlap s into the control bore  40 . Since the control piston  111  has a diameter that is only slightly smaller than that of the control bore  40 , a throttle gap  115  is formed between the control piston  111  and the control bore  40 , and by way of the throttle gap, the control chamber  10  communicates with the oil leakage chamber  20 . The overlap s of the edges  113  and  114  is less than the opening stroke h of the valve member  4 , so that when the fuel injection valve is fully open, the control piston  111  emerges from the control bore  40 . 
     The outward-opening fuel injection valve shown in FIG. 3 has the following mode of operation: The fuel introduced into the annular conduit  18  through the inlet conduit  2  acts upon both the upper pressure face  50  and the lower pressure face  51 . Since the lower pressure face  51  has a larger surface area operative in the axial direction, the force on the valve member  4  toward the combustion chamber predominates. If the fuel pressure is equal to an opening pressure, then the resultant force exceeds the closing force of the spring  21 . The valve sealing face  106  moves away from the valve seat  107 , and the injection opening  108  emerges from the bore  5 , until the stop ring  123  rests on the stroke stop  125 . In the open position of the valve member  4 , the control piston  111  is located outside the control bore  40 . By means of a pressure drop in the annular conduit  18  to below the opening pressure, the valve member  4  is accelerated in the closing direction by the spring  21 . As a result, the pressure face  112  moves into the control chamber  10 , and fuel is thus expelled into the oil leakage chamber  20  via the control bore  40 . Initially, this occurs with only a slight flow resistance; not until the damping edge  113  reaches the control edge  114  does the passage into the control bore  40  narrow down to the throttle gap  115 . The pressure in the control chamber  10  rises, and by the resultant force on the pressure face  112 , this causes a braked motion of the valve member  4  and thus a damped seating of the valve sealing face  106  on the valve seat  107 . 
     In FIG. 4 a , one exemplary embodiment of the outflow system  35  of the fuel from the oil leakage chamber  20  is shown schematically. In the course of the outflow line  31 , a pressure holding valve  32  is provided, which opens in the outflow direction toward the fuel tank  34  only at a certain pressure in the outflow line  31 . As a result, a certain holding pressure is maintained in the outflow line between the fuel injection valve and the pressure holding valve  32  and thus in the oil leakage chamber  20  as well. In FIG. 4 b , an alternative disposition of the pressure holding valve  32  is shown, which is disposed here in the outflow conduit  30  of the valve body  1 . In this arrangement, it is unnecessary for assembly purposes to adapt the existing outflow system  35  to the altered fuel injection valve. The holding pressure of the fuel injection valve in both embodiments amounts to approximately 0.15 to 1.0 MPa. By means of the holding pressure in the oil leakage chamber  20 , the outflow of the fuel from the control chamber  10  into the oil leakage chamber  20  during the closing motion of the valve member  4  is varied, since the outflow rate depends not only on the cross section of the throttle gap  15  but also on the pressure difference between the oil leakage chamber  20  and the control chamber  10 . 
     It can also be provided that the holding pressure is regulatable at the pressure holding valve  32 . This makes it possible to control the holding pressure as a function of the engine operating state and thus to adapt it in a purposeful way to various requirements. 
     The foregoing relates to preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the claims.