Patent Publication Number: US-7216815-B2

Title: Control valve for a fuel injector comprising a pressure exchanger

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a 35 USC 371 application of PCT/DE 2004/001255 filed on Jun. 17, 2004. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to an improved servo-valve, and more particularly to such a valve useful in a fuel injector equipped with a pressure booster. 
   2. Description of the Prior Art 
   Known stroke-controlled high-pressure accumulator injection systems (common rail) can be used to inject fuel in direct-injecting internal combustion engines. These injection systems are distinguished by the fact that the injection pressure can be adapted to the load and speed of the engine. A high injection pressure is required in order to reduce emissions and to achieve high specific outputs. Since the achievable pressure level in high-pressure fuel pumps is limited for strength reasons, a further pressure increase in high-pressure injection systems (common rail) can be achieved by means of pressure boosters in injectors. 
   DE 101 23 913 has disclosed a fuel injection apparatus for internal combustion engines, having a fuel injector that can be supplied from a high-pressure fuel source. A pressure boosting device that has a movable pressure booster piston is connected between the fuel injector and the high-pressure fuel source. The pressure booster piston divides a chamber that can be connected to the high-pressure fuel source from a high-pressure chamber connected to the fuel injector. The fuel pressure in the high-pressure chamber can be varied by filling a return chamber of the pressure boosting device with fuel or by emptying fuel from the return chamber. The fuel injector has a movable closing piston for opening and closing injection openings; the closing piston protrudes into a closing pressure chamber. Fuel pressure can be exerted on the closing piston to produce a force that acts on the closing piston in the closing direction. The closing pressure chamber and the return chamber are constituted by a combined closing pressure/return chamber; all of the partial regions of the closing pressure/return chamber are permanently connected to one another to permit the exchange of fuel. A pressure chamber is provided for supplying fuel to the injection openings and for exerting a force on the closing piston in the opening direction. The high-pressure chamber is connected to the high-pressure fuel source so that aside from pressure fluctuations, at least the fuel pressure of the high-pressure fuel source can continuously prevail in the high-pressure chamber. The pressure chamber and the high-pressure chamber are constituted by a combined injection chamber whose partial regions are permanently connected to one another to permit the exchange of fuel. 
   In fuel injectors, servo-valves can be used as on/off valves, which have a one-piece servo-valve piston whose control cross sections are embodied in a seat/slider design. In servo-valves of this kind, a significant amount of wear on the slider surfaces can occur since only short overlap lengths can be achieved. In addition, in servo-valves with a seat/slider design, high demands are placed on manufacturing precision, particularly with regard to the position of the control edges of the servo-valve piston in relation to each other. 
   SUMMARY OF THE INVENTION 
   The design proposed according to the present invention of an on/off valve, which is embodied as a servo-valve, in the form of a 3/2-way double seat valve for controlling a fuel injector, includes a valve piston to which a first valve piston is attached, which has a first sealing seat. The first valve piston is adjoined by an additional, second valve piston that performs the function of a sealing sleeve. The second valve piston has a second sealing seat embodied on it; the second valve piston is embodied so that it is pressed against a valve housing by a spring, which rests against the first valve piston, and, together with the valve housing against which it rests, constitutes the second sealing seat. Because of this embodiment of the valve piston of the 3/2-way double seat valve proposed according to the present invention, the second sealing seat closes after a significantly shorter partial stroke of the valve. Independent of the closing of the second sealing seat, however, the first sealing seat continues to open until a much greater stroke is reached. The design proposed according to the present invention, in which an on/off valve that controls a fuel injector is embodied in the form of a 3/2-way double seat valve, permits an optimal injector tuning without large leakage quantities. The two-part servo-valve embodied according to the present invention can advantageously be used in fuel injectors equipped with a pressure booster, regardless of whether this is integrated into the fuel injector or mounted onto it, which injectors are triggered by means of a relief or exertion of pressure in the differential pressure chamber (return chamber) of the pressure booster. 
   The design proposed according to the present invention avoids the disadvantages that occur with excessively short overlap lengths of slider sealing seats that frequently result in high leakage quantities and poor injector dynamics. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be described in greater detail below, in conjunction with the drawings, in which: 
       FIG. 1  shows an exemplary embodiment of a valve that is embodied in the form of a 3/2-way double seat valve for a fuel injector equipped with a pressure booster, in the deactivated state, and 
       FIG. 2  shows the 3/2-way double seat valve shown in  FIG. 1 , in the activated state. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The depiction in  FIG. 1  shows an exemplary embodiment of a 3/2-way double seat valve for a fuel injector. The fuel injector  1  includes a pressure booster  2  and an on/off valve, which is embodied in the form of a servo-valve  3 . The servo-valve  3  can be actuated by means of an actuator  4  which can be embodied in the form of either a solenoid valve or a piezoelectric actuator, possibly with the interposition of a hydraulic coupling chamber. 
   The fuel injector  1  is supplied with highly pressurized fuel by means of a pressure accumulator  5  (common rail). Via a high-pressure line  6 , the system pressure inside the pressure accumulator  5  prevails in the working chamber  7  of the pressure booster  2 . The pressure booster  2  also includes a differential pressure chamber  8  (return chamber), which is separated from the working chamber  7  by a two-part booster piston includes a first booster piston part  10  and a second booster piston part  11 . A spring element  12  resting against the bottom of the differential pressure chamber  8  acts on the second booster piston part  11  and moves the booster pistons  10 ,  11  back in the direction of their idle position against a stop ring  13  seated in the working chamber  7 . 
   The second booster piston part  11  acts on a compression chamber  9  of the pressure booster  2  with a pressure that is increased in accordance with the boosting ratio of the pressure booster  2 . A nozzle chamber inlet  14  extends from the compression chamber  9  to a nozzle chamber  17  of the fuel injector  1 . When the pressure booster  2  is deactivated, the compression chamber  9  is refilled via a filling valve  16 , which is embodied in the form of a check valve in the depiction in  FIG. 1 . The booster piston, which is comprised of two parts in the depiction in  FIG. 1  (see reference numerals  10 ,  11 ), can also be embodied in one piece. 
   The nozzle chamber  17  encompasses an injection valve member  18 , which is embodied in the form of a nozzle needle and has a pressure shoulder  19 . From the nozzle chamber  17 , an annular gap  20  extends to a seat  21  of the injection valve member  18 . Underneath the seat  21 , injection openings  22  are provided, through which fuel is injected into the combustion chamber of an internal combustion engine when the injection valve member  18  is lifted away from the seat  21 . The end surface of the injection valve member  18  is acted on by a closing piston  23  whose spherically embodied end surface contacts the end surface of the needle-shaped injection valve member  18 . The closing piston  23  contains an overflow throttle  34  via which a through bore  27  of the closing piston  23  communicates with a chamber containing a spring element  25 . The spring element  25  acts on the closing piston  23  in the closing direction. A control chamber line  15  containing a first throttle restriction  26  extends from the hydraulic chamber containing the spring element  25  to the differential pressure chamber  8  (return chamber) of the pressure booster  2 . 
   The pressure in the differential pressure chamber  8  of the pressure booster  2  is relieved via a discharge line  28 , which feeds into a valve housing  29  of the servo-valve  3  at a junction point  40 . The valve housing  29  of the servo-valve  3  includes a servo-valve piston  30  containing a through conduit  31  that includes a second throttle restriction  32  located at the point at which the through conduit  31  opens out into a control chamber  33  of the servo-valve  3 . A line that contains an outlet throttle  34  branches off from the control chamber  33  and leads into the first low-pressure return  35 . The pressure in the control chamber  33  of the servo-valve  3  can be relieved by actuating the actuator  4 , which can be embodied in the form of either a solenoid valve or a piezoelectric actuator. 
   The servo-valve piston  30  is encompassed by a servo-valve chamber  36  that has a second low-pressure return  37  branching off from it to permit control volumes to be discharged. The two returns  35 ,  37  can also be joined together inside the injector and connected to a combined return system. 
   The servo-valve housing  29  is provided with a first sealing seat  38  that cooperates with an annular surface of a first shaft region  46  of the servo-valve piston  30 . The first shaft region  46  of the servo-valve piston  30  is adjoined by a second reduced-diameter second shaft region  47 , which is encompassed by an annular chamber  39  inside the servo-valve housing  29 . The second shaft region  47  of the servo-valve piston has a stop surface  49  for a second servo-valve piston  41  accommodated in moving fashion on the first servo valve piston  30 . The second servo-valve piston  41  is supported so that it can move within the range of a third shaft region  48  on the first servo-valve piston  30  and is acted on by a spring element  42  that rests against a spring element support  43  at the bottom end of the third shaft region  48 . Oriented toward the working chamber, the third shaft region  48  of the first servo-valve piston  30  has an end surface  45  that is subjected to the pressure prevailing in the working chamber  7  of the pressure booster  2 . The second movably supported servo-valve piston  41  has a contoured piston surface  44 , which, together with the valve housing  29 , constitutes an additional, second sealing seat  50 . 
   In the deactivated idle position of the pressure booster  2  shown in  FIG. 1 , the open second sealing seat  50  below the servo-valve housing  29  allows the system pressure present in the working chamber  7  of the pressure booster  2  to travel via the junction point  40  and the discharge line  28  so that it also prevails in the differential pressure chamber  8  (return chamber) of the pressure booster  2 . As a result, the pressure booster is balanced due to the identical pressures prevailing in the working chamber  7  and in the differential pressure chamber  8  (return chamber) and no pressure boosting takes place. The movement of the first shaft region  46  of the first servo-valve piston  30  into the first sealing seat  38  closes the second low-pressure return  37 ; the movement of the actuator  4  into its closed position also closes the first low-pressure return  35 . 
   In the idle position of the pressure booster  2  shown in  FIG. 1 , no injection is taking place since the pressure prevailing in the differential pressure chamber  8  moves the closing piston  23  and the injection valve element  28 —assisted by the spring element  25 —into the closed position and no increased force of pressure acts in the opening direction on the pressure shoulder  19  of the injection valve member  18 . 
     FIG. 2  shows the activation of the pressure booster of the fuel injector when the actuator is triggered. 
   To trigger the pressure booster  2 , the pressure in the differential pressure chamber  8  of the pressure booster  2  is relieved via the discharge line  28 . To that end, the actuator  4 , which is embodied in the form of either a solenoid valve or a piezoelectric actuator, is triggered so that the first low-pressure return  35  is opened. Then fuel flows out of the control chamber  33  of the servo-valve  3  into the first low-pressure return  35  as a result of which the end surface of the first servo-valve piston  30  travels into the control chamber  33  of the servo-valve  3 . When the first servo-valve piston  30  moves upward, the second sealing seat  50  is closed before the first sealing seat  38  is finished opening. As a result, a fuel volume flows out of the differential pressure chamber  8 , via the discharge line  28 , the junction point  40 , and the annular chamber  39  into the second low-pressure return  37  so that the booster piston  10 ,  11  then travels into the compression chamber  9 . As a result, fuel travels into the nozzle chamber  17  at a pressure that is increased in accordance with the boosting ratio of the pressure booster  2 . This causes an increased hydraulic force acting on the pressure shoulder  9  in the opening direction to be exerted on the injection valve member  18 , which opens, thus unblocking the injection openings  22  that are located under the seat  21  of the injection valve member  18  and lead into the combustion chamber of the engine. 
   When the pressure in the control chamber  33  of the servo-valve  3  is relieved, even a slight upward stroke causes the second sealing seat  50  between the servo-valve housing  29  and the contoured surface  44  of the second servo-valve piston  41  to close. The force of pressure prevailing in the working chamber  7  of the pressure booster  2  and acting on the working chamber end surface  45  of the servo-valve piston  30  causes the first servo-valve piston  30  to continue moving after the second sealing seat  50  is closed so that the first sealing seat  38  opens further. 
   With the design according to present invention of the first servo-valve piston  30 , which is provided with a first sealing seat  38  and a moving second servo-valve piston  41  functioning as a sealing sleeve, the second sealing seat  50  can be completely closed even after a small valve stroke; independent of this, the first sealing seat  38  opens in accordance with a continuing stroke motion of the first servo-valve piston  30 . This makes a significant contribution to improving the injector dynamics of the fuel injector  1 . Furthermore, the design of the servo-valve  3  according to the present invention can significantly reduce the leakage quantities that occur when triggering the pressure booster  2 . 
   To terminate the injection, the actuator  4  is triggered so that the first low-pressure return  35  is closed again. This causes the pressure to increase again in the control chamber  33  of the servo-valve  3  as a result of the fuel flowing into it from the working chamber  7  via the through conduit  31 . The first servo-valve piston  30  travels into the first sealing seat  38  and closes it. During the inward to travel of the first servo-valve piston  30  into the first sealing seat  38 , the stop  49  provided at the piston end of the second shaft region  47  of the first servo-valve piston  30  strikes against the second servo-valve piston  41 , thus opening the second sealing seat  50 . As a result, fuel at system pressure can flow from the working chamber  7 , via the junction point  40  and the discharge line  28 , into the differential pressure chamber  8  of the pressure booster  2 . As a result, the two-part booster piston  10 ,  11  travels out of the compression chamber  9 , into which replenishing fuel now flows via the filling valve  16  from the chamber containing the spring element  25 . 
   Either a stop  49  or a spring element  42  can be provided to assure a definite starting position of the second servo-valve piston  41  accommodated in moving fashion on the first servo-valve piston  30 . Spring elements that are not shown in the embodiment variant according to  FIGS. 1 and 2  can be provided to assist the stroke motion of the first servo-valve piston  30 . Both the first sealing seat  38  and the second sealing seat  50  can be embodied in a multitude of ways. In the exemplary embodiment shown in  FIGS. 1 and 2 , the second servo-valve piston  41  is embodied, for example, with a contoured end surface  44  that cooperates with a flat seat on the servo-valve housing  29 . In addition to providing a flat seat on the servo-valve housing  29  in relation to the second sealing seat  50  or embodying the first sealing seat  38  in the form of a conical seat, as depicted in  FIGS. 1 and 2 , other seat geometries can also be used in the first sealing seat  38  and second sealing seat  50  in the servo-valve  3 . 
   The embodiment proposed according to the present invention of a servo-valve piston in the form of a two-part piston  30 ,  41  makes it possible to close the second sealing seat  50  after a short valve stroke of the first servo-valve piston  30 , whereas the first sealing seat  38  opens further, independent of the closing of the second sealing seat  50 . To reduce leakage quantities when triggering the pressure booster  2 , the servo-valve design proposed according to the present invention makes it possible for the second sealing seat  50  to be opened by means of the stop  49  oriented toward the piston only after the first sealing seat  38  leading to the second low-pressure return  37  is already partway closed. Only then is the second sealing seat  50  opened so that the system pressure prevailing in the working chamber  7 , traveling via the discharge line  28 , also prevails in the differential pressure chamber  8  of the pressure booster  2  and only a small amount of it escapes into the second low-pressure return  37 , which is already almost completely closed at the first sealing seat  38  by the first shaft region  46  of the first servo-valve piston  30 . 
   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 appended claims.