Abstract:
A fuel injection device for internal combustion engines, including a fuel injector that can be supplied by a high-pressure fuel source, and a pressure intensifying device that has a movable piston is connected between the fuel injector and the high-pressure fuel source. The movable piston separates a chamber connected to the high-pressure fuel source from a high-pressure chamber connected to the injector whereby the fuel pressure in the high-pressure chamber can be varied by filling a return chamber of the pressure intensifying device with fuel or by emptying fuel from the return chamber. A valve is provided with a valve body, which can be moved as a function of the fuel pressure prevailing in the return chamber so that the valve can connect the high-pressure chamber to the chamber. The invention also proposes a pressure intensifying device that is suitable for this purpose.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a 35 USC 371 application of PCT/DE 02/01535 filed on Apr. 26, 2002. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention is directed to an improved fuel injection device and a pressure intensifying device for use with internal combustion engines. 
   2. Description of the Prior Art 
   DE 199 10 970 has already disclosed fuel injection devices and pressure intensifying devices in which a pressure intensifying piston, by filling or emptying a return chamber, makes it possible to increase the fuel injection pressure beyond the level supplied by a common rail system. 
   SUMMARY OF THE INVENTION 
   The fuel injection device and pressure intensifying device according to the invention have the advantage over the prior art that the use of a valve, which connects the side of the pressure intensifying device connected to the high-pressure fuel source directly to the side connected to the fuel injector as a function of the fuel pressure prevailing in the return chamber, makes it possible to assure both a filling of the return chamber with fuel and a blocking of the side of the pressure intensifying device connected to the injector off from the high-pressure fuel source through the use of this one valve, without additional components. It must also be regarded as advantageous that the filling of the high-pressure chamber of the pressure intensifying device connected to the fuel injector does not take place by means of a for example spring-loaded separate check valve, but by means of a path that is continuously open in the reset phase. This assures an improved, particularly more rapid resetting of the piston of the pressure intensifying device. 
   Advantageous modifications and improvements of the fuel injection device and pressure intensifying device are also disclosed. 
   It is also advantageous to integrate a throttle into the piston of the pressure intensifying device so that it is no longer necessary to convey a line past the larger diameter end of the piston. This results in an even more compact design of the fuel injection device and the pressure intensifying device. 
   Furthermore, it is particularly advantageous to provide an additional control of the combination valve by means of the pressure increase in the high-pressure chamber so that in addition to the pressure drop in the return chamber, the pressure increase in the high-pressure chamber drives the valve body at the same time and consequently, the combination valve can switch in a particularly rapid fashion. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention are explained in detail in the subsequent description with references to the drawings, in which: 
       FIG. 1  shows a fuel injection device according to the invention, 
       FIG. 2  shows a pressure intensifying device when activated, and 
       FIG. 3  shows the pressure intensifying device of a different fuel injection device embodying the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a fuel injection device in which an injector  10  is connected to a high-pressure fuel source  60  by means of a pressure intensifying device  30 . The high-pressure fuel source includes a number of elements that are not shown in detail, such as a fuel tank, a pump, and the high-pressure rail of an intrinsically known common rail system in which the pump delivers fuel from the tank at a high fuel pressure of up to 1600 bar in the high-pressure rail. The injector  10  has a fuel injection valve with a valve element  12 , which protrudes with its injection openings  8  into the combustion chamber  11  of a cylinder of an internal combustion engine. The valve element is encompassed at a pressure shoulder  9  by a pressure chamber  13 , which is connected to the high-pressure chamber  40  of the pressure intensifying device  30  by means of a high-pressure line  21 . At its end oriented away from the combustion chamber, the schematically depicted valve element protudes into a working chamber  18 , which is connected by means of a throttle  20  to the high-pressure line  21  and is connected by means of a throttle  19  to a control valve  15  of the injector, the throttle  20  having a smaller opening cross section than the throttle  19 . The control valve  15  is embodied as a 2/2-port directional-control valve and is closed in the first position; in the second position, it connects the throttle  19  to a low-pressure line  17 . The valve element is flexibly supported by a return spring  14 , which presses the valve element against the injection openings  8 . The chamber of the injection valve of the injector containing the spring is connected to another low-pressure line  16 . The pressure intensifying device  30  has a flexibly supported piston  36 , which separates the high-pressure chamber  40  connected to the high-pressure line  21  from a chamber  35 , which is connected directly to the high-pressure fuel source  60 . The spring  39  used to support the piston is contained in a return chamber  38  of the pressure intensifying device  30 . The piston  36  has an extension piece  37  with a smaller diameter than the piston  36  has on its end oriented toward the chamber  35 . The return chamber  38  can be connected by means 2/2-port directional-control valve  31  to a low-pressure line  32 . In the same way as the low-pressure lines  16  and  17 , the low-pressure line  32  leads back to the fuel tank, which is not shown in detail. The chamber  35  of the pressure intensifying device is connected to the return chamber  38  by means of a throttle  47  that is integrated into the pistion in the form of a bore. In addition to the throttle bore  47 , a combination valve  50  is also integrated into a bore  58  of the piston  36 . The bore opens into the chamber  35  and contains a cylindrical valve body  51  in a movable fashion. A spring  54  is disposed between the piston  36  and the valve body  51  and when it is relaxed, this spring presses the valve body toward the chamber  35  just until the valve chamber  53  is connected on the one hand to a supply line  52 , which is embodied as a bore in the piston and leads to the chamber  35 , and is connected on the other hand to a high-pressure chamber line  56 , which is embodied as a bore through the extension piece  37  and leads to the high-pressure chamber  40 . In addition, a return chamber line  55 , which is embodied as a bore in the piston  36  and opens into the bore  58  at the end of the bore oriented away from the chamber  35 , connects the valve chamber  53  to the return chamber  38  independent of the position of the valve body  51  since the valve body  51 , on its end oriented toward the spring  54 , has an extension  57  that passes through the center of the spring and, as shown in  FIG. 2 , limits the movement of the valve bosy as soon as it has closed the lines  52  and  56 . 
   The operation of the stroke-controlled injector  10  is already known per se from the German patent application DE 199 10 970. A high fuel pressure prevails continuously in the high-pressure line  21 . Fuel travels from the pressure chamber  13 , through the injection openings  8 , into the combustion chamber  11  as soon as the valve element, at its end oriented away from the injection openings, is temporarily relieved of the fuel pressure through the opening of the 2/2-port directional-control valve  15  and consequently, the force acting in the opening direction engaging the pressure shoulder  9  is greater than the sum of the spring force ( 14 ) and the force resulting from the fuel pressure remaining in the working chamber  18 . In the neutral state, however, the valve  15  is closed, the injection valve is closed, and no injection occurs. If the intensifier control valve  31  is also closed, then the pressure of the high-pressure fuel source prevails in the return chamber  38  and the pressure intensifying device  30  is pressure balanced so that no pressure intensification occurs. The combination valve  50  is then open and the piston  36 ,  37  is in its starting position, characterized by a large volume of the return chamber  38 . The pressure of the high-pressure fuel source can travel through the open combination valve  50 , the supply line  52 , and the return chamber line  55 , into the return chamber  38 . The pressure of the high-pressure fuel source also travels through the supply line  52  and the high-pressure chamber line  56  to the high-pressure chamber  40  and from there, to the injector  10 . Consequently, an injection can occur at any time at the pressure of the high-pressure fuel source. In order for this to occur, it is only necessary for the control valve  15  of the injector to be actuated as has already been described at the beginning, which causes the injection valve to open. If it is necessary for an injection to now occur at an increased pressure, then the intensifier control valve  31  is opened so that the pressure in the return chamber  38  can decrease, as a result of which the combination valve  50  closes. When closed, the combination valve  50  closes the high-pressure chamber line  56  and the supply line  52 , as shown in FIG.  2 . As a result, the fuel to be compressed in the high-pressure chamber  40  cannot flow back (check valve function of the combination valve) and the fuel only flows out of the chamber  35  in a throttled fashion through the throttle  47  and into the return chamber  38  (filling valve function of the combination valve). As a result of the pressure relief of the return chamber  38 , the piston  36  is not pressure balanced and a pressure intensification occurs in the high-pressure chamber  40  in accordance with the pressure area ratio of the chamber  35  and high-pressure chamber  40 . If the pressure intensifying device  30  is switched off through the closing of the intensifier control valve  31 , then a pressure balance between the chambers  35 ,  38 , and  40  is produced by means of the throttle  47 . The combination valve  50  opens when the pressure in the return chamber  38  has reached the pressure in the chamber  35 , minus an opening pressure difference. The opening pressure difference of the combination valve is determined by the spring constant of the spring  54  and the hydraulic pressure areas of the valve body in relation to the chambers  35  and  53 . In the exemplary embodiment shown, the hydraulic pressure areas are equal in size. As soon as the combination valve has opened, the return chamber  38  and the high-pressure chamber  40  can be rapidly filled and consequently, the pressure intensifying device piston can be rapidly reset. Since the injection can occur at two different pressure levels (rail pressure and intensified pressure) and it is possible to switch on the pressure intensifying device at any time, this permits a flexible shaping of the course of the injection. This makes it possible to produce rectangular, ramp-shaped, or also boot-shaped injections with variable lengths of the boot phase. 
     FIG. 3  shows another embodiment of the fuel injection device according to the invention. The pressure intensifying device disposed between the high-pressure fuel source  60  and the high-pressure line  21  leading to the injector  10  has a piston  36  with an integrated alternative combination valve  70 . The valve body  78  of the combination valve  70  is movably supported in a cylindrical cavity  88  in the piston  36 . A supply line  72  embodied as a bore in the piston  36  leads from the chamber  35  into an annular groove  90  of the cavity  88 . The return chamber  38  is connected to the cavity  88  by means of the return chamber line  74  independent of the position of the valve body in the cavity so that the fuel pressure prevailing in the return chamber can constantly engage the valve body. A spring  80  is clamped between the wall of the cavity  88  and a shoulder of the valve body  78  so that if forces acting on the valve body in the spring force direction predominate, then a fluid exchange between the chamber  35  and the cavity  88  can occur by means of the annular groove  90 . As a result, a projection  94  on the valve body at its end oriented away from the spring  80  is pressed against the end of the cavity. A high-pressure chamber line  76  embodied as a bore in the piston connects the high-pressure chamber  40  to the part of the cavity  88  disposed between the piston wall and the pressure surface  92  bounded by the projection  94 . In the neutral state of the spring  80 , the region of the cavity  88 , which is bounded by the end of the valve body  78  oriented toward the spring, is connected by means of a central bore  86  in the valve body to the region of the cavity, which is bounded by the end of the valve body oriented away from the spring. If the forces acting on the valve body counter to the spring force direction predominate, then the flat sealing seat surfaces  82  are pressed against each other and the bore  86  is closed. At the same time, the annular groove  90  is closed off from the rest of the cavity  88  by the slide element sealing edges  84 . 
   Since the combination valve  70  has both a pressure surface oriented toward the high-pressure chamber  40 , i.e. the pressure surface  92 , and a pressure surface oriented toward the return chamber  38 , it is closed both by a decreasing pressure in the return chamber and by an increasing pressure in the high-pressure chamber. The opening spring force of the spring  80  determines the opening pressure difference between the return chamber and the high-pressure chamber up to which the combination valve is open. The sealing function is thus assured for the high-pressure chamber line  76  by the flat sealing seat surfaces  82  and is assured for the supply line  72  by the slide element sealing edges  84 . As in the exemplary embodiment described above, the opening of the intensifier control valve  31  in order to relieve the pressure in the return chamber  38  causes a pressure intensification in the high-pressure chamber to occur. 
   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.