Abstract:
The invention relates to a high-pressure fuel reservoir for a common rail fuel injection system of an internal combustion engine, having a plurality of connection openings, in particular connection openings for delivering and removing fuel and connection openings for sensors and valves and so forth. To increase the strength of the high-pressure fuel reservoir, the high-pressure fuel reservoir is equipped with a pulsation damping device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 USC 371 application of PCT/DE 00/02820 filed on Aug. 8, 2000. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a high-pressure fuel reservoir for a common rail fuel injection system of an internal combustion engine, having a plurality of connection openings, in particular connection openings for delivering and removing fuel and connection openings for sensors and valves and so forth. 
     2. Description of the Prior Art 
     In common rail injection systems for internal combustion engines, a high-pressure pump, optionally with the aid of a prefeed pump, pumps the fuel to be injected out of a tank into the central high-pressure fuel reservoir, which is called a common rail. From the rail, high-pressure lines lead to the individual injectors that are assigned one to each of the engine cylinders. The injectors are triggered individually by the engine electronics as a function of the operating parameters of the internal combustion engine, in order to inject fuel into the combustion chamber of the engine. By means of the high-pressure fuel reservoir, the pressure generation and the injection are decoupled from another. 
     A conventional high-pressure fuel reservoir is described in German Patent Disclosure DE 196 40 480, for instance. The known high-pressure fuel reservoir comprises an elongated, tubular body with a plurality of connections for supplying fuel injection valves, which are also called injectors. The tubular body has the simultaneous functions of pulsation damping over its volume and of distributing the fuel via the connections. Depending on the adaptation in the system, pressure pulsations occur, especially when the inside diameter of the tube is small and the length of the tube is great. The pressure pulsations mean that some injectors will inject too little, because of the development of a standing pressure wave. Pressure waves running back and forth in the rail can also mean that the injectors either in alternation or stochastically inject an overly small fuel quantity. To damp the pulsations in the rail, a relatively large volume is needed. The large volume makes it more difficult and expensive to design the rail to withstand high pressure. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     The object of the invention is to furnish a high-pressure fuel reservoir of the type defined at the outset that has greater strength and a longer service than conventional high-pressure fuel reservoirs. Nevertheless, the high-pressure fuel reservoir of the invention should be simple in design, and it should be possible to produce it economically. 
     In a high-pressure fuel reservoir for a common rail fuel injection system of an internal combustion engine, having a plurality of connection openings, in particular connection openings for delivering and removing fuel and connection openings for sensors and valves and so forth, this object is attained in that the high-pressure fuel reservoir is equipped with a pulsation damping device. By means of the pulsation damping device, the volume of the high-pressure fuel reservoir can be reduced markedly. As a result, the harmonics that occur in operation are damped, and thus the high-pressure strength of the high-pressure fuel reservoir is increased. 
     A particular embodiment of the invention is characterized in that the pulsation damping device is formed by interference geometries. By means of the interference geometries, the propagation of pressure waves in the high-pressure fuel reservoir is at least hindered. The interference geometries can be embodied in various ways. It is possible for the interference geometries to be formed by separate parts. However, it is also possible for the interference geometries to be embodied integrally with the high-pressure fuel reservoir. 
     A particular embodiment of the invention is characterized in that the high-pressure fuel reservoir includes a housing with an inner chamber in which the interference geometries are received. The inner chamber can be formed by a bore, for instance. The bore can be embodied as a through bore or as a blind bore. The open end or ends of the bore can be closed with suitable closing elements, to make them high-pressureproof, after the interference geometry is inserted. Alternatively, the inner chamber can be formed by a spherical chamber. In the case of a spherical inner chamber, the insertion of the interference geometries is made possible by a two-part housing. 
     A further embodiment of the invention is characterized in that the interference geometries are formed by at least one twisted metal sheet, a shaft with pierced transverse walls disposed on it, a wire coil, at least one sheet-metal strip with perforations, and/or a tube with perforations. In designing the interference geometries, care must be taken that the volume of the high-pressure fuel reservoir not be greatly reduced by the interference geometries. In other words, interference geometries that are not/very voluminous are to be preferred. 
     A further embodiment of the invention is characterized in that the interference geometries protrude through the connection openings or through additional openings from outside into the inner chamber of the housing. The interference geometries can for instance be screwed or welded onto the outside of the high-pressure fuel reservoir. The distribution of interference geometries in the high-pressure fuel reservoir can be regular or irregular, as needed. 
     A further embodiment of the invention is characterized in that the pulsation damping device is formed by at least one escape piston, which is received, movable back and forth counter to a spring, in the high-pressure fuel reservoir. The escape piston makes active pulsation damping possible. Thus even better results can be obtained than with the passive pulsation damping described above. 
     A further embodiment of the invention is characterized in that the pulsation damping device is formed by at least one escape piston, which is received, movable back and forth counter to a spring, in at least one bush which is mounted on the high-pressure fuel reservoir. This embodiment offers the advantage that the mounting of the escape piston is simplified. Furthermore, this embodiment can also be employed in conventional high-pressure fuel reservoirs without special changes being made. 
     A further embodiment of the invention is characterized in that the escape piston is provided with a through hole. The through hole assures that a static pressure equalization can be effected between the regions of the high-pressure fuel reservoir or bush that are separated by the escape piston. 
     A further embodiment of the invention is characterized in that the side of the through bore toward the spring is equipped with a flow promoter. The flow promoter can for instance be a rounded feature or a countersunk feature. The other side of the through bore can be embodied with sharp edges. As a result, it is attained that the deflection motion of the piston, in the event of a pressure surge occurring in the high-pressure fuel reservoir, takes place counter to the spring. 
     A further embodiment of the invention is characterized in that the escape piston is prestressed by the spring against a stroke stop. As a result, it is attained that only pressure surges beyond a certain intensity will be damped, as a function of the pressure difference. 
    
    
     Further advantages, characteristics and details of the invention will become apparent from the ensuing description, taken with the drawings, in which: 
     FIG. 1 is a longitudinal sectional view of a first embodiment of a high-pressure fuel reservoir of the invention; 
     FIGS. 2-6 illustrates different variants of the pulsation damping device used in FIG. 1, shown separately in each case; 
     FIG. 7 is a view similar to FIG.  1  and showing a second embodiment of a high-pressure fuel reservoir of the invention; and 
     FIGS. 8-10 are each fragmentary sectional views of further embodiments of a high-pressure fuel reservoir of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, a high-pressure fuel reservoir is shown that includes an elongated, tubular housing  1 . In the tubular housing  1 , a through bore  2  forms a storage chamber or reservoir for the fuel. The through bore  2  is closed so as to be high-pressureproof on both ends with the aid of closing stoppers or plugs  3  and  4 . The housing  1  is also equipped with a number of connections  5 - 10 . The connections  5 - 10  serve to connect the high-pressure fuel reservoir to the high-pressure pump and the individual injectors of an engine to be supplied. Also mounted on the housing  1  are a plurality of fastening elements  11 - 13 , which serve to secure the high-pressure fuel reservoir to the engine. 
     A pulsation damping device  14  is fastened in the through bore  2  between the two closing screws  3  and  4 . It is understood that the pulsation damping device  14  could also be fastened on only one side or could be braced radially. 
     In FIGS. 2-6, different variants of the pulsation damping device  14  are shown. In FIG. 2, the pulsation damping device  14  of FIG. 1 is shown by itself. As can be seen, the pulsation damping device  14  is a twisted metal sheet. 
     In FIG. 3, it can be seen that the pulsation damping device can also include a shaft  16 , on which transverse walls or baffles  17  are disposed, spaced apart by equal intervals. To allow fuel to flow through, a plurality of perforations  18  are provided in the transverse walls  17 . 
     FIG. 4 shows a pulsation damping device that is formed by a wire coil  20 . The wire coil  20  includes a plurality of wires, entwined irregularly with one another. Between individual wires, there is sufficient clearance to allow fuel to flow through. 
     The pulsation damping device shown in FIG. 5 is formed by a sheet-metal strip  22 , which is provided with a number of perforations, of which only two are provided in FIG. 5 with reference numerals  23  and  24 , to serve as examples. The perforations  23  and  24  are formed by folding sheet-metal pieces  25  and  26  outward. The folded-out sheet-metal pieces  25  and  26  form guide vanes for the fuel located in the high-pressure fuel reservoir. 
     The pulsation damping device shown in FIG. 6 is formed by a sheet-metal tube  30 . Many bores  31 - 33  are disposed in the tube  30 . Many tabs  34 - 36  are also folded outward out of the jacket face of the tube  30 . The bores  31 - 33  serve to allow fuel to flow through. The tabs  34 - 36  serve as guide vanes for the fuel. 
     The embodiment of a high-pressure fuel reservoir of the invention shown in FIG. 7 is largely equivalent to the embodiment shown in FIG.  1 . For the sake of simplicity, the same reference numerals have therefore been used to designate identical parts. To avoid repetition, see the above description of the exemplary embodiment shown in FIG.  1 . 
     In the embodiment shown in FIG. 7, the pulsation damping is achieved by a number of elongated damping elements, which protrude radially into the through bore  2 . One of these elongated damping elements is formed by a pin  42 , which is received in an additional connection opening  41 . The pin  42  can be screwed, welded, soldered or fitted into the connection opening  41 . On the outside, the connection opening  41  is closed in high-pressureproof fashion by a closing stopper  43 . Pegs  44  are also received in the connection openings  5 ,  6 ,  7  and  8 . Like the pin  42 , the pegs  44  also protrude into the through bore  2 . Unlike the pin  42 , however, the pegs  44  are each equipped with an internal bore  45 . The internal bore  45  allows fuel to flow through and thus makes the function of the connections  5 ,  6 ,  7  and  8  possible. 
     In FIG. 8, only part of a tubular housing  1  of a further embodiment of a high-pressure fuel reservoir of the invention is shown in longitudinal section. The housing  1  has a through bore  2 , which is closed on one end by a closing stopper  3 . Via a plurality of connections, the through bore  2  communicates with a high-pressure pump and with the individual injectors. For the sake of simplicity, only one connection  5  is shown in FIG.  8 . 
     An escape piston  50  is received, so that it can move back and forth, in the through bore  2 . A spring  51  is disposed between the escape piston  50  and the closing stopper  3 . The escape piston  50  is equipped with an axial through bore  52 . On the end of the through bore  52  toward the spring  51 , a countersunk feature  55  is provided. On the end remote from the spring  51 , the through bore  52  is embodied with sharp edges. As a result, the flat annular surface  54  on the side remote from the spring  51  is somewhat larger than on the side with the countersunk feature  55 . 
     By means of the through bore  52  in the escape piston  50 , a static pressure equalization can be performed. The countersunk feature  55  at the inlet to the through bore  52  forms a flow promoter in one direction. Upon a pressure surge on the side of the escape piston  50  remote from the spring  51 , the escape piston  50  is deflected counter to the force of the compression spring  51 . The quantity of fuel located on the side of the spring is positively displaced through the through bore  52  to the side of the escape piston  50  remote from the spring  51 . 
     In the embodiment shown in FIG. 9, the escape piston  50  is in contact with a stroke stop  60 . The spring  51  is also prestressed against the escape piston  50 . In this embodiment, only pressure surges beyond a certain pressure difference are damped. In this embodiment, a guide  61  is also formed on the escape piston  50 ; it results from a reduction of the outside diameter of the escape piston  50 . 
     In the embodiment shown in FIG. 10, the pulsation damping device is integrated with a bush  65 , which is screwed onto a connection  5  of the high-pressure fuel reservoir. By means of a closing stopper  66 , the bush  65  is sealed off from the environment. An escape piston  50  is received, so as to be movable back and forth, in the bush  65 . A compression spring  51  is located between the escape piston  50  and the closing stopper  66 . Otherwise, the escape piston  50  functions exactly the same as the escape piston received in the through bore  2 . Just like the escape piston describe above, the escape piston  50  shown in FIG. 10 has a through bore  52  with a countersunk feature  55 . 
     The function of the pulsation damping device can be optimized with the parameters of pressure area, spring rigidity, spring prestressing, internal bore diameter, and rounding of the bore. 
     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.