Abstract:
A pressure reserve for a common rail fuel supply system has outlet connections communicating with injection valves. The outlet connections are disposed in end pieces connected to an elongated hollow body. This disposition of the outlet connections assures that pressure surges that occur in the pressure reservoir have only a very slight influence on the injection events. In addition, economical production of the pressure reservoir is possible.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a pressure reservoir for a fuel supply system. The pressure reservoir is formed of an elongated hollow body with an inlet connection for communicating with a high-pressure pump and at least two outlet connections for communicating with injection valves. 
     Such pressure reservoirs are used above all in injection systems known by the name “common rail”, which makes it possible to keep the injection pressure and the injection quantity independent of the engine speed, and moreover to increase the injection pressure to above 1500 bar. In the common rail injection systems, fuel is pumped by a high-pressure pump out of a tank into the pressure reservoir, by way of which the fuel is present at injection valves that are each disposed in the cylinder heads of an engine. The pressure reservoir is generally tubular in shape and oriented parallel to the cylinder heads. The outlet connections for the injection valves disposed in the cylinder heads are generally disposed along the tubular body in a spacing equivalent to the spacings between individual injection valves. 
     The injection events into the cylinders are tripped by supplying current to the appropriate injection valves. The injection volume depends on the pressure prevailing at the injection valves and on the duration of the supply of electrical current. The injection events performed by the injection valves cause pressure fluctuations in the pressure reservoir. However, because of the position of the outlet connections that are distributed over the length of the tubular body, a variable effect on the individual injection valves and on the injection events performed by these injection valves can occur, and in particular can lead to variations in the respective injection volume. 
     To prevent such disadvantageous pressure fluctuations in the pressure reservoir that are tripped by the injection events, it is known from Published, Non-Prosecuted German Patent Application DE 195 32 599 A1 to divide the pressure reservoir into two individual reservoirs. In the application, each reservoir communicates with the common high-pressure pump via a respective distributor element. The individual reservoirs are then loaded in accordance with the ignition sequence of the engine, thus assuring that for the successive injection events, an unloaded individual reservoir will be available, and thus the pressure fluctuations tripped by one injection event cannot affect the next injection event. However, the embodiment involves increased production and installation expense, because both two pressure reservoirs and an additional distributor element have to be manufactured and installed in the engine compartment. 
     Furthermore, as in the conventional tubular pressure reservoirs, the outlet connections assigned to the various injection valves in the individual reservoirs used in Published, Non-Prosecuted German Patent Application DE 195 32 599 A1 are disposed along the tubular body. However, since in the region of the outlet connections the material load resulting from the internal pressure in the pressure reservoir is multiplied, the wall thickness and material strength in the region of the outlet connections must be oversized considerably compared with the other regions. This leads to both a high weight of the pressure reservoir and high costs for materials. Moreover, autofrettage is as a rule necessary as well. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a pressure reservoir for fuel supply systems, which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which is favorable in terms of production costs and reliably prevents changes in the outflow volume to the individual injection valve connections that might be tripped by pressure fluctuations resulting from the injection events. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, a pressure reservoir for a fuel supply system, including: an elongated hollow body having ends and an inlet connection for communicating with a high-pressure pump; and at least one end piece having at least two outlet connections for communicating with injection valves and disposed on at least one of the ends of the elongated hollow body, the at least two outlet connections disposed symmetrically about the elongated hollow body. 
     In the pressure reservoir of the invention, the outlet connections to the injection valves are disposed on the ends of the elongated hollow body that forms the pressure reservoir. In this manner, all of the outlet connections to the injection valves are subject to the same conditions with regard to possible pressure fluctuations in the pressure reservoir, and different outflow volumes are thus avoided. Moreover, by disposing the outlet connections in the region of the end portions of the pressure reservoir, a reduction in material costs can be achieved, since increased material loads occur not in the region of the circumferential wall of the hollow body but rather only in the region of outlet connections. 
     In accordance with an added feature of the invention, each of the at least two outlet connections have an axis and the elongated hollow body has an axis, the axis through each of the at least two outlet connections is inclined relative to the axis of the elongated hollow body. 
     In accordance with an additional feature of the invention, each of the at least two outlet connections have an axis and the elongated hollow body has an axis, the axis through each of the at least two outlet connections is laterally offset relative to the axis of the elongated hollow body. 
     In accordance with another feature of the invention, the at least one end piece has a tapered shape with a jacket face, and the at least two outlet connections are embodied on the jacket face. 
     In accordance with a further added feature of the invention, the at least one end piece includes a first end piece and a second end piece disposed respectively on the ends of the elongated hollow body, the first end piece and the second end piece each have at least one of the at least two outlet connections disposed thereon, and the at least two outlet connections disposed on the first end piece and the second end piece are recessed in mirror symmetry to one another. 
     In accordance with a further additional feature of the invention, there is a pressure sensor, and the elongated hollow body has a middle part and the pressure sensor and the inlet connection are embodied on the middle part. 
     In accordance with yet another feature of the invention, the injection valves have lines each with a diameter to be connected to the at least two outlet connections, and the at least two outlet connections each have a diameter larger than the diameter of the lines. 
     In accordance with yet another added feature of the invention, one of the ends of the elongated hollow body has an inside cone and the at least one end piece has an outside cone, a sealing point is created between the inside cone and the outside cone if the outside cone of the at least one end piece is screwed into the inside cone of the elongated hollow body. 
     In accordance with yet another additional features of the invention, the one end of the elongated hollow body and the at least one end piece each have male threads embodied in a same direction each with a thread pitch, and including a nut receiving the male threads for bracing the elongated hollow body against the at least one end piece, and the thread pitch of the at least one end piece is greater than the thread pitch of the one end of the elongated hollow body. 
     In accordance with a concomitant feature of the invention, there is a sealing element having two outside cones, one of the ends of the elongated hollow body and the at least one end piece each have an inside cone for receiving one of the two outside cones, the sealing element disposed between the one of the ends of the elongated hollow body and the at least one end piece forming sealing points between each of the two outside cones and the inside cone of the at least one end piece and the inside cone of the one of the ends of the elongated hollow body, respectively, when the at least one end piece is screwed onto the elongated hollow body. 
     With the foregoing and other objects in view there is also provided, in accordance with the invention, in combination with an engine having a block of in-line cylinders with cylinder heads, injection valves, and a high-pressure pump, a pressure reservoir including: an elongated hollow body having ends and an inlet connection for communicating with the high-pressure pump; a first end piece having at least one outlet connection for communicating with the injection valves and disposed symmetrically about the elongated hollow body on one of the ends; a second end piece having at least one outlet connection for communicating with the injection valves and disposed symmetrically about the elongated hollow body on another of the ends, the at least one outlet connection of the first end piece recessed in mirror symmetry to the at least one outlet connection of the second end piece; the elongated hollow body with the first end piece and the second end piece defining a given length; and the elongated hollow body oriented parallel to the cylinder heads, and the given length substantially equivalent to half a number of cylinders times a cylinder spacing. 
     With the foregoing and other objects in view there is further provided, in accordance with the invention, in combination with an engine having two blocks of cylinders with cylinder heads, injection valves, and a high-pressure pump, a pressure reservoir including: an elongated hollow body having ends and an inlet connection for communicating with the high-pressure pump; a first end piece having at least one outlet connection for communicating with the injection valves and disposed symmetrically about the elongated hollow body on one of the ends; a second end piece having at least one outlet connection for communicating with the injection valves and disposed symmetrically about the elongated hollow body on another of the ends, the at least one outlet connection of the first end piece recessed in mirror symmetry to the at least one outlet connection of the second end piece; and the elongated hollow body is disposed centrally crosswise to the engine, and the first end piece and the second end piece each end above a respective one of the cylinder heads of one of the two cylinder blocks of the engine. 
     Other features which are considered as characteristic for the invention arc set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a pressure reservoir for fuel supply systems, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a pressure reservoir in accordance with a first exemplary embodiment according to the invention; 
     FIG. 2 is a perspective view of the pressure reservoir in accordance with a second exemplary embodiment; 
     FIGS. 3A-3C are fragmentary, perspective views of various dispositions of outlet connections on the pressure reservoir; 
     FIGS. 4A-4C are sectional views through end portions of the pressure reservoir; 
     FIGS. 5A-5D are sectional views through end portions of the pressure reservoir; 
     FIGS. 6A and 6B are longitudinal sectional views through the end portions of the pressure reservoir; 
     FIG. 7 is a perspective view of a disposition of the pressure reservoir in a V-6 engine; 
     FIG. 8 is a perspective view of the disposition of the pressure reservoir in an in-line, six-cylinder engine; 
     FIG. 9 is a perspective view of the disposition of the pressure reservoir in an in-line, four-cylinder engine; and 
     FIG. 10 is a perspective view of a further disposition of the pressure reservoir in the in-line, four-cylinder engine. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In all the figures of the drawing, sub-features and integral parts that correspond to one another bear the same reference symbol in each case. Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a first embodiment of a pressure reservoir  10  according to the invention. The first embodiment has a tubular hollow body  11  to both ends of which hexagonal attachments  12  are attached. Neck-like outlet connections  21 , to which injection valves can be connected, are mounted on the side faces of the hexagonal attachments  12 . The outlet connections  21  on the attachments  12  are disposed in mirror symmetry to a center plane at right angles to the axis through the tubular hollow body  11  of the pressure reservoir. An inlet connection  20  is also mounted on the end face of one of the attachments  12  and can be connected to a high-pressure pump for supplying the pressure reservoir with fuel. The axis through the inlet connection  20  preferably coincides with the axis of the tubular hollow body  11 , which makes for a favorable disposition of the fuel supply line to the pressure reservoir in an engine compartment and for simple supply of fuel to the tubular hollow body. In mirror symmetry with the inlet connection  20 , a pressure sensor  22  is disposed on the other end face of the other attachment  12 , and by way of the sensor  22  the pressure in the pressure reservoir  10  can be determined. The pressure ascertained can be sent to an electronic control unit, which triggers the injection valves and the high-pressure pump. 
     As an alternative to the embodiment shown in FIG. 1, it is possible, as shown in FIG. 2, for the tubular hollow body  11  to be provided with an adapter  13  in the middle. The adapter  13  is preferably also hexagonal, and on which the inlet connection  20  and the pressure sensor  22  are disposed. In a modification of the embodiment shown in FIG. 1, it is also possible for only one of the arrangements  12  to be equipped with the outlet connections  21 , while the other attachment has only the inlet connection  20  or the pressure sensor  22  as well. It is thus possible to adapt the configuration of the pressure reservoir  10  to the spatial conditions prevailing in the engine compartment. However, it is essential that the outlet connections  21  are disposed in the end regions of the pressure reservoir  10  and geometrically identically with respect to the tubular hollow body  11 . This configuration assures that pressure fluctuations tripped in the pressure reservoir  10  by the injection events of the injection valves connected to the outlet connections  21  will not cause any differences in the outflow volumes of the individual outlet connections  21 , since all the outlet connections are spatially subject to the same conditions with regard to the pressure fluctuations. The embodiment shown in FIG. 2, in which the inlet connection  20  is disposed in the middle of the pressure reservoir  10 , also assures an increase in the uniformity of the pressure prevailing in the pressure reservoir  10 . The amplitude of the high-frequency pressure fluctuations in the pressure reservoir  10  that are tripped by the injection events can be still further reduced if the inside diameters of the outlet connections  21  are made greater than the inside diameters of the supply lines connected to them, leading to the injection valves. 
     Since in the region of the outlet connections  21 , the material load resulting from the internal pressure of the pressure reservoir  10  undergoes multiplication, it is necessary for the regions to be embodied with greater wall thicknesses and/or stronger materials, to suit the increased material load. By limiting the outlet connections  21  to the end regions of the pressure reservoir  10 , as provided by the invention, the additional material and productions costs can be reduced to a minimum. In addition, autofrettage can also be dispensed with. 
     FIGS. 3A-3C show especially favorable dispositions of the outlet connections  21  on the attachment  12  mounted on the tubular hollow body  11 . FIG. 3 c  shows essentially the same configuration of the outlet connections  21  on a hexagonal attachment  12  as has already been shown in FIGS. 1 and 2. The outlet connections  21  are disposed in a star pattern relative to one another on the side faces of the attachment  12  and axes of the outlet connections  21  are perpendicular to the axis of the tubular hollow body  11 . The inlet connection  20  is mounted on the end face, oriented perpendicular to the hollow body  11 , of the attachment  12 , in alignment with its axis. This embodiment is distinguished by especially simple production of the attachment  12  and of the outlet connections  21 . 
     Alternatively, as shown in FIG. 3 a , an attachment  112  may also be embodied in the form of a short tube with a cone mounted on it; the outlet connections  21  are mounted rotationally symmetrically on the jacket face of the cone. This configuration makes it possible to reduce the requisite wall thicknesses and material strength values for the attachment  112  and thus to reduce the production costs. This is possible since the inner bores in the outlet connections  21  meet in the end face of the tubular hollow body  11 , which is accordingly a region that is under compressive strain because of the internal pressure prevailing in the pressure reservoir  10 . However, the compressive strain dictates a lesser material load for the outlet connections  21 , compared with outlet connections  21  that open into the circumferential wall of the hollow body and are thus subject to a tensile strain because of the internal pressure in the pressure reservoir  10 . 
     In a further embodiment, shown in FIG. 3B, an attachment  212  has faces which converge obliquely on its end face and in which the outlet connections  21  are disposed rotationally symmetrically about the axis through the hollow body  11 . This embodiment has the same advantages as that shown in FIG. 3A, but it is simpler to produce and is especially suitable whenever only a small number of outlet connections  21  are to be disposed on the attachment  212 . 
     For production reasons, it is especially favorable if, as shown in FIGS. 4A-4C, that the bores of the outlet connections  21  are disposed radially to the inner bore of the attachment. To increase the strength of the outlet connections  21  in the attachment, it is also possible, however, as shown alternatively for various embodiments in FIGS. 5A-5D, for the inner bores of the outlet connections  21  to be laterally offset from the axis through the attachment. 
     The tubular hollow body  11  of the pressure reservoir  10  is generally formed by boring into rod material, or is already made in the form of a drawn tube. The form of a hollow body  11  can then be adapted to suit the space available in the engine compartment. The attachments  12 ,  112 ,  212  on the ends of the hollow body  11  may be mounted by friction welding, laser welding, or electric steel welding. However, there is also the possibility, which is often simpler from a production standpoint, of screwing the attachments  12 ,  112 ,  212  onto the ends of the hollow body  11 , as shown in FIGS. 6A and 6B. In that case, though, it is often difficult to assure that the attachments  12 ,  112 ,  212  and the outlet connections  21  disposed on them will be in the correct angular position for installation of the pressure reservoir  10  in the engine compartment. 
     In the embodiment shown in FIG. 6A, the hollow body  11  is provided in its end portion with a male thread, onto which a female thread provided in the attachment  12  is screwed. For sealing off the screw connection, a sealing element  14  is disposed between the hollow body  11  and the attachment  12 . The sealing element  14  has a continuous inner bore, which connects the interior of the hollow body  11  with the inner bore of the attachment  12 . The sealing element  14  is composed of two truncated cones  142 , joined together via a middle piece  141 , which are each adapted to inside cones  111 ,  121  embodied in the hollow body  11  and in the attachment  12 , respectively. When the attachment  12  is screwed onto the hollow body  11 , the attachment  12  is tightened up to a prescribed minimum torque, which assures adequate sealing of the screw connection, and is then tightened further until the desired angular position of the attachment  12  with the outlet connections  21  is attained. The conical configuration of the sealing element  14 , and the inside cones  111 ,  121  to suit in the hollow body  11  and the attachment  12  assure that the material loads resulting from the tightening moments will not become excessive. It is also advantageous to make the cone angles of the sealing element  14  more acute than the cone angles of the inside cones  111 ,  121  of the hollow body  11  and attachment  12 , so as to assure a sealing point of the least possible diameter between the sealing element  14  and the attachment  12  or the hollow body  11 , as applicable. The cone angles are preferably in a range from 30 to 60. It is also advantageous to make the sealing element  14  from a material that is softer than that of the attachment  12  and the hollow body  11 , so as to assure that when the attachment  12  is tightened onto the hollow body  11 , only the sealing element  14  will be deformed. For screwing together the attachment  12  and the hollow body  11 , thread pitches of 0.1 to 1.5 mm have proved to be advantageous, and using a male thread on the hollow body  11  has the advantage of averting soiling of the interior of the hollow body  11  as it is being screwed on. 
     In a further embodiment, shown in FIG. 6B, however, a screw connection between the hollow body  11  and the attachment  12  can also be made without using a sealing element. In this embodiment, the end portion of the hollow body  11  and the adjacent portion of the attachment  12  are each provided with male threads  51 ,  52  onto which the female thread of a nut  15  can be screwed. The two male threads  51 ,  52  can be embodied in contrary directions or in the same direction with different pitches; with threads of the same direction the thread pitch on the end portion of the hollow body  11  is always made greater than the thread pitch on the attachment  12 . The use of threads with the same direction has the advantage over contrary threads of less-expensive manufacture. For threads in the same direction, the relative motion of the hollow body  11  and the attachment  12  to one another is also determined by the difference between the two thread pitches, so that the motion between the attachment  12  and the hollow body  11  is stepped down. This increases the tightening force when the attachment  12  and the hollow body  11  are screwed together via the nut  15  and thus makes assembly easier. In contrast, contrary thread versions have the effect that the thread pitches are added together in the relative motion of the hollow body  11  and the attachment  12 , and thus a greater tightening moment is needed to an achieve equal contact-pressure and sealing force, in comparison with a thread constructed in the same direction. 
     To attain better sealing off of the screw connection, the hollow body  11  is provided with an inside cone  211 , which is engaged by an outside cone  221  on the attachment  12 . To screw the attachment  12  onto the hollow body  11 , the attachment  12  is first screwed into the nut  15 , until the nut  15  rests on a stop on the attachment  12 . Then the two parts are screwed together onto the hollow body  11 , until the outside cone  221  of the attachment  12  reaches the inside cone  211  of the hollow body  11 . Next, the nut  15  and the attachment  12  are unscrewed jointly far enough that the attachment  12  is in the desired angular position to the outlet connections. The attachment  12  is then held in this position and the nut  15  is tightened up to the prescribed torque, so that adequate sealing of the screw connection is attained. 
     In FIGS. 7-10, dispositions of the pressure reservoir  10  according to the invention for various engine constructions are shown. 
     FIG. 7 shows a V-6 engine  50  with two cylinder blocks  54 , in which the pressure reservoir  10  is disposed in the middle, transversely to an engine  50 , and extends essentially between the two middle cylinder heads. The outlet connections  21  disposed on the ends of the pressure reservoir  10  are connected via lines  32  to the injection valves  40  in the cylinder heads. Fuel is fed into the pressure reservoir  10  via a further supply line  31  coupled to a high-pressure pump  53  (FIG.  8 ). The injection sequence in the V-6 shown is selected such that in each case alternatingly via the two ends of the pressure reservoir  10 , fuel is supplied to the appropriate injection valve  40 . This assures that identical conditions with respect to pressure fluctuations occurring in the pressure reservoir  10  prevail at all the outlet connections  21  of the pressure reservoir  10 , and thus that all the cylinders are supplied with the same injection volume. The pressure reservoir  10  configuration shown in FIG. 7 is essentially suitable for all V-type and boxer-type engine configurations. 
     FIG. 8 shows the pressure reservoir  10  configuration in an in-line six-cylinder engine, in which the pressure reservoir  10  is disposed parallel to the cylinder heads. The length of the pressure reservoir  10  is advantageously selected such that it is approximately half the number of cylinders times the axial spacing between individual cylinders of the engine. The injection sequence in the in-line engine shown in FIG. 8 is advantageously selected such that in each case in alternation, fuel is supplied to the applicable injection valve first via one and then via the other side of the pressure reservoir  10 . In a way similar to the embodiment shown in FIG. 7, this assures that all the cylinders are supplied with the same injection volume. The embodiment shown in FIG. 8 is essentially suitable for all in-line engine configurations. 
     FIG. 9 shows a further possible pressure reservoir  10  configuration, which proves to be favorable particularly for two, three and four-cylinder in-line engines. The tubular hollow body  11  of the pressure reservoir  10  is embodied in curved fashion and is disposed with one end on the high-pressure pump. The other end of the pressure reservoir  10  is located essentially in the middle above a cylinder head of the engine. 
     FIG. 10 shows another pressure reservoir  10  configuration, in which the pressure reservoir  10  is disposed crosswise and in the middle with respect to an in-line four-cylinder engine. The injection valves of the inner cylinders are connected to one end of the pressure reservoir  10 , while the injection valves of the outer cylinders are connected to another end of the pressure reservoir  10 . The injection volumes for the cylinders can thus be supplied via the two ends of the pressure reservoir  10  in alternation.