Pressure reservoir for fuel supply systems

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.

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.

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. 3c 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. 3a, 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.