High-pressure pump, in particular for a common-rail injection system

Abstract

A high-pressure pump having a plurality of individual feed pumps is described, the feed pumps being designed as modular pump units and being able to be lined up next to one another via their housings, which are provided with fluid-connecting channels. At least one line module being provided which can be coupled at least on one side to a housing of a modular pump unit and in which the fluid-connecting channels of the respectively adjacent housings form intake and discharge channels which, on the one hand, lead on further and/or, on the other hand, lead outward.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a high-pressure pump for a common-rail injection system for internal combustion engines.

[0003] 2. Discussion of the Background

[0004] Common-rail injection systems are used in internal combustion engines, in which, in order to optimize the combustion power, the fuel is to be present in the combustion chambers of the individual cylinders in a finely atomized form. For this purpose, the fuel is compressed in a high-pressure pump and is distributed to the injectors of the individual cylinders via a rail. Finally, the process of injecting the fuel into the combustion chambers is triggered via an electric signal, the fuel, which is under high pressure, being finely distributed at high speed in the combustion chambers of the engine via the injection nozzles of the injectors.

[0005] A high-pressure pump of the type specified at the beginning which is suitable for common-rail injection systems for diesel engines is disclosed in EP-A-0 881 380. High-pressure pumps of this type which, as a rule, have a plurality of piston/cylinder feed elements make it possible to achieve high feed pressures with the required operational reliability, these main pumps having to be adapted in their design in a specific manner to the particular intended use, i.e. having to be constructed especially in each case.

[0006] Also known are high-performance diesel engines which are provided with a classical injection system, each cylinder in this system being assigned a pump feed element. A plurality of injection pumps is therefore generally necessary for high-performance diesel engines with a high number of cylinders. For example, in the case of a V-16 cylinder engine, two in-line injection pumps each having eight pump feed elements one behind another are arranged between the two cylinder banks. If an engine of this type is to be provided with a common-rail diesel injection system, a high-pressure pump which is specially adapted in terms of power and in terms of overall size and to the given spatial conditions is required for this.

[0007] U.S. Pat. No. 4,184,817 discloses a multicylinder high-pressure plunger pump, the plunger being sealed by means of two spaced apart lip seals. The seal on the feed-space side is lubricated by means of diesel oil and is intended at the same time to ensure that diesel oil does not pass into a space placed between these two lip seals and on the eccentric-drive side. An annular chamber which is connected via channels to a diesel induction chamber is furthermore connected upstream of this lip seal. The lower, second lip seal, i.e. the one placed on the eccentric-drive side, is used for sealing off the plunger against the lubricating oil present in the eccentric drive. Labyrinth-like elements are provided between the two lip seals and trap small, remaining overflow amounts of diesel and lubricating oil in the space which is placed between the two lip seals and is connected via a bore to the surroundings.

SUMMARY OF THE INVENTION

[0008] The object of the present invention is, especially, to provide a high-pressure pump which ensures high feed pressures, which can be realized in a particularly economic manner, and high operational reliability and can be adapted individually and without any problems to the requirements present in the individual case and also satisfies the exacting requirements placed on the service life.

[0009] This object is achieved essentially by a high-pressure pump having the features according to patent claim 1.

[0010] The modular manner of constructing the pump units and the combination options with specially designed line modules enable high-pressure pumps to be realized without any problems and in a space-saving manner, it being possible for said pumps to be adapted in the best possible manner to the requirements present in each case as a function of the particular combination of modules. Using this combination of modules and by appropriate design of the channels, optimum guides can also be achieved for the low-pressure supply and the high-pressure removal of fuel, in particular diesel oil, for the removal of leakages and for lubricating-oil supplies and oil return lines.

[0011] Each modular pump unit preferably in each case comprises at least two plungers which lie diametrically opposite each other and are actuated by the same eccentric section, together with an associated feed space and common housing, the feed space and plunger bore preferably being formed in a high-pressure part which can be screwed to the housing.

[0012] The line module or the plurality of line modules which may be present can be largely freely arranged within the overall construction of the particular high-pressure pump, with the result that, for example in the individual case, the connecting points can be positioned in an optimum position.

[0013] According to one preferred embodiment, line modules can simultaneously be configured with a bearing for the drive shaft, specifically either if a line module of this type is arranged between pump modules or if a line module of this type forms the end of a high-pressure pump constructed from individual modules.

[0014] According to the invention, a high-pressure pump, which is of modular construction particularly in the described manner, can be provided with a plurality of plungers which are moved to and fro via a common drive shaft provided with eccentric sections, are guided in each case in the plunger bore leading into a feed space and are actuated by an eccentric section counter to the action of a restoring spring in particular via a cup tappet guided in a bore in the housing, in which case, firstly, an eccentric space through which the drive shaft passes and, secondly, at least one annular lubricating channel which surrounds the respective plunger or cup tappet and is formed in the housing are connected to a lubricating-oil pressure supply, and an annular space which is connected to a lubricating-oil return flow is provided in the region of that section of the plunger or cup tappet which is on the feed-space side, and in which case, furthermore, an annular collecting space for overflow lubricating oil and overflow diesel oil is formed on the feed-space side in the wall of the plunger bore and is connected via channels to a diesel-oil tank, in particular.

[0015] A refinement of a high-pressure pump in such a way results, firstly, in a desired increase in the service life and, secondly, in the fact that virtually no diesel oil passes into that space of the eccentric drive which is filled with lubricating oil, and, conversely, that also virtually no lubricating oil mixes with the diesel oil, which mixture would sooner or later pass via the injection nozzles into the combustion chambers of the engine and would have a negative effect on the exhaust-gas emission of the engine.

[0016] The separation of diesel oil and lubricating oil is obtained in a simple manner and not prone to faults.

[0017] A further aspect which is essential for the invention and can be used in general in high-pressure pumps of this type resides in the fact that, instead of rolling rings which are conventionally provided between an eccentric drive and the plunger or cup tappet thereof which is to be actuated, use is made of sliding shoes of two-part design. This configuration of rolling elements in the form of two-part sliding shoes results especially in making installation easier and also permits installation of rolling elements of this type even if this is no longer possible using conventional rolling rings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Further particularly advantageous refinements of the invention and features which are significant to the invention are specified in the dependent claims and will also be explained in the following description of exemplary embodiments with reference to the drawings, in which:

[0019] FIG. 1 shows a schematic illustration of a pump unit with a common rail, the pump unit being illustrated in accordance with a section along the line I-I of FIG. 2,

[0020] FIG. 2 shows an axial longitudinal section through a high-pressure pump which is of modular construction according to the invention,

[0021] FIG. 3 shows an illustration of part of a high-pressure pump according to the invention with a centrally arranged line module (partially illustrated) and assigned diesel-oil tank and lubricating-oil tank,

[0022] FIG. 4 shows a schematic sectional illustration of a pump unit corresponding to a section along the line V-V of FIG. 2 in order to explain the profile of the low-pressure diesel intake line,

[0023] FIG. 5 shows an embodiment of a high-pressure pump according to the invention that is extended in comparison to the high-pressure pump shown in FIG. 2,

[0024] FIG. 6 shows an illustration of a refinement of a high-pressure pump according to the invention that is reduced in comparison to the embodiment according to FIG. 2, and

[0025] FIG. 7 shows a schematic illustration of a pump unit with rolling elements which are designed in the form of sliding shoes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] FIG. 1 shows, in the form of a schematic illustration, a pump unit 2 (illustrated in section) of a high-pressure pump which is constructed from pump units of this type and from line modules 1 which have yet to be explained in detail, for a common-rail injection system for internal combustion engines. The storage volume 6′ of a common rail 6 that is fed via a high-pressure output line 26 is respectively connected in a known manner via high-pressure connecting lines 4 to injectors 5.

[0027] The pump unit 2, which is shown in cross section, comprises two plunger units which are arranged diametrically opposite each other and are in each case formed by a plunger 14 which is guided in a reciprocating manner in a bore 37 and is assigned a cup tappet 36 which is guided in the housing 22. The plunger 14 with its cup tappet 36 is prestressed against an eccentric drive 10, 11 via a restoring spring 50. The plunger bore 37 leads into a feed space 18 which is connected via a pressure-controlled inlet valve 25 to a low-pressure supply line 24 and via a pressure-controlled outlet valve 27 to the high-pressure output line 26. The low-pressure supply line 24 is connected to a diesel-oil tank 33 having ventilating means 57, specifically via an intake line 23 which leads to a low-pressure pre-feed pump 21. A flow-regulating element 3 is arranged in the low-pressure supply line 24 for diesel oil.

[0028] The plunger bore 37, the feed space 18 and the accommodating regions for the valves 25 and 27 are formed in a high-pressure part 7 which is screwed to the housing 22.

[0029] The plunger 14 or the cup tappet 36 is driven via a drive shaft 9, the center of rotation of which is indicated by 63. The eccentric section acting on the cup tappet 36 bears the reference number 10. A rolling ring 11 is situated in a conventional manner between the eccentric section 10 and cup tappet 36, the sliding bearing 12 or a ball bearing being provided between the rolling ring 11 and eccentric element 10. The eccentric center is referred to by the letter E and the maximum eccentricity is indicated by H/2.

[0030] In the region separating the high-pressure part 7 and the housing 22, an annular space 34′ (which has yet to be explained in detail) is widened in such a manner that it ensures the passage of the high-pressure bore 26 in such a manner that should an overflow occur at the separating point of the high-pressure bore, the overflow quantity which arises can entirely escape into the space 34′.

[0031] The central-symmetrical design of the pump unit 2 which has already been discussed is clarified by FIG. 1 and it thus suffices to describe the upper part of this pump unit, since the same applies to the lower part of the pump unit. The measures undertaken for lubrication and for separating lubricating oil and diesel oil will be explained in detail with reference to the following figures.

[0032] The axial sectional illustration according to FIG. 2 shows a high-pressure pump which is constructed in a modular manner in accordance with the invention and has modular pump units 2 and a line module 1, which is arranged centrally in this case. All in all, there is therefore an arrangement of eight plungers which are combined to form a pump, and this arrangement is advantageous especially because it permits the construction of a narrow, tall pump similar to a classical in-line injection pump. This enables a pump according to the invention to be accommodated without any problem in a structural space which is already present, for example between the cylinder banks of a V-engine.

[0033] The lubrications which are effective in the individual pump units and the means of guiding the lubricating oil, diesel oil and leakages are explained with reference to the pump unit 2 (which is illustrated at the left end in FIG. 2) by way of representation for all of the pump units.

[0034] An annular space 45 arranged above the cup tappet 36 is connected via a forced-oil line 31, which extends through the entire construction of the high-pressure pump, to a lubricating-oil tank 40 (illustrated in FIG. 3), the lubricating oil being supplied at the required pressure via a feed pump 19. This feed pump 19 is used to supply the bearings of the drive shaft 9 (eccentric shaft) in the same manner with lubricating oil, specifically via the axial lubricating-oil channel 30 and the radial bores 46. Overflow oil from the bearings of the drive shaft 9 passes into the eccentric space 58.

[0035] The feed pump 19 can be the lubricating-oil pump of the engine. In this case, the lubricating-oil tank 40 is at the same time the engine lubricating-oil tank.

[0036] In the region of movement of the open end of the cup tappet 36, a further annular space 41′ is provided which leads via an axially parallel channel 41 to a channel section 41″, which runs perpendicularly outward thereto in the line module 1. Instead of the channel 41, openings could also be manufactured in the lower region of the cup tappet 36. In this case, overflow oil from the upper side of the cup tappet 36 would pass from the space 41′ through the inner empty space of the cup tappet 36 via the openings into the eccentric space 58.

[0037] An annular collecting and mixing space 35 is formed on the inner wall of the plunger bore 37 in the high-pressure part 7 and is connected via a channel 60 to an annular space 34′ which is connected via a channel 34, formed in the housing 22, to the channel 34″ which is perpendicular thereto, is formed in the line module 1 and is guided outward. An O-ring seal seals off the annular space 41′ from the annular space 34′.

[0038] The effect achieved by this refinement is that, firstly, the cup tappet 36 is reliably and satisfactorily lubricated and, secondly, it is ensured that no lubricating oil can pass into the annular space 34′ and consequently into the feed space 18.

[0039] In addition to the two channel sections 34″ and 41″, channels for the low-pressure supply line 24 (FIG. 1) for diesel oil and for a high-pressure output line 26″ are also formed in the line module 1. The channel 24″ which is assigned to the low-pressure supply line cannot be seen in the illustration according FIG. 2, but is illustrated by dashed lines in FIG. 1.

[0040] The lubricating-oil flow which is guided via the channels 31 and conducted to the annular space 45 passes during operation into the annular space 41′ and from there via the channels 41 and 41″ back to the oil tank 40, which may also be the oil sump of an engine provided with the high-pressure pump.

[0041] Both lubricating-oil leakages, via the extremely small gap between plunger 14 and plunger bore 37, and diesel-oil leakages can pass into the annular space 35, so that there is a corresponding leakage mixture in this annular space 35, said mixture being removed from the high-pressure pump via the channel 60, the space 34′ and the channels 34 and 34″. This mixture of overflow diesel oil and overflow lubricating oil can be conducted back into the diesel tank 33 shown in FIG. 3. The percentage amount of overflow lubricating oil in the overflow diesel oil can be kept very small, preferably smaller than 1% and, in certain places, even only 2%. The amount of overflow lubricating oil passing into the diesel tank 33 is further diluted therein and then passes into the feed space 18, into the injection system and is finally injected into the engine combustion chamber. The exhaust-gas quality is not negatively affected by this small amount of oil in the injected fuel. The overflow lubricating-oil amount is a priori small because the gap between the plunger 14 and plunger bore 37 is extremely small. Furthermore, the viscosity of the diesel oil is substantially lower than that of lubricating oil and, in addition, the pressure in the feed space 18 during the feed stroke is up to 1000 times higher than the lubricating-oil pressure. Both facts in themselves already bring about a dominance of the overflow diesel oil over the overflow lubricating oil. A further favorable refinement in order to keep the overflow lubricating-oil amount very small will be described in greater detail in conjunction with FIG. 3.

[0042] In the same manner as the high-pressure parts 7 are sealed off with respect to the housing 22 by high-pressure sealing elements 8, corresponding high-pressure sealing elements 8′ are also provided between the particular housing 22 and the adjoining line module 1. Further sealing elements (for example O-rings) are used as low-pressure seals for the bores 31, 34 and 41. In this manner, a leakproof, cohesive line system is provided by the bores, such as 24, 26, 31, 34 and 41, provided in the housing 22, said system being connected to the corresponding lines or channels 24″, 26″, 34″, 41″ in the line modules 1, it being possible for the line modules 1 to be designed in such a manner that they have pure lead-through channels and/or also channels leading outward. Furthermore, the central bearing 59 of the drive shaft 9 is formed in the line module 1, this bearing being dimensioned in such a manner and being of such a size that the drive shaft 9 together with the eccentric sections 10 can be pushed through it for installation purposes.

[0043] At one end of the high-pressure pump, the end piece 15, in which pressurized supply channels 30, 31 for the lubricating oil are provided, is fitted in a sealing manner onto the outer end wall 13 of the housing.

[0044] The illustration according to FIG. 3 shows, in conjunction with the high-pressure pump which has already been explained with reference to FIG. 2, the associated diesel-oil tank 33 with feed pump 21 and associated front pipe and the lubricating-oil tank 40 which is ventilated in a corresponding manner together with the feed pump 19 and forced-oil line 30. The forced-oil supply with the bearings of the drive shaft 9 via bores 46 is also indicated in FIG. 3.

[0045] It is particularly advantageous to arrange a pressure-maintaining valve 32 in the overflow line 34′, which guides the mixed leakage of diesel oil and smaller amount of lubricating oil and is connected to the annular collecting and mixing space 35. This pressure-maintaining valve 32, which is loaded, for example, by a compression spring, enables a somewhat increased pressure to be built up upstream of this valve and therefore also in the annular collecting and mixing space 35. Owing to this increase in pressure in the space 35, the direction of flow of the leakage can be affected in such a manner that virtually no lubricating oil at all can pass into the mixing space 35, this being an essential requirement in conjunction with the high-pressure pumps formed in accordance with the invention.

[0046] However, in this case, depending on the amount of increase in pressure, a very small amount of diesel oil can pass from the annular collecting space 35 into the oil return-flow annular space 41′ and therefore into the lubricating-oil tank 40. However, this amount of diesel oil is so small that the lubricating oil is thereby only insignificantly diluted, i.e. is virtually not diluted. In this case, the mixing of the very small amount of diesel oil with the lubricating oil is not a problem both with respect to the oiliness and also in terms of combustion.

[0047] Furthermore, the mixing of the diesel oil and lubricating oil in the annular collecting and mixing space 35 can be affected by the length “L” of the extremely small gap between the plunger 14 and plunger bore 37. It is particularly favorable if “L” is greater than 2×E=H, i.e. greater than the stroke of the eccentric 10 and therefore of the plunger 14. During a plunger stroke, particles are moved in the extremely small gap at most by the distance H. Together with the increase in pressure in the annular space 35, mixing can be effectively avoided.

[0048] Two measures of increase in pressure and length “L” may also be taken independently of each other.

[0049] In one variant (not illustrated) the pressure-maintaining valve 32 can be controlled (for example electrically or electronically) in order to be able to adapt the increase in pressure in the annular space 35 to the operating state of the pump and/or of the engine, in order to obtain a minimal mixing.

[0050] The sectional illustration according to FIG. 4 shows the position of the channels running axially parallel according to FIGS. 2 and 3 and, in particular, shows the bore 24″ which cannot be seen in FIG. 2 and which constitutes the low-pressure supply line for diesel oil.

[0051] FIG. 5 shows a refinement of a modularly constructed high-pressure pump according to the invention that is expanded in comparison to the embodiment according to FIG. 2. In this case, three modular pump units 2 are combined with two line modules 1, so that in total twelve cylinder/plunger units are in use. In this refinement, it can be seen that line modules 2 can be formed both with exclusively continuous channels and also with channels which are continuous and branch outward. Both line modules 1 can be used at the same time for the mounting of the drive shaft 9.

[0052] FIG. 6 shows a high-pressure pump which is reduced in comparison to the embodiment according to FIG. 2 and in which a total of just four plungers are used, said plungers being provided with high-pressure parts 7 in a housing 22 in the manner already explained.

[0053] The line module 1 used here is used, in turn, for mounting the shaft, but has, on the one hand, channel sections which lead outward and, on the other hand, continuous channels 31 for the forced-oil supply of the pump. The housing 22 remains identical to that according to FIGS. 1 and 2. Since the line module 1 takes on at the same time the function of an outer end wall of the housing, it is, by contrast, slightly modified, since not all of the channel sections can be permeable.

[0054] FIG. 7 shows a sectional illustration of a pump similar to FIG. 1, but instead of a rolling ring 11 a two-part sliding shoe 47, 47′ is used. The two sliding-shoe parts 47, 47′ are held together by means of screws 48. A sliding bearing or a ball bearing can be provided between the eccentric section 10 and this two-part sliding shoe 47, 47′. Since the eccentric space 58 is filled with lubricant, no annoying friction occurs between the flat sides 64 of the sliding shoe 47, 47′ and the cup tappet 36 or a plunger 14 which is optionally directly actuated.

[0055] A substantial advantage of the sliding-shoe arrangement resides in the fact that the sliding shoes can be fitted without any problem even if the rolling rings 11 used according to the figures explained above between the line modules 1 can no longer be pushed through the bearings 59 which are provided.

[0056] If appropriate, a combination of rolling rings and sliding shoes may also be used, but preferably all of the rolling rings are replaced by sliding shoes 47, 47′.

[0057] The present application claims priority to Swiss Patent Application 2002 1702/02 filed on Oct. 14, 2002, which is incorporated herein by reference in its entirety.

Claims

1. A high-pressure pump, in particular for a common-rail injection system for internal combustion engines, having a plurality of feed pumps which each comprises at least one plunger guided in a bore leading into a feed space, and are driven via a common drive shaft having eccentric sections assigned to the respective plungers, and each feed space is connected via a pressure-controlled inlet valve to a low-pressure supply line and via a pressure-controlled outlet valve to a high-pressure output line, wherein the individual feed pumps are designed as modular pump units and can be lined up next to one another via their housings, which are provided with fluid-connecting channels, and wherein at least one line module is provided which can be coupled at least on one side to a housing of a modular unit and in which the fluid-connecting channels of the respectively adjacent housings form intake and discharge channels which, on the one hand, lead on further and/or, on the other hand, lead outward.

2. The high-pressure pump as claimed in claim 1, wherein the plunger bore accommodating the plunger and the feed space are formed in a high-pressure part screwed to the housing.

3. The high-pressure pump as claimed in claim 1 or 2, wherein each modular pump unit in each case comprises at least two plungers which lie diametrically opposite each other and are actuated by the same eccentric section together with an associated feed space and common housing.

4. The high-pressure pump as claimed in claim 1, wherein each plunger is guided in the housing via a cup tappet and is prestressed against the associated eccentric section by means of a restoring spring.

5. The high-pressure pump as claimed claim 1, wherein the drive shaft is mounted at least in the outer end walls of the housings which are placed on the end side of a row of modules.

6. The high-pressure pump as claimed in claim 5, wherein, instead of the drive shaft being mounted at both ends in a respective housing end wall, it is mounted at one end in a line module forming one end of the housing and is mounted at the other end in a housing end wall.

7. The high-pressure pump as claimed in claim 1, wherein a bearing socket for the drive shaft is formed in each case in line modules which are arranged between adjacent housings.

8. The high-pressure pump as claimed in claim 7, wherein the diameter of the bearing socket is at least slightly larger than double the value of the largest radius of the eccentric sections of the drive shaft.

9. The high-pressure pump as claimed in claim 1, wherein a forced-oil supply into the bearings of the drive shaft, of the rolling rings or sliding shoes and preferably into annular lubricating channels of the cup tappets is provided via an end piece fitted onto a housing end wall or line module provided on the end side.

10. The high-pressure pump as claimed in claim 9, wherein the forced-oil supply to the bearings takes place via bores in the drive shaft and to the annular lubricating channels via channels in the housings and line modules.

11. The high-pressure pump as claimed in claim 1, wherein the channels, which are provided in the housings of the pump units and in the line modules, are mutually orientated in the axial direction of the high-pressure pump and are sealed at the transition points, are provided for the low-pressure supply and for the high-pressure removal of diesel oil, for the removal of leakage of a mixture of diesel oil and lubricating oil, for the forced-oil supply and for the oil return line.

12. The high-pressure pump as claimed in claim 1, having a plurality of plungers which are moved to and fro via a common drive shaft provided with eccentric sections, are guided in each case in a plunger bore leading into a feed space and are actuated by an eccentric section counter to the action of a restoring spring, wherein an annular collecting space for overflow lubricating oil and overflow diesel oil is formed on the feed-space side in the wall of the plunger bore and is connected via channels to a diesel-oil tank.

13. The high-pressure pump as claimed in claim 1, having a plurality of plungers which are moved to an fro via a common drive shaft provided with eccentric sections, are guided in each case in a plunger bore leading into a feed space and are actuated by an eccentric section counter to the action of a storing spring in particular via a cup tappet which is guided in a bore in the housing, wherein, firstly, an eccentric space through which the drive shaft passes and, secondly, at least one annular lubricating channel which surrounds the respective plunger or cup tappet and is formed in the housing are connected to a lubricating-oil pressure supply, and wherein an annular spaceconnected to a lubricating-oil return flow is provided in the region of that section of the plunger or of the cup tappet which is on the feed-space side.

14. The high-pressure pump as claimed in claim 12 or 13, wherein a pressure-maintaining valve is arranged in a channel section which is common to all of the channels conducting a mixture of lubricating- and diesel-oil leakages.

15. The high-pressure pump as claimed in claim 14, wherein the pressure-maintaining valve can be set or controlled.

16. The high-pressure pump as claimed in one claim 1, having a plurality of plungers which are moved to an fro via a common drive shaft provided with eccentric sections, are guided in each case through a plunger bore leading into a feed space and are actuated by an eccentric section counter to the action of a restoring spring with the interconnection of rolling elements, wherein sliding shoes which are of two-part design are provided as the rolling elements.

17. The high-pressure pump as claimed in claim 16, wherein the sliding-shoe halves which can be screwed to each other have planar bearing surfaces on the plunger side for the respective plunger or for a cup tappet assigned to the plunger.

18. The high-pressure pump as claimed in claim 16 or 17, wherein a sliding bearing or ball bearing is provided between the respective eccentric section and the associated sliding shoe.