Quantity-limiting valve

Abstract

In a quantity limiting valve for a fuel injection system of an internal combustion engine including a cylinder with an inflow region and an outflow region separated by a piston axially movably disposed in the cylinder and a flow limiting fluid flow path extending along the piston between the inflow and outflow regions wherein the piston is biased with its front surface into contact with a stop element, the contact area between the front surface and the stop surface includes between the piston and the stop element a contact structure providing for an intermediate space which is in communication with the inflow region thereby to expose the front surface of the piston to the pressure of the fluid in the inflow region.

Claims

1. A quantity limiting valve (1) for a fuel injection systems (6) of an internal combustion engine (8), the quantity limiting valve (1) including a cylinder (11) with an inflow region (7) and an outflow region (9) separated by a piston (13) which is movably guided in the cylinder (11), a fluid flow communication path (17) extending along the piston (13) between the inflow region (7) and an outflow region (9), the piston (13) having a front surface (25) and being biased toward a stop element (29) with a stop surface (27) holding the piston (13) in a first operating position thereof in contact with the stop surface (27), the contact area between the front surface (25) and the stop surface (27) being provided with a contact structure (39) which includes at least one intermediate space (41) which is disposed between the piston (13) and the stop element (29) and forming a gap in fluid communication with the inflow region (7) to permit the fluid to enter the intermediate space (41) between the piston (13) and the stop element (29) for rapid actuation of the piston (13).

2. The quantity limiting valve (1) according to claim 1, wherein the contact structure (39) includes at least one projection (43) which extends toward the stop surface (27) and on which at least part of the front surface (25) is formed and also a cavity (44) extending into the front surface (25).

3. The quantity limiting valve (1) according to claim 1, wherein the contact structure (39) has at least one projection extending from the stop element (29) toward the front surface (25) of the piston (13) and which forms at least part of the stop surface and at least one cavity (44, 56) extending into the stop surface (27).

4. The quantity limiting valve (1) according to claim 1, wherein the stop element (29) is in the form of a stop sleeve (48) extending onto the cylinder (11) and being provided with a collar (49) extending around the outer circumference of the stop sleeve (48) and being supported on a wall section (51) of the cylinder (11).

5. The quantity limiting valve (1) according to claim 1, wherein the piston (13) is provided with at least one projection (59) which extends toward the stop element (29) and which is provided with the front surface (25) and forms at least one cavity (56) extending into the front surface (25).

6. The quantity limiting valve (1) according to claim 4, wherein the stop sleeve (48) is provided with at least one projection (43) which extends toward the front surface of the piston (13) and which is provided with the stop surface (27) and with at least one cavity extending into the stop surface (27).

7. The quantity limiting valve (1) according to claim 3, wherein the at least one cavity (44, 56) is in the form of a radially extending groove (57).

8. The quantity limiting valve (1) according to claim 4, wherein the stop sleeve (48) is provided with a through-bore (45) which at least to some extent forms the inflow region (7).

9. The quantity limiting valve (1) according to claim 7, wherein the radially extending groove (57) is in fluid communication with the inflow region (7) and with the flow path (17) formed between circumferential surface area (19) of the piston (13) and the inner surface area (21) of the cylinder (11).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows, in a schematic representation, a first exemplary embodiment of the quantity limiting valve in a longitudinal sectional view,

(2) FIG. 2A is a bottom view of a stop element of the first exemplary embodiment,

(3) FIG. 2B is a side view of the stop element shown in FIG. 2A and,

(4) FIG. 3 shows, in a perspective exploded view, parts of a secondary exemplary embodiment of the quantity limiting valve.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT

(5) FIG. 1 is a cross-sectional view of an exemplary embodiment of a quantity limiting valve 1. The quantity limiting valve 1 is shown integrated into an injector 3 which includes an individual reservoir 5. The injector 3 is part of a fuel injection system 6 of an internal combustion engine 8 wherein the injection system 6 includes a common high pressure storage. The individual reservoir serves as additional buffer volume.

(6) The quantity limiting valve 1 has an inflow region 7 and an outflow region 9. It includes a cylinder 11 in which a piston 13 is guided so as to be movable in axial direction that is in the longitudinal direction shown vertically in FIG. 1 so as to separate the inflow region 7 from the outflow region 9.

(7) There is however a fluid communication path between the inflow region 7 and the outflow region 9. This path comprises a transfer channel 15 which extends at least partially through the piston 13, diagonally in the shown exemplary embodiment. The transfer channel 15 is at one end in communication with the inflow region 7 and at its other end with a flow path 17 which is formed between a circumferential surface area 19 of the piston 13 and an inner surface area 21 of the cylinder 11.

(8) The piston 13 is provided at its circumferential surface area 19 with projections 23 which extend circumferentially but not fully around the piston 13. The projections may overlap in the circumferential direction or gaps may be provided between the projections 23. In the shown exemplary embodiment, the projections 23 are displaced relative to one another in the longitudinal direction and do not extend longitudinally over the full length of the circumferential surface area 19. Alternatively, the projections 23 may be in the form of longitudinal webs provided on the circumferential surface area 19 to form the flow path 17 between the webs. However, if the projections 23 are axially displaced and overlapping in the circumferential direction, a tortuous flow path 17 is formed through which the fuel flow is conducted around the projections 23.

(9) In FIG. 1, the piston 13 is shown in its first operating position in which it is biased with its front surface 25 onto a stop surface 27 of a stop element 29. In the shown exemplary embodiment, the piston 13 is biased toward the stop element 29 by a spring 31.

(10) The piston 13 remains in its first operating position as long as the injector 3 is closed. When the injector 3 is opened fuel flows out of the outflow region 9 through an outflow area 33 to the injection arrangement of the injector 3 which includes for example an injection control needle. As a result, the pressure in the outflow region 9 drops. As long as the piston 13 is in its first operating position fuel can flow from the inflow region 7 to the outflow region 9 only via the transfer channel 15 and the flow path 17 which, in flow directionfollows the transfer channel 15. As a result of the pressure differential occurring in this way between the inflow region 7 and the outflow region 9, a pressure force is generated at the front surface of the piston 13 which exceeds the force of the spring 31. The piston 13 is then moved in the longitudinal direction toward the outflow region 9 or respectively, into the outflow region, that is in FIG. 1 downwardly. As soon as the piston 13 is lifted off the stop element 29 additional fuel can flow directly into the flow path 17 so that two fluid flow passages are provided between the inflow region 7 and the outflow region 9, that is the restricted fluid flow path via the transfer channel 15 and another path via which the fuel can flow from the inflow region directly into the flow path 17.

(11) The flow cross-sections of these flow paths are so selected that always more fuel can flow out of the outflow region via the outflow area 33 than fuel can flow via the fluid paths out of the inflow region 7. In this way, the pressure differential between the inflow region 7 and the outflow region 9 is maintained and the piston 13 is moved further into the outflow region 9 as long as the injection takes.

(12) When the injector 3 is closed again, a pressure differential first remains as fuel continues to flow out of the inflow region 7 to the outflow region 9 whereby the pressure differential becomes smaller until the piston is returned to its first operating position and the fuel flow from the inflow region to the outflow region stops while the piston 13 is again seated on the stop element 29preferably before the next injection takes place.

(13) Should the injector 3 become defective so that it remains open the pressure differential across the piston 13 remains so that the piston 13 is moved up to the sealing surface 35 against which it is sealingly pressed via an axial end face area 37. The piston is then in a second operating position wherein no fuel can flow from the inflow region 7 upstream of the piston 13 to the outflow region S downstream of the piston 13 or, respectively, the outflow area 33. As a result, the pressure in the outflow region and the outlet area drops whereby the pressure differential across the piston 7 is maximized and the piston remains firmly pressed into, and retained, in its second operating position. As a result, fuel can no longer flow via the injector 3 into the combustion chamber so that the internal combustion engine is effectively protected from being damaged by an excessive fuel supply.

(14) There is however a problem with such conventional quantity limiting valves in that, upon opening the injector, that is upon injection begin, the piston lifts off delayed and then suddenly from its first operating position. As a result, a so-called opening pressure wave is generated that is a time-wise local excess pressure is generated in an area of the individual reservoir 5 where the fuel pressure signal is detected.

(15) The development of such a pressure wave is prevented by the exemplary embodiment of the quantity limiting valve 1 according to the invention in that the piston front surface and/or the stop element is provided with a surface structure 39 which provides for at least one intermediate space 41 in the interface area between the piston 13 and the stop element 29. The intermediate space 41 is in communication with the inflow region 7. As a result, in the first operating position of the piston 13 fuel from the inflow region is admitted to the intermediate space 41 that is to the contact area between the front face 25 and the stop surface area 27. As a result, a larger surface area of the piston 13 is subjected to the high pressure of the fuel in the inflow area 7 as is the case in conventional quantity limiting valves. Therefore, the piston 13 lifts off without delay that is rapidly from its first-operating position. In addition, via the intermediate space 41 a fluid communication path is opened to the flow path 17 which is normally closed because the projections 23 do not extend along the full circumference of the piston 13. In addition to the transfer channel 15 therefore fuel can then flow also via the intermediate space 41 to the flow path 17 already with the injection begin. That is, an additional fluid flow path is provided whereby the responsiveness of the quantity limiting valve 1 is positively affected and whereby the piston 13 is no longer suddenly but softly moved out of its first operating position.

(16) In the exemplary embodiment of FIG. 1, the contact structure 39 is arranged, solely on the stop element 29 wherein in particular projections 43 are provided which extend, toward the front surface 25 and on which the stop surface 27 is provided. Between the projections 43, of which in FIG. 1 only one is shown, intermediate spaces 41 are formed of which in FIG. 1 also only one is shown. Alternatively cavities or grooves may be provided in the stop surface 27 which act as intermediate spaces 41.

(17) FIG. 2A is a bottom view of the stop element 29 according to FIG. 1. Identical or functionally identical elements are designated by the same reference numerals so that reference is made to the earlier description. In FIG. 2A, the projections 43 are indicated. The stop element 29 is in this case in the form of a stop sleeve 48 which has three projections 43 which are arranged symmetrically in a circumferential direction and, in particular, with an angular spacing of 120 relative to one another. Between the projections 43in the circumferential directionintermediate spaces 41 are provided. In the shown exemplary embodiment, the intermediate spaces may also be called cavities 44 which are provided on the stop surface 27. It is also apparent that the stop surface 27 is provided on the projections 43 and is interrupted by the cavities 44 or respectively, the intermediate spaces 41.

(18) It is also apparent that the stop element 29 has a through-bore 45 extending in the longitudinal direction which is also shown in FIG. 1. The through-bore 45 forms in part also the inflow region 7.

(19) FIG. 2B is a side view of the exemplary embodiment of the stop element 29 shown in FIG. 2A. Again, identical or functionally identical elements are designated by the same reference numeral so that in this respect reference can be made to the preceding description. Here, it is visible that the stop element 29 includes a collar 49 which preferably extends along an outer circumference 47 and which is also shown in FIG. 1. Herewith, it is visible from FIG. 1, that the stop sleeve 48 or respectively the contact element 29 is in contact with a wall 51 of the cylinder 11 via the collar 49.

(20) The effective flow path cross-section of the fluid communication path between the inflow region 7 and the outflow region 9 via the piston 13 is smaller than the flow path cross-section downstream of the outflow region 9. Accordingly, the projections 43 have a smaller height h. The height is preferably between at least a few tenths of a millimeter to at most two millimeters, but preferably only a few tenths of a millimeter.

(21) FIG. 3 shows in a three-dimensional perspective view a second exemplary embodiment of a quantity limiting valve 1. Identical or functionally identical elements are indicated again by the same numerals so that reference is made to the previous description. The representation according to FIG. 3 is in the form of an exploded view wherein only selected parts of the quantity limiting valve 1 are shown. In the upper area of FIG. 3, the stop element 29 in the form of a stop sleeve 48 with a collar 49 is shown.

(22) In the lower area of FIG. 3, the cylinder 11 is shown with the piston 13 movably guided therein. It is apparent therefrom that the circumferential surface area 19 of the piston 13 is not everywhere in sealing contact with the inner surface area 21 of the cylinder 11 but that there are rather recessed areas which form the flow path 17. In FIG. 3 such a recessed area 53 faces the viewer. In this area, the circumferential surface of the piston 13 is flattened so that an intermediate recessed area is formed between the piston 13 and the inner surface 21 of the cylinder 11.

(23) For a secure guidance of the piston 13, the piston 13 is provided with the projections of which one disposed next to the recessed area 53 is marked by the numeral 23.

(24) FIG. 3 also shows the transfer channel 15 whose one end opens in a center part 55 of the piston 13 which center part is also shown in FIG. 1 and whose other end opens into a recessed area 53 which is not visible in FIG. 3 as it is arranged at the side remote from the viewer.

(25) In the exemplary embodiment as shown in FIG. 3, the front surface 25 of the piston 13 has three cavities or recesses 56 in the form of radial grooves 57. When the piston 13 is pressed with its front surface 25 onto the stop surface 27, the grooves 57 form intermediate spaces 41 through which fuel may flow as the grooves 57 provide for a flow communication between the inflow region 7 and the flow path 17. This provides for an enlarged front surface area 25 which is subjected to the high pressure fuel in the inflow region 7 for lifting the piston off its first position whereby an additional fluid flow path is generated via which the inflow region 7 is in communication with the outflow region 9. A delayed reaction of the piston 13 as well as a sudden lift off of the piston 13 from the first operating position is therefore effectively prevented. The webs which remain between the grooves 57 which represent the front surface 25 may in the shown exemplary embodiment also be considered to be projections 59 on which the front surface 25 is provided.

(26) As already indicated, it is possible to combine the first exemplary embodiment according to FIGS. 1 and 2 and the second embodiment according to FIG. 3. In particular the projections 59 and/or the cavities 56 may be provided in the areas of the front surface 25 as well as in the area of the stop surface 27.

(27) It is noted that, with the quantity limiting valve 1 according to the invention, the problem caused by a valve opening wave which occurs in particular in connection with an individual reservoir analysis for determining an injection begins can be eliminated. The quantity limiting valve 1 as proposed herein opens smoothly and always in a timely fashion. The measurement of the pressure in the area of the individual reservoir 5 is not negatively affected so that a correct and reproducible determination of the injection begin from the pressure curve measured in the area of the individual reservoir 5 is made possible. The quantity limiting valve 1 is preferably used in connection with injectors 3 designed for the direct injection of the fuel into combustion chambers of internal combustion engines. However, the quantity limiting valve 1 may also be used in connection with a single point injector for injecting fuel into an intake duct serving all of the cylinders of an internal combustion engine or in connection with multipoint injectors for injecting fuel into the individual intake passages leading to the different combustion chambers. The actual use does not change the functions of the quantify limiting valve 1.