GB2328984A

GB2328984A - Fuel pressure intensifying device for an internal combustion engine

Info

Publication number: GB2328984A
Application number: GB9817918A
Authority: GB
Inventors: Karl Hofmann; Walter Egler; Joerg Schmidt
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1997-09-05
Filing date: 1998-08-18
Publication date: 1999-03-10
Anticipated expiration: 2018-08-18
Also published as: GB9817918D0; DE19738804A1; DE19738804B4; GB2328984B; JPH11159413A; FR2768185A1

Abstract

A fuel supply system for an internal combustion engine has a low pressure source 5, a high pressure pump 1, a fuel injection nozzle valve 7 and a hydraulic intensification device 13 positioned between the high pressure pump 1 and the nozzle valve 7. The intensification device comprises a stepped pistol, 19 whose end faces each define a pressure chamber 23, 27 and a supply duct, which contains a non return pressure valve 45 and preferably a rod filter 57, and allows chamber 27 to be filled with fuel from chamber 23. Pressure intensification results from the different surface areas D1, D2 of the end faces of the piston 19 and is proportional to their ratio. In this embodiment the supply duct is provided by a through-going bore 43 in the piston 19. In other embodiments (figure 2A, 3A, 3B) the supply duct may be provided in the housing of the device. A restoring force may be exerted on the stepped piston 19 by a spring 37 which abuts against an annular collar 29 on the piston 19.

Description

1 DESCREMQ 2328984 FUEL-INJECTION DEVICE FOR WERNAL COMBUSTION ENGINES The

invention relates to a fuel-injection device for internal combustion engines of the type having a high pressure pump, which delivers fuel from a lower pressure chamber by way of a high pressure line to a fuelinjection valve, and a hydraulic intensification device between the high pressure pump and the fuel-injection valve, which intensification device comprises a stepped Piston, which can be displaced in a bore and whose end faces in each case define a pressure chamber, wherein a first larger end face defines a first pressure chamber, which is connected to the pumpside part of the high pressure line, and a second opposite-lying smaller end face defines a second pressure chamber which is connected to the injection valve-side part of the high pressure line, and having a supply duct, which contains a pressure valve, for the purpose of filling with fuel the second pressure chamber.

In the case of this type of fuel-injection device, which is known from the document DE 41 18 237 AI, fuel is delivered from a low pressure chamber by way of a high pressure line to a fuel injection valve by means of a high pressure pump. In order to increase the pressure at the fuel- injection valve, a hydraulic intensification device is provided between the high pressure pump and the fuel-injection valve. This hydraulic intensification device comprises a stepped piston which can be displaced in a bore and whose end faces in each case define a pressure chamber, wherein a first larger end face defines a first pump-side pressure chamber and a second smaller end face 2 defines an injection-side pressure chamber. The hydraulic pressure intensification on the intensification device is dependent upon the surface ratio of the pump piston end faces adjacent to the pressure chambers, wherein the stepped piston is actuated by way of the supply of high pressure fuel on to the larger piston end face thereof.

The injection-side pressure chamber on the smaller end face of the stepped piston of the intensification device is filled by way of a valve arrangement from the fuel circuit of the injection device. The restoring movement of the stepped piston is also performed in a hydraulic manner by way of the fuel circuit and a corresponding valve arrangement in a supply line into the restoring chamber.

The known fuel-injection device for internal combustion engines has the disadvanta.e that it requires a plurality of control valves and thus comprises a complicated structure. Moreover, owing to the complicated valve control, the known fuel-injection device requires a tall installation space which is not often available in modern internal combustion engines.

A further disadvantage of the intensification device on the known fuelinjection device is the large volume, which is to be displaced, in the restoring chamber which volume reduces considerably the efficiency of the ice.

intensi ication dev In accordance with the present invention, the supply duct, which issues into the second pressure chamber leads off from the first pressure chamber.

In contrast to the known devices, a fuel-injection device in accordance 3 with the invention has the advantage that the injection pressure at the fuelinjection valve and the hydraulic efficiency can be increased as the ratio of injection energy and supplied power of the entire injection device, without substantially increasing the installation space with respect to injection systems which do not comprise an intensification device. Furthermore, with respect to known fuel-injection devices having an intensification device, a fuel-injection device in accordance with the invention can have the advantage of a substantially lower installation and assembly outlay owing to the straightforward structural formation. This can be achieved in particular by virtue of the fact that the second, injection valve-side pressure chamber is filled directly from the high pressure region between the high pressure pump and the intensification device. It is thus possible to omit an additional supply line from the low pressure region of the system. In so doing, it is particularly advantageous to fill the injection-side pressure chamber by way of a filling valve, which is provided as a pressure valve in the connection line or supply line between the high pressure line and the pressure chamber, parallel with the stepped piston. This supply line, which fills the injection-side pressure chamber, can be formed as a bypass line. This formation as a bypass line has the advantage that a bi-partite formation of the stepped piston is possible, so that the intensification device can be manufactured in a convenient manner. A bypass line of this type, which extends preferably in parallel with the stepped piston, functions in a problem-free manner and, furthermore, can be produced without narrow tolerances. A further possibility for the supply line is to 4 provide it directly as a through-going bore in the stepped piston, which has the advanta.e that the intensification device is extremely small. This renders it possible to retro-fit the intensification device into existing fuel-lines in known injection systems, such as distributor pumps, pump-line-nozzle systems or common rail systems. The filling valve which is inserted into the supply line is formed as a pressure valve, preferably as a non-return valve whose opening pressure can be adjusted by way of the valve spring. The stepped piston of the intensification device is disposed with the longest possible sliding surface in the guide bore, whereby in an advantageous manner only a small quantity of fuel can issue out of the pressure chambers by way of the play between the stepped piston and the guide bore thereof, whereby the intensification device only comprises slight leakage losses. The intensification ratio at the stepped piston is preferably in a ratio of the larger end face to the smaller end face between 1 to 3, wherein intensification ratios between 1. 5 and 2.2 are particularly suitable, since in this case the hydraulic efficiency is increased to a considerable extent without any substantial increases in the required delivery volume of the high pressure pump.

With respect to energy, a greater significance is attached to this increase in the efficiency than to a pure increase in pressure at the injection valve because as the drive energy requirement is reduced, the thermal load of the pump decreases along with its tendency to "seize", as it were. Therefore, smaller degrees of play between the piston and distributor shafts and their bushings can be produced, so that smaller leakages serve to increase the 0 efficiency once again. A further advantage is achieved by virtue of the integration of the rod filter into the supply duct leading to the injection-side pressure chamber, since the clearance volume in the injection-side high pressure region can be reduced once again.

The volume displaced on the piston ring end face of the spring chamber by the stepped piston is relieved in an advantageous manner, if possible without any counterpressure, into the low pressure circuit, so that hydraulic losses on the intensification device can be kept as low as possible.

Furthermore, in order to. ensure reliable function, a restrictor is provided within the supply line into the injection-side pressure chamber and is sufficiently large in order to guarantee a new filling procedure in the case of a returning stepped piston, and which restrictor is sufficiently small in order, during the pressure intensification stroke of the stepped piston, to build up a pressure difference which rapidly closes the non-return valve. This separate restrictor can be omitted if upstream of the non-return valve there is inserted a rod filter whose gaps are formed in such a manner that they perform the required restricting function.

The stepped piston of the intensification device is restored in an advantageous manner by means of a restoring spring so that no additional hydraulic restoring forces are required. Therefore, it is also possible to omit additional control lines and control valves, whereby the structural formation of the intensification device is simplified once more.

6 A further, advantageous embodiment of the fuel-injection device in accordance with the invention is the provision of the stepped piston in a guide bushing which for its part is inserted into a pipe connecting piece. The guide bushing comprises longitudinal slots through which a connection element, preferably a clamp, protrudes and engages a step of the stepped piston in a radial manner. The restoring spring of the stepped piston engages in a radial manner outside the guide bushing and in so doing is guided in an annular cbamber between the guide bushing and the inner wall of the pipe connecting piece. This spring arrangement renders possible a large winding diameter of the restoring spring and extensive spring travel. Furthermore, the components of the intensification device can be manufactured in a convenient manner as rotational ly-symmetrical parts, which reduces considerably the production outlay and the required installation space. The bypass duct is integrated in an advantageous manner into the guide bushing, wherein a restrictor is connected upstream of the pressure valve which opens in the direction of the injection valve-side pressure chamber. In so doing, the bypass duct is formed as a straialitforward longitudinal bore in the guide bushing and issues by way of widened parts of the bore of the guide bore, which receives the stepped piston, in the -ulde bushing into the respective pressure chambers. The stepped piston can be formed as one part as in the illustrated embodiment, however, owing to a more convenient manufacturing process, it is advantageous to form the stepped piston in two parts, which is similarly possible on the illustrated construction without performing any modifications.

7 A further advantage of the fuel-injection device in accordance with the invention is achieved by virtue of the most adjacent possible arrangement of the intensification device to the fuel-injection valve, so that the region having extremely high fuel pressures can be limited to an extremely small line region, in which this high pressure is actually required. Therefore, the waste space in the high pressure injection region and thus the lost hydraulic power are reduced. In the remaining, pump-side fuel line region the pressure remains reduced, which at this site results in lower component stresses so that said components can be dimensioned to be smaller whilst offering an equally long serviceable life.

The intensification devices of the individual fuel-injection valves can be mutually connected and the connection with respect to the high pressure fuel pump can be achieved by way of a common line.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which:- C Figure 1 shows a first exemplified embodiment of the fuel-injection device, wherein the supply line into the injection valve-side pressure chamber is formed by virtue of a through-going bore in the stepped piston of the intensification device, Figures 2A and 2B show a second exemplified embodiment in two views, wherein 8 the supply line into the injection valve-side pressure chamber is formed by virtue of a bypass duct which extends in parallel with the stepped piston, Figures 3A and 3B show a third exemplified embodiment in two positions of the stepped piston, wherein the supply line is disposed in a guide bushing which receives the stepped piston and which for its part is inserted into a pipe connecting piece, and Figure 4 shows an individual view of the clamp which connects the restoring spring and the stepped piston in the third exemplified embodiment.

Description of the exemplified embodiments

The fuel-injection device, illustrated in Figure 1, for internal combustion engines comprises a high pressure fuel pump 1, which delivers fuel by way of a high pressure line 3 from a low pressure chamber 5, preferably a fuel tank, to a fuelinjection valve 7. In order to control the supply of high pressure fuel to the injection valve 7, a control valve 9, preferably a solenoid valve, is inserted in the case of the described exemplified embodiments into a bypass line 11 which branches off from the high pressure line 3 and which 9 issues as a return line into the low pressure chamber 5. In so doing, a nonreturn valve 12, which opens in the direction of the low pressure chamber 5, is connected downstream of the control valve 9, and by way of said non-return valve it is possible to adjust a remaining static pressure in the bypass line 11 and in the high pressure line 3. In so doing, the control valve 9 can be switched in such a manner that, when the control valve 9 is closed, the fuel delivered by the high pressure pump 1 flows to the injection valve 7 or else flows back by way of the opened control valve 9 by way of the bypass line 11 into the low pressure chamber 5 (short circuit), wherein the non-return valve 12, which is disposed in the bypass line 11, maintains a predetermined static pressure in the system.

In order to increase the injection pressure at the injection valve 7 a hydraulic intensification device 13 is inserted into the high pressure line 3 between the high pressure pump 1 and the injection valve 7. This hydraulic intensification device 13 comprises a stepped piston 19, which is guided in an axial manner in a guide bore 15 of a housing 17 and defines with its axial end faces in each case a pressure chamber in the bore 15 in the housing 17 of the intensification device 13. A first larger end face 21 of the stepped piston 19 defines a first pressure chamber 23 which on the other side is connected to the part of the high pressure line 3 which leads to the high pressure pump 1. A second, smaller end face 25 of the stepped piston 19 defines a second pressure chamber 27 in the housing 17 of the intensification device 13, which second pressure chamber lies opposite to the first pressure chamber 23 and is connected to a second part of the high pressure line 3 which is connected to the injection valve 7. The single-piece stepped piston 19 illustrated in the first exemplified embodiment comprises, at its transition in crosssection from a large diameter D1 to a small diameter D2, an annular collar 29 which protrudes beyond the large diameter DI. With its annular end face 31, which is remote from the large diameter region on the stepped piston, the annular collar 29 defines in the direction of the second pressure chamber 27 a spring chamber 33, which on the other side is defined by virtue of a sleeve 35 which is pressed by the second chamber 27 into the bore 15 in the housing 17. The inner wall surface, which guides in an axial manner the stepped piston 19 with its small diameter D2, of the sleeve 35 deflines the second, injection-side pressure chamber 27. Furthermore, the annular end face, which defines the spring chamber 33, on the sleeve 35 serves as a spring support surface for a restoring spring 37 which is clamped in the spring chamber 33 and which acts upon the annular end face 31 of the annular collar 29 of the stepped piston 19 and holds same with the annular collar 29 in position against a housing-fixed bore step 39 of the bore 15 in the housing 17. Preferably two relief lines 41 lead off from the spring chamber 33 and issue into the low pressure chamber 5. In order to fill with fuel the second, injection-side pressure chamber 27, there is provided an axial through-going bore 43 in the stepped piston 19, which through-going bore, starting from the first pressure chamber 23, issues into the second pressure chamber 27. A non-return valve 45, which serves as a filling control valve is inserted into this through-going bore 43 and the valve 11 member 49 of said non-return valve can be raised from a valve seat 51 against the closing force of a valve spring 47 in the direction of the second pressure chamber 27. Furthermore, a fuel filter 57, which is formed as a rod filter, is inserted into the region, which is adjacent to the first pressure chamber 23, of the through-going bore 43 in the stepped piston 19 and the filter gaps of said rod filter are designed in such a manner, that in addition to the fuel filtering procedure the restricting function is performed which is required for the function of the intensification valve 13.

The intensification ratio, which is determined by virtue of the diameters D I with respect to D2 on the first end face 21 and of the second end face 25, on the stepped piston 19 ranges from the values 1 to 3 and should preferably amount to a value between 1.5 and 2.2.

The fuel-injection device in accordance with the invention functions in the following manner.

Prior to the commencement of the high pressure injection procedure at the fuel-injection valve 7, the second pressure chamber 27 is filled with fuel by way of supply line which is formed by virtue of the through-going bore 43 in the stepped piston 19. The pressure chamber 27 is filled for as long as until the pressure is compensated between the mutually connected pressure chambers 23 and 27, so that the non-return valve 45 closes the supply line. The injection procedure at the injection valve 7 is initiated, if the control valve 9 closes the bypass line 11 and the high pressure pump 1 delivers said fuel into the high pressure line 3 to the injection valve 7. Consequently, the high 12 pressure fuel flows initially into the first pressure chamber 23 on the stepped piston 19 of the hydraulic intensification device 13 and displaces the stepped piston 19 in the direction of the smaller second pressure chamber 27. Owing to the different annular end faces 21, 25 of the stepped piston 19 pressure is increased in the second pressure chamber 27 with respect to the fuel pressure which is built up by the high pressure pump. This increased fuel pressure passes by way of the second part of the high pressure line 3 to the injection vqlve 7 and passes at this site to the injection orifices for the purpose of injection into the combustion chamber of the internal combustion engine which is to be supplied. The fuel located in the spring chamber 33 is displaced without any significant counterpressure by way of the relief lines 41 and in so doing scarcely reduces the efficiency of the intensification device 13. The non-return valve 45 is kept closed by the force which is produced from the excess of the pressure force, which is effective from the pressure chamber 27, and the resilient force of the valve spring 47 with respect to the pressure force which is effective from the pressure chamber 21. As a result, the non-return valve 45 remains closed during the working stroke of the stepped piston 19.

The injection of high pressure fuel performed at the injection valve 7 is terminated in that the control valve 9 opens the bypass line 11 once again, so that the high pressure line 3 is connected by way thereof to the low pressure chamber 5 and the high pressure fuel, which is located in the high pressure line 3 and thus in the intensification device 13, is relieved to an adjustable static pressure into the low pressure chamber 5. This remaining residual static 13 pressure, which can be adjusted by way of the non-return valve 12 in the bypass line 11, in the high pressure line 3 is greater than the opening pressure of the non-return valve 45 so that the second pressure chamber 27, during the restoring movement of the stepped piston 19, is once again filled with fuel from the first pressure chamber 23 by way of the through-going bore 43. The restoring movement of the stepped piston 19 is performed mainly by virtue of the force of the restoring spring 37 which displaces the stepped piston 19 with its annular collar 29 back into position against the housing-fixed bore step 39 and thus back into its starting position. During its passage from the first pressure chamber 23 into the second pressure chamber 27 the fuel is filtered at the fuel filter 57 which is formed as a rod filter.

The second exemplified embodiment of the fuel-injection device, in accordance with the invention, for internal combustion engines differs from the first exemplified embodiment merely in the formation of the intensification device 13 in the high pressure line 3, for which reason Figure 2 is limited to the illustration of the intensification device 13. Figure 2A shows a sectional illustration of the second exemplified embodiment of the intensification device 13 and Figure 2B shows the intensification device 13 in a view which is rotated about 901 with respect to Figure 2A.

The intensification device 13 of the second exemplified embodiment differs from the intensification device 13 of the first exemplified embodiment, illustrated in Figure 1, in the arrangement of the supply line from the first, pump-side pressure chamber 23 into the second, injection valve-side pressure 14 chamber 27 on the now bi-partite stepped piston 19. This supply or filling duct for the second pressure chamber 27 in the second exemplified embodiment is formed as a bypass line which is disposed in parallel with the stepped piston 19 in the housing 17 of the hydraulic intensification device 13. The bypass line is formed by virtue of a first transverse bore 59, which leads off from the first pressure chamber 23, and by virtue of a second transverse bore 61, which leads off from the second pressure chamber 27, which tr4nsverse bores are mutually connected by virtue of a longitudinal bore 63 which preferably extends axis-parallel with the stepped piston 19. In a similar manner to the through-going bore 43 in the stepped piston 19 in the first exemplified embodiment, the non-return valve 45 and the fuel filter 57 are inserted in this longitudinal bore 63.

The hydraulic intensification device 13, which is illustrated in Figure 2, functions in the same manner as the intensification device 13, illustrated in Figure 1, of the fuel-injection device in accordance with the invention. The intensification ratio at the intensification device 13 is determined in turn by virtue of the surface ratio of the end faces 21 and 25 on the stepped piston 19 with respect to each other and is also in a range of 1 to 3, preferably in a range from 1.5 to 2.2.

In the case of the third exemplified embodiment, which is illustrated in Ficrures 3A and 3B, the stepped piston 19 is guided in a slidingdisplaceable manner in a guide bore 65 of a guide bushing 67, which for its part is inserted into a pipe connecting piece 69. The stepped piston 19 defines with its larger end face 21 the first, pump-side pressure chamber 23 and defines with its smaller end face 25 the second, injection valve-side pressure chamber 27. first pressure chamber 23 is disposed in a portion, which accordingly has an increased diameter, of the guide bore 65 and partially in the adjacent part of the pipe connecting piece 69 and the second pressure chamber 27 is provided in a through-going bore of a connecting branch 73, which is screwed on the injection valve-side into the pipe connecting piece 69 and clamps the guide btishing 67 in an axial manner against the step 75 of the pipe connecting piece 69. In the exemplified embodiment, a valve holding body 77 of the fuelinjection valve 7 is screwed into- the end, remote from the pipe connecting piece 69, of the connecting branch 73, wherein the sealing seat is guaranteed by way of a conical filling piece 79 which is clamped in an axial manner between the valve holding body 77 and the connecting branch 73 and which comprises an axial through-go ing orifice.

Furthermore, between the peripheral wall of the guide bushing 67 and the inner wall of the pipe connecting piece 69 there is provided an annular chamber 71, which in the third exemplified embodiment receives the restoring spring 37 of the stepped piston 19. The restoring spring 37 is supported in a fixed manner on the end face of the connecting branch 73 and on the other side influences the stepped piston 19 by way of a clamp 81 in the direction of the pressure chamber 23. This U-shaped clamp 81, which is illustrated individually in Figure 4, comprises a slot 83 whose dimension corresponds to the smaller diameter of the stepped piston 19 or to a receiving groove which is 16 provided on the cross-sectional transition on the stepped piston 19. The clamp 81 penetrates at the provided longitudinal slots [not illustrated] the guide bushing 67 in a radial manner and lies against the diameter step of the stepped piston 19.

The stroke movement of the stepped piston 19 in the direction of the pumpside pressure chamber 23 is defined by virtue of an annular step 85 on the periphery of the guide bushing 67, wherein the restoring spring 37 di places the stepped piston 19 into this starting position. The working stroke, which is directed in the direction of the injection valve-side pressure chamber 27, of the stepped piston 19 is defined by virtue of a step 91 of the guide bore 65, against which step the stepped piston 19 moves into position with the clamp 81 (Figure 3A).

The second chamber 27 is filled by way of a bypass or supply line which leads off from the first pressure chamber 23 and which is formed by virtue of an axial longitudinal bore 87 in the guide bushing 67. Depending upon the position of the stepped piston, the fuel then passes further directly into the pressure chambers 23, 27, which are defined by the end faces of the guide bushing 67, or by way of the remaining degree of play between the stepped piston 19 and the walls of the through-going bores in the pipe connecting piece 69 or connecting branch 73. A non- return valve 45, which opens in the direction of the injection-valve side pressure chamber 27, is inserted in the longitudinal bore 87 and, furthermore, a restrictor 89 is disposed upstream of said non-return valve in the direction of flow.

17 The manner in which the third exemplified embodiment functions is similar to the previous exemplified embodiments, wherein Figure 3A illustrates the position of the stepped piston 19 during the working stroke when the fu'ul position is achieved.

Figure 3B illustrates the stepped piston 19 a short time prior to reaching its starting position, wherein the procedure of refilling the pressure chamber 27 by way of the supply duct along the play between the stepped piston 19 in the pipe connecting piece 69, the longitudinal bore 87 and the non-return valve 45 can commence prior to the stepped piston 19 reaching its starting position.

l0(02 _: 4(2S 1

Claims

18 CLAIMS

1. A fuel-injection device for internal combustion engines, having a high pressure pump, which delivers fuel from a low pressure chamber by way of a high pressure line to a fuel-injection valve, and a hydraulic intensification device between the high pressure pump and the fuelinjection valve, which intensification device comprises a stepped piston, which can be displaced in a boe and whose end faces in each case define a pressure chamber, wherein a first larger end face defines a first pressure chamber, which is connected to the pump-side part of the high pressure line, and a second opposite-lying smaller end face defines a second pressure chamber which is connected to the injection valve-side part of the high pressure line, and having a supply duct, which contains a pressure valve, for the purpose of filling with fuel the second pressure chamber, and wherein the supply duct, which issues into the second pressure chamber, leads off from the first pressure chamber.

2. A fuel-injection device according to claim 1, wherein the pressure valve in the supply duct is connected in parallel with the stepped piston of the hydraulic intensification device.

3. A fuel-injection device according to claim 1, wherein the supply duct is formed as a bypass duct which bypasses the stepped piston.

4. A fuel-injection device according to claim 3, wherein the supply duct is disposed in parallel with the stepped piston.

5. A fuel-injection device according to claim 4, wherein the supply 19 duct is formed in each case by virtue of transverse bores, which lead off from the first pressure chamber and the second pressure chamber respectively, and a longitudinal bore which connects said transverse bores and which is disposed preferably axis-parallel with the bore which receives the stepped piston.

6. A fuel-injection device according to claim 1, wherein the supply duct is formed by virtue of a through-going bore in the stepped piston, wherein the pressure valve, which closes the supply duct, is disposed within the stepped piston.

7. A fuel-injection device according to claim 1, wherein the pressure valve is formed as a non-return valve which opens in the direction of the second pressure chamber and the opening pressure of said non-return valve is below the static pressure of the high pressure line.

8. A fuel-injection device according to claim 1, wherein the stepped piston is guided in a sealing and sliding displaceable manner in the bore in the housing of the intensification device.

9. A fuel-injection device according to claim 1, wherein the intensification ratio on the stepped piston between the larger piston end face and the smaller piston end face should amount to a value between 1 to 3, preferably between 1.5 and 2.2.

10. A fuel-injection device according to claim 1, wherein a fuel filter, preferably, a rod filter, is inserted into the supply duct.

11. A fuel-injection valve according to claim 1, wherein at the crosssectional transition of the stepped piston there is provided an annular collar which with its annular end face, facing the larger piston diameter part D 1, forms a stop surface which cooperates with a bore step of the bore and the annular end face, facing the smaller piston diameter part D2, of said annular collar defines a spring chamber in the bore.

12. A fuel-injection device according to claim 11, wherein a restoring spring, which surrounds the stepped piston preferably in a coaxial manner, is clamped in the spring chamber and is supported on a fixed bearing surface, irtfluences the stepped piston on the spring chamber-side annular end face in the direction of the bore step and, in dependence upon the static pressure in the high pressure line, the piston end faces and upon the opening pressure of the pressure valve in the supply duct, said restoring spring urges the stepped piston against its pump-side stop between injection procedures.

13. A fuelinjection device according to claim 11, wherein the fixed spring bearing surface is provided on a sleeve which is inserted into the bore.

14. A fuel-injection device according to claim 11, wherein at least one relief line leads off from the spring chamber into the low pressure chamber.

15. A fuel-injection device according to claim 1, wherein the stepped piston is guided in a displaceable manner in a guide bore of a guide bushing which is inserted into a pipe connecting piece.

16. A fuel-injection device according to claim 15, wherein an annular chamber is formed between the guide bushing and the inner wall of the pipe connecting piece and receives a restoring spring of the stepped piston.

17. A fuel-injection device according to claim 16, wherein the 21 restoring spring lies with its axial end face, which points in the direction of the small end face of the stepped piston, against afixed stop and with its oppositelying end face, facing the larger stepped piston end face influences a connection element which lies against the step of the stepped piston in such a manner as to penetrate in a radial manner the guide bushing at longitudinal slots.

18. A fuel-injection device according to claim 17, wherein the curiection element is formed as a U-shaped clamp.

19. A fuel-injection device according to claim 15, wherein the supply duct for the purpose of filling the injection valve-side pressure chamber is formed as a longitudinal bore in the guide bushing in a radial manner outside the guide bore which at the end faces of the guide bushing issues by way of widened parts in diameter of the guide bore into the pressure chambers.

20. A fuel-injection device according to claim 15, wherein the guide bushing is clamped by a connecting branch, which can be screwed into the pipe connecting piece, in an axial manner against a step in the pipe connecting piece.

21. A fuel-injection device according to claim 20, wherein the pumpside pressure chamber is provided in the part of the pipe connecting piece, which is adjacent to the guide bushing, and the injection-side pressure chamber is provided within the connecting branch.

22. A fuel-injection device according to claim 19, wherein in the longitudinal bore there is inserted a non-return valve, which opens in the 22 direction of the injection valve-side pressure chamber and a restrictor is connected upstream of said non-return valve in the direction of flow.

23. A fuel-injection device according to claim 1, wherein the hydraulic intensification device is disposed in a spatial manner in proximity to the fuelinjection valve.

24. A fuel-injection device substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.