EP1411238B1 - Pressure regulating valve for an injection system - Google Patents

Description

State of the art

The present invention relates to a fuel system of an internal combustion engine according to the preamble of claim 1.

Such a pressure relief valve is known from US 6,293,253 B1. It is preferably used in such fuel systems, which are used in internal combustion engines with gasoline direct injection. Such fuel systems usually have a low pressure range and a high pressure range. An electric prefeed pump delivers the fuel from a tank into the low-pressure area, from which the fuel is conveyed via a high-pressure pump into a fuel rail (called "common-rail".) The pressure in the fuel rail is usually controlled by a pressure regulator Quantity control valve regulated.
However, to provide a hedge against excessive pressure in the fuel rail, a pressure relief valve is provided in the high pressure region of the fuel system. This is generally a pressure relief valve with a pressed by a spring against a valve seat valve element. If the pressure in the fuel rail exceeds a certain limit, this will increase Valve element from the valve seat so that fuel can flow from the inlet of the pressure relief valve to the outlet and from there back to the low pressure region of the fuel system.

This known pressure relief valve is already working very well and above all very reliable. However, the possible arrangements of the pressure relief valve in the fuel system limits:

In general, the pressure limiting valve in the region of the fuel rail, ie at a certain distance from the high pressure pump, must be arranged. The reason for this is that during operation, the high-pressure pump generates pressure pulsations whose peaks can exceed the opening pressure of the pressure-limiting valve. If the pressure limiting valve were to be arranged directly at the high-pressure pump, there would be the danger that the pressure-limiting valve would open due to the pressure pulsations, although the maximum system pressure has not yet been reached. Only at a certain distance from the high-pressure pump does a smoothing of the pressure pulsations due to the throttle effects in the fuel line and due to the compressibility of the fuel.

Alternatively, it would also be possible to design the pressure relief valve so that its opening pressure is above the pressure peaks due to the pressure pulsations. This pressure limiting valve can then be arranged in the immediate vicinity of the high pressure pump or even integrated into it. In emergency mode, so if the pressure control of the fuel rail is no longer working properly and then there is a higher pressure in the fuel rail than the normal system pressure, safe operation of the internal combustion engine must still be ensured. This in turn would mean that the components of the high pressure area of the fuel system must be designed with respect to their function for the high opening pressure of the pressure relief valve. However, such components are relatively expensive.

From the subsequently published DE 101 18 936 a pressure limiting device is known in which the pressure pulsations are reduced by a compensation chamber, so that the pressure limiting device does not open during normal operation of the fuel pump despite the pressure pulsations caused by the high pressure pump. This allows the arrangement of the pressure relief device also in the vicinity of the high-pressure pump.

From EP 0 728 940 B1 a fuel injection system is known with a combined starter, bypass and safety pressure discharge valve, which is arranged between the high-pressure side output a high-pressure fuel pump and an electric prefeed pump.

In the pressure limiting valve according to the invention, it is provided that the outlet of the pressure limiting valve is hydraulically connected to a delivery chamber of a high pressure pump of the fuel system.

Advantages of the invention

In the pressure relief valve according to the invention an undesirable opening is prevented by the fact that caused by the high-pressure pump during the delivery stroke Pressure pulsations act on the valve member from both sides, that is, both the inlet and the outlet. As a result, the pressure pulsations, the maximum of which may be well above the opening pressure of the pressure limiting valve, do not cause a resultant hydraulic force on the valve member. This ensures that the valve member does not lift off its valve seat during the delivery stroke and thus does not open the pressure relief valve.

On the other hand, the pressure limiting valve according to the invention prevents the occurrence of unacceptably high pressures in the high pressure region of the fuel system during the intake stroke of the high pressure pump. For then the check valve between the delivery chamber of the high pressure pump and the high pressure region of the fuel system is closed and a possibly increased pressure in the high pressure region of the fuel system opens the valve member of the pressure relief valve, so that a pressure reduction takes place.

The pressure relief valve according to the invention is very simple and differs from other solutions known from the prior art essentially by the interconnection according to the invention. In principle, the advantages according to the invention can be realized both with poppet valves and with slide valves.

In a variant of the invention it is provided that the pressure relief valve has a housing with a valve seat and a spring chamber, that in the spring chamber, a spring is provided, which is supported at one end against the housing and the other end against the valve member, and that the spring chamber with the outlet hydraulically connected stands. This arrangement essentially corresponds to a known from the prior art pressure relief valve, which according to the invention is hydraulically in communication with the delivery chamber of the high-pressure pump of the fuel system.

A further embodiment of the pressure limiting valve according to the invention is characterized in that the pressure limiting valve has a spring holder, and that a spring is provided between the spring holder and the valve seat, which is supported at one end against the spring holder and the other end against the valve member, so that the pressure relief valve in different mounting positions in the High-pressure fuel pump can be integrated. In addition, the manufacture of the pressure relief valve is simplified.

A further supplement of the invention provides that the spring holder is connected to the valve seat, so that production, testing and calibration of the pressure relief valve outside the high-pressure fuel pump can be done. In addition, the performance of the high-pressure fuel pump is improved when the opening pressure of each pressure relief valve is measured and adjusted prior to assembly.

Alternatively, the spring holder can also be mounted in a bore of the housing, so that the number of components is reduced. In this case, the spring holder can be pressed into the bore and / or welded.

In order to prevent lateral deflection of the spring, the spring holder may have a support pin.

The production of the pressure relief valve will continue simplified if the valve seat is arranged in a seat sleeve and this seat sleeve in a bore of the housing z. B. by pressing and / or welding, is attached.

In a further feature of the invention, there is provided between the spring chamber and the outlet a sealing piston sealingly guided in the housing or the spring holder, and in that the separating piston rests on the valve member when there is a predetermined pressure difference between the outlet and the spring chamber. This means that the separating piston lifts off the valve member during the suction phase of the high pressure pump. As a result, pressure fluctuations in the delivery chamber are kept away from the valve member during the suction phase, which improves the control accuracy of the pressure relief valve.

In a particularly simple way, this effect can be further enhanced if between the separating piston and the valve member, a prestressed additional spring is present, which lifts the separating piston in the suction phase of the high-pressure fuel pump from the valve member.

The function of the pressure relief valve according to the invention can be further improved if a spring plate is provided between the spring and / or auxiliary spring and valve member. As a result, the dimensioning of the valve member and the springs can be decoupled from each other, which facilitates the design of the individual components. In addition, a buckling of the springs is prevented by the spring plate.

If the delivery level of the high-pressure pump to be optimized, the additional spring between separating piston and housing can be arranged so that the additional spring always brings the separating piston in abutment against the valve member.

The operation of the pressure relief valve according to the invention can be further improved when the spring chamber is in communication with a leakage line.

The present invention also relates to a fuel system for supplying fuel for an internal combustion engine, with a reservoir, with a first fuel pump, which is connected on the input side to the reservoir, with a second fuel pump, which is connected on the input side via a fuel connection to the first fuel pump, and with a pressure limiting valve which limits the pressure in a fuel line on the output side of the second fuel pump.

In order to build such a fuel system as variable as possible, without incurring additional costs, the invention proposes that the pressure relief valve is designed and connected in the manner described above.

It is proposed that the high-pressure pump comprises a 1-cylinder piston pump. In such a high pressure pump, the delivery pulsations are particularly pronounced, so that here the pressure relief valve according to the invention works very effectively.

In a particularly preferred embodiment of the fuel system according to the invention, the pressure relief valve is attached to the high-pressure pump, preferably integrated in this. Such an arrangement of the pressure relief valve within the fuel system has the advantage that a return line from the Pressure relief valve can be dispensed example, the low pressure region of the fuel system. As a result, the cost of the fuel system according to the invention are significantly reduced.

drawing

Figur 1:

eine Prinzipdarstellung eines Kraftstoffsystems mit einer Kraftstoffpumpe, an die ein Druckbegrenzungsventil angebaut ist;

Figur 2:

einen Schnitt durch einen Bereich der Hochdruckpumpe und ein erstes Ausführungsbeispiel eines Druckbegrenzungsventils von Figur 1;

Figur 3:

ein Diagramm, in dem der Druckverlauf im Förderraum und im Hochdruckbereich des Kraftstoffsystems über der Zeit dargestellt ist und

Figuren 4

bis 13: weitere Ausführungsbeispiele erfindungsgemäßer Druckbegrenzungsventile.

Hereinafter, an embodiment of the invention will be explained in detail with reference to the accompanying drawings. In the drawing show:

FIG. 1:

a schematic diagram of a fuel system with a fuel pump to which a pressure relief valve is attached;

FIG. 2:

a section through a portion of the high pressure pump and a first embodiment of a pressure relief valve of Figure 1;

FIG. 3:

a diagram in which the pressure curve in the delivery chamber and in the high pressure region of the fuel system over time is shown and

FIGS. 4

to 13: further embodiments of pressure relief valves according to the invention.

Description of the embodiments

In FIG. 1, a fuel system as a whole bears the reference numeral 10. It comprises a low-pressure region 12 and a high-pressure region 14.

The low-pressure region 12 comprises a reservoir 16 in which fuel 18 is stored. The fuel 18 is conveyed from the reservoir 16 by a first fuel pump 20. This is an electric fuel pump. The electric fuel pump 20 conveys into a low-pressure fuel line 22. In this, a filter 24 is initially provided after the electric fuel pump 20 as seen in the flow direction. Seen in the flow direction before the filter 24 branches off from the low-pressure fuel line 22 from a first branch line 26, which leads back to the reservoir 16. In the first branch line 26, a pressure limiting device 28 is arranged.

The low-pressure fuel line 22 leads to a high-pressure pump 30. This is driven in a manner not shown here by the camshaft of an internal combustion engine (not shown). The high-pressure pump 30 is a 1-piston high-pressure pump. Upstream of the high-pressure pump 30, a pressure damper 32 and a suction valve 34 are arranged in the low-pressure fuel line 22. Between the filter 24 and the pressure damper 32 branches off from the low-pressure fuel line 22 from a second branch line 36, in which a low-pressure regulator 38 is arranged. The second branch line 36 also leads to the reservoir 16. From the high-pressure pump 30, a leakage line 40 leads to the second branch line 36th

On the output side, the high-pressure pump 30 conveys into a high-pressure fuel line 42, which leads via a check valve 44 to a fuel manifold 46. Fuel injection valves 48 which in turn inject the fuel into a combustion chamber, not shown, of the internal combustion engine are in turn connected to the fuel manifold 46. The pressure in the Fuel rail 46 is detected by a pressure sensor 50.

To improve the performance of the high pressure section 14 of the fuel system 10, a throttle (not shown) may be provided in front of the fuel manifold 46 in the high pressure fuel line 42. The throttle avoids pressure oscillations and undesirable noise in the high-pressure region 14.

The pressure in the high pressure fuel line 42 and the fuel manifold 46, ie in the high pressure region 14 of the fuel system 10 is controlled in the embodiment of Figure 1 via a high pressure side flow control valve 52. This connects the region of the high pressure fuel line 42 between the check valve 44 and the fuel rail 46 to the region of the low pressure fuel line 22 between the suction valve 34 and the pressure damper 32. The connection is via a third branch line 54. The quantity control valve 52 is controlled by a control unit, not shown in Figure 1, which in turn receives signals from the pressure sensor 50. In this way, a closed loop for the regulation of the pressure in the high-pressure region 14 of the fuel system 10 is provided. In FIGS. 4 to 8, the pressure regulation in the high-pressure region is regulated by a quantity control valve arranged on the suction side.

In order to avoid an overpressure in the fuel collecting line 46 in the event of a failure of the quantity control valve 52, which could impair the functioning of the injection valves 48, a pressure limiting valve 56 is integrated in the high-pressure pump 30. The construction and the Function of the pressure relief valve 56 will be explained below with reference to Figures 2 and 4 to 8:

FIG. 2 shows a first exemplary embodiment of a pressure limiting valve 56 according to the invention, which is integrated in a housing 58 of the high-pressure pump 30. In the housing 58, a delivery chamber 60 is present, which is bounded on one side by a piston 62 of the high pressure pump 30. The piston 62 oscillates in a bore 64 of the housing 58. The drive of the piston 62 is not shown in Fig. 2. The oscillating movement of the piston 62 is indicated in Fig. 2 by a double arrow 66.

In the delivery chamber 60, the low-pressure fuel line 22 opens with a suction valve 34. From the delivery chamber 60 also goes from the third branch line 54, in which the quantity control valve 52 is arranged. Furthermore, the high-pressure fuel line 42 branches off from the delivery chamber 60 with the check valve 44.

As seen in the direction of flow behind the check valve 44, a fourth branch line 70, which connects the high-pressure fuel line 42 with the delivery chamber 60, leaves. The fourth branch 70 consists of sections 70a and 70b.

The pressure relief valve 56 is formed in the embodiment shown in Figure 2 as a ball valve. However, other forms of poppet valves and also slide valves can be used according to the invention.

In the housing 58, a valve seat 72 is worked out, which cooperates with a designed as a ball valve member 74 in a conventional manner. A spring 76, which at one end is supported against the housing 58 and the other end is supported against the valve member 74, determined by its bias the opening pressure of the pressure relief valve 56. The spring 76 is housed in a spring chamber 78 of the housing 58.

The fact that the spring chamber 78 and thus also the back of the valve member 74 are acted upon by the pressure prevailing in the delivery chamber 60, the valve member 74 does not lift off the valve seat 72 during the delivery stroke of the high-pressure fuel pump 30 when in the delivery chamber 60 or the fuel high pressure line 42 pressure pulsations occur. Namely, during the delivery stroke, the check valve 44 is opened, so that the pressure in the high-pressure fuel line 42, the fourth branch 70, the spring chamber 78 and the delivery chamber 60 is the same and thus cancel the hydraulic forces acting on the valve member 74.

Only during the suction stroke, namely, when the pressure in the delivery chamber 60 decreases and the check valve 44 closes, a pressure difference between the portion 70a of the fourth branch 70 and the spring chamber 78 and consequently a resultant hydraulic force on the valve member 74. If this resulting hydraulic force the pressure exerted by the spring 76 on the valve member 74 overcomes closing force, opens the pressure relief valve 56 and an impermissibly high pressure in the high-pressure fuel line 42 is degraded via the fourth branch line 70 in the delivery chamber 60.

As is apparent from the description of the first embodiment, the pressure relief valve 56 according to the invention is as simple as other known from the prior art pressure relief valves.

As a result of the interconnection according to the invention, the pressure limiting valve 56 according to the invention also remains closed during the occurrence of pressure pulsations during the delivery stroke of the high-pressure fuel pump 30. As a result, the pressure build-up in normal operation of the internal combustion engine takes place as desired. Only when during the suction stroke of the high-pressure pump 30, the pressure in the high-pressure fuel line 42 exceeds the opening pressure of the pressure relief valve 56, the pressure relief valve 56 opens, thus enabling a pressure reduction in the high pressure fuel line 42nd

In FIG. 3, the course of the pressure in the delivery chamber 60 and in the high-pressure fuel line 42 are applied downstream of the check valve 44 via the stroke of the piston 62 of the high-pressure pump 30.

A first line 80 shows the path of the piston 62 in the bore 64. The movement from bottom dead center (UT) to top dead center (TDC) is referred to as a delivery stroke and is indicated by double arrow 82 in FIG.

The path of the piston from TDC to TDC is referred to as suction stroke 84.

A second solid line 86 shows the pressure in the delivery chamber 60. FIG. 3 clearly shows that a so-called pressure pulsation 85 occurs during the delivery stroke. That is, it forms a pressure peak with a maximum value of P _max . which is significantly above an opening pressure P _{DBV of} the pressure limiting valve 56.

In Figure 3, a dashed third line 88 is entered, which the pressure in the high-pressure fuel line 42 behind the check valve 44 and in section 70a of the fourth branch 70. It can be clearly seen in FIG. 3 that the line 88, that is to say the pressure in the high-pressure fuel line 42, follows the pressure in the delivery chamber 60 (second line 86) during the delivery stroke 82, even if the pressure is the opening pressure P _{DBV of} the pressure-limiting valve 56 exceeds. Only when during the suction stroke 84, the pressure in the delivery chamber 60 drops sharply (see the second solid line 86), a pressure difference between the pressure in the high-pressure fuel line 42 and the delivery chamber 60 can form. In the operating state of the fuel system shown in Figure 3, the pressure in the high-pressure fuel line 42 during the intake stroke remains equal to the opening pressure P _{DBV of} the pressure relief valve 56, while the pressure in the delivery chamber 60, however, drops sharply. In other words, the pressure limiting valve 56 prevents the occurrence of impermissibly high pressures during the suction stroke in that the amount of fuel delivered into the fuel manifold 46 during the delivery stroke is released back into the delivery chamber 60 during the intake stroke.

In the illustrated in Figure 4 second embodiment of a pressure relief valve 56 according to the invention this is a preassembled unit consisting of a seat sleeve 102 with a seat 72 and a bore 104 and a spring holder 106 and a spring 76 and a valve member 74. In the lower part of Figure 4 Such a preassembled pressure relief valve 56 is shown enlarged outside of a high-pressure fuel pump, while it is integrated in the upper part of Figure 4 in the housing 58 of a high-pressure fuel pump.

As from the detailed representation of the pressure relief valve 56 can be seen in Figure 4, the spring holder 106 with the seat sleeve 102 by crimping and welding (see the weld 109) firmly connected. The spring 76 is supported at one end against the spring holder 106 and the other end against the valve member 74. If the seat sleeve 102 and the spring holder 106 are connected to each other, the opening pressure of the pressure limiting valve 56 can still be adjusted by the spring holder 76 is still slightly compressed in the direction of its longitudinal axis. As a result, the biasing force exerted by the spring 76 on the valve member 74 and, consequently, the opening pressure of the pressure relief valve increases. This pressure limiting valve 56 according to the invention can thus be mounted and adjusted completely outside the high-pressure fuel pump 30. This results in advantages in terms of manufacturing costs. In addition, the scattering of the operating behavior of various pressure relief valves 56 according to the invention in a series production is significantly reduced.

In the upper part of Figure 4, the pressure relief valve 56 is pressed into the housing 58 of a high pressure pump 30 with the seat sleeve 102 or attached in some other way. In this case, the pressure limiting valve 56 protrudes into the delivery chamber 60. The piston 62 has a cylindrical recess 108 into which the pressure limiting valve 56 is immersed when the piston 62 approaches its top dead center. This arrangement is particularly space-saving and at the same time the dead volume of the delivery chamber is very low. This increases the hydraulic efficiency of the high-pressure pump 30. Via the fourth branch line 70, the control side of the pressure-limiting valve 56, bypassing the check valve 44, is acted upon by the rail pressure prevailing in the high-pressure line 42 or the fuel manifold 46. In the sectional view of the high-pressure pump 30 shown in FIG. 4, the quantity control valve 52 is not visible. Likewise, in this illustration, the hydraulic connection between the low-pressure fuel line 22 and the delivery chamber 60 with the suction valve 34 connected therebetween is not visible. In Figure 4, the hydraulic connection between the pressure damper 32 and the low pressure fuel line 22 through a connecting hole 110, which is designed as a stepped bore, can be clearly seen.

FIG. 5 shows a further exemplary embodiment of a pressure limiting valve 56 according to the invention. In Figure 5, the housing 58 is shown perpendicular to the longitudinal axis of the piston 62 in a view from above. That is, one looks at the piston head of the piston 62. In this embodiment, the high-pressure fuel line 42, the low-pressure fuel line 22 and the fourth branch line 70, which is composed of the sections 70b and 70a, discharge into the delivery space 60. The rate control in this case is as described below by direct actuation of the suction valve 34:

The portion 70a of the fourth branch 70 is designed as a stepped bore. In this stepped bore, the seat sleeve 102 is pressed so that it is fixed to a shoulder of the stepped bore in the axial direction. The spring holder 106 is also pressed into the stepped bore and is then, when the arranged between the spring holder 106 and valve member 74 spring 76 has a sufficient bias, welded in this position. The weld is provided in Figure 5 by the reference numeral 109. In this embodiment of a pressure relief valve 56 according to the invention no direct connection between seat sleeve 102 and spring holder 106. So that the spring 76 can not escape laterally, a support pin 112 is provided on the spring holder 106. The third branch line 54 and the section 70b of the fourth branch line 70 lie on a common axis, so that these holes can be produced in one clamping and no additional sealing point is produced to the outside.

In this embodiment, the suction valve 34 is designed as a plate valve with a valve plate 111. The valve plate 111 is pressed by a spring 76 against a valve seat 115 of the suction valve 34. During the suction stroke of the high-pressure pump 30, the valve plate 111 lifts off from the valve seat 115 and fuel can flow out of the low-pressure fuel line 22 into the delivery chamber 60. The quantity control valve 52 is arranged on the suction side in this and the embodiments described below and lifts, if it is controlled accordingly, during the delivery stroke 82, the valve plate 111 by means of a plunger 113 from the valve seat 72. When the valve plate 111 does not rest on the valve seat 72, the suction valve 34 is opened. As a result, there is no pressure buildup in the delivery chamber 60 and no promotion of fuel in the high pressure fuel line 42, as long as the suction valve 34 is open. In this way, the regulation of the pressure in the fuel collecting line 46 can also be carried out by a quantity control valve 52 arranged on the intake side.

FIG. 6 shows a further exemplary embodiment of a pressure limiting valve according to the invention. The structural design of this pressure relief valve 6 substantially corresponds to the pressure relief valve 56 shown in Figure 5. However, the Installation situation in the embodiment of Figure 6 slightly different. In this embodiment, the low pressure fuel line 22, the suction valve 34, and the quantity control valve 52 are not shown.

The pressure limiting valve 56 according to the invention is arranged in a stepped bore 114 of the housing 58. The stepped bore 114 is arranged perpendicular to the high-pressure fuel line 42, which opens into the delivery chamber. The stepped bore 114, in turn, opens into the fourth branch line 70. In a similar manner to the exemplary embodiment according to FIG. 5, the seat sleeve 102 and the spring holder 106 are pressed into the stepped bore 114. The spring holder 106 is, as soon as it has reached the correct position, firmly connected to the housing 58 by a weld 109.

FIG. 7 shows a further exemplary embodiment of a pressure limiting valve 56 according to the invention. The same components are provided with the same reference numerals, and it applies that concerning the figures 2 and 3 said accordingly. Figure 7 shows a cross section through the housing 58 at the level of the delivery chamber 60. In this illustration, the piston 62, which is guided in the bore 64, visible. Perpendicular to branch off in the non-visible delivery chamber 60, the high-pressure fuel line 42 with the check valve 44 and the third branch line 54 with the quantity control valve 52, not shown. The low pressure fuel line 22 is not visible in this illustration. In the arrangement shown in Figure 7 a very compact design is possible, since the pressure relief valve (56) according to the invention at the same height as the delivery chamber (60) (not shown) is arranged.

In contrast, for example, to the first Embodiment of Figure 2 is provided between the delivery chamber 60 and the valve member 74 in the housing 58 sealingly guided separating piston 90. The separating piston 90 comprises a plunger 92, which protrudes into the spring chamber 78. Between the separating piston 90 and a spring plate 94, which rests on the valve member 74, an additional spring 96 is tensioned. The additional spring 96 causes the plunger 92 does not rest on the spring plate 94 when the same pressure prevails on both sides of the separating piston 90, that is, in the spring chamber 78 and in the portion 70b of the fourth branch 70 and the delivery chamber 60. Only when a pressure difference between the delivery chamber 60 and the spring chamber 78 prevails, the separating piston 90 is moved in the direction of the spring plate 94 and presses over the spring plate 94, the valve member 74 in its seat 72. By the arrangement of the separating piston 90, the dead volume in the delivery chamber 60 is reduced and thereby improves the volumetric efficiency of the high-pressure pump 30.

The spring chamber 78 is connected in this embodiment with a non-pressurized leakage line 98 or with the low-pressure fuel line 22. This means that the separating piston 90 presses on the valve member 74 during the delivery stroke of the high-pressure pump 30 and thus prevents opening of the pressure-limiting valve 56 during the delivery stroke 82. During the suction stroke 84 of the high-pressure pump 30, the additional spring 96 pushes the separating piston 90 in FIG. 7 to the left, so that it lifts off from the spring plate 94. As a result, a decoupling of the separating piston 90 and the valve member 74 is made so that during the suction stroke slight pressure fluctuations in the delivery chamber 60 of the high-pressure pump can not adversely affect the control behavior of the pressure relief valve 56.

By choosing the diameter of the separating piston 90 and the valve seat 72, a hydraulic reinforcement of the hydraulic force exerted by the separating piston 90 on the valve member 74 during the delivery stroke can also be achieved.

If the degree of delivery of the high-pressure pump 30 is to be maximized, the auxiliary spring 96 can also be arranged in the portion 70b of the fourth branch line 70 (see the arrow 100), so that it is supported on the one hand against the housing 58 and on the other hand against the separating piston 90 and this permanently in contact with the spring plate 94 holds. By this measure, the pressure build-up in the delivery chamber 60 and thus also in the high-pressure fuel line 42 during the delivery stroke of the high-pressure pump 30 is accelerated.

The embodiment of Figure 8 also shows a pressure relief valve 56 with separating piston 90. This pressure relief valve 56, as the embodiment of Figure 4, completely outside the high-pressure pump 30 are made and adjusted because between the seat sleeve 102 and spring holder 106, a sleeve 116 with at least one transverse bore 118 is provided. The sleeve 116 is welded to the spring holder 106 and the seat sleeve 102 when the bias of the spring 76 is so large that a desired opening pressure of the pressure limiting valve 56 has been reached. Of course, the sleeve 116 may also be connected to the spring holder 106 and / or the seat sleeve 102 by means other than a weld 109.

The preassembled and adjusted pressure relief valve 56 is press-fitted into the stepped bore portion 70a of the fourth branch and sealed to atmosphere through a plug 120 welded to the housing 58. In the stopper 120 grooves 122 are milled on the end face facing the pressure relief valve 56, which allows a hydraulic connection between the portion 70 b of the fourth branch line, which opens into the delivery chamber (not shown), and the separating piston 90. The diameter of the separating piston 90 is dimensioned such that the pressure limiting valve 56 does not open when pressure surges or pressure peaks in the delivery chamber (not shown in FIG. 8) occur during the delivery stroke of the high-pressure pump 30.

The low-pressure fuel line 22, not shown, goes upwards in this embodiment and opens into the pressure damper 32 (not shown, see FIG. 4).

The pressure relief valve according to the invention has the following main functions:

In normal operation, the system pressure of the fuel injection system is limited in overrun of the engine when the pressure in the fuel rail 46 increases due to the heating of the fuel by the engine heat.

In emergency operation, for example, if the quantity control valve 52 jams and in such a position that the high-pressure fuel pump 30 always delivers the full flow, the system pressure of the fuel injection system is also limited.

In the embodiment according to FIG. 2, in the overrun mode with the quantity control valve fully open (emergency operation), the maximum amount of fuel delivered by the high-pressure pump 30 can be discharged into the delivery chamber 60 again. A pressure increase, which by the Heating of the fuel is caused in the fuel rail 46 can not be compensated. It is therefore proposed to inject in this case via the injection valves 48 as much fuel into the combustion chambers (not shown) that an impermissible pressure increase in the high pressure region of the fuel system 10 is prevented.

In the pressure relief valves 56 according to FIGS. 7 and 8, it is possible to dissipate the entire amount of fuel both in normal operation and in emergency operation and thus to realize the pressure build-up under all circumstances and without additional intervention of the control unit of the engine control. However, it may be useful to reduce the maximum engine speed in emergency mode to have enough time for the pressure reduction in the fuel rail 46 during the suction phase of the high-pressure pump 30.

FIG. 9 shows a sectional view of a further exemplary embodiment of a pressure limiting valve 56 according to the invention. The exemplary embodiment according to FIG. 9 has parallels to the exemplary embodiment according to FIG. 2, so that only the further developments according to the invention will be described and otherwise reference is made to what has been said above regarding FIG. In the embodiment according to FIG. 9, a cylindrical guide section 124 adjoins the valve seat 72, which guides the valve member 74 in the axial direction as soon as it has lifted away from the valve seat 72. The diameter of the guide portion 124 and the diameter of the valve member 74 designed as a ball are matched to one another such that an annular throttle gap 126 is formed between valve member 74 and guide portion 124. The operation of this embodiment of an inventive Pressure relief valve is as follows:

When the pressure in the delivery chamber 60 is reduced in the emergency operation after completion of the delivery stroke, the pressure limiting valve 56 opens at the opening pressure resulting from the prestressing force of the spring 76 and the hydraulic force acting on the valve member 64. The amount of fuel flowing into the spring chamber 78 at the beginning of the opening of the pressure-limiting valve 56 from the section 70a of the fourth branch line is throttled in the throttle gap 126 and the entire projected area of the valve member 74 is subjected to the dynamic pressure. This leads to a very rapid opening movement of the valve member 74 and a sudden increase in the flow cross-section as soon as the valve member 74 has left the guide portion 124 in the direction of the spring chamber 78, because the guide portion 124 widens to the spring chamber 78 with a much larger diameter. Due to this rapid response of the pressure limiting valve 56, a large amount of fuel from the high-pressure region 14 can flow back into the delivery chamber 60 in a short time. Through the dimensioning of the throttle gap 126 and the length of the guide portion 124, the response of the pressure relief valve 26 can be optimized and adapted to a particular application. When dimensioning the throttle gap 126, however, it should be noted that when the pressure limiting valve 56 responds in normal operation due to a pressure increase due to heating of the fuel in the throttle gap 126 no throttling occurs, otherwise the pressure in the fuel manifold 46 correspondingly lowered according to the pressure level in the pressure relief valve 56 would become. Since, however, in this case are very small overflow rates, the throttle gap 126 can be designed so that the function described above is realized.

 In the embodiment according to FIG. 10, not the valve member 74 but the spring plate 94 is guided in a guide section 124 of the housing 58. As a result, the throttle gap 126 is formed between the guide portion 124 and the spring plate 94. In this way, the area acted upon by the back pressure can be selected independently of the diameter of the valve member. This results in a further degree of freedom in the optimization of the dynamic behavior of the pressure limiting valve 56. This constructive action solves the problem, which is that at high speeds (in case of failure with clamping quantity control valve 52) the time during the suction phase of the high pressure pump 30 is not is more sufficient to completely dissipate the previously funded in the high-pressure region 14 fuel amount in the delivery chamber 60 again. Especially in overrun operation of the internal combustion engine then a certain amount of fuel would still be sucked in via the suction valve 34 and as a result of which the pressure in the fuel manifold 46 to rise inadmissible.

In particular, by the embodiments of Figures 9 and 10 can be ensured that there is no unacceptable increase in pressure in the fuel manifold 46, even if the quantity control valve 52 jams and / or the controller operates incorrectly, since the pressure relief valves 56 has a sufficiently large backflow of Allow fuel from the high pressure region 14 in the delivery chamber 60 during the intake stroke of the high pressure pump 30.

A further embodiment of a pressure limiting valve 56 according to the invention will be explained with reference to FIGS. 11 and 12. This too Embodiment of a pressure relief valve 56 according to the invention is manufactured in cartridge construction. This results in the advantage that, similar to the embodiment shown in Figure 4, the pressure relief valve 56 mounted in the housing 58 of the high-pressure pump 30 before installation, tested and the opening pressure can be adjusted.

The pressure limiting valve according to FIG. 11 consists of a valve housing 128 which has a stepped central bore 130. At its outer diameter, the valve housing 128 has a first sealing bead 132, a second sealing bead 134 and a third sealing bead 136.

The central bore 130 is designed as a blind hole and closed in the position shown in Figure 11 of the pressure relief valve 56 on the right side. At the closed end of the central bore 130, the spring 76 is arranged. The spring 76 is guided on both sides by a respective guide sleeve 138 in the central bore 130. The spring force of the spring 76 is transmitted via the left in Figure 11 guide sleeve 138 and two pins 140 on the spring plate 94 and from there to the valve member 74.

Between the left in Figure 11 guide sleeve 138 and the spring plate 94, an intermediate piece 142 is pressed into the central bore 130. The intermediate piece 142 also serves, among other things, to guide the pins 140.

On the left in Figure 11 side of the valve housing 128 is a seat sleeve 102, in which the valve seat 72 is formed, pressed. The axial position of the seat sleeve 102 in the central bore 130 is defined by a paragraph of Center hole 130 and a shoulder in the seat sleeve 102 clearly defined. In the seat sleeve 102, a fuel strainer 144 is mounted, which keeps contaminants in the fuel from the sealing seat 72 and the valve member 74.

Hydraulically, the pressure relief valve 56 is integrated into the high-pressure pump 130 as follows. Via the section 70a of the fourth branch line, the left side of the valve member 74 is acted upon by the pressure of the fuel prevailing at the high-pressure region of the high-pressure pump 30. Via the section 70b of the fourth branch line, which continues in the valve housing 128 as far as the central bore 130, a radial bore 146 in the intermediate piece is acted upon by the pressure prevailing in the delivery chamber 60 of the high-pressure pump 30. In order to ensure a reliable hydraulic connection between the portion 70b of the fourth branch line and the radial bore 146 in the intermediate piece 142, the intermediate piece 142 has two sealing beads 148. Between these sealing beads 148 there is a circumferential groove which, together with the central bore 130 of the valve housing 128, forms a circumferential annular space. The portion 70b in the valve housing 128 is positioned so that it opens into this annulus. Also, the radial bore 146 is positioned so that it opens into the annulus, so that regardless of the angular position of the portion 70b and the radial bore 146 to each other, the hydraulic connection between the portion 70b and the radial bore 146 is always ensured. The radial bore 146 opens into a executed as a blind hole center bore 150 of the intermediate piece 142 in the separating piston 152 is slidably guided and sealing. The separating piston 152 is supported at one end on the spring plate 94. Thus, the separating piston 152 transmits a pressure proportional to the pressure in the delivery chamber 60 to the force Federteller 94 and thus causes the opening pressure of the pressure limiting valve 56 during the delivery stroke, namely, when the pressure in the delivery chamber is also high, is increased, so that the unwanted opening operations are suppressed during the delivery stroke.

When the pressure in the delivery chamber 60 drops during the suction stroke, no appreciable force is transmitted from the separating piston 152 to the spring plate 94, so that the opening pressure of the pressure limiting valve 56 is determined substantially only by the spring 76 in this period.

When the valve member 74 lifts from the sealing seat 72, fuel from the portion 70 a of the fourth branch 70, that is from the high pressure region 14 of the fuel system 10, via a transverse bore 154 in the valve housing 128 into the low pressure line 22 to flow. The transverse bore 154 is arranged between the first sealing bead 132 and the second sealing bead 134. The portion 70 b in the valve housing 128 is disposed between the second sealing bead 134 and the third sealing bead 136.

Between the third sealing bead 136 and a collar 156 of the valve housing 128, a circumferential groove 158 is provided so that fuel in a portion of the low-pressure line 22 in the housing 58 of the high-pressure pump 30 can flow around the valve housing 128 around and can flow to a pressure damper 32, not shown , The valve housing 128 is welded to the collar 58 at the collar 58. This is indicated in FIG. 11 by a stylized weld seam 160.

By the sealing beads 132, 134, 136 and 148 between the housing 58 and the valve housing 128 and between the Valve housing 128 and the intermediate piece 142 and the weld 160, seals are achieved by which no fuel diffusion takes place. In addition, this sealing compound does not age, as does, for example, an O-ring made of an elastomeric material.

FIG. 12 shows the pressure-limiting valve 56 according to FIG. 11 in a high-pressure pump 30. From this representation, the hydraulic connection of the pressure limiting valve 56 in the high-pressure pump 30 can be better recognized. Not all components of the pressure limiting valve 56 have been provided with reference numerals in FIG. 12 in order not to impair the clarity of FIG.

By a suitable choice of the diameter of the separating piston 152, the pressure of the spring plate 94 dependent on the pressure in the delivery chamber 60 can be adjusted to the valve member 64.

The opening pressure increase caused by the delivery chamber pressure of the pressure limiting valve 56 is matched to the flow resistance between the high pressure pump 30 and the fuel manifold 46 existing flow resistance that the pressure relief valve 56 does not open during the delivery stroke of the piston 62.

FIG. 13 shows a further exemplary embodiment of a pressure limiting valve 56 according to the invention. This exemplary embodiment has many embodiments parallel to the embodiment illustrated in FIGS. 11 and 12 and described with reference to these figures. Only the essential differences will be pointed out hereafter and otherwise referred to the previously described embodiments.

In the embodiment according to FIG. 13, the housing 58 of the pressure-limiting valve 56 is at the same time also the housing of the high-pressure pump 20; d. H. unlike in the embodiment according to FIGS. 11 and 12, the pressure limiting valve 56 in FIG. 13 is not designed as a cartridge. As a result, some components can be omitted. Nevertheless, the opening pressure of the pressure relief valve 56 can be adjusted during assembly thereof and thus the dispersion of the performance in series production can be minimized. These advantages are achieved in that the spring 76 is supported at one end against the spring plate 94 and the other end against the intermediate piece 142.

The spring plate 94 has at least one longitudinal groove 162 through which fuel, which flows from the section 70a into the pressure limiting valve 56 when the pressure limiting valve 56 is open, can be discharged into the negative pressure fuel line 22. The low-pressure fuel line 22 opens in the spring chamber 78 in this embodiment.

The intermediate piece is firmly pressed with the sealing beads 148 and liquid-tight in the center bore 130. Depending on how deep the intermediate piece is pressed into the central bore 130, a bias of the spring 76 and thus the opening pressure of the pressure relief valve 56 is set. After the setting of the opening pressure, the central bore 130 is closed by a cover 164. The lid 164 may be welded to the housing 58.

Between the sealing beads 148, the central bore 130 and the intermediate piece 142 an annular space is formed, which forms a hydraulic connection between the portion 70b of the fourth branch line and the radial bore 146 in the intermediate piece 142 ensures.

The exemplary embodiments according to FIGS. 7, 8, 11, 12, and 13 differ from the other exemplary embodiments in that the pressure reduction does not take place to the delivery chamber 60, but into the low-pressure fuel line 22.

All the features explained in the drawings, their description and the claims can be essential to the invention both individually and in conjunction with one another.

Claims (27)

1. Fuel system (10) for the delivery of fuel (18) for an internal combustion engine, with a storage tank (16), with a first fuel pump (20) which is connected on the inlet side to the storage tank (16), with a high-pressure pump (30) which is connected on the inlet side to the first fuel pump (20) via a fuel connection (22), with a high-pressure fuel line (42) which is arranged on the conveying side of the high-pressure pump (30) and has a non-return valve (44), and with a pressure-limiting valve (56) which limits the pressure in a fuel line (42, 46) on the outlet side of the high-pressure pump (30), a pressure side of the pressure-limiting valve (56) being acted upon by the pressure prevailing in a high-pressure region (14) of the fuel system (10), characterized in that downstream of the non-return valve (44), as seen in the direction of flow, a fourth branch line (70) branches off, which connects the high-pressure fuel line (42) to the conveying space (60), and in that an outlet of the pressure-limiting valve (56) is connected hydraulically to a conveying space (60) of the high-pressure pump (30) via a portion (70b) of the fourth branch line (70).
2. Fuel system according to Claim 1, characterized in that the pressure-limiting valve (56) has a housing (58) with a valve seat (72) and with a spring chamber (78), in that, in the spring chamber (78), a spring (76) is provided, which is supported at one end against the housing (58) and at the other end against the valve member (74), and in that the spring chamber (78) is connected hydraulically to the outlet (70b). (Figure 2)
3. Fuel system according to one of the preceding claims, characterized in that the pressure-limiting valve (56) has a spring holder (106), and in that, between the spring holder (106) and valve seat (72), a spring (76) is provided, which is supported at one end against the spring holder (106) and at the other end against the valve member (74). (Figure 4)
4. Fuel system according to Claim 3, characterized in that the spring holder (106) is connected to the valve seat (72). (Figures 4 and 8)
5. Fuel system according to Claim 3, characterized in that the spring holder (106) is fastened in a bore (70a, 114) of the housing (58, 128). (Figure 8)
6. Fuel system according to Claim 5, characterized in that the spring holder (106) is pressed and/or welded in the bore (70a, 114). (Figures 5 and 6)
7. Fuel system according to one of Claims 3 to 6, characterized in that the spring holder (106) has a supporting arbour (112). (Figures 5 and 6)
8. Fuel system according to one of Claims 2 to 7, characterized in that the valve seat (72) is arranged in a seat sleeve (102), and in that the seat sleeve (102) is fastened in a bore (70a, 114) of the housing (58, 128). (Figures 5, 6, 11, 12 and 13)
9. Fuel system according to Claim 8, characterized in that the seat sleeve (102) is pressed and/or welded in the bore (70a, 114). (Figures 5, 6, 11 and 13)
10. Fuel system according to one of Claims 2 to 9, characterized in that the valve seat (72) has adjoining it a guide portion (124), and in that a throttle gap (126) is formed between the guide portion (124) and the valve member (74). (Figure 9)
11. Fuel system according to one of Claims 2 to 10, characterized in that the valve seat (72) has adjoining it a guide portion (124), and in that a throttle gap (126) is formed between the guide portion (124) and the spring plate (94). (Figure 10)
12. Fuel system according to one of Claims 2 to 11, characterized in that, between the spring chamber (78) and outlet (70b), a sealingly guided separating piston (90) is provided, and in that the separating piston (90, 152) lies at least indirectly on the valve member (74) when a predetermined pressure difference prevails between the outlet (70b) and spring chamber (78). (Figures 7, 8, 11, 12 and 13)
13. Fuel system according to Claim 12, characterized in that the separating piston (90) is guided sealingly in the housing (58, 128). (Figure 7)
14. Fuel system according to Claim 13, characterized in that the separating piston (90) is guided sealingly in the spring holder (106). (Figure 8)
15. Fuel system according to one of Claims 12 to 14, characterized in that a prestressed additional spring (96) is provided between the separating piston (90) and valve member (74).
16. Fuel system according to one of Claims 2 to 15, characterized in that a spring plate (94) is provided between the spring (76) and/or additional spring (96) and valve member (74).
17. Fuel system according to either one of Claims 15 and 16, characterized in that the additional spring (96) lifts off the separating piston (90) from the valve member (74) in the suction phase.
18. Fuel system according to Claim 17, characterized in that the additional spring (96) holds the separating piston (90) in bearing contact against the valve member (74).
19. Fuel system according to one of Claims 12 to 18, characterized in that the separating piston (152) is connected hydraulically to the conveying space (60). (Figure 8)
20. Fuel system according to one of Claims 12 to 19, characterized in that, in the spring chamber (78), an intermediate piece (142) with a radial bore (146) and with a centre bore (150) is provided, in that the separating piston (152) is guided sealingly in the centre bore (150), in that the radial bore (146) and the centre bore (150) are connected hydraulically, in that the radial bore (146) is connected hydraulically to the conveying space (60) via the portion (70b) of the fourth branch line (70), and in that the outlet side of the pressure-limiting valve (56) is connected hydraulically to the low-pressure fuel line (22). (Figures 11, 12 and 13)
21. Fuel system according to Claim 20, characterized in that at least one pin (140) is guided in the intermediate piece (142), and in that the at least one pin (140) transmits the force of the spring (76) to the spring plate (4). (Figure 11)
22. Fuel system according to one of Claims 2 to 21, characterized in that the spring chamber (78) is connected to a leakage line (98).
23. Fuel system according to one of Claims 2 to 22, characterized in that the housing (128) has a plurality of peripheral sealing beads (132, 134, 136). (Figures 11, 12 and 13)
24. Fuel system according to one of Claims 1 to 23, characterized in that the housing (128) is welded to the high-pressure pump (30). (Figure 12)
25. Fuel system (10) according to Claim 24, characterized in that the high-pressure pump (30) comprises a single-cylinder piston pump.
26. Fuel system (10) according to one of the preceding claims, characterized in that the pressure-limiting valve (56) is mounted onto the high-pressure pump (30), preferably integrated into the latter.
27. Fuel system according to Claim 1, characterized in that the pressure-limiting valve (56) is designed as a slide valve.

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