EP1251266B1 - Pressure limiting device and fuel system with such a pressure limiting device - Google Patents

Description

State of the art

The present invention initially relates to a Pressure limiting device for a fuel system Internal combustion engine according to the preamble of claim 1 and a fuel system according to the preamble of claim 5 with a pressure limiting device.

Such a pressure limiting device is from the market known. It is preferably in such fuel systems used in internal combustion engines with gasoline direct injection be used. such Fuel systems usually have one Low pressure area and a high pressure area. A electric fuel pump promotes the fuel in the Low pressure range from which the fuel over a High-pressure pump in a fuel rail ("rail") called) is promoted. The pressure in the fuel rail is usually by a pressure control or a quantity control valve regulated.

However, a hedge against excessive pressure in the To create fuel manifold is in the High pressure area of the fuel system a Pressure limiting device provided. In this is it is generally a common one Pressure relief valve with one of a spring against a valve seat acted upon valve element. exceeds the pressure in the fuel rail a certain Limit value, lifts the valve element from the valve seat, so that fuel from the inlet of the pressure relief valve to Outlet and from there back to the low pressure area of the Fuel system can flow.

The known pressure limiting device is already working very good and above all very reliable. However, they are the possible arrangements of the pressure relief valve Limits set:

In general, the facility must be in the area of Fuel bus, so at a certain distance from the high pressure pump. The reason for this is that the high pressure pump in operation pressure pulsations produced, whose tips the opening pressure of Pressure relief valve can exceed. Would that be Pressure relief valve immediately at the high pressure pump there would be a risk that the Pressure relief valve due to the pressure pulsations opens, although the maximum system pressure has not yet reached is. Only at a certain distance from the High pressure pump, it comes to a smoothing of 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 do that Pressure relief valve designed to be that Opening pressure above due to the pressure pulsations existing pressure peaks is. In emergency mode, if So the pressure control of the fuel rail no longer works properly and then a higher pressure in the Fuel manifold as the normal system pressure prevails, Nevertheless, a safe operation of the internal combustion engine be assured. This in turn would reduce the interpretation of Components of the high pressure area of the fuel system for require correspondingly high pressures. Such components are but relatively expensive.

From DE 39 12 106 A1 is also a Fuel injection device according to the pump-nozzle principle known. It shows a pressure limiting device, which comprises a cylindrical valve pin, the partially received in a housing-side bore and at its end projecting into the bore a chamfer having. At an impermissible pressure increase deviates Valve pin out until the chamfer comes out of the hole. As a result, a fluid connection with a Low pressure area created.

In the known device is an evasive volume provided in which in a delivery pulsation of Fuel flow in and out of the fuel after the end the delivery pulsation can flow out again. A Pressure pulsation, so to speak, becomes a quantity pulsation "converted", so the pressure remains essentially constant.

However, it has turned out that it is also at the known pressure limiting device still undesirable Pressure pulsations can come.

From JP 09242639 A is a pressure relief valve with a Valve piston known which has a pressure stage. hereby ensures that when exceeding one Limit pressure in any case, the valve fully opens. One Evasion volume is not provided in this device.

The present invention therefore has the object, a Pressure limiting device of the type mentioned so to further develop that pressure pulsations as little as possible occur.

This object is in a pressure limiting device of by the type mentioned by the characterizing features of claim 1 solved. In a fuel system of the type mentioned is the task solved by the characterizing features of claim 5.

Advantages of the invention

According to the invention, a comparatively large hydraulic Effective equalization volume immediately after the withdrawal of the Sealing edge connected from the valve seat. This allows the effective damping even very hard pressure surges, which is through a steep gradient at low pressure difference distinguished. Furthermore, in this embodiment, the maximum possible evasion volumes by the maximum possible distance the control edge determined by the outlet opening. These Embodiment of the invention Pressure limiting device is also relatively inexpensive producible and can be more usual in the context of space requirements Pressure relief valves are realized.

Advantageous developments of the invention are in Subclaims specified.

In a first embodiment of the invention Pressure limiting device is proposed that the Pressure limiting device a hydraulic resistance, in particular, a flow restrictor, which, in the inlet is arranged to the escape volume. By such Flow restrictor prevents it in the escape volume too an overshoot comes. In the same direction also aims the antechamber provided in another development, which is present in the inlet to the evasive volume.

It is also possible that the inlet-side section of Piston has a rounded waisted area. By Such a design of the inlet-side section of Pistons can during operation of the pressure limiting device the Flow forces are largely compensated. So it is e.g. possible that virtually no increase in the opening pressure over the throughput takes place.

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 on the input side over a fuel connection with the first fuel pump is connected, and with a pressure limiting device, which the pressure in a fuel connection on the Output side of the second fuel pump limited.

To build such a fuel system as variable as possible can be without any additional costs According to the invention proposed that the Pressure limiting device in the manner described above is trained.

It is suggested that the second fuel pump includes a 1-cylinder piston pump. In such a Fuel pump are the delivery pulsations especially pronounced, so that here the inventive Pressure limiting device works very effectively.

In a particularly preferred embodiment of Fuel system according to the invention is the Pressure limiting device to the second fuel pump grown, preferably integrated into this. Such Arrangement of the pressure limiting device within the Fuel system has the advantage of being on a Return line from the pressure limiting device for example, to the low pressure region of the fuel system can be waived. This will be the cost of the Fuel system according to the invention significantly reduced.

drawing

Fig. 1:

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

Fig. 2:

einen Schnitt durch einen Bereich der Kraftstoffpumpe und der Druckbegrenzungseinrichtung von Fig. 1; und

Fig. 3:

ein Diagramm, in dem der Druck im Bereich des Auslasses der Kraftstoffpumpe von Fig. 1 über der Zeit dargestellt ist.

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 limiting device is attached;

Fig. 2:

a section through a portion of the fuel pump and the pressure limiting device of Fig. 1; and

3:

a diagram in which the pressure in the region of the outlet of the fuel pump of Fig. 1 over time is shown.

Description of the embodiment

In Fig. 1, a fuel system carries the whole Reference numeral 10. It includes a low-pressure region 12 and a high pressure area 14.

The low-pressure region 12 comprises a reservoir 16, is stored in the fuel 18. The fuel 18 is from the reservoir 16 of a first Fuel pump 20 promoted. This one is about an electric fuel pump. The electric Fuel pump 20 delivers into a low pressure fuel line 22. In this is after the electric Fuel pump 20 as seen in the flow direction first a filter 24 is provided. Seen in the flow direction yet before the filter 24 branches off the low-pressure fuel line 22 a branch line 26 from which, to the Reservoir 16 returns. In the branch line 26 is a pressure relief valve 28 is arranged.

The low-pressure fuel line 22 leads to a second Fuel pump 30. This will not be closer to here shown manner of the camshaft a Internal combustion engine (not shown) driven. In the second fuel pump 30 is a 1-piston high-pressure pump. Upstream of the high pressure pump 30 are still in the low pressure fuel line 22 a Pressure damper 32 and a check valve 34 is arranged. Between the filter 24 and the pressure damper 32 branches from the low-pressure fuel line 22 a branch line 36th from, in which a low pressure regulator 38 is arranged. The Branch line 36 also leads to the reservoir 16 for the fuel 18 back. From the high pressure pump 30 leads a leakage line 40 to the branch line 36th

On the output side promotes the high-pressure pump 30 in one Fuel line 42, which via a check valve 44th leads to a fuel manifold 46. To the Fuel manifold 46 are again fuel injectors 48 connected, which the fuel in a combustion chamber, not shown Inject internal combustion engine. The pressure in the Fuel manifold 46 is from a pressure sensor 50 detected.

The pressure in the fuel rail 42 and the fuel rail 46, ie in the high pressure region 14 of the Fuel system 10, via a quantity control valve 52nd controlled. This connects the between the Check valve 44 and the high-pressure pump 30 located Area of the fuel line 42 with the between the Check valve 34 and the pressure damper 32 located Low pressure fuel line area 22. The Connection takes place via a branch line 54. Das Quantity control valve 42 is not from a in Fig. 1 shown control unit, which in turn receives signals from the pressure sensor 50. In this way will be a closed loop for controlling the Pressure in the high pressure region 14 of the fuel system 10th created.

In case of failure of the quantity control valve 52 a To avoid overpressure in the fuel rail 46, which the functionality of the injectors 48th could interfere with the high pressure pump 30 Pressure relief valve 56 integrated. The exact structure of the Pressure relief valve 56 is shown in FIG. 2:

The high-pressure pump 30 and the pressure limiting valve 56 are housed in a common housing 58. Of the High-pressure pump 30 is in Fig. 2, only an area of one Delivery chamber 60 and the outlet side of the delivery chamber 60th arranged exhaust valve 44 visible. The exhaust valve 44 comprises a spherical valve element 64, which of a spring 66 is acted upon against a valve seat 68. Downstream of the exhaust valve 44 is the high pressure fuel line 42 visible. During a suction stroke will the delivery chamber 60 opposite the high-pressure fuel line 42 sealed by the outlet valve 44.

Seen in the direction of flow immediately behind the Exhaust valve 44 branches from the high pressure fuel line 42 a secondary line 70 from which to an antechamber 72nd leads. Between secondary line 70 and antechamber 72 is a Flow restrictor 74 is arranged.

In Fig. 2 above the antechamber 72 is a conical Extension 76 provided in a cylindrical Valve chamber 80 opens. Above the cylindrical Valve chamber 78 is coaxial with valve chamber 78 cylindrical recess 80 is present, which is a something smaller diameter than the valve chamber 78 has. The cylindrical recess 80 forms a guide for a also cylindrical piston 82. This is below described in detail.

Just above the transition from the cylindrical one Valve chamber 78 to the cylindrical guide 80 is in the Circumferential wall of the guide 80 has an annular groove 84. From this branches off a flow channel 86, the in Fig. 2 invisible way to the low pressure inlet side the high-pressure pump 30 leads. Above the cylindrical Guide 80 is a cylindrical to the guide 80 coaxial Recess 88 present, which has a smaller diameter as the guide 80 has. From the recess 88 leads a leakage channel 90 to the flow channel 86th

The elements from the secondary line 70 to the leakage channel 90 are part of the pressure relief valve 56. The piston 82nd the pressure limiting valve 56 is as follows built up:

It essentially has two sections, namely a - with respect to the pressure relief valve 56 - inlet-side section 92 and a - also on the Pressure relief valve 56 related - outlet side Section 94. The outlet side section 94 has a circular cylindrical outer contour with constant Diameter. In Fig. 2 is from above into the piston 82 a Blind hole 96 introduced. In this is a spring 98 guided, which on the one hand on the piston 82 and on the other hand, at the bottom of the upper recess 88 in the housing 58 supported. By this spring 98 is a free edge 100th 2 inlet-side portion 92 of the piston 82nd pressed against the conical extension 76. The conical Extension 76 thus forms a valve seat so far.

Towards the outlet-side section 94, the inlet side portion 92 of the piston 82 a Constriction 102 in the form of a rounded waisted Area on. This way, between the inlet side section 92 and the outlet side Section 94 a control edge 104 is formed, which the two sections 92 and 94 separated from each other. The Control edge 104 is from the free edge 100 of the inlet side Section 92 spaced so that when the free Edge 100 abuts the valve seat 76, the control edge 104 of the annular groove 84 is spaced.

The fuel system 10 with the pressure limiting valve 56 works as follows:

From the electric fuel pump 20, the fuel 18 from the reservoir 16 in the low-pressure fuel line 22 promoted. The pressure in the Low pressure fuel line 22 is typically about 4 bar. The fuel under this pressure continues in the high pressure pump 30 to a system pressure compressed by about 120 bar.

If on the outlet side of the high-pressure pump 30, ie for example, in the high pressure fuel line 42 and the fuel rail 46, a constant volume would prevail in the high pressure area 14 of the Fuel system 10 due to the delivery pulsations of High pressure pump 30 pressure peaks up to a peak of about 180 bar occur. Such a pressure peak is shown in FIG. 3 shown in dashed lines. These pressure peaks result from the acceleration of the fuel column in the High-pressure fuel line 42 through the high-pressure pump 30th These pressure peaks are in the illustrated in Fig. 2 Pressure relief valve 56 in the following manner avoided:

Basically, the pressure peak corresponds to one through the Delivery pulse of the high pressure pump 30 triggered flow rate. This flow rate flows into the secondary line 70 through which Flow restrictor 74 through the antechamber 72. There the flow rate causes the free edge 100 of the inlet side portion 92 of the piston 82 from the valve seat 78 lifts off and the entire piston 82 against the Beaufschlagungskraft of the spring 98 is moved. this leads to to an enlargement of the cylindrical valve chamber 78th The enlargement of the valve chamber 78 in turn corresponds an escape volume into which the fuel flows can.

After the end of the delivery pulse, the fuel flows out the cylindrical valve chamber 78 back into the high pressure fuel line 42 back. The piston moves 82 due to the spring action again with his free edge 100 against the valve seat 76. The distance between the control edge 104 and the annular groove 84 is thereby so dimensioned that with a usual pressure peak no Fuel via the annular groove 84 and the flow channel 86th flows. The maximum possible evasive volume corresponds thus the diameter of the outlet side portion 94 of Piston 82 multiplied by the maximum distance between the annular groove 84 and the control edge 104th

Through the antechamber 72 and the flow restrictor 74 is a prevents dynamic overshoot of the piston 82. Consequently is guaranteed even with very hard promotional impulses that the pressure relief valve 56 does not open, so no Fuel flows through the flow channel 86. falls However, for example, due to a disturbance of Mengensteuerventils 52 the pressure control in High-pressure region 14 of the fuel system 10 and is more fuel from the high pressure pump 30 into the high pressure fuel line 42 and the fuel rail 46 promoted as by the fuel injection valves 48 in the combustion chamber of the internal combustion engine is injected, then the total system pressure increases High pressure area 14 of the fuel system 10. Exceeds the actual system pressure is the maximum allowed System pressure, then the piston 82 against the Fed by the spring 98 so far moved until the Control edge 104 is above the annular groove 84.

Thus, the fuel from the secondary line 70 via the Flow channel 86 to the inlet side of the high-pressure pump 30th flow back. This will ensure that the System pressure total the allowable value, here for example, 120 bar, does not exceed. Thus, too in case of failure, for example, the quantity control valve 52 the safe operation of the fuel injection valves 48 guaranteed. By training the intake side Section 92 of the piston 82 with a constriction 102 is Ensures that flow forces are largely in operation be compensated. Thus, there is practically no increase in Opening pressure above the flow rate. Such a Rise would otherwise be limited during operation of the fuel system 10 or the Internal combustion engine lead when the quantity control valve 52 failed.

Claims (7)

1. Pressure-limiting device (56) for a fuel system (10) of an internal combustion engine, having a housing (58) which has an inlet (70) and an outlet (86), and having a prestressed element (82) which fluidically connects the inlet (70) to the outlet (86) starting from a specific pressure difference between the inlet (70) and outlet (86), the prestressed element being embodied as a cylindrical piston (82) which has an outlet-end section (94) and an inlet-end section (92) which are separated from one another by a control edge (104), characterized in that the outlet-end section (94) is guided in a sealed fashion in the housing (58), and in the closed state of the pressure-limiting device (56) said outlet-end section (94) covers an outlet opening (84) in the wall (80) of the housing, a free edge (100) of the inlet-end section (92) forming a sealing edge with a valve seat (76) on the housing, in such a way that a pressure pulsation is converted into a quantity pulsation and the pressure thus remains essentially constant by virtue of the fact that a bypass volume is made available in the pressure-limiting device (56) upstream of the prestressed element (82), viewed in the direction of flow, by movement of the prestressed element (82).
2. Pressure-limiting device (56) according to Claim 1, characterized in that it has a hydraulic resistor, in particular a flow restrictor (74) which is arranged in the inflow (70) to the bypass volume.
3. Pressure-limiting device (56) according to one of Claims 1 or 2, characterized in that it has an antechamber (72) which is provided in the inflow (70) to the bypass volume.
4. Pressure-limiting device (56) according to one of the preceding claims, characterized in that the inlet-end section (92) of the piston (82) has a region (102) which is shaped in a rounded fashion.
5. Fuel system (10) for supplying fuel (18) for an internal combustion engine, having a reservoir vessel (16), having a first fuel pump (20) which is connected at the input end to the reservoir vessel (16), having a second fuel pump (30) which is connected at the input end to the first fuel pump (20) via a fuel connection (22), and having a pressure-limiting device (56) which limits the pressure in a fuel connection (42, 46) at the output end of the second fuel pump (30), characterized in that the pressure-limiting device (56) is embodied according to one of Claims 1 to 4.
6. Fuel system (10) according to Claim 5, characterized in that the second fuel pump comprises a single cylinder piston pump (30).
7. Fuel system (10) according to one of Claims 5 or 6, characterized in that the pressure-limiting device (56) is attached to the second fuel pump (30), preferably integrated into it.

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