EP1394403B1 - Fuel system for an internal combustion engine - Google Patents

Description

State of the art

The invention relates to a fuel system for an internal combustion engine having a low-pressure region, a high-pressure fuel pump, and a high-pressure region, wherein the high-pressure fuel pump comprises: a housing, at least one movable conveyor element which delimits a delivery chamber, at least one drive which can set the delivery element in motion , a drive space in which the drive is at least partially disposed, and a lubricant supply device for supplying movable parts with fuel as a lubricant.

Such a fuel system is known from DE 197 05 205 A1. In this a radial piston pump is shown, the fuel is supplied from an electric feed pump with a certain form. The radial piston pump compresses the fuel to a very high level. The pistons of the radial piston pump are acted upon by a compression spring by means of sliding shoes against a lifting ring, which is placed on a rotating eccentric shaft. Over a Hole in the piston and in the shoe, the delivery chamber of a cylinder is connected to a discharge space, which is arranged between the shoe and the corresponding contact surface of the cam ring. In this way, the discharge space is pressurized in a delivery stroke of the piston and thereby reduces the bearing force of the shoe on the contact surface of the cam ring.

In the known piston pump eccentric shaft, cam ring, shoe, etc., are arranged in a drive space, which is connected to the low-pressure region and is present in the pressurized fuel under pressure. From this drive space, the fuel passes through an inlet valve into the delivery chamber of a respective cylinder. Due to the fuel present in the drive space, the moving parts located there are lubricated and cooled.

DE 197 39 653 A1 shows a system for high-pressure fuel production with a low-pressure pump and a high-pressure pump. The high-pressure pump has a flow-through pump housing. Between the low-pressure pump and the high-pressure pump, the pumped by the low-pressure pump fuel flow divides. Part of the fuel flow is passed through the pump inner casing via a flow control valve. This should be achieved under all operating conditions sufficient flow through the housing of the high-pressure pump.

Object of the present invention is to develop a fuel system of the type mentioned so that the lubrication and cooling of the moving parts is ensured in the drive compartment under all operating conditions.

This object is achieved in a fuel system of the type mentioned above in that is acted upon by the lubricant supply device of the drive chamber with a pressure which is higher than the pressure in the inlet channel of the high-pressure fuel pump.

Advantages of the invention

In the fuel system according to the invention, the lubrication and cooling of the moving parts of the high-pressure fuel pump is ensured even if in the low-pressure region, more precisely in the inlet channel of the high-pressure fuel pump, only a comparatively low pressure prevails. This is, for example, in such a fuel system possible, which has a low-pressure fuel supply, which provides a variable form. The background to this is the saving of fuel by reducing the drive power of the fuel pump used in the low-pressure fuel supply.

Without the measures according to the invention, such a fuel system would have the risk that, for example, in the bearing area of the drive shaft of the high-pressure fuel pump at a low fuel pressure in the drive chamber as a result of a local temperature increase, vapor formation of the fuel in the drive space could occur, which in turn causes a Inadmissible wear on the corresponding moving parts of the high-pressure fuel pump would result. This is reliably avoided by the measures according to the invention.

Advantageous developments of the invention are specified in subclaims.

First, it is proposed that the drive space is closed fluidically to the low pressure area. As a result, a small amount of fuel which is to be supplied to the drive space is sufficient to cause the pressure increase according to the invention in the drive space. This increases the efficiency of the fuel system.

It is also proposed that the lubricant supply device comprises a leakage gap from the delivery chamber to the drive chamber. The pressurization of the drive space is possible in this way without complicated additional measures, which keeps the manufacturing costs of the fuel system according to the invention low.

In concretization for this purpose, it is again proposed that the leakage gap between the conveyor element and the housing is arranged. As a result, the slide bearing between the conveyor element and housing is automatically lubricated and cooled.

It is also possible that the fuel system comprises a high-pressure region with a pressure control valve, and that the lubricant supply device comprises a flow path which connects the drive space with an outlet of the pressure control valve. To protect the components present in the high pressure area and to adjust the pressure, a pressure control valve is usually present there. According to the invention, the pressurized shut-off fluid of the pressure control valve is used for pressurizing the drive space. Thus, the pressurization of the drive space is ensured with very simple means and without complex and expensive additional devices.

It is also suggested that the fuel system include a quantity control valve with which a high-pressure side of the high-pressure fuel pump can be temporarily connected to the low-pressure region, and that the lubricant supply device comprises a flow path connecting the drive space with an outlet of the quantity control valve.

Such a quantity control valve is used for speed-independent adjustment of the delivery rate of the high-pressure fuel pump. This is useful in all those cases in which the high-pressure fuel pump is driven by the crankshaft or camshaft of an internal combustion engine. When the quantity control valve opens, flows under high pressure fuel from the high pressure side and thus does not reach, for example, to the fuel rail. This is exploited according to the invention for the lubrication and cooling of existing in the drive compartment components of the high-pressure fuel pump, so that a complex separate pressure supply for the drive space can be omitted. This development also saves costs.

In a further proposed development of the fuel system according to the invention, the lubricant supply device comprises a flow path which can connect the drive space with the low-pressure region, and in this flow path, a check valve is present, which blocks to the low-pressure region. In this way, the drive space can be subjected to a pressure, albeit comparatively low, even if the lubricant supply device can not yet provide the high pressure required in normal operation.

This is the case, for example, when the high-pressure fuel pump is driven by the internal combustion engine, and when the low-pressure fuel supply has an electrically driven fuel pump. In this case, even before starting the internal combustion engine by switching on the electric fuel pump generates a certain pressure in the drive space and there possibly existing gas bubbles can be reduced or eliminated.

By means of a very high pressure present in the drive space, an undesirable load, for example, can occur at sealing devices of the high-pressure fuel pump. In order to avoid this, the invention also proposes the fuel system comprises a pressure relief valve which limits the pressure in the drive space to a desired differential pressure.

Alternatively, it is possible that the fuel system comprises a pressure regulating valve, which adjusts the pressure in the drive space to a desired pressure. This has the advantage over a pressure relief valve that the maximum pressure in the drive chamber is lower.

In a further development of the two alternatives mentioned above, it is proposed that the outlet side of the pressure-limiting valve and / or the pressure-regulating valve be connected to the low-pressure fuel supply. In the first case, a pressure is set in the drive chamber which is higher by a certain differential pressure than the fuel pressure present in the low-pressure region (this usually corresponds to the prefeed pressure of an electric fuel pump). Such a pressure relief valve is simple and inexpensive. At high feed pressure, however, an undesirably high pressure may occur in the drive space. This is prevented if, instead of the pressure limiting valve, the pressure regulating valve is used, and if this is connected to the low-pressure fuel supply. In this case, the pressure in the drive chamber can not exceed the pressure prevailing in the low pressure range.

The invention further relates to a fuel system for an internal combustion engine having a high-pressure region and a high-pressure fuel pump comprising a housing and at least one movable conveying element, wherein between at least two relatively movable parts of the high-pressure fuel pump, a hydrostatic bearing is provided.

The operational safety of the fuel system is substantially improved if the hydrostatic bearing is connected to the outlet of a pressure control valve, which is arranged in the high-pressure region. The hydrostatic bearing significantly reduces the forces between two relatively moving parts. This reduces wear and the power required to drive the high pressure fuel pump.

The connection of the hydrostatic bearing to the pressure control valve of the high pressure area allows in all operating conditions of the high pressure fuel pump to build up a sufficient pressure in the hydrostatic bearing, which avoids the formation of vapor bubbles and lubrication and cooling is ensured at this point, regardless of actual pressure at the inlet of the high pressure fuel pump.

drawing

Figur 1

eine schematische Darstellung eines ersten Ausführungsbeispiels eines Kraftstoffsystems mit einer Hochdruck-Kraftstoffpumpe;

Figur 2

einen teilweisen Schnitt durch die Hochdruck-Kraftstoffpumpe von Figur 1;

Figur 3

einen teilweisen Schnitt durch einen Druckregler, welcher bei der Hochdruck-Kraftstoffpumpe von Figur 2 eingesetzt werden kann;

Figur 4

eine Darstellung ähnlich Figur 1 eines zweiten Ausführungsbeispiels eines Kraftstoffsystems;

Figur.5

eine Darstellung ähnlich Figur 1 eines dritten Ausführungsbeispiels eines Kraftstoffsystems; und

Figur 6

eine Darstellung ähnlich Figur 2 der Hochdruck-Kraftstoffpumpe von Figur 4.

Hereinafter, particularly preferred embodiments of the present invention will be explained in detail with reference to the accompanying drawings. In the drawing show:

FIG. 1

a schematic representation of a first embodiment of a fuel system with a high-pressure fuel pump;

FIG. 2

a partial section through the high-pressure fuel pump of Figure 1;

FIG. 3

a partial section through a pressure regulator, which can be used in the high-pressure fuel pump of Figure 2;

FIG. 4

a representation similar to Figure 1 of a second embodiment of a fuel system;

Figur.5

a representation similar to Figure 1 of a third embodiment of a fuel system; and

FIG. 6

a representation similar to Figure 2 of the high-pressure fuel pump of Figure 4.

Description of the embodiments

A fuel system carries the reference numeral 10 in FIG. 1. It comprises a tank 12, from which an electric fuel pump 14 delivers fuel. The fuel passes from the electric fuel pump 14 via a filter 16 in a low-pressure fuel line 18. From this branches off a branch line 20, in which a low-pressure fuel regulator 22 is arranged. The branch line 20 leads back to the tank 12.

The low-pressure fuel line 18 leads to a three-cylinder radial piston pump, which is referred to as high-pressure fuel pump 24. A high-pressure fuel line 26 leads from the high-pressure fuel pump 24 to a fuel rail 28 ("rail"). To the fuel manifold 28 a plurality of injectors 30 are connected, which inject the fuel directly into combustion chambers (not shown in Figure 1) of an internal combustion engine. The pressure in the fuel rail 28 is adjusted by a pressure control valve 32. This is about one Return line 34 is connected to the low pressure fuel line 18.

A pressure sensor 35 detects the pressure prevailing in the fuel rail 28 and transmits corresponding signals to a not shown in Figure 1 control and regulating device. This controls the electric fuel pump 14, the pressure control valve 32, the injectors 30, and other devices of the fuel system 10 depending on the fuel requirements.

The high-pressure fuel pump 24 is shown in detail in FIG. In the illustrated sectional plane, however, only one cylinder of the high-pressure fuel pump 24 is visible. In a radially extending stepped blind bore 36 in a housing 38, a cylinder head 40 and a cylinder liner 42 are fitted. In the cylinder liner 42, a piston 44 is slidably guided. Between piston 44 and cylinder liner 42, a leakage gap 45 is present. With its radially inner end of the piston 44 is supported on a shoe 46 from. Piston 44 and shoe 46 are pressed by a compression spring 48 against a contact surface (without reference numeral) a cam ring 50.

The cam ring 50 is seated on an eccentric portion 52 of a drive shaft 54. This is rotatably supported in the housing 38 via two shaft bearings 56 and 58. The drive shaft 54 is located in an axially present in the housing 38 blind bore 60. Between the housing 38 and the blind bore 60 on the one hand and the drive shaft 54, the cam ring 50, the shoe 46, the piston 44 and the cylinder liner 42 on the other hand, is a drive space 62nd educated. This is sealed by a shaft seal 64 to the outside. Between the cylinder head 40, the cylinder liner 42 and the piston 44, a delivery chamber 66 is present. This can be connected to the low-pressure fuel line 18 via an inlet channel 68 present in the housing 38 and an inlet check valve 70. Likewise, the delivery chamber 66 via an outlet channel 72 and an outlet check valve 74 with the high pressure fuel line 26 is connectable. Upstream of the inlet check valve 70, an auxiliary channel 76 branches off from the inlet channel 68, which opens into the drive chamber 72 via a check valve 78 blocking the inlet channel 68. From the auxiliary channel 76 also branches off an overflow 80, which also opens via a pressure relief valve 82 in the drive chamber 62.

The fuel system 10 shown in FIG. 1 and the high-pressure fuel pump 24 shown in FIG. 2 operate as follows:

As soon as the electric fuel pump 14 is put into operation, pressure is built up via the low-pressure fuel line 18 in the inlet channel 68. This is transmitted via the auxiliary channel 76 and the check valve 78 at this time (the high-pressure fuel pump 24 does not yet promote) in the drive chamber 62. This is thus under a certain pressure (prefeed pressure) standing fuel present, which lubricates their now in the onset of operation of the high-pressure fuel pump located in the drive chamber 62 moving parts. These include in particular the bearing 58, the cam ring 50 and the shoe 46.

By connecting the drive chamber 62 with the low-pressure fuel line 18 via the check valve 78 is a rapid actuation of the drive chamber 62nd with pressure, for example. At a first start-up or in the case possible in which when stopping the hot engine in the drive chamber 62, a larger vapor bubble has formed. The pressure in the drive chamber 62 then corresponds to the pre-pressure minus a small Duckabfalls of about 0.2 bar at the check valve 78th

The high pressure fuel pump 24 is operated by rotation of the drive shaft 54. Usually, the drive shaft 54 is driven by a crankshaft or a camshaft of the internal combustion engine, which is supplied by the fuel system 10 with fuel. By a rotation of the drive shaft 54, the piston 44 is set in a reciprocating motion. In a radially inwardly directed suction stroke of the piston 44, fuel is sucked into the delivery chamber 66 via the inlet channel 68 and the inlet valve 70. In a radially outwardly directed delivery stroke of the piston 44, the inlet valve 70 closes and the fuel trapped in the delivery chamber 66 is compressed.

As soon as the differential opening pressure of the exhaust valve 74 is exceeded, the exhaust valve 74 opens and the compressed fuel can escape from the delivery chamber 66 into the high pressure fuel line 26 and further into the fuel rail 28. A return flow of the compressed fuel from the fuel rail 28 into the delivery chamber 66 is prevented by the outlet valve 74. Thus, the fuel remains stored in the fuel manifold 28 under high pressure where it can be retrieved from the injectors 30 and injected into the combustion chambers of the engine under high pressure.

When the fuel in a delivery stroke of the piston 44 in Delivery chamber 66 is compressed, a small amount of fuel through the leakage gap 45 between the piston 44 and the cylinder liner 42 from the delivery chamber 66 is pressed into the drive chamber 62. As a result, the existing in the drive chamber 62 fuel is pressurized even more. Since the check valve 78 blocks to the inlet channel 68, no fuel can escape from the drive chamber 62. As a result, pressurization of the drive chamber 62 is made possible to a pressure level which is above the pressure level in the low-pressure fuel line 18. The normal operating pressure in the drive chamber 62 corresponds to the pressure in the low-pressure fuel line 18 plus the differential opening pressure of the pressure-limiting valve 82. The pressure-limiting valve 82 is prevented as an excessive increase in the pressure prevailing in the drive chamber 62 fuel pressure.

Typically, the fuel pressure that can be provided by the electric fuel pump 14 is approximately 1 to 6 bar. Thus, with a differential pressure of the pressure relief valve 82 of approximately 2 bar, a pressure in the drive space 62 will be approximately 3 to 8 bar.

It can easily be seen that the fuel pressure prevailing in the drive chamber 62 is in any case higher than the admission pressure generated by the electric fuel pump 14 in the low-pressure fuel line 18 and in the inlet channel 68. In this way, in normal operation, even when the electric fuel pump 14 is operated only at low power and the pressure in the low-pressure fuel line 18 is comparatively low, so sufficient pressure in the drive chamber 62 ensures that even with relatively warm components in the drive compartment 62 on Vaporizing the fuel and thus a collapse on the one hand the lubrication and on the other hand, the cooling is prevented at this point.

Due to the presence of the high pressure fuel pump 24, which is shown in Figure 2, existing pressure relief valve 82 between the drive chamber 62 and the inlet channel 68, the pressure in the drive chamber 62 ultimately depends to a considerable extent on the pressure prevailing in the inlet channel 68 form. If this form, for example, at a hot start of the internal combustion engine, relatively high, and the pressure in the drive chamber 62 is relatively high. Under certain circumstances, it is higher than would be necessary to avoid steam formation in the drive chamber 62 per se. By such a high pressure, however, in particular the shaft seal 64 is unnecessarily loaded, which could reduce their life. Therefore, instead of the pressure relief valve 82 shown in Figure 2, a pressure control valve can be used.

Such is exemplified in Figure 3 and there bears the reference numeral 84. It comprises a spring 86 acted upon by a membrane 88, which is acted upon by the spring 86 against a seat 90. The seat 90 is annular and separates a radially inward and connected to the inlet channel 68 portion of a radially outer and connected to the drive chamber 62 area. The drive chamber 62 and the inlet channel 68 are shown only symbolically in FIG. A vent line (not numbered) is also shown.

When using the pressure regulating valve 84 shown in FIG. 3, a change in the admission pressure prevailing in the intake passage 68 only has a weakened effect on the pressure in the intake passage 68 Drive space 62 off. The influencing factor can be determined by the choice of the pressure areas.

FIG. 4 shows a second exemplary embodiment of a fuel system 10. In this, such components, range, and parts having equivalent functions to components, regions, and parts of the fuel system shown in FIG. 1 carry the same reference numerals and will not be explained again in detail.

The high-pressure fuel pump 24 used in FIG. 4 is shown in detail in FIG. 6 and will be explained in more detail below. A significant difference of the fuel system 10 shown in Figure 4 to that of Figure 1 relates to the nature of the pressurization of the fuel present in the drive chamber 62. While in the high-pressure fuel pump used in Figure 1, this pressurization takes place solely through the leakage gap between the piston and cylinder liner, in the embodiment shown in Figure 4, the Absteuerkraftstoff the pressure control valve 32 is additionally used with the pressure in the fuel rail 28 is set , For this purpose, a branch line 92 leads from the return line 34 to the drive space 62.

FIG. 5 shows yet another embodiment of a fuel system 10. Also in his case, such components, regions, and parts which have equivalent functions to components, regions, and parts of the embodiment shown in Figure 1 or in Figure 4, the same reference numerals. They are not explained again in detail.

A significant difference of the fuel system 10 shown in Figure 5 to that of Figure 4 relates to the high-pressure fuel pump 24. This is therefore also shown in Figure 5 in somewhat greater detail. Thus, the delivery rate of the high-pressure fuel pump 24 can be adjusted independently of the speed of the drive shaft 54, a quantity control valve 94 is provided in the high-pressure fuel pump 24 shown in Figure 5. This is a solenoid-operated 2/2 shift valve whose inlet is connected to an area upstream of the exhaust valve 74, and whose outlet is connected to an area upstream of the intake valve 70.

The quantity control valve 94 can be opened for a certain period during a delivery stroke of the piston 44, so that during this opening period, the fuel is not conveyed into the fuel manifold 28, but with a correspondingly high pressure back into the low-pressure fuel line 18. As can be seen from FIG. 5, a branch line 92 is likewise provided, which leads from the outlet side of the quantity control valve 94 to the drive space 62 and thus pressurizes it.

For simplicity, in the present drawing, the arrangement of the quantity control valve is shown as it is the case with a single-cylinder pump. In a multi-cylinder pump, the input of the quantity control valve would have to open after the exhaust valve. Starting from this summation point then another check valve would have to be present to the fuel manifold.

A high pressure fuel pump 24, as in the embodiment of a fuel system shown in Figure 4 10 can be used is shown in Figure 6 in detail. The representation there corresponds in essential points to the high-pressure fuel pump of FIG. 2. Therefore, such components, regions, and parts which have the equivalent functions to components, regions, and parts of the high-pressure fuel pump shown in FIG are not explained again in detail.

In the case of the high-pressure fuel pump 24 shown in FIG. 6, the delivery chamber 66 is filled by an inlet channel 68, which extends in the longitudinal direction in the piston 44. Also, the inlet check valve 70 is disposed in the piston 44. Further, the drive space 62 is connected via a channel 76 directly to the low pressure fuel line 18. An auxiliary channel 96 also leads from the return line and the branch line 92 of the pressure control valve into the drive space 62.

In the auxiliary channel 96, a pressure limiting valve 82 is arranged. From a region of the auxiliary channel 96 located upstream of the pressure limiting valve 82, a channel 98 branches off, which opens into a space located between the axial end of the drive shaft 54 and the housing 38 (without reference numeral). In the drive shaft 54 itself, an outgoing from the axial end surface and extending to the eccentric portion 52 in the longitudinal direction in the drive shaft 54 extending channel 100 is present.

This opens via the longitudinal axis of the drive shaft 54 radially extending branch channels in the lateral surface of the drive shaft 54, on the one hand in the region of the bearing 58 and on the other in the region of the eccentric 52 and the cam ring 50th Since the pressure upstream of Pressure relief valve 82 in the auxiliary channel 96 is comparatively high (yes, it is provided by the Absteuerfluid the pressure relief valve 32), a good lubrication of the bearings on the lateral surface of the drive shaft 54 is ensured via the channels 98 and 100.

As can be seen from FIG. 6, the radial branch channels open into lubricating pockets which are present in the lateral surface of the drive shaft 54. The angular position of the lubrication pockets in the region of the shaft bearing 58 is diametrically opposite to the angular position of the lubricating pocket in the region of the eccentric portion 52. To avoid an axial force on the drive shaft 54, the channel 98 can open into the lateral surface of the drive shaft 54 and an annular groove with the channel 100th be connected in the drive shaft 54.

Characterized in that in the high-pressure fuel pump 24 shown in Figure 6, the drive chamber 62 is connected to the branch line 92 of the return line from the pressure control valve (see Figure 4), can be dispensed with a check valve between the drive chamber 62 and low-pressure fuel line 18. Nevertheless, a rapid admission of the fuel located in the drive chamber 62 is ensured and at the same time is also provided for an intensive flushing in the drive chamber 62. The same effect is achieved when the branch line 92 is connected to the outlet of the quantity control valve (see Figure 5).

Claims (11)

1. Fuel system (10) for an internal combustion engine, having a low-pressure region (18), a high-pressure fuel pump (24) and a high-pressure region (26, 28), the high-pressure fuel pump (24) comprising: a housing (38, 42) with an inlet duct (68) for conveying fuel out of the low-pressure region (18), at least one moveable feed element (44) which delimits a feed space (66), at least one drive (54) which can move the feed element (44), a working space (62) in which the drive (54) is at least partially arranged, and a lubricant supply device (45, 92, 96) for supplying moving parts with fuel as a lubricant, characterized in that the lubricant supply device (45, 92, 96) pressurizes the working space (62) with a pressure which is higher than the pressure in the inlet duct (68) of the high-pressure fuel pump (24).
2. Fuel system (10) according to Claim 1, characterized in that the working space (62) is fluidically closed off in the direction of the low-pressure region (18).
3. Fuel system (10) according to one of the preceding claims, characterized in that the lubricant supply device comprises a leakage gap (45) from the feed space (66) to the working space (62).
4. Fuel system (10) according to Claim 3, characterized in that the leakage gap (45) is arranged between the feed element (44) and the housing (42).
5. Fuel system (10) according to one of the preceding claims, characterized in that a pressure control valve (32) is arranged in the high-pressure region (26, 28), and in that the lubricant supply device comprises a flow path (92) which connects the working space (62) to an outlet of the pressure control valve (32).
6. Fuel system (10) according to one of the preceding claims, characterized in that it comprises a quantity control valve (94), by means of which a high-pressure side of the high-pressure fuel pump (24) can be connected, at times, to the low-pressure region (18), and in that the lubricant supply device comprises a flow path (92) which connects the working space (62) to an outlet of the quantity control valve (94).
7. Fuel system (10) according to one of the preceding claims, characterized in that a flow path (76) which can connect the working space (62) to the low-pressure region (18) is provided, and in that a non-return valve (78) is provided in said flow path (76), said non-return valve (78) effecting a blockage in the direction of the low-pressure region (18).
8. Fuel system (10) according to one of the preceding claims, characterized in that it comprises a pressure limiting valve (82) which limits the pressure in the working space (62) to a desired differential pressure.
9. Fuel system (10) according to one of the preceding claims, characterized in that it comprises a pressure limiting valve (84), by means of which the pressure in the working space (62) can be set to a desired pressure.
10. Fuel system (10) according to one of Claims 8 or 9, characterized in that the outlet side of the pressure limiting valve (82) and/or of the pressure regulating valve (84) are/is connected to the low-pressure region (18).
11. Fuel system (10) according to one of the preceding claims, characterized in that a hydrostatic mounting is provided between at least two parts (50, 52, 54, 58), which can move relative to one another, of the high-pressure fuel pump (24), the hydrostatic mounting being attached to the outlet of a pressure control valve (32) which is arranged in the high-pressure region (28).

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