WO2012155162A1

WO2012155162A1 - High-pressure pump arrangement for pumping combustible fuel from a tank into a high-pressure container

Info

Publication number: WO2012155162A1
Application number: PCT/AT2012/000125
Authority: WO
Inventors: Günther PRUMMER
Original assignee: Robert Bosch Gmbh
Priority date: 2011-05-18
Filing date: 2012-05-03
Publication date: 2012-11-22
Also published as: AT511504A1; EP2710252B1; EP2710252A1; AT511504B1

Abstract

In a high-pressure pump arrangement for pumping combustible fuel from a tank into a high-pressure container, wherein at least one pump element consisting of pump cylinder and pump piston is provided whose pump chamber can be connected via a suction valve to a pump suction chamber supplied by a fuel supply and via a pressure valve to the high-pressure container, wherein the pump element comprises a leakage line for returning into the pump suction chamber leakage fuel which flows off between pump piston and pump cylinder, and wherein the fuel supply has a metering unit, and at least one purging line, having a throttle, for evacuating a purging quantity coming from the metering unit into a low-pressure region leads off from the fuel supply downstream of the metering unit, the at least one purging line (24, 24') is connected to the pump suction chamber (12) such that the purging quantity flows through the pump suction chamber (12).

Description

High pressure pump assembly for pumping fuel from a tank into a high pressure vessel

The invention relates to a high-pressure pump arrangement for pumping fuel from a tank into a high-pressure vessel, wherein at least one of pump cylinder and pump piston existing pump element is provided, the pump chamber via a suction valve with a fed by a fuel supply pump suction and a pressure valve with the high-pressure vessel in combination wherein the pump element has a leakage line for returning leakage fuel flowing between the pump piston and the pump cylinder into the pump suction space, and wherein the fuel supply comprises a metering unit and at least one purge line having a throttle for discharging one of the metering unit from the fuel supply downstream of the metering unit Flushing leads away in a low pressure range.

Such high-pressure pump arrangements are used, for example, in so-called "common-rail systems" in which the high-pressure pump serves to pump fuel from a fuel tank into a high-pressure vessel, the so-called rail, the fuel in the high-pressure vessel being kept under sufficient pressure. to allow injection of the fuel into the combustion chamber of the internal combustion engine. The high pressure pump provides the high pressure fuel stored in the rail for all operating conditions of the engine. In some dynamic operating points, the flow rate of the high pressure pump must be above the full load required by the engine stationary. On the other hand, however, only a small flow rate of the high pressure pump is required at part load or idling of the engine.

The regulation of the flow rate of the high-pressure pump in the rail takes place via an electronically controlled metering unit which determines the inflow quantity to the high-pressure pump as a function of the fuel pressure in the rail. This has the advantage that only the respectively required amount of high pressure fuel in the rail replenished and not an excess of high-pressure fuel is generated, which is then relieved via a pressure control valve and returned to the tank. Such an approach would involve high energy losses and, moreover, would lead to excessive heating of the fuel.

A heating of the fuel is on the one hand in principle desirable when using fuel with high viscosity and high proportion of abrasive solids, so-called heavy oil, since the promotion and injection of heavy oil heating up to 150 ° is required to achieve the necessary injection viscosity , On the other hand, in the case of high-pressure pumps of conventional type, heating of the pump elements can be observed to an extent which can lead to undesirably high temperatures, especially at low flow rates. In the present type of control via a controlled metering unit of the high-pressure fuel supplied by the high-pressure pump, in spite of the lower losses, there is a significant heating of the pump units designed as piston pumps. This is due to the fact that the leakage currents generated at pressures of about 2000 bar during the pumping process cause a significant warming. The pump elements of a high pressure pump are usually arranged in series, with 2 to 6 cylinders side by side usual. A V or W arrangement in several rows is possible. In this case, the pump elements further away from the metering unit receive a low-pressure fuel, which has already flushed through one or more suction chambers of pump elements and was warmed up accordingly. With conventional high-pressure pumps, lent between the pump piston and pump cylinder from the pump room down through leaking fuel collected, for example, in an annular groove and returned through a leak oil hole in the suction chamber, as shown in Figure 2. At low metering quantities and high engine speeds, the leakage quantities are of the order of magnitude of the metering quantities and lead to an undesirably high and uneven heating of the high-pressure pump due to the said recirculation and the resulting circulation. In particular, the pump elements furthest from the fuel supply line are thereby heated the most. This reduces the delivery rate of these elements and also adversely affects their service life. High-pressure pump arrangements known from the prior art have a flushing line with a throttle arranged in the flushing line between the metering unit and the pump elements. This line is also referred to as a zero feed line, and the corresponding throttle as a zero feed throttle. This flushing line or zero delivery line comes into play when fuel is not to be delivered by the high-pressure pump arrangement, the metering unit is closed accordingly and systematically even with closed metering unit still fuel exiting from the outlet. To prevent it from reaching the working space of the high-pressure fuel, the purge line branches off from the fluid connection present between the metering unit and the suction valve, which leads to a low-pressure area. About the purge line exiting the closed metering unit leakage fuel is kept away from the high-pressure fuel pump. This happens because at relatively low differential pressure, the leakage quantity of the closed metering unit into the flushing line and from there into the low pressure rich, without the opening pressure of the suction valve is exceeded.

The minimum required opening pressure of the suction valve is thereby determined by the pressure level in the low pressure area plus the required pressure difference across the zero feed throttle, which is required to discharge the leaking from the metering leakage fuel, minus the minimum pressure in the working space of the high pressure fuel umpe during the intake.

Based on this prior art and the problems previously described of heating the pump elements by the heating of leakage fuel from the pump elements, it is an object of the present invention to improve the known high-pressure pump assemblies so that overheating and thus a reduction of the life of the pump elements in part-load operation the high pressure pump assembly is prevented.

To solve this problem, a high-pressure pump assembly of the type mentioned is inventively developed such that the at least one purge line is in communication with the pump suction, so that the pump suction is flowed through by the flushing. The invention thus consists essentially in that the flushing line. is connected to the pump suction of at least one pump element for discharging the leaking at the closed metering leakage fuel. As a result, the fuel coming from the metering unit is not already drawn off in the partial load range or completely closed metering unit before the pump elements and in particular before the pump suction of the respective pump elements and discharged into the low pressure range, but the pump suction chambers are traversed by this amount of fuel. Thereby, the leakage fuel, which is returned by the pump elements in the pump suction chambers, flushed in the low pressure area. The throttle in the purge line is in this case dimensioned such that the passing through the metering unit fuel quantity is dissipated so that the opening pressure of the suction valves of the pump elements is not exceeded when no high-pressure delivery is desired. Only when the metering unit meters larger amounts of fuel can not be discharged from the throttle in the purge line enough fuel, whereby the opening pressure of the suction valves is exceeded and fuel enters the pump chamber of the pump elements.

With the arrangement according to the invention, therefore, even for the case just mentioned, that no high-pressure delivery is desired, with appropriate dimensioning of the throttle in the purge line, a certain amount of purge from the metering unit is constantly metered, whereby even in Nullförderfall the pump pensaugräume the pump elements are flowed through and the formation of heating circuits can be virtually completely prevented.

The invention is preferably embodied such that a supply line of the fuel feed opens into the pump suction space and leads away from the pump suction space a separate discharge for the flushing quantity.

In the event that the high-pressure pump arrangement comprises a multi-piston pump, the invention is advantageously further developed in that a plurality of pump elements connected in at least one row are provided, the pump suction chambers of which are in communication with one another and are supplied with fuel from the fuel supply in succession , And that at the end of the row arranged pump element the Flush line is connected.

Advantageously, the high-pressure pump arrangement according to the invention is further developed such that downstream of the metering unit, another purge line having a throttle leads away into a low-pressure area for discharging a purge volume coming from the metering unit, this further purge line being arranged upstream of the pump suction chamber. This further purge line is thus arranged at a point in the circuit which corresponds to the order of the previously known purge line. By means of this flushing line, even with the metering unit closed, a certain amount of flushing can be provided for cooling the pump elements which flow according to the invention. The mentioned flushing quantities can be discharged directly into the low-pressure region of the high-pressure pump arrangement, however, a preferred embodiment of the present invention results if the flushing line is connected downstream of the restrictor to a cooling system of a high-pressure fuel line. Such cooling systems of high-pressure fuel lines are known from the prior art and are for example in a double-walled piping system of the high-pressure lines, wherein the relatively cool fuel from the purge line or from the purge lines is passed through the outer lumen of the double-walled high-pressure lines, whereby the inner fuel line and the therein high pressure fuel to be cooled.

The invention will be explained in more detail with reference to an embodiment schematically illustrated in the drawing. 2 shows a section according to the line II-II of Fig.l, Figure 3 shows the structure of a high-pressure pump assembly according to the present invention, 4 shows a block diagram of a high-pressure pump arrangement according to the prior art, and FIG. 5 shows a block diagram of the high-pressure pump arrangement according to the invention. In the high-pressure pump shown in Fig.l and Fig.2 is driven by the engine camshaft 1 can be seen, which is mounted in a pump housing 2 and roller tappet 3, the pump piston 4 moves in the pump cylinders 5 of the individual pump elements up and down. The contact between see roller tappet 3 and cam 1 is maintained by compression springs 6. During the downward movement of the pump piston 4, the quantity of fuel determined by the metering unit is sucked in via a suction valve 7 and then pressed into the rail during the upward gear via a pressure valve 8. In this high-pressure pump, the fuel pumping down between the pump piston 4 and the pump cylinder 5 from the pump chamber 9 is collected in an annular groove 10 and returned through a leakage oil bore 11 into the pump suction chamber 12, as shown in FIGS. 1 and 2. With small metering quantities and high engine speeds, the leakage quantities are of the order of magnitude of the metering quantities and lead to an undesirably high and uneven heating of the high-pressure pump. In particular, the pump elements furthest from the fuel supply line are thereby heated the most.

In Figure 3, a high pressure pump according to the invention is now shown, it can be seen that at the position 13, a line is connected, which is directly connected to the pump suction of the pump element 14 in connection. The metering unit 15 is located on the opposite side of the row of pumping elements, so that a flushing amount supplied from the metering unit 15 to the pumping elements passes through the pumping suction spaces 12 of the respective pumping elements, thereby removing the leakage amounts from the pumping suction spaces 12. In FIGS. 4 and 5, the interconnection of the individual components of the high-pressure pump arrangement can be seen particularly clearly. At the position 16, fuel is supplied from the tank to the low-pressure pump 17, which delivers the fuel at a constant rate to the metering unit 15. Depending on the fuel requirement, the metering unit 15 controls the amount of fuel that reaches the pump elements. In the flow direction in front of the metering unit, a return line 18 is provided with a suitable non-return valve 19 in order to reclaim unneeded fuel into the fuel feed from the tank. The fuel passes to the metering unit 15 to the pump elements 14 to 14c, where the promotion to high pressure and the high-pressure fuel in the Hochdrucksamm- ler 20 collected and fed via a line 21 to the injectors of the injection system. In the prior art, as can be seen from FIG. 4, a flushing or zero delivery line 22 with a zero feed throttle 23 is arranged between the metering unit 15 and the pump elements or their suction chambers, so that the fuel coming from the metering unit 15 is superfluously attributed to the pump elements 14 to 14c, is discharged into the low-pressure region of the injection system or the high-pressure pump assembly without the pump elements 14 to 14c are reached.

In the high-pressure pump arrangement according to the invention according to FIG. 5, it can now be seen that flushing lines 24, 24 'are arranged in the flow direction downstream of the pump elements 14 to 14c, so that a flushing quantity which is conducted from the metering unit 15 in the direction of the pump elements 14 to 14c Pump suction of the pump elements 14 to 14 c flows through before the flushing lines 24 and 24 'are achieved with the corresponding throttles 25 and 25'. After the throttles 25 or 25 ', a discharge of the flushing quantity takes place either directly into the low-pressure rich or the tank of the injection device, or the flushing amount is, as already described above, used for cooling the high-pressure fuel lines. At 26, a further bypass line is arranged at the position of the zero delivery line or purge line 22 from the prior art, which also has a throttle 27. As a result of this bypass line, even with the metering unit completely closed, a minimal amount of flushing can be conveyed to the pump elements 14 to 14c, so that corresponding cooling of the pump elements or the suction chambers of the pump elements takes place even in the zero flow case.

Claims

Claims:

1 . High-pressure pump arrangement for pumping fuel fuel from a tank into a high-pressure vessel, wherein at least one of pump cylinder and pump piston existing pump element is provided, the pump chamber is brought via a suction valve with a fed by a fuel supply pump suction and a pressure valve with the high-pressure vessel in combination, the Pump element having a leakage line for returning leakage between the pump piston and pump cylinder leakage in the pump suction, and wherein the fuel supply has a metering unit and leads away from the fuel supply downstream of the metering unit at least one throttle having a purge line for discharging a coming from the metering unit flushing in a low pressure region, characterized in that the at least one purge line (24, 24 ') communicates with the pump suction space (12), so that the pump suction space (12) flows through the flushing volume.

2. High-pressure pump assembly according to claim 1, characterized in that in the pump suction chamber (12) opens a supply line of the fuel supply and leads away from the pump suction a separate discharge for the flushing volume.

3. High-pressure pump arrangement according to claim 1 or 2, characterized in that a plurality of pump elements (14) connected in at least one row are provided, whose pump suction chambers (12) communicate with each other and are supplied with fuel from the fuel supply one after the other, and in that the flushing line (24, 24 ') is connected to the pump element arranged at the end of the row.

4. High-pressure pump arrangement according to claim 1, 2 or 3, characterized in that downstream of the metering unit (15) leads away a further having a throttle purge line for discharging one of the metering unit (15) coming flushing into a low pressure region, said further purge line upstream of the pump suction (12) is arranged.

5. High-pressure pump arrangement according to one of claims 1 to 4, characterized in that the flushing line (24, 24 ') downstream of the throttle (25, 25') is connected to a cooling system of a high-pressure fuel line.