EP1727978A1

EP1727978A1 - Fuel-injection system with reduced pressure pulsations in the return rail

Info

Publication number: EP1727978A1
Application number: EP04729610A
Authority: EP
Inventors: Patrick Mattes; Wolfgang Stoecklein; Holger Rapp; Hans Brekle; Markus Erhardt
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2003-06-21
Filing date: 2004-04-27
Publication date: 2006-12-06
Anticipated expiration: 2024-04-27
Also published as: JP2006523793A; DE502004012034D1; KR20060028699A; WO2005001280A1; DE10328000A1; EP1727978B1; ATE492720T1

Abstract

The invention relates to a fuel-injection system (1) for an internal combustion engine, comprising: at least one injector (3) for injecting fuel into a combustion chamber of a motor, said injector having a high-pressure connection (10), via which it receives a supply of fuel at high pressure, a control valve (64) for controlling the injections of the injector and a low-pressure connection (12) for discharging a controlled quantity of fuel that is accumulated during the control of the injection; and a leakage line (11), which is connected to a fuel-return line (17) by the interposition of a pressure-holding valve (15), which opens in the direction of the fuel-return line when a predefined pressure is exceeded. Said system is characterised in that it is equipped with a throttle device (20) in the vicinity of the pressure-holding valve (15), said device being configured and located in such a way that when the pressure-holding valve is open, a reflection of pressure waves emanating from the injector in the form of negative-pressure waves is damped. Negative-pressure waves emanating from the pressure-holding valve towards the leakage line of the injector are damped or prevented. This reduces the risk of damage caused by cavitation.

Description

Fuel injection system with reduced pressure fluctuations in the return rail

State of the art

The invention is based on a fuel injection system according to the preamble of claim 1. The pressure holding valve may be set to a pressure of 0.5 bar relative (ie relative to the ambient pressure of the fuel injection system), and then only serves to empty the at least one injector with a leakage line (= return rail) connecting the leakage line and / or the leakage line to be prevented. In such a system, the injector may be provided with an electrically operated solenoid valve that controls the injection process of the injector by changing the pressure in a control chamber. In other fuel injection systems, the pressure holding valve may be set relatively to a pressure of 30 bar, for example. In these systems, the injector is generally equipped with a hydraulic coupler that is actuated by a piezo actuator. The hydraulic coupler is functionally surrounded by fuel, which is under the pressure of about 30 bar, so that the hydraulic coupler is always functional. In both of the fuel injection systems mentioned, the fuel return line may lead directly to the fuel tank of the internal combustion engine. In a subset of the last-mentioned fuel injection systems, the line connected to the end of the pressure control valve facing away from the injector is connected to a connecting line between a fuel from the fuel tank to a moderate pressure of, for. B. 5 bar lifting first pump and the input of a high pressure pump. The invention can be used in the systems mentioned above. It is known (EP 0780 569 B1, Fig. 13B) to switch on the pressure accumulator a valve in the high-pressure line to the injector, which has a spherical movable valve member biased by a spring. This opens when fuel flows to the injector and closes almost completely when no fuel is flowing. A complete closing is prevented by the fact that the circularly circular cross-section behind the valve seat is radially expanded by grooves running in the longitudinal direction, which are not covered by the movable valve part. When the valve is closed, the valve thus forms a throttle which, as can be seen from the use of specialist knowledge, is suitable for damping the first pressure wave arriving on the high-pressure line from the injector, and which can therefore also prevent the formation of further pressure fluctuations in the high-pressure line.

Advantages of the invention

The advantage of the fuel injection system according to the invention is that a disadvantage recognized by the inventors is reduced or avoided. This disadvantage is due to the following processes: If the injector triggers an injection process, a control quantity flows into the leakage line when the above-mentioned control valve is actuated and, during operation, causes the counterpressure valve to open and essentially the same amount as the control quantity the pressure control valve flows off. The inflow of the above-mentioned control quantity causes a flow surge into the leakage line and triggers a pressure wave towards the counter-pressure valve, which is reflected there as a vacuum wave when it is opened (reflections of a pressure wave at an open line end or a pressure node as opposed to a pressure belly occur as a vacuum wave) , Such negative pressure waves can lead to cavitation, which in the long run causes damage to the injector and thereby reduces its service life. Cavitation occurs when the vapor pressure of the fuel falls below. It is believed that the lower the normal pressure in the leakage manifold and thus in the individual, the greater the risk of cavitation Leakage lines of the injectors is. The risk of cavitation is likely to be particularly great if a vacuum wave arrives at the control valve when it has just entered the blocking state and, because of the sudden interruption of the flow out of the control valve, the pressure behind the control valve falls below the vapor pressure of the fuel anyway.

According to the invention, negative pressure waves running from the pressure maintaining valve are weakened or prevented for the leakage connection of the injector.

By stating that the throttle should be in the vicinity of the pressure-maintaining valve, the following is understood: the distance should not be so great that the throttle's effect on the suppression of negative pressure waves is adversely affected thereby; in addition, the leakage quantities of several, preferably all, of the injectors which are connected to a single pressure holding valve are intended to flow through said throttle. In embodiments of the invention, the throttle may be arranged in front of the pressure-maintaining valve, or behind it, or be structurally combined with the valve element of the pressure-maintaining valve, seen from the injector.

In embodiments of the last-mentioned embodiment according to the invention, a slide is provided, which is preferably designed as a solid cylinder, and is displaceably guided in a recess, in particular a bore, against the force of a spring and has to be displaced against this spring force when coming out of the leakage collecting line should leak fuel through the pressure control valve. In a first modification, at least one groove is incorporated in the wall of the cylinder, which is closed by the wall of the bore at its rear end when the pressure holding valve is at rest and is open at its front end and with its rear end from the rear when the cylinder is displaced sufficiently Area of the hole so that the groove, which also forms a throttle, is completely continuous. In another modification, the solid cylinder is without grooves in its wall, instead a groove is incorporated in the wall of the bore, which is expediently closed at the front end by the cylinder surface of the cylinder when the valve is at rest, whereas its rear end is always free , and if the cylinder is shifted sufficiently, the front one Free end of the groove, which also forms a throttle. In a further combined modification, at least one of the above-mentioned grooves is present both in the wall of the cylinder and in the wall of the bore. It goes without saying that instead of a single groove, there can also be several grooves.

In all of the described embodiments, it is advantageous that the throttle, by exchanging generally a single part or selecting a suitable part of this type when mounting the valve, is based on the conditions prevailing in a specific fuel injection system and are generally known for every internal combustion engine , can be adjusted. This is because the characteristic impedance of the choke or, if there are several chokes, the combination of such chokes (as explained, a parallel connection of chokes, but also a series connection of such chokes is possible) should be adjusted correctly.

Further advantages and advantageous embodiments of the invention can be found in the description, the drawing and the claims.

drawing

Exemplary embodiments of the injection system or injection device according to the invention are illustrated with the aid of the drawing and are explained in more detail in the description below. Show it:

1 shows an illustration of a fuel injection system according to the invention with a plurality of injectors and a pressure holding valve, in the area of which a throttle is provided; Fig. 2 shows the combination of provided in the arrangement of Fig. 1

Pressure control valve and throttle in enlarged longitudinal section;

FIG. 3 shows a combination of pressure holding valve and throttle provided in another embodiment of the invention, modified from FIG. 2; 4 shows an arrangement provided in a further fuel injection system according to the invention instead of the valve arrangement according to FIGS. 2 and 3, in which a throttle is provided in a wall of a bore slidingly receiving a full cylinder,

5 modified embodiment of a pressure control valve, which is installed in a further embodiment of the invention, and in which a throttle is incorporated in the wall of said solid cylinder as a groove, and

Fig. 6 essential components of the injector of the fuel injection system used in Fig. 1 with an electromagnetically operated control valve.

Description of the embodiments

In Fig. 1, a fuel injection system 1, which is provided in the example for diesel fuel, has a number of known injectors 3 (6 injectors in the example) which, during operation, fuel through injection openings 5 (see FIG. 6) inside a respectively assigned combustion chamber Inject the diesel engine. A pressure accumulator 7 is filled with fuel under high pressure (1600 bar in the example) via a line 8. Fuel is fed to a high-pressure connection 10 of each injector 3 via a high-pressure line 9 in each case. Leakage quantities and control quantities of the injectors, which occur when a control valve that controls the injection process of the injectors are actuated, are each fed via a leakage line 11 from a low-pressure connection 12 to a leakage collection line 13 (leakage rail). In the example, the injectors 3 are such injectors which are controlled by an electrically operated solenoid valve which, when actuated in a known manner, the pressure within a

Control chamber lowers, whereby the injection process is started. When this control valve opens, fuel emerges from said control chamber and enters leakage line 11. All leakage lines of the injectors shown lead into the leakage line 13. One end of the leakage manifold 13 is closed, the other end, on the right in FIG. 1, is connected to a return line 17 for the fuel via a pressure holding valve 15, and this return line 17 leads to the fuel tank. Fuel is drawn in from the fuel tank in a known manner and finally brought to the high pressure with which the fuel is supplied to the pressure tank 7 by means of one or more pumps. In the example, the pressure-maintaining valve 15 opens at an overpressure within the leakage manifold 13 with respect to the pressure in the return line 17 of approximately 0.5 bar. This pressure of 0.5 bar serves to prevent the leakage lines from leaking. As far as the arrangement has been explained so far, it is known. What is new in relation to the prior art in the arrangement shown in FIG. 1 is that a throttle device 20 is provided in the vicinity of the counterbalance valve 15, which serves to largely prevent undesired pressure wave reflections in the leakage manifold 13. Fig. 2 shows the combination of throttle device and provided in Fig. 1

Back pressure holding valve as a structural unit 25. The throttle device is formed by a single throttle 27, which is introduced as a bore in a block 28 that can be selected appropriately during assembly. The block 28 is arranged in the flow direction of FIG. 1, that is to say from left to right, upstream of the back pressure holding valve. The assembly 25 is mounted pressure-tight in the arrangement according to FIG. 1 by screw connections.

The combination 30 shown in FIG. 3 of the counter pressure holding valve and throttle device differs from FIG. 2 only in that the throttle device is arranged downstream of the actual counter pressure holding valve.

The arrangements of FIGS. 2 and 3 can in embodiments of the invention in a completely identical manner by suitable connection, for. B. screwing of two separately manufactured parts, namely a component that essentially only contains the throttle bore, and a conventional counter pressure valve. In the arrangement according to FIG. 4, the throttle and the back pressure holding valve form a unit which cannot be separated from one another. The valve arrangement 40 opens again when there is a counter pressure on the left side in FIG. 4 compared to the pressure on the right side in FIG. 4. The valve arrangement is essentially designed as a slide valve. A slide 41 (full cylinder) is guided in the longitudinal direction of the essentially circular cylindrical valve arrangement 40 through a guide surface. For this purpose, the slide 41 is displaceable in a bore 42 in a center piece 43 against the force of a compression spring 44. In the rest position shown in FIG. 4, the slide 41 bears against a stop device 45, which is formed by a perforated plate and does not overall hinder the flow of the fuel. In the wall of the bore of part 43, a longitudinal groove 47 is machined, which is open to the right, but to the left ends before the end of the slide 41, so that in the position of the slide 41 shown, fuel does not enter the groove from the left 47, which simultaneously forms the throttle, can occur. If the pressure on the left-hand side of FIG. 4 is so great that the slide 41 moves sufficiently far to the right, the groove 47 is finally also free at its front end and fuel can enter there and flow through the groove 47, so that the valve assembly is now open. Functions, the throttle can be seen as lying behind the valve opening.

The embodiment of a combination 50 of a valve with a throttle shown in FIG. 5 differs from that shown in FIG. 4 only in that the throttle groove 51 is now arranged on the cylindrical outer surface of the slide 52, whereas the bore of the part 54 is smooth. Here the groove 51 is always open to the left and its right end is only for one

Flow through the groove is released when the slide 54 has moved sufficiently far to the right. Functions, the throttle can be seen as lying in front of the valve opening. In an embodiment that is not shown, both a groove 47 according to FIG

4, as well as a groove 51 according to FIG. 5 are provided. In this case, the two grooves must not overlap when the valve arrangement is locked. This configuration of the valve arrangement enables further actuation in such a way that no displacement of the cylinder is required to open the valve, but a rotation is possible, or in another embodiment only a slight displacement but in contrast a noticeable rotation. This would mean that the displacement movement per se does not lead to the release of the flow through the throttle, but the rotation coupled with the displacement, in which the throttle grooves come into an overlapping position. The easiest way to do this is to actuate it by moving it linearly.

The function of the arrangement is described with reference to FIGS. 1 and 2. It is assumed that a pressure has built up in the leakage collecting line 13, which leads to the back pressure holding valve 15 opening at a slightly higher pressure. If an injection is now initiated in one of the injectors, this is done, as mentioned above, by opening a control valve which enables a certain amount of fuel (control amount) to flow out of a control chamber of the injector. The outflow occurs on the one hand because the usual injectors

Control chamber is always connected via a throttle to the connection of the injector that is connected to the high-pressure line. On the other hand, an outflow also occurs because when the valve mentioned is opened, a force acting on the valve piston, which with its lower end opens and closes the injection openings, additionally leads to fuel being drawn out of the

Control chamber is pushed out. This opening of the control valve leads to a sudden increase in pressure in the leakage manifold. This increase in pressure opens the back pressure holding valve, the connection of which points to the right in FIGS. 1 and 2 then forms an open line end which reflects the pressure wave arriving from the injector as a vacuum wave. This reflection is mitigated by the throttle device and suppressed if the throttle is dimensioned exactly. For such a maximum suppression of the reflection, the following dimensioning is expedient for the throttle: In the invention, the anti-reflection effect of the throttle occurs when the pressure control valve is open (fuel-conducting). When the pressure control valve is blocked, no fuel flows through the throttle. In the exemplary embodiment, the leakage collecting line has a characteristic impedance of approximately 0.8 bar • ms / mm ³ . The flow coefficient of the throttle is 660 cm ³ / min at 100 bar differential pressure. The above values are based on a round cable cross section of 3 mm ² below

Use of diesel fuel. Accordingly, the single throttle provided in FIG. 2, which is designed as a round bore, has a diameter of approximately 0.4 mm. The length of the choke, which is 1 mm in the example, is chosen based on practical considerations; their length itself is less important for the function as a throttle.

As shown in FIG. 6, the injector 3 has a stroke-controlled valve piston 60, the movement of which is controlled by the pressure in a control chamber 62. If this pressure is reduced by opening a (in the example electromagnetic) control valve 64, the valve piston 60 opens and fuel is injected into the combustion chamber of a cylinder of the internal combustion engine via the injection openings 5.

In the example described so far, the fuel, which is at a pressure suitable for injection, is fed from a pressure accumulator to the injectors. However, the invention is also applicable to other fuel injection systems in which a control quantity in the leakage line causes a pressure surge when controlling the injection. For example, systems are known in which each cylinder is assigned its own pump-injector unit. A pump of this unit may already be supplied with a certain fuel pressure, but this is not sufficient for the injection and is increased by the pump to the required injection pressure. Since the beginning and / or end of the desired injection does not always coincide with the duration of a pump stroke, a control valve leading to a leakage channel is arranged in the injector or in the pump and is blocked during the duration of the desired injection, so that the pump supplies the fuel can promote the injection ports. When the control valve is opened, the fuel delivered by the pump is discharged to the leakage channel. Here, too, there is a pressure surge in the leakage line when opening the control valve, but also when the control valve is already open at the start of a pump stroke.

Claims

claims

I. Fuel injection system (1) for an internal combustion engine, comprising: at least one injector (3) for injecting fuel into a combustion chamber of the engine, the injector having a high-pressure connection (10) via which it is to be supplied with fuel under high pressure Control valve (64) for controlling injections of the injector, wherein a low-pressure connection (12) of the injector is provided for discharging a control amount which arises when controlling the injection, a leakage line (11) which is connected to a fuel return line (17) with the interposition of a Pressure-maintaining valve (15) is connected, which opens in the direction of the fuel return line when a predetermined pressure is exceeded, characterized in that a throttle device (20, 27, 47, 51) is provided in the vicinity of the pressure-maintaining valve (15), which is designed and is arranged that with the pressure holding valve open, a reflection of the pressure coming from the injector C waves is weakened as negative pressure waves.

2. Fuel injection system according to claim 1, characterized in that the throttle device is arranged in the flow direction from the injector to the fuel return line upstream of the pressure control valve.

3. Fuel injection system according to claim 1, characterized in that the throttle device is arranged downstream of the pressure control valve as seen in the flow direction from the injector to the fuel return line.

Fuel injection system according to claim 1, characterized in that the pressure holding valve as a slide valve with one to be derived Overpressure against a preload-displaceable slide (41, 52) is formed, which slides in a guide, at least one groove (47, 51) being provided in at least one of the slide and slide guide elements, and wherein a passage for fuel at one is open defined slide position is formed in that a groove is permeable to fuel, whereas in the

Closed position of the slide one end of the groove is closed by the part (slide guide, slide) of the slide valve in which the groove is not present.

Fuel injection system according to one of the preceding claims, characterized in that a channel forming part of the throttle device is provided in a separate part which can be used in the assembly of the valve or the throttle device.