DE10328000A1 - Fuel injection system with reduced pressure oscillations in the return rail - Google Patents

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

The Invention is based on a fuel injection system after the Preamble of claim 1. The pressure holding valve may on a pressure of 0.5 bar relative (i.e., relative to the ambient pressure of the Fuel injection system), and then serves only In addition, the emptying of the at least one injector with a Leakage manifold (= return ramp) connecting leakage line and / or the leakage manifold prevent. In such a system, the injector likes with a electrically operated Solenoid valve be provided that by changing the pressure in a control chamber controls the injection process of the injector. For other fuel injection systems like the pressure relief valve, for example, to a pressure of 30 bar relative be set. In these systems, the injector is generally equipped with a hydraulic coupler by a piezo actuator actuated becomes. The hydraulic coupler is functionally of fuel surrounded, which is under the said pressure of about 30 bar, so that the hydraulic coupler is always functional. In both mentioned Fuel injection systems like the fuel return line directly to the fuel tank lead the internal combustion engine. For a subgroup of the latter fuel injection systems is the end of the pressure relief valve facing away from the injector connected line with a connecting line between a Fuel from the fuel tank to a moderate pressure of z. B. 5 bar lifting first pump and the input of a high pressure pump connected. The invention can be used in the above-mentioned systems.

It is known ( EP 0780 569 B1 . 13B ) to turn on the pressure accumulator a valve in the high pressure line to the injector having a biased by a spring spherical movable valve member. This opens with a flow of fuel to the injector and closes almost completely when no fuel flows. A complete closing is prevented by the fact that the circular in cross-section flow is extended radially behind the valve seat by longitudinally extending grooves which are not covered by the movable valve member. When the valve is closed, the valve thus forms a throttle, which, as can be seen by taking into account the expertise, is suitable for damping the first incoming from the injector forth on the high pressure line pressure wave, and therefore can prevent the emergence of further pressure fluctuations in the high pressure line.

Of the Advantage of the fuel injection system according to the invention according to the claim 1 is that reduces a disadvantage recognized by the inventors or avoided. This disadvantage is due to the following operations: If the injector initiates an injection process, flows a control amount when pressing the above control valve in the leakage line and leads in progress Operation causes the backpressure valve to open and essentially the same size Quantity as the control amount flows through the pressure-maintaining valve. The pour in said control amount causes a flow into the leakage line and solve a pressure wave to the back pressure holding valve back out there at its opening is reflected as a negative pressure wave (reflections of a pressure wave at an open end of line or a pressure node in contrast to a pressure belly done as a vacuum wave). Such Vacuum waves can lead to cavitation, the permanent damage caused at the injector and thereby reduces its life. Cavitation occurs when the vapor pressure of the fuel falls below becomes. It is assumed that the risk of cavitation is greater, the lower the normal pressure in the leakage manifold and thus in the individual leakage lines of the injectors. The danger of cavitation is likely then be especially tall if a vacuum wave then arrives at the control valve, if this just got into the locked state and therefore because of the sudden Interruption of the flow from the control valve out the pressure behind the control valve anyway below the vapor pressure of the fuel. According to the invention to the leakage connection of the injector from the pressure holding valve ago running Low pressure waves attenuated or prevented.

Under indicating that the throttles are near the pressure relief valve should, the following is understood: the distance should not be so great that thereby the effect of the throttle with respect to the suppression of Negative pressure waves interfered with becomes; Furthermore should the leakage quantities of several, preferably all injectors, which communicate with a single pressure holding valve the said throttle flow. The throttle may be in embodiments of the invention seen from the injector forth before the pressure-holding valve be arranged, or behind this, or with the valve element be structurally united the pressure holding valve.

In embodiments of the last-mentioned embodiment of the invention, a slide is provided, which is preferably designed as a solid cylinder, and in a matching recess, in particular bore, against the force of a spring is displaceably guided and must be moved against this spring force, if from the leakage manifold Fuel should escape through the pressure holding valve. At a at least one groove is incorporated in the wall of the cylinder, which is closed at rest of the pressure holding valve through the wall of the bore at its rear end and is open at its front end and at sufficiently far displaced cylinder with its rear end of the Out hole, so that the groove, which also forms a throttle, is a total of continuous. In another modification, the solid cylinder without grooves in its wall, instead of a groove is incorporated in the wall of the bore, which is suitably closed at rest of the valve at its front end of the cylinder surface of the cylinder, while its rear end is always free , and with sufficiently strong displaced cylinder, the front end of the groove is free, 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 is understood that instead of a single groove and multiple grooves can be present.

at All the described embodiments beneficial to the throttle by replacing in general a single part or when selecting a suitable one Part in the assembly of the valve to the conditions in a given Fuel injection system prevail and for every internal combustion engine in the are generally known, adapt. It is supposed to be the Characteristic impedance of the choke, or in the presence of multiple chokes the combination of such chokes (as explained a parallel circuit of chokes, but also a series connection of such chokes is possible) in be properly adapted.

Further Advantages and advantageous embodiments of the invention are the Description, the drawings and claims removed.

drawing

embodiments the injection system according to the invention or injection device are shown with reference to the drawing and explained in more detail in the following description. Show it:

1 an illustration of a fuel injection system according to the invention with a plurality of injectors and a pressure-holding valve, in whose area a throttle is provided;

2 which in the arrangement of 1 provided combination of pressure-holding valve and throttle in the enlarged longitudinal section;

3 a provided in another embodiment of the invention, opposite 2 modified combination of pressure retention valve and throttle;

4 one in another fuel injection system according to the invention instead of the valve arrangement according to 2 and 3 provided arrangement in which a throttle is provided in a wall of a solid cylinder slidably receiving bore,

5 one opposite 4 modified embodiment of a pressure-maintaining 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

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

description the embodiments

In 1 has a fuel injection system 1 , which is provided in the example for diesel fuel, a number of known injectors 3 on (in the example 6 Injectors) which in operation fuel through injection ports 5 (please refer 6 ) inject into the interior of a respective associated combustion chamber of a diesel engine. An accumulator 7 is using fuel under high pressure (in the example 1600 bar) via a line 8th filled. Each with a high pressure line 9 Fuel is a high pressure connection 10 each injector 3 fed. Leakage quantities and control quantities of the injectors, which occur when a control valve is actuated, which controls the injection process of the injectors, are each via a leakage line 11 from a low pressure port 12 a leakage manifold 13 (Leckagerail) supplied. In the example are the injectors 3 such injectors, which are controlled by an electrically operated solenoid valve which, when operated in a known manner, the pressure within a control chamber lowers, whereby the injection process is started. When this control valve opens, fuel exits the control chamber and enters the leakage line 11 one. In the leakage line 13 lead all leakage lines of the injectors shown. An end of the leakage manifold 13 is closed, the other end, in 1 right, is via a pressure relief valve 15 with a return line 17 connected to the fuel, and this return line 17 leads to the fuel tank. From the fuel tank fuel is sucked in a known manner and finally brought by one or more pumps to the high pressure, with which the fuel to the pressure vessel 7 is supplied. The pressure hold Valve 15 opens in the example with an overpressure within the leakage manifold 13 opposite the pressure in the return line 17 of about 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. New compared to the state of the art is in the in 1 shown arrangement that in the vicinity of the counter-valve 15 a throttle device 20 is provided, which serves to unwanted pressure wave reflections in the leakage manifold 13 largely prevent.

2 shows the in 1 provided combination of throttle device and back pressure holding valve as a structural unit 25 , The throttle device is by a single throttle 27 formed in a suitably selectable during assembly block 28 is introduced as a bore. The block 28 is in the flow direction of 1 , So from left to right, upstream of the back pressure holding valve arranged. The construction unit 25 is in the arrangement 1 mounted pressure-tight by screw connections.

In the 3 shown combination 30 backpressure valve and throttle device is different from the 2 merely in that the throttle device is arranged downstream of the actual back pressure holding valve.

The arrangements after 2 and 3 may in embodiments of the invention in a completely similar manner by suitably connecting, for. B. screwing two separately manufactured parts, be realized, namely a component which contains only the throttle bore substantially, and a conventional back pressure holding valve.

In the arrangement according to 4 the throttle and the back pressure holding valve form a unit which can not be separated from each other. The valve arrangement 40 opens again at a back pressure on the in 4 left side opposite to the pressure on the 4 right side. The valve arrangement is designed essentially as a slide valve. A slider 41 (Solid cylinder) is in the longitudinal direction of the substantially circular cylindrical valve assembly 40 guided by a guide surface. This is the slider 41 in a hole 42 a centerpiece 43 against the force of a compression spring 44 displaceable. In the in 4 shown rest position is the slide 41 on a stop device 45 which is formed by a perforated plate and overall does not hinder the flow of the fuel. In the wall of the hole of the part 43 is a longitudinal groove 47 incorporated, which is open to the right, to the left but before the end of the slide 41 ends, so that in the illustrated position of the slider 41 Do not inject fuel from the left into the groove 47 , which simultaneously forms the throttle, can enter. When the pressure on the left side of the 4 so big is that the slider 41 moves sufficiently far to the right, eventually the groove 47 also free at its front end and there fuel can enter and through the groove 47 flow, so that now the valve assembly is open. Functionally, one can see the throttle lying behind the valve opening.

In the 5 shown embodiment of a combination 50 A valve with a throttle differs from the one in 4 shown only in that the throttle forming a groove 51 now on the cylindrical outer surface of the slider 52 is arranged, whereas the bore of the part 54 is smooth. Here is the groove 51 always open to the left and its right end is only then released for a flow through the groove when the slide 54 has shifted far enough to the right. Functionally, one can regard the throttle as lying in front of the valve opening.

In one embodiment, not shown, both a groove 47 according to 4 , as well as a groove 51 according to 5 intended. In this case, the two grooves must not overlap in the locked state of the valve assembly. This embodiment of the valve assembly allows further actuation in such a way that no opening of the valve, no displacement of the cylinder is required, 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 throttling grooves come into an overlapping position. The easiest way should be an operation by linear displacement.

Based on 1 and 2 the function of the arrangement will be described. It is believed that in the leakage manifold 13 has built up a pressure that causes the backpressure valve to be at a somewhat higher pressure 15 opens. If an injection is now initiated in one of the injectors, this is done, as mentioned above, by opening a control valve which allows the outflow of a certain amount of fuel (control quantity) from a control chamber of the injector. The outflow takes place on the one hand because in conventional injectors, the control chamber via a throttle always with that connection of the injector is in communication, which is connected to the high-pressure line. On the other hand, an outflow also occurs because, when the valve is opened, a valve piston which opens and closes the injection openings with its lower end, In addition, acting force causes fuel to be expelled from the control chamber. This opening of the control valve leads to a sudden increase in pressure in the leakage manifold. This pressure increase opens the back pressure holding valve, which in the 1 and 2 to the right-facing terminal then forms an open line end, which reflects the incoming from the injector forth overpressure wave as a vacuum wave. This reflection is mitigated by the throttle device and suppressed in a precisely fitting dimensioning of the throttle. For such a maximum suppression of the reflection, the following design is expedient for the throttle: In the invention, the reflection-preventing effect of the throttle occurs when the pressure-maintaining valve is open (fuel-conducting). When the pressure-retaining valve is locked, no fuel flows through the throttle.

In the exemplary embodiment, the leakage manifold has a characteristic impedance of about 0.8 bar · ms / mm ³ . The flow coefficient of the throttle has a value of 660 cm ³ / min at 100 bar differential pressure.

The above values are based on a round cable cross-section of 3 mm ² using diesel fuel. As a result, the in 2 provided single throttle, which is designed as a round bore, a diameter of about 0.4 mm. The length of the restrictor, which in the example is 1 mm, is chosen for practical reasons; their length itself is less essential for functioning as a throttle.

As 6 shows, points the injector 3 a stroke-controlled valve piston 60 on, whose movement by the pressure in a control chamber 62 is controlled. Is this pressure by opening a (in the example electromagnetic) control valve 64 reduced, so opens the valve piston 60 and it gets over the injection openings 5 Fuel injected into the combustion chamber of a cylinder of the internal combustion engine.

at the example described so far is the one under the injection suitable pressure fuel from a pressure accumulator the Supplied injectors. However, the invention is also in other fuel injection systems applicable, in which when controlling the injection, a control amount caused a surge in the leakage line. Such are, for example Plants are known in which each cylinder has its own pump-unit unit (Unit Pump Injector) assigned. A pump of this unit already likes with a be supplied to certain fuel pressure, but for the injection insufficient and from the pump to the required injection pressure elevated becomes. The beginning and / or end of the desired injection is not always agree with the duration of a pumping stroke is in the injector or arranged in the pump leading to a leakage channel control valve, that while the duration of the desired Injection is locked, allowing the pump to deliver the fuel Injection ports promote can. When the control valve is open is, then the funded by the pump fuel to the leakage channel dissipated. Again, there is a pressure surge in the leakage line when opening of the control valve, but also if at the beginning of a pumping stroke the control valve is already open.

Claims (5)

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, wherein the injector is a high pressure port ( 10 ), via which it is to be supplied with fuel under high pressure, a control valve ( 64 ) for controlling injections of the injector, wherein a low pressure port ( 12 ) of the injector for discharging a control amount, which is obtained in controlling the injection, a leakage line ( 11 ) fitted with a fuel return line ( 17 ) with the interposition of a pressure retaining valve ( 15 ) which opens in the direction of the fuel return line when a predetermined pressure is exceeded, characterized in that in the vicinity of the pressure retaining valve ( 15 ) a throttle device ( 20 . 27 . 47 . 51 ) is provided, which is designed and arranged such that, when the pressure holding valve is open, reflection of pressure waves coming from the injector is attenuated as vacuum waves. Fuel injection system according to claim 1, characterized characterized in that the throttle device in the flow direction from the injector to the fuel return line seen upstream the pressure holding valve is arranged. Fuel injection system according to claim 1, characterized characterized in that the throttle device in the flow direction from the injector to the fuel return line seen downstream the pressure holding valve is arranged. Fuel injection system according to claim 1, characterized in that the pressure-retaining valve as a slide valve with a displaceable by the overpressure against a bias slide slide ( 41 . 52 ), which slides in a guide, wherein at least one groove ( 47 . 51 ) is provided in at least one of the elements slide and slide guide, and wherein a passage for fuel in one defined as open Slider position is formed by a groove for fuel is permeable, whereas in the closed position of the slide one end of the groove is closed by that 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 part of the throttle device forming channel in a separate, during assembly of the valve or the throttle device insertable part is provided.