WO2008028706A1 - Arrangement for injecting fuel into cylinder combustion chambers of internal combustion engines - Google Patents

Abstract

An arrangement for injecting fuel into cylinder combustion chambers of internal combustion engines has an injector (11) whose nozzle outlet (13) is supplied with fuel from a high-pressure accumulator (10) (so-called common rail) via a high-pressure line (12). Throttling means are also interposed in the hydraulic connection (12, 14) between the high-pressure accumulator (10) and nozzle outlet (13). An essential peculiarity is that the throttling means are embodied as a return-flow throttling valve (15, 15a), in such a way that a large flow cross section is opened in the flow direction (16) to the injector (11) or to the nozzle outlet (13) thereof, and only a small (throttling) cross section (30) is opened in the opposite direction (20) - for the returning pressure wave.

Description

 description

title

Arrangement for injecting fuel into cylinder combustion chambers of internal combustion engines

State of the art

The invention relates to an arrangement according to the preamble of patent claim 1.

In fuel injections which take place in rapid succession, the respectively following injection is influenced by pressure waves in the injector and the line, which result from previous injections. This results in deviations in the injection quantity. In order not to let the amplitude of the pressure oscillations in the high-pressure system become too great, it is known to arrange throttles at the rail-side (upper) end of the high-pressure accumulator (common rail) leading to the injector high-pressure line.

Although the known throttles damp the amplitude of the pressure oscillations, but also reduce the flow, so that - in particular with a relatively long duration of the driving process of the injector - the respective fuel injection quantity decreases in comparison to an unthrottled system.

The object of the invention is to bring about a significant damping of the undesired pressure oscillations in the high-pressure line without having to accept one disadvantageous flow reduction. Disclosure of the invention

Advantages of the invention

According to the invention, the object is achieved in an arrangement of the initially described

Genus solved by the characterizing features of claim 1.

Advantageous developments of the basic idea of the invention can be taken from the patent claims 2 to 10.

The Rückströmdrosselventil invention has the advantageous effect that in the flow direction to the injector, a large flow cross-section is released. As a result, there is no obstruction of the fuel flow in the direction of the nozzle outlet of the injector. In the reverse direction, however, gives the Rückströmdrosselventil invention for the returning pressure wave only a small throttle cross-section, whereby advantageously returning pressure waves are damped.

In an embodiment of the basic idea of the invention, it is initially conceivable to arrange the return flow throttle valve on the high pressure accumulator side (upper) end of the high pressure line leading to the injector. Due to the time required by the pressure waves in the line system for their propagation, however, damping measures on the rail-side end of the high-pressure line become effective only after a certain time interval of two consecutive fuel injections. However, modern engine applications require very precisely metered injections in short time intervals. A preferred embodiment of the invention therefore provides the Rückströmdrosselventil foot (lower

End) of the riser within the injector body. The Rückströmdrosselventil is thus integrated into the injector itself. This measure provides the significant advantage that the pressure waves already near the place of their formation, namely immediately above the nozzle outlet, are damped, so that the hydraulic damping is fully effective even at short time intervals of the injections. In this way, the fuel

Zumessgenauigkeit at so-called. Combination points significantly improved. There is even the potential to eliminate (previously required) pressure wave compensation.

The great potential of the invention with respect to an improvement of fuel metering accuracy and smoothing of the line pressure curve can be easily determined by commercially available simulation software used for hydraulic simulations.

drawing

In the drawing, embodiments of the invention are shown, which are described in detail below. In detail shows:

1 - in a schematic (partial) representation - a common rail injection system,

2 - also schematically - an embodiment of a Rückströmdrosselventils, in relation to FIG. 1 enlarged view,

3 shows - in a vertical longitudinal section - another embodiment of a Rückströmdrosselventils, in relation to FIG. 1 and 2 greatly enlarged representation,

Fig. 4 - in diagram representation - the stroke of an integrated into an injector

Backflow restrictor (lower diagram) and the injection rate of the relevant injector (upper diagram), in each case plotted over time,

Fig. 5 shows the characteristics of an injector with and without Rückströmdrosselventil in the

Riser, wherein -in each case over time - in an upper diagram, the injection rate and in a lower diagram, the pressure in the connecting line high-pressure accumulator (common rail) / injector is applied, and

Fig. 6 - in diagram form - the fuel injection amount during the

Main injection, plotted against the time ("electrical") distance from the end of the pre-injection to the start of the main injection.

Description of the embodiments

In Fig. 1, 10 denotes a high pressure accumulator (so-called common rail) and 11 an injector of a fuel injection system, particularly for diesel engines. The high-pressure accumulator 10 is connected via a total of 12 numbered high-pressure line to the injector 11, the fuel supplied in a known and therefore not described in detail here way - A -

a nozzle outlet 13 with nozzle needle actuated spray holes (not shown) zuleitet. A running within the injector 11 section 14 of the high-pressure connecting line 12 will be referred to below as "riser".

1, a return flow throttle valve 15 is arranged in the riser 14, at the nozzle outlet side (lower) end thereof, the mode of operation of which essentially follows from FIG. 2 (but in particular also compare the embodiment according to FIG. 3).

To initiate the pilot injection opens the (not shown) nozzle needle of the injector.

Fuel then flows in the high-pressure connecting line 12 or in the riser 14 in the direction of the nozzle outlet 13 (arrow 16 in FIGS. 1 and 2). A by a compression spring 17 in the direction of arrow 20 (ie counter to the flow direction 16) acted upon - in the embodiment of FIG. 2 spherically formed - valve body 18 is moved against the spring force in the direction of arrow 16 and then releases a throttle valve seat 19 so that

Fuel (almost without throttle effect) can reach the nozzle outlet 13. As soon as the nozzle needle closes to complete the preinjection process, a pressure wave directed in the direction of the arrow 20 is created in the riser 14, which presses the valve body 18 of the return flow restrictor 15 into the throttle valve seat 19 so that it only releases a narrow throttle cross section. As a result, further flowing fuel is throttled strongly by the Rückströmdrosselventil 15. In the riser 14 and in the high pressure connection line 12 thus no large pressure fluctuations can occur; the system remains "quiet" (see Fig. 5 and its description below).

Similarly, the process of main injection proceeds. Since hardly any pressure waves are still present in the system from the pre-injection, a reproducible starting state is present, which does not depend on the time interval from the pre-injection. (See also FIG. 6 and the description below.) At the beginning of the injection process, fuel flows in the direction of the nozzle outlet. The Rückströmdrosselventil 15 opens, and the fuel is not appreciably throttled on the way to the nozzle outlet 13. After completion of the main injection process, the outlet nozzles are closed by the nozzle needle. As a result, an increase in pressure occurs at the nozzle outlet 13. Backflowing fuel closes the Rückströmdrosselventil 15. This continues to be greatly throttled back flowing fuel. As a result, omitted in riser 14 and high-pressure connection line 12 large pressure fluctuations; the system remains "quiet". In the above-described processes pre-injection main injection are only examples. The Rückströmdrosselventil invention 15 unfolds its effect in a corresponding manner, for example, even with a double pre-injection and / or a main injection post-injection.

The manner of operation of the variant of a return flow throttle valve which is shown in FIG. 3 and designated overall by 15a substantially corresponds to that of the return flow throttle valve 15 according to FIG. 2, as described above. However, differences exist in the structural design. The Rückströmdrosselventil 15 a has a remote one

Inner bore 21 having valve piston 22 which is guided axially displaceably in a valve housing 23. The guiding function for the valve piston 22 can also be taken over directly by the injector body (numbered 24 in FIG. 1). The valve piston 22 has a spherical end face 25 which cooperates with a conical valve seat 26. Fig. 3 shows the Rückströmdrosselventil 15a in its closed position

(Immediately after completion of a pilot injection or main injection operation), in which the valve piston 22 passes through the return from the nozzle outlet (13, Fig. 1) pressure wave. The closing operation of the Rückströmdrosselventils 15a is supported by a arranged in the stepped bore 21 of the valve piston 22 compression spring 27, which is supported on the rear side of a pressed into the valve housing 23 stop member 28 with continuous, coaxial bore 29 for the stepped bore 21 of the valve piston 22. The maximum displacement s of the valve piston 22 in its open position in which the valve piston 22 comes to rest with its rear end face on the stop member 28, on the one hand by the length of the valve piston 22, on the other hand determined by the mounting position of the stop member 28. The displacement s can be (about) 0.75 mm.

As further apparent from Fig. 3, the valve piston 22 has at its valve seat side (upper) end 25, a throttle bore 30 which is hydraulically connected on the one hand with the stepped bore 21 in the valve piston 22, on the other hand with a bore 31 of the valve housing 23 coaxial therewith. Due to the pressure wave (after closing the injection holes in the

Nozzle outlet 13, Fig. 1) in the direction of arrow 20 back flowing fuel passes through the holes 29 and 21 in the throttle bore 20 of the valve piston 22, where the pressure wave undergoes a strong damping due to the throttle effect. Only then can the fuel pass further through the housing bore 31 into the riser (eg 14, 1 and 2) of the relevant injector (eg 11 Fig. 1). During a fuel injection process (which may be the pilot injection or the main injection or also a post-injection), the valve piston 22 is pressed by the fuel flowing in the direction of arrow 16 against the resistance of the compression spring 27 by the displacement path s against the abutment member 28 and there at the valve seat

26 a corresponding flow area free. The fuel is now - unthrottled - passed into a formed between the outer wall of the valve piston 22 and the inner wall of the valve housing 23 annular space 32 and from there through radial bores 33, 34 in the stepped bore 21 of the valve piston 22. About the bore 29 of the stop member 28 of the fuel finally reaches the spray holes of the

Nozzle outlet (13, Fig. 1).

The characteristics shown in Fig. 4 were determined on an injector with Rückströmdrosselventil (eg 15 or 15a, Fig. 2 and 3) in the riser (eg 14, Fig. 1 and 2). In the curve of the upper diagram indicated as a whole by 35, a curve section 36 marks the pre-injection process and a curve section 37 the main injection process of the relevant injector. The pre-injection extends for a period of (about) 0.15 ms, while for the main injection (about) 20 ms are provided. The injection rate in the pre-injection - with about 30 mmVms - slightly lower than the injection rate achieved in the main injection, about 45 mmVms.

A curve labeled 38 in the lower diagram of Fig. 4 describes the piston stroke of a return flow throttle valve (eg 15, 15a, Fig. 2 or 3) arranged in the riser (eg 14, Fig. 1 and 2). , The curve 38 shows that the Rückströmdrosselventil during the preinjection - curve section 39 - and during the main injection process -

Curve section 40 - (substantially) is open and while the intervening periods - curve sections 41 and 42 - on the other hand assumes a throttle position (closed position with throttle opening).

The upper diagram in FIG. 5 shows the injection rate curve 43 - for an injector

(eg 11 Fig. 1) with Rückströmdrosselventil (eg 15, 15a, Fig. 2 and Fig. 3) in the riser (eg 14, Fig. 1 and 2) in comparison to the injection rate curve - Curve 44 - an injector without Rückströmdrosselventil in the riser. The extensive coverage of the Both curves 43 and 44 make it clear that a Rückströmdrosselventil exerts almost no (adverse) influence on the injection rate of the respective injector in the riser.

In the lower diagram of FIG. 5, curves 45 to 48 illustrate the pressure curve in the high-pressure connection line (12) between high-pressure accumulator (10) and injector (11).

The pressure was measured at curve 45 in the vicinity of the high pressure accumulator (10) and at curve 46 near the injector. The almost complete coverage of the curves 45, 46 and their nearly horizontal / straight course shows that the pressure remains practically identical and almost constant over the entire length of the high-pressure connection line (12), provided that in the riser (14) of the injector (11 ) a Rückströmdrosselventil (15, 15 a) is installed.

Line pressure waves are damped away. The line pressure shows only a slight decrease due to the ejection of the injector, no more "overshoots", which leads to a quieter rail pressure and thus to advantages for the rail pressure regulation.

Curves 47 and 48, on the other hand, illustrate the pressure curve in the high pressure

Connecting line (12) for an injector without Rückströmdrosselventil in the riser. In both cases, a non-constant pressure curve can be observed. Greater pressure rashes occur in the case of near-injection pressure measurement (curve 48), while the pressure excursions decrease near the rail near measurement (curve 47). The pressure excursions are the result of the pressure wave occurring at the nozzle exit (13, Fig. 1) upon closure of the injection holes, which can spread unthrottled in the high-pressure connection line (12) due to the absence of a Rückströmdrosselventils.

FIG. 6 shows the injection quantity obtained at the main injection (at the nozzle outlet 13) as a function of the time interval between the start of the main injection and the end of the injection

Pilot injection. The rail pressure (in the high-pressure accumulator 10) is 1800 bar in each case. The injection quantity of the pilot injection amounts to 2 mm ³ . The length of the high-pressure connecting line (12) is 150 mm and its diameter is 3 mm. Here, curve 49 represents the injection quantity high-pressure injection at an injector without Rückströmdrosselventil, but with throttle at the rail end of the high-pressure

Connecting line (12), and curve 50, the injection quantity main injection at an injector with Rückströmdrosselventil (15, 15 a, Fig. 2 and 3) in the riser (14). As shown by a comparison of curves 49 and 50, the "mass flow" (curve 49) has become substantially to a straight line (curve 50) by the action of placing a return flow restriction valve (15, 15a) in the riser (14). D. h., When changing the distance between the end of Pre-injection and the beginning of the main injection occurs no change in quantity of the second injection more. The readable from the curve 50, only very small injection quantity changes in distance variation are within the Hub-Hub-scattering, even with close successive injections. This advantageous result makes pressure wave compensation (DWK), as required in the prior art, dispensable.

The comparison of the two curves 49, 50 also makes it clear that when a Rückströmdrosselventils (15, 15a) in the riser (14) with the same drive duration (curve 50), the injection amount is even greater than in the absence of a Rückströmdrosselventils (curve 49). A decrease in quantity due to (additional) throttling is therefore not to be feared.

Claims

claims 1. Arrangement for injecting fuel into cylinder combustion chambers of internal combustion engines, with an injector (11), whose nozzle outlet (13) from a high-pressure accumulator (10) via a high-pressure line (12) fuel is supplied, and in the hydraulic connection (12, 14) between High-pressure accumulator (10) and nozzle outlet (13) interposed throttle means, characterized in that the throttle means are formed as Rückströmdrosselventil (15, 15a), such that in the flow direction (16) to the injector (11) or to the nozzle outlet (13) out a large flow cross-section and in the reverse direction (20) - for the returning pressure wave - only a small throttle cross-section (30) is released. 2. Arrangement according to claim 1, characterized in that the Rückströmdrosselventil is arranged at the high-pressure accumulator end of the high-pressure line (12) leading to the injector (11). 3. Arrangement according to claim 1, with an injector body (24) in which a riser (14) is formed, characterized in that the Rückströmdrosselventil (15, 15a) at the foot of the riser (14) within the injector body (24) is arranged (Fig. 1). 4. Arrangement according to claim 1, 2 or 3, characterized in that the Rückströmdrosselventil (15, 15 a) Valve body (18, 22) which on the one hand by spring force (17, 27) - in the closing direction (20) - and on the other hand by the fuel flow during the injection process - in the opening direction (16) - can be actuated, such that during the injection process, a large Opening cross-section and at Returning pressure wave only a small throttle cross-section (30) is released. 5. Arrangement according to claim 3 or 4, characterized in that the valve body (18, 22) of the Rückströmdrosselventils (15, 15a) is guided sealingly in the injector body (24). 6. Arrangement according to one or more of the preceding claims, characterized in that the valve body is designed as a ball (18) (Fig. 2). 7. Arrangement according to one or more of claims 1 to 4, characterized in that the valve body is a substantially hollow cylindrical piston (22) which is axially movably guided in a valve housing (23) (Fig. 3). 8. An arrangement according to claim 7, characterized in that in a stepped bore (21) of the valve piston (22) a valve piston (22) in the closing direction (20) acting on compression spring (27) is arranged, the back on Valve housing (23) or a component connected to this (28) is supported. 9. Arrangement according to claim 7 or 8, characterized in that in the valve housing (23) a the axial displacement (s) of the valve piston (22) in Öffhungsrichtung (16) limiting stop member (28) is sealingly secured and that the stop member (28 ) at the same time to the rear support of the compression spring (27). 10. Arrangement according to one or more of claims 7 to 9, characterized in that at the valve seat-side end of the valve piston (22) - Between the outer wall and the inner wall of the valve housing (23) - an annular channel (32) is formed, which via radial bores (33, 34) with the interior (21 or 29) of the valve piston (22) and the stop member (28) hydraulically connected.