EP1436498A1

EP1436498A1 - Fuel injector comprising a high-pressure resistant optimized control space

Info

Publication number: EP1436498A1
Application number: EP02748598A
Authority: EP
Inventors: Friedrich Boecking
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2001-06-29
Filing date: 2002-06-19
Publication date: 2004-07-14
Also published as: WO2003004859A1; DE10131631A1

Abstract

The invention relates to a fuel injector for storage-type injection systems on direct injection internal combustion engines. The fuel injector comprises an injector body (1) in which a control space (2) is provided. A nozzle needle/plunger assembly (6) inside the injector body (1) can be actuated by said space. The pressure inside the control space (2) can be relieved by an on-off valve (19), whereby a flow channel (14) runs between the control space (2) and the valve space (20) of the on-off valve (19). A high pressure-side inlet (16) with an integrated throttling element (17) leads into the flow channel/valve space area (14, 20).

Description

Fuel injector with control chamber optimized for high pressure resistance

Technical field

In air-compressing internal combustion engines, storage injection systems are increasingly being used today, which supply the individual fuel injectors assigned to the cylinders of the internal combustion engine with fuel under high pressure. By using a high-pressure storage space (common rail), pressure pulsations in the fuel can be damped, so that the fuel pressure at the individual injection openings of the fuel injectors can be kept almost constant. To control the movement of the nozzle needle, control rooms are integrated into the housing of the fuel injectors, the pressure relief of which allows a nozzle needle to be actuated to release or close injection openings. In general, the control chamber can be acted upon by a high-pressure fuel volume from the high-pressure source via an inlet throttle.

State of the art

EP 0 994 248 A2 relates to a fuel injector with injection course shaping by piezoelectric control of the nozzle needle stroke. A fuel injector includes a cylinder body on which an injection opening is formed. A nozzle needle is movably received in the injector body and moves by a stroke between an open position in which the injection openings are open and a closed position in which the injection openings are closed. A piezoelectric actuator is also accommodated in the injector body, the piezo element of which can be switched back and forth between a switch-on and a switch-off position. The nozzle needle and the piezoelectric actuator are connected to one another via a coupling element in the form of a pressure chamber in such a way that the movement of the piezo element of the piezoelectric actuator is translated into a larger axial stroke movement of the nozzle needle in the injector housing. DE 197 15 234 AI relates to a solenoid-controlled direct injection fuel injector for accumulator injection systems of Mel r cylinder internal combustion engines. In each valve housing, a feed line leads to a spring-loaded nozzle needle, the feed line being able to be shut off by a control piston with a valve function. Furthermore, a nozzle needle is provided which is supported in a spring chamber and presses the nozzle needle onto its needle seat. A control chamber is arranged on the rear side of the control piston under system pressure, a magnetic valve being provided through which the control chamber can be connected to a relief line and, at the same time, the injection line can be shut off by means of a high-pressure valve arranged on the control piston for the supply line leading to the nozzle needle. A throttled line connection is provided as a bypass between the supply line and the relief line, the line connection containing a leakage valve which is operatively connected to the solenoid valve and through which the line connection can be interrupted during the injection.

In both solutions known from the prior art, the control rooms are permanently connected to the high-pressure source via an inlet throttle element connected upstream of them. With regard to the fatigue strength of the injector body of a fuel injector, the permanent application of a very high pressure beyond 1000 bar is unfavorable and can lead to problems over the service life of a fuel injection system.

Presentation of the invention

The advantages that can be achieved with the solution according to the invention can be seen above all in that the high pressure that is permanently applied via the high-pressure source is present at a throttle element that acts as an inlet throttle, which opens into a flow channel from or to the control chamber and the flow channel is significantly less sensitive to one constant high pressure. With regard to the fatigue strength of the fuel injector, it is more favorable to allow high pressures to be advantageously applied to smaller-sized flow cross sections or pressure chambers, the wall thickness of which can be designed more favorably with regard to the high pressure load. As a result, the control chamber integrated into the injector body of a fuel injector can be relieved of a permanent and directly present high pressure level, which is considerably cheaper in terms of the fatigue strength of the injector body compared to the solutions known from the prior art. According to a first embodiment of the solution proposed according to the invention, the inlet throttle is arranged in the opening in the flow channel, which connects the control chamber and a switching valve to one another. The throttle element functioning as an inlet throttle is preferably arranged such that it opens at a distance from a further throttle, which functions as an outlet throttle and is integrated into the control chamber duct. Within this distance, ie this partial length of the flow channel, the fuel flow is able to contact the wall of the flow channel, ie an essentially laminar flow is formed.

In a further embodiment variant of the idea on which the invention is based, the throttle element acting as an inlet throttle can also open into the valve chamber of the switching valve which relieves pressure from the control chamber. The length of the flow channel connecting the valve chamber and the control chamber to one another is dimensioned such that a laminar flow state of the fuel in the flow channel also arises in the second embodiment variant.

In a particularly compact third embodiment variant of the idea on which the invention is based, the throttle element integrated into the flow channel according to the embodiment variants mentioned is connected downstream of the valve chamber of the switching valve which relieves the pressure in the control chamber. According to this embodiment variant, the calming section formed in the flow channel for the fuel flow can be dispensed with, since the throttle element assigned to the control chamber on the outlet side is arranged downstream of the valve chamber of the switching valve. A particularly compact and pressure-resistant injector is therefore possible, since the length of the flow channel between the valve chamber of the switching valve and the control chamber can be kept short.

drawing

The invention is explained in more detail below with the aid of the drawing.

It shows:

1 shows an injector arrangement, the control chamber of which is connected to a valve chamber by a flow channel, with an inlet opening into the flow channel at approximately half its length, FIG. 2 shows an injector design in which the inlet opens into the valve chamber of a switching valve which relieves the pressure in the control chamber and

3 shows a further injector design with the outlet throttle element connected downstream of the switching chamber to relieve pressure in the control chamber.

design variants

FIG. 1 shows an injector arrangement, the control chamber of which is connected to a valve chamber through a flow channel, in which an inlet on the high-pressure side with an integrated throttle element opens approximately at half its length.

The injector body 1 of a fuel injector comprises a control room 2 which is delimited by a control room wall 3 and a control room area 4. A stop 5 is formed on the control chamber surface 4, which is preferably configured as a projection which annularly surrounds a drain / inlet opening of the control chamber 2. An end face 8 of a nozzle needle / tappet arrangement 6 lies opposite the stop 5 on the control chamber surface 4. The nozzle needle / tappet arrangement 6 can be moved up and down in the injector body 1 in the vertical direction in accordance with the double arrow denoted by reference numeral 7. When the pressure in the control chamber 2 is released by actuating a switching valve 19, the end face 8 of the nozzle needle / tappet arrangement 6 moves into the control chamber 2; when pressure is applied to the control chamber 2 in the feed direction 12 of the fuel via an inlet 16 with an integrated throttle element 17, pressure builds up in the control chamber 2, so that the nozzle needle / tappet arrangement 6 moves downwards in the vertical direction and consequently injection openings (not shown) into the combustion chamber Closes internal combustion engine protruding fuel injector end.

The control chamber 2 of the fuel injector as shown in FIG. 1 is connected to a valve chamber 20 of the switching valve 19 via a flow channel 14 penetrating the injector body 1 in the vertical direction.

The flow channel 14, which connects the valve chamber 20 of the switching valve 19 with the control chamber 2 of the injector body 1, is formed in a channel cross section 15. In the illustration according to FIG. 1, a first throttle element 10 adjoining the outlet / inlet opening 9 is let into the flow channel 14. The throttle element 10 is formed in a throttle cross section 11, which is small in comparison to the channel cross section 15 of the flow channel 14. At a first distance 18 from the mungskanal 14 integrated first throttle element 10 opens an inlet 16 from a high pressure source, not shown here. The high pressure source can be a high pressure pump or a high pressure common rail of the fuel injection system. A further throttle element 17 is integrated in the inlet 16 from the high pressure source, the cross section of which is small compared to the cross section of the inlet 16 from the high pressure source. In the illustration of the first exemplary embodiment according to FIG. 1, the first distance 18 between the mouth of the inlet 16 from the high-pressure source in the flow channel 14 is selected such that the mouth of the high-pressure side inlet 16 is approximately half the length of the flow channel 14 between the control chamber 2 and the valve chamber 20 lies.

The flow channel 14, formed in the channel cross section 15, opens below a seat 22 into a valve chamber 20 of a switching valve 19. The switching valve 19 is preferably designed as a 2/2-way valve and comprises a spherically configured valve body 21. The valve body 21 is acted on the one hand by a prestressing element 23 which is supported on the upper wall of the valve chamber 20; actuation of the valve body 21 of the switching valve 19 is possible by means of a transmission element 24, the end face 25 of which rests on the peripheral surface of the valve body 21. The transmission element 24 can be moved in the vertical direction in the direction of the double arrow 26 shown in FIG. 1, for which purpose a piezoelectric actuator, a solenoid valve or a mechanical / hydraulic translator can preferably be used. From the valve chamber 20, which surrounds the spherically configured valve body 21, the pretensioning element 23 and the transmission element 24, a leakage oil drain 27 branches off at a branch point 28, via which a control volume flowing into the valve chamber 20 via the flow channel 14 leaves the control chamber 2 when the pressure in the control chamber 2 is released ,

If the valve body 21 of the switching valve 19 is placed in its seat 22 formed in the injector body 1, fuel flows in the inflow direction 12 in the direction of the control chamber 2 formed in the injector body 1 via the inlet 16 on the high-pressure side and the throttle element 17 integrated therein. The throttle element accommodated in the flow channel 14 10 acts as a further inlet throttle in the feed direction 12 of the fuel in relation to the control chamber 10. Pressure builds up in the control chamber 2, so that the end face 8 of the nozzle needle / plunger arrangement 6 is pressurized and the nozzle needle / plunger arrangement 6 can be moved into its closed position.

In order to relieve the pressure in the control chamber 2, the spherically configured valve body 21 of the switching valve 19 is actuated from its injector body 1 after an appropriate actuation of the transmission element 24 by an actuator (not shown here). drove the seat 22. From the control chamber 2, via the outlet / inlet opening 9, the throttle element 10, which acts as an outlet throttle in the flow direction 14 of the fuel, acts as an outlet throttle and then enters the flow channel 14. In this case, the throttle 17 accommodated in the high-pressure side inlet 16 and integrated therein acts as a leakage-reducing throttle element, since only a small part of the outflowing control volume can flow through it. When the valve body 21 of the switching valve 19 is open, that is to say from its seat 22, the control volume flows through the channel cross section 15 into the valve chamber 20 of the switching valve 19. Advantageously, the mouth of the inlet 16 on the high-pressure side is arranged at a first distance 18 with respect to the throttle element 10 integrated in the flow channel 14, so that, seen in the drain direction 13 of the fuel, fuel flow emerging from the throttle element 10 acting as an outlet throttle to the Wall of the flow channel 14 creates.

The illustration according to FIG. 2 shows an injector structure in which the inlet directly opens into the valve chamber of a switching valve that relieves the pressure in the control chamber.

According to this second embodiment variant of the idea on which the invention is based, the control chamber 2, which actuates the nozzle needle / tappet arrangement 6, and the valve chamber 20 of the switching valve 19 are connected to one another via a flow channel 14, in which a throttle element 10 is accommodated. Analogously to the illustration according to FIG. 1, the throttle element 10 is located in the flow channel 14 directly behind the outlet / inlet opening 9, which is enclosed in the control chamber 2 by an annularly configured stop surface 5.

According to this embodiment variant, a housing-side seat 30 of the spherical valve body 21 of the switching valve 19 is formed in the upper region of the valve chamber 20; the biasing element 23 is supported on the bottom of the valve chamber 20 and acts as a restoring element on the spherically configured valve body 21. In the second embodiment variant according to FIG. 2, the transmission element 24 is enclosed by an annular gap 31, via which the valve chamber 20 has entered, via the flow channel 14 controlled control volume flows into the drain oil drain.

In contrast to the first embodiment variant shown in FIG. 1, in the second embodiment variant according to FIG. 2, the inlet 16 on the high-pressure side with an integrated throttle element 17 is arranged to open into the valve chamber 20 of the switching valve 19. The inlet 16 on the high-pressure side opens at a second distance 32 with respect to the position of the throttle element 10 in the flow channel 14. Also in this second embodiment the flow channel 14, which connects the valve chamber 20 to the control chamber 2, can be flowed through by fuel both in the feed direction 12 with respect to the control chamber 2 and in the drain direction 13 when the pressure in the control chamber 2 is released by opening the valve body 21, preferably as 2/2 2-way valve procured switching valve 19. According to the variant shown in Figure 2, the second distance 32 between the mouth of the high-pressure side inlet 16 into the valve chamber 20 and the throttle element 10 provided in the flow channel 14 is dimensioned so that a laminar flow state, ie a Applying the fuel flow to the wall of the flow channel 14 adjusts.

Both of the embodiment variants shown in FIGS. 1 and 2 have in common that the inlet 16 on the high-pressure side opening into the flow channel 14 or the valve chamber 20 from a high-pressure source, not shown here, serves as a leak-reducing element in the discharge direction 13 when the control chamber 2 is depressurized. This is because a throttle element 17 is integrated in the high-pressure side inlet 16, the flow cross-section of which is dimensioned much smaller than the channel cross-section 15 of the flow channel 14. In the drainage direction 13, the integrated throttle element 17 of the high-pressure side inlet 16 acts in each case as a leakage-reducing throttle element; In both embodiment variants, the first throttle 10 integrated in the flow channel 14 acts as a second inlet throttle, which is connected downstream of the throttle 17 integrated in the inlet 16 on the high-pressure side. In the drain direction 13, the throttle element 10 integrated in the flow channel 14 acts as an outlet throttle for the control chamber 2.

According to a third injector embodiment variant which can be seen in FIG. 3, an outlet throttle element is integrated in a leakage oil outlet branching off from the valve chamber of a switching valve.

A particularly compact, high-pressure-resistant fuel injector can be realized with the embodiment variant shown in FIG. In this third embodiment variant of the idea on which the invention is based, the control chamber 2 and the valve chamber 20 of the switching valve 19, which is preferably configured as a 2/2-way valve, are connected via a flow channel 14, which both in the inflow direction 12 and in the outflow direction 13 in Fuel can flow through with respect to the control chamber 2. Halfway along the flow channel 14, a high-pressure inlet 16 opens into it, in which a throttle element 17 is integrated. In the feed direction 12 of the fuel into the control chamber 2, the integrated throttle element 17 functions as a feed throttle; with pressure relief of the control room 2, however, as a leakage reducing throttle element. In contrast to the embodiment variants of the invention shown in FIGS. 1 and 2 the underlying idea is that a downstream flow restrictor element 40 is installed in the leakage oil branch 27 from the control chamber 2. In the third embodiment variant of the idea on which the invention is based, the distance predetermined by the first distance 18 according to the first embodiment variant or by the second distance 32 according to the second embodiment variant, which serves as a calming section for the fuel flow, is no longer necessary, since that throttle element 10 provided in flow channel 14 according to these embodiment variants has been dispensed with and is let into leak oil drain 27. As a result, the length of the flow channel 14 between the valve chamber 20 and the outlet / inlet opening 9 of the control chamber 2 can be made shorter, since the distances 18 and 32 required to calm the fuel flow have been eliminated. The structure of the switching valve 19 according to the third embodiment variant shown in FIG. 3 of the idea on which the invention is based essentially corresponds to that of the switching valve 19 according to the first embodiment variant shown in FIG.

Claims

claims

1. Fuel injector for accumulator injection systems on direct-injection internal combustion engines with an injector body (1) in which a control chamber (2) is formed, with which a nozzle needle / tappet arrangement (6) in the injector body (1) can be actuated and with a switching valve (19 ), via which the control chamber (2) can be relieved of pressure and into the valve chamber (20) of which a flow channel (14) connecting the control chamber (2) and the switching valve (19) opens, characterized in that an inlet (16) on the high-pressure side also Integrated throttle element (17) opens into the flow channel / valve space area (14, 20).

2. Fuel injector according to claim 1, characterized in that the flow channel (14) in the feed direction (12) of the fuel and in the drain direction (13) of the fuel can be acted upon.

3. Fuel injector according to claim 1, characterized in that the flow channel (14) via an outlet / inlet opening (9) with the channel cross-section (15) of the flow channel (14) cross-sectional area opens into the control chamber (2).

4. Fuel injector according to claim 1, characterized in that in the flow channel (14) a throttle element (10) is received, which acts in the drain direction (13) of the fuel as a discharge throttle and in the feed direction (12) of the fuel as a second feed throttle.

5. Fuel injector according to claim 4, characterized in that the high-pressure side inlet (16) opens at a first distance (18) from the throttle element (10) of the flow channel (14) into the flow channel (14).

6. Fuel injector according to claim 4, characterized in that the high-pressure side inlet (16) opens at a second distance (32) from the throttle element (10) of the flow channel (14) into the valve chamber (20) of the switching valve (19).

7. Fuel injector according to claims 1 and 4, characterized in that the integrated throttle element (17) of the high-pressure side inlet (16) in the discharge direction

(13) of the fuel from the control chamber (2) has a leak-reducing effect.

8. Fuel injector according to claim 1, characterized in that the throttle element (10) is connected downstream of the switching valve (19) in the leakage oil outlet (27) branching off from the valve chamber (20) of the switching valve (19).

9. Fuel injector according to claim 1, characterized in that the switching valve (9) is designed as a 2/2-way valve, the valve body (21) via a biasing element (23) which is supported on the wall of the valve chamber (20) and can be moved into or out of its seat (22, 30) by means of a transmission element (24) which can be actuated by an actuator.