EP3184802B1 - Fuel injector - Google Patents

Description

The invention relates to a fuel injector of a fuel injection system of an internal combustion engine, wherein the fuel injector comprises a hydraulic coupler having a movable in a coupler body coupler piston and a coupled thereto via a coupler gap also movable in the coupler body working piston, and wherein the coupler gap via at least one filling channel with a is connected outside the coupler body arranged low pressure space.

State of the art

Such a fuel injector is from the DE 10 2009 001 266 A1 known. This fuel injector of a common rail fuel injection system has a hydraulic coupler which has a coupler piston movable in a coupler body and a piston which is also coupled to it in the coupler body via a coupler gap. The coupler gap is connected via a filling channel with a arranged outside the coupler body low pressure space. This filling channel is arranged in the coupler body, that the filling channel is closed during a downward movement of the coupler piston, while the filling channel is opened during an upward movement of the coupler piston. By means of this embodiment, it is to be achieved that the coupler gap is continuously filled with hydraulic fluid during operation of the fuel injector in order to compensate for leaks along the guides of the coupler piston and of the working piston in the coupler body.

From the DE 103 33 699 A1 a fuel injection device with a hydraulic coupler is known, wherein the filling of the filling space via a connecting line, in which a check valve may be arranged.

The invention has for its object to provide a fuel injector with a coupler, wherein the filling of the coupler gap space is improved with hydraulic fluid.

Disclosure of the invention

This object is achieved in that in the region of a connection of the filling channel with the Kopplerspaltraum a one-piece, non-deformable and switching by a change in position valve is arranged, which is designed as a sleeve or disc. This embodiment is based on the finding that with each switching operation in the coupler, a significantly higher pressure than in the surrounding low-pressure space arises. This results in the games on the piston guides of the coupler piston and the working piston in the coupler body to a leakage from the coupler, more precisely from the Kopplerspaltraum out. Since the requirements currently go in the direction of deducting more and more injections per injection cycle for low emissions, there is a Koppler gap with each injection to a Kopplerspaltraeu, which is why a lower output pressure in the coupler is available for the subsequent injection. This leads to a decrease in a possible injection quantity. Although in the injection pauses the coupler gap is basically filled again, but if a large number of injections are discontinued with short intermediate intervals, the coupler gap is more emptied than refilled. This can lead to the total absence of desired injections. Therefore, a hydraulic coupler has a speed limit, with which it can be operated at a required number of injections in dependence on the pressure of the fuel. The inventive design of the coupler a significantly improved refilling is achieved, which significantly improves the speed resistance of the coupler.

In one embodiment of the invention, the valve is designed as a sleeve. Such a sleeve is easy to manufacture and also has a high closing accuracy of the filling channel.

Furthermore, only a very small dead volume is represented by the arrangement of the sleeve within the coupler body on a stepped shoulder of the coupler piston. Furthermore, by a good fit of the sleeve (and the disc discussed later) in the coupler body to close the filling channel of the coupler gap, if at all, increased only very little, which is why the coupler function over other known solutions is improved. In addition, this does not weaken the stiffness of the coupler. It follows that the voltage requirement of the fuel injector for an operation is not increased, from which ultimately a pressure limit of the fuel injector is increased again and the speed stability is improved. During injection pauses, the pressure in the hydraulic fluid chamber is greater than in the coupler gap space, so that the sleeve and the sleeve explained later is pushed away from the inner wall of the coupler body by the pressure in the filling channel and thus a hydraulic connection between the hydraulic fluid chamber and the coupler gap is released. As a result, a very fast refilling is already achieved between partial injections with a quasi-constant or non-deteriorating coupler function.

According to the invention, the outer diameter of the sleeve or the disk is slightly smaller than the inner diameter of the coupler body in the region of the mouth of the filling channel in the coupler gap. Due to this slightly smaller outer diameter of the sleeve or the disc than the inner diameter of the coupler body that is the sleeve or disc in the case of closing flat against the inner wall of the coupler body in the region of the mouth of the filling channel at a higher pressure in the coupler gap than in the low pressure chamber and seals thus reliable from the filling channel. When an actuator of the fuel injector is actuated, a movement of the coupler piston into the coupler gap space results in an immediate buildup of pressure in the coupler, which, as described above, improves the function of the coupler.

According to the invention, the valve can - as already stated - be formed as a disc. With such a trained valve, the same advantageous properties are achieved as with the sleeve.

In a further embodiment of the invention, the valve designed as a sleeve or disk on the outer circumference on a frustoconical portion which cooperates with a corresponding conical wall portion of the coupler body in the region of the mouth of the filling channel in the coupler gap. In such an embodiment, the valve for the switching operation is moved axially. This section may extend in a further embodiment over the entire axial extent of the outer circumference of the sleeve or the disc. In the disc, a channel is also embedded in a development, which connects the two subspaces adjacent to the coupler piston and the working piston with each other.

Preferably, the material of the valve is a metallic material.

Further advantageous embodiments of the invention are described in the drawings, in which an illustrated in the figures embodiment of the invention is described in detail.

Figur 1

eine teilweise Schnittdarstellung eines Kraftstoffinjektors mit einem piezoelektrischen Aktuator und einem hydraulischen Koppler,

Figur 2

eine erste Schaltstellung eines Kopplers mit einem als Hülse ausgebildeten Ventil zur Befüllung eines Kopplerspaltraums,

Figur 3

eine zweite Schaltstellung eines Kopplers mit einem als Hülse ausgebildeten Ventil zur Befüllung eines Kopplerspaltraums,

Figur 4

eine dritte Schaltstellung eines Kopplers mit einem als Hülse ausgebildeten Ventil zur Befüllung eines Kopplerspaltraums,

Figur 5

eine erste Schaltstellung eines Kopplers mit einem als Scheibe ausgebildeten Ventil zur Befüllung eines Kopplerspaltraums,

Figur 6

eine zweite Schaltstellung eines Kopplers mit einem als Scheibe ausgebildeten Ventil zur Befüllung eines Kopplerspaltraums,

Figur 7

eine dritte Schaltstellung eines Kopplers mit einem als Scheibe ausgebildeten Ventil zur Befüllung eines Kopplerspaltraums,

Figur 8

einen Koppler mit einem als Scheibe ausgebildeten Ventil, wobei die Scheibe auf dem Außenumfang einen kegelstumpfförmigen Abschnitt aufweist,

Figur 9

einen Koppler mit einem als Scheibe ausgebildeten Ventil, wobei der Außenumfang der Scheibe insgesamt kegelförmig ausgebildet ist,

Figur 10

einen Koppler mit einem als Hülse ausgebildeten Ventil, wobei der Außenumfang der Hülse insgesamt kegelförmigen ausgebildet ist und

Figur 11

ein Diagramm zum Verlauf eines Injektornadelhubes eines Kraftstoffinjektors

Show it:

FIG. 1

a partial sectional view of a fuel injector with a piezoelectric actuator and a hydraulic coupler,

FIG. 2

a first switching position of a coupler with a sleeve designed as a valve for filling a Kopplererspaltraums,

FIG. 3

a second switching position of a coupler with a sleeve designed as a valve for filling a Kopplererspaltraums,

FIG. 4

a third switching position of a coupler with a valve designed as a sleeve for filling a coupler gap space,

FIG. 5

a first switching position of a coupler with a disk designed as a valve for filling a Kopplererspaltraums

FIG. 6

a second switching position of a coupler with a disk designed as a valve for filling a Kopplererspaltraums,

FIG. 7

a third switching position of a coupler with a disk designed as a valve for filling a Kopplererspaltraums

FIG. 8

a coupler having a disk-shaped valve, the disk having a frusto-conical portion on the outer circumference,

FIG. 9

a coupler with a valve designed as a disk, wherein the outer circumference of the disk is formed overall conical,

FIG. 10

a coupler with a sleeve formed as a valve, wherein the outer circumference of the sleeve is formed a conical overall and

FIG. 11

a diagram for the course of Injektornadelhubes a fuel injector

FIG. 1 shows a fuel injector 1 of a common rail injection system for injecting fuel into a combustion chamber, not shown, of an internal combustion engine. A high-pressure pump 2 conveys fuel from a tank 3 into a high-pressure accumulator 4. In the high-pressure accumulator 4, fuel, in particular diesel fuel, is stored under a high pressure of, for example, 2,000 bar or more. At the high pressure accumulator 4 of the fuel injector 1 is connected in addition to other, not shown fuel injectors via a high pressure line 5. The high-pressure line 5 opens into an axial supply channel 6 belonging to a high-pressure region of the fuel injector 1, through which fuel flows into a pressure chamber 7. During an injection process, the fuel flows from the pressure chamber 7 in the axial direction past an injector needle 8 through injection bores 16 into the combustion chamber of the internal combustion engine. The fuel injector 1 is connected via an injector return port 9 to a return line 10. About the return line 10 may be a subsequently explained control amount Flow fuel from the fuel injector 1 to the tank 3 and are fed from there again to the high-pressure circuit.

The injector needle 8 is guided axially adjustable within a stepped bore 11 of an injector needle body 12. The Injektornadelkörper 12 is clamped in conjunction with a throttle plate and a valve body against a holding body 13 by means of a clamping nut.

The Injektornadel 8 has at its needle tip 15 designed as a sealing surface closing surface with which the Injektornadel 8 is adjustable in a tight contact with a trained within the Injektornadelkörpers 12 Injektornadelkörpersitz. If the Injektornadel 8 rests against the Injektornadelkörpersitz, so is in the closed position, the fuel outlet from the at least one injection hole 16 is locked. By contrast, if the injector needle 8 is lifted off the injector needle body seat, fuel can flow from the pressure chamber 7, which is at least approximately under the pressure of the fuel in the high-pressure accumulator 4, into the combustion chamber.

From a plane in the drawing upper side of the Injektornadel 8 a control chamber 17 is limited, which is supplied via an inlet throttle 18 with fuel under high pressure from the supply channel 6. At the same time, a pressure chamber 14, from which fuel can flow into the combustion chamber when the injector needle 8 is open, is supplied with fuel from the supply channel 6. The pressure chamber 14 encloses a control chamber 17 limiting, spring-loaded sleeve body 32 radially outward. The formed in the sleeve body 32 control chamber 17 is connected via an outlet throttle 19 with a control valve chamber 20 which is connected by means of an axially adjustable control valve element 21 with a low-pressure chamber 22 and thus with the injector return port 9. The control valve element 21 is part of a control valve 23 which is normally designed as a 3/2-way valve. In a control valve element 21 located in a first (lower) switching position, fuel can flow from the control chamber 17 via the outlet throttle 19 and the control valve chamber 20 to the injector return port 9 in the low-pressure region , At the same time an opening out of the pressure chamber 14 and into the control valve chamber 20 opening bypass 35 of the control valve element 21 locked. When in a second (upper) switching position befindliches control valve element 21, the connection between the control valve chamber 20 and the low pressure chamber 22 is blocked and the bypass 35 is released, so that the control chamber 17 via the bypass 35, the control valve chamber 20, the outlet throttle 19 and the inlet throttle 18 is quickly brought to high pressure.

For adjusting the piston-shaped control valve element 21, a piezoelectric actuator 24 is provided, which is coupled via a hydraulic coupler 25 with the control valve element 21. In an alternative embodiment, not shown, the control valve 23 can be actuated directly by the hydraulic coupler 25, more precisely by a working piston 28 of the hydraulic coupler 25 which will be explained below. To open the control valve, so for moving the control valve member 21 in the plane of the drawing down, away from its upper control valve seat 26, the piezoelectric actuator 24 is energized and expands. As a result, an upper in the plane of the drawing, movable coupler piston 27 of the hydraulic coupler, which is hydraulically coupled via a coupler gap 29 with the coupler piston 27, moves in the drawing plane down. The working piston 28 presses on the control valve element 21, which is moved away in the sequence counter to the force of a control closing spring 30 from its upper control valve seat 26 and thus releases the flow of fuel from the control chamber 17 to the injector return port while blocking the bypass 35. By adjusting the flow cross-sections of the pressure in the control chamber 17 decreases rapidly, whereby the injector needle 8 lifts from her Injektornadelkörpersitz so that fuel can flow out of the pressure chamber 7 through the injection hole 16.

To end the injection process, the energization of the piezoelectric actuator 24 is terminated, whereby the piezocrystal stack of the actuator 24 contracts and the coupler piston 27 is supported by the spring force of a Bourdon tube 38 in the drawing plane moves upward. The working piston 28 presses supported by the control closing spring 30 in the plane of the drawing down against the control valve element 21. Between the working piston 28 and the control valve element 21 thus a permanent contact is ensured.

The working piston 28 and the control valve element 21 are moved at not energized actuator 24 upwards into the upper switching position in which the control valve element 21 rests against its upper control valve seat 26 and the hydraulic connection from the control chamber 17 to the injector return port 9 blocks. The fuel flowing in through the inlet throttle 18 and via the bypass 35 into the control chamber 17 ensures a rapid pressure increase in the control chamber 17 and a hydraulic closing force acting on the injector needle 8. The resulting closing movement of the Injektornadel 8 is supported by a closing spring 31 which is supported at one end to the Injektornadel 8 and the second end to a control chamber 17 limiting sleeve body 32.

The following FIGS. 2 to 4 show a first embodiment of the coupler 25 with the arranged in a stepped recess 34 in a coupler body 33 coupler piston 27 and working piston 28 in different switching positions. The coupler piston 27 has a larger outer diameter than the working piston 28 and is thus arranged in the stepped recess 34 with the larger inner diameter. However, the coupler piston 27 may also have a same or smaller diameter than the working piston 28. Between the coupler piston 27 and the piston 28 of the already mentioned Kopplerspaltraum 29 is arranged, which must be filled to transfer an executed by the coupler piston 27 axial movement of the piston 28 with hydraulic fluid in the form of fuel. This will be discussed below. The coupler piston 27 protrudes with an actuation-side end, on which an actuation plate 36 is arranged, out of the coupler body 33 and cooperates with the actuator 24 by means of the actuation plate 36. On the opposite side, the working piston 33 has an actuating nose 37, which - as described above - the control valve element 21 from the control valve seat 26 down ( FIG. 1 ) can press.

To set a defined Ausgangsruhelage and Aktorvorspannung, the coupler 25 has a Bourdon tube 38 which is supported on a lower annular shoulder 39 of the coupler body 33 and the actuator plate 36 and presses apart the two components. At the same time, a retaining ring for a working piston spring 40 is arranged on the working piston 28, the working piston 28th down from the coupler body 33 until the abutment of the actuating lug 37 presses on the control valve element 21. For filling or for refilling the Kopplerspaltraums 29 with fuel from the coupler 25 surrounding low pressure space 22 is preferably a filling channel 41 is inserted into the wall of the coupler body 33. The filling channel 41 is closed in the region of an orifice in the coupler gap 29 by a one-piece undeformable valve which opens in the direction of the coupler gap 29 and is switched by a position change in the form of a sleeve 42. The sleeve 42 has a slightly smaller outer diameter than the inner diameter of the coupler body 33 and the step recess 34. Due to the slightly smaller outer diameter of the sleeve 42, the pressure in the coupler gap 29 at rest is at least approximately equal to the pressure in the low pressure chamber 22 and the sleeve 42 is normally in this state the connection between the coupler gap 29 through the filling channel 41 to the low pressure space freely ( FIG. 2 ). The sleeve 42 is arranged in the region of a stepped shoulder 43 of the coupler piston 27, which saves space and has no effect on the function of the coupler 25. With regard to the arrangement of the sleeve 42 but other solutions are conceivable.

When the actuator 24 is actuated, the movement of the coupler piston 27 into the coupler gap 29 results in a pressure buildup in the coupler 25, which is transmitted to the working piston 28 (FIG. FIG. 3 ). Due to the only slightly smaller outer diameter of the sleeve 42 relative to the inner diameter of the coupler body 33, a small volume flow of fuel from the coupler gap 29 through the filling channel 41 in the low pressure chamber 22 causes and by a pressure drop in the mouth of the filling channel 41 in the coupler gap space 29 the sleeve 42 moves to the mouth of the filling channel 41 and closes the mouth or the filling channel 41. The valve is now closed and the pressure in the coupler gap 29 rises rapidly. In addition, the coupler gap space 29 is only very slightly increased by the exact fit of the sleeve 42, which is why an exact execution of the coupler function is ensured. On the other hand, it is the case that in this operating condition a low leakage from the coupler gap 29 along the coupler piston 27 and the working piston 28 from the coupler gap 29 space.

In FIG. 4 the operating state is shown in which in the injection pauses the pressure in the low pressure chamber 22 is greater or higher than in the coupler gap 29, which is why the sleeve 42 is pushed away by the pressure in the filling channel 41 of the inner wall in the region of the stepped recess 34 and the hydraulic Connection between the low-pressure chamber 22 and the coupler gap 29 space is released. The result is a very rapid refilling between injection processes or partial injection processes of the fuel injector 1 with a quasi-constant, non-decreasing coupler function. This is in the diagram in FIG. 11 , which applies to all embodiments of the valve according to the invention, is shown, wherein in the diagram the resulting needle stroke Nh of successive injections of a fuel injector 1 is reproduced. In this case, the needle stroke Nh of a conventional coupler 25 is shown with a solid line and the needle stroke Nh of a coupler 25 according to the invention is shown with a dashed line. It can be seen that in the second injection, the needle stroke Nh of the injector needle 8 with the conventional coupler 25 is significantly lower than in the first injection. In contrast, the dashed needle lift Nh, which can be represented by the embodiments according to the invention, shows no degradation.

The FIGS. 5 to 7 show an embodiment of the valve as a disc 44. In this case, the disc 44 performs the same function as the sleeve 42. Thus, reference may be made to the sleeve 42 with regard to the functional description.

The FIGS. 8 to 10 show an embodiment of the valve as a sleeve 42a or disc 44a, wherein on the outer periphery in the in FIG. 8 a frusto-conical portion 45 is provided, which cooperates with a corresponding conical wall portion 46 of the coupler body 33 in the region of the mouth of the filling channel 41 in the coupler gap space 29. The filling channel 41 is disposed obliquely in the coupler body 33 and terminates in the wall portion 46. In this and the other following embodiments, the disc 44a and the sleeve 42a is axially moved to close and open the mouth of the filling channel 41. In the disk 44a, a channel 47 is inserted, which connects the two subspaces adjacent to the coupler piston 27 and the working piston 28 with each other.
At the in FIG. 9 and 10 In the illustrated embodiment, the portion 45a extends over the entire axial extent of the outer circumference of the sleeve (42a) or the disc (44a). In this case, the valve in the embodiment according to FIG. 9 formed as a sleeve 42a and the filling channel 41 has a larger diameter. In the embodiment according to FIG. 10 In addition, the filling channel 41 is again arranged at right angles in the coupler body 33. With regard to the function, reference is additionally made to the previous description.

Claims (6)

1. Fuel injector (1) of a fuel injection system of an internal combustion engine, wherein the fuel injector (1) has a hydraulic coupler (25), said hydraulic coupler having a coupler piston (27) which is movable in a coupler body (33) and having a working piston (28) which is coupled to said coupler piston via a coupler gap chamber (29) and is likewise movable in the coupler body (33), and wherein the coupler gap chamber (29) is connected via at least one filling channel (41) to a low-pressure chamber (22) arranged outside the coupler body (33),
   characterized in that a unipartite, non-deformable valve, which switches by way of a positional change, is arranged in the region of a connection of the filling channel (41) to the coupler gap chamber (29), wherein the valve is formed as a sleeve (42) or as a disc (44) and the outer diameter of the sleeve (42) or the disc (44) is only slightly smaller than the inner diameter of the coupler body (33) in the region in which the filling channel (41) opens out into the coupler gap chamber (29), as a result of which a small volume flow of fuel from the coupler gap chamber (29) into the low-pressure chamber (22) through the filling channel (41) is brought about.
2. Fuel injector (1) according to Claim 1,
   characterized in that the valve formed as a sleeve (42) is arranged on a step shoulder (43) of the coupler piston (27).
3. Fuel injector (1) according to Claim 1,
   characterized in that the valve formed as a sleeve (42a) or disc (44a) has, on the outer periphery, a frustoconical section (45) which interacts with a corresponding frustoconical wall section (46) of the coupler body (33) in the region in which the filling channel (41) opens out into the coupler gap chamber (29) .
4. Fuel injector (1) according to Claim 3,
   characterized in that the section (45a) extends over the entire axial extent of the outer periphery of the sleeve (42a) or of the disc (44a).
5. Fuel injector (1) according to Claim 1 or 3,
   characterized in that the disc (44a) has an axial channel (47).
6. Fuel injector (1) according to one of the preceding claims,
   characterized in that the material of the valve is a metallic material.

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