EP1654453A1

EP1654453A1 - Injector for fuel injection systems of combustion engines, particularly direct injection diesel engines

Info

Publication number: EP1654453A1
Application number: EP04738750A
Authority: EP
Inventors: Sebastian Kanne; Godehard Nentwig
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2003-08-07
Filing date: 2004-06-22
Publication date: 2006-05-10
Also published as: WO2005014995A1; DE10336327A1; US20080163852A1; JP2007506897A; DE10336327B4; KR20060060675A

Abstract

An injector for fuel injection systems of combustion engines, particularly direct injection diesel engines, comprises a piezo actuator (16), which is placed inside an injector body (10) and which, via first spring means (35), is held in contact with the injector (10) and with a sleeve-like intensifier plunger (33). In addition, a nozzle body (20) is provided, which is connected to the injector body (10), has at least one nozzle discharge opening (26, 27), and inside of which a graduated (first) nozzle needle (21) is guided in an axially displaceable manner, and (second) spring means (54) are provided, which are placed inside the intensifier plunger (33) and which, together with the injection pressure acting on the rear side on the (first) nozzle needle (21), hold the (first) nozzle needle (21) in the closed position. In addition, the injector comprises an (outer) control space (47), which is formed at the nozzle needle-side end of the intensifier plunger (33), and which is connected, via at least one leakage gap, to a fuel supply (18) that is under injection pressure. The (first) nozzle needle (21) is displaced in the opening direction (36) by the fuel located inside the control space (47).

Description

INJECTOR FOR FUEL INJECTION SYSTEMS OF INTERNAL COMBUSTION ENGINES. ESPECIALLY OF DIRECT INJECTING DIESEL ENGINES

State of the art

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

An injector of the aforementioned type is the subject of (not previously published) DE ... (R.305 558). Advantages of this known injector are in its comp. uncomplicated construction (few individual parts) and direct control of the nozzle needle by the piezo actuator. The speed of the nozzle needle movement can be set via the voltage curve of the piezo actuator. In addition, the known injector is characterized in that it does not require a fuel return.

Advantages of the invention

The object of the present invention is to comp. simple means to create a way to gradually control and actuate the nozzle outlet.

According to the invention the object is achieved in an injector of the type described in the introduction by the characterizing features of patent claim 1. - 9 -

Advantageous refinements of the basic idea of the invention are contained in claims 2-9.

The invention advantageously makes it possible to actuate the nozzle outlet in stages by driving the two nozzle needles one after the other - by correspondingly applying voltage to the piezo actuator. The system according to the invention also has the advantage of not requiring a return.

DRAWING An exemplary embodiment of the invention is shown in the drawing and is described in detail below. It shows (each schematically):

1 shows an embodiment of a directly controlled common rail injector with a piezo actuator, in a vertical longitudinal section,

2 shows a lower part of the injector according to Mg. 1, in an enlarged view compared to FIG. 1, and

Fig. 3 - in a diagram - the force applied by the piezo actuator to the converter pistons, plotted over the stroke of the piezo actuator.

Description of the embodiment

1 and 2, 10 denotes a cylindrical injector body with a continuous recess 11, which is cylindrical over the major part of its longitudinal extent. At its upper end, the recess 11 initially has a conically tapering section 12, which merges into a section 13, 14 which is bent at a right angle and finally opens outwards. In the cylindrical section of the recess 11, which is numbered 15, a likewise cylindrical piezo actuator 16 is arranged with a comparatively large longitudinal extent, the diameter of which is smaller than the inside diameter of the recess section 15. This results in an annular space 17 between the outer wall of the piezo actuator 16 and the inner wall of the injector body 10 The conical section 12 of the axial recess 11 is used for centering the piezo actuator 16 within the injector body 10, and secondly, if necessary, fluid-permeable spacers (not shown) can be provided in the annular space 17 at certain axial distances from one another.

The upper, angled section 13, 14 of the recess 11 functions as a cable duct for the power supply of the piezo actuator 16. At the upper end of the injector body 10 there is a fuel supply 18, e.g. High-pressure connection of a common rail system is provided, which is in hydraulic connection with the annular space 17 via a pressure channel 19.

At the lower end of the injector body 10 and coaxially with it, there is a nozzle body 20 which receives a first nozzle needle 21. The nozzle body 20 is fastened to the injector body 10 by means of a union nut (clamping nut) 22 in such a way that it comes into sealing contact with a rear end face 23 on a lower end face 24 of the injector body 10.

In order to receive the first nozzle needle 21, the nozzle body 20 has an interior 25 that is open at the top and has multiple steps, the one below j _nm forms several nozzle outlet bores 26 to 29 opening out of the conical valve seat 30.

At its upper end, the first nozzle needle 21 has a section 31 of larger diameter, which is fitted into a cylindrical interior 32 of a sleeve-shaped, downwardly open booster piston 33. The upper end of the booster piston 33 is formed by a collar 34. A helical compression spring 35, which is arranged in the annular space 17 - here enclosing the booster piston 33 - is supported on the one hand on the end face 23 of the nozzle body 20 and on the other hand on the collar 34 of the booster piston 33 the piezo actuator on the front. Due to the pressure acting on the piezo actuator 16 in the direction of arrow 36 from the compression spring 35 via the booster piston 33, the top side 37 of the piezo actuator 16 is sealed against the injector body 10, and the electrical connection (not shown) can thus be made through the angled bores 13, 14 be led out of the injector body 10.

A special feature - particularly evident from FIG. 2 - consists in the fact that the first nozzle needle 21 has a continuous, concentric axial recess 39 which is stepped by a shoulder 38 and in which a second nozzle needle 41, which is likewise stepped by a shoulder 40, is axially displaceably fitted.

In the lower part of the nozzle body 20 - as part of the nozzle body interior 25 - a cylindrical pressure chamber 42 concentrically surrounding the first nozzle needle 21 is formed, which has holes 43, 44 in the nozzle body 20 and one between the nozzle body 20 and the nozzle body

Clamping nut 22 formed annular space 45 is hydraulically connected to the annular space 17 of the injector body 10. The interior 25 of the nozzle body 20 has a stepped diameter widening 46 at the top, in which the booster piston 33 is guided such that a first control chamber 47 formed in the widened interior part 46 below the booster piston 33 has a leakage gap 48 (see in particular FIG. 2). is in hydraulic connection with the annular space 17 of the injector body 10. A section 49 of the nozzle body interior 25 with a comparatively small diameter serves to guide the first nozzle needle 21 within the nozzle body 20. This guide fit 49 is also designed in such a way that a leakage gap results. The first control chamber 47 is thus hydraulically connected to the cylindrical chamber 42 via the second leakage gap 49, which in turn is subjected to high pressure from the annular chamber 17 of the injector body 10 via the recesses 43 to 45. The interior 32 of the booster piston 33, which extends above the nozzle needle 21, is also hydraulically connected to the high-pressure annular space 17 of the injector body 10, specifically via a lateral bore 50 in the booster piston 33. The upper (thickened) section 31 of the first nozzle needle 21 is thus in the Translator piston 33 guided that there is a (further) leakage gap 51 (see FIG. 2). A hydraulic connection between the first control chamber 47 and the pressurized annular chamber 17 of the injector body 10 is thus also established via this (third) leakage gap 51.

Another peculiarity is that within the

Axial recess 39 - between the shoulder 38 and the shoulder 40 of the second nozzle needle 41 - a (second) inner control chamber 52 is formed, which is in hydraulic connection with the first (outer) control chamber 47. The second (inner) control space 52 has a smaller volume than the first (outer) control space 47. The hydraulic connection of the two

Control rooms are provided through a bore 53 which penetrates the first nozzle needle 21 obliquely in the region of its shoulder 38. As can furthermore be seen in particular from FIG. 2, a (second) helical compression spring 54 is arranged in the interior 32 of the booster piston 33 and exerts a force directed in the closing direction (arrow 55) on the first nozzle needle 21. The (second) compression spring 54 keeps the first nozzle needle 21 closed during the breaks between the injection processes and when the vehicle is at a standstill. 1 and 2, the opening position of the two nozzle needles 21 and 41 is shown. In this position, an injection process takes place, in which all the outlet openings - in the example shown, the bores 26 to 29 - are involved. Here, fuel passes from the cylindrical pressure chamber 42 through the outlet bores 26 to 29 into the cylinder combustion chamber (not shown) of the internal combustion engine.

The first control chamber 47 formed at the lower end of the booster piston 33 serves for hydraulic length compensation and as a hydraulic booster for the expansion movement of the piezo actuator 16 with respect to the first nozzle needle 21.

1 and 2 (in particular FIG. 2) also make it clear that the (upper) end of the second nozzle needle 41 on the piezo actuator side is acted upon by third spring means 56 arranged in the interior of the booster piston 33 in the direction of the closed position (arrow 55). The third are

Spring means 56 around a helical compression spring, which is arranged concentrically with and encompassed by the second spring means (helical compression spring 54) and is supported on the one hand on the second nozzle needle 41, and on the other hand on the piezo actuator-side (upper) end of the booster piston interior 32. For this purpose, a shoulder 57 is formed at the (upper) end of the second nozzle needle 41 on the piezo actuator side, to which a pin part 58 with a smaller diameter is connected, on which the helical compression spring 56 is arranged. As can further be seen in particular from FIG. 2, the axial recess 39 of the first nozzle needle 21 penetrated by the second nozzle needle 41 has a diameter widening in its (lower) region on the nozzle outlet side. This creates an annular cylindrical cavity 59 surrounding the (lower) area of the second nozzle needle 41 on the nozzle outlet side. A radial bore 60 is machined into the first nozzle needle 21 and hydraulically connects the cylindrical pressure chamber 42 to the annular cylindrical cavity 59.

A further special feature is that the (lower) end region 61 of the nozzle body 20 containing the nozzle outlet openings 26 to 29 and the end sections 62, 63 of the two nozzle needles 21 and 41, each functioning as a closing body, are conical, so that complete the end sections 62, 63 of the nozzle needles 21 and 41 in the common closed or open position (FIGS. 1 and 2) to form a uniform conical surface. The nozzle outlet openings 26 to 29 and the conical end sections 62, 63 of the two nozzle needles 21 and 41 are matched to one another in terms of their dimensions and their position so that the two radially inner nozzle outlet openings 26, 27 extend from the conical end section 63 second nozzle needle 41 are actuated and the two radially outer nozzle outlet openings 28, 29 with the conical end portion 62 of the first

Interact nozzle needle 21.

The injector described above works as follows: The piezo actuator 16 is deenergized during spray breaks. If the piezo actuator 16 is now electrically controlled, it expands and moves it

Translator piston 33 against the force of the springs 35, 54 and 56 (in the direction of arrow 55) down. The volume of the control rooms 47 and 52 decreases and the pressure in the control rooms 47, 52 increases. Thereby a force in the opening direction (arrow 36) is exerted on the two nozzle needles 21 and 41. As soon as the opening force exceeds the closing pressure and spring forces, that nozzle needle moves in the opening direction (arrow 36) that requires less opening force. In the exemplary embodiment shown in FIGS. 1 and 2, this is the second (inner) nozzle needle 41. This is because the pressure surface facing the combustion chamber of the internal combustion engine is smaller than that of the first (outer) nozzle needle 21. As soon as the second (inner) nozzle needle 41 opens, the pressure in the control rooms 47, 52 does not decrease further. After a short stroke (approx. 0.1 mm, depending on the hydraulic flow), the second nozzle needle 41 strikes its upper stop, the pin part 58 coming into contact with the inner (upper) end face of the booster piston 33. In order to now also move the first (outer) nozzle needle 21 into its open position (FIGS. 1 and 2), a (further) increase in the electrical voltage applied to the piezo actuator 16 is required. As a result, the piezo actuator 16 expands again in the axial direction (arrow 55) to such an extent that the first nozzle needle 21 now also moves into the open position (FIGS. 1 and 2) and opens the nozzle outlet openings 28, 29. As a result of the path translation caused by the booster piston 33, the first nozzle needle 21 is able to carry out a maximum stroke which is clearly above the stroke of the piezo actuator 16. (Since the first nozzle needle 21 is supplied with fuel from the inside and outside, the stroke can be significantly less than 200 μm.) As soon as the nozzle needles 21, 41 have left the stroke region of the seat throttle, they are pressure-balanced. The piezo actuator 16 then has to keep the pressure in the control chambers 47, 52 only above the high pressure (rail pressure) of the fuel supplied at 18 (FIG. 1) via the booster piston 33 so that the resistances of the springs 35, 54 and 56 can be overcome. The longest possible activation period is determined by the leakage from the control rooms 47, 52. If the pressure in the control rooms 47, 52 drops to the rail pressure, the nozzle needles 21, 41 close. To actively close the nozzle needles 21, 41, the electrical voltage applied to the piezo actuator 16 must be reduced to zero. The piezo actuator 16 then contracts, and the pressure in the control rooms 47, 52 drops below the rail pressure. As a result, the nozzle needles 21, 41 experience closing forces, move in the direction of the arrow 55 and close the nozzle outlet openings 26 to 29. The first (outer) compression spring 35 prevents the piezo actuator 16 from separating from the booster piston 33.

In the exemplary embodiment shown in FIGS. 1 and 2, the volumes of the control chambers 47, 52 and the surfaces of the nozzle needles 21, 41 acted upon by the control chamber pressures or by the pressure of the fuel supply 18, 19 or by the spring medium pressure are coordinated such that the two nozzle needles 21, 41 open in succession by changing the electrical voltage applied to the piezo actuator 16 and can be closed simultaneously by removing the voltage from the piezo actuator 16.

In the following, a simple calculation example shows which

Forces and what services are required to perform the functions described:

With an outer diameter of the second (inner) nozzle needle 41 of 1.7 mm (seat diameter: 1.6 mm) at 1600 bar rail pressure 321 N are required to move the second nozzle needle 41 into the open position (FIGS. 1 and 2). With a stroke ratio of 4: 1 for the second nozzle needle 41, this corresponds to 1284 N piezo force, plus the spring forces. As soon as the second nozzle needle 41 is opened a few micrometers, the necessary (further) opening force decreases very strongly, since the pressure at the bottom of the needle increases. When the second nozzle needle 41 has reached its full stroke - 0.08 mm is sufficient because the radially inner nozzle outlet openings 26, 27 have the smaller hydraulic flow in this example - the piezo actuator 16 has been extended by 0.02 mm (neglecting the leakage losses and compressibility). In order to open the first (outer) nozzle needle 21 with an inner diameter (= inner seat diameter) of 2.0 mm and an outer diameter of 2.8 mm, a force of 482.54 N is required. With a stroke ratio of 1: 3, this corresponds to a force of 1450 N on the piezo actuator 16. This force is higher than the opening force of the second (inner) nozzle needle 41.

(If the stroke ratio for the first and the second nozzle needle (21 or 41) is selected differently, if necessary, it can also be achieved that first the first (outer) nozzle needle (21) and only then the second (inner) nozzle needle ( 41) opens.)

In order to achieve the necessary opening stroke of the first nozzle needle (21) of 0.15 mm - more is not necessary since the first nozzle needle (21) is supplied with fuel from the inside and outside - the piezo actuator (16) has to be turned again by 0 .05 mm long. This results in a necessary total stroke of the piezo actuator (16) of approximately 0.075 mm in this example, plus losses of leakage and compressibility. Assuming that a total of a further 0.025 mm piezo actuator stroke is required to compensate for the losses, a piezo actuator can be used, which can be seen in FIG

64 designated force-distance-KutNe fulfilled, can be used. If the seat angle is increased and the necessary strokes of the first and second nozzle needles (21 and 41) are made somewhat narrower, significantly lower values for maximum force and stroke can also be achieved. For example, with a seat angle of 90 ° (in the embodiment shown in FIGS. 1 and 2, the seat angles are somewhat smaller than 90 °), the second (inner) nozzle needle 41 would only have a stroke of 60 μm and the first (outer) nozzle needle 21 only need a stroke of 100 μm. This would result in a significantly smaller maximum stroke of the piezo actuator 16 of only 80 μm (s curve 65 in FIG. 3) with the same transmission ratios and the same surcharge for leakage.

Claims

1.Injector for fuel injection systems of internal combustion engines, in particular of direct-injection diesel engines, with a piezo actuator (16) arranged in an injector body (10), which via first spring means (35) on the one hand with the injector body (10) and on the other hand with a sleeve-like booster piston ( 33) is held in contact with a nozzle body (20) connected to the injector body (10) and having at least one nozzle outlet opening (26 - 29), in which a stepped (first) nozzle needle (21) is guided so as to be axially displaceable arranged inside the booster piston (33) are second spring means (54) which - together with the injection pressure acting on the rear of the (first) nozzle needle (21) - hold the (first) nozzle needle (21) in the closed position and with one at the end of the booster piston on the nozzle needle side (33) trained (outer) control chamber (47), which is at least under one injection gap and under injection pressure n fuel supply (18) is connected, the (first) nozzle needle (21) being acted upon by the fuel in the (outer) control chamber (47) in the opening direction (55), and the (first) nozzle needle (21) having a rear region (31), which has a larger diameter than a region on the nozzle outlet side of the (first) nozzle needle (21), is fitted into the interior (32) of the booster piston (33), characterized in that the first nozzle needle (21) is one has a continuous, concentric axial recess (39) stepped by a shoulder (38), in which a second nozzle needle (41), which is likewise stepped by a shoulder (40), is axially displaceably fitted, that within the axial recess (39) - between the shoulder (38) and the shoulder (40) of the second nozzle needle (41) - a (second) inner control chamber (52) is formed, which is in hydraulic connection with the outer (first) control chamber (47), and that the control chamber volumes and the The control chamber pressures or the pressure of the fuel supply (18, 19) or the surfaces of the nozzle needles (21, 41) acted upon by the spring mean pressure are so matched to one another that the two nozzle needles (21, 41) change by changing the values on the piezo actuator (16 ) open the applied voltage one after the other -

2. Injector according to claim 1, characterized in that the surfaces of the second nozzle needle (41) pressurized with liquid are designed in relation to the surfaces of the first nozzle needle (21) pressurized with liquid so that the second nozzle needle (41) is already at a comp. low control chamber pressure (cf. low piezo actuator voltage), the first nozzle needle (21), however, only when cf. high control room pressure (cf. high piezo actuator voltage) can be opened.

3. Injector according to claim 1 or 2, characterized in that the two control spaces (47, 52) are hydraulically connected to one another by a bore (53) penetrating the first nozzle needle (21).

4. Injector according to one or more of the preceding claims, wherein the interior (32) of the booster piston (33) with the fuel supply (18) is hydraulically connected, characterized in that the piezo actuator-side (upper) end of the second nozzle needle (41) from im The third spring means (56) arranged inside the booster piston (33) is acted upon in the direction of the closed position (arrow 55).

5. Injector according to claim 4, wherein as the first nozzle needle (21) in the closing direction (arrow 55) acting spring means a helical compression spring (54) is arranged coaxially to the first nozzle needle (21) and on the one hand on the rear end face, on the other hand supports the (upper) end of the translator piston interior (32), characterized in that the third spring means are also a helical compression spring (56) which is arranged concentrically with the second spring means (helical compression spring 54) and is enclosed by them and on the one hand adjoins the second nozzle needle (41) on the other hand on the piezo actuator-side (upper) end of the translator piston interior (32).

6. Injector according to claim 5, characterized in that at the piezo actuator-side (upper) end of the second nozzle needle (41) a shoulder (57) is formed, which is followed by a pin part (58) with a smaller diameter, and that as the third spring means Acting helical compression spring (56) is arranged on the pin part (58).

7. Injector according to one or more of the preceding claims, wherein in the region of the nozzle body (20) on the nozzle outlet side, a cylindrical pressure chamber (42) concentrically surrounding the first nozzle needle (21) is formed, which is connected to the fuel supply (18) under injection pressure (high pressure). is hydraulically connected, characterized in that the axial recess (39) of the first nozzle needle (21) penetrated by the second nozzle needle (41) has a diameter widening in its (lower) area on the nozzle outlet side, such that a region on the nozzle outlet side (lower) of the second Ring-cylindrical cavity (59) surrounding nozzle needle (41) is formed, and that in the first nozzle needle (21) at least one radial bore (60) is machined, which connects the cylindrical pressure chamber (42) with the ring-cylindrical cavity (59) hydraulically.

8. Injector according to one or more of the preceding claims, characterized in that the nozzle outlet (61) of the nozzle body (20) has one or more radially outer nozzle outlet openings (28, 29) actuated by the first (outer) nozzle needle (21) ) and one or more radially inner nozzle outlet openings (26, 27) which can be actuated by the second (inner) nozzle needle (41).

9. Injector according to one or more of the preceding claims, characterized in that the (lower) end region (61) of the nozzle body (20) containing the nozzle outlet openings (26-29) and the end sections (62, 63) of the two nozzle needles (21 or 41) are conical, the end sections (62, 63) of the nozzle needles (21 or 41) complementing one another in a common closed or open position to form a uniform conical surface.