EP1573196A1

EP1573196A1 - Injector comprising a device for sealing an actuator unit, and sealing ring

Info

Publication number: EP1573196A1
Application number: EP03813532A
Authority: EP
Inventors: Heinz Lixl; Johann Massinger; Willibald SCHÜRZ; Martin Simmet; Jürgen Dick
Original assignee: Siemens AG
Current assignee: Continental Automotive GmbH
Priority date: 2002-12-20
Filing date: 2003-12-16
Publication date: 2005-09-14
Anticipated expiration: 2023-12-16
Also published as: DE10260289A1; EP1573196B1; WO2004057179A1; DE50309597D1

Abstract

Disclosed is an injector for injecting fuel into a combustion engine, in which especially a piezoelectric actuator unit (2) actuates a servo valve or an injector needle by means of a lifting pin (3). The aim of the invention is to seal the actuator unit (2) against the high fuel pressure prevailing in a leakage space (6). Said aim is achieved by a device comprising a sealing ring that is provided with a flexible, fuel-resistant plastic ring (4) which tightly surrounds the lifting pin (3) in a centered and sealing manner against the effective fuel pressure. The plastic ring (4) is also tightly surrounded by a metal ring (5) which prevents axial displacement inside the housing (1). Said arrangement advantageously allows sealing against the fuel pressure as well as precise axial guidance of the actuator unit (2) or the lifting pin (3) without affecting the vertical mobility thereof.

Description

description

Injector with a device for sealing an actuator unit and a sealing ring

The invention is based on an injector for fuel injection into an internal combustion engine, in which an actuator unit is arranged in a housing, or a sealing ring according to the type of the independent claims 1 and 9. It is already known that when a control voltage is applied to a piezoelectric actuator, in particular, whose change in length is used to control a servo valve or a nozzle needle in such a way that a certain amount of fuel can emerge from a nozzle in a finely atomized manner. The moving parts of the actuator unit must be sealed to protect them from the leakage space located below the actuator unit, in which there is fuel with a high overpressure. Furthermore, the seal must allow a centering pin of the actuator unit to be guided as centered as possible and must not impair the linear expansion of the actuator unit, which is in the μm range.

To solve these problems, it has previously been proposed to seal the actuator unit with an O-ring which is arranged between the actuator unit and the inner wall of the housing of the injector. With this solution, however, it is disadvantageous that the O-ring shows a certain amount of wear over time, even though it moves slightly, and can then leak. Furthermore, cleaning problems already arise during the manufacturing process of the injector if the crank pin has to be reworked after assembly. For example, grinding residues cannot be washed out completely, so a reliability risk can arise here. It is also known to use a metal membrane instead of the O-ring. In particular, there are production-related problems here, some of which are also very cost-intensive. For example, the metal membrane can be pressed in. However, this requires large wall thicknesses of the metal membrane in order to achieve the required rigidity or strength. However, a high wall thickness results in less flexibility in the vertical direction, which in turn can impair the mobility of the actuator unit.

As an alternative solution, it was also known to weld the metal membrane into a frame and then press it into the housing bore of the injector. However, this solution is very labor intensive and therefore creates undesirable additional costs in the manufacture of the injector.

The invention is based on the object of improving the seal between the actuator unit and the leakage space on an injector for fuel injection into an internal combustion engine. This object is achieved with the features of the independent claims 1 and 9.

The injector according to the invention for fuel injection into an internal combustion engine or the sealing ring with the characterizing features of the independent claims 1 and 9 has the advantage that the device with the flexible plastic ring is inexpensive to manufacture and works without wear, since the crank pin is fixed to the plastic ring connected is. It is considered to be particularly advantageous that the crank pin can be cleaned easily and reliably after the post-processing, since the plastic ring has a simple geometric shape to which no dirt or grinding particles can adhere. Another advantage is the particularly simple assembly technique, as the metal ring that seals and firmly encloses the plastic ring fits exactly to the see position of the housing inner wall of the injector can be pushed and fixed here.

The measures listed in the dependent claims provide advantageous developments and improvements to the injector specified in the independent claims 1 and 9 and the sealing ring. It is considered to be particularly advantageous that the crank pin is connected to the plastic ring in a fuel-tight manner, so that no aggressive fuel can reach the sensitive actuator.

A particularly simple method for connecting the plastic ring to the crank pin is seen by vulcanizing or gluing. These manufacturing processes are easy to control and cost-effective to use.

With regard to its flexible properties and / or its geometric properties, the plastic ring is matched to the prevailing fuel pressure and / or the stroke of the actuator unit. Since, for example, a much higher pressure is used in diesel injection than in high-pressure gasoline injection, it is necessary to adapt the elasticity and / or the geometric properties of the plastic ring accordingly. The stroke of the actuator unit and thus the movement of the nozzle needle is also an important variable since the amount of fuel to be injected can be controlled very easily via the stroke.

A particularly advantageous solution is also seen in the choice of a suitable type of elastomer. The type of elastomer must in particular be resistant to the type of fuel used so that it can reliably perform its sealing function at least over the expected life of the injector.

The solution of designing the metal ring with regard to its dimensions in such a way that it fits in a drilling tion of the housing can be fixed by pressing. With a suitable tool, the metal ring can thus be easily pressed into the desired position of the bore and fixed there.

For simple assembly of the actuator unit, it is advantageous to specify the press-in depth for the metal ring in such a way that the lower end of the crank pin is flush with a sealing surface of the housing of the injector. This simplifies the assembly of the injector since there is no rework.

Alternatively, a predetermined press-in depth can also be used to generate a specific preload for the plastic ring. In this case, the flexible plastic ring acts like a resilient element in addition to its sealing and centering functions. A separate spring element can then advantageously be saved.

An embodiment of the invention is shown in the drawing and is explained in more detail in the following figures.

FIG. 1 shows, in a Scherriatic representation, sections of an injector with an actuator unit and with a device with a sealing ring and

Figure 2 shows the schematic structure of an injector for fuel injection.

With regard to the description of the invention, a section of an injector for fuel injection into an internal combustion engine can be seen from the sectional view in FIG. For reasons of clarity, FIG. 1 only shows the parts which relate to the actuator unit 2, the device with the sealing ring 4, 5 and the housing 1 of the injector. A servo valve, a nozzle needle with an The spray nozzle, fuel channels, etc. and the function of the injector will be explained in more detail in a later chapter.

In this case, the actuator unit 2 has a piezoelectric actuator 8, which is constructed from a piezoceramic with a large number of individual layers using PMA technology (piezoelectric multilayer actuator) in order to generate the largest possible stroke. The actuator is controlled with a pulsed control voltage, for example 160V, and changes its length in the axial direction in accordance with the applied control pulses. Its upper end is firmly connected to the housing 1 of the injector (not shown in FIG. 1), so that the change in length when the control voltage is applied to the actuator 8 can have a full downward effect.

The lower end of the actuator 8 is fixedly connected to a coupling element or base plate 2a, which is formed with a recess or bore and can receive the upper part of a crank pin 3. The coupling element and the crank pin 3 are matched to one another in such a way that the crank pin 3 completely retraces each movement of the actuator 8. The change in length of the actuator 8 can thus be tapped off at the lower end of the crank pin 3 and can be used to control a servo valve (not shown in the figure) or a nozzle needle.

In the area of the lower part of the crank pin 3, a leakage space 6 is arranged, in which the fuel is stored under a high pressure. Depending on the application, the pressure can be several hundred or more than a thousand bar. The crank pin 3 partially projects into this leakage space 6.

To seal the leakage space 6 against the actuator unit 2, a sealing ring is provided, which essentially has a plastic ring 4 and a metal ring 5. The plastic ring 4 has a central bore through which the crank pin 3 is passed. The plastic ring 4 is with the crank pin 3 is firmly connected to the crank pin 3, for example by vulcanizing or gluing, so that no fuel can penetrate. The plastic ring 4 is preferably disc-shaped, and has no inaccessible corners or edges on which solid particles can accumulate, which are produced, for example, by post-processing such as grinding.

A polymer type is provided as the material for the plastic ring 4, which is flexible or elastic and sufficiently resistant to aggressive fuels. Furthermore, the plastic ring 4 must have such flexible properties that are suitable against the prevailing pressure, occurring temperatures, etc., and allow a centered axial guidance of the crank pin 3.

The plastic ring 4 is encased by a metal ring 5 corresponding shape because of the better handling during assembly and is also firmly connected to this by vulcanizing or gluing. The dimensions of the metal ring 5 correspond to the opening width of the bore in the housing 1 into which the metal ring 5 is to be inserted. The metal ring 5 is preferably pressed into the bore and thereby fixed in such a way that it seals the leakage space 6 against leaking fuel with respect to the actuator unit 2.

The metal ring 5 is preferably pressed so deep into the bore that the lower end of the crank pin 3 is flush with a sealing surface 7 of the housing 1, which is used as a reference surface when pressed in. This ensures that the crank pin 3 functions reliably. In order to achieve this goal, the crank pin 3 can be re-ground after assembly until it is flush with the reference surface 7 of the housing 1. After the grinding process, the residues can be easily rinsed out because of the advantageous embodiment of the invention. Alternatively, it is also provided that the metal ring 5 is pressed in with an insertion depth which leads to a predetermined preload for the plastic ring 4.

Figure 2 shows a schematic representation of a longitudinal section through the aforementioned injector 20 for fuel injection into an internal combustion engine of a motor vehicle. The injector 20 has an injector housing 1, into which the piezoelectric actuator 8 or the actuator unit 2, which is preferably constructed using multilayer technology, is inserted. The upper part of the piezoelectric actuator 8 (head plate 16) is firmly connected to the upper part of the injector housing 1. The lower end of the actuator unit 2 is closed with a base plate 2a. The base plate 2a is arranged to be movable along the longitudinal axis and moves downward relative to the housing 1 when a corresponding control voltage is applied to the piezoelectric actuator 8. The piezoelectric actuator 8 is encased by a tubular spring 13 which, among other things, supports the reversible movement of the actuator 8 into its starting position when the control voltage is switched off.

A cutout (central bore) is made in the base plate 2a, which serves to receive the crank pin 3. The crank pin 3 is centered and guided by a plastic ring 4. For reasons of stability, the plastic ring 4 is encased by a metal ring 5, which is designed as a sealing ring and seals a leakage space 6 towards the injector 8. Position 7 symbolizes the sealing surface between the two parts of the injector housing 1.

A hydraulic or mechanical translator 15, on which the crank pin 3 can act, is arranged below the crank pin 3. The translator 15 is preferably designed as a stroke reverser. It moves its lower part upwards when the actuator 8 extends downwards. In the non-activated state of the actuator 8, the stroke reverser 15 presses one Ram 17 on a servo valve 18 so that it closes a control chamber 9 located below. Due to the pressure conditions in the control chamber 9 and the corresponding dimensioning of the nozzle needle 10, the nozzle needle 10 is pressed against injection openings 14 in the nozzle housing and closes the injection openings 14. A corresponding line 11 for supplying the fuel is arranged in the control chamber 9. In addition, the line 11 is led to an injection space 21, which is arranged above the sealing seat of the nozzle needle 10.

If the actuator 8 is activated by applying a control voltage, it expands and presses on the stroke reverser 15. This opens the servo valve 18, so that the fuel under pressure can partially flow off via an outlet 12. The fuel, which is under higher pressure at the lower end of the nozzle needle 10, lifts the nozzle needle 10 so that the fuel can escape from the injection openings 14.

Claims

claims

1. injector for fuel injection into an internal combustion engine, with a housing (1), with an actuator unit (2), which presses a crank pin (3) at its lower end when the actuator (8) is axially actuated, and with a device ( 5) for sealing the actuator unit (2) against a leakage space (6) filled with fuel, which is located below the device (5), characterized in that the device (5) has a flexible plastic ring (4) that the Plastic ring (4) is designed to center and tightly enclose the crank pin (3) in the axial direction, and that a metal ring (5) is provided which tightly encloses the plastic ring (4) and is arranged in a sealing manner to the housing and against an axial displacement inside the housing (1) ensures.

2. Injector according to claim 1, characterized in that the plastic ring is provided by the metal ring which tightly encloses the plastic ring (4) and arranged sealingly to the housing and secures against axial displacement in the interior of the housing (1).

3. Injector according to claim 1, characterized in that the plastic ring (4) with the crank pin (3) on the one hand and the metal ring (5) on the other hand is connected in a fuel-tight manner.

4. Injector according to claim 1 or 2, characterized in that the plastic ring (4) with the crank pin (3) and / or the metal ring (5) is vulcanized or glued.

5. Injector according to one of the preceding claims, characterized in that the plastic ring (4) with respect to its flexible properties and / or its geo etri- see dimensions on the prevailing fuel pressure and / or the stroke of the actuator unit (2) is tunable.

6. Injector according to one of the preceding claims, characterized in that the plastic ring (4) has a type of elastomer resistant to aggressive fuels.

7. Injector according to one of the preceding claims, characterized in that the metal ring (5) is designed with respect to its dimensions such that it can be fixed in a bore of the housing (1) by pressing.

8. Injector according to one of the preceding claims, characterized in that an insertion depth for the metal ring (5) can be predetermined such that the lower end of the

Crank pin (3) ends flush with a sealing surface (7) of the housing (1).

9. Injector according to one of the preceding claims, characterized in that a prestress for the plastic ring (4) is adjustable by the insertion depth for the metal ring (5).

10. Sealing ring for sealing a leakage space (6) from an actuator unit (2) of an injector, characterized in that the sealing ring has a flexible and fuel-resistant plastic ring (4), that the plastic ring (4) with an axial bore for Recording the crank pin (3) is formed and that the plastic ring (4) is surrounded by a metal ring (5).

11. Sealing ring according to claim 9, characterized in that the metal ring (5) in the housing (1) of the injector can be pressed.