EP1573196B1 - Injector comprising a device for sealing an actuator unit, and sealing ring - Google Patents

Description

The invention is based on an injector for fuel injection in an internal combustion engine, in which an actuator unit is arranged in a housing, according to the preamble of claim 1. It is already known that when a control voltage is applied to a particular piezoelectric actuator whose change in length is used to control a servo valve or a nozzle needle so that a certain amount of fuel can leak at a nozzle finely atomized. In this case, the moving parts of the actuator unit must be sealed to protect against the located in a located below the actuator unit leakage chamber in which fuel is at high pressure. Furthermore, the seal must allow the most centered possible guidance of a crank pin of the actuator and may not affect the length of the actuator actuator, which moves in the micron range.

To solve these problems, it has hitherto 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. In this solution, however, is disadvantageous that the O-ring has a certain wear due to its, albeit slight movement over time and then can be leaking. Furthermore arise during the manufacturing process of the injector problems with the cleaning when the crank pin must be reworked after assembly. For example, grinding residues can not be completely washed out, so that a reliability risk can arise here.

It is further known to use a metal membrane instead of the O-ring. Here, in particular manufacturing problems occur, which are sometimes very costly. For example, the metal membrane can be pressed. For this, however, large wall thicknesses of the metal membrane are required to achieve the required stiffness or strength. However, a high wall thickness causes less flexibility in the vertical direction, which in turn can affect the mobility of the actuator unit.

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

Out DE 37 422 241 A1 a fuel injector is known in which a piezo actuator actuates a valve piston. The valve piston is used to actuate a valve, via which fuel is discharged. The valve piston is guided in a housing of the injection valve, wherein a sealing element between the housing and the valve piston is arranged at the lower end of the valve piston. The sealing element hydraulically separates an upper area from a lower area. The sealing element is vulcanized to the valve piston and sealingly connected to the housing.

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

The injector according to the invention for fuel injection into an internal combustion engine or the sealing ring with the features of claim 1 has the advantage that the device with the flexible plastic ring cost can be produced and works wear-free, since the crank pin is firmly connected to the plastic ring. Furthermore, it is regarded as an advantage that the crank pin of the injector is centered and guided by the plastic ring. This can be dispensed with an additional guidance of the crank pin by a guide surface of the housing. It is considered to be particularly advantageous that a simple and reliable cleaning of the crank pin after the post-processing is possible, since the plastic ring has a simple geometric shape on which no dirt or abrasive particles can settle. Another advantage is also in a particularly simple assembly technique, since the plastic ring sealing and tightly enclosing metal ring exactly to the intended Position of the housing inner wall of the injector can be pushed and fixed here.

The measures listed in the dependent claims advantageous refinements and improvements of the claim 1 injector are given. Particularly advantageous is considered that the crank pin is connected to the plastic ring fuel-tight, 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 vulcanization or gluing. These manufacturing processes are easy to control and cost effective.

The plastic ring is tuned to the prevailing fuel pressure and / or the stroke of the actuator unit with regard to its flexible properties and / or its geometric properties. For example, since a much higher pressure is used in the diesel injection than in the high-pressure gasoline injection, it is necessary to adjust 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 an important factor, since the amount of fuel to be injected can be controlled very easily via the stroke.

A particularly advantageous solution is also seen by the choice of a suitable type of elastomer. The type of elastomer must be particularly 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.

Favorable also appears the solution to form the metal ring with respect to its dimensions such that it is in a bore of the housing can be fixed by pressing. With an appropriate tool thus the metal ring can be easily pressed to the desired location of the hole and fixed there.

For a simple assembly of the actuator unit, it is advantageous to specify the press-in depth for the metal ring such 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 no rework is required.

Alternatively, a predetermined offset can also be used to produce a certain bias for the plastic ring. In this case, the flexible plastic ring acts in addition to its sealing and centering functions like a resilient element. A separate spring element can then be saved in an advantageous manner.

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

FIG. 1 shows a schematic representation of a detail of an injector with an actuator and a device with a sealing ring and

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

With regard to the description of the invention is from the sectional view of FIG. 1 a fragmentary injector for fuel injection in an internal combustion engine recognizable. In the FIG. 1 For reasons of clarity, only those parts have been shown 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 injection 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 according to the PMA technique (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 according to the applied control pulses. Its upper end is fixedly connected to the housing 1 of the injector (in FIG. 1 not shown), so that the change in length when applying the control voltage to the actuator 8 can affect fully down.

The lower end of the actuator 8 is fixedly connected to a coupling element or bottom 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 every movement of the actuator 8. At the lower end of the crank pin 3 thus the change in length of the actuator 8 can be tapped off and can be used to control a (not shown in the figure) servo valve or a nozzle needle.

In the region of the lower part of the crank pin 3, a leakage chamber 6 is arranged, in which the fuel is stored under a high pressure. Depending on the application, the pressure may be several hundred or more than a thousand. The crank pin 3 protrudes partially into this leakage chamber 6 inside.

For sealing the leakage chamber 6 against the actuator unit 2, a sealing ring is provided which has a plastic ring 4 and a metal ring 5 substantially. The plastic ring 4 has a central bore through which the crank pin 3 is performed. The plastic ring 4 is with the crank pin 3, for example by vulcanization or gluing firmly connected to the crank pin 3, 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 be deposited, resulting for example by a post-processing such as grinding.

As the material for the plastic ring 4, a polymer is provided, 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 due to the better handling during assembly of a metal ring 5 corresponding shaping and firmly connected to this also by vulcanization or gluing. The dimensions of the metal ring 5 correspond to the opening width of the bore of the housing 1, in which the metal ring 5 is to be inserted. Preferably, the metal ring 5 is pressed into the bore and thereby fixed so that it seals the leakage chamber 6 against escaping fuel relative 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 during pressing as a reference surface. As a result, a secure operation of the crank pin 3 is ensured. To achieve this goal, the crank pin 3 can still be reground after installation 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 to press the metal ring 5 with a Einpresstiefe, which leads to a predetermined bias for the plastic ring 4.

FIG. 2 shows a schematic representation of a longitudinal section through the aforementioned injector 20 for the fuel injection in 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 piezoelectric actuator 8 is fixedly connected at its upper part (top plate 16) to the upper part of the injector housing 1. The lower end of the actuator unit 2 is closed with a bottom plate 2a. The bottom plate 2a is movably disposed along the longitudinal axis and moves downwardly relative to the housing 1 when a corresponding control voltage is applied to the piezoelectric actuator 8. The piezoelectric actuator 8 is surrounded by a tube spring 13, which among other things supports the reversible movement of the actuator 8 in its initial position when the control voltage is switched off.

In the bottom plate 2a a recess (central bore) is introduced, which serves to receive the crank pin 3. The crank pin 3 is centered and guided by a plastic ring 4. For stability reasons, the plastic ring 4 is encased by a metal ring 5, which is designed as a sealing ring and a leakage chamber 6 to the injector 8 sealingly closes. Position 7 symbolizes the sealing surface between the two parts of the injector housing. 1

Below the crank pin 3, a hydraulic or mechanical translator 15 is arranged, on which the crank pin 3 can act. The translator 15 is preferably designed as a Hubumkehrer. It moves its lower part upwards when the actuator 8 expands downwards. In the non-activated state of the actuator 8, the Hubumkehrer 15 presses on a Plunger 17 on a servo valve 18 so that it closes an underlying control chamber 9. Due to the pressure conditions in the control chamber 9 and 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. In the control chamber 9, a corresponding line 11 is arranged for an inlet of the fuel. In addition, the line 11 is guided 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, then it expands and presses on the Hubumkehrer 15. This opens the servo valve 18, so that the pressurized fuel can flow partially through a drain 12. The at the lower end of the nozzle needle 10 under higher pressure fuel raises the nozzle needle 10, so that the fuel can escape from the injection ports 14.

Claims (8)

1. Injector for injection of fuel into a combustion engine, with a housing (1), with an actuator unit (2), the lower end of which presses against a crank pin (3) when the actuator (8) is actuated axially, and with a device (5) for sealing the actuator unit (2) against a leakage area (6) filled with fuel which is located underneath the device (5), characterised in that the device (5) has a flexible plastic ring (4), the plastic ring (4) tightly encloses the crank pin (3), a metal ring (5) is provided which securely encloses and seals the plastic ring (4) and is arranged so as to seal the housing and prevent an axial displacement inside the housing (1), and the plastic ring (4) centres and guides the crank pin (3).
2. Injector according to claim 1, characterised in that the plastic ring (4) is connected on one side to the crank pin (3) and on the other side to the metal ring (5) in a fuel-tight manner.
3. Injector according to claim 1 or 2, characterised in that the plastic ring (4) is vulcanised or bonded to the crank pin (3) and/or the metal ring (5).
4. Injector according to one of the preceding claims, characterised in that the flexible attributes and/or the geometric dimensions of the plastic ring (4) can be aligned to the prevailing fuel pressure and/or the travel of the actuator unit (2).
5. Injector according to one of the preceding claims, characterised in that the plastic ring (4) is of an elastomer type which is resistant to aggressive fuels.
6. Injector according to one of the preceding claims, characterised in that the dimensions of the metal ring (5) are such that it can be fixed into a bore hole in the housing (1) by being pressed in.
7. Injector according to one of the preceding claims, characterised in that a depth for the metal ring (5) to be pressed in can be predefined such that the lower end of the crank pin (3) terminates flush with a sealing surface (7) of the housing (1).
8. Injector according to one of the preceding claims, characterised in that pretensioning for the plastic ring (4) can be set by the depth for the metal ring (5) to be pressed in.

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