EP2426349B1 - Fuel injector - Google Patents

Description

The invention relates to a fuel injector for a fuel injection system, in particular a common rail injection system, for injecting fuel into the combustion chamber of an internal combustion engine having the features of the preamble of claim 1, such as from the documents EP 393590 or EP 582993 known.

Fuel injectors of the aforementioned type have an axially movable nozzle needle for controlling the injection process. The nozzle needle is for this purpose in a high-pressure bore of a nozzle body for releasing or closing at least one injection opening guided in a liftable and limited with an end face formed within the high-pressure bore control chamber. About switchable inlet and outlet throttles pressure build-up or pressure reduction is realized in the control room, which causes an opening or closing of the nozzle needle.

Depending on the control concept of the inlet and outlet throttles or of the hydraulic overall tuning of the fuel injector, with relatively small injection periods of an electrical switching element, relatively large injection quantities can occur because the control chamber is deactivated too long and, consequently, the nozzle needle remains open too long. This problem (poor Kleinstmengenfähigkeit) occurs especially when using seat hole nozzles, as they have a high opening seat force even with small needle strokes.

State of the art

From the publication DE 101 64 123 A1 goes out a generic fuel injector, by means of which even very small injection quantities can be delivered with great precision. This is in the fuel injector between rule valve seat and control chamber arranged an elastic delay element, which delays the opening stroke of the nozzle needle at a pressure drop in the control chamber. In the closed position, the nozzle needle is pressed together with the elastic delay member due to the hydraulic pressure in the control chamber against the valve seat, wherein the elastic delay member is compressed. At a pressure drop in the control room, first relaxes the elastic delay element, wherein it expands and holds the nozzle needle in contact with the valve seat. Only when the elastic delay element has fully expanded to its largely relieved length, the nozzle needle lifts off the valve seat and thus releases the flow for the fuel. In this way, even very small pre-injection quantities can be realized.

From the publication DE 100 2005 027 853 A1 In addition, a fuel injector with a recorded in the control chamber stop member for adjusting the maximum stroke of the nozzle needle is known. On the interpretation of the stop element, a hydraulic damping can also be effected, which is to prevent it from bouncing after passing through the maximum stroke of the nozzle needle. On the one hand, the noise is reduced, on the other hand, the closing time can be set more precisely, since the state of the nozzle needle is known at the beginning of the closing movement. The control chamber is divided by the stop element into an upper and a lower partial space, which are hydraulically connected via a central bore formed in the stop element and / or an annular gap surrounding the stop element. About the size of the central bore and / or the annular gap, the damping effect is adjustable.

From the EP 2 275 665 A1 Furthermore, a fuel injector is known with a arranged in the control chamber of the nozzle needle movable element, wherein the element has a spherical surface.

Based on the above-mentioned prior art, the present invention seeks to provide a fuel injector of the type mentioned with improved Kleinstmengenfähigkeit. In addition, the fuel injector should be simple and inexpensive to produce.

The object is achieved by a fuel injector with the features of claim 1. Advantageous developments of the invention are specified in the dependent claims.

Disclosure of the invention

The proposed fuel injector has a nozzle needle, which is guided in a high-pressure bore of a nozzle body for releasing or closing at least one injection opening in a liftable manner. Further, the fuel injector has a control chamber which is axially bounded by the nozzle needle or a translating piston cooperating with the nozzle needle and can be connected to a low-pressure region for relief via a drainage channel. According to the invention a movable, axially biased delay element for forming a throttle between a first control chamber portion and a second control chamber portion is added in the control room. Also in the case of the fuel injector according to the invention, the control chamber is accordingly subdivided into two hydraulically connected sections via an additional element. The hydraulic connection of the two sections preferably takes place via a remaining annular gap between the retardation element and an inner circumferential surface radially delimiting the control chamber. The size of the annular gap is chosen such that the outflow of the fuel from the first control chamber section is throttled into the second control chamber section. In this case, a defined initial position and consequently a defined throttle effect on the volume ratio of the two control chamber sections is ensured via the axial bias of the delay element.

In order to prevent hydraulic adhesion of the delay element to the nozzle needle, the booster piston and / or the housing part, the delay element is spherically shaped. In contact with the nozzle needle, the booster piston and / or the housing part thus remains serving as a first control room section and second control chamber section pressure chamber. The applied to the nozzle needle, the booster piston and / or the housing part surface is thus reduced to a minimum.

According to a preferred embodiment of the invention, a spring element is received in the control chamber for the axial bias of the delay element. The spring element may for example be a coil spring, a plate spring or a corrugated spring. Alternatively or additionally, it may be provided that the delay element is at least partially elastically deformable. The axial bias of the delay element can accordingly Also caused or at least supported by an at least partially elastic deformation of the delay element.

When using a spring element is further preferably provided that the spring element is supported on the nozzle needle or on the booster piston or on a housing part of the fuel injector. The spring element can thus be arranged both in the first control chamber section and in the second control chamber section. To be advantageous, the arrangement of the spring element proves in the second control chamber section, if that for supporting the spring element provided housing part, for example, is a throttle plate and there is a cover of the formed in the throttle plate drainage channel or outlet throttle is to be prevented. The same applies with respect to an inlet channel or inlet throttle arranged in the throttle plate. Without the interposition of the spring element, the delay element could block the inflow or outflow of fuel.

According to a further preferred embodiment of the invention, the control chamber is bounded in the radial direction by a sleeve inserted into the high-pressure bore. The sleeve may for example serve as a sealing sleeve and be biased by a spring in the axial direction against the throttle plate.

Advantageously, the delay element and / or the spring element can be used to adjust the stroke of the nozzle needle. The delay element thus serves at the same time as a stop element, since it limits the stroke of the nozzle needle in the axial direction. Furthermore, the spring force of the spring element can be adjusted such that, alternatively or additionally, a stroke adjustment via the spring element can be effected.

The invention can be used to improve the minimum quantity capability, in particular in the case of fuel injectors with a large valve chamber volume and / or with a seat hole nozzle. In principle, however, the invention can be used in all known injector concepts. The delay element accommodated in the control chamber throttles the outflow of the fuel so that the pressure reduction and thus the opening of the nozzle needle is delayed. The adjustment of the throttling effect takes place via the size of the between the delay element and the Control chamber radially limiting inner peripheral surface remaining throttle gap. The delay of the Nadelöffnungshubes can be further set by setting the following parameters: volume ratio of the two control chamber sections, axial biasing force of the delay element, hydraulic design of the drain and / or the inlet throttle and / or needle seat diameter. Furthermore, by means of the delay element according to the invention, it is possible to cost-effectively correct copy-specific injection quantity scatterings.

• Fig. 1a, b jeweils einen Teillängsschnitt durch eine erste Ausführungsform eines erfindungsgemäßen Kraftstoffinjektors,
• Fig. 2a, b eweils einen Teillängsschnitt durch eine zweite Ausführungsform eines erfindungsgemäßen Kraftstoffinjektors und
• Fig. 3 ein Diagramm zur prinzipiellen Darstellung des Bewegungsablaufs des Verzögerungselementes bzw. der Düsennadel.

Preferred embodiments of the invention are explained below with reference to the drawings. These show:

• Fig. 1a, b each a partial longitudinal section through a first embodiment of a fuel injector according to the invention,
• Fig. 2a, b eweils a partial longitudinal section through a second embodiment of a fuel injector according to the invention and
• Fig. 3 a diagram for the basic representation of the movement of the delay element or the nozzle needle.

Detailed description of the drawings

A first embodiment of a fuel injector according to the invention is the Fig. 1 a and 1 b, where the Fig. 1b a section of the Fig. 1 a in the area of the control room 5 shows (see dashed line). The in the Fig. 1a and 1b shown fuel injector comprises a nozzle body 3 with a high-pressure bore 2, in which a nozzle needle 1 for releasing and closing at least one injection port 4 is received in a liftable manner.

The nozzle change 1 bounded in the axial direction of a control chamber 5, which is also formed in the high-pressure bore 2 and which is connected to the discharge via a drain passage 6 with a low pressure region 7. The drain channel 6 is formed in a housing part 11 which limits the control chamber 5 in the axial direction. In addition to the drainage channel 6, the housing part 11 has an opening into the control chamber 5 inlet channel 13, passes through the fuel into the control chamber 5. When connecting the control chamber 5 with the low pressure area 7, the control chamber 5 is relieved, that is, the prevailing in the control chamber 5 control chamber pressure drops. The pressure drop in the control chamber 5 in turn causes the nozzle needle 1 opens.

To realize even the smallest injection quantities of the opening stroke of the nozzle needle 1 is delayed in the fuel injector according to the invention. For this purpose, a spherical retardation element 8 is arranged in the control chamber 5, which is biased by the spring force of a spring element 10 in the form of a supported on the housing part 11 helical compression spring, axially against the nozzle needle 1. Due to the spherical shape of the delay element 8, a first control chamber section 5. 1 is formed between the ball and the nozzle needle 1, which is connected via a throttle 9 serving as an annular gap between the ball and the high pressure bore 2 in hydraulic communication with a second control chamber section 5.2. The throttle 9 causes that at a pressure drop in the second control chamber section 5.2, the pressure drop in the first control chamber section 5.1 occurs only with delay, so that the opening stroke of the nozzle needle 1 is also delayed. With the opening of the nozzle needle 1, the injection process begins, wherein fuel under high pressure is injected via the at least one injection opening 4 into the combustion chamber of the internal combustion engine. The fuel is supplied to the at least one injection port 4 via a fuel supply 14 and the high-pressure bore 2.

The in the Fig. 2a and 2b illustrated further embodiment of a fuel injector according to the invention differs from that of Fig. 1a and 1b merely in that the combustion chamber facing away from the end of the nozzle needle 1 is guided in a sleeve 12 which bears sealingly on the housing part 11 and thus the control chamber 5 radially limited. To ensure the sealing system, the sleeve 12 is biased by the spring force of a spring 15 axially against the housing part 11. For this purpose, the spring 15 is supported on the one hand on a radial shoulder of the nozzle needle 1 and on the other hand on an end face of the sleeve 12. The operation corresponds to that of the embodiment of Fig. 1a and 1b , which is why in connection with the description of the Fig. 1a and 1b referenced statements.

From the diagram of Fig. 3 can be the time-delayed opening stroke of the nozzle needle 1 read clearly. The time is plotted on the x-axis, while is plotted on the y-axis of the stroke of the nozzle needle 1 and the delay element 8 in conjunction with the pressure drop or Duck rise in the two control space sections 5.1 and 5.2. The curve b) shows the pressure drop or increase over time in the second control chamber section 5.2, which is connectable via the drain channel 6 with the low pressure region 7. The curve a) shows the contrast, delayed pressure drop in the first control chamber section 5.1, which is bounded by the nozzle needle 1 and the delay element 8. Similarly, the opening stroke of the nozzle needle 1 is delayed (see curve c). The needle opens when there is equilibrium between the needle seating force and the pressure force in the first control chamber 5.1. The needle opening is preceded by an "opening" of the delay element 8, when the pressure difference in both control space sections 5.1 and 5.2 corresponds to the axial biasing force of the delay element 8.

Claims (5)

1. Fuel injector for a fuel injection system, in particular a common-rail injection system, having a nozzle needle (1) which is guided, such that it can perform a stroke movement, in a high-pressure bore (2) of a nozzle body (3) for the purpose of opening up or closing off at least one injection opening (4), wherein the nozzle needle (1) or a transmitter piston that interacts with the nozzle needle (1) axially delimits a control chamber (5) which, for release of pressure, can be connected via an outflow duct (6) to a low-pressure region (7), wherein, in the control chamber (5), there is accommodated a movable, axially preloaded delay element (8) for forming a throttle (9) between a first control chamber section (5.1) and a second control chamber section (5.2), characterized in that the delay element (8) is of spherical form, such that, when in contact with the nozzle needle (1) or the transmitter piston at one side and/or with the housing part (11) at the other side, a pressure chamber remains which serves as first control chamber section (5.1) and as second control chamber section (5.2).
2. Fuel injector according to Claim 1, characterized in that, for the axial preload of the delay element (8), a spring element (10) is accommodated in the control chamber (5), and/or the delay element (8) is at least partially of elastically deformable form.
3. Fuel injector according to Claim 2, characterized in that the spring element (10) is supported on the nozzle needle (1) or on the transmitter piston or on a housing part (11) of the fuel injector.
4. Fuel injector according to one of the preceding claims, characterized in that the control chamber (5) is delimited, in a radial direction, by a sleeve (12) which is inserted into the high-pressure bore (2).
5. Fuel injector according to one of the preceding claims, characterized in that the delay element (8) and/or the spring element (10) can be used for setting the stroke of the nozzle needle (1).

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