Fuel injector

Abstract

The invention relates to a fuel injector for injecting highly pressurized fuel into the combustion chamber of an internal combustion engine, comprising a multipart housing (1), the housing parts (2; 3; 4; 5) thereof being clamped against each other in a liquid-tight manner. The housing (1) is equipped with a pressure chamber (8) that can be filled with fuel and comprises a nozzle needle (10) which is longitudinally movable in the pressure chamber and interacts with a nozzle seat (11) in order to open and close at least one injection opening (12) and the end of which facing away from nozzle seat (11) delimits a control chamber (18), said control chamber having a pressure which exerts a closing force on the nozzle needle (10) in the direction of the nozzle seat (11) and being hydraulically connected to a pressure chamber (32) in the housing (1). The housing (1) is additionally equipped with a pressure sensor (36) which is designed to measure the pressure in the pressure chamber (32). A diaphragm (30) which separates the pressure sensor (36) from the pressure chamber (32) in a liquid-tight manner is arranged between the pressure chamber (32) and the pressure sensor (36), said diaphragm (30) being clamped between two housing parts (3; 4).

Description

[0001] The invention relates to a fuel injector, such as is used for injecting fuel under high pressure into a combustion chamber of an internal combustion engine. State of the art

[0002] In modern compression-ignition internal combustion engines, the fuel is injected directly into a combustion chamber. This is achieved using fuel injectors, which inject the compressed, high-pressure fuel through narrow injection ports into the combustion chamber, where it is finely atomized. The finely atomized fuel, together with the air in the combustion chamber, forms an ignitable mixture that, due to the fine atomization, burns efficiently, thus enabling high engine performance. The fuel injector features a piston-shaped nozzle needle that is longitudinally displaceable within a pressure chamber filled with high-pressure fuel. The nozzle needle opens and closes the injection ports through its longitudinal movement. This movement is servo-hydraulically controlled, meaning that the fuel pressure in a control chamber exerts a hydraulic closing force on the nozzle needle.The fuel pressure in the control chamber is controlled by a control valve, which regulates the pressure in the control chamber electromagnetically or with the help of a piezo actuator.

[0003] For effective combustion of the fuel in the combustion chamber, it is necessary to meter the fuel into the combustion chamber at precisely the right time and in the exact required quantity. The electromagnet or piezo actuator of the control valve can be controlled very precisely by a control unit.

[0004] However, it must be taken into account that there is a time lag between the control current and the actual movement of the nozzle needle, since the actuation of the control valve only leads to the actual movement of the nozzle needle, and thus to the start or end of the injection, after a certain time delay. For precise control, it is therefore important to know the exact moment at which the nozzle needle moves and the injection begins, in order to readjust the control current for the control valve if necessary.

[0005] The movement of the nozzle needle can be precisely monitored, for example, via the pressure profile in the control chamber. For this purpose, a fuel injector is known from DE 10 2015 207 307 A1, in which the control chamber is connected to a pressure chamber via a connecting bore. The pressure chamber is separated from a pressure sensor by a diaphragm, which is deformable by pressure. A pressure change in the control chamber thus also causes a pressure change in the pressure chamber and consequently a pressure-dependent change in the diaphragm's deformation, which can be detected by the pressure sensor. By evaluating the pressure sensor signal, the precise time at which the nozzle needle opens and closes can then be determined, and the control signal at the control valve can be readjusted as needed.

[0006] The diaphragm that separates the pressure chamber from the pressure sensor is part of a valve plate that also houses the pressure sensor and the pressure chamber. Corresponding cutouts ensure that the diaphragm, which is integrally formed with the valve plate, remains between the pressure chamber and the pressure sensor. Disclosure of the invention Advantages of the invention

[0007] The fuel injector according to the invention has the advantage of enabling precise control of the injection while allowing considerable freedom in the injector's design. For this purpose, the fuel injector has a multi-part housing, the housing parts of which are clamped against each other in a liquid-tight manner. Within the housing is a pressure chamber, fillable with fuel, containing a longitudinally displaceable nozzle needle that interacts with a nozzle seat to open and close at least one injection orifice. At its end furthest from the nozzle seat, the nozzle needle defines a control chamber, the pressure of which exerts a closing force on the nozzle needle in the direction of the nozzle seat. The housing also includes a pressure chamber, which is hydraulically connected to the control chamber, and a pressure sensor designed to measure the pressure in the pressure chamber.A membrane is arranged between the pressure chamber and the pressure sensor, which separates the pressure sensor from the pressure chamber in a liquid-tight manner, with the membrane being clamped between two housing parts.

[0008] In the fuel injector according to the invention, the diaphragm is designed as a separate component, clamped between the two housing components. The diaphragm separates the pressure chamber from the pressure sensor, thus preventing the pressure sensor from being exposed to fuel. This design offers several advantages: The sensor preload, i.e., the force with which the piezoelectric pressure sensor is biased, can be adjusted directly without regard to the diaphragm. Furthermore, this design simplifies assembly and provides direct access to the pressure sensor. As a separate component, the diaphragm can be manufactured from any material, which is optimal for this application. Moreover, the design of the diaphragm requires little or no consideration of the geometric tolerances, material properties, and strength requirements of the other housing components.The thickness of the membrane is freely selectable and the manufacturing process of the adjacent components is hardly affected by the membrane, so that injectors with different membranes can be implemented without problems.

[0009] In a first advantageous embodiment, the membrane is designed such that it can be deformed by the pressure of the pressure chamber in the direction of the pressure sensor. In a further advantageous embodiment, a pin is arranged between the membrane and the pressure sensor, which transmits any deformation of the membrane to the pressure sensor. Such a pin increases the design freedom in arranging the pressure sensor and can also protect the sensor from excessive force, particularly from asymmetrical force, by acting as a damping element.

[0010] In a further advantageous embodiment, the pressure chamber is formed within a nozzle body, the nozzle body being abutted by a throttle plate. The nozzle body and the throttle plate are part of the housing, and the throttle plate defines the control chamber. Advantageously, the pressure chamber is formed by a recess in the throttle plate and connected to the control chamber via a connecting bore formed in the throttle plate. This design enables a compact form, and the connecting bore allows the pressure chamber to be positioned at virtually any location within the throttle plate.

[0011] In a further advantageous embodiment, the pressure sensor is arranged in a valve plate, which is also part of the housing and rests against the throttle plate. Since the pressure sensor is arranged in a separate housing component, its arrangement and mounting can be carried out independently of the throttle plate. The diaphragm is advantageously clamped between the valve plate and the throttle plate, ensuring a secure hold and separating the pressure chamber from the pressure sensor.

[0012] In a further advantageous embodiment, the diaphragm is designed as a circular disc. In this embodiment, several areas can also be left out so that only a portion of the interface between the valve plate and the throttle plate is covered. This is particularly advantageous if one or more high-pressure bores pass through the interface between the valve plate and the throttle plate and the diaphragm surrounds these passages, as this increases the overall surface pressure between the valve plate and the throttle plate and thus improves the seal. drawing

[0013] The drawing shows an embodiment of the fuel injector according to the invention. Figure 1 shows a longitudinal section through a fuel injector according to the invention, Figures 2 and 3 show sectional views of the fuel injector. Figure 1in the area of ​​the membrane, where parts of the housing are omitted, Figures 4 and 5 show further embodiments of the invention, wherein only the section designated A of the Figure 1 shown enlarged. Description of the exemplary embodiment

[0014] In Figure 1A fuel injector according to the invention is shown in longitudinal section, with only the essential areas of the injector being depicted. The fuel injector has a housing 1 comprising a valve body 2, a valve plate 3, a throttle plate 4, and a nozzle body 5, which are adjacent to one another in this order. The parts of the housing 1 are clamped against each other by a clamping nut 6, so that they seal against each other in a liquid-tight manner. A pressure chamber 8 is formed in the nozzle body 5, which can be filled with fuel under high pressure. The fuel is guided into the pressure chamber 8 via a high-pressure bore (not shown in the drawing) through the valve body 2, the valve plate 3, and the throttle plate 4. A piston-shaped nozzle needle 10 is arranged to be longitudinally displaceable in the pressure chamber 8, which interacts with a nozzle seat 11 formed at the combustion chamber-side end of the pressure chamber 8.At the combustion chamber end of the nozzle body 5, several injection openings 12 are formed, which open into a combustion chamber in the installed position of the fuel injector, wherein the nozzle needle 10, when in contact with the nozzle seat 11, closes the injection openings 12 against the pressure chamber 8, while fuel from the pressure chamber 8 can flow to the injection openings 12 when the nozzle needle 10 has lifted off the nozzle seat 11.

[0015] The nozzle needle 10, with its end face facing away from the nozzle seat 11, defines a control chamber 18. The control chamber 18 is radially bounded on the outside by a sleeve 16, which is guided on the nozzle needle 10, and at its end face by the throttle plate 4. A closing spring 14, under compressive preload, is arranged between the sleeve 16 and a support ring 15. This spring surrounds the nozzle needle 10 and exerts a closing force on the nozzle needle 10 in the direction of the nozzle seat 11. The control chamber 18 is connected to the pressure chamber 8 via an inlet throttle (not shown in detail in the drawing), so that when the nozzle needle 10 is closed, i.e., when it is in contact with the nozzle seat 11, the same pressure prevails in the control chamber 18 as in the pressure chamber 8. The inlet throttle can, for example, be formed within the sleeve 16.

[0016] To regulate the pressure in the control chamber 18, a control valve 18 is arranged in the valve body 2. The control valve 18 is located in a low-pressure chamber 21, which is formed in the valve body 2 and in which a low fuel pressure is always maintained, as the low-pressure chamber 21 is connected to a low-pressure return line via a line not shown in detail in the drawing. The control valve 18 comprises a magnetic armature 23, which is arranged to be longitudinally movable in the low-pressure chamber 21. The magnetic armature 23 interacts with a control valve seat 26 to open and close a drain bore 28, which connects the control chamber 18 to the low-pressure chamber 21. The electromagnet 24 serves to move the magnetic armature 23; when energized, it exerts an attractive force on the magnetic armature 23 and pulls the magnetic armature away from the control valve seat 26 against the force of the armature spring 25.When the magnetic armature 23 releases the drain bore 28, fuel flows from the control chamber 18 into the low-pressure chamber 21, thereby reducing the pressure in the control chamber 18. The nozzle needle 10 then lifts from the nozzle seat 11 – driven by the fuel pressure in the pressure chamber 8 – and opens the injection ports 12. When the current to the electromagnet 24 is cut off, the armature spring 25 pushes the magnetic armature 23 back into its closed position. The fuel pressure in the control chamber 18 then rises again to the level of the pressure chamber 8 and pushes the nozzle needle 10 back into its closed position.

[0017] A recess 35 is formed in the valve plate 3, in which a pressure sensor 36 is arranged. The pressure sensor 36 is designed as a piezoelectric sensor and is connected via an electrical connection line 40 to a control unit, which is located in Figure 1not shown. Opposite the pressure sensor 36, a pressure chamber 32 is formed by a recess on the front face of the throttle plate 4, with which it rests against the valve plate 3 with an interposed diaphragm 30. The pressure chamber 32 is connected to the control chamber 18 via a connecting bore 33, so that the same fuel pressure always prevails in the pressure chamber 32 as in the control chamber 18.

[0018] The diaphragm 30 is clamped between the valve plate 3 and the throttle plate 4 and is held in place there. The contact force of the housing parts, in particular the valve plate 3 and the throttle plate 4, seals the pressure chamber 32 through the diaphragm 30. A pin 38 is arranged between the pressure sensor 36 and the diaphragm 30. Any deformation of the diaphragm 30 is transmitted via this pin to the pressure sensor 36, triggering a corresponding signal that is then transmitted to the control unit via the electrical connection. The pressure in the control chamber 18, and thus also in the pressure chamber 32, deforms the diaphragm 30 in the area of ​​the pressure chamber 32 towards the pressure sensor 36. This exerts a force on the pressure sensor 36 via the pin 38, resulting in a corresponding signal there.The deformation of the membrane 30 changes depending on the pressure in the pressure chamber 32, so that the pressure in the pressure chamber 32 and thus also in the control room 18 can be measured with the pressure sensor 36.

[0019] The membrane 30 is designed as a separate component and essentially has the shape of a circular disc, with corresponding openings for the passage of the high-pressure channels and for other fastenings. For this purpose, in Figure 2 a partially cutaway view of the fuel injector of the Figure 1 This is shown to illustrate this. Here, the throttle plate 4 and the nozzle body 5 are omitted, and the valve body 2 and the valve plate 3 are partially cut away to show the structure of the pressure sensor 36 and its arrangement. The centering pins 42 serve as an assembly aid to ensure that the individual housing parts are mounted in precisely the correct orientation.

[0020] In Figure 3Figure 1 shows a further embodiment of the fuel injector according to the invention, wherein the diaphragm 30 has several recessed areas 130. In addition to sealing the pressure chamber 32 against the pressure sensor 36, the diaphragm 30 also serves as a sealing film between the valve plate 3 and the throttle plate 4. The recessed areas 130 significantly increase the surface pressure in the remaining areas, particularly in the area around the high-pressure bores 44, where these pass through the boundary layer between the valve plate 3 and the throttle plate 4. The increased surface pressure also improves the tightness in this area, reliably preventing high-pressure fuel from escaping and entering the space between the clamping nut 6 and the housing 1.

[0021] In Figure 4Another embodiment of the invention is shown in an enlargement of the section designated A of the Figure 1 . The pin 38 extends through the entire valve plate 3, while the pressure sensor 36 is arranged in a recess 35 in the valve body 2. The diaphragm 30 is also clamped between the valve plate 3 and the throttle plate 4 and separates the pressure sensor 36 from the fuel.

[0022] Figure 5 shows a further embodiment of the invention in the same representation as Figure 4 . As already in the exemplary embodiment of the Figure 4 The pressure sensor 36 is arranged in a recess 35 in the valve body 2, as is the pin 38. The diaphragm 30, which seals the pressure sensor against the fuel, is clamped here between the valve plate 3 and the valve body 2, with the connection to the connecting bore 33 being made by a rising bore 34.

[0023] The diaphragm 30 can be made of a different material than the other housing parts. In particular, the diaphragm 30 can be made of a stretchable and high-strength material with high flexural strength to optimally transmit the pressure signal from the pressure chamber 32 to the pressure sensor 36. Since the diaphragm 30 is designed as a separate component, the material can be freely selected during the design of the fuel injector, and it is not necessary to consider the other geometric tolerances and material properties of the other housing parts and other components of the fuel injector. The thickness of the diaphragm can be chosen as desired, as long as the necessary elasticity is ensured.

Claims

1. Fuel injector for injecting fuel at high pressure into a combustion chamber of an internal combustion engine, having a multi-part housing (1), wherein the housing parts (2; 3; 4; 5) are braced against one another in a fluid-tight manner, wherein a pressure space (8), which can be filled with fuel and has a nozzle needle (10) that can be moved longitudinally therein, is formed in the housing (1), said nozzle needle interacting with a nozzle seat (11) in order to open and close at least one injection opening (12) and delimiting, by way of its end facing away from the nozzle seat (11), a control chamber (18), the pressure of which exerts a closing force acting in the direction of the nozzle seat (11) on the nozzle needle (10), and having a pressure chamber (32), which is hydraulically connected to the control chamber (18), and a pressure sensor (36), which is designed to measure the pressure in the pressure chamber (32), characterized in that a diaphragm (30), which separates the pressure sensor (36) from the pressure chamber (32) in a fluid-tight manner, is arranged between the pressure chamber (32) and the pressure sensor (36), wherein the diaphragm (30) is clamped between two housing parts (3; 4).

2. Fuel injector according to Claim 1, characterized in that the diaphragm (30) can be deformed in the direction of the pressure sensor (36) as a result of the pressure in the pressure chamber (32).

3. Fuel injector according to Claim 1 or 2, characterized in that a pin (38), which transfers a deformation of the diaphragm (30) to the pressure sensor (36), is arranged between the pressure sensor (36) and the diaphragm (30).

4. Fuel injector according to Claim 1, characterized in that the pressure space (8) is formed in a nozzle body (5) and the nozzle body (5) bears against a throttle plate (4), wherein the nozzle body (5) and the throttle plate (4) are part of the housing (1) and the throttle plate (4) delimits the control chamber (18).

5. Fuel injector according to Claim 4, characterized in that the pressure chamber (32) is formed by a recess in the throttle plate (4) and is connected to the control chamber (18) via a connecting bore (33) formed in the throttle plate (4).

6. Fuel injector according to either of Claims 4 and 5, characterized in that the pressure sensor (36) is arranged in a valve plate (3), which is also part of the housing (1) and bears against the throttle plate (4).

7. Fuel injector according to Claim 6, characterized in that the diaphragm (30) is clamped between the valve plate (3) and the throttle plate (4).

8. Fuel injector according to Claim 7, characterized in that the diaphragm (30) is in the form of a circular disc.

9. Fuel injector according to Claim 8, characterized in that the diaphragm (30) has one or more regions (130) with cutouts, so that it covers only part of the interface between the valve plate (3) and the throttle plate (4).

10. Fuel injector according to Claim 9, characterized in that at least one highpressure bore (44) passes through the interface between the valve plate (3) and the throttle plate (4) and in that the diaphragm (30) surrounds this passage region, so that the surface pressure is increased around the passage region.

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