EP1656499A1

EP1656499A1 - Injection valve with a capacitive valve lift sensor

Info

Publication number: EP1656499A1
Application number: EP04742011A
Authority: EP
Inventors: Wolfgang Gerber; Uwe Leuteritz; Martin Neumaier; Jörg WONESCH
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2003-08-21
Filing date: 2004-07-29
Publication date: 2006-05-17
Also published as: WO2005021958A1; US7055762B2; US20050269422A1; DE10338489B3

Abstract

The invention relates to an injection valve in which the movable valve parts and the valve seat (4) form the electrodes of a capacitor that is connected in an electric circuit, the capacity of said capacitor changing with the valve lift of the closing element. According to the invention, the valve seat (4) is configured in the form of an electrically conductive nozzle body (2) that is connected to the electric circuit and the closing element is configured in the form of a valve needle (5) that is connected to the electric circuit by its end surface opposite the valve seat (4).

Description

description

Injection valve with capacitive valve lift sensor

The invention relates to an injection valve with a capacitive valve lift sensor for internal combustion engines.

Such an injection valve is already known from DE 198 30 667 AI.

In connection with the growing demands on a controlled engine injection system, it is becoming increasingly important to be able to build a stable control system for the precise control of the amount of fuel to be injected. In series operation, for example in a diesel piezo injector with a diesel engine control system, a sufficiently precise detection or determination of the time and the actual quantity of the individual injection cannot take place directly, but only indirectly by detecting the actual movement of the valve needle in the injection valve and a calculation of the injection quantity based on this.

For the purpose of detecting the actual movement of the valve needle, needle lift sensors have become known in recent years which are non-contact, for example on the

Based on optical elements or Hall elements. However, it is not without problems - also from a cost point of view - that such sensors with a relatively large space requirement are placed in an injector that is already narrowly dimensioned, where appropriate in an environment in which fuel pressures of up to

There is 2000 bar to install. On the other hand, installing a needle lift sensor increases the risk of leaks.

From DE 31 17 779 a needle stroke sensor with limited monitoring options in the form of a needle tip / valve seat contact switch is known, the two switching positions tion are correlated with the times of closing or opening of the valve needle, so that the actual injection duration, but not the exact injection course or the actual injection quantity, can be measured. Seat contact switches also require good electrical contact between the tip of the valve needle and the valve seat in the closed position, i.e. when the valve needle hits the valve seat, while newer efforts tend to reduce the high impact stresses in operation.

The invention is therefore based on the object of realizing a valve of the type specified at the outset as an injection valve, in particular as a piezo injector.

This object is achieved by an injection valve according to claim 1. Further training and preferred measures result from the subclaims.

According to the invention, it is accordingly provided in an injection valve of the type mentioned at the outset that there is an electrically conductive injector body connected to the circuit, on which a nozzle body with a valve seat is formed, and that the closure member is designed as a valve needle, which on its side Valve seat opposite, valve-facing end surface is connected to the circuit.

The invention is based on the premise of a valve needle which, apart from an electrical contact point at the end opposite the valve seat, is completely insulated from the nozzle body (housing). Valve needle and housing form a capacitor. The movement of the valve needle changes the distance between the tip of the valve needle and the valve seat, while the distance between the needle guide and the housing remains constant. Since the valve needle and nozzle body are both electrically conductive and in particular by an insulating de layer are separated from one another, they fulfill the characteristic of a capacitor with a variable capacitance value, the capacitance being indirectly proportional to the distance between the valve seat and valve needle tip. By means of an electrical signal, the start of movement and position during the movement of the valve needle can be detected in a reproducible and documentable manner. The injection process and the injection quantity can be calculated from these signals. As a result, a stable control system for regulating the amount of fuel to be injected can be set up for series production.

For further mechanical and electrical implementation, it is advantageous according to a first embodiment of the invention that the voltage connection of the capacitor circuit is carried out via a conductor which is insulated in an axial bore in the injector body and which is connected to an electrically conductive contact spring which is arranged insulated in the injector body which is supported in a contact-making manner on the underside of the head of a conductive injector piston which is pressed in a contact-making manner against the end face of the valve needle facing away from the valve. In particular, in this embodiment it is advantageous that the injector body is designed as an intermediate disk above the end face of the valve needle facing away from the valve, and that an electrically conductive contact part for the electrical connection between the conductor and the contact spring is provided on the side of the intermediate disk facing away from the valve is electrically insulated from the injector body and the washer and on which the contact spring is supported with its valve-side end. It is also advantageous to provide a seal at the beginning and end of the axial bore.

According to a second embodiment of the invention, it is advantageous to guide the capacitor circuit via a nozzle holding spring which is arranged in an electrically insulated manner in the injector body and which presses the valve needle against the valve seat, where the nozzle holding spring is supported with an end facing away from the valve on an adjusting disk, which is electrically connected to a further connection contact, and is supported on the valve side on a conductive injector piston which is pressed in a contacting manner against the end face of the valve needle facing away from the valve.

In these embodiments, the electrical insulation can be ensured or improved in a simple manner, in that in particular the valve needle and the injector piston have an insulating layer on at least part of the surfaces which are not used for contacting.

With regard to electrical decoupling of movable valve parts or valve-side regions of the injection valve from the condenser, it is particularly advantageous to provide a control piston which, with its valve-side end surface, presses on the central region of the head surface of the injector piston remote from the valve, at the same time on the head surface an insulating layer must be provided for the injector piston.

Within existing structural designs of injectors, the capacitive valve lift sensor can advantageously be integrated in that the injector body is designed as an intermediate disk above the end face of the valve needle facing away from the valve and that an axial annular shoulder is formed on the end face of the valve needle, which shoulder shoulder is formed on the underside of the intermediate disk Counter shoulder is assigned as a stop surface, wherein the underside of the washer can be provided with an insulating layer at least in the region of the stop surface.

With a view to avoiding leakage currents and corrosion, it is expedient for the valve lift present in each case to be ascertainable by measuring the voltage U- ^ dropping at the valve seat (R ₂ + C _va r), the operating voltage being voltage U _B an AC voltage is applied. The change in the complex resistance R ₂ + C _{var is} measured in a predetermined time window in order to determine the position of the nozzle needle or the valve lift.

The insulating layers can preferably be formed, at least in places, as diamond-like-carbon (DLC) or aluminum oxide or as a zirconium oxynitrite layer which, in addition to its insulating properties, is distinguished by high abrasion resistance and resistance to impact and does not move due to the movement of the corresponding parts Friction inhibits.

The valve stroke H of the nozzle needle present can be determined by measuring the voltage falling across the complex resistor R ₂ + C _var , an AC voltage being applied as the operating voltage U _B and the complex resistor being essentially formed between the nozzle needle and the nozzle body.

The axial position of the nozzle needle depends on the determined capacity and the resistance between the injector body and at least one valve part.

The point in time at which the nozzle needle is lifted off the valve seat depends on the determined change in the capacity between the nozzle needle and the nozzle body and can be determined in particular by the determined reduction in capacity.

The wear of the insulating layer between the nozzle needle and the nozzle body depends on the determined ohmic resistance between the nozzle needle and the nozzle body, a reduction in the resistance (R ₂ ) preferably being associated with increased wear.

The inside of the nozzle body and the nozzle needle are coated at least in the region of the valve seat. Further advantages and refinements of the invention are explained in more detail in the following description of the exemplary embodiment shown in the figures of the drawing. It shows :

FIG. 1 schematically shows a longitudinal section through the part of an injection valve on the nozzle side according to the invention,

FIG. 2 shows another embodiment of an injection valve according to the invention in the illustration according to FIG. 1,

Figure 3 is an electrical equivalent circuit diagram of the capacitor circuit used for the capacitive determination of the valve lift.

FIG. 1 shows in longitudinal section, for example, a piezoelectrically driven injection valve which, together with other piezo injectors, can be connected in a manner known per se to a central pressure accumulator (common rail) for diesel fuel, not shown, and its electrical actuation by means of an external one Control unit (ECU) takes place. The piezo actuator itself is usually located in the upper part of the injector body 14, which is not shown here.

The lower part of the injection valve shown is mainly made of electrically conductive materials and is preferably rotationally symmetrical with respect to the valve axis 1. It has a nozzle body 2, at the nozzle opening 3 of which a valve seat 4 is formed, on which a valve needle 5 is seated. The upper section of valve needle 5, which is enlarged in cross-section, is guided closely in nozzle body 2, an insulating layer 22 _r, however, providing abrasion-resistant and low-friction insulation between this section of valve needle 5 and nozzle body 2. At the transition from the upper to the lower section of the valve needle 5, which section is narrowed in cross section, a high-pressure fuel (via an inlet, not shown) is supplied with fuel. Pressure chamber 13 is provided, from which the supply of fuel can take place along the valve needle 5, via the valve seat 4, to the nozzle opening 3. As a result, sufficient electrical insulation to the nozzle body 2 is normally already provided along the lower section of the valve needle 5.

The upper end face of the valve needle 5 borders on an intermediate disk 6, which, together with the narrow guidance of the valve needle 5, in this embodiment separates a valve-side high-pressure region of the fuel injection valve from a low-pressure region located above it and the others with those arranged above and below it Areas of the nozzle body 2 and the injector body 14 is conductively connected. Above the intermediate disk 6, a spring space 7, which is open at the end and in which a nozzle holding spring 8 is arranged, is recessed in the injector body 14. The nozzle holding spring 8 is supported downwards on the upper side of an injector piston 9 designed as a T-piece, which is guided through a bore in the intermediate piece 6 and with it

Bottom presses on the upper end surface of the valve needle 5. On the opposite side, the nozzle holding spring 8 is supported on an adjusting disk 10 which is insulated from the injector body 14 and is electrically connected by a bore leading outwards to a connection contact 11 insulated from the injector body 14.

A control piston 12 is guided axially through the nozzle holding spring 8 and presses with one end surface on the upper side of the injector piston 9 and extends with the opposite end into the upper part of the injection valve.

The mode of operation of this construction, which is known per se in the mechanical-hydraulic aspects, is based on the fact that, as long as the injector is not actuated, the high fuel pressure is simultaneously applied to the tip of the valve needle 5 and in one to the upper end face of the control piston 12. orderly control room is present there, because of the larger area, but expresses itself with a greater effective pressure force and thus closes the valve. If the injector is actuated, the expanding piezo actuator opens a fuel return from the control chamber, as a result of which the pressure at the tip of the valve needle 5 becomes overweight, pushes the valve needle 5 upward and opens the nozzle valve. In principle, however, other designs are also possible according to the invention in which a piezo actuator or a solenoid valve is energized when the valve is closed.

As can be seen in FIG. 1, the cross section of the upper section of the valve needle 5 is somewhat larger than the cross section of the bore provided in the intermediate disk 6 for the injector piston 9. In this way, an axial ring shoulder is formed on the upper end surface of the valve needle 5, which is assigned a counter shoulder formed on the underside of the intermediate disk 6 as a stop surface.

FIG. 2 shows an embodiment of the injection valve according to the invention which differs in contact from the embodiment shown in FIG. 1. As can be seen, the voltage connection takes place via a connection 15 and an axial bore 19 in the injector body 14, through which an insulated conductor (wire) 16 is guided. On the side of the intermediate disk (stop disk) 6 facing away from the valve, an electrically conductive contact part 18 is incorporated, which is electrically insulated from the intermediate disk 6 and the injector body 14, for example by an insulating insert, and has a fixed electrical connection to the conductor 16. An electrically conductive contact spring 17 is supported on the contact part 18, which is supported at its other end on the underside of the head of the injector piston 9 and thus transfers the voltage to the injector piston 9. The injector piston 9 is electrically decoupled and to reduce the parasitic capacitances with respect to the control piston 12 on the head surface and the side surfaces of the head with an electrically risch insulating layer 21 provided. The voltage is passed to the valve needle 5 (which is laterally insulated to the nozzle body 2) via the valve-side end of the stroke adjustment bolt 9. Advantages of this contacting variant are the simpler installation in the engine compartment and the possibility of continuing the connection 15 in the injection valve upwards and thus in particular creating an electrical connection to the plug of the piezo actuator. The bore 19 should, as shown, be sealed from the inside to the outside and from the outside to the inside by means of a seal 20 in order to avoid the penetration of foreign substances or a loss of pressure.

The nozzle needle 5 and the injector body 14 (housing) of the described injection valve form a capacitor connected in a circuit, which acts as a capacitive valve lift sensor as follows:

In order to obtain an electrical signal corresponding to the position of the valve needle 5 and the valve stroke H associated therewith, the nozzle body 2 is connected to ground potential and the connection contact 11 is connected via a series resistor R _before to a voltage source U _B. In this circuit arrangement shown in Figure 3, the drop in voltage Uι _nj at R ₂ + C _{var is} measured directly and for evaluation, z. B. used as part of a central control unit (ECU). The voltage U _B is fed to the adjusting disk 10 of the nozzle holding spring 8 or the connection 15 and, depending on the contact variant, is passed on to the valve needle 5. It should be noted that all current-carrying parts apart from the contact points are sufficiently well insulated from the nozzle body 2. This is ensured by a sputtered diamond-like-carbon (DLC) - or an aluminum oxide or a zirconium oxynitrite layer, which has a high abrasion resistance and a low electrical conductivity and is therefore also suitable as an insulation layer, even if leakage currents cannot be excluded , An insulating layer must in particular which are provided at the locations of the shim 10 and the stroke adjustment bolt 9, at which there is a narrow guide to the nozzle body 2. With this insulating layer, it is also advantageous if it also has a very low coefficient of friction, which guarantees good running properties of the moving parts.

The electrical equivalent circuit diagram shown in FIG. 3 also makes the resistance conditions in the injector clear and shows the simple structure of the measuring circuit with the voltage source U _B , the capacitor C _var and the resistor R _VOr -R ₂ connected in series with C _var is the ohmic resistance component, C _{var is} the corresponding capacitive reactive component between the nozzle needle and the valve seat. R _IS0 denotes the insulation resistance of the insulating layer and R _FG the contact resistance between the guidance of the valve needle 5 and the nozzle body 2. R ₂ «(Riso + R _FG ) applies. • C _var and R ₂ essentially represent the complex resistance between the Valve seat is represented by the nozzle needle tip 4 and the associated inside of the nozzle body 2.

In order to avoid corrosion due to contact erosion and / or galvanic processes in exposed contact surfaces and since leakage currents are to be expected at the insulating layers, the operating voltage U _{B is designed} as an alternating voltage.

The total stroke of the valve needle 5 can be, for example, 100-250 μ. Apart from the measurement of the voltage drop Uinj already described, the electrical evaluation can also be based on another electrical principle or also in

Combination with a suitable coil can be realized by detuning the resonance frequency.

The electrical evaluation must take into account the fact that the relatively small changes in capacitance to be measured are also due to capacitances connected in parallel, cf. C | _<onst and associated Ri in Figure 3, - large Facing total capacity. It is therefore advantageous to reduce the total capacity in particular by inserting an insulating layer between the lower end face of the control piston 12 and the upper end face of the injector piston 9, which layer layer reduces the total capacity by connecting partial capacitances.

According to the invention, the position of the valve needle 5 can be detected in a direct manner with relatively simple means, in particular without major mechanical outlay. From this, a control chain can also be built, which uses a few arithmetic steps to infer the actual injection quantity from the measured values, compares this with the setpoints predefined according to the operating mode, and adjusts the control parameters accordingly by evaluating the differences.

Claims

claims

1. Injection valve with a capacitive valve lift sensor for internal combustion engines, with a valve seat (4) and movable valve parts, which comprise a longitudinally guided closure member assigned to the valve seat (4), which is guided in an electrically insulated manner, the closure member and the valve seat (4) each having electrodes of a capacitor connected in a circuit, the capacity of which changes with the valve stroke of the closure member, characterized in that an electrically conductive injector body (14) is provided, on which a nozzle body (2) with a valve seat (4) is provided. is formed, and that the closure member is designed as a valve needle (5), which is connected to the circuit at its valve face (4) opposite end face facing away from the circuit.

2. Injector according to claim 1, characterized in that the voltage connection of the

Circuit via an isolated in an axial bore (19) in the injector body (14) guided conductor (16), which is connected to an insulated in the injector body (14) arranged, electrically conductive contact spring (17), which makes contact on the underside of the Head of a conductive injector piston (9) is supported, which is pressed in contact with the end face of the valve needle (5) facing away from the valve.

3. Injection valve according to claim 1 or 2, characterized in that the injector body (14) above the valve-facing end face of the valve needle (5) is designed as an intermediate plate (6), and that on the valve-facing side of the intermediate plate (6) an electrically conductive contact part (18) for the electrical connection between the conductor (16) and the contact spring (17) is provided, which is opposite the injector body (14) and the washer (6) is electrically insulated and on which the contact spring (17) is supported with its valve-side end.

4. Injector according to claim 2 or 3, characterized in that a seal (20) is provided at the beginning and end of the axial bore (19).

5. Injection valve according to claim 1, characterized in that the circuit via an electrically insulated in the injector body (14) arranged nozzle holding spring (8), which presses the valve needle (5) against the valve seat (4), the nozzle holding spring ( 8) with an end facing away from the valve on an adjusting disc (10), which is electrically connected to a further connection contact (11), and is supported on the valve side on a conductive injector piston (9), which presses against the end face of the valve needle (5) facing away from the valve is.

6. Injection valve according to one of claims 2 to 5, characterized in that the valve needle (5) and the injector piston (9) have an insulating layer on at least part of the non-contacting surfaces.

7. Injection valve according to claim 5 or 6, characterized in that a control piston (12) is provided, which presses with its valve-side end surface onto the central region of the valve surface facing away from the injector piston (9), and that on the head surface of the stroke adjusting bolt ( 9) an insulating layer is provided.

8. Injection valve according to one of the preceding claims, characterized in that the injector body (14) above the valve-facing end face of the valve needle (5) is designed as an intermediate plate (6), and that on the end face of the valve needle (5) has an axial annular shoulder is formed, which is formed on the underside of the intermediate disc (6) Dete counter shoulder is assigned as a stop surface, the underside of the intermediate disc (6) is provided with an insulating layer at least in the region of the stop surface.

9. Injection valve according to one of claims 6 to 8, characterized in that the electrically insulating layer is designed as a diamond-like-carbon (DLC) or aluminum oxide or as a zirconium oxynitrite layer.

10. Injection valve according to one of the preceding claims, characterized in that the valve stroke (H) present in each case by measuring the respectively on the complex resistance

(R ₂ + C _var ) falling voltage Ui _nj can be determined, an AC voltage being applied as the operating voltage U _B and the complex resistance being essentially formed between the nozzle needle and the nozzle body.

11. Injection valve according to one of the preceding claims, characterized in that the axial position of the nozzle needle

(5) depends on the determined capacity (C _var ) and resistance (R ₂ ) between the injector body (14) and at least one valve part (5, 6, 9, 12).

12. Injection valve according to claim 10 or 11, characterized in that the time of lifting the nozzle needle from the valve seat depends on the determined change in the capacity between the nozzle needle and the nozzle body and in particular can be detected by the determined reduction in capacity.

13. Injection valve according to one of the preceding claims, characterized in that the wear of the insulating layer between the nozzle needle and the nozzle body depends on the determined ohmic resistance (R ₂ ) between the nozzle needle (5) and the nozzle body (2) and preferably with increased wear a reduction resistance (R ₂ ).

14. Injection valve according to one of the preceding claims, characterized in that the inside of the nozzle body (2) and the nozzle needle (5) are coated at least in the region of the valve seat (4).