EP1925814A1 - Fuel injector with a measuring device - Google Patents

Abstract

The fuel injector (1) has a moving device, which performs opening and closing movement for opening and closing a fuel injection opening (3) to inject fuel into a combustion chamber (4). A measuring device (5) formed as an eddy current sensor records the termination of fuel injection in the chamber. The sensor has a measuring body, which partially encloses the moving device. The device exhibits magnetization in the enclosing region over the body. An independent claim is also included for a method for recording the termination of injection of fuel into a combustion chamber.

Description

The present invention relates to a fuel injector for an internal combustion engine according to the preamble of claim 1. In particular, the present invention relates to a measuring device for detecting the movements of a moving means within the fuel injector.

State of the art

Fuel injectors of the type of interest here find particular application in internal combustion engines, which use such injectors to allow the metered injection of the fuel to be burned. Fuel injectors of the type of interest here can be subdivided into magnetically operated injectors and piezoelectrically operated injectors. Regardless of the type of execution of the fuel injector, this includes a nozzle needle, which is received within a nozzle body. By a lifting movement of the nozzle needle within the nozzle body fuel injection ports are released to inject pressurized fuel into the combustion chamber of the internal combustion engine.

From the publication DE 199 37 559 A1 discloses a fuel injector for an internal combustion engine, which is designed as a magnetically operated injector. The injector comprises a two-stage solenoid valve, wherein the solenoid valve moves a valve piston in a vertical axis of movement. The valve piston is operatively connected to a nozzle needle which abuts against a nozzle needle seat at the end and can release at least one fuel injection opening by means of a lifting movement for injecting the fuel into the combustion chamber and can also close it again. The problem with such executed fuel injectors oscillatory movements in the end positions of the nozzle needle, which may occur when triggered in the nozzle needle seat or when reaching the stroke stop, so that a precise dosage of the fuel quantity to be injected is hindered.

From the publication DE 10 2004 015 744 A1 a fuel injector is disclosed in the manner of a piezoelectrically operated injector. The nozzle needle is fluidly acted upon in the embodiment of the piezoelectrically operated fuel injector, and is controlled in the lifting movement via a nozzle needle control chamber, a nozzle spring and a pressure chamber surrounding the nozzle needle. Particularly in the case of common-rail systems (CRS), the injection quantity is controlled and adjusted merely by setting a rail pressure and a control duration determined from the setpoint quantity and rail pressure. In addition to the rail pressure and the activation duration, there are other parameters which influence the injection quantity of the fuel into the combustion chamber, such as the opening pressure of the nozzle, the armature or actuator stroke, occurring pressure waves and fluidic vibrations, which are caused by previous injections.

Such influences are currently either not at all or determined by controlled compensation of the driving time in response to the IMA code (information about quantity deviations) of an injector from the setpoint in the new state. The assumed interference interventions often do not match the actual interference and it comes to the fault compensation and thus deviations of the actual injected amount of the target amount of fuel, which is specified by the control unit of the engine. In the course of ever-tightening exhaust gas legislation but just the accuracy of the injection quantity is becoming increasingly important.

In CRS systems with a fully ballistic nozzle needle stroke, the nozzle needle essentially opens at a constant speed that is dependent on the rail pressure during the activation period and essentially closes at the end of the activation with a constant closing speed that is dependent on the rail pressure. Consequently, the closing delay duration, ie the time interval between the drive end and the injection end, is a measure of the injection duration and thus of the actually injected amount of the fuel into the combustion chamber. For non-ballistically operated nozzle needles, the delay time between the start of control and the stop of the nozzle needle at its stroke stop is a measure of the start of injection, so that over the time intervals between the Ansteuerbeginn and the stop of the nozzle needle on the stroke stop or between the Ansteuerende and the start of injection the actual amount injected can be determined.

For measuring the stroke of the moving means within the fuel injector measuring means are known, which are however mainly used for development purposes. The measuring devices are used for the design and structural design of the movement devices within a fuel injector, and are not suitable for a permanent operation within the fuel injector. In particular, known measuring devices in fuel injectors are not suitable for controlling an engine control unit in order to control an amount of fuel actually injected or injected into a combustion chamber via a control circuit. Although known measuring devices offer the possibility of sensing the stroke movement with regard to the direction and the speed of the movement devices, accurate detection of the stop of the nozzle needle in the nozzle seat and the achievement of the maximum opening in the stroke of the nozzle needle can not be detected with the known measuring devices.

It is therefore an object of the present invention to provide a fuel injector for an internal combustion engine, which provides information about the closing time or the opening time of the nozzle needle via an integrated measuring device. In particular, it is the object of the invention to provide a fuel injector with a measuring device which provides accurate information about the impact behavior of the nozzle needle in the nozzle needle seat and the behavior of the nozzle needle at the stop of the opening stroke.

Disclosure of the invention

This object is achieved on the basis of a fuel injector for an internal combustion engine according to the preamble of claim 1 in conjunction with its characterizing features. Advantageous developments of the invention are specified in the dependent claims.

The invention includes the technical teaching that the measuring device is designed as an eddy current sensor with a measuring body which at least partially surrounds the movement device, wherein the movement device has a magnetization at least in the region of the enclosure by the measuring body.

According to the present invention, the moving means is impressed with a magnetic field in the area enclosed by the measuring body. The magnetization can be effected either by a remanent magnetism or by energizing an exciting coil arranged inside the moving means, which can be referred to as external excitation. In addition, the magnetic field may be guided by the stationary component of the fuel injector in a magnetic core.

Now moves the moving means in the axial direction, i. in the direction of the movement axis, a signal is provided by the measuring device which is proportional to the movement speed of the movement device. In the case of permanent excitation as a consequence of remanence magnetism, the axial movement of the movement device induces a voltage in the sensor coil contained in the measuring body. In the case of external excitation by an excitation coil contained in the measuring body, eddy currents are generated by the axial movement of the movement device in the latter. Consequently, in this case as well, a voltage approximately proportional to the movement speed is induced in the sensor coil contained in the measuring body. If the Abklinkzeitkonstante the eddy currents greater than the injection duration, the decay of the eddy currents can be neglected. In the case of the external excitation, the functions of exciting and sensor coil can be summarized in an advantageous manner in a coil.

According to an advantageous embodiment of the present invention, it is provided that the measuring body comprises a magnetic yoke and the fuel injector is designed as a magnetically operated injector and the movement device is formed by a valve piston. After the design of a magnetically operated fuel injector, the valve piston moves in proportion to the movement of the nozzle needle. Therefore, the magnetic yoke can surround the valve piston, and the magnetization is carried out in the valve piston itself. The valve piston is guided in an injector body, so that the measuring device can be fixedly arranged within the injector. Alternatively, the fuel injector can be designed as a piezoelectrically operated injector with a fluidically actuated nozzle needle, and the movement device is formed by the nozzle needle itself. Here, too, a magnetization of the material of the nozzle needle can take place on at least a portion of the longitudinal extent, so that the measuring body of the measuring device in the form of the Magnetic yoke encloses the magnetized area of the nozzle needle. The measuring device is installed in the nozzle body stationary. Preferably, the measuring device is arranged on the low-pressure side of the nozzle body so as not to expose the measuring device to the high-pressure admission by the fuel, although an arrangement on the high-pressure side is likewise possible.

According to the operation of the measuring device, this comprises a coil body in addition to the magnetic yoke. The bobbin may be formed either as an excitation coil, as a sensor coil or as a combined exciter and sensor coil. On the part of the exciting coil, a magnetic field is generated within the moving device by energizing. The magnetic yoke is annular and has a U-shaped cross-section, wherein the opening of the U-shape points in the direction of the movement means. When using a separate sensor coil, the induced voltage can be removed directly from this. If the exciter and sensor coils are identical and this is supplied with a direct current, the induced voltage causes a deviation of the coil voltage from its value at rest. If, however, a constant DC voltage is applied to the coil, then the longitudinal movement of the movement device along the movement axis causes a deviation of the coil current from its value at rest. The striking of the nozzle needle or the valve piston at its stroke stop in the opening point and the closing of the nozzle needle are accompanied by extremely rapid changes in the piston speed, so that the measurement signal at these times each has a discontinuity. The time at which this discontinuity occurs is detected as Hubanschlags- or closing time and can then a higher-level controller, which is designed for example as an engine control unit or a part thereof, for this time or for the injection duration or the injection amount of the fuel in the Combustion chamber to be supplied.

According to a further advantageous embodiment of the invention, the magnetic yoke is designed radially slotted or has a material with a high resistivity, for example a powder composite material and / or a ferrite material.

The invention further relates to a method for detecting the end of the injection of a fuel into a combustion chamber and / or for detecting the stop of an opening stroke of a valve piston and / or a nozzle needle with a Measuring device, wherein the measuring device is operated with a constant DC current or a constant DC voltage, wherein the deviation from the constant DC voltage or from the constant DC serves as a measurement signal. In particular, the change in the periodic valve piston and / or nozzle needle movement results in a change in the measurement signal output by means of the measuring device in the form of the discontinuity. By means of this discontinuity, according to the present method, the stroke stop or closing times of periodically consecutive opening and closing cycles are determined.

Further, the invention improving measures will be shown together with the description of preferred embodiments of the invention with reference to the figures.

Embodiment:

Figur 1

einen Querschnitt eines brennraumseitigen Abschnitts eines Kraftstoffinjektors, welcher als magnetisch betriebener Kraftstoffinjektor ausgeführt ist, und eine Messeinrichtung einen innerhalb des Kraftstoffinjektors geführten Ventilkolben umschließt;

Figur 2

einen Kraftstoffinjektor gemäß Figur 1, wobei die Messeinrichtung im Düsenkörper integriert ist und die Düsennadel umschließt;

Figur 3

zeigt einen vergrößerten Ausschnitt der Anordnung der Messeinrichtung innerhalb des Kraftstoffinjektors gemäß der Figuren 1 und 2;

Figur 4

den Kurvenverlauf der Verwendung einer induzierten Spannung als Messsignal;

Figur 5

den Kurvenverlauf des Betriebes der Erreger- und Sensorspulen, welche mit einem Gleichstrom betrieben werden; und

Figur 6

den Kurvenverlauf des Betriebes der Erreger- und Sensorspule, welche mit einer Gleichspannung betrieben werden.

It shows:

FIG. 1

a cross section of a combustion chamber side portion of a fuel injector, which is designed as a magnetically operated fuel injector, and a measuring device encloses a valve piston guided within the fuel injector;

FIG. 2

a fuel injector according to Figure 1, wherein the measuring device is integrated in the nozzle body and surrounds the nozzle needle;

FIG. 3

shows an enlarged detail of the arrangement of the measuring device within the fuel injector according to Figures 1 and 2;

FIG. 4

the curve of the use of an induced voltage as a measurement signal;

FIG. 5

the waveform of the operation of the exciter and sensor coils, which are operated with a direct current; and

FIG. 6

the curve of the operation of the exciter and sensor coil, which are operated with a DC voltage.

The fuel injector shown in Figures 1 and 2 is formed in the manner of a magnetically operated injector and designated by the reference numeral 1. The housing of the fuel injector 1 is formed by an injector body 9 and a nozzle body 10.

Within the injector 9 and the nozzle body 10, a movement device is longitudinally movably guided along a movement axis 2, which is formed at least from a valve piston 7 and a nozzle needle 8. By a lifting movement of the nozzle needle 8 10 introduced fuel injection ports 3 are released in the nozzle body, so that the fuel can be injected into the combustion chamber 4. The lifting movement is controlled by a - not shown in the illustration - solenoid valve in the moving device.

FIG. 1 shows a measuring device 5, which is arranged at the level of the valve piston 7. The measuring device 5 comprises a magnetic yoke 6, in which a bobbin 11 is received. The bobbin 11 can be externally contacted via a connection line 12. According to the illustration, it can be seen that the measuring device 5 is introduced in a stationary manner within the injector body 9, and does not move along with the lifting movement of the movement device along the movement axis 2. The movement device is formed by the valve piston 7 as shown in FIG. 1 and the component relevant for the measuring device 5. The measuring device 5 encloses the valve piston 7 with the U-shaped magnet yoke 6. In the valve piston 7, magnetization has been impressed in a magnetization region 13, which has a north-south orientation along the movement axis 2. Now moves the valve piston 7 with the opening and closing movement of the nozzle needle 8 along the movement axis 2, the magnetic field changes in the magnetic yoke 6, so that in the bobbin 11, a voltage is induced, which can be tapped via the connecting lines 12. It is also possible that the bobbin 11 comprises both an exciter and a sensor coil, wherein the magnetic field within the valve piston 7 can be generated by energizing the exciter coil. By means of the sensor coil, a voltage is induced, which serves as a measured variable. Now opens the fuel injector 1, the fuel injection ports 3 by a vertical lifting movement of the nozzle needle 8, which is in interaction with the lifting movement of the valve piston 7, the magnetic flux in the magnetic yoke 6 changes.

In FIG. 2, the measuring device 5 is arranged at the level of the nozzle needle 8. Therefore, the magnetization region 13 is introduced into the nozzle needle 8 to produce a change in the magnetic field during a vertical movement of the nozzle needle 8 along the movement axis 2 in the same way as in the valve piston 7. The structure of the measuring device 5 as shown in Figure 2 in an arrangement around the nozzle needle 8 is similar to the structure in Figure 1, so that the measuring device 5 is also formed from a yoke 6, which receives a bobbin 11. The bobbin 11 is contacted via the connection line 12 externally. As shown, the measuring device 5 is fixedly connected to the nozzle body 10 in connection, so that the measuring device 5 does not move with the lifting movement of the nozzle needle 8.

To increase the Abklinkzeitkonstante the eddy currents within the valve piston or within the nozzle needle introduced in four circumferential grooves in the surface ring members 14 are provided in the region of the measuring device 5. These are made of a material with a very low specific resistance, such as aluminum. The ring elements 14 are introduced into grooves, so that the valve piston 7 in the region of the ring elements 14 has no diameter jumps. According to the illustration of the measuring device 5, this comprises a magnet yoke 6, which, due to the U-shaped design, comprises two subsections which adjoin the valve piston 7 directly. Between the two sections of the bobbin 11 is added. The ring elements 14 are in the idle state of the valve piston 7 at the height of the respective section of the magnetic yoke 6, which adjoin the valve piston 7, respectively. Thus, a total of four ring elements 14 are arranged within the valve piston 7, which adjoin the respective edge regions or the body edges of the U-shaped magnetic yoke 6.

Figures 4-6 show the relationship between the stroke of the valve piston (h _VK ) and the output signals through the measuring device. The abscissa is marked T and forms the time course. The stroke of the valve piston is shown on the ordinate in the upper graph and marked with h _VK . In Figs. 4 and 5, the lower graph represents the induced voltage which induces in the sensor coil and is output by the measuring device. In FIG. 6, the lower graph represents the current flow which flows through the bobbin.

The course of the induced voltage as shown in FIG. 4 initially begins with the beginning of the opening I, the opening period being characterized by the opening end II. Due to the ballistic behavior of the movement of the valve piston or the nozzle needle, the opening end II and the closing start III almost coincide in time. The closing operation extends from the closing start III to the closing end IV. The lower graph shows the induced voltage output by the measuring device. When reaching the end of a steep gradient with subsequent swinging motion is generated, which subsides by damping to zero. This vibration in the induced stress is generated by the dynamic behavior of the nozzle needle which strikes the nozzle seat. The steep gradient in the measurement signal can be detected by an evaluation device of the measurement signal, so that an accurate determination of the closing end 4 by the induced voltage signal is possible. If necessary, the damped oscillation can also be evaluated.

FIG. 5 shows the operation of the excitation and sensor coil with an impressed direct current. The course shows the induced voltage as a deviation from the value according to U = I _o · R. The respective swinging motion occurs both when reaching the opening end, ie at the time of Hubanschlages the nozzle needle in the open state, and at the end of closing, ie striking the nozzle needle in the nozzle seat , The deviation of the respective coil voltage from its value in the idle state serves as a measurement signal. The resting state is represented by a knotted dotted centerline.

Figure 6 shows the course of the coil current at a constant DC voltage, which is applied to the exciter and sensor coil. The deviation of the coil current from its value in the idle state serves as a measurement signal. The course therefore shows the constant value U _o / R in the idle state. The stroke stop times in the opening end II and in the closing time at the closing end IV generate steep gradients in the course of the current, which in turn are followed by damped oscillations. The gradients can be detected by an evaluation device, possibly together with the damped oscillation. This gives the possibility of an exact determination of the To create stroke stop or the closing end, so that the information obtained can be evaluated by an engine control unit.

The invention is not limited in its execution to the above-mentioned preferred embodiment. Rather, a number of variants is conceivable, which makes use of the illustrated solution even with fundamentally different types of use.

Claims (10)

A fuel injector (1) for an internal combustion engine having a movement device which performs an opening and closing movement in a movement axis (2) for opening and closing at least one fuel injection port (3) for injecting fuel into a combustion chamber (4), the fuel injector (1 ) has a measuring device (5) for detecting the end of the injection of the fuel into the combustion chamber and / or for detecting the stop of the opening stroke,
characterized in that the measuring device (5) is designed as an eddy current sensor with a measuring device at least partially enclosing the measuring body, wherein the moving device has a magnetization at least in the region of the enclosure by the measuring body. Fuel injector (1) according to claim 1,
characterized in that the measuring body comprises a magnetic yoke (6) and the fuel injector (1) is designed as a magnetically operated injector and the movement device is formed by a valve piston (7). Fuel injector (1) according to claim 1,
characterized in that the fuel injector (1) is designed as a piezoelectrically operated injector with a fluidically actuated nozzle needle (8), and the movement device is the nozzle needle (8). Fuel injector (1) according to one of the preceding claims,
characterized in that the fuel injector (1) comprises an injector body (9) and a nozzle body (10) arranged thereon, and the measuring device (5) is accommodated in the injector body (9) and / or in the nozzle body (10). Fuel injector (1) according to claim 4,
characterized in that the nozzle body (10) comprises a low pressure side, and the measuring device (5) is arranged in the low pressure side. Fuel injector (1) according to one of the preceding claims,
characterized in that the measuring device (5) comprises a coil body (11) embedded in the magnetic yoke (6), wherein the coil body (11) comprises a sensor coil and / or an exciter coil. Fuel injector (1) according to one of the preceding claims,
characterized in that the movement device in the region of the measuring device (5) in at least one circumferential groove in the surface introduced ring elements (14), which are formed of a material having a low resistivity. Fuel injector (1) according to one of the preceding claims,
characterized in that the magnetic yoke (6) is made radially slotted and / or has a material with a high resistivity, comprising a powder composite material and / or a ferrite material. Method for detecting the end of the injection of a fuel into a combustion chamber and / or for detecting the impact of an opening stroke of a valve piston (7) and / or a nozzle needle (9) with a measuring device (5) according to one of claims 1 to 8,
characterized in that the measuring device (5) is operated with a constant direct current or with a constant direct voltage, wherein the deviation from the direct current or the direct current serves as a measuring signal. Method according to claim 9,
characterized in that a change of the measuring device output by means of the measuring device (5) results in a discontinuity from a change in the periodic valve piston and / or nozzle needle movement, and by means of the discontinuity of the stroke stop or closing times periodically successive opening and closing cycles are determined ,

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