DE102017216942A1 - Method for calibrating a force or pressure sensor - Google Patents

Abstract

The invention relates to a method for calibrating a sensor (20) designed as a force or pressure sensor in or on a fuel injector (170) of an internal combustion engine (160) which is supplied with fuel from a high-pressure accumulator (175), wherein at least one event, comprising a fuel pressure change in the fuel injector (170), at least one signal trace (S, S ') of the sensor (20), and at least one associated reference trace (R ₁ , R ₂ ) of a reference sensor (190), one by a pressure in one Measured with the fuel injector (170) in fluid-communicating volume characterized size, are detected, and wherein the sensor (20) based on the at least one waveform (S, S '), the at least one reference curve (R ₁ , R ₂ ) and a Transfer function between the reference sensor (190) and the sensor (20) is calibrated.

Description

The present invention relates to a method for calibrating a designed as a force or pressure sensor sensor in or on a fuel injector of an internal combustion engine, which is intended to detect an opening and / or closing of the fuel injector, and a computing unit and a computer program for its implementation.

State of the art

Modern internal combustion engines have fuel injectors, with which fuel can be selectively introduced into combustion chambers. For precise control of the internal combustion engine and compliance with emission and performance requirements, it is advantageous to detect characteristic timing of the injection events, in particular opening and closing of the injectors of the fuel injectors and thus an injection start and an end of injection, or an output amount of fuel as accurately as possible.

From the DE 10 2010 000 827 A1 For example, a fuel injector is known in which a sensor is provided to detect pressure changes, so that such characteristic times can be closed.

Disclosure of the invention

According to the invention, a method for calibrating a sensor designed as a force or pressure sensor as well as a computing unit and a computer program for carrying it out with the features of the independent patent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

An inventive method is used to calibrate a designed as a force or pressure sensor sensor in or on a fuel injector of an internal combustion engine. The fuel injector is supplied from a high-pressure accumulator with fuel. Force or pressure sensors in or on a fuel injector of an internal combustion engine are usually provided to detect an opening and / or closing of the fuel injector. The sensor can be provided in the fuel injector in the same or similar manner, as in the DE 10 2010 000 827 A1 is described. By means of such a so-called needle-closing sensor (NC sensor), pressure changes in the control chamber of a valve of the fuel injector or in another position, for example the high-pressure bore of the injector, can be detected.

At least one event which comprises a pressure change in fuel in the fuel injector, at least one signal curve of the sensor and at least one associated reference profile of a reference sensor, which measures a variable characterized by a pressure in a volume in fluid communication with the fuel injector, are then detected , The sensor is then calibrated based on the at least one waveform, the at least one reference history, and a transfer function between the reference sensor and the sensor. The reference sensor can be arranged in particular away from the fuel injector.

With the mentioned sensors in or on the fuel injector, it is usually only possible to detect pressure changes, which is also sufficient for a detection of characteristic times such as injection start or end of injection. Elaborate electronic circuits are so far unnecessary. However, as soon as further functions, such as the exact determination of a pressure level to be met with the signals detected by the sensor, for example, a height of the pressure changes must be known (eg for a rail pressure, possibly for plausiblization), it is necessary, the absolute or at least relative height of the Pressure change or the sensor signal to know. Likewise, deviations over the lifetime of the sensor can be relevant.

The proposed calibration or adjustment using a reference sensor can now be achieved in a very simple manner that the sensor can be used in or on the fuel injector to a meaningful signal for absolute or relative pressure change in fuel in the fuel injector receive. As a reference sensor basically comes into question any sensor with which an absolute or relative pressure change in a fuel volume, which is in fluid communication with the injector, can be detected. Particularly suitable in this case is a pressure sensor (so-called rail pressure sensor, RDS) for the high-pressure accumulator (so-called rail), since such is already present anyway. The quantity characterized by a pressure in a volume in fluid communication with the fuel injector is then the rail pressure.

Since the reference sensor is provided away from the sensor, any different effects of the pressure change on the sensor on the one hand and the reference sensor on the other hand can be taken into account by means of the transfer function. Although the pressure changes propagate due to the fluidly connected fuel circuit, but can, for example, by throttling or volume effects or Pressure wave superposition different effects in the high pressure accumulator on the one hand and in the fuel injector on the other hand occur. Such a transfer function can be determined beforehand, for example in the context of a simulation and / or test measurements, and then stored in an executing arithmetic unit.

It is understood that a calibration for several or all sensors in or on fuel injectors of the internal combustion engine can take place in the same way. An assignment of a signal profile of the sensor to the actual change in pressure determined during the calibration can then be stored, for example, in a map or the like.

Preferably, the at least one event comprises a pressure change in an inlet of the high-pressure accumulator, which is caused in particular by a pump stroke of a high-pressure pump, or in the high-pressure accumulator. Such pressure changes before or in the high-pressure accumulator have a uniform effect on all fuel injectors, so that a particularly simple calibration can be carried out in this way. In addition, the value of the pressure change in such pump strokes is usually known.

Advantageously, the at least one event comprises a pressure relief (or a pressure drop) of the high pressure accumulator. For this purpose, for example, using a pressure regulator or a pressure control valve (DRV) a targeted pressure reduction in the high-pressure accumulator done, which then affects equally on all fuel injectors. This event is preferably timed to take place between the injections of the injectors to avoid being influenced by injection.

Alternatively to the procedure described above, e.g. if there is no DRV, or in addition, it is also preferable if the at least one event includes injection of fuel through the fuel injector or other fuel injector of the internal combustion engine. In this way, a pressure drop can be generated, which also propagates through the associated high-pressure line in the high-pressure accumulator and then also affects the other fuel injectors.

It is particularly preferred for a plurality of events which comprise different pressure changes to be detected in each case a signal course and a reference profile, based on which the sensor is calibrated. In this way, a calibration of the sensor can be done on the one hand more accurate and on the other hand in a larger area. Different pressure changes can be caused in the case of the pump stroke of the high-pressure pump, for example, by varying the amount of fuel delivered. In the case of deliberately caused drop in pressure In the high-pressure accumulator, the target pressure can be set to different values. And in the case of injection by the fuel injector, the pressure change can be varied by injection times of different lengths.

Preferably, the sensor is calibrated at predetermined, in particular regular, time intervals. In this way, any deviations that occur over the life of the sensor, be taken into account.

The calibration should preferably be performed outside of conventional injection processes, since for such a calibration usually pressure changes or periods are necessary, which are not common in the context of conventional injection operations or fuel delivery into the high-pressure accumulator.

An arithmetic unit according to the invention, e.g. a control device of a motor vehicle, is, in particular programmatically, adapted to perform a method according to the invention, e.g. by a so-called calibration mode.

Also, the implementation of the method in the form of a computer program is advantageous because this causes very low costs, especially if an executive controller is still used for other tasks and therefore already exists. Suitable data carriers for providing the computer program are in particular magnetic, optical and electrical memories, such as e.g. Hard drives, flash memory, EEPROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

The invention is illustrated schematically by means of embodiments in the drawing and will be described below with reference to the drawing.

list of figures

• 1 schematically shows an internal combustion engine with common rail system, which is suitable for carrying out a method according to the invention.
• 2 schematically shows a solenoid valve, in which a method according to the invention is feasible.
• 3 shows a waveform when performing a method according to the invention in a preferred embodiment.
• 4 shows reference curves and a waveform when performing a method according to the invention in a further preferred embodiment.
• 5 shows a calibration when performing a method according to the invention in a further preferred embodiment.

Embodiment (s) of the invention

In 1 is schematically an internal combustion engine 160 shown, which is suitable for carrying out a method according to the invention. By way of example, the internal combustion engine comprises 160 four combustion chambers or associated cylinders 165 , Every combustion chamber 165 is a fuel injector 170 with a sensor 20 assigned. Every fuel injector 170 is to a high-pressure accumulator 175 , a so-called rail or common rail, connected and is supplied by this with fuel. It is understood that a method according to the invention can also be carried out in an internal combustion engine with any other number of cylinders, for example one, two, three, five, six, eight, ten or twelve cylinders.

Next is the high-pressure accumulator 175 via a high-pressure pump 161 with fuel from a fuel tank 195 in which also a low pressure pump 196 can be provided, fed. The high pressure pump 161 is with the internal combustion engine 160 coupled, for example, such that the high-pressure pump via a crankshaft of the internal combustion engine, or via a camshaft, which in turn is coupled to the crankshaft, is driven.

A control of the fuel injectors 170 for metering or injecting fuel into the respective combustion chambers 165 via a motor control unit 180 trained computing unit. Every fuel injector 175 can be specifically controlled. Furthermore, the engine control unit 180 adapted to the fuel pressure in the high-pressure accumulator 175 by means of a pressure sensor 190 capture.

Furthermore, a pressure control valve 191 for the high-pressure accumulator 175 provided to regulate or adjust the pressure in the high-pressure accumulator. There is also an air supply system 140 for introducing air into the cylinders 165 and an air removal system 141 for discharging exhaust air or exhaust gases from the cylinders 165 shown, which here about a so-called turbocharger 141 and an exhaust gas recirculation valve 142 are connected.

In 2 is schematically a part of a fuel injector 170 out 1 shown in more detail. Here are within an injector body 1 a high pressure room 2 as well as a low-pressure room 3 arranged. These two spaces are separated by a valve piece 4 separated.

The high pressure room 2 communicates via an inlet channel 5 with the high-pressure accumulator or the common rail according to 1 , The low pressure room 3 is via a return line 21 or the like with the fuel tank according to 1 connected.

The high pressure room 2 is not shown injectors with the combustion chamber or the cylinder of the internal combustion engine according to 1 connectable. The injection nozzles are controlled in a known manner by means of a nozzle needle, from the in 2 only the nozzle-distal end, which is designed as a plunger (or control piston) 6, is shown. The plunger 6 is displacer effective in a valve piece 4 arranged control room 7 arranged. This control room 7 communicates via an inlet throttle 8th with the high pressure room 2 and via a preferably throttled drainage channel 9 with the low-pressure room 3 , wherein the drainage channel 9 by means of a control valve arrangement 10 is controlled.

When the drainage channel by means of the control valve assembly 10 is shut off and the nozzle needle is in its closed position, arises in the control room 7 the same high pressure as in the high pressure room 2 a, with the result that the plunger 6 in 2 pressed down and the associated nozzle needle is held in the shut-off the injectors closing position.

Becomes the drainage channel 9 by means of the control valve arrangement 10 (or by lifting the valve armature or closing body 11 ) opens in the control room 7 one opposite the high pressure room 2 reduced pressure and the plunger 6 moves together with the nozzle needle in 2 upward, that is, the nozzle needle is placed in its open position, so that fuel is injected through the injectors into the combustion chamber.

The control valve assembly 10 has a sleeve-shaped closing body 11 (Valve anchor), by a closing spring 12 , which is designed as a helical compression spring, against a to the outlet port of the drain channel 9 concentric seat is tensioned. In the example of 2 the seat is designed as a plane surface on which the sleeve-shaped closing body 11 is seated with a line-shaped annular edge. In principle, however, a differently shaped seat may be provided.

The sleeve-shaped closing body 11 is on one to the longitudinal axis 30 of the injector body 1 equiaxed guide rod 13 guided axially displaceable, wherein the annular gap between the inner periphery of the closing body 11 and the outer periphery of the guide rod 13 is designed as a practically leak-free throttle or sealing gap. When the closing body 11 in the 2 shown closed position assumes that within the closing body 11 formed pressure chamber 14 , which via the drainage channel 9 with the control room 7 communicates and then correspondingly the same fluid pressure as the control room 7 has, compared to the low pressure space 3 shut off.

On the closing body 11 is a star-shaped anchor 15 an electromagnet arrangement 16 arranged as an actuator for actuating the control valve assembly 10 is provided. This electromagnet arrangement 16 has in a known manner a magnetic coil 17 that are within a guide rod 13 concentric electromagnet arrangement with an annular outer pole 18 and an annular inner pole 19 is arranged. Will the solenoid coil 17 electrically energized, becomes the anchor 15 from the poles 18 and 19 magnetically attracted, leaving the closing body 11 against the force of the closing spring 12 lifted from its seat and the control valve assembly 10 is opened.

During the closed phase the with the plunger 6 connected nozzle needle, that is with closed injection nozzles, is the control valve assembly 10 closed, and in the pressure room 14 as well as in the control room 7 the same fluid pressures prevail. Immediately before the closing time of the nozzle needle, the pressure in the control chamber decreases 7 because of the low pressure at that time under the nozzle seat of the nozzle needle and the associated closing movement of the plunger 6 under the high pressure in the inlet channel 5 from. Immediately after closing the nozzle needle it comes because of the now stationary plunger 6 to a steep rise in pressure in the control room 7 , wherein the control chamber pressure on the pressure in the inlet channel 5 increases.

Because the pressure of the control room 7 with closed closing body 11 also in the pressure room 14 is present, the guide rod 13 inside the closing body 11 in this valve position the front side always loaded by the control chamber pressure. It is now provided, the control chamber pressure by means of the guide rod 13 on one in 2 schematically illustrated sensor 20 to transmit a force or pressure sensor. So can a signal from the sensor 20 can be obtained, which corresponds to the pressure curve in the control room and can at least recognize characteristic times such as opening and closing times.

In this construction, the guide rod has 13 So a double function, on the one hand, the sleeve-shaped closing body 11 axially leads and on the other hand as a power transmission member between the pressure chamber 14 or the control room communicating therewith 7 and the sensor 20 serves. Here it is furthermore advantageous that the sensor 20 in the low pressure region of the fuel injector, in the example shown in the drawing near the mouth of the return line 21 is arranged.

The sensor 20 may be suitably formed as a piezoelectric element, on which one of the pressure of the guide rod 13 dependent electrical voltage can be tapped off. Notwithstanding the illustrated embodiment, in which as actuator an electromagnet assembly 16 is provided, fuel injectors may be provided with other actuators. In particular, piezoelectric actuators are conceivable that are able to change their length as a function of an applied electrical voltage.

In 3 is a signal waveform when performing a method according to the invention shown in a preferred embodiment. This is a tension U of the sensor 20 applied over time t.

The waveform S In this case, the signal detected or output by the sensor, which represents the pressure or the pressure change in the fuel injector, is reproduced in the case of a pump stroke of the high-pressure pump. In the case shown is a period of time .delta.t after, for example, the beginning of the pump stroke, a change in the signal by one value .DELTA.U to see.

Now, when the pressure change caused by the pump stroke is known, for example, by detecting the rail pressure as one by pressure in one with the fuel injector 170 Size characterized in fluid communication by means of the pressure sensor 190 at the high-pressure accumulator and corresponding conversion, so can an assignment of voltage change in the waveform S to the actual pressure change. The mentioned transfer function must be taken into account for the conversion.

In 4 schematically reference curves and a waveform when performing a method according to the invention are shown in a further preferred embodiment. These are the pressure p in the high-pressure accumulator (left diagram) or the voltage U of the sensor (right diagram) respectively over time.

In the left diagram is starting from two different pressures p ₁ and p ₂ one each Pressure drop in the high-pressure accumulator provoked, for example using the pressure control valve. The associated pressure curves, as reference curves R ₁ respectively. R ₂ can be used in the context of the method according to the invention can be detected by the pressure sensor for the high-pressure accumulator. The respectively associated pressure drops in the high-pressure accumulator amount to this Δp ₁ respectively. Δp ₂ ,

In the right diagram is a to the reference history R ₂ associated signal curve S 'of the sensor shown in the fuel injector. This signal curve S 'includes a voltage change of .DELTA.U ' , In this way it is possible - similar to the case according to 3 - Make an assignment of voltage change in the waveform S 'to the actual pressure change. Again, a transfer function is taken into account in order to convert the pressure drop in the high-pressure accumulator to the pressure drop in the fuel injector. It should be emphasized that - even if in 3 Only one signal swing is shown - each pressure drop in the reference curve is associated with a corresponding signal swing in the waveform.

In 5 is a calibration when performing a method according to the invention shown in a further preferred embodiment, to an assignment of voltage changes .DELTA.U in the waveform to the actual pressure change Ap to be able to make. There are three characteristics for this K ₁ . K ₂ and K ₃ shown that allow for different output pressures in the high-pressure accumulator, a correlation of a voltage change of the sensor to an actual pressure change and thus a calibration. In this case, an adjustment for different amplitudes of the sensor signal is taken into account.

In addition, it is also considered that for different outlet pressures in the high-pressure accumulator, a pressure change in the fuel injector can have different effects on the sensor or the associated signal course.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102010000827 A1 [0003, 0005]

Claims (10)

Method for calibrating a sensor (20) designed as a force or pressure sensor in or on a fuel injector (170) of an internal combustion engine (160), which is supplied with fuel from a high-pressure accumulator (175), wherein at least one event involving a fuel pressure change in the fuel injector (170), at least one signal curve (S, S ') of the sensor (20) and at least one associated reference characteristic (R ₁ , R ₂ ) of a reference sensor (190), one by a pressure in one with the fuel injector ( 170), and wherein the sensor (20) based on the at least one waveform (S, S '), the at least one reference curve (R ₁ , R ₂ ) and a transfer function between the reference sensor (190) and the sensor (20) is calibrated. Method according to Claim 1 , wherein a pressure sensor for the high-pressure accumulator (175) is used as the reference sensor (190). Method according to Claim 1 or 2 wherein the at least one event comprises a pressure change in an inlet of the high-pressure accumulator (175), which is caused in particular by a pump stroke of a high-pressure pump (161), or in the high-pressure accumulator (176). The method of any one of the preceding claims, wherein the at least one event comprises pressure relief of the high pressure accumulator (175). The method of any one of the preceding claims, wherein the at least one event comprises injecting fuel through the fuel injector (175) or another fuel injector of the internal combustion engine (160). Method according to one of the preceding claims, wherein for a plurality of events which comprise mutually different pressure changes (Δp ₁ , Δp ₂ ), in each case a signal course (S, S ') and a reference course (R ₁ , R ₂ ) are detected, based on which the sensor (20) is calibrated. Method according to one of the preceding claims, wherein the sensor (20) is calibrated at predetermined, in particular regular, time intervals. Arithmetic unit (180) adapted to perform a method according to any one of the preceding claims. A computer program that causes a computing unit (180) to perform a method according to any one of Claims 1 to 7 when executed on the arithmetic unit (180). Machine-readable storage medium with a computer program stored thereon Claim 9 ,

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