DE102019206482A1 - Method for determining a fuel pressure in a high-pressure accumulator for equidistant crankshaft angle positions - Google Patents

Abstract

The invention relates to a method for determining a fuel pressure (p) in a high-pressure accumulator of an internal combustion engine, in which values for the fuel pressure are recorded repeatedly and in individual measured values (M), repeated after a predetermined interval (Δφ) of a crankshaft angle ( φ) of the internal combustion engine, a calculated value (M ') of the measured values (M) recorded in this interval (Δφ) is formed, and this calculated value (M') is provided as a value for the fuel pressure.

Description

The present invention relates to a method for determining a fuel pressure in a high-pressure accumulator of an internal combustion engine as well as a computing unit and a computer program for its implementation.

State of the art

The current fuel pressure in the high-pressure accumulator (e.g. common rail) of an internal combustion engine can be used or required for various applications or functions in a vehicle. This can involve, for example, the determination of an amount of fuel withdrawn from the high-pressure accumulator in the course of an injection of fuel into the internal combustion engine, a so-called injection amount.

From the DE 10 2014 215 618 A1 For example, a method is known in which such an injection quantity is determined on the basis of the fuel pressure in the high-pressure accumulator or its change. The fuel pressure or its course is recorded based on time and then transformed into a frequency-based course. Using the frequency-based profile, the injection quantity is then determined, for example, via the amplitude of the frequency-based profile associated with the ignition frequency of the internal combustion engine.

Disclosure of the invention

According to the invention, a method for determining a fuel pressure as well as a computing unit and a computer program for its implementation with the features of the independent patent claims are proposed. Advantageous configurations are the subject of the subclaims and the description below.

The invention is based on a method for determining a fuel pressure in a high-pressure accumulator of an internal combustion engine, in which the values for the fuel pressure are repeated and recorded in individual measured values. In particular, a pressure sensor can be used for detection, as is typically provided for high-pressure accumulators anyway. This can in particular be a so-called time-based detection of the fuel pressure. The fuel pressure is expediently recorded with a predetermined, in particular constant, sampling frequency for the individual measured values. A typical sampling frequency is 10 kHz, for example, but 1 kHz or a value in between or any values are also conceivable.

Since certain functions are related to the speed or crankshaft position when an internal combustion engine is operating, so-called leak effects occur when such time-related measured values are used. The background here is that the sampling frequency is generally not an integer multiple of the ultimately relevant evaluation frequency, for example the ignition frequency mentioned at the beginning. This applies in particular to speed-dependent functions, especially since the ratio between the sampling frequency and the relevant evaluation frequency can and will change during the operation of the internal combustion engine.

In other words, at the typically fixed sampling frequency, for example, a current measured value for the fuel pressure is not always recorded exactly at the ignition time, but rather something before or after. These time intervals from the ignition point are also not constant. Changes occurring in the meantime are not registered.

Another problem with the typical, time-based detection of the fuel pressure is that when converting recorded analog signals or measured values into digital, as is the case in modern computing units or control devices that read in sensors, often only a certain bandwidth is available stands. With a bandwidth of 10 bits and typical pressure ranges of up to 3000 bar to be covered, the resolution is only approx. 3 bar. A pressure drop in the high-pressure accumulator can sometimes also be, for example, only about 1 to 2 bar in the case of so-called pre-injections, and can therefore no longer be resolved or no longer recognized.

Within the scope of the invention, it is now proposed that a calculated value be formed from the measured values recorded in this interval and that this calculated value is provided as a value for the fuel pressure, in each case after a predetermined interval of a crankshaft angle of the internal combustion engine has elapsed in particular as soon as possible or exactly after the specified interval has expired.

In this way, despite the underlying time-based detection of the fuel pressure, values for the fuel pressure can be obtained which - at least significantly more precisely than before - correlate with the crankshaft angle and thus in particular with relevant evaluation frequencies such as the ignition frequency, in particular when several measured values are recorded per interval. Overall, an angle-synchronous detection or sampling of the fuel pressure is provided.

The calculated value is preferably provided as a value in addition to the repeatedly and individually recorded measured values.

The calculated value can then in particular be an arithmetic or geometric mean value. It can also be a weighted average, e.g. weight the most recent readings more heavily than the older ones. The calculation value formation also increases the possible resolution, since the values become independent of the bit widths and, in particular, intermediate values also occur.

It is expedient, in particular in terms of a simple implementation, if the same length is selected for each interval. The length of the interval is selected between 2 ° CA and 30 ° CA, preferably between 6 ° CA and 15 ° CA. A length of 6 ° CA, 10 ° CA or 15 ° CA, for example, can be particularly useful.

It is also advantageous if the length of the interval is an integer divisor of 360 ° CA or a full turn of the crankshaft (if necessary, instead of 360 ° CA it can also be set to 720 ° CA). In other words, 360 ° CA is an integral multiple of the length of the interval.

In particular, the length of the interval can also be made dependent on which evaluation frequency is to be used later. In the case of the ignition frequency, or also generally, the number of cylinders of an internal combustion engine can be taken into account here.

However, it is also preferred that the measured values are recorded with equidistant intervals with respect to the crankshaft angle, so-called angle-synchronous scanning. In particular, exactly one measured value is then recorded per interval, with the calculated value in particular corresponding to an identity mapping. In other words, a direct angle-synchronous detection of the pressure can also take place, in particular also without time-based detection. A sampling frequency that is advantageous for this is, for example, 6 ° CA, 5 ° CA, but 1 CA or a value in between or any values are also conceivable.

The individual measured values are preferably stored temporarily and deleted after the calculated value has been generated. For this purpose, a suitable memory of an executing computing unit can be used accordingly. A specific sequence can therefore be such that an interrupt is called every time after the interval, for example every 6 ° KW of a rotation of the crankshaft - such an angle is typically detected by means of a corresponding sensor. All measured values that have accumulated or recorded since the last interrupt can then be offset according to a calculation rule - the calculation value is thus formed. An appropriate counter can be used to obtain the number of measured values. The measured values, and possibly also the counter, are then deleted again and the calculated calculated value is provided as an (additional) value for the fuel pressure.

The values for the fuel pressure - this includes the values calculated on the basis of the calculation value formation, but in particular also the measured values obtained on the basis of the time-based detection - are advantageously used for at least one function in relation to the internal combustion engine.

The at least one function is in particular selected from: a determination and / or monitoring of an injection quantity that is taken from the high-pressure accumulator (and is then introduced into the internal combustion engine by means of a fuel injector), a correction of such an injection quantity (for example an adjustment due to too little or too high a quantity), a monitoring of a fuel pump that directly or indirectly supplies fuel to the high-pressure accumulator (a high-pressure pump is usually directly connected to the high-pressure accumulator and therefore delivers fuel there directly and, if necessary, is also controlled by an electric suction valve, whereas a low-pressure pump is supplied typically such a high-pressure pump with fuel and therefore supplies the fuel indirectly to the high-pressure accumulator), and a correction of a control of a fuel pump that supplies fuel directly or indirectly to the high-pressure accumulator (e.g. due to an adjustment due to too little or too much fuel delivered).

A computing unit according to the invention, e.g. a control unit of a motor vehicle is set up, in particular in terms of programming, to carry out a method according to the invention.

The implementation of a method according to the invention in the form of a computer program or computer program product with program code for performing all method steps is advantageous, since this causes particularly low costs, in particular if an executing control device is also used for other tasks and is therefore available anyway. Suitable data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, e.g. Hard disks, flash memories, EEPROMs, DVDs, etc. A program can also be downloaded from a computer network (Internet, intranet, etc.).

Further advantages and configurations of the invention emerge from the description and the accompanying drawing.

The invention is shown schematically in the drawing using an exemplary embodiment and is described below with reference to the drawing.

Figure list

• 1 shows schematically an internal combustion engine which is suitable for carrying out a method according to the invention in a preferred embodiment.
• 2 shows the frequency spectrum of a course of a fuel pressure for a high pressure accumulator of a four-cylinder internal combustion engine with time-synchronous recording of measurement data.
• 3 shows a frequency spectrum of a course of a fuel pressure with angle-synchronous measurement for a high pressure accumulator of a four-cylinder internal combustion engine.
• 4th shows schematically a relationship between the crankshaft angle and time-based detection of a fuel pressure to explain a method according to the invention in a preferred embodiment

Embodiment (s) of the invention

In 1 is schematically an internal combustion engine 100 shown, which is suitable for carrying out a method according to the invention in a preferred embodiment. The internal combustion engine includes, for example 100 three combustion chambers or associated cylinders 105 . Every combustion chamber 105 is a fuel injector 130 assigned, which in turn each to a high-pressure accumulator 120 connected via which it is supplied with fuel.

Next, the high pressure accumulator is operated by a high pressure pump 110 with fuel from a fuel tank 140 fed. The high pressure pump 110 is with the internal combustion engine 100 coupled in such a way that the high-pressure pump is driven via a crankshaft of the internal combustion engine, or via a camshaft, which in turn is coupled to the crankshaft. A fixed transmission ratio between crankshaft and camshaft is typically specified. In addition, a low-pressure pump, not shown here, can be installed between the tank 140 and the high pressure pump 110 be provided.

In each combustion cycle of the internal combustion engine with three cylinders, for example, three injection processes (from each fuel injector 130 one) executed. A control of the fuel injectors 130 for metering fuel into the respective combustion chambers 105 takes place via an engine control unit 180 trained computing unit. For the sake of clarity, only the connection from the engine control unit is shown 180 to a fuel injector 130 shown, however, it should be understood that any fuel injector 130 is connected to the engine control unit accordingly. Any fuel injector 130 can be specifically controlled. Furthermore, the engine control unit is 130 set up the fuel pressure in the high-pressure accumulator 120 by means of a pressure sensor 190 capture.

As already mentioned above, the determination of an injection quantity of fuel represents a typical case for which the most accurate possible knowledge of the fuel pressure in the high-pressure accumulator or its course with corresponding changes is relevant.

In 2 shows the frequency spectrum (Fourier spectrum) of a course of a fuel pressure p with time-based detection for a high-pressure accumulator or in a high-pressure accumulator of a four-cylinder internal combustion engine. For example, measured values over 100 camshaft revolutions were recorded synchronously and Fourier transformed.

In 3 shows the frequency spectrum of a fuel pressure with angle-synchronous measurement for a four-cylinder internal combustion engine. In the case of angle-synchronous detection, the crankshaft or the crankshaft angle is used as a basis. With a fixed, integer transmission ratio, however, the synchronicity also applies to the camshaft or the camshaft angle.

Since there is a correlation with the speed in this way, the values are plotted here as frequency f as a multiple of the camshaft frequency. Here too are - as with 2 - Measured values shown over 100 camshaft revolutions.

The frequency spectra or measured values in the 2 and 3 thus, in particular, represent the same fundamental curves of a fuel pressure (same internal combustion engine with high pressure accumulator), but in a different manner of detection.

Based on a comparison of the two 2 and 3 it can be clearly seen that with angle-synchronous acquisition, as in 3 to see, relevant usable frequencies such as camshaft frequency (at f = 1), crankshaft frequency (at f = 2) and ignition frequency (at f = 4) are clearly more pronounced than at 2 . As already mentioned, this depends on it together that with time-based recording of the fuel pressure, a measured value is typically not always recorded exactly at the relevant positions of the crankshaft or camshaft.

This knowledge with regard to angle-synchronous acquisition is made use of in the context of the present invention in that some (additional) angle-synchronous values are determined or calculated from a time-based acquisition of measured values. As already mentioned above, angle-synchronous detection can also take place directly within the scope of the present invention.

In 4th a connection between crankshaft angle φ and time-based detection (see time axis t) of a fuel pressure is shown schematically, on the basis of which a method according to the invention is to be explained in a preferred embodiment.

Measured values of the fuel pressure are represented by M, which, as can be seen, have a constant or equidistant interval in the period, as is the case with time-based detection with a constant sampling frequency. However, the associated crankshaft angle φ does not have to change linearly (or not proportionally to time), but can increase more or more slowly when the speed changes. In other words, a different number of measured values M can lie within a specific interval Δφ of the crankshaft angle.

Even at constant speed, the situation is that a measured value is not always recorded for a certain crankshaft angle or - to put it the other way around - that a measured value is not always recorded for a certain crankshaft angle (which is repeated every two full revolutions according to the usual count) or that the closest measured value is not always the same distance from the exact angle value. As mentioned at the beginning, this is due to the fact that the sampling frequency is generally not an integral multiple of the crankshaft frequency.

For the sake of completeness, it should be mentioned at this point that the camshaft angle can also be used instead of the crankshaft angle, only with a corresponding conversion according to the transmission ratio.

Within the scope of the invention, a computed value is now formed for all measured values M that occur within an interval Δφ, which is designated as M 'by way of example. This calculated value M 'is then provided - at the end of the relevant interval - as an additional value for the fuel pressure in the high-pressure accumulator. Due to the provision of this value or arithmetic value always as exactly as possible after the specified interval has elapsed, an angle-synchronous determination of the fuel pressure on the basis of a per se time-based measurement or sampling can be realized - with a corresponding selection of the length of the interval. For example, the arithmetic value is the arithmetic mean.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was 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.

Patent literature cited

• DE 102014215618 A1 [0003]

Claims (13)

Method for determining a fuel pressure (p) in a high-pressure accumulator (120) of an internal combustion engine (100), in which values for the fuel pressure (p) are repeated and recorded in individual measured values (M), wherein, after a predetermined interval (Δφ) of a crankshaft angle (φ) of the internal combustion engine (100) has elapsed, a calculated value (M ') of the measured values (M) recorded in this interval (Δφ) is formed, and this calculated value (M' ) is provided as a value for the fuel pressure (p). Procedure according to Claim 1 , the calculated value (M ') being provided as a value in addition to the repeatedly and individually recorded measured values (M). Procedure according to Claim 1 or 2 , where the same length is chosen for each interval (Δφ). Procedure according to Claim 3 , the length of the interval (Δφ) being selected as an integer divisor of 360 ° CA and / or between 2 ° CA and 30 ° CA, preferably between 6 ° CA and 15 ° CA. Method according to one of the preceding claims, wherein the fuel pressure (p) is detected with a predetermined, in particular constant, sampling frequency for the individual measured values (M). Method according to one of the Claims 1 to 4th , whereby the measured values are recorded with equidistant intervals in relation to the crankshaft angle. Method according to one of the preceding claims, wherein several measured values are recorded per interval (Δφ). Method according to one of the Claims 1 to 6th , whereby exactly one measured value is recorded per interval (Δφ), and wherein in particular the calculated value corresponds to an identity mapping. Method according to one of the preceding claims, wherein the individual measured values (M) are temporarily stored and deleted after the calculation value (M ') has been formed. Method according to one of the preceding claims, wherein the values for the fuel pressure (p) are used for at least one function in relation to the internal combustion engine (100), the at least function being selected in particular from: a determination and / or monitoring of an injection quantity, the the high-pressure accumulator (120) is taken, a correction of an injection quantity, a monitoring of a fuel pump (110), which directly or indirectly supplies fuel to the high-pressure accumulator (120), and a correction of a control of a fuel pump (110) that directly or indirectly delivers into the high pressure accumulator (120). Computing unit (180) which is set up to carry out all method steps of a method according to one of the preceding claims. Computer program that causes a computing unit (180) to perform all method steps of a method according to one of the Claims 1 to 10 to be carried out when it is executed on the arithmetic unit (180). Machine-readable storage medium with a computer program stored thereon Claim 12 .

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