DE10028884A1 - Combustion monitoring system for vehicle diesel engines uses ion current correction model corrects for contamination - Google Patents

Abstract

The combustion monitoring system subtracts the current due to contamination of the probes (3,4) from the measured ion current by using an adaptive theoretical model of the signal without combustion as a function of compression and temperature.

Description

The present invention relates to a method according to the preamble of claim 1 and a correspondingly designed device according to the preamble of Claim 10 for detecting the combustion process in an internal combustion engine, especially a diesel or gasoline engine.

Over the past few years, interest in ion current measurement has been in the range of Internal combustion engines increased. So recent studies have shown that Ion current signal can be used to generate the in a combustion chamber (cylinder) Internal combustion engine prevailing pressure (cylinder pressure) or the local lambda (λ) determine and thus the combustion process in the corresponding combustion chamber monitor. The local lambda provides information about the air-fuel ratio a certain local point in the combustion chamber.

DE 196 05 810 A1 describes an ion current measuring system for a combustion chamber Gasoline engine described, the spark plug provided for the combustion chamber at the same time is used as an ion current measuring sensor. The ion current measuring system includes one as an inverting amplifier connected differential amplifier, its inverting Input is connected to its output via a resistor. That the Output signal of the inverting amplifier corresponding ion current signal can can be used to detect the so-called knocking of the engine and over a suitable control of the ignition timing a corresponding knock control build up. In addition, this document proposes that Ion current signal to detect misfiring or to detect the Use camshaft position.

In contrast to gasoline engines, no suitable ion current Measuring system for use directly in the combustion chamber of a diesel engine suggested. A diesel engine is generally understood to be an internal combustion engine, at  which is the liquid fuel injected into the combustion chamber on an air charge ignited after this essentially by compression to one for the one line of ignition has been brought to a sufficiently high temperature.

In this respect, the evaluation of an ion current signal measured in a diesel engine is problematic than that when measuring ion current using modified glow the ion current signal in the diesel engine before the actual combustion Has a signal component, which consists of the soot of the measuring sensor used in each case, the compression pressure and the compression temperature is dependent. This annoying Signal component prevents an exact evaluation of the ion current signal before burning tion, so that no statement about the start of combustion can be made.

The present invention is therefore based on the object of an improved Method and an improved device for recording the combustion process in propose an internal combustion engine, with which in particular in a diesel engine by means of an ion current measurement a reliable statement about the Combustion process, especially about the start of combustion can.

This object is achieved by a method with the features of Claim 1 and a device with the features of claim 10 solved. The Subclaims define preferred and advantageous embodiments of the present invention.

According to the invention, it is contained in a measured ion current signal Interference signal component, which in particular from the soot of the particular used Measuring sensor, the compression pressure and the compression temperature, determined so that the measured ion current signal corresponding to this Interference signal component can be corrected. Then only the corrected ion current signal will evaluated, for example, the start of combustion and / or the Duration of combustion in a combustion chamber of an internal combustion engine, in particular of a diesel engine.

According to a preferred embodiment of the present invention, the Interference signal component adaptively calculated depending on the ion current signal and then subtracted from the measured ion current signal. To this end  can the interference signal component in the form of a theoretical course of the measured Ion current signal can be determined, which is without a combustion in each would consider the combustion chamber considered. This can be done, for example, by that the course of the measured ion current signal in a given crankshaft area recorded before crankshaft top dead center and synthetically up to one Crankshaft point continues near top dead center of the crankshaft the interference signal curve thus determined subsequently on the determined one Crankshaft point is mirrored to show a complete noise waveform Obtain dependence on the crankshaft angle.

The present invention ensures that the measured in a Ion current signal contained disturbing signal component, which the evaluation of the Prevents ion current signal from being calculated out of the measured ion current signal can be so that an "ideal" ion current signal is obtained, its evaluation a statement about the start of combustion and / or the duration of combustion in the each combustion chamber (cylinder) under consideration.

The invention is described below using a preferred exemplary embodiment Reference to the accompanying drawing explained in more detail.

Fig. 1 shows the basic structure of an apparatus for measuring and evaluating the ionic current occurring in a cylinder of a diesel engine according to a preferred embodiment of the present invention, and

FIG. 2 shows various signal profiles as a function of the crankshaft angle of a crankshaft shown in FIG. 1 to explain the present invention.

In Fig. 1 the basic structure of a device according to the invention a diesel engine by way of cylinder 1. A piston 8 located in the cylinder 1 is driven via a crankshaft 2 of the diesel engine. If, for example, it is assumed that the diesel engine works with four cycles, the crankshaft 2 and the piston 8 reach the so-called top dead center OT and the bottom dead center UT exactly twice within one work cycle, which corresponds to two complete revolutions of the crankshaft 2 . In automotive engineering, the angles of rotation ϕ of crankshaft 2 are specified in degrees crankshaft angle (° KW).

At least one ion current sensor is accommodated in the area of the cylinder head or the cylinder head gasket, the ion current occurring in the cylinder during a combustion process being detected via at least one cathode 3 and at least one anode 4 and being supplied to an ion current measuring unit 6 . In particular, the spark plug assigned to cylinder 1 can be used as the ion current sensor. It is also possible to use a modified glow plug or to arrange appropriate sensors in the cylinder head or in the cylinder head gasket. In this case, the glow tube or the tip of a correspondingly modified glow plug surrounded by insulation is used as the anode 4 and the cylinder head (or the cylinder housing) as the cathode 3 . The resistance of the gas mixture surrounded by the measuring electrodes is then measured via the glow plug, which changes depending on the combustion parameter and consequently on the ion current. Basically, an ion current can be measured if there is a flame in a mixture containing hydrocarbons between the two measuring electrodes (anode and cathode).

The ion current measuring unit 6 evaluates the detected ion current and, depending on this, deduces the current combustion state in the cylinder 1 . An engine control unit 7 is controlled via a corresponding control signal, which, depending on this, controls an injection valve 5 of the cylinder 1 coupled to a diesel line in order to influence the quantity of fuel supplied to the cylinder 1 accordingly. A crankshaft sensor 11 , which is connected to the engine control unit 7 , is provided for detecting the instantaneous position of the crankshaft 2 . The engine control unit 7 can thus infer the combustion chamber or cylinder volume depending on the crankshaft position and, taking into account the measured ion current, the combustion state in the cylinder 1 .

FIG. 2 shows the course of an ion current signal a measured in a conventional manner as a function of the crank angle of the crankshaft 2 shown in FIG. 1. It can be seen from FIG. 2 that the ion current signal a has a steep increase at approximately 360 ° KW at the time of the start of combustion, ie in the area of top dead center. The evaluation of the ion current signal a is, however, made more difficult by the fact that the measured ion current signal already has a signal component with an amplitude, in some cases clearly different from zero, before top dead center, ie before the actual start of combustion. This signal component depends, among other things, on the soot of the measuring electrodes 3 , 4 , the compression pressure and the compression temperature in the cylinder 1 . In order to obtain an ion current signal that is as ideal as possible, the measured ion current signal a must be eliminated from this interfering signal component.

For this purpose, the ion current measuring unit 6 shown in FIG. 1 comprises a correction unit 9 which on the one hand detects the interfering signal component and on the other hand subtracts it from the measured ion current signal in order to obtain an "ideal" ion current signal, the signal amplitude of which is as precise as possible with the start of combustion increases. The correction unit 9 adaptively calculates the interfering signal component as a function of the measured ion current signal a.

For this purpose, the correction unit 9 monitors the measured ion current signal a or its amplitude in order to determine when it rises significantly for the first time. In the case of the ion current signal a shown in FIG. 2, this is the case in the range between 300 ° KW and 320 ° KW. The correction unit 9 then detects the signal rise of the measured ion current signal a and uses this to calculate a virtual signal curve that would occur in the cylinder 1 without combustion. That is, the correction unit 9 theoretically continues the detected signal rise of the measured ion current signal a to a range where the sharp rise in the ion current signal a can be determined. This is the case in the area of top dead center, ie in the vicinity of 360 ° KW. Due to certain temperature influences, however, the crankshaft angle at which the sharp rise in the ion current signal a occurs can deviate slightly from the top dead center, ie from 360 ° KW. The interference signal curve thus determined by the correction unit 9 is reflected in the region of the steep rise in the measured ion current signal a in order to obtain the complete interference signal curve b shown in FIG. 2.

By subtracting the interference signal component b thus determined from the measured ion current signal a, the correction unit 9 calculates a corrected ion current signal c, the course of which is also shown in FIG. 2. As can be seen from FIG. 2, this difference signal c has no signal increase before the time of combustion, ie before the area of top dead center at approximately 360 ° KW. The amplitude of the difference signal c is relatively exactly zero at the time of the combustion and then increases abruptly with the start of combustion, so that the difference signal c can easily be evaluated to determine the start of combustion.

In the device shown in FIG. 1, the corrected ion current signal c (ie, the difference signal) determined by the correction unit 9 is fed to an evaluation unit 10 , which thus only evaluates the corrected ion current signal in order to make a dependent statement about the start of combustion and / or the duration of the combustion receive. The combustion duration can be determined, for example, by placing a secant at a certain signal amplitude over the course of the corrected ion current signal c and detecting the span between the two points between which the amplitude of the corrected ion current signal c is above the secant. The point at which the corrected ion current signal c intersects the secant from bottom to top corresponds to the start of combustion, while the point at which the corrected ion current signal c intersects the secant from top to bottom corresponds to the end of combustion.

In this way, the previously described correction of the ion current signal a reliable statement about the start of combustion and / or the Duration of combustion are taken.  

REFERENCE SIGN LIST

1

cylinder

2

crankshaft

3rd

cathode

4

anode

5

Injector

6

Unit of measurement

7

Control unit

8th

piston

9

Correction unit

10th

Evaluation unit

11

Crankshaft sensor
OT top dead center
UT bottom dead center
ϕ crankshaft angle
a measured ion current signal
b Interference signal
c corrected ion current signal

Claims (12)

1. A method for detecting the combustion process in an internal combustion engine, wherein an ion current measurement is carried out in a combustion chamber ( 1 ) of the internal combustion engine, and wherein the ion current signal (a) detected by the ion current measurement is evaluated to determine the combustion process in the combustion chamber ( 1 ) of the internal combustion engine to be detected, characterized in that an interference signal component (b) contained in the ion current signal (a) is determined, and that the ion current signal (a) is corrected prior to its evaluation in accordance with the interference signal component (b) and then the corrected ion current signal (c) for acquisition of the combustion process in the combustion chamber ( 1 ) of the internal combustion engine is evaluated. 2. The method according to claim 1, characterized in that the interference signal component (b) is subtracted from the ion current signal (a) by the corrected ion current signal (c) to get. 3. The method according to claims 1 or 2, characterized in that the interference signal component (b) is determined such that it approximately corresponds to a signal component of the ion current signal (a) by sooting an ion current sensor ( 3 , 4 ) provided for ion current measurement a compression pressure prevailing in the combustion chamber ( 1 ) and / or caused by the temperature in the combustion chamber ( 1 ) and is already contained in the ion current signal (a) before a combustion process occurs. 4. The method according to any one of the preceding claims, characterized in that by evaluating the corrected ion current signal (c) a statement is made about the start of combustion and / or the duration of combustion of a combustion process taking place in the combustion chamber ( 1 ) of the internal combustion engine. 5. The method according to claim 4, characterized in that on the Start of combustion is closed when the corrected ion current signal (c) shows a sharp increase. 6. The method according to claim 4 or 5, characterized in that the Burning time is equated to the time period in which the amplitude of the corrected ion current signal (c) is above a certain value. 7. The method according to any one of the preceding claims, characterized in that the interference signal component (b) adaptive depending on the current Ion current signal (a) is determined. 8. The method according to any one of the preceding claims, characterized in that the interference signal component (b) is determined in the form of a theoretical profile of the ion current signal (a), which would occur without a combustion process in the combustion chamber ( 1 ). 9. The method according to claim 8, characterized in that the interference signal component (b) is determined in that the course of the ion current signal (a) in a certain crankshaft area before the top dead center of the crankshaft ( 2 ) of the internal combustion engine is detected and continued and at one Crankshaft point is mirrored near the top dead center of the crankshaft ( 2 ). 10. Apparatus for detecting the combustion process in an internal combustion engine, with sensor means ( 3 , 4 ) for performing an ion current measurement in a combustion chamber ( 1 ) of the internal combustion engine, and with evaluation means ( 10 ) for evaluating the ion current signal (a) detected by the ion current measurement to detect the combustion process in the combustion chamber ( 1 ) of the internal combustion engine, characterized in that ion current signal correction means ( 9 ) are provided in order to include an interference signal component (b) contained in the ion current signal (a) detected by the sensor means ( 3 , 4 ) determine and correct the ion current signal (a) in accordance with the interference signal component (b), the corrected ion current signal (c) generated by the ion current signal correction means ( 9 ) being fed to the evaluation means ( 10 ) for evaluating the same. 11. The device according to claim 10, characterized in that the ion current signal correction means ( 9 ) are designed to carry out the method according to one of the methods 1-9. 12. The apparatus according to claim 10 or 11, characterized in that the Internal combustion engine is a diesel engine.