JP2001132520A - Monitoring method and device for fuel metering system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect even a small deviation in the monitoring method of a fuel metering system in an internal combustion engine and to heighten the precision in identification of errors. SOLUTION: When a first quantity characterizing the number of revolutions of an internal combustion engine is lowered larger value than a threshold value, and/or the number of revolutions after the filtering is larger than the threshold value, the error is identified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and a device for monitoring an internal combustion engine, for example a fuel metering system of a common rail system, as defined in the preamble of the independent claim.

[0002]

2. Description of the Related Art Methods and devices for monitoring a fuel metering system for an internal combustion engine are known. In doing so, various signals are monitored for threshold values. Above and / or below a predetermined threshold, an error is identified in the fuel metering system. For example, when the pressure in a so-called common rail system drops off very quickly, a leak in the common rail system is identified.

[0003] In certain injection systems, such as in common rail systems, for example, irregular combustion or misfires can occur in the cylinder under particularly unfavorable circumstances.
This can lead to damage to the internal combustion engine on the one hand due to excessively high cylinder pressures and, on the other hand, for exhaust gas emissions to rise above an acceptable value.

[0004]

It is an object of the present invention to identify such irregular combustions or persistent misfires, in particular even with small deviations, ie small, increased fuel quantities. Alternatively, it is desired to reliably identify even a small reduced fuel amount, that is, to realize high error identification accuracy.

[0005]

According to the present invention, this object is achieved by a method having the structure according to the characterizing part of claim 1 and the method having the structure according to the characterizing part of claim 8. Will be resolved.

[0006] With the method of the present invention, irregular combustion or misfire can be reliably detected.

[0007] Advantageous and advantageous embodiments and refinements of the invention are set out in the dependent claims.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

FIG. 1 shows a fuel metering system. At 100, an internal combustion engine is shown. Internal combustion engine 10
At 0, a pulse generator 110 is attached. The pulse generator consists essentially of a pulse wheel and a pulse detector. The pulse wheel is driven by an internal combustion engine or camshaft and / or crankshaft. The pulse detector scans a mark on the pulse wheel and outputs a signal at a fixed angular interval.
To send to. Advantageously, the pulse generator is realized as a so-called segment wheel. This delivers three pulses that define two segments for each combustion. In this case, one segment preferably comes before the combustion and one segment preferably comes after the combustion.

[0010] The rotation speed detecting section 120 sends out a signal N.
This characterizes the rotational speed of the internal combustion engine and is supplied to the comparator 130. The comparator provides an adjustment deviation to the first multiplexer 140. First multiplexer 140 selectively controls the first regulator or one of the z regulators. The z-th regulator is shown at 154. In this case, the number z of regulators preferably corresponds to the number of cylinders of the internal combustion engine. At least one for the regulator
Three integrators are included.

The regulators 151 to 154 supply signals DM1 to DMZ to the second multiplexer 160, respectively. These signals DM1 to DMZ are further supplied to a combustion identification unit 190.

The comparator 130, the first and second multiplexers and the regulators 151 to 154 are usually referred to as a quantity compensation regulator or a driving stability regulator. The output signal DM of the second multiplexer 160 reaches the quantity controller 170. The quantity control sends a signal QK to the injection system 180.
Supply S. Starting from this signal and other operating variables, the injection system of the internal combustion engine meters the fuel quantity QK. The injection system is advantageously a so-called common rail system.

Starting from the pulses of the pulse generator 10,
The rotation speed detector 120 obtains a rotation speed signal. Comparator 13
0 locates the adjustment deviation. First multiplexer 14
0 supplies this adjustment deviation to the respective regulator, where one regulator is assigned to each cylinder. The output signal of the regulator indicates how much fuel has to be supplied to the cylinders or how much must be supplied to the cylinders in order for all cylinders to contribute equally to the total torque. A measure for the amount of fuel that should be reduced. The quantity control 170 calculates the fuel quantity for the individual cylinders starting from various operating parameters and takes into account the correction quantity DM of the quantity compensation adjustment.

In this case, it is customary to start from a certain number of segments, preferably so that for the segment after combustion in a given cylinder, the actual value for the rotational speed of this cylinder is ascertained and compared to a target value. Has become. The desired value is preferably determined via a relatively large number of segments. Starting from a comparison of this desired value with the actual value, the difference DMZ for the z-th cylinder is ascertained and taken into account in the fuel metering in this cylinder. Such a quantity compensation adjustment or such a running stability adjustment is described in DE-OS 1962.
No. 7218 is described in detail.

In particular, in a common rail system, a situation in which the injector is caught and locked can occur. This means that the injector does not transition to its closed state or its open state or no longer transitions completely. For example, it may happen that the injector no longer closes or no longer closes completely. Such an error is also called an internal leak.

In an internal leak where at least one of the injectors gets stuck and locks, fuel reaches one of the cylinders over the entire crankshaft angle range. 100 °
The fuel reaching the cylinders in the region of the crankshaft and in the region of the top dead center is very well prepared by the swirl produced. At this point, there is so much fuel in the cylinder that rapid combustion can occur. The pressure profile of this rapid combustion has its center of gravity before top dead center. As a result, the upward movement of the piston is braked. This becomes remarkable due to a decrease in the number of revolutions. In addition, vibrations having a camshaft frequency are excited by such leaks. Leaks can be identified by evaluation of the rotational frequency oscillations with the camshaft frequency or comparison with a threshold value. It is particularly advantageous to combine the two methods. This means that a leak is only identified when a speed drop and a speed oscillation occur.

A corresponding device is shown in FIG. On the one hand, the signal of the rotation speed detection unit 120 reaches the filtering unit 200 and on the other hand reaches the rotation speed gradient unit 230. The output signal of the filtering unit is a rotation speed fluctuation detection unit 2
Then, the processing reaches the error identification unit 220 via the control unit 10. Correspondingly, the output signal of the speed gradient section 230 is output to the second error identification section 24.
Reaches 0. The error detector is additionally supplied with output signals of various sensors, such as the rotational speed N and / or the quantity of fuel QK to be injected.

The function of the device is shown in the flow charts of FIGS. FIG. 3 shows a rotational speed identification based on a rotational speed gradient caused by a decrease in the rotational speed.

In a first step 300, a counter K
Is set to zero. Subsequently, at step 310, a rotation value N (k) is determined. Subsequently, the counter K is incremented by one (K = k + 1). Step 330
, A rotation value N (k + 1) is obtained. Subsequently, in step 340, the difference DN between the two last determined rotational values N (k + 1) and N (k) is determined. In a subsequent interrogation section 350, it is checked whether this difference is smaller than a threshold value SW. If yes, the device identifies the error at step 360. Otherwise, in step 370, the memory N
The value NK plus 1 (NK = N (k + 1)) is set in K.

According to this embodiment, the speed detection is advantageously performed in one segment. The rotation values N (k) to N (k + 1) are determined for each segment. If the speed drops significantly within one segment or from one segment to the next, that is, if the speed difference is less than a threshold, a leak is identified.

A second embodiment is shown in FIG. After the rotation speed is detected in step 400, filtering using a band-pass filter is performed in step 410. This filter advantageously passes frequency components corresponding to the camshaft frequency. Frequency components above or below the camshaft frequency are not passed. In a following step 420, the maximum amplitude AM of this signal is formed. In a subsequent interrogation section 430, it is checked whether the maximum amplitude AM is greater than the threshold value SW. If yes, the device identifies the error at step 440.

An error is identified when the signal characterizing the speed includes a frequency component having a camshaft frequency greater than a threshold value.

It is particularly advantageous if the threshold value is predetermined according to the operating state of the internal combustion engine. Advantageously, the threshold value SW is predetermined in dependence on the first quantity characterizing the engine speed N and / or the second quantity characterizing the fuel quantity to be injected. Can be

Advantageously, the interrogation takes place only when the injection quantity is constant and no braking operation takes place, that is to say that the check is only performed in certain operating states. In such a predetermined operating state, a leak is identified when a significant decrease in the rotational speed occurs.

[Brief description of the drawings]

FIG. 1 is a block diagram of the device of the present invention.

FIG. 2 is a block diagram of a combustion identification unit.

FIG. 3 is a diagram showing a flowchart of the method of the present invention.

FIG. 4 shows another flowchart of the method of the present invention.

[Explanation of symbols]

100 internal combustion engine, 110 pulse generator, 120
Rotation speed detector, 130 comparator, 140 first multiplexer, 151-154 regulator, 160 second multiplexer, 170 quantity controller, 180
Injection system, 190 combustion discrimination unit, 200 filtering unit, 210 rotation speed fluctuation forming unit, 22
0,240 error identification unit, 230 rotation speed gradient unit

Claims (8)

[Claims] 1. A first characteristic of a rotation speed of an internal combustion engine.
Monitoring the fuel metering system of the internal combustion engine, characterized in that an error is identified when the quantity of fuel drops by a value greater than the threshold value and / or when the filtered rotational quantity is greater than the threshold value. 2. The method according to claim 1, wherein the number of rotations is filtered such that the frequency component is selected to be the same as the camshaft frequency.
A monitoring method for the fuel metering system according to the above. 3. The method according to claim 1, wherein the threshold value can be predetermined depending on an operating state of the internal combustion engine. 4. The method of monitoring a fuel metering system according to claim 1, wherein a leak is identified when a rotational speed decrease and / or rotational speed vibration having a camshaft frequency occurs. . 5. The method of monitoring a fuel metering system according to claim 1, wherein the inspection is performed only in a predetermined operating state. 6. The method according to claim 5, wherein the checking is performed only when the quantity characterizing the quantity of fuel to be injected is constant and no braking intervention takes place. 7. The threshold value (SW) can be predetermined depending on the quantity characterizing the rotational speed of the internal combustion engine and / or the quantity characterizing the quantity of fuel to be injected. Item 3. The monitoring method according to Item 3. 8. A first characteristic characterizing a rotational speed of the internal combustion engine.
Metering system for an internal combustion engine, characterized in that when the quantity of fuel drops by a value greater than the threshold value and / or when the filtered rotational quantity is greater than the threshold value, means are provided for identifying an error. Monitoring equipment.