DE4001333C1 - Cylinder-selective energy conversion monitoring of IC engine - k ascertaining instantaneous RPM and forming quadrant during stroke of each cylinder over certain crankshaft angle of rotation - Google Patents

Abstract

An ignition monitoring system for an engine monitors the actual engine speed during the firing cycle of each cylinder. The square of the engine speed is proportional to the cylinder energy and is used to determine the effectiveness of each cylinder. The measured square of the speed is subtracted from the mean square value to determine fluctuations in each cylinder. If the system detects misfiring, and if the rate of misfiring is above a threshold, a failure indication is activated, and/or the respective cylinder has its fuel supply cut. The system prevents damage to the exhaust scrubbing system (catalysator). ADVANTAGE - Responsive monitoring of each cylinder.

Description

The invention relates to a method for cylinder-selective monitoring of energy turnover a multi-cylinder internal combustion engine, for example with mixture-compressing internal combustion engines Misfires in one or more cylinders and with diesel internal combustion engines cylinders with different Energy turnover and resulting poor idling quality and poor smoothness to be able to identify.

Misfires in mixture-compressing internal combustion engines with lambda control and exhaust gas catalytic converter can cause significant thermal damage to the Carry catalyst, if this leads to after-reactions of the unburned fuel-air mixture in the exhaust system occur. High catalyst temperatures also pose pose a fire hazard to the vehicle. In addition is the exhaust gas quality due to misfires significantly deteriorated regardless of whether the Cause of misfires in errors of Fuel metering or ignition exists.

There are already methods for detecting misfires  known based on an analysis of the Course of the instantaneous speed of the internal combustion engine or the angular velocity of the crankshaft during based on a work cycle. Misfires lead to special changes in the speed curve compared to the normal state. The current speed will be determined from the length of time during these procedures while which extends the crankshaft around a defined crank angle range turns. The definition of this crank angle Areas are made using markings on one of the crankshaft driven wheel these marks from the teeth of the starter ring gear formed on the flywheel, but can also have its own, from the crankshaft driven disc with markings be provided. The markings generate a corresponding one Signal in an inductive pickup. The timing is done by counting the pulses of a pulse generator, that fall within the crank angle range. The determination the phase position required for the assignment of the individual Cylinder is necessary by means of a Phase signal, which occurs once per work cycle (with four-stroke Internal combustion engines with two revolutions of the crankshaft per work cycle z. B. triggered by the camshaft) becomes.

The known methods use a crank angle high-resolution curve of the instantaneous speed. The duration of very narrow crank angle ranges captures what for the necessary Accuracy high clock rates required for the pulse generator are. In a method described in US Pat. No. 4,532,592 become 6 ° crank angle ranges with a pulse rate sampled from 5 MHz. With such a high resolution However, instantaneous speed values represent interference due to cyclical fluctuations in the combustion process and significant due to manufacturing tolerances of the ring gear Problems.  

The same problems arise with the method according to DE 28 38 927 A1, in which a cylinder-selective comparison the target-actual performance based on the high-resolution instantaneous angular velocity or angular acceleration he follows.

A method is described in DE 37 24 420 A1 the current speed values within an engine cycle be determined at least twice as often as corresponds to the number of cylinders, and by comparison of minimum and maximum values assigned to each cylinder Misfires can be detected. This method requires a lot of calculation.

In a similar method according to DE 36 15 547 A1 from the maximum and assigned to each cylinder minimum instantaneous speed values for each cylinder Differences formed. For the detection of misfires is the difference value of a cylinder in relation to the difference in ignition order previous cylinder and it is checked whether this ratio falls below a threshold. However, when burning in two consecutive Exposing cylinders can be done with this Do not determine misfire in the second cylinder.

DE 34 24 692 A1 generally describes a method for Analysis of periodic or quasi-periodic Signals. This could give instantaneous speed values to each cylinder assigned to each cylinder individually compared continuously. In order to however, there is the disadvantage of a high level of interference due to cyclical fluctuations between the successive burns of the individual Cylinders. There are also continuous misfires in a cylinder  not recognizable in this way, because then none Fluctuations occur.

A major disadvantage of these known methods is in that the influence of dynamic engine operation (Acceleration, braking) on the detection of misfires is not taken into account.

A device for detection is known from EP 03 06 905 A1 known from ignition and flame misfires which a circuit for analyzing an electrical, analog Includes speed or power signal Differentiator and a downstream comparator has, which is exceeded when a predetermined Threshold value for deriving the speed signal Misfire of an output pulse indicating cylinder delivers. This known device also contains means to take dynamic engine operation into account to avoid creating an external, relative slow increase or decrease in speed Detection falsified. A disadvantage of this known Setup is that a cylinder selective Dropout detection, if at all, only with considerable additional effort is possible because of the electronic Analog circuits peculiar phase shift of the output signals compared to the input signals cannot be determined with certainty in which cylinder a misfire occurred. With the known Setup is relatively slower to suppress Speed changes with a high pass filter Cutoff frequency of about 10 Hz is provided. With such a However, high-pass filters can be misrecognized do not avoid, as the Speed changes constantly, with sudden speed changes while driving, for example when braking or when changing gear, similar frequencies as May have dropouts. If such speed changes  should be filtered out, so inevitably filtered out the speed changes caused by misfires, as far as they are in the same frequency range lie. But this means that dropouts in this Frequency range are not recognized.

The invention has for its object a method for cylinder-selective monitoring of energy turnover to create in a multi-cylinder internal combustion engine, with which a change in energy turnover in one  Cylinders caused by intermittent or bad Combustion, while avoiding faulty Detections especially in dynamic driving is reliably detected, so that appropriate countermeasures can be taken such. B. Interruption the fuel supply to the misfiring cylinder Avoid damage to the catalytic converter due to afterburning and to protect the vehicle, lighting up an error lamp in the dashboard to warn the driver Driver and saving the error for customer service Diagnosis.

This object is achieved by the in the license plate of the specified features solved.

The method according to the invention is based on the following simplifying physical consideration from:

The combustion that occurs in each cylinder Gas forces generate a torque on the crankshaft that during rotation by a crank angle range on the Crankshaft does the job. This crank angle range extends at most from the ignition TDC of the respective cylinder until the following subtitles. With intermittent combustion this work is not done, and accordingly takes the rotational energy from the crank mechanism and Flywheel mass in this crank angle range. The rotational energy is proportional to the square of the momentary Speed of the internal combustion engine.

In the method according to the invention is not as in the known methods the instantaneous speed or Angular velocity or its time derivative (acceleration) examined, but the fall of the square of Current speed within the specified crank angle range. Since each cylinder of the internal combustion engine has a corresponding one Angular range can be assigned is  cylinder-selective monitoring of energy turnover guaranteed.

With a constant cylinder charge, the n² drop is intermittent Combustion regardless of the (middle) Engine speed because the same amount of work the crankshaft is missing. This means with regard to the Setting detection thresholds is a significant simplification versus an analysis of the instantaneous speed Course, the strongly speed-dependent threshold values required makes.

In the method according to the invention, during each Working cycle of the engine for each cylinder is a current one Speed square value determined. The one to be checked Energy or n² waste results as a difference of the n² values of consecutive in firing order Cylinders. Thus, the internal combustion engine per work cycle determined only as many values as the number of cylinders corresponds to the internal combustion engine.

Each n² value is suitable from the duration of one selected crank angle range is calculated. The Duration results from the number of pulses one Pulse generator within the crank angle range, the for example, as is known, with the help of the tooth signal determined by the flywheel gear cross and a phase signal can be. Because every cylinder has a crank angle range assigned for the n² determination, follow Areas in the firing interval.

In contrast, in the method according to the invention wide crank angle ranges to the known methods used. The width should be chosen at least as large as that practically easy to implement count rates (e.g. 1 MHz) are sufficient for time measurement, and that interferences, for example due to cyclical  Fluctuations, manufacturing tolerances of the ring gear and retroactive bumps in the road surface are eliminated. The width of the crank angle ranges upwards limited by the requirement that an Combustion still clearly recognizable remains.

An essential feature of the method according to the invention is taking into account the influence of one dynamic engine operation on the n² curve, which for reliable detection of misfires is necessary because superimposed in the event of acceleration a possible misfire n² drop the acceleration-related increase in n², whereby misfire detection depending on the degree of acceleration difficult or would also be prevented. On the other hand occurs even with a faultless motor when braking n² drop, which leads to misdiagnosis of combustion misfires could lead. The method according to the invention therefore contains dynamic compensation. This will be done within of each working cycle of the internal combustion engine the mean linear of the actual n² curve n² increase (when accelerating) or n² decrease (when braking) subtracted within this working cycle, so that by accelerating or braking the vehicle engine caused n² change is eliminated. Then the difference between the corrected n² value in the ignition TDC of this cylinder and the corrected n² value in the ignition TDC of the ignition sequence next cylinder formed, and the difference values are compared with predetermined threshold values. A Failure diagnosis occurs when a critical relative Frequency of exceeding a or threshold multiple cylinders occurs.

The threshold values are preferably dependent on Load and speed of the internal combustion engine in a map  specified because the gas force is lower at partial load than with full load and therefore also with a misfire energy deficit occurring less is so that the threshold must be lower than at full load, and the frictional forces depend on the speed are.

The instantaneous speed is preferably determined via a crank angle corresponding to the ignition Area. In this way, the angular ranges limit successive cylinders together, with what the number of required crank angle marks (e.g. Tooth signal edges) reduced to half is because the end of each crank angle range with the Beginning of the next coincides.

The method according to the invention can be achieved by appropriate Extension of the digital engine control units common today in which the tooth and phase signals are already for the cylinder-selective control of the ignition and the Fuel injection are available without additional Sensors are carried out. A device for performing of the inventive method is in the claim 4 specified.

An embodiment of the invention is as follows described with reference to the drawings:

Fig. 1 is a schematic representation of an electronic control system with Verbrennungsaussetzer- detection for a mixture-compressing multi-cylinder internal combustion engine,

Fig. 2 is a schematic illustration of the starter ring gear of the engine,

Fig. 3 shows the program flow in the computing unit for the detection of combustion misfires,

Fig. 4 shows a working cycle of a 8-cylinder four-stroke internal combustion engine, the position and the duration of the crank angle ranges and the calculated therefrom n² values,

FIG. 5 is a diagram showing the course of the square of the instantaneous speed during an operating cycle of an 8-cylinder four-stroke internal combustion engine without dynamic compensation, and

FIG. 6 is a diagram corresponding to FIG. 5, but with dynamic compensation of the speed square curve over a work cycle.

In Fig. 1, 1 denotes the crankshaft of a four-stroke internal combustion engine, on which a gearwheel 2 is attached, the teeth 3 ( FIG. 2) or tooth flanks of which cooperate as a signal transmitter with a first sensor 4 . In Fig. 2 the ignition distance between successively firing cylinders is designated by β. In this exemplary embodiment, the segment width α for determining the instantaneous speed is equal to the ignition interval. In this case, the end of each crank angle range α coincides with the beginning of the next one, so that only a number of markings corresponding to the number of cylinders has to be provided. However, the segment width α can also deviate from the ignition interval β.

The crankshaft 1 drives a camshaft 5 at half the crankshaft speed, which carries a phase mark 6 which interacts with a second sensor 7 . The sensor 4 feeds the tooth signal to a digital control device 9 . The second sensor 7 receives a signal from the phase mark 6 after each revolution of the camshaft 5 , that is to say after every second revolution of the crankshaft 1 , which is also fed to the control unit 9 . The control unit 9 , which receives a load-dependent signal through a line 10 , determines the injection timing and the injection quantity and the ignition timing for each cylinder from the input signals and transmits corresponding signals to an electronic injection device 12 and an electronic ignition device 13 . In this respect, the device according to FIG. 1 corresponds to a known digital motor control. In addition, a computing unit 14 is provided, which transmits the tooth signal from the first sensor 4 through a first line 15, the phase signal from the second sensor 7 through a second line 16, the engine speed signal through a third line 17 and the engine load through a fourth line 18. Receives signal.

In the computing unit 14 from the tooth signal and the phase signal for each cylinder, the crank angle range α ( FIG. 2) is determined, the duration of which is determined by counting the pulses falling in it from a pulse generator present in the computing unit, and it is calculated for each cylinder from the Time period calculated the instantaneous speed and formed its square n², as shown schematically in Fig. 4. Here n₁² means the instantaneous speed square value for cylinder 1 before work performed by the gas force, n₂² the corresponding value for cylinder 2 , which also represents the n² value for cylinder 1 after work performed by its gas force etc. Any energy drop that may occur in Cylinder 1 due to intermittent combustion becomes the difference

(Δn²) ₁ = n₁² - n₂²

detected, this size positive with an n² drop is.  

In stationary engine operation, the quantities (Δn²) _i (i = 1... Z, z = number of cylinders of the internal combustion engine) can be used to detect misfires because, in the event of a misfire in cylinder i, the value of (Δn²) _i exceeds a threshold value . For reliable misfire detection in dynamic engine operation, however, a correction is necessary, since when accelerating there is an increase in n², which is superimposed on an n² drop caused by misfires. On the other hand, since an n² drop occurs when braking, this could lead to a misdiagnosis if the motor is faultless.

In order to compensate for these dynamic influences, the average linear n 2 increase or decrease in this work cycle is subtracted from the n 2 curve within each work cycle of the internal combustion engine. If n₁² and n _{1 ′} ² denote the current speed square values for the first cylinder in two successive work cycles, the formula gives

Δ _AS n² = n _{1 ′} ² - n₁²

the mean dynamic change in n² in the first of the two Working games.

The corrected cylinder-selective test variables f _i for the detection of misfires are thus

In Fig. 3, the program flow is illustrated in the arithmetic unit 14. If the processor detects misfires with a frequency greater than the critical frequency, it sends a signal to the control unit 9 via a line 19 , which lights up a fault light 20 and / or initiates other measures.

In FIG. 5, the n 2 curve during an operating cycle of an 8-cylinder, four-stroke internal combustion engine is represented by A during an acceleration process, it being assumed that no combustion takes place in cylinder 2 . The n² drop after cylinder 2 is superimposed by the n² increase due to the acceleration process and is therefore not very pronounced.

In order to achieve a clear misfire detection, the mean linear n² increase is calculated during each working cycle of the internal combustion engine. This mean linear curve is illustrated by curve B. If the linear n² increase according to curve B is subtracted from the actual n² curve A (or a corresponding n² drop when the vehicle is braked), the result is the dynamically compensated n² curve C shown in FIG now clearly shows a misfire in cylinder 2 .

It should also be noted that in FIGS. 2, 4, 5 and 6 the cylinders have been numbered consecutively according to their firing order and not, as usual, according to their arrangement.

Claims (5)

1. A method for cylinder-selective control of the energy conversion in a multi-cylinder internal combustion engine, characterized in that

• a) during the working cycle of each cylinder, the instantaneous speed is determined via a specific crankshaft rotation angle and its square (n²) is formed,
• b) subtracted from each actual cycle of the internal combustion engine from the actual n² curve the mean linear n² rise or fall to form a dynamically corrected n² curve,
• c) for each cylinder, the difference between the corrected n² value for the TDC of this cylinder and the corrected n² value for the TDC of the next cylinder in the firing order is formed,
• d) the difference values are compared with predetermined threshold values, and
• e) the relative frequencies of misfires in all cylinders are determined, an error display being triggered if a critical frequency threshold is exceeded.

2. The method according to claim 1, characterized in that that the threshold values depending on the load and the speed of the internal combustion engine can be determined. 3. The method according to claim 1, characterized in  that the determination of the instantaneous speed essentially over an ignition distance corresponding Crankshaft rotation angle takes place. 4. Device for performing the method according to claim 1 with

• a) a first device for identifying the crankshaft position, and
• b) a second device for detecting the instantaneous speed of the internal combustion engine via a specific crankshaft angle of rotation during the working cycle of each cylinder,
  marked by
• c) a third device for calculating the square of the determined instantaneous speed,
• d) a fourth device for the computationally dynamic correction of the instantaneous speed square by subtracting the mean linear increase or decrease in n² during a working cycle of the internal combustion engine from the actual n² curve during this working cycle,
• e) a fifth device for calculating the difference between successive corrected n² values for each cylinder, and
• f) a sixth device for comparing the difference values with predetermined threshold values.

5. The device according to claim 4, characterized in that all facilities in a common computing unit are integrated.