WO2014065743A1 - Cylinder diagnosis - Google Patents

Cylinder diagnosis Download PDF

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Publication number
WO2014065743A1
WO2014065743A1 PCT/SE2013/051221 SE2013051221W WO2014065743A1 WO 2014065743 A1 WO2014065743 A1 WO 2014065743A1 SE 2013051221 W SE2013051221 W SE 2013051221W WO 2014065743 A1 WO2014065743 A1 WO 2014065743A1
Authority
WO
WIPO (PCT)
Prior art keywords
test
torque contribution
cylinders
test variable
greatness
Prior art date
Application number
PCT/SE2013/051221
Other languages
French (fr)
Inventor
Björn Johansson
Original Assignee
Scania Cv Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Scania Cv Ab filed Critical Scania Cv Ab
Priority to DE112013004818.3T priority Critical patent/DE112013004818T5/en
Publication of WO2014065743A1 publication Critical patent/WO2014065743A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M15/00—Testing of engines
    • G01M15/04—Testing internal-combustion engines
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/008—Controlling each cylinder individually
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1497—With detection of the mechanical response of the engine
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1497—With detection of the mechanical response of the engine
    • F02D41/1498—With detection of the mechanical response of the engine measuring engine roughness
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/22—Safety or indicating devices for abnormal conditions
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M15/00—Testing of engines
    • G01M15/04—Testing internal-combustion engines
    • G01M15/042—Testing internal-combustion engines by monitoring a single specific parameter not covered by groups G01M15/06 - G01M15/12
    • G01M15/046—Testing internal-combustion engines by monitoring a single specific parameter not covered by groups G01M15/06 - G01M15/12 by monitoring revolutions
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/22—Safety or indicating devices for abnormal conditions
    • F02D2041/228—Warning displays
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D2200/00—Input parameters for engine control
    • F02D2200/02—Input parameters for engine control the parameters being related to the engine
    • F02D2200/10—Parameters related to the engine output, e.g. engine torque or engine speed
    • F02D2200/1002—Output torque
    • F02D2200/1004—Estimation of the output torque
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D2200/00—Input parameters for engine control
    • F02D2200/02—Input parameters for engine control the parameters being related to the engine
    • F02D2200/10—Parameters related to the engine output, e.g. engine torque or engine speed
    • F02D2200/101—Engine speed
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D35/00—Controlling engines, dependent on conditions exterior or interior to engines, not otherwise provided for
    • F02D35/02—Controlling engines, dependent on conditions exterior or interior to engines, not otherwise provided for on interior conditions
    • F02D35/023—Controlling engines, dependent on conditions exterior or interior to engines, not otherwise provided for on interior conditions by determining the cylinder pressure
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

Definitions

  • the present invention pertains generally to testing of combustion engines. Specifically, the invention pertains to a diagnostic system according to the preamble to patent claim 1 and a method according to the preamble to patent claim 1 3. The invention also pertains to a computer program according to patent claim 23 and a computer readable medium according to patent claim 24.
  • Modern combustion engines have advanced fuel injection systems in order to optimise the fuel utilisation rate and thus to conserve energy and mitigate the engine's environmental impact. If, however, a fault arises in the fuel injection system, there may be highly undesirable consequences. For example, a fuel injector to a certain cylinder may be jammed , so that the cylinder cannot receive any fuel . The result is that the engine provides an uneven torque, which in turn causes increased wear of the engine and its associated driveline. If the problem is not fixed , it may eventually lead to a breakdown . In any event, the engine's uneven operation gives rise to vi brations, which , if the engine is comprised in a vehicle, causes impaired comfort for the driver of the vehicle.
  • US 2012/0299051 describes a fault detection method , where so- called cylinder effect density values are determined during the operation of a combustion engine. By comparing the cylinder effect density values with a threshold value, it is determined whether there is an imbalance in the engine, which may indicate a fault in one of the cylinders.
  • JP 71 03047 shows a diagnostic method , where an abnormal engine condition is discovered which is due to a cylinder in the engine not consuming any fuel .
  • a signal representing the crankshaft speed is registered to measure a time interval corresponding to the combustion cycle of each cylinder. Any discrepancy between these time intervals and a reference value is deemed to indicate an anomaly in a cylinder
  • US 2002/0148441 shows a solution in which speed fluctuations in an engine's revolutions are studied in order to detect potential faults in the fuel injection system .
  • a band-pass filter is used to analyse amplitude variations at certain frequencies, which have been found to be especially characteristic for detecting faults in the fuel injection function .
  • US 2008/0228341 descri bes a method for the determination of a fault condition in the fuel system of a combustion engine.
  • One or several sensors here provide a signal representing combustion events in the cylinders. This signal is integrated , so that a first and second gradient for each cylinder is produced . By comparing the gradients for the same cylinder, conclusions are drawn as to whether or not a certain cylinder functions normally.
  • a combustion engine's speed signal is analysed in one way or another, in order to determine which torque contribution the respective cylinders in the engine provide. If the cylinders' torque contributions vary to an unacceptable degree in relation to each other, it is interpreted as a faulty state.
  • the prior art solutions for this type of analysis have difficulties in drawing correct conclusions when the engine is su bjected to e.g . transient processes. In such cases, the cylinders' torque contributions may seem to vary quite a lot among each other, even where the engine and its injection system functions perfectly. An alarm signal and/or error code may therefore be generated unnecessarily, which leads to unwarranted downtime.
  • the objective of the present invention is therefore to provide a solution , which mitigates the above mentioned problem and achieves a more reliable discovery of faulty cylinders in a combustion engine.
  • the objective is achieved through the diagnostic system described in the introduction , so that the processing device is configured to form a first test variable, based on a first pair of measuring values representing a respective torque contribution from two of the said at least three cylinders during a measuring period .
  • the processing device is also configured to form a second test variable, based on a second pair of measuring values representing one respective torque contribution from two of the said at least three cylinders during the measuring period .
  • the processing device is then configured to test the first and the second test variables against an alarm criterion , and provided that the alarm criterion is met, the processing device is configured to generate an alarm code indicating a fault in at least one of the said engine's cylinders.
  • This system is desirable since it may specify whether an identified fault involves a too high or too low torque contri bution from a certain cylinder. Additionally, the system may handle load and speed cases where many of the prior art solutions indicate a fault even though there is no fault.
  • the first test variable represents a difference between the biggest torque contribution and the second biggest torque contribution .
  • the second test variable preferably represents a difference between the second biggest torque contribution and the lowest torque contribution .
  • the processing device is configured to test the first and second test variables against the alarm criterion by forming a first test greatness representing a quota between the first test variable and the sum of the first test variable and the second test variable; and to form a second test greatness representing the sum of the first test variable and the second test variable.
  • the processing device is also configured to investigate whether the first test greatness exceeds a first threshold value, and to investigate whether the second test greatness exceeds a second threshold value.
  • the alarm criterion is deemed to be met here if the first test greatness exceeds the first threshold value and the second test greatness exceeds the second threshold value at the same time.
  • This test method has proved to be advantageous when the engine is su bject to transient operation . In these cases, the cylinders' torque contributions tend to fluctuate considerably (in particular if the torque contributions are not specifically measured , but only estimated ). Typically, however, the biggest as well as the second biggest torque contributions represent big values, so that the risk of a false alarm is relatively small .
  • the alarm code indicates an error in the cylinders of the engine, which gives the biggest torque contribution when the alarm criterion is met.
  • This type of discrepancy may be associated with too much fuel being fed into the cylinder, for example due to a fault in the fuel injection element.
  • the first test variable is formed based on a lowest torque contribution from the cylinder of the said at least tree cylinders which during a measuring period provides a lowest torque contribution , and a second lowest torque contribution from the cylinder of the said at least three cylinders which during the measuring period provides a second lowest torque contribution .
  • the second test variable is here formed based on the second lowest torque contribution and a highest torque contribution from the cylinder from the said at least three cylinders which during the measuring period gives a highest torque contribution .
  • the first test variable preferably represents a difference between the second lowest torque contribution and the lowest torque contribution
  • the second test variable represents a difference between the highest torque contribution and the second lowest torque contribution .
  • the processing device is suitably configured to test the first and second test variables against the alarm criterion by: forming a first test greatness representing a quota between the first test variable and the sum of the first test variable and the second test variable; forming a second test greatness representing the sum of the first test variable and the second test variable; investigating whether the first test greatness exceeds a third threshold value, and investigating [if] the second test greatness exceeds a fourth threshold value.
  • the alarm criterion is deemed to be fulfilled here if the first test greatness exceeds the third threshold value, and the second test greatness exceeds the fourth threshold value.
  • the alarm code indicates in this case a fault in the engine cylinder which provides the lowest torque contri bution when the alarm criterion is fulfilled .
  • the said sensor for registration of the measuring signal comprises at least one accelerometer and/or at least one cylinder pressure transmitter.
  • adequate data may be registered which reflect the respective cylinders' torque contributions.
  • the senor comprises a speed sensor, which is configured to generate a speed signal representing the speed of the combustion engine.
  • the processing device is here configured to deduce a torque contribution from each one of the engine cylinders based on the speed signal .
  • the diagnostic system comprises at least one filtering device configured to receive and linear filter (for example low-pass or band-pass filter) at least one original measuring signal from the combustion engine.
  • the filtering device is configured , in response to the signal received , to generate at least one resulting signal representing a filtered version of the measuring signal , where for example extreme signal values during the measuring period have been removed .
  • This further reduces the risk of false alarms.
  • the objective is achieved with the method described above, where a first test variable is formed based on a first pair of measuring values representing a respective torque contribution from two of the said at least three cylinders during a measuring period ; and a second test variable is formed based on a second pair of measuring values representing one respective torque contribution from two of the said at least three cylinders during the measuring period , where the first and second pair of measuring values originate from at least three different cylinders in the engine.
  • the first and the second test variables are tested against an alarm criterion , and given that the alarm criterion is met, an alarm code is generated indicating a fault in at least one of the engine's cylinders.
  • the objective is achieved with a computer program which may be downloaded to an internal memory of a computer, comprising software to control the steps according to the method suggested above when the said program is executed on a computer.
  • the objective is achieved with a computer readable medium with a stored program, where the program is adapted to induce a computer to control the steps according to the above method .
  • Figure 1 shows a schematic image of an engine and a diagnostic system according to a first embodiment of the invention
  • Figure 2 shows a schematic image of an engine and a diagnostic system according to a second embodiment of the invention ;
  • Figure 3 contains a diagram which illustrates a first example of different cylinders' torque contributions as a function of time
  • Figure 4 contains a diagram which illustrates a second example of different cylinders' torque contributions as a function of time
  • Figure 5 contains a flow diagram which illustrates an embodiment of the general method according to the invention .
  • Figure 1 shows a schematic image of a combustion engine 100 and a diagnostic system according to a first embodiment of the invention . It is assumed that the combustion engine 100 includes at least three cylinders.
  • the engine 100 illustrated in Figure 1 is equipped with six cylinders C1, C2, C3, C4, C5 and C6 in a straight configuration.
  • the invention is, however, also applicable to other numbers of cylinders ⁇ 3 and types of cylinder configurations, such as V, W, boxer and Wankel engines.
  • the proposed diagnostic system comprises at least one sensor s1, s2, s3, s4, s5 and s6, and one processing device 110.
  • a sensor s1, s2, s3, s4, s5 and s6 is configured to register a respective measuring signal T1, T2, T3, T4, T5 and T6, which represents a respective torque contribution from each cylinder C1, C2, C3, C4, C5 and C6.
  • Each sensor s1, s2, s3, s4, s5 and s6 may thus include an accelerometer and/or a cylinder pressure transmitter.
  • the processing device 110 is configured based on the measuring signals T1, T2, T3, T4, T5 and T6 to investigate whether or not the combustion engine 100 functions satisfactorily.
  • the processing device 110 is configured to form a first test variable a based on a first pair of measuring values representing one and two of the cylinders C1, C2, C3, C4, C5 and C6 during a measuring period.
  • the processing device 110 is also configured to form a second test variable b based on a second pair of measuring values representing one respective torque contribution from two of the cylinders C1, C2, C3, C4, C5 and C6 during the measuring period.
  • the measuring values may partly overlap, but the first and second pairs of measuring values must originate from at least three different cylinders of the cylinders C1 , C2, C3, C4, C5 and C6 of the engine 100.
  • the processing device 110 is configured to test the first and second test variables against an alarm criterion. If the alarm criterion is fulfilled, the processing device 110 is configured to generate an alarm code A, indicating a fault in at least one of the cylinders C1, C2, C3, C4, C5 or C6.
  • FIG. 3 shows a diagram illustrating a first example of the torque contribution T of the different cylinders C1 , C2 , C3, C4 , C5 and C6 as a respective function T1 , T2 , T3, T4 , T5 and T6 of time t.
  • the torque contribution T here is either the maximum torque which a cylinder generates during a combustion cycle (i .e. two crankshaft revolutions on a four-stroke engine), or an average torque which a cylinder generates during a combustion cycle.
  • the processing device 1 1 0 is specifically configured to form the first test variable a based on (i) a biggest torque contribution x from the cylinder which during a measuring period (for example corresponding to a certain number of sampling intervals for a respective digital sensor in the sensors s1 , s2 , s3, s4 , s5 and s6) produces the biggest torque contribution , and (ii ) a second biggest torque contribution y from the cylinder which during the measuring period produces the second biggest torque contribution .
  • the processing device 1 10 is also configured to form the second test variable b based on (i ) the second biggest torque contribution y, and (ii) a lowest torque contribution z from the cylinder which provides the lowest torque contribution during the measuring period .
  • Figure 3 shows how the allocation of the variables x, y, and z vary over time t.
  • a measuring signal T6 represents the variable x until a first time t-
  • the variable z represents a measuring signal T1 .
  • the variable x represents a measuring signal T5.
  • the variable z represents the measuring signal T6, following which the measuring signal T1 again represents the variable z.
  • a measuring signal T3 represents the variable x
  • the measuring signal T6 represents the variable x
  • the measuring signal T3 then represents the variable x.
  • the allocation of the variable y also varies over time t. For example, the measuring signal T3 represents the variable y between the fifth point in time t 5 and the sixth point in time t 6 , while the measuring signal T6 represents the variable y between and the sixth point in time t 6 and an eighth point in time t 8 .
  • the processing device 1 10 tests the first and second test variables a and b against an alarm criterion ; and if the alarm criterion is met, the processing device 1 1 0 generates an alarm code A.
  • the alarm criterion is met at a seventh point in time t 7 between the sixth point in time t 6 and the eighth point in time t 8 . This is because at the seventh point in time t 7 the relationship between the first test variable a and the second test variable b fulfils the alarm criterion .
  • the first test variable a represents a difference between the biggest torque contribution x and the second biggest torque contribution y
  • the second test variable b represents a difference between the second biggest torque contribution y and the lowest torque contribution z.
  • the processing device 1 1 0 is advantageously configured to test the first and second test variables a and b, respectively, against the alarm criterion by:
  • first test greatness representing a quota between the first test variable a and the sum of the first test variable a and the second test variable b, that is .
  • the processing device 1 1 0 then investigates whether the first test greatness a/(a+b) exceeds a first threshold value, and whether at the same time the second test greatness a+b exceeds a second threshold value. Provided that this is the case, the processing device 1 1 0 generates an alarm code A, which indicates a fault in at least one of the cylinders C1 , C2 , C3, C4 , C5 and C6. At the seventh point in time t 7 the current conditions are thus assumed to be fulfilled .
  • the measuring signal T3 from a third cylinder C3 in the combustion engine 100 represents the biggest torque contribution x.
  • the alarm code A thus indicates a fault in the third cylinder C3.
  • the alarm code A also specifies that the third cylinder C3 is receiving too much fuel , since its torque contribution T3 is too high .
  • Figure 4 shows a diagram illustrating a second example of how the torque contributions T1 , T2, T3, T4 , T5 and T6 of the different cylinders C1 , C2, C3, C4, C5 and C6 vary over time t.
  • the processing device 1 10 is configured to form a first test variable a, based on (i ) a lowest torque contribution z from the cylinder which during a measuring period (for example corresponding to a certain number of sampling intervals for a digital sensor in the sensors s1 , s2, s3, s4, s5 and s6) provides a lowest torque contribution , and (ii ) a second lowest torque contribution w from the cylinder which during a measuring period provides a second lowest torque contribution .
  • the processing device 1 1 0 is also configured to form a second test variable b based on (i) the second lowest torque contribution w, and (ii ) a highest torque contribution x from the cylinder which during the measuring period provides a lowest torque contri bution .
  • Figure 4 shows how the allocation of the variables x, w and z vary over time t.
  • the torque contribution T1 of the first cylinder C1 represents the variable z at the beginning
  • the torque contri bution T4 of the fourth cylinder C4 represent the variable w.
  • the torque contribution T3 of the third cylinder C3 represents the variable z
  • the alarm criterion is fulfilled .
  • the first test variable a represents a difference between the second lowest torque contribution z and the lowest torque contribution w; and the second test variable b represents a difference between the highest torque contribution x and the second lowest torque contribution w.
  • the processing device 1 10 is advantageously configured even here to test the first and second test variables a and b, respectively, against the alarm criterion by:
  • first test greatness representing a quota between the first test variable a and the sum of the first test variable a and the second test variable b, that is .
  • the processing device 1 1 0 then investigates whether the first test greatness a/(a+b) exceeds a third threshold value, and whether at the same time the second test greatness a+b exceeds a fourth threshold value. Provided that this is the case, the processing device 1 1 0 generates an alarm code A, which indicates a fault in at least one of the cylinders C1 , C2 , C3, C4 , C5 and C6. At the point in time t 0 these conditions are therefore assumed to be fulfilled .
  • the measuring signal T3 from the third cylinder C3 in the combustion engine 100 represents the lowest torque contribution z.
  • the alarm code A thus indicates a fault in the third cylinder C3.
  • the alarm code A also specifies that the third cylinder C3 is receiving insufficient fuel , since its torque contribution T3 is too low.
  • the diagnostic system comprises at least one filtering device 120, which is configured to receive and linear filter the original measuring signals from the combustion engine 100, and in response thereto to generate the resulting signals, which represent the measuring signals T1, T2, T3, T4, T5 and T6.
  • the filtering device 120 is installed to remove extreme measuring values, i.e. values which diverge strongly from other measuring values during the measuring period (so-called outliers), for example by low-pass or band-pass filtering of the incoming signals.
  • outliers for example by low-pass or band-pass filtering of the incoming signals.
  • the processing device 110 comprises, or is communicatively connected with, a memory device M, which comprises a computer program comprising software to control the processing device 110 so that it operates as described above.
  • Figure 2 shows a schematic image of a combustion engine 100 and a diagnostic system according to another embodiment of the invention. All references in Figure 2 which tally with references in Figure 1 use the same units, variables and signals as those described above with reference to Figure 1.
  • the embodiment in Figure 2 differs primarily from that in Figure 1 by the fact that the diagnostic system illustrated in Figure 2 includes a speed sensor s7 configured to generate a speed signal rpm representing the engine speed of the combustion engine 100.
  • the processing device 110 is thus configured to derive a respective torque contribution T1, T2, T3, T4, T5 and T6 from the cylinders C1, C2, C3, C4, C5 and C6 from the engine speed signal rpm. Examples of how this may be effectuated are described in the above mentioned patent documents.
  • a torque sensor may be arranged on the crankshaft of the engine 100 between the cylinders and the flywheel , the torque sensor of which is configured to measure the different torque contributions of the cylinders C1 , C2, C3, C4 , C5 and C6.
  • the diagnostic system also comprises a filtering device 220, which is configured to receive and linear filter the original measuring signal from the speed sensor, and in response thereto to generate resulting signals, which represent the measuring signals rpm.
  • the filtering device 220 is also here installed to remove extreme measuring values, i .e. values which diverge strongly from other measuring values during the measuring period (so-called outliers), for example through low- pass or band-pass filtering of the incoming signals.
  • At a first step 51 0 at least one measuring signal T1 , T2, T3, T4, T5 and T6 or rpm is registered , which represents a respective torque contribution from each cylinder C1 , C2, C3, C4 , C5 and C6 in a combustion engine. It is assumed that the engine is equipped with at least tree cylinders.
  • a first test variable a is formed in a step 520 based on a first pair of measuring values representing a respective torque contribution from two of the said cylinders during a measuring period .
  • the first pair of measuring values may represent a biggest torque contribution x from the cylinder which provides a biggest torque contribution during a measuring period and a second biggest torque contribution y from the cylinder which provides a second biggest torque contribution during the measuring period .
  • the first pair of measuring values may represent a lowest torque contribution z from the cylinder which provides a lowest torque contribution during a measuring period and a second lowest torque contribution w from the cylinder which provides a second lowest torque contribution du ring the measuring period .
  • a second test variable b is formed based on a second pair of measuring values representing a respective torque contribution from two of the said cylinders during the measuring period .
  • the first and second pairs of measuring values originate from at least three different cylinders of the said cylinders.
  • the second pair of measuring values may represent the second largest torque contribution y and a lowest torque contribution z from the cylinder which provides a lowest torque contribution during the measuring period .
  • the second pair of measuring values may represent the largest torque contribution x and the second lowest torque contribution w during the measuring period .
  • a subsequent step 540 investigates whether or not the combustion engine is deemed to function satisfactorily. Specifically, at step 540 the first and second test variables a and b, respectively, are tested against an alarm criterion . If the alarm criterion is met, a step 550 follows, otherwise the procedure loops back to step 510.
  • an alarm code indicating a fault in at least one of the engine's cylinders C1 , C2 , C3, C4 , C5 or C6 is generated , preferably the engine cylinder(s) which is/are associated with the most divergent torque contri bution(s) when the alarm criterion is fulfilled .
  • the procedure then ends.
  • the procedure after step 550 reverts to step 510 for continued testing .
  • the method steps described with reference to Figure 5 may be controlled with the help of a programmed computer apparatus.
  • the invention extends to software, in particular software on or in a carrier adapted to implement the invention practically.
  • the program may be in the form of a source code, object code, a code constituting a cross between source and object code, such as in partly compiled form, or in any other form whatsoever which is suitable for use in the implementation of the process according to the invention .
  • the carrier may be any type of entity or device which is capable of carrying the program .
  • the carrier may comprise a storage medium such as a flash memory, a ROM (Read Only Memory), for example a CD (Compact Disc) or a semiconductor ROM , EPROM (Electrically Programmable ROM ), EEPROM (Erasable EPROM), or a magnetic recording medium, for example a floppy disk or a hard disk.
  • the carrier may be a transmitting carrier such as an electric or optic signal , which may pass through an electric or optic cable or via radio or in another manner. Since the program is embodied by a signal that may be transmitted directly by a cable or another device or element, the carrier may consist of such a cable, device or element.
  • the carrier may be an integrated circuit into which the program is embedded , where the integrated circuit is adapted to carry out, or to be used in the performance of the relevant processes.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Combined Controls Of Internal Combustion Engines (AREA)

Abstract

A combustion engine (100) includes at least three cylinders (C1, C2, C3, C4, C5, C6). A diagnostic system for the engine (100) comprising at least one sensor (s7) configured to register a measuring signal (rpm) representing a respective torque contribution from each of the cylinders; and a processing device (110) configured, based on the measuring signal (rpm), to investigate whether or not the engine (100) functions satisfactorily. The processing device (110) forms a first test variable (a) based on a first pair of measuring values representing a respective torque contribution from two of the cylinders during a measuring period. The processing device (110) also forms a second test variable (b) based on a second pair of measuring values representing a respective torque contribution from two of the cylinders during the measuring period, where the said first and second pairs of measuring values originate from at least three different cylinders in the engine (100). The first and second test variable (a; b) are tested against an alarm criterion, and if the alarm criterion is met the processing device (110) generates an alarm code (A) indicating a fault in at least one of the cylinders.

Description

Cyl inder diagnosis
BACKGROUND OF THE I NVENTION AND PRI OR ART
The present invention pertains generally to testing of combustion engines. Specifically, the invention pertains to a diagnostic system according to the preamble to patent claim 1 and a method according to the preamble to patent claim 1 3. The invention also pertains to a computer program according to patent claim 23 and a computer readable medium according to patent claim 24. Modern combustion engines have advanced fuel injection systems in order to optimise the fuel utilisation rate and thus to conserve energy and mitigate the engine's environmental impact. If, however, a fault arises in the fuel injection system, there may be highly undesirable consequences. For example, a fuel injector to a certain cylinder may be jammed , so that the cylinder cannot receive any fuel . The result is that the engine provides an uneven torque, which in turn causes increased wear of the engine and its associated driveline. If the problem is not fixed , it may eventually lead to a breakdown . In any event, the engine's uneven operation gives rise to vi brations, which , if the engine is comprised in a vehicle, causes impaired comfort for the driver of the vehicle.
US 2012/0299051 describes a fault detection method , where so- called cylinder effect density values are determined during the operation of a combustion engine. By comparing the cylinder effect density values with a threshold value, it is determined whether there is an imbalance in the engine, which may indicate a fault in one of the cylinders.
JP 71 03047 shows a diagnostic method , where an abnormal engine condition is discovered which is due to a cylinder in the engine not consuming any fuel . A signal representing the crankshaft speed is registered to measure a time interval corresponding to the combustion cycle of each cylinder. Any discrepancy between these time intervals and a reference value is deemed to indicate an anomaly in a cylinder US 2002/0148441 shows a solution in which speed fluctuations in an engine's revolutions are studied in order to detect potential faults in the fuel injection system . Specifically, a band-pass filter is used to analyse amplitude variations at certain frequencies, which have been found to be especially characteristic for detecting faults in the fuel injection function .
US 2008/0228341 descri bes a method for the determination of a fault condition in the fuel system of a combustion engine. One or several sensors here provide a signal representing combustion events in the cylinders. This signal is integrated , so that a first and second gradient for each cylinder is produced . By comparing the gradients for the same cylinder, conclusions are drawn as to whether or not a certain cylinder functions normally.
PROBLEMS ASSOCIATED WITH PRIOR ART
In all of the above solutions, a combustion engine's speed signal is analysed in one way or another, in order to determine which torque contribution the respective cylinders in the engine provide. If the cylinders' torque contributions vary to an unacceptable degree in relation to each other, it is interpreted as a faulty state. The prior art solutions for this type of analysis, however, have difficulties in drawing correct conclusions when the engine is su bjected to e.g . transient processes. In such cases, the cylinders' torque contributions may seem to vary quite a lot among each other, even where the engine and its injection system functions perfectly. An alarm signal and/or error code may therefore be generated unnecessarily, which leads to unwarranted downtime.
SUM MARY OF TH E I NVENTION The objective of the present invention is therefore to provide a solution , which mitigates the above mentioned problem and achieves a more reliable discovery of faulty cylinders in a combustion engine. According to one aspect of the invention , the objective is achieved through the diagnostic system described in the introduction , so that the processing device is configured to form a first test variable, based on a first pair of measuring values representing a respective torque contribution from two of the said at least three cylinders during a measuring period . The processing device is also configured to form a second test variable, based on a second pair of measuring values representing one respective torque contribution from two of the said at least three cylinders during the measuring period . It is assumed that the first and second pairs of measuring values originate from at least three different cylinders in the engine. The processing device is then configured to test the first and the second test variables against an alarm criterion , and provided that the alarm criterion is met, the processing device is configured to generate an alarm code indicating a fault in at least one of the said engine's cylinders.
This system is desirable since it may specify whether an identified fault involves a too high or too low torque contri bution from a certain cylinder. Additionally, the system may handle load and speed cases where many of the prior art solutions indicate a fault even though there is no fault.
According to one embodiment of this aspect of the invention , the first test variable represents a difference between the biggest torque contribution and the second biggest torque contribution . Further, the second test variable preferably represents a difference between the second biggest torque contribution and the lowest torque contribution . Thus, stable detection criteria are obtained for the detection of cylinders which provide too high a torque contribution . According to another embodiment of this aspect of the invention , the processing device is configured to test the first and second test variables against the alarm criterion by forming a first test greatness representing a quota between the first test variable and the sum of the first test variable and the second test variable; and to form a second test greatness representing the sum of the first test variable and the second test variable. The processing device is also configured to investigate whether the first test greatness exceeds a first threshold value, and to investigate whether the second test greatness exceeds a second threshold value. The alarm criterion is deemed to be met here if the first test greatness exceeds the first threshold value and the second test greatness exceeds the second threshold value at the same time. This test method has proved to be advantageous when the engine is su bject to transient operation . In these cases, the cylinders' torque contributions tend to fluctuate considerably (in particular if the torque contributions are not specifically measured , but only estimated ). Typically, however, the biggest as well as the second biggest torque contributions represent big values, so that the risk of a false alarm is relatively small .
According to another embodiment of this aspect of the invention , the alarm code indicates an error in the cylinders of the engine, which gives the biggest torque contribution when the alarm criterion is met. This type of discrepancy may be associated with too much fuel being fed into the cylinder, for example due to a fault in the fuel injection element.
According to other embodiments of this aspect of the invention , the first test variable is formed based on a lowest torque contribution from the cylinder of the said at least tree cylinders which during a measuring period provides a lowest torque contribution , and a second lowest torque contribution from the cylinder of the said at least three cylinders which during the measuring period provides a second lowest torque contribution . The second test variable is here formed based on the second lowest torque contribution and a highest torque contribution from the cylinder from the said at least three cylinders which during the measuring period gives a highest torque contribution . In this case, the first test variable preferably represents a difference between the second lowest torque contribution and the lowest torque contribution , while the second test variable represents a difference between the highest torque contribution and the second lowest torque contribution .
Further, the processing device is suitably configured to test the first and second test variables against the alarm criterion by: forming a first test greatness representing a quota between the first test variable and the sum of the first test variable and the second test variable; forming a second test greatness representing the sum of the first test variable and the second test variable; investigating whether the first test greatness exceeds a third threshold value, and investigating [if] the second test greatness exceeds a fourth threshold value. The alarm criterion is deemed to be fulfilled here if the first test greatness exceeds the third threshold value, and the second test greatness exceeds the fourth threshold value. The alarm code indicates in this case a fault in the engine cylinder which provides the lowest torque contri bution when the alarm criterion is fulfilled . Thus a defective fuel injection element may be identified in an efficient manner. According to another embodiment of this aspect of the invention , the said sensor for registration of the measuring signal comprises at least one accelerometer and/or at least one cylinder pressure transmitter. Thus adequate data may be registered which reflect the respective cylinders' torque contributions.
According to another embodiment of this aspect of the invention , the sensor comprises a speed sensor, which is configured to generate a speed signal representing the speed of the combustion engine. The processing device is here configured to deduce a torque contribution from each one of the engine cylinders based on the speed signal . One advantage of this construction is that one and the same sensor may be used to measure signals from two or more cylinders. According to another embodiment of this aspect of the invention , the diagnostic system comprises at least one filtering device configured to receive and linear filter (for example low-pass or band-pass filter) at least one original measuring signal from the combustion engine. The filtering device is configured , in response to the signal received , to generate at least one resulting signal representing a filtered version of the measuring signal , where for example extreme signal values during the measuring period have been removed . This further reduces the risk of false alarms. According to another aspect of the invention , the objective is achieved with the method described above, where a first test variable is formed based on a first pair of measuring values representing a respective torque contribution from two of the said at least three cylinders during a measuring period ; and a second test variable is formed based on a second pair of measuring values representing one respective torque contribution from two of the said at least three cylinders during the measuring period , where the first and second pair of measuring values originate from at least three different cylinders in the engine. The first and the second test variables are tested against an alarm criterion , and given that the alarm criterion is met, an alarm code is generated indicating a fault in at least one of the engine's cylinders. The advantages of this method , as well as the preferred embodiments thereof, are apparent in the discussion above with reference to the proposed diagnostic system.
According to another aspect of the invention , the objective is achieved with a computer program which may be downloaded to an internal memory of a computer, comprising software to control the steps according to the method suggested above when the said program is executed on a computer.
According to another aspect of the invention , the objective is achieved with a computer readable medium with a stored program, where the program is adapted to induce a computer to control the steps according to the above method .
BRI EF DESCRI PTI ON OF DRAWI NGS
The present invention will now be explained in more detail through embodiments which are described as examples, and with reference to the enclosed drawings.
Figure 1 shows a schematic image of an engine and a diagnostic system according to a first embodiment of the invention ;
Figure 2 shows a schematic image of an engine and a diagnostic system according to a second embodiment of the invention ;
Figure 3 contains a diagram which illustrates a first example of different cylinders' torque contributions as a function of time;
Figure 4 contains a diagram which illustrates a second example of different cylinders' torque contributions as a function of time;
Figure 5 contains a flow diagram which illustrates an embodiment of the general method according to the invention .
DESCRI PTION OF EMBOD I MENTS ACCORD I NG TO TH E I NVENTI ON
We initially refer to Figure 1 , which shows a schematic image of a combustion engine 100 and a diagnostic system according to a first embodiment of the invention . It is assumed that the combustion engine 100 includes at least three cylinders. The engine 100 illustrated in Figure 1 is equipped with six cylinders C1, C2, C3, C4, C5 and C6 in a straight configuration. The invention is, however, also applicable to other numbers of cylinders≥ 3 and types of cylinder configurations, such as V, W, boxer and Wankel engines.
The proposed diagnostic system comprises at least one sensor s1, s2, s3, s4, s5 and s6, and one processing device 110. According to the embodiment in Figure 1, a sensor s1, s2, s3, s4, s5 and s6 is configured to register a respective measuring signal T1, T2, T3, T4, T5 and T6, which represents a respective torque contribution from each cylinder C1, C2, C3, C4, C5 and C6. Each sensor s1, s2, s3, s4, s5 and s6 may thus include an accelerometer and/or a cylinder pressure transmitter.
The processing device 110 is configured based on the measuring signals T1, T2, T3, T4, T5 and T6 to investigate whether or not the combustion engine 100 functions satisfactorily. Generally, the processing device 110 is configured to form a first test variable a based on a first pair of measuring values representing one and two of the cylinders C1, C2, C3, C4, C5 and C6 during a measuring period. The processing device 110 is also configured to form a second test variable b based on a second pair of measuring values representing one respective torque contribution from two of the cylinders C1, C2, C3, C4, C5 and C6 during the measuring period. According to the invention, the measuring values may partly overlap, but the first and second pairs of measuring values must originate from at least three different cylinders of the cylinders C1 , C2, C3, C4, C5 and C6 of the engine 100. Further, the processing device 110 is configured to test the first and second test variables against an alarm criterion. If the alarm criterion is fulfilled, the processing device 110 is configured to generate an alarm code A, indicating a fault in at least one of the cylinders C1, C2, C3, C4, C5 or C6.
We now refer to Figure 3, which shows a diagram illustrating a first example of the torque contribution T of the different cylinders C1 , C2 , C3, C4 , C5 and C6 as a respective function T1 , T2 , T3, T4 , T5 and T6 of time t. The torque contribution T here is either the maximum torque which a cylinder generates during a combustion cycle (i .e. two crankshaft revolutions on a four-stroke engine), or an average torque which a cylinder generates during a combustion cycle.
According to one embodiment of the invention the processing device 1 1 0 is specifically configured to form the first test variable a based on (i) a biggest torque contribution x from the cylinder which during a measuring period (for example corresponding to a certain number of sampling intervals for a respective digital sensor in the sensors s1 , s2 , s3, s4 , s5 and s6) produces the biggest torque contribution , and (ii ) a second biggest torque contribution y from the cylinder which during the measuring period produces the second biggest torque contribution . The processing device 1 10 is also configured to form the second test variable b based on (i ) the second biggest torque contribution y, and (ii) a lowest torque contribution z from the cylinder which provides the lowest torque contribution during the measuring period .
Figure 3 shows how the allocation of the variables x, y, and z vary over time t. Here, a measuring signal T6 represents the variable x until a first time t-| . Until a second point in time t2 the variable z represents a measuring signal T1 . Between the first point in time t-ι and a third point in time t3, the variable x represents a measuring signal T5. Between the second point in time t2 and a fourth point in time t4, the variable z represents the measuring signal T6, following which the measuring signal T1 again represents the variable z. Between the third point in time t3 and a fifth point in time t5, a measuring signal T3 represents the variable x, and between the fifth point in time t5 and a sixth point in time t6, the measuring signal T6 represents the variable x. As of the sixth point in time t6, the measuring signal T3 then represents the variable x. The allocation of the variable y also varies over time t. For example, the measuring signal T3 represents the variable y between the fifth point in time t5 and the sixth point in time t6, while the measuring signal T6 represents the variable y between and the sixth point in time t6 and an eighth point in time t8. During the entire process the processing device 1 10 tests the first and second test variables a and b against an alarm criterion ; and if the alarm criterion is met, the processing device 1 1 0 generates an alarm code A. In the example showed in Figure 3, the alarm criterion is met at a seventh point in time t7 between the sixth point in time t6 and the eighth point in time t8. This is because at the seventh point in time t7 the relationship between the first test variable a and the second test variable b fulfils the alarm criterion . According to embodiments of the invention , the first test variable a represents a difference between the biggest torque contribution x and the second biggest torque contribution y; and the second test variable b represents a difference between the second biggest torque contribution y and the lowest torque contribution z.
The processing device 1 1 0 is advantageously configured to test the first and second test variables a and b, respectively, against the alarm criterion by:
forming a first test greatness representing a quota between the first test variable a and the sum of the first test variable a and the second test variable b, that is .
a + b
and
forming a second test greatness representing the sum of the first test variable a and the second test variable b, i .e. a+b. The processing device 1 1 0 then investigates whether the first test greatness a/(a+b) exceeds a first threshold value, and whether at the same time the second test greatness a+b exceeds a second threshold value. Provided that this is the case, the processing device 1 1 0 generates an alarm code A, which indicates a fault in at least one of the cylinders C1 , C2 , C3, C4 , C5 and C6. At the seventh point in time t7 the current conditions are thus assumed to be fulfilled .
At this time t7 the measuring signal T3 from a third cylinder C3 in the combustion engine 100 represents the biggest torque contribution x. According to a preferred embodiment of the invention , the alarm code A thus indicates a fault in the third cylinder C3. Preferably, the alarm code A also specifies that the third cylinder C3 is receiving too much fuel , since its torque contribution T3 is too high .
Figure 4 shows a diagram illustrating a second example of how the torque contributions T1 , T2, T3, T4 , T5 and T6 of the different cylinders C1 , C2, C3, C4, C5 and C6 vary over time t.
According to this embodiment of the invention , the processing device 1 10 is configured to form a first test variable a, based on (i ) a lowest torque contribution z from the cylinder which during a measuring period (for example corresponding to a certain number of sampling intervals for a digital sensor in the sensors s1 , s2, s3, s4, s5 and s6) provides a lowest torque contribution , and (ii ) a second lowest torque contribution w from the cylinder which during a measuring period provides a second lowest torque contribution . The processing device 1 1 0 is also configured to form a second test variable b based on (i) the second lowest torque contribution w, and (ii ) a highest torque contribution x from the cylinder which during the measuring period provides a lowest torque contri bution .
Figure 4 shows how the allocation of the variables x, w and z vary over time t. For example, the torque contribution T1 of the first cylinder C1 represents the variable z at the beginning , while the torque contri bution T4 of the fourth cylinder C4 represent the variable w. At one point in time t9, however, the torque contribution T3 of the third cylinder C3 represents the variable z, and at a su bsequent point in time t 0 the alarm criterion is fulfilled .
According to this embodiment of the invention , the first test variable a represents a difference between the second lowest torque contribution z and the lowest torque contribution w; and the second test variable b represents a difference between the highest torque contribution x and the second lowest torque contribution w.
The processing device 1 10 is advantageously configured even here to test the first and second test variables a and b, respectively, against the alarm criterion by:
forming a first test greatness representing a quota between the first test variable a and the sum of the first test variable a and the second test variable b, that is .
a + b
and
forming a second test greatness representing the sum of the first test variable a and the second test variable b, i .e. a+b.
The processing device 1 1 0 then investigates whether the first test greatness a/(a+b) exceeds a third threshold value, and whether at the same time the second test greatness a+b exceeds a fourth threshold value. Provided that this is the case, the processing device 1 1 0 generates an alarm code A, which indicates a fault in at least one of the cylinders C1 , C2 , C3, C4 , C5 and C6. At the point in time t 0 these conditions are therefore assumed to be fulfilled .
At the point in time t 0 the measuring signal T3 from the third cylinder C3 in the combustion engine 100 represents the lowest torque contribution z. According to a preferred embodiment of the invention , the alarm code A thus indicates a fault in the third cylinder C3. Preferably, the alarm code A also specifies that the third cylinder C3 is receiving insufficient fuel , since its torque contribution T3 is too low.
According to one embodiment of the invention the diagnostic system comprises at least one filtering device 120, which is configured to receive and linear filter the original measuring signals from the combustion engine 100, and in response thereto to generate the resulting signals, which represent the measuring signals T1, T2, T3, T4, T5 and T6. The filtering device 120 is installed to remove extreme measuring values, i.e. values which diverge strongly from other measuring values during the measuring period (so-called outliers), for example by low-pass or band-pass filtering of the incoming signals. Thus the analysis of the processing device 110 may be based on data with higher reliability and relevance.
It is advantageous if the processing device 110 comprises, or is communicatively connected with, a memory device M, which comprises a computer program comprising software to control the processing device 110 so that it operates as described above.
Figure 2 shows a schematic image of a combustion engine 100 and a diagnostic system according to another embodiment of the invention. All references in Figure 2 which tally with references in Figure 1 use the same units, variables and signals as those described above with reference to Figure 1.
The embodiment in Figure 2 differs primarily from that in Figure 1 by the fact that the diagnostic system illustrated in Figure 2 includes a speed sensor s7 configured to generate a speed signal rpm representing the engine speed of the combustion engine 100. The processing device 110 is thus configured to derive a respective torque contribution T1, T2, T3, T4, T5 and T6 from the cylinders C1, C2, C3, C4, C5 and C6 from the engine speed signal rpm. Examples of how this may be effectuated are described in the above mentioned patent documents. As an alternative to the engine speed sensor s7, a torque sensor may be arranged on the crankshaft of the engine 100 between the cylinders and the flywheel , the torque sensor of which is configured to measure the different torque contributions of the cylinders C1 , C2, C3, C4 , C5 and C6.
Preferably, the diagnostic system also comprises a filtering device 220, which is configured to receive and linear filter the original measuring signal from the speed sensor, and in response thereto to generate resulting signals, which represent the measuring signals rpm. The filtering device 220 is also here installed to remove extreme measuring values, i .e. values which diverge strongly from other measuring values during the measuring period (so-called outliers), for example through low- pass or band-pass filtering of the incoming signals. For purposes of summarising , the general method according to the invention will now be described with reference to the flow diagram in Figure 5.
At a first step 51 0 at least one measuring signal T1 , T2, T3, T4, T5 and T6 or rpm is registered , which represents a respective torque contribution from each cylinder C1 , C2, C3, C4 , C5 and C6 in a combustion engine. It is assumed that the engine is equipped with at least tree cylinders.
Subsequently, a first test variable a is formed in a step 520 based on a first pair of measuring values representing a respective torque contribution from two of the said cylinders during a measuring period . For example, the first pair of measuring values may represent a biggest torque contribution x from the cylinder which provides a biggest torque contribution during a measuring period and a second biggest torque contribution y from the cylinder which provides a second biggest torque contribution during the measuring period . Alternatively, the first pair of measuring values may represent a lowest torque contribution z from the cylinder which provides a lowest torque contribution during a measuring period and a second lowest torque contribution w from the cylinder which provides a second lowest torque contribution du ring the measuring period .
In a step 530, which is preferably executed in parallel with step 520, a second test variable b is formed based on a second pair of measuring values representing a respective torque contribution from two of the said cylinders during the measuring period . It is assumed that the first and second pairs of measuring values originate from at least three different cylinders of the said cylinders. For example, the second pair of measuring values may represent the second largest torque contribution y and a lowest torque contribution z from the cylinder which provides a lowest torque contribution during the measuring period . Alternatively, the second pair of measuring values may represent the largest torque contribution x and the second lowest torque contribution w during the measuring period .
A subsequent step 540 investigates whether or not the combustion engine is deemed to function satisfactorily. Specifically, at step 540 the first and second test variables a and b, respectively, are tested against an alarm criterion . If the alarm criterion is met, a step 550 follows, otherwise the procedure loops back to step 510.
At step 550 an alarm code indicating a fault in at least one of the engine's cylinders C1 , C2 , C3, C4 , C5 or C6 is generated , preferably the engine cylinder(s) which is/are associated with the most divergent torque contri bution(s) when the alarm criterion is fulfilled . The procedure then ends. Alternatively, it is conceivable that the procedure after step 550 reverts to step 510 for continued testing . The method steps described with reference to Figure 5 may be controlled with the help of a programmed computer apparatus. In addition , even if the embodiments of the invention described above with reference to the figures comprise a computer and processes executed in a computer, the invention extends to software, in particular software on or in a carrier adapted to implement the invention practically. The program may be in the form of a source code, object code, a code constituting a cross between source and object code, such as in partly compiled form, or in any other form whatsoever which is suitable for use in the implementation of the process according to the invention . The carrier may be any type of entity or device which is capable of carrying the program . For example, the carrier may comprise a storage medium such as a flash memory, a ROM (Read Only Memory), for example a CD (Compact Disc) or a semiconductor ROM , EPROM (Electrically Programmable ROM ), EEPROM (Erasable EPROM), or a magnetic recording medium, for example a floppy disk or a hard disk. I n addition , the carrier may be a transmitting carrier such as an electric or optic signal , which may pass through an electric or optic cable or via radio or in another manner. Since the program is embodied by a signal that may be transmitted directly by a cable or another device or element, the carrier may consist of such a cable, device or element. Alternatively, the carrier may be an integrated circuit into which the program is embedded , where the integrated circuit is adapted to carry out, or to be used in the performance of the relevant processes.
The invention is not limited to the embodiments described with reference to the figures, but may be freely varied within the scope of the following patent claims.

Claims

Patent claims
1 . A diagnostic system for a combustion engine (100) including at least three cylinders (C1 , C2 , C3, C4, C5, C6), the system comprising :
at least one sensor (s1 , s2 , s3, s4, s5, s6; s7) configured to register at least one measuring signal (T1 , T2 , T3, T4 , T5, T6; rpm) representing a respective torque contribution from each cylinder of the said at least three cylinders, and
a processing device (1 1 0) configured to investigate, based on the said at least one measuring signal , whether or not the combustion engine (100) functions satisfactorily, characterised by the fact that the processing device ( 1 10) is configured to: form a first test variable (a) based on a first pair of measuring values representing a respective torque contribution (x, y; w, z) from two of the said at least three cylinders during a measuring period ;
form a second test variable (b) based on a second pair of measuring values representing a respective torque contribution (y, z; x, w) from two of the said at least three cylinders during the measuring period , where the said first and second pairs of measuring values originate from at least three different cylinders of the said at least three cylinders;
test the first test variable (a) and the second test variable (b) against an alarm criterion , and given that the alarm criterion is met
to generate an alarm code (A) indicating a fault in at least one of the said at least three cylinders.
2. Diagnostic system according to claim 1 , where:
the first test variable (a) is formed based on a biggest torque contribution (x) from the cylinder (C3) of the said at least three cylinders which during a measuring period provides a biggest torque contribution , and a second biggest torque contribution (y) from the cylinder of the said at least three cylinders which during the measuring period provides a second biggest torque contribution , and the second test variable (b) is formed based on the second biggest torque contribution (y), and a lowest torque contribution (z) from the cylinder of the said at least three cylinders which during the measuring period provides a lowest torque contribution .
3. Diagnostic system according to claim 2, where:
the first test variable (a) represents a difference between the biggest torque contribution (x) and the second biggest torque contribution (y), and
the second test variable (b) represents a difference between the second biggest torque contribution (y) and the lowest torque contribution (z).
4. Diagnostic system according to claim 3, where the processing device (1 1 0) is configured to test the first and second test variables (a; b) against the alarm criterion by:
forming a first test greatness representing a quota between the first test variable (a) and the sum of the first test variable (a) and the second test variable (b) ,
forming a second test greatness representing the sum of the first test variable (a) and the second test variable (b) ,
investigating whether the first test greatness exceeds a first threshold value, and
investigating whether the second test greatness exceeds a second threshold value,
where the alarm criterion is met if the first test greatness exceeds the first threshold value, and the second test greatness exceeds the second threshold value.
5. Diagnostic system according to any of the previous claims, where the alarm code (A) indicates a fault in the cylinder from the said at least three cylinders (C3) which provides the biggest torque contribution (x) when the alarm criterion is met.
6. Diagnostic system according to claim 1 , where: the first test variable (a) is formed based on a lowest torque contri bution (z) from the cylinder of the said at least three cylinders which during a measuring period provides the lowest torque contribution , and a second lowest torque contribution (w) from the cylinder from the said at least three cylinders which during the measuring period provides a second lowest torque contribution , and
the second test variable (b) is formed based on the second lowest torque contribution (w) and a highest torque contribution (x) from the cylinder from the at least three cylinders which during the measuring period provides a highest torque contribution .
7. Diagnostic system according to claim 6, where:
the first test variable (a) represents a difference between the second lowest torque contri bution (w) and the lowest torque contribution (z), and
the second test variable (b) represents a difference between the highest torque contribution (x) and the second lowest torque contribution (w).
8. Diagnostic system according to claim 7, where the processing device (1 1 0) is configured to test the first and second test variables (a; b) against the alarm criterion by:
forming a first test greatness representing a quota between the first test variable (a) and the sum of the first test variable (a) and the second test variable (b) ,
forming a second test greatness representing the sum of the first test variable (a) and the second test variable (b) ,
investigating whether the first test greatness exceeds a third threshold value, and
investigating whether the second test greatness exceeds a fourth threshold value,
where the alarm criterion is met if the first test greatness exceeds the third threshold value, and the second test greatness exceeds the fourth threshold value.
9. A diagnostic system according to any of claims 6 to 8, where the alarm code (A) indicates a fault in the cylinder from the said at least three cylinders (C3) which provides the lowest torque contribution (z) when the alarm criterion is met.
10. A diagnostic system according to any of the previous claims, where the said at least one sensor (s1 , s2, s3, s4 , s5, s6) includes at least either of an accelerometer and a cylinder pressure sensor.
1 1 . A diagnostic system according to any of claims 1 to 9, where:
the said at least one sensor comprises a speed sensor (s7) configured to generate a speed signal (rpm) representing the speed of the combustion engine (100), and
the processing device (1 1 0) is configured to deduce a respective torque contribution (T1 , T2 , T3, T4 , T5, T6) from each one of the said at least three cylinders from the speed signal (rpm).
12. A diagnostic system according to any of the previous claims, comprising at least one filtering device (120; 220) configured to receive and linear filter at least one original measuring signal from the combustion engine (100), and in response to generate at least one resulting signal representing the said at least one measuring signal (T1 , T2 , T3, T4, T5, T6; rpm).
13. A method to diagnose a combustion engine (1 00) including at least three numbers of cylinders (C1 , C2 , C3, C4 , C5, C6), the method comprising :
registration of at least one measuring signal (T1 , T2 , T3, T4 , T5, T6; rpm) representing a respective torque contribution from each cylinder of the said at least three cylinders, and
investigation , based on the said at least one measuring signal (T1 , T2 , T3, T4 , T5, T6; rpm), as to whether or not the combustion engine functions satisfactorily, characterised by formation of a first test variable (a based on a first pair of measuring values representing a respective torque contribution
(x, y; w, z) from two of the said at least three cylinders during a measuring period ;
formation of a second test variable (b) based on a second pair of measuring values representing a respective torque contribution (y, z; x, w) from two of the said at least three cylinders during the measuring period , where the said first and second pairs of measuring values originate from at least three different cylinders from the said at least three cylinders;
testing of the first test variable (a) and the second test variable (b) against an alarm criterion , and provided that the alarm criterion is met
generation of an alarm code (A) indicating a fault in at least one of the said at least three cylinders.
14. Method according to claim 13, where
the first test variable (a) is formed based on a biggest torque contribution (x) from the cylinder (C3) of the said at least three cylinders which during a measuring period provides a biggest torque contribution , and a second biggest torque contribution (y) from the cylinder of the said at least three cylinders which during the measuring period provides a second biggest torque contribution , and
the second test variable (b) is formed based on the second biggest torque contribution (y) and a lowest torque contribution (z) from the cylinder of the said at least three cylinders which during the measuring period provides a lowest torque contribution .
15. Method according to claim 14, where
the first test variable (a) represents a difference between the biggest torque contri bution (x) and the second biggest torque contribution (y), and
the second test variable (b) represents a difference between the second biggest torque contribution (y) and the lowest torque contribution (z).
16. Method according to claim 15, where the first and second test variables (a; b) are tested against the alarm criterion through :
formation of a first test greatness representing a quota between the first test variable (a) and the sum of the first test variable (a) and the second test variable (b) ,
formation of a second test greatness representing the sum of the first test variable (a) and the second test variable (b) ,
investigation as to whether the first test greatness exceeds a first threshold value, and
investigation as to whether the second test greatness exceeds a second threshold value,
where the alarm criterion is met if the first test greatness exceeds the first threshold value, and the second test greatness exceeds the second threshold value.
1 7. Method according to any of claims 13 to 16, where the alarm code (A) indicates a fault in the cylinder from the said at least three cylinders (C3) which provides the biggest torque contribution (x) when the alarm criterion is met.
18. Method according to claim 13, where
the first test variable (a) is formed based on a lowest torque contri bution (z) from the cylinder of the said at least three cylinders which during a measuring period provides the lowest torque contribution , and a second lowest torque contribution (w) from the cylinder from the said at least three cylinders which during the measuring period provides a second lowest torque contribution , and
the second test variable (b) is formed based on the second lowest torque contribution (w), and a highest torque contri bution (x) from the cylinder from the at least three cylinders which during the measuring period provides a highest torque contribution .
19. Method according to claim 18, where
the first test variable (a) represents a difference between the second lowest torque contri bution (w) and the lowest torque contribution (z), and
the second test variable (b) represents a difference between the highest torque contribution (x) and the second lowest torque contribution (w).
20. Method according to claim 19, where the first and second test variables (a; b) are tested against the alarm criterion through :
formation of a first test greatness representing a quota between the first test variable (a) and the sum of the first test variable (a) and the second test variable (b) ,
formation of a second test greatness representing the sum of the first test variable (a) and the second test variable (b) ,
investigation as to whether the first test greatness exceeds a third threshold value, and
investigation as to whether the second test greatness exceeds a fourth threshold value,
where the alarm criterion is met if the first test greatness exceeds the third threshold value, and the second test greatness exceeds the fourth threshold value.
21 . Method according to any of claims 18 to 20, where the alarm code (A) indicates a fault in the cylinder from said at least three cylinders (C3) which provides the lowest torque contribution (z) when the alarm criterion is met.
22. Method according to any of claims 13 to 21 , comprising linear filtering of at least one original measuring signal from the combustion engine (1 00) where at least one resulting signal is generated which represents the said at least one measuring signal (T1 , T2 , T3, T4, T5, T6; rpm).
23. A computer program which may be downloaded to the internal memory (M ) in a computer, comprising software to control the steps according to any of the claims 13 to 22 when the said program is executed in the computer.
24. A computer readable medium (M ) with a program stored thereon , where the program is adapted to induce a computer to control the steps according to any of the claims 13 to 22.
PCT/SE2013/051221 2012-10-24 2013-10-18 Cylinder diagnosis WO2014065743A1 (en)

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