DE102021212661A1 - Method for monitoring a traction device of an internal combustion engine - Google Patents

Abstract

The invention relates to a method for monitoring a traction device (20) of an internal combustion engine (100) with a crankshaft (1) and a camshaft (3), the traction device (20) connecting the crankshaft (1) and the camshaft (3) in a force-transmitting manner. wherein a reference angular position of the camshaft (3) is determined as a function of a crank angle of the crankshaft (1) over a specified number of revolutions of the camshaft (3), wherein a quality feature is determined from the reference angular positions determined over the specified number of revolutions of the camshaft (3). of the traction means (20) is determined.

Description

The present invention relates to a method for monitoring a traction mechanism of an internal combustion engine, as well as a computing unit and a computer program for carrying it out.

Background of the Invention

In 4-stroke internal combustion engines, the camshaft usually rotates at half the speed of the crankshaft. One revolution of the camshaft (360°NW) therefore corresponds to two revolutions of the crankshaft with a crank angle of 720°KW and thus a complete combustion cycle of the combustion engine. A reference position of the camshaft, for example a specific edge of a camshaft sensor wheel, can therefore be measured as a crank angle from 0 to 720° CA.

Camshaft and crankshaft can be connected in a power-transmitting manner by means of a so-called timing chain.

Disclosure of Invention

According to the invention, a method for monitoring a traction mechanism of an internal combustion engine and a computing unit and a computer program for its implementation with the features of the independent patent claims are proposed. Advantageous configurations are the subject of the dependent claims and the following description.

The internal combustion engine has a crankshaft and a camshaft, with a traction mechanism connecting the crankshaft and the camshaft in a force-transmitting manner. For this purpose, the traction means is in engagement with gear wheels, which are each connected in a rotationally fixed manner to the crankshaft or the camshaft or, if appropriate, to other elements in a traction means drive. For example, the traction means can be designed as a timing chain or as a toothed belt.

It goes without saying that the internal combustion engine can have other camshafts in addition to the camshaft used for monitoring (hereinafter referred to as “the camshaft”) and that the traction mechanism is coupled to multiple camshafts in a force-transmitting manner.

A reference angular position of the camshaft is determined as a function of a crank angle of the crankshaft over a predetermined number of revolutions of this camshaft. A quality feature of the traction means is determined from the reference angle positions determined over the predetermined number of revolutions of the camshaft.

The reference angle position depends in particular on a camshaft position or rotational angle position of the camshaft determined at a specific point in time and also on an associated crank angle determined at this specific point in time, ie the rotational angle position of the crankshaft determined at this point in time. Since the crankshaft and camshaft are coupled in a force-transmitting manner via the traction mechanism, the reference angular position represents a particularly expedient means of reliably deducing the synchronicity between the crankshaft and camshaft.

The predetermined number of revolutions of the camshaft is determined in particular in such a way that reference angle positions can expediently be detected at least during one complete revolution of the traction mechanism. The reference angle position can be determined particularly expediently via the predetermined number of camshaft revolutions in relation to different sections of the traction mechanism. In this way, individual traction element sections and individual traction element elements of the traction element can be monitored particularly effectively.

The quality feature determined from this large number of reference angle positions characterizes in particular a state or wear of the traction mechanism and in particular the ability of the traction mechanism to transmit force. The quality feature can be used in particular to assess whether the traction means is at least essentially fault-free or faulty or subject to wear. In particular, the quality feature allows conclusions to be drawn as to whether the traction means is being stretched or lengthened, in particular if individual links of the traction means or even an individual traction element are lengthened. With conventional methods for monitoring the traction device, it is often only possible to detect an elongation of the entire traction device. The invention advantageously makes it possible to also be able to detect an elongation of individual traction elements at an early stage. In particular, if individual traction element elements lengthen, the traction element can suddenly tear, which can lead to a defect or engine damage.

In order to determine the reference angle position of the camshaft as a function of the crank angle, sensor wheels are particularly expediently provided, in particular a crankshaft sensor wheel connected non-rotatably to the crankshaft for determining the current crank angle or the current rotational angle position of the crankshaft, and also expediently a non-rotatable ver Connected camshaft sensor wheel for determining the current angle of rotation of the camshaft. These encoder wheels can each have a large number of markings on their circumference, for example in the form of teeth and gaps. By scanning the respective rotating encoder wheel using a suitable sensor, eg a Hall sensor, an electrical measurement signal can be generated in the form of a voltage pulse signal in which the scanned markings are reflected, for example as rising and falling edges.

Advantageously, the reference angular position per revolution of the camshaft is determined depending on a specific or measured, detected or current actual angular position of a characteristic feature of a camshaft sensor wheel of the camshaft and on a target angular position of this characteristic feature.

In particular, the characteristic feature can be a special marking or edge of the camshaft encoder wheel, for example the rising or falling edge of a specific tooth or a specific gap. This characteristic feature is particularly expediently reflected in a corresponding electrical measurement signal or voltage pulse signal by scanning the sensor wheel, in particular as a rising or falling edge. The reference angular position is expediently determined once per revolution of the camshaft, or a current value for the respective reference angular position is determined per camshaft revolution.

The actual angular position and the setpoint angular position are expediently determined in each case as a function of or with reference to the crank angle (°CA) of the crankshaft. The camshaft revolution and the crankshaft revolution are in a predetermined relationship to one another, one revolution of the camshaft being able to correspond, for example, to two revolutions of the crankshaft. In this case, the camshaft circumference can be rolled out to 0° crankshaft to 720° crankshaft. Each characteristic feature, in particular each camshaft sensor wheel flank, therefore has a specific expected crank angle, that is to say a corresponding setpoint angular position.

By comparing these actual and target angular positions, it can be concluded in particular whether the crankshaft and camshaft rotate synchronously with one another, as expected. If this is not the case and if the actual and desired angular positions deviate from one another, this can indicate that individual traction element elements are lengthening.

Variations in the actual angular position in both directions are initially normal to a certain extent, because there are different traction element elements in the tight strand with each revolution of the camshaft. Depending on the number of traction elements, it therefore takes a certain number of camshaft revolutions until the respective sensor wheel flank is back at the original traction element point. With each revolution of the camshaft, therefore, different sections of the traction element are measured or monitored. The specified number of camshaft revolutions is therefore expediently selected in such a way that all sections of the traction mechanism can be measured and monitored once.

The reference angular position per revolution of the camshaft is advantageously determined in each case as a deviation between the determined actual angular position of the characteristic feature and the setpoint angular position. In particular, with each of these specific deviations over the predetermined number of camshaft revolutions, there is in each case a different traction means section and thus different traction means elements in the tight strand. In particular, based on these deviations, the length of the respective traction means section located in the tight strand can be evaluated.

The detected actual angular position of the camshaft sensor wheel in relation to the crank angle or the sensor wheel of the crankshaft enable a reliable diagnosis over the entire length of the traction mechanism. Deviations of the actual angular positions of the camshaft flanks from the expected target positions can be used particularly expediently to assess the quality of the traction mechanism.

The quality feature is preferably determined as a function of a maximum or a maximum positive reference angle position and a minimum or a maximum negative reference angle position of the reference angle position determined over the specified number of revolutions of the camshaft, preferably as a function of a difference between the maximum and the minimum reference angle position. In particular, differences in the reference angle positions indicate an elongation of individual traction elements. Maximum or minimum reference angle positions can indicate an elongation of that traction element section which is located in the tight strand during the determination of these specific reference angle positions.

The quality feature is particularly preferably dependent on a maximum positive deviation and a maximum negative deviation Calculation of the deviations between the actual angular position and the target angular position determined over the predetermined number of revolutions of the camshaft, particularly advantageously as a function of a difference between the maximum positive deviation and the maximum negative deviation. As explained above, slight variations in the reference angular position are normal due to tolerances. However, high deviations between the actual and desired angular position of the characteristic sensor wheel flank can indicate an elongation of the traction elements. The difference between the maximum positive and maximum negative deviation therefore represents a particularly expedient evaluation variable in order to be able to draw conclusions about an elongation of individual traction elements.

Alternatively or additionally, the quality feature can advantageously be determined as a function of a statistical value of the reference angle positions determined over the specified number of revolutions of the camshaft, preferably as a function of a variance in the reference angle positions. In particular, the differences in the individually determined reference angle positions, which can indicate the elongation of individual traction elements, can thus be effectively examined.

In a particularly advantageous manner, the quality feature is determined as a function of a statistical value of the deviations between the actual and the target angular position determined over the predetermined number of revolutions of the camshaft, preferably as a function of a variance of the determined deviations. Such a variance represents a particularly effective evaluation variable in order to recognize differences in the individual actual and target value deviations and to draw conclusions about an elongation of individual traction elements.

The specific quality feature is preferably compared with one or more threshold values. In particular, these individual threshold values can be selected in such a way that they represent elongations of different amounts of traction elements. For example, a first threshold value can be selected in such a way that an elongation of a traction element is probable and a more detailed examination of the traction element makes sense or the traction element should be replaced soon. A second threshold value can be specified, for example, in such a way that a traction element is greatly elongated and the traction element should be replaced immediately.

When the threshold value or threshold values are reached, a predetermined action is preferably carried out in each case. For example, when the first threshold value is reached, an error entry or an entry in an error memory of a control device can be created, so that the traction mechanism can be exchanged the next time you visit the workshop. When the second threshold value is reached, for example, a warning can be issued to a driver of the respective vehicle, for example by activating an engine control light (“Malfunction Indicator Light”, MIL). Furthermore, if necessary, emergency operation of the internal combustion engine can be initiated, for example.

Advantageously, the predetermined number of revolutions of the camshaft is predetermined as a function of a number of traction elements of the traction mechanism and of a ratio of a traction mechanism circulation to the revolutions of the camshaft that have taken place during this time. In particular, the number is specified such that each traction element can be examined, particularly expediently such that over the specified number of camshaft revolutions each traction element is at least once in the tight strand for determining the respective reference angular position. The camshaft drive wheel usually has fewer teeth than the traction mechanism has links, so that more than one camshaft revolution takes place during one rotation of the traction mechanism. In order to be able to examine all the traction elements, a large number of camshaft revolutions and traction element circulations are therefore expediently required, depending on the number of camshaft drive wheel teeth and the number of traction element elements.

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

The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is advantageous because this causes particularly low costs, especially if an executing control unit is also used for other tasks and is therefore available anyway. Finally, a machine-readable storage medium is provided with a computer program stored thereon as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical and electrical storage devices such as hard drives, flash memories, EEPROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.). Such a download can be wired or wired or wireless (e.g. via a WLAN network, a 3G, 4G, 5G or 6G connection, etc.).

Further advantages and refinements of the invention result from the description and the attached drawing.

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

character list

• 1 shows schematically an internal combustion engine, which can form the basis of a preferred embodiment of a method according to the invention.
• 2 shows schematically a preferred embodiment of a method according to the invention as a block diagram.
• 3 shows schematically a diagram of reference angle positions plotted against traction element sections, which can be determined in the course of a preferred embodiment of a method according to the invention.
• 4 shows schematically a camshaft sensor wheel signal that can be determined in the course of a preferred embodiment of a method according to the invention.

embodiment(s) of the invention

In 1 a section of an internal combustion engine is shown schematically and is denoted by 100 .

A crankshaft 1 of internal combustion engine 100 is non-rotatably connected to a first drive wheel 2a. A camshaft 3 is connected in a torque-proof manner to a second drive wheel 2b, it being possible for a phase adjustment device 11 to be provided between the drive wheel 2b and the camshaft 3 . The crankshaft 1 and the camshaft 3 are connected to one another in a force-transmitting manner via a timing chain 20 as a traction mechanism. For this purpose, individual chain links 21 (traction elements) of the timing chain 20 engage in a form-fitting manner in the drive wheels 2a and 2b.

It goes without saying that internal combustion engine 100 can have additional camshafts and that additional elements can also be provided in the chain drive and connected to timing chain 20 .

The internal combustion engine 100 also has cylinders 5, in each of which a movable piston 6 is arranged, which is fastened to the crankshaft 1 by means of a connecting rod 7 in each case. The cylinders 5 also have intake valves 8a and exhaust valves 8b which are opened or closed by cams 4 with cam flanks which are configured eccentrically with respect to the camshaft 3 . The intake and exhaust valves 8a and 8b are each urged toward a valve seat 10 by a valve spring 9 .

The camshaft 3 is connected in a torque-proof manner to a camshaft encoder wheel 14, the circumference or edge of which has markings 14a, for example in the form of teeth and gaps. A sensor 15, for example a Hall sensor, is arranged in the vicinity of the edge of the camshaft sensor wheel 14 and is connected to a control unit 30, in particular to an engine control unit. Analogously, the crankshaft 1 is non-rotatably connected to a crankshaft sensor wheel 12, the edge of which also has markings 12a, for example also teeth and gaps. A pick-up 13 is arranged near the edge of the crankshaft target wheel 12 and is connected to the control unit 30 .

During operation of internal combustion engine 100, crankshaft 1 and camshaft 3, and thus also crankshaft sensor wheel 12 and camshaft sensor wheel 14, rotate generate a voltage pulse signal. Analogously, pickup 15 scans camshaft encoder wheel 14, markings 14a generating a corresponding second measurement signal or camshaft encoder wheel signal. The measurement signals are evaluated by the control unit 30 (see also 4 ).

Over the course of its service life, the entire timing chain 20 or just individual chain links 21 can become longer. Such an elongation of individual links can often occur, for example, in vehicles with a high mileage and frequent use in city traffic, e.g. in taxis, buses, etc. An elongation of individual chain links of more than 1 mm, for example, increases the risk that the chain 20 will tear and that it will engine damage of internal combustion engine 100 occurs.

In order to be able to detect an elongation of individual chain links 21 at an early stage, control unit 30 is set up, in particular in terms of programming, to carry out a preferred embodiment of a method according to the invention, which 2 is shown schematically as a block diagram and below with reference to FIG 2 until 4 is explained.

In a step 201, a number of camshaft revolutions is specified, over wel che reference angle positions for chain monitoring can be determined.

This number is specified as a function of a number of chain links 21 of timing chain 20 and a number of teeth of drive wheel 2b of camshaft 3, for example as a ratio of the least common multiple to the number of teeth of drive wheel 2b.

For example, the timing chain 20 can have 102 chain links and the drive wheel 2b can have 48 teeth, i.e. the ratio of timing chain rotation to camshaft rotation is 2.125. In this case, for example, the chain 20 can be diagnosed in 17 sections, each with six chain links.

The camshaft rotates 17 times in eight timing chain revolutions (8*2.125 = 17). In these 17 camshaft revolutions, a reference angular position of the camshaft or camshaft sensor wheel can be determined in 17 different areas or sections of the chain, each with six chain links.

Thus, in step 201, for example, a number of 17 camshaft revolutions is specified.

In step 202, the internal combustion engine 100 is operated regularly and the counting of the number of 17 camshaft revolutions is started. With the rotation of the crankshaft and camshaft 1, 3, the crankshaft and camshaft encoder wheel 12, 14 are scanned and corresponding measurement signals are recorded.

In step 203, a characteristic feature of the camshaft target wheel 14 is identified in the camshaft target wheel signal, for example in the form of a falling edge of a specific tooth of the camshaft target wheel 14.

In step 204 the actual angular position of this characteristic feature is determined as a function of the crank angle, that is to say of the current angular position of the crankshaft 1 .

In step 205, a reference angular position of the current camshaft revolution is determined as a function of the actual angular position of the characteristic feature determined in step 204 and of its associated setpoint angular position, e.g. 153° CA. For example, this reference angular position per revolution of the camshaft 3 is determined in each case as a deviation between the determined actual angular position of the characteristic feature and the target angular position.

In step 206 it is checked whether the specified number of 17 camshaft revolutions has been carried out. If this is the case, there are a total of 17 values for the reference angular position.

In step 207, a quality feature is then determined from these 17 values for the reference angle position. The quality feature is particularly preferably determined as the difference between a maximum and a minimum reference angular position, in particular as a difference between the maximum positive and the maximum negative deviation of the deviations between the actual angular position and the target angular position determined via the number of camshaft revolutions.

A clear deviation from the actual and target angular positions indicates in particular the elongation of individual chain links. The difference between the maximum positive and the maximum negative deviation between the actual and target angular position therefore represents a particularly effective quality feature for assessing the elongation of individual chain links.

In step 208 it is checked whether the quality feature determined in step 207 reaches one of several threshold values. If this is not the case, it is determined in step 209 that the timing chain 20 is free of defects and there is no elongation of individual chain links.

If, on the other hand, the quality feature reaches a first threshold value in step 210, this indicates that individual chain links are elongating. In this case, a fault entry is created in control unit 30 and control chain 20 should be replaced when the opportunity arises. If, on the other hand, the quality feature reaches a second threshold value, this indicates that a chain link is elongating and a check engine light is activated, and the timing chain 20 should be replaced immediately. When the second threshold value is reached, internal combustion engine 100 can also be switched to emergency operation in order to protect the chain.

3 shows a schematic diagram 300 of the reference angular positions determined via the number of camshaft revolutions, ie the respective deviations Δ of the actual angular positions from the target angular position of, for example, 153° CA plotted against the chain sections d of the timing chain, each with six chain links.

For example, curve 310 was determined at an idle speed of 750 rpm, curve 320, for example, at a speed of 2,000 rpm.

Furthermore, both curves 310, 320 were determined, for example, using a timing chain which has a worn link with an elongation of 0.988 mm and another worn link with an elongation of 0.380 mm.

As can be seen in diagram 300, a maximum reference angular position or a maximum positive deviation from the actual and target angular position is approximately the value "+2" and a minimum reference angular position or a maximum negative deviation is approximately the value "-3". In this case, a value of "+5" can be determined as a quality feature.

4 shows a camshaft sensor wheel signal 410, which is determined over a large number of camshaft revolutions U _N , with each line corresponding to a chain revolution U _K .

Points 411, 412 characterize the falling edges of camshaft sensor wheel signal 410, points 411 characterizing those falling edges whose actual angular position is used to determine the reference angular position.

Furthermore, in 4 the timing chain 420 with chain links 1 to 102 is shown. As in 4 As can be seen, each of the 17 chain sections, each with six chain links, is located once in the tight strand when the reference angular position is determined.

Claims (14)

Method for monitoring a traction device (20) of an internal combustion engine (100) with a crankshaft (1) and a camshaft (3), the traction device (20) connecting the crankshaft (1) and the camshaft (3) in a force-transmitting manner, wherein a reference angular position of the camshaft (3) is determined as a function of a crank angle of the crankshaft (1) over a predetermined number of revolutions of the camshaft (3) (202, 203, 204, 205), a quality feature of the traction means (20) being determined (207) from the reference angle positions determined over the predetermined number of revolutions of the camshaft (3). procedure after claim 1 , wherein the reference angular position per revolution of the camshaft (3) is determined (202, 203, 204, 205). procedure after claim 2 , wherein the reference angular position per revolution of the camshaft (3) is determined in each case as a deviation between the determined actual angular position of the characteristic feature and the target angular position (202, 203, 204, 205). Method according to one of the preceding claims, wherein the quality feature is determined (207) as a function of a maximum reference angle position and a minimum reference angle position of the reference angle positions determined over the predetermined number of revolutions of the camshaft (3), in particular as a function of a difference between the maximum and the minimum reference angle position. procedure after claim 3 and 4 , the quality feature being determined (207) as a function of a maximum positive deviation and a maximum negative deviation of the deviations determined over the specified number of revolutions of the camshaft (3), in particular as a function of a difference between the maximum positive deviation and the maximum negative deviation . Method according to one of the preceding claims, in which the quality feature is determined as a function of a statistical value of the reference angle positions determined over the predetermined number of revolutions of the camshaft (3), in particular as a function of a variance in the reference angle positions. procedure after claim 6 if related to claim 3 , the quality feature being determined as a function of a statistical value of the deviations determined over the predetermined number of revolutions of the camshaft (3), in particular as a function of a variance of the determined deviations. Method according to one of the preceding claims, wherein the determined quality characteristic is compared with one or more threshold values (208). procedure after claim 8 , wherein a predetermined action is carried out (210) when the one or more threshold values are reached. The method according to any one of the preceding claims, wherein the predetermined number of revolutions of the camshaft (3) depending on a number of traction elements (21) of Zugmit by means (20) and by a ratio of a traction mechanism circulation to the revolutions of the camshaft (3) that have taken place during this (201). Method according to one of the preceding claims, wherein the specific quality feature characterizes an elongation of the traction means (20), in particular an elongation of individual traction means elements (21) of the traction means (20). Arithmetic unit (30) which is set up to carry out all method steps of a method according to one of the preceding claims. Computer program that causes a computing unit (30) to all method steps of a method according to one of Claims 1 until 11 to be carried out when it is executed on the computing unit (30). Machine-readable storage medium with a computer program stored on it Claim 13 .

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