Method for shutting down an internal combustion engine

Abstract

Method for switching off an internal combustion engine (20) in a vehicle which has an internal combustion engine (20) with a crankshaft (25) and an electric machine (30) which is connected to the crankshaft (25) via an operative connection (26), wherein a first torque (M1) is exerted on the crankshaft (25) by the electric machine (30) when the rotational speed of the crankshaft (25) is in a first rotational speed range (T2) which is below an idle speed of the internal combustion engine (20), wherein the first torque (M1) is specified as a function of an upper speed limit (n1) of the first speed range (T2), a lower speed limit (n2) of the first speed range (T2), a first crankshaft angle position (φ1) at the upper speed limit (n1) and a desired second crankshaft angle position (φ2) at the lower speed limit (n1), such that the lower speed limit (n2) is reached by the crankshaft (25) in the desired second crankshaft angle position (φ2), wherein in a second speed range (T3), which is located below the first speed range (T2), a second torque (M2) is exerted on the crankshaft (25) by the electric machine (30), wherein the second torque (M2) is specified as a function of a lower speed limit (n3) of the second speed range (T3) and a desired third crankshaft angle position (φ3) at the lower speed limit (n3) of the second speed range (T3), so that the lower speed limit (n3) of the second speed range (T3) is reached by the crankshaft (25) in the desired third crankshaft angle position (φ3).

Description

[0001] The present invention relates to a method for switching off an internal combustion engine using an electric machine in a vehicle. State of the art

[0002] When a vehicle's internal combustion engine is switched off, unwanted fluctuations in engine speed can occur. These fluctuations are transmitted to the vehicle's body, which is perceived as unpleasant by the occupants. Such fluctuations are particularly common, for example, in start-stop systems, where the vehicle's engine is automatically switched off when the vehicle is stationary.

[0003] A particularly unpleasant aspect is the backswing of the internal combustion engine, i.e., a brief rotation against the direction of travel at the end of the shutdown process.

[0004] Although dual-mass flywheels can be used in vehicles for vibration damping, due to their design they only develop special damping effects at and above idle speed, but not below.

[0005] In vehicles, electric machines are used, for example, as starters for internal combustion engines or as generators to produce electricity. In modern vehicles, electric machines are also used as a combination of starter and generator, known as starter-generators. Starter-generators are electric machines that can operate in a vehicle as either an electric motor or a generator, depending on the vehicle's needs. As a generator, a starter-generator must be able to perform all the tasks traditionally performed by an alternator, namely supplying the vehicle's electrical system and charging the vehicle battery. As an electric motor, a starter-generator must quickly bring the crankshaft of the internal combustion engine up to the required starting speed.

[0006] From DE 101 23 037 A1, for example, a device and a method for the controlled shutdown of an internal combustion engine are known. Here, the speed profile of the internal combustion engine is adapted to a predetermined speed profile by applying a torque to a crankshaft from an electric motor, thereby increasing or decreasing the speed of the internal combustion engine depending on the situation.

[0007] However, this method requires rapid adjustments to the applied torque in order to adapt the rotational speed in real time. Such rapid adjustments are difficult to implement due to the necessary communication within the vehicle.

[0008] Another possibility is to precisely set a rotational speed for the electric machine, but this is complicated to implement in real time.

[0009] DE 199 36 885 C2 describes a method for shutting down an internal combustion engine, wherein a crankshaft of the internal combustion engine is mechanically connected to at least one electric machine. After an interruption of the fuel supply, the crankshaft of the internal combustion engine is braked by the electric machine through a braking torque. The braking torque is controlled or regulated in such a way that the crankshaft comes to a standstill in a stable rest position.

[0010] DE 10 2005 062 500 A1 relates to a control unit for a motor vehicle internal combustion engine with a calculation / evaluation unit for determining the expected stop position of the piston in the respective cylinder, which it would assume when the rotating crankshaft comes to a stop after the motor vehicle internal combustion engine is switched off, without any corrective action. The control unit is coupled to an electric actuator by applying a corrective torque to the crankshaft in such a way that the piston of the respective cylinder can be actively moved into a corrected stop position close to its top dead center or close to its bottom dead center if the calculation / evaluation unit has determined that the piston in the respective cylinder would come to a stop position in a stop range close to its top dead center during its last compression stroke before the motor vehicle internal combustion engine comes to a standstill.

[0011] DE 10 2010 032 087 A1 describes a method and a device for stopping an internal combustion engine of a motor vehicle, which has an electric machine and an internal combustion engine braking device. The electric machine is coupled or can be coupled to a crankshaft of the internal combustion engine, and the method comprises a step in which a stop signal for stopping the internal combustion engine is detected, and a step in which the electric machine acts as a brake on the movement of the internal combustion engine by exerting a braking torque on the crankshaft of the internal combustion engine, and in which the internal combustion engine braking device additionally acts as a brake on the movement of the internal combustion engine.

[0012] It is therefore desirable to provide a way to prevent or at least reduce vibrations, especially those caused by rebounding, that are noticeable to vehicle occupants when an internal combustion engine is switched off. Disclosure of the invention

[0013] According to the invention, a method with the features of claim 1 is proposed. Advantageous embodiments are the subject of the dependent claims and the following description. Advantages of the invention

[0014] In an inventive method for shutting down an internal combustion engine in a vehicle, a first torque is exerted on the crankshaft by the electric motor during coasting, so that a specific rotational speed is reached by the crankshaft at a desired crankshaft angle position. The crankshaft angle position is advantageously selected to prevent any oscillation back to its original position. This increases comfort for the vehicle occupants.

[0015] The torque of the electric machine is advantageously set such that the change in the total torque per unit of time (i.e., the total torque gradient), which comprises at least the initial torque and the torque of the internal combustion engine, is minimized. A suitable unit of time can be in the single-digit or small double-digit millisecond range, e.g., 10 ms. In practice, the torque of the electric machine can be set such that the total torque gradient lies within a specific interval. This interval can be defined by an upper and a lower limit and / or by an interval around a target value. To minimize the total torque gradient, the upper and lower limits are advantageously close to zero, and the target value is advantageously zero.The width of the interval is expediently chosen to be as small as possible, but as large as necessary, in order to allow for a practical implementation.

[0016] In a preferred embodiment, the crankshaft angles at which torque output begins and ends (hereinafter referred to as the first and second crankshaft angle positions) are also selected such that the torque of the electric machine minimizes the overall torque gradient. This also reduces vibrations.

[0017] A reaction torque transmitted to the vehicle body via the engine mounts is equal to the product of the crankshaft's moment of inertia and angular acceleration. To prevent vibration and noise from being transmitted to the vehicle body, it would be sufficient to minimize the reaction torque, i.e., to minimize the crankshaft's angular acceleration. However, this conflicts with the desire to bring the internal combustion engine to a rapid standstill from idle speed. Therefore, instead of minimizing the reaction torque or angular acceleration itself, the temporal variation of the reaction torque or angular acceleration is minimized.

[0018] The magnitude of the electric machine's torque can be determined, for example, from an energy balance between the beginning and end of the speed range, as will be explained later in the figure description. This involves using the upper speed limit of the speed range, the lower speed limit of the speed range, the crankshaft angle position at the upper speed limit, and the crankshaft angle position at the lower speed limit.

[0019] If the vehicle has a dual-mass flywheel, the initial torque is advantageously set so that a speed range around the dual-mass flywheel's resonance speed is traversed as quickly as possible. This prevents or at least reduces noticeable vibrations when the internal combustion engine is switched off. The speed range is characterized by the fact that it contains a resonance speed, which results in an excitation frequency equal to the natural frequency of the dual-mass flywheel. This reduces vibrations transmitted to the vehicle through resonance of the dual-mass flywheel. The speed range is selected around the resonance frequency. An upper speed limit is advantageously set between the idle speed and the resonance speed plus 200 rpm. -1 A lower speed limit is expediently set between the resonance speed minus 200 rpm. -1and a speed from which the internal combustion engine can be stopped in at most half a crankshaft revolution.

[0020] In internal combustion engines, such as reciprocating piston engines, a flywheel is used to compensate for rotational irregularities, since torque is not transmitted to the crankshaft with every stroke. In modern vehicles, this flywheel is divided into two parts: a primary mass on the engine side and a secondary mass on the transmission side, forming a torsional vibration damper. This further reduces vibrations above idle speed. However, there is a speed range below idle speed where such a dual-mass flywheel can still generate or even amplify vibrations.

[0021] It is further advantageous if, during the shutdown of the internal combustion engine, different torques are exerted by the electric motor at different speed ranges. This can prevent or at least reduce noticeable vibrations when the internal combustion engine is switched off.

[0022] In a second speed range, which follows the first, a second torque from the electric motor can be selected so that the internal combustion engine comes to a standstill within a single power stroke (i.e., within half a crankshaft revolution). At standstill, a predetermined crankshaft angle should be reached so that the internal combustion engine remains stationary without any further torque being applied by the electric motor. This prevents the internal combustion engine from oscillating and thus avoids vibrations transmitted to the vehicle. This angle is defined by the number of cylinders and the gas forces in the cylinders.

[0023] Advantageously, a third speed range follows if the internal combustion engine cannot be brought to a standstill at the end of the second speed range, for example, if the electric motor is incapable of doing so due to its power output. In this case, the torque of the electric motor is set to zero, and the crankshaft angle reaches a specific position within a short time.

[0024] A computing unit according to the invention, e.g. a control unit of a motor vehicle, is, in particular in terms of programming, equipped to carry out a method according to the invention.

[0025] Implementing the process in software form is also advantageous, as this incurs particularly low costs, especially if the executing control unit is already used for other tasks and is therefore already present. Suitable data carriers for providing the computer program include floppy disks, hard drives, flash memory, EEPROMs, CD-ROMs, DVDs, etc. Downloading the program via computer networks (Internet, intranet, etc.) is also possible.

[0026] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0027] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0028] The invention is schematically illustrated in the drawing using an exemplary embodiment and is described in detail below with reference to the drawing. Brief description of the drawings Fig. Figure 1 schematically shows a part of a vehicle comprising an internal combustion engine, an electric machine, a functional connection and a computing unit in a preferred embodiment. Fig. Figure 2 schematically shows crankshaft angle, speed and torques during the coasting of an internal combustion engine, divided into different speed ranges. Fig. Figure 3 schematically shows a torque of the electric machine and two different total torques during the coasting of an internal combustion engine according to an advantageous embodiment of a method according to the invention. embodiment(s) of the invention

[0029] In Fig. Figure 1 schematically depicts part 10 of a vehicle. This part comprises an internal combustion engine 20 and an electric motor 30. The internal combustion engine 20 and the electric motor 30 are connected to each other via a operative connection designed as a crankshaft 25 in conjunction with a belt drive 26. A dual-mass flywheel 40, connected to the crankshaft 25 of the internal combustion engine 20, is also shown. Furthermore, a control unit 80, which enables the control of the electric motor 30 for specifying torque values, is shown.

[0030] In Fig. Figure 2 schematically depicts the coasting down of the internal combustion engine 20. The temporal progression is indicated to the right. The upper diagram shows the progression of the angle φ of the crankshaft 25 and the rotational speed n of the internal combustion engine 20. The middle diagram shows the progression of the torque M. 30of the electric machine 30. The lower diagram shows the curves of a torque M 20 of the internal combustion engine 20, of a dual-mass flywheel torque M 40 of the dual-mass flywheel 40 and a total torque M 25 , which acts on the crankshaft 25. The torque M 20 In addition to the torque exerted on the crankshaft 25 by the internal combustion engine 20, a frictional torque is also included. The diagrams are divided into speed ranges T1, T2, T3, and T4. Although these are shown on the time axis, they are defined by rotational speeds.

[0031] The relationship between the torques is such that the total torque M 25 from the other torques, the following results: M25=M20+M30+M40.

[0032] An upper speed range T1 represents the beginning of a coast-down phase for the internal combustion engine 20 and begins, for example, with a stop request for the internal combustion engine 20, i.e., after the engine speed falls below idle. This can be initiated, for example, by shutting off the fuel supply or closing a throttle valve. Before the upper speed range T1, the internal combustion engine 20 is still idling. During the upper speed range T1, no torque from the electric motor 30 acts on the engine; essentially, only the torque M is present. 20The internal combustion engine 20, which includes a frictional torque generated by the friction of the internal combustion engine 20, slows down the engine, as can be seen in the speed profile n during the upper speed range T1. Alternatively, a torque from the electric machine 30 (which is smaller than the first torque) is also applied in the upper speed range. This allows the shutdown of the internal combustion engine to be accelerated.

[0033] The first speed range T2 begins at a first speed n1, i.e., n1 is an upper speed limit of T2. The first speed range T2 is selected such that it includes a resonant frequency at which the dual-mass flywheel 40 is excited to resonant vibrations. The upper speed limit n1 is, for example, 600 rpm. -1(revolutions per minute) and is determined based on the design specifications. It is expediently located in a range between the idle speed and the resonance speed plus 200 rpm. -1 . As soon as a first crankshaft angle position φ1 is reached by the crankshaft 25 after the upper speed limit n1 has been undercut, a first torque M1 is exerted on the crankshaft by the electric machine.

[0034] The first crankshaft angle position φ1 is chosen such that the position of the crankshaft 25 lies in a range around top dead center, e.g., between 10° before top dead center and 10° after top dead center. In this range, a braking torque M 30 of the electric machine 30 a reduction in the change of the total torque M 25 .

[0035] The first torque M1 of the electric machine is selected such that a lower speed limit n2 of the first speed range T2 is reached by the crankshaft at a desired second crankshaft angle position φ2. The lower speed limit n2 of the first speed range T2 is expediently located between the resonance speed minus 200 min⁻¹. -1 and a speed from which the internal combustion engine can be stopped in at most half a crankshaft revolution. For example, it is 200 rpm. -1 The second crankshaft angle position φ2 is chosen such that the position of the crankshaft 25 lies within a specific range, e.g., between 20° after top dead center and 40° after top dead center if M2 < M1 (preferred case), or between 10° before top dead center and 10° after top dead center if M2 > M1

[0036] The initial torque M1 for the first speed range T2 is calculated by establishing an energy balance. The difference in energy E kin + E pot The energy E of the internal combustion engine 20 at the first crankshaft angle position φ1 and at the second crankshaft angle position φ2 corresponds exactly to the energy E R + E el , which is consumed by friction of the internal combustion engine 20 and by the braking effect of the electric machine 30 when passing through the first speed range T2: [Ekin(φ2)+Epot(φ2)]−[Ekin(φ1)+Epot(φ1)]=ER+Eel.

[0037] The energy of the internal combustion engine 20 consists of a kinetic energy E kin , i.e. the rotational energy of the rotating parts of the internal combustion engine 20 including the dual-mass flywheel 40, and a potential energy E pot of gas forces together.

[0038] The kinetic energy E kinresults from the product of half a moment of inertia J of the internal combustion engine 20 and the dual-mass flywheel 40 with the square of the angular velocity ω of the crankshaft 25: Ekin=12 J ω2

[0039] The moment of inertia J can be calculated theoretically using geometric measurements. The angular velocity ω can be measured using suitable means, such as a sensor.

[0040] The potential energy E pot is dependent on the position of the crankshaft 25, i.e., the angle φ. The potential energy E can be determined, for example, using a characteristic curve or a characteristic map. pot for the corresponding crankshaft angle positions φ j determine.

[0041] The energy E consumed by friction R results from the product of the frictional torque M R and the difference between the crankshaft angle positions φ1 and φ2: ER=MR(φ2−φ1).

[0042] The energy E consumed by the braking effect of the electric machine el results from the product of the first torque M1 and the difference between the crankshaft angle positions φ1 and φ2: Eel=M1(φ2−φ1)

[0043] The frictional torque M R This is determined, for example, by calculating an energy balance in the speed range T1 without electric torque, or, for example, by measuring on an engine test bench.

[0044] The first torque M1 can therefore be calculated from the other quantities.

[0045] The first torque M1 can, for example, be adjusted or recalculated during the speed range T2, either continuously or at specific time intervals of, for example, 10 ms. This allows for better compensation of inaccuracies and errors resulting from tolerances, etc. Changes to the total torque M 25During the T2 speed range, emissions can be reduced more effectively.

[0046] If the position of the crankshaft 25 is in a range around top dead center, e.g. between 10° before top dead center and 10° after top dead center, a reduction in torque M causes 30 of the electric machine 30 a reduction in the amplitude of the total torque M 25 . (Sign M > 0 if motor).

[0047] If the position of the crankshaft 25 is, for example, in a range after top dead center, e.g., between 20° and 160° after top dead center, an increase in the torque M causes 30 of the electric machine 30 a reduction in the amplitude of the total torque M 25 , i.e., a change in the total torque M 25 This reduces vibrations and thus also the noticeable vibrations in the vehicle.

[0048] It is important to ensure that the end of the first speed range T2 is reached at the desired angle φ2.

[0049] In Fig. Figure 3 shows exemplary torque curves during the execution of the method according to the invention. The time course is indicated to the right. The upper diagram shows a torque curve M. 30 of the electric machine 30. The lower diagram shows curves of a total torque M 25 and a total torque M 25 ', which act on the crankshaft 25. The total torque M includes 25 ' the torque M 30 , the total torque M 25 The torque M includes 30 No. It can be seen that with a cleverly chosen angle φ of the crankshaft 25, e.g. between 10° before and 10° after top dead center, a braking torque M 30The amplitude of the total torque is reduced. This is illustrated by the two vertical double arrows.

[0050] In the further course, the torque M can 30 further adjustments will be made to achieve a further adjustment of the overall torque.

[0051] The second speed range T3 begins at the second speed n2 and the second angle φ2, i.e. following the first speed range T2.

[0052] During the speed range T3, a second torque M2 is selected such that a third speed n3 and a third angle φ3 are reached at the end of the speed range T3.

[0053] The second torque M2 is calculated at the start of the speed range T3 by setting up an energy balance as for the speed range T2, but with the corresponding values ​​for speed and angle of the speed range T3: second speed n2, third speed n3, second angle φ2 and third angle φ3.

[0054] The second torque M2 can also be adjusted during the speed range T3, e.g., continuously or at specific time intervals of, for example, 10 ms. A gradient of the total torque M 25 During the speed range T3, this allows for better reduction. However, it is important to ensure that the end of the second speed range T3 is reached at the desired angle φ3. This is in Fig. The second torque M2 shown in the diagram changes over time within the speed range T3.

[0055] In a preferred embodiment, the rotational speed n3 should be zero, i.e., the internal combustion engine should be at rest at the end of the rotational speed range T3, and the angle φ3 should be, for example, 90° after top dead center (not in Fig. (2 shown). This angle φ3 should be reached within one revolution of the crankshaft 25. When the angle is at 90° after top dead center, the gas forces in the internal combustion engine are sufficiently balanced that the engine comes to a standstill without requiring any torque from the electric motor 30. It may be possible to deliberately create different gas ratios in the cylinders during coasting, resulting in a different balanced crank angle position, which is then defined as the desired crankshaft angle position φ3.

[0056] However, this depends on the electric machine 30. If the required second torque cannot be generated by the electric machine 30, for example due to insufficient power, a third speed range T4 is necessary. The speed limit n3 should then be selected to be as low as possible, depending on the available power of the electric machine 30. The crankshaft angle φ3 should be selected so that a preferred angle can be achieved in the following speed range T4.

[0057] The third speed range T4 begins at the speed limit n3 and the crankshaft angle position φ3, i.e. following the speed range T3.

[0058] During the T4 speed range, the torque M 30The speed is set to zero. At the end of the speed range T4, the speed should be zero, i.e., the internal combustion engine 20 should be at a standstill, and a desired crankshaft angle φ4 should be reached. The crankshaft angle φ4 should be, for example, 90° after top dead center in a four-cylinder internal combustion engine. When the angle is 90° after top dead center, the gas forces in the internal combustion engine are sufficiently balanced that the engine is at a standstill without requiring any torque from the electric motor 30.

[0059] The deceleration of the internal combustion engine 20 is achieved solely by frictional torque. The crankshaft angle position φ3 and the speed limit n3 must be selected in the preceding speed range T3 such that the crankshaft angle position φ4 is reached solely by frictional torque.

[0060] This prevents the internal combustion engine 20 from swinging back at the end of the shutdown process, which would be a particularly unpleasant vibration for occupants in the vehicle.

[0061] Calculating the required torque M 30 and the instruction to the electric machine 30 can be given to a control unit, e.g. the control unit 80, if all the necessary information is available directly in this control unit.

[0062] However, it is also conceivable that some of the required information, such as the crankshaft angle φ or the rotational speed n, is stored in another control unit, for example, a control unit configured to control the internal combustion engine 20. In this case, the transmission time required for the information to be transferred from the other control unit to the control unit for the electric motor should be taken into account. For this purpose, the angle φ and rotational speed n are pre-calculated for a later time by assuming a constant rotational speed.

[0063] It is also possible in this way to include the time required until a given torque is actually converted by the electric machine (so-called transfer function).

Claims

[1] Method for stopping an internal combustion engine (20) in a vehicle which has an internal combustion engine (20) with a crankshaft (25) and an electric machine (30) which is connected to the crankshaft (25) via an operative connection (26), wherein a first torque (M1) is exerted on the crankshaft (25) by the electric machine (30) when the rotational speed of the crankshaft (25) is in a first rotational speed range (T2) which is below an idle speed of the internal combustion engine (20), wherein the first torque (M1) is specified as a function of an upper speed limit (n1) of the first speed range (T2), a lower speed limit (n2) of the first speed range (T2), a first crankshaft angle position (φ1) at the upper speed limit (n1) and a desired second crankshaft angle position (φ2) at the lower speed limit (n1), such that the lower speed limit (n2) is reached by the crankshaft (25) in the desired second crankshaft angle position (φ2), wherein in a second speed range (T3), which is located below the first speed range (T2), a second torque (M2) is exerted on the crankshaft (25) by the electric machine (30), wherein the second torque (M2) is specified as a function of a lower speed limit (n3) of the second speed range (T3) and a desired third crankshaft angle position (φ3) at the lower speed limit (n3) of the second speed range (T3), so that the lower speed limit (n3) of the second speed range (T3) is reached by the crankshaft (25) in the desired third crankshaft angle position (φ3). [2] Method according to claim 1, wherein the first torque (M1) is exerted on the crankshaft (25) by the electric machine (30) as soon as the speed of the internal combustion engine (20) has reached the upper speed limit (n1) of the first speed range (T2). [3] Method according to claim 1 or 2, wherein the first torque (M1) is applied by the electric machine (30) to the crankshaft (25) until the speed of the internal combustion engine (20) reaches the lower speed limit (n2) of the first speed range (T2). [4] Method according to any of the preceding claims, wherein the first torque (M1) is specified such that a gradient of a total torque (M 25 ), which consists at least of a torque (M 20 ) of the internal combustion engine (20) and the first torque (M1), lies within a specified interval. [5] Method according to one of the preceding claims, wherein the internal combustion engine (20) has a dual-mass flywheel (40) connected to the crankshaft (25), wherein in the first speed range (T2) there is a resonance speed of the dual-mass flywheel (40) at which the dual-mass flywheel (40) is excited to a resonant oscillation. [6] Method according to claim 5, wherein the upper speed limit (n1) of the first speed range (T2) is between the idle speed and the resonance speed plus 200 min -1 lies and / or wherein the lower speed limit is between the resonance speed minus 200 min -1 and a speed from which the internal combustion engine can be stopped in at most half a crankshaft revolution. [7] Method according to one of the preceding claims, wherein the second torque (M2) is specified such that a gradient of a total torque (M 25 ), which consists at least of a torque (M 20 ) of the internal combustion engine (20) and the second torque (M2), lies within a specified interval. [8] Method according to one of the preceding claims, wherein the lower speed limit (n3) of the second speed range (T2) is zero. [9] Method according to any one of claims 1 to 7, wherein in a third speed range (T4) which is below the second speed range (T3) no torque is exerted by the electric machine (30) on the working connection (25, 26), wherein a lower speed limit of the third speed range (T4) is zero, and wherein the crankshaft (25) reaches the lower speed limit of the third speed range (T4) in a desired fourth crankshaft angle position (φ4). [10] Method according to one of the preceding claims, wherein in an upper speed range (T1) which is above the first speed range (T1) and below the idle speed, no torque or a lesser torque than the first torque is exerted on the working connection (25, 26) by the electric machine (30). [11] Method according to one of the preceding claims, wherein a time delay in the application of a torque (M1, M2) by the electric machine to the crankshaft (25) is taken into account when calculating the first and / or second torque (M1, M2). [12] Computing unit (80) configured to perform a method according to any of the preceding claims. [13] Computer program that causes a computing unit to perform a method according to any one of claims 1 to 11 when executed on the computing unit, in particular according to claim 12. [14] Machine-readable storage medium with a computer program stored thereon according to claim 13.

Images