Method for operating a hybrid system of a motor vehicle and corresponding hybrid system

Abstract

The invention relates to a method for operating a hybrid device for a motor vehicle and a corresponding hybrid device. The invention relates to a method for operating a hybrid device (1) for a motor vehicle, the hybrid device having an internal combustion engine (2) and an electric motor (3), wherein during a start attempt of the internal combustion engine (2), a separating clutch (4) arranged between the internal combustion engine (2) and the electric motor (3) is adjusted to a target clutch torque by at least partially engaging. It is proposed that during the start attempt, the actual clutch torque actually transmitted via the separating clutch (4) and the speed of the internal combustion engine (2) are determined, and the start attempt is interrupted if a characteristic value related to the actual clutch torque exceeds a threshold value and the time integral of the speed remains below a limit value during the start attempt. The invention also relates to a hybrid device (1) for a motor vehicle.

Description

Technical Field

[0001] The present invention relates to a method for operating a hybrid power unit of a motor vehicle, the hybrid power unit having an internal combustion engine and an electric machine, wherein during a starting attempt of the internal combustion engine, a separating clutch arranged between the internal combustion engine and the electric machine is adjusted to a target clutch torque by at least partially engaging the separating clutch. The present invention also relates to a hybrid power unit for a motor vehicle. Background Art

[0002] EP 2 689 157 B1, for example, is known from the prior art. It relates to a safety clutch for a motor vehicle, which is used to transmit drive torque between a motor shaft, an electric motor, and a wheel drive shaft driving at least one wheel of the vehicle. During fault-free normal operation, torque transmission between the motor shaft and the wheel drive shaft occurs via a releasable form-locking clutch. If a torque exceeding a limit value occurs, the releasable form-locking clutch is released, allowing an elastic clutch device to at least temporarily assume torque transmission. Summary of the Invention

[0003] The object of the present invention is therefore to provide a method for operating a hybrid drive unit of a motor vehicle which has advantages over other methods, in particular in that damage to the separator clutch due to blocking or stalling of the internal combustion engine during a starting attempt is avoided.

[0004] According to the invention, this aspect is achieved by a method for operating a hybrid power plant having the features of claim 1. It is proposed that during a start attempt, the actual clutch torque actually transmitted via the separating clutch and the speed of the internal combustion engine are detected, and the start attempt is interrupted if a characteristic value related to the actual clutch torque exceeds a threshold value and the time integral of the speed remains below a limit value during the start attempt.

[0005] A hybrid system is used to drive a motor vehicle, that is, to provide torque directly used to drive the motor vehicle. A hybrid system includes an internal combustion engine and an electric motor. These are configured and constructed to individually or at least temporarily jointly provide the drive torque supplied by the hybrid system. This means that the drive torque may be provided solely by the internal combustion engine without the electric motor, solely by the electric motor without the internal combustion engine, or jointly by the internal combustion engine and the electric motor.

[0006] As long as there is sufficient electrical energy available, for example, when the battery is fully charged, the electric motor can supply the drive torque alone, that is, without using the internal combustion engine. The internal combustion engine can be switched on to provide the drive torque alone or in conjunction with the electric motor. To this end, it is proposed to start the internal combustion engine with the help of the electric motor.

[0007] In order to start the internal combustion engine, a start attempt is performed. The start attempt begins when a variable indicating a request to switch on the internal combustion engine is sent to the hybrid device. The start attempt ends either with a successful start of the internal combustion engine or with the start attempt being aborted.

[0008] A start attempt is to be understood as a process in which an attempt is made to adjust the internal combustion engine in such a way that it subsequently provides or can provide at least a portion of the drive torque. During the start attempt, the speed of the internal combustion engine should be set from a standstill to a speed different from zero, in particular to a speed corresponding to at least the minimum speed, the idle speed, and / or the synchronous speed of the internal combustion engine.

[0009] From a minimum speed, the internal combustion engine can continue to increase its speed autonomously, i.e., without the need for an external drive such as a starter. The idle speed is the speed at which the internal combustion engine is operating without providing drive torque but simply to maintain its speed. The idle speed is preferably selected for quiet and / or low-vibration operation of the internal combustion engine. It is preferably greater than the minimum speed.

[0010] The synchronous speed is understood to be the speed of the internal combustion engine that corresponds to the current instantaneous speed of the electric machine. When the synchronous speed is present, there is no slip at the disconnect clutch, so the disconnect clutch can fully engage and a positive connection can be established between the internal combustion engine and the electric machine. The synchronous speed is preferably greater than the minimum speed. Thus, the synchronous speed can be comparable to or greater than the idle speed.

[0011] Preferably, the launch attempt is terminated with the disconnect clutch fully engaged when synchronous speed is present.

[0012] During the start attempt, the disconnect clutch is at least partially engaged. The disconnect clutch is adjusted to a target clutch torque. The target clutch torque is used to increase the speed of the internal combustion engine toward the minimum speed and preferably corresponds to a drag torque with which the speed of the internal combustion engine can reach the minimum speed, the idle speed, and / or the synchronous speed.

[0013] In the event of a malfunction or defect in the internal combustion engine, a situation may arise in which the speed of the internal combustion engine does not reach the minimum speed or only reaches the minimum speed briefly and then drops below the minimum speed.

[0014] A fault or defect may particularly take the form of a mechanical defect, such as a seizure of the output shaft and / or other rotating parts of the internal combustion engine. For example, a fault may be caused by insufficient lubrication of the internal combustion engine, which manifests itself as engine sluggishness or so-called piston seizure. In general, a fault is one that increases the drag torque required to reach the minimum speed compared to a fault-free internal combustion engine or prevents the minimum speed from being reached. Consequently, a start attempt cannot be successfully completed, or even if the internal combustion engine briefly reaches the minimum speed despite the engine fault, the start attempt is terminated without successfully starting the internal combustion engine.

[0015] This causes the disconnect clutch to be loaded with the target clutch torque for a long time during the startup attempt, or to be mistakenly fully engaged when the internal combustion engine speed briefly reaches the minimum speed. Thus, the disconnect clutch may be damaged, for example, due to high thermal and / or high mechanical loads.

[0016] In order to avoid the damage to the separating clutch, the method according to the present invention proposes to interrupt the starting attempt. At this, if the internal combustion engine does not successfully start and therefore has an internal combustion engine fault, then the starting attempt should be interrupted.

[0017] Identifying a fault or defect of an internal combustion engine is not simple. In order to identify a fault of the internal combustion engine, the method according to the invention therefore proposes at least two conditions, when these two conditions exist, the start attempt is interrupted.

[0018] The first condition for interrupting the start attempt is met when a characteristic value related to the actual clutch torque exceeds a threshold value. This condition checks whether the clutch torque actually transmitted by the disconnect clutch is at least as high as the torque required to start a healthy internal combustion engine. In other words, the first condition confirms the proper functioning of the disconnect clutch.

[0019] Here, it can be provided that as a second condition, a successful start of the internal combustion engine is detected when the speed of the internal combustion engine reaches or exceeds a minimum speed and / or an idle speed. However, the presence of a faulty internal combustion engine may result in the speed of the internal combustion engine briefly reaching the minimum speed and / or the idle speed during the start attempt, but then falling below these values again due to the fault.

[0020] Instead, the present invention proposes that the second condition is based on the integral of the rotational speed. If the time integral of the rotational speed continuously falls below a limit value during the start attempt, the second condition for interrupting the start attempt is met. Finally, if the engine speed, in particular, does not reach the minimum speed despite a sufficiently high actual clutch torque, or only briefly exceeds the minimum speed, a fault in the internal combustion engine is determined. In other words, the second condition confirms whether there is sufficient rotational movement of the internal combustion engine to start the engine.

[0021] To check the first condition, the method according to the present invention provides for determining the actual clutch torque actually transmitted by the disconnect clutch during the start attempt. The clutch torque actually transmitted by the disconnect clutch can be determined using a characteristic curve of the disconnect clutch, in particular in combination with an actual value of an actuating variable of the disconnect clutch, such as the contact pressure. For this purpose, for example, the actual value of the contact pressure can be determined and compared with a target contact pressure value determined based on the target clutch torque. Additionally or alternatively, the actual clutch torque can be calculated using a model that, for example, takes into account the rotational speeds prevailing on the input and output sides of the disconnect clutch and the moments of inertia of the corresponding rotating components.

[0022] The actual clutch torque is determined in the form of a time-dependent curve of the actual clutch torque. A corresponding instantaneous value of the actual clutch torque can be determined at any time during the start attempt, which corresponds to the actual clutch torque actually transmitted or at least approximately reflects it. A characteristic value is formed from the actual clutch torque or its time curve, the presence of which indicates that the first condition for aborting the start has been met. This characteristic value is used to identify the functional function of the disconnect clutch. If the characteristic value associated with the actual clutch torque exceeds the threshold, it can be assumed that the disconnect clutch is functioning properly.

[0023] For example, the characteristic value corresponds to the actual clutch torque. Preferably, however, the characteristic value is a variable derived from a curve of the actual clutch torque, which reflects or is approximately equal to the actual clutch torque transmitted during or immediately after at least partial engagement. The characteristic value can be, for example, the maximum value of the actual clutch torque within a defined time window, the difference between two values, or the gradient of the actual clutch torque.

[0024] To check the second condition for interrupting the start attempt, in addition to the actual clutch torque actually being transmitted, the internal combustion engine's speed is also detected. The internal combustion engine's speed is preferably also presented as a time-varying curve. The integral of the speed is determined based on this time-varying speed curve. In particular, the speed measurements are accumulated over time. According to the method of the present invention, for a successful start of the internal combustion engine, simply increasing the speed to a minimum speed is not sufficient; rather, the speed must remain nonzero for a sufficiently long time for the integral of the speed to exceed a limit value. By taking into account the integral of the speed, reliable detection of the internal combustion engine's rotational motion is achieved.

[0025] For both conditions to be met and the start attempt to be aborted, on the one hand, a characteristic value related to the actual clutch torque must exceed a threshold value, and on the other hand, the integral of the speed must remain continuously below a limit value during the start attempt. This approach ensures that malfunctions or defects in the internal combustion engine are detected during the start attempt. This reliably prevents damage to the disconnect clutch.

[0026] One refinement of the present invention provides for a start attempt to be interrupted only if the disconnect clutch temperature still exceeds a temperature threshold. Therefore, the disconnect clutch temperature is used to check a third condition for interrupting the start attempt, which must be met in addition to the first and second conditions. It is proposed that the start attempt be interrupted only if the disconnect clutch temperature exceeds the temperature threshold. In other words, the start attempt continues as long as the disconnect clutch temperature remains below the temperature threshold. This allows the start attempt to be interrupted before the disconnect clutch temperature reaches a critical value, thus preventing damage.

[0027] One refinement of the present invention provides that, in order to interrupt the start attempt, the disconnect clutch is disengaged and a fault entry is entered in the fault memory, and that the disconnect clutch is subsequently blocked from engaging as long as the fault entry is entered in the fault memory. Since the internal combustion engine is started by means of the electric machine, for which the disconnect clutch is at least partially engaged, the start attempt is interrupted by disengaging the disconnect clutch, in particular by completely disengaging the disconnect clutch in order to interrupt the start attempt.

[0028] At the same time, a fault entry is recorded in a fault memory, which is present, for example, in the controller of the internal combustion engine and / or the hybrid system. After the start attempt is interrupted, it is determined that a fault in the internal combustion engine is present. Therefore, as long as the fault entry is recorded in the fault memory, the separation clutch is subsequently prevented from engaging. This avoids repeated engagement of the separation clutch and the accompanying possible damage to the separation clutch. Instead of recording a fault entry, a fault state can be implemented. In this case, the fault state is marked as active when the start attempt is interrupted. Therefore, after the start attempt is interrupted, there is a fault state marked as active. While the active fault state exists, the internal combustion engine does not provide drive torque. The active fault state can be associated with the implementation of corresponding countermeasures, which enable the hybrid system to operate reliably without the use of the internal combustion engine.

[0029] One refinement of the present invention provides for deleting the fault entry from the fault memory after a defined period of time has elapsed since the start attempt was interrupted. As described above, as long as the fault entry is entered in the fault memory, engagement of the separating clutch and, therefore, a renewed start attempt of the internal combustion engine is prevented. A new start attempt is only possible after the fault entry has been deleted from the fault memory.

[0030] It is now proposed that the fault entry be deleted after a defined time period has elapsed after the start attempt is interrupted. Thus, engagement of the disconnect clutch is not permanently prevented after the start attempt is interrupted, but only for a defined time period. The length of this defined time period can be linked to other conditions, such as the hybrid system being shut down during this period. This prevents the situation where a restart attempt cannot be made after a defined time period has elapsed after the start attempt is interrupted. If a fault condition was active when the start attempt was interrupted, this fault condition is marked as failed after the defined time period has elapsed. While the failed fault condition is present, the aforementioned countermeasures are no longer implemented, thereby allowing for reliable operation of the hybrid system while using the internal combustion engine.

[0031] One refinement of the present invention provides that the fault entry is deleted from the fault memory only if the disconnect clutch temperature remains below a temperature threshold for a specific period of time. As described above, it can be provided that the start attempt is only interrupted if the disconnect clutch temperature still exceeds the temperature threshold. Thus, the fault entry is deleted from the fault memory only if the disconnect clutch temperature remains below the temperature threshold. If a fault state is active when the start attempt is interrupted, this fault state (as described above) is marked as a failure.

[0032] This ensures that a restart attempt is prevented as long as the disconnect clutch temperature is above a temperature threshold. In other words, after an interrupted start attempt, a restart attempt is prevented as long as the disconnect clutch temperature is within a critical temperature range and therefore there is a greater probability that the disconnect clutch will be damaged by the faulty internal combustion engine.

[0033] A refinement of the present invention provides for using the maximum value of the actual clutch torque occurring after the separating clutch is at least partially engaged as a characteristic value. As described above, the characteristic value represents a variable related to the actual clutch torque. It is proposed that the maximum value of the actual clutch torque occurring within a time window starting from the partial engagement of the separating clutch and ending at a predetermined time after the partial engagement of the separating clutch be used as the characteristic value. In other words, rather than using the maximum value of the actual clutch torque occurring during the entire start attempt as the characteristic value, only the maximum value of the actual clutch torque occurring within a predefined time window is used as the characteristic value. Since the characteristic value is used to check the proper functioning of the separating clutch, it is advantageous to perform this check within this time window. Alternatively, the gradient of the actual clutch torque occurring within the time window can be used as the characteristic value. This approach makes it possible to check whether the separating clutch exhibits a sufficiently fast reaction speed for its proper functioning.

[0034] One refinement of the present invention provides for using the difference between the maximum value and the minimum value of the actual clutch torque occurring before the disconnect clutch is partially engaged as a characteristic value. Since the determined actual clutch torque may have absolute and relative errors, the present invention provides for determining the minimum value in addition to the maximum value and using the difference between the maximum and minimum values as the characteristic value. This compensates for errors when determining the actually transmitted clutch torque, and improves the reliability of the characteristic value determination.

[0035] One refinement of the present invention provides that the target clutch torque is set to a first value during the engagement phase and is increased toward a second value during the start attempt until the speed of the internal combustion engine reaches a minimum speed. During the start attempt, the target clutch torque is initially set to the first value, in particular a predetermined first value. The target clutch torque is then increased until the separating clutch is fully engaged and a positive connection is established between the internal combustion engine and the electric machine, provided that the start attempt is not interrupted due to the aforementioned conditions.

[0036] In other words, as long as the internal combustion engine speed has not reached the minimum speed and the start attempt has not been interrupted, the target clutch torque is increased toward the second value. The increase in the target clutch torque can be performed continuously or in discrete steps. This ensures that sufficient actual clutch torque is available to start the internal combustion engine and that the internal combustion engine can be reliably started if a healthy internal combustion engine is present.

[0037] A refinement of the method provides that the target clutch torque is increased in defined target clutch torque steps, wherein the start attempt is interrupted if the target clutch torque reaches or exceeds a second value. The second value of the target clutch torque is in particular the maximum target clutch torque that can be transmitted by the separating clutch.

[0038] Therefore, the target clutch torque is not increased continuously, but rather in steps. In particular, the start attempt is interrupted when the target clutch torque reaches the second value and the internal combustion engine speed has not reached the minimum speed. This ensures that, on the one hand, the internal combustion engine start attempt by increasing the target clutch torque is successful, and, on the other hand, damage to the disconnect clutch is avoided because the start attempt is interrupted before the maximum target clutch torque that can be transmitted by the disconnect clutch is exceeded.

[0039] The invention also relates to a hybrid device for a motor vehicle, in particular for carrying out a method according to an embodiment within the scope of the present description, wherein the hybrid device has an internal combustion engine and an electric machine and is designed to: during a start attempt of the internal combustion engine, during a start attempt of the internal combustion engine (2), adjust a separating clutch arranged between the internal combustion engine and the electric machine in terms of drive technology to a target clutch torque by at least partially engaging it. It is proposed that the hybrid device is further designed to determine the actual clutch torque actually transmitted via the separating clutch and the speed of the internal combustion engine during the start attempt of the internal combustion engine, wherein the start attempt is interrupted if a characteristic value related to the actual clutch torque exceeds a threshold value and the time integral of the speed remains below a limit value during the start attempt.

[0040] The advantages of the design of the hybrid device and the method have been pointed out. The hybrid device and the method of operating it can be modified according to the embodiments within the scope of this description, in which respect reference is made to the above-described embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The present invention will be explained in more detail below with reference to the embodiments shown in the accompanying drawings, without limiting the present invention in any way.

[0042] The single FIGURE shows a schematic diagram of a hybrid device for carrying out the method according to the present description. DETAILED DESCRIPTION

[0043] The figures show a hybrid device 1 for a motor vehicle, comprising an internal combustion engine 2 and an electric motor 3. In terms of drive technology, a separating clutch 4, such as a multi-plate clutch, is arranged between the internal combustion engine 2 and the electric motor 3. The hybrid device 1 at least temporarily provides a drive torque for driving the motor vehicle. The drive torque can be provided by the internal combustion engine 2 and the electric motor 3 individually, or at least temporarily by both in a hybrid mode.

[0044] During the hybrid operation of the hybrid device 1 , the internal combustion engine 2 is at least temporarily shut down or stopped. In particular, it is proposed that the internal combustion engine 2 be started when corresponding demand variables are present and that at least part of the drive torque be generated by means of the internal combustion engine 2 .

[0045] A start attempt is performed to start internal combustion engine 2. The start attempt begins with the occurrence of a request variable or the at least partial engagement of disconnect clutch 4 for starting internal combustion engine 2 and ends with the successful start of internal combustion engine 2 or the abortion of the start attempt. In the event of a successful start, internal combustion engine 2 can then at least partially provide drive torque autonomously.

[0046] When the internal combustion engine 2 is successfully started, it reaches a minimum speed, an idle speed, or a synchronous speed. Synchronous speed is understood to be the speed of the internal combustion engine that corresponds to the current instantaneous speed of the electric machine 3. When the synchronous speed is reached, there is no slippage in the separating clutch 4, so the separating clutch 4 can be fully engaged and a positive connection can be established between the internal combustion engine 2 and the electric machine 3.

[0047] During the start attempt, the speed of the internal combustion engine 2 is increased from a standstill in the direction of the minimum speed. At the beginning of the start attempt, the internal combustion engine 2 is preferably at a standstill or has a speed below the minimum speed.

[0048] During the start attempt, the separating clutch 4 is at least partially engaged. Here, the separating clutch 4 is adjusted to a target clutch torque. The target clutch torque is used to increase the speed of the internal combustion engine 2 toward the minimum speed and preferably corresponds to a predefined drag torque at which the speed of the internal combustion engine 2 can be brought to the minimum speed.

[0049] By further engaging the separating clutch 4 , the target clutch torque increases from the first value toward the second value. The target clutch torque continues to increase until the speed of the internal combustion engine 2 reaches a minimum speed or the start attempt is interrupted. In particular, it can be provided that the target clutch torque is increased in steps with a defined target clutch torque step. The increase occurs in particular periodically, for example at fixed time intervals.

[0050] During the start attempt, the actual clutch torque actually transmitted via disconnect clutch 4 is determined. The actual clutch torque is determined, for example, based on a characteristic curve of disconnect clutch 4 or, alternatively, calculated based on a speed gradient and / or a moment of inertia. Based on the determined actual clutch torque, a time curve of the actual clutch torque can be formed. A characteristic value is determined from the time curve of the actual clutch torque, which corresponds to the maximum value of the actual clutch torque occurring after disconnect clutch 4 is at least partially engaged.

[0051] Preferably, the maximum value of the actual clutch torque occurring within a specific time window after the separation clutch 4 is engaged is used as the characteristic value instead of the maximum value occurring during the entire start attempt. Alternatively, the difference between the maximum value, in particular the maximum value occurring within the time window, and the minimum value of the actual clutch torque occurring before the separation clutch 4 is at least partially engaged is used as the characteristic value.

[0052] In addition, the time curve of the rotational speed of the internal combustion engine 2 is determined. An integral over time is determined from the time curve of the rotational speed of the internal combustion engine 2. In particular, for this purpose, the measured values of the rotational speed are accumulated over time.

[0053] It is provided that the start attempt is interrupted if the characteristic value exceeds a threshold value and the integral of the speed during the start attempt remains below a limit value. It can also be provided that the start attempt is interrupted only if the temperature of the disconnect clutch 4 also exceeds a temperature threshold value. The threshold value is determined, for example, in such a way that it corresponds to a torque or characteristic value at which the internal combustion engine 2 can normally be started.

[0054] To interrupt the start attempt, disconnect clutch 4 is disengaged and a fault entry is entered in the fault memory. Subsequently, as long as the fault entry is entered in the fault memory, disconnect clutch 4 is prevented from engaging. After a defined period of time has elapsed since the start attempt was interrupted and / or when the temperature of disconnect clutch 4 remains below a temperature threshold for a defined period of time, the fault entry is deleted from the fault memory.

[0055] The method according to the invention prevents damage or destruction of the separator clutch 4 in the event of a sluggishness or a jam of the internal combustion engine 2 .

[0056] List of reference numerals:

[0057] 1 Hybrid equipment

[0058] 2 Internal combustion engine

[0059] 3 Motor

[0060] 4 Disengagement clutch

Claims

1. A method for operating a hybrid device (1) of a motor vehicle, the hybrid device having an internal combustion engine (2) and an electric machine (3), wherein: During a start attempt of the internal combustion engine (2), a separating clutch (4) arranged between the internal combustion engine (2) and the electric motor (3) is adjusted to a target clutch torque by at least partially engaging, characterized in that during the start attempt, the actual clutch torque actually transmitted via the separating clutch (4) and the speed of the internal combustion engine (2) are obtained, and the start attempt is interrupted if a characteristic value related to the actual clutch torque exceeds a threshold value and the time integral of the speed remains continuously below a limit value during the start attempt.

2. The method according to claim 1, characterized in that The start attempt is only interrupted if the disconnect clutch (4) temperature still exceeds the temperature threshold value.

3. The method according to claim 1 or 2, characterized in that In order to interrupt the start attempt, the separating clutch (4) is disengaged and a fault entry is entered in the fault memory, and the separating clutch (4) is subsequently prevented from engaging as long as the fault entry is entered in the fault memory.

4. The method according to claim 3, characterized in that After a defined period of time has elapsed since the aborted start attempt, the fault entry is deleted from the fault memory.

5. The method according to claim 4, characterized in that The fault entry is deleted from the fault memory only when the temperature of the separator clutch (4) falls below a temperature threshold value for a specific period of time.

6. The method according to claim 1 or 2, characterized in that The actual maximum clutch torque occurring after at least partial engagement of the separator clutch (4) is used as the characteristic value.

7. The method according to claim 1 or 2, characterized in that The difference between the maximum value and the minimum value of the actual clutch torque occurring before the partial engagement of the separating clutch (4) is used as the characteristic value.

8. The method according to claim 1 or 2, characterized in that During engagement, the target clutch torque is adjusted to a first value, and during a start attempt, the target clutch torque is increased in the direction of a second value until the speed of the internal combustion engine (2) reaches a minimum speed.

9. The method according to claim 8, characterized in that The target clutch torque is increased in a defined target clutch torque increment, wherein the start attempt is interrupted if the target clutch torque reaches or exceeds a second value.

10. A hybrid device (1) for a motor vehicle, the hybrid device being adapted to carry out the method according to any one of claims 1 to 9, wherein: The hybrid device (1) has an internal combustion engine (2) and an electric motor (3), and is configured to adjust a separating clutch (4) arranged between the internal combustion engine (2) and the electric motor (3) in terms of drive technology to a target clutch torque by at least partially engaging it during a start attempt of the internal combustion engine (2), characterized in that the hybrid device (1) is also configured to obtain an actual clutch torque actually transmitted via the separating clutch (4) and a speed of the internal combustion engine (2) during a start attempt of the internal combustion engine (2), wherein the start attempt is interrupted if a characteristic value related to the actual clutch torque exceeds a threshold value and the time integral of the speed remains continuously below a limit value during the start attempt.

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