WO2014195089A1

WO2014195089A1 - Method for performing open-loop and/or closed-loop control of a hybrid drive arrangement of a motor vehicle

Info

Publication number: WO2014195089A1
Application number: PCT/EP2014/059638
Authority: WO
Inventors: Michael Zillmer; David Prochazka; Markus Fugel; Bernd Stiebels
Original assignee: Volkswagen Aktiengesellschaft
Priority date: 2013-06-08
Filing date: 2014-05-12
Publication date: 2014-12-11
Also published as: DE102013009649A1

Abstract

Method for performing open-loop and/or closed-loop control of a hybrid drive arrangement of a motor vehicle. The invention relates to a method for performing open-loop and/or closed-loop control of a hybrid drive arrangement (1) of a motor vehicle, having an internal combustion engine (2), having at least one electric machine (3), having an electric energy store (4) and having a clutch (K0), wherein the internal combustion engine (2) can be connected and disconnected by means of the clutch (K0), wherein the motor vehicle is driven in a purely electric fashion by the electric machine (3) in a first phase, and wherein the internal combustion engine (2) is tow-started without the combustion of fuel. An increased electrical energy requirement during tow-starting is avoided in that the tow-starting of the internal combustion engine (2) is carried out in a deceleration phase of the motor vehicle.

Description

description

Method for controlling and / or regulating a hybrid drive arrangement of a

motor vehicle

The invention relates to a method for controlling and / or regulating a

Hybrid drive arrangement of a motor vehicle, with an internal combustion engine, with at least one electric machine, with an electrical energy storage and with a disconnect clutch, wherein the internal combustion engine by means of the disconnect clutch can be engaged and disengaged, wherein the motor vehicle is driven purely electrically by the electric machine during an electric driving operation, and wherein the internal combustion engine is towed without combustion of fuel.

The hybrid drive is in particular a so-called "plug-in hybrid", wherein an electrical energy store, in particular a battery, can be externally charged via a power grid

Parallel hybrid, whereby significant distances can also be driven purely electrically. For the presentation or realization of high drive torques and powers, the internal combustion engine can be switched on from the initially electric driving operation in order to increase the maximum torque or the maximum power by the combined operation. For this, the internal combustion engine must be started. Of the

Internal combustion engine is also started, for example, when the residual energy content of the battery is low.

In the prior art, it has already been proposed to first start the internal combustion engine without combustion of fuel and thus to accelerate and only then to start the combustion of the fuel when a specific starting criterion is met. Because of the internal combustion engine without combustion of fuel first

is towed, the wear of the internal combustion engine is reduced. By the

Towing lubricates corresponding friction points and thus improves the lubricating properties for subsequent operation. From DE 198 14 402 A1 a hybrid drive arrangement of a motor vehicle and an associated method for controlling and / or regulating the hybrid drive arrangement is known. The hybrid drive assembly includes an internal combustion engine and an electric machine. The driver of the motor vehicle is at parked engine by pressing the accelerator pedal a start signal. The motor vehicle drives on virtually instantaneously and accelerates steadily. The first part of the starting process is carried out by the drive of the electric machine until the internal combustion engine takes over the further drive. The electric machine has a double function in the first phase of the starting process. On the one hand, the electric machine serves to accelerate the vehicle and, on the other hand, the electric machine also simultaneously turns on the internal combustion engine, which is non-rotatably connected to it, and this can be started in the course of the starting acceleration. In the first part of this phase, the internal combustion engine is turned up in the decompressed state, wherein the decompression can be done, for example, by keeping open an exhaust valve. Upon reaching a specific start criterion, namely a sufficient speed, the decompression is terminated, after which the injection of the fuel and the activation of the ignition takes place. Then the internal combustion engine starts and takes over the others

Vehicle acceleration.

From DE 10 2007 040 727 A a hybrid drive arrangement and a method for controlling and / or regulating the hybrid drive arrangement of a motor vehicle is known. It is a method for starting an internal combustion engine with a coupled electric machine described in a motor vehicle, wherein a certain desired torque is transmitted to a drive control of the internal combustion engine. After that, the

Internal combustion engine towed by the electric machine for take-off and thus pre-accelerated. In order to reduce exhaust emissions when starting the internal combustion engine, the internal combustion engine is trailed by the electric machine without injection of fuel until the engine torque convertible by the internal combustion engine substantially corresponds to the desired torque. Thereafter, only the injection of fuel in the engine is released. It will be the temperature of the

Internal combustion engine, in particular the coolant temperature measured. The temperature of the internal combustion engine also influences the torque of the internal combustion engine, so that the temperature of the internal combustion engine is included in the corresponding starting criterion.

From the generic DE 10 2010 038 086 A1 discloses a method for controlling and / or regulating a hybrid drive assembly of a motor vehicle is known. The

Hybrid drive assembly has an internal combustion engine and one with the Combustion engine operatively connected, electric machine on. The electric machine tows in a purely electric driving the disconnected internal combustion engine, whereby it is pre-accelerated. The electric machine drives the vehicle via a transmission alone. The internal combustion engine can be separated from the rest of the drive system by means of a separating clutch. This makes it possible in recuperation operation to decouple the internal combustion engine from the electric machine, wherein the internal combustion engine does not have to be carried along. As a result, the internal combustion engine generates no drag torque. This is intended to increase the efficiency of the hybrid drive arrangement.

In a plug-in hybrid drive arrangement, it is to be assumed that many journeys are purely electrical, that is to say without the assistance of the internal combustion engine. The start of the internal combustion engine is unpredictable in particular when it takes place through an interaction of the driver, for example by a high accelerator pedal / Radmoment- / Radleistungsanforderung or by a manual switchover from electrical operation in the engine operation or the like.

The generic method for controlling and / or regulating a hybrid drive arrangement of a motor vehicle is therefore not yet optimally designed. During the electric driving operation, the towing of the internal combustion engine leads to an increased electrical drive power requirement and thus to an increase in the electrical energy requirement. The electrical energy storage can thus be additionally burdened by the towing. Furthermore, it is conceivable that the towing leads to Drehunförmigkeiten, which could affect the ride comfort.

The invention is therefore based on the object, the aforementioned method in such a way and further develop that an increased electrical energy consumption

Towing, especially for preconditioning of the internal combustion engine is avoided.

This previously indicated object is now achieved in that the towing the

Internal combustion engine is performed in a deceleration phase of the motor vehicle. This has the advantage that for this purpose, no or only very little additional electrical energy from the energy storage, for example, the corresponding battery must be used. Although this also preferably the Rekuperationspotential to the drag torque of

Reduces internal combustion engine, this is effective but cheaper than the active removal of energy from the battery. In a deceleration phase of the motor vehicle, in particular during a braking phase, the towing of the internal combustion engine also becomes felt more comfortable than the coupling of the internal combustion engine in

Acceleration phases of the motor vehicle, in particular at low speeds or low drive power, as this rotational irregularities are reduced. The ride comfort is therefore increased accordingly. The electric machine is in particular a transmission, preferably arranged downstream of an automatic transmission. Now, if the motor vehicle decelerates, that is braked, the internal combustion engine is switched on or coupled by closing the disconnect clutch at a certain time. The internal combustion engine is subsequently towed. In order to keep the deceleration effect at the wheel substantially constant, the recuperation torque of the electric machine is preferably reduced accordingly. In a particularly preferred embodiment, the torque of the electric machine is briefly increased during the deceleration phase in order to accelerate the internal combustion engine. The internal combustion engine is pre-accelerated in particular by closing the separating clutch. A low load on the separating clutch by heat input and thus only a small amount of wear is achieved in particular by minimizing the slip of the separating clutch when towing (or entrainment). It is conceivable, in an alternative embodiment to adjust the slip on the separating clutch when entrainment while keeping the speed of the internal combustion engine substantially constant. The rotational speed of the internal combustion engine can fluctuate by a target rotational speed by, for example, +/- 150 revolutions, in particular +/- 50 revolutions, in particular +/- 20 revolutions per minute. This has the advantage that the engine speed when towing (or entrainment) is substantially constant. The clutch slip should not exceed 2,000, in particular 1,500, preferably 1 .000, in a particularly preferred embodiment 500 revolutions per minute. At another time, the

Disconnect now open and decoupled the engine again. The

Rekuperationsmoment is again increased accordingly. The decoupling takes place in particular when the internal combustion engine falls below a minimum speed threshold. This speed threshold can, for example, in response to the resonance speed of a

Dual mass flywheel or a torsion damper can be selected to

To avoid rotational irregularities when towing. Operation at very low engine speeds may be subject to greater rotational nonuniformities, which causes the

Could compromise ride comfort. Therefore, it is advantageous if the engine above the resonance speed of the dual-mass flywheel or the resonance speed of a

Torsionsdämpfers entrained. In particular, the towing may be terminated even if an engine towing time of more than 5 seconds or more than 10 seconds, or more than 30 seconds has been reached. Optionally, the towing can also after reaching the exceeding of a minimum speed of the engine be canceled. Furthermore, the towing can be terminated when the oil pressure, for example in the crankcase or in a cylinder head exceeds a pressure threshold of 0.3, in particular 0.6 or preferably 1, 2 bar. The pressure threshold should be exceeded for at least 5 seconds, in particular for at least 10 seconds, preferably for 20 seconds. Further abort criteria of Towing may be the achievement of a cumulative friction work of the towed internal combustion engine of a subsidized

Oil volume or a predefined oil temperature increase. The aforementioned disadvantages are therefore avoided and corresponding advantages are achieved.

There are now a variety of ways to design the inventive method in an advantageous manner and further. For this purpose may first on the the

Patent claim 1 subordinate claims are referenced. Hereinafter, a preferred embodiment of the method with reference to the drawings and the associated description is explained in detail. In the drawing shows:

1 is a schematic representation of a hybrid drive arrangement of a

Motor vehicle with an internal combustion engine, with a separating clutch and with an electric machine,

Fig. 2 is a diagram of the time-dependent speed curve and the time-dependent

Torque profile of the electric machine and the internal combustion engine during a deceleration phase of the motor vehicle without performing the method according to the invention,

Fig. 3 is a schematic diagram of the time-dependent speed curve and the time-dependent torque curve of the electric machine and the

Internal combustion engine during a deceleration phase of the motor vehicle, wherein the inventive method is performed and the separating clutch is closed, and

Fig. 4 is a schematic diagram of the time-dependent speed curve and the time-dependent torque curve of the electric machine and the

Internal combustion engine during a deceleration phase of the motor vehicle, wherein the inventive method is performed and the separating clutch is operated slipping. Before the method is explained in more detail with reference to FIGS. 2 and 3 and 4, may first be discussed in more detail on the hybrid drive assembly 1 with reference to FIG. 1.

The hybrid drive assembly 1 of a motor vehicle not shown here in detail has an internal combustion engine 2, in this embodiment, only an electrical

Machine 3 and a clutch K0 on. The internal combustion engine 2 may be designed as a gasoline engine or as a diesel engine.

The electric machine 3 and the internal combustion engine 2 can be coupled via the separating clutch K0. By opening the separating clutch K0, the internal combustion engine 2 can be decoupled. The separating clutch K0 is arranged functionally effective between the electric machine 3 and the internal combustion engine 2.

The electric machine 3 can be used as a motor and as a generator. The electric machine 3 is connected via an appropriate line (unspecified) to an energy store 4, in particular to a battery 5. The battery 5 is designed in particular as HV battery or high-voltage battery.

Furthermore, the hybrid drive arrangement 1 has a starting element, namely a coupling 6 or a corresponding converter. The clutch 6 is designed in particular as a double clutch. The clutch 6 is followed by a transmission 7. The transmission 7 is designed in particular as a double-clutch transmission.

For controlling the internal combustion engine 2, an engine control unit 8 is provided. to

Control of the electric machine 3 is an e-machine control unit 9 with

appropriate power electronics provided. For controlling or regulating the transmission 7, a transmission control unit 10 is provided. For controlling and / or regulating the battery 5, a battery management system 1 1 is provided.

The engine control unit 8 is via appropriate lines (not specified),

in particular via a bus 13, connected both to the internal combustion engine 2 and to the e-machine control unit 9 and to the transmission control unit 10. The

Transmission control unit 10 is connected via the line or the bus 13 to the transmission 7. The battery 5 is connected to a charger 12. The charger 12, the

Battery management 1 1, the transmission control unit 10, the E-machine control unit 9 and the engine control unit 8 are connected to each other via a common bus 13.

The hybrid drive arrangement 1 is designed in particular as a so-called "plug-in hybrid." In this case, the battery 5 can be charged via a power supply, not shown, in which case two energy sources are available for operating the motor vehicle, namely once in the form of the electrical energy store 4 and another in the form of the fuel (not shown), which can be supplied to the internal combustion engine 2.

It is a purely electric driving possible, the engine 2 can be switched on or disconnected by closing or opening the clutch K0.

The internal combustion engine 2 can now be towed without combustion of fuel. After reaching a corresponding start criterion, the internal combustion engine can be started, in which case fuel is burned.

Characterized in that in addition to the engine 2, a powerful electric drive in the form of the electric machine 3 is available and a suitably adapted battery 5, it is possible that significant distances can also be driven purely electrically. For the representation of high drive torques and drive powers, the internal combustion engine 2 can be switched on from the electric driving operation in order to increase the maximum torque or the maximum power by the combined operation. The internal combustion engine 2 is switched on by closing the separating clutch K0 in the boost mode. A start of the internal combustion engine 2 is preferably further then when the residual energy content of the battery 5 is low.

In order to reduce the engine wear, the internal combustion engine 2 is now towed and thus pre-accelerated and turned off a few revolutions without "firing" it in order to lubricate the corresponding friction points and thus to improve the lubricating properties for "post-fired" operation , which can reduce engine wear. The towing of the

Internal combustion engine 2 can be carried out in particular at low engine temperatures and / or low ambient temperatures. The engine temperature can be measured, for example by measuring the temperature of the coolant, the oil or corresponding engine components. These temperatures for use of the below Processes are preferably less than 20 ° C, in particular less than 10 ° C, preferably less than 0 ° C and especially less than -10 ° C.

The internal combustion engine 2 is preferably accelerated to a speed of at least 400, in particular 600, preferably 800, more preferably 1000, more preferably 1200, more preferably 1500 revolutions per minute and then operated towed without the combustion of fuel. The internal combustion engine 2 is operated without combustion of fuel preferably above a resonance speed of an optionally arranged dual-mass flywheel or the resonance speed of a corresponding torsional damper (not shown).

The towing and thus the acceleration of the internal combustion engine 2 takes place

in particular via a closed or preferably slipping operated separating clutch K0. Alternatively, it is conceivable to tow the internal combustion engine 2 via a separate, further electric machine (not shown) and thus to turn it over. The term "towing" therefore means the transmission of a torque to the internal combustion engine 2, in particular until the internal combustion engine 2 ignites, The corresponding torque can therefore be provided by the electric machine 3, which also drives the motor vehicle, or by another, For the former case, ie that the torque is provided by the electric machine 3, which also drives the motor vehicle, it is also conceivable to replace the term "towing" by the term "towing". Basically, however, applies here that the term "towing" should include both cases above. Furthermore, the term "towing" includes revving up the internal combustion engine and / or maintaining the internal combustion engine at a target speed.

In particular, towing may be terminated when an engine towing time of more than 30 seconds or 10 seconds or even just 5 seconds has been reached. This can also be done in combination with exceeding a minimum speed of the engine 2. Furthermore, the towing can be terminated when the oil pressure, for example in a crankcase or in a cylinder head exceeds a pressure threshold of 0.3, 0.6, or in particular 1, 2 bar. This pressure threshold should be exceeded in particular for at least 5, in particular 10, preferably 20 seconds.

Further towing launches may result in cumulative

Friction work of the towed internal combustion engine, a conveyed oil volume or a be predefined oil temperature increase. If the drive of the co-rotating internal combustion engine with a slipping separating clutch K0, however, high clutch slip speeds may result at high rotational speeds of the electric machine 3. In a preferred embodiment, co-rotation or towing of the internal combustion engine 2 takes place as long as the clutch slip does not exceed 2,000, in particular 1,500, 1,000, preferably 500 revolutions per minute.

The disadvantages mentioned above are now avoided in that the towing is carried out in a deceleration phase of the motor vehicle. This has the advantage that in particular no additional electrical energy from the energy store 4, for example, the battery 5 must be used. Although this also the Rekuperationspotential is reduced by the drag torque of the engine 2, this is effective but cheaper than the removal of energy from the battery 5 and the electric energy storage 4 during towing. Furthermore, the ride comfort is enhanced by the fact that the towing operation does not take place at low speeds, but during the deceleration phase of the motor vehicle, which may not be so important rotational irregularities are so significant. Preferably, this is done

Towing (or entrainment) at a speed that is above the resonance speed of the dual-mass flywheel.

In Fig. 2, which shows the prior art, the speed 14 and the exemplary are

Torque 15 of the electric machine 3 shown. It is also the speed 16 and the torque 17 of the engine 2 shown. In the deceleration phase, braking energy is converted into electrical energy by means of the electric machine 3. The electric machine 3 serves as a generator. This electrical energy is stored in the electrical energy storage 4, in particular in the battery 5. The electric machine 3 here provides a negative torque for the recuperation or generation of electrical energy, i. In this case, a recuperation occurs.

At the times t1 and t2, gear recirculations are made, for example from 4th gear to 3rd gear and from 3rd gear to 2nd gear. It occurs at the downshift, i. to the

Momentary t1 and t2 short-term torque increases 20. If no towing of the engine 2 is required, the internal combustion engine 2 in the

Deceleration phase decoupled by opening the clutch K0 to the

Increase recuperation potential. At time t4, the vehicle is at a standstill. In Fig. 3 and 4, the corresponding courses after execution of the method according to the invention for two variants are shown. Here, the internal combustion engine 2 is coupled to the drive train by closing the separating clutch K0 at the time t0. After this

At time tO, the internal combustion engine 2 is towed without combustion of fuel. In order to keep constant the deceleration effect on the wheel with a constant brake pedal actuation, the recuperation torque of the electric machine 4 is preferably reduced. A short-term torque intervention 21 of the electric machine 3 at the time t0 takes place, in particular, in order to compensate for the high speed turning of the internal combustion engine 2 in a torque-neutral manner.

There are now two embodiments possible and illustrated:

In the first embodiment (see Fig. 3), the slip of the separating clutch K0 during towing or during the pre-acceleration of the internal combustion engine 2 in about 0 or is below an upper limit of 50, preferably 20, preferably 5 revolutions per minute. It is also conceivable to completely close the separating clutch with a slip of "0." The speed curve 18 of the internal combustion engine 2 approaches by closing the separating clutch K0 and taking place in parallel

Torque engagement of the electric machine 3 quickly substantially the rotational speed 14 of the electric machine 3 at. Because the slip of the separating clutch K0 is extremely low here, only a slight load on the separating clutch K0 occurs due to heat input. As a result, the wear of the clutch K0 is minimized. Due to the varying speed

18 of the internal combustion engine 2 in the periods tO to t1 and t1 to t2 and t2 to t3 are also different drag torques or torques 17 of the

Internal combustion engine 2.

In the second embodiment (see Fig. 4), the slip at the separating clutch K0 is set such that the rotational speed 19 of the internal combustion engine 2 is substantially constant between the times t0 and t3. Substantially constant here means that the speed

19 of the internal combustion engine 2 is maintained in a speed range around a target speed. This can differ by preferably +/- 150 revolutions per minute, preferably +/- 50 revolutions per minute, in particular +/- 20 revolutions per minute from the target rotational speed. A uniform speed during towing is special

low-wear for the internal combustion engine 2. The fact that the speed 19 of the

Internal combustion engine 2 in the period tO to t3 is substantially constant, results As a result, a substantially constant drag torque or torque 17 of the internal combustion engine 2 during this period.

At time t3, the separating clutch K0 is now opened and the internal combustion engine 2 decoupled. The recuperation torque is again increased accordingly. The decoupling takes place when the electric machine 3 and thus the internal combustion engine 2 fall below a minimum speed threshold. This speed threshold can be defined for example by the resonance speed of an upstream dual-mass flywheel plus a distance value. The operation with very low engine speeds can also with strong

Rotationsleichformigkeiten be afflicted, which would disadvantage the ride comfort. Therefore, it is advantageous to carry out the towing at higher speeds.

Preferably, the internal combustion engine 2 is towed in a certain speed range of the electric machine 3. The speed range can in particular be between 1100 and 700 revolutions or between 1600 and 600 revolutions per minute. The coupling times for the coupling and uncoupling of the internal combustion engine 2 then arise in particular when the corresponding speed values 14 are undershot during the deceleration phase. The method can be used successively, in particular in several deceleration phases, in order to ensure adequate lubrication of the friction points

sure.

LIST OF REFERENCE NUMBERS

Hybrid propulsion system

internal combustion engine

electric machine

electrical energy storage

battery

clutch

transmission

Engine control unit

E-machine control device

Transmission Control Module

Battery Management System

charger

bus

Speed of the electric machine

Torque of the electric machine

Speed of the internal combustion engine

Torque of the internal combustion engine

Speed curve of the internal combustion engine (closed disconnect clutch) Speed curve of the internal combustion engine (with slipping disconnect clutch) Torque increase (downshift)

Torque increase (towing) Disconnect clutch

Claims

claims

A method for controlling and / or regulating a hybrid drive assembly (1) of a

Motor vehicle, with an internal combustion engine (2), with at least one electric machine (3), with an electrical energy store (4) and with a separating clutch (KO), wherein the internal combustion engine (2) by means of the separating clutch (KO) can be switched and disconnected, wherein the motor vehicle is driven purely electrically by the electric machine (3) during an electric driving operation, and wherein the

Internal combustion engine (2) at least temporarily without combustion of fuel

is towed, characterized in that the towing the

Internal combustion engine (2) is carried out in a deceleration phase of the motor vehicle.

2. The method according to claim 1, characterized in that the towing by

at least partial closing of the separating clutch (KO) takes place.

3. The method according to claim 1 or 2, characterized in that during the

Towing a short-term torque intervention of the electric machine (3) takes place, in particular to compensate for the spin-up of the internal combustion engine (2) radmomentenneutral.

4. The method according to claim 1 to 3, characterized in that when towing the clutch (KO) is slipping operated, wherein the rotational speed of the internal combustion engine (2) is kept almost constant, that is, the speed of the internal combustion engine (2) is no longer as +/- 150 revolutions per minute, in particular +/- 50 revolutions per minute, in particular +/- 20 revolutions per minute deviates from a target speed.

5. The method according to the preceding claim, characterized in that

Towing the internal combustion engine (2) to a target speed of at least 400, in particular 600, preferably 800, more preferably 1,000, more preferably 1,200, more preferably accelerates 1500 revolutions per minute and then operated towed.

6. The method according to claim 4 or 5, characterized in that the slip of the separating clutch (KO) 2000 revolutions per minute, in particular 1500 revolutions per minute, preferably does not exceed 500 revolutions per minute.

7. The method according to claim 1 to 3, characterized in that the towing by closing the separating clutch (K0) takes place, wherein the slip of the separating clutch (K0) under 50 revolutions per minute, less than 20 revolutions per minute, in particular less than 5 revolutions per minute or the separating clutch (K0) is completely closed (slip = "0").

8. The method according to any one of the preceding claims, characterized in that the hybrid drive assembly (1) a dual mass flywheel and / or a

Torsionsdämpfer having, wherein when towing the speed of the internal combustion engine (2) above a resonance speed of the dual mass flywheel or the

Torsionsdämpfers lies.

9. The method according to any one of the preceding claims, characterized in that the towing in a certain speed range of the electric machine (3), wherein when falling below an upper speed limit, the separating clutch (K0) is at least partially closed and falls below a lower speed limit, the separating clutch (K0) is opened.

10. The method according to the preceding claim, characterized in that the upper speed limit at about 1 .100 revolutions per minute, and the lower

Speed limit at about 700 revolutions per minute or the upper speed limit at about 1600 and the lower speed limit is about 600 revolutions per minute.

1 1. The method according to any one of the preceding claims, characterized in that in the deceleration phase by means of the electric machine (3) braking energy in an electrical energy storage (4), in particular in a battery (5) is stored, whereby a Rekuperationsmoment occurs and / or that the deceleration effect is kept constant at a constant brake pedal operation, that the

Rekuperationsmoment the electric machine (3) when towing the

Internal combustion engine (2) is reduced.

12. The method according to any one of the preceding claims, characterized in that at the beginning of towing a momentary torque increase (20) of the electric machine (3) takes place in order to accelerate the internal combustion engine (2).

13. The method according to any one of the preceding claims, characterized in that the towing is terminated when a towing time of more than 30 seconds, more than 10 seconds or more than 5 seconds has been reached and / or a minimum speed has been exceeded.

14. The method according to any one of the preceding claims, characterized in that the towing is terminated when an oil pressure, in particular in a crankcase or in a cylinder head a threshold of 0.3 bar, in particular 0.6 bar, preferably 1, 2 bar exceeded is for a period of at least 5, preferably 10, in particular 20 seconds.

15. The method according to any one of the preceding claims, characterized in that the engine temperature is measured, wherein the internal combustion engine (2) is towed when the measured temperature less than 20 degrees, in particular less than 10 degrees, preferably less than 0 degrees , more preferably less than -10 degrees.