DE102007052737A1 - Start-up method for an internal combustion engine in a hybrid drive train uses an electric motor and an internal combustion engine linked to the electric motor via a clutch - Google Patents

Abstract

Progression is measured for torque in an electric motor (EM) and an internal combustion engine (ICE) in a hybrid drive train during a start-up process. An X axis gives the time in seconds. A Y axis gives torque in Newton meters (Nm) in the electric motor and the internal combustion engine. The Y axis also gives the electric motor's speed (n) and that of the internal combustion engine as well as the position of a clutch. Clutch engagement process is started with generating a start signal through a control device. An independent claim is also included for a hybrid drive train with an electric motor, an internal combustion engine linked to the electric motor via a clutch and a unit for controlling the hybrid drive train.

Description

The The present invention relates to a method for starting at least an internal combustion engine of a hybrid drive train, wherein the Hybrid powertrain at least one electric motor and at least one via a Coupling with the electric motor connectable combustion engine. Furthermore, the invention relates to a hybrid powertrain with at least an electric motor and at least one via a coupling with the electric motor connectable internal combustion engine and with a control unit for controlling of the hybrid powertrain.

Out In the prior art, hybrid powertrains are well known. One Hybrid drive represents a combination of different drive principles for one Drive task within an application dar. As drive principles are usually in a hybrid drive at least one electric motor and an internal combustion engine or an internal combustion engine used.

One Hybrid drive becomes common used to operate a vehicle. In a hybrid drive with an internal combustion engine and an electric motor, the internal combustion engine in a very cheap Efficiency range are operated. Accumulating excess energy of the internal combustion engine can over a Generator for the battery charge can be used. Working while accelerating Combustion and electric motor in common. When braking and in overrun mode Part of the braking energy can be returned to the battery. If no drive power is required, for example, when the vehicle is at a standstill or when fully charged Battery, the internal combustion engine can be switched off. The electric motor can take over the function of a conventional starter. The electric motor already sets the maximum torque when starting to disposal, but leaves higher Speed in torque after. An internal combustion engine delivers against it from a certain speed range high torque. By combination Of the two drive principles, a vehicle can be about 10-20% faster be accelerated. The hybrid drive makes it possible to use the internal combustion engine under cheaper Operate conditions, for example in an optimal speed range, because the electric motor for the the combustion engine unfavorable Operating areas can cushion. The performance characteristics of an electric motor and an internal combustion engine itself, because the lower torque of an internal combustion engine in the lower Speed range offset by the high torque of the electric motor becomes. A hybrid drive can also only driven purely electrically become.

From the DE 37 37 192 C2 a hybrid drive for a motor vehicle is known in which the hybrid drive has an internal combustion engine and an electric motor designed as an asynchronous machine. The electric motor can be connected via a first clutch to a crankshaft of the internal combustion engine and with a second clutch to the transmission input shaft. The combustion engine does not have its own flywheel. Instead, the rotor of the electric motor is useful as a flywheel for the internal combustion engine when the first clutch is closed. The electric motor assumes the function of the starter of the internal combustion engine in the hybrid drive. For this purpose, the electric motor is brought to a relatively high speed when the first clutch is open, so that a high torque is generated in the rotating flywheel of the electric motor. After reaching the high torque, the first clutch between the electric motor and the engine is jerky closed, so that the engine is pulled up above the starting speed, and then continue to run independently. The Indian DE 37 37 192 C2 described hybrid drive can be operated such that a purely electric motor drive, a purely internal combustion engine drive or a simultaneous drive takes place. However, the jerky rupture of the internal combustion engine has the disadvantage that it comes to unwanted speed fluctuations on the electric motor. Furthermore, two clutches are needed, which leads to high costs.

From the DE 43 23 601 A1 is one compared to DE 37 37 192 C2 simplified or more compact hybrid drive disclosed. The hybrid drive described there requires no more two clutches, but only a clutch that makes the connection between the engine crankshaft and the drive shaft switchable. The stator of the electric motor is fixedly connected to the housing of the internal combustion engine or the associated gearbox, while the rotor of the electric motor rotatably seated on the transmission input shaft. The starting of the internal combustion engine can in the hybrid drive according to the DE 43 23 601 A1 done in two ways. At standstill of the vehicle and at zero position of the gearbox, the crankshaft can be accelerated together with the transmission input shaft and ignited the engine with the clutch closed due to the high engine torque of the electric motor. The starting process may also be such that the clutch is initially open and the hybrid vehicle is accelerated purely electric motor to a suitable minimum speed. That is, the electric motor generates a torque which is transmitted to the transmission input shaft. Upon reaching a certain torque of the electric motor, the clutch is closed, so that the Internal combustion engine is accelerated to the starting speed.

Starting from the DE 43 23 601 A1 As the closest prior art, the present invention seeks to improve the starting process of at least one internal combustion engine of a hybrid drive train, so that a torque fluctuation-free transition is made possible from a purely electrical operation in a pure engine operation or a combined operation. In particular, a speed fluctuation due to an engine start at the electric motor and thus at the transmission input shaft while driving should be avoided.

These The object is achieved by a Method for starting at least one internal combustion engine of a hybrid drive train with the features according to the independent claim 1 and by a hybrid powertrain having the features of the independent claim 8 solved. Further advantages, features, details, aspects and effects of the invention emerge from the subclaims, the drawing and the description. Features and details that in connection with the method for starting at least one internal combustion engine a hybrid powertrain according to claim 1 described, of course, apply in context with the hybrid powertrain according to the invention according to the claim 8, and vice versa.

• a) der Elektromotor wird mit einem ersten Drehmoment gefahren,
• b) mit der Erzeugung eines Startsignal durch ein Steuergerät wird der Schließvorgang der Kupplung gestartet, wobei während des Schließvorganges der Kupplung das Drehmoment des Elektromotors von dem ersten Drehmoment hochgefahren wird,
• c) durch das Schließen der Kupplung wird das zusätzlich zu dem ersten Drehmoment erzeugte, ansteigende Drehmoment auf den Verbrennungsmotor übertragen, wobei sich die Abtriebsdrehzahl des Verbrennungsmotors der Abtriebsdrehzahl des Elektromotors annähert,
• d) nach dem Erreichen einer vorgegebenen Drehzahl des Verbrennungsmotors wird das Drehmoment des Elektromotors auf ein Drehmoment, welches der Summe des Soll-Antriebsmomentes und des Schleppmomentes des Verbrennungsmotors, welches benötigt wird, um den Verbrennungsmotor auf der erreichten Drehzahl zu halten, entspricht, heruntergefahren und der Verbrennungsmotor gezündet, e) mit Beginn des Selbstlaufes des Verbrennungsmotors wird das Drehmoment des Elektromotors um das Schleppmoment verringert sowie das Drehmoment des Verbrennungsmotors hochgefahren und synchron zur Erhöhung des Drehmomentes des Verbrennungsmotors wird das Drehmoment des Elektromotors zurückgefahren, gelöst.

The object is according to the first aspect of the invention by a method for starting at least one internal combustion engine of a hybrid drive train, wherein the hybrid powertrain comprises at least one electric motor and at least one connectable via a clutch to the electric motor internal combustion engine, wherein the method by the following steps is characterized:

• a) the electric motor is driven with a first torque,
• b) with the generation of a start signal by a control unit of the closing operation of the clutch is started, wherein during the closing operation of the clutch, the torque of the electric motor is raised from the first torque,
• c) by closing the clutch, the increasing torque generated in addition to the first torque is transmitted to the internal combustion engine, wherein the output speed of the internal combustion engine approaches the output speed of the electric motor,
• d) after reaching a predetermined speed of the internal combustion engine, the torque of the electric motor to a torque which corresponds to the sum of the desired drive torque and the drag torque of the internal combustion engine, which is required to keep the internal combustion engine at the achieved speed, shut down and ignited the engine, e) with the beginning of the self-running of the internal combustion engine, the torque of the electric motor is reduced by the drag torque and the engine torque is ramped up and synchronously to increase the torque of the engine, the torque of the electric motor is reduced, solved.

First serves only the at least one electric motor as a drive, for example a motor vehicle. That is, it becomes a first torque of the Electric motor delivered to the drive train, which to fulfill the Target drive torque due to a driver-side power specification, such as for example, an accelerator pedal position, is used. The first torque corresponds to a limit torque or a limit torque range, from its performance-related excess initiated the process for switching on the engine becomes. That is, the first torque does not necessarily provide one Limit amount, but may be in a range of torque, within which the power electronics the method for connecting of the internal combustion engine initiates. The size of the first torque depends, for example, on how fast, e.g. by "kick-down" the accelerator accelerates is or is being driven uphill or in the plane. One low battery level, the limit torque may also be out. After reaching the first torque, preferred a relatively constant torque, the electric motor is the closing operation the clutch started while being of the closing process the coupling torque of the electric motor of the first torque is raised.

This generated on the part of the electric motor in addition to the first torque, advantageously linear or approximately linear, increasing torque is transmitted to the internal combustion engine when closing the clutch. Due to the linear or approximately linear increase in the transmitted torque of the electric motor, the output rotational speed of the internal combustion engine is brought closer to the output rotational speed of the electric motor, in particular without jerking continuously. The output speed of the internal combustion engine and the output speed of the electric motor correspond to the speed of the respective unit to the transmission input shaft. In this case, for example, intermediate planetary gear can be part of the unit. That is, the output speeds are the speeds of the respective motors on the transmission input shaft, which in particular with regard to the electromobility Tor can also be connected via, for example, planetary gear. Furthermore, a linear slope of the torque is particularly easy electronically controlled.

Becomes reaches a predetermined speed of the engine is the torque of the electric motor to a torque which is the sum the desired drive torque and the drag torque of the internal combustion engine that is needed to keep the combustion engine at the speed reached, corresponds, shut down and ignited the internal combustion engine. The Target drive torque is the torque required to implement the accelerator pedal position is. It is usually not constant as it is the performance target the driver over the accelerator or the specification of the speed-cruise control corresponds. Already during This method may change the desired drive torque, for example by a changed Accelerator pedal position or when driving uphill or downhill. Until the start the method for starting the internal combustion engine becomes the target torque solely applied by the electric motor. The desired torque can also by possible switching operations an automated transmission during operation of this Be affected method at least briefly.

that is, to start the self-running of the internal combustion engine increases from the Internal combustion engine generated torque down to an amount that that Drag torque to maintain the engine speed on Zero sinks. The internal combustion engine is running at synchronous speed E-motor without giving up power to the powertrain or receive. The electric motor no longer drags the combustion engine With. The drag torque is the part of the torque of the electric motor, which this applies to the non-ignited internal combustion engine to bring the predetermined speed or at the predetermined speed to keep. After the ignition of the Internal combustion engine is the torque of the electric motor to exactly This drag torque is reduced because the engine starts to run on its own and thus generates its own torque. Ignition of the internal combustion engine means fuel injection into the internal combustion engine. With beginning the internal combustion of the internal combustion engine is the torque of Engine started up and synchronous to increase the Torque of the engine is the torque of the electric motor scaled back. That is, the torque of the electric motor becomes exactly the same Amount shut down to the torque of the internal combustion engine elevated becomes. This leaves the total torque, i. the sum of Torques of the electric motor and the internal combustion engine, constant. It is particularly preferred if the torque of the internal combustion engine is ramped up continuously.

By the inventive method for Starting at least one internal combustion engine of a hybrid drive is the starting process of the hybrid powertrain improved such that a torque fluctuation-free transition of a purely electrical operation in a pure engine operation or a combined operation is possible. A speed fluctuation on the electric motor as a result of the engine start and thus on The transmission input shaft of the hybrid drive can through the previously described method can be avoided. Through the process can a starter for starting the internal combustion engine are omitted, whereby costs and installation space can be saved.

By such a method may be that of the two motors, i. from the electric motor and the internal combustion engine, output torque kept the transmission input shaft of the hybrid drive constant be simultaneously with the internal combustion engine is started. The torque output to the transmission input shaft is made first by the Electric motor and in the further course of the starting process of the internal combustion engine. That is, first, the hybrid drive is operated purely by electric motor and at the end of the starting process, the hybrid drive is purely internal combustion engine or partly driven by an electric motor and partly by an internal combustion engine. In this method, the engine can be switched smoothly become. This is done by the special procedure of the process. During the closing process the coupling becomes the torque curve, i.e. that in the electric motor generated torque, ramped up linearly or approximately linearly. The closing process the coupling, i. the closing path the clutch over the time, is tuned in such a way that the starting of the internal combustion engine, i.e. that bringing the engine to same speed as the electric motor, no waste of the on the transmission input shaft acting drive torque has the consequence. The one to crank and spin up required of the internal combustion engine Moment flux corresponds to the linear or approximately linear torque increase on the electric motor. Thus, when closing the clutch, the electric motor on one during the closing process almost Constantly increasing torque output is set and this increase of torque over the Continuously transfer the clutch to the combustion engine. The closing process The clutch is controlled in such a way that in each case that of the electric motor in addition at this time transmitted generated torque will, but not anymore. As a result, the internal combustion engine is jerk-free switched on.

During the entire starting phase is the torque output of the electric motor controlled insofar as the first of the omission of the drag torque for the Internal combustion engine back is regulated and with increasing torque output of the internal combustion engine to the drive train, the torque output of the electric motor on scaled back becomes. Overall, acting on the transmission drive train Performance, i. the transmitting torque, the two motors kept constant, which, for example, a constant Accelerator pedal position of a motor vehicle corresponds.

All in all the torque output curve of the electric motor should be within the entire Time window from the start of Entrainment of the engine to self-driving / alone Driving on the part of the internal combustion engine are controlled so that the Torque delivered thereby continuously almost the requirement corresponds on the part of the accelerator pedal.

With The beginning of the self-running of the internal combustion engine becomes the torque generation of the internal combustion engine gradually started up and the corresponding reduction of the drive of the vehicle remaining electric motor torque gradually lowered accordingly. It is used in this process to start the hybrid powertrain a sudden or unsteady torque jump on the part of the internal combustion engine at least from the point of no-load self-circulation avoided. In particular, flat ramps are considered torque changes for the electric motor and the internal combustion engine selected such that the added total torque line is nearly linear or at least free of torque jumps is.

The inventive method allows the simple starting of an internal combustion engine of a hybrid powertrain while the driving of the electric motor of the hybrid drive train. That is, a Hybrid powertrain is usually initially only by an electric motor driven. As soon as a signal for starting the internal combustion engine comes, the steps of the method described above are carried out. The Signal for starting the internal combustion engine may e.g. through a Performance call made by a driver of a motor vehicle, i.e. by accelerating when the power of the electric motor is not sufficient. It is also possible to start the internal combustion engine when a battery of the motor vehicle is almost empty, so this through the internal combustion engine again can be loaded.

Prefers is it when during of the closing process the coupling torque of the electric motor of the first torque linear or approximate ramped up linearly. The linear ramp-up of torque of the electric motor allows a particularly simple control of the closing process of the clutch. That the torque curve of the electric motor describes a linear or nearly linear increase during the closing process the clutch.

Prefers is a method for starting a hybrid powertrain, at the predetermined speed of the engine in a range between 85% to 100%, especially at about 95%, the speed of the Electric motor is located. In reaching such a high speed of the internal combustion engine becomes the coupling between the electric motor and the internal combustion engine completely closed, whereby in the remaining closing way, that can approx. 40% of the Clutch closing path be, no controlled control of the closing speed takes place more. That is, to the complete Shut down the clutch does not have to be considered more taken on the controlled torque build-up of the clutch become. It can be for the rest of the way a maximum closing speed the Kupplungsaktuatorik selected become. In this range of about 95% speed equality between electric motor and internal combustion engine becomes the increased electric motor torque down to an amount that corresponds to the current performance requirement. The current power request, i. the torque request or load request is made, for example, from the predetermined vehicle speed requirement, Here is the load according to the accelerator pedal position or during cruise control meant the set speed, and the negative current Engine torque, i. the internal combustion engine is dragged along empty on the corresponding electric motor speed, together.

Further is such a method advantageous in which after reaching the predetermined speed of the internal combustion engine, in particular at 95% of the electric motor speed, the clutch with maximum closing speed to achieve a 100% speed equality between the electric motor and the internal combustion engine is closed. To completely close the Coupling is no longer necessary control, so that preferably a maximum closing speed chosen can be.

A method for starting a hybrid powertrain, in which the transmission of the torque or a part of the torque of the electric motor to the internal combustion engine by means of a friction clutch, is particularly preferred. Such a friction clutch is switchable "during operation" of the hybrid drive train, ie, the clutch can be actuated to transmit an existing torque to the electric motor become. With such a friction clutch, in the closed state of the friction clutch, the energy of the electric motor can be transmitted to the internal combustion engine almost loss-free, ie with the same torque and speed itself. Particularly suitable is a dry friction clutch.

The Shut down the clutch, in particular the friction clutch, is preferably carried out hydraulically. A hydraulically actuated clutch worked exclusively with fluid friction and, except for an oil change, Maintenance and wear-free.

In another preferred embodiment of Procedure is closing the clutch, in particular the friction clutch, electronically. That the closing The clutch is electronically controlled by a clutch electronics.

Prefers is further a method in which that of the electric motor and / or the torque generated by the internal combustion engine to the Hybrid powertrain, in particular to a transmission input shaft, is delivered. During the Starting an internal combustion engine of the hybrid powertrain is the torque generated by the electric motor and the internal combustion engine at least partially and temporarily transferred to the transmission input shaft of the hybrid drive train. Of the Starting process of the internal combustion engine is carried out such that the torque output of the electric motor and / or the internal combustion engine to the transmission input shaft during the starting of the internal combustion engine is kept constant. Out For this reason, the torque of the electric motor is temporarily increased until the internal combustion engine itself generates enough torque. For this Reason becomes after the self-running of the internal combustion engine with rising Torque of the internal combustion engine, the torque synchronously to the same extent scaled back.

According to the second Aspect of the invention is the object by a hybrid powertrain with at least one electric motor and at least one via a Clutch with the electric motor connectable combustion engine and with a control unit for controlling the hybrid drive train, wherein the control unit means for carrying out the previously described Has method solved. Such a hybrid powertrain allows an improvement of the Starting operation of at least one internal combustion engine of a hybrid drive train, so that a torque fluctuation-free transition from a purely electrical Operation in a pure engine operation or a combined operation can be done. By such a hybrid powertrain can a speed fluctuation due to an engine start on Electric motor and thus avoided at the transmission input shaft. The connection of the internal combustion engine can by the control unit smoothly.

The Torque output curve of the electric motor can in such a Hybrid powertrain within the entire time window, i. from the beginning of the entrainment of the internal combustion engine until autonomous driving / alone driving on the part of the internal combustion engine, so controlled that the delivered Torque here constantly almost the requirement on the part of the accelerator pedal of a motor vehicle equivalent.

With The beginning of the internal combustion of the internal combustion engine is controlled by the control unit the torque generation of the internal combustion engine starts up gradually and the corresponding reduction of remaining to drive the vehicle e-motor torque gradually lowered accordingly. A sudden or unsteady torque jump on the part of the internal combustion engine at least from the point of no-load self-circulation is avoided. In particular, when flat ramps as torque changes for the electric motor and the Combustion engine selected be, the added total torque line is almost linear or at least free of torque jumps.

Prefers is also a hybrid powertrain, wherein the clutch is formed as a friction clutch is. The friction clutch can be closed, if already a first torque is applied to the electric motor. The friction clutch can hydraulically over Valves or electronically controlled by the control unit. A hydraulically operated Clutch worked exclusively with fluid friction and, except for an oil change, Maintenance and wear-free. Especially suitable is a dry friction clutch used.

Of the closing the clutch is tuned by the control unit such that the Ignition of the internal combustion engine does not waste the on the transmission input shaft acting drive torque of the electric motor has the consequence.

The closing operation of the friction clutch is controlled by the control unit in such a way that the torque flow required for starting up the internal combustion engine corresponds to the linear torque increase or the almost linear torque increase at the electric motor. Due to its performance, ie with regard to its controllability, the clutch electronics can represent a ramp / curve when the friction clutch closes, which corresponds to the increase / increase in the torque output at the electric motor. When closing the friction clutch of the electric motor is set to a nearly constant increasing torque output and transmit the increase of torque via the friction clutch to the engine. That is, the closing operation of the friction clutch is controlled by the control unit of the hybrid drive train such that each of the additional torque generated by the electric motor at this time is transmitted to the engine, but not more. As a result, the internal combustion engine is switched smoothly.

Of the Hybrid powertrain is preferably designed such that the Electric motor and the at least one internal combustion engine are connected in series. It can Also be provided several electric motors.

The Invention will now be described with reference to an embodiment with reference explained in more detail in the accompanying drawings. Show it:

1 the schematic course of the torque curves and the rotational speed curves of the electric motor and the internal combustion engine during the starting process of the internal combustion engine of a hybrid drive train;

2 a schematic theoretical flow of the torque curves of the electric motor and the internal combustion engine during the starting process of the internal combustion engine of a hybrid drive train;

3 a schematic theoretical sequence of the speed curves of the electric motor and the internal combustion engine during the starting process of the internal combustion engine of a hybrid drive train.

In 1 the schematic course of the torque curves of an electric motor EM and an internal combustion engine ICE of a hybrid drive train during the startup process is shown. The X-axis indicates the time in seconds. The Y axis indicates the torque in Newton meters Nm of the electric motor EM and the internal combustion engine ICE. Further, the Y-axis indicates the rotational speed n of the electric motor EM and the internal combustion engine ICE and the position x of the clutch.

The Curve 1 sets the target torque curve of the internal combustion engine ICE dar.

The Curve 4 represents the actual torque curve of the internal combustion engine ICE represents.

The Curve 2 represents the desired torque curve of the electric motor EM.

The Curve 3 represents the actual torque curve of the electric motor EM.

The Curve 5 shows the position of the clutch.

The Curve 6 represents the actual speed curve of the electric motor EM.

The Curve 7 represents the actual speed curve of the internal combustion engine ICE represents.

at a time of 5 seconds, the electric motor EM has a first Actual torque of approx. 120 Nm. The hybrid powertrain is driven purely electrically at this time. When the command to Starting the internal combustion engine comes from a control unit, becomes the closing process the clutch started while being of the closing process the clutch, the torque 3 of the electric motor EM of the first Actual torque is linear or approximate ramped up linearly. By closing the clutch is the addition to generated the first actual torque, linear or approximately linear transmit increasing torque 3 to the ICE internal combustion engine, wherein the speed 7 of the internal combustion engine ICE after a delay of approx. 1.3 seconds approximates the speed 6 of the electric motor EM. To reaching a given speed, here about one speed of almost 1,500 revolutions per minute, the internal combustion engine ICE, The torque of almost 300 Nm of the electric motor EM is on Torque of almost 200 Nm, which is the sum of the first torque of 120 Nm and the drag torque of the electric motor of about 80 Nm, which needs is to the internal combustion engine ICE at the achieved speed of about 1500 revolutions per minute, equals, shut down, and the internal combustion engine ICE ignited. After the ignition of the Internal combustion engine ICE after about 6.85 seconds, the current Torque of almost 200 Nm of the electric motor EM to the drag torque in height reduced by 80 Nm. Furthermore, with the beginning of the self-running of the Internal combustion engine ICE the torque 4 of the internal combustion engine ICE continuously from a value of 0 Nm up to a value of approx. 120 Nm raised after 7.2 seconds. Synchronous to increase the torque 4 of the internal combustion engine ICE becomes the torque 3 of the electric motor from a value of approx. 120 Nm back to a value of 0 Nm.

In the diagram shown 1 the ignition / the fuel injection, ie the self-running of the engine, takes place, for example, when the synchronous speed between the electric motor EM and the internal combustion engine ICE is reached. The synchronous speed is achieved here at 90% speed equality. By Be Beginning of the self-running of the internal combustion engine ICE increases the torque generated by the internal combustion engine ICE 4 to an amount that the drag torque of the electric motor EM to maintain the engine speed 7 decreases to zero. The internal combustion engine ICE runs at synchronous speed to the electric motor EM without, however, delivering or receiving power to the hybrid powertrain. The electric motor EM no longer tows the internal combustion engine ICE from this point on. The internal combustion engine ICE further increases, in particular continuously, its generated torque 4 and outputs this to the hybrid drive train, ie to the transmission input shaft from. During this overall phase, the torque output of the electric motor EM is controlled to the extent that the first omission of the drag torque for the internal combustion engine ICE is controlled back and with increasing torque output of the internal combustion engine ICE to the drive train, the torque output of the electric motor EM is further reduced. Overall, the force acting on the hybrid powertrain output, the output torque, the two motors should be consistent with the accelerator pedal position of a motor vehicle. That is, with a constant "accelerator pedal position", the sum of the torques of both motors acting on the transmission input shaft is kept constant.If the vehicle is then accelerating, the speed of the transmission input shaft but not the torque request changes, except for a torque-dependent torque request, eg At high speed as component protection, a reduction / limitation of the maximum torque.

All in all should the torque output curve of the electric motor EM within the entire time window from the start of entrainment of the internal combustion engine ICE until self-employed Running / alone driving on the part of the internal combustion engine ICE so be controlled by the method that the output torque here continually almost corresponds to the requirement on the part of the accelerator pedal.

With Start of the self-running of the internal combustion engine ICE is the torque generation 4 of the internal combustion engine ICE gradually started up and the corresponding reduction of remaining for driving the vehicle Electric motor torque 3 gradually lowered accordingly. It will be a sudden or unsteady torque jump on the part of the internal combustion engine ICE at least from the point of no-load Self-avoidance avoided. By choosing a flat ramp as torque changes 3 for the Electric motor EM and the ICE engine, is the added Total torque line 3 + 4 almost linear or at least free of Torque jumps.

The 2 shows a schematic theoretical flow of the torque curve 12 of the electric motor EM and the torque curve 14 of the internal combustion engine VM (ICE) during the starting process of the internal combustion engine VM of a hybrid drive train. In
3 a schematic theoretical sequence of the speed curve 26 of the electric motor EM and the speed curve 27 of the internal combustion engine VM during the starting process of the internal combustion engine VM of a hybrid drive train is shown. In both 2 and 3 Furthermore, the clutch travel 15, 25 of the clutch is schematically dargstellt.

Claims (14)

Method for starting at least one internal combustion engine a hybrid powertrain, wherein the hybrid powertrain at least one electric motor and at least one over a clutch with the electric motor connectable internal combustion engine characterized by the following steps: a) the electric motor is driven with a first torque, b) with production a start signal by a controller becomes the closing operation the clutch started while being of the closing process the coupling torque of the electric motor of the first torque being started up, c) by closing the clutch is in addition to transmitted to the first torque generated, increasing torque to the engine, wherein the output speed of the engine of the output speed approaching the electric motor, d) after reaching a predetermined speed of the internal combustion engine is the torque of the electric motor to a torque, which the sum of the nominal drive torque and the drag torque of the Internal combustion engine, which needs is to keep the internal combustion engine at the achieved speed, corresponds, shuts down and ignites the combustion engine, e) with the start of the self-running of the internal combustion engine, the torque the electric motor is reduced by the drag torque and the torque of the Engine started up and synchronous to increase the Torque of the engine is the torque of the electric motor scaled back. Method according to claim 1, characterized in that that while of the closing process the coupling torque of the electric motor of the first torque linear or approximate ramped up linearly. A method according to claim 1 or 2, characterized in that the predetermined speed of the Combustion engine 85% to 100% of the speed of the electric motor corresponds. Method according to claim 3, characterized that the predetermined speed of the engine 95% of the speed of the electric motor corresponds. Method according to one of claims 1 to 4, characterized that after reaching the predetermined speed of the internal combustion engine the clutch with maximum closing speed to reach a speed equality between the electric motor and the internal combustion engine is closed. Method according to one of claims 1 to 5, characterized that the transmission of the torque or a part of the torque of the electric motor on the internal combustion engine through a friction clutch. Method according to Claim 6, characterized that the friction clutch is formed as a dry friction clutch is. Method according to one of claims 1 to 7, characterized that closing the coupling, in particular the friction clutch, hydraulically. Method according to one of claims 1 to 7, characterized that closing the clutch, in particular the friction clutch, electronically. Method according to one of claims 1 to 9, characterized that of the electric motor and / or that of the internal combustion engine generated torque to the hybrid powertrain, in particular to a transmission input shaft is discharged. Hybrid powertrain with at least one electric motor and at least one over a clutch with the electric motor connectable internal combustion engine and with a control unit for controlling the hybrid drive train, characterized in that the control unit comprises means for carrying out the Method according to one of the claims 1 to 10. Hybrid drive train according to claim 11, characterized characterized in that the coupling is designed as a friction clutch is. Hybrid drivetrain according to claim 12, characterized characterized in that the friction clutch as a dry friction clutch is trained. Hybrid drive train according to one of claims 11 to 13, characterized in that the electric motor and the internal combustion engine are connected in series.