DE102014216984A1 - transmission - Google Patents

Abstract

Transmission (G) having an input shaft (GW1), an output shaft (GW2), an intermediate shaft (WZ), a first and a second planetary gear set (P1, P2), an electric machine (EM) with a stator (S) and a with the intermediate shaft (WZ) operatively connected rotor (R), a first switching element (K2), a second switching element (B2), a third switching element (K0), a fourth switching element (K1) and a fifth switching element (B1), wherein closing the second switching element (B2) torque between the first, second and third element (E12, E22, E32) of the second planetary gear set (P2) is transferable, wherein the input shaft (GW1) via the third switching element (K0) with the intermediate shaft (WZ) connectable is, wherein the output shaft (GW2) with the second element (E21) of the first planetary gear set (P1) is constantly connected, wherein the first element (E11) of the first planetary gear set (P1) with the intermediate shaft (WZ) constantly connected and via the fourth switching element (K1) with the second element (E22) of the second planetary gear set (P2) is connectable, wherein by closing the fifth switching element (B1) either the third element (E31) of the first planetary gear set (P1) or the second element (E22) of the second Planetary gear set (P2) rotationally fixed, wherein the third element (E31) of the first planetary gear set (P1) via the first switching element (K2) to the second element (E22) of the second planetary gear set (P2) is connectable, and wherein the second element ( E21) of the first planetary gear set (P1) with the third element (E32) of the second planetary gear set (P2) either permanently connected or via the fifth switching element (B1) is connectable.

Description

The invention relates to a transmission with an input shaft, an output shaft, an intermediate shaft, a first and a second planetary gear, an electric machine with a rotor and a stator and five switching elements. The invention further relates to a hybrid powertrain for a motor vehicle, and a method for controlling such a hybrid powertrain.

A transmission referred to here in particular a multi-speed transmission in which a predefined number of gears, ie fixed gear ratios between an input shaft and an output shaft, is preferably automatically switched by switching elements. The switching elements are, for example, clutches or brakes here. Such transmissions are mainly used in motor vehicles to adapt the speed and torque output characteristics of the drive unit to the driving resistance of the vehicle in a suitable manner.

From the still unpublished patent application DE 10 2014 204 795.1 the applicant is a transmission according to the preamble of claim 1 known. In addition, the above patent application teaches a hybrid powertrain of a motor vehicle having such a transmission, and a method of controlling the hybrid powertrain.

It is a first object of the invention to provide alternative embodiments of the aforementioned transmission. Another object of the invention is to provide suitable methods for operating such a transmission in a hybrid powertrain of a motor vehicle.

The first object is achieved by the features of claim 1. The further object is solved by the features of claim 13. Advantageous embodiments will become apparent from the dependent claims, the description and from the figures.

The transmission comprises at least one input shaft, an output shaft, an intermediate shaft, a first and a second planetary gear set, an electric machine having a rotor and a stator, and a first to fifth switching element.

A planetary gear set includes a sun gear, a land and a ring gear. Rotatably mounted on the web are planet gears, which mesh with the toothing of the sun gear and / or with the toothing of the ring gear. A minus wheel set denotes a planetary gear set with a web on which the planet gears are rotatably mounted, with a sun gear and with a ring gear, wherein the toothing of at least one of the planetary gears meshes with both the teeth of the sun gear, as well as with the teeth of the ring gear, whereby the ring gear and the sun gear rotate in opposite directions of rotation when the sun gear rotates at a fixed web. A plus gear set differs from the negative planetary gear set just described in that the plus gear set has inner and outer planet gears rotatably supported on the land. The toothing of the inner planet gears meshes on the one hand with the teeth of the sun gear and on the other hand with the teeth of the outer planetary gears. The toothing of the outer planetary gears also meshes with the teeth of the ring gear. This has the consequence that rotate at a fixed land, the ring gear and the sun gear in the same direction.

Both the first and the second planetary gear each have a first, second and third element. The first element is formed by a sun gear of the respective planetary gear set. If the planetary gear set is designed as a minus wheel set, then the second element is formed by a web of the planetary gear set, and the third element by a ring gear of the planetary gear set. If the planetary gear set is designed as a plus-wheel set, then the second element is formed by the ring gear of the planetary gear set, and the third element by the web of the planetary gear set.

By closing the second switching element, a torque transmission between the first, second and third element of the second planetary gear set is enabled so that the second planetary gear set is in the power flow between the input shaft and the output shaft. If the second switching element is open, then only a rotational speed transmission takes place between the elements of the second planetary gear set. Except for minor power losses, which may be caused for example by drag losses, no power is transmitted by the second planetary gear set with the second switching element open.

The input shaft of the transmission can be connected via the third switching element with the rotor of the electric machine, which is operatively connected to the intermediate shaft. The operative connection can be realized via a direct rotationally fixed connection, or via a transmission, for example via a planetary gear set. The output shaft is permanently connected to the second element of the first planetary gear set.

According to the invention, the first element of the first planetary gear set is constantly connected to the rotor of the electric machine, and via the fourth switching element with the second element of the second planetary gear set connectable. By closing the first and fifth switching element, both the third element of the first planetary gear set and the second element of the second planetary gear set is fixed in a rotationally fixed manner. The third element of the first planetary gear set is connectable via the first switching element with the second element of the second planetary gear set. The second element of the first planetary gear set is either permanently connected to the third element of the second planetary gear set or connectable via the second switching element.

A direct connection between the sun gear of the first planetary gear set and the rotor of the electric machine simplifies in particular the bearing structure of the transmission. Usually, the rotor of an electric machine is to be stored particularly rigidly in order to keep the air gap between the rotor and the stator as constant as possible under all operating conditions. By virtue of the solution according to the invention, the rotor bearing, which is in any case required for this purpose, can also take over the bearing of the sun gear of the first planetary gear set.

By closing the first switching element, a torque transmission between the first, second and third element of the first planetary gear set is enabled so that the first planetary gear set is in the power flow between the input shaft and the output shaft. Due to the now fixed connection of the first element of the first planetary gear set to the rotor, the first switching element according to the invention is arranged in the power flow between the third element of the first planetary gear set and the second element of the second planetary gear set.

A further coupling of the two planetary gear sets is effected by a connection between the second element of the first planetary gear set and the third element of the second planetary gear set. This connection is either constantly given, or switchable via the second switching element.

Preferably, the second element of the first planetary gear set is continuously connected to the third element of the second planetary gear set, wherein the first element of the second planetary gear set via the second switching element is rotatably fixable. In this way, the accessibility of the second switching element is facilitated, in particular if the first planetary gearset is arranged spatially between the input shaft and the second planetary gearset. In this arrangement, preferably, the second and the fifth switching element are arranged radially outside of the first and second planetary gear set. In this way, the second and fifth switching element can be arranged directly on the housing of the transmission, which is located radially outside the two planetary gear sets. If the second and / or the fifth shift element are designed as hydraulically actuated band brakes, the shift elements can be easily reached by hydraulic fluid near the housing. This simplifies the hydraulic fluid guidance of the transmission.

According to an alternative embodiment, the second switching element may be arranged in the connection between the second element of the first planetary gear set and the third element of the second planetary gear set, wherein the first element of the second planetary gear set is fixed permanently rotatably. By such a rotationally fixed connection of the first element of the second planetary gear set, the centering of the transmission components can be simplified.

According to one embodiment of the invention, four forward gears between the intermediate shaft and the output shaft are preferably automatically switched by selective actuation of the first, second, fourth and fifth switching element. When the third switching element is open, torque is applied solely to the intermediate shaft by the rotor of the electric machine. When the third switching element is closed, torque is applied to the intermediate shaft either solely by means of a drive unit which is connected to the input shaft or by the drive unit and the rotor of the electric machine. The first forward speed is formed by closing the fifth switching element and the first switching element. The second forward speed is formed by closing the second switching element and the first switching element. The third forward speed is formed by closing the fourth switching element and the first switching element. The fourth forward speed is formed by closing the second switching element and the fourth switching element. As a result, with a suitable choice of the stationary gear ratio of the first and second planetary gear, a well-suited for use in the motor vehicle translation series achieved. In addition, two adjacent gears always have a switching element that is closed in both of these gears. When switching to a neighboring gear, therefore, only one switching element must be opened and a switching element must be closed. This simplifies the switching process and shortens the switching time.

Preferably, the fifth switching element is designed as a form-locking switching element. Positive-locking switching elements make the connection in the closed state by positive locking, and are characterized in the open state by lower drag losses than non-positive switching elements. Due to the low drag in the open state of the Improved efficiency of the transmission, especially since the fifth switching element is closed only in the first forward gear. The fifth switching element is therefore predominantly open during operation of the transmission in the motor vehicle. Since the fifth shift element is closed only in the first forward gear, the fifth shift element is always opened during shifts to a higher gear, but not closed. Opening a claw-switching element is considerably easier than the closing process, since when closing the claws of the jaw switching element must first engage in the gaps provided, while the claws need to be made only load-free when opening. Both processes require time, with the switching time for driving dynamic reasons should be as short as possible, especially when switching from a low gear to a higher gear. However, since the fifth switching element in switching operations in a higher gear never closed, but only needs to be opened, there is no restriction on the switching duration by the formation of the fifth switching element as a form-locking switching element.

Preferably, the first switching element is designed as a form-locking switching element. Since the first switching element is open only in the fourth and thus the highest gear, the first switching element must never be closed in a shift to a higher gear. Therefore, even with the first switching element by the formation of a form-locking switching element no restriction with respect to the switching duration. In addition, the training as a positive switching element improves the efficiency of the transmission in the fourth forward gear.

According to one embodiment of the invention, a reverse gear of the transmission is formed by reverse rotation of the rotor of the electric machine, wherein the third switching element is open and one of the four forward gears is engaged. In other words, the transmission has no reverse gear formed by a selective actuation of the first, second, fourth and fifth shift element, in which a reversal of rotation between the intermediate shaft and the output shaft is generated. Instead, the electric machine is operated so that the rotor rotates counter to a preferred direction of rotation of the input shaft. When the gear is engaged, the output shaft rotates in the same direction as the rotor. As a result of this embodiment, a switching element can be saved compared to the prior art, which reduces the complexity of the transmission and also its weight.

According to one embodiment, the third switching element is designed as a dry or wet multi-plate clutch. A multi-plate clutch consists of an inner disk carrier and an outer disk carrier, wherein a plurality of inner disks is connected to the inner disk carrier, and a plurality of outer disks is connected to the outer disk carrier. The inner plates and outer plates are arranged alternately and overlap each other. If a force is applied to the lamellae as normal to the lamella surface of the lamellae, a torque is transferred from one lamella carrier to the other lamella carrier by friction between inner lamellae and outer lamellae. The torque transmitted from one disk carrier to the other disk carrier depends on the applied force. If the force is large enough to prevent a differential speed between the inner disk and the outer disk by frictional engagement, the entire torque is transmitted. If the force is insufficient, only a part of the torque is transmitted, resulting in a difference in speed between the inner disk and the outer disk. This condition is also called slip operation. By varying the force applied to the slats, the torque transmitting capability of the first switching element is adjustable.

In an alternative embodiment, the third switching element is designed as a form-locking switching element. As a result, the efficiency of the transmission can be improved because the first switching element in the open state generates significantly lower drag losses than a frictional switching element, such as a multi-plate clutch.

The transmission may be part of a hybrid powertrain of a motor vehicle. The hybrid powertrain has in addition to the transmission on an internal combustion engine, which is connected to the input shaft of the transmission. The output shaft of the transmission is connected to an axle transmission, which is connected to wheels of the motor vehicle. The hybrid powertrain allows multiple drive modes of the motor vehicle. In an electric driving operation, the motor vehicle is driven by the electric machine of the transmission, wherein the third switching element is open. In an internal combustion engine operation, the motor vehicle is driven by the internal combustion engine, wherein the third switching element is closed. In a hybrid operation, the motor vehicle is driven by both the internal combustion engine and the electric machine of the transmission.

In some operating conditions of the motor vehicle, a generator operation of the electric machine is required, wherein the rotor is driven by the internal combustion engine. For this purpose, the third switching element is closed. are both or one of the two switching elements, by which a gear is formed, not closed, so no torque is transmitted from the input shaft to the output shaft. If the motor vehicle is to start directly in this operating state, one of the switching elements closed in the first forward gear is transferred from the open state into a slip mode, while the other of the switching elements closed in the first forward gear remains closed or closed. By the switching element located in the slip mode torque is transmitted from the input shaft to the output shaft, wherein the rotational speed of the output shaft can be changed continuously by controlling the slip operation. The operated in the slip mode switching element is designed as a non-positive switching element.

Should be changed from the electric driving operation in the internal combustion engine or hybrid operation, the internal combustion engine must be started. This is preferably realized by a tow start, in which the crankshaft of the internal combustion engine is driven by the input shaft. For this purpose, one of the first, second, fourth or fifth switching elements, which is closed at this time, transferred into a slip operation in a first process step with gear engaged and open third switching element. The switched into the slip mode switching element is designed as a non-positive switching element, which is equipped with a variable torque transmission capability. In a second method step, the torque transmission capability of the third switching element is increased. The third switching element is also designed as a non-positive switching element with a variable torque transmission capability. The switching element converted from the closed state into the slip mode serves to achieve the necessary starting rotational speed of the crankshaft in the event of a low vehicle speed and to largely decouple any torque disturbances resulting from the starting process from the output shaft.

Preferably, in the drag start described above, the first switching element is transferred to the slip mode. Since the first shift element is closed in the first, second and third forward gear, the tow start can be performed in all these gears. In addition, the first shift element transmits the entire power flow from the intermediate shaft to the output shaft in the second and third forward gear. In other words, in the first and second gears, there is no power path between the intermediate shaft and the output shaft which does not pass over the first switching element. Thereby, the decoupling of the torque disturbances, which are caused by the start of the internal combustion engine, is improved to the output shaft.

Embodiments of the invention are described in detail below with reference to the accompanying figures.

1 schematically shows a transmission according to a first embodiment of the invention.

2 shows a circuit diagram of the transmission.

3 schematically shows a transmission according to a second embodiment of the invention.

4 schematically shows a transmission according to a third embodiment of the invention.

5 shows a hybrid powertrain of a motor vehicle.

1 schematically shows a transmission G according to a first embodiment of the invention. The transmission G has a first planetary gear P1, a second planetary gear P2 and an electric machine EM, which includes a stator S and a rotor R. First and second planetary P1, P2 are designed as minus wheelsets, and each have a first element E11, E12, a second element E21, E22 and a third element E31, E32. The first element E11, E12 is associated with a sun gear of the respective planetary gear set P1, P2. The second element E21, E22 is associated with a web of the respective planetary gear set P1, P2. The third element E31, E32 is associated with a ring gear of the respective planetary gear set P1, P2.

The transmission G has a total of five switching elements K2, B2, K0, K1, B1. By closing the first switching element K2, a rotationally fixed connection between the third element E31 of the first planetary gear set P1 and the second element E22 of the second planetary gear set P2 is produced. By closing the second switching element B2, a rotationally fixed connection between the first element E12 of the second planetary gear set P2 and a housing GG or another non-rotatable element of the transmission G is produced. The first element E12 of the second planetary gear set P2 can thus assume no rotational speed when the second switching element B2 is closed. By closing the third switching element K0 a rotationally fixed connection between an input shaft GW1 of the transmission G and an intermediate shaft WZ is produced. The rotor R of the electric machine EM and the first element E11 of the first Planetary gear P1 are constantly connected to the intermediate shaft WZ. By closing the fourth switching element K1, a rotationally fixed connection between the intermediate shaft WZ and the second element E22 of the second planetary gear set P2 is produced. By closing the fifth switching element B1, the second element E22 of the second planetary gear set P2 can be fixed in a rotationally fixed manner. The selected representation of the switching elements K2, B2, K0, K1, B1 is to be regarded only schematically, and is not intended to indicate the design of the switching element. For example, all switching elements K2, B2, K0, K1 B1 can be designed as non-positive switching elements. In particular, the first switching element K2, and / or the fifth switching element B1, and / or the third switching element K0 may be formed as a form-locking switching elements.

A transmission output shaft GW2 is permanently connected to the second element E21 of the first planetary gear set P1 and to the third element E32 of the second planetary gear set P2 in a rotationally fixed manner.

2 shows a circuit diagram of the transmission G. The transmission G has four forward gears 1 to 4, which are listed in the rows of the circuit diagram. In the columns of the circuit diagram is represented by an X, which of the switching elements B1, B2, K1, K2 are closed in which gear. In a first forward gear 1, the fifth switching element B1 and the first switching element K2 are closed. In a second forward gear 2, the second switching element B2 and the first switching element K2 are closed. In a third forward gear 3, the fourth switching element K1 and the first switching element K2 are closed. In a fourth forward gear 4, the second switching element B2 and the fourth switching element K1 are closed.

3 schematically shows a transmission G according to a second embodiment of the invention. This in 2 Schematic diagram also applies to the second embodiment. In contrast to the first embodiment, by closing the fifth switching element B1, the third element E31 of the first planetary gear set P1 instead of the second element E22 of the second planetary gearset fixed rotationally fixed. This change is possible without affecting the functionality of the transmission, since the fifth switching element B1 is closed only together with the first switching element K2. This is the case in the first forward gear 1. Therefore, the first switching element B1 may be disposed on both sides of the first switching element K2.

4 schematically shows a transmission G according to a third embodiment of the invention. This in 2 Schematic diagram also applies to the third embodiment. In contrast to the first embodiment, a rotationally fixed connection between the second element E21 of the first planetary gear set P1 and the third element E32 of the second planetary gear set P2 is produced by closing the second switching element B2. The first element E12 of the second planetary gear set P2 is permanently fixed against rotation.

5 shows a hybrid powertrain of a motor vehicle. The hybrid powertrain has an internal combustion engine VKM, which is connected via a torsional vibration damper TS to the input shaft GW1 of the transmission G.

The output shaft GW2 is connected to a Achsgetriebe AG. Starting from the axle drive AG, the torque which is applied to the output shaft GW2 is distributed to wheels DW of the motor vehicle. In the motor operation of the electric machine EM, electric power is supplied to the stator S via an inverter (not shown). During generator operation of the electric machine EM, the stator S supplies electrical power to the inverter. The inverter converts the DC voltage of a battery, not shown, into an AC voltage suitable for the electrical machine EM, and vice versa.

reference numeral

• G

  transmission

  LV1

  input shaft

  GW2

  output shaft

  GG

  casing

  WZ

  intermediate shaft

  P1

  First planetary gear set

  P2

  Second planetary gear set

  EM

  Electric machine

  R

  rotor

  S

  stator

  E11

  First element of the first planetary gear set

  E21

  Second element of the first planetary gear set

  E31

  Third element of the first planetary gear set

  E12

  First element of the second planetary gear set

  E22

  Second element of the second planetary gear set

  E32

  Third element of the second planetary gear set

  K2

  First switching element

  B2

  Second switching element

  K0

  Third switching element

  K1

  Fourth switching element

  B1

  Fifth switching element

  1

  First forward

  2

  Second forward speed

  3

  Third forward

  4

  Fourth forward

  VKM

  Internal combustion engine

  DW

  bikes

  AG

  transaxles

  TS

  torsional vibration damper

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102014204795 [0003]

Claims (15)

Transmission (G) having an input shaft (GW1), an output shaft (GW2), an intermediate shaft (WZ), a first and a second planetary gear set (P1, P2), an electric machine (EM) with a stator (S) and a with the intermediate shaft (WZ) operatively connected rotor (R), a first switching element (K2), a second switching element (B2), a third switching element (K0), a fourth switching element (K1) and a fifth switching element (B1), wherein the first and the second planetary gear set (P1, P2) each comprise a first element (E11, E12), a second element (E21, E22) and a third element (E31, E32), wherein the first element (E11, E21) is constituted by a sun gear of the planetary gear set (P1, P2) is formed, wherein the second element (E21, E22) in the case of a minus wheel set by a web and in the case of a plus-wheel set by a ring gear of the planetary gear set (P1, P2) is formed. wherein the third element (E31, E32) in the case of a minus wheel set by the ring gear and in the case of a Plus-wheelset through the web of the planetary gear set (P1, P2) is formed, closing by closing the second switching element (B2) torque between the first, second and third element (E12, E22, E32) of the second planetary gear set (P2) is transferable, wherein the input shaft (GW1) via the third switching element (K0) to the intermediate shaft (WZ) is connectable, the output shaft (GW2) with the second element (E21) of the first planetary gear set (P1) is constantly connected, characterized in that the first element (E11) of the first planetary gear set (P1) with the intermediate shaft (WZ) constantly connected and via the fourth switching element (K1) with the second element (E22) of the second planetary gear set (P2) is connectable, wherein by closing the first switching element (K2) and the fifth switching element (B1), the third element (E31) of the first planetary gear set (P1) and there s second element (E22) of the second planetary gear set (P2) are rotationally fixed, wherein the third element (E31) of the first planetary gear set (P1) via the first switching element (K2) to the second element (E22) of the second planetary gear set (P2) connectable is, and wherein the second element (E21) of the first planetary gear set (P1) with the third element (E32) of the second planetary gear set (P2) either constantly connected or via the second switching element (B2) is connectable. Transmission (G) according to claim 1, characterized in that the second element (E21) of the first planetary gear set (P1) with the third element (E32) of the second planetary gear set (P2) is constantly connected, wherein the first element (E12) of the second Planetenradsatzes on the second switching element (B2) rotatably fixed. Transmission (G) according to claim 2, characterized in that the fifth switching element (B1) and the second switching element (B2) are arranged radially outside of the first and second planetary gear set (P1, P2). Transmission (G) according to claim 1, characterized in that the second element (E21) of the first planetary gear set (P1) via the second switching element (B2) with the third element (E32) of the second planetary gear set (P2) is connectable, wherein the first Element (E12) of the second planetary gear set (P2) is fixed permanently rotatably. Transmission (G) according to one of claims 1 to 4, characterized in that by selectively operating the first, second, fourth and fifth switching element (K2, B2, K1, B1) four forward gears (1, 2, 3, 4) between the Intermediate shaft (WZ) and the output shaft (GW2) are switchable, wherein the first forward gear (1) by closing the fifth switching element (B1) and the first switching element (K2) is formed, wherein the second forward gear (2) by closing the second switching element (B2) and the first switching element (K2) is formed, wherein the third forward gear (3) by closing the fourth switching element (K1) and the first switching element (K2) is formed, and wherein the fourth forward gear (4) by closing the second Switching element (B2) and the fourth switching element (K1) is formed. Transmission (G) according to one of claims 1 to 5, characterized in that the second and / or the fifth switching element (B2, B1) is designed as a band brake. Transmission (G) according to one of claims 1 to 5, characterized in that the fifth switching element (B1) is designed as a form-locking switching element. Transmission (G) according to one of claims 1 to 7, characterized in that the first switching element (K2) is designed as a form-locking switching element. Transmission (G) according to one of claims 1 to 8, characterized in that a reverse gear of the transmission (G) by reverse rotation of the rotor (R) with the third switching element (K0) and operation in one of the four forward gears (1, 2, 3 , 4) is formed. Transmission (G) according to one of claims 1 to 9, characterized in that the third switching element (K0) is designed as a dry or wet multi-plate clutch. Transmission (G) according to one of claims 1 to 9, characterized in that the third switching element (K0) is designed as a form-locking switching element.  Hybrid powertrain for a motor vehicle, wherein the hybrid powertrain an internal combustion engine (VKM), a transmission (G) according to one of claims 1 to 11 and a wheel (DW) of the motor vehicle associated axle drive (AG), wherein the input shaft (GW1) of the transmission (G) is connected to the internal combustion engine (VKM) and the output shaft (GW2) is connected to the axle drive (AG), wherein the motor vehicle is drivable with the third switching element (K0) open in an electric driving operation of the electric machine (EM), wherein the motor vehicle with the third switching element (K0) is closed in an internal combustion engine operation of the internal combustion engine (VKM) driven alone, and wherein the motor vehicle with the third switching element (K0) in a hybrid operation of the internal combustion engine (VKM) and of the electric machine (EM) is drivable. Method for controlling a hybrid drive train according to claim 12, characterized in that for starting the motor vehicle with the third switching element (K0) closed, one of the first forward gear (1) closed switching elements (B1, K2) is transferred from the open state to a slip mode and the other the closed in the first forward gear (1) switching elements (B1, K2) is closed, whereby at a given speed of the input shaft (GW1) a speed of the output shaft (GW2) can be changed continuously, wherein the transferred into the slip operation switching element (B1, K2) is formed by a frictional switching element, which is equipped with a variable torque transmission capability. Method for controlling a hybrid drive train according to claim 13, wherein the third shift element (K0) is designed as a non-positive shift element with variable torque transmission capability, characterized in that in the electric drive mode of the motor vehicle in a first process step with engaged forward gear (1, 2, 3, 4) the first, second, fourth or fifth switching element (K2, B2, K1, B1), which is closed at this time, is put into a slip mode, wherein in a second method step, the torque transmission capability of the third switching element (K0) is increased, whereby the Internal combustion engine (VKM) is started, wherein the transferred in the first step in the slip mode switching element (K2, B2, K1, B1) is formed by a frictional switching element, which is equipped with a variable torque transmission capability. Method for controlling a hybrid drive train according to claim 14, characterized in that the switching element transferred into the slip mode in the first method step is the first switching element (K2).

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