Transmission for a motor vehicle, hybrid powertrain for a motor vehicle and method for controlling a hybrid powertrain

Abstract

Transmission (G) for a motor vehicle, comprising an input shaft (GW1), an output shaft (GW2), a gear set (RS), and switching elements (B1, B2, K0, K1, K2), wherein the gear set (RS) comprises a first planetary gear set (P1) and a second planetary gear set (P2) with a total of four shafts (W1, W2, W3, W4) designated as first, second, third, and fourth shafts in order of rotational speed, wherein the second shaft (W2) is connected to the output shaft (GW2), wherein the switching elements (B1, B2, K0, K1, K2) are selectively actuated, thereby enabling the transmission (G) to produce four selectable forward gears (1, 2, 3, 4) between the input shaft (GW1) and the output shaft (GW2), wherein the transmission (G) comprises an electric machine (EM) with a stator (S) and a rotor (R), wherein the input shaft (GW1) is connected via a first switching element (K0) can be connected to an intermediate shaft (WZ), wherein the rotor (R) is connected to the intermediate shaft (WZ),wherein the intermediate shaft (WZ) can be connected to the third shaft (W3) of the gear set (RS) via a second switching element (K1), wherein the intermediate shaft (WZ) can be connected to the first shaft (W1) of the gear set (RS) via a third switching element (K2), wherein the third shaft (W3) can be fixed against rotation by a fourth switching element (B1), and wherein the fourth shaft (W4) can be fixed against rotation by a fifth switching element (B2), wherein a sun gear (So-P1) of the first planet gear set (P1) is part of the first shaft (W1) of the gear set (RS), wherein a ring gear (St-P1) of the first planet gear set (P1) and a ring gear (Ho-P2) of the second planet gear set (P2) are parts of the second shaft (W2) of the gear set (RS), wherein a ring gear (Ho-P1) of the first planet gear set (P1) and a ring gear (Ho-P1) of the second planet gear set (P2) are parts of the second shaft (W2) of the gear set (RS), and wherein a ring gear (Ho-P1) of the first planet gear set (P1) and a ring gear (Ho-P1) of the first planet gear set (P1) are part of the second shaft (W2) of the gear set (RS). (St-P2) of the second planetary gear set (P2) components of the third shaft (W3) of the gear set (RS) are,and wherein a sun gear (So-P2) of the second planetary gear set (P2) is part of the fourth shaft (W4) of the gear set (RS), characterized in that four forward gears (1, 2, 3, 4) between the intermediate shaft (WZ) and the output shaft (GW2) can be automatically switched by selectively actuating the second, third, fourth and fifth switching element (K1, K2, B1, B2), that the first forward gear (1) is formed by closing the fourth switching element (B1) and the third switching element (K2), that , the second forward gear (2) is formed by closing the fifth switching element (B2) and the third switching element (K2), that the third forward gear (3) is formed by closing the second switching element (K1) and the third switching element (K2), and that the fourth forward gear (4) is formed by closing the fifth switching element (B2) and the second switching element (K1).

Description

[0001] The invention relates to a transmission having an input shaft, an output shaft, a gear set, and shifting elements. The gear set comprises a first planetary gear set and a second planetary gear set with a total of four shafts designated in speed order as the first, second, third, and fourth shafts. The second shaft is connected to the output shaft. The shifting elements are selectively operable, whereby the transmission can establish four preferably automatically shiftable forward gears between the input shaft and the output shaft. The invention further relates to a hybrid drive train for a motor vehicle, and to a method for controlling such a hybrid drive train.

[0002] A transmission, in this context, refers specifically to a multi-speed transmission in which a predefined number of gears—i.e., fixed gear ratios between a transmission input shaft and a transmission output shaft—can be shifted, preferably automatically, by shifting elements. These shifting elements include, for example, clutches or brakes. Such transmissions are primarily used in motor vehicles to appropriately adapt the speed and torque output of the drive unit to the vehicle's driving resistance.

[0003] From the specialist book LOOMAN Johannes, Zahnradgetriebe, 3rd edition: Springer, 1996, ISBN 3-540-60336-0, pages 236-239 a transmission is known which has an input shaft, an output shaft, a gear set and shifting elements, wherein the gear set has a first planetary gear set and a second planetary gear set with a total of four shafts referred to in speed order as the first, second, third and fourth shaft, wherein the second shaft is connected to the output shaft, and wherein the shifting elements are selectively actuable, whereby four automatically switchable forward gears can be produced between the input shaft and the output shaft by the transmission.

[0004] So-called plug-in hybrid vehicles or vehicles with range extenders often use only small internal combustion engines, which primarily serve to increase the vehicle's range through combustion engine operation. The main drive of such vehicles is an electric motor, which is capable of providing a wide range of the vehicle's power. Such vehicles are characterized by high drive efficiency.

[0005] Furthermore, DE 10 2011 006 940 A1 and JP 2007 - 315 466 A each disclose hybrid drivetrains for motor vehicles. The hybrid drivetrain of JP 2007 - 315 466 A provides a transmission with an input shaft, an output shaft, an intermediate shaft, an electric motor, a gear set, and shifting elements. The gear set comprises a first planetary gear set and a second planetary gear set, as well as four shafts. By selectively actuating the shifting elements, five different forward gears can be shifted between the input shaft and the output shaft of the transmission.

[0006] It is an object of the invention to design a transmission in such a way that a gear ratio series is achieved which is well suited for use in a motor vehicle, wherein the transmission is also characterized by a compact and simple design.

[0007] The object is achieved by the features of patent claim 1, whereby advantageous embodiments result from the subclaims, the description and the figures.

[0008] The transmission comprises at least one input shaft and one output shaft, a gear set, an electric machine with a rotor and a stator, and five shifting elements. The gear set has a first planetary gear set and a second planetary gear set with a total of four shafts, designated in speed order as the first, second, third, and fourth shafts. The gear set is designed as a two-carrier, four-shaft transmission. The second shaft of the gear set is continuously connected to the output shaft. The five shifting elements are selectively operable. By operating the shifting elements, a total of four gears can be established between the input shaft and the output shaft.

[0009] According to the invention, the input shaft can be connected to an intermediate shaft via a first shifting element, with the rotor of the electric motor being permanently connected to the intermediate shaft. The intermediate shaft can be connected to the third shaft of the gear set via a second shifting element. Furthermore, the intermediate shaft can be connected to the first shaft of the gear set via a third shifting element. The third shaft can be rotationally fixed by a fourth shifting element. The fourth shaft can be rotationally fixed by a fifth shifting element. The arrangement according to the invention results in a particularly simple and compact transmission design.

[0010] A two-carrier, four-shaft transmission is a planetary transmission consisting of two individual planetary gear sets kinematically coupled to one another via exactly two coupling shafts, and in which four of its elements ("shafts") are freely accessible to other transmission elements. A coupling shaft is defined as a permanent mechanical connection between an element—i.e., a sun gear, carrier, or ring gear—of the first individual planetary gear set and an element—i.e., a sun gear, carrier, or ring gear—of the second individual planetary gear set. The number of individual planetary gear sets and the number of free shafts are not defined by the visual appearance of the transmission, but rather by its kinematics. In each gear of a two-carrier, four-shaft transmission, two of the transmission shift elements connected to elements of the two-carrier, four-shaft transmission must be closed.To graphically represent the kinematics of the transmission, a speed diagram of the transmission is typically used, for example, the Kutzbach diagram known from transmission theory. Well-known examples of such a two-web, four-shaft transmission are the so-called Ravigneaux gear set and the so-called Simpson gear set.

[0011] A reduced two-carrier four-shaft transmission is a design of a two-carrier four-shaft transmission in which one element of the transmission—a sun gear, a carrier, or a ring gear—is omitted because another element of the transmission takes over its function without changing the kinematics. The element that takes over the function of the omitted element is thus simultaneously one of the transmission's coupling shafts. A well-known example of this is the Ravigneaux gear set, which has either two sun gears and only one ring gear, or two ring gears and only one sun gear.

[0012] In the following, a shaft is not exclusively understood to mean, for example, a cylindrical, rotatably mounted machine element for transmitting torque, but rather also general connecting elements that connect individual components or elements to one another, in particular connecting elements that connect several elements to one another in a rotationally fixed manner.

[0013] A planetary gear set comprises a sun gear, a carrier, and a ring gear. Planetary gears are rotatably mounted on the carrier and mesh with the teeth of the sun gear and / or the teeth of the ring gear. In the following, a negative gear set describes a planetary gear set with a carrier on which the planetary gears are rotatably mounted, with a sun gear, and with a ring gear. The teeth of at least one of the planetary gears mesh with both the teeth of the sun gear and the teeth of the ring gear, causing the ring gear and the sun gear to rotate in opposite directions when the sun gear rotates while the carrier is stationary.

[0014] A positive planetary gear set differs from the negative planetary gear set just described in that the positive planetary gear set has inner and outer planetary gears that are rotatably mounted on the carrier. The teeth of the inner planetary gears mesh with the teeth of the sun gear and the teeth of the outer planetary gears. The teeth of the outer planetary gears also mesh with the teeth of the ring gear. This means that when the carrier is stationary, the ring gear and the sun gear rotate in the same direction.

[0015] Four shafts, referred to in speed order as the first, second, third and fourth shaft, are characterized by the fact that the speeds of these shafts increase, decrease or are equal in a linear manner in the given order. In other words, the speed of the first shaft is less than or equal to the speed of the second shaft. The speed of the second shaft is in turn less than or equal to the speed of the third shaft. The speed of the third shaft is less than or equal to the speed of the fourth shaft. This sequence is also reversible, so that the fourth shaft has the highest speed, while the first shaft assumes a speed that is less than or equal to the speed of the fourth shaft. There is always a linear relationship between the speeds of all four shafts.

[0016] The speed of one or more shafts can also assume negative values, or even zero. The speed order is therefore always based on the signed value of the speeds, not their magnitude. The speeds of the four shafts are equal if two of the ring gear, carrier, and sun gear elements of one of the planetary gear sets are connected to each other.

[0017] An electrical machine consists of at least a rotationally fixed stator and a rotatably mounted rotor and is designed to convert electrical energy into mechanical energy in the form of speed and torque in motor operation, and to convert mechanical energy into electrical energy in the form of current and voltage in generator operation.

[0018] Depending on the actuation state, switching elements permit relative movement between two components or establish a connection for transmitting torque between the two components. Relative movement can be understood, for example, as the rotation of two components, where the speed of the first component and the speed of the second component differ from each other. Furthermore, rotation of only one of the two components is also conceivable, while the other component remains stationary or rotates in the opposite direction.

[0019] Two elements are referred to as connected to one another in particular when there is a fixed, particularly rotationally fixed, connection between the elements. Elements connected in this way rotate at the same speed. The various components and elements of the invention can be connected to one another via a shaft, a closed switching element, or a connecting element, but also directly, for example, by means of a welded, press-fit, or other connection.

[0020] Two elements are referred to as connectable if there is a rotationally fixed connection between them that can be released by a switching element. If the connection exists, such elements rotate at the same speed.

[0021] In this case, a sun gear of the first planetary gear set is a component of the first shaft of the gear set. A carrier of the first planetary gear set is connected to a ring gear of the second planetary gear set and forms a component of the second shaft of the gear set. A ring gear of the first planetary gear set is connected to a carrier of the second planetary gear set and forms a component of the third shaft of the gear set. A sun gear of the second planetary gear set forms a component of the fourth shaft of the gear set. This type of gear set design is characterized by good gearing efficiency and low component loads.

[0022] According to the invention, four forward gears can be automatically shifted between the intermediate shaft and the output shaft by selectively actuating the second to fourth shifting elements. When the first shifting element is open, torque is applied to the intermediate shaft by the rotor of the electric machine. When the first shifting element is closed, torque is applied to the intermediate shaft either by a drive unit connected to the input shaft or by the drive unit and the rotor of the electric machine. The first forward gear is formed by closing the fourth shifting element and the third shifting element. The second forward gear is formed by closing the fifth shifting element and the third shifting element. The third forward gear is formed by closing the second shifting element and the third shifting element.The fourth forward gear is formed by engaging the fifth shift element and the second shift element. By assigning the second to fourth shift elements to the individual forward gears, and with a suitable selection of the stationary gear ratios of the first and second planetary gear sets, a gear ratio series well-suited for automotive applications is achieved. Furthermore, two adjacent gears always have a shift element that is engaged in both of these gears. Therefore, when shifting into an adjacent gear, only one shift element needs to be opened and one shift element closed. This simplifies the shifting process and shortens the shifting time.

[0023] According to one embodiment, the fourth and fifth shifting elements are arranged radially outside the first and second planetary gear sets. Since both the fourth and fifth shifting elements ensure a rotationally fixed fixation of the shaft assigned to the respective shifting element, such an arrangement is particularly advantageous because the fourth and fifth shifting elements can thus be arranged directly on a transmission housing located radially outside the two planetary gear sets. If the fourth and / or fifth shifting elements are designed as hydraulically actuated band brakes, the shifting elements are easily accessible with hydraulic fluid due to their arrangement close to the housing. This simplifies the hydraulic fluid routing of the transmission.

[0024] The fourth shift element is preferably designed as a positive-locking shift element. When closed, positive-locking shift elements establish the connection through positive locking, and when open are characterized by lower drag losses than non-positive shift elements. For example, the fourth shift element can be designed as a dog-type shift element, which can be equipped with a synchronizing device. The low drag losses in the open state further improve the efficiency of the transmission, particularly since the fourth shift element is only closed in first forward gear. The fourth shift element is therefore predominantly open when the transmission is in operation. Since the fourth shift element is only closed in first forward gear, the shift element is always opened but not closed when shifting into a higher gear.Opening a claw shift element is considerably easier than closing it, as during closing, the claws of the claw shift element must first engage the designated gaps, whereas during opening, the claws simply need to be released from the load. Both processes require time, and for dynamic driving reasons, the shift time should be as short as possible, particularly when shifting from a lower gear to a higher gear. However, since the fourth shift element never needs to be closed when shifting to a higher gear, but only opened, the design of the fourth shift element as a positive-locking shift element means there is no limitation on the shift duration.

[0025] Preferably, the third shift element is designed as a positive-locking shift element. Since the third shift element is only open in the fourth and thus highest gear, the third shift element never needs to be closed when shifting to a higher gear. Therefore, the design of the third shift element as a positive-locking shift element also does not limit the shift duration. Furthermore, the design as a positive-locking shift element improves the efficiency of the transmission in the fourth forward gear.

[0026] 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 first shifting element is open and one of the four forward gears is engaged. In other words, the transmission does not have a reverse gear formed by selective actuation of the shifting elements. Instead, the electric machine is operated such that the rotor rotates counter to a preferred direction of rotation of the input shaft. When a gear is engaged, the output shaft rotates in the same direction of rotation as the rotor. This embodiment eliminates the need for a shifting element compared to the prior art, thereby reducing the complexity of the transmission and its weight.

[0027] According to one embodiment, the first shifting element is designed as a dry or wet multi-plate clutch. A multi-plate clutch consists of an inner plate carrier and an outer plate carrier, wherein a plurality of inner plates are connected to the inner plate carrier, and a plurality of outer plates are connected to the outer plate carrier. The inner and outer plates are arranged alternately and overlap one another. If a force is applied to the plates normal to the plate surface of the plates, a torque is transmitted from one plate carrier to the other plate carrier through friction between the inner and outer plates. The torque transmitted from one plate carrier to the other plate carrier depends on the applied force. If the force is large enough to prevent a difference in speed between the inner and outer plates through frictional connection, the entire torque is transmitted.If the force is insufficient, only a portion of the torque is transmitted, resulting in a speed differential between the inner and outer plates. This condition is also known as slippage. By varying the force applied to the plates, the torque transmission capacity of the first shift element can be adjusted.

[0028] In an alternative embodiment, the first shifting element is designed as a positive-locking shifting element. This can improve the efficiency of the transmission, since the first shifting element, when open, generates significantly lower drag losses than a non-positive shifting element, such as a multi-plate clutch.

[0029] Preferably, the third shifting element is arranged radially outside the second shifting element. The first and second shifting elements typically have a largely rotationally symmetrical design, with their axes coaxial with a central axis of the transmission, for example, coaxial with the axis of the input shaft. If the second shifting element is arranged radially outside the first shifting element, these two shifting elements do not need to be arranged axially offset from one another. Instead, it is possible to arrange the two shifting elements one above the other. This makes it possible to reduce the external dimensions of the transmission.

[0030] The transmission can be part of a hybrid drive train of a motor vehicle. In addition to the transmission, the hybrid drive train also has an internal combustion engine which is connected to the input shaft of the transmission. The output shaft of the transmission is connected to an output which is connected to the wheels of the motor vehicle. The hybrid drive train enables several drive modes of the motor vehicle. In electric drive mode, the motor vehicle is driven by the electric machine of the transmission, with the first shift element being open. In combustion engine mode, the motor vehicle is driven by the internal combustion engine, with the first shift element being closed. In hybrid mode, the motor vehicle is driven by both the internal combustion engine and the electric machine of the transmission.

[0031] In some operating states of the motor vehicle, generator operation of the electric machine is required, whereby the rotor is driven by the internal combustion engine. For this purpose, the first shift element is closed. If both or one of the two shift elements that form a gear are not closed, no torque is transferred from the input shaft to the output shaft. If the motor vehicle is to move off immediately in this operating state, one of the shift elements closed in first forward gear is changed from the open state to slip mode, while the other of the shift elements closed in first forward gear remains closed or is closed. The shift element in slip mode transfers torque from the input shaft to the output shaft, whereby the speed of the output shaft can be continuously varied by controlling the slip mode.The switching element operated in slip mode is designed as a force-locking switching element.

[0032] If you want to switch from electric drive mode to combustion engine or hybrid operation, the combustion engine must be started. This is preferably achieved by a drag start, in which the crankshaft of the combustion engine is driven by the input shaft. For this purpose, in a first method step, with the gear engaged and the first shift element open, one of the second to fifth shift elements, which is closed at this time, is transferred to slip mode. For this purpose, the shift element transferred to slip mode is designed as a non-positive shift element which is equipped with a variable torque transmission capacity. In a second method step, the torque transmission capacity of the first shift element is increased. For this purpose, the first shift element is also designed as a non-positive shift element with a variable torque transmission capacity.The switching element, which is transferred from the closed state to the slip mode, serves to achieve the necessary starting 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.

[0033] Preferably, during the tow-start described above, the third shift element is transferred to slip mode. Since the third shift element is engaged in the first, second, and third forward gears, the tow-start can be performed in all of these gears. Furthermore, in these gears, the third shift element transmits the entire power flow from the intermediate shaft to the output shaft. In other words, in the first, second, and third gears, there is no power path between the intermediate shaft and the output shaft that does not pass through the third shift element. This improves the decoupling of torque disturbances caused by the start of the internal combustion engine from the output shaft.

[0034] Embodiments of the invention are described in detail below with reference to the attached figures. Fig. 1 shows schematically a transmission according to an embodiment of the invention. Fig. 2 shows a shift diagram of the transmission. Fig. 3 shows a speed diagram of the gearbox Fig. 4 shows a hybrid powertrain of a motor vehicle.

[0035] Fig. 1 schematically shows a transmission G according to an embodiment of the invention. The transmission has a gear set RS with a first planetary gear set P1 and a second planetary gear set P2. The gear set RS has four shafts designated as first, second, third, and fourth shafts W1, W2, W3, W4. A sun gear So-P1 of the first planetary gear set P1 is part of the first shaft W1 of the gear set RS. A carrier St-P1 of the first planetary gear set P1 and a ring gear Ho-P2 of the second planetary gear set P2 are parts of the second shaft W2 of the gear set RS, wherein the second shaft W2 is connected to an output shaft GW2. A ring gear Ho-P1 of the first planetary gear set P1 and a carrier St-P2 of the second planetary gear set P2 are parts of the third shaft W3 of the gear set RS. A sun gear So-P2 of the second planetary gear set P2 is part of the fourth shaft W4 of the gear set RS.An input shaft GW1 of the gearbox G can be connected to an intermediate shaft WZ via a first switching element K0. An electric machine EM with a rotor R and a stator S that is fixed in rotation with respect to a housing GG of the gearbox G is also part of the gearbox G, with the rotor R being fixed in rotation with the intermediate shaft WZ. The intermediate shaft WZ can be connected to the third shaft W3 via a second switching element K1. The intermediate shaft WZ can be connected to the first shaft W1 via a third switching element K2. The third shaft W3 can be fixed in rotation with respect to the housing GG via a fourth switching element B1. The fourth shaft W4 can be fixed in rotation with respect to the housing GG via a fifth switching element.

[0036] Fig. Figure 2 shows a shift diagram of transmission G. In a first forward gear 1, the fourth shift element B1 and the third shift element K2 are engaged. In a second forward gear 2, the fifth shift element B2 and the third shift element K2 are engaged. In a third forward gear 3, the second shift element K1 and the third shift element K2 are engaged. In a fourth forward gear 4, the fifth shift element B2 and the second shift element K1 are engaged.

[0037] Fig. Figure 3 shows a speed diagram of transmission G. It plots the speeds of the four shafts W1, W2, W3, W4 of gear set RS in a vertical direction relative to the speed of the transmission input shaft GW1. The maximum occurring speed of the transmission input shaft GW1 is normalized to the value one. The distances between the four shafts W1, W2, W3, W4 are determined by the stationary gear ratios of the first and second planetary gear sets P1, P2. Speed ​​ratios belonging to a specific operating point can be connected by a straight line.

[0038] If two of the elements of a planetary gear set (ring gear, carrier, and sun gear) are connected to each other, the ring gear, carrier, and sun gear of this planetary gear set rotate at the same speed. In this state, the ratio between these elements assumes the value of one. For the sake of clarity, the horizontal arrangement of the shafts connected to these elements has not been shifted in the speed diagram. Consequently, this state can be identified in the speed diagram by a horizontal straight line connecting the shafts involved.

[0039] Fig.Figure 4 shows a hybrid drive train of a motor vehicle. The hybrid drive train has an internal combustion engine ICE, which is connected to the input shaft GW1 of the transmission G via a torsional vibration damper TS. The transmission output shaft GW2 is connected to an axle drive AG. Starting from the axle drive AG, the torque applied to the transmission output shaft GW2 is distributed to wheels DW of the motor vehicle. When the electric machine EM is in motor mode, electrical power is supplied to the stator S via an inverter (not shown). When the electric machine EM is in generator mode, the stator S supplies electrical power to the inverter. The inverter converts the direct voltage of a battery (not shown) into an alternating voltage suitable for the electric machine EM, and vice versa. Reference symbol G Gearbox GG case GW1 input shaft GW2 output shaft RS wheelset P1 First planetary gear set P2 Second planetary gear set So-P1 sun gear of the first planetary gear set St-P1 web of the first planetary gear set Ho-P1 ring gear of the first planetary gear set So-P2 sun gear of the second planetary gear set St-P2 web of the second planetary gear set Ho-P2 ring gear of the second planetary gear set W1 First Wave W2 Second Wave W3 Third Wave W4 Fourth Wave WZ intermediate shaft K0 First switching element K1 Second switching element K2 Third switching element B1 Fourth switching element B2 Fifth switching element EM Electric Machine R Rotor S Stator 1 First forward gear 2 Second forward gear 3 Third forward gear 4 Fourth forward gear ICE internal combustion engine DW Wheels AG axle drive TS torsional vibration damper

Claims

[1] Transmission (G) for a motor vehicle, which has an input shaft (GW1), an output shaft (GW2), a gear set (RS) and shifting elements (B1, B2, K0, K1, K2), wherein the gear set (RS) has a first planetary gear set (P1) and a second planetary gear set (P2) with a total of four shafts (W1, W2, W3, W4) designated in speed order as the first, second, third and fourth shafts, wherein the second shaft (W2) is connected to the output shaft (GW2), wherein the shifting elements (B1, B2, K0, K1, K2) are selectively actuable, whereby four shiftable forward gears (1, 2, 3, 4) can be produced between the input shaft (GW1) and the output shaft (GW2) by the transmission (G), wherein the transmission (G) has an electric machine (EM) with a stator (S) and a rotor (R), wherein the input shaft (GW1) is connectable to an intermediate shaft (WZ) via a first switching element (K0), wherein the rotor (R) is connected to the intermediate shaft (WZ),wherein the intermediate shaft (WZ) is connectable to the third shaft (W3) of the gear set (RS) via a second shifting element (K1), wherein the intermediate shaft (WZ) is connectable to the first shaft (W1) of the gear set (RS) via a third shifting element (K2), wherein the third shaft (W3) is rotatably fixed by a fourth shifting element (B1), and wherein the fourth shaft (W4) is rotatably fixed by a fifth shifting element (B2), wherein a sun gear (So-P1) of the first planetary gear set (P1) is a component of the first shaft (W1) of the gear set (RS), wherein a carrier (St-P1) of the first planetary gear set (P1) and a ring gear (Ho-P2) of the second planetary gear set (P2) are components of the second shaft (W2) of the gear set (RS), wherein a ring gear (Ho-P1) of the first planetary gear set (P1) and a web (St-P2) of the second planetary gear set (P2) are components of the third shaft (W3) of the gear set (RS),and wherein a sun gear (So-P2) of the second planetary gear set (P2) is part of the fourth shaft (W4) of the gear set (RS), , characterized by that by selectively actuating the second, third, fourth and fifth switching elements (K1, K2, B1, B2) four forward gears (1, 2, 3, 4) between the intermediate shaft (WZ) and the output shaft (GW2) can be automatically switched, that the first forward gear (1) is formed by closing the fourth switching element (B1) and the third switching element (K2), that the second forward gear (2) is formed by closing the fifth switching element (B2) and the third switching element (K2), that the third forward gear (3) is formed by closing the second switching element (K1) and the third switching element (K2), and that the fourth forward gear (4) is formed by closing the fifth switching element (B2) and the second switching element (K1). [2] Transmission (G) according to claim 1, characterized bythat the fourth and fifth switching elements (B1, B2) are arranged radially outside the two planetary gear sets (P1, P2). [3] Transmission (G) according to claim 1 or 2, characterized by that the fourth and / or fifth switching element (B1, B2) is designed as a band brake. [4] Transmission (G) according to claim 1 or 2, characterized by that the fourth switching element (B1) is designed as a positive-locking switching element. [5] Transmission (G) according to one of claims 1 to 4, characterized by that the third switching element (K2) is designed as a positive-locking switching element. [6] Transmission (G) according to one of claims 1 to 5, characterized by that a reverse gear of the transmission (G) is formed by reverse rotation of the rotor (R) with the first switching element (K0) open and operation in one of the four forward gears (1, 2, 3, 4). [7] Transmission (G) according to one of claims 1 to 6, characterized bythat the first switching element (K0) is designed as a dry or wet multi-plate clutch. [8] Transmission (G) according to one of claims 1 to 6, characterized by that the first switching element (K0) is designed as a positive-locking switching element. [9] Transmission (G) according to one of claims 1 to 8, characterized by that the third switching element (K2) is arranged radially outside the second switching element (K1). [10] Hybrid drive train for a motor vehicle, wherein the hybrid drive train has an internal combustion engine (ICE), a transmission (G) according to one of claims 1 to 9 and an output connected to wheels of the motor vehicle, wherein the input shaft (GW1) of the transmission (G) is connected to the internal combustion engine (ICE) and the output gear shaft (GW2) is connected to the output, wherein the motor vehicle can be driven by the electric machine (EM) in an electric driving mode when the first shifting element (K0) is open, wherein the motor vehicle can be driven by the internal combustion engine (ICE) alone in an internal combustion engine mode when the first shifting element (K0) is closed, and wherein the motor vehicle can be driven by the internal combustion engine (ICE) and the electric machine (EM) in a hybrid mode when the first shifting element (K0) is closed. [11] Method for controlling a hybrid drive train according to claim 10, characterized by in that, in order to start off the motor vehicle with the first shifting element (K0) closed, one of the shifting elements (B1, K2) closed in the first forward gear (1) is transferred from the open state into a slip mode and the other of the shifting elements (B1, K2) closed in the first forward gear (1) is closed, whereby at a given speed of the input shaft (GW1) a speed of the output shaft (GW2) can be continuously changed, wherein the shifting element (B1, K2) transferred into the slip mode is formed by a non-positive shifting element which is equipped with a variable torque transmission capacity. [12] Method for controlling a hybrid drive train according to claim 10 or claim 11, wherein the first switching element (K0) is designed as a force-locking switching element with variable torque transmission capacity, characterized byin that in the electric driving mode of the motor vehicle, in a first method step with the forward gear (1, 2, 3, 4) engaged, one of the second to fifth switching elements (K1, K2, B1, B2), which is closed at this time, is transferred into a slip mode, wherein in a second method step the torque transmission capacity of the first switching element (K0) is increased, whereby the internal combustion engine (VKM) is started, wherein the switching element (K1, K2, B1, B2 transferred into the slip mode in the first method step is formed by a non-positive switching element which is equipped with a variable torque transmission capacity. [13] Method for controlling a hybrid powertrain according to claim 12, characterized by that in the first method step the third switching element (K2), which is closed at this time, is transferred into a slip operation.

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