Vehicle powertrain, control arrangement and method for controlling the vehicle powertrain

Abstract

A vehicle powertrain (2) comprising an electric machine (3), an internal combustion engine (4), a planetary gear set (5), a first shaft (11), and a second shaft (12). The electric machine (3) is connected to the second shaft (12). The first shaft (11) is connected to a sun gear (20) of the planetary gear set (5), and the second shaft (12) is connectable to a ring gear (23) of the planetary gear set (5) via a ring gear coupling device (34). The second shaft (12) and an output shaft (13) of the internal combustion engine (4) are each connectable to the first shaft (11) via a coupling arrangement (30). The present disclosure also relates to a vehicle (1) with the vehicle powertrain (2), a method for controlling the vehicle powertrain (2), a control arrangement (100) designed to control the vehicle powertrain (2), a computer program, and a computer-readable medium.

Description

Field of TechnologyThe present disclosure generally relates to a vehicle powertrain and a vehicle including such a vehicle powertrain. The present disclosure also relates generally to a method of controlling the vehicle powertrain. Moreover, the present disclosure generally relates to a computer program and a computer readable medium. The present disclosure further relates generally to a control assembly configured to control the vehicle powertrain.BackgroundThe tendency to reduce emissions and improve fuel consumption of heavy duty vehicles such as trucks and buses has led to the development of vehicles including vehicle powertrains with one or more electric machines serving as propulsion units and configured to be powered by energy storage devices. Examples of such vehicles include battery electric vehicles (BEVs), as well as hybrid electric vehicles (HEVs), such as plug-in hybrid electric vehicles (PHEVs).One of the major obstacles in attempting to electrifying heavy vehicles is the considerable weight and high cost of the energy storage device (i.e. batteries) required to drive the heavy vehicle until it can be taken out of service for recharging the energy storage device. Vehicles designed for operation in very short-term cycles, such as city traffic or regional distribution vehicles, can often be converted to BEVs (battery electric vehicles) today, with the added weight and cost resulting from the size of the energy storage device required for the intended operation of the vehicle being acceptable. This is mainly due to the fact that the vehicle can be frequently charged by regenerative braking before it reaches the next charging station.However, for example for a long-distance truck, it is neither cost-effective nor energy-efficient to drive exclusively with stored electrical energy. Heavy vehicles consume a large portion of their available energy at high and constant speed, a condition that a long distance truck is often subject to over a considerable portion of a drive cycle. At the present energy density of batteries and assuming a long distance operation of about 500 km / day, the additional weight incurred by an energy storage device having sufficient capacity to ensure day operation would be on the order of about 3500 to 4000 kg. This would not only place a burden on the possible load weight, but also place space and vehicle specifications constraints due to the size of such an energy storage device. Also, this would result in significantly higher cost for the energy storage device, which is not offset by the cost reduction due to the omission of fuel cost. In addition, a larger energy storage device would have a suspect effect on sustainability. The use of a smaller energy storage device, the capacity of which is not sufficient for operation over a day, would lead to a charging process at a charging station being required in the course of the day. This, in turn, would increase the overall cost of the vehicle because the vehicle would be out of service during the charging operation and therefore does not present an option suitable for all types of heavy duty vehicles.One option that would allow electrification of a broader spectrum of heavy duty vehicle types would be to incorporate a range extender. A range extender typically includes an additional internal combustion engine that serves only to drive a generator that charges the energy storage device of the vehicle. This is sometimes also referred to as a series hybrid powertrain. However, this may result in unduly high emissions and such powertrains also often suffer from undesirable efficiency losses in converting the mechanical energy of the auxiliary internal combustion engine into the electrical energy to be stored.SUMMARY OF THE INVENTIONThe object of the present disclosure is to provide a cost and energy efficient (Wellto-Wheel) solution that can extend the types of vehicles that can be electrically powered.The object is achieved by the subject matter of the appended independent claim(s).According to the present disclosure, a vehicle powertrain is provided. The vehicle powertrain includes an electric machine configured to be selectively operated as a motor or a generator. The vehicle powertrain further includes an engine, a planetary gear, a first shaft, and a second shaft. The vehicle powertrain also includes a clutch assembly disposed at a first end of the first shaft. The vehicle powertrain also includes a driveshaft connected to at least one drive wheel. The above-mentioned first shaft is connected, at its second end, to a sun gear of the planetary gear set, and an output shaft of the planetary gear set is connected to a planet carrier of the planetary gear set. The electric machine is connected to the second shaft. The second shaft is connectable to the first shaft via the clutch arrangement. In addition, an output shaft of the internal combustion engine can be connected to the first shaft via the clutch arrangement. The second shaft is also connectable to a ring gear of the planetary gear set via a ring gear clutch device. In addition, the ring gear and the sun gear of the planetary gear are each configured to be selectively operated in a rotatable or a rotationally fixed state.The vehicle powertrain described herein is based on an electric vehicle powertrain supplemented by an internal combustion engine that can be directly connected to the driveshaft when longer trips are required for a vehicle including the vehicle powertrain. The vehicle drive train allows a purely electric drive in the case of a large part of the possible driving situations, wherein, in comparison with a battery-electric vehicle (BEV) with the same range, an energy storage device with significantly lower capacity can be used. This in turn leads, among other things, to a reduction in the additional weight and to lower costs for the energy storage device in comparison with a BEV. This also improves the effects on sustainability.The fact that the internal combustion engine can be directly connected to the drive shaft makes it possible to operate the internal combustion engine with a substantially constant load and in a limited speed range, such as about 80-90 km / h, and to use the electric machine to cycle all cases of transient energy consumption. This makes it possible to avoid transient emissions that are otherwise difficult to limit and at the same time sub-optimize the internal combustion engine for high energy efficiency.The configuration of the vehicle powertrain therefore allows for the control to be configured such that: (i) at higher power demands, at high vehicle speeds, the engine operates continuously and the electric machine provides additional power as assistance as needed; (ii) at lower power demands, at high vehicle speeds, the engine operates continuously and the electric machine regenerates the excess power; and (iii) at lower or medium vehicle speeds, the electric machine is used as the sole source of propulsion.Moreover, the vehicle powertrain enables a vehicle whose operation is less dependent on the charging infrastructure, as the vehicle's energy storage device is both in motion while the vehicle is in motion and can be charged when it is stationary, in which case the vehicle need not be at a charging station. More specifically, it is possible to charge the energy storage device using the internal combustion engine, and charging can be performed with a similar performance to a quick charger when the vehicle is at a standstill. In addition, charging may be performed while the vehicle is in motion by regenerative braking, but may be performed with a driving torque transmitted to the driving wheels and thus also during acceleration of the vehicle.The second shaft may be a hollow shaft, and the first shaft may be arranged to extend through the hollow second shaft. This allows for a more compact vehicle powertrain design because fewer gears and shafts are needed.The vehicle driveline may further include a first locking device configured to selectively lock the ring gear of the planetary gear set in the rotationally fixed state. This enables reliable operation of the ring gear in the rotationally fixed state and operation of the ring gear in a rotatable state, depending on the desired operating state of the vehicle drive train.The vehicle driveline may further include a second blocking device configured to selectively block the output shaft of the engine in a rotationally fixed state. In such a case, the sun gear of the planetary gear set may be configured to be locked in the rotationally fixed state by the output shaft of the internal combustion engine connected to the first shaft via the clutch arrangement when the output shaft of the internal combustion engine is locked in a rotationally fixed state. This eliminates the need to arrange a locking device, which is designed to lock the sun wheel in the rotationally fixed state, on or in the vicinity of the planetary gearing, where such a device is normally difficult to accommodate.The output shaft of the planetary gear mechanism can be connected via a differential to a drive shaft of the vehicle drive train. This has the advantage that a more compact design of the vehicle drive train is possible.Alternatively, the output shaft of the planetary gear set may be connected to a multi-speed transmission unit, the multi-speed transmission unit being connected to the drive shaft of the vehicle drive train via a differential. This allows further transmission ratios.The present disclosure further provides a method, performed by a control arrangement, for controlling the vehicle powertrain described above. The method comprises, in response to a command, charging an energy storage device configured to supply power to the electric machine while a drive torque to be transmitted to the drive shaft at a third transmission ratio is required, the following steps:controlling the ring gear to the rotatable state if it is not already in said rotatable state;controlling the sun gear to the rotatable state when it is not already in said rotatable state;controlling the ring gear clutch device to a closed state if it is not already closed;controlling the clutch assembly to connect the output shaft of the engine and the second shaft to the first shaft if this connection has not already been established;operating the electric machine as a generator; andoperating the internal combustion engine in such a way that it provides a drive torque.The method described herein enables efficient charging of an energy storage device while a vehicle comprising the vehicle powertrain is in motion, providing a drive torque to the drive wheels. In other words, charging of the energy storage device can be achieved without requiring regenerative braking of the vehicle, which would result in a decrease in the travel speed. In addition, the charging of the energy storage device does not depend on the presence of a separate generator, which is different from the electric machine, which may also serve as a drive unit.The method may further comprise, in response to a command to charge the energy storage device configured to supply power to the electric machine when no drive torque to be transmitted to the drive shaft is required, the following steps:controlling the ring gear to the rotatable state if it is not already in said rotatable state;controlling the sun gear to the rotatable state when it is not already in said rotatable state;controlling the ring gear clutch device to an open state when not already open;controlling the clutch assembly to connect the output shaft of the engine and the second shaft to the first shaft if this connection has not already been established;operating the engine to provide positive output torque; andoperating the electric machine as a generator.As a result, the energy storage device can be charged while a vehicle comprising the vehicle drive train is at a standstill, without charging at a charging station being required. This also enables charging of the energy storage device while the vehicle is in motion without having to transmit a drive torque to the drive shaft, such as during coasting, and without having to resort to regenerative braking, which could lead to a reduction in the travel speed.The method may further include, in response to a command regarding a first gear ratio electric-only drive, the steps of:controlling the ring gear in the rotationally fixed state if it is not already in the rotationally fixed state;controlling the sun gear to the rotatable state when it is not already in said rotatable state;controlling the ring gear clutch device to an open state when not already open;controlling the clutch assembly to connect the second shaft to the first shaft if this connection has not already been established; andoperating the electric machine as a motor.As a result, the greatest possible torque that is transmitted to the drive shaft and thus also to the drive wheel(s) is achieved without the internal combustion engine having to be used, and thus, inter alia, an environmentally friendly and energy-efficient driving at low driving speeds or when starting the vehicle comprising the vehicle drive train from a standstill is made possible.The method may further include, in response to a command regarding electric-only drive having a second gear ratio, the steps of:controlling the ring gear to the rotatable state if it is not already in said rotatable state;controlling the sun gear to the rotationally fixed state if it is not already in said rotationally fixed state;controlling the ring gear clutch device to a closed state if it is not already closed;controlling the clutch assembly to separate the second shaft and the first shaft if not already separated; andoperating the electric machine as a motor.This allows, among other things, an environmentally friendly and energy efficient driving at relatively low driving speeds, such as in city traffic or the like, without having to use the internal combustion engine, which would increase emissions.The method may further include, in response to a third ratio electric-only drive command, the steps of:controlling the ring gear to the rotatable state if it is not already in said rotatable state;controlling the sun gear to the rotatable state when it is not already in said rotatable state;controlling the ring gear clutch device to a closed state if it is not already closed;controlling the clutch assembly to connect the second shaft to the first shaft if this connection has not already been established; andoperating the electric machine as a motor.This allows an environmentally friendly and energy-efficient drive of a vehicle comprising the vehicle drive train at a relatively high driving speed to be achieved if the electric machine can provide a sufficient drive torque to maintain a desired driving speed of the vehicle.The method may further include, in response to a command regarding a hybrid drive having a first gear ratio, the steps of:controlling the ring gear in the rotationally fixed state if it is not already in the rotationally fixed state;controlling the sun gear to the rotatable state when it is not already in said rotatable state;controlling the ring gear clutch device to an open state when not already open;controlling the clutch assembly to connect the output shaft of the engine and the second shaft to the first shaft if this connection has not already been established;operating the electric machine as a motor; andoperating the internal combustion engine in such a way that it provides a drive torque.This makes it possible, inter alia, to set a vehicle comprising the vehicle drive train into motion on a steep gradient and / or under heavy load or at low travel speeds under such conditions. Using the engine to support the electric machine under such circumstances avoids the need to incorporate a more powerful (and thus more expensive) electric machine into the vehicle powertrain, which would likely be oversized for the most frequently occurring operating conditions of the vehicle.The method may further include the steps of, in response to a third gear ratio hybrid drive command:controlling the ring gear to the rotatable state if it is not already in said rotatable state;controlling the sun gear to the rotatable state when it is not already in said rotatable state;controlling the ring gear clutch device to a closed state if it is not already closed;controlling the clutch assembly to connect the output shaft of the engine and the second shaft to the first shaft if this connection has not already been established;operating the electric machine as a motor; andoperating the internal combustion engine in such a way that it provides a drive torque.As a result, at highest driving speeds or at high speeds on a steep gradient and / or at heavy loading, energy-efficient driving of a vehicle comprising the vehicle drive train can be achieved, since the internal combustion engine can be operated in its energy-efficient operating window, which also leads to low emissions while the electric machine is used to support the internal combustion engine. This also allows the use of a smaller energy storage device, resulting in lower cost for this and less additional weight for the vehicle.The method may further include the steps of, responsive to a variable ratio motor drive command:controlling the ring gear in the rotationally fixed state if it is not already in the rotationally fixed state;controlling the sun gear to the rotatable state when it is not already in said rotatable state;controlling the ring gear clutch device to a closed state if it is not already closed;controlling the clutch assembly to connect the output shaft of the internal combustion engine to the first shaft if this connection has not already been established and to disconnect the second shaft from the first shaft if they have not already been disconnected from one another;operating the internal combustion engine to provide a drive torque; andthe electric machine is variably operated as a motor or as a generator and at different rotational speeds in order to achieve a desired transmission ratio.Thus, by controlling the electric machine, a variable gear ratio may be achieved so as to affect the gear ratio achieved by the planetary gear. This can be used, for example, when maneuvering the vehicle comprising the vehicle drive train at very low travel speeds.The method may further include the steps of, responsive to a command regarding regenerative braking of the vehicle powertrain:controlling the ring gear to the rotatable state if it is not already in said rotatable state;controlling the sun gear to the rotatable state when it is not already in said rotatable state;controlling the ring gear clutch device to a closed state if it is not already closed;controlling the clutch assembly to connect the second shaft, and optionally the output shaft of the internal combustion engine, to the first shaft if this connection has not already been established; andoperating the electric machine as a generator; the method optionally further comprising the step of: when the output shaft of the internal combustion engine is connected to the first shaft, controlling the internal combustion engine to output a braking torque.This enables, inter alia, efficient charging of the energy storage device in situations in which a vehicle comprising the vehicle drive train has to be braked in order to reduce or at least maintain its travel speed (in the case of a downhill travel).The present disclosure also relates to a computer program comprising instructions which, when executed by a computer, cause the computer to carry out the method as described above.Furthermore, the present disclosure relates to a computer readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method as described above.Additionally, the present disclosure provides a control assembly configured to control the vehicle powertrain described above. The control arrangement is configured to charge an energy storage device in response to a command while it is required to transmit a drive torque to the input shaft in a third gear ratio, the energy storage device being configured to supply power to the electric machine:controlling the ring gear to the rotatable state if it is not already in said rotatable state;controlling the sun gear to the rotatable state when it is not already in said rotatable state;controlling the ring gear clutch device to a closed state if it is not already closed;controlling the clutch assembly to connect the output shaft of the engine and the second shaft to the first shaft if this connection has not already been established; andoperating the electric machine as a generator.The control arrangement provides the same advantages as described above with respect to the corresponding method of controlling the vehicle powertrain described herein.The present disclosure also relates to a vehicle including the vehicle powertrain described above and an energy storage device configured to provide power to the electric machine of the vehicle powertrain. Said vehicle may further comprise the control arrangement as described above. The vehicle may be, but is not limited to, a land-based heavy-duty vehicle such as a bus or truck. According to one embodiment, the vehicle may be a long-distance truck.Additionally, the vehicle may be a vehicle configured to be operated either partially or fully by a driver. Such a driver may be present on board the vehicle or remotely control the vehicle. Alternatively, the vehicle may also be a fully autonomous vehicle.Brief Description of the DrawingsFIG. 1 schematically illustrates a side view of an example of a vehicle, FIG. 2 schematically illustrates a first example embodiment of the vehicle powertrain described herein, FIG. 3 schematically illustrates a second example embodiment of the vehicle powertrain described herein, FIG. 4 is a flow chart schematically illustrating an example embodiment of the method described herein for controlling the vehicle powertrain in accordance with the present disclosure, FIG. 5 schematically illustrates an example embodiment of a device that may include, consist of, or be included in a control arrangement configured to carry out the method described herein for controlling the vehicle powertrain.DETAILED DESCRIPTIONThe invention will be described in more detail below with reference to exemplary embodiments and the accompanying drawings. The invention is not, however, limited to the exemplary embodiments discussed and / or shown in the drawings, but may be varied within the scope of the appended claims. Moreover, the drawings are not to be considered as drawn to scale, as some features may be exaggerated to more clearly illustrate the invention or features thereof.The present disclosure relates to a vehicle powertrain and a vehicle including such a vehicle powertrain. The vehicle powertrain includes an electric machine and an internal combustion engine, each configured to function as a propulsion unit. The present vehicle powertrain is thus a hybrid vehicle powertrain and may be operated, for example, as a parallel hybrid vehicle powertrain. The electric machine is designed to be operated selectively as a motor or as a generator. In addition, the electric machine is designed to be supplied with current from an energy storage device. It should be noted here that such an energy storage device is normally not considered part of the vehicle powertrain per se, but may be included in a vehicle comprising the vehicle powertrain. The vehicle powertrain further includes a planetary gear having a sun gear, a plurality of planet gears supported by a planet carrier, and a ring gear connected to / supported by a ring gear carrier. The planet carrier is in turn connected to an output shaft of the planetary gearing.The vehicle powertrain further includes a first shaft and a second shaft, and a driveshaft connected to one or more drive wheels. Normally, the drive shaft is connected to at least two drive wheels, the two drive wheels being connected to the drive shaft at opposite ends of the drive shaft. The electric machine is connected to the second shaft of the vehicle driveline. As a result, the second shaft is configured to be driven by the electric machine.The vehicle powertrain also includes a clutch assembly configured to selectively connect an output shaft of the engine to the first shaft. The clutch assembly is further configured to selectively connect the second shaft to the first shaft. The clutch assembly is disposed at a first end of the first shaft.The second end of the first shaft (i.e., the end opposite the first end of the first shaft) is connected to the sun gear of the planetary gear. Thus, the sun gear is configured to co-rotate with the rotation of the first shaft. The vehicle driveline also includes a ring gear clutch device configured to selectively connect the second shaft to the ring gear of the planetary gear set.The ring gear and the sun gear of the planetary gear can each be controlled to operate in both a rotationally fixed state and a rotatable state. For example, the vehicle drive train may include a first locking device configured to selectively lock the ring gear of the planetary gear set in a rotationally fixed state. This first locking device can be arranged on the ring gear. In addition, the sun gear of the planetary gear set may be locked in a rotationally fixed state by connecting the first shaft to the output shaft of the engine using the clutch assembly when the output shaft of the engine is locked in a rotationally fixed state. The output shaft of the internal combustion engine can be blocked in a rotationally fixed state by a second blocking device configured for this purpose.The second shaft of the vehicle drive train can expediently be a hollow shaft. In this case, the first shaft may be disposed within and through the hollow second shaft. As a result, a more compact design of the vehicle drive train can be achieved. The first and the second shaft can be coaxial or at least arranged in parallel.The output shaft of the planetary gear mechanism can be directly connected to a differential of the vehicle drive train, wherein the differential is designed to transmit a drive torque to the drive shaft. Alternatively, the output shaft of the planetary gear set may be connected to the differential via a multi-speed transmission unit of the vehicle drive train. Such a multi-speed transmission unit may be disposed in the vicinity of the input shaft. By means of such a multi-speed transmission unit, further transmission ratios of the vehicle drive train can be provided.By means of the vehicle powertrain described herein, the capacity of an energy storage device configured to provide power to the electric machine may be substantially reduced compared to, for example, a purely battery electric vehicle configured to provide the same range. This in turn leads to a lower weight of the vehicle and thus also to a higher possible charge weight as a result of the smaller size of the energy storage device. In addition, the cost of the energy storage device is reduced and as a result more space is available on board the vehicle, for example for the charge.In addition, the configuration of the powertrain described herein enables the engine to operate only within its most energy efficient operating window and under relatively stable operating conditions. Instead, the electric machine can be used to cycle all cases of transient energy demand. Generally, internal combustion engines for heavy vehicles have low energy efficiency at lower speeds and lower torque demands. Operation of the internal combustion engine outside the most energy efficient operating window and transient events during operation of the internal combustion engine may result in increased emissions. However, this may be minimized by the vehicle powertrain described herein.As mentioned above, the present disclosure also provides a vehicle including the vehicle powertrain described above. The vehicle may be a heavy truck such as, but not limited to, a bus or a truck and could therefore also be used for, for example, medium-size trucks. Importantly, the vehicle powertrain described herein provides an excellent solution to efforts to electrifying long-haul trucks that can be operated over an entire long-haul cycle without requiring a stop at a charging station. Therefore, according to an aspect of the present disclosure, the vehicle is a long distance truck. A long-route truck is understood here to mean a truck which is designed for transporting relatively heavy loads over long routes, for example 400 km or more.The present disclosure also relates to a method of controlling the vehicle powertrain described above. This control may be performed to achieve various operating conditions of the vehicle powertrain, depending on the desired operating condition of a vehicle including that vehicle powertrain. Depending on the desired operating condition, this method generally comprises the steps of: (a) driving the ring gear of the planetary gear set into a rotatable or a rotationally fixed condition; (b) driving the sun gear of the planetary gear set into a rotatable or a rotationally fixed condition; (c) driving the ring gear clutch device into a closed or an open condition, the closed condition connecting the second shaft to the ring gear of the planetary gear set and the open condition disconnecting the second shaft from the ring gear; (d) driving the clutch assembly to connect and / or disconnect one or both of the output shaft of the internal combustion engine and the second shaft to the first shaft; (e) driving the electric machine to operate as a motor, operate as a generator, or rotate only with the rotation of the second shaft; (f) controlling the engine to provide positive output torque, provide negative output torque, or shut down.It should be noted here that a positive output torque of the engine is also referred to herein as a drive torque, and a negative output torque of the engine is also referred to herein as a brake torque.The method described herein for controlling the vehicle powertrain is performed by a control assembly configured therefor.More specifically, the method described herein for controlling the vehicle powertrain includes, in response to a command, charging an energy storage device configured to supply power to the electric machine while requiring a drive torque to be transmitted to the driveshaft at a third gear ratio, the following steps:controlling the ring gear to the rotatable state if it is not already in said rotatable state;controlling the sun gear to the rotatable state when it is not already in said rotatable state;controlling the ring gear clutch device to a closed state if it is not already closed;controlling the clutch assembly to connect the output shaft of the engine and the second shaft to the first shaft if this connection has not already been established;operating the electric machine as a generator; andoperating the internal combustion engine in such a way that it provides a drive torque.The method described herein may further include controlling the vehicle powertrain to any of the operating conditions of the vehicle powertrain in response to a corresponding command, as will be described in more detail below with reference to the example embodiment of the vehicle powertrain shown in FIG. 2.Executing the method described herein for controlling the vehicle powertrain described herein may be controlled by programmed instructions. These programmed instructions may be in the form of a computer program that, when executed by a computer, causes the computer to execute desired forms of control operations. Such a computer may be included in the control arrangement described herein, for example. A computer in the present disclosure is understood to mean any type of hardware or hardware / firmware device realized using processing circuitry, such as, but not limited to, a processor, a central processing unit (CPU), a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable gate array (FPGA), a system-on-chip element (SoC), a programmable logic unit, a microprocessor, an application specific integrated circuit, or any other device capable of electronically executing operations in a defined manner.The programmed instructions described above, which may be in the form of a computer program, may be stored on a computer readable medium. Therefore, the present disclosure also relates to a computer readable medium storing instructions that, when executed by a computer, cause the computer to perform the method described herein for controlling the vehicle powertrain. The computer readable medium may be a non-transitory computer readable medium, such as a tangible electronic, magnetic, optical, infrared, electromagnetic, and / or semiconductor system, apparatus, and / or device.The present disclosure further relates to a control arrangement configured to carry out the method described herein for controlling the vehicle powertrain described above. The control arrangement may be configured to perform any of the steps of the method of controlling the vehicle powertrain described herein.More specifically, the present disclosure provides a control arrangement configured to control the vehicle powertrain described above. The control arrangement is configured to charge an energy storage device while it is required to transmit a drive torque to the drive shaft in a third gear ratio in response to a command, the energy storage device being configured to supply power to the electric machine, to carry out the following steps:controlling the ring gear to the rotatable state if it is not already in said rotatable state;controlling the sun gear to the rotatable state when it is not already in said rotatable state;controlling the ring gear clutch device to a closed state if it is not already closed;controlling the clutch assembly to connect the output shaft of the engine and the second shaft to the first shaft if this connection has not already been established; andoperating the electric machine as a generator.FIG. 1 schematically illustrates a side view of an example of a vehicle 1, which here is an example of a truck. The vehicle 1 comprises a vehicle drive train 2, the vehicle drive train 2 comprises a first drive unit in the form of an electric machine 3, the electric machine 3 being designed to be supplied with power from an energy storage device 10 of the vehicle when the electric machine 3 is operated as a motor. The electric machine 3 can also be operated as a generator for the purpose of charging the energy storage device 10. The vehicle drive train 2 further comprises a second drive unit in the form of an internal combustion engine 4. the vehicle drive train 2 also comprises a planetary gear 5, an output shaft 14 of the planetary gear 5 is connected to a drive shaft 6, which in turn is connected to drive wheels 7. The drive shaft 6 and the drive wheels 7 are components of the vehicle drive train 2.The vehicle 1 further includes a control assembly 100 configured to control the vehicle powertrain 2. The control assembly 100 may be configured to perform any of the steps of the method described herein for controlling the vehicle powertrain 2 according to the present disclosure.FIG. 2 schematically illustrates a first exemplary embodiment of the vehicle powertrain 2 according to the present disclosure. The vehicle powertrain 2 may be included in a vehicle, such as the vehicle 1 shown in FIG. 1.The vehicle powertrain 2 includes a plurality of shafts including a first shaft 11 and a second shaft 12. The first shaft 11 and the second shaft 12 may be connected to or disconnected from each other by a clutch assembly 30, depending on the operating state of the vehicle powertrain 2. The clutch assembly 30 is disposed at a first end 11 aof the first shaft 11. The second shaft 12 may be a hollow shaft, and the first shaft 11 may be arranged to extend longitudinally through the hollow second shaft 12. Thus, the first and second shafts 11, 12 may be coaxial, or at least substantially parallel. The plurality of shafts of the vehicle powertrain 2 also include a driveshaft 6 to which drive wheels 7 are connected. Two drive wheels 7 are shown in the figure. However, the vehicle drive train may comprise further drive wheels, such as two drive wheels at the respective ends of the drive shaft 6. In the case of a plurality of drive shafts 6, these drive shafts can expediently be arranged substantially parallel.The vehicle drive train 2 further comprises an electric machine 3. the electric machine 3 is operable as a motor to generate a drive torque to be transmitted to the drive wheels 7, and for this purpose is configured to be supplied with power from an energy storage device (such as the energy storage device 10 of the vehicle 1 shown in FIG. 1 ). The electric machine 3 may also be operated as a generator for the purpose of converting mechanical energy into electrical energy that may be used to charge the energy storage device. In other words, the electric machine is designed to be selectively operated as a motor or as a generator depending on the operating state of the vehicle drive train 2. The electric machine 3 comprises a rotor 16 and a stator 17. Thus, the second shaft 12 of the vehicle drive train 2 can alternatively also be referred to as an electric machine shaft. The second shaft 12 is arranged to extend outwardly on either side of the electric machine 3 to be selectively connectable to other components of the vehicle powertrain 2.The vehicle drive train 2 further comprises an internal combustion engine 4. the internal combustion engine 4 is designed to generate a drive torque to be transmitted to the drive wheels 7. The engine 4 may also be used to generate mechanical energy that may be converted to electrical energy by the electric machine 3 to charge an energy storage device (such as the energy storage device 10 of the vehicle 1 shown in FIG. 1 ). The engine 4 may also be used to provide braking torque to the vehicle powertrain 2, such as by engine drag or engine braking, if desired. The internal combustion engine 4 comprises an output shaft 13 which can be connected to the first shaft 11 and / or the second shaft 12 via the clutch arrangement 30.The vehicle powertrain 2 also includes a planetary gear set 5. the planetary gear set 5 includes a sun gear 20, a plurality of planet gears 21 supported by a planet carrier 22, and a ring gear 23 connected to a ring gear carrier 24. The sun gear 20 is connected to the first shaft 11 of the vehicle driveline 2 at the second end 11 bof the first shaft 11. In other words, the first shaft 11 is arranged to extend longitudinally from the clutch assembly 30 to the sun gear 20 of the planetary gear 5. Additionally, the ring gear 23 may be connected via the ring gear carrier 24 to the second shaft 12 of the vehicle powertrain 2 through a ring gear clutch device 34. This ring gear clutch device 34 is arranged on a side of the electric machine 3 which is opposite the side on which the clutch arrangement 30 is arranged. The ring clutch device 34 may be, for example, but is not limited to, a friction clutch, a viscous clutch, a positive clutch, or a dog clutch.The ring gear 23 of the planetary gear 5 can be locked in a rotationally fixed state by means of a first locking device 25. This first locking device 25 can alternatively also be referred to as a ring gear locking device. When the ring gear 23 is not locked by the first locking device 25 in the non-rotating state, the ring gear 23 is in a rotatable state. The ring gear carrier 24 is configured to co-rotate with the rotation of the ring gear 23.In addition, the planet carrier 22 is connected to a shaft which forms an output shaft 14 of the planetary gearing 5. This output shaft 14 is connected via a differential 8 to the drive shaft 6 of the vehicle drive train 2.As described above, the vehicle powertrain 2 includes a clutch assembly 30 disposed at a first end 11 aof the first shaft 11. The clutch arrangement 30 is designed to connect or disconnect the second shaft 12 and the output shaft 13 of the internal combustion engine 4 respectively to and from the first shaft 11. The clutch assembly 30 may be controlled into four different operating states, namely:(i) a first operating state in which the first shaft 11, the second shaft 12 and the output shaft 13 of the internal combustion engine 13 are respectively separated from each other,(ii) a second operating state in which the first shaft 11 is connected to the second shaft 12 and the output shaft 13 of the internal combustion engine is respectively disconnected from the first shaft 11 and the second shaft 12,(iii) a third operating state in which the output shaft 13 of the internal combustion engine 4 is connected to the first shaft 11 and the second shaft 12 is separated from the output shaft 13 and the first shaft 11, respectively; and(iv) a fourth operating state in which each of the second shaft 12 and the output shaft 13 of the internal combustion engine 4 is connected to the first shaft, which in turn also means that the output shaft 13 is connected to the second shaft 12.The clutch assembly 30 may include a first clutch device 31 and a second clutch device 32. The first clutch device 31 is configured to connect (disconnect) the output shaft 13 of the engine 4 to (or from) the first shaft 11. The second clutch device 32 of the clutch arrangement 30 is configured to connect (or disconnect) the first shaft 11 and the second shaft 12. Each of the first clutch device 31 and the second clutch device 32 may be selected from the group consisting of a friction clutch, a viscous clutch, a positive clutch, and a dog clutch, for example.As already mentioned, the sun gear 20 of the planetary gearing 5 is designed such that it can be operated selectively in a rotatable or a rotationally fixed state. Therefore, the vehicle drive train 2 also comprises means with which the sun wheel 20 can be locked in a rotationally fixed state. In the exemplary embodiment shown in FIG. 2, this is achieved by a gear wheel 41 arranged on the output shaft 13 of the internal combustion engine 4, which gear wheel can be locked in a rotationally fixed state by a second locking device 42. In other words, the vehicle drive train 2 comprises a second blocking device 42 which is designed to block the output shaft 13 of the internal combustion engine in a rotationally fixed state. Thus, controlling the clutch assembly 30 to connect the output shaft 13 of the engine 4 to the first shaft 11 of the vehicle powertrain 2 while the output shaft 13 of the engine 4 is locked in a rotationally fixed state by the second locking device 42 will forcibly lock the sun gear 20 in a rotationally fixed state.It should be appreciated that although the vehicle powertrain 2 illustrated in FIG. 2 has a configuration in which the first shaft 11 extends longitudinally within and through a hollow second shaft 12, other configurations in which the first and second shafts 11, 12 are arranged side-by-side are also contemplated. However, such configurations would require additional transmission assemblies and shafts to connect the second shaft 12 to the clutch assembly 30 as well as the ring gear clutch device, which in turn would result in, for example, a bulky vehicle powertrain 2.Various operating states of the vehicle drive train 2 illustrated in FIG. 2 are described below. These operating conditions are enabled by controlling the clutch device 30 and the ring gear clutch device 34, respectively, to connect / disconnect various shafts of the vehicle powertrain 2, controlling each of the sun gear 20 and ring gear 23 of the planetary gear set 5 to a rotatable or non-rotatable state, and operating the electric machine 3 (either as a motor or as a generator) and / or the engine 4 to provide a drive or brake torque.Purely electric drive with a first transmission ratioIn a purely electric drive with a first transmission ratio, the ring gear 23 is controlled into a rotationally fixed state, whereas the sun gear 20 is controlled into a rotatable state. In addition, the ring gear clutch device 34 is controlled to an open state, thereby disconnecting the second shaft 12 from the ring gear carrier 24 and thus also from the ring gear 23. Further, the clutch assembly 30 is controlled to connect the first shaft 11 to the second shaft 12. By operating the electric machine 3 as a motor, a drive torque is thus transmitted from the second shaft 12 via the first shaft 11 to the sun gear 20 of the planetary gearing 5. The drive torque is transmitted from the sun gear 20 via the planetary gears 21 to the planetary gear carrier 22 and the output shaft 14 of the planetary gear set 5 and then via the differential 8 to the drive shaft 6.In this operating state, the output shaft 13 of the internal combustion engine 4 is normally separated from the first shaft 11 by actuating the clutch arrangement 30. This prevents any braking torque resulting from engine drag from being applied to the vehicle driveline 2.The above-described operating state of an electric-only drive having a first transmission ratio can be used, for example, when the vehicle is set in motion and at low travel speeds. This operating state can lead to the highest torque at the drive wheels 7 while the vehicle drive train 2 is operated with purely electric drive.Purely electric drive with a second transmission ratioIn order to obtain a purely electric drive with a second transmission ratio, the ring gear 23 is controlled into a rotatable state, whereas the sun gear 20 is controlled into a rotationally fixed state. The sun gear 20 may be controlled to this non-rotational state by locking the output shaft 13 of the engine 4 in a non-rotational state using the second locking device 42 and controlling the clutch assembly 30 to connect the output shaft 13 of the engine 4 to the first shaft 11. The clutch assembly 30 is also controlled to disconnect the second shaft 12 from the first shaft 11. In addition, the ring gear clutch device 34 is controlled to a closed state, thereby connecting the second shaft 12 to the ring gear carrier 24 and thus also to the ring gear 23. By operating the electric machine 3 as a motor, a drive torque is transmitted from the second shaft 12 to the ring gear 23 of the planetary gear set 5. The drive torque is transmitted from the ring gear 23 (via the planetary gears 21) to the planetary gear carrier 22 and the output shaft 14 of the planetary gear 5, and further via the differential 8 to the drive shaft 6 and the associated drive wheels 7.The operating state of the electric drive with the second transmission ratio can be used, for example, at relatively low travel speeds, such as in city traffic or the like.Purely electric drive with a third transmission ratioIn order to obtain a purely electric drive with a third transmission ratio, the ring gear 23 and the sun gear 20 are each controlled into a rotatable state. In addition, the ring gear clutch device 34 is controlled to a closed state, thereby connecting the second shaft 12 to the ring gear carrier 24 and thus also to the ring gear 23. Also, the clutch assembly is controlled to connect the second shaft 12 to the first shaft 11. By operating the electric machine 3 as a motor, a drive torque is transmitted from the second shaft 12 to the ring gear 23 of the planetary gear set 5 and from the second shaft 12 via the clutch arrangement 30 to the first shaft 11 and thus also to the sun gear 20. Since the drive torque is transmitted both to the ring gear 23 and to the sun gear 20 of the planetary gearing 5, the planet gear carrier is connected to the ring gear 23 and to the sun gear 20 in a rotationally fixed manner. This leads to a direct drive for the purely electric drive of the vehicle drive train 2.Additionally, the clutch assembly 30 may be suitably controlled to disconnect the output shaft 13 of the engine 4 from the first shaft 11 (and thus also from the second shaft 12) to avoid any braking torque on the vehicle powertrain 2 caused by engine drag. However, should it be desired to drain the energy storage device configured to supply power to the electric machine, for example due to the prediction that the energy storage device has a state of charge too high to allow regenerative braking during an imminent braking operation, it may be reasonable to connect the output shaft 13 of the internal combustion engine 4 to the first and second shafts 11, 12 by controlling the clutch arrangement 30. As a result, the energy consumption of the electric machine 3 can be increased in order to compensate for a braking torque exerted by the internal combustion engine 4 on the vehicle drive train 2. Such a braking torque can be exerted either by engine drag or by engine braking. Engine braking is understood here to mean that the internal combustion engine 4 is operated in such a way that it outputs a braking torque, for example by using an exhaust brake, a decompression brake or a variable disk brake. During engine towing, the internal combustion engine 4 is controlled to a passive state and applies a braking torque to the vehicle driveline 2 by requiring energy therefrom to rotate the internal combustion engine.The operating state of the electric drive with a third transmission ratio can be used, for example, at higher travel speeds if the drive torque provided by the electric machine 3 is sufficient to maintain these higher travel speeds.Regenerative BrakingIn order to decelerate the vehicle powertrain 2 by regenerative braking, the ring gear 23 and the sun gear 20 are each controlled to a rotatable state. In addition, the ring gear clutch device 34 is controlled to a closed state, thereby connecting the second shaft 12 to the ring gear carrier 24 and thus also to the ring gear 23. Also, the clutch assembly is controlled to connect the second shaft 12 to the first shaft 11. By operating the electric machine 3 as a generator, a braking torque is then exerted on the vehicle drive train 2 by the conversion of mechanical energy into electrical energy achieved by means of the electric machine 3. The electrical energy generated by the electric machine 3 can be stored in the energy storage device in order to supply the electric machine 3 with current when it is intended to be operated as a motor.Depending on the desired level of braking torque, the clutch assembly 30 may be controlled to either connect or disconnect the output shaft 13 of the engine 4 from the first shaft 11. When the output shaft 13 of the engine 4 is disconnected from the first shaft 11, the engine 4 is not used to apply a braking torque to the vehicle powertrain 2. However, when the output shaft 13 of the engine 4 is connected to the first shaft 11, the engine may be used to further increase the braking torque applied to the vehicle powertrain 2 by either engine drag or engine braking. As already mentioned, engine braking is understood here to mean that the internal combustion engine 4 is operated in such a way that it delivers a braking torque, for example by using an exhaust brake, a decompression brake or a variable disk brake.Hybrid Drive with a First Transmission RatioTo obtain a hybrid drive with a first transmission ratio, the ring gear 23 is controlled to a rotationally fixed state, whereas the sun gear 20 is controlled to a rotatable state. In addition, the ring gear clutch device is controlled to an open state, thereby disconnecting the second shaft 12 from the ring gear 23 of the planetary gear 5. Further, the clutch assembly 30 is controlled to connect both the output shaft 13 of the engine 4 and the second shaft 12 to the first shaft 11. By operating both the internal combustion engine 4 and the electric machine 3 in such a way that a drive torque is provided (which means that the electric machine 3 is operated as a motor), the drive torque is transmitted both from the electric machine 3 and from the internal combustion engine 4 to the first shaft 11 and thus to the sun gear 20 of the planetary gearing 5. The drive torque is transmitted from the sun gear 20, via the planetary gears 21, to the planetary gear carrier 22 and the output shaft 14 of the planetary gear 5, and further via the differential 8 to the drive shaft 6.The operating state of the hybrid drive with a first transmission ratio can be used, for example, when the vehicle is set in motion on a steep gradient or at a steep gradient at a low driving speed. Use of the internal combustion engine to assist the electric machine may be considered here in order to ensure a sufficient drive torque. This operating state can lead to the highest drive torque at the drive wheels 7 while the vehicle drive train 2 is operated in hybrid drive.Hybrid Drive with a Third Transmission RatioIn order to obtain a hybrid drive having a third gear ratio, the ring gear 23 and the sun gear 20 are each controlled to a rotatable state. In addition, the ring gear clutch device 34 is controlled to a closed state, thereby connecting the second shaft 12 to the ring gear carrier 24 and thus also to the ring gear 23. Also, the clutch assembly 30 is controlled to connect both the output shaft 13 of the engine 4 and the second shaft 12 to the first shaft 11.By operating both the internal combustion engine 4 and the electric machine 3 in such a way that a drive torque is provided (which means that the electric machine 3 is operated as a motor), the drive torque is transmitted via the second shaft 12 to the ring gear 23 of the planetary gearing 5 and via the clutch arrangement 30 to the first shaft 11 and thus also to the sun gear 20. Since the drive torque is transmitted both to the ring gear 23 and to the sun gear 20 of the planetary gearing 5, the planet gear carrier is connected to the ring gear 23 and to the sun gear 20 in a rotationally fixed manner. This leads to a direct drive for the hybrid drive of the vehicle drive train 2.The operating state of the hybrid drive with a third transmission ratio can be used, for example, at the highest driving speeds, such as, for example, above 80 km / h, or during driving with high driving resistance, such as, for example, at high speed on a steep gradient.Pure motor drive with a third transmission ratioIn order to obtain a pure motor drive with a third transmission ratio, the ring gear 23 and the sun gear 20 are each controlled into a rotatable state. In addition, the ring gear clutch device 34 is controlled to a closed state, thereby connecting the second shaft 12 to the ring gear carrier 24 and thus also to the ring gear 23. Also, the clutch assembly 30 is controlled to connect both the output shaft 13 of the engine 4 and the second shaft 12 to the first shaft 11. In this operating state, the electric machine 3 is not supplied with current, but rather is allowed to rotate resulting from the rotation of the second shaft 12. The drive torque generated by the internal combustion engine is transmitted via the second shaft 12 to the ring gear and via the first shaft 11 to the sun gear 20 of the planetary gear mechanism 5. Since the drive torque is transmitted both to the ring gear 23 and to the sun gear 20 of the planetary gearing 5, the planet gear carrier 22 is connected to the ring gear 23 and to the sun gear 20 in a rotationally fixed manner. This leads to a direct drive for the pure engine drive of the vehicle drive train 2, and the drive torque is transmitted from the planetary gear carrier 22 and the output shaft 14 of the planetary gear set 5 via the differential 8 to the drive shaft 6.The operating state of the pure motor drive with a third transmission ratio can be used, for example, at high driving speeds, such as about 80-90 km / h, at which the internal combustion engine can be operated at or near its most energy efficient operating window. This is the most energy efficient driving mode for a heavy vehicle, with relatively low emissions, for longer trips at a relatively uniform travel speed. It also allows the use of a smaller size energy storage device, thereby adding less weight and costs as compared to electric propulsion under such driving conditions.It should be noted that the term "pure engine drive" is used herein to describe an operating state where the vehicle powertrain is powered solely by the internal combustion engine without the electric machine operating as a motor or as a generator.charging the energy storage device while simultaneously providing a drive torque for the drive shaftThe charging of an energy storage device 10, which is designed to supply the electric machine 3 with current, wherein at the same time a drive torque is also transmitted to the drive shaft 6 and the associated drive wheels 7, can be carried out in two different operating states of the vehicle drive train.According to the first alternative, a drive torque is transmitted to the drive shaft 6 at the third transmission ratio. This can be achieved by controlling the ring gear 23 and the sun gear 20 to a rotatable state, respectively, and controlling the ring gear clutch device 34 to a closed state, thereby connecting the second shaft 12 to the ring gear 23. In addition, the clutch assembly 30 is controlled to connect both the output shaft 13 of the engine 4 and the second shaft 12 to the first shaft 11. By operating the internal combustion engine 4 in such a way that it outputs a drive torque, a portion of the energy generated by the internal combustion engine can be converted into electrical energy by operating the electric machine 3 as a generator. The electric energy generated by the electric machine may be used to charge the energy storage device 10. The remaining part of the drive torque that is not consumed by the electric machine 3 is transmitted via the planetary gear 5 to the drive shaft 6 and the associated drive wheels 7. The first alternative can be used, for example, at high travel speeds of a vehicle having the vehicle drive train 2.According to the second alternative, a drive torque with the first transmission ratio is transmitted to the drive shaft 6. This can be achieved by controlling the ring gear 23 in a rotationally fixed state and the sun gear 20 in a rotatable state. Further, the ring gear clutch device 34 is controlled to an open state, thereby disconnecting the second shaft 12 from the ring gear 23. In addition, the clutch assembly 30 is controlled to connect both the output shaft 13 of the engine 4 and the second shaft 12 to the first shaft 11. As in the first alternative described above, the internal combustion engine 4 is operated to output a driving torque. As a result, a portion of the energy generated by the internal combustion engine can be converted into electrical energy by operating the electric machine 3 as a generator. The electrical energy generated by the electric machine 3 can thus be used for charging the energy storage device 10. The remaining part of the drive torque, which is generated by the internal combustion engine 4 and is not consumed by the electric machine 3, is transmitted via the planetary gear 5 to the drive shaft 6 and the associated drive wheels 7. The second alternative can be used, for example, at low travel speeds of a vehicle having the vehicle drive train 2.charging the energy storage device when no drive torque (or braking torque) has to be transmitted to the drive shaftIn order to enable charging of an energy storage device 10 configured to supply power to the electric machine 3, both the ring gear 23 and the sun gear 20 may be controlled to a rotatable state. Further, the ring gear clutch device 34 is controlled to an open state so that the second shaft 12 is separated from the ring gear 23. In addition, the clutch assembly 30 is controlled to connect both the output shaft 13 of the engine 4 and the second shaft 12 to the first shaft 11. By operating the engine 4 to produce a positive output torque, the energy produced by the engine 4 may be converted to electrical energy by operating the electric machine 3 as a generator.It should be noted that a positive output torque of the internal combustion engine corresponds to a drive torque of the internal combustion engine. However, since the torque generated by the engine is not used to drive the input shaft, the term "positive output torque" is used herein instead.This operating state can be used, for example, when the vehicle comprising the vehicle drive train 2 is stationary or while the vehicle is in motion, without a drive torque (or a brake torque) having to be transmitted to the drive shaft 6 with the associated drive wheels 7.Charging of the energy storage device 10 configured to supply power to the electric machine 3 while the vehicle is at a standstill with the vehicle powertrain 2 may alternatively be achieved as follows. Both the ring gear 23 and the sun gear 20 are controlled to a rotatable state. Further, the ring gear clutch device 34 is controlled to a closed state, whereby the second shaft 12 is connected to the ring gear 23. In addition, the clutch assembly 30 is controlled to connect the output shaft 13 of the engine 4 to the first shaft 11 but disconnect the second shaft 12 from the first shaft 11. Furthermore, the drive shaft 6 is controlled into a rotationally fixed state. This can be achieved, for example, by using service brakes to prevent the drive wheels 7 from rotating, thereby also locking the drive shaft 6. Controlling the input shaft 6 in a rotationally fixed state also means that the planet carrier 22 is controlled in a rotationally fixed state. The internal combustion engine 4 is then controlled in such a way that it exerts a positive torque and the electric machine 3 is operated as a generator. As a result, the mechanical energy coming from the internal combustion engine 4 can be converted by the electric machine 3 into electrical energy which can be stored in the energy storage device 10.Variable Ratio Motor DriveIn certain cases, it may be desirable to operate the vehicle powertrain 2 in a variable ratio operating mode. This may be carried out, for example, to use overdrive for the engine so that it may operate in a more efficient operating window. Alternatively, this may be desired when manoeuvring the vehicle comprising the vehicle drive train 2 at very low travel speeds.In this operating state, the ring gear 23 is controlled to a rotationally fixed state, whereas the sun gear 20 is controlled to a rotatable state. In addition, the ring gear clutch device 34 is controlled to a closed state to connect the second shaft 12 to the ring gear 23. In addition, the clutch assembly 30 is controlled to connect the output shaft 13 of the engine 4 to the first shaft 11 and disconnect the second shaft 12 from the first shaft 11. The internal combustion engine 4 is operated to provide a driving torque, whereas the electric machine 3 is controlled to provide different positive or negative torques (by operating as a motor or as a generator) and / or rotational speeds to the ring gear 23 so as to achieve the variable transmission ratio.emptying the energy storage deviceIn certain cases, it may be desirable to drain the energy storage device 10 configured to supply power to the electric machine, for example, based on the prediction that the energy storage device 10 has a state of charge that is too high to enable sufficient regenerative braking during an imminent braking operation. Depletion of the energy storage device 10 may be achieved by controlling the vehicle powertrain 2 to allow the electric machine 3 to consume more energy than would be required to provide the desired drive torque to the driveshaft 6 and the associated drive wheels 7. In this case, the purging is carried out while the vehicle is in motion. However, if desired, it is also possible to drain the energy storage device 10 while the vehicle is at a standstill.The emptying of the energy store can be achieved, according to a first alternative, as described above with regard to the operating state of the electric drive with the third transmission ratio. The emptying is carried out according to the first alternative while the vehicle 1 is in motion.According to a second alternative, the emptying of the energy store 10 can be achieved by controlling both the ring gear 23 and the sun gear 20 in a rotatable state. In addition, the ring gear clutch device 34 is controlled to an open state so that the second shaft 12 is separated from the ring gear 23. In addition, the clutch assembly 30 is controlled to connect both the output shaft 13 of the engine 4 and the second shaft 12 to the first shaft 11. The electric machine is then operated as an engine but does not transmit drive torque to the drive shaft 6. By having the engine have the ability to provide braking torque to the vehicle driveline 2, either as a result of engine drag or by controlling the engine 4 to provide braking torque, for example through the use of an exhaust brake, a decompression brake or a variable disc brake, the electric machine 3 may be controlled to compensate for the braking torque provided by the engine 4. This makes it possible to achieve emptying of the energy storage device 10. Emptying according to the second alternative can take place either when the vehicle 1 comprising the vehicle drive train 2 is at a standstill, or when the vehicle is in motion, without it being necessary to transmit a drive torque to the drive shaft 6.According to a third alternative, the emptying of the energy store 10 can be achieved by controlling both the ring gear 23 and the sun gear 20 in a rotatable state. In addition, the ring gear clutch device 34 is controlled to a closed state so that the second shaft 12 is connected to the ring gear 23. In addition, the clutch assembly 30 is controlled to connect the output shaft 13 of the engine 4 to the first shaft 11 but disconnect the second shaft 12 from the first shaft 11. In addition, the drive shaft 6 is controlled into a rotationally fixed state. This can be achieved, for example, by using service brakes to prevent the drive wheels 7 from rotating, thereby also locking the drive shaft 6. Controlling the input shaft 6 in a rotationally fixed state also means that the planet carrier 22 is controlled in a rotationally fixed state. The electric machine is then operated as a motor and controlled to compensate for a braking torque exerted by the internal combustion engine by either engine drag or engine braking. As a result, emptying of the energy storage device 10 can be achieved when the vehicle is at a standstill.According to a fourth alternative, the emptying of the energy store 10 can be achieved by controlling the ring gear 23 in a rotationally fixed state and the sun gear 20 in a rotatable state. In addition, the ring gear clutch device 34 is controlled to an open state, thereby disconnecting the second shaft 12 from the ring gear 23. In addition, the clutch assembly 30 is controlled to connect both the output shaft 13 of the engine 4 and the second shaft 12 to the first shaft 11. The electric machine is then operated as a motor in order to transmit a drive torque to the drive shaft 6. Moreover, the internal combustion engine 4 is controlled so as to exert a braking torque on the vehicle drive train 2 that must be compensated by the electric machine 3. As a result, the electric machine 3 consumes more energy from the energy storage device 10 than is absolutely necessary for the intended propulsion of the vehicle, which in turn leads to emptying of the energy storage device 10. As can be seen from the above, the emptying of the energy storage device 10 according to the fourth alternative takes place while the vehicle comprising the vehicle drive train 2 is in motion.It should be noted here that the above-described operating states of the vehicle powertrain 2 as depicted in FIG. 2 are not to be considered a full list of operating states of the vehicle powertrain according to the present disclosure.Controlling the vehicle powertrain 2 to each of the operating conditions described above may be performed in response to a command for such an operating condition of the vehicle powertrain 2. The command may be generated according to any suitable known method, for example, by a driver of the vehicle comprising the vehicle powertrain, or by any control system (including the control arrangement) of the vehicle.FIG. 3 schematically illustrates a second exemplary embodiment of the vehicle powertrain 2 according to the present disclosure. The second exemplary embodiment is similar to the first exemplary embodiment described above and illustrated in FIG. 2, except that the vehicle powertrain 2 additionally includes a multi-speed transmission unit 15.The multi-speed transmission unit 15 may be disposed between the planetary gear 5 and the differential 8. In other words, the output shaft 14 of the planetary gear 5 may be connected to the multi-speed transmission unit 15, and the multi-speed transmission unit 15 may be further connected to the input shaft 6 via the differential 8. The purpose of the multi-speed transmission unit 15 is to make it possible for the drive torque to be transmitted with more transmission ratios to the drive shaft 16 and thus also to the drive wheels 7. The multi-speed transmission unit 15 may be, but is not limited to, a two-stage transmission unit or a three-stage transmission unit, for example.The vehicle powertrain 2 according to the second exemplary embodiment shown in FIG. 3 may be controlled according to various operating conditions in the same manner as described above for the exemplary embodiment of the vehicle powertrain shown in FIG. 1. However, it can be controlled by controlling the multi-speed transmission unit 15 so that it transmits the drive torque to the drive shaft 6 with further transmission ratios.FIG. 4 is a flow chart schematically illustrating an example embodiment of the method described herein for controlling the vehicle powertrain according to the present disclosure, such as the example embodiment of the vehicle powertrain as shown in FIG. 2 or the example embodiment of the vehicle powertrain according to FIG. 3.The method comprises a first step S 101 in which it is determined whether a command has been generated to charge an energy storage device while it is required to transmit a drive torque to the drive shaft at a third transmission ratio. The energy storage device is an energy storage device which is designed to supply the electric machine with current if the electric machine is to be operated as a motor. If no such command has been generated, the method may return to the start. However, if such an instruction has been generated, the process proceeds to the following steps.The method comprises a step S 102 in which the ring gear of the planetary gear is controlled to the rotatable state if it is not already in this rotatable state.The method further comprises a step S 103 in which the sun gear of the planetary gear is controlled to the rotatable state if it is not already in this rotatable state.The method further comprises a step S 104 in which the ring gear clutch device is controlled to a closed state if it is not already in this closed state.Moreover, the method comprises a step S 105 in which the clutch arrangement is controlled such that it connects both the output shaft of the internal combustion engine and the second shaft to the first shaft of the vehicle drive train if this connection has not already been established.It should be noted here that although steps S 102-S 105 are illustrated in the figure as successive steps and in a particular order for clarity, these steps may be performed substantially in parallel or in any order without thereby departing from the present disclosure.The method further comprises a step S 106 in which the electric machine is operated as a generator and a step S 107 in which the internal combustion engine is operated in such a way that it provides a drive torque. As a result, the energy storage device can be charged while a drive torque is transmitted to the drive shaft. Steps S 106 and S 107 are normally carried out substantially in parallel and can be initiated respectively after completion of steps S 102-S 105, provided that the electric machine and / or the internal combustion engine are not already operated according to steps S 106 and S 107.The method can then be reset to start again.FIG. 5 schematically illustrates an example embodiment of a device 500. The control arrangement 100 described above can comprise, for example, the device 500, consist of the device 500 or be contained in the device 500.The apparatus 500 comprises a non-volatile memory 520, a data processing unit 510, and a read / write memory 550. The non-volatile memory 520 comprises a first memory element 530, in which a computer program, for example an operating system, is stored in order to control the function of the apparatus 500. The apparatus 500 further includes a bus controller, a serial communication port, I / O devices, an A / D converter, a time and date input and transmission unit, an event counter, and an interrupt controller (not shown). The non-volatile memory 520 also includes a second storage element 540.A computer program P is provided that includes instructions for controlling a vehicle powertrain. The vehicle powertrain includes an electric machine that is selectively operable as a motor or a generator. The vehicle powertrain further includes an engine, a planetary gear, a first shaft, and a second shaft. The vehicle powertrain also includes a clutch assembly disposed at a first end of the first shaft. The vehicle powertrain also includes a driveshaft connected to at least one drive wheel. The above-mentioned first shaft is connected at its second end to a sun gear of the planetary gear, and an output shaft of the planetary gear is connected to a planet carrier of the planetary gear. The electric machine is connected to the second shaft. The second shaft is connectable to the first shaft via the clutch arrangement. In addition, an output shaft of the internal combustion engine is connectable to the first shaft via the first clutch arrangement. The second shaft is additionally connectable via a ring gear clutch device to a ring gear of the planetary gearing. Furthermore, the ring gear and the sun gear of the planetary gear are each designed to be operated selectively in a rotatable or a rotationally fixed state. The computer program includes instructions to, in response to a command to charge an energy storage device configured to supply power to the electric machine while it is required to transmit a drive torque to the input shaft in a third gear ratio, execute the following steps:controlling the ring gear to the rotatable state if it is not already in said rotatable state;controlling the sun gear to the rotatable state when it is not already in said rotatable state;controlling the ring gear clutch device to a closed state if it is not already closed;controlling the clutch assembly to connect the output shaft of the engine and the second shaft to the first shaft if this connection has not already been established;operating the electric machine as a generator; andoperating the internal combustion engine in such a way that it provides a drive torque.The program P may be stored in executable form or in compressed form in a memory 560 and / or in a read / write memory 550.The data processing unit 510 may perform one or more functions, that is, the data processing unit 510 may perform a certain part of the program P stored in the memory 560 or a certain part of the program P stored in the read / write memory 550.The computing device 510 may communicate with a data port 599 via a data bus 515. The non-volatile memory 520 is provided for communication with the data processing unit 510 via a data bus 512. The separate memory 560 is provided for communication with the data processing unit 510 via a data bus 511. The read / write memory 550 is configured to communicate with the data processing unit 510 via a data bus 514. The communication between the individual components can be realized via a communication connection. A communication link may be a physical link, such as an optoelectronic communication line, or a non-physical link, such as a wireless link, for example a radio or microwave link.When data is received at the data port 599, they may be temporarily stored in the second storage element 540. When the received input data has been temporarily stored, the data processing unit 510 is ready to execute the code as described above.Portions of the methods described herein may be affected by the device 500 via the computing device 510 executing the program stored in the memory 560 or the read / write memory 550. When the device 500 executes the program, the methods described herein are performed.

Claims

Vehicle drive train (2) having: - an electric machine (3) which is designed to be operated selectively as a motor or as a generator, - an internal combustion engine (4), - a planetary transmission (5), - a first shaft (11), - a second shaft (12), - a clutch arrangement (30) which is arranged at a first end of the first shaft (11), and - a drive shaft (6) which is connected to at least one drive wheel (7), wherein the first shaft (11) is connected at a second end (11b) of the first shaft (11) to a sun wheel (20) of the planetary transmission (5), an output shaft (14) of the planetary transmission (5) is connected to a planet wheel carrier (22) of the planetary transmission (5), the electric machine (3) is connected to the second shaft (12), the second shaft (12) is connectable to the first shaft (11) via the clutch arrangement (30), an output shaft (13) of the internal combustion engine (4) is connectable to the first shaft (11) via the clutch arrangement (30), and the second shaft (12) is connectable to a ring gear (23) of the planetary gear set (5) via a ring gear clutch device (34), wherein the ring gear (23) and the sun gear (20) of the planetary gear set (5) are each configured to be selectively operated in a rotatable or a rotationally fixed state.The vehicle powertrain (2) of claim 1, wherein the second shaft (12) is a hollow shaft, and the first shaft (11) is arranged to extend through the hollow second shaft (12).Vehicle drive train (2) according to any one of claims 1 or 2, further comprising a first locking device (25) which is designed to lock the ring gear (23) of the planetary gearing (5) selectively in the rotationally fixed state.Vehicle drive train (2) according to any of the preceding claims, further comprising a second locking device (42) configured to selectively lock the output shaft (13) of the internal combustion engine (4) in a rotationally fixed state, and wherein the sun gear (20) of the planetary gear set (5) is configured to be locked in the rotationally fixed state by the output shaft (13) of the internal combustion engine (4) connected to the first shaft (11) via the clutch arrangement (30) when the output shaft (13) of the internal combustion engine is locked in a rotationally fixed state.Vehicle drive train (2) according to any of the preceding claims, wherein the output shaft (14) of the planetary gearing (5) is connected via a differential (8) to a drive shaft (6) of the vehicle drive train (2).The vehicle drive train (2) according to any one of claims 1 to 5, wherein the output shaft (14) of the planetary gear (5) is connected to a multi-speed transmission unit (15), and the multi-speed transmission unit (15) is further connected to the input shaft (6) of the vehicle drive train (2) via a differential (8).A method, performed by a control arrangement (100), for controlling the vehicle drive train (2) according to any of the preceding claims, the method comprising the steps of: in response to a command to charge an energy storage device (10) while a drive torque to be transmitted to the drive shaft (6) at a third gear ratio is required, the energy storage device (10) being configured to supply power to the electric machine (3): - controlling (S102) the ring gear (23) to the rotatable state if it is not already in said rotatable state; - controlling (S103) the sun gear (20) to the rotatable state if it is not already in said rotatable state; - controlling (S104) the ring gear clutch device (34) to a closed state if it is not already closed; controlling (S105) the clutch arrangement (30) so that it connects the output shaft (13) of the internal combustion engine and the second shaft (12) to the first shaft (11) if this connection has not already been established; operating the electric machine (3) as a generator; and operating the internal combustion engine (4) so that it provides a drive torque.Method according to claim 7, further comprising the steps of: in response to a command to charge the energy storage device (10) configured to supply power to the electric machine (3) when no drive torque to be transmitted to the drive shaft (6) is required: - driving the ring gear (23) into the rotatable state when it is not already in said rotatable state; - driving the sun gear (22) into the rotatable state when it is not already in said rotatable state; - driving the ring gear clutch device (34) into an open state when it is not already open; - driving the clutch arrangement (30) so as to connect the output shaft (13) of the internal combustion engine and the second shaft (12) to the first shaft (11) when this connection has not already been established; operating the internal combustion engine in such a way that it provides a positive output torque, and operating the electric machine (3) as a generator.The method according to any of claims 7 or 8, further comprising the steps of: in response to a command relating to a purely electric drive having a first transmission ratio: - driving the ring gear (23) into the non-rotatable state if it is not already in said non-rotatable state; - driving the sun gear (22) into the rotatable state if it is not already in said rotatable state; - driving the ring gear clutch device (34) into an open state if it is not already open; - controlling the clutch arrangement (30) to connect the second shaft to the first shaft if this connection has not already been established; and - operating the electric machine (3) as a motor.The method according to any of claims 7 to 9, further comprising the steps of: in response to a command relating to electric-only driving with a second transmission ratio: - driving the ring gear (23) into the rotatable state if it is not already in said rotatable state; - driving the sun gear (22) into the rotationally fixed state if it is not already in said rotationally fixed state; - driving the ring gear clutch device (34) into a closed state if it is not already closed; - controlling the clutch arrangement (30) to disconnect the second shaft (12) and that of the first shaft (11) from each other if they are not already disconnected from each other; and - operating the electric machine (3) as a motor.The method according to any of claims 7 to 10, further comprising the steps of: in response to a command relating to an electric-only drive having a third gear ratio: - driving the ring gear (23) into the rotatable state if it is not already in said rotatable state; - driving the sun gear (22) into the rotatable state if it is not already in said rotatable state; - driving the ring gear clutch device (34) into a closed state if it is not already closed; - controlling the clutch arrangement (30) to connect the second shaft (12) to the first shaft (11) if this connection has not already been established; and - driving the electric machine (3) as a motor.The method according to any of claims 7 to 11, further comprising the steps of: in response to a command relating to a hybrid drive having a first gear ratio: - driving the ring gear (23) into the non-rotatable state if it is not already in said non-rotatable state; - driving the sun gear (22) into the rotatable state if it is not already in said rotatable state; - driving the ring gear clutch device (34) into an open state if it is not already open; - controlling the clutch arrangement to connect the output shaft (13) of the internal combustion engine and the second shaft (12) to the first shaft (11) if this connection has not already been established; - driving the electric machine (3) as a motor; and - driving the internal combustion engine (4) to provide a driving torque.The method according to any of claims 7 to 12, further comprising the steps of: in response to a command relating to a hybrid drive having a third gear ratio: - driving the ring gear (23) into the rotatable state if it is not already in said rotatable state; - driving the sun gear (22) into the rotatable state if it is not already in said rotatable state; - driving the ring gear clutch device (34) into a closed state if it is not already closed; - driving the clutch arrangement (30) to connect the output shaft (13) of the internal combustion engine and the second shaft (12) to the first shaft (11) if this connection has not already been established; - driving the electric machine (3) as a motor; and - driving the internal combustion engine (4) to provide a driving torque.The method according to any of claims 7 to 13, further comprising the steps of: in response to a command relating to a variable ratio engine drive: - driving the ring gear (23) into the non-rotatable state if it is not already in said non-rotatable state; - driving the sun gear (22) into the rotatable state if it is not already in said rotatable state; - driving the ring gear clutch device (34) into a closed state if it is not already closed; - controlling the clutch arrangement (30) to connect the output shaft (13) of the internal combustion engine to the first shaft (11) if this connection has not already been established and disconnect the second shaft (12) from the first shaft (11) if they have not already been disconnected from each other; - driving the internal combustion engine (4) to provide a driving torque; and - to operate the electric machine (3) variably as a motor or as a generator and at different rotational speeds in order to achieve a desired transmission ratio.The method according to any of claims 7 to 14, further comprising the steps of: in response to a command regarding regenerative braking of the vehicle drive train (2): - controlling the ring gear (23) to the rotatable state if it is not already in said rotatable state; - controlling the sun gear (22) to the rotatable state if it is not already in said rotatable state; - controlling the ring gear clutch device (34) to a closed state if it is not already closed; - controlling the clutch arrangement (30) to connect the second shaft (12), and optionally the output shaft (13) of the internal combustion engine (4), to the first shaft (11) if this connection has not already been established; and - operating the electric machine (3) as a generator; wherein the method optionally further comprises the step of: when the output shaft (13) of the engine (4) is connected to the first shaft (11), controlling the engine (4) to output a braking torque.A computer program comprising instructions which, when executed by a computer, cause the computer to carry out the method of any of claims 7 to 15.A computer readable medium comprising instructions which, when executed by a computer, cause the computer to perform the method of any one of claims 7 to 15.A control arrangement (100) configured to control the vehicle powertrain (2) according to any of claims 1 to 6, the control arrangement (100) being configured to, in response to a command, charge an energy storage device (10) while it is required to transmit a driving torque at a third gear ratio to the drive shaft (6) - control the ring gear (23) to the rotatable state if it is not already in said rotatable state; - control the sun gear (22) to the rotatable state if it is not already in said rotatable state; - control the ring gear clutch device (34) to a closed state if it is not already closed; controlling the clutch arrangement (30) so that it connects the output shaft (13) of the internal combustion engine (4) and the second shaft (12) to the first shaft (11) if this connection has not already been established; and operating the electric machine (3) as a generator.A vehicle (1) comprising: the vehicle powertrain (2) of any of claims 1 to 6; and an energy storage device (10) configured to supply power to the electric machine (3) of the vehicle powertrain (2), optionally wherein the vehicle (1) further comprises the control assembly (100) of claim 18.

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