Powertrain for a motor vehicle, in particular for a motor car, and methods for operating such a powertrain

Abstract

Drive train (1) for a motor vehicle, comprising at least one internal combustion engine (2) having an output shaft (5) for providing torques for driving the motor vehicle and a full-load line, by means of which the motor vehicle can be driven via the output shaft (5), and comprising at least one electric machine (10) having an electrical operating voltage of at most 60 volts and designed to drive the output shaft (5) to assist the internal combustion engine (2) in driving the motor vehicle, characterized in that: - the powertrain has at least one first operating state in which the electric machine assists the internal combustion engine when driving the motor vehicle in at least one lower and / or upper speed range of the internal combustion engine compared to a medium speed range exhibiting the maximum torque of the full-load curve, such that a torque supplied by the output shaft exceeds the full-load curve and falls below the maximum torque of the full-load curve; and - the drive train has at least one second operating state in which the electric machine assists the internal combustion engine in driving the motor vehicle in the medium speed range in such a way that a torque provided by the output shaft exceeds the full load line and the maximum torque of the full load line.

Description

[0001] The invention relates to a drive train for a motor vehicle, in particular for a motor car, according to the preamble of claim 1. Furthermore, the invention relates to a method for operating such a drive train according to the preamble of claim 7.

[0002] A drivetrain for a motor vehicle, in particular for a car such as a passenger car, is known from the general state of the art and especially from series production vehicles. The drivetrain comprises at least one internal combustion engine, which has an output shaft. The motor vehicle can be driven by means of the internal combustion engine via the output shaft. For this purpose, the internal combustion engine, also referred to as an internal combustion motor, can provide torque via the output shaft by means of which the motor vehicle can be driven. In particular, the wheels of the motor vehicle can be driven by means of the internal combustion engine, thereby driving the motor vehicle as a whole. Furthermore, the drivetrain comprises at least one electric machine, by means of which, for example, the output shaft of the internal combustion engine can be driven to start it.As part of a method for operating such a drive train, it is therefore provided, for example, that the motor vehicle is driven by means of the internal combustion engine via its output shaft, so that the internal combustion engine is started by means of the electric machine by driving the output shaft by means of the electric machine.

[0003] Furthermore, EP 1 712 395 A2 discloses a device for temporarily increasing the acceleration of an internal combustion engine, with an electric motor connected to the internal combustion engine.

[0004] DE 10 2006 012 860 A1 discloses a method for operating a hybrid drive for a vehicle, with at least one internal combustion engine and at least one electric motor, wherein the internal combustion engine and the electric motor can be operated in hybrid mode.

[0005] DE 10 2010 046 048 A1 discloses a drive device comprising an internal combustion engine and an electric machine. DE 10 2008 027 620 A1 discloses a method for operating an electric machine. DE 10 2014 105 424 A1 discloses a method for controlling a drivetrain system comprising an electromechanical transmission, an internal combustion engine, and a turbocharger.

[0006] Furthermore, on November 13, 2017, an article was available on the internet at the URL (Uniform Resource Locator) “http: / / blog.mercedes-benz-passion.com / 2016 / 06 / entwicklung-des-48-volt-bordnetzes-bei-der-daimler-ag / ”, which described a drive train for a motor vehicle, comprising at least one internal combustion engine with an output shaft for providing torque to drive the motor vehicle and a full-load line, by means of which the motor vehicle can be driven via the output shaft, and at least one electric machine which has an electrical operating voltage of no more than 60 volts and is designed to drive the output shaft to assist the internal combustion engine in driving the motor vehicle.

[0007] Furthermore, on November 13, 2017, an article about 48-volt systems of hybrid vehicles was available on the internet at the URL "http: / / www.vdinachrichten.com / Technik-Wirtschaft / 48-Volt-Systeme-Hybridfahrzeugen-Durchbruchverhelfen".

[0008] Furthermore, a method for torque control of a hybrid drive unit is known from DE 10 2006 019 031 A1. US 2014 / 0067183 A1 discloses an energy storage system for a vehicle. A drive system is also known from DE 197 22 808 A1. In addition, DE 10 2016 217 955 A1 discloses a method for operating a hybrid vehicle. A hybrid drive is also known from DE 10 2014 220 862 A1.

[0009] The object of the present invention is to further develop a drive train and a method of the type mentioned above in such a way that a particularly advantageous operation can be realized in a particularly space-saving and weight-efficient manner.

[0010] This problem is solved according to the invention by a drive train with the features of claim 1 and by a method with the features of claim 7. Advantageous embodiments of the invention are the subject of the dependent claims.

[0011] A first aspect of the invention relates to a drivetrain for a motor vehicle, in particular for a car such as a passenger car. The drivetrain comprises an internal combustion engine which has an output shaft. The motor vehicle can be driven by means of the internal combustion engine via the output shaft. For this purpose, the internal combustion engine can, for example, provide torques via its output shaft by means of which the motor vehicle can be driven. In particular, the torques provided by the internal combustion engine via the output shaft can be used to drive the wheels of the motor vehicle and thus the motor vehicle as a whole. The drivetrain further comprises at least one electric machine.

[0012] Furthermore, the electric machine in question has an operating voltage of no more than 60 volts and is designed to drive the output shaft to assist the internal combustion engine in propelling the motor vehicle. In other words, the electric machine is designed to drive the output shaft, particularly while the motor vehicle is being propelled by the internal combustion engine via the output shaft, thereby assisting the internal combustion engine in propelling the motor vehicle. For this purpose, the output shaft can provide, at least temporarily, a particularly high torque for propelling, and especially accelerating, the motor vehicle. This high torque originates from the internal combustion engine itself, or rather from its powered operation, and from the driving of the output shaft effected by the electric machine.In other words, the torque provided by the output shaft is, for example, a total torque which includes a first torque provided by the internal combustion engine itself and a second torque provided by the electric machine and acting on the output shaft.

[0013] To achieve a particularly advantageous operation of the drivetrain and thus of the vehicle as a whole in a manner that is especially space-saving and weight-efficient, the invention provides that the drivetrain has at least one first operating state in which the electric machine assists the internal combustion engine when driving the vehicle in at least one speed range of the internal combustion engine such that the torque supplied by the output shaft exceeds the full-load line but falls below the maximum torque of the full-load line. Alternatively or additionally, the invention provides that the drivetrain has at least one second operating state in which the electric machine assists the internal combustion engine when driving the vehicle such that the torque supplied by the output shaft exceeds both the full-load line and the maximum torque of the full-load line.

[0014] As is generally known, the full-load curve is a speed-dependent curve, meaning it is dependent on the speed of the internal combustion engine or the output shaft. This curve represents the maximum torque that the internal combustion engine can deliver via the output shaft, particularly when operating alone (i.e., without assistance from an electric motor). This is especially evident in a torque or load-speed diagram, also known as an engine map. The maximum torque of the full-load curve is the highest torque or value on the full-load curve. In other words, the maximum torque of the full-load curve is the maximum torque of the internal combustion engine; that is, the maximum torque that the internal combustion engine can deliver via the output shaft, and thus the maximum of the full-load curve.As is also generally known, the full-load curve does not exhibit its maximum value in every speed range, i.e., at every speed of the internal combustion engine. Therefore, the internal combustion engine can only deliver its maximum torque in at least one part of the full-load curve that corresponds to a speed range of the output shaft or the internal combustion engine itself. The maximum torque is located in a middle part of the full-load curve and thus in a middle speed range, while the full-load curve exhibits lower values ​​than the maximum value in the lower and higher speed ranges.

[0015] According to the invention, the electric machine provides support to the internal combustion engine in at least one lower and / or upper speed range compared to the medium speed range exhibiting the maximum torque when driving the motor vehicle, such that the torque supplied by the output shaft of the internal combustion engine exceeds the full load line, but falls below the maximum torque, i.e. the maximum value of the full load line.

[0016] In addition, the electric machine assists the internal combustion engine in driving the vehicle in the medium speed range in such a way that the torque provided by the output shaft for driving the vehicle exceeds the full load line and the maximum torque, i.e. the maximum value of the full load line.

[0017] In particular, the operating voltage is a nominal voltage, and because the operating or nominal voltage is very low, requirements for touch protection can be avoided or kept to a minimum. In a recuperation scenario, where, for example, the electric machine is operated as a generator and driven by the kinetic energy of the vehicle, especially via at least one wheel of the moving vehicle, electrical voltages, especially operating voltages, of more than 58 volts can occur, but these are significantly below 60 volts and thus below the so-called touch protection threshold.

[0018] Thus, the electric machine makes it possible to increase the first torque by the second torque, thereby providing the total torque and enabling torque amplification. This allows, for example, the vehicle to be accelerated particularly strongly, at least temporarily, enabling a so-called boost function during or while propelling the vehicle. This allows the number of parts, the installation space required, the costs, and the weight of the powertrain to be kept particularly low.

[0019] The method according to the invention, or rather the respective exceedance of the full-load line, applies to the steady-state case, but especially also to the transient case, i.e., when the internal combustion engine, due to its potentially inert turbocharging technology, has not yet reached its maximum possible torque at the respective operating point or at the respective speed. Turbocharging technology refers in particular to the provision of, for example, a compressor by means of which the air supplied to the internal combustion engine is or can be compressed.

[0020] In order to achieve a particularly advantageous operation in a space-saving, weight-saving and cost-effective manner, it is preferably provided that the electrical operating voltage, in particular the nominal voltage, of the electrical machine is at most 50 volts, in particular at most 48 volts.

[0021] In a particularly advantageous embodiment of the invention, the electric machine is configured to drive the output shaft of the internal combustion engine for starting. In other words, to start the internal combustion engine and thus transition it from a deactivated state to an activated state, and in particular to a firing operation, the output shaft, which may be configured as a crankshaft, is driven by the electric machine. For this purpose, the electric machine is operated, for example, in motor mode and thus as an electric motor, which provides torque to drive the output shaft.During the starting process of the internal combustion engine, the output shaft is driven by the electric machine, for example, at least until combustion processes take place in at least one combustion chamber of the internal combustion engine, for example designed as a cylinder, by means of which the output shaft is then driven.

[0022] The electric machine can be designed, for example, as a belt-driven starter-generator or as a drive-driven or crankshaft-driven starter-generator, the rotor of which can be arranged, for example, on the output shaft, which is specifically designed as a crankshaft. Furthermore, it is conceivable that the electric machine is integrated into a transmission driven by the internal combustion engine via its output shaft, so that the electric machine can, for example, be designed as an integrated starter-generator. It is also conceivable that the electric machine is integrated into the internal combustion engine, particularly into its engine housing. In addition, the electric machine can be used with or without a disconnect clutch.

[0023] In principle, it is conceivable to start the internal combustion engine using at least one additional starting device, separate from the electric motor. Such a starting device could be, for example, a pinion starter, which is used to implement an engine starting function.

[0024] The number of parts, and therefore the installation space required and the weight, can be kept particularly low because the electric machine has at least a dual function. On the one hand, the electric machine is used to start the internal combustion engine. On the other hand, the electric machine is used to assist the internal combustion engine in propelling the vehicle, thus enabling, for example, boost operation. The electric machine is specifically designed to drive the output shaft, particularly mechanically and / or directly, to assist the internal combustion engine in propelling the vehicle. Thus, the electric machine acts mechanically on the output shaft, especially via its rotor.

[0025] The invention is based in particular on the following insight: Hybrid drives for motor vehicles typically comprise at least one internal combustion engine and at least one electric machine, preferably an electric motor. The use of such an electric machine in a hybrid drive makes it possible, particularly through skillful control of the electric machine, to avoid undesirable effects of the internal combustion engine. This is especially true for turbocharged internal combustion engines, since, for example, the so-called turbo lag can be bridged, i.e., compensated, by appropriate control of the electric machine and, in particular, by the aforementioned torque amplification. For this purpose, the internal combustion engine is assisted by the electric machine when propelling the motor vehicle.The electric machine makes it possible to feed additional power provided by the electric machine into the drive train, especially depending on a desired acceleration or a desired or required torque.

[0026] In such a conventional hybrid drive, the combustion engine is usually smaller than in a conventional powertrain, where only the combustion engine, and not an electric motor, is used to propel the vehicle. Due to this smaller design of the combustion engine compared to a conventional powertrain, it has a lower power output. However, the difference between the power output of the combustion engine in a conventional powertrain and the power output of the combustion engine in a hybrid drive can be at least partially, and in particular at least predominantly or completely, compensated for by the electric motor.

[0027] The electric motor is thus used as a hybrid motor to assist the combustion engine in propelling the vehicle. Typically, the hybrid motor is a high-voltage component, operating at a voltage of more than 50 volts, often several hundred volts. Therefore, such a hybrid motor is usually a separate or specially installed electric motor, which—especially compared to a conventional powertrain—requires additional installation space and contributes to the overall weight of the vehicle.

[0028] These problems and disadvantages can now be avoided by means of the drivetrain according to the invention, since the drivetrain is not implemented as a special hybrid drivetrain with a hybrid engine installed for propulsion purposes, but rather the drivetrain according to the invention is based on a conventional drivetrain and uses the internal combustion engine already intended for such a conventional drivetrain as the combustion engine. Furthermore, the drivetrain according to the invention – starting from a conventional drivetrain – uses the electric machine, whose function for starting the internal combustion engine is extended to include the function of assisting the internal combustion engine in propelling the motor vehicle.

[0029] The electric machine is, for example, a crankshaft starter generator (CSG), which is arranged coaxially to the output shaft (which may also be a crankshaft) and is or can be connected to it in a rotationally fixed manner. Alternatively, the electric machine could be a belt-driven starter generator whose axis of rotation is, for example, displaced from the axis of rotation of the output shaft and runs parallel to the axis of rotation of the output shaft.

[0030] In this system, for example, the electrical operating voltage of the electric machine is not increased, or only slightly increased, compared to the conventional drivetrain, and is at most 60 volts, particularly at most 50 volts, where the electrical operating voltage is preferably less than 60 volts, particularly less than 50 volts, and preferably at least 12 volts or greater than 12 volts. This provides the electric machine, which can preferably be operated as an electric motor, with sufficient power not only to start the internal combustion engine, but also to support the internal combustion engine, for example in dynamic load cases, by supplying additional torque, with the electric machine providing torque that is transmitted to the output shaft.This allows for torque assistance, whereby the output shaft is driven not only by combustion processes occurring in the internal combustion engine, particularly in at least one combustion chamber (e.g., a cylinder), but also by torque provided by the electric motor. This torque assistance can be used, for example, to overcome turbo lag and / or for the previously described torque amplification, in order to achieve a particularly high maximum drive torque for propelling the vehicle. Furthermore, it is conceivable to utilize the torque assistance in dynamic load cases to achieve a particularly advantageous response from the internal combustion engine.The torque support makes it possible, for example, to accelerate the output shaft and thus the vehicle to high speeds particularly strongly and therefore in a short time.

[0031] Unlike special hybrid vehicles, which typically have at least one high-voltage electric motor with several hundred volts that can be operated as both a generator and an electric motor, the powertrain according to the invention does not require an additional electric motor, since the electric machine already used in a conventional powertrain is employed, particularly as a low-voltage component with an operating voltage of less than 60 volts, and especially less than 50 volts. Compared to a conventional powertrain, the electric machine is, for example, simply made more powerful by increasing its operating voltage and / or by integrating the electric machine at a different point in the powertrain compared to the conventional powertrain.This allows both the installation space requirement and the weight of the drive train to be kept within a particularly low range.

[0032] In an advantageous embodiment of the invention, the electrical operating voltage of the electric machine is at most 48 volts. This allows, for example, the aforementioned boost function to be designed as a 48-volt boost function, so that, on the one hand, the installation space requirement and the weight of the drive train can be kept particularly low, and on the other hand, sufficiently strong accelerations of the output shaft and the vehicle as a whole can be ensured by means of the electric machine.

[0033] In particular, different types and levels of boost function are possible, especially the 48-volt boost function. For example, the boost function can be used to compensate for the transient behavior of a turbocharger or turbocharging system in an internal combustion engine, in order to avoid or at least minimize turbo lag. In this case, the steady-state full-load curve of the internal combustion engine is not exceeded, but a more dynamic response is achievable.

[0034] Furthermore, a temporary or at least brief exceedance of the internal combustion engine's full-load curve can be achieved, particularly in the lower and upper speed ranges, but not beyond the engine's maximum torque, which is typically present in the mid-range. Additionally, exceeding the engine's steady-state full-load curve beyond its maximum torque can be accomplished by adding, for example, a torque supplied by the electric motor and transmitted to the output shaft (also known as 48-volt torque) across virtually all speed ranges.

[0035] In a particularly advantageous embodiment of the invention, the electric machine comprises a stator and a rotor rotatable about an axis of rotation relative to the stator, which is arranged coaxially to the output shaft. This allows the installation space requirement to be kept particularly small. The rotor is, for example, arranged on the output shaft.

[0036] In order to keep the number of parts and the weight particularly low, a further embodiment of the invention provides that the rotor is connected to the output shaft in a rotationally fixed manner.

[0037] To achieve particularly efficient operation, a further embodiment of the invention provides that the electric machine can be operated in generator mode, driven by the output shaft. In generator mode, the output shaft, which is driven, for example, by combustion processes taking place in the internal combustion engine, provides mechanical energy that is supplied to the generator. Thus, the generator is driven by this mechanical energy. The generator converts at least a portion of the mechanical energy into electrical energy, which is then supplied by the generator.The electrical energy supplied by the generator can, for example, be supplied to at least one electrical consumer of the drive train, in particular directly, and / or fed into at least one energy storage device designed for storing electrical energy or electrical current, which is, for example, a battery, in particular a low-voltage battery. The energy storage device preferably has an electrical voltage, in particular an operating voltage, which is at most 60 volts, in particular at most 50 volts, and preferably less than 60 volts, in particular less than 50 volts, and at least 12 volts or greater than 12 volts. In particular, the electrical voltage, in particular the operating voltage, of the energy storage device is 48 volts.For example, the electric machine can be supplied with electrical energy stored in the energy storage system, which means that the electric machine can be operated in motor mode and thus as an electric motor using electrical energy stored in the energy storage system.

[0038] A second aspect of the invention relates to a method for operating a drivetrain for a motor vehicle, in particular a drivetrain according to the invention. In this method, the motor vehicle is driven by means of an internal combustion engine having an output shaft, for example, by the motor vehicle being driven by the internal combustion engine via the output shaft. Furthermore, the drivetrain includes at least one electric machine.

[0039] The electric machine is operated with an electrical operating voltage of no more than 60 volts, in particular no more than 50 volts, while the electric machine drives the output shaft in order to assist the internal combustion engine in propelling the motor vehicle.

[0040] In order to achieve a particularly advantageous operation in a space-saving and weight-efficient manner, the invention provides that the drive train is operated in at least one first operating state in which the internal combustion engine, when driving the motor vehicle, is supported by the electric machine in at least one lower and / or upper speed range of the internal combustion engine compared to a medium speed range exhibiting the maximum torque of the full-load line, such that a torque provided by the output shaft exceeds the full-load line and falls below the maximum torque of the full-load line.Additionally, it is provided that the drivetrain operates in at least one second operating state in which the internal combustion engine, when propelling the vehicle in the mid-range speeds, is assisted by the electric machine in such a way that the torque provided by the output shaft exceeds the full-load curve and the maximum torque of the full-load curve. Advantages and advantageous embodiments of the first aspect of the invention are to be regarded as advantages and advantageous embodiments of the second aspect of the invention, and vice versa.

[0041] It has proven particularly advantageous to start the internal combustion engine using the electric machine, by driving the output shaft using the electric machine.

[0042] Further details of the invention will become apparent from the following description of a preferred embodiment with the accompanying drawings. These show: Fig. 1 a schematic representation of a drive train according to the invention for a motor vehicle, in particular for a motor car; and Fig. 2 a schematic representation of the engine map of an internal combustion engine of the drive train.

[0043] Fig. Figure 1 shows a schematic representation of a drive train 1 for a motor vehicle, in particular for a car such as a passenger car. The drive train 1 comprises at least one internal combustion engine 2, which is also referred to as an internal combustion engine. In the embodiment illustrated in the figure, the internal combustion engine 2 is designed as a reciprocating piston engine. The internal combustion engine 2 comprises an engine housing 3, for example, designed as a crankcase, in particular as a cylinder crankcase, through which at least one combustion chamber 4 of the internal combustion engine 2 is formed. Fig. Figure 1 shows that the engine housing 3 forms several combustion chambers 4 of the internal combustion engine 2. Each combustion chamber 4 is designed as a cylinder.

[0044] The internal combustion engine 2 has an output shaft 5, which is designed, for example, as a crankshaft. The output shaft 5 is rotatably mounted on the engine housing 3 and can thus rotate about an axis of rotation 6 relative to the engine housing 3. In the respective combustion chamber 4, a piston (not visible in the figure) is movably mounted, in particular translationally, so that, for example, the respective piston can move translationally back and forth relative to the engine housing 3. The respective piston is articulated to a connecting rod, which in turn is articulated to the output shaft 5. Through this articulated coupling of the respective piston to the output shaft 5 via the respective connecting rod, the respective translational movements of the respective piston can be converted into a rotational movement of the output shaft 5 about its axis of rotation 6 relative to the engine housing 3.

[0045] During operation of the internal combustion engine 2, that is, while the internal combustion engine 2 is activated, combustion processes take place in the respective combustion chamber 4. These combustion processes drive the respective piston, which in turn exerts a torque on the output shaft 5 via the connecting rod. This, in turn, drives the output shaft 5 through the combustion processes occurring in the internal combustion engine 2, particularly in the combustion chambers 4, and causes it to rotate about the axis of rotation 6 relative to the engine housing 3. In this way, the output shaft 5, or rather the internal combustion engine 2, provides at least a torque via the output shaft 5 sufficient to drive the wheels 15 of the drivetrain 1 and thus the vehicle as a whole.

[0046] The drivetrain 1 comprises a transmission 7, also referred to as the main transmission, through which the torques supplied by the internal combustion engine 2 via the output shaft 5 are transmitted to the wheels 15. The wheels 15 are wheels of an axle 8 of the drivetrain 1, the axle 8 being configured, for example, as a rear axle or a front axle. The axle 8 has a differential 9, also referred to as an axle drive or differential gear, through which the wheels 15 can be driven by the internal combustion engine 2, i.e., by the output shaft 5.

[0047] The drive train 1 further comprises at least one electric machine 10, by means of which the output shaft 5 of the internal combustion engine 2 can be driven to start it. Within the framework of a method for operating the drive train 1, it is thus provided that the wheels 15, and therefore the motor vehicle as a whole, are driven by the internal combustion engine 2 via the output shaft 5. Furthermore, it is provided within the framework of the method that the internal combustion engine 2 is started, that is, brought to a running start, by means of the electric machine 10, by driving the output shaft 5. Starting the internal combustion engine 2 means that by starting the internal combustion engine 2, it is brought from its deactivated or unfired state to fired operation.During the starting of the internal combustion engine 2, the output shaft 5 is driven by the electric machine 10, for example, at least until the output shaft 5 is driven by the combustion processes taking place in the combustion chambers 4 via the pistons.

[0048] To drive the output shaft 5 and thus start the internal combustion engine 2, the electric machine 10 is operated in motor mode, i.e., as an electric motor. For this purpose, the drive train 1 includes, for example, an energy storage device 11 designed to store electrical energy or electrical current, which is, for example, a battery, in particular a low-voltage battery (LV battery). In motor mode, the electric machine 10 is supplied with electrical energy stored in the energy storage device 11 and is thus operated as an electric motor.

[0049] In order to achieve particularly advantageous operation of the powertrain 1 and thus of the vehicle as a whole, while keeping the weight and installation space requirements of the powertrain 1 especially low, the electric machine 10 has an operating voltage of at most 50 volts, and in particular an operating voltage of less than 50 volts. Specifically, the electrical operating voltage of the electric machine 10 is 48 volts, so that the electric machine 10 is designed, for example, as a 48-volt machine or as a 48-volt system. Preferably, the electrical operating voltage of the electric machine 10 is at least 12 volts or higher than 12 volts.

[0050] Furthermore, the electric machine 10 is designed to drive the output shaft 5 to assist the internal combustion engine 2 in driving the wheels 15 and thus the motor vehicle as a whole. In other words, within the framework of the aforementioned method, it is provided that the electric machine 11 is operated with an electrical operating voltage of at most 50 volts, preferably less than 50 volts, wherein, to assist the internal combustion engine 2 in driving the motor vehicle, the electric machine 10, as an electric motor, drives the output shaft 5.

[0051] The electric machine 10 is therefore preferably designed as a low-voltage component with an operating voltage of less than 50 volts, in particular direct current or alternating current. Similarly, the energy storage device 11 is preferably also designed as a low-voltage component with an operating voltage of less than 50 volts, in particular alternating current or direct current. In other words, the energy storage device 11 preferably provides a maximum voltage of 50 volts, which supplies the electric machine 10, particularly during motor operation.

[0052] Powertrain 1 is therefore not designed as a special hybrid drive with a less powerful internal combustion engine and an additional hybrid motor, but rather powertrain 1 is based on a conventional powertrain. Thus, in powertrain 1, the internal combustion engine 2 is a standard internal combustion engine used in a conventional powertrain, and the electric machine 10 is an electric machine already used or present in the conventional powertrain. Because the electrical operating voltage of the electric machine 10 is a maximum of 50 volts, the installation space and weight of powertrain 1 can be kept low.On the other hand, the electric machine 10 can provide sufficiently high electrical power and torque to assist the internal combustion engine 2 in propelling the motor vehicle.

[0053] To minimize the required installation space, the electric machine 10 has a stator 12 and a rotor 13, which is rotatable about an axis of rotation 14 relative to the stator 12 and, in particular, relative to the motor housing 3. The rotor 13 is arranged coaxially with the output shaft 5, so that the axis of rotation 14 coincides with the axis of rotation 6. For example, the rotor 13 is arranged on the output shaft 5 and / or non-rotatably connected to the output shaft 5.

[0054] Furthermore, it is conceivable that the electric machine 10 can be operated as a generator, driven by the output shaft 5. This allows, for example, a portion of the mechanical energy supplied by the internal combustion engine 2 via the output shaft 5 to be converted into electrical energy by the generator, which can then be stored, for instance, in the energy storage device 11. This enables load point shifting or recuperation operation.

[0055] Because the output shaft 5 can be driven both by the combustion processes taking place in the internal combustion engine 2 and by the electric motor 10, the output shaft 5 can provide a particularly high drive torque, which can be used to drive the axis of rotation 6. This drive torque is a total torque, comprising a first torque and a second torque. The first torque results from the piston driving the output shaft 5 via the combustion processes taking place in the internal combustion engine 2. The second torque is provided by the electric motor 10 and transmitted to the output shaft 5. This allows the first torque to be increased by the second torque to achieve the total torque, thus enabling torque amplification or torque support via the electric motor 10.This torque support allows, for example, the output shaft 5 to be accelerated particularly strongly, at least temporarily, and thus to high speeds in a short time, thereby accelerating the vehicle as a whole. This enables a particularly advantageous boost operation.

[0056] Furthermore, it is conceivable to compensate for turbo lag through torque support, particularly when the internal combustion engine 2 is designed as a turbocharged engine. For this purpose, an exhaust gas turbocharger is provided, which comprises a turbine and a compressor. The turbine can be driven, for example, by exhaust gas from the combustion chambers 4, with the compressor being driven by the turbine. The compressor can compress air supplied to the combustion chambers 4, thus enabling particularly efficient operation of the internal combustion engine 2. Furthermore, the electric machine 10 can be used in dynamic load cases through torque support to assist the internal combustion engine 2 in propelling the vehicle. This can result in a particularly advantageous response behavior of the internal combustion engine 2 and / or the drivetrain 1 as a whole.

[0057] Fig. Figure 2 schematically shows the engine map of the internal combustion engine 2. The engine map is a torque or load-speed diagram, on whose abscissa 16 the speed of the output shaft 5, and thus of the internal combustion engine 2, is plotted. On the ordinate 17 is the load or torque that is supplied by the output shaft 5, i.e., solely by the internal combustion engine 2 and thus without assistance from the electric motor 10, via the output shaft 5, in particular to drive the wheels 15 and thus the vehicle. The internal combustion engine 2 also has a full-load curve 18, which is shown in the engine map. The full-load curve 18 is a curve of the maximum torque that can be supplied by the internal combustion engine 2 alone, i.e., without assistance from the electric motor 10, via the output shaft 5, which depends on the speed of the internal combustion engine 2.The respective torque provided solely by the internal combustion engine 2 via the output shaft 5 is also referred to as the load, so that the load at or with which the internal combustion engine 2 is operated is plotted on the ordinate 17.

[0058] Out of Fig. Figure 2 clearly shows that the full-load curve 18 exhibits its maximum value, i.e., its highest or greatest value, in its central section T1. The central section T1 corresponds to a first or middle speed range B1 of the internal combustion engine 2. The maximum value of the full-load curve is the maximum torque max of the full-load curve 18, i.e., the highest or greatest torque on the full-load curve. In other words, the greatest value of the full-load curve 18, i.e., the maximum torque max of the full-load curve 18, is the total maximum torque that can be provided by the internal combustion engine 2 alone via the output shaft 5, relative to the full-load curve 18. In a second section T2 and a third section T3, the full-load curve exhibits only values ​​that are lower than the greatest value of the full-load curve 18.Part T2 corresponds to a lower speed range B2 compared to speed range B1, while part T3 corresponds to a higher speed range B3 compared to speed range B1. The internal combustion engine 2 alone can therefore only provide the maximum torque max via the output shaft 5 in speed range B1, but not in speed ranges B2 and B3.

[0059] To achieve particularly advantageous drivability, it is provided, for example, that the drive train 1 has at least one first operating state in which the electric machine 10 assists the internal combustion engine 2 when propelling the vehicle in the speed range B2 and / or in the speed range B3 such that a torque supplied by the output shaft 5 exceeds the full-load line 18 and the maximum torque max falls below the full-load line 18. The first operating state is in Fig. This is illustrated using the example of speed range B2. In speed range B2, the internal combustion engine 2 alone can provide at most the respective torque lying on the full-load line 18. However, the electric machine 10 now supports the internal combustion engine 2 in such a way that the output shaft 2 provides a torque D1 which exceeds the full-load line 18, but falls below the maximum torque max.

[0060] Alternatively or additionally, the drive train 1 may have at least one second operating state in which the electric machine 10 assists the internal combustion engine 2 in propelling the motor vehicle in such a way that a torque D2 provided by the output shaft 5 exceeds the full-load curve 18 and the maximum torque max of the full-load curve 18 or of the internal combustion engine 2 alone. The second operating state is also particularly well suited to Fig.2 recognizable. The electric machine 10 assists the internal combustion engine 10 in driving the motor vehicle in the speed range B1 such that the output shaft 5 provides the torque D2, which is greater than the maximum torque max, whereby in the speed range B1 the internal combustion engine 2 alone can provide at most the maximum torque max.In each operating state, the internal combustion engine 2 provides, for example, a first torque via the output shaft 5, either at or below the full-load line 18. Meanwhile, the electric machine 10 provides a second torque, so that the sum of the first torque provided solely by the internal combustion engine 2 and the second torque provided by the electric machine 10 yields the respective torques D1 and D2, respectively, which are each greater than the first torque and exceed the full-load line 18. This allows for a particularly advantageous operation of the motor vehicle in a cost-effective and weight-saving manner. Reference symbol list 1 Powertrain 2 Internal combustion engine 3 Motor housings 4 Combustion chamber 5 Output shaft 6 axis of rotation 7 gearboxes 8-axis 9 Differential 10 electric machine 11 Energy storage 12 Stator 13 Rotor 14 axis of rotation 15-inch wheel 16 Abscissa 17 ordinates 18 Full load line B1 Speed ​​range B2 Speed ​​range B3 Speed ​​range D1 torque D2 torque maximum torque T1 Part T2 Part T3 Part

Claims

[1] Drive train (1) for a motor vehicle, comprising at least one internal combustion engine (2) having an output shaft (5) for providing torques for driving the motor vehicle and a full-load line, by means of which the motor vehicle can be driven via the output shaft (5), and comprising at least one electric machine (10) having an electrical operating voltage of at most 60 volts and designed to drive the output shaft (5) to assist the internal combustion engine (2) in driving the motor vehicle, characterized by , that: - the powertrain has at least one first operating state in which the electric machine assists the internal combustion engine when driving the motor vehicle in at least one lower and / or upper speed range of the internal combustion engine compared to a medium speed range exhibiting the maximum torque of the full-load curve, such that a torque supplied by the output shaft exceeds the full-load curve and falls below the maximum torque of the full-load curve; and - the drive train has at least one second operating state in which the electric machine assists the internal combustion engine in driving the motor vehicle in the medium speed range in such a way that a torque provided by the output shaft exceeds the full load line and the maximum torque of the full load line. [2] Powertrain (1) according to claim 1, characterized by, that the electrical operating voltage of the electrical machine (10) is at most 50 volts, in particular at most 48 volts. [3] Powertrain (1) according to claim 1 or 2, characterized by , that the electric machine (10) is designed to drive the output shaft (5) of the internal combustion engine (2) in order to start it. [4] Powertrain (1) according to any one of the preceding claims, characterized by , that the electric machine (1) has a stator (12) and a rotor (13) rotatable about an axis of rotation (14) relative to the stator (12), which is arranged coaxially to the output shaft (5). [5] Drive train (1) according to claim 4, characterized by , that the rotor (13) is connected to the output shaft (5) in a rotationally fixed manner. [6] Powertrain (1) according to any one of the preceding claims, characterized by , that the electric machine (10) can be operated in generator mode as a generator which can be driven by the output shaft (5). [7] Method for operating a drive train (1) comprising at least one electric machine (10) for a motor vehicle, in which the motor vehicle is driven by means of an internal combustion engine (2) of the drive train (1) comprising an output shaft (5), wherein the electric machine (10) is operated with an electrical operating voltage of at most 60 volts and drives the output shaft (5) to assist the internal combustion engine (2) in driving the motor vehicle; characterized by , that: - the powertrain is operated in at least one first operating state in which the internal combustion engine, when driving the motor vehicle, is assisted by the electric machine in at least one lower and / or upper speed range of the internal combustion engine compared to a medium speed range exhibiting the maximum torque of the full-load line, such that a torque supplied by the output shaft exceeds the full-load line and falls below the maximum torque of the full-load line; and - the drive train is operated in at least one second operating state in which the internal combustion engine is supported by the electric machine when driving the motor vehicle in the medium speed range in such a way that a torque provided by the output shaft exceeds the full load line and the maximum torque of the full load line. [8] Method according to claim 7, characterized by, that the internal combustion engine (2) is started by means of the electric machine (10) by driving the output shaft (5) by means of the electric machine (10).

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