Method for operating a drive unit for a motor vehicle and corresponding drive unit

Abstract

The invention relates to a method for operating a drive train for a motor vehicle, wherein the drive train has at least one internal combustion engine, an electric motor which is drive-connected or can be connected to the internal combustion engine, and a starting clutch, wherein the internal combustion engine and the electric motor are drive-connected to an output shaft of the drive train via the starting clutch. It is provided that in a starting operating mode of the drive train, the internal combustion engine is operated in a non-ignited manner with the starter clutch disengaged and is dragged to a starting speed by means of the electric motor, the starting speed being higher than the idle speed of the internal combustion engine, wherein after reaching the starting speed, the internal combustion engine is operated in an ignited manner and the starter clutch is engaged. The invention also relates to a drive train for a motor vehicle.

Description

Technical Field

[0001] The invention relates to a method for operating a drive train for a motor vehicle, wherein the drive train has at least one internal combustion engine, an electric machine which is drive-connected or can be connected to the internal combustion engine, and a starting clutch, wherein the internal combustion engine and the electric machine are drive-connected to an output shaft of the drive train via the starting clutch. The invention also relates to a drive train for a motor vehicle. Background Art

[0002] Patent document DE 10 2017 203 623 A1 is known from the prior art, for example. This patent document describes a method for carrying out a starting process of a motor vehicle, which has a hybrid drive system, which comprises an output shaft, a starting element, an internal combustion engine with an output shaft, and an electric machine that can be connected to the output shaft of the internal combustion engine, wherein during a starting process for preloading the internal combustion engine, the electric machine is operated as a generator.

[0003] In addition, patent document US2013 / 0297105A1 is known from the prior art. This patent document describes a hybrid vehicle having an internal combustion engine, an electric motor coupled to the internal combustion engine via a first clutch, a transmission coupled to the electric motor via a second clutch, and a control device. The control device is designed to start the internal combustion engine by means of one of a plurality of start sequences, wherein the start sequence controls the electric motor, the first clutch, and the second clutch. The start sequence is selected according to the input speed of the transmission and the driver's demand. Summary of the invention

[0004] The object of the present invention is to provide a method for operating a drive unit for a motor vehicle which has the advantage over known methods that in particular a high drive torque can be made available very quickly at an output shaft in a particularly efficient manner.

[0005] It is provided here that in the starting operating mode of the power transmission device, the internal combustion engine is operated in a non-ignited manner with the starting clutch completely disengaged and is dragged to a starting speed by means of the electric machine, which is higher than the idle speed of the internal combustion engine, wherein, after reaching the starting speed, the internal combustion engine is operated in an ignited manner and the starting clutch is engaged.

[0006] The method is used to operate a drive unit that is a component of a motor vehicle or at least can be a component of a motor vehicle. The drive unit is used to drive the motor vehicle, that is, to provide a drive torque for driving the motor vehicle. To generate the drive torque, the drive unit has an internal combustion engine and an electric machine, which at least sometimes jointly provide the drive torque. However, sometimes it can also be provided that only the internal combustion engine is used and the electric machine is not used, and / or the electric machine is used and the internal combustion engine is not used to provide the drive torque.

[0007] The electric machine can be coupled to the internal combustion engine in terms of drive technology or at least can be coupled. In the first case, the electric machine is in particular rigidly and / or permanently connected to the internal combustion engine. For example, the electric machine is then directly coupled to the output shaft of the internal combustion engine and is preferably arranged coaxially with respect to the output shaft. However, it can also be provided that the electric machine is coupled to the output shaft in terms of drive technology via an intermediate transmission mechanism, wherein the intermediate transmission mechanism has a transmission ratio other than 1.

[0008] When the electric motor is coupled to the internal combustion engine, the internal combustion engine and the electric motor are coupled to the starting clutch together and can be coupled to the output shaft by means of the starting clutch. In this regard, in a first switching position of the starting clutch, the internal combustion engine and the electric motor are jointly disconnected from the output shaft, whereas in a second switching position of the starting clutch, the internal combustion engine and the electric motor are jointly coupled to the output shaft.

[0009] However, it can also be provided that the electric machine is only connectable to the internal combustion engine. For this purpose, the electric machine is connected to the internal combustion engine, more precisely to its output shaft, for example, via a separating clutch. Particularly preferably, the electric machine is coupled to the intermediate shaft in terms of drive technology, in particular rigidly and / or permanently, but particularly preferably via an intermediate transmission. The intermediate shaft is connected to the internal combustion engine, for example, on the one hand, via a separating clutch and on the other hand, via a starting clutch, to the output shaft of the drive unit.

[0010] Similar to the above embodiments, when the starting clutch is in the first switching position, the output shaft is disconnected from the intermediate shaft, and when the second switching position occurs, the output shaft is coupled to the intermediate shaft. In this regard, when the starting clutch is engaged, that is, when the second switching position occurs, at least the electric machine is coupled to the output shaft in terms of driving technology. If, in addition, the separating clutch between the internal combustion engine and the electric machine is at least partially or completely engaged, the internal combustion engine is also coupled to the output shaft of the drive unit in terms of driving technology.

[0011] The starting clutch is located in terms of drive technology between the internal combustion engine and the electric machine on the one hand and the output shaft of the drive unit on the other hand. The output shaft is preferably coupled in terms of drive technology to at least one wheel of the motor vehicle, particularly preferably to a plurality of wheels of the motor vehicle, for example via a transmission or a gearshift transmission. The transmission is used to set a transmission ratio selected from a plurality of transmission ratios between the output shaft and at least one wheel of the motor vehicle. This means that the transmission has a plurality of transmission ratios, one of which is selected and set on the transmission, so that the set transmission ratio then occurs between the output shaft and at least one wheel.

[0012] The drive train can now be operated, for example, in an idle operating mode. In the idle operating mode, the starting clutch is disengaged or completely disengaged, i.e., in its first switching position. Accordingly, both the internal combustion engine and the electric machine are completely disconnected from the output shaft. In the idle operating mode, the internal combustion engine is operated at an idle speed with ignition. This means that fuel is supplied to the internal combustion engine and the internal combustion engine is adjusted in such a way that it generates a torque corresponding to the drag torque of the internal combustion engine at the respective current speed of the internal combustion engine. In this respect, the speed of the internal combustion engine remains constant or at least approximately constant.

[0013] The speed of the internal combustion engine is adjusted to an idle speed, in particular to an idle speed. The idle speed is understood to be a speed of the internal combustion engine that is greater than the minimum speed of the internal combustion engine and is selected in such a way that a stable operation of the internal combustion engine occurs with low noise generation and low fuel consumption. Conversely, the minimum speed is a speed from which the internal combustion engine can be operated without an externally provided torque, i.e., from which the internal combustion engine can continue to increase its speed autonomously and without external torque intervention. Usually, when the motor vehicle is stationary, i.e., at a speed of zero, an idle speed is set on the drive train and is used to operate the drive train.

[0014] If, on the other hand, the motor vehicle is to be accelerated as quickly as possible, a starting operating mode is set at the drive train. The starting operating mode enables a so-called start-up control of the motor vehicle, which in particular causes a maximum and / or in particular effective acceleration of the motor vehicle. In the starting operating mode, the starting clutch is disengaged, i.e. completely disengaged, so that the internal combustion engine and the electric machine are completely disconnected from the output shaft. If the starting clutch is still engaged or at least partially engaged when the starting operating mode is initiated, the starting clutch is completely disengaged.

[0015] If the starting clutch is fully disengaged, the internal combustion engine is pulled to the starting speed by means of the electric machine, wherein the internal combustion engine is simultaneously operated in a misfire mode. The misfire mode operation is understood to mean the operation of the internal combustion engine without a fuel supply. In this respect, for the misfire mode operation, the fuel supply to the internal combustion engine is interrupted. During the misfire mode operation, there is no combustion of fuel in the internal combustion engine.

[0016] The internal combustion engine is thus driven to the starting speed solely by means of the electric machine, for which purpose electrical energy is supplied to the internal combustion engine, for example from an energy storage device of the motor vehicle, more precisely of the drive train. The starting speed is greater than the idle speed of the internal combustion engine, for example the starting speed is at least twice the idle speed. Particularly preferably, the starting speed is at least 5 times, at least 7.5 times or at least 10 times the idle speed.

[0017] If the internal combustion engine reaches the starting speed, i.e. its current speed corresponds to the starting speed, the internal combustion engine is operated in an ignited manner and the starting clutch is engaged. Therefore, the internal combustion engine is switched from operating in a non-ignited manner to operating in an ignited manner only after the starting speed has been reached. Only after this switch is the starting torque provided at least partially by the internal combustion engine. For this purpose, the starting clutch is additionally engaged. This method is extremely energy-saving and is also very comfortable for the occupants of the motor vehicle, because the operation of the internal combustion engine in a non-ignited manner and its acceleration by means of the electric machine are accompanied by very low noise generation and significantly lower noise and less vibration than the acceleration of the internal combustion engine to the starting speed in an ignited manner.

[0018] Usually, the starting mode is started from the idle mode, that is, the power transmission device is switched directly from the idle mode to the starting mode. In the idle mode, the internal combustion engine is operated in an ignited manner, whereas in the starting mode, the internal combustion engine is first set to operate in a non-ignited manner. Accordingly, when switching from the idle mode to the starting mode, the internal combustion engine switches from operating in an ignited manner to operating in a non-ignited manner, and at the same time begins to drag the internal combustion engine to the starting speed with the help of the electric motor. Here, the electric motor is operated in such a way that, although the internal combustion engine switches from operating in an ignited manner to operating in a non-ignited manner, there is no reduction in the speed, but the speed is continuously increased from the idle speed to the starting speed with the help of the electric motor. As a result, the advantages already described above are achieved.

[0019] For example, it is provided that the starting operating mode of the drive train is started as soon as the service brake of the motor vehicle is activated and the accelerator pedal of the motor vehicle is actuated. Thus, the internal combustion engine is operated without firing and is dragged to the starting speed by means of the electric machine with the service brake activated, so that the motor vehicle remains stationary. After reaching the starting speed, the starting clutch is initially also kept disengaged, so that the motor vehicle remains stationary. It can be provided that the internal combustion engine is still operated without firing and is kept at the starting speed by means of the electric machine.

[0020] However, it can also be provided that the internal combustion engine switches from non-ignition operation to ignition operation after reaching the starting speed. Particularly preferably, the starting clutch is not engaged until the service brake of the motor vehicle is released, ie, for example, the brake pedal of the motor vehicle is no longer actuated. Preferably, the starting clutch is disengaged just when the service brake is released, so that the torque provided by the internal combustion engine is present as drive torque at the output shaft and accelerates the motor vehicle.

[0021] A development of the invention provides that, after the starting speed is reached, the operation of the internal combustion engine with ignition is started directly. Reference is made to the above in this regard. Particularly preferably, after the starting speed is reached and the operation of the internal combustion engine with ignition is started, the starting clutch initially remains engaged, in particular until the service brake of the motor vehicle is released or completely released. By starting the operation with ignition directly after the starting speed is reached, it is ensured that a high drive torque is provided directly by means of the internal combustion engine when the starting clutch is engaged.

[0022] A further development of the invention provides that, with the start of the fired operation of the internal combustion engine, a torque is generated by means of the electric machine, which torque corresponds in magnitude to the torque provided by the internal combustion engine and is directed in the opposite direction thereto. By starting the fired operation, the internal combustion engine is preferably set in such a way that it delivers a torque. In other words, the torque generated by the internal combustion engine is greater than the friction torque of the internal combustion engine at the currently existing speed, in particular at the starting speed.

[0023] In order to keep the internal combustion engine at the starting speed despite this, the electric machine is controlled in such a way that a torque is generated that is opposite to the torque of the internal combustion engine. In other words, the electric machine is adjusted in such a way that the speed of the internal combustion engine is kept at the starting speed. For example, the internal combustion engine and the electric machine have the same rated power for this purpose. Preferably, the internal combustion engine is adjusted in such a way that it provides the maximum torque that can be achieved at the current speed, in particular at the starting speed. If the torque that can be provided by means of the electric machine is less than this torque, it is particularly preferred to adjust the torque of the internal combustion engine to the maximum torque that can be provided by means of the electric machine.

[0024] In other words, the internal combustion engine is already ready to provide a large drive torque, which is first suppressed by means of the electric machine. The electric machine is thus used to preload the internal combustion engine. This results in an extremely rapid provision of the drive torque, thereby achieving a high acceleration of the motor vehicle.

[0025] A further development of the invention provides that the torque is provided by means of the electric machine by operating the electric machine in the manner of a generator and that during generator operation the electrical energy provided by the electric machine is temporarily stored or converted into heat. As already explained above, the electric machine can be electrically connected to an energy accumulator which serves to temporarily store electrical energy. In this regard, the electric machine can be operated on the one hand with the electrical energy drawn from the energy accumulator. Conversely, the electrical energy provided by means of the electric machine can be supplied to the energy accumulator.

[0026] After the start of the internal combustion engine in the starting mode, the electric machine absorbs the torque generated by the internal combustion engine. In this process, the mechanical energy of the internal combustion engine is converted into electrical energy. The electrical energy is temporarily stored in an energy accumulator, for example. It is particularly advantageous to provide that in order to drag the internal combustion engine to the starting speed, the electric machine is operated with the electrical energy drawn from the energy accumulator. This means that the charge state of the energy accumulator decreases. During the generator operation of the electric machine in order to keep the internal combustion engine at the starting speed, electrical energy is supplied to the energy accumulator again, so that the electrical energy previously drawn is at least partially or even completely compensated.

[0027] However, it can also be provided that the electrical energy provided by the electric machine is converted directly into heat, for example by short-circuiting the electric machine. This process can be carried out in particular if the energy storage device is completely full, i.e. can no longer absorb electrical energy. For example, during operation of the internal combustion engine in ignition mode, the electrical energy provided by the electric machine is introduced into the energy storage device until the energy storage device is completely full. Subsequently, the electrical energy is converted into heat, in particular until the start clutch is engaged. This type of process always allows the internal combustion engine to be preloaded by means of the electric machine.

[0028] A further development of the invention provides that the starter clutch is engaged after the start of operation of the internal combustion engine with ignition. The starter clutch is therefore engaged only after the start of operation with ignition, so that there is a time interval. This ensures that the internal combustion engine provides a sufficiently large torque when the starter clutch is engaged. Particularly preferably, the starter clutch is engaged only when the internal combustion engine provides a preset theoretical torque, which is overcome by means of the electric machine. For example, the theoretical torque can correspond to the maximum torque that can be achieved at the starting speed. The described process again ensures rapid acceleration of the motor vehicle.

[0029] One refinement of the invention provides that when the starting clutch is engaged, the electric machine is deactivated or, starting from the engagement of the starting clutch, a torque assisting the torque of the internal combustion engine is applied by means of the electric machine. In particular, the electric machine is deactivated if a torque opposing the torque of the internal combustion engine was previously generated by means of the electric machine. Due to the deactivation of the electric machine, in this case the drive torque of the drive unit present at the output shaft is provided exclusively by means of the internal combustion engine.

[0030] Alternatively, it can be provided that the torque generated by the internal combustion engine is assisted by the electric machine, so that the drive torque occurring at the output shaft is composed of the torque generated by the internal combustion engine and the torque generated by the electric machine. Particularly preferably, the maximum torque achievable at the starting speed is generated by the internal combustion engine, whereas the electric machine is operated in such a way that the drive torque occurring at the output shaft corresponds to the theoretical drive torque. The theoretical drive torque is predetermined, for example, by the driver of the motor vehicle or a driver assistance device of the motor vehicle. It can obviously also be provided that the electric machine is controlled to generate its maximum torque, so that the maximum achievable drive torque occurs at the output shaft. In this way, a particularly high power output can be achieved.

[0031] A further development of the invention provides that the starting speed is selected to be identical to the speed at which the engine provides the maximum torque. The maximum torque corresponds to the maximum torque of the internal combustion engine at all possible speeds of the internal combustion engine. Identical to the maximum torque is not to be understood as the maximum torque at a specific speed. However, it is clear that the maximum torque coincides with the maximum torque for the speed at which the maximum torque on the internal combustion engine can be achieved. By means of the described process, a particularly high drive torque is ensured at the output shaft.

[0032] A further development of the invention provides that the starting speed is selected to be equal to the speed at which the maximum torque of the internal combustion engine corresponds to the maximum torque that can be provided by means of the electric machine. In this case, the maximum torque corresponds to the maximum torque that can be achieved by means of the internal combustion engine at the starting speed. The maximum torque can (but does not necessarily) correspond to the maximum torque. The maximum torque should now correspond to the maximum torque that can be provided by means of the electric machine, so that the torque generated by the internal combustion engine can be compensated by means of the electric machine, thereby achieving the described preloading of the internal combustion engine.

[0033] From this maximum torque (which corresponds to the maximum torque that can be provided by means of the electric machine), a speed is determined at which the maximum torque exists, which represents the maximum achievable torque of the internal combustion engine. The starting speed is then set equal to this speed. This ensures that a high drive torque is achieved despite the limitations of the electric machine.

[0034] A development of the invention provides that a separating clutch is present between the internal combustion engine and the electric motor in terms of drive technology, which is engaged in order to tow the internal combustion engine with the aid of the electric motor. The separating clutch has already been mentioned above. In a first switching position, the separating clutch is disengaged, so that the internal combustion engine is separated from the electric motor in terms of drive technology. In a second switching position, the separating clutch is engaged, in contrast, so that the internal combustion engine is preferably rigidly coupled to the electric motor in terms of drive technology. In order to enable towing the internal combustion engine with the aid of the electric motor, the separating clutch is engaged. This is the case in particular if the drive train has previously been operating in an idle operating mode in which the separating clutch was disengaged. The separating clutch enables a particularly high energy efficiency of the drive train.

[0035] The invention further relates to a drive train for a motor vehicle, in particular for carrying out a method according to an embodiment of the invention, wherein the drive train has at least one internal combustion engine, an electric machine which is drive-connected or can be connected to the internal combustion engine, and a starting clutch, wherein the internal combustion engine and the electric machine are drive-connected to an output shaft of the drive train via the starting clutch. It is provided that the drive train is designed to operate the internal combustion engine in a non-firing mode with the starting clutch disengaged in a starting operating mode of the drive train, and to drag the internal combustion engine to a starting speed by means of the electric machine, the starting speed being greater than the idling speed of the internal combustion engine, wherein after reaching the starting speed, the internal combustion engine is operated in a firing mode and the starting clutch is engaged.

[0036] The advantages of these embodiments of a power transmission device and a method of this type have already been pointed out. Both the power transmission device and the method for operating the same can be developed according to the embodiments within the scope of this description, so that reference is made to these embodiments.

[0037] Furthermore, the invention obviously also relates to a motor vehicle having such a drive unit. DETAILED DESCRIPTION

[0038] The motor vehicle has a drive train and at least one wheel that can be driven by means of the drive train. The drive train has an internal combustion engine and an electric machine, which is at least partially coupled to an output shaft of the drive train in terms of drive technology. In the embodiment shown here, the output shaft is coupled to an intermediate shaft in terms of drive technology via a starting clutch, which intermediate shaft is rigidly and permanently coupled to the electric machine.

[0039] For example, the electric machine is coupled to the intermediate shaft via an intermediate transmission. Conversely, the internal combustion engine is coupled to the intermediate shaft in terms of drive technology via a disconnect clutch. In this respect, when the disconnect clutch is disengaged, the intermediate shaft is completely disconnected from the internal combustion engine, and when the disconnect clutch is engaged, the intermediate shaft is rigidly connected to the internal combustion engine. Similarly, when the starting clutch is disengaged, the output shaft is completely disconnected from the intermediate shaft and is rigidly connected to the intermediate shaft when the starting clutch is engaged. The electric machine is electrically coupled to an energy accumulator, which serves to temporarily store electrical energy.

[0040] In the embodiment shown, the output shaft is coupled to at least one wheel of the motor vehicle via a transmission. Of course, the transmission can also be located at another location in the drive train or can be omitted entirely. It is also possible that the starting clutch is designed to be integrated into the transmission, so that the output shaft is also located in the transmission, for example as an intermediate shaft or the like.

[0041] It is now provided that in the starting operating mode of the drive unit, the starting clutch is completely disengaged, provided that it is not completely disengaged. The internal combustion engine is then driven by means of the electric machine to a starting speed which is greater than the idling speed of the internal combustion engine. In this case, the internal combustion engine is operated in a non-firing mode. This means that no fuel is burned in the internal combustion engine, in particular no fuel is supplied to the internal combustion engine. Preferably, the electrical energy for driving the internal combustion engine by means of the electric machine is taken from an energy accumulator.

[0042] After reaching the starting speed, the internal combustion engine is switched from operation in a non-ignited mode to operation in an ignited mode. Preferably, the internal combustion engine is adjusted in such a way that it outputs a torque greater than 0 Nm. At the same time, the electric motor is adjusted in such a way that the torque generated by the electric motor reacts against the torque of the internal combustion engine and corresponds in magnitude to the torque of the internal combustion engine. Accordingly, despite the torque generated by the electric motor, the speed of the internal combustion engine is kept constant, i.e., at the starting speed.

[0043] Next, in order to accelerate the motor vehicle, the starting clutch is engaged and the electric machine is either deactivated or adjusted to assist the torque generated by the internal combustion engine. In the latter case, the drive torque provided by the internal combustion engine and the electric machine is present at the output shaft. Due to the previous preloading of the internal combustion engine, a very large drive torque can be provided very quickly at the output shaft.

Claims

1. A method for operating a drive train for a motor vehicle, in, The power transmission device has at least one internal combustion engine, an electric motor that is drive-connected or can be connected to the internal combustion engine, and a starting clutch, wherein the internal combustion engine and the electric motor are drive-connected to an output shaft of the power transmission device via the starting clutch, and is characterized in that, in a starting operating mode of the power transmission device, the internal combustion engine is operated in a non-ignited manner with the starting clutch completely disengaged and is dragged to a starting speed by means of the electric motor, which starting speed is higher than the idle speed of the internal combustion engine, wherein, after reaching the starting speed, the internal combustion engine is operated in an ignited manner and the starting clutch is engaged, wherein the starting speed is selected to be the same as the speed at which the internal combustion engine provides a maximum torque.

2. The method according to claim 1, It is characterized in that After the starting speed has been reached, fired operation of the internal combustion engine begins immediately.

3. The method according to claim 1 or 2, It is characterized in that When the internal combustion engine starts to operate in an ignition mode, a torque is generated by the electric machine, which is equal in magnitude to the torque provided by the internal combustion engine and opposite in direction.

4. The method according to claim 3, It is characterized in that The torque is provided by means of the electric machine by operating the electric machine as a generator, the electrical energy provided by the electric machine in generator operation being temporarily stored or converted into heat.

5. The method according to claim 1 or 2, It is characterized in that After the internal combustion engine begins to operate in an ignited manner, the starting clutch is engaged.

6. The method according to claim 1 or 2, It is characterized in that When the starting clutch is engaged, the electric machine is deactivated or, starting from the engagement of the starting clutch, an auxiliary torque is applied to the torque of the internal combustion engine by means of the electric machine.

7. The method according to claim 1 or 2, It is characterized in that The starting speed is selected to be equal to the speed at which the maximum torque of the internal combustion engine corresponds to the maximum torque that can be provided by means of the electric machine.

8. The method according to claim 1 or 2, It is characterized in that In terms of drive technology, there is a separating clutch between the internal combustion engine and the electric machine, which is engaged in order to drag the internal combustion engine by means of the electric machine.

9. A power transmission device for a motor vehicle, for implementing the method according to any one of claims 1 to 8.