Method and control device for operating a drive train

Abstract

Method for operating a drive train (1) of a motor vehicle, wherein the drive train (1) comprises a first drive unit designed as an internal combustion engine (2), a second drive unit designed as an electric machine (3), a starting element (6), and a transmission (4), wherein the starting element (6) comprises a converter (6A) and a lock-up clutch (6B), wherein the starting element (6) is connected between the electric machine (3) and the transmission (4), wherein the electric machine (3) is connected between the internal combustion engine (2) and the starting element (6), and wherein, when a decoupling of the lock-up clutch (6B) is requested, the lock-up clutch (6B) is brought into slip and a target speed is specified for the electric machine (3), characterized in that first the bridging clutch (6B) of the starting element (6) is brought into slippage; Then, when the slip at the bridging clutch (6B) of the starting element (6) reaches a limit value or becomes greater than the limit value, a target speed is then specified for the electric machine (3) and the speed of the electric machine (3) is adjusted to this target speed.

Description

[0001] The invention relates to a method for operating a drive train according to the preamble of claim 1. Furthermore, the invention relates to a control device for operating a drive train.

[0002] German patent application DE 10 2006 018 057 A1 discloses a method for operating a parallel hybrid drivetrain of a motor vehicle. Such a parallel hybrid drivetrain comprises a first drive unit designed as an internal combustion engine, a second drive unit designed as an electric machine, a starting element, and a transmission, wherein the starting element is connected between the electric machine and the transmission, and the electric machine is connected between the internal combustion engine and the starting element. According to DE 10 2006 018 057 A1, the starting element is a hydrodynamic starting element with a torque converter and a lock-up clutch. To decouple the internal combustion engine when it is switched off, a disconnect clutch is connected between the internal combustion engine and the electric machine.If the combustion engine is to be started during purely electric driving, this state of the art proposes starting the combustion engine via the electric motor by at least partially engaging the clutch between the combustion engine and the electric motor, while simultaneously allowing the lock-up clutch of the starting element to slip in order to direct the torque generated by the electric motor partly through the torque converter and partly through the lock-up clutch of the starting element. The slippage of the lock-up clutch of the starting element ensures that the starting of the combustion engine via the electric motor does not result in any discomfort from sudden jolts at the drivetrain output.According to DE 10 2006 018 057 A1, the bridging clutch of the starting element is kept in a slipping mode during the entire starting process of the combustion engine by means of a speed control of the electric machine. A differential speed is specified for the starting element, namely its bridging clutch.

[0003] DE 11 2010 000 430 T5 discloses a hybrid drive device which allows a power machine to be started by a driving force of an electric rotary machine in an EV driving state, and which allows a torque which corresponds exactly to a target torque which is to be transmitted to a transmission device.

[0004] DE 10 2009 054 468 A1 describes a method for operating a powertrain comprising at least a hybrid drive with an internal combustion engine and an electric machine, a clutch connected between the internal combustion engine and the electric machine, a transmission, a starting element and a brake pedal.

[0005] Although a convenient start of an internal combustion engine via the electric machine is already possible using the method known from the prior art, there is a need to enable decoupling of the jump-start clutch within a shorter time and with greater comfort in the event of a control-side requirement for decoupling.

[0006] Based on this, the invention aims to provide a method for operating a drive train and a control device for carrying out the method. This objective is achieved by a method for operating a drive train according to claim 1. According to the invention, the bypass clutch of the starting element is first brought into slip, and then, when the slip at the bypass clutch of the starting element reaches or exceeds a limit value, a target speed is set for the electric machine and the speed of the electric machine is regulated to this target speed. The method according to the invention proposes first bringing the bypass clutch into a defined slip and only then setting a target speed for the electric machine and regulating the speed of the electric machine to this target speed.This allows for a faster and more convenient decoupling of the bridging clutch of the starting element.

[0007] According to an advantageous embodiment of the invention, when the disengagement of the lock-up clutch is requested, a first target differential speed level for the lock-up clutch of the starting element is specified by the control system, wherein the first target differential speed level is greater than zero in magnitude. Preferably, when the disengagement of the lock-up clutch is requested, a motor control system specifies the first target differential speed level for the lock-up clutch, with a starting element control system specifying a target differential speed profile, particularly along a ramp, leading to the first target differential speed level. This allows the lock-up clutch to be brought into slippage particularly advantageously before subsequent speed control takes place at the electric machine.

[0008] According to an advantageous embodiment of the invention, when the decoupling of the lock-up clutch is no longer required, a second target differential speed level for the lock-up clutch is specified by the control system. This second target differential speed level is smaller in magnitude than the first target differential speed level and greater than or equal to zero in magnitude. Preferably, the starting element control system ramps the target differential speed from the first target differential speed level to the second target differential speed level. This allows the decoupling of the lock-up clutch to be ended particularly advantageously and conveniently.

[0009] Then, when the slip at the lock-up clutch reaches or exceeds the limit value, a target speed profile is subsequently set for the electric machine. Starting from the electric machine's current speed when the slip limit is reached or exceeded, the target speed is preferably ramped up to a speed dependent on the first target differential speed level of the lock-up clutch. This speed remains constant as long as the lock-up clutch is disengaged. Then, when the lock-up clutch is no longer disengaged, the target speed for the electric machine is preferably ramped down from this speed to a speed dependent on the second target differential speed level of the lock-up clutch. This speed control of the electric machine is particularly advantageous.

[0010] Following a beneficial further development, if the driver's requested torque changes during a requested disengagement of the lock-up clutch, a starting element control adjusts the torque transmitted by the lock-up clutch to match the driver's requested torque. This allows for convenient adaptation to changing driver requests. Because the torque transmitted by the lock-up clutch is adjusted to match the driver's requested torque, rather than being regulated, disturbances introduced into the drivetrain—such as those occurring during engine start-up, engine shutdown, or cylinder deactivation—are prevented from affecting the slip at the lock-up clutch.

[0011] According to an advantageous embodiment of the invention, during a requested disengagement of the lock-up clutch, a target transmission input torque is determined based on a driver-requested torque. The torque transmitted by the lock-up clutch is adjusted during slippage of the lock-up clutch to compensate for the increase in torque transmitted by the torque converter caused by the slippage of the lock-up clutch. This prevents an impermissible change in the transmission input torque due to the slippage of the lock-up clutch.

[0012] The control device according to the invention is defined in claim 10.

[0013] Preferred embodiments are described in the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail with reference to the drawing, without being limited thereto. The drawing shows: Fig. 1. A diagram of a powertrain; and Fig. 2 a time diagram to illustrate the method according to the invention.

[0014] The invention relates to a method for operating a drive train of a motor vehicle, and to a control device for carrying out the method.

[0015] Fig. Figure 1 schematically shows a parallel hybrid powertrain 1 of a motor vehicle. The powertrain 1 has a first drive unit designed as an internal combustion engine 2 and a second drive unit designed as an electric machine 3, with a disconnect clutch 5 being connected between the internal combustion engine 2 and the electric machine 3. Furthermore, the powertrain 1 includes the Fig. Figure 1 comprises a gearbox 4 and a starting element 6, wherein the starting element 6 is connected between the electric machine 3 and the gearbox 4. The starting element 6 is a hydrodynamic starting element with a converter 6A and a lock-up clutch 6B connected in parallel to the converter 6A, wherein a pump impeller 6C and a turbine impeller 6D of the converter 6A are shown.

[0016] Then, when the drivetrain... Fig. When the vehicle is driven purely electrically, the combustion engine 2 is typically switched off and the disconnect clutch 5 between the combustion engine 2 and the electric machine 3 is fully open. In hybrid operation, however, in which both the combustion engine 2 and the electric machine 3 are running and providing drive torque, the disconnect clutch 5 between the combustion engine 2 and the electric machine 3 is closed.

[0017] The operation of the combustion engine 2 is controlled by an engine control unit, and the operation of the transmission 4 is controlled by a transmission control unit. A hybrid control unit is typically present to control and / or regulate the operation of the electric machine 3. The starting element 6 is controlled by a starting element control unit.

[0018] Typically, the starting element control and the transmission control are implemented in a common control unit, namely a transmission control unit. The hybrid control unit can also be part of the transmission control unit. The engine control unit is typically part of a separate control unit, namely an engine control unit. The engine control unit and the transmission control unit exchange data with each other.

[0019] In the operation of such a parallel hybrid drive train, operating situations arise in which the control system requests a decoupling of the lock-up clutch 6B, for example when the combustion engine 2 is to be started via the electric machine 3 from purely electric driving, in order to make the start-up of the combustion engine 2 as comfortable as possible by means of this decoupling of the lock-up clutch 6B.

[0020] If a decoupling of the bridging clutch 6B is requested, the bridging clutch 6b of the starting element 6 is first brought into slip according to the invention.

[0021] Only when the slip at the bridging clutch 6b of the starting element 6 exceeds or reaches a defined limit value, is a target speed then specified for the electric machine 3, and the electric machine 3 is regulated to this target speed via a speed control. In this way, a control-side decoupling of the bridging clutch 6b can be provided quickly and conveniently.

[0022] Further details of the method according to the invention are described below with reference to Fig. 2 described, whereby Fig. Figure 2 over time t shows several curves 7 to 18, namely torque curves with curves 7 to 10, speed curves with curves 11 to 16, and status signals with curves 17 and 18. The in Fig. The curves 7 to 18 shown here occur when, to start the combustion engine 2 from purely electric driving mode, the control system requests decoupling of the lock-up clutch 6B in order to make the start of the combustion engine 2 as comfortable as possible. Curve 7 shows a torque transmitted by the lock-up clutch 6B of the starting element 6. Curve 8 corresponds to the torque curve requested by the driver. Curve 9 illustrates the time course of an input torque of the transmission 4. Curve 10 visualizes the torque curve transmitted by the disconnect clutch 5. Curve 11 illustrates a speed curve over time for the turbine wheel 6D of the torque converter 6A. Curve 12 shows the speed curve over time of the electric machine 3. Curve 14 shows the speed curve over time of the combustion engine 2.Curves 13, 15, and 16 represent control-side speed specifications: curve 13 represents the target speed profile for the electric machine 3, curve 15 represents a control-side specification of a target differential speed level for the lock-up clutch 6B, and curves 16 and 16a represent a target differential speed profile of the lock-up clutch 6B. Curve 18 visualizes a control-side request for decoupling of the lock-up clutch 6B, and curve 17 visualizes a status signal regarding the implementation or effectiveness of this requested decoupling.

[0023] As already explained, this illustrates Fig. 2 Details of the inventive method for the case in which the combustion engine 2 is to be started via the electric machine 3 from purely electric driving.

[0024] Before time t1, the internal combustion engine 2 is stationary; therefore, its rotational speed 14 is zero before time t1. With the internal combustion engine 2 stationary, the disconnect clutch 5 is fully open before time t1, so that it transmits no torque according to curve 10. Before time t1, the driver-requested torque 8 is provided exclusively by the electric machine 3, with the lock-up clutch 6B fully closed according to curve 7. Before time t1, the rotational speed 12 of the electric machine 3 corresponds to the rotational speed 11 of the turbine wheel 6D of the converter 6A. Before time t1, as can be seen from curve 8, the driver-requested torque increases. The increase in the driver-requested torque is shown in Fig. 2 such that it cannot be provided solely by the electric machine 3, so that a start of the combustion engine 2 is therefore required. A maximum torque M EM-MAX of the electric machine 3 is in Fig. 2 is shown as a dashed line. For the start-up of the combustion engine 2, a decoupling of the bridging clutch 6B is requested at time t1 in order to start the combustion engine 2 particularly smoothly via the electric machine 3. The curve 18 of the Fig. Figure 2 clarifies that at time t1 the decoupling of the bridging coupling 6B is requested, whereby this request for decoupling of the bridging coupling 6B remains requested until time t3 and only at time t3 is this decoupling no longer requested.

[0025] In order to implement the requested decoupling of the bridging clutch 6B quickly and conveniently, the bridging clutch 6B of the starting element 6 is first brought into slip between times t1 and t2, whereby only subsequently between times t2 and t3 a target speed is specified for the electric machine 3 and the speed of the electric machine 3 is adjusted to the target speed in the sense of a speed control.

[0026] Then, when the decoupling of the lock-up clutch 6B is requested at time t1 according to signal curve 18, a first target differential speed level for the lock-up clutch 6B of the starting element 6 is specified by the control system, which is greater than zero in magnitude. For this purpose, the motor control system specifies the first target differential speed level for the lock-up clutch 6B of the starting element 6 according to curve 15, whereby the starting element control system specifies a target differential speed profile for the lock-up clutch 6B to this first target differential speed level 15 according to curve 16 or 16a.

[0027] According to the curve profile 16, this occurs in stages at time t1, whereby in this case the starting element control converts the first target differential speed level specified in stages by the motor control into a target differential speed profile 16 in stages.

[0028] Alternatively, as can be seen from the curve 16a, it is possible that the starting element control converts the first target differential speed level specified by the motor control in steps into a target differential speed curve such that the target differential speed for the bridging clutch 6B of the starting element 6 is guided linearly along a ramp to the first target differential speed level 15.

[0029] By specifying the first target differential speed level 15 via the motor control and by converting this first target differential speed level 15 into the target differential speed profile 16 or 16a via the starting element control, the speed of the electric machine 3 can deviate from the turbine speed of the converter 6A between times t1 and t2 according to the curve profiles 11, 12, so that a slip develops at the starting element 6, namely at the lock-up clutch 6B of the starting element 6, which corresponds to the difference between the two speed profiles 11, 12. For this purpose, the transmission capacity of the lock-up clutch 6B is reduced so that the slip builds up at it.

[0030] At time t2, it is detected that the slip at the bridging clutch 6B of the starting element 6 reaches or exceeds a limit value. Then, starting at time t2, i.e., immediately after the bridging clutch 6B is engaged, a target speed 13 is specified for the electric machine 3, whereby the speed 12 of the electric machine 3 is regulated to this target speed 13. As can be seen from the signal waveform 17, if the differential speed at the bridging clutch 6B reaches or exceeds the limit value at time t2, the status signal 17 is changed, so that the decoupling of the bridging clutch 6B requested at time t1 is then implemented or becomes effective at time t2.

[0031] According to Fig. Starting at time t2, the target speed 13 for the electric machine 3 is initially increased in steps, namely to the speed of the electric machine at time t2. From this point, the target speed 13 for the electric machine 3 is increased linearly or ramp-wise and subsequently held constant until time t3. The speed to which the target speed is ramp-wise increased from the speed of the electric machine 3 at time t2 depends on the first target differential speed level of the bridging clutch 6B.

[0032] In Fig. 2 Between times t2 and t3, as can be seen from the curve 10, after the engagement of the bridging clutch 6b and after a defined period of speed control of the electric machine 3, the transmission capacity of the clutch 5 connected between the internal combustion engine 2 and the electric machine 3 is increased in order to start the internal combustion engine 2 via the electric machine 3, whereby the internal combustion engine 2 is towed according to the curve 14, which corresponds to the speed profile of the internal combustion engine 2.

[0033] As already explained, the decoupling of the bridging clutch 6B is in Fig. 2. Decoupling is requested between times t1 and t3; after time t3, this decoupling is no longer requested.

[0034] Starting at time t3, the engine control unit no longer requests the first target speed level according to curve 15.

[0035] Rather, starting at time t3, a second target differential speed level 19 for the lock-up clutch 6B of the starting element 6 is specified or requested by the control system, namely by the starting element control. This second target differential speed level 19 is smaller in magnitude than the first target differential speed level 15, which, depending on the operating situation of the powertrain or vehicle, can be greater than zero or zero. The second target differential speed level depends on the current operating situation of the powertrain and the desired comfort level. Fig. 2. The second target differential speed level 19 is greater than zero, with the starting element control linearly increasing the target differential speed 16 along a ramp from the first target differential speed level 15 to the second target differential speed level 19, namely between times t3 and t4. Between times t3 and t4, the target speed for the electric machine 3 is also linearly reduced according to the curve 13, whereby at time t4 the speed control for the electric machine 13 ends and, according to the signal tracing 17, the decoupling of the lock-up clutch 6B ends at time t4 and is no longer effective. Then, if the decoupling of the lock-up clutch 6B is no longer required, the target speed for the electric machine 3 is reduced, preferably in a ramp-like manner, to a speed dependent on the second target differential speed level of the lock-up clutch 6B, starting at time t3.

[0036] It is therefore in line with the present invention that, for example, when a decoupling of the bridging clutch 6B is requested for a start-up of the combustion engine 2 via the electric machine 3 in a parallel hybrid drive train, the bridging clutch 6B of the hydrodynamic starting element 6 is first brought into defined slip and only afterwards the electric machine 3 is regulated to a target speed in the sense of speed control.

[0037] Preferably, when the decoupling of the bridging clutch 6B is no longer requested by the control system, the speed control is maintained at the target speed for a defined period of time. Fig. 2 between times t3 and t4, maintained to guide the slip at the bridging clutch 6B to the second target differential speed level in a defined and controlled manner.

[0038] Then, if the driver's requested torque 8 changes during a requested decoupling, the starting element control adjusts a torque transmitted by the lock-up clutch 6b to match the driver's requested torque, i.e., in the sense of control and not regulation. Because the torque transmitted by the lock-up clutch 6b is adjusted to match the driver's requested torque and not regulated, disturbances introduced into the drivetrain, e.g., during starting or stopping of the combustion engine 2 or during cylinder deactivation of the combustion engine 2, are prevented from affecting the slip at the lock-up clutch 6b.

[0039] Preferably, during a requested decoupling of the lock-up clutch 6B, a target transmission input torque is determined based on the driver's requested torque. When the lock-up clutch 6B is slipping, the torque transmitted by it is adjusted to compensate for the increase in torque transmitted by the torque converter 6A caused by the slippage of the lock-up clutch 6B, ensuring that the actual transmission input torque does not exceed the target transmission input torque.

[0040] The invention further relates to a control device for carrying out the method according to the invention. The control device comprises hardware and software components that serve to carry out the method according to the invention. The hardware components include data interfaces for exchanging data with the assemblies involved in carrying out the method, in particular with the starting element 6 and with the electric machine 3. The hardware components also include a processor for data processing and a memory for data storage. The software components include program modules for carrying out the method.

[0041] The control device according to the invention is in particular a transmission control device in which the starting element control, the transmission control, and the hybrid control are implemented. Such a transmission control device exchanges data with an engine control device, wherein the engine control device in particular transmits the status signal 18 to the transmission control device via the control-side request for the decoupling of the lock-up clutch 6B in order to initiate the execution of the method according to the invention. Reference sign 1 Powertrain 2 Internal combustion engine 3 electric machine 4 gearboxes 5 Clutch 6 Starting element 6A converter 6B Jumper coupling 6C Pump impeller 6D turbine wheel 7 Curve pattern 8 Curve path 9 Curve pattern 10 Curve pattern 11 Curve path 12 Curve path 13 Curve path 14 Curve path 15 Curve path 16 Curve path 17 Curve pattern 18 Curve path

Claims

[1] Method for operating a powertrain (1) of a motor vehicle, wherein the powertrain (1) comprises a first drive unit designed as an internal combustion engine (2), a second drive unit designed as an electric machine (3), a starting element (6) and a transmission (4), wherein the starting element (6) comprises a converter (6A) and a lock-up clutch (6B), wherein the starting element (6) is connected between the electric machine (3) and the transmission (4), wherein the electric machine (3) is connected between the internal combustion engine (2) and the starting element (6), and wherein, when a decoupling of the lock-up clutch (6B) is requested, the lock-up clutch (6B) is made to slip and a target speed is specified for the electric machine (3), characterized by , that first the bridging clutch (6B) of the starting element (6) is brought into slippage; Then, when the slip at the bridging clutch (6B) of the starting element (6) reaches a limit value or becomes greater than the limit value, a target speed is then specified for the electric machine (3) and the speed of the electric machine (3) is adjusted to this target speed. [2] Method according to claim 1, characterized by , that when the decoupling of the bridging clutch (6B) is requested, a first target differential speed level for the bridging clutch (6B) of the starting element (6) is specified on the control side, wherein the first target differential speed level is greater than zero in magnitude. [3] Method according to claim 2, characterized by, that when the decoupling of the lock-up clutch (6B) is requested, a motor control unit specifies the first target differential speed level for the lock-up clutch (6B) of the starting element (6), and that a starting element control unit specifies a target differential speed profile to the first target differential speed level. [4] Method according to claim 3, characterized by , that the starting element control specifies a ramp-like progression of the target differential speed to the first target differential speed level. [5] Method according to any one of claims 2 to 4, characterized by, that if the decoupling of the bridging clutch (6B) is no longer requested, a second target differential speed level for the bridging clutch (6B) of the starting element (6) is specified on the control side, wherein the second target differential speed level is smaller in magnitude than the first target differential speed level and greater than zero or equal to zero in magnitude. [6] Method according to claim 5, characterized by , that the starting element control specifies a ramp-like progression of the target differential speed from the first target differential speed level to the second target differential speed level. [7] Method at least according to claims 2 and 5, characterized by, that when the slip at the lock-up clutch (6B) reaches or exceeds the limit value, a target speed profile is subsequently specified for the electric machine (3) such that the target speed is preferably ramped up from the current speed of the electric machine (3) to a speed dependent on the first target differential speed level of the lock-up clutch (6B), which remains constant as long as the decoupling of the lock-up clutch (6B) is requested, and that when the decoupling of the lock-up clutch (6B) is no longer requested, the target speed for the electric machine (3) is preferably ramped down from this speed to a speed dependent on the second target differential speed level of the lock-up clutch (6B). [8] Method according to any one of claims 1 to 7, characterized by, that if a driver request torque changes during a requested decoupling of the lock-up clutch (6B), a torque transmitted by the lock-up clutch (6B) is adjusted to the driver request torque. [9] Method according to any one of claims 1 to 8, characterized by , that during a requested decoupling of the lock-up clutch (6B) a target transmission input torque is determined depending on a driver request torque, and that a torque transmitted by the lock-up clutch (6B) is adjusted in the event of slipping lock-up clutch (6B) in such a way as to compensate for an increase in the torque transmitted by the converter (6A) caused by the slip of the lock-up clutch (6B). [10] Control device for operating a drive train, characterized by Means for carrying out the method according to any one of claims 1 to 9.

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