Method for operating a motor vehicle powertrain and electronic control unit for implementing the method

Abstract

This invention relates to a method for operating a powertrain of a motor vehicle, the powertrain having at least one internal combustion engine (VM), an electric motor (EM), a transmission (G) having a drive shaft (GW1) and a driven shaft (GW2), starting elements (WK, SCI, DC1, DC2) in the power flow between the electric motor (EM) and the driven shaft (GW2), and a disengagement clutch (K0) in the power flow between the internal combustion engine (VM) and the electric motor (EM). At the start of an electric starting process, the motor vehicle is driven solely by the electric motor (EM), and the disengagement clutch (K0) is open. During the electric starting process, the disengagement clutch (K0) is engaged... K0) tows the internal combustion engine (VM) by means of the electric motor (EM), and then the disengagement clutch (K0) is reopened. After towing the internal combustion engine (VM), the vehicle continues to be driven only by the electric motor (EM). The speed (n_EM) of the driven side of the disengagement clutch (K0) is less than the no-load speed (n_VM_LL) of the internal combustion engine (VM). In order to assist the driving of the vehicle by the internal combustion engine (VM), the disengagement clutch (K0) is only closed when the rated driving torque (M_soll) of the vehicle reaches or exceeds the limit value (M_lim). The method also relates to an electronic control unit (ECU) for implementing such a method.

Description

Technical Field

[0001] This invention relates to a method for operating a motor vehicle powertrain (particularly for a motor vehicle with a hybrid drive system). The invention also relates to an electronic control unit for implementing this method. Background Technology

[0002] Patent application EP2065244A2 teaches a method for operating a hybrid vehicle that uses an internal combustion engine and an electric motor for vehicle propulsion. A clutch is provided between the internal combustion engine and the electric motor. A second clutch is provided between the electric motor and the drive wheels. Furthermore, a temperature acquisition device is provided to detect the temperature of the second clutch. Based on the temperature of the second clutch, two different operating modes are selected. In a first operating mode, the first clutch is engaged and the second clutch operates with slippage, wherein the internal combustion engine operates at a first speed. In a second operating mode, the first clutch is disengaged and the second clutch operates with slippage, and the electric motor operates at a second speed lower than the first speed. This method should prevent the second clutch from overheating, wherein the speed difference on the second clutch decreases in relation to temperature.

[0003] However, this temperature-dependent mode switching of the second clutch cannot be implemented with high dynamism without compromising ride comfort. Therefore, this method cannot provide reliable protection against clutch overheating, as the clutch temperature rises very rapidly during slippery operation. Summary of the Invention

[0004] Therefore, the object of the present invention is to provide a method by which reliable overload protection for such a clutch can be achieved. Another object of the present invention is to provide a control device suitable for this purpose.

[0005] Therefore, the present invention proposes a method for operating a powertrain of a motor vehicle, wherein the powertrain includes at least one internal combustion engine, an electric motor, a transmission for providing different gears between a drive shaft and a driven shaft of a transmission, a starting element in the power flow between the electric motor and the driven shaft, and a disengaging clutch in the power flow between the internal combustion engine and the electric motor, wherein the rotor of the electric motor is coupled to the drive shaft.

[0006] At the start of the electric starting process, the vehicle is driven solely by the electric motor, and the starting element is engaged or in a slippery state, while the disengagement clutch is disengaged.

[0007] During the electric starting process, the internal combustion engine is towed by the motor by engaging the disengagement clutch, and

[0008] After the disengagement clutch is opened again, the motor vehicle continues to be driven by the electric machine alone after the internal combustion engine is dragged, the rotational speed of the driven side of the disengagement clutch is less than the no-load rotational speed of the internal combustion engine, and

[0009] After the internal combustion engine is dragged and the disengagement clutch is opened, the disengagement clutch is closed only when the nominal drive torque of the motor vehicle reaches or exceeds a limit value in order to assist the motor vehicle drive by the internal combustion engine.

[0010] The application also proposes an electronic control unit for open-loop and closed-loop control of a motor vehicle powertrain, wherein the control unit is designed to implement the method according to the application.

[0011] A method is proposed for operating a motor vehicle powertrain having an internal combustion engine, an electric machine and a transmission. The transmission is designed to provide different gear ratios between a drive shaft and a driven shaft of the transmission. The rotor of the electric machine is coupled to the drive shaft of the transmission. This coupling can be implemented directly, so that the rotor rotational speed is equal to the drive shaft rotational speed. Alternatively, the rotor and the drive shaft can be connected to one another by means of a variable transmission.

[0012] A start-up element is provided in the power flow between the electric machine and the driven shaft. The start-up element can be configured, for example, as a hydrodynamic torque converter having a parallel- connected lock-up clutch. Alternatively, a separate friction clutch can constitute the start-up element. According to a further alternative, the start-up element can be constituted by a gear shift element of the transmission which forms a gear ratio, provided that this gear shift element is configured as a friction clutch or as a friction brake. The start-up element allows torque to be transmitted between at least one of the drive sources of the powertrain and the driven shaft in the event of a rotational speed difference. A disengagement clutch is provided in the power flow between the internal combustion engine and the electric machine, which is configured as a friction clutch.

[0013] At the start of the electric start-up process, the motor vehicle is driven by the electric machine alone. The disengagement clutch is open in this case. The start-up element can be closed, so that there is no rotational speed difference on the start-up element. In this state, the rotational speed of the electric machine is directly related to the rotational speed of the engaged gear ratio in the transmission and the driven shaft. Alternatively, the start-up element can be operated in a slip state.

[0014] During the electric start-up process, the internal combustion engine is dragged by the electric machine by means of the closed disengagement clutch. When the rotational speed of the internal combustion engine is sufficient, the internal combustion engine can start up and be maintained independently. The disengagement clutch is then opened again.

[0015] According to the application, it is now provided that, after the internal combustion engine is being dragged, the motor vehicle continues to be driven by the electric machine alone. Here, the rotational speed of the driven side of the decoupling clutch is less than the no-load rotational speed of the internal combustion engine. In order to assist the motor vehicle drive by the internal combustion engine, the decoupling clutch is closed only when the required drive torque of the motor vehicle reaches or exceeds a limit value.

[0016] By this method, the energy input into the starting element can be kept small, since the rotational speed of the driven side of the decoupling clutch after the internal combustion engine is being dragged is less than the no-load rotational speed of the internal combustion engine. Thus, overheating of the starting element can be avoided. If the required drive torque exceeds the limit value, the already running internal combustion engine can be coupled to the powertrain with high dynamics.

[0017] Preferably, the rotational speed of the driven side of the decoupling clutch is maintained at least below the no-load rotational speed of the internal combustion engine after the internal combustion engine is being dragged until the required drive torque reaches or exceeds the limit value. Thereby, the energy input into the starting element can be kept even smaller.

[0018] Preferably, the starting element is operated in a slip state during the dragging of the internal combustion engine, wherein the slip on the starting element is reduced again, in particular to zero, after the decoupling clutch is opened. Thereby, torsional vibrations generated when the internal combustion engine is being dragged can be decoupled from the driven shaft. The rapid establishment of the starting element-slip can be accelerated by a corresponding control of the electric machine.

[0019] According to one preferred design, the slip on the starting element is increased when the required drive torque reaches or exceeds the limit value. Thus, the rotational speed difference on the decoupling clutch when the decoupling clutch is closed is minimized, so that the decoupling clutch is thermally stressed as little as possible. The rapid establishment of the starting element-slip can be accelerated by a corresponding control of the electric machine.

[0020] According to one alternative design, the slip on the starting element remains unchanged when the required drive torque of the motor vehicle reaches or exceeds the limit value, so that the decoupling clutch is closed during the slip operation of the decoupling clutch. According to another alternative design, not only the starting element but also the decoupling clutch is operated in a slip operation when the required drive torque of the motor vehicle reaches or exceeds the limit value.

[0021] Which of the three above-mentioned method flows is used depends on the thermal stressability of the starting element and the decoupling clutch. In addition, there can be a correlation to the value of the required drive torque.

[0022] Preferably, the internal combustion engine is actively operated after the towing without contributing to the drive of the motor vehicle. Thus, the internal combustion engine is coupled to the powertrain only when the desired drive torque reaches or exceeds a limit value. Here, the internal combustion engine is preferably operated in a speed-regulated manner, wherein the desired rotational speed of the internal combustion engine is dependent on the current desired drive torque. Thereby, the driver of the motor vehicle can be provided with an acoustic feedback on the desired drive torque even if the internal combustion engine does not contribute to the drive of the motor vehicle.

[0023] To solve the stated task, an electronic control unit is also proposed, which is designed to implement the method described at the outset. The electronic control unit can be provided to implement other functions of the powertrain control. BRIEF DESCRIPTION OF DRAWINGS

[0024] The individual embodiments of the application are described in detail below. In the drawings:

[0025] Figures 1 to 3 a powertrain of a motor vehicle is respectively shown; and

[0026] Figures 4 to 6 a time flow of different variables of the powertrain is respectively shown. DETAILED DESCRIPTION

[0027] Figure 1 A schematic diagram of a hybrid powertrain for a motor vehicle is shown. The hybrid powertrain has an internal combustion engine VM and an electric machine EM. Between the internal combustion engine VM and the electric machine EM, a separating clutch K0 is provided. By means of the separating clutch K0, the power flow between the internal combustion engine VM and the electric machine EM can be switched. The hybrid powertrain also comprises a transmission G with a drive shaft GW1 and a driven shaft GW2. The driven shaft GW2 is connected to a differential AG, by means of which the power present on the driven shaft GW2 is distributed to the drive wheels DW of the motor vehicle. In the power flow between the electric machine EM and the drive shaft GW1, a torque converter TC is provided. The torque converter TC comprises a pump wheel P connected to the electric machine EM. A turbine wheel TR of the torque converter TC is connected to the drive shaft GW1. The pump wheel P and the turbine wheel TR interact in a fluid-dynamic manner, such that the power of the pump wheel P can be transferred to the turbine wheel TR in a fluid-dynamic manner. The pump wheel P and the turbine wheel TR can be connected to one another mechanically by means of a closed lock-up clutch WK.

[0028] The transmission G is designed to form different gear steps between the drive shaft GW1 and the driven shaft GW2. To form these gear steps, a plurality of shift elements are provided. One of the shift elements is exemplarily shown in Figure 1 and is denoted there as SCI. The shift elements, including the shift element SCI, are connected to a shift actuator S in Figure 1A planetary gear set, not shown, is acting in cooperation in order to form different gears between the drive shaft GW1 and the driven shaft GW2. This should only be considered as exemplary. Instead of or in addition to the planetary gear set, spur gear stages and / or one or more frictional power transmission mechanisms can be used, which act in cooperation with shift elements, including the shift element SCI, in order to form the gears.

[0029] Furthermore, an electronic control unit ECU is provided. This control unit ECU is in communication connection with the inverter INV, which is provided to the electric machine EM for controlling the electric machine. The control unit ECU is also in communication connection with the transmission G. The transmission G comprises an actuator for actuating the shift element SCI. Furthermore, the transmission G also comprises an actuator for actuating the lock-up clutch WK and an actuator for actuating the disconnect clutch K0. This can also only be considered as exemplary. The disconnect clutch K0 can also be actuated by an actuator which is independent of the transmission G. The same applies to the actuation of the lock-up clutch WK.

[0030] The lock-up clutch WK constitutes an element for transmitting torque between the electric machine EM and the driven shaft GW2. If the lock-up clutch is operated in slip, torque can be transmitted from the internal combustion engine VM and / or the electric machine EM onto the drive wheels DW, without a fixed rotational speed relationship between the driven shaft GW2 and the electric machine EM. The lock-up clutch WK can thus function as a launch element.

[0031] Figure 2 A schematic diagram of a further hybrid powertrain for a motor vehicle is shown, which essentially corresponds to the powertrain shown in Figure 1 The torque converter is now cancelled, so that the electric machine EM is directly connected to the drive shaft GW1. If the shift element SCI participates in the gear formation in the transmission G, the shift element SCI constitutes an element for transmitting torque between the electric machine EM and the driven shaft GW2. If the shift element SCI is operated in slip, torque can be transmitted from the internal combustion engine VM and / or from the electric machine EM onto the drive wheels DW, without a fixed rotational speed relationship between the driven shaft GW2 and the drive shaft GW1. The shift element SCI can thus function as a launch element.

[0032] Figure 3 A schematic diagram of a further hybrid powertrain for a motor vehicle is shown, which essentially corresponds to the powertrain shown in Figure 1 The torque converter is now cancelled, so that the electric machine EM is directly connected to the drive shaft GW1. The transmission G is now listed as a dual clutch transmission, wherein the dual clutch is constituted by the clutches DC1 and DC2. Each of the clutches DC1, DC2 is provided with a shift clutch unit SK1, SK2. Each shift clutch unit SK1, SK2 comprises at least two positively locking clutches, which can haveFigure 3 The synchronization unit is not shown. On the driven side, the shift clutch units SK1, SK2 are connected with the driven shaft GW2. If one of the clutches DC1, DC2 in the dual clutch DC1, DC2 is operated in a slip, torque can be transmitted from the internal combustion engine VM and / or from the electric machine EM onto the drive wheels DW, without a fixed rotational speed relationship between the driven shaft GW2 and the drive shaft GW1. The clutches DC1, DC2 can thus function as a starting element.

[0033] Figure 4 The time curves of different variables of the powertrain according to Figure 1 , Figure 2 or Figure 3 are shown during a starting process, wherein the rated drive torque M_soll, the torque M_EM of the electric machine EM, the limit value M_lim, the torque M_K0 transmitted by the disconnect clutch K0, the rotational speed n_EM of the electric machine EM, the rotational speed n_GW2*i of the driven shaft GW2 relative to the current gear ratio of the transmission G, the rotational speed n_VM of the internal combustion engine VM, the no-load rotational speed n_VM_LL of the internal combustion engine VM and the starting rotational speed n_VM_AN of the internal combustion engine VM are included.

[0034] At the time t1, a starting process of the motor vehicle having one of the powertrains according to Figure 1 , Figure 2 or Figure 3 is started. In the starting process, the vehicle is driven only by the electric machine EM, wherein the disconnect clutch K0 is open and the transmission torque M_K0 of the disconnect clutch is thus equal to zero. Possible drag losses of the open disconnect clutch K0 are not taken into account in this schematic diagram. The starting elements WK, SCI, DC1, DC2 are completely closed, so that the rotational speed n_GW2*i is equal to the rotational speed n_EM of the electric machine EM. The torque M_EM of the electric machine EM is thus transmitted without slip to the driven device GW2.

[0035] At the time t2, the torque M_EM of the electric machine EM is increased for a short time, so that the starting elements WK, SCI, DC1, DC2 assume a slip state. The electric machine EM is operated at a constant rotational speed n_EM after reaching a defined rotational speed value. Such a manner can be necessary, for example, in order to transmit the rated drive torque M_soll in the transmission G. Since the required clamping force of the hydraulically actuated shift elements of the transmission G increases with the rated drive torque M_soll, the hydraulic pump driven by the drive shaft GW1 is operated at a corresponding rotational speed in order to provide the required pressure and the required volume flow.

[0036] At time t3, the rotational speed n_GW2*i reaches the defined rotational speed value of the electric machine EM. While the rotational speed n_GW2*i now continues to increase, the starting elements WK, SCI, DC1, DC2 are closed in order to avoid a thermal input into the starting elements WK, SCI, DC1, DC2. The torque M_EM of the electric machine EM is thus transmitted without slip to the driven device GW2.

[0037] At time t4, the starting of the internal combustion engine VM is requested by the operating strategy of the vehicle. For this purpose, the separating clutch K0 is actuated in such a way that the torque M_K0 is transmitted to the internal combustion engine VM by means of the separating clutch K0. The torque required for the dragging of the internal combustion engine VM is provided by increasing the torque M_EM of the electric machine EM. Here, the starting elements WK, SCI, DC1, DC2 are operated in a slip state in order to decouple the driven shaft GW2 from the vibrations of the starting of the internal combustion engine. The separating clutch K0 is opened again after the dragging process, so that the motor vehicle continues to be driven by the electric machine EM alone. The slip state on the starting elements WK, SCI, DC1, DC2 is reduced again, so that the starting elements WK, SCI, DC1, DC2 are operated without slip from time t5. The rotational speed n_EM of the electric machine EM is less than the no-load rotational speed n_VM_LL here.

[0038] If the internal combustion engine VM is started at time t5 and can be operated automatically, the rotational speed VM_n of the internal combustion engine VM is selected in accordance with the setpoint driving torque M_soll, so that the rotational speed VM_n of the internal combustion engine VM also increases with the increase in the setpoint driving torque M_soll. As a result, an acoustic feedback is transmitted to the driver of the motor vehicle about the increased setpoint driving torque M_soll.

[0039] At time t6, the setpoint driving torque M_soll is increased significantly, for example as a result of a corresponding actuation of the accelerator pedal of the motor vehicle. Here, the setpoint driving torque M_soll exceeds the limit value M_lim. In reaction to this, the torque M_K0 transmitted by the separating clutch K0 is increased from time t7, so that the internal combustion engine VM can contribute to the driving of the motor vehicle. In order to keep the rotational speed difference on the separating clutch K0 small or reduce it to zero, the rotational speed n_EM of the electric machine EM is increased, so that the starting elements WK, SCI, DC1, DC2 are placed in a slip state. At time t8, the rotational speed n_GW2*i reaches the rotational speed n_EM of the electric machine EM, whereupon the starting elements WK, SCI, DC1, DC2 are again switched to the closed state.

[0040] Figure 5 Further time curves of different variables of the powertrain according to Figure 1 , Figure 2 or Figure 3 are shown during the starting process. In Figure 5The parameters and processes shown largely correspond to those in Figure 4 The variation curve shown in the figure, and thus refer to the variation curve for... Figure 4 The description.

[0041] According to Figure 5 In the process, and according to Figure 4 The process is different. The speed n_EM of motor EM is already greater than zero at time t1 and takes a constant value. As the rated driving torque M_soll increases, the starting elements WK, SCI, DC1, and DC2 are driven and controlled, so that the torque is transmitted through the starting elements WK, SCI, DC1, and DC2, thereby causing the speed n_GW2*i to increase - the motor vehicle starts to move.

[0042] According to Figure 5 In the process, and according to Figure 4 The process is different; the rated driving torque M_soll only slightly exceeds the limit value M_lim at time t6. Because it only slightly exceeds the limit, the starting elements WK, SCI, DC1, and DC2 remain closed after time t7, so the speed difference on the disengaging clutch K0 does not decrease until time t8.

[0043] Figure 6 Showing the time during the start-up process according to Figure 1 , Figure 2 or Figure 3 Other time-varying curves of different parameters of the powertrain. Figure 6 The parameters and processes shown largely correspond to those in Figure 4 The variation curve shown in the figure, and thus refer to the variation curve for... Figure 4 The description.

[0044] According to Figure 6 In the process, and according to Figure 4 The process is different. The motor EM is driven and controlled in this way after time t7, which causes slippage in the starting elements WK, SCI, DC1, and DC2, but the speed difference in the disengagement clutch K0 is not completely reduced. More precisely, the disengagement clutch K0 and the starting elements WK, SCI, DC1, and DC2 are all operating in a slippage state, thereby distributing the heat load to the starting elements WK, SCI, DC1, DC2, and the disengagement clutch K0.

[0045] Reference signs

[0046] VM internal combustion engine

[0047] n_VM is the engine speed of the internal combustion engine.

[0048] n_VM_LL is the no-load speed of the internal combustion engine.

[0049] n_VM_AN rotational speed of the internal combustion engine at start-up

[0050] G transmission

[0051] GW1 drive shaft

[0052] GW2 driven shaft

[0053] n_GW2*i rotational speed of the driven shaft GW2 relative to the transmission ratio of the transmission G

[0054] K0 separating clutch

[0055] M_K0 transmission torque of the separating clutch

[0056] EM electric machine

[0057] n_EM rotational speed of the electric machine

[0058] TC torque converter

[0059] P pump wheel

[0060] TR turbine wheel

[0061] WK lock-up clutch

[0062] SCI shift element

[0063] DC1, DC2 clutches

[0064] SK1, SK2 shift clutch unit

[0065] M_soll rated drive torque

[0066] M_lim limit value

[0067] AG differential

[0068] DW drive wheel

[0069] ECU control unit

[0070] INV inverter

Claims

1. Method for operating a powertrain of a motor vehicle, wherein The powertrain has at least one internal combustion engine (VM), an electric machine (EM), a transmission (G) for providing different gear ratios between a drive shaft (GW1) and a driven shaft (GW2) of the transmission (G), a starting element (WK, SCI, DC1, DC2) in the power flow between the electric machine (EM) and the driven shaft (GW2), and a disconnect clutch (K0) in the power flow between the internal combustion engine (VM) and the electric machine (EM), the rotor (R) of the electric machine (EM) being coupled to the drive shaft (GW1), At the start of the electric starting process, the motor vehicle is driven only by the electric machine (EM), and here the starting element (WK, SCI, DC1, DC2) is closed or is operated in a slip state, and the disconnect clutch (K0) is open, During the electric starting process, the internal combustion engine (VM) is dragged by the electric machine (EM) by closing the disconnect clutch (K0), and Subsequently, the disconnect clutch (K0) is opened again, characterized in that, after the internal combustion engine (VM) is dragged and during the electric starting process, the motor vehicle continues to be driven only by the electric machine (EM), the rotational speed (n_EM) of the driven side of the disconnect clutch (K0) is less than the no-load rotational speed (n_VM_LL) of the internal combustion engine (VM), and After the internal combustion engine (VM) is dragged and the disconnect clutch (K0) is opened and during the electric starting process, in order to assist the motor vehicle drive by the internal combustion engine (VM), the disconnect clutch (K0) is closed only when the desired drive torque (M_soll) of the motor vehicle reaches or exceeds a limit value (M_lim).

2. The method of claim 1, wherein, The rotational speed (n_EM) of the driven side of the disconnect clutch (K0) after the internal combustion engine (VM) is dragged is at least maintained to be less than the no-load rotational speed (n_VM_LL) of the internal combustion engine (VM) until the desired drive torque (M_soll) of the motor vehicle reaches or exceeds the limit value (M_lim).

3. The method of claim 1 or claim 2, wherein, The starting element (WK, SCI, DC1, DC2) is operated in a slip state during the dragging of the internal combustion engine (VM), the slip on the starting element (WK, SCI, DC1, DC2) is reduced again after the disconnect clutch (K0) is opened.

4. The method of claim 3, wherein, The slip on the starting element (WK, SCI, DC1, DC2) is reduced to zero after the disconnect clutch (K0) is opened.

5. The method of claim 1, wherein, When the desired drive torque (M_soll) of the motor vehicle reaches or exceeds the limit value (M_lim), the slip on the starting element (WK, SCI, DC1, DC2) is increased in order to minimize the rotational speed difference at the disconnect clutch (K0) when the disconnect clutch (K0) is closed.

6. The method of claim 1, wherein, When the desired drive torque (M_soll) of the motor vehicle reaches or exceeds the limit value (M_lim), the slip on the starting element (WK, SCI, DC1, DC2) remains unchanged, so that the disconnect clutch (K0) is closed during the slip operation of the disconnect clutch (K0).

7. The method of claim 1, wherein, When the setpoint driving torque (M_soll) of the motor vehicle reaches or exceeds the limit value (M_lim), not only the starting elements (WK, SCI, DC1, DC2) but also the separating clutch (K0) are operated in a slip state.

8. The method according to any one of claims 5 to 7, characterized in that, The selection of the method according to claim 5, claim 6 or claim 7 depends on the value of the current setpoint driving torque (M_soll).

9. The method of claim 1 or 2, wherein, The internal combustion engine (VM) is actively operated after towing without contributing to the driving of the motor vehicle and is coupled to the powertrain only when the setpoint driving torque (M_soll) of the motor vehicle reaches or exceeds the limit value (M_lim).

10. The method of claim 9, wherein, The internal combustion engine (VM) is operated in a speed-regulated manner after towing at least until the internal combustion engine (VM) is coupled to the powertrain by closing the separating clutch (K0).

11. The method of claim 10, wherein, The setpoint speed of the internal combustion engine (VM) in the speed-regulated operation is dependent on the current setpoint driving torque (M_soll).

12. An electronic control unit (ECU) for open loop and closed loop control of a motor vehicle powertrain, characterized by, The control unit (ECU) is designed to implement the method according to any one of claims 1 to 11.

Images