METHOD AND DEVICE FOR OPERATING A DRIVE DEVICE, DRIVE DEVICE

Abstract

The invention relates to a method for operating a drive device (1) of a motor vehicle, having an internal combustion engine (2), an electric machine (3), and a dual-clutch transmission (4). The dual-clutch transmission (4) has two clutches (K1, K2), by means of which the transmission can be connected to the internal combustion engine (2). At least the internal combustion engine (2) is actuated in a driving operation in order to generate a target drive torque, and the clutches (K1, K2) are actuated in opposite directions for a gear shift. During a gear shift, the electric machine (3) which is connected to the dual-clutch transmission (4) without a clutch is actuated such that the electric machine completely or partly generates the target torque at least temporarily.

Claims

1. A method for operating a drive device of a motor vehicle, which drive device has an internal combustion engine, an electric machine and a dual-clutch transmission, wherein the dual-clutch transmission has two clutches by which it can be connected to the internal combustion engine, and the electric machine is connected to the dual-clutch transmission without a clutch, the method comprising: actuating, in a driving mode, the internal combustion engine to generate a target drive torque, activating the two clutches in opposite directions during a gear shifting process, wherein during the gear shifting process the electric machine is actuated in such a way that the electric machine at least partly generates the target torque.

2. The method as claimed in claim 1, wherein the electric machine is actuated in such a way that said electric machine completely or partially takes over that portion of the target drive torque which is provided by the internal combustion engine.

3. The method as claimed in claim 1, wherein to initiate the gear shifting process the torque which is transmitted by the internal combustion engine to the dual-clutch transmission is reduced.

4. The method as claimed in claim 3, wherein the torque is reduced by opening the clutch which currently connects the internal combustion engine to the dual-clutch transmission.

5. The method as claimed in claim 3, wherein the torque is reduced by reducing an engine torque which is predefined by the internal combustion engine.

6. The method as claimed in claim 1, wherein the clutch which connects the internal combustion engine to the dual-clutch transmission is not opened until the engine torque of the internal combustion engine is reduced to zero.

7. The method as claimed in claim 1, wherein during a rotational speed synchronization of the dual-clutch transmission during the gear shifting process both clutches are opened completely.

8. The method as claimed in claim 1, wherein in order to initiate the gear shifting process the clutch which connects the internal combustion engine to the dual-clutch transmission is opened and at the same time the other clutch is at least partially closed.

9. A device for operating a drive device of a motor vehicle which has an internal combustion engine, an electric machine and a dual-clutch transmission, wherein the dual-clutch transmission has two clutches by which the internal combustion engine can be operatively connected to the dual-clutch transmission, with a control unit configured to actuate, in a driving mode, the internal combustion engine to generate a target drive torque, activate the two clutches in opposite directions during a gear shifting process, wherein during the gear shifting process the electric machine is actuated in such a way that the electric machine at least partly generates the target torque.

10. A drive device for a motor vehicle, having an internal combustion engine, an electric machine and a dual-clutch transmission, wherein the dual-clutch transmission has two clutches by which it can be operatively connected to the internal combustion engine, and wherein the electric machine is operatively connected to the dual-clutch transmission without a clutch, and having a device as claimed in claim 9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In the text which follows, the advantages of the inventions will be explained further on the basis of an exemplary embodiment. In this respect:

[0017] FIG. 1 shows a drive device of a motor vehicle in a functional illustration,

[0018] FIG. 2 shows a diagram explaining an advantageous method for operating the drive device,

[0019] FIG. 3 shows a further diagram explaining the method,

[0020] FIG. 4 shows a further diagram explaining the method,

[0021] FIG. 5 shows a diagram explaining a variant of the method,

[0022] FIG. 6 shows a further diagram explaining the further variant of the method, and

[0023] FIG. 7 shows a flowchart explaining a further advantageous method for operating the drive device.

DETAILED DESCRIPTION

[0024] FIG. 1 shows a drive device 1 of a motor vehicle, which drive device 1 is embodied as a hybrid drive device. For this purpose, the drive device 1 has an internal combustion engine 2 and an electric machine 3, which are connected by a dual-clutch transmission 4, which is illustrated only functionally in FIG. 1, to at least one driven wheel 5 of the motor vehicle. The dual-clutch transmission 4 has two clutches K1 and K2 by which it can be operatively connected to the internal combustion engine 2. In this context, the dual-clutch transmission 4 has two partial transmissions TG1 and TG2 which each have different transmission ratios and are operatively connected to the driven wheel 5. Thus, the partial transmission TG1 here has, for example, the transmission ratios for the gears 1, 3, 5, the reverse gear and a neutral gear N, while the partial transmission TG2 has the transmission ratios for the gears 2, 4 and 6 and a neutral gear N. In particular, the dual-clutch transmission 4 is embodied in such a way that, as shown here, the next highest or the next lowest transmission ratio is located in each case on the other partial transmission. An input shaft of the partial transmission TG1 is connected here to the clutch K1, and an input shaft of the partial transmission TG2 is connected to the clutch K2, with the result that the internal combustion engine 2 is operatively connected either to the partial transmission TG1 or to the partial transmission TG2 as a function of which of the two clutches K1 and K2 is closed. If both clutches K1 and K2 are opened, the internal combustion engine 2 is completely disconnected from the dual-clutch transmission 4 and cannot transmit either a positive or a negative torque to the driven wheel 5. The electric machine 3 is connected to the input shaft of the partial transmission TG2 permanently or without a clutch. The electric machine 3 is coupled to the input shaft here, for example, by a belt drive or by a gear mechanism. Alternatively, the electric machine 3 can, however, also be connected to the partial transmission TG2 at the output shaft or at another location in the partial transmission TG2. Furthermore, a starter motor 6 is assigned to the internal combustion engine 2 here.

[0025] In the case of a gear shifting process from a relatively low to a relatively high gear, for example from the gear 3 to the gear 4, the procedure adopted is usually as follows: in the initial state in the partial transmission TG2 the gear 4 is already engaged. In the partial transmission TG1 the gear 3 is engaged, the clutch K2 is opened and the clutch K1 is closed, and the internal combustion engine 2 makes available a positive engine torque which is transmitted to the driven wheel 5 according to the transmission ratio of the gear 3. In this context, the torque or the power flows from the internal combustion engine 2 through the clutch K1, the partial transmission TG1 to the driven wheel 5. In the final state, the flow of torque is to be transmitted from the internal combustion engine 2 through the clutch K2 and the partial transmission TG2 to the driven wheel 5 with the transmission ratio of the gear 4. In order to pass from the initial state to the final state, the following steps are carried out:

[0026] For the sake of simplification, a constant driver's request torque and a constant velocity are assumed, with the result that the rotational speeds of the partial transmissions TG1 and TG2 as well as the required torques in the respective gears do not change. In the case of shifting up from the third into the fourth gear, a differentiation is made between a torque transfer from the partial transmission TG1 to the partial transmission TG2 and subsequent synchronization of the rotational speed of the internal combustion engine to the rotational speed of the partial transmission TG2. Since the torque request by the driver at the driven wheel 5 of the entire shifting operation is to remain constant, the torque of the internal combustion engine 2 has to be raised during the torque transfer. The required raising of the torque can be calculated from the transmission ratio of the fourth gear in the partial transmission TG2 and the desired driver's request torque. During the synchronization of the rotational speed of the internal combustion engine 2 with the partial transmission TG2, the torque of the internal combustion engine 2 is lowered so far that the rotational speed of the internal combustion engine 2 is lowered to the input rotational speed of the partial transmission TG2. The clutch torque of the partial transmission TG1 or the torque which is transmitted by the clutch K1 is lowered during the torque transfer to zero and the clutch torque of the partial transmission TG2 or of the clutch K2 is raised from zero to the required drive torque. In this context it is advantageously necessary to ensure that the sum of the two clutch torques during the torque transfer is equal to the desired driver's torque so that an interruption in the tractive force and therefore a reduction in the comfort do not occur. Furthermore, the clutch torque of the partial transmission TG2 has to be kept constant during the synchronization of the rotational speed in order to prevent the tractive force from being interrupted. During the transfer of torque, the rotational speed of the internal combustion engine has to be kept constant, or must be slightly increased so that the slip of the clutch K1 is always positive. This is important so that the sign of the transmitted torque of a slipping clutch depends on the sign of the difference in rotational speed. There is therefore expediently provision that the rotational speed of the internal combustion engine 2 is higher than or equal to the input rotational speed of the partial transmission TG1, in order to transmit a positive torque. If the rotational speed of the internal combustion engine 2 drops below the input rotational speed of the partial transmission TG1, the sign of the transmitted torque changes and a significantly perceptible dip occurs in the drive torque at the driven wheel 5, which in turn leads to an interruption in the tractive force which can be clearly felt by the driver and other occupants of the motor vehicle. In this context, the rotational speed cannot be synchronized until the entire engine torque of the internal combustion engine 2 has been transferred to the clutch K2 of the partial transmission TG2. For the partial transmission TG2, in the case of a tractive upshift, that is to say a gear shifting process to a relatively high gear, the rotational speed of the internal combustion engine is always higher than the rotational speed of the input shaft of the partial transmission TG2, in order to ensure a positive transmission of torque. During the synchronization of the rotational speed, the rotational speed of the internal combustion engine 2 must be lowered to the input rotational speed of the partial transmission TG2, in order to be able to close the clutch K2 completely.

[0027] The required driver's request torque at the driven wheel 5 can be distributed between the electric machine 3 and the internal combustion engine 2 by the electric machine 3, in order to be able to operate the internal combustion engine 2, for example, at an operating point which is optimum in terms of consumption. The target drive torque which is to be made available overall at the driven wheel 5 by the drive device 1 can therefore be provided jointly by the internal combustion engine 2 and the electric machine 3. Depending on the operating strategy, the portions of the target drive torque provided by the internal combustion engine 2 and electric machine 3 change here.

[0028] In order to increase further the comfort for a driver and further occupants of the motor vehicle during the shifting up, to relieve the loading of the internal combustion engine 2 and the clutches K1 and K2 and therefore to obtain a lower level of wear of the clutches K1 and K2, there is provision here that during the gear shifting process the torque of the internal combustion engine 2 is transferred completely or partially to the electric machine 3 as a function of the efficiency of the electric machine 3. As a result, low torques or no torques have to be transmitted between the clutches K1 and K2 of the partial transmissions TG1 and TG2 during the torque transfer. This has the advantage that the comfort is increased and the wear reduced. Furthermore, smaller dimensioning of the drive device, in particular of the clutches K1, K2, is possible, which gives rise to improved installation space conditions and lower manufacturing costs. The advantageous method is to be explained in more detail with reference to FIGS. 2 to 7. In this context, the initial state and final state described above are used as the starting points.

[0029] FIG. 2 shows in a diagram plotted against the time t the machine torque Md.sub.3 of the electric machine 3 and the engine torque Md.sub.2 of the internal combustion engine 2 during a gear shifting process, wherein it is assumed here that the transmission ratio of the electric machine 3 to the partial transmission TG2 is equal to 1. Furthermore, the torques of the partial transmissions TG1 and TG2 for the third gear Md.sub.G3 and the fourth gear Md.sub.G4 are shown. During the shifting up from the third to the fourth gear, that is to say during a changeover from the partial transmission TG1 to the partial transmission TG2, the torque Md.sub.2 of the internal combustion engine 2 is firstly transmitted to the electric machine 3 in a phase I, so that the electric machine 3 makes available the entire driver's request torque through the partial transmission TG2 and the driven wheel 5. After this, in phase II the rotational speed synchronization of the internal combustion engine 2 and of the partial transmission TG2 occurs. If the rotational speeds are synchronized, in phase III the clutch K2 of the partial transmission TG2 is completely closed, and the torque is transmitted from the electric machine 3 again to the internal combustion engine 2 or, if the target drive torque is to be provided jointly by the internal combustion engine 2 and the electric machine 3, it is distributed between the internal combustion engine 2 and the electric machine 3.

[0030] FIG. 3 shows in a further diagram plotted against the time t the torques Md.sub.K1 and Md.sub.K2 which are transmitted by the clutches K1 and K2. The torque of the clutch K1 of the partial transmission TG1 is lowered to zero to the same degree as the torque Md.sub.2 of the internal combustion engine 2. If the clutch K1 is load-free, it can be opened, or the clutch K2 can already be adjusted beforehand in order to implement a faster shifting process. In contrast to a conventional gear shifting process in which the internal combustion engine torque is transferred to the clutch K2 of the partial transmission TG2 with an associated increase in the torque, the transmitted torque of the clutch K2 of the partial transmission TG2 is here equal to zero in the phases I and II. The clutch K2 is still completely opened and there is no slip and therefore no wear present. During the synchronization of the rotational speed in the phase II, both clutches K1 and K2 are completely opened. The clutch K2 of the partial transmission TG2 is completely closed, in particular, before the torque transfer from the electric machine 3 to the internal combustion engine 2 and is optionally increased with the internal combustion engine torque Md.sub.2 in order to permit a faster shifting process.

[0031] FIG. 4 shows in a further diagram plotted against the time t the rotational speed n2 of the internal combustion engine 2 during the described gear shifting process. Here, the input rotational speeds n.sub.TG2 and n.sub.TG1 which remain the same owing to the constant velocity of the motor vehicle are also shown with the respectively engaged gear 3 or 4 by dashed lines. The rotational speed profile of the internal combustion engine 2 corresponds to the rotational speed profile during a conventional shifting process. However, because the clutches K1 and K2 have to operate with very much less slip and as a result the wear and the loading of the clutches K1 and K2 is reduced compared to the conventional gear shifting process, the advantages already specified above are obtained.

[0032] In the event of the electric machine 3 not being able to completely provide the entire target drive torque or driver's request torque, a reduction in the necessary clutch torques during the torque transfer from the partial transmission TG1 to the partial transmission TG2 is always possible using the electric machine 3. The sequence of the gear shifting process is explained below with reference to FIG. 5 in a way analogous to the shifting sequences described above.

[0033] FIG. 5 shows again the diagram which is also shown in FIG. 2, with the difference that the electric machine 3 is not able to take over completely the torque of the electric motor 2. In the phase I at the same time part of the torque Md.sub.2 of the internal combustion engine 2 is transmitted to the electric machine 3, while the remaining part of the torque of the internal combustion engine is also transmitted to the partial transmission TG2. After this, the synchronization of the rotational speed in phase II takes place. If the rotational speeds are synchronized, the clutch K2 of the partial transmission TG2 can be closed completely, and the target drive torque can be distributed again between the electric machine 3 and the internal combustion engine 2 to phase III.

[0034] The associated torques which are transmitted by the clutches K1 and K2 are shown in FIG. 6. The transmitted torque of the clutch K1 is initially lowered to zero in the phase I. As soon as the clutch K1 is load-free, it can be opened, or the clutch can already be adjusted beforehand in order to implement a faster shifting process. At the same time, the internal combustion engine torque Md.sub.2 is taken over by the clutch K2. In contrast to a conventional gear shifting process in which the internal combustion engine torque Md.sub.2 is transferred to the clutch K2 (with the associated increase in the torque), the torque Md.sub.K2 of the clutch K2 is lower here. In the slip, a relatively low power loss, which is proportional to the transmitted torque Md.sub.K2, is input into the clutch K2 and therefore a lower wear of the clutch K2 with respect to the conventional gear shifting process is achieved. The torque of the clutch K2 is also lower during the synchronization of the internal combustion engine 2. As a result, a lower power loss in the clutch K2 is achieved over the entire shifting process or gear shifting process. This gives rise to a reduced wear of the clutch K2 and therefore to an increased service life.

[0035] FIG. 7 shows in a flowchart an advantageous method for operating the drive device during shifting down, that is to say during a gear shifting process from a relatively high gear to a relatively low gear, by which process shifting of the gear of the partial transmission TG2 without an interruption in the tractive force is made possible during a recuperation mode of the electric machine 3. In this context, the following initial state is taken as the starting point: in the partial transmission TG2 a gear, for example gear 4, is engaged, the clutch K2 is opened, and the internal combustion engine 2 is switched off, the clutch K1 is opened and the electric machine 3 is operated as a generator. As a final state, a relatively low gear, for example gear 2, is to be engaged in the partial transmission TG2, the clutches K1 and K2 are to be opened and the internal combustion engine is to be switched off and the electric machine 3 is to continue to be operated as a generator, and in this respect a negative torque is to be generated.

[0036] In the step S1, the method is started with the abovementioned initial state. In the following step S2 in a partial transmission TG1 a low gear is engaged, in particular a gear which is lower than the gear which is engaged in the partial transmission TG2, in particular the lowest available gear with the highest transmission ratio of the partial transmission TG1, in order to achieve the highest possible rotational speed at the clutch K1.

[0037] Subsequently, in a step S3 for the gear shifting process the electric machine 3 is actuated to provide a zero torque, that is to say to run in an idling mode. In this context, the clutch K1 is operated in a slipping fashion in a step S4, without the internal combustion engine 2 being operated. The slipping operation of the clutch K1 generates a decelerating torque in the partial transmission TG1 in that energy is destroyed in the clutch K1 by the slip, and therefore an interruption in the tractive force is compensated by the zero torque of the electric machine 3.

[0038] Subsequently, the current gear, for example gear 4, is disengaged in the partial transmission TG2 in a step S5, and a new, relatively low gear, in particular the next lowest gear, here gear 2, is engaged in a subsequent step S6. In parallel with this, the decelerating target drive torque continues to be made available by the slipping operation of the clutch K1.

[0039] In a subsequent step S7, the electric machine 3 is again actuated to be operated as a generator, and in this context to make available a decelerating drive torque, which acts on the driven wheel 5 for the partial transmission TG2. While the torque of the electric machine 3 is increased again, the clutch K1 is opened again, in order to reduce the deceleration torque which is generated by the slip. As soon as the clutch K1 is completely opened, the engaged gear of the partial transmission TG1 is preferably disengaged again in a step S8, and the partial transmission TG1 is shifted, in particular, into a neutral gear or state. As a result, the method is ended in a step S9. The shifting process is advantageously carried out as quickly as possible so that as little energy as possible is destroyed in the clutch K1 by the slipping operation, and the wear is kept small. Alternatively, there can be provision that the internal combustion engine 2 also rotates as long as the clutch K1 generates a decelerating torque.

[0040] By means of this method, a gear shifting process of the partial transmission TG2 which is free of an interruption in the tractive force is made possible during a recuperation mode, as a result of which the electric machine can be operated in a high gear at high speeds, with better efficiency and a high torque. As a result, purely electric driving is optimized even at relatively high speeds, in particular with respect to the driving comfort. The comfort of the dual-clutch transmission 4, specifically the shifting which is free of an interruption in the tractive force, is therefore ensured even in the purely electric mode of the motor vehicle, with just one electric machine which is assigned to just one of the partial transmissions TG1 or TG2.