METHOD AND DEVICE FOR OPERATING A DRIVE DEVICE, AND DRIVE DEVICE

Abstract

The invention relates to a method for operating a drive device (1) of a motor vehicle, comprising an internal combustion engine (2) having a first exhaust gas turbocharger (5) and a second exhaust gas turbocharger (6), and comprising at least one electric machine (3), wherein the exhaust gas turbochargers (5, 6) are connected in series, wherein at least the second exhaust gas turbocharger (6) has means for varying the output thereof, and wherein the output at least of the second exhaust gas turbocharger (6) is varied in accordance with a required target torque of the drive device (1). According to the invention, the electric machine (3) is controlled in accordance with the time of the variation, in order to compensate for a deviation of an actual torque of the drive device (1) from the target torque.

Claims

1. A method for operating a drive device (1) of a motor vehicle, which drive device (1) has an internal combustion engine (2) with a first exhaust gas turbocharger (5) and a second exhaust gas turbocharger (6), and at least one electric machine (3), the first and second exhaust gas turbochargers (5, 6) being connected in series, at least the second exhaust gas turbocharger (6) having means for varying performance of the second exhaust gas turbocharger, and the method comprising varying the performance of at least the second exhaust gas turbocharger (6) in a manner which is dependent on a requested setpoint torque of the drive device (1), and actuating the electric machine (3) in a manner which is dependent on a time of the variation, in order to compensate for a deviation of an actual torque of the drive device (1) from the setpoint torque.

2. The method as claimed in claim 1, characterized in that the performance of the second exhaust gas turbocharger (6) is varied in such a way that the performance of the second exhaust gas turbocharger (6) is increased if a first limit value is exceeded by the requested setpoint torque.

3. The method as claimed in claim 1, characterized in that the performance of the second exhaust gas turbocharger (6) is varied in such a way that the second exhaust gas turbocharger (6) is not switched on until the first limit value is exceeded.

4. The method as claimed in claim 1, characterized in that the first exhaust gas charger (5) has means for varying performance of the first exhaust gas turbocharger, the performance of the first exhaust gas turbocharger (5) being varied in a manner which is dependent on the requested setpoint torque.

5. The method as claimed in claim 1, further comprising detecting a current actual rotational speed of at least the second exhaust gas turbocharger (6), and determining the time of the variation in a manner which is dependent on the detected actual rotational speed.

6. The method as claimed in claim 1, further comprising monitoring an actual actuating state of the means of at least the second exhaust gas turbocharger (6), and determining the time of the variation in a manner which is dependent on the actual actuating state.

7. The method as claimed in claim 1, characterized in that the actuation of the electric machine (3) is ended in a manner which is dependent on a hysteresis when the actual rotational speed and/or the actual actuating state correspond/corresponds to a setpoint rotational speed and a setpoint actuating state, respectively.

8. The method as claimed in claim 1, characterized in that the electric machine (3) is actuated in a manner which is dependent on a requested gear change.

9. A device for operating a drive device of a motor vehicle, wherein the drive device comprises a control unit configured to carry out the method as claimed in claim 1, and wherein the drive device has an internal combustion engine (2) with a first exhaust gas turbocharger (5) and a second exhaust gas turbocharger (6), and at least one electric machine (3), the first and second exhaust gas turbochargers (5, 6) being connected in series, and at least the second exhaust gas turbocharger (6) having means for varying performance of the second exhaust gas turbocharger.

10. A drive device (1) for a motor vehicle, the drive device comprising a device as claimed in claim 9, and the drive device having an internal combustion engine (2) which has a first exhaust gas turbocharger (5) and a second exhaust gas turbocharger (6), and having an electric machine (3), the first and second exhaust gas turbochargers (5, 6) being connected in series, and at least the second exhaust gas turbocharger (6) having means for varying performance of the second exhaust gas turbocharger.

Description

[0016] In the following text, the invention and its advantages are to be described in greater detail using the drawing, in which:

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

[0018] FIG. 2 shows a method for operating the drive device, and

[0019] FIG. 3 shows a further method for operating the drive device.

DETAILED DESCRIPTION

[0020] FIG. 1 shows a simplified illustration of a drive device 1 of a motor vehicle (not shown in greater detail here). The drive device 1 has an internal combustion engine 2 which is configured as a reciprocating piston engine. The internal combustion engine 2 or a crankshaft of the internal combustion engine 2 is connected to an electric machine 3. In particular, a rotor of the electric machine 3 is directly arranged fixedly on the crankshaft 2 or the output shaft of the internal combustion engine 2 so as to rotate with it. The electric machine 3 is in turn connected to a transmission 4 which connects the drive device 1 to drive wheels of the motor vehicle. Here, in particular, the transmission 4 has a plurality of transmission stages, between which shifting can be carried out.

[0021] The internal combustion engine 2 is assigned two exhaust gas turbochargers 5 and 6 which are connected in series to one another. The two exhaust gas turbochargers 5, 6 have in each case one turbine T.sub.5, T.sub.6 and a compressor V.sub.5 and V.sub.6 which is connected to the turbine. The exhaust gas turbochargers 5 and 6 are connected in series to one another, with the result that exhaust gas which comes from the internal combustion engine 2 is first of all fed to the turbine T.sub.6 of the exhaust gas turbocharger 6 and subsequently to the turbine T.sub.5 of the exhaust gas turbocharger 5. Accordingly, fresh air is first of all fed to the compressor V.sub.5 of the exhaust gas turbocharger 5 and subsequently to the compressor V.sub.6 of the exhaust gas turbocharger 6, with the result that the fresh air is compressed by way of the compressor V.sub.5 and subsequently the compressor V.sub.6 and is only then fed to the internal combustion engine 2.

[0022] The turbines T.sub.5 and T.sub.6 are in each case assigned a bypass B.sub.5 and B.sub.6, respectively, which in each case have a switchable wastegate valve W.sub.5 and W.sub.6, respectively, by way of which a throughflow cross section of the respective bypass B.sub.5, B.sub.6 can be set. If the respective bypass B.sub.5, B.sub.6 is closed completely by way of the respective wastegate valve W.sub.5, W.sub.6, the exhaust gas or the exhaust gas mass flow of the internal combustion engine 2 is guided completely through the turbines T.sub.6 and T.sub.5, in order to drive the two exhaust gas turbochargers T.sub.5 and T.sub.6.

[0023] In the present case, the compressor V.sub.6 is also assigned a further bypass BV.sub.6 with a further valve WV.sub.6, by way of which the fresh air flow which is fed to the compressor V.sub.6 can be regulated.

[0024] The wastegate valves W.sub.5, W.sub.6 and WV.sub.6 are, in particular, means for varying the performance of the respective exhaust gas turbocharger 5, 6. By way of the actuation of the wastegate valves W.sub.5 and W.sub.6, for example, a switchover can be carried out during operation of the drive device 1 from two stage operation, in which the two exhaust gas turbochargers 5, 6 are operated, to one stage operation, in which only one of the exhaust gas turbochargers 5 or 6 is still operated. In the case of a switchover of this type, a delayed build up of boost pressure of the internal combustion engine 2 occurs on account of the dynamic flow conditions in the air guiding system. As a result, the actual torque of the drive device 1 follows a setpoint torque of the drive device 1 in a delayed manner, which setpoint torque is stipulated by a driver or is requested by a driver.

[0025] It is provided in the present case that, in the case of a switchover, the electric machine 3 is actuated to compensate for said deviation of the actual torque from the setpoint torque. To this end, it is provided in the present case that the electric machine is actuated in a manner which is dependent on the time of the variation of the performance of at least one of the exhaust gas turbochargers 5, 6, in order to generate an additional torque which compensates for the delayed build up of torque of the internal combustion engine 2. Here, in the present case, the example is assumed that a switchover is carried out between the exhaust gas turbochargers 5 and 6 if a predefinable limit value is exceeded by the requested setpoint torque, the high pressure stage, in particular, being decoupled in the case of a high performance request. For the switchover, the performance of the exhaust gas turbochargers 6 is varied by way of the actuation of the bypass. It is provided here that the wastegate valve W.sub.6, and the other wastegate valves, are assigned an, in particular, electropneumatic actuator which moves or actuates the respective valve accordingly. The actuator is actuated, in particular, with a predefinable duty factor, a predefinable position of the respective valve resulting in a manner which is dependent on said duty factor.

[0026] The duty factor is monitored continuously by way of the control unit 7, in order to determine the performance of the exhaust gas turbocharger or a variation of the performance of the exhaust gas turbocharger 6 in a manner which is dependent on the actuating position of the actuator. In particular, the time, at which the performance of the exhaust gas turbocharger 6 is actually changed, can be determined by way of monitoring of the boost pressure deviation which results as a consequence of the performance of the exhaust gas turbocharger. In a manner which is dependent on said time, the electric machine 3 is actuated to compensate for that proportion of the torque increase which cannot be provided immediately by the internal combustion engine 2. As a result, the electric machine 3 is started up at an early stage such that a uniform torque increase and, in particular, no traction interruption are noticeable for the driver or occupants of a motor vehicle which has the drive device 1. The time of the switchover is advantageously fixed in such a way that the additional torque of the electric machine 3 acts in a manner which is controlled in advance, and a drop in the rotational speed is avoided as a result. This can be implemented, for example, by way of an actuating logic means of the control unit 7 in a manner which is dependent on the determined time of the variation or the boost pressure deviations and/or the actuating position of the actuator system, as has already been described above.

[0027] FIG. 2 shows a simplified illustration of a method for operating the drive device 1, in which method the time of the switchover is determined in a manner which is dependent on the duty factor. To this end, FIG. 2 shows a simplified flow diagram. First of all, in a step 8, the actuator of the wastegate valve 6 is actuated to set a setpoint duty factor (EPW.sub.soll). In a manner which is dependent on the electric current, the characteristic curve which is inherent to the actuator results in a setpoint duty factor, from which an actual duty factor TV or an actual position of the wastegate valve 6 arises. As a result, the duty factor TV of the actuator is determined and, as a consequence of this, the time T, at which a variation of the performance of the exhaust gas turbocharger 6 takes place. The electric machine 3 is actuated in a manner which is dependent on said duty factor TV or time, a release hysteresis being used in the following step 9 to actuate the electric machine 3. Said hysteresis provides that the electric machine 3 is actuated (on) over a defined duty factor or time, at which the variation is detected, in order to compensate for the missing torque Md. The operation of the electric machine 3 is ended (off), however, in a delayed manner at the time, at which it can be assumed that the exhaust gas turbocharger 6 generates the desired performance.

[0028] For an improved connection of the torque during a shifting operation of the transmission 4, the compensation which is described in this regard by way of the electric machine 3 is likewise advantageous because the brief traction interruption of the transmission 4 during the shifting operation is bridged. As a result, the torque of the drive device 1 can also be kept at a higher level during the shifting operation, which improves the connection of the next transmission ratio and avoids downshifts. The advantage of an additional torque assistance by way of the electric machine 3 in a manner which is dependent on a gear change is the avoidance of the traction loss and the avoidance of a downshift, that is to say a higher gear can be utilized for a longer time by way of the electric additional drive.

[0029] In the case of a request for a gear change for a downshift, that is to say, for example, from third gear into second gear, a check is advantageously carried out as to whether said downshift can be avoided by way of the generation of an additional torque by way of the electric machine 3. Conversely, the required electric additional performance can be determined in the case of an upshift, in order to compensate for the delayed build up of boost pressure in an optimum manner.

[0030] To this end, for example, FIG. 3 shows the additional performance P which is to be provided by the electric machine 3 or the additional torque which is to be provided in a manner which is dependent on different gear changes G between the gears 1, 2, 3, 4 and 5 of the transmission 4.