Method for operating a drive train

This application claims priority from German patent application serial no. 10 2008 043 733.6 filed Nov. 14, 2008.

The invention concerns a process for operating at least one transmission and a drive train comprising a hybrid drive of a motor vehicle.

The primary components of a drive train of a motor vehicle are a drive unit and a transmission. A transmission provides a speed-power conversion and thus converts the supply of traction force of the drive unit. The invention concerns a process for operating a drive train, which comprises at least one transmission and a hybrid drive as drive unit with an internal combustion engine and an electric machine that can be operated as an electric motor and/or generator.

FIG. 1 shows a drive train diagram of a drive train known from the state of the art having a hybrid drive comprising an internal combustion engine 1 and an electric motor 2 , wherein a transmission 4 is connected between the electric motor 2 of the hybrid drive and an output 3 of the drive train. The transmission 4 is an automatic transmission, in which the gear changes or shifts are preferably carried out with an interruption of traction force. A clutch 5 , which is disengaged during purely electric motor-based driving in order to decouple the internal combustion engine 1 from the output 3 , is connected between the internal combustion engine 1 and the electric motor 2 of the hybrid drive. A drive train such as this typically comprises furthermore either a starting element located in the interior of transmission, which is not shown, or a starting element located outside of the transmission, which is not shown. Such a drive train is also referred to as parallel hybrid drive train.

FIG. 2 shows a diagram, which illustrates the mode of operation known from the state of the art for carrying out a shift in the drive train shown in FIG. 1 . In FIG. 2 are shown three torque trends over the time t, namely a time torque trends 6 of a torque that can be transmitted by the clutch 5 connected between the internal combustion engine 1 and the electric motor 2 is shown as a dashed line, a time torque trend 7 of a torque made available by the internal combustion engine 1 is shown as a solid line, and a time torque trend 8 of a torque made available by the electric motor 2 is shown as a dash-dotted line, each specifically during a gear change in the form of a traction shift when the electric motor 2 is operated as a generator.

It is thus apparent from FIG. 2 that in order to carry out a shift in the automatic transmission 4 with previously engaged clutch 5 , first the load at the internal combustion engine 1 is reduced (see torque trend 7 ), and simultaneously the load at the electric motor 2 is reduced (see signal trend 8 ), while in addition also the torque transmitted by the clutch 5 is reduced according to the signal trend 6 . According to FIG. 2 , the load made available by the internal combustion engine 1 , or the torque made available by the internal combustion engine 1 , and the load made available by the electric motor 2 , or the torque made available by the electric motor 2 , each have a value of zero at the time t 1 , while the torque that can be transmitted by the clutch 5 amounts to zero only later at time t 2 . According to the state of the art, the clutch 5 is accordingly disengaged with time delay at time t 2 in order to reduce the load at the internal combustion engine 1 and at the electric motor 2 , while a gear change is carried out in the automatic transmission between the times t 2 and t 3 . The gear change is completed in the transmission 4 at time t 3 , while the torque that can be transmitted by the clutch 5 (see signal trend 6 ) is again built up at time t 3 . The loads or torques at the internal combustion engine 1 (see signal trend 7 ) and at the electric motor 2 (see signal trend 8 ) are again built up delayed in time starting at time t 4 , according to signal trends 7 and 8 .

In the mode of operation of FIG. 2 known from the state of the art for operating a parallel hybrid drive train having an automatic transmission 4 , the shift in the transmission 4 is carried out accordingly during the time span Δt 23 , but the duration of an interruption of traction force at the output 3 corresponds to the time span Δt 14 . The duration of the interruption of traction force Δt 14 accordingly comprises the duration Δt 23 for gear change in the automatic transmission 4 , plus the duration until the clutch 5 can be opened at time t 2 after the reduction in load at the internal combustion engine 1 and at the electric motor 2 at time t 1 , and plus the time frame until the clutch 5 can transmit torque after the shift time span t 3 has been carried out and torque has built up at the internal combustion engine at time t 4 .

Based on this state of the art, there is a need for a process for operating a drive train comprising a hybrid drive and an automatic transmission, wherein the interruption of traction force at the output can be shortened.

Based on this, it is the object of the invention to create a novel process for operating a drive train with a transmission and a hybrid drive. The object is attained by means of a process according to claim 1 . According to the invention, a load transfer by means of the electric motor is carried out before carrying out a gear change in the automatic transmission and/or after carrying out a gear change in the automatic transmission.

The duration of the traction force interruption at the output can be shortened with the process for operating a drive train of the invention. A further advantage of the process according to the invention is that discrepancies in the clutch torque of the clutch connected between the internal combustion engine and the electric motor of the hybrid drive have a reduced impact on the shifting comfort.

Exemplar embodiments of the invention will be explained in more detail with reference to the figures, without being limited to these. In the drawings:

FIG. 1 shows a drive train diagram of a motor vehicle known from the state of the art, in which the process according to the invention can be utilized; and

FIG. 2 shows a diagram to illustrate a process for operating the drive train of FIG. 1 , which is known from the state of the art; and

FIG. 3 shows a diagram to illustrate the process according to the invention for operating the drive train of FIG. 1 .

FIG. 3 shows a diagram to illustrate the process according to the invention for operating the parallel hybrid drive train shown in FIG. 1 , whose transmission 4 is configured as an automatic transmission, which preferably carries out shifts or gear changes with interruption of traction force.

Thus, in FIG. 3 , three different torque trends are shown again over the time t, namely a time torque trend 9 of the torque that can be transmitted by the clutch 5 connected between the internal combustion engine 1 and the electric motor 2 is shown as a dashed line, a time-based torque trend 10 of a torque made available by the internal combustion engine 1 is shown as a solid line, and a time torque trend 11 of a torque made available by the electric motor 2 is shown as a dash-dotted line, while FIG. 3 again concerns the case of a traction shift.

According to FIG. 3 , the torque made available by the internal combustion engine 1 is again reduced according to the torque trend 10 until it amounts to zero at time t 1 before a shift is carried out in the automatic transmission 4 . The torque that can be transmitted by the clutch 5 (see signal trend 9 ) is likewise reduced, while the torque is zero with time delay at time t 2 and the clutch 5 is disengaged at time t 2 .

After carrying out a shift in the automatic transmission 4 , at time t 3 , the torque that can be transmitted by the clutch 5 (see signal trend 9 ) is also increased again, and the torque made available by the internal combustion engine 1 (see signal trend 10 ) is increased again with time delay, starting at the time t 4 .

A load transfer by means of the electric motor 2 is carried out in the sense of the invention before a gear change in the automatic transmission 4 is carried out and/or after a gear change in the automatic transmission 4 has been carried out, while this transfer takes place both before the gear change is carried and after the gear change has been carried out according to FIG. 3 .

The torque trends 11 of the torque made available by the electric machine show in FIG. 3 that a load transfer is carried out by means of the electric motor 2 , both before the gear change is carried out and after the gear change has carried been out.

It is apparent from FIG. 3 that the load transfer by means of the electric motor 2 before the gear change is carried out is carried out in such a way that after the load reduction at the internal combustion engine 1 at time t 1 , and after the reduction of the torque that can be transmitted by the clutch 5 at time t 2 , the electric motor makes available a torque having the same algebraic sign as the previously reduced torque of the internal combustion engine 1 .

The load transfer by means of the electric motor 2 is also takes place after a gear change has been carried out in such a way that the electric motor 2 makes available a torque, which has the same algebraic sign as the torque of the internal combustion engine 1 to be built up, before the load buildup at the internal combustion engine 1 at time t 4 , and before the buildup of torque that can be transmitted by the clutch 5 at time t 3 .

Before a gear change is carried out, the torque provided by the electric motor 2 at the output is therefore not zero until time t 5 . Furthermore, after a gear change has been carried out, the torque provided at the output is zero only until the time t 6 , so that the duration of the interruption of traction force, that is, the time during which the shift is carried out in the automatic transmission 4 is limited.

In FIG. 3 , the time during which a shift is carried out in the automatic transmission 4 corresponds accordingly to the duration of the interruption of traction force, which are each characterized by the time span Δt 56 .

It is therefore practical according to invention to carry out a load transfer by means of the electric motor 2 from the internal combustion engine 1 before the actual shift is carried out in the automatic transmission 4 and/or after the actual shift has been carried out in the automatic transmission 4 . The load transfer is limited by the capacity of the electric motor 2 and by an electric energy accumulator of the drive train. In dependence upon the dimensions of the electric motor 2 as well as the energy accumulator, this leads indeed in most cases to a reduction of the traction force at the output, but not to a complete interruption of traction force before and/or after the actual shift in the automatic transmission 4 has been carried out.

The shifting comfort can be increased, since the load reduction at the internal combustion engine 1 before the shift and the disengagement of the clutch 5 are no longer time-critical.

The actual shift in the automatic transmission 4 is carried out with interruption of traction force and active synchronization by varying the torque made available by the electric motor 2 . The duration of the interruption of traction force at the output 3 is limited to the time during which the shift is carried out in the automatic transmission 4 .

Even though the load transfer by means of the electric motor 2 takes place both before the shift and after the shift in the automatic transmission are carried out in the embodiment of FIG. 3 , these steps are also possible independent of each other. It is therefore possible to take advantage of the load transfer by means of the electric motor 2 exclusively before the shift in the automatic transmission 4 is carried out or also exclusively after the shift in the automatic transmission 4 has been carried out.

According to an advantageous further development of the invention, a charge state of the electric accumulator of the hybrid drive train is monitored in connection with the process according to the invention, wherein a load transfer by means of the electric motor 2 takes place before the gear change is carried out and/or after the gear change has been carried out, only if the charge state of the electric accumulator is greater than a threshold value. To this end is taken into consideration the energy required by the electric motor 2 for synchronization while the gear change in the automatic transmission 4 is carried out. If the charge state of the electric energy accumulator is lower than the threshold value, a load transfer is not carried out by the electric motor 2 before the gear change is carried out and after the gear change has been carried out, because then the energy stored in the energy accumulator is not sufficient to do so.

In this connection, it can be provided that an energy management system of the drive train ensures that sufficient energy reserves are always available in the energy accumulator in order to ensure a load transfer by means of the electric motor before and/or after a shift.

In the exemplary embodiment shown in FIG. 3 , the time t 5 at which the output torque is zero before a shift is carried out, is located after the time t 2 , at which the clutch 5 disengages. This means that the time point at which a shift is carried out is delayed with respect to the state of the art of FIG. 2 by the time span between the times t 2 and t 5 . However, the times t 2 and t 5 , and optionally the times t 6 and t 3 , can coincide by means of an appropriate configuration of the load transfer by means of the electric motor 2 ,

According to a further advantageous further development of the invention, a driver input can be monitored if the time t 5 is located after the time t 2 , and a load transfer by means of the electric motor is only performed if no dynamic or spontaneous gear changes are requested in accordance with FIG. 3 , before a gear change is carried out and/or after a gear change has been carried out. If, in contrast, dynamic or spontaneous gear changes are desired, a load transfer by means of the electric motor 2 does not take place before a gear change is carried out or after a gear change has been carried out, but rather a conventional shift as defined by FIG. 2 is carried out.

The process according to the invention can be used for traction shifting and overrun shifting.

1 Internal combustion engine

2 Electric motor

3 Output

4 Transmission

5 Clutch

6 Torque trend

7 Torque trend

8 Torque trend

9 Torque trend

10 Torque trend

11 Torque trend