Method for operating a drive train for a mobile vehicle

Abstract

With a torque-controlled internal combustion engine and a variable-speed transmission having fixed shift gear ratios, during a shift, the internal combustion engine is controlled in such manner that the drive output torque of the transmission remains the same before and after the shift.

Claims

1. A method of operating a drive-train of a mobile vehicle with an internal combustion engine and a transmission having at least shiftable first and second fixed gear ratios for powering a driving operation such that, when the transmission is shifted, the transmission shifts from the first fixed gear ratio to the second fixed gear ratio, the method comprising: controlling the internal combustion engine with an electronic control unit so that the internal combustion engine is operated in a torque-controlled manner as a function of a position of an accelerator pedal; during the shift from the first fixed gear ratio to the second fixed gear ratio, and with the accelerator pedal position unchanged, the electronic control unit controls torque of the internal combustion engine as a function of a gear ratio change in such a manner that the torque of the internal combustion engine is either increased or reduced such that delivered torque of the transmission remains the same; and maintaining the torque of the internal combustion engine during the shift if a rotational speed of the internal combustion engine is below a predefined value before the shift.

2. The method of operating the drive-train according to claim 1, further comprising, defining the shift as a downshift; and during the downshift, reducing the torque delivered by the internal combustion engine by a factor of the gear ratio change.

3. The method of operating the drive-train according to claim 1, further comprising, defining the shift as an upshift; and during the upshift, increasing the torque delivered by the internal combustion engine by a factor of the gear ratio change.

4. The method of operating the drive-train according to claim 1, further comprising limiting a maximum rotational speed that is reachable by the internal combustion engine as a function of the position of the accelerator pedal, and the limited rotational speed is lower than a theoretically possible rotational speed of the internal combustion engine.

5. A method of operating a drive-train of a mobile vehicle with an internal combustion engine and a transmission having at least shiftable first and second fixed gear ratios for powering a driving operation such that, when the transmission is shifted, the transmission shifts from the first fixed gear ratio to the second fixed gear ratio, the method comprising: controlling the internal combustion engine with an electronic control unit so that the internal combustion engine is operated in a torque-controlled manner as a function of a position of an accelerator pedal; during the shift from the first fixed gear ratio to the second fixed gear ratio, and with the accelerator pedal position unchanged, the electronic control unit controls torque of the internal combustion engine as a function of a gear ratio change in such a manner that the torque of the internal combustion engine is either increased or reduced such that delivered torque of the transmission remains the same; limiting a maximum rotational speed that is reachable by the internal combustion engine as a function of the position of the accelerator pedal, and the limited maximum rotational speed is lower than a theoretically possible rotational speed of the internal combustion engine; and limiting the maximum rotation speed of the internal combustion engine in such a manner that the internal combustion engine brakes the vehicle when the accelerator pedal position is set below a predefined value.

6. The method of operating the drive-train according to claim 5, further comprising additionally actuating a retarder when the accelerator pedal position is set below a predefined value.

7. The method of operating the drive-train according to claim 6, further comprising controlling the torque produced by the retarder as a function of the accelerator pedal position.

8. A method of operating a drive-train of a mobile vehicle with an internal combustion engine and a transmission having at least first and second fixed gear ratios that are shiftable for powering a driving operation, the method comprising: initiating a transmission gear shift from the first fixed gear ratio to the second fixed gear ratio; controlling a torque of the internal combustion engine with an electronic control unit as a function of a position of an accelerator pedal; during the transmission gear shift from the first fixed gear ratio to the second gear ratio, and when the position of the accelerator pedal is unchanged, controlling the torque of the internal combustion engine with the electronic control unit as a function of a gear ratio change such that the torque of the internal combustion engine is either increased or reduced to maintain torque output by the transmission unchanged during the transmission gear shift from the first fixed gear ratio to the second gear ratio; and maintaining the torque of the internal combustion engine during the transmission gear shift, if a rotational speed of the internal combustion engine is below a predefined value before the shift.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further characteristics emerge from the description of the figures, which show:

(2) FIG. 1: A rotational speed-torque diagram of a torque-regulated internal combustion engine;

(3) FIG. 2: A rotational speed-torque diagram of a torque-regulated internal combustion engine with limited maximum and minimum rotational speeds; and

(4) FIG. 3: A rotational speed-torque diagram of a torque-regulated internal combustion engine with limited maximum and minimum rotational speeds, also showing the retarder braking torque.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) FIG. 1:

(6) The drive output torque of the internal combustion engine is plotted along the ordinate and the drive output rotational speed is plotted along the abscissa.

(7) The line 1 represents the maximum possible torque curve of the internal combustion engine. Since the internal combustion engine torque is regulated, without the method according to the invention the internal combustion engine would be operated for example along the line 2 or the line 3 depending on the position of the accelerator pedal. In that case, when operating along line 2 the accelerator pedal would be pressed down harder than when operating along line 3. The line 4 is the upshift line at which the variable-speed transmission with the fixed shift gear ratio stages is upshifted. The line 5 is the shift line at which the transmission with the fixed gear ratios is downshifted. If now the vehicle is operated using the accelerator pedal, with which the internal combustion engine is torque-regulated along the line 2, and the vehicle reaches the shifting point 6, then an upshift takes place by the gear ratio of the gear to be changed, for example 1.4. Since due to the inertial mass the driving speed, i.e. the drive output rotational speed of the transmission hardly changes, both the rotational speed and also the torque required change by the factor of the gear ratio change, in this case by the factor 1.4. The change of torque and rotational speed during the shift is represented by the line 7. If the vehicle were now to be operated further with constant torque regulation along the line 2 whereas, however, the torque increases along the line 7 due to the shift of the transmission, then the vehicle would immediately reach the line 5 for downshifting and a downshift would immediately take place again. This would produce the so-termed shifting shock. Now however, according to the invention the internal combustion engine in its torque regulation is controlled in such manner that during the shift the torque is increased sufficiently for the torque increase to equal the gear ratio change during the upshift. Thus, the torque changes along the line 7. Consequently the drive output shaft of the transmission has the same torque after the shift as it had before the shift. This reliably prevents shifting shock. The lines 8 and 9 show upshifts at other positions of the accelerator pedal.

(8) FIG. 2:

(9) Along the ordinate is plotted the torque, whereas the rotational speed of the internal combustion engine is plotted along the abscissa. For torque adaptation during the shift by the factor of the gear ratio change of the transmission, FIG. 2 also shows the limitation of the maximum rotational speed, which begins for example from the limitation point 10, 11, 12, 13 and 14. For example, if the vehicle drives over a crest and the vehicle were to have no maximum rotational speed limitation of the internal combustion engine, then after the crest the vehicle would accelerate sharply and not reach the overdrive operating condition. By limiting the maximum rotational speed, for example above the limiting point 11, the vehicle can be brought to overdrive operation so that the vehicle is braked by the internal combustion engine, whereby a driving sense is conveyed to the driver that he can slow the vehicle down by means of the accelerator pedal. To prevent the vehicle from stalling when starting off, the vehicle is operated along the lines 15 and 16.

(10) FIG. 3:

(11) Along the ordinate is plotted the torque, whereas the rotational speed of the internal combustion engine is plotted along the abscissa. In addition, the braking torque from the retarder is shown along the negative extension of the ordinate. The course of the lines in the positive zone of the ordinate corresponds to the representation if FIG. 2. In addition, as a function of the accelerator pedal a braking torque is produced by the retarder, which is shown along the lines 17, 18, 19, 20, 21, 22 and 23. The more the accelerator pedal actuation is reduced, the greater is the braking action of the retarder.

INDEXES

(12) 1 Line 2 Line 3 Line 4 Line 5 Line 6 Shifting point 7 Line 8 Line 9 Line 10 Limiting point 11 Limiting point 12 Limiting point 13 Limiting point 14 Limiting point 15 Line 16 Line 17 Line 18 Line 19 Line 20 Line 21 Line 22 Line 23 Line