METHOD FOR OPERATING A DRIVELINE

Abstract

A method is disclosed for operating a drivetrain of a working machine with a continuously variable transmission. The method comprises a step of detecting a current drive output rotation speed (10). The drivetrain is controlled (14) in such manner as to simulate a drivetrain with a fixed-gear transmission and a bridged converter transmission when the drive output rotation speed detected is higher than or equal to a drive output rotation speed limit. The drivetrain is controlled (16) in such manner as to simulate a drivetrain with a fixed-gear transmission and a coupled converter transmission when the drive output rotation speed detected is lower than the drive output rotation speed limit. In addition, the invention relates to a control unit for a drivetrain of a working machine with a continuously variable transmission, and a drivetrain for a working machine.

Claims

1. A method for operating a drivetrain of a working machine with a continuously variable transmission, wherein the method comprises at least the following steps: detecting (10) a current drive output rotation speed; determining that the current drive output rotation speed is higher than or equal to a drive output rotation speed limit; and controlling (14) the drivetrain to simulate a drivetrain with a fixed-gear transmission and a bridged converter transmission.

2. The method according to claim 1, wherein controlling the drivetrain to simulate the bridged converter transmission includes the continuously variable transmission having a fixed transmission ratio.

3. The method according to claim 2, comprising: detecting a decreasing drive output rotation speed; and reducing the transmission ratio in response to determining the decreasing drive output rotation speed, wherein controlling (16) the drivetrain to simulate the coupled converter transmission includes the continuously variable transmission having a variable transmission ratio.

4. The method according to claim 1, wherein simulating the bridged converter transmission and the coupled converter transmission includes controlling the drivetrain with reference to an accelerator-pedal-dependent target drive output rotation speed.

5. The method according to claim 1, wherein the drive output rotation speed limit is specified as a function of a detected accelerator pedal position.

6. The method according to claim 1, wherein the drive output rotation speed limit is specified as a function of the drive output rotation speed.

7. A control unit for a drivetrain of a working machine with a continuously variable transmission, wherein the control unit is configured to control (14) the drivetrain so as to simulate a drivetrain with a fixed-gear transmission and a bridged converter transmission when the drive output rotation speed detected is higher than or equal to a drive output rotation speed limit, and wherein the control unit is further configured to control (16) the drivetrain so as to simulate a drivetrain with a fixed-gear transmission and a coupled converter transmission when the drive output rotation speed detected is lower than the drive output rotation speed limit.

8. A drivetrain for a working machine, wherein the drivetrain comprises: a drive motor configured to provide a driving force; a continuously variable transmission configured to transmit the driving force from the drive motor to a drive output with a continuously adjustable transmission ratio, a detection device configured to detect (10) a current drive output rotation speed of the drivetrain, and a control unit configured to simulate a drivetrain with a fixed-gear transmission and a bridged converter transmission by controlling (14) the drivetrain when the drive output rotation speed detected is higher than or equal to a drive output rotation speed limit, and is configured to simulate a drivetrain with a fixed-gear transmission and a coupled converter transmission by controlling (16) the drivetrain when the drive output rotation speed detected is lower than the drive output rotation speed limit.

9. A method for operating a drivetrain of a working machine with a continuously variable transmission, wherein the method comprises at least the following steps: detecting (10) a current drive output rotation speed; determining that the current drive output rotation speed is lower than a drive output rotation speed limit; and controlling (16) the drivetrain to simulate a drivetrain with a fixed-gear transmission and a coupled converter transmission.

10. The method according to claim 9, wherein controlling the drivetrain to simulate the bridged converter transmission includes the continuously variable transmission having a fixed transmission ratio.

11. The method according to claim 10, comprising: detecting a decreasing drive output rotation speed; and reducing the transmission ratio in response to determining the decreasing drive output rotation speed, wherein controlling (16) the drivetrain to simulate the coupled converter transmission includes the continuously variable transmission having a variable transmission ratio.

12. The method according to claim 9, wherein simulating the bridged converter transmission and the coupled converter transmission includes controlling the drivetrain with reference to an accelerator-pedal-dependent target drive output rotation speed.

13. The method according to claim 9, wherein the drive output rotation speed limit is specified as a function of a detected accelerator pedal position.

14. The method according to claim 9, wherein the drive output rotation speed limit is specified as a function of the drive output rotation speed.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0025] FIG. 1 illustrates schematically in a diagram a control method for simulating a converter transmission in accordance with a first embodiment, wherein motor rotation speeds and transmission ratios are plotted against drive output rotation speeds as control characteristics.

[0026] FIG. 2 illustrates schematically in a diagram a control method for simulating a converter transmission in accordance with a second embodiment, wherein motor rotation speeds and transmission ratios are plotted against drive output rotation speeds as control characteristics.

[0027] FIG. 3 illustrates schematically in a diagram a control method for simulating a converter transmission in accordance with a third embodiment, wherein motor rotation speeds and transmission ratios are plotted against drive output rotation speeds as control characteristics.

[0028] FIG. 4 illustrates schematically a method for operating a drivetrain.

DETAILED DESCRIPTION OF EMBODIMENTS

[0029] FIG. 4 illustrates schematically a method for operating a drivetrain of a working machine, wherein the drivetrain comprises a continuously variable transmission. In a step 10 a current drive output rotation speed is detected. In a step 12 it is determined whether the drive output rotation speed detected is higher than or equal to a drive output rotation speed limit. If the drive output rotation speed detected is higher than or equal to the drive output rotation speed limit, the system moves on to step 14. In step 14 the drivetrain is controlled so as to simulate a drivetrain with a fixed-gear transmission and a bridged converter transmission. For this, a fixed transmission ratio is set, and a motor rotation speed is specified as a function of a detected accelerator pedal position. In an embodiment the motor rotation speed and alternatively or in addition the fixed transmission ratio is/are also specified or set as a function of a gear of a selected fixed-gear transmission that is to be simulated. Provided that the drive output rotation speed detected is lower than the drive output rotation speed limit, the system moves on to step 16. In step 16 the drivetrain is controlled so as to simulate a drivetrain with a fixed-gear transmission and a coupled converter transmission. In this range, for the motor rotation speed with the accelerator pedal not actuated, i.e., with the accelerator pedal in its starting position, the transmission ratio is reduced as the drive output rotation speed decreases and a minimum motor rotation speed is specified which simulates an idling behavior. If the accelerator pedal is actuated, then an increasing motor rotation speed and a decreasing transmission ratio are set in order to simulate the behavior of the coupled converter transmission.

[0030] In FIG. 1, along the ordinate a motor rotation speed is shown by the upper characteristic line, and the lower characteristic line shows a reciprocal transmission ratio of the continuously variable transmission. Along the abscissa a drive output rotation speed is shown. A first characteristic line 30 shows the motor rotation speed during a simulation of the fixed-gear transmission with the converter transmission bridged. Depending on the load applied, when power is called for a corresponding drive output rotation speed is produced. A target drive output rotation speed that depends on a current accelerator pedal position N_ab_Ziel(FP) on the first characteristic line 30, here at the point 32, is calculated using the following formula:

[00001]$\mathrm{N\_ab}\mathrm{\_Ziel}\left(\mathrm{FP}\right)=\left(\left(\mathrm{n\_mot}\mathrm{\_high}\mathrm{\_idle}*\mathrm{i\_rez}\mathrm{\_festgang}\right)-\left(\mathrm{n\_mot}\mathrm{\_low}\mathrm{\_idle}*\mathrm{i\_rez}\mathrm{\_festgang}\right)\right)*\mathrm{FP}/100+\mathrm{n\_mot}\mathrm{\_low}\mathrm{\_idle}*\mathrm{i\_rez}\mathrm{\_festgang}$

[0031] in which n_mot_high_idle is a load-free motor rotation speed when the accelerator pedal is fully actuated, i_rez_festgang is the fixed transmission ratio set, by virtue of which a transmission ratio by which a fixed-gear transmission with a particular gear is simulated by the continuously variable transmission, and n_mot_low_idle is a load-free motor rotation speed when the accelerator pedal is not actuated. FP stands for an accelerator pedal position wherein zero corresponds to a non-actuated accelerator pedal and 100 to a fully actuated accelerator pedal. A drive output rotation speed determined in that way for the point 32 is shown by the vertical line 34. From a minimum motor rotation speed represented by a vertical line 40 even during the simulation of the bridged converter transmission the transmission ratio is no longer constant but varies in order to be able to operate the drive motor with the load-free motor rotation speed when the accelerator pedal is not actuated n_mot_low_idle and to avoid stalling. However, this no longer corresponds to an operating behavior that a driver would expect from a drivetrain with a fixed-gear transmission and a converter transmission that can be bridged.

[0032] A target motor rotation speed corresponding to this as a function of the current accelerator pedal position n_Mot_Ziel(FP) can be calculated using the formula:

[00002]$\mathrm{n\_Mot}\mathrm{\_Ziel}\left(\mathrm{FP}\right)=\mathrm{n\_ab}\mathrm{\_Ziel}\left(\mathrm{FP}\right)*\mathrm{i\_rez}\mathrm{\_festgang}$

[0033] Correspondingly, there is a control value for the drive motor when simulating the drivetrain with a fixed-gear transmission and a bridged converter transmission. For the target motor rotation speed when simulating the drivetrain with a fixed-gear transmission and a coupled converter transmission, the corresponding converter rotation speed is calculated using the following formula:

[00003]$\mathrm{Converter}\mathrm{rotation}\mathrm{speed}=(\mathrm{n\_ab}\mathrm{\_Ziel}\left(\mathrm{FP}\right)-\mathrm{n\_ab}\mathrm{\_ist}/\mathrm{n\_ab}\mathrm{\_Ziel}\left(\mathrm{FP}\right)*\left(\mathrm{n\_mot}\mathrm{\_Ziel}\left(\mathrm{FP}\right)-\mathrm{n\_mot}\mathrm{\_low}\mathrm{\_idle}\right)+\mathrm{n\_mot}\mathrm{\_low}\mathrm{\_idle}$

[0034] In this case the converter rotation speed is a function of a current drive output rotation speed n_ab_ist. The drive output rotation speed limit corresponds to that drive output rotation speed at which the converter rotation speed corresponds to the target motor rotation speed that depends on the current accelerator pedal position n_Mot_Ziel(FP) when simulating the drivetrain with a fixed-gear transmission and a bridged converter transmission. Thus, the values of these two rotation speeds are always used for controlling the drive motor. The converter rotation speed corresponds to the target motor rotation speed while simulating the coupled converter transmission.

[0035] With a fixed-gear transmission ratio in this case selected as 0.42, an idling rotation speed with the accelerator pedal fully actuated, n_mot_high_idle, of 1800 rpm and an idling rotation speed with the accelerator pedal not actuated, n_mot_low_idle, of 800 rpm, we obtain for the fully actuated accelerator pedal a characteristic line 36 and for a half-way actuated accelerator pedal a characteristic line 38. Further characteristic lines can also be calculated or extrapolated or interpolated. Thus, the change from the simulation with a bridged converter transmission and with a coupled converter transmission depends on the accelerator pedal position, so that the drive output rotation speed limit too is determined as a function of the accelerator pedal position.

[0036] For the sake of clarity, the control behavior will now be explained with reference to an example. At first the working machine is travelling with the motor rotation speed and drive output rotation speed represented by the point 32. The load at the drive output now increases over a permissible traction force, in this example owing to a higher grading resistance. The drive output rotation speed decreases correspondingly and the target motor rotation speed N_Mot_Ziel(FP) decreases linearly along with it, since the gear ratio i_rez_festgang remains constant in order to simulate the fixed-gear transmission. During this the accelerator pedal is fully actuated. At a point 42 the drive output rotation speed limit for that accelerator pedal position is then reached and the simulation of a coupled converter transmission begins. Even with an actual drivetrain with a bridged converter transmission and a fixed-gear transmission, at that point the converter transmission would be coupled, and the bridging terminated automatically. With a further reduction of the drive output rotation speed owing to the load applied, the motor rotation speed now increases in accordance with the characteristic line 36 and corresponds to the calculated converter rotation speed. For this, the reciprocal transmission ratio in the continuously variable transmission is reduced, as shown by the characteristic line 46. At point 44 the working machine is at rest and the drive motor rotates at the idling rotation speed with the fully actuated accelerator pedal, n_mot_high_idle.

[0037] The course when the accelerator pedal is only half-actuated is analogous to the above, but the drive output rotation speed limit is not reached until the point 48. Correspondingly, as the load increases and the drive output rotation speed decreases, the motor rotation speed follows the characteristic line 38 as far as the point 50. At point 50 the working machine is at rest and the drive motor rotates, in this example, at an idling rotation speed of 1300 rpm with the accelerator pedal half-actuated. With the accelerator pedal half-actuated, the course of the reciprocal transmission ratio is shown by the characteristic line 52.

[0038] If the load decreases again, a reverse sequence takes place. With a half-actuated accelerator pedal, an operating point 56 is obtained as the operating point when there is no suppression due to an applied load, for which point the corresponding drive output rotation speed is shown by a vertical line 54. With this control logic a drivetrain with a fixed-gear transmission and a converter transmission that can be bridged can be simulated by the drivetrain with a continuously variable transmission, such that the simulated drivetrain automatically couples the converter transmission.

[0039] FIG. 2 illustrates the same characteristic lines with the same diagram structure as FIG. 1. In addition, however, a modification of the control parameters is shown, by virtue of which a transition point from the simulation of the fixed-gear transmission ratio with the bridged converter transmission to the coupled converter transmission is displaced. In that way the drive output rotation speed limit can be changed by way of a parameterization. The converter rotation speed in the simulation of the coupled converter transmission is now calculated using the following formula:

[00004]$\mathrm{Converter}\mathrm{rotation}\mathrm{speed}=\left(\mathrm{n\_ab}\mathrm{\_Ziel}\left(\mathrm{FP}\right)-\mathrm{n\_ab}\mathrm{\_ist}\right)/\mathrm{n\_ab}\mathrm{\_Ziel}\left(\mathrm{FP}\right)*\left(\mathrm{n\_mot}\mathrm{\_Ziel}\left(\mathrm{FP}\right)-\mathrm{n\_mot}\mathrm{\_Wandler}\mathrm{\_base}\right)+\mathrm{n\_mot}\mathrm{\_Wandler}\mathrm{\_base}$

[0040] Instead of the load-free motor rotation speed with a non-actuated accelerator pedal n_mot_low_idle, a converter basis rotation speed n_mot_Wandler_base is now used for the calculation. The converter basis rotation speed n_mot_Wandler_base is here determined as a function of the drive output rotation speed and in the example illustrated decreases in a linear manner with the drive output rotation speed. Thereby, the accelerator-pedal-dependent characteristic lines 36, 38 for the motor control when simulating a coupled converter transmission are displaced to the characteristic lines 36, 38 as shown in FIG. 2. Correspondingly, the corresponding characteristic lines 46, 52 for the reciprocal transmission ratio in the continuously variable transmission, which are set for the simulation, are changed to the characteristic lines 46, 52. The accelerator-pedal-dependent transition point and the drive output rotation speed limit are then displaced from the points 42, 48 to the points 42, 48.

[0041] FIG. 3 illustrates the same characteristic lines with the same diagram structure as FIG. 2. In addition, however, a modification of the control parameters is shown, with which a motor rotation speed while stationary is displaced. For this, during the simulation of the coupled converter transmission the converter rotation speed is now calculated using the following formula:

[00005]$\mathrm{Converter}\mathrm{rotation}\mathrm{speed}=\left(\mathrm{n\_ab}\mathrm{\_Ziel}\left(\mathrm{FP}\right)-\mathrm{n\_ab}\mathrm{\_ist}\right)/\mathrm{n\_ab}\mathrm{\_Ziel}\left(\mathrm{FP}\right)*\mathrm{FP\_Factor}*\left(\mathrm{n\_mot}\mathrm{\_Ziel}\left(\mathrm{FP}\right)-\mathrm{n\_mot}\mathrm{\_Wandler}\mathrm{\_base}\right)+\mathrm{n\_mot}\mathrm{\_Wandler}\mathrm{\_base}$

[0042] An addition to this is an accelerator-pedal-dependent scaling factor in the simulation of the coupled converter transmission. In the example shown, this decreases progressively with increasing actuation of the accelerator pedal. Correspondingly, the points 44, 50 when the working machine is at rest are displaced to the points 44, 50, wherein the motor rotation speed at point 44 is now 1600 rpm and at point 50 it is now 1350. The corresponding reciprocal transmission ratio is displaced correspondingly.

INDEXES

[0043] 10 Detection of a current drive output rotation speed [0044] 12 Comparison of the current drive output rotation speed with the drive output rotation speed limit [0045] 14 Control of a drivetrain: simulation of a fixed-gear transmission and a bridged converter transmission [0046] 16 Control of a drivetrain: simulation of a fixed-gear transmission and a coupled converter transmission [0047] 30 Characteristic line for the target drive output rotation speed [0048] 32 Point for calculating the target drive output rotation speed with reference to the first formula [0049] 34 Line for the drive output rotation speed determined at point 32 [0050] 36. 36 Characteristic line for a fully actuated accelerator pedal [0051] 38, 38 Characteristic line for a half-actuated accelerator pedal [0052] 40 Line for the minimum motor rotation speed [0053] 42, 42 Point for the drive output rotation speed limit with a fully actuated accelerator pedal [0054] 44, 44 Point for idling rotation speed with a fully actuated accelerator pedal while at rest [0055] 46, 46 Characteristic line for the reciprocal transmission ratio [0056] 48, 48 Point for the drive output rotation speed limit with a half-actuated accelerator pedal [0057] 50, 50 Point for idling rotation speed with a half-actuated accelerator pedal while at rest [0058] 52, 52 Characteristic line for the reciprocal transmission ratio with a half-actuated accelerator pedal [0059] 54 Line for the drive output rotation speed that corresponds to the operating point [0060] 56 Operating point