Method for operating drive train

Abstract

The invention relates to a method for operating a drive train. The method has a step of detecting a current output rotational speed (10). When the detected output speed is greater than or equal to the boundary output speed, the drive train is controlled (14) in order to simulate a drive train having a fixed gear transmission and a locked torque converter transmission. If the detected output speed is less than the boundary output speed, the drive train is controlled (16) in order to simulate a drive train having a fixed gear transmission and a coupled torque converter transmission. The invention further relates to a control device for a drive train of a work machine having a continuously variable transmission and to a drive train for a work machine.

Description

Technical Field

[0001] The invention relates to a method for operating a drive train of a working machine. The invention also relates to a control device for a drive train and a drive train of a working machine. Prior art

[0002] In working machines, such as excavators, graders or agricultural machines, the drive train is used to provide propulsion. In drive trains with fixed-gear transmissions, which can provide different gears with fixed transmission ratios, torque converter transmissions are often used. The torque converter transmission can act as a starting element. In addition, the torque converter transmission can prevent the drive motor of the drive train from being overloaded and stalling under high loads.

[0003] In addition, some work machines have a drive train with a continuously variable transmission. This means, for example, that the drive motor of such a work machine will run at a nearly constant speed. As a result, the work machine can be operated very efficiently. In addition, starting elements, such as a torque converter transmission, can be omitted in such a drive train. In the event of excessive load, the transmission ratio of the transmission can then be reduced, for example, in order to increase the torque at the output and prevent the motor from being overloaded. However, it can be difficult for the driver to recognize when the drive train can no longer overcome the existing load.

[0004] Often, drivers of work machines mainly or even exclusively use the same work machine for a long time. Accordingly, the driver is accustomed to the characteristics of the drive train of the work machine. In this case, for example, the behavior of the work machine is known and used to achieve the desired control of the work machine. If these drivers then switch to a work machine with different characteristics, incorrect operation may occur. In general, the driver may feel uncomfortable when using a work machine whose behavior does not meet his expectations. Summary of the invention

[0005] A first aspect of the invention relates to a method for operating a drive train of a working machine. The working machine can be configured as an agricultural machine or a construction machine, for example. Examples of working machines are tractors, graders and wheel loaders. The drive train can be configured to provide a driving force for the working machine to travel. The drive train can include, for example, a drive motor, such as an internal combustion engine or an electric motor. The drive train can also have multiple drive motors.

[0006] The drive train has a transmission device, by means of which, for example, the driving force can be transmitted from the drive motor to the driven end of the working machine. The transmission device is configured as a continuously variable transmission device. The transmission device can be configured as a power-dividing type for this purpose. For example, the transmission device can be configured as a hydraulic power-dividing transmission device with a hydrostatic device. The driven end of the working machine can also form the driven end of the drive train. The driven end can be configured, for example, as a shaft connected to the differential of the working machine. The driven end can also be configured as a driven axle, wheel or track. For example, when the drive train is enabled, the drive motor can always provide the driving force. This can be the case, for example, if the drive motor is configured as an internal combustion engine. However, the drive train can also be configured to generate the driving force without using the drive motor in a specific state. This can be the case, for example, if the drive motor is configured as an electric motor and does not require propulsion and does not require auxiliary electrical appliances to be driven by the drive motor.

[0007] The force transmission and, alternatively or additionally, the drive force generation can be controllable, for example, by means of a gas pedal. The gas pedal can also be designed as a lever or other operating element. The gas pedal can be designed, for example, as a virtual gas pedal, which is operated by hand on a touch screen. The drive train can also have a reversing gear, by means of which, for example, the direction of rotation of the output end can be reversed with respect to the drive end. The drive train can, for example, not contain a torque converter or a starting clutch.

[0008] The method comprises the step of detecting the current output speed. The output speed can be detected directly, for example, by means of a speed sensor. However, the output speed can also be calculated indirectly based on other state variables, such as the motor speed and the current transmission ratio, to determine the output speed. The output speed can correspond to the rotation speed of the output of the drive train. The output speed can correspond to the travel speed of the working machine.

[0009] The method comprises the step of controlling a drive train. When the detected driven end speed is greater than or equal to a limit driven end speed, the drive train is controlled to simulate a drive train with a fixed gear transmission and a locked torque converter transmission. When the detected driven end speed is less than the limit driven end speed, the drive train is controlled to simulate a drive train with a fixed gear transmission and a coupled torque converter transmission. In addition, the drive motor can be controlled to simulate an internal combustion engine. For example, the drive motor always runs at a minimum speed even when the accelerator pedal is not depressed and propulsion is not required.

[0010] The boundary output speed can be a threshold value of the detected current output speed. The boundary output speed can be, for example, a fixed predetermined value. The boundary output speed can also be determined, for example, depending on other influencing factors (such as the load present). In simulation, the drive train with a continuously variable transmission can be controlled as follows, that is, the behavior of the drive train basically corresponds to the actual drive train with a fixed gear transmission and a lockable torque converter transmission. The lockable torque converter transmission can, for example, participate in the transmission of driving force by means of a torque converter lockup clutch. The locked torque converter transmission, for example, does not participate in the transmission of driving force from the drive motor to the output. For this purpose, the torque converter lockup clutch can be closed. In contrast, the coupled torque converter transmission can, for example, participate in the transmission of driving force from the drive motor to the output, and thus provide another transmission ratio. The transmission ratio of the coupled torque converter transmission can be related to the load and alternatively or additionally to the speed. As a result, the torque converter transmission can provide assistance as needed during starting and when preventing the unwanted motor from being suppressed. In other driving conditions, however, a high efficiency is achieved by decoupling. The torque converter transmission can be designed, for example, as a hydrodynamic torque converter. The torque converter transmission can be designed as a starting element.

[0011] Therefore, by this method, corresponding driving behavior can be simulated in a continuously variable transmission. The torque converter transmission can change the transmission ratio as the load increases, so that the motor speed can be increased as the output speed decreases. Therefore, the torque converter transmission can prevent the drive motor constructed as an internal combustion engine from stalling under high load and low driving speed. During the simulation, a drive train with an internal combustion engine as the drive motor can be simulated. Here, the drive train can actually have an internal combustion engine. The fixed gear transmission can, for example, provide one or more transmission ratio levels (such as gears) for torque transmission. The drive train can be controlled as follows, that is, the driver can select the gear by means of the driving operating element, based on which the fixed gear transmission is controlled to simulate. The driver can, for example, choose between the first gear and the second gear during the simulation. Different fixed transmission ratios can be provided between the drive motor and the output. For example, if the current output speed is greater than or equal to the limit output speed, these transmission ratios can be provided by the continuously variable transmission accordingly during the simulation. However, a unique virtual gear can also be fixedly predetermined during the simulation. This makes it possible to simulate a drive train with a fixed gear transmission with only one gear.

[0012] The method makes it possible to provide different operating behaviors through the drive train and, for example, simulate behaviors that are not originally caused by the structural form of the drive train. In this way, different behaviors and customary behaviors of the drive train can be realized for different drivers. Each driver can, for example, select the desired behavior according to his preferences or the current usage situation. At the same time, the advantages of a drive train with a continuously variable transmission can be utilized. For example, when using a rear-end subsoiler or roughing machine with a continuously variable transmission, more efficient operation and more functional flexibility can be achieved. In contrast, when simulating a drive train with a fixed gear transmission and a torque converter transmission, for example, fine leveling can be performed more easily. When the speed of the driven end decreases, the driver can recognize when there is a large load by the pressure and thus the increase in the motor speed. In this way, direct and, for example, acoustic feedback about the existing load can be achieved during leveling. During fine leveling, the driver controls the load, for example, by adjusting the scraper and thus controlling the material flow, rather than by stepping on the travel pedal. Uneven leveling and drive wheel slip can thus be reliably avoided.

[0013] The method may include a step of selecting an operating mode for the drive train. For this purpose, the drive train may be configured to operate using different operating modes. The operating mode may, for example, predetermine the control of the drive train. The drive train may, for example, be configured to operate in a normal mode and a simulation mode. In the normal mode, the drive train may be controlled in the manner commonly seen in continuously variable transmissions. Here, the motor speed, for example, remains essentially constant, and the driving speed is controlled via a stepless adjustment of the transmission ratio. In contrast, in the simulation mode, the behavior of a drive train having a fixed gear transmission and a lockable torque converter transmission may be simulated. For example, a boost mode may still be used in both the normal mode and the simulation mode. By means of the boost mode, for example, a higher power may be provided for a short period of time compared to continuous operation. The selection may cause the activation of one of the two operating modes. The selection may, for example, be performed by the driver of the work machine by means of a switch or other operating element. For example, the normal mode may always be activated until the driver activates the simulation mode. The normal mode may be automatically reselected by deactivating the simulation mode. The operating mode can also be selected automatically, for example as a function of the identity of the driver, the location of the work machine or an ID, an activation code or a key for activating the work machine. The operating mode can also be predetermined at the factory, for example. For example, the work machine can be delivered to the customer with one of the two operating modes as the selected operating mode, and the driver can no longer change it. This operating mode can then only be switched within the scope of maintenance, for example.

[0014] In another embodiment of the method, it can be provided that a fixed transmission ratio is provided by means of a continuously variable transmission when the drive train is controlled to simulate a locked torque converter transmission. Here, the fixed transmission ratio can be selected by the driver in a discrete step, for example. Here, even during the simulation, the transmission ratio can be changed by the driver in order to simulate a gear shift. If the current output speed is greater than or equal to the limit output speed, the output speed can be proportional to the motor speed. In this way, the driver can simply control the driving speed directly using the accelerator pedal. Optionally, the driving speed can be controlled via the currently selected virtual gear. In a variant, the simulation is used only in a specific gear (for example, the lowest gear).

[0015] In another embodiment of the method, it can be provided that a variable transmission ratio is provided by means of a continuously variable transmission when the control drive train is used to simulate a coupled torque converter transmission. For example, if the current output speed is less than the limit output speed, the transmission ratio can be adjusted on the continuously variable transmission depending on the detected current output speed. Thus, a partial separation of the output from the drive motor can be simulated by the torque converter transmission. For example, as the detected output speed decreases, the transmission ratio of the continuously variable transmission will decrease. In this way, the motor speed can be increased as the output speed decreases. For example, when the accelerator pedal is fully depressed and the output speed decreases, when the working machine is stationary due to an excessive load (which prevents the working machine from moving), the motor speed will increase to the maximum idling speed. In contrast, if the current output speed is less than the limit output speed, the motor speed can correspond to the idling speed or the minimum motor speed substantially constantly when the accelerator pedal is not depressed. By depressing the accelerator pedal, it is possible to scale between these extreme values. For example, when the accelerator pedal is half depressed, the speed of the drive motor can be between the minimum motor speed and the maximum motor speed when stationary.

[0016] In another embodiment of the method, it can be provided that the drive train is controlled in dependence on the target output speed when simulating a locked torque converter transmission and alternatively or additionally when simulating a coupled torque converter transmission. The target output speed can be determined separately, for example, for simulating a coupled torque converter transmission and a locked torque converter transmission. The respectively larger of the two target output speeds is then used for the actual control. Thus, a boundary output speed can also be determined from this. Thus, the boundary output speed corresponds, for example, to the speed at which the two target output speeds are equal. Thus, the drive train can be speed-controlled. The target output speed can be dependent on the gas pedal. For example, the respective target output speed can be determined in dependence on the detected gas pedal position. The method can also have a step of detecting the gas pedal position. The gas pedal position can correspond to the degree of depression of the gas pedal. The gas pedal can be designed, for example, as an accelerator pedal. Optionally, the respective target output speed can additionally be determined in dependence on the transmission ratio selected for simulating a fixed gear transmission. As a function of the target output speed for the control, a target motor speed can be determined, for example as a function of the current transmission ratio of the continuously variable transmission.

[0017] In another embodiment of the method, it can be provided that a limit output speed is predetermined in dependence on the detected gas pedal position. As a result, it is possible to simulate when the torque converter transmission is locked or coupled in dependence on the power required by the drive motor. For example, when the gas pedal is depressed to a greater extent, i.e., when the gas pedal position is greater, a greater limit output speed is determined. When the power requirement of the drive motor is higher, the suppression of the motor in the drive train to be simulated can occur, for example, at a higher speed, at which the torque converter transmission is automatically coupled in. Alternatively, the limit output speed can be predetermined independently of the gas pedal position, for example as a fixed threshold value.

[0018] In another embodiment of the method, it can be provided that the limit output speed is predetermined as a function of the output speed. For example, a characteristic curve is shifted for the limit output speed. This makes it possible to easily predetermine the gas pedal-dependent and load-dependent limit output speed. Thus, a simple switchover from a coupled torque converter transmission to a locked torque converter transmission simulation and vice versa can be easily parameterized.

[0019] A second aspect relates to a control device for a drive train of a working machine. The control device can be configured, for example, to carry out the method according to the first aspect. The corresponding advantages and other features can be seen from the description of the first aspect, wherein the design of the first aspect also forms the design of the second aspect, and vice versa.

[0020] The control device is configured to control the drive train when the detected output speed is greater than or equal to the boundary output speed so as to simulate a drive train with a fixed gear transmission and a locked torque converter transmission. The control device is configured to control the drive train when the detected output speed is less than the boundary output speed so as to simulate a drive train with a fixed gear transmission and a coupled torque converter transmission. The control device may have one or more microprocessors. The control device may be configured to control a continuously variable transmission and alternatively or additionally to control a drive motor. The control device may be configured to obtain and process the detected current output speed.

[0021] The third aspect relates to a drive train for a working machine. The drive train can be configured, for example, for operation using the method according to the first aspect. The drive train can have a control device according to the second aspect. The corresponding advantages and other features can be seen from the description of the first aspect or the second aspect, wherein the embodiments of the first aspect and the second aspect also form the embodiments of the third aspect, and vice versa.

[0022] The drive train has a drive motor, a continuously variable transmission, a detection device and a control device. In addition, the drive train may also have a driven end. The drive motor is configured to provide a driving force for the travel of the working machine, for example. The transmission device is configured to transmit the driving force generated by the drive motor to the driven end using a continuously adjustable transmission ratio. To this end, the transmission device can provide a mechanical operative connection between the drive motor and the driven end. The driving force can be provided to the motor shaft by the drive motor, for example. The drive train can be configured to operate as an operating mode selectively in a normal mode and a simulation mode. To this end, the drive train can have a mode selection element, for example, configured as a switch.

[0023] The control device can be configured to simulate a drive train with a fixed gear transmission and a torque converter transmission by controlling the drive train, for example, when the simulation mode is activated. When the detected output speed is greater than or equal to the limit output speed, the control device controls the drive train to simulate a drive train with a fixed gear transmission and a locked torque converter transmission. When the detected output speed is less than the limit output speed, the control device controls the drive train to simulate a drive train with a fixed gear transmission and a coupled torque converter transmission. The transmission device can be configured as a hydraulic power split transmission, for example. The control device can be configured to control the drive train in normal mode depending on the accelerator pedal position and the optionally selected driving range. In this case, the control device can determine the rated output speed and adjust the motor speed and the transmission ratio depending thereon. In this case, for example, a substantially constant motor speed can be predetermined for the motor speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A control method for simulating a torque converter transmission according to a first specific embodiment is schematically explained in diagram form, wherein the motor speed and the transmission ratio are shown as a control characteristic curve as a function of the output speed;

[0025] Figure 2 A control method for simulating a torque converter transmission according to a second embodiment is schematically explained in diagram form, wherein the motor speed and the transmission ratio are shown as a control characteristic curve as a function of the output speed;

[0026] Figure 3 A control method for simulating a torque converter transmission according to a third embodiment is schematically illustrated in diagram form, wherein the motor speed and the transmission ratio are shown as a control characteristic curve in relation to the output speed;

[0027] Figure 4 A method for operating a drive train is explained schematically. DETAILED DESCRIPTION

[0028] Figure 4 A method for operating a drive train of a working machine is schematically explained, wherein the drive train has a continuously variable transmission. In step 10, the current output speed is detected. In step 12, it is determined whether the detected output speed is greater than or equal to the limit output speed. If the detected output speed is greater than or equal to the limit output speed, the method continues with step 14. In step 14, the drive train is controlled to simulate a drive train with a fixed gear transmission and a locked torque converter transmission. For this purpose, the fixed transmission ratio is adjusted and the motor speed is predetermined depending on the detected accelerator pedal position. In one embodiment, the motor speed is also predetermined or adjusted depending on the selected gear of the fixed gear transmission to be simulated and the fixed transmission ratio is predetermined or adjusted alternatively or additionally. If the detected output speed is less than the limit output speed, the method continues with step 16. In step 16, the drive train is controlled to simulate a drive train with a fixed gear transmission and a coupled torque converter transmission. In this range, for the motor speed, when the accelerator pedal is not depressed (i.e. the accelerator pedal is in the starting position), the transmission ratio changes as the output speed decreases, and a minimum motor speed is predefined, which simulates the idling behavior. If the accelerator pedal is depressed, an increased motor speed and a reduced transmission ratio are set as the output speed decreases, in order to simulate the behavior of a coupled torque converter transmission.

[0029] exist Figure 1In the diagram, the motor speed is shown on the vertical axis for the upper characteristic curve and the inverse transmission ratio of the continuously variable transmission is shown for the lower characteristic curve. The output speed is shown on the horizontal axis. The first characteristic curve 30 shows the motor speed when simulating a fixed gear transmission and a locked torque converter transmission. Depending on the load present, the corresponding output speed is obtained with a predetermined power. The target output speed N_ab_Ziel(FP), which is dependent on the current pedal position, is calculated on the first characteristic curve 30, here at point 32, using the following formula:

[0030] N_ab_Ziel(FP) = ((n_mot_high_idle* i_rez_festgang) – (n_mot_low_idle* i_rez_festgang)) * FP / 100 + n_mot_low_idle * i_rez_festgang,

[0031] Here, n_mot_high_idle is the unloaded motor speed when the gas pedal is fully depressed. i_rez_festgang is the set fixed transmission ratio with which the transmission ratio achieved by a fixed-gear transmission in a specific gear is simulated by the continuously variable transmission. n_mot_low_idle is the unloaded motor speed when the gas pedal is not depressed. FP stands for the gas pedal position, with zero corresponding to a gas pedal not depressed and 100 corresponding to a gas pedal fully depressed. The output speed thus determined for point 32 is indicated by a vertical line 34. Starting from the minimum motor speed, which is indicated by a vertical line 40, the transmission ratio is no longer constant even in the case of a locked torque converter transmission, but changes in order to be able to operate the drive motor at the unloaded motor speed n_mot_low_idle when the gas pedal is not depressed and to avoid stalling. However, this no longer corresponds to the operating behavior of a drive train with a fixed-gear transmission and a lockable torque converter transmission that the driver expects.

[0032] The corresponding target motor speed n_Mot_Ziel(FP) which is dependent on the current accelerator pedal position is calculated using the following formula:

[0033] n_Mot_Ziel(FP) = n_ab_Ziel(FP)* i_rez_festgang,

[0034] Accordingly, the control variables for the drive motor are obtained when simulating a drive train with a fixed gear transmission and a locked torque converter transmission. For the target motor speed when simulating a drive train with a fixed gear transmission and a coupled torque converter transmission, the corresponding torque converter speed is calculated using the following formula:

[0035] Torque converter speed = (n_ab_Ziel(FP) – n_ab_ist) / n_ab_Ziel(FP) * (n_mot_Ziel(FP) – n_mot_low_idle) + n_mot_low_idle,

[0036] The torque converter speed is dependent on the current output speed n_ab_ist. The limit output speed corresponds to a output speed in which the torque converter speed corresponds to a target motor speed n_Mot_Ziel(FP) in dependence on the current gas pedal position when simulating a drive train with a fixed gear transmission and a locked torque converter transmission. The drive motor is therefore always controlled with the larger of the two speeds. The torque converter speed corresponds to the target motor speed when simulating a coupled torque converter transmission.

[0037] In the case of a fixed gear ratio of 0.42 selected here, at an idling speed n_mot_high_idle of 1800 rpm when the gas pedal is fully depressed and at an idling speed n_mot_low_idle of 800 rpm when the gas pedal is not depressed, a characteristic curve 36 is obtained for a fully depressed gas pedal and a characteristic curve 38 is obtained for a half depressed gas pedal. The other characteristic curves can thus also be calculated in this way or by extrapolation or interpolation. Thus, the switch from simulation with a locked torque converter transmission to simulation with a coupled torque converter transmission is dependent on the gas pedal position, so that the limit output speed is also determined in dependence on the gas pedal position.

[0038] The control behavior will now be described with an example for explanation. The work machine is initially traveling at a motor speed and output speed as indicated by point 32. In this example, the load on the output now increases beyond the permissible traction force due to the increased leveling resistance. The output speed decreases accordingly and the rated motor speed N_Mot_Ziel(FP) decreases linearly with it, since the transmission ratio i_rez_festgang remains constant in order to simulate a fixed gear transmission. In this case, the accelerator pedal is fully depressed. Then, at point 42, the limit output speed for this accelerator pedal position is reached and the coupled torque converter transmission begins to be simulated. Even in a real drive train with a lockable torque converter transmission and a fixed gear transmission, the torque converter transmission is coupled at this point or the locking is automatically terminated. As the output speed now decreases further due to the presence of the load, the motor speed increases according to the characteristic curve 36 and corresponds to the calculated torque converter speed. For this purpose, the reciprocal transmission ratio of the continuously variable transmission is reduced, which is illustrated by the characteristic curve 46. At point 44, the working machine is stationary and the drive motor rotates at the idling speed n_mot_high_idle when the accelerator pedal is fully depressed.

[0039] The curve is similar when the accelerator pedal is only half depressed, but the limit output speed is not reached until point 48. Accordingly, as the load increases and the output speed decreases, the motor speed follows the characteristic curve 38 up to point 50. At point 50, the work machine is at a standstill and the drive motor rotates at an idling speed of 1300 rpm when the accelerator pedal is half depressed in this example. The curve of the reciprocal transmission ratio is illustrated by the characteristic curve 52 when the accelerator pedal is half depressed.

[0040] If the load is reduced again, the reverse sequence is obtained. When the accelerator pedal is half-pressed, an operating point 56 is obtained as an operating point without being depressed by the existing load, which is indicated by the vertical line 54 with respect to the corresponding output speed. With this control logic, a drive train with a fixed gear transmission and a lockable torque converter transmission can be simulated by a drive train with a continuously variable transmission, wherein the simulated drive train is automatically coupled to the torque converter transmission.

[0041] Figure 2 Explains the Figure 1 Same characteristic curve with same diagram structure. In addition, however, a modification of the control parameters is described, by means of which the transition point from the simulation with a locked torque converter transmission to the fixed gear transmission with a coupled torque converter transmission is shifted. This allows the limiting output speed to be varied by parameterization. When simulating a coupled torque converter transmission, the torque converter speed is now calculated using the following formula:

[0042] Torque converter speed = (n_ab_Ziel(FP) – n_ab_ist) / n_ab_Ziel(FP) * (n_mot_Ziel(FP) – n_mot_Wandler_base)+ n_mot_Wandler_base,

[0043] Instead of the unloaded motor speed n_mot_low_idle when the accelerator pedal is not depressed, the torque converter base speed n_mot_Wandler_base is now used for calculation. The torque converter base speed n_mot_Wandler_base is determined as a function of the output speed and decreases linearly with the output speed in the example shown. As a result, the accelerator-dependent characteristic curves 36, 38 for the motor control are shifted to characteristic curves 36', 38' when simulating a coupled torque converter transmission, as shown in FIG. Figure 2 As shown. Correspondingly, for the reciprocal transmission ratio on the continuously variable transmission (which is adjusted for the simulation), a corresponding change of the characteristic curve 46, 52 to the characteristic curve 46', 52' is also obtained. Thus, the transition point or the limit output speed associated with the accelerator pedal depression is moved from the point 42, 48 to the point 42', 48'.

[0044] Figure 3 Explains the Figure 2 Same characteristic curve with same diagram structure. In addition, however, a modification of the control parameters is described, by means of which the motor speed at rest is shifted. For this purpose, the torque converter speed is calculated using the following formula when simulating a coupled torque converter transmission:

[0045] Torque converter speed = (n_ab_Ziel(FP) – n_ab_ist) / n_ab_Ziel(FP) * FP_factor*(n_mot_Ziel(FP) - n_mot_Wandler_base) + n_mot_Wandler_base,

[0046] When simulating a coupled torque converter transmission, a scaling factor is added that is dependent on the accelerator pedal. In the example shown, this scaling factor decreases gradually as the accelerator pedal is depressed more gradually. Accordingly, the points 44, 50 with the work machine stationary are shifted to points 44', 50', wherein the motor speed at point 44' is now 1600 rpm and the motor speed at point 50' is now 1350 rpm. The corresponding reciprocal transmission ratios are also shifted accordingly.

[0047] Reference numerals list

[0048] 10 Detect the current driven end speed

[0049] 12 Compare the current driven end speed with the boundary driven end speed

[0050] 14 Control drive system: simulate fixed gear transmission and locked torque converter transmission

[0051] 16 Controlled drive train: Simulation of fixed gear transmission and coupled torque converter transmission

[0052] 30 Characteristic curve of target driven end speed

[0053] 32 Calculate the target driven end speed point according to the first formula

[0054] 34 The line of the driven end speed determined at point 32

[0055] 36, 36' Characteristic curve when the travel pedal is fully depressed

[0056] 38, 38' Characteristic curve of half-pressing the driving pedal

[0057] 40Minimum motor speed line

[0058] 42, 42' When the travel pedal is fully depressed, the point at the limit driven end speed

[0059] 44, 44' Points for stationary and idling speeds when the throttle pedal is fully depressed

[0060] 46, 46' The characteristic curve of the reciprocal transmission ratio

[0061] 48, 48' When the driving pedal is half-pressed, the point at the boundary driven end speed

[0062] 50, 50' points for static and idling speeds when the travel pedal is half depressed

[0063] 52, 52' The characteristic curve of the reciprocal transmission ratio when the travel pedal is half-pressed

[0064] 54 The line of the driven end speed corresponding to the operating point

[0065] 56 operating points

Claims

1. A method for operating a drive train of a working machine having a continuously variable transmission, the method comprising at least the following steps: - Detect (10) the current driven end speed; - when the detected driven end speed is greater than or equal to the limit driven end speed, controlling (14) the drive train so as to simulate a drive train having a fixed gear transmission and a locked torque converter transmission; as well as - If the detected output speed is less than the limit output speed, the drive train is controlled (16) in order to simulate a drive train having a fixed gear transmission and a coupled torque converter transmission.

2. The method according to claim 1, characterized in that When the drive train is controlled (14) to simulate a locked torque converter transmission, a fixed transmission ratio is provided by means of the continuously variable transmission.

3. The method according to claim 1 or 2, characterized in that: When the drive train is controlled (16) to simulate a coupled torque converter transmission, a variable transmission ratio is provided by means of the continuously variable transmission, wherein the transmission ratio of the continuously variable transmission decreases as the detected output speed decreases.

4. The method according to any one of the preceding claims, characterized in that When simulating a locked torque converter transmission and an engaged torque converter transmission, the drive train is controlled as a function of a target output speed that is dependent on the gas pedal.

5. The method according to any one of the preceding claims, characterized in that The limit output speed is predetermined as a function of the detected gas pedal position.

6. The method according to any one of the preceding claims, characterized in that The limit output speed is predetermined as a function of the output speed.

7. A control device for a drive train of a working machine having a continuously variable transmission, wherein: The control device is configured to control (14) the drive train to simulate a drive train having a fixed gear transmission and a locked torque converter transmission when the detected output end speed is greater than or equal to a limit output end speed, and wherein the control device is configured to control (16) the drive train to simulate a drive train having a fixed gear transmission and a coupled torque converter transmission when the detected output end speed is less than the limit output end speed.

8. A drive system for a working machine, wherein: The drive system comprises: a drive motor configured to provide a driving force; a continuously variable transmission device configured to transmit the driving force from the drive motor to a driven end using a continuously adjustable transmission ratio; A detection device configured to detect (10) a current driven end rotation speed of the drive system; And a control device, which is configured to simulate a drive system with a fixed gear transmission and a locked torque converter transmission by controlling (14) the drive system when the detected driven end speed is greater than or equal to the boundary driven end speed, and the control device is configured to simulate a drive system with a fixed gear transmission and a coupled torque converter transmission by controlling (16) the drive system when the detected driven end speed is less than the boundary driven end speed.

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