Method for operating a power-split transmission

Abstract

The present invention relates to a method for operating a power-split transmission (1) for a working machine. The power-split transmission (1) has a first driving range for slower driving speeds and a further driving range for faster driving speeds. The transmission (1) further comprises a first clutch (6) for shifting the first driving range, a further clutch (7) for shifting the further driving range, and a variator (3) for varying the gear ratio within the driving ranges. The method includes detecting (I) a switching request to switch from the first to the further driving range, opening (II) the first clutch (6), adjusting (V) the variator (3) to a target gear ratio, and closing (VII) the further clutch (7).Furthermore, the present invention relates to a control device (8) for carrying out such a method and to a power-split transmission (1) with such a control device (8).

Description

Technical field

[0001] The present invention relates to a method for operating a power-split transmission for a working machine. The working machine may be a construction or agricultural machine. Furthermore, the present invention relates to a control device configured to carry out such a method and to a power-split transmission with such a control device. State of the art

[0002] Power-split continuously variable transmissions (CVTs), such as hydrostatic-mechanical CVTs, are frequently used in construction machinery. These hydromechanical transmissions allow for stepless adjustment of the gear ratio with relatively high efficiency, but they have a comparatively narrow gear ratio spread. The gear ratio spread of a transmission is the ratio between the highest and lowest gear ratios. To increase the gear ratio spread, it is known to incorporate several operating ranges in a CVT, each with a different gear ratio. The transmission uses a clutch to switch between these operating ranges. Traditionally, the transmission is designed so that switching between the operating ranges occurs at the clutch's synchronization point.The object of the present invention was to provide a method for operating a power-split transmission for a working machine, with which the torque that can be transmitted through the transmission can be increased with minimal wear. Description of the invention

[0003] The present invention relates to a method for operating a power-split transmission for a working machine. The working machine can be a construction or agricultural machine. For example, the working machine is a tractor or a wheel loader. The power-split transmission can be a continuously variable transmission in which the gear ratio is infinitely variable. The power split can be, for example, a hydrostatic-mechanical power split. Alternatively or additionally, it can be an electromechanical power split. The transmission can have an input, at which the quantity to be translated is fed into the transmission, and an output, at which the quantity translated by the transmission is discharged. A drive unit, for example an internal combustion or electric motor, can be mechanically coupled to the input.

[0004] The transmission has a driving range for lower speeds and another driving range for higher speeds. The transmission can be designed such that the driving speed correlates with a reciprocal transmission ratio, for example, a linear correlation. The reciprocal transmission ratio can be the inverse of the transmission's gear ratio. A driving range of the transmission can be understood as a state in which a fixed mechanical gear ratio exists between the input and output of the transmission, whereby the transmission ratio can be continuously varied within the driving range by the variator. The driving range for lower speeds can therefore be provided for lower reciprocal transmission ratios, and the driving range for higher speeds for higher reciprocal transmission ratios.The transmission can also have additional driving ranges. In one embodiment, the transmission has three driving ranges, and the method of the present invention allows switching between the second and third driving ranges.

[0005] Furthermore, the power-split transmission includes a first clutch for shifting between the first driving range and a second clutch for shifting between the second driving range. These clutches can be friction clutches, such as multi-plate clutches. In one embodiment, the transmission switches from the driving range for slower speeds to the second driving range for faster speeds when the first clutch opens and the second clutch closes. The transmission also includes a variator for varying the gear ratio within the driving ranges. If the transmission is a hydrostatic-mechanical power-split transmission, the variator can be a hydrostatic unit. In this case, the hydrostatic unit can have two hydraulic units to enable stepless variation of the transmission's gear ratio within the driving ranges.In an alternative embodiment, the variator can have two electric machines, each of which can be operated as a motor and generator. In this configuration as well, the variator allows the transmission ratio to be continuously varied within the driving ranges.

[0006] The process involves detecting a switching requirement to change from the first to the next driving range. Such detection can be based on various measured values. For example, a switching requirement can be detected when a specific speed of the machine or a specific reciprocal gear ratio is requested or present. Alternatively or additionally, a specific load condition of the transmission may be required, such as a certain load reserve. For this purpose, the vehicle's acceleration dynamics and the transmission's torque load can be determined. The transmission's torque load can be determined based on a measurement from the transmission's variator.In one embodiment, a pressure value of the variator, provided it is designed as a hydrostatic transmission, is determined as part of this measurement. This pressure value can be the differential pressure between a high-pressure and a low-pressure section of the variator. Additionally, the engine load (actual engine percent torque) can also be determined and evaluated. This can include checking the current engine torque. If the engine torque exceeds a maximum threshold, the shift cannot be enabled. Furthermore, the shift can only be enabled if a minimum threshold for engine torque is exceeded.

[0007] The detection of a shift requirement can involve a shift requirement for asynchronous switching from the lower-speed range to the higher-speed range. During asynchronous shifting of the clutch, it is not at its synchronization point, meaning that the rotational speeds of the components being coupled are different. Due to the asynchronous shifting of the drive ranges, the transmission can transmit torque that would result in an impermissible load on the clutch if the clutch were shifted synchronously.If the power transmitted by the transmission is to be increased while simultaneously synchronizing the clutch, the tractive force would have to be reduced when switching between driving ranges to prevent damage to the clutch or a condition that would compromise its reliability. This would result in an uneven tractive force curve and a corresponding drop in the transmission's performance. However, by asynchronously engaging the clutch to switch between driving ranges while maintaining the same power transmission, a largely continuous tractive force curve without significant drops can be provided, preventing impermissible stresses. The result is an increase in the transmission's performance.

[0008] The method includes opening the first clutch. Opening the first clutch reduces the force required to fully close it, which may, but does not necessarily, lead to clutch slippage. In other words, opening the clutch in the present embodiment also includes a process in which the force required to fully close the clutch is reduced, but the clutch still does not exhibit differential rotation. However, in one embodiment, opening the clutch according to the present invention includes a state in which the clutch is opened to such an extent that differential rotation occurs at the clutch.

[0009] The method further comprises adjusting the variator to a target gear ratio. This adjustment can be performed with the first clutch disengaged, for example, in such a way that the first clutch exhibits a differential speed. Adjusting the variator changes the transmission's gear ratio. The variator adjustment can be performed, at least partially, in a state where both the first and subsequent clutches exhibit a differential speed, thus preventing torque transmission from the input to the output of the transmission. Consequently, the method of the present invention can result in a brief interruption of traction. During this interruption, when the drivetrain is disengaged, intermediate synchronization of the transmission can be achieved by adjusting the variator, thereby setting the transmission to a target gear ratio.Furthermore, the procedure includes closing the second clutch to eliminate any differential speed at that clutch and thus re-enabling torque transmission via the drivetrain. Closing the second clutch can occur during or after the variator adjustment.

[0010] The method of the present invention provides asynchronous shifting with the potential increase in transmission performance described above. Intermediate synchronization via the variator significantly reduces the load on the secondary clutch compared to a pure powershift transmission, thus preventing overload. Simultaneously, intermediate synchronization allows for essentially continuous acceleration of the vehicle even with asynchronous shifting, since, unlike a pure powershift transmission, the variator can be adjusted to the speed required in the next driving range. However, a brief period can occur when both clutches are open, i.e., not engaged. During this time, there may be a brief period of no power transmission, and the output may therefore decelerate briefly according to the external load.If, on the other hand, a pure load switching operation were performed, the variator in the asynchronous circuit would, for example, be in a position within its wider operating range that corresponds to a slower speed than required. This would lead to an unwanted deceleration in the asynchronous load switching operation. However, by incorporating the intermediate synchronization described above, such an unwanted deceleration in the asynchronous circuit can be effectively avoided.

[0011] In one embodiment, the driving range for slower speeds is extended up to a reciprocal gear ratio, i.e., up to a driving speed greater than the reciprocal gear ratio or the driving speed at which the secondary clutch is at its synchronization point. Consequently, the transmission is designed such that the driving range for slower speeds extends up to a maximum reciprocal gear ratio greater than the reciprocal gear ratio at the transmission's synchronization point. This extension of the driving range for slower speeds up to a reciprocal gear ratio greater than the reciprocal gear ratio at the secondary clutch's synchronization point can be achieved in one embodiment by adjusting the variator beyond a position at which the clutch is at its synchronization point.

[0012] In one embodiment, the method further comprises determining the target gear ratio to which the variator is adjusted, based on the output speed of the transmission present at the time the switching requirement is detected and a load-dependent override value. The asynchronous shifting within the scope of the present invention can be performed such that the output speed of the transmission at the end of the shift corresponds to the output speed of the transmission at the beginning of the shift. The target gear ratio can be determined in such a way that this condition is met. The override value is load-dependent and, in one embodiment, serves to compensate for a drop in speed due to external loads acting on the drivetrain. If the shifting occurs, for example, in a plane where output speed losses due to external driving resistances are very low, no override value can be parameterized in one embodiment.If, however, a shift is performed under full load on an incline, a drop in speed can occur during the interruption of traction. To compensate for such a drop, the override value can be parameterized accordingly in this case. When shifting under deceleration, for example, when descending a hill, the target gear ratio can be determined based solely on the output speed at the start of the asynchronous shift. In an alternative embodiment, an override value is also parameterized under deceleration, but this is used as an acceleration override, not as a deceleration override as in traction operation. This embodiment ensures that the asynchronous shifting within the scope of the present invention is performed with particularly high efficiency and quality, as a constant output speed can be maintained during the shift.

[0013] In one embodiment, adjusting the variator to the target gear ratio reduces the differential speed at the secondary clutch. This significantly reduces the loads occurring during shifting compared to a pure load shift. The method can include checking whether the differential speed at the secondary clutch falls below a threshold value. In other words, this embodiment can verify whether a load occurring during shifting is less than a threshold value, with the test based on the differential speed at the clutch. Only if this test step is successful can the secondary clutch be fully engaged. However, before the secondary clutch is fully engaged, it may already be partially engaged.The present embodiment offers the advantage that an asynchronous circuit with the advantages described above can be implemented in a gentle and safe manner.

[0014] In one embodiment, closing the secondary clutch comprises an initial closing with a lower gradient to reduce any differential rotational speed present at the secondary clutch, followed by a closing with a higher gradient. Closing the secondary clutch with an initial low gradient allows the remaining differential rotational speed to be reduced in a particularly gentle manner. Only when the differential rotational speed is below a threshold value can the clutch then be closed with a higher gradient and thus at a higher speed. This provides a good balance between reducing the load during switching and ensuring a fast switching process, and therefore, above all, minimizing the time interrupted by traction.

[0015] In one embodiment, the method further includes pre-filling the secondary clutch to reduce its response time. The secondary clutch can be pre-filled while the first clutch is opening, or alternatively or additionally while the variator is being adjusted. Pre-filling can reduce the subsequent response time of the clutch, but it cannot create a state in which the clutch is already transmitting torque. In other words, the clutch still exhibits a differential speed even after pre-filling. Pre-filling of the secondary clutch can occur as soon as the differential speed at the secondary clutch is less than a configurable threshold for a configurable period of time. Alternatively or additionally, pre-filling of the secondary clutch can occur when a configurable period of time has elapsed since the shift activation.

[0016] In one embodiment, opening the first clutch involves a gradient opening to prevent a sudden release of load on the drive train of the driven machine. The first clutch can open immediately after detecting the switching requirement described above. Subsequently, a target pressure of the first clutch can be ramped down depending on the load. This load-dependent ramping can initially be performed with a large gradient to quickly bring the clutch into a state where it begins to slip. Once such a slipping state is reached, the ramp gradient can be reduced to allow for smooth slippage and thus a smooth opening of the drive train. Due to this smooth opening, the output speed now begins to decrease, corresponding to the slippage of the clutch and the external driving resistances.This embodiment therefore offers the advantage that asynchronous switching can be provided with high speed and at the same time high comfort.

[0017] In one embodiment, the method further includes monitoring a switching load during the switchover from the first to the further driving range.

[0018] When monitoring the shift load, the shifting power and, alternatively or additionally, the shifting work occurring during shifting can be monitored. If the shift load exceeds a limit value, i.e., if the shifting load (i.e., the shifting power and / or shifting work) exceeds a threshold value, for example, a value critical for the clutch structure, the shift can be aborted. When the shift is aborted, the variator can be reset to its initial position at the start of the shift, i.e., resynchronized to the output speed in the gear for lower driving speeds. The first clutch can then be re-engaged. Furthermore, the second clutch, if already partially engaged or pre-filled, can subsequently be completely emptied.Furthermore, if such a limit value is exceeded, the driving range for higher speeds can subsequently be blocked, for example, for a parameterizable period of time. This allows the other clutch to cool down before it can be engaged again. Only after this period has elapsed can a switch from the driving range for slower speeds to the driving range for higher speeds be permitted. The present embodiment offers the advantage that a method for switching the transmission can be provided with a particularly high level of safety.

[0019] The present invention further relates to a control device that is configured, i.e., specifically programmed, to execute the method according to one of the embodiments described above. The control device may include a memory, for example, non-volatile memory, on which a program for executing the method according to one of the embodiments described above may be stored. The control device may include one or more microprocessors, which may be arranged and programmed at the same or different locations to execute the method according to one of the embodiments described above. The control device may be part of a transmission control unit. Alternatively or additionally, the control device may be provided separately from the transmission control unit.The control unit can have one or more interfaces to communicate with the different components of the transmission, for example via a bus system.

[0020] The control unit's memory can store a characteristic map of the transmission, based on which the various components of the transmission can be controlled according to the embodiments described above. For example, the characteristic map can contain a relationship between the reciprocal gear ratio, a state variable of the variator (e.g., the differential pressure of the variator mentioned above), and a torque applied to the transmission output. Furthermore, the present invention relates to a power-split transmission for a machine with a driving range for slower speeds and another driving range for higher speeds. The power-split transmission has a first clutch for shifting the first driving range and a second clutch for shifting the second driving range, as well as a variator for varying the gear ratio within the driving ranges.Furthermore, the power-split transmission includes a control unit according to the embodiment described above. For an understanding of the individual features and their advantages, reference is made to the above explanations in connection with the method for operating a power-split transmission. Short description of the characters Fig. Figure 1 shows a power-split transmission according to an embodiment of the present invention. Fig. Figure 2 shows a schematic flowchart of a procedure for operating the power-split transmission. Fig. 1. Fig. Figure 3 shows the curves of different gear sizes when performing the operation in Fig. 2 of the procedures shown. Detailed description of embodiments

[0021] Fig. Figure 1 shows a power-split transmission 1 according to an embodiment of the present invention. The power-split transmission 1 is designed for use in a working machine, in this case a tractor or wheel loader. In the present embodiment, the power-split transmission 1 is a hydrostatic-mechanical power-split transmission 1. Accordingly, the power-split transmission 1 has a mechanical power path 2 and a hydraulic power path with a variator 3. In the present embodiment, the variator 3 is designed as a hydrostatic unit. Furthermore, the transmission 1 includes a drive 4, which is mechanically connected to the mechanical 2 and the hydraulic power path 3. Both the mechanical 2 and the hydraulic power path 3 are also mechanically connected to an output 5 of the power-split transmission 1.In the present embodiment, the drive 4 of the transmission 1 is mechanically connected to a motor (not shown), in this case an internal combustion engine. The output 5 is mechanically connected to the wheels of the working machine.

[0022] The power-split transmission 1 comprises several driving ranges, between which switching is possible by means of a first clutch 6 and a further clutch 7. In the present embodiment, the clutches 6 and 7 are designed as friction clutches, for example, as multi-plate clutches. The clutches 6 and 7 can be actuated via a hydraulic system (not shown). The present embodiment has three driving ranges, with the second driving range being selected by means of the first clutch 6 and the third driving range being selected by means of the further clutch 7. In addition, the transmission 1 has a further clutch (not shown) for selecting the first driving range.

[0023] The transmission 1 further comprises a control unit 8, which is electronically connected via a clutch interface 9 to the first clutch 6 and the second clutch 7 for shifting between the first and second driving ranges. The control unit 8 also has a variator interface 10, through which the variator 3 can be adjusted. The control unit 8 can read the differential speed of the clutches 6 and 7 via the clutch interface 9. The differential pressure of the variator 3 between a high-pressure and a low-pressure section of the variator 3 can be read via the variator interface 10, based on which the pressure / torque load of the transmission 1 can be determined. The control unit 8 is designed to monitor the shifting operation and the shifting performance during a shift using the clutch 6 and / or the clutch 7.Such monitoring can be performed via the clutch interface 9 of the control unit 8. Furthermore, the control unit 8 is designed to detect the rotational speed at the output 5 of the transmission 1, for example, via a speed interface (not shown). The control unit 8 also receives the target clutch pressure from a transmission control unit in order to calculate the corresponding shifting work / shifting power using the differential speed in the clutch. Alternatively, the shifting work / shifting power calculated by the transmission control unit can be used directly. In addition, the control unit 8 can receive the torque load from the engine.

[0024] The control unit 8 is set up and specifically programmed in this case to perform the following with reference to Fig. 2 and Fig. 3 described methods for operating the power-split transmission 1 from Fig. 1. In this procedure, the second driving range is extended up to a reciprocal gear ratio that is greater than the reciprocal gear ratio at the synchronization point of the further clutch 7. As from Fig. As can be seen in Figure 3, the motor mechanically connected to the drive 4 of the gearbox 1 has a substantially constant speed 26 during the entire asynchronous switching process.

[0025] In a first step I, the control unit 8 detects a switching request to change from one driving range, in this case the second driving range, to another driving range, in this case the third driving range. In the present embodiment, a switching request for asynchronous switching between these driving ranges is detected in step I. Such a switching request for asynchronous switching occurs in the present embodiment when the requested reciprocal gear ratio, i.e., the requested vehicle speed, is greater than a threshold value and simultaneously the acceleration dynamics and the torque utilization of the transmission 1 are less than their respective threshold values. In other words, the asynchronous switching 25 occurs when the requested speed is greater than a threshold value and the transmission 1 has a power reserve.In one embodiment, the motor load is additionally checked, and switching is only permitted if it is below a threshold. If these conditions are met, a trigger 11 is first set in step I, as shown in [reference]. Fig. 3 in the lower section of the drawing. This trigger 11 initiates the asynchronous switching 25 from the second to the third driving range of the transmission 1. Reference drawing 25 is shown in Fig. Figure 3 shows the period during which the asynchronous switching is active.

[0026] In a subsequent step II, the first clutch 6 is now ramped down via the control unit 8 depending on the load, as determined by the target pressure profile 12 of the first clutch 6. Fig. 3 is evident in order to avoid a sudden release of the drivetrain and thus a noticeable jerk. The ramp-off phase of the target pressure 12 of the clutch 6 is in Fig. 3 is represented by reference numeral 13. During load-dependent ramping 13, the load transmitted by the gearbox 1 can first be determined, whereby this is done in this case by measuring the differential pressure in the variator 3 described above via the variator interface 10. Depending on the applied load, the target pressure 12 of the clutch 6 is ramped down. This ramping initially takes place with a larger and then with a smaller gradient. At the time shown at position 14 in Fig. 3 the clutch pressure 12 at the clutch 6 has dropped so far that the clutch 6 begins to slip, causing the output speed 22 to slow down according to the slippage of the clutch 6 and the external driving resistances.

[0027] As from Fig. As can be seen in Figure 3, during the ramping down 13 of the target pressure 12 of the clutch 6, the pre-filling III of the further clutch 7 is triggered, as by the target pressure profile 15 of the further clutch 7. Fig. 3 is evident. This pre-filling phase of the clutch 7 is in Fig. Figure 3 is shown with reference numeral 16. In the present embodiment, the pre-filling III of the further clutch 7 begins after a predetermined time period following activation by the trigger signal 11. The time period is designed such that the pre-filling III of the further clutch 7 begins after the ramping 13 of the clutch 6 has begun, in this case approximately from the point at which the gradient of the ramping 13 decreases significantly, as described above. However, the pre-filling III can also occur earlier in the steep section of the ramping 13. In the present embodiment, the differential rotational speed applied to the clutch 6, which is in Fig. 3 is shown by reference numeral 17, during pre-filling III in the pre-filling phase 16 of the further coupling 7 has not yet dropped significantly.

[0028] During the asynchronous switching 25, a tractive force interruption occurs, during which the clutch 6 is already partially open and begins to slip, i.e., temporally following point 14 in Fig. 3, the further clutch 7, however, is not yet fully closed for torque transmission. The duration of the interruption of traction force during the asynchronous switching 25, in which there is no frictional coupling in the gearbox 1, is less than 1 s in the present embodiment, and less than 200 ms in this case.

[0029] Furthermore, in step IV, the control unit 8 determines the target gear ratio to which the variator 3 is to be synchronized during the asynchronous switching. For this purpose, the control unit 8 detects the output speed 22 present at the output 5 of the transmission 1 at the beginning of the asynchronous switching, i.e., at the time of triggering 11. Additionally, at an adjustable time after triggering 11, when the clutch 6 is still fully engaged, the output speed 22 present at the output 5 of the transmission 1 can be detected. Furthermore, it determines a load-dependent override value 23. The asynchronous switching 25 is designed such that the output speed 22 present at the beginning of the asynchronous switching 25 should also be present after the asynchronous switching, as indicated by reference numeral 23 in the figure. Fig. 3 shown. The target value for synchronization is always the maintained output speed plus the load-dependent surcharge value 23, which can be negative in traction operation and positive in thrust operation.

[0030] In the present embodiment, the load-dependent override value is determined based on the pressure load of the variator 3 at the beginning of the asynchronous switching 25, i.e., at the time of triggering 11. The greater the pressure load and thus the load applied to the gearbox 1, the larger the override value is parameterized. If the asynchronous switching takes place, for example, on level ground, no override value is parameterized, since the output speed loss due to external resistances is very low during the switching process. In contrast, in the present embodiment, a relatively large override value is parameterized for switching under full load on an incline, since the output speed drop during the switching process is significantly higher due to the higher external driving resistances.If a thrust condition is detected at the time of triggering 11, which would correspond, for example, to a downhill drive, the determination step of the present invention can be suspended. The target transmission ratio can then be determined solely on the basis of the current output speed. In an alternative embodiment, the determination step can continue, whereby a positive overrun value 23 can be set, as described above.

[0031] From the beginning of the circuit 25, in this case shortly after the start of ramping II of clutch 6 in ramping phase 13 and before the start of pre-filling III of the further clutch 7 in pre-filling phase 16, the hydrostatic drive 3 is adjusted and synchronized to the new target gear ratio in a step V. The adjustment process of the variator 3 is in Fig. 3 is represented by reference numeral 21. While the clutch 6 is still engaged, the actual variator ratio VR, which hydraulically follows the target variator ratio VS, must not move at all or only very slightly towards the new target ratio, as this would lead to a delay in the old driving range. For this reason, only small gradients are permitted for the target variator ratio VS in the first stage of synchronization, in order to bring the control valve of the hydrostatic unit 3 to the correct control edge and reduce the hydraulic delay time. The basic gradient of the target variator ratio VS depends on how long the asynchronous switching 25 has been active since the start of the switching trigger 11.

[0032] As from Fig. As can be seen in Figure 3, the target variator ratio VS is adjusted from the beginning of the asynchronous switching 25. However, due to the hydraulic delay, the actual variator ratio VR is only adjusted at a point in time when the target pressure 12 at the clutch 6 has already been partially ramped down. From point 14 onwards, the gradient of the target variator ratio VS is increased to achieve an adjustment to the target ratio with maximum possible adjustment dynamics. Since the hydrostatic drive is now being adjusted with maximum slewing dynamics, it is necessary to decelerate it again before reaching the new target ratio to prevent overshoot in the actual variator ratio VR. For this purpose, the gradient of the target variator ratio VS is gradient-limited depending on the distance 19 to the target value 20. The smaller the distance 19 from the target value 20, the smaller the permissible gradient in the target variator ratio VS.The gradient can be adjusted via a characteristic curve.

[0033] At the beginning of the in Fig. In the area marked with reference numeral 24, the pre-filling 16 of the further clutch 7 is completed, so that it is ready to build up torque. The procedure includes a check VI to see if the time-debounced differential speed 18 at the further clutch 7 falls below a threshold value. If the differential speed 18 is below the threshold value, the closing of the further clutch 7 is started in step VII. As shown in Fig. As can be seen in Figure 3, the target pressure 15 of the additional clutch 7 is initially increased via a shallower gradient during the closing phase 24. It is then determined whether the differential speed 18 at the clutch 7 has largely decreased, i.e., is essentially zero. As soon as this condition is met, the target pressure 15 of the additional clutch 7 is increased with a steeper gradient up to a parameterizable torque level. The additional clutch 7 is then fully closed again with a shallower gradient. Once the additional clutch 7 has reached its closing pressure, the asynchronous switching is complete, as indicated by the switching activity signal 25 in Figure 3. Fig. 3 is visible. The translation can then be adjusted normally again. Following step VII, the procedure returns to step I.

[0034] During the asynchronous shifting operation 25, the shifting performance and shifting work of the transmission 1 are monitored in step VIII. If either of these parameters exceeds a critical value, the shifting operation 25 is aborted and the hydrostatic drive 3 is resynchronized to the output speed 22 at the beginning of the shifting operation 25. The clutch 6 is then closed again, and if the other clutch 7 has already closed, this clutch 7 is fully opened again. The third driving range is then locked for a configurable time, allowing the other clutch 7 sufficient time to cool down. Only after this configurable time has elapsed is another asynchronous shifting operation 25 possible. Reference sign 1 power-split gearbox 2 mechanical power branch 3 Variator 4 Drive 5 Drive 6 first clutch 7 more clutches 8 Control unit 9 Coupling interface 10 Variator interface 11 Trigger signal 12 Target pressure first clutch 13 Ramping Target pressure first clutch 14 Time of difference in speed first clutch 15 Target pressure further clutch 16 Pre-filling further clutch 17 Differential speed first clutch 18 Differential speed further clutch 19 Distance Target Value 20 Target value 21 Variator adjustment for intermediate synchronization 22 Output speed 23 Load-dependent surcharge value 24 Close another coupling 25 Asynchronous circuit VS Target Variator Translation VR Ist-Variator Translation 26 Engine speed I Capture switch requirement II Open first clutch III Pre-filling further clutch IV Determine target translation V Adjust variator VI Check for differential speed VII Close further coupling VIII Monitor switching load

Claims

[1] Method for operating a power-split transmission (1) for a work machine, wherein the power-split transmission (1) has a first driving range for slower driving speeds and a further driving range for faster driving speeds, a first clutch (6) for shifting the first driving range, a further clutch (7) for shifting the further driving range and a variator (3) for varying the gear ratio within the driving ranges, comprising detecting (I) a shift requirement for switching from the first to the further driving range, opening (II) the first clutch (6), adjusting (V) the variator (3) to a target gear ratio and closing (VII) the further clutch (7). [2] Method according to claim 1, characterized by that the method comprises extending from the first driving range to a reciprocal gear ratio greater than that at the synchronization point of the further clutch (7). [3] Method according to one of the preceding claims, characterized by that the method comprises determining (IV) the target gear ratio based on an output speed of the transmission (1) present at the time of detecting (I) the switching requirement and a load-dependent surcharge value. [4] Method according to one of the preceding claims, characterized by in that the adjustment (V) of the variator (3) to the target gear ratio leads to a reduction in a differential speed (18) at the further clutch (7), and in that the method comprises checking (VI) whether the differential speed present at the further clutch (7) falls below a threshold value. [5] Method according to one of the preceding claims, characterized bythat the closing (VII) of the further clutch (7) comprises a closing with an initially smaller gradient in order to reduce a differential speed present at the further clutch (7) and then a closing with a larger gradient. [6] Method according to one of the preceding claims, characterized by that the method comprises pre-filling (III) the further clutch (7) to reduce its response time. [7] Method according to one of the preceding claims, characterized by that the opening (II) of the first clutch (6) comprises an opening with a gradient to avoid a sudden unloading of a drive train of the working machine. [8] Method according to one of the preceding claims, characterized bythat the method comprises monitoring (VIII) a switching load during switching from the first to the further driving range and, if the switching load limit is exceeded, resetting the variator (3) to the gear ratio present when the switching requirement was detected (I). [9] Control device (8) arranged to carry out the method according to one of the preceding claims. [10] Power-split transmission (1) for a work machine with a first driving range for slower driving speeds and a further driving range for faster driving speeds, a first clutch (6) for switching the first driving range, a further clutch (7) for switching the further driving range, a variator (3) for varying the gear ratio within the driving ranges and a control device (8) according to claim 9.

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