Method for determining the emptying behavior of a hydraulically actuated switching element of a transmission

Abstract

Method for determining the emptying behavior of a hydraulically actuated switching element (9, 10) of a transmission (3), one half of which of the switching element is operatively connected to a transmission input shaft (6) that can be coupled to a drive motor (2) and the other half of which of the switching element can be connected to an output shaft (4) of a vehicle drive train (1) implemented with the transmission, characterized in that The switching element (9, 10) is switched from an open and completely empty operating state to a closed and completely filled operating state by applying an actuating pressure (p9) when the speed of the transmission input shaft (6) is greater than a threshold and when the switching element half is decoupled from the output (4). The reference filling time (tf) until this operating state of the switching element (9, 10) is reached is determined. wherein the closed operating state of the switching element (9, 10) is recognized when a rotational speed (n11) of the switching element half connectable to the output (4) reaches a predefined threshold value (n11_threshold), wherein the switching element (9, 10) is brought into its fully emptied and open operating state by adjusting the actuating pressure (p9) for a predefined emptying period upon detection of the closed operating state of the switching element (9, 10) and is subsequently fully filled and closed again, wherein the switching element (9, 10) is again guided in the direction of the emptied and open operating state by lowering the actuating pressure (p9) upon detection of the fully filled and closed operating state, and wherein the switching element (9, 10) is returned to its fully filled and closed operating state before reaching the fully emptied and open operating state, and the filling period is determined until the partially emptied switching element again has its fully filled and closed operating state.

Description

[0001] The invention relates to a method for determining the emptying behavior of a hydraulically actuated switching element of a transmission according to the type defined in more detail in the preamble of claim 1.

[0002] In conventional continuously variable transmissions (CVTs) and construction machinery transmissions, hydraulically actuated friction-locked switching elements are typically used. These elements are filled with hydraulic fluid in piston chambers and pressurized accordingly. The fill level of the piston chamber of such a switching element significantly influences its transmission capacity and the torque it can transmit. Furthermore, the actuation sequence of a switching element affects its closing behavior and thus also the shifting comfort, which is largely determined by the torque applied to a vehicle's output shaft and its torque curve.

[0003] Since manufacturing tolerances of components used in shift elements, as well as of hydraulic lines manufactured in series, are known to vary undesirably, each shift element in a transmission must be individually calibrated to determine its specific filling behavior and to ensure it can be actuated to the required extent for optimal shifting comfort. The parameters characterizing the clutch filling, determined through calibration, are stored in the non-volatile memory of the transmission control unit and used to actuate each shift element during every gear change.

[0004] Two parameters are particularly characteristic of the filling behavior of a switching element. The first parameter is the so-called rapid filling time, during which a switching element is subjected to a rapid filling pulse to fill it within a short operating time. The piston chamber of a switching element is pressurized with a defined rapid filling pressure for the duration of the rapid filling time. This rapid filling phase is followed by a so-called filling equalization phase, during which the actuating pressure in the piston chamber is reduced from the level of the rapid filling pressure to a level of a filling equalization pressure (represented by the second parameter) and maintained for a further defined filling equalization time.At the end of the filling equalization phase, the switching element is ideally in a defined operating state in which the transmission capability of the switching element is essentially zero and from which an increase in the actuating force of the switching element results in an immediate increase in the transmission capability of the switching element.

[0005] In previously known calibration methods, the rapid filling time is determined iteratively. Starting with a very short rapid filling time, the time is increased step by step until the switching element transmits torque at the end of the rapid filling phase. This operating state of a switching element can be easily verified as a function of various speed profiles of transmission components. Speed ​​monitoring is implemented using a suitable detection function. All calibration methods are based on the assumption that the switching element, whose rapid filling time is currently being calibrated, transitions to a completely empty operating state between the individual iteration steps for determining the rapid filling times.

[0006] Besides its filling behavior, the emptying behavior of a switching element also has a significant influence on the quality of shifting. This results from the fact that, especially in construction machinery, the same clutch is engaged in rapid succession within the power flow of a vehicle's drivetrain, which is particularly common during multiple consecutive reversing operations. If the same clutch is engaged and disengaged after very short operating times, it is possible that the clutch will not fully empty before being engaged again and will have to be engaged from a partially filled operating state. This means that existing engagement routines for switching elements are not suitable for preparing a switching element to the extent required for the desired high level of shifting comfort.

[0007] From DE10036510 A1, a method for operating an automatic transmission of a motor vehicle with a hydraulic system is known. An electronic control unit is connected to the hydraulic system. It has at least one switching element that can be controlled via the hydraulic system using predefined time-pressure profiles, wherein the switching element is switched on or off via the time-pressure profiles. Depending on a time-pressure profile underlying a previous control of the switching element and an associated profile representing the operating point of the switching element with respect to a fill level and / or a position of a piston of the switching element, a current operating point of the respective switching element is determined by an algorithm stored in the electronic control unit, based on which the switching element is then controlled.

[0008] The present invention is based on the objective of providing a method for determining the emptying behavior of a hydraulically actuated switching element of a transmission, in order to be able to actuate even partially emptied switching elements to an extent required for high shifting comfort during a shifting process.

[0009] According to the invention, this problem is solved by a method having the features of claim 1.

[0010] In the inventive method for determining the emptying behavior of a hydraulically actuated switching element of a transmission, one half of which is operatively connected to a transmission input shaft that can be coupled to a drive motor and the other half of which can be connected to an output of a vehicle drive train carried out with the transmission, the switching element is, when the rotational speed of the transmission input shaft is greater than a threshold and when the switching element half is decoupled from the transmission output shaft, transferred from an open and completely empty operating state to a closed and completely filled operating state by applying an actuating pressure and the reference filling time until this operating state of the switching element is reached is determined.The closed operating state of the switching element is detected when the rotational speed of the switching element half connected to the transmission output shaft reaches a predefined limit due to the closed operating state of the switching element. Upon detection of the closed operating state, the switching element is moved to its fully emptied and open operating state for a predefined emptying period by adjusting the actuation pressure. It is then fully filled and closed again. Once the fully filled and closed operating state is detected, the switching element is moved back towards the emptied and open operating state by reducing the actuation pressure.Before reaching the fully emptied and open operating state, the switching element is then returned to its fully filled and closed operating state, and at the same time the filling period is determined until the partially emptied switching element again has its fully filled and closed operating state.

[0011] The inventive method allows for the simple determination of the discharge behavior of a switching element, particularly reversing clutches in a continuously variable transmission (CVT). The parameters determined by the method can be taken into account during the actuation of a switching element to improve the shifting quality, especially of reversing clutches in CVTs. This is particularly advantageous for rapid successive shifts, as significantly improved shifting behavior can be achieved by considering the discharge time of a switching element. For the first time, the method makes it possible to explicitly account for variations in switching elements manufactured in series production and in the hydraulic actuation system.

[0012] In the method according to the invention, a detection function monitors the secondary-side rotational speed of the switching element. When the switching element transitions to its closed operating state, the switching element half that can be connected to the transmission output rotates essentially at the same speed as the switching element half connected to the transmission input shaft, and a speed sensor, preferably arranged on the output side, measures the increase in the rotational speed of the output-side switching element half.

[0013] Furthermore, during the process, a sufficiently high actuating pressure is applied to the switching element until its secondary-side rotational speed exceeds the limit. At this point, it is detected that the switching element is filled to the point where it can transmit torque. The time elapsed up to this point is stored as a reference filling time in a transmission control unit. Subsequently, the actuating pressure is adjusted to a level that ensures the switching element empties completely. Following this, the switching element is filled completely again, and the previously determined reference filling time is verified, thus confirming that the switching element was indeed completely emptied.

[0014] In addition, during the actual emptying time determination, the emptying time from the fully filled operating state of the switching element until the next filling process is significantly reduced, meaning the switching element does not have enough time to empty completely. This approach allows the actual emptying behavior of a switching element to be precisely determined with minimal effort, and a method for filling and closing a switching element can be easily adapted to the extent required for high switching comfort.

[0015] If the reference filling time is determined at least twice in succession, incorrect activation of a switching element due to measurement errors can be easily avoided.

[0016] The method according to the invention can preferably be used in vehicle drive trains with continuously variable transmissions (CVTs), but it is also possible to use the method according to the invention in vehicle drive trains with transmissions with shift clutches, such as transmissions with a hydrodynamic torque converter, preferably with a closed converter lock-up clutch. The transmission also has a friction-based shifting element.

[0017] In an advantageous embodiment of the method according to the invention, the switching element is returned to its fully filled and closed operating state after a predefined emptying time has elapsed, whereby the degree of filling of the switching element after the predefined emptying time has elapsed is determined with minimal effort based on the ratio between the filling period and the reference filling time.

[0018] In a further advantageous variant of the method according to the invention, the determination of the filling level of the switching element is carried out iteratively until the emptying time corresponding to a predefined filling level of the switching element is determined.

[0019] In a further variant of the method according to the invention, the determination of the filling level of the switching element is carried out iteratively until the emptying time until the switching element reaches the completely empty and open operating state is determined, whereby a switching element can be actuated with high accuracy.

[0020] In a variant of the method according to the invention that can be carried out with minimal effort, a characteristic curve depicting the emptying behavior of the switching element is determined by linear interpolation between the fully filled and closed operating state, which the switching element has at an emptying time of zero, the fully emptied and open operating state of the switching element, which the switching element has after the emptying period has elapsed, and a determined intermediate value of the degree of filling at a corresponding emptying time.

[0021] Depending on the specific application, a characteristic curve depicting the emptying behavior of a switching element is used as a second-degree polynomial, which is determined based on the fully filled and closed operating state that the switching element has at an emptying time of zero, the fully emptied and open operating state of the switching element that the switching element has after the emptying period has elapsed, and a determined intermediate value of the degree of filling at a corresponding emptying time.

[0022] In an advantageous variant of the inventive method, the filling level of the switching element corresponding to a predefined emptying time and / or the emptying time corresponding to a predefined filling level of the switching element is or are adapted as a function of the speed of the transmission input shaft and / or the operating temperature of the transmission, making it possible to actuate a switching element over the entire operating range of a transmission to an extent required for high shifting comfort.

[0023] In order to be able to actuate a switching element to an extent required for high switching comfort, a rapid filling time and / or a pressure level of the actuating pressure of the switching element during a rapid filling phase of the switching element is adapted via the characteristic curve to the degree of filling of the switching element determined at the beginning of the rapid filling phase via the characteristic curve in a simple variant of the method according to the invention.

[0024] It is possible that the pressure level of the actuation pressure and / or the rapid filling time will be reduced depending on the respective degree of filling of the switching element determined at the beginning of the rapid filling phase.

[0025] Both the features specified in the patent claims and the features specified in the following embodiment of the invention are each suitable, either individually or in any combination with one another, to further develop the invention.

[0026] Further advantages and beneficial developments of the invention result from the patent claims and the exemplary embodiments described in principle with reference to the drawing.

[0027] It shows: Fig. 1 a highly schematic block diagram representation of a vehicle powertrain with a continuously variable power-split transmission; Fig. 2 a gear scheme of a continuously variable transmission; Fig. 3 an actuation chain of one of the switching elements of the transmission according to Fig. 2; Fig. 4 several curves of different operating condition variables of the gearbox according to Fig. 2 over time t, which occurs during the execution of the procedure according to the invention; Fig. 5 the course of a filling level of a switching element of the transmission according to Fig. 2, wherein the emptying behavior of the switching element is determined according to a first variant of the method according to the invention; Fig. 6 a Fig. 5. Corresponding representation of a course of a filling level of the switching element of the transmission according to Fig. 2, wherein the region of the characteristic curve representing the discharge behavior of the switching element is determined via a second variant of the method according to the invention; and Fig. 7 a Fig. 5 or Fig. 6 corresponding filling and emptying characteristic curve of the switching element of the transmission according to Fig. 2 and progressions of two successive actuation phases of the switching element, wherein the second actuation phase of the switching element is adapted depending on the filling and emptying characteristic curve.

[0028] Fig. Figure 1 shows a schematic representation of a vehicle drive train with a drive unit 2 and a transmission 3, designed as a continuously variable power-split transmission, which can be coupled to it. The drive unit 2 is designed as an internal combustion engine, preferably as a diesel internal combustion engine, and in further embodiments of the vehicle drive train 1 can also be designed as an electric machine or as a combination of an internal combustion engine of any type and an electric machine.

[0029] On the output side, the gearbox 3 is operatively connected to an output 4, whereby a drive torque provided by the drive unit 2 is converted, depending on the gear ratio set in the gearbox 3, into an output torque in the output 4, representing the corresponding tractive force. In the area between the drive unit 2 and the gearbox 3, a power take-off 5 or a working hydraulic system can be supplied with torque from the drive unit 2.

[0030] In Fig. Figure 2 is a gear scheme of a possible embodiment of the transmission 3 according to Fig. Figure 1 shows a drive unit 2 that is non-rotatably connected to a transmission input shaft or transmission input 6 in the region of the transmission input shaft. The transmission input shaft 6 drives the auxiliary output 5, a further auxiliary output 8, and first switching element halves of friction-fit switching elements 9 and 10 via a fixed gear 7 and a fixed gear 8A. The friction-fit switching element 9 is arranged coaxially with the transmission input shaft 6, while the friction-fit switching element 10, or the reverse direction clutch, is positioned on the shaft of the auxiliary output 5, which is arranged coaxially with the transmission input shaft 6. In the closed operating state of the friction-fit switching element 9, or the forward direction clutch, the transmission input shaft 6 drives a loose gear 12, which is rotatably mounted on the transmission input shaft 6, via a loose gear 11 that is rotatably mounted on the transmission input shaft 6. The loose gear 12 is non-rotatably coupled to a planet carrier 13.In the closed operating state of the friction-fit switching element 10, the transmission input shaft 6 drives the loose gear 12 via a loose gear 14.

[0031] Several double planetary gears 15 are rotatably mounted on the planet carrier 13. The double planetary gears 15 mesh with a first sun gear 16, a second sun gear 17, and a ring gear 18. The first sun gear 16 is non-rotatably connected to a shaft 19 of a first hydraulic unit 20 of a hydrostatic unit 21. The ring gear 18 is operatively connected via a fixed gear 22 and a fixed gear 23 to a shaft 24 of a second hydraulic unit 25 of the hydrostatic unit 21.

[0032] Within the continuously variable power-split transmission 3, several gear ratio ranges are adjustable, within which the gear ratio of the transmission 3 can be continuously varied by adjusting the hydrostatic unit 21. The transmission 3 can be operated independently of the illustration according to Fig. 2. The transmission may be designed as a continuously variable transmission coupled both as a primary and as a secondary coupled transmission, whereby the power splitting may be hydraulic or electrical or by means of a combination thereof.

[0033] A transmission output or transmission output shaft 26 of the transmission 3 can be connected to the second shaft 24 of the hydrostatic unit 21 via a friction-fit switching element 27 arranged coaxially to the transmission output shaft 26 for a first driving range of the transmission 3, a loose gear 28, and a fixed gear 29. Furthermore, the transmission output shaft 26 can be coupled to the second sun gear 17 via a fixed gear 30, a fixed gear 31, and another friction-fit switching element 32 for a second driving range of the transmission 3, as well as a loose gear 33 and a fixed gear 34. The fixed gear 34 is arranged coaxially with the second sun gear 17, while the fixed gear 31, the friction-fit switching element 32 for the second driving range, and the loose gear 33 are arranged coaxially with each other. The fixed gear 30, the friction-locked switching element 27 for the first driving range and the loose gear 28 are in turn provided coaxially to the transmission output shaft 26.In addition, the fixed gear 30 meshes with both the fixed gear 31 and the fixed gear 34 of a shaft 35, which in turn can be connected to the driven vehicle axle or to several driven vehicle axles of the output 4.

[0034] The direction-of-travel couplings 9 and 10 are designed as wet couplings, which are not only intended to establish the power flow between the drive unit 2 and the output 4, but also simultaneously determine the direction of travel. According to their capacitive design, the friction-locking switching elements 9 and 10 of the vehicle drive train 1 are configured as follows: Fig. 2 can also be used as starting elements. This is the case when a driver, starting from a neutral operating state of the transmission 3, in which the switching elements 27 and 32 are open, selects a direction of travel and simultaneously depresses an accelerator pedal to indicate a desired speed. The friction-locking switching elements 9 and 10 are designed in such a way that a change of direction or a so-called reversing process is also possible via them, starting from higher speeds in either the forward or reverse direction.

[0035] During such a reversing process, the vehicle speed is initially reduced from its current speed towards zero. For this purpose, the transmission capability of both the friction-locked switching element 9 and the friction-locked switching element 10 is adjusted accordingly. The two friction-locked switching elements 9 and 10 operate predominantly in a slipping manner during the reversing process. Once the vehicle speed is essentially zero, the transmission capabilities of the two switching elements 9 and 10 are adjusted so that the vehicle moves forward in the opposite direction to its previous direction of travel until the desired vehicle speed is reached.

[0036] To enable a start-up process from a standstill and the neutral operating state of the transmission 3 within short operating times and essentially without delay, the shift element 27 of the first gear range of the transmission 3 is closed, and, depending on the driver's request for forward or reverse travel, the shift element 9 or the shift element 10 is additionally moved to its closed operating state. During the engagement of the shift element 27 and the shift element 9 or 10, the two hydraulic units 20 and 25 are adjusted via an adjustable yoke 36 such that the desired starting gear ratio is set in the transmission 3. During this process, the transmission capacity of the friction-fit shift element 9 or 10 is set to values ​​greater than zero to ensure a connection with the vehicle drivetrain 1. Fig. 1. The vehicle being driven is already in motion during a closing process of the friction-locking switching element 9 or 10.

[0037] Fig. Figure 3 shows a part of an electro-hydraulic control device 37, via which, among other things, the friction-locked switching elements 9 and 10 can be actuated to implement the functionalities described above. In this case, to actuate the switching element 9, a setpoint value i9 for the actuating current i9 of the switching element 9 is output in the area of ​​an electrical control unit 38 and applied in the area of ​​a valve assembly 39. In the area of ​​the valve assembly 39, an actuating pressure p9 is thus set depending on the setpoint value i9 for the actuating current i9, which is applied in the area of ​​the switching element 9 or in the area of ​​a piston chamber of the switching element 9.

[0038] The valve assembly 39 comprises a proportional pressure regulator 40, the valve spool 41 of which can be displaced by an electromagnet 42 against the spring force of a spring assembly 43. The electromagnet 42 is actuated depending on the setpoint i9 of the actuating current i9. A supply pressure signal p_red or a reducing pressure is present in the area of ​​the proportional pressure regulator 40, which, depending on the setpoint i9 of the actuating current i9, can be applied to a hydraulic amplifier 44 of the valve assembly 39 in the area of ​​a control surface 45 of a valve spool 46 of the hydraulic amplifier 44 at the respective levels required for actuating the switching element 9.Additionally, a supply pressure signal p_sys is present at the hydraulic amplifier 44, which corresponds to a system pressure of a primary pressure circuit of the electro-hydraulic control and regulating device 37 and which, due to the valve amplification present in the area of ​​the hydraulic amplifier 44, can be increased by a factor of 2.7 in the present case as actuation pressure p9 at the switching element 9.

[0039] Depending on the specific application, it may also be possible for the switching element 9 to be actuated directly, i.e. without the additional hydraulic amplifier, by the system pressure p_sys, if this pressure is sufficiently high.

[0040] Since it is quite common in construction machinery for the same clutch or switching elements 9 and 10 to be engaged in rapid succession, such as during quick reversals of the direction of travel, there is a possibility that switching elements 9 and 10 will not empty sufficiently between two consecutive engagement processes for the actuation processes stored in a control unit. To ensure that switching elements 9 and 10 are actuated to the extent required for a high level of shifting comfort, depending on their current operating state when a request is made to engage one of them, the following procedure or calibration process is carried out. During the calibration process, the emptying behavior of switching elements 9 and 10 can be determined individually for each clutch and taken into account when actuating the switching elements.The characteristic values ​​determined by means of the calibration procedure are subsequently stored in the electro-hydraulic control and regulating device 37 and taken into account when actuating the switching elements 9 and 10, which makes it possible to improve the switching quality of the reversing clutches or the switching elements 9 and 10 with little effort.

[0041] For better understanding, the calibration procedure for determining the emptying behavior of the switching elements 9 and 10 is first illustrated according to the diagram. Fig. 4 explained in more detail, whereby the calibration procedure, which is carried out identically for switching elements 9 and 10, is described below only with reference to switching element 9 for the sake of clarity.

[0042] At time T0, when the calibration procedure is started, a so-called detection function monitors the rotational speed n11 of the switching element half of the switching element 9 coupled to the loose gear 11. This half can be brought into operative contact with the output via the friction-fit switching element 27 or the friction-fit switching element 32 to the extent described above. When the calibration procedure is activated, the rotational speed of the drive machine 2 is greater than a threshold value, whereby the switching element half of the switching element 9 operatively connected to the transmission input shaft 6 rotates at the rotational speed of the drive machine 2. Since both the switching element 27 and the switching element 32 are open, the switching element half of the switching element 9 coupled to the loose gear 11 is stationary when the switching element 9 is fully open. Therefore, the detection function then determines a rotational speed n11 of this switching element half that is essentially zero.

[0043] At time T0, the electrical control unit 38 outputs a target value i9 of the actuating current i9 of the switching element 9, and the switching element 9 is subjected to a corresponding actuating pressure p9 in the area of ​​the clutch chamber. The actuating pressure p9 is measured in the Fig. In the manner shown in Figure 4, the pressure is ideally increased abruptly and maintained at a constant pressure level p9. With increasing operating time t, the degree of filling of the switching element 9 and its transmission capacity also increase. This increase in transmission capacity, in turn, causes an increase in the rotational speed n11 of the switching element half of the switching element 9, which is rotationally fixed to the loose gear 11. At time T1, the rotational speed n11 of the switching element half of the switching element 9 exceeds a defined threshold value n11_threshold, which is empirically determined. At time T1, it is recognized that the switching element 9 is filled sufficiently to transmit torque. The reference filling time tf is determined from the difference between times T1 and T0, which is 250 ms in the example considered here.

[0044] After determining the reference filling time tf, the target value i9 of the actuating current i9 and thus the actuating pressure p9 is set in Fig. The range shown in Figure 4 is again abruptly reduced to a level p9, at which the switching element 9 transitions to its open operating state. The target value i9 of the actuating current 9 is held constant at the current value corresponding to the opening pressure level p9 of the actuating pressure p9 for such a long time interval that the switching element 9 is completely emptied. In the example considered here, the target value i9 is set to this level for 10 s until time T2. From time T2 onwards, the target value i9 of the actuating current i9 is abruptly increased to the same extent as at time T0, and the switching element 9 is then subjected to the actuating pressure p9.

[0045] At time T3, the rotational speed n11 of the switching element half of switching element 9 again exceeds the threshold value n11_threshold, and the period between times T3 and T2 is determined. If the period bounded by times T3 and T2 corresponds to the reference filling time tf determined at time T1, the reference phase, during which the reference filling time tf is determined, ends at time T3.

[0046] Depending on the specific application, the reference filling time tf is determined either after a single filling operation of the switching element 9 or after several consecutive filling operations, with a waiting period between each filling operation sufficient to ensure that the switching element 9 is in its fully open and emptied operating state before each subsequent filling operation. Tests have advantageously shown that determining the reference filling time tf after a single filling operation already achieves the accuracy required for the calibration procedure.

[0047] After completion of the reference phase, the actual emptying time determination is started, and the switching element 9 is filled with the actuating pressure p9 at time T4, approximately 2 seconds after time T3, by applying the target value i9 of the actuating current i9 to the proportional pressure regulator 40. This pressure is the same as during the reference phase. The shorter waiting time of 2 seconds means that the piston chamber of the switching element 9 is not completely empty at time T4, and the rotational speed n11 of the switching element half of the switching element 9 exceeds the threshold value n11_threshold after only 125 ms. The currently determined filling time of 125 ms is divided by the previously determined reference filling time tf of 250 ms, with the result corresponding to the remaining fill level of the switching element 9 at time T4, which is 50% in this example.

[0048] Subsequently, further filling phases of the switching element 9 are carried out, whereby the emptying time between the further filling phases of the switching element 9 is gradually increased until one of the filling phases of the switching element 9 again lasts the full reference filling time tf, until the switching element 9 is completely filled.

[0049] At the in Fig. In the exemplary iterative procedure for determining the emptying time of switching element 9, shown in section 4, switching element 9 is re-pressurized with the pressure value p9 after an emptying time of 3 s at time T5. The rotational speed n11 of the switching element half of switching element 9 exceeds the threshold value n11_threshold at time T7, which corresponds to a filling time of 187 ms. This means that switching element 9 still has a residual fill level of 25% after the emptying time of 3 s, or at time T6.

[0050] At time T7, the setpoint i9 of the actuating current i9 is again reduced to the opening level of the switching element 9. After a discharge time of 4 s, the switching element 9 is then subjected to the actuating pressure p9 at time T8. The switching element transitions to its fully filled and closed operating state at time T9, as the rotational speed n11 of the switching element half of the switching element 9 then exceeds the threshold value n11_threshold. The period between times T9 and T8 corresponds to the reference filling time tf of 250 ms. The measured values ​​show that the switching element 9 is completely discharged after a discharge time of between 3 and 4 s. Knowing that the emptying of switching element 9 takes between 3 and 4 s, the actual emptying time of switching element 9 in this time interval can be determined iteratively very accurately with a reduced step size.

[0051] The step change in the setpoint i9 of the actuating current 9, and thus of the actuating current p9, shown here is merely an example. It is within the discretion of a person skilled in the art to change the actuating current, and thus also the actuating pressure of the switching element 9, in another suitable manner, for example, in a ramped manner.

[0052] Furthermore, it is also possible to adapt the values ​​determined via the calibration procedure depending on various operating condition variables, such as the speed of the transmission input shaft 6, which essentially corresponds to the speed of the drive machine, and the respective operating temperature of the transmission 3, and to actuate the switching elements 9 and 10 depending on the adapted values.

[0053] After determining the emptying times of the switching elements 9 and 10 and any necessary adaptation, the determined calibration values ​​are stored in a non-volatile memory, such as an EPROM or an EEPROM, of the electro-hydraulic control and regulating device 37 and used as parameters for the actuation of the switching elements 9 and 10.

[0054] Fig. Figure 5 shows an example of a filling and emptying characteristic curve of the switching element 9 over time t. The curve illustrates the filling behavior of the switching element 9 between times T10 and T13 during a rapid filling phase and during a subsequent leveling phase. Additionally, the curve shows the emptying behavior of the switching element 9 after time T14.

[0055] The present case in Fig. The filling behavior shown in Figure 5 results from the procedure whereby the switching element 9, which is completely empty at time T10 and in the open operating state, is filled as quickly as possible from time T10 onwards in a known manner during the rapid filling phase with a rapid filling pressure for a rapid filling time that ends at time T11. Following the rapid filling phase, a so-called filling equalization phase begins at time T11 and extends until time T13, during which the switching element 9 is subjected to a filling equalization pressure for an empirically determined filling equalization time.

[0056] Ideally, at the end of the filling equalization phase, the switching element 9 is in a defined operating state in which its transmission capability is zero, and from which a further increase in the actuation pressure p9 of the switching element results in an immediate increase in its transmission capability. At time T13, the switching element 9 is definitely completely filled.

[0057] To determine the characteristic curve according to Fig. 5 is initially set to a predetermined residual fill level of 25% for the switching element 9 via the Fig. The procedure described in section 4 determines the corresponding emptying time. In the section described in Fig. In the example considered, this emptying time is 3 s. Additionally, a period is defined after which the switching element 9 is definitively completely empty. Subsequently, a linear interpolation is performed between the operating point at time T14, at which the switching element 9 is completely filled, the operating point at time T15 (i.e., 3 s after time T14), at which the switching element has a residual fill level of 25%, and at time T16, which follows time T14 after 10 s, and at which the clutch is completely empty and open. Fig. The discharge curve shown in Figure 5 over time t is defined with minimal effort. During subsequent operation of the transmission 3 or a vehicle drivetrain equipped with the transmission 3, the switching element 9 can be actuated to a degree favorable for high shifting comfort, depending on such a characteristic curve, as described later.

[0058] The in Fig. Figure 6 shows the filling and emptying characteristic of the switching element, which between times T10 and T14 essentially corresponds to that shown in Fig. The filling and emptying characteristic curve shown in Figure 5. The section of the filling and emptying characteristic curve shown from time T14 onwards is shown according to... Fig. 6 is also determined by linear interpolation between three operating points of the switching element 9. The parameters for determining the characteristic curve correspond to... Fig. 6 operating points of the switching element 9 used at times T14 and T16 the operating points of the switching element 9 which at times T14 and T16 for determining the filling and emptying characteristic curve according to Fig. 5. Only the one at time T17 for determining the filling and emptying characteristic curve according to Fig. The operating point used in point 6 differs from the one used to determine the filling and emptying characteristic curve according to Fig. 5 operating point used at time T15.

[0059] The determination of the filling and emptying characteristic curve according to Fig. The underlying operating point at time T17 is defined by the residual fill level of the switching element 9 after the expiry of a defined emptying time, which in this case starts after time T14 and is 3 s.

[0060] Fig. Figure 7 shows a possible consideration of the calibrated residual filling behavior of the switching elements 9 and 10, as previously described, when initially switching a completely empty switching element 9 or 10. In this case, Fig. Figure 7 shows the upper section of the curve of the target value i9 of the actuating current i9 over time t during a rapid filling phase occurring between times T10 and T11, followed by a filling equalization phase that takes place between times T11 and T13. After time T13, the target value i9 of the actuating current i9 is ramped up during a so-called pressure modulation phase, which in this case lasts until time T30, in order to bring the switching element 9 or 10 into its fully closed operating state.

[0061] At time T14, a request is again made to switch off the switching element 9 or 10, which is why the setpoint i9 of the actuating current i9 is ramped down to the level required for opening and emptying the switching element 9 or 10. For this reason, the switching element 9 or 10 empties from time T14 onwards in the Fig. 7 in the lower area, the extent shown by the depicted filling and emptying characteristic curve. The in Fig. The characteristic curve shown in section 7 can be found in the... Fig. 5 or in the to Fig. 6. It can be created by linear interpolation.

[0062] After an emptying time of approximately 2 s, a new request to activate switching element 9 is issued at time T18. Switching element 9 or 10 exhibits the filling and emptying characteristic curve according to Fig. 7 accordingly, at time T18, there is still a residual fill level of approximately 25%. Due to the knowledge of the non-negligible residual fill level of the switching element 9, the setpoint value i9 of the actuating current i9 at time T18 is maintained at the current level corresponding to the rapid fill pressure for a period shorter than the period between times T10 and T11, i.e., a reduced rapid fill time, until time T19. At time T19, it is ramped down to the level of the equalization pressure until time T20, and the switching element 9 is subjected to the corresponding rapid fill pressure.

[0063] At the end of the filling equalization phase, or after the filling equalization time has elapsed (which in this case is also shorter than the filling equalization phase between times T11 and T13), the switching element 9 or 10 is again in its defined operating state. In this state, the transmission capacity of the switching element 9 or 10 is essentially zero, and increasing the actuating pressure of the switching element 9 or 10 results in an immediate increase in the transmission capacity. The switching element 9 or 10 is in this operating state at time T21, from which the target value i9 of the actuating current i9 is increased to the same extent as between times T13 and T30, to the closing level of the switching element 9 or 10, at which time the switching element 9 or 10 is subjected to closing pressure.Subsequently, the setpoint i9 of the actuating current i9 is reduced again at time T23, according to a requirement, to the current level to which the switching element 9 or 10 transitions in its open operating state.

[0064] By means of the Fig. The procedure described in more detail in section 7 prevents, with minimal effort, the switching element 9 or 10 from being overfilled due to a renewed activation request that occurs when the switching element 9 or 10 is not yet completely empty, and avoids a switching shock that is perceived as disturbing by a driver.

[0065] In general, the inventive method achieves improved switching behavior in rapidly successive switching operations of a switching element by determining or calibrating the discharge time. Furthermore, by implementing the inventive method in existing vehicle systems, variations in component tolerances present in mass-produced components can, for the first time, be explicitly taken into account during the actuation of switching elements in transmissions, thus achieving a desired high level of switching comfort.

[0066] In addition, it is generally possible to determine the filling and emptying characteristics of switching elements using other methods, such as heuristic, statistical or other approaches, in order to be able to actuate a switching element to the extent described above in order to achieve a high switching quality. Reference sign 1 Vehicle powertrain 2 Drive unit 3 gearboxes 4 Drive 5 Power take-off 6 Gearbox input shaft 7 Fixed wheel 8 additional auxiliary drives 8A Fixed Wheel 9 friction-fit switching element 10 friction-fit switching element 11 Loose wheel 12 Loose wheel 13 planetary carriers 14 Loose wheel 15 double planetary carriers 16 first sun wheel 17 second sun wheel 18 Ring gear 19th wave 20 first hydraulic unit 21 Hydrostatic unit 22 Fixed wheel 23 Fixed wheel 24 wave 25 second hydraulic unit 26 Gearbox output shaft 27 friction-fit switching element 28 Loose wheel 29" fixed wheel 30 fixed wheel 31 Fixed wheel 32 friction-fit switching element 33 Loose wheel 34 Fixed wheel 35 wave 36 adjustable yoke 37 electro-hydraulic control and regulating device 38 electrical control unit 39 Valve assembly 40 Proportional pressure regulators 41 Valve slide of the proportional pressure regulator 42 Electromagnet 43 Spring mechanism 44 hydraulic amplifiers 45 Control area 46 valve slides i9 Actuation current i9soll Target value of the actuation current n11 Rotational speed of the switching element half of the switching element n11_threshold Threshold p9 Actuation pressure p_red supply pressure signal p_sys supply pressure signal T0 - T30 discrete time point t time

Claims

[1] Method for determining an emptying behavior of a hydraulically actuated shifting element (9, 10) of a transmission (3), one shifting element half of which is operatively connected to a transmission input shaft (6) which can be coupled to a drive engine (2) and the other shifting element half of which can be connected to an output (4) of a vehicle drive train (1) which is implemented with the transmission, characterized by , that the switching element (9, 10) is transferred from an open and completely emptied operating state into a closed and completely filled operating state by applying an actuating pressure (p9) when the speed of the transmission input shaft (6) is greater than a threshold and the switching element half is decoupled from the output (4), and the reference filling time (tf) is determined until this operating state of the switching element (9, 10) is reached, wherein the closed operating state of the switching element (9, 10) is detected when a rotational speed (n11) of the switching element half connectable to the output (4) reaches a predefined threshold value (n11_schwell), wherein the switching element (9, 10) is transferred to its completely emptied and open operating state upon detection of the closed operating state of the switching element (9, 10) by setting the actuating pressure (p9) for a predefined emptying period to a level and is then completely filled and closed again, wherein the switching element (9, 10) is again guided towards the emptied and open operating state by lowering the actuating pressure (p9) upon detection of the fully filled and closed operating state, and wherein the switching element (9, 10) is again transferred into its fully filled and closed operating state before reaching the fully emptied and open operating state and the filling period is determined until the partially emptied switching element again has its fully filled and closed operating state. [2] Method according to claim 1, characterized by that the reference filling time (tf) is determined at least twice consecutively. [3] Method according to claim 1 or 2, characterized by that the switching element (9, 10) is returned to its fully filled and closed operating state after a predefined emptying time has elapsed and the degree of filling of the switching element (9, 10) after the predefined emptying time has elapsed is determined on the basis of the relationship between the filling period and the reference filling time (tf). [4] Method according to claim 3, characterized bythat the determination of the filling level of the switching element (9, 10) is carried out iteratively until the emptying time corresponding to a predefined filling level of the switching element (9, 10) is determined. [5] Method according to claim 3, characterized by that the determination of the degree of filling of the switching element (9, 10) is carried out iteratively until the emptying time until the completely emptied and open operating state of the switching element (9, 10) is reached is determined. [6] Method according to one of claims 3 to 5, characterized bythat a characteristic curve depicting the emptying behavior of the switching element (9, 10) is determined by linear interpolation between the completely filled and closed operating state, which the switching element (9, 10) has when the emptying time is zero, the completely emptied and open operating state of the switching element (9, 10) that the switching element (9, 10) has after the emptying period has elapsed, and a determined intermediate value of the filling level at a corresponding emptying time. [7] Method according to one of claims 3 to 5, characterized bythat a characteristic curve representing the emptying behavior of the switching element is used as a second-degree polynomial, which is determined as a function of the completely filled and closed operating state that the switching element has at an emptying time equal to zero, the completely emptied and open operating state of the switching element that the switching element has after the emptying period has elapsed, and a determined intermediate value of the filling level at a corresponding emptying time. [8] Method according to one of claims 3 to 7, characterized by that the filling level of the switching element (9, 10) corresponding to a predefined emptying time and / or the emptying time corresponding to a predefined filling level of the switching element (9, 10) is adapted as a function of the speed of the transmission input shaft (6) and / or the operating temperature of the transmission (3). [9] Method according to one of claims 6 to 8, characterized by that a rapid filling time and / or a pressure level of the actuating pressure (p9) of the switching element (9, 10) during a rapid filling phase of the switching element (9, 10) is adapted via the characteristic curve to the filling degree of the switching element (9, 10) determined via the characteristic curve at the beginning of the rapid filling phase. [10] Method according to claim 9, characterized by that at least the pressure level of the actuating pressure (p9) and / or the rapid filling time is or are reduced depending on the respectively determined degree of filling of the switching element (9, 10) at the beginning of the rapid filling phase.

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