Method and control device for operating a transmission with at least one positive shift element

Abstract

Method for operating a transmission (3) with at least one positive switching element (A, F), which has two switching element halves (10, 11), wherein at least one switching element half (10) is designed to be displaceable between two end positions and the switching element (A, F) is open in the first end position and closed in the second end position, and wherein the travel of the switching element half (10) is detected by means of a sensor and a power flow in the transmission (3) is interrupted if a fault in the sensor is detected, characterized in that is checked if a sensor fault is detected, whether the switching element half (10) was in an end position as required before the fault and was actuated with an actuating force acting in the direction of this end position, wherein, if the test is positive, the power flow in the gear (3) is maintained until the switching element half (10) is actuated from the current end position in the direction of the other end position or the actuating force acting in the direction of the current end position is less than a threshold value.

Description

[0001] The invention relates to a method for operating a transmission with at least one positive shifting element according to the type defined in more detail in the preamble of patent claim 1. Furthermore, the invention relates to a control unit for carrying out the method and a corresponding computer program product.

[0002] DE 10 2005 002 337 A1 discloses an 8-speed multi-stage transmission with frictional shifting elements. The shifting elements are designed as multi-disk clutches or multi-disk brakes. When a gear change is requested in the transmission, at least one of the frictional shifting elements is to be disengaged from the power flow of the transmission device, and at least one further frictional shifting element is to be engaged in the power flow of the transmission device in order to transmit torque.

[0003] In general, when a request to open a frictional switching element is received, it can be assumed that the frictional switching element will actually transition to the open operating state, regardless of the torque currently applied to the frictional switching element. To the same extent, a request to close a frictional switching element can also be implemented with comparatively little control and regulation effort.

[0004] For this reason, a simple software-based evaluation of the control current of a pressure regulator of a friction-locked shift element is sufficient. By determining a corresponding opening control signal or a corresponding closing control signal for transferring the friction-locked shift element to its open or closed operating state, such an evaluation can easily verify whether a shift or gear change was successful.

[0005] Unfortunately, friction-locked shift elements in the open operating state cause drag torques, which adversely affect the overall efficiency of an automatic transmission.

[0006] For this reason, transmission devices, such as those known from DE 10 2008 000 429 A1, are increasingly being designed with positive-locking shifting elements in addition to frictional shifting elements. Such positive-locking shifting elements typically comprise two shifting element halves. The shifting element halves can be brought into positive engagement with one another by axially adjusting at least one movable shifting element half relative to the other, then axially immovable, shifting element half in the region of claw elements or the like. The positive-locking shifting element is then closed and transmits an applied torque. Furthermore, it is also possible for both shifting element halves to be designed to be axially movable relative to one another.

[0007] If the positive-locking shift element is to be deactivated from the power flow, the positive connection between the shift element halves is again canceled by axially displacing the movable shift element half relative to the axially immovable shift element half. The reason for the use of positive-locking shift elements is that, in contrast to friction-locking shift elements, there is essentially no drag torque in the area of ​​open positive-locking shift elements, which impairs the overall efficiency of a transmission. However, it should be noted that, in contrast to friction-locking shift elements, positive-locking shift elements can only be converted from an open operating state, in which no torque can be transmitted via the positive-locking shift elements, to their closed operating state near their synchronization point.

[0008] In addition, positive-locking shift elements connected to the power flow of a transmission device can be disengaged from the power flow with low shifting forces or transferred to their open operating state if the applied torque is sufficiently low. During shifting operations or so-called gear disengagement operations, the power flow between a transmission input shaft and a transmission output shaft in the area of ​​a transmission must be interrupted. In this case, a positive-locking shift element must be transferred from its closed operating state to its open operating state if necessary. If the torque applied in the area of ​​the positive-locking shift element builds up too quickly or incorrectly, or if the applied torque is released incorrectly, the positive-locking shift element may not be able to be transferred to its open operating state.Furthermore, mechanical, hydraulic, or electrical malfunctions may prevent a positive-locking switching element from opening. Therefore, unlike friction-locking switching elements, positive-locking switching elements do not necessarily transition to an open operating state when a corresponding opening control signal is present.

[0009] In addition, there is also the possibility that an open positive-locking switching element cannot be converted into its closed operating state within the desired short operating time. This is the case, for example, if the desired positive connection between the switching element halves cannot be achieved due to a so-called tooth-on-tooth position. In such a tooth-on-tooth position, claw elements of the switching element halves rest against one another in the area of ​​their end faces and the differential speed between the switching element halves is zero. Such a tooth-on-tooth position only resolves when a torque applied to the positive-locking switching element is greater than the static friction torque between the end faces of the claw elements of the switching element halves.

[0010] Furthermore, the creation of a complete positive connection or the complete closure of a positive-locking switching element can also be prevented by what is known as flank clamping between the flanks of the claw elements. With such flank clamping, the two switching elements have a certain axial overlap in the area of ​​their claw elements. However, the static friction between the adjacent flanks of the claw elements of the switching element halves is so high that the closing force acting on the switching elements in the closing direction is insufficient to overcome the static friction and completely close the positive-locking switching element.

[0011] Sensors are installed to monitor the current operating state of a positive-locking switching element. These sensors include, for example, a permanent magnet and a measuring device for sensing the permanent magnet's magnetic field. The sensors also include a ferromagnetic encoder contour that influences the permanent magnet's magnetic field depending on the operating states of the switching element halves. Various magnetic field sensing elements are known, such as elements based on a Hall effect or magnetoresistance elements. Magnetic field sensors generally include magnetic field sensing elements or other electronic components, with some magnetic field sensors comprising permanent magnets in a so-called back-biased arrangement.

[0012] Such magnetic field sensors provide electrical signals that reflect the state of a sensed magnetic field. In some designs, magnetic field sensors interact with ferromagnetic objects. The magnetic field sensors detect magnetic field fluctuations caused by an object moving through the magnetic field of a magnet in a magnetic field sensor. The magnetic field monitored by the magnetic field sensor is known to vary depending on the shape or profile of the moving ferromagnetic object. The position determination of the switching element halves is calculated directly from the raw signals of the sensors using applicable thresholds.

[0013] The values ​​of the sensor signal exhibit a non-negligible scatter, which makes it impossible to determine the current claw position with pinpoint accuracy. For this reason, a sensor signal value range is used to determine the current claw position on the sensor side. This range is limited for the respective claw position by the maximum and minimum sensor signals received. In addition, the signal values ​​of such a sensor also vary depending on a change in the position of the entire positive-locking shift element of a transmission relative to the sensor. Such a change in position results from what is known as gear play, which varies depending on the torque to be transmitted via the transmission as well as on the manufacturing tolerances of the transmission and the positive-locking shift element.

[0014] If a sensor malfunction is detected based on the raw sensor signals, the power flow in known transmission systems is interrupted. For this purpose, for example, in a transmission of the type described in more detail above, all shifting elements are suddenly switched to their open operating state. This ensures that an actuation routine called by the software due to an incorrectly determined operating state of a positive-locking shifting element neither causes a potentially overdetermined operating state of the transmission nor damage to the positive-locking shifting element.

[0015] The disadvantage, however, is that even very brief electrical disturbances can cause the transmission to open completely. If the sensor subsequently detects proper operation again, in the worst-case scenario, two positive-locking shift elements in the transmission described above would have to be transferred to their closed operating state. Closing the two positive-locking shift elements is very time-consuming due to the engagement strategy required. For this reason, the transmission is only available for driving again after an undesirably long operating period.

[0016] Based on the prior art described above, the invention seeks to provide a method for operating a transmission with at least one positive shifting element, by means of which the probability of transmission failure can be reduced. In addition, a control unit configured to implement the method and a computer program for implementing the method are to be specified.

[0017] From a process engineering perspective, this problem is solved based on the preamble of patent claim 1 in conjunction with its characterizing features. A control unit and a computer program product are also the subject of the further independent claims. Advantageous further developments are the subject of the subclaims and the following description.

[0018] A method is proposed for operating a transmission with at least one positive-locking shifting element comprising two shifting element halves. At least one shifting element half is designed to be movable between two end positions. The shifting element is open in the first end position of the shifting element half and closed in the second end position. The travel of the shifting element half is detected by a sensor. A force flow in the transmission is interrupted if a sensor fault is detected.

[0019] The term "positive-locking switching element" includes, for example, claw switching elements, which each transmit a torque via a positive-locking connection. Furthermore, the term "frictional switching element" includes switching elements designed as clutches or brakes, which each transmit a torque via a frictional connection. The torque that can be transmitted via such a frictional switching element varies depending on the closing force applied to the frictional switching element and is preferably continuously adjustable. The closing force corresponds, for example, to a hydraulic pressure applied to the switching element. In contrast, the torque that can be transmitted via a positive-locking switching element is not continuously adjustable.

[0020] The invention now encompasses the technical teaching that, upon detection of a sensor malfunction, a check is carried out to determine whether the switching element half was in a limit position as required prior to the malfunction and was actuated with an actuating force acting toward this limit position. If the check is positive, the power flow in the transmission is maintained until the switching element half is actuated from the current limit position toward the other limit position and / or the actuating force acting toward the current limit position is less than a threshold value.

[0021] In other words, the procedure according to the invention is used to decide which information the sensor signal provides and whether it is necessary to open the power flow in the transmission based on this information.

[0022] If the switching element half is in the requested end position until the point in time at which, for example, an electrical fault is detected based on the course of the sensor signal, and if the switching element half has also been actuated in the direction of the requested end position with a sufficiently high actuating force up to this point, the engaged end position is maintained and there is no need to interrupt the power flow in the transmission.

[0023] Thus, the power flow in the gearbox only needs to be interrupted and an unknown position of the switching element half needs to be indicated if the last known position of the switching element half does not correspond to an end position, the actuation direction of the switching element half does not correspond to the last known position of the switching element half or if no actuation force sufficient to control the switching element half can be provided.

[0024] This means that the probability of the power flow in the transmission being interrupted is reduced in a simple way compared to conventionally operated transmissions.

[0025] In an advantageous variant of the method according to the invention, a sensor malfunction is detected when a sensor signal exhibits values ​​that lie outside a specified range. The values ​​of the range correspond to the entire travel range of the switching element half between its end positions. This allows a sensor malfunction to be detected with minimal control and regulation effort.

[0026] If the sensor signal is a pulse-width modulated signal, a sensor malfunction can be detected with little effort.

[0027] If the power flow in the transmission is interrupted when the sensor fault persists for longer than a predefined period, short-term sensor faults are ignored, meaning that transmission operation is only affected when longer-term sensor faults occur.

[0028] Typically, the actuating force that can be applied to the shifting element corresponds to a hydraulic pressure provided by a hydraulic pump driven by a prime mover of a vehicle drivetrain. In an advantageous variant of the method according to the invention, the power flow in the transmission is interrupted when the drive torque of the prime mover is less than a threshold value. It is possible to define the threshold value such that the power flow in the transmission is interrupted when the prime mover is deactivated, during which the drive torque is essentially zero.

[0029] The invention further relates to a control unit designed to carry out the method according to the invention. The control unit comprises, for example, means used to carry out the method according to the invention. These means can be hardware-based means or software-based means. The hardware-based means of the control unit or control device are, for example, data interfaces for exchanging data with the components of the vehicle drive train involved in carrying out the method according to the invention. Further hardware-based means are, for example, a memory for data storage and a processor for data processing. Software-based means can be, among other things, program modules for carrying out the method according to the invention.

[0030] To implement the method according to the invention, the control unit can be configured with at least one receiving interface designed to receive signals from signal generators. The signal generators can be designed, for example, as sensors that detect measured variables and transmit them to the control unit. A signal generator can also be referred to as a signal sensor. Thus, the receiving interface can receive a signal from a signal generator, which indicates that a sensor malfunction has occurred.

[0031] The control unit may also have a data processing unit to evaluate and / or process the received input signals or the information of the received input signals.

[0032] The control unit can also be designed with a transmission interface configured to output control signals to actuators. Actuators are defined as actuators that implement the control unit's commands. The actuators can be designed, for example, as electromagnetic valves.

[0033] The control unit is designed to operate a transmission with at least one positive-locking shift element comprising two shift element halves. At least one shift element half is designed to be movable between two end positions. The shift element is open in the first end position of the shift element half and closed in the second end position. The travel of the shift element half is detected by a sensor. A power flow in the transmission is interrupted by the control unit if the control unit detects a sensor fault based on received input signals.

[0034] The control unit is designed in such a way that, upon detection of a sensor fault, it uses input signals to check whether the shift element half was in its end position as required prior to the fault and was actuated with an actuating force acting toward this end position. If the check is positive, the control unit maintains the power flow in the transmission until the shift element half is actuated from the current end position toward the other end position and / or the actuating force acting toward the current end position is less than a threshold value.

[0035] This simply reduces the probability that the power flow in the transmission is interrupted when a control of the sensor is detected.

[0036] The aforementioned signals are to be considered only as examples and are not intended to limit the invention. The detected input signals and the output control signals can be transmitted via a vehicle bus, for example, via a CAN bus. The control device or control unit can be designed, for example, as a central electronic control unit of the vehicle drive train or as an electronic transmission control unit.

[0037] The solution according to the invention can also be embodied as a computer program product which, when running on a processor of a control device, instructs the processor via software to carry out the associated method steps according to the invention. In this context, the subject matter of the invention also includes a computer-readable medium on which a computer program product described above is stored in a retrievable manner.

[0038] The invention is not limited to the specified combination of features of the independent claims or the dependent claims. Furthermore, possibilities arise for combining individual features, even if they emerge from the claims, the following description of embodiments, or directly from the drawings. The reference of the claims to the drawings by the use of reference symbols is not intended to limit the scope of protection of the claims.

[0039] Preferred developments emerge from the dependent claims and the following description. An exemplary embodiment of the invention is explained in more detail with reference to the drawing, without being limited thereto. Herein: Fig. 1 a schematic representation of a vehicle drive train with a prime mover, with a transmission and with an output; Fig. 2 a tabular circuit logic of the Fig. 1 shown gearbox; Fig. 3a to Fig. 3e shows different operating states of a highly schematically represented positive switching element between a fully open state and a fully closed state; and Fig. 4a to Fig. 4f each Fig. 3a corresponding representations of different operating states of a positive-locking switching element whose claw elements are designed with different lengths.

[0040] Fig. 1 shows a schematic representation of a vehicle drive train 1 with a prime mover 2, a transmission 3 and an output 4. The prime mover 2 is in the present case embodied as an internal combustion engine. The transmission 3 is an automatic transmission in which a plurality of gear ratios “1” to “9” for forward travel and at least one gear ratio “R” for reverse travel can be represented. Depending on the respective configuration of the vehicle drive train 1, the output 4 comprises one, two or more drivable vehicle axles which can be acted upon by the torque of the prime mover 2 via the transmission 3. During a gear ratio change in the transmission 3, i.e. during upshifts or downshifts in the transmission 3, hydraulically actuated shifting elements A to F are actuated. The gear ratio changes should be carried out essentially without any interruption in tractive force while at the same time providing a high level of driving comfort and with the desired performance.The term performance refers to a gear ratio change in gearbox 3 that is implemented within a defined operating time.

[0041] In order to be able to carry out the requested shift to the desired extent, the shift elements A to F are each subjected to shift sequences stored in a transmission control unit and a corresponding shift pressure.

[0042] The transmission 3 comprises a transmission input shaft 5 and a transmission output shaft 6. The transmission output shaft 6 is connected to the output shaft 4. Between the transmission input shaft 5 and the drive motor 2, a torsional damper 7 and a hydrodynamic torque converter 8 with an associated torque converter lock-up clutch 9 are arranged as a starting element.

[0043] In addition, the transmission 3 comprises four planetary gear sets P1 to P4. The first planetary gear set P1 and the second planetary gear set P2, which are preferably designed as negative planetary gear sets, form a shiftable primary gear set. The third planetary gear set P3 and the fourth planetary gear set P4 constitute a so-called main gear set. The shifting elements C, D, and F of the transmission 3 are designed as brakes, while the shifting elements A, B, and E are so-called clutches.

[0044] The switching elements A to F are connected in accordance with the Fig. Selective switching of gear ratios "1" to "R" is possible using the switching logic shown in more detail in Figure 2. To establish a power flow in the transmission, essentially three of the switching elements A to F must be simultaneously moved or maintained in a closed operating state.

[0045] In this case, shift elements A and F are designed as positive-locking shift elements without additional synchronization. As a result, the drag torques caused by open frictional shift elements are reduced in transmission 3 compared to transmissions equipped only with frictional shift elements.

[0046] As is known, positive-locking shift elements can generally only be converted from an open operating state to a closed operating state within a very narrow differential speed band around the synchronous speed between the shift element halves that are to be brought into positive-locking operative connection with one another. If the synchronization of a positive-locking shift element to be engaged cannot be implemented by means of additional structural designs, synchronization is achieved by a corresponding actuation of the other frictionally engaged shift elements involved in the shift and / or a so-called engine intervention. During such an engine intervention, for example, the drive torque provided by the prime mover 2 is varied to the extent required for synchronization in both overrun and traction mode of the vehicle drive train 1.This also applies to the actuation of the frictional switching elements during the execution of requested pull or push switching operations.

[0047] Fig. 3a to Fig. 3e show two switching element halves 10, 11 of the positive switching element A and F in different operating states. Fig. 3a shows the fully open operating state of the positive-locking switching element A or F, in which there is no positive connection between the two switching element halves 10 and 11 and in which the switching element halves 10 and 11 are spaced apart from one another in the axial direction x.

[0048] The switching element halves 10 and 11 each comprise claw elements 10A and 11A. Depending on the respective application, the claw elements 10A and 11A can be brought into positive engagement with one another by axially adjusting the switching element half 10 and / or the switching element half 11 with respect to the switching element half 11 or the switching element half 10, in order to be able to transmit a torque applied to the positive switching element A or F to the desired extent.

[0049] When a corresponding requirement exists to close the positive-locking switching element A or F, a corresponding actuating force is applied in the closing direction to the respective displaceable switching element half 10 or 11. This results in the axial distance between the mutually facing end faces 10B and 11B of the claw elements 10A and 11A being progressively reduced.

[0050] If the difference in speed between the switching element halves 10 and 11 is too large, the claw elements 10A and 11A cannot be brought into positive engagement with each other. In such a case, a so-called ratcheting occurs, during which the claw elements 10A and 11A Fig. 3b, in the region of their facing end faces 10B and 11B in the circumferential direction of the switching element halves 10 and 11. However, such ratcheting is undesirable, since it causes irreversible damage in the area of ​​the claw elements 10A and 11A with increasing operating time.

[0051] For this reason, the differential speed between the shift element halves 10 and 11 is set to values ​​within a differential speed window by correspondingly actuating the frictional shift elements B to E involved in the change of operating state in the transmission 3, which differential speed window is arranged around the synchronous speed of the positive shift element A or F. Within this differential speed window, the claw elements 10A and 11A of the shift element halves 10 and 11 can be brought into positive engagement with one another to the desired extent.

[0052] However, it should be noted that the form fit to be achieved can be prevented by a so-called tooth-on-tooth position between the switching element halves 10 and 11. The tooth-on-tooth position is as in Fig. 3c, characterized in that the claw elements 10A and 11A abut one another in the region of their end faces 10B and 11B and the differential speed between the switching element halves 10 and 11 is zero. During such a tooth-on-tooth position of the positive switching element A or F, the static friction between the end faces 10B and 11B of the claw elements 10A and 11A is so great that the torque applied to the positive switching element A or F is transmitted via the positive switching element A or F, respectively, without the tooth-on-tooth position being disrupted.

[0053] To release the tooth-on-tooth position, it is advantageous if the actuating force applied to the positive-locking switching element A or F in the closing direction is reduced and / or the torque applied to the positive-locking switching element A or F is increased. In this case, the static friction in the area between the end faces 10B and 11B of the claw elements 10A and 11A is reduced by reducing the closing force. At the same time, increasing the torque applied to the positive-locking switching element A or F leads to the static friction between the end faces 10B and 11B being overcome and the differential speed between the switching element halves 10 and 11 increasing to an extent that enables the positive connection between the claw elements 10A and 11A to be established.

[0054] In Fig. Figure 3d shows an operating state of the positive-locking switching element A or F, in which a positive connection with a so-called partial overlap of the claw elements 10A and 11A exists between the switching element halves 10 and 11. Such an operating state exists both during an opening process and during a closing process of the positive-locking switching element A or F.

[0055] The torque acting on switching element A or F and the friction coefficients of flanks 10C and 11C result in a static friction force acting between flanks 10C, 11C. If the actuating force acting on switching element halves 10 and 11 in the opening or closing direction of the positive-locking switching element A or F is too low in relation to the static friction force between flanks 10C and 11C of the claw elements 10A and 11A, so-called flank jamming occurs. During such flank jamming, the axial relative positioning movement between switching element halves 10 and 11 in the closing or opening direction is zero, thus preventing the requested operating state change of the positive-locking switching element A or F. In order to avoid or resolve such edge clamping, the actuating force applied to the switching element A or F can be increased and / or the force applied to the positive-locking switching element A or F can be increased.F the torque applied in each case must be reduced to the extent required.

[0056] The fully closed operating state of the positive switching element A or F is in Fig. 3e, in which the full overlap between the claw elements 10A and 11A is present in the axial direction x.

[0057] Fig. 4a to Fig. 4f each show a Fig. 3a shows a representation of the positive-locking switching element A or F. In the switching element A or F, the claw elements 10A and 11A of the switching element halves 10 and 11, which are arranged side by side in the circumferential direction of the switching element halves 10 and 11, each have a different length in the axial direction x. The longer claw elements are identified in more detail below by the reference symbols 10A1 and 11A1, respectively, and the shorter claw elements by the reference symbols 10A2 and 11A2, respectively.

[0058] This design of the positive-locking switching elements A and F offers the advantage that the positive locking between the switching element halves 10 and 11 can be achieved at higher differential speeds between the switching element halves 10 and 11 than in the Fig. 3a to Fig. 3e shown design of the positive switching elements A and F. In contrast, the design of the positive switching element A or F according to Fig. 4a to Fig. 4f compared to the design of the positive switching element A or F according to Fig. 3a to Fig. 3e has a lower robustness compared to ratchets.

[0059] Due to the different lengths of the claw elements 10A1, 10A2 as well as 11A1 and 11A2, the switching element A or F can be used in addition to the Fig. 3a to Fig. 3e described operating states of the positive switching element A or F have further operating states, which will be referred to in the following description. Fig. 4a to Fig. 4f will be discussed in more detail.

[0060] First of all, Fig. 4a again shows the fully open operating state of the switching element A or F. Fig. Figure 4b again shows the operating state of the positive-locking switching element A or F during ratcheting operation. During ratcheting operation, the switching element halves 10 and 11 slide against each other in the circumferential direction in the area of ​​the end faces 10B1 and 11B1 of the longer claw elements 10A1 and 11A1. As a result, the positive locking between the switching element halves 10 and 11 cannot be established. This ratcheting operation is again in the Fig. 3b can be avoided or stopped by reducing the differential speed between the switching element halves 10 and 11.

[0061] Furthermore, Fig. 4c and Fig. 4d each have a tooth-on-tooth position, which prevents the establishment of the positive connection between the switching element halves 10 and 11. In this case, Fig. 4c, the tooth-on-tooth position between the end faces 10B1 and 11B1 of the longer claw elements 10A1 and 11A1 is present. In contrast, the tooth-on-tooth position between the switching element halves 10 and 11 is present in the operating state of the positive switching element A or F shown in Fig. 4d, the operating state of the positive switching element A or F between the end faces 11B1 of the longer claw elements 11A1 of the switching element half 11 and the end faces 10B2 of the shorter claw elements 10A2 of the switching element half 10.

[0062] Irrespective of this, the respective tooth-to-tooth position between the switching element halves 10 and 11 is in the Fig. 3c can be resolved or avoided in the manner described.

[0063] Fig. 4e shows an intermediate operating state of the positive-locking switching element A or F between the fully open operating state and the fully closed operating state of the positive-locking switching element A or F. During this intermediate operating state, the edge clamping described in more detail above can again occur between the claw elements 10A1, 10A2 and the claw elements 11A1, 11A2. The edge clamping is again in the Fig. 3d described extent can be avoided or resolved in order to be able to open or close the positive switching element A or F to the requested extent.

[0064] The fully closed operating state of the positive switching element A or F is in Fig. 4f.

[0065] If a fault in one or both sensors is detected based on the signal from the sensor assigned to the positive-locking switching element A and / or the signal from the sensor assigned to the positive-locking switching element F, a test routine is started. The test routine determines the operating state of the switching element A or F, or of both switching elements A and F, as it existed before the fault in the sensor or sensors was detected. For the sake of clarity, the test routine is described in more detail below using only the positive-locking switching element A, since the operating state of the other positive-locking switching element F is tested in the same way as for the switching element A.

[0066] First, if a fault is detected in the sensor assigned to switching element A, the test routine checks whether the switching element half 10 was in an end position as required prior to the fault and was actuated with an actuating force acting in the direction of this end position. If the test is positive, the power flow in the gearbox 3 is maintained until the switching element half 10 is actuated from its current end position towards the other end position and / or the actuating force acting in the direction of its current end position is less than a threshold value. If the test result is negative, the power flow in the gearbox 3 is interrupted. For this purpose, all switching elements A to F are transferred to their open operating state in order to reliably prevent possible incorrect actuation of the gearbox 3.

[0067] If an electrical fault occurs in the sensor of switching element A, the logic of the test routine decides, depending on the situation, which information can be derived from the sensor signal and whether the transmission 3 should be fully opened for this reason. If the switching element half 10 is in one of the two end positions at the time the electrical fault in the sensor occurs, the switching element half 10 is additionally actuated in the direction of the corresponding end position and if the actuating force acting in the direction of the current end position is sufficiently large to hold the switching element half 10 in the end position, the transmission 3 will not be opened. The transmission 3 will only be fully opened if there is a request according to which the switching element half 10 is to be moved out of the current end position or if the actuating force applied to the switching element half 10 falls below a threshold value.

[0068] The latter event occurs, for example, when the hydraulic pump of the transmission 3, which provides the actuating pressure for the shift element A, is no longer supplied with sufficient torque by the drive engine 2. Reference symbol 1 vehicle powertrain 2 drive machine 3 gearboxes 4 downforce 5 Gearbox input shaft 6 Gearbox output shaft 7 torsion dampers 8 hydrodynamic torque converter 9 torque converter lock-up clutch 10, 11 Switching element half 10A, 10A1, 10A2 claw element 11A, 11A1, 11A2 claw element 10B, 10B1, 10B2 End face of the claw element 10C Flank of the claw element 11B, 11B1, 11B2 End face of the claw element 11C Flank of the claw element “1” to “9” gear ratio for forward drive A to F switching element P1 to P4 planetary gear set “R” gear ratio for reverse

Claims

[1] Method for operating a transmission (3) with at least one positive switching element (A, F), which has two switching element halves (10, 11), wherein at least one switching element half (10) is designed to be displaceable between two end positions and the switching element (A, F) is open in the first end position and closed in the second end position, and wherein the travel of the switching element half (10) is detected by means of a sensor and a power flow in the transmission (3) is interrupted if a fault in the sensor is detected, characterized by , that is checked if a sensor fault is detected, whether the switching element half (10) was in an end position as required before the fault and was actuated with an actuating force acting in the direction of this end position, wherein, if the test is positive, the power flow in the gear (3) is maintained until the switching element half (10) is actuated from the current end position in the direction of the other end position or the actuating force acting in the direction of the current end position is less than a threshold value. [2] Method according to claim 1, characterized by that a fault in the sensor is detected if a signal from the sensor has values ​​that lie outside a value range whose values ​​correspond to the entire travel range of the switching element half (10) between its end positions. [3] Method according to claim 1 or 2, characterized by that the sensor signal is a pulse width modulated signal. [4] Method according to one of claims 1 to 3, characterized by that the power flow in the gearbox (3) is interrupted if the sensor fault persists for longer than a predefined period of time. [5] Method according to one of claims 1 to 4, characterized by that the actuating force that can be applied to the switching element (A, F) corresponds to a hydraulic pressure that is made available by a hydraulic pump that can be driven by a drive motor (2) of a vehicle drive train (1), wherein the power flow in the transmission (3) is interrupted when the drive torque of the drive motor (2) is less than a threshold value. [6] Control unit for operating a transmission (3) with at least one positive switching element (A, F), which has two switching element halves (10, 11), wherein at least one switching element half (10) is designed to be displaceable between two end positions and the switching element (A, F) is open in the first end position and closed in the second end position, and wherein the travel of the switching element half (10) is detected by means of a sensor and a power flow in the transmission (3) is interrupted if a fault in the sensor is detected, characterized by , that the control unit is designed in such a way that if a fault in the sensor is detected, whether the switching element half (10) was in an end position as required before the fault and was actuated with an actuating force acting in the direction of this end position, wherein, if the test is positive, the power flow in the gear (3) is maintained until the switching element half (10) is actuated from the current end position in the direction of the other end position or the actuating force acting in the direction of the current end position is less than a threshold value. [7] Control device according to claim 6, characterized by that it carries out the method according to one of claims 1 to 5 on the control side. [8] Computer program product with program code means stored on a computer-readable data carrier in order to carry out all the steps of a method according to one of claims 1 to 5 when the computer program product is executed on a computer or on a corresponding computing unit, in particular a control device according to claim 6.

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