METHOD FOR OPERATING A DUAL CLUTCH TRANSMISSION OF A MOTOR VEHICLE AND MOTOR VEHICLE

Description

[0001] The invention relates to a method for operating a dual-clutch transmission of a motor vehicle according to the preamble of patent claim 1. Furthermore, the invention relates to a motor vehicle.

[0002] DE 10 2016 221 794 A1 discloses a motor vehicle transmission with a parking lock device comprising a transmission output shaft, a transmission housing and a transmission gear set which can be connected to the transmission output shaft or is connected to it in a torque-conducting manner.

[0003] DE 10 2007 019 241 A1 discloses a method for controlling an automated dual-clutch transmission. Furthermore, DE 199 50 696 A1 discloses a dual-clutch transmission for a motor vehicle, comprising a first transmission input shaft having a starting gear and connected to a first clutch, a second transmission input shaft having a driving gear and connected to a second clutch, and a common transmission output shaft.

[0004] Furthermore, DE 10 2011 108 013 A1 discloses a gear-tensioning method for testing a transmission having at least two partial transmissions.

[0005] Furthermore, EP 3 287 669 A1 discloses a method for controlling an automated drive train of a motor vehicle in order to immobilize the motor vehicle. The drive train has a transmission arrangement with a plurality of gear stages that can be shifted at least partially independently of one another. For immobilization, a gear stage pairing is engaged, which has a first pairing gear stage and a second pairing gear stage to block the drive train. For immobilization, a plurality of gear stage pairings are available, which are stored in a priority list.The method comprises the steps of first attempting to shift the first pairing gear of a gear pairing to be used and, depending on whether this attempt was successful, either attempting to shift the second pairing gear or attempting to shift a first pairing gear of a gear pairing following in the priority list.

[0006] Furthermore, DE 199 50 696 A1 discloses a dual-clutch transmission, in particular for a motor vehicle, comprising a first transmission input shaft having a starting gear and connected to a first clutch, a second transmission input shaft having a driving gear and connected to a second clutch, and a common transmission output shaft. At least one of the transmission input shafts is assigned multiple gears, and in a parking lock function, two gears assigned to one of the transmission input shafts can be engaged simultaneously.

[0007] The object of the present invention is to provide a method for operating a dual-clutch transmission and a motor vehicle with such a dual-clutch transmission, so that a parking lock of the dual-clutch transmission can be realized in a particularly advantageous manner.

[0008] This object is achieved according to the invention by a method having the features of patent claim 1 and by a motor vehicle having the features of patent claim 8. Advantageous embodiments with expedient further developments of the invention are specified in the remaining claims.

[0009] A first aspect of the invention relates to a method for operating a dual-clutch transmission of a motor vehicle, preferably designed as a motor vehicle, in particular as a passenger car. For example, at least one wheel of the motor vehicle can be driven via the dual-clutch transmission. In particular, at least or exactly two wheels of the motor vehicle can be driven via the dual-clutch transmission, whereby, for example, the motor vehicle as a whole can be driven. This means that the motor vehicle, in its fully manufactured state, has the dual-clutch transmission and the wheel or wheels, also referred to as the vehicle wheel. The respective wheel is, for example, a ground contact element, via which the motor vehicle is or can be supported downwards on a ground in the vertical direction of the vehicle.If the motor vehicle is driven along the ground while the vehicle is supported vertically downwards on the ground, the wheel will roll along the ground.

[0010] The dual-clutch transmission has a first sub-transmission and a second sub-transmission. The dual-clutch transmission also has a first clutch assigned to the first sub-transmission and a second clutch assigned to the second sub-transmission. For example, the motor vehicle has a drive motor by which the motor vehicle can be driven via the dual-clutch transmission. The drive motor comprises an output shaft, designed, for example, as a crankshaft. The feature that the first clutch is assigned to the first sub-transmission can be understood in particular to mean that the first sub-transmission, in particular a first transmission input shaft of the first sub-transmission, can be coupled to the output shaft in a torque-transmitting manner via the first clutch or by means of the first clutch, in particular while the second clutch is disengaged.The feature that the second clutch is assigned to the second partial transmission can be understood in particular to mean that the second partial transmission, in particular a second transmission input shaft of the second partial transmission, can be coupled to the output shaft in a torque-transmitting manner via the second clutch or by means of the second clutch, in particular while the first clutch is disengaged. Thus, for example, the motor vehicle can be driven by the drive engine via the dual-clutch transmission and in particular via the first partial transmission, while driving of the motor vehicle by the drive engine via the second partial transmission is omitted. Furthermore, the motor vehicle can be driven by the drive engine via the dual-clutch transmission and thereby via the second partial transmission, while driving of the motor vehicle by the drive engine via the first partial transmission is omitted.The respective clutch is preferably designed as a friction clutch, in particular as a multi-plate clutch, which allows for particularly high levels of comfort, particularly driving comfort, of the motor vehicle. In the method, the dual-clutch transmission is switched to a parking lock state, which will be explained in more detail below.

[0011] Through or in the parking lock state, a parking lock, in particular a mechanical one, of the dual-clutch transmission is implemented, activated, or engaged. The parking lock clamps the dual-clutch transmission, in particular in such a way that the aforementioned wheels are secured against rotation. In particular, the engaged or activated parking lock secures or is to be secured against unwanted rolling away, particularly when the motor vehicle is parked, for example, on a slope or downhill gradient.

[0012] In order to be able to implement the parking lock particularly advantageously and, in particular, to engage it particularly safely, the invention provides that the dual-clutch transmission is shifted in the parking lock state through the following steps, i.e. by means of the following steps. In a first of the steps, while a first gear of one of the sub-transmissions is engaged, a first engagement process is carried out for engaging a second gear of one of the sub-transmissions. During the engagement process, for example, at least one actuator is controlled and thereby operated, in particular with the basic aim of moving, for example, a shift element, also referred to as a gear selector, and assigned to the second gear.

[0013] In a second step, it is determined that, despite the engagement process being performed, second gear is not engaged or has not been engaged. In other words, in the second step, it is determined that, despite the engagement process being performed, second gear was not engaged or the fundamentally desired engagement of second gear was prevented. In other words, in the second step, it is determined or recognized that the engagement process was unsuccessful with regard to engaging second gear.This means that, within the scope of the invention, the engagement process per se or the execution of the engagement process per se does not necessarily mean that the execution of the engagement process per se leads to the engagement of second gear, but in particular, within the scope of the invention, the engagement process or the execution of the engagement process per se is to be understood as an attempt or an attempt being made to engage second gear. However, the engagement of second gear can be prevented or omitted, for example, if the previously described activation of the actuator does not result in a movement of the gear selector intended or required for engaging second gear, or if a movement of the gear selector caused by the activation of the actuator does occur but does not result in the actual engagement of second gear.This is determined, in particular detected or recognized, in the second step, for example. For example, in the second step it is determined that the second gear is not engaged despite the engagement process being carried out by detecting at least one position of the gear selector using at least one position sensor. For example, the second gear is engaged when the gear selector is in an engagement position. In other words, the second gear is engaged, for example, by the gear selector being moved or being moved into the engagement position, in particular by means of the actuator and in particular by controlling the actuator. For example, the position of the gear selector detected by means of the position sensor is compared with the engagement position.If the comparison shows that the current or actual position of the gear selector detected by the position sensor deviates from the engagement position, it can be concluded that, despite the engagement process being carried out, the gear selector did not move into the engagement position and thus the second gear was not engaged, i.e., it did not occur.

[0014] In a third of the steps of the method, a third gear of the dual-clutch transmission that is different from the first gear and the second gear is selected, in particular depending on the fact that it is determined in the second step that, despite the engagement process being carried out, the second gear is not engaged. In a fourth of the steps, the selected third gear is engaged, so that in the parking lock state, the first gear and the third gear are at least temporarily engaged simultaneously. As a result, the dual-clutch transmission is tensioned or the dual-clutch transmission can be tensioned as a result, as a result of which the parking lock, in particular a mechanical parking lock, is engaged or activated. It is preferably provided that in the parking lock state, both clutches are disengaged simultaneously, in particular while the first gear and the third gear are engaged simultaneously.Preferably, the second gear and the third gear, also known as the alternative gear, are gears of the same partial transmission.

[0015] The parking lock state, in which, for example, first gear and third gear are engaged simultaneously, allows a mechanical parking lock to be implemented without the need for an additional mechanical parking lock. The parking lock is preferably engaged when the motor vehicle is stationary in order to secure the motor vehicle against rolling away, particularly independently of a locking device, also known as a parking brake. In particular, when the motor vehicle is parked on an uphill or downhill gradient and the parking lock is engaged, the dual-clutch transmission is tensioned by the motor vehicle's own weight and by a downhill force resulting from the motor vehicle's own weight and acting on the motor vehicle, particularly in the vehicle's longitudinal direction.In particular, the downhill force can result in a downhill torque, which is introduced into the dual-clutch transmission, for example, via a transmission output shaft of the dual-clutch transmission. For example, to deactivate or disengage the parking lock, i.e., to terminate the parking lock state, one of the gears simultaneously engaged in the parking lock state is disengaged, in particular while the other of the gears simultaneously engaged in the parking lock state remains engaged.

[0016] The gear selector provided for engaging second gear is, for example, a gear selector for positively engaging second gear. The gear selector is, for example, movable, in particular relative to a housing of the dual-clutch transmission, in order to thereby move, for example, a shifting element, in particular a positive-locking one. For example, the shifting element, which is in particular formed separately from the gear selector, is movable, in particular translationally, relative to the housing in order to thereby engage second gear. The shifting element can, for example, be a shift sleeve. In particular, it is conceivable for the shifting element to have a first toothing. The shifting element is, for example, connected in a rotationally fixed manner to a transmission shaft of the dual-clutch transmission, also simply referred to as a transmission, wherein the shifting element is movable, in particular translationally, relative to the housing and relative to the transmission shaft.

[0017] To actually engage second gear, for example, the gear selector is moved in such a way that the shifting element is moved in such a way that the first toothing engages and thus interacts positively with a corresponding second toothing, which is provided, for example, on a gearwheel of the second gear. The aim of the engagement process is fundamentally to connect the gearwheel to the transmission shaft in a rotationally fixed manner using the toothing and the shifting element. This is because when second gear is engaged, the gearwheel is rotatable relative to the transmission shaft and is therefore not rotationally fixedly connected to the transmission shaft but rather rotatably mounted on the transmission shaft.

[0018] In this case, engagement of the second gear can be prevented by a so-called tooth-on-tooth position. The tooth-on-tooth position can be understood in particular to mean that at least one first tooth of the first toothing is overlapped or covered in the direction of movement of the gear selector by at least one tooth of the second toothing, wherein the gear selector has to be moved or is moved in the direction of movement in order to engage the second gear. Because the tooth of the first toothing is overlapped or covered in the direction of movement by the tooth of the second toothing, the tooth of the first toothing is in support contact with the tooth of the second toothing along the direction of movement or the tooth of the first toothing comes into support contact with the tooth of the second toothing along the direction of movement, in particular when the gear selector is moved a short distance and in the process is moved towards the engagement position.However, the tooth-on-tooth position prevents the gear selector from fully moving into the engaged position. Such a tooth-on-tooth position is statistically rather unlikely, but certainly possible. In other words, the engagement of second gear can be prevented due to a statistically possible geometric position of the gear selector, with the aforementioned tooth-on-tooth position, for example, being one such statistically possible geometric position of the gear selector.

[0019] For example, the engagement process or reaching the engagement position does not necessarily have to be prevented by a tooth-on-tooth alignment. Rather, even if there is no tooth-on-tooth alignment, there may be insufficient backlash and thus insufficient rotational travel, especially of the gear, so that second gear cannot be engaged. This may be the case because the goal of modern transmissions is usually to avoid excessive backlash and thus excessive noises such as rattling.

[0020] The method according to the invention now makes it possible to bring about the parking lock state, or to engage the parking lock safely, even when engaging second gear is not possible and thus prevented, particularly due to a statistically possible geometric position of the parking actuator. Consequently, the method according to the invention makes it possible to particularly advantageously secure the motor vehicle against undesired rolling away, thus ensuring particularly safe operation.

[0021] In particular, it can be provided that after performing the engagement process or after the engagement process has ended, the shift lever is moved into a neutral position and, for example, is moved in a further movement direction opposite to the movement direction, whereupon, for example, finally the third gear is engaged. Overall, it can be seen that engaging the parking lock, that is, shifting the dual-clutch transmission into the parking lock state, is possible in at least almost all geometric positions of the shift lever. This can be done, for example, starting from conventional transmissions without further component adaptations, since the method according to the invention can be implemented, for example, by components that are already present and in particular via an existing actuator control.Preferably, the dual-clutch transmission is an automatic transmission, i.e., an automated or automatic dual-clutch transmission, so that, for example, the engagement process and the engagement of the respective gear are performed automatically, in particular by means of an electronic computing device. Thus, for example, it is provided that the steps are performed by means of an electronic computing device of the dual-clutch transmission, in particular of the motor vehicle, and in doing so, it is determined, in particular, that despite the engagement process, the second gear is not engaged.

[0022] The aforementioned first gear may, but does not necessarily have to, be a starting gear or the forward gear with the highest gear ratio of the dual-clutch transmission, and accordingly, the aforementioned second or third gears do not necessarily have to be the forward gear with the second or third highest gear ratios. Rather, the first, second, and third gears can be any gears, in particular forward gears, of the dual-clutch transmission, in particular of the same sub-transmission.

[0023] It is provided that after the third gear is engaged, the third gear is disengaged and the second gear is engaged, in particular while the first gear remains engaged. This method is based on the knowledge that, for example, engaging the third gear or as a result of the engagement of the third gear causes such a movement of the gear selector assigned to the second gear that the gear selector is moved, for example, out of the previously described position preventing the engagement of the second gear and into a position in which the second gear can actually be engaged. If the second gear is then engaged, for example by repeating the engagement process, the parking lock can subsequently be engaged particularly securely. It is preferably provided that, for example, the second gear is engaged first and then the third gear is disengaged, or vice versa.Preferably, the first gear and the second gear are then engaged simultaneously in the parking lock state, in particular while all other gears of the dual-clutch transmission are disengaged or while at least or exactly one gear of the other partial transmission is engaged.

[0024] Furthermore, it is conceivable that, particularly after engaging third gear, first gear is disengaged and a fourth gear of the dual-clutch transmission is engaged, which is different from first gear, second gear, and third gear, so that third gear and fourth gear are engaged simultaneously in the parking lock state. This makes it possible, for example, to secure the motor vehicle particularly securely against unwanted rolling away. Third gear and fourth gear are preferably gears of the same sub-transmission. In particular, it can be provided that one sub-transmission or the other sub-transmission can be used selectively or as needed to effect the parking lock.

[0025] In order to be able to activate or engage the parking lock particularly reliably, one embodiment of the invention provides for the third gear to be a gear of the first sub-transmission. Thus, in the parking lock state, the first gear and the third gear of one sub-transmission are at least temporarily engaged simultaneously, so that one sub-transmission is also referred to as a locked sub-transmission. Preferably, the first gear and the third gear are at least temporarily engaged simultaneously in the parking lock state, while preferably all gears of the other sub-transmission are disengaged, or while at least or exactly one gear is engaged in the other sub-transmission. Thus, the other sub-transmission is, for example, a so-called unlocked sub-transmission.

[0026] It has also proven advantageous if the third gear is a gear of the second sub-transmission. This also allows the parking lock state to be activated particularly reliably.

[0027] A further embodiment is characterized in that, in the parking lock state, first gear is engaged by a first gearwheel of the first gear, designed as an idler gear and rotatably arranged on a first shaft of the dual-clutch transmission, being rotationally fixedly connected to the first shaft by means of a first shifting element assigned to the first gear, arranged on the first shaft, and connected in a rotationally fixed manner to the first shaft. Third gear is engaged, for example, in such a way that a second gearwheel of the third gear, designed as an idler gear and rotatably arranged on a second shaft of the dual-clutch transmission, is rotationally fixedly connected to the second shaft by means of a second shifting element assigned to the third gear, arranged on the second shaft, and connected in a rotationally fixed manner to the second shaft.This makes it particularly advantageous to ensure or engage the parking lock when second gear cannot be engaged.

[0028] In order to be able to engage the parking lock particularly safely and thus to secure the motor vehicle particularly safely against unwanted rolling away, it is provided in a further embodiment of the invention that the respective switching element is a positive-locking switching element, in particular a claw clutch.

[0029] It has also proven particularly advantageous if, in the parking lock state, at least one of the clutches, or both clutches, are engaged simultaneously. Preferably, one of the clutches is engaged while the other clutch is disengaged. This allows the parking lock to be securely held engaged.

[0030] A further embodiment is characterized in that the method is carried out when the motor vehicle is stationary.

[0031] A second aspect of the invention relates to a motor vehicle, preferably designed as a motor vehicle, in particular as a passenger car, which is designed to carry out a method according to the first aspect of the invention. Advantages and advantageous embodiments of the first aspect of the invention are to be regarded as advantages and advantageous embodiments of the second aspect of the invention, and vice versa.

[0032] The invention also includes further developments of the motor vehicle according to the invention that have features already described in connection with the further developments of the method according to the invention. For this reason, the corresponding further developments of the motor vehicle according to the invention are not described again here. The motor vehicle according to the invention is preferably designed as a motor vehicle, in particular as a passenger car or truck, or as a passenger bus or motorcycle. The invention also encompasses combinations of the features of the described embodiments.

[0033] An exemplary embodiment of the invention is described below. The single figure shows a schematic representation of a dual-clutch transmission of a motor vehicle, wherein the dual-clutch transmission is operated according to a method according to the invention.

[0034] The exemplary embodiment explained below is a preferred embodiment of the invention. In the exemplary embodiment, the described components of the embodiment each represent individual features of the invention that can be considered independently of one another, each of which also develops the invention independently of one another. Therefore, the disclosure is intended to encompass combinations of the features of the embodiment other than those shown. Furthermore, the described embodiment can also be supplemented by further features of the invention already described.

[0035] The single figure shows a schematic representation of a dual-clutch transmission 10 of a motor vehicle, which is preferably designed as a motor vehicle or preferably as a passenger car. The motor vehicle has at least one drive motor, by means of which at least two wheels of the motor vehicle can be driven via the dual-clutch transmission 10. By driving the wheels, the motor vehicle as a whole can be driven or is driven. The wheels are ground contact elements by means of which the motor vehicle can be or is supported on a ground in the vertical direction of the vehicle downwards. The wheels, also referred to as vehicle wheels, roll on the ground when the motor vehicle is driven along the ground, while the motor vehicle is supported on the ground via the wheels in the vertical direction of the vehicle downwards. The drive motor is shown particularly schematically in the figure and designated 12 there.The drive motor 12 can be an internal combustion engine, for example, designed as a reciprocating piston engine, or an electric motor. The drive motor 12 has an output shaft 14, for example, designed as a crankshaft.

[0036] The dual-clutch transmission 10 has a first sub-transmission 16, which, for example, comprises three first gears 18a-c. In addition, the first sub-transmission 16 has a first transmission input shaft 20. The dual-clutch transmission 10 further comprises a second sub-transmission 22, which has a second transmission input shaft 24 and second gears 26a-c. The gears 18a-c are, for example, odd gears or are also referred to as odd gears, wherein, for example, gear 18a can be the so-called first gear, gear 18b the so-called third gear, and gear 18c the so-called fifth gear of the dual-clutch transmission 10. The gears 26a-c are, for example, also referred to as even gears or are so-called even gears of the dual-clutch transmission 10, wherein, for example, gear 26a can be the second gear, gear 26b the fourth gear, and gear 26c the sixth gear of the dual-clutch transmission 10.Gears 18a-c and 26a-c can also be designated as forward gears for driving the motor vehicle forward, or at least one or exactly one of gears 18a-c and 26a-c can be a reverse gear for driving the motor vehicle backward. The first gear is a forward starting gear, by means of which the motor vehicle can be driven forward. The reverse gear is a reverse starting gear, by means of which the motor vehicle can be driven backward.

[0037] The dual-clutch transmission 10 has a first clutch 28 assigned to the sub-transmission 16, which, for example, with respect to the sub-transmissions 16 and 22, in particular with respect to the transmission input shafts 20 and 24, is assigned exclusively to the sub-transmission 16 or exclusively to the transmission input shaft 20, but not to the sub-transmission 22 or not to the transmission input shaft 24. The dual-clutch transmission 10 further comprises a second clutch 30 assigned to the sub-transmission 22, which, for example, with respect to the sub-transmissions 16 and 20, in particular with respect to the transmission input shafts 20 and 24, is assigned exclusively to the sub-transmission 22 or exclusively to the transmission input shaft 24, but not to the sub-transmission 16 or not to the transmission input shaft 20.This means that, with respect to the transmission input shafts 20 and 24, only the transmission input shaft 20 can be connected to the output shaft 14 in a torque-transmitting manner by means of the clutch 28. With respect to the transmission input shafts 20 and 24, only the transmission input shaft 24 can be connected or coupled to the output shaft 14 in a torque-transmitting manner by means of the clutch 30. Furthermore, the transmission input shaft 24 is designed as a hollow shaft, which in this case is at least partially, in particular at least predominantly or completely, penetrated by the transmission input shaft 20, which is designed, for example, as a solid shaft. The respective sub-transmission 16 or 22 also has a side shaft 32 or 34. The dual-clutch transmission 10 has a transmission output shaft 36 which is common to the sub-transmissions 16 and 20, in particular the side shafts 32 and 34, and which can be driven by the side shafts 32 and 34.

[0038] The drive motor 12 can provide at least one drive torque via its output shaft 14, which can be introduced into the sub-transmission 16 or 22 via the respective clutch 28 or 30 and transmitted therefrom to the transmission output shaft 36. In this way, the aforementioned wheels can be driven by the drive motor 12 via the dual-clutch transmission 10. Preferably, the clutch 30 is disengaged when the clutch 28 is engaged. Furthermore, it is provided, for example, that the clutch 28 is disengaged when the clutch 30 is engaged. Thus, preferably only one of the sub-transmissions 16 and 20 is always connected to the output shaft 14 via the respective clutch 28 or 30 in a torque-transmitting manner.

[0039] A method for operating the dual-clutch transmission 10 is described below. In the method, the dual-clutch transmission 10 is switched to a parking lock state, so that in the method, the dual-clutch transmission 10 is at least temporarily in the parking lock state.

[0040] In order to be able to engage the parking lock state and thus a mechanical parking lock particularly securely, by means of which, for example, the aforementioned wheels can be secured against rotation and thereby the motor vehicle can be secured against unwanted rolling away, the dual clutch transmission 10 is shifted into the parking lock state by the following steps. In a first of the steps, while, for example, gear 18a of the partial transmission 16 is engaged, an engagement process provided for engaging, for example, gear 18b is carried out. In a second of the steps, it is determined that, despite carrying out the engagement process, the engagement of the second gear 18b fails to occur or does not take place.In a third of the steps, for example, gear 18c is selected, and in a fourth of the steps, the selected gear 18c is engaged, so that in the parking lock state, gear 18a and gear 18c are at least temporarily engaged simultaneously. It can be seen that the gears 18a and 18c, which are at least temporarily engaged simultaneously in the parking lock state, are gears of the same sub-transmission 16.

[0041] In the parking lock state, gear 18a is preferably engaged by a first gear 38 of gear 18a, designed as a loose wheel and rotatably arranged on the side shaft 32 of the dual-clutch transmission 10, in particular of the sub-transmission 16, being connected in a rotationally fixed manner to the side shaft 32 by means of a first shift element 40 assigned to the first gear 18a, arranged on the side shaft 32, and connected in a rotationally fixed manner to the side shaft 32. The shift element 40 is a shift sleeve. The gear 18c is preferably engaged by a second gear 42 of the gear 18c, which is designed as a loose wheel and is rotatably arranged on the transmission input shaft 20 of the dual-clutch transmission 10, in particular of the sub-transmission 16, being connected in a rotationally fixed manner to the transmission input shaft 20 by means of a second shift element 44 assigned to the gear 18c, which is arranged on the transmission input shaft 20 and is connected in a rotationally fixed manner to the transmission input shaft 20.The shifting element 44 is preferably a second shift sleeve. The shifting elements 40 and 44 are gear selectors, in particular positive-locking gear selectors, which are moved into a respective engagement position to engage the gears 18a and 18c. As a result, the shifting element 40 is positively connected to the gearwheel 38 and the shifting element 44 is positively connected to the gearwheel 42, so that the gearwheel 38 is positively connected to the side shaft 32 via the shifting element 40 and the gearwheel 42 is positively connected to the transmission input shaft 20 via the shifting element 44. The side shaft 32 and the transmission input shaft 20 are respective shafts of the dual-clutch transmission 10, in particular of the sub-transmission 16, which are different from one another and formed separately from one another. The shafts are arranged off-axis with respect to one another and run at least substantially parallel to one another.In addition, the respective shifting element 40 or 44 is a positive-locking shifting element, in particular a claw clutch, by means of which the respective gearwheel 38 or 42 can be connected or is connected in a positive-locking, rotationally fixed manner to the side shaft 32 or to the transmission input shaft 20.

[0042] In principle, it is conceivable that after gear 18c is engaged, gear 18c is disengaged and, for example, gear 18b is engaged, in particular while gear 18a remains engaged, so that in the parking lock state, gears 18a and 18b are engaged simultaneously, at least temporarily. Furthermore, it is conceivable that, in particular after gear 18c is engaged, first gear 18a is disengaged and a fourth gear of the dual-clutch transmission 10 that is different from gear 18a, gear 18b, and gear 18c is engaged, so that in the parking lock state, for example, gear 18c or gear 18b and the fourth gear are at least temporarily engaged simultaneously. The fourth gear is, for example, one of the gears 26a-c and thus a gear of the sub-transmission 22 or a gear of the sub-transmission 16.

[0043] Overall, it can be seen that the parking lock state can be safely activated even if engagement of gear 18b, which is actually intended as a locking gear, is not possible, for example due to an unforeseen event such as an unfavorable location or position of a gear selector assigned to gear 18b. Then, instead of the actually intended locking gear, gear 18c is engaged, for example, at least temporarily, in order to tension the dual-clutch transmission 10, in particular the sub-transmission 16. This tensioning activates or engages a mechanical parking lock, which can secure the motor vehicle against unwanted rolling away.

Claims

1. Method for operating a dual clutch transmission (10) of a motor vehicle, having first sub-transmission (16), a second sub-transmission (22), a first clutch (28) assigned to the first sub-transmission (16), and a second clutch (30) assigned to the second sub-transmission (22), wherein the dual clutch transmission (10) is shifted to a parking lock state, characterized in that the dual clutch transmission (10) is shifted to the parking lock state by the following steps: - while a first gear (18a) of one of the sub-transmissions (16, 20) is engaged: carrying out an engagement procedure provided for engaging a second gear (18b) of the one sub-transmission (16); - determining that the engagement of the second gear (18b) does not happen, despite carrying out the engagement procedure; - selecting a third gear (18c) of the dual clutch transmission (10), different from the first gear (18a) and from the second gear (18b); and - engaging the selected third gear (18c) such that, in the parking lock state, the first gear (18a) and the third gear (18c) are temporarily engaged simultaneously, wherein: ∘ after the third gear (18c) has been engaged, the third gear (18c) is disengaged and the second gear (18b) is engaged, while the first gear (18a) remains engaged, or ∘ after the third gear (18c) has been engaged, the first gear (18a) is disengaged and a fourth gear (26a-c) of the dual clutch transmission (10), different from the first gear (18a), the second gear (18b) and the third gear (18c), is engaged such that, in the parking lock state, the third gear (18c) and the fourth gear (26a-c) are engaged simultaneously.

2. Method according to Claim 1, characterized in that the third gear (18c) is a gear of the first sub-transmission (16).

3. Method according to Claim 1, characterized in that the third gear (18c) is a gear of the second sub-transmission (20).

4. Method according to one of the preceding claims, characterized in that in the parking lock state, the first gear (18a) is engaged in that a first gearwheel (38) of the first gear (18a), which is designed as an idler gearwheel and is rotatably disposed on a first shaft (32) of the dual clutch transmission (10), is co-rotationally connected to the first shaft (32) by means of a first shifting element (40) which is assigned to the first gear (18a), is disposed on the first shaft (32) and co-rotationally connected to the first shaft (32), wherein the third gear (18c) is engaged in that a second gearwheel (42) of the third gear (18c), which is designed as an idler gearwheel and is rotatably disposed on a second shaft (20) of the dual clutch transmission (10), is co-rotationally connected to the second shaft (20) by means of a second shifting element (44) which is assigned to the third gear (18c), is disposed on the second shaft (20) and co-rotationally connected to the second shaft (20).

5. Method according to Claim 4, characterized in that the respective shifting element (40, 44) is a form-fitting shifting element.

6. Method according to one of the preceding claims, characterized in that in the parking lock state, at least or exactly one of the clutches (28, 30) is closed, or both clutches (28, 30) are closed simultaneously.

7. Method according to one of the preceding claims, characterized in that the method is carried out when the motor vehicle is stationary.

8. Motor vehicle having a dual clutch transmission (10) which is designed to carry out a method according to one of the preceding claims.