Emergency braking of a motor vehicle using a dual-clutch transmission

Abstract

Method for emergency braking of a motor vehicle (50) by means of a dual-clutch transmission (56) of a powertrain (52) of the motor vehicle (50), wherein the dual-clutch transmission (56) comprises a first actuable clutch unit (24) and a second clutch unit (26) actuable independently of the first clutch unit (24), as well as two sub-transmissions (28, 30), wherein each of the clutch units (24, 26) is coupled on one side to each of the sub-transmissions (28, 30) and on the other side to an input shaft (20) of the dual-clutch transmission (56) in order to couple the input shaft (20) to the respective of the sub-transmissions (28, 30) depending on a respective clutch state, and the sub-transmissions (28, 30) are coupled on the output side to an output shaft (22) of the dual-clutch transmission (56), wherein the method for providing a redundant braking system comprises the steps: - Receiving an emergency signal to trigger emergency braking outside of a standstill of the motor vehicle (50) when the motor vehicle is in use in its intended operation, - Deactivating a drive unit (58) of the powertrain (52) which has a drive unit shaft (54) coupled to the input shaft (20) of the dual clutch transmission (56), - Activating the first and second clutch units (24, 26) to establish at least partial coupling between the input shaft (20) and the respective sub-transmission (28, 30) by means of the respective clutch units (24, 26), wherein at least one of the clutch units (24, 26) provides clutch slip, characterized in that - at least one change in rotational speed and / or at least one wheel slip of at least one wheel (40) of the motor vehicle (50) driven by means of the drive train (52) via the output shaft (22) is detected, and - a torque of the output shaft (22) is reduced by means of the first and / or the second clutch unit (24, 26) depending on at least one detected speed change and / or at least one detected wheel slip.

Description

[0001] The invention relates to a method for emergency braking of a motor vehicle by means of a dual-clutch transmission of a drive train of the motor vehicle, wherein the dual-clutch transmission has a first actuatable clutch unit and a second clutch unit that can be actuated independently of the first clutch unit, as well as two sub-transmissions, wherein a respective one of the clutch units is coupled on the one hand to a respective one of the sub-transmissions and on the other hand to an input shaft of the dual-clutch transmission in order to couple the input shaft to the respective one of the sub-transmissions depending on a respective clutch state, and the sub-transmissions are coupled on the output side to an output shaft of the dual-clutch transmission, wherein the method comprises the steps of: receiving an emergency signal for triggering the emergency braking when the motor vehicle is not at a standstill, deactivating a drive unit of the drive train that has a drive unit shaft,which is coupled to the input shaft of the dual-clutch transmission, and activating the first and second clutch units to at least partially establish a coupling between the input shaft and the respective sub-transmission by means of the respective clutch unit, wherein at least one of the clutch units provides clutch slip. The invention further relates to a control device for emergency braking of a motor vehicle by means of a dual-clutch transmission of a drive train of the motor vehicle, wherein the dual-clutch transmission has a first actuatable clutch unit and a second clutch unit actuatable independently of the first clutch unit, as well as two sub-transmissions, wherein each of the clutch units is coupled, on the one hand, to a respective one of the sub-transmissions and, on the other hand, to an input shaft of the dual-clutch transmission.to couple the input shaft to the respective sub-transmission depending on a respective clutch state, and the sub-transmissions are coupled on the output side to an output shaft of the dual-clutch transmission, wherein the control device is designed to receive an emergency signal for triggering emergency braking when the motor vehicle is not at a standstill, to deactivate a drive unit of the drive train, which has a drive unit shaft coupled to the input shaft of the dual-clutch transmission, and to activate the first and second clutch units in order to at least partially establish a coupling between the input shaft and the respective sub-transmission by means of the respective clutch unit, wherein at least one of the clutch units provides clutch slip. Finally, the invention also relates to a motor vehicle with a drive train,which has a drive unit with a drive shaft and a dual-clutch transmission with an input shaft coupled to the drive shaft, and with at least one wheel of the motor vehicle that can be driven by means of the drive train via an output shaft of the dual-clutch transmission, wherein the dual-clutch transmission has a first actuatable clutch unit and a second clutch unit that can be actuated independently of the first clutch unit, as well as two sub-transmissions, wherein a respective one of the clutch units is coupled on the one hand to a respective one of the sub-transmissions and on the other hand to the input shaft of the dual-clutch transmission in order to couple the input shaft to the respective one of the sub-transmissions depending on a respective clutch state, and the sub-transmissions are coupled on the output side to the output shaft of the dual-clutch transmission, and with a control device for emergency braking of the motor vehicle by means of the dual-clutch transmission.

[0002] Methods of the generic type, generic control devices, and generic motor vehicles are extensively known in the prior art, so that separate written documentation is not required. The motor vehicle generally has a drive train by means of which at least one wheel of the motor vehicle can be driven during normal driving operation. For this purpose, the drive train comprises, in addition to the drive unit, which can be formed, for example, by an internal combustion engine, an electric motor, and / or the like, a dual-clutch transmission having an input shaft coupled to a drive shaft of the drive unit in order to be able to transmit a torque provided by the drive unit to the dual-clutch transmission.The dual-clutch transmission also has an output shaft, via which a torque can be provided depending on a gear ratio. The output shaft is coupled to the driven wheel of the motor vehicle, so that the desired drive function can be achieved. Two-track motor vehicles typically have at least one axle with at least two wheels, which are arranged at a distance from one another transversely to the direction of travel of the motor vehicle and which are jointly driven by the drive train.

[0003] In addition to providing a force that maintains normal driving operation, the drive unit can generally also decelerate the motor vehicle. However, the torque achievable in this way proves to be limited, particularly when the drive unit is designed as an internal combustion engine, so that the braking effect achievable in this way is insufficient for emergency braking. This does not allow the motor vehicle to be brought to a standstill in the desired short time and / or with the desired short braking distance. During normal operation of the motor vehicle, this function is therefore generally performed by a service brake device, which can be implemented, for example, using hydraulic brakes or the like.

[0004] If a malfunction occurs in a motor vehicle, for example with regard to the service brake system, there is a need for additional safety functionality or redundancy with regard to braking. This is particularly relevant if the motor vehicle is at least partially automated, for example using a driver assistance system or the like. However, even in braking systems implemented using X-by-Wire, a malfunction can lead to the failure of the service brake system. In order to improve safety when using the motor vehicle for its intended purpose, it is therefore desirable to be able to provide redundant braking functionality, particularly in the event of emergency braking. The prior art can provide for the installation of a separate, independent braking device for this purpose. However, this is associated with considerable effort and expense.

[0005] From EP 1 658 454 B1, it is known to bring a motor vehicle to a standstill in an emergency braking situation using a transmission via a defined switching of trigger switching elements. A torque is to be determined as a function of a brake pedal actuation force or an ACC radar sensor in conjunction with an actual vehicle deceleration. In this context, DE 10 2013 102 706 A1 discloses that a dual-clutch transmission can be used to brake the motor vehicle by mutually clamping the corresponding clutches when gears of the respective sub-transmissions are engaged. DE 10 2014 016 470 A1 uses this clamping to brake the motor vehicle if the service brake system is defective. Furthermore, DE 10 2008 045 627 A1 discloses a method for controlling a dual-clutch transmission. Finally, DE 10 2012 212 282 A1 discloses a method for braking a motor vehicle with a dual-clutch transmission.

[0006] Even though this state-of-the-art technology has proven itself, it does have its drawbacks. Using a dual-clutch transmission to brake the vehicle can result in a significant braking effect, which can lead to at least one driven wheel locking or experiencing significant slippage relative to the road surface. This results in disadvantages in terms of braking distance and / or vehicle steerability.

[0007] The invention is therefore based on the object of developing a generic method, a generic control device and a generic motor vehicle in such a way that the shortest possible braking distance and / or steerability can be achieved during emergency braking.

[0008] As a solution, the invention proposes a method, a control device and a motor vehicle according to the independent claims.

[0009] Further advantageous developments arise from features of the dependent claims.

[0010] With regard to a generic method, the invention proposes in particular that at least one speed jump and / or at least one wheel slip of at least one wheel of the motor vehicle driven by the drive train via the output shaft is detected, and a torque of the output shaft is reduced by means of the first and / or the second clutch unit depending on the at least one detected speed jump and / or at least one detected wheel slip.

[0011] With regard to a generic control device, the invention proposes in particular that the control device is further designed to detect at least one speed jump and / or at least one wheel slip of at least one wheel of the motor vehicle that can be driven by the drive train via the output shaft, and to reduce a torque of the output shaft by means of the first and / or the second clutch unit depending on the at least one detected speed jump and / or at least one detected wheel slip.

[0012] With regard to a generic motor vehicle, the invention proposes in particular that the control device is designed according to the invention.

[0013] The invention utilizes, among other things, the idea that the braking effect achievable by means of the dual-clutch transmission can be varied by simultaneously actuating the clutch units of the dual-clutch transmission. At least one of the clutch units can be operated with a variable clutch state. This means that in addition to a disengaged clutch state in which the coupling is interrupted, and an engaged clutch state in which the coupling is fully established, an intermediate state can be set in which clutch engagement is only partial, resulting in clutch slip. This clutch slip can preferably be adjusted. As a result, a torque transmitted via the respective clutch unit can also be adjusted. This allows the braking effect that can be achieved in this way to be adjusted as needed during a respective braking operation.

[0014] In this case, it can advantageously be taken into account that the braking effect should be selected to be as great as possible in order to keep the braking distance as short as possible. At the same time, however, the aim should be to prevent locking of the driven wheel as far as possible and / or to ensure that wheel slip does not exceed a predetermined comparison value. This makes it possible to achieve a short braking distance on the one hand and steerability during braking on the other. In particular, the locking of the driven wheel that occurs in the prior art can be detected and largely avoided with the invention. Furthermore, it can also be achieved that excessive wheel slip can lead to the vehicle no longer being braked optimally and / or no longer being able to be steered sufficiently.

[0015] The invention therefore makes it possible to provide a redundant braking system that can be actuated independently of a service brake system. This also allows for the fulfillment of special safety requirements, such as those specified by ISO 26262. Overall, this improves safety when driving a motor vehicle, particularly with regard to emergency braking.

[0016] To ensure the desired effect of the dual-clutch transmission, it is preferably provided that at least one gear is engaged in each of the sub-transmissions, i.e., a mechanical coupling is established between the output shaft of the dual-clutch transmission and the respective clutch unit assigned to the sub-transmission. However, at least provision can be made for the emergency signal to engage a correspondingly suitable gear in the sub-transmissions, especially if no gear is engaged.

[0017] The clutch unit can have a dry clutch or a hydraulic clutch or the like. Activating the clutch unit, for the purposes of this disclosure, means that the clutch transmits a torque between elements connected to it, for example, shafts or the like. Activating the clutch therefore encompasses not only the clutch state in which a torque is transmitted essentially completely, but also a partially coupled clutch state in which only a portion of the torque is transmitted. These are thus engaged clutch states. In contrast, in a disengaged clutch state, torque transmission through the clutch unit is interrupted.

[0018] Deactivating the drive unit means that the drive unit no longer provides any torque that serves to propel the motor vehicle. Preferably, the drive unit provides no torque or a torque that serves to decelerate the motor vehicle, for example, assisting it, or the like. For this purpose, an internal combustion engine as the drive unit can deactivate the ignition and / or interrupt the fuel supply.

[0019] Clutch slip occurs when the clutch, in the engaged state, only partially transmits the supplied torque. In this case, the speeds on the clutch input and output sides are different, even though torque is being transmitted. In this clutch state, a significant amount of heat is generated compared to the deactivated and fully engaged states, which must be dissipated accordingly.

[0020] Wheel slip is a quantity whose value depends on the actual instantaneous speed of the driven wheel and the speed of the driven wheel that can be assigned to the instantaneous movement of the motor vehicle. If the instantaneous speed of the driven wheel corresponds to the speed that can be assigned to the instantaneous speed of the motor vehicle, the wheel slip is zero. During strong acceleration or deceleration, however, the wheel slip can be very large. Furthermore, the wheel slip can also depend on the properties of the road surface on which the driven wheel is moving. A sudden change in speed occurs when sliding friction occurs between the road surface and a surface of the driven wheel, causing the wheel speed to essentially zero. This can also be referred to as wheel locking.Using a sensor unit that detects the current speed of the driven wheel, these aforementioned events can be detected by evaluating the corresponding sensor signal. A suitable evaluation device can be provided for this purpose. The evaluation device can be part of a control system used for emergency braking of the motor vehicle using the dual-clutch transmission.

[0021] The torque of the output shaft is reduced by means of the first and / or the second clutch unit depending on at least the detected speed jump and / or at least the detected wheel slip. This can ensure that a locked wheel is released for rotation again or that sufficient rotation of the driven wheel is ensured so that a comparison value for the wheel slip is not exceeded. For this purpose, it can be provided that the first and the second clutch unit are controlled in a suitable manner by means of the control device so that the torque provided to the output shaft is adjusted so that the driven wheel does not lock or a predetermined maximum wheel slip is not exceeded.For this purpose, one of the two clutch units can be provided in the activated state to provide complete coupling, allowing the supplied torque to be transmitted essentially completely. In such an operating state of the dual-clutch transmission, the desired setting can then be achieved by appropriately controlling the other clutch unit. In principle, however, it is also possible to use both clutch units together to adjust the torque. However, this is more complex in terms of control, particularly considering stability conditions.

[0022] Overall, the invention thus makes it possible to keep the braking distance as short as possible during emergency braking and / or to maintain the steerability of the motor vehicle during emergency braking.

[0023] It is further proposed that, in order to detect the at least one speed jump and / or the at least one wheel slip, a rotation of the driven wheel is compared with a rotation of a free-running wheel. In this case, it can be assumed, among other things, that the free-running wheel, due to its low braking contribution during emergency braking, can serve as an indicator of the current speed that the driven wheel should also have. This allows the non-driven or free-running wheel to be used as a reference with regard to the rotation. In principle, the free-running wheel can of course also contribute to the braking effect. However, it is preferably provided that the braking effect is lower, so that phenomena such as the speed jump and / or wheel slip occur significantly later than with the driven wheel.This allows this wheel to contribute to the braking effect during emergency braking, while also serving as a reference for the rotation of the driven wheel. Overall, this allows for control of the rotation of the driven wheel, thus achieving the greatest possible braking effect and / or steerability.

[0024] Furthermore, it is proposed that the clutch slip and / or a transmitted torque of the first and / or second clutch unit be adjusted depending on a last detected speed before the speed jump was detected and / or depending on a speed difference between the driven wheel and the freewheeling wheel. This embodiment allows emergency braking to be further improved by a control function with regard to the braking effect. From the speed difference, for example, a slip between the wheel and the road surface on which the wheel rolls can be determined. Based on this slip, a comparison function can be implemented that compares the determined wheel slip with a comparison value for the wheel slip. As soon as the wheel slip is greater than the comparison value, the first and / or second clutch unit can be actuated accordingly to reduce the transmission of torque.This can be achieved by increasing the clutch slip of at least one of the two clutch units. The braking effect does not need to be completely lost, but can be appropriately adjusted so that a speed jump at the driven wheel can be largely avoided.

[0025] It is also possible, of course, to adjust the clutch slip depending on the last detected speed before the speed jump is detected. The clutch slip can then be adjusted, for example, so that the braking effect is temporarily suspended. However, it can also be set so that adjusting the clutch slip reduces the braking effect to the extent that it achieves the same effect as shortly before the speed jump. This can cause the driven wheel to transition from sliding against the road surface to rolling, thus reactivating the braking effect.

[0026] Activating the clutch units preferably involves one of the clutch units coupling the input shaft to the respective sub-transmission without slippage. This creates a rotationally fixed coupling between the input shaft and the output shaft of the dual-clutch transmission via the aforementioned sub-transmission with the associated clutch unit. The braking effect can then be adjusted accordingly using the clutch slip of the respective other clutch unit. This reduces the complexity of the control process and allows a stabilized emergency braking function to be implemented with a simple control system. In particular, the risk of control instability can be minimized.

[0027] Furthermore, it is proposed that the activation of the clutch units include alternating operation of the clutch units between clutch slip and clutch operation without clutch slip. This refinement has the advantage that the thermal energy generated during clutch slip can be distributed among the clutch units. This makes it possible to reliably apply the braking effect to a standstill even at high vehicle speeds, largely avoiding damage to the dual-clutch transmission. The thermal and mechanical loads on the clutch units can thus be more evenly distributed.

[0028] Furthermore, it is proposed that the switching occurs depending on the temperature of one or both of the clutch units. For this purpose, the clutch units can have temperature sensors that are correspondingly coupled to the control device. The control device can evaluate the detected temperatures and, if a predetermined temperature difference between the two clutch units is exceeded, can switch between clutch engagement with and without clutch engagement. Furthermore, the switching can, of course, also depend on other parameters, such as the wear status of a respective clutch unit, the currently engaged gear of a respective sub-transmission, and / or the like.

[0029] According to a further development, it is proposed that during a transition period, both clutch units are operated in a coupling with clutch slip. This has the advantage that the braking effect can be maintained even during the transition period for emergency braking. The transition period can, for example, be approximately one second or less, preferably less than 0.1 s, particularly preferably less than 0.01 s. However, the transition period can also be selected to be longer than one second if a smooth transfer from one clutch unit to the other clutch unit is to take place. This can have advantages with regard to the stress on the other components.

[0030] It is further proposed that the provision of the emergency signal be triggered by a driver of the motor vehicle and / or a driver assistance system of the motor vehicle. This has the advantage that both the driver and the driver assistance system, preferably independently of one another, can trigger the emergency signal and thus initiate emergency braking according to the invention. For this purpose, it can be provided that the driver actuates an actuating element, for example, by depressing a brake pedal to a predetermined level or the like. Furthermore, a separate actuating element can of course also be provided to trigger emergency braking, for example, a switching element on the steering wheel or the like.Furthermore, it is of course also possible that the driver assistance system triggers the emergency signal, for example, if an analysis of the vehicle's surroundings indicates that an accident, particularly a collision with an object external to the vehicle, appears imminent. Furthermore, the emergency braking signal can also be triggered if the driver assistance system or a higher-level vehicle control system of the vehicle issues an error message regarding an important piece of equipment, such as the service brake system.

[0031] The advantages and effects stated for the method according to the invention naturally also apply equally to the control device according to the invention and the motor vehicle equipped with the control device according to the invention, and vice versa. Method features can therefore also be formulated as device features, and vice versa.

[0032] The invention also includes the control device for the motor vehicle. The control device has a processor device configured to carry out an embodiment of the method according to the invention. For this purpose, the processor device can have at least one microprocessor and / or at least one microcontroller and / or at least one FPGA (Field Programmable Gate Array) and / or at least one DSP (Digital Signal Processor). Furthermore, the processor device can have program code configured to carry out the embodiment of the method according to the invention when executed by the processor device. The program code can be stored in a data memory of the processor device.

[0033] The invention also includes further developments of the control device 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 control device according to the invention are not described again here.

[0034] 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.

[0035] The invention also includes combinations of the features of the described embodiments.

[0036] Exemplary embodiments of the invention are described below. Shown are: Fig. 1 shows a schematic side view of an internal combustion engine-driven motor vehicle with a drive train comprising an internal combustion engine and a dual-clutch transmission, a control device for the dual-clutch transmission, and two wheels that can be driven by the drive train via the output shaft and two non-driven wheels of the motor vehicle; Fig. 2 a schematic flow diagram representation for an emergency braking of the motor vehicle according to Fig. 1; and Fig. 3 a schematic block diagram of the drive train of the motor vehicle according to Fig. 1.

[0037] The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments 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 embodiments other than those shown. Furthermore, the described embodiments can also be supplemented by further features of the invention already described.

[0038] In the figures, the same reference symbols designate elements with the same function.

[0039] Fig. 1 shows a schematic side view of an internal combustion engine-powered motor vehicle 50. The motor vehicle 50 has a drive train 52, which includes an internal combustion engine 58 for driving the motor vehicle 50 in a normal driving mode. The drive train 52 further includes a dual-clutch transmission 56, which has an input shaft 20, which is connected in a rotationally fixed manner to a drive shaft 54 ​​of the internal combustion engine 58 ( Fig. 3). The dual-clutch transmission 56 further comprises an output shaft 22, which is drive-coupled to wheels 40 of a front axle 44 of the motor vehicle 50. For this purpose, a differential gear can be additionally provided, for example. The motor vehicle 50 further comprises two wheels 42 of a rear axle 46, which are not driven. Furthermore, the motor vehicle 50 comprises a control device 10, which serves to control the dual-clutch transmission 56.

[0040] Fig. 3 shows in a schematic block diagram the drive train 52 of the motor vehicle 50 according to Fig. 1. From Fig. 3 shows that the drive train 52 includes the internal combustion engine 58 as the drive unit, which provides its drive power to the drive shaft 54. The drive train 52 further includes the dual-clutch transmission 56, which has the input shaft 20, which is rotationally fixedly connected to the drive shaft 54. The dual-clutch transmission 56 further includes the output shaft 22, which is coupled, in a manner not shown, to the driven wheels 40 of the motor vehicle 50 of the front axle 44.

[0041] The dual-clutch transmission 56 has a first actuatable clutch unit 24 and a second clutch unit 26 actuatable independently of the first clutch unit 24, as well as two sub-transmissions 28, 30. By means of the first clutch unit 24, the first of the sub-transmissions 28 can be coupled to the input shaft 20 depending on the clutch state of the first clutch unit 24. Correspondingly, by means of the second clutch unit 26, the second of the sub-transmissions 30 can be coupled to the input shaft 20 depending on its clutch state. Both sub-transmissions 28, 30 are furthermore coupled in a rotationally fixed manner to the output shaft 22 of the dual-clutch transmission 56. This makes it possible to couple the input shaft 20 to the respective one of the sub-transmissions 28, 30 depending on the respective clutch states of the clutch units 24, 26.

[0042] In the present embodiment, the clutch units 24, 26 are designed as dry clutches. In alternative embodiments, this may, of course, be different; for example, hydraulic clutch units or the like may also be provided for the clutch units 24, 26. In principle, the two clutch units 24, 26 do not need to be designed identically.

[0043] Fig.Figure 2 now shows, in a schematic flowchart, a method for emergency braking of the motor vehicle 50, as executed by the control device 10. In a first step 12, the control device 10 receives an emergency signal for triggering the emergency braking when the motor vehicle 50 is not stationary. This emergency signal can be provided in the present case by a driver assistance system (not shown) that monitors the function of the motor vehicle during normal operation. Alternatively or additionally, this can also be a vehicle control system that monitors, for example, a service brake device of the motor vehicle 50. In principle, however, the emergency braking signal can also be triggered by a driver of the motor vehicle 50.

[0044] In a second step 14, a warning signal is emitted by the motor vehicle 50, which can be implemented, for example, by activating hazard warning lights and / or a horn. Of course, several corresponding warning signals can also be emitted by the motor vehicle 50.

[0045] In a third step 16, the internal combustion engine 58 is then deactivated. The control device 10 delivers a control signal to the vehicle control system, which then deactivates the internal combustion engine 58 of the drive train 52. For this purpose, an ignition and / or a fuel supply can be deactivated. At the same time, it is determined whether a gear is engaged in the first and second sub-transmissions 28, 30. If no gear is engaged in one of the sub-transmissions 28, 30, this is done automatically by engaging a suitable gear.

[0046] The control device 10 then detects a rotational speed of the wheels 40, 42 using a rotational speed sensor (not shown in the figures). By evaluating the detected rotational speeds, a speed jump and / or at least one wheel slip of the driven wheels 40 of the motor vehicle 50 can be determined. In the present embodiment, it is provided that, in particular, the rotational speeds of the non-driven wheels 40 are also detected.

[0047] The control device 10 then first determines in a comparison step 38 whether the motor vehicle 50 has come to a standstill. If the motor vehicle 50 has come to a standstill, the method ends in step 48.

[0048] If, however, the motor vehicle 50 has not yet come to a standstill, a comparison step 34 determines whether the wheel slip, which can be determined by calculating the difference between the rotational speeds of the wheels 42 and the respective wheels 40, reaches or exceeds a predetermined comparison value. Alternatively or additionally, it can also simply be determined whether the rotational speed of one of the driven wheels 40 exhibits a speed jump, so that the rotational speed becomes zero.

[0049] If this is not the case, the procedure branches off and continues in step 32.

[0050] If the condition according to step 34 is met, the method continues in step 36. In the present case, it is provided that the first clutch unit 24 is in the fully coupled clutch state, so that the input shaft 20 is firmly coupled to the first sub-transmission 28. The second clutch unit 26, on the other hand, is in a partially coupled state, which allows clutch slip via the second clutch unit 26. By adjusting the clutch slip of the second clutch unit 26, the braking function during emergency braking can now be controlled. This makes it possible to reduce the braking torque provided for the wheels 40 in step 36. The reduction is selected such that, when the wheel slip is taken into account for the adjustment, it is reduced to such an extent that the value remains below the comparison value. With regard to the speed jump, the braking torque is reduced to such an extent that both wheels 40 rotate again.The procedure is then continued in step 32.

[0051] The process is repeated until the motor vehicle 50 reaches a standstill, which is determined in step 38.

[0052] The emergency signal can be activated, for example, via a vehicle's surroundings sensor system, such as a presence function, but also via a standard distance sensor system, such as in conjunction with a parking assistant or similar. The surroundings sensor system is preferably taken into account in order to obtain the most objective and accurate decision possible as to whether a critical situation exists that would require emergency braking.

[0053] Not shown is that the control device 10 further detects a temperature of the first and second clutch units 24, 26. Depending on the detected respective temperatures, the clutch states of the two clutch units 24, 26 can be swapped or changed, so that thermal stress on the clutch units 24, 26 during emergency braking can be distributed across both clutch units 24, 26.

[0054] Finally, after the motor vehicle 50 has reached a standstill, a parking brake or the like can be used to secure the vehicle against rolling away. Furthermore, it can be provided that, to secure the motor vehicle 50 against rolling away after reaching a standstill, one of the two clutch units 24, 26 is moved to the disengaged clutch state, while the other of the two clutch units 24, 26 remains in the fully engaged state. Two gears can then be engaged on the free input shaft, and both clutch units 24, 26 can then be switched to the disengaged clutch state.

[0055] The embodiments described above serve solely to explain the invention and are not intended to limit it.

Claims

[1] Method for emergency braking of a motor vehicle (50) by means of a dual-clutch transmission (56) of a drive train (52) of the motor vehicle (50), wherein the dual-clutch transmission (56) has a first actuatable clutch unit (24) and a second clutch unit (26) actuatable independently of the first clutch unit (24), as well as two partial transmissions (28, 30), wherein a respective one of the clutch units (24, 26) is coupled on the one hand to a respective one of the partial transmissions (28, 30) and on the other hand to an input shaft (20) of the dual-clutch transmission (56) in order to couple the input shaft (20) to the respective one of the partial transmissions (28, 30) depending on a respective clutch state, and the partial transmissions (28, 30) are coupled on the output side to an output shaft (22) of the dual-clutch transmission (56), wherein the method for providing a redundant braking system the steps include: - receiving an emergency signal for triggering the emergency braking outside of a standstill of the motor vehicle (50) when the motor vehicle is used in its intended operation, - Deactivating a drive unit (58) of the drive train (52) having a drive unit shaft (54) coupled to the input shaft (20) of the dual-clutch transmission (56), - activating the first and second clutch units (24, 26) in order to at least partially establish a coupling between the input shaft (20) and the respective partial transmission (28, 30) by means of the respective clutch unit (24, 26), wherein at least one of the clutch units (24, 26) provides a clutch slip, characterized by , that - at least one speed jump and / or at least one wheel slip of at least one wheel (40) of the motor vehicle (50) driven by the drive train (52) via the output shaft (22) is detected, and - a torque of the output shaft (22) is reduced by means of the first and / or the second clutch unit (24, 26) depending on the at least one detected speed jump and / or at least one detected wheel slip. [2] Method according to claim 1, characterized by in that, in order to detect the at least one speed jump and / or the at least one wheel slip, a rotation of the driven wheel (40) is compared with a rotation of a free-running wheel (42). [3] Method according to claim 2, characterized by that the clutch slip and / or a transmitted torque of the first and / or the second clutch unit (24, 26) is adjusted as a function of a last detected speed before the speed jump is detected and / or as a function of a speed difference between the driven wheel (40) and the free-running wheel (42). [4] Method according to one of the preceding claims, characterized bythat the activation of the clutch units (24, 26) comprises one of the clutch units coupling the input shaft (20) to the respective partial transmission (28, 30) without slip. [5] Method according to one of the preceding claims, characterized by that the activation of the clutch units (24, 26) comprises that the clutch units (24, 26) are operated alternately between a coupling with clutch slip and a coupling without clutch slip. [6] Method according to claim 5, characterized by that the changeover takes place depending on a temperature of one or both of the coupling units (24, 26). [7] Method according to claim 5 or 6, characterized by that in a transition period during the changeover both clutch units (24, 26) are operated in a coupling with clutch slip. [8] Method according to one of the preceding claims, characterized bythat the provision of the emergency signal is triggered by a driver of the motor vehicle (50) and / or a driver assistance system of the motor vehicle (50). [9] Control device (10) for emergency braking of a motor vehicle (50) by means of a dual-clutch transmission (56) of a drive train (52) of the motor vehicle (50), wherein the dual-clutch transmission (56) has a first actuatable clutch unit (24) and a second clutch unit (26) actuatable independently of the first clutch unit (24), as well as two partial transmissions (28, 30), wherein a respective one of the clutch units (24, 26) is coupled on the one hand to a respective one of the partial transmissions (28, 30) and on the other hand to an input shaft (20) of the dual-clutch transmission (56) in order to couple the input shaft (20) to the respective one of the partial transmissions (28, 30) depending on a respective clutch state, and the partial transmissions (28, 30) are coupled on the output side to an output shaft (22) of the dual-clutch transmission (56), wherein the control device (10) is designed to provide a redundant braking system: - when using the motor vehicle in its intended operation, to receive an emergency signal for triggering the emergency brake outside of a standstill of the motor vehicle (50), - to deactivate a drive unit (58) of the drive train (52) having a drive unit shaft (54) coupled to the input shaft (20) of the dual-clutch transmission (56), - to activate the first and the second clutch unit (24, 26) in order to establish at least a partial coupling between the input shaft (20) and the respective partial transmission (28, 30) by means of the respective clutch unit (24, 26), wherein at least one of the clutch units (24, 26) provides a clutch slip, characterized by that the control device (10) is further designed - to detect at least one speed jump and / or at least one wheel slip of at least one wheel (40) of the motor vehicle (50) that can be driven by the drive train (52) via the output shaft (22), and - to reduce a torque of the output shaft (22) by means of the first and / or the second clutch unit (24, 26) depending on the at least one detected speed jump and / or at least one detected wheel slip. [10] Motor vehicle (50) with a drive train (52) which has a drive unit (58) with a drive shaft (54) and a dual-clutch transmission (56) with an input shaft (20) coupled to the drive shaft (54), and with at least one wheel (40) of the motor vehicle (50) which can be driven by means of the drive train (52) via an output shaft (22) of the dual-clutch transmission (56), wherein the dual-clutch transmission (56) has a first actuatable clutch unit (24) and a second clutch unit (26) which can be actuated independently of the first clutch unit (24), as well as two partial transmissions (28, 30), wherein a respective one of the clutch units (24, 26) is coupled on the one hand to a respective one of the partial transmissions (28, 30) and on the other hand to the input shaft (20) of the dual-clutch transmission (56) in order to drive the input shaft (20) depending on a respective Clutch state with the respective one of the partial transmissions (28, 30), and the partial transmissions (28,30) are coupled on the output side to the output shaft (22) of the dual-clutch transmission (56), and with a control device (10) for emergency braking of the motor vehicle (50) by means of the dual-clutch transmission (56), , characterized by that the control device (10) is designed according to claim 9.

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