Method and control unit for operating a motor vehicle's powertrain

Abstract

Method for operating a motor vehicle drivetrain comprising a drive unit (1) and a transmission (3) with multiple shift elements (4) connected between the drive unit (1) and an output (2), wherein, when driving with a frictionally engaged gear in the transmission (3) with a gear-dependent, defined target gear ratio, it is monitored whether, despite the gear being engaged, the actual gear ratio deviates from the target gear ratio by more than a limit value, wherein, if it is determined that the actual gear ratio deviates from the target gear ratio by more than the limit value, a flare condition of the transmission (3) is detected, wherein, upon or after detection of the flare condition of the transmission (3), the following steps are performed: determining the shift element (4) of the transmission (3) which exhibits a reduced transmission capability, determining a reduced transmission capability torque for that shift element (4) of the transmission (3).which exhibits the reduced transmission capability, Determining a compensation torque for that switching element (4) of the transmission (3) which exhibits the reduced transmission capability, Actuating that switching element (4) of the transmission (3) which exhibits the reduced transmission capability, depending on the determined reduced transmission capability torque and depending on the determined compensation torque, in order to approximate the actual transmission ratio to the target transmission ratio and thus to exit the flare state of the transmission (3).

Description

The invention relates to a method for operating a drive train of a motor vehicle. The invention furthermore relates to a control device for carrying out the method.Drive trains of motor vehicles having a transmission connected between a drive unit and an output are sufficiently known from practice. It is also known that a transmission comprises a plurality of shift elements, which can be designed as frictional shift elements or also as form-locking shift elements. Then, when a force-locking gear is engaged in a transmission, a first number of the shift elements of the transmission is closed and a second number of the shift elements of the transmission is opened. When a force-locking gear is engaged in the transmission, the gear is driven with a defined gear-dependent transmission ratio. Depending on this gear-dependent transmission ratio, rotational speeds and torques are converted and thus the traction force supply of the drive unit is provided by the transmission at the output. Due to a defect on a switching element, the transfer capability of a switching element may be reduced. In this case, it may be that the transmission can no longer transmit a torque offered by the drive unit completely in the direction of the output, wherein this torque that can no longer be transmitted then leads to an increase in the rotational speed at the transmission input. In this case, an actual transmission ratio is then formed when the force-locking gear is engaged, which transmission ratio deviates from the gear-dependent desired transmission ratio. Such a state of the transmission is referred to as the flare state. It is already known from practice to monitor the transmission capacity of shift elements of a transmission with the aid of so-called gear monitoring. If it is determined at a transmission that one of the shift elements must have a reduced transmission capacity, then according to practice gear changes are carried out in order to identify in the exclusion method that shift element whose transmission capacity is limited. Such unnecessary circuits may cause consequent damage to switching elements and should be avoided.DE 10 2016 212 359 B4 discloses a method for determining transmission-internal torques at shift elements of a transmission, with the aid of which a shift element of a transmission can be determined by calculation, the transmission capacity of which is reduced, which thus has a low transmission capacity.DE 10 2008 000 209 A1 describes a method for operating an automatic transmission of a drive train of a motor vehicle having a plurality of shift elements.DE 10 2014 105 701 A1 discloses a transmission clutch control method including a transfer function that relates clutch torque to a control signal under transmission operating conditions.US 2010 / 0 318 269 A1 discloses a closed loop shift control apparatus and method based on frictional element load that controls the torque transfer transition phase.Although it is already known in principle to determine a shift element of a transmission by calculation, which has a low transmission capacity, it has hitherto been difficult to leave the flare state of the transmission in a defined manner.There is therefore a need for a method for operating a drive train and for a control device for carrying out the method, with the aid of which, when a flare state of the transmission is detected and that shift element of the transmission which has a low transmission capacity is determined, it is possible to leave the flare state of the transmission properly.Proceeding from this, the object of the invention is to create a novel method and a control device of a drive train of a motor vehicle.This object is achieved by a method for operating a drive train of a motor vehicle according to patent claim 1.According to the invention, when driving with a gear-dependent, defined desired transmission ratio in a force-locking gear engaged in the transmission, it is monitored whether an actual transmission ratio deviates from the desired transmission ratio by more than a limit value despite the firmly engaged gear.If it is determined that the actual transmission ratio deviates from the setpoint transmission ratio by more than the limit value, a flare state of the transmission is detected, the following steps being carried out when or after the flare state of the transmission is detected:determining that shift element of the transmission which has a low transmission capability.determining a torque of low transmission capability for that shift element of the transmission which has the low transmission capability.determining a compensation torque for that shift element of the transmission which has the low transmission capability.activating that shift element of the transmission which has the low transmission capacity as a function of the low transmission capacity torque determined and as a function of the compensation torque determined in order to bring the actual transmission ratio closer to the desired transmission ratio and thus to leave the flare state of the transmission.The present invention proposes determining, for the shifting element which has a low transmission capacity when a flare state of the transmission is detected, on the one hand a low transmission capacity torque and, on the other hand, a compensation torque and subsequently controlling, as a function of these two torques, the shifting element which has the low transmission capacity in order to bring the actual transmission ratio of the transmission closer to the setpoint transmission ratio of the engaged, force-locking gear and thus to leave the flare state of the transmission in a defined manner.According to an advantageous development, for that shifting element of the transmission which has the low transmission capacity, a first dynamic torque is determined as a function of a temporal actual gradient and desired gradient of the transmission input rotational speed and a mass inertia relating to the drive unit, from which the low transmission capacity torque is determined. The torque of reduced transmission capability is preferably determined from this first dynamic torque as a function of a gear-dependent and / or shifting element-dependent support factor. The torque of reduced transmission capability can thereby be determined particularly advantageously.According to an advantageous development, for that shifting element of the transmission which has the low transmission capability, a second dynamic torque is determined as a function of a temporal setpoint compensation gradient of the transmission input rotational speed and a mass inertia relating to the drive unit, from which the compensation torque is determined. The compensation torque is preferably determined from this second dynamic torque as a function of a gear-dependent and / or shifting element-dependent support factor. The compensation torque can thereby be determined particularly advantageously.According to an advantageous development, temporal setpoint compensation gradients of the transmission input rotational speed are preferably determined as a function of a temperature of the shift element which has the low transmission capability and / or as a function of a torque of the shift element which has the low transmission capability and / or as a function of a differential rotational speed of the shift element which has the low transmission capability and / or as a function of a transmission input torque. This is preferred in order to determine the temporal setpoint compensation gradient of the transmission input rotational speed.The control device according to the invention is defined in claim 10.Preferred refinements emerge from the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail with reference to the drawings, without being restricted thereto. The following shows: FIG. 1 shows a block diagram of a drive train of a motor vehicle; FIG. 2 shows a signal flow diagram to illustrate the method according to the invention; FIG. 3 shows a time diagram for further clarification of the method according to the invention.The invention relates to a method and a control device for operating a drive train of a motor vehicle.FIG. 1 shows a highly schematic block diagram of a drive train of a motor vehicle, wherein the drive train comprises a drive unit 1 and a transmission 3 connected between the drive unit 1 and an output 2. The transmission 3 is an automated or automatic transmission, which converts rotational speeds and torques and thus provides the traction force available to the drive unit 1 at the output 2.The transmission 3 comprises a plurality of shift elements 4, wherein only one shift element 4 is shown in FIG. 1. The shift elements 4 of the transmission 3 are frictional shift elements and, if appropriate, form-locking shift elements, wherein in each engaged, force-locking gear of the transmission 3 a first number of the shift elements 4 is closed and a second number of the shift elements 4 is opened. To carry out a gear change in the transmission 3, a previously closed shifting element is opened and a previously opened shifting element is closed. According to FIG. 1, a separating clutch 5 is connected between the drive unit 1 and the transmission 3.The operation of the drive unit 1 is controlled and / or regulated by an engine control unit 6. The operation of the transmission 3 is controlled and / or regulated by a transmission control unit 7. For this purpose, according to the double arrows shown, the engine control unit 6 exchanges data with the drive unit 1 and the transmission control unit 7 exchanges data with the transmission 3. Furthermore, engine control unit 6 and transmission control unit 7 exchange data with one another.When, in the drive train shown in FIG. 1, a force-locking gear is firmly engaged in the transmission 3 and is driven with a defined desired transmission ratio dependent on the force-locking gear, it is monitored whether an actual transmission ratio deviates from a desired transmission ratio by more than a limit value despite the force-locking gear being firmly engaged. If this is the case, it is concluded that a so-called flare state exists for the transmission 3.Upon or after detection of such a flare state in the transmission 3, the following steps are carried out:determining that shift element 4 of the transmission 3 which has a low transmission capability.determining a torque of low transmission capability for that shift element 4 of the transmission 3 which has the low transmission capability.determining a compensation torque for that shift element 4 of the transmission 3 which has the low transmission capability.activating that shift element 4 of the transmission 3 which has a low transmission capacity as a function of the low transmission capacity torque determined and as a function of the compensation torque determined in order to bring the actual transmission ratio of the transmission closer to the desired transmission ratio of the engaged, force-locking gear and to leave the flare state of the transmission 3.Further details of the invention are described below with reference to the signal flow diagram of FIG. 2.In a block 8, 12 a check is made as to whether a flare condition occurs at the transmission 3 during travel in a firmly engaged, force-locking gear. For this purpose, a plurality of input variables 9, 10 and 11 are provided to block 8, namely the setpoint transmission ratio of the firmly engaged, force-locking gear of transmission 3 with input variable 9, the actual rotational speed of the transmission output with input variable 10, and the actual rotational speed of the transmission input with input variable 11. In block 8, an actual transmission ratio is then calculated as a function of the actual rotational speed of the transmission output and the actual rotational speed of the transmission input, which is compared with the desired transmission ratio in block 12. In a block 12, it is checked whether the actual transmission ratio deviates from the desired transmission ratio by more than a limit value.If this is not the case, the system branches back from block 12 to block 8. If, on the other hand, it is determined in block 12 that the actual transmission ratio deviates from the setpoint transmission ratio by more than the limit value, a flare state of the transmission is detected and, starting from block 12, the system branches to block 13.In block 13, that shift element of the transmission 3 is determined which is closed during travel in the engaged, force-locking gear and has a low transmission capacity.The determination of this switching element, which has the low transmission capability, is preferably carried out in the manner known from DE 10 2016 212 359 B4. Details of how a switching element which has a low transmission capability can be determined mathematically on the basis of a system of equations are accordingly known to the person skilled in the art addressed here from DE 10 2016 212 359 B4, so that reference is made at this point to DE 10 2016 212 359 B4.As an output variable, the block 13 outputs that shifting element of an engaged, force-locking gear which is closed in the engaged, force-locking gear and has a low transmission capacity.In a subsequent block 14, a torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the torque of the.For this purpose, block 14 is provided, on the one hand, as input variable 15 with an actual time gradient of the transmission input rotational speed and, as a further input variable 16, with a mass inertia relating to drive unit 1, as a function of which a first dynamic torque is ascertained for shift element 4 which has the low transmission capability. The mass inertia, which is provided to block 14 as input variable 16, is that mass inertia of the drive train which it has between drive unit 1 and shift element 4 with the low transmission capability.The first dynamic torque, which is determined in block 14, is also dependent on a temporal setpoint gradient of the transmission input rotational speed. This temporal setpoint gradient of the transmission input rotational speed is determined as a function of the setpoint transmission input rotational speed, which corresponds to the product of the setpoint transmission ratio and the actual output rotational speed at the output 2.The first dynamic torque corresponds to the product of the mass inertia and the difference between the difference between the actual gradient and the setpoint gradient of the transmission input rotational speed. The first dynamic torque is calculated with a support factor of the transmission 3 in order to calculate the torque with which the transmission is less than this first dynamic torque, wherein the support factor of the transmission 3 is dependent on the engaged force-locking gear and on the shift element which has the transmission is less than this.The block 14 outputs the torque of low transmission capability as an output variable.In a subsequent block 17, a check is again carried out, analogously to block 12, as to whether the flare state of the transmission 3 is present.Subsequently, in a block 18, the compensation torque is determined for that shifting element 4 of the transmission 3 which has the low transmission capability. This compensation torque 18 is determined as a function of input variables, namely, as a function of the input variables 19 and 16. The input variable 16 is in turn the mass inertia of the output train starting from the drive unit 1 in the direction of the shifting element 4 with the low transmission capability. The input variable 19 is a temporal setpoint compensation gradient of the transmission input rotational speed.From the product of these input variables 16 and 19, a second dynamic torque is determined, which is initially related to the drive and is converted into the compensation torque by calculation with the support factor of the transmission 3, wherein the support factor of the transmission 3 is again gear-dependent. Block 18 accordingly outputs the compensation torque as an output variable.In a block 20, the shifting element 4 of the transmission 3 which has the low transmission capacity is subsequently activated as a function of the low transmission capacity torque determined in block 14 and as a function of the compensation torque determined in block 18, in order to bring the actual transmission ratio closer to the desired transmission ratio as a result of this activation and thus to leave the flare state at the transmission 3.Consequently, in block 17 a continuous monitoring is carried out as to whether a flare condition is present at the transmission 3, wherein if a flare condition is still present at the transmission 3, the compensation torque is continuously recomputed in block 18 in order to adapt the actuation of the shift element 4. For the actuation of the switching element 4 with low transmission capability, the low transmission capability torque ascertained in block 14 accordingly remains unchanged, and the compensation torque ascertained in block 18 is continuously adapted.The adaptation of the compensation torque in block 18 is dependent on the setpoint compensation gradient 19 for the transmission input rotational speed, which is determined in block 21 of FIG. 2. The setpoint compensation gradient 19 of the transmission input rotational speed is ascertained in block 21 as a function of the input variables 22 and / or 23 and / or 24 and / or 25, the input variable 22 being a current actual differential rotational speed at the shift element 4 which has the low transmission capability, the input variable 23 being a current temperature of the shift element 4 which has the low transmission capability, the input variable 24 being a current transmitted torque at the shift element 4 which has the low transmission capability, and the input variable 25 being a current torque of the transmission input. The setpoint compensation gradient 19 of the transmission input rotational speed is preferably determined as a function of these four input variables 22, 23, 24 and 25. However, it is also possible to take into account only some of these input variables for the determination of the setpoint compensation gradient 19 of the transmission input rotational speed or to add further input variables.In a block 26 of the signal flow diagram of FIG. 2, the low-transmission-capability torque ascertained in block 14 is stored in order to determine in this regard an adaptation value for the activation of that shift element of transmission 3 which has the low-transmission capability.When using the method described above, the temporal signal curves shown in FIG. 3 can form. Thus, three time signal curves are shown in FIG. 3 over time t, namely with a signal curve 27 a curve of a setpoint transmission input rotational speed of the transmission 3, which corresponds to a product of the setpoint transmission ratio of the gear engaged in the transmission 3 and a measured actual output rotational speed at the output 2. A curve profile 28 visualizes an actual profile of the transmission input rotational speed. It can be seen from the signal curves 27 and 28 that the actual curve of the transmission input rotational speed deviates from the gear-dependent setpoint curve, so that a flare state in the transmission 3 is concluded at the time t 1 in FIG. 3.Signal curve 29 visualizes a torque curve in transmission 3, namely at that shifting element 4 of transmission 3, which has a low transmission capability when the force-locking gear is firmly engaged. Thus, FIG. 3 visualizes with the reference numeral 30 a torque of low transmission capability, which causes the flare state in the transmission 3. When the flare state is detected in the transmission 3 at the time t 1, the low transmission capability torque and the compensation torque are determined for that shifting element 4 of the transmission 3 which has the low transmission capability, as described above, in order to change the actuation of the shifting element which has the low transmission capability as a function of these variables. Thus, the torque of low transmission capability is visualized with reference numeral 31 and the compensation torque with reference numeral 32. With increasing flare degradation and increasing reduction of a rotational speed difference at the shifting element 4 with recognized low transmission capability, the compensation torque 32 is continuously reduced in the sense of blocks 17, 18 and 20.The invention further relates to a control device for operating the drive train of the motor vehicle, wherein the control device executes the method described above on the control side. The control device according to the invention is in particular the transmission control device 7.The transmission control unit 7 has hardware-side means and software-side means for carrying out the method on the control side, the hardware-side means being data interfaces, a processor and a memory. The data interfaces serve to exchange data with the modules involved in carrying out the method according to the invention. The processor is used for data processing and the memory is used for data storage. Software-side means include program modules for carrying out the method according to the invention.The control device 7 monitors when a force-locking gear is engaged in the transmission 3 and when the gear is driven in this force-locking gear how the desired transmission ratio behaves to the actual transmission ratio, wherein, when the control device 7 establishes that the actual transmission ratio deviates from the desired transmission ratio by more than a limit value, it recognizes a flare state of the transmission 3. Then, when the control device 7 recognizes the flare state of the transmission 3, it executes the following steps: ascertaining that shift element 4 of the transmission 3 which has the low transmission capability. determining the torque of the low transmission capability for that shift element 4 of the transmission 3 which has the low transmission capability. determining the compensation torque for that shift element 4 of the transmission 3 which has the low transmission capability. Actuating that shifting element 4 of the transmission 3 which has the low transmission capacity, namely as a function of the low transmission capacity torque determined and the compensation torque determined, in order to bring the actual transmission ratio closer to the desired transmission ratio and thus to leave the flare state of the transmission 3.Reference numerals denote reference numerals1 Drive unit 2 Transmission 3 Output 4 Shifting element 5 Separating clutch 6 Engine control unit 7 Transmission control unit 8 Block Setpoint transmission ratio ascertainment 9 Input variable Setpoint transmission ratio 10 Input variable Actual rotational speed Transmission output 11 Input variable Actual rotational speed Transmission input 12 Block Query Flare state 13 Block Shifting element ascertainment 14 Block Torque capability Torque ascertainment 15 Input variable Actual gradient Transmission input rotational speed 16 Input variable Mass inertia 17 Block Query Flare state 18 Block Compensation torque ascertainment 19 Input variable Setpoint compensation gradient Transmission input rotational speed 20 Block Shifting element control 21 Block Setpoint compensation gradient ascertainment 22 Input variable Actual differential rotational speed Shifting element 23 Input variable Temperature Shifting element 24 Input variable Torque Shifting element 25 Input variable Torque Transmission input 26 block adaptation value 27 setpoint curve profile transmission input rotational speed 28 actual curve profile transmission input rotational speed 29 curve profile torque 30 low transmission capability torque 31 low transmission capability torque 32 compensation torque

Claims

Method for operating a drive train of a motor vehicle, having a drive unit (1) and a transmission (3) which is connected between the drive unit (1) and an output (2) and has a plurality of shift elements (4), wherein, when driving with a gear-dependent, defined desired transmission ratio when a force-locking gear is engaged in the transmission (3), it is monitored whether an actual transmission ratio deviates from the desired transmission ratio by more than a limit value despite the gear being fixedly engaged, wherein, when it is determined that the actual transmission ratio deviates from the desired transmission ratio by more than the limit value, a flare state of the transmission (3) is detected, wherein the following steps are carried out when or after detecting the flare state of the transmission (3): determining that shift element (4) of the transmission (3), which has a low transmission capability, ascertaining a low transmission capability torque for that shifting element (4) of the transmission (3) which has the low transmission capability, ascertaining a compensation torque for that shifting element (4) of the transmission (3) which has the low transmission capability, activating that shifting element (4) of the transmission (3) which has the low transmission capability, as a function of the ascertained low transmission capability torque and as a function of the ascertained compensation torque, in order to approximate the actual transmission ratio to the setpoint transmission ratio and thus to leave the flare state of the transmission (3).Method according to Claim 1, characterized in that a dynamic torque is determined for that shifting element (4) of the transmission (3) which has the low transmission capacity, as a function of a temporal actual gradient of a transmission input rotational speed, a temporal setpoint gradient of the transmission input rotational speed and a mass inertia relating to the drive unit (1), from which dynamic torque the low transmission capacity torque is determined.Method according to Claim 2, characterized in that the torque with which the low transmission capability is able to be determined from this dynamic torque as a function of a gear-dependent and / or shifting-element-dependent supporting factor.Method according to Claim 2 or 3, characterized in that the setpoint gradient of the transmission input rotational speed is determined from the setpoint transmission input rotational speed which corresponds to the product of the setpoint transmission ratio and the output rotational speed.Method according to one of Claims 1 to 4, characterized in that a dynamic torque is determined for that shifting element (4) of the transmission (3) which has the low transmission capability, as a function of a temporal setpoint compensation gradient of the transmission input rotational speed and a mass inertia relating to the drive unit (1), from which dynamic torque the compensation torque is determined.Method according to Claim 5, characterized in that the compensation torque is determined from this dynamic torque as a function of a gear-dependent and / or shift-element-dependent supporting factor.Method according to Claim 5 or 6, characterized in that the temporal setpoint compensation gradient of the transmission input rotational speed is determined as a function of a temperature of the shift element (4) which has the low transmission capability and / or as a function of a torque of the shift element (4) which has the low transmission capability and / or as a function of a differential rotational speed of the shift element (4) which has the low transmission capability and / or as a function of a transmission input torque.Method according to one of Claims 1 to 7, characterized in that, for the actuation of that shift element (4) of the transmission (3) which has the low transmission capacity, the low transmission capacity torque determined is kept unchanged and the compensation torque is continuously ascertained anew.Method according to one of Claims 1 to 8, characterized in that the low transmission capability torque determined is used as an adaptation value for actuating that shift element (4) of the transmission (3) which has the low transmission capability.Control device (7) for operating a drive train of a motor vehicle, having a drive unit (1) and a transmission (3) which is connected between the drive unit (1) and an output (2) and has a plurality of shift elements (4), wherein the control device (7) monitors, when a frictional gear engaged in the transmission (3) is driven with a gear-dependent, defined desired transmission ratio, whether an actual transmission ratio deviates from the desired transmission ratio by more than a limit value despite the gear being fixedly engaged, wherein the control device (7) detects, when the same establishes that the actual transmission ratio deviates from the desired transmission ratio by more than the limit value, a flare state of the transmission (3), wherein the control device (7) carries out the following steps upon or after detection of the flare state of the transmission (3): ascertaining that shift element (4) of the transmission (3) which has a low transmission capability, ascertaining a low transmission capability torque for that shift element (4) of the transmission (3) which has the low transmission capability, ascertaining a compensation torque for that shift element (4) of the transmission (3) which has the low transmission capability, activating that shift element of the transmission (3) which has the low transmission capability in dependence on the ascertained low transmission capability torque and the ascertained compensation torque in order to approximate the actual transmission ratio to the setpoint transmission ratio and thus to leave the flare state of the transmission (3).Control device according to Claim 10, characterized in that it carries out the method according to one of Claims 1 to 9 on the control side.

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