Method and control device for operating a drive train

Abstract

A method for operating a motor vehicle powertrain, wherein the powertrain comprises a drive unit (1) and an automatic or automated transmission (3) connected between the drive unit (1) and an output (2), wherein in each engaged gear of the transmission (3) a number N switching elements (9) of the transmission (3) are closed, wherein, depending on operating parameters of the powertrain, the same can be automatically converted into a coasting mode, wherein in the coasting mode the drive unit (1) rotates with the transmission (3) not engaged or the drive unit (1) is stationary with the transmission (3) not engaged, and wherein, to terminate the coasting mode, a target gear is specified for the transmission (3) and a speed control is specified for the drive unit (1) such thatthat, in order to establish a synchronous condition for the transmission (3), the drive unit speed is increased via the speed control such that the drive unit speed or a transmission input speed dependent on it approaches and / or reaches a defined target synchronous speed adapted to the target gear, characterized in that during the speed control, it is monitored, on the basis of control currents of switching element controllers (10) which serve to control the switching elements (9) of the transmission (3), which switching elements (9) of the transmission (3) are to be considered closed, wherein when it is detected that a number N switching elements (9) of the transmission (3) are to be considered closed, a monitoring function is triggered, wherein a switching element (9) of the transmission (3) is then considered closed if the control current of the switching element controller (10) of the respective switching element (9) is greater than a limit value,where the monitoring function , the actual gear of the transmission that corresponds to these closed switching elements (9) is determined, Depending on this actual gear, an actual synchronous speed is determined for the drive unit speed or for the transmission input speed dependent on the same, and the actual drive unit speed or the actual transmission input speed is monitored. Then, when the actual drive unit speed or the actual transmission input speed reaches the actual synchronous speed or a speed dependent on it, a monitoring period is started and it is monitored whether the speed control is terminated within the monitoring period.

Description

[0001] The invention relates to a method for operating a drive train according to the preamble of claim 1. Furthermore, the invention relates to a control device for carrying out the method.

[0002] A motor vehicle's powertrain comprises a drive unit and a transmission, the transmission being connected between the drive unit and an output shaft of the powertrain. The transmission converts rotational speeds and torques and provides the tractive force of the drive unit at the output shaft of the powertrain. The present invention relates to a method and a control device for operating such a motor vehicle powertrain, in which the transmission is designed as an automatic or automated transmission. In each gear of the transmission, a number N of switching elements of the transmission are closed and a number M of switching elements of the transmission are open, where N+M is the total number of switching elements of the transmission.It is already known in practice to automatically select an operating mode for such a drivetrain depending on its operating parameters and to control and / or regulate the functions of the transmission and / or the drive unit based on this operating mode. For example, depending on operating parameters, coasting can be automatically selected as the operating mode for the drivetrain. Hereinafter, the term coasting will be understood as an operating mode in which the drive unit rotates at idle speed when the transmission is not engaged, or is stationary when the transmission is not engaged.

[0003] From DE 10 2011 005 320 A1, the sailing operating mode for a drive train with a drive unit and a transmission connected between the drive unit and an output is generally known. Furthermore, it is known from this prior art that when the drive unit is decoupled from the output in the case of a non-friction-engaged transmission, it can either run at idle speed or be completely stopped. DE 10 2011 005 320 A1 also proposes that, when sailing mode is active, exiting sailing mode can occur depending on the gradient of the driver's requested torque.

[0004] From DE 10 2010 000 857 A1 it is known that when a drive train exits a sailing mode, the power flow is restored in the transmission, i.e., the transmission is returned to a friction-locked state. According to this prior art, the switching elements required to provide the requested gear ratio in the transmission are closed, and then a still-open switching element of the gear to be engaged is closed or synchronized.

[0005] US 2004 / 0138027 A1 also reveals details on exiting a sailing mode of a propulsion system, in particular details on gear selection when ending the sailing mode.

[0006] Further procedures for exiting a sailing operation of a propulsion train are disclosed in documents DE 10 2013 202 710 A1, DE 10 2012 212 230 A1 and DE 10 2011 078 085 A1.

[0007] It is known that, in order to exit the sailing mode, a target gear is specified for the transmission on the one hand and a speed control is specified for the drive unit on the other hand, whereby the speed control increases the drive unit speed in such a way as to create a synchronous condition for the transmission, so that the drive unit speed or a transmission input speed dependent on it approaches or reaches a defined target synchronous speed adapted to the target gear.

[0008] If, for example, engine speed control is applied to the drive unit to end or exit sailing mode, this can cause unintended acceleration of the vehicle if the engine speed control remains active for too long or is applied too strongly. This must be avoided for safety reasons.

[0009] Therefore, there is a need for a method for operating a motor vehicle's drivetrain that allows the sailing mode to be safely terminated without the risk of the vehicle unintentionally accelerating.

[0010] Based on this, the present invention aims to create a novel method for operating a drive train and a control device for carrying out the method.

[0011] This problem is solved by a method according to claim 1.

[0012] According to the invention, during speed control, it is determined, on the basis of control currents from switching element controllers which serve to control the switching elements of the transmission, which switching elements of the transmission are to be considered closed, wherein when it is recognized that a number N switching elements of the transmission are to be considered closed, a monitoring function is triggered.The monitoring function determines the actual gear of the transmission corresponding to these closed switching elements. Depending on this actual gear, an actual synchronous speed is determined for the drive unit speed or for the transmission input speed dependent on it, and the actual drive unit speed or the actual transmission input speed is monitored. When the actual drive unit speed or the actual transmission input speed reaches the actual synchronous speed or a speed dependent on it, a monitoring period is started, and it is monitored whether the speed control is terminated within this period. Therefore, when exiting the coasting operating mode, the system, according to the invention, uses protected signals—namely, the control currents of the switching element controllers of the transmission's switching elements—to monitor which switching elements of the transmission are actually considered closed.The monitoring function is triggered when the number N of switching elements in the transmission are considered closed, i.e., when the transmission must be considered frictionally engaged. A switching element is considered closed when the control current of its switching element controller exceeds a certain threshold. The monitoring function determines the corresponding actual gear of the transmission for each switching element considered closed and, based on this actual gear, the corresponding actual synchronous speed, which depends on the output speed and the gear ratio of the actual gear. During the monitoring process, the system checks whether the actual drive unit speed or the actual transmission input speed reaches the actual synchronous speed or a speed dependent on the actual synchronous speed. If this occurs, a monitoring period is initiated.The system then monitors whether the engine speed control is terminated within the monitoring period. This allows for a particularly simple and reliable way to monitor the proper termination of the coasting mode, thereby preventing unintended acceleration of the vehicle.

[0013] Following a further advantageous development, if the monitoring function detects that the speed control is terminated within the monitoring period, the system concludes that the coasting mode has been properly terminated and no compensatory measure is initiated. However, if the monitoring function detects that the speed control is not terminated within the monitoring period, the system concludes that the coasting mode has not been properly terminated and at least one compensatory measure is initiated. Therefore, if an improper termination of the coasting mode is detected, a compensatory measure is initiated for safety reasons. This measure is valid for the current termination of the coasting mode and / or for the entire current driving cycle. This prevents safety-critical conditions in the powertrain.

[0014] Preferably, as a countermeasure, the engine speed control is forcibly deactivated during the termination of the current coasting mode and / or the coasting mode is disabled for the current driving cycle and / or engine speed control is disabled in all operating modes for the current driving cycle. Forcibly deactivating the engine speed control during the termination of the current coasting mode prevents unwanted acceleration of the vehicle when coasting ends. Furthermore, disabling the coasting mode for the current driving cycle and / or disabling engine speed control in all operating modes for the current driving cycle can further enhance the vehicle's operational safety.

[0015] According to an advantageous embodiment of the invention, if the monitoring of the control currents of the switching element controllers reveals that fewer than the number N of switching elements of the transmission are to be considered closed, a conclusion is drawn that the transmission is not frictionally engaged, and the monitoring function is not triggered. This embodiment of the invention is based on the understanding that an undesired acceleration of the vehicle cannot occur in a non-frictionally engaged transmission.

[0016] According to a further advantageous embodiment of the invention, if the monitoring of the control currents of the switching element controllers reveals that more than the number N of switching elements of the transmission are to be considered closed, a conclusion is drawn that the transmission is under load and the monitoring function is not triggered. This embodiment of the invention is based on the understanding that even with a transmission under load, undesired acceleration of the vehicle cannot occur.

[0017] The control device according to the invention is defined in claim 10.

[0018] Preferred embodiments are described in the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail with reference to the drawing, without being limited thereto. The drawing shows: Fig. 1. A diagram of a powertrain.

[0019] The invention relates to a method for operating a drive train of a motor vehicle and a control device for carrying out the method.

[0020] Fig. Figure 1 shows a highly schematic representation of a motor vehicle's powertrain, where the powertrain of Fig. 1 comprises a drive unit 1 and a gearbox 3 positioned between the drive unit 1 and an output 2.

[0021] The gearbox 3 converts speeds and torques, thus providing the tractive force of the drive unit 1 at the output 2.

[0022] The operation of the drive unit 1 is controlled and / or regulated by an engine control unit 4, and the operation of the transmission 3 by a transmission control unit 5. For this purpose, the engine control unit 4 exchanges data with the drive unit 1, as indicated by the double arrow 6, and the transmission control unit 5 exchanges data with the transmission 3, as indicated by the double arrow 7. Furthermore, the transmission control unit 5 and the engine control unit 4 exchange data with each other, as indicated by the double arrow 8, to control and / or regulate the operation of the drive unit 1 and the transmission 3.

[0023] The transmission 3 comprises several switching elements 9, wherein in Fig. Figure 1 shows an example of such a switching element 9. Each switching element 9 is assigned a switching element controller 10, for example a pressure controller, which outputs a control current 11 to control the corresponding switching element 9.

[0024] In each engaged gear of the transmission 3, a first number N of switching elements 9 of the transmission 3 are closed and a second number M of switching elements 9 of the transmission 3 are open, where M+N corresponds to the total number of switching elements 9 of the transmission 3. The switching elements 9 can be positive-locking switching elements or friction-locking switching elements. Friction-locking switching elements can be designed as clutches or brakes.

[0025] Depending on defined operating parameters of the drive train, which are familiar to the person skilled in the art, the drive train can automatically switch to a sailing mode, also known as coasting mode. In sailing mode, the drive unit 1 is decoupled from the output 2 when the transmission 3 is not engaged, and the drive unit 1 can rotate at idle speed or remain stationary.

[0026] Furthermore, depending on defined operating parameters, which are also known to the person skilled in the art, the sailing mode can be automatically terminated. For this purpose, a target gear is specified for transmission 3 via the control system, and a speed control is specified for the drive unit 1 via the control system, such that, to establish synchronization conditions for transmission 3, the drive unit speed is increased via the speed control to such an extent that the drive unit speed or a transmission input speed dependent on the drive unit speed approaches and / or reaches a defined target synchronous speed adapted to the target gear.

[0027] The invention aims to carry out the termination of the sailing mode or the exit from the sailing mode with the required functional reliability, in particular to avoid the motor vehicle being unintentionally accelerated when the sailing mode is terminated.

[0028] In order to ensure a safe exit from the sailing operating mode according to the invention, after the speed control has been specified on the control side and during the execution of the speed control for the drive unit 1 on the control side, the switching element controllers 10 of the switching elements 9 of the gearbox 3 are monitored on the basis of the control currents 11 to determine which switching elements 9 of the gearbox 3 are to be considered as closed.

[0029] Then, if a control current 11 of a switching element controller 10 is greater than a limit value, the corresponding switching element 9 can be considered closed, whereas if the respective control current 11 of the corresponding switching element controller 10 of the respective switching element 9 is less than the limit value, the corresponding switching element 9 of the gearbox 3 is considered not closed.

[0030] Then, when it is recognized that a number N of switching elements 9 of the gearbox 3 are to be considered closed, a monitoring function is subsequently triggered.

[0031] The number N of switching elements 9, which are to be considered closed for the purpose of triggering the monitoring function, corresponds to the number N of switching elements 9 of the transmission 3 that are closed in each gear of the transmission 3.

[0032] Then, if the monitoring of the control currents 11 of the switching element controller 10 detects that fewer than the number N switching elements or more than the number N switching elements 9 of the transmission 3 are to be considered closed, the monitoring function described below is not triggered. This is because, if fewer than the number N switching elements 9 of the transmission 3 are to be considered closed, the entire transmission 3 is to be considered non-engaged, and if more than the number N switching elements 9 of the transmission 3 are to be considered closed, the transmission 3 is to be considered preloaded. In both cases, it is not expected that the vehicle will unintentionally accelerate when the coasting mode is terminated.

[0033] Then, when it is recognized that a number N of switching elements 9 of the gearbox 3 are to be considered closed as a result of the evaluation of the control currents 11 of the switching element controllers 10, the monitoring function is triggered.

[0034] The monitoring function determines the actual gear of the transmission 3 that corresponds to the switching elements 9 that are to be assessed as closed.

[0035] Depending on the actual gear position, an actual synchronous speed is then determined for the drive unit speed or for the transmission input speed dependent on the same, whereby the actual synchronous speed depends on the output speed and the gear ratio of the actual gear position matching the closed switching elements 9. This actual synchronous speed will then differ from the target synchronous speed if the actual gear position deviates from the target gear position.

[0036] The actual drive unit speed or the actual transmission input speed is then monitored. When the actual drive unit speed or the actual transmission input speed reaches the corresponding actual synchronous speed or a speed dependent on it, a monitoring period is started. During this monitoring period, it is checked whether the speed control is terminated within the monitoring time.

[0037] If it is determined that the speed control is terminated within the monitoring period, the monitoring function concludes that the sailing mode has been properly terminated and does not initiate any compensatory action. However, if it is determined that the speed control is not terminated within the monitoring period, the monitoring function concludes that the sailing mode has not been properly terminated and initiates at least one compensatory action.

[0038] For example, as a substitute measure during the termination of the current sailing mode, the speed control for the drive unit 1 can be forcibly terminated, which in particular ensures that no unwanted acceleration of the vehicle occurs.

[0039] As an alternative or additional measure, the coasting mode can be deactivated or locked for the current driving cycle, preventing re-entry into coasting mode for the current cycle. This also increases operational reliability.

[0040] Additionally or alternatively, it can be provided that, as a substitute measure for the current driving cycle, speed control is prevented in all operating modes, including outside of the coasting mode. This can also further increase operational reliability.

[0041] It is therefore in accordance with the present invention to determine, when speed control is initiated for the drive unit 1 to exit sailing mode, which and how many of the switching elements 9 of the transmission 3 are to be considered closed, from the control currents of switching element controllers 10 of the switching elements 9 of the transmission 3. Then, when a number N of switching elements of the transmission are to be considered closed, the actual gear of the transmission 3 corresponding to these switching elements, as well as an actual synchronous speed corresponding to this actual gear (i.e., the gear ratio of the actual gear) and the output speed, are determined. As soon as the drive unit speed or the transmission input speed reaches the actual synchronous speed or a speed dependent on it, it is monitored whether the speed control for the drive unit 1 is terminated within a monitoring period.If this is not the case, at least one alternative measure will be taken or initiated to increase the functional safety of the motor vehicle.

[0042] The actual synchronous speed calculated from the actual gear or the translation of the actual gear and the output speed is preferably offset with a negative offset value to determine the speed at which the monitoring time is started. Reference sign 1 drive unit 2 Drive 3 gearboxes 4 Engine control unit 5 Transmission control unit 6 Data exchange 7 Data exchange 8 Data exchange 9 Switching element 10 switching element controllers 11 Control current

Claims

[1] Method for operating a drive train of a motor vehicle, wherein the drive train comprises a drive unit (1) and an automatic or output gear connected between the drive unit (1) and a drive gear (2).an automated transmission (3) wherein in each engaged gear of the transmission (3) a number N switching elements (9) of the transmission (3) are closed, wherein, depending on operating parameters of the drive train, the same can be automatically converted into a coasting operating mode, wherein in the coasting operating mode the drive unit (1) rotates with the transmission (3) not engaged or the drive unit (1) is stationary with the transmission (3) not engaged, and wherein, to terminate the coasting operating mode, a target gear is specified for the transmission (3) and a speed control is specified for the drive unit (1) such that, in order to establish a synchronous condition for the transmission (3), the drive unit speed is increased via the speed control such that the drive unit speed or a transmission input speed dependent on it approaches and / or reaches a defined target synchronous speed adapted to the target gear.characterized by , that during speed control, the control currents of switching element controllers (10), which serve to control the switching elements (9) of the transmission (3), are monitored to determine which switching elements (9) of the transmission (3) are to be considered closed, wherein when it is detected that a number N switching elements (9) of the transmission (3) are to be considered closed, wherein a switching element (9) of the transmission (3) is then considered closed if the control current of the switching element controller (10) of the respective switching element (9) is greater than a limit value, wherein the monitoring function the actual gear of the transmission that corresponds to these closed switching elements (9) is determined, Depending on this actual gear, an actual synchronous speed is determined for the drive unit speed or for the transmission input speed dependent on the same, and the actual drive unit speed or the actual transmission input speed is monitored. Then, when the actual drive unit speed or the actual transmission input speed reaches the actual synchronous speed or a speed dependent on it, a monitoring period is started and it is monitored whether the speed control is terminated within the monitoring period. [2] Method according to claim 1, characterized by , that if the monitoring function determines that the speed control is terminated within the monitoring time, a proper termination of the sailing operating mode is concluded and no alternative measure is initiated. [3] Method according to claim 1 or 2, characterized by, that if the monitoring function determines that the speed control is not terminated within the monitoring time, an improper termination of the sailing operating mode is concluded and at least one alternative measure is initiated. [4] Method according to claim 3, characterized by , that as a replacement measure during the termination of the current sailing operating mode, the speed control is forcibly terminated. [5] Method according to claim 3 or 4, characterized by , that as a substitute measure for the current driving cycle, the sailing mode is prevented by the control system, so that therefore it is not possible to re-enter the sailing mode for the current driving cycle. [6] Method according to any one of claims 3 to 5, characterized by , that as a substitute measure for the current driving cycle, speed control is prevented in all operating modes. [7] Method according to any one of claims 1 to 6, characterized by , that if, during the monitoring of the control currents of the switching element controller (10), it is determined that fewer than the number N switching elements (9) of the transmission (3) are to be considered closed, a conclusion is drawn that the transmission (3) is not frictionally engaged and the monitoring function is not triggered. [8] Method according to any one of claims 1 to 7, characterized by , that if, during the monitoring of the control currents of the switching element controller (10), it is determined that more than the number N switching elements (9) of the gearbox (3) are to be considered closed, a conclusion is drawn that the gearbox (3) is jammed and the monitoring function is not triggered. [9] Control device, in particular transmission control device (5), characterized by Means for carrying out the method according to any one of claims 1 to 8.

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