Method and device for controlling a parallel hybrid drive train of a vehicle

Abstract

Method for controlling a parallel hybrid drivetrain of a vehicle, comprising an automatic transmission (5) and an internal combustion engine (2), which can be connected via a first switching device (3) functioning as a disconnect clutch to an electric machine (4), which is connected via a drive shaft to a second switching device (6) arranged within the transmission (5) and functioning as a starting clutch, wherein fault monitoring is carried out to detect switching errors of the starting clutch (6), and wherein, in the event of a detected fault, predetermined substitute measures are initiated and carried out, enabling the vehicle to be decelerated to a standstill, wherein, in the event of a detected opening fault of the starting clutch (6), a forced neutral shift of the transmission (5) via an alternative power branch of the drivetrain is triggered as a substitute measure, characterized in thatthat in the event of a sudden demand for drive torque from the internal combustion engine (2) and / or the electric machine (4), where, without a corresponding actuation of an accelerator pedal and / or without a significant deviation of the speed of the internal combustion engine (2) from a predetermined target idle speed, a torque monitoring threshold is exceeded for a specified minimum period, the occurrence of an opening fault is inferred.

Description

[0001] The invention relates to a method and a device for controlling a parallel hybrid drive train of a vehicle according to the preamble of claim 1.

[0002] German patent DE 10 2006 033 087 A1 discloses a vehicle with such a powertrain, in which a first clutch is arranged between an internal combustion engine and an electric motor that can be operated as both a motor and a generator, and a second clutch is arranged within an 8-speed automatic transmission with four partially coupled planetary gear sets. During a starting maneuver using the electric motor, the first clutch is engaged, and the second clutch, integrated into the transmission, is activated to perform a temporary slip operation. The power flow for several gears also branches via this integrated starting clutch. A comparable parallel hybrid powertrain with a slip-controlled integrated starting clutch is also disclosed in German patent DE 10 2006 005 468 A1.

[0003] DE 198 18 108 A1 discloses a different hybrid powertrain in which an internal combustion engine, an electric motor, and a vehicle transmission are arranged in a controllable drive relationship via a planetary gear set. On the input side, the internal combustion engine is connected to a ring gear via a first shaft, and the electric motor is connected to a sun gear of the planetary gear set via a second shaft. On the output side, a planetary gear carrier is connected to the vehicle transmission via a third shaft. A controllable clutch is arranged between the internal combustion engine and the electric motor, which selectively connects the input shafts of the internal combustion engine and the electric motor. To avoid a clutch shock when starting the vehicle, the electric motor is operated as a generator while the internal combustion engine is running and the clutch is initially disengaged.Its braking torque keeps the combustion engine at a predetermined idle speed via the planetary gear, so that the speeds of the three drive shafts approach each other and, when the speeds are equal, the clutch can be closed comfortably, i.e. completely without jerking.

[0004] DE 10 2007 050 229 A1 describes a hybrid vehicle with an internal combustion engine, an electric motor, and an automatic transmission, wherein a disconnect clutch is arranged between the internal combustion engine and the electric motor. A starting clutch is arranged on the side of the electric motor associated with the automatic transmission. In the event of a transmission malfunction, the disconnect clutch is held in a closed position by means of a disconnect clutch holding hydraulic system, and the starting clutch is held in a closed position by means of a starting clutch hydraulic system.

[0005] German patent DE 10 2006 042 608 A1 describes a method for determining the state of a starting clutch. During the vehicle's braking process, the torque curve of the drive system and / or "stall information" from the combustion engine is observed and correlated with the current transmission state of the starting clutch. If it is determined that the starting clutch could not be disengaged during braking, a restart of the engine is not permitted without restrictions for safety reasons.

[0006] EP 1 177 931 A2 describes a hybrid vehicle control system for the event of a clutch failure between the combustion engine and the drive wheel. If a clutch between the combustion engine and the transmission cannot be disengaged due to a fault, the system shifts into the highest possible gear to maximize the vehicle's range. Alternatively, it shifts into a lower gear to facilitate starting. If a gear change is not possible, the maximum possible vehicle speed for the current gear is determined and limited accordingly.

[0007] The constant operational readiness of the switching device, which functions as a controllable starting clutch, is particularly important in such hybrid systems, especially in those where the starting clutch is integrated into the vehicle transmission as a multifunctional component. However, a failure of such a controllable switching element cannot be completely ruled out.

[0008] If a vehicle is brought to a stop from a standstill with the integrated starting clutch engaged, this clutch should normally open at a specific engine speed above or equal to the target idle speed. However, if this clutch fails to open despite appropriate control signals, for example, due to a hydraulic valve being blocked by contamination in the hydraulic oil, the engine speed could drop below the target idle speed when the vehicle decelerates. To prevent the engine from stalling, a conventional idle speed control would then demand higher engine torque, ultimately resulting in the vehicle accelerating. A driver who presses the brake pedal would therefore initially experience the expected deceleration, followed by a surprising acceleration.

[0009] Such vehicle behavior, which is irritating to the driver, can lead to a loss of comfort in known parallel hybrid vehicles, even to the point of rendering the vehicle undrivable.

[0010] Against this background, the invention is based on the objective of presenting a method and a device for controlling a parallel hybrid vehicle with an internal transmission starting clutch, in which a high level of operational reliability and the highest possible driving comfort of the vehicle is ensured, especially in the event of a failure of the integrated starting clutch.

[0011] The solution to this problem arises from the features of the independent claims, while advantageous embodiments and further developments of the invention can be derived from the respective dependent claims.

[0012] The invention is based on the finding that in vehicles with modern automatic transmissions with a relatively high number of gears, a failure to open an integrated starting clutch in the drivetrain can in many cases be compensated at least temporarily by switching substitute gears, taking into account the closed integrated starting clutch, or that at least a disengagement of the power transmission by bypassing the closed integrated starting clutch is possible.

[0013] This can be done by entering detected errors into an error memory of a suitable control and monitoring device, which can be determined event-oriented by evaluating disturbances of the regular power transmission in the drive train that can be clearly attributed to the clutch failure, or preventively by means of a direct cyclical functional check of the clutch, in close temporal proximity to the failure event or even predictively in the case of a likely imminent failure.

[0014] The invention is based on a method for controlling a parallel hybrid drivetrain of a vehicle, comprising an automatic transmission and an internal combustion engine. The engine is connected to an electric motor via a first switching device functioning as a disconnect clutch. This electric motor is connected via a drive shaft to a second switching device, located within the transmission and functioning as a starting clutch. To solve the stated problem, the invention provides for fault monitoring to detect switching errors of the starting clutch. Upon detection of a fault, predetermined compensatory measures are initiated and executed to allow the vehicle to continue driving or to brake to a standstill.

[0015] The invention further relates to a device for controlling a parallel hybrid drivetrain of a vehicle, comprising an automatic transmission and an internal combustion engine. The engine can be connected to an electric motor via a first switching device functioning as a disconnect clutch. This electric motor is connected via a drive shaft to a second switching device, located within the transmission and functioning as a starting clutch. To solve the stated problem with regard to the device, the invention provides a fault monitoring device. This device includes sensor and evaluation means for detecting switching errors of the starting clutch, as well as control means for initiating and executing compensatory measures that enable the continuation of driving or the braking of the vehicle to a standstill.

[0016] The fault monitoring according to the invention makes it advantageous to reliably detect a switching fault of the starting clutch that has currently occurred or that is expected to occur during an upcoming switching operation, in which in particular a requested clutch opening fails to occur.

[0017] In particular, in the event of a sudden torque demand, i.e., a short-term, strong increase in the drive torque of the combustion engine and / or the electric machine, where a torque monitoring threshold is exceeded for a defined minimum period, for example 50 milliseconds, without corresponding actuation of an accelerator pedal and / or without a significant deviation of the speed of the combustion engine from a predetermined target idle speed, a conclusion is drawn that an opening fault of the integrated starting clutch has occurred and an error memory entry is triggered, which initiates a replacement measure.

[0018] In response to a detected opening fault of the starting clutch, measures are first checked and, if necessary, implemented to enable the vehicle to continue driving.

[0019] In particular, it may be provided that a transmission monitoring system, which is frequently present in modern transmissions, is advantageously used in the event of a failure of a regular shifting operation in which the integrated starting clutch is intended to be engaged, in order to avoid gears with a shifting participation of the integrated starting clutch and to modify the shift control accordingly.

[0020] If, during deceleration, the clutch opening speed falls below a certain threshold, threatening to stall the engine, a forced neutral shift is prepared and initiated as the next step. In a forced neutral shift, the power transmission in the remaining transmission, independent of the integrated starting clutch (i.e., in the power-split transmission), is disengaged as quickly as possible, bypassing the branch in which the starting clutch is active.

[0021] Furthermore, as an additional vehicle-side safety measure, in the event of a safety-critical deceleration or a failure of the forced neutral shift, the driver is permitted to stall the combustion engine using the vehicle brakes. The drive torque of the combustion engine and / or the electric motor is pre-limited to a maximum value, depending on the accelerator pedal position or another parameter corresponding to the driver's input. This allows for a relatively gentle stalling of the engine. For idle control purposes, the permissible drive torque is limited to a maximum value, for example, 50 Nm when stationary. If the vehicle fails to disengage the traction or does not do so quickly enough, the vehicle engine is stalled by the vehicle brakes, thus preventing the vehicle from potentially sliding forward in a potentially safety-critical manner.

[0022] In addition to event-driven fault detection, preventive fault detection regarding the functionality of the integrated starting clutch is possible. For this purpose, it can be provided that, during driving operation, a slip test is performed and evaluated at predetermined intervals on those gears whose power flow branches via the integrated starting clutch, and if necessary, an error message is issued or an error entry is made in an electronic memory.

[0023] Accordingly, during driving, the clutch is cyclically brought into a slip state in the gears relevant to the vehicle's transmission system, where speed measurement and thus slip determination at the integrated starting clutch is possible. Starting from a closed position, the excessive pressure normally present at the starting clutch in this state, which is higher than required for the current torque load, is reduced by a corresponding pressure reduction. The test determines whether and, if so, at what control pressure—i.e., at what transmission capacity relative to the transmission load torque or engine torque—slip occurs. It should be noted that the slip initiation point determined during the slip test can also be advantageously used to adapt the actual coefficient of friction of the integrated starting clutch.

[0024] If the clutch slip with respect to the control pressure is within a predefined, plausible test range, it is not expected that the pressure modulation or the release of the contact pressure between the friction partners for opening the integrated starting clutch will fail during the next relevant shifting or stopping operation. Should opening of the integrated starting clutch nevertheless unexpectedly fail, at least the previously described event-oriented fault detection will take effect.

[0025] If, however, the slip test indicates that the integrated starting clutch is unlikely to open during the next necessary gear change, an error message is logged in the corresponding electronic data storage device while the vehicle is in operation, and a suitable alternative measure is prepared. Again, all gear changes that require opening the integrated starting clutch are initially avoided, and if necessary, a suitable alternative gear is pre-selected.

[0026] When braking and falling below the opening speed of the starting clutch, the disengagement of the power transmission in the drivetrain is ensured not only by attempting to open the starting clutch but also by proactively requesting a forced neutral in the rest of the transmission.

[0027] To further increase the availability of the drive for continuing to drive or starting after braking to a standstill when the starting clutch cannot be opened, it can also be provided that, in the event of a detected opening error of the integrated starting clutch, the combustion engine is decoupled from the drive train as required by opening the disconnect clutch and a purely electric drive is temporarily used, and that the combustion engine is coupled back to the rest of the drive train by closing the disconnect clutch when a suitable transmission input speed for the combustion engine drive has been established.

[0028] Accordingly, due to an event-driven or preventative fault entry in an electronic data storage device, the disconnect clutch is opened at a pre-calculated opening speed when a gear is engaged and the integrated starting clutch is involved. An auxiliary electric pump, located in hybrid drive systems, can advantageously take over the supply of lubrication, cooling, and hydraulic oil to the transmission during the period when a hydraulic pump mechanically driven by the combustion engine is decoupled. With the disconnect clutch open and the integrated starting clutch closed, the vehicle is then decelerated in an electric driving mode.

[0029] After a standstill, the vehicle can start electrically, and once a suitable transmission input speed is reached, the combustion engine can be re-engaged. In principle, it is even possible to restart the combustion engine without the clutch slipping (since it remains engaged) if stalling could not be prevented despite opening the disconnect clutch.

[0030] To illustrate the invention, the method for fault detection and for carrying out replacement measures on a parallel hybrid drive train of a vehicle in the event of a shift failure of an internal transmission starting clutch is described in more detail below using the example of an 8-speed automatic transmission, as is known per se from the applicant's DE 10 2006 033 087 A1 mentioned at the outset.

[0031] The single figure shows a highly simplified schematic of such a parallel hybrid drivetrain. The parallel hybrid drive system 1 comprises, as essential components in the direction of power flow, an internal combustion engine 2, a disconnect clutch 3, an electric machine 4 capable of both motor and generator operation, an 8-speed automatic transmission 5 with gear ratio monitoring 8, a starting clutch 6 integrated into the automatic transmission 5 and controllable by a fault monitoring device 9, and an output shaft 7. The fault monitoring device 9 can be designed as a component of other existing control units. In this transmission 5, the integrated starting clutch 6 is involved in torque transmission to gears 1 to 5 as well as to a reverse gear.

[0032] The following scenario assumes a vehicle with the integrated starting clutch 6 engaged or nearly engaged, and is then decelerated by the driver applying the brake pedal. The starting clutch 6 should open at a specific engine speed, defined as the opening speed, slightly above or equal to the target idle speed to prevent the combustion engine 2 from stalling. Despite appropriate control signals, the starting clutch 6 does not open, for example, because a connected hydraulic valve is blocked by contamination in the hydraulic oil. Consequently, the torque transmission via the starting clutch 6 cannot be released to the required extent.

[0033] As a result, the engine speed would be reduced below the target idle speed when the vehicle decelerates. Therefore, the drive torque would be increased via an idle speed control of the internal combustion engine 2 to prevent the engine 2 from stalling, with the consequence that the vehicle would accelerate abruptly.

[0034] The fault monitoring device 9 performs a clutch diagnosis, concluding that there is an opening fault in the integrated starting clutch 6, since the driver does not operate the accelerator pedal and the engine speed is initially in the range of an idle speed, after which the drive torque increases sharply and exceeds a defined monitoring threshold for a predetermined period.

[0035] The clutch problem may also have been detected by the transmission ratio monitoring system 8 or may have already been indicated by a preventive cyclic slip test at the starting clutch 6, in which slippage does not occur at all or not to the expected extent despite reduced contact pressure. In any case, the clutch fault triggers a corresponding fault memory entry in an electronic data storage device, which necessitates the preparation and subsequent execution of a compensatory measure in the drivetrain.

[0036] If the transmission ratio monitoring system 8 detects a problem with the starting clutch 6, for example, if the starting clutch 6 fails to disengage during an upshift attempt into 6th gear or a higher gear, or if the starting clutch 6 fails to engage during a downshift attempt from 6th gear or a higher gear to a lower gear, a gear is selected as a substitute measure in which no shifting of the starting clutch 6 is necessary. The starting clutch 6 is therefore no longer considered an active clutch.

[0037] If the opening speed is undershot during braking, or if undershot opening speed is unavoidable in driving operation restricted by the inactive starting clutch 6, a forced neutral shift is triggered in the automatic transmission, in which the power transmission in the rest of the transmission is immediately terminated, i.e. by bypassing the control-blocked starting clutch 6.

[0038] In the event of preventive fault detection based on the aforementioned slip test, which assesses the necessary opening of the starting clutch 6 during upshifts into 6th gear or higher gears, or during braking to a standstill, as unsafe, a compensatory measure is implemented during driving. Upshifts involving the integrated starting clutch 6 are then preferentially avoided. During braking and when the opening speed is undershot, an appropriate control signal is used to attempt to open the clutch. Simultaneously, however, an additional requirement for forced neutral in the rest of the transmission ensures the disengagement of the power transmission in the drivetrain.

[0039] If the transmission ratio monitoring 8 detects that it is not possible to open the starting clutch 6, which is otherwise required, the disconnect clutch 3 can be activated as a further embodiment of the method, provided that a necessary hydraulic supply is ensured with the combustion engine 2 disconnected, e.g. by an electric supply pump.

[0040] The disconnect clutch 3 is opened at a predetermined opening speed, thereby switching the vehicle or its drive system into a purely electric driving mode. In this mode, the vehicle is decelerated to a standstill, whereby downshifts from 5th gear down to 1st gear are still possible without the involvement of the starting clutch 6. Any subsequent acceleration is also purely electric. The combustion engine 2 can continue to run at idle during the disconnection process by opening the disconnect clutch 3 and can be re-engaged at a transmission input 10 after acceleration once a sufficient speed is reached. If the combustion engine 2 was previously stalled, it can also be restarted by closing the disconnect clutch 3. Reference symbol list 1 parallel hybrid drive system 2 Internal combustion engine 3 Switching device, disconnect clutch 4 Electric machine 5 gearboxes 6. Switching device, starting clutch 7 Drive 8 Gear ratio monitoring 9 Fault monitoring device 10 Gearbox input

Claims

[1] Method for controlling a parallel hybrid drive train of a vehicle, comprising an automatic transmission (5) and an internal combustion engine (2), which can be connected via a first switching device (3) functioning as a disconnect clutch to an electric machine (4), which is connected via a drive shaft to a second switching device (6) arranged inside the transmission (5) functioning as a starting clutch, wherein fault monitoring is carried out to detect switching faults of the starting clutch (6), and wherein, in the event of a detected fault, predetermined substitute measures are initiated and carried out, enabling the vehicle to be decelerated to a standstill, wherein, in the event of a detected opening fault of the starting clutch (6), a forced neutral shift of the transmission (5) via an alternative power branch of the drive train is triggered as a substitute measure. characterized by, that in the event of a sudden demand for drive torque from the internal combustion engine (2) and / or the electric machine (4), where, without a corresponding actuation of an accelerator pedal and / or without a significant deviation of the speed of the internal combustion engine (2) from a predetermined target idle speed, a torque monitoring threshold is exceeded for a specified minimum period, the occurrence of an opening fault is inferred. [2] Method for controlling a parallel hybrid drivetrain of a vehicle, comprising an automatic transmission (5) and an internal combustion engine (2), which can be connected via a first switching device (3) functioning as a disconnect clutch to an electric machine (4), which is connected via a drive shaft to a second switching device (6) arranged inside the transmission (5) functioning as a starting clutch, wherein fault monitoring is carried out to detect switching faults of the starting clutch (6), and wherein, in the event of a detected fault, predetermined substitute measures are initiated and carried out, enabling the continuation of driving or the braking of the vehicle to a standstill, wherein, in the event of a detected opening fault of the starting clutch (6), the internal combustion engine (2) is decoupled from the drivetrain as required by opening the disconnect clutch (3) and a purely electric drive is temporarily provided,wherein the internal combustion engine (2) is re-coupled to the drive train by closing the disconnect clutch (3) when a transmission input speed suitable for internal combustion engine drive has been established, characterized by , that in the event of a safety-critical deceleration, the combustion engine (2) may be stalled by a driver using a vehicle brake, wherein the drive torque of the combustion engine (2) and / or the electric machine (4) is limited in advance to a maximum value, depending on an accelerator pedal position or another quantity corresponding to a driver request. [3] Method according to claim 1 or claim 2, characterized by , that the fault monitoring detects the currently occurring or a likely to occur opening fault of the starting clutch (6) during an upcoming switching operation, in which a requested clutch opening fails to occur. [4] Method according to any one of claims 1 to 3, characterized by, that during driving operation for at least one gear whose power flow branches via the starting clutch (6), a slip test is carried out and evaluated at the starting clutch (6) at predetermined intervals. [5] Method according to any one of claims 1 to 4, characterized by , that a transmission ratio monitoring system (8) will issue an error message if a regular shifting operation, in which a shifting of the starting clutch (6) is intended, fails. [6] Method according to any one of claims 1 to 4, characterized by , that if an impending opening fault of the starting clutch (6) is detected, an error message is issued and the preventive replacement measure is initiated. [7] Method according to any one of claims 2 to 6, characterized by , that as a further preventive alternative measure, switching operations in which switching of the starting clutch (6) is intended are avoided. [8] Method according to any one of claims 2 to 6, characterized by , that when the starting clutch (6) is activated in the opening direction, a forced neutral switching of a residual transmission is prepared as a further preventive replacement measure in the event of a predetermined clutch opening speed being undershot. [9] Method according to any one of claims 2 to 7, characterized by , that as a further preventive replacement measure a switchable substitute gear is preselected via the transmission ratio monitoring (8), and that a forced neutral shift is initiated if a predetermined clutch opening speed is undershot.

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