Method for controlling a hybrid powertrain

Abstract

The invention relates to a method for controlling a hybrid powertrain of a motor vehicle with a drive unit comprising at least one internal combustion engine and at least one first electric motor effectively connected to drive wheels and powered by a battery whose functionality is continuously monitored, as well as an automatically controlled disconnect clutch arranged between the drive unit and the at least one first electric motor. In order to enable the motor vehicle to continue operating in specific driving situations in the event of battery failures, the disconnect clutch, which may be open, is closed when a battery fault impairing functionality occurs, and the drive wheels are then driven by the internal combustion engine.

Description

[0001] The invention relates to a method for controlling a hybrid drive train of a motor vehicle with a drive unit containing at least one internal combustion engine and at least one first electric machine which is effectively connected to drive wheels and fed by a battery which is continuously monitored for its functionality, and with an automatically controlled separating clutch arranged between the drive unit and the at least one first electric machine.

[0002] CN 1 15 923 771 A describes a method for starting an internal combustion engine in the event of a battery failure in a hybrid vehicle.

[0003] DE 10 2017 221 245 A1 describes a control method for emergency driving for a hybrid vehicle.

[0004] US 2018 / 0 178 806 A1 describes a method for starting an internal combustion engine and for electric driving with the internal combustion engine switched off in a hybrid vehicle.

[0005] For example, DE 10 2019 122 170 A1 discloses a hybrid drivetrain for a motor vehicle with a drive unit containing an internal combustion engine and an electric motor, and another electric motor that drives the drive wheels directly or via a transmission. A separating clutch is arranged between the drive unit and the electric motor that directly drives the drive wheels. Depending on the driving situation of the motor vehicle, the electric motors are powered by a battery, and / or the battery, such as an accumulator, is charged by one or both generator-driven electric motors.

[0006] The object of the invention is to further develop a method for controlling such a powertrain. In particular, the object of the invention is to propose a method for controlling such a powertrain that takes battery faults into account.

[0007] The object is solved by the subject matter of claim 1. The claims dependent on claim 1 represent advantageous embodiments of the subject matter of claim 1.

[0008] The proposed method is used to control a hybrid drive train of a motor vehicle. The hybrid drive train controlled by the method includes a drive unit containing at least one internal combustion engine. The drive unit preferably includes at least one electric machine, preferably a single electric machine, referred to below as the second electric machine. The internal combustion engine and the second electric machine can be connected to each other permanently or via a separating clutch, and are preferably arranged coaxially with each other.

[0009] At least one further, subsequently at least one first electric motor is operatively connected directly to the drive wheels, for example, as a hub motor or arranged in a transmission. A separating clutch is arranged between the drive unit and the at least one first electric motor, which is controlled automatically, for example, by a hydraulic actuation device according to the prevailing driving situation and depending on a desired torque of the driver of the motor vehicle or a higher-level autonomous control device.

[0010] The electric motors are powered by a battery, for example, a high-voltage battery or accumulator, which is continuously monitored for faults that impair its functionality (hereinafter referred to simply as faults). Depending on the charge level, the following driving situations may arise (not an exhaustive list): - Electric driving, for example, up to a speed threshold of, for example, 70 km / h with the clutch open and the internal combustion engine switched off by means of at least one electric motor, recuperation possible. - Electric driving with charging of the battery with the clutch open, the internal combustion engine drives the second electric machine, which charges the battery, driving and, if necessary, recuperation is carried out by means of at least one first electric machine. - Hybrid driving preferably at speeds above the desired speed threshold with the separating clutch closed, the internal combustion engine and optionally at least one first and / or second electric machine drive the drive wheels, recuperation by means of the at least one first and / or second electric machine is possible.

[0011] In an emergency driving situation superimposed on these normal driving situations, when a battery failure occurs that impairs its functionality, the disconnect clutch, if open, is engaged, and the drive wheels are driven by the internal combustion engine. To compensate for the battery failure or to protect a damaged battery, the vehicle is operated exclusively by the internal combustion engine. If the battery's charge level is particularly impaired, the second electric motor can also be used to charge the battery, provided the driving situation and the detected battery failure permit.

[0012] Particularly in city traffic or when driving below the speed threshold, the emergency driving situation is selected, for example, within the framework of the ecological specifications and the drive wheels are driven by the internal combustion engine below the specified speed threshold if a fault occurs in the battery that impairs its functionality, by starting the internal combustion engine, shutting down at least a first electric motor and closing the separating clutch.

[0013] Depending on a fault that impairs the functionality of the battery, the battery can be charged by the second electric machine in a generator mode or the second electric machine can be switched off.

[0014] According to the invention, if a battery fault is detected, the first thing to check is whether the disconnect clutch is open.

[0015] According to the invention, when the disconnect clutch is engaged—this generally means that the internal combustion engine is already driving the drive wheels—opening of the disconnect clutch is prevented even when the motor vehicle decelerates below the speed threshold, i.e., at all speeds of the motor vehicle, as long as the battery fault persists. In this case, preferably the at least one first and second electric motor are shut down.

[0016] When the separating clutch is open and there is a speed difference between the drive unit and at least one first electric machine below a predetermined speed difference threshold, the separating clutch is immediately closed.

[0017] According to the invention, when the separating clutch is open and when the speed difference between the drive unit and the at least one first electric machine is greater than or equal to the predetermined speed difference threshold, the speed difference is brought below the speed difference threshold, after which the separating clutch is closed. Depending on the existing battery fault, the speed difference can be adjusted by means of at least one of the electric machines, for example if the battery has residual capacity or residual function. Alternatively or additionally, particularly when emergency operation occurs in the event of a total battery failure, the speed difference can be brought below the speed difference threshold, for example ideally below 50 rpm, by means of the internal combustion engine and / or by braking the drive wheels according to the invention.In an emergency, such as a total battery failure, the speed difference can be as high as 1000 rpm, depending on the load capacity of the separating clutch. Furthermore, if the speed of the drive wheels is too low, the engine cannot provide sufficient torque, such as drive torque. In this case, the separating clutch can remain open or be opened to prevent the engine from stalling. The engine can charge the battery while stationary—to the extent that the battery failure allows it.

[0018] The invention is explained in more detail using the exemplary embodiment illustrated in the single figure. This shows a block diagram of a routine for implementing the method.

[0019] The block diagram 1 shows the routine 2 for handling a fault of the battery of a hybrid drive train with the separating clutch TK between the drive unit and the at least one first electric machine driving the drive wheels of the drive train.

[0020] Routine 2 is started in the START block. In branch 3, the functionality FT of the drive train battery is continuously checked. If the functionality FT corresponds to the required quality Q, for example, an insufficient state of charge or a defect, the program branches off to branch 3. If the functionality FT does not correspond to quality Q, i.e., there is an acute, intolerable fault such that continued operation of the battery is not plausible, branch 4 checks whether the separating clutch TK is open. If the separating clutch TK is closed, branch 5 checks whether the torque M available at the corresponding speed of the drive wheels is greater than the torque threshold S1. The torque threshold S1 specifies the torque M of the internal combustion engine at which stalling is avoided.If the torque M is less than or equal to the torque threshold S1, the separating clutch is opened in block 6 and the vehicle goes into emergency mode. When the vehicle is stationary, an attempt can be made to charge the battery using the internal combustion engine. If the torque M is greater than S1, the KEEP condition is set in block 10. This condition keeps the separating clutch TK closed in all speed ranges, particularly at speeds below a speed threshold of, for example, less than 70 km / h, where the separating clutch TK is opened in normal operation and purely electric operation of the drive train is carried out, until the battery fault is rectified. Routine 2 is terminated in block 11.

[0021] If the separating clutch TK is open, branch 7 queries whether the speed difference Δn is less than or equal to a predefined speed difference threshold S. In the event of an emergency closure due to a battery fault, this speed difference Δn can be increased, if the design of the separating clutch TK permits, compared to the speed difference Δn typical in normal operation of less than or equal to 50 rpm, for example, up to 1000 rpm. If the speed difference Δn is less than or equal to this adaptable speed difference threshold S, the separating clutch TK is closed in block 9, and routine 2 is terminated in block 11.

[0022] If the speed difference Δn is greater than the speed difference threshold S, the speed difference Δn is reduced in block 8 and the separating clutch TK is closed in block 9 and routine 2 is ended in block 6. List of reference symbols 1 block diagram 2 Routine 3 Branching 4 Branching 5 Branching 6 blocks 7 Branching 8 blocks 9 Blocks 10 blocks 11 blocks FT functionality KEEP condition M Moment Q Quality TK separating coupling S Speed ​​difference threshold S1 torque threshold Δn speed difference

Claims

[1] Method for controlling a hybrid drive train of a motor vehicle with a drive unit containing at least one internal combustion engine and at least one first electric machine operatively connected to drive wheels and fed by a battery continuously monitored for its functionality (FT), and with an automatically controlled separating clutch (TK) arranged between the drive unit and the at least one first electric machine, wherein the possibly opened separating clutch (TK) is closed upon the occurrence of a fault in the battery that impairs the functionality (FT) and the drive wheels are driven by the internal combustion engine, wherein, if a fault in the battery is detected, it is checked whether the separating clutch (TK) is open, and wherein, if the separating clutch (TK) is closed, opening of the separating clutch (TK) is prevented at all speeds of the motor vehicle as long as the fault in the battery persists,and wherein, when the separating clutch (TK) is open and when the speed difference (Δn) between the drive unit and the at least one first electric machine is greater than or equal to the predetermined speed difference threshold (S), the speed difference (Δn) is brought below the speed difference threshold (S) and then the separating clutch (TK) is closed, , characterized by that, depending on the battery fault, the speed difference (Δn) is adjusted by braking the drive wheels. [2] Method according to claim 1, characterized by that the drive wheels are driven by the at least one electric machine with the separating clutch (TK) open below a predetermined speed threshold and when the separating clutch (TK) is open, and when a fault occurs in the battery which impairs the functionality (FT), the internal combustion engine is started, the at least one first electric machine is shut down and the separating clutch (TK) is closed. [3] Method according to claim 1 or 2, characterized by that the drive unit contains, in addition to the internal combustion engine, at least a second electric machine which, depending on a fault affecting the functionality (FT) of the battery, charges the battery in a generator manner or is switched off. [4] Method according to one of claims 1 to 3, characterized by that when the separating clutch (TK) is open and when the speed difference (Δn) between the drive unit and at least one first electric machine is below a predetermined speed difference threshold (S), the separating clutch (TK) is immediately closed.

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