Method for performing a load change of an internal combustion engine in hybrid vehicles

Abstract

The invention relates to a method for performing a load change in an internal combustion engine in hybrid vehicles. The method according to the invention comprises several steps. In a first step, a driver-requested torque is detected. Subsequently, a target torque of the internal combustion engine is increased by establishing a first target torque gradient as a function of the driver-requested torque or the filtered driver-requested torque. Furthermore, the start of a system change in a drivetrain connected to the internal combustion engine is detected, and a system change gradient of the target torque is determined as a function of the driver-requested torque and / or the current target torque and / or the rotational speed of the internal combustion engine and applied to the target torque until the system change is complete.Furthermore, the target torque is increased to the driver's desired torque by building up a second target torque gradient after the end of the system change, whereby a difference between the driver's desired torque and the target torque is compensated by a torque of the electric motor.

Description

[0001] The invention relates to a method for performing a load change of an internal combustion engine in hybrid vehicles. For the purposes of this application, hybrid vehicles are understood to be vehicles with hybrid drives, i.e., vehicles that can be operated independently via either an electric motor or an internal combustion engine.

[0002] In the context of this application, load changes in an internal combustion engine (combustion engine) refer to processes in which the torque provided by the internal combustion engine changes sign. If no power is required from the internal combustion engine, it is typically in a state in which it exerts a drag torque on the drivetrain. Only when a driver requests power from the internal combustion engine will it operate in such a way that its torque changes sign and the drivetrain is driven. The same applies to negative load changes, in which the sign changes from a positive torque to a drag torque, and the internal combustion engine thus slightly brakes the drivetrain.

[0003] In hybrid vehicles, such a load change occurs in particular when switching from a purely electric operation of the drive train to a combustion engine operation, in which only the combustion engine is used to propel the vehicle, or at least to a hybrid operation, in which both types of drive are used to propel the vehicle, or vice versa.

[0004] Such load changes, according to the state of the art, result in a change in the drivetrain. Modern vehicles with combustion engines typically have a so-called dual-mass flywheel (DMF), which is located between the combustion engine and the rest of the drivetrain to prevent rotational irregularities or similar caused by the combustion engine from being transmitted to the drivetrain and thus to the rest of the vehicle. Such DMFs are also found in hybrid vehicles, where they are located between the combustion engine and the electric motor or drivetrain. A DMF can improve comfort and also reduce the mechanical stress on the drivetrain. The DMF thus decouples the drivetrain from vibrations and the combustion engine.There are different concepts for the DMF, but they all have in common that when changing gears, a certain amount of play must be overcome between the drivetrain and the output of the combustion engine. This means that during the change of gear and thus the load change in the combustion engine, there is no or only a partial frictional connection with the drivetrain. Consequently, the full torque of the combustion engine can only be transferred to the drivetrain after the change of gear, which leads to torque disturbances during the change of gear. Once the change of gear has been completed and the frictional connection in the drivetrain has been established, this can lead to loud noises and acceleration excitations, which can be considered disadvantageous, particularly with regard to comfort and the mechanical stress on the components in the drivetrain.

[0005] The problem and its origins are discussed particularly with regard to theFig. 1a and Fig. 1b clearly. Fig. Figure 1a shows a diagram in which a torque curve during a load change of the combustion engine is plotted over time. The dotted line corresponds to an unfiltered driver request, the dash-dotted line to a filtered driver request, the dashed line to a target torque curve (target torque) of the combustion engine set based on the filtered driver request, and the solid line corresponds to the actual torque curve of the combustion engine during the load change, which deviates from the target torque due to the change in the drive train, here in particular in the DMF. Fig. 1a, a positive load change is considered, i.e., one in which the torque of the combustion engine is increased. Such a load change can occur, for example, when the combustion engine is engaged, when a hybrid vehicle switches from purely electric operation to at least mixed operation. However, other driving situations are also conceivable in which such a load change occurs, such as when a torque requirement is increased from 0 and the combustion engine switches from coasting operation to power operation, in which it delivers power to the drivetrain.

[0006] As in Fig. As can be seen in Figure 1a, the combustion engine is initially in idle mode, i.e. before the load change, and thus delivers a negative torque to the drivetrain. If a power demand is now placed on the combustion engine by increasing the driver's desired torque, a target torque demand is made to the combustion engine, which is represented by the dashed line. The driver's desired torque is usually first filtered (dash-dotted line) in order to provide the combustion engine with a sensible target torque demand with regard to the comfort or dynamic requirements. Due to physical limits and because the combustion engine is not immediately ready to deliver power as soon as the driver's desired torque is available, for example, there is a time offset between the target torque of the combustion engine and the filtered driver's desired torque.The difference in torque during load change between the filtered driver request torque and the target torque of the combustion engine is compensated by an increase in the torque of the electric motor, so that overall there is no loss of performance due to the delayed build-up of the target torque of the combustion engine.

[0007] When the torque of the combustion engine increases, a change in engagement occurs in the drivetrain, particularly in the DMF. The DMF has several spring elements for damping purposes, which are stretched and compressed when the engagement changes. The stretching and compression of the springs, as well as the movement in the DMF, is therefore subject to friction and thus causes hysteresis behavior during the engagement change, which is why this only occurs after a breakaway torque is exceeded and is slightly positive. The breakaway torque can therefore be understood as a limit torque above which the engagement change in the DMF occurs. During the engagement change, however, the torque to be transmitted drops and can therefore no longer follow the target torque specification, resulting in torque disturbances.

[0008] This is also in the Fig. This can be seen from the speed curve over time shown in Figure 1b, since the combustion engine speed is higher than that of the electric motor during the system change. As soon as the system change is complete, a force-locking connection is suddenly formed, which, in conjunction with the briefly sharp increase in speed, transmits a strong impulse to the drivetrain. This impulse also causes the speed of the electric motor and thus the drivetrain to briefly increase, resulting in annoying clicking noises and acceleration impulses.

[0009] Various systems for controlling the electric motor and combustion engine in hybrid vehicles are known in the prior art, which particularly address the load changes of the combustion engine. Patent document DE 10 2005 015 484 A1 discloses a hybrid drivetrain for a vehicle with a fully automatic transmission. The drivetrain is intended to prevent jerky vibrations in the low frequency range up to 20 Hertz by pre-controlling the electric motor. Furthermore, the torque of the electric motor is to be controlled in such a way that the transition from a positive to a negative total torque is as smooth as possible.

[0010] Document DE 10 2009 020 794 A1 also describes a system for optimizing drivetrain dynamics. For this purpose, the future behavior of the drivetrain is predicted using a dual-mass torsional oscillator model based on the required torques for the individual components of the affected axle. At the same time, an optimal progression plan for the drivetrain dynamics is created based on a modified torsional oscillator model. The error between the two predictions and plans results in a correction torque that changes the total torque of the axle. A brake interface generates corresponding signals for the brake control by extrapolating the raw braking torque into the future and generating a standby request for the brake.

[0011] Patent DE 10 2016 215 787 A1 proposes an alternative method for improving the performance of electric drive systems in vehicles. This document refers to problems caused by the timing of the separating clutch and the electric motor when the motor speed drops or increases (a drop in speed causes an unpleasant jerk in the driveline, while an increase in speed results in an acoustic disturbance). These timing problems are known to change with the vehicle's mileage. The method is therefore intended to identify any constant deviation between the actual and target torque of the separating clutch and prevent it from being mistakenly attributed to a timing problem. To avoid compensating for the drive's speed response resulting from such a deviation, the clutch's speed gradient is observed and evaluated in various phases during restart.

[0012] Document DE 10 2008 052 058 B3 relates to a damping device and an associated method for suppressing torsional vibrations in the drivetrain of motor vehicles. A nonlinear physical model of the torsional vibration state is used for this purpose, which is intended to enable more accurate prediction and response to vibrations. The system is suitable for various drivetrain configurations, including multi-motor and electric drives, with the clutch or transmission input torque serving as a control variable. Furthermore, the system allows the driver to select between different driving styles and thus influence the vehicle's load-change behavior. This vibration damping does not require sensors for directly measuring the torsional vibrations or the vehicle's longitudinal acceleration.

[0013] Against the background of the prior art described above, it is the object of the present invention to provide a method by means of which the negative effects on comfort, mechanical stress on the components and longitudinal dynamics during load changes of an internal combustion engine in a hybrid vehicle can be eliminated.

[0014] This object is achieved by the subject matter of the independent claim. Advantageous embodiments of the invention are contained in the subclaims.

[0015] The method according to the invention for carrying out a load change of an internal combustion engine in a hybrid vehicle with the internal combustion engine and an electric motor comprises several steps. In a first method step, a raw driver command torque is detected, which is preferably filtered to a filtered driver command torque. Subsequently, a target torque of the internal combustion engine is increased by establishing a first target gradient of the target torque of the internal combustion engine as a function of the driver command torque or the filtered driver command torque.Furthermore, the start of a shift in a drive train connected to the internal combustion engine, in particular in a dual-mass flywheel, is detected, and a shift gradient of the target torque is determined as a function of the driver's desired torque and / or the current target torque and / or the speed of the internal combustion engine and applied to the target torque of the internal combustion engine until the shift is completed. Preferably, a damping countertorque is applied to the internal combustion engine during the shift in order to reduce an impulse of the shift in torque. Furthermore, the target torque is increased to the driver's desired torque by building up a second target gradient of the target torque after the end of the shift in torque, wherein a difference between the driver's desired torque and the target torque is compensated by a torque of the electric motor.

[0016] The method according to the invention reduces the gradient of the target torque in the internal combustion engine during the shift, and thus around the breakaway torque range. This results in a more controlled shift, which significantly reduces the impulse after the shift and the resulting power connection. This can improve both mechanical load and comfort and power development. The difference in power between the target torque of the internal combustion engine and the preferably filtered driver-desired torque is supplied by the electric motor, so that the reduced magnitude of the gradient in the target torque curve during the shift does not result in any dynamic losses.

[0017] Preferably, the system transition gradient is represented as a nonlinear curve and defined as a nonlinear function over time. This allows for smooth transitions in the target torque, which can be easily compensated by adjusting the torque provided by the electric motor to achieve the driver's desired torque.

[0018] In an advantageous embodiment of the invention, the start and / or end of the shift in the drive train is detected by comparing the speed of the internal combustion engine and the speed of the drive train, and the start and / or end of the shift in the dual-mass flywheel is detected by comparing the speed of the internal combustion engine and the speed of the electric motor. If the speed of the internal combustion engine exceeds the speed of the electric motor, this marks the start of the shift and the exceeding of the breakaway torque, i.e. the torque necessary to overcome friction and similar effects in the drive train or, in particular, in the dual-mass flywheel. If a change in speeds is detected at the dual-mass flywheel, a damping counter-torque is introduced on the internal combustion engine to reduce the shift impulse.

[0019] Another advantageous embodiment of the invention is one in which the first and second target gradients are identical. In such an embodiment, the speed of the internal combustion engine increases or decreases at the same rate before and after the load change. Preferably, a gradient with the maximum possible value is selected here, particularly during positive load changes, in order to reach the detected and driver-specified driver desired torque as quickly as possible and thus keep the time of electric motor support as short as possible. This ensures that the hybrid system comprising an electric motor and internal combustion engine can be used in the optimum power range. The maximum possible value is understood to be the value of the gradient that can be provided by the internal combustion engine within the physical possibilities.

[0020] Furthermore, an embodiment of the method according to the invention is preferred in which the amount of the second target gradient is reduced before the driver's desired torque is reached, thus enabling a smooth and comfortable transition to the final driver's desired torque to be achieved.

[0021] In a preferred embodiment of the invention, the hysteresis behavior of the dual-mass flywheel provided in the drivetrain of the hybrid vehicle is taken into account to determine the shift gradient. This allows a more accurate prediction of the breakaway torque and, accordingly, when the shift gradient is applied to the target torque and when it is not. Accordingly, the shift gradient can be further improved.

[0022] Advantageous embodiments and aspects of the invention are explained in more detail below with reference to the accompanying figures. These show Fig. 1a shows a diagram with a torque curve during a positive load change in the drive train according to the state of the art Fig. 1b shows a diagram with a speed curve during a positive load change in the drive train according to the state of the art Fig. 2a shows a diagram with a torque curve during a positive load change in the drive train when applying the method according to the invention Fig. 2b shows a diagram with a speed curve during a positive load change in the drive train when applying the method according to the invention Fig. 3a shows a diagram with a torque curve during a negative load change in the drive train when applying the method according to the invention Fig. 3b shows a diagram with a speed curve during a negative load change in the drive train when applying the method according to the invention

[0023] On the Fig. 1a and Fig. 1b has already been discussed in more detail in the explanations of the state of the art, which is why a further description is omitted here.

[0024] Fig. Figure 2a shows a diagram with a torque curve during a positive load change in the drive train when applying the method according to the invention. The individual curves correspond to the respective Fig. 1a already explained torque curves. Until the breakaway torque is reached during load change, the Fig. 2a the already in Fig. 1a. Therefore, the driver's desired torque is first detected and filtered accordingly. If the internal combustion engine is ready to ignite and thus deliver power to the drivetrain, the target torque of the internal combustion engine is slowly increased, applying a predetermined initial gradient of the target torque. The internal combustion engine is shifted from coasting mode to power mode.

[0025] Due to the change in sign of the combustion engine's torque, a change in the drivetrain occurs, particularly in the DMF, as soon as a certain breakaway torque is exceeded. Shortly before the change in the drivetrain, the gradient of the target torque (dashed curve) is reduced, so that the target torque is only slowly increased. In the diagram according to Fig. 2a, this is evident from the level of the target torque in the area of ​​the breakaway torque. This makes the system change much smoother than in the case of Fig. 1a and Fig. 1b, the state-of-the-art method, and the impulse acting on the drive train after the force connection in the DMF is restored, can be significantly reduced. Nevertheless, a slight drop in torque occurs when changing the system, as shown in Fig. 2b, since there is no traction during the system change and therefore the torque cannot be transferred to the drive train. However, due to the reduced system change gradient, the drop is significantly smaller than in comparison to the state of the art according to Fig. 1a and Fig. 1b. Fig. 2b shows that the speed of the ICE is only slightly increased during the load change and the curve has a strong peak as in Fig. 1b. Accordingly, the pulse during load change only slightly increases the speed of the electric motor.

[0026] Once the system change has been completed and traction is restored, the target torque is increased again by building up a second target torque gradient. The first and second target gradients are preferably maximum to ensure the fastest possible load change and to produce the driver's desired torque as quickly as possible by the combustion engine. The difference between the target torque curve and the filtered driver's desired torque curve is absorbed at all times by a torque provided by the electric motor (EM support), so that the torque perceived by the driver always corresponds to the filtered driver's desired torque. By calculating the system change gradient and applying it to the target torque curve of the combustion engine, targeted support through the torque of the electric motor can be easily implemented.

[0027] Analogously, in the diagram according to Fig. 3a shows a negative load change using the method according to the invention. The individual curves in the diagram correspond to the curves already described in Fig. 1a and Fig. 2a. If the driver's desired torque drops, a filtered driver's desired torque is specified accordingly. At the beginning of the torque reduction, this also corresponds to the target torque of the combustion engine, so the first target gradient at the beginning of the load change corresponds to the gradient of the filtered driver's desired torque.

[0028] Shortly before reaching the system change, the target torque is specified by a corresponding system change gradient. The system change gradient is even more clearly not to be described as a linear function, but rather is designed in such a way that the target torque curve gradually separates from the driver's desired torque and becomes increasingly flatter. Accordingly, the system change can be carried out smoothly, whereby the actual torque only collapses slightly (i.e., decreases in magnitude), as shown in Fig. 3b in an analogous manner to Fig.3a. Once the system change is complete, a second target gradient is established, which is again significantly larger in magnitude (i.e., regardless of the sign) than the system change gradient, whereby the filtered driver-desired torque curve is reached as quickly as possible. Here, too, the corresponding drag torque between the target torque and the filtered driver-desired torque is taken over by the electric motor. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2005 015 484 A1

[0009] DE 10 2009 020 794 A1

[0010] DE 10 2016 215 787 A1

[0011] DE 10 2008 052 058 B3

[0012]

Claims

[1] Method for carrying out a load change of an internal combustion engine in a hybrid vehicle with the internal combustion engine and an electric motor, Detecting a driver's desired torque, Increasing a target torque of the internal combustion engine by building up a first target gradient of the target torque of the internal combustion engine depending on the detected driver request torque, Detecting the start of a system change in a drive train connected to the internal combustion engine, Determining a system change gradient of the target torque of the internal combustion engine as a function of the driver's desired torque and / or the current target torque of the internal combustion engine and / or the speed of the internal combustion engine, Applying the system change gradient of the target torque of the internal combustion engine to the target torque of the internal combustion engine until the system change is completed, Increasing the target torque of the internal combustion engine to the driver's desired torque by building up a second target gradient of the target torque of the internal combustion engine after the end of the system change, whereby a difference between the driver's desired torque and the target torque of the combustion engine is compensated by a torque from the electric motor. [2] Method according to the preceding claim, wherein the detection of the beginning and / or the end of the system change in the drive train is carried out by a speed comparison between the speed of the internal combustion engine and the speed of the drive train. [3] Method according to one of the preceding claims, wherein the first target gradient and the second target gradient of the target torque of the internal combustion engine are identical. [4] Method according to one of the preceding claims, wherein the first target gradient and / or the second target gradient of the target torque of the internal combustion engine have the maximum possible amount. [5] Method according to one of the preceding claims, wherein the amount of the second target gradient of the target torque of the internal combustion engine is reduced before the driver's desired torque is reached. [6] Method according to one of the preceding claims, wherein during the system change a damping counter-torque is applied to the internal combustion engine in order to reduce an impulse of the system change. [7] Method according to one of the preceding claims, wherein the system change takes place in a dual-mass flywheel of the drive train. [8] Method according to the preceding claim, wherein the determination of the system change gradient is carried out taking into account the hysteresis behavior of the dual-mass flywheel. [9] Method according to one of the preceding claims, wherein the determination of the system change gradient is carried out taking into account a determined breakaway torque. [10] Method according to one of the preceding claims, wherein the detected driver request torque is filtered to a filtered driver request torque.

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