Method for controlling the powertrain of a motor vehicle

Abstract

Method for controlling a drive train of a motor vehicle with at least one engine and at least one transmission, wherein the transmission has at least one first forward gear (I) and one second forward gear (II), and wherein the first forward gear (I) is freewheeling, characterized in that when the motor vehicle starts moving, if a certain temperature (T) is below a certain threshold (TS), the second forward gear (II) is engaged, so that in the event of a slippage of a freewheel (F) of the first forward gear (I), the second forward gear (II) enables the motor vehicle to start moving.

Description

The invention relates to a method for controlling a drive train of a motor vehicle with the features of the preamble of claim 1. From EP 0 321 873 A2, a dual-clutch transmission and a method for its control are known. In this transmission, a first forward gear is integrated into the power transmission path via a first clutch, and a second forward gear via a second clutch, and can be effectively controlled in this way. The first and second forward gears can each be shifted by means of a switchable freewheel. The transmission can be configured so that when the vehicle starts moving, the first and second clutches are actuated simultaneously. From DE 10 2005 039 383 A1 a method for clutch control for wet clutches is known, wherein, if a viscosity of a clutch fluid is above a certain threshold value, the clutch / gearbox control is adapted in such a way that additional clutch energy is transferred to the clutch fluid and the clutch fluid is then heated by the additional energy. A freewheel synchronizing device is known from DE 11 2009 005 205 T5. From DE 10 2004 042 399 A1 a clutch assembly for torque transmission between a motor and a gearbox with two friction clutches is known. However, the methods known in the prior art for controlling a motor vehicle's drivetrain are not yet optimally designed. For example, at very low temperatures, when starting a motor vehicle with a freewheel or a first forward gear that can be engaged via a freewheel, the freewheel can slip. In this case, no power can be transmitted via the freewheel and the motor vehicle cannot start moving. The invention is therefore based on the objective of further developing and refining the aforementioned method for controlling a motor vehicle's drive train in such a way that starting the motor vehicle can be ensured in a simple and cost-effective manner even at very low temperatures. The problem underlying the invention is solved by a method for controlling a drive train of a motor vehicle with the features of claim 1. The drivetrain comprises, in particular, at least one engine and at least one transmission. The transmission has at least one first forward gear and one second forward gear. The first forward gear is designed with a freewheel mechanism or has a freewheel function. In this process, if the temperature of the motor vehicle is below a certain threshold when it starts moving, then the second forward gear is engaged. In the event of slippage of the first forward gear's freewheel, the vehicle can be moved forward again using the second forward gear. The second forward gear can be designed without a freewheel mechanism. Alternatively, the second forward gear can be equipped with a switchable freewheel, in which case the freewheel is also deactivated and / or locked when the second forward gear is engaged. The specified temperature can be, for example, a transmission (oil) temperature, an engine (oil) temperature, an ambient temperature, or a vehicle interior temperature, or it can be determined from one of these. In a preferred embodiment, the specified temperature is the gear oil temperature. The gear oil temperature can be easily determined, for example, by a temperature sensor. Furthermore, the gear oil temperature can provide a relatively reliable assessment of the freewheel's operational readiness. The transmission can be, in particular, an automatic and / or an automatable transmission. In a further highly preferred embodiment, the transmission is designed as a dual-clutch transmission. In this configuration, the first forward gear can be engaged via a first clutch and the second forward gear via a second clutch. For example, one clutch component of the first clutch can be non-rotatably connected to an engine shaft driven by the engine, and another clutch component of the first clutch can be non-rotatably connected to a first transmission input shaft. Similarly, one clutch component of the second clutch can be non-rotatably connected to the engine shaft driven by the engine, while another clutch component of the second clutch can be non-rotatably connected to a second transmission input shaft. The first forward gear can be specifically assigned to the first transmission input shaft, and the second forward gear to the second transmission input shaft.The first transmission input shaft and / or the first forward gear, as well as the second transmission input shaft and / or the second forward gear, can be connected to a transmission output shaft in a rotationally effective manner, possibly via an intermediate shaft. For example, the transmission can be an automatic and / or automatable dual-clutch transmission, for example with a manual shift function, such as a so-called Tiptronic function. In a further embodiment, the second clutch engages, in particular, only at a starting speed that is higher than the starting speed of the first clutch. This ensures that the two clutches do not engage or, in particular, are not engaged simultaneously. In this procedure, if the vehicle's temperature is below a certain threshold when starting off, the second forward gear is engaged. This allows at least an attempt to determine whether the freewheel mechanism of the first forward gear is still functional despite the low temperature, and in particular whether it can engage. If the freewheel mechanism of the first forward gear is not functional due to the low temperature, and in particular whether it can engage, then starting off can be ensured by using the second forward gear. In one embodiment, if the vehicle's temperature is below a certain threshold when starting off, only the second clutch is engaged. This ensures that starting off directly in second forward gear is a simple and straightforward process. In another embodiment, when the vehicle starts moving and the temperature is below a certain threshold, the first clutch (and later the second clutch) is engaged, or the first and second clutches are actuated in parallel. When the engine speed reaches or exceeds the engagement speed of the second clutch, the second clutch engages. This allows testing to determine whether the freewheel of the first forward gear is functional despite the low temperature, and in particular whether it engages. If the freewheel of the first forward gear is not functional due to the low temperature, or in particular whether it engages, starting can be ensured using the second forward gear. In a preferred embodiment, the first forward gear can be engaged by a freewheel, particularly one that transmits only traction torque, or is itself engaged by a freewheel mechanism. A freewheel that transmits only traction torque can be designed more simply and cost-effectively than a freewheel that can be switched on and off. The freewheel of the first forward gear can, for example, be built into or integrated within the first forward gear itself. It is also conceivable that the freewheel of the first forward gear can be designed to be switched on and off. In another embodiment, the motor vehicle is an electric vehicle with at least one electric motor. In another embodiment, the motor vehicle is a hybrid vehicle with an internal combustion engine and at least one electric motor. The disadvantages mentioned at the beginning are therefore avoided and corresponding advantages are achieved. There are now numerous possibilities for advantageously designing and further developing the method according to the invention. For this purpose, reference may first be made to the claims subordinate to claim 1. In the following, some preferred embodiments of the method according to the invention are explained in more detail with reference to the drawing and the accompanying description. In the drawing: Fig. 1 shows, in a schematic flowchart, an embodiment of a method in which – if a certain temperature is below a certain threshold when the motor vehicle starts moving – the second forward gear is engaged and only the second clutch is engaged (starting via the second clutch); and Fig.2 in a schematic flowchart another embodiment of a method according to the invention, in which - when a certain temperature is below a certain threshold when starting the motor vehicle - the first and second forward gears are engaged and the first clutch is closed first, wherein if the freewheel of the first forward gear slips, the second clutch is closed (starting via both clutches). Fig. 1 and Fig. 2 illustrate different embodiments of the inventive method for controlling a drive train of a motor vehicle with at least one engine and at least one transmission. For example, the motor vehicle can be an electric vehicle with at least one electric motor and / or a hybrid vehicle with an internal combustion engine and at least one electric motor. The transmission has at least one first forward gear (I) and one second forward gear (II). The first forward gear (I) can be engaged by a freewheel (F), which is designed to transmit traction torque (only), or is specifically configured as a freewheel mechanism. The transmission can in particular be designed as a dual-clutch transmission, in which the first forward gear I is integrated into the power transmission path via a first clutch K1 and the second forward gear II via a second clutch K2. In both embodiments, a specific temperature T, for example the transmission oil temperature, is first determined when the motor vehicle starts moving. Fig. 1 illustrates an embodiment of the method in which, when the specific temperature T, for example the transmission oil temperature, is below a certain threshold TS, (at least) the second forward gear II is engaged and, in particular, only the second clutch K2 is engaged, so that the vehicle can start moving in the second forward gear II. This prevents slippage of the freewheel F of the first forward gear I. Fig. 1 further illustrates that when the vehicle starts moving, if the specific temperature T, for example the transmission oil temperature, is greater than or equal to the specific threshold TS, then – particularly as is conventional – the first forward gear I or the freewheel of the first forward gear I can be effectively engaged and the first clutch K1 can be closed, so that the vehicle can start moving in the first forward gear I. Fig. 2 illustrates another embodiment of the method, in which, if the specific temperature T, for example the transmission oil temperature, is below a specific threshold TS, the first forward gear I is effectively "engaged" or realized by the freewheel, and the second forward gear II is effectively engaged, and initially the first clutch K1 (and later the second clutch) is closed, or the first clutch K1 and the second clutch K2 are engaged in parallel.The two clutches K1 and K2 are designed such that the second clutch K2 only engages at a starting speed UK2 that is higher than the starting speed UK1 of the first clutch K1. This ensures that the two clutches K1 and K2 do not engage simultaneously, and in particular, that clutch K2 only engages when clutch K1 cannot regulate the starting speed UK1. Fig. 2 illustrates that the first attempt to start is made – particularly as is conventional – via clutch K1, provided that the engine speed UM is greater than or equal to the starting speed UK1 of the first clutch K1 and less than the starting speed UK2 of the second clutch K2, and the freewheel F does not slip despite the low temperature T. Thus, the vehicle can still start in first forward gear I via the freewheel F, if necessary, despite the low temperature. Fig. 2 further illustrates that if the engine speed UM is greater than or equal to the starting speed UK1 of the first clutch K1 and less than the starting speed UK2 of the second clutch K2, and the freewheel F slips, for example due to low temperature T, the first clutch K1 cannot maintain the engine speed UM and the engine speed U increases until it reaches or exceeds the starting speed UK2 of the second clutch K2, at which point the second clutch K2 engages. Thus, even with the freewheel F of first forward gear I slipping, the vehicle can still start in second forward gear II. To engage the second clutch K2, a starting governor can, for example, adjust the torque of the second clutch K2 and regulate the engine speed U. Fig. 2 further illustrates that when the motor vehicle starts moving, if the certain temperature T, for example the transmission oil temperature, is greater than or equal to the certain threshold TS, - in particular as is conventional - the first forward gear I can be engaged and the first clutch K1 can be closed, so that the motor vehicle can start moving in the first forward gear I. Reference symbol list I First forward gear with freewheel II Second forward gear F Freewheel T Specific temperature, in particular transmission oil temperature TS Threshold of the specific temperature, in particular transmission temperature K1 First clutch K2 Second clutch UK1 Starting speed of the first clutch UK2 Starting speed of the second clutch UM Engine speed

Claims

Method for controlling a drive train of a motor vehicle with at least one engine and at least one transmission, wherein the transmission has at least one first forward gear (I) and one second forward gear (II), and wherein the first forward gear (I) is freewheeling, characterized in that when the motor vehicle starts moving, if a certain temperature (T) is below a certain threshold (TS), the second forward gear (II) is engaged, so that in the event of a slippage of a freewheel (F) of the first forward gear (I), the second forward gear (II) enables the motor vehicle to start moving. Method according to claim 1, characterized in that the specified temperature (T) is a gear oil temperature. Method according to claim 1 or 2, characterized in that the transmission is designed as a dual-clutch transmission, wherein the first forward gear (I) is integrated into the power transmission path via a first clutch (K1) and the second forward gear (II) via a second clutch (K2). Method according to claim 3, characterized in that the second clutch (K2) only closes at a starting speed (UK2) which is higher than a starting speed (UK1) of the first clutch (K1). Method according to one of claims 3 to 4, characterized in that when the motor vehicle starts moving and the certain temperature (T) is below the certain threshold (TS), only the second clutch (K2) is closed or is closed. Method according to one of claims 3 to 4, characterized in that when the motor vehicle starts moving, if the certain temperature (T) is below the certain threshold (TS), the first clutch (K1) is closed first, or the first clutch (K1) and the second clutch (K2) are controlled in parallel, wherein when an engine speed (UM) of the engine reaches or exceeds the starting speed (UK2) of the second clutch (K2), the second clutch (K2) is closed. Method according to one of the preceding claims, characterized in that the first forward gear (I) is switchable or designed by a freewheel (F) that transmits, in particular, only traction torque. Method according to one of the preceding claims, characterized in that the motor vehicle is an electric vehicle with at least one electric motor. Method according to one of the preceding claims, characterized in that the motor vehicle is a hybrid vehicle with an internal combustion engine and with at least one electric motor.

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