Method for controlling and control unit for operating an automatic transmission in a motor vehicle

Abstract

Method for controlling an automatic transmission (3) with an electronic transmission control unit (8) for operating this transmission (3) in a motor vehicle (1) with an engine (2) for driving this transmission (3), wherein the transmission (3) is controlled and / or regulated by means of at least one function (9) implemented in the transmission control unit (8) which, in calculating its control and / or regulated variables, uses at least one reference temperature (c_ref) based on an oil temperature (c_sensor) currently measured in the transmission (3), wherein, from a first engine start (M_an1) which occurs after initialization of the transmission control unit (8), a filtered oil temperature (c_PT2) is calculated from the currently measured oil temperature (c_sensor) using a mathematical filter function, characterized in thatthat the function (9) uses the filtered oil temperature (c_PT2) as the reference temperature (c_ref) when calculating its control and / or regulated variables from the first engine start (M_an1) until the beginning of an engine stop phase (M_stopp) following the first engine start (M_an1), during which the transmission control unit (8) remains in operation at least temporarily; that the filtered oil temperature (c_PT2) valid at the beginning of this engine stop phase (M_stopp) is stored as a shutdown temperature (c_aus) in the electronic transmission control unit (8); and that predefined criteria for an engine restart (M_an2_w) are checked when a second engine start (M_an2) ends this engine stop phase (M_stopp); and that if the second engine start (M_an2) is not identified as an engine restart (M_an2_w), the function (9) uses the filtered oil temperature (c_PT2) as the reference temperature when calculating its control and / or regulated variables. (c_ref) continues to use the filtered oil temperature (c_PT2),However, if the second engine start (M_an2) is identified as an engine restart (M_an2_w), function (9) uses the stored shutdown temperature (c_aus) as the reference temperature (c_ref) when calculating its control variables as long as the currently measured oil temperature (c_sensor) does not exceed the stored shutdown temperature (c_aus), and then, if the currently measured oil temperature (c_sensor) is greater than the stored shutdown temperature (c_aus) for a predefined time period (t_def), it uses the filtered oil temperature (c_PT2) again as the reference temperature (c_ref).

Description

The present invention relates to a method for controlling an automatic transmission in a motor vehicle, according to the preamble of claim 1. The present invention further relates to a control unit for carrying out this method. In modern automatic transmissions, it is necessary and common practice for various reasons to measure the temperature of the lubricating and cooling oil used in the transmission—for example, by means of a semiconductor sensor located in the transmission's oil sump—and to supply this measurement to the transmission's control unit. For instance, in known automatic transmissions, it is common practice to only allow the transmission's torque converter lock-up clutch to engage once a predetermined minimum transmission oil temperature has been reached or exceeded. Furthermore, it is also common practice in known automatic transmissions to switch the transmission to a so-called "hot mode" and implement measures to reduce the transmission oil temperature when a predetermined upper limit for the transmission oil temperature has been reached or exceeded.Furthermore, it is common practice in automatic transmissions to adjust control parameters based on the transmission oil temperature, as the transmission oil temperature determines the viscosity of the transmission oil. Depending on the transmission oil temperature, different filling times and pressures result for the transmission's shift elements, which are actuated during gear changes. Therefore, a corresponding adjustment of these control parameters is necessary to ensure smooth shifting. In order to be able to regulate or control as accurately as possible depending on the transmission oil temperature, the temperature sensor(s) integrated into the transmission should be as accurate as possible and have the smallest possible measurement tolerance, so that the required temperature reserve for the temperature-dependent adjustment or triggering of transmission functions is as low as possible and the temperature-dependent function adjustments or triggerings are as effective as possible. However, it's important to consider that the actual transmission temperature varies across different components within the transmission. In practice, the oil temperature is often measured in the transmission's oil sump or in the intake line of a hydraulic control unit. However, for the individual functions of the transmission control system, the actual temperatures of precisely those components affected by the control mechanism are required. For example, during a gear change, it's very helpful to know both the actual component temperature at or near the shift element being closed by pressure control, and the actual component temperature at or near the pressure control valve that performs this pressure control.Although attributed to the same event, these two actual component temperatures differed considerably from each other and also from the oil temperature measured at the same time in the transmission oil sump or in the intake line of the hydraulic transmission control unit. To better measure the temperature in the various areas and components of the transmission, additional sensors would need to be installed at relevant points, which is expensive. A practical alternative is to simulate the component temperature required for calculating a control variable, based on the oil temperature measured at a single point in the transmission using only one sensor, and employing suitable mathematical models. An example of a highly simplified simulation is gradient limitation of the heating and cooling curves of the oil temperature measured in an intake line of the hydraulic transmission control unit. The result is that the actual component heating in the transmission is relatively well represented when the engine is started with the transmission already at operating temperature, but noticeably less accurately when the engine is started with a cold transmission.In this context, a comfort-critical aspect is the engine restart performed by the vehicle's automatic start-stop system after a temporary engine stop phase. During this restart, the transmission's shift elements, which were open during the engine stop phase, must close again to allow the vehicle to move forward. Due to insufficient oil circulation within the transmission when the engine is off, the oil at the measuring point typically cools down more significantly than at the rotating internal components of the transmission, which are heated during operation. This results in a temperature gradient within the transmission.Because the transmission control software, when controlling and / or regulating the transmission's shift elements, does not calculate based on the actual local temperatures present at the shift elements, but rather uses the value measured at the temperature sensor, shifting comfort deteriorates as the temperature gradient increases when closing the previously open shift elements. Particularly at low starting temperatures, the deviation is so significant that both the actuation of the pressure control valves used for the hydraulic actuation of the shift elements and the effective filling of the pressure chambers of the shift elements to be closed are severely impaired, resulting in a significant decrease in shift quality. Documents DE 195 45 888 A1 and the subsequently published DE 10 2018 209 786 A1 also disclose methods for controlling an automatic transmission, wherein the temperature of the lubricating and cooling oil used in the transmission is measured and this measured value is supplied to the control unit of the transmission. The present invention is based on the objective of improving the accuracy of using a temperature signal to control an automatic transmission in a motor vehicle, both in a method and in a control unit operated by this method. This problem is solved by a method with the features of claim 1 and by a control unit with the features of claim 15. Preferred embodiments and further developments of the invention are described in the dependent claims and the following description. The invention relates to a method for controlling an automatic transmission with an electronic transmission control unit for operating this transmission in a motor vehicle with an engine for driving this transmission, in which the transmission is controlled and / or regulated by means of at least one function implemented in the transmission control unit, which uses at least one reference temperature in calculating its control and / or regulated variables, based on an oil temperature currently measured in the transmission. From the first engine start, which occurs after initialization of the transmission control unit, a filtered oil temperature is calculated from the currently measured oil temperature using a mathematical filter function. According to the invention, it is proposed that the function, when calculating its control and / or regulated variables from the first engine start until the beginning of an engine stop phase following the first engine start, during which the transmission control unit remains in operation at least temporarily, uses the filtered oil temperature as a reference temperature. According to the invention, it is also proposed that the filtered oil temperature valid at the beginning of this engine stop phase be stored as a shutdown temperature in the electronic transmission control unit. Furthermore, the invention proposes that, during a second engine start that ends this engine stop phase, predefined criteria for an engine restart are checked. If the second engine start is not identified as an engine restart, the function uses the filtered oil temperature as the reference temperature when calculating its control variables – as it did before the engine stop phase. However, if the second engine start is identified as an engine restart, the function uses the stored shutdown temperature as the reference temperature when calculating its control variables as long as the currently measured oil temperature does not exceed the stored shutdown temperature. Then, if the currently measured oil temperature exceeds the stored shutdown temperature for a predefined period, the function again uses the filtered oil temperature as the reference temperature.When the engine restarts, a reset is performed on the reference temperature currently used in the calculation of the control variables. This reset marks the switch to a different calculation method for the transmission control function, specifically the temporary suspension of filtering the measured oil temperature in favor of the filtered oil temperature that was last valid when the engine stopped, provided the measured oil temperature has not yet exceeded this last valid filtered oil temperature. In most cases, the measured oil temperature drops after an engine stop due to the lack of oil circulation in the transmission; the extent of this drop depends on the location and flow of the measuring point.However, it is also possible that the measured oil temperature rises after an engine stoppage due to the lack of oil circulation in the transmission, for example, at a correspondingly high ambient temperature or in proximity to a hot exhaust system. Restarting the engine restores oil circulation in the transmission, with the result that the measured oil temperature returns to the stored cutoff temperature that was present at the time of the engine stoppage. Exceeding this stored value for a predefined period signals the transmission control function to revert to the original calculation method, which is also used during and after a normal engine start without a preceding temporary engine stop phase. Incidentally, the predefined period can also be set to zero. The engine stop phase and engine restart occur, for example, as part of an automatic engine stop-start system in the motor vehicle. During the predefined time period, within which the currently measured oil temperature must be higher than the stored shutdown temperature for the second engine start to be considered an engine restart, the function preferably uses the currently measured oil temperature as a reference temperature when calculating its control and / or regulated variables. As a first alternative, the function could use a modified shutdown temperature as a reference temperature when calculating its control variables during the predefined time period. This modified shutdown temperature is calculated from the stored shutdown temperature using a predefined correction function. Such a correction function could, for example, be a constant multiplier, a constant offset value, a time-dependent multiplier, or a time-dependent offset. In a simplified second alternative, it can be provided that the function continues to use the stored shutdown temperature as a reference temperature when calculating its control and / or regulated variables during the predefined time period. In a preferred embodiment of the invention, it is proposed that the time of commencement of this engine stop phase is also stored in the electronic transmission control unit, and that the second engine start is only identified as an engine restart if the second engine start occurs within a predefined maximum duration of the engine stop phase that begins at this stored time. Alternatively or additionally, it can be provided that the second engine start is only identified as an engine restart if the temperature difference between the also stored shutdown temperature and the oil temperature measured at the time of the second engine start has not yet reached a predefined temperature drop.If these predefined criteria are not met, the function intended for operating the automatic transmission treats the second engine start as a normal initial engine start, just like the first engine start, when internally calculating the control variables. In a further embodiment of the invention, it is proposed that both the beginning of the temporary engine stop phase and the second engine start ending this engine stop phase be detected by monitoring the engine speed of the engine intended to drive the transmission, such that when a predefined first engine speed threshold is undershot, the beginning of the temporary engine stop phase is inferred, and when a predefined second engine speed threshold is exceeded during the ongoing engine stop phase, the second engine start is inferred. Advantageously, this method also reliably detects engine shutdown in the event of disturbances in the engine's ignition signal. Preferably, the function is an electro-hydraulic pressure control of switching elements of the transmission by means of an electro-hydraulic control unit of the automatic transmission. Advantageously, a PT2 filter can be used for the mathematical filtering of the measured oil temperature, the parameters of which are predefined as a function of the measured oil temperature, particularly when the oil temperature is measured by means of a sensor that is located in an oil flow at or inside the electro-hydraulic control unit of the transmission or inside an oil sump of the transmission. In an advantageous embodiment of the invention, it is proposed that the function, when calculating its control variables, uses both a transmission reference temperature and a hydraulic reference temperature as reference temperatures, both of which are based on an oil temperature currently measured in the transmission. For this purpose, for example, two different sensors can be provided within the transmission, one of which is arranged, for example, in the oil sump for measuring the oil sump temperature or near a switching element for measuring the component temperature, whereas the other is arranged, for example, in an oil flow within the electro-hydraulic control unit or on a valve housing of the electro-hydraulic control unit for measuring the control unit temperature. Alternatively, using empirically determined parameters from the measured values ​​of a temperature sensor, both the transmission reference temperature and the hydraulic reference temperature can be derived. For example, when using separate reference temperatures for the transmission and hydraulics, it can be provided that, starting from the first engine start, a filtered transmission temperature is calculated from the currently measured oil temperature using a first PT2 filter with shift-element-specific parameterization, and a filtered hydraulic temperature is calculated using a second PT2 filter with hydraulic-specific parameterization. Accordingly, when using separate reference temperatures for the transmission and hydraulics, the function can be configured to use the filtered transmission temperature as the transmission reference temperature and the filtered hydraulic temperature as the hydraulic reference temperature when calculating its control variables from the first engine start until the beginning of the engine stop phase. The filtered transmission temperature valid at the beginning of the engine stop phase is then stored as a transmission shutdown temperature in the transmission control unit, whereas the filtered hydraulic temperature valid at the beginning of the engine stop phase is then stored as a hydraulic shutdown temperature in the transmission control unit. If the second engine start is not identified as an engine restart, the function continues to use the filtered gearbox temperature as the gearbox reference temperature and the filtered hydraulic temperature as the hydraulic reference temperature when calculating its control variables. If the second engine start is identified as an engine restart, the function uses the stored transmission cutoff temperature as the transmission reference temperature when calculating its control variables, as long as the currently measured oil temperature does not exceed the stored transmission cutoff temperature. If the currently measured oil temperature is higher than the stored transmission cutoff temperature for a time period predefined by the shift element, the function reverts to using the filtered transmission temperature as the transmission reference temperature when calculating its control variables.The same applies to the hydraulic reference temperature: If the second engine start is identified as an engine restart, the function uses the stored hydraulic cut-off temperature as the hydraulic reference temperature when calculating its control variables, as long as the currently measured oil temperature has not exceeded the stored hydraulic cut-off temperature in terms of value, and the filtered hydraulic temperature again as the hydraulic reference temperature if the currently measured oil temperature is higher than the stored hydraulic cut-off temperature for a hydraulically specific predefined period of time. While the inventive method already noticeably improves the shifting quality of the transmission compared to the prior art, the use of separate reference temperatures for the transmission and hydraulics further improves the shifting quality of the transmission. The invention further relates to a transmission control unit for carrying out the method according to the invention. This transmission control unit is preferably an electronic control device for the automatic transmission. Such a transmission control device comprises means for carrying out the method, wherein these means are hardware-related and software-related. The hardware-related means include data interfaces for exchanging data with the assemblies involved in carrying out the method according to the invention, for example, to control switching elements of the automatic transmission for locking or unlocking. Furthermore, the hardware-related means include a data memory for storing data and a processor for processing data. The software-related means include program modules that are stored in the memory and executed by the processor.The transmission control unit serves to carry out the above-described procedure on the control side and thus to operate the automatic transmission. The invention will now be explained in more detail with reference to the accompanying exemplary figures, without being limited thereto. These figures show: Fig. 1 a simplified schematic representation of a motor vehicle with an automatic transmission, which is operated by means of the method and control unit according to the invention; Fig. 2 an exemplary time course of temperature signals as used in the prior art; Fig. 3 an exemplary time course of the temperature signals used in a first embodiment of the method according to the invention; Fig. 4 a block diagram of an exemplary functional sequence using the first embodiment of the method according to the invention; and Fig. 5 a block diagram of an exemplary functional sequence using a second embodiment of the method according to the invention. The following section, with reference to Fig. 1, describes in more detail the integration of the inventive method and the inventive control unit into the overall concept of the motor vehicle in which the automatic transmission to be controlled is located. Fig. 1 shows a simplified schematic representation of a motor vehicle 1 with an automatic transmission 3 driven by an engine 2. This transmission 3 comprises an electro-hydraulic control unit 4, which, by way of example, is immersed in an oil sump 5 of the transmission 3 and is designed to actuate the pressure-side switching elements 6 of the transmission 3. The calculation of the control variables required for this is carried out in a specially designed electronic transmission control unit 8, which, in the schematic shown here, is designed as a separate component by way of example, but in another embodiment can also be an integral part of the electro-hydraulic control unit 4.At least one data line 10 is provided for communication between the electronic transmission control unit 8 and the electro-hydraulic control unit 4. Accordingly, the electro-hydraulic control unit 4 implements the control commands of the electronic transmission control unit 8. The transmission 3 then includes at least one temperature sensor 7, which, by way of example, is arranged in the oil sump 5 on the electro-hydraulic control unit 4 and thus senses the current oil temperature of the transmission and makes this sensed signal available to the electronic transmission control unit 8. The electronic transmission control unit 8 implements at least one function 9, which is intended for controlling the automatic transmission 3 and calculates its required control variables using a reference temperature based on this sensed current oil temperature. To illustrate these physical relationships between the temperatures actually measured in the transmission and the fictitious transmission temperature used in calculating control variables for transmission control, an exemplary time course of the affected temperature signals is described in more detail below with reference to Fig. 2, as known and used in the prior art. The dotted line describes the time course of the current oil temperature c_sensor actually measured by the temperature sensor 7, whereas the dashed line describes the time course of a filtered oil temperature c_PT2, which results when the measured oil temperature c_sensor shown is mathematically filtered using a PT2 filter.The solid line describes the time course of the temperature c_coupling actually occurring in the pressure chamber of one of the switching elements 6, which typically corresponds to the time course of the sensed oil temperature c_sensor. The problems of the prior art are explained in more detail below with reference to Fig. 2. The fact that, within the framework of functions 9, which generate control and regulation variables for controlling the transmission taking into account the oil temperature c_sensor measured in the transmission 3, it must be taken into account that the actual transmission temperature at the components relevant for the respective function 9 can deviate significantly from the oil temperature c_sensor measured at a point in the transmission 3 by the single temperature sensor 7 used here as an example, was already discussed at the beginning of the description. The present invention is based on investigations showing that the reference temperature required for calculating the control variables of the functions 9 provided for controlling the transmission 3 can be represented relatively well from the measured oil temperature c_sensor using a mathematical PT2 filter. The necessary filter parameters of this PT2 filter vary considerably depending on the location of the components affected by the control. Thus, for example, even when engaging a gear after starting the engine at low ambient temperatures, the actual component temperature present in the electro-hydraulic control unit 4 can be determined differently than the oil temperature responsible for filling the shift elements 6 of the transmission 3. This is particularly advantageous when the electro-hydraulic control unit 4 contains pressure control valves that are kept in oscillation with frequency and amplitude depending on the temperature by means of a so-called dither function. As a result, the PT2 filtering of the oil temperature c_sensor measured in the oil flow in the electro-hydraulic control unit 4 enables consistent shift quality even at different engine start temperatures. However, the investigations underlying the present invention have also shown that the consistent use of an oil temperature c_PT2 filtered by a PT2 filter in calculating the control variables of the transmission control is problematic if the engine stops and restarts during the warm-up phase. Such an event can occur, for example, within the context of an engine stop-start system in a motor vehicle, which is well known from the prior art. Fig. 2 shows a typical time course of the measured oil temperature c_sensor (dotted line) and the corresponding filtered oil temperature c_PT2 (dashed line) for such an engine stop-start process, as it results from the measured value c_sensor when using a PT2 filter.Also shown (in a solid line) is a typical time course of the clutch temperature c_kuppl, which corresponds to the time course of the sensed oil temperature c_sensor shown. At time t_0, the electronic transmission control unit 8 of the automatic transmission 3 is initialized and operating without errors. Time t_0 marks the first engine start M_an1 of engine 2 of vehicle 1 after the initialization of the transmission control unit 8. Therefore, the engine start M_an1 can also be called the engine initial start. Subsequently, engine 2 runs without errors. The currently measured oil temperature c_sensor and the filtered oil temperature c_PT2, mathematically calculated from the currently measured oil temperature c_sensor using a PT2 filter, are at least largely identical. In calculating its control variables, function 9, which is designed to control the transmission 3 – in particular the pressure control of the shift elements 6 of the transmission 3 – uses the filtered oil temperature c_PT2 as the current reference temperature. As can be clearly seen in Fig. 2, the filtered oil temperature c_PT2 accurately reflects the actual clutch temperature c_cuppl until time t_1, when the engine 2 is switched off as part of the motor vehicle 1's engine stop-start system. The electronic transmission control unit 8 of the automatic transmission 3 remains operational even after this engine stop M_off and consequently continues to maintain its implemented functional sequences and perform the corresponding internal calculations. During the subsequent engine stop phase M_stop, the oil temperature c_sensor measured in the oil sump 5 at the electro-hydraulic control unit 4 of the transmission 3 drops relatively quickly in this example. This is because the measuring point where the temperature sensor 7 is located is no longer supplied with fresh oil due to the transmission 3's oil pump no longer being driven by the engine 2. In this example, the temperature sensor 7 is located in a tiny blind hole inside the electro-hydraulic control unit 4. The cooling of the minimal amount of oil remaining at the temperature sensor 7 is accelerated the colder the aluminum block of the electro-hydraulic control unit 4 is.The filtered oil temperature c_PT2, mathematically calculated from the currently measured oil temperature c_sensor using a PT2 filter, is then filtered back according to its respective filter parameters. In this case, this results in a temperature profile that decreases somewhat more slowly than the profile of the measured oil temperature c_sensor. As can be easily seen in Fig. 2, the deviation between the two temperatures c_sensor and c_PT2 is comparatively large at times, but it evens out again over time.However, the difference between the actual clutch temperature c_kuppl and the corresponding filtered oil temperature c_PT2 is more dramatic in the time course after the engine stop M_aus, since the rotating internal components of the gearbox 3, which are heated during operation, behave comparatively sluggishly with regard to their cooling - due to their mass - and the actual clutch temperature c_kuppl only drops relatively slowly. If the function 9 intended for controlling the transmission 3 continues to use the filtered oil temperature c_PT2 as the current reference temperature when calculating its control variables, a gear engagement controlled simultaneously with or only slightly delayed after the engine restart in the transmission 3 becomes more critical to comfort the greater the deviation between the filtered oil temperature c_PT2 used in the calculation and the current temperature c_kuppl of the shift element 6 which is controlled by the function 9 during this gear engagement. The following section, with reference to Fig. 3, describes in more detail an exemplary temporal profile of the temperature signals used in a first embodiment of the method according to the invention. Fig. 3 again shows a time / temperature diagram, where the time axis is labeled t and the temperature axis is labeled c. Again, the dotted line describes the temporal profile of the actual oil temperature c_sensor measured by the temperature sensor 7, whereas the dashed line describes the temporal profile of the filtered oil temperature c_PT2, which results when the depicted sensed oil temperature c_sensor is mathematically filtered using a PT2 filter. Again, the solid line describes the temporal profile of the temperature c_kuppl actually occurring in the pressure chamber of one of the switching elements 6, corresponding to the temporal profile of the sensed oil temperature c_sensor. Based on Fig.3. The particular advantages of the method according to the invention will be explained in more detail below. The illustration in Fig. 3 begins at time t_1, which marks the engine stop M_off performed as part of the motor vehicle 1's automatic engine stop-start system. The electronic transmission control unit 8 of the automatic transmission 3 continues to operate, at least temporarily, even after this engine stop M_off, and consequently maintains its implemented functional sequences, at least temporarily, and continues the corresponding internal calculations, at least temporarily. The engine stop M_off thus marks the beginning of a temporary engine stop phase M_stop. The method according to the invention provides that, when calculating its control and / or regulation variables intended for controlling the transmission 3, the function 9 uses a filtered oil temperature c_PT2 as the reference temperature c_ref during the operating period from the initialization of the transmission control unit 8, at the latest from time t_0 of the first engine start M_an1 after the initialization of the transmission control unit 8, until time t_1, at which the engine 2 of the motor vehicle 1 is switched off again. This filtered oil temperature is calculated from the currently measured oil temperature c_sensor using a mathematical filter function. The method according to the invention also provides that, in the event of an engine stop M_off occurring after the first engine start M_on1, which marks the starting point of a temporary engine stop phase M_stop, during which the electronic transmission control unit 8 remains in operation at least temporarily, the filtered oil temperature c_PT2 valid at the time of this engine stop M_off or at the beginning of the engine stop phase M_stop is stored as a shutdown temperature c_off in the electronic transmission control unit 8 for subsequent use. Additionally, the time t_1 of this engine stop M_off or of the beginning of the engine stop phase M_stop can also be stored in the transmission control unit 8 in the form of a timestamp for further use. Typically, such an engine stop M_off with a subsequent engine stop phase M_stop, during which the electronic transmission control unit 8 remains in operation at least temporarily, occurs as part of an engine stop-start system of the motor vehicle 1. The inventive method then provides that the function 9, which remains active during the engine stop phase M_stop, uses the previously stored shutdown temperature c_off as a reference temperature c_ref when calculating its control and / or regulation variables for controlling the transmission 3, starting from time t_1 of the engine stop M_off or from the beginning of the engine stop phase M_stop, and continues to do so until the currently measured oil temperature c_sensor reaches the stored shutdown temperature c_off. Only when the currently measured oil temperature c_sensor is higher than the stored shutdown temperature c_off for a predefined time period t_def does the function 9 again use the filtered oil temperature c_PT2 as the reference temperature c_ref when calculating its control and / or regulation variables for controlling the transmission 3.In the first embodiment of the method according to the invention shown here, function 9 uses the currently measured oil temperature c_sensor as a reference temperature c_ref when calculating its control and / or regulation variables intended for controlling the gearbox 3 during this predefined time period t_def v. In the present example, at time t_2, the engine restart command M_an2 is issued by the automatic engine stop-start system of vehicle 1. The engine 2 of vehicle 1 now drives the oil pump of the transmission 3 again, with the result that the area of ​​the measuring point where the temperature sensor 7 is located is once again supplied with fresh oil, causing the measured oil temperature c_sensor to rise again. The actual clutch temperature c_kuppl also rises again and reaches the level of the shutdown temperature c_aus at time t_3. At time t_3, however, the difference between c_kuppl and c_sensor is still relatively large. Only at time t_4 does the measured oil temperature c_sensor reach the level of the shutdown temperature c_aus again, i.e., the level of the measured oil temperature c_sensor prevailing at time t_1 of the start of the engine stop phase M_stop.From time t_4 onwards, a timer runs, during which function 9, in its internal calculation of the control variables intended for controlling the gearbox 3, preferably uses the currently measured oil temperature c_sensor as the reference temperature c_ref. After the predefined time interval t_def of the timer has elapsed, which in this example is marked as time t_5, function 9, according to the invention, again uses the filtered oil temperature c_PT2 as the reference temperature c_ref in its internal calculation of the control variables intended for controlling the gearbox 3. In Fig.It can be clearly seen that during the timer runtime between times t_4 and t_5, the currently measured oil temperature c_sensor accurately reflects the actual clutch temperature c_kuppl, which is essential for the control and / or regulation of the switching elements 6 of the transmission 3, whereas from time t_5 onwards, the filtered oil temperature c_PT2 accurately reflects the actual clutch temperature c_kuppl, which is essential for the control and / or regulation of the switching elements 6 of the transmission 3. As a result, the inventive method achieves a very accurate representation of the real temperature conditions of the components of the automatic transmission 3 to be controlled and / or regulated, without additional costs, for use in the control and / or regulation of these components. Fig. 4 shows a largely self-explanatory block diagram of the exemplary functional sequence described above, using the first embodiment of the method according to the invention. The individual process steps are designated by reference numerals v1 to v14. In the first process step v1, the first start of engine 2 after initialization of the electronic transmission control unit 8 is detected as a first engine start M_an1. At the latest now, when engine 2 is running, the oil temperature c_sensor is continuously measured in the second process step v2 using the temperature sensor 7. Using a known mathematical PT2 filter, the filtered oil temperature c_PT2 is continuously calculated in the third process step v3 based on the currently measured oil temperature c_sensor. Provided that the engine 2 and the electronic transmission control unit 8 remain in operation, the previously calculated current filtered oil temperature c_PT2 is supplied to the function 9 implemented in the electronic transmission control unit 8 for controlling and regulating the automatic transmission 3 and is used in the fourth process step v4 by the function 9 as the current reference temperature c_ref in the calculation of its control and / or regulated variables, until in the fifth process step v5 an engine stop M_aus is detected, which was initiated by a start-stop system of the vehicle 1 and in the temporal sequence of which the electronic transmission control unit 8 remains in operation. If such an engine stop M_off occurs, in the sixth process step v6 the last valid value of the filtered oil temperature c_PT2 – i.e., at the time of engine shutdown – is stored as the shutdown temperature c_off in the electronic transmission control unit 8 and, in the subsequent seventh process step v7, is supplied to function 9, which is responsible for controlling and regulating the automatic transmission 3, as the new reference temperature c_ref. From then on, the reference temperature c_ref used by function 9 is frozen at the constant value of the shutdown temperature c_off until, in the eighth process step v8, a second engine start M_an2 (occurring after the first engine start M_an1) is detected and, in the subsequent ninth process step v9, it is checked whether this second engine start M_an2 is an engine restart M_an2_w initiated by the start-stop system of the vehicle 1 or not. One criterion for not classifying an engine start as an engine restart M_an2 could be, for example, exceeding a predefined maximum duration of the temporary engine stop phase. Similarly, reaching or exceeding a predefined temperature drop in the continuously measured oil temperature c_sensor relative to the stored shutdown temperature c_aus is a suitable criterion for classifying the engine start as not being classified as an engine restart M_an2 and instead treating it as a normal engine initial start M_an1 in the subsequent operating sequence. Thus, process steps v5 and v9 frame a temporary engine stop phase (M_stop), the planned end of which depends, in a manner known per se, on parameters of the start-stop system of the vehicle 1. During the engine stop phase, the oil temperature c_sensor, which has been continuously measured since process step v2, typically decreases, and the decrease is greater the longer the engine stop phase lasts. A premature interruption of the ignition circuit of the engine 2, and thus an interruption of the power supply to the electronic transmission control unit 8 within this temporary engine stop phase, can lead to the termination of the process, since the electronic transmission control unit can no longer operate without a power supply, or at best only for a very short time.If, after the ignition circuit of engine 2 is interrupted, the electronic transmission control unit 8 has sufficient time during a run-on process to store the process-relevant data in the writable non-volatile memory of the electronic transmission control unit 8, a premature termination of the process is not necessary. After the engine restart M_an2 is detected in the ninth process step v9, the reference temperature c_ref used in the internal calculations of function 9 remains frozen at the constant value of the stored shutdown temperature c_aus in the subsequent tenth process step v10 until it is determined in the subsequent eleventh process step v11 that the oil temperature c_sensor, which has been continuously measured since process step v2, has reached or exceeded the stored shutdown temperature c_aus in terms of its current value. When the measured oil temperature c_sensor reaches or exceeds the cut-off temperature c_off, a timer is started in the subsequent twelfth process step v12, and simultaneously, in the thirteenth process step v13, the currently measured oil temperature c_sensor is set as the reference temperature c_ref. Function 9 then uses the continuously measured oil temperature c_sensor as the reference temperature c_ref in its internal calculations until the timer reaches its predefined time interval t_def in the fourteenth process step v14. If the timer in process step v14 has expired, a return to the fourth process step v4 occurs, so that the filtered oil temperature c_PT2 calculated from the currently measured oil temperature c_sensor is subsequently specified as the reference temperature c_ref in function 9, until a new engine stop M_off is detected. Furthermore, the relationships described as examples for the temporal profile of the temperature c_kuppl actually occurring at the switching elements 6 of the transmission are also transferable to the temporal profile of temperatures in the electro-hydraulic control unit 4 of the transmission 3. To achieve consistently high shifting quality, it is important, within the framework of the pressure control of the switching elements 6, to provide the function 9 implemented in the electronic transmission control unit 8 for pressure control of the switching elements 6 with a reference temperature c_ref. This reference temperature not only accurately reflects the temperature behavior in the area of ​​the switching elements 6 during their filling, but also accurately reflects the temperature behavior in the area of ​​those hydraulic valves of the electro-hydraulic control unit 4 that are intended for controlling the switching elements 6.Depending on the position of the temperature sensor 7, which is provided for continuously measuring the oil temperature c_sensor, in the oil flow and relative to the electro-hydraulic transmission control unit 4 and relative to the transmission shift elements 6, significant differences can arise between a transmission mechanics-specific temperature and a transmission hydraulics-specific temperature, both of which are relevant for the function 9 during the operation of the transmission 3. The second embodiment of the method according to the invention, described in more detail below with reference to Fig. 5, takes particular account of this circumstance. As previously shown in Fig. 4, Fig. 5 shows a block diagram for an exemplary functional sequence of the method according to the invention. For the sake of comparability of individual process steps with Fig. 4, the individual process steps in Fig. 5 are designated by the reference numerals v1' to v9', v10' to v14' and v10'' to v14''. It is readily apparent that the process steps v1' to v9' of the second embodiment shown in Fig. 5 are similar to the process steps v1' to v9' of the first embodiment shown in Fig. 4, whereas the process steps v10' to v14' and v10'' to v14'' of the second embodiment shown in Fig. 5 represent a kind of division of the process steps v10 to v14 of the first embodiment shown in Fig. 4. The first process step v1' in Fig. 5 marks the starting point of the process with the detection of the first engine start M_an1 after initialization of the electronic transmission control unit 8. Now, with the engine 2 running, the oil temperature c_sensor is continuously measured in the second process step v2' using the temperature sensor 7. In contrast to Fig. 4, in Fig. 5 the third process step v3' calculates a filtered transmission temperature c_PT2_getr based on the currently measured oil temperature c_sensor using a first mathematical PT2 filter with shift element-specific parameterization, and a filtered hydraulic temperature c_PT2_hydr. using a second mathematical PT2 filter with hydraulic-specific parameterization. Provided that engine 2 and electronic transmission control unit 8 remain in operation, both the previously calculated current filtered transmission temperature c_PT2_getr and the previously calculated current filtered hydraulic temperature c_PT2_hydr are fed to the function 9 implemented in the electronic transmission control unit 8 for controlling and regulating the automatic transmission 3 and, in the fourth process step v4', are used by the function 9 as the current transmission temperature c_getr and the current hydraulic temperature c_hydr when calculating its control and / or regulated variables, until, in the fifth process step v5', an engine stop (see M_aus in Fig. 4) is detected, which was initiated by a start-stop system of the vehicle 1 and, as a consequence, the electronic transmission control unit 8 remains in operation.In this second embodiment, an engine stop is inferred when the continuously measured engine speed n_mot of engine 2 falls below a predefined engine speed threshold n_mot_aus. The engine stop detection method proposed here, based on monitoring the engine speed n_mot, is a very robust and reliable method for determining whether engine 2 has actually been switched off. Potential misinterpretations of a shutdown signal from the ignition circuit are reliably avoided; after all, the driver of the vehicle 1 can close the ignition circuit, which was previously interrupted to switch off the engine, even before engine 2 has actually come to a complete stop. If such an engine stop occurs, three values ​​are stored in the electronic transmission control unit 8 in the sixth process step v6': the time t_M_off of the engine stoppage, the filtered transmission temperature c_PT2_getr value valid at the time of the engine stoppage as transmission stoppage temperature c_off_getr, and the filtered hydraulic temperature c_PT2_hydr value valid at the time of the engine stoppage as hydraulic stoppage temperature c_off_hydr. These three stored values ​​t_M_off, c_PT2_getr, and c_PT2_hydr are subsequently fed to function 9, which is intended for controlling and regulating the automatic transmission 3, for further use.In the seventh process step v7', function 9 sets the transmission temperature c_getr, which it uses to calculate its control variables, to the constant value of the stored transmission shutdown temperature c_aus_getr, and the hydraulic temperature c_hydr, which it uses to calculate its control variables, to the constant value of the stored hydraulic shutdown temperature c_aus_hydr. Function 9 then holds these two calculated values ​​c_getr and c_hydr frozen until, in the eighth process step v8', a second engine start (occurring after the first engine start M_an1) is detected (see M_an2 in Fig. 4). In the present second embodiment, the detection of the second engine start is again achieved by observing the engine speed n_mot: A second engine start is inferred when the continuously measured engine speed n_mot of engine 2 has exceeded a predefined engine speed threshold n_mot_an. Again, the proposed detection of the engine stop via observation of the engine speed n_mot proves to be a very robust and reliable method for determining whether engine 2 actually restarts. Potential misinterpretations of an ignition circuit activation signal are reliably avoided; after all, the driver of vehicle 1 can interrupt the ignition circuit, which was previously closed for starting the engine, even before engine 2 actually starts running again. In the following ninth process step v9', it is checked whether this second engine start is an engine restart initiated by the start-stop system of the motor vehicle 1 (see M_an2_w in Fig. 4) or not. In the present second embodiment, an engine restart is detected if the time of the second engine start, i.e., the time at which the current engine speed n_mot has exceeded the predefined engine speed threshold n_mot_an, occurs within a predefined maximum duration t_stop of the engine stop phase, which starts at time t_M_aus, or if the difference between the continuously measured oil temperature c_sensor and at least one of the two stored shutdown temperatures c_aus_getr, c_aus_hydr has not yet reached a predefined differential temperature c_delta. This differential temperature c_delta represents the permissible temperature drop so that the second engine start is not treated as a normal engine initial start M_an1. Preferably, the maximum duration t_stop is also predefined separately for the transmission mechanics and transmission hydraulics.If the second engine start is not recognized as an engine restart, the process returns to the first step v1'. Thus, process steps v5' and v9' frame a temporary engine stop phase (M_stop), the planned end of which depends, in a manner known per se, on parameters of the start-stop system of the vehicle 1. During the engine stop phase, the oil temperature c_sensor, which has been continuously measured since process step v2', typically decreases, and the longer the engine stop phase lasts, the greater the decrease. Due to differing masses, different convection, and possibly different materials, the switching elements 6 and the electro-hydraulic transmission control unit 4 cool down at different rates. The second embodiment of the invention, shown in Fig. 5, takes this circumstance into account by adjusting the process, upon detection of an engine restart, in accordance with the model shown in Fig.The four known process steps v10 to v14 are now continued in two sub-branches, such that the two shutdown temperatures c_off_gear and c_off_hydrar are advantageously considered separately. Process steps v10' to v14' are assigned to the branch that concerns the gear temperature c_gear, whereas process steps v10'' to v14'' are assigned to the other branch that concerns the hydraulic temperature c_hydrar. Accordingly, in the tenth process step v10', the transmission temperature c_getr used in the internal calculations of function 9 remains frozen at the constant value of the stored transmission shutdown temperature c_aus_getr until, in the subsequent eleventh process step v11', it is determined that the oil temperature c_sensor, which has been continuously measured since process step v2', has not yet reached the stored transmission shutdown temperature c_aus_getr in terms of its current value.In the parallel process step v10'', however, the hydraulic temperature c_hydr used in the internal calculations of function 9 remains frozen at the constant value of the stored hydraulic shutdown temperature c_aus_hydr until, in the subsequent process step v11'', it is determined that the oil temperature c_sensor, which has been continuously measured since process step v2', has again reached or exceeded the stored transmission shutdown temperature c_aus_getr in terms of its current value. When the measured oil temperature c_sensor reaches or exceeds the transmission cutoff temperature c_aus_getr, a timer is started in the subsequent twelfth process step v12', and simultaneously, in the thirteenth process step v13', the currently measured oil temperature c_sensor is set as the transmission temperature c_getr. Function 9 then uses the continuously measured oil temperature c_sensor as the transmission temperature c_getr in its internal calculations until the timer reaches a time interval t_def_getr, specifically predefined for the transmission shift elements 6, in the fourteenth process step v14'.Accordingly, function 9 also uses the continuously measured oil temperature c_sensor as the hydraulic temperature c_hydr in its internal calculations, until the timer in process step v14'' reaches a time interval t_def_hydr specifically predefined for the electro-hydraulic transmission control unit 4. These two time intervals t_def_getr and t_def_hydr, individually predefined for the transmission mechanics and the transmission hydraulics, advantageously take into account that the switching elements 6 and the electro-hydraulic transmission control unit 4 heat up again at different rates after the resumption of oil circulation in the transmission 3. If the respective timer in the process steps v14' and v14'' has expired, a return to the fourth process step v4' occurs, so that subsequently the function 9 is again given the filtered transmission temperature c_PT2_getr calculated from the currently measured oil temperature c_sensor as the transmission temperature c_getr and the filtered hydraulic temperature c_PT2_hydr calculated from the currently measured oil temperature c_sensor as the hydraulic temperature c_hydr, until another engine stop is detected. As a result, the second embodiment of the method according to the invention achieves a further improved representation of the actual temperature conditions of the components of the automatic transmission 3 to be controlled and / or regulated, without additional costs, compared to the first embodiment of the method according to the invention, for use in the control and / or regulation of these components. Reference sign 1 Motor vehicle 2 Motor vehicle engine 3 Automatic transmission of the motor vehicle 4 Electro-hydraulic control unit of the transmission 5 Transmission oil sump 6 Transmission shift element 7 Transmission temperature sensor 8 Electronic transmission control unit 9 Function for controlling and / or regulating the transmission 10 Data line c Temperature c_off Shutdown temperature; filtered oil temperature at the start of the engine stop phase c_off_tr Transmission shutdown temperature; filtered transmission temperature at the start of the engine stop phase c_off_hydr Hydraulic shutdown temperature; filtered hydraulic temperature at the start of the engine stop phase c_delta Temperature drop c_cuppl Actual temperature at a transmission shift element c_PT2 Filtered oil temperature, calculated from the measured oil temperature c_PT2_tr Filtered transmission temperature, calculated from the measured oil temperature c_PT2_hydr Filtered hydraulic temperature,c_ref reference temperature, calculated from the measured oil temperature; c_ref_getr gearbox reference temperature, used by the function in calculating its control and / or regulated variables; c_ref_hydr hydraulic reference temperature.The following parameters are used by the function when calculating its control and / or regulated variables: c_sensor (oil temperature measured by the function), n_mot (engine speed), n_mot_an (engine speed threshold for engine start detection), n_mot_aus (engine speed threshold for engine stop detection), M_an1 (first engine start after initialization of the transmission control unit), M_an2 (second engine start). Engine start at the end of the engine stop phase M_on2_w Engine restart M_off Engine stop M_stop Temporary engine stop phase t Time t_0 Time of an engine initial start t_1 Time of an engine stop t_2 Time of an engine restart t_3 Time t_4 Time t_5 Time t_def Predefined time span t_def_getr Predefined time span t_def_hydr Predefined time span t_M_off Start time of the engine stop phase t_stop Maximum duration of the engine stop phase v1 to v14 Process step v1' to v14' Process step v10'' to v14'' Process step,

Claims

Method for controlling an automatic transmission (3) with an electronic transmission control unit (8) for operating this transmission (3) in a motor vehicle (1) with an engine (2) for driving this transmission (3), wherein the transmission (3) is controlled and / or regulated by means of at least one function (9) implemented in the transmission control unit (8) which, in calculating its control and / or regulated variables, uses at least one reference temperature (c_ref) based on an oil temperature (c_sensor) currently measured in the transmission (3), wherein, from a first engine start (M_an1) which occurs after initialization of the transmission control unit (8), a filtered oil temperature (c_PT2) is calculated from the currently measured oil temperature (c_sensor) using a mathematical filter function, characterized in thatthat the function (9) uses the filtered oil temperature (c_PT2) as the reference temperature (c_ref) when calculating its control and / or regulated variables from the first engine start (M_an1) until the beginning of an engine stop phase (M_stopp) following the first engine start (M_an1), during which the transmission control unit (8) remains in operation at least temporarily; that the filtered oil temperature (c_PT2) valid at the beginning of this engine stop phase (M_stopp) is stored as a shutdown temperature (c_aus) in the electronic transmission control unit (8); and that predefined criteria for an engine restart (M_an2_w) are checked when a second engine start (M_an2) ends this engine stop phase (M_stopp); and that if the second engine start (M_an2) is not identified as an engine restart (M_an2_w), the function (9) uses the filtered oil temperature (c_PT2) as the reference temperature when calculating its control and / or regulated variables. (c_ref) continues to use the filtered oil temperature (c_PT2),However, if the second engine start (M_an2) is identified as an engine restart (M_an2_w), function (9) uses the stored shutdown temperature (c_aus) as the reference temperature (c_ref) when calculating its control variables as long as the currently measured oil temperature (c_sensor) does not exceed the stored shutdown temperature (c_aus), and then, if the currently measured oil temperature (c_sensor) is greater than the stored shutdown temperature (c_aus) for a predefined time period (t_def), it uses the filtered oil temperature (c_PT2) again as the reference temperature (c_ref). Method according to claim 1, characterized in that the function (9) uses the currently measured oil temperature (c_sensor) as the reference temperature (c_ref) when calculating its control and / or regulated variables during the predefined time period (t_def). Method according to claim 1, characterized in that the function (9) uses a modified switch-off temperature as a reference temperature (c_ref) when calculating its control and / or regulated variables during the predefined time period (t_def), which is calculated from the stored switch-off temperature (c_off) using a predefined correction function. Method according to claim 1, characterized in that the function (9) continues to use the stored switch-off temperature (c_off) as the reference temperature (c_ref) when calculating its control and / or regulated variables during the predefined time period (t_def). Method according to one of claims 1 to 4, characterized in that a PT2 filter is used for the mathematical filtering of the measured oil temperature (c_sensor), the parameters of which are predefined as a function of the measured oil temperature (c_sensor). Method according to claim 5, characterized in that the function (9) uses both a transmission reference temperature (c_ref_getr) and a hydraulic reference temperature (c_ref_hdyr) as reference temperatures (c_ref_ref) when calculating its control variables, both of which are based on an oil temperature (c_sensor) currently measured in the transmission (3), wherein, from the first engine start (M_an1), a filtered transmission temperature (c_PT2_getr) is calculated from the currently measured oil temperature (c_sensor) using a first PT2 filter with shift element-specific parameterization, and a filtered hydraulic temperature (c_PT2_hydr) is calculated using a second PT2 filter with hydraulic-specific parameterization.wherein the function (9) uses the filtered transmission temperature (c_PT2_getr) as the transmission reference temperature (c_ref_getr) and the filtered hydraulic temperature (c_PT2_hydr) as the hydraulic reference temperature (c_ref_hydr) when calculating its control and / or regulated variables from the first engine start (M_an1) until the beginning of the engine stop phase (M_stopp), wherein the filtered transmission temperature (c_PT2_getr) valid at the beginning of the engine stop phase (M_stopp) is stored as a transmission shutdown temperature (c_aus_getr) and the filtered hydraulic temperature (c_PT2_hydr) valid at the beginning of the engine stop phase (M_stopp) is stored as a hydraulic shutdown temperature (c_aus_hydr) in the transmission control unit (8), wherein if the second engine start (M_an2) is not identified as an engine restart (M_an2_w),Function (9) continues to use the filtered transmission temperature (c_PT2_getr) as the transmission reference temperature (c_ref_getr) and the filtered hydraulic temperature (c_PT2_hydr) as the hydraulic reference temperature (c_ref_hydr), whereas when the second engine start (M_an2) is identified as an engine restart (M_an2_w), function (9) uses the stored transmission shutdown temperature (c_aus_getr) as the transmission reference temperature (c_ref_getr) as long as the currently measured oil temperature (c_sensor) does not exceed the stored transmission shutdown temperature (c_aus_getr), and then uses the filtered transmission temperature (c_PT2_getr) again as the transmission reference temperature (c_ref_getr).If the currently measured oil temperature (c_sensor) is higher than the stored transmission cut-off temperature (c_aus_getr) over a switching element-specific predefined time period (t_def_getr), the stored hydraulic cut-off temperature (c_aus_hydr) is used as the hydraulic reference temperature (c_ref_hydr) as long as the currently measured oil temperature (c_sensor) does not exceed the stored hydraulic cut-off temperature (c_aus_hydr), and the filtered hydraulic temperature (c_PT2_hydr) is used again as the hydraulic reference temperature (c_ref_hydr) if the currently measured oil temperature (c_sensor) is higher than the stored hydraulic cut-off temperature (c_aus_hydr) over a hydraulically-specific predefined time period (t_def_hydr). Method according to one of claims 1 to 6, characterized in that the time (t_M_off) of the start of the engine stop phase (M_stop) is stored in the electronic transmission control unit (8), wherein the second engine start (M_on2) is identified as an engine restart (M_on2_w) if the second engine start (M_on2) occurs within a predefined maximum duration (t_stop) of the engine stop phase (M_stop) starting at this time (t_M_off). Method according to claim 7, characterized in that the maximum duration (t_stop) of the engine stop phase (M_stop) is individually predefined separately for transmission mechanics and transmission hydraulics. Method according to one of claims 1 to 8, characterized in that the second engine start (M_an2) is identified as an engine restart (M_an2_w) if a temperature difference between the stored shutdown temperature (c_off; c_off_getr, c_off_hydr) and the oil temperature (c_sensor) measured at the time of the second engine start (M_an2) has not yet reached a predefined temperature drop (c_delta). Method according to one of claims 1 to 9, characterized in that when a predefined first engine speed threshold (n_mot_off) is undershot, the beginning of the temporary engine stop phase (M_stop) is inferred, wherein when a predefined second engine speed threshold (n_mot_on) is exceeded during the engine stop phase (M_stop), the second engine start (M_on2) ending the engine stop phase (M_stop) is inferred. Method according to one of claims 1 to 10, characterized in that the function (9) is an electro-hydraulic pressure control of switching elements (6) of the transmission (3). Method according to one of claims 1 to 11, characterized in that the oil temperature (c_sensor) is measured by means of a temperature sensor (7) which is arranged in an oil flow of an electro-hydraulic control unit (4) of the transmission (3). Method according to one of claims 1 to 11, characterized in that the oil temperature (c_sensor) is measured by means of a temperature sensor (7) which is arranged in an oil sump (5) of the transmission (3). Method according to one of claims 1 to 13, characterized in that engine stop (M_off) and engine restart (M_on2_w) take place within the framework of an engine stop-start automatic system of the motor vehicle (1). Transmission control unit (8) for operating an automatic transmission (3) in a motor vehicle (1) comprising an engine (2) for driving this transmission (3), characterized in that a method according to one of claims 1 to 14 is implemented in the transmission control unit (8).

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