Method and control unit for operating a motor vehicle transmission

Abstract

Method for operating a transmission (3) of a motor vehicle, wherein a current actual rotational speed is recorded at a gearbox output (6) of the gearbox (3), wherein a time gradient of the actual speed at the gearbox output (6) is determined depending on a respective current actual speed at the gearbox output (6) and a respective previously recorded actual speed at the gearbox output (6), where, if the magnitude of a negative gradient of the actual rotational speed at the gearbox output (6) is greater than a first limit value, an unwanted binding of the gearbox (3) is detected, wherein, if the magnitude of a positive gradient of the actual rotational speed at the gearbox output (6) is greater than a second limit value, a slip condition on the output side is detected and the respective currently detected actual rotational speed is not used for the detection of an unwanted preload of the gearbox (3), characterized by the fact that Then, when a slip condition on the output side is detected, the respective previously recorded actual speed at the gearbox output (6) is used as the current actual speed for the detection of an unwanted preloading of the gearbox (3) as long as the actual currently recorded actual speed at the gearbox output (6) is greater by a defined offset than the respective previously recorded actual speed at the gearbox output (6).

Description

[0001] The invention relates to a method for operating a transmission of a motor vehicle according to the preamble of claim 1. The invention further relates to a control unit for operating a transmission of a motor vehicle.

[0002] A motor vehicle's powertrain consists of a drive unit and a transmission positioned between the drive unit and an output shaft. The transmission converts speed and torque, thus providing tractive force from the drive unit to the output shaft.

[0003] Motor vehicle transmissions have several switching elements. These switching elements can be friction-based, such as clutches or brakes, or positive-locking, such as dog clutches. In each engaged, friction-based gear of a transmission, a first set of switching elements is closed and a second set of switching elements is open. To perform a gear change in a transmission, at least one previously closed switching element is opened and at least one previously open switching element is closed.

[0004] If at least one shift element in a transmission is closed more than necessary to provide a positive gear engagement, this can lead to transmission binding, which can then block the vehicle's output shaft. Such a safety-critical condition must be avoided.

[0005] To detect gearbox binding, it is already known in practice to record the actual speed at the gearbox output and, depending on the recorded actual speed, to determine a time gradient of this speed at the gearbox output. If a strongly negative time gradient of the actual speed at the gearbox output is detected, the magnitude of which is greater than a threshold value, then a gearbox binding can be concluded.

[0006] Particularly in vehicles equipped with vehicle stability programs, a strongly negative time gradient of the actual rotational speed at the transmission output can develop even if there is no transmission binding. Therefore, in vehicles with stability programs, the aforementioned monitoring or detection of unwanted transmission binding is suppressed when the vehicle stability programs are active.

[0007] However, there are also vehicles without such driving stability programs; it is particularly common for trucks to lack them. In such vehicles without driving stability programs, a strongly negative temporal gradient of the actual speed at the transmission output can develop, especially if the vehicle is initially driven on a surface with a relatively low coefficient of friction and subsequently on a surface with a relatively high coefficient of friction. In this case, the transition from the surface with the relatively low coefficient of friction to the relatively high coefficient of friction can result in a sharp deceleration of the output shaft, thus reducing the speed at the transmission output. This could then be falsely detected as transmission binding, even though there is actually no binding in the transmission. This is disadvantageous.

[0008] Therefore, there is a need for a method and control unit for operating a motor vehicle transmission, especially a motor vehicle without driving stability programs, which can detect unwanted tension in the transmission with higher reliability and robustness.

[0009] DE 199 58 075 A1 relates to a method for operating a motor vehicle with wheel speed detection to monitor whether the vehicle's wheels are spinning or locked. It proposes analyzing gradients of wheel speeds recorded over time. A correlation test is performed between engine speed and wheel speeds to detect wheel spinning and wheel locking.

[0010] DE 10 2012 216 305 A1 discloses a method and a control device for controlling a positive-locking switching element of a gearbox.

[0011] DE 10 2019 203 961 A1 discloses a method for avoiding error memory entries in an output speed monitoring system in the event of a collision between a driven wheel of a motor vehicle and a small obstacle.

[0012] DE 10 2011 075 588 A1 discloses a control device for a motor vehicle. The control device stores a defined number of consecutive signal values ​​and, depending on an observation period defined for the control function, calculates a difference between the most recent signal value and the oldest signal value within that observation period. The control device triggers the control function when the absolute value of this difference exceeds a limit defined for the control function, whereas it does not trigger the control function when the absolute value of this difference is less than the limit defined for the control function.

[0013] Based on this, the invention aims to create a novel method and control unit for operating a motor vehicle transmission.

[0014] This problem is solved by a method according to claim 1. According to the invention, if the magnitude of a positive gradient of the actual rotational speed at the gearbox output is greater than a second limit value, a slip condition on the output side is detected, and the respective currently detected actual rotational speed is not used for the detection of an unwanted binding of the gearbox.

[0015] According to the invention, it is proposed that if, during the determination of the gradient of the actual rotational speed at the transmission output, a positive speed gradient is determined whose magnitude is greater than the second limit value, a slip condition on the output side is detected. The respective currently detected actual rotational speed is then assigned to a slip condition and subsequently not used for the detection of unwanted binding of the transmission.

[0016] This is based on the understanding that slippage can occur, for example, due to insufficient road surface friction, and that if the road surface friction subsequently increases, a strongly negative speed gradient can develop at the transmission output, even without transmission binding. This makes it possible to detect transmission binding more reliably.

[0017] When a slip condition on the output side is detected, the previously recorded actual speed at the gearbox output is used as the current actual speed for detecting unwanted gearbox binding, as long as the actual current recorded speed at the gearbox output is higher than the previously recorded actual speed at the gearbox output by a defined offset. This is preferred in order to disregard a possible slip condition at the output when determining or detecting unwanted gearbox binding.

[0018] When a slip condition on the output side is detected, the previously recorded actual speed at the gearbox output, which was compared to the currently recorded actual speed when the slip condition was detected, is used as the current actual speed as long as the actual current recorded speed at the gearbox output is higher than the previously recorded actual speed at the gearbox output by the defined offset. This allows for the advantageous suppression of slip conditions when an unwanted gearbox binding is detected.

[0019] Preferably, the actual current speed measured at the gearbox output is only used again for detecting unwanted gearbox binding when it falls below the previously measured actual speed at the gearbox output (increased by the offset and reduced by a hysteresis value). Only when the current measured actual speed at the gearbox output falls below the previously measured actual speed at the gearbox output, which was the basis for the initial slip detection, is the current measured actual speed at the gearbox output used again for detecting unwanted binding. It is specifically stipulated that the current measured actual speed at the gearbox output must fall below the previously measured actual speed (increased by the offset and reduced by the hysteresis value).The hysteresis value can be zero, but preferably its absolute value is greater than zero.

[0020] The control unit according to the invention is defined in claim 7.

[0021] Preferred embodiments are described in the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail with reference to the drawing, without being limited thereto. The drawing shows: Fig. 1. A powertrain diagram of a motor vehicle.

[0022] Fig. Figure 1 shows a schematic diagram of a motor vehicle's powertrain. The motor vehicle has a drive unit 1 and a transmission 3 connected between the drive unit 1 and an output 2. The transmission 3 is an automatic or automated manual transmission. A transmission input 4, an exemplary shift element 5, and a transmission output 6 of the transmission 3 are shown. The transmission 3 has several shift elements 5, which can be designed as friction-based shift elements, such as brakes or clutches, or as positive-locking shift elements, such as dog clutches. In each friction-based gear of the transmission 3, a first number of shift elements 5 are closed and a second number of shift elements 5 are open, whereby in each engaged gear of the transmission 3, the same element converts rotational speeds and torques and provides the tractive force of the drive unit 1 at the output 2.

[0023] The operation of the drive unit 2 is controlled and / or regulated by an engine control unit 7 and the operation of the transmission 3 by a transmission control unit 8.

[0024] For this purpose, the engine control unit 7 exchanges data with the drive unit 1, and the transmission control unit 8 exchanges data with the transmission 3. Furthermore, the engine control unit 7 and the transmission control unit 8 exchange data with each other.

[0025] The invention relates to a method and a control unit for operating a transmission 3 of a motor vehicle, by means of which an unwanted tensioning of the transmission 3, which can lead to a blockage of the output 2, can be reliably detected.

[0026] According to the invention, the current actual rotational speed at the transmission output 6 is preferably acquired at defined time intervals, in particular at time intervals corresponding to the sampling rate of the transmission control unit 8. Acquisition can be carried out using a speed sensor 9, which measures the actual rotational speed and provides it to the transmission control unit 8, preferably via a corresponding data interface 10 of the transmission control unit 8. The transmission control unit 8 exchanges data via data interfaces 10 in Fig. 1 not only with the speed sensor 9 but also with the engine control unit 7 and the transmission 3 data.

[0027] Depending on the respective currently recorded actual speed at the transmission output 6 and depending on a respective previously recorded actual speed at the transmission output 6, which was recorded in particular by an integer multiple of the sampling rate of the transmission control unit 8, a temporal gradient of the actual speed at the transmission output 6 is preferably determined at the defined time intervals.

[0028] Then, if the magnitude of a negative gradient of the actual rotational speed at the gearbox output 6 is greater than a first limit value, an unwanted tensioning of the gearbox 3 is detected.

[0029] According to the invention, if a positive speed gradient of the actual speed at the transmission output 6 is determined based on a comparison of a respective currently detected actual speed at the transmission output 6 with a respective previously detected actual speed at the transmission output 6, the magnitude of which is greater than a second limit value, a slip condition on the output side is detected, wherein the respective currently detected actual speed, on the basis of which the slip condition on the output side was detected, is then not used for the detection of an unwanted binding of the transmission 3.

[0030] Rather, in this case, the respective previously recorded actual speed at the gearbox output 6, on the basis of which in combination with the respective currently recorded actual speed at the gearbox output 6, the output-side slip state was recognized, is used as the current actual speed for the detection of an unwanted binding of the gearbox 3, as long as the actual currently recorded actual speed at the gearbox output 6 is greater than this respective previously recorded actual speed at the gearbox output 6 by a defined offset.

[0031] Only when the actual current measured speed at gearbox output 6 becomes lower than the previously measured speed at gearbox output 6 (increased by the offset and reduced by a hysteresis value) is the actual current measured speed subsequently used again for detecting unwanted binding of the gearbox 3. The hysteresis value can be zero, but is preferably greater than zero in absolute value.

[0032] The above procedural details allow for the detection of unwanted gear binding 3 by masking or suppressing possible slip conditions at output 2. This enables a more reliable and robust conclusion to be drawn about unwanted gear binding 3. Slip conditions that could impair the detection of unwanted gear binding are thus masked.

[0033] Preferably, each currently recorded actual rotational speed of the gearbox output 6, which is in Fig. 1 is detected using the speed sensor 9 and provided to the transmission control unit 8 via a data interface 10, and stored in a memory 12 via a processor 11.

[0034] To determine the time gradient of the actual rotational speed at the gearbox output 6, the respective stored, currently recorded actual rotational speed and the respective stored, previously determined actual rotational speed are read from memory 10 and compared with each other.

[0035] Then, when a slip condition on the output side is detected, the respective previously recorded actual speed at the gearbox output 6, on the basis of which the slip condition on the output side was detected in combination with the respective currently recorded actual speed, is stored as a reference value or as a reference speed.

[0036] This reference value, or reference speed, is used as the current actual speed for detecting unwanted binding of the gearbox 3 as long as the actual, currently measured speed at the gearbox output 6 is greater than this reference value by the defined offset. Only when the currently measured speed falls below the reference speed (increased by the offset and reduced by the hysteresis value) is the actual, currently measured speed used again for detecting unwanted binding of the gearbox 3.

[0037] Alternatively, to determine the time gradient of the actual rotational speed at gearbox output 6, the respective stored, currently recorded actual rotational speed and the respective previously recorded actual rotational speed from memory 10 can be read and calculated together. If a slip condition is detected on the output side, the respective current actual rotational speed is overwritten by the respective previously recorded actual rotational speed in memory 10 as long as the actual current recorded rotational speed at gearbox output 6 is greater than the respective previously recorded actual rotational speed by the defined offset. In this case, no reference value is temporarily stored; instead, a memory location in memory 12 is overwritten.

[0038] Alternatively, before storing the currently recorded actual speed, it is possible to compare the current recorded actual speed at gearbox output 6 with a previously determined actual speed at gearbox output 6 to determine the gradient of the actual speed. The currently recorded actual speed is only stored in memory 12 if no output-side slip condition is detected. If an output-side slip condition is detected, the previously recorded actual speed is stored in memory 10 instead of the currently recorded actual speed.

[0039] Memory 10 is preferably a ring buffer with a defined number of storage locations, which are then successively overwritten when the ring buffer is completely filled, namely in such a way that the oldest stored actual speed is replaced by a new actual speed.

[0040] The invention further relates to a control unit of a transmission 3, which is configured to automatically execute the method described above. This control unit is in particular the electronic transmission control unit 8, which comprises hardware and software components.

[0041] The hardware means include the data interfaces 10 for exchanging data with the assemblies involved in the execution of the method according to the invention, for example with the speed sensor 9.

[0042] Furthermore, the hardware components include the processor 11 for data processing and the memory 12 for data storage.

[0043] The software-related means include program modules that are implemented in the transmission control unit 8 for carrying out the method according to the invention. Reference sign 1 drive unit 2 Drive 3 gearboxes 4 Gearbox input 5 switching element 6 Gearbox output 7 Engine control unit 8 Transmission control unit 9 Speed ​​sensor 10 Data interface 11 processor 12 memory / ring buffers

Claims

Method for operating a transmission (3) of a motor vehicle, wherein a current actual rotational speed is detected at a transmission output (6) of the transmission (3), wherein, depending on a respective current actual rotational speed at the transmission output (6) and a respective previously detected actual rotational speed at the transmission output (6), a temporal gradient of the actual rotational speed at the transmission output (6) is determined, wherein, if the magnitude of a negative gradient of the actual rotational speed at the transmission output (6) is greater than a first limit value, an unwanted binding of the transmission (3) is detected, wherein, if the magnitude of a positive gradient of the actual rotational speed at the transmission output (6) is greater than a second limit value, a slip condition on the output side is detected and the respective currently detected actual rotational speed is not used for the detection of an unwanted binding of the transmission (3), characterized in that, if a slip condition on the output side is detected,The respective previously recorded actual speed at the gearbox output (6) is used as the current actual speed for the detection of an unwanted binding of the gearbox (3), as long as the actual currently recorded actual speed at the gearbox output (6) is greater than the respective previously recorded actual speed at the gearbox output (6) by a defined offset. Method according to claim 1, characterized in that only when the actual current detected actual speed at the gearbox output (6) becomes smaller than the respective previously detected actual speed at the gearbox output (6) increased by the offset and reduced by a hysteresis value, is the actual current detected actual speed used again for the detection of an unwanted binding of the gearbox (3). Method according to claim 1 or 2, characterized in that each currently detected actual speed of the transmission output (6) is stored in a memory (12), to determine the time gradient of the actual speed at the transmission output (6) the respective stored currently detected actual speed and the respective previously detected actual speed are read from the memory (12) and calculated together, then, when a slip condition on the output side is detected, the respective previously detected actual speed at the transmission output (6) is stored as a reference speed and is used as the current actual speed for the detection of an unwanted binding of the transmission (3) as long as the actual currently detected actual speed at the transmission output (6) is greater than the reference value by the defined offset. Method according to claim 1 or 2, characterized in that each currently detected actual speed of the transmission output (6) is stored in a memory (12), to determine the temporal gradient of the actual speed at the transmission output (6), the respective stored currently detected actual speed and the respective previously detected actual speed are read from the memory (12) and calculated together, then, when a slip condition on the output side is detected, the respective currently detected actual speed is overwritten by the respective previously detected actual speed at the transmission output (6) and used as the current actual speed for the detection of an unwanted binding of the transmission (3) as long as the actual currently detected actual speed at the transmission output (6) is greater than the respective previously detected actual speed by the defined offset. Method according to claim 1 or 2, characterized in that a currently detected actual speed of the transmission output (6) is stored in a memory (12) only if no output-side slip condition is detected, and if an output-side slip condition is detected, the respective previously detected actual speed at the transmission output (6) is stored in the memory (12) instead of the respective currently detected actual speed, namely as long as the actual currently detected actual speed at the transmission output (6) is greater than the respective previously detected actual speed by the defined offset. Method according to one of claims 3 to 5, characterized in that a ring buffer is used as the storage device (12). Control unit (8) of a transmission (3) which is configured to automatically execute the method according to one or more of claims 1 to 6.

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