Method for operating an automatic transmission of a motor vehicle and motor vehicle

Abstract

The invention relates to a method for operating an automatic transmission of a motor vehicle, in which the automatic transmission has at least one multi-plate shift element, wherein, when it is determined that a temperature (14) associated with the multi-plate shift element exceeds a first upper temperature threshold (T1), downshifts of the automatic transmission requested by means of the multi-plate shift element are prevented for a subsequent period of time and downshifts of the automatic transmission requested by means of the multi-plate shift element are carried out, and then, when it is determined that the temperature (14) associated with the multi-plate shift element exceeds a second upper temperature threshold (T2) higher than the first upper temperature threshold (T1), only such downshifts and downshifts of the automatic transmission to be carried out by means of the multi-plate shift element are executed.which are performed in a speed range close to idle speed, and all other downshifts and downshifts of the automatic transmission that are to be carried out by means of the multi-plate shift element are prevented.

Description

[0001] The invention relates to a method for operating an automatic transmission of a motor vehicle. Furthermore, the invention relates to a motor vehicle with such an automatic transmission.

[0002] In DE 10 2006 046 164 A1 a method for protecting switching elements in an automatic transmission of a motor vehicle is disclosed, in which separate load characteristics are determined for individual switching elements of the transmission and then, if the load characteristic of a switching element exceeds a limit value, a protective function is activated for the overloaded switching element.

[0003] DE 10 2004 051 639 A1 discloses a device for controlling an automatically shifting transmission for a motor vehicle as known, with a first selection device with which at least the driving stages adjustable in an automatic mode can be determined.

[0004] The object of the present invention is to provide a method for operating an automatic transmission of a motor vehicle and a motor vehicle with such an automatic transmission, so that a particularly advantageous operation of the automatic transmission can be realized.

[0005] This problem is solved by a method with the features of claim 1 and by a motor vehicle with the features of claim 4. Advantageous embodiments with expedient further developments of the invention are specified in the remaining claims.

[0006] A first aspect of the invention relates to a method for operating an automatic transmission, also referred to simply as a transmission, of a motor vehicle, also referred to simply as a vehicle. This means that the motor vehicle, preferably designed as a motor vehicle, in particular as a passenger car, has the automatic transmission in its fully manufactured state. For example, the motor vehicle has a drive engine by means of which the motor vehicle can be driven via the automatic transmission. In particular, it is provided that in the method the motor vehicle is driven via the automatic transmission by means of the drive engine. The drive engine can be or comprise an internal combustion engine. Furthermore, it is conceivable that, in particular alternatively or additionally, the drive engine can be or comprise at least or exactly an electric machine.

[0007] The automatic transmission has at least one multi-plate shift element. For example, the automatic transmission has several, and thus at least two, selectable gears. The characteristic that each gear is selectable means that the respective gear can be either engaged or disengaged. Each gear has a specific gear ratio. Preferably, the gear ratios differ from one another, in particular such that the ratio of the first gear is higher than the ratio of the second gear. The ratio of the first gear is also referred to as the first gear ratio, and the ratio of the second gear is also referred to as the second gear ratio.In particular, the automatic transmission and the drive engine can drive vehicle wheels, especially those on the same axle, of the motor vehicle, where, for example, the first gear ratio from the drive engine to the vehicle wheels is higher than the second gear ratio. An upshift of the automatic transmission is understood to be a gear change in which the initially engaged first gear is disengaged and the initially engaged second gear is engaged. A downshift of the automatic transmission is understood to be a gear change in which the initially engaged second gear is disengaged and the initially engaged first gear is engaged. If the upshift is performed while the drive engine is under load, it is called a load upshift. If the upshift is performed while the drive engine is under overrun, it is called an overrun upshift.If the downshift is performed during traction operation of the drive motor, the downshift is a traction downshift. If the downshift is performed during deceleration operation of the drive motor, the downshift is a deceleration downshift.

[0008] A multi-plate shift element is a shifting element comprising plates, particularly friction plates, and is designed, for example, as a multi-plate clutch. Specifically, the respective downshift is performed by means of the multi-plate shift element, also simply referred to as a shifting element, in order to engage the initially engaged first gear and to disengage the initially engaged second gear. In particular, during the respective downshift, the first gear is engaged by means of the multi-plate shift element, specifically by closing the initially open multi-plate shift element. Thus, it is conceivable, for example, that during the respective upshift, the initially closed multi-plate shift element is opened, thereby engaging the first gear.

[0009] The method provides that, if it is determined that a temperature associated with the multi-plate shift element exceeds a first upper temperature threshold, i.e., the temperature associated with the multi-plate shift element is greater than the first upper temperature threshold, then, for a specified or specifiable subsequent period, in particular, downshifts of the automatic transmission to be carried out by means of the multi-plate shift element are prevented, in particular continuously, i.e., without interruption, and downshifts requested by means of the multi-plate shift element are carried out and thus permitted.In particular, the term "subsequent time" refers to a period of time that follows, for example, directly and thus immediately, a point in time at which it is determined, particularly by means of an electronic computing device (designated as a control unit) by which the procedure is carried out, that the temperature associated with the lamellar switching element exceeds the first upper temperature threshold, i.e., is greater than the first upper temperature threshold. When the term "temperature" is used below, unless otherwise specified, it refers to the temperature associated with the lamellar switching element, also known as the element temperature.For example, it is intended that in an automatic program of the automatic transmission, also referred to as automatic mode, the requested downshifts by the automatic transmission, which are to be carried out by the multi-plate shift element, are subsequently prevented, and the requested downshifts by the multi-plate shift element are carried out and thus permitted. In the automatic program, the gear changes are carried out automatically and thus without human intervention. Alternatively or additionally, it is conceivable that in a manual program of the automatic transmission, also referred to as manual mode, the requested downshifts by the automatic transmission, which are to be carried out by the multi-plate shift element, are subsequently prevented, and the requested downshifts by the multi-plate shift element are carried out and thus permitted.In manual mode, the gear changes of the automatic transmission can be manually controlled by a person, such as the driver, by manually operating a control element of the vehicle. The term "requested downshift" or "replacement downshift" refers specifically to the fact that a component of the vehicle provides a signal, particularly an electrical one, requesting the downshift. This signal is also known as a request signal. The component in question is, for example, the control unit or a part thereof.In the automatic program, the request signal results, for example, from the detection of a gear change by the automatic transmission, which is then specifically requested by the transmission using this signal. In the manual program, the request signal results, for example, from the operator's activation of the control element. In other words, if a downshift is requested while the temperature exceeds the first upper temperature threshold, this downshift will be prevented and not performed. However, if the downshift is a coasting downshift, it will be performed. This is because downshifts place a greater thermal load on the clutch plates than coasting downshifts.In other words, more heat is introduced into the clutch plate shift element during downshifts than during deceleration downshifts. Since the inventive method differentiates between deceleration and downshifts by preventing downshifts while allowing deceleration downshifts when the temperature exceeds the first upper temperature threshold, downshifts of the automatic transmission are more frequent or better available compared to conventional solutions, thus ensuring particularly advantageous operation.

[0010] The invention is based in particular on the following findings and considerations: In a powershift transmission, such as the automatic transmission of the invention, energy and thus temperature are introduced into the respective shifting element participating in each shift. Depending on the type of shift, different temperature inputs occur: Upshifts and downshifts under load drive a great deal of heat into the shifting element, whereas upshifts and downshifts under engine braking result in hardly any temperature input. For example, if, on a racetrack during racing, an upshift from third to fourth gear and a downshift from fourth to third gear are frequently performed under load, the shifting element involved heats up quickly and can thus reach its maximum permissible friction plate temperature.When this point is reached, the shift element must be protected. Conventionally, downshifting is prevented and / or the downshift speed is significantly reduced, giving the shift element more time to cool down or, in extreme cases, preventing it from shifting altogether. This effectively means the transmission remains stuck in fourth gear for a certain period. This can be particularly undesirable on the racetrack, negatively impacting consistent performance and fast lap times, as fourth gear is intermittently unavailable. In both automatic and manual modes, a distinction is made between downshifts during acceleration, which are typically temperature-sensitive, and downshifts during deceleration, which are typically less so. This differentiation prevents the automatic transmission from completely preventing downshifts.Downshifts during acceleration are prevented to avoid excessive heating of the clutch plate, but downshifts during deceleration are permitted and performed. Additionally, the option can be implemented to prevent an already initiated deceleration downshift during a load change in the shift sequence—for example, a change from deceleration to acceleration by moving the vehicle's accelerator pedal—from being converted into a full acceleration downshift, which would again lead to excessively high temperatures of the clutch plate.

[0011] Furthermore, it is preferably provided, particularly in or for the manual program, that a purely time-dependent suppression of manually actuated shifting operations of the automatic transmission is avoided, wherein, preferably, a suppression of manually actuated shifting operations of the automatic transmission is carried out depending on the element temperature. It is preferably provided that manually actuated shifting operations of the automatic transmission are suppressed as long as, and preferably only as long as, the temperature is greater than the first upper temperature threshold. Then, and preferably always when the temperature is less than or equal to the first upper temperature threshold, manually actuated shifting operations of the automatic transmission are permitted and, in particular, carried out.During a period in which manually controlled shifting of the automatic transmission is continuously and thus uninterrupted, a warning signal, perceptible visually and / or audibly to a person inside the vehicle, is emitted, for example, by means of an electrical or electronic display device, particularly in the vehicle's interior. This signal informs the person that manually controlled shifting of the transmission is temporarily disabled and therefore not possible. By preventing manually controlled shifting of the automatic transmission in this way, which is not solely dependent on time, the transmission's shifting capabilities can be improved, resulting in particularly advantageous operation.

[0012] Preferably, it is provided that train upshifts are permitted in order to avoid, for example, excessively long operation of the drive motor in a speed limiter.

[0013] To achieve particularly advantageous operation, the invention further provides that, if it is determined that the temperature associated with the lamellar switching elements exceeds a second upper temperature threshold that is higher than the first upper temperature threshold, only those pull-down and push-down switching operations to be performed and, for example, requested by the lamellar switching element, which are carried out in a speed range close to idle speed, are executed and thus permitted. This prevents, for example, the stalling of the drive motor. All other pull-down and push-down switching operations to be performed and, for example, requested by the lamellar switching element are, however, prevented in order to avoid, in particular, thermal overload of the lamellar switching element.

[0014] It has proven particularly advantageous if, when the temperature assigned to the lamellar switching element exceeds the second upper temperature threshold, an information value, for example 1, is set in the control unit, whereby the information value is deleted or changed, for example set to 0, when the temperature assigned to the lamellar switching element falls to or below the second upper temperature threshold. This ensures particularly efficient operation.

[0015] Finally, it has proven particularly advantageous for realizing a particularly beneficial operation if, when it is determined that the temperature assigned to the lamellar switching element is in a temperature range between a lower temperature threshold and the first upper temperature threshold, a trigger speed in a switching program, in particular of the control unit, at which a pull-back switching to be carried out by means of the switching element is performed, is shifted, i.e. changed, towards lower values ​​depending on the temperature assigned to the lamellar switching element.

[0016] A second aspect of the invention relates to a motor vehicle, also referred to simply as a vehicle, and preferably configured as a motor car, in particular a passenger car, which has an automatic transmission configured to carry out the method according to the first aspect of the invention. Advantages and advantageous embodiments of the first aspect of the invention are to be regarded as advantages and advantageous embodiments of the second aspect of the invention and vice versa.

[0017] Further advantages, features, and details of the invention will become apparent from the following description of a preferred embodiment and from the drawing. The features and combinations of features mentioned above in the description, as well as those mentioned below in the figure description and / or shown in the single figure alone, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention.

[0018] The drawing shows in the only Fig. 1. A diagram illustrating a procedure for operating an automatic transmission of a motor vehicle.

[0019] The following will be based on Fig. 1. A method for operating an automatic transmission of a motor vehicle is explained. Fig. Figure 1 shows a diagram where time is plotted on the abscissa 10, relative to the image plane. Fig. 1. From left to right, increasingly so, that is, continuously. This is in Fig. The diagram shown has an ordinate 12. In the method, the automatic transmission, also referred to simply as a gearbox, has at least one multi-plate shift element, also referred to simply as a shifting element, where a temperature associated with the multi-plate shift element is plotted on the ordinate 12, specifically with respect to the plane of the diagram. Fig.The temperature increases from bottom to top, i.e., it rises. A curve 14 is plotted in the diagram. This curve illustrates the temporal progression of the temperature associated with the lamella switching element. Temperature thresholds are plotted in the diagram: a first upper temperature threshold T1, a second upper temperature threshold T2, and a lower temperature threshold T3. It can be seen that the temperature threshold T1 is higher than the temperature threshold T3 and lower than the temperature threshold T2, so the temperature threshold T2 is higher than the temperature threshold T1 and higher than the temperature threshold T3. The latter, i.e., the temperature threshold T3, is lower than the temperature thresholds T1 and T2. A temperature range between the temperature thresholds T3 and T1 is designated TB. A limit temperature GT is also plotted in the diagram.The temperature assigned to the lamellar switching element should ideally not exceed the limit temperature GT, as otherwise damage, particularly mechanical damage, to the lamellar switching element could occur. Unless otherwise specified, the term "temperature" refers to the temperature assigned to the lamellar switching element.

[0020] The method is designed so that if it is determined that the temperature associated with the multi-plate shift element exceeds the temperature threshold T1 and is, for example, lower than the temperature threshold T2, then, for a predetermined or predefinable interval, requested downshifts of the automatic transmission, to be performed by the multi-plate shift element, are prevented, and requested overrun downshifts of the automatic transmission, to be performed by the multi-plate shift element, are carried out and thus permitted. On the one hand, this prevents excessive thermal stress on the multi-plate shift element, thus preventing, for example, the temperature from reaching or exceeding the limit temperature GT. On the other hand, it ensures a high and therefore advantageous availability of downshifts of the automatic transmission.

[0021] Furthermore, it is provided, for example, that if it is determined that the temperature exceeds the temperature threshold T2, which is, for example, 180°C, only those downshifts and downshifts performed by the multi-plate clutch that occur at speeds close to idle will be executed, and all other downshifts and downshifts of the automatic transmission performed by the multi-plate clutch will be prevented. The temperature threshold T1 is, for example, 120°C. The temperature threshold T3 is, for example, 70°C.

[0022] In particular, this method can prevent such frequent shifting of the automatic transmission, which leads to excessive heating of the clutch plates. Frequent shifting, also simply called shifting, refers to gear changes between adjacent gears of the automatic transmission, such as an upshift from third to fourth gear followed by a downshift from fourth to third. Frequent shifting can cause the temperature to approach the critical limit temperature (GT). Therefore, downshifts should be prevented once a certain distance is reached from the maximum permissible limit temperature (GT), as an upshift immediately following such a downshift could cause the temperature to reach or exceed the limit temperature (GT).Upshifting during acceleration should be permitted to prevent the engine, which drives the vehicle via the automatic transmission, from remaining excessively locked into the rev limiter for an extended period. Downshifting during deceleration is permitted, however, because it places less thermal stress on the clutch plate compared to downshifting during acceleration. Therefore, the procedure differentiates between downshifting during deceleration and downshifting during acceleration with regard to performing these downshifts when the temperature exceeds the temperature threshold T1.

Claims

[1] Method for operating an automatic transmission of a motor vehicle, wherein: - the automatic transmission has at least one multi-plate shift element; - then, when it is determined that a temperature (14) associated with the multi-plate shift element exceeds a first upper temperature threshold (T1), downshifts of the automatic transmission requested by the multi-plate shift element during a subsequent period are prevented and downshifts of the automatic transmission requested by the multi-plate shift element are carried out, and - then, if it is determined that the temperature (14) assigned to the multi-plate shift element exceeds a second upper temperature threshold (T2) that is higher than the first upper temperature threshold (T1), only those downshifts and downshifts to be carried out by means of the multi-plate shift element that are carried out in a speed range close to idle speed are carried out, and all other downshifts and downshifts of the automatic transmission to be carried out by means of the multi-plate shift element are prevented. [2] Method according to claim 1, characterized by, that if the second upper temperature threshold (T2) is exceeded by the temperature (14) assigned to the lamella switching element in a control unit, an information value is set which is deleted or changed when the temperature (14) assigned to the lamella switching element falls to or below the second upper temperature threshold (T2). [3] Method according to any one of the preceding claims, characterized by , that when it is determined that the temperature (14) assigned to the lamellar switching element is in a temperature range (TB) between a lower temperature threshold (T3) and the first upper temperature threshold (T1), a trigger speed in a switching program, at which a pull-back switching to be carried out by means of the switching element is performed, is shifted to lower values ​​depending on the temperature (14) assigned to the lamellar switching element. [4] Motor vehicle, with an automatic transmission configured to perform a method according to any of the preceding claims.

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