Method for performing shifts in an automated transmission of a vehicle

Abstract

Method for performing gear changes in an automated transmission of a commercial vehicle, wherein, upon a requested downshift, the expected engine speed of the commercial vehicle after the downshift is determined and compared with a maximum permissible engine speed of the commercial vehicle, wherein, if the maximum permissible engine speed is exceeded, a vehicle brake is activated in such a way that the maximum engine speed is not exceeded after the downshift, characterized in that a brake intervention to reduce the engine speed is carried out when a deceleration request from the driver is detected by sensing a position of a brake lever of an engine brake to a maximum value.

Description

[0001] The present invention relates to a method for performing gearshifts in an automated transmission of a vehicle. Upon a requested downshift, an expected engine speed of the vehicle after the downshift is determined and compared with a maximum permissible engine speed of the vehicle. Furthermore, the invention relates to a control unit for implementing the method.

[0002] Methods for performing gear changes in a vehicle's automated transmission are also referred to as shift strategies, which can be used to perform gear changes in the vehicle automatically. As part of the shift strategy, downshifts are also performed in order to use the wear-free engine brake to slow the vehicle down, for example, on a downhill slope. However, with such a downshift, the braking effect of the engine brake is lost, causing the vehicle to accelerate during the downshift. The occurring acceleration of the vehicle is determined as part of the shift strategy before the downshift is performed, making it possible to determine what the engine speed will be after the downshift.If this engine speed is above a maximum permissible engine speed of the vehicle, the downshift is not triggered with known shift strategies, since triggering the shift would result in the maximum permissible engine speed being exceeded, which could damage the vehicle's engine.

[0003] This results in the disadvantage that, with the known shifting strategy, certain downshifts are not triggered on downhill gradients, thus reducing the number of available gears, particularly on downhill gradients. As a result, the use of the wear-free engine brake in the vehicle is significantly limited, requiring the wear-prone service brake to be used to permanently limit the vehicle's deceleration on downhill gradients. This can cause the service brake to overheat, which can lead to the failure of the separate service brake.

[0004] DE 10 2020 204 282 A1 discloses a method for controlling the operation of a motor vehicle, wherein a speed profile and / or an acceleration profile of the motor vehicle is determined as a function of at least one driving resistance parameter for a current transmission gear and at least one further transmission gear, and a change or a maintenance of the current transmission gear is carried out based on the determined speed profile and / or the determined acceleration profile.

[0005] DE 10 2011 080 712 A1 discloses a method for influencing a transmission shift strategy of a motor vehicle, wherein the operation of the transmission is controlled using driving state data and / or driver request data. To improve the shift strategy, road class-related information and / or temporal traffic control information and / or route-related information assumed to be probable are recorded, where available.

[0006] DE 10 2017 221 887 A1 discloses a method for operating a drive train of a motor vehicle, wherein an operating strategy is designed in a forward-looking manner taking into account detected environmental conditions of the motor vehicle.

[0007] DE 10 2014 009 725 A1 discloses a motor vehicle drivetrain device with an automatic transmission designed to shift gears at least partially automatically. A control and / or regulating unit is provided, in at least one operating mode, to actively reduce a vehicle speed for a downshift.

[0008] DE 10 2015 211 996 A1 discloses a method for automatically actuating a service brake of a motor vehicle, wherein the actuation is performed before a downshift, which takes place in a motor vehicle transmission of the motor vehicle to a target gear. In this process, the actuation of the service brake causes a drive motor of the motor vehicle to be shifted from a speed that is impermissibly high for the target gear to a speed that is permissible for the target gear. The present invention is based on the object of proposing a method of the type described above and a control device for carrying out the method, which expand the use of an engine brake.

[0009] This object is achieved according to the invention by the features of patent claims 1 and 4. Advantageous and claimed developments emerge from the subclaims and the description as well as the drawings.

[0010] Thus, a method for performing gearshifts or a gearshift strategy in an automated transmission or an automatic transmission of a vehicle is proposed, wherein, upon a requested downshift, an expected engine speed of the vehicle after the downshift is determined and compared with a maximum permissible engine speed of the vehicle. To expand the use of the wear-free engine brake and the number of gears available for downshifting, it is provided that, if the maximum permissible speed is exceeded, a vehicle brake is activated in such a way that the maximum engine speed is not exceeded after the downshift.

[0011] In this way, the proposed method enables downshifts, for example, on downhill slopes or on a descending road gradient, without the risk of exceeding the maximum permissible engine speed. This is achieved by limiting vehicle acceleration during this downshift through the automated application of the vehicle brake or the vehicle's service brake. This enables downshifts that would not have been initiated without the use of the vehicle brake, increasing the number of available gears, particularly on routes with a descending road gradient.

[0012] In order to determine the expected engine speed of the vehicle after the downshift as accurately as possible, the engine speed is determined based on certain vehicle characteristics. For example, the proposed method can use the vehicle speed and / or the vehicle mass and / or the driving resistance and / or the ratio of the requested idle gear.

[0013] To further determine the expected engine speed of the vehicle after the downshift, the proposed method can also use current and / or future route information from the vehicle. For example, route information from the vehicle's electronic horizon can be used for this purpose.

[0014] To further optimize the proposed method, braking intervention to reduce the engine speed is performed when a driver deceleration request is detected. Consequently, the braking function is only applied if this request can be interpreted from the driver's actions. For example, this can occur if the driver of a commercial vehicle has set the engine brake lever to a maximum value.

[0015] The proposed method is preferably used in commercial vehicles, in particular in trucks or the like, where the use of the engine brake is essential in order to relieve the load on the service brake when the road gradient decreases.

[0016] The object underlying the invention is also achieved by a control unit for implementing the method described above. A multitude of vehicle data and route information are available to the control unit, or the engine or transmission control unit, so that if the maximum permissible engine speed is exceeded, the vehicle brake is applied automatically to prevent the maximum engine speed from being exceeded after the downshift.

[0017] The proposed procedure is further explained below using the drawing.

[0018] The single figure shows a possible flow diagram of a method according to the invention for carrying out a downshift on a downhill slope, for example from a sixth gear to the fifth gear on a falling road gradient of, for example, 10% in an automated transmission of a commercial vehicle.

[0019] The figure shows that, in order to enable downshifting, the method according to the invention determines the expected engine speed after the downshift. This check takes into account the vehicle speed, the ratio of the requested target gear, the road gradient or road surface cleanliness, and the vehicle mass.

[0020] This results in an expected engine speed after shifting down to fifth gear of, for example, 2600 revolutions per minute. The maximum permissible engine speed of the vehicle is approximately 2500 revolutions per minute. Therefore, shifting down to fifth gear would exceed the maximum permissible engine speed.

[0021] Within the framework of the proposed method, an automated braking intervention is activated or executed by appropriately activating the vehicle brake during the downshift to fifth gear, so that the expected engine speed after the downshift due to the automated braking intervention is approximately 2400 rpm. Thus, the expected engine speed is below the maximum permissible engine speed of 2500 rpm. This does not result in the maximum permissible engine speed being exceeded, so the downshift is triggered within the framework of the proposed method.

[0022] To enable downshifting on a downhill slope, the commercial vehicle's service brake is automatically activated during the shift. This prevents the commercial vehicle from accelerating too quickly. The downshift can be initiated and executed because the expected engine speed does not exceed the maximum permissible engine speed due to the braking intervention. Since the service brake is only activated during the downshift, there is no overloading of the service brake.

[0023] When calculating the engine speed after the downshift, the driver takes into account whether the aforementioned braking intervention occurs during the downshift. This automatically adapts the shift strategy of the automated transmission system to the proposed braking function. For example, driving resistance can be taken into account to adjust the braking component of the function accordingly.

[0024] The braking function is only activated when the commercial vehicle is on a downhill route or is about to reach one, requiring engine braking. This route information can be provided, for example, from the vehicle's electronic horizon. Furthermore, the braking function is only activated when a corresponding driver request can be interpreted, for example, by detecting the position of the engine braking lever at a maximum value and, optionally, when the vehicle is only slightly decelerating.

Claims

[1] Method for carrying out gear shifts in an automated transmission of a commercial vehicle, wherein, in the case of a requested downshift, an expected engine speed of the commercial vehicle after the downshift is determined and compared with a maximum permissible engine speed of the commercial vehicle, wherein, if the maximum permissible speed is exceeded, a vehicle brake is activated in such a way that the maximum engine speed is not exceeded after the downshift, characterized by that a braking intervention is carried out to reduce the engine speed when a deceleration request of the driver is detected by detecting a position of a brake lever of an engine brake to a maximum value. [2] Method according to claim 1, characterized bythat the expected engine speed of the commercial vehicle after the downshift is determined as a function of a vehicle speed and / or a vehicle mass and / or a driving resistance and / or a ratio of the requested target gear. [3] Method according to claim 1 or 2, characterized by that the expected engine speed of the commercial vehicle after the downshift is determined depending on predetermined route information. [4] Control device designed to carry out a method according to one of the preceding claims.

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