Control procedure and control device in a motor vehicle for shifting an automatic transmission

Abstract

Control method in a motor vehicle (F) for shifting an automatic transmission (7) having at least two gears (GH, GN), in which data from a vehicle speed-related data source (10) are received by means of at least one electronic control unit (5, 8) for a defined foresight range (BV), in which an area (U) lying at least within the foresight range (BV) is derived from the data v_limit ) with a limiting speed (v_limit) below the maximum speed (v_max) of the lower gear (GN) is recognizable and in which the lower gear (GN) is maintained or downshifted to the lower gear (GN) when such an area (U) is detected in the foresight range (BV). v_limit ) was detected, characterized in that the control unit (5, 8) only shifts down to the lower gear (GN) if a driver performance requirement value (FP) is below a defined first threshold (S1).

Description

[0001] The invention relates to a control method and a control device in a motor vehicle for shifting an automatic, in particular non-powershift transmission.

[0002] Vehicles with non-powershift transmissions generally cannot use all gears, as the long gearshift pauses lead to an interruption in traction, which is perceived as annoying, especially during upshifts. The BMW i8 serves as an example. It has an electric motor on the front axle that transfers power to the road via a two-speed transmission (non-powershift). Due to an engine speed limit, first gear can only be used up to approximately 120 km / h. At this point at the latest, second gear must be shifted to increase the vehicle speed. To avoid this shifting, the automatic mode with the combustion engine that can be switched on as needed ("Auto eDrive") always starts off in second gear. Only in purely electric mode ("Max eDrive") is first gear used at limited vehicle speeds. For further technical background, please refer to the unpublished document DE 10 2014 203 668.2 of the applicant, DE 10 2006 030 528 A1 and DE 10 2014 019 543 A1.

[0003] Starting off in second gear has the following disadvantages, especially in the BMW i8: For one thing, starting off requires less wheel torque. This results in the combustion engine starting more frequently in automatic mode ("Auto eDrive"), resulting in a lesser electric driving experience.

[0004] Secondly, during full-throttle acceleration from a standstill in second gear, the electric motor can only deliver maximum power at a higher speed than in first gear. It cannot accelerate as quickly as in first gear.

[0005] The object of the invention is to improve comfort on the one hand and acceleration capability on the other hand, particularly in non-powershift transmissions.

[0006] This object is achieved according to the invention by the subject matter of claim 1. Dependent claims are advantageous developments of the invention.

[0007] In the control method according to the invention or in the control device according to the invention for shifting an automatic and, in particular, non-powershift transmission having at least two gears, data from a driving speed-related data source for a defined look-ahead area is received by at least one electronic control unit. Such data sources include, for example, navigation systems, car-to-car systems, transmitting traffic signs, or other digital, remotely transmitted data. The data is such that the control unit can use it to determine an area located at least within the look-ahead area with a limit speed below the maximum speed of the lower gear. If such an area is actually detected in the look-ahead area, either the lower gear is maintained or a shift is made from the higher to the lower gear.

[0008] The downshift to the lower gear only occurs if a driver performance demand value (in particular, the accelerator pedal angle) is below a defined (first) threshold, preferably if the driving speed is at least below the maximum speed of the lower gear. The first threshold can be defined in such a way that the presence of constant speed or coasting operation is ensured.

[0009] The driver preferentially changes from the lower gear to the higher gear if, within a transition area between the area with a limit speed below the maximum speed of the lower gear and an area with a limit speed or a possible expected driving speed above the maximum speed of the lower gear, a driver performance requirement value is below a defined (second) threshold and the driving speed is below the maximum speed of the lower gear.

[0010] The first threshold and the second threshold can be defined the same or similarly but differently in the sense of hysteresis.

[0011] The invention is based on the following considerations: The disadvantages of a gearshift with a comparatively long gearshift interruption only arise when, in the example vehicle described above, acceleration exceeds 120 km / h – i.e., above the maximum speed of the lower (e.g., first) gear. The invention therefore provides a navigation-based gearshift strategy. The vehicle detects when it is in an area with a speed limit below the maximum speed of the lower gear or when it is approaching such an area (e.g., speed limit 50, 60, or 80 km / h). In this area, the driver's desire to accelerate beyond the maximum speed (e.g., 120 km / h) is unlikely.

[0012] For example, in an urban environment, the invention maintains the low gear or shifts back to it.

[0013] If the vehicle detects that it is approaching the city limits and leaving the urban area (speed limit equal to or above 100 km / h), the transmission shifts into the higher (e.g. second) gear in a comfort-oriented moment, particularly when driving at a constant speed and / or during a coasting phase.

[0014] This makes it possible to drive with higher electric wheel torque, especially in urban environments, making the hybrid vehicle described above more robust at start-up and achieving a more enjoyable electric driving experience. Furthermore, the vehicle's absolute acceleration capability in urban environments increases.

[0015] Details of the invention are explained in more detail in the following exemplary embodiment with reference to the drawing. It shows Fig. 1 a schematic representation of a road-coupled hybrid vehicle with the components essential for the invention and Fig. 2 a schematic representation of the operation of the control method according to the invention.

[0016] In Fig. Figure 1 shows a so-called road-coupled hybrid vehicle F (e.g., a BMW i8) with an electric motor 1, which acts as the first drive motor, for example, on the front axle (VA), and with an internal combustion engine 3, which acts as the second drive motor on the rear axle (RA). The electric motor 1 interacts with a two-speed transmission 7 without an intermediate clutch. This two-speed transmission 7 is an example of a non-powershift transmission, to which the invention preferably relates.

[0017] A second electric motor 2 can be provided in addition to the combustion engine 3. Furthermore, a second transmission 4, preferably in the form of an electronically controllable automatic transmission (as already known from the prior art of BMW production vehicles), is connected to the input side of the combustion engine 3. Analogously, the invention is also applicable to a different arrangement of components 2, 3, and 4. The electric motor 1 could also be arranged on the rear axle and the combustion engine 3 on the front axle.

[0018] The hybrid vehicle F also has a driver-operated selector device (“Max-E-Drive” button) for manually switching between a purely electric operating mode (E-mode) and an automatic operating mode (A-mode) with the combustion engine 3 that can be switched on as needed, and a navigation system 10.

[0019] Furthermore, the hybrid vehicle has an electronic transmission selector 9 which is known per se (e.g. from BMW series vehicles), via which the driver can select the usual driving positions P, R, N and D for the automatic transmission 4 as well as a switch position “S” for selecting a sporty automatic mode.

[0020] Finally, in Fig. 1 schematically shows a known accelerator pedal FP, the deflection of which is known to be detected, for example, via a potentiometer.

[0021] The drive control of the hybrid vehicle is preferably carried out by a first electronic control unit 5, by means of which a wheel torque-related overall drive control for all existing drive motors can be carried out (known, for example, from patent applications DE 10 2011 004 862 and DE 10 2011 005 962). Furthermore, according to the invention, a function module GS-E ("E-drive transmission control") is also contained, for example, in the control unit 5 or preferably (as shown here) in an additional control unit 8 that is mechatronically assigned closer to the two-speed transmission 7. The function module GS-E is designed, for example, as a software program module. By means of the function module GS-E and the control units 5 and / or 8, the two-speed transmission 7 is preferably connected to the Fig. 2 shown particularly advantageous sequence control.

[0022] Control units 5 and 8 are preferably connected to each other via a data bus (e.g., CAN) and exchange sensor and control signals as needed. For example, control unit 8 can receive the vehicle speed v as information from control unit 5.

[0023] The control unit 8 has a functional module which is designed (in particular programmed) in such a way that a change between the first gear GN and the second gear GH can be initiated depending on the operation of the selector device (Max-E-Drive button).

[0024] However, the GS-E functional module is also designed (in particular programmed) in such a way that a change between the first gear GN and the second gear GH can be initiated depending on further predetermined conditions.

[0025] To change gears, the torque of the electric motor 1 is reduced to at least almost zero, since the two-speed transmission 7 does not have a clutch that can be opened to interrupt the traction.

[0026] A gear change is initiated, for example, with a target gear jump (e.g. in the form of a digital upshift or downshift command within a software program).

[0027] The control of the gear change according to the invention is explained in detail in the embodiment according to Fig. 2 explains: In the electronic control unit, for example in the form of a single control unit or here in the form of the main control unit 5 and the additional control unit 8, data from a driving speed-related data source, here e.g. the on-board navigation system 10, are received for a defined preview area BV in front of the vehicle F. These data are evaluated to determine whether at least in the preview area BV an area U v_limit with a limit speed v_limit below the maximum speed v_max of the lower gear GN. Let the limit speed v_limit be, for example, 50 km / h (urban area) and the maximum speed v_max (= maximum possible driving speed due to the engine speed) of the lower gear GN be 120 km / h. The look-ahead area BV is preferably defined at approximately 500 m to 1000 m. If the vehicle F is in a transition area B1 before the area U v_limit or in area U v_limit, the lower gear GN is shifted or the lower gear GN is maintained if the accelerator pedal angle FP is below a defined first threshold S1 and the driving speed v is at least below the maximum speed v_max of the lower gear GN of 120 km / h.

[0028] The lower gear GN is changed to the higher gear GH if, within a transition area B2 between the area U v_limit and an area U v_max with a possible driving speed v above the maximum speed v_max, the accelerator pedal angle FP is below a defined second threshold S2 and the driving speed v is below the maximum speed v_max.

[0029] The first threshold S1 and the second threshold S2 are defined differently in the sense of a hysteresis and ensure, for example, overrun during gear changes.

Claims

[1] Control method in a motor vehicle (F) for shifting an automatic transmission (7) having at least two gears (GH, GN), in which method data from a driving speed-related data source (10) are received for a defined look-ahead area (BV) by means of at least one electronic control unit (5, 8), in which method an area (U v_limit ) with a limit speed (v_limit) below the maximum speed (v_max) of the lower gear (GN) and in which the lower gear (GN) is maintained or shifted back to the lower gear (GN) if such an area (U v_limit ) was detected, characterized by that the control unit (5, 8) only switches back to the lower gear (GN) if a driver power demand value (FP) is below a defined first threshold (S1). [2] Control method according to claim 1, characterized by that the control unit (5, 8) only switches back to the lower gear (GN) when the driving speed (v) is below the maximum speed (v_max) of the lower gear (GN). [3] Control method according to one of the preceding claims, characterized by that the control unit (5, 8) is used to change from the lower gear (GN) to the higher gear (GH) if, within a transition area (B2) between the area (U v_limit ) with a limit speed (v_limit) below the maximum speed (v_max) and an area (U v_max ) with a limit speed (v_limit) or possible driving speed (v) above the maximum speed (v_max), the driving speed (v) is below the maximum speed (v_max) of the lower gear (GN). [4] Control method according to one of the preceding claims, characterized bythat the control unit (5, 8) is used to change from the lower gear (GN) to the higher gear (GH) if, within a transition area (B2) between the area (U v_limit ) with a limit speed (v_limit) below the maximum speed (v_max) and an area (U v_max ) with a limit speed (v_max) or possible driving speed (v) above the maximum speed (v_max) a driver performance requirement value (FP) is below a defined second threshold (S2). [5] Control method according to one of the preceding claims, characterized by that the first threshold (S1) and the second threshold (S2) are the same or are defined differently in the sense of a hysteresis. [6] Control device in a motor vehicle for shifting an automatic transmission (7) having at least two gears (GH, GN), with at least one electronic control unit (5, 8) in such a way that it can receive data from a driving speed-related data source (10) for a defined look-ahead area (BV), that it can determine from the data an area (U) lying ahead at least in the look-ahead area (BV) v_limit ) with a limit speed (v_limit) below the maximum speed (v_max) of the lower gear (GN) and that the lower gear (GN) can be maintained or shifted back from the higher gear (GN) to the lower gear (GN) if such an area (U v_limit ) is recognized, characterized bythat the control unit (5, 8) only switches back to the lower gear (GN) if a driver power demand value (FP) is below a defined first threshold (S1). [7] Control unit (5, 8) for a motor vehicle (F) with a programmable function module for controlling an automatic transmission (7) for use in a control device according to claim 6.

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