DE102012208155A1 - Method for performing downshift operation of automatic load switching stage automatic gearbox, involve assigning gears with identical switching elements and presetting start speed by control unit on fully opening common switching element - Google Patents

Abstract

The method involves assigning multiple gears (G2,G4) with identical switching elements (A,B,C,D,E) and performing gear changes in the form of overlapping circuits in a normal mode. The start speed is preset by the control unit (6) on fully opening the common switching element. The speed setting is carried out for keeping the engine speed of the actual gear and for adjusting the engine speed theoretically of the next target gear. The common switching element is closed after reaching the engine speed assigned to the final target gear. An independent claim is included for a device for performing a downshift operation of an automatic load switching stage automatic gearbox.

Description

The invention relates to a method for performing a downshifting of an automatic power-shift stage automatic transmission in a motor vehicle.

Under automatic power-shift stage automatic transmissions are understood in the context of the invention, all transmissions in which a gear change automatically or automatically and without interrupting the torque transmission between the output shaft of a drive motor (or the transmission input shaft) and the transmission output shaft takes place and the more than two load Own switching elements. These include, in particular, automatic transmissions with planetary gear sets and automated starting clutch or converter clutch. In the following, these transmission devices are subsumed under the name automatic transmission.

The gear changes found in known automatic transmissions (especially step machines with planetary gear sets), in the form of so-called overlapping circuits - also called load circuits - instead. This form of gear change is referred to below as the normal mode.

From the DE 10 2006 057 666 A1 is a method for performing an automated downshift during a vehicle deceleration with at least temporarily activated service brake known. According to this known method, a reduction of the braking torque generated by the at least temporarily activated service brake occurs during the downshifting process, whereby the reduction of the braking torque takes place depending on the occurring speed change of the internal combustion engine or a correlated therewith during torque transmission between the drive unit and the transmission device. As a result, a jerk-free downshift during a deceleration process, especially at higher engine speeds, are possible.

The invention has for its object to provide a method for performing automated downshifts in a motor vehicle with automatic transmission, in which the fastest possible and jerk-free downshifting, especially in multiple downshifts, is possible.

According to the invention the object is solved by the features of claim 1, while in the dependent claims preferred developments of the invention are given.

The inventive method for performing an automatic downshifting of an automatic transmission, in which closed by an electronic transmission control unit for engaging a gear more than one switching element between the input shaft and the output shaft of the automatic transmission, wherein the same switching elements are associated with multiple gears and wherein in one Normal mode, the gear changes are performed in the form of overlapping circuits is characterized in a different mode from the normal mode by the following features:
In a multiple-downshift (downshifts over more than one gear), in which a switching element of the current gear is also assigned to (each next and preferably also the final) target gear, this common switching element is fully opened by the electronic transmission control unit first and Simultaneously or immediately thereafter, a speed specification is preferably made to the electronic engine control unit of a cooperating with the automatic transmission drive first to hold the engine speed of the current gear and then to set the (respectively next or final) target gear theoretically present engine speed, while on the rest respectively required switching elements of each next target gear is inserted as soon as possible. Upon reaching the (final) target gear then a rapid closing of the common switching element can be carried out as a slip-free by the previous speed specification in terms of a regulation of the engine torque and / or engine speed respectively to achieve the engine speed value that is expected in the respective target gear Close the common switching element is possible.

According to the invention, therefore, a switching element is always selected as the common switching element, which is assigned during the multiple-downshift to smaller gears as many courses in a row.

The inventive method is used in motor vehicles with an example of an internal combustion engine or hybrid drive (especially internal combustion engine and electric motor) formed drive unit (drive motor including electronic engine control unit), with a transmission device (automatic transmission including electronic transmission control unit) for performing automated gear changes and with between the input shaft and the output shaft of the automatic transmission arranged controllable switching elements (so-called transmission clutches or brakes) for establishing a separation or connection between the input shaft and the output shaft of the transmission device. A coupling unit between Drive motor (especially internal combustion engine) and automatic transmission is designed for example as an automated disconnect clutch (especially multi-plate clutches) or converter clutch.

The invention is used in particular when multiple downshifts are required during driving, in particular by a braking intervention of the service brake. An intervention of the service brake can be done by the manual operation of a brake pedal by the driver or due to an automatic braking intervention by a driver assistance system for longitudinal and / or lateral dynamics control.

The implementation of the automatic downshift according to the invention is carried out as a special mode in contrast to the normal mode according to the prior art preferably not always, but only at predetermined conditions, especially if the length of the switching time in normal mode when reaching the target gear, the engine speed below or too close to the Idle speed threatens to lie.

The invention is based on the following considerations, findings and ideas:
Affected are automatic transmissions in the form of planetary gears, regardless of whether, for example, in combination with converter, starting clutch or as a hybrid module. Circuits with this type of transmission are usually designed as so-called load circuits or overlapping circuits, in which the torque transmission during the switching operation is transferred from a disconnecting to an engaging switching element (clutch or brake), without the adhesion being interrupted. For reasons of comfort, these circuits can not be performed arbitrarily fast. This leads to problems with greater braking of the vehicle because the required duration, especially of several successive downshifts can lead to unwanted pressure of the engine speed. If this leads to critical underspeeding, it must be provided for a decoupling of the engine, which can be done by opening the converter lockup clutch, any existing startup or disconnect clutch or neutral switching of the transmission (opening all or individual selected switching elements). With renewed load addition in one of these partially or completely decoupled states results in often very unpleasant restart behavior with regard to response and comfort, because the one or more decoupling elements must be closed in conjunction with the switching of a suitable gear again.

If, due to the switching time required for the above-described load circuits or overlapping circuits, the danger of the rotational speed is below a desired threshold, then according to the method proposed according to the invention, only one switching element should be used (ideally the switching element which is common to all or most of the (intermediate or final) In this state, the engine is to be adjusted by torque or speed specification on the theoretically present engine speed in the current target gear. In this state, the respective target gear is to be engaged as quickly as possible (with the exception of one decoupling switching element) via the other switching elements required in each case Ideally, no or only temporary clinking occurs by switching the switching elements and synchronous engine speed control ger slip on the remaining open switching element. As long as the braking stops, the decoupling should remain in order to represent the described much faster feasible gear changes with parallel speed control of the engine can. From this state, the open switching element can now be closed directly (no slippage reduction necessary) with load addition or when reaching the target gear without risk of speed depression or withdrawal of braking, and thus a spontaneous restart behavior can be displayed.

Advantages of the invention:

• - Gear changes can be made much faster (decoupling and supporting engine speed control);
• - It can come to no speed pressing, as there is a decoupling and the drive motor is more or less freely rotating set to the speed level of each target gear;
• - Coupling with load addition can be displayed much faster and more comfortable than, for example, after neutral switching or opening the lock-up clutch according to the prior art, ie without inventive speed specification while the common switching element is open;
• - The driver has the same perception by the engine speed control at target gear level as if the gears were switched normally with existing traction.

In the drawing, an embodiment of the invention is shown. It shows

1 a schematic representation of the existing in a motor vehicle components for carrying out the method according to the invention,

2 a tabular representation of the assignment of switching elements within an automatic transmission for engaging the individual gears,

3 a comparative comparison of the resulting switching times during downshifts of the prior art (normal mode) and according to the invention (special mode) and

4 a comparative comparison of the resulting switching times in multiple downshifts with a comfort-optimized alternative and with a switching time minimized alternative of the invention.

In 1 above is schematically a motor vehicle 1 shown, which is a drive motor 2 , an automatic transmission 3 and, for example, a converter clutch as a coupling unit 4 between drive motor 2 (especially internal combustion engine) and automatic transmission 3 having. The drive motor 2 is an electronic engine control unit 5 and the automatic transmission 3 is an electronic transmission control unit 6 assigned. The two control units 5 and 6 For example, they communicate with each other via a CAN data bus and thus exchange information and commands.

That via the coupling unit 4 with the drive motor 2 cooperating automatic transmission 3 includes the switching elements A, B, C, D and E between its input shaft and its output shaft for engaging the gears G1 to G8 and GR (reverse), by the electronic transmission control unit 6 are controllable. The switching elements A and B, for example, transmission brakes and the switching elements C, D and E gear couplings. The electronic control unit 6 contains a program module for carrying out the method according to the invention, wherein it is an interface to the engine control unit via the CAN data bus, for example 5 for controlling the engine speed n_M of the drive motor 2 having.

In 2 is a table for an exemplary automatic transmission 3 which shows in which gear which of the switching elements A, B, C, D and E are closed (= X). For the invention, the fact is exploited that the same switching elements are required for multiple gears. In the illustrated embodiment, in this regard, the switching element B for the first five gears G1 to G5 is particularly relevant. The following embodiment according to the inventive method is based on the fifth gear G5 as the current gear before a downshift.

First, based on 3 , above, the normal mode for a multiple downshift G5 => G4, G4 => G3 and G3 => G2 shown with respect to the clutch torque M_K the respective switching elements concerned. At the same time, the course of the engine speed n_M of the drive motor resulting from these multiple downshifts becomes 2 shown. These multiple downshifts in normal mode result in engine speed pressures below idle speed n_LL and may stall the drive motor 2 or to an emergency decoupling (traction interruption) to prevent stalling of the drive motor 2 to lead. Furthermore, there is a relatively long switching time ts for all required consecutively executed downshifts.

Based on 3 , bottom, for comparison, the effect on the curves of the clutch torque M_K and the engine speed n_M in the special mode according to the inventive method is shown. According to the invention, in a downshift from gear G5, in which the shifting element B of the current gear G5 is also assigned to all further lower target gears G4, G3 and G2, this common shifting element B is completely opened as quickly as possible in a first step. At the same time or at least immediately thereafter, a speed specification is made by the transmission control unit 6 to the engine control unit 5 is started and carried out in such a way that first the engine speed n_M of the (previously engaged) current gear (start gear) is held and then the engine speed n_M of the next and finally final target gear in multiple downshifts - here from gear G5 to gear G2 - is adjusted , The engine speed n_M of the respective target gear G4, G3 and G2 should be reached before or at least until the time t4, t3 or t2 at which the respective other shift elements for setting the respective target gear are finished. The predetermined engine speeds n_M for speed specification can be determined from the transmission ratio of the target gear and the current vehicle speed.

Another embodiment is based on 4 explains:
If a downshift over several gears - for example, a G4 to G2 gear change - requested, this can be minimized switching time (alternative 1 ) or comfort-optimized (alternative 2 ) be performed. These two alternatives will be in 4 compared. alternative 1 ( 4 , bottom) achieves a considerably reduced switching time ts3 compared to the prior art normal mode, whereby, however, a clear howling of the engine speed n_M would be audible to the driver (see dash-dotted n_M line in FIG 3 , Opposite the alternative 1 achieved alternative 2 ( 4 , above), although a reduced compared to the normal mode according to the prior art switching time ts2, which is greater than ts3. By the alternative 2 becomes despite switching time reduction, however, achieved a better and more habitual acoustics. The alternative 1 can be used if even the alternative 2 too slow and thus lead to speed in the target gear.

Second step according to alternative 1 ( 4 below):
In a second step, when switching back from fourth gear G4 directly into second gear G2, the other shifting element D of the current gear G4 is opened as target gear and the other shifting element A of the target gear G2 is closed (see also FIG 1 below, G4 to G2 gear change). The curves of the clutch torques M_K of the switching elements relevant for this G4 to G2 downshift are shown in FIG 4 shown below. The affected switching elements are also in 1 below, G4 to G2 gear change, shown in bold in connection with the component overview.

Second step according to alternative 2 ( 4 above):
In a second step, the switching element D of the current gear G4 are opened and the switching element C of the target gear G3 closed in a downshift from fourth gear G4 first in the third gear G3 as a target gear. In a final downshift from the gear G3 in the gear G2 as (final) target gear, the switching element C of the current gear G3 is opened and the switching element A of the target gear G2 closed.

In the second step, the switching element B remains open for traction interruption in both alternatives, while those associated with 3 explained speed specification is performed. In a third step, the common switching element B is then closed when the engine speed n_M of the final target gear G2 is reached.

The special mode is performed here only by the corresponding constellation of the switching elements and by the advantageous effect of the special mode, especially in lower gears, if more than one downshift command below the fifth gear G5 (in the example 3 ) or fourth gear G4 (in the example 4 ) is present.

Additionally or alternatively, the special mode is performed only if the length of the switching time ts in the normal mode in the target gear, the engine speed n_M threatens to fall below or too close to the idle speed n_LL. This may be the electronic transmission control unit 6 precalculate by the information available to her.

• – Zunächst wird als erstes gemeinsames Schaltelement das Schaltelement D ausgewählt, da dieses ausgehend von Gang G8 den meisten folgenden niedrigeren Gängen nacheinander zugeordnet ist. Das Schaltelement D wird somit geöffnet und bleibt bis zum Gang G4, wenn dies ein nächster oder endgültiger Zielgang wäre, geöffnet.
• – Letzter endgültiger Zielgang ist in diesem Beispiel G2, dem das Schaltelement D nicht zugeordnet ist.
• – Als nächstes gemeinsames Schaltelement wird das Schaltelement B gewählt, da dieses ausgehend vom Gang G4 den meisten folgenden niedrigeren Gängen nacheinander zugeordnet ist. Das Schaltelement B wird bei Gang G3, dem das Schaltelement D erstmalig nicht mehr zugeordnet ist, geöffnet; Schaltelement D bleibt geöffnet und das Schaltelement C wird geschlossen.

If, during the multiple downshift operation (eg, by a brake pedal being depressed longer), the next or final target gear predicted by the controller changes in such a manner that the (first or previous) common shift element is no longer associated with the changed target gear a new common switching element for the next courses determined and decoupling - preferably when the previous common switching element would not be assigned to the next gear for the first time - opened. This particularly advantageous embodiment of the invention is based on the following embodiment (see also 2 ) - in the form of a multiple-downshift from G8 to G2 - explained in more detail:

• - First, the switching element D is selected as the first common switching element, since this is assigned starting from gear G8 most successive lower gears in succession. The shift element D is thus opened and remains open until the gear G4, if this would be a next or final target gear.
• Last final target gear is in this example G2 to which the shift element D is not assigned.
• - The next common switching element, the switching element B is chosen, since this is assigned starting from the gear G4 most successive lower gears in succession. The switching element B is at gear G3, the switching element D is not assigned for the first time, opened; Switching element D remains open and the switching element C is closed.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102006057666 A1 [0004]

Claims (4)

Method for carrying out a downshifting process of an automatic load-switching step automatic transmission ( 3 ), in which by an electronic control unit ( 6 ) for engaging a gear (G1 to G8) more than one switching element (A, B, C, D, E) between the input shaft and the output shaft of the automatic transmission ( 3 ) are closed at the same time, wherein the same switching elements (A, B, C, D, E) are assigned to multiple gears and wherein in a normal mode, the gear changes are performed in the form of overlapping circuits, characterized in that in a different mode from the normal mode in a multiple -Return operation, in which a switching element (B; D) of the current gear (G5, G4; G8) is also assigned to the respectively next and final target gear (G4 to G2; G8 to G4), by the control unit ( 6 ) First, this common switching element (B; D) is fully opened and simultaneously or immediately thereafter a speed command is started, the speed setting first to hold the engine speed (n_M) of the current gear and then to set the theoretically present in the next target gear engine speed (n_M ), while the next target gear required in each case is inserted as quickly as possible, and after reaching the final target gear associated engine speed (n_M), the common switching element (B) is closed as soon as possible. Method according to Patent Claim 1, characterized in that, during the multiple downshifting operation (G8 to G2), the next or final target gear (G3, G2) predetermined by the control unit changes in such a way that the previous common shift element (D) is changed Target gear (G3, G2) is no longer assigned, a new common switching element (B) for the next courses determined and opened. Method according to one of the preceding claims, characterized in that the special mode is performed only if the engine speed (n_M) would be below or too close to the idling speed (n_LL) by the length of the switching time (ts) in normal mode on reaching the target gear , Device in a motor vehicle with a drive motor ( 2 ), with one with the drive motor ( 2 ) cooperating automatic transmission ( 3 ), which has more than one switching element (A, B, C, D, E) between its input shaft and its output shaft for engaging a gear (G1 to G8), and with at least one electronic control unit ( 6 ), in which a program module for carrying out the method according to one of the preceding claims is contained, wherein the program module has an interface for controlling the engine speed (n_M) of the drive motor ( 2 ) having.

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