[001] METHOD FOR CONTROLLING SHIFTING OF A
STEPPED AUTOMATIC TRANSMISSION
[002]
[003]
[004] The invention concerns a method for controlling gear shifts in an automated
stepped gear transmission of a motor vehicle, in which operating parameters of the motor vehicle are continuously monitored and in each case evaluated for the purpose of initiating and carrying out a shift from a currently engaged gear to a target gear, such that before any shift, in each case, the shift speed for initiating the gear shift and the target gear are determined,
[005]
[006] To initiate and carry out a transmission gear shift, it is first necessary to
determine the speed of the drive engine at which the shift should begin, known as the shift speed, and the target gear into which the shift should be made from the gear currently actually engaged. For this purpose, it is usual for operating parameters of the motor vehicle, such as the current driving speed, the current acceleration or deceleration of the motor vehicle, the current rotation speed of the drive engine (engine speed), the load condition or torque of the drive engine, the accelerator pedai position, the change or rate of change of the accelerator pedal position, the actual on of a kick-down switch; if necessary, also the actuation of a vehicle brake, the current driving resistance, in particular in tns case of commercial vehicles also the loading condition or mass of the motor vehicle and th 3 inclination of the road, eitherto be determined directly by corresponding sensors cr calculated by the evaluation of control magnitudes, in particular of the drive engire, and/or of the measured values of other operating parameters.
[007] In determining the shift speed and the target gear, a distinction is generally
made between a "shift-speed-orientated shift" and a "target-speed-orientated shift".
[008] For a "shift-speed-orientated shift" the shift speed, i.e., the engine speed at
which the gear shift should take place or be initiated, is first determined as a function of relevant operating parameters. Then a gear step appropriate for the

momentary driving situation and, in particular the momentary vehicle acceleration is determined and hence, starting from the gear currently engaged, the target gear to which the transmission is to be shifted is identified.
[009] The advantage of a "shift-speed-orientated shift" consists in the relatively
spontaneous reaction of the automated stepped gear transmission to changing operation conditions and to commands input by the driver. For example, when moving from flat ground onto a rising slope with a corresponding increase of the driving resistance and sometimes a deceleration of the motor vehicle a downshift is initiated relatively quickly. Likewise, when the kick-down switch is actuated, via the accelerator pedal, to initiate the kick-down function, an immediate downshift takes place as expected by the driver, since in such a case the current engine speed is regarded as the shift speed. In motor vehicles for whose stepped gear transmissions more than one shift program is available, for example E n ecological mode and a sporty mode, the shift speed and the target gear are also influenced by the shift program that is active at the time. Thus, when the ecological mode is active, to achieve low fuel consumption the shift speed is generally bwer than in the sporty mode, in the latter of which the achievement of high drive dynamics is paramount.
[010] In contrast, in a "target-speed-orientated shift" the target speed,
i.e., the engine speed that should exist after a shift operation, is determined first. Starting from this, a suitable gear step from the current actually engaged gear, and hence the target gear and the shift speed, are determined as a function of current operating parameters, in particular the acceleration of tne vehicle. The ad vantage of a "target-speed-orientated shift" consists in the possibility of being able to operate the drive engine within an optimum speed range, in particular one that is favorable for consumption, under any operating conditions.
[011] A method for a "target-speed-orientated shift" is described in
DE 196 38 064 C2. In that document, for an upshift to the next-higher gear it is provided that to reach the same target gear, when driving with low load and high acceleration a shift is initiated at a lower shift speed and, when driving with a high load and low acceleration, it is initiated at a higher shift speed.

[012] In both shift types, respective speed limits must be complied with, namely
in a "shift-speed-crientated shift", a target speed limit and in a "target-speed-orientated shift", a shift speed limit, in order to keep the engine speed and therefore the desired operating behavior of the drive engine within a desired range, for example with low fuel consumption and/or a high traction force of the drive engine. In extreme cases, these speed limits can be identical to the engine speed limits, i.e., the acceptable minimum speed and the acceptable maximum speed of the drive engine, however, they are usually inside those engine speed limits.
[013] Since in the known methods for controlling gear shifts of automated stepped
gear transmissions, in each case only one shift type is envisaged. The possibilities for adapting to tne respective existing driving or operating situation are insufficiently utilized. Thus, the purpose of the present invention is ;o indicate a method of the type mentioned at the start, with which gear shifts, in p articular the determination of shift speed and target gear, can be better adapted to the driving or operating situation at the time.
[014]
[015] Thus, in accordance with the characteristics of the principal claim the
invention concerns a method for controlling gear shifts in an automated stepped gear transmission of a motor vehicle, in which operating parameters are continuously detected and, in each case, evaluated for the purpose of initiating and carrying out a shift from a currently engaged gearto a target gear, such that before any shift, in each case, the shift speed for initiating the gear shift ard the target gear are determined.
[016] In addition, in this method the shift types "shift-speed-orientated shift" and
"target-speed-orientated shift" are both available and it is decided immediately before a shift, as a function of at least one of the operating parameters, by which of the two shift types the gear shift is to be carried out.
[017] Thanks to the availability of the two shift types the respective shift can be
adapted better to existing operating conditions, in particular to the arrant driving resistance, the current load condition of the drive engine and the driver's current power demand. Thus, depending on the driving situation and the driver's power

demand, it is possible to achieve optimum driving dynamics or low fuel consumption of the motor vehicle.
[018] Advantageous features and further developments of the method according
to the invention are indicated in Claims 2 to 13.
[019] To determine the current driving situation and an optimum adaptation of the
gear shifts, it is expediently provided that the driving resistance of the motor vehicle is monitored continuously white driving and that, when the driving resistance is low, a gear shift is carried out as a Mtarget-speed-ohentated shift" and, when the driving resistance is high, the shift is carried out as a 'shift-speed-orientated shift", In this way, the circumstance is taken into account that when the driving resistance is high the driving dynamics, i.e., a rapid reaction to changed operating conditions, is paramount. This is fulfilled by "shift-speed-orientated shifts". Thus in such a case, for example when driving from level grcund onto an uphill stretch, a rapid reaction to the increasing driving resistance takes place in the form of a shift-speed-orientated downshift and this avoids an undes;ired slowing down of the motor vehicle.
[020] In contrast, when the driving resistance is Sow, sufficient latitude is available
for following a superimposed driving strategy and this can best be attained by "target-speed-orientated shifts". For example, by controlling the gear shifts appropriately, the crive engine can be kept largely within a speed range in which its specific fuel consumption is low, so enabling the motor vehicle to be operated particularly economically.
[021] Since the driving resistance of a motor vehicle, especially a commercial
vehicle, is decisively influenced by the inclination of the road in the driv ng direction and by the loading condition or mass of the vehicle, it is expediently provided that while driving the road inclination is continuously determined and a gear shift is carried out in the "target-speed-orientated shift" mode when driving on level ground or downhill, and in the "shift-speed-orientated shift" mode when driving uphill.
[022] In addition, it is advantageous for the loading condition or mass of the motor
vehicle to be continuously determined and for a shift to be carried out in the "target-speed-orientated shift" mode under low load or when the mass of the

vehicle is low, and in the "shift-speed-orientated shift" mode under heavy loading or when the vehicle mass is high.
[023] Likewise, the current load situation of the drive engine influences the driving
dynamics and the fuel consumption of the motor vehicle. Accordingly, it is also expediently provided that while driving, the load condition of the drive engine is continuously determined, and that if the drive engine is operating under part load at the time a "target-speed-orientated shift" is carried out, whereat; if the drive engine is operating under full load, a "shift-speed-orientated shift" is carried out.
[024] Finally, the available latitude for transmission control is also influenced by
the driver's power demand at the time. It is therefore advantageously provided that while driving, the driver's power demand is also continuously determined and that when the driver's power demand is low a gear shift is carried out as a "target-speed-orientated shift" and when the driver's power demand is high it is carried out as a 'shift-speed-orientated shift", in this, it can be provided in particular that a downshift initiated by actuating the kick-down switch is carried out as a "shift-speed-orientated shift" so that the downshift takes place spontaneously, as expected by the driver.
[025] Advantageously, in at least one of the shift types and preferably in both shift
types, the shift mode "comply with a gear-step specification" and the; shift mode "fully utilize the available speed range" are provided, such that immed ately before a gear shift it is decided as a function of at least one operating parameter in which shift mode the shift is to be carried out.
[026] in this context, the shift mode "comply with a gear-step specincetio'i" means
that a gear-step specification determined for a given driving situation is complied with so far as possible. For example, in the case of a commercial vehicle equipped with a stepped gear transmission whose gear steps are small, when driving on level ground with low load a gear-step specification G3-G6-G3-G11-G12 with the third gear G3, the sixth gear G6, etc., may be determined since the lower gears G1 and G2 are only needed for starting off and the intermediate gears G4, G5, G7, G9, G10 are only needed when driving uphill and downhill or when driving with a heavy toad.

[027] In this case it is expedient, before carrying out a shift in the "comply with a
gear-step specification" shift mode, to check whether the associated speed limits, i.e., in the case of a "shift-speed-orientated shift", the target-speed limits and in a "target-speed-orientated shift", the shift-speed limits, would be exceeded. If the speed limits would indeed be exceeded, then the gear step envisaged is reduced until the speed limits concerned are complied with. By virtue of the gear step specification, the gear step of the shift can even be smaller thar the largest possible gear step permitted within the speed limits.
[028] In the shift mode "fully utilize the available speed range", in contrast, the
gear shift in question is always carried out with the largest possible gear step permitted within the speed limits.
(029] The shift mode is determined independently of the shift type, preferably as
a function of the load condition and the engine speed of the drive engine. For this, it is expediently provided that while driving, the load condition and the speed of the drive engine are continuously determined, and that if the drive engire is working under full load and at a low engine speed or when the speed of the drive engine is high, a shift is carried out in the "fully utilize the available speed range" shift mode, whereas if the engine speed is intermediate the shift takes place in the "comply with a gesr-step specification" shift mode.
[030] This ensures that unfavorable operating conditions of the drive engine, such
as operating at fuli load with an extremely low engine speed or operating at an extremely high encine speed, are exited by the largest possible speed margin by way of the largest possible gear step in each case, it is also ensured that if the engine speed is intermediate, a driving strategy determined implicitly by the gear step specification, which can be aimed for example at low fuel consumption, is complied with.
[031] In simply automated variable-speed transmissions, a gear shift is
necessarily associated with a traction force interruption during which in the drive train on the drive output side, a speed change occurs which is negati/e when the driving resistance is positive, i.e., such as to slow down the motor vehicle and is positive when the driving resistance is negative, i.e., such as to drive the motor vehicle onward. To a lesser extent, such a gear-shift-related speed change also

takes place in automated change-under-load transmissions, such a-; dual-clutch transmissions and automatic planetary transmissions since, in these stepped gear transmissions, owing to transmission-interval stresses and friction losses during a gear shift, there is some faltering of the torque on the output side :as a rule.
[032] To take this effect into account, when determining the target gear and the
shift speed, it is expediently provided that before a gear shift the effective driving resistance during Ihe shift is determined and the resulting speed change on the drive output side is calculated, and that using this speed change the :arget speed is corrected during a "shift-speed-orientated shift" and the shift speec is corrected during a "target-speed-orientated shift".
[033] Accordingly, for a "shift-speed-orientated shift" the target speed is reduced
when the driving resistance is high when driving uphill, and increased when the driving resistance is low when driving downhill.
[034] In contrast for a "target-speed-orientated shift", the shift speed is
correspondingly increased when the driving resistance is high and reduced when the driving resistance is low.
[035] During this, if the relevant speed limits are exceeded, i.e., in a'shift-speed-
orientated shift", the target-speed limits or in a "target-speed-orientated shift", the shift speed limts, then the gear step envisaged must be reduced by at least one gear, i.e., the shift must be carried out for an upshift to a lower gear and for a downshift to a higher gear than envisaged.
[035]
[037] To clarify the invention the description of a drawing is given below. The
drawing shows:
[038] FIG. 1 is a synopsis to indicate the degrees of freedom of the method
according to the invention;
[039] FIG. 2 is a speed diagram to illustrate shift-relevant speeds, considering the
example of a downshift;
[040] FIG. 3 is a speed diagram to show two shift types, considering :he example
of an upshift, and

[041] FIG. 4 is a speed diagram to illustrate two shift types, considering the
example of a downshift.
[042]
[043] As can be seen in FIG. 1, in the method according to the invention, two
types of gear shifts are available and, in each case, two shift modes, where a corresponding determination of the shift speed, i.e., the engine speed at which the shift is initiated, the target gear to be engaged as a result of the s'lift, and the target speed, i.e., the engine speed reached at the end of the shift, a gear shift can be better adapted to the current driving and operating conditions than with previous shift control methods.
[044] For a "shift-speed-orientated shift", the shift speed n_schalt is determined
first. Starting from the shift speed n_schalt, the gear step and hence the target gear and the target speed n_ziel are then determined. In doing this, the shift speed n_schalt and the target speed n_ziel must lie within a speed range delimited by a shift speed limit n_schalt_grenz and a target speed limit n_ziel_grenz. This speed range is specified by the control program of the stepped gear transmission as the permissible operating range of the drive engine. In extreme cases, it may be the same as the speed range between the minimum acceptaole and the maximum acceptable speed of the drive engine. Usually, however, the speed range is narrower than that and can correspond to the speed range in which the specific fuel consumption of the engine is low or the speed range in which a high drive engine torque is obtained.
[045] In a "shift-speed-orientated shift", the shift speed n_schalt is usually
identical to the shift speed limit n_schalt_grenz, but it can also be different from the latter. Owing to the discrete transmission ratio steps between the gears, in the target gear determined the target speed limit n_ziel_grenz is, as a rule, not reached, but rather the target speed n_ziel is usually above the target speed limit n_ziel_grenz in an upshift and below it in a downshift.
[046] FIG. 2 illustrates a "shift-speed-orientated shift", considering the example
of a downshift. The Figure shows the variation of an engine speed n with a time t from a downshiftfrom the eighth gearG8down to sixth gearG-3. Thegear

shift is initiated when the shift speed n_schait is reached and, in this case, the shift speed n_schalt can correspond to the shift speed limit n_schalt_grerz applicable for this one gear shift or for several similar shifts. Owing to :he discrete transmission ratio change between G8 and G6, the target speed limit n_ztel__grenz is not reached, rather the target speed n_ziel obtainedin the sixth gear G6 is lower than the target speed limit n_ziel...grenz.
[047] In contrast, in a "target-speed-orientated shift", the target spoed n_ziel is
determined first and starting from that, the gear step and hence the target gear and the shift speed n_schalt are determined correspondingly. Once again, the relevant shift speed limit n_schalt_grenz and target speed limit n_ziel_grenz must be complied with, i.e., they must not be exceeded.
[048] In a "target-speed-orientated shift", the target speed n_ziel is usually
identical to the target speed limit n_ziel_grenz, but may also be different from it. Owing to the discrete steps between the gears, starting from the shift speed limit n_schalt_grenz, the target speed n_ziel in the target gear determined is as a rule not reached, rather the shift speed n_schalt must be changed in \he direction toward the target speed limit n_ziel_grenz in order for the target speed n_ziel to be reached at the end of the gear shift.
[049] Sn both shift types, the shift modes "comply with a gear-step specification"
and "fulty utilize the available speed range" are, in each case, additionally available (see also FIG. 1). In the shift mode "comply with a gear-step specification", a gear step specification established for a given driving situation is complied with, insofar as the respective speed limit, i.e., in a "shift-speed-orientated shift', the tsrget speed limit n_ziel_grenz and in a "target-speed-orientated shift", the shift speed limit n_schalt_grenz, is complied with. If the speed limit concerned is exceeded, the gear step envisaged is then reduced in steps until the speed limit is complied with. In contrast, in the shift mode "fully utilize the available speed range", the shift in question is carried out with the largest possible gear step as defined by the speed limits.
[050] Since both the shift type and the shift mode are selected as a function of
current operating parameters before a gear shift is carried out, the shif is optimally adapted to the current driving situation.

[051} Considering the influence of road inclination as an example, this is
illustrated in FIG. 2 for an upshift and in FIG. 4 for a downshift, in each case for a "target-speed-orientated shift" and for a "shift-speed-orientated shift".
[052] In the target-speed-orientated upshift, according to FIG. 3, owing to the
discrete transmission ratio steps available the shift speed n_schalt is lower than the shift speed limit n__schalt_grenz, in order to reach the target speed limit n_ziel_grenz in the target gear without any topographiCEl influence. However, since during the traction-force-free phase of the gear shirt, the motor vehicle slows down when moving uphill and accelerates when moving downhill, and a corresponding speed change of the output shaft of the slepped gear transmission takes place in order to compensate for this, i.e., in order still to reach the target speed limit n_ziel_grenz by way of the same shirt, the shift speed n_schalt is increased when driving uphill and reduced when driv ng downhill. In the extreme case, to do this a previous downshift may be necessary when driving uphill and a previous upshift when driving downhill.
[053] The analogous relationship is illustrated in FIG. 4 for a tsirget-speed-
orientated downshift.
[054] In the shift-speed-orientated upshift according to FIG. 3, cwing to the
discrete transmission ratio steps available, the target speed n_ziei is higher than the target speed limit n_ziel_grenz and for that reason, without any influence of road topography, the target speed limit n_ziel_grenz is not reached. When driving uphill, the target speed n__ziel decreases because of the deceleration of the motor vehicle during the gear shift When driving downhill, the target soeed n_ziei increases because of the acceleration of the motor vehicle during the gear shift. In this case when driving up a steep hill, a previous downshift may be needed in order to avoid falling below the target speed limit n_ziel_grenz in the target gear. Likewise when driving down a steep hill, a previous upshift may be needed in order to prevent the speed in the target gear from increasing too much.
[055] The analogous relationship is shown in FIG. 4 for a shift-speed-orientated
downshift.

CLAIMS
1. A method for controlling gear shifts in an automated stepped gear
transmission of a motor vehicle, in which operating parameters of the notor vehicle
are detected and in each case evaluated for initiating and carrying out a gear shift
from a currently engaged gear to a target gear, such that before a shift in each
case the shift speed n_schalt for initiating the shift and the tarcet gear are
determined, characterized in that the shift types "shift-speed-orientated shift" and
"target-speed-orientated shift" are provided, and immediately before a gear shift
it is decided as a function of at least one of the operating parameters in which of
the said two shift types the shift is to be carried out. ■
2. The method according to claim 1, characterized in that while driving, the
driving resistance of the motor vehicle is continuously determined, and if the
driving resistance is low the gear shift is carried out as a "target-speed-orientated
shift", whereas if the driving resistance is high, the gear shift is carried out as a
"shift-speed-orientated shift".
3. The method according to claims 1 or 2, characterized in that while driving, the road inclination is continuously determined, and when dri /ing on level ground or downhiii a gear shift is carried out as a "target-speed-orientated shift", whereas when driving uphill the shift is carried out as a "shift-speed-orientated shift".
4. The method according to claims 2 or 3, characterized in that while driving, the load condition or mass of the motor vehicle is continuously determined, and when the loading or the vehicle mass is low a gear shift is carried out as a "target-speed-orientated shift", whereas if the loading or the vehicle mass is high the shift is carried out as a "shift-speed-orientated shift".
5. The method according to at least one of claims 1 to 4, characterized in
that while driving, the load condition of the drive engine is continuously determined,
and when the drive engine is operating under part-load at the time a gear shift is
carried out as a "target-speed-orientated shift", whereas if the drive engine is
operating under full load at the time the shift is carried out as a "shift-speed-
orientated shift".

The method according to at least one of claims 1 to 5, cha-acterized in that while driving, the driver's power demand is continuously determined, and when the driver's power demand is low a gear shift is carried out as a "target-speed-orientated shift", wnereas if the driver's power demand is high the shift is carried out as a "shift-speed-orientated shift".
7. The method according to at least one of claims 1 to 6,cha-acterized in that while driving, the actuation or not of a kick-down switch is continuously checked, and a downshift initiated by the actuation of the kick-down switch is carried out as a "shift-speed-orientated shift".
8. The method according to at least one of claims 1 to 7, characterized in that with at least one of the two shift types the shift mode "comply with a gear-step specification" or the shift mode "fully utilize the available speed range" are provided, and directly before a shift it is decided as a function of at least one of the operating parameters in which shift mode the shift is to be carried out.
9. The metnod according to claim 8, characterized in that belore carrying out a gear shift in the shift mode "comply with a gear-step specification" it is checked whether the associated speed limit will be exceeded, and if the speed limit wouid be exceeded the gear step envisaged is reduced in steps until the speed limit is complied with.

10. The method according to claims 8 or 9, characterized in that while driving the load condition and the engine speed of the drive engine are continuously determined, and when the drive engine is operating under full load and the engine speed is low or when the engine speed is high, a ;ear shift :s carried out in the shift mode "fully utilize the available speed range", wiereas if the engine speed is intermediate a gear shift is carried out in the shift mode "comply with a gear-step specification".
11. The method according to at least one of claims 1 to 10, characterized in that before a gear shift the driving resistance existing during the shift is determined and the speed change on the drive output side that resul s therefrom is calculated, and using the speed change on the drive output side the target speed n_ziel is corrected in a "shift-speed-orientated shift" and the shift speed n_schalt is corrected in a "target-speed-orientated shift".

12. The method according to claim 11, characterized in that in a "shift-
speed-orientated shift" the target speed n_scha.lt is reduced when the driving
resistance is high and increased when the driving resistance is low.
13. The method according to claim 11, characterized in that in a "target-
speed-orientated shift" the shift speed n_schalt is increased when the driving
resistance is high and reduced when the driving resistance is low.