Hydraulically-assisted automatic skip shifting method of a multi-path toothed-wheel gear change box

A method for the automatic shifting of a multi-path toothed-wheel gear change box between two gears which are formed in a first gearbox subunit temporarily engages a middle gear formed in a second, parallel gearbox subunit. It is simultaneously ensured, by control of the working pressures for actuating the power-shift clutches connecting the gearbox subunits to the input shaft, that the speed characteristic of the input shaft shifting is essentially steady without remaining at the middle gear speed value.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention generally relates to a hydraulically-assisted 
automatic shifting method and associated apparatus in accordance and, more 
particularly, to a method for the hydraulically-assisted automatic 
shifting of a multi-path toothed-wheel gear change box with a gearbox 
arrangement in which an input shaft can be brought into driving connection 
with an output shaft via at least on of at least two gearbox subunits 
arranged in parallel to one another in a force flux, one power-shift 
clutch is arranged in the force flux between the input shaft and in each 
case one gearbox subunit, at least one of the gearbox subunits has at 
least two gearwheel stages with in each case one loose wheel which can be 
coupled to its shaft by a positively engaging gearwheel clutch, and the 
transmission ratios of the gearwheel stages are configured such that, in 
each case in relation to two gears adjacent in terms of their transmission 
ratio, in one gear one associated gearbox subunit: and, in the adjacent 
gear, another gearbox subunit associated with the latter is connected into 
the driving connection by subjecting in each case one clutch actuator 
actuating the associated power-shift clutch to working pressure. 
In a known shifting method, as shown in VDI Report No. 672, 1988, page 383, 
with a gearbox arrangement having two gearbox subunits, it is regarded as 
disadvantageous that shifts without an interruption to the tractive force 
are only possible between two gears in which the flux of force does not 
take place via one and the same gearbox subunit and a crossover control 
for the power-shift clutches ca consequently be effected. For this reason, 
skipping gears has only been considered to be possible over two gears. 
EP 0 273 735 A2 discloses a method for electronic control of a 
toothed-wheel gear change box which is connected downstream in an engine 
flux of force, via a power-shift clutch and in which an optimum gear is 
selected as a function of shift characteristics which take account of 
driving speed and accelerator-pedal position. When a shift command for an 
upshift via two or more gears is issued, a shift is first effected into 
the next-highest gear for a predetermined period of time, during which the 
upshift of the shift command is suppressed. 
DE 34 06 218 A1 discloses a method for hydraulically assisted automatic 
downshifting from the fourth gear to the second gear of a multi-path 
planetary gear change box with a gearbox arrangement in which, in fourth 
gear, an input shaft can be brought into driving connection with an output 
shaft via a first, simple planetary gearbox subunit by engaging a first 
frictional shifting clutch situated between the input shaft and this 
gearbox subunit in the flux of force. In second gear, it is brought into 
driving connection with the input shaft additionally via a second simple 
planetary gearbox subunit by a direct connection between the input shaft 
and the inner sun gear of the second gearbox subunit and by engaging a 
second frictional shifting clutch connected to the planet carrier of the 
first gearbox subunit and to the outer sun gear of the second gearbox 
unit. In the intermediate third gear, the input shaft and the output shaft 
are coupled to one another by engaging both shifting clutches via the two 
gearbox subunits which, as a result, revolve as a block. During the shift 
from fourth to second, a restriction device comes into effect which 
retards the engagement of the second shifting clutch relative to its 
engagement during the shift from fourth to third. 
An underlying object of the present invention consists essentially in 
providing a shifting method in which a shift is made possible without an 
interruption to the tractive force, between two gears which, in terms of 
their transmission ratio, are nonadjacent and for which one and the same 
gearbox subunit is connected into the driving connection between the input 
shaft and the output shaft. Consequently, in a gearbox arrangement having, 
for example, only two gearbox subunits, only a single gear is skipped 
(shifts via two gears). 
The foregoing object has been explained is achieved in an advantageous 
manner by utilizing a shifting method and associated apparatus in which 
the purpose of changing over between two nonadjacent gears, in each case 
another associated gearwheel stage of the sam gearbox subunit is connected 
into the driving connection, a middle gear which lies between the two 
nonadjacent gears in its transmission ratio and in which a gearwheel stage 
of another gearbox subunit is connected into the driving connection and 
temporarily engaged, and the working pressure in the clutch actuators of 
the power-shift clutches of the two gearbox subunits taking part in the 
changeover is controlled in such that the characteristic of the speed of 
the input shaft between the speed value corresponding to the old gear and 
the speed value corresponding to the new gear is at least approximately 
steady, without remaining at the speed value of the middle gear. 
In the method of the present invention, unpleasant torque fluctuations at 
the output shaft are largely avoided because, on one hand, a direct jump 
of the torque between the torque values associated with the two 
nonadjacent gears is avoided and, on the other hand, the torque in the 
middle gear which is engaged and disengaged transitorily, in each case by 
a crossover control i.e. without interruption to the tractive force is 
adjusted to a torque value by the working pressure for the actuation of 
the power-shift clutch associated with this gear such that a low-jerk 
transmission between this torque value and the two torque values of the 
nonadjacent gears is in each case obtained. 
The method of the present invention can be used both for upshifts and for 
downshifts. For upshifts, the clutch torque in the middle gear in the 
sense according to the invention is held above the value associated with 
this middle gear whereas, for downshifts, the clutch torque is held 
correspondingly below the value associated with the middle gear. 
In the event of a downshift via two gears which are nonadjacent in terms of 
their transmission ratio in the method according to the present invention, 
it is ensured that, in a first shifting phase, the engine can increase its 
revs by virtue of a reduction in the working pressure, i.e. the speed of 
the input shaft rises steadily from the beginning of the shift. 
In the first shifting phase, the clutch actuator for actuating the 
power-shift clutch of the gearbox subunit which is connected into the 
driving connection in the middle gear can be filled or placed under an 
application pressure. 
When the engine speed and thus the speed of the input shaft reaches the 
speed value of the middle gear during the increase in revs, it is possible 
with the present invention for a changeover in the actuation of the 
power-shift clutches to take place. The middle gear is engaged with 
reduced excitation of the power-shift clutch concerned without the steady 
rise in the speed of the input shaft being interrupted, with the result 
that no significant torque jumps at the output of the gearbox occur 
either. 
When the speed of the input shaft has risen almost to the speed value of 
the new gear, the engine can be levelled off, i.e. the increase in the 
revs of the engine reduced. 
When the filling of the clutch actuator for actuating the power-shift 
clutch of the gearbox subunit connected into the driving connection in 
both nonadjacent gears is complete, this being indicated by a pressure 
rise in the clutch actuator, it is possible, according to the present 
invention, for a crossover control to be triggered for the purpose of 
shifting to the new gear without an interruption to the tractive force. 
In the case of shifts of multi-path toothed-wheel gear change boxes having 
loose wheels which can in each case be coupled to their shaft by a 
gearwheel clutch, it is customary, in a gearbox subunit in each case not 
connected into the driving connection between the input shaft and the 
output shaft, to, as it were, preselect the loose wheel of a gearwheel 
stage adjacent to the respectively selected gear as regards the 
transmission ration by engaging its associated gearwheel clutch. 
In the case of a downshift via two nonadjacent gears in the method 
according to the invention, the gearwheel stage of the middle gear is 
engaged. 
With a downshift via two nonadjacent gears in the method according to the 
invention, the gearwheel clutch of the gearwheel stage of the lower of the 
two nonadjacent gears is engaged. 
With an upshift via two gears which are nonadjacent in terms of their 
transmission ratio in the method according to the invention, measures are 
first taken as a preparation for a shift to the middle gear. A subsequent 
engagement of the middle gear without an interruption to the tractive 
force then takes place in accordance with the crossover control. 
When the power-shift clutch of the middle gear is capable of transmitting 
the torque of the input shaft on its own, the other power-shift clutch or 
the associated working pressure of the latter is disconnected completely, 
with the result that the middle gear can be engaged and the torque fed in 
to a level which is sufficiently high above the torque value associated 
with the middle gear for the engine or its speed to be steadily retarded. 
In preparation for an engagement of the higher of the two nonadjacent gears 
in the method according to the present invention, a clutch-control signal 
for filling the power-shift clutch associated with the higher gear or the 
clutch actuator concerned is produced in the third shifting phase. This is 
followed by a shift from the middle to the higher gear without an 
interruption to the tractive force while the characteristic of the engine 
speed continues to fall steadily. 
In a following shifting phase, the engine continues to be steadily retarded 
in its speed. The upshift via two nonadjacent gear is ended when the 
engine speed has fallen to the speed value corresponding to the higher 
gear. 
With an upshift via two nonadjacent gears in the method according to the 
present invention, the gearwheel clutch of the gearwheel stage of the 
middle gear can be actuated o controlled and the gearwheel clutch of the 
gearwheel stage of the higher gear actuated or controlled. 
In the case of an upshift via two nonadjacent gears, the clutch-control 
signal for the beginning of filling of the power-shift clutch or of the 
clutch actuator of the higher gear in the third shifting phase can be 
produced.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring to FIG. 1, an input shaft 5, which can be driven by a motor 
vehicle engine via a hydrodynamic torque converter, is connected, with the 
interposition of, in each case, one power-shift clutch 9 and 10 
respectively, via two gearbox subunits 7, 8 arranged in parallel to one 
another in the flux of force to an output shaft 6 which can be in or be 
brought into driving connection in the customary manner with at least one 
vehicle axle of the motor vehicle. 
One gearbox subunit 7 has four gearwheel stages 11 to 14, by means of which 
the reverse gear R and the three forward gears I, III and V respectively 
can be formed. The two loose wheels 22, 23 of the spatially adjacent 
gearwheel stages 11, 12 can be coupled optionally to their countershaft 17 
by an intermediate gearwheel clutch 19, which is shown in the neutral, 
disengaged position. The two loose wheels 24, 25 of the spatially adjacent 
gearwheel stages 13, 14 can be coupled optionally to the countershaft 17 
by an intermediate gearwheel clutch 20, which is also shown in its 
neutral, disengaged position. 
The other gearbox subunit 8 has a gearwheel stage 15 with a loose wheel 26 
for the formation of the second gear, and a spatially adjacent gearwheel 
stage 16 with a loose wheel 27 for the formation of the fourth gear. The 
two loose wheels 26, 27 can be coupled optionally to their countershaft 18 
by an intermediate gearwheel clutch 21, shown in its neutral, disengaged 
position. 
The gearwheel clutches 19, 20 of one gearbox subunit 7 are engaged when the 
associated power-shift clutch 9 has been disengaged and the force flux has 
been directed via one of the gear wheel stages 15, 16 of gearbox subunit 8 
by engagement of the other power-shift clutch 10. 
The gearwheel clutch 21 of the other gearbox subunit 8 is engaged by 
preselection when the associated power-shift clutch 10 has been disengaged 
and the force flux has been directed via one of the gearwheel stages 11 to 
14 of gearbox subunit 7 by engagement of the other power-shift clutch 9. 
In order to be able to perform a crossover control of the two power-shift 
clutches 9, 10 for the gear change between two gears which are adjacent in 
terms of the transmission ratio without interruption to the tractive force 
the transmission ratios of gearwheel stages 11 to 16 are matched to one 
another in such a way that, for these gear changes, a changeover of the 
force flux from one gearbox subunit to the other also occurs. Crossover 
controls are per se known, as shown, for example, in Forster "Das 
kraftschlussige Schalten von Ubersetzungsstufen von Fahrzeuggetrieben" 
(The frictional shifting of transmission stages of vehicle gearboxes) 
VDI-Zeitung 99 No. 27; 21st September (1957). 
In contrast, the method according to the invention makes possible a 
changeover without interruption to the tractive force between two gears 
which are formed in the same gearbox subunit and, due to the 
above-mentioned configuration of the transmission ratios of the gearwheel 
stages, are not adjacent to one another. The method is described below for 
a downshift, for example from fourth to second gear, with particular 
reference to FIG. 3 and for an upshift, for example from second to fourth 
gear, with particular reference to FIG. 4. All the possible upshifts and 
downshifts via two nonadjacent gears can, of course, also be carried out 
in accordance with the method according to the present invention in the 
illustrated embodiment of a gearbox arrangement. 
First, however, a more detailed explanation of the block diagram in FIG. 2 
will be given insofar as it is necessary of the understanding of the two 
shifts between second and fourth gear. The power-shift clutch 9 for 
connecting the gearbox subunit 7 into the driving connection between the 
input shaft 5 and the output shaft 6 can be engaged by resilient means 
(not shown). Connected to the clutch actuator 28 for the purpose of 
subjecting its axial piston to working pressure is a working-pressure line 
60 which leads to a clutch-shift valve 62 fed by a main pressure line 64 
and controlled via a control-pressure line 65 by an electromagnetic 
proportional valve 67. 
The power-shift clutch 10 for connecting the gearbox subunit 8 into the 
driving connection between the input shaft 5 and the output shaft 6 is 
engaged by a clutch actuator 29 of the axial-piston type and is disengaged 
by resilient means (not shown). Connected to the clutch actuator 29 for 
the purpose of subjecting its axial piston to pressure is a 
working-pressure line 61 which leads to a clutch-shift valve 63 fed by the 
main pressure line 64 and controlled via a control-pressure line 66 by an 
electromagnetic proportional valve 68. 
A conventional gearbox control 86, which operates in a known manner with 
the aid of stored shift characteristics as a function of input signals, in 
particular relating to the driving speed, the engine load, the power 
requirement, the gearbox condition and a selection device, has outputs 87, 
90 which are connected via an output stage 88, 91 respectively to, in each 
case, one of the proportional valves 67, 68 by control lines 89, 92 which 
are supplied with pressure via a secondary pressure line 69. 
The gearwheel clutch 20 of the gearbox subunit 8 can be actuated by a 
shifting actuator 70 of the axial-piston type which is held by resilient 
means in the illustrated central neutral position, in which position loose 
wheels 24, 25 are uncoupled from the countershaft 17. The shifting 
actuator 70 can be shifted into its two end positions via connected 
working-pressure lines 71, 72 which lead to a shift valve 73. The shift 
valve 73, which is fed by a secondary pressure line 74, can be controlled 
via a control-pressure line 75 by an electromagnetic shift-control valve 
76 which is fed by a further secondary pressure line 77 and can be 
controlled by a output 93 of the gearbox control 86 via an output stage 94 
and a connected control line 95. 
The gearwheel clutch 21 of the gearbox subunit 8 can be actuated by a 
shifting actuator 78 of the axial-piston type, which is held by resilient 
means in the illustrated central neutral position. In this neutral 
position, both loose wheels 26 and 27 are uncoupled from the countershaft 
18. The shifting actuator 78 can be shifted into its two end positions via 
connected working-pressure lines 79, 80 which lead to a shift valve 81 
which is fed by the secondary pressure line 74 and are controlled via 
connected control-pressure lines 82, 84 by electromagnetic shift-control 
valves 83 and 85 which are fed by the secondary pressure line 77. The 
shift-control valves 83, 85 are controlled from outputs 96, 99 of the 
gearbox control 86 by connected control lines 98, 101 with output stages 
97 and 100. 
The course of a downshift from fourth gear to second gear in the 
toothed-wheel gear change box of FIG. 1 is shown in five shifting phases 
in FIG. 3. The characteristic of the working pressure p.sub.28 in the 
clutch actuator 28 of power-shift clutch 9 and the characteristic of the 
working pressure p.sub.29 in the clutch actuator 29 of power-shift clutch 
10 are shown plotted against time t in FIG. 3a. The characteristic of the 
clutch torque M.sub.K9 of power-shift clutch 9 and the characteristic of 
the clutch torque M.sub.K10 of power-shift clutch 10 are shown plotted 
against time t in FIG. 3b. The characteristic of the output torque M.sub.6 
of the output shaft 6 is shown plotted against time t in FIG. 3c. Finally, 
FIG. 3d shows the characteristic of the speed n.sub.5 of the input shaft 5 
plotted against time t. 
In the initial condition of the toothed wheel gear change box (i.e. in 
fourth gear), the power-shift clutch 10 is engaged, and the working 
pressure p.sub.29 in the associated clutch actuator 29 is set to an 
engagement pressure value 37 by the proportional valve 68. At this 
engagement pressure 37 the power-shift clutch 10 transmits only the torque 
of the input shaft 5. In the associated gearbox subunit 8, the loose wheel 
27 of the gearwheel stage 16 of the fourth gear is connected by the 
gearwheel clutch 21 to the countershaft 18, with the result that the 
gearbox subunit 8 is connected to the driving connection between the input 
shaft 5 and the output shaft 6. For this purpose, the working-pressure 
line 80 of the shifting actuator 78 is connected by the shift valve 81 to 
the secondary pressure line 74 in order to actuate the gearwheel clutch 21 
into the position in which it couples the loose wheel 27 to the 
countershaft 18. The shift-control valve 85 for the fourth gear, excited 
by the gearbox control 86, controls this shaft valve 81 in the appropriate 
fashion. In the case of the gearbox subunit 7, the power-shift clutch 9 is 
disengaged because the working pressure p.sub.28 in the associated clutch 
actuator 28 is shut off by the clutch control valve 62 at the instigation 
of the proportional valve 67. The electromagnetic shift control valve 
excited by the gearbox control 86 has switched shift valve 73 into the 
position in which the working-pressure line 71 for actuating the shifting 
actuator 70 into the end position for coupling the loose wheel 24 of the 
gearwheel stage 13 of the third gear by way of gearwheel clutch 20 is 
connected to the secondary pressure line 74, with the result that third 
gear is preselected in gearbox subunit 7. 
When a shift signal for shifting down from fourth gear into second gear 
occurs in the gearbox control 86, corresponding signals at outputs 87, 90 
trigger a first shifting phase 36, in which proportional valve 68 causes a 
reduction in the working pressure p.sub.29 of the clutch actuator 29 of 
power-shift clutch 10 to a constant phase pressure value 38 which is 
between the engagement pressure value 37 and a low application value 43 
and permits a steady increase in the revs of the engine, as the steady 
rise 30 in the speed n.sub.5 between the speed value 32 corresponding to 
fourth gear and the speed value 34 corresponding to third gear shows. With 
the beginning of the first shifting phase 36, the proportional valve 67 
continues to cause working pressure p.sub.28 to be fed into the clutch 
actuator 28 of power-shift clutch 9 via clutch control valve 62, this 
working pressure p.sub.28 coming to an application pressure value 39 
during the filling process. 
When the speed n.sub.5 of the input shaft 5 has reached the speed value 34 
corresponding to third gear, a second shifting phase 40, following the 
first phase 36, is triggered, in which the working pressure p.sub.29 of 
the clutch actuator 29 of power-shift clutch 10 is shut off in accordance 
with a ramp function 41 and the working pressure p.sub.28 of the clutch 
actuator 28 of power-shift clutch 9 is correspondingly increased by a 
known type of crossover control. In this way, a temporary shift from 
fourth gear to third gear is initiated without interruption to the 
tractive force, and the pressure level is set only high enough to allow 
the engine to continue the steady increase in revs. 
When the working pressure p.sub.29 has fallen to the application pressure 
value 43, a third shifting phase 42, following the second phase 40, is 
triggered, in which the working pressure p.sub.29 of the clutch actuator 
29 of power-shift clutch 10 is shut off completely, and the working 
pressure p.sub.28 of the clutch actuator 28 of power-shift clutch 9 is 
adjusted to a phase pressure value 44 of the engagement pressure value 
associated with third gear and is only high enough for the characteristic 
30 of the speed n.sub.5 of the input shaft 5 to continue to rise steadily 
without remaining at the speed value of the third gear. In the third 
shifting phase 42, a preselective changeover to the gearwheel stage 15 of 
second gear is performed in the gearbox subunit 8, in particular when the 
working pressure p.sub.29 of the clutch actuator 29 of the associated 
power-shift clutch 10 has been completely shut off. This changeover is 
performed by the gearbox control 86 exciting the shift-control valve 83 of 
the second gear instead of the shift-control valve 85, with the shift 
valve 81 thereby being switched over into the position in which secondary 
pressure line 74 is connected to the working-pressure line 79 of the 
shifting actuator 78, and the gear wheel clutch 21 thereby being actuated 
into the position in which it couples the loose wheel 26 of the gearwheel 
stage 15 of second gear to the countershaft 18. 
When, after a uniformly steady variation, the speed n.sub.5 of the input 
shaft 5 has reached a speed lead value 46, which is lower by a fixed 
differential speed 47 than the speed value 33 corresponding to second 
gear, a fourth shifting phase 45 following the third phase 42 is triggered 
in which proportional valve 67, under appropriate influence from the 
gearbox control 86, causes an increase, via clutch-shift valve 62, in the 
working pressure p.sub.28 in the clutch actuator 28 of power-shift clutch 
9 to a phase pressure value 48 higher than the phase pressure value 44 of 
the previous shifting phase. At the same time, proportional valve 68, 
likewise controlled in appropriate fashion by the gearbox control 86, 
initiates the filling process for the clutch actuator 29 of power-shift 
clutch 10 by causing working pressure p.sub.28 to be fed in via 
clutch-shift valve 63, with the pressure coming in the process to the 
application pressure value 43. 
In order to level off the engine, the increased phase pressure value 48 of 
the working pressure p.sub.28 is matched to the application pressure value 
43 of the working pressure p.sub.29 such that both power-shift clutches 9 
and 10 together transmit the engine torque, i.e. the torque of the input 
shaft 5, and the speed n.sub.5 of the input shaft 5 is held at the speed 
value 33 of the second gear. 
When the filling process in the clutch actuator 29 of power-shift clutch 10 
is complete, this being indicated by a rise in the working pressure 
p.sub.29 beyond the application pressure value 43, a fifth shifting phase 
49 following the fourth phase 45 is working pressures p.sub.28, p.sub.29, 
the power-shift clutch 9 of the third gear is disconnected and the 
power-shift clutch 10 of the second gear is connected fully, i.e. with 
expiration of the fifth shifting phase 49, power-shift clutch 10 is 
transmitting the full torque of the input shaft 5, at which time the 
working pressure p.sub.29 has reattained the corresponding engagement 
pressure value 37. 
The characteristic of the clutch torques M.sub.K9 and M.sub.K10 of the two 
power-shift clutches 9, 10 in FIG. 3b is self-explanatory by virtue of the 
above-explained curves in FIG. 3a for the associated working pressures 
p.sub.28 and p.sub.29. FIG. 3c illustrates the low-jerk characteristic 35 
of the output torque M.sub.6 of the output shaft 6 during the shift from 
fourth to second according to the present invention. 
The method according to the present invention is also explained below, with 
reference to the five shifting phases of FIG. 4, for a second embodiment 
for an upshift via two gears, i.e. from second to fourth gear, in the 
two-path toothed-wheel gear change box of FIG. 1. 
In the initial condition of the toothed-wheel gear change box (that is to 
say, in second gear), the power-shift clutch 9 in the gearbox subunit 7 is 
disengaged, because the working pressure p.sub.28 in the associated clutch 
actuator 28 is completely shut off by the clutch-shift valve 62. The loose 
wheel 24 of the gearwheel stage 13 of the third gear is preselectively 
coupled to its countershaft 17 by gearwheel clutch 20 because the 
shift-control valve 76 of the third gear is excited by the gearbox control 
86. As a result, the shift-control valve 76 has switched the shift valve 
73 into the position in which the secondary pressure line 74 is connected 
to the working-pressure line 71 of shifting actuator 70, via which 
pressurization for actuation of gearwheel clutch 20 into the position in 
which it couples loose wheel 24 to countershaft 17 occurs. 
When a shift signal for an upshift from second gear to fourth gear occurs 
in the gearbox control 86, then a first shifting phase 51 is triggered, 
via corresponding signals at the outputs 87 and 90, in which the working 
pressure p.sub.29 in the clutch actuator 29 of power-shift clutch 10 is 
adjusted at the instigation of proportional valve 68 to an engagement 
pressure value 52, at which power-shift clutch 10 still transmits the full 
torque of the input shaft while proportional valve 67 initiates the 
filling process in the case of the clutch actuator 28 of power-shift 
clutch 9 by feeding in working pressure p.sub.28, the latter coming in the 
course of the filling process to an application pressure value 39. During 
this process, the speed n.sub.5 of the input shaft 5 does not yet change 
i.e. remains constant. 
When the filling process in the clutch actuator 28 of power-shift clutch 9 
is complete, this being indicated by a rise in the working pressure 
p.sub.28 beyond the application pressure value 39, a second shifting phase 
53 following the first phase 51 is triggered. In the second phase 53, 
using the customary crossover control for the relevant working pressures 
p.sub.28, p.sub.29, the power-shift clutch 9 is engaged and the 
power-shift clutch 10 is disengaged. This shifting phase thus proceeds 
without interruption to the tractive force and remains at a constant speed 
(i.e. speed value 33 of the second gear) of the input shaft 5. 
When the working pressure p.sub.29 in the clutch actuator 29 of the 
power-shift clutch 10 has fallen to the application pressure value 43, to 
which the working pressure p.sub.29 comes during the filling of the clutch 
actuator 29 and at which the working pressure p.sub.28 of the clutch 
actuator 28 of power-shift clutch 9 has risen to the second engagement 
pressure value 50 of the third gear, the power-shift clutch 9 is then 
capable of transmitting the full torque of the input shaft 5 on its own. A 
third shifting phase 54 following the second phase 53 is then triggered in 
which, although third gear is selected, the working pressure p.sub.28 of 
the clutch actuator 28 of the power-shift clutch 9 transmitting the power 
during this process is adjusted to a phase pressure value 55 which is 
higher than the second engagement pressure value 50, with the result that 
the engine is retarded to such an extent that, starting from the speed 
value 33 at the end of the second shifting phase 53, its speed and thus 
the speed n.sub.5 of the input shaft 5 takes a steadily falling or 
declining course 31 without remaining at the speed value of the third 
gear. 
In the third shifting phase 54, in particular when the working pressure 
p.sub.29 of the clutch actuator 29 of power-shift clutch 10 is completely 
shut off and gearbox subunit 8 is thus completely without driving torque, 
a changeover from the gearwheel stage 15 of the second gear to the 
gearwheel stage 16 of the fourth gear is performed in the gearbox subunit 
8 by the gearwheel clutch 21. This changeover is effected by subjecting 
the shifting actuator 78 to pressure via the working-pressure line 80. The 
shift-control valve 85 of the fourth gear is now excited by the gearbox 
control 8 instead of the shift-control valve 83 of the second gear. When, 
under these circumstances, the gearwheel clutch 21 reaches the position in 
which it couples the loose wheel 27 to the countershaft 18, a clutch 
control signal is produced, due to which the proportional valve 68 causes 
pressurization with working pressure p.sub.29, via the clutch-shift valve 
63, and a pressure rise to at least the application pressure value 43 in 
the clutch actuator 29 of power-shift clutch 10. 
When the filling process in the clutch actuator 29 is complete in the third 
shifting phase 54, this being indicated by a rise in the working pressure 
p.sub.29 beyond the application pressure value 43, a fourth shifting phase 
56 following the third shifting phase 54 is triggered. In this fourth 
phase 56, using the customary crossover control for the relevant working 
pressures p.sub.28, p.sub.29, the power-shift clutch 9 of the third gear 
is disengaged and the power-shift clutch 10 of the fourth gear is engaged. 
This shifting phase also consequently proceeds without interruption to the 
tractive force, but with the required pressure level being fed in, with a 
characteristic 31 of the speed n.sub.5 of the input shaft 5 which 
continues to fall steadily. 
In order to continue to retard the engine steadily to the speed value 32 of 
the fourth gear, a fifth shifting phase 57 following the fourth shifting 
phase 56 is triggered when the working pressure p.sub.28 in the clutch 
actuator 28 of power-shift clutch 9 has fallen to the application pressure 
value 39, the working pressure p.sub.29 already having been adjusted 
upwards beyond the engagement pressure value 52 for the reasons mentioned. 
In this phase, the working pressure p.sub.29 in the clutch actuator 29 of 
power-shift clutch 10 is adjusted to a phase pressure value 58 which is 
above the engagement pressure value 52. 
Whereas the upshift is now complete in the fifth shifting phase 57 to the 
extent that the changeover of power transmission from the power-shift 
clutch 9 of the third gear to the power-shift clutch 10 of the fourth gear 
has been completed, the engine continues to be steadily retarded by the 
increased pressure level. 
When the speed n.sub.5 of the input shaft 5 has fallen to the speed value 
32 corresponding to the fourth gear, however, the proportional valve 68 is 
caused by the gearbox control 86 to reduce the working pressure p.sub.29 
in the clutch actuator 29 of the power-shift clutch 10 of the fourth gear, 
to, for example, the engagement pressure value 52, for example, with the 
result that the speed n.sub.5 is held at the speed value 32 of the fourth 
gear. 
Due to the explanation of the pressure characteristics of the associated 
working pressures p.sub.28, p.sub.29 in FIG. 4a, FIG. 4b is 
self-explanatory as regards the respective characteristic of the clutch 
torque M.sub.K9 of power-shift clutch 9 and of the clutch torque M.sub.K10 
of power-shift clutch 10. Likewise, FIG. 4c illustrates in a 
self-explanatory manner the low-jerk characteristic 59 of the output 
torque M.sub.6 of the output shaft 6 during the upshift according to the 
present invention via two gears. The said characteristic deviates only to 
a small extent from a jerk-free characteristic. 
Although the invention has been described and illustrated in detail, it is 
to be clearly understood that the same is by way of illustration and 
example, and is not to be taken by way of limitation. The spirit and scope 
of the present invention are to be limited only by the terms of the 
appended claims.