Lock-up control device

A lock-up control device controls an engaging force of a lock-up clutch, which shares engine output with a torque converter to transmit it toward an input shaft of a transmission of a car. First, target driving force is produced based on accelerator pedal opening and car velocity. Then, required torque is produced based on a gear ratio and the target driving force. Target engine speed is produced based on the required torque, wherein the target engine speed is set to avoid occurrence of abnormal sounds and abnormal vibrations. Thus, the lock-up clutch is controlled in such a way that real engine speed does not become less than the target engine speed in case of a gear change corresponding to a shift-up operation, for example. Basically, the lock-up clutch is controlled to have engaging force, which is made as maximal as possible to improve fuel efficiency. In other words, the lock-up clutch is controlled to be as tightly as possible. Or, the lock-up clutch which is initially set at a tight state is turned off just after the gear change start timing if it is predicted that the real engine speed after the gear change will become lower than the target engine speed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to lock-up control devices that control the engaging 
force of lock-up clutches, which share engine outputs with torque 
converters to transmit engine output toward input shafts of transmissions 
of cars. This application is based on Patent Application No. Hei 9-252534 
and Patent Application No. 9-257224 both filed in Japan, the contents of 
which are incorporated herein by reference. 
2. Description of the Related Art 
Japanese Patent Application, Publication No. Hei 7-332479 discloses an 
example of a lock-up control device. This lock-up control device has a map 
of target slip ratios, which are considered effective to avoid occurrence 
of abnormal sounds such as indistinct sounds and abnormal vibrations such 
as surging. Herein, the target slip ratios are created in advance by 
experiments regarding real car travel profiles, wherein they are produced 
in connection with car speeds and accelerator pedal openings. Thus, the 
lock-up control device controls the lock-up clutch to provide the target 
slip, which is read from the map in connection with the car speed and 
accelerator pedal opening. 
As described above, the map for controlling the lock-up clutch is created 
based on experimental data. So, considerable amounts of labor and cost are 
required to create such a map. 
Even in the same type of the car, different maps are required in response 
to changes of gear ratios. So, every time the gear ratio is changed, it is 
necessary to provide a specific map whose content is created through 
experiments. As a result, enormous amounts of labor and cost are required 
to create multiple maps with regard to the same type of the car. 
At a shift-up event, the aforementioned lock-up control device 
unconditionally turns off the lock-up clutch so as to set the engaging 
force at zero, so that only the torque converter works to transmit the 
engine output toward the input shaft. 
In consideration of the improvement of fuel efficiency, it is preferable 
that the lock-up clutch is set at a "tight" side, in other words, the 
lock-up clutch should be set as tightly as possible. 
For this reason, even if the lock-up clutch is set at the tight side before 
a gear change event, a gear change is performed while the lock-up clutch 
is maintained at the tight side. 
However, in the case of the gearshift which is performed while the lock-up 
clutch is maintained at the tight side, a shift-up operation reduces a 
number of revolutions of the input shaft of the transmission, so engine 
speed is reduced as well. In such a case, it is predicted that the engine 
speed is reduced to a critical one that will easily induce occurrence of 
abnormal sounds such as indistinct sounds and abnormal vibrations such as 
surging. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a lock-up control device that 
is capable of remarkably reducing amounts of labor and cost, which are 
required to make the setting to avoid occurrence of abnormal sounds such 
as indistinct sounds and abnormal vibrations such as surging, regardless 
of changes of gear ratios. 
It is another object of the invention to provide a lock-up control device 
that is capable of avoiding occurrence of abnormal sounds such as 
indistinct sounds and abnormal vibrations such as surging at shift-up 
operations where the lock-up clutch is set as tightly as possible to 
improve fuel efficiency. 
A lock-up control device of the present invention is provided to control 
the engaging force of a lock-up clutch, which shares engine output with a 
torque converter to transmit engine output toward an input shaft of a 
transmission of a car. Now, target driving force is produced based on 
accelerator pedal opening and car velocity. Then, required torque is 
produced based on a gear ratio and the target driving force. Target engine 
speed is produced based on the required torque, wherein the target engine 
speed is set to avoid occurrence of abnormal sounds and abnormal 
vibrations. Thus, the lock-up clutch is controlled in such a way that real 
engine speed does not become less than the target engine speed in case of 
a gear change corresponding to a shift-up operation, for example. 
Basically, the lock-up clutch is controlled to have an engaging force, 
which is made as maximum as possible to improve fuel efficiency. 
In another aspect of the invention, the lock-up clutch is controlled based 
on comparison between the target engine speed and a predicted input shaft 
speed. Herein, the input shaft speed after the gear change is predicted at 
the gear change start timing. If the predicted input shaft speed is 
greater than the target engine speed, the lock-up clutch is controlled as 
tightly as possible during the gear change. If the predicted input shaft 
speed is smaller than the target engine speed, the lock-up clutch which is 
initially set at a tight state is turned off just after the gear change 
start timing. 
Thus, it is possible to avoid occurrence of the abnormal sounds such as the 
indistinct sounds and the abnormal vibrations such as the surging while it 
is possible to improve the fuel efficiency.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
This invention will be described in further detail by way of examples with 
reference to the accompanying drawings. 
Before specifically describing the lock-up control devices of this 
invention, a description will be given with respect to mechanical 
construction regarding the torque converter, transmission and lock-up 
clutch with reference to FIG. 1. 
In FIG. 1, a cover 11 is connected to a crank shaft, which corresponds to 
an output shaft of an engine (not shown). A pump impeller 12 is fixed to 
the cover 11 and is rotated by a driving force of the engine together with 
the cover 11. A turbine runner 13 is arranged at an opposite side of the 
pump impeller 12. An input shaft 14 of a transmission (not shown) is fixed 
to the turbine runner 13. A stator 15 is arranged at interior portions of 
the pump impeller 12 and turbine runner 13. Incidentally, the pump 
impeller 12, turbine runner 13 and stator 15 are assembled together to 
construct a torque converter 16. 
A lock-up clutch 18 shares engine output with the torque converter 16 to 
transmit engine output toward the input shaft 14 of the transmission. The 
lock-up clutch 18 is arranged between the cover 11 and the turbine runner 
13, while it is also fixed to the input shaft 14 of the transmission. In 
response to a hydraulic pressure difference between the cover 11 and the 
turbine runner 13, the lock-up clutch 18 comes in contact with or leaves 
from the cover 11. 
In a fixed state where the lock-up clutch 18 is placed in contact with the 
cover 11, the lock-up clutch 18 is capable of directly transmitting 
driving force, input thereto from the engine, to the input shaft 14 of the 
transmission without intervening with the torque converter 16. In a 
separated state where the lock-up clutch 18 completely separates from the 
cover 11, the driving force input from the engine is fully transmitted to 
the pump impeller 12. In addition, fluid movement due to rotation of the 
pump impeller 12 makes the turbine runner 13 to rotate. Thus, the driving 
force is transmitted to the input shaft 14 of the transmission (by means 
of the torque converter 16). 
As the aforementioned hydraulic pressure difference is controlled, a 
contact state established between the lock-up clutch 18 and the cover 11 
(in other words, engaging force of the lock-up clutch 18) is controlled. 
Thus, it is possible to control distribution between a first amount of 
transmitted force that the driving force input from the engine is directly 
transmitted to the input shaft 14 of the transmission via the lock-up 
clutch 18 and a second amount of transmitted force that the driving force 
is transmitted to the input shaft 14 via the torque converter 16. 
[Embodiment 1] 
Now, a description will be given with respect to a lock-up control device 
20 according to a first embodiment of the invention with reference to FIG. 
2. The lock-up control device 20 controls duty solenoid (not shown) to 
control the aforementioned hydraulic pressure difference, so that engaging 
force established between the lock-up clutch 18 and the cover 11 is 
controlled. As shown in FIG. 2, the lock-up control device 20 is 
configured using a target driving force calculation unit 21, a required 
engine torque calculation unit 22, a target engine speed calculation unit 
23 and a control value calculation unit 24. 
The target driving force calculation unit 21 produces target driving force 
of a car based on multiple parameters for estimating a driving state such 
as accelerator pedal opening AP and car velocity V. Based on detected 
values of the accelerator pedal opening AP and car velocity V, the target 
driving force calculation unit 21 calculates target driving force of the 
car suited to driver's intention to accelerate the car in accordance with 
a characteristic map, which is determined in advance as shown in FIG. 3. 
Thus, the target driving force calculation unit 21 outputs a signal 
representing the target driving force. In a graph of FIG. 3, a horizontal 
axis represents the car velocity V, while a vertical axis represents the 
target driving force. Herein, each of curves is drawn in response to each 
of present accelerator pedal openings. Incidentally, the accelerator pedal 
opening becomes large with respect to the curve which is positioned on the 
upper right portion of the graph. So, the upper-rightmost curve is drawn 
in response to a full opening state, where accelerator pedal opening AP is 
represented by "WOT" (representing "Wide Open Throttle"). 
The required engine torque calculation unit 22 produces required engine 
torque (hereinafter, simply referred to as "required torque") Tin, which 
is required to obtain the target driving force calculated by the target 
driving force calculation unit 21. Herein, the required torque Tin is 
calculated from a gear ratio corresponding to a shift position. Thus, the 
required engine torque calculation unit 22 outputs a signal representing 
the required torque Tin. 
Based on the required torque Tin produced by the required engine torque 
calculation unit 22, the target engine speed calculation unit 23 produces 
a target engine speed NA, which allows capability of outputting the 
required torque Tin and which also meets a prescribed condition. Thus, the 
target engine speed calculation unit 23 produces the target engine speed 
NA, by which it is possible to avoid occurrence of abnormal sounds such as 
indistinct sounds and abnormal vibrations such as surging. This engine 
speed NA is read from a table, which is provided in connection with the 
required torque Tin. FIG. 4 shows an example of the content of the table, 
which is set in advance based on experimental data. That is, FIG. 4 shows 
a characteristic curve, which is produced through experiments and is 
established between the required torque Tin and the target engine speed 
NA. The characteristic of FIG. 4 represents variations of the target 
engine speed NA, by which it is possible to avoid occurrence of the 
abnormal sounds such as the indistinct sounds and abnormal vibrations such 
as the surging. In general, the aforementioned abnormal sounds and 
abnormal vibrations occur if the engine speed is relatively low, while 
they are unlikely to occur if the engine speed is relatively high. For 
this reason, the target engine speed NA is set at minimum engine speed 
that is capable of suppressing the abnormal sounds and abnormal vibrations 
within allowable levels. In other words, if the actual engine speed is 
greater than the target engine speed NA, it is possible to suppress the 
abnormal sounds and abnormal vibrations within the allowable levels, that 
is, it is possible to substantially avoid occurrence of the abnormal 
sounds and abnormal vibrations. 
Based on the target engine speed NA produced by the target engine speed 
calculation unit 23, the control value calculation unit 24 produces a 
control value for engaging force of the lock-up clutch 18. Herein, the 
control value calculation unit 24 determines the control value in the 
following manner. 
(i) First case where the target engine speed NA is greater than a number of 
revolutions "Nin" of the input shaft 14 of the transmission. 
In this case, when the lock-up clutch 18 works to directly connect the 
input shaft 14 to the engine, real engine speed is reduced down to the 
number of revolutions Nin of the input shaft 14, which is determined by 
the "present" car velocity. At this time, the real engine speed should be 
smaller than the target engine speed NA, which in turn causes occurrence 
of the aforementioned abnormal sounds and abnormal vibrations. In 
consideration of such a phenomenon, the control value calculation unit 24 
determines the control value to let the lock-up clutch 18 slip while 
retaining the engaging force at an optimum state, which will be described 
later. 
(ii) Second case where the target engine speed NA is smaller than the 
number of revolutions Nin of the input shaft 14 of the transmission. 
In this case, when the lock-up clutch 18 works to directly connect the 
input shaft 14 to the engine, real engine speed becomes identical to the 
number of revolutions Nin, which is determined by the "present" car 
velocity. At this time, however, there is no possibility that the real 
engine speed becomes smaller than the target engine speed NA. For this 
reason, the aforementioned abnormal sounds and abnormal vibrations do not 
occur. So, to improve the fuel efficiency, the control value calculation 
unit 24 determines the control value that makes the engaging force maximal 
to establish direct connection of the lock-up clutch 18. 
Based on the control value that is determined by the control value 
calculation unit 24, the lock-up control device of the present embodiment 
electrically controls the duty solenoid (not shown), which is used to 
control the lock-up clutch. Thus, it is possible to control the engaging 
force of the lock-up clutch 18. 
The foregoing required torque Tin produced by the required engine torque 
calculation unit 22 and the foregoing engaging force of the lock-up clutch 
18 produced by the control value calculation unit 24 are supplied to an 
engine torque calculation unit 26. 
Based on the required torque Tin and engaging force, the engine torque 
calculation unit 26 produces required throttle opening TH, by which a 
throttle is electrically controlled. 
Next, operation of the lock-up control device 20 will be described with 
reference to a flowchart of FIG. 5. As described before, the target 
driving force calculation unit 21 produces target driving force based on 
accelerator pedal opening AP and car velocity V. In step S1, the required 
engine torque calculation unit 22 produces required torque Tin, which is 
required to obtain the target driving force. In addition, the lock-up 
control device 20 detects a number of revolutions "Nin" of the input shaft 
14 of the transmission, which will be referred to as input shaft speed 
Nin. 
Then, the lock-up control device 20 transfers control to step S2, wherein 
based on the required torque Tin produced by the required engine torque 
calculation unit 22, the target engine speed calculation unit 23 produces 
a target engine speed NA in accordance with the foregoing table, the 
content of which is shown in FIG. 4. 
In step S3, the control value calculation unit 24 makes a decision as to 
whether the target engine speed NA produced by the target engine speed 
calculation unit 23 is greater than the number of revolutions Nin of the 
input shaft 14 of the transmission or not. In the case where the target 
engine speed NA is not greater than the number of revolutions Nin of the 
input shaft 14 of the transmission, there is no possibility that the 
aforementioned abnormal sounds and abnormal vibrations occur because real 
engine speed would not be smaller than the target engine speed NA even if 
the lock-up clutch 18 works to directly connect the input shaft 14 to the 
engine. In this case, the control device 20 transfers control to step S4. 
Herein, in order to improve the fuel efficiency, the control value 
calculation unit 24 determines a control value to be maximal to establish 
the direct connection of the lock-up clutch 18. 
In the case where the step S3 makes a decision that the target engine speed 
NA is greater than the number of revolutions Nin of the input shaft 14 of 
the transmission, the control device 20 transfers control to step S5. 
Herein, the control value calculation unit 24 performs a calculation of 
"(number of revolutions Nin)/(target engine speed NA)" to produce a value 
ET for a target slip ratio, which places the real engine speed within a 
specific range where the real engine speed would not be smaller than the 
target engine speed NA. 
In step S6, the control device 20 produces tor-con absorption torque Tp, 
which is absorbed by the torque converter 16, in accordance with a formula 
as follows: 
EQU T.sub.p =.tau.(ET)*(NA/1000).sup.2 
Herein, .tau. represents torque absorption coefficient of the torque 
converter 16, so .tau.(ET) is produced in consideration of a slip ratio e 
(=Nin/Ne, see FIG. 6) and a table which is prepared in advance with 
respect to .tau.. 
In step S7, the control device 20 produces transmission torque TLC in 
accordance with a formula as follows: 
EQU TLC=Tin-Tp 
That is, the transmission torque TLC of the lock-up clutch 18 is calculated 
by subtracting the torque which is transmitted by the torque converter 16 
from the required torque Tin. 
In step S8, the control value calculation unit 24 determines a control 
value to provide the lock-up clutch 18 with engaging force corresponding 
to the transmission torque TLC. 
By controlling the aforementioned control value, it is possible to obtain 
the maximum engaging force within a certain range of amounts of engaging 
force that the real engine speed would not be smaller than the target 
engine speed NA. 
Using the aforementioned control value determined by the control value 
calculation unit 24, the lock-up control device 20 electrically controls 
the duty solenoid (not shown) for controlling the lock-up clutch 18. Thus, 
the control device 20 controls the engaging force of the lock-up clutch 
18. 
Operations of the lock-up control device 20 can be summarized as follows: 
When the required engine torque calculation unit 22 produces the required 
engine torque Tin which is required to obtain the target driving force, 
the target engine speed calculation unit 23 performs the foregoing 
calculation based on the required engine torque Tin to produce the target 
engine speed NA, which is effective to avoid occurrence of the abnormal 
sounds such as indistinct sounds and the abnormal vibrations such as 
surging. Then, the control value calculation unit 24 produces the control 
value for the engaging force of the lock-up clutch 18 to make the real 
engine speed to be greater than the target engine speed NA. Using the 
control value, the control device 20 controls the lock-up clutch 18. 
Therefore, it is possible to normally provide the "effective" engine speed 
against the occurrence of the abnormal sounds such as the indistinct 
sounds and the abnormal vibrations such as the surging. In other words, 
the engine controls the lock-up clutch 18 to cope with the occurrence of 
the abnormal sounds such as the indistinct sounds and the abnormal 
vibrations such as the surging. For this reason, it is unnecessary to cope 
with changes of the gear ratios by using the control characteristic of the 
lock-up clutch 18. 
In addition, the present embodiment is basically designed such that the 
engaging force of the lock-up clutch 18 is made maximal to improve fuel 
efficiency. Further, when the abnormal sounds such as the indistinct 
sounds and the abnormal vibrations such as the surging occur due to the 
"maximum" setting of the engaging force of the lock-up clutch 18, the 
present embodiment allows the lock-up clutch 18 slip to control 
revolutions of the engine such that the abnormal sounds and abnormal 
vibrations can be limited within allowable levels. For this reason, the 
present embodiment does not require the map for controlling the lock-up 
clutch 18 based on the car velocity and accelerator pedal opening. Thus, 
it is possible to remarkably reduce amounts of labor and cost required for 
the setting to avoid occurrence of the abnormal sounds such as the 
indistinct sounds and the abnormal vibrations such as the surging. 
[Embodiment 2] 
Next, a description will be given with respect to a lock-up control device 
in accordance with a second embodiment of the invention with reference to 
FIG. 7. In FIG. 7, parts equivalent to those of FIG. 2 will be designated 
by the same reference symbols; hence, the description thereof will be 
omitted. 
As compared with the first embodiment of FIG. 2, the second embodiment of 
FIG. 7 is characterized by providing an input shaft speed prediction unit 
25 and a control unit 27, wherein "input shaft speed" is a number of 
revolutions of the input shaft 14 of the transmission. 
The input shaft speed prediction unit 25 predicts a number of revolutions 
NM of the input shaft 14 of the transmission after a shift-up operation of 
gears, in other words, the input shaft speed prediction unit 25 predicts 
an input shift speed NM after a gear change that is made between third 
gear position and fourth gear position, for example. Herein, the input 
shaft speed prediction unit 25 performs prediction at the start timing of 
the gear change. Based on the input shift speed at the start timing of the 
gear change as well as the gear ratio, the input shaft speed prediction 
unit 25 calculates a changed input shift speed NM as a prediction value. 
In the case where a certain gear change condition that allows a gear change 
is established while it is detected that the gear change corresponds to 
the shift-up operation of gears, the control unit 27 performs operations 
as follows: 
At the start timing of the gear change, the input shaft speed prediction 
unit 25 produces a predicted input shaft speed NM after the gear change. 
On the other hand, the target driving force calculation unit 21 produces 
target driving force based on accelerator pedal opening AP and car 
velocity V which are detected at the start timing of the gear change. 
Based on the target driving force, the required engine torque calculation 
unit 22 performs a calculation using the gear ratio, corresponding to the 
changed gear position, to produce required torque Tin. So, based on the 
required torque Tin, the target engine speed calculation unit 23 produces 
target engine speed NES, by which it is possible to avoid occurrence of 
abnormal sounds and abnormal vibrations. Thus, the control unit 27 
performs comparison between the predicted input shaft speed NM and the 
target engine speed NES. 
If the predicted input shaft speed NM is less than the target engine speed 
NES, the control unit 27 turns off the lock-up clutch 18 during the gear 
change. In addition, the control unit 27 controls the duty solenoid (not 
shown) in such a way that the OFF state of the lock-up clutch 18 is 
maintained until completion of the gear change. 
If the predicted input shaft speed NM is greater than the target engine 
speed NES, the control unit 27 controls the duty solenoid in such a way 
that engaging force of the lock-up clutch 18 that is established before 
the gear change is maintained after completion of the gear change. 
After the completion of the gear change, the control unit 27 controls the 
lock-up clutch 18 in accordance with another control routine (which is not 
specifically described herein) until another gear change condition that 
allows a next gear change is established. 
The engine torque calculation unit 26 for controlling the engine is 
supplied with the required torque Tin produced by the required engine 
torque calculation unit 22 as well as the engaging force of the lock-up 
clutch 18 produced by the control unit 27. 
Based on the required torque Tin and the engaging force of the lock-up 
clutch 18, the engine torque calculation unit 26 produces required 
throttle opening TH, by which the throttle is electrically controlled. 
Next, real operations (or effects) of the aforementioned lock-up control 
device 20 of FIG. 7 will be described in a concrete manner by taking 
examples of FIG. 7 and FIG. 8. 
(i) First example shown in FIG. 8 where the engine speed which is initially 
high is reduced during a gear change corresponding to a shift-up 
operation. 
FIG. 8 shows a transition of the engine speed, wherein the lock-up clutch 
18 which is initially set at a tight state (or ON state) prior to the gear 
change is controlled to cope with the shift-up operation. At time t.sub.0, 
a gear change condition is established while a shift-up command signal is 
issued. At time t.sub.1 when the gear change is initiated, the input shaft 
speed prediction unit 25 produces a predicted input shaft speed NM that 
the input shaft 14 is predicted to have at time t.sub.2 which is after the 
gear change. Based on accelerator pedal opening AP and car velocity 
detected at the time t.sub.1 to start the gear change, the target driving 
force calculation unit 21, the required engine torque calculation unit 22 
and the target engine speed calculation unit 23 cooperate together to 
produce target engine speed NES, by which it is possible to avoid 
occurrence of abnormal sounds and abnormal vibrations. If the predicted 
input shaft speed NM is greater than the target engine speed NES, the 
control unit 27 controls the lock-up clutch 18 in such a way that the 
lock-up clutch 18 which is initially set at the tight state prior to the 
gear change continues the tight state during the gear change. In response 
to the input shaft speed NM, the engine speed NE is reduced during the 
gear change. However, even if the lock-up clutch 18 is retained in the 
tight state during the gear change, there is no possibility that the 
engine speed NE at the time t.sub.2 when the gear change is ended would 
not be smaller than the target engine speed NES. Therefore, it is possible 
to avoid occurrence of the abnormal sounds and abnormal vibrations. 
(ii) Second example shown in FIG. 9 where the engine speed which is 
initially low is reduced during a gear change corresponding to a shift-up 
operation. 
FIG. 9 shows a transition of the engine speed, wherein the lock-up clutch 
18 which is initially set at a tight state (or ON state) is controlled to 
cope with the shift-up operation. At time t.sub.0, a gear change condition 
is established while a shift-up command signal is issued. At time t.sub.1 
when the gear change is initiated, the input shaft speed prediction unit 
25 produces predicted input shaft speed NM that the input shaft 14 is 
predicted to have at time t.sub.2 which is after the gear change. Based on 
accelerator pedal opening AP and car velocity V detected at the time 
t.sub.1 to start the gear change, the target driving force calculation 
unit 21, the required engine torque calculation unit 22 and the target 
engine speed calculation unit 23 cooperate together to produce target 
engine speed NES, by which it is possible to avoid occurrence of abnormal 
sounds and abnormal vibrations. If the predicted input shaft speed NM is 
smaller than the target engine speed NES, the control unit 27 controls the 
lock-up clutch 18, which is set at the tight state prior to the gear 
change, to be in an OFF state (where engaging force is zero) at prescribed 
time t.sub.3 which comes just after the time t.sub.1 to start the gear 
change. If the lock-up clutch 18 is retained in the tight state during the 
gear change, the engine speed NE would be smaller than the target engine 
speed NES, which is shown by a dotted line in FIG. 9. In contrast, the 
present embodiment controls the lock-up clutch 18 to turn OFF, so that as 
shown by a solid line in FIG. 9, it is possible to secure relatively high 
engine speed, which is not reduced so much as compared with the input 
shaft speed NM. Therefore, it is possible to avoid an event that the 
engine speed NE becomes smaller than the target engine speed NES at the 
time t.sub.2 when the gear change is ended. Thus, it is possible to avoid 
occurrence of the abnormal sounds and abnormal vibrations. 
Moreover, the input shaft speed prediction unit 25 predicts the "future" 
input shaft speed NM at the gear change start timing for the shift-up 
operation. At the gear change start timing, the target driving force 
calculation unit 21, the required engine torque calculation unit 22 and 
the target engine speed calculation unit 23 cooperate together to produce 
the "future" target engine speed NES after the gear change. Then, the 
present embodiment compares them to turn OFF the lock-up clutch 18 during 
the gear change. Therefore, the driver does not have a feeling of 
wrongness due to the aforementioned operation of the lock-up clutch 18 in 
the shift-up operation. 
As described heretofore, the present embodiment controls the lock-up clutch 
18 as tightly as possible in the shift-up operation to improve the fuel 
efficiency. In addition, the present embodiment avoids occurrence of 
abnormal sounds like indistinct sounds and abnormal vibrations like 
surging after the shift-up operation. 
The aforementioned description is made by taking examples that the lock-up 
clutch 18 is initially set at the tight state to start the gear change. Of 
course, the present embodiment works well even in a slip control state 
where the lock-up clutch 18 is currently slipping to have a certain amount 
of engaging force. In such a state, the present embodiment retains the 
engaging force during the gear change as long as the predicted input shaft 
speed NM is greater than the target engine speed NES, while the present 
embodiment controls the lock-up clutch 18 to turn OFF if the predicted 
input shaft speed NM is smaller than the target engine speed NES. 
Moreover, it is possible to modify the present embodiment in the case where 
the predicted input shaft speed NM is smaller than the target engine speed 
NES, as follows: 
Instead of the aforementioned control of the control the lock-up clutch 18 
which is merely turned OFF to cancel the engaging force, the control unit 
27 controls the lock-up clutch 18 to reduce the engaging force up to the 
minimally required limit so that the engine speed NE after the gear change 
is continued to be greater than the target engine speed NES. 
As this invention may be embodied in several forms without departing from 
the spirit of essential characteristics thereof, the present embodiments 
are therefore illustrative and not restrictive, since the scope of the 
invention is defined by the appended claims rather than by the description 
preceding them, and all changes that fall within metes and bounds of the 
claims, or equivalence of such metes and bounds are therefore intended to 
be embraced by the claims.