Control of a vehicle automatic transmission

A vehicle automatic transmission including a hydraulic torque converter and a multiple stage transmission gear mechanism connected with the torque converter, and an electronic control unit for automatically shifting the gear stages of the gear mechanism in accordance with the vehicle operating condition. The electronic control unit has a plurality of gear shift patterns for a plurality of operating modes, such as a normal mode, a power mode and an economy mode. A manual switch is provided for selecting one of the operating modes. The control unit controls the gear mechanism so that different gear ratios are obtained between corresponding gear stages in different operating modes.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to control means for automatic transmissions 
and more particularly to control means for automatic transmissions having 
a hydraulic torque converter and a multiple-stage transmission gear 
mechanism connected with the hydraulic torque converter. More 
specifically, the present invention pertains to control means for 
determining the gear stage of the transmission gear mechanism in 
accordance with the vehicle operating condition. 
2. Description of the Prior Art 
Conventional automatic transmissions generally include a hydraulic torque 
converter having an output shaft connected with a multiple-stage gear 
transmission mechanism, such as a planetary gear mechanism. For selecting 
a desired one of the gear stages, the transmission usually includes a 
hydraulic system which has hydraulically operated and electromagnetically 
operated valves for appropriately selecting hydraulic circuits to thereby 
engage selected ones of friction devices such as clutches and brakes. 
Where the hydraulic system includes electromagnetically operated solenoid 
valves, electronic means is generally provided for detecting that the 
vehicle operating condition has been shifted from one zone to another, 
crossing a shifting line and producing electric signals for energizing 
appropriate ones of the solenoid valves. 
Generally, such a shifting line is determined in terms of the vehicle speed 
and the engine load. 
It has been known in automatic transmissions of the aforementioned type to 
provide more than one shift pattern, each having a plurality of shift 
lines. For example, Japanese patent publication No. 52-182 proposes an 
automatic transmission control which includes two shift patterns which can 
be manually selected for governing gear shifting operations, so that the 
gear mechanism is shifted at a lower vehicle speed under one of the shift 
patterns than under the other shift pattern. Since the shift pattern 
wherein the shifting is carried out at a lower vehicle speed can give 
economical operation, it may be called an economy mode, whereas the other 
shift pattern may be called a power mode, since it can give a stronger 
acceleration. 
It has been proposed to select the shift pattern automatically in 
accordance with a vehicle condition. For example, in Japanese patent 
application No. 54-34643 filed on Mar. 24, 1979, and disclosed for public 
inspection on Oct. 7, 1980, under the disclosure No. 55-129645, there is 
disclosed a control system for automatic transmissions wherein the shift 
pattern is switched to the economy mode when the fuel quantity decreases 
below a predetermined level. It should, however, be noted that in the 
known control systems, accelerating characteristics cannot substantially 
be changed by selectively switching the shifting pattern from one to 
another. Particularly in the vehicle starting period, the transmission 
gear mechanism is in the first stage both in the power mode and the 
economy mode, so that there will be no difference in acceleration between 
the two modes. 
OBJECT OF THE INVENTION 
It is an object of the present invention to provide a vehicle automatic 
transmission provided with a control system having a plurality of gear 
shift patterns with which vehicle operating characteristics can be 
substantially varied. 
Another object of the present invention is to provide a control system for 
a vehicle automatic transmission having a plurality of gear shift patterns 
which can provide different series of gear ratios in the transmission gear 
mechanism to produce different feelings in acceleration and deceleration. 
A further object of the present invention is to provide a control system 
for a vehicle automatic transmission having power and economy modes which 
can provide significantly different operating characteristics. 
SUMMARY OF THE INVENTION 
According to the present invention, the above and other objects can be 
accomplished by an automatic transmission for motor vehicles which 
comprises a torque converter having an input member adapted to be 
connected with an engine and an output member, a transmission gear 
mechanism having a plurality of gear trains of different gear ratios, said 
transmission gear mechanism including an input member connected with the 
output member of the torque converter, hydraulic actuator means for 
selecting one of said gear trains in the transmission gear mechanism, 
electromagnetic means for controlling a supply of hydraulic fluid to said 
hydraulic actuator means, sensing means for detecting vehicle operating 
conditions and producing an operating condition signal, control means 
provided with mode selecting manual switch means for determining an 
operating mode and producing a mode signal depending on an actuated 
position of the switch means, said control means including gear train 
series selecting means responsive to said mode signal for selecting one of 
a plurality of series of the gear trains in accordance with the operating 
mode, a plurality of shift patterns for governing gear shifting operations 
depending on the vehicle operating condition, shift pattern selecting 
means responsive to said mode signal and selecting one of said shift 
patterns, shifting means for comparing the operating condition signal with 
the selected one of the shift patterns and producing a shift signal when 
it is judged that gear shifting is necessary, said shift signal being 
applied to said electromagnetic means to effect the gear shifting in 
accordance with the selected series of the gear trains. 
Preferably, the plurality of series of the gear trains have first gear 
stages of different gear ratios. The transmission gear mechanism may 
include a first gear unit which can provide three gear trains and a second 
gear unit which is connected with the first gear unit and can provide two 
gear trains so that six different combinations of the gear trains can be 
obtained as a whole. The gear train series selecting means may select four 
of such combinations of the gear trains in accordance with the selected 
operating mode. The transmission gear mechanism may be of a planetary type 
which is conventionally used in vehicle automatic transmissions.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
General Arrangement 
Referring to the drawings, particularly to FIG. 1, there is shown a vehicle 
automatic transmission 1 connected with an engine 2. In order to control 
the transmission 1, there is provided a control unit 100. 
Basic Structure of the Transmission 
Referring now to FIG. 2, there is shown an automatic transmission which 
comprises a hydraulic torque converter 10, a multiple stage transmission 
gear mechanism 20, and a planetary gear type over-drive transmission 
mechanism 40 arranged between the torque converter 10 and the multiple 
stage transmission gear mechanism 20. 
The torque converter 10 has a pump 13 connected with an output shaft 3 of 
an engine 2 through a drive plate 11 and a converter casing 12, a turbine 
14 provided in the casing 12 to face to the pump 13 and a stator 15 
disposed between the pump 13 and the turbine 14. A converter output shaft 
16 is connected with the turbine 14. A lock-up clutch 17 is provided 
between the converter output shaft 16 and the casing 12 which is connected 
to the pump 13. The lock-up clutch 17 is normally engaged with the casing 
12 under a pressure of hydraulic fluid which circulates in the torque 
converter 10, and is released by a hydraulic pressure, which is drawn to a 
space between the casing 12 and the clutch 17 from an external pressure 
source. 
The multiple stage transmission gear mechanism 20 has a front planetary 
gear unit 21 and a rear planetary gear unit 22. The front planetary gear 
unit 21 has a sun gear 23 connected with a sun gear 24 of the rear 
planetary gear unit 22 though a connecting rod 25. The gear mechanism 20 
has an input shaft 26 connected through a front clutch 27 with the 
connecting rod 25 and through a rear clutch 28 with an internal gear 29 of 
the front planetary gear unit 21. A front brake 31 is provided between the 
connecting rod 25 of the sun gears 23, 24 of the gear units 21 and 22, and 
a casing 30 of the transmission. The gear mechanism 20 also has an output 
shaft 34 connected with a planetary carrier 32 of the front planetary gear 
unit 21 and an internal gear 33 of the rear planetary gear unit 22. The 
rear planetary gear unit 22 has a planetary carrier 35, and there are 
provided between the planetary carrier 35 and the transmission casing 30 a 
rear brake 36 and a one-way clutch 37. 
The planetary gear type over-drive transmission mechanism 40 includes 
planetary gears 41a, a planetary carrier 41 rotatably carrying the 
planetary gears 41a and connected with the output shaft 16 of the torque 
converter 10, a sun gear 42 engaged with the planetary gears 41a, and an 
internal gear 43 which is also engaged with the planetary gears 41a and 
connected with the sun gear 42 through a direct connecting clutch 44. An 
over-drive brake 45 is provided between the sun gear 42 and the 
transmission casing 30. The internal gear 43 is connected with the input 
shaft 26 of the multiple stage transmission gear mechanism 20. 
The multiple stage transmission gear mechanism 20 is of known type and can 
provide three forward driving gear stages and one reverse stage through 
selective engagements of the clutches and brakes. The relationships 
between the forward gear stages and the engagements of the clutches and 
brakes are shown in Table 1 together with typical values of gear ratios in 
the gear stages. The planetary gear type over-drive transmission mechanism 
40 connects the shafts 16 and 26 directly when the direct connection 
clutch 44 is engaged and the brake 45 is released, and provides an 
over-drive connection between the shafts 16 and 26 when the brake 45 is 
engaged and the clutch 44 is released. This function is shown in Table 2 
together with typical values of the gear ratios. 
TABLE 1 
______________________________________ 
FRONT REAR FRONT REAR GEAR 
GEAR CLUTCH CLUTCH BRAKE BRAKE RA- 
STAGE 27 28 31 36 TIO 
______________________________________ 
1 o o 2.841 
2 o o 1.541 
3 o o 1.000 
______________________________________ 
TABLE 2 
______________________________________ 
DIRECT 
CONNECT OVER-DRIVE 
GEAR CLUTCH BRAKE 
STAGE 44 45 GEAR RATIO 
______________________________________ 
DIRECT o 1.000 
OVER-DRIVE o 0.720 
______________________________________ 
It will be understood that, by combining the three forward gear stages in 
the gear mechanism 20 and the two gear stages in the over-drive 
transmission gear mechanism 40, it becomes possible to obtain six gear 
stages of different overall gear ratios. 
Hydraulic Control Circuit 
The above-mentioned automatic transmission is provided with a hydraulic 
control circuit as shown in FIG. 2. The hydraulic control circuit has an 
oil pump 50 which is driven by the engine output shaft 3. Hydraulic oil is 
discharged under pressure from the pump 50 into a pressure line 51. The 
oil pressure is reduced by a pressure regulating valve 52 and applied to a 
select valve 53. The select valve 53 has a plunger which can be 
selectively positioned in one of the shift positions 1, 2, D, N, R and P. 
When the plunger is positioned in one of the shift positions 1, 2 and D, 
the pressure line 51 is communicated with ports a, b, c of the select 
valve 103. The port a is communicated with a hydraulic actuator 28a for 
the rear clutch 28 through a line 54. When the select valve 53 is 
positioned in the above mentioned position, the actuator 28a makes the 
rear clutch 28 engage. The port a is also communicated with the left-hand 
end portion of a 1-2 shift valve 61 having a spool which is now biased 
rightward in FIG. 2 under the oil pressure from the port a. The port a is 
further communicated with the right-hand end portion of the 1-2 shift 
valve 61 through a first line 56, the right-hand end portion of a 2-3 
shift valve 62 through a second line 57, and the upper end portion of a 
3-4 shift valve 63 through a third line 58. First, second and third drain 
lines 66, 67 and 68 are provided in the first, second and third lines 56, 
57 and 58, respectively. These drain lines 66, 67 and 68 are respectively 
provided with a first, second and third solenoid valves 71, 72 and 73 for 
opening and closing them. When the port a is communicated with the line 
51, the solenoid valves 71, 72 and 73 are energized to close the drain 
lines 66, 67, 68 and as a result, the pressure is built up in the first, 
second and third line 56, 57, 58. 
The port b is communicated with a second lock valve 78 through a line 80. 
The oil pressure which is applied from the port b to the second lock valve 
78 acts to bias the spool 78a of the valve 78 downwards. When the spool 
78a of the valve 78 is in the lower position, the line 80 is communicated 
with the line 79 so that the oil pressure is introduced into a brake 
engaging pressure chamber 31a' of an actuator 31a to engage the front 
brake 31. The port c is communicated with the second lock valve 78 through 
a line 81. The oil pressure which is applied from the port c to the second 
lock valve 78 acts to bias the spool 78a of the valve 78 upward. The port 
c is also communicated with the 2-3 shift valve 62 through a pressure line 
81a having an orifice check valve 82. The line 81a is communicated with a 
line 83 when the spool of the 2-3 shift valve 120 is moved leftward by the 
pressure in the second line 57, which increases upon energizing the 
solenoid valve 72 in the drain line 67. The line 83 is communicated with 
the releasing pressure chamber 31a" of the actuator 31a. When oil pressure 
is introduced into the releasing pressure chamber 31a", the actuator 31a 
is moved to release the brake 31 against the pressure in the engaging 
pressure chamber 31a'. Additionally, the pressure in the line 83 is 
introduced into the actuator 27a for the front clutch 27 to make the 
clutch 27 engage. 
The select valve 53 has a port d which is communicated with the pressure 
line 51 when the valve 53 is positioned in the position 1. The port d is 
communicated with the 1-2 shift valve 61 through a line 86, and with an 
actuator 36a for the rear brake 36 through a further line 87. When the 
solenoid valves 71 and 72 are energized, the spools of the 1-2 shift valve 
61 and the 2-3 shift valve 62 are moved to thereby change the port 
connections for engaging appropriate brakes and/or clutches to establish 
1-2, 2-3 shifting operations, respectively. The hydraulic control circuit 
is also provided with a cut-back valve 95 for making the oil pressure from 
the pressure regulating valve 52 stable, a vacuum throttle valve 96 for 
varying the line pressure from the pressure regulating valve 52 according 
to the suction pressure in the engine intake passage, and a valve 97 for 
backing up the throttle valve 96. 
Furthermore, this hydraulic control circuit is provided with an actuator 
44a for controlling the clutch 44 and an actuator 45a for the brake 45 of 
the planetary gear type over-drive transmission mechanism 40. The actuator 
45a has an engaging pressure chamber 45a' communicated with the pressure 
line 51 through a line 90. The brake 45 is operated when the actuator 45a 
is moved under the pressure in the line 51. The pressure line 51 is 
connected through a line 89 with the 3-4 shift valve 63. When the solenoid 
valve 73 is energized, the spool 63a of the 3-4 shift valve 63 is moved 
downward to communicate the pressure line 51 through the line 89 with a 
line 91 so that the oil pressure is introduced into the line 91. The oil 
pressure introduced into the line 91 acts on a releasing pressure chamber 
45a" of the actuator 45a to release the brake 45, and on the actuator 44a 
to make the clutch 44 engage. 
Still further, the present hydraulic control circuit is provided with a 
lock-up control valve 64, which is communicated with a port a of the 
select valve 53 through a line 59. From the line 59, a branch drain line 
69 extends and is provided with a solenoid valve 74. When the pressure in 
the line 59 increases by closing the drain line 69 with the solenoid valve 
74 being energized, the lock-up control valve 64 has its spool 64a moved 
upward to cut the communication between lines 93 and 94 and drain the 
pressure in the line 94 so that the lock-up clutch 17 is engaged. 
In the above arrangement, the relations of the overall gear ratios and the 
operations of the solenoids, the brakes and the clutches are shown in 
Table 3. 
TABLE 3 
__________________________________________________________________________ 
DIRECT 
FRONT REAR FRONT 
CONNECT 
OVER-DRIVE 
SOLENOID 
SOLENOID 
SOLENOID 
CLUTCH 
CLUTCH 
BRAKE 
CLUTCH BRAKE GEAR 
71 72 73 27 28 31 44 45 RATIO 
__________________________________________________________________________ 
OFF OFF OFF o o 2.841 
ON OFF OFF o o o 1.541 
OFF ON OFF o o o 1.000 
OFF OFF ON o o 2.046 
ON ON OFF o o o 1.000 
ON OFF ON o o o 1.110 
OFF ON ON o o o 0.720 
ON ON ON o o o 0.720 
__________________________________________________________________________ 
It will be understood in the Table 3 that six different gear ratios can be 
obtained through selective energization of the three solenoids 71, 72 and 
73. Thus, it is possible to selectively combine the gear ratios to provide 
a plurality of operating modes as, for example, shown in Table 4. 
TABLE 4 
______________________________________ 
GEAR POWER NORMAL ECONOMY ECONOMY 
STAGE MODE MODE MODE A MODE B 
______________________________________ 
1 2.841 2.841 2.046 2.046 
2 2.046 1.541 1.541 1.541 
3 1.541 1.000 1.000 1.110 
4 1.000 0.720 0.720 1.000 
5 0.720 0.720 
______________________________________ 
In Table 5, there is shown a relationship between the operation of the 
solenoid 74 and the torque converter lock-up. 
TABLE 5 
______________________________________ 
SOL 74 Lock-up 
______________________________________ 
ON engage 
OFF release 
______________________________________ 
Electronic Control Circuit 
Referring to FIG. 1, there is shown an electronic control circuit 100 for 
controlling the above hydraulic control circuit. The electronic control 
circuit 100 can be constituted by a microcomputer which is provided with 
an input-output device (I/O) 101, a random access memory (RAM) 102 and a 
central processing unit (CPU) 103. For supplying signals to the I/O, there 
are provided an engine load sensor 104, and a torque converter turbine 
speed sensor 105. The engine load sensor 104 detects the load on the 
engine 2 in terms of the opening of an engine throttle valve 5 provided in 
the intake passage 4 of the engine 2 to produce an engine load signal 
S.sub.1. The turbine speed sensor 105 senses the rotating speed of the 
converter output shaft 16 to produce a turbine speed signal S.sub.2. There 
is also provided a manually operated mode select switch 106 which applies 
a mode signal S.sub.5 to the I/O 101. 
The I/O receives the engine load signal S.sub.1, the turbine speed signal 
S.sub.2 and the mode signal S.sub.5, processes these signals, and applies 
them to the RAM 102. The RAM memorizes the signals S.sub.1, S.sub.2 and 
S.sub.5 and applies these signals and other data pre-stored in the RAM 102 
to the CPU 103 in accordance with demands of the CPU 103. As examples of 
the prestored data, there is a gear shift control map including a shift 
pattern comprised of a gear shift up control line X, a gear shift down 
control line Y, a torque converter lock up line Le and a torque converter 
lock up release line Le' as shown in FIG. 3. 
It should be noted that the map shown in FIG. 3 is drawn in terms of the 
engine throttle valve position and the torque converter turbine speed, 
however, the map may be drawn in terms of the vehicle speed instead of the 
torque converter turbine speed. 
The CPU 103 processes the input data and produces output signals S.sub.3 
and S.sub.4 which are applied to the solenoids 71, 72, 73 and 74 to 
control the transmission. Although only one shift pattern is shown in FIG. 
3, one or more shift patterns are further provided. For example, there may 
be provided a second shift pattern having shift-up and shift-down control 
lines and lock-up control lines which are shifted toward a low speed side 
as compared with corresponding lines shown in FIG. 3. There may further be 
provided a shift pattern having control lines shifted toward a high speed 
side. The CPU 103 selects one of such shift patterns in accordance with 
the mode signal S.sub.5 from the switch 106. For example, when a normal 
mode is selected by the switch 106, the CPU 103 may select the shift 
pattern shown in FIG. 3. Under an economy mode, the CPU 103 may then 
select the shift pattern shifted toward the low speed side, whereas it may 
select the shift pattern shifted toward the high speed side under a power 
mode. 
The operation of the control unit will now be described with reference to 
FIGS. 4 through 10. 
General Operation 
FIG. 4 shows in general the operation of the control unit. When the program 
is initialized at the step A.sub.1, the ports in the respective hydraulic 
control valves and the counters in the circuit are brought into intialized 
positions to thereby hold the gear mechanism at the first stage and 
release the torque converter lock-up clutch 17. Thereafter, the gear shift 
timer is set to T at the step A.sub.2 and the shift range or the position 
of the select valve 53 is read in the Step A.sub.3 and a judgement is 
carried out in the step A.sub.4 as to whether the shift range is at the 
"1" range. If the judgement is YES, a signal is produced in the step 
A.sub.5 to de-energize the solenoid 74 so as to release the lock-up clutch 
17. Then, a calculation is made in the step A.sub.6 to determine whether 
the engine will overrun if the gear mechanism is shifted down to the first 
stage. A judgement is then made in the step A.sub.7 as to whether the 
engine will overrun based on the result of the calculation in the step 
A.sub.6. If the judgement in the step A.sub.7 is NO, a signal is produced 
to shift the gear mechanism to the first stage in the step A.sub.8. If the 
judgement is NO, a signal is produced to shift the gear mechanism to the 
second stage in the step A.sub.9. If the judgement in the step A.sub.4 is 
NO, a further judgement is carried out in the step A.sub.10 as to whether 
the shift range is at "2" range. If the judgement is YES, a signal is 
applied in the step A.sub.11 to energize the solenoid valve 74 to release 
the lock-up clutch 17 and to fix the gear mechanism at the second stage. 
If the judgement in step A.sub.10 is that the shift range is not at the 
second stage, it is interpreted that the shift valve 53 is in the "D" 
range. 
Then, the operation mode is read in the step A.sub.13 and a judgement is 
read in the step A.sub.14 as to whether the mode is in the economy mode. 
If the result of the judgement is NO, it is interpreted that the normal 
mode is selected and the shift pattern for the normal mode as shown in 
FIG. 3 is selected in the step A.sub.15. Thereafter, operations of the 
solenoids 71, 72, 73 and 74 are determined in the step A.sub.16 for the 
normal mode in accordance with the Tables 3 and 4. For example, in the 
normal mode, all of the solenoids are de-energized for the first gear 
stage to obtain the gear ratio 2.841, but the solenoid 71 is energized for 
the second gear stage to obtain the gear ratio 1.541. For the third gear 
stage, the solenoid 72 is energized instead of the solenoid 71 to obtain 
the gear ratio 1.000 whereas the solenoids 72 and 73 are energized for the 
fourth gear stage to obtain the overdrive gear ratio. If the judgement in 
the step A.sub.14 is YES, the shift pattern for the economy mode is 
selected in the step A.sub.15 and the operations of the solenoids 71, 72, 
73 and 74 are determined in the step A.sub.16' for the economy mode. Then, 
the shift up control, the shift down control and the torque converter lock 
up control are carried out respectively in the steps A.sub.17, A.sub.18 
and A.sub.19. Finally, a predetermined time delay, for example 50 m sec., 
is provided in the step A.sub.20 and the step A.sub.2 is repeated. In the 
step A.sub.2, the value in the timer is substracted by one and a new value 
T is set. 
Shift-up Control 
Referring to FIG. 5, the gear position of the transmission gear mechanism 
20 is at first read and a judgement is made in the step B as to whether 
the gear mechanism 20 is at the fourth stage. If the judgement is YES, the 
shift-up control is terminated because no further shift-up is possible. If 
the fourth gear stage judgement in the step B.sub.1 is NO, the engine 
throttle valve position is read in the step B.sub.2 and a reference 
turbine speed, Tmap, is read in the step B.sub.3 from the selected 
shift-up control line MU which is shown in FIG. 6. Thereafter, the actual 
turbine speed T is read in the step B.sub.4 and a judgement is made in the 
step B.sub.5 as to whether the actual turbine speed T is greater than the 
reference turbine speed Tmap. If the judgement is YES, a further judgement 
is made in the step B.sub.6 as to whether the shift-up flag F.sub.1 is set 
to zero. If the result of the judgement is NO, the procedure is terminated 
but, if the judgement is YES, the shift-up flag F.sub.1 is set to one in 
the step B.sub.7 and one stage shift up is carried out in the step B.sub.8 
by appropriately energizing the solenoids 71, 72 and 73, as determined in 
the step A.sub.16, or A.sub.16' and the shift timer is set to the initial 
value T in the step B.sub.9. 
If the judgement in the step B.sub.5 is NO, a new shift up control line Mu' 
is provided as shown in FIG. 6 by multiplying in the step B.sub.10 the 
reference turbine speed, Tmap, with a constant 0.8 to obtain a new 
reference speed Tmap. Then, a judgement is made in the step B.sub.11 as to 
whether the actual turbine speed is greater than the new reference speed 
Tmap. If the result of the judgement is YES, the procedure is terminated 
but, if the judgement is NO, the shift up flag F.sub.1 is reset to zero in 
the step B.sub.12. The steps B.sub.10 through B.sub.12 are performed in 
order to prevent the gear shifting operations to be repeatedly carried out 
when the turbine speed T is close to the reference turbine speed Tmap. 
Shift Down Control 
As shown in FIG. 7, in the gear shift down control, the gear position of 
the transmission gear mechanism 20 is at first read and judgement is made 
in the step C.sub.1 as to whether the gear mechanism is at the first 
stage. If the judgement is YES, no further control can be carried out so 
that the control is finished. 
If the aforementioned judgement is NO, the engine throttle valve position 
is read in the step C.sub.2 and a reference turbine speed, Tmap, is read 
in the step C.sub.3 from the selected shift down control line Md, which is 
shown in FIG. 8. Thereafter, the actual turbine speed T is read in the 
step C.sub.4. Then, a judgement is made in the step C.sub.5 as to whether 
the actual turbine speed T is smaller than the reference turbine speed 
Tmap. If the result of the judgement is YES, a further judgement is made 
in the step C.sub.6 as to whether the shift down flag F.sub.2 in the zero 
position. If the result of the judgement is NO, the procedure is 
terminated, but if the result of the judgement is YES, the shift down flag 
F.sub.2 is set to one in the step C.sub.7 and a one-stage shift down is 
carried out in the step C.sub.8. Thereafter, the shift timer is set to the 
initial value in the step C.sub.9. 
If the judgement in the step C.sub.5 is NO, a new shift down control line 
Md' is provided as shown in FIG. 8. This is in effect carried out by 
multiplying in the step C.sub.10 the turbine speed T with a constant 0.8 
to obtain a new turbine speed T. Then, a judgement is made as to whether 
the new turbine speed T is smaller than the reference speed Tmap. If the 
result of the judgement is YES, the procedure is terminated, but if the 
result of the judgement is NO, the shift down flag F.sub.2 is reset to 
zero in the step C.sub.12. 
Lock Up Control 
Referring to FIG. 9, a judgement is at first made in the step D.sub.1 as to 
whether the count value in the shift timer T is zero. If the result of the 
judgement is NO, a signal is produced in the step D.sub.2 to release the 
lock up clutch 17. If the result of the judgement is YES, the engine 
throttle valve position is read in the step D.sub.3 and a reference 
turbine speed, Tmap, is read in the step D.sub.4 from the lock up release 
line Moff as shown in FIG. 10. Then, the actual turbine speed T is read in 
the step D.sub.5 and a judgement is made in the step D.sub.6 as to whether 
the actual turbine speed T is smaller than the reference turbine speed 
Tmap. If the result of the judgement is YES, the step D.sub.2 is carried 
out, but if the result of the judgement is NO, a further reference turbine 
speed Tmap is read in the step D.sub.7 from the lock up engage line Mon. 
Thereafter, a judgement is made in the step D.sub.8 as to whether the 
actual turbine speed T is greater than the reference turbine speed Tmap. 
If the result of the judgement is NO, the procedure is finished. If the 
judgement is YES, a signal is produced in the step D.sub.9 to engage the 
lock up clutch 17. 
The above descriptions have been made with respect to the operations 
wherein the normal and economy modes are alternatively selected. If 
should, however, be noted that other combinations of the modes may be 
chosen in Table 4. For example, the power mode and the economy mode A may 
be combined. In this instance, the gear ratios in any gear stage are 
different between the two modes, so that substantially different 
acceleration and deceleration feelings can be provided by the two modes. 
Further, three or more modes may be alternatively selected by the switch 
106. It should therefore be understood that the invention is in no way 
limited to the details of the illustrated embodiment, but changes and 
modifications may be made without departing from the scope of the appended 
claims.