System for controlling rate of speed change in automatic transmission

A control system for an automatic transmission employed in a vehicle comprises a torque converter coupled with an engine, power transmitting gear arrangement disposed at an output end of the torque converter, a speed change mechanism for giving rise to speed change in the power transmitting gear arrangement, a fluid servo control device having an applying chamber and a releasing chamber to each of which a fluid is supplied and operative to cause the speed change mechanism to work, and an additional control device for controlling the fluid servo control device under a situation in which the fluid in the releasing chamber of the fluid servo control device is so controlled as to have one of speeds in the power transmitting gear arrangement. The fluid servo control device is controlled by the additional control device to be in a first condition wherein the fluid is supplied to the applying chamber and in a second condition wherein the fluid is drained from the applying chamber selectively in response to the operating condition of the engine or the travelling condition of the vehicle.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to control systems for automatic 
transmissions employed in vehicles, and more particularly, to a system for 
controlling an automatic transmission provided in a vehicle to have a 
speed position selected automatically in accordance with the operating 
condition of an engine employed in the vehicle and the travelling 
condition of the vehicle. 
2. Description of the Prior Art 
There has been commonly used in vehicles an automatic transmission which 
comprises a torque converter coupled with an output shaft of an engine, a 
power transmitting gear arrangement including a planetary gear mechanism 
connected to an output shaft of the torque converter, a speed change 
mechanism including clutch and brake elements and operative to switch over 
power transmitting paths from one to another in the power transmitting 
gear arrangement so that speed change is carried out, a hydraulic servo 
control device provided in an oil hydraulic control circuit for causing 
the speed change mechanism to work, and a valve arrangement for 
controlling an operation oil to be supplied to and drained from the speed 
change mechanism and the hydraulic servo control device. The valve 
arrangement is operative to cause the hydraulic servo control device to 
act on the speed change mechanism in response to the operating condition 
of the engine and the travelling condition of the vehicle, so that the 
speed change mechanism works to switch over the power transmitting paths 
from one to another in the power transmitting gear arrangement under the 
control by the hydraulic servo control device. 
For such an automatic transmission employed in the vehicle, it is desired 
that the shock of great degree, which may arise on the occasion of, for 
example, a kick-down operation in which the speed is shifted down in the 
power transmitting gear arrangement, is avoided and in addition a superior 
responsibility for speed changes is obtained. For fulfilling these 
desires, it is required that the timing of each speed change is adjusted 
appropriately in accordance with the operating condition of the engine and 
the travelling condition of the vehicle. 
In view of this, for example, as disclosed in the Japanese patent 
application published before examination under publication number 
59/183160, there has been proposed a control device for an automatic 
transmission in which a control valve mechanism for controlling the 
velocity of an oil flowing into or from a hydraulic servo control device 
which has an applying chamber and a releasing chamber to each of which an 
oil is supplied and is operative to cause a speed change mechanism 
comprising friction elements to work for changing a power transmitting 
path in a power transmitting gear arrangement, so as to control the acting 
speed of the hydraulic servo control device, is provided with the 
intention of adjusting the timing of each speed change caused by the speed 
change mechanism in response to the operating condition of an engine. 
However, although the acting speed of the hydraulic servo control device 
is influenced by the presence or absence of oil pressure in the applying 
chamber, such a fact has not been taken into consideration in the 
previously proposed control device. Therefore, the previously proposed 
control device has failed to realize the anticipated result. 
OBJECTS AND SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a control 
system for an automatic transmission which avoids the aforementioned 
problems encountered with the prior art. 
Another object of the present invention is to provide a control system for 
an automatic transmission employed in a vehicle, wherein the shifting-down 
in a power transmitting gear arrangement is so performed on the occasion 
of, for example, a kick-down operation that the shock can be effectively 
moderated. 
A further object of the present invention is to provide a control system 
for an automatic transmission employed in a vehicle, wherein the acting 
speed of a fluid servo control device which is operative to cause a speed 
change mechanism to work for switching over power transmitting paths from 
one to another in power transmitting gear arrangement is controlled 
appropriately in accordance with the operating condition of an engine with 
which the control system is coupled and the travelling condition of the 
vehicle. 
According to the present invention, there is provided a control system for 
an automatic transmission employed in a vehicle comprising a torque 
converter coupled with an output shaft of an engine, a power transmitting 
gear arrangement disposed at an output end of the torque converter, a 
speed change mechanism for changing over power transmitting paths to one 
from another in the power transmitting gear arrangement to give rise to 
speed change, a fluid servo control device having an applying chamber and 
a releasing chamber to each of which a fluid is supplied and operative to 
act on the speed change mechanism, and an additional control device for 
causing the fluid servo control device to be in a first condition wherein 
the fluid is supplied to the applying chamber and in a second condition 
wherein the fluid is drained from the applying chamber selectively in 
response to at least one of the operating condition of the engine and the 
travelling condition of the vehicle during a period in which the fluid in 
the releasing chamber of the fluid servo control device is so controlled 
as to have one of speeds in the power transmitting gear arrangement. 
With the control system for an automatic transmission thus constituted in 
accordance with the present invention, when the fluid is drained from the 
releasing chamber of the fluid servo control device so as to conduct a 
speed change of shifting down in the power transmitting gear arrangement, 
the applying chamber of the fluid servo control device has been previously 
set to be in one of the first and second conditions in accordance with at 
least one of the operating condition of the engine and the travelling 
condition of the vehicle. This results in that the acting speed of the 
fluid servo control device which is appropriate for the operating 
condition of the engine and the travelling condition of the vehicle is 
automatically obtained on the occasion of the speed change of shifting 
down and consequently the timing of the speed chage caused by the speed 
change mechanism is properly and accurately adjusted so that the speed 
change is so performed that the shock can be effectively moderated. 
The above, and other objects, features and advantages of the present 
invention will become apparent from the following detailed description 
which is to be read in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention will now be desribed by way of example with reference to the 
accompanying drawings. 
Referring to FIG. 1, an automatic transmission employed in a vehicle 
comprises a torque converter 2 coupled with a crank shaft 1 of an engine 
and a multi-stage power transmitting gear arrangement 10 connected to an 
output end of the torque converter 2. 
The torque converter 2 includes a pump impeller 3, a turbine runner 4 and a 
stator 5, and the pump impeller 3 is secured to the crank shaft 1. The 
stator 5 is coupled rotatably through a one-way clutch 6 with a fixed 
shaft 7 incorporated with a case 11 of the multi-stage power transmitting 
gear arrangement 10. The one-way clutch 6 permits the stator 5 to revolve 
only in a direction common to the rotation of the pump impeller 3. 
The multi-stage power transmitting gear arrangement 10 includes a central 
shaft 12 which has one end thereof connected to the crank shaft 1 and 
elongates to pass through a central part of the arrangement 10 and engage 
at the other end thereof with an oil pump 100 disposed on a side wall of 
the arrangement 10. Further, a tubular turbine shaft 13 is disposed to 
surround the central shaft 12. One end of the tubular turbine shaft 13 is 
coupled with the turbine runner 4 and the other end of the tubular turbine 
shaft 13 reaches to the side wall of the arrangement 10 to be supported 
rotatably by the same. 
On the tubular turbine shaft 13, a planetary gear unit 14 comprising a 
small sun gear 15, a large sun gear 16 disposed behind the small sun gear 
15 with a short distance between, a long pinion gear 17, a short pinion 
gear 18 and a ring gear 19 is mounted. Further, first and second clutch 
devices 20 and 21 are disposed behind the planetary gear unit 14 on the 
tubular turbine shaft 13. The first clutch device 20 is provided for 
forward driving and operative to make selectively power transmission 
through a one-way clutch device 22 between the tubular turbine shaft 13 
and the small sun gear 15. The second clutch device 21 is operative to 
making selectively another power transmission between the tubular turbine 
shaft 13 and the small sun gear 15. A first brake device 23 is disposed at 
the outside of the second clutch device 21. The first brake device 23 is 
formed into a band brake having a brake drum 23-1 connected to the large 
sun gear 16 and a brake band 23-2 engaged with the brake drum 23-1. A 
third clutch device 24 is disposed at the outside of the first clutch 
device 20 and on the side of the first brake device 23. The third clutch 
device 24 is provided for backward driving and operative to making 
selectively power transmission through the brake drum 23-1 of the first 
brake device 23 between the tubular turbine shaft 13 and the large sun 
gear 16. 
At the outside of the planetary gear unit 14, a second brake device 25 is 
provided for engaging selectively a carrier 14a of the planetary gear unit 
14 with a case 10a of the multi-stage power transmitting gear arrangement 
10. Between the first and second brake devices 23 and 25, a second one-way 
clutch device 26 is provided in parallel with the second brake device 25 
for engaging selectively the carrier 14a of the planetary gear unit 14 
with the case 10a of the multi-stage power transmitting gear arrangement 
10. 
A fourth clutch device 27 is disposed in front of the planetary gear unit 
14 for making selectively power transmission between the tubular turbine 
shaft 13 and the carrier 14a of the planetary gear unit 14. Further, an 
output gear 28 connected to the ring gear 19 is disposed in front of the 
fourth clutch device 27 to be coupled with an output shaft. 
The tubular turbine shaft 13 is so arranged as to be coupled through a 
lock-up clutch device 29 with the crank shaft 1 without passing through 
the torque converter 2, as occasion demands. 
The multi-stage power transmitting gear arrangement 10 constituted as 
described above provides four forward speeds and one backward speed, and 
the automatic transmission comprising the torque converter 2 and the 
multi-stage power transmitting gear arrangement 10 can provide a large 
number of speeds at a plurality of shift ranges arranged ordinarily by 
causing the first to fourth clutch devices 20, 21, 24 and 27, and the 
first and second brakes devices 23 and 25 to work selectively. 
In the following Table 1, there are given the relationship in operation of 
the respective shift ranges with the clutches and the brakes in the above 
configuration: 
TABLE 1 
______________________________________ 
One-way 
Shift Clutch Brake Clutch 
position 24 20 21 27 25 23 26 22 
______________________________________ 
R o o 
N 
D first o o (o) (o) 
speed 
second o o o (o) 
speed 
third o o o (o) 
speed 
overdrive o o o 
2nd 
first o o (o) (o) 
speed 
second o o o (o) 
speed 
third o o o (o) 
speed 
1st 
first o o o (o) (o) 
speed 
second o o o (o) 
speed 
______________________________________ 
FIG. 2 shows an oil hydraulic control circuit used for the automatic 
transmission shown in FIG. 1 and described above. 
The oil hydraulic control circuit includes an oil pump 100 adapted to be 
driven by the crank shaft 1 of the engine and an operation oil is 
discharged from the oil pump 100 into a pressure line 101. The operation 
oil discharged into the pressure line 101 is led to a pressure valve 102 
to be adjusted in pressure thereby and then passed into a selector valve 
103 through a port g thereof. The selector valve 103 is a manual shift 
valve having the 1st, 2nd, D, N, R and P shift positions to be selected 
manually and also ports a, c, d, e and f in addition to the port g. The 
port g is permitted to communicate with the ports a, d and e, when the 
selector valve 103 is in the 1st shift position, with the ports a, c and d 
when the selector valve 103 is in the 2nd shift position, with the ports a 
and c when the selector valve 103 is in the D shift position, and with the 
port f when the selector valve 103 is in the R shift position. 
The port a of the selector valve 103 is connected to a 1-2 shift valve 110 
for supplying thereto with the operation oil against a spring 110a 
provided therein. The 1-2 shift valve 110 is put in the 1st shift position 
when a solenoid valve 110b is deenergized and in the 2nd shift position 
when the solenoid valve 110b is energized. The operation oil discharged 
from the port a of the selector valve 103, for example, under the 
situation wherein the selector valve 103 is in the D shift position, is 
supplied through, the 1-2 shift valve 110 to an applying chamber 23a of a 
hydraulic servo control device 23A which is provided for causing the first 
brake device 23 to operate when the solenoid valve 110b is energized so 
that the speed change to the second speed from the third speed is carried 
out. In the case where the solenoid valve 110b is deenergized under the 
situation wherein the selector valve 103 is in the D shift position, the 
operation oil discharged from the port a of the selector valve 103 
bypasses the 1-2 shift valve 110 to be supplied to the first and second 
clutch devices 20 and 21, so that the first speed is selected. 
Further, the 1-2 shift valve 110 is operative to supply the operation oil 
which is introduced thereto through a pressure reducing valve 140 from the 
port e of the selector valve 103 to the second brake device 25 and also a 
signal pressure to throttle backup valve 141 when the second speed is 
selected under the situation wherein the selector valve 103 is in the 1st 
shift position. 
The port a of the selector valve 103 is also connected to a 2-3 shift valve 
120 for supplying thereto with the operation oil against a spring 120a 
provided therein. The 2-3 shift valve 120 is put in the 2nd shift position 
when a solenoid valve 120b is energized and in the 3rd shift position when 
the solenoid valve 120b is deenergized. In the case where the speed change 
to the third speed from the second speed is carried out, the operation oil 
discharged from the port c of the selector valve 103 is supplied through a 
servo control valve 142 and a 2-3 timing valve 143 to the fourth clutch 
device 27 to engage the same and also to the releasing chamber 23b of the 
hydraulic servo control device 23A so as to disengage the first brake 
device 23. 
The port a of the selector valve 103 is further connected to a 3-4 shift 
valve 130 for supplying thereto with the operation oil against a spring 
130a provided therein. The 3-4 shift valve 130 is put in the 3rd shift 
position when a solenoid valve 130b is deenergized and in the 4the shift 
position (overdrive position) when the solenoid valve 130b is energized. 
When the 3-4 shift valve 130 is in the 3rd shift position, the operation 
oil having passed through the 1-2 shift valve 110 is supplied to the 
applying chamber 23a of the hydraulic servo control device 23A without 
passing through any orifice and the operation oil discharged from the port 
a of the selector valve 103 to bypass the 1-2 shift valve 110 is supplied 
through the 3-4 shift valve 130 and an N-D accumulator 144 to the first 
and second clutch devices 20 and 21. 
When the solenoid valve 130b is energized to drain the operation oil from 
the 3-4 shift valve 130, the operation oil having passed through the 1-2 
shift valve 110 is supplied through a line provided with an orifice and a 
check valve to the applying chamber 23a of the hydraulic servo control 
device 23A, and the speed change to the fourth speed from the third speed 
is performed. Simultaneously, the operating oil in the releasing chamber 
23b of the hydraulic servo control device 23A is drained through an 
orifice or a 3-4 cavity valve 145 and the 3-4 shift valve 130 so as to 
engage the first brake device 23, and the operating oil acting on the 
second clutch device 21 is also drained through the N-D accumulator 144, a 
neutral valve 160 and the 3-4 shift valve 130 so that the second clutch 
device 21 is disengaged. 
The pressure reducing valve 140 receives the operation oil discharged from 
the port e of the selector valve 103 to reduce the pressure of the same by 
self-adjusting function and supplies the operation oil reduced in pressure 
to the 1-2 shift valve 110 when the selector valve 103 is in the 1st shift 
position. The operation oil thus supplied to the 1-2 shift valve 110 is 
supplied therethrough to the second brake device 25 when the first speed 
is selected. Since the operation oil which is supplied through the 1-2 
shift valve 110 to the second brake device 25 is reduced in pressure by 
the pressure reducing valve 140, the shock caused on the occasion of the 
speed change is moderated. The pressure reducing valve 140 is operative 
also to supply the operation oil having passed through the 1-2 shift valve 
110 to the throttle backup valve 141 as the signal pressure, but is not 
caused to work when the selector valve 103 is in the D shift position. 
The throttle backup valve 141 receives the signal pressure from the 
pressure reducing valve 140 to cause the same to act against the pressure 
by a spring contained therein, and supplies the operation oil discharged 
from the port d of the selector valve 103 to the pressure regulator valve 
102 only when the signal pressure supplied from the pressure reducing 
valve 140 acts practically against the pressure by the spring contained 
therein. Accordingly, the throttle backup valve 141 is operative to supply 
the operation oil discharged rom the port d of the selector valve 103 to 
the pressure regulator valve 102 for increasing the pressure of the 
operation oil so that an engine braking operation is obtained effectively 
when the selector valve 103 in the 1st or 2nd shifting position and in 
addition the signal pressure is not supplied to the throttle backup valve 
141. 
The pressure regulator valve 102 is connected through a throttle modulator 
valve 147 to a throttle valve 146. The throttle valve 146 works in 
conjunction with an accelerator so as to produce a hydraulic pressure in 
proportion to the opening degree of a throttle (hereinafter, referred to 
as the throttle opening degree). The throttle modulator valve 147 reduces 
appropriately the hydraulic pressure produced by the throttle valve 146 
and supplies the reduced hydraulic pressure to the pressure regulator 
valve 102 so that a hydraulic pressure which matches the engine torque is 
obtained. 
The servo control valve 142 and the 2-3 timing valve 143 are provided for 
moderating the shock arising on the occasion of the speed change to the 
third speed from the second speed. In the event of the speed change to the 
third speed from the second speed, it is required that the fourth clutch 
device 27 is engaged and the first brake device 23 is disengaged and 
therefore the operation oil is supplied to both the fourth clutch device 
27 and the releasing chamber 23b of the hydraulic servo control device 
23A. However, in such case, since an orifice and an accumulator 148 are 
provided in a line for supplying the operation oil to the fourth clutch 
device 27 for the purpose of reducing the shock resulting from the 
engagement of the fourth clutch device 27, the operation oil which is 
supplied to the fourth clutch device 27 is apt to be delayed to affect 
with a proper hydraulic pressure on the fourth clutch device 27 and 
therefore it is feared that the timing of the engagement of the fourth 
clutch device 27 is undesirably delayed. Accordingly, the servo control 
valve 142 is provided in a line for supplying the operation oil to the 
releasing chamber 23b of the hydraulic servo control device 23A so as to 
receive the hydraulic pressure from the fourth clutch device 27 and 
prevent the operation oil from acting to the releasing chamber 23b of the 
hydraulic servo control device 23A until the hydraulic pressure from the 
fourth clutch device 27 becomes relatively high. 
The 2-3 timing valve 143 is operative to control the timing of the 
engagement of the fourth clutch device 27 in response to the throttle 
opening degree, so as to moderate the shock which is caused on the 
occasion on the speed change and unable to be moderated by the servo 
control valve 142. In fact, in the event of such a shift-up to the third 
speed from the second speed as arising when the throttle is returned 
quickly to reduce is opening degree at a relatively small opening degree, 
a quick engagement of the fourth clutch device 27 would give rise to a 
shock. In view of this, the 2-3 timing valve 143 is arranged for 
controlling the fourth clutch device 27 to have a relatively long engaging 
time when the throttle opening degree is small and a relatively short 
engaging time when the throttle opening degree is large. 
The 3-4 capacity valve 145 is provided for moderating the shock arising on 
the occasion of the shift-up to the fourth speed from the third speed. 
When the operation oil in the 3-4 shift valve 130 is drained through the 
solenoid valve 130b which is energized so that the 3-4 shift valve 130 is 
shifted to the 4the shift position from the 3rd shift position and 
therefore the operation oil in the second clutch device 21 is drained 
through the N-D accumulator 144, the neutral valve 160 and the 3-4 shift 
valve 130 and the operation oil in the releasing chamber 23b of the 
hydraulic servo control device 23A is drained through the orifice or the 
3-4 capacity valve 145 and the 3-4 shift valve 130. The drain of the 
operation oil from the releasing chamber 23b of the hydraulic servo 
control device 23A is controlled by the 3-4 capacity valve 145 so that the 
above mentioned shock is moderated. In the 3-4 capacity valve 145, a spool 
is placed at such a position as shown in FIG. 2 to connect a line l.sub.1 
with a line l.sub.2 at the beginning of a period of the drain of the 
operation oil from the releasing chamber 23b because the hydraulic 
pressure of the operation oil drained from the second clutch device 21 is 
still relatively large and accordingly the hydraulic pressure acting upon 
the 3-4 capacity valve 145 is kept relatively large. Therefore, the 
operation oil from the releasing chamber 23b is drained through the 3-4 
capacity valve 145. Then, when the drain of the operation oil from the 
releasing chamber 23b is advanced to a certain degree, the spool in the 
3-4 capacity valve 145 is moved to the left in the drawing to disconnect 
the line l.sub.1 from the line l.sub.2 and accordingly the operation oil 
from the releasing chamber 23b is drained through an orifice. Under such a 
control by the 3-4 capacity valve 145, the hydraulic pressure in the 
releasing chamber 23b of the hydraulic servo control device 23A is reduced 
rapidly at the beginning of the period of the drain of the operation oil 
from the releasing chamber 23b and then further reduced gradually during 
that period of the drain. Consequently, the first brake device 23 is 
controlled by the hydraulic servo control device 23A to have has a 
relatively long engaging time, so that the shock resulting from the 
engagement of the first brake device 23 is moderated. 
A 3-2 capacity valve 149 and a 3-2 timing valve 150 are provided for 
moderating the shock arising on the occasion of the shift-down to the 
second speed from the third speed in response to the throttle opening 
degree. In the 3-2 capacity valve 149, the hydraulic pressure from the 
throttle modulator valve 147 is applied to act against the total amount of 
the hydraulic pressure produced by a spring contained in the 3-2 capacity 
valve 149 and the hydraulic pressure of the drain of the operation oil 
from the releasing chamber 23b of the hydraulic servo control device 23A. 
Therefore, the drain of the operation oil from the releasing chamber 23b 
of the hydraulic servo control device 23A is controlled by the 3-2 
capacity valve 149 in such a manner that the operation oil from the 
releasing chamber 23b is drained through the 3-2 capacity valve 149 at the 
beginning of the period of the drain of the operation oil from the 
releasing chamber 23b and then further drained through an orifice. The 
operation oil drained from the 3-2 capacity valve 149 is controlled 
through the 3-2 timing valve 150 by the 2-3 shift valve 120. 
In the 3-2 timing valve 150, the hydraulic pressure from the throttle 
modulator valve 147 acts against the hydraulic pressure produced by a 
spring contained in the 3-2 timing valve 150. The operation oil having 
passed through or bypassed the 3-2 capacity valve 149 is drained through 
an orifice when the hydraulic pressure from the throttle modulator valve 
147 is higher than the hydraulic pressure produced by the spring contained 
in the 3-2 timing valve 150 and drained through the 3-2 timing valve 150 
when the hydraulic pressure from the throttle modulator valve 147 is equal 
to or lower than the hydraulic pressure produced by the spring contained 
in the 3-2 timing valve 150. In the situation wherein the hydraulic 
pressure from the throttle modulator valve 147 is higher than the 
hydraulic pressure produced by the spring contained in the 3-2 timing 
valve 150 and therefore the operation oil passes through the orifice, the 
operation oil from the releasing chamber 23b of the hydraulic servo 
control device 23A is drained gradually through the orifice. As a result, 
the first brake device 23 is controlled to have has a relatively long 
engaging time, so that the shock resulting from the engagement of the 
first brake device 23 is moderated. 
The operation of each of the solenoid valves 110b, 120b and 130b are 
controlled by a controller 200 which is constituted with, for example, a 
microcomputer, in response to at least one of the operating condition of 
the engine and the travelling condition of the vehicle. The controller 200 
is supplied with a turbine speed signal St obtained from a turbine speed 
sensor, throttle opening degree signal Sh obtained from a throttle sensor, 
shift position signal Sr obtained from a shift position sensor, and a 
vehicle speed signal Ss obtained from a speed sensor, to produces shift-up 
and shift-down signals selectively based on the signals St, Sh, Sr and Ss 
and forwards the shift-up or shift-down signal to the solenoid valves 
110b, 120b and 130b when the speed change is carried out. 
Further, for the purpose of moderating effectively the shock arising on the 
occasion of the speed change, for example, to the second speed from the 
third speed which is performed by causing the operation oil in the 
releasing chamber 23b of the hydraulic servo control device 23A to be 
drained and also improving the responsibility for the timing of each speed 
change, the controller 200 is operative to supply a control signal 
obtained in response to, for example, the vehicle travelling speed to the 
solenoid valve 110b when the third speed is selected in the multi-stage 
power transmitting gear arrangement 10, so as to cause the hydraulic servo 
control device 23A to be in a first condition wherein the operation oil is 
supplied to the releasing chamber 23b thereof and in a second condition 
wherein the operation oil is drained from the releasing chamber 23b 
thereof selectively in response to the travelling condition of the 
vehicle. 
FIG. 3 shows the flow of such control operation for supplying the control 
signal to the solenoid valve 110b by the controller 200. In this control 
operation, first, it is checked based on the shift position signal Sr 
whether the third speed is selected in the multi-stage power transmitting 
gear arrangement 10 or not in decision D1. When the third speed is 
selected, the vehicle speed signal Ss is stored in process P1 and then it 
is checked based on the vehicle speed signal Ss whether a vehicle 
travelling speed VN is equal to or higher than 40 km/h or not in decision 
D2. To the contrary, if it is clarified in the decision D1 that the third 
speed in not selected in the multi-stage power transmitting gear 
arrangement 10, the check at the decision D1 is repeated. 
When it is clarified in the decision D2 that the vehicle travelling speed 
VN is equal to or higher than 40 km/h, that is, the vehicle travels at 
high speed, a first group of control signals by which the solenoid valve 
110b is energized and both of the solenoid valves 120b and 130b are 
deenergized, as shown in Table 2, are forwarded to the solenoid valves 
110b, 120b and 130b,respectively, in process P2. On the other hand, if it 
is clarified in the desicion D2 that the vehicle travelling speed VN is 
lower than 40 km/h, that is, the vehicle travels at low speed, a second 
group of control signals by which the solenoid valves 110b, 120b and 130b 
are deenergized, as shown in Table 2, are forwarded to the solenoid valves 
110b, 120b and 130b, respectively, in process P3. 
TABLE 2 
______________________________________ 
Solenoid Solenoid Solenoid 
valve 110b 
valve 120b valve 130b 
______________________________________ 
First group 
energized deenergized deenergized 
of control 
signals 
Second group 
deenergized deenergized deenergized 
of control 
signals 
______________________________________ 
As described above, when the vehicle travels at high speed (equal to or 
higher than 40 km/h) with the shift position selecting the third speed, 
the solenoid valve 110b is energized so as to supply previously the 
operation oil to the applying chamber 23a of the hydraulic servo control 
device 23A. Accordingly, the first brake device 23 can be engaged quickly 
when the solenoid valve 130b is energized to cause the operation oil in 
the releasing chamber 23b of the hydraulic servo control device 23A to be 
drained through the solenoid valve 130b for the purpose of engaging the 
first brake device 23 so that the shift-down to the second speed from the 
third speed is carried out. Futher, when the vehicle travels at low speed 
(lower than 40 km/h) with the shift position selecting the third speed, 
the solenoid valve 110b is deenergized so as to prevent the operation oil 
from being supplied therethrough to the applying chamber 23a and cause the 
operation oil to be drained from the applying chamber 23a. Accordingly, 
the operation oil is commenced to be supplied to the applying chamber 23a 
when the solenoid valve 110b is turned to be energized for the shift-down 
to the second speed from the third speed and therefore the first brake 
device 23 has a relatively long engaging time so that the shock resulting 
from the engagement of the first brake device can be moderated 
effectively. 
In such a control operation, the first brake device 23 is in its 
disengaging state regardless of the condition of the operation oil in the 
applying chamber 23a when the operation oil is supplied to the releasing 
chamber 23b and then changed to be in its engaging state when the 
operation oil is supplied to the applying chamber 23a and simultaneously 
the operation oil in the releasing chamber 23b is drained. In this 
connection, a period of time necessitated for completion of the engagement 
of the first brake device 23 is influenced to be varied in length by the 
presence or absence of the operation oil in the applying chamber 23a, and 
therefore the timing of the engagement of the first brake device 23 can be 
appropriately set by controlling the presence and absence of the operation 
oil in the applying chamber 23a previously in response to the vehicle 
travelling speed. 
Accordingly, with a control device which includes the controller 200 and 
the solenoid valve 110b and is operative to cause the hydraulic servo 
control device 23A to be in the first condition wherein the operation oil 
is supplied to the applying chamber 23a and in the second condition 
wherein the operation oil is drained from the applying chamber 23a 
selectively in response to the vehicle travelling speed, a quick response 
to the speed change can be obtained when the vehicle travels at high speed 
and the shock caused on the occasion of the speed change can be 
effectively moderated when the vehicle travels at low speed. 
Although the aforementioned control to the applying chamber 23a of the 
hydraulic servo control device 23A is performed in response to the vehicle 
travelling speed, it is also possible to apply an engine load or the like 
representing the operating condition of the engine for the control in 
place of the vehicle travelling speed. In the control performed in 
response to the engine load, the operation oil is supplied to the applying 
chamber 23a of the hydraulic servo control device 23A so that the quick 
response for the speed change is obtained when the engine load is 
relatively heavy and the operation oil in the applying chamber 23a is 
drained so that the shock caused on the occasion of the speed change is 
moderated when the engine load is relatively light. 
Further, the timing of the shift-up to the third speed from the second 
speed which caused with the operation oil supplied to the releasing 
chamber 23b of the hydraulic servo control device 23A can be also 
appropriately controlled by selecting the condition of the operation oil 
in the applying chamber 23a of the hydraulic servo control device 23A. 
In the embodiment shown in FIG. 2, the N-D accumulator 144 is provided to 
be connected with lines for supplying the operation oil to the first and 
second clutch devices 20 and 21 for delaying slightly the supply of the 
operation oil to the second clutch device 21 compared with the supply of 
the operation oil to the first clutch device 20. With such a control by 
the N-D accumulator 144, the second clutch device 21 is prevented from 
being engaged prior to the engagement of the first clutch device 20 and 
thereby worn abnormally when the selector valve 103 is moved to the D 
shift position from the N shift position under the situation wherein the 
throttle opening degree is rapidly increased. 
Further, a lock-up control valve 151 is provided in a line for supplying 
the operation oil to the lock-up clutch diveice 29. In the lock-up control 
valve 151, the hydraulic pressure of the operating oil supplied through 
the line is applied to act against the total amount of the hydraulic 
pressure produced by a spring contained in the lock-up control valve 151 
and the hydraulic pressure applied to the first clutch device 20. The 
lock-up clutch device 29 is provided with an applying chamber and a 
releasing chamber each connected to the lock-up control valve 151. When 
the operation oil in the releasing chamber of the lock-up clutch device 29 
is drained through the lock-up control valve 151 controlled by a solenoid 
valve 151a which is in its energized state, the lock-up clutch device 29 
is in the lock-up state.