Control system for automatic transmission

A control system for an automatic transmission which includes a fluid transmission unit. The control system includes a clutch applied in a forward running range; a hydraulic servo for applying the clutch responsive to an oil pressure; input and output R.P.M. sensors for detecting the input and output R.P.M.s of the fluid transmission unit; a stop state detector for detecting that the vehicle is stopped; a start detector for detecting start of the vehicle from a stop; and a control unit for controlling the oil pressure fed to the hydraulic servo. The oil pressure of the hydraulic servo is reduced, when the vehicle is stopped, to establish a neutral control state in which the clutch is released. A completely applied state of the clutch is established by boosting the oil pressure fed to the hydraulic servo when the shift of the vehicle from a stop to start is detected, in two stages. In the first stage the oil pressure fed to the hydraulic servo is boosted by adding a set shelf pressure to the base pressure until the clutch comes into a partially applied state and then, in the second stage, the oil pressure fed to the hydraulic servo is further boosted until the clutch becomes completely applied.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a control system for an automatic 
transmission. 
2. Prior Art 
A typical prior art automatic transmission includes a torque converter, 
acting as a fluid transmission unit for receiving the rotation generated 
by an engine, and a speed change unit for changing the speed of the 
rotation transmitted from the torque converter. The speed change unit has 
a planetary gear unit composed of gear elements for changing the speed in 
accordance with a shift pattern determined in accordance with the vehicle 
speed, the throttle opening and so on. 
The automatic transmission allows for selection of ranges including a P 
(parking) range, a R (reverse) range, a N (neutral) range, a D (drive) 
range, a S (second) range and a L (low) range. If the range is changed 
from the N-range to the D-range by the shift lever, for example, the 
rotation of the engine at idle is transmitted through the torque converter 
to the gear change unit, to cause a "creep phenomenon" wherein the vehicle 
inches forward without the accelerator pedal being depressed. 
The prior art seeks to prevent such a creep phenomenon by releasing a 
forward clutch, i.e. a first clutch which is applied in the forward ranges 
of the speed change unit (as disclosed in Japanese Patent Laid-Open No. 
21458/1986). The release of the first clutch is effected by reducing the 
oil pressure of the hydraulic servo of the first clutch when one of the 
D-range, the S-range and the L-range (hereinafter "forward running range") 
is selected while the vehicle is substantially stopped. 
If the oil pressure fed to the hydraulic servo of the first clutch is 
abruptly boosted to shift the first clutch from a released state to a 
completely applied state, the engine R.P.M. drops, or a serious shock 
occurs as the first clutch is applied. On the other hand, if the oil 
pressure fed to the hydraulic servo of the first clutch is gradually 
boosted, the time period until the end of the application of the first 
clutch is prolonged to cause engine racing. 
Thus, an oil pressure lower than that at the end of the application of the 
first clutch is fed to the hydraulic servo for a predetermined time period 
to establish a partially applied state, and the oil pressure is then 
boosted to end the application of the first clutch. In this case, the oil 
pressure for establishing the partially applied state is set by adding a 
shelf pressure to the oil pressure (hereinafter "base pressure") at the 
instant when the starting action is detected. The shelf pressure is set to 
avoid both engaging shock and engine racing. 
In the control system for the automatic transmission of the prior art, 
however, the oil pressure fed to the hydraulic servo is fed back and 
slightly adjusted so as to maintain the released state of the first 
clutch. As a result, the aforementioned base pressure fluctuates to cause 
engaging shock and engine racing. 
For example, if the application is started when the first clutch is in a 
relatively released state, the time period for completing the application 
of the first clutch is prolonged because of the low base pressure so that 
engine racing occurs. On the other hand, if application is started when 
the first clutch is in a relatively applied state, engaging shock is 
caused because of the high base pressure. 
SUMMARY OF THE INVENTION 
The present invention has as its objective solution of the aforementioned 
problems of the prior art control systems, i.e. to provide a control 
system for an automatic transmission which is free from engaging shock and 
engine racing in the case of a transition of a first clutch from the 
released state to the completely applied state. 
In order to achieve the above-described objective, the present invention, 
in one aspect, provides a control system for an automatic transmission, 
including a fluid transmission unit, which includes: a clutch which is 
applied responsive to selection of a forward running range; a hydraulic 
servo for applying the clutch when fed with an oil pressure; an input 
R.P.M. sensor for detecting the input R.P.M. of the fluid transmission 
unit; an output R.P.M. sensor for detecting the output R.P.M. of the fluid 
transmission unit; stop state detection means for detecting that the 
vehicle has stopped; start detection means for detecting a shift of the 
vehicle from stopped to start; and a control unit for controlling the oil 
pressure fed to the hydraulic servo. The oil pressure of the hydraulic 
servo is reduced, when the vehicle is at a stop, to establish a neutral 
control state in which the clutch is released. 
The control system further includes clutch release means for releasing the 
clutch by reducing the oil pressure fed to the hydraulic servo, responsive 
to detection of a stop, and clutch application means for completely 
applying the clutch by boosting the oil pressure fed to the hydraulic 
servo, when a shift of the vehicle from a stop to start is detected. 
The clutch release means includes: differential rotation calculation means 
for calculating the difference between the input R.P.M. of the fluid 
transmission unit and the output R.P.M. of the fluid transmission unit 
("differential rotation"); differential rotation change decision means for 
deciding whether or not the differential rotation has changed; pressure 
boosting means for boosting the oil pressure fed to the hydraulic servo if 
it is decided that the differential rotation has not changed; pressure 
reducing means for reducing the oil pressure fed to the hydraulic servo if 
it is decided that the differential rotation has changed; and base 
pressure storage means for storing the detected oil pressure, before 
reduction, as a base pressure, when the oil pressure fed to the hydraulic 
servo is boosted by the pressure boosting means and then reduced by the 
pressure reducing means. 
On the other hand, the clutch application means includes: first clutch 
pressure boosting means for boosting the oil pressure fed to the hydraulic 
servo, by adding set shelf pressure increments to the base pressure until 
the clutch comes into a partially applied state after detection of a shift 
of the vehicle from a stop to start; and second clutch pressure boosting 
means for further boosting the oil pressure fed to the hydraulic servo, 
until the clutch becomes completely applied subsequent to the partially 
applied state. 
Preferably, the control system of the present invention also includes an 
oil temperature sensor for detecting the oil temperature of the automatic 
transmission. If the oil temperature is excessively low, for example, the 
viscosity of the oil is far higher than ordinary and causes a high 
dragging resistance. The result may be an erroneous decision that the 
application of the clutch has been started when the clutch application has 
not actually started. In this case, the base pressure storage means stores 
an oil pressure, as the base pressure, which is lower than that for the 
actual start of the clutch application. As a result, the time period until 
the end of the clutch application is prolonged to cause engine racing due 
to the delay in the engagement. Therefore, if the oil temperature is lower 
than the set value, the oil pressure corresponding to the normal oil 
temperature, as stored, is used as the base pressure. As a result, it is 
possible to prevent engine racing. 
The base pressure storage means updates the base pressure if the oil 
temperature is higher than the set value, each time the oil pressure fed 
to the hydraulic servo is boosted by the pressure boosting means and then 
reduced by the pressure reducing means, and holds the stored base pressure 
without change if the oil temperature is lower than the set value. Thus, 
if the oil pressure fed to the hydraulic servo is boosted by the pressure 
boosting means and then reduced by the pressure reducing means, the oil 
pressure before reduction is used as the base pressure. When the oil 
pressure fed to the hydraulic servo is boosted by the pressure boosting 
means and then reduced by the pressure reducing means, the clutch just 
starts to be applied. Therefore, if the oil pressure before reduction is 
used as the base pressure, the oil pressure at the instant of starting the 
application of the clutch is used as the base pressure. Thus, the oil 
pressure at the time of starting the clutch application is used as the 
base pressure so that the base pressure will not fluctuate and the 
partially applied state of the clutch can be stably achieved at all times. 
This makes it possible to prevent engaging shock and engine racing. 
When the oil pressure controlled by the control system is fed to the 
hydraulic servo the clutch is applied, whereby the rotation of the engine 
is transmitted to the speed change unit through the fluid transmission 
unit and the clutch. 
While the clutch is released, the oil pressure fed to the hydraulic servo 
can be boosted to apply the clutch, if the difference between the input 
R.P.M. and the output R.P.M. has not changed, but can be reduced to 
release the clutch if the difference has changed. Moreover, when the oil 
pressure fed to the hydraulic servo is reduced, the oil pressure before 
the reduction is used as the base pressure. 
When start of a shift of the vehicle from stop to start state is detected, 
the shelf pressure, as set to the base pressure, is fed to the hydraulic 
servo so that the oil pressure is boosted to bring the clutch into a 
partially applied state. Subsequently, the oil pressure fed to the 
hydraulic servo is further boosted to bring the clutch into the completely 
applied state.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiments of the present invention will now be described in 
detail with reference to FIG. 1. 
As shown in FIG. 1, the automatic transmission includes: a torque converter 
12 acting as a fluid transmission unit for transmitting the rotation of 
engine 10 to a speed change unit 16; a first clutch C1 which is applied 
when a forward running range is selected; a hydraulic servo C-1 for 
applying the first clutch C1 upon receipt of oil pressure; an input R.P.M. 
sensor 91 for detecting the input R.P.M. of the torque converter 12; an 
output R.P.M. sensor 92 for detecting the output R.P.M. of the torque 
converter 12; stop state detection means 93 for detecting that the vehicle 
has stopped; start state detection means 94 for detecting the shift of the 
vehicle from a stop to a start; and a control unit 95 for controlling the 
oil pressure fed to the hydraulic servo C-1. 
The control unit 95 includes: clutch release means 951 for releasing the 
first clutch C1 by reducing the oil pressure to the hydraulic servo C-1, 
when the vehicle is detected to be stopped; and clutch application means 
952 for applying the first clutch C1 by boosting the oil pressure fed to 
the hydraulic servo C-1 when a shift of the vehicle from stop to start is 
detected. 
The clutch release means 951 is composed of: differential rotation 
calculation means 953 for calculating the difference, i.e. "differential 
rotation," between the input R.P.M. and the output R.P.M.; differential 
rotation change decision means 954 for deciding whether or not the 
differential rotation has changed; pressure boosting means 955 for 
boosting the oil pressure fed to the hydraulic servo C-1 if it is decided 
that the differential rotation has not changed; pressure reducing means 
956 for reducing the oil pressure fed to the hydraulic servo C-1 if it is 
decided that the differential rotation has changed; and base pressure 
storage means 958 for storing, in a storage unit 957, the oil pressure 
before reduction, as a base pressure, when the oil pressure fed to the 
hydraulic servo C-1 is boosted by the pressure boosting means 955 and then 
reduced by the pressure reducing means 956. 
The clutch application means 952 is composed of: first clutch pressure 
boosting means 959 for boosting the oil pressure fed to the hydraulic 
servo C-1, by adding the shelf pressure, set to the base pressure, until 
the first clutch C1 is brought to a partially applied state after 
detection of shift of the vehicle from a stop to a start; and second 
clutch pressure boosting means 960 for further boosting the oil pressure 
fed to the hydraulic servo C-1 until the first clutch C1 becomes 
completely applied. 
As shown in FIG. 2, the rotation generated by the engine 10, is transmitted 
through an output shaft 11 to the torque converter 12, acting as the fluid 
transmission unit. The torque converter 12 transmits the rotation of the 
engine 10 to an output shaft 14 through a fluid (or working oil). However, 
if the vehicle speed exceeds a set value, a lockup clutch L/C is applied 
so that the rotation can be transmitted directly to the output shaft 14. 
The output shaft 14 is connected to the speed change unit 16. The speed 
change unit 16 includes a main transmission 18 for establishing three 
forward and one reverse gear stages, and an underdrive auxiliary 
transmission 19. The rotation of the main transmission 18 is transmitted 
through a counter drive gear 21 and a counter driven gear 22 to the 
auxiliary transmission 19, the output shaft 23 of which transmits its 
rotation through an output gear 24 and a ring gear 25 to a differential 
unit 26. 
In differential unit 26, the rotation, as received from the output gear 24 
and the ring gear 25, is differentiated so that the differential rotations 
are transmitted through left and right drive shafts 27 and 28 to the drive 
wheels (not shown). 
The main transmission 18 has a first planetary gear unit 31, a second 
planetary gear unit 32, a first clutch C1, a second clutch C2, a first 
brake B1, a second brake B2, a third brake B3, a one-way clutch F1 and a 
one-way clutch F2 for transmitting the torque selectively between the 
individual components of the two planetary gear units 31 and 32. 
The first planetary gear unit 31 is composed of: a ring gear R1 connected 
to drive unit case 34 through the third brake B3 and the one-way clutch 
F2, arranged in parallel; a sun gear 2 formed on a sun gear shaft 36 
fitted on and rotatably supported by the outer shaft 14; a carrier 
CR.sub.1 connected to the counter drive gear 21; and pinions P.sub.1A and 
P.sub.1B interposed to mesh with each other between the ring gear R.sub.1 
and the sun gear 2 and rotatably supported by the carrier CR.sub.1. 
The sun gear shaft 36 is connected through the second clutch C2 to the 
output shaft 14 and is further connected through the first brake B1 to the 
drive unit case 34 and through the one-way clutch F1 and the second brake 
B2, arranged in series with each other, to the drive unit case 34. 
On the other hand, the second planetary gear unit 32 is composed of: a ring 
gear R.sub.2 connected through the first clutch C1 to the output shaft 14; 
a sun gear 4 formed on the sun gear shaft 36 integrally with the sun gear 
2; a carrier CR.sub.2 connected to the carrier CR.sub.1 ; and a pinion 
P.sub.2 interposed to mesh with the ring gear R.sub.2 and the sun gear 4, 
rotatably supported by the carrier CR.sub.2 and formed integrally with the 
pinion P.sub.1B. 
The counter drive gear 21 is in meshing engagement with the counter driven 
gear 22 in the auxiliary transmission 19, to transmit the rotation, 
received from the main transmission 18, to the auxiliary transmission 19. 
Auxiliary transmission 19 includes a third planetary gear unit 38, a third 
clutch C3, a fourth brake B4 and a one-way clutch F3 for transmitting the 
torque selectively between the individual components of the third 
planetary gear unit 38. 
The third planetary gear unit 38 is composed of: a ring gear R.sub.3 
connected to the counter driven gear 22; a sun gear 6 formed on a sun gear 
shaft 39 fitted rotatably on the output shaft 23; a carrier CR.sub.3 fixed 
on the output shaft 23; and a pinion P.sub.3 interposed between the ring 
gear R.sub.3 and the sun gear 6 and rotatably supported by the carrier 
CR.sub.3. 
The operations of the above-described automatic transmission will now be 
described with reference to FIG. 3 wherein: S1 is the first solenoid 
valve; S2 is the second solenoid valve; S3 is the third solenoid valve; C1 
is the first clutch; C2 is the second clutch; C3 is the third clutch; B1 
is the first brake; B2 is the second brake; B3 is the third brake; B4 is 
the fourth brake; and F1 to F3 are the one-way clutches. Moreover: R is 
reverse range; N is the neutral range; D is the drive range; 1ST is a gear 
stage at the 1st speed; 2ND is a gear stage at the 2nd speed; 3RD is a 
gear stage at the 3rd speed; and 4TH is a gear stage at the 4th speed. 
Symbols "O" indicate that a first solenoid signal S.sub.1, a second 
solenoid signal S.sub.2 and a third solenoid signal S.sub.3 for 
opening/closing the first solenoid valve S1, the second solenoid valve S2 
and the third solenoid valve S3, respectively, are ON; that the first 
clutch C1, the second clutch C2, the third clutch C3, the first brake B1, 
the second brake B2, the third brake B3 and the fourth brake B4 are 
applied; and that the one-way clutches F1 to F3 are locked. 
On the other hand, symbols "X" indicate: that the first solenoid signal 
S.sub.1, the second solenoid signal S.sub.2 and the third solenoid signal 
S.sub.3 for opening/closing the first solenoid valve S1, the second 
solenoid valve S2 and the third solenoid valve S3, respectively, are OFF; 
that the first clutch C1, the second clutch C2, the third clutch C3, the 
first brake B1, the second brake B2, the third brake B3 and the fourth 
brake B4 are released; and that the one-way clutches F1 to F3 are free. 
Incidentally, symbols ".DELTA." indicate ON/OFF for when the neutral 
control state is established, and a parenthesized circle "(O)" indicates 
that the third brake B3 is applied at the time of engine braking. 
At the 1st speed in the D-range, the first clutch C1 and the fourth brake 
B4 are applied to lock the one-way clutches F2 and F3. Then, the rotation 
of the output shaft 14 is transmitted through the first clutch C1 to the 
ring gear R.sub.2. In this state, the rotation of the ring gear R.sub.1 is 
blocked by the one-way clutch F2 so that the rotation of the carrier 
CR.sub.2 is drastically decelerated, while rotating the sun gear 4 idly, 
and is transmitted to the counter drive gear 21. 
The rotation is transmitted from the counter drive gear 21 to the counter 
driven gear 22 to the ring gear R.sub.3. However, the rotation of the sun 
gear 6 is blocked by the fourth brake B4 so that the rotation of the 
carrier CR.sub.3 is further decelerated and transmitted to the output 
shaft 23. 
At the 2nd speed in the D-range, on the other hand, the first clutch C1, 
the first brake B1, the second brake B2 and the fourth brake B4 are 
applied to lock the one-way clutches F1 and F3. Then, the rotation of the 
output shaft 14 is transmitted through the first clutch C1 to the ring 
gear R.sub.2, and the rotation of the sun gear 4 is blocked by the second 
brake B2 and the one-way clutch F1. As a result, the rotation of the ring 
gear R.sub.2 is decelerated and transmitted to the carrier CR.sub.2, the 
rotation of which is transmitted to the counter drive gear 21 while 
rotating the ring gear R.sub.1 idly. 
As in 1ST speed, the rotation is transmitted from the counter drive gear 21 
to the counter driven gear 22 and then to the ring gear R.sub.3. However, 
in the 2nd speed also, the rotation of the sun gear 6 is blocked by the 
fourth brake B4 so that the rotation of the carrier CR.sub.3 is 
decelerated and transmitted to the output shaft 23. 
At the 3rd speed in the D-range, the first clutch C1, the third clutch C3, 
the first brake B1 and the second brake B2 are applied to lock the one-way 
clutch F1. Then, the rotation of the output shaft 14 is transmitted 
through the first clutch C1 to the ring gear R.sub.2, and the rotation of 
the sun gear 4 is blocked by the second brake B2 and the one-way clutch 
F1. As a result, the rotation of the ring gear R.sub.2 is decelerated and 
transmitted to the carrier CR.sub.2 so that the rotation of the carrier 
CR.sub.2 is transmitted to the counter drive gear 21 while rotating the 
ring gear R.sub.1 idly. 
Again, as in 1st and 2nd speeds, rotation is transmitted from the counter 
drive gear 21 to the counter driven gear 22 to the ring gear R3. However, 
the relative rotation of the carrier CR3 and the sun gear 6 is blocked by 
the third clutch C3 so that the third planetary gear unit 38 comes into a 
directly connected state. As a result, the rotation of the counter driven 
gear 22 is transmitted as is to the output shaft 23. 
At 4th speed in D-range, the first clutch C1, the second clutch C2, the 
third clutch C3 and the second brake B2 are applied. Then, the rotation of 
the output shaft 14 is transmitted through the first clutch C1 to the ring 
gear R.sub.2 and through the second clutch C2 to the sun gear 4, so that 
the first planetary gear unit 31 and the second planetary gear unit 32 
come into the directly connected state. As a result, the rotation of the 
output shaft 11 is transmitted as is to the counter drive gear 21. 
As in the lower speeds, rotation is transmitted from the counter drive gear 
21 to the counter driven gear 22 to the ring gear R.sub.3. However, the 
relative rotation of the carrier CR.sub.3 and the sun gear 6 is blocked by 
the third clutch C3 so that the third planetary gear unit 38 comes into 
the directly connected state. As a result, the rotation of the counter 
driven gear 22 is transmitted as is to the output shaft 23. 
The automatic transmission, as is conventional, also includes a hydraulic 
circuit for applying/releasing the first clutch C1, the second clutch C2, 
the third clutch C3, the first brake B1, the second brake B2, the third 
brake B3 and the fourth brake B4. The hydraulic circuit, in turn, is 
controlled by a hydraulic control unit 40. This hydraulic control unit 40 
corresponds to the control unit 95 of FIG. 1. 
On the other hand, the engine 10 is controlled by an electronic control 
unit 43. 
Both the hydraulic control unit 40 and the electronic control unit 43 are 
connected to an automatic transmission control unit (ECU) 41 so that they 
are operated according to the control program of the automatic 
transmission control unit 41. 
The automatic transmission control unit 41 receives signals from a neutral 
start switch (N.S.S.W.) 45, an oil temperature sensor 46, an R.P.M. sensor 
47, a brake switch 48, an engine R.P.M. sensor 49, a throttle opening 
sensor 50 and a vehicle speed sensor 51. Incidentally, the engine R.P.M. 
sensor 49 and the R.P.M. sensor 47 correspond to the input R.P.M. sensor 
91 and the output R.P.M. sensor 92 of FIG. 1, respectively. 
Thus, the shift position of the shift lever (not shown), i.e., the selected 
range, is detected by the neutral start switch 45; the temperature of the 
oil in the hydraulic circuit is detected by the oil temperature sensor 46; 
and the R.P.M. of the input side of the first clutch C1, i.e., the R.P.M. 
of the output shaft 14 (hereinafter "clutch input side R.P.M.") N.sub.C1, 
is detected by the R.P.M. sensor 47. 
Moreover, depression of the brake pedal is detected by the brake switch 48; 
the engine R.P.M. NE is detected by the engine R.P.M. sensor 49; the 
throttle opening .theta. is detected by the throttle opening sensor 50; 
and the vehicle speed is detected by the vehicle speed sensor 51. 
FIGS. 4 and 5 show a hydraulic circuit for use in the present invention 
which includes a primary valve 59 for adjusting the oil pressure coming 
from an oil pressure source and for outputting the adjusted oil pressure 
as the line pressure to a line L-21. A manual valve 55 is provided with 
ports 1, 2, 3, D, P.sub.L and R so that the line pressure fed from the 
primary valve 59 via lines L-21 and L-4 to the port P.sub.L is supplied as 
the 1-range pressure, the 2-range pressure, the 3-range pressure, the 
D-range pressure and the R-range pressure, respectively, at the ports 1, 
2, 3, D and R, by operating the shift lever. 
When the shift lever is placed in the forward drive position, the D-range 
oil pressure, supplied at port D, is fed via a line L-1 to the second 
solenoid valve S2, via a line L-2 to a 1-2 shift valve 57 and via a line 
L-3 to a B-1 sequence valve 56. On the other hand, the line pressure from 
the primary valve 59 is fed via the line L-21 to the third solenoid valve 
S3. 
Moreover, the line pressure from the line L-21 is fed via the line L-4 to a 
solenoid modulator valve 58 and further via a line L-5 to the first 
solenoid valve S1 and a 2-3 shift valve 60. 
The first solenoid signal S1, the second solenoid signal S2 and the third 
solenoid signal S3 for opening/closing the first solenoid valve S1, the 
second solenoid valve S2 and the third solenoid valve S3 are turned ON/OFF 
in response to the signals coming from the hydraulic control unit 40 (FIG. 
2), so that the first solenoid valve S1 feeds the signal oil pressure via 
a line L-8 to the 1-2 shift valve 57 and a 3-4 shift valve 62, the second 
solenoid valve S2 feeds the signal oil pressure via a line L-9 to the 2-3 
shift valve 60, and the third solenoid valve S3 feeds the signal oil 
pressure via a line L-10 to a neutral relay valve 64. 
The 1-2 shift valve 57 takes the depicted upper half position in the 1st 
speed and the depicted lower half position in the 2nd ton 4th speeds; the 
2-3 shift valve 60 takes the lower half position at the 1st and 2nd speeds 
and the upper half position at the 3rd and 4th speeds; the 3-4 shift valve 
62 takes the upper half position at the 1st and 4th speeds and the lower 
half position at the 2nd and 3rd speeds; and the neutral relay valve 64 
takes the upper half position in the neutral control state and the lower 
half position at the 1st to 4th speeds. 
The solenoid module valve 58 is connected via a line L-12 to a linear 
solenoid valve 66, which is connected via a line L-13 to a C-1 control 
valve 67. The linear solenoid valve 66 is further connected via a line 
L-22 to the primary valve 59. 
In response to the signal from the hydraulic control unit 40, the linear 
solenoid valve 66 is controlled to feed a throttle pressure PTH as the 
control oil pressure to the control valve 67 via the line L-13. On the 
other hand, the C-1 control valve 67 is fed with the D-range pressure via 
the lines L-3 and L-14, adjusts the received D-range pressure to an oil 
pressure P.sub.C1 (hereinafeter the "C-1 oil pressure"), in accordance 
with the throttle pressure P.sub.TH coming from the linear solenoid valve 
66, and feeds the adjusted oil pressure P.sub.C1 through line L-15 and 
through the neutral relay valve to the hydraulic servo C-1. 
The B-1 sequence valve 56 has a spring, located at its left end, applying a 
load on the spool, and a control oil chamber, located at its right end. 
The control oil chamber of the B-1 sequence valve 56 receives the D-range 
pressure via the line L-3 and takes the lower half position at the 1st 
speed. When the oil pressure is fed at the 2nd speed to the hydraulic 
servo B-2 so that its pressure rises, the B-1 sequence valve 56 is fed 
with the sequence pressure from the hydraulic servo B-2 so that it has its 
spool pushed to the right by the sequence pressure and the spring load to 
take the upper half position. 
As a result, the oil pressure from the 1-2 shift valve 57 is fed through 
the B-1 sequence valve 56 to the 3-4 shift valve 62 and further through 
the 1-2 shift valve 57 and the neutral relay valve 64 to a hydraulic servo 
B-1. Thus, the hydraulic servo B-1 receives an oil pressure in accordance 
with the rise of the oil pressure in the hydraulic servo B-2. 
The neutral relay valve 64 takes the upper half position when in the 
neutral control state. In this neutral control state, therefore, the C-1 
oil pressure P.sub.C1 is fed through line L-15, line L-16, neutral relay 
valve 64 and line L-17 to the hydraulic servo C-1. Moreover, the oil at 
the C-1 oil pressure P.sub.C1 is fed via lines L-23 and L-24 to a B-1 
control valve 70. 
The neutral relay valve 64 takes the lower half position at the 1st to 4th 
speeds. At the 1st to 4th speeds, therefore, oil at D-range pressure is 
fed through the line L-3, the neutral relay valve 64 and the line L-17 to 
the hydraulic servo C-1. In the neutral control state, on the other hand, 
the neutral relay valve 64 is switched to the upper half position to 
connect the line L-16 and the line L-17. 
A damper valve 68 is provided in the line L-17 for smoothing the discharge 
pressure of the oil from the hydraulic servo C-1. Hydraulic servo B-1 
operates the first brake B1. Hydraulic servo B-2 operates the second brake 
B2. Hydraulic servo B-4 operates the fourth brake B4. 
In the main routine, illustrated in FIG. 6, simultaneously as the ignition 
of the engine 10 (FIG. 2) is turned ON, the main routine is started to 
repeat the N-D change control and the neutral control until the ignition 
is turned OFF. 
Step S1: The N-D change control is executed; and 
Step S2: The neutral control is executed. 
The N-D change control subroutine of Step S1 of FIG. 6 will now be 
described with reference to FIGS. 7-11. In FIG. 7: 
Step S1-1: The start detection means 94 (FIG. 1) decides, on the basis of 
the signal from the neutral start switch 45 (FIG. 2), whether or not the 
N-D change has been initiated by starting from a stop. This N-D change 
control subroutine advances to Step S1-2, if the N-D change has been made, 
but is ended if NOT. 
Step S1-2: The clutch input side R.P.M. NC1S at the N-D change time is 
detected by the input R.P.M. sensor 91. 
Step S1-3: The third solenoid signal S3 for opening/closing the third 
solenoid valve S3 is turned ON. 
Step S1-4: The throttle pressure P.sub.TH according to the input torque is 
output with reference to the map of FIG. 9. On the other hand, the 
throttle pressure P.sub.TH is output at idling ON with reference to the 
map of FIG. 10 and at idling OFF with reference to the map of FIG. 11. 
Step S1-5: The current clutch input side R.P.M. N.sub.C1 is detected, and 
it is decided whether or not the difference between the clutch input side 
R.P.M. N.sub.C1S at the time of a N-D change, and the detected clutch 
input side R.P.M. N.sub.C1 (N.sub.C1S -N.sub.C1) exceeds a set value 
.DELTA.N.sub.R1. The subroutine advances to Step S1-7, if the value 
(N.sub.C1S -N.sub.C1) is over the set value .DELTA.N.sub.R1, but to Step 
S1-6 if the value (N.sub.C1S -N.sub.C1) is below the set value 
.DELTA.N.sub.R1. 
Step S1-6: It is decided whether or not the throttle opening .theta. is 
over a set value .theta..sub.R. The subroutine advances to Step S1-7, if 
the throttle opening .theta. is over the set value .theta..sub.R, but 
returns to Step S1-4 if the throttle opening .theta. is below the set 
value .theta..sub.R. 
.DELTA.N.sub.R1 is set to the value at which the first clutch C1 starts its 
application (or engagement) after the piston of the hydraulic servo C-1 
has reached the end of its stroke, and .theta..sup.R is set to a value 
which indicates that the driver intends to start. 
Thus, in the state where the first clutch C1 has not yet started to engage, 
the subroutine advances to Step S1-7 when the accelerator pedal is 
depressed to increase the throttle opening .theta.. 
Step S1-7: The speed ratio e of the torque converter 12 is calculated from 
the engine R.P.M. N.sub.E and the turbine R.P.M. N.sub.T using the 
following Equation: 
EQU e=N.sub.E /N.sub.T. (I) 
A map is utilized to read out a torque ratio t.sub.R and a capacity 
coefficient C which correspond to the speed ratio e, and an output torque 
T.sub.O is calculated by the following Equation, in which letter i 
designates the gear ratio of the speed change unit 16: 
EQU T.sub.O =t.sub.R .multidot.C.multidot.N.sub.E.sup.2 .multidot.i 
Step S1-8: It is decided whether or not the output torque T.sub.O is below 
a preset N-D control end torque T.sub.ND. The subroutine advances to Step 
S1-10, if the output torque T.sub.O is below the preset N-D control end 
torque T.sub.ND, but to Step S1-9 if the output torque T.sub.O is over the 
preset N-D control end torque T.sub.ND. 
Step S1-9: It is decided whether or not the neutral control starting 
conditions are satisfied. The subroutine is ended to quickly execute the 
neutral control of Step S2 of FIG. 6, if all the starting conditions are 
satisfied, but advances to Step S1-10 if NOT. 
The starting conditions which must be satisfied are: the accelerator pedal 
is released so that the throttle opening .theta. is below a predetermined 
value; the oil temperature detected by the oil temperature sensor 46 is 
over a predetermined value; and the brake pedal is depressed to turn ON 
the brake switch 48. 
Step S1-10: The throttle pressure P.sub.TH is swept up. In this case, the 
application of the first clutch C1 is continued by changing the control 
oil pressure from the linear solenoid valve 6 (FIG. 4) to boost the C-1 
oil pressure P.sub.C1 and by boosting the C-1 oil pressure P.sub.C1 by a 
set pressure .DELTA.P each lapse of time t. 
Step S1-11: It is decided on the basis of the output R.P.M. N.sub.O of the 
speed change unit 16 whether or not the application of the first clutch C1 
has ended. In this case, the R.P.M. of the output side of the first clutch 
C1 is estimated as N.sub.O .multidot.i, wherein i is the gear ratio of the 
speed change unit 16. Hence, it is decided whether or not the clutch input 
side R.P.M. N.sub.C1 is smaller than the sum of the output side R.P.M. 
N.sub.O .multidot.i and a set value .DELTA.N.sub.R2 : 
N.sub.C1 .ltoreq.N.sub.O .multidot.i+.DELTA.N.sub.R2. 
The subroutine advances to Step S1-13, if the application of the first 
clutch C1 has ended, but to Step S1-12 if NOT. 
Step S1-12: It is decided whether or not the throttle pressure P.sub.TH has 
reached a set value P.sub.THR. The subroutine advances to Step S1-13, if 
the throttle pressure P.sub.TH has reached the set value P.sub.THR, but 
returns to Step S1-7, if NOT. 
Step S1-13: The third solenoid signal S.sub.3 is turned OFF. 
Step S1-14: The throttle pressure P.sub.TH is returned to the normal value 
corresponding to the gear stage, the throttle opening .theta. and so on. 
In the N-D change, the application of the first clutch C1 is started when 
the third solenoid signal S.sub.3 for opening/closing the third solenoid 
valve S3 (FIG. 5) is turned ON so that the C-1 oil pressure PC1 
corresponding to the input torque is fed to the hydraulic servo C-1. Then, 
as the clutch input side R.P.M. NC1 is reduced and as the throttle opening 
.theta. is increased by depression of the accelerator pedal by the driver, 
the C-1 oil pressure PC1 is gradually boosted. 
At the end of the application of the first clutch C1, the third solenoid 
signal S.sub.3 is then turned OFF to start the vehicle. 
Meanwhile, the output torque T.sub.O is calculated, and it is decided if 
the starting conditions for neutral control are satisfied, when the 
calculated output torque T.sub.O is over the N-D control ending torque 
T.sub.ND. If the starting conditions are satisfied, the subroutine quickly 
shifts to the neutral control. In case the N-D change is made, therefore, 
performance is improved because the neutral control is not started before 
the output torque TO exceeds the N-D control ending torque TND so that the 
driver feels the N-D change. 
After the N-D change, the subroutine quickly goes to the neutral control if 
the conditions for starting the neutral control are satisfied, so that the 
effects of reduction of fuel consumption and suppression of the vibration 
are enhanced. 
The neutral control subroutine which is Step S2 of FIG. 6 will now be 
described with reference to FIGS. 13 and 25. In FIG. 13: 
Step S2-1: The release state establishing means 951 (FIG. 1) executes the 
first clutch release control. In this case, with the vehicle speed zero 
being assumed at zero, the 2nd speed shift output signal is issued at a 
set time to start the applications of the second brake B2 (FIG. 2) and the 
third brake B3, to thereby effect the hill hold control. Further, the 
throttle pressure P.sub.TH is swept down at a set timing. 
For these operations, the engine R.P.M. N.sub.E corresponding to the input 
torque is determined, and the throttle pressure P.sub.TH, corresponding to 
the engine R.P.M. N.sub.E, is determined and set to a set oil pressure 
P.sub.1 so that the C-1 oil pressure P.sub.C1 is also set to P.sub.1 and 
then is gradually reduced. 
The input torque can be detected, not only from the engine R.P.M. N.sub.E, 
but also indirectly from the engine air intake, the fuel injection rate 
and so on. Moreover, the input torque of the speed change unit 16 can also 
be directly detected by a torque sensor (not-shown). In this case, the 
torque sensor is attached to the output shaft 14 of the torque converter 
12. 
Step S2-2: The clutch release means 951 executes the in-neutral control to 
establish the neutral control state. Here, stabilization of the engine 
R.P.M. N.sub.E and the clutch input side N.sub.C1 is awaited and the C-1 
oil pressure P.sub.C1 is then boosted or reduced by set pressure 
increments on the basis of those stabilized values for engine R.P.M. 
N.sub.E and clutch input side R.P.M. N.sub.C1. 
Step S2-3: The clutch application means 952 executes the first clutch apply 
control. In this case, the C-1 oil pressure P.sub.C1 is boosted by set 
increments, which are determined on the basis of the throttle opening, the 
engine R.P.M. N.sub.E and so on, to complete the piston stroke of the 
hydraulic servo C-1 (FIG. 5). After the completion of the piston stroke of 
the hydraulic servo C-1, the C-1 oil pressure P.sub.C1 is boosted by the 
set pressure increments to prevent shock. 
The first clutch release control subroutine, i.e. Step S2-1 of FIG. 13, 
will be described with reference to FIGS. 14 to 16. In FIGS. 14 and 15: 
Step S2-1-1: It is decided whether or not the third solenoid valve S3 is 
ON. The subroutine advances to Step S2-1-6, if ON, but to Step S2-1-2 if 
OFF. If the conditions for starting the neutral control are satisfied in 
the decision of Step S1-9 of FIG. 8, the third solenoid signal S.sub.3 is 
already ON so that the subroutine transfers directly to the neutral 
control to start the hill hold function. 
Step S2-1-2: The stop state decision means 93 (FIG. 1) estimates the 
vehicle speed to be zero on the basis of the change in the clutch input 
side R.P.M. N.sub.C1. 
Step S2-1-3: Satisfaction of the neutral control starting conditions, i.e., 
the conditions for starting the hill hold control and the neutral control, 
is awaited. If the starting conditions are satisfied, the timing operation 
of the first timer (not shown) is started, and the subroutine advances to 
Step S2-1-4. 
The starting conditions which must be satisfied are: the clutch input side 
R.P.M. N.sub.C1 is substantially 0; the accelerator pedal is released so 
that the throttle opening .theta. is below a predetermined value; the oil 
temperature detected by the oil temperature sensor 46 (FIG. 2) is over a 
predetermined value; and the brake pedal is depressed to turn ON the brake 
switch 48. Incidentally, whether or not the clutch input side R.P.M. 
N.sub.C1 is substantially 0 is decided depending upon whether or not the 
detection limit is detected by the R.P.M. sensor 47. In this preferred 
embodiment, it is decided that the detection limit has been detected if 
the actual vehicle speed reaches a set value of, for example, 2 km/h. 
Step S2-1-4: The lapse of the time period T.sub.1 measured by the first 
timer is awaited, and the subroutine advances to Step S2-1-5 upon lapse of 
the time period T.sub.1. The time period T.sub.1 is calculated by the 
vehicle speed zero estimation, and it is estimated that the vehicle speed 
is 0 when the time period T.sub.1 has elapsed. 
Step S2-1-5: The third solenoid signal S3 is turned ON to bring the neutral 
relay valve 64 (FIG. 5) to the upper half position, where the C-1 oil 
pressure P.sub.C1 is controlled. 
Step S2-1-6: The 2nd speed shift output for starting the hill hold control 
is issued to turn ON the first solenoid signal S.sub.1 for opening/closing 
the first solenoid valve S1, so that oil pressure is fed to the hydraulic 
servo B-2 of the second brake B2 to apply the second brake B2. In 
accordance with the rise of the oil pressure in the hydraulic servo B-2, 
moreover, the sequence pressure in the hydraulic servo B-2 is fed to the 
B-1 sequence valve 56 so that oil pressure is fed to the hydraulic servo 
B-1 to apply the first brake B1. 
Thus, the hill hold control is executed to establish the 2nd speed gear 
stage in the speed change unit 16 so that the first clutch C1, the first 
brake B1, the second brake B2 and the fourth brake B4 are applied to lock 
the one-way clutches F1 and F3. In this state, if the vehicle is were to 
roll backward on a hill, reverse rotation would be transmitted to the 
output shaft 23 of the auxiliary transmission 19 to rotate the ring gear 
R.sub.1 forward. However, this rotation is blocked by the one-way clutch 
F2 so that the vehicle will not roll backward. 
Step S2-1-7: As shown in FIG. 16, the engine R.P.M. N.sub.E, corresponding 
to the input torque T.sub.T, is detected to set the value of the engine 
R.P.M. N.sub.E to a reference engine R.P.M. N.sub.Em. FIG. 16 plots the 
input torque T.sub.T (=t.multidot.C.multidot.N.sub.E.sup.2) 
Kg.multidot.m! and the throttle pressure P.sub.TH Kg.multidot.cm.sup.2 ! 
against the engine R.P.M. N.sub.E rpm!. 
Step S2-1-8: The throttle pressure P.sub.TH, just before the start of 
release of the first clutch C1, is determined in a manner to correspond to 
the engine R.P.M. N.sub.E and is used as the set oil pressure P.sub.1 to 
reduce the C-1 oil pressure P.sub.C1 to the set oil pressure P.sub.1. 
Step S2-1-9: It is decided whether or not the speed ratio e, as expressed 
by the foregoing equation (I), is larger than a constant e.sub.2 (=0.25). 
The subroutine advances to Step S2-1-10, if the speed ratio e is larger 
than the constant e.sub.2, but to Step S2-1-12 if NOT. 
The constant e.sub.2 is a value at the instant when the release of the 
first clutch C1 is slightly started. Incidentally, the speed ratio e may 
be replaced by the clutch input side R.P.M. N.sub.C1. 
Step S2-1-10: It is decided whether or not the PNC1 signal is ON. The 
subroutine advances to Step S2-1-12, if the PNC1 signal is ON, but to Step 
S2-1-11 if OFF. 
Step S2-1-11: The engine control unit 43 turns ON the PNC1 signal to reduce 
the fuel injection rate in the engine 10. 
The first clutch C1 is released in the N-range but applied in the D-range, 
so that the load upon the engine 10 is different between the two ranges. 
Therefore, the R.P.M. control is executed by the engine control unit 43 so 
that the idle R.P.M. remains constant in the N-range and the D-range. The 
fuel injection rate is made higher in the D-range and lower in the 
N-range. 
In the neutral control, the first clutch C1 is released to lighten the load 
upon the engine 10. In the neutral control, therefore, it is also 
necessary to reduce the fuel injection rate. Because of the poor 
responsiveness of the R.P.M. control by the engine control unit 43, 
however, the fuel injection rate is liable to remain as is, in spite of 
the fact that the release of the first clutch C1 has started. This may 
increase fuel consumption and may cause engine racing. Accordingly, as 
previously described, the PNC1 signal is promptly turned ON upon 
initiation of release of the first clutch C1. 
Step S2-1-12: The engine R.P.M. N.sub.E corresponding to the input torque 
T.sub.T is again detected. 
Step S2-1-13: It is decided whether or not the engine R.P.M. N.sub.E has 
changed, as compared with the reference engine R.P.M. N.sub.Em. The 
subroutine advances to Step S2-1-14, if the answer is YES, but to Step 
S2-1-15 if NO. 
Step S2-1-14: The reference engine R.P.M. N.sub.Em is set at the value of 
the engine R.P.M. N.sub.E at the instant when it is decided at Step 
S2-1-13 that the engine R.P.M. N.sub.E has changed with respect to the 
reference engine R.P.M. N.sub.Em, and the C-1 oil pressure P.sub.C1 is 
changed to the throttle pressure P.sub.TH corresponding to the new 
reference engine R.P.M. N.sub.Em. 
Step S2-1-15: The throttle pressure P.sub.TH, i.e., the C-1 oil pressure 
P.sub.C1, is reduced (or swept down) by set pressure increments 
P.sub.THDOWN at each lapse of a set time period T.sub.DOWN, as expressed 
by the following Equation: 
EQU P.sub.TH =P.sub.TH -P.sub.THDOWN. 
S2-1-16: After release of the first clutch C1 has been established, the 
pressure reduction of Step S2-1-15 is continued until the speed ratio e 
exceeds a constant e.sub.1. This pressure reduction of Step S2-1-15 is 
stopped when the gear ratio e exceeds the constant e.sub.1. This constant 
e.sub.1 is set to 0.75, for example, in consideration of the delay of the 
change of the clutch input side R.P.M. N.sub.C1 when the first clutch C1 
is released. Incidentally, the speed ratio e may be replaced by the clutch 
input side R.P.M. N.sub.C1. 
The applied state of the first clutch C1 can not be determined based simply 
on the basis of whether or not the differential rotation .DELTA.N has 
changed, because this differential rotation .DELTA.N will not change 
regardless of whether the first clutch C1 is completely applied or 
released. As a result, it is difficult to distinguish between the state in 
which the first clutch C1 is completely applied and the state in which the 
first clutch C1 is released. Therefore, the state just before the 
application of the first clutch C1 is started is reliably restored by 
waiting for the speed ratio e to exceed the constant e.sub.1. 
The subroutine for the vehicle speed zero estimation, i.e. Step S2-1-2 of 
FIG. 14, will now be described with reference to FIG. 17. 
Step S2-1-2-1: The R.P.M. Difference .DELTA.N.sub.C1(i) is calculated by 
subtracting a clutch input side R.P.M. N.sub.C1(i-1), at a time At 
earlier, from the present clutch input side R.P.M. N.sub.C1(i). For this 
purpose, a clock in the automatic transmission control unit 41 (FIG. 2) 
detects the clutch input side R.P.M. N.sub.C1 every time period .DELTA.t. 
Step S2-1-2-2: Deceleration A of the vehicle is calculated by dividing the 
R.P.M. Difference .DELTA.N.sub.C1(i) by the time period .DELTA.t. 
Step S2-1-2-3: The time period T.sub.1 until stop of the vehicle is 
calculated by dividing the present clutch input side R.P.M. N.sub.C1(i) by 
the deceleration A. 
The subroutine for the in-neutral control of Step S2-2 of FIG. 13 will now 
be described with reference to FIGS. 18 to 21. In FIGS. 18 and 19: 
Step S2-2-1: An oil pressure control flag F, the count C of a counter (not 
shown), and the reference R.P.M. difference .DELTA.N.sub.m are set to the 
following initial values: 
F.rarw.Off; 
C.rarw.0; and 
.DELTA.N.sub.m .rarw.the value (N.sub.E -N.sub.C1) at that time. 
Steps S2-2-2 and S2-2-3: The C-1 oil pressure P.sub.C1 is held at the final 
value of the first clutch release control. After it has been confirmed 
that the first clutch C1 has been released to a predetermined extent, a 
decision is promptly made as to whether the differential rotation .DELTA.N 
has been changed. However, this decision may be mistaken due to the change 
in the differential rotation .DELTA.N deriving from the pressure reduction 
in the first clutch release control. Therefore, a second timer (not shown) 
is used to continue the holding of the C-1 oil pressure P.sub.C1 until the 
time period T.sub.2 has elapsed. As a result, the decision as to whether 
or not the differential rotation .DELTA.N has been changed is postponed to 
prevent the C-1 oil pressure P.sub.C1 from being adjusted while in an 
unstable state just after the first clutch C1 has been released. When the 
time period T.sub.2 has elapsed, the subroutine advances to Step S2-2-4. 
Step S2-2-4: the differential rotation calculation means 953 (FIG. 1) 
calculates the differential rotation .DELTA.N between the engine R.P.M. 
N.sub.E and the clutch input side R.P.M. N.sub.C1. 
Step S2-2-5: It is decided whether or not a preset sampling time has been 
reached, that is, whether or not a time period of, for example, 1.0 sec or 
0.5 sec has elapsed. The subroutine advances to Step S2-2-6, if the 
sampling time is reached, but to Step S2-2-14 if NOT. 
Step S2-2-6: The differential rotation change decision means 954 decides 
whether or not the absolute value of the difference between the 
differential rotation .DELTA.N and the reference differential rotation 
.DELTA.N.sub.m is below a set value .DELTA.N.sub.R, that is, whether or 
not the change in the differential rotation .DELTA.N is below the set 
value .DELTA.N.sub.R. The subroutine advances to Step S2-2-7, if below the 
set value .DELTA.N.sub.R, but to Step S2-2-9 if over the set value 
.DELTA.N.sub.R. The value .DELTA.N.sub.R is set in advance to discriminate 
between the active state and the inactive state of the first clutch C1, as 
shown in FIG. 20. 
The calculation of the differential rotation .DELTA.N may be erroneous, if 
the signal from the engine R.P.M. sensor 49 (FIG. 2) or that from the 
R.P.M. sensor 47 is in error, or if the calculation itself is in error. 
Because the differential rotation .DELTA.N will abruptly change if the 
application of the first clutch C1 is started prematurely, error in the 
decision that the differential rotation .DELTA.N has changed can be 
prevented by making the decision only after the differential rotation 
.DELTA.N exceeds the set value .DELTA.N.sub.R. 
Moreover, if the set value .DELTA.N.sub.R is varied according to the oil 
temperature, the C-1 oil pressure P.sub.C1 can be properly controlled 
regardless of the temperature of the oil. 
Step S2-2-7: It is decided whether or not the count C of the counter is 
below a set value C.sub.R. The subroutine advances to 
Step S2-2-8, if below the set value C.sub.R, but to Step S2-2-19 if over 
the set value C.sub.R. 
Step S2-2-8: The pressure boosting means 955 decides that the first clutch 
C1 is inactive, because of no change in the differential rotation 
.DELTA.N. In this state, to avoid return of the piston to an excessive 
extent, the C-1 oil pressure P.sub.C1 is boosted, as shown in FIG. 21, by 
a set pressure .DELTA.P.sub.UP, as follows: 
P.sub.C1 .rarw.P.sub.C1 +P.sub.UP. 
Moreover, the reference differential rotation .DELTA.N.sub.m is set to the 
differential rotation .DELTA.N, and the oil pressure control flag F is 
turned ON: 
.DELTA.N.sub.m .rarw..DELTA.N; and 
F.rarw.ON. 
Step S2-2-9: It is decided whether or not the change in the differential 
rotation .DELTA.N has a tendency to decrease, that is, whether or not the 
difference between the differential rotation .DELTA.N and the reference 
differential rotation .DELTA.N.sub.m is below the set value 
.DELTA.N.sub.R. The subroutine advances to Step S2-2-10, if below the set 
value .DELTA.N.sub.R, but to Step S2-2-11 if over the set value 
.DELTA.N.sub.R. 
Step S2-2-10: If it is decided that the first clutch C1 is in transition 
from the active state to the inactive state, the C-2 oil pressure P.sub.C1 
is held at its present value of that time, and the oil pressure control 
flag F is turned OFF: 
F.rarw.OFF. 
If the differential rotation .DELTA.N has changed, this change is in the 
direction of a decrease in the case of transition of the first clutch C1 
from the active state to the inactive state. At this time, if the C-1 oil 
pressure P.sub.C1 is further reduced, the piston may abruptly return to 
the extent of an excessive stroke loss. Therefore, the reduction of the 
C-1 oil pressure P.sub.C1 is once inhibited and held at its current value 
while the first clutch C1 is in transition from the active to the inactive 
state. 
Step S2-2-11: The pressure reducing means 956 reduces the C-1 oil pressure 
P.sub.C1 by a set pressure .DELTA.P.sub.DOWN because of a decision that 
the first clutch C1 is in transition from the inactive to the active 
state, as follows: 
P.sub.C1 .rarw.P.sub.C1 -.DELTA.P.sub.DOWN. 
Moreover, the reference differential rotation .DELTA.N.sub.m is set to the 
differential rotation .DELTA.N, and the oil pressure control flag F is 
turned OFF whereas the value "1" is subtracted from the count value of the 
counter: 
.DELTA.N.sub.m .rarw..DELTA.N; 
F.rarw.OFF; and 
C.rarw.C -1(or C=0 for C&lt;0). 
Step S2-2-12: It is decided whether or not the oil temperature is over a 
set value, e.g. 50.degree. C. The subroutine advances to Step S2-2-13, if 
the oil temperature is over the set value, but to Step S2-2-19 if NOT. 
Step S2-2-13: The base pressure storage means 958 sets the C-1 oil pressure 
P.sub.C1, which has previously been reduced at Step S2-2-11, as a 
reference C-1 oil pressure P.sub.C1m and stores it in the storage unit 
957: 
P.sub.C1m .rarw.P.sub.C1 before reduction. 
Step S2-2-14: It is decided whether or not the oil pressure control flag F 
is ON, that is, whether or not the C-1 oil pressure P.sub.C1 was boosted 
at the previous sampling. The subroutine advances to Step S2-2-15, if the 
oil pressure control flag F is ON, but to Step S2-2-19 if OFF. 
Step S2-2-15: The differential rotation change decision means 954 decides 
whether or not the difference between the differential rotation .DELTA.N 
and the reference differential rotation .DELTA.N, is below the set value 
.DELTA.N.sub.R, because the C-1 oil pressure P.sub.C1 was boosted at the 
previous sampling. The subroutine advances to Step S2-2-16, if below he 
set value .DELTA.N.sub.R, but to Step S2-2-19 if over the set value 
.DELTA.N.sub.R. 
Step S2-2-16: The differential rotation .DELTA.N is changed by boosting the 
C-1 oil pressure P.sub.C1 of the previous sampling. As a result, the 
pressure reducing means 956 decides that the first clutch C1 is in the 
applied state, and reduces the C-1 oil pressure P.sub.C1 by the set 
pressure .DELTA.P.sub.DOWN : 
P.sub.C1 .rarw.P.sub.C1 -.DELTA.P.sub.DOWN. 
Moreover, the reference differential rotation .DELTA.N.sub.m is set with 
the differential rotation .DELTA.N, and the oil pressure control flag F is 
turned OFF whereas the value "1" is added to the count value of the 
counter, as follows: 
.DELTA.N.sub.m .rarw..DELTA.N; 
F.rarw.OFF; and 
C.rarw.C+1. 
As previously described, it is decided whether or not the differential 
rotation .DELTA.N has been changed at the instant of each sampling. When 
the C-1 oil pressure P.sub.C1 is boosted in accordance with the decision, 
the application of the first clutch C1 may be instantly started from the 
released state, in which case vibration may be generated by initiation of 
torque transmission. Therefore, if the differential rotation .DELTA.N is 
increased while the application of the first clutch C1 is being started, 
the C-1 oil pressure P.sub.C1 is reduced without awaiting the subsequent 
sampling. Thus, the first clutch C1 is prevented from being released and 
idle vibration is prevented. 
Moreover, the C-1 oil pressure P.sub.C1 is changed when the change in the 
differential rotation .DELTA.N is higher than the set value .DELTA.N.sub.R 
at each sampling instant, as previously described. In this case, if the 
differential rotation changes only in small increments, i.e. little by 
little, the C-1 oil pressure P.sub.C1 may not be changed in spite of the 
fact that the first clutch C1 has transferred to the applied state. 
Therefore, the reference differential rotation .DELTA.Nm is updated only 
when the C-1 oil pressure P.sub.C1 is changed. As a result, the change of 
the C-1 oil pressure P.sub.C1 can be ensured, even if the differential 
rotation .DELTA.N is changed in small increments. 
Step S2-2-17: It is decided whether or not the oil temperature is over the 
set value, e.g. 50.degree. C. The subroutine advances to Step S2-2-18, if 
the oil temperature is over the set value, but to Step S2-2-19 if below 
the set value. 
Step S2-2-18: The base pressure storage means 958 sets the C-1 oil pressure 
P.sub.C1, at the level before reduction at Step S2-2-16, as the reference 
C-1 oil pressure P.sub.C1m, and stores it in the storage unit 957, as 
follows: 
P.sub.C1m .rarw.P.sub.C1 before reduction. 
Step S2-2-19: It is decided whether or not the conditions for ending the 
in-neutral control of the first clutch C1 are satisfied. If the ending 
conditions are satisfied, the in-neutral control is ended. Otherwise, the 
subroutine returns to Step S2-2-4, and the foregoing steps are repeated. 
Incidentally, if the oil temperature is below the set value at Steps 
S2-2-12 and S2-2-17, the individual discs of the first clutch C1 have a 
higher than normal viscous resistance, which is seen as a dragging 
resistance. As a result, it may be erroneously decided that the 
application of the first clutch C1 has started. In this case, the base 
pressure storage means 958 will store, in the storage unit 957, a 
reference C-1 oil pressure P.sub.C1m which is lower than the oil pressure 
before the application of the first clutch C1 is actually started. As a 
result, the time period for ending the application of the first clutch C1 
is prolonged to cause engine racing due to the delay in the application. 
Therefore, when the oil temperature is lower than the set value, the 
reference C-1 oil pressure P.sub.C1m is not updated, but the reference C-1 
oil pressure P.sub.C1m, as stored in the storage unit 957 corresponding to 
normal oil temperature, is read out for use. As a result, it is possible 
to prevent the engine from racing. 
The subroutine of the first clutch apply control, i.e. Step S2-3 of FIG. 
13, will now be described with reference to FIGS. 22 to 24. In FIG. 23: 
Step S2-3-1: When the application of the first clutch C1 is started at time 
t1, the signal PNC.sub.1 is promptly turned OFF to restore the R.P.M. 
control of the engine 10 (FIG. 1) in the D-range state. 
Step S2-3-2: The clutch input side R.P.M. N.sub.C1(i) at the instant when 
the in-neutral control ending conditions are satisfied is stored as a 
value N.sub.5 in the memory of the automatic transmission control unit 41 
(FIG. 2). 
Step S2-3-3: The first clutch pressure boosting means 959 adds a constant 
P.sub.C1S as a shelf pressure to the reference C-1 oil pressure P.sub.C1m 
as the base pressure set at Steps S2-2-13 and S2-2-18, and sets the sum as 
the C-1 oil pressure P.sub.C1. Incidentally, the constant P.sub.C1S is set 
to a value which ensures movement of the piston of the hydraulic servo C-1 
(FIG. 5) and which minimizes the engaging shock generated by application 
of the clutch. 
As a result, when the driver starts the vehicle from a stop, the constant 
P.sub.C1S is added to the reference C-1 oil pressure P.sub.C1m so that the 
oil pressure fed to the hydraulic servo C-1 is boosted to bring the first 
clutch C1 into a partially applied state. Subsequently, the oil pressure 
fed to the hydraulic servo C-1 is further boosted to bring the first 
clutch C1 into the completely applied state. 
In this case, the reference C-1 oil pressure P.sub.C1m, as set at Steps 
S2-2-13 and S2-2-18, is the C-1 oil pressure P.sub.C1 before reduction, in 
case it is boosted by the pressure boosting means 955 and then reduced by 
the pressure reducing means 956. It is at the start of the application of 
the first clutch C1 that the C-1 oil pressure P.sub.C1 is boosted by the 
pressure boosting means 955 and then reduced by the pressure reducing 
means 956. Thus, if the C-1 oil pressure P.sub.C1 before reduction is set 
to the reference C-1 oil pressure P.sub.C1m, the C-1 oil pressure P.sub.C1 
at the time of starting the application of the first clutch C1 is the 
reference C-1 oil pressure P.sub.C1m. 
Thus, because the C-1 oil pressure P.sub.C1 at the time of starting the 
application of the first clutch C1 is used as the reference C-1 oil 
pressure P.sub.C1m, the reference C-1 oil pressure P.sub.C1m does not 
fluctuate so that the partially applied state of the first clutch C1 can 
always be stably achieved. As a result, it is possible to prevent engaging 
shock and engine racing. 
Step S2-3-4: the subroutine awaits the clutch input side R.P.M. N.sub.C1 to 
become smaller than the difference between the value N.sub.5 and a 
constant DSN. If the clutch input side R.P.M. N.sub.C1 becomes smaller 
than the difference between the value N.sub.5 from the constant DSN at 
time t2, the start of application of the first clutch C1 is decided, and 
the subroutine advances to Step S2-3-5. 
Step S2-3-5: The 1st-speed shift output signal is issued. 
Step S2-3-6: The second clutch pressure boosting means 960 changes the 
throttle pressure P.sub.TH coming from the linear solenoid valve 66 (FIG. 
4) to boost the C-1 oil pressure P.sub.C1 to a pressure P.sub.B and then 
boosts the C-1 oil pressure P.sub.C1 by set pressure increments 
.DELTA.P.sub.B at each lapse of a time period .DELTA.t.sub.B to thereby 
continue the application of the first clutch C1. 
Step S2-3-7: The subroutine waits until the clutch input side R.P.M. 
N.sub.C1 becomes smaller than a constant DEN. 
Step S2-3-8: A third timer (not shown) measures the time period T.sub.3, 
the lapse of which is awaited. 
In this case, the set values of the constant P.sub.C1S, the pressure 
P.sub.B, the set pressure .DELTA.P.sub.B and so on are set on the basis of 
variables corresponding to the input torque T.sub.T such as the throttle 
opening .theta.. 
The invention may be embodied in other specific forms without departing 
from the spirit or essential characteristics thereof. The present 
embodiments are therefore to be considered in all respects as illustrative 
and not restrictive, the scope of the invention being indicated by the 
appended claims rather than by the foregoing description, and all changes 
which come within the meaning and range of equivalency of the claims are 
therefore intended to be embraced therein.