Shift control system of automatic transmission

In a shift control system of an automatic transmission, wherein the shift control system includes at least a first and a second transmissions capable of automatically switching speeds separately of one another, and the first and the second transmissions are shifted simultaneously or alternately, to thereby achieve multi-speed shifts, there is provided means for starting and completing changes in rpm for the shift of rotary members of the second transmission during the operation of changes in rpm for the shift of rotary members of the first transmission, particularly when the first transmission is low gear shifted and the second transmission is shifted simultaneously, whereby the automatic transmission as a whole is down shifted, so that the shift characteristics can be maintained satisfactorily.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a shift control system of an automatic 
transmission, and more particularly to improvements in a shift control 
system of an automatic transmission, wherein the shift control system 
includes at least a first and a second transmissions capable of 
automatically switching speeds separately of one another, and the first 
and the second transmissions are shifted simultaneously or alternately, to 
thereby achieve multi-speed shifts. 
2. Description of the Prior Art 
Along with a rapid spread in use of the automatic transmissions for motor 
vehicles in recent years, there have been commonly adopted such 
transmissions wherein a so-called over drive device, in which a 
transmission gear ratio is less than 1, is connected in series to the 
first transmission capable of automatic switching the shift speeds in 
association with a vehicle speed, a throttle opening, etc. as the second 
transmission. 
Furthermore, there is also known such a transmission wherein, based on a 
function of the second transmission capable of switching from lower speed 
to higher speed and vice versa as the above-described over drive device, 
shift controls shown in FIG. 2A for example are performed, so that 
multi-speed shifts of six forward speeds can be achieved. This 
transmission is of such arrangement that a shift of the second 
transmission is actively cooperated with a shift of the first 
transmission, whereby the first transmission and the second transmission 
are shifted simultaneously or alternately, so that multi-speed shifts can 
be achieved. 
The above-described arrangement makes it possible that the existing 
automatic transmission is utilized as the basis, and changes in design are 
minimized for manufacturing advantage, so that multi-speed shifts can be 
achieved. As the result, such advantages can be offered that the fuel 
consumption rate is improved, the power performance is bettered, and the 
burden of frictional materials is relieved due to making the speed shifts 
into multi-speed shifts, and the like. 
However, in the automatic transmission wherein the first and the second 
transmissions are shifted simultaneously or alternately to achieve the 
multi-speed shifts, as shown in FIG. 2, there occurs a case where the 
first transmission is low gear shifted and the second transmission is high 
gear shifted, for example, like a shift from a third speed to a second 
speed and like a shift from a fifth speed to a fourth speed, to thereby 
down shift the automatic transmission as a whole. At this time, if only 
the respective shifts are controlled separately of one another, an 
increase in shift shock is not avoidable. Furthermore, for example, while 
a down shift is in operation, the shift is started from an up shift, or an 
up shift after a down shift is performed, thus presenting such a 
disadvantage that there may be experienced the shift characteristics of a 
strange driving feeling. 
SUMMARY OF THE INVENTION 
The present invention has been developed to obviate the above-described 
disadvantages of the prior art and has its object that the provision of a 
shift control system of an automatic transmission, wherein a first 
transmission is down gear shifted and a second transmission is shifted 
simultaneously, whereby, when the automatic transmission as a whole is 
down shifted, shifts are reliably started from the down shift, the shift 
shock is low and the shift feeling of the up shift does not remain. 
To this end, the present invention contemplates that, in a shift control 
system of an automatic transmission, wherein the shift control system 
includes at least first and second transmissions capable of automatically 
switching shift speeds separately of one another, and the first and the 
second transmissions are shifted simultaneously, to thereby achieve 
multi-speed shifts, there is provided means for starting and completing 
changes in rpm (revolutions per minute) for the shift of rotary members of 
the second transmission during the operation of changes in rpm for the 
shift of rotary members of the first transmission, when the first 
transmission is low gear shifted and the second transmission is shifted 
simultaneously, whereby the automatic transmission as a whole is down 
shifted. Also included are means for instructing the first transmission to 
switch speeds so that such rpm changes therein subsequently occur, and 
means for judging such changes. At least the starting of the starting of 
such changes in rpm in the second transmission is in response to such 
judging of such rpm changes in the first transmission. 
A preferable specific form in the above-described arrangement is such that 
the start of changes in rpm for shifts of the rotary members of the first 
transmission is judged from a pressure switch adapted to be turned on when 
the hydraulic pressure of a frictionally engaging device associated with 
the aforesaid shifts reaches a predetermined pressure. 
Or, the aforesaid start of changes in rpm for shifts of the rotary members 
of the first transmission is judged from whether or not a detected value 
reaches a predetermined value upon continuous detection of the hydraulic 
pressure of the frictionally engaging device associated with the aforesaid 
shifts. 
Or, the aforesaid start is judged from a lapse of time measured by a timer 
referenced from a time of judgment of the aforesaid shift. 
Or, the aforesaid start is judged from a lapse of time measured by a timer 
referenced from a time of command of the aforesaid shift. 
Or, the aforesaid start is judged from the return of a piston of an 
accumulator of the frictionally engaging device associated with the 
aforesaid shift. 
Or, the aforesaid start is judged from a torque of an output shaft. 
Or, the aforesaid start is judged from a change in rpm of an engine 
revolution speed. 
Or, the aforesaid start is judged from a change in rpm of a specific rotary 
member in the automatic transmission. 
Additionally, the better setting of the timer can be obtained when the 
timer is set as commensurate to at least one of an engine load and a 
vehicle speed. 
According to the present invention, changes in rpm of the rotary members of 
the second transmission for the shift are started and completed while the 
rotary members of the first transmission are performing the changes for 
the shift, whereby the shift shock is reduced and the feeling of only the 
down shift should necessarily be given to the driver.

DETAILED DESCRIPTION OF THE INVENTION 
Detailed description will hereunder be given of embodiment of the present 
invention with reference to the drawings. 
FIG. 1 shows the general arrangement of the automatic transmission for a 
motor vehicle, to which is applied the present invention. 
This automatic transmission includes a torque converter 20, a second 
transmission 40 and a first transmission 60 having three forward speeds 
and one rearward speed. The torque converter 20 includes a pump 21, a 
turbine 22, a stator 23 and a lock-up clutch 24. The pump 21 is connected 
to a crankshaft 10 of an engine 1, and the turbine 22 is connected to a 
carrier 41 of a planetary gear train in the second transmission 40. 
In the second transmission 40, a planetary pinion 42 rotatably supported by 
this carrier 41 is in mesh with a sun gear 43 and a ring 44. Furthermore, 
a clutch C0 and a one-way clutch F0 are interposed between the sun gear 43 
and the carrier 41. And a brake B0 is interposed between the sun gear 43 
and a housing Hu. 
In the first transmission 60, there are provided two rows including one on 
the front side and the other on the rear side as the planetary gear train. 
This planetary gear train includes a sun gear 61 being commonly used, ring 
gears 62 and 63, planetary pinions 64 and 65, and carrier 66 and 67. 
The ring gear 44 of the second transmission 40 is connected to the ring 
gear 62 through a clutch C1. Furthermore, a clutch C2 is interposed 
between the ring gear 44 and the sun gear 61. Further, the carrier 66 is 
connected to the ring gear 63, and the carrier 66 and the ring gear 63 are 
connected to an output shaft 70. 
On the other hand, a brake B3 and a one-way clutch F2 are interposed 
between the carrier 67 and the housing Hu. Further, a brake B2 is provided 
between the sun gear 61 and the housing Hu, through a one-way clutch F1. 
Furthermore, a brake B1 is interposed between the sun gear 61 and the 
housing Hu. 
This automatic transmission has the above-described transmission section, 
and solenoid valves S1-S4 in a hydraulic control circuit 106 are driven 
and controlled in accordance with a shift pattern preset by a central 
processing unit (CPU) 104 to which are inputted signals from a throttle 
sensor 100 for detecting a throttle opening representing a load condition 
of the engine 1, a vehicle speed sensor 102 for detecting a vehicle speed, 
and the like. As a result, combinations of engagements between the 
clutches, brakes and the like as shown in the B portion in FIG. 2 are 
performed for shift control. 
Additionally, in FIG. 2, indicated by marks "o" are engagements and marks 
"x" engagements only when an engine brake is used. 
The solenoid valves S1 and S2 perform controls of shift of the first 
transmission 60, the solenoid valve S3 performs controls on the higher 
speed side and the lower speed side of the second transmission 40 and the 
solenoid S4 performs control of the lock-up clutch 24 of the torque 
converter 20, respectively. 
Additionally, in FIG. 1, designated at 110 is a shift position sensor for 
detecting positions of N (Neutral), D (Drive) and R (Reverse), which are 
operated by the driver, 112 a pattern select switch for detecting position 
of E (Economical running), P (Power running) and the like, 114 a water 
temperature sensor for detecting a cooling water temperature of the 
engine, 116 a brake switch for detecting operations of a foot brake and 
118 another brake switch for detecting operation of a side brake, 
respectively. 
Here, in this embodiment, in addition to the above-described input signals, 
the CPU 104 has inputted thereto a signal from a pressure switch 120 for 
detecting a hydraulic pressure in an oil line directed to the brake B2, 
which will hereunder be described, in order to confirm the start of a 
change in rpm of the rotary members in the first transmission 60 due to a 
shift command. 
FIG. 3 shows the essential portions of the hydraulic control circuit 106. 
In the drawing, designated at 200 is a first shift valve for switching 
between a first speed condition and a second speed condition of the first 
transmission 60, S1 a solenoid valve for controlling the switching of the 
first shift valve, 300 a third shift valve for switching between the 
higher speed side and the lower speed side of the second transmission 40, 
400, 500 and 600 are respectively accumulators for B2, B0, and C0, S3 a 
solenoid valve for controlling the transition characteristics of the 
hydraulic pressure in oil lines to the brakes B2, B0 and the clutch C0, 
respectively, and 700 a manually operated valve interlocked with a shift 
lever operated by a driver. The arrangements and actions of these 
components are identical with the conventional ones, so that detailed 
description of the respective components need not be repeated. 
Additionally, the pressure switch 120 is provided on an oil line to the 
brake B2. This pressure switch 120 is preset to output an ON signal to CPU 
104 when a hydraulic pressure PB2 in the oil line to the brake B2 reaches 
a predetermined pressure PB2' (which would better be set as commensurate 
to the throttle opening) at which the rotary members of the first 
transmission 60 start changes in rpm. 
Description will hereunder be given of action of this control system with 
reference to FIGS. 4 and 5. In the case where the first transmission 60 is 
low gear shifted and the second transmission 40 is shifted simultaneously, 
whereby, when the automatic transmission as a whole is down shifted, there 
are various shifts as apparent from FIG. 2. However, since the gist of the 
invention relating to shifts is common to all of these shifts, explanation 
is given of a shift from the third speed to the second speed as an 
example, here. 
Firstly, in Step 900, a judgment of shift (judgment of shift from the third 
speed to the second speed) is made from a vehicle speed, a throttle 
opening or a signal of a pattern select switch, etc. through an action 
similar to a conventional one. Upon making this judgment, a delay for a 
predetermined time duration T1 is taken in Step 902, and thereafter, the 
solenoid valve S1 is turned off to switch the first shift valve 200 for 
controlling the first transmission 60 (Step 904). The reason why the delay 
for a time duration T1 is taken is that, when two or more judgments of 
shift are made for a short period of time, only the last judgment should 
be selected 
Turn-off of the solenoid valve S1 firstly lowers the hydraulic pressure PB2 
of the brake B2, the first transmission 60 begins to be low gear shifted 
at a predetermined pressure PB2', whereby changes in rpm of the respective 
rotary members of the first transmission 60 begin (at point a). 
On the other hand, when the pressure switch 120 is actuated at the 
predetermined pressure PB2' due to a decrease of the hydraulic pressure 
PB2 of the brake B2, the CPU 104 confirms the start of an inertia phase 
(the period of time, during which changes in rpm of the respective rotary 
members are performed) of the first transmission 60 in Step 906. When the 
inertia phase is confirmed, a shift command is delivered to the solenoid 
valve S3, and the third shift valve 300 is switched, whereby the hydraulic 
line pressure is fed to the brake B0 and the hydraulic pressure of the 
clutch C0 is drained. As the result, high gear shift of the second 
transmission 40 is started at a point b and the engagement is completed at 
a point c. 
On the other hand, the first transmission 60, which has begun the inertia 
phase at the point a, completes the inertia phase at a point d where the 
rotation (Refer to the revolution numbers of the rotary members) of the 
output shaft of the turbine 22 comes into synchronism therewith. 
As a result, the second transmission 40 starts changes in rpm after the 
start of changes in rpm of the first transmission 60, and completes the 
changes in rpm thereof while the first transmission 60 is performing the 
changes in rpm. 
In the foregoing, description has been given of the arrangement and action 
when the shift is performed from the third speed to the second speed, 
however, the gist of the invention is applicable to a shift from the fifth 
speed to the fourth speed or another shift wherein the first transmission 
60 is low gear shifted and the second transmission 40 is shifted 
simultaneously, whereby the automatic transmission as a whole is down 
shifted. 
Furthermore, in the above embodiment, as the means for detecting the 
inertia phase of the first transmission 60, the pressure switch 120 
adapted to be turned on when the hydraulic pressure PB2 of the brake B2 
reaches the predetermined pressure PB2' has been used, the means for 
detecting the inertia phase of the first transmission 60 according to the 
present invention need not necessarily be limited to this, and, for 
example, the hydraulic pressure of the brake B2 may be continuously 
detected by a hydraulic pressure sensor. In addition, in the case where 
the inertia phase is detected through pressure by use of the pressure 
switch 120, the hydraulic sensor or the like as described above, when a 
time duration T (corresponding to a deflection region of a return spring 
of a brake) shown in FIG. 4 is prolonged, the high gear shift of the 
second transmission 40 may not be completed during the inertia phase of 
the first transmission 60. In consequence, the predetermined pressure may 
be set at PB2" which is higher. Furthermore, as another detecting means, 
the detection may be made by a timer (which would better be set as 
commensurate to the throttle opening) referenced from an OFF time of the 
solenoid valve S1 (at the time of a shift command) or the time of shift 
judgment. Or, as shown in FIG. 6, the return of the accumulator 400 may be 
detected. More specifically, in FIG. 6, designated at 402 is a rod with a 
stopper, 404 a return spring, 406 a housing and 408 a contact point. When 
an accumulator piston 410 returns in a direction indicated by an arrow X0 
due to the drain of the brake B2, the rod 402 is urged in a direction 
indicated by an arrow X against the return spring 404, whereby the rod 402 
comes into contact with the contact point 408, so that the operation of 
the accumulator 400 can be detected (a point a.sub.0 in FIG. 4). In this 
case, it is the time before the inertia phase of the first transmission 60 
is started, whereby the start of inertia is detected by a timer referenced 
from the time of detection of the accumulator 400 and set as commensurae 
to the throttle opening. 
Additionally, the changes in rpm of the engine, or the respective rotary 
members of the automatic transmission may be detected directly, and, the 
detection may be made from the torque of the output shaft of the automatic 
transmission. 
And, in the above embodiment, the throttle opening has represented "the 
engine load", however, the present invention need not necessarily be 
limited to this, and, for example, the output shaft torque of the engine 
detected by a torque sensor may represent "the engine load".