Daihatsu 1997 Terios J100 Service Manual page 421

AT–20
10) Servo control valve
When gear shift takes place between the 3rd gear and the 4th gear, the servo control valve turns ON and
OFF the C1 pressure and B1' pressure (at released side) simultaneously.
Moreover, in order to prevent downshift from the 4th gear to the 2nd gear from taking place all at once (be-
cause it will apply a great torque to the forward clutch suddenly), the servo control valve causes downshift
to the 3rd gear to take place first. Then, the transmission is shifted to the 2nd gear.
When the transmission is in the 3rd gear, the forces applied to the valve are the spring force (force pushing
to the left side), line pressure o (force pushing to the left side) from the 3-4 shift valve, and the line pres-
sure q (force pushing to the right side) from the 2-3 shift valve.
When conditions for upshifting to the 4th gear are satisfied and the 3-4 shift valve is switched, the line pres-
sure o will be drained. Therefore, the valve moves to the right side. At this time, u and i are connected
to each other. Consequently, the pressure B1' u will be drained from the 3-4 shift valve via i. At the same
time, the pressure C1 w will be drained, too.
Moreover, although the vehicle speed decreases and conditions for switching the 2-3 shift valve (downshift
to the 2nd gear) are satisfied, the servo control valve allows the 2-3 shift valve be switched only after the 3-
4 shift valve has been switched (downshift to the 3rd gear has taken place). The servo control valve does
this by making the line pressure, instead of governor pressure, applied to the 2-3 shift valve from r.
<Except for 4th gear>
q q w
q
Line pressure , From 2-3 shift valve (3rd and 4th gears)
w
To C1
e
Governor pressure (From governor valve)
r
To 2-3 shift valve
Line pressure , From manual valve (Î, x and Ò ranges)
t
u i
r t o
y
e
<4th gear>
r t
q q w
e
y
Line pressure , From 2-3 shift valve (3rd and 4th gears)
u
To B1'
To 3-4 & select timing valve
}
i
Line pressure , From 3-4 shift valve
o
(1st, 2nd and 3rd gears)
u i
o
y
JAT00032-00025