Honda Acura NSX 1991 Service Manual page 429

Partial Lock-up
Lock-up Control Solenoid Valve A: ON
The control unit switches the solenoid valve A to ON to release the modulator pressure in the left cavity of the lock-up
shift valve. The modulator pressure in the right cavity of the lock-up shift valve overcomes the spring force, thus the
lock-up shift valve is moved to the left side.
The torque converter pressure is spearated into two passages:
Torque Converter Inner Pressure: entered into right side-to engage lock-up clutch
Torque Converter Back Pressure: entered into left side-to disengage lock-up clutch
The back pressure (F2) is regulated by the lock-up control valve whereas the position of the lock-up timing valve B is
determined by the throttle B pressure, tension of the valve spring and pressure regulated by the modulator. Also the
position of the lock-up control valve is determind by the throttle valve B pressure, back pressure of the lock-up control
valve and torque converter pressure regulated by the check valve. In low speed range, the throttle B pressure working
on the right side of the lock-up control valve is low, causing the valve to be moved to the right side. With the lock-up
control solenoid valve B kept OFF, the modulator pressure is maintained in the left end of the lock-up control valve; in
other words, the lock-up control valve is moved slightly to the left side. This slight movement of the lock-up control
valve causes the back pressure to be lowered slightly, resulting in partial lock-up.
NOTE: When used, "left" or "right" indicates direction on the flow chart.
Lock-up Control Solenoid Valve B: OFF
THROTTLE P R E S S U R E
- M O D U L A T O R P R E S S U R E