Honda 2004 Odyssey, Service Manual

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Lock-up System
General Operation
14-62
Automatic Transmission
System Description (cont’d)
MAINSHAFT
To ATF cooler
INLET
OUTLET
TURBINE
DAMPER SPRING
LOCK-UP PISTON
TORQUE CONVERTER
COVER
Power flow
The power flows by way of:
Engine
Drive plate
Torque converter cover
Lock-up piston
Damper spring
Turbine
Mainshaft
Power flow
Engine
Drive plate
Torque converter cover
Pump
Turbine
Mainshaft
MAINSHAFT
To ATF cooler
INLET
TURBINE
TORQUE CONVERTER
COVER
PUMP
The lock-up mechanism operates in D4 position (3rd and 4th), and D3 position (3rd). The pressurized fluid is drained
from the back of the torque converter through a fluid passage, causing the torque converter clutch piston to be held
against the torque converter cover. As this takes place, the mainshaft rotates at the same speed as the engine
crankshaft. Together with hydraulic control, the PCM optimizes the timing of the lock-up mechanism. When the torque
converter clutch solenoid valve activates, modulator pressure changes to switch lock-up ON and OFF. The lock-up
control valve and the lock-up timing valve control the amount of lock-up according to A/T clutch pressure control
solenoid valves A and B. The torque converter clutch solenoid valve is mounted on the torque converter housing, and
A/T clutch pressure control solenoid valves A and B are mounted on the transmission housing. They are controlled by
the PCM.
1. Operation (clutch on)
With the torque converter clutch on, fluid in the chamber between the torque converter clutch cover and the
torque converter clutch piston is drained off, and the converter fluid exerts pressure through the piston against
the torque converter cover. As a result, the converter turbine is locked to the converter cover. The effect is to
bypass the converter, placing the vehicle in direct drive.
2. Operation (clutch off)
With the torque converter clutch off, fluid flows in the reverse of CLUTCH ON. As a result, the torque converter
clutch piston moves away from the converter cover, and torque converter lock-up is released.
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