System Description; General Operation - Honda 2004 Odyssey Service Manual

Automatic Transmission

System Description

General Operation

The automatic transmission is a combination of a 3-element torque converter and triple-shaft electronically controlled
unit which provides 4 speeds forward and 1 reverse. The entire unit is positioned in line with the engine.
Torque Converter, Gears, and Clutches
The torque converter consists of a pump, turbine, and stator assembly in a single unit. The converter housing (pump)
is connected to the engine crankshaft and turn as the engine turns. Around the outside of the torque converter is a ring
gear which meshes with the starter pinion when the engine is being started. The entire torque converter assembly
serves as a flywheel, transmitting power to the transmission mainshaft. The transmission has three parallel shafts: the
mainshaft, the countershaft, and the secondary shaft. The mainshaft is in line with the engine crankshaft. The
mainshaft includes the 3rd and 4th clutches, and gears for 3rd, 4th, reverse, and idler (reverse gear is integral with the
4th gear). The countershaft includes the final drive, 1st, 3rd, 4th, reverse, 2nd, park, and idler gears (the final drive gear
is integral with the countershaft). The secondary shaft includes the 1st and 2nd clutches, and gears for 1st, 2nd, and
idler. The countershaft 4th gear and the countershaft reverse gear can be locked to the countershaft at its center,
providing 4th gear or reverse, depending which way the selector moved. The gears on the mainshaft and the
secondary shaft are in constant mesh with those on the countershaft. When certain combinations of gears in the
transmission are engaged by the clutches, power is transmitted through the mainshaft, then to the secondary shaft to
the countershaft to provide drive.
Electronic Control
The electronic control system consists of the powertrain control module (PCM), sensors, and six solenoid valves.
Shifting and lock-up are electronically controlled for comfortable driving under all conditions. The PCM is located
below the dashboard, under the front lower panel behind the center console.
Hydraulic Control
The valve bodies include the main valve body, the regulator valve body, the servo body, and the accumulator body.
They are bolted to the torque converter housing. The main valve body contains the manual valve, the modulator valve,
the shift valve C, the shift valve D, the shift valve E, the servo control valve, the torque converter check valve, the
reverse Clutch Pressure Control C (CPC) valve, the lock-up shift valve, the relief valve, the cooler check valve, and the
ATF pump gears. The regulator valve body contains the regulator valve, the lock-up timing valve, and the lock-up
control valve. The servo body contains the servo valve, the shift valve A, the shift valve B, the CPC valves A and B, and
3rd and 4th accumulators. The accumulator body contains the 1st and 2nd accumulators and lubrication check valve.
Fluid from the regulator passes through the manual valve to the various control valves. The 1st, 3rd, and 4th clutches
receive fluid from their respective feed pipes, and the 2nd clutch receives fluid from the internal hydraulic circuit.
Shift Control Mechanism
To shift gears, the PCM controls shift solenoid valves A, B, and C, and A/T clutch pressure control solenoid valves A
and B while receiving input signals from various sensors and switches located throughout the vehicle. The shift
solenoid valves shift the positions of the shift valves to switch the port leading hydraulic pressure to the clutch. The
A/T clutch pressure control solenoid valves A and B control the CPC valves A and B to shift smoothly between lower
gear and higher gear. This pressurizes a line to one of the clutches, engaging the clutch and its corresponding gear.
Lock-up Mechanism
The lock-up mechanism operates in the 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 all controlled
by the PCM.
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