System Description - Honda Accord 2008 Manual

07/11/02 08:46:25 61TA0000_140_0028
Automatic Transmission

System Description

General Operation
The automatic transmission is a combination of a three-element torque converter and triple-shaft electronically
controlled unit which provides five speeds forward and one in 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 turns as the engine turns. Around the outside of the torque converter is a
ring gear which meshes with the starter drive gear when the engine is being started. The entire torque converter
assembly serves as a flywheel while 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, and includes the 4th and 5th clutches, and gears for 5th, 4th, reverse, and idler. The mainshaft reverse gear
is integral with the mainshaft 4th gear. The countershaft includes the gears for 1st, 2nd, 3rd, 4th, 5th, reverse, park,
and the final drive. The final drive gear is integral with the countershaft. The countershaft 4th gear and the
countershaft reverse gear can be locked to the countershaft providing 4th or reverse gear, depending on which way
the selector is moved. The secondary shaft includes the 1st, 2nd, and 3rd clutches, and gears for 1st, 2nd, 3rd, and
idler. The idler shaft is located between the mainshaft and the secondary shaft, and the idler gear transmits power
between the mainshaft and the secondary shaft. 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, or through
mainshaft to countershaft to provide drive.
Electronic Control
The electronic control system consists of the powertrain control module (PCM), sensors, and solenoid valves. Shifting
and lock-up are electronically controlled for comfortable driving under all conditions. The PCM is located in the engine
compartment.
Hydraulic Control
The valve bodies include the main valve body, the regulator valve body, and the servo body. They are bolted to the
torque converter housing. The main valve body contains the manual valve, shift valves A, B, C, and E, the relief valve,
the lock-up control valve, the cooler check valve, the servo control valve, and the ATF pump gears. The regulator valve
body contains the regulator valve, the torque converter check valve, the lock-up shift valve, and the 1st and 3rd
accumulators. The servo body contains the servo valve, shift valve D, the accumulators for 2nd, 4th, and 5th, and shift
solenoid valves A, B, C, D, and E. Fluid from the regulator passes through the manual valve to the various control
valves. The 1st, 3rd, and 5th clutches receive fluid from their respective feed pipes, and the 2nd and 4th clutches
receive fluid from the internal hydraulic circuit.
Shift Control Mechanism
To shift gears, the PCM controls shift solenoid valves A, B, C, D, and E, and A/T clutch pressure control solenoid valves
A, B, and C, 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. A/T
clutch pressure control solenoid valves A, B, and C regulate their respective pressure, and pressurize the clutches to
engage them and their corresponding gears. The pressures of the A/T clutch pressure control solenoid valves also
apply to the shift valves to switch the port.
Lock-up Mechanism
The lock-up mechanism operates in D (2nd, 3rd, 4th, and 5th gears), and in D3 (2nd and 3rd gears). 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 the hydraulic control, the PCM optimizes the timing and volume of the lock-up
mechanism. When shift solenoid valve E is turned on by the PCM, shift solenoid valve E pressure switches the lock-up
shift valve on and off. A/T clutch pressure control solenoid valve A and the lock-up control valve control the volume of
the lock-up conditions.
14-26
ＴＡ０８ＡＥＢＥ１０４００００００００ＣＡＡＴ００