Automatic Transmission Description - Honda 2002 Accord Manual

Automatic Transmission
System Description
General Operation
The automatic transmission is a combination of a 3-element t o r q u e converter and triple-shaft electronically controlled
automatic transmission which provides 4 speeds f o r w a r d and 1 reverse. The entire unit is positioned in line w i t h the
engine.
Torque Converter, Gears, and Clutches
The torque converter consists of a p u m p , turbine, and stator assembly in a single unit. They are connected to the
engine crankshaft so they turn together as a unit as the engine turns. Around the outside of the torque converter is a
ring gear w h i c h meshes w i t h the starter pinion w h e n 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 w i t h the engine crankshaft.
The mainshaft includes the 3rd and 4th clutches, and gears for 3rd, 4th, reverse, and idler (reverse gear is integral w i t h
4th the gear). The countershaft includes the final drive, 1st, 3 r d , 4th, reverse, 2nd, park, and idler gears (the final drive
gear is integral w i t h 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 on w h i c h w a y the selector moved. The gears on the mainshaft and the
secondary shaft are in constant mesh w i t h those on the countershaft. When certain combinations of gears in the
transmission are engaged by the clutches, power is transmitted f r o m the mainshaft and the secondary shaft to the
countershaft to provide E L S , H I Q D and E positions.
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 f r o n t lower panel behind the center console.
Hydraulic Control
The valve bodies include the m a i n 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 CPC valve, the lock-up shift valve, the lock-up control valve, the cooler check valve, and the ATF p u m p gears.
The regulator valve body contains the regulator valve, the lock-up t i m i n g valve, and the relief valve. The servo body
contains the servo valve, the shift valve A, the shift valve B, the CPC valves A and B, and the 3rd and 4th accumulators.
The accumulator body contains the 1st and 2nd accumulators, and the lubrication check valve. Fluid f r o m the
regulator passes through the manual valve to the various control valves. The 1st, 3rd, and 4th clutches receive fluid
f r o m their respective feed pipes, and the 2nd clutch receives fluid f r o m the internal hydraulic circuit.
Shift Control Mechanism
The PCM controls shift solenoid valves A, B, and C, and A/T clutch pressure control solenoid valves A and B, while
receiving input signal f r o m various sensors located t h r o u g h o u t 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 t o one of the clutches, engaging the clutch and its corresponding gear.
Lock-up Mechanism
In E position (3rd and 4th), and (H position (3rd), pressurized fluid is drained f r o m the back of the torque converter
through a fluid passage, causing the lock-up 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 w i t h hydraulic control, the PCM optimizes
the t i m i n g of the lock-up m e c h a n i s m . W h e n 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 t i m i n g valve control the range of
lock-up according t o A/T clutch pressure control solenoid valves A and B. The torque converter clutch solenoid valve is
m o u n t e d on the torque converter h o u s i n g , 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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