A/T System Description - General Description (A/T)
A/T System Description - General Description
General Operation
General description
The automatic transmission is a transversely mounted three-shaft design, implementing an electronically controlled hydraulic circuit that provides five forward speeds and one in reverse. Engine power is transmitted through the torque converter, a combination of shafts which hold gears and clutches and a differential that transmits power to the driving wheels.
Shaft, Gears and Clutches
Three parallel shafts hold gears and clutches. The gears on the input shaft (mainshaft) and secondary shaft are in constant mesh with those on the output shaft (countershaft). When specific gears are engaged by the clutches, power is transmitted through the mainshaft, to the secondary shaft, and/or the countershaft, then to the final drive gear of the differential to provide drive.
Shift Control Mechanism
To shift gears, the PCM controls shift solenoid valves A, B, C, D, and E, and automatic transmission (A/T) clutch pressure control solenoid valves A, B, and C. The shift solenoid valves change the positions of the shift valves in the valve body which open and close ports to send hydraulic pressure to the appropriate clutch. A/T clutch pressure control solenoid valves A, B, and C change the position of their respective CPC valves A, B, and C to control hydraulic pressure going to the clutches, which allows smooth shifts between gears.
Electronic Control
Shifting and lock-up is achieved by a system of solenoid valves driven by the PCM to control ATF flow through various valves in the valve bodies to select the appropriate gears for all driving conditions.
Hydraulic Control
The valve bodies include the main valve body, the regulator valve body, and the servo valve body. They are mounted to the torque converter housing. Fluid from the regulator valve passes through the manual valve to the various control valves. All the clutches receive fluid from the internal hydraulic circuit.
Torque Converter
The torque converter is a fluid coupling, which allows the engine to spin independently of the transmission yet connects them together as needed. It is an assembly that consists of an impeller (pump), turbine, stator and lock-up clutch, which uses automatic transmission fluid (ATF) to transmit engine power to the input shaft (mainshaft), and acts as a flywheel to help the engine run smoothly. During certain conditions the lock-up clutch is engaged by the PCM to mechanically connect the engine's crankshaft with the input shaft (mainshaft) which improves fuel economy. Around the outside of the torque converter housing is a ring gear which meshes with the starter ring gear, when the engine is being started.
Lock-up Mechanism
The lock-up mechanism causes the input shaft (mainshaft) to rotate at the same speed as the engine crankshaft. Pressurized ATF is drained from between the torque converter cover and the torque converter clutch piston through a fluid passage, causing the torque converter clutch piston to be held against the torque converter housing. Together with the hydraulic control, the PCM optimizes the timing and degree of lock-up. The lock-up mechanism operates in D (2nd, 3rd, 4th, and 5th gears) and S (2nd, 3rd, and 4th gears).
Gear Selection
The shift lever has five positions; P: PARK, R: REVERSE, N: NEUTRAL, D: DRIVE 1st through 5th gear with automatic shift mode and D-paddle shift mode, S: DRIVE 1st through 4th gear with automatic shift mode and 1st through 5th gear with sequential sportshift mode.
Starting is possible only in P and N because of a neutral-safety switch.
Automatic Transmission (A/T) Gear Position Indicator
The A/T gear position indicator in the gauge control module shows which shift lever position has been selected.
Shift Indicator and M Indicator
When the transmission is switched into the sequential sportshift mode, the shift indicator in the gauge control module display the gear selected, and the M indicator next to the shift indicator comes on. The shift indicator also displays the gear selected in the D-paddle shift mode, but the M indicator does not come on.