A/T System Description - General Operation
A/T System Description - General Operation
General Description
The automatic transmission is a transverse-mounted five-shaft design with an electronically controlled hydraulic circuit that provides six forward speeds and one in reverse. Engine output 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. This model also has a transfer assembly which transmits power to the SH-AWD differential.
Shaft, Gears, and Clutches
The clutches and gears are installed on the input shaft (mainshaft), the secondary shaft, the third shaft, and the idler gear shaft. These gears 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, the third shaft, the idler gear shaft, and/or the countershaft, then to the final driven gear of the differential to provide drive.
Shift Control Mechanism
To perform hydraulic control, shift control, and lock-up control of the automatic transmission, the PCM controls shift solenoid valves A, B, and C, line pressure solenoid valve A, and automatic transmission (A/T) clutch pressure control solenoid valves A, B, C, and D. The PCM switches each solenoid valve ON and OFF. This changes the positions of the shift valves in the valve bodies which open and close ports to send hydraulic pressure to the appropriate clutch. A/T clutch pressure control solenoid valves A, B, C, and D control the clutch pressure regulated by each of them, which allows smooth shifts and lock-up of the torque converter.
Electronic Control
Shifting and lock-up are achieved by a system of solenoid valves driven by the PCM, which controls ATF flow through various valves in the valve bodies to select the appropriate gears for all driving conditions.
Hydraulic Control
The valve bodies consist of the main valve body, the regulator valve body, the secondary valve body, the stator shaft support, and the manual valve body. They are installed to the torque converter housing. Fluid regulated by the regulator valve passes through the manual valve to the various control valves. All the clutches receive fluid from the shaft internal hydraulic circuit. Also, the hydraulic control body is adapted to the secondary valve body, which includes the main shift hydraulic circuit, the solenoid valve, the hydraulic switch, etc. to shorten the fluid passage and optimize the hydraulic pressure.
Torque Converter
The torque converter is connected to the flywheel. It is an assembly that consists of an impeller (pump), turbine, stator, and torque converter clutch, which uses ATF to transmit engine power to the input shaft (mainshaft). Around the outside of the torque converter housing, the starter ring gear is installed, which is used to start the engine.
Lock-Up Mechanism
The lock-up causes the input shaft (mainshaft) to rotate at the same speed as the engine crankshaft by engaging the torque converter cover with the turbine by the torque converter clutch. Together with the hydraulic control, the PCM optimizes the timing and degree of lock-up. The lock-up mechanism operates in D (during accelerating: 1st, 2nd, 3rd, 4th, 5th, and 6th gears/during decelerating: 2nd, 3rd, 4th, 5th, and 6th gears), S with automatic shift mode (during accelerating: 1st, 2nd, 3rd, 4th, and 5th gears/during decelerating: 2nd, 3rd, 4th, and 5th gears), and S with sequential sportshift mode (during accelerating: 1st, 2nd, 3rd, 4th, 5th, and 6th gears/during decelerating: 2nd, 3rd, 4th, 5th, and 6th gears). The torque converter clutch is in the torque converter. The multi-plate torque converter clutch increases the torque capacity and extends the lock-up area, improving fuel economy.
Gear Selection
The shift lever has five positions; P: PARK, R: REVERSE, N: NEUTRAL, D: DRIVE 1st through 6th gear ranges with automatic shift mode and D-paddle shift mode, and S: DRIVE 1st through 5th gear ranges with automatic shift mode and 1st through 6th gear ranges with sequential sportshift mode.
Starting the engine 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 displays 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.
Transfer Assembly
The transfer assembly consists of the transfer hypoid drive gear/shaft assembly, the transfer output shaft (hypoid gear), and the companion flange. The transfer assembly is on the rear side of the transmission, beside the differential. The transfer drive gear on the differential drives the transfer output shaft in the transmission. The transfer output shaft in the transmission is connected to the transfer hypoid drive gear/shaft assembly by splines. Power is transmitted from the transfer drive gear on the differential to the rear differential via the transfer assembly and the propeller shaft.