## Automatic Transmission

#### System Description

14-24

General Operation

The automatic transmission is a combination of a 3-element torque converter and electronically controlled automatic transmission that provides 4 speeds forward and 1 reverse. The 6-position transmission is dual-shaft automatic transmission and the 7-position is triple-shaft. 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. 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 which meshes with the starter pinion, when the engine is being started. The entire torque converter assembly serves as a flywheel while transmitting power to the transmissioNmainshaft.

The 6-position transmission has two parallel shafts: the mainshaft and the countershaft. The 7-position transmission has three parallel shafts: the mainshaft, the countershaft and the sub-shaft. The mainshaft is in line with the engine crankshaft. The mainshaft includes the 1st, 2nd and 4th clutches and gears for 3rd, 2nd, 4th, reverse and 1st (3rd gear is integral with the mainshaft, while reverse gear is integral with the 4th gear). The countershaft includes the 3rd clutch and gears for 3rd, 2nd, 4th, reverse, 1st and park. Reverse and 4th gears can be locked to the countershaft at its centre, providing 4th gear or reverse, depending on which way the selector is moved. The sub-shaft includes the 1st-hold clutch and gears for 1st and 4th. The gears on the mainshaft are in constant mesh with those on the countershaft. When certain combinations of gears are engaged by the clutches, power is transmitted from the mainshaft to the countershaft to provide , , and positions (6-position) and , , , and positions (7-position).

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 below the dashboard, behind the glove box.

Hydraulic Control

The valve bodies include the main valve body, the regulator valve body, the secondary valve body, the servo body and the lock-up valve body. They are bolted to the torque converter housing. The main valve body contains the manual valve, the modulator valve, the 1-2 shift valve, the 2nd orifice control valve, the servo control valve, the Clutch Pressure Back-up (CPB) valve and the ATF pump gears. The regulator valve body contains the regulator valve, the lock-up control valve, the torque converter check valve and the cooler relief valve. The secondary valve body contains the 2-3 shift valve, the 3-4 shift valve, 3-4 orifice control valve, the 4th exhaust valve and the Clutch Pressure Control (CPC) valve. The servo body contains the servo valve and the 1st, 2nd, 3rd and 4th accumulators. The lock-up valve body contains the lock-up shift valve and the lock-up timing valve. Fluid from the regulator passed through the manual valve to the various control valves. The 1st, 3rd and 4th clutches receive fluid from their respective feed pipe and the 2nd clutch receives fluid from the internal hydraulic circuit.

Shift Control Mechanism

The PCM controls to shift gears the shift solenoid valves A and B and A/T clutch pressure control solenoid valve A, while receiving input signal from various sensors 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 valve A controls the CPC valve to regulate the CPC pressure and to shift smoothly between lower gear and higher gear. This pressurises a line to one of the clutches, engaging the clutch and its corresponding gear.

Lock-up Mechanism

In position (3rd and 4th) and position (3rd), pressurised fluid is drained from 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 with hydraulic control, the PCM optimises 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 range of the lock-up according to A/T clutch pressure control solenoid valve B. The torque converter clutch solenoid valve is mounted on the torque converter housing and A/T clutch pressure control solenoid valve B is mounted on the transmission housing with solenoid valve A as an assembly. They are all controlled by the PCM.