Description Part 1

DESCRIPTION
The automatic transmission is a 3-element torque converter and triple-shaft electronically controlled unit which provides 4 speeds forward and 1 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. 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 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. The mainshaft includes the 3rd and 4th clutches, and gears for 3rd, 4th, reverse, and idler (reverse gear is integral with the 4th gear). The countershaft includes the final drive, 1st, 3rd, 4th, reverse, 2nd, parking, and idler gears (the final drive gear is integral with 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 which way the selector moved. 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 from the mainshaft and the secondary shaft to the countershaft to provide [D4], [D3], [2], [1], and [R] positions.

Electronic Control
The electronic control system consists of the Transmission Control Module (TCM), sensors, and six solenoid valves. Shifting and lock-up are electronically controlled for comfortable driving under all conditions. The TCM is located below the dashboard, under the front lower panel on the passenger's side.

Hydraulic Control
The valve bodies include the main valve body, the regulator valve body, the servo body, and the accumulator body. They are bolted on 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 pump gears. The regulator valve body contains the regulator valve, the lock-up timing 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 from the regulator passes through the manual valve to the various control valves. The 1st, 3rd, and 4th clutches receive fluid from their respective feed pipes, and the 2nd clutch receives fluid from the internal hydraulic circuit.

Shift Control Mechanism
The TCM controls shift control solenoid valves A, B, and C, and A/T clutch pressure control solenoid valves A and B, while receiving input signals from various sensors located throughout the vehicle. The shift control 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 to one of the clutches, engaging the clutch and its corresponding gear.





Lock-Up Mechanism
In [D4] position, and sequential sportshift mode (2nd, 3rd and 4th), and [D3] position (2nd and 3rd), pressurized 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 TCM optimizes the timing of the lock-up mechanism. When the lock-up control 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 lock-up according to A/T clutch pressure control solenoid valves A and B. The lock-up control solenoid valve is mounted on the torque converter housing, and A/T clutch pressure control solenoid valves A and B are mounted on the transmission housing. They are all controlled by the TCM.

CLUTCHES





The four-speed automatic transmission uses hydraulically-actuated clutches to engage or disengage the transmission gears. When hydraulic pressure is introduced into the clutch drum, the clutch piston moves. This presses the friction discs and steel plates together, locking them so they don't slip, Power is then transmitted through the engaged clutch pack to its hub-mounted gear. Likewise, when the hydraulic pressure is bled from the clutch pack, the piston releases the friction discs and the steel plates, and they are free to slide past each other. This allows the gear to spin independently on its shaft, transmitting no power.

1st Clutch
The 1st clutch engages/disengages 1st gear, and is located at the middle of the secondary shaft. The 1st clutch is joined back-to-back to the 2nd clutch. The 1st clutch is supplied hydraulic pressure by its ATF feed pipe within the secondary shaft.

2nd Clutch
The 2nd clutch engages/disengages 2nd gear, and is located at the middle of the secondary shaft. The 2nd clutch is joined back-to-back to the 1st clutch. The 2nd clutch is supplied hydraulic pressure through the secondary shaft by a circuit connected to the internal hydraulic circuit.

3rd Clutch
The 3rd clutch engages/disengages 3rd gear, and is located at the middle of the mainshaft. The 3rd clutch is joined back-to-back to the 4th clutch. The 3rd clutch is supplied hydraulic pressure by its ATF feed pipe within the mainshaft.

4th Clutch
The 4th clutch engages/disengages 4th gear, as well as reverse gear, and is located at the middle of the mainshaft. The 4th clutch is joined back-to-back to the 3rd clutch. The 4th clutch is supplied hydraulic pressure by its ATF feed pipe within the mainshaft.
POWER FLOW





Gear Operation

Gears on the mainshaft:
- The 3rd gear is engaged/disengaged with the mainshaft by the 3rd clutch.
- The 4th gear is engaged/disengaged with the mainshaft by the 4th clutch.
- The reverse gear is engaged/disengaged with the mainshaft by the 4th clutch.
- The idler gear is splined to the mainshaft and rotates with the mainshaft.

Gears on the countershaft:
- The final drive gear is integral with the countershaft.
- The 1st gear, 3rd gear, 2nd gear, and park gear are splined to the countershaft, and rotate with the countershaft.
- The 4th gear and reverse gear rotate freely from the countershaft. The reverse selector engages the 4th gear or the reverse gear with the reverse selector hub. The reverse selector hub is splined with the countershaft so that the 4th gear or reverse gear engage with the countershaft.
- The idler gear rotates freely from the countershaft.





Gears on the secondary shaft:
- The 1st gear is engaged/disengaged with the secondary shaft by the 1st clutch.
- The 2nd gear is engaged/disengaged with the secondary shaft by the 2nd clutch.
- The idler gear is splined to the secondary shaft and rotates with the secondary shaft.

In [D4] or [D3] position, the optimum gear is automatically selected from 1st, 2nd, 3rd, and 4th gears, according to conditions such as the balance between the throttle opening (engine loading) and vehicle speed.

[D4] or [D3] Position in 1st gear and [1] Position





1. Hydraulic pressure is applied to the 1st clutch, then the 1st clutch engages the secondary shaft 1st gear with the secondary shaft.
2. The mainshaft idler gear drives the secondary shaft via the countershaft idler gear and secondary shaft idler gear.
3. The secondary shaft 1st gear drives the countershaft 1st gear and the countershaft.
4. Power is transmitted to the final drive gear, which in turn drives the final driven gear.

[D4] or [D3] Position in 2nd gear and [2] Position





1. Hydraulic pressure is applied to the 2nd clutch, then the 2nd clutch engages the secondary shaft 2nd gear with the secondary shaft.
2. The mainshaft idler gear drives the secondary shaft via the countershaft idler gear and secondary shaft idler gear.
3. The secondary shaft 2nd gear drives the countershaft 2nd gear and the countershaft.
4. Power is transmitted to the final drive gear, which in turn drives the final driven gear.





[D4] or [D3] Position in 3rd gear
1. Hydraulic pressure is applied to the 3rd clutch, then the 3rd clutch engages the mainshaft 3rd gear with the mainshaft.
2. The mainshaft 3rd gear drives the countershaft 3rd gear and the countershaft.
3. Power is transmitted to the final drive gear, which in turn drives the final driven gear.

[D4] Position in 4th gear





1. Hydraulic pressure is applied to the servo valve to engage the reverse selector with the countershaft 4th gear while the shift lever is in the forward range ([D4], [D3], [2] and [1] position).
2. Hydraulic pressure is also applied to the 4th clutch, then the 4th clutch engages the mainshaft 4th gear with the mainshaft.
3. The mainshaft 4th gear drives the countershaft 4th gear, which drives the reverse selector hub and the countershaft.
4. Power is transmitted to the final drive gear, which in turn drives the final driven gear.

[R] Position





1. Hydraulic pressure is applied to the servo valve to engage the reverse selector with the countershaft reverse gear while the shift lever is in the [R] position.
2. Hydraulic pressure is also applied to the 4th clutch, then the 4th clutch engages the mainshaft reverse gear with the mainshaft.
3. The mainshaft reverse gear drives the countershaft reverse gear via the reverse idler gear.
4. The rotation direction of the countershaft reverse gear is changed via the reverse idler gear.
5. The countershaft reverse gear drives the countershaft via the reverse selector, which drives the reverse selector hub.
6. Power is transmitted to the final drive gear, which in turn drives the final driven gear.