Description and Operation Part 1

DESCRIPTION
Part 1

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.

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.

SHIFT CONTROL





Shifting is related to engine torque through the A/T clutch pressure control solenoids, which are controlled by the TCM. The TCM instantly determines which gear should be selected, by various signals sent from sensors, and actuates the shift control solenoid valves A, B, and C to control shifting. Also, a sequential sportshift mode has been adopted to shift gears up and down manually in [D4] position while using the shift lever.
The combination of driving signals to shift control solenoid valves A, B, and C are shown in the table below.

SEQUENTIAL SPORTSHIFT MODE
In [D4] position while sliding the shift lever to the sequential sportshift mode position, the driver can use the shift lever to shift gears up and down, much like a manual transmission.
- Pushing the shift lever toward the "+" mark: Transmission upshifts to the next higher gear.
- Pulling the shift lever toward the "-" mark: Transmission downshifts.

The number of the selected gear is displayed in the shift indicator next to the [D4] indicator.
The transmission does not automatically upshift and downshift, and remains in the selected gear position (4th, 3rd 2nd and 1st). However, the transmission will automatically downshift as follows:
- Downshift from 4th gear to 3rd gear to get more power when climbing or to provide engine braking when going down a steep hill.
- Downshift to 1st gear when the vehicle comes to stop.

To prevent engine over-revving, the transmission has 4-3, 3-2 and 2-1 downshift allowable speeds. When the vehicle is coasting over the 4-3 downshift allowable speed, 3-2 downshift allowable speed, and 2-1 downshift allowable speed, the TCM does not input the downshift signal from the shift switch, and the transmission does not downshift. When the vehicle is coasting over the 4-3 downshift allowable speed in 4th gear, and the 3-2 downshift allowable speed in 3rd gear, the TCM inputs the signal to wait until it reaches the downshift allowable speed, then the shift indicator blinks several times to indicate the lower gear position.

LOCK-UP CONTROL
The lock-up control solenoid valve controls modulator pressure to switch the lock-up shift valve and lock-up on and off. The TCM controls the lock-up control solenoid valve and the A/T clutch pressure control solenoid valves A and B. When the lock-up control solenoid valve is turned on, the condition of lock-up starts. The A/T clutch pressure control solenoid valves A and B regulate A/T clutch pressure control solenoid pressure, and apply pressure to the lock-up control valve and the lock-up timing valve; those of the lock-up control mechanism come into operation in 2nd, 3rd, and 4th gear in [D4] and sequential sportshift mode, and in 2nd and 3rd gear in [D3] positions.

GRADE LOGIC CONTROL SYSTEM





How it works:
The TCM compares actual driving conditions with driving conditions memorized in the TCM, based on the input from the vehicle speed sensor, the throttle position sensor, the brake switch signal, and the shift lever position signal, to control shifting while the vehicle is ascending or descending a slope, or reducing speed.

ASCENDING CONTROL
When the TCM determines that the vehicle is climbing a hill in [D4] position, the shift-up speed from 3rd to 4th gear becomes faster than the set speed for normal mode (flat road) driving to widen the 3rd gear driving area, so the vehicle can run smooth and have more power when needed. There are three ascending modes with different 3rd gear driving areas. The modes are based on information stored in the TCM.

DESCENDING CONTROL
When the TCM determines that the vehicle is going down a hill in [D4] position, the shift-up speed from 3rd to 4th gear when the throttle is closed becomes faster than the set speed for normal mode (flat road) driving to widen the 3rd gear driving area. This, in combination with engine braking from the deceleration lock-up, achieves smooth driving when the vehicle is descending. There are two descending modes with different 3rd gear driving areas. The modes are based on information stored in the TCM. When the vehicle is in 4th gear, and you are decelerating on a gradual hill, or when you are applying the brakes on a steep hill, the transmission will downshift to 3rd gear. When you accelerate, the transmission will then return to 4th gear.

DECELERATION CONTROL





When the vehicle goes around a corner, and needs to decelerate first and then accelerate, the TCM sets the data for deceleration control to reduce the number of times the transmission shifts. When the vehicle is decelerating from speeds above 30 mph (48 km/h), the TCM shifts the transmission from 4th to 2nd earlier than normal to cope with upcoming acceleration.

ENGINE CONTROL IN COOPERATION WITH ECM





The TCM also sends signals of the following transmission conditions to the ECM which controls the engine.
- When the transmission shifts gears, the TCM causes the ECM to control the engine ignition timing.
- When the transmission is in [N] position, the TCM causes the ECM to control engine rpm.
- When the transmission shifts into [D4], [D3], [2], [1] or [R] position at high rpm, the TCM causes the ECM to control the engine ignition timing.
- During a stall test, the TCM causes the ECM to control engine torque.

HYDRAULIC CONTROL





The valve body includes the main valve body, the regulator valve body, the servo body, and the accumulator body. The ATF pump is driven by splines on the right end of the torque converter which is attached to the engine. Fluid flows through the regulator valve to maintain specified pressure, through the main valve body, to the manual valve, directing pressure to each of the clutches. The shift control solenoid valves B and C are mounted on the outside of the torque converter housing. The shift control solenoid valve A and the lock-up control solenoid valve are mounted on the torque converter housing as an assembly. The A/T clutch pressure control solenoid valves A and B are mounted on the transmission housing.

Main Valve Body





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 primary function of the main valve body is to switch fluid pressure on and off and to control hydraulic pressure going to the hydraulic control system.

Regulator Valve Body





The regulator valve body is located on the main valve body. The regulator valve body contains the regulator valve, the lock-up timing valve, and the relief valve.

Regulator Valve





The regulator valve maintains constant hydraulic pressure from the ATF pump to the hydraulic control system, while also furnishing fluid to the lubricating system and torque converter. The fluid from the ATF pump flows through B and B'. Fluid entering from B flows through the valve orifice to the A cavity. This pressure of the A cavity pushes the regulator valve to the right side, and this movement of the regulator valve uncovers the fluid port to the torque converter and the relief valve. The fluid flows out to the torque converter and the relief valve, and the regulator valve moves to the left side. According to the level of the hydraulic pressure through B, the position of the regulator valve changes and the amount of the fluid from B' through torque converter also changes. This operation is continued, maintaining the line pressure.

Stator Reaction Hydraulic Pressure Control





Increases in hydraulic pressure according to torque are performed by the regulator valve using stator torque reaction. The stator shaft is splined with the stator in the torque converter, and its arm end contacts the regulator spring cap. When the vehicle is accelerating or climbing (Torque Converter Range), the stator torque reaction acts on the stator shaft, and the stator arm pushes the regulator spring cap in the direction of the arrow in proportion to the reaction. The stator reaction spring compresses, and the regulator valve moves to increase the line pressure which is regulated by the regulator valve. The line pressure reaches its maximum when the stator torque reaction reaches its maximum.

Servo Body
The servo body is on the main valve body. It contains the servo valve, the shift valve A, the shift valve B, the CPC valves A and B, and the 3rd and 4th accumulators.