Description Part 3

POWER FLOW

ELECTRONIC CONTROL SYSTEM





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

Shift Control





The Powertrain Control Module (PCM) instantaneously determines which gear should be selected by various signals sent from sensors, and actuates the shift control solenoid valves A and B to control shifting. Also, a Grade Logic Control System has been adopted to control shifting in [D4] position while the vehicle is ascending or descending a slope, or reducing speed.

Lock-up Control





From sensor input signals, the Powertrain Control Module (PCM) determines whether to turn the lock-up ON or OFF, and activates lock-up control solenoid valve A and/or B accordingly. The combination of driving signals to lock-up control solenoid valves A and B and the linear solenoid pressure is shown in the table.

GRADE LOGIC CONTROL SYSTEM





How it works:
The Powertrain Control Module (PCM) compares actual driving conditions with driving conditions memorized in the PCM, based on the input from the vehicle speed sensor, the throttle position sensor, the barometoric pressure sensor, the engine coolant temperature sensor, the brake switch signal, and the shift lever position signal, to control shifting while a vehicle is ascending or descending a slope, or reducing speed.

Ascending Control
When the Powertrain Control Module (PCM) determines that the vehicle is climbing a hill in [D4] position, the system extends the engagement area of 2nd gear and 3rd gear to prevent the transmission from frequently shifting between 2nd and 3rd gears, and between 3rd and 4th gears, so the vehicle can run smooth and have more power when needed. There are two ascending modes with different 3rd gear driving areas according to the magnitude of a gradient stored in the PCM.

NOTE:
- The PCM memory contains shift schedules between 2nd and 3rd gears, and between 3rd and 4th gears that enable the PCM's fuzzy logic to automatically select the most suitable gear according to the magnitude of a gradient.
- Fuzzy logic is a form of artificial intelligence that lets computers respond to changing conditions much like a human mind would.

Descending Control





When the Powertrain Control Module (PCM) 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 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 downshift (4 - 3) schedules according to the magnitude of a gradient stored in the PCM. 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 first decelerate and then accelerate, the Powertrain Control Module (PCM) sets the data for deceleration control to reduce the number of times the transmission shifts. When the vehicle is decelerating from speeds above 26 mph (41 km/h), the PCM shifts the transmission from 4th to 2nd earlier than normal to cope with upcoming acceleration.


HYDRAULIC CONTROL





The hydraulic control system is controlled by the Automatic Transmission Fluid (ATF) pump, valves, accumulators, and electronically controlled solenoids. The ATF pump is driven by splines on the end of the torque converter which is attached to the engine. Fluid from the ATF pump 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 valve body includes the main valve body, the regulator valve body, the lock-up valve body, the secondary valve body, the servo body, the linear solenoid, the shift control solenoid valve A/B assembly, and the lock-up control solenoid valve A/B assembly. The shift control solenoid valve A/B assembly and the linear solenoid are bolted on the outside of the transmission housing. The lock-up control solenoid valve A/B assembly is bolted on the outside of the torque converter housing.

Main Valve Body





The main valve body houses the manual valve, the 1-2 shift valve, the 2nd orifice control valve, the Clutch Pressure Back-up (CPB) valve, the modulator valve, the servo control valve, and the relief valve. The primary functions of the main valve body is to switch fluid pressure on and off and to control the hydraulic pressure going to the hydraulic control system.

Secondary Valve Body





The secondary valve body is located on the main valve body. The secondary valve body houses the 2-3 shift valve, the 3-4 shift valve, the 3-4 orifice control valve, the 4th exhaust valve, and Clutch Pressure Control (CPC) valve.

Regulator Valve Body





The regulator valve body is located on the main valve body. The regulator valve body consists of the regulator valve, the torque converter check valve, the cooler relief valve, and the lock-up control valve.

Lock-up Valve Body





The lock-up valve body with the lock-up shift valve and the lock-up timing valve is located on the regulator valve body.

Regulator Valve
The regulator valve maintains a constant hydraulic pressure from the Automatic Transmission Fluid (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'. The regulator valve has a valve orifice, The fluid entering from B flows through the 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 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 D and C also changes. This operation is continued, maintaining the line pressure.





NOTE: When used, "left" or "right" indicates direction on the illustration.

Stator Reaction Hydraulic Pressure Control





Hydraulic pressure increases according to torque, are performed by the regulator valve using the 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 located on the secondary valve body. The servo body contains the servo valve which is integrated with the reverse shift fork, and the accumulators.

HYDRAULIC FLOW





[N] Position





As the engine turns, the ATF pump also starts to operate. Automatic Transmission Fluid (ATF) is drawn from (99) and discharged into (1). Then, ATF flowing from the ATF pump becomes the line pressure (1). The line pressure (1) is regulated by the regulator valve. The torque converter inlet pressure (92) enters (94) of the torque converter through the lock-up shift valve and discharges into (90). The torque converter check valve prevents the torque converter pressure from rising. Under this condition, the hydraulic pressure is not applied to the clutches.

NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.

[2] Position





The line pressure (1) flows to the manual valve and the modulator valve. The line pressure (1) changes the line pressure (4) and (25) at the manual valve, and changes to the modulator pressure at the modulator valve. But the modulator pressure (6) does not flow to each shift valve because shift control solenoid valves A and B are turned ON by the Powertrain Control Module (PCM). The line pressure (4) passes through the CPB valve and the Clutch Pressure Control (CPC) valve, and changes to the line pressure (5), then flows to the 1-2 shift valve. The line pressure (5) from the 1-2 shift valve changes to the 2nd clutch pressure (20) at the 2-3 shift valve. The 2nd clutch pressure (20) is applied to the 2nd clutch, and the 2nd clutch is engaged. The line pressure (4) passes through the 1-2 shift valve and the orifice, and changes the 1st clutch pressure. The 1st clutch pressure (10) also flows to the 1st clutch. However, no power is transmitted because of the one-way clutch.

NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.

[D4] or [D3] Position
1. 1st Gear





The flow of fluid through the torque converter circuit is same as in [N] position. The line pressure flows to the manual valve and the modulator valve. The line pressure changes to the modulator pressure (6) at the modulator valve and to the line pressure (4) at the manual valve. The modulator pressure (6) flows to the left end of the 1-2 shift valve and the 3-4 shift valve because shift control solenoid valve A is turned OFF and B is turned ON by the PCM. The 1-2 shift valve is moved to the right side. The line pressure (4) changes to the 1st clutch pressure (10) at the 1-2 shift valve and the orifice. The 1st clutch pressure (10) is applied to the 1st clutch and the 1st accumulator; consequently, the vehicle will move as the engine power is transmitted.

NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.

2. 2nd Gear





As the speed of the vehicle reaches the prescribed value, shift control solenoid valve A is turned ON by means of the Powertrain Control Module (PCM). The modulator pressure (6A) in the left end of the 1-2 shift valve is released by turning shift control solenoid valve A ON. The 1-2 shift valve is moved to the left side and uncovers the port to allow line pressure (5) to the 2-3 shift valve. The line pressure (5) changes to the 2nd clutch pressure (20) at the 2-3 shift valve. The 2nd clutch pressure (20) is applied to the 2nd clutch, and the 2nd clutch is engaged.
Fluid flows by way of:
- Line Pressure (4) -> CPB Valve - Line Pressure (5) -> 1-2 Shift Valve - Line Pressure (5) - 2-3 Shift Valve
- 2nd Clutch Pressure (20) -> 2nd Clutch

The hydraulic pressure also flows to the 1st clutch. However, no power is transmitted because of the one-way clutch.

NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.

3. 3rd Gear





As the speed of the vehicle reaches the prescribed value, shift control solenoid valve B is turned OFF by means of the Powertrain Control Module (PCM). Shift control solenoid valve A remains ON. The modulator pressure (6) flows to the right end of the 1-2 shift valve and the left end of the 2-3 shift valve. The 2-3 shift valve is moved to the right side by the modulator pressure (6B). The 2-3 shift valve covers the port to stop line pressure (5) to the 2nd clutch and uncovers to the 3-4 shift valve as the 2-3 shift valve is moved to the right side. The line pressure (5) becomes the 3rd clutch pressure (30) at the 3-4 shift valve. The 3rd clutch pressure (30) is applied to the 3rd clutch, and the 3rd clutch is engaged.
Fluid flows by way of:
- Line pressure (4) -> CPB Valve - Line Pressure (5) -> 1-2 Shift Valve - Line Pressure (5) -> 2-3 Shift Valve
- Line Pressure (5) -> 3-4 Shift Valve -> 3rd Clutch Pressure (30)-> 3rd Clutch
The hydraulic pressure also flows to the 1st clutch. However, no power is transmitted because of the one-way clutch as in 2nd gear.

NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.

4. 4th Gear ([D4] Position)





As the speed of the vehicle reaches the prescribed value, shift control solenoid valve A is turned OFF by means of the PCM. Shift control solenoid valve B remains OFF. The modulator pressure (6) flows to the left end of the 1-2 shift valve and the left end of the 3-4 shift valve. The modulator pressure (6A) in the left end of the 1-2 shift valve equals the modulator pressure (6B) in the right end of the 1-2 shift valve, the 1-2 shift valve remains at left side by the tension of the valve spring. The 3-4 shift valve is moved to the right side by the modulator pressure (6A). The 3-4 shift valve covers the port to the 3rd clutch and uncovers the port to the 4th clutch as this valve is moved to the right side. The 4th clutch pressure (41) from the 3-4 shift valve becomes the 4th clutch pressure (40) at the manual valve. The 4th clutch pressure (40) is applied to the 4th clutch, and the 4th clutch is engaged.
Fluid flows by way of:
- Line pressure (4) -> CPB Valve - Line Pressure (5) -> 1-2 Shift Valve - Line Pressure (5) -> 2-3 Shift Valve
- Line Pressure (5) -> 3-4 Shift Valve - 4th Clutch Pressure (41) -> Manual Valve - 4th Clutch Pressure (40) -> 4th Clutch
The hydraulic pressure also flows to the 1st clutch. However, no power is transmitted because of the one-way clutch as in 2nd and 3rd gear.

NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.

[R] Position
The flow of fluid through the torque converter circuit is the same as in [N] position. The line pressure (1) changes to the line pressure (3) and flows to the 1-2 shift valve. The line pressure (3) changes to the line pressure (3') at the 1-2 shift valve and flows to the servo valve. The servo valve is moved to the right side (Reverse range position) and uncovers the port to allow line pressure (3") to the manual valve. The line pressure (31 from the 1-2 shift valve flows through the servo valve to the manual valve and changes the 4th clutch pressure (40). The 4th clutch pressure (40) is applied to the 4th clutch, and the 4th clutch is engaged.

Reverse Inhibitor Control





When the [R] position is selected while the vehicle is moving forward at speeds over 6 mph (10 km/h), the PCM outputs the 1st speed signal to shift control solenoid valves A and B; shift control solenoid valve A is turned OFF, shift control solenoid valve B is turned ON. The 1-2 shift valve is moved to the right side and covers the port to stop line pressure (3') to the servo valve. The line pressure (3') is not applied to the servo valve, and the 4th clutch pressure (40) is not applied to the 4th clutch, as a result, power is not transmitted to the reverse direction.

NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.

[P] Position





The flow of fluid through the torque converter circuit is the same as in [N] position. The line pressure (1) changes to the line pressure (3) and flows to the 1-2 shift valve. The line pressure (3) changes to the line pressure (3') at the 1-2 shift valve and flows to the servo valve. The servo valve is moved to the right side (Reverse range position) and uncovers the port to allow line pressure (3") to the manual valve as in [R] position. The line pressure (3") from the servo valve is intercepted by the manual valve. However, hydraulic pressure is not supplied to the clutches, and the power is not transmitted.

NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.

LOCK-UP SYSTEM
Lock-up Clutch
1. Operation (clutch on)





With the lock-up clutch on, the fluid in the chamber between the torque converter cover and the lock-up piston is drained off, and the converter fluid exerts pressure through the piston against the torque converter cover. As a result, the converter turbine is locked to the converter cover. The effect is to bypass the converter, thereby placing the vehicle in direct drive.
2. Operation (clutch off)





With the lock-up clutch off, the fluid flows in the reverse of "clutch on." As a result, the lock-up piston moves away from the converter cover, and the torque converter lock-up is released.





Lock-up Conditions/Lock-up Control Solenoid Valves/ Linear Solenoid Pressure

In [D4] position, in 3rd and 4th, and [D3] position in 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 the hydraulic control, the PCM optimized the timing of the lock-up system. Under certain conditions, the lock-up clutch is applied during deceleration, in 3rd and 4th gear.
The lock-up system controls the range of lock-up according to lock-up control solenoid valves A and B, and the linear solenoid. When lock-up control solenoid valves A and B activate, modulator pressure changes. Lock-up control solenoid valves A and B and the linear solenoid are mounted on the outside of the torque converter housing, and are controlled by the Powertrain Control Module (PCM).

No Lock-up
- Lock-up Control Solenoid Valve A: OFF
- Lock-up Control Solenoid Valve B: OFF
- Linear Solenoid Pressure: High





The pressurized fluid regulated by the modulator works on both ends of the lock-up shift valve. Under this condition, the pressures working on both ends of the lock-up shift valve are equal, the lock-up shift valve is moved to the right side by the tension of the valve spring alone. The fluid from the Automatic Transmission Fluid (ATF) pump will flow through the left side of the lock-up clutch to the torque converter; that is, the lock-up clutch is in OFF condition.

NOTE: When used, "left" and "right" indicates direction on the hydraulic circuit.

Half Lock-up
- Lock-up Control Solenoid Valve A: ON
- Lock-up Control Solenoid Valve B: Duty Operation OFF <-> ON
- Linear Solenoid Pressure: Low





The Powertrain Control Module (PCM) switches the solenoid valve A on to release the modulator pressure in the left cavity of the lock-up shift valve. The modulator pressure in the right cavity of the lock-up shift valve overcomes the spring force; thus the lock-up shift valve is moved to the left side.
The line pressure is then separated into the two passages to the torque converter:
- Torque Converter Inner Pressure: enters into right side to engage lock-up clutch.
- Torque Converter Back Pressure: enters into left side to disengage lock-up clutch
The back pressure (F2) is regulated by the lock-up control valve, whereas the position of the lock-up timing valve is determined by the linear solenoid pressure and tension of the valve spring. Also the position of the lockup control valve is determined by the back pressure of the lock-up control valve, torque converter pressure regulated by the torque converter check valve, and modulator pressure determined by the lock-up control solenoid valve B. The PCM switches the lock-up control solenoid valve B on and off rapidly (duty operation) under certain conditions to regulate the back pressure (F2) to lock the torque converter properly.

NOTE: When used, "left" and "right" indicates direction on the hydraulic circuit.

Full Lock-up
- Lock-up Control Solenoid Valve A: ON
- Lock-up Control Solenoid Valve B: ON
- Linear Solenoid Pressure: High





When the vehicle speed further increases, the linear solenoid pressure is increased to high in accordance with the linear solenoid controlled by the Powertrain Control Module (PCM).
The lock-up timing valve overcomes the spring force and moves to the left side. Also, this valve closes the fluid port leading to the left side of the lock-up control valve.
Under this condition, the modulator pressure in the left side of the lock-up control valve had already been released by the lock-up control solenoid valve B; the lock-up control valve is moved to the left side. As this takes place, the torque converter back pressure is released fully, causing the lock-up clutch to be engaged fully.

NOTE: When used, "left" and "right" indicates direction on the hydraulic circuit.

Deceleration Lock-up
- Lock-up Control Solenoid Valve A: ON
- Lock-up Control Solenoid Valve B: Duty Operation OFF <-> ON
- Linear Solenoid Pressure: Low





The Powertrain Control Module (PCM) switches solenoid valve B on and off rapidly under certain conditions. The slight lock-up and half lock-up regions are maintained so as to lock the torque converter properly.

NOTE: When used, "left" and "right" indicates direction on the hydraulic circuit.