Part 2
System Description (Continued)Electronic Control System
Functional Diagram
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 receives input signals from the sensors, switches, and other control units, processes data, and outputs signals for the engine control System and A/T control system. The A/T control system includes shift control, grade logic control, clutch pressure control, and lock-up control. The PCM switches the shift solenoid valves and the A/T clutch pressure control solenoid valves to control shifting transmission gears and lock-up torque converter clutch.
Shift Control
The PCM instantly determines which gear should be selected by various signals sent from sensors and switches, and it actuates shift solenoid valves A, B, C, and D to control shifting transmission gear.
The shift solenoid valves have two types:
^ Shift solenoid valves A and D use ON-OPEN/OFF-CLOSE type; shift solenoid valve opens the port of shift solenoid valve pressure while shift solenoid valve is turned ON by the PCM, and closes the port when shift solenoid valve is OFF.
^ Shift solenoid valves B and C use ON-CLOSE/OFF-OPEN type; shift solenoid valve closes the port of shift solenoid valve pressure while shift solenoid valve is turned ON by the PCM, and opens the port when shift solenoid valve is OFF.
The combination of driving signals to shift solenoid valves A, B, C, and D are shown in the table.
Shift Control - Grade Logic Control
The grade logic control system has been adopted to control shifting in the D position. To control shifting while the vehicle is ascending or descending a slope the PCM compares actual driving conditions with programmed driving conditions, based on the input from the accelerator pedal position sensor, the engine coolant temperature sensor, the barometric pressure sensor, the brake pedal position switch signal, and the shift lever position signal.
Grade Logic Control: Ascending Control
When the PCM determines that the vehicle is climbing a hill in the D position, the system extends the engagement area of 2nd gear, 3rd gear, and 4th gear to prevent the transmission from frequently shifting between 2nd and 3rd gears, between 3rd and 4th gears, and between 4th and 5th gears, so the vehicle can run smooth and have more power when needed.
NOTE: Shift commands stored in the PCM between 2nd and 3rd gears, between 3rd and 4th gears, and between 4th and 5th gears, enable the PCM to automatically select the most suitable gear according to the magnitude of a gradient.
Grade Logic Control: Descending Control
When the PCM determines that the vehicle is going down a hill in the D position, the shift-up speed from 4th to 5th gear, 3rd to 4th gear, and from 2nd to 3rd (when the throttle is closed) becomes faster than the set speed for flat road driving to widen the 4th gear, 3rd gear, and 2nd gear driving areas. This, in combination with engine braking from the deceleration lock-up, achieves smooth driving when the vehicle is descending. There are three descending modes with different 4th gear driving areas, 3rd gear driving areas, and 2nd gear driving areas according to the magnitude of a gradient stored in the PCM. When the vehicle is in 5th or 4th gear and you are decelerating while applying the brakes on a steep hill, the transmission will downshift to a lower gear. When you accelerate, the transmission will then return to a higher gear.
Deceleration Control
When the vehicle goes around a corner and needs to decelerate first and then accelerate, the PCM sets the data for deceleration control to reduce the number of times the transmission shifts. When the vehicle is decelerating from speeds above 27 mph (43 km/h), the PCM shifts the transmission from 5th or 4th to 2nd earlier than normal to cope with upcoming acceleration.
Shift-Hold Control
When negotiating winding roads, the throttle is suddenly released and the brakes are applied, as is the case when decelerating at the entrance of a corner, Shift-Hold Control keeps the transmission in its current (lower) ratio as it negotiates the corner and accelerates out.
When the vehicle is driven aggressively on a winding road, the PCM will extend the engagement time of 3rd gear and 4th gear to prevent the transmission from frequently shifting between 3rd, 4th, and 5th gears. This allows the driver to have more control for both acceleration and deceleration.
The PCM monitors the average change in vehicle speed and throttle over time. When these values exceed those for normal driving conditions, the shift-up from 3rd to 4th gear and 4th to 5th gear is delayed. This gives more control over power, and engine braking when the driver is driving aggressively around winding roads. The transmission will resume the normal shift-up pattern after the PCM determines that normal driving has resumed.
Shift Control - Sequential Shift Made
The transmission is provided a sequential shift mode in the D position. In the D position, the transmission has two modes; the automatic shift mode and sequential shift mode. The transmission is switched to the sequential shift mode by moving the shift lever into the M position from the D, and the driver can shift up and down manually 1st through 5th gears with the shift lever, and by using the steering wheel shift switches (Type-S); much like a manual transmission.
The vehicle can start off in 1st and 2nd gear in the M position.
The sequential shift upshift switch and downshift switch are in the shift lever, and steering wheel upshift (+) switch and steering wheel downshift (-) switch are installed on the back of the steering wheel. The driver can shift gears by moving the shift lever by hand, or by pressing the steering wheel shift switches without taking either hand off the steering wheel.
The M indicator and shift indicator are in the tachometer in the gauge control module.
In the M position; sequential shift mode, the M indicator comes on, and the shift indicator displays the number of the gear selected.
Clutch Pressure Control
The PCM actuates A/T clutch pressure control solenoid valves A, B, and C to control the clutch pressure. When shifting between gears, the clutch pressure regulated by A/T clutch pressure control solenoid valves A, B, and C engages and disengages the clutch smoothly. The PCM receives input signals from the various sensors and switches, performs processing data, and outputs current to A/T clutch pressure control solenoid valves A, B, and C.
Lock-up Control
Shift solenoid valve D controls the hydraulic pressure to switch the lock-up shift valve and lock-up ON and OFF. The PCM actuates shift solenoid valve D and A/T clutch pressure control solenoid valve C ON, the condition of lock-up starts. A/T clutch pressure control solenoid valve C regulates and apply the hydraulic pressure to the lock-up control valve to control the volume of the lock-up.
The lockup mechanism operates in the D position (2nd, 3rd, 4th, and 5th) and the D position with sequential shift (M position) (3rd, 4th, and 5th).
PCM A/T Control System Electrical Connections:
PCM A/T Control System Inputs and Outputs (Part 1):
PCM A/T Control System Inputs and Outputs (Part 2):
PCM A/T Control System Inputs and Outputs (Part 3):
PCM A/T Control System Inputs and Outputs (Part 4):
Hydraulic Controls
The valve body includes the main valve body, the regulator valve body, the secondary valve body, and the accumulator body. The ATF pump is driven by splines on the 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. Shift solenoid valves A, B, C, and D are mounted on the accumulator body. A/T clutch pressure control solenoid valves A, B, and C are mounted on the transmission housing.
Main Valve Body
The main valve body contains the manual valve, the modulator valve, shift valve A, shift valve B, shift valve E, CPC valve A, the servo control valve, the lubrication check valve, the lubrication control valve, the torque converter check valve, the lock-up timing valve, the relief valve, the lock-up shift valve, and the ATF pump gears. The primary function of the main valve body is to switch fluid pressure on and off 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 cooler check valve, the lock-up control valve, the servo valve, and the 3rd accumulator.
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. 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 spring 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 returns under spring force. According to the level of the hydraulic pressure through B, the position of the regulator valve changes, and the amount of fluid from B' through the torque converter changes. This operation is continued, maintaining the line pressure.
Increases in hydraulic pressure according to torque are performed by the regulator valve using stator torque reaction. The stator shaft is splined to 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), 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.
Secondary Valve Body
The secondary valve body is on the main valve body. The secondary valve body contains shift valve C, shift valve D, CPC valve B, CPC valve C, the reverse control valve, and the reverse CPC valve.
Accumulator Body
The accumulator body is on the secondary valve body, and contains the 1st, 1st-hold, 2nd, 4th, and 5th accumulators. The 3rd accumulator is in the regulator valve body.
Hydraulic Flow
Distribution of Hydraulic Pressure
As the engine turns, the ATF pump starts to operate. Automatic transmission fluid (ATF) is drawn through the ATF strainer (filter) and discharged into the hydraulic circuit. Then, ATF flowing from the ATF pump becomes line pressure that is regulated by the regulator valve. Torque converter pressure from the regulator valve enters the torque converter through the lock-up shift valve and lock-up control valve, and it is discharged from the torque converter. The torque converter check valve prevents torque converter pressure from rising. The PCM controls shift solenoid valves A, B, C, and D ON and OFF, and the shift solenoid valves control shift solenoid pressure to the shift valves. Applying shift solenoid pressure to the shift valves moves the position of the shift valve, and switches the port of hydraulic pressure.
The PCM also controls A/T clutch pressure control solenoid valves A, B, and C. The A/T clutch pressure control solenoid valves regulate the A/T clutch pressure control solenoid valve pressure and apply A/T clutch pressure control solenoid valve pressure to CPC valves A, B, and C.
When shifting between gears, the clutch is engaged by pressure from the CPC pressure mode. The PCM controls one of the shift solenoid valves to move the position of the shift valve. This movement switches the port of CPC pressure and line pressure. Line pressure is then applied to the clutch, and CPC pressure is released. Engaging the clutch with line pressure mode happens when shifting is completed.
Hydraulic pressure at the ports:
N Position
Line pressure (1) regulated by the regulator valve flows to shift solenoid valves. The PCM controls the shift solenoid valves ON and OFF. The conditions of the shift solenoid valves and positions of the shift valve are as follows:
^ Shift solenoid valve A is OFF, and closes the port of shift solenoid valve A pressure (SA); shift valve A stays on the left side.
^ Shift solenoid valve B is turned ON, and closes the port of shift solenoid valve B pressure (SB); shift valve B and shift valve E stay on the left side.
^ Shift solenoid valve C is OFF, and opens the port of shift solenoid valve C pressure (SC); shift valve C and shift valve D move to the right side.
^ Shift solenoid valve D is OFF, and closes the port of shift solenoid valve D pressure (SD).
Line pressure (1) also flows to the modulator valve and becomes modulator pressure (6). Modulator pressure (6) flows to the A/T clutch pressure control solenoid valves. The manual valve covers the port leading pressure to the clutches, and hydraulic pressure is not applied to the clutches.
NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.
D Position: 1st gear shifting from the N position
The shift solenoid valves remain the same as in the N position when shifting to the D position from the N position. The manual valve is moved to the D position, and uncovers the port of line pressure (4) leading to CPC valves A and C. The PCM controls A/T clutch pressure control solenoid valves A and C, A/T clutch pressure control solenoid valve A pressure (56) flows to CPC valve A, and A/T clutch pressure control solenoid valve C pressure (58) flows to CPC valve C. CPC valves A and C regulate line pressure (4), line pressure (4) becomes CPC C pressure (4C) at CPC valve C, and becomes CPC A pressure at CPC valve A. CPC C pressure (4C) becomes 1st clutch pressure (10) at shift valve D, and 1st clutch pressure flows to the 1st clutch. CPC A pressure (4A) becomes 2nd clutch pressure (20) at shift valve B via shift valves A and C. The 1st clutch and 2nd clutch engage gently with the CPC pressure mode.
NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.
D Position: Driving in 1st gear
The PCM turns shift solenoid valve C ON, and shift solenoid valve C covers the port of shift solenoid valve C pressure (SC) to shift valve, C and shift valve D via shift valve E. Shift solenoid valve A keeps OFF, and shift solenoid valve B keeps ON. Shift valves C and D are moved to the left side, shift valve D switches the port of line pressure (4) and CPC C pressure (4C) leading to the 1st clutch, and shift valve C switches the port of CPC A pressure (4A) releasing 2nd clutch pressure. Line pressure (4) becomes 1st clutch pressure (10) at shift valve D, and flows to the 1st clutch. The 1st clutch is engaged securely with the line pressure mode.
NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.
D Position: Shifting between 1st gear and 2nd gear
As the speed of the vehicle reaches the programmed value, the PCM turns shift solenoid valve A ON, and shift solenoid valve A uncovers the port of shift solenoid valve A pressure (SA) to shift valve A. Shift solenoid valves B and C remain ON. Shift valve A is moved to the right side to uncover the port of CPC A pressure (4A) leading to the 2nd clutch. The PCM controls A/T clutch pressure control solenoid valve A, and A/T clutch pressure control solenoid valve A pressure (56) is applied to CPC valve A. CPC valve A regulates line pressure (4), and line pressure (4) becomes CPC A pressure (4A). CPC A pressure (4A) flows to shift valve B via shift valves C and A, and becomes 2nd clutch pressure (20) at shift valve B. The 2nd clutch is engaged with the CPC pressure mode. The 1st clutch is also engaged, but no power is transmitted because of the one-way clutch.
NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.
