Automatic Transmission/Transaxle: Description and Operation

DESCRIPTION

The advanced alpha automatic transaxle is for a 1.6 DOHC engine. The advanced alpha AT is popularly used among small sized vehicles.
Nowadays PCM(power-train control module), which which integrates the ECU and TCU inside, is new trend of the power-train system.
The merge of two system guarantees stable quality of the AT as well as better shift feeling and faster response to ECU information.

COMPONENTS(1)

COMPONENTS(2)

Mechanical system

COMPONENTS

Function

Front clutch

Rear clutch

End clutch

Kick down brake

Low&Reverse brake

One Way Clutch (O.W.C)

Planetary Gear
The planetary gear set incorporated in this transaxle consists of a forward sun gear, a reverse sun gear, a short pinion, a carrier to support both pinions, and an annulus gear.
The reverse sun gear is connected to the front clutch retainer via the kickdown drum, while the forward sun gear is connected to the rear clutch hub.
The carrier is built in one unit with the low reverse brake's hub and the outer race of the one-way clutch. The carrier is connected to the end clutch via the end clutch shaft.
The annulus gear, to which the output flange is connected, conveys driving force to the transfer drive gear installed on the output flange. And the parking sprag is provided on the outer circumference of the annulus gear.
The Ravigneaux type planetary gear set consists of two sun gears, each meshing with one of two sets of planetary pinion gears in a single carrier, and a single annulus gear that meshes with one of the sets of pinions. The two sun gears are called the forward and the reverse sun gears, for the gear conditions they operate in. Power input is to either of these two sun gears. Power output is through the annulus gear, which has the parking sprag on the outer circumstance. Various holding elements are built into gear set components.- Ravigneaux type planetary gear ratio.

Parking Mechanism
When the shaft is in the "P" range, the parking pawl engages with the parking sprag provided on outer circumference of the annulus gear to fasten the output shaft, to prevent the wheels from rotating. In other words, when the select lever is set to the "P" range, the detent plate and the parking sprag rod move in the direction of arrow, causing the cam on the parking sprag rod to push up the parking pawl to engage with the sprag.
In case the parking pawl collides against a crest of the sprag, only the rod moves because the parking pawl cannot be moved upward, and the cam, while pressing the spring, collides with the parking pawl and the support, and is with held in this condition. If the car is moved even slightly in this condition, the turning of wheels causes the annulus gear to turn as well. Since the cam is pressed in the direction of arrow, the parking pawl is pushed up as a bottom of the sprag aligns with the parking sprag to engage with the sprag.
In this way, the parking mechanism eliminates any chances of the vehicle from being.

Power flow

* - Engine start possible
+ - Parking mechanism
o - Element engaged in each gear position
x - Pre-engaged element
- F/C : Front Clutch
- R/C : Rear Clutch
- E/C : End Clutch
- OWC : One Way Clutch
- K/D : Kickdown brake
- L&R : Low&Reverse brake
For each shift condition, certain holding units in the transaxle are used. Knowing which holding element is used and how they are connected in the transaxle, we can trace the power flow through the transaxle for each shift condition. One set of pinions, the short pinions, meshes with the reverse sun gear.
The other set, the long pinions, meshes with both the forward sun gear and with the annulus gear. The two sets of pinions also mesh with each other in pairs. The pinion carrier is built as a unit with the low reverse brake hub and the outer race of the one-way clutch. Power input is to either of the two sun gears.
The reverse sun gear is connected to the front clutch retainer through the kick-down drum. The forward sun gear is connected to the rear clutch hub. So by engaging either the front or the rear clutch, power is directed to either the reverse or the forward sun gear. When both front and rear clutches are engaged, the gear set is locked, and power passes directly through the transaxle. Power output is through the annulus gear, which has the parking sprag on the outer circumference and is connected to the output flange.

1st Gear ("D" and "2" range)
Operating elements: Rear Clutch, One-Way Clutch

1st Gear ("L" range)
Operating elements: Rear Clutch, Low & Reverse Brake

2nd Gear ("D" and "2" range)
Operating elements: Rear Clutch, Kick Down Brake

3rd Gear ("D" range)
Operating elements: Front Clutch, Rear Clutch, End Clutch

4th Gear ("D" range)
Operating elements: Front Clutch, Rear Clutch, End Clutch

"R" range
Operating elements: Front Clutch, Low & Reverse Brake

Hydraulic Control System

1. The hydraulic pressure during gear shifting engages the clutches and applies the brakes. It is regulated by the pressure control valve. The hydraulic pressure that works on the pressure control valve is further regulated by the pressure control solenoid valve which functions under the control of the transaxle control module. The transaxle control module controls the solenoid valve using a duty cycle signal, thus providing appropriate regulation of the hydraulic pressure.
2. The transaxle control module decides the timing of the gear-shifting period (during which it performs hydraulic pressure control for gear shifting) according to the change in the kickdown drum rotating speed that it detects. The module identifies the time just before the kickdown brake is applied and uses that as the timing for initiating control of the hydraulic pressure that is to be applied to the kickdown brake.
3. TCM detects torque change ratio (turbine speed change ratio in torque converter). If input torque is larger than the pre-set torque in TCM, TCM controls the duty of PCSV and changes oil pressure. Shift shock will be alleviated due to torque control. Torque change ratio is applied differently according to each pattern.
4. When the transaxle is cold, the fluid viscosity is high, causing slower oil pressure response. In such conditions, the transaxle control module provides a correction for the oil pressure by changing the control duty of the pressure control solenoid valve. This control is performed when the fluid temperature as indicated by the oil temperature sensor is lower than 60°C(140°F).
5. After the engine has been started and the vehicle is in motion, the transaxle control module continues to refine its performance for smoothest possible gear shifting.
The hydraulic control system consists of an oil pump that generates hydraulic pressure for A/T. It also has valves and solenoid valves that control the hydraulic pressure or switch the oil passage. The valves and solenoid valves are all built into the valve body.
For better and smoother shift quality, the rear clutch pressure is controlled independently, 4th->2nd gear skip shift is available and the line pressure at 3rd/4th gear is reduced.
There are 6 solenoid valves are incorporated on the valve body. 2 of those are duty-controlled type and the rest are ON/OFF type.
A. Duty control type: Pressure control solenoid valve A/B, Damper clutch control solenoid valve
B. ON/OFF type: Shift control solenoid valve A/B/C
If the mechanical malfunction such as valve sticking occurred, the fail-safe valve has been adopted to prevent interlock. The line pressure is regulated at the 4th speed to improve the efficiency of power transmission. This function is performed by High-low pressure valve and regulator valve.

Oil Pump
Oil pump generates pressure for supplying oil to the torque converter, for lubricating frictional parts of the planetary gearing set and the overrunning clutch, etc., and for activating the hydraulic control system.
The pump is one of the inner-teeth engaging trochoid type. It always generates the oil pressure when the engine is running since the drive gear is driven by 2 pawls of the pump drive hub welded at the center of the torque converter shell.

MANUAL VALVE

PRESSURE CONTROL VALVE-A, B
Pressure control valve A, B regulate the pressure supplied to each clutch under the control of the pressure control solenoid valve A, B to eliminate shock at the time of shifting.
1. Pressure control valve A - Not operated

PRESSURE CONTROL VALVE-A, B
1. Pressure control valve A - Operation

PRESSURE CONTROL VALVE-A, B
1. Pressure control valve B - Not Operated

PRESSURE CONTROL VALVE-A, B
1. Pressure control valve B - Operation
The main function of this valve controls the rear clutch independently.

SHIFT CONTROL VALVE(SCV) AND SOLENOID VALVE-A, B, C (SCSV-A,B,C)
The line pressure acting upon the shift control valve is controlled by the two shift control solenoid valves(which are switch ON and OFF according to the shifting gear by the transaxle control module command), and the shift control valve is activated according to the shifting gear, thus switching the oil passages.

The relationship of the shifting gear and the ON-OFF switch of shift control solenoid valve "A", "B" and "C" is shown in the table below.

CONTROL SWITCH VALVE(CSV) & END CLUTCH(E/C) VALVE
- Function
Switching the pressure of E/C and SA

CONTROL SWITCH VALVE(CSV) & E/C VALVE
- 2nd Gear
- 2nd pressure is supplied from SA through the CSV.
- SCSV-C maintains OFF as well as 2nd gear.

CONTROL SWITCH VALVE(CSV) & E/C VALVE
- 2nd -> 3rd gear
- SCSV-C maintains OFF as well as 2nd gear.
- The E/C pressure from shift control valve is intercepted at the E/C valve during up-shifting from 2nd to 3rd gear.
- SA pressure is supplied from 1-2 shift valve, but the front clutch and SR pressure is also supplied from the 2-3/4-3 shift valve, so the both SR and SA pressure will be set off.

CONTROL SWITCH VALVE(CSV) & E/C VALVE
- 3rd gear
- SCSV-C is changed from OFF to ON.
- The E/C pressure is supplied from 1-2 shift valve at the CSV after finishing the up-shifting from 2nd to 3rd gear.
- SA pressure is supplied from shift control valve, but the front clutch and SR pressure is also supplied from the 2-3/4-3shift valve, so the both SR and SA pressure will be set off.

4 -> 2 SKIP SHIFT
1. Operating elements

2. Controls
A. R/C engaging duty control
B. E/C releasing duty control
C. Continuous switching to SA
3. Description
A. R/C engaging duty control

B. E/C releasing duty control
4 -> 2 Skip shift only (SCSV-C ON)
When releasing the E/C clutch pressure, it is controlled by duty of PCSV-A only in case of 4 -> 2 skip shift.

C. Continuous switching to SA
From (SCV) to SA through (CSV)

Fail Safe Function
1. TCM malfunction in 1st or 2nd gear
CUTTING OFF THE E/C PRESSURE BY E/C VALVE

A. F/C, SR : from 2-3/4-3 shift valve
B. R/C : from PCV-B
C. SA : from 1-2 shift valve

2. TCM malfunction in 1st or 2nd gear
If the hydraulic pressure is supplied to E/C and the F/C, SR pressure is delayed

A. R/C, E/C, S/A : interlock

NOTE:
- SA : Servo Apply pressure
- F/C : Front Clutch pressure
- R/C : Rear Clutch pressure
- K/D : Kick Down
- SCV : Shift Control Valve
- CSV : Control Switch Valve
- PCSV : Pressure Control Solenoid Valve
- SCSV : Shift Control Solenoid Valve
- PCV : Pressure Control Valve
- RCEV : Rear Clutch Exhaust Valve

AUTOMATIC TRANSAXLE HYDRAULIC CIRCUIT

PARKING AND NEUTRAL