Download Fundamentals of Automatic Transmissions PDF

TitleFundamentals of Automatic Transmissions
Tags Vehicle Parts Transmission (Mechanics) Automatic Transmission Clutch
File Size5.1 MB
Total Pages220
Table of Contents
                            Fundamentals of Automatic Transmissions
	Section 1 Fundamentals of Automatic Transmissions
	Section 2 Torque Converter
	Section 3 Simpson Planetary Gear Unit
	Section 4 Gear Selection and Function
	Section 5 Power Flow
	Section 6 Automatic Transmission Fluid
	Section 7 Transmission Oil Pump
	Section 8 Valve Body Circuits
	Section 9 A340H Transfer
	Section 10 Electrical Control
	Section 11 Transmission Check, Adjustments and Diagnosis
	Section 12 Shift Lock System
	Appendix A Glossary of Terms
	Appendix B Micrometers
	Appendix C Diagnostic Reference
	Appendix D Automatic Transmission Air Check
	Appendix E General Reference
                        
Document Text Contents
Page 1

Automatic Transmissions - Course 262

1. Compare the function of automatic transmission systems of front- and
rear-wheel drive transmissions.

2. List the three major component systems used in Toyota automatic
transmissions which:
a. Transfer torque from the engine.
b. Provide varying gear ratios.
c. Regulate shift quality and timing.

3. Identify the three types of holding devices used in Toyota automatic
transmissions.

Section 1

FUNDAMENTALS OF
AUTOMATIC TRANSMISSIONS

Lesson Objectives

Page 2

Section 1

2 TOYOTA Technical Training

Automatic transmissions can be basically divided into two types: those

used in front−engine, front−wheel drive (FF) vehicles and those used in

front−engine, rear−wheel drive (FR) vehicles.

Transmissions used in front−wheel drive vehicles are designed to be

more compact than transmissions used in rear−wheel drive vehicles

because they are mounted in the engine compartment. They are

commonly referred to as a "transaxle."

Automatic
Transmission

Types

The basic function and
purpose for either front or

rear drive automatic
transmissions are the

same.

The differential is an integral part of the front−wheel drive

transmission, whereas the differential for the rear−wheel drive

transmission is mounted externally. The external differential is

connected to the transmission by a driveshaft.

The basic function and purpose for either front or rear drive automatics

are the same. They share the same planetary gear train design which

is used in all Toyota automatic transmissions and the majority of

automatics in production today.

Types of
Automatic

Transmissions

Page 110

Section 8

106 TOYOTA Technical Training

Pressure modulating valves change controlling pressures to tailor

operational characteristics of the automatic transmission. Line

pressure, throttle pressure and governor pressure all have an effect on

how the automatic transmission operates.

This valve modifies line pressure from the pump to the accumulators

based on engine load. It reduces shift shock by lowering the back

pressure of the direct clutch (C2) accumulator and second brake (B2)

accumulator when the throttle opening is small. Since the torque

produced by the engine is low when the throttle opening is small,

accumulator back pressure is reduced. This prevents shift shock when

the brakes and clutches are applied.

Conversely, engine torque is high when the throttle angle is large,

during moderate to heavy acceleration. Not only is line pressure

increased, but throttle pressure acting at the base of the accumulator

control valve increases back pressure to the accumulators.

Accumulator pressure is increased to prevent slippage when the

clutches and brakes are applied.

Accumulator Control
Valve

Modifies line pressure to
the accumulators based on

engine load.

− On all transmissions, hydraulically controlled or ECT with the

exception of the A40 Series, throttle pressure acts directly on the

bottom of the accumulator control valve to increase accumulator

control pressure.

− There is no accumulator control valve in the A40 Series automatic

transmissions; line pressure acts directly on the rear of each

accumulator.

Pressure
Modulating

Valves

Accumulator
Control valve

Reference:

Page 111

VALVE BODY CIRCUITS

Automatic Transmissions - Course 262 107

This valve is located between the governor valve and the cut−back

valve. It modifies the governor pressure generated by the governor

valve. The governor modulator valve is pushed to the right by a spring,

while governor modulator pressure acts on the right side of the valve,

pushing it toward the left. The governor modulator valve maintains a

pressure constant between governor pressure and spring tension.

Governor Modulator
Valve and Cut-Back

Valve

Governor modulator valve
provides the aspect of

vehicle speed to the
cut-back valve which acts

to reduce throttle pressure.

This valve modifies throttle pressure. It regulates the cut−back

pressure acting on the throttle valve and is actuated by governor

pressure and throttle pressure. Applying cut−back pressure to the

throttle valve in this manner lowers the throttle pressure and

ultimately lowers line pressure to prevent unnecessary power loss due

to the transmission oil pump at higher speeds.

Governor pressure acts on the upper portion of this valve. As the valve

is pushed downward, a passage from the throttle valve is opened and

throttle pressure is applied. The cut−back valve is pushed upward as a

result of the difference in the diameters of the valve pistons. The

balance between the downward force due to governor pressure and the

throttle pressure becomes the cut−back pressure.

Governor Modulator
Valve

Cut-Back Valve

Page 219

Automatic Transmissions - Course 262 215

OVERALL COMPARISON OF TOYOTA’S VARIOUS AUTOMATIC
TRANSMISSIONS
1. A40 SERIES

*1 The gear ratio has been changed.
*2 The A40D is an A40 with added overdrive unit, but without brake No. 2 (B2) and one-way clutch
No. 1 (F1).
*3 The A42D is an A40 (including brake No. 2 (B2) and one-way clutch No. 1 (F1) with added
overdrive unit.
*4 To enable it to be used with larger, higher-performance engines, the capacity and performance
of the A42D have been upgraded (i.e., the planetary gear has been made larger, the number of
discs used has been increased, the two C2 pistons have been combined into one double-acting
piston, and the surface area of this piston to which hydraulic pressure is applied in 3rd gear or
overdrive (in the ”D” range) has been increased).
*5 The gear ratio has been changed and a three-stage governor valve used.
*6 The gear ratio has been changed.
*7 The A45DF is on A45DL modified for 4WD vehicles.

Page 220

216 TOYOTA Technical Training

5. A100, 200 SERIES

*1 The A140L is an A130L with added overdrive unit on the rear of transaxle case.
*2 The A240L is an A130L with added underdrive (4th speed) unit on the inside of transaxle case.

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