• By: Abd Alrhman Al-Fawaer

AUTOMATICTRANSMISSIONS

AND TRANSAXLES

AUTOMATICTRANSMISSIONS

Introduction An automatic transmission or transaxle selects gear ratios according to engine speed, power train load, vehicle speed, and other operating factors. Little effort is needed on the part of the driver, because both up shifts and downshifts occur automatically.A driver-operated clutch is not needed to change gears, and the vehicle can be brought to a stop without shifting to neutral.

This is a great convenience, particularly in stop-and-go traffic.

Today’s automatic transmissions have four to eight forward speeds. Five- and six-speed units are the most common. Seven- and eight-speed units are mostly found in luxury vehicles. Today’s transmissions have at least one overdrive gear to reduce fuel consumption, lower emission levels, and reduce noise while the vehicle is cruising.

TORQUE CONVERTER

• 1-DesignNearly all torque converters, or T/Cs, are one-piece, welded units that can only be repaired by specialty shops.

• 2-ComponentsA standard torque converter consists of three elements the pump assembly, often called an impeller, the stator assembly, and the turbine.1-The impeller assembly is the input (drive) member. It receives power from the engine.

• 2-The turbine is the output (driven) member. It is splined to the transmission’s turbine shaft.

• 3-The stator assembly is the reaction member or torque multiplier. The stator is supported on a one-way clutch, which operates as an overrunning clutch and permits the stator to rotate freely in one direction and lock up in the opposite direction.

• 3- Theory Of Operation• Rotary oil flow is the oil flow around the circumference of the torque converter

caused by the rotation of the torque converter on its axis.• Vortex oil flow is the oil flow occurring from the impeller to the turbine and back

to the impeller, at a 90-degree angle from (A) engine rotation.

Rotary flow is at its greatest at the coupling stage and The difference between rotary and

vortex flow.

PLANETARY GEARS

Theory Of Operation

• How Planetary Gears WorkEach member of a planetary gear set can spin (revolve) or be held at rest. Power transfer through a planetary gear set is only possible when one of the members is held at rest, or if two of the members are locked together.

•Any one of the three members can be used as the driving or input member. At the same time, another member might be kept from rotating and thus becomes the reaction, held, or stationary member.

•The third member then becomes the driven or output member. Depending on which member is the driver, which is held, and which is driven, either a torque increase (underdrive) or a speed increase (overdrive) is produced by the planetary gear set.Output direction can also be reversed through various combinations.

LAWS OF SIMPLE PLANETARY GEAR OPERATION

Simpson planetary gear set

CONTINUOUSLY VARIABLETRANSMISSIONS (CVT)

The Benefits Of CVT

A typical compound servo design

A typical band and servo assembly

APPLICATION OF HYDRAULICSIN TRANSMISSIONS

Oil Pump• Oil Pump

The source of fluid flow through the transmission isthe oil pump .

• Three types of oil pumps are commonly used in automatic transmissions: gear type rotor type, and vane type. Oil pumps are driven by the pump drive hub of the T/C or oil pump shaft and/or converter cover on transaxles. Therefore, whenever the T/C cover is rotating, the oil pump is driven.

• The oil pumpcreates fluid flow throughout the transmission.

Theory Of Operation

Fluid flows in the neutral gear range

In drive range first gear, the rear clutch and overrunning clutch are engaged

In drive range second gear, the rear clutch and front kickdown band are applied.

Drive range third gear with the lockup torque converter clutch disengaged and front and rear clutches

engaged.

Reverse line pressure is increased to keep the front clutch, which has no Belleville spring, from slipping.