TTransChev1971 - page 4 of 76

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AUTOMATIC TRANSMISSION

CONTENTS

Torque Converters ...........................

Powerglide .................................

The 3-element torque converter (Fig. 1) consists of a pump

or driving member, a turbine or driven member, and a stator

assembly.

The torque converter unit is filled with oil and is attached

to the engine crankshaft by a flex plate, thus always rotates at

engine speed. The converter pump is an integral part of the

welded converter cover; therefore, the pump blades, rotating

at engine speed, set the oil within the converter into motion

and direct it to the turbine, causing the turbine to rotate. The

converter pump also drives the hydraulic oil pump of the

transmission.

The driven member of the converter is the turbine and

turbine shaft. The turbine is driven by the oil forced against it

by the rotating converter pump-there is no mechanical con

nection between these two elements of the converter.

The third and final element of the converter is the stator.

The stator (Fig. 2) is mounted on a one-way (overrunning)

roller clutch and attached to the transmission by the stator

shaft. The overrunning roller clutch locks the stator stationary

against counterclockwise forces, but permits it to rotate freely

with clockwise forces. The reasons for this arrangement are

more clearly evident when considering the hydraulic forces

that occur within the converter from stall, or standstill, to

normal cruising speed.

With the engine running, the converter pump sets the oil

within the converter into motion and directs it to the turbine,

TURBINE STATOR

(REACTION MEMBER)

(DRIVEN MEMBER)

CONVERTER PUMP

COVER

(DRIVING MEMBER)

Fig. 1-Torque Converter

ROLLER CLUTCH

COUNTER CLOCKWISE FORCES ON CAM, LOCK

ROLLERS TO INNER RACE

CLOCKWISE FORCES ON CAM CAUSE

STATOR ASSEMBLY

ROLLERS TO OVERRUN INNER RACE

STATOR

OVERRUNS

Fig. 2-Stator Overrunning Clutch Operation

causing the turbine and shaft to rotate. As the oil passes

through the turbine, it is traveling in such a direction that it

would hit the rear of the converter pump blades and impede

its pumping action. So at low speeds, the oil is redirected by

the stator to the converter pump in such a manner that it

actually assists the converter pump to deliver power, or multi

ply engine torque. At stall, the torque multiplication of this

converter assembly is a ratio of approximately two-to-one.

As turbine speed-and accordingly vehicle speed-increases,

the direction of the oil leaving the turbine changes and flows

against the rear side of the stator vanes. Since the stator is now

hindering the smooth flow of oil, its roller clutch releases, and

the stator revolves freely on its shaft. Once the stator becomes

inactive, there is no further multiplication of engine torque

within the converter. At this point, the converter is merely

acting as a fluid coupling as both the converter pump and the

turbine are being driven at the same speed- or at approxi

mately one-to-one ratio.

The torque converter and turbine shaft actually form a

simple transmission as they provide a means of transmitting

engine power to the rear wheels and a small degree of torque

multiplication. Transmissions nearly identical to this are used

in some light industrial applications, but automobiles have far

greater torque requirements and need a reverse as well. These

requirements are provided by the components housed in the

transmission case.

TORQUE CONVERTERS

THEORY OF OPERATION

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