The foregoing discussion of torque converters is
general, and is adaptable to the operational
understanding of any hydraulic torque converter.
Actually, the changeover from stall speed to coupling
speed in the converter, as outlined above, is not sudden
but gradual and is determined by the power demands of
the load and/or operator. When the vehicle begins to
move, there is one power demand. Then, as the turbine
speed begins to increase, the oil flow direction in the
converter begins to shift. The shifting oil pattern
Figure 2-54.--Typical radiator-type oil cooler.
reflects changing power demands, and is similar to a
members on an overrunning clutch. In most cases,
gear-type transmission with an infinite number of gear
either an overrunning (one-way) clutch of the roller
type or a sprag unit type is used.
The torque converter, like the fluid coupling, can
A typical roller-type overrunning clutch is shown
be used as a coupling between the engine and a
in figure 2-55. Notice the shape of the spaces
m e c h a n i c a l c l u t c h . H ow eve r, s i n c e t h e t o r q u e
surrounding the rollers in the clutch cam. When the
converter can effectively vary torque ratios, a
member overruns, the rollers move against light
transmission is not always required. There is no reverse
springs into the larger spacing in the cam, thus
or neutral on the torque converter; therefore, a
allowing freewheeling. If the member slows down, the
transmission is normally used to meet the demands
rollers are wedged into the smaller spaces by light
springs and clutch hub rotation. This action locks the
also incorporate a lockup clutch and a retarding device
rotating member to the shaft.
within the converter hydraulic system.
A sprag unit assembly is shown in figure 2-56. This
Converter Hydraulic System
assembly consists of an inner and outer race, thrust
washers, snap ring, and the required number of sprag
The converter hydraulic (oil) system usually
units. The sprags (fig. 2-56, view A) are usually held in
consists of a reservoir, a supply pump, a filter, and a
alignment and on a slight angle between the inner and
cooler. When the converter is used in conjunction with
outer race by an energizing spring.
an automatic transmission, the sump of the
The operation of a sprag assembly can be seen in
transmission is used as the reservoir, since the oil is
detail in of figure 2-56, view B. As long as the inner or
circulated to the converter and other hydraulic units of
the transmission by the supply pump.
The cooler, or heat exchanger, is used to dissipate
the heat that is generated by the converter. The oil is
constantly subjected to agitation and motion when the
vehicle is operating, thus it becomes very hot. Some
converters have fins on the pump housing similar to the
fins on an air-cooled engine to dissipate the heat.
Others use the circulating coolant of the vehicle's
engine for cooling, while still others use a heat
exchanger of the radiator type. A typical radiator-type
heat exchanger is shown in figure 2-54. This type of
cooler is mounted with the radiator for the vehicle's
For the torque converter to function properly, the
stator or stators and the secondary members must be
Figure 2-55.--Roller-type overrunning clutch.
able to overrun. This is made possible by mounting the