THE losses that occur in torque converters are
of two types: flow losses and shock losses.
The causes of these losses and how they are
minimized in the polyphase converter are dis-
cussed in this paper.
O. K. KELLEY (M' 26) is in charge of Automatic Trans-
mission Development of General Motors Central Engineer-
ing. He has held this position since 1940. He served a
year as assistant chief engineer of Detroit Transmission
Division manufacturing the Hydra-Matic, before his ap-
pointment to his present position.Polyphase
THE efficiency of the hydrokinetic torque con-
verter is the efficiency of its fluid flow-from
pump to turbine to stator and back to the pump.
The best efficiency results from getting the greatest
weight of fluid through the path with the least
amount of energy expenditure. Density and vis-
cosity of the fluid are naturally important. The
denser the fluid and the freer flowing the fluid, the
better the efficiency.
The only practical fluids for torque converters at
the present time seem to be the petroleum oils,
which leave quite a bit to be desired from both
density and viscosity considerations. The torque
converter designers can do nothing to improve this
situation, beyond continuing to urge the oil and
chemical industries to search for a more suitable
fluid. The torque converter designers can merely
analyze and learn to control the inevitable losses
taking place in the flow of such liquids as have
been made available to them. These losses can be
grouped into two major categories: the flow losses
and the shock losses.
The flow losses are the minimum, unavoidable
losses suffered through the path of the converter
when all the blades are receiving the flow from the
most efficient direction. These losses are due to the
following:
1. Wall friction of the core and shell and both
sides of all the blades contacting the flow.
2. Edge losses of the entrances and exits of all
the blades.
3. Bend loss due to the circular path around the
core ring.
4. Loading loss due to the specific curvature and
the change in radius of the working blades.5. Expansion and contraction losses due to the
change in cross-section of various flow channels.
6. Turbulence caused by cross-flows due to un-
even blade loading.
7. Labyrinth leaks which short-circuit a part of
the flow.
8. Cavitation losses due to inadequate charging
pressure in the converter.
For any given path design, the summation of all
flow losses is in proportion to the square of the
flow velocity.
The shock losses, as the name implies, are the
additional entrance losses suffered from a wrong
angle of entrance in relation to the blades. All
blade shapes receive the flow best in only one direc-
tion. When this direction is deviated from, addi-
tional losses result. These additional losses, re-
ferred to as shock losses, deteriorate the efficiency
of the converter very rapidly as they develop under
the conditions of a radically wrong angle of en-
trance. Like the flow losses, the shock losses are
also proportional to the square of the flow velocity.
Careful attention can be paid to the efficiency
of the flow path to minimize the flow losses. We
shall assume that in the following illustrations the
flow losses have been designed to an irreducible
point. The remaining losses then? left to consider
are the shock losses as they form with the changing
direction and velocity of the flow and the changing
speed of rotation of the members.
If we consider a simple, three-element converter
as in Fig. 1, we can see the fundamental trend of
the entrance shock losses and their importance
relative to the flow loss. First, we note the gener-
ally diminishing flow loss. This is due to the dimn-
138 SAE Quarterly TransactionsDownloaded from SAE International by Larry Glover, Saturday, November 24, 2018Torque Converter
O. K. Kelley, Transmission Division, CMC
This paper was presented at the SAE Summer Meeting, French Lick, Ind., June 4, 1951
ishing flow velocity as the turbine speed picks up
and leaves
SAE_1952-01-01_520218_GM_Polyphase Torque Converter
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