Subaru SVX 1992 Manual page 395

3- 2 [V2A0]
AUTOMATIC TRANSMISSION AND DIFFERENTIAL
2 . Torque Converter
A: CONSTRUCTION
" The torque converter is composed of impeller, tur-
bine, stator, and lock-up clutch. It is filled with oil ;
therefore it must not be disassembled .
" The impeller is directly coupled to the crankshaft via
a drive plate . A sleeve for driving the oil pump, which
is the source of the hydraulic pressure for the auto-
matic transmission, is welded to the rear of the
impeller .
" The turbine transmits multiplied engine torque in the
torque converter range, unmultiplied engine torque
in the coupling range, or engine torque itself directly
through the lock-up clutch to the automatic transmis-
sion via the input shaft spline fitted to the internal
spline of the turbine hub .
The stator incorporates a Sprague type one-way
clutch . The stator is spline-fitted to the oil pump cover
via the inner race of the one-way clutch, and secured
to the torque converter case .
B : FUNCTION
Rotating direction
Turbine Impeller
-~ a
Stator
6
u
:/ Oil flow
B3-447
Fig. 2 Function of torque converter
When the impeller rotates, centrifugal force pushes out
oil which then enters the turbine . The oil flows along the
turbine blade and exerts force on the blade . This causes
the turbine to rotate and power is transmitted to the
input shaft.
If turbine speed is below impeller speed, the oil leaving
the turbine flows in the direction impeding impeller
rotation (a in Fig . 2). This direction is then changed by
the stator so that the oil will assist impeller rotation (b in
Fig . 2) . With this action, the torque is multiplied .
The stator is subject to reverse torque when it changes
the direction of oil flow, hence it must be secured to the
casing . As turbine speed increases and approaches
impeller speed, the oil from the turbine begins to push
directly on the back of the stator blade . (This change-
over point is called the "coupling point' .) If the stator is
still fixed under this condition, the oil flow will be
impeded by the stator . To avoid this, the stator is
mounted to the case via a one-way clutch so that it can
rotate freely in the same direction as the impeller and
turbine .
C : PERFORMANCE
Converter range Coupling range
Big i
Torque ratio
i
100
Torque ratio
I Efficiency (%)
?-- 50
Efficiency j
I
I
I 0
Small
0 0.5 1 .0
Speed ratio
C3-094
Fig. 3
The torque converter characteristics are shown in the
above graph. The torque converter range refers to a
range where the impeller and turbine rotate at different
speeds and the torque is multiplied by a fixed stator . In
the coupling range, on the other hand, the turbine
rotates at high speed, and the stator is also rotating . The
coupling range provides no torque multiplication be-
cause the torque converter functions as a fluid coupling
in this range.
If the impeller (engine side) alone is rotating with sta-
tionary turbine (vehicle standstill) when the speed ratio
is zero (0), this state is called the stall point. In this state,
the torque ratio of impeller and turbine is the largest .
The torque ratio in this state is called the stall torque
ratio, and the engine rpm is called the stall rpm.
4