Hudson 1948 - 1952, Service Manual

Page: 213 / 333

OVERDRIVE 9 - 5
speed of the latter, the sun gear will stand still; if it turns faster than
this, relatively, the sun gear will turn forward; and if it turns slower,
the sun gear will turn backward. If the engine is idling with the car
moving forward, this reverse rotation may be quite fast.
FIGURE 7
OVERDRIVE
If the sun gear is held against rotation, Figure 6, the pinion cage,
and also the engine, will revolve through only 0.7 turn for each turn
of the propeller shaft, Figure 7. The action of the control elements
involved is as follows:
FIGURE 8
Assuming that the car is being driven with the dash
control pushed in, Figure 4, the sun gear control plate
revolves along with the sun gear at the speed of the
transmission main-shaft. Under such circumstances, the
blocker ring, by its frictional drag upon the hub of the
control plate, is rotated into such a position as to latch
the control pawl against inward movement, Figure 8-A.
When the car reaches a predetermined speed (the
"cut-in" speed, which varies between 18 and 21 mph.) the
governor contacts close, acting through the overdrive
electrical circuit to energize the solenoid. The latter sets
up a spring pressure against the pawl, tending to push it
into engagement. This movement is prevented by the
blocker. However, the driver either consciously, or un-
consciously, and according to his own choice, may mo-
mentarily close the throttle, whereupon the roller clutch
releases, and the engine slows down. At the same time,
the sun gear slows down, more rapidly, so that the sun
gear passes through the stand-still condition when the
engine speed has fallen 30%, and then reverse its motion.
Upon the instant of reversal, the blocker ring, moved by
its frictional drive from the control plate hub, also rotates
slightly in this direction and releases the pawl which
snaps into the first notch of the backwardly-rotating
control plate, Figure 8-B.
The extreme rapidity of this action insures that the
control plate cannot rotate backward more than 1/3 turn
at the most; usually, it will be less. This engagement, at
nearly perfect synchronism, accounts for the smooth
action this control. Once engaged, under the conditions
of normal driving, the overdrive is in action until the car
speed falls to a value 2 or 3 mph lower than the cut-in
speed, when the governor contacts open, releasing the
solenoid, which withdraws the pawl (if throttle is closed),
whereupon the condition of freewheeling direct drive is
resumed.
DRIVER-CONTROLLED DOWNSHIFT (kickdown)
It has been noted above that when the overdrive is
engaged, the engine only turns 0.7 as fast as when in
direct drive. This reduces the power available (excepting
at high car speeds) and although this reduced power is
usually sufficient for all purposes,there are