TM-9-2520-234-35
POWER TRAIN ASSEMBLY; ALLISON MODEL XTG411-2A
TECHNICAL MANUAL; FIELD AND DEPOT MAINTENANCE MANUAL
JULY 1962
TM-9-2520-234-35 - Page 49 of 323
PAR 20-21
DESCRIPTION AND OPERATION OF
CHAP 2, SEC II
MAIN TRANSMISSION ASSEMBLY
will result in maximum pressure.
Steer
valves 29 and 34, and passages in valve
body 40, are so constructed that either
valve, moving toward cover 10, directs
pressure to the clutch or brake being ap-
plied while exhausting the clutch which
must be released at the same side of the
transmission. Movement of either valve
29 or 34 toward the opposite end of its
bore has no effect on the brake or clutch
which it supplies or exhausts. Movement
of either steer regulator valve 26 or 37
away from cover 10 will direct coolant to
the steering member (brake or clutch)
being applied for steer.
21. CONTROL VALVE BODY ASSEMBLY
a . Components (fig. 383, fold-out 12)
(1) The control valve body assem-
bly includes valves and other components
which perform four different functions.
All of these components are installed in a
common valve body 54. The range selector
valve group includes valve assembly 75,
selector shaft assembly 56, indicator 49,
ball 59 and spring 60. Valve assembly 75
operates in a bore of the valve body. Its
lengthwise movements are manually con-
trolled by shaft assembly 56 which engages
a slot in the stem of the valve. Ball 59
and spring 60 retain the lever in any posi-
tion to which it is manually shifted.
(2) Lockup cutoff valve 80 is a
simple, spool-type valve which move s
lengthwise in its bore. Its movement is
controlled entirely by hydraulic pressures
to which it is subjected.
(3) The downshift inhibitor group
includes inhibitor plunger 79, spring 78 and
valve 76. Plunger 79 is fitted in a bore of
the valve body which is alined with a
stepped projection on shaft assembly 56.
Spring 78 is installed on plunger 79 and
acts against retaining ring 77 on the plun-
ger. The plunger seats against valve 76.
(4) The throttle valve 61 an d
throttle regulator valve assembly 63 fit
into a common bore and are separated by
spring 62. Both valves act against spring
68. Both valves are moved lengthwise
toward spring 68 by shaft assembly 58.
b . Operation (fig. 372, fold-out 1 and
fig. 383, fold-out 12)
(1) For range selection, the ve-
hicle operator shifts the range selector
control to the desired range.
Selector
shaft assembly 56, being linked to the
operator’s control, moves to a correspond-
ing position. In each range position, hy-
draulic pressure is directed to the range
clutch to be applied. Simultaneously, other
range clutches are exhausted through
passages controlled by valve 75.
(2)
When
any
shift
from
one
range to another occurs, the oil required
to apply the oncoming clutch must pass
through the bore in which lockup clutch
cutoff valve 80 operates. This flow moves
the valve to a position which interrupts
the flow of oil to the lockup clutch and
exhausts the lockup clutch pressure. When
the oncoming range clutch fills, the rising
pressure returns valve 80 to its original
position and restores pressure to the lock-
up clutch.
(3) Governor
pressure
act s
against shift inhibitor valve 76. When the
speed of the turbine shaft is sufficient,
governor pressure
will overcome th e
resistance of spring 78. Valve 76 then
pushes plunger 79 into the path of the
stepped lug on shaft 56, preventing its
movement to a lower range position.
(4) Throttle valve 61 and throttle
regulator valve assembly 63 are acted
upon by three forces. Throttle valve shaft
assembly 58 pushes throttle valve 61 into
its bore. Throttle regulator valve assembly
63 is, in turn, pushed by spring 62 against
spring 68 .
Hydraulic pressure reacts
against the throttle regulator valve. Two
control pressures (T and TV) arise in the
action of these two valves. TV pressure
results from the position of throttle regu-
lator valve assembly 63 and compression
of spring 62. T pressure results from the
position of throttle valve 61. TV pressure
varies according to throttle opening, be-
ginning early in throttle movement and
continuing through full throttle. T pres-
sure is merely TV pressure introduced to
the hydraulic system during the late
phases of throttle opening.
21
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