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Home > Ordnance Documents and other related manuals > > Figure 1-52. Authomatic Shift Circuit.
Automatic  Shifts
Figure 1-54. Lockup Shift Circuit.

Introduction to the X1100-3B Transmission, M1A1 Abrams Tank
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In any downshift the signal acts first and exhausts the shift signal
pressure that is holding the shift valve up.
The shift then moves
down and exhausts the applied clutch and applying the clutch for the
next lower range.
When  operating  the  transmission  in  low  (L)  or  reverse  (R),  the
transmission downshifts at a higher vehicle speed than in "drive."
Hold pressure, applied to the 1-2, 2-3, and 3-4 signal valves, causes
these transmission downshifts at a higher vehicle speed.  A decrease
or  increase  in  modulator  pressure  does  not  affect  the  automatic
upshifts when the selector is in "low" or "reverse."
Figure 1-52.
Automatic Shift Circuit.
f. G1 Governor Circuit (fig. 1-53).
The G1 governor circuit
originates at the front pitot.  Rotation of the vane pitot collector
ring, located on the forward clutch housing, directs oil against and
into  the  pitot  orifice.
This  produces  a  pressure  in  the  front
governor  circuit  that  varies  with  the  rotational  speed  of  the
collector ring.  This pressure is applied to the bottom of the lockup
shift valve and front pitot modulating regulator.
g. Lockup  Shift  Circuit  (fig.  1-54).
When  front  governor
pressure (or front governor pressure assisted by modulator pressure)
overcomes spring pressure and compresses the spring at the top of the
valve, the lockup shift valve moves up.  In this position, the valve
directs pressure through the lockup cutoff valve to the lockup piston
and causes the lockup clutch to engage.  To apply the lockup clutch,
the transmission uses clutch apply pressure from the engaged range
clutch.
52
OD1710






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