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 TM 9-8000
(2) Low. When the gearshift lever is
(c) Because the input and low sun gears are
placed in low, the direct and reverse clutches are
both locked, the planetary pinions are locked and unable
released and the low brake band is applied, locking the
to rotate. This forces the planetary carrier and the
low sun gear. Power flow through the drive train is as
attached output shaft to rotate at a 1:1 ratio with the input
follows:
shaft.
(4) Reverse. When the gearshift lever is
(a) From the input sun gear to the
placed in reverse, the low brake band and the direct
long planetary pinions.
clutch are released. The reverse clutch is applied,
locking the internal gear of the planetary gearset. Power
(b) From the long planetary pinions to
flow through the drive train is as follows:
the short planetary pinions.
(a) From the input sun gear to the
(c) The locked sun gear then provides
long planetary pinions.
a reaction point so that the planetary pinions and carrier
(b) From the long planetary pinions to
can walk around it, rotating the output shaft.
the short planetary pinions.
The result is a speed reduction ratio from the input shaft
(c) The short planetary pinions walk
to the output shaft of about 1.8:1. The low- gear power
flow also is used when the gearshift lever is in the drive
around the inside of the locked internal gear, rotating the
position before the vehicle attains sufficient speed for the
planetary carrier and the attached output shaft in the
transmission to shift to direct drive.
opposite direction of the input shaft. The speed
reduction ratio of the input to the output shafts is
(3) Direct Drive. When the gearshift lever
approximately 1.8:1.
is placed in drive, the transmission is in low gear until the
vehicle reaches a speed sufficient to allow the
23-10. Simpson Drive Train.
transmission to automatically shift to direct drive. The
shift to direct drive releases the low brake band and
a. General (Fig. 23-9). This arrangement
applies the direct clutch, locking the low sun gear to the
combines two multiple-disk clutches, two brake bands,
input shaft. The reverse clutch remains released. Power
an overrunning clutch, and two planetary gearsets
flow through the drive train is as follows:
operating on a common sun gear. The simpson drive
train is the standard for virtually all three-speed
(a) From the input sun gear to the
automatic transmissions that are currently produced.
long planetary pinions.
b. Operation (Fig. 23-9). The simpson drive
(b) From the long planetary pinions to
train provides three forward speeds, reverse, and
the short planetary pinions.
neutral. Power flow is outlined by the following chart and
accompanying text.
FRONT
REAR
KICKDOWN
LOW-REVERSE
OVERRUNNING
RANGE
GEAR
CLUTCH
CLUTCH
BAND
BAND
CLUTCH
Reverse
on
off
off
on
no movement
Neutral
off
off
off
off
no movement
D-drive
first
off
on
off
off
holds
second
off
on
on
off
overruns
third
on
on
off
off
overruns
2-drive
second
off
on
on
off
overruns
first
off
on
off
off
holds
1-low
first
off
on
off
on
holds
23-8
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