POWER TRAIN
-
Automatic Transaxle
Solenoid Driver Logic
Electronic solenoid valves connect the clutches to
either a hydraulic source or a vent. Solenoid coils,
when energized, exert force on a push rod which
in turn opens or closes a ball valve and/or vent.
To increase efficiency, the current through the sole-
noid coil is pulse-width modulated. The
microcom-
Pulsing the Solenoids
The Full ON pulse time is normally around 8 millisec-
onds and provides rapid pull-in response time.
Pull-
in response time is dependent upon battery voltage.
The pull-in response time will increase with reduced
battery voltage to maintain pull in power.
To protect against inadvertent drop-out of an ener-
gized solenoid, each ON solenoid is issued a re-
fresher pulse every 50 milliseconds. The refresher
pulse is used to prevent hydraulic pressure from
overcoming the solenoids strength. The frequency
is increased during shifts and as certain faults start
to occur.
The hold-in duty cycle is also dependent on battery
voltage as well as the in-gear condition. The
percent-
puter within the TCM is responsible for providing
this modulation (pulsing) signal as well as an initial
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pull-in current pulse each time a solenoid is ener-
gized.
age of solenoid on-time is normally 38%. In third
or fourth gear, the typical percentage is 30%. This
is because less power is required to overcome the
reduced hydraulic line pressure in third and fourth
gear ranges.
Current efficiency is maximized by the use of the
inductive energy of the solenoid during the OFF
portion of the cycle.
The turn OFF command opens the circuit to provide
for rapid drop-out response time. The circuit is moni-
tored to permit checking the continuity of the sole-
noid and its power return line.
SOLENOID DRIVER LOGIC
Solenoid control logic:
FFJ
Driver pulse logic:
Ek-
n
J
H-u-Ln
Solenoid voltage:
-+I
Full
on
pulse
W-
Hold-in
duty
cycle
+j
VL
1
0
Inductive current flow
-H
I+
from ground
Solenoid current:
Inductive path opened
--C
+
(1) provides rapid ON pull-in response time
(2) reduces power level
(3) refresh pulse
-
a periodic reissue of the FULL ON
pulse to any energized
solenlcid
(4) provides for rapid OFF drop-out response time;
inductive OFF voltage spike monitored
to confirm circuit continuity
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