Mitsubishi Eclipse. Technical Information Manual (1994) — part 43
POWER TRAIN
Automatic Transaxle
Underdrive
clutch
Underdrive
solenoide
(de-energized)
solenoid
(energized)
Orifice located
in piston
Reverse
. .
Torque converter
apply pressure
Reverse and Underdrive Solenoids
When these two solenoids are not energized by the TCM,
their check balls prevent venting of a clutch. In this position
the check balls allow line pressure to reach the desired clutch.
These solenoids allow oil pressure to the clutch when de-ener-
gized and are referred to as normally applied valves. When
the solenoids are energized, the plunger forces the check ball
down and prevents line pressure from reaching the clutch.
At the same time, pressure is vented from the clutch.
Similar to the normally vented valves, these normally applied
valves are also cycled to modulate clutch pressure to any
value between line pressure and zero.
Dribbler Circuits
Two dribbler circuits feed low flow rate oil (residual pressure)
from the torque converter to the overdrive and reverse clutches
at all times. The low flow rate oil provided by the dribbler circuits
keeps both clutches full of oil. These clutches share a common
piston. If there is a difference in the amount of oil on either
side of the piston, the piston would tend to move toward the
clutch with less oil and cause that clutch to drag. If oil is only
on one side of the piston, and the retainer is spinning at high
speed, the spinning action will force oil to the outer diameter
of the retainer and cause the piston to move. The oil pressure
build-up caused by spinning is called centrifugal pressure.
Another feature added to avoid this situation is a small orifice
in the overdrive/reverse piston that helps equalize pressure
on both sides of the piston. The dribbler circuits only involve
low flow rates, which do not have any significant effect when
the clutches receive full line pressure.
POWER TRAIN
Automatic Transaxle
c
2
r
Fluid venting
from UD clutch
(through
orifice
and thermal valve)
Cold-open
from UD clutch
Hot-closed
No pressure
switch off
With pressure
switch on
Thermal Valve
The thermal valve is a bi-metallic shutter valve that helps control
the venting rate of oil pressure in the underdrive clutch passage
during release of the clutch. When the oil temperature is approxi-
mately 20 degrees Fahrenheit or less, the valve will be fully
open to assist in venting oil past the orifice. At temperatures
above 20 degrees, the valve starts to close and becomes fully
closed at approximately 140 degrees, The thermal valve is
located in the transfer plate of the valve body.
Pressure Switches
The pressure switches in the solenoid assembly supply informa-
tion to the TCM. When pressure is applied to a hydraulic circuit
where there is a pressure switch, the switch is forced to the
“on” or closed position. The switches do not tell the TCM how
much pressure there is in a circuit, but rather that pressure
does exist. Basically, the switches confirm to the TCM that
the intended solenoid action did occur. They can also be used
to determine a hydraulic problem.
POWER TRAIN
Automatic Transaxle
VALVE AND SOLENOID HYDRAULIC CONTROL IN SELECTED GEAR RANGES
Park/Neutral
In either of these gear selections, the transaxle has
lube pressure. To provide smoother engagement,
the low/reverse clutch is pressurized, anticipating
a shift to a forward or reverse gear. The
solenoid is energized which permits line pressure
to the low/reverse clutch. The
solenoid is
energized to close off the circuit to the manual valve.
Hydraulically, this internal transaxle condition is
identical for both the Park and Neutral positions.
The only mechanical difference is that the parking
pawl is engaged in the Park position.
PARK/NEUTRAL
Speed under mph
LR Low reverse
UD Underdrive
R Reverse
AC Accumulator
PT Pressure tap
S Solenoid
24 2-4 clutch
OD Overdrive
SW Switch
CC Converter CL
D Dribbler
V Vent
PARK/NEUTRAL
SPEED UNDER 8 MPH
.
POWER TRAIN
Automatic Transaxle
Rolling Neutral Above Eight MPH
When the transaxle is in neutral, and vehicle speed
the
solenoid to vent the LR circuit. This
b
IS
a ove eight mph, all friction elements are
figuration is ready to engage any forward gear,
gaged to minimize or reduce drag and to avoid
pending on vehicle speed and throttle position.
excessive element speed. The TCM de-energizes
NEUTRAL
Speed over 8 mph
LR Low reverse
UD Underdrive
Reverse
AC Accumulator
PT Pressure tap
S Solenoid
24 2-4 clutch
OD Overdrive
SW Switch
CC Converter CL
D Dribbler
V Vent
NEUTRAL
SPEED OVER 8 MPH
l - 2 - 3 ) O G
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