model Chrysler A-500/A-518 transmissions and the transaxles used in most
Chrysler/Mitsubishi vehicles rely on electronics to control the shifting into
overdrive gear. Electronics are also involved in the control of the converter
clutch in all late-model Chrysler transmissions.
A-500 and A-518 transmissions are fully automatic units with an overdrive
attached to the rear of the transmission. The first through third gear shifts
are controlled hydraulically through apply devices in the main body of the
Fourth gear operation is controlled by a manually operated overdrive switch on
the instrument panel, center console, or shift lever. The overdrive switch is
wired into a circuit with an overdrive solenoid, located on the valve body, and
the single board engine controller (SBEC). The torque converter clutch lockup
solenoid is also wired into this circuit. The overdrive switch prevents a shift
into fourth gear when the switch if off. Therefore, the operation of the torque
converter clutch is also inhibited when the overdrive switch is off.
shift from third to fourth gears is electronically controlled and hydraulically
activated by the SBEC. The SBEC controls the overdrive solenoid using
information received from several sensors.
Chrysler A-604/41TE Controls The A-604/41TE transaxle is an electronically
controlled 4-speed transaxle. The transaxle uses hydraulically operated
clutches, which are controlled by the transaxle controller. The controller
receives information from various inputs and controls a solenoid assembly
through the electronic automatic transaxle (EATX) relay. The solenoid assembly
consists of four solenoids that control hydraulic pressure to four of the five
clutches in the transaxle and to the lockup clutch of the torque converter.
controller has an adaptive learning characteristic that learns the release rate
and application rate of various transaxle components during various operating
conditions. Adaptive learning allows the controller to compensate for wear and
other events that might occur and cause the normal shift programming to be
controller may receive information from two different sources: directly from a
sensor, or through a twisted-pair bus circuit, which connects all of the vehicle
computer systems. This modulated bi-directional bus system is called Chrysler
collision detection (CCD) bus and allows the various computers in the vehicle to
the controller receives an ignition run from the ignition switch, it performs a
series of circuit and relay checks. If a problem is found, the controller will
provide voltage to the EATX relay, which causes its contacts to close. This
sends voltage to the solenoid assembly.
Direct battery voltage is supplied to the controller. If the controller loses
source voltage, the transaxle will enter into limp-in mode. The transaxle will
also enter into limp-in if the controller senses a transmission failure. At this
point, a fault code will be stored in the memory of the controller and the
transaxle will remain in limp-in until the transaxle is repaired. While in
limp-in, the transaxle will operate only in park, neutral, reverse, and second
gears. The transaxle will not upshift or downshift. This allows the vehicle to
be operated, although its efficiency and performance is hurt.
solenoids are controlled by the controller, which sends voltage to the EATX
relay. The EATX relay, in turn, send voltage to the solenoid assembly. The
controller also completes the ground circuit of the solenoids when a particular
solenoid should be activated. The controller also monitors the operation of the
solenoids through inputs from low-reverse, 2-4 pressure, and overdrive switches.
These switches are located in the solenoid assembly and inform the controller
when a hydraulic circuit is open.
Inputs The direct inputs are those sensors that provide information to the
controller and do not use the CCD bus circuit. The CCD bus inputs use the bus
circuit to supply the controller and other computers with information.
Typical CCD bus inputs used by the transaxle controller are from an ambient or
battery temperature sensor, brake switch, coolant temperature sensor (CTS), and
manifold absolute pressure (MAP) sensor. Other information, such as engine and
body identification, the SBEC's target idle speed, and speed control operation
are not the result of monitoring by sensors, rather these have been calculated
or determined by the SBEC and made available on the bus. The ambient or battery
temperature sensor monitors intake air temperature. The SBEC uses the
temperature of intake air and current flow to calculate the temperature of the
battery. The SBEC uses this temperature calculation to estimate transaxle fluid
brake switch is used to disengage the torque converter clutch when the brakes
are applied. Its input has little to do with the up and down shifting of gears.
The input from the CTS is critical to the operation of the transaxle. If the
engine's coolant temperature is cold, the controller may delay upshifts to
improve driveability. The controller may also lock the converter clutch in
second or third gear if the coolant temperature rises. The MAP sensor keeps the
controller informed of changes in engine load.
Although engine speed information is available at the bus, the controller
receives this signal directly from the distributor pick-up coil or crank angle
sensor. With the direct feed, any time delay at the bus circuit is avoided and
the controller is aware of current engine speeds.
direct inputs to the controller include battery voltage, selector lever
positions, throttle position, turbine shaft speed, output shaft speed, and
information from the low-reverse, overdrive, and 2-4 pressure switches at the
solenoid assembly. The output shaft and turbine shaft speed sensors are magnetic
pick-up type sensors that generate an AC voltage.
controller processes these inputs and selects the proper shift schedule for the
transaxle. The controller will then control the power feed to the solenoid
assembly through the EATX relay and the ground circuit of the solenoids to force
upshifts and downshifts. The controller will also activate the backup lamp relay
based on these inputs.
42LE Controls The 42LE four-speed transaxle, released in 1994 by
Chrysler for use in the their New Yorker, Intrepid, LHS, and Vision models, also
uses fully adaptive controls. Like the 41TE, this transaxle uses hydraulically
applied clutches to shift gear but controls the hydraulics electornically.
hydraulics of the transaxle provide for the control of torque converter fluid
flow and oil cooler flow, the regulation of mainline pressure, and the movement
of the manual shift valve. Fluid flow to the various apply devices is directly
controlled by the solenoids. The basic hydraulic system also includes a
logic-controlled solenoid switch valve, which locks out first gear when second,
direct, or overdrive gears are engaged. This solenoid switch also redirects
fluid to the torque converter lockup clutch. To regain access to first gear, a
special sequence of solenoid commands from the control unit must be used to
unlock and move the solenoid switch. This prevents the engagement of first gear
when other gears are engaged.
solenoids act directly on steel poppet and ball valves. Two of the solenoid
valves are normally venting and the other two are normally applying. This
combination allows for a fault mode of operation. If electrical power to the
transaxle is lost, the transaxle will only provide second gear in all forward
are three pressure switches that give input to the transaxle controller. They
are all located within the solenoid assembly. One speed sensor reads input speed
at the turbine shaft and another speed sensor reads output speed. The third
sensor monitors the position of the manual shift valve.
Engine speed, throttle position, temperature, engine load, and other typical
engine-related inputs are also used by the controller to determine the best
shift points. Many of these inputs are available through multiplexing and are
inputted from the common bus.
adaptive learning takes place as the controller reads input and output speeds
over 140 times per second. The controller responds to each new reading. This
learning process allows the transaxle controller to make adjustments to its
program so quality shifting always occurs.
basic shift logic of the controller allows the releasing apply device to slip
slightly during the engagement of the engaging apply device. Once the apply
device has engaged and the next gear is driven, the releasing apply device is
pulled totally away from its engaging member and the transmission is fully into
its next gear. This allows for smooth shifting into all gears. The adaptive
learning capability of the transaxle controller allows for this smooth shifting
throughout the life of the transmission. The controller learns the
characteristics of the transaxle and changes its programming accordingly.