Chrysler 2005 Crossfire SRT6 Service Manual page 3407

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The solenoids used in transmission applications are attached to valves which can be classified as normally open
or normally closed. The normally open solenoid valve is defined as a valve which allows hydraulic flow when no
current or voltage is applied to the solenoid. The normally closed solenoid valve is defined as a valve which does
not allow hydraulic flow when no current or voltage is applied to the solenoid. These valves perform hydraulic con-
trol functions for the transmission and must therefore be durable and tolerant of dirt particles. For these reasons, the
valves have hardened steel poppets and ball valves. The solenoids operate the valves directly, which means that
the solenoids must have very high outputs to close the valves against the sizable flow areas and line pressures
found in current transmissions. Fast response time is also necessary to ensure accurate control of the transmission.
The strength of the magnetic field is the primary force that determines the speed of operation in a particular sole-
noid design. A stronger magnetic field will cause the plunger to move at a greater speed than a weaker one. There
are basically two ways to increase the force of the magnetic field:
1. Increase the amount of current applied to the coil or
2. Increase the number of turns of wire in the coil.
The most common practice is to increase the number of turns by using thin wire that can completely fill the available
space within the solenoid housing. The strength of the spring and the length of the plunger also contribute to the
response speed possible by a particular solenoid design.
A solenoid can also be described by the method by which it is controlled. Some of the possibilities include variable
force, pulse-width modulated, constant ON, or duty cycle. The variable force and pulse-width modulated versions
utilize similar methods to control the current flow through the solenoid to position the solenoid plunger at a desired
position somewhere between full ON and full OFF. The constant ON and duty cycled versions control the voltage
across the solenoid to allow either full flow or no flow through the solenoid's valve.
UPSHIFT/DOWNSHIFT SOLENOID VALVES
The solenoid valves for upshifts and downshifts are
located in the shell of the electric control unit and
pressed against the shift plate with a spring.
The solenoid valves (1) initiate the upshift and down-
shift procedures in the shift plate.
The solenoid valves (1) are sealed off from the valve
housing of the shift plate (5) by two O-rings (4, 6). The
contact springs (8) at the solenoid valve engage in a
slot in the conductor tracks (7). The force of the con-
tact spring (8) ensures safe contacts.
AUTOMATIC - NAG1 SERVICE INFORMATION 21 - 337