Electronic Transmission Control Introduction 1-10-03.qxd - GE39

Pressure Regulation
Pressure regulating solenoids modify line pressure for hydraulic operation. Solenoids for
pressure regulation are referred to as EDS valves in ZF transmissions. GM transmissions
have a few terms such as Force Motor Solenoid, Variable Bleed Solenoid, and DR solenoid.
Regardless of the name used, they are all used to control main line pressure based on throttle
position and engine load.
On ZF transmissions, EDS valves are also used to control “Overlap Shifting”. This allows
for improved shift comfort by controlling pressures during shifting.
Depending upon transmission application, pressure regulating solenoids can be controlled
using Pulse Width Modulation on B+ or B-.
The TCM will increase line pressure by regulating current flow to the pressure regulator.
Current flow is controlled by pulse width modulation. When the duty cycle is low, the current
flow to the solenoid is low. This allows spring pressure to close the valve. Therefore
maximum line pressure is achieved. As the duty cycle increases, the current flow also
increases. The valve opening increases, which allows pressure to be released through the
pressure discharge which in turn decreases line pressure.
Main line pressure is also increased during failsafe operation and when needed during
“Adaptive Hydraulic Pressure Control” functions. Mainline pressure will also default to maximum
pressure when power to the TCM is switched off.
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Electronic Transmission Control