Modern automatic transmissions use various methods to estimate
fluid line pressures in order to improve shift quality and reduce
energy losses. These estimations lead to improvements in fuel
economy, customer satisfaction and reduced exhaust emissions. The
further addition of pressure feedback switches improves operational
knowledge by verifying when clutches have received their commanded
pressures.
Product reliability above the industry standard for transmission
pressure switches was developed through the use of multiple FEA
platforms combined with advanced design optimization software,
robust optimization and Shainin® tools. In this optimized design,
ferromagnetic non-contact pressure switches operate by translating
fluid pressure into piston motion, isolated by a sealed proprietary
diaphragm. The more traditional contact point type switch is prone
to failures from short circuit conditions that can cause permanent
or temporary switch failures; there are also cases of switch dither
or what is sometimes known as bounce. This condition is
intermittent and generally unpredictable, providing hard to manage
information to a controller. Any of these conditions can trigger a
diagnostic failure, leading to a compromise in shift performance
and ultimately to the end vehicle owner needing to return the
vehicle for service.
Besides the elimination of contact points, unique to this design
is the patent-pending magnetic package which provides a flux
direction transition through zero-gauss instead of the more common
flux gain measurement. By monitoring the zero gauss transition,
air-gap and temperature sensitivity are significantly reduced,
simplifying manufacturing tolerances and improving switch point
accuracy. Pressure switch sensitivity to fluid-born contaminants is
virtually eliminated by avoiding mechanically conductive contact
points in the design. The greater stroke used in this mechanization
was proven robust against bouncing conditions, verified through
dynamic simulations and empirical confirmation.
Product stack-up tolerances are absorbed through the use of a
non-magnetic cylinder that was designed in Solid Edge and optimized
by a Heeds-Ansys interface to maintain the optimum compression on a
diaphragm. The tolerances of mechanical components in the design
were prioritized based on their contribution to the system
performance as identified in an L18 Robust Optimization study. A
Shainin Green Y® system analysis was used throughout the product
development to identify failure modes early and target specific
tests to eliminate risk. Production intent assemblies are available
and have passed stringent confirmation tests.