Non-contact Pressure Switch Package Optimization for Improved Reliability of Diagnostics in Automatic Transmissions 2010-01-0187

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.