Non-contacting Transmission Range Selector Sensor Package Optimization for Improved Reliability in Automatic Transmissions

Steve Thomson; Daniel Martinez; Duane Collins

doi:10.4271/2010-01-0189

Ever since the implementation of diagnostics and electronic control systems on automatic transmissions, various forms of transmission gear selection feedback has been used. The traditional mechanization uses a feedback switch with mechanical contacts that indicate the selected gear discretely or through a grey code output.

Switch reliability above the industry standard was made possible through the use of non-contact technology. Multi-Hall mechanizations have been used by others in recent years however this type of product has been simplified by using a single linear Hall device; reducing component count and the number of connector interfaces. Furthermore, a reduction in the number of electrical connections led to improved system reliability and cost.

Optimization of this package was made possible through the use of a multi-tool, multi-objective, single field focus using advanced design optimization software, robust engineering techniques and Shainin® tools.

In this optimized design a unique system of magnets and shaped-flux concentrators surround a linear-Hall device to provide a sensor package which is robust to stray external ferromagnetic fields. Flux strength is measured by the linear-Hall element held within a constant air-gap. Shaped flux concentrators then minimize the fringe effects that are common to magnetic fields which occur even when ferromagnetic concentrators are used. More importantly concentrator shapes linearize the flux output and eliminate the need for external compensation tables.

For added diagnostic capability it will be shown that the magnetic package accepts single or multiple linear-Hall devices in order to provide redundant outputs. With this design's flexibility single or multiple linear output signals can be provided over a range of up to 80 degrees of rotation or 50 mm of linear travel.

Re-shaping this magnetic package into a linear motion sensor was made possible by a robust optimization using an L18 array that was then completed using Ansoft's Maxwell 3D tools. Linearity was further enhanced using a Heeds advanced optimization tool.

Although beyond the scope of this paper, it can be mentioned that the final mechanization is very robust against external sources that typically cause electromagnetic interference. The shaped concentrators, to be described, affectively buffer a magnetic field over a large area. Because the sensing device is encompassed within a strong magnetic field, this package has also proven itself robust against any ferromagnetic particle build-up which may occur over several lifetimes of durability tests.

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Non-contacting Transmission Range Selector Sensor Package Optimization for Improved Reliability in Automatic Transmissions 2010-01-0189

SAE MOBILUS