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.