SCIS: Small & Compact Inductive Sensors for Position Sensing in the Automatic Gear Shifters
ZF-Friedricshafen AG is one of the biggest supplier of Automatic Gear Shifters for the modern cars and ZF-Automatic Gear Shifter needs sensing of five or seven positions (e.g. P, R, N, D, S) and (M+, M-) etc. Hall Sensors and Inductive Sensors are two automatic choices for such position sensing applications. Inductive Position Sensors [1] are ZF-Patented technology and are very robust & cheaper in price but they occupy a large area on a Printed Circuit Board (PCB). For instance, Inductive sensors presented at COMSOL® Cambridge Conference in 2014 [1] required approximately 200 square-mm of PCB space for sensing the five positions.
Hall Sensors, although much more expensive than inductive sensors, are frequently used as they occupy less PCB-area and space. For instance, 10 or more Hall-ICs will cost approximately double in comparison to 10 Inductive Sensors' cost.
On the other Hand, Magnets of Hall Sensors become weaker (loss of Remanence Br-field [mT]) with time, temperature, humidity & corrosion etc.
PCB-Area Optimization and Design of Fault Tolerant behavior of the inductive sensors are the driving forces for the SCIS Project.
In order to achieve the above goals instead of using a row of several (seven) square or rectangular planar coils in X-axis direction as implemented in [1], only two or utmost three planar trapezoidal/rectangular coils were arranged in the Y-direction as depicted in [2] and in Figures -1a & 1b. A very specific contour of sliding Cu-activator is used which produces a scissor-like two curves (L [nH] vs. X-off [mm]) [Fig.-2].
The COMSOL Multiphysics® Software with the Magnetic Fields interface and a frequency domain study at 10 MHz were used for first optimum design of the contour of the Cu-activator element. Thereafter, aforementioned "scissor or X" like curves/functions were obtained from COMSOL® simulation. The Simulation-results were verified with the real measurements of planar-coils under the influence of proposed Cu-activator element. Shape of the aforementioned curves resemble very much with the FEM-simulation results, although the inductance values differed by approximately 10% to 15%.
The proposed/(patented-[2]) arrangement of planar-coils reduced the PCB-area approximately by 50% and yet can sense all five positions with high accuracy.
