Variable-reluctance position sensor
A variable reluctance analog position device designed to determine the position variation of a target made from a ferromagnetic material. The device includes at least one magnet, the target and the magnet defining a gap therebetween. A magnetosensitive element detects induction variation produced in the gap by relative movement of the target relative to the magnet. The magnet is magnetized in a direction essentially perpendicular to the front surface of the magnet, which defines one edge of the gap. The magnet includes a cavity open at the front surface thereof and the magnetosensitive element is housed in the cavity. Moreover, the target is provided with a specific geometric configuration determined such that the induction variation according to the position of the target corresponds to a pre-defined function.
1. A variable-reluctance analog position transducer configured to determine a position of a target, comprising:
a target made of a ferromagnetic material, the target being rotationally mobile around a shaft perpendicular to an axis of magnetization of at least one magnet, the target including three spiral teeth, each disposed at an angle of 120°;
the target and the at least one magnet defining between one another an air gap; and
a magnetosensitive element detecting a magnetic induction caused by a presence of the target and related to the air gap between the target and the at least one magnet, wherein the at least one magnet has a unidirectional magnetization along a direction substantially perpendicular to a front surface of the at least one magnet bounding one edge of the air gap, the at least one magnet having a cavity opening on the front surface of the at least one magnet, the magnetosensitive element being seated in the cavity, the target having a geometric configuration such that the induction as a function of the position of the target corresponds to a predefined linear function.
2. A variable-reluctance analog position transducer according to claim 1 , wherein the target is rotationally mobile around a shaft parallel to an axis of magnetization of the at least one magnet.
3. A variable-reluctance analog position transducer according to claim 1 , wherein a plane in which displacement of the target takes place is included in a plane passing through the center of the magnetosensitive element.
4. A variable-reluctance analog position transducer according to claim 1 , further comprising a ferromagnetic piece adhesively bonded to a back of the at least one magnet.
5. A variable-reluctance analog position transducer according to claim 4 , wherein the at least one magnet is adhesively bonded to a T-shaped ferromagnetic piece.
6. A variable-reluctance analog position transducer target according to claim 1 , wherein the target has a particular or optimized shape, configured to deliver a linear induction as a function of the displacement of the target.
7. A variable-reluctance analog position transducer according to claim 1 , wherein the magnetosensitive element is placed in the cavity in a zone of minimal induction.
8. A variable-reluctance analog position transducer according to claim 1 , wherein a maximum measurable angular travel is close to 360°.
9. An angular position transducer for a camshaft or crankshaft, provided with an analog position sensor according to claim 1 .
10. A variable-reluctance analog position transducer according to claim 1 , wherein the induction as a function of the position of the target is a linear function across the entire maximum measurable angular travel.
11. A variable-reluctance analog position transducer according to claim 1 , wherein a maximum measurable angular travel is 360°, and the induction as a function of the position of the target is a linear function across the entire maximum measurable angular travel.
12. A method for construction of a target for an analog position transducer made of a ferromagnetic material, having a desired induction signal, the transducer including,
a target made of a ferromagnetic material;
at least one magnet, the target and the at least one magnet defining between one another an air gap;
a magnetosensitive element detecting a magnetic induction caused in the air gap by displacement of the target relative to the at least one magnet, wherein the at least one magnet is magnetized along a direction substantially perpendicular to a front surface of the at least one magnet bounding one edge of the air gap, the at least one magnet having a cavity opening on the front surface of the at least one magnet, the magnetosensitive element being seated in the cavity, the target having a geometric configuration such that the induction as a function of the position of the target corresponds to a predefined function,
the method comprising:
establishing a first geometric shape for the target;
positioning points on the target, the points having coordinates in a viewing plane of spatial coordinates;
calculating a magnetic induction signal as a function of linear or rotary displacement of the target, the displacement of the target being effected over a predefined trajectory;
modifying coordinates of one of the points and recalculating the induction as a function of the position of the target to determine influence of this point on the induction measured by the at least one magnet;
determining a matrix and solving an equation configured to define a new geometric shape of the first shape determined previously for the target; and
repeating the calculating, modifying, and determining until a magnetic induction as a function of the linear or rotary displacement of the target is obtained satisfying in conformity with desired linearity criteria, or until a nonlinear function is obtained.