Ferrite core coil device, sensor device for determining rotational speed of a rotatable object with such a ferrite core coil device and turbocharger with such a sensor device

1. A ferrite core coil device as a sensing element for a sensor device determining a rotational speed of a metallic rotatable object, comprising:

a coil having a first sector and a second sector; and

a ferrite core holding the coil, the ferrite core has a shape of a disk lacking a disk sector and defined by a contour of the disk and a chord of the disk, the chord forms a bending edge of the ferrite core, the first sector of the coil is not arranged on a bed of the ferrite core and the second sector of the coil is arranged on the bed, the first sector is bent around the bending edge at a bending angle with respect to the second sector.

2. The ferrite core coil device of claim 1 , wherein the ferrite core has a pin protruding from the bed, the pin has a same axis as the ferrite core.

3. The ferrite core coil device of claim 2 , wherein the coil is wound around the pin.

4. The ferrite core coil device of claim 2 , wherein the bed is delimited by a supporting edge wall of the ferrite core extending along the contour of the disk and by the bending edge.

5. The ferrite core coil device of claim 4 , wherein the pin has substantially a same height from the bed as the supporting edge wall.

6. The ferrite core coil device of claim 1 , wherein a radius of the coil is smaller than a radius of the ferrite core.

7. The ferrite core coil device of claim 1 , wherein a ratio between the first sector of the coil and the second sector of the coil is between 1:1 and 1.5:1.

8. The ferrite core coil device of claim 1 , wherein the bending angle is between 70 and 110 degrees.

9. The ferrite core coil device of claim 8 , wherein the coil is a substantially L-shaped coil with a bending angle of 90°.

10. The ferrite core coil device of claim 1 , wherein the coil has between ten and thirty windings.

11. The ferrite core coil device of claim 1 , wherein the coil has a plurality of windings each in contact with the bed.

12. The ferrite core coil device of claim 1 , wherein the coil is printed on a flexible polymer substrate.

13. The ferrite core coil device of claim 1 , wherein the ferrite core has a thickness between 0.2 mm and 2 mm.

14. The ferrite core coil device of claim 1 , wherein the ferrite core has a relative permeability between 50 and 3000.

15. A sensor device for determining rotational speed of a rotatable object, comprising:

a sensor segment;

a mounting segment;

a connector segment; and

a ferrite core coil device arranged at a sensor tip of the sensor segment, the ferrite core coil device including a coil having a first sector and a second sector and a ferrite core holding the coil, the ferrite core has a shape of a disk lacking a disk sector and defined by a contour of the disk and a chord of the disk, the chord forms a bending edge of the ferrite core, the first sector of the coil is not arranged on a bed of the ferrite core and the second sector of the coil is arranged on the bed, the first sector is bent around the bending edge at a bending angle with respect to the second sector.

16. A turbocharger, comprising:

a turbocharger housing;

a compressor impeller arranged in the turbocharger housing; and

a sensor device including a sensor segment, a mounting segment, a connector segment, and a ferrite core coil device arranged at a sensor tip of the sensor segment, the ferrite core coil device including a coil having a first sector and a second sector and a ferrite core holding the coil, the ferrite core has a shape of a disk lacking a disk sector and defined by a contour of the disk and a chord of the disk, the chord forms a bending edge of the ferrite core, the first sector of the coil is not arranged on a bed of the ferrite core and the second sector of the coil is arranged on the bed, the first sector is bent around the bending edge at a bending angle with respect to the second sector, the sensor segment is arranged in a wall of the turbocharger housing that has a recess, the ferrite core coil device protrudes through the wall and faces the compressor impeller at a predefined distance from the compressor impeller.

17. The turbocharger of claim 16 , wherein the predefined distance is between 0.5 and 1 mm.

18. A method for determining a rotational speed of a rotatable object, comprising:

providing a sensor device including a sensor segment, a mounting segment, a connector segment, and a ferrite core coil device arranged at a sensor tip of the sensor segment, the ferrite core coil device including a coil having a first sector and a second sector and a ferrite core holding the coil, the ferrite core has a shape of a disk lacking a disk sector and defined by a contour of the disk and a chord of the disk, the chord forms a bending edge of the ferrite core, the first sector of the coil is not arranged on a bed of the ferrite core and the second sector of the coil is arranged on the bed, the first sector is bent around the bending edge at a bending angle with respect to the second sector;

placing the sensor device with the sensor tip at a predefined distance from the rotatable object;

applying an electrical input current to the ferrite core coil device;

reading an amplitude modulated output voltage signal output from the sensor device; and

determining the rotational speed by evaluating a demodulated output voltage signal of the sensor device.