US-12618862-B2 - Front bias magnetic speed sensor with true-power-on capability

US12618862B2US 12618862 B2US12618862 B2US 12618862B2US-12618862-B2

Abstract

A magnetic sensor system includes a toothed wheel configured to rotate about a rotation axis that extends in an axial direction, wherein the toothed wheel includes a plurality of teeth and a plurality of notches arranged that define a circumferential perimeter, wherein the toothed wheel further includes an interior cavity arranged within the circumferential perimeter; a front-bias magnet arranged within the interior cavity of the toothed wheel, wherein the front-bias magnet is rotationally fixed and is magnetized with a magnetization direction that extends along a radial axis of the toothed wheel; and a magnetic sensor arranged exterior to the toothed wheel, wherein the magnetic sensor includes a sensor element arranged on the radial axis that coincides with the magnetization direction of the front-bias magnet and the first sensor element is sensitive to a magnetic field of the front-bias magnet that is aligned with the radial axis.

Inventors

Gernot Binder
Rocio Elisa DE LA TORRE RODRIGUEZ

Assignees

INFINEON TECHNOLOGIES AG

Dates

Publication Date: 20260505
Application Date: 20240422

Claims (20)

1 . A magnetic sensor system, comprising: a wheel, configured to rotate about a rotation axis, wherein the wheel comprises a plurality of teeth and a plurality of notches arranged in an alternating tooth-notch pattern, wherein the plurality of teeth and the plurality of notches define a circumferential perimeter, and wherein the wheel further comprises an interior cavity arranged within the circumferential perimeter; a front-bias magnet; and a first sensor element, wherein the front-bias magnet and the first sensor element are arranged opposing each other in a first direction with a gap between the front-bias magnet and the first sensor element such that a tooth, of the plurality of teeth of the wheel, or a notch, of the plurality of notches of the wheel, is located in the gap between the front-bias magnet and the first sensor element when the wheel is rotating about the rotation axis, wherein the front-bias magnet is magnetized in the first direction, wherein the first sensor element is sensitive in the first direction, wherein the wheel causes a magnetic field of the front-bias magnet to oscillate at a location of the first sensor element, and wherein the magnetic sensor system is configured to determine a rotation speed of the wheel based on the oscillation.
2 . The magnetic sensor system of claim 1 , wherein one of the front-bias magnet or the first sensor element is in an interior of the wheel, and wherein another one of the front-bias magnet or the first sensor element is exterior to the wheel.
3 . The magnetic sensor system of claim 2 , wherein the first sensor element is exterior to the wheel.
4 . The magnetic sensor system of claim 2 , wherein the plurality of teeth of the wheel shields the first sensor element from the magnetic field of the front-bias magnet, and wherein the plurality of notches of the wheel exposes the first sensor element to the magnetic field of the front-bias magnet.
5 . The magnetic sensor system of claim 1 , wherein at least one of the front-bias magnet or the first sensor element is rotationally fixed and does not rotate with the wheel.
6 . The magnetic sensor system of claim 1 , further comprising: a second sensor element, wherein the first sensor element and the second sensor element are arranged on a radial axis that coincides with a same magnetization direction.
7 . A magnetic sensor system, comprising: a wheel, comprising a plurality of teeth and a plurality of notches, configured to rotate about a rotation axis, wherein the plurality of teeth and the plurality of notches define a circumferential perimeter, and wherein the wheel further comprises an interior cavity arranged within the circumferential perimeter; a front-bias magnet, arranged inside of the interior cavity, having a magnetization direction that extends along a symmetry axis of the front-bias magnet that is orthogonal to the rotation axis; and a magnetic sensor, arranged external to the wheel, including at least one sensor element arranged on an extension of the symmetry axis that coincides with the magnetization direction.
8 . The magnetic sensor system of claim 7 , further comprising: a molded package encapsulating the front-bias magnet and the magnet sensor.
9 . The magnetic sensor system of claim 8 , wherein the molded package has a one-piece integral construction that holds the symmetry axis of the front-bias magnet in alignment with a symmetry axis of the magnetic sensor.
10 . The magnetic sensor system of claim 8 , wherein the molded package comprises a notch between the front-bias magnet and the magnet sensor.
11 . The magnetic sensor system of claim 10 , wherein, during a rotation of the wheel, the plurality of teeth passes through the notch.
12 . The magnetic sensor system of claim 8 , wherein the magnetic sensor is configured to: generate, in response to sensing a magnetic field of the front-bias magnet, a first signal having a signal pattern representative of a pattern of the plurality of teeth.
13 . The magnetic sensor system of claim 12 , wherein the magnetic sensor comprises a sensor circuit configured to: receive the first signal, and generate a pulsed output signal based on the first signal crossing at least one threshold, or determine whether a tooth, of the plurality of teeth of the wheel, is located between the front-bias magnet and the magnetic sensor based on the first signal.
14 . The magnetic sensor system of claim 8 , wherein a rotation of the wheel causes a magnetic field of the front-bias magnet to oscillate between a first extremum value and a second extremum value at a location of the magnetic sensor.
15 . The magnetic sensor system of claim 14 , wherein the magnetic sensor comprises a sensor circuit configured to: generate a first signal that has the first extremum value when any tooth, of the plurality of teeth of the wheel, is interposed between the front-bias magnet and the magnetic sensor; and generate a second signal that has the second extremum value when any tooth, of the plurality of teeth of the wheel, is interposed between the front-bias magnet and the magnetic sensor.
16 . The magnetic sensor system of claim 15 , wherein the sensor circuit is further configured to: generate a differential signal based on a combination of the first signal and the second signal; and generate a pulsed output signal based on the differential signal crossing at least one threshold.
17 . A magnetic sensor system, comprising: a wheel, comprising a plurality of teeth and a plurality of notches, configured to rotate about a rotation axis, wherein the plurality of teeth and the plurality of notches define a circumferential perimeter, and wherein the wheel further comprises an interior cavity arranged within the circumferential perimeter, a front-bias magnet, arranged external to the interior cavity, having a magnetization direction that extends along a symmetry axis of the front-bias magnet that is orthogonal to the rotation axis; and a magnetic sensor, arranged inside of the wheel, including at least one sensor element arranged on an extension of the symmetry axis that coincides with the magnetization direction.
18 . The magnetic sensor system of claim 17 , further comprising: a molded package encapsulating the front-bias magnet and the magnet sensor.
19 . The magnetic sensor system of claim 18 , wherein the molded package has a one-piece integral construction that holds the symmetry axis of the front-bias magnet in alignment with a symmetry axis of the magnetic sensor.
20 . The magnetic sensor system of claim 18 , wherein the molded package comprises a notch between the front-bias magnet and the magnet sensor.

Description

RELATED APPLICATION This application is a continuation of U.S. patent application Ser. No. 17/727,979, filed Apr. 25, 2022, which is incorporated herein by reference in its entirety. FIELD The present disclosure relates generally to sensing a rotational speed of a target object, and, more particularly, to magnetic speed sensors. BACKGROUND To measure a rotational speed of a toothed wheel, for example, typically a ferromagnetic toothed wheel is used in combination with a magnetic sensitive sensor and a back-bias magnet mounted to the sensor. The sensor generates output-pulses. A control unit counts the pulses and is able to calculate the rotational speed and actual angle of the rotating wheel, as well as optionally determine the rotation direction of the wheel. In camshaft sensing applications, a Hall monocell configuration may be used that enables output switching at the tooth edge of a toothed wheel. A z-magnetized back-bias sensor in combination with the Bz-sensitive monocell sensor generates a sinusoidal signal as the ferrous target wheel rotates in front of the sensor. A back-bias magnet produces a static magnetic bias field at the sensing elements, which is deflected and modulated when the tooth wheel rotates. The maximum amplitude is achieved when a tooth center passes the sensor, while the minimum signal is achieved when the sensor faces a notch center of the toothed wheel. Thus, the sensor device switches on the tooth edge. A benefit in using a Hall monocell sensor is that the sensor is twist-insensitive such that the sensor will work independent from a mounting position regardless of its rotational orientation around its z-axis. Thus, an air-gap between the sensor module and the wheel can be adjusted during mounting using a screw. That is, twisting the sensor module like a screw will adjust the air-gap and the rotational orientation of the sensor can be disregarded. Accordingly, the assembly tolerances are relaxed during mounting of the sensor due to the twist-insensitivity. On the downside, Hall monocell sensors have a disadvantage in terms of stray-field robustness. Stray-fields are magnetic fields that are introduced by external means located in the proximal environment of the sensor. For example, components located within a vehicle (e.g., for hybrid cars due to current rails driving high electrical currents close to the sensing device or due to inductive battery charging) or a currents flowing through a railway of a train system that generates magnetic fields may cause stray-field disturbance. External magnetic stray-fields directly affect the magnetic signal and in worst case could lead to wrong position information. In camshaft sensing applications, an engine control unit (ECU) can use the magnetic speed sensors to detect the exact position of the camshaft. This precise information helps to control the fuel injection and the intake and exhaust valves, thereby increasing the overall performance and efficiency of a vehicle and ultimately reduces the emissions. True-power-on (TPO) is a feature that enables a fast start up. Directly at start-up, the magnetic speed sensor can provide the precise position of the camshaft (e.g., information indicating whether the sensor is facing a tooth or a notch of the cam target wheel). Providing this information to the ECU with high accuracy enables advanced control schemes like variable camshaft adjustment (variable valve timing (VVT)) which improves the performance, fuel economy, or emissions of a vehicle by a precise timing of the injection and ignition phase. Typical camshaft sensors use a “zero-gauss” magnet for the back-bias magnet, which is typically a magnet that has a center axis with a center bore or a center cavity that extends axially along the center axis. The magnet needs to be axially magnetized and a sensing element (e.g., a Hall monocell) is concentrically aligned with the magnet's center axis. As a result of the center bore, the magnet produces essentially a 0 mT magnetic field in the sensor plane at the position of one or more sensing elements. This zero magnetic field in the sensor plane is referred to as a zero magnetic offset and is intended to be present in the absence of a ferromagnetic target. In the case of a toothed wheel, the zero magnetic offset occurs in the sensor plane in the absence of a tooth or, alternatively, in the presence of a notch. This special magnet is required for the TPO feature. At a notch center of the toothed wheel, the back-bias magnet produces essentially a 0 mT magnetic offset at the Hall plate location. If a tooth passes the sensor, the magnetic offset increases. Therefore, the magnetic signal is an imprint of the mechanical wheel shape (e.g., an imprint of the tooth-notch pattern directly visible in the magnetic signal). The low magnetic offset in the notch center is crucial for a reliable TPO functionality over lifetime. A small magnetic offset (ideally 0 mT) is less affected by temperature drifts and aging