Ferromagnetic speed sensor

Details Ferromagnetic speed sensor Ferromagnetic speed sensor

1994-06-21

1997-10-28

Snow, Walter E.

Electricity: measuring and testing

Electrical speed measuring

Including speed-related frequency generator

3242072, 32420712, 324235, G01D 514, F02P 706, G01B 730, G01P 3487

Patent

active

056820950

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a rotational speed sensor, in particular a gear wheel sensor, including a magnet and two Hall effect elements cooperating therewith and arranged in laterally spaced relationship one to the other, wherein a component part made of ferromagnetic material, in particular a gear wheel, which has an irregular periphery or a periphery with points of discontinuity, and the angle of rotation or rotational speed of which is to be determined, is movable past the Hall effect elements in the direction of the lateral distance.
The rotational speed of a component part or only its special position on standstill can be determined by means of such a rotational speed sensor and can be converted into a corresponding signal which can be processed further in a corresponding electronic device. Rotational speed sensors of this type are used whereever it is intended to sense rotational speeds or only angles of rotation. A special field of application are automotive vehicles and, more particularly, the automatic brake system (ABS) or the traction slip control (TSC) for driven wheels, or even engine management and gear management.
Such rotational speed sensors are high-precision apparatus, the elements of which need not only be manufactured very accurately, but also must be assigned one to the other. This applies in particular to the magnets and the two Hall effect elements.
In the case of a gear wheel sensor, the teeth of the gear wheel one after the other move past the Hall IC with the two Hall effect elements, the magnets and the electronic devices, such as a protective wiring, for example. Each tooth produces a pulse, and the rotational speed can be determined by computing the pulses. However, to be more precise, the matter is that the rotational speed sensor does not recognize the tooth as such, but recognizes each respective transition from tooth to tooth space, or vice versa. Thus, a complete signal results when a tooth and a tooth space each have moved past the rotational speed sensor or, in other words, when the gear wheel has been rotated further by one unit consisting of tooth and tooth space.
First of all, the sensor senses the so-called basic field of the magnet. Added to the field intensity of the basic field is still a field density which originates from the mass of the gear wheel or any similar component part. If, instead of a tooth space, a tooth is assigned to the sensor, this results in a repeated amplification of the magnetic field for the time the tooth is assigned to the sensor. Thus, when the gear wheel rotates, the field intensity varies in dependence on the teeth and tooth spaces moving past the sensor.
However, as the two Hall effect elements of the rotational speed sensor are offset in the circumferential direction of the gear wheel or the component part, respectively, when viewed in the direction of rotation of the gear wheel, the tooth first arrives at the first Hall effect element and, after a certain angle of rotation, at the second one. The resultant oscillations of the magnetic field of the two sensors are deferred in relation to each other.
If, however, a stationary tooth is simultaneously opposite to both Hall effect elements, the total magnet intensity at both Hall effect elements is of equal size. When forming the difference in a corresponding sum-and-difference amplifier, the value zero results. As stated before, when the gear wheel or any component part of the like rotates, the two oscillations are deferred in relation to each other, a sum-and-difference amplifier issuing a finite signal as a result. However, the values for the basic field and the mass of the component part neutralize each other so that the oscillation comprises only the increase in the magnetic field density which is due to the tooth.
The analog signal, which is furnished to the two Hall effect elements in a deferred manner, as stated above, and which a sum-and-difference amplifier emits, can be converted into a digital pulse train by means of a so-called Schmitt trigger. The pulse train can the

REFERENCES:
patent: 3252057 (1966-05-01), Hoeppel
patent: 4518918 (1985-05-01), Avery
patent: 5045920 (1991-09-01), Vig et al.
patent: 5325005 (1994-06-01), Denk

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