Rotation angle sensor

Details Rotation angle sensor Rotation angle sensor

2004-02-11

2004-08-24

LeDynh, Bot (Department: 2862)

Electricity: measuring and testing

Magnetic

Displacement

C324S207250

Reexamination Certificate

active

06781368

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the detection of rotation angles, such as e.g. the rotation angle of a throttle flap of a throttle valve. In particular, the present invention relates to apparatus or sensors for detecting rotation angles operating on an analogue magnetic basis.
2. Description of Prior Art
Nowadays, the orientation of a rotary part as an absolute value and/or the rotation angle, which the rotary part includes with a fixed reference point, is often required for further processing, such as, for example, a feedback control or similar. These rotatable parts include both freely rotatable parts, such as, for example, axes and shafts of drives, and parts which are only rotatable in a partial area of the full circle, i.e. by less than 360°, such as, for example, rotary regulators or throttle flap valves. For measuring the rotation angle varying sensor systems or arrangements are currently known, which differ from each other both with respect to their accuracy, their reliability and their manufacturing cost. Basically, these sensor types may be organized into two different types, i.e. contact systems on the one hand and contactless systems on the other.
Contact systems are mostly based on a potentio-metric measurement and, due to their simple structure, characterize themselves by very low manufacturing costs. However, a great disadvantage of the contact systems consists in that high temperature drifts result in these systems and, when vibrations and oscillations occur, such as, for example, in a valve in a motor vehicle, even when the measuring system comprises a fixed rotary position, small movements of high frequencies may occur, which may result in a great wearout and in a premature failure of the system.
Contactless systems, in turn, can be subdivided into those of the analog and of the digital type. In contactless systems of the digital type, a more complex transducer is required, which logically subdivides the desired circle area, i.e. the area of possible rotation angles, into several partial segments. A known possibility includes, for example, a transducer structure in the form of a tooth gear or shaft gear which has a tooth missing at a certain position. Both the “vacancy” and the existing teeth may be detected by a suitable sensor technology operating on an optical or magnetic basis, with an angle position being detected by counting the teeth following the vacancy. Although only a transducer and a sensor are required for this, a disadvantage of this solution consists in that the determination of the angle may not be carried out until after the first pass or the first detection of the specifically marked position, i.e. of the missing tooth.
A further prior art realization of a contactless system of a digital type includes a complex transducer consisting of several transducer parts as well as one sensor each per transducer part. Each transducer part subdivides the desired circle area, i.e. the area of possible rotation angles, into various partial segments. The detection of the partial segments by the sensors may be carried out optically or magnetically, for example, via slot metal sheets. When suitably subdividing the desired circle areas, for example, by halving, quartering, etc. of the same, it may be achieved that the output signals of all sensors together indicate the value of the rotation angle in a digitally encoded form with a solution of one bit per sensor/transducer pair. For a resolution of approximately 1°, nine bits (512 possibilities) have to be encoded, and, as a consequence, nine transducer components and nine sensors are required for this purpose. On the basis of the suitable subdivision into partial segments, the signal is consequently available in digital form without any further A/C conversion. However, a disadvantage of these solutions consists in that an increase of the resolution may only be carried out by adding further transducer components and sensors. The higher the resolution to be achieved, the more complicated the required transducer is.
Conventionally, contactless analog systems operate with a simple magnet as a transducer and two analog magnetic-field sensors arranged to each other under 90°. Typically, magneto-resistive (MR) or Hall sensors are used. The transducer magnet is arranged such that its north/south axis runs in a radial direction, such that the magnetic-field sensors output signals of a sine and/or cosine course, from which the current rotation angle may be calculated. The resolution will be determined from the accuracy of the magnetic-field sensors, the environment influences and the conversion depth of the subsequent analog/digital conversion. Dependent on the arrangements of two sensors under exactly 90°, a great deal of labour and time is necessary for realizing this solution, making it relatively cost intensive.
On the basis of the technical conditions, contactless measurements are frequently necessary in many fields of applications and are of a considerable advantage. On the other hand, these contactless measurements are more complex and thus more expensive. For applications with an extremely high number of pieces, manufacturing costs for a rotation angle sensor play a very important role. Therefore, there is a need for a less complex contactlessly measuring rotation angle sensor.
In accordance with DE 3244891 C1, a system for detecting positions with linear motions is known, in which a simple magnet arranged in direction of the linear motion and a series of sensors arranged equidistantly and parallel to the linear motion, together defining a scale, are used. The sensors arranged in series detect the magnetic field, with the zero crossing of the vertical field component, which results from a central level through the magnet, being determined from the measurement, with the locus of the zero crossing indicating the locus of the magnet.
SUMMARY OF THE INVENTION
The object of the present invention consists in providing an apparatus for detecting a rotation angle of a rotation around an axis of rotation, which is less complex with comparable measuring qualities.
In accordance with the present invention this is achieved by an apparatus for detecting a rotation angle of a rotation around an axis of rotation, comprising a transducer magnet for generating a magnetic field and a plurality of magnetic-field-sensitive sensor elements for detecting the magnetic field, with the transducer magnet and the plurality of magnetic-field-sensitive sensor elements being arranged such that, when rotating around the axis of rotation, the plurality of magnetic-field-sensitive sensor elements circles around the same relative to the transducer magnet, and wherein the plurality of magnetic-field-sensitive sensor elements define a scale. The transducer magnet are arranged such that the generated magnetic field comprises a characteristic at a locus on the scale, and the locus on the scale uniquely depends on the rotary angle at least for a partial area of a full rotation. The transducer magnet is magnetized inclined to the axis of rotation.
The present invention is based on the recognition that the susceptibility of the potentio-metric systems, the complexity of contactless systems of the digital type with respect to the transducer structure, and the analog/digital conversion in the analog sine/cosine signal systems may be eliminated in that a transducer magnet and a scale defined by a plurality of magnetic-field-sensitive sensor elements which are arranged such to each other that the generated magnetic field comprises a characteristic at one location on the scale and that the locus on the scale uniquely depends at least for a partial area of a full rotation on the rotation angle. In this manner, it is on the one hand possible to use a simple transducer structure as is for example the case in the sine/cosine signal systems and to determine, and, on the other hand, to determine the rotation angle position from the measured magnetic-field data in a manner which is both simple and may be ada

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