Geometrical instruments – Miscellaneous – Light direction
Reexamination Certificate
1998-12-31
2001-04-10
Bennett, G. Bradley (Department: 2859)
Geometrical instruments
Miscellaneous
Light direction
C324S207200
Reexamination Certificate
active
06212783
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an arrangement for the contactless determination of an angle of rotation of a rotatable element, in particular a shaft of an internal combustion engine, in which, comprising means for generating a magnetic field rotating with the rotatable element, a magnetic field sensor for detection of magnetic field intensity and an evaluation circuit for determining the angular orientation or position of the rotatable element from the magnetic field sensor output signals.
2. Prior Art
Arrangements of this kind, with which a determination of an angle of rotation can be performed, are known for instance from Published, Non-Examined German Patent Application DE-OS 195 43 562. In these arrangements, a magnet is connected to the rotatable shaft whose angular position is to be ascertained. The magnetic field, which varies with the angle of rotation of the shaft, is measured with the aid of two sensor elements. These sensor elements are either two Hall sensor elements, which are rotatable by an angle of 90° from one another, or two magnetoresistive sensor elements, which are rotated by 45° from one another. The sensor elements are supplied with alternating voltage signals phase offset from one another in a suitable way. The superposition of the output signals of the sensor elements produces a signal course which is representative for the angular position. By suitable linkage of the signals of the two sensor elements, an angle measurement over an angular range of 360° can be obtained. One special application of the known arrangements for contactless determination of an angle of rotation is to detect the angular position of the camshaft of an internal combustion engine. The arrangements described in DE-OS 195 43 562 for contactless determination of an angle of rotation each have two identical sensor elements. This could have disadvantages, because Hall sensors, for instance, have great temperature dependency and great pressure dependency. Magnetoresistive sensor elements, conversely, have better properties with regard to temperature and pressure dependency, being less temperature- and pressure-dependent than Hall sensors, but have the disadvantage that because of the physical effect, only an angular range of 180° can be detected unambiguously. Such an angular range is too small for detecting the position of the camshaft of an internal combustion engine.
Since with the present invention the angle of rotation of the camshaft of an internal combustion engine is intended in particular to be detected, the problems involved in detecting the camshaft angle will first be described below.
To meet the demands for functionality of modern engine controllers, the rpm and the angular position of the crankshaft and camshaft must be detected with high precision at all times. For rpm detection at the crankshaft, a transducer disk with 60-2 angle markings is used, which rotates with the crankshaft and is scanned by a sensor; as the sensor, a sensor that utilizes the inductive, magnetoresistive, or Hall effect is employed.
So that sufficient information about the current operating play of the engine can be obtained, the absolute camshaft position (NW position) must additionally be ascertained. In present engine control systems, the camshaft positions are detected segmentally. A disk that rotates with the camshaft and has one angle marking per cylinder, for instance, is scanned with the aid of a sensor. This sensor outputs an output signal which has one pulse multiple times per camshaft revolution; as a result, current accurate-angle information about the camshaft position is always obtained at the segment boundaries, that is, at the points where pulses occur in the camshaft sensor signal. At the angular positions between segment boundaries, accurate absolute angle information on the camshaft position is unavailable.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an arrangement for contactless determination of an angular position of a rotatable element that does not have the above-described disadvantages.
It is also an object of the present invention to provide an arrangement for continuous contactless determination of the angular position of a camshaft of an internal combustion engine that is less sensitive to changes in temperature and pressure but nevertheless provides an unambiguous determination of angular position between 0° and 360°.
According to the invention the arrangement for contactless determination of an angular position of a rotatable element, especially a camshaft of an internal combustion engine, comprises
means for generating a magnetic field comprising at least one magnetic field-producing element arranged to rotate with the rotatable element;
a magnetic field sensor stationary in relation to the rotatable element and including a first sensor element and a second sensor element, wherein the first sensor element operates according to a magnetoresistive effect so as to generate a first output signal linearly dependent on an angle between the magnetic field and the magnetic field sensor, whereby the first output signal has respective values between 0° and 180° that repeat between 180° and 360°, the second sensor element operates according to a Hall effect to generate a second output signal which has a high value between 0° and 180° and a low value between 180° and 360°; and
an evaluation circuit comprising means for analyzing the output signals of both sensor elements to determine the angular position of the rotatable element between 0° and 360°.
In preferred embodiments of the arrangement according to the invention sensor elements are mounted so that magnetic field lines from the magnet are oriented approximately parallel to the first sensor element and perpendicularly penetrate the second sensor element.
In a preferred embodiment of the arrangement according to the invention the evaluating circuit finds that the absolute angular position is either of two angular orientations spaced 180° from each other only from the signals from the first sensor element and then selects one of them as the absolute angular position using the second output signal.
With continuous determination of an angle of rotation at the camshaft by means of the arrangement for contactless determination of angular position according to the invention, an improvement in the engine control system can be attained, since the current angle information is available at all times in the control unit. The functionality of existing engine control functions can thus be improved, and additional functions can optionally be achieved. For instance, with such continuous determination of an angle of rotation at the camshaft, fast diagnosis of the rpm transducer can be performed; simple, rapid diagnosis of the absolute angle encoder itself is possible by monitoring the plausibility of the signal. Safe and simple detections of starting can also be performed. Both engine stalling and underspeed can be reliably detected; it is possible to detect the direction of rotation, and faster synchronization in fast-start operations can be achieved.
Better emergency operation of an rpm transistor can also be achieved, and direct starting of the engine is possible only using an absolute angle encoder. Such an absolute angle encoder, with which the angular position of the camshaft can be ascertained at any time, can be achieved with the aid of the present invention. By using the sensor of the invention as a camshaft sensor, an engine control system can thus be constructed which is distinguished by a better fast start, so that the battery, starter and generator are not so severely burdened and can therefore be made smaller. Reliable detection of the rotational direction makes it possible to prevent intake tube splatting, and as a result the intake tube and throttle valve of the engine can for instance be made to less stringent specifications.
With the arrangement for contactless determination of an angle of rotation according to the invention, an angle deter
Lehner Michael
Ott Karl
Bennett G. Bradley
Robert & Bosch GmbH
Striker Michael J.
Verbitsky Gail
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