Electricity: measuring and testing – Electrical speed measuring – Including speed-related frequency generator
Reexamination Certificate
1999-05-04
2001-01-30
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Electrical speed measuring
Including speed-related frequency generator
C324S163000, C324S165000, C324S174000, C324S207250, C324S207260
Reexamination Certificate
active
06181127
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and a circuit for checking the width of the air gap between a coded rotor, which varies a magnetic flux, and at least one sensor element which is sensitive to magnetic fields and is provided for recording the rotary movement of the rotor, and to which a circuit is connected and in which measurement signals are generated by the magnetic variation during rotation of the rotor, the measurement signals being converted by the circuit into output signals which can be evaluated by a connected control device.
2. Description of the Related Art
Magnetically based speed sensors are used, for example, in motor vehicles in connection with antilock systems. A circuit for such a sensor is known, for example, from WO 96/10751. The circuit changes the shape or the strength of the output signal as a function of the air gap width. The output signal is evaluated by the connected control device. However, the expenditure for the evaluation is very high in the case of such a mode of procedure, since the output signal is not present in discrete form. Moreover, the direct modulation of information on direction of rotation is an unreliable method, since interference has a strong influence.
It is the object of the present invention to specify a method and a simple, cost-effective circuit for a magnetic speed sensor for generating a discrete speed signal which contains information for the width of the air gap, two lines sufficing to relay this signal to other devices via a cable connection.
This object is achieved by means of the method according to the invention by virtue of the fact that square-wave output signals are generated from the measurement signals by means of at least one prescribable threshold value, wherein the pulse duty factor of the square-wave output signals is kept within a prescribed range in the case of an air gap width lying within a tolerance band, and wherein the pulse duty factor deviates in a reliably measurable fashion from the prescribed range in the case of amplitudes of the measurement signal outside prescribed limits.
SUMMARY OF THE INVENTION
The purposes and advantages of the invention will be set forth in and apparent from the descriptions and drawings that follow below, as well as will be learned from the practice of the invention. Additional advantages of the invention will be realized and obtained from the elements of the apparatus particularly pointed out in the appended claims.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and described herein, a method and circuit for checking the width of an air gap is provided. In a first refinement of the method according to the invention, it is provided that the pulse duty factor lies at 50% within a tolerance band of ±15% in the case of an air gap width lying within a tolerance band, and wherein the pulse duty factor deviates at least by 10% from the respective limits of the tolerance band in the case of amplitudes of the measurement signal outside the prescribed limits. A pulse duty factor of 50% yields a high reliability against interference.
The circuit according to the invention, which is provided for implementing the method according to the invention, comprises
a comparator circuit which generates the square-wave signals from the measurement signals by means of at least one prescribable threshold value,
a detector circuit which determines the threshold value from the amplitude of the measurement signals in such a way that the pulse duty factor of the output signals lies within a prescribed range, the detector circuit prescribing the threshold value for the comparator circuit and
an amplitude discriminator which in the case of amplitudes of the measurement signal outside prescribed limits generates signals for changing the threshold value in such a way that the pulse duty factor deviates in a reliably measurable fashion from the prescribed range.
In a first refinement of the circuit according to the invention, there is provided as output stage a current source to which a voltage is applied by the control device via a first line, and which feeds a current forming the output signals to the control device via a second line. As a result, it is possible without a large outlay on circuitry for the circuit to receive an approximately constant operating voltage via the same lines via which the output signals in the form of current pulses are also transmitted to the control device. There is thus no need for any additional lines for transmitting the signals.
The signal for the direction of rotation can be transmitted without additional outlay on cables if, as is provided in a first development of the invention, the current source can be set to different level values of the output current as a function of the direction of rotation of the rotor. The information on the direction of rotation can thereby be transmitted via the same lines as all other information.
In a next development of the invention, it is provided that the sensor has two sensor elements which are sensitive to magnetic fields and are arranged in such a way that their measurement signals are phase-offset. A signal for the direction of rotation is yielded from the logic combination of the resulting square-wave signals by means of an exclusive- or function.
In order to be able to control the current source with the signal for the direction of rotation, in a next development of the invention means are provided for generating a signal for the direction of rotation for the purpose of representing the direction of rotation of the rotor. Furthermore, it is provided that the detector circuit transmits to the current source the signal for the direction of rotation, and wherein the current source changes the amplitude of the output current as a function of the signal for the direction of rotation.
The output signals contain the information on the direction of rotation. Consequently, in a next advantageous development of the invention it is provided that the control device determines the direction of rotation of the rotor with the aid of the amplitude of the output current of the circuit.
In the case of two further, alternative developments of the invention it is provided that the change in the threshold value is performed continuously or discontinuously by the amplitude discriminator in the case of amplitudes of the measurement signal outside prescribed limits. The person skilled in the art can decide in the individual case whether he prefers the discontinuous change for the benefit of a sharper delimitation of the pulse duty factor, or whether he prefers the continuous change for the benefit of enabling intermediate values to be represented.
It is preferably provided that the rotor is a magnet wheel.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and are provided for purposes of explanation only, and are not restrictive of the invention as claimed.
REFERENCES:
patent: 4902970 (1990-02-01), Suquet
patent: 6008638 (1999-12-01), Bleckmann et al.
patent: 2459749 (1976-07-01), None
patent: 3226073A1 (1983-04-01), None
patent: 3201811A1 (1983-09-01), None
patent: 4216142A1 (1993-11-01), None
patent: 4308031A1 (1994-04-01), None
patent: 196 23 101A1 (1997-10-01), None
patent: 196 18 867A (1997-12-01), None
patent: 196 34 715A1 (1998-03-01), None
patent: 0282732A2 (1988-09-01), None
patent: 0569924A (1993-11-01), None
patent: 9610751 (1996-04-01), None
Mannesmann VDO AG
Mayer Brown & Platt
Patidar Jay
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