Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
2002-03-01
2003-11-18
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C324S225000, C324S239000, C324S207170, C361S143000
Reexamination Certificate
active
06650113
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a detector which detects a magnetic flux generated by an exciting coil being supplied with an excitation current, and it relates also to a method used for detection of the magnetic flux.
BACKGROUND OF THE INVENTION
Electromagnetic devices whose solenoids are supplied with excitation currents to generate magnetic fluxes are well known, and electromagnetic clutches, which utilize electromagnetic forces generated by such electromagnetic devices for engaging the clutch discs, are also well known. For example, Japanese Laid-Open Patent Publication No. H04(1992)-312217 discloses an arrangement in which a differential limiter that is activated by the engagement of a main clutch is provided to the rear differential gears of an automobile, the main clutch being operated by a pilot clutch which comprises an electromagnetic clutch. In this arrangement, the duty value for the excitation current supplied to the solenoid of the electromagnetic clutch is controlled in feedback of the engaging force (clutching force) of the electromagnetic clutch, which force is being detected. The detection of the engaging force of the clutch for this feedback control is performed by detecting a leakage flux of the main magnetic flux, which is being generated by the solenoid, with a magnetic flux density sensor comprising a Hall element.
In such an arrangement, as a leakage flux based on the main magnetic flux is determined in magnetic flux density by a hall element, in the assemblage, a little misalignment of the magnetic flux density sensor, which comprises a hall element, affects the accuracy of the detection. This is a problem that affects accuracy in detecting the magnetic flux. In addition, if an attempt to improve the efficiency of the magnetic circuit is attempted, then such an attempt will cause a reduction in the magnitude of the leakage flux and thus will also lead to a reduction in the accuracy of the detection. In other words, although the efficiency of the magnetic circuit is improved when the leakage flux is reduced, the reducing of the leakage flux can reduce the accuracy of the magnetic flux detection.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a magnetic flux detector and a method for magnetic flux detection which is used to detect directly a main magnetic flux itself in a magnetic path.
Another object of this invention is to provide a magnetic flux detector and a method for magnetic flux detection which achieves a highly accurate magnetic flux detection even if a leakage flux is minimized.
To achieve these objectives, a magnetic flux detector according to the present invention comprises a magnetic flux generator (for example, the armature member
11
and the core member
12
described in the following embodiment), an excitation current controller, a search coil and a magnetic flux calculator. The magnetic flux generator includes an exciting coil, to which an excitation current is supplied to generate a magnetic flux, and the excitation current controller controls the excitation current supplied to the exciting coil. The search coil is placed in a magnetic path where the magnetic flux generated by the magnetic flux generator passes, such that an electromotive force is induced in the search coil by a change in the magnetic flux, and the magnetic flux calculator determines the magnitude of the magnetic flux generated by the magnetic flux generator by measuring the electromotive force induced in the search coil. In this arrangement, the excitation current controller controls the excitation current to increase from zero to a predetermined current value during a first predetermined time period and thereafter to decrease from the predetermined current value to zero during a second predetermined time period. The magnetic flux calculator determines the magnitude of the magnetic flux generated by the magnetic flux generator based on the difference between the increasing electromotive force integral value which is the integral of the electromotive force induced in the search coil during the first predetermined time period and the decreasing electromotive force integral value which is the integral of the electromotive force induced in the search coil during the second predetermined time period.
In the magnetic flux detector, the search coil is placed in the magnetic path of the magnetic flux (so-called main magnetic flux) generated by the magnetic flux generator. Because of this arrangement, an electromotive force is induced in the search coil when there is a change in the magnetic flux. When this electromotive force is integrated for a time period, the magnetic flux that is passing through the magnetic path is determinable accurately. This arrangement effectively eliminates a problem or errors which may otherwise occur if the sensor is misaligned as in a case of prior art where the sensor comprises a Hall element to detect a leakage flux for determination of the magnitude of the magnetic flux. Also, this arrangement secures the accuracy of the magnetic flux detector because it is immune to a flux leakage reduction, which can result from an improvement in the efficiency of the magnetic circuit.
Furthermore, because the magnetic flux calculator determines the magnitude of the magnetic flux based on the difference between the increasing electromotive force integral value and the decreasing electromotive force integral value, even if a drift exists in the reading of the electromotive force induced in the search coil while the excitation current is nil or even if the electromotive force is offset, the drift or offset value is canceled out when the difference is obtained from these two integral values. Therefore, the magnetic flux detector can perform accurate magnetic flux detection without any adverse effect from a drift or offset which may exist. As the magnetic flux detector does not require any calculation for the cancellation of the effect of a drift or offset, it can perform magnetic flux detection in a quick and simple manner.
Preferably, the excitation current controller controls the excitation current to make the integral value for the increased part, which corresponds to the increased part of the electromotive force induced in the search coil during the first predetermined time period, equal to the integral value for the decreased part, which corresponds to the decreased part of the electromotive force induced in the search coil during the second predetermined time period.
To achieve this, more specifically, the excitation current controller controls the excitation current to make the first and second predetermined time periods equal to each other, and to make the absolute value of the rate of increase of the excitation current during the first predetermined time period, equal to the absolute value of the rate of decrease of the excitation current during the second predetermined time period.
Theoretically, the determination of the magnitude of the magnetic flux is possible either based on the integral value for the increased part, which corresponds to the increased part of the electromotive force in the increasing electromotive force integral value, or the integral value for the decreased part, which corresponds to the decreased part of the electromotive force in the decreasing electromotive force integral value, because the integral value of either the increased part or the decreased part corresponds to the magnetic flux. However, in reality, the integral value for the increased part and the integral value for the decreased part differ from each other because the real excitation current applied can differ from the target excitation current, and the characteristics of the magnetic flux generated are affected by the excitation current being applied. To avoid such a problem, the integral value for the increased part and the integral value for the decreased part are averaged to determine the magnitude of the magnetic flux by calculating the difference between these two values. In this way, the magnetic flux detector
Armstrong Westerman & Hattori, LLP.
Honda Giken Kogyo Kabushiki Kaisha
Strecker Gerard R.
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