Electricity: measuring and testing – Electrical speed measuring – Including speed-related frequency generator
Patent
1999-02-02
2000-11-07
Oda, Christine K.
Electricity: measuring and testing
Electrical speed measuring
Including speed-related frequency generator
324174, 32420721, G01P 348
Patent
active
06144197&
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a rotational speed-detecting device provided with a signal processing circuit for detecting a variation of magnetic leakage flux produced by a rotating or moving multi-polar magnet or a variation of magnetic leakage flux produced between a gear of magnetic moving body and a fixed magnet by utilizing a magneto-electric element, and for executing a voltage-current conversion by shaping waveform of the detected signal.
BACKGROUND OF THE INVENTION
A detecting element of the prior art for detecting rotation of a gear is a magnetic coil 102 coupled with a bias magnet 103, as shown in FIG. 6, so as to gain an induced voltage across the coil by detecting a variation of magnetic flux density due to a change of magneto-resistance produced by projections and depressions of a rotating gear 101. In this instance, the rotating gear 101, the bias magnet 103 and the magnetic coil 102 are considered as a generator, and a magnitude of the induced voltage depends upon a rotational speed, and a signal is detectable with two lines. Although it is a simple and inexpensive structure, it has a fundamental problem in that the induced voltage decreases at low speed.
It is also known that a ferromagnetic magneto-resistance element 104 is used as a detecting element in combination with a signal processing circuit 105 for superposing a rectangular wave current on a power supply line by a constant-current drive, as shown in FIG. 7. It utilizes a pair of current-miller circuits for the constant-current drive, in which a current of one of the current-miller circuits is kept flown at all the time, while a current of the other current-miller circuit is turned on and off by an output signal at a midpoint of the ferromagnetic magneto-resistance element 104 of a half bridge, so as to produce a rectangular wave current, and superposes the rectangular wave current on the power supply line in order to reduce a signal output line and to convert three lines into two lines.
In recent years, a performance required of a rotational sensor for vehicle installation is an ability to detect rotation at an extremely low speed.
Detecting elements suitable for this purpose are so-called magneto-electric elements of positional detection type, such as a Hall element, a ferromagnetic magneto-resistance element, and a semiconductor magneto-resistance element. The semiconductor magneto-resistance element, in particular, is one of the most suitable for detecting a rotational gear, since it produces a high detection signal voltage. If a magneto-electric element of positional detection type is used for the rotational sensor, two current supply lines and one signal output line, for a sum of three lines are generally needed to constitute the circuit. A rotational sensor capable of detecting an extremely low speed with two lines is desirable, however, in consideration of compatibility with a magnetic coil, reduction of a vehicle weight, effective usage of a cab space, etc. A two-line system in a rotational speed-detecting device of the positional detection type detects a variation of magnetic leakage flux produced by a rotating or moving body with a magneto-electric element, and superposes a rectangular wave current on the power supply line after signal processing, so as to reduce a number of a signal output line by way of calculating the number of rotations or the amount of movement of the rotating or moving body with a computer by detecting a voltage across a resistor inserted in the power supply line at a power supply terminal. This method requires to reduce absolute values and a relative difference of a high current value and a low current value of the rectangular wave as small as possible, in order to reduce a power consumption of the entire circuit and to hold down heat generation of the circuit elements as little as possible. On the other hand, the smaller it is to keep an absolute current value of the rectangular wave current, the more important a preciseness of the current value of the rectangular cur
REFERENCES:
patent: 5168274 (1992-12-01), Wakamatsu
Japanese search report for Int'l Appln No. PCT/JP98/02403 dated Aug. 25, 1998.
Copy of Form PCT/ISA/210.
Shimamura Hiroshi
Ueda Shinjiro
Matsushita Electric - Industrial Co., Ltd.
Oda Christine K.
Zaveri Subhash
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