Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2001-11-28
2002-05-21
Han, Jessica (Department: 2838)
Electricity: measuring and testing
Magnetic
Displacement
C324S207250
Reexamination Certificate
active
06392407
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rotation angle detecting device capable of magnetically detecting, for instance, a rotation angle of a gear-shaped magnetic rotation member.
2. Description of the Related Art
Referring now to a drawing, a conventional rotation angle detecting device will be described. FIG.
4
(
a
) to FIG.
4
(
c
) are diagrams for illustratively showing a magnetic circuit of a conventional rotation angle detecting device.
FIG. 5
represents a signal processing circuit employed in the conventional rotation angle detecting device.
In
FIG. 4
, reference numeral
1
shows a rotation shaft corresponding to a crank shaft of a vehicle engine, reference numeral
2
represents a magnetic rotation member, reference numeral
3
indicates a magnet, reference numeral
4
denotes a chip, and reference numeral
5
shows a magnetic detecting element (will be referred to as an “MR element” hereinafter).
In
FIG. 5
, reference numeral
10
shows a bridge circuit, reference numeral
20
indicates a differential amplifying circuit, reference numeral
30
represents an AC coupling circuit, reference numeral
40
indicates another differential amplifying circuit, reference numeral
50
shows a comparing circuit, reference numeral
60
indicates an output circuit, and also reference numeral
70
is an initiating circuit.
As illustrated in
FIG. 4
, the conventional rotation angle detecting circuit contains the magnet
3
having a rectangular solid shape, the chip
4
, and the magnetic detecting element
5
. This chip
4
is mounted on an upper surface of this magnet
3
, and a semiconductor integrated circuit (namely, signal processing circuit) is built in this chip
4
.
Since the magnetic rotation member
2
having the gear shape is rotated which is provided in the vicinity of the above-explained rotation angle detecting device, a concave portion and a convex portion of the magnetic rotation member
2
are alternatively positioned in the vicinity of the magnetic detecting element
5
. As a result, a magnetic field, which is applied from the magnet
3
to the magnetic detecting element
5
, is changed. This change in the magnetic fields may be detected as a change in voltages by the magnetic detecting element
5
.
This change in the voltages is outputted as a pulsatory electric signal through the differential amplifying circuit
20
, the AC coupling circuit
30
, the differential amplifying circuit
40
, the comparing circuit
50
, and the output circuit
60
, which are provided in the chip
4
, to an external circuit. This pulsatory electric signal is supplied to a computer unit (not shown), so that a rotation angle of the magnetic rotation member
2
may be detected.
Generally speaking, as the magnetic detecting element
5
, either a magnetic resistance element (will be referred to as a “MR element” hereinafter) or a giant magnetic resistance element (will be referred to as a “GMR element” hereinafter) is employed. However, since the operations of these MR element and GMR element are substantially identical to each other, operations of the rotation detecting device in the case that the MR element is employed will be explained in detail.
An MR element (magnetic resistance element) corresponds to such an element whose resistance value is changed based upon an angle defined between a magnetization direction of a thin film of a ferromagnetic material (for example, Ni—Fe, Ni—Co etc.) and a current direction thereof. The resistance value of this MR element becomes minimum when the current direction is intersected with the magnetization direction at a right angle, whereas the resistance value of the MR element becomes maximum in the case that the current direction is intersected with the magnetization direction at an angle of 0 degree. In other words, when both the current direction and the magnetization direction are intersected along the same direction, or completely opposite directions, this resistance value becomes maximum. This change in the resistance values will be referred to as an MR change rate. Generally speaking, the MR change rate of Ni—Fe is equal to 2 to 3%, and the MR change rate of Ni—Co is equal to 5 to 6%.
Since the magnetic rotation member
2
is rotated, a magnetic field applied to the MR element
5
is changed, so that the magnetic resistance value of this MR element
5
is changed. Accordingly, in order to detect the change in the magnetic fields, as indicated in
FIG. 5
, the bridge circuit
10
is constituted by employing the MR element
5
. While this bridge circuit
10
is connected to a power supply capable of supplying a constant voltage and a constant current, the resistance value change of the MR element
5
is converted into a voltage change, and then, a change in magnetic fields which is exerted to this MR element
5
may be detected.
The conventional rotation angle detecting device is arranged by employing the bridge circuit
10
, the differential amplifying circuit
20
, the AC coupling circuit
30
, the differential amplifying circuit
40
, the comparing circuit
50
, the initiating circuit
70
, and the output circuit
60
. The bridge circuit
10
is constructed of the MR element
5
. The differential amplifying circuit
20
amplifies the output signal of this bridge circuit
10
. The AC coupling circuit
30
removes a DC component from the output signal of the differential amplifying circuit
20
. The differential amplifying circuit
40
amplifies the output signal of this AC coupling circuit
30
. The comparing circuit
50
compares the output signal of this differential amplifying circuit
40
with a reference value to output either a signal of “0” or a signal of “1”. The initiating circuit
70
sets the output signal of this comparing circuit
50
to a preselected level. The output circuit
60
is operated in a switching mode in response to the output signal of this comparing circuit
50
.
The bridge circuit
10
contains a resistor
11
and the above-described MR element
5
. The resistor
11
is connected to a power supply terminal VCC; the MR element
5
is connected to the ground; and the other respective terminals of the resistor
11
and the MR element
5
are connected to a junction point “A.”
Then, the connection point “A” of the bridge circuit
10
is connected via a resistor
21
to an inverting input terminal of an operational amplifier
20
employed in the differential amplifying circuit
20
. Also, a non-inverting input terminal of this operational amplifier
22
is connected via a resistor
27
to a voltage dividing circuit which constitutes a reference power supply, and is further connected via a resistor
24
to the ground. The output terminal of the operational amplifier
22
is connected via the resistor
23
to the own inverting input terminal, and also is connected to a capacitor
31
employed in the AC coupling circuit
30
.
The AC coupling circuit
30
is arranged by one capacitor
31
and a resistor
34
. A junction point between the capacitor
31
and the resistor
34
is connected via the resistor
41
to an inverting input terminal of an operational amplifier
42
employed in the differential amplifying circuit
40
. Also, another terminal of the resistor
34
is connected to a voltage dividing circuit which constitutes a reference power supply.
Also, a non-inverting input terminal of the operational amplifier
42
provided in the differential amplifying circuit
40
is connected via a resistor
47
to the voltage dividing circuit which constitutes the reference power supply, and further, is connected via a resistor
44
to the ground. An output terminal of this operational amplifier
42
employed in the differential amplifying circuit
40
is connected via a resistor
43
to the own inverting input terminal, and also is connected to an inverting input terminal of an operational amplifier
51
employed in the comparing circuit
50
.
Both a non-inverting input terminal and an output terminal of an operational amplifier
77
employed in the initiating circuit
70
a
Mishiro Naohiro
Shinjo Izuru
Yokotani Masahiro
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