Electricity: measuring and testing – Electrical speed measuring – Including speed-related frequency generator
Reexamination Certificate
2000-09-11
2002-01-15
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Electrical speed measuring
Including speed-related frequency generator
C324S207200, C324S207250
Reexamination Certificate
active
06339324
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic object motion sensor including a pair of magnetoelectric transducer elements for detecting for example the rotation of a cam shaft of an internal combustion engine, and more particularly, to a magnetic object motion sensor which can output a high-precision pulse signal which precisely corresponds to the motion of the object to be detected, and which can be produced with a greater tolerance in structure and production and thus at low cost.
2. Description of the Related Arts
FIG. 12
is a cross-sectional view illustrating a conventional magnetic object motion sensor as disclosed in Japanese Patent Laid-Open Nos.7-198736 and 6-273437. In this specific example, the magnetic object motion sensor is disposed opposite to a rotating magnetic object so as to serve as a rotation detector for detecting the rotation of the rotating magnetic object.
FIG. 13
is a side view illustrating the position of the rotation sensor relative to the position of the rotating magnetic object shown in FIG.
12
.
As shown in
FIGS. 12 and 13
, a moving magnetic object serving as a rotating magnetic object
1
has a plurality of magnetic material protrusions
1
a
disposed at equal intervals along its periphery.
A pair of magnetoelectric transducer elements, such as Hall devices,
2
a
and
2
b
are disposed a predetermined distance D apart from each other in the direction, denoted by “A”, of the motion of the rotating magnetic object
1
so that the magnetoelectric transducer elements
2
a
and
2
b
face the magnetic material protrusions
1
a
disposed along the periphery of the rotating magnetic object
1
. Each magnetoelectric transducer element
2
a
and
2
b
detects a change in magnetic field caused by the motion of the magnetic material protrusions
1
a
, and outputs an electric signal (which will be described in detail later) corresponding to the change in the magnetic field.
Both magnetoelectric transducer elements
2
a
and
2
b
are included in an integral fashion in a sensor IC
3
, which also includes other various circuit elements (which will be described later).
A permanent magnet
4
magnetized in the direction denoted by the arrow B (refer to
FIG. 13
) is disposed adjacent to the sensor IC
3
so that a bias magnetic field is supplied to each magnetoelectric transducer element
2
a
and
2
b.
The rotation sensor is constructed with the sensor IC
3
including the pair of magnetoelectric transducer elements
2
a
and
2
b
and the permanent magnet
4
for generating the bias magnetic field. The rotation sensor is held in an integral fashion by a holding member
5
so that the rotation sensor is maintained at the specific position described below relative to the rotating magnetic object
1
.
The above components are disposed so that the central axis of the sensor IC
3
and the permanent magnet
4
passing between the center of the magnetoelectric transducer elements
2
a
and
2
b
is coincident with the central axis C in a radial direction of the rotating magnetic object
1
. The side face of the permanent magnet
4
facing the rotating magnetic object
1
is parallel to the line from one element to the other of the two magnetoelectric transducer elements
2
a
and
2
b
and also parallel to the tangential direction E of rotation movement of the rotating magnetic object
1
.
Therefore, the magnetization direction of the permanent magnet
4
is coincident with the direction of the central axis C.
FIG. 14
is a circuit diagram illustrating a typical circuit configuration of the sensor IC
3
.
As shown in
FIG. 14
, the sensor IC
3
has a power supply terminal Vcc via which a power supply voltage is supplied from an external circuit (not shown), a ground terminal GND connected to ground, and an output terminal Vout via which a pulse signal P is output.
The sensor IC
3
also includes: a pair of amplifiers
6
a
and
6
b
for separately amplifying electric signals Fa and Fb output by the pair of magnetoelectric transducer elements
2
a
and
2
b
; a differential amplifier
7
for amplifying in a differential fashion the electric signals Ga and Gb output by the respective amplifiers
6
a
and
6
b
; a waveform shaping circuit
8
for converting the differential signal H output by the differential amplifier
7
into a pulse signal J corresponding to the edges of the magnetic material protrusions
1
a
; and a transistor
9
with a grounded emitter for,inverting the pulse signal J and outputting the resulting signal as a pulse signal P.
The magnetoelectric transducer elements
2
a
and
2
b
, the amplifiers
6
a
and
6
b
, the differential amplifier
7
, and the waveform shaping circuit
8
are connected to the power supply terminal Vcc and also to the ground terminal GND so that electric power is supplied to these circuit elements.
The pulse signal P output from the transistor
9
via the output terminal Vout is further converted by an external circuit to a pulse signal having a final form.
The operation of the conventional magnetic object motion sensor shown in
FIGS. 12
to
14
is described below with reference to the waveform diagrams of
FIGS. 15 and 16
.
FIGS. 15 and 16
illustrate the relationships among the magnetic material protrusions
1
a
of the rotating magnetic object
1
, the differential signal H input to the waveform shaping circuit
8
, and the pulse signal J shaped by the waveform shaping circuit, wherein
FIG. 16
illustrates those relationships for the case in which the rotating magnetic object
1
rotates at a low speed.
In
FIGS. 15 and 16
, TH denotes a threshold level at which the pulse signal J is switched from a high level (H-level) to a low level (L-level), TL denotes a threshold level at which the pulse signal J is switched from a low level to a high level, and &Dgr;T denotes the hysteresis or the difference between the above threshold levels TH and TL.
As shown in
FIG. 16
, the circuit characteristic of the sensor IC
3
has the feature that undershoot Ho and overshoot occur in the differential signal H in particular when the rotating magnetic object
1
rotates at a low speed.
When the rotating magnetic object
1
rotates in the direction indicated by the arrow A, the pair of magnetoelectric transducer elements
2
a
and
2
b
detects the change in the magnetic field caused by the motion of the magnetic material protrusions
1
a
of the rotating magnetic object
1
, and outputs electric signals Fa and Fb whose voltage changes in response to the change in the magnetic field.
The electric signals Fa and Fb are amplified by the amplifiers
6
a
and
6
b
and output as electric signals Ga and Gb, which are further amplified in a differential fashion by the differential amplifier
7
and output as a differential signal H. The differential signal H is then applied to the waveform shaping circuit
8
constructed with for example a Schmitt trigger circuit.
The waveform shaping circuit
8
compares the differential signal H with the threshold levels TH and TL, and converts the differential signal H to a pulse signal J corresponding to the edges of the magnetic material protrusions
1
a.
More specifically, when the differential signal H has become higher than the threshold TH, the pulse signal J is made to fall down to a low level (L level). On the other hand, when the differential signal H has become lower than the threshold TL, the pulse signal J is made to rise up to a high level (H level).
The pulse signal J is then inverted by the transistor
9
into a pulse signal P which is then supplied via the output terminal Vout to an external computer unit or a similar device so as to detect the rotation speed or the rotation angle of the rotating magnetic object
1
.
However, as can be seen from
FIG. 15
, the threshold levels TH and TL associated with the waveform shaping circuit
8
are located in the range in which the differential signal H changes rather gradually. As a result, a small change in level of the differential signal H results in a shift of the pulse signal J i
Fukui Wataru
Hayashi Noriaki
Hiraoka Naoki
Ohashi Yutaka
Sakanoue Hiroshi
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