Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
2001-05-30
2004-08-03
Chapman, John E. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
C073S035110
Reexamination Certificate
active
06769305
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an acceleration sensor, and more particularly to an acceleration sensor for detecting an acceleration caused by an object with a piezoelectric element mounted on an oscillation plate accommodated in a sensor casing.
2. Description of the Related Art
In general, the acceleration sensor now known and in use includes various types such as an electromagnetic type, a piezoelectric element type, and a semiconductor type, all of which are designed to detect the acceleration. Among these types of acceleration sensors, the piezoelectric element type of acceleration sensor is known as detecting acceleration with a piezoelectric element when it is deformed to generate a voltage indicative of the acceleration. These types of acceleration sensors are usually mounted on automobiles to be used for controlling knockings of engines and airbag systems.
The acceleration sensor of this type is raised for example as a first conventional acceleration sensor and shown in
FIGS. 25 and 26
. The acceleration sensor
800
comprises a fixed case member
801
, an oscillation plate
802
, a piezoelectric element
803
, electrodes
804
, a metal wire
805
, a cover member
806
, an output terminal pin
807
and a resilient ring
808
. The fixed case member
801
formed in a cylindrical shape is made of a metal and has a supporting portion
801
a
upwardly projecting from and integrally formed with the bottom portion of the fixed case member
801
. The oscillation plate
802
formed in an annular shape is made of a metal and securely mounted on the supporting portion
801
a
of the fixed case member
801
by welding. The piezoelectric element
803
formed in an annular shape is provided on the oscillation plate
802
in axial alignment with the oscillation plate
802
. The piezoelectric element
803
is covered with the electrodes
804
. One of the electrodes
804
is electrically connected with the oscillation plate
802
, while the other of the electrodes
804
is electrically connected with the output terminal pin
807
. The electrical connection between the other of the electrodes
804
and the output terminal pin
807
is established by the metal wire
805
having both ends soldered at
805
a
by wire bonding and like. The cover member
806
formed in a cylindrical shape is made of a plastic material and has an exterior object mounted thereon and electrically connected with the output terminal pin
807
. The output terminal pin
807
is mounted on the cover member
806
. The fixed case member
801
and the cover member
806
have respectively peripheral edge portions
801
c
and
806
c
bent and fixedly coupled with each other with the resilient ring
808
intervening between the peripheral edge portions
801
c
and
806
c
to hermetically seal the gap and define a closed space in which the oscillation plate
802
and the piezoelectric element
803
are operatively accommodated. Therefore, no water enters the closed space through the gap.
Another acceleration sensor of the piezoelectric element type is raised for example as a second conventional acceleration sensor and shown in FIG.
27
.
The acceleration sensor
900
comprises a fixed case member
901
, a metal base member
902
, an oscillation plate
802
, a piezoelectric element
803
, electrodes
804
, a metal plate
903
, a cover member
904
, an output terminal pin
807
and a resilient ring
905
. The fixed case member
901
formed in a cylindrical shape has an annular ledge portion
901
c
radially inwardly bent. The metal base member
902
formed in a circular shape and provided on the fixed case member
901
at the annular ledge portion
901
c
of the fixed case member
901
. The cover member
904
formed in a circular shape has a peripheral edge portion
904
a
fixedly connected with the annular ledge portion
901
c
of the fixed case member
901
with the metal base member
902
intervening between the fixed case member
901
and the cover member
904
. The fixed case member
901
, the metal base member
902
and the cover member
904
collectively define a closed space to accommodate the oscillation plate
802
and the piezoelectric element
803
to be oscillatable by an oscillation exerted on the acceleration sensor. On the cover member
904
formed in a circular shape is mounted the output terminal pin
807
electrically connected with the piezoelectric element
803
and connectable with an exterior connecting member. The metal base member
902
has a supporting portion
902
a
projecting toward the fixed case member
901
into the closed space and has the oscillation plate
802
and the piezoelectric element
803
securely supported thereon. In this example, both of the oscillation plate
802
and the piezoelectric element
803
are formed in an annular shape, and the cover member
904
is made of a plastic material to ensure that the output terminal pin
807
is electrically insulated from the metal base member
902
. Through the supporting portion
902
a
of the metal base member
902
is extending the output terminal pin
807
which has one end electrically connected with one of the electrodes
804
of the piezoelectric element
803
through the metal plate
903
soldered by
903
a
and thus electrically connected with one of the electrodes
804
of the piezoelectric element
803
so that the oscillation plate
802
and the piezoelectric element
803
can be oscillated when they are exerted by an acceleration. The resilient ring
905
is interposed between the inner surface of the fixed case member
901
and the outer surface of the metal base member
902
to ensure that the resilient ring
905
hermetically seals the closed space. The rigidity of the metal plate
903
is preferably as small as possible and may be replaced by the metal wire
805
electrically connected with the electrode
804
of the piezoelectric element
803
and the output terminal pin
807
, while the oscillation plate
802
may be connected to the supporting portion
902
a
by welding.
The above two type of acceleration sensors
800
and
900
have male screws
801
b
and
901
b
, respectively formed on its exterior side of the fixed case member
801
and
901
to be screwed into a female screw portion formed in a detectable object such as engine. Thus, the oscillation plate
802
is oscillated and deformed by an oscillation from the detectable object such as engine to have the piezoelectric element
803
generate a voltage indicative of the acceleration, thereby enabling the voltage to be outputted from the electrodes
804
through the output terminal pin
807
with the fixed case member
801
,
901
and the metal base member
902
earthed to the ground.
FIG. 28
is a graph showing a characteristic of the resonance frequency fo with respect to the oscillation under a predetermined acceleration of the acceleration sensor of these types, for example, obtaining a relatively high sharpness of resonance Q in the vicinity of a point of the resonance frequency fo while obtaining a relatively low and flat sharpness of resonance Q at intermediate and lower frequency range. Here, the sharpness of resonance Q means sensitivity of resonance. Generally available is the relatively high sharpness of resonance Q at around the point of the resonance frequency fo and the relatively low and flat sharpness of resonance Q at intermediate and lower frequency range any one of which is selected depending upon the acceleration sensor in use. Accordingly, the upper limit of the frequency range in substantial use is the point of the resonance frequency fo. For example, the sharpness of resonance Q in the vicinity of the point of the resonance frequency fo used for obtaining the desirable frequency makes it impossible to detect a frequency slightly out of the point of the resonance frequency fo. Generally, the disadvantages inherent in the foregoing apparatus is overcome with the resistance R and the piezoelectric element
803
connected in parallel relationship with each other to have the output volta
Baba Hiroyuki
Murata Noriyuki
Chapman John E.
Pearne & Gordon LLP
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