Measuring and testing – Engine detonation – Specific type of detonation sensor
Reexamination Certificate
2001-06-05
2002-08-27
Solis, Erick (Department: 3747)
Measuring and testing
Engine detonation
Specific type of detonation sensor
Reexamination Certificate
active
06439030
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to a signal processing device for use in a physical force measuring system which is designed to measure an applied physical force such as pressure or vibration using a piezoelectric device which may be employed in combustion pressure measuring device for measuring the combustion pressure of an internal combustion engine.
2. Background Art
Typical combustion pressure measuring devices for internal combustion engines use a charge amplifier designed as a signal processing circuit which handles an output of a combustion pressure sensor. The charge amplifier works to monitor a current outputted by a combustion pressure sensor in response to an applied pressure and integrate it to produce a voltage signal indicative of the combustion pressure. An example of a combustion pressure measuring device of this type is shown in FIG.
11
.
A combustion pressure sensor
61
is coupled to an integrating circuit
62
made by a charge amplifier. An output of the integrating circuit
62
is transmitted to an external device through a high-pass filter
63
, an amplifier
64
, and a low-pass filter
65
. The integrating circuit
62
is made up of an operational amplifier
66
, a resistor
67
, and a capacitor
68
and designed to integrate a charge produced in the combustion pressure sensor
61
to provide a voltage signal.
Specifically, the integrating circuit
62
integrates a weak current signal. Therefore, in order to prevent the capacitor
68
from being charged by a bias current from the operational amplifier
66
, the operational amplifier
66
having a high input impedance is used to store the charges in the capacitor
68
. The time constant of the integration depends upon the capacitor
68
and the resistor
67
. The cut-off frequency of the integrating circuit
62
is relatively low, so that the resistance value of the resistor
67
will be several M &OHgr; to several tens M &OHgr;. For instance, when the cut-off frequency of the integrating circuit
62
is 0.8 Hz, and the capacitance of the capacitor
68
is 0.1 &mgr;F, the resistance value of the resistor
67
will be approximately 2M &OHgr;.
The resistance value of the resistor
67
may be determined, as discussed below, in terms of a combustion cycle of the engine. The combustion cycle f of the engine using an engine speed during idling is
f=750 rpm/(60 sec.×2 cycles)=6.25 Hz
Considering the fact that ensuring the integrating operation requires the cut-off frequency of the integrating circuit
62
to be one-tenth ({fraction (1/10)}) of a frequency of a detected signal (i.e., the combustion cycle f), the resistance value Rin of the resistor
67
may be expressed by
Rin≧
1/(2&pgr;×0.1×
f×Cin
)
where Cin is 0.1 &mgr;F. The resistance value Rin of the resistor
67
is, thus, 2.5M &OHgr;.
The input impedance of the integrating circuit
62
is equal to that of the resistor
67
and thus has a higher value. The integrating circuit
62
is, therefore, undermined easily by the leakage current from the combustion pressure sensor
61
or an external device due to the humidity. This problem will be described in detail below with reference to time charts in FIGS.
12
(
a
) to
12
(
d
).
Usually, the combustion pressure of the engine, as shown in FIG.
12
(
a
), rises every combustion in each cylinder. In the absence of the leakage current, the output of the integrating circuit
62
changes, as shown in FIG.
12
(
b
), within a voltage range (e.g., 0 to 12V) defined near the voltage of a power supply of the operational amplifier
66
. Specifically, the output of the integrating circuit
62
changes following each change in level of the combustion pressure. Since the output of the combustion pressure sensor
61
is inputted to an inverting input (−) of the operational amplifier
66
, the output of the integrating circuit
62
is reverse in level to the input thereinto. The operational amplifier
66
needs to be actuated on ±12V. Specifically, a negative (−) power supply voltage must be prepared, therefore, this system is unsuitable for automotive vehicles.
In the presence of the leakage current, the output of the integrating circuit
62
is, as shown in FIG.
12
(
c
), shifted in level to a negative side. This will result in an unwanted change in output of the combustion pressure measuring device even though a dc component is removed by the high-pass filter
63
.
If the leakage current increases greatly, it will cause the waveform of the output of the integrating circuit
62
, as shown in FIG.
12
(
d
), to be deformed greatly, so that the output indicative of the combustion pressure will be saturated at a minimum output voltage VL of the operational amplifier
66
(i.e., the voltage of the negative power supplied to the operational amplifier
66
). Specifically, a great leakage current causes an error in the output of the combustion pressure measuring device to be produced.
Further, if electric noises arise in a driver for fuel injectors of the engine, it will cause the output of the integrating circuit
62
to change, thus resulting in decreased accuracy of measuring the combustion pressure.
Japanese Patent First Publication No. 4-97614 teaches a signal processing circuit for a touch sensor equipped with an piezoelectric element. The signal processing circuit consists of a differentiating circuit, a diode, an integrating circuit, and a comparator. The differentiating circuit receives the electromotive force produced by the piezoelectric element. The diode rectifies an output of the differentiating circuit. The integrating circuit receives an output of the diode. The comparator compares an output of the integrating circuit with a reference voltage. Specifically, the differentiating circuit extracts only a change in electromotive force produced by the piezoelectric element. The integrating circuit stabilizes of the change in electromotive force for increasing the reliability of the output of the sensor.
The above system is designed to determine whether a cumulative value of loads applied to the piezoelectric element is greater than a reference level or not, meaning that the output of the diode only shows an increase in load applied to the piezoelectric element and thus unsuitable for processing a sensor signal indicating the pressure containing a vibrational component such as the combustion pressure of the engine.
SUMMARY OF THE INVENTION
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide a signal processing device capable of processing an output of a piezoelectric element without errors caused by the leakage current and/or electric noises.
According to one aspect of the invention, there is provided a signal processing device which processes an output of a piezoelectric sensor to produce a signal indicative of a load applied to the piezoelectric sensor. The signal processing device comprises: (a) a differentiating circuit differentiating the output of the piezoelectric sensor; and (b) an integrating circuit integrating an output of the differentiating circuit to produce an output signal as a function of the output of the piezoelectric sensor. A frequency range of the output signal is determined based on a frequency range of the load applied to the piezoelectric sensor.
In the preferred mode of the invention, a cut-off frequency of the differentiating circuit is determined based on an upper limit of the frequency range of the load applied to the piezoelectric sensor. A cut-off frequency of the integrating circuit is determined based on a lower limit of the frequency range of the load applied to the piezoelectric sensor.
The piezoelectric sensor includes a piezoelectric element which provides the output changing with a change in physical pressure applied to the piezoelectric element.
The piezoelectric sensor may be installed in a combustion engine to produce the output in response to a change i
Kurokawa Eiichi
Murai Hiroyuki
Suzuki Toshiyuki
Denso Corporation
Nixon & Vanderhye P.C.
Solis Erick
LandOfFree
Signal processing device for piezoelectric sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Signal processing device for piezoelectric sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Signal processing device for piezoelectric sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2952032