Measuring and testing – Engine detonation – Specific type of detonation sensor
Reexamination Certificate
2002-10-02
2004-05-25
McCall, Eric S. (Department: 2855)
Measuring and testing
Engine detonation
Specific type of detonation sensor
Reexamination Certificate
active
06739181
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based on Japanese Patent Application No. 2001-362656 filed on Nov. 28, 2001 the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a combustion detecting apparatus of an engine for determining a combustion condition of the engine based on ion current.
2. Description of Related Art
Conventionally, in order to detect a combustion condition of an engine, there has been developed a technology of detecting ion current flowing in an electrode of an spark plug at each ignition and determining firing/misfire or the like based on an ion current detecting signal thereof.
Further, as a combustion detecting apparatus of an engine using a technology of this kind, according to, for example, JP-A-11-13616, there is described an apparatus in which an ion current detecting signal is inputted to a filter for passing only a signal equal to or larger than a predetermined threshold and having a width equal to or larger than a predetermined time period, an output signal of the filter is inputted to a peak hold circuit, an output of the peak hold circuit is subjected to A/D conversion at a predetermined timing after ignition (for example, timing of ATDC60° CA), when the A/D conversion value (that is, a peak hold value of the output signal of the filter by the peak hold circuit) is equal to or larger than a determining reference value, a firing is determined, otherwise, a misfire is determined.
However, there poses the following problem according to the apparatus described in the publication.
That is, the peak hold circuit is constructed by a constitution of storing electric charge in a capacitor and therefore, when peak hold time is long, by leak current of the circuit or discharging the electric charge of the capacitor, peak hold voltage is lowered and a correct peak hold value is not provided. Particularly, when the output of the peak hold circuit is subjected to A/D conversion at a timing of a specific crank angle after ignition (ATDC60° CA in the above-described example), in accordance with rotational speed (rotational number) of the engine, the lower the rotational number, the longer the time period from ignition to the timing of the specific crank angle and therefore, the peak hold voltage is liable to lower. Therefore, the apparatus is disadvantageous in accurately determining the combustion condition of the engine.
Hence, it is conceivable to construct a constitution as shown by
FIG. 16
without using an analog peak hold circuit.
That is, first, the ion current detecting signal is inputted to a low pass filter
101
and an output signal of the low pass filter
101
is subjected to A/D conversion at every constant time period by an A/D converter
103
. Further, it is conceivable to adopt a constitution in which CPU
105
carries out a peak hold processing of calculating a maximum value (peak value) of an A/D conversion value at the every constant time period by the A/D converter
103
, compares a maximum value provided in the peak hold processing with a predetermined determinant (threshold) Vth, determines a firing when the maximum value is larger and determines a misfire otherwise.
However, in the case of the constitution, as exemplified in
FIG. 17
, (b), (c), and (d), there is a case in which a period of generating noise in the ion current detecting signal and an A/D conversion timing by the A/D converter
103
are synchronized. In this case, a signal of the noise is erroneously determined as a signal indicating a firing. That is, even in the case of a misfire, the misfire is erroneously determined as a firing. Further, in
FIG. 17
, (b), (c) and (d), the A/D conversion timing is indicated by a black circle mark (&Circlesolid;). In
FIG. 17
, (b) shows normal combustion. In
FIG. 17
, (c) shows the case of a misfire. In
FIG. 17
, (d) shows a case of increasing the time constant of the low pass filter. In
FIG. 17
, (a) shows an ignition signal and time t
0
is the ignition timing.
Therefore, although it is conceivable to construct a constitution of setting an A/D conversion period (time interval of A/D conversion) to be short and determining whether a noise signal is constituted from a state of changing each A/D conversion value, there is needed an A/D converter capable of carrying out high-speed A/D conversion or CPU capable of carrying out high-speed processing, which results in a significant increase in cost.
Further, although it is also conceivable to enhance a filter effect (voltage smoothing effect) of the low pass filter
101
, thereby, as exemplified in (d) of
FIG. 17
, an original waveform of the ion current detecting signal is significantly blunted, an accurate peak hold value is not provided and therefore, the combustion condition cannot accurately be determined.
Meanwhile, the above-described respective problem is not limited to the constitution of subjecting the ion current detecting signal to peak holding but is similarly posed also in the case of, for example, an integrating constitution. That is, in the apparatus described in the publication, even in the case of providing an integrating circuit in place of the peak hold circuit and determining firing/misfire based on an output of the integrating circuit, the integrating circuit is constructed by a constitution of storing electric charge in a capacitor and therefore, when an integrating time period is long, output voltage in correspondence with an integrated value is lowered and a correct integrated value is not provided. Further, in the constitution of
FIG. 16
, even in a case in which CPU
105
carries out an integrating processing for calculating an integrated value of the A/D conversion value at every constant time period and determining firing/misfire based on the integrated value provided by the processing, the problems described in reference to
FIG. 17
, (b), (c) and (d) are similarly posed.
SUMMARY OF THE INVENTION
The invention has been carried out in view of the problems and it is an object thereof to provide a combustion detecting apparatus capable of accurately determining a combustion condition of an engine from an ion current detecting signal without shortening an A/D conversion period for excluding influence of noise.
According to an aspect of the invention, ion current detecting means detects an ion current flowing in electrodes of a spark plug of the engine and outputs an ion current detecting signal of a voltage in accordance with the ion current. Further, A/D conversion means subjects the ion current detecting signal outputted from the ion current detecting means at every predetermined time period to A/D conversion and A/D conversion value storing means stores an A/D conversion value by the A/D conversion means.
Further, reference voltage producing means produces a reference voltage large or small of which is compared with the ion current detecting signal and voltage change storing means stores that the ion current detecting signal traverses the reference voltage by comparing the ion current detecting signal and the reference voltage.
Further, at every timing of subjecting the ion current detecting signal to A/D conversion by the A/D conversion means (A/D conversion timing), erasing means determines whether the ion current detecting signal is stored to traverse the reference voltage in the voltage change storing means, erasing a stored value of the A/D conversion value storing means prior to an A/D conversion timing at a current time and erasing a memory of the voltage change storing means when the ion current detecting signal is stored to traverse the reference voltage. Further, combustion condition determining means determines a combustion condition of the engine based on the stored value of the A/D conversion value storing means which has not been erased continuously over A/D conversion timings more than a predetermined number of times M by the erasing means.
Further, when the traversing of the reference voltage by the ion current detecting signal i
Denso Corporation
McCall Eric S.
Nixon & Vanderhye P.C.
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