Measuring and testing – Engine detonation – Specific type of detonation sensor
Reexamination Certificate
1999-06-25
2001-03-20
Moller, Richard A. (Department: 2856)
Measuring and testing
Engine detonation
Specific type of detonation sensor
C073S116070, C324S378000
Reexamination Certificate
active
06202474
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ion current detector to detect the ionization of combustion gas generated by the combustion of an internal combustion engine as an ion current, and thus to detect a combustion status on the basis of the ion current.
2. Description of Related Art
An ignition-type internal combustion engine (hereinafter referred to as engine) compresses a mixed gas of air and fuel for introduction into a combustion chamber (hereinafter referred to as cylinder) by a piston and ignites and burns the compressed gas with an ignition plug to produce power. An output from an engine and ignition timing for a cylinder position share a close relationship. Generally, when the ignition timing is advanced, higher output is attainable. However, in the presence of an excess advance angle, an abnormal combustion condition called knocking takes place. In the case of repeated knocking, the engine can be destroyed.
When the mixed gas burns inside the cylinder, the burning gas is ionized. Therefore, when a voltage is applied to the burning gas, a current flows within the burning gas due to the ions' action. This current is called an ion current, and it varies according to the burning condition inside the cylinder. Accordingly, the burning condition can be determined by detecting the ion current.
The ion current sharply increases immediately after ignition, and reaches its peak in a short period of time, and thereafter gradually decreases. In the case where knocking occurs, an oscillating component of several kilohertz is superposed onto the ion current. It is indispensable to extract only the oscillating component caused by knocking from the sharply varying ion current. In Japanese Patent Laid-Open No. 7-63869, an ion current-to-voltage conversion part comprising an ion current detecting part to detect an ion current, and a diode, has been proposed. This ion current-to-voltage conversion part outputs a voltage in proportion to the ratio of an alternating component (oscillating component) included in the ion current which has been detected in the ion current detecting part by using logarithmic characteristics of a forward voltage of the diode.
BRIEF SUMMARY OF THE INVENTION
Object of the Invention
As described above, the voltage outputs of an ion current-to-voltage conversion part are set to present such characteristics as a voltage in proportion to the ratio of an alternating component included in the ion current which has been detected in the ion current detecting part by using the logarithmic characteristics of the forward voltage of the diode, then the oscillating component due to knocking is superposed onto the ion current in proportion to the ion current quantity. Thus extraction of the oscillating component from the ion current can be conducted.
However, only in the case of very large knocking is the oscillating component due to knocking superposed onto the ion current in proportion to the ion current quantity. It has been experimentally resolved that in the case of small to medium knocking, which must be detected as a top priority to conduct regulation of the ignition timing, the oscillating component due to knocking is not superposed onto the ion current in proportion to the ion current quantity, but the oscillating component is approximately the same size from the region with a large ion current quantity to the region with a small ion current quantity superposed onto the ion current.
Therefore, when the ion current-to-voltage conversion part is given characteristics to conduct a voltage conversion at a size in proportion to the ratio between the ion current quantity and the oscillating component to detect the oscillation component, it is difficult to detect the oscillating component in the region with a large ion current quantity unless the oscillation has a large amplitude. In addition, in the region with a small ion current quantity, even oscillation with a tiny amplitude is to be detected, even for a slight variation of the ion current. Thus, it will be detected as an oscillating component.
Therefore, when the ion current-to-voltage conversion part is given characteristics to detect the oscillating component in proportion to the ratio between the ion current quantity and the oscillating component, there was a problem in that the accuracy of the detection of the oscillating component for small to medium knocking, which must be detected as a top priority to regulate the ignition timing, got worse.
The present invention has been made to overcome such problems as described above, and its purpose is to obtain an ion current detector for an internal combustion engine which can improve the characteristics of detecting the oscillating component due to small to medium knocking.
SUMMARY OF THE INVENTION
An ion current detector in accordance with the invention, which detects an ion current generated around an ignition plug just after mixed gas inside a cylinder has been ignited with a spark discharge at the ignition plug due to a voltage generated by an ignition coil, comprises a voltage generating part to generate a high voltage for an ion current detection to be applied to the ignition plug via the ignition coil, an ion current-to-voltage conversion part to convert an ion current flowing between electrodes of the ignition plug by this high voltage into a voltage, which is output as an ion signal, and a signal processing part to conduct signal processing for the ion signals, wherein the ion current-to-voltage conversion part makes the voltage conversion ratio of the ion current smaller in the region with less ion current quantity.
The ion current-to-voltage conversion part of the ion current detector in accordance with the invention, further, makes the voltage conversion ratio of the ion current fixed when the ion current quantity is not less than a predetermined value.
The ion current-to-voltage conversion part of the ion current detector in accordance with the invention, also can make the voltage conversion ratio of the ion current decrease in proportion to the ion current quantity when the ion current quantity is not more than a predetermined value.
The ion current-to-voltage conversion part of the ion current detector in accordance with the invention also can make the voltage conversion ratio of the ion current decrease as the ion current quantity increases in the region with a large ion current quantity, and can further make the voltage conversion ratio of the ion current decrease as the ion current quantity diminishes in the region with a small ion current quantity.
The ion current-to-voltage conversion part of the ion current detector in accordance with the invention also can make the voltage conversion ratio of the ion current decrease as the ion current quantity increases in the region with an ion current quantity of not less than the first predetermined value, can make the voltage conversion ratio of the ion current decrease as the ion current quantity diminishes in the region with an ion current quantity of not more than a second predetermined value, and can make the voltage conversion ratio of the ion current fixed when the ion current quantity is not less than the second predetermined value and not more than the first predetermined value.
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Koiwa Mituru
Ohashi Yutaka
Okamura Koichi
Takahashi Yasuhiro
Mitsubishi Denki & Kabushiki Kaisha
Moller Richard A.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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