Measuring and testing – Vehicle chassis – Steering
Reexamination Certificate
2002-05-01
2004-08-17
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Vehicle chassis
Steering
Reexamination Certificate
active
06776032
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field the Invention
The present invention relates to a misfire deciding method and system for an internal combustion engine.
2. Description of the Related Art
As a misfire deciding method in an internal combustion engine, a method has been proposed for directly measuring the pressure in a combustion chamber, for example, by forming a pressure conduit leading to the combustion chamber in a cylinder head and by arranging a partition type pressure sensor in the pressure conduit. The formation of this pressure conduit in the cylinder head, however, involves complex machining which inevitably raises the manufacturing cost. A more convenient method for measuring the internal pressure uses a pressure sensor (hereinafter called a “gasket type pressure sensor”) which is mounted on the mounting seat of a spark plug, as disclosed, for example, in Japanese Patent Laid-Open No. 290853/1994.
FIG. 3
exemplifies an internal pressure profile as measured by an internal pressure sensor for one cycle in the combustion engine. The solid curve indicates the profile for normal combustion timing, and the single-dotted curve indicates the profile for a misfire timing. When an intake valve is closed, the inside of the combustion chamber is sealed, and the mixture is compressed as a piston rises, so that the internal pressure rises. Moreover, the spark plug sparks at a crank angle (or an ignition timing) before top dead center (TDC). When the mixture is normally ignited with that spark, the internal pressure is further raised by the explosion of the mixture. By this pressure rise, the rise in the internal pressure is continued for a while, even after the piston passes through the TDC and turns downward, and the internal pressure is reduced after the piston goes down to some extent. Therefore, the internal pressure measured profile assumes an asymmetric shape in which the peak position is shifted to a larger angle side than the crank angle (i.e., an &agr;TDC) corresponding to the TDC. When the ignition ends unsuccessfully with a misfire, on the other hand, no pressure rise due to the explosion occurs so that the pressure assumes a maximum value at the TDC where the volume in the combustion chamber is at a minimum. After this, the piston moves down with the pressure change merely following a profile which is inverted relative to that of the rising time. Therefore, the internal pressure measured profile thus obtained is generally symmetric so as to have a peak position at the &agr;TDC. Thus, between the normal combustion time and the misfire time, differences apparently occur both in the peak value of the internal pressure measured profile and in the symmetry of the profile.
However, the misfire decision using only one point of the internal pressure peak value level has numerous error factors and lacks accuracy because it does not take into consideration the tendency of the entire profile. Japanese Patent Laid-Open Nos. 321752/1992, 72448/1992 and 325755/1992, therefore, discloses a method for deciding a misfire by comparing the magnitudes of a before top dead center pressure integrated value S
1
obtained by integrating the internal pressure measured values for a constant integration period defined in the before top dead center period and an after top dead center pressure integrated value S
2
obtained by integrating the average pressure information for a constant integration period defined in the after top dead center period. In short, by using the integrated values, the tendency of the entire internal pressure measured profile can be reflected in an average form on the decision result so that a more accurate misfire decision can be made.
Here, the method using the gasket type pressure sensor indirectly measures the internal pressure, in that the fastening force of the spark plug fixing the sensor is loosened by the internal pressure. As compared with the method of measuring the internal pressure directly through the pressure conduit by using the partition type sensor, therefore, there are a number of factors causing the absolute value of the measured pressure value to fluctuate. More specifically, variations in the force for fastening the spark plug and in the performance of individual piezoelectric elements easily cause the measured value level of the internal pressure to fluctuate, such that the measured value and its integrated value vary for a given internal pressure, easily resulting in an erroneous decision. In the above-specified patent publications, however, there is no disclosure of any specific means for reducing the adverse influences of these variation-causing factors.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a misfire decision method and system for an internal combustion engine, which can be executed conveniently and inexpensively by using a gasket type pressure sensor and which can at all times make an accurate misfire decision while being hardly influenced by variations in the mounting arrangement or performance of the piezoelectric elements.
In order to achieve the above-specified object, the invention provides a misfire deciding method for an internal combustion engine, characterized by:
acquiring an internal pressure measured value based on the internal pressure of an internal combustion engine, to which a spark plug is attached, from the output of a pressure sensor mounted in a mounting seat of the spark plug;
calculating the integrated value of the internal pressure measured values for a first constant integration period in a period (as will be called the “before top dead center period”) after an intake valve is closed and before a crank angle reaches top dead center, and setting the calculated value to a before top dead center integrated value S
1
;
calculating the integrated value of the internal pressure measured values for a second constant integration period in a period (as will be called the “after top dead center period”) after the crank angle reaches top dead center and before an exhaust valve is opened, and setting the calculated value to an after top dead center integrated value S
2
;
calculating a differential integrated value S
1
−S
2
between the after top dead center integrated value S
2
and the before top dead center integrated value S
1
; and
calculating a first correction reference value using the internal pressure measured value at a correction measurement point set for the before top dead center period, to correct the differential integrated value with the first correction reference value, to thereby make a misfire decision on the basis of the corrected differential integrated value.
The invention provides a misfire deciding system for an internal combustion engine, comprising:
a pressure sensor mounted in a mounting seat of a spark plug for acquiring an internal pressure measured value based on the internal pressure of an internal combustion engine having the spark plug mounted therein; and
a decision unit for: calculating the integrated value of the internal pressure measured values for a first constant integration period in a period (as will be called the “before top dead center period”) after an intake valve is closed and before a crank angle reaches the top dead center, and setting the calculated value to a before top dead center integrated value S
1
; calculating the integrated value of the internal pressure measured values for a second constant integration period in a period (as will be called the “after top dead center period”) after the crank angle reaches top dead center and before an exhaust valve is opened, and setting the calculated value to an after top dead center integrated value S
2
; calculating a differential integrated value S
1
−S
2
between the after top dead center integrated value S
2
and the before top dead center integrated value S
1
; and calculating a first correction reference value using the internal pressure measured value at a correction measurement point set for the before top dead center period, to correct the differential integrated value
Matsui Masayoshi
Okazaki Koji
Davis Octavia
NGK Spark Plug Co. Ltd.
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