Electricity: measuring and testing – Internal-combustion engine ignition system or device – In situ testing of spark plug
Reexamination Certificate
1999-04-08
2001-05-22
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Internal-combustion engine ignition system or device
In situ testing of spark plug
C324S399000
Reexamination Certificate
active
06236213
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a method and an apparatus for inspecting a spark plug or ignition plug for defects thereof such as defects of a discharge gap and a porcelain thereof, and more particularly to such method and apparatus which permit the inspection of the spark plug while the spark plug is installed in an engine.
2. Discussion of related Art
Since spark plugs are relatively likely to be defective during installation thereof in an engine, the inspection of the spark plugs is desirably conducted after the installation in the engine. An example of a method of inspecting spark plugs for their discharge gaps while the spark plugs are installed in an engine. According to this inspection method, the secondary voltage of an ignition coil is detected by an exclusive probe while the engine is operated by combustion of an air-fuel mixture, so that the spark plug is inspected for adequacy of the discharge gap based on a time duration of an inductive discharge component of the detected secondary voltage.
This inspection method permits the inspection of the spark plug as installed in the engine. However, this method is a so-called “firing check” in which the engine is operated by combustion of the air-fuel mixture. Further, the method relies on only the time duration of the discharging. Therefore, the conventional inspection method cannot be considered satisfactory. The discharging in the spark plug tends to be influenced by the pressure and the fuel concentration of the air-fuel mixture surrounding the discharge gap of the spark plug. In the firing state of the engine, there exists a relatively strong fluid flow within the cylinder of the engine, which may cause considerable variations in the pressure and fuel concentration around the discharge gap, leading to insufficient accuracy of inspection of the discharge gap.
It is desirable to inspect the spark plug for a defect of the porcelain, as well as for the adequacy of the discharge gap. The conventional inspection method indicated above cannot satisfy this need.
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a method of inspecting a spark plug, which is improved over the conventional method disclosed in JP-A-50-74034.
A second object of the invention is to provide an apparatus suitable for practicing the method of the invention.
The first object indicated above may be achieved according to any one of the following features of the present invention, which are numbered to indicate possible combinations of the features:
(1) A method of inspecting a spark plug while the spark plug is installed in an engine, characterized in that a state of the spark plug is determined on the basis of at least one voltage-related quantity relating to a voltage which is applied to the spark plug without the engine being supplied with a fuel, such that a level of the voltage is high enough to cause the spark plug to generate a spark.
The present method may be practiced while the pressure within a cylinder of the engine for which the spark plug is provided is maintained at the atmospheric pressure or at a level higher than the atmospheric pressure. Further, the method may be practiced while the engine is held at rest or operated by an external drive device. The operation of the engine by the external drive device is performed, without a fuel being supplied to the engine, namely, without firing of the engine, so as to raise the cylinder pressure at which the engine is fired during normal operation by combustion of the fuel. The inspecting apparatus for practicing the present method may be adapted to utilize the ignition system of the engine per se. However, where the inspection of the spark plug is effected by simply raising the cylinder pressure of the engine, this may be accomplished by closing at least one of the intake and exhaust ports and introducing a compressed gas such as compressed air into the cylinder through the closed port.
In any of the above cases, the inspection is effected without the engine being supplied with a fuel, whereby the inspection would not be influenced by the fuel concentration of the air-fuel mixture. Further, since the engine is held at rest or operated by the external drive device without firing thereof, the amount of flow of the fluid within the cylinder is made smaller than where the inspection is effected with the engine being fired, so that the pressure variation in the vicinity of the discharge gap of the spark plug is reduced, resulting in an improvement in the accuracy of inspection of the spark plug for the discharge gap size, and leading to enhanced reliability of the inspection.
For inspecting the spark plug, it may be energized with a secondary voltage which is generated by a voltage applying device on the basis of a primary voltage lower than the secondary voltage. In this case, the above-indicated at least one voltage-related quantity may consist of at least one of the primary and secondary voltages and a time duration of a discharge which occurs on the energized spark plug. This arrangement utilizing the two or more kinds of information permits a further improvement in the inspection reliability. Even where the inspection is based on at least one of the primary and secondary voltages, without utilizing the discharge time duration, the number of kinds of the information that can be utilized for the inspection is larger than where the inspection is based on only the discharge time duration. For instance, the voltage information may include an average of the primary or secondary voltage, a rate of change of the voltage and a waveform of the voltage.
(2) A method of inspecting a spark plug while the spark plug is installed in an engine, characterized in that the spark plug is energized with a secondary voltage which is generated by a voltage applying device on the basis of a primary voltage lower than said secondary voltage, such that a level of said secondary voltage is high enough to cause the spark plug to generate a spark, and that a state of the spark plug is determined on the basis of at least one of the primary and secondary voltages.
In the method according to the feature (2) of the invention which utilizes at least one of the primary and secondary voltages, the number of kinds of the information on which the inspection is effected is larger than where the inspection is based on only the discharge time duration, as described above with respect to the feature (1) of the invention. Accordingly, the inspection reliability is improved. However, it is to be understood that the method according to the present feature (2) does not exclude the inspection while the engine is fired by combustion of a fuel, and the inspection which utilizes the discharge time duration as well as the at least one of the primary and secondary voltages.
(3) A method according to the above feature (1) or (2), wherein the spark plug is energized by application of the primary voltage or secondary voltage thereto while the engine is operated by an external drive device.
(4) A method according to any one of the above features (1)-(3), wherein the spark plug is energized by application of the primary voltage or secondary voltage thereto while the engine is held at rest.
The method according to the features (3) and (4) may include a step of inspecting the spark plug while the engine is held at rest, and a step of inspecting the spark plug while the engine is operated. Since a relatively large number of kinds of information may be obtained while the engine is held at rest and while the engine is operated, the number of items of the inspection may be increased, and the inspection reliability is accordingly improved.
(5) A method according to any one of the above features (1)-(4), wherein the spark plug is energized by application of the primary voltage or secondary voltage thereto while a pressure in a cylinder of the engine for which the spark plug is provided is held at an atmospheric level.
The method according to this feature
Maruta Naoyuki
Suzuki Nobuaki
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Metjahic Safet
Nguyen Vincent Q.
Toyota Jidosha & Kabushiki Kaisha
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