Method of testing assembled internal combustion engine

Details Method of testing assembled internal combustion engine Method of testing assembled internal combustion engine

2002-09-17

2004-03-30

McCall, Eric S. (Department: 2855)

Measuring and testing

Test stand

For engine

Reexamination Certificate

active

06711944

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a method of checking or testing the assembled state of an internal combustion engine.
BACKGROUND ART
When the assembling of an internal combustion engine (hereinafter, referred to as the “engine”) finishes, it is necessary to judge whether there is a fault with the assembling of the engine, such as missing of any part of the engine, or asynchronism of respective operations of two or more parts of the same. If the engine has a fault, it cannot perform as designed. One example of the assembled engine testing method is disclosed in U.S. Pat. No. 5,355,713. In the disclosed method, an assembled engine is rotated in a “cool” state in which no fuel is fired, a pressure waveform is obtained from an exhaust-valve or intake-valve side space of the engine, and the obtained pressure waveform is compared with a reference pressure waveform which is obtained in advance from a normal engine. Thus, whether or not there is a fault with the assembling of the engine is judged. The U.S. patent discloses the technique of comparing a characteristic of the obtained waveform with a corresponding characteristic of the reference waveform. The characteristic may be the amplitude of at least one of a (positive) pressure pulse and a vacuum (negative pressure) pulse contained in each pressure waveform. In addition, the U.S. patent discloses the technique of judging that an assembled engine has a fault if the pressure in the exhaust-valve side space of the engine (hereinafter, referred to as the “exhaust pressure”) does not exceed a reference value at a predetermined angular phase of a crank shaft of the engine (hereinafter, referred to as the “crank-shaft (CS) angle”) where the exhaust pressure would exceed the reference value if the engine were normal. That is, the engine testing method disclosed in the U.S. patent consists in comparing a measured characteristic value of exhaust or intake pressure of an assembled engine, such as maximal or minimal value or a value corresponding to a particular CS angle, with a reference value obtained from a normal engine.
The U.S. patent teaches finding a fault with an assembled engine based on a pressure waveform obtained from either one of the exhaust-valve or intake-valve side space of the engine. However, it fails to teach finding a fault based on respective pressure waveforms obtained from the exhaust-valve and intake-valve side spaces of the engine. In addition, if the disclosed method finds a fault, it ends. Therefore, if an assembled engine has different sorts of faults, the method cannot find those faults.
DISCLOSURE OF INVENTION
It is therefore an object of the present invention to provide an assembled engine testing method which is different from that disclosed in the above-identified U.S. patent.
According to a first aspect of the present invention, there is provided a method of testing an assembled internal combustion engine having an intake valve and an exhaust valve, being characterized by rotating the assembled engine, measuring a timing of occurrence of at least one predetermined condition of a pressure in at least one of an external intake-valve side space which communicates with the intake valve and an external exhaust-valve side space which communicates with the exhaust valve, and judging, based on the measured timing, whether there is at least one fault with the assembling of the engine.
In the testing method in accordance with the first aspect of the invention, the timing of occurrence of the at least one predetermined condition of the pressure in the intake-valve side space or the external exhaust-valve side space (hereinafter, referred to as “the intake pressure” or the “exhaust pressure”) changes depending upon the changing pressure in a cylinder (hereinafter, referred to as the “cylinder pressure”) in which a piston reciprocates linearly and the opening and closing timings of the intake and exhaust valves. The cylinder pressure increases as the piston moves up toward its top dead position, and decreases as the piston moves down toward its bottom dead position. In the reciprocating engine, after the intake and exhaust valves close, first, the exhaust valve starts opening and subsequently the intake valve starts opening. After the exhaust valve closes, the intake valve closes. During each cycle, if, e.g., the timing of commencement of opening of the intake valve is earlier (i.e., corresponds to a smaller CS angle) than a reference timing obtained from a normal engine, the exhaust pressure takes a maximal value smaller than a reference value obtained from the normal engine and takes a less time to reach the maximal value. To the contrary, if the timing of commencement of opening of the intake valve is later (i.e., corresponds to a larger CS angle) than the reference timing obtained from the normal engine, the exhaust pressure takes a maximal value greater than the reference value and takes a more time to reach the maximal value. Therefore, if, e.g., the timing when the exhaust pressure takes a maximal value is known, the relationship between the opening and closing timings of the intake valve and the CS angle is known. Thus, it can be judged that the assembled engine has the assembling fault of an incorrect phase difference between a crank shaft and a cam shaft. In addition, if, e.g., the opening and closing timings of the exhaust valve change relative to the CS angle, the change influences the intake pressure. Thus, the fault of incorrect phase difference between the crank and cam shafts can be identified based on the timing of occurrence of at least one predetermined condition of the intake pressure. In this way, it is possible to judge whether there is at least one fault with an assembled engine, based on the timing of occurrence of one or more predetermined conditions of the intake pressure and/or the exhaust pressure, without having to take the engine apart. The present testing method does not exclude finding an assembling fault by taking into account an intake or exhaust pressure value corresponding to the predetermined condition. For example, an exhaust pressure value at the timing when the exhaust valve starts opening, a maximal value of the exhaust pressure, etc. may be taken into account. The assembled engine may be rotated in a “hot” state, i.e., by firing of fuel therein, or in a “cool” state, i.e., by being connected to a separate rotating device and compulsorily rotated by the device. Generally, the “cool” test is easier than the “hot” test. In the hot test, it is cumbersome to supply fuel to the engine and treat the exhaust gas emitted therefrom. In addition, in the “hot” test, the pressure signals obtained from the intake-side and exhaust-side spaces contain more noise. The “cool” test is free from those problems, and accordingly can be carried out more easily.
According to a preferred feature of the first aspect of the invention, the judging step comprises comparing the measured timing with a reference timing and judging, based on the comparison result, whether there is at least one fault with the assembling of the engine. The reference timing may be a timing which is actually measured from a normal engine having no assembling fault, or may be a timing which is prescribed by a designer. An incorrect phase of a crank shaft may be caused by an incorrect relative phase between the crank shaft and a crank pulley due to inappropriate attachment of the pulley to the shaft, an incorrect relative phase between the crank pulley and a timing belt or chain due to inappropriate engagement thereof, etc. An incorrect phase of a cam shaft may be caused by an incorrect relative phase between the cam shaft and a cam pulley due to inappropriate attachment of the cam pulley to the cam shaft, an incorrect relative phase between the cam pulley and a timing belt or chain due to inappropriate engagement thereof, etc. As will be described later on the preferred embodiments, the incorrect phase of the cam shaft may also be caused by an incorrect relative phase between a drive gear attached to one of an inta

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