Process for determining and evaluating the combustion pressure o

Details Process for determining and evaluating the combustion pressure o Process for determining and evaluating the combustion pressure o

1990-04-27

1991-06-04

Myracle, Jerry W.

Measuring and testing

Vehicle drive train

Rear end

G01M 1500

Patent

active

050203606

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates generally to a process for determining and evaluating the combustion pressure, and, more particularly, to a process for measuring the incremental pressure caused by combustion in such a way that the ignition angle can be accurately adjusted even if the pressure sensors are not particularly accurate. [as generically defined by the preamble to claim 1.]
Processes for determining the combustion chamber are known in which very sturdy, accurate sensors are used. Particularly if the combustion pressure is to be used for controlling and/or monitoring engine functions, the requirements for accuracy of the measured pressure values are very stringent. It is also essential that the measurement sensitivity and accuracy be constant over a wide temperature range. The known processes therefore have the disadvantage that very expensive sensors must be used, if the measure pressure values are to be usable for controlling and/or monitoring the engine.
From Patent Abstracts of Japan, Vol. 9, No. 320 (p-413) (2043), Dec. 14, 1985, JP-A 60 147 631, an apparatus for determining the combustion pressure is known. To this end, on the one hand the pressure in the combustion chamber is detected by means of a pressure sensor; on the other, the compression pressure at specific crankshaft angle positions is calculated continuously. By subtracting the compression pressure from the measured combustion chamber pressure, the combustion pressure can then be determined, which is finally used for determining the instant of ignition. This apparatus thus requires computer-aided determination of the compression pressure and makes use of variables that are not stable for long periods of time, because over the life of an internal combustion engine, sealing problems repeatedly occur at inlet and outlet valves, and moreover the piston rings are subject to wear over the life of the engine.


ADVANTAGES OF THE INVENTION

The process for determining the combustion pressure of an internal combustion engine according to the present invention has the advantage over the prior art that even simple, relatively inaccurate pressure pickups can be used, in which the measurement sensitivity varies during operation. This is attained by providing that the combustion pressure is found by determining the compression pressure prevailing in the combustion chamber of a cylinder, that is, the pressure that prevails in the combustion chamber without the influence of an ignition event. These pressure values are stored in memory and are subtracted from the combustion chamber pressure instantaneously prevailing during engine operation, to produce the instantaneous combustion pressure values. All the pressure values are determined as a function of the crankshaft angle .alpha.. Thus the course of the combustion pressure is calculated from the difference between the instantaneous combustion chamber pressure p(.alpha.) and the compression pressure p.sub.k (.alpha.). The combustion pressure is therefore also called the differential combustion pressure.
In a particularly preferred process, the compression pressure is measured as a function of the crankshaft angle .alpha. up to a predetermined crankshaft angle and stored in memory. The resultant pressure course is reflected at an axis extending through the predetermined crankshaft angle, and the values stored in memory before the predetermined crankshaft angle is attained are recalled as soon as this crankshaft angle is exceeded. This value of the compression pressure, extending along a symmetrical curve, is used to calculate the value of the combustion pressure. In other words, the compression pressure values obtained in this calculation are subtracted from the instantaneous combustion pressure in order to determine the combustion pressure value.
Preferably, this process can be used to regulate the ignition angle in an internal combustion engine. To this end, the maximum value of the combustion pressure over the crankshaft angle is determined. By shifting the ignition ang

REFERENCES:
patent: 4403505 (1983-09-01), Hattori et al.
patent: 4633707 (1987-01-01), Haddox et al.
patent: 4936137 (1990-06-01), Iwata et al.
Yamamoto/Nissan, Patent Abstracts of Japan, vol. 9, No. 320 (P-413)[2043], Dec. 14, 1985.
Nakatomi/Toyota, Patent Abstracts of Japan, vol. 10, No. 237 (P-487)[2293], Aug. 15, 1986.

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