Measuring and testing – Vehicle chassis – Steering
Patent
1994-10-07
1996-04-09
Chilcot, Richard
Measuring and testing
Vehicle chassis
Steering
73116, 36443107, G01M 1500, F02D 4114
Patent
active
055050794
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a process for detecting combustion irregularities in an internal combustion engine in order to make a combustion diagnosis, particularly at medium and high speed. It extends to a device for implementing said process and to injection engine control systems equipped with such devices.
Combustion irregularities in an internal combustion engine (misfires and partial combustion) are interesting to diagnose because they are indicative of various disorders liable to affect either the preparation of the air/fuel mixture, or the ignition means, or a mechanical component (tightness of a valve). Moreover, these combustion defects increase pollutant emissions and can lead to external combustion causing damage to catalytic exhaust systems.
The following vocabulary is used below: which precedes the expansion of the gases, corresponding to the minimum distance between the piston and the top of the cylinder head, gases occurs after ignition, this phase extending at medium and high speeds from ignition to about half of expansion,
Partial combustion in a given cycle causes a variation of the drive torque in an engine and hence a variation in the engine speed in comparison with the average speed considered over many cycles. Today, it is known how to detect these speed variations, on the one hand, at low engine speed (below 3000 rpm), irrespective of the load applied, and, on the other, at medium speed under high load. For example, the publication by Gunther Plapp et al, `Methods of on-board misfire detection, SAE 900232, 1990`, describes a process in which the average engine speed is compared during successive combustion phases in order to detect significant variations. However, at high speed or under low load, these variations in average speed have relatively low values and are impossible to detect. Furthermore, irrespective of the speed, these relative variations are not necessarily indicative of a combustion irregularity, and may be confused with variations in the engine speed. To make a reliable diagnosis, it is accordingly necessary to equip the engine with an additional displacement transducer (French Patent No. 91.12743) or with an accelerometer, to invalidate the fault detection in the transient phases. Another publication, by W. B. Ribbens and C. Rizzoni, `Applications of precise crankshaft position measurements for engine testing, control and diagnosis, SAE 890885, 1989`, describes a process in which matrix algebra calculations are carried out on a set of instantaneous speed measurements taken during each engine cycle, in order to determine the absolute value of the drive torque for each cylinder and thus to determine abnormal variations in said torque. However, these calculations are highly complex and demand powerful computation resources, which cannot conceivably be mounted onboard an automotive vehicle. Moreover, according to this publication, it appears that the process is only usable at low speed (less than 3500 rpm).
SUMMARY OF THE INVENTION
The present invention proposes to enable a combustion diagnosis irrespective of the engine speed and the load applied to the engine. It aims in particular to detect combustion irregularities at medium and high speed, for which the process of the invention is ideally applicable. For low speeds, the process of the invention could possibly be applied, although it is highly sensitive. It can also be supplanted by a process of a known type, particularly a simplified torque estimation process.
The detection process concerned by the invention is of the type consisting in measuring the time intervals between predetermined angular positions of a rotating part integral with the crankshaft, in calculating from these intervals a parameter representative of a variation in speed, and in comparing this parameter with a fault threshold. The process according to this invention is characterized in that: defined, centered on an angular position, called the reference position, corresponding to a predetermined moment of the combustion ph
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Chilcot Richard
Dombroske George
Siemens Automotive S.A.
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