Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
1997-04-03
2001-02-13
Denion, Thomas E. (Department: 3745)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C123S463000, C123S436000, C073S117020
Reexamination Certificate
active
06185928
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method and to a device for detecting misfires in an internal combustion engine of the so-called controlled-ignition, or alternatively spark-ignition, type for a motor vehicle, and in particular for a vehicle in which the engine is, on the one hand, associated with a catalytic exhaust system, called a catalytic converter in the rest of the description and, on the other hand, equipped with a fuel-injection type fuel supply system, preferably of the so-called “multi-point” type, and such that the engine injection and preferably also ignition are controlled by an electronic control and management system known as an engine management system.
BACKGROUND OF THE INVENTION
The detection of misfires in all combustion engines has become a major problem, owing to the most recent or pending legislation regarding environmental protection with which these engines, associated with catalytic converters, have to comply.
Now it is known that the occurrence of misfires may lead to deterioration of the catalytic converter, or even destruction thereof in the event of successive misfires on account of quantities, which may be excessive, of unburnt fuel mixtures resulting from these misfires reaching the catalytic converter. This deterioration or destruction of the catalytic converter leads to uncontrolled emanation of pollutants in the exhaust gases, and therefore to the vehicle no longer complying with legislation.
The overall problem upon which the invention is based is that of proposing a method and a device for detecting misfires, making it possible to alert the driver in the event of a risk of degrading the catalytic converter through misfiring and/or of excessively increasing a polluting emission.
From WO-A-94 16209, there is already known a method for detecting misfires in a controlled-ignition internal combustion engine, comprising the steps consisting in:
a) formulating, for each combustion/expansion phase in each cylinder of the engine, a signal representative of the value of the gas torque Cg produced in the corresponding cylinder by the corresponding combustion,
b) measuring the rotational speed N of the engine and formulating a signal representative of this speed for at least the inlet phase which preceded the combustion/expansion phase in the corresponding cylinder,
c) measuring a parameter representative of the unitary filling of the corresponding cylinder and formulating a signal representative of this unitary filling for at least the inlet phase which preceded the combustion/expansion phase during the same engine cycle in the corresponding cylinder,
d) entering the signals representative of speed N and of unitary filling as addresses in a reference theoretical gas torque map, and deducing therefrom a signal representative of a reference torque Cref.
This known method consists additionally in:
e) assigning to the reference torque Cref a multiplicative weighting coefficient K associated with the corresponding cylinder and/or with whether the engine is running in stabilized or transient mode, and in deducing therefrom a signal representative of an expected theoretical torque Cpr, and
f) comparing the signals of the measured gas torque Cg and of the expected theoretical torque Cpr and deeming there to be a misfire when the ratio of the gas torque Cg to the expected theoretical torque Cpr drops below a given ratio threshold.
SUMMARY OF THE INVENTION
The object of the invention is to improve the detection and the ability to discern misfires of the aforementioned known method, particularly so as to take account of whether the engine is running in transient or in stabilized mode.
To this end, the method according to the invention, which comprises the steps a) to d) of the known method given hereinabove, is characterized in that it additionally comprises the steps consisting in:
e) assigning to at least one of the signals representative of the value of the gas torque Cg and of the reference torque Cref a respective multiplicative correction factor KM associated with the corresponding cylinder 80 as to obtain signals which are proportional to the value of the gas torque Cg and to the reference torque Cref, and, in addition, assigning to at least one of the proportional signals, an additive correction factor KA when the engine is running in transient mode, and deducing therefrom a signal representative of an expected theoretical torque Cpr on the basis of the signal which is proportional to the reference torque-Cref, and a signal representative of a calculated gas torque Cgc on the basis of the signal which is proportional to the value of the gas torque Cg,
f) calculating the ratio of the signal representative of the expected theoretical torque Cpr to the signal representative of the calculated gas torque Cgc, and deeming there to be a misfire when this ratio is higher than a given ratio threshold.
This ratio threshold may be constant, for example equal to 2, but it is advantageously taken from a map established as a function of the rotational speed N of the engine and of a parameter representative of the unitary filling of the cylinders of the engine.
This parameter representative of the unitary filling of the cylinders may be the flow rate of air let into the engine or the degree of openness of a rotary choke or butterfly valve regulating the air supply to the engine, but advantageously this parameter is the pressure Pim at the air inlet manifold for the corresponding cylinder.
Although the signal representative of the value of the gas torque Cg may be the only one to have assigned to it the multiplicative correction factor KM and, in transient mode, the additive correction factor KA, in which event the expected theoretical torque Cpr is equal to the reference torque Cref and Cref/Cgc is calculated so as to compare it to the aforementioned threshold, advantageously the signal representative of the reference torque Cref is the only one of the representative signals to have assigned to it the multiplicative correction factor and, when the engine is running in transient mode, the corresponding proportional signal is also the only one to have assigned to it the additive correction factor. In such an event, Cg=Cgc, and Cpr/Cg is compared with the aforementioned threshold.
It will be understood that the idea upon which the invention is based consists in anticipating or estimating, for each combustion/expansion phase, an expected theoretical gas torque as a function of the rotational speed of the engine, or speed, of the chosen parameter representative of the unitary filling of the cylinders, and of correction factors, of which a first, multiplicative factor, takes into account the state of each of the cylinders of the engine for the corresponding combustion/expansion phases, while the second, additive factor, is taken into account when the engine is running in a transient mode, and that this expected torque is then advantageously compared with the calculated gas torque for the combustion/expansion phase under consideration in order to deduce, from the value of their ratio, whether or not there has been a misfire during this phase, as a function of the result of the comparison of this ratio with the threshold.
Advantageously too, the signal representative of the calculated gas torque Cgc for each combustion/expansion phase in each cylinder of the engine is formulated on the basis of the signal relating to the angular position of the crankshaft or of the shaft of the engine. This characteristic is advantageous in that it makes it possible to calculate the gas torque on the basis of this angular position signal alone, without it being necessary to provide other means such as pressure sensors taking pressure readings in the combustion chambers.
However, when the signal relating to the angular position of the shaft of the engine is obtained with the aid of a known sensor comprising a target rotating integrally with the crankshaft or with the flywheel, the formulation of the signal representative of the calculated gas torque Cgc is disturbed by t
Genin Christophe
Wallerand Philippe
Denion Thomas E.
Larson & Taylor PLC
Magneti Marelli France
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