Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – With indicator or control of power plant
Reexamination Certificate
1999-07-06
2001-02-20
Dolinar, Andrew M. (Department: 3747)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
With indicator or control of power plant
C060S276000, C073S001070
Reexamination Certificate
active
06192310
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to internal combustion engines of the fuel-injection type equipped with a catalytic exhaust converter preceded by a sensor and, more particularly in such engines, a device and a process for diagnosis of the condition of the sensor disposed upstream from the catalytic converter.
2. Discussion of the Background
It is known how to use systems for modifying the quantity of fuel injected into an engine as a function of the exhaust-gas composition and, more particularly, of the oxygen content of these gases. To this end, the oxygen content is measured by means of a nonlinear sensor known as the “lambda” sensor or EGO sensor, where EGO is an English-language acronym for “Exhaust Gas Oxygen”. Such a sensor is disposed upstream from the catalytic exhaust converter, and the signal delivered by this sensor is used to modify the quantity of fuel injected into the engine cylinders via a first feedback loop. For this reason, the sensor is also known as a richness-regulating sensor.
It is clear that poor condition of this sensor leads to poor operation of the engine and of the catalytic converter, in turn leading to pollutant emissions at abnormally high levels. It is therefore important to determine the condition of this sensor at all times in order to diagnose poor operation thereof when its condition has deteriorated beyond certain limits. The present solutions for diagnosis of the condition of the upstream sensor comprise analyzing the behavior of the sensor in response to richness excitations in open loop or closed loop and monitoring the following parameters:
the minimum voltage delivered by the sensor: if too high, a fault is indicated;
the maximum voltage delivered by the sensor: if too low, a fault is indicated;
the lean-to-rich transition time; if too long, a fault is indicated;
the rich-to-lean transition time; if too long, a fault is indicated;
the period of the signal delivered by the sensor in closed loop: if too long, a fault is indicated.
The diagnosis then comprises declaring failure of the sensor if one or more faults are detected.
Such a diagnostic process is based on analysis of the sensor behavior in order co deduce therefrom a sensor condition on the basis of assumed degradation mechanisms. For example, as a sensor ages, its dynamic voltage range is reduced and/or its transition times become longer The disadvantage of such a diagnostic process is that a perfect correlation does not exist between these measurements and the emissions of pollutants.
In addition, calibration of fault detection thresholds proves to be very tricky and necessitates:
perfect knowledge of the mechanisms of aging of the sensors,
numerous tests to establish a relationship between the measured degradations of parameters and their effects on pollutant emissions.
In addition, it is not possible in all cases to guarantee that the diagnosis is reliable. For example, a sensor with reduced dynamic voltage range may prove to be good with regard to pollutant emission if only that characteristic is affected.
SUMMARY OF THE INVENTION
One object of the present invention is therefore to provide, for diagnosis of the condition of a sensor disposed upstream from a catalytic converter associated with an internal combustion engine of the fuel-injection type, a device and a process which do not exhibit the aforesaid disadvantages of the devices and processes of the prior art.
Another object of the present invention is also to provide, for diagnosis of the condition of an upstream sensor, a device and a process which does not depend on measurements of intrinsic characteristics of the sensor. The process of the invention is based on monitoring of characteristics of the richness feedback loop which have an influence on pollutant emission, or in other words the mean period and mean richness of the feedback loop. In this way, the condition of the upstream sensor is evaluated on the basis of effects that it produces on the richness feedback loop, or in other words on the emissions of pollutants, and not on the basis of its intrinsic characteristics.
The effects of the condition of the upstream sensor are capable of causing pollutant emissions by exceeding the limits of the “window” of good operation of the catalytic converter, this exceeding being due to drift of the mean operating richness and/or to excessively long mean period of the richness loop.
To detect drift of the mean operating richness, the invention proposes to provide a second nonlinear sensor disposed downstream from the catalytic converter and constituting an integral part of a second feedback loop, by virtue of which the output voltage V
downstream
of the second sensor, called downstream sensor hereinafter, is slaved to a setpoint voltage VC
downstream
corresponding to the center of the window of good operation of the catalytic converter. The signal delivered by this loop is used to modify the signal of the first feedback loop containing the upstream sensor.
Such a system of richness slaving with double control loop is described in the patent application filed today by the Applicant and entitled: “SYSTEM AND PROCESS WITH DOUBLE CONTROL LOOP FOR INTERNAL COMBUSTION ENGINE”. The invention relates to a device for diagnosis of the condition of a nonlinear sensor disposed upstream from a catalytic converter associated with an internal combustion engine of the fuel-injection type controlled by an electronic computer, the said engine containing a first control loop, including the said nonlinear sensor, to deliver to the computer a first signal KCL for correction of the quantity of fuel injected, and a second control loop, including a second nonlinear sensor disposed downstream from the said catalytic converter, to deliver a second signal KRICH for correction of the quantity of fuel injected, the said diagnostic device being characterized in that it comprises:
a filter circuit to which there is applied the second correction signal KRICH in order to deliver a filtered signal KRICH
F
,
a measuring circuit to which there is applied the output signal V
upstream
of the upstream sensor in order to determine the mean value T
m
of the period of correction of the first control loop, and
a logic circuit to determine, as a function of the values of the filtered signal KRICH
F
and of the mean period T
m
, whether the condition DIAG of the upstream sensor is good or defective.
In one embodiment of the invention, the logic circuit determines that the upstream sensor is defective if the filtered signal is larger than a maximum value or smaller than a minimum value or else if the mean period is longer than a maximum value.
In another embodiment of the invention, the maximum and minimum values of the filtered signal KRICH
F
are determined by calibration as a function of the value of the mean period and are stored in a memory. This memory is addressed by the value of the mean period in order to deliver the maximum and minimum values, with which the value of the filtered signal is compared.
The invention also relates to a process which comprises the following stages:
filtering of the second correction signal KRICH to obtain a filtered signal KRICH
F
,
calculation of the mean value T
m
of the period of the output signal V
upstream
of the upstream sensor,
comparison of the said filtered signal KRICH
F
with two values, the maximum KRICH
max
and the minimum KRICH
min
, to determine whether the condition DIAG of the said upstream sensor is correct or defective, according to whether the filtered signal KRICH
F
is respectively within the limits defined by the maximum and minimum values or outside the said limits for the value of the mean period T
m
.
REFERENCES:
patent: 5341642 (1994-08-01), Kurihara et al.
patent: 5399961 (1995-03-01), Wild et al.
patent: 5656765 (1997-08-01), Gray
Afonso Vasco
Marcheguet Eric
Ratinet Francois
Dolinar Andrew M.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Renault
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