Measuring and testing – Simulating operating condition – Marine
Reexamination Certificate
2001-02-27
2003-01-21
McCall, Eric S. (Department: 2855)
Measuring and testing
Simulating operating condition
Marine
Reexamination Certificate
active
06508111
ABSTRACT:
BACKGROUND OF THE INVENTION:
1. Technical Field
The present invention relates to a failure diagnosis apparatus for an exhaust gas recirculation system of an internal combustion engine.
2. Prior Art
An art disclosed in Japanese Patent Application Laid-Open Publication No. HEI 10-115259 (1998) represents a conventional failure diagnosis apparatus of this type for an exhaust gas recirculation system.
FIG. 16
is a block diagram of the functional configuration of a conventional failure diagnosis apparatus for an exhaust gas recirculation system.
Shown in the figure are an EGR valve controlling means
2703
, an internal combustion engine condition parameter detecting means
2702
, an internal combustion engine condition parameter estimating means
2701
, an internal combustion engine condition parameter comparing means
2704
for comparing the detected and estimated internal combustion engine parameters, an EGR flow judging means
2706
for diagnosing an EGR flow on the basis of the above comparison result, and an internal combustion engine condition parameter modifying means
2705
for modifying the internal combustion engine condition parameter estimating means.
When an EGR valve opening is judged greater than a specified value by the EGR controlling means, the actual suction air pressure at that time is detected by the internal combustion engine condition parameter detecting. means
2702
and a suction air pressure under the EGR not working is estimated by the internal combustion engine condition parameter estimating means
2701
.
A difference in outputs between the above two means represents an EGR pressure. If this pressure is higher than the threshold searched from an atmospheric pressure table, the EGR flow is judged normal. If it is lower than the threshold, the EGR flow is judged lower and faulty.
In the above step, in order to improve the accuracy of the internal combustion engine condition parameter estimating means
2701
, the estimated suction air pressure under the EGR not working is adjusted with gains so that the EGR pressure becomes zero under a condition that the EGR valve is almost fully opened.
The above-mentioned failure analysis apparatus for an exhaust gas recirculation system of an internal combustion engine considers that a discrepancy between the measured and estimated fresh air suction pipe pressures is caused by a discrepancy between gains in the fresh air pressure estimating calculation, and accordingly aims to adjust the gains so that the estimated suction pipe pressure under the EGR not working becomes equal to the measured pressure.
However, there are various factors that cause an error in an estimated suction pipe pressure in practice, including dispersion of suction/exhaust temperature, dispersion. of post-exhaust-stroke cylinder residual gas pressure, dispersion of actual throttle valve opening area, and error in air-flow meter, and consequently influence on the estimated pressure is different.
For example, because the post-exhaust-stroke cylinder. residual gas pressure
2801
is nearly proportional to the atmospheric pressure as shown in
FIG. 17
, it remains consistent even if the cylinder suction volumetric flow varies. As a result, an estimated pressure error
2803
caused by this dispersion also remains consistent irrespective of the cylinder suction volumetric flow. Besides, the influence of a measurement error of the air-flow meter appears as an error on an intake air flow dependent portion
2807
of the estimated suction pipe pressure.
For the above reasons, there has been a limitation of accuracy in correcting the estimated pressure simply by adjusting the estimated pressure with gains as in the above-mentioned known art.
There has been another problem that, if the EGR gas temperature is lower than expected like in a case that the exhaust gas recirculation system has not yet been warmed up sufficiently and therefore heat of the EGR gas is absorbed by the exhaust gas recirculation system, the EGR flow may be wrongly judged lower and faulty because the actual pressure of the EGR gas becomes lower even if. the EGR mass flow is normal.
There has been. another problem that, since the purge valve mounted on the suction pipe is operated under a duty control, pulses are caused in the suction pipe pressure by the incoming gas through the valve and the accuracy of diagnosis is badly affected. There remains a further problem that, if purging is stopped during the diagnosis so as to prevent the above, the purge gas discharge increases.
According to the above-mentioned known art, the suction air pressure is sampled at the time when the EGR valve opening area becomes greater than a specified value and the sampled result is judged. Because of this, the diagnosis is commenced as soon as the EGR valve opening area has reached from a fully closed state up to the specified value while the suction pipe has not yet been charged sufficiently with the EGR gas.
The measured suction pipe pressure sampled as above is a pressure at the time when the EGR gas pressure has not yet increased sufficiently. Because of this, the EGR pressure calculated from the measured suction pipe pressure and estimated fresh air pressure results in a smaller value, and consequently there remains a possibility that the EGR flow is wrongly judged lower and faulty.
Since the EGR ratio is generally specified for each operation range, different EGR pressure applies in each operating range. As a result, the normal-state minimum and faulty-state maximum EGR pressures calculated from the difference between the measured suction pipe pressure and the estimated fresh air pressure under the EGR working are also different in each operation range.
Consequently, a threshold for judging the calculated EGR pressure must be specified for each operation range. Because the above-mentioned known art does not consider this point, diagnosis is available only in a limited operation range where a similar threshold applies to the judgment.
Delay of the estimated fresh air pressure is of another problem. Generally, a system configuration in
FIG. 7
is used for estimating a fresh air pressure. The estimated fresh air pressure is calculated from a suction air flow, detected by a suction air flow detecting means
902
for measuring the suction air flow of a suction pipe
206
, and an engine speed. Since the detected suction air. flow contains a suction pulse component, a filtering process is needed to eliminate it.
Since the filtered suction air flow includes a delay as compared to the actual suction air flow, the estimated fresh air pressure
1302
calculated from this air flow is accompanied also with a delay from the actual fresh air pressure
1301
. A response delay pressure between the two is proportional to an increase of the suction air flow per unit time. Because of this, if an acceleration/deceleration condition varies at time
1303
, a response delay also varies accordingly.
As a result, the EGR pressure calculated by deducting the estimated fresh air pressure
1302
from the measured pressure
1307
contains an error
1311
dependent upon the operating condition. This error causes a problem that, even if the estimated fresh air pressure is corrected by an internal combustion engine parameter modifying means
2705
, the estimated value shifts as the operating condition varies.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a failure diagnosis apparatus for an exhaust gas recirculation system which is capable of eliminating the influence of various disturbance factors that vary the suction air pressure, diagnosing a failure of the exhaust gas recirculation system on the basis of the suction air pressure, and preventing wrong diagnosis.
In order to achieve the above objective, a failure diagnosis apparatus for an exhaust gas recirculation system of the present invention has a characteristic feature that the apparatus consists of a fresh air pressure estimating means for calculating an estimated fresh air pressure inside a suction pipe from the operating condition detected of an
Hori Toshio
Matsuno Osamu
Osaki Satoru
Tsuyuki Takeshi
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