Method and system for monitoring an O2 sensor of a vehicle

Details Method and system for monitoring an O2 sensor of a vehicle Method and system for monitoring an O2 sensor of a vehicle

2001-05-11

2002-07-02

Wu, Daniel J. (Department: 2632)

Communications: electrical

Land vehicle alarms or indicators

C340S439000, C060S274000, C123S486000

Reexamination Certificate

active

06414590

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority of Korea patent Application No. 2000-25356, filed on May 12, 2000.
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a method for monitoring an O
2
sensor of a vehicle and a system thereof, and more particularly, to a method for detecting a malfunction of a front O
2
sensor of a vehicle and warning of the malfunction, and a system thereof.
(b) Description of the Related Art
Exhaust gas of a vehicle, being understood as a main cause of atmospheric pollution, is under strict regulation along with smoke and noxious gases from factories, and in some leading nations, only vehicles that satisfy regulations are permitted to be sold.
Accordingly, recently produced vehicles are provided with a catalytic converter in their exhaust systems to accomplish more complete combustion. Furthermore, an engine is electronically controlled to reduce noxious exhaust gas and to improve mileage at the same time, an example of which is that fuel supply to the engine is controlled by an electronic control unit (written as ECU hereinafter) to maintain an appropriate Air/Fuel ratio based on signals from an oxygen sensor (written as O
2
sensor hereinafter) disposed in front of the catalytic converter in the exhaust system.
Methods for detecting malfunctions of the front O
2
sensor and methods for compensating values of variables used by the ECU to control fuel supply are investigated because if the front O
2
sensor malfunctions, an appropriate Air/Fuel ratio cannot be maintained.
As an example of the methods, the exhaust system includes another O
2
sensor (written as rear O
2
sensor hereinafter) at the rear of the catalytic converter, and the exemplary method includes steps of:
measuring lean/rich durations of the rear O
2
sensor at a predetermined driving condition, the condition being dependent on engine revolution speed and load;
calculating reference durations from a predetermined table recorded in the ECU;
accumulating the measured durations and the calculated reference durations respectively for a predetermined number of occurrences; and
determining the front O
2
sensor to be malfunctioning if the accumulated measured durations are greater than the accumulated reference durations.
FIG. 3
is a flowchart showing an O
2
sensor monitoring method according to the prior art.
Referring to
FIG. 3
, an ECU determines whether a monitoring condition is satisfied at step S
300
. If the monitoring condition is satisfied, the ECU measures lean duration L and/or rich duration R of a front O
2
sensor and calculates lean reference duration TL and/or rich reference duration TR on the basis of a predetermined reference table at step S
310
.
Each of the durations L and R and the reference durations TL and TR are accumulated at step S
320
and the number of accumulations is counted at step S
330
. If the count is greater than a predetermined number at step S
340
, the ECU compares the accumulated duration L with the accumulated reference duration TL and/or the accumulated duration R with the accumulated reference duration TR at step S
350
. If one of the accumulated durations is greater than the corresponding accumulated reference duration, the ECU determines at step S
360
that a front O
2
sensor is malfunctioning.
The lean reference duration TL and the rich reference duration TR are calculated from predetermined functions of the engine state, of which independent variables to determine the engine state are engine speed and load, for example.
FIG. 4
is a set of graphs explaining a change of a fuel supply pattern according to a state of exhaust gas, especially when exhaust gas is determined to be lean.
The algorithm to change the fuel supply pattern is variously called P-Jump Delay or PTV/ATV, etc., depending on the manufacturer of the ECU, and hereinafter it is denoted as P-Jump Delay.
Because the Air/Fuel ratio of an engine is basically controlled on the basis of the signal from the front O
2
sensor, a theoretical Air/Fuel ratio is not maintained in the case that the front O
2
sensor malfunctions, for example through thermal breakdown. Therefore, a basic concept of the P-Jump Delay is that the ECU compensates for the malfunctioning of the front O
2
sensor by feedback signals of a rear O
2
sensor, the rear O
2
sensor detecting the state of exhaust gas after the catalytic converter.
FIG. 4
a
is related to a normal state that a learned parameter (denoted as PJ_AD hereinafter) equals zero.
A dotted line shown in
FIG. 4
a
indicates a target amount of fuel supply. In a normal state, the amount of fuel supply fluctuates around the dotted line as time passes, so that an average fuel supply over a period coincides with the dotted line. Therefore the target amount of fuel supply is achieved by injectors injecting fuel into an engine according to the fuel supply pattern of
FIG. 4
a.
An area above the dotted line, the area corresponding to an oversupply of fuel, is described as a positive area, and an area below the dotted line, the area corresponding to an insufficient supply of fuel, is described as a negative area.
A time division, in which fuel is injected constantly at a predetermined amount, is defined in each of the positive and negative areas. The time divisions are defined as delay time DLY_POS and DLY_NEG for the positive and negative areas respectively.
The delay times DLY_POS and DLY_NEG in a normal state are determined as base values POS and NEG respectively, the base values POS and NEG being predetermined values based on functions of the engine state, the functions having independent variables of, for example, engine speed and load.
Furthermore, a learning algorithm for compensating malfunctioning of the front O
2
sensor is provided because if the front O
2
sensor malfunctions, an appropriate Air/Fuel ratio is not maintained so that exhaust gas becomes rich or lean.
As a learning algorithm pointed out above, a learned parameter PJ_AD is learned on the basis of the history of detecting lean and rich states of exhaust gas from the rear O
2
sensor, and the fuel supply pattern is modified on the basis of the learned parameter PJ_AD.
The fuel supply pattern is modified by modifying the delay time DLY_POS and/or DLY_NEG so that the amount of fuel-supplied is increased or decreased.
Normally, if the front O
2
sensor malfunctions, the Air/Fuel ratio, basically controlled by the front O
2
sensor, is controlled so that lean exhaust gas results.
To compensate the Air/Fuel ratio for the case exhaust gas is lean, the fuel supply pattern can be modified from the graph shown in
FIG. 4
a
so that the delay time DLY_POS of the positive area is increased or the delay time DLY_NEG of the negative area is decreased by a value of the learned parameter PJ_AD.
Of the two ways of modifying, the latter is preferable because increasing the delay time DLY_POS causes a period of the fuel supply pattern to be unnecessarily increased, accordingly reducing frequency of control. Therefore, the fuel supply pattern is principally changed to one as shown in
FIG. 4
b
if the exhaust gas is determined to be lean.
FIG. 4
c
is a graph of a fuel supply pattern relating to a state in which a learned parameter PJ_AD is greater than the base delay time NEG in the negative area.
If the learned parameter PJ_AD is greater than the base delay time NEG, insufficient fuel is supplied even if the delay time DLY_NEG is set to be 0. In such a case, as shown in
FIG. 4
c
, the delay time DLY_POS must be increased by the value of the learned parameter PJ_AD minus the base time NEG, and the delay time DLY_NEG is set to be 0.
A method for changing the fuel supply pattern from
FIGS. 4
a
to
FIG. 4
b
or
FIG. 4
c
is described hereinafter in further detail, referring to FIG.
5
.
The ECU determines whether a signal from an O
2
sensor satisfies a P-Jump Delay condition at step S
400
. The P-Jump Delay condition is preferably set to be such that the signal from the O
2
sensor is changed from rich to lean.
If the signal from the

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