Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2000-08-02
2001-09-25
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C204S424000, C205S784500
Reexamination Certificate
active
06293093
ABSTRACT:
TECHNICAL FIELD
This invention relates to on-board diagnostics and, more particularly, to an on-board diagnostic method and system on motor vehicles that can diagnose the efficiency of a catalyst having negligible oxygen storage capacity.
BACKGROUND ART
Today's engineers strive toward the goal of perfecting the efficiency of automotive engines by achieving lower emissions, better fuel efficiency, and improved performance. Government regulations require on-board diagnostics computers (On-Board Diagnostics or OBD) to further these goals. OBDs have been employed in motor vehicles since the late 1980s. The OBD system has been vastly improved to On-Board Diagnostics Level
2
(“OBD II”). OBD II not only monitors the partial failure of components but the deterioration of components as well.
With respect to the goal of lowering emissions, feedback control has been implemented with the engine/emission system to ensure that the optimum mixture of the gases is delivered to the catalytic converter. In general, an emissions system includes a three-way catalyst in the exhaust path to target particular components of the exhaust gases for the purpose of converting the targeted components to more environmentally friendly gases. For example, the three way catalysts convert HC, CO and NO, from the exhaust gas to H
2
O, CO
2
and N
2
.
Oxygen sensors have proven helpful in providing feedback control in emissions systems. In
FIG. 1
a
, a typical oxygen sensor of the prior art and its conventional implementation in an emissions system are illustrated. The oxygen sensor
12
includes an oxygen permeable material and is generally mounted onto the exhaust system
14
near the exhaust manifold (not shown). The oxygen sensor
12
is used to maintain a stoichiometric air-fuel ratio by monitoring the oxygen content of the exhaust gas
16
. The sensor
12
compares the oxygen level in the outside air
18
to the oxygen level in the exhaust gases
16
. The sensor may further include a platinum tip
20
which is in direct contact with the exhaust gases
16
. The platinum in the tip
20
equilibrates the gases and develops a voltage signal which is sent to a powertrain control module (not shown) for purposes of providing feedback to the air-fuel delivery system.
With reference to
FIG. 1
b,
a prior art OBDII monitoring system
13
is illustrated. This prior art system monitors the oxygen storage ability of the catalyst. This indirect system and method of the prior art infers the deterioration in the hydrocarbon efficiency from changes in oxygen storage in the catalyst over time. As shown in
FIG. 1
b,
a first oxygen sensor
22
is positioned at the upstream end
23
of a catalyst
24
and a second oxygen sensor
26
is positioned at the downstream end
28
of the catalyst. The first oxygen sensor
22
and the second oxygen sensor
26
measure the change in oxygen storage across the catalyst. The catalyst
24
may include oxygen storage material such as cerium. The first oxygen sensor
22
and the second oxygen sensor
26
collect data which track the oscillation between a rich condition and a lean condition of the exhaust gas. The collected data may be transmitted to a corresponding first signal processing means
28
and a second signal processing means
30
which are in communication with a means
32
for determining the switch ratio of the outlet sensor
26
to the inlet sensor
22
. In determining the switch ratio, the system compares the rich-lean oscillation of the exhaust gas at the upstream side to the rich-lean oscillation at the downstream side of the catalyst.
However, as described above, this system and method do not provide a direct means of measuring oxidation efficiency given that the two sensors infer the oxidation efficiency based upon the catalyst oxygen storage capacity determined from a measurable quantity such as a voltage difference or a switch ratio. This indirect method assumes that the hydrocarbon efficiency of the system is adverse where the oxygen storage capacity of the catalyst is also adverse. However, the correlation between these two factors is approximately 0.6 to 0.7 at best. As known by those skilled in the art, the oxygen storage capacity may greatly vary despite very little change in the hydrocarbon efficiency.
Under a new emission-control system, a conditioning catalyst may be implemented for purposes of preventing “lean shift” in the control air-fuel ratio. “Lean shift” is a problem which occurs when the sensor incorrectly indicates that the hydrogen-laden exhaust gas is too rich and causes the engine control system to provide a leaner air fuel mixture. Conditioning catalysts help ensure accurate air-fuel control where very low emissions levels are mandated (e.g., California's Super Ultra Low Emission Vehicle (SULEV) standards). In this type of system, the exhaust gas stream is conditioned by a catalyst before the exhaust gas stream gets to the oxygen sensor by oxidizing the hydrogen and some of the hydrocarbons so that the sensor may more accurately measure the true air-fuel ratio of the exhaust. However, the catalyst in this system does not contain oxygen storage material given that the sensor must detect the oscillation between a rich condition and a lean condition at the downstream end of the conditioning catalyst to provide feedback control to the engine.
With negligible oxygen storage capacity in the catalyst, the conventional OBDII method of monitoring the deterioration of a catalyst (with dual sensors as described above) is no longer useful given that oscillation between a rich condition and a lean condition at the upstream side of the catalyst will be the same as the oscillation at the downstream side of the catalyst. Accordingly, a need has developed for a system and direct method that accurately diagnose the efficiency of a conditioning catalyst having negligible oxygen storage capacity.
DISCLOSURE OF THE INVENTION
It is a principal object of the present invention to provide a system that precisely and directly diagnoses the oxidation efficiency of a catalyst having negligible oxygen storage capacity.
It is another object of the present invention to provide a method of precisely and directly monitoring the efficiency of a catalyst having negligible oxygen storage capacity.
It is still another object of the present invention to provide a system that precisely and directly diagnoses the oxidation efficiency of a catalyst.
It is yet another object of the present invention to provide a method of precisely and directly monitoring the efficiency of a catalyst.
It is yet another object of the present invention to provide a new method of implementing an oxygen sensor in a vehicle.
It is still another object of the present invention to provide a system which implements a differential oxygen sensor that simultaneously compares oxygen levels at the upstream end and the downstream end of a catalyst.
In carrying out the above objects and other objects and features, a system for directly monitoring the efficiency of a catalyst having negligible oxygen storage capacity is provided. The monitoring system includes an oxygen sensor mounted in the vehicle exhaust system near a first end of a catalyst and an exhaust gas catalyst bypass. The oxygen sensor includes a first side and a second side. The first side detects the oxygen levels in the exhaust gases at the first end of the catalyst. The exhaust gas catalyst bypass transfers a small amount of exhaust gas from the second end of the catalyst to the second side of the oxygen sensor. The oxygen sensor performs an instantaneous comparison of the oxygen levels between the exhaust gases at the first end of the catalyst and the exhaust gases at the second end of the catalyst thereby producing a voltage signal. The voltage signal generated by the sensor is proportional to the difference in oxygen levels between the gases at the first end and the second end of the oxygen sensor. The voltage signal may then be transmitted to the vehicle's powertrain control module to provide feedback to the engine.
A method is also p
Boone William P.
Goralski Christian Thomas
Soltis Richard E.
Bejin Gigette M
Denion Thomas
Ford Global Technologies, Inc
Melotik Lorraine S.
Tran Diem
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