Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
2000-01-20
2001-10-16
Denion, Thomas (Department: 3747)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S276000, C060S285000, C123S443000
Reexamination Certificate
active
06301880
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to electronic control of an internal combustion engine having first and second groups of cylinders. In particular, this invention relates to a system and method of controlling the air/fuel ratio in the second group of cylinders based on a feedback signal received from an oxygen exhaust sensor located downstream of the second group of cylinders and a feedback signal from at least one exhaust gas oxygen sensor located downstream of the first group of cylinders.
BACKGROUND
To meet current emission regulations, automotive vehicles must regulate the air/fuel ratio (A/F) supplied to the vehicles' cylinders so as to achieve maximum efficiency of the vehicles' catalysts. For this purpose, it is known to control the air/fuel ratio of internal combustion engines using an exhaust gas oxygen (EGO) sensor positioned in the exhaust stream from the engine. The EGO sensor provides feedback data to an electronic controller that calculates preferred A/F values over time to achieve optimum efficiency of a catalyst in the exhaust system. It is also known to have systems with two EGO sensors in the exhaust stream in an effort to achieve more precise A/F control with respect to the catalyst window. Normally, a pre-catalyst EGO sensor is positioned upstream of the catalyst and a post-catalyst EGO sensor is positioned downstream of the catalyst. Finally, in connection with engines having two groups of cylinders, it is known to have a two-bank exhaust system coupled thereto where each exhaust bank has a catalyst as well as pre-catalyst and post-catalyst EGO sensors. Each of the exhaust banks corresponds to a group of cylinders in the engine. The feedback signals received from the EGO sensors are used to calculate the desired A/F values in their respective group of cylinders at any given time. The controller uses these desired A/F values to control the amount of liquid fuel that is injected into the cylinders by the vehicle's fuel injector. It is a known methodology to use the EGO sensor feedback signals to calculate desired A/F values that collectively, when viewed over time, form A/F waveforms having ramp portions, jumpback portions and hold portions, as shown in FIG.
4
.
In order to build two-bank exhaust systems more economically, it is known to eliminate one of the post-catalyst EGO sensors in a two-bank, four-EGO sensor system. Specifically, it is known to eliminate the post-catalyst EGO sensor in one of the banks and move the post-catalyst EGO sensor from the other bank downstream in the system to where the exhaust gases from the two banks are combined prior to being expelled from the system. This system is known as the so-called Y-pipe system and is shown generally in FIG.
2
. In the Y-pipe system, the single downstream EGO sensor performs the function of monitoring the oxygen content of the post-catalyst exhaust gases for both banks. However, because the exhaust gases from the two banks are combined prior to reaching the downstream EGO sensor, the data provided from the downstream EGO sensor is derived from the mixture of the exhaust gases from the two banks. Thus, because the downstream EGO sensor is unable to distinguish between the oxygen contents of the separate banks, the feedback data provided by the downstream EGO sensor is not specific to either bank. Accordingly, the A/F levels for the individual banks cannot be monitored and controlled as closely, and, as a result, the potential performance of the system is limited.
Therefore, it is desirable to have an improved system and methodology for controlling the A/F levels in each exhaust bank of a two-bank system using only three EGO sensors.
SUMMARY OF THE INVENTION
The present invention is directed toward a new system and methodology for adjusting the A/F level in an internal combustion engine coupled to a two-bank exhaust system using only three EGO sensors. Specifically, the system includes a first and a second exhaust bank with each bank including a catalyst. Each exhaust bank corresponds to a respective group of cylinders in the engine. The first exhaust bank includes a pre-catalyst EGO sensor and a post-catalyst EGO sensor. The second exhaust bank includes only a post-catalyst EGO sensor. The system operates generally by calculating A/F values for the group of cylinders corresponding to the first bank using feedback signals from both its pre-catalyst and its post-catalyst EGO sensors. These calculated A/F values together form an A/F waveform over time. An electronic controller, in cooperation with a fuel injector, uses this A/F waveform to control the A/F levels in the group of cylinders corresponding to the first exhaust bank. The controller also calculates A/F values for the group of cylinders corresponding to the second bank based on feedback signals from the EGO sensors in the first bank and the EGO sensor in the second bank. Specifically, the system uses the A/F waveform calculated for the first bank as the A/F waveform for the second bank, except that a portion of the second bank A/F waveform is modified based on the feedback signal from the second bank's post-catalyst EGO sensor.
In particular, the controller uses well-known methodologies to calculate a desired A/F waveform for the first bank that has ramp portions, jumpback portions and hold portions, as shown in FIG.
4
. Then, the controller uses the feedback signal provided by the second bank's post-catalyst EGO sensor to modify the hold portions of the A/F waveform calculated for the first bank to generate an A/F waveform for the second bank, as shown in FIG.
5
. Thus, the A/F waveform for the second bank has A/F ramp portions and A/F jumpback portions that are identical to the A/F ramp portions and A/F jumpback portions of the first bank. However, the A/F values for the hold portions of the second bank are modified based on the feedback signal provided by the second bank's post-catalyst EGO sensor. This system and methodology provides more responsive A/F values, and, as a result, permits both catalysts to operate more efficiently compared to the known so-called Y-pipe system.
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U.S.P.A. for “Method And System For Compensating For Degraded Pre-Catalyst Oxygen Sensor In A Two-Bank Exhaust System” filed on the same date hereof; Inventors: Booth, et al.; Attorney Docket No. 198-0963 (65080-0005).
U.S.P.A. for “Method And System For Controlling Air/Fuel Level In Two-Bank Exhaust System” filed on the same date hereof; Inventors: Booth, et al.; Attorney Docket No. 199-1619 (65080-0006).
U.S.P.A. for “Method For Controlling Air/Fuel Mixture” filed on the same date hereof; Inventors: Booth, et al.; Attorney Docket No. 199-1803 (65080-0008).
U.S.P.A. for “Diagnostic System For Detecting Catalyst Failure Using Switch Ratio” filed on the same date hereof; Inventors: Booth, et al.; Attorney Docket No. 199-1788 (65080-0009).
U.S.P.A. for “Diagnostic System For Monitoring Catalyst Operation Using Arc Length Ratio” filed on the same date he
Behr Kenneth John
Booth Richard Andrew
Cullen Michael John
Sealy Brent Edward
Buckert John F.
Denion Thomas
Ford Global Technologies Inc.
Lippa Allan J.
Tran Binh
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