Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2000-07-31
2002-03-26
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S435000, C073S116070
Reexamination Certificate
active
06360726
ABSTRACT:
TECHNICAL FIELD
This invention relates to a process to be executed with the microprocessor of a vehicular engine- or powertrain-control module for determining the volatility of a gasoline fuel for use in adjusting air-to-fuel ratio during cold engine start.
BACKGROUND OF THE INVENTION
Despite the development of catalytic converters for the treatment of exhaust gases from automotive internal combustion engines and sophisticated computer-based controls for engine spark timing and air-to-fuel ratio management, there remains a need for improvement in reducing emissions during the starting and warm-up of a cold engine. A significant amount of carbon monoxide and unburned hydrocarbon emissions is exhausted to the atmosphere during the first minute or so of start up and operation of a cold gasoline-powered engine when the catalyst has not reached its light-off temperature. The actual temperature of a “cold” engine may vary greatly depending upon the ambient conditions, but even a tropic environment does not heat an engine and exhaust system to their effective operating regime. During a cold start, the noble metal-based catalytic converter is not hot enough to affect the oxidation of incompletely burned fuel. Furthermore, it is difficult to adjust the air/fuel ratio in the engine because the oxygen sensor in the exhaust system is not warmed up, and there is no information available to the engine controller concerning the ratio of air to fuel being admitted into the cylinders for combustion.
The amount of liquid fuel being introduced into the engine can be controlled by the activation times of the engine's calibrated fuel injectors. But during cold start, only a portion of the injected fuel actually vaporizes for efficient combustion, and that portion depends largely on the volatility of the fuel being delivered to the cylinders of a cold engine.
Commercial fuel volatility varies by season and location. Usually, lower volatility fuels are supplied in the summer and warmer locations. To avoid driveability problems at lower temperatures, higher volatility fuels are provided in winter. Such fuel volatility variation, however, is a cause of concern for the auto industry in regard to both emissions compliance and good driveability for customer satisfaction. Designers of automotive vehicles have to provide engine controls and calibrations that enable rapid and smooth engine start-up to satisfy the customer, and such controls and calibrations must also lead to ever lower exhaust discharges of carbon monoxide and incompletely burned fuel species. Indeed, the design of engine controls would have been simpler had the actual volatility of the fuel used in the vehicle were known to engine controller in real time.
A well-recognized measure of fuel volatility is the familiar Driveability Index (DI)
DI=
1.5
T
10
+3
T
50
+T
90
where T
10
, T
50
and T
90
represent temperatures in ° F. at which 10%, 50% and 90%, respectively, of fuel has vaporized during ASTM D86 distillation test. It is seen by inspection of the above equation that high volatility fuels have lower DI values and vice versa. In general, fuels with higher DI values, i.e., lower volatility properties, are harder to start and may cause rougher engine operation during warm-up.
Current engine computer control strategy is to calibrate engines for low-volatility fuel (worst case scenario) to avoid potential engine stall and/or driveability problems with lower volatility fuels in the market. This requires significant fuel enrichment during the initial cold-start transient phase of engine control and operation. In such a fuel-blind calibration procedure, the emission levels for high-volatility fuels (used in most emission certification tests) are much higher than would otherwise be possible. On the other hand, had the engine been calibrated for the certification fuel, there could have been driveability problems in real-world vehicle operation and hence potential customer complaints. Thus, an adaptive engine control strategy based on real-world estimation of DI would help both emissions and driveability.
In the absence of a reliable and cost-effective sensor for direct measurement of fuel volatility, optimal fuel control during initial cold-start transients is a difficult task. Without knowledge of how much vaporized fuel is being pumped into the combustion chamber of the engine during cold start, control of the proportions of air and fuel is difficult, if not impossible. With the lack of knowledge of fuel DI, all current engine control strategies have resorted to a conservative high DI calibration base. This assures a fuel rich start-up for driver satisfaction but with increased exhaust emissions. As a result, in practice, on some systems additional costly after-treatment processes (such as the Air Injection Reactor system) are added to the emissions control system to reduce non-methane hydrocarbons (NMHC) and carbon monoxide (CO) to acceptable levels given by the relevant mandated emission standards.
It is clear that there is a significant need for a soft sensor or computer-based process for the real time detection of fuel volatility, especially during cold engine start, to insure simultaneous customer driveability satisfaction and compliance with emissions standards.
SUMMARY OF THE INVENTION
This invention provides a generic process for detecting the fuel volatility, or equivalently the driveability index DI, of the gasoline actually being pumped to and injected into the intake port or the combustion cylinders of a vehicle engine during start-up. The invention also provides a compensation process for adjusting or compensating for the low volatility fuel-based calibration with a reliable estimate of the actual volatility of the fuel in establishing the rate of fuel injection to the engine. These detection and compensation processes are preferably carried out within about one second of engine start-up using crankshaft position sensor information (raw rpm data) in the suitably programmed engine control module or powertrain control module of the vehicle.
When a vehicle operator turns the ignition key to start a current gasoline-powered, internal combustion engine (preferably without touching the throttle pedal) under the management of an engine or powertrain control module, the starter motor cranks the engine a few revolutions to enable starting. The powertrain control module (PCM) is activated. It has been pre-calibrated to control the ignition system and air and gasoline flow to start the cold engine. As part of its operation, the PCM receives and processes raw signals from the crankshaft position sensor to time ignition events and ascertain engine start and idle. During the first few events after cranking, fuel is injected into the air inlet ports of all cylinders (asynchronous fuel injection) until the PCM has processed sufficient sensor data to learn crankshaft position. Synchronous fuel injection then begins. The mass of fuel injected per port has been predetermined by the calibration of the engine control designer, but the amount of fuel vapor actually available for combustion in any given engine depends mostly on the actual volatility of the fuel at the ambient temperature.
The proportion of vapor generated by the injected fuel is relatively low in low volatility (high DI) fuels and relatively high in high volatility (low DI) fuels. The PCM has been calibrated to inject a relatively large mass of fuel because of the designer's assumption that the vehicle may contain a low volatility fuel. The fuel-rich engine quickly starts idling. As soon as the PCM detects the engine run condition, the rate of fuel injection is sharply cut back over a specified number of engine ignition or fuelling events. The engine is now operating in a more fuel-lean condition and engine speed in revolutions per minute (rpm) decreases to a pre-specified level.
As stated, a part of PCM operation involves noting and counting engine events and the time between them. An engine event refers to the timing of ignition or fuel injection into a cyl
General Motors Corporation
Grove George A.
Sedlar Jeffrey A.
Wolfe Willis R.
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