Internal-combustion engines – Charge forming device – Including means responsive to instantaneous change in engine...
Reexamination Certificate
2002-05-16
2004-01-20
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Charge forming device
Including means responsive to instantaneous change in engine...
C123S478000, C123S486000, C123S491000
Reexamination Certificate
active
06679225
ABSTRACT:
TECHNICAL FIELD
This invention relates to internal combustion engine operation and control, and more specifically, to engine operation and control responsive to fuel volatility.
BACKGROUND OF THE INVENTION
The need to be able to effectively start and run an internal combustion (IC) engine using fuels with a range of properties has been a problem that continually challenges engine calibrators. The fuel properties that pose problems include the vaporization pressure of the fuel, which is quantified by the Reid Vapor Pressure (RVP) or the Driveability Index (DI). Fuel refiners and distributors adjust the fuel vaporization pressure to correspond to seasonal ambient temperatures in order to optimize the cold start capability of IC engines in various geographic regions. This variation in vaporization pressure is created by balancing the amount of lower-, mid-, and heavier-weight hydrocarbon molecules in the fuel. The lower weight hydrocarbon molecules vaporize at lower temperatures, thus leading to more effective engine startability at low ambient temperatures. The fuel available can range in DI from under 1000 (highly volatile) in cooler areas to over 1250 (very stable) in hotter areas.
In addition, the fuel in a fuel tank may change vaporization characteristics over time, through a process called ‘weathering’. The lower-weight hydrocarbon molecules may evaporate in the fuel tank. Passenger cars and trucks have evaporative systems that capture and store these evaporated hydrocarbons in a carbon canister and subsequently consume them by purging the canister through the engine. In engine applications where there is no evaporative system, these lower weight molecules may be vented to the atmosphere. Either way, the evaporative characteristics of the fuel remaining will have changed, and the suitability of the fuel for cold start operation will have also changed.
Engine manufacturers are faced with meeting requirements for stable start and run conditions. To meet the driveability requirements, engine management systems are calibrated using a sufficient amount of fuel to be robust when fuels of varying volatility are encountered. A typical approach to managing varying levels of fuel volatility has been to calibrate the system with excess fuel to ensure good driveability during engine start and initial operation. This use of excess fuel increases engine-out hydrocarbon and carbon monoxide emissions. In addition, the vehicle manufacturers must also comply with more stringent exhaust emissions regulations. An important strategy in meeting these emission regulations is to ensure that the engine runs at an air/fuel (AF) ratio that is at or near stoichiometry at the start of the engine, or soon thereafter. This is necessary to minimize engine out emissions and also to provide an exhaust gas feedstream to the catalytic converter that allows the converter to perform at optimum levels.
Engine and vehicle manufacturers accomplish this balance between meeting requirements for stable operation and meeting emissions regulations several ways. Extensive testing and calibration during the engine development phase is conducted. Hardware such as air injection pumps are added. The amount of precious metals (Palladium, Rhodium, and Platinum) contained in the catalytic converter is increased to improve effective conversion of pollutants. Each of these methods adds complexity and cost to the vehicle or engine.
Optimal operation and control of an engine occurs when the engine is in a warmed up state and is using an exhaust gas sensor to provide feedback to the engine controller for closed loop control of the engine. During the initial operation of the engine after start, especially a cold start, an engine may not be able to operate in closed loop fashion based on feedback from the exhaust gas sensor. This may happen for several reasons. The exhaust gas sensor typically takes a certain amount of time to become functional, i.e. to warm up or ‘light-off’. This sensor light-off may take a few seconds, or it may take more than 30 seconds, depending on sensor design and placement, ambient conditions, and the temperature of the exhaust gas from the engine.
In addition to the exhaust gas sensor not being functional, the engine itself may not be sufficiently warmed up to operate at or near stoichiometry immediately after start. An engine that has high internal friction may require that there be more power to operate the engine when it is cold. This can lead to a need for corresponding rich AF operation to overcome the friction. Another factor is the design of the intake manifold, including placement of the fuel injectors. This can affect the amount of fuel that must be delivered to have a sufficient quantity of fuel vaporized to effectively operate the engine. Also, the design of the exhaust catalytic converter system may require the engine to operate in a manner that enables the catalyst to quickly light off and become chemically active. Balanced against this is the need to provide smooth, stable engine operation and the need to minimize tailpipe emissions.
Prior to sensor light-off the engine controller relies upon information other than the input from the exhaust gas sensor to control the engine. This includes inputs from other sensors and calibrations that are internal to the controller, e.g. crankshaft sensor, manifold absolute pressure sensor, and throttle position sensor. The engine controller can control the engine to a commanded AF ratio by monitoring input from the sensors and by using internal calibrations. This control will be based on the engine operating conditions that can be measured directly and conditions that are inferred from predictable behavior of the engine under the measured conditions.
The engine controller is still unable to manage engine roughness resulting from incomplete vaporization of the fuel and mixture with the air in individual cylinders that can occur as the result of unanticipated fuel volatility. This engine roughness will be manifested as instability in the engine crank speed during initial engine operation. Variations in crankshaft speed can also be related to design of the engine and variation in components of each cylinder due to part-to-part variability, deterioration of engine components and sensors, or various component or system malfunctions.
The prior art has sought to measure and compensate for fuel volatility by monitoring engine performance during initial engine operation. This is accomplished by monitoring the engine speed immediately after starting and comparing it to predetermined engine speed values that have been determined by testing prototype engines. This type of method will provide fuel compensation during initial operation based only on the measured engine speed. However, it is recognized that variations in fuel volatility affect the initial operation of the engine in several ways beyond the initial engine run speed. The prior art does not provide compensation for fuel volatility during engine cranking. Nor does it compensate for other effects of variation in fuel volatility, including engine roughness, and instability in engine firing during initial operation. The prior art also does not address a root cause of varying engine performance as a result varying fuel volatility, which is the effect of intake valve temperature on the incoming fuel.
Accordingly, a need exists for a more complete method to compensate for the variation in fuel volatility during engine start and initial operation.
SUMMARY OF THE INVENTION
The present invention provides an improvement over conventional engine controls by adjusting engine air/fuel [AF] ratio, as a function of fuel volatility, during engine start and initial operation. The AF ratio is used in the calculation of the engine fueling. Engine fueling is calculated by determining the air intake to the engine and dividing this value by the AF ratio.
The present invention is a method that is comprised of three detection tests to determine the volatility of the fuel and provide compensation to the AF ratio in proportio
Burleigh Darrell W.
Carlson Craig A.
Garcia Sergio Eduardo
Robertson William R.
Argenbright Tony M.
Delphi Technologies Inc.
Funke Jimmy L.
LandOfFree
Compensation for fuel volatility for internal combustion... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Compensation for fuel volatility for internal combustion..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Compensation for fuel volatility for internal combustion... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3194705